Investigation of component failure rates for pulsed versus steady state tokamak operation
Cadwallader, L.C.
1992-07-01
This report presents component failure rate data sources applicable to magnetic fusion systems, and defines multiplicative factors to adjust these data for specific use on magnetic fusion experiment designs. The multipliers address both long pulse and steady state tokamak operation. Thermal fatigue and radiation damage are among the leading reasons for large multiplier values in pulsed operation applications. Field failure rate values for graphite protective tiles are presented, and beryllium tile failure rates in laboratory testing are also given. All of these data can be used for reliability studies, safety analyses, design tradeoff studies, and risk assessments.
Progress toward steady-state tokamak operation exploiting the high bootstrap current fraction regime
NASA Astrophysics Data System (ADS)
Ren, Q. L.; Garofalo, A. M.; Gong, X. Z.; Holcomb, C. T.; Lao, L. L.; McKee, G. R.; Meneghini, O.; Staebler, G. M.; Grierson, B. A.; Qian, J. P.; Solomon, W. M.; Turnbull, A. D.; Holland, C.; Guo, W. F.; Ding, S. Y.; Pan, C. K.; Xu, G. S.; Wan, B. N.
2016-06-01
Recent DIII-D experiments have increased the normalized fusion performance of the high bootstrap current fraction tokamak regime toward reactor-relevant steady state operation. The experiments, conducted by a joint team of researchers from the DIII-D and EAST tokamaks, developed a fully noninductive scenario that could be extended on EAST to a demonstration of long pulse steady-state tokamak operation. Improved understanding of scenario stability has led to the achievement of very high values of βp and βN , despite strong internal transport barriers. Good confinement has been achieved with reduced toroidal rotation. These high βp plasmas challenge the energy transport understanding, especially in the electron energy channel. A new turbulent transport model, named TGLF-SAT1, has been developed which improves the transport prediction. Experiments extending results to long pulse on EAST, based on the physics basis developed at DIII-D, have been conducted. More investigations will be carried out on EAST with more additional auxiliary power to come online in the near term.
Advances in multi-megawatt lower hybrid technology in support of steady-state tokamak operation
NASA Astrophysics Data System (ADS)
Delpech, L.; Achard, J.; Armitano, A.; Artaud, J. F.; Bae, Y. S.; Belo, J. H.; Berger-By, G.; Bouquey, F.; Cho, M. H.; Corbel, E.; Decker, J.; Do, H.; Dumont, R.; Ekedahl, A.; Garibaldi, P.; Goniche, M.; Guilhem, D.; Hillairet, J.; Hoang, G. T.; Kim, H. S.; Kim, J. H.; Kim, H.; Kwak, J. G.; Magne, R.; Mollard, P.; Na, Y. S.; Namkung, W.; Oh, Y. K.; Park, S.; Park, H.; Peysson, Y.; Poli, S.; Prou, M.; Samaille, F.; Yang, H. L.; The Tore Supra Team
2014-10-01
It has been demonstrated that lower hybrid current drive (LHCD) systems play a crucial role for steady-state tokamak operation, owing to their high current drive (CD) efficiency and hence their capability to reduce flux consumption. This paper describes the extensive technology programmes developed for the Tore Supra (France) and the KSTAR (Korea) tokamaks in order to bring continuous wave (CW) LHCD systems into operation. The Tore Supra LHCD generator at 3.7 GHz is fully CW compatible, with RF power PRF = 9.2 MW available at the generator to feed two actively water-cooled launchers. On Tore Supra, the most recent and novel passive active multijunction (PAM) launcher has sustained 2.7 MW (corresponding to its design value of 25 MW m-2 at the launcher mouth) for a 78 s flat-top discharge, with low reflected power even at large plasma-launcher gaps. The fully active multijunction (FAM) launcher has reached 3.8 MW of coupled power (24 MW m-2 at the launcher mouth) with the new TH2103C klystrons. By combining both the PAM and FAM launchers, 950 MJ of energy, using 5.2 MW of LHCD and 1 MW of ICRH (ion cyclotron resonance heating), was injected for 160 s in 2011. The 3.7 GHz CW LHCD system will be a key element within the W (for tungsten) environment in steady-state Tokamak (WEST) project, where the aim is to test ITER technologies for high heat flux components in relevant heat flux density and particle fluence conditions. On KSTAR, a 2 MW LHCD system operating at 5 GHz is under development. Recently the 5 GHz prototype klystron has reached 500 kW/600 s on a matched load, and studies are ongoing to design a PAM launcher. In addition to the studies of technology, a combination of ray-tracing and Fokker-Planck calculations have been performed to evaluate the driven current and the power deposition due to LH waves, and to optimize the N∥ spectrum for the future launcher design. Furthermore, an LHCD system at 5 GHz is being considered for a future upgrade of the ITER
NASA Astrophysics Data System (ADS)
Freidberg, Jeffrey; Dogra, Akshunna; Redman, William; Cerfon, Antoine
2016-10-01
The development of high field, high temperature superconductors is thought to be a game changer for the development of fusion power based on the tokamak concept. We test the validity of this assertion for pilot plant scale reactors (Q 10) for two different but related missions: pulsed operation and steady-state operation. Specifically, we derive a set of analytic criteria that determines the basic design parameters of a given fusion reactor mission. As expected there are far more constraints than degrees of freedom in any given design application. However, by defining the mission of the reactor under consideration, we have been able to determine the subset of constraints that drive the design, and calculate the values for the key parameters characterizing the tokamak. Our conclusions are as follows: 1) for pulsed reactors, high field leads to more compact designs and thus cheaper reactors - high B is the way to go; 2) steady-state reactors with H-mode like transport are large, even with high fields. The steady-state constraint is hard to satisfy in compact designs - high B helps but is not enough; 3) I-mode like transport, when combined with high fields, yields relatively compact steady-state reactors - why is there not more research on this favorable transport regime?
Non-Inductive Current Drive Modeling Extending Advanced Tokamak Operation to Steady State
Casper, T.A.; Lodestro, L.L.; Pearlstein, L.D.; Porter, G.D.; Murakami, M.; Lao, L.L.; Lin-Lui, Y.R.; St. John, H.E.
2000-06-06
A critical issue for sustaining high performance, negative central shear (NCS) discharges is the ability to maintain current distributions that are maximum off axis. Sustaining such hollow current profiles in steady state requires the use of non-inductively driven current sources. On the DIII-D experiment, a combination of neutral beam current drive (NBCD) and bootstrap current have been used to create transient NCS discharges. The electron cyclotron heating (ECH) and current drive (ECCD) system is currently being upgraded from three gyrotrons to six to provide more than 3MW of absorbed power in long-pulse operation to help sustain the required off-axis current drive. This upgrade SuPporrs the long range goal of DIII-D to sustain high performance discharges with high values of normalized {beta}, {beta}{sub n} = {beta}/(I{sub p}/aB{sub T}), confinement enhancement factor, H, and neutron production rates while utilizing bootstrap current fraction, f{sub bs}, in excess of 50%. At these high performance levels, the likelihood of onset of MHD modes that spoil confinement indicates the need to control plasma profiles if we are to extend this operation to long pulse or steady state. To investigate the effectiveness of the EC system and to explore operating scenarios to sustain these discharges, we use time-dependent simulations of the equilibrium, transport and stability. We explore methods to directly alter the safety factor profile, q, through direct current drive or by localized electron heating to modify the bootstrap current profile. Time dependent simulations using both experimentally determined [1] and theory-based [2] energy transport models have been done. Here, we report on simulations exploring parametric dependencies of the heating, current drive, and profiles that affect our ability to sustain stable discharges.
NASA Astrophysics Data System (ADS)
Kuzmin, A.; Zushi, H.; Takagi, I.; Sharma, S. K.; Rusinov, A.; Inoue, Y.; Hirooka, Y.; Zhou, H.; Kobayashi, M.; Sakamoto, M.; Hanada, K.; Yoshida, N.; Nakamura, K.; Fujisawa, A.; Matsuoka, K.; Idei, H.; Nagashima, Y.; Hasegawa, M.; Onchi, T.; Banerjee, S.; Mishra, K.
2015-08-01
Hydrogen wall pumping is studied in steady state tokamak operation (SSTO) of QUEST with all metal plasma facing materials PFMs at 100 °C. The duration of SSTO is up to 820 s in fully non-inductive plasma. Global gas balance analysis shows that wall pumping at the apparent (retention-release) rate of 1-6 × 1018 H/s is dominant and 70-80% of injected H2 can be retained in PFMs. However, immediately after plasma termination the H2 release rate enhances to ∼1019 H/s. In order to understand a true retention process the direct measurement of retention flux has been carried out by permeation probes. The comparison between the evaluated wall retention and results from global analysis is discussed.
System studies for quasi-steady-state advanced physics tokamak
Reid, R.L.; Peng, Y.K.M.
1983-11-01
Parametric studies were conducted using the Fusion Engineering Design Center (FEDC) Tokamak Systems Code to investigate the impact of veriation in physics parameters and technology limits on the performance and cost of a low q/sub psi/, high beta, quasi-steady-state tokamak for the purpose of fusion engineering experimentation. The features and characteristics chosen from each study were embodied into a single Advanced Physics Tokamak design for which a self-consistent set of parameters was generated and a value of capital cost was estimated.
Steady-state inductive spheromak operation
Janos, A.C.; Jardin, S.C.; Yamada, M.
1985-02-20
The inductively formed spheromak configuration (S-1) can be maintained in a highly stable and controlled fashion. The method described eliminates the restriction to pulsed spheromak plasmas or the use of electrodes for steady-state operation, and, therefore, is a reactor-relevant formation and sustainment method.
Steady-state inductive spheromak operation
Janos, Alan C.; Jardin, Stephen C.; Yamada, Masaaki
1987-01-01
The inductively formed spheromak plasma can be maintained in a highly stable and controlled fashion. Steady-state operation is obtained by forming the plasma in the linked mode, then oscillating the poloidal and toroidal fields such that they have different phases. Preferably, the poloidal and magnetic fields are 90.degree. out of phase.
Simulations of KSTAR high performance steady state operation scenarios
NASA Astrophysics Data System (ADS)
Na, Yong-Su; Kessel, C. E.; Park, J. M.; Yi, Sumin; Becoulet, A.; Sips, A. C. C.; Kim, J. Y.
2009-11-01
We report the results of predictive modelling of high performance steady state operation scenarios in KSTAR. Firstly, the capabilities of steady state operation are investigated with time-dependent simulations using a free-boundary plasma equilibrium evolution code coupled with transport calculations. Secondly, the reproducibility of high performance steady state operation scenarios developed in the DIII-D tokamak, of similar size to that of KSTAR, is investigated using the experimental data taken from DIII-D. Finally, the capability of ITER-relevant steady state operation is investigated in KSTAR. It is found that KSTAR is able to establish high performance steady state operation scenarios; βN above 3, H98(y, 2) up to 2.0, fBS up to 0.76 and fNI equals 1.0. In this work, a realistic density profile is newly introduced for predictive simulations by employing the scaling law of a density peaking factor. The influence of the current ramp-up scenario and the transport model is discussed with respect to the fusion performance and non-inductive current drive fraction in the transport simulations. As observed in the experiments, both the heating and the plasma current waveforms in the current ramp-up phase produce a strong effect on the q-profile, the fusion performance and also on the non-inductive current drive fraction in the current flattop phase. A criterion in terms of qmin is found to establish ITER-relevant steady state operation scenarios. This will provide a guideline for designing the current ramp-up phase in KSTAR. It is observed that the transport model also affects the predictive values of fusion performance as well as the non-inductive current drive fraction. The Weiland transport model predicts the highest fusion performance as well as non-inductive current drive fraction in KSTAR. In contrast, the GLF23 model exhibits the lowest ones. ITER-relevant advanced scenarios cannot be obtained with the GLF23 model in the conditions given in this work. Finally
Simulations of KSTAR high performance steady state operation scenarios
Na, Y S; Kessel, C. E.; Park, Jin Myung; Yi, Sumin; Becoulet, A.; Sips, A C C; Kim, J Y
2009-01-01
We report the results of predictive modelling of high performance steady state operation scenarios in KSTAR. Firstly, the capabilities of steady state operation are investigated with time-dependent simulations using a free-boundary plasma equilibrium evolution code coupled with transport calculations. Secondly, the reproducibility of high performance steady state operation scenarios developed in the DIII-D tokamak, of similar size to that of KSTAR, is investigated using the experimental data taken from DIII-D. Finally, the capability of ITER-relevant steady state operation is investigated in KSTAR. It is found that KSTAR is able to establish high performance steady state operation scenarios; beta(N) above 3, H-98(y, 2) up to 2.0, f(BS) up to 0.76 and f(NI) equals 1.0. In this work, a realistic density profile is newly introduced for predictive simulations by employing the scaling law of a density peaking factor. The influence of the current ramp-up scenario and the transport model is discussed with respect to the fusion performance and non-inductive current drive fraction in the transport simulations. As observed in the experiments, both the heating and the plasma current waveforms in the current ramp-up phase produce a strong effect on the q-profile, the fusion performance and also on the non-inductive current drive fraction in the current flattop phase. A criterion in terms of q(min) is found to establish ITER-relevant steady state operation scenarios. This will provide a guideline for designing the current ramp-up phase in KSTAR. It is observed that the transport model also affects the predictive values of fusion performance as well as the non-inductive current drive fraction. The Weiland transport model predicts the highest fusion performance as well as non-inductive current drive fraction in KSTAR. In contrast, the GLF23 model exhibits the lowest ones. ITER-relevant advanced scenarios cannot be obtained with the GLF23 model in the conditions given in this work
NASA Astrophysics Data System (ADS)
Hu, J. S.; Sun, Z.; Guo, H. Y.; Li, J. G.; Wan, B. N.; Wang, H. Q.; Ding, S. Y.; Xu, G. S.; Liang, Y. F.; Mansfield, D. K.; Maingi, R.; Zou, X. L.; Wang, L.; Ren, J.; Zuo, G. Z.; Zhang, L.; Duan, Y. M.; Shi, T. H.; Hu, L. Q.; East Team
2015-02-01
A critical challenge facing the basic long-pulse high-confinement operation scenario (H mode) for ITER is to control a magnetohydrodynamic (MHD) instability, known as the edge localized mode (ELM), which leads to cyclical high peak heat and particle fluxes at the plasma facing components. A breakthrough is made in the Experimental Advanced Superconducting Tokamak in achieving a new steady-state H mode without the presence of ELMs for a duration exceeding hundreds of energy confinement times, by using a novel technique of continuous real-time injection of a lithium (Li) aerosol into the edge plasma. The steady-state ELM-free H mode is accompanied by a strong edge coherent MHD mode (ECM) at a frequency of 35-40 kHz with a poloidal wavelength of 10.2 cm in the ion diamagnetic drift direction, providing continuous heat and particle exhaust, thus preventing the transient heat deposition on plasma facing components and impurity accumulation in the confined plasma. It is truly remarkable that Li injection appears to promote the growth of the ECM, owing to the increase in Li concentration and hence collisionality at the edge, as predicted by GYRO simulations. This new steady-state ELM-free H -mode regime, enabled by real-time Li injection, may open a new avenue for next-step fusion development.
Steady state plasma operation in RF dominated regimes on EAST
Zhang, X. J.; Zhao, Y. P.; Gong, X. Z.; Hu, C. D.; Liu, F. K.; Hu, L. Q.; Wan, B. N. Li, J. G.
2015-12-10
Significant progress has recently been made on EAST in the 2014 campaign, including the enhanced CW H&CD system over 20MW heating power (LHCD, ICRH and NBI), more than 70 diagnostics, ITER-like W-monoblock on upper divertor, two inner cryo-pumps and RMP coils, enabling EAST to investigate long pulse H mode operation with dominant electron heating and low torque to address the critical issues for ITER. H-mode plasmas were achieved by new H&CD system or 4.6GHz LHCD alone for the first time. Long pulse high performance H mode has been obtained by LHCD alone up to 28s at H{sub 98}∼1.2 or by combing of ICRH and LHCD, no or small ELM was found in RF plasmas, which is essential for steady state operation in the future Tokamak. Plasma operation in low collision regimes were implemented by new 4.6GHz LHCD with core Te∼4.5keV. The non-inductive scenarios with high performance at high bootstrap current fraction have been demonstrated in RF dominated regimes for long pulse operation. Near full non-inductive CD discharges have been achieved. In addition, effective heating and decoupling method under multi-transmitter for ICRF system were developed in this campaign, etc. EAST could be in operation with over 30MW CW heating and current drive power (LHCD ICRH NBI and ECRH), enhanced diagnostic capabilities and full actively-cooled metal wall from 2015. It will therefore allow to access new confinement regimes and to extend these regimes towards to steady state operation.
Steady state plasma operation in RF dominated regimes on EAST
NASA Astrophysics Data System (ADS)
Zhang, X. J.; Zhao, Y. P.; Gong, X. Z.; Hu, C. D.; Liu, F. K.; Hu, L. Q.; Wan, B. N.; Li, J. G.
2015-12-01
Significant progress has recently been made on EAST in the 2014 campaign, including the enhanced CW H&CD system over 20MW heating power (LHCD, ICRH and NBI), more than 70 diagnostics, ITER-like W-monoblock on upper divertor, two inner cryo-pumps and RMP coils, enabling EAST to investigate long pulse H mode operation with dominant electron heating and low torque to address the critical issues for ITER. H-mode plasmas were achieved by new H&CD system or 4.6GHz LHCD alone for the first time. Long pulse high performance H mode has been obtained by LHCD alone up to 28s at H98˜1.2 or by combing of ICRH and LHCD, no or small ELM was found in RF plasmas, which is essential for steady state operation in the future Tokamak. Plasma operation in low collision regimes were implemented by new 4.6GHz LHCD with core Te˜4.5keV. The non-inductive scenarios with high performance at high bootstrap current fraction have been demonstrated in RF dominated regimes for long pulse operation. Near full non-inductive CD discharges have been achieved. In addition, effective heating and decoupling method under multi-transmitter for ICRF system were developed in this campaign, etc. EAST could be in operation with over 30MW CW heating and current drive power (LHCD ICRH NBI and ECRH), enhanced diagnostic capabilities and full actively-cooled metal wall from 2015. It will therefore allow to access new confinement regimes and to extend these regimes towards to steady state operation.
Steady-state and non-steady state operation of counter-current chromatography devices.
Kostanyan, Artak E; Ignatova, Svetlana N; Sutherland, Ian A; Hewitson, Peter; Zakhodjaeva, Yulya A; Erastov, Andrey A
2013-11-01
Different variants of separation processes based on steady-state (continuous sample loading) and non-steady state (batch) operating modes of CCC columns have been analyzed and compared. The analysis is carried out on the basis of the modified equilibrium cell model, which takes into account both mechanisms of band broadening - interphase mass transfer and axial mixing. A full theoretical treatment of the intermittent counter-current chromatography with short sample loading time is performed. Analytical expressions are presented allowing the simulation of the intermittent counter-current chromatography separations for various experimental conditions. Chromatographic and extraction separations have been compared and advantages and disadvantages of the two methods have been evaluated. Further technical development of the CCC machines to implement counter-current extraction separations is considered.
A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium
NASA Astrophysics Data System (ADS)
Reed, Mark; Parker, Ronald R.; Forget, Benoit
2012-06-01
This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more
A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium
Reed, Mark; Parker, Ronald R.; Forget, Benoit
2012-06-19
This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more
Tokamak burn cycle study: a data base for comparing long pulse and steady-state power reactors
Ehst, D.A.; Brooks, J.N.; Cha, Y.; Evans, K. Jr.; Hassanein, A.; Kim, S.; Majumdar, S.; Misra, B.; Stevens, H.C.
1983-11-01
Several distinct operating modes (conventional ohmic, noninductive steady state, internal transformer, etc.) have been proposed for tokamaks. Our study focuses on capital costs and lifetime limitations of reactor subsystems in an attempt to quantify sensitivity to pulsed operation. Major problem areas considered include: thermal fatigue on first wall, limiter/divertor; thermal energy storage; fatigue and eddy current heating in toroidal field coils; electric power supply costs; and noninductive driver costs. We assume a high availability and low cost of energy will be mandatory for a commercial fusion reactor, and we characterize improvements in physics (current drive efficiency) and engineering (superior materials) which will help achieve these goals for different burn cycles.
Steady-state hollow electron temperature profiles in the Rijnhuizen Tokamak Project
Hogeweij, G.M.; Oomens, A.A.; Barth, C.J.; Beurskens, M.N.; Chu, C.C.; van Gelder, J.F.; Lok, J.; Lopes Cardozo, N.J.; Pijper, F.J.; Polman, R.W.; Rommers, J.H.
1996-01-01
In the Rijnhuizen Tokamak Project steady-state hollow electron temperature ({ital T}{sub {ital e}}) profiles have been sustained with strong off-axis electron cyclotron heating, creating a region of reversed magnetic shear. In this region the effective electron thermal diffusivity ({chi}{sub {ital e}}{sup {ital pb}}) is close to neoclassical in high density plasmas. For medium density, {chi}{sub {ital e}}{sup {ital pb}} is lower than neoclassical and may even be negative, indicating that off-diagonal elements in the transport matrix drive an electron heat flux up the {ital T}{sub {ital e}} gradient. {copyright} {ital 1996 The American Physical Society.}
Steady-state operation of spheromaks by inductive techniques
Janos, A.
1984-04-01
A method to maintain a steady-state spheromak configuration inductively using the S-1 Spheromak device is described. The S-1 Spheromak formation apparatus can be utilized to inject magnetic helicity continuously (C.W., not pulsed or D.C.) into the spheromak configuration after equilibrium is achieved in the linked mode of operation. Oscillation of both poloidal- and toroidal-field currents in the flux core (psi-phi Pumping), with proper phasing, injects a net time-averaged helicity into the plasma. Steady-state maintenance relies on flux conversion, which has been earlier identified. Relevant experimental data from the operation of S-1 are described. Helicity flow has been measured and the proposed injection scheme simulated. In a reasonable time practical voltages and frequencies can inject an amount of helicity comparable to that in the initial plasma. Plasma currents can be maintained or increased. This pumping technique is similar to F-THETA Pumping of a Reversed-Field-Pinch but is applied to this inverse-pinch formation.
NASA Astrophysics Data System (ADS)
Moreau, D.; Artaud, J. F.; Ferron, J. R.; Holcomb, C. T.; Humphreys, D. A.; Liu, F.; Luce, T. C.; Park, J. M.; Prater, R.; Turco, F.; Walker, M. L.
2015-06-01
This paper shows that semi-empirical data-driven models based on a two-time-scale approximation for the magnetic and kinetic control of advanced tokamak (AT) scenarios can be advantageously identified from simulated rather than real data, and used for control design. The method is applied to the combined control of the safety factor profile, q(x), and normalized pressure parameter, βN, using DIII-D parameters and actuators (on-axis co-current neutral beam injection (NBI) power, off-axis co-current NBI power, electron cyclotron current drive power, and ohmic coil). The approximate plasma response model was identified from simulated open-loop data obtained using a rapidly converging plasma transport code, METIS, which includes an MHD equilibrium and current diffusion solver, and combines plasma transport nonlinearity with 0D scaling laws and 1.5D ordinary differential equations. The paper discusses the results of closed-loop METIS simulations, using the near-optimal ARTAEMIS control algorithm (Moreau D et al 2013 Nucl. Fusion 53 063020) for steady state AT operation. With feedforward plus feedback control, the steady state target q-profile and βN are satisfactorily tracked with a time scale of about 10 s, despite large disturbances applied to the feedforward powers and plasma parameters. The robustness of the control algorithm with respect to disturbances of the H&CD actuators and of plasma parameters such as the H-factor, plasma density and effective charge, is also shown.
An Operational Definition of the Steady State in Enzyme Kinetics.
ERIC Educational Resources Information Center
Barnsley, E. A.
1990-01-01
The Briggs-Haldane assumption is used as the basis for the development of a kinetic model for enzyme catalysis. An alternative definition of the steady state and examples of realistic mechanisms are provided. (KR)
NASA Astrophysics Data System (ADS)
Lee, G. S.; Na, Yong-Su; Becoulet, A.; Ide, S.; Kessel, C. E.; Komori, A.; Kuteev, B. V.; Mank, G.; Olstad, R. A.; Sarkar, B.; Sips, A. C. C.; van Houtte, D.; Vdovin, V. L.
2008-08-01
This report summarizes the contributions presented at the 5th IAEA Technical Meeting on Steady State Operation of Magnetic Fusion Devices, held in Daejeon, Republic of Korea, 14-17 May 2007. The main topics of the meeting were overview and superconducting devices, long pulse operation and advanced tokamak, steady state fusion technology, heating and current drive, particle control and power exhaust and ITER-related issues.
DIII-D research towards resolving key issues for ITER and steady-state tokamaks
NASA Astrophysics Data System (ADS)
Hill, D. N.; the DIII-D Team
2013-10-01
The DIII-D research program is addressing key ITER research needs and developing the physics basis for future steady-state tokamaks. Pellet pacing edge-localized mode (ELM) control in the ITER configuration reduces ELM energy loss in proportion to 1/fpellet by inducing ELMs at up to 12× the natural ELM rate. Complete suppression of ELMs with resonant magnetic perturbations has been extended to the q95 expected for ITER baseline scenario discharges, and long-duration ELM-free QH-mode discharges have been produced with ITER-relevant co-current neutral-beam injection (NBI) using external n = 3 coils to generate sufficient counter-Ip torque. ITER baseline discharges at βN ˜ 2 and scaled NBI torque have been maintained in stationary conditions for more than four resistive times using electron cyclotron current drive (ECCD) for tearing mode suppression and disruption avoidance; active tracking with steerable launchers and feedback control catch these modes at small amplitude, reducing the ECCD power required to suppress them. Massive high-Z gas injection into disruption-induced 300-600 kA 20 MeV runaway electron (RE) beams yield dissipation rates ˜10× faster than expected from e-e collisions and demonstrate the possibility of benign dissipation of such REs should they occur in ITER. Other ITER-related experiments show measured intrinsic plasma torque in good agreement with a physics-based model over a wide range of conditions, while first-time main-ion rotation measurements show it to be lower than expected from neoclassical theory. Core turbulence measurements show increased temperature fluctuations correlated with sharply enhanced electron transport when \
Simulation of the hybrid and steady state advanced operating modes in ITER
NASA Astrophysics Data System (ADS)
Kessel, C. E.; Giruzzi, G.; Sips, A. C. C.; Budny, R. V.; Artaud, J. F.; Basiuk, V.; Imbeaux, F.; Joffrin, E.; Schneider, M.; Murakami, M.; Luce, T.; St. John, Holger; Oikawa, T.; Hayashi, N.; Takizuka, T.; Ozeki, T.; Na, Y.-S.; Park, J. M.; Garcia, J.; Tucillo, A. A.
2007-09-01
Integrated simulations are performed to establish a physics basis, in conjunction with present tokamak experiments, for the operating modes in the International Thermonuclear Experimental Reactor (ITER). Simulations of the hybrid mode are done using both fixed and free-boundary 1.5D transport evolution codes including CRONOS, ONETWO, TSC/TRANSP, TOPICS and ASTRA. The hybrid operating mode is simulated using the GLF23 and CDBM05 energy transport models. The injected powers are limited to the negative ion neutral beam, ion cyclotron and electron cyclotron heating systems. Several plasma parameters and source parameters are specified for the hybrid cases to provide a comparison of 1.5D core transport modelling assumptions, source physics modelling assumptions, as well as numerous peripheral physics modelling. Initial results indicate that very strict guidelines will need to be imposed on the application of GLF23, for example, to make useful comparisons. Some of the variations among the simulations are due to source models which vary widely among the codes used. In addition, there are a number of peripheral physics models that should be examined, some of which include fusion power production, bootstrap current, treatment of fast particles and treatment of impurities. The hybrid simulations project to fusion gains of 5.6-8.3, βN values of 2.1-2.6 and fusion powers ranging from 350 to 500 MW, under the assumptions outlined in section 3. Simulations of the steady state operating mode are done with the same 1.5D transport evolution codes cited above, except the ASTRA code. In these cases the energy transport model is more difficult to prescribe, so that energy confinement models will range from theory based to empirically based. The injected powers include the same sources as used for the hybrid with the possible addition of lower hybrid. The simulations of the steady state mode project to fusion gains of 3.5-7, βN values of 2.3-3.0 and fusion powers of 290 to 415 MW
NASA Astrophysics Data System (ADS)
Sonnino, G.
2011-03-01
Fully ionized L-mode tokamak plasmas in the fully collisional (Pfirsch-Schlüter) and in the low-collisional (banana) nonlinear transport regimes are analyzed. We derive the expressions for particles and heat losses together with the steady-state particle distribution functions in the several collisional transport regimes. The validity of the nonlinear closure equations, previously derived, has been indirectly tested by checking that the obtained particle distribution functions are indeed solutions of the nonlinear, steady-state, Vlasov-Landau gyro-kinetic equations. A quite encouraging result is the fact that, for L-mode tokamak plasmas a dissymmetry appears between the ion and electron transport coefficients: the latter submits to a nonlinear correction, which makes the radial electron coefficients much larger than the former. In particular we show that when the L-mode JET plasma is out of the linear region, the Pfirsch-Schlüter electron transport coefficients are corrected by an amplification factor, which may reach values of order 102. Such a correction is absent for ions. On the contrary, in the banana regime, the ion transport coefficients are increased by a factor 2 and the nonlinear corrections for electrons are negligible. These results are in line with experiments.
Diagnostics and control for the steady state and pulsed tokamak DEMO
NASA Astrophysics Data System (ADS)
Orsitto, F. P.; Villari, R.; Moro, F.; Todd, T. N.; Lilley, S.; Jenkins, I.; Felton, R.; Biel, W.; Silva, A.; Scholz, M.; Rzadkiewicz, J.; Duran, I.; Tardocchi, M.; Gorini, G.; Morlock, C.; Federici, G.; Litnovsky, A.
2016-02-01
The present paper is devoted to a first assessment of the DEMO diagnostics systems and controls in the context of pulsed and steady state reactor design under study in Europe. In particular, the main arguments treated are: (i) The quantities to be measured in DEMO and the requirements for the measurements; (ii) the present capability of the diagnostic and control technology, determining the most urgent gaps, and (iii) the program and strategy of the research and development (R&D) needed to fill the gaps. Burn control, magnetohydrodynamic stability, and basic machine protection require improvements to the ITER technology, and moderated efforts in R&D can be dedicated to infrared diagnostics (reflectometry, electron cyclotron emission, polarimetry) and neutron diagnostics. Metallic Hall sensors appear to be a promising candidate for magnetic measurements in the high neutron fluence and long/steady state discharges of DEMO.
Hybrid and Steady-State Operation on JET and Tore Supra
NASA Astrophysics Data System (ADS)
Bécoulet, A.
2003-12-01
Producing fusion energy requires to simultaneously sustain in a tokamak environment fully non inductive regimes at the highest Q-values and a "significant" fusion performance level under MHD-stable conditions, while insuring a satisfactory confinement of the fast alpha particles. This ambitious goal is being investigated on many devices worldwide, particularly focusing on the role played by the current density profile. The paper reports on the recent experimental progress of both the JET and Tore Supra devices towards i) long to very long pulse operation relying on a careful use of lower hybrid current drive under various current profile tailoring conditions (namely so-called "hybrid" peaked current density profiles and so-called "steady-state" hollow current density profiles) and ii) discharges performed with real-time controlled pressure and/or current density profiles. Such discharges are detailed and interpreted using the CRONOS integrated modelling suite. Its fully predictive capability, including real time control features, is used to provide keys to future experiments.
Advanced tokamak operating modes in TPX and ITER
Nevins, W.M.
1994-12-31
A program is described to develop the advanced tokamak physics required for an economic steady-state fusion reactor on existing (short-pulse) tokamak experiments; to extend these operating modes to long-pulse on TPX; and finally to demonstrate them in a long-pulse D-T plasma on ITER.
Advanced operation scenarios toward high-beta, steady-state plasmas in KSTAR
NASA Astrophysics Data System (ADS)
Yoon, Si-Woo; Jeon, Y. M.; Woo, M. H.; Bae, Y. S.; Kim, H. S.; Oh, Y. K.; Park, J. M.; Park, Y. S.; Kstar Team
2016-10-01
For the realization of the fusion reactor, solving issues for high-beta steady-state operation is one of the essential topics for the present superconducting tokamaks and in this regard, KSTAR has been focusing on maximizing performance and increasing pulse length simultaneously. Typically, study on high beta operation has been focusing on advanced scenario limited at relatively short pulse discharge and partial success has been reported previously. However, it must be stressed that it is critical to verify compatibility of the developed scenario to long-pulse operation and compared with that of the short-pulse, it is turned out stable long-pulse operation is possible only with a reduced level of beta. In this work, the results of recent approaches in long-pulse operation are presented focusing respectively on high betaN, high betap and high li scenarios. For high betaN, the achieved level is close to 3 with Ip =0.4 MA, BT =1.4T and Pext 6MW and it is found to be limited by m/n =2/1 tearing mode and is also sensitive on the internal inductance. For high betap, conditions of the maximum betap is investigated mainly by parametric scans of plasma current (Ip =0.4-0.7 MA) and also neutral beam injection power (3-5MW). The achieved betap is also close to 3 with Ip =0.4 MA, BT =2.9T and Pext 6MW and it is found to be limited by heating power and without indication of MHD activities. Finally, attempt for high li discharge will be addressed on scenario development and transient results.
A ``Stepladder'' Approach to a Steady State Tokamak Fusion Power Plant
NASA Astrophysics Data System (ADS)
Zohm, Hartmut; Bock, Alexander; Fable, Emiliano; Stober, Joerg; Traeuble, Frederik
2016-10-01
In the EU strategy to an FPP, DEMO is the single step between ITER and an FPP. It is not obvious how to arrive at a DEMO design point in this strategy. We propose to avoid large scenario development steps in an ITER-DEMO-FPP step-ladder, since no other machines can qualify the scenarios. Thus, DEMO becomes a technology demonstrator, not a plasma physics experiment. We characterize the plasma scenario in terms of the quantities βN, q, H and fGW. To ensure adequate divertor performance, constant ne is chosen. Different from previous approaches, ρ* and ν* will vary throughout the stepladder based on physics arguments that below minimum values, their variation is no longer important. This leaves open the choice of machine parameters A, R and B. Fixing A to the ITER value, constant fGW and absolute ne lead to B/R = const. At constant q, βN and A, B and R increase proportional to Pfus1 / 7 in the stepladder. The power needed to drive the current in steady state varies similarly, so from DEMO to an FPP a significant decrease in recirculating power fraction occurs. A viable divertor solution and access to H-mode are considered explicitly. An example for such a stepladder is discussed, based on recent ASDEX Upgrade results in steady state. Also at Faculty of Physics, Ludwig-Maximilians-Universität, D-80799 München, Germany.
Not Available
1988-01-01
Critical issues for the steady state operation of plasma confinement devices exist in both the physics and technology fields of fusion research. Due to the wide range and number of these issues, this technical assessment has focused on the crucial issues associated with the plasma physics and the plasma interactive components. The document provides information on the problem areas that affect the design and operation of a steady state ETR or ITER type confinement device. It discusses both tokamaks and alternative concepts, and provides a survey of existing and planned confinement machines and laboratory facilities that can address the identified issues. A universal definition of steady state operation is difficult to obtain. From a physics point of view, steady state is generally achieved when the time derivatives approach zero and the operation time greatly exceeds the characteristic time constants of the device. Steady state operation for materials depends on whether thermal stress, creep, fatigue, radiation damage, or power removal are being discussed. For erosion issues, the fluence and availability of the machine for continuous operation are important, assuming that transient events such as disruptions do not limit the component lifetimes. The panel suggests, in general terms, that steady state requires plasma operation from 100 to 1000 seconds and an availability of more than a few percent, which is similar to the expectations for an ETR type device. The assessment of critical issues for steady state operation is divided into four sections: physics issues; technology issues; issues in alternative concepts; and devices and laboratory facilities that can address these problems.
Woolley, R.D.
1996-12-31
A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.
Woolley, Robert D.
1998-01-01
A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.
Woolley, R.D.
1998-09-08
A method and apparatus are disclosed for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators. 6 figs.
Sengupta, A.; Ranjan, P
2001-01-15
In this paper, we examine the possibility of using a multilayered feedforward neural network to extract tokamak plasma parameters from magnetic measurements as an improvement over the traditional methodology of function parametrization. It is also used to optimize the number and locations of the magnetic diagnostics designed for the tokamak. This work has been undertaken with the specific purpose of application of the neural network technique to the newly designed (and currently under fabrication) Superconducting Steady-State Tokamak-1 (SST-1). The magnetic measurements will be utilized to achieve real-time control of plasma shape, position, and some global profiles. A trained neural network is tested, and the results of parameter identification are compared with function parametrization. Both techniques appear well suited for the purpose, but a definite improvement with neural networks is observed. Although simulated measurements are used in this work, confidence regarding the network performance with actual experimental data is ensured by testing the network's noise tolerance with Gaussian noise of up to 10%. Finally, three possible methods of ranking the diagnostics in decreasing order of importance are suggested, and the neural network is used to optimize the number and locations of the magnetic sensors designed for SST-1. The results from the three methods are compared with one another and also with function parametrization. Magnetic probes within the plasma-facing side of the outboard limiter have been ranked high. Function parametrization and one of the neural network methods show a distinct tendency to favor the probes in the remote regions of the vacuum vessel, proving the importance of redundancy. Fault tolerance of the optimized network is tested. The results obtained should, in the long run, help in the decision regarding the final effective set of magnetic diagnostics to be used in SST-1 for reconstruction of the control parameters.
Steady state off-axis sawtoothing in the Rijnhuizen Tokamak project
NASA Astrophysics Data System (ADS)
Meulenbroeks, R. F. G.; de Baar, M. R.; Beurskens, M. N. A.; de Blank, H. J.; Deng, B. H.; Donné, A. J. H.; Hogeweij, G. M. D.; Lopes Cardozo, N. J.; Montvai, A.; Oyevaar, Th.
1999-10-01
A family of off-axis, or annular, instabilities has been studied using Thomson scattering, soft X-ray emission, and two electron cyclotron emission diagnostic systems. In the Rijnhuizen tokamak (RTP) [N. J. Lopes Cardozo et al., Plasma Physics and Controlled Nuclear Fusion Research 1992 (International Atomic Energy Agency, Vienna, 1993), Vol. 1, p. 271] these phenomena are invoked in a controlled way in discharges with specific (off-axis) deposition of electron cyclotron heating (ECH) and persist during most of the heating period, or during many current diffusion times. Based on coherent mode analysis at the crash time, the instabilities are associated with resonant surfaces near simple rational values of q (3/2, 2, and 3). A parameter study shows an increase of reheat rate and a decrease of sawtooth period with increasing ECH power and — in contrast to observations in other experiments — with increASING density as well.
Non-steady-state operation of polymer/TiO2 photovoltaic devices
NASA Astrophysics Data System (ADS)
Kirov, Kiril R.; Burlakov, Victor M.; Xie, Zhibin; Henry, Bernard M.; Carey, Michelle J.; Grovenor, Christopher R. M.; Burn, Paul L.; Assender, Hazel E.; Briggs, G. Andrew D.
2004-11-01
We present data on the initial period of operation of Gilch-route MEH-PPV/TiO2 composite solar cells (CSCs) which show that during this period the CSCs operate in a non-steady state regime. The behavior is complex and may include a gradual rise of the open circuit voltage (Voc) and of the short-circuit current density (Jsc) with time, a passage through a maximum of either or both parameters, and even a sign reversal. The mechanisms most probably contributing to the transient processes are: i) diffusion driven redistribution of charges resulting in the build up of a quasi steady state charge density profile across the device; ii) photo-doping resulting in a relatively slow increase of the average charge carrier concentration and consequently of the conductivity of the device. The latter is responsible for a strong decrease in Voc, and is evidenced by the significant increase in dark current after device illumination.
Quantitative, steady-state properties of Catania's computational model of the operant reserve.
Berg, John P; McDowell, J J
2011-05-01
Catania (2005) found that a computational model of the operant reserve (Skinner, 1938) produced realistic behavior in initial, exploratory analyses. Although Catania's operant reserve computational model demonstrated potential to simulate varied behavioral phenomena, the model was not systematically tested. The current project replicated and extended the Catania model, clarified its capabilities through systematic testing, and determined the extent to which it produces behavior corresponding to matching theory. Significant departures from both classic and modern matching theory were found in behavior generated by the model across all conditions. The results suggest that a simple, dynamic operant model of the reflex reserve does not simulate realistic steady state behavior.
Demonstration of Steady State Operation with 1 MW of 170 GHz gyrotron for ITER
Kasugai, Atsushi; Takahashi, Koji; Kajiwara, Ken; Kobayashi, Noriyuki; Sakamoto, Keishi
2007-09-28
A quasi-steady-state operation of 1 MW/800 s with the efficiency of 55%, which exceeded 1 MW/500 s/50% of the performance required in ITER, was demonstrated in a 170 GHz gyrotron. The oscillation characteristics in the long pulse operation was clarified, and the operation scenario to the hard self-excitation region for the high efficiency oscillation was newly established by controlling a pitch factor of the electron and the cavity magnetic field during the pulse with fixed beam voltage in the triode MIG. The result gives a clear outlook for the success of ECH and ECCD in ITER.
High-power and steady-state operation of ICRF heating in the large helical device
Mutoh, T. Seki, T.; Saito, K.; Kasahara, H.; Seki, R.; Kamio, S.; Kumazawa, R.; Kubo, S.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Takahashi, H.; Ii, T.; Makino, R.; Nagaoka, K.; Nomura, G.; Shinya, T.
