General Atomics (United States)

"Mathematical Handbook for Scientists and Engineers." Nuclear Science and Engineering, 13(2), pp. 202–203

The impact of radially sheared poloidal flows on ambient edge turbulence in tokamaks is investigated analytically. In the regime where poloidal shearing exceeds turbulent radial scattering, a hybrid time scale weighted toward the former is found to govern the decorrelation process. The coupling between radial and poloidal decorrelation results in a suppression of the turbulence below its ambient value. The turbulence quench mechanism is found to be insensitive to the sign of either the radial electric field or its shear.

The concept of fast ignition with inertial confinement fusion (ICF) is a way to reduce the energy required for ignition and burn and to maximize the gain produced by a single implosion. Based on recent experimental findings at the PETAWATT laser at Lawrence Livermore National Laboratory, an intense proton beam to achieve fast ignition is proposed. It is produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.

One of the scientific success stories of fusion research over the past decade is the development of the E×B shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high) mode to VH (very high) mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with E×B velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of E×B shear on the growth, radial extent, and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number of ways to change the radial electric field Er. An important theme in this area is the synergistic effect of E×B velocity shear and magnetic shear. Although the E×B velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of E×B velocity shear and facilitate turbulence stabilization. Considerable experimental work has been done to test this picture of E×B velocity shear effects on turbulence; the experimental results are generally consistent with the basic theoretical models.

The central event in the cellular immune response to invading microorganisms is the specific recognition of foreign peptides bound to major histocompatibility complex (MHC) molecules by the alphabeta T cell receptor (TCR). The x-ray structure of the complete extracellular fragment of a glycosylated alphabeta TCR was determined at 2.5 angstroms, and its orientation bound to a class I MHC-peptide (pMHC) complex was elucidated from crystals of the TCR-pMHC complex. The TCR resembles an antibody in the variable Valpha and Vbeta domains but deviates in the constant Calpha domain and in the interdomain pairing of Calpha with Cbeta. Four of seven possible asparagine-linked glycosylation sites have ordered carbohydrate moieties, one of which lies in the Calpha-Cbeta interface. The TCR combining site is relatively flat except for a deep hydrophobic cavity between the hypervariable CDR3s (complementarity-determining regions) of the alpha and beta chains. The 2C TCR covers the class I MHC H-2Kb binding groove so that the Valpha CDRs 1 and 2 are positioned over the amino-terminal region of the bound dEV8 peptide, the Vbeta chain CDRs 1 and 2 are over the carboxyl-terminal region of the peptide, and the Valpha and Vbeta CDR3s straddle the peptide between the helices around the central position of the peptide.

Chapter 3: MHD stability, operational limits and disruptions, Hender, T.C., Wesley, J.C, Bialek, J., Bondeson, A., Boozer, A.H., Buttery, R.J., Garofalo, A., Goodman, T.P, Granetz, R.S., Gribov, Y., Gruber, O., Gryaznevich, M., Giruzzi, G., Günter, S., Hayashi, N., Helander, P., Hegna, C.C., Howell, D.F., Humphreys, D.A., Huysmans, G.T.A., Hyatt, A.W., Isayama, A., Jardin, S.C., Kawano, Y., Kellman, A., Kessel, C., Koslowski, H.R., La Haye, R.J., Lazzaro, E., Liu, Y.Q., Lukash, V., Manickam, J., Medvedev, S., Mertens, V., Mirnov, S.V., Nakamura, Y., Navratil, G., Okabayashi, M., Ozeki, T., Paccagnella, R., Pautasso, G., Porcelli, F., Pustovitov, V.D., Riccardo, V., Sato, M., Sauter, O., Schaffer, M.J., Shimada, M., Sonato, P., Strait, E.J., Sugihara, M., Takechi, M., Turnbull, A.D., Westerhof, E., Whyte, D.G., Yoshino, R., Zohm, H., the ITPA MHD, Disruption and Magnetic Control Topical Group

The predictions of gyrokinetic and gyrofluid simulations of ion-temperature-gradient (ITG) instability and turbulence in tokamak plasmas as well as some tokamak plasma thermal transport models, which have been widely used for predicting the performance of the proposed International Thermonuclear Experimental Reactor (ITER) tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 1, p. 3], are compared. These comparisons provide information on effects of differences in the physics content of the various models and on the fusion-relevant figures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simplified plasma model and geometry which is an idealization of the plasma conditions and geometry in a Doublet III-D [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high confinement (H-mode) experiment. Most of the models show good agreements in their predictions and assumptions for the linear growth rates and frequencies. There are some differences associated with different equilibria. However, there are significant differences in the transport levels between the models. The causes of some of the differences are examined in some detail, with particular attention to numerical convergence in the turbulence simulations (with respect to simulation mesh size, system size and, for particle-based simulations, the particle number). The implications for predictions of fusion plasma performance are also discussed.

