The Experts below are selected from a list of 153 Experts worldwide ranked by ideXlab platform

L. A. G. Aylmore - One of the best experts on this subject based on the ideXlab platform.

  • studies of soil water drawdowns by single radish roots at decreasing soil water content using Computer Assisted Tomography
    Soil Research, 2001
    Co-Authors: M A Hamza, S H Anderson, L. A. G. Aylmore
    Abstract:

    Application of Computer-Assisted Tomography to the attenuation of X-rays has been used to compare the drawdowns in soil water content associated with radish roots at starting soil water contents (θv) of 0.3 cm3/cm3 and 0.1 cm3/cm3, respectively. Decreasing soil water content results in an increase in the appearance of ‘beam hardening’. Decreasing soil water content from 0.3 to 0.1 cm3/cm3 caused the transpiration rate to decrease by 6–10 times. This was presumably due to a reduction in the water potential gradient across the root membrane. The transpiration rate decreased less rapidly than did the water content at the soil–root interface, suggesting some osmotic adjustment by the leaves. This osmotic adjustment would allow the plant to maintain transpiration rate even at relatively low soil water content. The drawdown distances associated with roots growing at the lower soil water content were 8 times smaller than those at the high soil water content and the value of θv at the soil–root interface at the end of the transpiration period was 2.5 times lower. The radish roots exhibited a temporary slight decrease in diameter after the transpiration commenced followed by a significant temporary increase. However, root diameter stabilised around its original value when the plant attained an almost steady water uptake rate. Despite the complexity arising from ‘beam hardening’, CAT scanning can provide valuable information on processes at the root–soil interface.

  • Computer Assisted Tomography and magnetic resonance imaging
    2000
    Co-Authors: S Asseng, L. A. G. Aylmore, J S Macfall, J W Hopmans, P J Gregory
    Abstract:

    Until recently, techniques for direct measurements on roots and soil water in the rooting zone have been largely destructive, or simply lacked the spatial resolution necessary for meaningful definition of root and water content distributions. With advances in X-ray physics, detector technology and mathematical reconstruction theory, a solution to this problem was essentially achieved by Hounsfield (1972), who developed the technique known as Computer-Assisted Tomography (CAT) or computed Tomography (CT). In addition to X- and γ-rays (photons), tomographic imaging is also applicable to other types of energy such as electrons, protons, alpha particles, lasers, radar, seismic and nuclear magnetic resonance (NMR).

  • Computation of hydraulic conductivity of porous materials using Computer-Assisted Tomography
    Soil Research, 1996
    Co-Authors: V. K. Phogat, L. A. G. Aylmore
    Abstract:

    The spatial distribution of porosity and continuity of pore space in glass bead and soil aggregate systems has been characterised by application of Computer-Assisted Tomography to gamma-ray attenuation measurements. It has been demonstrated that a useful empirical relationship between hydraulic conductivity and pore size and continuity for the glass bead system as measured by CAT scanning can be derived.

  • use of Computer Assisted Tomography in studying water movement around plant roots
    Advances in Agronomy, 1993
    Co-Authors: L. A. G. Aylmore
    Abstract:

    Publisher Summary Application of Computer-Assisted Tomography to X- and y-ray attenuation measurements has provided an exciting new method for nondestructive imaging within a solid matrix, with considerable potential for studying soil behavior and soil/plant/water relations in space and time. However, the information provided is currently limited by the capabilities of the instrumentation available. Commercially available medical CT scanners have proved useful for visual studies of soil structure, the advancement and stability of wetting fronts, and the structural changes following wetting and drying. However, the usefulness of these systems and of single-source CAT scanning systems in studying soil systems is invariably restricted by their inability to distinguish between changes in water content and bulk density in swelling and shrinking soils and by the associated physical relocation of soil elements that can occur. Thus their quantitative applications have been limited to the measurement of water drawdowns in proximity to plant roots in nonswelling soils and statistical assessments of macroporosity distributions before and after complete wetting and drying cycles. Though fast in operation, the quantitative usefulness of X-ray scanners is limited by the polychromatic nature of the beam and the process known as “beam hardening.” Furthermore, the proprietary nature of these commercial systems usually makes software modification or extensions impossible.

A Kantzas - One of the best experts on this subject based on the ideXlab platform.

