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Nitrogen control of chloroplast development and differentiation

Description: The growth and development of plants and photosynthetic microorganisms is commonly limited by the availability of nitrogen. Our work concerns understanding the mechanisms by which plants and algae that are subjected to nitrogen deprivation alter the composition of photosynthetic membranes and enzymes involved in photosynthetic carbon metabolism. Toward these ends, we study biosynthetic and gene expression processes in the unicellular green alga Chlamydomonas reinhardtii which is grown in an ammonium-limited continuous culture system. We have found that the expression of nuclear genes, including those encoding for light-harvesting proteins, are severely repressed in nitrogen-limited cells whereas, in general, chloroplast protein synthesis is attenuated primarily at the level of mRNA translation. Conversely, nitrogen deprivation appears to lead to enhanced synthesis of enzymes that are involved in starch and storage lipid deposition. In addition, as a possible means by which photosynthetic electron transport activities and ATP synthesis is sustained during chronic periods of nitrogen deprivation, thylakoid membranes become enriched with components for chlororespiration. Characterization of the chlororespiratory electron transport constituents, including cytochrome complexes and NAD(P)H dehydrogenase is a major current effort. Also, we are striving to isolate the genes encoding chlororespiration proteins toward determining how they and others that are strongly responsive to nutrient availability are regulated.
Date: December 1, 1991
Creator: Schmidt, G.W.
Partner: UNT Libraries Government Documents Department

Investigations of transitions from order to chaos in dynamical systems. [Dept. of Physics/Engineering Physics, Stevens Inst. of Technology, Hoboken, New Jersey]

Description: Work was carried out in the following areas: The Arter flow and fast dynamo in connection with astrophysical magnetic fields, chaotic ion motion in the magnetosphere, nonlinear waves in two-dimensional plasmas, stochastic webs and transport phenomena, and chaotic mixing.
Date: March 1, 1993
Creator: Schmidt, G.
Partner: UNT Libraries Government Documents Department

Nitrogen control of chloroplast differentiation

Description: This project is directed toward understanding how the availability of nitrogen affects the accumulation of chloroplast pigments and proteins functioning in energy transduction and carbon metabolism. Molecular analyses performed with Chlamydomonas reinhardtii grown in a continuous culture system such that ammonium concentration is maintained at a low steady-state concentration so as to limit cell division. As compared to chloroplasts from cells of non-limiting nitrogen provisions, chloroplasts of N-limited cells are profoundly chlorophyll-deficient but still assimilate carbon for deposition of as starch and as storage lipids. Chlorophyll deficiency arises by limiting accumulation of appropriate nuclear-encoded mRNAs of and by depressed rates of translation of chloroplast mRNAs for apoproteins of reaction centers. Chloroplast translational effects can be partially ascribed to diminished rates of chlorophyll biosynthesis in N-limited cells, but pigment levels are not determinants for expression of the nuclear light-harvesting protein genes. Consequently, other signals that are responsive to nitrogen availability mediate transcriptional or post-transcriptional processes for accumulation of the mRNAs for LHC apoproteins and other mRNAs whose abundance is dependent upon high nitrogen levels. Conversely, limited nitrogen availability promotes accumulation of other proteins involved in carbon metabolism and oxidative electron transport in chloroplasts. Hence, thylakoids of N-limited cells exhibit enhanced chlororespiratory activities wherein oxygen serves as the electron acceptor in a pathway that involves plastoquinone and other electron carrier proteins that remain to be thoroughly characterized. Ongoing and future studies are also outlined.
Date: July 1, 1992
Creator: Schmidt, G.W.
Partner: UNT Libraries Government Documents Department

