Showing papers by "David W. Johnson published in 1988"

Bootstrap current in TFTR.

Abstract: Neutral-beam--heated plasmas in TFTR show evidence of substantial non-Ohmically driven toroidal current, even for balanced beam momentum input. The observations are inconsistent with calculations including only Ohmic and beam-driven currents, and presently can only be matched by models including the neoclassical bootstrap current.

Critical Thinking through Structured Controversy.

Abstract: U sing academic conflicts for in structional purposes is one of the most dynamic and involv ing, yet least-used teaching strategies. Although creating a conflict is an ac cepted writer's tool for capturing an audience, teachers often suppress stu dents' academic disagreements and consequently miss out on valuable op portunities to capture their own audi ences and enhance learning. Teachers generally avoid and sub due students' academic conflicts for several reasons. For instance, they may view conflicts as divisive, alienating students from each other, with the least capable feeling defeated and hu miliated (Collins 1970, DeCecco and Richards 1974). Another reason is that teachers do not have an instructional model for structuring and controlling academic controversies to stimulate learning. Over the past 10 years, we have developed and tested a theory about how controversy promotes positive

Impact of Positive Interdependence and Academic Group Contingencies on Achievement

Abstract: The effects of positive goal interdependence and positive goal and positive reward interdependence on achievement were investigated. The control group (n = 26) consisted of American students in a 10th-grade social studies class, and the experimental group (n = 28) consisted of American students in a 10th-grade social studies class that included four academically disabled and isolated 10th-grade students (3 male and 1 female). The results indicated that cooperation promotes higher achievement than competition does, and that both positive goal and reward interdependence are needed to maximize student achievement.

Accumulation of pristanic acid (2, 6, 10, 14 tetramethylpentadecanoic acid) in the plasma of patients with generalised peroxisomal dysfunction

Abstract: The plasma of some patients with biochemical evidence of a generalised peroxisomal dysfunction (GPD) show greatly increased levels of phytanic acid as well as its α-oxidation product, pristanic acid (2, 6, 10, 14-tetramethylpentadecanoic acid). Increased amounts of 14- and 16- carbon branched chain fatty acids are also found in some of these patients. As pristanic acid is present in normal or near-normal amounts in classical Refsum disease and rhizomelic chondrodysplasia, two disorders characterised by deficiencies in phytanic acid oxidation, we speculate that its accumulation is not secondary to a defect in the α-oxidation of phytanic acid, but is indicative of a block in the peroxisomal β-oxidation of pristanic acid. The finding of phytanic acid, as well as a number of its metabolites in patients with inherited defects in peroxisomal biogenesis indicates that a number of the steps in phytanic acid degradation may be confined to peroxisomes.

The occurrence of polyenoic very long chain fatty acids with greater than 32 carbon atoms in molecular species of phosphatidylcholine in normal and peroxisome-deficient (Zellweger's syndrome) brain.

Abstract: The n-6 tetra- and pentaenoic fatty acids with carbon chain lengths greater than 32 found in normal brain are located predominantly in a separable species of phosphatidylcholine A similar phospholipid is found in increased amounts in the brain of peroxisome-deficient (Zellweger's syndrome) patients, but the fatty acid composition differs in that penta- and hexaenoic derivatives predominate Our data strongly suggest that the polyenoic very long chain fatty acids are confined to the sn-1 position of the glycerol moiety, while the sn-2 position is enriched in saturated, monounsaturated and polyunsaturated fatty acids with less than 24 carbon atoms It is postulated that these unusual molecular species of phosphatidylcholine may play some, as yet undefined, role in brain physiology

Experimental investigation of nonlinear dynamics in the Fermilab Tevatron.

Abstract: The nonlinear dynamics of transverse particle oscillations in the Fermilab Tevatron is studied experimentally and compared with prediction. Accurate measurements of various phase-space features are obtained. A theoretically expected metastable state of the accelerator, with particles captured on nonlinear resonance islands, is demonstrated experimentally, and stability of the state is investigated.

Measurements of radial profiles of the ion temperature and the plasma rotation velocity with the TFTR vertical x‐ray crystal spectrometer

Abstract: The TFTR vertical x‐ray crystal spectrometer has now been operating with three crystals and position‐sensitive detectors according to the original design specifications. The observed spectra of heliumlike Ti xxi, Cr xxiii, Fe xxv, and Ni xxvii have permitted a detailed comparison with the predictions from atomic theories, and they have provided data on the radial profiles of the ion temperature and toroidal rotation velocity, as well as the radial ion charge‐state distribution in TFTR discharges. Central ion temperatures of 20 keV and central plasma rotation velocities of 5×105 m/s have been recorded from plasmas with auxiliary neutral beam heating. These experimental results are presented. Also discussed are further instrumental improvements, such as the installation of two additional crystals and detectors and the installation of γ and neutron shielding, which will make it possible to measure under full DD and DT operation with 27 MW of neutral beam injection where neutron production rates of 1019 neutr...