  • monitoring bitumen solvent interactions with low field nuclear magnetic resonance and x ray Computer Assisted Tomography
    Energy & Fuels, 2005
    Co-Authors: A Kantzas
    Abstract:

    This work involves the detection and monitoring of solvent interactions with heavy oil and bitumen. Two nondestructive methodslow-field nuclear magnetic resonance (NMR) and X-ray Computer-Assisted Tomography (CAT)were used. It is shown that low-field NMR can be a very useful tool in understanding the relationship of viscosity, density, and asphaltene precipitation in bitumen−solvent mixtures. Such mixtures are present in solvent-related heavy oil and bitumen recovery processes, such as vapor extraction (VAPEX). As a solvent comes into contact with a heavy oil or bitumen sample, the mobility of hydrogen-bearing molecules of both solvent and oil changes. These changes are detectable through changes in the NMR relaxation characteristics of both the solvent and the oil and can be correlated to mass flux and concentration changes. Based on Fick's second law, diffusion coefficients were calculated for combinations of three oils and six solvents. X-ray CAT scanning was also used in parallel for analysis of solve...

  • the application of Computer Assisted Tomography in the analysis of fracture geometry
    Geotechnical Testing Journal, 1998
    Co-Authors: D A Walters, R C K Wong, A Kantzas
    Abstract:

    An experimental study was conducted to investigate the surface characteristics of an oil sand fracture. The oil sand fracture was induced in core samples along the axis of the sample using the Brazilian tension test. A Computer-Assisted Tomography scanning analysis was performed to determine the fracture geometry. The fracture was shown to be a variable aperture system that would have significant effects of the permeability of the fracture. The aperture distributions of the fractures were found to follow a log-normal distribution, similar to that of previously studied rock fractures.

  • CHARACTERIZATION OF MACROPORE MORPHOLOGY IN A SANDY LOAM SOIL USING X-RAY Computer Assisted Tomography AND GEOSTATISTICAL ANALYSIS
    Canadian Water Resources Journal, 1998
    Co-Authors: Johan Perret, A Kantzas, Shiv O. Prasher, Cooper H. Langford
    Abstract:

    Our understanding of the factors affecting the leaching of chemicals such as pesticides and fertilizers into soils is limited, due in part to a lack of adequate non-destructive measurements of soil pore size distribution. The recent application of X-Ray Computer Assisted Tomography scanning to non-medical fields such as soil physics has allowed the development of a new and non-destructive technique with considerable potential for quantification of soil and water processes. The present study was undertaken to develop an innovative protocol for the characterization and visualization of soil macropores. It focuses primarily on the characterization of macropore morphology in large undisturbed soil columns using a 4th generation X-ray CAT scanner. The objective of the study is to assess, in quantitative terms, variations in the morphology of macropores as a function of depth. In order to evaluate these variations, the number of macropores, soil macroporosity, macropore size, hydraulic radius, and circularity h...

  • computation of holdups in fluidized and trickle beds by Computer Assisted Tomography
    Aiche Journal, 1994
    Co-Authors: A Kantzas
    Abstract:

    A fourth-generation X-ray Computer-Assisted Tomography (CAT) scanner was used for the study of fluidized and trickle beds. A variety of exploratory experiments were performed, and images of density and holdup were obtained in three dimensions as a function of time. The gas/solid fluidized beds were glass bead/nitrogen and polyethylene/nitrogen systems. The trickle bed was a glass bead/nitrogen/water system. The algorithms presented can be used to determine holdup from X-ray absorption data. These algorithms—extensions of similar algorithms used for the calculation of fluid saturations in porous media—are applied on data of CAT scanner images as they are generated by the scanner and after they are transferred to a workstation. The results of the presented tests demonstrate how detailed holdup calculations can be performed in a chemical reactor. Radial and longitudinal variances of the holdup can be easily defined. The proposed algorithms can assist in the design of chemical reactor prototypes.

  • Computation of holdups in fluidized and trickle beds by Computer‐Assisted Tomography
    Aiche Journal, 1994
    Co-Authors: A Kantzas
    Abstract:

    A fourth-generation X-ray Computer-Assisted Tomography (CAT) scanner was used for the study of fluidized and trickle beds. A variety of exploratory experiments were performed, and images of density and holdup were obtained in three dimensions as a function of time. The gas/solid fluidized beds were glass bead/nitrogen and polyethylene/nitrogen systems. The trickle bed was a glass bead/nitrogen/water system. The algorithms presented can be used to determine holdup from X-ray absorption data. These algorithms—extensions of similar algorithms used for the calculation of fluid saturations in porous media—are applied on data of CAT scanner images as they are generated by the scanner and after they are transferred to a workstation. The results of the presented tests demonstrate how detailed holdup calculations can be performed in a chemical reactor. Radial and longitudinal variances of the holdup can be easily defined. The proposed algorithms can assist in the design of chemical reactor prototypes.

