The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Gerik Scheuermann - One of the best experts on this subject based on the ideXlab platform.

  • Hot Lines tracking Lines in higher order tensor fields
    IEEE Visualization, 2005
    Co-Authors: Mario Hlawitschka, Gerik Scheuermann
    Abstract:

    Tensors occur in many areas of science and engineering. Especially, they are used to describe charge, mass and energy transport (i.e. electrical conductivity tensor, diffusion tensor, thermal conduction tensor resp.) If the locale transport pattern is complicated, usual second order tensor representation is not sufficient. So far, there are no appropriate visualization methods for this case. We point out similarities of symmetric higher order tensors and spherical harmonics. A spherical harmonic representation is used to improve tensor glyphs. This paper unites the definition of streamLines and tensor Lines and generalizes tensor Lines to those applications where second order tensors representations fail. The algorithm is tested on the tractography problem in diffusion tensor magnetic resonance imaging (DT-MRI) and improved for this special application.

  • IEEE Visualization - Hot-Lines: tracking Lines in higher order tensor fields
    IEEE Visualization 2005 - (VIS'05), 1
    Co-Authors: Mario Hlawitschka, Gerik Scheuermann
    Abstract:

    Tensors occur in many areas of science and engineering. Especially, they are used to describe charge, mass and energy transport (i.e. electrical conductivity tensor, diffusion tensor, thermal conduction tensor resp.) If the locale transport pattern is complicated, usual second order tensor representation is not sufficient. So far, there are no appropriate visualization methods for this case. We point out similarities of symmetric higher order tensors and spherical harmonics. A spherical harmonic representation is used to improve tensor glyphs. This paper unites the definition of streamLines and tensor Lines and generalizes tensor Lines to those applications where second order tensors representations fail. The algorithm is tested on the tractography problem in diffusion tensor magnetic resonance imaging (DT-MRI) and improved for this special application.

Mario Hlawitschka - One of the best experts on this subject based on the ideXlab platform.

  • Hot Lines tracking Lines in higher order tensor fields
    IEEE Visualization, 2005
    Co-Authors: Mario Hlawitschka, Gerik Scheuermann
    Abstract:

    Tensors occur in many areas of science and engineering. Especially, they are used to describe charge, mass and energy transport (i.e. electrical conductivity tensor, diffusion tensor, thermal conduction tensor resp.) If the locale transport pattern is complicated, usual second order tensor representation is not sufficient. So far, there are no appropriate visualization methods for this case. We point out similarities of symmetric higher order tensors and spherical harmonics. A spherical harmonic representation is used to improve tensor glyphs. This paper unites the definition of streamLines and tensor Lines and generalizes tensor Lines to those applications where second order tensors representations fail. The algorithm is tested on the tractography problem in diffusion tensor magnetic resonance imaging (DT-MRI) and improved for this special application.

  • IEEE Visualization - Hot-Lines: tracking Lines in higher order tensor fields
    IEEE Visualization 2005 - (VIS'05), 1
    Co-Authors: Mario Hlawitschka, Gerik Scheuermann
    Abstract:

    Tensors occur in many areas of science and engineering. Especially, they are used to describe charge, mass and energy transport (i.e. electrical conductivity tensor, diffusion tensor, thermal conduction tensor resp.) If the locale transport pattern is complicated, usual second order tensor representation is not sufficient. So far, there are no appropriate visualization methods for this case. We point out similarities of symmetric higher order tensors and spherical harmonics. A spherical harmonic representation is used to improve tensor glyphs. This paper unites the definition of streamLines and tensor Lines and generalizes tensor Lines to those applications where second order tensors representations fail. The algorithm is tested on the tractography problem in diffusion tensor magnetic resonance imaging (DT-MRI) and improved for this special application.

S Patsourakos - One of the best experts on this subject based on the ideXlab platform.