2015-12-10
Recent progress in an ion cyclotron range of frequencies (ICRF) heating system and experiment results in a Large Helical Device (LHD) are reported. Three kinds of ICRF antenna pairs were installed in the LHD, and the operation power regimes were extended up to 4.5 MW; also, the steady-state operation was extended for more than 45 min in LHD at a MW power level. We studied ICRF heating physics in heliotron configuration using a Hand Shake type (HAS) antenna, Field Aligned Impedance Transforming (FAIT) antenna, and Poloidal Array (PA) antenna, and established the optimum minority-ion heating scenario in an LHD. The FAIT antenna having a novel impedance transformer inside the vacuum chamber could reduce the VSWR and successfully injected a higher power to plasma. We tested the PA antennas completely removing the Faraday-shield pipes to avoid breakdown and to increase the plasma coupling. The heating performance was almost the same as other antennas; however, the heating efficiency was degraded when the gap between the antenna and plasma surface was large. Using these three kinds of antennas, ICRF heating could contribute to raising the plasma beta with the second- and third-harmonic cyclotron heating mode, and also to raising the ion temperature as discharge cleaning tools. In 2014, steady-state operation plasma with a line-averaged electron density of 1.2 × 10{sup 19} m{sup −3}, ion and electron temperature of 2 keV, and plasma sustainment time of 48 min was achieved with ICH and ECH heating power of 1.2 MW for majority helium with minority hydrogen. In 2015, the higher-power steady-state operation with a heating power of up to 3 MW was tested with higher density of 3 × 10{sup 19} m{sup −3}.
NASA Astrophysics Data System (ADS)
Tani, K.; Shinohara, K.; Oikawa, T.; Tsutsui, H.; McClements, K. G.; Akers, R. J.; Liu, Y. Q.; Suzuki, M.; Ide, S.; Kusama, Y.; Tsuji-Iio, S.
2016-11-01
As part of the verification and validation of a newly developed non-steady-state orbit-following Monte-Carlo code, application studies of time dependent neutron rates have been made for a specific shot in the Mega Amp Spherical Tokamak (MAST) using 3D fields representing vacuum resonant magnetic perturbations (RMPs) and toroidal field (TF) ripples. The time evolution of density, temperature and rotation rate in the application of the code to MAST are taken directly from experiment. The calculation results approximately agree with the experimental data. It is also found that a full orbit-following scheme is essential to reproduce the neutron rates in MAST.
Isayama, A.
2005-05-15
Recent results from steady-state sustainment of high-{beta} plasma experiments in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) tokamak [A. Kitsunezaki et al., Fusion Sci. Technol. 42, 179 (2002)] are described. Extension of discharge duration to 65 s (formerly 15 s) has enabled physics research with long time scale. In long-duration high-{beta} research, the normalized beta {beta}{sub N}=2.5, which is comparable to that in the steady-state operation in International Thermonuclear Experimental Reactor (ITER) [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], has been sustained for about 15 s with confinement enhancement factor H{sub 89PL} above 2, where the duration is about 80 times energy confinement time and {approx}10 times current diffusion time ({tau}{sub R}). In the scenario aiming at longer duration with {beta}{sub N}{approx}1.9, which is comparable to that in the ITER standard operation scenario, duration has been extended to 24 s ({approx}15{tau}{sub R}). Also, from the viewpoint of collisionality and Larmor radius of the plasmas, these results are obtained in the ITER-relevant regime with a few times larger than the ITER values. No serious effect of current diffusion on instabilities is observed in the region of {beta}{sub N} < or approx. 2.5, and in fact neoclassical tearing modes (NTMs), which limit the achievable {beta} in the stationary high-{beta}{sub p} H-mode discharges, are suppressed throughout the discharge. In high-{beta} research with the duration of several times {tau}{sub R}, a high-{beta} plasma with {beta}{sub N}{approx}2.9-3 has been sustained for 5-6 s with two scenarios for NTM suppression: (a) NTM avoidance by modification of pressure and current profiles, and (b) NTM stabilization with electron cyclotron current drive (ECCD)/electron cyclotron heating (ECH). NTM stabilization with the second harmonic X-mode ECCD/ECH has been performed, and it is found that EC current
Water-cooled target modules for steady-state operation of the W7-X divertor
NASA Astrophysics Data System (ADS)
Boscary, J.; Greuner, H.; Czerwinski, M.; Mendelevitch, B.; Pfefferle, K.; Renner, H.
2003-09-01
The stellarator WENDELSTEIN 7-X (W7-X) includes water-cooled plasma facing components (PFCs) to allow steady-state operation and to provide an efficient particle and power exhaust up to 10 MW for a maximum pulse duration of 30 min. Ten divertor units are arranged along the helical edge of the fivefold periodic plasma column. The three-dimensional shape and positioning of the target surfaces are optimized to address physics issues for a wide range of experimental parameters, which influence the topology of the boundary. The three-dimensional target surfaces are reproduced by a series of consecutive plane target elements as a set of parallel water-cooled elements positioned onto the frameworks of target modules. The design and arrangement of target modules and elements are described.
Extending unified-theory-of-reinforcement neural networks to steady-state operant behavior.
Calvin, Olivia L; McDowell, J J
2016-06-01
The unified theory of reinforcement has been used to develop models of behavior over the last 20 years (Donahoe et al., 1993). Previous research has focused on the theory's concordance with the respondent behavior of humans and animals. In this experiment, neural networks were developed from the theory to extend the unified theory of reinforcement to operant behavior on single-alternative variable-interval schedules. This area of operant research was selected because previously developed neural networks could be applied to it without significant alteration. Previous research with humans and animals indicates that the pattern of their steady-state behavior is hyperbolic when plotted against the obtained rate of reinforcement (Herrnstein, 1970). A genetic algorithm was used in the first part of the experiment to determine parameter values for the neural networks, because values that were used in previous research did not result in a hyperbolic pattern of behavior. After finding these parameters, hyperbolic and other similar functions were fitted to the behavior produced by the neural networks. The form of the neural network's behavior was best described by an exponentiated hyperbola (McDowell, 1986; McLean and White, 1983; Wearden, 1981), which was derived from the generalized matching law (Baum, 1974). In post-hoc analyses the addition of a baseline rate of behavior significantly improved the fit of the exponentiated hyperbola and removed systematic residuals. The form of this function was consistent with human and animal behavior, but the estimated parameter values were not.
NASA Technical Reports Server (NTRS)
Simon, Donald L.; Litt, Jonathan S.
2010-01-01
This paper presents an algorithm that automatically identifies and extracts steady-state engine operating points from engine flight data. It calculates the mean and standard deviation of select parameters contained in the incoming flight data stream. If the standard deviation of the data falls below defined constraints, the engine is assumed to be at a steady-state operating point, and the mean measurement data at that point are archived for subsequent condition monitoring purposes. The fundamental design of the steady-state data filter is completely generic and applicable for any dynamic system. Additional domain-specific logic constraints are applied to reduce data outliers and variance within the collected steady-state data. The filter is designed for on-line real-time processing of streaming data as opposed to post-processing of the data in batch mode. Results of applying the steady-state data filter to recorded helicopter engine flight data are shown, demonstrating its utility for engine condition monitoring applications.
D0 Silicon Upgrade: Control Dewar Steady State Thermodynamic Operating Goals
Rucincki, Russ; /Fermilab
1995-10-20
This engineering note documents the thermodynamic operating parameter goals for the steady state operation of the control dewar/solenoid system. Specifically, how the control dewar pressure control valve, PV-3062-H and the magnet flow control valve EVMF are operated to give the lowest possible temperature fluid at the solenoid magnet. The goals are: (1) For PV-3062-H - The process variable is the helium reservoir pressure, minimize the reservoir pressure, provide only enough pressure plus a little margin to ensure leads flow; and (2) For EVMF - The process variable is firstly a manual setpoint of flowrate as read by the flow venturi, FE3253-H, and secondly the reservoir liquid level, minimize the pressure drop thru the solenoid cooling tubes, provide at least enough flow to maintain reservoir level and stable operation of the magnet. The thermodynamic states for the fluid thru the system are shown on the Pressure versus Temperature graph. Lines of constant enthalpy are also shown. State A is shown as two phase liquid entering the inlet of the subcooler. The subcooler subcools the fluid to State B. State B to State C is caused by the pressure drop across EVMF. State C to D is the estimated pressure drop from the outlet of EVMF thru the solenoid cooling tubes and back up to the helium reservoir inlet. To give the coolest fluid in the cooling tubes, the two phase fluid in the reservoir should be at the lowest pressure (and thus temperature). This lowest pressure is limited by the required pressure for leads flow and if this does not dominate, the low pressure side pressure drop thru the refrigerator and suction pressure set point. My guess is the lead flow requirement will dominate. I suggest putting the PV-3062-H set point such that the lead flow control valves operate at about 80% open. The second parameter that will give the coolest fluid in the cooling tubes is a minimized pressure drop thru the cooling tubes. This can be accomplished by providing a minimized
Radioactivity computation of steady-state and pulsed fusion reactors operation
Attaya, H.
1994-06-01
Different mathematical methods are used to calculate the nuclear transmutation in steady-state and pulsed neutron irradiation. These methods are the Schuer decomposition, the eigenvector decomposition, and the Pade approximation of the matrix exponential function. In the case of the linear decay chain approximation, a simple algorithm is used to evaluate the transition matrices.
Development of steady-state operation using ICH in the LHD
Kasahara, H.; Seki, T.; Saito, K.; Seki, R.; Yoshimura, Y.; Kubo, S.; Shimozuma, T.; Igami, H.; Takahashi, H.; Tokitani, M.; Ashikawa, N.; Shoji, M.; Kamio, S.; Tsuchiya, H.; Tanaka, H.; Yoshimura, S.; Tamura, N.; Yamada, I.; Suzuki, C.; Mutoh, T.; and others
2014-02-12
Long-pulse discharge with the electron density n{sub e0} of 1 × 10{sup 19} m{sup −3}, electron temperature T{sub e0} of 2.5 keV, discharge length t{sub dis} of 19 minutes and heating power P{sub inject} of 1MW, is demonstrated using the HAS antenna and the PA antenna for ion cyclotron heating (ICH) and increasing in the power of electron cyclotron heating (ECH). The HAS antenna is designed to phase dipole and excite ideal fast wave with parallel electric field kept small, and low impurity generation and accumulation are achieved on the steady-state discharge by weak parasitic heating around antennas. On the long-pulse discharge, the radiation measured by bolometer is kept smaller than 20% for injection power, and the heat load to divertor is approximately 60 % with low energetic particle losses. The heat load ratio to divertor is not as a function of injection power around 1MW, and energy confinement has been kept during the steady-state discharge.
Rodatos, A; Greuner, H; Jakubowski, M W; Boscary, J; Wurden, G A; Pedersen, T S; König, R
2016-02-01
Wendelstein 7-X (W7-X) aims to demonstrate the reactor capability of the stellarator concept, by creating plasmas with pulse lengths of up to 30 min at a heating power of up to 10 MW. The divertor plasma facing components will see convective steady state heat flux densities of up to 10 MW/m(2). These high heat flux target elements are actively cooled and are covered with carbon fibre reinforced carbon (CFC) as plasma facing material. The CFC is bonded to the CuCrZr cooling structure. Over the life time of the experiment this interface may weaken and cracks can occur, greatly reducing the heat conduction between the CFC tile and the cooling structure. Therefore, there is not only the need to monitor the divertor to prevent damage by overheating but also the need to detect these fatigue failures of the interface. A method is presented for an early detection of fatigue failures of the interface layer, solely by using the information delivered by the IR-cameras monitoring the divertor. This was developed and validated through experiments made with high heat flux target elements prior to installation in W7-X.
NASA Astrophysics Data System (ADS)
Rodatos, A.; Greuner, H.; Jakubowski, M. W.; Boscary, J.; Wurden, G. A.; Pedersen, T. S.; König, R.
2016-02-01
Wendelstein 7-X (W7-X) aims to demonstrate the reactor capability of the stellarator concept, by creating plasmas with pulse lengths of up to 30 min at a heating power of up to 10 MW. The divertor plasma facing components will see convective steady state heat flux densities of up to 10 MW/m2. These high heat flux target elements are actively cooled and are covered with carbon fibre reinforced carbon (CFC) as plasma facing material. The CFC is bonded to the CuCrZr cooling structure. Over the life time of the experiment this interface may weaken and cracks can occur, greatly reducing the heat conduction between the CFC tile and the cooling structure. Therefore, there is not only the need to monitor the divertor to prevent damage by overheating but also the need to detect these fatigue failures of the interface. A method is presented for an early detection of fatigue failures of the interface layer, solely by using the information delivered by the IR-cameras monitoring the divertor. This was developed and validated through experiments made with high heat flux target elements prior to installation in W7-X.
NASA Astrophysics Data System (ADS)
Radosavljević, Jordan; Klimenta, Dardan; Jevtić, Miroljub
2012-07-01
This paper proposed a multi-objective genetic algorithm (MOGA) based approach for determining the steady-state performance characteristics of three-phase self-excited induction generators (SEIGs) operating in parallel and supplying an unbalanced load. The symmetrical component theory is used for the transformation of a complex three-phase generators-capacitances-load system to a simple equivalent circuit. The MOGA has been employed for the determination of unknown variables by minimizing the impedance module of the equivalent circuit. Using this approach, effects of various parameters on the terminal voltage control characteristics are examined for two parallel SEIGs with C2C connection under a single phase load.
The capabilities of steady state operation at the stellarator W7-X with emphasis on divertor design
NASA Astrophysics Data System (ADS)
Renner, H.; Boscary, J.; Erckmann, V.; Greuner, H.; Grote, H.; Sapper, J.; Speth, E.; Wesner, F.; Wanner, M.; W7-X Team
2000-06-01
The stellarator Wendelstein 7-X (W7-X) is presently under construction at Greifswald, Germany, and the start of operation is planned in 2006. W7-X is a large `advanced stellarator' of the HELIAS type (R = 5.5 m, a = 0.55 m, B0 = 3 T, five periods, moderate shear and variable rotational transform 5/6 <= ι <= 5/4 at the boundary) with the aims of demonstrating the reactor potential of this stellarator line in steady state operation close to fusion relevant parameters. The capability of stationary operation requires the realization of a superconducting magnet system consisting of 50 modular coils and 20 planar coils, the operation of a 140 GHz ECR CW heat source of 10 MW, the installation of a divertor to handle the power and particle flux, and to limit the impurity fraction to tolerable levels. Additional heating schemes, ICRF and NBI, will be provided for flexible experimentation.
Steady state thermal radiometers
NASA Technical Reports Server (NTRS)
Loose, J. D. (Inventor)
1974-01-01
A radiometer is described operating in a vacuum under steady state conditions. The front element is an aluminum sheet painted on the outer side with black or other absorptive material of selected characteristics. A thermocouple is bonded to the inner side of the aluminum sheet. That is backed by highly insulative layers of glass fiber and crinkled, aluminized Mylar polyester. Those layers are backed with a sturdy, polyester sheet, and the entire lamination is laced together by nylon cords. The device is highly reliable in that it does not drift out of calibration, and is significantly inexpensive.
Steady-state operation of 170 GHz 1 MW gyrotron for ITER
NASA Astrophysics Data System (ADS)
Kasugai, A.; Sakamoto, K.; Takahashi, K.; Kajiwara, K.; Kobayashi, N.
2008-05-01
A 170 GHz gyrotron has been developed at JAEA, which has achieved operation of 1 MW/800 s and up to 55% efficiency. This is the first demonstration of a gyrotron achieving and even exceeding the ITER operating requirements of 1 MW/500 s and 50% efficiency. In addition the gyrotron demonstrated operation for 1 h with an output power of 0.6 MW. The oscillation was stable with all cooling water temperatures and vacuum pressure reaching equilibrium conditions during the pulse length at either power level. The successful operation was aided by a very low level of stray radiation (~2% of the output power), which contributed to fast conditioning and stable operation. The output power from the gyrotron was coupled into an ITER sized corrugated waveguide (phi = 63.5 mm) via a matching optics unit with a total of 0.97 MW transmitted to the dummy load after two miter bends and ~7 m of a waveguide without any trouble. These results give an encouraging outlook for the success of the ITER electron cyclotron heating and current drive system.
Lumen and Chromaticity Maintenance of LED PAR38 Lamps Operated in Steady-State Conditions
Royer, Michael P.
2014-12-01
The lumen depreciation and color shift of 38 different lamps (32 LED, 2 CFL, 1 ceramic metal halide [CMH], 3 halogen) were monitored in a specially developed automated long-term test apparatus (ALTA2) for nearly 14,000 hours. Five samples of each lamp model were tested, with measurements recorded on a weekly basis. The lamps were operated continuously at a target ambient temperature between 44°C and 45°C.
Steady state operation simulation of the Francis-99 turbine by means of advanced turbulence models
NASA Astrophysics Data System (ADS)
Gavrilov, A.; Dekterev, A.; Minakov, A.; Platonov, D.; Sentyabov, A.
2017-01-01
The paper presents numerical simulation of the flow in hydraulic turbine based on the experimental data of the II Francis-99 workshop. The calculation domain includes the wicket gate, runner and draft tube with rotating reference frame for the runner zone. Different turbulence models such as k-ω SST, ζ-f and RSM were considered. The calculations were performed by means of in-house CFD code SigmaFlow. The numerical simulation for part load, high load and best efficiency operation points were performed.
Development of steady-state operation using ion cyclotron heating in the Large Helical Device
Kasahara, H.; Seki, T.; Saito, K.; Seki, R.; Kumazawa, R.; Yoshimura, Y.; Kubo, S.; Shimozuma, T.; Igami, H.; Takahashi, H.; Tokitani, M.; Ashikawa, N.; Shoji, M.; Kamio, S.; Tsuchiya, H.; Yoshimura, S.; Tamura, N.; Suzuki, C.; Yamada, H.; Mutoh, T.; and others
2014-06-15
Using a handshake shape (HAS) antenna phasing dipole for ion cyclotron heating (ICH), the heating efficiency was higher than that using a previous poloidal array antenna in the Large Helical Device. In order to sustain the dipole operation, real-time feedback for impedance matching and maintaining the same phase and power was adopted during long-pulse discharge. The HAS antenna was designed to reduce parasitic losses associated with energetic particle and radio-frequency (RF) sheath effects by field-aligned current concentration on the midplane. Local hot spots and the inhomogeneity of the diverter heat profile in the toroidal direction were reduced. The long-pulse discharge with an electron density (n{sub e0}) of 1 × 10{sup 19} m{sup −3}, center electron temperature (T{sub e0}) of 2.5 keV, a plasma duration time (t{sub d}) of 19 min, and RF heating power (P{sub RF}) of 1 MW was achieved by ICH and electron cyclotron heating.
Evaluation of performance of a BLSS model in long-term operation in dynamic and steady states
NASA Astrophysics Data System (ADS)
Gros, Jean-Bernard; Tikhomirov, Alex; Ushakova, Sofya; Velitchko, Vladimir; Tikhomirova, Natalia; Lasseur, Christophe
Evaluation of performance of a BLSS model, including higher plants for food production and biodegradation of human waste, in long-term operation in dynamic and steady states was performed. The model system was conceived for supplying vegetarian food and oxygen to 0.07 human. The following data were obtained in steady-state operating conditions. Average rate of wheat, chufa, radish, lettuce and Salicornia edible biomass accumulation were 8.7, 5.5, 0.6, 0.6 and metricconverterProductID2.5 g2.5 g per day respectively. Thus, to mimic the vegetarian edible biomass consumption by a human it was necessary to withdraw 17.9 g/d from total mass ex-change. Simultaneously, human mineralized exometabolites (artificial mineralized urine, AMU) in the amount of approximately 7% of a daily norm were introduced into the nutrient solu-tion for irrigation of the plants cultivated on a neutral substrate (expanded clay aggregate). The estimated value of 5.8 g/d of wheat and Salicornia inedible biomass was introduced in the soil-like substrate (SLS) to fully meet the plants need in nitrogen. The rest of wheat and Salicornia inedible biomass, 5.7 g/d, was stored. Thus in all, 23.6g of vegetarian dry matter had been stored. Assuming edible biomass is eaten up by the human, the closure coefficient of the vegetarian biomass inclusion into matter recycling amounted to 88%. The analysis of the long-term model operation showed that the main factors limiting increase of recycling processes were the following: a) Partly unbalanced mineral composition of daily human waste with daily needs of plants culti-` vated in the system. Thus, when fully satisfied with respect to nitrogen, the plants experienced a lack of macro elements such as P, Mg and Ca by more than 50%; b) Partly unbalanced mineral composition of edible biomass of the plants cultivated in the SLS with that of inedible biomass of the plants cultivated by hydroponic method on neutral substrate introduced in the SLS; c) Accumulation of
Holcomb, C T; Ferron, J R; Luce, T C; Petrie, T W; Politzer, P A; Rhodes, T L; Doyle, E J; Makowski, M A; Kessel, C; DeBoo, J C; Groebner, R J; Osborne, T H; Snyder, P B; Greenfield, C M; La Haye, R J; Murakami, M; Hyatt, A W; Challis, C; Prater, R; Jackson, G L; Park, J; Reimerdes, H; Turnbull, A D; McKee, G R; Shafer, M W; Groth, M; Porter, G D; West, W P
2008-12-19
Recent studies on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] have elucidated key aspects of the dependence of stability, confinement, and density control on the plasma magnetic configuration, leading to the demonstration of nearly noninductive operation for >1 s with pressure 30% above the ideal no-wall stability limit. Achieving fully noninductive tokamak operation requires high pressure, good confinement, and density control through divertor pumping. Plasma geometry affects all of these. Ideal magnetohydrodynamics modeling of external kink stability suggests that it may be optimized by adjusting the shape parameter known as squareness ({zeta}). Optimizing kink stability leads to an increase in the maximum stable pressure. Experiments confirm that stability varies strongly with {zeta}, in agreement with the modeling. Optimization of kink stability via {zeta} is concurrent with an increase in the H-mode edge pressure pedestal stability. Global energy confinement is optimized at the lowest {zeta} tested, with increased pedestal pressure and lower core transport. Adjusting the magnetic divertor balance about a double-null configuration optimizes density control for improved noninductive auxiliary current drive. The best density control is obtained with a slight imbalance toward the divertor opposite the ion grad(B) drift direction, consistent with modeling of these effects. These optimizations have been combined to achieve noninductive current fractions near unity for over 1 s with normalized pressure of 3.5<{beta}{sub N}<3.9, bootstrap current fraction of >65%, and a normalized confinement factor of H{sub 98(y,2)}{approx}1.5.
NASA Astrophysics Data System (ADS)
Bergan, Carl; Goyal, Rahul; Cervantes, Michel J.; Dahlhaug, Ole G.
2016-11-01
Francis-99 is a set of workshops aiming to determine the state of the art of high head Francis turbine simulations (flow and structure) under steady and transient operating conditions as well as promote their development and knowledge dissemination openly. The first workshop (Trondheim, 2014) focused on steady state conditions. Some concerns were raised regarding uncertainty in the measurements, mainly that there was no clear vortex rope at the Part Load (PL) condition, and that the flow exhibited relatively large asymmetry. The present paper addresses these concerns in order to ensure the quality of the data presented in further workshops. To answer some of these questions, a new set of measurements were performed on the Francis- 99 model at Waterpower Laboratory at the Norwegian University of Science and Technology (NTNU). In addition to PL, two other operating conditions were considered, for further use in transient measurements, Best Efficiency (BEP) and High Load (HL). The experiments were carried out at a head of 12 m, with a runner rotational speed of 333 revolutions per minute (rpm). The guide vane opening angle were 6.72°, 9.84° and 12.43° for PL, BEP and HL, respectively. The part load condition has been changed from the first workshop, to ensure a fully developed Rotating Vortex Rope (RVR). The velocity and pressure measurements were carried out in the draft tube cone using 2D PIV and six pressure sensors, respectively. The new PL condition shows a fully developed rotating vortex rope (RVR) in both the frequency analysis and in the phase resolved data. In addition, the measurements confirm an asymmetric flow leaving the runner, as was a concern in the first Francis-99 workshop. This asymmetry was detected at both design and off-design conditions, with a stronger effect during off design.
An on-line monitoring method, jet resonance-enhanced multi-photon ionization (REMPI) with time-of-flight mass spectrometry (TOFMS) was used to measure emissions of organic air toxics from a medium-duty (60 kW)diesel generator during transient and steady state operations. Emission...
NASA Astrophysics Data System (ADS)
Simonin, A.; Achard, Jocelyn; Achkasov, K.; Bechu, S.; Baudouin, C.; Baulaigue, O.; Blondel, C.; Boeuf, J. P.; Bresteau, D.; Cartry, G.; Chaibi, W.; Drag, C.; de Esch, H. P. L.; Fiorucci, D.; Fubiani, G.; Furno, I.; Futtersack, R.; Garibaldi, P.; Gicquel, A.; Grand, C.; Guittienne, Ph.; Hagelaar, G.; Howling, A.; Jacquier, R.; Kirkpatrick, M. J.; Lemoine, D.; Lepetit, B.; Minea, T.; Odic, E.; Revel, A.; Soliman, B. A.; Teste, P.
2015-11-01
Since the signature of the ITER treaty in 2006, a new research programme targeting the emergence of a new generation of neutral beam (NB) system for the future fusion reactor (DEMO Tokamak) has been underway between several laboratories in Europe. The specifications required to operate a NB system on DEMO are very demanding: the system has to provide plasma heating, current drive and plasma control at a very high level of power (up to 150 MW) and energy (1 or 2 MeV), including high performances in term of wall-plug efficiency (η > 60%), high availability and reliability. To this aim, a novel NB concept based on the photodetachment of the energetic negative ion beam is under study. The keystone of this new concept is the achievement of a photoneutralizer where a high power photon flux (~3 MW) generated within a Fabry-Perot cavity will overlap, cross and partially photodetach the intense negative ion beam accelerated at high energy (1 or 2 MeV). The aspect ratio of the beam-line (source, accelerator, etc) is specifically designed to maximize the overlap of the photon beam with the ion beam. It is shown that such a photoneutralized based NB system would have the capability to provide several tens of MW of D0 per beam line with a wall-plug efficiency higher than 60%. A feasibility study of the concept has been launched between different laboratories to address the different physics aspects, i.e. negative ion source, plasma modelling, ion accelerator simulation, photoneutralization and high voltage holding under vacuum. The paper describes the present status of the project and the main achievements of the developments in laboratories.
Ogata, R.; Liu, H. Q.; Ishiguro, M.; Ikeda, T.; Hanada, K.; Zushi, H.; Nakamura, K.; Fujisawa, A.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Nishino, N.; Collaboration: QUEST Group
2011-09-15
A study of radial propagation and electric fields induced by charge separation in blob-like structures has been performed in a non-confined cylindrical electron cyclotron resonance heating plasma on Q-shu University Experiment with a Steady-State Spherical Tokamak using a fast-speed camera and a Langmuir probe. The radial propagation of the blob-like structures is found to be driven by E x B drift. Moreover, these blob-like structures were found to have been accelerated, and the property of the measured radial velocities agrees with the previously proposed model [C. Theiler et al., Phys. Rev. Lett. 103, 065001 (2009)]. Although the dependence of the radial velocity on the connection length of the magnetic field appeared to be different, a plausible explanation based on enhanced short-circuiting of the current path can be proposed.
none,
2014-12-31
This CALiPER report examines lumen depreciation and color shift of 17 different A lamps in steady-state conditions (15 LED, 1 CFL, 1 halogen). The goal of this investigation was to examine the long-term performance of complete LED lamps relative to benchmark halogen and CFL lamps—in this case, A lamps emitting approximately 800 lumens operated continuously at a relatively high ambient temperature of 45°C.
NASA Astrophysics Data System (ADS)
Oishi, Tetsutarou; Yamazaki, Kozo; Arimoto, Hideki; Mano, Junji
We applied the TOTAL (toroidal transport analysis linkage) simulation code for the analysis of the operational scenario of D-3He spherical tokamak reactors with high beta values and high bootstrap current fractions. Several technical elements, such as the control of the fuel ratio or selective exhaust of the α particle, need to be developed to establish steady-state burning. Negative magnetic shear configuration is a candidate for the high bootstrap current fraction operation.
Overview of the National Centralized Tokamak programme
NASA Astrophysics Data System (ADS)
Kikuchi, M.; Tamai, H.; Matsukawa, M.; Fujita, T.; Takase, Y.; Sakurai, S.; Kizu, K.; Tsuchiya, K.; Kurita, G.; Morioka, A.; Hayashi, N.; Miura, Y.; Itoh, S.; Bialek, J.; Navratil, G.; Ikeda, Y.; Fujii, T.; Kurihara, K.; Kubo, H.; Kamada, Y.; Miya, N.; Suzuki, T.; Hamamatsu, K.; Kawashima, H.; Kudo, Y.; Masaki, K.; Takahashi, H.; Takechi, M.; Akiba, M.; Okuno, K.; Ishida, S.; Ichimura, M.; Imai, T.; Hashizume; Miura, Y. M.; Horiike, H.; Kimura, A.; Tsutsui, H.; Matsuoka, M.; Uesugi, Y.; Sagara, A.; Nishimura, A.; Shimizu, A.; Sakamoto, M.; Nakamura, K.; Sato, K.; Okano, K.; Ida, K.; Shimada, H. R.; Kishimoto, Y.; Azechi, H.; Tanaka, S.; Yatsu, K.; Yoshida, N.; Inutake, M.; Fujiwara, M.; Inoue, N.; Hosogane, N.; Kuriyama, M.; Ninomiya, H.
2006-03-01
An overview is given of the National Centralized Tokamak (NCT) programme as a research programme for advanced tokamak research to succeed JT-60U. The mission of NCT is to establish high beta steady-state operation for DEMO and to contribute to ITER. The machine flexibility is pursued in aspect ratio and shape controllability for the demonstration of the high-β steady-state, feedback control of resistive wall modes, wide current and pressure profile control capability and also very long pulse steady-state operation. Existing JT-60 infrastructure such as the heating and current drive system, power supplies and cooling systems will be best utilized for this modification.
NASA Astrophysics Data System (ADS)
Cesario, R.; Amicucci, L.; Fonseca, A.; Chapman, I. T.; Jenko, F.; Marinucci, M.; Saarelma, S.; Smeulders, P.; Told, D.; Zagorski, R.; Baranov, Y.; Beurskens, M.; De Angelis, R.; McDonald, D.; Challis, C.; Galli, A.; Mailloux, J.; Pericoli, V.; Zerbini, M.; EFDA-JET Contributors, the
2013-04-01
In this paper, we discuss the phenomena that link particle recycling from the vessel walls in the L-mode during discharge start-up and the core confinement in the H-mode during the subsequent main heating phase. We consider available data of JET experiments that aimed at approaching fully non-inductive ITER-relevant steady-state conditions and show that the high electron temperature produced at the edge by a low recycling during start-up tends to favour the build-up of high normalized β(βN) regimes in the H-mode, the confinement being improved in a large plasma volume. To provide an insight into this complex phenomenon we have modelled the relation between particle recycling in the scrape-off layer and the evolution of plasma transport, plasma current density and shear as well as the stability properties for such experimental conditions. The results confirm the existence of a link between the confinement in the H-mode phase and the values at the edge of electron temperature, bootstrap current density and local magnetic shear during start-up. Such a link could favour these regimes to be self-sustained in time.
RF-driven tokamak reactor with sub-ignited, thermally stable operation
Harten, L.P.; Bers, A.; Fuchs, V.; Shoucri, M.M.
1981-02-01
A Radio-Frequency Driven Tokamak Reactor (RFDTR) can use RF-power, programmed by a delayed temperature measurement, to thermally stabilize a power equilibrium below ignition, and to drive a steady state current. We propose the parameters for such a device generating approx. = 1600 MW thermal power and operating with Q approx. = 40 (= power out/power in). A one temperature zero-dimensional model allows simple analytical formulation of the problem. The relevance of injected impurities for locating the equilibrium is discussed. We present the results of a one-dimensional (radial) code which includes the deposition of the supplementary power, and compare with our zero-dimensional model.
NASA Astrophysics Data System (ADS)
Ishida, S.; JT-60 Team, JFT-2M Group
2004-05-01
In the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U), a high- β p ELMy H-mode (high-poloidal-beta high-confinement-mode with edge localized mode) plasma was sustained with β N ˜2.7 for 7.4 s. Real-time neoclassical tearing mode (NTM) stabilization system was established and effective NTM suppression by early electron cyclotron (EC) wave injection was demonstrated. High fusion triple product of n i (0)τ E T i (0)=3.1×10 20 keVṡsṡm -3 was achieved using the negative-ion based neutral beam current drive with β N ˜2.5 and the bootstrap current fraction f BS ˜50%. In a hot electron regime, a high electron cyclotron current drive efficiency of 4.2×10 18 A/W/m 2 was achieved at T e ˜21 keV . Innovative current start-up scenario produced a current hole plasma with a very high f BS ˜90%. No accumulation of helium and carbon impurities was observed for internal transport barrier (ITB) plasmas. While argon impurity was accumulated, EC injection effectively exhausted it across ITB. In a regime of ELM disappearance, a clear correlation between the ELM frequency and the toroidal velocity at pedestal was observed. In the Japan Atomic Energy Research Institute Fusion Torus-2 Modified (JFT-2M), high beta plasmas were produced with full ferritic inside wall up to β N =3.3, where high recycling steady H-mode discharges were developed up to β N H 89 P ˜6 at n e /n GW ˜0.7-1.0 with ITB. JT-60U started long pulse experiment in late 2003 and JFT-2M will conduct wall stabilization experiment in early 2004. The modification of JT-60 to a fully superconducting coil tokamak is regarded as the national centralized tokamak facility program to accomplish the high beta steady-state research in a collisionless regime.
2010-03-01
organization and shared situational awareness 15 is sought between organizations and others. It is a metacognition of the operating environment that...understanding of a situation and perceives it, its history, and potential future(s), in the same way. It is a metacognition of the operating environment that...This assessment should culminate in the creation of a risk portfolio that includes a hierarchical prioritization of hazards, based upon their
Wyrzykowska-Ceradini, Barbara; Gullett, Brian K; Tabor, Dennis; Touati, Abderrahmane
2011-07-01
Concentrations of polybrominated dibenzo-p-dioxins, and -dibenzofurans (PBDDs/Fs) and polychlorinated dibenzo-p-dioxins, and -dibenzofurans (PCDDs/Fs), were determined in the pre- and post-air pollution control system (APCS) flue gas of a municipal waste combustor (MWC). Operational transients of the combustor were found to considerably increase levels of PBDDs/Fs and PCDDs/Fs compared to steady state operation, both for the raw and clean flue gas; ΣPBDDs/Fs increased from 72.7 to 700 pg dscm(-1) in the raw, pre-APCS gas and from 1.45 to 9.53 pg dscm(-1) in the post-APCS flue gas; ΣPCDDs/Fs increased from 240 to 960 ng dscm(-1) in the pre-APCS flue gas, and from 1.52 to 16.0 ng dscm(-1) in the post-APCS flue gas. The homologue profile of PBDDs/Fs and PCDDs/Fs in the raw flue gas (steady state and transients) was dominated by hexa- and octa-isomers, while the clean flue gas homologue profile was enriched with tetra- and penta-isomers. The efficiency of the APCS for PBDD/F and PCDD/F removal was estimated as 98.5% and 98.7%, respectively. The cumulative TEQ(PCDD/F+PBDD/F) from the stack was dominated by PCDD/F: the TEQ of PBDD/F contributed less than 0.1% to total cumulative toxic equivalency of MWC stack emissions.
Baker, C.C.
1981-01-01
This paper presents an overview of tokamak reactor studies with particular attention to commercial reactor concepts developed within the last three years. Emphasis is placed on DT fueled reactors for electricity production. A brief history of tokamak reactor studies is presented. The STARFIRE, NUWMAK, and HFCTR studies are highlighted. Recent developments that have increased the commercial attractiveness of tokamak reactor designs are discussed. These developments include smaller plant sizes, higher first wall loadings, improved maintenance concepts, steady-state operation, non-divertor particle control, and improved reactor safety features.
NASA Technical Reports Server (NTRS)
Olson, Walter T; Childs, J Howard
1950-01-01
Some of the systematic research conducted by the NACA on aircraft gas-turbine combustors is reviewed. Trends depicting the effect of inlet-air pressure, temperature, and velocity and fuel-air ratio on performance characteristics, such as combustion efficiency, maximum temperature rise attainable, pressure loss, and combustor-outlet temperature distribution are described for a variety of turbojet combustors of the liquid-fuel type. These trends are further discussed as effects significant to the turbojet engine, such as altitude operational limits, specific fuel consumption, thrust, acceleration, and turbine life.
NASA Technical Reports Server (NTRS)
Khonsari, M. M.
1983-01-01
Thermohydrodynamic effects in journal bearings operating under steady load in laminar regime are investigated. An analytical model for the finite and infinitely long journal bearings is formulated. The model includes correction factors for the cavitation effects in the unloaded region of the bearing and the mixing of the recirculating oil and supply oil at the oil inlet. A finite difference computer program is developed to numerically solve the governing equations of the continuity, Reynolds, energy, Laplace heat conduction, and a viscosity-temperature relation simultaneously. The program includes a numerical technique for obtaining an isothermal shaft temperature. The numerical results of temperature distribution and the heat effects on the bearing load carrying capacity agree closely with those of experimental findings. Several different sets of simpler boundary conditions for the energy equation are studied.
NASA Astrophysics Data System (ADS)
Houde, S.; Fraser, R.; Ciocan, G. D.; Deschênes, C.
2012-11-01
A good evaluation of the unsteady pressure field on hydraulic turbine blades is critical in evaluating the turbine lifespan and its maintenance schedule. Low-head turbines such as Kaplan and Propeller, using a relatively low number of blades supported only at the hub, may also undergo significant deflections at the blade tips which will lead to higher amplitude vibration compared to Francis turbines. Furthermore, the precise evaluation of the unsteady pressure distribution on low-head turbines is still a challenge for computational fluid dynamics (CFD). Within the framework of an international research consortium on low-head turbines, a research project was instigated at the Hydraulic Machines Laboratory in Laval University (LAMH) to perform experimental measurements of the unsteady pressure field on propeller turbine model runner blades. The main objective of the project was to measure the pressure fluctuations on a wide band of frequencies, both in a blade-to-blade channel and on the pressure and suction side of the same blade, to provide validation data for CFD computations. To do so, a 32 channels telemetric data transmission system was used to extract the signal of 31 pressure transducers and two strain gages from the rotating part at an acquisition frequency of 5 KHz. The miniature piezoelectric pressure transducers were placed on two adjacent runner blades according to an estimated pressure distribution coming from flow simulations. Two suction sides and one pressure side were instrumented. The strain gages were mounted in full-bridge on both pressure and suction sides to measure the blade span wise deflection. In order to provide boundary conditions for flow simulations, the test bench conditions during the measurements were acquired. The measurements were made in different operating conditions ranging from part load, where a cavitating vortex occurs, to full load under different heads. The results enabled the identification and the quantification of the
NASA Technical Reports Server (NTRS)
Foster, Winfred A., Jr.; Crowder, Winston; Steadman, Todd E.
2014-01-01
This paper presents the results of statistical analyses performed to predict the thrust imbalance between two solid rocket motor boosters to be used on the Space Launch System (SLS) vehicle. Two legacy internal ballistics codes developed for the Space Shuttle program were coupled with a Monte Carlo analysis code to determine a thrust imbalance envelope for the SLS vehicle based on the performance of 1000 motor pairs. Thirty three variables which could impact the performance of the motors during the ignition transient and thirty eight variables which could impact the performance of the motors during steady state operation of the motor were identified and treated as statistical variables for the analyses. The effects of motor to motor variation as well as variations between motors of a single pair were included in the analyses. The statistical variations of the variables were defined based on data provided by NASA's Marshall Space Flight Center for the upgraded five segment booster and from the Space Shuttle booster when appropriate. The results obtained for the statistical envelope are compared with the design specification thrust imbalance limits for the SLS launch vehicle.
NASA Technical Reports Server (NTRS)
Foster, Winfred A., Jr.; Crowder, Winston; Steadman, Todd E.
2014-01-01
This paper presents the results of statistical analyses performed to predict the thrust imbalance between two solid rocket motor boosters to be used on the Space Launch System (SLS) vehicle. Two legacy internal ballistics codes developed for the Space Shuttle program were coupled with a Monte Carlo analysis code to determine a thrust imbalance envelope for the SLS vehicle based on the performance of 1000 motor pairs. Thirty three variables which could impact the performance of the motors during the ignition transient and thirty eight variables which could impact the performance of the motors during steady state operation of the motor were identified and treated as statistical variables for the analyses. The effects of motor to motor variation as well as variations between motors of a single pair were included in the analyses. The statistical variations of the variables were defined based on data provided by NASA's Marshall Space Flight Center for the upgraded five segment booster and from the Space Shuttle booster when appropriate. The results obtained for the statistical envelope are compared with the design specification thrust imbalance limits for the SLS launch vehicle
Steady-state spheromak reactor studies. Revision
Krakowski, R.A.; Hagenson, R.L.
1985-01-01
After summarizing the essential elements of a gun-sustained spheromak, the potential for a steady-state is explored by means of a comprehensive physics/engineering/costing model. A range of cost-optimized reactor design point is presented, and the sensitivity of cost to key physics, engineering, and operational variables is reported.
Einstein's steady-state cosmology
NASA Astrophysics Data System (ADS)
O'Raifeartaigh, Cormac
2014-09-01
Last year, a team of Irish scientists discovered an unpublished manuscript by Einstein in which he attempted to construct a "steady-state" model of the universe. Cormac O'Raifeartaigh describes the excitement of finding this previously unknown work.
NASA Astrophysics Data System (ADS)
Marmar, Earl
2011-10-01
I-mode operation on Alcator C-Mod combines a strong edge thermal transport barrier with L-mode levels of particle and impurity transport, allowing access to very high performance discharges with low pedestal collisionality and central temperatures up to 8 keV, and without large ELMs or other intermittent edge instabilities. In recent campaigns, C-Mod I-modes have been extended to quasi-steady-state, with access in both favorable and unfavorable ion drift directions and typical normalized energy confinement quality factor H98 ~ 1.0 to 1.2. Adding ICRF mode-conversion flow-drive enhances toroidal flow shear near the plasma edge and confinement is further enhanced. I-mode has been maintained with input power up to nearly 2x the I-mode threshold power, with the largest accessible range in closed divertor geometry at modest triangularity. Simple extrapolations at fixed field imply that ITER in unfavorable drift could access I-mode with available power, and stay in I-mode with alpha-dominant heating. Detailed pedestal fluctuation measurements reveal changes in the turbulence, with decreases in the power at some frequencies and size scales, and growth of a weakly coherent mode (WCM) (kθ ~ 1.5 cm-1, δf/f ~.3) which propagates in the electron diamagnetic direction in the plasma frame. The WCM, which has density, temperature and magnetic signatures, appears to play a key role in pedestal density and impurity regulation, and detailed experimental results and associated modeling are presented. The distribution of divertor exhaust power depends on ion drift direction; new measurements of I-mode heat flux footprints on the outer divertor are compared with those in H-mode. Pedestal stability analyses will be shown for I-modes, including some which exhibited small ELMs. Supported by USDOE Award DE-FC02-99-ER54512.
