Search Results - (Author, Cooperation:M. Chu)

2018-05-18

Institute of Physics Publishing (IOP)

1748-0221

Physics

2018-08-01

National Academy of Sciences

0027-8424

1091-6490

Biology

Medicine

Natural Sciences in General

2013-03-23

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Amino Acid Motifs ; Amino Acid Sequence ; Arrestin/metabolism ; Arrestins/metabolism ; Binding Sites ; Crystallography, X-Ray ; Ergolines/chemistry/metabolism ; Ergotamine/chemistry/*metabolism ; HEK293 Cells ; Humans ; Ligands ; Lysergic Acid Diethylamide/chemistry/metabolism ; Models, Molecular ; Molecular Sequence Data ; Protein Conformation ; Protein Structure, Secondary ; Receptor, Serotonin, 5-HT1B/chemistry/*metabolism ; Receptor, Serotonin, 5-HT2B/*chemistry/*metabolism ; Receptors, Serotonin/chemistry/metabolism ; Signal Transduction

2012-10-23

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Disulfides/chemistry/metabolism ; Enzyme Activation ; Heterotrimeric GTP-Binding Proteins/metabolism ; Humans ; Interleukin-8/chemistry/metabolism ; Lipid Bilayers/chemistry/*metabolism ; Models, Molecular ; Molecular Conformation ; Nuclear Magnetic Resonance, Biomolecular ; Phospholipids/chemistry/*metabolism ; Receptors, Interleukin-8A/*chemistry/*metabolism ; Signal Transduction

2016-04-14

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; Child, Preschool ; Chronic Disease ; Clostridium symbiosum/isolation & purification/physiology ; Diet/adverse effects/methods ; Feces/microbiology ; Female ; Germ-Free Life ; Growth Disorders/*diet therapy/etiology/*microbiology ; Healthy Volunteers ; Humans ; Infant ; Intestines/drug effects/*microbiology ; Liver/metabolism ; Malawi ; Malnutrition/complications/*diet therapy/*microbiology ; Mice ; Microbiota/drug effects/genetics/*physiology ; Milk, Human/chemistry/microbiology ; Mothers ; Oligosaccharides/analysis/pharmacology/therapeutic use ; Ruminococcus/isolation & purification/physiology ; Somatomedins/biosynthesis ; Weight Gain/drug effects

1752-7325

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Objectives: The objectives of this study were: (1) to compare the mercury levels in general dentists with the mercury levels in other health professionals using toenail clippings as a biomarker, (2) to identify risk factors associated with high mercury levels, and (3) to compare practice characteristics of dentists with high and low mercury levels. Methods: A sample of 579 men was randomly selected from the 33,737 men participating in the Health Professionals Follow-up Study who had provided toenail samples in 1987. A questionnaire was sent to these male subjects in 1991 to obtain information on fish consumption, tooth-brushing frequency, number of teeth, number of amalgam restorations, general practice or specialty status, number of amalgam restorations placed and removed per week, mercury storage and handling procedures, and mercury spillage incidents. A measure of long-term mercury exposure was obtained from toenail samples using neutron activation analysis for the 410 respondents (71% response rate). The 90th percentile mercury level in toenails (0.88 ppm) was selected as the threshold for elevated toenail mercury level. Results: No relationship was found between the number of dental amalgams and toenail mercury levels among general dentists, dental specialists, and nondental health professionals. General dentists were found to have more than twice the level of mercury in toenails than nondental health professionals (mean level=0.94 vs 0.45) and 60 percent higher than dental specialists (mean=0.59). The combined use of disposable capsules and water storage of scrap amalgam appeared to reduce the risk of elevated mercury levels. Regardless of professional status, consumption of tuna and saltwater fish were the primary exposure factors that were positively associated with toenail mercury levels. Conclusions: As shown by the associations with dental profession and fish consumption, the mercury content of toenails is a stable biomarker of cumulative long-term mercury exposure. The lack of association between nail mercury levels and number of amalgam restorations suggests that avoidance of mercury amalgam restorative materials cannot be justified by the presence of mercury released from dental amalgams.

Electronic Resource

2018-02-16

Cold Spring Harbor Laboratory Press

0890-9369

Biology

2018-03-14

Oxford University Press

0022-1899

1537-6613

Medicine

2018-08-03

Institute of Physics (IOP)

1757-8981

1757-899X

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

2018-07-13

Institute of Physics (IOP)

1757-8981

1757-899X

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

2018-10-23

The American Association of Immunologists (AAI)

0022-1767

1550-6606

Medicine

1089-7674

AIP Digital Archive

Physics

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.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

A new approach to the study of linear resistive magnetohydrodynamics stability is described. The approach is based on the traditional toroidal plasma model where the plasma resistivity and mass effects are essential only in thin layers around resonance surfaces, whereas the outer plasma is ideal and inertia free. This leads to differential equations with singular points. A new technique to solve these equations is proposed and it is shown that it has superior numerical convergence and accuracy properties to previous methods. The new technique is generally applicable to other problems in which differential equations with singular points arise. © 2000 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

