Showing papers by "David W. Johnson published in 1990"
01 Jun 1990
TL;DR: Oxygen plasma-treated polydimethylsiloxane surfaces were aged in a low energy (air) and in a high energy (water) medium, and the results showed that when aging was performed in water, a high surface tension was maintained as discussed by the authors.
Abstract: Oxygen plasma-treated polydimethylsiloxane surfaces were aged in a low-energy (air) and in a high-energy (water) medium. Treated samples were characterized using a combination of surface-sensitive techniques: X-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, and contact angle measurements. Plasma treatments cause large increases in surface tension of treated samples. When aged in air (low-surface-energy medium) the samples returned to a low-surface-tension situation. The mechanism was a combination of diffusive burial of polar groups in the bulk and condensation of silanol groups formed by plasma treatment and consequent crosslinking. When aging was performed in water, a high surface tension was maintained.
485 citations
Journal Article•
TL;DR: In a 4th grade classroom the teacher is trying out learning groups and she sighs, "This is a mess,\" she thinks as mentioned in this paper, "My stu dents do not know how to work coop eratively".
Abstract: I n a 4th grade classroom the teacher is trying out learning groups \"This is a mess,\" she thinks. In one group, students are bickering over who is going to do the writing. In another group, one child sits quietly, too shy to participate Two members of a third group are talking about football while the third member works on the assignment \"My stu dents do not know how to work coop eratively,\" she sighs What is a teacher to do in such a situation? Simply placing students in groups and telling them to work to gether does not, in and of itself, pro duce cooperation and certainly not the higher achievement and positive social outcomes that can result from cooperative learning groups The rea son? Traditional group efforts may go wrong in many ways. Group members sometimes seek a free ride on others' work by \"leaving it to George\" to complete the group's tasks. Students who are stuck doing all the work sometimes decrease their efforts to avoid being suckers. High-ability group members may take over in ways that benefit themselves at the expense of lower achieving group members (the \"rich get richer\" effect). Pressures to conform may suppress individual Social skills—like other skills—must be teamed. But once learned, the abilities to cooperate and to work effectively with others will serve students well in school and later on in their careers
260 citations
TL;DR: The combination of teacher- and student-led processing resulted in greater problem-solving success and achievement in the cooperative conditions.
Abstract: Group processing was examined as a variable mediating the relationship between cooperative learning and achievement. Group processing may be defined as a review of a group session to describe the member actions that were helpful and unhelpful and to decide what actions to continue or change. Four conditions were included in the study: cooperative learning with no processing, cooperative learning with teacher-led processing (the teacher specified what cooperative skills to use, observed, and gave whole-class feedback about how well students were using the skills), cooperative learning with teacher- and student-led processing (the teacher specified what cooperative skills to use, observed, gave whole-class feedback about how well students were using the skills, and had groups discuss how well they interacted as a group), and individual learning. Forty-eight high-ability Black American high-school seniors and entering college freshmen at Xavier University were given a complex computer-assisted problem-solving assignment. Students in the three cooperative conditions performed better than those in the individual condition. The combination of teacher- and student-led processing resulted in greater problem-solving success and achievement in the cooperative conditions.
242 citations
TL;DR: In this article, a histological and immunocytochemically examined multiple sclerosis (MS) and control brains for the presence of mast cells and IgE-positive cells, but not in controls.
96 citations
TL;DR: In this paper, the average parallel resistivity and the location of the q=1 surface are found to be consistent with the predictions of neoclassical transport theory and inconsistent with classical resistivity (uncorrected for toroidal effects) for Ohmic plasmas in the TFTR tokamak.
Abstract: The average parallel resistivity and the location of the q=1 surface are found to be consistent with the predictions of neoclassical transport theory and inconsistent with classical resistivity (uncorrected for toroidal effects) for Ohmic plasmas in the TFTR tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. I, p. 51], both in near‐equilibrium and during ramping of the plasma current. These observations are incompatible with theories predicting anomalous parallel resistivity in concert with anomalous perpendicular transport.
