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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of carotenoid and porphyrin pigments of geochemical interest by high-performance liquid chromatography (1978)
    s.l. : American Chemical Society
    Analytical chemistry 50 (1978), S. 549-553 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac50026a004
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental studies of plasma transport across a magnetic island in the Compact Auburn Torsatron (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2405-2409 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of experiments on the Compact Auburn Torsatron [Gandy et al., Fusion Technol. 18, 281 (1990)] has investigated plasma particle transport properties across a magnetic island. The size of the island was systematically varied and the resulting changes in plasma transport were determined. Measurements of plasma density, electron and ion temperature, and plasma rotation speed were performed. Using a simple diffusion model, these measurements were used to deduce the diffusion coefficients for ions and electrons. With a factor of 2 increase in island width, the ion diffusion coefficient remained nearly constant whereas the electron diffusion coefficient increased by a factor of 4. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872916
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  • 3
    Electronic Resource
    Electronic Resource
    An experimental counter-example to the local transport paradigm (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2292-2298 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response of a tokamak discharge to a sharp drop in edge temperature differs significantly from that expected from typical local transport models in several important respects. Laser ablation of carbon induces large (ΔT/T≤70%), rapid (〈200 μs) electron temperature drops in the outermost region of the plasma, r/a≥0.9. This cold pulse proceeds through the outer plasma (r/a≥0.75), rapidly compared with power balance or sawtooth predictions. However, the pulse shrinks markedly thereafter, disappearing near r/a∼0.5. Within r/a∼0.3, the temperature rises promptly. The results are inconsistent with conventional local transport models; a nonlocal phenomenology, in which transport coefficients increase in the edge and decrease in the core, is suggested. The turbulence levels measured with a heavy ion beam probe increase near the edge but are unchanged in the core. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871252
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  • 4
    Electronic Resource
    Electronic Resource
    Core temperature fluctuations and related heat transport in the Texas Experimental Tokamak-Upgrade (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 720-726 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism(s) responsible for anomalous heat transport in the tokamak plasma core has remained elusive to experimental verification. In this paper the hypothesis that high-frequency electrostatic turbulence can account for the measured electron heat transport in Ohmically heated tokamak discharges of the Texas Experimental Tokamak-Upgrade (TEXT-U) [Proceedings of the 15th Symposium on Fusion Technology, Utrecht (Elsevier, Amsterdam, 1989), Vol. 1, p. 342] is tested. To accomplish this, core temperature fluctuations have been determined from the measured correlation between two electron cyclotron radiation signals detected by a multichannel high-frequency-resolution heterodyne radiometer. It is found that long wavelength modes (poloidal wave number (approximately-less-than)1 cm−1) are present, with an electron temperature fluctuation amplitude comparable to the density fluctuation amplitude. However, these modes cannot account for observed transport. An extrapolation of the observed turbulent temperature spectrum to the shorter wavelengths measured by far infrared scattering shows that shorter-wavelength electrostatic turbulence could still be responsible for transport. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871423
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  • 5
    Electronic Resource
    Electronic Resource
    Vertical viewing of electron-cyclotron emissions for diagnosing fast-electron dynamics in TEXT-U : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 427-429 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A system for vertically observing the second-harmonic electron-cyclotron emissions from the TEXT-U tokamak in conjunction with fundamental electron-cyclotron heating is described. Using external collection optics and heterodyne receivers, measurements of the distribution function can be performed over two-thirds of the plasma radius and on transport time scales. Observations are typically of electrons with energy E〈100 keV and either steep or shallow pitch angle, depending upon the toroidal viewing angle relative to the plasma current. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146368
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  • 6
    Electronic Resource
    Electronic Resource
    High resolution electron cyclotron emission temperature profile and fluctuation diagnostic for Alcator C-Mod : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1011-1013 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new second harmonic heterodyne electron cyclotron emission system with high spatial resolution (≤15 mm) and a large number of channels (32) for dense profile coverage will be installed on Alcator C-Mod. The system will provide detailed radial electron temperature profiles and core temperature fluctuation measurements. The collection system is composed of elliptical and parabolic mirrors coupled to two overmoded waveguides to provide high poloidal spatial resolution necessary for T˜e measurements. Four radiometer sections cover the frequency range of 234–306 GHz, coupled to four optimized intermediate frequency modules with eight channels of detectors, amplifiers, dividers, and filters providing the profile information. A separate filter arrangement allows for temperature fluctuation measurements utilizing correlation techniques. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149368
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  • 7
    Electronic Resource
    Electronic Resource
