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Sample records for eddy correlation technique

  1. DEVELOPMENT OF TECHNIQUES FOR EDDY-CORRELATION MEASUREMENTS OF NON-METHANE VOLATILE ORGANIC COMPOUND FLUXED IN THE ATMOSPHERE

    EPA Science Inventory

    An analytical technique for the measurement of the exchange (flux) of trace gases between the earth's surface and the atmosphere will be developed. Measurements will rely on the eddy correlation method (ECM). Target compounds are biogenically and anthropogenically emitted v...

  2. Assessing maize crop coefficient through eddy correlation technique in Northern Italy

    NASA Astrophysics Data System (ADS)

    Horeschi, D.; Mancini, M.; Corbari, C.; Montaldo, N.

    2009-04-01

    The evapotranspiration (ET), also known as latent heat (LE) in energetic terms, has a key role in eco-hydrological processes. Direct measurements of ET, owing to the technique adopted (for instance the lysimeters), were not reliable, nor immediate. For this reason new methods developed by the scientific community suggested to estimate ET from energy budget using atmospheric data and parameters. Among these methods the FAO Penman-Monteith, which is largely diffused, evaluates the potential evapotranspiration of a generic crop as a product of a reference evapotranspiration (ET0) multiplied by a coefficient kc. Kc, called crop coefficient, should embody all the physiologic characteristics of a specific plant and should allow to pass from the reference ET0 to the potential ET of each crop. Such coefficients have been evaluated only in some regions of the planet, which may be quite different from the one in which they are applied. This means that available kc coefficients in literature, despite a correction procedure to adapt them to the local meteo-climate conditions, are yet not completely reliable (Katerji and Rana, 2006). Besides in this context the Eddy correlation technique (eddy-corr for simplicity), was developed in the last years. This method, built through a dimensional analysis application, demonstrated that the latent heat is proportional to the covariance of some measurable atmospheric variables. The paper discusses the reliability of the kc of maize, assessed by the FAO method comparing it with the eddy-corr analysis.

  3. Airborne eddy correlation gas flux measurements - Design criteria for optical techniques

    NASA Technical Reports Server (NTRS)

    Ritter, John A.; Sachse, Glen W.; Anderson, Bruce E.

    1993-01-01

    Although several methods exist for the determination of the flux of an atmospheric species, the airborne eddy correlation method has the advantage of providing direct flux measurements that are representative of regional spatial domains. The design criteria pertinent to the construction of chemical instrumentation suitable for use in airborne eddy correlation flux measurements are discussed. A brief overview of the advantages and limitations of the current instrumentation used to obtain flux measurements for CO, CH4, O3, CO2, and water vapor are given. The intended height of the measurement within the convective boundary layer is also shown to be an important design criteria. The sensitivity, or resolution, which is required in the measurement of a scalar species to obtain an adequate species flux measurement is discussed. The relationship between the species flux resolution and the more commonly stated instrumental resolution is developed and it is shown that the standard error of the flux estimate is a complicated function of the atmospheric variability and the averaging time that is used. The use of the recently proposed intermittent sampling method to determine the species flux is examined. The application of this technique may provide an opportunity to expand the suite of trace gases for which direct flux measurements are possible.

  4. Assessment of benthic flux of dissolved organic carbon in wetland and estuarine sediments using the eddy-correlation technique

    NASA Astrophysics Data System (ADS)

    Swett, M. P.; Amirbahman, A.; Boss, E.

    2009-12-01

    Wetland and estuarine sediments release significant amounts of dissolved organic carbon (DOC) due to high levels of microbial activity, particularly sulfate reduction. Changes in climate and hydrologic conditions have a potential to alter DOC release from these systems as well. This is a concern, as high levels of DOC can lead to mobilization of toxic metals and organics in natural waters. In addition, source waters high in DOC produce undesirable disinfection byproducts in water treatment. Various in situ methods, such as peepers and sediment core centrifugation, exist to quantify vertical benthic fluxes of DOC and other dissolved species from the sediment-water interface (SWI). These techniques, however, are intrusive and involve disturbance of the sediment environment. Eddy-correlation allows for real-time, non-intrusive, in situ flux measurement of important analytes, such as O2 and DOC. An Acoustic Doppler Velocimeter (ADV) is used to obtain three-dimensional fluid velocity measurements. The eddy-correlation technique employs the mathematical separation of fluid velocity into mean velocity and fluctuating velocity components, with the latter representing turbulent eddy velocity. DOC concentrations are measured using a colored dissolved organic matter (CDOM) fluorometer, and instantaneous vertical flux is determined from the correlated data. This study assesses DOC flux at three project sites: a beaver pond in the Lower Penobscot Watershed, Maine; a mudflat in Penobscot River, Maine; and a mudflat in Great Bay, New Hampshire. Eddy flux values are compared with results obtained using peepers and centrifugation, as well as vertical profiling.

  5. Eddy current technique for predicting burst pressure

    DOEpatents

    Petri, Mark C.; Kupperman, David S.; Morman, James A.; Reifman, Jaques; Wei, Thomas Y. C.

    2003-01-01

    A signal processing technique which correlates eddy current inspection data from a tube having a critical tubing defect with a range of predicted burst pressures for the tube is provided. The method can directly correlate the raw eddy current inspection data representing the critical tubing defect with the range of burst pressures using a regression technique, preferably an artificial neural network. Alternatively, the technique deconvolves the raw eddy current inspection data into a set of undistorted signals, each of which represents a separate defect of the tube. The undistorted defect signal which represents the critical tubing defect is related to a range of burst pressures utilizing a regression technique.

  6. Eddy Correlation Flux Measurement System (ECOR) Handbook

    SciTech Connect

    Cook, DR

    2011-01-31

    The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration.

  7. Geohydrology and evapotranspiration at Franklin Lake playa, Inyo County, California; with a section on estimating evapotranspiration using the energy-budget eddy-correlation technique

    USGS Publications Warehouse

    Czarnecki, John B.; Stannard, David I.

    1997-01-01

    Franklin Lake playa is one of the principal discharge areas of the ground-water-flow system associated with Yucca Mountain, Nevada, the potential site of a high-level nuclear-waste repository. By using the energy-budget eddy-correlation technique, measurements made between June 1983 and April 1984 to estimate evapotranspiration were found to range from 0.1 centimeter per day during winter months to about 0.3 centimeter per day during summer months; the annual average was 0.16 centimeter per day. These estimates were compared with evapotranspiration estimates calculated from six other methods.

  8. Energy budget measurements using eddy correlation and Bowen ratio techniques at the Kinosheo Lake tower site during the Northern Wetlands Study

    NASA Technical Reports Server (NTRS)

    Den Hartog, G.; Neumann, H. H.; King, K. M.; Chipanshi, A. C.

    1994-01-01

    Fluxes of heat and water vapor were measured on a 20-m tower at Kinosheo Lake in the Hudson Bay lowlands using eddy correlation and Bowen ratio energy balance techniques. The study period was June 25 to July 28, 1990. Measurements were made over a peat bog consisting of a mixture of sphagnum moss and lichen hummocks and black pools. About 200 m west of the tower were several shallow ponds. The hummocks had a dry, insulating surface and were underlain by an ice layer near 50 cm depth until mid-July. At the beginning of the period the black pools were covered with water, and although the free water gradually disappeared over the study period, they remained saturated to the end of July. The depth of peat near the tower was about 3 m. Despite the ice layer under the hummocks, their daytime surface temperatures were high, near 35 C, and after the middle of July, above 40 C. Inspection of temperature, precipitation, and radiation data showed that the midsummer period of 1990 was warmer, drier, and sunnier than usual at Moosonee and so by influence at Lake Kinosheo. When all the data were combined to yield average diurnal energy balance components, the eddy correlation fluxes accounted for 90% of the available energy. Latent heat flux averaged 46% of the total available energy and the sensible heat flux averaged 34%. Daytime Bowen ratios were near 1 for the experimental period, suggesting that the bog behaved more like a dryland than a wetland. Eddy correlation measurements of sensible heat and latent heat flux were less than those measured using the Bowen ratio energy balance technique, the average ratios being 0.81 and 0.86 respectively. These differences were possibly due to the difficulty in measuring energy balance components of net radiation and ground heat flux over the mosaic surface.

  9. Effects of Eddy Viscosity on Time Correlations in Large Eddy Simulation

    NASA Technical Reports Server (NTRS)

    He, Guowei; Rubinstein, R.; Wang, Lian-Ping; Bushnell, Dennis M. (Technical Monitor)

    2001-01-01

    Subgrid-scale (SGS) models for large. eddy simulation (LES) have generally been evaluated by their ability to predict single-time statistics of turbulent flows such as kinetic energy and Reynolds stresses. Recent application- of large eddy simulation to the evaluation of sound sources in turbulent flows, a problem in which time, correlations determine the frequency distribution of acoustic radiation, suggest that subgrid models should also be evaluated by their ability to predict time correlations in turbulent flows. This paper compares the two-point, two-time Eulerian velocity correlation evaluated from direct numerical simulation (DNS) with that evaluated from LES, using a spectral eddy viscosity, for isotropic homogeneous turbulence. It is found that the LES fields are too coherent, in the sense that their time correlations decay more slowly than the corresponding time. correlations in the DNS fields. This observation is confirmed by theoretical estimates of time correlations using the Taylor expansion technique. Tile reason for the slower decay is that the eddy viscosity does not include the random backscatter, which decorrelates fluid motion at large scales. An effective eddy viscosity associated with time correlations is formulated, to which the eddy viscosity associated with energy transfer is a leading order approximation.

  10. Eddy Correlation Flux Measurement System Handbook

    SciTech Connect

    Cook, D. R.

    2016-01-01

    The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration. The instruments used are: • a fast-response, three-dimensional (3D) wind sensor (sonic anemometer) to obtain the orthogonal wind components and the speed of sound (SOS) (used to derive the air temperature) • an open-path infrared gas analyzer (IRGA) to obtain the water vapor density and the CO2 concentration, and • an open-path infrared gas analyzer (IRGA) to obtain methane density and methane flux at one SGP EF and at the NSA CF. The ECOR systems are deployed at the locations where other methods for surface flux measurements (e.g., energy balance Bowen ratio [EBBR] systems) are difficult to employ, primarily at the north edge of a field of crops. A Surface Energy Balance System (SEBS) has been installed collocated with each deployed ECOR system in SGP, NSA, Tropical Western Pacific (TWP), ARM Mobile Facility 1 (AMF1), and ARM Mobile Facility 2 (AMF2). The surface energy balance system consists of upwelling and downwelling solar and infrared radiometers within one net radiometer, a wetness sensor, and soil measurements. The SEBS measurements allow the comparison of ECOR sensible and latent heat fluxes with the energy balance determined from the SEBS and provide information on wetting of the sensors for data quality purposes. The SEBS at one SGP and one NSA site also support upwelling and downwelling PAR measurements to qualify those two locations as Ameriflux sites.

  11. Eddy Diffusivities for Sensible Heat, Ozone and Momentum from Eddy Correlation and Gradient Measurements.

    NASA Astrophysics Data System (ADS)

    Zeller, Karl Frederick

    Micrometeorological field measurements of the fluxes and the gradients of momentum, sensible heat and ozone are presented and discussed. The eddy-correlation measurement technique was used to obtain the flux data at the heights of three and eight meters. A method to accurately measure mass (ozone) gradients from surface -layer based meteorological towers was developed and used. Both flux and gradient measurements are used for the determination of eddy diffusivities. Exploratory analyses were made with the data to investigate similarity relationships between the eddy diffusivities of momentum K_{ rm m}, sensible heat K_ {rm h}, and mass K_ {rm c}, where ozone was used as the mass tracer. Eddy-diffusivity ratios were computed using dimensionless -gradient ratios classified from the data and from regression models. These ratios were classified by atmospheric stability determined at the geometric mean of the measurement heights. The assumption of similarity between the eddy diffusivities of ozone and sensible heat, K_ {rm c} = K_{ rm h}, based on scalar turbulent transfer theory, was verified for unstable atmospheric conditions. The results for eddy diffusivities of sensible heat and ozone for stable atmospheric conditions however, show that diffusivities of sensible heat are 50% greater than diffusivities of ozone. Chemical reaction of ozone, and/or the need for flux-measurement corrections, decrease the resulting values for ozone diffusivities during stable periods. Established eddy-diffusivity ratios for water vapor and momentum are valid for ozone and momentum under stable-atmospheric conditions over smooth-terrain but not under unstable conditions for flow disturbed by irregular terrain. The relationships between the eddy diffusivities of momentum and the eddy diffusivities of ozone, as well as those between momentum and sensible heat are controlled by free-convection conditions, K_{ rm m} < K_ {rm c} and K_{ rm m} < K_ {rm h}; these results are inconclusive for

  12. Ergodicity test of the eddy correlation method

    NASA Astrophysics Data System (ADS)

    Chen, J.; Hu, Y.; Yu, Y.; Lü, S.

    2014-07-01

    The turbulent flux observation in the near-surface layer is a scientific issue which researchers in the fields of atmospheric science, ecology, geography science, etc. are commonly interested in. For eddy correlation measurement in the atmospheric surface layer, the ergodicity of turbulence is a basic assumption of the Monin-Obukhov (M-O) similarity theory, which is confined to steady turbulent flow and homogenous surface; this conflicts with turbulent flow under the conditions of complex terrain and unsteady, long observational period, which the study of modern turbulent flux tends to focus on. In this paper, two sets of data from the Nagqu Station of Plateau Climate and Environment (NaPlaCE) and the cooperative atmosphere-surface exchange study 1999 (CASE99) were used to analyze and verify the ergodicity of turbulence measured by the eddy covariance system. Through verification by observational data, the vortex of atmospheric turbulence, which is smaller than the scale of the atmospheric boundary layer (i.e., its spatial scale is less than 1000 m and temporal scale is shorter than 10 min) can effectively meet the conditions of the average ergodic theorem, and belong to a wide sense stationary random processes. Meanwhile, the vortex, of which the spatial scale is larger than the scale of the boundary layer, cannot meet the conditions of the average ergodic theorem, and thus it involves non-ergodic stationary random processes. Therefore, if the finite time average is used to substitute for the ensemble average to calculate the average random variable of the atmospheric turbulence, then the stationary random process of the vortex, of which spatial scale was less than 1000 m and thus below the scale of the boundary layer, was possibly captured. However, the non-ergodic random process of the vortex, of which the spatial scale was larger than that of the boundary layer, could not be completely captured. Consequently, when the finite time average was used to substitute

  13. PHREATOPHYTE WATER USE ESTIMATED BY EDDY-CORRELATION METHODS.

    USGS Publications Warehouse

    Weaver, H.L.; Weeks, E.P.; Campbell, G.S.; Stannard, D.I.; Tanner, B.D.

    1986-01-01

    Water-use was estimated for three phreatophyte communities: a saltcedar community and an alkali-Sacaton grass community in New Mexico, and a greasewood rabbit-brush-saltgrass community in Colorado. These water-use estimates were calculated from eddy-correlation measurements using three different analyses, since the direct eddy-correlation measurements did not satisfy a surface energy balance. The analysis that seems to be most accurate indicated the saltcedar community used from 58 to 87 cm (23 to 34 in. ) of water each year. The other two communities used about two-thirds this quantity.

  14. Open-path tunable diode laser absorption for eddy correlation flux measurements of atmospheric trace gases

    NASA Technical Reports Server (NTRS)

    Anderson, Stuart M.; Zahniser, Mark S.

    1991-01-01

    Biogenic emissions from and dry deposition to terrestrial surfaces are important processes determining the trace gas composition of the atmosphere. An instrument has been developed for flux measurements of gases such as CH4, N2O, and O3 based on the eddy correlation technique which combines trace gas fluctuation measurements with simultaneous windfield measurements. The instrument combines a tunable diode laser infrared light source with an open-path multipass absorption cell in order to provide the fast time response and short base pathlength required for the eddy correlation method. Initial field tests using the instrument to measure methane emissions from a local wetland demonstrate the capability for high precision eddy correlation flux measurements.

  15. Non-Destructive Techniques Based on Eddy Current Testing

    PubMed Central

    García-Martín, Javier; Gómez-Gil, Jaime; Vázquez-Sánchez, Ernesto

    2011-01-01

    Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future. PMID:22163754

  16. Non-destructive techniques based on eddy current testing.

    PubMed

    García-Martín, Javier; Gómez-Gil, Jaime; Vázquez-Sánchez, Ernesto

    2011-01-01

    Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future. PMID:22163754

  17. Ergodicity test of the eddy-covariance technique

    NASA Astrophysics Data System (ADS)

    Chen, J.; Hu, Y.; Yu, Y.; Lü, S.

    2015-09-01

    The ergodic hypothesis is a basic hypothesis typically invoked in atmospheric surface layer (ASL) experiments. The ergodic theorem of stationary random processes is introduced to analyse and verify the ergodicity of atmospheric turbulence measured using the eddy-covariance technique with two sets of field observational data. The results show that the ergodicity of atmospheric turbulence in atmospheric boundary layer (ABL) is relative not only to the atmospheric stratification but also to the eddy scale of atmospheric turbulence. The eddies of atmospheric turbulence, of which the scale is smaller than the scale of the ABL (i.e. the spatial scale is less than 1000 m and temporal scale is shorter than 10 min), effectively satisfy the ergodic theorems. Under these restrictions, a finite time average can be used as a substitute for the ensemble average of atmospheric turbulence, whereas eddies that are larger than ABL scale dissatisfy the mean ergodic theorem. Consequently, when a finite time average is used to substitute for the ensemble average, the eddy-covariance technique incurs large errors due to the loss of low-frequency information associated with larger eddies. A multi-station observation is compared with a single-station observation, and then the scope that satisfies the ergodic theorem is extended from scales smaller than the ABL, approximately 1000 m to scales greater than about 2000 m. Therefore, substituting the finite time average for the ensemble average of atmospheric turbulence is more faithfully approximate the actual values. Regardless of vertical velocity or temperature, the variance of eddies at different scales follows Monin-Obukhov similarity theory (MOST) better if the ergodic theorem can be satisfied; if not it deviates from MOST. The exploration of ergodicity in atmospheric turbulence is doubtlessly helpful in understanding the issues in atmospheric turbulent observations and provides a theoretical basis for overcoming related difficulties.

  18. Characterization of Magnetron Sputtered Coatings by Pulsed Eddy Current Techniques

    SciTech Connect

    Mulligan, Chris; Lee Changqing; Danon, Yaron

    2005-04-09

    A method that uses induced pulsed eddy currents for characterization of thick magnetron sputtered Nb coatings on steel is presented in this paper. The objectives of this work are to develop a system for rapid quantitative nondestructive inspection of coatings as well as to determine the correlation between coating properties, such as density and purity, and eddy current measured resistivity of coatings. A two-probe differential system having higher sensitivity and less noise than a one-probe system with 2-D scanning ability was developed.

  19. Eddy Current Rail Inspection Using AC Bridge Techniques

    PubMed Central

    Liu, Ze; Koffman, Andrew D; Waltrip, Bryan C; Wang, Yicheng

    2013-01-01

    AC bridge techniques commonly used for precision impedance measurements have been adapted to develop an eddy current sensor for rail defect detection. By using two detection coils instead of just one as in a conventional sensor, we can balance out the large baseline signals corresponding to a normal rail. We have significantly enhanced the detection sensitivity of the eddy current method by detecting and demodulating the differential signal of the two coils induced by rail defects, using a digital lock-in amplifier algorithm. We have also explored compensating for the lift-off effect of the eddy current sensor due to vibrations by using the summing signal of the detection coils to measure the lift-off distance. The dominant component of the summing signal is a constant resulting from direct coupling from the excitation coil, which can be experimentally determined. The remainder of the summing signal, which decreases as the lift-off distance increases, is induced by the secondary eddy current. This dependence on the lift-off distance is used to calibrate the differential signal, allowing for a more accurate characterization of the defects. Simulated experiments on a sample rail have been performed using a computer controlled X-Y moving table with the X-axis mimicking the train’s motion and the Y-axis mimicking the train’s vibrational bumping. Experimental results demonstrate the effectiveness of the new detection method. PMID:26401427

  20. Eddy Current Rail Inspection Using AC Bridge Techniques.

    PubMed

    Liu, Ze; Koffman, Andrew D; Waltrip, Bryan C; Wang, Yicheng

    2013-01-01

    AC bridge techniques commonly used for precision impedance measurements have been adapted to develop an eddy current sensor for rail defect detection. By using two detection coils instead of just one as in a conventional sensor, we can balance out the large baseline signals corresponding to a normal rail. We have significantly enhanced the detection sensitivity of the eddy current method by detecting and demodulating the differential signal of the two coils induced by rail defects, using a digital lock-in amplifier algorithm. We have also explored compensating for the lift-off effect of the eddy current sensor due to vibrations by using the summing signal of the detection coils to measure the lift-off distance. The dominant component of the summing signal is a constant resulting from direct coupling from the excitation coil, which can be experimentally determined. The remainder of the summing signal, which decreases as the lift-off distance increases, is induced by the secondary eddy current. This dependence on the lift-off distance is used to calibrate the differential signal, allowing for a more accurate characterization of the defects. Simulated experiments on a sample rail have been performed using a computer controlled X-Y moving table with the X-axis mimicking the train's motion and the Y-axis mimicking the train's vibrational bumping. Experimental results demonstrate the effectiveness of the new detection method. PMID:26401427

  1. Technique for temperature compensation of eddy-current proximity probes

    NASA Technical Reports Server (NTRS)

    Masters, Robert M.

    1989-01-01

    Eddy-current proximity probes are used in turbomachinery evaluation testing and operation to measure distances, primarily vibration, deflection, or displacment of shafts, bearings and seals. Measurements of steady-state conditions made with standard eddy-current proximity probes are susceptible to error caused by temperature variations during normal operation of the component under investigation. Errors resulting from temperature effects for the specific probes used in this study were approximately 1.016 x 10 to the -3 mm/deg C over the temperature range of -252 to 100 C. This report examines temperature caused changes on the eddy-current proximity probe measurement system, establishes their origin, and discusses what may be done to minimize their effect on the output signal. In addition, recommendations are made for the installation and operation of the electronic components associated with an eddy-current proximity probe. Several techniques are described that provide active on-line error compensation for over 95 percent of the temperature effects.

  2. Correlation Between Eddy Current Signal Noise and Peened Surface Roughness

    NASA Astrophysics Data System (ADS)

    Wendt, S. E.; Hentscher, S. R.; Raithel, D. C.; Nakagawa, N.

    2007-03-01

    For advanced uses of eddy current (EC) NDE models in, e.g., model-assisted POD, there is a need to understand the origin of EC noise sources so that noise estimations can be made for a given set of inspection conditions, in addition to defect signal predictions. This paper focuses on the material-oriented noise sources that exhibit some universality when isolated from electrical and mechanical noises. Specifically, we report on experimental measurements that show explicit correlations between surface roughness and EC noise as seen in post-peen EC measurements of shot-peened roughness specimens. The samples are 3″-by-3″ Inconel 718 and Ti-6A1-4V blocks, pre-polished and shot-peened at Almen intensities ranging from a low of 4N to as high as 16A, created by smaller (˜350 μm) and larger (˜1 mm) diameter zirconium oxide shots. Strong correlations are observed between the Almen intensities and the measured surface roughness. The EC noise correlates equally strongly with the Almen intensities for the superalloy specimens. The correlation for the Ti-alloy samples is only apparent at higher intensities, while being weak for lower intensities, indicating the grain noise dominance for smoother surfaces.

  3. Correlation Between Eddy Current Signal Noise and Peened Surface Roughness

    SciTech Connect

    Wendt, S. E.; Hentscher, S. R.; Raithel, D. C.; Nakagawa, N.

    2007-03-21

    For advanced uses of eddy current (EC) NDE models in, e.g., model-assisted POD, there is a need to understand the origin of EC noise sources so that noise estimations can be made for a given set of inspection conditions, in addition to defect signal predictions. This paper focuses on the material-oriented noise sources that exhibit some universality when isolated from electrical and mechanical noises. Specifically, we report on experimental measurements that show explicit correlations between surface roughness and EC noise as seen in post-peen EC measurements of shot-peened roughness specimens. The samples are 3''-by-3'' Inconel 718 and Ti-6A1-4V blocks, pre-polished and shot-peened at Almen intensities ranging from a low of 4N to as high as 16A, created by smaller ({approx}350 {mu}m) and larger ({approx}1 mm) diameter zirconium oxide shots. Strong correlations are observed between the Almen intensities and the measured surface roughness. The EC noise correlates equally strongly with the Almen intensities for the superalloy specimens. The correlation for the Ti-alloy samples is only apparent at higher intensities, while being weak for lower intensities, indicating the grain noise dominance for smoother surfaces.

  4. Initial results from the Pawnee eddy correlation system for acid deposition research

    SciTech Connect

    Zeller, K.; Massman, W.; Stocker, D.; Fox, D.G.; Stellman, D.; Hazlett, D.

    1989-01-01

    The Pawnee grassland eddy correlation dry deposition project is described. Instrumentation, methods of analysis, and initial data and research findings are presented. Data from this eddy correlation system show agreement with previous observations of deposition velocities for atmospheric ozone, NO{sub 2}, and NO{sub x}; micrometeorological theory; and micrometeorological site characteristics.

  5. Analysis techniques for eddy current imaging of carbon fiber materials

    NASA Astrophysics Data System (ADS)

    Schulze, Martin H.; Meyendorf, Norbert; Heuer, Henning

    2010-04-01

    Carbon fiber materials become more and more important for many applications. Unlike metal the technological parameters and certified quality control mechanisms for Raw Carbon Fiber Materials (RCF) have not yet been developed. There is no efficient and reliable testing system for in-line inspections and consecutive manual inspections of RCF and post laminated Carbon Fiber Reinforced Plastics (CFRP). Based upon the multi-frequency Eddy Current system developed at Fraunhofer IZFP, structural and hidden defects such as missing carbon fiber bundles, lanes, suspensions, fringes, missing sewing threads and angle errors can be detected. Using an optimized sensor array and intelligent image pre-processing algorithms, the complex impedance signal can be allocated to different carbon fiber layers. This technique enables the detection of defects in depths of up to 5 layers, including the option of free scale measuring resolution and testing frequency. Appropriate parameter lists for optimal error classifications are available. The dimensions of the smallest detectable flaws are in the range of a few millimeters. Algorithms and basic Eddy Current C-Scan processing techniques for carbon fiber material testing are described in this paper.

  6. Eddy current techniques for super duplex stainless steel characterization

    NASA Astrophysics Data System (ADS)

    Camerini, C.; Sacramento, R.; Areiza, M. C.; Rocha, A.; Santos, R.; Rebello, J. M.; Pereira, G.

    2015-08-01

    Super duplex stainless steel (SDSS) is a two-phase material where the microstructure consists of grains of ferrite (δ) and austenite (γ). SDSS exhibit an attractive combination of properties, such as: strength, toughness and stress corrosion cracking resistance. Nevertheless, SDSS attain these properties after a controlled solution heat treatment, leading to a similar volumetric fraction of δ and γ. Any further heat treatment, welding operation for example, can change the balance of the original phases, or may also lead to precipitation of a deleterious phase, such as sigma (σ). For these situations, the material corrosion resistance is severely impaired. In the present study, several SDSS samples with low σ phase content and non-balanced microstructure were intentionally obtained by thermally treating SDSS specimens. Electromagnetic techniques, conventional Eddy Current Testing (ECT) and Saturated Low Frequency Eddy Current (SLOFEC), were employed to characterize the SDSS samples. The results showed that ECT and SLOFEC are reliable techniques to evaluate σ phase presence in SDSS and can provide an estimation of the δ content.

  7. The ARM eddy correlation system for monitoring surface fluxes

    SciTech Connect

    Hart, R.L.; Cook, D.R.; Wesely, M.L.

    1998-12-31

    The Atmospheric Radiation Measurement (ARM) Program was established by the Department of Energy as part of the US Global Climate Change Research Program to improve methods of determining radiative transfer and cloud processes in large-scale models. The ARM observational facility in the Southern Great Plains (SGP) of the US uses various types of instrument systems to make continuous measurements of the state of the atmosphere, cloud properties, radiative transfer, and other forms of energy transfer. Most of the instrument systems for these continuous observations come from commercial sources; many are adaptations of systems that have been used previously, mostly in short-term field campaigns. Eddy correlation systems (ECORs) are used to measure the air-surface exchange rates of heat, moisture, and momentum at eight locations in the overall area (350 km by 400 km) of the SGP site. At most locations, measurements are made at a height of about three meters above the ground over tilled agricultural land. At 14 other locations, air-surface exchange is measured above grasslands with an energy balance Bowen ratio system.

  8. Direct measurement of biosphere-atmosphere isotopic CO2 exchange using the eddy covariance technique

    NASA Astrophysics Data System (ADS)

    Griffis, T. J.; Sargent, S. D.; Baker, J. M.; Lee, X.; Tanner, B. D.; Greene, J.; Swiatek, E.; Billmark, K.

    2008-04-01

    Quantifying isotopic CO2 exchange between the biosphere and atmosphere presents a significant measurement challenge, but has the potential to provide important constraints on local, regional, and global carbon cycling. Past approaches have indirectly estimated isotopic CO2 exchange using relaxed eddy accumulation, the flask-based isoflux method, and flux-gradient techniques. Eddy covariance (EC) is an attractive method because it has the fewest theoretical assumptions and the potential to give a direct measure of isotopic CO2 flux, but it requires a highly sensitive and relatively fast response instrument. To date, no such field measurements have been reported. Here we describe the use of a closed-path tunable diode laser absorption spectroscopy and eddy covariance (EC-TDL) system for isotopic (C16O2, 13CO2, C18O16O) flux measurements. Results are presented from an intensive field experiment conducted over a soybean canopy from 18 July to 20 September 2006. This experiment represents a rigorous field test of the EC-TDL technique because the transport was dominated by relatively high frequency eddies. Net ecosystem CO2 exchange (FN) measured with the EC-TDL system showed strong correlation (r2 = 0.99) in the half-hourly fluxes with an EC open-path infrared gas analyzer (EC-IRGA) over the 60-d period. Net CO2 flux measured with the EC-IRGA and EC-TDL systems agreed to within 9%. Flux loss associated with diminished frequency response beyond 1 Hz for the EC-TDL system was approximately 8% during daytime windy (>4 m s-1) conditions. There was no significant evidence of a kinetic-type fractionation effect related to a phase shift among isotopologues due to tube attenuation. Investigation of isotopic spectral similarity in the flux ratio (δNx) for both 13CO2 and C18O16O transport showed that δNx was relatively independent of eddy scale for this ecosystem type. Flux loss, therefore, did not significantly bias δNx. There was excellent agreement between isofluxes (F

  9. Eddy correlation measurements of NO, NO{sub 2}, and O{sub 3} fluxes

    SciTech Connect

    Gao, W.; Wesely, M.L.; Cook, D.R.; martin, T.J.

    1996-06-01

    The micrometeorological technique of eddy correlation was used to measure the vertical fluxes of NO, NO{sub 2}, and ozone in rural North Carolian during spring 1995 as part of the Natural emission of Oxidant precurssors-Validation of techniques and Assessment (NOVA) field experiment. Net flux densities were measured at heights 5 and 10 m above an agricultural field with short corn plants and large amount of exposed bare soil between the rows. Large upward eddy fluxes of NO{sub 2} were seen, and strong NO emissions from the soil were measured by collaborators using environmental enclosures on the soil surface. Data indicate that about 50% of the nitrogen emitted from the soil as NO was converted into NO{sub 2} at 5 m. Rest of the emitted nitrogen may remain as NO flux and be returned back to the vegetation and soil by deposition. Divergence of the NO{sub 2} and O{sub 3} fluxes were detected between 5 and 10 m. This is consistent with likely net NO{sub 2} and O{sub 3} destruction rates. The data will be used to help develop parameterizations of the flux of nitrogen oxides into the lower troposphere.

  10. Correlative Techniques in Microscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Imaging is an important component in basic research, product development and understanding structure/function relationships in agricultural commodities and products. An array of microscopes and techniques can be used illustrate the structure and microchemistry of diverse samples. Examples of the var...

  11. Isoprene Fluxes Measured By Eddy-correlation Over A Mixed Deciduous Forest In Italy

    NASA Astrophysics Data System (ADS)

    Finco, A.; Cieslik, S.

    A measuring campaign was conducted from July to September 2001 at a mixed de- ciduous forest located at a flat site (Nonantola, 4441' N; 1107' E) in the North- ern Italian plain to determine isoprene fluxes. The measuring station, operated by the CNR-ISAO (Bologna ) and CNR-IATA (Florence) was part of the CARBOEU- ROFLUX network, whose main goal is the study of the carbon balance in European forests. The flux measuring system used the eddy-correlation technique and consisted of a Gill sonic anemometer installed at 13 m a.g.l., and a LI-COR CO2/H2O analyser. For isoprene, a Hills Fast Isoprene Sensor was used.In this forest, about 50% of the trees (oaks, poplars and willows) are isoprene emitters. The canopy is very dense and homogeneous; its average height is 8 meters a.g.l. The general daily course of isoprene concentrations consisted in an increase during morning hours, followed with a sharp maximum and a rapid decrease. Maximum val- ues were quite high (around 15 ppb) in July and August, decreasing in September. During daytime, fluxes appeared to be strongly correlated with latent heat fluxes, con- firming the hypothesis of emission through stomata. The concentration decrease ob- served in the afternoon shows exponential decay, suggesting that no emission occurs after the concentration maximum, when stomata are progressively closing. A resistance analysis confirmed the above hypothesis : the role of stomatal emission appears essential, practically excluding other pathways. A mathematical investigation of the stationarity state of the lower atmosphere dur- ing the observations was made in order to draw attention on limitations of the eddy- correlation method. During nighttime, non-stationary situations are frequent, causing apparent peaks of isoprene flux, not due to an emission from the plants. The method developed permits to eliminate these biases.

  12. Eddy current signal deconvolution technique for the improvement of steam generator tubing burst pressure predictions.

    SciTech Connect

    Petri, M. C.; Wei, T. Y. C.; Kupperman, D. S.; Reifman, J.; Morman, J. A.

    2000-01-01

    Eddy current techniques are extremely sensitive to the presence of axial cracks in nuclear power plant steam generator tube walls, but they are equally sensitive to the presence of dents, fretting, support structures, corrosion products, and other artifacts. Eddy current signal interpretation is further complicated by cracking geometries more complex than a single axial crack. Although there has been limited success in classifying and sizing defects through artificial neural networks, the ability to predict tubing integrity has, so far, eluded modelers. In large part, this lack of success stems from an inability to distinguish crack signals from those arising from artifacts. We present here a new signal processing technique that deconvolves raw eddy current voltage signals into separate signal contributions from different sources, which allows signals associated with a dominant crack to be identified. The signal deconvolution technique, combined with artificial neural network modeling, significantly improves the prediction of tube burst pressure from bobbin-coil eddy current measurements of steam generator tubing.

  13. Tests of a robust eddy correlation system for sensible heat flux

    NASA Astrophysics Data System (ADS)

    Blanford, J. H.; Gay, L. W.

    1992-03-01

    Sensible heat flux estimates from a simple, one-propeller eddy correlation system (OPEC) were compared with those from a sonic anemometer eddy correlation system (SEC). In accordance with similarity theory, the performance of the OPEC system improved with increasing height of the sensor above the surface. Flux totals from the two systems at sites with adequate fetch were in excellent agreement after frequency response corrections were applied. The propeller system appears suitable for long periods of unattended measurement. The sensible heat flux measurements can be combined with net radiation and soil heat flux measurements to estimate latent heat as a residual in the surface energy balance.

  14. Remote field eddy current technique - Phantom exciter model calculations

    NASA Astrophysics Data System (ADS)

    Atherton, D. L.; Czura, W.

    1993-03-01

    High resolution results of finite element calculations for remote field eddy current 'phantom exciter' simulations of slit defect interactions using single through wall transit are presented. These show that fine circumferential slits cause almost no field perturbations in the case of nonferromagnetic tubes but big perturbations in ferromagnetic tubes where high magnetic H fields occur in the slits. Defect-induced magnetic field perturbations must therefore be considered in addition to eddy current perturbations when ferromagnetic materials are inspected, particularly in the case of fine slits orthogonal to the magnetic field direction. Additional details seen are the funnelling of energy into slits in ferromagnetic pipes and precursor disturbances of fields approaching defects. It is suggested that these are due to the reflection of the electromagnetic waves dictated by boundary conditions at the near-side defect boundary.

  15. Parametric Studies and Optimization of Eddy Current Techniques through Computer Modeling

    SciTech Connect

    Todorov, E. I.

    2007-03-21

    The paper demonstrates the use of computer models for parametric studies and optimization of surface and subsurface eddy current techniques. The study with high-frequency probe investigates the effect of eddy current frequency and probe shape on the detectability of flaws in the steel substrate. The low-frequency sliding probe study addresses the effect of conductivity between the fastener and the hole, frequency and coil separation distance on detectability of flaws in subsurface layers.

  16. Aquatic eddy correlation: quantifying the artificial flux caused by stirring-sensitive O2 sensors.

    PubMed

    Holtappels, Moritz; Noss, Christian; Hancke, Kasper; Cathalot, Cecile; McGinnis, Daniel F; Lorke, Andreas; Glud, Ronnie N

    2015-01-01

    In the last decade, the aquatic eddy correlation (EC) technique has proven to be a powerful approach for non-invasive measurements of oxygen fluxes across the sediment water interface. Fundamental to the EC approach is the correlation of turbulent velocity and oxygen concentration fluctuations measured with high frequencies in the same sampling volume. Oxygen concentrations are commonly measured with fast responding electrochemical microsensors. However, due to their own oxygen consumption, electrochemical microsensors are sensitive to changes of the diffusive boundary layer surrounding the probe and thus to changes in the ambient flow velocity. The so-called stirring sensitivity of microsensors constitutes an inherent correlation of flow velocity and oxygen sensing and thus an artificial flux which can confound the benthic flux determination. To assess the artificial flux we measured the correlation between the turbulent flow velocity and the signal of oxygen microsensors in a sealed annular flume without any oxygen sinks and sources. Experiments revealed significant correlations, even for sensors designed to have low stirring sensitivities of ~0.7%. The artificial fluxes depended on ambient flow conditions and, counter intuitively, increased at higher velocities because of the nonlinear contribution of turbulent velocity fluctuations. The measured artificial fluxes ranged from 2-70 mmol m(-2) d(-1) for weak and very strong turbulent flow, respectively. Further, the stirring sensitivity depended on the sensor orientation towards the flow. For a sensor orientation typically used in field studies, the artificial flux could be predicted using a simplified mathematical model. Optical microsensors (optodes) that should not exhibit a stirring sensitivity were tested in parallel and did not show any significant correlation between O2 signals and turbulent flow. In conclusion, EC data obtained with electrochemical sensors can be affected by artificial flux and we

  17. Aquatic Eddy Correlation: Quantifying the Artificial Flux Caused by Stirring-Sensitive O2 Sensors

    PubMed Central

    Holtappels, Moritz; Noss, Christian; Hancke, Kasper; Cathalot, Cecile; McGinnis, Daniel F.; Lorke, Andreas; Glud, Ronnie N.

    2015-01-01

    In the last decade, the aquatic eddy correlation (EC) technique has proven to be a powerful approach for non-invasive measurements of oxygen fluxes across the sediment water interface. Fundamental to the EC approach is the correlation of turbulent velocity and oxygen concentration fluctuations measured with high frequencies in the same sampling volume. Oxygen concentrations are commonly measured with fast responding electrochemical microsensors. However, due to their own oxygen consumption, electrochemical microsensors are sensitive to changes of the diffusive boundary layer surrounding the probe and thus to changes in the ambient flow velocity. The so-called stirring sensitivity of microsensors constitutes an inherent correlation of flow velocity and oxygen sensing and thus an artificial flux which can confound the benthic flux determination. To assess the artificial flux we measured the correlation between the turbulent flow velocity and the signal of oxygen microsensors in a sealed annular flume without any oxygen sinks and sources. Experiments revealed significant correlations, even for sensors designed to have low stirring sensitivities of ~0.7%. The artificial fluxes depended on ambient flow conditions and, counter intuitively, increased at higher velocities because of the nonlinear contribution of turbulent velocity fluctuations. The measured artificial fluxes ranged from 2 - 70 mmol m-2 d-1 for weak and very strong turbulent flow, respectively. Further, the stirring sensitivity depended on the sensor orientation towards the flow. For a sensor orientation typically used in field studies, the artificial flux could be predicted using a simplified mathematical model. Optical microsensors (optodes) that should not exhibit a stirring sensitivity were tested in parallel and did not show any significant correlation between O2 signals and turbulent flow. In conclusion, EC data obtained with electrochemical sensors can be affected by artificial flux and we recommend

  18. Initial results from the Pawnee Eddy Correlation system for dry acid-deposition research. Forest Service research paper

    SciTech Connect

    Zeller, K.; Massman, W.; Stocker, D.; Fox, D.G.; Stedman, D.

    1988-01-01

    The Pawnee Grassland Eddy Correlation Dry Deposition Project is described. Instrumentation, methods of analysis, and initial data and research findings are presented. Data from this eddy correlation system show agreement with: previously observations of deposition velocities for atmospheric ozone, NO/sub 2/ and NOx; micrometeorological theory; micrometeorological site characteristics.

  19. The eddy-current technique for nondestructive evaluation of generator retaining rings: Feasibility study: Interim report

    SciTech Connect

    Elmo, P.M.; Nottingham, L.D.

    1988-05-01

    An evaluation of the feasibility of using eddy current nondestructive inspection techniques to detect intergranular stress corrosion in generator rotor retaining rings was conducted by the EPRI NDE Center. Experiments were conducted using a bend-bar containing representative stress corrosion damage, a calibration block containing electrical discharge machined (EDM) notches, and four retired retaining rings containing EDM notches and stress corrosion damage. An eddy current transducer transport was designed and fabricated to interface with an existing computer-controlled, two-axis positioner and digital eddy current data acquisition system. Test results of experiments performed with this equipment on the retaining ring test-bed provided experimental validation of the eddy current method's feasibility as a retaining ring inspection method. Details are given of the system and its performance under laboratory and simulated service-inspection conditions. 9 refs., 47 figs.

  20. Using the Cross-Correlation Function to Evaluate the Quality of Eddy-Covariance Data

    NASA Astrophysics Data System (ADS)

    Qi, Yongfeng; Shang, Xiaodong; Chen, Guiying; Gao, Zhiqiu; Bi, Xueyan

    2015-11-01

    A cross-correlation test is proposed for evaluating the quality of 30-min eddy-covariance data. Cross-correlation as a function of time lag is computed for vertical velocity paired with temperature, humidity, and carbon dioxide concentration. High quality data have a dominant peak at zero time lag and approach zero within a time lag of 20 s. Poor quality data have erratic cross-correlation functions, which indicates that the eddy flux may no longer represent the energy and mass exchange between the atmospheric surface layer and the canopy, and such data should be rejected in post-data analyses. Eddy-covariance data over grassland in July 2004 are used to evaluate the proposed test. The results show that 17, 29, and 36 % of the available data should be rejected because of poor quality measurements of sensible heat, latent heat, and CO2 fluxes, respectively. The rejected data mainly occurred on calm nights and day/night transitions when the atmospheric surface layer became stable or neutrally stratified. We found no friction velocity (u_*) threshold below which all data should be rejected, a test that many other studies have implemented for rejecting questionable data. We instead found that some data with low u_* were reliable, whereas other data with higher u_* were not. The poor quality measurements collected under less than ideal conditions were replaced by using the mean diurnal variation gap-filling method. The correction for poor quality data shifted the daily average CO2 flux by +0.34 g C m^{-2} day^{-1}. After applying the quality-control test, the eddy CO2 fluxes did not display a clear dependence on u_*. The results suggest that the cross-correlation test is a potentially valuable step in evaluating the quality of eddy-covariance data.

  1. On physical interpretation of two dimensional time-correlations regarding time delay velocities and eddy shaping

    SciTech Connect

    Fedorczak, N.; Manz, P.; Thakur, S. C.; Xu, M.; Tynan, G. R.; Xu, G. S.; Liu, S. C.

    2012-12-15

    Time delay estimation (TDE) techniques are frequently used to estimate the flow velocity from fluctuating measurements. Tilted structures carried by the flow lead to misinterpretation of the time delays in terms of velocity direction and amplitude. It affects TDE measurements from probes, and is also intrinsically important for beam emission spectroscopy and gas puff imaging measurements. Local eddy shapes estimated from 2D fluctuating field are necessary to gain a more accurate flow estimate from TDE, as illustrated by Langmuir probe array measurements. A least square regression approach is proposed to estimate both flow field and shaping parameters. The technique is applied to a test case built from numerical simulation of interchange fluctuations. The local eddy shape does not only provide corrections for the velocity field but also quantitative information about the statistical interaction mechanisms between local eddies and E Multiplication-Sign B flow shear. The technique is then tested on gaz puff imaging data collected at the edge of EAST tokamak plasmas. It is shown that poloidal asymmetries of the fluctuation fields-velocity and eddy shape-are consistent at least qualitatively with a ballooning type of turbulence immersed in a radially sheared equilibrium flow.

  2. Temperature and humidity flux-variance relations determined by one-dimensional eddy correlation

    NASA Astrophysics Data System (ADS)

    Weaver, Harold L.

    1990-10-01

    It may be possible to estimate surface fluxes of scalar quantities from measurement of their variance and mean wind speed. The flux-variance relation for temperature and humidity was investigated over prairie and desert-shrub plant communities. Fluxes were measured by one-dimensional eddy correlation, humidity by fast-response wet-bulb psychrometers and Krypton open-path hygrometers, temperature by fine-wire thermocouples, and mean windspeed by a cup anemometer. The quality of the flux-variance relation proved to be good enough for application to flux measurement. Regressions of flux estimated by the variance technique versus measured flux usually had r 2 values greater than 0.97 for sensible heat flux and greater than 0.88 for water vapor flux. More uniform surfaces tended to yield the same flux-variance relations except when fluxes were small. This exception supported the hypothesis that sparse sources of flux may increase variance downwind. Nonuniform surfaces yielded flux-variance relations that were less predictable, although reasonably accurate once determined. The flux-variance relation for humidity was quite variable over dry surfaces with senescent vegetation.

  3. Dry Deposition of Fine Aerosol Nitrogen to an Agricultural Field Measured by Eddy-Correlation Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Gonzales, D. A.; Allen, J. O.

    2005-12-01

    In urban areas high emissions of reactive nitrogen species cause an increase in atmospheric aerosol nitrogen formation and deposition. This nitrogen is eventually removed from the atmosphere by wet or dry deposition, with dry deposition often accounting for more than half of the total deposition of particulate nitrate. Total N deposition is not adequately characterized, in part because dry deposition is difficult to measure or model. For example measured fine particle deposition to a forest canopy differs from predicted values by an order of magnitude. The eddy-correlation technique is a micrometeorological method used to directly measure fluxes from measurements made above the surface. Eddy-correlation mass spectrometry (ECMS) has been developed to directly measure aerosol particle deposition velocities from fast response aerosol concentration and wind velocity measurements. Using an Aerodyne Aerosol Mass Spectrometer (AMS), the size and composition of ambient aerosols were measured at 10~Hz. The AMS signal is proportional to non-refractory PM1.0 mass. Aerosol deposition fluxes for a given averaging period are then calculated directly as the covariance of the vertical wind velocity with the AMS signal (F = -\\overline{w'S'}). A field study was conducted to measure aerosol nitrogen dry deposition to an agricultural field immediately downwind of the Phoenix metropolitan area using eddy-correlation mass spectrometry. The study was supplemented with aerosol composition measurements including bulk deposition collectors and filter bank samplers. Here we compare the results of the flux estimates from bulk collection with inferential measurements (filter samples and modeled deposition velocities) and direct micrometeorological measurements (ECMS) in order to improve nitrogen deposition estimates.

  4. Dry Deposition of Fine Aerosol Nitrogen to an Agricultural Field Measured by Eddy-Correlation Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Gonzales, D. A.; Allen, J. O.; Smith, K. A.; Hope, D.

    2004-12-01

    In urban areas high emissions of reactive nitrogen species cause an increase in atmospheric aerosol nitrogen formation and deposition. This nitrogen is eventually removed from the atmosphere by wet or dry deposition, with dry deposition often accounting for more than half of the total deposition of particulate nitrate (Lovett, 1994). Total N deposition is not adequately characterized, in part because dry deposition is difficult to measure or model. For example measured fine particle deposition to a forest canopy differs from predicted values by an order of magnitude (Gallagher et al., 1997). The eddy-correlation technique is a micrometeorological method used to directly measure fluxes from measurements made above the surface (Wesely and Hicks, 2000). Eddy-correlation mass spectrometry (ECMS) has been developed to directly measure aerosol particle deposition velocities from fast response aerosol concentration and wind velocity measurements. Using an Aerodyne Aerosol Mass Spectrometer (AMS) (Jayne et al., 2000), the size and composition of ambient aerosols is measured at a high frequency. The AMS signal is proportional to non-refractory PM1.0 mass. Aerosol deposition fluxes for a given averaging period are then calculated directly as the covariance of the vertical wind velocity with the AMS signal (F = -/line{w'S'}). A field study was conducted to measure aerosol nitrogen dry deposition to an agricultural field immediately downwind of the Phoenix metropolitan area using eddy-correlation mass spectrometry. The study was supplemented with aerosol composition measurements including bulk deposition collectors and filter bank samplers. Bulk deposition samples and 24-hour filter samples were analyzed for ammonia and nitrogen. Here we compare the results of the flux estimates from bulk collection with inferential measurements (filter samples and modeled deposition velocities) and direct micrometeorological measurements (ECMS) in order to improve N deposition estimates.

  5. A Fast, Portable, Fiber Optic Spectrofluorometer for Eddy Correlation Flux Measurement in the Aquatic Environment

    NASA Astrophysics Data System (ADS)

    Hu, I. H.; Senft-Grupp, S.; Hemond, H.

    2014-12-01

    The measurement of chemical fluxes between natural waters and their benthic sediments by most existing methods, such as benthic chambers and sediment core incubations, is slow, cumbersome, and often inaccurate. One promising new method for determining benthic fluxes is eddy correlation (EC), a minimally invasive, in situ technique based on high-speed velocity and concentration measurements. Widespread application of EC to a large range of chemicals of interest is currently limited, however, by the availability of rapid, high-resolution chemical sensors capable of precisely measuring concentrations at a point location and at sufficient speed (several Hz). A proof of concept spectrofluorometry instrument has been created that is capable of high-frequency concentration measurements of naturally fluorescent substances. Designed with the EC application in mind, the system utilizes optical fibers to transmit excitation and emission light, enabling in situ measurements at high spatial resolution. Emitted fluorescence light is passed through a tunable monochromator before reaching a photomultiplier tube; photons are quantified by a custom miniaturized, low-power photon counting circuit board. Preliminary results indicate that individual measurements made at 100 Hz of a 10 ppm humic acid solution were precise within 10%, thus yielding a precision of the order of +/- 1% in a second. Used in an EC system, this instrument will enable flux measurements of substances such as naturally occurring fluorescent dissolved organic material (FDOM). Measurement of fluxes of FDOM is significant in its own right, and also will allow the indirect measurement of the numerous other chemical fluxes that are associated with FDOM by using tracer techniques. The use of a tunable monochromator not only allows flexibility in detection wavelength, but also enables full wavelength scans of the emission spectrum, making the spectrofluorometer a dual-function device capable of both characterizing the

  6. The in-service inspection of coated steel welds using Eddy-Current Techniques

    NASA Astrophysics Data System (ADS)

    Brown, B. J.; Zaid, M.; Picton, P. D.; Mabbutt, S. J.

    2012-05-01

    Traditionally surface crack detection in coated Ferritic Steel Welds with Eddy-Current Techniques has been difficult due to the change in material properties in the Heat Affected Zone. These typically produce signals larger than crack signals. Sophisticated probe design and construction, combined with modern electronic equipment, have largely overcome the traditional problems and now enable the advantages of Eddy-Current Techniques to be applied to In-Service Inspection of Coated Ferritic Steel Structures in the as-we!ded conditions. Specifically, the advantage of the technique is that under quantifiable conditions an inspection may now be carried out through corrosion protection systems. It is the intention of this paper to review the current information available, establish the limiting parameters of the technique and detail the practical experiments conducted to determine the extent of the limiting parameters. The results of these experiments are detailed. Having determined the limiting factors, outline testing procedures have been established together with relative sensitivity settings.

  7. Pulsed remote eddy current field array technique for nondestructive inspection of ferromagnetic tube

    NASA Astrophysics Data System (ADS)

    Yang, Binfeng; Li, Xuechao

    2010-03-01

    One pick-up coil with a large inner diameter is usually used in pulsed remote field eddy current technique, which decreases the identification ability to defect. With the purpose of overcoming this problem, array pulsed remote field eddy current technique is proposed to enhance the precision in quantification of defect. The finite element method is used to optimise the structure of probe and analyse of the influence effect of response signal with the variation of the defect depths. The results of experimental work confirm that the array pulsed remote field technique has the advantages of high precision and sensitivity, which can be used as an effective method for quantification of defect in tube.

  8. Application of Resonant Frequency Eddy Current Technique on a Shot-Peened Nickel-Based Engine-Grade Material

    SciTech Connect

    Ko, Ray T.; Sathish, Shamachary; Boehnlein, Thomas R.; Blodgett, Mark P.

    2007-03-21

    The shot peening conditions of a nickel-based engine-grade material were evaluated using a novel eddy current measurement technique. With this technique, the shift of a resonant frequency was found to be dependent on variables which also affect conventional eddy current testing. The cable effect is another important variable, which is often neglected in a routine eddy current testing, is also discussed. Experimental results showed that at high frequencies, the shot peening conditions were easily distinguishable using this frequency shift technique.

  9. Inter-comparison of ammonia fluxes obtained using the relaxed eddy accumulation technique

    NASA Astrophysics Data System (ADS)

    Hensen, A.; Nemitz, E.; Flynn, M. J.; Blatter, A.; Jones, S. K.; Sørensen, L. L.; Hensen, B.; Pryor, S.; Jensen, B.; Otjes, R. P.; Cobussen, J.; Loubet, B.; Erisman, J. W.; Gallagher, M. W.; Neftel, A.; Sutton, M. A.

    2008-10-01

    The exchange of NH3 between grassland and the atmosphere was determined using Relaxed Eddy Accumulation (REA) measurements. The use of REA is of special interest for NH3, since the determination of fluxes at one height permits multiple systems to be deployed to quantify vertical flux divergence (either due to effects of chemical production or advection). During the Braunschweig integrated experiment four different continuous-sampling REA systems were operated during a period of about 10 days and were compared against a reference provided by independent application of the Aerodynamic Gradient Method (AGM). The experiment covered episodes before, after cutting and fertilising and provided a wide range of fluxes -60 3600 ng NH3 m-2 s-1 for testing the REA systems. The REA systems showed moderate to good correlation with the AGM estimates, with r2 values for the linear regressions between 0.3 and 0.82. For the period immediately after fertilization, the REA systems showed average fluxes 20% to 70% lower than the reference. At periods with low fluxes REA and AGM can agree within a few %. Overall, the results show that the continuous REA technique can now be used to measure NH3 surface exchange fluxes. While REA requires greater analytical precision in NH3 measurement than the AGM, a key advantage of REA is that auto-referencing periods can be introduced to remove bias between sampling inlets. However, while the data here indicate differences consistent with advection effects, further improvements in sampling precision are needed to allow measurement of flux divergence. Wet chemical techniques will be developed further since they use the sticky and reactive properties of NH3 that impedes development of cheaper optical systems.

  10. Inter-comparison of ammonia fluxes obtained using the Relaxed Eddy Accumulation technique

    NASA Astrophysics Data System (ADS)

    Hensen, A.; Nemitz, E.; Flynn, M. J.; Blatter, A.; Jones, S. K.; Sørensen, L. L.; Hensen, B.; Pryor, S. C.; Jensen, B.; Otjes, R. P.; Cobussen, J.; Loubet, B.; Erisman, J. W.; Gallagher, M. W.; Neftel, A.; Sutton, M. A.

    2009-11-01

    The exchange of Ammonia (NH3) between grassland and the atmosphere was determined using Relaxed Eddy Accumulation (REA) measurements. The use of REA is of special interest for NH3, since the determination of fluxes at one height permits multiple systems to be deployed to quantify vertical flux divergence (either due to effects of chemical production or advection). During the Braunschweig integrated experiment four different continuous-sampling REA systems were operated during a period of about 10 days and were compared against a reference provided by independent application of the Aerodynamic Gradient Method (AGM). The experiment covered episodes before and after both cutting and fertilizing and provided a wide range of fluxes -60-3600 ng NH3 m-2 s-1 for testing the REA systems. The REA systems showed moderate to good correlation with the AGM estimates, with r2 values for the linear regressions between 0.3 and 0.82. For the period immediately after fertilization, the REA systems showed average fluxes 20% to 70% lower than the reference. At periods with low fluxes REA and AGM can agree within a few %. Overall, the results show that the continuous REA technique can now be used to measure NH3 surface exchange fluxes. While REA requires greater analytical precision in NH3 measurement than the AGM, a key advantage of REA is that reference sampling periods can be introduced to remove bias between sampling inlets. However, while the data here indicate differences consistent with advection effects, significant improvements in sampling precision are essential to allow robust determination of flux divergence in future studies. Wet chemical techniques will be developed further since they use the adsorptive and reactive properties of NH3 that impedes development of cheaper optical systems.

  11. Studies of the eddy structure in the lower ionosphere by the API technique

    NASA Astrophysics Data System (ADS)

    Bakhmetieva, Nataliya V.; Grigoriev, Gennadii I.; Lapin, Victor G.

    2016-07-01

    We present a new application of the API technique to study of turbulent phenomena in the lower ionosphere. The main objective of these studies is experimental diagnostics of natural ordered eddy structures at the altitudes of the mesosphere and lower thermosphere, such as those that occur when internal gravity waves propagate in stratified flows in the atmospheric boundary layer. To this end, we considered the impact of eddy motions in the mesosphere and lower thermosphere on the relaxation time and the frequency of the signal scattered by periodic irregularities. Theoretical study of eddy structures base on experiments using SURA heating facility (56,14 N; 44,1 W). It is known, artificial periodic irregularities (APIs) are formed in the field of the powerful standing wave as a result of the interference of the incident wave and reflected from the ionosphere (Belikovich et al., Ionospheric Research by Means of Artificial Periodic Irregularities - 2002. Katlenburg-Lindau, Germany. Copernicus GmbH. 160 p.). The relaxation or decay of the periodic structure is specified by the ambipolar diffusion process. The atmospheric turbulence causes reduction of the amplitude and decay time of the API scattered signal in comparison with the diffusion time. We found a relation between the eddy period and the characteristic decay time of scattered signal, for which the synchronism of the waves scattered by a periodic structure is broken. Besides, it is shown, when the eddy structure moves by a horizontal wind exists at these heights, the frequency of the radio wave scattered by API structure will periodically increase and decrease compared with the frequency of the radiated diagnostic (probing) radio-wave. The work was supported by the Russian Science Foundation under grant No 14-12-00556.

  12. Application of Eddy Current Techniques for Orbiter Reinforced Carbon-Carbon Structural Health Monitoring

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Simpson, John

    2005-01-01

    The development and application of advanced nondestructive evaluation techniques for the Reinforced Carbon-Carbon (RCC) components of the Space Shuttle Orbiter Leading Edge Structural Subsystem (LESS) was identified as a crucial step toward returning the shuttle fleet to service. In order to help meet this requirement, eddy current techniques have been developed for application to RCC components. Eddy current technology has been found to be particularly useful for measuring the protective coating thickness over the reinforced carbon-carbon and for the identification of near surface cracking and voids in the RCC matrix. Testing has been performed on as manufactured and flown RCC components with both actual and fabricated defects representing impact and oxidation damage. Encouraging initial results have led to the development of two separate eddy current systems for in-situ RCC inspections in the orbiter processing facility. Each of these systems has undergone blind validation testing on a full scale leading edge panel, and recently transitioned to Kennedy Space Center to be applied as a part of a comprehensive RCC inspection strategy to be performed in the orbiter processing facility after each shuttle flight.

  13. Pulsed remote field eddy current technique applied to non-magnetic flat conductive plates

    NASA Astrophysics Data System (ADS)

    Yang, Binfeng; Zhang, Hui; Zhang, Chao; Zhang, Zhanbin

    2013-12-01

    Non-magnetic metal plates are widely used in aviation and industrial applications. The detection of cracks in thick plate structures, such as multilayered structures of aircraft fuselage, has been challenging in nondestructive evaluation societies. The remote field eddy current (RFEC) technique has shown advantages of deep penetration and high sensitivity to deeply buried anomalies. However, the RFEC technique is mainly used to evaluate ferromagnetic tubes. There are many problems that should be fixed before the expansion and application of this technique for the inspection of non-magnetic conductive plates. In this article, the pulsed remote field eddy current (PRFEC) technique for the detection of defects in non-magnetic conducting plates was investigated. First, the principle of the PRFEC technique was analysed, followed by the analysis of the differences between the detection of defects in ferromagnetic and non-magnetic plain structures. Three different models of the PRFEC probe were simulated using ANSYS. The location of the transition zone, defect detection sensitivity and the ability to detect defects in thick plates using three probes were analysed and compared. The simulation results showed that the probe with a ferrite core had the highest detecting ability. The conclusions derived from the simulation study were also validated by conducting experiments.

  14. Impact of water use efficiency on eddy covariance flux partitioning using correlation structure analysis

    NASA Astrophysics Data System (ADS)

    Anderson, Ray; Skaggs, Todd; Alfieri, Joseph; Kustas, William; Wang, Dong; Ayars, James

    2016-04-01

    Partitioned land surfaces fluxes (e.g. evaporation, transpiration, photosynthesis, and ecosystem respiration) are needed as input, calibration, and validation data for numerous hydrological and land surface models. However, one of the most commonly used techniques for measuring land surface fluxes, Eddy Covariance (EC), can directly measure net, combined water and carbon fluxes (evapotranspiration and net ecosystem exchange/productivity). Analysis of the correlation structure of high frequency EC time series (hereafter flux partitioning or FP) has been proposed to directly partition net EC fluxes into their constituent components using leaf-level water use efficiency (WUE) data to separate stomatal and non-stomatal transport processes. FP has significant logistical and spatial representativeness advantages over other partitioning approaches (e.g. isotopic fluxes, sap flow, microlysimeters), but the performance of the FP algorithm is reliant on the accuracy of the intercellular CO2 (ci) concentration used to parameterize WUE for each flux averaging interval. In this study, we tested several parameterizations for ci as a function of atmospheric CO2 (ca), including (1) a constant ci/ca ratio for C3 and C4 photosynthetic pathway plants, (2) species-specific ci/ca-Vapor Pressure Deficit (VPD) relationships (quadratic and linear), and (3) generalized C3 and C4 photosynthetic pathway ci/ca-VPD relationships. We tested these ci parameterizations at three agricultural EC towers from 2011-present in C4 and C3 crops (sugarcane - Saccharum officinarum L. and peach - Prunus persica), and validated again sap-flow sensors installed at the peach site. The peach results show that the species-specific parameterizations driven FP algorithm came to convergence significantly more frequently (~20% more frequently) than the constant ci/ca ratio or generic C3-VPD relationship. The FP algorithm parameterizations with a generic VPD relationship also had slightly higher transpiration (5 Wm-2

  15. On the Computation of Space-Time Correlations by Large-Eddy Simulation

    NASA Technical Reports Server (NTRS)

    He, Guo-Wei; Wang, Meng; Lele, Sanjiva K.

    2003-01-01

    Numerical comparisons in decaying isotropic turbulence suggest that there exist discrepancies in time correlations evaluated by DNS and LES using eddy-viscosity-type SGS models. This is consistent with the previous observations in forced isotropic turbulence. Therefore, forcing is not the main cause of the discrepancies. Comparisons among different SGS models in the LES also indicate that the model choice affects the time correlations in the LES. The multi-scale LES method using the dynamic Smagorinsky model on the small scale equation is the most accurate of the all models, the classic Smagorinsky model is the least accurate and the dynamic Smagorinsky model and spectral eddy viscosity model give intermediate results with small differences. The generalized sweeping hypothesis implies that time correlations in decaying isotropic turbulence are mainly determined by the instantaneous energy spectra and sweeping velocities. The analysis based on the sweeping hypothesis explains the discrepancies in our numerical simulations: the LES overpredicts the decorrelation time scales because the sweeping velocities are smaller than the DNS values, and underpredicts the magnitudes of time correlations because the energy spectrum levels are lower than the DNS ones. Since the sweeping velocity is determined by the energy spectra, one concludes that an accurate prediction of the instantaneous energy spectra guarantees the accuracy of time correlations. An analytical expression of sound power spectra based on Lighthill's theory and the quasi-normal closure assumption suggests that the sound power spectra are sensitive to errors in time correlations. Small errors in time correlations can cause significant errors in the sound power spectra, which exhibit a sizable drop at moderate to high frequencies accompanied by a shift of the peaks to lower frequencies. Based on the above analysis, two possible ways to improve the acoustic power spectrum predictions can be considered. The first

  16. A comparison of short-term measurements of lake evaporation using eddy correlation and energy budget methods

    USGS Publications Warehouse

    Stannard, D.I.; Rosenberry, D.O.

    1991-01-01

    Concurrent short-term measurements of evaporation from a shallow lake, using eddy correlation and energy budget methods, indicate that sensible and latent heat flux between lake and atmosphere, and energy storage in the lake, may vary considerably across the lake. Measuring net radiation with a net radiometer on the lake appeared to be more accurate than measuring incoming radiation nearby and modeling outgoing radiation. Short-term agreement between the two evaporation measurements was obtained by using an energy storage term that was weighted to account for the area-of-influence of the eddy correlation sensors. Relatively short bursts of evaporation were indicated by the eddy correlation sensors shortly after midnight on two of three occasions. ?? 1991.

  17. Direct Measurement of Biosphere-Atmosphere Isotopic CO2 Exchange using the Eddy Covariance Technique

    NASA Astrophysics Data System (ADS)

    Griffis, T.; Sargent, S.; Tanner, B.; Greene, J.; Swiatek, E.; Baker, J.; Lee, X.

    2006-12-01

    Quantifying isotopic CO2 exchange between the biosphere and atmosphere presents a significant measurement challenge, but has the potential to provide important constraints on local, regional, and global carbon cycling. Such measurements are rare because of the difficulties quantifying CO2 isotope ratios or individual isotopomer mixing ratios at the precision and frequency required for continuous scalar flux estimation. This limitation has slowed the understanding of key isotope discrimination mechanisms and carbon cycle processes. Past approaches have indirectly estimated isotopic CO2 exchange using relaxed eddy accumulation, the flask-based isoflux method, and flux-gradient techniques. Eddy covariance is an attractive method because it has the fewest theoretical assumptions and the potential to give a direct measurement of isotopic CO2 exchange, but requires a highly sensitive and relatively fast-response instrument. To date, no such field measurements have been reported. Here, we describe the use of a closed- path tunable diode laser absorption spectroscopy system (Trace Gas Analyzer, TGA100A, Campbell Scientific Inc.) and a sampling manifold optimized for eddy covariance isotopic (C16O2, 13CO2, C18O16O) flux measurements. The sampling system was designed to preserve frequency response, to avoid excessive consumption of expensive calibration gases and, more importantly, to avoid bias between the air sample and three calibration gas measurements. Results are presented from an intensive field experiment conducted at the University of Minnesota from July 18 to September 18, 2006. The field experiment was designed to evaluate: 1) the feasibility of making continuous isotopic flux measurement over extended periods of time; 2) differences in isotopic composition of ecosystem respiration and net ecosystem CO2 exchange using the Keeling plot, flux-gradient, and eddy covariance methods, and 3) the potential for isotopic flux partitioning of net ecosystem CO2 exchange.

  18. Development of "active correlation" technique

    NASA Astrophysics Data System (ADS)

    Tsyganov, Yu. S.

    2016-01-01

    With reaching to extremely high intensities of heavy-ion beams new requirements for the detection system of the Dubna Gas-Filled Recoil Separator (DGFRS) will definitely be set. One of the challenges is how to apply the "active correlations" method to suppress beam associated background products without significant losses in the whole long-term experiment efficiency value. Different scenarios and equations to develop the method according this requirement are under consideration in the present paper. The execution time to estimate the dead time parameter associated with the optimal choice of the life-time parameter is presented.

  19. Development of Airborne Eddy-Correlation Flux Measurement Capabilities for Reactive Oxides of Nitrogen

    NASA Technical Reports Server (NTRS)

    Sandholm, Scott

    1998-01-01

    This report addresses the Tropospheric Trace Gas and Airborne Measurement Group (TTGAMG) endeavors to continue to push the evolution of the Georgia Institute of Technology's Airborne Laser Induced Fluorescence Experiment (GITALIFE) into a sensor capable of making airborne eddy correlation measurements of nitrogen oxides. It will mainly address the TTGAMG successes and failures as well as its participation in the summer 1998 Wallops Island test flights on board the P3-B. Due to the restructuring and reorganization of the TTGAMG since the original funding of this grant, some of the objectives and the deliverables can not be achieved as proposed in the original funding of this grant. Most of these changes have been driven by the passing away of John Bradshaw, the original principal investigator.

  20. Application of an eddy correlation system for the estimation of oxygen benthic fluxes in coastal permeable sediments impacted by submarine groundwater discharge

    NASA Astrophysics Data System (ADS)

    Donis, D.; Janssen, F.; Böttcher, M.; McGinnis, D.; Holtappels, M.; Wenzhöfer, F.

    2012-04-01

    Measurements of solute exchange across the sediment-water interface are crucial for marine environment monitoring. This interface has fundamental filter functions for the mass exchange between the seafloor and the water column. Being a non-invasive technique, the eddy correlation method, is probably the most accurate measurement for benthic fluxes. It does not interfere with local hydrodynamics and integrates over large areas, showing considerable advantages compared to traditional methods, i.e., microprofiles and benthic chambers. One of the most important exchange processes across the sediment-water interface is flux of oxygen, which is a predominant control factor for the biogeochemical activity in the sediment, carbon processing and the composition of benthic communities. The eddy correlation method performs simultaneous recordings of vertical velocities and oxygen concentrations at a specific distance to the seafloor and is becoming a standard method for resolving dissolved oxygen fluxes in aquatic systems. However, data treatment and interpretation, especially in shallow environments, is still challenging. One major concern in eddy correlation studies of coastal environments is how to consider surface wave motions that can dominate the turbulence range and that may bias flux calculations. A critical part of the data treatment thus is the removal of wave biases from the vertical velocity component, by separating the wave frequency oscillations (due to a tilted or miss-aligned sensor) from those containing meaningful flux contributions. Here we present in situ benthic oxygen exchange rates as determined by an eddy correlation system (ECS) and simultaneously deployed stirred benthic chambers. The study was carried out in a coastal ecosystem of the southern Baltic Sea that was impacted by low salinity groundwater discharge (Hel peninsula, Poland). Oxygen fluxes determined with ECS compared well with results from benthic chambers. Flux data and seepage rates are

  1. Development of airborne eddy-correlation flux measurement capabilities for reactive oxides of nitrogen

    NASA Technical Reports Server (NTRS)

    Bradshaw, John (Principal Investigator); Zheng, Xiaonan; Sandholm, Scott T.

