Search Results - (Author, Cooperation:G. Porter)

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  1. 1
    Staff View
    Publication Date:
    2018-09-26
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    1098-0121
    Electronic ISSN:
    1095-3795
    Topics:
    Physics
    Keywords:
    Electronic structure and strongly correlated systems
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Staff View
    Publication Date:
    2018-07-27
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    1098-0121
    Electronic ISSN:
    1095-3795
    Topics:
    Physics
    Keywords:
    Magnetism
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  3. 3
    Staff View
    Publication Date:
    2013-05-15
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Adult ; Case-Control Studies ; Child ; Chromatin/chemistry/metabolism ; DNA Mutational Analysis ; Enhancer Elements, Genetic/genetics ; Exome/genetics ; Female ; Genes, Developmental/genetics ; Heart Diseases/*congenital/*genetics/metabolism ; Histones/chemistry/*metabolism ; Humans ; Lysine/chemistry/metabolism ; Male ; Methylation ; Mutation ; Odds Ratio ; Promoter Regions, Genetic/genetics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  4. 4
    Y. Fainman ; G. Porter
    American Association for the Advancement of Science (AAAS)
    Published 2013
    Staff View
    Publication Date:
    2013-10-12
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  5. 5
    Staff View
    Publication Date:
    2018-05-02
    Publisher:
    Genetics Society of America (GSA)
    Print ISSN:
    0016-6731
    Topics:
    Biology
    Published by:
    http://www.genetics-gsa.org/

    Latest Papers from Table of Contents or Articles in Press
  6. 6
    T. A. Porter, G. P. Rowell, G. Jóhannesson, and I. V. Moskalenko
    American Physical Society (APS)
    Published 2018
    Staff View
    Publication Date:
    2018-09-01
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    0556-2821
    Electronic ISSN:
    1089-4918
    Topics:
    Physics
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  7. 7
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Detailed measurements in two dimensions by probes and Thomson scattering reveal unexpected local electric potential and electron pressure (pe) maxima near the divertor X point in L-mode plasmas in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. The potential drives E×B circulation about the X point, thereby exchanging plasma between closed and open magnetic surfaces at rates that can be comparable to the total cross-separatrix transport. The potential is consistent with the classical parallel Ohm's law. A simple model is proposed to explain the pressure and potential hills in low power, nearly detached plasmas. Recent two-dimensional edge transport modeling with plasma drifts also shows X-point pressure and potential hills but by a different mechanism. These experimental and theoretical results demonstrate that low power tokamak plasmas can be far from poloidal uniformity in a boundary layer just inside the separatrix. Additional data, although preliminary and incomplete, suggest that E×B circulation across the separatrix might be a common feature of low confinement behavior. © 2001 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1352597

    Articles: DFG German National Licenses
  8. 8
    Porter, G. D. ; Isler, R. ; Boedo, J. ; Rognlien, T. D.

    [S.l.] : American Institute of Physics (AIP)
    Published 2000
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The results of detailed comparisons between experimental measurements of the scrape-off layer and divertor plasmas and simulations using the UEDGE code for a DIII-D discharge [J. Luxon et al., Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986), Vol. I, p. 159] are reported. The simulations focus on understanding the flow of both fuel and impurity particles throughout the edge and scrape-off layer (SOL) plasma. The core impurity content and the core hydrogen ionization rate can be explained by sputtering and recycling in the divertor region alone. The model reproduces most of the detailed experimental measurements. The simulations include the effect of intrinsic impurities, assumed to be carbon originating from sputtering of the plasma facing surfaces. The simulations accurately reproduce the total radiated power, although the spatial profile of radiation is somewhat narrower in the simulation. The measured carbon density on closed field lines is reproduced well with the simulation. Comparison of carbon emission lines indicates the total carbon sputtering yield is a factor of 2 to 4 less than expected, although the total radiated power and core carbon content are insensitive to the sputtering yield. The agreement between simulation and experiment permits more meaningful interpretation of the experimental measurements. © 2000 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1286509