Nitrogen control of chloroplast differentiation. Final report

Description: This project was directed toward understanding at the physiological, biochemical and molecular levels of how photosynthetic organisms adapt to long-term nitrogen-deficiency conditions is quite incomplete even though limitation of this nutrient is the most commonly restricts plant growth and development. For our work on this problem, the unicellular green alga, Chlamydomonas reinhardtii, was grown in continuous cultures in which steady-state levels of nitrogen can be precisely controlled. N-limited cells exhibit the classical symptoms of deficiency of this nutrient, chlorosis and slow growth rates, and respond to nitrogen provision by rapid greening and chloroplast differentiation. We have addressed three aspects of this problem: (1) the regulation of pigment synthesis; (2) control of expression of nuclear genes encoding photosynthetic proteins; (3) changes in metabolic and electron transport pathways that enable sustained CO{sub 2} fixation even though they cannot be readily converted into amino and nucleic acids. For the last, principle components are: (a) enhanced mitochondrial respiratory activity intimately associated with photosynthates, and (b) the occurrence in thylakoids of a supplemental electron transport pathway that facilitates reduction of the plastoquinone pool. Together, these distinguishing features of N-limited cells are likely to enable cell survival, especially under conditions of high irradiance stress.
Date: May 1, 1998
Creator: Schmidt, G.W.
Partner: UNT Libraries Government Documents Department

Plasma density measurements using FM-CW millimeter wave radar techniques

Description: Modified FM-CW radar techniques using swept millimeter-wave oscillators are useful for determining when a particular density has been reached in a plasma. Narrowband measurements on the Princeton Large Torus (PLT) demonstrate the suitability of these techniques for controlling high-power auxiliary plasma heating systems. Broadband measurements using these same techniques are proposed, by which the density profile could be determined.
Date: September 1, 1980
Creator: Doane, J.L.; Mazzucato, E. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Measurement of emitted power in the divertor region in PBX

Description: In strongly indented PBX plasmas, radiated power profiles are calculated by combining data obtained from two bolometer arrays in order to study poloidal asymmetries arising from plasma indentation and characterize emission from the divertor region. A compact, 15-channel bolometer array that views the plasma tangentially along the midplane complements a 19-channel array that scans the plasma vertically in a poloidal plane. Assuming that radiated power density is constant along a magnetic flux surface, the contributions to the irradiance viewed by the poloidal array from the region inside the separatrix can be calculated from the midplane measurements. The difference between this contribution and the measured poloidal distribution is assumed to originate in the expanded boundary divertor. In general, the total radiated power loss constitutes 40% of the total input power, and is independent of beam geometry. However, the radiation profiles in the main plasma and divertor region depend on operating conditions such as beam geometry and gas puffing rates. Radiation from the main plasma accounts for 20% of the input power and radiation from the divertor region accounts for 20%. Accumulation of impurities during neutral-beam-heated discharges can cause peak radiation levels to exceed 1 W/cm/sup 3/, leading to a thermal collapse of the plasma.
Date: September 1, 1986
Creator: Paul, S.F.; Fonck, R.J. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Operation of a tangential bolometer on the PBX tokamak

Description: A compact 15-channel bolometer array that views plasma emission tangentially across the midplane has been installed on the PBX tokamak to supplement a 19-channel poloidal array which views the plasma perpendicular to the toroidal direction. By comparing measurements from these arrays, poloidal asymmetries in the emission profile can be assessed. The detector array consists of 15 discrete 2-mm x 2-mm Thinistors, a mixed semiconductor material whose temperature coefficient of resistance is relatively high. The accumulated heat incident on a detector gives rise to a change in the resistance in each active element. Operated in tandem with an identical blind detector, the resistance in each pair is compared in a Wheatstone bridge circuit. The variation in voltage resulting from the change in resistance is amplified, stored on a CAMAC transient recorder during the plasma discharge, and transferred to a VAX data acquisition computer. The instantaneous power is obtained by digitally smoothing and differentiating the signals in time, with suitable compensation for the cooling of the detector over the course of a plasma discharge. The detectors are ''free standing,'' i.e., they are supported only by their electrical leads. Having no substrate in contact with the detector reduces the response time and increases the time it takes for the detector to dissipate its accumulated heat, reducing the compensation for cooling required in the data analysis. The detectors were absolutely calibrated with a tungsten-halogen filament lamp and were found to vary by +-3%. The irradiance profiles are inverted to reveal the radially resolved emitted power density from the plasma, which is typically in the 0.1 to 0.5 W/cm/sup 3/ range.
Date: April 1, 1987
Creator: Paul, S.F.; Fonck, R.J. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Nuclear Merchant Ship Reactor Final Safeguards Report, Volume 6: Environmental Analysis OF NS "Savannah" Operation at Camden