    1996-01-01

    This research is aimed at producing a fundamental new research tool for characterizing the source strength of the most important compound controlling the hemispheric and global scale distribution of tropospheric ozone. Specifically, this effort seeks to demonstrate the proof-of-concept of a new general purpose laser-induced fluorescence based spectrometer for making airborne eddy-correlation flux measurements of nitric oxide (NO) and other reactive nitrogen compounds. The new all solid-state laser technology being used in this advanced sensor will produce a forerunner of the type of sensor technology that should eventually result in highly compact operational systems. The proof-of-concept sensor being developed will have over two orders-of-magnitude greater sensitivity than present-day instruments. In addition, this sensor will offer the possibility of eventual extension to airborne eddy-correlation flux measurements of nitrogen dioxide (NO2) and possibly other compounds, such as ammonia (NH3), peroxyradicals (HO2), nitrateradicals (NO3) and several iodine compounds (e.g., I and IO). Demonstration of the new sensor's ability to measure NO fluxes will occur through a series of laboratory and field tests. This proof-of-concept demonstration will show that not only can airborne fluxes of important ultra-trace compounds be made at the few parts-per-trillion level, but that the high accuracy/precision measurements currently needed for predictive models can also. These measurement capabilities will greatly enhance our current ability to quantify the fluxes of reactive nitrogen into the troposphere and significantly impact upon the accuracy of predictive capabilities to model O3's distribution within the remote troposphere. This development effort also offers a timely approach for producing the reactive nitrogen flux measurement capabilities that will be needed by future research programs such as NASA's planned 1999 Amazon Biogeochemistry and Atmospheric Chemistry

  2. Investigation of correlation classification techniques

    NASA Technical Reports Server (NTRS)

    Haskell, R. E.

    1975-01-01

    A two-step classification algorithm for processing multispectral scanner data was developed and tested. The first step is a single pass clustering algorithm that assigns each pixel, based on its spectral signature, to a particular cluster. The output of that step is a cluster tape in which a single integer is associated with each pixel. The cluster tape is used as the input to the second step, where ground truth information is used to classify each cluster using an iterative method of potentials. Once the clusters have been assigned to classes the cluster tape is read pixel-by-pixel and an output tape is produced in which each pixel is assigned to its proper class. In addition to the digital classification programs, a method of using correlation clustering to process multispectral scanner data in real time by means of an interactive color video display is also described.

  3. Flux of organic compounds from grass measured by relaxed eddy accumulation technique.

    PubMed

    Olofsson, Marcus; Ek-Olausson, Birgitta; Ljungström, Evert; Langer, Sarka

    2003-12-01

    Fluxes of some Volatile Organic Compounds (VOC) from grass were measured at a golf course in western Sweden, using the Relaxed Eddy Accumulation (REA) technique. The sampling was done by collecting VOC onto adsorbent tubes and the analysis was performed by thermal desorption followed by GC/MS. High emissions were observed after cutting. Transient fluxes of (Z)-3-hexenyl acetate (0.51 microg m(-2) s(-1)), (Z)-3-hexen-1-ol (0.14 microg m(-2) s(-1)) and (Z)-3-hexenal (0.40 microg m(-2) s(-1)) were measured, even at low temperatures. The REA technique requires a relatively large fetch area that is sometimes not available. Therefore, a procedure for correcting measured fluxes from a limited fetch is suggested. PMID:14710940

  4. Remote field eddy current technique applied to the inspection of nonmagnetic steam generator tubes

    NASA Astrophysics Data System (ADS)

    Shin, Young-Kil; Chung, Tae-Eon; Lord, William

    2001-04-01

    As steam generator (SG) tubes have aged, new and subtle degradations have appeared. Most of them start growing from outside the tubes. Since outer diameter defects might not be detected by conventional eddy current testing due to skin effect phenomena, this paper studies the feasibility of using the remote field eddy current (RFEC) technique, which has shown equal sensitivity to inner diameter (ID) and outer diameter (OD) defects in ferromagnetic pipe inspection. Finite element modeling studies show that the operating frequency needs to be increased up to a few hundred kHz in order for RFEC effects to occur in the nonmagnetic SG tube. The proper distance between exciter and sensor coils is also found to be 1.5 OD, which is half of the distance used in ferromagnetic pipe inspection. The resulting defect signals show equal sensitivity to ID and OD defects. These results demonstrate superior capability of the proposed RFEC probe compared to the differential ECT probe in detecting OD defects.

  5. Eddy Correlation Measurements of the Dry Deposition of Particles in Wintertime.

    NASA Astrophysics Data System (ADS)

    Duan, B.; Fairall, C. W.; Thomson, D. W.

    1988-05-01

    Eddy correlation measurements of the vertical fluxes of particles, momentum, heat and water vapor, were conducted over a partially snow covered field in central Pennsylvania during December 1985. The PMS ASASP-300 and CSASP-100-HV optical counters were used as sensors to measure particle-number fluxes. Overall, average dry deposition velocities for 28 half-hour runs were found to be 0.034 ± 0.014 and 0.021 ± 0.005 cm s1 for particles in two size ranges, 0.15-30 and 0.5-1.0 m, respectively. The average deposition velocity was close to results from prior wind-tunnel and theoretical investigations. These results were also comparable with those reported by other authors over grass. Relatively large sampling rates reduced the effects of counting noise on deposition measurements of 0.5-;1.0 m particles. Small correlation coefficients between vertical velocity and the particle concentration were found even after corrections for the effects of counting noise. The normalized average surface deposition velocity vds/u( for particles in diameter of 0.15-0.30 and 0.5-1.0 m appeared to be 0.006 and 0.002, respectively, in nearly neutral and stable conditions.

  6. [Research progress on urban carbon fluxes based on eddy covariance technique].

    PubMed

    Liu, Min; Fu, Yu-Ling; Yang, Fang

    2014-02-01

    Land use change and fossil fuel consumption due to urbanization have made significant effect on global carbon cycle and climate change. Accurate estimating and understanding of the carbon budget and its characteristics are the premises for studying carbon cycle and its driving mechanisms in urban system. Based on the theory of eddy covariance (EC) technique, the characteristics atmospheric boundary layer and carbon cycle in urban area, this study systematically reviewed the principles of CO2 flux monitoring in urban system with EC technique, and then summarized the problems faced in urban CO2 flux monitoring and the method for data processing and further assessment. The main research processes on urban carbon fluxes with EC technique were also illustrated. The results showed that the urban surface was mostly acting as net carbon source. The CO2 exchange between urban surface and atmosphere showed obvious diurnal, weekly and seasonal variation resulted from the vehicle exhaust, domestic heating and vegetation respiration. However, there still exist great uncertainties in urban flux measurement and its explanation due to high spatial heterogeneity and complex distributions of carbon source/sink in urban environments. In the end, we suggested that further researches on EC technique and data assessment in complex urban area should be strengthened. It was also requisite to develop models of urban carbon cycle on the basis of the system principle, to investigate the influencing mechanism and variability of urban cycle at regional scale with spatial analysis technique. PMID:24830264

  7. Very Large Eddy Simulation Technique for Noise Prediction and Control in Turbomachinery and Propulsion

    NASA Technical Reports Server (NTRS)

    Golubev, Vladimir V.

    2003-01-01

    The summer fellowship research project focused on further developing an advanced computational technique based on Very Large Eddy Simulation (VLES) for analysis and control of major sources of noise in turbomachinery and propulsion systems, including jet noise and fan noise. Major part of the work during the 10-week tenure dealt with implementing a low-order, implicit A-stable time-stepping scheme in the existing explicit VLES code of Dr. Ray Hixon. The preliminary plan of the work also included application of a new time marching formulation to the problem of viscous gust-airfoil interaction. Other research items selected for implementation (possibly in the future) included investigating a set of new subgrid turbulent models for the code, and code application to a number of test cases, including a supersonic jet and swirling flow downstream of a rotor stage.

  8. Eddy current technique applied to the nondestructive evaluation of turbine blade wall thickness

    NASA Astrophysics Data System (ADS)

    Le Bihan, Yann; Joubert, Pierre-Yves; Placko, Dominique

    2000-05-01

    The high pressure turbine blades of jet engines show internal channels designed for air cooling. These recesses define the internal walls (partitions) and external walls of the blade. The external wall thickness is a critical parameter which has to be systematically checked in order to ensure the blade strength. The thickness evaluation is usually lead by ultrasonic technique or by X-ray tomography. Nevertheless, both techniques present some drawbacks related to measurement speed and automation capability. These drawbacks are bypassed by the eddy current (EC) technique, well known for its robustness and reliability. However, the wall thickness evaluation is made difficult because of the complexity of the blade geometry. In particular, some disturbances appear in the thickness evaluation because of the partitions, which exclude the use of classical EC probes such as cup-core probe. In this paper, we show the main advantages of probes creating an uniformly oriented magnetic field in order to reduce the partition disturbances. Furthermore, we propose a measurement process allowing to separate the wall thickness parameter from the EC signals. Finally, we present some experimental results validating the proposed technique.

  9. Eddy-correlation measurements of fluxes of CO 2 and H 2O above a spruce stand

    NASA Astrophysics Data System (ADS)

    Ibrom, A.; Schütz, C.; Tworek, T.; Morgenstern, K.; Oltchev, A.; Falk, M.; Constantin, J.; Gravenhorst, G.

    1996-12-01

    Atmospheric fluxes of CO 2 and H 2O above a mature spruce stand ( Picea abies (L.) Karst.) have been investigated using the eddy- correlation technique. A closed path sensor adapted to the special requirements of long-term studies has been developed and tested. Field measurements have been performed since April 1995. Estimates of fetch showed a very narrow source area dimension under instable stratification (≤ 200 m). Fetch requirements at night are not met in some directions. Energy balance closure was influenced systematically by the wind direction indicating a substantial attenuation of the vertical wind motion by the tower (up to 40 %). Even for optimal flow directions, energy balance closure was about 88%. Intercomparison of the used ultra sonic anemometer (USAT-3) with a GILL - anemometer showed systematically lower values of vertical wind speed fluctuations (13 %). Average CO 2-fluxes ranged between -13 at noon to 3 μ mol m-2, s-1 at night in summer. In November and December the stand released CO 2 on a daily basis. A preliminary estimate of the cumulative net carbon balance over the observed period of 9 months is 4-5 t, Cha-1.

  10. Evaluation of sensible heat flux from remote sensing and eddy correlation data for two Portuguese cork-oak forests

    NASA Astrophysics Data System (ADS)

    Cunha, John; Paço, Teresa A.; Silva, Filipe Costa e.; David, Jorge S.; Pereira, João S.; Rufino, Iana; Galvão, Carlos; Valente, Fernanda

    2015-04-01

    Energy balance is a major determinant of Earth surface temperature and climate. However, the physics of energy balance computations are complex and vary in space and in time. Most of the data available on the energy balance of non-agricultural systems is from local measurements, only representative of the area around the measuring point. To overcome this, remote sensing techniques have been widely used, particularly in studies on the temporal land-cover changes and on their influences on the energy and water balances. Several remote sensors with different spatial, temporal and spectral resolutions have been used to understand these processes. In many applications, the main objective is to understand how landscape's changes over time can influence regional climate. Orbital information enables the analysis of the spatial and temporal features of the Earth's surface, and to understand the interactions between different land-cover types with topography, atmospheric and anthropogenic action. However, to test for accuracy and precision, data from satellite sensors and their derivatives need to be compared with ground-level field data. This study evaluates and tests sensible heat flux data obtained from the SEBAL algorithm using images by Thematic Mapper (TM) sensor aboard Landsat 5 satellite. These sensible heat flux data were compared with those of two ground level experiments, with the Eddy Covariance technique, in Évora and Coruche, Portugal. The footprints of the sensible heat flux measurements were calculated for six scenes of sensor TM, allowing the comparison between satellite data and surface flux data. Results showed a high correlation between sensible heat flux data derived from remote sense and ground-level measurements (R2=0.94). We conclude that the remote sensing technique is useful in estimating this energy balance component and may contribute to the understanding of vegetation dynamics.

  11. Nuclear Technology. Course 32: Nondestructive Examination (NDE) Techniques II. Module 32-6, Operation of Eddy Current Test Equipment.

    ERIC Educational Resources Information Center

    Espy, John; Selleck, Ben

    This sixth in a series of six modules for a course titled Nondestructive Examination (NDE) Techniques II details eddy current examination of steam generator tubing. The module follows a typical format that includes the following sections: (1) introduction, (2) module prerequisites, (3) objectives, (4) notes to instructor/student, (5) subject…

  12. Nuclear Technology. Course 32: Nondestructive Examination (NDE) Techniques II. Module 32-5, Fundamentals of Eddy Current Testing.

    ERIC Educational Resources Information Center

    Espy, John

    This fifth in a series of six modules for a course titled Nondestructive Examination (NDE) Techniques II describes the fundamental concepts applicable to eddy current testing in general. The module follows a typical format that includes the following sections: (1) introduction, (2) module prerequisites, (3) objectives, (4) notes to…

  13. Optimizing correlation techniques for improved earthquake location

    USGS Publications Warehouse

    Schaff, D.P.; Bokelmann, G.H.R.; Ellsworth, W.L.; Zanzerkia, E.; Waldhauser, F.; Beroza, G.C.

    2004-01-01

    Earthquake location using relative arrival time measurements can lead to dramatically reduced location errors and a view of fault-zone processes with unprecedented detail. There are two principal reasons why this approach reduces location errors. The first is that the use of differenced arrival times to solve for the vector separation of earthquakes removes from the earthquake location problem much of the error due to unmodeled velocity structure. The second reason, on which we focus in this article, is that waveform cross correlation can substantially reduce measurement error. While cross correlation has long been used to determine relative arrival times with subsample precision, we extend correlation measurements to less similar waveforms, and we introduce a general quantitative means to assess when correlation data provide an improvement over catalog phase picks. We apply the technique to local earthquake data from the Calaveras Fault in northern California. Tests for an example streak of 243 earthquakes demonstrate that relative arrival times with normalized cross correlation coefficients as low as ???70%, interevent separation distances as large as to 2 km, and magnitudes up to 3.5 as recorded on the Northern California Seismic Network are more precise than relative arrival times determined from catalog phase data. Also discussed are improvements made to the correlation technique itself. We find that for large time offsets, our implementation of time-domain cross correlation is often more robust and that it recovers more observations than the cross spectral approach. Longer time windows give better results than shorter ones. Finally, we explain how thresholds and empirical weighting functions may be derived to optimize the location procedure for any given region of interest, taking advantage of the respective strengths of diverse correlation and catalog phase data on different length scales.

  14. Nitrous oxide emissions from a commercial cornfield (Zea mays) measured using the eddy covariance technique

    NASA Astrophysics Data System (ADS)

    Huang, H.; Wang, J.; Hui, D.; Miller, D. R.; Bhattarai, S.; Dennis, S.; Smart, D.; Sammis, T.; Reddy, K. C.

    2014-12-01

    Increases in observed atmospheric concentrations of the long-lived greenhouse gas nitrous oxide (N2O) have been well documented. However, information on event-related instantaneous emissions during fertilizer applications is lacking. With the development of fast-response N2O analyzers, the eddy covariance (EC) technique can be used to gather instantaneous measurements of N2O concentrations to quantify the exchange of nitrogen between the soil and atmosphere. The objectives of this study were to evaluate the performance of a new EC system, to measure the N2O flux with the system, and finally to examine relationships of the N2O flux with soil temperature, soil moisture, precipitation, and fertilization events. An EC system was assembled with a sonic anemometer and a fast-response N2O analyzer (quantum cascade laser spectrometer) and applied in a cornfield in Nolensville, Tennessee during the 2012 corn growing season (4 April-8 August). Fertilizer amounts totaling 217 kg N ha-1 were applied to the experimental site. Results showed that this N2O EC system provided reliable N2O flux measurements. The cumulative emitted N2O amount for the entire growing season was 6.87 kg N2O-N ha-1. Seasonal fluxes were highly dependent on soil moisture rather than soil temperature. This study was one of the few experiments that continuously measured instantaneous, high-frequency N2O emissions in crop fields over a growing season of more than 100 days.

  15. Sediment-water gas exchange in two Swedish lakes measured by Eddy Correlation

    NASA Astrophysics Data System (ADS)

    Kokic, J.; Sahlee, E.; Brand, A.; Sobek, S.

    2014-12-01

    Lake sediments are hotspots for carbon (C) cycling, acting both as sinks and sources through C burial and production of carbon dioxide (CO2) and methane. The fate of this CO2 in the water column is controlled by bottom water turbulence, a factor not accounted for in current estimates of sediment CO2 fluxes. This study is aimed to quantify the turbulent CO2 flux across the sediment-water interface (SWI) by measuring the oxygen (O2) flux with the non-invasive Eddy Correlation (EC) method that combines measurements of 3D velocity (ADV) and O2 fluctuations with a microsensor. Using the metabolic relation (respiratory quotient, RQ) of O2 and CO2 derived from a sediment incubation experiment we present the first estimates of turbulent lake sediment CO2 flux from two boreal lakes in Sweden (Erssjön and Erken, 0.07 km2 and 23.7 km2 respectively). Only ~10 % of the total dataset was extracted for flux calculations due to poor signal-to-noise ratio in the velocity and O2 signals. The sediment in Lake Erssjön was both consuming and producing O2, related to bacterial respiration and photosynthesis. Mean O2 flux was -0.19 and 0.17 μmol O2 m-2 sec-1, comparing to 0.04 μmol O2 m-2 sec-1 derived from the sediment incubation experiment. Fluxes for Lake Erken are still to be determined. Experimentally derived RQ of the both lake sediments were close to unity implying that in-situ CO2 fluxes are of similar magnitude as O2 fluxes, varying between -0.15 and 0.18 μmol C m-2 sec-1. The first measurement of turbulent sediment O2 flux and estimate of turbulent CO2 flux from a small boreal lake show higher and more variable fluxes than previously found in experimental studies. The low amount of data extracted for flux calculations (~10%) point towards the difficulties in EC measurement in low-turbulence environments. On-going work focuses on the turbulence structure in lakes and its influence on the gas fluxes at the SWI.

  16. Non destructive technique for cracks detection by an eddy current in differential mode for steel frames

    SciTech Connect

    Harzalla, S. Chabaat, M.; Belgacem, F. Bin Muhammad

    2014-12-10

    In this paper, a nondestructive technique is used as a tool to control cracks and microcracks in materials. A simulation by a numerical approach such as the finite element method is employed to detect cracks and eventually; to study their propagation using a crucial parameter such as the stress intensity factor. This approach has been used in the aircraft industry to control cracks. Besides, it makes it possible to highlight the defects of parts while preserving the integrity of the controlled products. On the other side, it is proven that the reliability of the control of defects gives convincing results for the improvement of the quality and the safety of the material. Eddy current testing (ECT) is a standard technique in industry for the detection of surface breaking flaws in magnetic materials such as steels. In this context, simulation tools can be used to improve the understanding of experimental signals, optimize the design of sensors or evaluate the performance of ECT procedures. CEA-LIST has developed for many years semi-analytical models embedded into the simulation platform CIVA dedicated to non-destructive testing. The developments presented herein address the case of flaws located inside a planar and magnetic medium. Simulation results are obtained through the application of the Volume Integral Method (VIM). When considering the ECT of a single flaw, a system of two differential equations is derived from Maxwell equations. The numerical resolution of the system is carried out using the classical Galerkin variant of the Method of Moments. Besides, a probe response is calculated by application of the Lorentz reciprocity theorem. Finally, the approach itself as well as comparisons between simulation results and measured data are presented.

  17. Non destructive technique for cracks detection by an eddy current in differential mode for steel frames

    NASA Astrophysics Data System (ADS)

    Harzalla, S.; Belgacem, F. Bin Muhammad; Chabaat, M.

    2014-12-01

    In this paper, a nondestructive technique is used as a tool to control cracks and microcracks in materials. A simulation by a numerical approach such as the finite element method is employed to detect cracks and eventually; to study their propagation using a crucial parameter such as the stress intensity factor. This approach has been used in the aircraft industry to control cracks. Besides, it makes it possible to highlight the defects of parts while preserving the integrity of the controlled products. On the other side, it is proven that the reliability of the control of defects gives convincing results for the improvement of the quality and the safety of the material. Eddy current testing (ECT) is a standard technique in industry for the detection of surface breaking flaws in magnetic materials such as steels. In this context, simulation tools can be used to improve the understanding of experimental signals, optimize the design of sensors or evaluate the performance of ECT procedures. CEA-LIST has developed for many years semi-analytical models embedded into the simulation platform CIVA dedicated to non-destructive testing. The developments presented herein address the case of flaws located inside a planar and magnetic medium. Simulation results are obtained through the application of the Volume Integral Method (VIM). When considering the ECT of a single flaw, a system of two differential equations is derived from Maxwell equations. The numerical resolution of the system is carried out using the classical Galerkin variant of the Method of Moments. Besides, a probe response is calculated by application of the Lorentz reciprocity theorem. Finally, the approach itself as well as comparisons between simulation results and measured data are presented.

  18. Development of Eddy Current Techniques for Detection of Deep Fatigue Cracks in Multi-Layer Airframe Components

    NASA Technical Reports Server (NTRS)

    Wincheski, Russell A.

    2008-01-01

    Thick, multi-layer aluminum structure has been widely used in aircraft design in critical wing splice areas. The multi-layer structure generally consists of three or four aluminum layers with different geometry and varying thickness, which are held together with fasteners. The detection of cracks under fasteners with ultrasonic techniques in subsurface layers away from the skin is impeded primarily by interlayer bonds and faying sealant condition. Further, assessment of such sealant condition is extremely challenging in terms of complexity of structure, limited access, and inspection cost. Although Eddy current techniques can be applied on in-service aircraft from the exterior of the skin without knowing sealant condition, the current eddy current techniques are not able to detect defects with wanted sensitivity. In this work a series of low frequency eddy current probes have been designed, fabricated and tested for this application. A probe design incorporating a shielded magnetic field sensor concentrically located in the interior of a drive coil has been employed to enable a localized deep diffusion of the electromagnetic field into the part under test. Due to the required low frequency inspections, probes have been testing using a variety of magnetic field sensors (pickup coil, giant magneto-resistive, anisotropic magneto-resistive, and spin-dependent tunneling). The probe designs as well as capabilities based upon a target inspection for sub-layer cracking in an airframe wing spar joint is presented.

  19. Active Correlation Technique: Status and Development

    SciTech Connect

    Tsyganov, Yury

    2010-04-30

    During the recent years, at the FLNR (JINR) a successful cycle of experiments has been accomplished on the synthesis of the superheavy elements with Z = 112-118 with {sup 48}Ca beam. From the viewpoint of the detection of rare decays and background suppression, this success was achieved due to the application of a new radical technique--the method of active correlations. The method employs search in a real-time mode for a pointer to a probable correlation like recoil-alpha for switching the beam off. In the case of detection in the same detector strip an additional alpha-decay event, of 'beam OFF' time interval is prolonged automatically.

  20. Development of Eddy Current Techniques for the Detection of Cracking in Space Shuttle Primary Reaction Control Thrusters

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz A.; Simpson, John W.; Koshti, Ajay

    2007-01-01

    A recent identification of cracking in the Space Shuttle Primary Reaction Control System (PRCS) thrusters triggered an extensive nondestructive evaluation effort to develop techniques capable of identifying such damage on installed shuttle hardware. As a part of this effort, specially designed eddy current probes inserted into the acoustic cavity were explored for the detection of such flaws and for evaluation of the remaining material between the crack tip and acoustic cavity. The technique utilizes two orthogonal eddy current probes which are scanned under stepper motor control in the acoustic cavity to identify cracks hidden with as much as 0.060 remaining wall thickness to the cavity. As crack growth rates in this area have been determined to be very slow, such an inspection provides a large safety margin for continued operation of the critical shuttle hardware. Testing has been performed on thruster components with both actual and fabricated defects. This paper will review the design and performance of the developed eddy current inspection system. Detection of flaws as a function of remaining wall thickness will be presented along with the proposed system configuration for depot level or on-vehicle inspection capabilities.

  1. Development of Eddy Current Technique for the Detection of Stress Corrosion Cracking in Space Shuttle Primary Reaction Control Thrusters

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Simpson, John; Koshti, Ajay

    2006-01-01

    A recent identification of stress corrosion cracking in the Space Shuttle Primary Reaction Control System (PRCS) thrusters triggered an extensive nondestructive evaluation effort to develop techniques capable of identifying such damage on installed shuttle hardware. As a part of this effort, specially designed eddy current probes inserted into the acoustic cavity were explored for the detection of such flaws and for evaluation of the remaining material between the crack tip and acoustic cavity. The technique utilizes two orthogonal eddy current probes which are scanned under stepper motor control in the acoustic cavity to identify cracks hidden with as much as 0.060 remaining wall thickness to the cavity. As crack growth rates in this area have been determined to be very slow, such an inspection provides a large safety margin for continued operation of the critical shuttle hardware. Testing has been performed on thruster components with both actual and fabricated defects. This paper will review the design and performance of the developed eddy current inspection system. Detection of flaws as a function of remaining wall thickness will be presented along with the proposed system configuration for depot level or on-vehicle inspection capabilities.

  2. Correlative visualization techniques for multidimensional data

    NASA Technical Reports Server (NTRS)

    Treinish, Lloyd A.; Goettsche, Craig

    1989-01-01

    Critical to the understanding of data is the ability to provide pictorial or visual representation of those data, particularly in support of correlative data analysis. Despite the advancement of visualization techniques for scientific data over the last several years, there are still significant problems in bringing today's hardware and software technology into the hands of the typical scientist. For example, there are other computer science domains outside of computer graphics that are required to make visualization effective such as data management. Well-defined, flexible mechanisms for data access and management must be combined with rendering algorithms, data transformation, etc. to form a generic visualization pipeline. A generalized approach to data visualization is critical for the correlative analysis of distinct, complex, multidimensional data sets in the space and Earth sciences. Different classes of data representation techniques must be used within such a framework, which can range from simple, static two- and three-dimensional line plots to animation, surface rendering, and volumetric imaging. Static examples of actual data analyses will illustrate the importance of an effective pipeline in data visualization system.

  3. Eddy correlation measurements of methane fluxes using a tunable diode laser at the Kinosheo Lake tower site during the Northern Wetlands Study (NOWES)

    NASA Technical Reports Server (NTRS)

    Edwards, G. C.; Neumann, H. H.; Den Hartog, G.; Thurtell, G. W.; Kidd, G.

    1994-01-01

    As part of the Canadian Northern Wetlands Study (NOWES) measurements of methane flux were made at the Kinosheo Lake tower site for a 1-month period during the 1990 summer intensive. The measurements were made with a diode-laser-based methane sensor using the eddy correlation technique. Measurements of the methane fluxes were made at two levels, 5 or 18 m. Approximately 900 half-hour average methane flux measurements were obtained. Weak temporal and diurnal trends were observed in the data. Fluxes averaged over the study period showed an overall methane emission of 16 mg CH4 m(exp -2)/d with a daytime average of 20 mg CH4 m(exp -2)/d and a nighttime average of 9 mg CH4 m(exp -2)/d. The effect of emission footprint was evident in the data. A strong relationship between the daily average methane flux and wet bog temperature at 20-cm depth was observed.

  4. Nitrous oxide emissions from a commercial cornfield (Zea mays) measured using the eddy-covariance technique

    NASA Astrophysics Data System (ADS)

    Huang, H.; Wang, J.; Hui, D.; Miller, D. R.; Bhattarai, S.; Dennis, S.; Smart, D.; Sammis, T.; Reddy, K. C.

    2014-08-01

    Increases in observed atmospheric concentrations of the long-lived greenhouse gas, nitrous oxide (N2O), have been well documented. However, information on event-related instantaneous emissions during fertilizer applications is lacking. With the development of fast-response N2O analyzers, the eddy covariance (EC) technique can be used to gather instantaneous measurements of N2O concentrations to quantify the exchange of nitrogen between the soil and atmosphere. The objectives of this study were to evaluate the performance of a new EC system, to measure the N2O flux with the system, and finally to examine relationships of the N2O flux with soil temperature, soil moisture, precipitation, and fertilization events. We assembled an EC system that included a sonic anemometer and a fast-response N2O analyzer (quantum cascade laser spectrometer) in a cornfield in Nolensville, Tennessee during the 2012 corn growing season (4 April-8 August). Fertilizer amounts totaling 217 kg N ha-1 were applied to the experimental site. The precision of the instrument was 0.066 ppbv for 10 Hz measurements. The seasonal mean detection limit of the N2O flux measurements was 2.10 ng N m-2 s-1. This EC system can be used to provide reliable N2O flux measurements. The cumulative emitted N2O for the entire growing season was 6.87 kg N2O-N ha-1. The 30 min average N2O emissions ranged from 0 to 11 100 μg N2O{-}N m-2 h-1 (mean = 257.5, standard deviation = 817.7). Average daytime emissions were much higher than night emissions (278.8 ± 865.8 vs. 100.0 ± 210.0 μg N2O-N m-2 h-1). Seasonal fluxes were highly dependent on soil moisture rather than soil temperature, although the diurnal flux was positively related to soil temperature. This study was one of the few experiments that continuously measured instantaneous, high-frequency N2O emissions in crop fields over a growing season of more than 100 days.

  5. New cyberinfrastructure for studying land-atmosphere interactions using eddy covariance techniques

    NASA Astrophysics Data System (ADS)

    Jaimes, A.; Salayandia, L.; Gallegos, I.; Gates, A. Q.; Tweedie, C.

    2010-12-01

    Eddy covariance (EC) methods are used to measure the exchanges of mass and energy across the atmospheric boundary layer. EC is the basis of several large national and international flux networks of micrometeorological tower sites (i.e. FLUXNET, AMERIFLUX), that provide continuous observations and measurements to understand and quantify the spatial and temporal variations in carbon storage in plants, soils, and the exchanges of carbon dioxide, water vapor, and energy, in major vegetation types across a range of disturbance historic and climatic conditions. A consistent quality assurance and quality control (QA/QC) procedure of micrometeorological data is essential for measurement networks such as these. Although, a QA/QC procedure is very much a site-specific activity, there are a variety of components available to implement Eddy covariance methods, as well as, limited documentation about best practices or standards, results in different approaches being adopted throughout data capturing sites. In some cases, this can lead to a limited or inefficient data reusability and knowledge transfer among related projects. The amount of data being collected is rapidly increasing, and the ability to evaluate proper instrument operation and data accuracy is critical to ensure the results are not bias due to factors such as, instrument malfunction, erroneous definition of optimal measurement ranges, calibration errors and differences, and environmental conditions that can affect data quality (i.e. wind directions are not from the footprint of interest, heavy precipitation, dust/snow storms, etc). This study presents findings from Cyberinfrastructure research conducted on a data stream from a newly established Eddy Covariance Tower, located on the Jornada basin Experimental Range (JER), Las Cruces, NM. Specifically, property characterization and specification was developed under a series of laboratory and field experiments. Our intent was to characterize thresholds and range

  6. Correlative stitching interferometer and its key techniques

    NASA Astrophysics Data System (ADS)

    Yu, Yingjie; Chen, Mingyi

    2002-06-01

    Correlative stitching is on the fact that the same area has the same information. This testing thought is meaningful in extending spatial measurement ranges, keeping high resolutions, high precision and low cost. So in order to test large-scale optical workpiece, people are designing large-scale interferometer, at the same time, they are also designing stitching interferometer. The keys to realize stitching measurement are to obtain high precision wavefront of each sub-aperture and apply appropriate stitching algorithm. There are many techniques to test sub-apertures, among which phase-shifting technique has high precision, and is applied widely. How to reduce its system error is a central problem. The paper will utilize difference of two testing results to remove the system error. How to reduce the accumulative error is a key problem in stitching. The paper will apply the stitching algorithm in Descartes coordinates presented by M. Otsubo and K. Okada to realize the connecting of sub-apertures. And the paper presents a method to deal with the main random errors in sub-aperture testing. Finally, the paper does some tests.

  7. Applying a simple three-dimensional eddy correlation system for latent and sensible heat flux to contrasting forest canopies

    NASA Astrophysics Data System (ADS)

    Bernhofer, Ch.

    1992-06-01

    A simple eddy correlation system is presented that allows on-line calculation of latent and sensible heat fluxes. The system is composed of a three dimensional propeller anemometer, a thermocouple and a capacitance relative humidity sensor. Results from two contrasting sites demonstrate the capability of the system to measure turbulent fluxes under varying conditions. A dry mixed (dominantly coniferous) forest in hilly terrain in Austria is compared to a well irrigated, heavily transpiring, deciduous pecan orchard in the Southwest of the US. The US site shows insufficient closure of the energy balance that is attributed to non-turbulent fluxes under advective conditions in a stable boundary layer (Blanford et al., 1991) while the Austrian site exhibits almost perfect closure with the use of the very same instruments when the boundary layer is convective and advection is negligible.

  8. A comparison of methane emission measurements using Eddy Covariance and manual and automated chamber-based techniques in Tibetan Plateau alpine wetland.

    PubMed

    Yu, Lingfei; Wang, Hao; Wang, Guangshuai; Song, Weimin; Huang, Yao; Li, Sheng-Gong; Liang, Naishen; Tang, Yanhong; He, Jin-Sheng

    2013-10-01

    Comparing of different CH4 flux measurement techniques allows for the independent evaluation of the performance and reliability of those techniques. We compared three approaches, the traditional discrete Manual Static Chamber (MSC), Continuous Automated Chamber (CAC) and Eddy Covariance (EC) methods of measuring the CH4 fluxes in an alpine wetland. We found a good agreement among the three methods in the seasonal CH4 flux patterns, but the diurnal patterns from both the CAC and EC methods differed. While the diurnal CH4 flux variation from the CAC method was positively correlated with the soil temperature, the diurnal variation from the EC method was closely correlated with the solar radiation and net CO2 fluxes during the daytime but was correlated with the soil temperature at nighttime. The MSC method showed 25.3% and 7.6% greater CH4 fluxes than the CAC and EC methods when measured between 09:00 h and 12:00 h, respectively. PMID:23838484

  9. Combined investigation of Eddy current and ultrasonic techniques for composite materials NDE

    SciTech Connect

    Davis, C.W.; Nath, S.; Fulton, J.P.; Namkung, M.

    1993-12-31

    Advanced composites are not without trade-offs. Their increased designability brings an increase in the complexity of their internal geometry and, as a result, an increase in the number of failure modes associated with a defect. When two or more isotropic materials are combined in a composite, the isotropic material failure modes may also combine. In a laminate, matrix delamination, cracking and crazing, and voids and porosity, will often combine with fiber breakage, shattering, waviness, and separation to bring about ultimate structural failure. This combining of failure modes can result in defect boundaries of different sizes, corresponding to the failure of each structural component. This paper discusses a dual-technology NDE (Non Destructive Evaluation) (eddy current (EC) and ultrasonics (UT)) study of graphite/epoxy (gr/ep) laminate samples. Eddy current and ultrasonic raster (Cscan) imaging were used together to characterize the effects of mechanical impact damage, high temperature thermal damage and various types of inserts in gr/ep laminate samples of various stacking sequences.

  10. Combined investigation of Eddy current and ultrasonic techniques for composite materials NDE

    NASA Technical Reports Server (NTRS)

    Davis, C. W.; Nath, S.; Fulton, J. P.; Namkung, M.

    1993-01-01

    Advanced composites are not without trade-offs. Their increased designability brings an increase in the complexity of their internal geometry and, as a result, an increase in the number of failure modes associated with a defect. When two or more isotropic materials are combined in a composite, the isotropic material failure modes may also combine. In a laminate, matrix delamination, cracking and crazing, and voids and porosity, will often combine with fiber breakage, shattering, waviness, and separation to bring about ultimate structural failure. This combining of failure modes can result in defect boundaries of different sizes, corresponding to the failure of each structural component. This paper discusses a dual-technology NDE (Non Destructive Evaluation) (eddy current (EC) and ultrasonics (UT)) study of graphite/epoxy (gr/ep) laminate samples. Eddy current and ultrasonic raster (Cscan) imaging were used together to characterize the effects of mechanical impact damage, high temperature thermal damage and various types of inserts in gr/ep laminate samples of various stacking sequences.

  11. Prospects and Techniques for Eddy-Resolving Acoustic Tomography in the Eastern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Caruthers, J. W.; Nechaev, D.; Roman, D. A.; Sidorovskaia, N. A.; Ioup, G. E.; Ioup, J.; Yaremchuk, M.

    2007-05-01

    For several decades monitoring and modeling the dynamics and physical structure of the Gulf of Mexico have been major efforts undertaken by oceanographers of the United States and other American countries. There are very interesting physical oceanographic features in the Gulf, not the least of which are the Gulf Loop Current and the eddies it spawns. Satellite sensing of IR and altimeter imagery has been a major input to modeling those features. Such efforts are very important to the economy and well being of much of the United States and Mexico, including fisheries, mineral economies, hurricane strengths and paths in the summer, and severe snow storms in the eastern US in the winter. A major shortcoming of the present monitoring of the Gulf is the lack of subsurface input to the dynamic models of the Gulf. Acoustic tomography is a viable means of providing that missing input. Several universities have come together to investigate the prospects for establishing a Gulf Eddy Monitoring System (GEMS) for the deep eastern half of the Gulf using acoustic tomography. The group has conducted several acoustics experiments and propagation studies to determine the feasibility of long-range propagation in the eastern Gulf and the mitigation of adverse effects on marine mammal populations in that region under the Office of Naval Research project entitled the Littoral Acoustic Demonstration Center (LADC). The group has also convened an invited session for the 9th World Multiconference on Systemics, Cybernetics and Informatics (WMSCI 2005) Orlando, FL, July 2005. This paper discusses prospects for establishing the GEMS tomographic system, its technical characteristics, and its contributions to advancing the knowledge of the dynamics of the Gulf. This presentation will concentrate on the characteristics of a single-slice tomographic system, called GEMS Phase I, across the approaches to the DeSoto Canyon in the northeastern Gulf and its prospect for monitoring the movements of

  12. Nonlinear, non-stationary image processing technique for eddy current NDE

    NASA Astrophysics Data System (ADS)

    Yang, Guang; Dib, Gerges; Kim, Jaejoon; Zhang, Lu; Xin, Junjun; Udpa, Lalita

    2012-05-01

    Automatic analysis of eddy current (EC) data has facilitated the analysis of large volumes of data generated in the inspection of steam generator tubes in nuclear power plants. The traditional procedure for analysis of EC data includes data calibration, pre-processing, region of interest (ROI) detection, feature extraction and classification. Accurate ROI detection has been enhanced by pre-processing, which involves reducing noise and other undesirable components as well as enhancing defect indications in the raw measurement. This paper presents the Hilbert-Huang Transform (HHT) for feature extraction and support vector machine (SVM) for classification. The performance is shown to significantly better than the existing rule based classification approach used in industry.

  13. Failure of the Cross Correlation Measurement Technique

    NASA Astrophysics Data System (ADS)

    McGill, Ken; Ham, Katie; Schock, Kris

    2014-03-01

    The experiment involves creating a sound wave that propagates down a pipe with 8 transducers attached at equally spaced intervals of 0.01016 meters. The numerical method used to solve for the phase component, the Cross Correlation Method, creates a high correlation value, but the speed of sound varies immensely. The method involves a Fast Fourier Transform of the collected data, which is used to find the phase of the sound wave, and the slope of the position versus time graph, which is used to calculate the speed of sound. This high correlation values shows that the data is correct, but the numerical method for analyzing the data is incorrect. We would like to thank Dr. Ken McGill for all of his time, help, and guidance with this research project. We would also like to thank Georgia College and State University for both the resources and space necessary for this experiment.

  14. Fluxes by eddy correlation over heterogeneous landscape: How shall we apply the Reynolds average?

    NASA Astrophysics Data System (ADS)

    Dobosy, R.

    2007-12-01

    Top-down estimates of carbon exchange across the earth's surface are implicitly an integral scheme, deriving bulk exchanges over large areas. Bottom-up estimates explicitly integrate the individual components of exchange to derive a bulk value. If these approaches are to be properly compared, their estimates should represent the same quantity. Over heterogeneous landscape, eddy-covariance flux computations from towers or aircraft intended for comparison with top-down approach face a question of the proper definition of the mean or base state, the departures from which yield the fluxes by Reynolds averaging. 1)≠Use a global base state derived over a representative sample of the surface, insensitive to land use. The departure quantities then fail to sum to zero over any subsample representing an individual surface type, violating Reynolds criteria. Yet fluxes derived from such subsamples can be directly composed into a bulk flux, globally satisfying Reynolds criteria. 2)≠Use a different base state for each surface type. satisfying Reynolds criteria individually. Then some of the flux may get missed if a surface's characteristics significantly bias its base state. Base state≠(2) is natural for tower samples. Base state≠(1) is natural for airborne samples over heterogeneous landscape, especially in patches smaller than an appropriate averaging length. It appears (1) incorporates a more realistic sample of the flux, though desirably there would be no practical difference between the two schemes. The schemes are related by the expression w¯*a*)C - w¯'a¯')C = w¯'ã¯)C+ wtilde ¯a¯')C+ wtilde ¯ã¯)C Here w is vertical motion, and a is some scalar, such as CO2. The star denotes departure from the global base state≠(1), and the prime from the base state≠(2), defined only over surface class≠C. The overbar with round bracket denotes average over samples drawn from class≠C, determined by footprint model. Thus a¯')C = 0 but a¯*)C ≠ 0 in general. The

  15. Investigation of Frequency Mixing Techniques for Eddy Current Testing of Steam Generator Tubes in Nuclear Power Plants

    NASA Astrophysics Data System (ADS)

    Jung, H. J.; Kong, Y. B.; Song, S.-J.; Kim, C.-H.; Choi, Y. H.; Kang, S.-C.; Song, M. H.

    2007-03-01

    In eddy current testing (ECT) of steam generator tubes in nuclear power plants, it is very important to extract flaw signals from the signals compound by flaws and supporting structures. To perform such an important task, the multifrequency ECT methods are widely adopted since they have a well-known capability of extracting the flaw signal from the compound signals. Therefore, various frequency mixing algorithms have been proposed up to now. In the present work, two different frequency mixing algorithms, a time-domain optimization method and a discrete cosine transform (DCT) based optimization method, are investigated using experimental signals captured from a ASME standard tube. In this paper, we discuss the basic principles and the performances of these two frequency mixing techniques.

  16. Impact of water use efficiency on eddy covariance flux partitioning using correlation structure analysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Partitioned land surfaces fluxes (e.g. evaporation, transpiration, photosynthesis, and ecosystem respiration) are needed as input, calibration, and validation data for numerous hydrological and land surface models. However, one of the most commonly used techniques for measuring land surface fluxes,...

  17. Frequency Optimization for Enhancement of Surface Defect Classification Using the Eddy Current Technique

    PubMed Central

    Fan, Mengbao; Wang, Qi; Cao, Binghua; Ye, Bo; Sunny, Ali Imam; Tian, Guiyun

    2016-01-01

    Eddy current testing is quite a popular non-contact and cost-effective method for nondestructive evaluation of product quality and structural integrity. Excitation frequency is one of the key performance factors for defect characterization. In the literature, there are many interesting papers dealing with wide spectral content and optimal frequency in terms of detection sensitivity. However, research activity on frequency optimization with respect to characterization performances is lacking. In this paper, an investigation into optimum excitation frequency has been conducted to enhance surface defect classification performance. The influences of excitation frequency for a group of defects were revealed in terms of detection sensitivity, contrast between defect features, and classification accuracy using kernel principal component analysis (KPCA) and a support vector machine (SVM). It is observed that probe signals are the most sensitive on the whole for a group of defects when excitation frequency is set near the frequency at which maximum probe signals are retrieved for the largest defect. After the use of KPCA, the margins between the defect features are optimum from the perspective of the SVM, which adopts optimal hyperplanes for structure risk minimization. As a result, the best classification accuracy is obtained. The main contribution is that the influences of excitation frequency on defect characterization are interpreted, and experiment-based procedures are proposed to determine the optimal excitation frequency for a group of defects rather than a single defect with respect to optimal characterization performances. PMID:27164112

  18. Frequency Optimization for Enhancement of Surface Defect Classification Using the Eddy Current Technique.

    PubMed

    Fan, Mengbao; Wang, Qi; Cao, Binghua; Ye, Bo; Sunny, Ali Imam; Tian, Guiyun

    2016-01-01

    Eddy current testing is quite a popular non-contact and cost-effective method for nondestructive evaluation of product quality and structural integrity. Excitation frequency is one of the key performance factors for defect characterization. In the literature, there are many interesting papers dealing with wide spectral content and optimal frequency in terms of detection sensitivity. However, research activity on frequency optimization with respect to characterization performances is lacking. In this paper, an investigation into optimum excitation frequency has been conducted to enhance surface defect classification performance. The influences of excitation frequency for a group of defects were revealed in terms of detection sensitivity, contrast between defect features, and classification accuracy using kernel principal component analysis (KPCA) and a support vector machine (SVM). It is observed that probe signals are the most sensitive on the whole for a group of defects when excitation frequency is set near the frequency at which maximum probe signals are retrieved for the largest defect. After the use of KPCA, the margins between the defect features are optimum from the perspective of the SVM, which adopts optimal hyperplanes for structure risk minimization. As a result, the best classification accuracy is obtained. The main contribution is that the influences of excitation frequency on defect characterization are interpreted, and experiment-based procedures are proposed to determine the optimal excitation frequency for a group of defects rather than a single defect with respect to optimal characterization performances. PMID:27164112

  19. Eddy correlation measurements of methane fluxes using a tunable diode laser at the Kinosheo Lake tower site during the Northern Wetlands Study (NOWES)

    SciTech Connect

    Edwards, G.C.; Kidd, G.; Thurtell, G.W.; Neumann, H.H.; Hartog, G. den

    1994-01-20

    As part of the Canadian Northern Wetlands Study (NOWES) measurements of methane flux were made at the Kinosheo Lake tower site for a 1-month period during the 1990 summer intensive. The measurements were made with a diode-laser-based methane sensor using the eddy correlation technique. Measurements of the methane fluxes were made at two levels, 5 or 18 m. Approximately 900 half-hour average methane flux measurements were obtained. Weak temporal and diurnal trends were observed in the data. Fluxes averaged over the study period showed an overall methane emission of 16 mg CH{sub 4} m{sup {minus}2} d{sup {minus}1} with a daytime average of 20 mg CH{sub 4} m{sup {minus}2} d{sup {minus}1} and a nighttime average of 9 mg CH{sub 4} m{sup {minus}2} d{sup {minus}1}. The effect of emission footprint was evident in the data. A strong relationship between the daily average methane flux and wet bog temperature at 20-cm depth was observed. 41 refs., 6 figs.

  20. The role of airborne eddy correlation measurements in global change studies

    NASA Technical Reports Server (NTRS)

    Ritter, J. A.; Barrick, J. D. W.; Sachse, G. W.; Collins, J. E., Jr.; Anderson, B. E.; Hill, G. F.; Woerner, M. A.; Harkleroad, J. E., Jr.

    1994-01-01

    We have obtained measurements of the mean and turbulent quantities of heat, moisture, momentum, O3, CO, and CH4 from an airborne platform. Species flux measurements obtained from these data provide unique regional-scale information which can be used to evaluate 'scaled-up' flux estimates based on smaller scale observations. Airborne flux data also provide a basis for assessing the uncertainties associated with large-scale ground level flux extrapolations. Airborne constituent budget analyses are possible with this suite of measurements. The local change in the mean value of a parameter can be explained in terms of horizontal advection, vertical turbulent transport, and, in the case of chemically reactive species (i.e., O3), in situ production or destruction. This technique is used to indicate a direct relationship between O3 precursors and the measured in situ production rate.

  1. Pulsed eddy current testing

    NASA Astrophysics Data System (ADS)

    Workman, G. L.

    1980-10-01

    Since a large number of the procedures used for inspecting the external tank are concerned with determining flaws in welds, there is a need to develop an inspection technique, which can be automated, to determine flaws in welds and structures with complex geometries. Techniques whereby an eddy current is generated in a metallic material and the changes in the circuit parameters due to material differences are observed, were chosen as one possible approach. Pulsed eddy current and its relationship to multifrequency techniques is discussed as well as some preliminary results obtained from observing pulsed waveforms with apparatus and algorithms currently in use for ultrasonic testing of welds. It can be shown the pulsed eddy current techniques can provide similar results, can eliminate some of the noncritical parameters affecting the eddy current signals, and can facilitate in the detection of critical parameter such as flaws, subsurface voids, and corrosion.

  2. Optical correlator techniques applied to robotic vision

    NASA Technical Reports Server (NTRS)

    Hine, Butler P., III; Reid, Max B.; Downie, John D.

    1991-01-01

    Vision processing is one of the most computationally intensive tasks required of an autonomous robot. The data flow from a single typical imaging sensor is roughly 60 Mbits/sec, which can easily overload current on-board processors. Optical correlator-based processing can be used to perform many of the functions required of a general robotic vision system, such as object recognition, tracking, and orientation determination, and can perform these functions fast enough to keep pace with the incoming sensor data. We describe a hybrid digital electronic/analog optical robotic vision processing system developed at Ames Research Center to test concepts and algorithms for autonomous construction, inspection, and maintenance of space-based habitats. We discuss the system architecture design and implementation, its performance characteristics, and our future plans. In particular, we compare the performance of the system to a more conventional all digital electronic system developed concurrently. The hybrid system consistently outperforms the digital electronic one in both speed and robustness.

  3. Eddy Covariance Flux Measurements of Pollutant Gases in the Mexico City Urban Area: a Useful Technique to Evaluate Emissions inventories

    NASA Astrophysics Data System (ADS)

    Velasco, E.; Grivicke, R.; Pressley, S.; Allwine, G.; Jobson, T.; Westberg, H.; Lamb, B.; Ramos, R.; Molina, L.

    2007-12-01

    Direct measurements of emissions of pollutant gases that include all major and minor emissions sources in urban areas are a missing requirement to improve and evaluate emissions inventories. The quality of an urban emissions inventory relies on the accuracy of the information of anthropogenic activities, which in many cases is not available, in particular in urban areas of developing countries. As part of the MCMA-2003 field campaign, we demonstrated the feasibility of using eddy covariance (EC) techniques coupled with fast-response sensors to measure fluxes of volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City. Those flux measurements demonstrated to be also a valuable tool to evaluate the emissions inventory used for air quality modeling. With the objective to confirm the representativeness of the 2003 flux measurements in terms of magnitude, composition and diurnal distribution, as well to evaluate the most recent emissions inventory, a second flux system was deployed in a different district of Mexico City during the 2006 MILAGRO field campaign. This system was located in a busy district surrounded by congested avenues close to the center of the city. In 2003 and 2006 fluxes of olefins and CO2 were measured by the EC technique using a Fast Isoprene Sensor calibrated with a propylene standard and an open path Infrared Gas Analyzer (IRGA), respectively. Fluxes of aromatic and oxygenated VOCs were analyzed by Proton Transfer Reaction-Mass Spectroscopy (PTR-MS) and the disjunct eddy covariance (DEC) technique. In 2006 the number of VOCs was extended using a disjunct eddy accumulation (DEA) system. This system collected whole air samples as function of the direction of the vertical wind component, and the samples were analyzed on site by gas chromatography / flame ionization detection (GC-FID). In both studies we found that the urban surface is a net source of CO2 and VOCs. The diurnal patterns were similar, but the 2006 fluxes

  4. Detection of Anomalous Machining Damages in Inconel 718 and TI 6-4 by Eddy Current Techniques

    NASA Astrophysics Data System (ADS)

    Lo, C. C. H.; Shimon, M.; Nakagawa, N.

    2010-02-01

    This paper reports on an eddy current (EC) study aimed at detecting anomalous machining damages in Inconel 718 and Ti 6-4 samples, including (i) surface discontinuities such as re-depositing of chips onto the machined surface, and (ii) microstructural damages manifested as a white surface layer and a subsurface layer of distorted grains, typically tens of microns thick. A series of pristine and machine-damaged coupons were studied by EC scans using a differential probe operated at 2 MHz to detect discontinuous surface anomalies, and by swept high frequency EC (SHFEC) measurements from 0.5 MHz to 65.5 MHz using proprietary detection coils to detect surface microstructural damages. In general, the EC c-scan data from machine-damaged surfaces show spatial variations with larger standard deviations than those from the undamaged surfaces. In some cases, the c-scan images exhibit characteristic bipolar indications in good spatial correlation with surface anomalies revealed by optical microscopy and laser profilometry. Results of the SHFEC measurements indicate a reduced near-surface conductivity of the damaged surfaces compared to the undamaged surfaces.

  5. Semidiurnal and seasonal variations in methane emissions from a sub-tropical hydroelectric reservoir (Nam Theun 2, Laos) measured by eddy covariance technique

    NASA Astrophysics Data System (ADS)

    Deshmukh, C.; Serca, D.; Guerin, F.; Meyerfeld, Y.; Descloux, S.; Chanudet, V.; Pighini, S.; Godon, A.; Guedant, P.

    2012-12-01

    The quantification of sources and sinks of greenhouse gases (GHG) have become an important scientific issue. Hydroelectric reservoirs have been identified as considerable methane (CH4) sources to the atmosphere, especially in the tropics. Assessing these emissions and their variations on small and large time scale represent important challenges in our understanding of water-atmosphere exchange. In this context, objectives of this study are (i) to quantify the CH4 emissions, (ii) to determine the variations in the emissions on daily and seasonal time scale, and link these variations to environmental driving forces (iii) to compare different methodologies to assess CH4 emissions. Measurements of CH4 emissions were made in a recently impounded (in 2009) subtropical hydroelectric reservoir, Nam Theun 2 (NT2), in Lao PDR, Asia. The sampling strategy included three different types of flux measurement techniques: floating chambers, submerged funnels, and a micrometeorological station allowing for flux determination based on the eddy covariance technique (EC). We carried out flux measurements during four intensive field campaigns conducted in between May 2009 and June 2011. Eddy covariance system, composed by a 3D sonic anemometer coupled with a cavity ring-down spectroscopy (CRDS) analyzer, was deployed on the mast in a large surface of open water corresponding to an homogeneous ecosystem (floodplain). Diffusive and bubbling fluxes were measured using respectively floating chambers and submerged funnel techniques around the mast. Our results from the all four field campaigns show that individual 30-min EC fluxes varied by 4 order of magnitude (from 0.01 to 102 mmol.m-2.day-1). Average EC fluxes of individual campaigns varied inversely with water depth, from 5±3.5 to 28±16 mmol.m-2.day-1 for respectively from 10.5 to 2 m of water depths. Diffusive fluxes measured by floating chambers ranged between 0.2 and 3.2 mmol.m-2.day-1. Bubbling fluxes were found to be highly

  6. Correlation of Three Techniques for Determining Soil Permeability

    ERIC Educational Resources Information Center

    Winneberger, John T.

    1974-01-01

    Discusses problems of acquiring adequate results when measuring for soil permeability. Correlates three relatively simple techniques that could be helpful to the inexperienced technician dealing with septic tank practices. An appendix includes procedures for valid percolation tests. (MLB)

  7. Component greenhouse gas fluxes and radiative balance from two deltaic marshes in Louisiana: Pairing chamber techniques and eddy covariance

    NASA Astrophysics Data System (ADS)

    Krauss, Ken W.; Holm, Guerry O.; Perez, Brian C.; McWhorter, David E.; Cormier, Nicole; Moss, Rebecca F.; Johnson, Darren J.; Neubauer, Scott C.; Raynie, Richard C.

    2016-06-01

    Coastal marshes take up atmospheric CO2 while emitting CO2, CH4, and N2O. This ability to sequester carbon (C) is much greater for wetlands on a per area basis than from most ecosystems, facilitating scientific, political, and economic interest in their value as greenhouse gas sinks. However, the greenhouse gas balance of Gulf of Mexico wetlands is particularly understudied. We describe the net ecosystem exchange (NEEc) of CO2 and CH4 using eddy covariance (EC) in comparison with fluxes of CO2, CH4, and N2O using chambers from brackish and freshwater marshes in Louisiana, USA. From EC, we found that 182 g C m-2 yr-1 was lost through NEEc from the brackish marsh. Of this, 11 g C m-2 yr-1 resulted from net CH4 emissions and the remaining 171 g C m-2 yr-1 resulted from net CO2 emissions. In contrast, -290 g C m2 yr-1 was taken up through NEEc by the freshwater marsh, with 47 g C m-2 yr-1 emitted as CH4 and -337 g C m-2 yr-1 taken up as CO2. From chambers, we discovered that neither site had large fluxes of N2O. Sustained-flux greenhouse gas accounting metrics indicated that both marshes had a positive (warming) radiative balance, with the brackish marsh having a substantially greater warming effect than the freshwater marsh. That net respiratory emissions of CO2 and CH4 as estimated through chamber techniques were 2-4 times different from emissions estimated through EC requires additional understanding of the artifacts created by different spatial and temporal sampling footprints between techniques.

  8. Development of Quality Assessment Techniques for Large Eddy Simulation of Propulsion and Power Systems in Complex Geometries

    SciTech Connect

    Lacaze, Guilhem; Oefelein, Joseph

    2015-03-01

    Large-eddy-simulation (LES) is quickly becoming a method of choice for studying complex thermo-physics in a wide range of propulsion and power systems. It provides a means to study coupled turbulent combustion and flow processes in parameter spaces that are unattainable using direct-numerical-simulation (DNS), with a degree of fidelity that can be far more accurate than conventional engineering methods such as the Reynolds-averaged Navier-Stokes (RANS) approx- imation. However, development of predictive LES is complicated by the complex interdependence of different type of errors coming from numerical methods, algorithms, models and boundary con- ditions. On the other hand, control of accuracy has become a critical aspect in the development of predictive LES for design. The objective of this project is to create a framework of metrics aimed at quantifying the quality and accuracy of state-of-the-art LES in a manner that addresses the myriad of competing interdependencies. In a typical simulation cycle, only 20% of the computational time is actually usable. The rest is spent in case preparation, assessment, and validation, because of the lack of guidelines. This work increases confidence in the accuracy of a given solution while min- imizing the time obtaining the solution. The approach facilitates control of the tradeoffs between cost, accuracy, and uncertainties as a function of fidelity and methods employed. The analysis is coupled with advanced Uncertainty Quantification techniques employed to estimate confidence in model predictions and calibrate model's parameters. This work has provided positive conse- quences on the accuracy of the results delivered by LES and will soon have a broad impact on research supported both by the DOE and elsewhere.

  9. Application of Self Nulling Eddy Current Probe Technique to the Detection of Fatigue Crack Initiation and Control of Test Procedures

    NASA Technical Reports Server (NTRS)

    Namkung, M.; Nath, S.; Wincheski, B.; Fulton, J. P.

    1994-01-01

    A major part of fracture mechanics is concerned with studying the initiation and propagation of fatigue cracks. This typically requires constant monitoring of crack growth during fatigue cycles and the knowledge of the precise location of the crack tip at any given time. One technique currently available for measuring fatigue crack length is the Potential Drop method. The method, however, may be inaccurate if the direction of crack growth deviates considerably from what was assumed initially or the curvature of the crack becomes significant. Another popular approach is to optically view the crack using a high magnification microscope, but this entails a person constantly monitoring it. The present proposed technique uses an automated scheme, in order to eliminate the need for a person to constantly monitor the experiment. Another technique under development elsewhere is to digitize an optical image of the test specimen surface and then apply a pattern recognition algorithm to locate the crack tip. A previous publication showed that the self nulling eddy current probe successfully tracked a simulated crack in an aluminum sample. This was the impetus to develop an online real time crack monitoring system. An automated system has been developed which includes a two axis scanner mounted on the tensile testing machine, the probe and its instrumentation and a personal computer (PC) to communicate and control all the parameters. The system software controls the testing parameters as well as monitoring the fatigue crack as it propagates. This paper will discuss the experimental setup in detail and demonstrate its capabilities. A three dimensional finite element model is utilized to model the magnetic field distribution due to the probe and how the probe voltage changes as it scans the crack. Experimental data of the probe for different samples under zero load, static load and high cycle fatigue load will be discussed. The final section summarizes the major accomplishments

  10. Estimates of evapotranspiration in alkaline scrub and meadow communities of Owens Valley, California, using the Bowen-ratio, eddy-correlation, and Penman-combination methods

    USGS Publications Warehouse

    Duell, L. F. W., Jr.

    1988-01-01

    In Owens Valley, evapotranspiration (ET) is one of the largest components of outflow in the hydrologic budget and the least understood. ET estimates for December 1983 through October 1985 were made for seven representative locations selected on the basis of geohydrology and the characteristics of phreatophytic alkaline scrub and meadow communities. The Bowen-ratio, eddy-correlation, and Penman-combination methods were used to estimate ET. The results of the analyses appear satisfactory when compared to other estimates of ET. Results by the eddy-correlation method are for a direct and a residual latent-heat flux that is based on sensible-heat flux and energy budget measurements. Penman-combination potential ET estimates were determined to be unusable because they overestimated actual ET. Modification in the psychrometer constant of this method to account for differences between heat-diffusion resistance and vapor-diffusion resistance permitted actual ET to be estimated. The methods may be used for studies in similar semiarid and arid rangeland areas in the Western United States. Meteorological data for three field sites are included in the appendix. Simple linear regression analysis indicates that ET estimates are correlated to air temperature, vapor-density deficit, and net radiation. Estimates of annual ET range from 300 mm at a low-density scrub site to 1,100 mm at a high-density meadow site. The monthly percentage of annual ET was determined to be similar for all sites studied. (Author 's abstract)

  11. Component greenhouse gas fluxes and radiative balance from two deltaic marshes in Louisiana: Pairing chamber techniques and eddy covariance

    USGS Publications Warehouse

    Krauss, Ken W.; Holm, Guerry O.; Perez, Brian C.; McWhorter, David E.; Cormier, Nicole; Moss, Rebecca; Johnson, Darren; Neubauer, Scott C; Raynie, Richard C

    2016-01-01

    Coastal marshes take up atmospheric CO2 while emitting CO2, CH4, and N2O. This ability to sequester carbon (C) is much greater for wetlands on a per-area basis than from most ecosystems, facilitating scientific, political, and economic interest in their value as greenhouse gas sinks. However, the greenhouse gas balance of Gulf of Mexico wetlands is particularly understudied. We describe the net ecosystem exchange (NEEc) of CO2 and CH4 using eddy covariance (EC) in comparison with fluxes of CO2, CH4, and N2O using chambers from brackish and freshwater marshes in Louisiana, USA. From EC, we found that 182 g C m-2 y-1 was lost through NEEc from the brackish marsh. Of this, 11 g C m-2 y-1 resulted from net CH4 emissions and the remaining 171 g C m-2 y-1 resulted from net CO2 emissions. In contrast, -290 g C m2 y-1 was taken up through NEEc by the freshwater marsh, with 47 g C m-2 y-1 emitted as CH4 and -337 g C m-2 y-1 taken up as CO2. From chambers, we discovered that neither site had large fluxes of N2O. Sustained-flux greenhouse gas accounting metrics indicated that both marshes had a positive (warming) radiative balance, with the brackish marsh having a substantially greater warming effect than the freshwater marsh. That net respiratory emissions of CO2 and CH4 as estimated through chamber techniques were 2-4 times different from emissions estimated through EC requires additional understanding of the artifacts created by different spatial and temporal sampling footprints between techniques.

  12. Energy balance closure on a winter wheat stand: comparing the eddy covariance technique with the soil water balance method

    NASA Astrophysics Data System (ADS)

    Imukova, K.; Ingwersen, J.; Hevart, M.; Streck, T.

    2015-05-01

    The energy balance of eddy covariance (EC) flux data is typically not closed. The nature of the gap is usually not known, which hampers using EC data to parameterize and test models. The present study elucidates the nature of the energy gap of EC flux data from winter wheat stands in southwest Germany. During the vegetation periods 2012 and 2013, we continuously measured, in a half-hourly resolution, latent (LE) and sensible (H) heat fluxes using the EC technique. Measured fluxes were adjusted with either the Bowen-ratio (BR), H or LE post-closure method. The adjusted LE fluxes were tested against evapotranspiration data (ETWB) calculated using the soil water balance (WB) method. At sixteen locations within the footprint of an EC station, the soil water storage term was determined by measuring the soil water content down to a soil depth of 1.5 m. In the second year, the volumetric soil water content was also continuously measured in 15 min resolution in 10 cm intervals down to 90 cm depth with sixteen capacitance soil moisture sensors. During the 2012 vegetation period, the H post-closed LE flux data (ETEC = 3.4 ± 0.6 mm day-1) corresponded closest with the result of the WB method (3.3 ± 0.3 mm day-1). ETEC adjusted by the BR (4.1 ± 0.6 mm day-1) or LE (4.9 ± 0.9 mm day-1) post-closure method were higher than the ETWB by 20 and 33%, respectively. In 2013, ETWB was in best agreement with ETEC adjusted with the H post-closure method during the periods with low amount of rain and seepage. During these periods the BR and LE post-closure methods overestimated ET by about 30 and 40%, respectively. During a period with high and frequent rainfalls, ETWB was in-between ETEC adjusted by H and BR post-closure methods. We conclude that, at most vegetation periods on our site, LE is not a~major component of the energy balance gap. Our results indicate that the energy balance gap other energy fluxes and unconsidered or biased energy storage terms.

  13. Energy balance closure on a winter wheat stand: comparing the eddy covariance technique with the soil water balance method

    NASA Astrophysics Data System (ADS)

    Imukova, K.; Ingwersen, J.; Hevart, M.; Streck, T.

    2016-01-01

    The energy balance of eddy covariance (EC) flux data is typically not closed. The nature of the gap is usually not known, which hampers using EC data to parameterize and test models. In the present study we cross-checked the evapotranspiration data obtained with the EC method (ETEC) against ET rates measured with the soil water balance method (ETWB) at winter wheat stands in southwest Germany. During the growing seasons 2012 and 2013, we continuously measured, in a half-hourly resolution, latent heat (LE) and sensible (H) heat fluxes using the EC technique. Measured fluxes were adjusted with either the Bowen-ratio (BR), H or LE post-closure method. ETWB was estimated based on rainfall, seepage and soil water storage measurements. The soil water storage term was determined at sixteen locations within the footprint of an EC station, by measuring the soil water content down to a soil depth of 1.5 m. In the second year, the volumetric soil water content was additionally continuously measured in 15 min resolution in 10 cm intervals down to 90 cm depth with sixteen capacitance soil moisture sensors. During the 2012 growing season, the H post-closed LE flux data (ETEC = 3.4 ± 0.6 mm day-1) corresponded closest with the result of the WB method (3.3 ± 0.3 mm day-1). ETEC adjusted by the BR (4.1 ± 0.6 mm day-1) or LE (4.9 ± 0.9 mm day-1) post-closure method were higher than the ETWB by 24 and 48 %, respectively. In 2013, ETWB was in best agreement with ETEC adjusted with the H post-closure method during the periods with low amount of rain and seepage. During these periods the BR and LE post-closure methods overestimated ET by about 46 and 70 %, respectively. During a period with high and frequent rainfalls, ETWB was in-between ETEC adjusted by H and BR post-closure methods. We conclude that, at most observation periods on our site, LE is not a major component of the energy balance gap. Our results indicate that the energy balance gap is made up by

  14. Exchange of nitrous oxides and carbon dioxide measured using the eddy covariance technique in a high-latitude city

    NASA Astrophysics Data System (ADS)

    Järvi, Leena; Nordbo, Annika; Rannik, Üllar; Haapanala, Sami; Pihlatie, Mari; Mammarella, Ivan; Riikonen, Anu; Nikinmaa, Eero; Vesala, Timo

    2014-05-01

    In Helsinki, Finland, carbon dioxide (CO2) fluxes have been measured continuously using the eddy covariance (EC) technique since 2005. In summer 2012, the measurements were supplemented with the fluxes of nitrous oxide (N2O) in order to examine how the exchanges of these two important greenhouse gases behave in urban environment. The EC measurements are made at the semi-urban measurement station SMEAR III Kumpula site located four kilometres north-east from the Helsinki city centre. The measurements are made on the top level of a 31 meters high lattice tower (60°12.17'N, 24°57.67'E) located on a hill, 26 m above sea level. The area around the tower can be divided into three surface cover sectors: built, road and vegetation, each representing the typical surface cover of the area. These areas allow us to examine the effect of different urban surface covers to the exchange of CO2 and N2O. The measurement setup includes an ultrasonic anemometer (USA-1, Metek GmbH) and a closed-path infrared gas analyzer (LI-7000, LI-COR) to measure the CO2 flux. During the summer 2012 measurement campaign lasting from 21 June till 27 November, the N2O flux was measured using a TDL spectrometer. Commonly accepted procedures were used to post-process the raw 10 Hz data. Overall, the measurement surroundings act as a source for both CO2 and N2O. The long-term measurements of the CO2 flux show a strong seasonal variation with clear effect from vegetation. In summer in the direction of high fraction of vegetation cover, the CO2 uptake exceeds its emissions and a downward flux reaching on average 10 μmol m-2 s-1 is observed. N2O on the other hand reaches its maxima values (campaign median 2.0 μmol m-2 h-1) in the same direction. This indicates that vegetation cannot be neglected in the urban greenhouse exchange studies. Traffic had a clear role emitting both N2O and CO2 with higher emissions during the rush hours than at other times. In the direction of the heavily trafficked road

  15. Study of eddy current probes

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Wang, Morgan

    1992-01-01

    The recognition of materials properties still presents a number of problems for nondestructive testing in aerospace systems. This project attempts to utilize current capabilities in eddy current instrumentation, artificial intelligence, and robotics in order to provide insight into defining geometrical aspects of flaws in composite materials which are capable of being evaluated using eddy current inspection techniques.

  16. Digital image correlation techniques applied to LANDSAT multispectral imagery

    NASA Technical Reports Server (NTRS)

    Bonrud, L. O. (Principal Investigator); Miller, W. J.

    1976-01-01

    The author has identified the following significant results. Automatic image registration and resampling techniques applied to LANDSAT data achieved accuracies, resulting in mean radial displacement errors of less than 0.2 pixel. The process method utilized recursive computational techniques and line-by-line updating on the basis of feedback error signals. Goodness of local feature matching was evaluated through the implementation of a correlation algorithm. An automatic restart allowed the system to derive control point coordinates over a portion of the image and to restart the process, utilizing this new control point information as initial estimates.