ELM induced tungsten melting and its impact on tokamak operation
NASA Astrophysics Data System (ADS)
Coenen, J. W.; Arnoux, G.; Bazylev, B.; Matthews, G. F.; Jachmich, S.; Balboa, I.; Clever, M.; Dejarnac, R.; Coffey, I.; Corre, Y.; Devaux, S.; Frassinetti, L.; Gauthier, E.; Horacek, J.; Knaup, M.; Komm, M.; Krieger, K.; Marsen, S.; Meigs, A.; Mertens, Ph.; Pitts, R. A.; Puetterich, T.; Rack, M.; Stamp, M.; Sergienko, G.; Tamain, P.; Thompson, V.
2015-08-01
In JET-ILW dedicated melt exposures were performed using a sequence of 3MA/2.9T H-Mode JET pulses with an input power of PIN = 23 MW, a stored energy of ∼6 MJ and regular type I ELMs at ΔWELM = 0.3 MJ and fELM ∼ 30 Hz. In order to assess the risk of starting ITER operations with a full W divertor, one of the task was to measure the consequences of W transients melting due to ELMs. JET is the only tokamak able to produce transients/ ELMs large enough (>300 kJ per ELM) to facilitate melting of tungsten. Such ELMs are comparable to mitigated ELMs expected in ITER. By moving the outer strike point (OSP) onto a dedicated leading edge the base temperature was raised within ∼1 s to allow transient ELM-driven melting during the subsequent 0.5 s. Almost 1 mm (∼6 mm3) of W was moved by ∼ 150 ELMs within 5 subsequent discharges. Significant material losses in terms of ejections into the plasma were not observed. There is indirect evidence that some small droplets (∼ 80 μm) were ejected. The impact on the main plasma parameters is minor and no disruptions occurred. The W-melt gradually moved along the lamella edge towards the high field side, driven by j × B forces. The evaporation rate determined is 100 times less than expected from steady state melting and thus only consistent with transient melting during individual ELMs. IR data, spectroscopy, as well as melt modeling point to transient melting. Although the type of damage studied in these JET experiments is unlikely to be experienced in ITER, the results do strongly support the design strategy to avoid exposed edges in the ITER divertor. The JET experiments required a surface at normal incidence and considerable pre-heating to produce tungsten melting. They provide unique experimental evidence for the absence of significant melt splashing at events resembling mitigated ELMs on ITER and establish a unique experimental benchmark for the simulations being used to study transient shallow melting on ITER W
Gravitational steady states of solar coronal loops
NASA Astrophysics Data System (ADS)
Sugiyama, Linda E.; Asgari-Targhi, M.
2017-02-01
Coronal loops on the surface of the sun appear to consist of curved, plasma-confining magnetic flux tubes or "ropes," anchored at both ends in the photosphere. Toroidal loops carrying current are inherently unstable to expansion in the major radius due to toroidal-curvature-induced imbalances in the magnetic and plasma pressures. An ideal MHD analysis of a simple isolated loop with density and pressure higher than the surrounding corona, based on the theory of magnetically confined toroidal plasmas, shows that the radial force balance depends on the loop internal structure and varies over parameter space. It provides a unified picture of simple loop steady states in terms of the plasma beta βo, the inverse aspect ratio ɛ =a /Ro , and the MHD gravitational parameter G ̂≡g a /vA2 , all at the top of the loop, where g is the acceleration due to gravity, a the average minor radius, and vA the shear Alfvén velocity. In the high and low beta tokamak orderings, βo=2 noT /(Bo2/2 μo)˜ɛ1 and ɛ2 , that fit many loops, the solar gravity can sustain nonaxisymmetric steady states at G ̂˜ɛ βo that represent the maximum stable height. At smaller G ̂≤ɛ2βo , the loop is axisymmetric to leading order and stabilized primarily by the two fixed loop ends. Very low beta, nearly force-free, steady states with βo˜ɛ3 may also exist, with or without gravity, depending on higher order effects. The thin coronal loops commonly observed in solar active regions have ɛ ≃0.02 and fit the high beta steady states. G ̂ increases with loop height. Fatter loops in active regions that form along magnetic neutral lines and may lead to solar flares and Coronal Mass Ejections have ɛ ≃0.1 -0.2 and may fit the low beta ordering. Larger loops tend to have G ̂>ɛ βo and be unstable to radial expansion because the exponential hydrostatic reduction in the density at the loop-top reduces the gravitational force -ρG ̂ R ̂ below the level that balances expansion, in agreement with
Royer, Michael P.; McCullough, Jeffrey J.; Tucker, Joseph C.
2014-12-01
The lumen depreciation and color shift of 17 different A lamps (15 LED, 1 CFL, 1 halogen) was monitored in the automated long-term test apparatus (ALTA) for more than 7,500 hours. Ten samples of each lamp model were tested, with measurements recorded on a weekly basis. The lamps were operated continuously at an ambient temperature of 45°C (-1°C). Importantly, the steady-state test conditions were not optimized for inducing catastrophic failure for any of the lamp technologies—to which thermal cycling is a strong contributor— and are not typical of normal use patterns—which usually include off periods where the lamp cools down. Further, the test conditions differ from those used in standardized long-term test methods (i.e., IES LM-80, IES LM-84), so the results should not be directly compared. On the other hand, the test conditions are similar to those used by ENERGY STAR (when elevated temperature testing is called for). Likewise, the conditions and assumptions used by manufacturers to generated lifetime claims may vary; the CALiPER long-term data is informative, but cannot necessarily be used to discredit manufacturer claims. The test method used for this investigation should be interpreted as one more focused on the long-term effects of elevated temperature operation, at an ambient temperature that is not uncommon in luminaires. On average, the lumen maintenance of the LED lamps monitored in the ALTA was better than benchmark lamps, but there was considerable variation from lamp model to lamp model. While three lamp models had average lumen maintenance above 99% at the end of the study period, two products had average lumen maintenance below 65%, constituting a parametric failure. These two products, along with a third, also exhibited substantial color shift, another form of parametric failure. While none of the LED lamps exhibited catastrophic failure—and all of the benchmarks did—the early degradation of performance is concerning, especially with a
Intense steady state electron beam generator
Hershcovitch, Ady; Kovarik, Vincent J.; Prelec, Krsto
1990-01-01
An intense, steady state, low emittance electron beam generator is formed by operating a hollow cathode discharge plasma source at critical levels in combination with an extraction electrode and a target electrode that are operable to extract a beam of fast primary electrons from the plasma source through a negatively biased grid that is critically operated to repel bulk electrons toward the plasma source while allowing the fast primary electrons to move toward the target in the desired beam that can be successfully transported for relatively large distances, such as one or more meters away from the plasma source.
Bootstrapped tokamak with oscillating field current drive
Weening, R.H. )
1993-07-01
A magnetic helicity conserving mean-field Ohm's law is used to study bootstrapped tokamaks with oscillating field current drive. The Ohm's law leads to the conclusion that the tokamak bootstrap effect can convert the largely alternating current of oscillating field current drive into a direct toroidal plasma current. This plasma current rectification is due to the intrinsically nonlinear nature of the tokamak bootstrap effect, and suggests that it may be possible to maintain the toroidal current of a tokamak reactor by supplementing the bootstrap current with oscillating field current drive. Steady-state tokamak fusion reactors operating with oscillating field current drive could provide an alternative to tokamak reactors operating with external current drive.
Posaconazole Plasma Concentrations on Days Three to Five Predict Steady-State Levels
Prattes, Jürgen; Duettmann, Wiebke
2016-01-01
Low posaconazole plasma concentrations (PPCs) have been associated with breakthrough invasive fungal infections. We assessed the correlation between pre-steady-state PPCs (obtained between days 3 and 5) and PPCs obtained during steady state in 48 patients with underlying hematological malignancies receiving posaconazole oral-solution prophylaxis. Pre-steady-state PPCs correlated significantly with PPCs obtained at steady state (Spearman r = 0.754; P < 0.001). Receiver operating characteristic (ROC) curve analysis of pre-steady-state PPCs revealed an area under the curve (AUC) of 0.884 (95% confidence interval [CI], 0.790 to 0.977) for predicting satisfactory PPCs at steady state. PMID:27324763
Inconsistencies in steady state thermodynamics
NASA Astrophysics Data System (ADS)
Dickman, Ronald; Motai, Ricardo
2014-03-01
We address the issue of extending thermodynamics to nonequilibrium steady states. Using driven stochastic lattice gases, we ask whether consistent definitions of an effective chemical potential μ, and an effective temperature Te, are possible. These quantities are determined via zero-flux conditions of particles and energy between the driven system and a reservoir. For the models considered here, the fluxes are given in terms of certain stationary average densities, eliminating the need to perturb the system by actually exchanging particles; μ and Te are thereby obtained via open-circuit measurements, using a virtual reservoir. In the lattice gas with nearest-neighbor exclusion, temperature is not relevant, and we find that the effective chemical potential, a function of density and drive strength, satisfies the zeroth law, and correctly predicts the densities of coexisting systems. In the Katz-Lebowitz-Spohn driven lattice gas, both μ and Te need to be defined. We show analytically that the zeroth law is violated, and determine the size of the violations numerically. Our results highlight a fundamental inconsistency in the extension of thermodynamics to nonequilibrium steady states. Research supported by CNPq, Brazil.
High-beta, steady-state hybrid scenario on DIII-D
Petty, C. C.; Kinsey, J. E.; Holcomb, C. T.; ...
2015-12-17
Here, the potential of the hybrid scenario (first developed as an advanced inductive scenario for high fluence) as a regime for high-beta, steady-state plasmas is demonstrated on the DIII-D tokamak. These experiments show that the beneficial characteristics of hybrids, namely safety factor ≥1 with low central magnetic shear, high stability limits and excellent confinement, are maintained when strong central current drive (electron cyclotron and neutral beam) is applied to increase the calculated non-inductive fraction to ≈100% (≈50% bootstrap current). The best discharges achieve normalized beta of 3.4, IPB98(y,2) confinement factor of 1.4, surface loop voltage of 0.01 V, and nearlymore » equal electron and ion temperatures at low collisionality. A zero-dimensional physics model shows that steady-state hybrid operation with Qfus ~ 5 is feasible in FDF and ITER. The advantage of the hybrid scenario as an Advanced Tokamak regime is that the external current drive can be deposited near the plasma axis where the efficiency is high; additionally, good alignment between the current drive and plasma current profiles is not necessary as the poloidal magnetic flux pumping self-organizes the current density profile in hybrids with an m/n=3/2 tearing mode.« less
High-beta, steady-state hybrid scenario on DIII-D
Petty, C. C.; Kinsey, J. E.; Holcomb, C. T.; DeBoo, J. C.; Doyle, E. J.; Ferron, J. R.; Garofalo, A. M.; Hyatt, A. W.; Jackson, G. L.; Luce, T. C.; Murakami, M.; Politzer, P. A.; Reimerdes, H.
2015-12-17
Here, the potential of the hybrid scenario (first developed as an advanced inductive scenario for high fluence) as a regime for high-beta, steady-state plasmas is demonstrated on the DIII-D tokamak. These experiments show that the beneficial characteristics of hybrids, namely safety factor ≥1 with low central magnetic shear, high stability limits and excellent confinement, are maintained when strong central current drive (electron cyclotron and neutral beam) is applied to increase the calculated non-inductive fraction to ≈100% (≈50% bootstrap current). The best discharges achieve normalized beta of 3.4, IPB98(y,2) confinement factor of 1.4, surface loop voltage of 0.01 V, and nearly equal electron and ion temperatures at low collisionality. A zero-dimensional physics model shows that steady-state hybrid operation with Q_{fus} ~ 5 is feasible in FDF and ITER. The advantage of the hybrid scenario as an Advanced Tokamak regime is that the external current drive can be deposited near the plasma axis where the efficiency is high; additionally, good alignment between the current drive and plasma current profiles is not necessary as the poloidal magnetic flux pumping self-organizes the current density profile in hybrids with an m/n=3/2 tearing mode.
High-beta, steady-state hybrid scenario on DIII-D
NASA Astrophysics Data System (ADS)
Petty, C. C.; Kinsey, J. E.; Holcomb, C. T.; DeBoo, J. C.; Doyle, E. J.; Ferron, J. R.; Garofalo, A. M.; Hyatt, A. W.; Jackson, G. L.; Luce, T. C.; Murakami, M.; Politzer, P. A.; Reimerdes, H.
2016-01-01
The potential of the hybrid scenario (first developed as an advanced inductive scenario for high fluence) as a regime for high-beta, steady-state plasmas is demonstrated on the DIII-D tokamak. These experiments show that the beneficial characteristics of hybrids, namely safety factor ⩾1 with low central magnetic shear, high stability limits and excellent confinement, are maintained when strong central current drive (electron cyclotron and neutral beam) is applied to increase the calculated non-inductive fraction to ≈100% (≈50% bootstrap current). The best discharges achieve normalized beta of 3.4, IPB98(y,2) confinement factor of 1.4, surface loop voltage of 0.01 V, and nearly equal electron and ion temperatures at low collisionality. A 0D physics model shows that steady-state hybrid operation with Qfus ~ 5 is feasible in FDF and ITER. The advantage of the hybrid scenario as an advanced tokamak regime is that the external current drive can be deposited near the plasma axis where the efficiency is high; additionally, good alignment between the current drive and plasma current profiles is not necessary as the poloidal magnetic flux pumping self-organizes the current density profile in hybrids with an m/n=3/2 tearing mode.
Multimode optical fibers: steady state mode exciter.
Ikeda, M; Sugimura, A; Ikegami, T
1976-09-01
The steady state mode power distribution of the multimode graded index fiber was measured. A simple and effective steady state mode exciter was fabricated by an etching technique. Its insertion loss was 0.5 dB for an injection laser. Deviation in transmission characteristics of multimode graded index fibers can be avoided by using the steady state mode exciter.
Irreversible processes at nonequilibrium steady states
Fox, Ronald Forrest
1979-01-01
It is shown that a Liapunov criterion exists for the stability of nonequilibrium steady states. This criterion is based upon the fluctuation-dissipation relation, as was first pointed out by Keizer. At steady states, the Liapunov function is constructed from the covariance matrix for the thermodynamic variables. Unlike the situation around equilibrium, at steady states the covariance matrix and the “excess entropy” matrix are not equivalent. The excess entropy, which serves as the Liapunov function around equilibrium, does not work in this capacity at steady states. Keizer's Liapunov function must be viewed as the first correct candidate for a proper Liapunov function for steady states. PMID:16592649
Progress Towards High-Performance, Steady-State Spherical Torus
Lawrence Livermore National Laboratory
2004-01-04
Research on the spherical torus (or spherical tokamak) (ST) is being pursued to explore the scientific benefits of modifying the field line structure from that in more moderate aspect ratio devices, such as the conventional tokamak. The ST experiments are being conducted in various US research facilities including the MA-class National Spherical Torus Experiment (NSTX) at Princeton, and three medium sized ST research facilities: PEGASUS at University of Wisconsin, HIT-II at University of Washington, and CDX-U at Princeton. In the context of the fusion energy development path being formulated in the US, an ST-based Component Test Facility (CTF) and, ultimately a Demo device, are being discussed. For these, it is essential to develop high performance, steady-state operational scenarios. The relevant scientific issues are energy confinement, MHD stability at high beta ({beta}), non-inductive sustainment, Ohmic-solenoid-free start-up, and power and particle handling. In the confinement area, the NSTX experiments have shown that the confinement can be up to 50% better than the ITER-98-pby2 H-mode scaling, consistent with the requirements for an ST-based CTF and Demo. In NSTX, CTF-relevant average toroidal beta values {beta}{sub T} of up to 35% with a near unity central {beta}{sub T} have been obtained. NSTX will be exploring advanced regimes where {beta}{sub T} up to 40% can be sustained through active stabilization of resistive wall modes. To date, the most successful technique for non-inductive sustainment in NSTX is the high beta poloidal regime, where discharges with a high non-inductive fraction ({approx}60% bootstrap current+NBI current drive) were sustained over the resistive skin time. Research on radio-frequency (RF) based heating and current drive utilizing high harmonic fastwave and electron Bernstein wave is also pursued on NSTX, PEGASUS, and CDX-U. For non-inductive start-up, the coaxial helicity injection, developed in HIT/HIT-II, has been adopted on NSTX
Analysis and Simulation of ITER Steady-State Discharges on DIII-D
NASA Astrophysics Data System (ADS)
Diem, S. J.; Murakami, M.; Park, J. M.; Sontag, A. C.
2013-10-01
One of the primary goals of the ITER project is to demonstrate a reactor scale steady-state operation for future tokamaks. This is a challenging task which requires simultaneous operation with fully noninductive current drive, a fusion gain of Q >= 5 and IBS for discharges approximately 3000s in length. Previously, DIII-D has demonstrated fully noninductive scenario in ITER-like shaped plasmas at relatively high q95 ~ 6 . 5 and moderate βN ~ 3 but with low fusion performance (G =βNH89 /q952 ~ 0 . 15). Recent high qmin experiment and modeling indicate that the goal of G = 0 . 3 predicted for Q = 5 operation on ITER can be achieved noninductively at reduced q95 and at higher βN. An optimum choice of q95 and βN for the ITER steady-state mission will be discussed based on the experimental scaling from ITER demonstration discharges on DIII-D, as well as predictive FASTRAN scenario modeling using TGLF coupled to the Integrated Plasma Simulator. FASTRAN is a new iterative numerical procedure that integrates a variety of models (transport, heating, CD, equilibrium and stability) and has been shown to reproduce most features of DIII-D high beta discharges with a stationary current profile. ORNL is managed by UT-Battelle, LLC for the US DOE under DE-AC02-05ER22725 and DE-FC02-04ER54698.
Modelling of pulsed and steady-state DEMO scenarios
NASA Astrophysics Data System (ADS)
Giruzzi, G.; Artaud, J. F.; Baruzzo, M.; Bolzonella, T.; Fable, E.; Garzotti, L.; Ivanova-Stanik, I.; Kemp, R.; King, D. B.; Schneider, M.; Stankiewicz, R.; Stępniewski, W.; Vincenzi, P.; Ward, D.; Zagórski, R.
2015-07-01
Scenario modelling for the demonstration fusion reactor (DEMO) has been carried out using a variety of simulation codes. Two DEMO concepts have been analysed: a pulsed tokamak, characterized by rather conventional physics and technology assumptions (DEMO1) and a steady-state tokamak, with moderately advanced physics and technology assumptions (DEMO2). Sensitivity to impurity concentrations, radiation, and heat transport models has been investigated. For DEMO2, the impact of current driven non-inductively by neutral beams has been studied by full Monte Carlo simulations of the fast ion distribution. The results obtained are a part of a more extensive research and development (R&D) effort carried out in the EU in order to develop a viable option for a DEMO reactor, to be adopted after ITER for fusion energy research.
JET, the largest tokamak on the eve of DT operation
NASA Astrophysics Data System (ADS)
Horton, L. D.
2016-11-01
The Joint European Torus (JET) is the world's largest operating tokamak and the only such machine capable of operating with the fuel mixture (deuterium-tritium) foreseen for a fusion reactor. Since it came into operation in 1983, JET has explored fusion plasmas "in conditions and dimensions approaching those of a fusion reactor" [1]. JET has demonstrated world-record levels of fusion power and energy production, in conditions where the ratio of the fusion power generated to the input power to the plasma, Q, approaches unity.
Multiple steady states in coupled flow tank reactors
NASA Astrophysics Data System (ADS)
Hunt, Katharine L. C.; Kottalam, J.; Hatlee, Michael D.; Ross, John
1992-05-01
Coupling between continuous-flow, stirred tank reactors (CSTR's), each having multiple steady states, can produce new steady states with different concentrations of the chemical species in each of the coupled tanks. In this work, we identify a kinetic potential ψ that governs the deterministic time evolution of coupled tank reactors, when the reaction mechanism permits a single-variable description of the states of the individual tanks; examples include the iodate-arsenous acid reaction, a cubic model suggested by Noyes, and two quintic models. Stable steady states correspond to minima of ψ, and unstable steady states to maxima or saddle points; marginally stable states typically correspond to saddle-node points. We illustrate the variation in ψ due to changes in the rate constant for external material intake (k0) and for exchange between tanks (kx). For fixed k0 values, we analyze the changes in numbers and types of steady states as kx increases from zero. We show that steady states disappear by pairwise coalescence; we also show that new steady states may appear with increasing kx, when the reaction mechanism is sufficiently complex. For fixed initial conditions, the steady state ultimately reached in a mixing experiment may depend on the exchange rate constant as a function of time, kx(t) : Adiabatic mixing is obtained in the limit of slow changes in kx(t) and instantaneous mixing in the limit as kx(t)→∞ while t remains small. Analyses based on the potential ψ predict the outcome of mixing experiments for arbitrary kx(t). We show by explicit counterexamples that a prior theory developed by Noyes does not correctly predict the instability points or the transitions between steady states of coupled tanks, to be expected in mixing experiments. We further show that the outcome of such experiments is not connected to the relative stability of steady states in individual tank reactors. We find that coupling may effectively stabilize the tanks. We provide
Non-Markovianity-assisted steady state entanglement.
Huelga, Susana F; Rivas, Ángel; Plenio, Martin B
2012-04-20
We analyze the steady state entanglement generated in a coherently coupled dimer system subject to dephasing noise as a function of the degree of Markovianity of the evolution. By keeping fixed the effective noise strength while varying the memory time of the environment, we demonstrate that non-Markovianity is an essential, quantifiable resource that may support the formation of steady state entanglement whereas purely Markovian dynamics governed by Lindblad master equations lead to separable steady states. This result illustrates possible mechanisms leading to long-lived entanglement in purely decohering, possibly local, environments. We present a feasible experimental demonstration of this noise assisted phenomenon using a system of trapped ions.
Steady-State Squeezing in the Micromaser Cavity Field
NASA Technical Reports Server (NTRS)
Nayak, N.
1996-01-01
It is shown that the radiation field in the presently operated micromaser cavity may be squeezed when pumped with polarized atoms. The squeezing is in the steady state field corresponding to the action similar to that of the conventional micromaser, with the effect of cavity dissipation during entire t(sub c) = tau + t(sub cav).
Prospects for Tokamak Fusion Reactors
Sheffield, J.; Galambos, J.
1995-04-01
This paper first reviews briefly the status and plans for research in magnetic fusion energy and discusses the prospects for the tokamak magnetic configuration to be the basis for a fusion power plant. Good progress has been made in achieving fusion reactor-level, deuterium-tritium (D-T) plasmas with the production of significant fusion power in the Joint European Torus (up to 2 MW) and the Tokamak Fusion Test Reactor (up to 10 MW) tokamaks. Advances on the technologies of heating, fueling, diagnostics, and materials supported these achievements. The successes have led to the initiation of the design phases of two tokamaks, the International Thermonuclear Experimental Reactor (ITER) and the US Toroidal Physics Experiment (TPX). ITER will demonstrate the controlled ignition and extended bum of D-T plasmas with steady state as an ultimate goal. ITER will further demonstrate technologies essential to a power plant in an integrated system and perform integrated testing of the high heat flux and nuclear components required to use fusion energy for practical purposes. TPX will complement ITER by testing advanced modes of steady-state plasma operation that, coupled with the developments in ITER, will lead to an optimized demonstration power plant.
Yongky, Andrew; Lee, Jongchan; Le, Tung; Mulukutla, Bhanu Chandra; Daoutidis, Prodromos; Hu, Wei-Shou
2015-07-01
Continuous culture for the production of biopharmaceutical proteins offers the possibility of steady state operations and thus more consistent product quality and increased productivity. Under some conditions, multiplicity of steady states has been observed in continuous cultures of mammalian cells, wherein with the same dilution rate and feed nutrient composition, steady states with very different cell and product concentrations may be reached. At those different steady states, cells may exhibit a high glycolysis flux with high lactate production and low cell concentration, or a low glycolysis flux with low lactate and high cell concentration. These different steady states, with different cell concentration, also have different productivity. Developing a mechanistic understanding of the occurrence of steady state multiplicity and devising a strategy to steer the culture toward the desired steady state is critical. We establish a multi-scale kinetic model that integrates a mechanistic intracellular metabolic model and cell growth model in a continuous bioreactor. We show that steady state multiplicity exists in a range of dilution rate in continuous culture as a result of the bistable behavior in glycolysis. The insights from the model were used to devise strategies to guide the culture to the desired steady state in the multiple steady state region. The model provides a guideline principle in the design of continuous culture processes of mammalian cells.
On the possibility of a steady state tokamak
NASA Astrophysics Data System (ADS)
Dawson, J. M.; Nunan, W. J.; Ma, S.
1994-08-01
It is a great pleasure for me to speak at this symposium in honor of Tom Stix. I have had the privilege of knowing Tom ever since I started working in plasma physics and fusion at the Princeton Plasma Physics Lab almost 36 years ago. He was a leader of the fusion effort when I arrived and has remained so up to the present time. I vividly remember our interesting discussions on plasma physics. Particularly, I remember how many new and original ideas came from Tom, his ideas for ICRH: the Stix coil, the magnetic beach, and many, many others. Tom not only originated ideas but he built and carried out experiments to these ideas, as well as many other fundamental concepts in plasma physics. Tom's experiments were always firsts, and many pioneering advances were made by him. Tom's enthusiasm for plasma physics and fusion is infectious; it stimulates and inspires his co-workers and has touched all of Princeton's plasma students. Tom has had a deep interest in teaching plasma physics from the beginning. His excellent course on plasma waves launched many careers. His book on plasma waves, which came from this course, is the standard on the subject, and is an invaluable reference for everyone working in plasma physics. Tom is a generous and caring person which made him an ideal person to lead the Princeton Plasma Physics Graduate Program. It is my great good fortune to have known and worked with Tom, and to have him as a friend. This symposium is particularly honoring Tom for his guiding of the graduate program in plasma physics at Princeton. For this reason I thought it would be appropriate for me to speak about some work a graduate student of mine, Bill Nunan, is doing, at UCLA. In a real sense the UCLA graduate program in Plasma Physics has many roots in the Princeton program which Tom so skillfully guided.
Dust remobilization in fusion plasmas under steady state conditions
NASA Astrophysics Data System (ADS)
Tolias, P.; Ratynskaia, S.; De Angeli, M.; De Temmerman, G.; Ripamonti, D.; Riva, G.; Bykov, I.; Shalpegin, A.; Vignitchouk, L.; Brochard, F.; Bystrov, K.; Bardin, S.; Litnovsky, A.
2016-02-01
The first combined experimental and theoretical studies of dust remobilization by plasma forces are reported. The main theoretical aspects of remobilization in fusion devices under steady state conditions are analyzed. In particular, the dominant role of adhesive forces is highlighted and generic remobilization conditions—direct lift-up, sliding, rolling—are formulated. A novel experimental technique is proposed, based on controlled adhesion of dust grains on tungsten samples combined with detailed mapping of the dust deposition profile prior and post plasma exposure. Proof-of-principle experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are presented. The versatile environment of the linear device Pilot-PSI allowed for experiments with different magnetic field topologies and varying plasma conditions that were complemented with camera observations.
Practical steady-state enzyme kinetics.
Lorsch, Jon R
2014-01-01
Enzymes are key components of most biological processes. Characterization of enzymes is therefore frequently required during the study of biological systems. Steady-state kinetics provides a simple and rapid means of assessing the substrate specificity of an enzyme. When combined with site-directed mutagenesis (see Site-Directed Mutagenesis), it can be used to probe the roles of particular amino acids in the enzyme in substrate recognition and catalysis. Effects of interaction partners and posttranslational modifications can also be assessed using steady-state kinetics. This overview explains the general principles of steady-state enzyme kinetics experiments in a practical, rather than theoretical, way. Any biochemistry textbook will have a section on the theory of Michaelis-Menten kinetics, including derivations of the relevant equations. No specific enzymatic assay is described here, although a method for monitoring product formation or substrate consumption over time (an assay) is required to perform the experiments described.
Network inference in the nonequilibrium steady state
NASA Astrophysics Data System (ADS)
Dettmer, Simon L.; Nguyen, H. Chau; Berg, Johannes
2016-11-01
Nonequilibrium systems lack an explicit characterization of their steady state like the Boltzmann distribution for equilibrium systems. This has drastic consequences for the inference of the parameters of a model when its dynamics lacks detailed balance. Such nonequilibrium systems occur naturally in applications like neural networks and gene regulatory networks. Here, we focus on the paradigmatic asymmetric Ising model and show that we can learn its parameters from independent samples of the nonequilibrium steady state. We present both an exact inference algorithm and a computationally more efficient, approximate algorithm for weak interactions based on a systematic expansion around mean-field theory. Obtaining expressions for magnetizations and two- and three-point spin correlations, we establish that these observables are sufficient to infer the model parameters. Further, we discuss the symmetries characterizing the different orders of the expansion around the mean field and show how different types of dynamics can be distinguished on the basis of samples from the nonequilibrium steady state.
Steady state response of unsymmetrically laminated plates
Hosokawa, Kenji; Kawashima, Katsuya; Sakata, Toshiyuki
1995-11-01
A numerical approach for analyzing the forced vibration problem of a symmetrically laminated FRP (fiber reinforced plastic) composite plate was proposed by the authors. In the present paper, this approach is modified for application to an unsymmetrically laminated FRP composite plate. Numerical calculations are carried out for the clamped antisymmetrically laminated rectangular and elliptical plates which are a kind of unsymmetrically laminated plate. Then,, the effects of the lamina material and the fiber orientation angle on the steady state response are discussed. Furthermore, it is investigated that what structural damping factor is most influenced on the steady state response of an antisymmetrically laminated plate.
Firestone, M.A.; Mau, T.K.; Conn, R.W.
1985-04-01
A small steady-state tokamak capable of producing power in the 100 to 300 MWe range and relying on electron cyclotron RF heating (ECH) for both heating and current drive is described. Working in the first MHD stability regime for tokamaks, the approach adheres to the recently discovered maximum beta limit. An appropriate figure of merit is the ratio of the fusion power to absorbed RF power. Efficient devices are feasible at both small and large values of fusion power, thereby pointing to a development path for an attractive commercial fusion reactor.
Magnetic confinement experiment. I: Tokamaks
Goldston, R.J.
1995-08-01
Reports were presented at this conference of important advances in all the key areas of experimental tokamak physics: Core Plasma Physics, Divertor and Edge Physics, Heating and Current Drive, and Tokamak Concept Optimization. In the area of Core Plasma Physics, the biggest news was certainly the production of 9.2 MW of fusion power in the Tokamak Fusion Test Reactor, and the observation of unexpectedly favorable performance in DT plasmas. There were also very important advances in the performance of ELM-free H- (and VH-) mode plasmas and in quasi-steady-state ELM`y operation in JT-60U, JET, and DIII-D. In all three devices ELM-free H-modes achieved nT{tau}`s {approximately} 2.5x greater than ELM`ing H-modes, but had not been sustained in quasi-steady-state. Important progress has been made on the understanding of the physical mechanism of the H-mode in DIII-D, and on the operating range in density for the H-mode in Compass and other devices.
The Politics of the Steady State
ERIC Educational Resources Information Center
Taylor, Charles
1978-01-01
A steady state society has limits pertaining to population size, non-renewable resources, and production which emits heat or substances into soil, water, or the atmosphere. Respecting these limits means renouncing exponential quantitative growth and accepting a universally available consumption standard. (SW)
Runov, A.M.; Kasilov, S.V.; Helander, P.
2015-11-01
A kinetic Monte Carlo model suited for self-consistent transport studies is proposed and tested. The Monte Carlo collision operator is based on a widely used model of Coulomb scattering by a drifting Maxwellian and a new algorithm enforcing the momentum and energy conservation laws. The difference to other approaches consists in a specific procedure of calculating the background Maxwellian parameters, which does not require ensemble averaging and, therefore, allows for the use of single-particle algorithms. This possibility is useful in transport balance (steady state) problems with a phenomenological diffusive ansatz for the turbulent transport, because it allows a direct use of variance reduction methods well suited for single particle algorithms. In addition, a method for the self-consistent calculation of the electric field is discussed. Results of testing of the new collision operator using a set of 1D examples, and preliminary results of 2D modelling in realistic tokamak geometry, are presented.
Harmonic coupling of steady-state visual evoked potentials.
Krusienski, Dean J; Allison, Brendan Z
2008-01-01
Steady-state visual evoked potentials (SSVEPs) are oscillating components of the electroencephalogram (EEG) that are detected over the occipital areas, having frequencies corresponding to visual stimulus frequencies. SSVEPs have been demonstrated to be reliable control signals for operating a brain-computer interface (BCI). This study uses offline analyses to investigate the characteristics of SSVEP harmonic amplitude and phase coupling and the impact of using this information to construct a matched filter for continuously tracking the signal.
Krachkovskiy, Sergey A; Bazak, J David; Werhun, Peter; Balcom, Bruce J; Halalay, Ion C; Goward, Gillian R
2016-06-29
Accurate modeling of Li-ion batteries performance, particularly during the transient conditions experienced in automotive applications, requires knowledge of electrolyte transport properties (ionic conductivity κ, salt diffusivity D, and lithium ion transference number t(+)) over a wide range of salt concentrations and temperatures. While specific conductivity data can be easily obtained with modern computerized instrumentation, this is not the case for D and t(+). A combination of NMR and MRI techniques was used to solve the problem. The main advantage of such an approach over classical electrochemical methods is its ability to provide spatially resolved details regarding the chemical and dynamic features of charged species in solution, hence the ability to present a more accurate characterization of processes in an electrolyte under operational conditions. We demonstrate herein data on ion transport properties (D and t(+)) of concentrated LiPF6 solutions in a binary ethylene carbonate (EC)-dimethyl carbonate (DMC) 1:1 v/v solvent mixture, obtained by the proposed technique. The buildup of steady-state (time-invariant) ion concentration profiles during galvanostatic experiments with graphite-lithium metal cells containing the electrolyte was monitored by pure phase-encoding single point imaging MRI. We then derived the salt diffusivity and Li(+) transference number over the salt concentration range 0.78-1.27 M from a pseudo-3D combined PFG-NMR and MRI technique. The results obtained with our novel methodology agree with those obtained by electrochemical methods, but in contrast to them, the concentration dependences of salt diffusivity and Li(+) transference number were obtained simultaneously within the single in situ experiment.
Steady state compact toroidal plasma production
Turner, William C.
1986-01-01
Apparatus and method for maintaining steady state compact toroidal plasmas. A compact toroidal plasma is formed by a magnetized coaxial plasma gun and held in close proximity to the gun electrodes by applied magnetic fields or magnetic fields produced by image currents in conducting walls. Voltage supply means maintains a constant potential across the electrodes producing an increasing magnetic helicity which drives the plasma away from a minimum energy state. The plasma globally relaxes to a new minimum energy state, conserving helicity according to Taylor's relaxation hypothesis, and injecting net helicity into the core of the compact toroidal plasma. Controlling the voltage so as to inject net helicity at a predetermined rate based on dissipative processes maintains or increases the compact toroidal plasma in a time averaged steady state mode.
Variational methods in steady state diffusion problems
Lee, C.E.; Fan, W.C.P.; Bratton, R.L.
1983-01-01
Classical variational techniques are used to obtain accurate solutions to the multigroup multiregion one dimensional steady state neutron diffusion equation. Analytic solutions are constructed for benchmark verification. Functionals with cubic trial functions and conservational lagrangian constraints are exhibited and compared with nonconservational functionals with respect to neutron balance and to relative flux and current at interfaces. Excellent agreement of the conservational functionals using cubic trial functions is obtained in comparison with analytic solutions.
On Typicality in Nonequilibrium Steady States
NASA Astrophysics Data System (ADS)
Evans, Denis J.; Williams, Stephen R.; Searles, Debra J.; Rondoni, Lamberto
2016-08-01
From the statistical mechanical viewpoint, relaxation of macroscopic systems and response theory rest on a notion of typicality, according to which the behavior of single macroscopic objects is given by appropriate ensembles: ensemble averages of observable quantities represent the measurements performed on single objects, because " almost all" objects share the same fate. In the case of non-dissipative dynamics and relaxation toward equilibrium states, " almost all" is referred to invariant probability distributions that are absolutely continuous with respect to the Lebesgue measure. In other words, the collection of initial micro-states (single systems) that do not follow the ensemble is supposed to constitute a set of vanishing, phase space volume. This approach is problematic in the case of dissipative dynamics and relaxation to nonequilibrium steady states, because the relevant invariant distributions attribute probability 1 to sets of zero volume, while evolution commonly begins in equilibrium states, i.e., in sets of full phase space volume. We consider the relaxation of classical, thermostatted particle systems to nonequilibrium steady states. We show that the dynamical condition known as Ω T-mixing is necessary and sufficient for relaxation of ensemble averages to steady state values. Moreover, we find that the condition known as weak T-mixing applied to smooth observables is sufficient for ensemble relaxation to be independent of the initial ensemble. Lastly, we show that weak T-mixing provides a notion of typicality for dissipative dynamics that is based on the (non-invariant) Lebesgue measure, and that we call physical ergodicity.
Theory of Steady-State Superradiance
NASA Astrophysics Data System (ADS)
Xu, Minghui
In this thesis, I describe the theoretical development of the superradiant laser, or laser in the extreme bad-cavity regime. In this regime, the cavity decay rate is much greater than the atomic dynamics. The atoms emit photons into the cavity mode superradiantly in steady state. We develop group-theoretic methods that enable us to exactly solve mesoscopic systems with hundreds of atoms. We demonstrate the synchronization of atomic dipoles in steady-state superradiance. With this synchronized system, we propose conditional Ramsey spectroscopy which allows us to observe Ramsey fringes indefinitely, even in the presence of atomic decoherence. Furthermore, we explore manifestations of synchronization in the quantum realm with two superradiant atomic ensembles. We show that two such ensembles exhibit a dynamical phase transition from two disparate oscillators to quantum phase-locked dynamics. Finally, we study the mechanical eect of the light-atom interaction in the steady-state superradiance. We find efficient many-body cooling of atoms. The work described in this thesis lays the theoretical foundation for the superradiant laser and for a potential future of active optical frequency standards.
Advanced tokamak scenario developments for the next step
NASA Astrophysics Data System (ADS)
Joffrin, E.
2007-12-01
The objective of advanced tokamak scenario research is to provide a candidate plasma scenario for continuous operation in a fusion power plant. The optimization of the self-generated non-inductive current by the bootstrap mechanism up to a level of 50% and above using high plasma pressure and improved confinement are the necessary conditions to achieve this goal. The two main candidate scenarios for continuous operation, the steady state scenario and long duration (up to 3000 s) high neutron fluency scenario (the hybrid scenario), both face physics challenges in terms of confinement, stability, power exhaust and plasma control. Resistive wall modes and Alfvénic fast ion driven instabilities are the main limitations for operating the steady state scenario at high pressure and low magnetic shear. In addition, this scenario demands a high degree of control over the plasma current and pressure profile and the steady state heat load on in-vessel plasma facing components. Understanding the confinement properties of hybrid scenario is still an outstanding issue as well as its modelling for ITER in particular with regard to the H-mode pedestal parameters. This scenario will also require active current profile control, although, less demanding than for the steady state scenario. To operate advanced tokamak scenario, broad current and pressure profile control appears as a necessary requirement on ITER actuators, in addition to the tools required for instability control such as error field coils or electron cyclotron current drive.
Technical challenges in the construction of the steady-state stellarator Wendelstein 7-X
Bosch, H.-S.; Wolf, R. C.; Andreeva, T.; Cardella, A; Erckmann, V.; Gantenbein, G; Hathiramani, D; Kasparek, W; Klinger, T.; Koenig, R; Kornejew, P; Laqua, H P; Lechte, C; Michel, G; Peacock, A.; Sunn Pedersen, T; Thumm, M; Turkin, Yu.; Wegener, Lutz; Werner, A.; Zhang, D; Beidler, C.; Bozhenkov, S.; Brown, T.; Geiger, J.; Harris, Jeffrey H; Heitzenroeder, P.; Lumsdaine, Arnold; Maassberg, H.; Marushchenko, N B; Neilson, G. H.; Otte, M; Rummel, Thomas; Spong, Donald A; Tretter, Jorg
2013-01-01
The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, currently under construction in Greifswald, Germany. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7-X mission is to demonstrate steady-state operation under plasma conditions relevant for a fusion power plant. Steady-state operation of a fusion device, on the one hand, requires the implementation of special technologies, giving rise to technical challenges during the design, fabrication and assembly of such a device. On the other hand, also the physics development of steady-state operation at high plasma performance poses a challenge and careful preparation. The electron cyclotron resonance heating system, diagnostics, experiment control and data acquisition are prepared for plasma operation lasting 30 min. This requires many new technological approaches for plasma heating and diagnostics as well as new concepts for experiment control and data acquisition.
