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  • 1
    Electronic Resource
    Electronic Resource
    Recursive algorithm for fast evaluation of the Abel inversion integral in broadband reflectometry : 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. 1047-1050 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The application of Kalman filtering is proposed for the numerical evaluation of plasma density profiles using noisy group delay data obtained from O-mode frequency-modulated broadband reflectometry. This method allows faster computation of the Abel inversion integral than the usual numerical methods (e.g., the trapezoidal rule) while maintaining a good accuracy in the presence of noise. In addition, density profiles with different degrees of smoothing can be produced by adjusting a single parameter. The algorithm seems promising in applications to plasma control in real time. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149306
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  • 2
    Electronic Resource
    Electronic Resource
    Automatic evaluation of plasma density profiles from microwave reflectometry on ASDEX upgrade based on the time-frequency distribution of the reflected signals : 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. 1060-1063 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new data analysis technique has been developed for the evaluation of the density profiles from broadband reflectometry in the presence of plasma turbulence. The method is based on the spectrogram of the reflected signals and uses the complete information of the beat frequency spectrum. The application of the Floyd best path algorithm, that takes into account the history of the beat frequency curve, enables us to extract the slow component due to the plasma profile. The statistics of the group delay data points is also considered to validate (or reject) data with great confidence. The results obtained in a wide range of plasma regimes show that accurate and detailed profiles can be measured automatically. One and two dimensional moving averaging over consecutive sweeps is also available to reduce the variance of the inverted profile while retaining a good temporal resolution. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149520
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  • 3
    Electronic Resource
    Electronic Resource
    Neural network evaluation of reflectometry density profiles for control purposes : 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. 521-524 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Broadband reflectometry is a diagnostic that is able to measure the density profile with high spatial and temporal resolutions, therefore it can be used to improve the performance of advanced tokamak operation modes and to supplement or correct the magnetics for plasma position control. To perform these tasks real-time processing is needed. Here we present a method that uses a neural network to make a fast evaluation of radial positions for selected density layers. Typical ASDEX Upgrade density profiles were used to generate the simulated network training and test sets. It is shown that the method has the potential to meet the tight timing requirements of control applications with the required accuracy. The network is also able to provide an accurate estimation of the position of density layers below the first density layer which is probed by an O-mode reflectometer, provided that it is trained with a realistic density profile model. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149379
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  • 4
    Electronic Resource
    Electronic Resource
    Data processing techniques for density profile evaluation from FM–CW reflectometry : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 910-913 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Microwave reflectometry is an important diagnostic to measure the plasma density profile on present fusion experiments and on next devices like ITER. Several data processing techniques, currently employed to evaluate the density profile, use filtering algorithms to overcome the effect of plasma fluctuations. However, in these processes the detailed profile structure may be altered or even lost. In order to study this problem we applied two different data analysis methods to experimental results obtained in ASDEX, when a locked magnetohydrodynamic mode is present. The first method uses a software implementation of a frequency discriminator to estimate continuously the evolution of the group delay versus frequency and the second applies a sliding fast Fourier transform method to determine an averaged group delay curve. It is shown that the profile exhibits a density plateau due to the magnetic island, which can be lost due to filtering or averaging procedures. Next we perform a numerical study for a profile with a small rotating density plateau, disturbed by random noise to simulate the effect of plasma fluctuations. The frequency discriminator is used to obtain group delay sweeps from consecutive sweeps and a two-dimensional (2-D) regularization technique is applied to the multiple samples. It is shown that the 2-D method has advantages in the routine evaluation of the detailed profile structure masked under the effect of plasma turbulence, due to the combined averaging (over space and time), based on the correlation between neighboring data points. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147767
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  • 5
    Electronic Resource
    Electronic Resource