Transport and stability studies on TFTR

Abstract: During the 1987 run, TFTR reached record values of QDD, neutron source strength, and Ti(0). Good confinement together with intense auxiliary heating has resulted in a plasma pressure greater than 3*105 Pascals on axis, which is at the ballooning stability boundary. At the same time improved diagnostics, especially ion temperature profile measurements, have led to increased understanding of tokamak confinement physics. Ion temperature profiles are much more peaked than previously thought, implying that ion thermal diffusivity, even in high ion temperature supershot plasmas, is greater than electron thermal diffusivity. Based on studies of the effect of beam orientation on plasma performance, one of the four neutral beamlines has been re-oriented from injecting co-parallel to counter parallel, which will increase the available balanced neutral injection power from 14 MW to 27 MW. With this increase in balanced beam power, and the addition of 7 MW of ICRF power it is planned to increase the present equivalant QDT of 0.25 to close to break-even conditions in the coming run.

Determination of the structure of magnetic islands on TFTR (invited)

Abstract: The Mirnov coil array, the horizontal soft x‐ray camera, and the ECE (electron cyclotron emission) grating polychromator are used to unfold the structure of m≥2 coherent magnetic fluctuations (assumed to be tearing modes) observed in TFTR. The modes are found predominantly in the enhanced confinement, or supershot, regime, and when present seriously degrade confinement. The poloidal and toroidal mode numbers (m and n) are determined with the Mirnov coil array. The radial structure is found by calculating the theoretical radial eigenmode (based on the calculated current‐density profile) and scaling the resulting linear eigenmode with the measured fluctuation amplitude at the plasma edge. The presence of rotating magnetic islands is detected as fluctuations on both the chord‐averaged soft‐x‐ray emissivity measurements and the fast grating polychromator electron temperature measurements. The ECE and soft‐x‐ray systems are used to identify coherent modes as islands and confirm estimates of the islands’ locati...

Social interdependence, psychological adjustment, and marital satisfaction in second marriages.

Abstract: Attitudes toward cooperative, competitive, and individualistic situations were correlated with measures of psychological health, orientation toward negative life stress, and marital satisfaction among 44 American stepcouples. Cooperativeness was unrelated to measures of wives' psychological pathology and orientation toward negative life stress but was positively related to wives' and husbands' marital satisfaction and husbands' overall psychological adjustment and positive orientation toward life events. Competitiveness was significantly related to wives' and husbands' psychological pathology and marital dissatisfaction, and was unrelated to orientation toward negative life stress. Individualistic attitudes were significantly related to wives' and husbands' psychological pathology and maladjustment, orientation toward negative life stress, and marital dissatisfaction. The results were stronger for the wives than for the husbands.

Regulation of intraganglionic synapses among rabbit parasympathetic neurones.

Abstract: 1. The response of parasympathetic neurones to the removal of preganglionic innervation was studied in the ciliary ganglia of adult rabbits. After section of the preganglionic oculomotor nerve, individual ciliary neurones were characterized electrophysiologically by intracellular recording, and morphologically by intracellular injection of horseradish peroxidase. 2. Within the first 24-48 h after nerve section, only two of fifty-nine neurones responded to antidromic stimulation of the postganglionic ciliary nerve with synaptic potentials. This result indicates that synaptic connections between principal neurones are rare in normal ganglia. 3. One week after denervation, however, excitatory postsynaptic potentials were recorded in thirty-nine out of fifty-three cells examined. Thus there is a rapid and extensive formation of intraganglionic connections after denervation. Morphological analysis of these ganglion cells showed numerous fine processes arising from the cell bodies and dendrites; such neurites were not present among control neurones. Many of these newly formed processes appeared to form synapses on neighbouring cells. 4. A similar proportion of neurones (about two-thirds of the cells) showed antidromically evoked excitatory postsynaptic potentials 2 weeks after denervation. Dendrites were still longer and more complex than controls at this time. After several months the morphology and prevalence of intraganglionic connections returned to normal as the ganglion became reinnervated. 5. Thus, denervation of rabbit ciliary ganglion cells induces the rapid formation of large numbers of functional synaptic connections among ganglion cells. It is postulated that local regulatory factors govern connections between parasympathetic ganglion cells. After denervation, these trophic signals are no longer modulated by presynaptic axons and they exert a stimulus for sprouting and synapse formation among this population of cholinergic neurones.