Description: "An analysis is presented of the accidental release of activity following the operation of the NS "Savannah" at the New York Shipbuilding Corporation docks in Camden, New Jersey. Although a number of accidents are considered, the report is primarily concerned with the environmental activity levels and subsequent exposures which would result from the "maximum credible accident" (p. v).
Date: January 24, 1961
Creator: Cottrell, W. B.; Parker, F. L.; Mann, L. A. & Schmidt, G. D.
Partner: UNT Libraries Government Documents Department

First evidence of collective alpha particle effect on TAE modes in the TFTR D-T experiment

Description: The alpha particle effect on the excitation of toroidal Alfven eigenmodes (TAE) was investigated in deuterium-tritium (d-t) plasmas in the Tokamak Fusion Test Reactor (TFTR). RF power was used to position the plasma near the instability threshold, and the alpha particle effect was inferred from the reduction of RF power threshold for TAE instability in d-t plasmas. Initial calculations indicate that the alpha particles contribute 10--30% of the total drive in a d-t plasma with 3 MW of peak fusion power.
Date: August 1, 1995
Creator: Wong, K.L.; Schmidt, G. & Batha, S.H.
Partner: UNT Libraries Government Documents Department

Supershot performance with reverse magnetic shear in TFTR

Description: Discharges with large regions of reversed magnetic shear and good energy and particle confinement have been produced in the Tokamak Fusion Test Reactor. These plasmas were created by heating the plasma during a rapid plasma current increase. The stability of these discharges is dependent on the shape of the q profile, in particular the value and location of the minimum value of q. Control of the q profile by optimizing the plasma startup, prelude start time, the neutral-beam directionality during the prelude heating phase, and the plasma current ramp rate is demonstrated. High-performance discharges, created by injecting more than 18 to 25 MW of neutral beam power into a plasma with reverse shear, are also described.
Date: August 1, 1995
Creator: Batha, S.H.; Levinton, F.M.; Zarnstorff, M.C. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Potential safe termination by injection of polypropylene pellets in JET

Description: Thermal energy and the magnetic field energy associated with the plasma current must be dissipated safely when a tokamak discharge is terminated in a disruption. Magnetic energy can be dissipated by impurity radiation if position control is maintained. Prior to the dissipation of magnetic energy, thermal energy is usually conducted to the plasma contact points on a 1ms time scale in a thermal quench. A resistive, highly radiating plasma formed prior to the thermal quench, might dissipate both the thermal and magnetic energy by radiation minimizing damage due to local deposition. High speed injection of a low Z material can produce a resistive, highly radiating plasma on a 1ms time scale. Neon has recently been used in such an application on JT60-U. A large carbon pellet producing dilution temperatures < 1 keV is a possible alternative. This paper summarizes the results of an initial experiment performed in JET using carbon injected at high speed, as a 6mm polypropylene pellet, to investigate this potential approach to a safe plasma termination.
Date: October 1, 1995
Creator: Schmidt, G.L.; Ali-Arshad, S. & Bartlett, D.
Partner: UNT Libraries Government Documents Department

Radiated energy and impurity density changes during intensive hydrogen influx in the PLT tokamak