  • spectroscopic observations of Hot Lines constraining coronal heating in solar active regions
    The Astrophysical Journal, 2009
    Co-Authors: S Patsourakos, James A Klimchuk
    Abstract:

    Extreme-ultraviolet observations of warm coronal loops suggest that they are bundles of unresolved strands that are heated impulsively to high temperatures by nanoflares. The plasma would then have the observed properties (e.g., excess density compared with static equilibrium) when it cools into the 1-2MK range. If this interpretation is correct, then very Hot emission should be present outside of proper flares. It is predicted to be very faint, however. A critical element for proving or refuting this hypothesis is the existence of Hot, yet faint plasmas which should be at amounts predicted by impulsive heating models. We report on the first comprehensive spectroscopic study of Hot plasmas in active regions (ARs). Data from the Extreme-ultraviolet Imaging Spectrometer on Hinode were used to construct emission measure (EM) distributions in quiescent ARs in the 1-5 MK temperature range. The distributions are flat or slowly increasing up to approximately 3 MK and then fall off rapidly at higher temperatures. We show that AR models based on impulsive heating can reproduce the observed EM distributions relatively well. Our results provide strong new evidence that coronal heating is impulsive in nature.

  • spectroscopic observations of Hot Lines constraining coronal heating in solar active regions
    The Astrophysical Journal, 2009
    Co-Authors: S Patsourakos, James A Klimchuk
    Abstract:

    Extreme-ultraviolet observations of warm coronal loops suggest that they are bundles of unresolved strands that are heated impulsively to high temperatures by nanoflares. The plasma would then have the observed properties (e.g., excess density compared with static equilibrium) when it cools into the 1-2MK range. If this interpretation is correct, then very Hot emission should be present outside of proper flares. It is predicted to be very faint, however. A critical element for proving or refuting this hypothesis is the existence of Hot, yet faint plasmas which should be at amounts predicted by impulsive heating models. We report on the first comprehensive spectroscopic study of Hot plasmas in active regions (ARs). Data from the Extreme-ultraviolet Imaging Spectrometer on Hinode were used to construct emission measure (EM) distributions in quiescent ARs in the 1-5 MK temperature range. The distributions are flat or slowly increasing up to approximately 3 MK and then fall off rapidly at higher temperatures. We show that AR models based on impulsive heating can reproduce the observed EM distributions relatively well. Our results provide strong new evidence that coronal heating is impulsive in nature.

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

  • High Resolution Soft X-ray Spectroscopy and the Quest for the Hot (5–10 MK) Plasma in Solar Active Regions
    Frontiers in Astronomy and Space Sciences, 2021
    Co-Authors: Giulio Del Zanna, James A Klimchuk, Vincenzo Andretta, Peter J. Cargill, Alain J. Corso, Adrian N. Daw, Leon Golub, Helen E. Mason
    Abstract:

    We discuss the diagnostics available to study the 5–10 MK plasma in the solar corona, which is key to understanding the heating in the cores of solar active regions. We present several simulated spectra, and show that excellent diagnostics are available in the soft X-rays, around 100 Å, as six ionization stages of Fe can simultaneously be observed, and electron densities derived, within a narrow spectral region. As this spectral range is almost unexplored, we present an analysis of available and simulated spectra, to compare the Hot emission with the cooler component. We adopt recently designed multilayers to present estimates of count rates in the Hot Lines, with a baseline spectrometer design. Excellent count rates are found, opening up the exciting opportunity to obtain high-resolution spectroscopy of Hot plasma.

  • spectroscopic observations of Hot Lines constraining coronal heating in solar active regions
    The Astrophysical Journal, 2009
    Co-Authors: S Patsourakos, James A Klimchuk
    Abstract:

    Extreme-ultraviolet observations of warm coronal loops suggest that they are bundles of unresolved strands that are heated impulsively to high temperatures by nanoflares. The plasma would then have the observed properties (e.g., excess density compared with static equilibrium) when it cools into the 1-2MK range. If this interpretation is correct, then very Hot emission should be present outside of proper flares. It is predicted to be very faint, however. A critical element for proving or refuting this hypothesis is the existence of Hot, yet faint plasmas which should be at amounts predicted by impulsive heating models. We report on the first comprehensive spectroscopic study of Hot plasmas in active regions (ARs). Data from the Extreme-ultraviolet Imaging Spectrometer on Hinode were used to construct emission measure (EM) distributions in quiescent ARs in the 1-5 MK temperature range. The distributions are flat or slowly increasing up to approximately 3 MK and then fall off rapidly at higher temperatures. We show that AR models based on impulsive heating can reproduce the observed EM distributions relatively well. Our results provide strong new evidence that coronal heating is impulsive in nature.