    Microwave reflectometry diagnostic for density profile and fluctuation measurements on ASDEX Upgrade : 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. 1072-1075 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The broadband microwave reflectometry system on ASDEX Upgrade has been recently upgraded with new channels. It has now 12 channels that probe simultaneously the high and low fields plasma, with ultrafast sweeping (20–100 μs). X mode (33–75 GHz) is used for the scrape off layer, and the O mode (16–110 GHz) is reflected from densities between 0.3×1019 and 1.5×1019 m−3. A fast sweeping heterodyne system was developed for the highest frequency channels (50–110 GHz) to cope with higher losses and lower incident power. Fixed frequency operation is employed for fluctuation measurements. A dedicated channel (33–55 GHz) operating in fixed frequency provides a signal to continuously monitor the level of density fluctuations (e.g., L–H transition), during the whole discharge. The diagnostic is fully operated by remote control. The acquisition system is based on specially developed VME boards with up to 1 Gsamp/s sampling rates. Automatic profile inversion was recently implemented using data validation and rejection algorithms. Experimental results are presented to illustrate the profile measurements with O mode and with O and X mode combined operation. We present density profiles measured in a wide range of plasma regimes. Profile modifications due to rotating magnetic islands illustrates the potentialities of the reflectometry to estimate the location of the rational q surfaces. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149439
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  • 6
    Electronic Resource
    Electronic Resource
    A two-dimensional regularization algorithm for density profile evaluation from broadband reflectometry : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 906-909 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Broadband reflectometry is a current technique that uses the round-trip group delays of reflected frequency-swept waves to measure density profiles of fusion plasmas. The main factor that may limit the accuracy of the reconstructed profiles is the interference of the probing waves with the plasma density fluctuations: plasma turbulence leads to random phase variations and magneto hydrodynamic activity produces mainly strong amplitude and phase modulations. Both effects cause the decrease, and eventually loss, of signal at some frequencies. Several data processing techniques can be applied to filter and/or interpolate noisy group delay data obtained from turbulent plasmas with a single frequency sweep. Here, we propose a more powerful algorithm performing two-dimensional regularization (in space and time) of data provided by multiple consecutive frequency sweeps, which leads to density profiles with improved accuracy. The new method is described and its application to simulated data corrupted by noise and missing data is considered. It is shown that the algorithm improves the identification of slowly varying plasma density perturbations by attenuating the effect of fast fluctuations and noise contained in experimental data. First results obtained with this method in ASDEX Upgrade tokamak are presented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147766
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  • 7
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    A Ministry and its Community: Tobago - A Case Study in Participation (1974)
    Kingston, Jamaica : Periodicals Archive Online (PAO)
    Social and economic studies. 23:2 (1974:June) 176 
    Details
    ISSN: 0037-7651
    Topics: Sociology , Economics
    Notes: SPECIAL NUMBER ISSUES OF PUBLIC POLICY AND PUBLIC ADMINISTRATION IN THE COMMONWEALTH CARIBBEAN
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:5209-1974-023-02-000003
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  • 8
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    The Declining Status of the Jamaican Civil Service (1974)
    Kingston, Jamaica : Periodicals Archive Online (PAO)
    Social and economic studies. 23:2 (1974:June) 344 
    Details
    ISSN: 0037-7651
    Topics: Sociology , Economics
    Notes: SPECIAL NUMBER ISSUES OF PUBLIC POLICY AND PUBLIC ADMINISTRATION IN THE COMMONWEALTH CARIBBEAN
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:5209-1974-023-02-000011
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  • 9
    Electronic Resource
    Electronic Resource
    Radiating spherical collapse with shear and heat flow (1993)
    Springer
    Astrophysics and space science 199 (1993), S. 215-223 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider a spherical body consisting of a fluid with heat flow which radiates in its exterior a null fluid described by the outgoing Vaidya's metric, we prove that this solution matched with the outgoing Vaidya's metric represents a physically reasonable collapsing model. Our model has the remarkable property: it is shear-free and the motion of the fluid is geodesic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00613196
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of deflocculants on the characteristics of alumina bodies obtained by slip casting (1992)
    Springer
    Journal of materials science 27 (1992), S. 6662-6666 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Conformation of alumina bodies with differential porosities was carried out using a slip-casting technique. Preliminary results, showing the relationship between changes of rheological properties of the suspensions caused by pH variation and wall characteristics of the bodies, have been reported previously. The research was continued in order to establish the dependence of the structure of flow units in suspension on type and amount of deflocculants and its influence on the porosity of the walls obtained by slip casting. Rheometry, sedimentometry and electrophoresis were used to characterize the suspensions. Mercury porosimetry enabled the determination of porous structure. Results show a strong correlation between the properties of the suspensions and the characteristics of the presintered bodies and corroborate the possibility of fabrication of articles with differential porosities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165951
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