Technical challenges in the construction of the steady-state stellarator Wendelstein 7-X
NASA Astrophysics Data System (ADS)
Bosch, H.-S.; Wolf, R. C.; Andreeva, T.; Baldzuhn, J.; Birus, D.; Bluhm, T.; Bräuer, T.; Braune, H.; Bykov, V.; Cardella, A.; Durodié, F.; Endler, M.; Erckmann, V.; Gantenbein, G.; Hartmann, D.; Hathiramani, D.; Heimann, P.; Heinemann, B.; Hennig, C.; Hirsch, M.; Holtum, D.; Jagielski, J.; Jelonnek, J.; Kasparek, W.; Klinger, T.; König, R.; Kornejew, P.; Kroiss, H.; Krom, J. G.; Kühner, G.; Laqua, H.; Laqua, H. P.; Lechte, C.; Lewerentz, M.; Maier, J.; McNeely, P.; Messiaen, A.; Michel, G.; Ongena, J.; Peacock, A.; Pedersen, T. S.; Riedl, R.; Riemann, H.; Rong, P.; Rust, N.; Schacht, J.; Schauer, F.; Schroeder, R.; Schweer, B.; Spring, A.; Stäbler, A.; Thumm, M.; Turkin, Y.; Wegener, L.; Werner, A.; Zhang, D.; Zilker, M.; Akijama, T.; Alzbutas, R.; Ascasibar, E.; Balden, M.; Banduch, M.; Baylard, Ch.; Behr, W.; Beidler, C.; Benndorf, A.; Bergmann, T.; Biedermann, C.; Bieg, B.; Biel, W.; Borchardt, M.; Borowitz, G.; Borsuk, V.; Bozhenkov, S.; Brakel, R.; Brand, H.; Brown, T.; Brucker, B.; Burhenn, R.; Buscher, K.-P.; Caldwell-Nichols, C.; Cappa, A.; Cardella, A.; Carls, A.; Carvalho, P.; Ciupiński, Ł.; Cole, M.; Collienne, J.; Czarnecka, A.; Czymek, G.; Dammertz, G.; Dhard, C. P.; Davydenko, V. I.; Dinklage, A.; Drevlak, M.; Drotziger, S.; Dudek, A.; Dumortier, P.; Dundulis, G.; Eeten, P. v.; Egorov, K.; Estrada, T.; Faugel, H.; Fellinger, J.; Feng, Y.; Fernandes, H.; Fietz, W. H.; Figacz, W.; Fischer, F.; Fontdecaba, J.; Freund, A.; Funaba, T.; Fünfgelder, H.; Galkowski, A.; Gates, D.; Giannone, L.; García Regaña, J. M.; Geiger, J.; Geißler, S.; Greuner, H.; Grahl, M.; Groß, S.; Grosman, A.; Grote, H.; Grulke, O.; Haas, M.; Haiduk, L.; Hartfuß, H.-J.; Harris, J. H.; Haus, D.; Hein, B.; Heitzenroeder, P.; Helander, P.; Heller, R.; Hidalgo, C.; Hildebrandt, D.; Höhnle, H.; Holtz, A.; Holzhauer, E.; Holzthüm, R.; Huber, A.; Hunger, H.; Hurd, F.; Ihrke, M.; Illy, S.; Ivanov, A.; Jablonski, S.; Jaksic, N.; Jakubowski, M.; Jaspers, R.; Jensen, H.; Jenzsch, H.; Kacmarczyk, J.; Kaliatk, T.; Kallmeyer, J.; Kamionka, U.; Karaleviciu, R.; Kern, S.; Keunecke, M.; Kleiber, R.; Knauer, J.; Koch, R.; Kocsis, G.; Könies, A.; Köppen, M.; Koslowski, R.; Koshurinov, J.; Krämer-Flecken, A.; Krampitz, R.; Kravtsov, Y.; Krychowiak, M.; Krzesinski, G.; Ksiazek, I.; Kubkowska, M.; Kus, A.; Langish, S.; Laube, R.; Laux, M.; Lazerson, S.; Lennartz, M.; Li, C.; Lietzow, R.; Lohs, A.; Lorenz, A.; Louche, F.; Lubyako, L.; Lumsdaine, A.; Lyssoivan, A.; Maaßberg, H.; Marek, P.; Martens, C.; Marushchenko, N.; Mayer, M.; Mendelevitch, B.; Mertens, Ph.; Mikkelsen, D.; Mishchenko, A.; Missal, B.; Mizuuchi, T.; Modrow, H.; Mönnich, T.; Morizaki, T.; Murakami, S.; Musielok, F.; Nagel, M.; Naujoks, D.; Neilson, H.; Neubauer, O.; Neuner, U.; Nocentini, R.; Noterdaeme, J.-M.; Nührenberg, C.; Obermayer, S.; Offermanns, G.; Oosterbeek, H.; Otte, M.; Panin, A.; Pap, M.; Paquay, S.; Pasch, E.; Peng, X.; Petrov, S.; Pilopp, D.; Pirsch, H.; Plaum, B.; Pompon, F.; Povilaitis, M.; Preinhaelter, J.; Prinz, O.; Purps, F.; Rajna, T.; Récsei, S.; Reiman, A.; Reiter, D.; Remmel, J.; Renard, S.; Rhode, V.; Riemann, J.; Rimkevicius, S.; Riße, K.; Rodatos, A.; Rodin, I.; Romé, M.; Roscher, H.-J.; Rummel, K.; Rummel, Th.; Runov, A.; Ryc, L.; Sachtleben, J.; Samartsev, A.; Sanchez, M.; Sano, F.; Scarabosio, A.; Schmid, M.; Schmitz, H.; Schmitz, O.; Schneider, M.; Schneider, W.; Scheibl, L.; Scholz, M.; Schröder, G.; Schröder, M.; Schruff, J.; Schumacher, H.; Shikhovtsev, I. V.; Shoji, M.; Siegl, G.; Skodzik, J.; Smirnow, M.; Speth, E.; Spong, D. A.; Stadler, R.; Sulek, Z.; Szabó, V.; Szabolics, T.; Szetefi, T.; Szökefalvi-Nagy, Z.; Tereshchenko, A.; Thomsen, H.; Thumm, M.; Timmermann, D.; Tittes, H.; Toi, K.; Tournianski, M.; Toussaint, U. v.; Tretter, J.; Tulipán, S.; Turba, P.; Uhlemann, R.; Urban, J.; Urbonavicius, E.; Urlings, P.; Valet, S.; Van Eester, D.; Van Schoor, M.; Vervier, M.; Viebke, H.; Vilbrandt, R.; Vrancken, M.; Wauters, T.; Weissgerber, M.; Weiß, E.; Weller, A.; Wendorf, J.; Wenzel, U.; Windisch, T.; Winkler, E.; Winkler, M.; Wolowski, J.; Wolters, J.; Wrochna, G.; Xanthopoulos, P.; Yamada, H.; Yokoyama, M.; Zacharias, D.; Zajac, J.; Zangl, G.; Zarnstorff, M.; Zeplien, H.; Zoletnik, S.; Zuin, M.
2013-12-01
The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, currently under construction in Greifswald, Germany. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7-X mission is to demonstrate steady-state operation under plasma conditions relevant for a fusion power plant. Steady-state operation of a fusion device, on the one hand, requires the implementation of special technologies, giving rise to technical challenges during the design, fabrication and assembly of such a device. On the other hand, also the physics development of steady-state operation at high plasma performance poses a challenge and careful preparation. The electron cyclotron resonance heating system, diagnostics, experiment control and data acquisition are prepared for plasma operation lasting 30 min. This requires many new technological approaches for plasma heating and diagnostics as well as new concepts for experiment control and data acquisition.
Intensity fluctuations in steady-state superradiance
Meiser, D.; Holland, M. J.
2010-06-15
Alkaline-earth-metal-like atoms with ultranarrow optical transitions enable superradiance in steady state. The emitted light promises to have an unprecedented stability with a linewidth as narrow as a few millihertz. In order to evaluate the potential usefulness of this light source as an ultrastable oscillator in clock and precision metrology applications, it is crucial to understand the noise properties of this device. In this paper, we present a detailed analysis of the intensity fluctuations by means of Monte Carlo simulations and semiclassical approximations. We find that the light exhibits bunching below threshold, is to a good approximation coherent in the superradiant regime, and is chaotic above the second threshold.
Steady state stresses in ribbon parachute canopies
NASA Technical Reports Server (NTRS)
Garrard, W. L.; Wu, K. Y.; Muramoto, K. K.
1984-01-01
An experimental study of the steady state stresses in model ribbon parachute canopies is presented. The distribution of circumferential stress was measured in the horizontal ribbons of two parachutes using Omega sensors. Canopy pressure distributions and overall drag were also measured. Testing was conducted in the University of Minnesota Low-Speed Wind Tunnel at dynamic pressures ranging from 1.0 to 1.5 inches of water. The stresses in the parachute canopies were calculated using the parachute structural analysis code, CANO. It was found that the general shape of the measured and calculated stress distributions was fairly similar; however, the measured stresses were somewhat less than the calculated stresses.
Energy repartition in the nonequilibrium steady state
NASA Astrophysics Data System (ADS)
Yan, Peng; Bauer, Gerrit E. W.; Zhang, Huaiwu
2017-01-01
The concept of temperature in nonequilibrium thermodynamics is an outstanding theoretical issue. We propose an energy repartition principle that leads to a spectral (mode-dependent) temperature in steady-state nonequilibrium systems. The general concepts are illustrated by analytic solutions of the classical Heisenberg spin chain connected to Langevin heat reservoirs with arbitrary temperature profiles. Gradients of external magnetic fields are shown to localize spin waves in a Wannier-Zeemann fashion, while magnon interactions renormalize the spectral temperature. Our generic results are applicable to other thermodynamic systems such as Newtonian liquids, elastic solids, and Josephson junctions.
Resistive demountable toroidal-field coils for tokamak reactors
Jassby, D.L.; Jacobsen, R.A.; Kalnavarns, J.; Masson, L.S.; Sekot, J.P.
1981-07-01
Readily demountable TF (toroidal-field) coils allow complete access to the internal components of a tokamak reactor for maintenance of replacement. The requirement of readily demountable joints dictates the use of water-cooled resistive coils, which have a host of decisive advantages over superconducting coils. Previous papers have shown that resistive TF coils for tokamak reactors can operate in the steady state with acceptable power dissipation (typically, 175 to 300 MW). This paper summarizes results of parametric studies of size optimization of rectangular TF coils and of a finite-element stress analysis, and examines several candidate methods of implementing demountable joints for rectangular coils constructed of plate segments.
Operation of a tangential bolometer on the PBX tokamak
Paul, S.F.; Fonck, R.J.; Schmidt, G.L.
1987-04-01
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.
Statistical steady state in turbulent droplet condensation
NASA Astrophysics Data System (ADS)
Siewert, Christoph; Bec, Jérémie; Krstulovic, Giorgio
2017-01-01
Motivated by systems in which droplets grow and shrink in a turbulence-driven supersaturation field, we investigate the problem of turbulent condensation in a general manner. Using direct numerical simulations we show that the turbulent fluctuations of the supersaturation field offer different conditions for the growth of droplets which evolve in time due to turbulent transport and mixing. Based on that, we propose a Lagrangian stochastic model for condensation and evaporation of small droplets in turbulent flows. It consists of a set of stochastic integro-differential equations for the joint evolution of the squared radius and the supersaturation along the droplet trajectories. The model has two parameters fixed by the total amount of water and the thermodynamic properties, as well as the Lagrangian integral timescale of the turbulent supersaturation. The model reproduces very well the droplet size distributions obtained from direct numerical simulations and their time evolution. A noticeable result is that, after a stage where the squared radius simply diffuses, the system converges exponentially fast to a statistical steady state independent of the initial conditions. The main mechanism involved in this convergence is a loss of memory induced by a significant number of droplets undergoing a complete evaporation before growing again. The statistical steady state is characterised by an exponential tail in the droplet mass distribution. These results reconcile those of earlier numerical studies, once these various regimes are considered.
An Intuitive Approach to Steady-State Kinetics.
ERIC Educational Resources Information Center
Raines, Ronald T.; Hansen, David E.
1988-01-01
Attempts to provide an intuitive understanding of steady state kinetics. Discusses the meaning of steady state and uses free energy profiles to illustrate and follow complex kinetic and thermodynamic relationships. Provides examples with explanations. (MVL)
Exploration of steady-state scenarios for the Fusion Development Facility (FDF)
NASA Astrophysics Data System (ADS)
Chan, V. S.; Garofalo, A. M.; Stambaugh, R. D.; Choi, M.; Kinsey, J. E.; Lao, L. L.; Snyder, P. B.; St. John, H. E.; Turnbull, A. D.
2011-10-01
A Fusion Nuclear Science Facility (FNSF) has to operate at 105 times longer duration than that of present tokamak discharges. The scalability of plasma sustainment to such a long time is an issue that needs to be resolved by scientific understanding. We carry out steady-state (SS) scenario development of the FDF (a candidate for FNSF-AT) using an iterative process toward a self-consistent solution via alternating temperature profiles and current profile evolution. The temperature profile evolves according to a physics-based transport model GLF23. SS requires large off-axis current drive (CD). To achieve this with no NBI is highly challenging. It however simplifies tritium containment, increases area for tritium breeding, and avoids costly negative-ion NBI technology. We find that with ECH/ECCD only, too much power is required. A SS baseline equilibrium is found by adding LHCD: Qfus ~ 4 , H98 y 2 ~ 1 . 2 , fBS ~ 70 %, Pfus ~ 260 MW, PEC = 35 MW, PLH = 21 MW. The GATO ideal MHD code finds the equilibrium stable to n = 1 internal kink at κ = 2 . 3 . Work supported by General Atomics internal funds.
Steady State Vacuum Ultraviolet Exposure Facility With Automated Calibration Capability
NASA Technical Reports Server (NTRS)
Stueber, Thomas J.; Sechkar, Edward A.; Dever, Joyce A.; Banks, Bruce A.
2000-01-01
NASA Glenn Research Center at Lewis Field designed and developed a steady state vacuum ultraviolet automated (SSVUVa) facility with in situ VUV intensity calibration capability. The automated feature enables a constant accelerated VUV radiation exposure over long periods of testing without breaking vacuum. This test facility is designed to simultaneously accommodate four isolated radiation exposure tests within the SSVUVa vacuum chamber. Computer-control of the facility for long, term continuous operation also provides control and recording of thermocouple temperatures, periodic recording of VUV lamp intensity, and monitoring of vacuum facility status. This paper discusses the design and capabilities of the SSVUVa facility.
Non-steady-state aerosol filtration in nanostructured fibrous media.
Przekop, Rafal; Gradoń, Leon
2011-06-28
The filtration of aerosol particles using composites of nano- and microsized fibrous structures is a promising method for the effective separation of nanoparticles from gases. A multi-scale physical system describing the flow pattern and particle deposition at a non-steady-state condition requires an advanced method of modelling. The combination of lattice Boltzmann and Brownian dynamics was used for analysis of the particle deposition pattern in a fibrous system. The dendritic structures of deposits for neutral and charged fibres and particles are present. The efficiency of deposition, deposit morphology, porosity and fractal dimension were calculated for a selected operational condition of the process.
TPX diagnostics for tokamak operation, plasma control and machine protection
Edmonds, P.H.; Medley, S.S.; Young, K.M.
1995-08-01
The diagnostics for TPX are at an early design phase, with emphasis on the diagnostic access interface with the major tokamak components. Account has to be taken of the very severe environment for diagnostic components located inside the vacuum vessel. The placement of subcontracts for the design and fabrication of the diagnostic systems is in process.
Steady State Turbulent Transport in Magnetic Fusion Plasmas
Lee, W. W.; Ethier, S.; Kolesnikov, R.; Wang, W. X.; Tang, W. M.
2007-12-20
For more than a decade, the study of microturbulence, driven by ion temperature gradient (ITG) drift instabilities in tokamak devices, has been an active area of research in magnetic fusion science for both experimentalists and theorists alike. One of the important impetus for this avenue of research was the discovery of the radial streamers associated the ITG modes in the early nineties using a Particle-In-Cell (PIC) code. Since then, ITG simulations based on the codes with increasing realism have become possible with the dramatic increase in computing power. The notable examples were the demonstration of the importance of nonlinearly generated zonal flows in regulating ion thermal transport and the transition from Bohm to GyroBoham scaling with increased device size. In this paper, we will describe another interesting nonlinear physical process associated with the parallel acceleration of the ions, that is found to play an important role for the steady state turbulent transport. Its discovery is again through the use of the modern massively parallel supercomputers.
Steady-state models of photosynthesis.
von Caemmerer, Susanne
2013-09-01
In the challenge to increase photosynthetic rate per leaf area mathematical models of photosynthesis can be used to help interpret gas exchange measurements made under different environmental conditions and predict underlying photosynthetic biochemistry. To do this successfully it is important to improve the modelling of temperature dependencies of CO₂ assimilation and gain better understanding of internal CO₂ diffusion limitations. Despite these shortcomings steady-state models of photosynthesis provide simple easy to use tools for thought experiments to explore photosynthetic pathway changes such as redirecting photorespiratory CO₂, inserting bicarbonate pumps into C₃ chloroplasts or inserting C₄ photosynthesis into rice. Here a number of models derived from the C₃ model by Farquhar, von Caemmerer and Berry are discussed and compared.
A closed-loop control scheme for steering steady states of glycolysis and glycogenolysis pathway.
Panja, Surajit; Patra, Sourav; Mukherjee, Anirban; Basu, Madhumita; Sengupta, Sanghamitra; Dutta, Pranab K
2013-01-01
Biochemical networks normally operate in the neighborhood of one of its multiple steady states. It may reach from one steady state to other within a finite time span. In this paper, a closed-loop control scheme is proposed to steer states of the glycolysis and glycogenolysis (GG) pathway from one of its steady states to other. The GG pathway is modeled in the synergism and saturation system formalism, known as S-system. This S-system model is linearized into the controllable Brunovsky canonical form using a feedback linearization technique. For closed-loop control, the linear-quadratic regulator (LQR) and the linear-quadratic gaussian (LQG) regulator are invoked to design a controller for tracking prespecified steady states. In the feedback linearization technique, a global diffeomorphism function is proposed that facilitates in achieving the regulation requirement. The robustness of the regulated GG pathway is studied considering input perturbation and with measurement noise.
Steady state multiplicity of two-step biological conversion systems with general kinetics.
Volcke, E I P; Sbarciog, M; Noldus, E J L; De Baets, B; Loccufier, M
2010-12-01
This study analyses the steady state behaviour of biological conversion systems with general kinetics, in which two consecutive reactions are carried out by two groups of micro-organisms. The model considered is a realistic description of wastewater treatment processes. A step-wise procedure is followed to reveal the mechanisms affecting the occurrence of steady states in terms of the process input variables. It is clearly demonstrated how taking into account inhibition effects by simply including additional inhibition terms to the kinetic expressions, a common practice, influences the model's long term behaviour. The overall steady state behaviour of the model has been summarized in easy-to-interpret operating diagrams, depicting the occurrence of steady states in terms of the reactor dilution rate and the influent substrate concentration, with well-defined boundaries between distinct operating regions. This knowledge is crucial for modelers as steady state multiplicity--in the sense that more than one steady state can be reached depending on the initial conditions--may remain undetected during simulation. The obtained results may also serve for experimental design and for model validation based on experimental findings.
Bohm, P; Aftanas, M; Bilkova, P; Stefanikova, E; Mikulin, O; Melich, R; Janky, F; Havlicek, J; Sestak, D; Weinzettl, V; Stockel, J; Hron, M; Panek, R; Scannell, R; Frassinetti, L; Fassina, A; Naylor, G; Walsh, M J
2014-11-01
The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to ∼1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.
Economic analyses of alpha channeling in tokamak power plants.
Ehst, D.A.
1998-09-17
The hot-ion-mode of operation [1] has long been thought to offer optimized performance for long-pulse or steady-state magnetic fusion power plants. This concept was revived in recent years when theoretical considerations suggested that nonthermal fusion alpha particles could be made to channel their power density preferentially to the fuel ions [2,3]. This so-called anomalous alpha particle slowing down can create plasmas with fuel ion temperate T{sub i} somewhat larger than the electron temperature T{sub e}, which puts more of the beta-limited plasma pressure into the useful fuel species (rather than non-reacting electrons). As we show here, this perceived benefit may be negligible or nonexistent for tokamaks with steady state current drive. It has likewise been argued [2,3] that alpha channeling could be arranged such that little or no external power would be needed to generate the steady state toroidal current. Under optimistic assumptions we show that such alpha-channeling current drive would moderately improve the economic performance of a first stability tokamak like ARIES-I [4], however a reversed-shear (advanced equilibrium) tokamak would likely not benefit since traditional radio-wave (rf) electron-heating current drive power would already be quite small.
NASA Lewis Steady-State Heat Pipe Code Architecture
NASA Technical Reports Server (NTRS)
Mi, Ye; Tower, Leonard K.
2013-01-01
NASA Glenn Research Center (GRC) has developed the LERCHP code. The PC-based LERCHP code can be used to predict the steady-state performance of heat pipes, including the determination of operating temperature and operating limits which might be encountered under specified conditions. The code contains a vapor flow algorithm which incorporates vapor compressibility and axially varying heat input. For the liquid flow in the wick, Darcy s formula is employed. Thermal boundary conditions and geometric structures can be defined through an interactive input interface. A variety of fluid and material options as well as user defined options can be chosen for the working fluid, wick, and pipe materials. This report documents the current effort at GRC to update the LERCHP code for operating in a Microsoft Windows (Microsoft Corporation) environment. A detailed analysis of the model is presented. The programming architecture for the numerical calculations is explained and flowcharts of the key subroutines are given
New models for fast steady state magnetic reconnection
NASA Technical Reports Server (NTRS)
Priest, E. R.; Forbes, T. G.
1986-01-01
A new unified family of models for incompressible, steady-state magnetic reconnection in a finite region is presented. The models are obtained by expanding in powers of the Alfven Mach number and may be used to elucidate some of the puzzling properties of numerical experiments on reconnection which are not present in the classical models. The conditions imposed on the inflow boundary of the finite region determine which member of the family occurs. Petscheklien and Sonnerup like solutions are particular members. The Sonneruplike regime is a special case of a weak slow mode expansion in the inflow region, and it separates two classes of members with reversed currents. The Petscheklike regime is a singular case of a weak fast mode expansion, and it separates the hybrid regime from a regime of slow mode compressions. Care should be taken in deciding which type of reconnection is operating in a numerical experiment. Indeed, no experiment to date has used boundary conditions appropriate for demonstrating steady state Petschek reconnection.
Steady State Vapor Bubble in Pool Boiling
Zou, An; Chanana, Ashish; Agrawal, Amit; Wayner, Peter C.; Maroo, Shalabh C.
2016-01-01
Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics. PMID:26837464
Inconsistencies in steady-state thermodynamics
NASA Astrophysics Data System (ADS)
Dickman, Ronald; Motai, Ricardo
2014-03-01
We address the issue of extending thermodynamics to nonequilibrium steady states. Using driven stochastic lattice gases, we ask whether consistent definitions of an effective chemical potential μ, and an effective temperature Te, are possible. μ and Te are determined via coexistence, i.e., zero flux of particles and energy between the driven system and a reservoir. In the lattice gas with nearest-neighbor exclusion, temperature is not relevant, and we find that the effective chemical potential, a function of density and drive strength, satisfies the zeroth law, and correctly predicts the densities of coexisting systems. In the Katz-Lebowitz-Spohn driven lattice gas both μ and Te need to be defined. We show analytically that in this case the zeroth law is violated for Metropolis exchange rates, and determine the size of the violations numerically. The zeroth law appears to be violated for generic exchange rates. Remarkably, the system-reservoir coupling proposed by Sasa and Tasaki [J. Stat. Phys. 125, 125 (2006), 10.1007/s10955-005-9021-7] is free of inconsistencies, and the zeroth law holds. This is because the rate depends only on the state of the donor system, and is independent of that of the acceptor.
Maximal lactate steady state in Judo
de Azevedo, Paulo Henrique Silva Marques; Pithon-Curi, Tania; Zagatto, Alessandro Moura; Oliveira, João; Perez, Sérgio
2014-01-01
Summary Background: the purpose of this study was to verify the validity of respiratory compensation threshold (RCT) measured during a new single judo specific incremental test (JSIT) for aerobic demand evaluation. Methods: to test the validity of the new test, the JSIT was compared with Maximal Lactate Steady State (MLSS), which is the gold standard procedure for aerobic demand measuring. Eight well-trained male competitive judo players (24.3 ± 7.9 years; height of 169.3 ± 6.7cm; fat mass of 12.7 ± 3.9%) performed a maximal incremental specific test for judo to assess the RCT and performed on 30-minute MLSS test, where both tests were performed mimicking the UchiKomi drills. Results: the intensity at RCT measured on JSIT was not significantly different compared to MLSS (p=0.40). In addition, it was observed high and significant correlation between MLSS and RCT (r=0.90, p=0.002), as well as a high agreement. Conclusions: RCT measured during JSIT is a valid procedure to measure the aerobic demand, respecting the ecological validity of Judo. PMID:25332923
Steady State Vapor Bubble in Pool Boiling.
Zou, An; Chanana, Ashish; Agrawal, Amit; Wayner, Peter C; Maroo, Shalabh C
2016-02-03
Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics.
Steady state volcanism - Evidence from eruption histories of polygenetic volcanoes
NASA Technical Reports Server (NTRS)
Wadge, G.
1982-01-01
Cumulative volcano volume curves are presented as evidence for steady-state behavior at certain volcanoes and to develop a model of steady-state volcanism. A minimum criteria of five eruptions over a year was chosen to characterize a steady-state volcano. The subsequent model features a constant head of magmatic pressure from a reservoir supplied from depth, a sawtooth curve produced by the magma arrivals or discharge from the subvolcanic reservoir, large volume eruptions with long repose periods, and conditions of nonsupply of magma. The behavior of Mts. Etna, Nyamuragira, and Kilauea are described and show continuous levels of plasma output resulting in cumulative volume increases. Further discussion is made of steady-state andesitic and dacitic volcanism, long term patterns of the steady state, and magma storage, and the lack of a sufficient number of steady-state volcanoes in the world is taken as evidence that further data is required for a comprehensive model.
Fast-ion transport in qmin>2, high- β steady-state scenarios on DIII-D
Holcomb, C. T.; Heidbrink, W. W.; Ferron, J. R.; ...
2015-05-22
The results from experiments on DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] aimed at developing high β steady-state operating scenarios with high-qminqmin confirm that fast-ion transport is a critical issue for advanced tokamak development using neutral beam injection current drive. In DIII-D, greater than 11 MW of neutral beam heating power is applied with the intent of maximizing βN and the noninductive current drive. However, in scenarios with qmin>2 that target the typical range of q95= 5–7 used in next-step steady-state reactor models, Alfvén eigenmodes cause greater fast-ion transport than classical models predict. This enhanced transport reducesmore » the absorbed neutral beam heating power and current drive and limits the achievable βN. Conversely similar plasmas except with qmin just above 1 have approximately classical fast-ion transport. Experiments that take qmin>3 plasmas to higher βP with q95= 11–12 for testing long pulse operation exhibit regimes of better than expected thermal confinement. Compared to the standard high-qmin scenario, the high βP cases have shorter slowing-down time and lower ∇βfast, and this reduces the drive for Alfvénic modes, yielding nearly classical fast-ion transport, high values of normalized confinement, βN, and noninductive current fraction. These results suggest DIII-D might obtain better performance in lower-q95, high-qmin plasmas using broader neutral beam heating profiles and increased direct electron heating power to lower the drive for Alfvén eigenmodes.« less
Fast-ion transport in qmin>2, high- β steady-state scenarios on DIII-D
Holcomb, C. T.; Heidbrink, W. W.; Ferron, J. R.; Van Zeeland, M. A.; Garofalo, A. M.; Solomon, W. M.; Gong, X.; Mueller, D.; Grierson, B.; Bass, E. M.; Collins, C.; Park, J. M.; Kim, K.; Luce, T. C.; Turco, F.; Pace, D. C.; Ren, Q.; Podesta, M.
2015-05-22
The results from experiments on DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] aimed at developing high β steady-state operating scenarios with high-qminqmin confirm that fast-ion transport is a critical issue for advanced tokamak development using neutral beam injection current drive. In DIII-D, greater than 11 MW of neutral beam heating power is applied with the intent of maximizing β_{N} and the noninductive current drive. However, in scenarios with q_{min}>2 that target the typical range of q_{95}= 5–7 used in next-step steady-state reactor models, Alfvén eigenmodes cause greater fast-ion transport than classical models predict. This enhanced transport reduces the absorbed neutral beam heating power and current drive and limits the achievable β_{N}. Conversely similar plasmas except with q_{min} just above 1 have approximately classical fast-ion transport. Experiments that take q_{min}>3 plasmas to higher β_{P} with q_{95}= 11–12 for testing long pulse operation exhibit regimes of better than expected thermal confinement. Compared to the standard high-q_{min} scenario, the high β_{P} cases have shorter slowing-down time and lower ∇β_{fast}, and this reduces the drive for Alfvénic modes, yielding nearly classical fast-ion transport, high values of normalized confinement, β_{N}, and noninductive current fraction. These results suggest DIII-D might obtain better performance in lower-q_{95}, high-q_{min} plasmas using broader neutral beam heating profiles and increased direct electron heating power to lower the drive for Alfvén eigenmodes.
Transient and steady state modelling of a coupled WECS
NASA Astrophysics Data System (ADS)
Nathan, G. K.; Tan, J. K.
The paper presents a method for simulation of a wind turbine using a dc motor. The armature and field voltages of the dc motor are independently regulated to obtain torque-speed characteristics which correspond to those of a wind turbine at different wind speeds. The mass moment of inertia of the wind turbine is represented by adding a rotating mass to a parallel shaft which is positively coupled to the motor shaft. To verify the method of simulation, an American multiblade wind turbine is chosen, loaded by coupling to a centrifugal pump. Using the principle of conservation of energy and characteristics of both constituent units, two mathematical models are proposed: one for steady state operation and another for the transient state. The close comparison between the theoretical and the experimental results validates the proposed models and the method of simulation. The experimental method is described and the results of the experimental and theoretical investigation are presented.
Exact Nonequilibrium Steady State of a Strongly Driven Open XXZ Chain
NASA Astrophysics Data System (ADS)
Prosen, Tomaž
2011-09-01
An exact and explicit ladder-tensor-network ansatz is presented for the nonequilibrium steady state of an anisotropic Heisenberg XXZ spin-1/2 chain which is driven far from equilibrium with a pair of Lindblad operators acting on the edges of the chain only. We show that the steady-state density operator of a finite system of size n is—apart from a normalization constant—a polynomial of degree 2n-2 in the coupling constant. Efficient computation of physical observables is facilitated in terms of a transfer operator reminiscent of a classical Markov process. In the isotropic case we find cosine spin profiles, 1/n2 scaling of the spin current, and long-range correlations in the steady state. This is a fully nonperturbative extension of a recent result [Phys. Rev. Lett. 106, 217206 (2011)PRLTAO0031-900710.1103/PhysRevLett.106.217206].
Defining Features of Steady-State Timbres
NASA Astrophysics Data System (ADS)
Hall, Michael D.
1995-01-01
Three experiments were conducted to define steady -state features of timbre for a group of well-trained musicians. Experiment 1 evaluated whether or not pairs of three critical dimensions of timbre--spectral slope (6 or 12 dB/octave), formant structure (/a/ or /i/ vowel), and inharmonicity of partials (harmonic or inharmonic)--were processed in a separable or integral fashion. Accuracy and speed for classification of values along one dimension were examined under different conditions of variability along a second dimension (fixed, correlated, or orthogonal). Spectral slope and formant structure were integral, with classification speed for the target dimension depending upon variability along the orthogonal dimension. In contrast, evidence of asymmetric separability was obtained for inharmonicity. Classification speed for slope and formant structure did not depend on inharmonicity, whereas RT for the target dimension of inharmonicity was strongly influenced by variability along either slope or formant structure. Since the results of Experiment 1 provided a basis for manipulating spectral slope and formant structure as a single feature, these dimensions were correlated in Experiment 2. Subjects searched for targets containing potential features of timbre within arrays of 1-4 inharmonic distractor pitches. Distractors were homogeneous with respect to the dimensions of timbre. When targets had /a/ formants with shallow spectral slopes, search time increased nonlinearly with array size in a manner consistent with the parallel processing of items, and thus feature search. Feature search was not obtained for targets with /i/ formants and steep slopes. Thus, the feature was coded as the presence or absence of /a/ formants with shallow spectral slopes. A search task using heterogeneous distractor values along slope/formant structure was used in Experiment 3 to evaluate whether or not the feature of timbre and pitch were automatically conjoined (integral). Search times for
NASA Astrophysics Data System (ADS)
Yamazaki, K.; Uemura, S.; Oishi, T.; Garcia, J.; Arimoto, H.; Shoji, T.
2009-05-01
Reference 1-GWe DT reactors (tokamak TR-1, spherical tokamak ST-1 and helical HR-1 reactors) are designed using physics, engineering and cost (PEC) code, and their plasma behaviours with internal transport barrier operations are analysed using toroidal transport analysis linkage (TOTAL) code, which clarifies the requirement of deep penetration of pellet fuelling to realize steady-state advanced burning operation. In addition, economical and environmental assessments were performed using extended PEC code, which shows the advantage of high beta tokamak reactors in the cost of electricity (COE) and the advantage of compact spherical tokamak in life-cycle CO2 emission reduction. Comparing with other electric power generation systems, the COE of the fusion reactor is higher than that of the fission reactor, but on the same level as the oil thermal power system. CO2 reduction can be achieved in fusion reactors the same as in the fission reactor. The energy payback ratio of the high-beta tokamak reactor TR-1 could be higher than that of other systems including the fission reactor.
The steady-state assumption in oscillating and growing systems.
Reimers, Alexandra-M; Reimers, Arne C
2016-10-07
The steady-state assumption, which states that the production and consumption of metabolites inside the cell are balanced, is one of the key aspects that makes an efficient analysis of genome-scale metabolic networks possible. It can be motivated from two different perspectives. In the time-scales perspective, we use the fact that metabolism is much faster than other cellular processes such as gene expression. Hence, the steady-state assumption is derived as a quasi-steady-state approximation of the metabolism that adapts to the changing cellular conditions. In this article we focus on the second perspective, stating that on the long run no metabolite can accumulate or deplete. In contrast to the first perspective it is not immediately clear how this perspective can be captured mathematically and what assumptions are required to obtain the steady-state condition. By presenting a mathematical framework based on the second perspective we demonstrate that the assumption of steady-state also applies to oscillating and growing systems without requiring quasi-steady-state at any time point. However, we also show that the average concentrations may not be compatible with the average fluxes. In summary, we establish a mathematical foundation for the steady-state assumption for long time periods that justifies its successful use in many applications. Furthermore, this mathematical foundation also pinpoints unintuitive effects in the integration of metabolite concentrations using nonlinear constraints into steady-state models for long time periods.
Global migration of impurities in tokamaks
NASA Astrophysics Data System (ADS)
Hakola, A.; Airila, M. I.; Björkas, C.; Borodin, D.; Brezinsek, S.; Coad, J. P.; Groth, M.; Järvinen, A.; Kirschner, A.; Koivuranta, S.; Krieger, K.; Kurki-Suonio, T.; Likonen, J.; Lindholm, V.; Makkonen, T.; Mayer, M.; Miettunen, J.; Müller, H. W.; Neu, R.; Petersson, P.; Rohde, V.; Rubel, M.; Widdowson, A.; the ASDEX Upgrade Team; Contributors, JET-EFDA
2013-12-01
The migration of impurities in tokamaks has been studied with the help of tracer-injection (13C and 15N) experiments in JET and ASDEX Upgrade since 2001. We have identified a common pattern for the migrating particles: scrape-off layer flows drive impurities from the low-field side towards the high-field side of the vessel. Migration is also sensitive to the density and magnetic configuration of the plasma, and strong local variations in the resulting deposition patterns require 3D treatment of the migration process. Moreover, re-erosion of the deposited particles has to be taken into account to properly describe the migration process during steady-state operation of the tokamak.
Assessment of the LH wave for demo in pulsed and steady state scenario
Cardinali, A.; Barbato, E.; Castaldo, C.; Cesario, R.; Marinucci, M.; Ravera, G. L.; Tuccillo, A. A.; Ceccuzzi, S.; Mirizzi, F.; Panaccione, L.; Santini, F.; Schettini, G.
2014-02-12
The Lower Hybrid Current Drive (LHCD) has been analysed in DEMO tokamak plasma in the 'pulsed and steady state regime' considering two plasma scenarios characterized, respectively, by flat density profile and peaked density profiles. We have obtained LH deposition profiles in cases of neglecting the effect of spectral broadening produced by PI at the edge. By comparing the Power Deposition Profiles for both DEMO scenarios ('flat' and 'peaked'), the SOL of DEMO does not play any role in the absorption of the LH wave. In all cases the deposition is localized inside the separatrix layer r/a≤1. By lowering the parallel wave-number peak of the power spectrum from 1.8 to 1.5, the accessibility condition in both case prevents the power from reaching the deposition layer apart from a small fraction which pertains to the higher n∥ of the power spectrum. The spectrum centred at 1.8 is suggested to be useful in DEMO. More realistically, as supported by available data of LHCD in a wide range of operating densities, the effect of parametric decay instability (PDI) can produce a spectral broadening which should be included in the simulations. Further studies would be necessary for assessing the temperature profiles in the SOL at reactor-graded conditions. This is because, if the SOL temperature is at least of the order of 50 to 100 eV, the effect of PDI broads the spectrum up to n∥≤10, and the deposition profile is slightly wider but not much shifted outwards.
Assessment of the LH wave for demo in pulsed and steady state scenario
NASA Astrophysics Data System (ADS)
Cardinali, A.; Barbato, E.; Castaldo, C.; Ceccuzzi, S.; Cesario, R.; Marinucci, M.; Mirizzi, F.; Panaccione, L.; Ravera, G. L.; Santini, F.; Schettini, G.; Tuccillo, A. A.
2014-02-01
The Lower Hybrid Current Drive (LHCD) has been analysed in DEMO tokamak plasma in the "pulsed and steady state regime" considering two plasma scenarios characterized, respectively, by flat density profile and peaked density profiles. We have obtained LH deposition profiles in cases of neglecting the effect of spectral broadening produced by PI at the edge. By comparing the Power Deposition Profiles for both DEMO scenarios ("flat" and "peaked"), the SOL of DEMO does not play any role in the absorption of the LH wave. In all cases the deposition is localized inside the separatrix layer r/a≤1. By lowering the parallel wave-number peak of the power spectrum from 1.8 to 1.5, the accessibility condition in both case prevents the power from reaching the deposition layer apart from a small fraction which pertains to the higher n∥ of the power spectrum. The spectrum centred at 1.8 is suggested to be useful in DEMO. More realistically, as supported by available data of LHCD in a wide range of operating densities, the effect of parametric decay instability (PDI) can produce a spectral broadening which should be included in the simulations. Further studies would be necessary for assessing the temperature profiles in the SOL at reactor-graded conditions. This is because, if the SOL temperature is at least of the order of 50 to 100 eV, the effect of PDI broads the spectrum up to n∥≤10, and the deposition profile is slightly wider but not much shifted outwards.
Saturated internal instabilities in advanced-tokamak plasmas
NASA Astrophysics Data System (ADS)
Hua, M.-D.; Chapman, I. T.; Pinches, S. D.; Hastie, R. J.; MAST Team
2010-06-01
"Advanced tokamak" (AT) scenarios were developed with the aim of reaching steady-state operation in future potential tokamak fusion power plants. AT scenarios exhibit non-monotonic to flat safety factor profiles (q, a measure of the magnetic field line pitch), with the minimum q (qmin) slightly above an integer value (qs). However, it has been predicted that these q profiles are unstable to ideal magnetohydrodynamic instabilities as qmin approaches qs. These ideal instabilities, observed and diagnosed as such for the first time in MAST plasmas with AT-like q profiles, have far-reaching consequences like confinement degradation, flattening of the toroidal core rotation or enhanced fast ion losses. These observations motivate the stability analysis of advanced-tokamak plasmas, with a view to provide guidance for stability thresholds in AT scenarios. Additionally, the measured rotation damping is compared to the self-consistently calculated predictions from neoclassical toroidal viscosity theory.
Steady states of solar coronal loops as nonaxisymmetric toroidal flux ropes
NASA Astrophysics Data System (ADS)
Sugiyama, Linda; Asgari-Targhi, M.
2016-10-01
Consistent MHD steady states for coronal loops on the surface of the sun, modeled as magnetic flux ropes, are derived for the first time, based on the equilibrium and stability of toroidal magnetically confined fusion plasmas. Coronal loops, like magnetic tori, are unstable to expansion in major radius. The solar gravity and plasma beta, previously ignored, are crucual parameters in the steady state. For loops with a predominantly axisymmetric magnetic axis, three analytical steady states exist in terms of beta and the normalized solar gravity parameter Ĝ = ga /vA2 , where g is the acceleration due to gravity, ordered in inverse aspect ratio: high beta (β ɛ) and small gravity Ĝ ɛ3 , which resembles a nearly axisymmetric high-beta tokamak, and high beta with larger Ĝ ɛ2 , and low beta (β ɛ2) with Ĝ ɛ3 , which are more strongly nonaxisymmetric. Comparison with observations shows that the two high beta states bracket the range of thin coronal loops in solar active regions ɛ 0.02 and Ĝ orders the loops by height. The low beta solution may describe certain thicker loops ɛ 0.1 that grow to solar flares or Coronal Mass Ejections. Work partially supported by the U.S. DOE OFES under Award DE-SC-0007883.
A new hybrid inductive scenario for a nearly steady-state Reversed Field Pinch
NASA Astrophysics Data System (ADS)
Sarff, J. S.
2007-11-01
Steady-state current sustainment is challenging for the Reversed Field Pinch (RFP). The current magnitude is large, while the pressure-driven (bootstrap) current is small, even at the RFP's high beta >20%. In the TITAN (RFP) system study [1], the current was designed steady-state using Oscillating Field Current Drive (OFCD), i.e., steady magnetic helicity injection using phased AC induction. Experiments and theory for OFCD are so far promising, but OFCD's reliance on magnetic relaxation could turn out incompatible with energy confinement requirements. Meanwhile inductive current profile control has demonstrated tokamak-like confinement in the RFP. Such control is inherently not steady-state. A hybrid scheme is proposed using OFCD to ramp the current, followed by a pulsed-burn during which inductive profile control maintains high confinement. The current is not constant but never goes to zero (sawtooth-like waveform). The current drive (and profile control) is efficient induction, simply applied at the plasma surface. The pulsed-burn phases could be separated by only a few seconds. Optimization of the hybrid cycle and other issues will be discussed. [1] http://aries.ucsd.edu/LIB/REPORT/TITAN/final.shtml
Tokamak Physics Experiment divertor design
Anderson, P.M.