Equilibrium and stability analyses have identified a class of tokamak configurations with conventional safety factor profiles (q0∼qmin(approximately-greater-than)1) at moderately high li(li∼1.0), and high normalized β(βN∼3.5–4.0), that are stable to the ideal n=1 kink without the requirement of wall stabilization. In contrast to previously identified high li, high βN equilibria, these configurations have high bootstrap current fractions (fBS∼50%–70%); they require only modest central current drive for maintaining steady state and are therefore compatible with advanced tokamak (AT) operation. Strong plasma shaping is crucial for achieving the high β and high bootstrap fraction simultaneously. © 1999 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

A tokamak equilibrium model, local to a flux surface, is introduced which is completely described in terms of nine parameters including aspect ratio, elongation, triangularity, and safety factor. By allowing controlled variation of each of these nine parameters, the model is particularly suitable for localized stability studies such as those carried out using the ballooning mode representation of the gyrokinetic equations. © 1998 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

The maximum normalized beta achieved in long-pulse tokamak discharges at low collisionality falls significantly below both that observed in short pulse discharges and that predicted by the ideal MHD theory. Recent long-pulse experiments, in particular those simulating the International Thermonuclear Experimental Reactor (ITER) [M. Rosenbluth et al., Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1995), Vol. 2, p. 517] scenarios with low collisionality νe*, are often limited by low-m/n nonideal magnetohydrodynamic (MHD) modes. The effect of saturated MHD modes is a reduction of the confinement time by 10%–20%, depending on the island size and location, and can lead to a disruption. Recent theories on neoclassical destabilization of tearing modes, including the effects of a perturbed helical bootstrap current, are successful in explaining the qualitative behavior of the resistive modes and recent results are consistent with the size of the saturated islands. Also, a strong correlation is observed between the onset of these low-m/n modes with sawteeth, edge localized modes (ELM), or fishbone events, consistent with the seed island required by the theory. We will focus on a quantitative comparison between both the conventional resistive and neoclassical theories, and the experimental results of several machines, which have all observed these low-m/n nonideal modes. This enables us to single out the key issues in projecting the long-pulse beta limits of ITER-size tokamaks and also to discuss possible plasma control methods that can increase the soft β limit, decrease the seed perturbations, and/or diminish the effects on confinement. © 1997 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

Detailed analysis of recent high beta discharges in the DIII-D [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] tokamak demonstrates that the resistive vacuum vessel can provide stabilization of low n magnetohydrodynamic (MHD) modes. The experimental beta values reaching up to βT=12.6% are more than 30% larger than the maximum stable beta calculated with no wall stabilization. Plasma rotation is essential for stabilization. When the plasma rotation slows sufficiently, unstable modes with the characteristics of the predicted "resistive wall'' mode are observed. Through slowing of the plasma rotation between the q=2 and q=3 surfaces with the application of a nonaxisymmetric field, it has been determined that the rotation at the outer rational surfaces is most important, and that the critical rotation frequency is of the order of Ω/2π=1 kHz. © 1995 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

Sustained stabilization of the n=1 kink mode by plasma rotation at beta approaching twice the stability limit calculated without a wall has been achieved in DIII-D by a combination of error field reduction and sufficient rotation drive. Previous experiments have transiently exceeded the no-wall beta limit. However, demonstration of sustained rotational stabilization has remained elusive because the rotation has been found to decay whenever the plasma is wall stabilized. Recent theory [Boozer, Phys. Rev. Lett. 86, 5059 (2001)] predicts a resonant response to error fields in a plasma approaching marginal stability to a low-n kink mode. Enhancement of magnetic nonaxisymmetry in the plasma leads to strong damping of the toroidal rotation, precisely in the high-beta regime where it is needed for stabilization. This resonant response, or "error field amplification" is demonstrated in DIII-D experiments: applied n=1 radial fields cause enhanced plasma response and strong rotation damping at beta above the no wall limit but have little effect at lower beta. The discovery of an error field amplification has led to sustained operation above the no-wall limit through improved magnetic field symmetrization using an external coil set. The required symmetrization is determined both by optimizing the external currents with respect to the plasma rotation and by use of feedback to detect and minimize the plasma response to nonaxisymmetric fields as beta increases. Ideal stability analysis and rotation braking experiments at different beta values show that beta is maintained 50% higher than the no wall stability limit for durations greater than 1 s, and approaches beta twice the no-wall limit in several cases, with steady-state rotation levels. The results suggest that improved magnetic-field symmetry could allow plasmas to be maintained well above no-wall beta limit for as long as sufficient torque is provided. © 2002 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

A proof of principle magnetic feedback stabilization experiment has been carried out to suppress the resistive wall mode (RWM), a branch of the ideal magnetohydrodynamic (MHD) kink mode under the influence of a stabilizing resistive wall, on the DIII-D tokamak device [Plasma Phys. Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159; Phys. Plasmas 1, 1415 (1994)]. The RWM was successfully suppressed and the high beta duration above the no-wall limit was extended to more than 50 times the resistive wall flux diffusion time. It was observed that the mode structure was well preserved during the time of the feedback application. Several lumped parameter formulations were used to study the feedback process. The observed feedback characteristics are in good qualitative agreement with the analysis. These results provide encouragement to future efforts towards optimizing the RWM feedback methodology in parallel to what has been successfully developed for the n=0 vertical positional control. Newly developed MHD codes have been extremely useful in guiding the experiments and in providing possible paths for the next step. © 2001 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

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.

Electronic Resource