"Isospin in Nuclear Physics." Nuclear Science and Engineering, 42(1), pp. 116–117

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular Recognition of Protein−Ligand Complexes: Applications to Drug DesignRobert E. Babine and Steven L. BenderView Author Information Agouron Pharmaceuticals, Inc., 3565 General Atomics Court, San Diego, California 92121-1122 Cite this: Chem. Rev. 1997, 97, 5, 1359–1472Publication Date (Web):August 5, 1997Publication History Received14 February 1997Revised19 May 1997Published online5 August 1997Published inissue 1 August 1997https://pubs.acs.org/doi/10.1021/cr960370zhttps://doi.org/10.1021/cr960370zresearch-articleACS PublicationsCopyright © 1997 American Chemical SocietyRequest reuse permissionsArticle Views7012Altmetric-Citations789LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Inhibitors,Ligands,Monomers,Noncovalent interactions,Peptides and proteins Get e-Alerts

The recent FCC frequency allocation for UWB has generated a lot of interest in UWB technologies. There is 7,500 MHz of spectrum for unlicensed use. The main limitations are provided by the low-power spectral density and by the fact that the transmit signal must occupy at least 500 MHz at whole times. IEEE 802.15.3a is being developed for high-bit-rate PAN applications, and UWB is the most promising technology to support the stringent requirements: 110, 200, and 480 Mb/s. Two UWB multiband systems, frequency hopping and Spectral Keying, have been described in this article. Both systems meet the stringent requirements provided by IEEE 802.15.

A stochastic magnetic boundary, produced by an applied edge resonant magnetic perturbation, is used to suppress most large edge-localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H mode transport barrier and core confinement are unaffected by the stochastic boundary, despite a threefold drop in the toroidal rotation. These results demonstrate that stochastic boundaries are compatible with H modes and may be attractive for ELM control in next-step fusion tokamaks.

Expressions for the neoclassical resistivity and the bootstrap current coefficients in terms of aspect ratio and collisionality are widely used in simulating toroidal axisymmetric equilibria and transport evolution. The formulas used are in most cases based on works done 15–20 years ago, where the results have been obtained for large aspect ratio, small or very large collisionality, or with a reduced collision operator. The best expressions to date and to our knowledge are due to Hirshman [S. P. Hirshman, Phys. Fluids 31, 3150 (1988)] for arbitrary aspect ratio in the banana regime and Hinton–Hazeltine [F. L. Hinton and R. D. Hazeltine, Rev. Mod. Phys. 48, 239 (1976)] for large aspect ratio and arbitrary collisionality regime. A code solving the Fokker–Planck equation with the full collision operator and including the variation along the magnetic field line, coupled with the adjoint function formalism, has been used to calculate these coefficients in arbitrary equilibrium and collisionality regimes. The coefficients have been obtained for a wide variety of plasma and equilibrium parameters and a comprehensive set of formulas, which have been fitted to the code results within 5%, is proposed for evaluating the neoclassical conductivity and the bootstrap current coefficients. This extends previous works and also highlights inaccuracies in the previous formulas in this wide plasma parameter space.

Myeloid cell activation by lipopolysaccharides (LPS) involves two proteins, plasma LPS-binding protein (LBP) and cell-membrane CD14. Cell membrane CD14, anchored by a glycerophosphatidylinositol tail, is the cellular receptor for LPS-LBP complexes. Another form of CD14, without the lipid tail, circulates as a soluble plasma protein. In this work we show that soluble CD14 (sCD14) is required for activation of endothelial and epithelial cells by LPS. We propose that LPS-LBP complexes transfer LPS to sCD14, and the LPS-sCD14 complexes then bind to a cellular receptor. Support for this pathway comes from experiments in which LBP and CD14 in normal human serum are blocked by specific antibodies, experiments in which serum is replaced by purified LBP and sCD14, and experiments in which specific binding of [3H]LPS to epithelial cells is quantitated.

Chapter 2: Plasma confinement and transport, Doyle, E.J., Houlberg, W.A., Kamada, Y., Mukhovatov, V., Osborne, T.H., Polevoi, A., Bateman, G., Connor, J.W., Cordey, J.G., Fujita, T., Garbet, X., Hahm, T.S., Horton, L.D., Hubbard, A.E., Imbeaux, F., Jenko, F., Kinsey, J.E., Kishimoto, Y., Li, J., Luce, T.C., Martin, Y., Ossipenko, M., Parail, V., Peeters, A., Rhodes, T.L., Rice, J.E., Roach, C.M., Rozhansky, V., Ryter, F., Saibene, G., Sartori, R., Sips, A.C.C., Snipes, J.A., Sugihara, M., Synakowski, E.J., Takenaga, H., Takizuka, T., Thomsen, K., Wade, M.R., Wilson, H.R., ITPA Transport Physics Topical Group, ITPA Confinement Database and Modelling Topical Group, ITPA Pedestal and Edge Topical Group