4-Hydroxybutyric aciduria in a patient without ataxia or convulsions.

Abstract: A child presenting with mild psychomotor retardation, hypotonia, microcephaly and hyperkinesis is described. Urinary organic acid analysis by combined gas chromatography-mass spectrometry revealed 4-hydroxybutyric aciduria. Succinic semialdehyde dehydrogenase activity in extracts of white cells derived from the patient was less than 10% of control values.

Role of Mast Cells in Peripheral Nervous System Demyelination

Abstract: It was previously reported that degranulation of peripheral nerve mast cells is an early event in the development of experimental allergic neuritis (EAN).’-’ We examined the possible consequences of this degranulation and ways in which it may be initiated. Vasoactive amines released by degranulating mast cells have been implicated in the development of demyelination by contributing to increased permeability of blood vessels.’-3 We examined the effects of another granule component, neutral protease, on PNS myelin. Rat serosal mast cells were degranulated with Compound 48/80, a standard mast cell secretagogue, and the supernatant was incubated with freshly prepared bovine PNS myelin. The proteases released on degranulation degraded 72 t 1.7% of P, protein in 3 hours. As Po is the major PNS myelin protein, such extensive degradation may be expected to be associated with significant structural disruption. As basic peptides can stimulate degranulation of mast cells: we also examined the effects of the cationic myelin proteins P, and myelin basic protein (MBP) on isolated serosal mast cells. Degranulation was assayed by measuring the release of the granule enzyme 0-hexosaminidase. Incubation of mast cells with either P, or MBP led to the release of approximately 50% of total mast cell P-hexosaminidase, which was comparable to the effect obtained with Compound 48/80 (TABLE 1). Myelin-

The Measurement of Poverty in Australia: 1981–82 and 1985–86

Abstract: In this paper I discuss indices used to measure the level of poverty in Australia among demographic groups and over time. The strengths and deficiencies of indices in current use are noted and alternative indices are presented. The theoretical properties of the indices are compared and discussed. The discussion is extended to include a brief review of poverty lines paying particular attention to the method used to update them. Poverty is measured for 1981–82 and 1985–86 for broad demographic groups. Differences between groups in each year and trends over time are noted and discussed. The performance of alternative indices are compared.

Characteristics of radiated power for various Tokamak Fusion Test Reactor regimes

Abstract: Power loss studies were carried out to determine the impurity radiation and energy transport characteristics of various Tokamak Fusion Test Reactor (TFTR) operation and confinement regimes including low mode, detached plasma, co‐only neutral beam injection (energetic ion regime), and the enhanced confinement (‘‘supershot’’) regime. Combined bolometric, spectroscopic, and infrared photometry measurements provide a picture of impurity behavior and power accounting in TFTR. The purpose of this paper is to make a survey of the various regimes with the aim of determining the radiated power signatures of each.

Effects of inhibitors on chloride outflux from cerebrospinal fluid.

Abstract: Movement of chloride from cerebrospinal fluid (CSF) to brain or blood is one of the factors that may be involved in regulation of CSF [Cl-], which is important to CSF acid-base balance We made quantitative measurements of the unidirectional outflux of radiolabeled chloride (38Cl, half-life 373 min) from CSF in anesthetized dogs, using ventriculocisternal perfusion (VCP) The outflux of 38Cl from CSF was determined from the difference between the movements of 38Cl and dextran using a one-compartment model VCP was performed at a rate of 14 ml/min for 14 min, and then slowed to 028 ml/min The 38Cl activity decreased to a steady-state level approximately 12% lower than that of dextran within 40-50 min Under control conditions for the first run (n = 24), the flux was 0042 +/- 0003 (SE) ml/min The outflux under control conditions (n = 6) tended to increase over three separate determinations in a 6-h period, being 136 +/- 19% of the first run on the second run, and 143 +/- 24% on the third There were no significant changes in 38Cl outflux compared with control ratios after the inclusion of bumetanide in the VCP fluid (n = 6), which inhibits sodium-coupled Cl- transport, with acetazolamide (n = 6), which inhibits carbonic anhydrase, or with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (n = 6), an inhibitor of carrier-mediated anion exchange These results suggest that the outward movement of chloride from CSF occurs mostly by passive diffusion and is not by mediated transport