72 citations
TL;DR: Left atrial dilatation, a normal development in healthy elderly subjects, plays a significant role in the pathophysiology of the increased incidence of atrial arrhythmias, and increased left ventricular mass is not associated with an increased frequency and/or complexity of ventricular arrh rhythmias.
65 citations
TL;DR: Results support the conclusion that both gE and gI are required for full Fc receptor activity, although gE alone can bind IgG to a lesser extent.
58 citations
TL;DR: Measurements of the spatial structure of the transport coefficients of He²+ on the Tokamak Fusion Test Reactor is reported, showing that the helium diffusivity is on the order of the ion momentum and thermaldiffusivity and is greater than the electron thermal diffuivity.
Abstract: Measurements of the spatial structure of the transport coefficients of He²+ on the Tokamak Fusion Test Reactor is reported. He²+ profiles were measured using charge-exchange spectroscopy after a helium puff into corotating L-mode plasmas. Modeling shows that the He²+ diffusivity is about 10 m²/s near the plasma edge and drops to below 1 m²/s inside of the q =1 surface. The convective velocity ranges from 1–3 m/s near q =1 to 20–40 m/s near the edge. The helium diffusivity is on the order of the ion momentum and thermal diffusivity and is greater than the electron thermal diffusivity.
58 citations
TL;DR: It is concluded that exposure to environmental tobacco smoke, particularly at the workplace, adversely affects the pulmonary function of adults.
Abstract: The effects of exposure to environmental tobacco smoke (passive smoking) on pulmonary function of non-smoking, healthy Iranian men (n = 167) and women (n = 108) were investigated. There were significant reductions in % predicted FEV1 (5.7%), forced vital capacity (FVC, 4.6%) and forced expiratory flow 25-75% (FEF25-75, 9.9%) among men exposed to cigarette smoke (n = 78). The adverse effect of passive smoking was greatest among men exposed at the workplace (reduction in % predicted FEV1 9.4%, FVC 7.6%, and FEF25-75 15.3%). No significant difference in pulmonary function was found among the 54 women exposed to passive smoke, but only eight women had smoke exposure at work. It is concluded that exposure to environmental tobacco smoke, particularly at the workplace, adversely affects the pulmonary function of adults.
56 citations
TL;DR: The data presented indicate that the oxidation of alpha- and gamma-methyl isoprenoid-derived fatty acids takes place largely in peroxisomes in human skin fibroblasts.
TL;DR: Polyenoic VLCFA phosphatidylcholine appears to be predominantly confined to nervous tissue in rats, and it is envisaged that this phospholipid is of physiological significance.
Abstract: Rat brain has been shown to contain polyenoic very-long-chain fatty acids (VLCFA) belonging to the n-3 and n-6 series with four, five and six double bonds and even-carbon chain lengths from 24 to 38. These fatty acids are almost exclusively located in unusual molecular species of phosphatidylcholine at the sn-1 position of the glycerol backbone, whereas saturated, monoenoic and polyenoic fatty acids with less than 24 carbon atoms are present at the sn-2 position. Polyenoic VLCFA phosphatidylcholine in neonatal rat brain is enriched with n-6 pentaenoic and n-3 hexaenoic VLCFA with up to 36 carbon atoms, whereas the corresponding phospholipid in adult rat brain mainly contains n-6 tetraenoic and n-3 pentaenoic VLCFA with up to 38 carbon atoms. The total amount of polyenoic VLCFA associated with phosphatidylcholine is highest in the brain of immature animals. Polyenoic VLCFA phosphatidylcholine appears to be predominantly confined to nervous tissue in rats, and it is envisaged that this phospholipid is of physiological significance.
TL;DR: In this paper, the toroidal rotation speed vφ(r) driven by neutral beam injection in tokamak plasmas and, in particular, simultaneous profile measurements have provided new insights into the nature of anomalous transport in TOkamaks.