Description: During a discharge a puff of hydrogen is admitted, sufficient to more than triple the plasma density, and the resulting changes in various plasma parameters are determined. The absolute densities of various wall and limiter (carbon) materials are found to decrease by a substantial fraction, probably as a result of lowered peripheral temperature. The radiation pattern deduced from spectroscopically determined plasma composition is in good quantitative agreement with direct bolometric measurements. In the interior of the discharge radiation constitutes only a small part of the power input. Neither the radiated power nor the power input changes very markedly as a result of the density rise, since the effects of temperature and plasma composition changes tend to compensate each other.
Date: December 1, 1981
Creator: Hinnov, E.; Hosea, J.; Hsuan, H.; Jobes, F.; Meservey, E.; Schmidt, G. et al.
Partner: UNT Libraries Government Documents Department

Neutron and hard x-ray measurements during pellet deposition in TFTR

Description: Measurements of neutrons and hard x rays are made with a pair of plastic scintillators during injection of deuterium pellets into deuterium TFTR plasmas. Three cases are investigated. During ohmic heating in plasmas with few runaway electrons, the neutron emission does not increase when a pellet is injected, indicating that strong acceleration of the pellet ions does not occur. In ohmic plasmas with low but detectable levels of runaway electrons, an x-ray burst is observed on a detector near the pellet injector as the pellet ablates, while a detector displaced 126/sup 0/ toroidally from the injector does not measure a synchronous burst. Reduced pellet penetration correlates with the presence of x-ray emission, suggesting that the origin of the burst is bremsstrahlung from runaway electrons that strike the solid pellet. In deuterium beam-heated discharges, an increase in the d-d neutron emission is observed when the pellet ablates. In this case, the increase is due to fusion reactions between beam ions and the high density neutral and plasma cloud produced by ablation of the pellet; this localized density perturbation equilibrates in about 700 ..mu..sec. Analysis of the data indicates that the density propagates without forming a sharp shock front with a rapid initial propagation velocity (greater than or equal to 2 x 10/sup 7/ cm/sec) that subsequently decreases to around 3 x 10/sup 6/ cm/sec. Modelling suggests that the electron heat flux into the pellet cloud is much less than the classical Spitzer value.
Date: June 1, 1986
Creator: Heidbrink, W.W.; Milora, S.L.; Schmidt, G.L.; Schneider, W. & Ramsey, A.
Partner: UNT Libraries Government Documents Department

Gas injection in PLT: experimental overview

Description: Cold gas injection serves both the obvious role of a particle source at the surface of the plasma and a more subtle role as one element in the process by which the relative impurity concentration and the MHD activity of a discharge are determined. Evidence offered by PLT experiments in support of these two widely recognized roles is considered.
Date: January 1, 1977
Creator: Schmidt, G.L.; Bretz, N.I.; Hawryluk, R.J.; Hosea, J.C. & Johnson, D.W.
Partner: UNT Libraries Government Documents Department

Transport simulations of ohmic TFTR experiments with profile-consistent microinstability-based models for chi/sub e/ and chi/sub i/. [BALDUR]

Description: Transport simulations of ohmically heated TFTR experiments with recently developed profile-consistent microinstability models for the anomalous thermal diffusivities, chi/sub e/ and chi/sub i/, give good agreement with experimental data. The steady-state temperature profiles and the total energy confinement times, tau/sub e/, were found to agree for each of the ohmic TFTR experiments simulated, including three high radiation cases and two plasmas fueled by pellet injection. Both collisional and collisionless models are tested. The trapped-electron drift wave microinstability model results are consistent with the thermal confinement of large plasma ohmic experiments on TFTR. We also find that transport due to the toroidal ion temperature gradient (eta/sub i/) modes can cause saturation in tau/sub E/ at the highest densities comparable to that observed on TFTR and equivalent to a neoclassical anomaly factor of 3. Predictions based on stabilized eta/sub i/-mode-driven ion transport are found to be in agreement with the enhanced global energy confinement times for pellet-fueled plasmas. 33 refs., 26 figs., 4 tabs.
Date: March 1, 1987
Creator: Redi, M.H.; Tang, W.M.; Efthimion, P.C.; Mikkelsen, D.R. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Tritium pellet injection sequences for TFTR