1995-12-31
The Tokamak Physics Experiment (TPX) tokamak requires a symmetric up/down double-null divertor capable of operation with steady-state heat flux as high as 7.5 MW/m{sup 2}. The divertor is designed to operate in the radiative mode and employs a deep slot configuration with gas puffing lines to enhance radiative divertor operation. Pumping is provided by cryopumps that pump through eight vertical ports in the floor and ceiling of the vessel. The plasma facing surface is made of carbon-carbon composite blocks (macroblocks) bonded to multiple parallel copper tubes oriented vertically. Water flowing at 6 m/s is used, with the critical heat flux (CHF) margin improved by the use of enhanced heat transfer surfaces. In order to extend the operating period where hands on maintenance is allowed and to also reduce dismantling and disposal costs, the TPX design emphasizes the use of low activation materials. The primary materials used in the divertor are titanium, copper, and carbon-carbon composite. The low activation material selection and the planned physics operation will allow personnel access into the vacuum vessel for the first 2 years of operation. The remote handling system requires that all plasma facing components (PFCs) are configured as modular components of restricted dimensions with special provisions for lifting, alignment, mounting, attachment, and connection of cooling lines, and instrumentation and diagnostics services.
A stability analysis of the power-law steady state of marine size spectra.
Datta, Samik; Delius, Gustav W; Law, Richard; Plank, Michael J
2011-10-01
This paper investigates the stability of the power-law steady state often observed in marine ecosystems. Three dynamical systems are considered, describing the abundance of organisms as a function of body mass and time: a "jump-growth" equation, a first order approximation which is the widely used McKendrick-von Foerster equation, and a second order approximation which is the McKendrick-von Foerster equation with a diffusion term. All of these yield a power-law steady state. We derive, for the first time, the eigenvalue spectrum for the linearised evolution operator, under certain constraints on the parameters. This provides new knowledge of the stability properties of the power-law steady state. It is shown analytically that the steady state of the McKendrick-von Foerster equation without the diffusion term is always unstable. Furthermore, numerical plots show that eigenvalue spectra of the McKendrick-von Foerster equation with diffusion give a good approximation to those of the jump-growth equation. The steady state is more likely to be stable with a low preferred predator:prey mass ratio, a large diet breadth and a high feeding efficiency. The effects of demographic stochasticity are also investigated and it is concluded that these are likely to be small in real systems.
Diehl, S; Zambrano, J; Carlsson, B
2016-01-01
A reduced model of a completely stirred-tank bioreactor coupled to a settling tank with recycle is analyzed in its steady states. In the reactor, the concentrations of one dominant particulate biomass and one soluble substrate component are modelled. While the biomass decay rate is assumed to be constant, growth kinetics can depend on both substrate and biomass concentrations, and optionally model substrate inhibition. Compressive and hindered settling phenomena are included using the Bürger-Diehl settler model, which consists of a partial differential equation. Steady-state solutions of this partial differential equation are obtained from an ordinary differential equation, making steady-state analysis of the entire plant difficult. A key result showing that the ordinary differential equation can be replaced with an approximate algebraic equation simplifies model analysis. This algebraic equation takes the location of the sludge-blanket during normal operation into account, allowing for the limiting flux capacity caused by compressive settling to easily be included in the steady-state mass balance equations for the entire plant system. This novel approach grants the possibility of more realistic solutions than other previously published reduced models, comprised of yet simpler settler assumptions. The steady-state concentrations, solids residence time, and the wastage flow ratio are functions of the recycle ratio. Solutions are shown for various growth kinetics; with different values of biomass decay rate, influent volumetric flow, and substrate concentration.
Current Control in ITER Steady State Plasmas With Neutral Beam Steering
R.V. Budny
2009-09-10
Predictions of quasi steady state DT plasmas in ITER are generated using the PTRANSP code. The plasma temperatures, densities, boundary shape, and total current (9 - 10 MA) anticipated for ITER steady state plasmas are specified. Current drive by negative ion neutral beam injection, lower-hybrid, and electron cyclotron resonance are calculated. Four modes of operation with different combinations of current drive are studied. For each mode, scans with the NNBI aimed at differing heights in the plasma are performed to study effects of current control on the q profile. The timeevolution of the currents and q are calculated to evaluate long duration transients. Quasi steady state, strongly reversed q profiles are predicted for some beam injection angles if the current drive and bootstrap currents are sufficiently large.
A Note on Equations for Steady-State Optimal Landscapes
Liu, H.H.
2010-06-15
Based on the optimality principle (that the global energy expenditure rate is at its minimum for a given landscape under steady state conditions) and calculus of variations, we have derived a group of partial differential equations for describing steady-state optimal landscapes without explicitly distinguishing between hillslopes and channel networks. Other than building on the well-established Mining's equation, this work does not rely on any empirical relationships (such as those relating hydraulic parameters to local slopes). Using additional constraints, we also theoretically demonstrate that steady-state water depth is a power function of local slope, which is consistent with field data.
Steady-state decoupling and design of linear multivariable systems
NASA Technical Reports Server (NTRS)
Thaler, G. J.
1974-01-01
A constructive criterion for decoupling the steady states of a linear time-invariant multivariable system is presented. This criterion consists of a set of inequalities which, when satisfied, will cause the steady states of a system to be decoupled. Stability analysis and a new design technique for such systems are given. A new and simple connection between single-loop and multivariable cases is found. These results are then applied to the compensation design for NASA STOL C-8A aircraft. Both steady-state decoupling and stability are justified through computer simulations.
SUPERENERGY-2: a multiassembly, steady-state computer code for LMFBR core thermal-hydraulic analysis
Basehore, K.L.; Todreas, N.E.
1980-08-01
Core thermal-hydraulic design and performance analyses for Liquid Metal Fast Breeder Reactors (LMFBRs) require repeated detailed multiassembly calculations to determine radial temperature profiles and subchannel outlet temperatures for various core configurations and subassembly structural analyses. At steady-state, detailed core-wide temperature profiles are required for core restraint calculations and subassembly structural analysis. In addition, sodium outlet temperatures are routinely needed for each reactor operating cycle. The SUPERENERGY-2 thermal-hydraulic code was designed specifically to meet these designer needs. It is applicable only to steady-state, forced-convection flow in LMFBR core geometries.
Steady-state creep of complexly reinforced shallow metal-composite shells
NASA Astrophysics Data System (ADS)
Yankovskii, A. P.
2010-05-01
The problem of deformation of shallow shells of variable thickness reinforced with fibers of constant cross section, whose all phases operate under the conditions of steady-state creep, is formulated. The system of resolving equations and the corresponding boundary conditions are analyzed, and the procedure for solving this problem is developed. A way of approximate solution of such problems in the case of transient creep is indicated. The particular calculations performed show that the compliance of thin-walled structures, under the conditions of steady-state creep, greatly depends on the structure of reinforcement.
Bootstrap current in a tokamak
Kessel, C.E.
1994-03-01
The bootstrap current in a tokamak is examined by implementing the Hirshman-Sigmar model and comparing the predicted current profiles with those from two popular approximations. The dependences of the bootstrap current profile on the plasma properties are illustrated. The implications for steady state tokamaks are presented through two constraints; the pressure profile must be peaked and {beta}{sub p} must be kept below a critical value.
High beta, sawtooth-free tokamak operation using energetic trapped particles
White, R.B.; Bussac, M.N.; Romanelli, F.
1988-08-01
It is shown that a population of high energy trapped particles, such as that produced by ion cyclotron heating in tokamaks, can result in a plasma completely stable to both sawtooth oscillations and the fishbone mode. The stable window of operation increases in size with plasma temperature and with trapped particle energy, and provides a means of obtaining a stable plasma with high current and high beta. 13 refs., 2 figs.
The operation of the Tokamak Fusion Test Reactor Tritium Facility
Gentile, C.A.; LaMarche, P.H.; Anderson, J.L.
1995-07-01
The TFTR tritium operations staff has successfully received, stored, handled, and processed over five hundred thousand curies of tritium for the purpose of supporting D-T (Deuterium-Tritium) operations at TFTR. Tritium operations personnel nominally provide continuous round the clock coverage (24 hours/day, 7 days/week) in shift complements consisting of I supervisor and 3 operators. Tritium Shift Supervisors and operators are required to have 5 years of operational experience in either the nuclear or chemical industry and to become certified for their positions. The certification program provides formal instruction, as well as on the job training. The certification process requires 4 to 6 months to complete, which includes an oral board lasting up to 4 hours at which time the candidate is tested on their knowledge of Tritium Technology and TFTR Tritium systems. Once an operator is certified, the training process continues with scheduled training weeks occurring once every 5 weeks. During D-T operations at TFTR the operators must evacuate the tritium area due to direct radiation from TFTR D-T pulses. During `` time operators maintain cognizance over tritium systems via a real time TV camera system. Operators are able to gain access to the Tritium area between TFTR D-T pulses, but have been excluded from die tritium area during D-T pulsing for periods up to 30 minutes. Tritium operators are responsible for delivering tritium gas to TFRR as well as processing plasma exhaust gases which lead to the deposition of tritium oxide on disposable molecular sieve beds (DMSB). Once a DMSB is loaded, the operations staff remove the expended DMSB, and replace it with a new DMSB container. The TFIR tritium system is operated via detailed procedures which require operator sign off for system manipulation. There are >300 procedures controlling the operation of the tritium systems.
Conn, R.W.; Ghoniem, N.M.; Firestone, M.A.
1986-09-01
Reactor system operation and procedures have a profound impact on the conception and design of power plants. These issues are studied here using a model tokamak system employing a solid-breeder blanket. The model blanket is one which has evolved from the STARFIRE and BCSS studies. The reactor parameters are similar to those characterizing near-term fusion engineering reactors such as INTOR or NET (Next European Tokamak). Plasma startup, burn analysis, and methods for operation at various levels of output power are studied. A critical, and complicating, element is found to be the self-consistent electromagnetic response of the system, including the presence of the blanket and the resulting forces and loadings. Fractional power operation, and the strategy for burn control, is found to vary depending on the scaling law for energy confinement, and an extensive study is reported. Full-power reactor operation is at a neutron wall loading pf 5 MW/m/sup 2/ and a surface heat flux of 1 MW/m/sup 2/. The blanket is a pressurized steel module with bare beryllium rods and low-activation HT-9-(9-C-) clad LiAlO/sub 2/ rods. The helium coolant pressure is 5 MPa, entering the module at 297/sup 0/C and exiting at 550/sup 0/C. The system power output is rated at 1000 MW(e). In this report, we present our findings on various operational scenarios and their impact on system design. We first start with the salient aspects of operational physics. Time-dependent analyses of the blanket and balance of plant are then presented. Separate abstracts are included for each chapter.
TRANSIENT AND STEADY STATE STUDY OF PURE AND MIXED REFRIGERANTS IN A RESIDENTIAL HEAT PUMP
The report gives results of an experimental and theoretical investigation of the transient and steady state performance of a residential air-conditioning/heat pump (AC/HP) operating with different refrigerants. (NOTE: The project was motivated by environmental concerns related to...
The Enlisted Steady State-Simulation (ESS-SIM) Tool
2014-07-01
The Enlisted Steady State-Simulation ( ESS -SIM) Tool David M. Rodney • Peggy A. Golfin • Molly F. McIntosh DIM-2014-U-007587-Final July 2014 This...situation. We built and made use of a simulation model, ESS -Sim (Enlisted Steady- State Simulation), to obtain insights into attainable levels of...fleet manning and estimate the impact of policy changes on fleet man- ning. This information memorandum describes this model. Model overview We built ESS
Development of high poloidal beta, steady-state scenario with ITER-like W divertor on EAST
NASA Astrophysics Data System (ADS)
Garofalo, A. M.; Lanctot, M.; Gong, X. Z.; Ding, S.; Li, G.; Liu, H.; Lyu, B.; Qian, J.; Bonoli, P. T.; Shiraiwa, S.; Holcomb, C.; McClenaghan, J.
2016-10-01
Experiments on EAST have started to adapt the fully-noninductive high poloidal beta scenario developed on DIII-D, in order to demonstrate steady state tokamak operation at high performance on metal walls. Unlike on DIII-D, where the creation of a broad current profile requires early heating at low density, on EAST a broad current profile can be obtained simply by increasing the electron density, when most of the current drive is provided by lower hybrid wave. Systematic scans yield lower internal inductance with higher density. The hypothesis is that the LHCD profile becomes more off-axis with higher density. With the newly commissioned POINT (polarimeter-interferometer) diagnostic for q-profile measurements, these experiments enable strict tests of LHCD deposition models. Supported by US DOE under DE-SC0010685, DE-SC0010492 DE-FC02-04ER54698, DE-AC02-09-CH11466, DE-AC52-07NA27344, DE-AC05-00OR22725, and the National Magnetic Confinement Fusion Program of China (No. 2015GB110001 and 2015GB102000).
Steady State Analysis of Small Molten Salt Reactor
NASA Astrophysics Data System (ADS)
Yamamoto, Takahisa; Mitachi, Koshi; Suzuki, Takashi
The Molten Salt Reactor (MSR) is a thermal neutron reactor with graphite moderation and operates on the thorium-uranium fuel cycle. The feature of the MSR is that fuel salt flows inside the reactor during the nuclear fission reaction. In the previous study, the authors developed numerical model with which to simulate the effects of fuel salt flow on the reactor characteristics. In this study, we apply the model to the steady-state analysis of a small MSR system and estimate the effects of fuel flow. The model consists of two-group neutron diffusion equations for fast and thermal neutron fluxes, transport equations for six-group delayed neutron precursors and energy conservation equations for fuel salt and the graphite moderator. The following results are obtained: (1) in the rated operation condition, the peaks of the neutron fluxes slightly move toward the bottom from the center of the reactor and the delayed neutron precursors are significantly carried by the fuel salt flow, and (2) the extension of residence time in the external-loop system and the rise of the fuel inflow temperature show weak negative reactivity effects, which decrease the neutron multiplication factor of the small MSR system.
Tokamak operation with safety factor q95 < 2 via control of MHD stability.
Piovesan, P; Hanson, J M; Martin, P; Navratil, G A; Turco, F; Bialek, J; Ferraro, N M; La Haye, R J; Lanctot, M J; Okabayashi, M; Paz-Soldan, C; Strait, E J; Turnbull, A D; Zanca, P; Baruzzo, M; Bolzonella, T; Hyatt, A W; Jackson, G L; Marrelli, L; Piron, L; Shiraki, D
2014-07-25
Magnetic feedback control of the resistive-wall mode has enabled the DIII-D tokamak to access stable operation at safety factor q(95) = 1.9 in divertor plasmas for 150 instability growth times. Magnetohydrodynamic stability sets a hard, disruptive limit on the minimum edge safety factor achievable in a tokamak, or on the maximum plasma current at a given toroidal magnetic field. In tokamaks with a divertor, the limit occurs at q(95) = 2, as confirmed in DIII-D. Since the energy confinement time scales linearly with current, this also bounds the performance of a fusion reactor. DIII-D has overcome this limit, opening a whole new high-current regime not accessible before. This result brings significant possible benefits in terms of fusion performance, but it also extends resistive-wall mode physics and its control to conditions never explored before. In present experiments, the q(95) < 2 operation is eventually halted by voltage limits reached in the feedback power supplies, not by intrinsic physics issues. Improvements to power supplies and to control algorithms have the potential to further extend this regime.
Predictive Modeling of Tokamak Configurations*
NASA Astrophysics Data System (ADS)
Casper, T. A.; Lodestro, L. L.; Pearlstein, L. D.; Bulmer, R. H.; Jong, R. A.; Kaiser, T. B.; Moller, J. M.
2001-10-01
The Corsica code provides comprehensive toroidal plasma simulation and design capabilities with current applications [1] to tokamak, reversed field pinch (RFP) and spheromak configurations. It calculates fixed and free boundary equilibria coupled to Ohm's law, sources, transport models and MHD stability modules. We are exploring operations scenarios for both the DIII-D and KSTAR tokamaks. We will present simulations of the effects of electron cyclotron heating (ECH) and current drive (ECCD) relevant to the Quiescent Double Barrier (QDB) regime on DIII-D exploring long pulse operation issues. KSTAR simulations using ECH/ECCD in negative central shear configurations explore evolution to steady state while shape evolution studies during current ramp up using a hyper-resistivity model investigate startup scenarios and limitations. Studies of high bootstrap fraction operation stimulated by recent ECH/ECCD experiments on DIIID will also be presented. [1] Pearlstein, L.D., et al, Predictive Modeling of Axisymmetric Toroidal Configurations, 28th EPS Conference on Controlled Fusion and Plasma Physics, Madeira, Portugal, June 18-22, 2001. * Work performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
On the time to steady state: insights from numerical modeling
NASA Astrophysics Data System (ADS)
Goren, L.; Willett, S.; McCoy, S. W.; Perron, J.
2013-12-01
How fast do fluvial landscapes approach steady state after an application of tectonic or climatic perturbation? While theory and some numerical models predict that the celerity of the advective wave (knickpoint) controls the response time for perturbations, experiments and other landscape evolution models demonstrate that the time to steady state is much longer than the theoretically predicted response time. We posit that the longevity of transient features and the time to steady state are controlled by the stability of the topology and geometry of channel networks. Evolution of a channel network occurs by a combination of discrete capture events and continuous migration of water divides, processes, which are difficult to represent accurately in landscape evolution models. We therefore address the question of the time to steady state using the DAC landscape evolution model that solves accurately for the location of water divides, using a combination of analytical solution for hillslopes and low-order channels together with a numerical solution for higher order channels. DAC also includes an explicit capture criterion. We have tested fundamental predictions from DAC and show that modeled networks reproduce natural network characteristics such as the Hack's exponent and coefficient and the fractal dimension. We define two steady-state criteria: a topographic steady state, defined by global, pointwise steady elevation, and a topological steady state defined as the state in which no further reorganization of the drainage network takes place. Analyzing block uplift simulations, we find that the time to achieve either topographic or topological steady state exceeds by an order of magnitude the theoretical response time of the fluvial network. The longevity of the transient state is the result of the area feedback, by which, migration of a divide changes the local contributing area. This change propagates downstream as a slope adjustment, forcing further divide migrations
Maximally reliable spatial filtering of steady state visual evoked potentials.
Dmochowski, Jacek P; Greaves, Alex S; Norcia, Anthony M
2015-04-01
Due to their high signal-to-noise ratio (SNR) and robustness to artifacts, steady state visual evoked potentials (SSVEPs) are a popular technique for studying neural processing in the human visual system. SSVEPs are conventionally analyzed at individual electrodes or linear combinations of electrodes which maximize some variant of the SNR. Here we exploit the fundamental assumption of evoked responses--reproducibility across trials--to develop a technique that extracts a small number of high SNR, maximally reliable SSVEP components. This novel spatial filtering method operates on an array of Fourier coefficients and projects the data into a low-dimensional space in which the trial-to-trial spectral covariance is maximized. When applied to two sample data sets, the resulting technique recovers physiologically plausible components (i.e., the recovered topographies match the lead fields of the underlying sources) while drastically reducing the dimensionality of the data (i.e., more than 90% of the trial-to-trial reliability is captured in the first four components). Moreover, the proposed technique achieves a higher SNR than that of the single-best electrode or the Principal Components. We provide a freely-available MATLAB implementation of the proposed technique, herein termed "Reliable Components Analysis".
NASA Lewis steady-state heat pipe code users manual
NASA Technical Reports Server (NTRS)
Tower, Leonard K.; Baker, Karl W.; Marks, Timothy S.
1992-01-01
The NASA Lewis heat pipe code was developed to predict the performance of heat pipes in the steady state. The code can be used as a design tool on a personal computer or with a suitable calling routine, as a subroutine for a mainframe radiator code. A variety of wick structures, including a user input option, can be used. Heat pipes with multiple evaporators, condensers, and adiabatic sections in series and with wick structures that differ among sections can be modeled. Several working fluids can be chosen, including potassium, sodium, and lithium, for which monomer-dimer equilibrium is considered. The code incorporates a vapor flow algorithm that treats compressibility and axially varying heat input. This code facilitates the determination of heat pipe operating temperatures and heat pipe limits that may be encountered at the specified heat input and environment temperature. Data are input to the computer through a user-interactive input subroutine. Output, such as liquid and vapor pressures and temperatures, is printed at equally spaced axial positions along the pipe as determined by the user.
Residual gas analysis for long-pulse, advanced tokamak operation.
Klepper, C C; Hillis, D L; Bucalossi, J; Douai, D; Oddon, P; Vartanian, S; Colas, L; Manenc, L; Pégourié, B
2010-10-01
A shielded residual gas analyzer (RGA) system on Tore Supra can function during plasma operation and is set up to monitor the composition of the neutral gas in one of the pumping ducts of the toroidal pumped limited. This "diagnostic RGA" has been used in long-pulse (up to 6 min) discharges for continuous monitoring of up to 15 masses simultaneously. Comparison of the RGA-measured evolution of the H(2)/D(2) isotopic ratio in the exhaust gas to that measured by an energetic neutral particle analyzer in the plasma core provides a way to monitor the evolution of particle balance. RGA monitoring of corrective H(2) injection to maintain proper minority heating is providing a database for improved ion cyclotron resonance heating, potentially with RGA-base feedback control. In very long pulses (>4 min) absence of significant changes in the RGA-monitored, hydrocarbon particle pressures is an indication of proper operation of the actively cooled, carbon-based plasma facing components. Also H(2) could increase due to thermodesorption of overheated plasma facing components.
NASA Technical Reports Server (NTRS)
Garrett, Floyd B; Gyorgak, Charles A; Weeton, John Waldemar
1953-01-01
An investigation was conducted to determine the behavior of recently produced, forged S-816 turbine blades in a full-scale turbojet engine, and in particular, the scatter in performance of the alloy. The turbine blades were operated as continuously as possible at a temperature of 1500 degrees F and a centrifugal stress of 21,500 pounds per square inch. The operating lives of the turbine blades varied from 181 to 539 hours, a range of 358 hours. Stress-rupture properties of specimens cut from blade airfoils also varied considerably, as much as 1257 hours at 20,000 pounds per square inch and 1500 degrees F. Since the variability of scatter of stress-rupture data is greater than that of blade performance, the scatter is probably caused by variations in the properties of the forged blades rather than by variations caused by engine operation or installation of the blades. Metallographic examinations were made to determine possible causes of the scatter and although numerous differences in microstructures of blades were found, no consistent tendencies were observed and the findings did not permit an explanation of the scatter of blade performance. The results of the metallographic examinations and of the physical tests indirectly indicated variables in the fabricating method caused the scatter in properties.
Impurity shielding criteria for steady state hydrogen plasmas in the LHD, a heliotron-type device
NASA Astrophysics Data System (ADS)
Nakamura, Y.; Kobayashi, M.; Yoshimura, S.; Tamura, N.; Yoshinuma, M.; Tanaka, K.; Suzuki, C.; Peterson, B. J.; Sakamoto, R.; Morisaki, T.; the LHD Experiment Group
2014-07-01
Impurity behavior has so far been investigated in steady state hydrogen plasmas in the Large Helical Device, which is a heliotron-type device and excellent for steady state operation. There was always found to be an impurity accumulation window, as observed before (Nakamura et al 2002 Plasma Phys. Control. Fusion 44 2121, Nakamura et al 2003 Nucl. Fusion 43 219). To clarify the boundary conditions, the dependences of impurity transport on edge plasma parameters are investigated with a database of steady state hydrogen discharges, and the boundary conditions for the impurity accumulation window are discussed. It is found that two different types of impurity screening effects are essential for preventing intrinsic impurities from entering the core plasma. One of them is due to positive radial electric field at the plasma edge on the low collisionality side and the other is impurity retention caused by friction force in the ergodic layer on the high collisionality side. The classification of steady state discharges on n-T space shows that the impurity behavior can be predicted by the impurity shielding criteria based on each empirical scaling.
NASA Astrophysics Data System (ADS)
Hershey, Kyle W.; Holmes, Russell J.
2016-11-01
Phosphorescent organic light-emitting devices (OLEDs) can suffer a significant reduction in device efficiency under high current density excitation. This steady-state efficiency roll-off is frequently modeled by including losses from exciton-exciton and exciton-polaron quenching. Despite success in modeling the steady-state efficiency roll-off, the corresponding transient electroluminescence behavior has not been modeled as effectively using the same quenching processes. In this work, both the steady-state and transient electroluminescence behavior of phosphorescent OLEDs based on tris[2-phenylpyridinato-C2,N]Iridium(III) (Ir(ppy)3) are successfully reproduced by considering a dynamic polaron population. Within this model, polarons are able to either form excitons or leak through the device emissive layer, reducing the overall efficiency. This formalism permits a natural and rigorous connection between exciton and polaron dynamics and device charge balance, with the charge balance cast as the efficiency of exciton formation. The full dynamics model reproduces both the rise and decay of transient electroluminescence, as well as the full dependence of the external quantum efficiency on current density. Fit parameters are independently verified using separate studies of transient and steady-state photoluminescence. The model provides a complete picture for the dynamics present during the electrical operation of phosphorescent OLEDs, while also offering a direct route to elucidate exciton formation.
Proteome analysis of the Escherichia coli heat shock response under steady-state conditions
Lüders, Svenja; Fallet, Claas; Franco-Lara, Ezequiel
2009-01-01
In this study a proteomic approach was used to investigate the steady-state response of Escherichia coli to temperature up-shifts in a cascade of two continuously operated bioreactors. The first reactor served as cell source with optimal settings for microbial growth, while in the second chemostat the cells were exposed to elevated temperatures. By using this reactor configuration, which has not been reported to be used for the study of bacterial stress responses so far, it is possible to study temperature stress under well-defined, steady-state conditions. Specifically the effect on the cellular adaption to temperature stress using two-dimensional gel electrophoresis was examined and compared at the cultivation temperatures of 37°C and 47.5°C. As expected, the steady-state study with the double bioreactor configuration delivered a different protein spectrum compared to that obtained with standard batch experiments in shaking flasks and bioreactors. Setting a high cut-out spot-to-spot size ratio of 5, proteins involved in defence against oxygen stress, functional cell envelope proteins, chaperones and proteins involved in protein biosynthesis, the energy metabolism and the amino acid biosynthesis were found to be differently expressed at high cultivation temperatures. The results demonstrate the complexity of the stress response in a steady-state culture not reported elsewhere to date. PMID:19772559
System and method for generating steady state confining current for a toroidal plasma fusion reactor
Bers, Abraham
1981-01-01
A system for generating steady state confining current for a toroidal plasma fusion reactor providing steady-state generation of the thermonuclear power. A dense, hot toroidal plasma is initially prepared with a confining magnetic field with toroidal and poloidal components. Continuous wave RF energy is injected into said plasma to estalish a spectrum of traveling waves in the plasma, where the traveling waves have momentum components substantially either all parallel, or all anti-parallel to the confining magnetic field. The injected RF energy is phased to couple to said traveling waves with both a phase velocity component and a wave momentum component in the direction of the plasma traveling wave components. The injected RF energy has a predetermined spectrum selected so that said traveling waves couple to plasma electrons having velocities in a predetermined range .DELTA.. The velocities in the range are substantially greater than the thermal electron velocity of the plasma. In addition, the range is sufficiently broad to produce a raised plateau having width .DELTA. in the plasma electron velocity distribution so that the plateau electrons provide steady-state current to generate a poloidal magnetic field component sufficient for confining the plasma. In steady state operation of the fusion reactor, the fusion power density in the plasma exceeds the power dissipated inthe plasma.
System and method for generating steady state confining current for a toroidal plasma fusion reactor
Fisch, Nathaniel J.
1981-01-01
A system for generating steady state confining current for a toroidal plasma fusion reactor providing steady-state generation of the thermonuclear power. A dense, hot toroidal plasma is initially prepared with a confining magnetic field with toroidal and poloidal components. Continuous wave RF energy is injected into said plasma to establish a spectrum of traveling waves in the plasma, where the traveling waves have momentum components substantially either all parallel, or all anti-parallel to the confining magnetic field. The injected RF energy is phased to couple to said traveling waves with both a phase velocity component and a wave momentum component in the direction of the plasma traveling wave components. The injected RF energy has a predetermined spectrum selected so that said traveling waves couple to plasma electrons having velocities in a predetermined range .DELTA.. The velocities in the range are substantially greater than the thermal electron velocity of the plasma. In addition, the range is sufficiently broad to produce a raised plateau having width .DELTA. in the plasma electron velocity distribution so that the plateau electrons provide steady-state current to generate a poloidal magnetic field component sufficient for confining the plasma. In steady state operation of the fusion reactor, the fusion power density in the plasma exceeds the power dissipated in the plasma.
NASA Technical Reports Server (NTRS)
Sellers, J. F.; Daniele, C. J.
1975-01-01
The DYNGEN, a digital computer program for analyzing the steady state and transient performance of turbojet and turbofan engines, is described. The DYNGEN is based on earlier computer codes (SMOTE, GENENG, and GENENG 2) which are capable of calculating the steady state performance of turbojet and turbofan engines at design and off-design operating conditions. The DYNGEN has the combined capabilities of GENENG and GENENG 2 for calculating steady state performance; to these the further capability for calculating transient performance was added. The DYNGEN can be used to analyze one- and two-spool turbojet engines or two- and three-spool turbofan engines without modification to the basic program. A modified Euler method is used by DYNGEN to solve the differential equations which model the dynamics of the engine. This new method frees the programmer from having to minimize the number of equations which require iterative solution. As a result, some of the approximations normally used in transient engine simulations can be eliminated. This tends to produce better agreement when answers are compared with those from purely steady state simulations. The modified Euler method also permits the user to specify large time steps (about 0.10 sec) to be used in the solution of the differential equations. This saves computer execution time when long transients are run. Examples of the use of the program are included, and program results are compared with those from an existing hybrid-computer simulation of a two-spool turbofan.
A unified theory of tokamak transport via the generalized Balescu--Lenard collision operator
Mynick, H.E.; Duvall, R.E.
1988-06-01
A unified basis from which to study the transport of tokamaks at low collisionality is provided by specializing the ''generalized Balescu--Lenard'' collision operator to toridal geometry. Explicitly evaluating this operator, ripple, turbulent, and neoclassical transport coefficients are obtained, simply by further specializing the single operator to different particular classes of fluctuation wavelength and mode structure. For each class of fluctuations, the operator possesses a diffusive, test-particle contribution D, and in addition a dynamic drag term F, which makes the operator self-consistent, and whose presence is accordingly essential for the resultant fluxes to possess the appropriate conservation laws and symmetrics. These properties, well-known for axisymmetric transport, are demonstrated for one type of turbulent transport, chosen for definiteness, by explicit evaluation of both ''anomalous diffusion'' term arising from D, as well as the closely related test particle calculations, but is shown to have an important impact on the predicted fluxes. 16 refs., 1 fig.
Structural simplification of chemical reaction networks in partial steady states.
Madelaine, Guillaume; Lhoussaine, Cédric; Niehren, Joachim; Tonello, Elisa
2016-11-01
We study the structural simplification of chemical reaction networks with partial steady state semantics assuming that the concentrations of some but not all species are constant. We present a simplification rule that can eliminate intermediate species that are in partial steady state, while preserving the dynamics of all other species. Our simplification rule can be applied to general reaction networks with some but few restrictions on the possible kinetic laws. We can also simplify reaction networks subject to conservation laws. We prove that our simplification rule is correct when applied to a module of a reaction network, as long as the partial steady state is assumed with respect to the complete network. Michaelis-Menten's simplification rule for enzymatic reactions falls out as a special case. We have implemented an algorithm that applies our simplification rules repeatedly and applied it to reaction networks from systems biology.
Poissonian steady states: from stationary densities to stationary intensities.
Eliazar, Iddo
2012-10-01
Markov dynamics are the most elemental and omnipresent form of stochastic dynamics in the sciences, with applications ranging from physics to chemistry, from biology to evolution, and from economics to finance. Markov dynamics can be either stationary or nonstationary. Stationary Markov dynamics represent statistical steady states and are quantified by stationary densities. In this paper, we generalize the notion of steady state to the case of general Markov dynamics. Considering an ensemble of independent motions governed by common Markov dynamics, we establish that the entire ensemble attains Poissonian steady states which are quantified by stationary Poissonian intensities and which hold valid also in the case of nonstationary Markov dynamics. The methodology is applied to a host of Markov dynamics, including Brownian motion, birth-death processes, random walks, geometric random walks, renewal processes, growth-collapse dynamics, decay-surge dynamics, Ito diffusions, and Langevin dynamics.
NASA Astrophysics Data System (ADS)
Nieto, M.; Allain, J. P.; Hassanein, A.; Titov, V.; Hendricks, M.; Gray, T.; Kaita, R.; Kugel, H.; Majeski, R.; Mansfield, D.; Spaleta, J.; Timberlake, J.
2006-12-01
The role of lithium on the modification of recycling regimes in fusion reactors has renewed interest of previous lithium supershot experiments carried out in TFTR. There is a need to understand the interaction between edge plasmas and lithiated plasma-facing components (PFCs), which have the potential of enabling fusion reactors to operate at low-recycling regimes. The Interaction of Materials with Particles and Components Testing (IMPACT) facility at Argonne National Laboratory is currently collaborating with Princeton Plasma Physics Laboratory (PPPL) to conduct lithiated surface studies for the National Spherical Tokamak Experiment (NSTX) and the Current Drive eXperiment — Upgrade (CDX-U). IMPACT has the necessary tools to perform experiments that diagnose the surface dynamics of lithium thin films on metallic and non-metallic substrates, and can be monitored with multiple in-situ techniques (LEISS, AES, QMS and XPS) capturing real-time surface dynamics. Therefore, these techniques are available during He+ and D+ irradiation. Surface sputtering measurements can be performed using a quartz crystal microbalance — dual crystal unit (QCM-DCU) with very high sensitivity. Initial results suggest that lithium intercalation into graphite occurs quite rapidly and only a fraction lithium can be kept on the surface. On metallic substrates this intercalation is absent. Additional results of Li/metal systems show lithium surface self-healing with temperature. It was also found that the presence of lithium seems to inhibit hydrocarbon formation during D+ bombardment of graphite. Experiments in CDX-U have tested the effect of both solid and liquid lithium PFCs on tokamak plasmas, and significant changes in tokamak operation are observed. These include a strong reduction in both recycling and impurity levels in the gas phase, lowered loop voltage during ohmic operation, and an increased electron temperature at the edge.
A simplified approach to estimating the maximal lactate steady state.
Snyder, A C; Woulfe, T; Welsh, R; Foster, C
1994-01-01
The exercise intensity associated with an elevated but stable blood lactate (HLa) concentration during constant load work (the maximal steady state, MSS) has received attention as a candidate for the "optimal" exercise intensity for endurance training. Identification of MSS ordinarily demands direct measurement of HLa or respiratory metabolism. The purpose of this study was to test the ability of heart rate (HR) to identify MSS during steady state exercise, similar to that used in conventional exercise prescription. Trained runners (n = 9) and cyclists (n = 12) performed incremental and steady state exercise. MSS was defined as the highest intensity in which blood lactate concentration increased < 1.0 mM from minutes 10 to 30. The next higher intensity workbout completed was defined as > MSS. HR models related to the presence or absence of steady state conditions were developed from the upper 95% confidence interval of MSS and the lower 95% confidence interval of > MSS. Cross validation of the model to predict MSS was performed using 21 running and 45 cycling exercise bouts in a separate group. Using the MSS upper 95% confidence interval model 84% and 76% of workbouts were correctly predicted in cyclists and runners, respectively. Using the > MSS lower 95% confidence interval model, 76% and 81% of workbouts were correctly predicted in cyclists and runners, respectively. Prediction errors tended to incorrectly predict non-steady state conditions when steady state had occurred (16/26) (62%). We conclude that use of these simple HR models may predict MSS with sufficient accuracy to be useful when direct HLa measurement is not available.
Remote operation of the GOLEM tokamak with hydrogen and helium plasmas
NASA Astrophysics Data System (ADS)
Svoboda, V.; Dvornova, A.; Dejarnac, R.; Prochazka, M.; Zaprianov, S.; Akhmethanov, R.; Bogdanova, M.; Dimitrova, M.; Dimitrov, Zh; Grover, O.; Hlavata, L.; Ivanov, K.; Kruglov, K.; Marinova, P.; Masherov, P.; Mogulkin, A.; Mlynar, J.; Stockel, J.; Volynets, A.
2016-10-01
The GOLEM tokamak was operated remotely via Internet connection during the 6th International Workshop and Summer School on Plasma Physics. Performances of hydrogen and helium discharges are compared in this paper. It is found, at similar vacuum conditions, that helium discharges are shorter but the breakdown of the working gas can be quite easily achieved at almost the same loop voltage. The plasma current in helium discharges is slightly lower than in the case of hydrogen. Turbulent fluctuations of the floating potential measured by means of an array of Langmuir probes reveal a noticeably different character in the two discharges.
Steady-state error of a system with fuzzy controller.
Butkiewicz, B S
1998-01-01
We consider the problem of control error of a fuzzy system with feedback. The system consists of a plant, linear or nonlinear, fuzzy controller, and feedback loop. As controller we use both PD and PI fuzzy type controllers. We apply different t-norm and co-norm: logic, algebraic, Yager, Hamacher, bounded, drastic, etc. in the process of fuzzy reasoning. Triangular shape of membership functions is supposed, but we generalize the results obtained. Steady-state error of a system is calculated. We have obtained very interesting results. The steady-state error is identical for pairs of triangular t- and co-norms.
Mapping current fluctuations of stochastic pumps to nonequilibrium steady states
NASA Astrophysics Data System (ADS)
Rotskoff, Grant M.
2017-03-01
We show that current fluctuations in a stochastic pump can be robustly mapped to fluctuations in a corresponding time-independent nonequilibrium steady state. We thus refine a recently proposed mapping so that it ensures equivalence of not only the averages, but also optimal representation of fluctuations in currents and density. Our mapping leads to a natural decomposition of the entropy production in stochastic pumps similar to the "housekeeping" heat. As a consequence of the decomposition of entropy production, the current fluctuations in weakly perturbed stochastic pumps are shown to satisfy a universal bound determined by the steady state entropy production.
Descriptive Linear modeling of steady-state visual evoked response
NASA Technical Reports Server (NTRS)
Levison, W. H.; Junker, A. M.; Kenner, K.
1986-01-01
A study is being conducted to explore use of the steady state visual-evoke electrocortical response as an indicator of cognitive task loading. Application of linear descriptive modeling to steady state Visual Evoked Response (VER) data is summarized. Two aspects of linear modeling are reviewed: (1) unwrapping the phase-shift portion of the frequency response, and (2) parsimonious characterization of task-loading effects in terms of changes in model parameters. Model-based phase unwrapping appears to be most reliable in applications, such as manual control, where theoretical models are available. Linear descriptive modeling of the VER has not yet been shown to provide consistent and readily interpretable results.
Karst, Daniel J; Steinhoff, Robert F; Kopp, Marie R G; Serra, Elisa; Soos, Miroslav; Zenobi, Renato; Morbidelli, Massimo
2016-12-20
Perfusion cell culture processes allow the steady-state culture of mammalian cells at high viable cell density, which is beneficial for overall product yields and homogeneity of product quality in the manufacturing of therapeutic proteins. In this study, the extent of metabolic steady state and the change of the metabolite profile between different steady states of an industrial Chinese hamster ovary (CHO) cell line producing a monoclonal antibody (mAb) was investigated in stirred tank perfusion bioreactors. Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) of daily cell extracts revealed more than a hundred peaks, among which 76 metabolites were identified by tandem MS (MS/MS) and high resolution Fourier transform ion cyclotron resonance (FT-ICR) MS. Nucleotide ratios (Uridine (U)-ratio, nucleotide triphosphate (NTP)-ratio and energy charge (EC)) and multivariate analysis of all features indicated a consistent metabolite profile for a stable culture performed at 40 × 10(6) cells/mL over 26 days of culture. Conversely, the reactor was operated continuously so as to reach three distinct steady states one after the other at 20, 60, and 40 × 10(6) cells/mL. In each case, a stable metabolite profile was achieved after an initial transient phase of approximately three days at constant cell density when varying between these set points. Clear clustering according to cell density was observed by principal component analysis, indicating steady-state dependent metabolite profiles. In particular, varying levels of nucleotides, nucleotide sugar, and lipid precursors explained most of the variance between the different cell density set points. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 2016.
ADX - Advanced Divertor and RF Tokamak Experiment
NASA Astrophysics Data System (ADS)
Greenwald, Martin; Labombard, Brian; Bonoli, Paul; Irby, Jim; Terry, Jim; Wallace, Greg; Vieira, Rui; Whyte, Dennis; Wolfe, Steve; Wukitch, Steve; Marmar, Earl
2015-11-01
The Advanced Divertor and RF Tokamak Experiment (ADX) is a design concept for a compact high-field tokamak that would address boundary plasma and plasma-material interaction physics challenges whose solution is critical for the viability of magnetic fusion energy. This device would have two crucial missions. First, it would serve as a Divertor Test Tokamak, developing divertor geometries, materials and operational scenarios that could meet the stringent requirements imposed in a fusion power plant. By operating at high field, ADX would address this problem at a level of power loading and other plasma conditions that are essentially identical to those expected in a future reactor. Secondly, ADX would investigate the physics and engineering of high-field-side launch of RF waves for current drive and heating. Efficient current drive is an essential element for achieving steady-state in a practical, power producing fusion device and high-field launch offers the prospect of higher efficiency, better control of the current profile and survivability of the launching structures. ADX would carry out this research in integrated scenarios that simultaneously demonstrate the required boundary regimes consistent with efficient current drive and core performance.
A steady-state model of the lunar ejecta cloud
NASA Astrophysics Data System (ADS)
Christou, Apostolos
2014-05-01
Every airless body in the solar system is surrounded by a cloud of ejecta produced by the impact of interplanetary meteoroids on its surface [1]. Such ``dust exospheres'' have been observed around the Galilean satellites of Jupiter [2,3]. The prospect of long-term robotic and human operations on the Moon by the US and other countries has rekindled interest on the subject [4]. This interest has culminated with the - currently ongoing - investigation of the Moon's dust exosphere by the LADEE spacecraft [5]. Here a model is presented of a ballistic, collisionless, steady state population of ejecta launched vertically at randomly distributed times and velocities and moving under constant gravity. Assuming a uniform distribution of launch times I derive closed form solutions for the probability density functions (pdfs) of the height distribution of particles and the distribution of their speeds in a rest frame both at the surface and at altitude. The treatment is then extended to particle motion with respect to a moving platform such as an orbiting spacecraft. These expressions are compared with numerical simulations under lunar surface gravity where the underlying ejection speed distribution is (a) uniform (b) a power law. I discuss the predictions of the model, its limitations, and how it can be validated against near-surface and orbital measurements.[1] Gault, D. Shoemaker, E.M., Moore, H.J., 1963, NASA TN-D 1767. [2] Kruger, H., Krivov, A.V., Hamilton, D. P., Grun, E., 1999, Nature, 399, 558. [3] Kruger, H., Krivov, A.V., Sremcevic, M., Grun, E., 2003, Icarus, 164, 170. [4] Grun, E., Horanyi, M., Sternovsky, Z., 2011, Planetary and Space Science, 59, 1672. [5] Elphic, R.C., Hine, B., Delory, G.T., Salute, J.S., Noble, S., Colaprete, A., Horanyi, M., Mahaffy, P., and the LADEE Science Team, 2014, LPSC XLV, LPI Contr. 1777, 2677.