Abstract: Measurements of the toroidal rotation speed vφ(r) driven by neutral beam injection in tokamak plasmas and, in particular, simultaneous profile measurements of vφ, Ti, Te, and ne, have provided new insights into the nature of anomalous transport in tokamaks. Low‐recycling plasmas heated with unidirectional neutral beam injection exhibit a strong correlation among the local diffusivities, χφ≊χi>χe. Recent measurements have confirmed similar behavior in broad‐density L‐mode plasmas. These results are consistent with the conjecture that electrostatic turbulence is the dominant transport mechanism in the tokamak fusion test reactor tokamak (TFTR) [Phys. Rev. Lett. 58, 1004 (1987)], and are inconsistent with predictions both from test‐particle models of strong magnetic turbulence and from ripple transport. Toroidal rotation speed measurements in peaked‐density TFTR ‘‘supershots’’ with partially unbalanced beam injection indicate that momentum transport decreases as the density profile becomes more peaked. In hi...
TL;DR: In this paper, the authors studied the magnetic reconnection in TFTR tokamak plasmas and found that the shape of the q profile is a good indicator of the presence of sawteeth.
Abstract: Magnetohydrodynamic (MHD) activity within three zones (core, half‐radius, and edge) of TFTR [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 51] tokamak plasmas are discussed. Near the core of the plasma column, sawteeth are often observed. Two types of sawteeth are studied in detail; one with complete, and the other with incomplete, magnetic reconnection. Their characteristics are determined by the shape of the q profile. Near the half‐radius the m/n=3/2 and 2/1 resistive ballooning modes are found to correlate with a beta collapse. The pressure and the pressure gradient at the mode rational surface are found to play an important role in stability. MHD activity is also studied at the plasma edge during limiter H modes. The edge localized modes (ELM’s) are found to have a precursor mode with a frequency between 50–200 kHz and a mode number m/n=1/0. The mode does not show a ballooning structure. While these instabilities have been studied on many other machines, ...
TL;DR: This work seeks to answer the following questions: 1) Are the cardiorespiratory effects of adrenergic agents secondary to possible changes in ACh release? 2) Does cAMP production have an intermediate role?
Abstract: The ventrolateral medulla, which functions as integrator of cardiorespiratory control, contains cholinergic and adrenergic neurons. Exogenously administered cholinergic and adrenergic agents affect...
TL;DR: In this article, a detailed analysis of the profile consistency of the measured values of Te(r), F1, F2 and F3 for sawtoothing TFTR discharges is presented.
Abstract: The principle of profile consistency states that for fixed limiter safety factor qa there are unique natural equilibrium profile shapes for the current density j(r) (and consequently q(r)) and the electron temperature Te(r) for any tokamak plasma, independent of the shapes of the heating power deposition profiles. The mathematical statements of the three basic consequences of this principle for sawtoothing discharges (i.e. discharges with q(0) ? 1) are: (1) r1/a = F1(l/qa) (? 1/qa, empirically); (2) Te/Te0 = F2(l/qa); and (3) a unique scaling law for the central electron temperature , where q(r1) = 1, Te is the volume average electron temperature, and F3(qa) = qa/q0. Since Ohm's law relates j(r) to Te(r), the principle of profile consistency dictates that this unique set of functions F1, F2 and F3 remain the same for all sawtoothing discharges in any tokamak, regardless of its size (i.e. a and R), Ip, VL, BT, etc. The paper presents a rather complete and detailed analysis of this self-consistency of the measured values of Te(r), F1, F2 and F3 for sawtoothing TFTR discharges. In particular, the analytical predictions of the profiles of Coppi's Gaussian, exponential, modified exponential and trapezoidal models, as well as the model profiles of Kadomtsev and Campbell et al. are compared with TFTR and TFR data. Some of the principal results are: (1) The empirical profile consistency relation r1/a = 1/qa is an acceptable solution of q(r1) = 1 for all qa dependent profiles. (2) A comparison between experiment and the present analytic results yields [Te/Te0]EXP ? [Te/Te0]AN + 0.05 for the profiles of Coppi's Gaussian model, and for the profiles of the models of Kadomtsev and Campbell et al. (3) For all qa independent profiles, F3(qa) = qa/q0 = constant, and, consequently, for all qa dependent profiles, F3(qa) = qa/q0 ~ qa when r1/a ? 1/qa, and, consequently, . (4) Coppi's and Ohkawa's forms of xe(r) yield , while the INTOR value of xe(r) yields . (5) For r1/a ? 1/qa, the profiles of Coppi's Gaussian model and those of the models of Kadomtsev and Campbell et al. all predict that the normalized sawtooth amplitude ?Te/Te ~ 1/qa, in agreement with the experimental observations. (6) For qa dependent models, universality of profiles exists in suitably reduced co-ordinates when r1/a ? 1/qa.