  17. Weak value amplification via second-order correlated technique

    NASA Astrophysics Data System (ADS)

    Ting, Cui; Jing-Zheng, Huang; Xiang, Liu; Gui-Hua, Zeng

    2016-02-01

    We propose a new framework combining weak measurement and second-order correlated technique. The theoretical analysis shows that weak value amplification (WVA) experiment can also be implemented by a second-order correlated system. We then build two-dimensional second-order correlated function patterns for achieving higher amplification factor and discuss the signal-to-noise ratio influence. Several advantages can be obtained by our proposal. For instance, detectors with high resolution are not necessary. Moreover, detectors with low saturation intensity are available in WVA setup. Finally, type-one technical noise can be effectively suppressed. Project supported by the Union Research Centre of Advanced Spaceflight Technology (Grant No. USCAST2013-05), the National Natural Science Foundation of China (Grant Nos. 61170228, 61332019, and 61471239), and the High-Tech Research and Development Program of China (Grant No. 2013AA122901).

  18. Estimates of evapotranspiration in alkaline scrub and meadow communities of Owens Valley, California, using the Bowen-ratio, eddy-correlation, and penman-combination methods

    USGS Publications Warehouse

    Duell, Lowell F. W., Jr.

    1990-01-01

    In Owens Valley, evapotranspiration (ET) is one of the largest components of outflow in the hydrologic budget and the least understood. ET estimates for December 1983 through October 1985 were made for seven representative locations selected on the basis of geohydrology and the characteristics of phreatophytic alkaline scrub and meadow communities. The Bowen-ratio, eddy-correlation, and Penman-combination methods were used to estimate ET. The results of the analyses appear satisfactory when compared with other estimates of ET. Results by the eddy-correlation method are for a direct and a residual latent-heat flux that is based on sensible-heat flux and energy-budget measurements. Penman-combination potential-ET estimates were determined to be unusable because they overestimated actual ET. Modification of the psychrometer constant of this method to account for differences between heat-diffusion resistance and vapor-diffusion resistance permitted actual ET to be estimated. The methods described in this report may be used for studies in similar semiarid and arid rangeland areas in the Western United States. Meteorological data for three field sites are included in the appendix of this report. Simple linear regression analysis indicates that ET estimates are correlated to air temperature, vapor-density deficit, and net radiation. Estimates of annual ET range from 301 millimeters at a low-density scrub site to 1,137 millimeters at a high-density meadow site. The monthly percentage of annual ET was determined to be similar for all sites studied.

  19. Application of optical correlation techniques to particle imaging velocimetry

    NASA Technical Reports Server (NTRS)

    Wernet, Mark P.; Edwards, Robert V.

    1988-01-01

    Pulsed laser sheet velocimetry yields nonintrusive measurements of velocity vectors across an extended 2-dimensional region of the flow field. The application of optical correlation techniques to the analysis of multiple exposure laser light sheet photographs can reduce and/or simplify the data reduction time and hardware. Here, Matched Spatial Filters (MSF) are used in a pattern recognition system. Usually MSFs are used to identify the assembly line parts. In this application, the MSFs are used to identify the iso-velocity vector contours in the flow. The patterns to be recognized are the recorded particle images in a pulsed laser light sheet photograph. Measurement of the direction of the partical image displacements between exposures yields the velocity vector. The particle image exposure sequence is designed such that the velocity vector direction is determined unambiguously. A global analysis technique is used in comparison to the more common particle tracking algorithms and Young's fringe analysis technique.

  20. Application of optical correlation techniques to particle imaging

    NASA Technical Reports Server (NTRS)

    Wernet, Mark P.; Edwards, Robert V.

    1988-01-01

    Pulsed laser sheet velocimetry yields noninstrusive measurements of velocity vectors across an extended 2-dimensional region of the flow field. The application of optical correlation techniques to the analysis of multiple exposure laser light sheet photographs can reduce and/or simplify the data reduction time and hardware. Here, Matched Spatial Filters (MSF) are used in a pattern recognition system. Usuallay MSFs are used to identify the assembly line parts. In this application, the MSFs are used to identify the iso-velocity vector contours in the flow. The patterns to be recognized are the recorded particle images in a pulsed laser light sheet photograph. Measurement of the direction of the particle image displacements between exposures yields the velocity vector. The particle image exposure sequence is designed such that the velocity vector direction is determined unambiguously. A global analysis technique is used in comparison to the more common particle tracking algorithms and Young's fringe analysis technique.

  1. Evaluation of the Advanced-Canopy-Atmosphere-Surface Algorithm (ACASA Model) Using Eddy Covariance Technique Over Sparse Canopy

    NASA Astrophysics Data System (ADS)

    Marras, S.; Spano, D.; Sirca, C.; Duce, P.; Snyder, R.; Pyles, R. D.; Paw U, K. T.

    2008-12-01

    Land surface models are usually used to quantify energy and mass fluxes between terrestrial ecosystems and atmosphere on micro- and regional scales. One of the most elaborate land surface models for flux modelling is the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) model, which provides micro-scale as well as regional-scale fluxes when imbedded in a meso-scale meteorological model (e.g., MM5 or WRF). The model predicts vegetation conditions and changes with time due to plant responses to environment variables. In particular, fluxes and profiles of heat, water vapor, carbon and momentum within and above canopy are estimated using third-order equations. It also estimates turbulent profiles of velocity, temperature, humidity within and above canopy, and CO2 fluxes are estimated using a combination of Ball-Berry and Farquhar equations. The ACASA model is also able to include the effects of water stress on stomata, transpiration and CO2 assimilation. ACASA model is unique because it separates canopy domain into twenty atmospheric layers (ten layers within the canopy and ten layers above the canopy), and the soil is partitioned into fifteen layers of variable thickness. The model was mainly used over dense canopies in the past, so the aim of this work was to test the ACASA model over a sparse canopy as Mediterranean maquis. Vegetation is composed by sclerophyllous species of shrubs that are always green, with leathery leaves, small height, with a moderately sparse canopy, and that are tolerant at water stress condition. Eddy Covariance (EC) technique was used to collect continuous data for more than 3 years period. Field measurements were taken in a natural maquis site located near Alghero, Sardinia, Italy and they were used to parameterize and validate the model. The input values were selected by running the model several times varying the one parameter per time. A second step in the parameterization process was the simultaneously variation of some parameters

  2. A comparison of airborne eddy correlation and bulk aerodynamic methods for ocean-air turbulent fluxes during cold-air outbreaks

    NASA Technical Reports Server (NTRS)

    Chou, Shu-Hsien

    1993-01-01

    The viscous interfacial-sublayer model of Liu et al. (1979) is used to derive four bulk schemes (LKB, FG, D, and DB), with the flux-profile relationships of Lie et al., Francey and Garratt (1981), Dyer (1974), and Dyer and Bradley (1982). These schemes, with stability-dependent transfer coefficients, are tested against the eddy-correlation fluxes measured at the 50-m flight level above the western Atlantic Ocean during cold-air outbreaks. The bulk fluxes of momentum (tau), sensible heat (H), and latent heat (E) are found to increase with various von Karman constants. The dependence of transfer coefficients on wind speeds and roughness lengths is discussed. The transfer coefficients for tau and E agree excellently between LKB and FG. The ratio of the coefficent for H of LKB to that of FG, increasing with decreasing stability, is very sensitive to stability at low winds, but approaches the neutral value of 1.25 at high winds.

  3. Verifying eddy-correlation measurements of dry deposition: A study of the energy-balance components of the Pawnee grasslands. Forest Service research paper

    SciTech Connect

    Massman, W.J.; Fox, D.G.; Zeller, K.F.; Lukens, D.

    1990-02-01

    At the Central Plains Experimental Range/Long-Term Ecological Research (CPER/LTER) site at the Pawnee National Grasslands, scientists from both the Rocky Mountain Station and the Natural Resources Ecology Laboratory of Colorado State University are independently attempting to measure several major components of the surface energy balance. The report describes how well independent measurements of radiation and the transport of heat and water vapor achieve closure of the surface energy balance and, thereby, account for the gross energy available to and processed by an ecosystem. The motivation behind the study is to evaluate the eddy correlation technology which the authors have been using to measure the exchange of gaseous pollutants (NO{sub 2}, NOx, and O{sub 3}) between the atmosphere and the grassland ecosystem.

  4. Latitude dependence of eddy variances

    NASA Technical Reports Server (NTRS)

    Bowman, Kenneth P.; Bell, Thomas L.

    1987-01-01

    The eddy variance of a meteorological field must tend to zero at high latitudes due solely to the nature of spherical polar coordinates. The zonal averaging operator defines a length scale: the circumference of the latitude circle. When the circumference of the latitude circle is greater than the correlation length of the field, the eddy variance from transient eddies is the result of differences between statistically independent regions. When the circumference is less than the correlation length, the eddy variance is computed from points that are well correlated with each other, and so is reduced. The expansion of a field into zonal Fourier components is also influenced by the use of spherical coordinates. As is well known, a phenomenon of fixed wavelength will have different zonal wavenumbers at different latitudes. Simple analytical examples of these effects are presented along with an observational example from satellite ozone data. It is found that geometrical effects can be important even in middle latitudes.

  5. Investigations of eddy coherence in jet flows

    NASA Technical Reports Server (NTRS)

    Yule, A. J.

    1980-01-01

    In turbulent shear flow the term coherent structures refers to eddies which are both spatially coherent, i.e., large eddies, aand also temporally coherent, i.e., they retain their identities for times which are long compared with their time scales in fixed point measurements. In transitional flows, the existence of such structures is evident from flow visualizations. In many other flows, such structures are not so evident. The reasons for the existence of these two classes of flows are discussed and attention is focused upon the more difficult flows, where coherent structures are not so evident. Techniques by which the existence (or nonexistence) of such structures in these flows can be established from point measurements, are also discussed. A major problem is shown to be the need to discriminate between real losses in eddy coherence and apparent losses in coherence introduced by phase scrambling effects which 'smear' multipoint correlations. The analysis of multiprobe time dependent data in cold and reacting round turbulent jets is described and it is shown how evidence of strong eddy coherence can be extracted from data.

  6. On the estimate of the transpiration in Mediterranean heterogeneous ecosystems with the coupled use of eddy covariance and sap flow techniques.

    NASA Astrophysics Data System (ADS)

    Corona, Roberto; Curreli, Matteo; Montaldo, Nicola; Oren, Ram

    2013-04-01

    Mediterranean ecosystems are commonly heterogeneous savanna-like ecosystems, with contrasting plant functional types (PFT) competing for the water use. Mediterranean regions suffer water scarcity due to the dry climate conditions. In semi-arid regions evapotranspiration (ET) is the leading loss term of the root-zone water budget with a yearly magnitude that may be roughly equal to the precipitation. Despite the attention these ecosystems are receiving, a general lack of knowledge persists about the estimate of ET and the relationship between ET and the plant survival strategies for the different PFTs under water stress. During the dry summers these water-limited heterogeneous ecosystems are mainly characterized by a simple dual PFT-landscapes with strong-resistant woody vegetation and bare soil since grass died. In these conditions due to the low signal of the land surface fluxes captured by the sonic anemometer and gas analyzer the widely used eddy covariance may fail and its ET estimate is not robust enough. In these conditions the use of the sap flow technique may have a key role, because theoretically it provides a direct estimate of the woody vegetation transpiration. Through the coupled use of the sap flow sensor observations, a 2D foot print model of the eddy covariance tower and high resolution satellite images for the estimate of the foot print land cover map, the eddy covariance measurements can be correctly interpreted, and ET components (bare soil evaporation and woody vegetation transpiration) can be separated. The case study is at the Orroli site in Sardinia (Italy). The site landscape is a mixture of Mediterranean patchy vegetation types: trees, including wild olives and cork oaks, different shrubs and herbaceous species. An extensive field campaign started in 2004. Land-surface fluxes and CO2 fluxes are estimated by an eddy covariance technique based micrometeorological tower. Soil moisture profiles were also continuously estimated using water

  7. NO2 flux evaluation using laser induced fluorescence measurements and eddy covariance technique, in the Borneo forest during OP3 campaign

    NASA Astrophysics Data System (ADS)

    Dari Salisburgo, Cesare; di Carlo, Piero; Aruffo, E.; Langford, Ben; Dorsey, James; Giammaria, F.

    2010-05-01

    Emissions (both anthropogenic and biogenic) are extremely important to reduce the uncertainty of most models used to predict the atmospheric chemical species evolution. Measurements of emission of compounds such as nitrogen dioxide (NO2) are very rare because they require measures with high sensitivity and frequencies (above 5 Hz). Direct measurements of NO2 using laser-induced fluorescence (at 10Hz) combined with those of three components of wind are used to quantify directly the NO2 flux applying the eddy covariance technique. In this presentation will be described the technique of measurements and results of the observations made in the forests of Borneo (Malaysia) during the OP3 campaign in summer 2008.

  8. Recent advances in remote field eddy current NDE techniques and their applications in detection, characterization, and monitoring of deeply hidden corrosion in aircraft structures

    NASA Astrophysics Data System (ADS)

    Sun, Yushi; Ouyang, Tianhe; Udpa, Satish S.

    1999-01-01

    The remote field eddy current (RFEC) technique is based on the RFEC phenomenon which is characterized by differences in the energy flow patterns in the near and remote field regions. The energy released by the probe excitation coil traverses the pipe al twice before reaching the pickup coil. The RFEC technique, currently used in metallic tube inspection, is therefore characterized by its equal sensitivity to a flaw irrespective to its location in the tube wall. It can be used for detecting defects located several skin-depths away from the excitation source, since its inspection capacity is limited by the skin-depth of the specimen, but by the signal-to-noise ratio for a particular measurement condition.

  9. Nuclear material safeguards surveillance and accountancy by isotope correlation techniques

    SciTech Connect

    Persiani, P.J.; Goleb, J.A.; Kroc, T.K.

    1981-11-01

    The purpose of this study is to investigate the applicability of isotope correlation techniques (ICT) to the Light Water Reactor (LWR) and the Liquid Metal Fast Breeder Reactor (LMFBR) fuel cycles for nuclear material accountancy and safeguards surveillance. The isotopic measurement of the inventory input to the reprocessing phase of the fuel cycle is the primary direct determination that an anomaly may exist in the fuel management of nuclear material. The nuclear materials accountancy gap which exists between the fabrication plant output and the input to the reprocessing plant can be minimized by using ICT at the dissolver stage of the reprocessing plant. The ICT allows a level of verification of the fabricator's fuel content specifications, the irradiation history, the fuel and blanket assemblies management and scheduling within the reactor, and the subsequent spent fuel assembly flows to the reprocessing plant. The investigation indicates that there exist relationships between isotopic concentration which have predictable, functional behavior over a range of burnup. Several cross-correlations serve to establish the initial core assembly-averaged composition. The selection of the more effective functionals will depend not only on the level of reliability of ICT for verification, but also on the capability, accuracy and difficulty of developing measurement methods. The propagation of measurement errors on the correlation functions and respective sensitivities to isotopic compositional changes have been examined and found to be consistent with current measurement methods.

  10. Estimation of mixing parameters for cancellation of discretized eddy current signals using time and frequency domain techniques

    SciTech Connect

    Sword, C.K.; Simaar, M.

    1985-03-01

    In this paper, we present two methods for estimating the mixing parameters used in scaling, rotating, and time shifting discrete time eddy current impedance plane trajectories in order to suppress unwanted support plate signals. One method operates directly on the time signals. The other method operates on the frequency domain representation of these signals and consequently is computationally more involved. Both methods require the minimization of a functional which measures the energy difference between the horizontal and vertical components of the high and low frequency data. Three illustrative examples are presented, and it is shown that the use of the frequency domain method is justified if the data are corrupted with random noise as well as with unknown multisample time shifts.

  11. Methane fluxes measured by eddy covariance and static chamber techniques at a temperate forest in central ontario, Canada

    NASA Astrophysics Data System (ADS)

    Wang, J. M.; Murphy, J. G.; Geddes, J. A.; Winsborough, C. L.; Basiliko, N.; Thomas, S. C.

    2012-12-01

    Methane flux measurements were carried out at a temperate forest (Haliburton Forest and Wildlife Reserve) in central Ontario (45°17´11´´ N, 78°32´19´´ W) from June-October, 2011. Continuous measurements were made by an off-axis integrated cavity output spectrometer Fast Greenhouse Gas Analyzer (FGGA) from Los Gatos Research Inc. that measures methane (CH4) at 10 Hz sampling rates. Fluxes were calculated from the gas measurements in conjunction with wind data collected by a 3-D sonic anemometer using the eddy covariance (EC) method. Observed methane fluxes showed net uptake of CH4 over the measurement period with an average uptake flux (± standard deviation of the mean) of -2.7 ± 0.13 nmol m-2 s-1. Methane fluxes showed a seasonal progression with average rates of uptake increasing from June through September and remaining high in October. This pattern was consistent with a decreasing trend in soil moisture content at the monthly time scale. On the diurnal timescale, there was evidence of increased uptake during the day, when the mid-canopy wind speed was at a maximum. These patterns suggest that substrate supply of CH4 and oxygen to methanotrophs, and in certain cases hypoxic soil conditions supporting methanogenesis in low-slope areas, drive the observed variability in fluxes. A network of soil static chambers used at the tower site showed close agreement with the eddy covariance flux measurements. This suggests that soil-level microbial processes, and not abiological leaf-level CH4 production, drive overall CH4 dynamics in temperate forest ecosystems such as Haliburton Forest.

  12. Buckling prediction of panels using the vibration correlation technique

    NASA Astrophysics Data System (ADS)

    Abramovich, H.; Govich, D.; Grunwald, A.

    2015-10-01

    The Vibration Correlation Technique (VCT) for experimentally nondestructive determination of buckling loads of thin-walled structures is applied to stringer stiffened curved panels manufactured both from aluminum and laminated composite material. The modal behavior of the panels is investigated by exciting the structures using the modal hammer method. Natural frequencies of the panels are recorded as a function of the applied axial compression load. Unlike shell structures which present a non-stable post-buckling behavior, the stringer stiffened panels show a stable post-buckling behavior, enabling the measurement of the natural frequencies up to the actual experimental buckling load. The modal behavior of compressed panels is compared for reference to shells, yielding areas of applicability for VCT to predict efficiently the buckling loads of thin-walled structures. Guidelines are then formulated for the application of the VCT.

  13. Comparison of Bowen-ratio, eddy-correlation, and weighing-lysimeter evapotranspiration for two sparse-canopy sites in eastern Washington

    USGS Publications Warehouse

    Tomlinson, S.A.

    1996-01-01

    This report compares evapotranspiration estimated with the Bowen-ratio and eddy-correlation methods with evapotranspiration measured by weighing lysimeters for two sparse-canopy sites in eastern Washington. The sites are located in a grassland area (grass lysimeter site) and a sagbrush- covered area (sage lysimeter site) on the Arid Lands Ecology Reserve in Benton County, Washington. Lysimeter data were collected at the sites from August 1990 to November 1994. Bowen-ratio data were collected for varying periods from May 1993 to November 1994. Additional Bowen-ratio data without interchanging air- temperature and vapor-pressure sensors to remove sensor bias (fixed-sensor system) were collected from October 1993 to June 1994. Eddy-correlation data were collected at the grass lysimeter site from March to April 1994, and at the sage lysimeter site from April to May 1994. The comparisons of evapotranspiration determined by the various methods differed considerably, depending on the periods of record being compared and the sites being analyzed. The year 1993 was very wet, with about 50 percent more precipitation than average; 1994 was a very dry year, with only about half the average precipitation. The study showed that on an annual basis, at least in 1994, Bowen-ratio evapotranspiration closely matched lysimeter evapotranspiration. In 1993, Bowen-ratio and lysimeter evapotranspiration comparisons were variable. Evapotranspiration estimated with the Bowen-ratio method averaged 5 percent more than evapotranspiration measured by lysimeters at the grass lysimeter site from October 1993 to November 1994, and 3 percent less than lysimeters at the sage lysimeter site from November 1993 to October 1994. From March 24 to April 5, 1994, at the grass lysimeter site, the Bowen-ratio method estimated 11 percent less, the Bowen-ratio method utilizing the fixed sensor system about 7 percent more, and the eddy-correlation method about 28 percent less evapotranspiration than the

  14. Remote field eddy current detection of stress-corrosion cracks

    SciTech Connect

    Nestleroth, J.B.

    1990-02-01

    The feasibility of detecting stress-corrosion cracks (SSC) using the Remote Field Eddy Current (RFEC) technique was demonstrated. The RFEC technique interrogates the entire thickness of the pipe and is applicable for in-line inspection. If it can be shown that the RFEC technique is effective in detecting SSC, then the technique is an ideal method for detecting the defects of interest. A defect detection model is proposed for explaining the mechanism for crack detection. For axially oriented, closed cracks, such as SCC, the conventional defect detection model proved to be too simplistic and not applicable. Therefore, a new detection mode that examines the flow of circumferential eddy currents was developed based on experimental results. This model, though not rigorous, provides a general understanding of the applicability of the RFEC technique for finding SSC. The data from the cracks and various artificial defects is presented in three formats: isometric projections, pseudocolor images and line-of-sight data. Though only two cracks were found, the experimental results correlate well with the circumferential eddy current theory. A theoretical analysis of the effects of motion on the output signal of the receiver is presented. This analysis indicates that inspection speed of simple implementations may be limited to a few miles per hour. Remote field eddy current inspection has excellent potential for inspection of gas transmission lines for detecting stress corrosion cracks that should be further developed.

  15. Non-contact online thickness measurement system for metal films based on eddy current sensing with distance tracking technique

    NASA Astrophysics Data System (ADS)

    Li, Wei; Wang, Hongbo; Feng, Zhihua

    2016-04-01

    This paper proposes an online, non-contact metal film thickness measurement system based on eddy current sensing. The slope of the lift-off curve (LOC) is used for characterizing target thickness. Theoretical derivation was conducted to prove that the slope is independent of the lift-off variation. In practice, the measurement has some immunity to the lift-off, but not perfect. The slope of LOC is still affected at some extent by the lift-off. Hence, a height tracking system was also proposed, which could stabilize the distance between the sensor and the target and significantly reduce the lift-off effect. The height tracking system contains a specially designed probe, which could vibrate rapidly to obtain a fast measurement speed, and its height can be adjusted up and down continuously to stabilize the lift-off. The sensor coil in the thickness measurement system was also used as the height sensor in the height tracking system. Several experiments were conducted to test the system performances under static and dynamic conditions. This measurement system demonstrated significant advantages, such as simple and clear conversion between the slope of LOC and target thickness, high resolution and stability, and minimized effect of lift-off variation.

  16. Non-contact online thickness measurement system for metal films based on eddy current sensing with distance tracking technique.

    PubMed

    Li, Wei; Wang, Hongbo; Feng, Zhihua

    2016-04-01

    This paper proposes an online, non-contact metal film thickness measurement system based on eddy current sensing. The slope of the lift-off curve (LOC) is used for characterizing target thickness. Theoretical derivation was conducted to prove that the slope is independent of the lift-off variation. In practice, the measurement has some immunity to the lift-off, but not perfect. The slope of LOC is still affected at some extent by the lift-off. Hence, a height tracking system was also proposed, which could stabilize the distance between the sensor and the target and significantly reduce the lift-off effect. The height tracking system contains a specially designed probe, which could vibrate rapidly to obtain a fast measurement speed, and its height can be adjusted up and down continuously to stabilize the lift-off. The sensor coil in the thickness measurement system was also used as the height sensor in the height tracking system. Several experiments were conducted to test the system performances under static and dynamic conditions. This measurement system demonstrated significant advantages, such as simple and clear conversion between the slope of LOC and target thickness, high resolution and stability, and minimized effect of lift-off variation. PMID:27131700

  17. Transient eddies in the MACDA Mars reanalysis

    NASA Astrophysics Data System (ADS)

    Mooring, Todd A.; Wilson, R. John

    2015-10-01

    We present a survey of the transient eddy activity in the Mars Analysis Correction Data Assimilation (MACDA) reanalysis. The spatial structure and propagation characteristics of the eddies are emphasized. Band-pass-filtered variance and covariance fields are found to be zonally modulated, indicating a longitude dependence of the typical amplitudes of Martian transient eddies. Considerable repeatability of the eddy field spatial structures is found across Mars years, including a roughly wave number 3 pattern of low-level eddy meridional temperature transport (v'T'¯) in the northern hemisphere that is evident before and after winter solstice and a possible tendency for northern hemisphere eddy kinetic energy maxima to be located above low-lying areas. Southern hemisphere eddy fields tend to feature two local maxima, one roughly south of Tharsis and the other associated with Hellas. Eddies are weakened near winter solstice in both hemispheres and were generally weakened in the northern hemisphere during the 2001 (Mars year 25) global dust storm, albeit with little change in spatial patterns. Because the transient eddies propagate in space, we also used a teleconnection map-based technique to estimate their phase velocities. Eddy propagation at the surface is found to follow topography, a phenomenon less evident at higher altitude. Possible physical mechanisms underlying the documented eddy phenomena are discussed.

  18. Flap noise characteristics measured by pressure cross correlation techniques

    NASA Astrophysics Data System (ADS)

    Miller, W. R.

    1980-03-01

    The aerodynamic sound generated by a realistic aircraft flap system was investigated through the use of cross correlations between surface pressure fluctuations and far field sound. Measurements were conducted in two subsonic wind tunnel studies to determine the strength, distribution, and directivity of the major sources of flap noise at speeds up to 79.0 m/sec. A pilot study was performed on a single flap model to test the measurement technique and provide initial data on the characteristics of flap noise. The major portion of this investigation studied the sound radiated by a realistic large scale model of a triple slotted flap system mounted on a sweptback 6.7 meter semispan model wing. The results of this investigation have identified the major sources of flap generated noise and their dependence of flow defining parameters. In addition, a possible avenue toward the reduction of flap generated noise has been identified via the placement of the flap actuator fairings on the flap system.

  19. Inexpensive Eddy-Current Standard

    NASA Technical Reports Server (NTRS)

    Berry, Robert F., Jr.

    1985-01-01

    Radial crack replicas serve as evaluation standards. Technique entails intimately joining two pieces of appropriate aluminum alloy stock and centering drilled hole through and along interface. Bore surface of hole presents two vertical stock interface lines 180 degrees apart. These lines serve as radial crack defect replicas during eddy-current technique setup and verification.

  20. Eddies in the Red Sea: A statistical and dynamical study

    NASA Astrophysics Data System (ADS)

    Zhan, Peng; Subramanian, Aneesh C.; Yao, Fengchao; Hoteit, Ibrahim

    2014-06-01

    Sea level anomaly (SLA) data spanning 1992-2012 were analyzed to study the statistical properties of eddies in the Red Sea. An algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks. Statistics suggest that eddies are generated across the entire Red Sea but that they are prevalent in certain regions. A high number of eddies is found in the central basin between 18°N and 24°N. More than 87% of the detected eddies have a radius ranging from 50 to 135 km. Both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase. The averaged eddy lifespan is approximately 6 weeks. AEs and cyclonic eddies (CEs) have different deformation features, and those with stronger intensities are less deformed and more circular. Analysis of long-lived eddies suggests that they are likely to appear in the central basin with AEs tending to move northward. In addition, their eddy kinetic energy (EKE) increases gradually throughout their lifespans. The annual cycles of CEs and AEs differ, although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in February and August, respectively. The seasonal cycle of EKE is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate, suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the Red Sea.

  1. Analysis of carbon dioxide, water vapour and energy fluxes over an Indian teak mixed deciduous forest for winter and summer months using eddy covariance technique

    NASA Astrophysics Data System (ADS)

    Jha, Chandra Shekhar; Thumaty, Kiran Chand; Rodda, Suraj Reddy; Sonakia, Ajit; Dadhwal, Vinay Kumar

    2013-10-01

    In the present study, we report initial results on analysis of carbon dioxide (CO2), water vapour (H2O), and energy fluxes (sensible and latent heat flux) over teak mixed deciduous forests of Madhya Pradesh, central India, during winter (November 2011 and January 2012) and summer (February-May 2012) seasons using eddy covariance flux tower datasets. During the study period, continuous fast response measurements of CO2, H2O and heat fluxes above the canopy were carried out at 10 Hz and averaged for 30 minutes. Concurrently, slow response measurements of meteorological parameters are also being carried out. Diurnal and seasonal variations of CO2, H2O and heat fluxes were analysed and correlated with the meteorological variables. The study showed strong influence of leaf off and on scenario on the CO2, H2O and energy fluxes due to prevalence of deciduous vegetation type in the study area. Maximum amount of CO2 was sequestered for photosynthesis during winter (monthly mean of mol/m2/s) compared to summer (monthly mean of mol/m2/s). Energy flux analysis (weekly mean) showed more energy being portioned into latent heat during winter (668 W/m2) and sensible heat during summer (718 W/m2).

  2. Exploring Eddy-Covariance Measurements Using a Spatial Approach: The Eddy Matrix

    NASA Astrophysics Data System (ADS)

    Engelmann, Christian; Bernhofer, Christian

    2016-04-01

    Taylor's frozen turbulence hypothesis states that "standard" eddy-covariance measurements of fluxes at a fixed location can replace a spatial ensemble of instantaneous values at multiple locations. For testing this hypothesis, a unique turbulence measurement set-up was used for two measurement campaigns over desert (Namibia) and grassland (Germany) in 2012. This "Eddy Matrix" combined nine ultrasonic anemometer-thermometers and 17 thermocouples in a 10 m × 10 m regular grid with 2.5-m grid distance. The instantaneous buoyancy flux derived from the spatial eddy covariance of the Eddy Matrix was highly variable in time (from -0.3 to 1 m K s^{-1} ). However, the 10-min average reflected 83 % of the reference eddy-covariance flux with a good correlation. By introducing a combined eddy-covariance method (the spatial eddy covariance plus the additional flux of the temporal eddy covariance of the spatial mean values), the mean flux increases by 9 % relative to the eddy-covariance reference. Considering the typical underestimation of fluxes by the standard eddy-covariance method, this is seen as an improvement. Within the limits of the Eddy Matrix, Taylor's hypothesis is supported by the results.

  3. Numerical techniques for the study of long-time correlations

    SciTech Connect

    Karney, C.F.F.

    1985-05-01

    In the study of long-time correlations extremely long orbits must be calculated. This may be accomplished much more reliably using fixed-point arithmetic. Use of this arithmetic on the Cray-1 computer is illustrated.

  4. Assessment of the soil water balance by the combination of cosmic ray neutron sensing and eddy covariance technique in an irrigated citrus orchard (Marrakesh, Morocco)

    NASA Astrophysics Data System (ADS)

    Mroos, Katja; Baroni, Gabriele; Er-Raki, Salah; Francke, Till; Khabba, Said; Jarlan, Lionel; Hanich, Lahoucine; Oswald, Sascha E.

    2014-05-01

    Irrigation water requirement plays a crucial role in many agricultural areas and especially in arid and semi-arid landscapes. Improvements in the water management and the performance of the irrigation systems require a correct evaluation of the hydrological processes involved. However, some difficulties can arise due to the heterogeneity of the soil-plant system and of the irrigation scheme. To overcome these limitations, in this study, the soil water balance is analyzed by the combination of the Eddy Covariance technique (EC) and Cosmic Ray neutron Sensing (CRS). EC provides the measurement of the actual evapotranspiration over the area as it was presented in many field conditions. Moreover CRS showed to be a valuable approach to measure the root zone soil moisture integrated in a footprint of ~30 ha. In this way, the combination of the two methodologies should provide a better analysis of the soil water balance at field scale, as opposed to point observations, e.g. by TDR, evaporimeter and fluxmeter. Then, this could increase the capability to assess the irrigation efficiency and the agricultural water management. The study is conducted in a citrus orchard situated in a semi-arid region, 30 km southwest of Marrakesh (Morocco). The site is flat and planted with trees of same age growing in parallel rows with drip irrigation lines and application of fertilizer and pesticides. The original soil seems modified on the surface by the agricultural use, creating differences between trees, rows and lines. In addition, the drip irrigation creates also a spatial variability of the water flux distribution in the field, making this site an interesting area to test the methodology. Particular attention is given to the adaptation of the standard soil sampling campaign used for the calibration of the CRS and the introduction of a weighing function. Data were collected from June to December 2013, which corresponds to the high plant transpiration. Despite the intention of the

  5. Simultaneous Flux Measurements of CO2, its Stable Isotope Ratios and Trace Gases Based on Eddy Accumulation Technique for Flux Partitioning

    NASA Astrophysics Data System (ADS)

    Takahashi, Y.; Hirata, R.

    2007-12-01

    for on-site measurement. Therefore, as a first step, we are planning to measure those fluxes based on an eddy accumulation technique coupled with flask sampling and high precision lab analysis. We report current progress of the development.

  6. The Fate of Ozone at a Ponderosa Pine Plantation: Partitioning Between Stomatal and Non-stomatal Deposition Using Sap Flow and Eddy Covariance Techniques

    NASA Astrophysics Data System (ADS)

    Kurpius, M. R.; McKay, M. M.; Goldstein, A. H.

    2001-12-01

    Major advances in quantifying ozone deposition to vegetated ecosystems have been made using above-canopy techniques -- such as eddy covariance -- that allow for the direct measure of ozone flux into natural systems. However, from above-canopy flux measurements alone, it is impossible to differentiate between deposition through stomatal openings of trees versus non-stomatal surfaces or within canopy chemical loss. Therefore, there is a need to partition ozone fluxes into plant stomatal and non-stomatal components. Sap flow measurements provide a direct measurement of stomatal conductance from which we can infer ozone uptake by trees: this represents a novel way to determine pollutant loading on stomatal surfaces of trees that is inexpensive, reliable, and can be deployed in a multitude of environments. Sap flow measurements were used to determine ozone uptake by ponderosa pine trees in the Sierra Nevada Mountains year-round starting in June 2000 at Blodgett Forest, an Ameriflux site located ~75 miles downwind of Sacramento, CA. Concurrently, total ecosystem ozone flux was measured using eddy covariance. Mean total ozone flux to the ecosystem was 46.6 μ mol m-2 h-1 (+/-15.1) in summer 2000, 27.6 μ mol m-2 h-1 (+/-14.2) in fall 2000, 8.2 μ mol m-2 h-1 (+/-5.1) in winter 2001, and 21.1 μ mol m-2 h-1 (+/-11.6) in spring 2001. Mean ozone flux through the stomata was 14.6 μ mol m-2 h-1 (+/-4.1) during summer 2000, 12.9 μ mol m-2 h-1 (+/-5.8) during fall 2000, 5.6 μ mol m-2 h-1 (+/-2.8) during winter 2001, and 12.7 μ mol m-2 h-1 (+/-3.7) during spring 2001. The percentage of total ozone deposition which occurred through the stomata was 31% in summer, 47% in fall, 69% but highly variable in winter, and 60% in spring. The difference between total ozone flux to the ecosystem and stomatal ozone flux to the trees varied exponentially with air temperature, suggesting that much of the non-stomatal deposition was actually due to chemical loss either on surfaces or within

  7. Problems and solutions in analyzing partial-reflection drift data by correlation techniques

    NASA Technical Reports Server (NTRS)

    Meek, C. E.

    1984-01-01

    Solutions in analyzing partial reflection drift data by correlation techniques are discussed. The problem of analyzing spaced antenna drift data breaks down into the general categories of raw data collection and storage, correlation calculation, interpretation of correlations, location of time lags for peak correlation, and velocity calculation.

  8. Exploring underwater target detection by imaging polarimetry and correlation techniques.

    PubMed

    Dubreuil, M; Delrot, P; Leonard, I; Alfalou, A; Brosseau, C; Dogariu, A

    2013-02-10

    Underwater target detection is investigated by combining active polarization imaging and optical correlation-based approaches. Experiments were conducted in a glass tank filled with tap water with diluted milk or seawater and containing targets of arbitrary polarimetric responses. We found that target estimation obtained by imaging with two orthogonal polarization states always improves detection performances when correlation is used as detection criterion. This experimental study illustrates the potential of polarization imaging for underwater target detection and opens interesting perspectives for the development of underwater imaging systems. PMID:23400061

  9. Accurate prediction of unsteady and time-averaged pressure loads using a hybrid Reynolds-Averaged/large-eddy simulation technique

    NASA Astrophysics Data System (ADS)

    Bozinoski, Radoslav

    Significant research has been performed over the last several years on understanding the unsteady aerodynamics of various fluid flows. Much of this work has focused on quantifying the unsteady, three-dimensional flow field effects which have proven vital to the accurate prediction of many fluid and aerodynamic problems. Up until recently, engineers have predominantly relied on steady-state simulations to analyze the inherently three-dimensional ow structures that are prevalent in many of today's "real-world" problems. Increases in computational capacity and the development of efficient numerical methods can change this and allow for the solution of the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations for practical three-dimensional aerodynamic applications. An integral part of this capability has been the performance and accuracy of the turbulence models coupled with advanced parallel computing techniques. This report begins with a brief literature survey of the role fully three-dimensional, unsteady, Navier-Stokes solvers have on the current state of numerical analysis. Next, the process of creating a baseline three-dimensional Multi-Block FLOw procedure called MBFLO3 is presented. Solutions for an inviscid circular arc bump, laminar at plate, laminar cylinder, and turbulent at plate are then presented. Results show good agreement with available experimental, numerical, and theoretical data. Scalability data for the parallel version of MBFLO3 is presented and shows efficiencies of 90% and higher for processes of no less than 100,000 computational grid points. Next, the description and implementation techniques used for several turbulence models are presented. Following the successful implementation of the URANS and DES procedures, the validation data for separated, non-reattaching flows over a NACA 0012 airfoil, wall-mounted hump, and a wing-body junction geometry are presented. Results for the NACA 0012 showed significant improvement in flow predictions

  10. Utility of correlation techniques in gravity and magnetic interpretation

    NASA Technical Reports Server (NTRS)

    Chandler, V. W.; Koski, J. S.; Braice, L. W.; Hinze, W. J.

    1977-01-01

    Internal correspondence uses Poisson's Theorem in a moving-window linear regression analysis between the anomalous first vertical derivative of gravity and total magnetic field reduced to the pole. The regression parameters provide critical information on source characteristics. The correlation coefficient indicates the strength of the relation between magnetics and gravity. Slope value gives delta j/delta sigma estimates of the anomalous source. The intercept furnishes information on anomaly interference. Cluster analysis consists of the classification of subsets of data into groups of similarity based on correlation of selected characteristics of the anomalies. Model studies are used to illustrate implementation and interpretation procedures of these methods, particularly internal correspondence. Analysis of the results of applying these methods to data from the midcontinent and a transcontinental profile shows they can be useful in identifying crustal provinces, providing information on horizontal and vertical variations of physical properties over province size zones, validating long wavelength anomalies, and isolating geomagnetic field removal problems.

  11. Comparative analysis of matter and energy fluxes determined by Bowen Ratio and Eddy Covariance techniques at a crop site in eastern Germany

    NASA Astrophysics Data System (ADS)

    Brust, K.; Hehn, M.; Bernhofer, C.

    2012-04-01

    The measurement of atmospheric fluxes is an important means to evaluate ecosystem exchanges. In 2009 and 2010, fluxes and gradients of heat, water vapour, and CO2 over winter barley and rapeseed were measured simultaneously at the Klingenberg cropland site in Germany. A Bowen Ratio (BR) system was employed alongside to an existing Eddy Covariance (EC) tower. The BR system is required to account for the longer response time of the chemiluminescence analysers measuring other trace gases, e.g. NOx. To test and evaluate the application of the NOx measurement setup, the two independent systems (BR/EC) are compared with respect to energy and CO2 fluxes. We show a regression and differences analysis, diurnal cycles of the obtained fluxes, and interpret their coherence to the growth stage of the crops. The regression analysis depicts that differences between the systems are largest for latent heat LE (BR detects apparently higher LE due to the forced closure of energy balance), whereby the matter fluxes of CO2 show fairly little differences. Both measurement systems are able to capture the fluctuations of fluxes adequately well. Additionally, a multiple linear regression revealed that differences between the obtained fluxes are not induced by atmospheric conditions. The results of the differences analysis for sensible and latent heat point out that the observed differences of fluxes between both systems are mainly due to deviations in the mean, while differences in variability and timing/shape are of smaller importance. The differences of CO2 fluxes between both measurement systems are particularly caused by deviations in timing and shape, which can be explained with the linear cross-correlation coefficient (R2=0.8). From the good results of the comparison of matter fluxes (CO2) we conclude that the use of the Bowen Ratio method is applicable to other matter fluxes (like NOx).

  12. Eddy current scanning at Fermilab

    SciTech Connect

    Boffo, C.; Bauer, P.; Foley, M.; Brinkmann, A.; Ozelis, J.; /Jefferson Lab

    2005-07-01

    In the framework of SRF cavity development, Fermilab is creating the infrastructure needed for the characterization of the material used in the cavity fabrication. An important step in the characterization of ''as received'' niobium sheets is the eddy current scanning. Eddy current scanning is a non-destructive technique first adopted and further developed by DESY with the purpose of checking the cavity material for sub-surface defects and inclusions. Fermilab has received and further upgraded a commercial eddy current scanner previously used for the SNS project. The upgrading process included developing new filtering software. This scanner is now used daily to scan the niobium sheets for the Fermilab third harmonic and transverse deflecting cavities. This paper gives a status report on the scanning results obtained so far, including a discussion of the typology of signals being detected. We also report on the efforts to calibrate this scanner, a work conducted in collaboration with DESY.

  13. Correlation techniques and measurements of wave-height statistics

    NASA Technical Reports Server (NTRS)

    Guthart, H.; Taylor, W. C.; Graf, K. A.; Douglas, D. G.

    1972-01-01

    Statistical measurements of wave height fluctuations have been made in a wind wave tank. The power spectral density function of temporal wave height fluctuations evidenced second-harmonic components and an f to the minus 5th power law decay beyond the second harmonic. The observations of second harmonic effects agreed very well with a theoretical prediction. From the wave statistics, surface drift currents were inferred and compared to experimental measurements with satisfactory agreement. Measurements were made of the two dimensional correlation coefficient at 15 deg increments in angle with respect to the wind vector. An estimate of the two-dimensional spatial power spectral density function was also made.

  14. An Approach to Minimizing Artifacts Caused by Cross-Sensitivity in the Determination of Air-Sea CO2 Flux Using the Eddy-Covariance Technique

    NASA Astrophysics Data System (ADS)

    Duan, Ziqiang; Gao, Huiwang; Gao, Zengxiang; Wang, Renlei; Xue, Yuhuan; Yao, Xiaohong

    2013-07-01

    The air-sea CO2 flux was measured from a research vessel in the North Yellow Sea in October 2007 using an open-path eddy-covariance technique. In 11 out of 64 samples, the normalized spectra of scalars (C}2, water vapour, and temperature) showed similarities. However, in the remaining samples, the normalized CO2 spectra were observed to be greater than those of water vapour and temperature at low frequencies. In this paper, the noise due to cross-sensitivity was identified through a combination of intercomparisons among the normalized spectra of three scalars and additional analyses. Upon examination, the cross-sensitivity noise appeared to be mainly present at frequencies {<}0.8 Hz. Our analysis also suggested that the high-frequency fluctuations of CO2 concentration (frequency {>}0.8 Hz) was probably less affected by the cross-sensitivity. To circumvent the cross-sensitivity issue, the cospectrum in the high-frequency range 0.8-1.5 Hz, instead of the whole range, was used to estimate the CO2 flux by taking the contribution of the high frequency to the CO2 flux to be the same as the contribution to the water vapour flux. The estimated air-sea CO2 flux in the North Yellow Sea was -0.039 ± 0.048 mg m^{-2} s^{-1}, a value comparable to the estimates using the inertial dissipation method and Edson's method (Edson et al., J Geophys Res 116:C00F10, 2011).

  15. Utility of correlation techniques in gravity and magnetic interpretation

    NASA Technical Reports Server (NTRS)

    Chandler, V. W.; Koski, J. S.; Braile, L. W.; Hinze, W. J.

    1977-01-01

    Two methods of quantitative combined analysis, internal correspondence and clustering, are presented. Model studies are used to illustrate implementation and interpretation procedures of these methods, particularly internal correspondence. Analysis of the results of applying these methods to data from the midcontinent and a transcontinental profile show they can be useful in identifying crustal provinces, providing information on horizontal and vertical variations of physical properties over province size zones, validating long wave-length anomalies, and isolating geomagnetic field removal problems. Thus, these techniques are useful in considering regional data acquired by satellites.

  16. Vortex metrology using Fourier analysis techniques: vortex networks correlation fringes.

    PubMed

    Angel-Toro, Luciano; Sierra-Sosa, Daniel; Tebaldi, Myrian; Bolognini, Néstor

    2012-10-20

    In this work, we introduce an alternative method of analysis in vortex metrology based on the application of the Fourier optics techniques. The first part of the procedure is conducted as is usual in vortex metrology for uniform in-plane displacement determination. On the basis of two recorded intensity speckled distributions, corresponding to two states of a diffuser coherently illuminated, we numerically generate an analytical signal from each recorded intensity pattern by using a version of the Riesz integral transform. Then, from each analytical signal, a two-dimensional pseudophase map is generated in which the vortices are located and characterized in terms of their topological charges and their core's structural properties. The second part of the procedure allows obtaining Young's interference fringes when Fourier transforming the light passing through a diffracting mask with multiple apertures at the locations of the homologous vortices. In fact, we use the Fourier transform as a mathematical operation to compute the far-field diffraction intensity pattern corresponding to the multiaperture set. Each aperture from the set is associated with a rectangular hole that coincides both in shape and size with a pixel from recorded images. We show that the fringe analysis can be conducted as in speckle photography in an extended range of displacement measurements. Effects related with speckled decorrelation are also considered. Our experimental results agree with those of speckle photography in the range in which both techniques are applicable. PMID:23089799

  17. Anisotropic eddy viscosity models

    NASA Technical Reports Server (NTRS)

    Carati, D.; Cabot, W.

    1996-01-01

    A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.

  18. Large Eddy Simulation of a Turbulent Jet

    NASA Technical Reports Server (NTRS)

    Webb, A. T.; Mansour, Nagi N.

    2001-01-01

    Here we present the results of a Large Eddy Simulation of a non-buoyant jet issuing from a circular orifice in a wall, and developing in neutral surroundings. The effects of the subgrid scales on the large eddies have been modeled with the dynamic large eddy simulation model applied to the fully 3D domain in spherical coordinates. The simulation captures the unsteady motions of the large-scales within the jet as well as the laminar motions in the entrainment region surrounding the jet. The computed time-averaged statistics (mean velocity, concentration, and turbulence parameters) compare well with laboratory data without invoking an empirical entrainment coefficient as employed by line integral models. The use of the large eddy simulation technique allows examination of unsteady and inhomogeneous features such as the evolution of eddies and the details of the entrainment process.

  19. Unified Ultrasonic/Eddy-Current Data Acquisition

    NASA Technical Reports Server (NTRS)

    Chern, E. James; Butler, David W.

    1993-01-01

    Imaging station for detecting cracks and flaws in solid materials developed combining both ultrasonic C-scan and eddy-current imaging. Incorporation of both techniques into one system eliminates duplication of computers and of mechanical scanners; unifies acquisition, processing, and storage of data; reduces setup time for repetitious ultrasonic and eddy-current scans; and increases efficiency of system. Same mechanical scanner used to maneuver either ultrasonic or eddy-current probe over specimen and acquire point-by-point data. For ultrasonic scanning, probe linked to ultrasonic pulser/receiver circuit card, while, for eddy-current imaging, probe linked to impedance-analyzer circuit card. Both ultrasonic and eddy-current imaging subsystems share same desktop-computer controller, containing dedicated plug-in circuit boards for each.

  20. Tracking Loop Current eddies with satellite altimetry

    NASA Astrophysics Data System (ADS)

    Leben, Robert R.; Born, George H.

    1993-11-01

    Geosat altimeter derived sea surface height (SSH) anomaly fields have been optimally interpolated onto a regular space time grid using both crossover data from the nonrepeating Geodetic Mission (Geosat-GM) and collinear data from the Exact Repeat Mission (Geosat-ERM). Over four years of data were collected from the combined missions, spanning the time period from April 1985 through August 1989, during which six major and at least two minor Loop Current eddies were directly observed. Eddy paths determined by automated tracking of the local maximum values in the SSH anomaly fields were compared with eddy centers estimated from drifting buoy trajectories, validating the data processing and tracking techniques. Accurate tracking of eddy centers allowed transits of 90°W to be used as a benchmark for determination of eddy shedding periods. For this data set the average period between major eddy transits was 9.8 months, with individual separation periods ranging from 6 to 14 months. The two minor eddies observed were associated with the deepest penetrations of the Loop Current into the gulf, and were nearly coincident with the shedding of the strongest major Loop Current eddies.

  1. Southern Ocean eddy phenomenology

    NASA Astrophysics Data System (ADS)

    Frenger, I.; Münnich, M.; Gruber, N.; Knutti, R.

    2015-11-01

    Mesoscale eddies are ubiquitous features in the Southern Ocean, yet their phenomenology is not well quantified. To tackle this task, we use satellite observations of sea level anomalies and sea surface temperature (SST) as well as in situ temperature and salinity measurements from profiling floats. Over the period 1997-2010, we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more. The Antarctic Circumpolar Current (ACC), the boundary current systems, and the regions where they interact are hot spots of eddy presence, representing also the birth places and graveyards of most eddies. These hot spots contrast strongly to areas shallower than about 2000 m, where mesoscale eddies are essentially absent, likely due to topographical steering. Anticyclones tend to dominate the southern subtropical gyres, and cyclones the northern flank of the ACC. Major causes of regional polarity dominance are larger formation numbers and lifespans, with a contribution of differential propagation pathways of long-lived eddies. Areas of dominance of one polarity are generally congruent with the same polarity being longer-lived, bigger, of larger amplitude, and more intense. Eddies extend down to at least 2000 m. In the ACC, eddies show near surface temperature and salinity maxima, whereas eddies in the subtropical areas generally have deeper anomaly maxima, presumably inherited from their origin in the boundary currents. The temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring.

  2. Eddy current inspection of graphite fiber components

    NASA Technical Reports Server (NTRS)

    Workman, G. L.; Bryson, C. C.

    1990-01-01

    The recognition of defects in materials properties still presents a number of problems for nondestructive testing in aerospace systems. This project attempts to utilize current capabilities in eddy current instrumentation, artificial intelligence, and robotics in order to provide insight into defining geometrical aspects of flaws in composite materials which are capable of being evaluated using eddy current inspection techniques. The unique capabilities of E-probes and horseshoe probes for inspecting probes for inspecting graphite fiber materials were evaluated and appear to hold great promise once the technology development matures. The initial results are described of modeling eddy current interactions with certain flaws in graphite fiber samples.

  3. Remote field eddy current detection of stress-corrosion cracks. Final report

    SciTech Connect

    Nestleroth, J.B.

    1990-02-01

    The feasibility of detecting stress-corrosion cracks (SSC) using the Remote Field Eddy Current (RFEC) technique was demonstrated. The RFEC technique interrogates the entire thickness of the pipe and is applicable for in-line inspection. If it can be shown that the RFEC technique is effective in detecting SSC, then the technique is an ideal method for detecting the defects of interest. A defect detection model is proposed for explaining the mechanism for crack detection. For axially oriented, closed cracks, such as SCC, the conventional defect detection model proved to be too simplistic and not applicable. Therefore, a new detection mode that examines the flow of circumferential eddy currents was developed based on experimental results. This model, though not rigorous, provides a general understanding of the applicability of the RFEC technique for finding SSC. The data from the cracks and various artificial defects is presented in three formats: isometric projections, pseudocolor images and line-of-sight data. Though only two cracks were found, the experimental results correlate well with the circumferential eddy current theory. A theoretical analysis of the effects of motion on the output signal of the receiver is presented. This analysis indicates that inspection speed of simple implementations may be limited to a few miles per hour. Remote field eddy current inspection has excellent potential for inspection of gas transmission lines for detecting stress corrosion cracks that should be further developed.

  4. Phase demodulation from a single fringe pattern based on a correlation technique.

    PubMed

    Robin, Eric; Valle, Valéry

    2004-08-01

    We present a method for determining the demodulated phase from a single fringe pattern. This method, based on a correlation technique, searches in a zone of interest for the degree of similarity between a real fringe pattern and a mathematical model. This method, named modulated phase correlation, is tested with different examples. PMID:15298408

  5. Seasonal Dynamics of N2O and CO2 Emissions from a Corn Production System measured with the Eddy covariance and Chamber techniques

    NASA Astrophysics Data System (ADS)

    Iwuozo, S. A.; Hui, D.; Dennis, S.

    2013-12-01

    Agricultural Practices play a major role in the global fluxes of the greenhouse gases carbon dioxide, nitrous oxide, and methane. The use of fertilizer in Corn production has generated concerns about its contribution to global climate change. Thus, farmers and others concerned have become interested in more efficient fertilization management practice and reduced greenhouse gas emissions. To understand best management practices, in the 2012 and 2013 corn growing seasons, field experiments was conducted at Tennessee State University Agricultural Research and Demonstration Center in Nashville, TN. The study examines the seasonal variations of (N2O) and (CO2) emissions from soil as a function of six treatment that include inorganic nitrogen fertilizer, chicken litter and biochar application. The combinations were: regular URAN 32-0-0 liquid fertilizer (2 times) no till, regular URAN 32-0-0 liquid fertilizer (2 times) conventional till, multiple URAN applications (4 times) no till, Denitrification inhibitor with regular URAN application in no till, chicken litter with regular URAN application no till and URAN application with biochar in no tilled plots. Each treatment was replicated 6 times. N2O and CO2 emissions were measured using a closed chamber method after rainfall event(s), fertilizer applications or every two weeks whichever was shorter. Corresponding soil NH4+-N and NO3--N, soil temperature and moisture were also measured during gas sampling. Plant physiological and growth parameters were measured as appropriate and meteorological records were kept. N2O flux was also continuously measured in a commercial corn field using the eddy covariance (EC) technique fitted with a fast response N2O analyzer to check the N2O emissions at the large scale and compare it to the chamber method. Results obtained with the EC technique were comparable with the chamber methods. Preliminary data indicate that N2O and CO2 fluxes were significantly influenced by the agricultural

  6. Joint transform correlator based on CIELAB model with encoding technique for color pattern recognition

    NASA Astrophysics Data System (ADS)

    Lin, Tiengsheng; Chen, Chulung; Liu, Chengyu; Chen, Yuming

    2010-10-01

    The CIELAB standard color vision model instead of the traditional RGB color model is utilized for polychromatic pattern recognition. The image encoding technique is introduced. The joint transform correlator is set to be the optical configuration. To achieve the distortion invariance in discrimination processes, we have used the minimum average correlation energy approach to yield sharp correlation peak. From the numerical results, it is found that the recognition ability based on CIELAB color specification system is accepted.

  7. Optimized swimmer tracking system by a dynamic fusion of correlation and color histogram techniques

    NASA Astrophysics Data System (ADS)

    Benarab, D.; Napoléon, T.; Alfalou, A.; Verney, A.; Hellard, P.

    2015-12-01

    To design a robust swimmer tracking system, we took into account two well-known tracking techniques: the nonlinear joint transform correlation (NL-JTC) and the color histogram. The two techniques perform comparably well, yet they both have substantial limitations. Interestingly, they also seem to show some complementarity. The correlation technique yields accurate detection but is sensitive to rotation, scale and contour deformation, whereas the color histogram technique is robust for rotation and contour deformation but shows low accuracy and is highly sensitive to luminosity and confusing background colors. These observations suggested the possibility of a dynamic fusion of the correlation plane and the color scores map. Before this fusion, two steps are required. First is the extraction of a sub-plane of correlation that describes the similarity between the reference and target images. This sub-plane has the same size as the color scores map but they have different interval values. Thus, the second step is required which is the normalization of the planes in the same interval so they can be fused. In order to determine the benefits of this fusion technique, first, we tested it on a synthetic image containing different forms with different colors. We thus were able to optimize the correlation plane and color histogram techniques before applying our fusion technique to real videos of swimmers in international competitions. Last, a comparative study of the dynamic fusion technique and the two classical techniques was carried out to demonstrate the efficacy of the proposed technique. The criteria of comparison were the tracking percentage, the peak to correlation energy (PCE), which evaluated the sharpness of the peak (accuracy), and the local standard deviation (Local-STD), which assessed the noise in the planes (robustness).

  8. Eddy fluxes in baroclinic turbulence

    NASA Astrophysics Data System (ADS)

    Thompson, Andrew F.

    The eddy heat flux generated by the statistically equilibrated baroclinic instability of a uniform, horizontal temperature gradient is studied using a two-mode quasigeostrophic model. An overview of the dependence of the eddy diffusivity of heat Dtau on the planetary potential vorticity gradient beta, the bottom friction kappa, the deformation radius lambda, the vertical shear of the large-scale flow 2U and the domain size L is provided at 70 numerical simulations with beta = 0 (f-plane) and 110 simulations with beta ≠ 0 (beta-plane). Strong, axisymmetric, well-separated baroclinic vortices dominate the equilibrated barotropic vorticity and temperature fields of f-plane turbulence. The heat flux arises from a systematic northward (southward) migration of anti-cyclonic (cyclonic) eddies with warm (cold) fluid trapped in the cores. Zonal jets form spontaneously on the beta-plane, and stationary, isotropic, jet-scale eddies align within the strong eastward-flowing regions of the jets. In both studies, the vortices and jets give rise to a strong anti-correlation between the barotropic vorticity zeta and the temperature field tau. The baroclinic mode is also an important contributor to dissipation by bottom friction and energizes the barotropic mode at scales larger than lambda. This in part explains why previous parameterizations for the eddy heat flux based on Kolmogorovian cascade theories are found to be unreliable. In a separate study, temperature and salinity profiles obtained with expendable conductivity, temperature and depth (XCTD) probes within Drake Passage, Southern Ocean are used to analyze the turbulent diapycnal eddy diffusivity kappa rho to a depth of 1000 meters. The Polar Front separates two dynamically different regions with strong, surface-intensified mixing north of the Front. South of the Polar Front mixing is weaker and peaks at a depth of approximately 500 m, near the local temperature maximum. Peak values of kapparho are found to exceed 10-3 m

  9. "Audibilization" in the Chemistry Laboratory: An Introduction to Correlation Techniques for Data Extraction

    ERIC Educational Resources Information Center

    Hovick, James W.; Murphy, Michael; Poler, J. C.

    2007-01-01

    The study describes the development and advantages of various correlation techniques that are used for data extraction and are integral to all modern instrumentation. The "Audibilization" of the electronic signals in such cases is found to be very essential for the technique.

  10. Novel Optical Technique Developed and Tested for Measuring Two-Point Velocity Correlations in Turbulent Flows

    NASA Technical Reports Server (NTRS)

    Zimmerli, Gregory A.; Goldburg, Walter I.

    2002-01-01

    A novel technique for characterizing turbulent flows was developed and tested at the NASA Glenn Research Center. The work is being done in collaboration with the University of Pittsburgh, through a grant from the NASA Microgravity Fluid Physics Program. The technique we are using, Homodyne Correlation Spectroscopy (HCS), is a laser-light-scattering technique that measures the Doppler frequency shift of light scattered from microscopic particles in the fluid flow. Whereas Laser Doppler Velocimetry gives a local (single-point) measurement of the fluid velocity, the HCS technique measures correlations between fluid velocities at two separate points in the flow at the same instant of time. Velocity correlations in the flow field are of fundamental interest to turbulence researchers and are of practical importance in many engineering applications, such as aeronautics.

  11. A comparison of image registration techniques for the correlation of radiolabelled antibody distribution with tumour morphology.

    PubMed

    Flynn, A A; Green, A J; Boxer, G; Pedley, R B; Begent, R H

    1999-07-01

    Image registration is a powerful tool for correlating functional images with images of anatomical structure. This facilitates more accurate quantitation of regional radiopharmaceutical uptake. Similarly, registration of images of radiolabelled antibody distribution, in tissue sections, with the equivalent histological images allows the comparison and measurement of radiopharmaceutical distribution with morphological structure. The images used were obtained by storage phosphor plate technology, for the radiopharmaceutical distribution, and by digitization of the stained histological sections. Here we compare four fully automatic registration techniques and one manual technique in terms of their spatial accuracy. We have found that there was no difference in accuracy between cross-correlation, minimization of variance and mutual information. These techniques were more accurate than principal axes and the manual technique. However, minimization of variance and mutual information were more time-consuming than the other methods. Consequently, cross-correlation is the method of choice for automatic registration of large numbers of these image pairs. PMID:10442718

  12. Remote field eddy current inspection

    SciTech Connect

    Atherton, D.L.

    1995-11-01

    The Remote Field Eddy Current (RFEC) technique uses an internal probe to inspect conducting tubes nondestructively. A coaxial solenoidal exciter, energized with low frequency AC, and detector coils near the inside of the pipe wall are separated by about two pipe diameters to obtain through wall transmission and equal sensitivity to defects on the outside or inside of the pipe wall. Calculation methods are outlined and the voltage plane polar plot signal representation for defect measurement is described. Slit defect interactions in ferromagnetic and non-ferromagnetic tubes are discussed. Defect-induced anomalous fields are interpreted in terms of anomalous source eddy current and missing magnetization defect models. The use of computer animations to represent the time variations of high resolution field measurements and calculations is described.

  13. Automated eddy current analysis of materials

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.

    1991-01-01

    The use of eddy current techniques for characterizing flaws in graphite-based filament-wound cylindrical structures is described. A major emphasis was also placed upon incorporating artificial intelligence techniques into the signal analysis portion of the inspection process. Developing an eddy current scanning system using a commercial robot for inspecting graphite structures (and others) was a goal in the overall concept and is essential for the final implementation for the expert systems interpretation. Manual scans, as performed in the preliminary work here, do not provide sufficiently reproducible eddy current signatures to be easily built into a real time expert system. The expert systems approach to eddy current signal analysis requires that a suitable knowledge base exist in which correct decisions as to the nature of a flaw can be performed. A robotic workcell using eddy current transducers for the inspection of carbon filament materials with improved sensitivity was developed. Improved coupling efficiencies achieved with the E-probes and horseshoe probes are exceptional for graphite fibers. The eddy current supervisory system and expert system was partially developed on a MacIvory system. Continued utilization of finite element models for predetermining eddy current signals was shown to be useful in this work, both for understanding how electromagnetic fields interact with graphite fibers, and also for use in determining how to develop the knowledge base. Sufficient data was taken to indicate that the E-probe and the horseshoe probe can be useful eddy current transducers for inspecting graphite fiber components. The lacking component at this time is a large enough probe to have sensitivity in both the far and near field of a thick graphite epoxy component.

  14. Mesoscale eddies in the NE Pacific tropical-subtropical zone.

    NASA Astrophysics Data System (ADS)

    Kurczyn, J. A.; Beier, E.; Lavín, M. F.; Chaigneau, A.

    2012-04-01

    Mesoscale eddy characteristics in the NE Pacific tropical-subtropical zone (16-30N) are analyzed using nearly 20 years of satellite altimetry maps and an automated eddy detection algorithm known as "the closed contours of sea-level anomaly (SLA)". The mean eddy characteristics of the study region are described based on the analysis of 1055 anticyclonic and 1097 cyclonic eddy trajectories. Eddies are preferentially formed near the coast in three main subregions: Punta Eugenia, Cabo San Lucas and Cabo Corrientes. The seasonally highest eddy generation occurs during spring in the three subregions, when surface winds are upwelling-favorable and strong upwelling events occur, thus promoting strong vertical shear between currents. Being highly non-linear and propagating toward the open ocean, mesoscale eddies can thus transport near-coastal seawater properties and plankton toward remote regions. In general, Punta Eugenia and Cabo San Lucas show the highest eddy occurrence. Long-lived eddies, having a life span greater than 16 weeks, are preferentially formed in Punta Eugenia. On average, eddy radii are larger than the Rossby internal radius of deformation, probably due to an up-scale energy cascade of geostrophic turbulence. Mean eddy propagation speeds in Cabo San Lucas and Punta Eugenia regions show higher values than the first baroclinic Rossby waves, while eddies south of ~19N travel slightly slower. The seasonal eddy generation and the eddy-prolific areas can be explained by the climatology of surface currents, where the eddy-prolific areas coincide with sites of strongest surface speeds, and the timing of the highest seasonal eddy generation corresponds with the strongest seasonal surface currents. Although relatively strong interannual variability is observed in terms of the local eddy activity index, no clear correlation is observed between eddy-generation events and large-scale climate indices such as the Pacific Decadal Oscillation index or the Multivariate

  15. Multispectral image sharpening using wavelet transform techniques and spatial correlation of edges

    USGS Publications Warehouse

    Lemeshewsky, George P.; Schowengerdt, Robert A.

    2000-01-01

    Several reported image fusion or sharpening techniques are based on the discrete wavelet transform (DWT). The technique described here uses a pixel-based maximum selection rule to combine respective transform coefficients of lower spatial resolution near-infrared (NIR) and higher spatial resolution panchromatic (pan) imagery to produce a sharpened NIR image. Sharpening assumes a radiometric correlation between the spectral band images. However, there can be poor correlation, including edge contrast reversals (e.g., at soil-vegetation boundaries), between the fused images and, consequently, degraded performance. To improve sharpening, a local area-based correlation technique originally reported for edge comparison with image pyramid fusion is modified for application with the DWT process. Further improvements are obtained by using redundant, shift-invariant implementation of the DWT. Example images demonstrate the improvements in NIR image sharpening with higher resolution pan imagery.

  16. Study of photon correlation techniques for processing of laser velocimeter signals

    NASA Technical Reports Server (NTRS)

    Mayo, W. T., Jr.

    1977-01-01

    The objective was to provide the theory and a system design for a new type of photon counting processor for low level dual scatter laser velocimeter (LV) signals which would be capable of both the first order measurements of mean flow and turbulence intensity and also the second order time statistics: cross correlation auto correlation, and related spectra. A general Poisson process model for low level LV signals and noise which is valid from the photon-resolved regime all the way to the limiting case of nonstationary Gaussian noise was used. Computer simulation algorithms and higher order statistical moment analysis of Poisson processes were derived and applied to the analysis of photon correlation techniques. A system design using a unique dual correlate and subtract frequency discriminator technique is postulated and analyzed. Expectation analysis indicates that the objective measurements are feasible.

  17. Non-degenerated photoluminescence excitation correlation spectroscopy using an optical sampling technique

    SciTech Connect

    Hasegawa, Takayuki; Masumoto, Naofumi; Harada, Tomonori; Makino, Takayuki; Takagi, Yoshihiro

    2012-10-15

    We have developed a highly time-resolved photoluminescence spectroscopy based on the excitation correlation method. Successive irradiation of a pair of ultrashort light pulses with different wavelength combinations taken from two sub-picosecond lasers has exposed both temporal and energetic correlation in photoluminescence intensity associated with a nonlinear response of a sample. An optical sampling technique has been introduced successfully in order to avoid consideration of the synchronization control of ultrashort light pulses. We have demonstrated the abilities of this technique by applying to the nonlinear photoluminescence dynamics of organic dye molecules in solution.

  18. Correlation of the deply technique with ultrasonic imaging of impact damage in graphite-epoxy composites

    NASA Technical Reports Server (NTRS)

    Smith, B. T.; Heyman, J. S.; Buoncristiani, A. M.; Blodgett, E. D.; Miller, J. G.

    1989-01-01

    The ultrasonic quantitative NDE of graphite-epoxy composites is difficult because of the inherent inhomogeneity of the material. An examination technique must discriminate between inherent scattering centers in an undamaged region and the scattering centers due to defects or damage. Two NDE techniques that can make this distinction were used to image and quantify the extent of damage resulting from a low-energy impact. These results were then compared with those from a destructive technique. The first NDE technique, polar backscatter, employed a nonzero polar angle insonifying method to reduce specular reflection from the surface of the sample; the second NDE technique used a normal-incidence ultrasonic beam. Results from both NDE methods were subsequently correlated with those from a destructive technique, the deply method. Both the qualitative and quantitative agreement of the methods was excellent.

  19. Pitch evaluation of gratings based on a digital image correlation technique

    NASA Astrophysics Data System (ADS)

    Lu, Yancong; Jia, Wei; Wei, Chunlong; Yu, Junjie; Li, Shubin; Li, Yanyang; Li, Minkang; Qiu, Jucheng; Wang, Shaoqing; Zhou, Changhe

    2016-04-01

    The digital image correlation (DIC) technique used for metrological grating evaluation is presented in this paper. A CCD camera is used to acquire the grating image, and the DIC technique together with the peak-position detection method is used to evaluate the grating pitches. The theoretical analysis and simulations are performed to confirm that the performance of our technique is as accurate as the Fourier transform (FT) technique, and is capable of noise resistance. As an example, the uniformity of the grating fabricated in our laboratory is measured using this method. The experimental results show that this grating has a peak-to-valley uniformity of 48 nm during a long range of 35 mm, and our technique has a higher repeatability than the FT technique in our measurement strategy. This work should be of great significance for the evaluation of metrological grating for optical encoders.

  20. A new gauge-invariant method for diagnosing eddy diffusivities

    NASA Astrophysics Data System (ADS)

    Mak, J.; Maddison, J. R.; Marshall, D. P.

    2016-08-01

    Coarse resolution numerical ocean models must typically include a parameterisation for mesoscale turbulence. A common recipe for such parameterisations is to invoke mixing of some tracer quantity, such as potential vorticity or buoyancy. However, it is well known that eddy fluxes include large rotational components which necessarily do not lead to any mixing; eddy diffusivities diagnosed from unfiltered fluxes are thus contaminated by the presence of these rotational components. Here a new methodology is applied whereby eddy diffusivities are diagnosed directly from the eddy force function. The eddy force function depends only upon flux divergences, is independent of any rotational flux components, and is inherently non-local and smooth. A one-shot inversion procedure is applied, minimising the mis-match between parameterised force functions and force functions derived from eddy resolving calculations. This enables diffusivities associated with the eddy potential vorticity and Gent-McWilliams coefficients associated with eddy buoyancy fluxes to be diagnosed. This methodology is applied to multi-layer quasi-geostrophic ocean gyre simulations. It is found that: (i) a strictly down-gradient scheme for mixing potential vorticity and quasi-geostrophic buoyancy has limited success in reducing the mis-match compared to one with no sign constraint on the eddy diffusivity or Gent--McWilliams coefficient, with prevalent negative signals around the time-mean jet; (ii) the diagnostic is successful away from the jet region and wind-forced top layer; (iii) the locations of closed mean stream lines correlate with signals of positive eddy potential vorticity diffusivity; (iv) there is indication that the magnitude of the eddy potential vorticity diffusivity correlates well with the eddy energy. Implications for parameterisation are discussed in light of these diagnostic results.