Pre-Steady-State Decoding of the Bicoid Morphogen Gradient
Bergmann, Sven; Sandler, Oded; Sberro, Hila; Shnider, Sara; Schejter, Eyal; Shilo, Ben-Zion; Barkai, Naama
2007-01-01
Morphogen gradients are established by the localized production and subsequent diffusion of signaling molecules. It is generally assumed that cell fates are induced only after morphogen profiles have reached their steady state. Yet, patterning processes during early development occur rapidly, and tissue patterning may precede the convergence of the gradient to its steady state. Here we consider the implications of pre-steady-state decoding of the Bicoid morphogen gradient for patterning of the anterior–posterior axis of the Drosophila embryo. Quantitative analysis of the shift in the expression domains of several Bicoid targets (gap genes) upon alteration of bcd dosage, as well as a temporal analysis of a reporter for Bicoid activity, suggest that a transient decoding mechanism is employed in this setting. We show that decoding the pre-steady-state morphogen profile can reduce patterning errors caused by fluctuations in the rate of morphogen production. This can explain the surprisingly small shifts in gap and pair-rule gene expression domains observed in response to alterations in bcd dosage. PMID:17298180
Steady-State Multiplicity Features of Chemically Reacting Systems.
ERIC Educational Resources Information Center
Luss, Dan
1986-01-01
Analyzes steady-state multiplicity in chemical reactors, focusing on the use of two mathematical tools, namely, the catastrophe theory and the singularity theory with a distinguished parameter. These tools can be used to determine the maximum number of possible solutions and the different types of bifurcation diagrams. (JN)
Pressure updating methods for the steady-state fluid equations
NASA Technical Reports Server (NTRS)
Fiterman, A.; Turkel, E.; Vatsa, V.
1995-01-01
We consider the steady state equations for a compressible fluid. Since we wish to solve for a range of speeds we must consider the equations in conservation form. For transonic speeds these equations are of mixed type. Hence, the usual approach is to add time derivatives to the steady state equations and then march these equations in time. One then adds a time derivative of the density to the continuity equation, a derivative of the momentum to the momentum equation and a derivative of the total energy to the energy equation. This choice is dictated by the time consistent equations. However, since we are only interested in the steady state this is not necessary. Thus we shall consider the possibility of adding a time derivative of the pressure to the continuity equation and similar modifications for the energy equation. This can then be generalized to adding combinations of time derivatives to each equation since these vanish in the steady state. When using acceleration techniques such as residual smoothing, multigrid, etc. these are applied to the pressure rather than the density. Hence, the code duplicates the behavior of the incompressible equations for low speeds.
CONTROL OF CRYPTOSPORIDIUM OOCYSTS BY STEADY-STATE CONVENTIONAL TREATMENT
Pilot-scale experiments have been performed to assess the ability of conventional treatment to control Cryptosporidium oocysts under steady-state conditions. The work was performed with a pilot plant that was designed to minimize flow rates and, as a result, the number of oocyst...
Steady-State Pharmacokinetics of Bupropion SR in Juvenile Patients
ERIC Educational Resources Information Center
Daviss, W. Burleson; Perel, James M.; Rudolph, George R.; Axelson, David A.; Gilchrist, Richard; Nuss, Sharon; Birmaher, Boris; Brent, David A.
2005-01-01
Objective: To examine the steady-state pharmacokinetic properties of bupropion sustained release (SR) and their potential developmental differences in youths. Method: Eleven boys and eight girls aged 11 to 17 years old were prescribed bupropion SR monotherapy for attention-deficit/hyperactivity disorder (n = 16) and/or depressive disorders (n =…
The concave river long profile: a morphodynamic steady state?
NASA Astrophysics Data System (ADS)
Blom, A.
2011-12-01
By definition, a morphodynamic steady state is governed by a spatially constant sediment transport rate. As the sediment transport rate is a function of shear stress associated with skin friction, the morphodynamic steady state has been considered to be governed by a spatially constant bed slope. For this reason, the typical concave river long profile has been considered to be a quasi-steady state. The river's steady state has been considered to be one with a spatially constant bed slope, with tributaries inducing a stepwise decrease in bed slope in streamwise direction. Yet, for the sediment transport rate to be spatially constant, it rather is the product of water surface slope and water depth associated with skin friction that needs to be constant. This implies that physical mechanisms that induce streamwise variation in the sediment transport rate can be compensated by a streamwise variation in bed slope so as to guarantee a spatially constant sediment transport rate. Following the river course, such physical mechanisms can be bedrock exposure, partial transport, and a spatially lagging bedform growth. At locations where tributaries increase the water discharge, the above mechanisms cause the river bed profile to be upward concave over a significant reach. At bifucations or at locations where river widening prevails, the river bed profile is upward convex.
Combined Steady-State and Dynamic Heat Exchanger Experiment
ERIC Educational Resources Information Center
Luyben, William L.; Tuzla, Kemal; Bader, Paul N.
2009-01-01
This paper describes a heat-transfer experiment that combines steady-state analysis and dynamic control. A process-water stream is circulated through two tube-in-shell heat exchangers in series. In the first, the process water is heated by steam. In the second, it is cooled by cooling water. The equipment is pilot-plant size: heat-transfer areas…
Equilibrium Binding and Steady-State Enzyme Kinetics.
ERIC Educational Resources Information Center
Dunford, H. Brian
1984-01-01
Points out that equilibrium binding and steady-state enzyme kinetics have a great deal in common and that related equations and error analysis can be cast in identical forms. Emphasizes that if one type of problem solution is taught, the other is also taught. Various methods of data analysis are evaluated. (JM)
Identification of enzyme inhibitory mechanisms from steady-state kinetics.
Fange, David; Lovmar, Martin; Pavlov, Michael Y; Ehrenberg, Måns
2011-09-01
Enzyme inhibitors are used in many areas of the life sciences, ranging from basic research to the combat of disease in the clinic. Inhibitors are traditionally characterized by how they affect the steady-state kinetics of enzymes, commonly analyzed on the assumption that enzyme-bound and free substrate molecules are in equilibrium. This assumption, implying that an enzyme-bound substrate molecule has near zero probability to form a product rather than dissociate, is valid only for very inefficient enzymes. When it is relaxed, more complex but also more information-rich steady-state kinetics emerges. Although solutions to the general steady-state kinetics problem exist, they are opaque and have been of limited help to experimentalists. Here we reformulate the steady-state kinetics of enzyme inhibition in terms of new parameters. These allow for assessment of ambiguities of interpretation due to kinetic scheme degeneracy and provide an intuitively simple way to analyze experimental data. We illustrate the method by concrete examples of how to assess scheme degeneracy and obtain experimental estimates of all available rate and equilibrium constants. We suggest simple, complementary experiments that can remove ambiguities and greatly enhance the accuracy of parameter estimation.
Steady States of the Parametric Rotator and Pendulum
ERIC Educational Resources Information Center
Bouzas, Antonio O.
2010-01-01
We discuss several steady-state rotation and oscillation modes of the planar parametric rotator and pendulum with damping. We consider a general elliptic trajectory of the suspension point for both rotator and pendulum, for the latter at an arbitrary angle with gravity, with linear and circular trajectories as particular cases. We treat the…
Steady State Load Characterization Fact Sheet: 2012 Chevy Volt
Scoffield, Don
2015-03-01
This fact sheet characterizes the steady state charging behavior of a 2012 Chevy Volt. Both level 1 charging (120 volt) and level 2 charging (208 volts) is investigated. This fact sheet contains plots of efficiency, power factor, and current harmonics as vehicle charging is curtailed. Prominent current harmonics are also displayed in a histogram for various charge rates.
Density Functional Theory for Steady-State Nonequilibrium Molecular Junctions
Liu, Shuanglong; Nurbawono, Argo; Zhang, Chun
2015-01-01
We present a density functional theory (DFT) for steady-state nonequilibrium quantum systems such as molecular junctions under a finite bias. Based on the steady-state nonequilibrium statistics that maps nonequilibrium to an effective equilibrium, we show that ground-state DFT (GS-DFT) is not applicable in this case and two densities, the total electron density and the density of current-carrying electrons, are needed to uniquely determine the properties of the corresponding nonequilibrium system. A self-consistent mean-field approach based on two densities is then derived. The theory is implemented into SIESTA computational package and applied to study nonequilibrium electronic/transport properties of a realistic carbon-nanotube (CNT)/Benzene junction. Results obtained from our steady-state DFT (SS-DFT) are compared with those of conventional GS-DFT based transport calculations. We show that SS-DFT yields energetically more stable nonequilibrium steady state, predicts significantly lower electric current, and is able to produce correct electronic structures in local equilibrium under a limiting case. PMID:26472080
Fast-ion transport in q{sub min}>2, high-β steady-state scenarios on DIII-D
Holcomb, C. T.; Heidbrink, W. W.; Collins, C.; Ferron, J. R.; Van Zeeland, M. A.; Garofalo, A. M.; Bass, E. M.; Luce, T. C.; Pace, D. C.; Solomon, W. M.; Mueller, D.; Grierson, B.; Podesta, M.; Gong, X.; Ren, Q.; Park, J. M.; Kim, K.; Turco, F.
2015-05-15
Results from experiments on DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] aimed at developing high β steady-state operating scenarios with high-q{sub min} confirm that fast-ion transport is a critical issue for advanced tokamak development using neutral beam injection current drive. In DIII-D, greater than 11 MW of neutral beam heating power is applied with the intent of maximizing β{sub N} and the noninductive current drive. However, in scenarios with q{sub min}>2 that target the typical range of q{sub 95}= 5–7 used in next-step steady-state reactor models, Alfvén eigenmodes cause greater fast-ion transport than classical models predict. This enhanced transport reduces the absorbed neutral beam heating power and current drive and limits the achievable β{sub N}. In contrast, similar plasmas except with q{sub min} just above 1 have approximately classical fast-ion transport. Experiments that take q{sub min}>3 plasmas to higher β{sub P} with q{sub 95}= 11–12 for testing long pulse operation exhibit regimes of better than expected thermal confinement. Compared to the standard high-q{sub min} scenario, the high β{sub P} cases have shorter slowing-down time and lower ∇β{sub fast}, and this reduces the drive for Alfvénic modes, yielding nearly classical fast-ion transport, high values of normalized confinement, β{sub N}, and noninductive current fraction. These results suggest DIII-D might obtain better performance in lower-q{sub 95}, high-q{sub min} plasmas using broader neutral beam heating profiles and increased direct electron heating power to lower the drive for Alfvén eigenmodes.
Steady-state and dynamic models of unified power flow controller (UPFC) for power system studies
Nabavi-Niaki, A.; Iravani, M.R.
1996-11-01
This paper provides comprehensive development procedures and final forms of mathematical models of unified power flow controller (UPFC) for steady-state, transient stability and eigenvalue studies. Based on the developed models, the impacts of control strategy, parameters and location of UPFC on power system operating conditions are discussed. The accuracy of the developed models is verified through comparing the study results with those obtained from detailed time-domain simulation using the Electromagnetic Transients Program (EMTP).
Cooperative Effects in Models of Steady-State Transport across Membranes
Hill, Terrell L.; Chen, Yi-Der
1971-01-01
Several different one-site, two-site, and multisite models of steady-state ion transport across a membrane are investigated. The basic features, including cooperative interactions between channels, are the same as in earlier papers in this series. In particular, the present paper represents a considerable elaboration of part III. The models might apply to artificial or possibly to biological membranes, but particular applications must await further elucidation of the molecular structure and operation of these membranes. PMID:5132496
Characterization of the Radiation Environment During and Following Operation of the DIII-D Tokamak
NASA Astrophysics Data System (ADS)
Riso, Victoria; Pace, D. C.; Cooper, C. M.
2015-11-01
A survey of the gamma ray spectrum throughout the machine hall of the DIII-D tokamak provides a detailed mapping of its energy and temporal evolution. Engineering issues related to the structural effects of radiation produced by a fusion power plant will significantly affect the cost-effectiveness of the resulting energy. While existing magnetic confinement facilities produce considerably less neutron and gamma radiation than that expected from a power plant-scale facility, it remains useful to examine the latent gamma spectrum of the surrounding structures. The DIII-D tokamak produces ~1016 neutrons per run day (resulting primarily from beam-target DD fusion), with ~75 run days per year, leading to the activation of support structures with a short half-life. Measurements are made using bismuth germinate scintillator detectors operated in pulse height analysis mode. These detectors are placed throughout the machine hall and acquire gamma data both during experiments and for some time afterward. Results of these surveys from the 2015 experiments will be presented. Supported in part by US DOE under DE-FC02-04ER54698.
Steady state volcanism: Evidence from eruption histories of polygenetic volcanoes
Wadge, G.
1982-05-10
Some volcanoes erupt magma at average rates which are constant over periods of many years, even through this magma may appear in a complex series of eruptions. This constancy of output is tested by construction of a curve of cumulative volume of erupted magma, which is linear for steady state volcanism, and whose gradient defines the steady state rate Q/sub s/s. The assumption is made that Q/sub s/s is the rate at which magma is supplied to these polygenetic volcanoes. Five general types of eruptive behavior can be distinguished from the cumulative volume studied. These types are interpreted in terms of a simple model of batches of magma rising buoyantly through the crust and interacting with a small-capacity subvolcanic magma reservoir. Recognition of previous steady state behavior at a volcano may enable the cumulative volume curve to be used empirically as a constraint on the timing and volume of the next eruption. The steady state model thus has a limited predictive capability. With the exception of Kilauea (O/sub s/s = 4m/sup 3/ s/sup -1/) all the identified steady state volcanoes have values of Q/sub s/s of a few tenths of one cubic meter per second. These rates are consistent with the minimum flux rates required by theoretical cooling models of batches of magma traversing the crust. The similarity of these Q/sub s/s values of volcanoes (producing basalt, andesite, and dacite magmas) in very different tectonic settings suggests that the common factors of crustal buoyancy forces and the geotherm-controlled cooling rates control the dynamics of magma supply through the crust. Long-term dormancy at active volcanoes may be a manifestation of the steady accumulation of magma in large crustal reservoirs, a process that complements the intermittent periods of steady state output at the surface. This possibility has several implications, the most important of which is that it provides a constraint on the supply rate of new magma to the bases of plutons.
Realization of minute-long steady-state H-mode discharges on EAST
NASA Astrophysics Data System (ADS)
Xianzu, GONG; Baonian, WAN; Jiangang, LI; Jinping, QIAN; Erzhong, LI; Fukun, LIU; Yanping, ZHAO; Mao, WANG; Handong, XU; A, M. GAROFALO; Annika, EKEDAH; Siye, DING; Juan, HUANG; Ling, ZHANG; Qing, ZANG; Haiqing, LIU; Long, ZENG; Shiyao, LIN; Biao, SHEN; Bin, ZHANG; Linming, SHAO; Bingjia, XIAO; Jiansheng, HU; Chundong, HU; Liqun, HU; Liang, WANG; Youwen, SUN; Guosheng, XU; Yunfeng, LIANG; Nong, XIANG; EAST Team
2017-03-01
In the 2016 EAST experimental campaign, a steady-state long-pulse H-mode discharge with an ITER-like tungsten divertor lasting longer than one minute has been obtained using only RF heating and current drive, through an integrated control of the wall conditioning, plasma configuration, divertor heat flux, particle exhaust, impurity management, and effective coupling of multiple RF heating and current drive sources at high injected power. The plasma current (I p ∼ 0.45 MA) was fully-noninductively driven (V loop < 0.0 V) by a combination of ∼2.5 MW LHW, ∼0.4 MW ECH and ∼0.8 MW ICRF. This result demonstrates the progress of physics and technology studies on EAST, and will benefit the physics basis for steady state operation of ITER and CFETR.
Dynamic relaxation of a levitated nanoparticle from a non-equilibrium steady state.
Gieseler, Jan; Quidant, Romain; Dellago, Christoph; Novotny, Lukas
2014-05-01
Fluctuation theorems are a generalization of thermodynamics on small scales and provide the tools to characterize the fluctuations of thermodynamic quantities in non-equilibrium nanoscale systems. They are particularly important for understanding irreversibility and the second law in fundamental chemical and biological processes that are actively driven, thus operating far from thermal equilibrium. Here, we apply the framework of fluctuation theorems to investigate the important case of a system relaxing from a non-equilibrium state towards equilibrium. Using a vacuum-trapped nanoparticle, we demonstrate experimentally the validity of a fluctuation theorem for the relative entropy change occurring during relaxation from a non-equilibrium steady state. The platform established here allows non-equilibrium fluctuation theorems to be studied experimentally for arbitrary steady states and can be extended to investigate quantum fluctuation theorems as well as systems that do not obey detailed balance.
Steady-State Dynamic Behavior of a Flexible Rotor With Auxiliary Support From a Clearance Bearing
NASA Technical Reports Server (NTRS)
Xie, Huajun; Flowers, George T.; Feng, Li; Lawrence, Charles T.
1996-01-01
This paper investigates the steady-state responses of a rotor system supported by auxiliary bearings in which there is a clearance between the rotor and the inner race of the bearing. A simulation model based upon the rotor of a production jet engine is developed and its steady-state behavior is explored over a wide range of operating conditions for various parametric configurations. Specifically, the influence of rotor imbalance, clearance, support stiffness and damping is studied. Bifurcation diagrams are used as a tool to examine the dynamic behavior of this system as a function of the afore mentioned parameters. The harmonic balance method is also employed for synchronous response cases. The observed dynamical responses is discussed and some insights into the behavior of such systems are presented.
Steady-state bumpless transfer under controller uncertainty using the state/output feedback topology
Zheng, K.; Lee, A.H.; Bentsman, J.; Taft, C.W.
2006-01-15
Linear quadratic (LQ) bumpless transfer design introduced recently by Turner and Walker gives a very convenient and straightforward computational procedure for the steady-state bumpless transfer operator synthesis. It is, however, found to be incapable of providing convergence of the output of the offline controller to that of the online controller in several industrial applications, producing bumps in the plant output in the wake of controller transfer. An examination of this phenomenon reveals that the applications in question are characterized by a significant mismatch, further referred to as controller uncertainty, between the dynamics of the implemented controllers and their models used in the transfer operator computation. To address this problem, while retaining the convenience of the Turner and Walker design, a novel state/output feedback bumpless transfer topology is introduced that employs the nominal state of the offline controller and, through the use of an additional controller/model mismatch compensator, also the offline controller output. A corresponding steady-state bumpless transfer design procedure along with the supporting theory is developed for a large class of systems. Due to these features, it is demonstrated to solve a long-standing problem of high-quality steady-state bumpless transfer from the industry standard low-order nonlinear multiloop PID-based controllers to the modern multiinput-multioutput (MIMO) robust controllers in the megawatt/throttle pressure control of a typical coal-fired boiler/turbine unit.
Extending Molecular Theory to Steady-State Diffusing Systems
FRINK,LAURA J. D.; SALINGER,ANDREW G.; THOMPSON,AIDAN P.
1999-10-22
Predicting the properties of nonequilibrium systems from molecular simulations is a growing area of interest. One important class of problems involves steady state diffusion. To study these cases, a grand canonical molecular dynamics approach has been developed by Heffelfinger and van Swol [J. Chem. Phys., 101, 5274 (1994)]. With this method, the flux of particles, the chemical potential gradients, and density gradients can all be measured in the simulation. In this paper, we present a complementary approach that couples a nonlocal density functional theory (DFT) with a transport equation describing steady-state flux of the particles. We compare transport-DFT predictions to GCMD results for a variety of ideal (color diffusion), and nonideal (uphill diffusion and convective transport) systems. In all cases excellent agreement between transport-DFT and GCMD calculations is obtained with diffusion coefficients that are invariant with respect to density and external fields.
Multiplying steady-state culture in multi-reactor system.
Erm, Sten; Adamberg, Kaarel; Vilu, Raivo
2014-11-01
Cultivation of microorganisms in batch experiments is fast and economical but the conditions therein change constantly, rendering quantitative data interpretation difficult. By using chemostat with controlled environmental conditions the physiological state of microorganisms is fixed; however, the unavoidable stabilization phase makes continuous methods resource consuming. Material can be spared by using micro scale devices, which however have limited analysis and process control capabilities. Described herein are a method and a system combining the high throughput of batch with the controlled environment of continuous cultivations. Microorganisms were prepared in one bioreactor followed by culture distribution into a network of bioreactors and continuation of independent steady state experiments therein. Accelerostat cultivation with statistical analysis of growth parameters demonstrated non-compromised physiological state following distribution, thus the method effectively multiplied steady state culture of microorganisms. The theoretical efficiency of the system was evaluated in inhibitory compound analysis using repeated chemostat to chemostat transfers.
Optimal Control of Transitions between Nonequilibrium Steady States
Zulkowski, Patrick R.; Sivak, David A.; DeWeese, Michael R.
2013-01-01
Biological systems fundamentally exist out of equilibrium in order to preserve organized structures and processes. Many changing cellular conditions can be represented as transitions between nonequilibrium steady states, and organisms have an interest in optimizing such transitions. Using the Hatano-Sasa Y-value, we extend a recently developed geometrical framework for determining optimal protocols so that it can be applied to systems driven from nonequilibrium steady states. We calculate and numerically verify optimal protocols for a colloidal particle dragged through solution by a translating optical trap with two controllable parameters. We offer experimental predictions, specifically that optimal protocols are significantly less costly than naive ones. Optimal protocols similar to these may ultimately point to design principles for biological energy transduction systems and guide the design of artificial molecular machines. PMID:24386112
Hydrodynamics of stratified epithelium: Steady state and linearized dynamics
NASA Astrophysics Data System (ADS)
Yeh, Wei-Ting; Chen, Hsuan-Yi
2016-05-01
A theoretical model for stratified epithelium is presented. The viscoelastic properties of the tissue are assumed to be dependent on the spatial distribution of proliferative and differentiated cells. Based on this assumption, a hydrodynamic description of tissue dynamics at the long-wavelength, long-time limit is developed, and the analysis reveals important insights into the dynamics of an epithelium close to its steady state. When the proliferative cells occupy a thin region close to the basal membrane, the relaxation rate towards the steady state is enhanced by cell division and cell apoptosis. On the other hand, when the region where proliferative cells reside becomes sufficiently thick, a flow induced by cell apoptosis close to the apical surface enhances small perturbations. This destabilizing mechanism is general for continuous self-renewal multilayered tissues; it could be related to the origin of certain tissue morphology, tumor growth, and the development pattern.
Nonequilibrium Steady States of a Stochastic Model System.
NASA Astrophysics Data System (ADS)
Zhang, Qiwei
We study the nonequilibrium steady state of a stochastic lattice gas model, originally proposed by Katz, Lebowitz and Spohn (Phys. Rev. B 28: 1655 (1983)). Firstly, we solve the model on some small lattices exactly in order to see the general dependence of the steady state upon different parameters of the model. Nextly, we derive some analytical results for infinite lattice systems by taking some suitable limits. We then present some renormalization group results for the continuum version of the model via field theoretical techniques, the supersymmetry of the critical dynamics in zero field is also explored. Finally, we report some very recent 3-D Monte Carlo simulation results, which have been obtained by applying Multi-Spin-Coding techniques on a CDC vector supercomputer - Cyber 205 at John von Neumann Center.
Turnover of messenger RNA: Polysome statistics beyond the steady state
NASA Astrophysics Data System (ADS)
Valleriani, A.; Ignatova, Z.; Nagar, A.; Lipowsky, R.
2010-03-01
The interplay between turnover or degradation and ribosome loading of messenger RNA (mRNA) is studied theoretically using a stochastic model that is motivated by recent experimental results. Random mRNA degradation affects the statistics of polysomes, i.e., the statistics of the number of ribosomes per mRNA as extracted from cells. Since ribosome loading of newly created mRNA chains requires some time to reach steady state, a fraction of the extracted mRNA/ribosome complexes does not represent steady state conditions. As a consequence, the mean ribosome density obtained from the extracted complexes is found to be inversely proportional to the mRNA length. On the other hand, the ribosome density profile shows an exponential decrease along the mRNA for prokaryotes and becomes uniform in eukaryotic cells.
Feedback-assisted extension of the tokamak operating space to low safety factor
Hanson, J. M. Bialek, J. M.; Navratil, G. A.; Olofsson, K. E. J.; Shiraki, D.; Turco, F.; Baruzzo, M.; Bolzonella, T.; Marrelli, L.; Martin, P.; Piovesan, P.; Piron, C.; Piron, L.; Terranova, D.; Zanca, P.; Hyatt, A. W.; Jackson, G. L.; La Haye, R. J.; Lanctot, M. J.; Strait, E. J.; and others
2014-07-15
Recent DIII-D and RFX-mod experiments have demonstrated stable tokamak operation at very low values of the edge safety factor q(a) near and below 2. The onset of n = 1 resistive wall mode (RWM) kink instabilities leads to a disruptive stability limit, encountered at q(a) = 2 (limiter plasmas) and q{sub 95} = 2 (divertor plasmas). However, passively stable operation can be attained for q(a) and q{sub 95} values as low as 2.2. RWM damping in the q(a) = 2 regime was measured using active MHD spectroscopy. Although consistent with theoretical predictions, the amplitude of the damped response does not increase significantly as the q(a) = 2 limit is approached, in contrast with damping measurements made approaching the pressure-driven RWM limit. Applying proportional gain magnetic feedback control of the n = 1 modes has resulted in stabilized operation with q{sub 95} values reaching as low as 1.9 in DIII-D and q(a) reaching 1.55 in RFX-mod. In addition to being consistent with the q(a) = 2 external kink mode stability limit, the unstable modes have growth rates on the order of the characteristic wall eddy-current decay timescale in both devices, and a dominant m = 2 poloidal structure that is consistent with ideal MHD predictions. The experiments contribute to validating MHD stability theory and demonstrate that a key tokamak stability limit can be overcome with feedback.
Analytic Steady-State Accuracy of a Spacecraft Attitude Estimator
NASA Technical Reports Server (NTRS)
Markley, F. Landis
2000-01-01
This paper extends Farrenkopf's analysis of a single-axis spacecraft attitude estimator using gyro and angle sensor data to include the angle output white noise of a rate-integrating gyro. Analytic expressions are derived for the steady-state pre-update and post-update angle and drift bias variances and for the state update equations. It is shown that only part of the state update resulting from the angle sensor measurement is propagated to future times.
The approach to steady state using homogeneous and Cartesian coordinates.
Gochberg, D F; Ding, Z
2013-01-01
Repeating an arbitrary sequence of RF pulses and magnetic field gradients will eventually lead to a steady-state condition in any magnetic resonance system. While numerical methods can quantify this trajectory, analytic analysis provides significantly more insight and a means for faster calculation. Recently, an analytic analysis using homogeneous coordinates was published. The current work further develops this line of thought and compares the relative merits of using a homogeneous or a Cartesian coordinate system.
Intense steady state neutron source. The CNR reactor
Difilippo, F.C.; Moon, R.M.; Gambill, W.R.; Moon, R.M.; Primm, R.T. III; West, C.D.
1986-01-01
The Center for Neutron Research (CNR) has been proposed in response to the needs - neutron flux, spectrum, and experimental facilities - that have been identified through workshops, studies, and discussions by the neutron-scattering, isotope, and materials irradiation research communities. The CNR is a major new experimental facility consisting of a reactor-based steady state neutron source of unprecedented flux, together with extensive facilities and instruments for neutron scattering, isotope production, materials irradiation, and other areas of research.
MUTATION RATES OF BACTERIA IN STEADY STATE POPULATIONS
Fox, Maurice S.
1955-01-01
The breeder and the chemostat have been used to measure mutation rates for two mutations under a variety of steady state growth conditions. These rates have been found to be higher in complex medium than in minimal (F) medium. The effects of changes in nutritional conditions on these high rates have been described. In addition, the mutation rates at short generation times, in complex medium, have been shown to decrease with increasing generation time. PMID:13271726
Steady state equivalence among autocatalytic peroxidase-oxidase reactions.
Méndez-González, José; Femat, Ricardo
2016-12-14
Peroxidase-oxidase is an enzymatic reaction that can exhibit dynamical scenarios such as bistability, sustained oscillations, and Shilnikov chaos. In this work, we apply the chemical reaction network theory approach to find kinetic constants such that the associated mass action kinetics ordinary differential equations induced by three four dimensional structurally different enzymatic reaction systems can support the same steady states for several chemical species despite differences in their chemical nature.
Steady state equivalence among autocatalytic peroxidase-oxidase reactions
NASA Astrophysics Data System (ADS)
Méndez-González, José; Femat, Ricardo
2016-12-01
Peroxidase-oxidase is an enzymatic reaction that can exhibit dynamical scenarios such as bistability, sustained oscillations, and Shilnikov chaos. In this work, we apply the chemical reaction network theory approach to find kinetic constants such that the associated mass action kinetics ordinary differential equations induced by three four dimensional structurally different enzymatic reaction systems can support the same steady states for several chemical species despite differences in their chemical nature.
A correspondence principle for steady-state wave problems
NASA Technical Reports Server (NTRS)
Schmerr, L. W.
1976-01-01
A correspondence principle was developed for treating the steady state propagation of waves from sources moving along a plane surface or interface. This new principle allows one to obtain, in a unified manner, explicit solutions for any source velocity. To illustrate the correspondence principle in a particular case, the problem of a load moving at an arbitrary constant velocity along the surface of an elastic half-space is considered.
Multiple Color Stimulus Induced Steady State Visual Evoked Potentials
2007-11-02
MULTIPLE COLOR STIMULUS INDUCED STEADY STATE VISUAL EVOKED POTENTIALS M. Cheng, X. Gao, S. Gao, D. Xu Institute of Biomedical Engineering...characteristics of high SNR and effectiveness in short-term identification of evoked responses. In most of the SSVEP experiments, single high...frequency stimuli are used. To characterize the complex rhythms in SSVEP, a new multiple color stimulus pattern is proposed in this paper. FFT and
Multiple steady states for characteristic initial value problems
NASA Technical Reports Server (NTRS)
Salas, M. D.; Abarbanel, S.; Gottlieb, D.
1984-01-01
The time dependent, isentropic, quasi-one-dimensional equations of gas dynamics and other model equations are considered under the constraint of characteristic boundary conditions. Analysis of the time evolution shows how different initial data may lead to different steady states and how seemingly anamolous behavior of the solution may be resolved. Numerical experimentation using time consistent explicit algorithms verifies the conclusions of the analysis. The use of implicit schemes with very large time steps leads to erroneous results.
Transition of unsteady flows of evaporation to steady state
NASA Astrophysics Data System (ADS)
d'Almeida, Amah
2008-07-01
We investigate the half-space problem of evaporation and condensation in the scope of discrete kinetic theory. Exact solutions are found to the boundary value problem and the initial boundary value problems of the flow in the half space for a discrete velocity model. The results are used to analyze the transition of the unsteady solutions towards steady states. To cite this article: A. d'Almeida, C. R. Mecanique 336 (2008).
Steady-state superradiance with alkaline-earth-metal atoms
Meiser, D.; Holland, M. J.
2010-03-15
Alkaline-earth-metal-like atoms with ultranarrow transitions open the door to a new regime of cavity quantum electrodynamics. That regime is characterized by a critical photon number that is many orders of magnitude smaller than what can be achieved in conventional systems. We show that it is possible to achieve superradiance in steady state with such systems. We discuss the basic underlying mechanisms as well as the key experimental requirements.
Steady state magnetic field configurations for the earth's magnetotail
NASA Technical Reports Server (NTRS)
Hau, L.-N.; Wolf, R. A.; Voigt, G.-H.; Wu, C. C.
1989-01-01
A two-dimensional, force-balance magnetic field model is presented. The theoretical existence of a steady state magnetic field configuration that is force-balanced and consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD is demonstrated. A numerical solution is obtained for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The results are consistent with the convection time sequences reported by Erickson (1985).
Adaptive control of unknown unstable steady states of dynamical systems.
Pyragas, K; Pyragas, V; Kiss, I Z; Hudson, J L
2004-08-01
A simple adaptive controller based on a low-pass filter to stabilize unstable steady states of dynamical systems is considered. The controller is reference-free; it does not require knowledge of the location of the fixed point in the phase space. A topological limitation similar to that of the delayed feedback controller is discussed. We show that the saddle-type steady states cannot be stabilized by using the conventional low-pass filter. The limitation can be overcome by using an unstable low-pass filter. The use of the controller is demonstrated for several physical models, including the pendulum driven by a constant torque, the Lorenz system, and an electrochemical oscillator. Linear and nonlinear analyses of the models are performed and the problem of the basins of attraction of the stabilized steady states is discussed. The robustness of the controller is demonstrated in experiments and numerical simulations with an electrochemical oscillator, the dissolution of nickel in sulfuric acid; a comparison of the effect of using direct and indirect variables in the control is made. With the use of the controller, all unstable phase-space objects are successfully reconstructed experimentally.
Cavitation modeling for steady-state CFD simulations
NASA Astrophysics Data System (ADS)
Hanimann, L.; Mangani, L.; Casartelli, E.; Widmer, M.
2016-11-01
Cavitation in hydraulic turbomachines is an important phenomenon to be considered for performance predictions. Correct analysis of the cavitation onset and its effect on the flow field while diminishing the pressure level need therefore to be investigated. Even if cavitation often appears as an unsteady phenomenon, the capability to compute it in a steady state formulation for the design and assessment phase in the product development process is very useful for the engineer. In the present paper the development and corresponding application of a steady state CFD solver is presented, based on the open source toolbox OpenFOAM®. In the first part a review of different cavitation models is presented. Adopting the mixture-type cavitation approach, various models are investigated and developed in a steady state CFD RANS solver. Particular attention is given to the coupling between cavitation and turbulence models as well as on the underlying numerical procedure, especially the integration in the pressure- correction step of pressure-based solvers, which plays an important role in the stability of the procedure. The performance of the proposed model is initially assessed on simple cases available in the open literature. In a second step results for different applications are presented, ranging from airfoils to pumps.
STEADY-STATE MODEL OF SOLAR WIND ELECTRONS REVISITED
Yoon, Peter H.; Kim, Sunjung; Choe, G. S.
2015-10-20
In a recent paper, Kim et al. put forth a steady-state model for the solar wind electrons. The model assumed local equilibrium between the halo electrons, characterized by an intermediate energy range, and the whistler-range fluctuations. The basic wave–particle interaction is assumed to be the cyclotron resonance. Similarly, it was assumed that a dynamical steady state is established between the highly energetic superhalo electrons and high-frequency Langmuir fluctuations. Comparisons with the measured solar wind electron velocity distribution function (VDF) during quiet times were also made, and reasonable agreements were obtained. In such a model, however, only the steady-state solution for the Fokker–Planck type of electron particle kinetic equation was considered. The present paper complements the previous analysis by considering both the steady-state particle and wave kinetic equations. It is shown that the model halo and superhalo electron VDFs, as well as the assumed wave intensity spectra for the whistler and Langmuir fluctuations, approximately satisfy the quasi-linear wave kinetic equations in an approximate sense, thus further validating the local equilibrium model constructed in the paper by Kim et al.
Steady state statistical correlations predict bistability in reaction motifs.
Chakravarty, Suchana; Barik, Debashis
2017-03-01
Various cellular decision making processes are regulated by bistable switches that take graded input signals and convert them to binary all-or-none responses. Traditionally, a bistable switch generated by a positive feedback loop is characterized either by a hysteretic signal response curve with two distinct signaling thresholds or by characterizing the bimodality of the response distribution in the bistable region. To identify the intrinsic bistability of a feedback regulated network, here we propose that bistability can be determined by correlating higher order moments and cumulants (≥2) of the joint steady state distributions of two components connected in a positive feedback loop. We performed stochastic simulations of four feedback regulated models with intrinsic bistability and we show that for a bistable switch with variation of the signal dose, the steady state variance vs. covariance adopts a signatory cusp-shaped curve. Further, we find that the (n + 1)th order cross-cumulant vs. nth order cross-cumulant adopts a closed loop structure for at least n = 3. We also propose that our method is capable of identifying systems without intrinsic bistability even though the system may show bimodality in the marginal response distribution. The proposed method can be used to analyze single cell protein data measured at steady state from experiments such as flow cytometry.
Addressable nanoelectrode membrane arrays: fabrication and steady-state behavior.
Zoski, Cynthia G; Yang, Nianjun; He, Peixin; Berdondini, Luca; Koudelka-Hep, Milena
2007-02-15
An addressable nanoelectrode membrane array (ANEMA) based on a Au-filled track-etched polycarbonate membrane was fabricated. The Au-filled membrane was secured to a lithographically fabricated addressable ultramicroelectrode (UME) array patterned with 25 regularly spaced (100 microm center to center spacing), 10 microm diameter recessed Pt UMEs to create 25 microregions of 10 microm diameter nanoelectrode ensembles (NEEs) on the membrane. The steady-state voltammetric behavior of 1.0 mM Ru(NH(3))(6)Cl(3) and 1.0 mM ferrocene methanol in 0.1 M KCl on each of the micro NEEs resulted in sigmoidal-shaped voltammograms which were reproducible across the ANEMA. This reproducibility of the steady-state current was attributed to the overlapping hemispherical diffusion layers at the Au-filled nanopores of each 10 microm diameter NEE of a ANEMA. The track-etched polycarbonate membranes were filled using a gold electroless deposition procedure into the 30 nm diameter pores in the membrane. Electrical connection between the Au-filled template array and the lithographic UME platform array was achieved by potentiostatic electrodeposition of Cu from an acidic copper solution into each of the 25 recessed Pt UMEs on the UME array platform. A multiplexer unit capable of addressing 64 individual micro NEEs on an ANEMA is described. ANEMAs have advantages of high reproducibility, facile fabrication, multitime reuse of lithographically fabricated UME arrays, and purely steady-state behavior.
Numerical computation of steady-state acoustic disturbances in flow
NASA Technical Reports Server (NTRS)
Watson, W. R.; Myers, M. K.
1992-01-01
Two time domain methods for computing two dimensional steady-state acoustic disturbances propagating through internal subsonic viscous flow fields in the presence of variable area are investigated. The first method solves the Navier-Stokes equations for the combined steady and acoustic field together and subtracts the steady flow to obtain the acoustic field. The second method solves a system of perturbation equations to obtain the acoustic disturbances, making use of a separate steady flow computation as input to the system. In each case the periodic steady-state acoustic fluctuations are obtained numerically on a supercomputer using a second order unsplit explicit MacCormack predictor-corrector method. Results show that the first method is not very effective for computing acoustic disturbances of even moderate amplitude. It appears that more accurate steady flow algorithms are required for this method to succeed. On the other hand, linear and nonlinear acoustic disturbances extracted from the perturbation approach are shown to exhibit expected behavior for the problems considered. It is also found that inflow boundary conditions for an equivalent uniform duct can be successfully applied to a nonuniform duct to obtain steady-state acoustic disturbances.
Nonequilibrium Steady State Thermodynamics and Fluctuations for Stochastic Systems
NASA Astrophysics Data System (ADS)
Taniguchi, Tooru; Cohen, E. G. D.
2008-02-01
We use the work done on and the heat removed from a system to maintain it in a nonequilibrium steady state for a thermodynamic-like description of such a system as well as of its fluctuations. Based on an extended Onsager-Machlup theory for nonequilibrium steady states we indicate two ambiguities, not present in an equilibrium state, in defining such work and heat: one due to a non-uniqueness of time-reversal procedures and another due to multiple possibilities to separate heat into work and an energy difference in nonequilibrium steady states. As a consequence, for such systems, the work and heat satisfy multiple versions of the first and second laws of thermodynamics as well as of their fluctuation theorems. Unique laws and relations appear only to be obtainable for concretely defined systems, using physical arguments to choose the relevant physical quantities. This is illustrated on a number of systems, including a Brownian particle in an electric field, a driven torsion pendulum, electric circuits and an energy transfer driven by a temperature difference.
Basin stability measure of different steady states in coupled oscillators
Rakshit, Sarbendu; Bera, Bidesh K.; Majhi, Soumen; Hens, Chittaranjan; Ghosh, Dibakar
2017-01-01
In this report, we investigate the stabilization of saddle fixed points in coupled oscillators where individual oscillators exhibit the saddle fixed points. The coupled oscillators may have two structurally different types of suppressed states, namely amplitude death and oscillation death. The stabilization of saddle equilibrium point refers to the amplitude death state where oscillations are ceased and all the oscillators converge to the single stable steady state via inverse pitchfork bifurcation. Due to multistability features of oscillation death states, linear stability theory fails to analyze the stability of such states analytically, so we quantify all the states by basin stability measurement which is an universal nonlocal nonlinear concept and it interplays with the volume of basins of attractions. We also observe multi-clustered oscillation death states in a random network and measure them using basin stability framework. To explore such phenomena we choose a network of coupled Duffing-Holmes and Lorenz oscillators which are interacting through mean-field coupling. We investigate how basin stability for different steady states depends on mean-field density and coupling strength. We also analytically derive stability conditions for different steady states and confirm by rigorous bifurcation analysis. PMID:28378760
The VERRUN and VERNAL software systems for steady-state visual evoked response experimentation
NASA Technical Reports Server (NTRS)
Levison, W. H.; Zacharias, G. L.
1984-01-01
Two digital computer programs were developed for use in experiments involving steady-state visual evoked response (VER): VERRUN, whose primary functions are to generate a sum-of-sines (SOS) stimulus and to digitize and store electro-cortical response; and VERNAL, which provides both time- and frequency-domain metrics of the evoked response. These programs were coded in FORTRAN for operation on the PDP-11/34, using the RSX-11 Operating System, and the PDP-11/23, using the RT-11 Operating System. Users' and programmers' guides to these programs are provided, and guidelines for model analysis of VER data are suggested.