TL;DR: Tangential imaging is pursued on TFTR as a method to study instabilities with high poloidal mode number m, which cannot be seen with conventional perpendicular viewing soft x-ray diode arrays because the emission is integrated along a line of sight.
Abstract: Tangential imaging is being pursued on TFTR as a method to study instabilities with high poloidal mode number m. These instabilities cannot be seen with conventional perpendicular viewing soft x‐ray diode arrays because the emission is integrated along a line of sight. Computer simulations of tangential imaging indicate that excellent spatial resolution can be obtained. Prerequisites are (a) that the line of sight is nearly parallel to a magnetic field line at the point of closest approach to the center of the plasma, and (b) that there exists a steep gradient of the plasma radiation that is used for the measurements. The TFTR plans for a tangential, two‐dimensional imaging, soft x‐ray diode array will be outlined.
TL;DR: The data suggest that polyenoic VLCFA are synthesized in brain from shorter-chain precursor fatty acids and undergo beta-oxidation.
Abstract: Rat brain was recently found to contain polyenoic very-long-chain fatty acids (VLCFA) belonging to the n-3 and n-6 series with four, five and six double bonds and even-carbon chain lengths from 24 to 38 [Robinson, Johnson & Poulos (1990) Biochem. J. 265, 763-767]. In the present paper, the metabolism in vivo of hexacosatetraenoic acid (C26:4,n-6) was studied in neonatal rat brain. Rats were injected intracerebrally with [1-14C]C26:4,n-6 and the labelled metabolites were examined after 4 h. Radioactivity was detected mainly in non-esterified fatty acids, with smaller amounts in other neutral lipids and phospholipids. Radiolabelled fatty acid products included C28-36 tetraenoic and C26-28 pentaenoic VLCFA formed by elongation and desaturation of the substrate, and C14-24 saturated, C16-24 monoenoic, C18-24 dienoic, C18-22 trienoic and C20-24 tetraenoic fatty acids formed from released [1-14C]acetate either by synthesis de novo or by elongation of endogenous fatty acids. The data suggest that polyenoic VLCFA are synthesized in brain from shorter-chain precursor fatty acids and undergo beta-oxidation.
TL;DR: In this paper, three chemically prepared polyanilines (PANIs) have been studied by static secondary ion mass spectrometry under low "damage" conditions, and the results suggest consecutive doping of amine and imine nitrogen atoms in parts of the poly-aniline chain.
TL;DR: A curved-linear Fresnel lens was investigated to test the effect of concentrated solar radiation on surface and buried weed seed and found it had the greatest potential for affecting weed seed on the soil surface.
Abstract: A curved-linear Fresnel lens was investigated to test the effect of concentrated solar radiation on surface and buried weed seed. The lens produced a line focus 1 by 150 cm with a mean temperature of 309 C. A 20-s exposure to seed on the soil surface was 100% lethal to green foxtail, kochia, common lambsquarters, common purslane, and wild buckwheat. In a separate study, emergence from kochia and yellow foxtail seed was reduced 100% at 10 mm soil depth after 15 mm in soil of 35 and 93 g/kg moisture and 20 to 40% at 178 g/kg moisture content. Concentrated solar radiation from a Fresnel lens has the greatest potential for affecting weed seed on the soil surface. A series of Fresnel lenses and/or larger lenses may be required for many practical field applications. Nomenclature: Green foxtail, Setaria viridis (L.)Beauv. #3 SETVI; kochia, Kochia scoparia (L.)Schrad. # KCHSC; common lambsquarters, Chenopodium album L. # CHEAL; common purslane, Portulaca oleracea L. # POROL; wild buckwheat, Polygonum convolvulus L. # POLCO; yellow foxtail, Setaria glauca (L.)Beauv. # SETLU. Additional index words: Germination, temperature response, emergence, curved linear lens, SETVI, KCHSC, CHEAL, POROL, POLCO, AMARE, PANMI, BROTE, SETLU, AVEFA.
