Non-existence of normal tokamak equilibria with negative central current

Recent tokamak experiments employing off-axis, non-inductive current drive have found that a large central current hole can be produced. The current density is measured to be approximately zero in this region, though in principle there was sufficient current drive power for the central current density to have gone significantly negative. Recent papers have used a large aspect-ratio expansion to show that normal MHD equilibria (with axisymmetric nested flux surfaces, non-singular fields, and monotonic peaked pressure profiles) can not exist with negative central current. We extend that proof here to arbitrary aspect ratio, using a variant of the virial theorem to derive a relatively simple integral constraint on the equilibrium. However, this constraint does not, by itself, exclude equilibria with non-nested flux surfaces, or equilibria with singular fields and/or hollow pressure profiles that may be spontaneously generated.Comment: 5 pages, 3 figures. Submitted to Physics of Plasmas, Feb. 14, 2003. Revised Feb. 24, 2003. Vers. 2: revised May 29 to clarify points raised by referee, add references to recent work. July 18, accepted for publicatio

Recognition Memory Revisited: An Aging and Electrophysiological Investigation

This study provides a better understanding of contributing factors to age differences in human episodic memory. A recurrent finding in recognition memory is that older adults tend to have lower overall accuracy and tend to make fewer false-alarm errors in judging new items, relative miss errors (Coyne, Allen & Wickens, 1986; Danziger, 1980; Poon and Fozard 1980). Two possible causes for decline in these abilities include an age-related decrement in speed of processing (Salthouse 1991) and changes in information processing ability due to entropy (Allen, Kaufman, Smitch, & Propper 1998a; Mallik et al., in preparation). Additionally, age differences may be partially explained by a tendency for older adults to exhibit a conservative response bias. Surprisingly this study found no age-related differences in recognition memory accuracy, and older adults did not show a more conservative response bias. Due to these null results for age, the study examined the role of response bias (propensity to indicate a probe as being recognized, or new) on recognition memory accuracy and the role of the release from proactive interference (PI) across age. This study introduces a new ERP (Event-Related Potential) component to measure the recognition of “miss” responses called “FN400 Below Threshold”. This component, when looked at collapsed across Experiment 1 & Experiment 2 was positively correlated to behavioral accuracy suggesting that a more conservative response criterion hurts overall behavioral accuracy. Experiment 2 found that words learned from four categories were easier to remember than words from a single category due to a reduction in interference across items. This effect was found for both age groups

Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations

A self-regulating magnetic flux pumping mechanism in tokamaks that maintains the core safety factor at $q\approx 1$, thus preventing sawteeth, is analyzed in nonlinear 3D magnetohydrodynamic simulations using the M3D-C$^1$ code. In these simulations, the most important mechanism responsible for the flux pumping is that a saturated $(m=1,n=1)$ quasi-interchange instability generates an effective negative loop voltage in the plasma center via a dynamo effect. It is shown that sawtoothing is prevented in the simulations if $\beta$ is sufficiently high to provide the necessary drive for the $(m=1,n=1)$ instability that generates the dynamo loop voltage. The necessary amount of dynamo loop voltage is determined by the tendency of the current density profile to centrally peak which, in our simulations, is controlled by the peakedness of the applied heat source profile.Comment: submitted to Physics of Plasmas (23 pages, 15 Figures

The TULIP project : first on-line result and near future

The TULIP project aims to produce radioactive ion beams of short-lived neutron-deficient isotopes by using fusion-evaporation reactions in an optimized Target Ion Source System (TISS). The first step consisted of the design of a TISS to produce rubidium isotopes. It was tested with a primary beam of $^{22}$[email protected] MeV/A irradiating a natural Ni target at the SPIRAL1/GANIL facility in March 2022. Rates of $^{76,78}$Rb were measured as well as an exceptionally short atom-to-ion transformation time for an ISOL system, of the order of 200 \mathrm{\micro}s. The second step of the project aims at producing neutron-deficient short-lived metallic isotopes in the region of $^{100}$Sn. A "cold" prototype has been realized to study the electron impact ionization in the TISS cavity and a "hot" version is under construction to prepare an on-line experiment expected in the near future

A new explanation of the sawtooth phenomena in tokamaks

The ubiquitous sawtooth phenomena in tokamaks are so named because the central temperature rises slowly and falls rapidly, similar to the blades of a saw. First discovered in 1974, it has so far eluded a theoretical explanation that is widely accepted and consistent with experimental observations. We propose here a new theory for the sawtooth phenomena in auxiliary heated tokamaks, which is motivated by our recent understanding of "magnetic flux pumping." In this theory, the role of the (m, n) = (1, 1) mode is to generate a dynamo voltage, which keeps the central safety factor, q(0), just above 1.0 with low central magnetic shear. When central heating is present, the temperature on axis will increase until at some point, and the configuration abruptly becomes unstable to ideal MHD interchange modes with equal poloidal and toroidal mode numbers, m = n &gt; 1. It is these higher order modes and the localized magnetic stochasticity they produce that cause the sudden crash of the temperature profile, not magnetic reconnection. Long time 3D MHD simulations demonstrate these phenomena, which appear to be consistent with many experimental observations.</p

Cetuximab-induced aseptic meningitis: case report and review of a rare adverse event.

BACKGROUND: Cetuximab is a commonly used antibody agent in the treatment of colorectal or head and neck cancer. Although it is generally well tolerated in most patients, cetuximab has been associated with some rare but serious adverse events. Aseptic meningitis is one such distinctly uncommon adverse drug reaction. CASE PRESENTATION: We present the case of a middle-aged Caucasian patient, who presented with fever and headache within a few hours of starting cetuximab therapy and was diagnosed with cetuximab-induced aseptic meningitis after a complete workup. CONCLUSION: To our knowledge, this is the ninth case of cetuximab-induced aseptic meningitis reported in literature. Because of a nonspecific clinical presentation, this adverse drug reaction can be easily misdiagnosed. It is important to increase awareness of this potentially severe reaction among oncologists

Optimisation de la transformation génétique de la pomme de terre par Agrobacterium tumefaciens. Utilisation de la résistance à l'hygromycine comme marqueur sélectif

Optimization of potato genetic transformation by Agrobacterium tumefaciens using hygromycin resistance as selective marker. The objective of this work is the optimization of a genetic transformation and a regeneration protocol of transgenic plants in Solanum tuberosum cv Désirée using hygromycin resistance as selective marker. The gene Cat2 of Nicotiana plumbaginifolia and the gene SU2 of Gossypium hirsutum, both coding for catalases, have been used. Two antibiotic concentrations (5 and 10 mg . l -1 of culture medium) combined with two preculture periods (5 and 20 days) on non-selective medium were tested. Coculture medium was supplemented with 10 mg . l -1 of acetosyringone to test its effect on potato transformation. The addition of this phenolic compound to the coculture medium affected positively the regeneration aptitude of transgenic SU2 plants. Only the combination of 5 mg . l -1 of hygromycin and 20 days of preculture without antibiotic allowed the obtention of plants transformed with the gene SU2. Screening of the rooted shoots with PCR showed 45% of transgenic plants for both molecular constructions used