Description: Tritium pellet injection into neutral deuterium, beam heated deuterium plasmas in the Tokamak Fusion Test Reactor (TFTR) is shown to be an attractive means of (1) minimizing tritium use per tritium discharge and over a sequence of tritium discharges; (2) greatly reducing the tritium load in the walls, limiters, getters, and cryopanels; (3) maintaining or improving instantaneous neutron production (Q); (4) reducing or eliminating deuterium-tritium (D-T) neutron production in non-optimized discharges; and (5) generally adding flexibility to the experimental sequences leading to optimal Q operation. Transport analyses of both compression and full-bore TFTR plasmas are used to support the above observations and to provide the basis for a proposed eight-pellet gas gun injector for the 1986 tritium experiments.
Date: January 1, 1983
Creator: Houlberg, W.A.; Milora, S.L.; Attenberger, S.E.; Singer, C.E. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Particle transport analysis of pellet fueled JET plasmas

Description: An understanding of the mechanism controlling particle transport in tokamaks is of crucial importance in projecting the fueling requirements and performance of such devices. Multiple pellet injection experiments have been carried out on JET to determine heating and confinement characteristics of pellet fueled plasmas. We report in this paper on the analysis of electron particle transport in these multi-pellet fueled JET plasmas under ohmic heating, ICRF heating, and NBI heating conditions in primarily limiter configurations. The study of particle transport in JET plasmas is based on measurements by a 6-channel far-infrared interferometer for density profile evolution and H/sub ..cap alpha../ detectors for edge source magnitude. Fluctuation induced transport is frequently suggested as the mechanism responsible for the anomalous particle and heat fluxes observed in tokamaks. As part of our analysis, we compare the determined electron particle and heat fluxes with fluctuation induced transport calculations using electron and ion drift wave mechanisms as the dominant fluctuation spectrum. The Onsager symmetry found in the neoclassical transport theory of fluctuations can be used to determine a connection between the anomalous electron particle and heat flux. 9 refs., 3 figs.
Date: January 1, 1988
Creator: Baylor, L.R.; Houlberg, W.A.; Milora, S.L. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

A Fast Shutdown Technique for Large Tokamaks

Description: A practical method is proposed for the fast shutdown of a large ignited tokamak. The method consists of injecting a rapid series of 30-50 deuterium pellets doped with a small ( 0.0005%) concentration of Krypton impurity, and simultaneously ramping the plasma current and shaping fields down over a period of several seconds using the poloidal field system. Detailed modeling with the Tokamak Simulation Code using a newly developed pellet mass deposition model shows that this method should terminate the discharge in a controlled and stable way without producing significant numbers of runaway electrons. A partial prototyping of this technique was accomplished in TFTR.
Date: September 1, 1999
Creator: Fredrickson, E.; Schmidt, G.L.; Hill, K.; Jardin, S.C. & al, et
Partner: UNT Libraries Government Documents Department

New techniques for calculating heat and particle source rates due to neutral-beam injection in axisymmetric tokamaks

Description: A set of numerical techniques are described for calculating heat and particle source rates due to neutral beam injection in axisymmetric tokamaks. While these techniques consume a substantial amount of computer time, they take into account a number of significant, and normally neglected, effects. Examples of these effects are reionization of escaping charge exchanged beam particles, finite fast ion orbit excursions, beam deposition through collisions of beam neutrals with circulating beam ions, and the transport of thermal neutrals in the plasma due to charge changing collisions with beam ions.
Date: February 1, 1981
Creator: Goldston, R.J.; McCune, D.C.; Towner, H.H.; Davis, S.L.; Hawryluk, R.J. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Gas-fueling studies in the PDX tokamak