  • spectroscopic observations of Hot Lines constraining coronal heating in solar active regions
    The Astrophysical Journal, 2009
    Co-Authors: S Patsourakos, James A Klimchuk
    Abstract:

    Extreme-ultraviolet observations of warm coronal loops suggest that they are bundles of unresolved strands that are heated impulsively to high temperatures by nanoflares. The plasma would then have the observed properties (e.g., excess density compared with static equilibrium) when it cools into the 1-2MK range. If this interpretation is correct, then very Hot emission should be present outside of proper flares. It is predicted to be very faint, however. A critical element for proving or refuting this hypothesis is the existence of Hot, yet faint plasmas which should be at amounts predicted by impulsive heating models. We report on the first comprehensive spectroscopic study of Hot plasmas in active regions (ARs). Data from the Extreme-ultraviolet Imaging Spectrometer on Hinode were used to construct emission measure (EM) distributions in quiescent ARs in the 1-5 MK temperature range. The distributions are flat or slowly increasing up to approximately 3 MK and then fall off rapidly at higher temperatures. We show that AR models based on impulsive heating can reproduce the observed EM distributions relatively well. Our results provide strong new evidence that coronal heating is impulsive in nature.

Josef Pelzl - One of the best experts on this subject based on the ideXlab platform.

  • Thermal expansion imaging and finite element simulation of Hot Lines in high power AlGaN HEMT devices
    Superlattices and Microstructures, 2004
    Co-Authors: D. Dietzel, Ralf Meckenstock, S. Chotikaprakhan, J. Bolte, Josef Pelzl, R. Aubry, J.c. Jacquet, S. Cassette
    Abstract:

    Abstract The temperature and thermo-elastic expansion of the heated area in a high power, high electron mobility transistor (HEMT) device have been investigated by means of finite element calculations and scanning thermal expansion microscopy. With both procedures a Hot line is located near the gate line of the transistor. To determine the absolute temperature, the thermo-elastic response was calibrated on the basis of the force–distance curve of the AFM and the thermal expansion of the gold layer on top of the heated areas. The maximum temperatures deduced by the two procedures are in reasonable agreement whereas discrepancies are found for the temperature profile of the Hot line, pointing towards a possible influence of the large aspect ratio of the device on the thermo-elastic measurement.

  • Higher harmonic thermal wave detection in thermoreflectance microscopy with combined electrical and optical heating
    Superlattices and Microstructures, 2004
    Co-Authors: D. Dietzel, B. K. Bein, Josef Pelzl
    Abstract:

    Abstract Insulating Lines and channels prepared by focused ion beam implantation on SIMOX wafers have been investigated by thermally modulated optical reflectance microscopy using optical and electrical excitation. Continuous Hot Lines and Hot spots can be visualized by modulated electrical heating, whereas insulating Lines forming channels can be imaged only with simultaneous optical and electrical excitation. Three different schemes have been investigated for the combined excitation: (i) optical modulation with additional DC voltage, (ii) optical and electrical pumps modulated at the same frequency with the detection effected at higher harmonics and (iii) two different modulation frequencies used for optical and electrical excitation with the detection effected at sum and difference frequencies. When detecting at higher frequencies, best contrast for the observation of the insulating Lines adjacent to a channel is achieved by recording the modulated reflectance signal at the fourth harmonic 4f where f is the modulation frequency of the optical and electrical pump. The observed contrast enhancement of the double excited thermoreflectance signal is found to be mainly of a thermal origin.