John T. Nagurney - One of the best experts on this subject based on the ideXlab platform.

  • sex differences in the effectiveness of early coronary computed tomographic angiography compared with standard emergency department evaluation for acute chest pain the rule out myocardial infarction with Computer Assisted Tomography romicat ii trial
    Circulation, 2013
    Co-Authors: Quynh A Truong, John T. Nagurney, Douglas Hayden, Pamela K Woodard, Ruth Kirby, Eric T Chou, Stephen D Wiviott, Jerome L Fleg, David A Schoenfeld, James E Udelson
    Abstract:

    BACKGROUND: We evaluate sex-based differences in the effectiveness of early cardiac computed tomographic angiography (CCTA) and standard emergency department (ED) evaluation in patients with acute chest pain. METHODS AND RESULTS: In the Rule-Out Myocardial Infarction With Computer-Assisted Tomography (ROMICAT)-II multicenter, controlled trial, we randomized 1000 patients (47% women) 40 to 74 years of age with symptoms suggestive of acute coronary syndrome to an early CCTA or standard ED evaluation. In this prespecified analysis, women in the CCTA arm had a greater reduction in length of stay, lower hospital admission rates, and lesser increased cumulative radiation dose than men in a comparison of ED strategies (P for interaction ≤0.02). Although women had lower acute coronary syndrome rates than men (3% versus 12%; P<0.0001), sex differences in length of stay persisted after adjustment for baseline differences, including acute coronary syndrome rate (P for interaction <0.03). Length of stay was similar between sexes with normal CCTA findings (P=0.11). There was no missed acute coronary syndrome for either sex. No difference was observed in major adverse cardiac events between sexes and ED strategies (P for interaction =0.39). Women had more normal CCTA examinations than men (58% versus 37%; P<0.0001), less obstructive coronary disease by CCTA (5% versus 17%; P=0.0001), but similar normalcy rates for functional testing (P=0.65). Men in the CCTA arm had the highest rate of invasive coronary angiography (18%), whereas women had comparable low 5% rates regardless of ED strategy. CONCLUSIONS: This trial provides data supporting an early CCTA strategy as an attractive option in women presenting to the ED with symptoms suggestive of acute coronary syndrome. The findings may be explained by lower CAD prevalence and severity in women than men. CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT01084239.

  • comparison of exercise treadmill testing with cardiac computed Tomography angiography among patients presenting to the emergency room with chest pain the rule out myocardial infarction using Computer Assisted Tomography romicat study
    Circulation-cardiovascular Imaging, 2012
    Co-Authors: Ron Blankstein, Waleed Ahmed, Fabian Bamberg, Ian S. Rogers, Christopher L. Schlett, Khurram Nasir, João D. Fontes, Ahmed Tawakol, Thomas J. Brady, John T. Nagurney
    Abstract:

    Background— The aims of our study were to (1) examine how data from exercise treadmill testing (ETT) can identify patients who have coronary plaque or stenosis, using CT angiography (CTA) as the reference standard, and (2) identify patient characteristics that may be used in selecting ETT versus CTA. Methods and Results— The Rule Out Myocardial Infarction Using Computer-Assisted Tomography (ROMICAT) trial was an observational cohort study of acute chest pain patients presenting to the emergency department with normal initial troponin and a nonischemic ECG. Univariate and multivariable analyses were performed to assess the relationship of baseline clinical data and ETT parameters with coronary plaque and stenosis on CTA. Of the 220 patients who had ETT (mean age, 51 years; 63% men), 21 (10%) had positive results. A positive ETT had a sensitivity of 30% and specificity of 93% to detect >50% stenosis. The sensitivity increased to 83% after excluding uninterpretable segments and evaluating the ability to detect a >70% stenosis. Predictors of plaque included older age, male sex, diabetes, hypertension, hyperlipidemia, lower functional capacity, and a lower Duke Treadmill Score. Both a positive ETT and a low Duke Treadmill Score were significant univariate and multivariable predictors of stenosis >50% on CTA Whereas the prevalence of stenosis by CTA was greater among patients with more risk factors, coronary stenosis was not present among men <40 years old or women <50 years old or individuals who achieved at least 13 metabolic equivalents on ETT. Conclusions— Among low- to intermediate-risk patients with acute chest pain, a positive ETT has a limited sensitivity but high specificity for the detection of >50% stenosis by CTA. Although patients with a high number of clinical risk factors are more likely to have obstructive coronary artery disease, those who are young or who would be expected to have a very high exercise capacity are unlikely to have coronary stenosis and therefore may benefit from initial ETT testing instead of CTA.