    Correlation radiometry of electron cyclotron radiation in TEXT-U (invited) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 798-801 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Very low level plasma density and temperature fluctuations can be responsible for anomalous transport in thermonuclear magnetic traps. Measuring these fluctuations by detecting plasma electron cyclotron emission (ECE) might indicate where, in ω−k space, the most dangerous instabilities are located. The most attractive feature of ECE is the good localization of the source, unique to this range of frequencies among plasma radiation. However, to maintain spatial resolution, only a small number of radiation modes should be detected. The consequent poor statistics of the ECE measurement allows one to measure only the average value for the temperature fluctuation amplitude via correlation analysis of two ECE signals with suitable correlation properties. Initial measurements of this kind have been performed successfully. But, results have only been partially conclusive as to the relevance of electrostatic turbulence to heat transport, due to still too limited poloidal spatial resolution and the inability to correlate the measured signals with corresponding potential fluctuations. Suggestions of how to extend the present results to correct for these drawbacks are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146225
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  • 8
    Electronic Resource
    Electronic Resource
    Soil friability: theory, measurement and the effects of management and organic carbon content (1998)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 49 (1998), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The weakest link between particles or aggregates determines the strength of soil. We have re-examined the theory and, as a result, have re-defined friability, F, as the coefficient of variation of soil tensile strength. The formal relationship between the parameter 1/α of the weakest link theory of strength, which has previously been used as a measure of friability, and the newly defined measure, F, is described by a simple equation which has an accuracy of within 2% over the range of interest. The quantity F is used to show that friability reaches maximum at water contents around the lower plastic limit, that mechanical disturbance of wet soil by tillage reduces the friability, and that friability is strongly positively correlated with the organic carbon content of the soil. These results show the merit of measuring friability for determining the optimum water content for tillage, for quantifying the damage done by different tillage practices, and as a theoretically based index of soil physical quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1998.00129.x
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  • 9
    Electronic Resource
    Electronic Resource
    The design of porous material sensors to measure the matric potential of water in soil (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 52 (2001), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In recent years the use of porous material sensors for matric potential, which were originally intended for soil drier than −100 kPa, has been extended to wet soils. In these wetter soils, unpredictable behaviour of the sensors has been reported. We have studied the design of porous material sensors of matric potential in soil and propose a hypothesis to explain this unpredictability, and suggest recommendations for a design of sensor which will behave more reliably. The development of an experimental porous material sensor of matric potential based on this design is described. It operates between 0 and −60 kPa, and both the drying and wetting moisture characteristics were measured. In this sensor the porous material was a ceramic and its water content was measured with a dielectric water content sensor. We tested a simple closed-form hysteresis model to convert the measured water content of the porous material into matric potential under laboratory conditions. This was shown to give better results than using a calibration based on the drying moisture characteristic curve, where the predicted matric potentials were too small. The use of the experimental sensors in the field environment is described. Both types of sensor were installed using the same procedure. As far as we are aware the experimental sensor described in this paper is the first porous material sensor of matric potential that can be installed in the same way as a conventional tensiometer. Both conventional tensiometers and the experimental porous material sensors gave similar estimates of matric potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2001.00397.x
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  • 10
    Electronic Resource
    Electronic Resource
    The effect of iron concentration, hindered settling, saturating cation and aggregate density of clays on the size distribution determined by gravitation X-ray sedimentometry (2000)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 51 (2000), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: X-ray sedimentation is potentially attractive for estimating the particle-size distribution of soil, but has been thought to overestimate clay fractions because of the iron they contain. We have examined X-ray sedimentation for estimating the particle-size distribution of fully dispersed and of aggregated clay. We obtained good agreement between the pipette and X-ray sedimentation methods using two different kaolinite samples with a small iron concentration. We also studied montmorillonite saturated with Li, Na, K, Mg or Ca to investigate possible effects of hindered settling. For the Ca montmorillonite, we obtained good agreement between X-ray sedimentation and the pipette method at concentrations up to 40 g l−1. We also found that X-ray sedimentation could be used at concentrations less than those recommended by the manufacturer. Hindered settling was observed at concentrations 〉 20 g l−1 for Li- and Na-saturated montmorillonite. Our data suggest that conducting experiments at different mass concentrations is a sensitive test to detect such problems. Finally we used a fractal model to investigate the possible errors that might result from the size dependence of aggregate density and show that the error caused by assuming a single value for particle density of solids is small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2000.00311.x
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