Description: The characteristics of gas-fueling of high power discharges in the PDX tokamak have been investigated using gas-flow, neutral pressure, plasma density, and H..cap alpha.. emission measurements. The efficiency of gas-fueling was measured for various plasma configurations by comparison of the measured gas-influx rates to the particle exhaust rates inferred from particle decay time measurements. We observe that the fueling efficiency decreases significantly with increasing plasma density as the ionization length for thermal neutrals becomes shorter than the width of the boundary plasma. Gas fueling rates required to maintain a given plasma density are considerably higher (by factors of 5 to 10) for diverted discharges compared to limiter discharges. This result is attributed to a lower effective recycling coefficient for diverted plasmas. We discuss the dependence of the particle balance on the following experimentally measured parameters: the particle containment time, system-pumping speed, and neutral pressure in the vicinity of the active pumps.
Date: August 1, 1982
Creator: Dylla, H.F.; Blanchard, W.R.; Budny, R.; Fonck, R.J.; Owens, D.K. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Stable water isotope simulation by current land-surface schemes:Results of IPILPS phase 1

Description: Phase 1 of isotopes in the Project for Intercomparison of Land-surface Parameterization Schemes (iPILPS) compares the simulation of two stable water isotopologues ({sup 1}H{sub 2} {sup 18}O and {sup 1}H{sup 2}H{sup 16}O) at the land-atmosphere interface. The simulations are off-line, with forcing from an isotopically enabled regional model for three locations selected to offer contrasting climates and ecotypes: an evergreen tropical forest, a sclerophyll eucalypt forest and a mixed deciduous wood. Here we report on the experimental framework, the quality control undertaken on the simulation results and the method of intercomparisons employed. The small number of available isotopically-enabled land-surface schemes (ILSSs) limits the drawing of strong conclusions but, despite this, there is shown to be benefit in undertaking this type of isotopic intercomparison. Although validation of isotopic simulations at the land surface must await more, and much more complete, observational campaigns, we find that the empirically-based Craig-Gordon parameterization (of isotopic fractionation during evaporation) gives adequately realistic isotopic simulations when incorporated in a wide range of land-surface codes. By introducing two new tools for understanding isotopic variability from the land surface, the Isotope Transfer Function and the iPILPS plot, we show that different hydrological parameterizations cause very different isotopic responses. We show that ILSS-simulated isotopic equilibrium is independent of the total water and energy budget (with respect to both equilibration time and state), but interestingly the partitioning of available energy and water is a function of the models' complexity.
Date: October 31, 2005
Creator: Henderson-Sellers, A.; Fischer, M.; Aleinov, I.; McGuffie, K.; Riley, W.J.; Schmidt, G.A. et al.
Partner: UNT Libraries Government Documents Department

Lower Hybrid Current Drive Experiments in Alcator C-Mod

Description: A Lower Hybrid Current Drive (LHCD) system has been installed on the Alcator C-MOD tokamak at MIT. Twelve klystrons at 4.6 GHz feed a 4x22 waveguide array. This system was designed for maximum flexibility in the launched parallel wave-number spectrum. This flexibility allows tailoring of the lower hybrid deposition under a variety of plasma conditions. Power levels up to 900 kW have been injected into the tokomak. The parallel wave number has been varied over a wide range, n|| ~ 1.6–4. Driven currents have been inferred from magnetic measurements by extrapolating to zero loop voltage and by direct comparison to Fisch-Karney theory, yielding an efficiency of n20IR/P ~ 0.3. Modeling using the CQL3D code supports these efficiencies. Sawtooth oscillations vanish, accompanied with peaking of the electron temperature (Te0 rises from 2.8 to 3.8 keV). Central q is inferred to rise above unity from the collapse of the sawtooth inversion radius, indicating off-axis cd as expected. Measurements of non-thermal x-ray and electron cyclotron emission confirm the presence of a significant fast electron population that varies with phase and plasma density. The x-ray emission is observed to be radialy broader than that predicted by simple ray tracing codes. Possible explanations for this broader emission include fast electron diffusion or broader deposition than simple ray tracing predictions (perhaps due to diffractive effects).
Date: October 9, 2007
Creator: J.R. Wilson, S. Bernabei, P. Bonoli, A. Hubbard, R. Parker, A. Schmidt, G. Wallace, J. Wright, and the Alcator C-Mod Team
Partner: UNT Libraries Government Documents Department