  • Comparison of Exercise Treadmill Testing With Cardiac Computed Tomography Angiography Among Patients Presenting to the Emergency Room With Chest Pain The Rule Out Myocardial Infarction Using Computer-Assisted Tomography (ROMICAT) Study
    Circulation-cardiovascular Imaging, 2012
    Co-Authors: Ron Blankstein, Waleed Ahmed, Fabian Bamberg, Ian S. Rogers, Christopher L. Schlett, Khurram Nasir, João D. Fontes, Ahmed Tawakol, Thomas J. Brady, John T. Nagurney
    Abstract:

    Background— The aims of our study were to (1) examine how data from exercise treadmill testing (ETT) can identify patients who have coronary plaque or stenosis, using CT angiography (CTA) as the reference standard, and (2) identify patient characteristics that may be used in selecting ETT versus CTA. Methods and Results— The Rule Out Myocardial Infarction Using Computer-Assisted Tomography (ROMICAT) trial was an observational cohort study of acute chest pain patients presenting to the emergency department with normal initial troponin and a nonischemic ECG. Univariate and multivariable analyses were performed to assess the relationship of baseline clinical data and ETT parameters with coronary plaque and stenosis on CTA. Of the 220 patients who had ETT (mean age, 51 years; 63% men), 21 (10%) had positive results. A positive ETT had a sensitivity of 30% and specificity of 93% to detect >50% stenosis. The sensitivity increased to 83% after excluding uninterpretable segments and evaluating the ability to detect a >70% stenosis. Predictors of plaque included older age, male sex, diabetes, hypertension, hyperlipidemia, lower functional capacity, and a lower Duke Treadmill Score. Both a positive ETT and a low Duke Treadmill Score were significant univariate and multivariable predictors of stenosis >50% on CTA Whereas the prevalence of stenosis by CTA was greater among patients with more risk factors, coronary stenosis was not present among men

Edward P Delikat - One of the best experts on this subject based on the ideXlab platform.

  • liquid distribution in trickle beds an experimental study using Computer Assisted Tomography
    Industrial & Engineering Chemistry Research, 1991
    Co-Authors: Pierre G Lutran, Ka M Ng, Edward P Delikat
    Abstract:

    Liquid distribution in trickle beds with a quiescent gaseous phase was visualized by using Computer-Assisted Tomography. The model system was made up of a column packed with uniform, nonporous glass spheres, distilled water, or a mixture of water and ethanol for a lower surface tension. Flow patterns at the bed scale were recorded as a function of various parameters (liquid flow rate, particle size, type of liquid inlet distributor used, and surface tension)

Apostolos Kantzas - One of the best experts on this subject based on the ideXlab platform.

  • study of diffusivity of hydrocarbon solvent in heavy oil saturated sands using x ray Computer Assisted Tomography
    Journal of Canadian Petroleum Technology, 2008
    Co-Authors: Apostolos Kantzas
    Abstract:

    Hydrocarbon solvent-Assisted processes are thought to be effective EOR technologies for heavy oil and bitumen production. In order to describe those processes quantitatively, the diffusivity of hydrocarbon solvent in oil sands is a crucial required parameter. Computer-Assisted Tomography (CAT), as a nonintrusive method, is a useful tool to obtain the physical properties of cores (density, porosity, heterogeneities) and the fluids within the cores (saturation or concentration profiles). However, the concentration profiles obtained from diffusion experiments of solvent in oil sands were fluctuating and could not be used to evaluate the diffusivity. In order to solve the problem, during the data processing of CAT scanning, porosity heterogeneity of porous media and volume changes on mixing are considered to improve the accuracy of concentration profiles dramatically. Subsequently, the diffusivity of hydrocarbon solvent in heavy-oil saturated sands is determined based on an updated mathematical model, which considers porosity heterogeneity of porous media in the major diffusion direction and volume changes on mixing. Thus, the diffusivity as a function of concentration and porosity is evaluated precisely and the impact of porosity heterogeneity of porous media on diffusivity determination of hydrocarbon solvent in heavy-oil saturated sands is investigated.