Steady state thermal radiation analysis between the TOPAZ-II radiator and a heat exchanger
Maveety, J.G.; Wold, S.K.
1995-12-31
In this study the authors investigate the feasibility and efficiency of coupling a single-pass heat exchanger to the TOPAZ-II space power system operating at steady state conditions. A first and second law analysis was performed in order to determine the optimal operating conditions which minimize the pumping power and maximize the flow exergy of the working fluid. The results of this study show that (1) the space power system is basically unaffected by the addition of this heat exchanger and (2) as much as 60% of the availability is destroyed by irreversibilities while operating at optimal flow conditions.
Haaland, Ben; Min, Wanli; Qian, Peter Z. G.; Amemiya, Yasuo
2011-01-01
Temperature control for a large data center is both important and expensive. On the one hand, many of the components produce a great deal of heat, and on the other hand, many of the components require temperatures below a fairly low threshold for reliable operation. A statistical framework is proposed within which the behavior of a large cooling system can be modeled and forecast under both steady state and perturbations. This framework is based upon an extension of multivariate Gaussian autoregressive hidden Markov models (HMMs). The estimated parameters of the fitted model provide useful summaries of the overall behavior of and relationships within the cooling system. Predictions under system perturbations are useful for assessing potential changes and improvements to be made to the system. Many data centers have far more cooling capacity than necessary under sensible circumstances, thus resulting in energy inefficiencies. Using this model, predictions for system behavior after a particular component of the cooling system is shut down or reduced in cooling power can be generated. Steady-state predictions are also useful for facility monitors. System traces outside control boundaries flag a change in behavior to examine. The proposed model is fit to data from a group of air conditioners within an enterprise data center from the IT industry. The fitted model is examined, and a particular unit is found to be underutilized. Predictions generated for the system under the removal of that unit appear very reasonable. Steady-state system behavior also is predicted well. PMID:22076026
Arc plasma generator of atomic driver for steady-state negative ion source
Ivanov, A. A.; Belchenko, Yu. I.; Davydenko, V. I.; Ivanov, I. A.; Kolmogorov, V. V.; Listopad, A. A. Mishagin, V. V.; Shulzhenko, G. I.; Putvinsky, S. V.; Smirnov, A.
2014-02-15
The paper reviews the results of development of steady-state arc-discharge plasma generator with directly heated LaB{sub 6} cathode. This arc-discharge plasma generator produces a plasma jet which is to be converted into an atomic one after recombination on a metallic plate. The plate is electrically biased relative to the plasma in order to control the atom energies. Such an intensive jet of hydrogen atoms can be used in negative ion sources for effective production of negative ions on a cesiated surface of plasma grid. All elements of the plasma generator have an augmented water cooling to operate in long pulse mode or in steady state. The thermo-mechanical stresses and deformations of the most critical elements of the plasma generator were determined by simulations. Magnetic field inside the discharge chamber was optimized to reduce the local power loads. The first tests of the steady-state arc plasma generator prototype have performed in long-pulse mode.
Arc plasma generator of atomic driver for steady-state negative ion source.
Ivanov, A A; Belchenko, Yu I; Davydenko, V I; Ivanov, I A; Kolmogorov, V V; Listopad, A A; Mishagin, V V; Putvinsky, S V; Shulzhenko, G I; Smirnov, A
2014-02-01
The paper reviews the results of development of steady-state arc-discharge plasma generator with directly heated LaB6 cathode. This arc-discharge plasma generator produces a plasma jet which is to be converted into an atomic one after recombination on a metallic plate. The plate is electrically biased relative to the plasma in order to control the atom energies. Such an intensive jet of hydrogen atoms can be used in negative ion sources for effective production of negative ions on a cesiated surface of plasma grid. All elements of the plasma generator have an augmented water cooling to operate in long pulse mode or in steady state. The thermo-mechanical stresses and deformations of the most critical elements of the plasma generator were determined by simulations. Magnetic field inside the discharge chamber was optimized to reduce the local power loads. The first tests of the steady-state arc plasma generator prototype have performed in long-pulse mode.
Agarwalla, Bijay Kumar; Li, Baowen; Wang, Jian-Sheng
2012-05-01
We study the statistics of heat transferred in a given time interval t_{M}, through a finite harmonic chain, called the center, which is connected to two heat baths, the left (L) and the right (R), that are maintained at two temperatures. The center atoms are driven by external time-dependent forces. We calculate the cumulant generating function (CGF) for the heat transferred out of the left lead, Q_{L}, based on the two-time quantum measurement concept and using the nonequilibrium Green's function method. The CGF can be concisely expressed in terms of Green's functions of the center and an argument-shifted self-energy of the lead. The expression of the CGF is valid in both transient and steady-state regimes. We consider three initial conditions for the density operator and show numerically, for a one-atom junction, how their transient behaviors differ from each other but, finally, approach the same steady state, independent of the initial distributions. We also derive the CGF for the joint probability distribution P(Q_{L},Q_{R}), and discuss the correlations between Q_{L} and Q_{R}. We calculate the CGF for total entropy production in the reservoirs. In the steady state we explicitly show that the CGFs obey steady-state fluctuation theorems. We obtain classical results by taking ℏ→0. We also apply our method to the counting of the electron number and electron energy, for which the associated self-energy is obtained from the usual lead self-energy by multiplying a phase and shifting the contour time, respectively.
Steady-State and Pre-Steady-State Kinetic Analysis of Mycobacterium smegmatis Cysteine Ligase (MshC)
Fan, Fan; Luxenburger, Andreas; Painter, Gavin F.; Blanchard, John S
2008-01-01
Mycobacterium tuberculosis and many other members of the Actinomycetes family produce mycothiol, i.e., 1-D-myo-inosityl-2-(N-acetyl-L-cysteinyl)amido-2-deoxy-α-D-glucopyranoside (MSH or AcCys-GlcN-Ins), to act against oxidative and antibiotic stress. The biosynthesis of MSH is essential for cell growth, and has been proposed to proceed via a biosynthetic pathway involving four key enzymes, MshA-D. The MSH biosynthetic enzymes present potential targets for inhibitor design. With this as a long-term goal, we have carried out a kinetic and mechanistic characterization, using steady state and pre-steady state approaches, of the recombinant Mycobacterium smegmatis MshC. MshC catalyzes the ATP-dependent condensation of GlcN-Ins and cysteine to form Cys-GlcN-Ins. Initial velocity and inhibition studies show that the steady state kinetic mechanism of MshC is a Bi Uni Uni Bi Ping Pong mechanism, with ATP binding followed by cysteine binding, release of PPi, binding of GlcN-Ins, followed by the release of Cys-GlcN-Ins and AMP. The steady state kinetic parameters were determined to be: kcat equal to 3.15 s−1, and Km values of 1.8, 0.1, and 0.16 mM for ATP, cysteine, and GlcN-Ins, respectively. A stable bisubstrate analog, 5′-O-[N-(L-cysteinyl)sulfamonyl]adenosine, exhibits competitive inhibition versus ATP and non-competitive inhibition versus cysteine, with an inhibition constant of ~306 nM versus ATP. Single-turnover reactions of the first and second half reactions were determined using rapid quench techniques, giving rates of ~9.4 s−1 and ~5.2 s−1, respectively, consistent with the cysteinyl adenylate being a kinetically competent intermediate in the reaction by MshC. PMID:17848100
Experiments on steady state particle control in Tore Supra and DIII-D
Mioduszewski, P.K.; Hogan, J.T.; Owen, L.W.
1994-12-31
Particle control is playing an increasingly important role in tokamak plasma performance. The present paper discusses particle control of hydrogen/deuterium by wall pumping on graphite or carbonized surfaces, as well as by external exhaust with pumped limiters and pumped divertors. Wall pumping is ultimately a transient effect and by itself not suitable for steady state particle exhaust. Therefore, external exhaust techniques with pumped divertors and limiters are being developed. How wall pumping phenomena interact and correlate with these inherently steady state, external exhaust techniques, is not well known to date. In the present paper, the processes involved in wall pumping and in external pumping are investigated in an attempt to evaluate the effect of external exhaust on wall pumping. Some of the key elements of this analysis are: (1) charge-exchange fluxes to the wall play a crucial role in the core-wall particle dynamics, (2) the recycling fluxes of thermal molecules have a high probability of ionization in the scrape-off layer, (3) thermal particles originating from the wall, which are ionized within the scrape-off layer, can be directly exhausted, thus providing a direct path between wall and exhaust which can be used to control the wall inventory. This way, the wall can be kept in a continuous pumping state in the sense that it continuously absorbs energetic particles and releases thermal molecules which are then removed by the external exhaust mechanism. While most of the ingredients of this analysis have been observed individually before, the present evaluation is an attempt to correlate effects of wall recycling and external exhaust.
Scott, T.C.; Hill, C.G. Jr.; Amundson, C.H.
1985-01-01
Analysis of the steady-state behavior of immobilized ..beta..-galactosidase by integral reactor techniques has yielded a model which allows one to predict reactor performance under normal operating conditions. Values of the mechanistic rate constants for enzymatic hydrolysis of lactose were determined as a function of temperature by fitting the reactor model to experimental lactose conversion profiles. Use of this model along with the activity decay characteristics of the immobilized enzyme which have been presented in a previous publication could prove to be a useful tool in determining appropriate operating strategies for industrial applications of the immobilized enzyme catalyst. 18 refs., 5 figs., 6 tabs.
Mimicking Nonequilibrium Steady States with Time-Periodic Driving
NASA Astrophysics Data System (ADS)
Raz, O.; Subaşı, Y.; Jarzynski, C.
2016-04-01
Under static conditions, a system satisfying detailed balance generically relaxes to an equilibrium state in which there are no currents. To generate persistent currents, either detailed balance must be broken or the system must be driven in a time-dependent manner. A stationary system that violates detailed balance evolves to a nonequilibrium steady state (NESS) characterized by fixed currents. Conversely, a system that satisfies instantaneous detailed balance but is driven by the time-periodic variation of external parameters—also known as a stochastic pump (SP)—reaches a periodic state with nonvanishing currents. In both cases, these currents are maintained at the cost of entropy production. Are these two paradigmatic scenarios effectively equivalent? For discrete-state systems, we establish a mapping between nonequilibrium stationary states and stochastic pumps. Given a NESS characterized by a particular set of stationary probabilities, currents, and entropy production rates, we show how to construct a SP with exactly the same (time-averaged) values. The mapping works in the opposite direction as well. These results establish a proof of principle: They show that stochastic pumps are able to mimic the behavior of nonequilibrium steady states, and vice versa, within the theoretical framework of discrete-state stochastic thermodynamics. Nonequilibrium steady states and stochastic pumps are often used to model, respectively, biomolecular motors driven by chemical reactions and artificial molecular machines steered by the variation of external, macroscopic parameters. Our results loosely suggest that anything a biomolecular machine can do, an artificial molecular machine can do equally well. We illustrate this principle by showing that kinetic proofreading, a NESS mechanism that explains the low error rates in biochemical reactions, can be effectively mimicked by a constrained periodic driving.
Typical pure nonequilibrium steady states and irreversibility for quantum transport.
Monnai, Takaaki; Yuasa, Kazuya
2016-07-01
It is known that each single typical pure state in an energy shell of a large isolated quantum system well represents a thermal equilibrium state of the system. We show that such typicality holds also for nonequilibrium steady states (NESS's). We consider a small quantum system coupled to multiple infinite reservoirs. In the long run, the total system reaches a unique NESS. We identify a large Hilbert space from which pure states of the system are to be sampled randomly and show that the typical pure states well describe the NESS. We also point out that the irreversible relaxation to the unique NESS is important to the typicality of the pure NESS's.
Stabilizing unstable steady states using multiple delay feedback control.
Ahlborn, Alexander; Parlitz, Ulrich
2004-12-31
Feedback control with different and independent delay times is introduced and shown to be an efficient method for stabilizing fixed points (equilibria) of dynamical systems. In comparison to other delay based chaos control methods multiple delay feedback control is superior for controlling steady states and works also for relatively large delay times (sometimes unavoidable in experiments due to system dead times). To demonstrate this approach for stabilizing unstable fixed points we present numerical simulations of Chua's circuit and a successful experimental application for stabilizing a chaotic frequency doubled Nd-doped yttrium aluminum garnet laser.
Nonequilibrium steady-state circulation and heat dissipation functional.
Qian, H
2001-08-01
A nonequilibrium steady-state (NESS), different from an equilibrium, is sustained by circular balance rather than detailed balance. The circular fluxes are driven by energy input and heat dissipation, accompanied by a positive entropy production. Based on a Master equation formalism for NESS, we show the circulation is intimately related to the recently studied Gallavotti-Cohen symmetry of heat dissipation functional, which in turn suggests a Boltzmann's formulalike relation between rate constants and energy in NESS. Expanding this unifying view on NESS to diffusion is discussed.
Steady-State-Preserving Simulation of Genetic Regulatory Systems
Hou, Xilin
2017-01-01
A novel family of exponential Runge-Kutta (expRK) methods are designed incorporating the stable steady-state structure of genetic regulatory systems. A natural and convenient approach to constructing new expRK methods on the base of traditional RK methods is provided. In the numerical integration of the one-gene, two-gene, and p53-mdm2 regulatory systems, the new expRK methods are shown to be more accurate than their prototype RK methods. Moreover, for nonstiff genetic regulatory systems, the expRK methods are more efficient than some traditional exponential RK integrators in the scientific literature. PMID:28203268
Thermodynamic formalism and linear response theory for nonequilibrium steady states.
Speck, Thomas
2016-08-01
We study the linear response in systems driven away from thermal equilibrium into a nonequilibrium steady state with nonvanishing entropy production rate. A simple derivation of a general response formula is presented under the condition that the generating function describes a transformation that (to lowest order) preserves normalization and thus describes a physical stochastic process. For Markov processes we explicitly construct the conjugate quantities and discuss their relation with known response formulas. Emphasis is put on the formal analogy with thermodynamic potentials and some consequences are discussed.
Quantum-classical correspondence in steady states of nonadiabatic systems
Fujii, Mikiya; Yamashita, Koichi
2015-12-31
We first present nonadiabatic path integral which is exact formulation of quantum dynamics in nonadiabatic systems. Then, by applying the stationary phase approximations to the nonadiabatic path integral, a semiclassical quantization condition, i.e., quantum-classical correspondence, for steady states of nonadiabatic systems is presented as a nonadiabatic trace formula. The present quantum-classical correspondence indicates that a set of primitive hopping periodic orbits, which are invariant under time evolution in the phase space of the slow degree of freedom, should be quantized. The semiclassical quantization is then applied to a simple nonadiabatic model and accurately reproduces exact quantum energy levels.
Steady State Creep of Zirconium at High and Intermediate Temperatures
Rosen, R.S.; Hayes, T.A.
2000-04-08
Creep of zirconium and zirconium alloys has been labeled ''anomalous.'' Researchers often report that zirconium and its alloys never reach true steady state creep and have stress exponents that continuously change with stress and temperature. Many varied interpretations have been offered explaining the creep behavior of zirconium. Some have suggested that creep is diffusion controlled, while others maintain that creep is dislocation glide controlled. Cumulative zirconium creep data will be presented based on an extensive literature review. An interpretation of results will be presented and compared to previous interpretations.
Steady-State Solution of a Flexible Wing
NASA Technical Reports Server (NTRS)
Karkehabadi, Reza; Chandra, Suresh; Krishnamurthy, Ramesh
1997-01-01
A fluid-structure interaction code, ENSAERO, has been used to compute the aerodynamic loads on a swept-tapered wing. The code has the capability of using Euler or Navier-Stokes equations. Both options have been used and compared in the present paper. In the calculation of the steady-state solution, we are interested in knowing how the flexibility of the wing influences the lift coefficients. If the results of a flexible wing are not affected by the flexibility of the wing significantly, one could consider the wing to be rigid and reduce the problem from fluid-structure interaction to a fluid problem.
Steady-state grain growth in UO{sub 2}
Galinari, C.M.; Lameiras, F.S.
1998-06-05
The authors have observed steady-state grain growth in sintered UO{sub 2} pellets of nuclear purity at 2,003 K under H{sub 2}. The behavior of the grain size distribution at different instants is consistent with the grain growth model proposed by one of the authors. The total number of grains was estimated using the Saltykov`s method, and the evolution is in accordance with the model proposed by Rhines and Craig. The parabolic growth law was observed for the mean intercept length with n = 0.4.
Linear modeling of steady-state behavioral dynamics.
Palya, William L; Walter, Donald; Kessel, Robert; Lucke, Robert
2002-01-01
The observed steady-state behavioral dynamics supported by unsignaled periods of reinforcement within repeating 2,000-s trials were modeled with a linear transfer function. These experiments employed improved schedule forms and analytical methods to improve the precision of the measured transfer function, compared to previous work. The refinements include both the use of multiple reinforcement periods that improve spectral coverage and averaging of independently determined transfer functions. A linear analysis was then used to predict behavior observed for three different test schedules. The fidelity of these predictions was determined. PMID:11831782
NASA Technical Reports Server (NTRS)
Sargent, N. B.; Dustin, M. O.
1981-01-01
Steady state tests were run to characterize the system and component efficiencies over the complete speed-torque capabilities of the propulsion system in both motoring and regenerative modes of operation. The steady state data were obtained using a battery simulator to separate the effects on efficiency caused by changing battery state-of-charge and component temperature. Transient tests were performed to determine the energy profiles of the propulsion system operating over the SAE J227a driving schedules.
Steady-State ALPS for Real-Valued Problems
NASA Technical Reports Server (NTRS)
Hornby, Gregory S.
2009-01-01
The two objectives of this paper are to describe a steady-state version of the Age-Layered Population Structure (ALPS) Evolutionary Algorithm (EA) and to compare it against other GAs on real-valued problems. Motivation for this work comes from our previous success in demonstrating that a generational version of ALPS greatly improves search performance on a Genetic Programming problem. In making steady-state ALPS some modifications were made to the method for calculating age and the method for moving individuals up layers. To demonstrate that ALPS works well on real-valued problems we compare it against CMA-ES and Differential Evolution (DE) on five challenging, real-valued functions and on one real-world problem. While CMA-ES and DE outperform ALPS on the two unimodal test functions, ALPS is much better on the three multimodal test problems and on the real-world problem. Further examination shows that, unlike the other GAs, ALPS maintains a genotypically diverse population throughout the entire search process. These findings strongly suggest that the ALPS paradigm is better able to avoid premature convergence then the other GAs.
Ecological Implications of Steady State and Nonsteady State Bioaccumulation Models.
McLeod, Anne M; Paterson, Gordon; Drouillard, Ken G; Haffner, G Douglas
2016-10-18
Accurate predictions on the bioaccumulation of persistent organic pollutants (POPs) are critical for hazard and ecosystem health assessments. Aquatic systems are influenced by multiple stressors including climate change and species invasions and it is important to be able to predict variability in POP concentrations in changing environments. Current steady state bioaccumulation models simplify POP bioaccumulation dynamics, assuming that pollutant uptake and elimination processes become balanced over an organism's lifespan. These models do not consider the complexity of dynamic variables such as temperature and growth rates which are known to have the potential to regulate bioaccumulation in aquatic organisms. We contrast a steady state (SS) bioaccumulation model with a dynamic nonsteady state (NSS) model and a no elimination (NE) model. We demonstrate that both the NSS and the NE models are superior at predicting both average concentrations as well as variation in POPs among individuals. This comparison demonstrates that temporal drivers, such as environmental fluctuations in temperature, growth dynamics, and modified food-web structure strongly determine contaminant concentrations and variability in a changing environment. These results support the recommendation of the future development of more dynamic, nonsteady state bioaccumulation models to predict hazard and risk assessments in the Anthropocene.
Steady-state mushy layers: Experiments and theory
NASA Astrophysics Data System (ADS)
Peppin, S.; Aussillous, P.; Huppert, Herbert E.; Grae Worster, M.
2006-11-01
A new facility has been developed to investigate mushy layers formed during the steady directional solidification of transparent aqueous solutions in a quasi-two-dimensional system. Experiments have been conducted on NaCl--H20 solutions by translating a Hele-Shaw cell at prescribed rates between fixed heat exchangers providing a temperature gradient of approximately 1,^0C/mm. Ice formed the primary solid phase and the dense residual fluid ponded within the mushy layer at the base of the system. Mathematical predictions of the steady-state temperature profile and mushy layer thickness as functions of freezing rate are in excellent agreement with experimental results. Experiments have also been performed on aqueous NH4Cl solutions, with the salt forming the primary solid phase, yielding buoyancy-driven convection in the mushy layer and the development of chimneys. The lifetime of the chimneys increased with decreasing freezing rate; however, no steady-state chimneys have been observed. Rather, a convecting chimney appears to deplete the surrounding solution and is eventually extinguished. At freezing rates larger than about 5.5,μm/s a uniform mushy layer develops with no chimneys. However, at rates larger than about 5,μm/s a second mode of behaviour is observed in which the mushy layer is thin and there is significant supercooling and nucleation above it. There is hysteresis between the two modes.
Integrated stoichiometric, thermodynamic and kinetic modelling of steady state metabolism
Fleming, R.M.T.; Thiele, I.; Provan, G.; Nasheuer, H.P.
2010-01-01
The quantitative analysis of biochemical reactions and metabolites is at frontier of biological sciences. The recent availability of high-throughput technology data sets in biology has paved the way for new modelling approaches at various levels of complexity including the metabolome of a cell or an organism. Understanding the metabolism of a single cell and multi-cell organism will provide the knowledge for the rational design of growth conditions to produce commercially valuable reagents in biotechnology. Here, we demonstrate how equations representing steady state mass conservation, energy conservation, the second law of thermodynamics, and reversible enzyme kinetics can be formulated as a single system of linear equalities and inequalities, in addition to linear equalities on exponential variables. Even though the feasible set is non-convex, the reformulation is exact and amenable to large-scale numerical analysis, a prerequisite for computationally feasible genome scale modelling. Integrating flux, concentration and kinetic variables in a unified constraint-based formulation is aimed at increasing the quantitative predictive capacity of flux balance analysis. Incorporation of experimental and theoretical bounds on thermodynamic and kinetic variables ensures that the predicted steady state fluxes are both thermodynamically and biochemically feasible. The resulting in silico predictions are tested against fluxomic data for central metabolism in E. coli and compare favourably with in silico prediction by flux balance analysis. PMID:20230840
Zonal Flow Growth Rates: Modulational Instability vs Statistical Steady States.
NASA Astrophysics Data System (ADS)
Krommes, J. A.; Kolesnikov, R. A.
2002-11-01
The nonlinear growth rate of zonal flows has been the subject of various investigations. The calculations can be grouped into two major classes: those based on modulational instability of a fixed pump wave;(L. Chen et al., Phys. Plasmas 7), 3129 (2000); P. N. Guzdar et al., Phys. Rev. Lett. 87, 015001 (2001); C. N. Lashmore-Davies et al., Phys. Plasmas 8, 5121 (2001). and those employing statistical formalism to describe a self-consistent, energy-conserving steady state.(J. A. Krommes and C.--B. Kim, Phys. Rev. E 62), 8508 (2000), and references therein. The results from these two approaches do not necessarily agree either in their dependence on parameters like the plasma pressure β, on the threshold for instability, or even, in some cases, on the sign. The reasons for such disagreements are isolated, and it is shown to what extent the steady-state statistical approach can be reconciled with a generic modulational instability calculation. Generalizations of the statistical formalism to the multifield systems appropriate for finite β are described. Specific calculations based on model systems are used to illustrate the general arguments.
Steady States and Universal Conductance in a Quenched Luttinger Model
NASA Astrophysics Data System (ADS)
Langmann, Edwin; Lebowitz, Joel L.; Mastropietro, Vieri; Moosavi, Per
2017-01-01
We obtain exact analytical results for the evolution of a 1+1-dimensional Luttinger model prepared in a domain wall initial state, i.e., a state with different densities on its left and right sides. Such an initial state is modeled as the ground state of a translation invariant Luttinger Hamiltonian {H_{λ}} with short range non-local interaction and different chemical potentials to the left and right of the origin. The system evolves for time t > 0 via a Hamiltonian {H_{λ'}} which differs from {H_{λ}} by the strength of the interaction. Asymptotically in time, as {t to ∞}, after taking the thermodynamic limit, the system approaches a translation invariant steady state. This final steady state carries a current I and has an effective chemical potential difference {μ+ - μ-} between right- (+) and left- (-) moving fermions obtained from the two-point correlation function. Both I and {μ+ - μ-} depend on {λ} and {λ'}. Only for the case {λ = λ' = 0} does {μ+ - μ-} equal the difference in the initial left and right chemical potentials. Nevertheless, the Landauer conductance for the final state, {G = I/(μ+ - μ-)}, has a universal value equal to the conductance quantum {e^2/h} for the spinless case.
Modeling steady-state methanogenic degradation of phenols in groundwater
Bekins, Barbara A.; Godsy, E. Michael; Goerlitz, Donald F.
1993-01-01
Field and microcosm observations of methanogenic phenolic compound degradation indicate that Monod kinetics governs the substrate disappearance but overestimates the observed biomass. In this paper we present modeling results from an ongoing multidisciplinary study of methanogenic biodegradation of phenolic compounds in a sand and gravel aquifer contaminated by chemicals and wastes used in wood treatment. Field disappearance rates of four phenols match those determined in batch microcosm studies previously performed by E.M. Godsy and coworkers. The degradation process appears to be at steady-state because even after a sustained influx over several decades, the contaminants still are disappearing in transport downgradient. The existence of a steady-state degradation profile of each substrate together with a low biomass density in the aquifer indicate that the bacteria population is exhibiting no net growth. This may be due to the oligotrophic nature of the biomass population in which utilization and growth are approximately independent of concentration for most of the concentration range. Thus a constant growth rate should exist over much of the contaminated area which may in turn be balanced by an unusually high decay or maintenance rate due to hostile conditions or predation.
Steady-state wear and friction in boundary lubrication studies
NASA Technical Reports Server (NTRS)
Loomis, W. R.; Jones, W. R., Jr.
1980-01-01
A friction and wear study was made at 20 C to obtain improved reproducibility and reliability in boundary lubrication testing. Ester-base and C-ether-base fluids were used to lubricate a pure iron rider in sliding contact with a rotating M-50 steel disk in a friction and wear apparatus. Conditions included loads of 1/2 and 1 kg and sliding velocities of 3.6 to 18.2 m/min in a dry air atmosphere and stepwise time intervals from 1 to 250 min for wear measurements. The wear rate results were compared with those from previous studies where a single 25 min test period was used. Satisfactory test conditions for studying friction and wear in boundary lubrication for this apparatus were found to be 1 kg load; sliding velocities of 7.1 to 9.1 m/min (50 rpm disk speed); and use of a time stepwise test procedure. Highly reproducible steady-state wear rates and steady-state friction coefficients were determined under boundary conditions. Wear rates and coefficients of friction were constant following initially high values during run-in periods.
2005-12-01
choice of a steady state control is completely independent from the choice of a stabilizing control law. This separation is key for the methods we will...develop for steady state optimization in later sections. Combining the steady state with the stabilizing control , we can express the control law as u...for stabilizing control and optimization methods for steady state control, both unconstrained and constrained, we were able to produce promising results
40 CFR 86.1362-2010 - Steady-state testing with a ramped-modal cycle.
Code of Federal Regulations, 2012 CFR
2012-07-01
... Torque(percent) 2 3 1a Steady-state 170 Warm Idle 0 1b Transition 20 Linear Transition Linear Transition. 2a Steady-state 173 A 100 2b Transition 20 Linear Transition Linear Transition. 3a Steady-state 219 B 50 3b Transition 20 B Linear Transition. 4a Steady-state 217 B 75 4b Transition 20 Linear...
Tabiś, Bolesław; Skoneczny, Szymon
2013-07-20
Nonlinear properties of a bioreactor with a developed microbiological predator-prey food chain are discussed. The presence of the predator microorganism completely changes the position and stability of the stationary states. A wide range of unstable steady states appears, associated with high amplitude oscillations of the state variables. Without automatic control such a system can only operate in transient states, with the yield undergoing periodic changes following the dynamics of the stable limit cycle. Technologically, this is undesirable. It has been shown that the oscillations can be removed by employing continuous P or PI controllers. Moreover, with a PI-controller, the predator can be eliminated from the system.
40 CFR Appendix II to Part 1042 - Steady-State Duty Cycles
Code of Federal Regulations, 2014 CFR
2014-07-01
...%. 1bTransition 20 Linear transition Linear transition in torque. 2aSteady-state 166 63% 25%. 2bTransition 20 Linear transition Linear transition in torque. 3aSteady-state 570 91% 75%. 3bTransition 20 Linear transition Linear transition in torque. 4aSteady-state 175 80% 50%. 1 Speed terms are defined...
40 CFR Appendix II to Part 1042 - Steady-State Duty Cycles
Code of Federal Regulations, 2010 CFR
2010-07-01
...%. 1bTransition 20 Linear transition Linear transition in torque. 2aSteady-state 166 63% 25%. 2bTransition 20 Linear transition Linear transition in torque. 3aSteady-state 570 91% 75%. 3bTransition 20 Linear transition Linear transition in torque. 4aSteady-state 175 80% 50%. 1 Speed terms are defined...
40 CFR Appendix II to Part 1042 - Steady-State Duty Cycles
Code of Federal Regulations, 2013 CFR
2013-07-01
...%. 1bTransition 20 Linear transition Linear transition in torque. 2aSteady-state 166 63% 25%. 2bTransition 20 Linear transition Linear transition in torque. 3aSteady-state 570 91% 75%. 3bTransition 20 Linear transition Linear transition in torque. 4aSteady-state 175 80% 50%. 1 Speed terms are defined...
Son of IXION: A Steady State Centrifugally Confined Plasma for Fusion*
NASA Astrophysics Data System (ADS)
Hassam, Adil
1996-11-01
A magnetic confinement scheme in which the inertial, u.grad(u), forces effect parallel confinement is proposed. The basic geometry is mirror-like as far as the poloidal field goes or, more simply, multipole (FM-1) type. The rotation is toroidal in this geometry. A supersonic rotation can effect complete parallel confinement, with the usual magnetic mirror force rendered irrelevant. The rotation shear, in addition, aids in the suppression of the flute mode. This suppression is not complete which indicates the addition of a toroidal field, at maximum of the order of the poloidal field. We show that at rotation in excess of Mach 3, the parallel particle and heat losses can be minimized to below the Lawson breakeven point. The crossfield transport can be expected to be better than tokamaks on account of the large velocity shear. Other advantages of the scheme are that it is steady state and disruption free. An exploratory experiment that tests equilibrium, parallel detachment, and MHD stability is proposed. The concept resembles earlier (Geneva, 1958) experiments on "homopolar generators" and a mirror configuration called IXION. Ixion, Greek mythological king, was forever strapped to a rotating, flaming wheel. *Work supported by DOE
Microchemostat array with small-volume fraction replenishment for steady-state microbial culture.
Park, Jaewon; Wu, Jianzhang; Polymenis, Michael; Han, Arum
2013-11-07
A chemostat is a bioreactor in which microorganisms can be cultured at steady-state by controlling the rate of culture medium inflow and waste outflow, thus maintaining media composition over time. Even though many microbial studies could greatly benefit from studying microbes in steady-state conditions, high instrument cost, complexity, and large reagent consumption hamper the routine use of chemostats. Microfluidic-based chemostats (i.e. microchemostats) can operate with significantly smaller reagent consumption while providing accurate chemostatic conditions at orders of magnitude lower cost compared to conventional chemostats. Also, microchemostats have the potential to significantly increase the throughput by integrating arrays of microchemostats. We present a microchemostat array with a unique two-depth culture chamber design that enables small-volume fraction replenishment of culture medium as low as 1% per replenishment cycle in a 250 nl volume. A system having an array of 8 microchemostats on a 40 × 60 mm(2) footprint could be automatically operated in parallel by a single controller unit as a demonstration for potential high throughput microbial studies. The model organism, Saccharomyces cerevisiae, successfully reached a stable steady-state of different cell densities as a demonstration of the chemostatic functionality by programming the dilution rates. Chemostatic functionality of the system was further confirmed by quantifying the budding index as a function of dilution rate, a strong indicator of growth-dependent cell division. In addition, the small-volume fraction replenishment feature minimized the cell density fluctuation during the culture. The developed system provides a robust, low-cost, and higher throughput solution to furthering studies in microbial physiology.
CONTROL OF MHD STABILITY IN DIII-D ADVANCED TOKAMAK DISCHARGES
STRAIT,EJ; BIALEK,J; CHANCE,MS; CHU,MS; EDGELL,DH; FERRON,JR; GREENFIELD,CM; GAROFALO,AM; HUMPHREYS,DA; JACKSON,GL; JAYAKUMAR,RJ; JERNIGAN,TC; KIM,JS; LA HAYE,RJ; LAO,LL; LUCE,TC; MAKOWSKI,MA; MURAKAMI,M; NAVRATIL,GA; OKABAYASHI,M; PETTY,CC; REIMERDES,H; SCOVILLE,JT; TURNBULL,AD; WADE,MR; WALKER,ML; WHYTE,DG; DIII-D TEAM
2003-06-01
OAK-B135 Advanced tokamak research in DIII-D seeks to optimize the tokamak approach for fusion energy production, leading to a compact, steady state power source. High power density implies operation at high toroidal beta, {beta}{sub T}=
2{micro}{sub 0}/B{sub T}{sup 2}, since fusion power density increases roughly as the square of the plasma pressure. Steady-state operation with low recirculating power for current drive implies operation at high poloidal beta, {beta}{sub P} =
2{micro}{sub 0}/{sup 2}, in order to maximize the fraction of self-generated bootstrap current. Together, these lead to a requirement of operation at high normalized beta, {beta}{sub N} = {beta}{sub T}(aB/I), since {beta}{sub P}{beta}{sub T} {approx} 25[(1+{kappa}{sup 2})/2] ({beta}{sub N}/100){sup 2}. Plasmas with high normalized beta are likely to operate near one or more stability limits, so control of MHD stability in such plasmas is crucial.
Steady-state dynamic behavior of an auxiliary bearing supported rotor system
NASA Technical Reports Server (NTRS)
Xie, Huajun; Flowers, George T.; Lawrence, Charles
1995-01-01
This paper investigates the steady-state responses of a rotor system supported by auxiliary bearings in which there is a clearance between the rotor and the inner race of the bearing. A simulation model based upon the rotor of a production jet engine is developed and its steady-state behavior is explored over a wide range of operating conditions for various parametric configurations. Specifically, the influence of rotor imbalance, support stiffness, and damping is studied. It is found that imbalance may change the rotor responses dramatically in terms of frequency contents at certain operating speeds. Subharmonic responses of 2nd order through 10th order are all observed except the 9th order. Chaotic phenomenon is also observed. Jump phenomena (or double-valued responses) of both hard-spring type and soft-spring type are shown to occur at low operating speeds for systems with low auxiliary bearing damping or large clearance even with relatively small imbalance. The effect of friction between the shaft and the inner race of the bearing is also discussed.
[Auditory steady-state responses--the state of art].
Szymańska, Anna; Gryczyński, Maciej; Pajor, Anna
2010-01-01
The auditory steady-state responses (ASSR) is quite a new method of electrophysiological threshold estimation with no clinical standards. It was the aim of this study to review practical and theoretical thesis of ASSR and mention recent recommendations and achievements of this technique. The most common application of ASSR is diagnosis of hearing loss in children together with ABR test. In this paper we mentioned information about influence of physiological factors (age, sex, state of arousal, handedness) and type of recording technique (electrodes placement, air and bone stimulation, occlusion effect, amplitude and frequency stimulation, multiple or single frequency stimulation, dichotic and monotic recording technique and type of hearing loss) on ASSR. We conclude that putting ASSR in clinical use as an standardized method it is necessary to do research with numerous groups of patients using the same equipment and parameters of tests.
Characterization of a class of stellarator steady states
Weitzner, Harold
2011-01-15
A stellarator steady state is obtained for a specific class of magnetic fields by a formal expansion in the small Larmor radius parameters of the coupled ion-electron Fokker-Planck equations. A system of relatively simple ordinary differential equations is given to determine the plasma profile functions, the number density, the temperature, and the electrostatic potential. A particular low collisionality ordering is used. The magnetic field is assumed to have stellarator symmetry of N periods in the toroidal direction and is approximated by a closed magnetic line configuration with rotational transform N/R. The magnetic field is nearly quasisymmetric. The chosen magnetic field also includes a small additional component leading to a configuration without closed lines or closed flux surfaces. The theoretical logic behind this choice of magnetic fields is also presented.
Steady-state magma discharge at Etna 1971-81
NASA Technical Reports Server (NTRS)
Wadge, G.; Guest, J. E.
1981-01-01
Throughout the past decade Mount Etna has been in almost continuous activity and even during periods of repose incandescent lava has often been visible in at least one of the summit vents. Using observations by Italian, British and French volcanological teams, the volumes of lava produced by each eruption from 1971 to July 1981 have been estimated. The computed output of magma for this period approximates to a rate of 0.7 cu m/s. This is compared with the output rate estimates for Etna's historic past. The steady-state nature of the output during the past decade has implications for the interpretation of the volcano's internal plumbing and the petrology of its lavas, and the assumption that this state will be maintained allows a discussion of the timing and magnitude of future eruptions.
Extending the definition of entropy to nonequilibrium steady states
Ruelle, David P.
2003-01-01
We study the nonequilibrium statistical mechanics of a finite classical system subjected to nongradient forces ξ and maintained at fixed kinetic energy (Hoover–Evans isokinetic thermostat). We assume that the microscopic dynamics is sufficiently chaotic (Gallavotti–Cohen chaotic hypothesis) and that there is a natural nonequilibrium steady-state ρξ. When ξ is replaced by ξ + δξ, one can compute the change δρ of ρξ (linear response) and define an entropy change δS based on energy considerations. When ξ is varied around a loop, the total change of S need not vanish: Outside of equilibrium the entropy has curvature. However, at equilibrium (i.e., if ξ is a gradient) we show that the curvature is zero, and that the entropy S(ξ + δξ) near equilibrium is well defined to second order in δξ. PMID:12629215
Extending the definition of entropy to nonequilibrium steady states.
Ruelle, David P
2003-03-18
We study the nonequilibrium statistical mechanics of a finite classical system subjected to nongradient forces xi and maintained at fixed kinetic energy (Hoover-Evans isokinetic thermostat). We assume that the microscopic dynamics is sufficiently chaotic (Gallavotti-Cohen chaotic hypothesis) and that there is a natural nonequilibrium steady-state rho(xi). When xi is replaced by xi + deltaxi, one can compute the change deltarho of rho(xi) (linear response) and define an entropy change deltaS based on energy considerations. When xi is varied around a loop, the total change of S need not vanish: Outside of equilibrium the entropy has curvature. However, at equilibrium (i.e., if xi is a gradient) we show that the curvature is zero, and that the entropy S(xi + deltaxi) near equilibrium is well defined to second order in deltaxi.
Steady state asymmetric planetary electrical induction. [by solar wind
NASA Technical Reports Server (NTRS)
Horning, B. L.; Schubert, G.
1974-01-01
An analytic solution is presented for the steady state electric and magnetic fields induced by the motional electric field of the solar wind in the atmosphere or interior of a planet that is asymmetrically surrounded by solar wind plasma. The electrically conducting ionosphere or interior must be in direct electrical contact with the solar wind over the day side of the planet. The conducting region of the planet is modeled by a sphere or a spherical shell of arbitrarily stratified electrical conductivity. A monoconducting cylindrical cavity is assumed to extend downstream on the night side of the planet. The solar wind is assumed to be highly conducting so that the induced fields are confined to the planet and cavity. Induced currents close as sheet currents at the solar wind-cavity and solar wind-planet interfaces. Numerical evaluations of the analytic formulas are carried out for a uniformly conducting spherical model.
Steady-state mushy layers: experiments and theory
NASA Astrophysics Data System (ADS)
Peppin, S. S. L.; Aussillous, P.; Huppert, Herbert E.; Grae Worster, M.
A new facility has been developed to investigate the directional solidification of transparent aqueous solutions forming mushy layers in a quasi-two-dimensional system. Experiments have been conducted on NaCl H_{2}O solutions by translating a Hele-Shaw cell at prescribed rates between fixed heat exchangers providing a temperature gradient of approximately 1 (°) C mm(-1) . The mush liquid interface remained planar at all freezing velocities larger than 8 umum s(-1) , while steepling occurred at lower velocities. No significant undercooling of the mush liquid interface was detected at freezing velocities up to 12 umum s(-1) . Mathematical predictions of the steady-state temperature profile and mushy-layer thickness as functions of freezing rate are in excellent agreement with experimental measurements.
Entropy Production and Non-Equilibrium Steady States
NASA Astrophysics Data System (ADS)
Suzuki, Masuo
2013-01-01
The long-term issue of entropy production in transport phenomena is solved by separating the symmetry of the non-equilibrium density matrix ρ(t) in the von Neumann equation, as ρ(t) = ρs(t) + ρa(t) with the symmetric part ρs(t) and antisymmetric part ρa(t). The irreversible entropy production (dS/dt)irr is given in M. Suzuki, Physica A 390(2011)1904 by (dS/dt)irr = Tr( {H}(dρ s{(t)/dt))}/T for the Hamiltonian {H} of the relevant system. The general formulation of the extended von Neumann equation with energy supply and heat extraction is reviewed from the author's paper (M. S.,Physica A391(2012)1074). irreversibility; entropy production; transport phenomena; electric conduction; thermal conduction; linear response; Kubo formula; steady state; non-equilibrium density matrix; energy supply; symmetry-separated von Neumann equation; unboundedness.
Steady-State Density Functional Theory for Finite Bias Conductances.
