Rotational resonance of nonaxisymmetric magnetic braking in the KSTAR tokamak.

One of the important rotational resonances in nonaxisymmetric neoclassical transport has been experimentally validated in the KSTAR tokamak by applying highly nonresonant n=1 magnetic perturbations to rapidly rotating plasmas. These so-called bounce-harmonic resonances are expected to occur in the presence of magnetic braking perturbations when the toroidal rotation is fast enough to resonate with periodic parallel motions of trapped particles. The predicted and observed resonant peak along with the toroidal rotation implies that the toroidal rotation in tokamaks can be controlled naturally in favorable conditions to stability, using nonaxisymmetric magnetic perturbations.

Effects of electron-cyclotron-resonance-heating-induced internal kink mode on the toroidal rotation in the KSTAR Tokamak.

It is observed that the magnitude of the toroidal rotation speed is reduced by the central electron cyclotron resonance heating (ECRH) regardless of the direction of the toroidal rotation. The magnetohydrodynamics activities generally appear with the rotation change due to ECRH. It is shown that the internal kink mode is induced by the central ECRH and breaks the toroidal symmetry. When the magnetohydrodynamics activities are present, the toroidal plasma viscosity is not negligible. The observed effects of ECRH on the toroidal plasma rotation are explained by the neoclassical toroidal viscosity in this Letter. It is found that the neoclassical toroidal viscosity torque caused by the internal kink mode damps the toroidal rotation.

Near-infrared spectroscopy as a possible device for continuous monitoring of arterial carbon dioxide tension during cardiac surgery.

BACKGROUND: Insufflation of carbon dioxide (CO(2)) to the operative field has been used to prevent major organ injury attributed to air embolisms in cardiac surgery. However, it may be preferable to avoid hypercapnia induced by CO(2) insufflation, owing to its potentially harmful effect. To investigate the effectiveness of near-infrared spectroscopy (NIRS) as a possible method for continuous monitoring of arterial CO(2) tension during cardiac surgery, we evaluated the correlation between the change in arterial CO(2) tension and the change in regional cerebral oxygen saturation (rScO(2)) obtained from NIRS in as controlled a condition as possible. METHODS: Thirty patients who underwent surgical correction for atrial or ventricular septal defects were enrolled in this study. Patients who had pulmonary hypertension or other intracardiac anomalies were excluded. Anesthetic and cardiopulmonary bypass (CPB) management were conducted according to our standard institutional practice. Data obtained from arterial blood gas analyses and corresponding regional cerebral oxygen saturation (rScO(2)) recorded from NIRS before and after the insufflations of CO(2) during CPB were used for analysis. RESULTS: The change in arterial CO(2) tension correlated with the change in rScO(2) in the left hemisphere (r = 0.681, p <0.001, y = -1.393 + 0.547x) and right hemisphere (r = 0.690, p <0.001, y = -1.999 + 0.486x). To control the effects of other variables, including hematocrit and temperature, these relationship were not reduced (left hemisphere: r=0.678, p<0.001; right hemisphere: r=0.634, p<0.001). CONCLUSIONS: Since the change in regional cerebral oxygen saturation was correlated with the change in arterial CO(2) tension during mild hypothermic CPB, NIRS might be a possible non-invasive method for monitoring of arterial CO(2) tension without incurring additional cost in this setting.

Rotation characteristics during the resonant magnetic perturbation induced edge localized mode suppression on the KSTAR.

Measuring rotation profiles with a reliable spatial resolution is one of the critical diagnostics in understanding the plasma behavior especially for the edge transport. In the KSTAR experiments, it has been consistently observed from the charge exchange spectroscopy measurements that the magnetic perturbations not only suppresses edge localized modes (ELMs) but also reduces toroidal rotations. In this paper, toroidal velocities of the carbon impurity and their profile evolutions during ELMy and ELM-suppressed phases are presented. The rotation profiles are shown to collapse immediately after an ELM burst and continue to build up until the next burst that accompanies another collapse. Toroidal rotations following the resonant magnetic perturbations applications are observed to be reduced along with the ELMs suppressed.

Digital I/Q demodulation for KSTAR ion cyclotron range of frequency system.

An ion cyclotron range of frequency system requires rf diagnostics for a rf-plasma coupling or for maintaining a correct operation. A detector based on a digital I/Q demodulation technique collects the rf amplitude and phase at the same time without errors from the I/Q imbalance inherent in an analog counterpart. The theory of such a detector was studied and implemented for the first campaign of the KSTAR tokamak. Experimental results of the rf and other diagnostics are presented and discussed.

Phospholipase A2 engineering. X-ray structural and functional evidence for the interaction of lysine-56 with substrates.

Site-directed mutagenesis studies of bovine pancreatic phospholipase A2 (PLA2, overproduced in Escherichia coli) showed that replacement of surface residue Lys-56 by a neutral or hydrophobic amino acid residue resulted in an unexpected and significant change in the function of the enzyme. The kcat for phosphatidylcholine micelles increases 3-4-fold for K56M, K56I, and K56F and ca. 2-fold for K56N and K56T but does not change for K56R. These results suggest that the side chain of residue 56 has significant influence on the activity of PLA2. In order to probe the structural basis for the enhanced activity, the crystal structures of wild-type and K56M PLA2 were determined by X-ray crystallography to a resolution of 1.8 A. The results suggest that the mutation has not only perturbed the conformation of the side chain of Met-56 locally but also caused conformational changes in the neighboring loop (residues 60-70), resulting in the formation of a hydrophobic pocket by residues Met-56, Tyr-52, and Tyr-69. Docking of a phosphatidylcholine inhibitor analogue into the active site of K56M, according to the structure of the complex of cobra venom PLA2-phosphatidylethanolamine inhibitor analogue [White, S.P., Scott, D. L., Otwinowski, Z., Gleb, M. H., & Sigler, P. (1990) Science 250, 1560-1563], showed that the choline moiety [N(CH3)3]+ is readily accommodated into the newly formed hydrophobic pocket with a high degree of surface complementarity. This suggests a possible interaction between residue 56 and the head group of the phospholipid, explaining the enhanced activities observed when the positively charged Lys-56 is substituted by apolar residues, viz., K56M, K56I, and K56F. Further support for this interpretation comes from the 5-fold enhancement in kcat for the mutant K56E with a negatively charged side chain, where there would be an attractive electrostatic interaction between the side chain of Glu-56 and the positively charged choline moiety. Our results also refute a recent report [Tomasselli, A. G., Hui, J., Fisher, J., Zürcher-Neely, H., Reardon, I.M., Oriaku, E., Kézdy, F.J., & Heinrikson, R.L. (1989) J. Biol. Chem. 264, 10041-10047] that substrate-level acylation of Lys-56 is an obligatory step in the catalysis by PLA2.