  1. Correlation between near infrared spectroscopy and electrical techniques in measuring skin moisture content

    NASA Astrophysics Data System (ADS)

    Mohamad, M.; Sabbri, A. R. M.; Mat Jafri, M. Z.; Omar, A. F.

    2014-11-01

    Near infrared (NIR) spectroscopy technique serves as an important tool for the measurement of moisture content of skin owing to the advantages it has over the other techniques. The purpose of the study is to develop a correlation between NIR spectrometer with electrical conventional techniques for skin moisture measurement. A non-invasive measurement of moisture content of skin was performed on different part of human face and hand under control environment (temperature 21 ± 1 °C, relative humidity 45 ± 5 %). Ten healthy volunteers age between 21-25 (male and female) participated in this study. The moisture content of skin was measured using DermaLab® USB Moisture Module, Scalar Moisture Checker and NIR spectroscopy (NIRQuest). Higher correlation was observed between NIRQuest and Dermalab moisture probe with a coefficient of determination (R2) above 70 % for all the subjects. However, the value of R2 between NIRQuest and Moisture Checker was observed to be lower with the R2 values ranges from 51.6 to 94.4 %. The correlation of NIR spectroscopy technique successfully developed for measuring moisture content of the skin. The analysis of this correlation can help to establish novel instruments based on an optical system in clinical used especially in the dermatology field.

  2. Correlations Between Teacher and Student Backgrounds and Teacher Perceptions of Discipline Problems and Disciplinary Techniques.

    ERIC Educational Resources Information Center

    Moore, W. L.; Cooper, Harris

    1984-01-01

    A study in Columbia, Missouri, revealed that many teacher and student background characteristics correlated weakly but significantly with teachers' perceptions of the frequency of discipline infractions and the effectiveness of disciplinary techniques. The data (derived from school records and from a questionnaire to which 162 elementary teachers…

  3. Time-Correlated Photon Counting (TCPC) technique based on a photon-number-resolving photodetector

    NASA Astrophysics Data System (ADS)

    Li, Baicheng; Miao, Quanlong; Wang, Shenyuan; Hui, Debin; Zhao, Tianqi; Liang, Kun; Yang, Ru; Han, Dejun

    2016-05-01

    In this report, we present Time-Correlated Photon Counting (TCPC) technique and its applications in time-correlated Raman spectroscopy. The main difference between TCPC and existing Time-Correlated Single Photon Counting (TCSPC) is that the TCPC employs a photon-number-resolving photodetector (SiPM, silicon photomultiplier) and measures exact photon number rather than counting single photon by reducing pulse light intensity, thus high measurement speed and efficiency can be expected. A home-made Raman spectrometer has demonstrated an Instrument Response Function (IRF) ~100ps (FWHM) based on TCPC with a strip SiPM (1mm×0.05mm, containing 500 micro cells), fast and weak Raman signals was separated from slow and strong fluorescence background of bulk trinitrotoluene TNT sample. The original Raman spectrum of bulk TNT, measured by TCPC technique, is compared with the result obtained by a commercial Micro-Raman Spectrometer.

  4. Field transients of coherent terahertz synchrotron radiation accessed via time-resolving and correlation techniques

    NASA Astrophysics Data System (ADS)

    Pohl, A.; Semenov, A.; Hübers, H.-W.; Hoehl, A.; Ries, M.; Wüstefeld, G.; Ulm, G.; Ilin, K.; Thoma, P.; Siegel, M.

    2016-03-01

    Decaying oscillations of the electric field in repetitive pulses of coherent synchrotron radiation in the terahertz frequency range was evaluated by means of time-resolving and correlation techniques. Comparative analysis of real-time voltage transients of the electrical response and interferograms, which were obtained with an ultrafast zero-bias Schottky diode detector and a Martin-Puplett interferometer, delivers close values of the pulse duration. Consistent results were obtained via the correlation technique with a pair of Golay Cell detectors and a pair of resonant polarisation-sensitive superconducting detectors integrated on one chip. The duration of terahertz synchrotron pulses does not closely correlate with the duration of single-cycle electric field expected for the varying size of electron bunches. We largely attribute the difference to the charge density oscillations in electron bunches and to the low-frequency spectral cut-off imposed by both the synchrotron beamline and the coupling optics of our detectors.

  5. Eddy-current testing

    NASA Technical Reports Server (NTRS)

    Pasley, R. L.; Birdwell, J. A.

    1973-01-01

    Eddy-current inspection is discussed as a method for locating subsurface flaws in electrically conductive materials. The physical principles and electrical circuitry are described along with the test equipment.

  6. The eddy cannon

    NASA Astrophysics Data System (ADS)

    Pichevin, Thierry; Nof, Doron

    1996-09-01

    A new nonlinear mechanism for the generation of "Meddies" by a cape is proposed. The essence of the new process is that the flow-force associated with any steady current that curves back on itself around a cape cannot be balanced without generating and shedding eddies. The process is modeled as follows. A westward flowing density current advances along a zonal wall and turns eastward after reaching the edge of the wall (i.e. the Cape of St Vincent). Integration of the steady (and inviscid) momentum equation along the wall gives the long-shore flow-force and shows that, no matter what the details of the turning process are, such a scenario is impossible. It corresponds to an unbalanced flow-force and, therefore, cannot exist. Namely, in an analogy to a rocket, the zonal longshore current forces the entire system to the west. A flow field that can compensate for such a force is westward drifting eddies that push the system to the east. In a similar fashion to the backward push associated with a firing cannon, the westward moving eddies (bullets) balance the integrated momentum of the flow around the cape. Nonlinear solutions are constructed analytically using an approach that enables one to compute the eddies' size and generation frequency without solving for the incredibly complicated details of the generation process itself. The method takes advantage of the fact that, after each eddy is generated, the system returns to its original structure. It is based on the integration of the momentum equation (for periodic flows) over a control volume and a perturbation expansion in ɛ, the ratio between the eddies' westward drift and the parent current speed. It is found that, because of the relatively small size of the Mediterranean eddies, β is not a sufficiently strong mechanism to remove the eddies (from the Cape of St Vincent) at the observed frequency. It is, therefore, concluded that westward advection must also take place. Specifically, it is found that an advection

  7. Full-field detection of surface defects using real-time holography and optical correlation techniques

    NASA Astrophysics Data System (ADS)

    Blackshire, James L.; Duncan, Bradley D.

    1999-02-01

    Innovative optical NDE techniques are being developed for the full-field detection and evaluation of surface defects and defect precursors in titanium and aluminum based alloys. The techniques are based on frequency-translated holography and optical correlation principles, and use bacteriohodopsin (bR) holographic films and temporal correlation techniques for real-time storage and retrieval of Surface Acoustic Waves (SAW) features and embedded surface defect information. The SAW waves induced on the material surface being studied are made to interfere with optical light waves, and fringes are produced that are a function of optical Doppler shifts induced by phonon-photon interaction on the surface of the materials. Visualization of these SAW patterns allow for NDE characterization of features on and near the surface of the materials, including defect and defect precursor sites. Preliminary results are provided for real-time bR holographic recordings of acoustic patterns induced on Al2024-T3 material surfaces.

  8. Revolving Eddy-Current Probe Detects Cracks Near Rivets

    NASA Technical Reports Server (NTRS)

    Namkung, Min; Wincheski, Buzz; Fulton, James P.; Nath, Shridhar; Simpson, John

    1995-01-01

    Scanning eddy-current probe in circular pattern increases sensitivity with which probe indicates fatigue cracks and other defects in metal surfaces in vicinity of rivets. Technique devised to facilitate inspection of riveted joints in aircraft. Eddy-current probe in question described in "Electro-magnetic Flaw Detector Is Easier To Use" (LAR-15046).

  9. Remote field eddy current inspection of support plate fretting wear

    SciTech Connect

    Shatat, A.; Atherton, D.L.

    1997-03-01

    This article demonstrates how the remote field eddy current technique might be extended to measure support plate fretting wear in heat exchanger tubes. A finite element analysis was used to examine the plate`s effect on the eddy current signal. Experimental data lend support to a suggested multifrequency method for sizing fretting grooves.

  10. Automated eddy current analysis of materials

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.

    1990-01-01

    This research effort focused on the use of eddy current techniques for characterizing flaws in graphite-based filament-wound cylindrical structures. A major emphasis was on incorporating artificial intelligence techniques into the signal analysis portion of the inspection process. Developing an eddy current scanning system using a commercial robot for inspecting graphite structures (and others) has been a goal in the overall concept and is essential for the final implementation for expert system interpretation. Manual scans, as performed in the preliminary work here, do not provide sufficiently reproducible eddy current signatures to be easily built into a real time expert system. The expert systems approach to eddy current signal analysis requires that a suitable knowledge base exist in which correct decisions as to the nature of the flaw can be performed. In eddy current or any other expert systems used to analyze signals in real time in a production environment, it is important to simplify computational procedures as much as possible. For that reason, we have chosen to use the measured resistance and reactance values for the preliminary aspects of this work. A simple computation, such as phase angle of the signal, is certainly within the real time processing capability of the computer system. In the work described here, there is a balance between physical measurements and finite element calculations of those measurements. The goal is to evolve into the most cost effective procedures for maintaining the correctness of the knowledge base.

  11. Transient eddy current flow metering

    NASA Astrophysics Data System (ADS)

    Forbriger, J.; Stefani, F.

    2015-10-01

    Measuring local velocities or entire flow rates in liquid metals or semiconductor melts is a notorious problem in many industrial applications, including metal casting and silicon crystal growth. We present a new variant of an old technique which relies on the continuous tracking of a flow-advected transient eddy current that is induced by a pulsed external magnetic field. This calibration-free method is validated by applying it to the velocity of a spinning disk made of aluminum. First tests at a rig with a flow of liquid GaInSn are also presented.

  12. Casimir Interaction from Magnetically Coupled Eddy Currents

    SciTech Connect

    Intravaia, Francesco; Henkel, Carsten

    2009-09-25

    We study the quantum and thermal fluctuations of eddy (Foucault) currents in thick metallic plates. A Casimir interaction between two plates arises from the coupling via quasistatic magnetic fields. As a function of distance, the relevant eddy current modes cross over from a quantum to a thermal regime. These modes alone reproduce previously discussed thermal anomalies of the electromagnetic Casimir interaction between good conductors. In particular, they provide a physical picture for the Casimir entropy whose nonzero value at zero temperature arises from a correlated, glassy state.

  13. The statistical behaviour of attached eddies

    NASA Astrophysics Data System (ADS)

    Woodcock, J. D.; Marusic, I.

    2015-01-01

    Townsend's attached eddy hypothesis forms the basis of an established model of the logarithmic layer in wall-bounded turbulent flows in which this inertially dominated region is characterised by a hierarchy of geometrically self-similar eddying motions that scale with their distance to the wall. The hypothesis has gained considerable support from high Reynolds number measurements of the second-order moments of the fluctuating velocities. Recently, Meneveau and Marusic ["Generalized logarithmic law for high-order moments in turbulent boundary layers," J. Fluid Mech. 719, R1 (2013)] presented experimental evidence that all even-ordered moments of the streamwise velocity will exhibit a logarithmic dependence on the distance from the wall. They demonstrated that this was consistent with the attached eddy hypothesis, so long as the velocity distribution is assumed to be Gaussian (which allows the use of the central limit theorem). In this paper, we derive this result from the attached eddy model without assuming a Gaussian velocity distribution, and find that such logarithmic behaviours are valid in the large Reynolds number limit. We also revisit the physical and mathematical basis of the attached eddy hypothesis, in order to increase rigour and minimise the assumptions required to apply the hypothesis. To this end, we have extended the proof of Campbell's theorem to apply to the velocity field corresponding to a forest of variously sized eddies that are randomly placed on the wall. This enables us to derive all moments of the velocity in the logarithmic region, including cross-correlations between different components of the velocity. By contrast, previous studies of the attached eddy hypothesis have considered only the mean velocity and its second order moments. From this, we obtain qualitatively correct skewnesses and flatnesses for the spanwise and wall-normal fluctuations. The issue of the Reynolds number dependence of von Kármán's constant is also addressed.

  14. Relationships among the slopes of lines derived from various data analysis techniques and the associated correlation coefficient

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.

    1980-01-01

    A technique for fitting a straight line to a collection of data points is given. The relationships between the slopes and correlation coefficients, and between the corresponding standard deviations and correlation coefficient are given.

  15. A simple cross-correlation technique between infrared and hard x-ray pulses.

    SciTech Connect

    Kraessig, B.; Dunford, R. W.; Kanter, E. P.; Landahl, E. C.; Southworth, S. H.; Young, L.; Chemical Sciences and Engineering Division

    2009-04-27

    We report a gas phase technique to establish the temporal overlap of ultrafast infrared laser and hard x-ray pulses. We use tunnel ionization of a closed shell atom in the strong field at the focus of an infrared laser beam to open a distinct x-ray absorption resonance channel with a clear fluorescence signature. The technique has an intrinsic response of a few femtoseconds and is nondestructive to the two beams. It provides a step-functionlike cross-correlation result. The details of the transient provide a diagnostic of the temporal overlap of the two pulses.

  16. Active-passive correlation spectroscopy - A new technique for identifying ocean color algorithm spectral regions

    NASA Technical Reports Server (NTRS)

    Hoge, F. E.; Swift, R. N.

    1986-01-01

    A new active-passive airborne data correlation technique has been developed which allows the validation of existing in-water oceoan color algorithms and the rapid search, identification, and evaluation of new sensor band locations and algorithm wavelength intervals. Thus far, applied only in conjunction with the spectral curvature algorithm (SCA), the active-passive correlation spectroscopy (APCS) technique shows that (1) the usual 490-nm (center-band) chlorophyll SCA could satisfactorily be placed anywhere within the nominal 460-510-nm interval, and (2) two other spectral regions, 645-660 and 680-695 nm, show considerable promise for chlorophyll pigment measurement. Additionally, the APCS method reveals potentially useful wavelength regions (at 600 and about 670 nm) of very low chlorophyll-in-water spectral curvature into which accessory pigment algorithms for phycoerythrin might be carefully positioned. In combination, the APCS and SCA methods strongly suggest that significant information content resides within the seemingly featureless ocean color spectrum.

  17. Homogeneous and inhomogeneous eddies

    SciTech Connect

    Pavia, E.G.

    1994-12-31

    This work deals with mesoscale warm oceanic eddies; i.e., self-contained bodies of water which transport heat, among other things, for several months and for several hundreds of kilometers. This heat transport is believed to play an important role in the atmospheric and oceanic conditions of the region where it is being transported. Here the author examines the difference in evolution between eddies modeled as blobs of homogeneous water and eddies in which density varies in the horizontal. Preliminary results suggest that instability is enhanced by inhomogeneities, which would imply that traditional modeling studies, based on homogeneous vortices have underestimated the rate of heat-release from oceanic eddies to the surroundings. The approach is modeling in the simplest form; i.e., one single active layer. Although previous studies have shown the drastic effect on stability brought by two or more dynamically-relevant homogeneous layers, the author believes the single-layer eddy-model has not been investigated thoroughly.

  18. Optical Measurement Techniques for Rocket Engine Testing and Component Applications: Digital Image Correlation and Dynamic Photogrammetry

    NASA Technical Reports Server (NTRS)

    Gradl, Paul

    2016-01-01

    NASA Marshall Space Flight Center (MSFC) has been advancing dynamic optical measurement systems, primarily Digital Image Correlation, for extreme environment rocket engine test applications. The Digital Image Correlation (DIC) technology is used to track local and full field deformations, displacement vectors and local and global strain measurements. This technology has been evaluated at MSFC through lab testing to full scale hotfire engine testing of the J-2X Upper Stage engine at Stennis Space Center. It has been shown to provide reliable measurement data and has replaced many traditional measurement techniques for NASA applications. NASA and AMRDEC have recently signed agreements for NASA to train and transition the technology to applications for missile and helicopter testing. This presentation will provide an overview and progression of the technology, various testing applications at NASA MSFC, overview of Army-NASA test collaborations and application lessons learned about Digital Image Correlation.

  19. Earthquake-explosion discrimination using waveform cross-correlation technique for mines in southeast of Tehran

    NASA Astrophysics Data System (ADS)

    Kahbasi, A.; Moradi, A.

    2016-04-01

    The presence of man-made explosions in a seismic catalogue leads to errors in statistical analyses of seismicity. Recently, the need to monitor man-made explosions used for mining, road excavating, and other constructional applications has been become a demanding challenge for the seismologists. In this way, we gain new insight into the cross-correlation technique and conduct this approach to discriminate explosions from seismic datasets. Following this, improved P-wave arrival times are used for more precise relocation. In this study, the waveform cross-correlation technique provides a reliable means for discriminating explosions which have cross-correlation coefficients (CC) of 0.6 or greater with their own corresponding stacked waveforms. The results illustrate that approximately 80 % of seismicity of southeast of Tehran, recorded by the Iranian Seismological Center (IRSC), includes events which have cross-correlation coefficients of ≥0.6 with their corresponding stacked waveforms. Furthermore, with improved P-wave arrival time, there is a better chance to relocate explosions precisely in the region under study.

  20. Eddy current heating in magnetic refrigerators

    NASA Technical Reports Server (NTRS)

    Kittel, Peter

    1990-01-01

    Eddy current heating can be a significant source of parasitic heating in low temperature magnetic refrigerators. To study this problem a technique to approximate the heating due to eddy currents has been developed. A formula is presented for estimating the heating within a variety of shapes commonly found in magnetic refrigerators. These shapes include circular, square, and rectangular rods; cylindrical and split cylindrical shells; wire loops; and 'coil foil. One set of components evaluated are different types of thermal radiation shields. This comparison shows that a simple split shield is almost as effective (only 23 percent more heating) as using a shield, with the same axial thermal conductivity, made of 'coil foil'.

  1. The Tundra is a Net Source of CO2 Measured by Autochambers and Eddy Covariance Techniques During Five Years in a Site With Permafrost Thawing.

    NASA Astrophysics Data System (ADS)

    Celis, G.; Mauritz, M.; Bracho, R. G.; Salmon, V. G.; Webb, E.; Hutchings, J. A.; Natali, S.; Crummer, K. G.; Schuur, E.; Schaedel, C.

    2015-12-01

    Current and future warming of high latitude tundra ecosystems will play an important role in climate change through feedbacks to the global carbon (C) cycle. Long-term observational and experimental studies are pivotal for detecting and understanding changes in the coming decades. Yet studies of the C feedbacks from observational studies and manipulative experiments made on tundra plant communities often have significantly different conclusions with regards to impacts of warming on the ecosystem. Comparing results from these two study types, however, often involves integrating CO2 flux measurements that were collected on different spatial scales using a variety of methods. The process of data assimilation for landscape level analysis is often complicated by the fact that many projects only utilize one method for measuring CO2 fluxes at a given site. This study compares five years of C dynamics in a moist acidic tundra from control plots in a manipulative warming experiment (CiPEHR - plot-scale) and landscape-level natural permafrost thaw gradient (Gradient - Eddy covariance) observations all within a 1km distance from each other. We found net ecosystem exchange (NEE) to be an annual net source of carbon using both methods (Gradient 12.3 - 125.6 g CO2-C m-2 and CiPEHR warming manipulation 80.2 - 175.8 g CO2-C m-2). The differences between sites were biggest in the first three years of observation, and can be explained by lower growing season gross primary production (GPP - first three years) from the manipulation (CiPEHR), and lower ecosystem respiration (Reco) from CiPEHR in the first year only. Suppressed GPP and Reco could be from the impact of experimental setup (chamber soil collars - root damage), which lowered the plant community's capacity to fix C, but recovered within three years. This warrants caution of making generalization of short-term experiments in the tundra and more research is needed evaluating coupling of belowground and aboveground C dynamics.

  2. Extraction of correlated count rates using various gate generation techniques: Part II Experiment

    NASA Astrophysics Data System (ADS)

    Henzlova, D.; Croft, S.; Menlove, H. O.; Swinhoe, M. T.

    2012-11-01

    This paper presents an experimental comparison of different neutron pulse train analysis methods developed to extract correlated count rates from the detected neutron arrival times. This work comprises a sequel to the previous paper (Part I Theory) [1], where the complete formalism of different analysis methods was presented. In the current paper, the signal triggered inspection (STI), randomly triggered inspection (RTI) and MIXED techniques (implemented in current shift register hardware) are compared using list mode data acquired from series of 252Cf sources. In addition, three techniques of randomly triggered inspection are investigated: gates generated at fixed clock frequency, i.e., consecutive (non-overlapping) gates and overlapping gates (known as fast accidentals sampling (FAS)), as well as gates generated after a long delay following each trigger pulse (delayed-signal gates). The average correlated count rates (singles (S), doubles (D) and triples (T)) are extracted using the STI, RTI and MIXED analysis techniques and compared to demonstrate their equivalence. In addition, an influence of different gate generation and pulse train analysis techniques on the precision of the measured S, D and T rates is investigated.

  3. Micromagnetics with eddy currents

    NASA Astrophysics Data System (ADS)

    Iyer, R.; Millhollon, J.; Long, K.

    2011-01-01

    In this paper, we study the modified Landau-Lifshitz-Gilbert (LLG) equation for of a conducting, magnetic body. The modified LLG equations include the magnetic field due to eddy currents in the total effective magnetic field. We derive an expression for the magnetic field due to eddy current losses and show that it is well defined. We then show that the work done by the eddy currents in opposing the change of magnetization is a Rayleigh type dissipation function, and derive the modified LLG equations using the calculus of variations. Finally, we show that the modified LLG equations lead to a decrease in the Gibbs energy. This implies that the LLG equations describes a dynamic process proceeding spontaneously forward in time.

  4. F2DPR: a fast and robust cross-correlation technique for volumetric PIV

    NASA Astrophysics Data System (ADS)

    Earl, Thomas; Jeon, Young Jin; Lecordier, Bertrand; David, Laurent

    2016-08-01

    The current state-of-the-art in cross-correlation based time-resolved particle image velocimetry (PIV) techniques are the fluid trajectory correlation, FTC (Lynch and Scarano 2013) and the fluid trajectory evaluation based on an ensemble-averaged cross-correlation, FTEE (Jeon et al 2014a). These techniques compute the velocity vector as a polynomial trajectory Γ in space and time, enabling the extraction of beneficial quantities such as material acceleration whilst significantly increasing the accuracy of the particle displacement prediction achieved by standard two-frame PIV. In the context of time-resolved volumetric PIV, the drawback of trajectory computation is the computational expense of the three-dimensional (3D) cross-correlation, exacerbated by the requirement to perform N  ‑  1 cross-correlations, where N (for typically 5≤slant N≤slant 9 ) is the number of sequential particle volumes, for each velocity field. Therefore, the acceleration of this calculation is highly desirable. This paper re-examines the application of two-dimensional (2D) cross-correlation methods to three-dimensional (3D) datasets by Bilsky et al (2011) and the binning techniques of Discetti and Astarita (2012). A new and robust version of the 2D methods is proposed and described, called fast 2D projection—re-projection (f2dpr). Performance tests based on computational time and accuracy for both two-frame and multi-frame PIV are carried out on synthetically generated data. The cases presented herein include uniaxial uniform linear displacements and shear, and simulated turbulence data. The proposed algorithm is shown to be in the order of 10 times faster than a standard 3D FFT without loss of precision for a wide range of synthetic test cases, while combining with the binning technique can yield 50 times faster computation. The algorithm is also applied to reconstructed synthetic turbulent particle fields to investigate reconstruction noise on its performance and no

  5. Eddy current damper

    NASA Technical Reports Server (NTRS)

    Ellis, R. C.; Fink, R. A.; Rich, R. W.

    1989-01-01

    A high torque capacity eddy current damper used as a rate limiting device for a large solar array deployment mechanism is discussed. The eddy current damper eliminates the problems associated with the outgassing or leaking of damping fluids. It also provides performance advantages such as damping torque rates, which are truly linear with respect to input speed, continuous 360 degree operation in both directions of rotation, wide operating temperature range, and the capability of convenient adjustment of damping rates by the user without disassembly or special tools.

  6. Large eddy simulation of incompressible turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Moin, P.; Reynolds, W. C.; Ferziger, J. H.

    1978-01-01

    The three-dimensional, time-dependent primitive equations of motion were numerically integrated for the case of turbulent channel flow. A partially implicit numerical method was developed. An important feature of this scheme is that the equation of continuity is solved directly. The residual field motions were simulated through an eddy viscosity model, while the large-scale field was obtained directly from the solution of the governing equations. An important portion of the initial velocity field was obtained from the solution of the linearized Navier-Stokes equations. The pseudospectral method was used for numerical differentiation in the horizontal directions, and second-order finite-difference schemes were used in the direction normal to the walls. The large eddy simulation technique is capable of reproducing some of the important features of wall-bounded turbulent flows. The resolvable portions of the root-mean square wall pressure fluctuations, pressure velocity-gradient correlations, and velocity pressure-gradient correlations are documented.

  7. Pulsed eddy current testing. [nondestructive tests of the external tank

    NASA Technical Reports Server (NTRS)

    Workman, G. L.

    1980-01-01

    Since a large number of the procedures used for inspecting the external tank are concerned with determining flaws in welds, there is a need to develop an inspection technique, which can be automated, to determine flaws in welds and structures with complex geometries. Techniques whereby an eddy current is generated in a metallic material and the changes in the circuit parameters due to material differences are observed, were chosen as one possible approach. Pulsed eddy current and its relationship to multifrequency techniques is discussed as well as some preliminary results obtained from observing pulsed waveforms with apparatus and algorithms currently in use for ultrasonic testing of welds. It can be shown the pulsed eddy current techniques can provide similar results, can eliminate some of the noncritical parameters affecting the eddy current signals, and can facilitate in the detection of critical parameter such as flaws, subsurface voids, and corrosion.

  8. Techniques for estimating the unknown functions of incomplete experimental spectral and correlation response matrices

    NASA Astrophysics Data System (ADS)

    Antunes, Jose; Borsoi, Laurent; Delaune, Xavier; Piteau, Philippe

    2016-02-01

    In this paper, we propose analytical and numerical straightforward approximate methods to estimate the unknown terms of incomplete spectral or correlation matrices, when the cross-spectra or cross-correlations available from multiple measurements do not cover all pairs of transducer locations. The proposed techniques may be applied whenever the available data includes the auto-spectra at all measurement locations, as well as selected cross-spectra which implicates all measurement locations. The suggested methods can also be used for checking the consistency between the spectral or correlation functions pertaining to measurement matrices, in cases of suspicious data. After presenting the proposed spectral estimation formulations, we discuss their merits and limitations. Then we illustrate their use on a realistic simulation of a multi-supported tube subjected to turbulence excitation from cross-flow. Finally, we show the effectiveness of the proposed techniques by extracting the modal responses of the simulated flow-excited tube, using the SOBI (Second Order Blind Identification) method, from an incomplete response matrix 1

  9. Methane fluxes above the Hainich forest by True Eddy Accumulation and Eddy Covariance

    NASA Astrophysics Data System (ADS)

    Siebicke, Lukas; Gentsch, Lydia; Knohl, Alexander

    2016-04-01

    Understanding the role of forests for the global methane cycle requires quantifying vegetation-atmosphere exchange of methane, however observations of turbulent methane fluxes remain scarce. Here we measured turbulent fluxes of methane (CH4) above a beech-dominated old-growth forest in the Hainich National Park, Germany, and validated three different measurement approaches: True Eddy Accumulation (TEA, closed-path laser spectroscopy), and eddy covariance (EC, open-path and closed-path laser spectroscopy, respectively). The Hainich flux tower is a long-term Fluxnet and ICOS site with turbulent fluxes and ecosystem observations spanning more than 15 years. The current study is likely the first application of True Eddy Accumulation (TEA) for the measurement of turbulent exchange of methane and one of the very few studies comparing open-path and closed-path eddy covariance (EC) setups side-by-side. We observed uptake of methane by the forest during the day (a methane sink with a maximum rate of 0.03 μmol m‑2 s‑1 at noon) and no or small fluxes of methane from the forest to the atmosphere at night (a methane source of typically less than 0.01 μmol m‑2 s‑1) based on continuous True Eddy Accumulation measurements in September 2015. First results comparing TEA to EC CO2 fluxes suggest that True Eddy Accumulation is a valid option for turbulent flux quantifications using slow response gas analysers (here CRDS laser spectroscopy, other potential techniques include mass spectroscopy). The TEA system was one order of magnitude more energy efficient compared to closed-path eddy covariance. The open-path eddy covariance setup required the least amount of user interaction but is often constrained by low signal-to-noise ratios obtained when measuring methane fluxes over forests. Closed-path eddy covariance showed good signal-to-noise ratios in the lab, however in the field it required significant amounts of user intervention in addition to a high power consumption. We

  10. Vector correlation technique for pixel-wise detection of collagen fiber realignment during injurious tensile loading.

    PubMed

    Quinn, Kyle P; Winkelstein, Beth A

    2009-01-01

    Excessive soft tissue loading can produce adverse structural and physiological changes in the absence of any visible tissue rupture. However, image-based analysis techniques to assess microstructural changes during loading without any visible rupture remain undeveloped. Quantitative polarized light imaging (QPLI) can generate spatial maps of collagen fiber alignment during loading with high temporal resolution and can provide a useful technique to measure microstructural responses. While collagen fibers normally realign in the direction that tissue is loaded, rapid, atypical fiber realignment during loading may be associated with the response of a local collagenous network to fiber failure. A vector correlation technique was developed to detect this atypical fiber realignment using QPLI and mechanical data collected from human facet capsular ligaments (n=16) loaded until visible rupture. Initial detection of anomalous realignment coincided with a measurable decrease in the tissue stiffness in every specimen and occurred at significantly lower strains than those at visible rupture (p<0.004), suggesting this technique may be sensitive to a loss of microstructural integrity. The spatial location of anomalous realignment was significantly associated with regions where visible rupture developed (p<0.001). This analysis technique provides a foundation to identify regional differences in soft tissue injury tolerances and relevant mechanical thresholds. PMID:19895112

  11. Interview with Eddie Reisch

    ERIC Educational Resources Information Center

    Owen, Hazel

    2013-01-01

    Eddie Reisch is currently working as a policy advisor for Te Reo Maori Operational Policy within the Student Achievement group with the Ministry of Education in New Zealand, where he has implemented and led a range of e-learning initiatives and developments, particularly the Virtual Learning Network (VLN). He is regarded as one of the leading…

  12. Eddies off Tasmania

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This true-color satellite image shows a large phytoplankton bloom, several hundred square kilometers in size, in the Indian Ocean off the west coast of Tasmania. In this scene, the rich concentration of microscopic marine plants gives the water a lighter, more turquoise appearance which helps to highlight the current patterns there. Notice the eddies, or vortices in the water, that can be seen in several places. It is possible that these eddies were formed by converging ocean currents flowing around Tasmania, or by fresh river runoff from the island, or both. Often, eddies in the sea serve as a means for stirring the water, thus providing nutrients that help support phytoplankton blooms, which in turn provide nutrition for other organisms. Effectively, these eddies help feed the sea (click to read an article on this topic). This image was acquired November 7, 2000, by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) flying aboard the Orbview-2 satellite. Tasmania is located off Australia's southeastern coast. Image courtesy SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  13. Fracture analysis of plastic-bonded explosive by digital image correlation technique

    NASA Astrophysics Data System (ADS)

    Li, M.; Zhang, J.; Xiong, Chun-Yang; Fang, J.; Hao, Y.; Wen, M. P.

    2002-05-01

    Plastic-bonded explosive is a kind of energy material used in military and civil engineering. It serves also as structures or components to sustain external loads. Safety and reliability of the material is of importance to prevent damage and fracture during both manufacturing and usage procedure. Digital image correlation technique was applied to analyze the deformation field of the material near crack tip. The specimen was loaded by uniaxial compression and a slot was preset at the specimen edge with 45 degrees orientation. The speckle images were captured during the load and the surface patterns were matched by correlation computation to obtain the displacement components. The stress intensity factors of the crack tip were evaluated by the deformation in the near region of the crack. By the comparison of the strain field and the surface profile, the damage form of the material can be analyzed that showed brittle behavior with axial splitting fracture.

  14. Emission-rotation correlation in pulsars: new discoveries with optimal techniques

    NASA Astrophysics Data System (ADS)

    Brook, P. R.; Karastergiou, A.; Johnston, S.; Kerr, M.; Shannon, R. M.; Roberts, S. J.

    2016-02-01

    Pulsars are known to display short-term variability. Recently, examples of longer term emission variability have emerged that are often correlated with changes in the rotational properties of the pulsar. To further illuminate this relationship, we have developed techniques to identify emission and rotation variability in pulsar data, and determine correlations between the two. Individual observations may be too noisy to identify subtle changes in the pulse profile. We use Gaussian process (GP) regression to model noisy observations and produce a continuous map of pulse profile variability. Generally, multiple observing epochs are required to obtain the pulsar spin frequency derivative (dot{ν }). GP regression is, therefore, also used to obtain dot{ν }, under the hypothesis that pulsar timing noise is primarily caused by unmodelled changes in dot{ν }. Our techniques distinguish between two types of variability: changes in the total flux density versus changes in the pulse shape. We have applied these techniques to 168 pulsars observed by the Parkes radio telescope, and see that although variations in flux density are ubiquitous, substantial changes in the shape of the pulse profile are rare. We reproduce previously published results and present examples of profile shape changing in seven pulsars; in particular, a clear new example of correlated changes in profile shape and rotation is found in PSR J1602-5100. In the shape changing pulsars, a more complex picture than the previously proposed two state model emerges. We conclude that our simple assumption that all timing noise can be interpreted as dot{ν } variability is insufficient to explain our data set.

  15. Interrogation of fiber Bragg grating sensors using a VCSEL and correlation techniques

    NASA Astrophysics Data System (ADS)

    Triana, Cristian; Varón, Margarita; Pastor, Daniel

    2015-09-01

    We describe a demodulation technique for optical fiber Bragg grating (FBG) sensors based in the utilization of a long wavelength Vertical Cavity Surface Emitting Laser (VCSEL). The identification of the FBG wavelength is performed by sweeping the VCSEL wavelength over the operation range of the sensors and correlating its raising and falling periods in order to automatically determine the initial and final points of the wavelength to time mapping readout. The process is carried out by a simple computational routine, which allows the identification of the FBGs' spectral position leading to a cost-effective scheme.

  16. Correlation techniques to determine model form in robust nonlinear system realization/identification

    NASA Technical Reports Server (NTRS)

    Stry, Greselda I.; Mook, D. Joseph

    1991-01-01

    The fundamental challenge in identification of nonlinear dynamic systems is determining the appropriate form of the model. A robust technique is presented which essentially eliminates this problem for many applications. The technique is based on the Minimum Model Error (MME) optimal estimation approach. A detailed literature review is included in which fundamental differences between the current approach and previous work is described. The most significant feature is the ability to identify nonlinear dynamic systems without prior assumption regarding the form of the nonlinearities, in contrast to existing nonlinear identification approaches which usually require detailed assumptions of the nonlinearities. Model form is determined via statistical correlation of the MME optimal state estimates with the MME optimal model error estimates. The example illustrations indicate that the method is robust with respect to prior ignorance of the model, and with respect to measurement noise, measurement frequency, and measurement record length.

  17. Comparisons of neural networks to standard techniques for image classification and correlation

    NASA Technical Reports Server (NTRS)

    Paola, Justin D.; Schowengerdt, Robert A.

    1994-01-01

    Neural network techniques for multispectral image classification and spatial pattern detection are compared to the standard techniques of maximum-likelihood classification and spatial correlation. The neural network produced a more accurate classification than maximum-likelihood of a Landsat scene of Tucson, Arizona. Some of the errors in the maximum-likelihood classification are illustrated using decision region and class probability density plots. As expected, the main drawback to the neural network method is the long time required for the training stage. The network was trained using several different hidden layer sizes to optimize both the classification accuracy and training speed, and it was found that one node per class was optimal. The performance improved when 3x3 local windows of image data were entered into the net. This modification introduces texture into the classification without explicit calculation of a texture measure. Larger windows were successfully used for the detection of spatial features in Landsat and Magellan synthetic aperture radar imagery.

  18. Automatic detection and classification of damage zone(s) for incorporating in digital image correlation technique

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Sudipta; Deb, Debasis

    2016-07-01

    Digital image correlation (DIC) is a technique developed for monitoring surface deformation/displacement of an object under loading conditions. This method is further refined to make it capable of handling discontinuities on the surface of the sample. A damage zone is referred to a surface area fractured and opened in due course of loading. In this study, an algorithm is presented to automatically detect multiple damage zones in deformed image. The algorithm identifies the pixels located inside these zones and eliminate them from FEM-DIC processes. The proposed algorithm is successfully implemented on several damaged samples to estimate displacement fields of an object under loading conditions. This study shows that displacement fields represent the damage conditions reasonably well as compared to regular FEM-DIC technique without considering the damage zones.

  19. Forest Ecosystem respiration estimated from eddy covariance and chamber measurements under high turbulence and substantial tree mortality from bark beetles

    USGS Publications Warehouse

    Speckman, Heather N.; Frank, John M.; Bradford, John B.; Miles, Brianna L.; Massman, William J.; Parton, William J.; Ryan, Michael G.

    2015-01-01

    Eddy covariance nighttime fluxes are uncertain due to potential measurement biases. Many studies report eddy covariance nighttime flux lower than flux from extrapolated chamber measurements, despite corrections for low turbulence. We compared eddy covariance and chamber estimates of ecosystem respiration at the GLEES Ameriflux site over seven growing seasons under high turbulence (summer night mean friction velocity (u*) = 0.7 m s−1), during which bark beetles killed or infested 85% of the aboveground respiring biomass. Chamber-based estimates of ecosystem respiration during the growth season, developed from foliage, wood and soil CO2 efflux measurements, declined 35% after 85% of the forest basal area had been killed or impaired by bark beetles (from 7.1 ±0.22 μmol m−2 s−1 in 2005 to 4.6 ±0.16 μmol m−2 s−1 in 2011). Soil efflux remained at ~3.3 μmol m−2 s−1 throughout the mortality, while the loss of live wood and foliage and their respiration drove the decline of the chamber estimate. Eddy covariance estimates of fluxes at night remained constant over the same period, ~3.0 μmol m−2 s−1 for both 2005 (intact forest) and 2011 (85% basal area killed or impaired). Eddy covariance fluxes were lower than chamber estimates of ecosystem respiration (60% lower in 2005, and 32% in 2011), but the mean night estimates from the two techniques were correlated within a year (r2 from 0.18-0.60). The difference between the two techniques was not the result of inadequate turbulence, because the results were robust to a u* filter of > 0.7 m s−1. The decline in the average seasonal difference between the two techniques was strongly correlated with overstory leaf area (r2=0.92). The discrepancy between methods of respiration estimation should be resolved to have confidence in ecosystem carbon flux estimates.

  20. Measuring the thermal expansion coefficient of tubular steel specimens with digital image correlation techniques

    NASA Astrophysics Data System (ADS)

    De Strycker, M.; Schueremans, L.; Van Paepegem, W.; Debruyne, D.

    2010-10-01

    In this contribution it is investigated whether it is possible to measure the coefficient of thermal expansion (CTE) of steel with the aid of the digital image correlation (DIC) technique. DIC is first used to obtain reference values of the CTE of well-known steels (S235 and SS304) on simple geometries (rectangular blocks) within a low temperature interval (up to 120 °C). Although the strains that occur in this process are small, the CTE can be determined with good accuracy if enough images are available. The influence of the different parameters that control the correlation process showed no influence on the results. The values for the CTE are compared to available literature references and strain gauge measurements. The technique is extended to measure within a higher temperature interval (up to 600 °C), three-dimensional geometries (tubular samples), and a third material (SS409). It is shown that also in these cases, the results obtained are reliable. This contribution is part of a larger research effort predicting the residual stress in tubes coming from the welding process with finite element (FE) simulation. The goal of this research is therefore twofold: firstly obtaining the CTE in function of temperature, which can be used as input for the FE simulations; and secondly exploring the possibilities of measuring small thermal strains with DIC.

  1. Time reversal imaging and cross-correlations techniques by normal mode theory

    NASA Astrophysics Data System (ADS)

    Montagner, J.; Fink, M.; Capdeville, Y.; Phung, H.; Larmat, C.

    2007-12-01

    Time-reversal methods were successfully applied in the past to acoustic waves in many fields such as medical imaging, underwater acoustics, non destructive testing and recently to seismic waves in seismology for earthquake imaging. The increasing power of computers and numerical methods (such as spectral element methods) enables one to simulate more and more accurately the propagation of seismic waves in heterogeneous media and to develop new applications, in particular time reversal in the three-dimensional Earth. Generalizing the scalar approach of Draeger and Fink (1999), the theoretical understanding of time-reversal method can be addressed for the 3D- elastic Earth by using normal mode theory. It is shown how to relate time- reversal methods on one hand, with auto-correlation of seismograms for source imaging and on the other hand, with cross-correlation between receivers for structural imaging and retrieving Green function. The loss of information will be discussed. In the case of source imaging, automatic location in time and space of earthquakes and unknown sources is obtained by time reversal technique. In the case of big earthquakes such as the Sumatra-Andaman earthquake of december 2004, we were able to reconstruct the spatio-temporal history of the rupture. We present here some new applications at the global scale of these techniques on synthetic tests and on real data.

  2. Extraction of correlated count rates using various gate generation techniques: Part I theory

    NASA Astrophysics Data System (ADS)

    Croft, S.; Henzlova, D.; Hauck, D. K.

    2012-11-01

    This paper presents an overview of different gate generation techniques that can be used to extract correlated counting rates from neutron pulse trains in the context of Passive Neutron Multiplicity Counting (PNMC). PNMC based on shift register pulse train time autocorrelation analyzers is an important Non-Destructive Assay (NDA) method used in the quantification of plutonium and other spontaneously fissile materials across the nuclear fuel cycle. Traditionally PNMC employs signal-triggered gate generation followed by a random gate, separated from the trigger pulse by a long delay, to extract the totals rate (gross or singles), the pairs (coincidences or doubles) rate, and the triplets (or triples) rate of correlated neutron pulse trains. In this paper we provide expressions for singles, doubles and triples rates using the information available in both, the random and signal-triggered gates (traditional shift register analysis), in the randomly triggered gates only, and introduce a third approach to extract the correlated rates using signal-triggered gates only. In addition, we expand the formalism for randomly triggered gate generation to include Fast Accidental Sampling (FAS) and consecutive gate generation.

  3. Determination of correlation functions of turbulent velocity and sound speed fluctuations by means of ultrasonic technique

    NASA Astrophysics Data System (ADS)

    Andreeva, Tatiana A.; Durgin, William W.

    2011-12-01

    An experimental study of the propagation of high-frequency acoustic waves through grid-generated turbulence by means of an ultrasound technique is discussed. Experimental data were obtained for ultrasonic wave propagation downstream of heated and non-heated grids in a wind tunnel. A semi-analytical acoustic propagation model that allows the determination of the spatial correlation functions of the flow field is developed based on the classical flowmeter equation and the statistics of the travel time of acoustic waves traveling through the kinematic and thermal turbulence. The basic flowmeter equation is reconsidered in order to take into account sound speed fluctuations and turbulent velocity fluctuations. It allows deriving an integral equation that relates the correlation functions of travel time, sound speed fluctuations and turbulent velocity fluctuations. Experimentally measured travel time statistics of data with and without grid heating are approximated by an exponential function and used to analytically solve the integral equation. The reconstructed correlation functions of the turbulent velocity and sound speed fluctuations are presented. The power spectral density of the turbulent velocity and sound speed fluctuations are calculated.

  4. Correlation and registration of ERTS multispectral imagery. [by a digital processing technique

    NASA Technical Reports Server (NTRS)

    Bonrud, L. O.; Henrikson, P. J.

    1974-01-01

    Examples of automatic digital processing demonstrate the feasibility of registering one ERTS multispectral scanner (MSS) image with another obtained on a subsequent orbit, and automatic matching, correlation, and registration of MSS imagery with aerial photography (multisensor correlation) is demonstrated. Excellent correlation was obtained with patch sizes exceeding 16 pixels square. Qualities which lead to effective control point selection are distinctive features, good contrast, and constant feature characteristics. Results of the study indicate that more than 300 degrees of freedom are required to register two standard ERTS-1 MSS frames covering 100 by 100 nautical miles to an accuracy of 0.6 pixel mean radial displacement error. An automatic strip processing technique demonstrates 600 to 1200 degrees of freedom over a quater frame of ERTS imagery. Registration accuracies in the range of 0.3 pixel to 0.5 pixel mean radial error were confirmed by independent error analysis. Accuracies in the range of 0.5 pixel to 1.4 pixel mean radial error were demonstrated by semi-automatic registration over small geographic areas.

  5. Measuring water velocity using DIDSON and image cross-correlation techniques

    SciTech Connect

    Deng, Zhiqun; Mueller, Robert P.; Richmond, Marshall C.

    2009-08-01

    To design or operate hydroelectric facilities for maximum power generation and minimum ecological impact, it is critical to understand the biological responses of fish to different flow structures. However, information is still lacking on the relationship between fish behavior and flow structures despite many years of research. Existing field characterization approaches conduct fish behavior studies and flow measurements separately and coupled later using statistical analysis. These types of studies, however, lack a way to determine the specific hydraulic conditions or the specific causes of the biological response. The Dual-Frequency Identification Sonar (DIDSON) has been in wide use for fish behavior studies since 1999. The DIDSON can detect acoustic targets at long ranges in dark or turbid dark water. PIV is a state-of-the-art, non-intrusive, whole-flow-field technique, providing instantaneous velocity vector measurements in a whole plane using image cross-correlating techniques. There has been considerable research in the development of image processing techniques associated with PIV. This existing body of knowledge is applicable and can be used to process the images taken by the DIDSON. This study was conducted in a water flume which is 9 m long, 1.2 m wide, and 1.2 m deep when filled with water. A lab jet flow was setup as the benchmark flow to calibrate DIDSON images. The jet nozzle was 6.35 cm in diameter and core jet velocity was 1.52 m/s. Different particles were used to seed the flow. The flow was characterized based on the results using Laser Doppler Velocimetry (LDV). A DIDSON was mounted about 5 meters away from the jet nozzle. Consecutive DIDSON images with known time delay were divided into small interrogation spots after background was subtracted. Across-correlation was then performed to estimate the velocity vector for each interrogation spot. The estimated average velocity in the core zone was comparable to that obtained using a LDV. This proof

  6. Turbulent fluxes by "Conditional Eddy Sampling"

    NASA Astrophysics Data System (ADS)

    Siebicke, Lukas

    2015-04-01

    for the field (one to two orders of magnitude lower compared to current closed-path laser based eddy covariance systems). Potential applications include fluxes of CO2, CH4, N2O, VOCs and other tracers. Finally we assess the flux accuracy of the Conditional Eddy Sampling (CES) approach as in our real implementation relative to alternative techniques including eddy covariance (EC) and relaxed eddy accumulation (REA). We further quantify various sources of instrument and method specific measurement errors. This comparison uses real measurements of 20 Hz turbulent time series of 3D wind velocity, sonic temperature and CO2 mixing ratio over a mixed decidious forest at the 'ICOS' flux tower site 'Hainich', Germany. Results from a simulation using real wind and CO2 timeseries from the Hainich site from 30 April to 3 November 2014 and real instrument performance suggest that the maximum flux estimates error (50% and 75% error quantiles) from Conditional Eddy Sampling (CES) relative to the true flux is 1.3% and 10%, respectively for monthly net fluxes, 1.6% and 7%, respectively for daily net fluxes and 8% and 35%, respectively for 30-minute CO2 flux estimates. Those results from CES are promising and outperform our REA estimates by about a factor of 50 assuming REA with constant b value. Results include flux time series from the EC, CES and REA approaches from 30-min to annual resolution.

  7. Interannual forcing mechanisms of California Current transports II: Mesoscale eddies

    NASA Astrophysics Data System (ADS)

    Davis, Andrew; Di Lorenzo, Emanuele

    2015-02-01

    Mesoscale eddies exert dominant control of cross-shelf exchanges, yet the forcing dynamics underlying their interannual and decadal variability remain uncertain. Using an ensemble of high-resolution ocean model hindcasts of the central and eastern North Pacific from 1950 to 2010 we diagnose the forcing mechanisms of low-frequency eddy variability in the California Current System (CCS). We quantify eddy activity by developing eddy counts based on closed contours of the Okubo-Weiss parameter and find that the spatial and temporal features of model-derived counts largely reproduce the short AVISO observational record. Comparison of model ensemble members allows us to separate the intrinsic and deterministic fractions of eddy variability in the northern CCS (34.5-50°N) and in the southern CCS (28.5-34.5°N). In the North, a large fraction of low-frequency eddy variability (30% anticyclones, 20% cyclones) is deterministic and shared with satellite observations. We develop a diagnostic model based on indices of the large-scale barotropic and baroclinic states of the CCS which recovers this deterministic variance. This model also strongly correlates with local atmospheric forcing. In contrast to the North, Southern CCS eddy counts exhibit very little deterministic variance, and eddy formation closely resembles a red-noise process. This new understanding of the external forcings of eddy variability allows us to better estimate how climate variability and change impact mesoscale transports in the California Current. The skill of our diagnostic model and its close association with local wind stress curl indicate that local atmospheric forcing is the dominant driver of eddy activity on interannual and decadal time scales north of pt. conception (~33°N).

  8. Application and correlation of nano resolution microscopy techniques to viral protein localization

    NASA Astrophysics Data System (ADS)

    Hodges, Jeffery Allen

    This dissertation is primarily focused on the application of super-resolution microscopy techniques to localization of viral proteins within envelope viruses. Advances in optical super-resolution microscopy techniques have enabled scientists to observe phenomena much smaller than the Abbe diffraction limit by stochastically limiting the number of molecules excited at a given instance and localizing their positions one at a time. Additionally, methods such as Atomic Force Microscopy (AFM) allow scientists to measure the topological features and material properties of samples through contact with a force probe. This dissertation describes the application of these two techniques to virology in order to localize internal viral proteins of enveloped virions, and measure their effect on the elastic properties of the virion. By utilizing super-resolution microscopy techniques such as Fluorescent Photo-Activated Localization Microscopy (fPALM) on virions, which have had their surface glycoproteins labeled with a photo-switchable label, the viral envelope may be accurately recovered. This dissertation describes the development and application of this technique as it applies to envelope recovery of Vesicular Stomatitis Virus (VSV) and Human Immunodeficiency Virus-1 (HIV-1). By fluorescently labeling proteins, which are internal to each of these viruses, I have been able to localize a variety of viral proteins within their recovered envelopes. This is done without significant damage to the virion, making this method a highly effective in vivo technique. In the case of VSV, an asymmetric localization along the central axis towards the blunt 5' end was found to exist for both the polymerase and phosphoproteins. These have been determined to occupy a region in the central cavity of ˜57 +/- 12 nm on the 5' end. This inhomogeneity of the underlying proteins such an asymmetry would predict that the Young's modulus would vary along the central axis of the virion. This dissertation

  9. Probing Cytoskeletal Structures by Coupling Optical Superresolution and AFM Techniques for a Correlative Approach

    PubMed Central

    Chacko, Jenu Varghese; Zanacchi, Francesca Cella; Diaspro, Alberto

    2013-01-01

    In this article, we describe and show the application of some of the most advanced fluorescence superresolution techniques, STED AFM and STORM AFM microscopy towards imaging of cytoskeletal structures, such as microtubule filaments. Mechanical and structural properties can play a relevant role in the investigation of cytoskeletal structures of interest, such as microtubules, that provide support to the cell structure. In fact, the mechanical properties, such as the local stiffness and the elasticity, can be investigated by AFM force spectroscopy with tens of nanometers resolution. Force curves can be analyzed in order to obtain the local elasticity (and the Young's modulus calculation by fitting the force curves from every pixel of interest), and the combination with STED/STORM microscopy integrates the measurement with high specificity and yields superresolution structural information. This hybrid modality of superresolution-AFM working is a clear example of correlative multimodal microscopy. PMID:24027190

  10. Lithographically fabricated silicon microreactor for in situ characterization of heterogeneous catalysts—Enabling correlative characterization techniques

    NASA Astrophysics Data System (ADS)

    Baier, S.; Rochet, A.; Hofmann, G.; Kraut, M.; Grunwaldt, J.-D.

    2015-06-01

    We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies.

  11. Lithographically fabricated silicon microreactor for in situ characterization of heterogeneous catalysts—Enabling correlative characterization techniques.

    PubMed

    Baier, S; Rochet, A; Hofmann, G; Kraut, M; Grunwaldt, J-D

    2015-06-01

    We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies. PMID:26133867

  12. Core noise source diagnostics on a turbofan engine using correlation and coherence techniques

    NASA Technical Reports Server (NTRS)

    Karchmer, A. M.; Reshotko, M.

    1976-01-01

    Fluctuating pressure measurements at several locations within the core of a turbofan engine were made simultaneously with far field acoustic measurements. Correlation and coherence techniques were used to determine the relative amplitude and phase relationships between core pressures at these various locations and between the core pressures and far field acoustic pressure. The combustor is a low frequency source region for acoustic propagation through the core nozzle and out to the far field. The relation between source pressure and the resulting sound pressure involves a 180 degree phase shift and an amplitude transfer function which varies approximately as frequency squared. This is consistent with a simplified model using fluctuating entropy as a source term.

  13. Assessment of two-filter technique for correlating actinium-227 concentrations in soils

    SciTech Connect

    Fraizer, W.K.; Patch, K.D.; Reynolds, B.A.

    1980-02-01

    Concentrations of actinium-227 in soil samples from waste-disposal sites for uranium procession plants were successfully correlated with radon-219 measurements obtained by the two-filter technique, thus avoiding time-consuming and difficult radiochemical analyses. A flow-through sampling device and procedure were developed which determined actinium levels with a precision of 2 pCi/g +- 50%. Theoretical relations for the production of radon from actinium, the decay of radon, and the decay and diffusion of radon daughters in the two-filter apparatus were formulated. Measurements indicated that the emanation fraction for radon-219 was about 15%. Sampling filters collected radon daughters with a 93% efficiency while radon could be scrubbed from air samples by use of an activated-charcoal canister.

  14. Core noise source diagnostics on a turbofan engine using correlation and coherence techniques

    NASA Technical Reports Server (NTRS)

    Karchmer, A.; Reshotko, M.

    1976-01-01

    Fluctuating pressure measurements at several locations within the core of a turbofan engine were made simultaneously with far-field acoustic measurements. Correlation and coherence techniques were used to determine the relative amplitude and phase relationships between core pressures at these various locations and between the core pressures and far-field acoustic pressure. The results indicate that the combustor is a low-frequency source region for acoustic propagation through the core nozzle and out to the far-field. Specifically, it was found that the relation between source pressure and the resulting sound pressure involves a 180 deg phase shift and an amplitude transfer function which varies approximately as frequency squared. This is shown to be consistent with a simplified model using fluctuating entropy as a source term.

  15. Optical cryptographic system employing multiple reference-based joint transform correlation technique

    NASA Astrophysics Data System (ADS)

    Islam, Mohammed Nazrul; Karim, Mohammad Ataul; Alam, Mohammad Showkat; Asari, K. Vijayan

    2011-06-01

    An optical joint transform correlation-based cryptographic system is a used to feed multiple phase-shifted encryption keys into four parallel channels along with a to-be-encrypted signal in the form of an image. The resulting joint power spectra (JPS) signals are phase-shifted and then combined to yield a modified JPS signal. Inverse Fourier transformation of the modified JPS signal yields the secured encrypted image. For decryption purpose, the received encrypted signal is first Fourier transformed and multiplied by the encryption key used in encryption. The derived signal is then inverse Fourier transformed to generate the output signal. The proposed system offers a nonlinear encryption without the involvement of any complex mathematical operation on the encryption key otherwise required in similar encryption techniques and is invariant to noise. Computer simulation results are presented to show the effectiveness of the proposed scheme with binary, as well as gray images in both noise-free and noisy environment.

  16. Neutron multiplicity equation and its application for (n,2n) multiplication measurements by statistical correlation techniques

    SciTech Connect

    Kumar, A.; Srinivasan, M.

    1986-07-01

    A new equation, called the neutron multiplicity equation (NME), has been derived starting from basic physics principles. Neutron multiplicity v is defined as the integral number of neutrons leaking from a neutron multiplying system for a source neutron introduced into it. Probability distribution of neutron multiplicities (PDNMs) gives the probability of leakage of neutrons as a function of their multiplicity v. The PDNM is directly measurable through statistical correlation techniques. In a specific application, the NME has been solved for PDNM as a function of v for /sup 9/Be spheres of varying radii and driven by a centrally located 14-MeV deuterium-tritium neutron source. The potential of NME for sensitivity analysis is demonstrated through a particular modification of secondary neutron transfer cross sections of /sup 9/Be. It turns out that PDNM is very sensitive, even as the ''average'' neutron leakage is practically insensitive to it.

  17. Lithographically fabricated silicon microreactor for in situ characterization of heterogeneous catalysts—Enabling correlative characterization techniques

    SciTech Connect

    Baier, S.; Rochet, A.; Hofmann, G.; Kraut, M.; Grunwaldt, J.-D.

    2015-06-15

    We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies.

  18. Eddy current pulsed phase thermography and feature extraction

    NASA Astrophysics Data System (ADS)

    He, Yunze; Tian, GuiYun; Pan, Mengchun; Chen, Dixiang

    2013-08-01

    This letter proposed an eddy current pulsed phase thermography technique combing eddy current excitation, infrared imaging, and phase analysis. One steel sample is selected as the material under test to avoid the influence of skin depth, which provides subsurface defects with different depths. The experimental results show that this proposed method can eliminate non-uniform heating and improve defect detectability. Several features are extracted from differential phase spectra and the preliminary linear relationships are built to measure these subsurface defects' depth.

  19. Nanoscale deformation measurement of microscale interconnection assemblies by a digital image correlation technique.

    PubMed

    Sun, Yaofeng; Pang, John H L; Fan, Wei

    2007-10-01

    The continuous miniaturization of microelectronic devices and interconnections demand more and more experimental strain/stress analysis of micro- and nanoscale components for material characterization and structure reliability analysis. The digital image correlation (DIC) technique, with the aid of scanning probe microscopes, has become a very promising tool to meet this demand. In this study, an atomic force microscope (AFM) was used to scan and digitally image micro-interconnection assemblies in a micro-thermoelectric cooler. AFM images of the scan region of interest were obtained separately when the microelectronic device was operated before and after the cooling and heating stages. The AFM images were then used to obtain the in-plane deformation fields in the observed region of the micro-assembly. AFM image correlation is performed for nanoscale deformation analysis using the authors' AFM-DIC program. The results show that the observed region was subjected to cyclic strains when the device worked between its cooling and heating stages, and cyclic strain in the vertical direction was found to be a significant deformation mode. The thermally induced deformation behavior of the micro-assembly device was modeled by finite element analysis (FEA). Both thermal-electric analysis and thermal stress analysis were conducted on a 3D finite element model of the device. It is shown that the experimental results were able to validate the finite element analysis results. PMID:21730419

  20. Digital Image Correlation Techniques Applied to Large Scale Rocket Engine Testing

    NASA Technical Reports Server (NTRS)

    Gradl, Paul R.

    2016-01-01

    Rocket engine hot-fire ground testing is necessary to understand component performance, reliability and engine system interactions during development. The J-2X upper stage engine completed a series of developmental hot-fire tests that derived performance of the engine and components, validated analytical models and provided the necessary data to identify where design changes, process improvements and technology development were needed. The J-2X development engines were heavily instrumented to provide the data necessary to support these activities which enabled the team to investigate any anomalies experienced during the test program. This paper describes the development of an optical digital image correlation technique to augment the data provided by traditional strain gauges which are prone to debonding at elevated temperatures and limited to localized measurements. The feasibility of this optical measurement system was demonstrated during full scale hot-fire testing of J-2X, during which a digital image correlation system, incorporating a pair of high speed cameras to measure three-dimensional, real-time displacements and strains was installed and operated under the extreme environments present on the test stand. The camera and facility setup, pre-test calibrations, data collection, hot-fire test data collection and post-test analysis and results are presented in this paper.

  1. Tensile-shear correlations obtained from shear punch test technique using a modified experimental approach

    NASA Astrophysics Data System (ADS)

    Karthik, V.; Visweswaran, P.; Vijayraghavan, A.; Kasiviswanathan, K. V.; Raj, Baldev

    2009-09-01

    Shear punch testing has been a very useful technique for evaluating mechanical properties of irradiated alloys using a very small volume of material. The load-displacement data is influenced by the compliance of the fixture components. This paper describes a modified experimental approach where the compliances of the punch and die components are eliminated. The analysis of the load-displacement data using the modified setup for various alloys like low carbon steel, SS316, modified 9Cr-1Mo, 2.25Cr-1Mo indicate that the shear yield strength evaluated at 0.2% offset of normalized displacement relates to the tensile YS as per the Von Mises yield relation ( σys = 1.73 τys). A universal correlation of type UTS = mτmax where m is a function of strain hardening exponent, is seen to be obeyed for all the materials in this study. The use of analytical models developed for blanking process are explored for evaluating strain hardening exponent from the load-displacement data. This study is directed towards rationalizing the tensile-shear empirical correlations for a more reliable prediction of tensile properties from shear punch tests.

  2. Digital image correlation: a technique for determining local mechanical conditions within early bone callus.

    PubMed

    Thompson, M S; Schell, H; Lienau, J; Duda, G N

    2007-09-01

    Local mechanical conditions are known to play a role during the regeneration of musculoskeletal tissues, and histomorphometrical investigations of the time course of healing have enabled specific conclusions regarding the mechanosensitivity of tissue differentiation. However, the mechanism for this influence is not clearly understood. In order to extend this analysis, it is essential to link local histological understanding with direct characterisation of the local mechanical environment. Digital image correlation (DIC) is a computer-based image analysis technique that enables the non-contact measurement of strains on material surfaces and is finding application in many areas of biomechanics. Here we report a DIC technique to investigate the local distribution of mechanical strain within regenerating soft tissue sections. We provide exemplary data from analysis of a section of sheep bone callus. An assessment of displacement measurement accuracy gave an RMS error of 4.2 microm, corresponding to an estimated strain error of 1.4%. The sections showed concentrations of up to four times the applied strain and comparison of the strain patterns with histological analysis confirmed that these concentrations reflected boundaries between hard and soft callus. PMID:17045512

  3. Automation of a McBain-Bakr-type thermogravimetric analyzer using a digital image correlation technique

    NASA Astrophysics Data System (ADS)

    Trexler, M. D.; Sanders, T. H.; Singh, P. M.

    2006-02-01

    Thermogravimetric analysis was used to obtain corrosion kinetics data for several materials in high-temperature environments. A thermogravimetric analyzer has been developed that uses a McBain-Bakr quartz spring balance in conjunction with a digital image acquisition and analysis package to accurately characterize materials through image correlation. This provides a new method for automatically measuring mass changes continuously with a variable resolution depending on the spring component. The decomposition of calcium oxalate was used to verify the validity of the technique. The results show two reactions, whose reaction temperatures were determined by the intercept method, upon heating to 650 °C. The mass loss at the first reaction temperature, 200 °C, was 20% and a 30% loss was observed at 500 °C. Comparison of the experimentally obtained results with those of other researchers who used commercial instruments suggests that the method of using digital image analysis in conjunction with a spring to monitor mass change is a viable and accurate replacement for automatic electrobalances and cathetometers for thermal analysis of materials. Additional comparison between corrosion tests performed on SA210 steel in H2S using both a commercial thermobalance and the developed technique confirmed that high-temperature corrosion can be monitored accurately with the proposed method.

  4. Automation of a McBain-Bakr-type thermogravimetric analyzer using a digital image correlation technique

    SciTech Connect

    Trexler, M.D.; Sanders, T.H. Jr.; Singh, P.M.

    2006-02-15

    Thermogravimetric analysis was used to obtain corrosion kinetics data for several materials in high-temperature environments. A thermogravimetric analyzer has been developed that uses a McBain-Bakr quartz spring balance in conjunction with a digital image acquisition and analysis package to accurately characterize materials through image correlation. This provides a new method for automatically measuring mass changes continuously with a variable resolution depending on the spring component. The decomposition of calcium oxalate was used to verify the validity of the technique. The results show two reactions, whose reaction temperatures were determined by the intercept method, upon heating to 650 deg. C. The mass loss at the first reaction temperature, 200 deg. C, was 20% and a 30% loss was observed at 500 deg. C. Comparison of the experimentally obtained results with those of other researchers who used commercial instruments suggests that the method of using digital image analysis in conjunction with a spring to monitor mass change is a viable and accurate replacement for automatic electrobalances and cathetometers for thermal analysis of materials. Additional comparison between corrosion tests performed on SA210 steel in H{sub 2}S using both a commercial thermobalance and the developed technique confirmed that high-temperature corrosion can be monitored accurately with the proposed method.

  5. Eddy current correction in volume-localized MR spectroscopy

    NASA Technical Reports Server (NTRS)

    Lin, C.; Wendt, R. E. 3rd; Evans, H. J.; Rowe, R. M.; Hedrick, T. D.; LeBlanc, A. D.

    1994-01-01

    The quality of volume-localized magnetic resonance spectroscopy is affected by eddy currents caused by gradient switching. Eddy currents can be reduced with improved gradient systems; however, it has been suggested that the distortion due to eddy currents can be compensated for during postprocessing with a single-frequency reference signal. The authors propose modifying current techniques for acquiring the single-frequency reference signal by using relaxation weighting to reduce interference from components that cannot be eliminated by digital filtering alone. Additional sequences with T1 or T2 weighting for reference signal acquisition are shown to have the same eddy current characteristics as the original signal without relaxation weighting. The authors also studied a new eddy current correction method that does not require a single-frequency reference signal. This method uses two free induction decays (FIDs) collected from the same volume with two sequences with opposite gradients. Phase errors caused by eddy currents are opposite in these two FIDs and can be canceled completely by combining the FIDs. These methods were tested in a phantom. Eddy current distortions were corrected, allowing quantitative measurement of structures such as the -CH = CH- component, which is otherwise undetectable.

  6. Remote-field eddy current signal representation

    SciTech Connect

    Atherton, D.L.; Mackintosh, D.D.; Sullivan, S.P.; Dubois, J.M.S.; Schmidt, T.R. . Dept. of Physics.)

    1993-07-01

    While conventional reflected impedance eddy current testing (ET) techniques are limited by skin depth considerations to near surface defects, the RFEC (remote field eddy current) technique exploits skin effects. The RFEC method is a through-wall inspection technique. Only the field which has made a double transit of the pipe wall is detected. The skin depth equation can be used to predict the approximate effect of metal loss on the RFEC signal. Metal loss effectively reduces the shielding so that the attenuation and phase lag of the field is less. A method of analyzing RFEC defect signals is therefore to compare the signals with the phase and amplitude in uncorroded pipe. RFEC probes are used for inspecting ferromagnetic and nonferromagnetic tubulars for corrosion and, since eddy current detectors are generally well suited to crack detection, there is considerable interest in their potential to detect stress corrosion cracking in pipelines. Here the authors first of all summarize the impedance plane representation and scope monitor displays customarily used for conventional exploring coil ET probes in tubes. They then present the normalized voltage plane and monitor displays that are most appropriate for RFEC probes. They discuss the similarities and differences between the preferred monitor displays.

  7. Correlations between forced oscillation technique parameters and pulmonary densitovolumetry values in patients with acromegaly

    PubMed Central

    Camilo, G.B.; Carvalho, A.R.S.; Machado, D.C.; Mogami, R.; Kasuki, L.; Gadelha, M.R.; Melo, P.L.; Lopes, A.J.

    2015-01-01

    The aims of this study were to evaluate the forced oscillation technique (FOT) and pulmonary densitovolumetry in acromegalic patients and to examine the correlations between these findings. In this cross-sectional study, 29 non-smoking acromegalic patients and 17 paired controls were subjected to the FOT and quantification of lung volume using multidetector computed tomography (Q-MDCT). Compared with the controls, the acromegalic patients had a higher value for resonance frequency [15.3 (10.9-19.7) vs 11.4 (9.05-17.6) Hz, P=0.023] and a lower value for mean reactance [0.32 (0.21-0.64) vs 0.49 (0.34-0.96) cm H2O/L/s2, P=0.005]. In inspiratory Q-MDCT, the acromegalic patients had higher percentages of total lung volume (TLV) for nonaerated and poorly aerated areas [0.42% (0.30-0.51%) vs 0.25% (0.20-0.32%), P=0.039 and 3.25% (2.48-3.46%) vs 1.70% (1.45-2.15%), P=0.001, respectively]. Furthermore, the acromegalic patients had higher values for total lung mass in both inspiratory and expiratory Q-MDCT [821 (635-923) vs 696 (599-769) g, P=0.021 and 844 (650-945) vs 637 (536-736) g, P=0.009, respectively]. In inspiratory Q-MDCT, TLV showed significant correlations with all FOT parameters. The TLV of hyperaerated areas showed significant correlations with intercept resistance (rs=−0.602, P<0.001) and mean resistance (rs=−0.580, P<0.001). These data showed that acromegalic patients have increased amounts of lung tissue as well as nonaerated and poorly aerated areas. Functionally, there was a loss of homogeneity of the respiratory system. Moreover, there were correlations between the structural and functional findings of the respiratory system, consistent with the pathophysiology of the disease. PMID:26445330

  8. Correlations between forced oscillation technique parameters and pulmonary densitovolumetry values in patients with acromegaly.

    PubMed

    Camilo, G B; Carvalho, A R S; Machado, D C; Mogami, R; Kasuki, L; Gadelha, M R; Melo, P L; Lopes, A J

    2015-10-01

    The aims of this study were to evaluate the forced oscillation technique (FOT) and pulmonary densitovolumetry in acromegalic patients and to examine the correlations between these findings. In this cross-sectional study, 29 non-smoking acromegalic patients and 17 paired controls were subjected to the FOT and quantification of lung volume using multidetector computed tomography (Q-MDCT). Compared with the controls, the acromegalic patients had a higher value for resonance frequency [15.3 (10.9-19.7) vs 11.4 (9.05-17.6) Hz, P=0.023] and a lower value for mean reactance [0.32 (0.21-0.64) vs 0.49 (0.34-0.96) cm H2O/L/s2, P=0.005]. In inspiratory Q-MDCT, the acromegalic patients had higher percentages of total lung volume (TLV) for nonaerated and poorly aerated areas [0.42% (0.30-0.51%) vs 0.25% (0.20-0.32%), P=0.039 and 3.25% (2.48-3.46%) vs 1.70% (1.45-2.15%), P=0.001, respectively]. Furthermore, the acromegalic patients had higher values for total lung mass in both inspiratory and expiratory Q-MDCT [821 (635-923) vs 696 (599-769) g, P=0.021 and 844 (650-945) vs 637 (536-736) g, P=0.009, respectively]. In inspiratory Q-MDCT, TLV showed significant correlations with all FOT parameters. The TLV of hyperaerated areas showed significant correlations with intercept resistance (rs=-0.602, P<0.001) and mean resistance (rs=-0.580, P<0.001). These data showed that acromegalic patients have increased amounts of lung tissue as well as nonaerated and poorly aerated areas. Functionally, there was a loss of homogeneity of the respiratory system. Moreover, there were correlations between the structural and functional findings of the respiratory system, consistent with the pathophysiology of the disease. PMID:26445330

  9. Gyrokinetic large eddy simulations

    SciTech Connect

    Morel, P.; Navarro, A. Banon; Albrecht-Marc, M.; Carati, D.; Merz, F.; Goerler, T.; Jenko, F.