TL;DR: The time history of the central toroidal plasma rotation velocity in TFTR experiments with auxiliary heating by neutral deuterium beam injection and major radius compression has been measured from the Doppler shift of the emitted Ti XXI Kα line radiation as discussed by the authors.
Abstract: The time history of the central toroidal plasma rotation velocity in Tokamak Fusion Test Reactor (TFTR) experiments [Phys. Rev. Lett. 55, 2587 (1985)] with auxiliary heating by neutral deuterium beam injection and major‐radius compression has been measured from the Doppler shift of the emitted Ti XXI Kα line radiation. The experiments were conducted for neutral beam powers in the range 2.1–3.8 MW and line‐averaged densities in the range 1.8–3.0×1019 m−2. The observed rotation velocity increase during compression is consistent with theoretical estimates.
TL;DR: It is reported that the r-oxidation of isoprenoid-derived fatty acids is defective in fibroblasts from patients with inherited defects in peroxisomal biogenesis, and the defect in a-Oxidation is not confined to isop Renoid- derived fatty acids alone.
Abstract: In vivo and in vitro studies indicate that fatty acids with more than 22 carbon atoms (VLCFA) are degraded mainly in peroxisomes (Singh and Poulos, 1988). Recently we observed that not only VLCFA but also branched chain fatty acids such as phytanic and pristanic acids accumulate in the plasma of patients with inherited defects in peroxisomal biogenesis (Zellweger's syndrome, infantile Refsum's disease, and neonatal adrenoleukodystrophy (ALD)), indicating the probable involvement of peroxisomes in the aand r-oxidation of branched chain fatty acids (Poulos et al., 1988). However, while there have been some reports on the a-oxidation of phytanic acid by normal and peroxisomal disease fibroblasts, the degradation of r-methyl fatty acids other than phytanic acid, and of branched chain fatty acids with methyl groups in the aand ?-positions, has not been investigated. In the present paper we report that the r-oxidation of isoprenoid-derived fatty acids is defective in fibroblasts from patients with inherited defects in peroxisomal biogenesis. In addition we find that the defect in a-oxidation is not confined to isoprenoid-derived fatty acids alone.
TL;DR: In this article, the authors used beam attenuation codes and charge exchange cross sections to measure local metallic impurity concentrations, which were in good agreement with iron concentrations obtained from impurity transport code modeling of the brightnesses of EUV electron impact excited lines.
Abstract: Charge exchange excited lines of Fe23+ in the EUV region have been observed on the TFTR tokamak. These lines are emitted by Δn=1 transitions between levels with n=6–10 following charge exchange recombination of He‐like iron ions (Fe24+) with deuterium atoms injected by neutral beams. Iron concentrations are obtained by modeling the line brightnesses using a beam attenuation code and iron charge exchange cross sections. The results are in good agreement with iron concentrations obtained from impurity transport code modeling of the brightnesses of EUV electron impact excited lines, demonstrating that charge exchange excited lines may be reliably used to measure local metallic impurity concentrations.
TL;DR: For shots 18528 and 20345 the limiter is believed to have had a high recycling coefficient; shot 21790 occurred after modest limiter 'conditioning', which produced some reduction in recycling, though much less than for'supershots'; shot 22871 is a super-shot as discussed by the authors.
Abstract: (1) For shots 18528 and 20345 the limiter is believed to have had a high recycling coefficient; shot 21790 occurred after modest limiter 'conditioning', which produced some reduction in recycling, though much less than for 'supershots'; shot 22871 is a 'supershot'. These plasma regimes have been described previously [1, 2]. The older work does not include the 1987 corrections to the TVTS [2] electron temperatures (and Te dependent quantities) and so those data cannot be directly compared with the corrected data in the present tables.