  • Laboratory Investigation of Pipeline/Soil Interactions Using X-Ray Computer Assisted Tomography
    Volume 2: Design Construction and Operation Innovations; Compression and Pump Technology; SCADA Automation and Measurement; System Simulation; Geotech, 1996
    Co-Authors: Apostolos Kantzas, Allan Trigg
    Abstract:

    X-ray Computer Assisted Tomography (CAT) Scanning has been used successfully for the determination of physical properties of porous rocks and for flow visualization in a variety of porous media including soils. CAT scanning has also been demonstrated as an effective tool for the visualization of different stress conditions in porous rocks with greater accuracy when dealing with unconsolidated media. This success was the motivation in trying to expand the diagnostic capabilities of CAT scanning in the phenomena associated with pipeline/soil interactions. For this purpose, a physical model was built. The model consisted of a X-ray transparent holder which had to pistons, one at each end. The pistons were mounted on a cylindrical rod of variable diameter. The holder was then filled with sand. The entire apparatus was placed in the CAT scanner gantry. A series of experiments were performed whereby the rod was forced through the sand pack. The holder was scanned from end to end and the images of various cross-sections were acquired and analyzed for bulk density and porosity. The experiments were coupled with calibration experiments where a uniformly packed sand was loaded under hydrostatic load in given increments. As the sand pack compacted, its bulk density increased.more » The normalized change in density (strain) was monitored as a function of the pressure load (stress). The results of the calibration tests were used to identify the levels of stress on the sand surrounding the moving rod. It was discovered that areas of compaction ahead of the moving rod and discovered that areas of compaction ahead of the moving rod and dilation behind the moving rod could be successfully identified and mapped. The stress/strain calibration data allowed the translation of the bulk density images into stress maps around the pipeline. This type of experimental work could be successfully used to calibrate complicated field scale Computer models.« less

  • monitoring the fluidization characteristics of polyolefin resins using x ray Computer Assisted Tomography scanning
    Chemical Engineering Science, 1996
    Co-Authors: Apostolos Kantzas, Nicolas Kalogerakis
    Abstract:

    Flow visualization of chemical reactor phenomena was given a new direction with the implementation of process Tomography techniques. These techniques can provide valuable information on flow phenomena in heterogeneous reactors. In particular, visualization and understanding of flow phenomena in gas phase polymerization reactors can aid us in achieving a better temperature distribution in the reactor and higher quality of products. In this study, the fluidization characteristics of a series of commercially available LLDPE, HDPE and IPP resins were investigated. The experiments were run in a small column of 10 cm in diameter (D) and variable bed heights (L), at L/D ratios of one, two and three. The fluidization velocities were varied between one and three times the minimum fluidization velocity of each sample. The particle size distributions varied from very narrow mesh sizes to full particle size distributions as they came out of commercial gas phase polymerization reactors. The resins also varied in sphericity. In several samples, there was some rubber present in the particles resulting in a “stickiness” characteristic of the resin. All experiments were performed at ambient conditions and inside the x-ray Computer Assisted Tomography (CAT) scanner facility. The CAT scanner images provided areal gas voidage distributions as a function of position and operating conditions at a resolution of 400 μm by 400 μm in cross section and 3 mm in thickness. A large number of images were collected and analyzed. Experimental results clearly established a set of fluidization experiments that gave relatively uniform voidage distributions, whereas other experiments had extremely non-uniform voidage distributions. Segregation and channeling were also observed under various operating conditions. It was found that certain regions of the bed were characterized by high voidage while others by very low voidage. These regions varied with experiments using the same resin but different velocities and L/Ds. The spatial variability of the voidage was also described in terms of statistical moments, frequency distributions and variograms. The voidage distributions were found to vary from wide unimodal to tri-modal of the same range for experimental conditions that, at first sight, did not appear to be significantly different. This paper describes the various categories of voidage distributions observed and provides some first correlations between voidage and operating parameters. A discussion of the implications of such phenomena to the performance of a gas phase polymerization reactor is also presented.