    2011-07-15

    The large eddy simulation approach is adapted to the study of plasma microturbulence in a fully three-dimensional gyrokinetic system. Ion temperature gradient driven turbulence is studied with the GENE code for both a standard resolution and a reduced resolution with a model for the sub-grid scale turbulence. A simple dissipative model for representing the effect of the sub-grid scales on the resolved scales is proposed and tested. Once calibrated, the model appears to be able to reproduce most of the features of the free energy spectra for various values of the ion temperature gradient.

  10. NOTE: A comparison of image registration techniques for the correlation of radiolabelled antibody distribution with tumour morphology

    NASA Astrophysics Data System (ADS)

    Flynn, A. A.; Green, A. J.; Boxer, G.; Pedley, R. B.; Begent, R. H. J.

    1999-07-01

    Image registration is a powerful tool for correlating functional images with images of anatomical structure. This facilitates more accurate quantitation of regional radiopharmaceutical uptake. Similarly, registration of images of radiolabelled antibody distribution, in tissue sections, with the equivalent histological images allows the comparison and measurement of radiopharmaceutical distribution with morphological structure. The images used were obtained by storage phosphor plate technology, for the radiopharmaceutical distribution, and by digitization of the stained histological sections. Here we compare four fully automatic registration techniques and one manual technique in terms of their spatial accuracy. We have found that there was no difference in accuracy between cross-correlation, minimization of variance and mutual information. These techniques were more accurate than principal axes and the manual technique. However, minimization of variance and mutual information were more time-consuming than the other methods. Consequently, cross-correlation is the method of choice for automatic registration of large numbers of these image pairs.

  11. Zone wise local characterization of welds using digital image correlation technique

    NASA Astrophysics Data System (ADS)

    Saranath, K. M.; Sharma, Abhay; Ramji, M.

    2014-12-01

    The process of welding is associated with high and varying thermal gradients across the weld, resulting in inhomogeneous material properties surrounding the weldment. A proper understanding of the varying mechanical properties of the weld and surrounding materials is important in designing and modelling of components with weld. In the present study the characterization of different zones such as fusion zone, heat affected zones and unaffected base material of a deposited weld is carried out using digital image correlation (DIC) technique. A methodology using the micrographic observation and image processing is proposed for accurate identification of various weld zones. The response of welded samples in the elastic and plastic region is compared with the virgin sample. Full range stress-strain curves are obtained for each zone using the whole field strain measurement involving DIC. The parameters investigated are Young's modulus, Poisson's ratio, yield stress, strain hardening exponent and strength coefficient. A study regarding the variation of properties with respect to varying weld currents of 100 A, 130 A and 150 A is carried out. The Vickers microhardness measurement is also conducted to obtain the variation in hardness across weldment. Fusion zone of all the welded samples have reported lower Young's modulus and higher yield strength compared to virgin samples. The Vickers hardness values obtained for fusion and heat affected zones are in line with the yield stress variation obtained zone wise. Proposed zone wise local characterization of welds using digital image correlation. Weld zones are identified using a strain based method coupled with micrographs. Full range stress-strain curves are extracted for each local weld zones. Local elastic, plastic properties and microhardness across the weld are extracted. Local properties of welds produced using different current ratings are compared.

  12. Are Eddy Covariance series stationary?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Spectral analysis via a discrete Fourier transform is used often to examine eddy covariance series for cycles (eddies) of interest. Generally the analysis is performed on hourly or half-hourly data sets collected at 10 or 20 Hz. Each original series is often assumed to be stationary. Also automated ...

  13. Remote field eddy current-crack and defect detection

    SciTech Connect

    Lord, W.

    1989-03-16

    No single nondestructive evaluation (NDE) technique is currently capable of detecting and characterizing all the defect types that can occur in gas pipeline. Conventional in-line inspection tools for example, have not shown significant sensitivity to intergranular stress corrosion cracking. For this reason considerable research and development work is still needed in order to provide the in-line inspection tools whose results are essential for structural integrity evaluations. The remote field eddy current method shows more promise than conventional eddy current methods, in gas pipeline inspection, due to the increased sensitivity to inner and outer pipe wall inhomogeneities. Even though the fundamental physical principles governing the conventional eddy current method and the remote field eddy current method is one and the same (that of electromagnetic induction), the differences in operating frequencies in the two methods result in field patterns that have different characteristic properties, such as extremely small skin depths associated with conventional eddy currents testing and the phenomena of potential valley'' and phase knot'' associated with remote field eddy current technique. 20 refs., 26 figs.

  14. Modified Multilook Cross Correlation technique for Doppler centroid estimation in SAR image signal processing

    NASA Astrophysics Data System (ADS)

    Bee Cheng, Sew

    Synthetic Aperture Radar (SAR) is one of the widely used remote sensing sensors which produces high resolution image by using advance signal processing technique. SAR managed to operate in all sorts of weather and cover wide range of area. To produce a high-quality image, accurate parameters such as Doppler centroid are required for precise SAR signal processing. In the azimuth matched filtering of SAR signal processing, Doppler centroid is an important azimuth parameter that helps to focus the image pixels. Doppler centroid has always been overlooked during SAR signal processing. It is due to the fact that estimation of Doppler centroid involved complicated calculation and increased computational load. Therefore, researcher used to apply only the approximate Doppler value which is not precise and cause defocus effort in the generated SAR image. In this study, several conventional Doppler centroid estimation algorithms are reviewed and developed using Matlab software program to extract the Doppler parameter from received SAR data, namely Spectrum Fit Algorithm, Wavelength Diversity Algorithm (WDA), Multilook Cross Correlation Algorithm (MLCC), and Multilook Beat Frequency Algorithm (MLBF). Two sets of SAR data are employed to evaluate the performance of each estimator, i.e. simulated point target data and RADARSAT-1 Vancouver scene raw data. These experiments gave a sense of accuracy for the estimated results together with computational time consumption. Point target is simulated to generate ideal case SAR data with pre-defined SAR system parameters.

  15. Correlation techniques as applied to pose estimation in space station docking

    NASA Astrophysics Data System (ADS)

    Rollins, John M.; Juday, Richard D.; Monroe, Stanley E., Jr.

    2002-08-01

    The telerobotic assembly of space-station components has become the method of choice for the International Space Station (ISS) because it offers a safe alternative to the more hazardous option of space walks. The disadvantage of telerobotic assembly is that it does not necessarily provide for direct arbitrary views of mating interfaces for the teleoperator. Unless cameras are present very close to the interface positions, such views must be generated graphically, based on calculated pose relationships derived from images. To assist in this photogrammetric pose estimation, circular targets, or spots, of high contrast have been affixed on each connecting module at carefully surveyed positions. The appearance of a subset of spots must form a constellation of specific relative positions in the incoming image stream in order for the docking to proceed. Spot positions are expressed in terms of their apparent centroids in an image. The precision of centroid estimation is required to be as fine as 1/20th pixel, in some cases. This paper presents an approach to spot centroid estimation using cross correlation between spot images and synthetic spot models of precise centration. Techniques for obtaining sub-pixel accuracy and for shadow and lighting irregularity compensation are discussed.

  16. Correlation Techniques as Applied to Pose Estimation in Space Station Docking

    NASA Technical Reports Server (NTRS)

    Rollins, J. Michael; Juday, Richard D.; Monroe, Stanley E., Jr.

    2002-01-01

    The telerobotic assembly of space-station components has become the method of choice for the International Space Station (ISS) because it offers a safe alternative to the more hazardous option of space walks. The disadvantage of telerobotic assembly is that it does not provide for direct arbitrary views of mating interfaces for the teleoperator. Unless cameras are present very close to the interface positions, such views must be generated graphically, based on calculated pose relationships derived from images. To assist in this photogrammetric pose estimation, circular targets, or spots, of high contrast have been affixed on each connecting module at carefully surveyed positions. The appearance of a subset of spots essentially must form a constellation of specific relative positions in the incoming digital image stream in order for the docking to proceed. Spot positions are expressed in terms of their apparent centroids in an image. The precision of centroid estimation is required to be as fine as 1I20th pixel, in some cases. This paper presents an approach to spot centroid estimation using cross correlation between spot images and synthetic spot models of precise centration. Techniques for obtaining sub-pixel accuracy and for shadow, obscuration and lighting irregularity compensation are discussed.

  17. Fracture toughness of the nickel-alumina laminates by digital image-correlation technique

    NASA Astrophysics Data System (ADS)

    Mekky, Waleed

    The purpose of this work is to implement the digital image correlation technique (DIC) in composite laminate fracture testing. The latter involves measuring the crack opening displacement (COD) during stable crack propagation and characterizing the strain development in a constrained nickel layer under applied loading. The major challenge to measure the COD of alternated metal/ceramic layers is the elastic-mismatch effect. This leads to oscillating COD measurement. Smoothing the result with built-in modules of commercial software leads to a loss of data accuracy. A least-squares fitting routine for the data output gave acceptable COD profiles. The behavior of a single Ni ligament sandwiched between two Al2O3 layers was determined for two Ni thicknesses (0.125 and 0.25mm). Modeling of the behavior via a modified Bridgman approach for rectangular cross section samples, proved limited as different mechanisms are operating. Nevertheless, the behavior is however captured to a point, but the model underestimates the results vis a vis experimental ones. The fracture-resistance curves for Nickel/Alumina laminates were developed experimentally and modeled via LEFM using the weight function approach and utilizing single-ligament-, and COD-, data. The crack-tip toughness was found to increase with Ni layer thickness due to crack-tip-shielding. The crack-initiation-toughness was estimated from the stress field and the crack-opening-displacement of the main crack.

  18. Obituary: John Allen Eddy (1931-2009)

    NASA Astrophysics Data System (ADS)

    Gingerich, Owen

    2011-12-01

    , "This Mercury is Hot! Red Shift, Black Body, and a Perfect Radiator." Ironically, within a few years he was laid off from his HAO position as a result of budget cuts at its parent organization, the National Center for Atmospheric Research (NCAR). In an interview a quarter of a century later Eddy remarked, "I found out how hard it is for a person with a Ph.D. to get another job at that time, and often wished I didn't have one, for I was often told, true or not, that I was overqualified for the few jobs that turned up." Eddy found a temporary job writing a book for NASA as part of a series on the Skylab spacecraft; the book, The New Sun, was published in 1979. Again, working on his own time, he revived an earlier finding, namely, that between 1645 and 1715 the sun was almost devoid of spots, and he greatly extended the previous work of Gustav Spörer and Walter Maunder by showing during that period a dearth of aurorae and atmospheric carbon-14, a diminution of the solar corona during eclipses, and probably a correlation with cooling of the earth. For onomatopoiec reasons, the rhythm of the m's, Eddy chose the title "the Maunder Minimum" for the phenomenon, and for his unusually long cover story in the 18 June 1976 issue of Science. The paper was well received, and for a while Eddy was an invited speaker fifty times a year. In 1977, Eddy scored yet again, with his third cover story in Science, a jointly authored paper on solar rotation in the early 17th century. In 1977-78 Eddy had a fellowship at the Harvard-Smithsonian Center for Astrophysics in Cambridge, and during that time Ken Brecher and I had a series of conversations with Jack in which we worked out a proposal for a historical astronomy division within the AAS; since I had just been an AAS Councilor, I negotiated with the Society for its actualization, and Eddy became the first HAD president, in 1981-83. He introduced the logo, Dürer's ancient astronomer, and at the end of his term, the plaque with the motto "Ich

  19. Eddy current detection of pitting corrosion around fastener holes

    NASA Astrophysics Data System (ADS)

    Heida, J. H.; Thart, W. G. J.

    1995-01-01

    An evaluation of the eddy current technique for the detection and depth assessment of corrosion around fastener holes in F-16 lower wing skins is described. The corrosion type in this structure is pitting corrosion at the countersink edge of the fastener holes. Due to a corrosion clean-up limit of only 1.5 - 2.5 percent, a maximum thickness reduction in the range of 0.08 - 0.32 mm is allowed (depending on local skin thickness). This specifies the needed sensitivity for in-service corrosion inspection. In the evaluation use was made of specimens cut out of the F-16 lower wing skin structure. In total twelve specimens were exposed to an accelerated corrosion test (EXCO-test). Eddy current inspection of the specimens with installed fasteners was performed with a standard eddy scope and four different eddy current probes. After the eddy current inspection cross-sections of the twelve-specimens were made to determine the extent of pitting corrosion at the countersink edges. After evaluation of the inspection results the following conclusions can be drawn: for in-service detection of countersink edge corrosion standard visual inspection is the preferred technique regarding the simplicity, sensitivity and reliability of inspection; and for the purpose of depth assessment the eddy current technique is capable of detecting countersink edge corrosion with a depth from about 0.1 mm. Due to the corrosion clean-up limit of only 1.5 - 2.5 percent (0.08 - 0.32 mm), however, the eddy current technique is considered not applicable for in-service depth assessment of countersink edge corrosion in F-16 lower wing skins.

  20. Characteristic eddy decomposition of turbulence in a channel

    NASA Technical Reports Server (NTRS)

    Moin, Parviz; Moser, Robert D.

    1991-01-01

    The proper orthogonal decomposition technique (Lumley's decomposition) is applied to the turbulent flow in a channel to extract coherent structures by decomposing the velocity field into characteristic eddies with random coefficients. In the homogeneous spatial directions, a generaliztion of the shot-noise expansion is used to determine the characteristic eddies. In this expansion, the Fourier coefficients of the characteristic eddy cannot be obtained from the second-order statistics. Three different techniques are used to determine the phases of these coefficients. They are based on: (1) the bispectrum, (2) a spatial compactness requirement, and (3) a functional continuity argument. Results from these three techniques are found to be similar in most respects. The implications of these techniques and the shot-noise expansion are discussed. The dominant eddy is found to contribute as much as 76 percent to the turbulent kinetic energy. In both 2D and 3D, the characteristic eddies consist of an ejection region straddled by streamwise vortices that leave the wall in the very short streamwise distance of about 100 wall units.

  1. Anomalous eddy heat and freshwater transport in the Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Lyman, John M.; Johnson, Gregory C.

    2015-02-01

    Characteristics of eddies in the Gulf of Alaska are assessed from January 2003 through April 2012. Ensemble statistics for eddy subsurface water properties on isopycnals are computed using temperature and salinity profiles from Argo profiling floats located within eddies, which are identified in sea-surface height using objective techniques. Ninety cyclonic and 154 anticyclonic eddies are identified during this period. The anticyclonic eddies are strongly nonlinear and exhibit significant warm subsurface temperature anomalies and associated salty anomalies on isopycnals while no clear distinguishing subsurface anomalies on isopycnals are detected in association with the cyclonic eddies. Heat and freshwater fluxes for the eddies are estimated from integrations in depth coordinates. The anticyclonic eddies transport heat both westward off the continental shelf into the Subarctic Gyre and westward within the Alaskan Stream. However, they transport salt into the Subarctic Gyre and freshwater within the Alaskan Stream. In both pathways eddy heat and freshwater transport show possible year-to-year fluctuations, varying from 0 to 50.4 × 1018 J a-1 and -16.8 to +7.4 km3 a-1, respectively. The anticyclonic eddies are capped by relatively fresh water year-round.

  2. Annular modes and apparent eddy feedbacks in the Southern Hemisphere

    NASA Astrophysics Data System (ADS)

    Byrne, Nicholas J.; Shepherd, Theodore G.; Woollings, Tim; Plumb, R. Alan

    2016-04-01

    Lagged correlation analysis is often used to infer intraseasonal dynamical effects but is known to be affected by nonstationarity. We highlight a pronounced quasi 2 year peak in the anomalous zonal wind and eddy momentum flux convergence power spectra in the Southern Hemisphere, which is prima facie evidence for nonstationarity. We then investigate the consequences of this nonstationarity for the Southern Annular Mode and for eddy momentum flux convergence. We argue that positive lagged correlations previously attributed to the existence of an eddy feedback are more plausibly attributed to nonstationary interannual variability external to any potential feedback process in the midlatitude troposphere. The findings have implications for the diagnosis of feedbacks in both models and reanalysis data as well as for understanding the mechanisms underlying variations in the zonal wind.

  3. Method and apparatus for correcting eddy current signal voltage for temperature effects

    DOEpatents

    Kustra, Thomas A.; Caffarel, Alfred J.

    1990-01-01

    An apparatus and method for measuring physical characteristics of an electrically conductive material by the use of eddy-current techniques and compensating measurement errors caused by changes in temperature includes a switching arrangement connected between primary and reference coils of an eddy-current probe which allows the probe to be selectively connected between an eddy current output oscilloscope and a digital ohm-meter for measuring the resistances of the primary and reference coils substantially at the time of eddy current measurement. In this way, changes in resistance due to temperature effects can be completely taken into account in determining the true error in the eddy current measurement. The true error can consequently be converted into an equivalent eddy current measurement correction.

  4. Lagrangian analysis of formation, structure, evolution and splitting of anticyclonic Kuril eddies

    NASA Astrophysics Data System (ADS)

    Prants, S. V.; Lobanov, V. B.; Budyansky, M. V.; Uleysky, M. Yu.

    2016-03-01

    We studied in detail a mesoscale anticylonic eddy that has been sampled in the R/V Professor Gagarinskiy cruise (June-July 2012) in the area east of the Kuril Islands in the northwestern subarctic Pacific. Lagrangian approach was applied to study formation, structure and evolution of this feature called the eddy A and of its parent eddy B using a simulation with synthetic tracers advected by the AVISO velocity field. We used different Lagrangian methods and techniques to identify those eddies and their boundaries, to know their structure and to document their deformation, metamorphoses and splitting. It has been found that the eddy A was born as a result of splitting of the eddy B with the core water to be borrowed from the eddy B which, in turn, was influenced by the Okhotsk Sea water flowing into the ocean through the Kuril straits. The periphery of the eddy A was formed mainly by East Kamchatka Current water in the process of its winding onto the eddy A core by portions. All these processes have been documented in detail with the help of drift and tracking Lagrangian maps computed forward and backward in time with a large number of synthetic tracers distributed over the studied area. We have found a Lagrangian structure of those eddies and the ways how they have gained and released water. Simulated and measured locations of the center of the eddy A and its boundary have been be estimated to coincide with the accuracy of ≈ 7-10 and ≈ 15-20 km, respectively. Our simulations were validated in part by tracks of available surface drifters and Argo floats. We presented CTD hydrographic observations of the Kuril eddy A from the surface to deep waters and compared observed and simulated results in order to establish origin and properties of water masses constituting that eddy.

  5. Fast patient-specific Monte Carlo brachytherapy dose calculations via the correlated sampling variance reduction technique

    SciTech Connect

    Sampson, Andrew; Le Yi; Williamson, Jeffrey F.

    2012-02-15

    Purpose: To demonstrate potential of correlated sampling Monte Carlo (CMC) simulation to improve the calculation efficiency for permanent seed brachytherapy (PSB) implants without loss of accuracy. Methods: CMC was implemented within an in-house MC code family (PTRAN) and used to compute 3D dose distributions for two patient cases: a clinical PSB postimplant prostate CT imaging study and a simulated post lumpectomy breast PSB implant planned on a screening dedicated breast cone-beam CT patient exam. CMC tallies the dose difference, {Delta}D, between highly correlated histories in homogeneous and heterogeneous geometries. The heterogeneous geometry histories were derived from photon collisions sampled in a geometrically identical but purely homogeneous medium geometry, by altering their particle weights to correct for bias. The prostate case consisted of 78 Model-6711 {sup 125}I seeds. The breast case consisted of 87 Model-200 {sup 103}Pd seeds embedded around a simulated lumpectomy cavity. Systematic and random errors in CMC were unfolded using low-uncertainty uncorrelated MC (UMC) as the benchmark. CMC efficiency gains, relative to UMC, were computed for all voxels, and the mean was classified in regions that received minimum doses greater than 20%, 50%, and 90% of D{sub 90}, as well as for various anatomical regions. Results: Systematic errors in CMC relative to UMC were less than 0.6% for 99% of the voxels and 0.04% for 100% of the voxels for the prostate and breast cases, respectively. For a 1 x 1 x 1 mm{sup 3} dose grid, efficiency gains were realized in all structures with 38.1- and 59.8-fold average gains within the prostate and breast clinical target volumes (CTVs), respectively. Greater than 99% of the voxels within the prostate and breast CTVs experienced an efficiency gain. Additionally, it was shown that efficiency losses were confined to low dose regions while the largest gains were located where little difference exists between the homogeneous and

  6. Digital speckle-photography, LASCA and cross-correlation techniques for study of blood microflow in isolated vessel

    NASA Astrophysics Data System (ADS)

    Ganilova, Yulia; Li, Pengcheng; Zhu, Dan; Lin, Nisong; Chen, Haiying; Luo, Qingming; Ulyanov, Sergey

    2006-08-01

    Different methods of speckle-metrology, which may be used in biomedical diagnostics, are considered in this paper. Cross-correlation technique, digital speckle-photography, LASCA are compared. Advantages and disadvantages of these methods are demonstrated; the limits for minimal resolution are studied.

  7. Tone Burst Eddy-Current Thermography (tbet)

    NASA Astrophysics Data System (ADS)

    Kumar, Ch. N. Kiran; Krishnamurthy, C. V.; Maxfield, Bruce W.; Balasubramaniam, Krishnan

    2008-02-01

    This paper reports on a Tone Burst Eddycurrent Thermography (TBET) technique that uses short-time bursts of eddy-currents induced in conducting media to generate local heating inside the material. The transient diffusion of the heat inside the material, induced by pulsed/short-time induction heating, is imaged by measuring the transient temperature profiles on the surface of the material. The presence and characteristics of the defects inside the materials changes the surface temperature transients and thus can be used for the nondestructive evaluation (NDE) of conducting materials. Axisymmetric numerical models of the conventional transient thermography technique are used to benchmark the TBET technique. From the temperature profile data, temperature contrast information is obtained for the different defect depths. Temperature contrast data obtained for TBET, in this process, was compared with that obtained from conventional transient thermography data. It was found that the frequency of the eddy-current and, consequently, the skin-depth of the induced field play an important role in the effective utilization of this technique. Simulation details and the experimental results are presented in the paper. Possible advantages of TBET over conventional flash thermography are also discussed and supported by experimental data.

  8. Hot-cell design considerations for interfacing eddy-current systems

    SciTech Connect

    Franklin, E.M.; Webb, J.P.; Larson, J.M.

    1985-01-01

    The Hot Fuel Examination Facility/North conducts remote eddy-current examination of irradiated fuel elements. Applications include cladding breach detection and irradiation-induced ferrite examination. The seccussful use of remote eddy-current techniques is achieved by applying basic test parameters and interfacing considerations. These include impedance matching, operating frequency, and feedthrough considerations.

  9. Eddy current pulsed thermography for fatigue evaluation of gear

    NASA Astrophysics Data System (ADS)

    Tian, Gui Yun; Yin, Aijun; Gao, Bin; Zhang, Jishan; Shaw, Brian

    2014-02-01

    The pulsed eddy current (PEC) technique generates responses over a wide range of frequencies, containing more spectral coverage than traditional eddy current inspection. Eddy current pulsed thermography (ECPT), a newly developed non-destructive testing (NDT) technique, has advantages such as rapid inspection of a large area within a short time, high spatial resolution, high sensitivity and stand-off measurement distance. This paper investigates ECPT for the evaluation of gear fatigue tests. The paper proposes a statistical method based on single channel blind source separation to extract details of gear fatigue. The discussion of transient thermal distribution and patterns of fatigue contact surfaces as well as the non-contact surfaces have been reported. In addition, the measurement for gears with different cycles of fatigue tests by ECPTand the comparison results between ECPT with magnetic Barkhausen noise (MBN) have been evaluated. The comparison shows the competitive capability of ECPT in fatigue evaluation.

  10. CO2 and CH4 fluxes along a latitudinal transect in Northern Alaska using eddy covariance technique in challenging conditions: first results of a long term experiment in the Arctic tundra

    NASA Astrophysics Data System (ADS)

    Moreaux, V.; Oechel, W. C.; Losacco, S.; McEwing, R.; Murphy, P.; Zona, D.

    2013-12-01

    the first year of a new long-term study that includes the results of the upgrading of 5 sites in Northern Alaska across a latitudinal transect (Barrow, Atqasuk, and Ivotuk) and across a moisture gradient (Barrow) in the Arctic. These sites are equipped with different eddy covariance systems to follow CO2 and CH4 fluxes, combined with a full data set of meteorological and soil measurements. The study summarizes a full analysis of energy balance, CO2 and CH4 fluxes correlated to changes in meteorological and soil conditions on the 5 sites of the transect. Based on the results available, CH4 fluxes averaged approximatively 8 mgC m-2 d-1 in the north (Barrow) to 13 mgC m-2 d-1 in the south (Ivotuk). In between these two sites, a daily value of about 20 mgC m-2 d-1 in the wetter, vegetated drained lake basin was observed. Surprisingly, from our preliminary data investigation, the southernmost and warmer site (Ivotuk) did not present the highest CH4 emission, which instead was the highest in the 200 km north site (Atqasuk) with a mean daily value of 25 mgC m-2 d-1. The importance of fall season CH4 emissions will also be presented and their importance relative to summertime emissions.

  11. NONDESTRUCTIVE EDDY CURRENT TESTING

    DOEpatents

    Renken, C.J. Jr.

    1961-05-23

    An eddy current testing device is described for measuring metal continuity independent of probe-to-sample spacing. An inductance would test probe is made a leg of a variable impedance bridge and the bridge is balanced with the probe away from the sample. An a-c signal is applied across the input terminals of the bridge circuit. As the probe is brought into proximity with the metal sample, the resulting impedance change in the probe gives an output signal from the bridge whose phase angle is proportional to the sample continuity and amplitude is proportional to the probe-tosample spacing. The output signal from the bridge is applied to a compensating network where, responsive to amplitude changes from the bridge output signal, a constant phased voltage output is maintained when the sample is continuous regardless of probe-to-sample spacing. A phase meter calibrated to read changes in resistivity of the metal sample measures the phase shift between the output of the compensating network and the original a-c signal applied to the bridge.

  12. A new technique to determine the correlation between the QT interval and heart-rate for control and SIDS babies

    NASA Technical Reports Server (NTRS)

    Sadeh, D.; Shannon, D. C.; Abboud, S.; Akselrod, S.; Cohen, R. J.

    1987-01-01

    The ability of the autonomic nervous system to alter the QT interval in response to heart rate changes is essential to cardiovascular control. An accurate way to determine the relation between QT intervals and their corresponding RR intervals is described. A computer algorithm measures the RR intervals using digital filtering and cross-correlating the QRS sections of consecutive waveforms. The QT intervals is calculated by choosing a section of, the ECG that includes the T wave and cross-correlating it with all the consecutive T waves. At least 4000 pairs of QT-RR intervals are computed for each subject and a best fit correlation function determines the relations between the QT and RR intervals. This technique enables to establish a precise correlation between RR and QT in order to distinguish between control and SIDS babies.

  13. Pulse shape measurement by a non-collinear third-order correlation technique

    NASA Astrophysics Data System (ADS)

    Priebe, G.; Janulewicz, K. A.; Redkorechev, V. I.; Tümmler, J.; Nickles, P. V.

    2006-03-01

    A third-order correlator suitable for detailed shape measurements of picosecond laser pulses has been developed. The working principle in both the single shot and the scanning mode is based on detection of the phase-matched difference frequency non-collinear generated signal in a non-linear crystal. This third-order OPA correlator was applied for the characterization of the specifically shaped picosecond laser pulses from the MBI CPA Nd: glass laser system.

  14. High frequency eddy current device for near surface material characterizations

    NASA Astrophysics Data System (ADS)

    Hillmann, S.; Heuer, H.; Meyendorf, N.

    2009-03-01

    For near surface characterization a new high frequency eddy current device was been developed. By using a measurement frequency up to 100 MHz information of near surface areas can be acquired. Depending on the investigated material high resolution depth profiles can be derived. The obtained data with the new device were compared to those obtained with a high precision impedance analyser. It could be demonstrated that the new device measures the eddy current conductivity signal in the high frequencies much better than the impedance analyser. By sweeping the frequency from 100 kHz up to 100 MHz the technique delivers a depth profile of the electrical conductivity of the material. This kind of high frequency eddy current technique can be used for quality assurance, surface contamination control or near surface material characterization e.g. microstructure and cold work influences. It can be a powerful tool to obtain information for process control or a good / bad decision in mass production processes like for example rolling, coating, and surface treatments. The big advantage of the high frequency eddy current method is that it is fast und precise. This paper presents results with a new developed prototype Eddy-Current-Device for measurement frequencies up to 100 MHz which is first time suitable in rough industrial environment and makes expensive lab network analysers unnecessary for this kind of investigations.

  15. Measuring evapotranspiration: comparison of eddy covariance, scintillometers and enclosed chambers

    NASA Astrophysics Data System (ADS)

    Yee, Mei Sun; Beringer, Jason; Pauwels, Valentijn R. N.; Daly, Edoardo; Walker, Jeffrey P.; Rüdiger, Christoph

    2014-05-01

    Evapotranspiration (ET) is the combination of evaporation from the soil surface and transpiration from plants. It is an important component of the hydrological cycle, particularly in arid and semi-arid areas where most of the precipitation is returned to the atmosphere via ET. It also drives the land-surface energy balance, largely affecting soil temperature and the heat exchange between the land and atmosphere. Therefore, the ability to quantify ET is important for accurate climate and weather predictions, as well as improving the management of water resources. Various methods for measuring ET are available, including gas chambers, lysimeters, Bowen-ratio energy balance stations, eddy-covariance systems, scintillometers, and space-borne sensors. These methods differ in spatial scales (from leaf to basin scale), time scales (seconds to days), principles (water-balance, mass-transfer, eddy-correlation, energy balance) and have their own strengths and limitations. For instance, point scale measurements, such as those obtained using lysimeters, assume that the sample is representative of a larger area, whereas measurements at a basin scale assume that the spatial average of all the other components in the water or energy balance equations can be measured accurately. The purpose of this study is to compare different techniques to measure ET across their respective scales and to identify causes of discrepancies between measurements. The final aim is to identify a technique or a combination of techniques to be used for verification of remote sensing evapotranspiration products. The study area is located in the Yanco Study Area (34.561°S, 35.170°S, 145.826°E, 146.439°E), situated within the western plains of the Murrumbidgee River catchment, in New South Wales, Australia. This area has been extensively monitored and a series of field experiments have been performed in the past to contribute to the pre- and post-launch algorithm development of earth observing

  16. TODCOR: A New Two-Dimensional Correlation Technique to Analyze Stellar Spectra in Search for Faint Companions

    NASA Astrophysics Data System (ADS)

    Mazeh, T.; Zucker, S.; Smith, H.

    1993-12-01

    TODCOR is a new TwO-Dimensional CORrelation technique to measure radial velocities of two components of a spectroscopic binary (Zucker and Mazeh 1993, ApJ, in press). Assuming the spectra of the two components are known, the technique correlates an observed binary spectrum against a combination of the two spectra with different shifts. TODCOR measures simultaneously the radial velocities of the two stars by finding the maximum correlation. A few real single-line spectroscopic binaries already have been turned into double-line systems with TODCOR, demonstrating the power of the technique. One of the advantages of TODCOR is its ability to detect a very faint companion in a combined spectrum, and to measure its radial velocity. We present numerical tests in which we applied TODCOR to simulated spectra which were prepared as combinations of two observed infrared spectra with various luminosity ratios, together with random noise. These tests show that TODCOR can detect in principle a very faint secondary spectrum and measure correctly its velocity, provided the combined spectrum has adequate spectral coverage and S/N. Measuring the radial velocity of the faint secondary will enable us to estimate its mass, making the technique a very useful tool in the search for brown dwarfs and giant planets around nearby stars.

  17. Giant Magnetoresistance Sensors: A Review on Structures and Non-Destructive Eddy Current Testing Applications

    PubMed Central

    Rifai, Damhuji; Abdalla, Ahmed N.; Ali, Kharudin; Razali, Ramdan

    2016-01-01

    Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper. PMID:26927123

  18. Giant Magnetoresistance Sensors: A Review on Structures and Non-Destructive Eddy Current Testing Applications.

    PubMed

    Rifai, Damhuji; Abdalla, Ahmed N; Ali, Kharudin; Razali, Ramdan

    2016-01-01

    Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper. PMID:26927123

  19. Remote Field Eddy Current Transition Zone

    NASA Astrophysics Data System (ADS)

    Dubois, Joseph Maurice Stephane

    1992-01-01

    The Remote Field Eddy Current (RFEC) technique is a non-destructive inspection technique used for anomaly detection in tubulars. The RFEC technique uses exciter and detector coils, both located inside the pipe, to detect interior and exterior corrosion with approximately equal sensitivity. The presence of both direct and indirect electromagnetic coupling paths distinguishes the RFEC technique from conventional reflected impedance eddy current techniques. The RFEC pipe inspection technique normally operates with the detector coil in the remote field region at distances of two or more pipe diameters from the internal exciter coil. At this spacing, the direct coupled field, dominant near the exciter (less than 1 pipe ID), is strongly attenuated and is overshadowed by the indirect field generated by an indirect energy transmission path which diffuses outwardly at the exciter coil location and tends to be guided by the pipe wall. In the remote field region, the field energy is greater outside than inside the pipe and some of the energy diffuses back inside the pipe. In the intermediate region (from 1 to 2 pipe diameters), called the transition zone, direct and indirect fields interact. The transition zone interaction produces a resultant field which is very sensitive to variations in pipe properties or wall thickness. The effect is maximal at the point where the indirect and direct fields have equal magnitudes and opposite phases. Small variations in the indirect field at this crossover point produce large changes in the resultant field. Experimental examples of the resultant axial magnetic field are presented to demonstrate the transition zone characteristics. An improved understanding of the effects of localized inner and outer wall defects and of pipe wall thinning on the direct and indirect field components in the transition zone is needed to better exploit the RFEC technique. Operating the RFEC probe in the transition zone with carefully selected frequency and

  20. Applied large eddy simulation.

    PubMed

    Tucker, Paul G; Lardeau, Sylvain

    2009-07-28

    Large eddy simulation (LES) is now seen more and more as a viable alternative to current industrial practice, usually based on problem-specific Reynolds-averaged Navier-Stokes (RANS) methods. Access to detailed flow physics is attractive to industry, especially in an environment in which computer modelling is bound to play an ever increasing role. However, the improvement in accuracy and flow detail has substantial cost. This has so far prevented wider industrial use of LES. The purpose of the applied LES discussion meeting was to address questions regarding what is achievable and what is not, given the current technology and knowledge, for an industrial practitioner who is interested in using LES. The use of LES was explored in an application-centred context between diverse fields. The general flow-governing equation form was explored along with various LES models. The errors occurring in LES were analysed. Also, the hybridization of RANS and LES was considered. The importance of modelling relative to boundary conditions, problem definition and other more mundane aspects were examined. It was to an extent concluded that for LES to make most rapid industrial impact, pragmatic hybrid use of LES, implicit LES and RANS elements will probably be needed. Added to this further, highly industrial sector model parametrizations will be required with clear thought on the key target design parameter(s). The combination of good numerical modelling expertise, a sound understanding of turbulence, along with artistry, pragmatism and the use of recent developments in computer science should dramatically add impetus to the industrial uptake of LES. In the light of the numerous technical challenges that remain it appears that for some time to come LES will have echoes of the high levels of technical knowledge required for safe use of RANS but with much greater fidelity. PMID:19531503

  1. In-vivo measuring of blood-flow changes using diffusing wave correlation techniques

    NASA Astrophysics Data System (ADS)

    Meglinski, Igor V.; Boas, David A.; Yodh, Arjun G.; Chance, Britton

    1997-02-01

    We have non-invasively measured in vivo blood flow changes using photon correlation spectroscopy with a simple correlation diffusion model to study and quantify blood flow in the human arm during cuff ischemia. The method utilizes the Doppler broadening of light that arises in a multiply scattering dynamic media, and is also responsive to changes in absorption and scattering coefficients. Our measurements clearly show blood flow changes with cuff pressures, including the hyperemic overshoot after cuff release, that qualitatively agree with the physiological behavior of the cardiovascular system. In this paper, we present our method, results and discuss the clinical relevance of our findings.

  2. Evaluation of a wind-tunnel gust response technique including correlations with analytical and flight test results

    NASA Technical Reports Server (NTRS)

    Redd, L. T.; Hanson, P. W.; Wynne, E. C.

    1979-01-01

    A wind tunnel technique for obtaining gust frequency response functions for use in predicting the response of flexible aircraft to atmospheric turbulence is evaluated. The tunnel test results for a dynamically scaled cable supported aeroelastic model are compared with analytical and flight data. The wind tunnel technique, which employs oscillating vanes in the tunnel throat section to generate a sinusoidally varying flow field around the model, was evaluated by use of a 1/30 scale model of the B-52E airplane. Correlation between the wind tunnel results, flight test results, and analytical predictions for response in the short period and wing first elastic modes of motion are presented.

  3. Might eddies dominate carbon export ?

    NASA Astrophysics Data System (ADS)

    Allen, J.; Rixen, M.; Fielding, S.; Mustard, A.; Brown, L.; Sanders, R.

    2003-04-01

    Yes - from a review of recent data sets we present a scale analysis of the potential for globally integrated carbon export, from the surface ocean, due to the vertical transports of mesoscale eddies. Mesoscale eddies are the oceanic equivalent of atmospheric storms, most are a fundamental result of horizontally unstable density gradients on the surface of a rotating sphere (baroclinic instability) and ~ 90% of the oceans energy exchanges take place at this scale. Recent studies from satellite remote sensing and high resolution models show that mesoscale eddies are a ubiquitous feature of the open ocean in both time and space; they are even present in sub-tropical oligotrophic gyres. Individual atmospheric weather systems generally have little ecological impact on terrestrial or marine biological systems. Grass grows and herbivores munch through many cyclone and anticyclone periods. In the open ocean we have a very different picture. The primary producers and herbivores have shorter time scales; time scales that coincide with those of mesoscale eddies. Plankton can have either good or bad weather lifetimes associated with just a single cyclone or anticyclone period. Furthermore, although the spring bloom may be the single largest source of material for the export of carbon from the upper ocean, it is short lived and may not be dominant everywhere in the annual export budget. The magnitude of vertical motion associated with mesoscale eddies is significant on biological timescales both for phytoplankton growth and the development of zooplankton grazing pressure. Critically this motion does not form a closed vertical circulation; baroclinic instability releases potential energy and thus water masses are exchanged both vertically and horizontally across water mass boundaries. Thus mesoscale eddies have been shown to provide a mechanism for export both in the direct transport of biomass downwards out of the surface mixed layer and the fertilisation of an exhausted

  4. Correlation of breast tissue histology and optical signatures to improve margin assessment techniques

    NASA Astrophysics Data System (ADS)

    Kennedy, Stephanie; Caldwell, Matthew; Bydlon, Torre; Mulvey, Christine; Mueller, Jenna; Wilke, Lee; Barry, William; Ramanujam, Nimmi; Geradts, Joseph

    2016-06-01

    Optical spectroscopy is sensitive to morphological composition and has potential applications in intraoperative margin assessment. Here, we evaluate ex vivo breast tissue and corresponding quantified hematoxylin & eosin images to correlate optical scattering signatures to tissue composition stratified by patient characteristics. Adipose sites (213) were characterized by their cell area and density. All other benign and malignant sites (181) were quantified using a grid method to determine composition. The relationships between mean reduced scattering coefficient (<μs‧>), and % adipose, % collagen, % glands, adipocyte cell area, and adipocyte density were investigated. These relationships were further stratified by age, menopausal status, body mass index (BMI), and breast density. We identified a positive correlation between <μs‧> and % collagen and a negative correlation between <μs‧> and age and BMI. Increased collagen corresponded to increased <μs‧> variability. In postmenopausal women, <μs‧> was similar regardless of fibroglandular content. Contributions from collagen and glands to <μs‧> were independent and equivalent in benign sites; glands showed a stronger positive correlation than collagen to <μs‧> in malignant sites. Our data suggest that scattering could differentiate highly scattering malignant from benign tissues in postmenopausal women. The relationship between scattering and tissue composition will support improved scattering models and technologies to enhance intraoperative optical margin assessment.

  5. Carrier Noise Reduction in Speckle Correlation Interferometry by a Unique Averaging Technique

    SciTech Connect

    Pechersky, M.J.

    1999-01-20

    We present experimental result of carrier speckle noise averaging by a novel approach to generate numerous identical correlation fringes with randomly different speckles. The surface under study is sprayed with a new dry paint or a layer each time for the repetitive experiments to generate randomly different surfaces of the carrier speckle patterns.

  6. A new eddy-covariance method using empirical mode decomposition

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We introduce a new eddy-covariance method that uses a spectral decomposition algorithm called empirical mode decomposition. The technique is able to calculate contributions to near-surface fluxes from different periodic components. Unlike traditional Fourier methods, this method allows for non-ortho...

  7. Biospecimen use correlates with emerging techniques in cancer research: impact on planning future biobanks.

    PubMed

    Cole, Alexandra; Cheah, Stefanie; Dee, Simon; Hughes, Shevaun; Watson, Peter H

    2012-12-01

    The average cohort size for tissue biospecimens used in cancer research studies has increased significantly over the last 20 years. To understand some of the factors behind changes in biospecimen use, we examined cancer research publications to characterize the relationship between specific assay techniques and biospecimen formats and products. We assessed a representative cross section of 378 publications in the journal Cancer Research that used tissue biospecimens, selected from 6 intervals between 1988 and 2010. Publications were categorized by biospecimen utilization, format type (Frozen, Formalin-Fixed Paraffin-Embedded, and Fresh), product type (RNA, DNA, Protein, Cells, and Metabolites), and types of research techniques performed. There was an increase in average biospecimen cohort size (p=0.001); relative use of Formalin-Fixed Paraffin-Embedded biospecimens (24%-68%, p<0.0001); and the proportion of techniques assaying RNA products from biospecimens (Frozen and Fresh formats, p<0.05), from 1988 to 2008. However, these trends have not continued and there has been no further increase from 2008 to 2010. While specific techniques such as 'tissue microarray' analysis appear to have driven some changes in format requirements, there is an overall trend towards techniques requiring RNA products across all formats of biospecimens in basic cancer research. Since pre-analytical variables influence gene expression (RNA levels) more than gene structure (DNA sequence), recognition of these research trends is important for biobanks when deciding priorities for the optimal preservation format and annotation of biospecimens. PMID:24845138

  8. Coolant-side heat-transfer rates for a hydrogen-oxygen rocket and a new technique for data correlation

    NASA Technical Reports Server (NTRS)

    Schacht, R. L.; Quentmeyer, R. J.

    1973-01-01

    An experimental investigation was conducted to determine the coolant-side, heat transfer coefficients for a liquid cooled, hydrogen-oxygen rocket thrust chamber. Heat transfer rates were determined from measurements of local hot gas wall temperature, local coolant temperature, and local coolant pressure. A correlation incorporating an integration technique for the transport properties needed near the pseudocritical temperature of liquid hydrogen gives a satisfactory prediction of hot gas wall temperatures.

  9. Variations of global mesoscale eddy energy observed from Geosat

    NASA Technical Reports Server (NTRS)

    Shum, C. K.; Werner, R. A.; Sandwell, D. T.; Zhang, B. H.; Tapley, B. D.; Nerem, R. S.

    1990-01-01

    Data on oceanic-current variability were extracted from Geosat altimeter observations for 44 17-day repeat cycles, using the Sandwell and Zhang (1989) technique to process the altimeter data and to produce a sea-surface-slope profile having an estimated accuracy of 0.2 microrad. These were used to generate a series of global eddy kinetic energy maps, each averaged over 3 months, together with their mean. It was found that the maximum mean eddy kinetic energy per unit mass exceeds 2000 sq cm/sq sec for most of the western boundary currents; for the Antarctic Circumpolar Current, however, this value reaches only 500 sq cm/sq sec.

  10. Correlation between macroscopic porosity location and liquid metal pressure in centrifugal casting technique.

    PubMed

    Vaidyanathan, T K; Schulman, A; Nielsen, J P; Shalita, S

    1981-01-01

    Radiographic analysis of uniform cylindrical castings fabricated by the centrifugal casting technique has revealed that the macroscopic porosity is dependent on the location of the sprue attachment to the casting. This is attributed to the significant pressure gradient associated with the centrifugal casting technique. The pressure gradient results in different heat transfer rates at portions of the castings near and away from the free surface of the button. Consequently, the macroscopic porosity is invariably at portions of the casting close to the free surface of the button. In addition, some optimized sprue-reservoir combinations could be predicted and proved, based on this pressure gradient concept. PMID:7002971

  11. Acoustic source location in a jet-blown flap using a cross-correlation technique

    NASA Technical Reports Server (NTRS)

    Becker, R. S.; Maus, J. R.

    1977-01-01

    The acoustic source strength distribution in a turbulent flow field was measured for two far field microphones at 45 deg above and below the plane of the flap surface. A processed signal from an inclined hot-film anemometry probe was cross correlated with the signal from the appropriate far field microphone. The contribution made by the sources associated with the fluctuating pressure on the flap surface to the sound received at far field microphone was estimated by cross correlating the processed signals of microphones which were embedded in the flap surface with the far field microphone signals. In addition, detailed fluid dynamic measurements were made in the flow field of the jet flap using dual sensor hot-film anemometry probes.

  12. Composite pseudocolor images: a technique to enhance the visual correlation between ventilation-perfusion lung images

    NASA Astrophysics Data System (ADS)

    Vaz de Carvalho, Carlos; Costa, Antonio A.; Seixas, M.; Ferreira, F. N.; Guedes, M. A.; Amaral, I.

    1993-07-01

    Lung ventilation and perfusion raw nuclear medicine images obtained from a gamma camera can be difficult to analyze on a per si basis. A method to optimize the visual correlation between these images was established through the use of new combination images: Composite Pseudo-Color (CPC) images. The major topic of this study is the assessment of the usefulness of this method in the detection of lung malfunction.

  13. Eddy Current Testing for Detecting Small Defects in Thin Films

    SciTech Connect

    Obeid, Simon; Tranjan, Farid M.; Dogaru, Teodor

    2007-03-21

    Presented here is a technique of using Eddy Current based Giant Magneto-Resistance sensor (GMR) to detect surface and sub-layered minute defects in thin films. For surface crack detection, a measurement was performed on a copper metallization of 5-10 microns thick. It was done by scanning the GMR sensor on the surface of the wafer that had two scratches of 0.2 mm, and 2.5 mm in length respectively. In another experiment, metal coatings were deposited over the layers containing five defects with known lengths such that the defects were invisible from the surface. The limit of detection (resolution), in terms of defect size, of the GMR high-resolution Eddy Current probe was studied using this sample. Applications of Eddy Current testing include detecting defects in thin film metallic layers, and quality control of metallization layers on silicon wafers for integrated circuits manufacturing.

  14. Tomographic correlation of the Magerl technique for C1-C2 arthrodesis in rheumatoid arthritis

    PubMed Central

    Marchese, Luiz Roberto Delboni; Bonadio, Marcelo Batista; Letaif, Olavo Biraghi; Cristante, Alexandre Fogaça; Oliveira, Reginaldo Perilo; de Barros, Tarcísio Eloy Pessoa

    2013-01-01

    OBJECTIVE: To use the tomographic analysis of C1 and C2 vertebrae to assess the possibility of using Magerl's technique in patients with rheumatoid arthritis. Other objectives were to obtain anatomical data for the choice of the surgical technique in general, to establish safety parameters and obtain epidemiological data of the population in question. METHODS: We retrospectively reviewed the CT scans of 20 patients with rheumatoid arthritis of the Outpatient Spine Group, IOT-HCFMUSP. Data were analyzed statistically to obtain the mean values and the variance of each measurement: the length of the C2 pedicle to the C1 lateral mass, the thickness of the pedicle and the angle of attack of the screw in the isthmus of C2 to the horizontal. RESULTS: The mean values were, respectively: right 23.08 mm and left 23.16 mm, right 6.46 mm and left 6.50 mm, right 44.50o and left 44.95o. Discussion: The leading screw's manufacturers have implants compatible with the anatomical measurements found in this work. Considering the wide diffusion and mastery of Magerl's technique in our country and around the world, this is a safe surgical option that provides mechanical stability. CONCLUSION: Magerl's technique, according to tomographic analysis, can be used in patients with rheumatoid arthritis. Levels of Evidence IV,Case Series. PMID:24453667

  15. The thyroid: review of imaging features and biopsy techniques with radiologic-pathologic correlation.

    PubMed

    Nachiappan, Arun C; Metwalli, Zeyad A; Hailey, Brian S; Patel, Rishi A; Ostrowski, Mary L; Wynne, David M

    2014-01-01

    Knowledge of the normal and abnormal imaging appearances of the thyroid gland is essential for appropriate identification and diagnosis of thyroid lesions. Thyroid nodules are often detected incidentally at computed tomography, magnetic resonance imaging, and positron emission tomography; however, ultrasonography (US) is the most commonly used imaging modality for characterization of these nodules. US characteristics that increase the likelihood of malignancy in a thyroid nodule include microcalcifications, solid composition, and central vascularity. Nuclear scintigraphy is commonly used for evaluation of physiologic thyroid function and for identification of metabolically active and inactive nodules. When fine-needle aspiration biopsy (FNAB) of a lesion is indicated based on clinical and radiologic features, appropriate US-guided biopsy technique and careful cytologic analysis are crucial for making the diagnosis. FNAB and core biopsy are the two percutaneous techniques used to obtain a specimen, with the latter technique being indicated following nondiagnostic or indeterminate FNAB. Specimen adequacy and diagnostic accuracy vary due to several factors, including location of aspiration and biopsy technique used. The radiologist must have a basic knowledge of thyroid disease, be familiar with specimen processing, and recognize the cytologic and radiologic appearances of thyroid lesions, all of which will facilitate the management of these lesions. Online supplemental material is available for this article. PMID:24617678

  16. Improvements in the chronology, geochemistry and correlation techniques of tephra in Antarctic ice

    NASA Astrophysics Data System (ADS)

    Iverson, N. A.; Dunbar, N. W.; McIntosh, W. C.; Pearce, N. J.; Kyle, P. R.

    2013-12-01

    Visible and crypto tephra layers found in West Antarctic ice provide an excellent record of Antarctic volcanism over the past 100ka. Tephra layers are deposited almost instantaneously across wide areas creating horizons that, if found in several locations, provide 'pinning points' to adjust ice time scales that may otherwise be lacking detailed chronology. Individual tephra layers can have distinct chemical fingerprints allowing them to correlate over great distances. Advances in sample preparation, geochemical analyses (major and trace elements) of fine grained tephra and higher precision 40Ar/39Ar dating of young (<100ka) proximal volcanic deposits are improving an already established tephra record in West Antarctica. Forty three of the potential hundreds of silicate layers found in a recently drilled deep West Antarctic Ice Sheet Divide core (WDC06A) have been analyzed for major elements and a subset for trace elements. Of these layers, at least 16 are homogenous tephra that could be correlated to other ice cores (e.g. Siple Dome, SDMA) and/or to source volcanoes found throughout Antarctica and even extra-continental eruptions (e.g. Sub-Antarctic islands and South America). Combining ice core tephra with those exposed in blue ice areas provide more locations to correlate widespread eruptions. For example, a period of heightened eruptive activity at Mt. Berlin, West Antarctica between 24 and 28ka produced a set of tephra layers that are found in WDC06A and SDMA ice cores, as well as at a nearby blue ice area at Mt. Moulton (BIT-151 and BIT-152). Possible correlative tephra layers are found at ice ages of 26.4, 26.9 and 28.8ka in WDC06A and 26.5, 27.0, and 28.7ka in SDMA cores. The geochemical similarities of major elements in these layers mean that ongoing trace element analyses will be vital to decipher the sequence of events during this phase of activity at Mt. Berlin. Sample WDC06A-2767.117 (ice age of 28.6×1.0ka) appears to correlate to blue ice tephra BIT

  17. Eddy diffusion at Saturn's homopause

    NASA Technical Reports Server (NTRS)

    Sandel, B. R.; Mcconnell, J. C.; Strobel, D. F.

    1982-01-01

    Measurements of Saturn's He 584 A dayglow and the CH4 density profile deduced from stellar occultation data near the homopause have been combined to infer an eddy diffusion coefficient of 8 + or - 4 x 10 to the 7th sq cm/s and a temperature of 125 + 40 or - 25 K near the homopause at Voyager 2 encounter. It appears that the eddy diffusion coefficient may have increased between the Voyager encounters. Saturn's H Ly-alpha dayglow is qualitatively compatible with this increase and the interpretation of the He 584 A dayglow and CH4 absorption measurement.

  18. Experimental correlations for transient soot measurement in diesel exhaust aerosol with light extinction, electrical mobility and diffusion charger sensor techniques

    NASA Astrophysics Data System (ADS)

    Bermúdez, Vicente; Pastor, José V.; López, J. Javier; Campos, Daniel

    2014-06-01

    A study of soot measurement deviation using a diffusion charger sensor with three dilution ratios was conducted in order to obtain an optimum setting that can be used to obtain accurate measurements in terms of soot mass emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement settings in steady-state operating conditions; evaluation of the proposed setting under the New European Driving Cycle; and a study of correlations for different measurement techniques. These correlations provide a reliable tool for estimating soot emission from light extinction measurement or from accumulation particle mode concentration. There are several methods and correlations to estimate soot concentration in the literature but most of them were assessed for steady-state operating points. In this case, the correlations are obtained by more than 4000 points measured in transient conditions. The results of the new two correlations, with less than 4% deviation from the reference measurement, are presented in this paper.

  19. Role of eddy pumping in enhancing primary production in the ocean

    NASA Technical Reports Server (NTRS)

    Falkowski, Paul G.; Kolber, Zbigniew; Ziemann, David; Bienfang, Paul K.

    1991-01-01

    Eddy pumping is considered to explain the disparity between geochemical estimates and biological measurements of exported production. Episodic nutrient injections from the ocean into the photic zone can be generated by eddy pumping, which biological measurements cannot sample accurately. The enhancement of production is studied with respect to a cyclonic eddy in the subtropical Pacific. A pump-and-probe fluorimeter generates continuous vertical profiles of primary productivity from which the contributions of photochemical and nonphotochemical processes to fluorescence are derived. A significant correlation is observed between the fluorescence measurements and radiocarbon measurements. The results indicate that eddy pumping has an important effect on phytoplankton production and that this production is near the maximum relative specific growth rates. Based on the production enhancement observed in this case, eddy pumping increases total primary production by only 20 percent and does not account for all enhancement.

  20. Eddy current array probe for corrosion mapping on ageing aircraft

    NASA Astrophysics Data System (ADS)

    Leclerc, Rémi; Samson, Rock

    2000-05-01

    The life of an airplane in the civil and military fleet is expanding by many years. The corrosion on aircraft is becoming a serious problem. The corrosion can also lead to the development of "multi-site damage" (MSD) and catastrophic failure. The need for a fast and reliable nondestructive technique for the detection of corrosion is a prime concern. A simple eddy current or ultrasonic probe can be very time consuming in the inspection because of the small area covered by the probe. The use of an eddy current array probe can cut the time use for an inspection or increase the surface scanned. Because it is an eddy current technology, the surface preparation is minimal compared to other techniques like ultrasound. It is also possible to detect defects beyond the first layer in a multiple layer panel. A flexible probe was employed to demonstrate the capacities of an eddy current array probe. This flexible probe can also match the profile of the structure to inspect limiting the lift-off. The C-scan technique is used in the display to see all the data on the same screen. The interpretation is also simplified.

  1. Tomographic correlation for Magerl's technique in C1-C2 arthrodesis in children

    PubMed Central

    Chiaramonti, Bárbara Camargo; Kim, So Yeon; Marchese, Luiz Roberto Delboni; Letaif, Olavo Biraghi; Marcon, Raphael Martus; Cristante, Alexandre Fogaça

    2013-01-01

    OBJECTIVE: To analyze through tomographic studies, the morphology and dimensions of the C1-C2 vertebrae in pediatric patients, to evaluate the possibility of application of Magerl's technique in these patients, and to contribute with data for the usage of the technique in safety. METHOD: Forty normal cervical tomographies, from patients at an age range of 24-120 months of age and from both genders, were retrospectively analyzed. Data was statistically analyzed to obtain mean value and variations of each measurement: length from the C2's pedicle to C1's lateral mass, thickness of the pedicle of C2, the attack angle of the screw at the C2 isthmus with the horizontal axis and the distance from the odontoid to the anterior arch of C1. RESULTS: The mean values obtained were: length right 30.86 mm, left 31.47 mm; thickness right 5.28 mm, left 5.26 mm; attack angle right 46.250 , left 44.500 ; distance from odontoid to anterior arch of C1 2,17 mm. CONCLUSION: The Magerl technique, after tomographic study, seems to be a viable option to be used in pediatric patients. Level of Evidence IV, Case Series. PMID:24453677

  2. Eddy current distributions in cylindrical samples: effect on equivalent sample resistance.

    PubMed

    Harpen, M D

    1989-09-01

    We present a general technique for the determination of eddy current distributions within an irregularly shaped conducting sample in the uniform field of an NMR RF coil. Also presented is a general expression for the sample-induced coil resistance. The technique is applied specifically to a conducting cylindrical solid. Unlike previous descriptions of cylindrical samples in solenoidal coils where the induction is parallel to the axis of the cylinder and eddy current streamlines are circular, we treat the case where the induction is perpendicular to the cylindrical axis and where consequently eddy current streamlines take on an irregular shape. PMID:2798558

  3. An Automated Parallel Image Registration Technique Based on the Correlation of Wavelet Features

    NASA Technical Reports Server (NTRS)

    LeMoigne, Jacqueline; Campbell, William J.; Cromp, Robert F.; Zukor, Dorothy (Technical Monitor)

    2001-01-01

    With the increasing importance of multiple platform/multiple remote sensing missions, fast and automatic integration of digital data from disparate sources has become critical to the success of these endeavors. Our work utilizes maxima of wavelet coefficients to form the basic features of a correlation-based automatic registration algorithm. Our wavelet-based registration algorithm is tested successfully with data from the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) and the Landsat/Thematic Mapper(TM), which differ by translation and/or rotation. By the choice of high-frequency wavelet features, this method is similar to an edge-based correlation method, but by exploiting the multi-resolution nature of a wavelet decomposition, our method achieves higher computational speeds for comparable accuracies. This algorithm has been implemented on a Single Instruction Multiple Data (SIMD) massively parallel computer, the MasPar MP-2, as well as on the CrayT3D, the Cray T3E and a Beowulf cluster of Pentium workstations.

  4. Validation of the shear punch-tensile correlation technique using irradiated materials

    SciTech Connect

    Hankin, G.L.; Faulkner, R.G.; Toloczko, M.B.; Hamilton, M.L.

    1998-03-01

    It was recently demonstrated that tensile data could be successfully related to shear punch data obtained on transmission electron microscopy (TEM) discs for a variety of irradiated alloys exhibiting yield strengths that ranged from 100 to 800 MPa. This implies that the shear punch test might be a viable alternative for obtaining tensile properties using a TEM disk, which is much smaller than even the smallest miniature tensile specimens, especially when irradiated specimens are not available or when they are too radioactive to handle easily. The majority of the earlier tensile-shear punch correlation work was done using a wide variety of unirradiated materials. The current work extends this correlation effort to irradiated materials and demonstrates that the same relationships that related shear punch tests remain valid for irradiated materials. Shear punch tests were performed on two sets of specimens. In the first group, three simple alloys from the {sup 59}Ni isotopic doping series in the solution annealed and cold worked conditions were irradiated at temperatures ranging from 365 to 495 C in the Fast Flux Test Facility. The corresponding tensile data already existed for tensile specimens fabricated from the same raw materials and irradiated side-by-side with the disks. In the second group, three variants of 316 stainless steel were irradiated in FFTF at 5 temperatures between 400 and 730 C to doses ranging from 12.5 to 88 dpa. The specimens were in the form of both TEM and miniature tensile specimens and were irradiated side-by-side.

  5. Spatial patterns of historical temperature variability: Global correlations using spectral and wavelet techniques

    SciTech Connect

    Park, J.

    1995-12-31

    In order to assess man`s impact on global climate, we need to understand natural climate variability more fully. Using 100 years of global temperature data, we have developed time-series methods that identify coherent spatio-temporal {open_quotes}modes{close_quotes} of temperature variability e.g., El Nino-Southern Oscillation (ENSO) cycles. Methods based on multiple-taper spectral analysis estimate the correlated temperature variability within narrow frequency bands. Methods based on a multiple wavelet analysis identify short-term global temperature {open_quotes}events{close_quotes} on a range of time scales. We assess the statistical significance of narrow-band and event correlations from Monte Carlo confidence limits, which are derived from stochastic variations of uncorrelated white-noise time series. Significant patterns of variability with 2.8 to 5.7 year duration exhibit the characteristic ENSO pattern: warming in the tropics, followed by temperature excursions in middle latitudes. An interdecadal mode (15-18 years) appears to represent long-term ENSO variability, an interpretation supported by the persistence of warm Pacific Ocean surface water in the decade after the large 1982-3 El Nino episode. The interdecadal mode appears to explain much of the anomalous global warmth of the 1980s. North Atlantic variability dominates quasi-biennial (2.2 years) and decadal (7-12 years) modes.

  6. Expert system for analyzing eddy current measurements

    DOEpatents

    Levy, Arthur J.; Oppenlander, Jane E.; Brudnoy, David M.; Englund, James M.; Loomis, Kent C.

    1994-01-01

    A method and apparatus (called DODGER) analyzes eddy current data for heat exchanger tubes or any other metallic object. DODGER uses an expert system to analyze eddy current data by reasoning with uncertainty and pattern recognition. The expert system permits DODGER to analyze eddy current data intelligently, and obviate operator uncertainty by analyzing the data in a uniform and consistent manner.

  7. Expert system for analyzing eddy current measurements

    SciTech Connect

    Levy, A.J.; Oppenlander, J.E.; Brudnoy, D.M.; Englund, J.M.; Loomis, K.C.

    1994-08-16

    A method and apparatus (called DODGER) analyzes eddy current data for heat exchanger tubes or any other metallic object. DODGER uses an expert system to analyze eddy current data by reasoning with uncertainty and pattern recognition. The expert system permits DODGER to analyze eddy current data intelligently, and obviate operator uncertainty by analyzing the data in a uniform and consistent manner. 21 figs.

  8. In situ characterization of organic matter in two primitive chondrites through correlated microanalytical techniques

    NASA Astrophysics Data System (ADS)

    Wende, A. M.; Nittler, L.; Steele, A.; Herd, C. D.

    2009-12-01

    Primitive meteorites contain up to 2 wt % C, much of it in the form of insoluble organic matter (IOM). Bulk analyses have revealed the IOM to be marked by large D and 15N enrichments relative to terrestrial values. Isotopic imaging studies have revealed the presence of `hotspots’, sub-μm to μm-sized regions of IOM exhibiting extreme isotope enrichments. An interesting subpopulation of organic grains, ’nanoglobules’, which have hollow, spherical morphologies, is known to account for a portion of these hot spots. Previous work has suggested that nanoglobules can be identified in situ by native UV fluorescence. The isotopic enrichments are believed to point to low-T chemical fractionations either in the interstellar medium (ISM) or the outer regions of the early Solar System. As part of a larger study investigating the origin and evolution of IOM in the Solar System, a correlated, in situ, microanalytical approach was employed to characterize local isotopic and morphological heterogeneities in IOM in the highly primitive chondrites QUE 99177 (CR3) and Tagish Lake (C-ung). Previous NanoSIMS ion imaging of a QUE 99177 section revealed the spatial and isotopic distribution of C in the matrix with a spatial resolution of 200 nm. Manual definition of >3300 C-rich regions in the NanoSIMS images indicates that grains smaller than 1 μm across, which account for 80% of the IOM area, have a size distribution that is similar to estimates of the size distribution of carbonaceous dust in the diffuse ISM, supporting an interstellar origin for the IOM. Micro-Raman spectroscopy, which is highly sensitive to the degree of disorder in carbonaceous materials, was attempted on the same regions analyzed by NanoSIMS in QUE 99177. Unfortunately, surface damage due to both the prior SIMS analyses and removal of a prior C coat precluded acquisition of useful Raman spectra. Consequently, future correlated work will entail performing Raman analyses on uncoated samples prior to SIMS

  9. Full-field speckle correlation technique as applied to blood flow monitoring

    NASA Astrophysics Data System (ADS)

    Vilensky, M. A.; Agafonov, D. N.; Timoshina, P. A.; Shipovskaya, O. V.; Zimnyakov, D. A.; Tuchin, V. V.; Novikov, P. A.

    2011-03-01

    The results of experimental study of monitoring the microcirculation in tissue superficial layers of the internal organs at gastro-duodenal hemorrhage with the use of laser speckles contrast analysis technique are presented. The microcirculation monitoring was provided in the course of the laparotomy of rat abdominal cavity in the real time. Microscopic hemodynamics was analyzed for small intestine and stomach under different conditions (normal state, provoked ischemia, administration of vasodilative agents such as papaverine, lidocaine). The prospects and problems of internal monitoring of micro-vascular flow in clinical conditions are discussed.

  10. Applications of digital image processing techniques to problems of data registration and correlation

    NASA Technical Reports Server (NTRS)

    Green, W. B.

    1978-01-01

    An overview is presented of the evolution of the computer configuration at JPL's Image Processing Laboratory (IPL). The development of techniques for the geometric transformation of digital imagery is discussed and consideration is given to automated and semiautomated image registration, and the registration of imaging and nonimaging data. The increasing complexity of image processing tasks at IPL is illustrated with examples of various applications from the planetary program and earth resources activities. It is noted that the registration of existing geocoded data bases with Landsat imagery will continue to be important if the Landsat data is to be of genuine use to the user community.

  11. Heat Transport and Long-Term Change in the Southern Ocean: Assessing the Role of Eddies

    NASA Astrophysics Data System (ADS)

    Gwiazda, R.; Paull, C. K.; Dallimore, S.; Melling, H.; Jin, Y. K.

    2014-12-01

    Long-term change in the Southern Ocean can be difficult to evaluate because of both the paucity of historic observations and the magnitude of eddy variability. The low stratification of the Southern Ocean means that eddies detected by altimetry at the ocean surface extend through the top 2 km of the ocean. Sea surface height anomalies are more strongly correlated with sub-surface variability at depths between about 600 and 1400 dbars than they are with variability in the upper 200 dbars. Altimetric variability can thus be used to remove eddy-related anomalies from individual Argo profiles, resulting in a smoother estimate of mean temperature and salinity. This "eddy-free" mean field serves as a benchmark against which to assess decadal-scale changes in the Southern Ocean, and we use historic hydrographic data to evaluate temperature and salinity changes through the second half of the 20th century. We also evaluate the behavior of Southern Ocean eddies themselves: Although in most parts of the ocean closed oceanic eddies appear to result in thermally indirect heat transport, eddies that are carried eastward by the ACC tend to propagate in the opposite direction, resulting in thermally direct, poleward heat transport across the ACC. Evidence suggests that this cell is maintained by the effective eastward propagation of eddies relative to the mean flow at deep levels.

  12. Seismic observations from a Yakutat eddy in the northern Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Tang, Q. S.; Gulick, S. P. S.; Sun, L. T.

    2014-06-01

    Recent works show that the seismic oceanography technique allows us to relate water column seismic reflections to oceanic finescale structures. In this study, finescale structures of a surface anticyclonic eddy have been unveiled by reprocessing two seismic transects acquired in the northern Gulf of Alaska using an 8 km hydrophone streamer and 6600 cu in linear airgun array in September 2008. The eddy was a typical bowl-like structure with around 55 km width and 700 m depth. It has two fringes around the eddy base and a spiral arm at the NE edge. The in situ sea surface temperature and salinity data from a shipboard thermosalinograph help to confirm our interpretations of a spiral arm shed from the warm eddy and the entrained cold water from elsewhere. Nearby the eddy and offshore the shelf-break, there is a strong frontal feature, probably the Alaska Current. The eddy likely formed offshore Yakutat shelf and transported along the offshore shelf-break by tracking the sea level anomalies. Its equivalent diameter of 65 km was measured using the along-track altimeter and the seismic constraints. It was comparable with results from the representative conventional algorithms of eddy detection. Geostrophic velocities of the eddy were estimated from the dipping seismic reflections under the assumptions of approximate isopycnals and geostrophic balance. Measured water properties including sea surface temperature, salinity, and chlorophyll revealed that eddy translation transports coastal water to the pelagic regions. Structures synthesized from CTD profiles that sampled an earlier eddy suggest that thin striae around the base might be a common feature in Gulf of Alaska eddies.

  13. Studies of continuum states in 16 Ne using three-body correlation techniques

    NASA Astrophysics Data System (ADS)

    Marganiec, J.; Wamers, F.; Aksouh, F.; Aksyutina, Yu.; Álvarez-Pol, H.; Aumann, T.; Beceiro-Novo, S.; Boretzky, K.; Borge, M. J. G.; Chartier, M.; Chatillon, A.; Chulkov, L. V.; Cortina-Gil, D.; Emling, H.; Ershova, O.; Fraile, L. M.; Fynbo, H. O. U.; Galaviz, D.; Geissel, H.; Heil, M.; Hoffmann, D. H. H.; Hoffmann, J.; Johansson, H. T.; Jonson, B.; Karagiannis, C.; Kiselev, O. A.; Kratz, J. V.; Kulessa, R.; Kurz, N.; Langer, C.; Lantz, M.; Le Bleis, T.; Lemmon, R.; Litvinov, Yu. A.; Mahata, K.; Müntz, C.; Nilsson, T.; Nociforo, C.; Nyman, G.; Ott, W.; Panin, V.; Paschalis, S.; Perea, A.; Plag, R.; Reifarth, R.; Richter, A.; Rodriguez-Tajes, C.; Rossi, D.; Riisager, K.; Savran, D.; Schrieder, G.; Simon, H.; Stroth, J.; Sümmerer, K.; Tengblad, O.; Weick, H.; Wiescher, M.; Wimmer, C.; Zhukov, M. V.

