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  • 1
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    Positive regulation of T cell activation and integrin adhesion by the adapter Fyb/Slap (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-09-22
    Description: The molecular adapter Fyb/Slap regulates signaling downstream of the T cell receptor (TCR), but whether it plays a positive or negative role is controversial. We demonstrate that Fyb/Slap-deficient T cells exhibit defective proliferation and cytokine production in response to TCR stimulation. Fyb/Slap is also required in vivo for T cell-dependent immune responses. Functionally, Fyb/Slap has no apparent role in the activation of known TCR signaling pathways, F-actin polymerization, or TCR clustering. Rather, Fyb/Slap regulates TCR-induced integrin clustering and adhesion. Thus, Fyb/Slap is the first molecular adapter to be identified that couples TCR stimulation to the avidity modulation of integrins governing T cell adhesion.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Griffiths, E K -- Krawczyk, C -- Kong, Y Y -- Raab, M -- Hyduk, S J -- Bouchard, D -- Chan, V S -- Kozieradzki, I -- Oliveira-Dos-Santos, A J -- Wakeham, A -- Ohashi, P S -- Cybulsky, M I -- Rudd, C E -- Penninger, J M -- New York, N.Y. -- Science. 2001 Sep 21;293(5538):2260-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Amgen Institute, 620 University Avenue, Toronto, Ontario, Canada M5G 2C1.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11567140" target="_blank"〉PubMed〈/a〉
    Keywords: Actins/metabolism ; *Adaptor Proteins, Signal Transducing ; Animals ; Antigens, CD/metabolism ; Antigens, CD3/metabolism ; Antigens, Differentiation, T-Lymphocyte/metabolism ; B-Lymphocytes/immunology ; Carrier Proteins/genetics/*physiology ; Cell Adhesion ; Cell Adhesion Molecules/metabolism ; Chimera ; Gene Targeting ; Humans ; Immunization ; Immunoglobulin G/biosynthesis ; Integrins/*metabolism ; Intercellular Adhesion Molecule-1/metabolism ; Interferon-gamma/biosynthesis ; Interleukin-2/biosynthesis/pharmacology ; Lectins, C-Type ; *Lymphocyte Activation ; Lymphocyte Function-Associated Antigen-1/metabolism ; Mice ; Phosphoproteins/genetics/*physiology ; Receptors, Antigen, T-Cell/immunology/metabolism ; Receptors, Interleukin-2/metabolism ; Recombinant Proteins/metabolism ; Signal Transduction ; T-Lymphocytes/immunology/metabolism/*physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 2
    Electronic Resource
    Electronic Resource
    Kinetic theory of interaction of high frequency waves with a rotating plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 596-608 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The equations of motion of charged particles of a strongly magnetized flowing plasma under the influence of high frequency waves are derived in the guiding center approximation. A quasilinear theory of the interactions of waves with rotating plasmas is formulated. This is applied to investigate the effect of radio frequency waves on a rotating tokamak plasma with a heated minority species. The angular momentum drive is mainly due to the rf-induced radial minority current. The return current by the bulk plasma gives an equal and opposite rotation drive on the bulk. Using moment equations and a small banana width approximation, the J×B drive was evaluated for the bulk plasma. Quite remarkably, although collisions are included, the net rotation drive is due to a term which can be obtained by neglecting collisions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873846
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  • 3
    Electronic Resource
    Electronic Resource
    Gyrokinetic theory in the White–Chance–Boozer coordinates (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4609-4615 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The noncanonical Lagrangian theory of guiding center orbits is applied to the coordinate system of White–Chance–Boozer. The result is a generalized set of equations of motion which eliminates certain approximations of the static field and includes the effects of large rotations and high frequency waves. A quasilinear gyrokinetic theory is shown to readily follow from these equations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287740
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  • 4
    Electronic Resource
    Electronic Resource
    Erratum: "Radio frequency forces and wave helicity'' [Phys. Fluids B 5, 3590 (1993)] (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 805-805 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870778
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  • 5
    Electronic Resource
    Electronic Resource
    Radio-frequency-driven radial current and plasma rotation in a tokamak (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 501-510 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma rotational shear is potentially important for controlling the formation and positioning of internal transport barriers that could stabilize tokamak microturbulence and improve plasma confinement. A new physical mechanism capable of inducing plasma rotation and rotational shear via the ion cyclotron resonance frequency (ICRF) heating of minority ion species in a tokamak has been proposed [Perkins, White, Bonoli, and Chan, Phys. Plasmas 8, 2181 (2001)]. The present work evaluates the validity of this mechanism under the realistic condition when fast ions are continuously heated and slowed down in a driven system. Ion dynamics are calculated with a Monte Carlo code in which wave-induced diffusion in velocity space is accounted for by a quasilinear operator. The code follows the drift trajectories of test particles in a tokamak geometry under the influence of given rf fields and collisions with the background plasma. When the heating geometry is such that no net toroidal wave momentum is injected, the rotational characteristics described in Perkins et al. are reproduced. A physical picture emerges which ascribes the directionality of the rotation as a consequence of finite drift orbit width. The stochastic nature of the wave-induced diffusion can result in a net toroidal torque on the bulk plasma. A number of predicted features can be experimentally tested as a validation of finite orbit drift physics and radio-frequency-induced orbit diffusion. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1429633