Chapter 1: Overview and summary, Shimada, M., Campbell, D.J., Mukhovatov, V., Fujiwara, M., Kirneva, N., Lackner, K., Nagami, M., Pustovitov, V.D., Uckan, N., Wesley, J., Asakura, N., Costley, A.E., Donné, A.J.H., Doyle, E.J., Fasoli, A., Gormezano, C., Gribov, Y., Gruber, O., Hender, T.C., Houlberg, W., Ide, S., Kamada, Y., Leonard, A., Lipschultz, B., Loarte, A., Miyamoto, K., Mukhovatov, V., Osborne, T.H., Polevoi, A., Sips, A.C.C.

While the results of early work on the density limit in tokamaks from the ORMAK and DITE groups have been useful over the years, results from recent experiments and the requirements for extrapolation to future experiments have prompted a new look at this subject. There are many physical processes which limit the attainable densities in tokamak plasmas. These processes include: (1) radiation from low Z impurities, convection, charge exchange and other losses at the plasma edge; (2) radiation from low or high Z impurities in the plasma core; (3) deterioration of particle confinement in the plasma core; and (4) inadequate fuelling, often exacerbated by strong pumping by walls, limiters or divertors. Depending upon the circumstances, any of these processes may dominate and determine a density limit. In general, these mechanisms do not show the same dependence on plasma parameters. The multiplicity of processes leading to density limits with a variety of scaling has led to some confusion when comparing density limits for different machines. The authors attempt to sort out the various limits and to extend the scaling law for one of them to include the important effects of plasma shaping, i.e. ; e = k , where n e is the line average electron density (10 20 m −3 ), κ is the plasma elongation and (MA·m −2 ) is the average plasma current density, defined as the total current divided by the plasma cross-sectional area. In a sense, this is the most important density limit since, together with the q-limit, it yields the maximum operating density for a tokamak plasma. It is shown that this limit may be caused by a dramatic deterioration in core particle confinement occurring as the density limit boundary is approached. This mechanism can help explain the disruptions and Marfes that are associated with the density limit.

A model based on magnetohydrodynamic (MHD) stability of the tokamak plasma edge region is presented, which describes characteristics of edge localized modes (ELMs) and the pedestal. The model emphasizes the dual role played by large bootstrap currents driven by the sharp pressure gradients in the pedestal region. Pedestal currents reduce the edge magnetic shear, stabilizing high toroidal mode number (n) ballooning modes, while at the same time providing drive for intermediate to low n peeling modes. The result is that coupled peeling–ballooning modes at intermediate n (3

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe "One-Bead-One-Compound" Combinatorial Library MethodKit S. Lam, Michal Lebl, and Viktor KrchňákView Author Information Arizona Cancer Center, Department of Medicine, Department of Microbiology and Immunology, 1501 N. Campbell Avenue, Tucson, Arizona 85724, and Houghten Pharmaceuticals Inc., 3550 General Atomics Court, San Diego, California 92121 Cite this: Chem. Rev. 1997, 97, 2, 411–448Publication Date (Web):April 1, 1997Publication History Received19 November 1996Revised21 January 1997Published online1 April 1997Published inissue 1 April 1997https://pubs.acs.org/doi/10.1021/cr9600114https://doi.org/10.1021/cr9600114research-articleACS PublicationsCopyright © 1997 American Chemical SocietyRequest reuse permissionsArticle Views8528Altmetric-Citations601LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Assays,Monomers,Organic polymers,Peptides and proteins,Receptors Get e-Alerts

We show that linear collisionless processes do not damp poloidal flows driven by ion-temperature-gradient (ITG) turbulence. Since these flows play an important role in saturating the level of the turbulence, this level, as well as the transport caused by ITG modes, may be overestimated by gyrofluid simulations, which employ linear collisionless rotation damping.

An efficient method is given for self-consistent reconstruction of the tokamak current profiles and their associated magnetic topology using the magnetohydrodynamic (MHD) equilibrium constraint from external magnetic measurements, kinetic profile measurements, internal poloidal magnetic field measurements, and topological information from soft X-ray (SXR) measurements. Illustrative examples for beam heated H-mode divertor discharges in the DIII-D tokamak are presented, using the experimentally measured kinetic profile information and external magnetic data from the existing diagnostics. Comparative reconstructions of the current profile using various combinations of diagnostics are given. Also presented is an alternative magnetic analysis method in which the MHD equilibrium is reconstructed using external magnetic data and a constraint on the edge pressure gradient. The results of a sensitivity study are given which show that the axial safety factor q(0) can be more accurately determined when additional information from internal poloidal magnetic measurements is used in conjunction with the external magnetic, kinetic and SXR topological data.