    2015-01-01

    Two-proton decay of the unbound nucleus 16Ne , produced in one-neutron knockout from a 500 MeV/u 17Ne beam, has been studied at GSI. The ground state, at a resonance energy 1.388(15) MeV, ( MeV) above the 14O +p+p threshold, and two narrow resonances at MeV and 7.57(6) MeV have been investigated. A comparison of the energy difference between the first excited 2+ state and the 0+ ground state in 16Ne with its mirror nucleus 16C reveals a small Thomas-Ehrman shift (TES) of keV. A trend of the TES for the T = 2 quintet is obtained by completing the known data with a prediction for 16F obtained from an IMME analysis. The decay mechanisms of the observed three resonances were revealed from an analysis of the energy and angular correlations of the 14O +p+p decay products. The ground state decay can be considered as a genuine three-body (democratic) mode and the excited states decay sequentially via states in the intermediate nucleus 15F , the 3.22 MeV state predominantly via the 15F ground-state resonance, while the 7.57 MeV state decays via the 5/2+ resonance in 15F at 2.8 MeV above the 14O +p+p threshold. Further, from an analysis of angular correlations, the spin-parity of the 7.57 MeV state has been determined as and assigned as the third 2+ state in 16Ne based on a comparison with 16C.

  14. From Phenomena to Objects: Segmentation of Fuzzy Objects and its Application to Oceanic Eddies

    NASA Astrophysics Data System (ADS)

    Wu, Qingling

    A challenging image analysis problem that has received limited attention to date is the isolation of fuzzy objects---i.e. those with inherently indeterminate boundaries---from continuous field data. This dissertation seeks to bridge the gap between, on the one hand, the recognized need for Object-Based Image Analysis of fuzzy remotely sensed features, and on the other, the optimization of existing image segmentation techniques for the extraction of more discretely bounded features. Using mesoscale oceanic eddies as a case study of a fuzzy object class evident in Sea Surface Height Anomaly (SSHA) imagery, the dissertation demonstrates firstly, that the widely used region-growing and watershed segmentation techniques can be optimized and made comparable in the absence of ground truth data using the principle of parsimony. However, they both have significant shortcomings, with the region growing procedure creating contour polygons that do not follow the shape of eddies while the watershed technique frequently subdivides eddies or groups together separate eddy objects. Secondly, it was determined that these problems can be remedied by using a novel Non-Euclidian Voronoi (NEV) tessellation technique. NEV is effective in isolating the extrema associated with eddies in SSHA data while using a non-Euclidian cost-distance based procedure (based on cumulative gradients in ocean height) to define the boundaries between fuzzy objects. Using this procedure as the first stage in isolating candidate eddy objects, a novel "region-shrinking" multicriteria eddy identification algorithm was developed that includes consideration of shape and vorticity. Eddies identified by this region-shrinking technique compare favorably with those identified by existing techniques, while simplifying and improving existing automated eddy detection algorithms. However, it also tends to find a larger number of eddies as a result of its ability to separate what other techniques identify as connected

  15. Eddy current thickness measurement apparatus

    DOEpatents

    Rosen, Gary J.; Sinclair, Frank; Soskov, Alexander; Buff, James S.

    2015-06-16

    A sheet of a material is disposed in a melt of the material. The sheet is formed using a cooling plate in one instance. An exciting coil and sensing coil are positioned downstream of the cooling plate. The exciting coil and sensing coil use eddy currents to determine a thickness of the solid sheet on top of the melt.

  16. Eddy-Current Inspection of Narrow Metal Tubes

    NASA Technical Reports Server (NTRS)

    Ambrose, H. H.; Kleint, R. E.; Kirkham, K. E.

    1984-01-01

    Inspection technique for narrow-bore metal tubing involves use of small internal eddy-current probe. Probe consists of thin copper wire wrapped on bobbin. Probe small enough to pass through bends in tube being measured. Technique useful for strain measurements where operating conditions or inaccessibility prevent use of such conventional methods as X-ray diffraction, electrical-resistance measurements, strain gages, or holography.

  17. Community differentiation and population enrichment of Sargasso Sea bacterioplankton in the euphotic zone of a mesoscale mode-water eddy.

    PubMed

    Nelson, Craig E; Carlson, Craig A; Ewart, Courtney S; Halewood, Elisa R

    2014-03-01

    Eddies are mesoscale oceanographic features (∼ 200 km diameter) that can cause transient blooms of phytoplankton by shifting density isoclines in relation to light and nutrient resources. To better understand how bacterioplankton respond to eddies, we examined depth-resolved distributions of bacterial populations across an anticyclonic mode-water eddy in the Sargasso Sea. Previous work on this eddy has documented elevated phytoplankton productivity and diatom abundance within the eddy centre with coincident bacterial productivity and biomass maxima. We illustrate bacterial community shifts within the eddy centre, differentiating populations uplifted along isopycnals from those enriched or depleted at horizons of enhanced bacterial and primary productivity. Phylotypes belonging to the Roseobacter, OCS116 and marine Actinobacteria clades were enriched in the eddy core and were highly correlated with pigment-based indicators of diatom abundance, supporting developing hypotheses that members of these clades associate with phytoplankton blooms. Typical mesopelagic clades (SAR202, SAR324, SAR406 and SAR11 IIb) were uplifted within the eddy centre, increasing bacterial diversity in the lower euphotic zone. Typical surface oligotrophic clades (SAR116, OM75, Prochlorococcus and SAR11 Ia) were relatively depleted in the eddy centre. The biogeochemical context of a bloom-inducing eddy provides insight into the ecology of the diverse uncultured bacterioplankton dominating the oligotrophic oceans. PMID:24589288

  18. Swept frequency eddy current (SFEC) measurements of Inconel 718 as a function of microstructure and residual stress

    NASA Astrophysics Data System (ADS)

    Chandrasekar, Ramya

    The goal of this thesis was to determine the dependency of swept frequency eddy current (SFEC) measurements on the microstructure of the Ni-based alloy, Inconel 718 as a function of heat treatment and shot peening. This involved extensive characterization of the sample using SEM and TEM coupled with measurements and analysis of the eddy current response of the various sample conditions using SFEC data. Specific objectives included determining the eddy current response at varying depths within the sample, and this was accomplished by taking SFEC measurements in frequencies ranging from 100 kHz to 50 MHz. Conductivity profile fitting of the resulting SFEC signals was obtained by considering influencing factors (such as surface damage). The problems associated with surface roughness and near surface damage produced by shot peening were overcome by using an inversion model. Differences in signal were seen as a result of precipitation produced by heat treatment and by residual stresses induced due to the shot peening. Hardness of the material, which is related both to precipitation and shot peening, was seen to correlate with the measured SFEC signal. Surface stress measurement was carried out using XRD giving stress in the near surface regions, but not included in the calculations due to shallow depth information provided by the technique compared to SFEC. By comparing theoretical SFEC signal computed using the microstructural values (precipitate fraction) and experimental SFEC data, dependency of the SFEC signals on microstructure and residual stress was obtained.

  19. Effects of correlated noise on the full-spectrum combining and complex-symbol combining arraying techniques

    NASA Technical Reports Server (NTRS)

    Vazirani, P.

    1995-01-01

    The process of combining telemetry signals received at multiple antennas, commonly referred to as arraying, can be used to improve communication link performance in the Deep Space Network (DSN). By coherently adding telemetry from multiple receiving sites, arraying produces an enhancement in signal-to-noise ratio (SNR) over that achievable with any single antenna in the array. A number of different techniques for arraying have been proposed and their performances analyzed in past literature. These analyses have compared different arraying schemes under the assumption that the signals contain additive white Gaussian noise (AWGN) and that the noise observed at distinct antennas is independent. In situations where an unwanted background body is visible to multiple antennas in the array, however, the assumption of independent noises is no longer applicable. A planet with significant radiation emissions in the frequency band of interest can be one such source of correlated noise. For example, during much of Galileo's tour of Jupiter, the planet will contribute significantly to the total system noise at various ground stations. This article analyzes the effects of correlated noise on two arraying schemes currently being considered for DSN applications: full-spectrum combining (FSC) and complex-symbol combining (CSC). A framework is presented for characterizing the correlated noise based on physical parameters, and the impact of the noise correlation on the array performance is assessed for each scheme.

  20. Acoustic source location in the secondary mixing region of a jet-blown flap using a cross-correlation technique

    NASA Technical Reports Server (NTRS)

    Becker, R. S.; Maus, J. R.

    1977-01-01

    An experimental investigation of the acoustic sources in the secondary mixing region of a laboratory-scale jet-flap was made using a causality correlation technique. The processed signal of a hot-film anemometer probe was cross correlated with the output signal of a far-field microphone. Axial acoustic source strength distributions were measured for three far-field microphone locations: plus or minus 45 deg in the flyover plane and 45 deg in the sideline plane. These measurements showed that the acoustic sources in the secondary mixing region are highly directional, radiating much more effectively to the -45 deg-microphone, located below the plane of the flap surface. A relative maximum in the acoustic source strength measured for the microphones in the flyover plane occurred very near the flap trailing edge, which may be due to an edge amplification effect predicted by the theoretical work of Ffowcs Williams and Hall.

  1. Tissue deformation analysis using a laser based digital image correlation technique.

    PubMed

    Kerl, Johannes; Parittotokkaporn, Tassanai; Frasson, Luca; Oldfield, Matthew; y Baena, Ferdinando Rodriguez; Beyrau, Frank

    2012-02-01

    A laser based technique for planar time-resolved measurements of tissue deformation in transparent biomedical materials with high spatial resolution is developed. The approach is based on monitoring the displacement of micrometer particles previously embedded into a semi-transparent sample as it is deformed by some form of external loading. The particles are illuminated in a plane inside the tissue material by a thin laser light sheet, and the pattern is continuously recorded by a digital camera. Image analysis yields the locally and temporally resolved sample deformation in the measurement plane without the need for any in situ measurement hardware. The applicability of the method for determination of tissue deformation and material strain during the insertion of a needle probe into a soft material sample is demonstrated by means of an in vitro trial on gelatin. PMID:22301185

  2. Correlative Microscopy Techniques for the Analysis of Particles in Safeguards Environmental Samples

    NASA Astrophysics Data System (ADS)

    Dzigal, N.; Chinea-Cano, E.

    2015-10-01

    This paper presents a novel approach to environmental particle analysis for safeguards by means of a combination of micro-analytical techniques. It includes the tandem utilization of two separate light microscopes, a scanning electron microscope and a femtosecond laser-ablation ICP-MS. These are: a light microscopy automated particle relocation device (Zeiss Z2m); an optical-microscopy-based laser micro-dissection system (IX83 MMI+Olympus); a focussed ion beam scanning electron microscope equipped with a time-of-flight mass spectrometer extension (Tescan Lyra3) and a fs LA-ICP-MS (J200 from Applied Spectra Inc. and Thermofisher Scientific iCap Q). The samples examined in this contribution are analysed for their nuclear material signatures, in particular the presence of uranium isotopes.

  3. Use of double correlation techniques for the improvement of rotation speed measurement based on electrostatic sensors

    NASA Astrophysics Data System (ADS)

    Li, Lin; Wang, Xiaoxin; Hu, Hongli; Liu, Xiao

    2016-02-01

    Electrostatic sensing technology using correlation signal processing offers an approach to the measurement of rotational speed in the automatic control system of large generators and centrifugal machines. In this article, a double autocorrelation method was proposed to improve the accuracy and robustness of the measurement on the designed test rig. An electrostatic sensor was used to obtain signals from the rotor surface. Then, the rotational speed was determined from the period of rotational motion calculated from a double autocorrelation method. At the same time, experiments with sampling rates of 2ksps (kilo samples per second), 5ksps, 10ksps, 20ksps were carried out on a laboratory-scale test rig under a rotational speed range from 400 r min-1 to 4200 r min-1. The results show that the double autocorrelation method improves the accuracy and robustness. The measurement accuracy also improves with the sampling rate-the relative errors using 2ksps, 5ksps, 10ksps, and 20ksps are within 1.5%, 1%, 0.4%, and 0.3% respectively. The linearity of them is 1.47%, 0.61%, 0.28%, 0.17% correspondingly. The experiments also reveal that the measurement error has a tendency to increase with the rotational speed.

  4. Comparison of infrared and 3D digital image correlation techniques applied for mechanical testing of materials

    NASA Astrophysics Data System (ADS)

    Krstulović-Opara, Lovre; Surjak, Martin; Vesenjak, Matej; Tonković, Zdenko; Kodvanj, Janoš; Domazet, Željko

    2015-11-01

    To investigate the applicability of infrared thermography as a tool for acquiring dynamic yielding in metals, a comparison of infrared thermography with three dimensional digital image correlation has been made. Dynamical tension tests and three point bending tests of aluminum alloys have been performed to evaluate results obtained by IR thermography in order to detect capabilities and limits for these two methods. Both approaches detect pastification zone migrations during the yielding process. The results of the tension test and three point bending test proved the validity of the IR approach as a method for evaluating the dynamic yielding process when used on complex structures such as cellular porous materials. The stability of the yielding process in the three point bending test, as contrary to the fluctuation of the plastification front in the tension test, is of great importance for the validation of numerical constitutive models. The research proved strong performance, robustness and reliability of the IR approach when used to evaluate yielding during dynamic loading processes, while the 3D DIC method proved to be superior in the low velocity loading regimes. This research based on two basic tests, proved the conclusions and suggestions presented in our previous research on porous materials where middle wave infrared thermography was applied.

  5. Application of Video Image Correlation Techniques to the Space Shuttle External Tank Foam Materials

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Nemeth, Michael P.

    2005-01-01

    Results that illustrate the use of a video-image-correlation-based displacement and strain measurement system to assess the effects of material nonuniformities on the behavior of the sprayed-on foam insulation (SOFI) used for the thermal protection system on the Space Shuttle External Tank are presented. Standard structural verification specimens for the SOFI material with and without cracks and subjected to mechanical or thermal loading conditions were tested. Measured full-field displacements and strains are presented for selected loading conditions to illustrate the behavior of the foam and the viability of the measurement technology. The results indicate that significant strain localization can occur in the foam because of material nonuniformities. In particular, elongated cells in the foam can interact with other geometric or material discontinuities in the foam and develop large-magnitude localized strain concentrations that likely initiate failures. Furthermore, some of the results suggest that continuum mechanics and linear elastic fracture mechanics might not adequately represent the physical behavior of the foam, and failure predictions based on homogeneous linear material models are likely to be inadequate.

  6. Application of Video Image Correlation Techniques to the Space Shuttle External Tank Foam Materials

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Nemeth, Michael P.

    2006-01-01

    Results that illustrate the use of a video-image-correlation-based displacement and strain measurement system to assess the effects of material nonuniformities on the behavior of the sprayed-on foam insulation (SOFI) used for the thermal protection system on the Space Shuttle External Tank are presented. Standard structural verification specimens for the SOFI material with and without cracks and subjected to mechanical or thermal loading conditions were tested. Measured full-field displacements and strains are presented for selected loading conditions to illustrate the behavior of the foam and the viability of the measurement technology. The results indicate that significant strain localization can occur in the foam because of material nonuniformities. In particular, elongated cells in the foam can interact with other geometric or material discontinuities in the foam and develop large-magnitude localized strain concentrations that likely initiate failures. Furthermore, some of the results suggest that continuum mechanics and linear elastic fracture mechanics might not adequately represent the physical behavior of the foam, and failure predictions based on homogeneous linear material models are likely to be inadequate.

  7. Refinement of digital image correlation technique to investigate the fracture behaviour of refractory materials

    NASA Astrophysics Data System (ADS)

    Belrhiti, Y.; Pop, O.; Germaneau, A.; Doumalin, P.; Dupré, J. C.; Huger, M.; Chotard, T.

    2016-03-01

    Refractory materials exhibit a heterogeneous microstructure consisting in coarse aggregates surrounded by fine grains that form an aggregate/matrix composite. This heterogeneous microstructure often leads to a complex mechanical behaviour during loading. This paper is devoted to the study, thanks to an optical method, Digital Image Correlation (DIC), of the fracture behaviour of two industrial refractory materials in relation with their microstructure resulting from both the chosen constituents and the sintering process. The aim is here, specifically, to highlight and to characterize the evolution of kinematic fields (displacement and strain) observed at the surface of sample during a wedge splitting test typically used to quantify the work of fracture. DIC is indeed a helpful and effective tool, in the topic of experimental mechanics, for the measurement of deformation in a planar sample surface. This non-contact optical method directly provides full-field displacements by comparing the digital images of the sample surface obtained before and during loading. In the present study, DIC has been improved to take into account the occurrence of cracks and performed so as to better identify the early stage of the cracking behaviour. The material transformation, usually assumed homogeneous inside each DIC subset, is thus more complex and a discontinuity of displacement should be taken into account. Then each subset which crosses a crack can be cut in two parts with different kinematics. By this way, it is possible to automatically find the fracture paths and follow the crack geometries (length, opening).

  8. A new climatological oceanic eddy census

    NASA Astrophysics Data System (ADS)

    Mason, Evan; Pascual, Ananda; Pujol, Isabel; Faugère, Yannice; Delepoulle, Antoine; Briol, Frederic

    2015-04-01

    We present a new climatological oceanic eddy census dataset based on gridded sea level anomalies from satellite altimeter observations that is due for release by Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO). The identification and automated tracking of oceanic eddies is carried out using the py-eddy-tracker of Mason et al. (2014). Daily outputs of eddy properties (including position, radius, amplitude and nonlinearity) covering the period 1993-2013 over the global domain are presented and discussed. Validation and comparison is made with the published global eddy track database of Chelton et al. (2011).

  9. Synthesis of dynamic phase profile by the correlation technique for spatial control of optical beams in multiplexing and switching

    NASA Astrophysics Data System (ADS)

    Bugaychuk, Svitlana A.; Gnatovskyy, Vladimir O.; Sidorenko, Andrey V.; Pryadko, Igor I.; Negriyko, Anatoliy M.

    2015-11-01

    New approach for the correlation technique, which is based on multiple periodic structures to create a controllable angular spectrum, is proposed and investigated both theoretically and experimentally. The transformation of an initial laser beam occurs due to the actions of consecutive phase periodic structures, which may differ by their parameters. Then, after the Fourier transformation of a complex diffraction field, the output diffraction orders will be changed both by their intensities and by their spatial position. The controllable change of output angular spectrum is carried out by a simple control of the parameters of the periodic structures. We investigate several simple examples of such management.

  10. Time-correlated single photon counting: an advancing technique in a plate reader for assay development and high throughput screening

    NASA Astrophysics Data System (ADS)

    Näther, Dirk U.; Fenske, Roger; Hurteaux, Reynald; Majno, Sandra; Smith, S. Desmond

    2006-10-01

    A new plate reader (Nanotaurus) has been developed by Edinburgh Instruments that has the principle design features of a confocal microscope and utilises the technique of Time Correlated Single Photon Counting for data acquisition. The advantages of Fluorescence Lifetime Measurements in the nanosecond time scale and analysis methods to recover lifetime parameters are discussed based on experimental data. First working assays using changes of lifetime parameters are presented that clearly demonstrate the advantages of the new instrument for biochemical assays and show strong promise for cell-based assays, by utilising the independence of lifetime parameters from sample volume and concentration.

  11. Pulsed eddy current thickness measurements of transuranic waste containers

    SciTech Connect

    O`Brien, T.K.; Kunerth, D.C.

    1995-12-31

    Thickness measurements on fifty five gallon waste drums for drum integrity purposes have been traditionally performed at the INEL using ultrasonic testing methods. Ultrasonic methods provide high resolution repeatable thickness measurements in a timely manner, however, the major drawback of using ultrasonic techniques is coupling to the drum. Areas with severe exterior corrosion, debonded paper labels or any other obstacle in the acoustic path will have to be omitted from the ultrasonic scan. We have developed a pulsed eddy current scanning system that can take thickness measurements on fifty five gallon carbon steel drums with wall thicknesses up to 65 mils. This type of measurement is not susceptible to the problems mentioned above. Eddy current measurements in the past have excluded ferromagnetic materials such as carbon steel because of the difficulty in penetrating the material and in compensating for changes in permeability from material to material. New developments in data acquisition electronics as well as advances in personal computers have made a pulsed eddy current system practical and inexpensive. Certain aspects of the pulsed eddy current technique as well as the operation of such a system and features such as real time pass/fail thresholds for overpacking identification and full scan data archiving for future evaluation will be discussed.

  12. Progress of a Cross-correlation Based Optical Strain Measurement Technique for Detecting Radial Growth on a Rotating Disk

    NASA Technical Reports Server (NTRS)

    Clem, Michelle M.; Woike, Mark; Abdul-Aziz, Ali

    2013-01-01

    The Aeronautical Sciences Project under NASAs Fundamental Aeronautics Program is extremely interested in the development of fault detection technologies, such as optical surface measurements in the internal parts of a flow path, for in situ health monitoring of gas turbine engines. In situ health monitoring has the potential to detect flaws, i.e. cracks in key components, such as engine turbine disks, before the flaws lead to catastrophic failure. In the present study, a cross-correlation imaging technique is investigated in a proof-of-concept study as a possible optical technique to measure the radial growth and strain field on an already cracked sub-scale turbine engine disk under loaded conditions in the NASA Glenn Research Centers High Precision Rotordynamics Laboratory. The optical strain measurement technique under investigation offers potential fault detection using an applied background consisting of a high-contrast random speckle pattern and imaging the background under unloaded and loaded conditions with a CCD camera. Spinning the cracked disk at high speeds induces an external load, resulting in a radial growth of the disk of approximately 50.8-m in the flawed region and hence, a localized strain field. When imaging the cracked disk under static conditions, the disk will appear shifted. The resulting background displacements between the two images will then be measured using the two-dimensional cross-correlation algorithms implemented in standard Particle Image Velocimetry (PIV) software to track the disk growth, which facilitates calculation of the localized strain field. In order to develop and validate this optical strain measurement technique an initial proof-of-concept experiment is carried out in a controlled environment. Using PIV optimization principles and guidelines, three potential backgrounds, for future use on the rotating disk, are developed and investigated in the controlled experiment. A range of known shifts are induced on the

  13. Investigation of a Cross-Correlation Based Optical Strain Measurement Technique for Detecting radial Growth on a Rotating Disk

    NASA Technical Reports Server (NTRS)

    Clem, Michelle M.; Woike, Mark R.

    2013-01-01

    The Aeronautical Sciences Project under NASA`s Fundamental Aeronautics Program is extremely interested in the development of novel measurement technologies, such as optical surface measurements in the internal parts of a flow path, for in situ health monitoring of gas turbine engines. In situ health monitoring has the potential to detect flaws, i.e. cracks in key components, such as engine turbine disks, before the flaws lead to catastrophic failure. In the present study, a cross-correlation imaging technique is investigated in a proof-of-concept study as a possible optical technique to measure the radial growth and strain field on an already cracked sub-scale turbine engine disk under loaded conditions in the NASA Glenn Research Center`s High Precision Rotordynamics Laboratory. The optical strain measurement technique under investigation offers potential fault detection using an applied high-contrast random speckle pattern and imaging the pattern under unloaded and loaded conditions with a CCD camera. Spinning the cracked disk at high speeds induces an external load, resulting in a radial growth of the disk of approximately 50.0-im in the flawed region and hence, a localized strain field. When imaging the cracked disk under static conditions, the disk will be undistorted; however, during rotation the cracked region will grow radially, thus causing the applied particle pattern to be .shifted`. The resulting particle displacements between the two images will then be measured using the two-dimensional cross-correlation algorithms implemented in standard Particle Image Velocimetry (PIV) software to track the disk growth, which facilitates calculation of the localized strain field. In order to develop and validate this optical strain measurement technique an initial proof-of-concept experiment is carried out in a controlled environment. Using PIV optimization principles and guidelines, three potential speckle patterns, for future use on the rotating disk, are developed

  14. Studies of cytochrome c-551 unfolding using fluorescence correlation spectroscopy and other biophysical techniques.

    PubMed

    Sil, Pallabi; Paul, Simanta Sarani; Silvio, Eva Di; Travaglini-Allocatelli, Carlo; Chattopadhyay, Krishnananda

    2016-09-21

    In this paper, we have studied the equilibrium unfolding transitions of cytochrome c from Pseudomonas aeruginosa (cytc551), a small bacterial protein. Similar to eukaryotic cytochrome c, cytc551 folds sequentially, although significant differences exist in the order of folding units (foldons). There are two regions of cytc551 (N-terminal helix with residue number 3 to 10 and the loop 2 region containing residues 34 to 45), in which no foldon unit could be assigned. In addition, the helix containing the Cys-X-X-Cys-His motif, adjacent to the N-terminal helix (residue number 3 to 10), shows unexplained ultra-fast collapse. To obtain further insights, we have studied cytc551 site-directed mutants using fluorescence correlation spectroscopy (FCS) and molecular dynamics simulation. We have found out that cytc551 unfolds through the formation of a fluorescently dark intermediate state and the amplitude of the dark component depends on the position of labeling. We have utilized this position dependence to propose a shape change model during the unfolding of cytc551. The present results show that the N-terminal helix remains in a collapsed position even in the completely unfolded state and this helix may act as a rigid support to guide the folding of its adjacent helix. This rigid support may be responsible for the ultra-fast collapse of the adjacent helix region, which occurs during the initial events of folding. The present results also show that the C-terminal end of loop 2 traverses a large distance during unfolding compared to the N-terminal end, which justifies the observed flexibility of the loop 2 region. PMID:27538920

  15. Small-strain measurement in bridge connections using the digital image correlation (DIC) technique

    NASA Astrophysics Data System (ADS)

    Desai, Niranjan

    2016-04-01

    Structural health monitoring (SHM) is emerging as a vital tool to help civil engineers improve the safety, maintainability, and reliability of critical structures and assists infrastructure owners with timely information for the continued safe and economic operation of their structure. SHM involves implementing a strategy that identifies and characterizes damage or undesirable performance in engineering structures. The goal of this research project was to determine the smallest strains measurable using standard digital image correlation (DIC) based SHM equipment. This practical investigation that had strong ties to the industry was motivated by damage observed in a real-world bridge, which was initially undetected. Its early detection would have led to reduced repair costs. To accomplish the aforementioned goal, tests were performed on a laboratory specimen that replicated a steel beam-to-column connection of the concerned bridge, involving progressively loading it in a manner in which it was loaded in the actual bridge, while simultaneously measuring the strains that developed in it using the aforementioned DIC-based equipment and software. Under the controlled conditions in the laboratory, the minimum resolution of the state-of-the-art system used in this investigation was determined. Due to the challenges faced in making these small-strain measurements even under highly controlled laboratory conditions, it was concluded that it is currently unrealistic to use the existing DIC technology in a real-world situation to measure strains as small as those that would need to be measured to detect the onset of damage in bridge connections. More work needs to be done in this area.

  16. Obituary: John Allen Eddy (1931-2009)

    NASA Astrophysics Data System (ADS)

    Gingerich, Owen

    2011-12-01

    , "This Mercury is Hot! Red Shift, Black Body, and a Perfect Radiator." Ironically, within a few years he was laid off from his HAO position as a result of budget cuts at its parent organization, the National Center for Atmospheric Research (NCAR). In an interview a quarter of a century later Eddy remarked, "I found out how hard it is for a person with a Ph.D. to get another job at that time, and often wished I didn't have one, for I was often told, true or not, that I was overqualified for the few jobs that turned up." Eddy found a temporary job writing a book for NASA as part of a series on the Skylab spacecraft; the book, The New Sun, was published in 1979. Again, working on his own time, he revived an earlier finding, namely, that between 1645 and 1715 the sun was almost devoid of spots, and he greatly extended the previous work of Gustav Spörer and Walter Maunder by showing during that period a dearth of aurorae and atmospheric carbon-14, a diminution of the solar corona during eclipses, and probably a correlation with cooling of the earth. For onomatopoiec reasons, the rhythm of the m's, Eddy chose the title "the Maunder Minimum" for the phenomenon, and for his unusually long cover story in the 18 June 1976 issue of Science. The paper was well received, and for a while Eddy was an invited speaker fifty times a year. In 1977, Eddy scored yet again, with his third cover story in Science, a jointly authored paper on solar rotation in the early 17th century. In 1977-78 Eddy had a fellowship at the Harvard-Smithsonian Center for Astrophysics in Cambridge, and during that time Ken Brecher and I had a series of conversations with Jack in which we worked out a proposal for a historical astronomy division within the AAS; since I had just been an AAS Councilor, I negotiated with the Society for its actualization, and Eddy became the first HAD president, in 1981-83. He introduced the logo, Dürer's ancient astronomer, and at the end of his term, the plaque with the motto "Ich

  17. Correlation of Air Displacement Plethysmography with Alternative Body Fat Measurement Techniques in Men and Women

    PubMed Central

    REINERT, BRITTANY L.; POHLMAN, ROBERTA; HARTZLER, LYNN

    2012-01-01

    Obesity has reached epidemic proportions with serious health consequences. Techniques used to measure body fat (BF) yield variable BF estimates, and this variability may lead to underestimation or overestimation of BF and subsequent treatment options. The measurements that are most accurate (Dual-Energy X-ray Absorptiometry (DEXA) and Air Displacement Plethysmography (ADP)) are expensive and often unavailable. The purpose of this study is to find the commonly available BF measurement that is the most accurate and practical for individual body types in the general population and compare these measurements to ADP (BOD POD®) as the standard. Field measurements include skinfolds (SKF), upper, lower, and whole body bioelectrical impedance (BI), waist and hip circumference ratios, body mass index calculations (BMI), and ADP. Our data indicate that BI is the least accurate measurement of body fat in males and females (paired t-tests of % body fat: BI vs. ADP, p0.05). However, preliminary data suggest female- specific SKF equations more accurately predict body fat in obese males than male-specific SKF equations. Given the current obesity trends, it is imperative to update these formulae to accurately reflect the current population. PMID:27182394

  18. Practical application of cross correlation technique to measure jitter of master-oscillator-power-amplifier laser system

    SciTech Connect

    Młyńczak, J.; Sawicz-Kryniger, K.; Fry, A. R.; Glownia, J.; Leemans, S.

    2014-01-01

    The Linac coherent light source (LCLS) at the SLAC National Accelerator Laboratory (SLAC) is the world’s first hard X-ray free electron laser (XFEL) and is capable of producing high-energy, femtosecond duration X-ray pulses. A common technique to study fast timescale physical phenomena, various “pump/probe” techniques are used. In these techniques there are two lasers, one optical and one X-ray, that work as a pump and as a probe to study dynamic processes in atoms and molecules. In order to resolve phenomena that occur on femtosecond timescales, it is imperative to have very precise timing between the optical lasers and X-rays (on the order of ~ 20 fs or better). The lasers are synchronized to the same RF source that drives the accelerator and produces the X-ray laser. However, elements in the lasers cause some drift and time jitter, thereby de-synchronizing the system. This paper considers cross-correlation technique as a way to quantify the drift and jitter caused by the regenerative amplifier of the ultrafast optical laser.

  19. Trace elemental correlation study in malignant and normal breast tissue by PIXE technique

    NASA Astrophysics Data System (ADS)

    Raju, G. J. Naga; Sarita, P.; Kumar, M. Ravi; Murty, G. A. V. Ramana; Reddy, B. Seetharami; Lakshminarayana, S.; Vijayan, V.; Lakshmi, P. V. B. Rama; Gavarasana, Satyanarayana; Reddy, S. Bhuloka

    2006-06-01

    Particle induced X-ray emission technique was used to study the variations in trace elemental concentrations between normal and malignant human breast tissue specimens and to understand the effects of altered homeostasis of these elements in the etiology of breast cancer. A 3 MeV proton beam was used to excite the biological samples of normal and malignant breast tissues. The elements Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb and Sr were identified and their relative concentrations were estimated. Almost all the elements were found to be elevated (p < 0.05, Wilcoxon signed-ranks test) in the cancerous tissues when compared with normal tissues. The excess levels of trace elements observed in the cancerous breast tissues could either be a cause or a consequence of breast cancer. Regarding their role in the initiation or promotion of breast cancer, one possible interpretation is that the elevated levels of Cu, Fe and Cr could have led to the formation of free radicals or other reactive oxygen species (ROS) that adversely affect DNA thereby causing breast cancer, which is mainly attributed to genetic abnormalities. Moreover, since Cu and Fe are required for angiogenesis, elevated concentrations of these elements are likely to promote breast cancer by increasing the blood supply for tumor growth. On the other hand elevated concentrations of elements in breast cancer tissues might also be a consequence of the cancer. This can be understood in terms of the biochemical and histological differences between normal and cancerous breast tissues. Tumors, characterized by unregulated multiplication of cells, need an ever-increasing supply of essential nutrients including trace elements. This probably results in an increased vascularity of malignant tissues, which in turn leads to enhancement of elemental concentrations in tumors.

  20. Raman correlation spectroscopy: A feasibility study of a new optical correlation technique and development of multi-component nanoparticles using the reprecipitation method

    NASA Astrophysics Data System (ADS)

    Nishida, Maki

    The feasibility of Raman correlation spectroscopy (RCS) is investigated as a new temporal optical fluctuation spectroscopy in this dissertation. RCS analyzes the correlations of the intensity fluctuations of Raman scattering from particles in a suspension that undergo Brownian motion. Because each Raman emission line arises from a specific molecular bond, the RCS method could yield diffusion behavior of specific chemical species within a dispersion. Due to the nature of Raman scattering as a coherent process, RCS could provide similar information as acquired in dynamic light scattering (DLS) and be practical for various applications that requires the chemical specificity in dynamical information. The theoretical development is discussed, and four experimental implementations of this technique are explained. The autocorrelation of the intensity fluctuations from a beta-carotene solution is obtained using the some configurations; however, the difficulty in precise alignment and weak nature of Raman scattering prevented the achievement of high sensitivity and resolution. Possible fluctuations of the phase of Raman scattering could also be affecting the results. A possible explanation of the observed autocorrelation in terms of number fluctuations of particles is also examined to test the feasibility of RCS as a new optical characterization method. In order to investigate the complex systems for which RCS would be useful, strategies for the creation of a multicomponent nanoparticle system are also explored. Using regular solution theory along with the concept of Hansen solubility parameters, an analytical model is developed to predict whether two or more components will form single nanoparticles, and what effect various processing conditions would have. The reprecipitation method was used to demonstrate the formation of the multi-component system of the charge transfer complex perylene:TCNQ (tetracyanoquinodimethane) and the active pharmaceutical ingredient cocrystal

  1. Eddy transport of reacting substances

    NASA Astrophysics Data System (ADS)

    Flierl, Glenn

    2015-11-01

    We examine an exact formulation of eddy fluxes but extended to tracers which react with each other. The resulting formula is evaluated using the lattice model approach, allowing not only control (including elimination) of sub-grid-scale diffusion and efficient enough computation to generate an adequate ensemble. The theory predicts that the flux is a non-local average of the mean gradients, even for passive scalars, and we can calculate the averaging kernel. The reaction terms alter the effective transport for a single scalar depending on decay time scale compared to that of the Lagrangian covariance. But, in addition, the eddies produce ``cross-fluxes'' whereby the transport of each tracer depends on the gradients of all of them.

  2. Development of an ultralow frequency eddy current instrument for the detection and sizing of stress corrosion cracks

    SciTech Connect

    Hayford, D.T.

    1988-01-01

    This book describes an investigation of the potential to use remote field eddy currents at low frequencies that would permit penetration of pipeline steels and use this technique to detect stress corrosion cracking on coated pipelines without requiring coating to be removed. The report describes development of a prototype eddy current instrument.

  3. Large eddy simulation applications in gas turbines.

    PubMed

    Menzies, Kevin

    2009-07-28

    The gas turbine presents significant challenges to any computational fluid dynamics techniques. The combination of a wide range of flow phenomena with complex geometry is difficult to model in the context of Reynolds-averaged Navier-Stokes (RANS) solvers. We review the potential for large eddy simulation (LES) in modelling the flow in the different components of the gas turbine during a practical engineering design cycle. We show that while LES has demonstrated considerable promise for reliable prediction of many flows in the engine that are difficult for RANS it is not a panacea and considerable application challenges remain. However, for many flows, especially those dominated by shear layer mixing such as in combustion chambers and exhausts, LES has demonstrated a clear superiority over RANS for moderately complex geometries although at significantly higher cost which will remain an issue in making the calculations relevant within the design cycle. PMID:19531505

  4. electromagnetics, eddy current, computer codes

    Energy Science and Technology Software Center (ESTSC)

    2002-03-12

    TORO Version 4 is designed for finite element analysis of steady, transient and time-harmonic, multi-dimensional, quasi-static problems in electromagnetics. The code allows simulation of electrostatic fields, steady current flows, magnetostatics and eddy current problems in plane or axisymmetric, two-dimensional geometries. TORO is easily coupled to heat conduction and solid mechanics codes to allow multi-physics simulations to be performed.

  5. The morphology of shelfbreak eddies

    NASA Astrophysics Data System (ADS)

    Garvine, R. W.; Wong, K.-C.; Gawarkiewicz, G. G.; McCarthy, R. K.; Houghton, R. W.; Aikman, F.

    1988-12-01

    We used a combination of buoy tracking, intensive hydrography, satellite thermal imagery, and moored current meters to resolve the structure of eddies at the shelfbreak front in the Middle Atlantic Bight south of New England. Eddylike features were always present at the front in our study area throughout the 15-day period of observations in June 1984. We found that hydrographic features in our across-shelf hydrographic transects that appeared to represent the detached parcels of shelf water often reported in the literature were, in fact, part of the three-dimensional structure of shelfbreak eddies. Adequate alongshelf resolution, in particular, enabled us to determine that no detached parcels were present. The two prominent features of the eddy groups we found were plumes of lighter shelf water that protruded into slope water, curling "backward" opposite the direction of mean shelf flow, and neighboring cyclones with warmer, saltier slope water in their cores, partly or wholly encircled by the plumes. The plumes have the potential especially for producing vigorous across-front exchange of heat, salt, and nutrients and may play roles analogous to the "squirts" found on the California shelf.

  6. Eddy covariance based methane flux in Sundarbans mangroves, India

    NASA Astrophysics Data System (ADS)

    Jha, Chandra Shekhar; Rodda, Suraj Reddy; Thumaty, Kiran Chand; Raha, A. K.; Dadhwal, V. K.

    2014-06-01

    We report the initial results of the methane flux measured using eddy covariance method during summer months from the world's largest mangrove ecosystem, Sundarbans of India. Mangrove ecosystems are known sources for methane (CH4) having very high global warming potential. In order to quantify the methane flux in mangroves, an eddy covariance flux tower was recently erected in the largest unpolluted and undisturbed mangrove ecosystem in Sundarbans (India). The tower is equipped with eddy covariance flux tower instruments to continuously measure methane fluxes besides the mass and energy fluxes. This paper presents the preliminary results of methane flux variations during summer months (i.e., April and May 2012) in Sundarbans mangrove ecosystem. The mean concentrations of CH4 emission over the study period was 1682 ± 956 ppb. The measured CH4 fluxes computed from eddy covariance technique showed that the study area acts as a net source for CH4 with daily mean flux of 150.22 ± 248.87 mg m-2 day-1. The methane emission as well as its flux showed very high variability diurnally. Though the environmental conditions controlling methane emission is not yet fully understood, an attempt has been made in the present study to analyse the relationships of methane efflux with tidal activity. This present study is part of Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP) initiative under `National Carbon Project'.

  7. Eddy Covariance Measurements of the Sea-Spray Aerosol Flu

    NASA Astrophysics Data System (ADS)

    Brooks, I. M.; Norris, S. J.; Yelland, M. J.; Pascal, R. W.; Prytherch, J.

    2015-12-01

    Historically, almost all estimates of the sea-spray aerosol source flux have been inferred through various indirect methods. Direct estimates via eddy covariance have been attempted by only a handful of studies, most of which measured only the total number flux, or achieved rather coarse size segregation. Applying eddy covariance to the measurement of sea-spray fluxes is challenging: most instrumentation must be located in a laboratory space requiring long sample lines to an inlet collocated with a sonic anemometer; however, larger particles are easily lost to the walls of the sample line. Marine particle concentrations are generally low, requiring a high sample volume to achieve adequate statistics. The highly hygroscopic nature of sea salt means particles change size rapidly with fluctuations in relative humidity; this introduces an apparent bias in flux measurements if particles are sized at ambient humidity. The Compact Lightweight Aerosol Spectrometer Probe (CLASP) was developed specifically to make high rate measurements of aerosol size distributions for use in eddy covariance measurements, and the instrument and data processing and analysis techniques have been refined over the course of several projects. Here we will review some of the issues and limitations related to making eddy covariance measurements of the sea spray source flux over the open ocean, summarise some key results from the last decade, and present new results from a 3-year long ship-based measurement campaign as part of the WAGES project. Finally we will consider requirements for future progress.

  8. An automated cross-correlation based event detection technique and its application to surface passive data set

    USGS Publications Warehouse

    Forghani-Arani, Farnoush; Behura, Jyoti; Haines, Seth S.; Batzle, Mike

    2013-01-01

    In studies on heavy oil, shale reservoirs, tight gas and enhanced geothermal systems, the use of surface passive seismic data to monitor induced microseismicity due to the fluid flow in the subsurface is becoming more common. However, in most studies passive seismic records contain days and months of data and manually analysing the data can be expensive and inaccurate. Moreover, in the presence of noise, detecting the arrival of weak microseismic events becomes challenging. Hence, the use of an automated, accurate and computationally fast technique for event detection in passive seismic data is essential. The conventional automatic event identification algorithm computes a running-window energy ratio of the short-term average to the long-term average of the passive seismic data for each trace. We show that for the common case of a low signal-to-noise ratio in surface passive records, the conventional method is not sufficiently effective at event identification. Here, we extend the conventional algorithm by introducing a technique that is based on the cross-correlation of the energy ratios computed by the conventional method. With our technique we can measure the similarities amongst the computed energy ratios at different traces. Our approach is successful at improving the detectability of events with a low signal-to-noise ratio that are not detectable with the conventional algorithm. Also, our algorithm has the advantage to identify if an event is common to all stations (a regional event) or to a limited number of stations (a local event). We provide examples of applying our technique to synthetic data and a field surface passive data set recorded at a geothermal site.

  9. Differential distribution of diatoms and dinoflagellates in a cyclonic eddy confined in the Bay of La Paz, Gulf of California

    NASA Astrophysics Data System (ADS)

    Coria-Monter, Erik; Monreal-Gómez, María. Adela; Salas-de-León, David Alberto; Aldeco-Ramírez, Javier; Merino-Ibarra, Martín.

    2014-09-01

    The differential distribution of diatoms and dinoflagellates in the Bay of La Paz, Gulf of California, Mexico, was analyzed in summer of 2009, when a cyclonic eddy confined in the bay dominated the circulation. An uplift of the nutricline in the eddy drove high concentrations of nutrients to the euphotic layer. A differential phytoplankton distribution was observed to be associated with the eddy: there was an abundance of dinoflagellates close to the center of the cyclonic eddy, whereas diatoms were more abundant at the periphery. A significant inverse correlation (R = -0.62, p < 0.002) was found between the temperature at 25 m depth and the dinoflagellates abundance. Based on the temporal evolution of chlorophyll measured by MODIS satellite images, and a conceptual model proposed for the lifecycle of eddies, the cyclonic eddy may have been an old decaying structure. The effect of the cyclonic eddy on the phytoplankton distribution in this small semienclosed region was apparently similar to that found in larger eddies in the open ocean, but this is the first time such a differential distribution has been found associated to a confined eddy.

  10. Strain distribution in the intervertebral disc under unconfined compression and tension load by the optimized digital image correlation technique.

    PubMed

    Liu, Qing; Wang, Tai-Yong; Yang, Xiu-Ping; Li, Kun; Gao, Li-Lan; Zhang, Chun-Qiu; Guo, Yue-Hong

    2014-04-01

    The unconfined compression and tension experiments of the intervertebral disc were conducted by applying an optimized digital image correlation technique, and the internal strain distribution was analysed for the disc. It was found that the axial strain values of different positions increased obviously with the increase in loads, while inner annulus fibrosus and posterior annulus fibrosus experienced higher axial strains than the outer annulus fibrosus and anterior annulus fibrosus. Deep annulus fibrosus exhibited higher compressive and tensile axial strains than superficial annulus fibrosus for the anterior region, while there was an opposite result for the posterior region. It was noted that all samples demonstrated a nonlinear stress-strain profile in the process of deforming, and an elastic region was shown once the sample was deformed beyond its toe region. PMID:24718863

  11. Progress of a Cross-Correlation Based Optical Strain Measurement Technique for Detecting Radial Growth on a Rotating Disk

    NASA Technical Reports Server (NTRS)

    Clem, Michelle M.; Abdul-Aziz, Ali; Woike, Mark R.; Fralick, Gustave C.

    2015-01-01

    The modern turbine engine operates in a harsh environment at high speeds and is repeatedly exposed to combined high mechanical and thermal loads. The cumulative effects of these external forces lead to high stresses and strains on the engine components, such as the rotating turbine disks, which may eventually lead to a catastrophic failure if left undetected. The operating environment makes it difficult to use conventional strain gauges, therefore, non-contact strain measurement techniques is of interest to NASA and the turbine engine community. This presentation describes one such approach; the use of cross correlation analysis to measure strain experienced by the engine turbine disk with the goal of assessing potential faults and damage.

  12. Three dimensional imaging and analysis of a single nano-device at the ultimate scale using correlative microscopy techniques

    SciTech Connect

    Grenier, A.; Barnes, J. P.; Serra, R.; Audoit, G.; Cooper, D.; Duguay, S.; Rolland, N.; Blavette, D.; Vurpillot, F.; Morin, P.; Gouraud, P.

    2015-05-25

    The analysis of a same sample using nanometre or atomic-scale techniques is fundamental to fully understand device properties. This is especially true for the dopant distribution within last generation nano-transistors such as MOSFET or FINFETs. In this work, the spatial distribution of boron in a nano-transistor at the atomic scale has been investigated using a correlative approach combining electron and atom probe tomography. The distortions present in the reconstructed volume using atom probe tomography have been discussed by simulations of surface atoms using a cylindrical symmetry taking into account the evaporation fields. Electron tomography combined with correction of atomic density was used so that to correct image distortions observed in atom probe tomography reconstructions. These corrected atom probe tomography reconstructions then enable a detailed boron doping analysis of the device.

  13. Correlation between the dielectric constant and porosity of nanoporous silica thin films deposited by the gas evaporation technique

    NASA Astrophysics Data System (ADS)

    Si, J. J.; Ono, H.; Uchida, K.; Nozaki, S.; Morisaki, H.; Itoh, N.

    2001-11-01

    Nanoporous silica thin films with low dielectric constants were deposited by gas evaporation of SiO2 nanoparticles in an argon atmosphere. With increasing gas pressure during the evaporation, the dielectric constant decreases, while the porosity increases. The correlation between the dielectric constant and porosity is well modeled by a serial connection of two capacitors, one with air and the other with SiO2 as the dielectric medium. This suggests that the dielectric constant of the nanoporous silica thin film using the gas evaporation technique is more effectively lowered by forming "uniformly" distributed voids of closed gaps than those of the nanoporous silica films with pores extending from the back to front surface. Therefore, the former nanoporous silica thin film requires less porosity to obtain a low dielectric constant and is regarded as an ideal low-k material.

  14. EDDY CURRENT INVERSION AND ESTIMATION METRICS FOR EVALUATING THERMAL BARRIER COATINGS

    SciTech Connect

    Sabbagh, Harold A.; Murphy, R. Kim; Sabbagh, Elias H.; Knopp, Jeremy S.; Aldrin, John C.; Nyenhuis, John

    2010-02-22

    In this paper, sophisticated eddy-current techniques incorporating model-based inverse methods were successfully demonstrated to measure the thickness and remaining-life of high-temperature coatings. To further assure the performance of these inverse methods, several estimation metrics including Fisher Information, Cramer-Rao Lower Bound (CRLB), covariance, and singular value decomposition (SVD) are introduced. The connections and utility of these metrics are illustrated in the design of eddy current methods for estimating layer thickness, conductivity and probe liftoff.

  15. Finite Element Modeling of Pulsed Eddy Current Signals from Aluminum Plates Having Defects

    NASA Astrophysics Data System (ADS)

    Babbar, V. K.; Harlley, D.; Krause, T. W.

    2010-02-01

    The pulsed eddy current technique is being developed for detection of flaws located at depth within conducting structures. The present work investigates the pulsed eddy current response from flat-plate conductors having defects by using finite element modeling. Modeling revealed the optimum probe position with respect to a multilayer defect geometry. Models were also produced to investigate the effect of changing some probe parameters on pickup signal and penetration depth.

  16. Eddy Current Inversion and Estimation Metrics for Evaluating Thermal Barrier Coatings

    NASA Astrophysics Data System (ADS)

    Sabbagh, Harold A.; Knopp, Jeremy S.; Aldrin, John C.; Murphy, R. Kim; Sabbagh, Elias H.; Nyenhuis, John

    2010-02-01

    In this paper, sophisticated eddy-current techniques incorporating model-based inverse methods were successfully demonstrated to measure the thickness and remaining-life of high-temperature coatings. To further assure the performance of these inverse methods, several estimation metrics including Fisher Information, Cramer-Rao Lower Bound (CRLB), covariance, and singular value decomposition (SVD) are introduced. The connections and utility of these metrics are illustrated in the design of eddy current methods for estimating layer thickness, conductivity and probe liftoff.

  17. Evaluation and Improvement of Eddy Current Position Sensors in Magnetically Suspended Flywheel Systems

    NASA Technical Reports Server (NTRS)

    Dever, Timothy P.; Palazzolo, Alan B.; Thomas, Erwin M., III; Jansen, Ralph H.; McLallin, Kerry (Technical Monitor); Soeder, James (Technical Monitor)

    2001-01-01

    Eddy current position sensor performance is evaluated for use in a high-speed flywheel development system. The flywheel utilizes a five axis active magnetic bearing system. The eddy current sensors are used for position feedback for the bearing controller. Measured characteristics include sensitivity to multiple target materials and susceptibility to noise from the magnetic bearings and from sensor-to-sensor crosstalk. Improvements in axial sensor configuration and techniques for noise reduction are described.

  18. Optimisation of a Stirred Bioreactor through the Use of a Novel Holographic Correlation Velocimetry Flow Measurement Technique

    PubMed Central

    Ismadi, Mohd-Zulhilmi; Higgins, Simon; Samarage, Chaminda R.; Paganin, David; Hourigan, Kerry; Fouras, Andreas

    2013-01-01

    We describe a method for measuring three dimensional (3D) velocity fields of a fluid at high speed, by combining a correlation-based approach with in-line holography. While this method utilizes tracer particles contained within the flow, our method does not require the holographic reconstruction of 3D images. The direct flow reconstruction approach developed here allows for measurements at seeding densities in excess of the allowable levels for techniques based on image or particle reconstruction, thus making it suited for biological flow measurement, such as the flow in bioreactor. We outline the theory behind our method, which we term Holographic Correlation Velocimetry (HCV), and subsequently apply it to both synthetic and laboratory data. Moreover, because the system is based on in-line holography, it is very efficient with regard to the use of light, as it does not rely on side scattering. This efficiency could be utilized to create a very high quality system at a modest cost. Alternatively, this efficiency makes the system appropriate for high-speed flows and low exposure times, which is essential for imaging dynamic systems. PMID:23776534

  19. Identification and measurement of combustion noise from a turbofan engine using correlation and coherence techniques. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Karchmer, A. M.

    1977-01-01

    Fluctuating pressure measurements within the combustor and tailpipe of a turbofan engine are made simultaneously with far field acoustic measurements. The pressure measurements within the engine are accomplished with cooled semi-infinite waveguide probes utilizing conventional condenser microphones as the transducers. The measurements are taken over a broad range of engine operating conditions and for 16 far field microphone positions between 10 deg and 160 deg relative to the engine inlet axis. Correlation and coherence techniques are used to determine the relative phase and amplitude relationships between the internal pressures and far field acoustic pressures. The results indicate that the combustor is a low frequency source region for acoustic propagation through the tailpipe and out to the far field. Specifically, it is found that the relation between source pressure and the resulting sound pressure involves a 180 deg phase shift. The latter result is obtained by Fourier transforming the cross correlation function between the source pressure and acoustic pressure after removing the propagation delay time. Further, it is found that the transfer function between the source pressure and acoustic pressure has a magnitude approximately proportional to frequency squared. These results are shown to be consistent with a model using a modified source term in Lighthill's turbulence stress tensor, wherein the fluctuating Reynolds stresses are replaced with the pressure fluctuations due to fluctuating entropy.

  20. Charm and beauty searches using electron -D{sup 0} azimuthal correlations and microvertexing techniques in STAR experiment at RHIC

    SciTech Connect

    Geromitsos, Artemios

    2010-12-22

    The energy loss of heavy quarks in the hot and dense matter created at RHIC, can be used to probe the properties of the medium. Both charm and beauty quarks contribute to the non-photonic electrons through their semi-leptonic decays. It is essential to determine experimentally the relative contribution of charm and beauty quarks to understand the suppression of heavy flavors at high p{sub T} in central Au+Au collisions. The azimuthal angular correlations of non-photonic electrons with the reconstructed D{sup 0} allow to disentangle the contribution of charm and beauty and to reduce the background below the D{sup 0} invariant mass as well. We discuss the STAR measurement of non-photonic electron and D{sup 0{yields}}K{sup -{pi}+} azimuthal correlations in p+p collisions at 200 GeV. Furthermore, we show results from the application of microvertexing techniques for charm and beauty searches in Cu+Cu and Au+Au collisions at 200 GeV using the information of the Silicon tracker of STAR.

  1. Observations of Three Dimensional Surfzone Eddies

    NASA Astrophysics Data System (ADS)

    Arnold, J. L.; Henderson, S. M.; Solovitz, S.

    2012-12-01

    We present measurements of the vertical structure of surfzone eddies (frequencies 0.0005-0.01 Hz). From 16 Oct to 07 Nov 2011, an array of 12 Acoustic Doppler Profilers (ADPs) measured velocity profiles in 0-6 m water depth on a natural beach near Duck, North Carolina. We will analyze and describe vertical variations in eddy velocity. Vertical variability of eddy magnitude will be presented, as well as coherence and phase between near-surface and near-bed velocities. We aim to shed light on the causes and consequences of vertical eddy variability, which has recently been recognized in observations, but is not yet well understood.

  2. Software compensation of eddy current fields in multislice high order dynamic shimming

    PubMed Central

    Sengupta, Saikat; Avison, Malcolm J.; Gore, John C.; Welch, E. Brian

    2011-01-01

    Dynamic B0 shimming (DS) can produce better field homogeneity than static global shimming by dynamically updating slicewise shim values in a multislice acquisition. The performance of DS however is limited by eddy current fields produced by the switching of 2nd and 3rd order unshielded shims. In this work, we present a novel method of eddy field compensation (EFC) applied to higher order shim induced eddy current fields in multislice DS. This method does not require shim shielding, extra hardware for eddy current compensation or subject specific prescanning. The interactions between shim harmonics are modeled assuming steady state of the medium and long time constant, cross and self term eddy fields in a DS experiment and ‘correction factors’ characterizing the entire set of shim interactions are derived. The correction factors for a given time between shim switches are shown to be invariable with object scanned, shim switching pattern and actual shim values, allowing for their generalized prospective use. Phantom and human head, 2nd and 3rd order DS experiments performed without any hardware eddy current compensation using the technique show large reductions in field gradients and offsets leading to significant improvements in image quality. This method holds promise as an alternative to expensive hardware based eddy current compensation required in 2nd and 3rd order DS. PMID:21458339

  3. Magnetic activity cycles in solar-like stars: The cross-correlation technique of p-mode frequency shifts

    NASA Astrophysics Data System (ADS)

    Régulo, C.; García, R. A.; Ballot, J.

    2016-04-01

    Aims: We set out to study the use of cross-correlation techniques to infer the frequency shifts that are induced by changing magnetic fields in p-mode frequencies and to provide a precise estimation of error bars. Methods: This technique and the calculation of the associated errors is first tested and validated on the Sun where p-mode magnetic behaviour is very well known. These validation tests are performed on 6000-day time series of Sun-as-a-star observations delivered by the SoHO spacecraft. Errors of the frequency shifts are quantified through Monte Carlo simulations. The same methodology is then applied to three solar-like oscillating stars: HD 49933, observed by CoRoT, as well as KIC 3733735 and KIC 7940546, observed by Kepler. Results: We first demonstrate the reliability of the error bars computed with the Monte Carlo simulations using the Sun. From the three stars analyzed, we confirm the presence of a magnetic activity cycle in HD 49933 with this methodology and we unveil the seismic signature of ongoing magnetic variations in KIC 3733735. Finally, the third star, KIC 7940546, seems to be in a quiet regime.

  4. Eddy current system for inspection of train hollow axles

    SciTech Connect

    Chady, Tomasz; Psuj, Grzegorz; Sikora, Ryszard; Kowalczyk, Jacek; Spychalski, Ireneusz

    2014-02-18

    The structural integrity of wheelsets used in rolling stock is of great importance to the safety. In this paper, electromagnetic system with an eddy current transducer suitable for the inspection of hollow axles have been presented. The transducer was developed to detect surface braking defects having depth not smaller than 0.5 mm. Ultrasound technique can be utilized to inspect the whole axle, but it is not sufficiently sensitive to shallow defects located close to the surface. Therefore, the electromagnetic technique is proposed to detect surface breaking cracks that cannot be detected by ultrasonic technique.

  5. Progress of a Cross-Correlation Based Optical Strain Measurement Technique for Detecting Radial Growth on a Rotating Disk

    NASA Technical Reports Server (NTRS)

    Clem, Michelle M.; Woike, Mark R.; Abdul-Aziz, Ali

    2014-01-01

    The Aeronautical Sciences Project under NASA's Fundamental Aeronautics Program is interested in the development of novel measurement technologies, such as optical surface measurements for the in situ health monitoring of critical constituents of the internal flow path. In situ health monitoring has the potential to detect flaws, i.e. cracks in key components, such as engine turbine disks, before the flaws lead to catastrophic failure. The present study, aims to further validate and develop an optical strain measurement technique to measure the radial growth and strain field of an already cracked disk, mimicking the geometry of a sub-scale turbine engine disk, under loaded conditions in the NASA Glenn Research Center's High Precision Rotordynamics Laboratory. The technique offers potential fault detection by imaging an applied high-contrast random speckle pattern under unloaded and loaded conditions with a CCD camera. Spinning the cracked disk at high speeds (loaded conditions) induces an external load, resulting in a radial growth of the disk of approximately 50.0-µm in the flawed region and hence, a localized strain field. When imaging the cracked disk under static conditions, the disk will be undistorted; however, during rotation the cracked region will grow radially, thus causing the applied particle pattern to be 'shifted'. The resulting particle displacements between the two images is measured using the two-dimensional cross-correlation algorithms implemented in standard Particle Image Velocimetry (PIV) software to track the disk growth, which facilitates calculation of the localized strain field. A random particle distribution is adhered onto the surface of the cracked disk and two bench top experiments are carried out to evaluate the technique's ability to measure the induced particle displacements. The disk is shifted manually using a translation stage equipped with a fine micrometer and a hotplate is used to induce thermal growth of the disk, causing the

  6. Instantaneous Wavelet Energetic Transfers between Atmospheric Blocking and Local Eddies.

    NASA Astrophysics Data System (ADS)

    Fournier, Aimé

    2005-07-01

    A new wavelet energetics technique, based on best-shift orthonormal wavelet analysis (OWA) of an instantaneous synoptic map, is constructed for diagnosing nonlinear kinetic energy (KE) transfers in five observed blocking cases. At least 90% of the longitudinal variance of time and latitude band mean 50-kPa geopotential is reconstructed by only two wavelets using best shift. This superior efficiency to the standard OWAs persists for time-evolving structures. The cases comprise two categories, respectively dominated by zonal-wavenumber sets {1} and {1, 2}. Further OWA of instantaneous residual nonblocking structures, combined with new “nearness” criteria, yields three more orthogonal components, representing smaller-scale eddies near the block (upstream and downstream) and distant structures. This decomposition fulfills a vision expressed to the author by Saltzman. Such a decomposition is not obtainable by simple Fourier analysis.Eddy patterns apparent in the components' contours suggest inferring geostrophic energetic interactions, but the component Rossby numbers may be too large to support the inference. However, a new result enabled by this method is the instantaneous attribution of blocking strain-field effects to particular energetically interactive eddies, consistent with Shutts' hypothesis. Such attribution was only possible before in simplified models or in a time-average sense. In four of five blocks, the upstream eddies feed KE to the block, which in turn, in three of four cases, transmits KE to the downstream eddies. The small case size precludes statistically significant conclusions. The appendixes link low-order blocking structure and dynamics to some wavelet design principles and propose a new interaction diagnosis, similar to E-vector analysis, but instantaneous.

  7. Video Analysis of Eddy Structures from Explosive Volcanic Eruptions

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Kobs-Nawotniak, S. E.

    2013-12-01

    We present a method of analyzing turbulent eddy structures in explosive volcanic eruptions using high definition video. Film from the eruption of Sakurajima on 25 September 2011 was analyzed using a modified version of FlowJ, a Java-based toolbox released by National Institute of Health. Using the Lucas and Kanade algorithm with a Gaussian derivative gradient, it tracks the change in pixel position over a 23 image buffer to determine the optical flow. This technique assumes that the optical flow, which is the apparent motion of the pixels, is equivalent to the actual flow field. We calculated three flow fields per second for the duration of the video. FlowJ outputs flow fields in pixels per frame that were then converted to meters per second in Matlab using a known distance and video rate. We constructed a low pass filter using proper orthogonal decomposition (POD) and critical point analysis to identify the underlying eddy structure with boundaries determined by tracing the flow lines. We calculated the area of each eddy and noted its position over a series of velocity fields. The changes in shape and position were tracked to determine the eddy growth rate and overall eddy rising velocity. The eddies grow in size 1.5 times quicker than they rise vertically. Presently, this method is most successful in high contrast videos when there is little to no effect of wind on the plumes. Additionally, the pixel movement from the video images represents a 2D flow with no depth, while the actual flow is three dimensional; we are continuing to develop an algorithm that will allow 3D reprojection of the 2D data. Flow in the y-direction lessens the overall velocity magnitude as the true flow motion has larger y-direction component. POD, which only uses the pattern of the flow, and analysis of the critical points (points where flow is zero) is used to determine the shape of the eddies. The method allows for video recorded at remote distances to be used to study eruption dynamics

  8. Toward finding a universally applicable parameterization of the β factor for Relaxed Eddy Accumulation applications

    NASA Astrophysics Data System (ADS)

    Vogl, Teresa; Hrdina, Amy; Thomas, Christoph

    2016-04-01

    -dioxide, latent and sensible heat fluxes across the contrasting environments. First, the choice of an appropriate scalar to calculate β0 is discussed considering the sources and sinks of each scalar with an emphasis on the carbon dioxide flux, which shows strongly dissimilar dynamics between the Antarctic ecosystem and the grassland. Secondly, the impact of atmospheric stability on both β models is investigated. In a next step, we attempt to find a physically meaningful explanation for the overestimation of the REA scalar fluxes compared to those from EC for using βw. We do so by analyzing the probability density function (pdf) and its statistical moments for the vertical wind speed. We found its pdf to be non-Gaussian for the majority of cases, and detected a close to linear relationship of its kurtosis with βw. Finally, in an attempt to provide practical guidance for field measurements, we integrate our findings and propose an enhanced model parameterization, and evaluate the differences between our new model and a constant β. Ammann, C. and Meixner, F.X. (2002) Stability dependence of the relaxed eddy accumulation coefficient for various scalar quantities. J. Geophys. Res. 107. ACL7.1-ACL7.9 doi:10.1029/2001JD000649 Businger, J.A., Oncley, S.P. (1990) Flux measurement with conditional sampling. J. Atmos. Ocean. Tech. 7:349-352. Desjardins, R. L. (1972) A study of carbon-dioxide and sensible heat fluxes using the eddy correlation technique, Ph.D. dissertation, Cornell University, 189 pp. Desjardins, R.L. (1977) Description and evaluation of sensible heat flux detector. Boundary-Layer Meteorol. 11:147-154. Katul, G., Finkelstein, P. L., Clarke, J. F., and Ellestad, T. G. (1996) An Investigation of the Conditional Sampling Methods Used to Estimate Fluxes of Active, Reactive and Passive Scalars. J. Appl. Meteorol. 35: 1835-1845. Milne, R., Beverland, I. J., Hargreaves, K., and Moncrieff, J. B. (1999) Variation of the beta coefficient in the relaxed eddy accumulation method

  9. Hydrographic Description and Habitat use of Eddies by Northern Elephant Seals in the North East Pacific

    NASA Astrophysics Data System (ADS)

    Costa, D. P.; Simmons, S.; Robinson, P.; Tremblay, Y.; Hassrick, J.; Walli, A.

    2006-12-01

    Northern elephant seals range widely over the North East Pacific Ocean. As part of the Tagging of Pacific Pelagics program we have followed the migratory patterns and habitat utilization of these animals. Habitat utilization has been defined by a combination of satellite remote sensing and animal bourn sensors. Previous work has shown that elephant seals forage around frontal systems and regions of high thermal gradients. Here we examine the foraging behavior of 4 elephant seals that were found to forage within eddies that formed along the coast of Southeastern Alaska (Haida & Sitka) and the Alaska Peninsula. Animal movements were observed using ARGOS locations and were correlated with eddies that were defined by satellite derived sea surface height anomaly data. All animals carried time depth and temperature sensors, while one animal carried a CTD instrument. We used these in situ data to examine the thermal profile of these eddies and the variation in the animals diving behavior as it migrated through the eddy.

  10. The relationship between sea-level and bottom pressure variability in an eddy permitting ocean model

    NASA Astrophysics Data System (ADS)

    Bingham, Rory J.; Hughes, Chris W.

    2008-02-01

    We investigate the relationship between sea-level (after application of an inverse-barometer correction) and ocean bottom pressure, in an eddy-permitting ocean model. We find the presence of eddies can disrupt this relationship even on timescales as short as 10-20 days, but only in the regions of most energetic eddy variability. Away from eddies, the relationship is similar to that seen in a coarser-resolution model, with a tight relationship between sea-level and bottom pressure at high frequencies, but with significant correlations between sea-level and bottom pressure at interannual timescales seen only in shelf sea regions. In the deep ocean, regions where sea-level and bottom pressure remain related out to the longest timescales are in the Arctic Ocean and regions of the Southern Ocean, where particularly large amplitude barotropic fluctuations are found but where the mesoscale signal is weak.

  11. Improved Imaging With Laser-Induced Eddy Currents

    NASA Technical Reports Server (NTRS)

    Chern, Engmin J.

    1993-01-01

    System tests specimen of material nondestructively by laser-induced eddy-current imaging improved by changing method of processing of eddy-current signal. Changes in impedance of eddy-current coil measured in absolute instead of relative units.

  12. Toward large eddy simulation of turbulent flow over an airfoil

    NASA Technical Reports Server (NTRS)

    Choi, Haecheon

    1993-01-01

    The flow field over an airfoil contains several distinct flow characteristics, e.g. laminar, transitional, turbulent boundary layer flow, flow separation, unstable free shear layers, and a wake. This diversity of flow regimes taxes the presently available Reynolds averaged turbulence models. Such models are generally tuned to predict a particular flow regime, and adjustments are necessary for the prediction of a different flow regime. Similar difficulties are likely to emerge when the large eddy simulation technique is applied with the widely used Smagorinsky model. This model has not been successful in correctly representing different turbulent flow fields with a single universal constant and has an incorrect near-wall behavior. Germano et al. (1991) and Ghosal, Lund & Moin have developed a new subgrid-scale model, the dynamic model, which is very promising in alleviating many of the persistent inadequacies of the Smagorinsky model: the model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model has been remarkably successful in prediction of several turbulent and transitional flows. We plan to simulate turbulent flow over a '2D' airfoil using the large eddy simulation technique. Our primary objective is to assess the performance of the newly developed dynamic subgrid-scale model for computation of complex flows about aircraft components and to compare the results with those obtained using the Reynolds average approach and experiments. The present computation represents the first application of large eddy simulation to a flow of aeronautical interest and a key demonstration of the capabilities of the large eddy simulation technique.

  13. A priori tests of a new dynamic subgrid-scale model for finite-difference large-eddy simulations

    NASA Astrophysics Data System (ADS)

    Salvetti, M. V.; Banerjee, S.

    1995-11-01

    This work focuses on subgrid-scale (SGS) modeling for finite-difference large-eddy simulations, employing filters in physical space. When a filter in physical space is used, an overlap is allowed between the unresolved and the resolved scales. For such a filter, all the three terms in the classical decomposition of the SGS stress tensor are present: the Leonard and cross-terms, due to the overlap between scales, and the true SGS Reynolds tensor, expressing the pure effect of the small scales. A dynamic subgrid-scale stress model is proposed, for finite-difference large-eddy simulation of incompressible and compressible flows in which the Leonard and cross-parts of the SGS stress tensor are assumed to be proportional to the resolved part (the ``modified Leonard term''), which is computed explicity. The SGS Reynolds stress is modeled by the eddy-viscosity Smagorinsky model. The two unknown parameters in this model are computed dynamically, as in Germano et al. [Phys. Fluids A 3, 1790 (1991)], but using a least squares technique. The model is tested using direct numerical simulation data for fully developed turbulent incompressible flows in presence of solid boundaries and free surfaces, and for compressible homogeneous turbulence. A ``box filter'' in physical space is used. Other SGS models are also tested, viz. the dynamic model of Germano et al. (DSM), and its compressible extension by Moin et al. [Phys. Fluids A 3, 2746 (1991)], and the dynamic mixed model in Zang et al. [Phys. Fluids A 5, 3186 (1993)] (DMM) and its compressible version developed here. Results on the behavior of the different models with regard to energy exchanges and correlation with the exact SGS stresses are presented for different filter widths. In particular high correlation is found between the modified Leonard and cross-terms thus justifying the basic assumption made in the model.

  14. Visualization and Analysis of Wireless Sensor Network Data for Smart Civil Structure Applications Based On Spatial Correlation Technique

    NASA Astrophysics Data System (ADS)

    Chowdhry, Bhawani Shankar; White, Neil M.; Jeswani, Jai Kumar; Dayo, Khalil; Rathi, Manorma

    2009-07-01

    Disasters affecting infrastructure, such as the 2001 earthquakes in India, 2005 in Pakistan, 2008 in China and the 2004 tsunami in Asia, provide a common need for intelligent buildings and smart civil structures. Now, imagine massive reductions in time to get the infrastructure working again, realtime information on damage to buildings, massive reductions in cost and time to certify that structures are undamaged and can still be operated, reductions in the number of structures to be rebuilt (if they are known not to be damaged). Achieving these ideas would lead to huge, quantifiable, long-term savings to government and industry. Wireless sensor networks (WSNs) can be deployed in buildings to make any civil structure both smart and intelligent. WSNs have recently gained much attention in both public and research communities because they are expected to bring a new paradigm to the interaction between humans, environment, and machines. This paper presents the deployment of WSN nodes in the Top Quality Centralized Instrumentation Centre (TQCIC). We created an ad hoc networking application to collect real-time data sensed from the nodes that were randomly distributed throughout the building. If the sensors are relocated, then the application automatically reconfigures itself in the light of the new routing topology. WSNs are event-based systems that rely on the collective effort of several micro-sensor nodes, which are continuously observing a physical phenomenon. WSN applications require spatially dense sensor deployment in order to achieve satisfactory coverage. The degree of spatial correlation increases with the decreasing inter-node separation. Energy consumption is reduced dramatically by having only those sensor nodes with unique readings transmit their data. We report on an algorithm based on a spatial correlation technique that assures high QoS (in terms of SNR) of the network as well as proper utilization of energy, by suppressing redundant data transmission

  15. Statistical correlations and risk analyses techniques for a diving dual phase bubble model and data bank using massively parallel supercomputers.