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear three-dimensional self-consistent simulations of negative central shear discharges in the DIII-D tokamak (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3605-3619 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonlinear simulations of experimentally observed magnetohydrodynamic (MHD) bursts in DIII-D [J. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] L-mode negative central magnetic shear (NCS) discharges were performed with a full three-dimensional nonlinear MHD code. The effects of plasma rotation in the presence of resistivity and viscosity are included and an effectively implicit numerical scheme allows the transport profile to evolve self-consistently with the nonlinear MHD instabilities and externally applied sources and sinks. The simulations follow the MHD bursts and disruptions through the linear and nonlinear phases and identify the connections between the early MHD bursts and the ultimate disruption phase. Specific predictions of the growth and saturation of the modes are directly compared with experimental diagnostic measurements in DIII-D. The simulations show that the bursts observed in experiments are triggered by MHD instability of a resistive interchange mode and a resistive kink mode that are excited for critical plasma profiles. The critical profiles are determined by the balance between inductive and noninductive sources of current density. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380235
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  • 7
    Electronic Resource
    Electronic Resource
    Stable equilibria for bootstrap-current-driven low aspect ratio tokamaks (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1062-1068 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low aspect ratio tokamaks (LATs) can potentially provide a high ratio of plasma pressure to magnetic pressure β and high plasma current I at a modest size. This opens up the possibility of a high-power density compact fusion power plant. For the concept to be economically feasible, bootstrap current must be a major component of the plasma current, which requires operating at high βp. A high value of the Troyon factor βN and strong shaping is required to allow simultaneous operation at a high-β and high bootstrap fraction. Ideal magnetohydrodynamic stability of a range of equilibria at aspect ratio 1.4 is systematically explored by varying the pressure profile and shape. The pressure and current profiles are constrained in such a way as to assure complete bootstrap current alignment. Both βN and β are defined in terms of the vacuum toroidal field. Equilibria with βN≥8 and β∼35%–55% exist that are stable to n=∞ ballooning modes. The highest β case is shown to be stable to n=0,1,2,3 kink modes with a conducting wall. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872193
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  • 8
    Electronic Resource
    Electronic Resource
    Rotational and magnetic shear stabilization of magnetohydrodynamic modes and turbulence in DIII-D high performance discharges (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1951-1958 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The confinement and the stability properties of the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high-performance discharges are evaluated in terms of rotational and magnetic shear, with an emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped-electron-ηi mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the ηi mode suggests that the large core E×B flow shear can stabilize this mode and broaden the region of reduced core transport. Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low βN≤2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges, which has a broad region of weak or slightly negative magnetic shear (WNS), is described. The WNS discharges have broader pressure profiles and higher β values than the NCS discharges, together with high confinement and high fusion reactivity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871991
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  • 9
    Electronic Resource
    Electronic Resource
    Finite orbit analysis in tokamak plasmas (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 877-887 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The orbits of particles in the core region of a rotating tokamak plasma are analyzed. It is found that the phase space topologies of finite orbits differ significantly from those of thin orbit considerations. Specifically, in the absence of rotations, the trapped-passing boundary of co-moving particles has a finite extent in energies and disappears above a critical energy; and the pitch angle of the boundary has a rather strong energy dependence. Rotation and rotation shear cause significant shifts of this boundary in phase space so that above certain thresholds this boundary disappears. The finite orbit analysis also leads to improved analytic formulas for orbit averaged quantities of interest. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1447920
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  • 10
    Electronic Resource
    Electronic Resource
    Runaway electron production in DIII-D killer pellet experiments, calculated with the CQL3D/KPRAD model (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4590-4599 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Runaway electrons are calculated to be produced during the rapid plasma cooling resulting from "killer pellet" injection experiments, in general agreement with observations in the DIII-D [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] tokamak. The time-dependent dynamics of the kinetic runaway distributions are obtained with the CQL3D [R. W. Harvey and M. G. McCoy, "The CQL3D Code," in Proceedings of the IAEA Technical Committee Meeting on Numerical Modeling, Montreal, 1992 (International Atomic Energy Agency, Vienna, 1992), p. 489] collisional Fokker–Planck code, including the effect of small and large angle collisions and stochastic magnetic field transport losses. The background density, temperature, and Zeff are evolved according to the KPRAD [D. G. Whyte and T. E. Evans et al., in Proceedings of the 24th European Conference on Controlled Fusion and Plasma Physics, Berchtesgaden, Germany (European Physical Society, Petit-Lancy, 1997), Vol. 21A, p. 1137] deposition and radiation model of pellet–plasma interactions. Three distinct runway mechanisms are apparent: (1) prompt "hot-tail runaways" due to the residual hot electron tail remaining from the pre-cooling phase, (2) "knock-on" runaways produced by large-angle Coulomb collisions on existing high energy electrons, and (3) Dreicer "drizzle" runaway electrons due to diffusion of electrons up to the critical velocity for electron runaway. For electron densities below (approximate)1×1015 cm−3, the hot-tail runaways dominate the early time evolution, and provide the seed population for late time knock-on runaway avalanche. For small enough stochastic magnetic field transport losses, the knock-on production of electrons balances the losses at late times. For losses due to radial magnetic field perturbations in excess of (approximate)0.1% of the background field, i.e., δBr/B≥0.001, the losses prevent late-time electron runaway. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1312816
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