    Articles: DFG German National Licenses
  9. 9
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Experiments to explore the long-time evolution of noninductive, high βp plasmas in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159], have identified a new, quiescent, high performance regime. The experiments were carried out at low current (400–800 kA) with medium power neutral beam injection (3–10 MW). This regime is characterized by high q0 ((approximately-greater-than)2) and moderate li(∼1.3). It is reached by slow relaxation of the current profile, on the resistive time scale. As the profiles relax, q0 rises and li falls. When q0 goes above 2 (approximately), magnetohydrodynamic (MHD) activity disappears, and the stored energy rises. Most dramatic is the strong peaking of the central density, which increases by as much as a factor of 2. The improved central confinement appears similar to the PEP/reversed central shear/second stable core modes seen in tokamak experiments, but in this case without external intervention or transient excitation. At high current, a similar, but slower relaxation is seen. Also notable in connection with these discharges is the behavior of the edge and scrape-off layer (SOL). The edge localized modes (ELM's) as seen previously, are small and very rapid (to 1 kHz). The SOL exhibits high density (≥1×1019 m−3), which shows little or no falloff with radius. Also the power deposition at the divertor surface is very broad, up to four times the width usually seen. This regime is of particular interest for the development of steady-state tokamak operating scenarios, for the Tokamak Physics Experiment (TPX), and following reactors.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.870937

    Articles: DFG German National Licenses
  10. 10
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Intermittent plasma objects (IPOs) featuring higher pressure than the surrounding plasma, and responsible for ∼50% of the E×BT radial transport, are observed in the scrape off layer (SOL) and edge of the DIII-D tokamak [J. Watkins et al., Rev. Sci. Instrum. 63, 4728 (1992)]. Conditional averaging reveals that the IPOs, produced at a rate of ∼3×103 s−1, are positively charged and also polarized, featuring poloidal electric fields of up to 4000 V/m. The IPOs move poloidally at speeds of up to 5000 m/s and radially with E×BT/B2 velocities of ∼2600 m/s near the last closed flux surface (LCFS), and ∼330 m/s near the wall. The IPOs slow down as they shrink in radial size from 4 cm at the LCFS to 0.5 cm near the wall. The IPOs appear in the SOL of both L and H mode discharges and are responsible for nearly 50% of the SOL radial E×B transport at all radii; however, they are highly reduced in absolute amplitude in H-mode conditions. © 2001 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1406940

    Articles: DFG German National Licenses
  11. 11
    Porter, G. D. ; Moller, J. ; Brown, M. ; Lasnier, C.

    [S.l.] : American Institute of Physics (AIP)
    Published 1998
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Characterization of the plasma density and temperature at the last closed flux surface (the separatrix) of a tokamak requires accurate knowledge of the location of the separatrix. In this paper we discuss the effect of inaccuracy in the separatrix location on the measured parameters in DIII-D [Luxon et al., International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986), p. 159] An uncertainty in the separatrix position of ±0.5 cm, as expected in this device using magnetic reconstruction to determine the location of the separatrix, leads to unacceptably large uncertainty in the plasma parameters. Several techniques to improve the accuracy obtained from magnetic reconstruction are discussed. A new technique that is based on a characterization of the electron temperature profile is proposed. A comparison of the separatrix location defined in this manner with that obtained using magnetic reconstruction techniques suggests a systematic error in the reconstruction when the plasma is far from the walls and magnetic diagnostics. Determination of the perpendicular transport coefficients is given as an example of the improved statistics obtained using the new technique of defining the separatrix position.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.872830

    Articles: DFG German National Licenses
  12. 12
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The radiation of divertor heat flux on DIII-D [J. Luxon et al., in Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987), p. 159] is shown to greatly exceed the limits imposed by assumptions of energy transport dominated by electron thermal conduction parallel to the magnetic field. Approximately 90% of the power flowing into the divertor is dissipated through low-Z radiation and plasma recombination. The dissipation is made possible by an extended region of low electron temperature in the divertor. A one-dimensional analysis of the parallel heat flux finds that the electron temperature profile is incompatible with conduction-dominated parallel transport. Plasma flow at up to the ion acoustic speed, produced by upstream ionization, can account for the parallel heat flux. Modeling with the two-dimensional fluid code UEDGE [T. Rognlien, J. L. Milovich, M. E. Rensink, and G. D. Porter, J. Nucl. Mater. 196–198, 347 (1992)] has reproduced many of the observed experimental features. © 1998 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.872842

    Articles: DFG German National Licenses
  13. 13
    Porter, G. D.