    PubMed

    Wienke, B R; O'Leary, T R

    2008-05-01

    Linking model and data, we detail the LANL diving reduced gradient bubble model (RGBM), dynamical principles, and correlation with data in the LANL Data Bank. Table, profile, and meter risks are obtained from likelihood analysis and quoted for air, nitrox, helitrox no-decompression time limits, repetitive dive tables, and selected mixed gas and repetitive profiles. Application analyses include the EXPLORER decompression meter algorithm, NAUI tables, University of Wisconsin Seafood Diver tables, comparative NAUI, PADI, Oceanic NDLs and repetitive dives, comparative nitrogen and helium mixed gas risks, USS Perry deep rebreather (RB) exploration dive,world record open circuit (OC) dive, and Woodville Karst Plain Project (WKPP) extreme cave exploration profiles. The algorithm has seen extensive and utilitarian application in mixed gas diving, both in recreational and technical sectors, and forms the bases forreleased tables and decompression meters used by scientific, commercial, and research divers. The LANL Data Bank is described, and the methods used to deduce risk are detailed. Risk functions for dissolved gas and bubbles are summarized. Parameters that can be used to estimate profile risk are tallied. To fit data, a modified Levenberg-Marquardt routine is employed with L2 error norm. Appendices sketch the numerical methods, and list reports from field testing for (real) mixed gas diving. A Monte Carlo-like sampling scheme for fast numerical analysis of the data is also detailed, as a coupled variance reduction technique and additional check on the canonical approach to estimating diving risk. The method suggests alternatives to the canonical approach. This work represents a first time correlation effort linking a dynamical bubble model with deep stop data. Supercomputing resources are requisite to connect model and data in application. PMID:18371945

  16. Mesoscale Ocean Large Eddy Simulations

    NASA Astrophysics Data System (ADS)

    Pearson, Brodie; Fox-Kemper, Baylor; Bachman, Scott; Bryan, Frank

    2015-11-01

    The highest resolution global climate models (GCMs) can now resolve the largest scales of mesoscale dynamics in the ocean. This has the potential to increase the fidelity of GCMs. However, the effects of the smallest, unresolved, scales of mesoscale dynamics must still be parametrized. One such family of parametrizations are mesoscale ocean large eddy simulations (MOLES), but the effects of including MOLES in a GCM are not well understood. In this presentation, several MOLES schemes are implemented in a mesoscale-resolving GCM (CESM), and the resulting flow is compared with that produced by more traditional sub-grid parametrizations. Large eddy simulation (LES) is used to simulate flows where the largest scales of turbulent motion are resolved, but the smallest scales are not resolved. LES has traditionally been used to study 3D turbulence, but recently it has also been applied to idealized 2D and quasi-geostrophic (QG) turbulence. The MOLES presented here are based on 2D and QG LES schemes.

  17. Observed deep energetic eddies by seamount wake

    NASA Astrophysics Data System (ADS)

    Chen, Gengxin; Wang, Dongxiao; Dong, Changming; Zu, Tingting; Xue, Huijie; Shu, Yeqiang; Chu, Xiaoqing; Qi, Yiquan; Chen, Hui

    2015-11-01

    Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

  18. Observed deep energetic eddies by seamount wake.

    PubMed

    Chen, Gengxin; Wang, Dongxiao; Dong, Changming; Zu, Tingting; Xue, Huijie; Shu, Yeqiang; Chu, Xiaoqing; Qi, Yiquan; Chen, Hui

    2015-01-01

    Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport. PMID:26617343

  19. Southern Ocean Eddies as Weather Makers

    NASA Astrophysics Data System (ADS)

    Frenger, Ivy; Byrne, David; Gruber, Nicolas; Knutti, Reto; Münnich, Matthias; Papritz, Lukas

    2013-04-01

    Several hundred mesoscale eddies populate the Southern Ocean south of 30°S at any time, however, little is known about their effect on the overlying atmosphere. As these eddies feature sea surface temperature (SST) anomalies one can expect them to play a role in the coupling of the atmosphere and the ocean. Here we show based on satellite observations of about 600,000 eddies occurring between 1997 and 2010, that these ocean eddies significantly alter near surface wind, cloud properties and rainfall by several percent. Relative to the atmospheric variability, the magnitude of the anomalies related to ocean eddies represents ±13-15 % (wind, cloud fraction), ±6-10 % (cloud water content) and ±2-6 % (rain). This impact on the atmosphere is striking given the fact that oceanic eddies constitute non-stationary SST fronts of moderate size relative to the much larger atmospheric low pressure systems which are constantly passing by at these latitudes. The spatial pattern of these changes is consistent with a mechanism labeled downward momentum mechanism in which the SST anomalies related to eddies modify the stability and thus turbulence of the atmospheric boundary layer. We will investigate the mechanisms and impact of the atmospheric modifications associated with ocean eddies in a regional high-resolution coupled atmosphere-ocean model (COSMO-ROMS) over the Southern Ocean.

  20. Observed deep energetic eddies by seamount wake

    PubMed Central

    Chen, Gengxin; Wang, Dongxiao; Dong, Changming; Zu, Tingting; Xue, Huijie; Shu, Yeqiang; Chu, Xiaoqing; Qi, Yiquan; Chen, Hui

    2015-01-01

    Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport. PMID:26617343

  1. Mesoscale Eddies in the Solomon Sea

    NASA Astrophysics Data System (ADS)

    Hristova, H. G.; Kessler, W. S.; McWilliams, J. C.; Molemaker, M. J.

    2011-12-01

    Water mass transformation in the strong equatorward flows through the Solomon Sea influences the properties of the Equatorial Undercurrent and subsequent cold tongue upwelling. High eddy activity in the interior Solomon Sea seen in altimetric sea surface height (SSH) and in several models may provide a mechanism for these transformations. We investigate these effects using a mesoscale (4-km resolution) sigma-coordinate (ROMS) model of the Solomon Sea nested in a basin solution, forced by a repeating seasonal cycle, and evaluated against observational data. The model generates a vigorous upper layer eddy field; some of these are apparently shed as the New Guinea Coastal Undercurrent threads through the complex topography of the region, others are independent of the strong western boundary current. We diagnose the scales and vertical structure of the eddies in different parts of the Solomon Sea to illuminate their generation processes and propagation characteristics, and compare these to observed eddy statistics. Hypotheses tested are that the Solomon Sea mesoscale eddies are generated locally by baroclinic instability, that the eddies are shed as the South Equatorial Current passes around and through the Solomon Island chain, that eddies are generated by the New Guinea Coastal Undercurrent, or that eddies occurring outside of the Solomon Sea propagate into the Solomon Sea. These different mechanisms have different implications for the resulting mixing and property fluxes. They also provide different interpretations for SSH signals observed from satellites (e.g., that will be observed by the upcoming SWOT satellite).

  2. Correlation between the Temperature Dependence of Intrsinsic Mr Parameters and Thermal Dose Measured by a Rapid Chemical Shift Imaging Technique

    PubMed Central

    Taylor, Brian A.; Elliott, Andrew M.; Hwang, Ken-Pin; Hazle, John D.; Stafford, R. Jason

    2011-01-01

    In order to investigate simultaneous MR temperature imaging and direct validation of tissue damage during thermal therapy, temperature-dependent signal changes in proton resonance frequency (PRF) shifts, R2* values, and T1-weighted amplitudes are measured from one technique in ex vivo tissue heated with a 980-nm laser at 1.5T and 3.0T. Using a multi-gradient echo acquisition and signal modeling with the Stieglitz-McBride algorithm, the temperature sensitivity coefficient (TSC) values of these parameters are measured in each tissue at high spatiotemporal resolutions (1.6×1.6×4mm3,≤5sec) at the range of 25-61 °C. Non-linear changes in MR parameters are examined and correlated with an Arrhenius rate dose model of thermal damage. Using logistic regression, the probability of changes in these parameters is calculated as a function of thermal dose to determine if changes correspond to thermal damage. Temperature calibrations demonstrate TSC values which are consistent with previous studies. Temperature sensitivity of R2* and, in some cases, T1-weighted amplitudes are statistically different before and after thermal damage occurred. Significant changes in the slopes of R2* as a function of temperature are observed. Logistic regression analysis shows that these changes could be accurately predicted using the Arrhenius rate dose model (Ω=1.01±0.03), thereby showing that the changes in R2* could be direct markers of protein denaturation. Overall, by using a chemical shift imaging technique with simultaneous temperature estimation, R2* mapping and T1-W imaging, it is shown that changes in the sensitivity of R2* and, to a lesser degree, T1-W amplitudes are measured in ex vivo tissue when thermal damage is expected to occur according to Arrhenius rate dose models. These changes could possibly be used for direct validation of thermal damage in contrast to model-based predictions. PMID:21721063

  3. Wind changes above warm Agulhas Current eddies

    NASA Astrophysics Data System (ADS)

    Rouault, M.; Verley, P.; Backeberg, B.

    2016-04-01

    Sea surface temperature (SST) estimated from the Advanced Microwave Scanning Radiometer E onboard the Aqua satellite and altimetry-derived sea level anomalies are used south of the Agulhas Current to identify warm-core mesoscale eddies presenting a distinct SST perturbation greater than to 1 °C to the surrounding ocean. The analysis of twice daily instantaneous charts of equivalent stability-neutral wind speed estimates from the SeaWinds scatterometer onboard the QuikScat satellite collocated with SST for six identified eddies shows stronger wind speed above the warm eddies than the surrounding water in all wind directions, if averaged over the lifespan of the eddies, as was found in previous studies. However, only half of the cases showed higher wind speeds above the eddies at the instantaneous scale; 20 % of cases had incomplete data due to partial global coverage by the scatterometer for one path. For cases where the wind is stronger above warm eddies, there is no relationship between the increase in surface wind speed and the SST perturbation, but we do find a linear relationship between the decrease in wind speed from the centre to the border of the eddy downstream and the SST perturbation. SST perturbations range from 1 to 6 °C for a mean eddy SST of 15.9 °C and mean SST perturbation of 2.65 °C. The diameter of the eddies range from 100 to 250 km. Mean background wind speed is about 12 m s-1 (mostly southwesterly to northwesterly) and ranging mainly from 4 to 16 m s-1. The mean wind increase is about 15 %, which corresponds to 1.8 m s-1. A wind speed increase of 4 to 7 m s-1 above warm eddies is not uncommon. Cases where the wind did not increase above the eddies or did not decrease downstream had higher wind speeds and occurred during a cold front associated with intense cyclonic low-pressure systems, suggesting certain synoptic conditions need to be met to allow for the development of wind speed anomalies over warm-core ocean eddies. In many cases

  4. A turnkey data logger program for field-scale energy flux density measurements using eddy covariance and surface renewal

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Micrometeorological methods and ecosystem-scale energy and mass flux density measurements have become increasingly important in soil, agricultural, and environmental sciences. For many scientists without formal training in atmospheric science, these techniques are relatively inaccessible. Eddy cov...

  5. Intense submesoscale upwelling in anticyclonic eddies

    NASA Astrophysics Data System (ADS)

    Brannigan, L.

    2016-04-01

    Observations from around the global ocean show that enhanced biological activity can be found in anticyclonic eddies. This may mean that upwelling of nutrient-rich water occurs within the eddy, but such upwelling is not captured by models that resolve mesoscale processes. High-resolution simulations presented here show intense submesoscale upwelling from the thermocline to the mixed layer in anticyclonic eddies. The properties of the upwelling are consistent with a process known as symmetric instability. A simple limiting nutrient experiment shows that this upwelling can drive much higher biological activity in anticyclonic eddies when there is a high nutrient concentration in the thermocline. An estimate for the magnitude of upwelling associated with symmetric instability in anticyclonic eddies in the Sargasso Sea shows that it may be of comparable magnitude to other processes, though further work is required to understand the full implications for basin-scale nutrient budgets.

  6. Effects of Mesoscale Eddies in the Active Mixed Layer: Test of the Parametrisation in Eddy Resolving Simulations

    NASA Technical Reports Server (NTRS)

    Luneva, M. V.; Clayson, C. A.; Dubovikov, Mikhail

    2015-01-01

    In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200-207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1-2 degrees and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher (0.5-0.74) correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes from the parametrisation is controlled by dimensionless parameter estimating the ratio of vertical turbulent mixing term to mesoscale advection. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux

  7. Observed characteristics of Mozambique Channel eddies

    NASA Astrophysics Data System (ADS)

    Swart, N. C.; Lutjeharms, J. R. E.; Ridderinkhof, H.; de Ruijter, W. P. M.

    2010-09-01

    The flow in the Mozambique Channel is dominated by large, southward propagating, anti-cyclonic eddies, as opposed to a steady western boundary current. These Mozambique Channel eddies feed their waters into the Agulhas Current system, where they are thought to have a significant influence on the formation of the Natal Pulse and Agulhas Ring shedding. Here we use in situ hydrographic and nutrient data, together with satellite altimetry and surface velocity profilers to provide a detailed characterization of the Mozambique Channel eddies. Two warm eddies in the Channel at 20°S and 24°S had diameters of over 200 km. They rotated anti-cyclonically with a tangential velocity of over 0.5 m.s-1. Vertical sections show that the eddies reached to the bottom of the water column. Relative to the surrounding waters, the features were warm and saline. The total heat and salt anomalies for the southernmost eddy were computed relative to a reference station close by. At 24°S the total anomalies were 1.3 × 1020 J and 6.9 × 1012 kg, respectively, being on par with Agulhas rings. Mozambique Channel eddies thus have the potential to form a major contribution to the southward eddy heat flux in the Agulhas Current system. The feature also had positive nutrient and negative oxygen anomalies. The large magnitude of the water mass anomalies within the eddy suggests that interannual variability in Mozambique Channel eddy numbers would have a significant impact on downstream water mass characteristics.

  8. Combining and Correlating DC, Modulated, and Transient Measurement Techniques to Disentangle and Quantify Key Physical Properties for Organic Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Gundlach, David

    2015-03-01

    Organic thin film electronics offer the potential to significantly impact how humans interface with their surroundings and society in general. Substantial contributions over the past two decades in this highly multidisciplinary area of research have led to significant improvements in discrete device performance and several impressive advanced technology demonstrations. However, fundamental understanding and quantification of the physical properties and processes that govern device operation remains limited compared to conventional semiconductors, such as silicon. In this presentation I will discuss our recent development and application of combined and correlated optical-electrical measurement methods to obtain a more nuanced understanding and quantification of the critical properties and fundamental processes relevant to device operation. In particular, I will discuss the use of steady state and pulsed light techniques combined with modulated and DC electrical measurements tailored to the specific operating regimes and device structures of organic diodes (solar cells and light emitters) and transistors to provide greater understanding of charge injection, transport, lifetime, density, and recombination kinetics.

  9. Correlation study of structural, optical and electrical properties of amorphous carbon thin films prepared by ion beam sputtering deposition technique

    NASA Astrophysics Data System (ADS)

    Mohagheghpour, E.; Rajabi, M.; Gholamipour, R.; Larijani, M. M.; Sheibani, S.

    2016-01-01

    The correlation of structural, optical and electrical properties of amorphous carbon thin films deposited by ion beam sputtering technique on the glass substrate was investigated. The film thickness varied over a wide range from 57 to 408 nm by controlling the deposition time. Raman spectra and X-ray photoelectron spectroscopy showed that the size of the graphite crystallites with sp2 bonds (La) and the sp3/sp2 fraction are smaller than 1.5 nm and 1.4, respectively. The values of ID/IG ratio, the 'G' peak position, and surface roughness depend on the film thickness; all of them increased by increasing film thickness up to 360 nm, and then decreased by increasing time and thickness. Furthermore, the resistivity followed similar trends of these structural properties. According to Tauc equation the optical band gap of these films was in the range of 3.2-3.9 eV. A broad emission peak at around 2.94 eV was observed on a photoluminescence spectrum of amorphous carbon film with highest resistivity.

  10. On the standardization of crystal-field parameters and the multiple correlated fitting technique: Applications to rare-earth compounds

    NASA Astrophysics Data System (ADS)

    Rudowicz, C.; Chua, M.; Reid, M. F.

    2000-09-01

    This work investigates the crystal-field parameter (CFP) sets for rare-earth (RE) ions doped at orthorhombic and/or lower symmetry, i.e. monoclinic or triclinic sites. Two important questions are addressed: (1) How do you compare CFP sets reported by different authors when there can be as many as six numerically different equivalent sets? and (2) How do you distinguish between global and local minima in the multi-parameter fittings? To answer the first question we propose to adopt the standardization of CFP sets. The orthorhombic and/or monoclinic standardization has been carried out for several illustrative CFP sets, including the contributions from various mechanisms, for NdF 3, RE 2Te 4O 11, and RE 3+ in garnet materials. It is shown that adopting a well-defined standardization convention enables meaningful comparison of CFP sets taken from various sources. The analysis of literature data reveals also cases when the CF parameters may be misinterpreted due to the choice of a different representation in the multi-parameter fittings. To answer the second question we propose the multiple correlated fitting technique (MCFT). Using experimental data for Nd 3+ in YAG and LaF 3, MCFT is employed to probe for more reliable CFP sets.

  11. Davisson-Germer Prize in Atomic or Surface Physics: The COLTRIMS multi-particle imaging technique-new Insight into the World of Correlation

    NASA Astrophysics Data System (ADS)

    Schmidt-Bocking, Horst

    2008-05-01

    The correlated many-particle dynamics in Coulombic systems, which is one of the unsolved fundamental problems in AMO-physics, can now be experimentally approached with so far unprecedented completeness and precision. The recent development of the COLTRIMS technique (COLd Target Recoil Ion Momentum Spectroscopy) provides a coincident multi-fragment imaging technique for eV and sub-eV fragment detection. In its completeness it is as powerful as the bubble chamber in high energy physics. In recent benchmark experiments quasi snapshots (duration as short as an atto-sec) of the correlated dynamics between electrons and nuclei has been made for atomic and molecular objects. This new imaging technique has opened a powerful observation window into the hidden world of many-particle dynamics. Recent multiple-ionization studies will be presented and the observation of correlated electron pairs will be discussed.

  12. Conformable eddy current array delivery

    NASA Astrophysics Data System (ADS)

    Summan, Rahul; Pierce, Gareth; Macleod, Charles; Mineo, Carmelo; Riise, Jonathan; Morozov, Maxim; Dobie, Gordon; Bolton, Gary; Raude, Angélique; Dalpé, Colombe; Braumann, Johannes

    2016-02-01

    The external surface of stainless steel containers used for the interim storage of nuclear material may be subject to Atmospherically Induced Stress Corrosion Cracking (AISCC). The inspection of such containers poses a significant challenge due to the large quantities involved; therefore, automating the inspection process is of considerable interest. This paper reports upon a proof-of-concept project concerning the automated NDT of a set of test containers containing artificially generated AISCCs. An Eddy current array probe with a conformable padded surface from Eddyfi was used as the NDT sensor and end effector on a KUKA KR5 arc HW robot. A kinematically valid cylindrical raster scan path was designed using the KUKA|PRC path planning software. Custom software was then written to interface measurement acquisition from the Eddyfi hardware with the motion control of the robot. Preliminary results and analysis are presented from scanning two canisters.

  13. Rotating concave eddy current probe

    DOEpatents

    Roach, Dennis P.; Walkington, Phil; Rackow, Kirk A.; Hohman, Ed

    2008-04-01

    A rotating concave eddy current probe for detecting fatigue cracks hidden from view underneath the head of a raised head fastener, such as a buttonhead-type rivet, used to join together structural skins, such as aluminum aircraft skins. The probe has a recessed concave dimple in its bottom surface that closely conforms to the shape of the raised head. The concave dimple holds the probe in good alignment on top of the rivet while the probe is rotated around the rivet's centerline. One or more magnetic coils are rigidly embedded within the probe's cylindrical body, which is made of a non-conducting material. This design overcomes the inspection impediment associated with widely varying conductivity in fastened joints.

  14. Toward the large-eddy simulation of compressible turbulent flows

    NASA Technical Reports Server (NTRS)

    Erlebacher, G.; Hussaini, M. Y.; Speziale, C. G.; Zang, T. A.

    1990-01-01

    New subgrid-scale models for the large-eddy simulation of compressible turbulent flows are developed and tested based on the Favre-filtered equations of motion for an ideal gas. A compressible generalization of the linear combination of the Smagorinsky model and scale-similarity model, in terms of Favre-filtered fields, is obtained for the subgrid-scale stress tensor. An analogous thermal linear combination model is also developed for the subgrid-scale heat flux vector. The two dimensionless constants associated with these subgrid-scale models are obtained by correlating with the results of direct numerical simulations of compressible isotropic turbulence performed on a 96(exp 3) grid using Fourier collocation methods. Extensive comparisons between the direct and modeled subgrid-scale fields are provided in order to validate the models. A large-eddy simulation of the decay of compressible isotropic turbulence (conducted on a coarse 32(exp 3) grid) is shown to yield results that are in excellent agreement with the fine grid direct simulation. Future applications of these compressible subgrid-scale models to the large-eddy simulation of more complex supersonic flows are discussed briefly.

  15. Eddy Covariance Method: Overview of General Guidelines and Conventional Workflow

    NASA Astrophysics Data System (ADS)

    Burba, G. G.; Anderson, D. J.; Amen, J. L.

    2007-12-01

    Atmospheric flux measurements are widely used to estimate water, heat, carbon dioxide and trace gas exchange between the ecosystem and the atmosphere. The Eddy Covariance method is one of the most direct, defensible ways to measure and calculate turbulent fluxes within the atmospheric boundary layer. However, the method is mathematically complex, and requires significant care to set up and process data. These reasons may be why the method is currently used predominantly by micrometeorologists. Modern instruments and software can potentially expand the use of this method beyond micrometeorology and prove valuable for plant physiology, hydrology, biology, ecology, entomology, and other non-micrometeorological areas of research. The main challenge of the method for a non-expert is the complexity of system design, implementation, and processing of the large volume of data. In the past several years, efforts of the flux networks (e.g., FluxNet, Ameriflux, CarboEurope, Fluxnet-Canada, Asiaflux, etc.) have led to noticeable progress in unification of the terminology and general standardization of processing steps. The methodology itself, however, is difficult to unify, because various experimental sites and different purposes of studies dictate different treatments, and site-, measurement- and purpose-specific approaches. Here we present an overview of theory and typical workflow of the Eddy Covariance method in a format specifically designed to (i) familiarize a non-expert with general principles, requirements, applications, and processing steps of the conventional Eddy Covariance technique, (ii) to assist in further understanding the method through more advanced references such as textbooks, network guidelines and journal papers, (iii) to help technicians, students and new researchers in the field deployment of the Eddy Covariance method, and (iv) to assist in its use beyond micrometeorology. The overview is based, to a large degree, on the frequently asked questions

  16. An experimental search for near-wall boundary conditions for large eddy simulation

    NASA Technical Reports Server (NTRS)

    Robinson, S. K.

    1982-01-01

    Instantaneous wall shear stress and streamwise velocities have been measured simultaneously in a flat plate, turbulent boundary layer at moderate Reynolds number in an effort to provide experimental support for large eddy simulations. Data were obtained by using a buried-wire wall shear gage and a hot-wire rake positioned in the log region of the flow. All data processing was accomplished with digital data analysis techniques on a minicomputer. Fluctuations of the instantaneous U plus versus Y plus profiles about a mean law of the wall are shown to be significant and complex. Peak cross-correlation values between wall shear stress and the velocities are high and reflect the passage of a large structure inclined at a small angle to the wall. Estimates of this angle are consistent with those made by other investigators. Conditional sampling techniques were used to detect the passage of various sizes and types of flow disturbances (events) and to estimate their mean frequency of occurrence. Events characterized by large and sudden streamwise accelerations were found to be highly coherent throughout the log region and were strongly correlated with large fluctuations in wall shear-stress. Phase randomness between the near-wall quantities and the outer velocities was small. The results suggest that the flow events detected by conditional sampling applied to velocities in the log region may be related to the bursting process.

  17. Multiple dipole eddies in the Alaska Coastal Current detected with Landsat thematic mapper data

    NASA Technical Reports Server (NTRS)

    Ahlnas, Kristina; Royer, Thomas C.; George, Thomas H.

    1987-01-01

    Seventeen dipole eddies, including five large, well-formed ones, three second-generation eddies, and two double eddies, were observed in the Alaska Coastal Current near Kayak Island in one single scene of the Landsat thematic mapper (TM) on April 22, l985. The digital Landsat TM satellite data were computer analyzed to extract details in the near coastal circulation in the northern Gulf of Alaska. Enhancement techniques were applied to the visible and thermal IR bands. The features are evident only in the visible bands because of the ability of these bands to detect the distribution of sediments in the near surface. These eddies did not have a significant thermal signature.The sources of these sediments are the glacial streams found throughout the Gulf of Alaska coast. Eddies of this configuration and frequency have never been observed here previously. However, the oceanographic and meteorological conditions are typical for this time of year. These eddies should be important to the cross-shelf mixing processes in the Alaska Coastal Current and are an indicator that the flow here can be unstable at certain times of the year.

  18. Eddy current scanning of niobium for SRF cavities at Fermilab

    SciTech Connect

    Boffo, C.; Bauer, P.; Foley, M.; Antoine, C.; Cooper, C.; Brinkmann, A.; /DESY

    2006-08-01

    In the framework of SRF cavity development, Fermilab is creating the infrastructure needed for the characterization of the material used in the cavity fabrication. An important step in the characterization of ''as received'' niobium sheets is eddy current scanning. Eddy current scanning is a non-destructive technique first adopted and further developed by DESY with the purpose of checking the cavity material for subsurface defects and inclusions. Fermilab has received and further upgraded a commercial eddy current scanner previously used for the SNS project. This scanner is now used daily to scan the niobium sheets for the Fermilab third harmonic, the ILC, and the Proton Driver cavities. After optical inspection, more than 400 squares and disks have been scanned and when necessary checked at the optical and electron microscopes, anodized, or measured with profilometers looking for surface imperfections that might limit the performance of the cavities. This paper gives a status report on the scanning results obtained so far, including a discussion of the classification of signals being detected.

  19. Subsurface Defect Detection in Metals with Pulsed Eddy Current

    SciTech Connect

    Plotnikov, Yuri A.; Bantz, Walter J.

    2005-04-09

    The eddy current (EC) method is traditionally used for open surface crack detection in metallic components. Subsurface voids in bulk metals can also be detected by the eddy current devices. Taking into consideration the skin effect in conductive materials, a lower frequency of electromagnetic excitation is used for a deeper penetration. A set of special specimens was designed and fabricated to investigate sensitivity to subsurface voids. Typically, flat bottom holes (FBHs) are used for subsurface defect simulation. This approach is not very representative of real defects for eddy current inspection because the FBH depth extends to the bottom of the specimen. Two-layer specimens with finite depth FBHs were fabricated and scanned with conventional EC of variable frequency. Sensitivity and spatial resolution of EC diminish with flaw depth. The pulsed EC approach was applied for flaw detection at variable distance under the surface. The transient response from multi-layer model was derived and compared to experiments. The multi-frequency nature of pulsed excitation provides effective coverage of a thick layer of material in one pass. Challenging aspects of subsurface flaw detection and visualization using the EC technique are discussed.

  20. Eddy current inspection of bonded composite crack repair

    NASA Astrophysics Data System (ADS)

    Smith, Thomas K., Jr.; Guijt, Cornelius; Fredell, Robert

    1996-11-01

    The aging of the US aircraft fleet poses serious economic and safety challenges. Fatigue cracks in the 7079-T6 aluminum fuselage skin of aging transports have presented zn opportunity to test a prototype repair. GLARE, a fiber metal laminate, has been applied to repair fuselage cracks in the fuselage skin of a US transport aircraft. This affordable prototype solution to extend the life of aging aircraft requires an inspection method to track crack growth and monitor the effectiveness of the patch on repaired fuselage skin. The fiber metal laminate patch is opaque and the fuselage skin at the damage location generally can only be accessed from the outside surface requiring the use of a non-destructive means to monitor crack length. Advances in eddy current inspection technology have provided a means to detect and track crack growth beneath patches on fuselage skins. This paper describes the development of low-frequency eddy current techniques to monitor cracks under bonded composite repair patches applied to stiffened fuselage structures. The development involved the use of a rugged portable eddy current inspection unit. The results show crack growth can be monitored to ensure the continued structural integrity of repaired flawed structures; however, the influence of substructure present a challenge to the inspector in detecting crack growth.

  1. Seasonal variability in global eddy diffusion and the effect on neutral density

    NASA Astrophysics Data System (ADS)

    Pilinski, M. D.; Crowley, G.

    2015-04-01

    We describe a method for making single-satellite estimates of the seasonal variability in global-average eddy diffusion coefficients. Eddy diffusion values as a function of time were estimated from residuals of neutral density measurements made by the Challenging Minisatellite Payload (CHAMP) and simulations made using the thermosphere-ionosphere-mesosphere electrodynamics global circulation model (TIME-GCM). The eddy diffusion coefficient results are quantitatively consistent with previous estimates based on satellite drag observations and are qualitatively consistent with other measurement methods such as sodium lidar observations and eddy diffusivity models. Eddy diffusion coefficient values estimated between January 2004 and January 2008 were then used to generate new TIME-GCM results. Based on these results, the root-mean-square sum for the TIME-GCM model is reduced by an average of 5% when compared to density data from a variety of satellites, indicating that the fidelity of global density modeling can be improved by using data from a single satellite like CHAMP. This approach also demonstrates that eddy diffusion could be estimated in near real-time from satellite observations and used to drive a global circulation model like TIME-GCM. Although the use of global values improves modeled neutral densities, there are limitations to this method, which are discussed, including that the latitude dependence of the seasonal neutral-density signal is not completely captured by a global variation of eddy diffusion coefficients. This demonstrates the need for a latitude-dependent specification of eddy diffusion which is also consistent with diffusion observations made by other techniques.

  2. Seasonal Variability in Global Eddy Diffusion and the Effect on Thermospheric Neutral Density

    NASA Astrophysics Data System (ADS)

    Pilinski, M.; Crowley, G.

    2014-12-01

    We describe a method for making single-satellite estimates of the seasonal variability in global-average eddy diffusion coefficients. Eddy diffusion values as a function of time between January 2004 and January 2008 were estimated from residuals of neutral density measurements made by the CHallenging Minisatellite Payload (CHAMP) and simulations made using the Thermosphere Ionosphere Mesosphere Electrodynamics - Global Circulation Model (TIME-GCM). The eddy diffusion coefficient results are quantitatively consistent with previous estimates based on satellite drag observations and are qualitatively consistent with other measurement methods such as sodium lidar observations and eddy-diffusivity models. The eddy diffusion coefficient values estimated between January 2004 and January 2008 were then used to generate new TIME-GCM results. Based on these results, the RMS difference between the TIME-GCM model and density data from a variety of satellites is reduced by an average of 5%. This result, indicates that global thermospheric density modeling can be improved by using data from a single satellite like CHAMP. This approach also demonstrates how eddy diffusion could be estimated in near real-time from satellite observations and used to drive a global circulation model like TIME-GCM. Although the use of global values improves modeled neutral densities, there are some limitations of this method, which are discussed, including that the latitude-dependence of the seasonal neutral-density signal is not completely captured by a global variation of eddy diffusion coefficients. This demonstrates the need for a latitude-dependent specification of eddy diffusion consistent with diffusion observations made by other techniques.

  3. Eddy Current Testing, RQA/M1-5330.17.

    ERIC Educational Resources Information Center

    National Aeronautics and Space Administration, Huntsville, AL. George C. Marshall Space Flight Center.

    As one in the series of classroom training handbooks, prepared by the U.S. space program, instructional material is presented in this volume concerning familiarization and orientation on eddy current testing. The subject is presented under the following headings: Introduction, Eddy Current Principles, Eddy Current Equipment, Eddy Current Methods,…

  4. Linkages between controlled floods, eddy sandbar dynamics, and riparian vegetation along the Colorado River in Marble Canyon, Arizona

    NASA Astrophysics Data System (ADS)

    Mueller, E. R.; Grams, P. E.; Hazel, J. E., Jr.; Schmeeckle, M. W.

    2015-12-01

    Controlled floods are released from Glen Canyon Dam to build and maintain eddy sandbars along the Colorado River in Grand Canyon National Park. Long-term monitoring shows that the topographic response to controlled floods varies considerably between eddies, likely reflecting different geometric configurations and flow hydraulics. Differences in eddy sandbar response also reflect the degree of vegetation establishment since the 1980s when reservoir spills more than double the magnitude of controlled floods cleared most sandbars of vegetation. Here we explore the geomorphology of sandbar responses in the context of controlled floods, debris fan-eddy geometry, and riparian vegetation establishment. In Marble Canyon, the proportion of eddy area stabilized by vegetation is negatively correlated with water surface slope and the rate of stage change with discharge. Less vegetated sites are more dynamic; they tend to build open sandbars during controlled floods and show greater topographic variability in the eddy compared to the main channel. In contrast, deposition of open sandbars is limited where vegetation establishment has decreased channel width, altering the pattern of eddy recirculation and sediment redistribution. In these locations, deposition during controlled floods is more akin to floodplain sedimentation, and the elevation of vegetated bar surfaces increases with successive floods. Changes in sand storage in the main channel are greater than storage change in the eddy at these lower gradient sites, and controlled floods tend to evacuate sand that has accumulated on the bed. The degree to which vegetation has stabilized sandbar surfaces may thus provide a proxy for different hydraulic conditions and a better canyon-wide assessment of controlled flood response. Our results apply primarily to large eddies in Marble Canyon, and ongoing flow modeling and vegetation composition mapping will allow further assessment of eddy sandbar-riparian vegetation interactions

  5. Adaptation of a speciation sampling cartridge for measuring ammonia flux from cattle feedlots using relaxed eddy accumulation

    NASA Astrophysics Data System (ADS)

    Baum, K. A.; Ham, J. M.

    Improved measurements of ammonia losses from cattle feedlots are needed to quantify the national NH 3 emissions inventory and evaluate management techniques for reducing emissions. Speciation cartridges composed of glass honeycomb denuders and filter packs were adapted to measure gaseous NH 3 and aerosol NH 4+ fluxes using relaxed eddy accumulation (REA). Laboratory testing showed that a cartridge equipped with four honeycomb denuders had a total capture capacity of 1800 μg of NH 3. In the field, a pair of cartridges was deployed adjacent to a sonic anemometer and an open-path gas analyzer on a mobile tower. High-speed valves were attached to the inlets of the cartridges and controlled by a datalogger so that up- and down-moving eddies were independently sampled based on direction of the vertical wind speed and a user-defined deadband. Air flowed continuously through the cartridges even when not sampling by means of a recirculating air handling system. Eddy covariance measurement of CO 2 and H 2O, as measured by the sonic and open-path gas analyzer, were used to determine the relaxation factor needed to compute REA-based fluxes. The REA system was field tested at the Beef Research Unit at Kansas State University in the summer and fall of 2007. Daytime NH 3 emissions ranged between 68 and 127 μg m -2 s -1; fluxes tended to follow a diurnal pattern correlated with latent heat flux. Daily fluxes of NH 3 were between 2.5 and 4.7 g m -2 d -1 and on average represented 38% of fed nitrogen. Aerosol NH 4+ fluxes were negligible compared with NH 3 emissions. An REA system designed around the high-capacity speciation cartridges can be used to measure NH 3 fluxes from cattle feedlots and other strong sources. The system could be adapted to measure fluxes of other gases and aerosols.

  6. Anomalous chlorofluorocarbon uptake by mesoscale eddies in the Drake Passage region

    NASA Astrophysics Data System (ADS)

    Song, Hajoon; Marshall, John; Gaube, Peter; McGillicuddy, Dennis J.

    2015-02-01

    The role of mesoscale eddies in the uptake of anthropogenic chlorofluorocarbon-11 (CFC-11) gas is investigated with a 1/20° eddy-resolving numerical ocean model of a region of the Southern Ocean. With a relatively fast air-sea equilibrium time scale (about a month), the air-sea CFC-11 flux quickly responds to the changes in the mixed layer CFC-11 partial pressure (pCFC-11). At the mesoscale, significant correlations are observed between pCFC-11 anomaly, anomalies in sea surface temperature (SST), net heat flux, and mixed layer depth. An eddy-centric analysis of the simulated CFC-11 field suggests that anticyclonic warm-core eddies generate negative pCFC-11 anomalies and cyclonic cold-core eddies generate positive anomalies of pCFC-11. Surface pCFC-11 is modulated by mixed layer dynamics in addition to CFC-11 air-sea fluxes. A negative cross correlation between mixed layer depth and surface pCFC-11 anomalies is linked to higher CFC-11 uptake in anticyclones and lower CFC-11 uptake in cyclones, especially in winter. An almost exact asymmetry in the air-sea CFC-11 flux between cyclones and anticyclones is found.

  7. Production and destruction of eddy kinetic energy in forced submesoscale eddy-resolving simulations

    NASA Astrophysics Data System (ADS)

    Mukherjee, Sonaljit; Ramachandran, Sanjiv; Tandon, Amit; Mahadevan, Amala

    2016-09-01

    We study the production and dissipation of the eddy kinetic energy (EKE) in a submesoscale eddy field forced with downfront winds using the Process Study Ocean Model (PSOM) with a horizontal grid resolution of 0.5 km. We simulate an idealized 100 m deep mixed-layer front initially in geostrophic balance with a jet in a domain that permits eddies within a range of O(1 km-100 km). The vertical eddy viscosities and the dissipation are parameterized using four different subgrid vertical mixing parameterizations: the k - ɛ , the KPP, and two different constant eddy viscosity and diffusivity profiles with a magnitude of O(10-2m2s-1) in the mixed layer. Our study shows that strong vertical eddy viscosities near the surface reduce the parameterized dissipation, whereas strong vertical eddy diffusivities reduce the lateral buoyancy gradients and consequently the rate of restratification by mixed-layer instabilities (MLI). Our simulations show that near the surface, the spatial variability of the dissipation along the periphery of the eddies depends on the relative alignment of the ageostrophic and geostrophic shear. Analysis of the resolved EKE budgets in the frontal region from the simulations show important similarities between the vertical structure of the EKE budget produced by the k - ɛ and KPP parameterizations, and earlier LES studies. Such an agreement is absent in the simulations using constant eddy-viscosity parameterizations.

  8. Large-eddy Advection in Evapotranspiration Estimates from an Array of Eddy Covariance Towers

    NASA Astrophysics Data System (ADS)

    Lin, X.; Evett, S. R.; Gowda, P. H.; Colaizzi, P. D.; Aiken, R.

    2014-12-01

    Evapotranspiration was continuously measured by an array of eddy covariance systems and large weighting lysimeter in a sorghum in Bushland, Texas in 2014. The advective divergence from both horizontal and vertical directions were measured through profile measurements above canopy. All storage terms were integrated from the depth of soil heat flux plate to the height of eddy covariance measurement. Therefore, a comparison between the eddy covariance system and large weighing lysimeter was conducted on hourly and daily basis. The results for the discrepancy between eddy covariance towers and the lysimeter will be discussed in terms of advection and storage contributions in time domain and frequency domain.

  9. Thin film eddy current impulse deicer

    NASA Technical Reports Server (NTRS)

    Smith, Samuel O.; Zieve, Peter B.

    1990-01-01

    Two new styles of electrical impulse deicers has been developed and tested in NASA's Icing Research Tunnel. With the Eddy Current Repulsion Deicing Boot (EDB), a thin and flexible spiral coil is encapsulated between two thicknesses of elastomer. The coil, made by an industrial printed circuit board manufacturer, is bonded to the aluminum aircraft leading edge. A capacitor bank is discharged through the coil. Induced eddy currents repel the coil from the aluminum aircraft structure and shed accumulated ice. A second configuration, the Eddy Current Repulsion Deicing-Strip (EDS) uses an outer metal erosion strip fastened over the coil. Opposite flowing eddy currents repel the strip and create the impulse deicing force. The outer strip serves as a surface for the collection and shedding of ice and does not require any structural properties. The EDS is suitable for composite aircraft structures. Both systems successfully dispelled over 95 percent of the accumulated ice from airfoils over the range of the FAA icing envelope.

  10. Process Specification for Eddy Current Inspection

    NASA Technical Reports Server (NTRS)

    Koshti, Ajay

    2011-01-01

    This process specification establishes the minimum requirements for eddy current inspection of flat surfaces, fastener holes, threaded fasteners and seamless and welded tubular products made from nonmagnetic alloys such as aluminum and stainless steel.

  11. Eddies and vortices in ocean basin dynamics

    NASA Astrophysics Data System (ADS)

    Siegel, A.; Weiss, Jeffrey B.; Toomre, Juri; McWilliams, James C.; Berloff, Pavel S.; Yavneh, Irad

    A wind-driven, closed-basin quasi-geostrophic ocean model is computed at very high horizontal resolution to study the effect of increasing Reynolds number (Re) on eddy variability. Five numerical simulations are performed with identical configurations, varying only in horizontal resolution and viscosity coefficient (and therefore Re). Qualitative changes in the structure of eddy variability are evident in the dramatic increase of isolated vortex structures at the highest Re. While the time-mean kinetic energy is relatively independent of Re, the vortex emergence contributes to a continual increase with Re of eddy kinetic energy and meridional vorticity flux. The rate of increase slows somewhat at the highest Re, indicating the possibility of a regime where eddy variability becomes insensitive to further increases in Re.

  12. Detection of subsurface eddies from satellite observations

    NASA Astrophysics Data System (ADS)

    Assassi, Charefeddine; Morel, Yves; Chaigneau, Alexis; Pegliasco, Cori; Vandermeirsch, Frederic; Rosemary, Morrow; Colas, François; Fleury, Sara; Cambra, Rémi

    2014-05-01

    This study aims to develop an index that allows distinguishing between surface and subsurface intensified eddies from surface data only, in particular using the sea surface height and the sea surface temperature available from satellite observations. To do this, we propose the use of a simple index based on the ratio of the sea surface temperature anomaly (SSTa) and the sea level anomaly (SLA). This index is first derived using an academic approach, based on idealized assumptions of geostrophic balance and Gaussian-shaped vortices. This index depends on the vertical extent (or decreasing rate) of the eddy and because of its sensitivity to the exact shape of the vortex, we were not able to evaluate these depths from the surface fields and our results remain qualitative. Then, in order to examine the pertinence and validity of the proposed index, SSTa and SLA were computed using outputs of a realistic regional circulation model in the Peru-Chile upwelling system where both surface and subsurface eddies coexist. Over a seven year simulation, the statistics shows that 71% of eddies are correctly identified as surface or subsurface intensified. Multi-core eddies are also largely present and represent an average of 37% of all vortices. These multi-core eddies contribute to a large number of the wrong identification (15%). Finally, the index was successfully applied on in-situ data to detect a previously observed subsurface-intensified Swoddy (slope water eddy) in the Bay of Biscay. This study suggests that the index can be successfully used to determine the exact nature of mesoscale eddies (surface or subsurface- intensified) from satellite observations only.

  13. Eddy-current sensor measures bolt loading

    NASA Technical Reports Server (NTRS)

    Burr, M. E.

    1980-01-01

    Thin wire welded to bottom of hole down center of bolt permits measurement of tension in bolt. Bolt lengthens under strain, but wire is not loaded, so gap between wire and eddy-current gap transducer mounted on bolt head indicates bolt loading. Eddy-current transducer could measure gap within 0.05 mm. Method does not require separate "standard" for each bolt type, and is not sensitive to dirt or oil in bolt hole, unlike ultrasonic probes.

  14. Eddy viscosity measurements in a rectangular jet

    NASA Technical Reports Server (NTRS)

    Swan, David H.; Morrison, Gerald L.

    1988-01-01

    The flow field of a rectangular jet with a 2:1 aspect ratio was studied at a Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry (LDV). Velocity gradients, Reynolds stress tensor components, and scalar eddy viscosities are presented for the major and minor axis planes of the jet. The eddy viscosity model was found to be applicable only in the direction of maximum mean velocity gradient.

  15. Eddy currents in a conducting sphere

    NASA Technical Reports Server (NTRS)

    Bergman, John; Hestenes, David

    1986-01-01

    This report analyzes the eddy current induced in a solid conducting sphere by a sinusoidal current in a circular loop. Analytical expressions for the eddy currents are derived as a power series in the vectorial displacement of the center of the sphere from the axis of the loop. These are used for first order calculations of the power dissipated in the sphere and the force and torque exerted on the sphere by the electromagnetic field of the loop.

  16. Eddies in eastern boundary subtropical upwelling systems

    NASA Astrophysics Data System (ADS)

    Capet, X.; Colas, F.; McWilliams, J. C.; Penven, P.; Marchesiello, P.

    Over the last decade, mesoscale-resolving ocean models of eastern boundary upwelling systems (EBS) have helped improve our understanding of the functioning of EBS and, in particular, assess the role of eddy activity in these systems. We review the main achievements in this regard and highlight remaining issues and challenges. In EBS, eddy activity arises from baroclinic/barotropic instability of the inshore and also offshore currents. Mesoscale eddies play a significant (although not leading) role in shaping the EBS dynamical structure, both directly and through associated submesoscale activity (i.e., primarily frontal). They do so by modifying both momentum and tracer balances in ways that cannot simply be understood in terms of diffusion. The relative degree to which these assertions about eddy activity and eddy role apply to each of the four major EBS (Canary, Benguela, Peru-Chile, and California Current Systems) remains to be established. Besides resolving the eddies, benefits from EBS high-resolution modeling include the possibility of accounting for the fine-scale structures of the nearshore wind, a better representation of the Ekman-driven coastal divergence, and (at resolution σ (1 km) or lower) inclusion of submesoscale (i.e., mainly frontal) processes. Recent numerical experiments suggest that accounting for these various processes in climate models, through resolution increase (possibly locally) or parameterization, would lead to significant basin-scale bias reduction. The mechanisms involved in upscaling from EBS toward the larger scale remain to be fully elucidated.

  17. Mesoscale eddies transport deep-sea sediments

    PubMed Central

    Zhang, Yanwei; Liu, Zhifei; Zhao, Yulong; Wang, Wenguang; Li, Jianru; Xu, Jingping

    2014-01-01

    Mesoscale eddies, which contribute to long-distance water mass transport and biogeochemical budget in the upper ocean, have recently been taken into assessment of the deep-sea hydrodynamic variability. However, how such eddies influence sediment movement in the deepwater environment has not been explored. Here for the first time we observed deep-sea sediment transport processes driven by mesoscale eddies in the northern South China Sea via a full-water column mooring system located at 2100 m water depth. Two southwestward propagating, deep-reaching anticyclonic eddies passed by the study site during January to March 2012 and November 2012 to January 2013, respectively. Our multiple moored instruments recorded simultaneous or lagging enhancement of suspended sediment concentration with full-water column velocity and temperature anomalies. We interpret these suspended sediments to have been trapped and transported from the southwest of Taiwan by the mesoscale eddies. The net near-bottom southwestward sediment transport by the two events is estimated up to one million tons. Our study highlights the significance of surface-generated mesoscale eddies on the deepwater sedimentary dynamic process. PMID:25089558

  18. Eddies and variability in the Mozambique Channel

    NASA Astrophysics Data System (ADS)

    Schouten, Mathijs W.; de Ruijter, Wilhelmus P. M.; van Leeuwen, Peter Jan; Ridderinkhof, Herman

    2003-07-01

    Between 1995 and 2000, on average 4 eddies per year are observed from satellite altimetry to propagate southward through the Mozambique Channel, into the upstream Agulhas region. Further south, these eddies have been found to control the timing and frequency of Agulhas ring shedding. Within the Mozambique Channel, anomalous SSH amplitudes rise to 30 cm, in agreement with in situ measured velocities. Comparison of an observed velocity section with GCM model results shows that the Mozambique Channel eddies in these models are too surface intensified. Also, the number of eddies formed in the models is in disagreement with our observational analysis. Moored current meter measurements observing the passage of three eddies in 2000 are extended to a 5-year time series by referencing the anomalous surface currents estimated from altimeter data to a synoptic LADCP velocity measurement. The results show intermittent eddy passage at the mooring location. A statistical analysis of SSH observations in different parts of the Mozambique Channel shows a southward decrease of the dominant frequency of the variability, going from 7 per year in the extension of the South Equatorial Current north of Madagascar to 4 per year south of Madagascar. The observations suggest that frequency reduction is related to the Rossby waves coming in from the east.

  19. Eddies off the Queen Charlotte Islands

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The bright red, green, and turquoise patches to the west of British Columbia's Queen Charlotte Islands and Alaska's Alexander Archipelago highlight the presence of biological activity in the ocean. These colors indicate high concentrations of chlorophyll, the primary pigment found in phytoplankton. Notice that there are a number of eddies visible in the Pacific Ocean in this pseudo-color scene. The eddies are formed by strong outflow currents from rivers along North America's west coast that are rich in nutrients from the springtime snowmelt running off the mountains. This nutrient-rich water helps stimulate the phytoplankton blooms within the eddies. (For more details, read Tracking Eddies that Feed the Sea.) To the west of the eddies in the water, another type of eddy-this one in the atmosphere-forms the clouds into the counterclockwise spiral characteristic of a low pressure system in the Northern Hemisphere. (Click on the image above to see it at full resolution; or click to see the scene in true-color.) The snow-covered mountains of British Columbia are visible in the upper righthand corner of the image. This scene was constructed using SeaWiFS data collected on June 13, 2002. SeaWiFS image courtesy the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  20. Non-Destructive Evaluation of Thermal Spray Coating Interface Quality By Eddy Current Method

    SciTech Connect

    B. Mi; G. Zhao; R. Bayles

    2006-08-10

    Thermal spray coating is usually applied through directing molten or softened particles at very high velocities onto a substrate. An eddy current non-destructive inspection technique is presented here for thermal spray coating interface quality characterization. Several high-velocity-oxy-fuel (HVOF) coated steel plates were produced with various surface preparation conditions or spray process parameters. A quad-frequency eddy current probe was used to manually scan over the coating surface to evaluate the bonding quality. Experimental results show that different surface preparation conditions and varied process parameters can be successfully differentiated by the impedance value observed from the eddy current probe. The measurement is fairly robust and consistent. This non-contact, nondestructive, easy-to-use technique has the potential for evaluating the coating quality immediately after its application so that any defects can be corrected immediately.

  1. Alignment issues, correlation techniques and their assessment for a visible light imaging-based 3D printer quality control system

    NASA Astrophysics Data System (ADS)

    Straub, Jeremy

    2016-05-01

    Quality control is critical to manufacturing. Frequently, techniques are used to define object conformity bounds, based on historical quality data. This paper considers techniques for bespoke and small batch jobs that are not statistical model based. These techniques also serve jobs where 100% validation is needed due to the mission or safety critical nature of particular parts. One issue with this type of system is alignment discrepancies between the generated model and the physical part. This paper discusses and evaluates techniques for characterizing and correcting alignment issues between the projected and perceived data sets to prevent errors attributable to misalignment.

  2. Coherent-vortex dynamics in large-eddy simulations of turbulence

    NASA Astrophysics Data System (ADS)

    Lesieur, M.; Begou, P.; Briand, E.; Danet, A.; Delcayre, F.; Aider, J. L.

    2003-04-01

    We present a review of coherent-vortex dynamics obtained thanks to large-eddy simulations (LES) associated with simple and effective vortex-identification and animation techniques. LES of a large class of constant-density or weakly compressible three-dimensional flows have been carried out. In isotropic turbulence, we present the formation and evolution of spaghetti-type vortices, seen thanks toQ, vorticity and pressure, together with the time evolution of the kinetic energy, enstrophy and skewness. In a spatially growing boundary layer on a flat plate, one observes during transition big ? vortices lying on the wall (with very well correlated oblique induced low- and high-speed streaks) shedding smaller hairpin vortices around their tips. In the developed boundary layer, we show animations of the purely longitudinal low- and high-speed streaks, as well as animations of low-pressure regions. In a backwards-facing step, we examine the influence of upstream conditions upon the flow structure, by comparing two inflow conditions: a white noise superposed on a mean velocity profile and a realistic turbulent boundary layer. The latter three-dimensionalizes the flow downstream of the step and reduces the reattachment length. In both cases big staggered arch vortices form, impinge the lower wall and are carried away downstream. In a two-dimensional(2D) square cavity, spanwisely oriented vortices are shed behind the upstream edge, and impinge the downstream edge, transforming into arch vortices very similar to the back-step case. These arch vortices are also found behind a 2D rectangular obstacle with wall effect. We discuss the relevance of the vortices found with respect to reality. All these eddies are very important in terms of drag and noise reduction in aerodynamics and aeroacoustics.

  3. Non-Destructive Evaluation of Thermal Spray Coating Interface Quality by Eddy Current Method

    SciTech Connect

    B.Mi; X. Zhao; R. Bayles

    2006-05-26

    Thermal spray coating is usually applied through directing molten or softened particles at very high velocities onto a substrate. An eddy current non-destructive inspection technique is presented here for thermal spray coating interface quality characterization. Several high-velocity-oxy-fuel (HVOF) coated steel plates were produced with different surface preparation conditions before applying the coating, e.g., grit-blasted surface, wire-brush cleaned surface, and a dirty surface. A quad-frequency eddy current probe was used to manually scan over the coating surface to evaluate the bonding quality. Experimental results show that the three surface preparation conditions can be successfully differentiated by looking into the impedance difference observed from the eddy current probe. The measurement is fairly robust and consistent. More specimens are also prepared with variations of process parameters, such as spray angle, stand-off distance, and application of corrosion protective sealant, etc. They are blindly tested to evaluate the reliability of the eddy current system. Quantitative relations between the coating bond strength and the eddy current response are also established with the support of destructive testing. This non-contact, non-destructive, easy to use technique has the potential for evaluating the coating quality immediately after its application so that any defects can be corrected immediately.

  4. Investigating electrical resonance in eddy-current array probes

    NASA Astrophysics Data System (ADS)

    Hughes, R.; Fan, Y.; Dixon, S.

    2016-02-01

    The sensitivity enhancing effects of eddy-current testing at frequencies close to electrical resonance are explored. Var-ied techniques exploiting the phenomenon, dubbed near electrical resonance signal enhancement (NERSE), were experimentally investigated to evaluate its potential exploitation for other interesting applications in aerospace materials, in particular its potential for boosting the sensitivity of standard ECT measurements. Methods for setting and controlling the typically unstable resonant frequencies of such systems are discussed. This research is funded by the EPSRC, via the Research Centre for Non-Destructive Evaluation RCNDE, and Rolls-Royce plc.

  5. Solving time-dependent two-dimensional eddy current problems

    NASA Technical Reports Server (NTRS)

    Lee, Min Eig; Hariharan, S. I.; Ida, Nathan

    1990-01-01

    Transient eddy current calculations are presented for an EM wave-scattering and field-penetrating case in which a two-dimensional transverse magnetic field is incident on a good (i.e., not perfect) and infinitely long conductor. The problem thus posed is of initial boundary-value interface type, where the boundary of the conductor constitutes the interface. A potential function is used for time-domain modeling of the situation, and finite difference-time domain techniques are used to march the potential function explicitly in time. Attention is given to the case of LF radiation conditions.

  6. Correlation-based continuous-wave technique for optical fiber distributed strain measurement using Brillouin scattering (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Hotate, Kazuo

    2005-05-01

    We have been developing "fiber optic nerve systems" for "smart structures and smart materials", in which an optical fiber acts as sensor to measure distribution of strain along it. The original technology, "Brillouin Optical Correlation Domain Analysis: BOCDA" has been proposed and developed to analyze the distributed strain along the fiber by use of synthesis of correlation characteristics of continuous lightwave. Adopting this technology, "fiber optic nerve systems" with quite a high spatial resolution and measurement speed, have been established.

  7. Anticyclonic eddies are more productive than cyclonic eddies in subtropical gyres because of winter mixing

    PubMed Central

    Hardman-Mountford, Nick J.; Greenwood, Jim; Richardson, Anthony J.; Feng, Ming; Matear, Richard J.

    2016-01-01

    Mesoscale eddies are ubiquitous features of ocean circulation that modulate the supply of nutrients to the upper sunlit ocean, influencing the rates of carbon fixation and export. The popular eddy-pumping paradigm implies that nutrient fluxes are enhanced in cyclonic eddies because of upwelling inside the eddy, leading to higher phytoplankton production. We show that this view does not hold for a substantial portion of eddies within oceanic subtropical gyres, the largest ecosystems in the ocean. Using space-based measurements and a global biogeochemical model, we demonstrate that during winter when subtropical eddies are most productive, there is increased chlorophyll in anticyclones compared with cyclones in all subtropical gyres (by 3.6 to 16.7% for the five basins). The model suggests that this is a consequence of the modulation of winter mixing by eddies. These results establish a new paradigm for anticyclonic eddies in subtropical gyres and could have important implications for the biological carbon pump and the global carbon cycle. PMID:27386549

  8. Anticyclonic eddies are more productive than cyclonic eddies in subtropical gyres because of winter mixing.

    PubMed

    Dufois, François; Hardman-Mountford, Nick J; Greenwood, Jim; Richardson, Anthony J; Feng, Ming; Matear, Richard J

    2016-05-01

    Mesoscale eddies are ubiquitous features of ocean circulation that modulate the supply of nutrients to the upper sunlit ocean, influencing the rates of carbon fixation and export. The popular eddy-pumping paradigm implies that nutrient fluxes are enhanced in cyclonic eddies because of upwelling inside the eddy, leading to higher phytoplankton production. We show that this view does not hold for a substantial portion of eddies within oceanic subtropical gyres, the largest ecosystems in the ocean. Using space-based measurements and a global biogeochemical model, we demonstrate that during winter when subtropical eddies are most productive, there is increased chlorophyll in anticyclones compared with cyclones in all subtropical gyres (by 3.6 to 16.7% for the five basins). The model suggests that this is a consequence of the modulation of winter mixing by eddies. These results establish a new paradigm for anticyclonic eddies in subtropical gyres and could have important implications for the biological carbon pump and the global carbon cycle. PMID:27386549

  9. Carbon dioxide emissions in fallow periods of a corn-soybean rotation: eddy-covariance versus chamber methods

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Carbon dioxide (CO2) fluxes at terrestrial surface are typically quantified using eddy-covariance (EC) or chamber (Ch) techniques; however, long-term comparisons of the two techniques are not available. This study was conducted to assess the agreement between EC and Ch techniques when measuring CO2 ...

  10. Temporal Large-Eddy Simulation

    NASA Technical Reports Server (NTRS)

    Pruett, C. D.; Thomas, B. C.

    2004-01-01

    In 1999, Stolz and Adams unveiled a subgrid-scale model for LES based upon approximately inverting (defiltering) the spatial grid-filter operator and termed .the approximate deconvolution model (ADM). Subsequently, the utility and accuracy of the ADM were demonstrated in a posteriori analyses of flows as diverse as incompressible plane-channel flow and supersonic compression-ramp flow. In a prelude to the current paper, a parameterized temporal ADM (TADM) was developed and demonstrated in both a priori and a posteriori analyses for forced, viscous Burger's flow. The development of a time-filtered variant of the ADM was motivated-primarily by the desire for a unifying theoretical and computational context to encompass direct numerical simulation (DNS), large-eddy simulation (LES), and Reynolds averaged Navier-Stokes simulation (RANS). The resultant methodology was termed temporal LES (TLES). To permit exploration of the parameter space, however, previous analyses of the TADM were restricted to Burger's flow, and it has remained to demonstrate the TADM and TLES methodology for three-dimensional flow. For several reasons, plane-channel flow presents an ideal test case for the TADM. Among these reasons, channel flow is anisotropic, yet it lends itself to highly efficient and accurate spectral numerical methods. Moreover, channel-flow has been investigated extensively by DNS, and a highly accurate data base of Moser et.al. exists. In the present paper, we develop a fully anisotropic TADM model and demonstrate its utility in simulating incompressible plane-channel flow at nominal values of Re(sub tau) = 180 and Re(sub tau) = 590 by the TLES method. The TADM model is shown to perform nearly as well as the ADM at equivalent resolution, thereby establishing TLES as a viable alternative to LES. Moreover, as the current model is suboptimal is some respects, there is considerable room to improve TLES.

  11. Correlation of the deply technique with the ultrasonic imaging of impact damage in graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

    Smith, B. T.; Heyman, J. S.; Moore, J. G.; Cucura, S. J.; Freeman, S. M.

    1986-01-01

    A quantitative ultrasonic technique for the nondestructive assessment of impact damage is described. The method, which involves digitizing the entire backscattered ultrasonic wave from a sample, was applied to two test panels removed from a 16-ply graphite/epoxy laminate and impacted with an aluminum ball fired at a velocity of 150 ft/sec. The results of the ultrasonic NDE were compared with the results obtained using the destructive deply technique of Freeman (1984). The NDE method provides through-the-thickness information on damage and only requires access to a single side of the material, while the deply technique gives exact information on the actual damage. Good quantitative agreement between the two techniques was obtained.

  12. Eddy-Kuroshio interaction processes revealed by mooring observations off Taiwan and Luzon

    NASA Astrophysics Data System (ADS)

    Tsai, Cheng-Ju; Andres, Magdalena; Jan, Sen; Mensah, Vigan; Sanford, Thomas B.; Lien, Ren-Chieh; Lee, Craig M.

    2015-10-01

    The influence and fate of westward propagating eddies that impinge on the Kuroshio were observed with pressure sensor-equipped inverted echo sounders (PIESs) deployed east of Taiwan and northeast of Luzon. Zero lag correlations between PIES-measured acoustic travel times and satellite-measured sea surface height anomalies (SSHa), which are normally negative, have lower magnitude toward the west, suggesting the eddy-influence is weakened across the Kuroshio. The observational data reveal that impinging eddies lead to seesaw-like SSHa and pycnocline depth changes across the Kuroshio east of Taiwan, whereas analogous responses are not found in the Kuroshio northeast of Luzon. Anticyclones intensify sea surface and pycnocline slopes across the Kuroshio, while cyclones weaken these slopes, particularly east of Taiwan. During the 6 month period of overlap between the two PIES arrays, only one anticyclone affected the pycnocline depth first at the array northeast of Luzon and 21 days later in the downstream Kuroshio east of Taiwan.

  13. Retrieval of eddy dynamics from SMOS sea surface salinity measurements in the Algerian Basin (Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Isern-Fontanet, Jordi; Olmedo, Estrella; Turiel, Antonio; Ballabrera-Poy, Joaquim; García-Ladona, Emilio

    2016-06-01

    The circulation in the Algerian Basin is characterized by the presence of fresh-core eddies that propagate along the coast or at distances between 100 and 200 km from the coast. Enhancements in the processing of the Soil Moisture and Ocean Salinity (SMOS) data have allowed to produce, for the first time, satellite sea surface salinity (SSS) maps in the Mediterranean Sea that capture the signature of Algerian eddies. SMOS data can be used to track them for long periods of time, especially during winter. SMOS SSS maps are well correlated with in situ measurements although the former has a smaller dynamical range. Despite this limitation, SMOS SSS maps capture the key dynamics of Algerian eddies allowing to retrieve velocities from SSS with the correct sign of vorticity.

  14. A connection between the South Equatorial Current north of Madagascar and Mozambique Channel Eddies

    NASA Astrophysics Data System (ADS)

    Backeberg, B. C.; Reason, C. J. C.

    2010-02-01

    Combining high resolution model output and geostrophic currents derived from satellite altimeter data, it is shown that the formation of mesoscale eddies in the Mozambique Channel (MZC) is connected to variability in the transport of the South Equatorial Current (SEC). Lagged cross-correlations of the currents north of Madagascar and vorticities in the MZC, combined with a composite analysis of the model output, show that eddies form in the narrows of the channel approximately 20 weeks following a westward transport pulse in the SEC. A relationship between MZC eddies and the large-scale variability of the South Indian Ocean may have downstream impacts on the Agulhas leakage, the Atlantic Meridional overturning circulation, and thus climate.

  15. Turbulent eddies in a compressible jet in crossflow measured using pulse-burst particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Beresh, Steven J.; Wagner, Justin L.; Henfling, John F.; Spillers, Russell W.; Pruett, Brian O. M.

    2016-02-01

    Pulse-burst Particle Image Velocimetry (PIV) has been employed to acquire time-resolved data at 25 kHz of a supersonic jet exhausting into a subsonic compressible crossflow. Data were acquired along the windward boundary of the jet shear layer and used to identify turbulent eddies as they convect downstream in the far-field of the interaction. Eddies were found to have a tendency to occur in closely spaced counter-rotating pairs and are routinely observed in the PIV movies, but the variable orientation of these pairs makes them difficult to detect statistically. Correlated counter-rotating vortices are more strongly observed to pass by at a larger spacing, both leading and trailing the reference eddy. This indicates the paired nature of the turbulent eddies and the tendency for these pairs to recur at repeatable spacing. Velocity spectra reveal a peak at a frequency consistent with this larger spacing between shear-layer vortices rotating with identical sign. The spatial scale of these vortices appears similar to previous observations of compressible jets in crossflow. Super-sampled velocity spectra to 150 kHz reveal a power-law dependency of -5/3 in the inertial subrange as well as a -1 dependency at lower frequencies attributed to the scales of the dominant shear-layer eddies.

  16. Turbulent Eddies in a Compressible Jet in Crossflow Measured using Pulse-Burst PIV

    NASA Astrophysics Data System (ADS)

    Beresh, Steven; Wagner, Justin; Henfling, John; Spillers, Russell; Pruett, Brian

    2015-11-01

    Pulse-burst Particle Image Velocimetry (PIV) has been employed to acquire time-resolved data at 25 kHz of a supersonic jet exhausting into a subsonic compressible crossflow. Data were acquired along the windward boundary of the jet shear layer and used to identify turbulent eddies as they convect downstream in the far-field of the interaction. Eddies were found to have a tendency to occur in closely-spaced counter-rotating pairs and are routinely observed in the PIV movies, but the variable orientation of these pairs makes them difficult to detect statistically. Correlated counter-rotating vortices are more strongly observed to pass by at a larger spacing, both leading and trailing the reference eddy. This indicates the paired nature of the turbulent eddies and the tendency for these pairs to convect through the field of view at repeatable spacings. Velocity spectra reveal a peak at a frequency consistent with this larger spacing between shear-layer vortices rotating with identical sign. Super-sampled velocity spectra to 150 kHz reveal a power-law dependency of -5/3 in the inertial subrange as well as a -1 dependency at lower frequencies attributed to the scales of the dominant shear-layer eddies.

  17. An alternative eddy-viscosity representation and its implication to turbulence modeling

    NASA Astrophysics Data System (ADS)

    Jakirlic, Suad; Jovanovic, Jovan; Basara, Branislav

    2013-11-01

    Large majority of turbulence models in the RANS framework (it holds also in the case of the LES method) is based on the eddy-viscosity rationale. The principle task of modeling the Reynolds stress tensor reduces to modeling the eddy-viscosity, representing, according to Boussinesq (1877), the ``coefficient of proportionality'' between the Reynolds stress and mean rate of strain tensors. In the present contribution an extended formulation based on the least square approach applied to the Boussinesq's correlation is presented. Furthermore, a Taylor-microscale-based formulation is derived originating from the equilibrium assumption related to the equality between the production and dissipation rates of kinetic energy of turbulence. Finally, an expression is proposed reflecting the Reynolds stress anisotropy influence on the eddy-viscosity damping by approaching the solid wall as well as including an appropriate length-scale switch accounting for the viscosity effects through inclusion of the Kolmogorov scales blended with those of the energy-containing eddies. The latter formulation is successfully applied in the framework of an instability-sensitive Reynolds stress model of turbulence. The afore-mentioned eddy-viscosity definitions are comparatively assessed in a series of wall-bounded flow configurations (including separation) in a Reynolds number range.

  18. Calibration of diffuse correlation spectroscopy with a time-resolved near-infrared technique to yield absolute cerebral blood flow measurements.

    PubMed

    Diop, Mamadou; Verdecchia, Kyle; Lee, Ting-Yim; St Lawrence, Keith

    2011-07-01

    A primary focus of neurointensive care is the prevention of secondary brain injury, mainly caused by ischemia. A noninvasive bedside technique for continuous monitoring of cerebral blood flow (CBF) could improve patient management by detecting ischemia before brain injury occurs. A promising technique for this purpose is diffuse correlation spectroscopy (DCS) since it can continuously monitor relative perfusion changes in deep tissue. In this study, DCS was combined with a time-resolved near-infrared technique (TR-NIR) that can directly measure CBF using indocyanine green as a flow tracer. With this combination, the TR-NIR technique can be used to convert DCS data into absolute CBF measurements. The agreement between the two techniques was assessed by concurrent measurements of CBF changes in piglets. A strong correlation between CBF changes measured by TR-NIR and changes in the scaled diffusion coefficient measured by DCS was observed (R(2) = 0.93) with a slope of 1.05 ± 0.06 and an intercept of 6.4 ± 4.3% (mean ± standard error). PMID:21750781

  19. Calibration of diffuse correlation spectroscopy with a time-resolved near-infrared technique to yield absolute cerebral blood flow measurements

    PubMed Central

    Diop, Mamadou; Verdecchia, Kyle; Lee, Ting-Yim; St Lawrence, Keith

    2011-01-01

    A primary focus of neurointensive care is the prevention of secondary brain injury, mainly caused by ischemia. A noninvasive bedside technique for continuous monitoring of cerebral blood flow (CBF) could improve patient management by detecting ischemia before brain injury occurs. A promising technique for this purpose is diffuse correlation spectroscopy (DCS) since it can continuously monitor relative perfusion changes in deep tissue. In this study, DCS was combined with a time-resolved near-infrared technique (TR-NIR) that can directly measure CBF using indocyanine green as a flow tracer. With this combination, the TR-NIR technique can be used to convert DCS data into absolute CBF measurements. The agreement between the two techniques was assessed by concurrent measurements of CBF changes in piglets. A strong correlation between CBF changes measured by TR-NIR and changes in the scaled diffusion coefficient measured by DCS was observed (R2 = 0.93) with a slope of 1.05 ± 0.06 and an intercept of 6.4 ± 4.3% (mean ± standard error). PMID:21750781

  20. Corrosion Assessment of Steel Bars Used in Reinforced Concrete Structures by Means of Eddy Current Testing.

    PubMed

    de Alcantara, Naasson P; da Silva, Felipe M; Guimarães, Mateus T; Pereira, Matheus D

    2015-01-01

    This paper presents a theoretical and experimental study on the use of Eddy Current Testing (ECT) to evaluate corrosion processes in steel bars used in reinforced concrete structures. The paper presents the mathematical basis of the ECT sensor built by the authors; followed by a finite element analysis. The results obtained in the simulations are compared with those obtained in experimental tests performed by the authors. Effective resistances and inductances; voltage drops and phase angles of wound coil are calculated using both; simulated and experimental data; and demonstrate a strong correlation. The production of samples of corroded steel bars; by using an impressed current technique is also presented. The authors performed experimental tests in the laboratory using handmade sensors; and the corroded samples. In the tests four gauges; with five levels of loss-of-mass references for each one were used. The results are analyzed in the light of the loss-of-mass and show a strong linear behavior for the analyzed parameters. The conclusions emphasize the feasibility of the proposed technique and highlight opportunities for future works. PMID:26712754

  1. Eddy current characterization of small cracks using least square support vector machine

    NASA Astrophysics Data System (ADS)

    Chelabi, M.; Hacib, T.; Le Bihan, Y.; Ikhlef, N.; Boughedda, H.; Mekideche, M. R.

    2016-04-01

    Eddy current (EC) sensors are used for non-destructive testing since they are able to probe conductive materials. Despite being a conventional technique for defect detection and localization, the main weakness of this technique is that defect characterization, of the exact determination of the shape and dimension, is still a question to be answered. In this work, we demonstrate the capability of small crack sizing using signals acquired from an EC sensor. We report our effort to develop a systematic approach to estimate the size of rectangular and thin defects (length and depth) in a conductive plate. The achieved approach by the novel combination of a finite element method (FEM) with a statistical learning method is called least square support vector machines (LS-SVM). First, we use the FEM to design the forward problem. Next, an algorithm is used to find an adaptive database. Finally, the LS-SVM is used to solve the inverse problems, creating polynomial functions able to approximate the correlation between the crack dimension and the signal picked up from the EC sensor. Several methods are used to find the parameters of the LS-SVM. In this study, the particle swarm optimization (PSO) and genetic algorithm (GA) are proposed for tuning the LS-SVM. The results of the design and the inversions were compared to both simulated and experimental data, with accuracy experimentally verified. These suggested results prove the applicability of the presented approach.

  2. Corrosion Assessment of Steel Bars Used in Reinforced Concrete Structures by Means of Eddy Current Testing

    PubMed Central

    de Alcantara, Naasson P.; da Silva, Felipe M.; Guimarães, Mateus T.; Pereira, Matheus D.

    2015-01-01

    This paper presents a theoretical and experimental study on the use of Eddy Current Testing (ECT) to evaluate corrosion processes in steel bars used in reinforced concrete structures. The paper presents the mathematical basis of the ECT sensor built by the authors; followed by a finite element analysis. The results obtained in the simulations are compared with those obtained in experimental tests performed by the authors. Effective resistances and inductances; voltage drops and phase angles of wound coil are calculated using both; simulated and experimental data; and demonstrate a strong correlation. The production of samples of corroded steel bars; by using an impressed current technique is also presented. The authors performed experimental tests in the laboratory using handmade sensors; and the corroded samples. In the tests four gauges; with five levels of loss-of-mass references for each one were used. The results are analyzed in the light of the loss-of-mass and show a strong linear behavior for the analyzed parameters. The conclusions emphasize the feasibility of the proposed technique and highlight opportunities for future works. PMID:26712754

  3. Eddy Current, Magnetic Particle and Hardness Testing, Aviation Quality Control (Advanced): 9227.04.

    ERIC Educational Resources Information Center

    Dade County Public Schools, Miami, FL.

    This unit of instruction includes the principles of eddy current, magnetic particle and hardness testing; standards used for analyzing test results; techniques of operating equipment; interpretation of indications; advantages and limitations of these methods of testing; care and calibration of equipment; and safety and work precautions. Motion…

  4. Eddy stirring in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Naveira Garabato, A. C.; Ferrari, R.; Polzin, K. L.

    2011-09-01

    There is an ongoing debate concerning the distribution of eddy stirring across the Antarctic Circumpolar Current (ACC) and the nature of its controlling processes. The problem is addressed here by estimating the isentropic eddy diffusivity κ from a collection of hydrographic and altimetric observations, analyzed in a mixing length theoretical framework. It is shown that, typically, κ is suppressed by an order of magnitude in the upper kilometer of the ACC frontal jets relative to their surroundings, primarily as a result of a local reduction of the mixing length. This observation is reproduced by a quasi-geostrophic theory of eddy stirring across a broad barotropic jet based on the scaling law derived by Ferrari and Nikurashin (2010). The theory interprets the observed widespread suppression of the mixing length and κ in the upper layers of frontal jets as the kinematic consequence of eddy propagation relative to the mean flow within jet cores. Deviations from the prevalent regime of mixing suppression in the core of upper-ocean jets are encountered in a few special sites. Such `leaky jet' segments appear to be associated with sharp stationary meanders of the mean flow that are generated by the interaction of the ACC with major topographic features. It is contended that the characteristic thermohaline structure of the Southern Ocean, consisting of multiple upper-ocean thermohaline fronts separated and underlaid by regions of homogenized properties, is largely a result of the widespread suppression of eddy stirring by parallel jets.

  5. Effect of mesoscale eddies and streamers on sardine spawning habitat and recruitment success off Southern and central California

    NASA Astrophysics Data System (ADS)

    Nieto, Karen; McClatchie, Sam; Weber, Edward D.; Lennert-Cody, Cleridy E.

    2014-09-01

    We quantified the effect of mesoscale eddies and streamers on the spatial distribution of Pacific sardine spawning habitat using a merged altimetry data set and a statistical spawning habitat model. The distribution of eggs could be predicted using sea-surface temperature, chlorophyll concentration, and eddy kinetic energy (EKE) similarly to previous studies. Eddies alone did not have a significant additional or emergent effect on the probability of capturing eggs beyond these predictors. Rather, mesoscale features (eddies and streamers) entrained water with the appropriate conditions in terms of temperature, chlorophyll, and EKE. These dynamic features moved appropriate spawning habitat for sardine offshore to areas where appropriate habitat otherwise would not exist. Using centroids of predicted sardine habitat, we showed that sardine recruitment success was inversely correlated with distance from shore of predicted sardine habitat centroids. This indicates that offshore transport has a negative effect on sardine recruitment, despite expanding favorable spawning habitat further offshore.

  6. Eddy Fluxes and Sensitivity of the Water Cycle to Spatial Resolution in Idealized Regional Aquaplanet Model Simulations

    SciTech Connect

    Hagos, Samson M.; Leung, Lai-Yung R.; Gustafson, William I.; Singh, Balwinder

    2014-02-28

    A multi-scale moisture budget analysis is used to identify the mechanisms responsible for the sensitivity of the water cycle to spatial resolution using idealized regional aquaplanet simulations. In the higher resolution simulations, moisture transport by eddies fluxes dry the boundary layer enhancing evaporation and precipitation. This effect of eddies, which is underestimated by the physics parameterizations in the low-resolution simulations, is found to be responsible for the sensitivity of the water cycle both directly, and through its upscale effect, on the mean circulation. Correlations among moisture transport by eddies at adjacent ranges of scales provides the potential for reducing this sensitivity by representing the unresolved eddies by their marginally resolved counterparts.

  7. Eddy viscosity and flow properties of the solar wind: Co-rotating interaction regions, coronal-mass-ejection sheaths, and solar-wind/magnetosphere coupling

    SciTech Connect

    Borovsky, Joseph E.

    2006-05-15

    The coefficient of magnetohydrodynamic (MHD) eddy viscosity of the turbulent solar wind is calculated to be {nu}{sub eddy}{approx_equal}1.3x10{sup 17} cm{sup 2}/s: this coefficient is appropriate for velocity shears with scale thicknesses larger than the {approx}10{sup 6} km correlation length of the solar-wind turbulence. The coefficient of MHD eddy viscosity is calculated again accounting for the action of smaller-scale turbulent eddies on smaller scale velocity shears in the solar wind. This eddy viscosity is quantitatively tested with spacecraft observations of shear flows in co-rotating interaction regions (CIRs) and in coronal-mass-ejection (CME) sheaths and ejecta. It is found that the large-scale ({approx}10{sup 7} km) shear of the CIR fractures into intense narrow ({approx}10{sup 5} km) slip zones between slabs of differently magnetized plasma. Similarly, it is found that the large-scale shear of CME sheaths also fracture into intense narrow slip zones between parcels of differently magnetized plasma. Using the solar-wind eddy-viscosity coefficient to calculate vorticity-diffusion time scales and comparing those time scales with the {approx}100-h age of the solar-wind plasma at 1 AU, it is found that the slip zones are much narrower than eddy-viscosity theory says they should be. Thus, our concept of MHD eddy viscosity fails testing. For the freestream turbulence effect in solar-wind magnetosphere coupling, the eddy-viscous force of the solar wind on the Earth's magnetosphere is rederived accounting for the action of turbulent eddies smaller than the correlation length, along with other corrections. The improved derivation of the solar-wind driver function for the turbulence effect fails to yield higher correlation coefficients between measurements of the solar-wind driver and measurements of the response of the Earth's magnetosphere.

  8. Distributed fiber Brillouin strain sensing by correlation-based continuous-wave technique: cm-order spatial resolution and dynamic strain measurement

    NASA Astrophysics Data System (ADS)

    Hotate, Kazuo; Ong, Sean S.

    2002-09-01

    This paper describes a novel correlation-based technique for fiber optic distributed strain sensors using Brillouin scattering. Conventional Brillouin-based sensors utilize a pulsed-pump similar to that of OTDR and are capable of distributed strain sensing over large distances, but suffer an inherent spatial resolution limit of around 1m. In addition, unlike FBG-based strain sensors which are competent of measuring dynamic strain, the pulse-based Brillouin sensors have large measurement times of several minutes, making them inadequate for dynamic strain measurements. On the other hand, using the correlation-based continuous-wave technique, we have achieved static distributed strain measurements of up to 1cm spatial resolution, and dynamic strain measurements of up to 8.8Hz from a 5cm strained section.

  9. Procedure for Automated Eddy Current Crack Detection in Thin Titanium Plates

    NASA Technical Reports Server (NTRS)

    Wincheski, Russell A.

    2012-01-01

    This procedure provides the detailed instructions for conducting Eddy Current (EC) inspections of thin (5-30 mils) titanium membranes with thickness and material properties typical of the development of Ultra-Lightweight diaphragm Tanks Technology (ULTT). The inspection focuses on the detection of part-through, surface breaking fatigue cracks with depths between approximately 0.002" and 0.007" and aspect ratios (a/c) of 0.2-1.0 using an automated eddy current scanning and image processing technique.

  10. Finite Element Modeling of Pulsed Eddy Current Signals from Conducting Cylinders and Plates

    NASA Astrophysics Data System (ADS)

    Babbar, V. K.; Kooten, P. V.; Cadeau, T. J.; Krause, T. W.

    2009-03-01

    Pulsed eddy current technique is being developed for detection of flaws located at depth within conducting structures. The present work investigates the pulsed eddy current response from cylindrical and flat-plate conductors by using finite element modeling employing COMSOL Multiphysics commercial package. The benchmark case of a driver/pick-up coil configuration encircling a solid conducting cylinder is used to model the transient electromagnetic response of cylinders of different diameters and lengths. A good comparison with experimental results validates the model. The work was extended to model a planar coil response to flat-plate aluminum structures.

  11. Correlative Förster Resonance Electron Transfer-Proximity Ligation Assay (FRET-PLA) Technique for Studying Interactions Involving Membrane Proteins.

    PubMed

    Ivanusic, Daniel; Denner, Joachim; Bannert, Norbert

    2016-01-01

    This unit provides a guide and detailed protocol for studying membrane protein-protein interactions (PPI) using the acceptor-sensitized Förster resonance electron transfer (FRET) method in combination with the proximity ligation assay (PLA). The protocol in this unit is focused on the preparation of FRET-PLA samples and the detection of correlative FRET/PLA signals as well as on the analysis of FRET-PLA data and interpretation of correlative results when using cyan fluorescent protein (CFP) as a FRET donor and yellow fluorescent protein (YFP) as a FRET acceptor. The correlative application of FRET and PLA combines two powerful tools for monitoring PPI, yielding results that are more reliable than with either technique alone. © 2016 by John Wiley & Sons, Inc. PMID:27479505

  12. Eddy analysis in the Eastern China Sea using altimetry data

    NASA Astrophysics Data System (ADS)

    Qin, Dandi; Wang, Jianhong; Liu, Yu; Dong, Changming

    2015-12-01

    Statistical characteristics of mesoscale eddies in the Eastern China Sea (ECS) are analyzed using altimetry sea surface height anomaly (SSHA) data from 1993 to 2010. A velocity geometry-based automated eddy detection scheme is employed to detect eddies from the SSHA data to generate an eddy data set. About 1,096 eddies (one lifetime of eddies is counted as one eddy) with a lifetime longer than or equal to 4 weeks are identified in this region. The average lifetime and radius of eddies are 7 weeks and 55 km, respectively, and there is no significant difference between cyclonic eddies (CEs) and anticyclonic eddies (AEs) in this respect. Eddies' lifetimes are generally longer in deep water than in shallow water. Most eddies propagate northeastward along the Kuroshio (advected by the Kuroshio), with more CEs generated on its western side and AEs on its eastern side. The variation of the Kuroshio transport is one of the major mechanisms for eddy genesis, however the generation of AEs on the eastern side of the Kuroshio (to the open ocean) is also subject to other factors, such as the wind stress curl due to the presence of the Ryukyu Islands and the disturbance from the open ocean.

  13. Estimation of rainfall interception in grassland using eddy flux measurements

    NASA Astrophysics Data System (ADS)

    Maruyama, A.; Miyazawa, Y.; Inoue, A.

    2014-12-01

    Rainfall interception plays an important role in the water cycle in natural ecosystems. Interception by the forest canopies have been widely observed or estimated over various ecosystems, such as tropical rainforest, evergreen forest and deciduous forest. However interception by the short canopies, e.g. shrubby plant, grassland and crop, has been rarely observed since it has been difficult to obtain reliable precipitation measurements under the canopy. In this study, we estimated monthly and annual rainfall interception in grassland using evapotranspiration data of eddy flux measurements. Experiments were conducted in grassland (Italian ryegrass) from 2010 to 2012 growing season in Kumamoto, Japan. Evapotranspiration (latent heat flux) were observed throughout the year based on the eddy covariance technique. A three dimensional sonic anemometer and an open path CO2/H2O analyzer were used to calculate 30 min flux. Other meteorological factors, such as air temperature, humidity and solar radiation, were also observed. Rainfall interception was estimated as follows. 1) Using evapotranspiration data during dry period, environmental response of surface conductance (gc) was inversely calculated based on the big-leaf model. 2) Evapotranspiration without interception during precipitation period was estimated using above model and environmental response of gc. 3) Assuming that evaporation of intercepted rainfall is equal to the difference in evapotranspiration between above estimation and actual measurements, rainfall interception was estimated over experimental period. The account of rainfall interception in grassland using this technique will be presented at the meeting.

  14. Anticyclonic eddy energy and pathways in the Algerian basin (1993-2007)

    NASA Astrophysics Data System (ADS)

    Pessini, Federica; Perilli, Angelo; Olita, Antonio

    2016-04-01

    use in the study area. This automated method allowed the investigation of mesoscale eddy variability using several years (1993-2007) of satellite altimetry observations. To verify the reliability of the technique, we compared the eddy pathways derived from the application of the modified Penven method with independent observations. Preliminary results suggest that AEs, moving anticlockwise within the sub-basin, complete as many as two or three laps, depending on their lifetime, following the Algerian Gyre path. We suppose that AEs acquire kinetic energy from the Algerian current, occasionally in sufficient magnitude to cause their detachment. This phenomenon mainly takes place near the Sardinian Channel. Eddies formed on the thermal front, called Frontal Anticyclonic Eddies (FAEs), remain localized in the northern part of the sub-basin and have lower energy and shorter life than AEs. They usually don't interact with AEs. Basic statistics on eddy trajectories and energy characteristics allow the evaluation of these mesoscale structures' relevance of on (sub-) basin circulation.

  15. Long-lived mesoscale eddies in the eastern Mediterranean Sea: Analysis of 20 years of AVISO geostrophic velocities

    NASA Astrophysics Data System (ADS)

    Mkhinini, Nadia; Coimbra, Andre Louis Santi; Stegner, Alexandre; Arsouze, Thomas; Taupier-Letage, Isabelle; Béranger, Karine

    2014-12-01

    We analyzed 20 years of AVISO data set to detect and characterize long-lived eddies, which stay coherent more than 6 months, in the eastern Mediterranean Sea. In order to process the coarse gridded (1/8°) AVISO geostrophic velocity fields, we optimized a geometrical eddy detection algorithm. Our main contribution was to implement a new procedure based on the computation of the Local and Normalized Angular Momentum (LNAM) to identify the positions of the eddy centers and to follow their Lagrangian trajectories. We verify on two mesoscale anticyclones, sampled during the EGYPT campaign in 2006, that our methodology provides a correct estimation of the eddy centers and their characteristic radius corresponding to the maximal tangential velocity. Our analysis reveals the dominance of anticyclones among the long-lived eddies. This cyclone-anticyclone asymmetry appears to be much more pronounced in eastern Mediterranean Sea than in the global ocean. Then we focus our study on the formation areas of long-lived eddies. We confirm that the generations of the Ierapetra and the Pelops anticyclones are recurrent and correlated to the Etesian wind forcing. We also provide some evidence that the smaller cyclonic eddies formed at the southwest of Crete may also be induced by the same wind forcing. On the other hand, the generation of long-lived eddies along the Libyo-Egyptian coast are not correlated to the local wind-stress curl but surprisingly, their initial formation points follow the Herodotus Trough bathymetry. Moreover, we identify a new formation area, not discussed before, along the curved shelf off Benghazi.

  16. Toward finding a universally applicable parameterization of the β factor for Relaxed Eddy Accumulation applications

    NASA Astrophysics Data System (ADS)

    Vogl, Teresa; Hrdina, Amy; Thomas, Christoph

    2016-04-01

    -dioxide, latent and sensible heat fluxes across the contrasting environments. First, the choice of an appropriate scalar to calculate β0 is discussed considering the sources and sinks of each scalar with an emphasis on the carbon dioxide flux, which shows strongly dissimilar dynamics between the Antarctic ecosystem and the grassland. Secondly, the impact of atmospheric stability on both β models is investigated. In a next step, we attempt to find a physically meaningful explanation for the overestimation of the REA scalar fluxes compared to those from EC for using βw. We do so by analyzing the probability density function (pdf) and its statistical moments for the vertical wind speed. We found its pdf to be non-Gaussian for the majority of cases, and detected a close to linear relationship of its kurtosis with βw. Finally, in an attempt to provide practical guidance for field measurements, we integrate our findings and propose an enhanced model parameterization, and evaluate the differences between our new model and a constant β. Ammann, C. and Meixner, F.X. (2002) Stability dependence of the relaxed eddy accumulation coefficient for various scalar quantities. J. Geophys. Res. 107. ACL7.1-ACL7.9 doi:10.1029/2001JD000649 Businger, J.A., Oncley, S.P. (1990) Flux measurement with conditional sampling. J. Atmos. Ocean. Tech. 7:349-352. Desjardins, R. L. (1972) A study of carbon-dioxide and sensible heat fluxes using the eddy correlation technique, Ph.D. dissertation, Cornell University, 189 pp. Desjardins, R.L. (1977) Description and evaluation of sensible heat flux detector. Boundary-Layer Meteorol. 11:147-154. Katul, G., Finkelstein, P. L., Clarke, J. F., and Ellestad, T. G. (1996) An Investigation of the Conditional Sampling Methods Used to Estimate Fluxes of Active, Reactive and Passive Scalars. J. Appl. Meteorol. 35: 1835-1845. Milne, R., Beverland, I. J., Hargreaves, K., and Moncrieff, J. B. (1999) Variation of the beta coefficient in the relaxed eddy accumulation method

  17. An advanced synthetic eddy method for the computation of aerofoil-turbulence interaction noise

    NASA Astrophysics Data System (ADS)

    Kim, Jae Wook; Haeri, Sina

    2015-04-01

    This paper presents an advanced method to synthetically generate flow turbulence via an inflow boundary condition particularly designed for three-dimensional aeroacoustic simulations. The proposed method is virtually free of spurious noise that might arise from the synthetic turbulence, which enables a direct calculation of propagated sound waves from the source mechanism. The present work stemmed from one of the latest outcomes of synthetic eddy method (SEM) derived from a well-defined vector potential function creating a divergence-free velocity field with correct convection speeds of eddies, which in theory suppresses pressure fluctuations. In this paper, a substantial extension of the SEM is introduced and systematically optimised to create a realistic turbulence field based on von Kármán velocity spectra. The optimised SEM is then combined with a well-established sponge-layer technique to quietly inject the turbulent eddies into the domain from the upstream boundary, which results in a sufficiently clean acoustic field. Major advantages in the present approach are: a) that genuinely three-dimensional turbulence is generated; b) that various ways of parametrisation can be created to control/characterise the randomly distributed eddies; and, c) that its numerical implementation is efficient as the size of domain section through which the turbulent eddies should be passing can be adjusted and minimised. The performance and reliability of the proposed SEM are demonstrated by a three-dimensional simulation of aerofoil-turbulence interaction noise.

  18. Quantification and compensation of eddy-current-induced magnetic-field gradients.

    PubMed

    Spees, William M; Buhl, Niels; Sun, Peng; Ackerman, Joseph J H; Neil, Jeffrey J; Garbow, Joel R

    2011-09-01

    Two robust techniques for quantification and compensation of eddy-current-induced magnetic-field gradients and static magnetic-field shifts (ΔB0) in MRI systems are described. Purpose-built 1-D or six-point phantoms are employed. Both procedures involve measuring the effects of a prior magnetic-field-gradient test pulse on the phantom's free induction decay (FID). Phantom-specific analysis of the resulting FID data produces estimates of the time-dependent, eddy-current-induced magnetic field gradient(s) and ΔB0 shift. Using Bayesian methods, the time dependencies of the eddy-current-induced decays are modeled as sums of exponentially decaying components, each defined by an amplitude and time constant. These amplitudes and time constants are employed to adjust the scanner's gradient pre-emphasis unit and eliminate undesirable eddy-current effects. Measurement with the six-point sample phantom allows for simultaneous, direct estimation of both on-axis and cross-term eddy-current-induced gradients. The two methods are demonstrated and validated on several MRI systems with actively-shielded gradient coil sets. PMID:21764614

  19. A non-monotonic eddy diffusivity profile of Titan's atmosphere revealed by Cassini observations

    NASA Astrophysics Data System (ADS)

    Li, Cheng; Zhang, Xi; Kammer, Joshua A.; Liang, Mao-Chang; Shia, Run-Lie; Yung, Yuk L.

    2014-12-01

    Recent measurements from the limb-view soundings of Cassini/CIRS and the stellar occultations from Cassini/UVIS revealed the complete vertical profiles of minor species (e.g., C2H2 and C2H4) from 100 to 1000 km in the atmosphere of Titan. In this study, we developed an inversion technique to retrieve the eddy diffusion profile using C2H2 as a tracer species. The retrieved eddy profile features a low eddy diffusion zone near the altitude of the detached haze layer (~ 550 km), which could be a consequence of stabilization through aerosol heating. Photochemical modeling results using the retrieved eddy profile are in better agreement with the Cassini measurements than previous models. The underestimation of C2H4 in the stratosphere has been a long-standing problem in planetary photochemical modeling, and the new eddy diffusion profile does not solve this problem. In order to match the observations, we suggest a new expression for the rate coefficient of the key reaction, H +C2H4 + M ⟶C2H5 + M. The new reaction rate coefficient is estimated to be ~ 10 times lower than that used by Moses et al. (2005)'s model, and should be validated in the laboratory and tested against the hydrocarbon chemistry of giant planets.

  20. Deep Eddies in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Furey, H. H.; Bower, A. S.; Perez-Brunius, P.; Hamilton, P.

    2014-12-01

    A major Lagrangian program is currently underway to map the deep (1500-2500 m) circulation of the entire Gulf of Mexico. Beginning in 2011, more than 120 acoustically tracked RAFOS floats have been released in the eastern, central and western Gulf, many in pairs and triplets. Most floats are programmed to drift for two years, obtaining position fixes and temperature/pressure measurements three times daily. More than 80 floats have completed their missions, and results from the trajectories will be described with a focus on mesoscale eddying behavior. In particular, the first-ever observations of deep energetic anticyclonic eddies (possibly lenses) forming at and separating from a northeastward-flowing boundary current west of Campeche Bank will be discussed. The existence of these eddies has major implications for exchange between the continental slope and interior Gulf. The project is being supported by the U.S. Bureau of Ocean Energy Management (BOEM).

  1. Analysis of a California Catalina eddy event

    NASA Technical Reports Server (NTRS)

    Bosart, L. F.

    1983-01-01

    During the period 26-29 May 1968 a shallow cyclonic circulation, known locally as a Catalina eddy, developed in the offshore waters of southern California. A synoptic and mesoscale analysis of the event establishes the following: (1) the incipient circulation forms on the coast near Santa Barbara downwind of the coastal mountains, (2) cyclonic shear vorticity appears offshore in response to lee troughing downstream of the coastal mountains between Vandenberg and Pt. Mugu, California, (3) mountain wave activity may be aiding incipient eddy formation in association with synoptic-scale subsidence and the generation of a stable layer near the crest of the coastal mountains, (4) a southeastward displacement and offshore expansion of the circulation occurs following the passage of the synoptic-scale ridge line, and (5) dissipation of the eddy occurs with the onset of a broad onshore flow.

  2. Solitonlike solutions in loop current eddies

    NASA Technical Reports Server (NTRS)

    Nakamoto, Shoichiro

    1989-01-01

    The application of the nonlinear quasi-geostrophic equations to an isolated eddy in the western continental slope region in the Gulf of Mexico is examined for a two-layer ocean model with bottom topography. In the linear limit, solutions are topographic nondispersive waves. Form-preserving solutions, or solitons, have been found. The solution is shown to be a limiting form for a nonlinear dispersive system propagating northward along the topographic waveguide in the western continental slope region in the Gulf of Mexico. Using satellite-tracked drifter data, a linear relationship is found between the amplitude of the deduced stream function of the eddy and its observed translational velocity over the continental slope, which supports the hypothesis that some mesoscale eddies interacting with the continental slope behave as solitons.

  3. Improving the Correction of Eddy Current-Induced Distortion in Diffusion-Weighted Images by Excluding Signals from the Cerebral Spinal Fluid

    PubMed Central

    Liu, Wei; Liu, Xiaozheng; Yang, Guang; Zhou, Zhenyu; Zhou, Yongdi; Li, Gengying; Dubin, Marc; Bansal, Ravi; Peterson, Bradley. S.; Xu, Dongrong

    2012-01-01

    Iterative Cross-Correlation (ICC) is the most popularly used schema for correcting eddy current (EC)-induced distortion in diffusion-weighted imaging data, however, it cannot process data acquired at high b-values. We analyzed the error sources and affecting factors in parameter estimation, and propose an efficient algorithm by expanding the ICC framework with a number of techniques: (1) Pattern recognition for excluding brain ventricles; (2) ICC with the extracted ventricle for parameter initialization; (3) Gradient-based Entropy Correlation Coefficient (GECC) for optimal and finer registration. Experiments demonstrated that our method is robust with high accuracy and error tolerance, and outperforms other ICC-family algorithms and popular approaches currently in use. PMID:22835646

  4. Development and Application of Wide Bandwidth Magneto-Resistive Sensor Based Eddy Current Probe

    NASA Technical Reports Server (NTRS)

    Wincheski, Russell A.; Simpson, John

    2010-01-01

    The integration of magneto-resistive sensors into eddy current probes can significantly expand the capabilities of conventional eddy current nondestructive evaluation techniques. The room temperature solid-state sensors have typical bandwidths in the megahertz range and resolutions of tens of microgauss. The low frequency sensitivity of magneto-resistive sensors has been capitalized upon in previous research to fabricate very low frequency eddy current sensors for deep flaw detection in multilayer conductors. In this work a modified probe design is presented to expand the capabilities of the device. The new probe design incorporates a dual induction source enabling operation from low frequency deep flaw detection to high frequency high resolution near surface material characterization. Applications of the probe for the detection of localized near surface conductivity anomalies are presented. Finite element modeling of the probe is shown to be in good agreement with experimental measurements.

  5. Evaluation and field validation of Eddy-Current array probes for steam generator tube inspection

    SciTech Connect

    Dodd, C.V.; Pate, J.R.

    1996-07-01

    The objective of the Improved Eddy-Current ISI for Steam Generator Tubing program is to upgrade and validate eddy-current inspections, including probes, instrumentation, and data processing techniques for inservice inspection of new, used, and repaired steam generator tubes; to improve defect detection, classification, and characterization as affected by diameter and thickness variations, denting, probe wobble, tube sheet, tube supports, copper and sludge deposits, even when defect types and other variables occur in combination; to transfer this advanced technology to NRC`s mobile NDE laboratory and staff. This report describes the design of specialized high-speed 16-coil eddy-current array probes. Both pancake and reflection coils are considered. Test results from inspections using the probes in working steam generators are given. Computer programs developed for probe calculations are also supplied.

  6. Computer programs for the acquisition and analysis of eddy-current array probe data

    SciTech Connect

    Pate, J.R.; Dodd, C.V.

    1996-07-01

    Objective of the Improved Eddy-Curent ISI (in-service inspection) for Steam Generators Tubing program is to upgrade and validate eddy-current inspections, including probes, instrumentation, and data processing techniques for ISI of new, used, and repaired steam generator tubes; to improve defect detection, classification and characterization as affected by diameter and thickness variations, denting, probe wobble, tube sheet, tube supports, copper and sludge deposits, even when defect types and other variables occur in combination; to transfer this advanced technology to NRC`s mobile NDE laboratory and staff. This report documents computer programs that were developed for acquisition of eddy-current data from specially designed 16-coil array probes. Complete code as well as instructions for use are provided.

  7. Digital volume correlation and micro-CT: An in-vitro technique for measuring full-field interface micromotion around polyethylene implants.

    PubMed

    Sukjamsri, Chamaiporn; Geraldes, Diogo M; Gregory, Thomas; Ahmed, Farah; Hollis, David; Schenk, Samuel; Amis, Andrew; Emery, Roger; Hansen, Ulrich

    2015-09-18

    Micromotion around implants is commonly measured using displacement-sensor techniques. Due to the limitations of these techniques, an alternative approach (DVC-μCT) using digital volume correlation (DVC) and micro-CT (μCT) was developed in this study. The validation consisted of evaluating DVC-μCT based micromotion against known micromotions (40, 100 and 150 μm) in a simplified experiment. Subsequently, a more clinically realistic experiment in which a glenoid component was implanted into a porcine scapula was carried out and the DVC-μCT measurements during a single load cycle (duration 20 min due to scanning time) was correlated with the manual tracking of micromotion at 12 discrete points across the implant interface. In this same experiment the full-field DVC-μCT micromotion was compared to the full-field micromotion predicted by a parallel finite element analysis (FEA). It was found that DVC-μCT micromotion matched the known micromotion of the simplified experiment (average/peak error=1.4/1.7 μm, regression line slope=0.999) and correlated with the micromotion at the 12 points tracked manually during the realistic experiment (R(2)=0.96). The DVC-μCT full-field micromotion matched the pattern of the full-field FEA predicted micromotion. This study showed that the DVC-μCT technique provides sensible estimates of micromotion. The main advantages of this technique are that it does not damage important parts of the specimen to gain access to the bone-implant interface, and it provides a full-field evaluation of micromotion as opposed to the micromotion at just a few discrete points. In conclusion the DVC-μCT technique provides a useful tool for investigations of micromotion around plastic implants. PMID:26113290

  8. Assessment of Mixed Layer Mesoscale Parameterization in Eddy Resolving Simulations.

    NASA Astrophysics Data System (ADS)

    Clayson, C. A.; Luneva, M. V.; Dubovikov, M. S.

    2014-12-01

    In eddy resolving simulations we test a mixed layer mesoscale parameterization, developed recently by Canuto and Dubovikov (2011). The parameterization yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy. An expression for the later in terms of mean fields has been found too to get a closed parameterization in terms of the mean fields only. In 40 numerical experiments we simulated the two types of flows: idealized flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow in shallow and narrow straits. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1o - 2o and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are highly correlated with the parameterization. After averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations, are quite consistent with the parameterization for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parameterization unless vertical turbulent mixing in the upper layer becomes strong enough to compare with mesoscale advection. In the later case, numerical simulations demonstrate that the deviation of the fluxes from the parameterization is controlled by the dimensionless parameter γ, estimating the ratio of vertical diffusion term to a mesoscale advection. The empirical dependence of vertical flux on γ is found. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.

  9. Binary phase masks on self-developing photopolymers: the technique for formation and testing in an optical correlator

    SciTech Connect

    Yezhov, P V; Il'in, O A; Smirnova, T N; Tikhonov, E A

    2003-06-30

    Binary phase masks (PMs) of size 256x256 cells with a random distribution of elements, formed on the self-developing FPK-488 photopolymer, are studied. The masks were prepared by the projection method using amplitude transparencies. The phase shift between the mask elements corresponding to the regions of the amplitude transparency with the optical density D = 0 and 2 was (0.85{+-}0.05){pi} at the wavelength of 0.633 {mu}m. Holographic matched filters were recorded for PMs obtained. The diffraction efficiency of holographic matched PM filters was 40 %. The signal-to-noise ratio for recognition signals for PMs in the Vander Lugt correlator was 20 dB. The normalised power density of the recognition signal is studied as a function of the rotation angle of a PM in the input plane of the Vander Lugt correlator. (laser applications and other topics in quantum electronics)

  10. Tracking the PRIME eddy using satellite altimetry

    NASA Astrophysics Data System (ADS)

    Wade, Ian P.; Heywood, Karen J.

    The PRIME cruise to the North Atlantic during June/July 1996 surveyed and sampled an extremely vigorous and deep-reaching eddy with a significant barotropic component. Although it exhibited anticyclonic flow and featured a warm core at depth, it had been capped at some point during its lifetime, so appeared as a cold feature in the upper 500 m. Satellite-derived sea-surface temperatures (SST) showed it to have moved little during the few weeks prior to the cruise. In this paper we discuss the origin of the PRIME eddy including where and when it is likely to have formed. Consistently large amounts of cloud cover restrict the use of SST imagery to track such features. Altimetry provides a better method to trace this eddy back in time and space since microwave radiation is not significantly affected by cloud cover. Sea-level anomaly (SLA) data from the TOPEX/POSEIDON and European Remote Sensing (ERS) satellites were used. Results show that the eddy remained almost stationary in the Iceland Basin since first being detected in late 1995 and that it almost certainly formed locally, probably as a result of an instability in the current flow around the northwest of the Hatton Bank. Comparisons between satellite SLAs and hydrographic estimates of sea-surface elevation confirm that the eddy had a substantial barotropic flow. Both the altimeter data and the sea-surface height derived from the acoustic Doppler current profiler agree that the PRIME eddy had a sea-surface elevation of about 20 cm and that its diameter was about 120 km.

  11. Projected changes of wintertime synoptic-scale transient eddy activities in the East Asian eddy-driven jet from CMIP5 experiments

    NASA Astrophysics Data System (ADS)

    Xiao, Chuliang; Zhang, Yaocun

    2015-07-01

    The wintertime East Asian eddy-driven jet (EAEJ) responding to climate change in the 21st century is studied using model outputs from the Coupled Model Intercomparison Project phase 5 (CMIP5). Compared to the location displacement in oceanic eddy-driven jets, the magnitude change of synoptic-scale transient eddy activities, measured by eddy kinetic energy (EKE), is a more striking feature in EAEJ. An intensified EKE is projected unanimously by CMIP5 models, suggesting that potential strong winter storm events are likely to happen in East Asian midlatitude in a warming climate. The future change of EKE in EAEJ can be understood in terms of growing baroclinicity wave. The upper level EKE is highly correlated to the low-level static stability, Brunt-Väisälä frequency (BVF). CMIP5 models generally project an intensified upper evel EKE with a reduced low-level BVF (ΔEKE ∝ -ΔBVF). Meanwhile, the enhancement of EKE is also constrained by its historical state (ΔEKE ∝ -EKE). Intermodel variabilities among CMIP5 models reveal a similar but weaker relationship between ΔBVF (or EKE) and ΔEKE, indicating relatively large model diversities and independencies among CMIP5 models.

  12. Development of a Field Concentrator Coil by Finite Element Modeling for Power Efficiency Optimization in Eddy Current Thermography Inspection

    NASA Astrophysics Data System (ADS)

    Grenier, M.; Ibarra-Castanedo, C.; Luneau, F.; Bendada, H.; Maldague, X.

    2010-02-01

    Eddy current thermography is a relatively new inspection technique that takes advantage of the electromagnetic induction phenomenon to generate heat in electro conductive materials during inspection. An interesting advantage of eddy current heating compared to classical optical or ultrasonic heating is that the excitation source is smaller and can be conveniently shaped in order to provide energy efficient localized heating. Such excitation source is more suitable for the development of portable instruments and to perform field inspections. In this paper, finite element modeling (FEM) is used to optimize the eddy current coil configuration in terms of heating power efficiency. The performances of air-core coils, normally used in eddy current thermography, and a new field concentrator coil are compared and discussed. FEM results demonstrate that the proposed field concentrator coil improves the magnetic coupling with the inspected material and requires less energy than air-core coils to generate the same temperature variation.

  13. Visualization and analysis of eddies in a global ocean simulation

    SciTech Connect

    Williams, Sean J; Hecht, Matthew W; Petersen, Mark; Strelitz, Richard; Maltrud, Mathew E; Ahrens, James P; Hlawitschka, Mario; Hamann, Bernd

    2010-10-15

    Eddies at a scale of approximately one hundred kilometers have been shown to be surprisingly important to understanding large-scale transport of heat and nutrients in the ocean. Due to difficulties in observing the ocean directly, the behavior of eddies below the surface is not very well understood. To fill this gap, we employ a high-resolution simulation of the ocean developed at Los Alamos National Laboratory. Using large-scale parallel visualization and analysis tools, we produce three-dimensional images of ocean eddies, and also generate a census of eddy distribution and shape averaged over multiple simulation time steps, resulting in a world map of eddy characteristics. As expected from observational studies, our census reveals a higher concentration of eddies at the mid-latitudes than the equator. Our analysis further shows that mid-latitude eddies are thicker, within a range of 1000-2000m, while equatorial eddies are less than 100m thick.

  14. Characterization of eddy current distortion effects on magnetic resonance axonography of human brain

    NASA Astrophysics Data System (ADS)

    Elshafiey, Ibrahim; Narayana, Ponnada A.

    2002-05-01

    Axonography of human brain, based on diffusion tensor magnetic resonance imaging (DT-MRI), has recently gained popularity because of its potential in providing crucial information about intercommunication between different regions of brain. This technique exploits the sensitivity of MRI to random water diffusion in tissues in the presence of diffusion gradient pulses incorporated into the imaging sequence. Large diffusion weighting that is necessary for the generation of axonography with high SNR is achieved by increasing the magnitude of diffusion pulses. However large diffusion gradients induce strong eddy currents in the metallic structure of the cryostat that houses the superconducting coil of the scanner magnet, resulting in distortion of magnetic resonance images. The purpose of this study was to characterize the effect of eddy currents on images obtained using the DT-MRI of human brain. Characterization of eddy current effects is essential for optimizing the scanning parameters and improving image quality. All MRI studies were performed on 1.5-T GE scanner, using single shot diffusion weighed echo planar imaging sequence. All acquisitions were cardiac gated for minimizing the pulsation effect of cerebrospinal fluid (CSF) on the images. Diffusion gradient- or b-space was explored using a set of 62 directions along the two poles, and 60 other directions. Total scan time was less than three minutes. The exploration of the b-space helps quantify the relationship between the orientation of diffusion gradients and eddy current levels. Experimental results demonstrate that certain directions are more prone to eddy current-induced image distortions. Determining the optimum gradient directions should present a powerful technique for reducing eddy current distortion, and thus enhance the use of MRI axonography for a noninvasive assessment of human brain.

  15. Application of finite element models to eddy current probe design for aircraft inspection

    NASA Astrophysics Data System (ADS)

    Sharma, Sarit

    Eddy current nondestructive testing (NDT) methods are used extensively in the inspection of aircraft structures. Improvements and innovations in probe design are constantly required for detection of flaws in complex multilayer aircraft structures. This thesis investigates alternate designs of eddy current probes for addressing some of these problems. An important aspect of probe design is the capability to simulate probe performance. Numerical computation and visualization of the electromagnetic fields can provide valuable insight into the design of new probes. Finite element methods have been used in this dissertation to numerically compute the electromagnetic fields associated with the probe coils, and the eddy current probe signals. A major contribution of this thesis is development of techniques to reduce the computer resource requirement in the finite element modeling: of the eddy current phenomenon. The first flaw detection problem is addressed by focusing the flux of the probe using active compensation techniques. A novel eddy current probe using a combination of coils is proposed and studied using: the 3D model simulation. The probe consists of two current carrying concentric coils to detect flaws closer to the sample edges. Detection of defects in second and third layer of samples has been demonstrated using: the remote field eddy current (RFEC) method. In the RFEC method the pickup coils are located in the far field region which leads to a large volume to be modeled numerically with large number of elements. A method involving partitioning the volume in the 3D finite element model is demonstrated for the RFEC detection of defects. Magneto-optic/eddy current imaging (MOI) techniques have shown considerable promise in the detection of corrosion in the second layer. MOI is a nondestructive testing method currently in use in aircraft frame inspection and it involves optically sensing the magnetic field induced by the eddy currents in the test sample. A

  16. Determination of linear defect depths from eddy currents disturbances

    NASA Astrophysics Data System (ADS)

    Ramos, Helena Geirinhas; Rocha, Tiago; Pasadas, Dário; Ribeiro, Artur Lopes

    2014-02-01

    One of the still open problems in the inspection research concerns the determination of the maximum depth to which a surface defect goes. Eddy current testing being one of the most sensitive well established inspection methods, able to detect and characterize different type of defects in conductive materials, is an adequate technique to solve this problem. This paper reports a study concerning the disturbances in the magnetic field and in the lines of current due to a machined linear defect having different depths in order to extract relevant information that allows the determination of the defect characteristics. The image of the eddy currents (EC) is paramount to understand the physical phenomena involved. The EC images for this study are generated using a commercial finite element model (FLUX). The excitation used produces a uniform magnetic field on the plate under test in the absence of defects and the disturbances due to the defects are compared with those obtained from experimental measurements. In order to increase the limited penetration depth of the method giant magnetoresistors (GMR) are used to lower the working frequency. The geometry of the excitation planar coil produces a uniform magnetic field on an area of around the GMR sensor, inducing a uniform eddy current distribution on the plate. In the presence of defects in the material surface, the lines of currents inside the material are deviated from their uniform direction and the magnetic field produced by these currents is sensed by the GMR sensor. Besides the theoretical study of the electromagnetic system, the paper describes the experiments that have been carried out to support the theory and conclusions are drawn for cracks having different depths.

  17. Ultra High Precision Laser Monitor for Oxygen Eddy Flux Measurements

    NASA Astrophysics Data System (ADS)

    Nelson, David; Herndon, Scott; McManus, Barry; Roscioli, Rob; Jervis, Dylan; Zahniser, Mark

    2016-04-01

    Atmospheric oxygen provides one of the most powerful tracers to study the carbon cycle through its close interaction with carbon dioxide. Keeling and co-workers demonstrated this at the global scale by using small variations in atmospheric oxygen content to disentangle oceanic and terrestrial carbon sinks. It would be very exciting to apply similar ideas at the ecosystem level to improve our understanding of biosphere-atmosphere exchange and our ability to predict the response of the biosphere and atmosphere to climate change. The eddy covariance technique is perhaps the most effective approach available to quantify the exchange of gases between these spheres. Therefore, eddy covariance flux measurements of oxygen would be extremely valuable. However, this requires a fast response (0.1 seconds), high relative precision (0.001% or 10 per meg) oxygen sensor. We report recent progress in developing such a sensor using a high resolution visible laser to probe the oxygen A-band electronic transition. We have demonstrated precision of 1 ppmv or 5 per meg for a 100 second measurement duration. This sensor will enable oxygen flux measurements using eddy covariance. In addition, we will incorporate a second laser in this instrument to simultaneously determine the fluxes of oxygen, carbon dioxide and water vapor within the same sampling cell. This will provide a direct, real time measurement of the ratio of the flux of oxygen to that of carbon dioxide. This ratio is expected to vary on short time scales and small spatial scales due to the differing stoichiometry of processes producing and consuming carbon dioxide. Thus measuring the variations in the ratio of oxygen and carbon dioxide fluxes will provide mechanistic information to improve our understanding of the crucial exchange of carbon between the atmosphere and biosphere.

  18. Application of Neutron Correlation Techniques to Warhead Authentication: Feasibility and Conceptual Requirements?Monte Carlo Simulations and Statistical Analysis

    SciTech Connect

    Frank, M I; Wolford, J K

    2004-08-05

    We explore the feasibility of using Feynman moments as attributes of fissile material in warhead authentication measurements. We present results of computer simulations of neutron correlation measurements to validate and inform the application of the method to measurements in an arms control scenario. We establish the robustness of the method for use in automated measuring equipment that protects classified or sensitive data using an information barrier. Drawing from our results, we define high-level requirements to govern the design process, and guide the construction of a prototype.

  19. Flaw Imaging Using the Massively Multiplexed Eddy Current Technique

    SciTech Connect

    Hils, C.M.; Brown, D.J.

    2004-02-26

    This paper details an investigation into using up to 32 frequencies to characterize defects originating from the outside diameter of a tube. Measurements are made from the inside diameter. Analysis of the data will show that this approach offers at least two methods for using the +Point registered coil for defect depth estimation. One method is referenced against the bobbin probe. The other method involves defect imaging and phase analysis.

  20. Two contra-rotating eddies of the Mozambique Ridge Current

    NASA Astrophysics Data System (ADS)

    Gründlingh, Marten L.

    1989-01-01

    The combined existence of a cyclonic and anticyclonic eddy pair on the Mozambique Ridge tends to confirm the hypothesis that they are created by a westward-flowing Mozambique Ridge Current. The eddies are mutually comparable in size but smaller than cyclonic eddies previously observed in the region.

  1. Gulf Stream eddies - Recent observations in the western Sargasso Sea.

    NASA Technical Reports Server (NTRS)

    Richardson, P. L.; Knauss, J. A.; Strong, A. E.

    1973-01-01

    A cyclonic Gulf Stream eddy was observed in the western Sargasso Sea by satellite infrared measurements and later confirmed by ship measurements. Fourteen months of observations indicate that the eddy moved southwestward at an average rate of 1 mile per day. The evidence suggests that the eddy was absorbed by the Gulf Stream off Florida.

  2. The influence of eddy currents on magnetic actuator performance

    NASA Technical Reports Server (NTRS)

    Zmood, R. B.; Anand, D. K.; Kirk, J. A.

    1987-01-01

    The present investigation of the effects of eddy currents on EM actuators' transient performance notes that a transfer function representation encompassing a first-order model of the eddy current influence can be useful in control system analysis. The method can be extended to represent the higher-order effects of eddy currents for actuators that cannot be represented by semiinfinite planes.

  3. Eddy-Current Inspection Of Graphite-Fiber Composites

    NASA Technical Reports Server (NTRS)

    Workman, G. L.; Bryson, C. C.

    1993-01-01

    NASA technical memorandum describes initial research on, and proposed development of, automated system for nondestructive eddy-current inspection of parts made of graphite-fiber/epoxy-matrix composite materials. Sensors in system E-shaped or U-shaped eddy-current probes like those described in "Eddy-Current Probes For Inspecting Graphite-Fiber Composites" (MFS-26129).

  4. An expert system for analyzing eddy current measurements

    SciTech Connect

    Levy, A.J.; Oppenlander, J.E.; Brudnoy, D.M.; Englund, J.M.; Loomis, K.C.

    1991-12-31

    A method and apparatus (called DODGER) analyzes eddy current data for heat exchanger tubes or any other metallic object. DODGER uses an expert system to analyze eddy current data by reasoning with uncertainty and pattern recognition. The expert system permits, DODGER to analyze eddy current data intelligently, an obviate operator uncertainty by analyzing the data in a uniform and consistent manner.

  5. Scale-Similar Models for Large-Eddy Simulations

    NASA Technical Reports Server (NTRS)

    Sarghini, F.

    1999-01-01

    Scale-similar models employ multiple filtering operations to identify the smallest resolved scales, which have been shown to be the most active in the interaction with the unresolved subgrid scales. They do not assume that the principal axes of the strain-rate tensor are aligned with those of the subgrid-scale stress (SGS) tensor, and allow the explicit calculation of the SGS energy. They can provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses in regions that are well correlated with the locations where large Reynolds stress occurs. In this paper, eddy viscosity and mixed models, which include an eddy-viscosity part as well as a scale-similar contribution, are applied to the simulation of two flows, a high Reynolds number plane channel flow, and a three-dimensional, nonequilibrium flow. The results show that simulations without models or with the Smagorinsky model are unable to predict nonequilibrium effects. Dynamic models provide an improvement of the results: the adjustment of the coefficient results in more accurate prediction of the perturbation from equilibrium. The Lagrangian-ensemble approach [Meneveau et al., J. Fluid Mech. 319, 353 (1996)] is found to be very beneficial. Models that included a scale-similar term and a dissipative one, as well as the Lagrangian ensemble averaging, gave results in the best agreement with the direct simulation and experimental data.

  6. Stochastic Ocean Eddy Perturbations in a Coupled General Circulation Model.

    NASA Astrophysics Data System (ADS)

    Howe, N.; Williams, P. D.; Gregory, J. M.; Smith, R. S.

    2014-12-01

    High-resolution ocean models, which are eddy permitting and resolving, require large computing resources to produce centuries worth of data. Also, some previous studies have suggested that increasing resolution does not necessarily solve the problem of unresolved scales, because it simply introduces a new set of unresolved scales. Applying stochastic parameterisations to ocean models is one solution that is expected to improve the representation of small-scale (eddy) effects without increasing run-time. Stochastic parameterisation has been shown to have an impact in atmosphere-only models and idealised ocean models, but has not previously been studied in ocean general circulation models. Here we apply simple stochastic perturbations to the ocean temperature and salinity tendencies in the low-resolution coupled climate model, FAMOUS. The stochastic perturbations are implemented according to T(t) = T(t-1) + (∆T(t) + ξ(t)), where T is temperature or salinity, ΔT is the corresponding deterministic increment in one time step, and ξ(t) is Gaussian noise. We use high-resolution HiGEM data coarse-grained to the FAMOUS grid to provide information about the magnitude and spatio-temporal correlation structure of the noise to be added to the lower resolution model. Here we present results of adding white and red noise, showing the impacts of an additive stochastic perturbation on mean climate state and variability in an AOGCM.

  7. The turbulent cascade of individual eddies

    NASA Astrophysics Data System (ADS)

    Huertas-Cerdeira, Cecilia; Lozano-Durán, Adrián; Jiménez, Javier

    2014-11-01

    The merging and splitting processes of Reynolds-stress carrying structures in the inertial range of scales are studied through their time-resolved evolution in channels at Reλ = 100 - 200 . Mergers and splits coexist during the whole life of the structures, and are responsible for a substantial part of their growth and decay. Each interaction involves two or more eddies and results in little overall volume loss or gain. Most of them involve a small eddy that merges with, or splits from, a significantly larger one. Accordingly, if merge and split indexes are respectively defined as the maximum number of times that a structure has merged from its birth or will split until its death, the mean eddy volume grows linearly with both indexes, suggesting an accretion process rather than a hierarchical fragmentation. However, a non-negligible number of interactions involve eddies of similar scale, with a second probability peak of the volume of the smaller parent or child at 0.3 times that of the resulting or preceding structure. Funded by the Multiflow project of the ERC.

  8. Eddy current sensing of intermetallic composite consolidation

    NASA Technical Reports Server (NTRS)

    Dharmasena, Kumar P.; Wadley, Haydn N. G.

    1991-01-01

    A finite element method is used to explore the feasibility and optimization of a probe-type eddy current sensor for determining the thickness of plate specimens during a hot isostatic pressing cycle. The dependence of the sensor's impedance upon sample-sensor separation in the high frequency limit is calculated, and factors that maximize sensitivity to the final stages of densification are identified.

  9. Large-Eddy Simulation and Multigrid Methods

    SciTech Connect

    Falgout,R D; Naegle,S; Wittum,G

    2001-06-18

    A method to simulate turbulent flows with Large-Eddy Simulation on unstructured grids is presented. Two kinds of dynamic models are used to model the unresolved scales of motion and are compared with each other on different grids. Thereby the behavior of the models is shown and additionally the feature of adaptive grid refinement is investigated. Furthermore the parallelization aspect is addressed.

  10. Understanding positive feedback between PNA and synoptic eddies by eddy structure decomposition method

    NASA Astrophysics Data System (ADS)

    Zhou, Fang; Ren, Hong-Li; Xu, Xiao-Feng; Zhou, You

    2016-08-01

    In the upper troposphere during winter, positive synoptic eddy (SE) feedback plays an indispensible role in maintaining the Pacific-North American (PNA) pattern that dominates climate variability on inter-annual timescales over the North Pacific and downstream regions. This study shows that the eddy forcing, induced by eddy-vorticity (EV) fluxes, is not only in-phase with, but also downstream to the PNA pattern in terms of its northeast Pacific lobe. We employ the eddy structure decomposition method to understand such an observed PNA-SEs feedback, and propose a kinematic mechanism that can depict dynamical processes associated with the eddy structure change and its induced positive eddy feedback relative to the PNA flow pattern. With this method, the winter-mean PNA-related SE structures are separated into climatological (basic) and anomalous SE structures, and these two parts can be used to represent the changes in SE structure in a statistical sense and then to calculate the EV fluxes in order to further elucidate the feedback mechanism. It is demonstrated that, on one hand, the winter-mean PNA flow tends to systematically deform the structures of SEs and induce anomalous EV fluxes, and these winter-mean EV fluxes primarily converge into the PNA cyclonic center, which, in return enhances the PNA flow. On the other hand, the PNA-related northeast Pacific flow is featured by a stronger zonal wind shear in the east than the west, which can induce larger zonal-slanting eddy structure change and then stronger meridional EV fluxes that converge to form downstream feedback. This kinematic mechanism may help to deeply understand the dynamical eddy feedback between the low-frequency PNA flow and high-frequency SEs.

  11. Correlation of clinical and angiographic findings in brain ischemia with regional cerebral blood flow measured by the xenon inhalation technique

    SciTech Connect

    Awad, I.; Little, J.R.; Furlan, A.J.; Weinstein, M.

    1982-07-01

    Eighty-eight patients with brain ischemia underwent cerebral angiography and measurement of regional cerebral blood flow (rCBF) after /sup 133/Xe inhalation. A fast compartment flow rate and an initial slope index were computed for each detector and for each hemisphere. The clinical presentation, angiographic findings, and rCBF results were then examined for significant correlations. Patients with hemispheric infarction most frequently showed bilateral diffusely decreased rCBF. In patients with transient ischemic attacks, no specific pattern emerged. Patients with unilateral internal carotid artery occlusion frequently hd bilateral diffusely decreased rCBF. Patients with severe internal carotid artery stenosis were more likely to show decreased rCBF than were patients with mild or moderate stenosis. The initial slope index seemed to be a more sensitive indicator of brain ischemia than the fast compartment flow rate. The possible pathophysiological significance and relationship to patient management of the various rCBF patterns are discussed.

  12. Fragment-based identification of druggable ‘hot spots’ of proteins using Fourier domain correlation techniques

    PubMed Central

    Brenke, Ryan; Kozakov, Dima; Chuang, Gwo-Yu; Beglov, Dmitri; Hall, David; Landon, Melissa R.; Mattos, Carla; Vajda, Sandor

    2009-01-01

    Motivation: The binding sites of proteins generally contain smaller regions that provide major contributions to the binding free energy and hence are the prime targets in drug design. Screening libraries of fragment-sized compounds by NMR or X-ray crystallography demonstrates that such ‘hot spot’ regions bind a large variety of small organic molecules, and that a relatively high ‘hit rate’ is predictive of target sites that are likely to bind drug-like ligands with high affinity. Our goal is to determine the ‘hot spots’ computationally rather than experimentally. Results: We have developed the FTMAP algorithm that performs global search of the entire protein surface for regions that bind a number of small organic probe molecules. The search is based on the extremely efficient fast Fourier transform (FFT) correlation approach which can sample billions of probe positions on dense translational and rotational grids, but can use only sums of correlation functions for scoring and hence is generally restricted to very simple energy expressions. The novelty of FTMAP is that we were able to incorporate and represent on grids a detailed energy expression, resulting in a very accurate identification of low-energy probe clusters. Overlapping clusters of different probes are defined as consensus sites (CSs). We show that the largest CS is generally located at the most important subsite of the protein binding site, and the nearby smaller CSs identify other important subsites. Mapping results are presented for elastase whose structure has been solved in aqueous solutions of eight organic solvents, and we show that FTMAP provides very similar information. The second application is to renin, a long-standing pharmaceutical target for the treatment of hypertension, and we show that the major CSs trace out the shape of the first approved renin inhibitor, aliskiren. Availability: FTMAP is available as a server at http://ftmap.bu.edu/. Contact: vajda@bu.edu Supplementary

  13. Subsurface hydrographic structures and the temporal variations of Aleutian eddies

    NASA Astrophysics Data System (ADS)

    Saito, Rui; Yasuda, Ichiro; Komatsu, Kosei; Ishiyama, Hiromu; Ueno, Hiromichi; Onishi, Hiroji; Setou, Takeshi; Shimizu, Manabu

    2016-05-01

    Aleutian eddies are mesoscale anticyclonic eddies formed within the Alaskan Stream region between 180° meridian and 170° E south of the Aleutian Islands. They propagate southwestward after the isolation from the Alaskan Stream and pass through the Western Subarctic Gyre. We compared hydrographic structures of three Aleutian eddies observed during summer, west of 170° E (Eddy A) and east of 170° E (Eddies B and C). In each eddy, a subsurface dichothermal water (3.0-4.0 °C) was observed above a subsurface mesothermal water (4.0-4.5 °C). The minimum temperature in the dichothermal water at around a depth of 100 m was colder in Eddy A (2.8 °C) than in Eddies B and C (3.0-3.2 °C). This difference could be ascribed to wintertime cooling and influence of surrounding waters during spring warming period. The wintertime cooling makes the dichothermal water colder for eddies isolated from the Alaskan Stream region for a longer time. Particle-tracking experiments using re-analysis products from a data-assimilative eddy resolving ocean model suggested that the dichothermal water within Eddy A was cooled by the entrainment of surrounding colder water even during the spring warming period. The mesothermal waters at depth around 250 m demonstrated similarity among the observed eddies, and the maximum temperature in the mesothermal water within Eddy A (4.3 °C) was close to that of Eddies B and C (4.2 °C) in the in situ observations. These results indicated that the dichothermal water of Aleutian eddies modifies over time, whereas the mesothermal water maintains the original feature as they propagate southwestward from the Alaskan Stream region to the Western Subarctic Gyre.

  14. Eddies in the southern Mozambique Channel

    NASA Astrophysics Data System (ADS)

    Quartly, G. D.; Srokosz, M. A.

    2004-01-01

    The Agulhas Current system contains one of the world's strongest western boundary currents, and plays an important part in the warm water path of the global thermohaline circulation. However, there have been few surveys of the source regions of the Agulhas Current, and thus little in situ measurement of their variability. Utilizing the more than 5-year record of SeaWiFS data, we examine the eddy activity present in the southern portion of the Mozambique Channel. The two sources of Agulhas input from the central Indian Ocean (southward flow through the Mozambique Channel and westward flow around the southern limit of Madagascar) both show great temporal variability, with no clear seasonal signal. A number of large (˜200 km diameter) anticyclonic rings intermittently propagate poleward along the western edge of the channel, sweeping coastal waters into mid-channel. Their passage past Maputo appears to affect the circulation of the lee eddy in the Delagoa Bight. The eastern side of the channel is mainly characterized by cyclonic eddies. These are made manifest in the lee of the southern tip of Madagascar, although it is not clear whether many form there or just develop a visible presence due to entrainment of high-chlorophyll coastal waters. Several of these cyclonic eddies then appear to move in west-southwesterly direction. The chlorophyll data do reveal the apparent East Madagascar Retroflection on occasions, but do not show clear examples of the pinching off of anticyclonic eddies. However, surface waters from the East Madagascar Current may reach the African mainland on occasions when no retroflection is present.

  15. Carbon balance of surfaces vs. ecosystems: advantages of measuring eddy covariance and soil respiration simultaneously in dry grassland ecosystems

    NASA Astrophysics Data System (ADS)

    Nagy, Z.; Pintér, K.; Pavelka, M.; Darenová, E.; Balogh, J.

    2011-02-01

    An automated open system for measurement of soil CO2 efflux (Rsc) was developed and calibrated against known fluxes and tested in the field, while measuring soil respiration also by the gradient method (Rsg) at a dry sandy grassland (Bugac, Hungary). Ecosystem respiration (Reco) was measured by the eddy covariance technique. Small chamber size (5 cm in diameter) of the chamber system made it possible to use the chambers also in vegetation gaps, thereby avoiding the necessity of removing shoots, the disturbance of the spatial structure of vegetation and the upper soil layer. Low air flow rates associated with small chamber volume and chamber design allowed the overpressure range to stabilize between 0.05-0.12 Pa. While the correlation between ecosystem and soil CO2 efflux rates as measured by the independent methods was significant, Reco rates were similar or even lower than Rsc in the low flux (up to 2 μmol CO2 m-2 s-1) range, probably due to the larger than assumed storage flux. The gradient method showed both up and downward CO2 fluxes originating from the main rooting zone after rains. Downward fluxes within the soil profile amounted to 15% of the simultaneous upward fluxes and to ~ 7.6% of the total (upward) effluxes during the 3 months study. The upper 5 cm soil layer contributed to ~ 50% of the total soil CO2 efflux. The continuously operated automatic open chamber system and the gradient system makes possible the detection of situations when the eddy system underestimates Reco, gives the lower limit of underestimation (chamber system) and helps in quantifying the downward flux component of soil respiration (gradient method) between the soil layers. These latter (downward) fluxes are expected to seriously affect (1) the Reco vs. temperature response functions and (2) the net ecosystem exchange of CO2 (NEE) vs. photon flux density response functions, therefore potentially affecting also the gap filling procedures and to led to a situation (3) when the

  16. Spatially correlated structural and optical characterization of a single InGaAs quantum well fin selectively grown on Si by microscopy and cathodoluminescence techniques

    NASA Astrophysics Data System (ADS)

    David, S.; Roque, J.; Rochat, N.; Bernier, N.; Piot, L.; Alcotte, R.; Cerba, T.; Martin, M.; Moeyaert, J.; Bogumilowizc, Y.; Arnaud, S.; Bertin, F.; Bassani, F.; Baron, T.

    2016-05-01

    Structural and optical properties of InGaAs quantum well fins (QWFs) selectively grown on Si using the aspect ratio trapping (ART) method in 200 nm deep SiO2 trenches are studied. A new method combining cathodoluminescence, transmission electron microscopy, and precession electron diffraction techniques is developed to spatially correlate the presence of defects and/or strain with the light emission properties of a single InGaAs QWF. Luminescence losses and energy shifts observed at the nanoscale along InGaAs QWF are correlated with structural defects. We show that strain distortions measured around threading dislocations delimit both high and low luminescent areas. We also show that trapped dislocations on SiO2 sidewalls can also result in additional distortions. Both behaviors affect optical properties of QWF at the nanoscale. Our study highlights the need to improve the ART growth method to allow integration of new efficient III-V optoelectronic components on Si.

  17. Theoretical prediction of remote-field eddy current response for the nondestructive evaluation of metallic tubes

    NASA Astrophysics Data System (ADS)

    Palanisamy, R.

    1987-04-01

    The remote-field eddy current effect refers to low-frequency eddy current nondestructive testing (NDT) phenomenon in tubular conductors in which the behavior of both amplitude and phase of induced magnetic field are in apparent contradiction to the well-known ``skin-effect'' theory. Near-equal detection sensitivity across the wall thickness, the ability to measure wall thickness, and the absence of lift-off problems are some of the attractive features of this technique. Despite its early recognition and useful application in down-hole inspection of oil-well casing, no development of adequate scientific basis that could explain this phenomenon has been reported in the open literature. Modeling of the remote-field eddy current phenomenon using the axisymmetric finite element computer code is described in this paper. The results presented show that the finite element numerical technique originally developed for the computation of fields in electrical and magnetic devices can be used as well for the modeling of remote-field eddy current NDT problems.

  18. Coupled circuit numerical analysis of eddy currents in an open MRI system

    NASA Astrophysics Data System (ADS)

    Akram, Md. Shahadat Hossain; Terada, Yasuhiko; Keiichiro, Ishi; Kose, Katsumi

    2014-08-01

    We performed a new coupled circuit numerical simulation of eddy currents in an open compact magnetic resonance imaging (MRI) system. Following the coupled circuit approach, the conducting structures were divided into subdomains along the length (or width) and the thickness, and by implementing coupled circuit concepts we have simulated transient responses of eddy currents for subdomains in different locations. We implemented the Eigen matrix technique to solve the network of coupled differential equations to speed up our simulation program. On the other hand, to compute the coupling relations between the biplanar gradient coil and any other conducting structure, we implemented the solid angle form of Ampere’s law. We have also calculated the solid angle for three dimensions to compute inductive couplings in any subdomain of the conducting structures. Details of the temporal and spatial distribution of the eddy currents were then implemented in the secondary magnetic field calculation by the Biot-Savart law. In a desktop computer (Programming platform: Wolfram Mathematica 8.0®, Processor: Intel(R) Core(TM)2 Duo E7500 @ 2.93 GHz; OS: Windows 7 Professional; Memory (RAM): 4.00 GB), it took less than 3 min to simulate the entire calculation of eddy currents and fields, and approximately 6 min for X-gradient coil. The results are given in the time-space domain for both the direct and the cross-terms of the eddy current magnetic fields generated by the Z-gradient coil. We have also conducted free induction decay (FID) experiments of eddy fields using a nuclear magnetic resonance (NMR) probe to verify our simulation results. The simulation results were found to be in good agreement with the experimental results. In this study we have also conducted simulations for transient and spatial responses of secondary magnetic field induced by X-gradient coil. Our approach is fast and has much less computational complexity than the conventional electromagnetic numerical

  19. Coupled circuit numerical analysis of eddy currents in an open MRI system.

    PubMed

    Akram, Md Shahadat Hossain; Terada, Yasuhiko; Keiichiro, Ishi; Kose, Katsumi

    2014-08-01

    We performed a new coupled circuit numerical simulation of eddy currents in an open compact magnetic resonance imaging (MRI) system. Following the coupled circuit approach, the conducting structures were divided into subdomains along the length (or width) and the thickness, and by implementing coupled circuit concepts we have simulated transient responses of eddy currents for subdomains in different locations. We implemented the Eigen matrix technique to solve the network of coupled differential equations to speed up our simulation program. On the other hand, to compute the coupling relations between the biplanar gradient coil and any other conducting structure, we implemented the solid angle form of Ampere's law. We have also calculated the solid angle for three dimensions to compute inductive couplings in any subdomain of the conducting structures. Details of the temporal and spatial distribution of the eddy currents were then implemented in the secondary magnetic field calculation by the Biot-Savart law. In a desktop computer (Programming platform: Wolfram Mathematica 8.0®, Processor: Intel(R) Core(TM)2 Duo E7500 @ 2.93GHz; OS: Windows 7 Professional; Memory (RAM): 4.00GB), it took less than 3min to simulate the entire calculation of eddy currents and fields, and approximately 6min for X-gradient coil. The results are given in the time-space domain for both the direct and the cross-terms of the eddy current magnetic fields generated by the Z-gradient coil. We have also conducted free induction decay (FID) experiments of eddy fields using a nuclear magnetic resonance (NMR) probe to verify our simulation results. The simulation results were found to be in good agreement with the experimental results. In this study we have also conducted simulations for transient and spatial responses of secondary magnetic field induced by X-gradient coil. Our approach is fast and has much less computational complexity than the conventional electromagnetic numerical simulation

  20. A Comparison of GHG Flux Measurements by Relaxed Eddy Accumulation and Eddy Covariance Methods Using FTIR and QCL Analyzers

    NASA Astrophysics Data System (ADS)

    Vermeulen, A. T.; Laborde, M.; Hensen, A.; van den Bulk, P.; Famulari, D.; Griffith, D. W.; Nemitz, E.

    2013-12-01

    In this presentation results obtained with a novel system for Relaxed Eddy Accumulation (REA) measurements using an Ecotech Spectronus FTIR analyzer (Griffth et al, 2012) will be compared to eddy covariance fluxes using an Aerodyne QCL and a Licor 6262 NDIR analyzer. The REA FTIR system can be easily combined with other standard (e.g. NDIR) analyzers suited for eddy covariance measurements to allow for scaling of the obtained up/down concentration differences with the directly measured fluxes. Furthermore the FTIR system allows for on-line simultaneous high precision concentration measurement of a large number of different gases and even isotope composition, next to the measurement of CO2, CH4 and N2O mixing ratios. The final design goal for the REA FTIR system is an attractive fully automated, low maintenance system for long-term monitoring of Greenhouse Gas fluxes at the hourly time scale and a spatial scale of about 1 km2. During a campaign of four weeks in June 2013 (in the framework of the InGOS EU project) at a grazed grassland site at Easter Bush, Scotland (UK), simultaneous surface flux measurements of N2O and additionally CO2 and CH4 have been performed using our systems and a number of setups from other groups.. Weather conditions during the campaign were excellent and after the application of fertilizer at the field and some rainfall the increased emission of N2O was detected clearly by all systems. Both the eddy covariance and REA methods performed well during the campaign and the measured fluxes compare satisfactorily. In general the resulting fluxes from the FTIR system are lower then the QCL based results. Reasons for these deviations will be discussed together with implications of the results for the design of future REA measurements using the FTIR system. Griffith, D.W.T., N.M. Deutscher, C.G.R. Caldow, G. Kettlewell, M. Riggenbach and S. Hammer, A Fourier transform infrared trace gas analyser for atmospheric applications. Atmospheric Measurement