    [S.l.] : American Institute of Physics (AIP)
    Published 1998
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The importance of radial particle flow on the power flowing across the last closed flux surface (separatrix) in DIII-D [Luxon et al., International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986), Vol. I, p. 159] is considered. The perpendicular thermal diffusivity at the separatrix is near 1 m2/s in low confinement operation (L-mode), and 0.1 m2/s in high confinement (H-mode). The particle diffusivity is about one-fourth of the thermal diffusivity producing radial particle fluxes of the order of kilo-amperes. The particle flux is 10 to 100 times the particle input from neutral beam sources, consistent with core fueling being dominated by neutral recycling. The radial particle flux scales with the neutral pressure in the private flux region, suggesting the core is fueled predominantly from neutrals which recycle from the divertor, through the private flux, and into the core near the singular point where the poloidal field is zero (X-point). There is significant core power loss associated with the large particle flux across the separatrix. The electron temperature measured at the top of the edge pedestal in H-mode operation scales inversely with the particle flux. In turn, the core energy confinement scales with the pedestal temperature, and hence inversely with the particle flux. The results presented here indicate the global particle confinement time is between 0.5 and 2 times the global energy confinement time. © 1998 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.873169

    Articles: DFG German National Licenses
  14. 14
    Rognlien, T. D. ; Ryutov, D. D. ; Mattor, N. ; Porter, G. D.

    [S.l.] : American Institute of Physics (AIP)
    Published 1999
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A two-dimensional calculation is presented for the transport of plasma in the edge region of a divertor tokamak solving continuity, momentum, and energy balance fluid equations. The model uses classical processes of parallel transport along the magnetic field and cross-field drifts together with anomalous radial diffusion, including perpendicular ion viscosity. The self-consistent electrostatic potential is calculated on both sides of the magnetic separatrix via quasineutrality and current continuity. Outside the separatrix, the model extends to material divertor plates where the incident plasma is recycled as neutral gas and where the plate sheath and parallel currents dominate the potential structure. Inside the separatrix, various radial current terms—from anomalous viscosity, collisional damping, inertia, and ∇B drifts—contribute to determining the potential. The model rigorously enforces cancellation of gyroviscous and magnetization terms from the transport equations. The results emphasize the importance of E×B particle flow under the X-point which depends on the sign of the toroidal magnetic field. Radial electric field profiles at the outer midplane show strong variation with the magnitude of the anomalous diffusion coefficients and the core toroidal rotation velocity, indicating that shear stabilization of edge turbulence can likewise be sensitive to these parameters.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.873488

    Articles: DFG German National Licenses
  15. 15
    Porter, G. D. ; Casper, T. A. ; Moller, J. M.

    [S.l.] : American Institute of Physics (AIP)
    Published 2001
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Particle losses associated with edge localized mode (ELM) activity on the DIII-D tokamak [J. Luxon et al., Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986, Vol. I, p. 159] are evaluated quantitatively using density profile data obtained from a Thomson scattering system. It is shown that up to 10% of the total core particle content is lost with each ELM. The particle loss varies inversely with ELM frequency. The temporally averaged ELM particle loss is shown to be about 25% of the total particle loss from the confined region under a wide variety of plasma conditions. Although this ELM loss is a small fraction of the total ion flux, it is large compared to the particle input from neutral beam heating. Hence ELM particle losses are sufficient to control the density rise associated with H-mode plasma operation with neutral beam heating. In addition to controlling the average density by enhancing the total ion flow, albeit only by 25%, it is posited that the ELMs play a role in determining the density profile in the H-mode pedestal region. © 2001 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1412863

    Articles: DFG German National Licenses
  16. 16
    Higginbottom, J. ; Slater, J. ; Porter, G. ; Whitfield, C. R.

    Oxford, UK : Blackwell Publishing Ltd
    Published 1975
    Staff View
    ISSN:
    1471-0528
    Source:
    Blackwell Publishing Journal Backfiles 1879-2005
    Topics:
    Medicine
    Notes:
    A new method of estimating fetal weight from the circumference of the fetal trunk, measured by ultrasound, is described. Comparison of weights estimated in this way with the actual birth weights of 50 fetuses, delivered not more than 48 hours later, shows a mean error in prediction of only 75 g, and in 94 per cent the error was less than 145 g. With such accuracy, the method is of clinical value, particularly in anticipating difficult delivery and in monitoring growth of the fetus at risk.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1111/j.1471-0528.1975.tb00709.x

    Articles: DFG German National Licenses
  17. 17
    Houlberg, W. A. ; Ross, D. W. ; Bateman, G. ; Cowley, S. C. ; Efthimion, P. C. ; Pfeiffer, W. W. ; Porter, G. D. ; Shumaker, D. E. ; Sugiyama, L. E. ; Wiley, J. C.

    New York, NY : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1089-7666
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The scope and detail of physics contained in computational models for fluid (density, momentum, energy) transport in toroidal plasmas have steadily increased during the past two decades. There has been considerable success in the development and verification of models for sources and sinks of particles, energy, momentum, and magnetic flux. Transport codes have collectively become very useful tools in interpreting experimental data and in providing guidance for new experiments. However, a more thorough understanding of the fundamental transport processes of magnetically confined plasmas and development of improved computational models are needed to enhance the predictive capabilities of transport codes. It is argued that fluid transport modeling by itself cannot lead to a complete understanding of transport—there must be a very strong collaboration among theory, experiment, and modeling on both the fluid and kinetic levels.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.859360

    Articles: DFG German National Licenses
  18. 18
    Rensink, M. E. ; Allen, S. L. ; Futch, A. H. ; Hill, D. N. ; Porter, G. D. ; Mahdavi, M. A.

    New York, NY : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1089-7666
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    In this paper an investigation of the particle confinement for beam-heated single-null discharges in the open divertor configuration of Doublet III-D (DIII-D) [E. J. Doyle et al., Phys. Fluids B 3, 2300 (1991)] is described. Results are based on a Monte Carlo neutral transport model with a relatively simple plasma model that utilizes experimental data on density, temperature, and heat flux profiles in the edge plasma. For a typical discharge, it is found that the particle confinement time in the quiescent H-mode phase is only about a factor of 2 larger than during the L-mode phase, an increase comparable to the energy confinement time increase. For both H-mode and L-mode phases the particle confinement time is about a factor of 4 larger than the energy confinement time. It is also found that the core plasma fueling rate is higher in the H mode due to the increased transparency of a thinner scrape-off layer. The longer particle confinement time and the increased fueling rate both contribute to the observed density rise during the quiescent period following the L–H transition. Flux surface-averaged transport modeling of the time evolution for the core plasma density profile during H mode suggests that a strong inward particle pinch is necessary near the separatrix.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.860751

    Articles: DFG German National Licenses
  19. 19
    Gupta, S. ; Francis, J. D. ; Porter, G. E. ; Valentine, J. M. J.

    Oxford : Blackwell Science Ltd
    Published 2000
    Staff View
    ISSN:
    1365-2044
    Source:
    Blackwell Publishing Journal Backfiles 1879-2005
    Topics:
    Medicine
    Notes:
    This study was designed to evaluate the therapeutic response, as perceived by patients and their general practitioners, to a supraregional residential pain management programme (INPUT). Twenty patients who completed the INPUT programme and their general practitioners, were sent locally designed questionnaires. Eighteen patients and 16 general practitioners responded. Patients were assessed for the effects of the programme on a wide variety of treatment targets reflecting quality of life. General practitioners were questioned about changes in dependence upon healthcare services. The mean time from attending INPUT to assessment was 11.4 (5.7) months. Thirteen patients indicated a moderate or maximal improvement in quality of life. General practitioners reported a reduced use of healthcare services and improvement in quality of life. The majority of our patients attending INPUT gained benefits that improved their quality of life. Healthcare services appeared to benefit from the patients' greater independence in managing their symptoms.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1046/j.1365-2044.2000.01126.x

    Articles: DFG German National Licenses
  20. 20
    Raper, Porter G.

    Charlottesville : Periodicals Archive Online (PAO)
    Published 1992
    Staff View
    ISSN:
    0042-675X
    Topics:
    English, American Studies
    URL:
    http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:1240-1992-068-01-000007

    Articles: DFG German National Licenses