Stefanucci, G; Kurth, S
2015-12-09
In the framework of density functional theory, a formalism to describe electronic transport in the steady state is proposed which uses the density on the junction and the steady current as basic variables. We prove that, in a finite window around zero bias, there is a one-to-one map between the basic variables and both local potential on as well as bias across the junction. The resulting Kohn-Sham system features two exchange-correlation (xc) potentials, a local xc potential, and an xc contribution to the bias. For weakly coupled junctions the xc potentials exhibit steps in the density-current plane which are shown to be crucial to describe the Coulomb blockade diamonds. At small currents these steps emerge as the equilibrium xc discontinuity bifurcates. The formalism is applied to a model benzene junction, finding perfect agreement with the orthodox theory of Coulomb blockade.
Steady-state plasma transition in the Venus ionosheath
NASA Technical Reports Server (NTRS)
Perez-De-tejada, H.; Intriligator, D. S.; Strangeway, R. J.
1991-01-01
The results of an extended analysis of the plasma and electric field data of the Pioneer Venus Orbiter (PVO) are presented. The persistent presence of a plasma transition embedded in the flanks of the Venus ionosheath between the bow shock and the ionopause is reported. This transition is identified by the repeated presence of characteristic bursts in the 30 kHz channel of the electric field detector of the PVO. The observed electric field signals coincide with the onset of different plasma conditions in the inner ionosheath where more rarified plasma fluxes are measured. The repeated identification of this intermediate ionosheath transition in the PVO data indicates that it is present as a steady state feature of the Venus plasma environment. The distribution of PVO orbits in which the transition is observed suggests that it is more favorably detected in the vicinity of and downstream from the terminator.
Locating CVBEM collocation points for steady state heat transfer problems
Hromadka, T.V.
1985-01-01
The Complex Variable Boundary Element Method or CVBEM provides a highly accurate means of developing numerical solutions to steady state two-dimensional heat transfer problems. The numerical approach exactly solves the Laplace equation and satisfies the boundary conditions at specified points on the boundary by means of collocation. The accuracy of the approximation depends upon the nodal point distribution specified by the numerical analyst. In order to develop subsequent, refined approximation functions, four techniques for selecting additional collocation points are presented. The techniques are compared as to the governing theory, representation of the error of approximation on the problem boundary, the computational costs, and the ease of use by the numerical analyst. ?? 1985.
A Steady-state Trio for Bretherton Equation
NASA Astrophysics Data System (ADS)
Niu, Zhao; Liu, Zeng; Cui, Jifeng
2016-12-01
To investigate if steady-state resonant solution exist for any system of weakly interacting waves in a dispersive medium, a trio is considered in the Bretherton equation based on the homotopy analysis method (HAM). Time-independent spectrum was found when all components were travelling in the same direction. Within the trio, the amplitude of longer component is larger than that of shorter one. As the difference of wave number between components in trio increases or the nonlinearity of whole system increases, the amplitudes of all components tends to increase simultaneously. These findings are helpful to enrich and deepen our understanding about resonant solutions in any dispersive medium, especially for a two-dimensional scenario.
Relativistic hydrodynamics and non-equilibrium steady states
NASA Astrophysics Data System (ADS)
Spillane, Michael; Herzog, Christopher P.
2016-10-01
We review recent interest in the relativistic Riemann problem as a method for generating a non-equilibrium steady state. In the version of the problem under consideration, the initial conditions consist of a planar interface between two halves of a system held at different temperatures in a hydrodynamic regime. The new double shock solutions are in contrast with older solutions that involve one shock and one rarefaction wave. We use numerical simulations to show that the older solutions are preferred. Briefly we discuss the effects of a conserved charge. Finally, we discuss deforming the relativistic equations with a nonlinear term and how that deformation affects the temperature and velocity in the region connecting the asymptotic fluids.
Petri nets for steady state analysis of metabolic systems.
Voss, Klaus; Heiner, Monika; Koch, Ina
2011-01-01
Computer assisted analysis and simulation of biochemical pathways can improve the understanding of the structure and the dynamics of cell processes considerably. The construction and quantitative analysis of kinetic models is often impeded by the lack of reliable data. However, as the topological structure of biochemical systems can be regarded to remain constant in time, a qualitative analysis of a pathway model was shown to be quite promising as it can render a lot of useful knowledge, e. g., about its structural invariants. The topic of this paper are pathways whose substances have reached a dynamic concentration equilibrium (steady state). It is argued that appreciated tools from biochemistry and also low-level Petri nets can yield only part of the desired results, whereas executable high-level net models lead to a number of valuable additional insights by combining symbolic analysis and simulation.
Steady state analysis of metabolic pathways using Petri nets.
Voss, Klaus; Heiner, Monika; Koch, Ina
2003-01-01
Computer assisted analysis and simulation of biochemical pathways can improve the understanding of the structure and the dynamics of cell processes considerably. The construction and quantitative analysis of kinetic models is often impeded by the lack of reliable data. However, as the topological structure of biochemical systems can be regarded to remain constant in time, a qualitative analysis of a pathway model was shown to be quite promising as it can render a lot of useful knowledge, e. g., about its structural invariants. The topic of this paper are pathways whose substances have reached a dynamic concentration equilibrium (steady state). It is argued that appreciated tools from biochemistry and also low-level Petri nets can yield only part of the desired results, whereas executable high-level net models lead to a number of valuable additional insights by combining symbolic analysis and simulation.
Steady-state thermodynamics for population growth in fluctuating environments
NASA Astrophysics Data System (ADS)
Sughiyama, Yuki; Kobayashi, Tetsuya J.
2017-01-01
We report that population dynamics in fluctuating environments is characterized by a mathematically equivalent structure to steady-state thermodynamics. By employing the structure, population growth in fluctuating environments is decomposed into housekeeping and excess parts. The housekeeping part represents the integral of the stationary growth rate for each condition during a history of the environmental change. The excess part accounts for the excess growth induced by environmental fluctuations. Focusing on the excess growth, we obtain a Clausius inequality, which gives the upper bound of the excess growth. The equality is shown to be achieved in quasistatic environmental changes. We also clarify that this bound can be evaluated by the "lineage fitness", which is an experimentally observable quantity.
Evidence for Anomalous Effects on the Current Evolution in Tokamak Operating Scenarios
Casper, T; Jayakumar, R; Allen, S; Holcomb, C; Makowski, M; Pearlstein, L; Berk, H; Greenfield, C; Luce, T; Petty, C; Politzer, P; Wade, M; Murakami, M; Kessel, C
2006-10-03
Alternatives to the usual picture of advanced tokamak (AT) discharges are those that form when anomalous effects alter the plasma current and pressure profiles and those that achieve stationary characteristics through mechanisms so that a measure of desired AT features is maintained without external current-profile control. Regimes exhibiting these characteristics are those where the safety factor (q) evolves to a stationary profile with the on-axis and minimum q {approx} 1 and those with a deeply hollow current channel and high values of q. Operating scenarios with high fusion performance at low current and where the inductively driven current density achieves a stationary configuration with either small or non-existing sawteeth may enhance the neutron fluence per pulse on ITER and future burning plasmas. Hollow current profile discharges exhibit high confinement and a strong ''box-like'' internal transport barrier (ITB). We present results providing evidence for current profile formation and evolution exhibiting features consistent with anomalous effects or with self-organizing mechanisms. Determination of the underlying physical processes leading to these anomalous effects is important for scaling of current experiments for application in future burning plasmas.
Implementing a Finite-State Off-Normal and Fault Response System for Robust Tokamak Operation
NASA Astrophysics Data System (ADS)
Eidietis, N. W.; Humphreys, D. A.; Sammuli, B.; Walker, M. L.
2015-11-01
The initial implementation and testing of a finite state off-normal & fault response (ONFR) system on the DIII-D and KSTAR tokamaks is presented. Robust ONFR will be critical to the operation of ITER as the physical consequences of unexpected events will be far more extreme than in present devices. ``Off-normal'' refers to unexpected plasma events (e.g. disruptions) and plasma events that are expected but still require asynchronous response (e.g. neoclassical tearing modes). ``Fault'' refers to hardware failure. ONFR priorities are to (1) protect the device from damage, (2) minimize recovery time between shots by avoiding unnecessary initiation of mitigation procedures, and (3) maximize the useful pulse length of a given shot by providing for discharge recovery after deleterious events. The detailed implementation of finite-state ONFR using Matlab/Simulink and Stateflow exported to the DIII-D and KSTAR plasma control systems is described, as are initial tests of multi-stage locked mode handling on both devices. Work supported by the US DOE under DE-FC02-04ER54698.
A mathematical model of pan evaporation under steady state conditions
NASA Astrophysics Data System (ADS)
Lim, Wee Ho; Roderick, Michael L.; Farquhar, Graham D.
2016-09-01
In the context of changing climate, global pan evaporation records have shown a spatially-averaged trend of ∼ -2 to ∼ -3 mm a-2 over the past 30-50 years. This global phenomenon has motivated the development of the "PenPan" model (Rotstayn et al., 2006). However, the original PenPan model has yet to receive an independent experimental evaluation. Hence, we constructed an instrumented US Class A pan at Canberra Airport (Australia) and monitored it over a three-year period (2007-2010) to uncover the physics of pan evaporation under non-steady state conditions. The experimental investigations of pan evaporation enabled theoretical formulation and parameterisation of the aerodynamic function considering the wind, properties of air and (with or without) the bird guard effect. The energy balance investigation allowed for detailed formulation of the short- and long-wave radiation associated with the albedos and the emissivities of the pan water surface and the pan wall. Here, we synthesise and generalise those earlier works to develop a new model called the "PenPan-V2" model for application under steady state conditions (i.e., uses a monthly time step). Two versions (PenPan-V2C and PenPan-V2S) are tested using pan evaporation data available across the Australian continent. Both versions outperformed the original PenPan model with better representation of both the evaporation rate and the underlying physics of a US Class A pan. The results show the improved solar geometry related calculations (e.g., albedo, area) for the pan system led to a clear improvement in representing the seasonal cycle of pan evaporation. For general applications, the PenPan-V2S is simpler and suited for applications including an evaluation of long-term trends in pan evaporation.
Steady-state spectroscopy of new biological probes
NASA Astrophysics Data System (ADS)
Abou-Zied, Osama K.
2007-02-01
The steady state absorption and fluorescence spectroscopy of 2-(2'-hydroxyphenyl)benzoxazole (HBO) and (2,2'-bipyridine)-3,3'-diol (BP(OH) II) were studied here free in solution and in human serum albumin (HSA) in order to test their applicability as new biological probes. HBO and BP(OH) II are known to undergo intramolecular proton transfers in the excited state. Their absorption and fluorescence spectra are sensitive to environmental change from hydrophilic to hydrophobic, thus allowing the opportunity to use them as environment-sensitive probes. The effect of water on the steady state spectra of the two molecules also shows unique features which may position them as water sensors in biological systems. For HBO in buffer, fluorescence is only due to the syn-keto tautomer, whereas in HSA the fluorescence is due to four species in equilibrium in the excited state (the syn-keto tautomer, the anti-enol tautomer, the solvated syn-enol tautomer, and the anion species of HBO). Analysis of the fluorescence spectra of HBO in HSA indicates that HBO is exposed to less water in the HBO:HSA complex. For the BP(OH) II molecule, unique absorption due to water was observed in the spectral region of 400-450 nm. This absorption decreases in the presence of HSA due to less accessibility to water as a result of binding to HSA. Fluorescence of BP(OH) II is due solely to the di-keto tautomer after double proton transfer in the excited state. The fluorescence peak of BP(OH) II shows a red-shift upon HSA recognition which is attributed to the hydrophobic environment inside the binding site of HSA. We discuss also the effect of probe-inclusion inside well-defined hydrophobic cavities of cyclodextrins.
Automatic Fault-Checking System on the DIII-D Tokamak
Scoville, J.T.; Walker, M.L.
2005-04-15
Modern tokamaks are highly sophisticated devices consisting of a large number of state-of-the-art systems that must function in unison to obtain a successful plasma discharge. An unsuccessful discharge can result if one or more systems fail, and diagnosis in an efficient and timely manner can be difficult. The resulting reduction in tokamak availability and productivity can be expensive, justifying a significant effort for automated fault diagnosis.For the DIII-D tokamak, a software system has been used for the past 5 years to automatically monitor and test the performance of hundreds of tokamak systems. The Fault Identification and Communication System (FICS) is automatically triggered to run immediately after each tokamak discharge and report its results via a simple color-coded graphical user interface. In addition to saving the operator time, the significant advantage of FICS is its ability to detect insipient faults that could lead to future machine failures. It has been estimated that FICS has saved an average of one to two shots per day, which equates to approximately 5% of all DIII-D pulses. The significant experience gained through the development and use of this post-discharge analysis tool also provides insight into future methods for on-line process monitoring of steady state devices.
Xu, Lu; Choi, Sunju; Xie, Yusu; Sze, Ji Ying
2015-01-01
Heterotrimeric G proteins regulate a vast array of cellular functions via specific intracellular effectors. Accumulating pharmacological and biochemical studies implicate Gβ subunits as signaling molecules interacting directly with a wide range of effectors to modulate downstream cellular responses, in addition to their role in regulating Gα subunit activities. However, the native biological roles of Gβ-mediated signaling pathways in vivo have been characterized only in a few cases. Here, we identified a Gβ GPB-1 signaling pathway operating in specific serotonergic neurons to the define steady state serotonin (5-HT) synthesis, through a genetic screen for 5-HT synthesis mutants in Caenorhabditis elegans. We found that signaling through cell autonomous GPB-1 to the OCR-2 TRPV channel defines the baseline expression of 5-HT synthesis enzyme tryptophan hydroxylase tph-1 in ADF chemosensory neurons. This Gβ signaling pathway is not essential for establishing the serotonergic cell fates and is mechanistically separated from stress-induced tph-1 upregulation. We identified that ADF-produced 5-HT controls specific innate rhythmic behaviors. These results revealed a Gβ-mediated signaling operating in differentiated cells to specify intrinsic functional properties, and indicate that baseline TPH expression is not a default generic serotonergic fate, but is programmed in a cell-specific manner in the mature nervous system. Cell-specific regulation of TPH expression could be a general principle for tailored steady state 5-HT synthesis in functionally distinct neurons and their regulation of innate behavior. PMID:26402365
Steady-state performance characteristics of latent heat TES/heat pump systems
NASA Astrophysics Data System (ADS)
Sigmon, T. W.
1982-03-01
Two projects are currently being completed that wholly or in part address various technical issues involved in the implementation of heat pump systems combined with thermal energy storage (TES). The first of these involves the determination of steady state performance characteristics for six generic TES/heat pump configurations and the comparison of the operational performance of these systems with other space heating and cooling TES technologies. Of these latter systems four are commercial or near commerical air conditioner or heat pump coupled TES systems. Steady state performance has been established for all systems. Operational performance and system life cycle cost has been determined for the six generic designs for a limited set of application conditions. The intent of the second project is to establish a reliable method of estimating seasonal energy use by TES/heat pump systems, to utilize this methodology to evaluate a large number of possible system designs, identify a small number of systems that merit more detailed analysis, and, to the extent possible, conduct these detailed studies.
Stability of Elevated-qmin Steady-State Scenarios on DIII-D
NASA Astrophysics Data System (ADS)
Holcomb, C. T.; Victor, B.; Ferron, J. R.; Luce, T. C.; Schuster, E.
2016-10-01
Limits to high performance steady-state operation with qmin >1.4 and βN <= 3.5 are identified and explained. Various βN and q-profile histories were produced while testing feedback control of these profiles. Ten pulses had no core MHD at βN=3.4-3.5, with qmin=1.4-1.8, and q95=5-5.8. These have predicted ideal-wall kink βN limits between 4 and 5. One pulse had an n=1 tearing mode (TM) at βN=3.5 with no clear trigger. Five pulses developed n=1 TMs when βN=2, qmin=2, and q95=4.7. Stability calculations for these latter cases will be shown. In seven other shots, additional NBI power from sources with more normal injection was used, and these had off-axis fishbone (OAFB) modes at βN=3.5. These sources produce more large-radius trapped ions whose precession can drive OAFB. Preliminary analysis suggests a threshold power or voltage exists. In some cases OAFB appear to trigger n=1 TMs. These studies seek to clarify the operational limits of a steady-state scenario for next step devices. Supported by US DOE under DE-AC52-07NA27344, DE-FC02-04ER54698, DE-FG02-09ER55064.
Wernsman, B.
1997-01-01
A comparison between steady-state and dynamic I-V measurements from a single-cell thermionic fuel element (TFE) is made. The single-cell TFE used in this study is the prototype for the 40kW{sub e} space nuclear power system that is similar to the 6kW{sub e} TOPAZ-II. The steady-state I-V measurements influence the emitter temperature due to electron cooling. Therefore, to eliminate the steady-state I-V measurement influence on the TFE and provide a better understanding of the behavior of the thermionic energy converter and TFE characteristics, dynamic I-V measurements are made. The dynamic I-V measurements are made at various input power levels, cesium pressures, collector temperatures, and steady-state current levels. From these measurements, it is shown that the dynamic I-V{close_quote}s do not change the TFE characteristics at a given operating point. Also, the evaluation of the collector work function from the dynamic I-V measurements shows that the collector optimization is not due to a minimum in the collector work function but due to an emission optimization. Since the dynamic I-V measurements do not influence the TFE characteristics, it is believed that these measurements can be done at a system level to understand the influence of TFE placement in the reactor as a function of the core thermal distribution. {copyright} {ital 1997 American Institute of Physics.}
Wernsman, Bernard
1997-01-10
A comparison between steady-state and dynamic I-V measurements from a single-cell thermionic fuel element (TFE) is made. The single-cell TFE used in this study is the prototype for the 40 kW{sub e} space nuclear power system that is similar to the 6 kW{sub e} TOPAZ-II. The steady-state I-V measurements influence the emitter temperature due to electron cooling. Therefore, to eliminate the steady-state I-V measurement influence on the TFE and provide a better understanding of the behavior of the thermionic energy converter and TFE characteristics, dynamic I-V measurements are made. The dynamic I-V measurements are made at various input power levels, cesium pressures, collector temperatures, and steady-state current levels. From these measurements, it is shown that the dynamic I-V's do not change the TFE characteristics at a given operating point. Also, the evaluation of the collector work function from the dynamic I-V measurements shows that the collector optimization is not due to a minimum in the collector work function but due to an emission optimization. Since the dynamic I-V measurements do not influence the TFE characteristics, it is believed that these measurements can be done at a system level to understand the influence of TFE placement in the reactor as a function of the core thermal distribution.
NASA Glenn Steady-State Heat Pipe Code GLENHP: Compilation for 64- and 32-Bit Windows Platforms
NASA Technical Reports Server (NTRS)
Tower, Leonard K.; Geng, Steven M.
2016-01-01
A new version of the NASA Glenn Steady State Heat Pipe Code, designated "GLENHP," is introduced here. This represents an update to the disk operating system (DOS) version LERCHP reported in NASA/TM-2000-209807. The new code operates on 32- and 64-bit Windows-based platforms from within the 32-bit command prompt window. An additional evaporator boundary condition and other features are provided.
The Budyko functions under non-steady-state conditions
NASA Astrophysics Data System (ADS)
Moussa, Roger; Lhomme, Jean-Paul
2016-12-01
The Budyko functions relate the evaporation ratio E / P (E is evaporation and P precipitation) to the aridity index Φ = Ep / P (Ep is potential evaporation) and are valid on long timescales under steady-state conditions. A new physically based formulation (noted as Moussa-Lhomme, ML) is proposed to extend the Budyko framework under non-steady-state conditions taking into account the change in terrestrial water storage ΔS. The variation in storage amount ΔS is taken as negative when withdrawn from the area at stake and used for evaporation and positive otherwise, when removed from the precipitation and stored in the area. The ML formulation introduces a dimensionless parameter HE = -ΔS / Ep and can be applied with any Budyko function. It represents a generic framework, easy to use at various time steps (year, season or month), with the only data required being Ep, P and ΔS. For the particular case where the Fu-Zhang equation is used, the ML formulation with ΔS ≤ 0 is similar to the analytical solution of Greve et al. (2016) in the standard Budyko space (Ep / P, E / P), a simple relationship existing between their respective parameters. The ML formulation is extended to the space [Ep / (P - ΔS), E / (P - ΔS)] and compared to the formulations of Chen et al. (2013) and Du et al. (2016). The ML (or Greve et al., 2016) feasible domain has a similar upper limit to that of Chen et al. (2013) and Du et al. (2016), but its lower boundary is different. Moreover, the domain of variation of Ep / (P - ΔS) differs: for ΔS ≤ 0, it is bounded by an upper limit 1 / HE in the ML formulation, while it is only bounded by a lower limit in Chen et al.'s (2013) and Du et al.'s (2016) formulations. The ML formulation can also be conducted using the dimensionless parameter HP = -ΔS / P instead of HE, which yields another form of the equations.
Mantle Sulfur Cycle: A Case for Non-Steady State ?
NASA Astrophysics Data System (ADS)
Cartigny, Pierre; Labidi, Jabrane
2016-04-01
Data published over the last 5 years show that the early inference that mantle is isotopically homogeneous is no more valid. Instead, new generation data on lavas range over a significant 34S/32S variability of up to 5‰ with δ 34S values often correlated to Sr- and Nd-isotope compositions. This new set of data also reveals the Earth's mantle to have a sub-chondritic 34S/32S ratio, by about ˜ 1‰. We will present at the conference our published and unpublished data on samples characterizing the different mantle components (i.e. EM1, EM2, HIMU and LOMU). All illustrate 34S-enrichments compared to MORB with Δ 33S and Δ 36S values indistinguishable from CDT or chondrites at the 0.03‰ level. These data are consistent with the recycling of subducted components carrying sulfur with Δ 33S and Δ 36S-values close to zero. Archean rocks commonly display Δ 33S and Δ 36S values deviating from zero by 1 to 10 ‰. The lack of variations for Δ 33S and Δ 36S values in present day lava argue against the sampling of any subducted protolith of Archean age in their mantle source. Instead, our data are consistent with the occurrence of Proterozoic subducted sulfur in the source of the EM1, EM2, LOMU and HIMU endmember at the St-Helena island. This is in agreement with the age of those components early derived through the use of the Pb isotope systematic. Currently, the negative δ 34S-values of the depleted mantle seem to be associated with mostly positive values of enriched components. This would be inconsistent with the concept a steady state of sulfur. Assuming that the overall observations of recycled sulfur are not biased, the origin of such a non-steady state remains unclear. It could be related to the relatively compatible behavior of sulfur during partial melting, as the residue of present-day melting can be shown to always contain significant amounts of sulfide (50{%} of what is observed in a fertile source). This typical behavior likely prevents an efficient
Critical Concavity of a Drainage Basin for Steady-State
NASA Astrophysics Data System (ADS)
Byun, Jongmin; Paik, Kyungrock
2015-04-01
Longitudinal profiles of natural streams are known to show concave forms. Saying A as drainage area, channel gradient S can be expressed as the power-law, S≈A-θ (Flint, 1974), which is one of the scale-invariant features of drainage basin. According to literature, θ of most natural streams falls into a narrow range (0.4 < θ < 0.7) (Tucker and Whipple, 2002). It leads to fundamental questions: 'Why does θ falls into such narrow range?' and 'How is this related with other power-law scaling relationships reported in natural drainage basins?' To answer above questions, we analytically derive θ for a steady-state drainage basin following Lane's equilibrium (Lane, 1955) throughout the corridor and named this specific case as the 'critical concavity'. In the derivation, sediment transport capacity is estimated by unit stream power model (Yang, 1976), yielding a power function of upstream area. Stability of channel at a local point occurs when incoming flux equals outgoing flux at the point. Therefore, given the drainage at steady-state where all channel beds are stable, the exponent of the power function should be zero. From this, we can determine the critical concavity. Considering ranges of variables associated in this derivation, critical concavity cannot be resolved as a single definite value, rather a range of critical concavity is suggested. This range well agrees with the widely reported range of θ (0.4 < θ < 0.7) in natural streams. In this theoretical study, inter-relationships between power-laws such as hydraulic geometry (Leopold and Maddock, 1953), dominant discharge-drainage area (Knighton et al., 1999), and concavity, are coupled into the power-law framework of stream power sediment transport model. This allows us to explore close relationships between their power-law exponents: their relative roles and sensitivity. Detailed analysis and implications will be presented. References Flint, J. J., 1974, Stream gradient as a function of order, magnitude
Self-induced longitudinal current in the perpendicular ion cyclotron heating in a tokamak
NASA Astrophysics Data System (ADS)
Gott, Yu. V.; Yurchenko, E. I.
2016-11-01
In this paper, we give an estimation of the longitudinal current in a tokamak due to high-energy minority ions obtained by perpendicular ICR heating. To illustrate this current, which is known as the banana-drift current, we give an estimation of this effect in an ITER-like tokamak. It is shown that by changing the number of accelerated minority ions, by selecting the position and energy of the resonant layer in which they are accelerated, it is possible to completely replace the noninductive current driven by other methods (for example, with RF power and high-energy neutrals beams). Thus, it is shown that the self-induced currents (bootstrap, asymmetry, and banana-drift currents) driving by continuous HF sources can provide steady-state operation of a fusion reactor.
Modeling of high harmonic fast wave current drive on EAST tokamak
Li, J. C.; Gong, X. Y. Li, F. Y.; Dong, J. Q.; Gao, Q. D.; Zhang, N.
2015-10-15
High harmonic fast waves (HHFW) are among the candidates for non-inductive current drive (CD), which is essential for long-pulse or steady-state operation of tokamaks. Current driven with HHFW in EAST tokamak plasmas is numerically studied. The HHFW CD efficiency is found to increase non-monotonically with the wave frequency, and this phenomenon is attributed to the multi-pass absorption of HHFW. The sensitivity of CD efficiency to the value of the parallel refraction index of the launched wave is confirmed. The quasilinear effects, assessed as significant in HHFW current drive with the GENRAY/CQL3D package, cause a significant increase in CD efficiency as RF power is increased, which is very different from helicon current drive. Simulations for a range of toroidal dc electric fields, in combination with a range of fast wave powers, are also presented and indicate that the presence of the DC field can also enhance the CD efficiency.
DIII-D Upgrade to Prepare the Basis for Steady-State Burning Plasmas
NASA Astrophysics Data System (ADS)
Buttery, R. J.; Guo, H. Y.; Taylor, T. S.; Wade, M. R.; Hill, D. N.
2014-10-01
Future steady-state burning plasma facilities will access new physics regimes and modes of plasma behavior. It is vital to prepare for this both experimentally using existing facilities, and theoretically in order to develop the tools to project to and optimize these devices. An upgrade to DIII-D is proposed to address the three critical aspects where research must go beyond what we can do now: (i) torque free electron heating to address the energy, particle and momentum transport mechanisms of burning plasmas using electron cyclotron (EC) heating and full power balanced neutral beams; (ii) off-axis heating and current drive to develop the path to true fusion steady state by reorienting neutral beams and deploying EC and helicon current drive; (iii) a new divertor with hot walls and reactor relevant materials to develop the basis for benign detached divertor operation compatible with wall materials and a high performance fusion core. These elements with modest incremental cost and enacted as a user facility for the whole US program will enable the US to lead on ITER and take a decision to proceed with a Fusion Nuclear Science Facility. Work supported by the US Department of Energy under DE-FC02-04ER54698 and DE-AC52-07NA27344.
Modeling of Steady-State Non-Inductive ITB Discharges with Application to DIII-D
NASA Astrophysics Data System (ADS)
St John, H. E.; Lao, L. L.; Murakami, M.; Kinsey, J. E.
2001-10-01
Establishment of near steady-state high-performance discharges with internal transport barriers in the electron and ion heat and the toroidal momentum channels is investigated using the GLF23 and Weiland confinement models. A combination of neutral beam and electron cyclotron heating and current drive is used to optimally shape the current profile for near non-inductive steady-state operation. The GLF23 and Weiland confinement models have had some success in modeling DIII-D discharges and consequently represents our best choice for DIII-D AT scenario development at this time. By starting the modeling with actual high-performance DIII-D discharges, we expect to obtain experimentally realized results. The stability of our simulations is monitored with the BALOO and GATO codes and rf heating and current drive is modelled with TORAY-GA. This computationally instensive modeling approach requires concurrent computing methods in order to be used routinely. We discuss our efforts to date in producing a parallel computational transport environment.
The Steady State Challenge for Soft X-Ray Diagnostics on Wendelstein 7-X Stellarator
Thomsen, H.; Broszat, T.; Mohr, S.; Weller, A.; Ye, M. Y.; Carvalho, P.
2008-03-19
The steady state operation of Wendelstein 7-X stellarator presently under construction in Greifswald poses special challenges to the diagnostics development [1, 2]. A critical issue is the heat load on plasma facing components ({approx}500 kW/m{sup 2}) over a long discharge time (up to 30 min), which leads to the necessity of active cooling. As result, the design of the 400 channel soft X-Ray Multi Camera Tomography System (XMCTS) [2, 3] has to cope with dark currents and amplifier drifts due to the heating of active components like photo diodes and in-vessel preamplifiers. In order to allow for a quantitative measurement of dynamic drifts and offsets, a shutter system and blind diodes are considered to compensate these effects. Another important issue is the large amount of data gathered by the XMCT system during long pulse discharges. A fast but less precise online reconstruction is planned, which will give information on the plasma shape and position on a human time scale. The two options under investigation are a Cormack-Inversion method and an approach based on neural networks [4]. Dependent on the available hardware, as much information as possible should be stored for more accurate offline-analysis. An intelligent way of marking interesting data is required. In case that the steady-state storage of all measured data is not feasible, at least this marked data will be stored in high time resolution.
NASA Technical Reports Server (NTRS)
Gainer, Patrick A.; Aiken, William S., Jr.
1959-01-01
A method is presented for shortening the computations required to determine the steady-state span loading on flexible wings in subsonic flight. The method makes use of tables of downwash factors to find the necessary aerodynamic-influence coefficients for the application of lifting-line theory. Explicit matrix equations of equilibrium are converted into a matrix power series with a finite number of terms by utilizing certain characteristic properties of matrices. The number of terms in the series is determined by a trial-and-error process dependent upon the required accuracy of the solution. Spanwise distributions of angle of attack, airload, shear, bending moment, and pitching moment are readily obtained as functions of qm(sub R) where q denotes the dynamic pressure and mR denotes the lift-curve slope of a rigid wing. This method is intended primarily to make it practical to solve steady-state aeroelastic problems on the ordinary manually operated desk calculators, but the method is also readily adaptable to automatic computing equipment.
Steady state solutions to dynamically loaded periodic structures
NASA Technical Reports Server (NTRS)
Kalinowski, A. J.
1980-01-01
The general problem of solving for the steady state (time domain) dynamic response (i.e., NASTRAN rigid format-8) of a general elastic periodic structure subject to a phase difference loading of the type encountered in traveling wave propagation problems was studied. Two types of structural configurations were considered; in the first type, the structure has a repeating pattern over a span that is long enough to be considered, for all practical purposes, as infinite; in the second type, the structure has structural rotational symmetry in the circumferential direction. The theory and a corresponding set of DMAP instructions which permits the NASTRAN user to automatically alter the rigid format-8 sequence to solve the intended class of problems are presented. Final results are recovered as with any ordinary rigid format-8 solution, except that the results are only printed for the typical periodic segment of the structure. A simple demonstration problem having a known exact solution is used to illustrate the implementation of the procedure.
Steady state quantum discord for circularly accelerated atoms
Hu, Jiawei; Yu, Hongwei
2015-12-15
We study, in the framework of open quantum systems, the dynamics of quantum entanglement and quantum discord of two mutually independent circularly accelerated two-level atoms in interaction with a bath of fluctuating massless scalar fields in the Minkowski vacuum. We assume that the two atoms rotate synchronically with their separation perpendicular to the rotating plane. The time evolution of the quantum entanglement and quantum discord of the two-atom system is investigated. For a maximally entangled initial state, the entanglement measured by concurrence diminishes to zero within a finite time, while the quantum discord can either decrease monotonically to an asymptotic value or diminish to zero at first and then followed by a revival depending on whether the initial state is antisymmetric or symmetric. When both of the two atoms are initially excited, the generation of quantum entanglement shows a delayed feature, while quantum discord is created immediately. Remarkably, the quantum discord for such a circularly accelerated two-atom system takes a nonvanishing value in the steady state, and this is distinct from what happens in both the linear acceleration case and the case of static atoms immersed in a thermal bath.
Grand canonical steady-state simulation of nucleation
NASA Astrophysics Data System (ADS)
Horsch, Martin; Vrabec, Jadran
2009-11-01
Grand canonical molecular dynamics (GCMD) is applied to the nucleation process in a metastable phase near the spinodal, where nucleation occurs almost instantaneously and is limited to a very short time interval. With a variant of Maxwell's demon, proposed by McDonald [Am. J. Phys. 31, 31 (1963)], all nuclei exceeding a specified size are removed. In such a steady-state simulation, the nucleation process is sampled over an arbitrary time span and all properties of the metastable state, including the nucleation rate, can be obtained with an increased precision. As an example, a series of GCMD simulations with McDonald's demon is carried out for homogeneous vapor to liquid nucleation of the truncated-shifted Lennard-Jones (tsLJ) fluid, covering the entire relevant temperature range. The results are in agreement with direct nonequilibrium MD simulation in the canonical ensemble. It is confirmed for supersaturated vapors of the tsLJ fluid that the classical nucleation theory underpredicts the nucleation rate by two orders of magnitude.
Nonequilibrium steady states of ideal bosonic and fermionic quantum gases
NASA Astrophysics Data System (ADS)
Vorberg, Daniel; Wustmann, Waltraut; Schomerus, Henning; Ketzmerick, Roland; Eckardt, André
2015-12-01
We investigate nonequilibrium steady states of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013), 10.1103/PhysRevLett.111.240405]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state.
Steady-state and dynamic network modes for perceptual expectation
Choi, Uk-Su; Sung, Yul-Wan; Ogawa, Seiji
2017-01-01
Perceptual expectation can attenuate repetition suppression, the stimulus-induced neuronal response generated by repeated stimulation, suggesting that repetition suppression is a top-down modulatory phenomenon. However, it is still unclear which high-level brain areas are involved and how they interact with low-level brain areas. Further, the temporal range over which perceptual expectation can effectively attenuate repetition suppression effects remains unclear. To elucidate the details of this top-down modulatory process, we used two short and long inter-stimulus intervals for a perceptual expectation paradigm of paired stimulation. We found that top-down modulation enhanced the response to the unexpected stimulus when repetition suppression was weak and that the effect disappeared at 1,000 ms prior to stimulus exposure. The high-level areas involved in this process included the left inferior frontal gyrus (IFG_L) and left parietal lobule (IPL_L). We also found two systems providing modulatory input to the right fusiform face area (FFA_R): one from IFG_L and the other from IPL_L. Most importantly, we identified two states of networks through which perceptual expectation modulates sensory responses: one is a dynamic state and the other is a steady state. Our results provide the first functional magnetic resonance imaging (fMRI) evidence of temporally nested networks in brain processing. PMID:28079163
Visual steady state in relation to age and cognitive function.
Horwitz, Anna; Dyhr Thomsen, Mia; Wiegand, Iris; Horwitz, Henrik; Klemp, Marc; Nikolic, Miki; Rask, Lene; Lauritzen, Martin; Benedek, Krisztina
2017-01-01
Neocortical gamma activity is crucial for sensory perception and cognition. This study examines the value of using non-task stimulation-induced EEG oscillations to predict cognitive status in a birth cohort of healthy Danish males (Metropolit) with varying cognitive ability. In particular, we examine the steady-state VEP power response (SSVEP-PR) in the alpha (8Hz) and gamma (36Hz) bands in 54 males (avg. age: 62.0 years) and compare these with 10 young healthy participants (avg. age 27.6 years). Furthermore, we correlate the individual alpha-to-gamma difference in relative visual-area power (ΔRV) with cognitive scores for the older adults. We find that ΔRV decrease with age by just over one standard deviation when comparing young with old participants (p<0.01). Furthermore, intelligence is significantly negatively correlated with ΔRV in the older adult cohort, even when processing speed, global cognition, executive function, memory, and education (p<0.05). In our preferred specification, an increase in ΔRV of one standard deviation is associated with a reduction in intelligence of 48% of a standard deviation (p<0.01). Finally, we conclude that the difference in cerebral rhythmic activity between the alpha and gamma bands is associated with age and cognitive status, and that ΔRV therefore provide a non-subjective clinical tool with which to examine cognitive status in old age.
Visual steady state in relation to age and cognitive function
Dyhr Thomsen, Mia; Wiegand, Iris; Horwitz, Henrik; Klemp, Marc; Nikolic, Miki; Rask, Lene; Lauritzen, Martin; Benedek, Krisztina
2017-01-01
Neocortical gamma activity is crucial for sensory perception and cognition. This study examines the value of using non-task stimulation-induced EEG oscillations to predict cognitive status in a birth cohort of healthy Danish males (Metropolit) with varying cognitive ability. In particular, we examine the steady-state VEP power response (SSVEP-PR) in the alpha (8Hz) and gamma (36Hz) bands in 54 males (avg. age: 62.0 years) and compare these with 10 young healthy participants (avg. age 27.6 years). Furthermore, we correlate the individual alpha-to-gamma difference in relative visual-area power (ΔRV) with cognitive scores for the older adults. We find that ΔRV decrease with age by just over one standard deviation when comparing young with old participants (p<0.01). Furthermore, intelligence is significantly negatively correlated with ΔRV in the older adult cohort, even when processing speed, global cognition, executive function, memory, and education (p<0.05). In our preferred specification, an increase in ΔRV of one standard deviation is associated with a reduction in intelligence of 48% of a standard deviation (p<0.01). Finally, we conclude that the difference in cerebral rhythmic activity between the alpha and gamma bands is associated with age and cognitive status, and that ΔRV therefore provide a non-subjective clinical tool with which to examine cognitive status in old age. PMID:28245274
Attentional Modulation of Auditory Steady-State Responses
Mahajan, Yatin; Davis, Chris; Kim, Jeesun
2014-01-01
Auditory selective attention enables task-relevant auditory events to be enhanced and irrelevant ones suppressed. In the present study we used a frequency tagging paradigm to investigate the effects of attention on auditory steady state responses (ASSR). The ASSR was elicited by simultaneously presenting two different streams of white noise, amplitude modulated at either 16 and 23.5 Hz or 32.5 and 40 Hz. The two different frequencies were presented to each ear and participants were instructed to selectively attend to one ear or the other (confirmed by behavioral evidence). The results revealed that modulation of ASSR by selective attention depended on the modulation frequencies used and whether the activation was contralateral or ipsilateral. Attention enhanced the ASSR for contralateral activation from either ear for 16 Hz and suppressed the ASSR for ipsilateral activation for 16 Hz and 23.5 Hz. For modulation frequencies of 32.5 or 40 Hz attention did not affect the ASSR. We propose that the pattern of enhancement and inhibition may be due to binaural suppressive effects on ipsilateral stimulation and the dominance of contralateral hemisphere during dichotic listening. In addition to the influence of cortical processing asymmetries, these results may also reflect a bias towards inhibitory ipsilateral and excitatory contralateral activation present at the level of inferior colliculus. That the effect of attention was clearest for the lower modulation frequencies suggests that such effects are likely mediated by cortical brain structures or by those in close proximity to cortex. PMID:25334021
Quasi-steady state aerodynamics of the cheetah tail.
Patel, Amir; Boje, Edward; Fisher, Callen; Louis, Leeann; Lane, Emily
2016-08-15
During high-speed pursuit of prey, the cheetah (Acinonyx jubatus) has been observed to swing its tail while manoeuvring (e.g. turning or braking) but the effect of these complex motions is not well understood. This study demonstrates the potential of the cheetah's long, furry tail to impart torques and forces on the body as a result of aerodynamic effects, in addition to the well-known inertial effects. The first-order aerodynamic forces on the tail are quantified through wind tunnel testing and it is observed that the fur nearly doubles the effective frontal area of the tail without much mass penalty. Simple dynamic models provide insight into manoeuvrability via simulation of pitch, roll and yaw tail motion primitives. The inertial and quasi-steady state aerodynamic effects of tail actuation are quantified and compared by calculating the angular impulse imparted onto the cheetah's body and its shown aerodynamic effects contribute to the tail's angular impulse, especially at the highest forward velocities.
Quasi-steady state aerodynamics of the cheetah tail
Boje, Edward; Fisher, Callen; Louis, Leeann; Lane, Emily
2016-01-01
ABSTRACT During high-speed pursuit of prey, the cheetah (Acinonyx jubatus) has been observed to swing its tail while manoeuvring (e.g. turning or braking) but the effect of these complex motions is not well understood. This study demonstrates the potential of the cheetah's long, furry tail to impart torques and forces on the body as a result of aerodynamic effects, in addition to the well-known inertial effects. The first-order aerodynamic forces on the tail are quantified through wind tunnel testing and it is observed that the fur nearly doubles the effective frontal area of the tail without much mass penalty. Simple dynamic models provide insight into manoeuvrability via simulation of pitch, roll and yaw tail motion primitives. The inertial and quasi-steady state aerodynamic effects of tail actuation are quantified and compared by calculating the angular impulse imparted onto the cheetah's body and its shown aerodynamic effects contribute to the tail's angular impulse, especially at the highest forward velocities. PMID:27412267
The Path of Carbon in Photosynthesis XX. The Steady State
DOE R&D Accomplishments Database
Calvin, M.; Massini, Peter
1952-09-01
The separation of the phenomenon of photosynthesis in green plants into a photochemical reaction and into the light-dependent reduction of carbon dioxide is discussed, The reduction of carbon dioxide and the fate of the assimilated carbon were investigated with the help of the tracer technique (exposure of the planks to the radioactive C{sup 14}O{sub 2}) and of paper chromatography. A reaction cycle is proposed in which phosphoglyceric acid is the first isolable assimilations product. Analyses of the algal extracts which had assimilated radioactive carbon dioxide in a stationary condition ('steady-state' photosynthesis) for a long time provided further information concerning the proposed cycle and permitted the approximate estimation, for a number of compounds of what fraction of each compound was taking part in the cycle. The earlier supposition that light influences the respiration cycle was confirmed. The possibility of the assistance of {alpha}-lipoic acid, or of a related substance, in this influence and in the photosynthesis cycle, is discussed.
Ising game: Nonequilibrium steady states of resource-allocation systems
NASA Astrophysics Data System (ADS)
Xin, C.; Yang, G.; Huang, J. P.
2017-04-01
Resource-allocation systems are ubiquitous in the human society. But how external fields affect the state of such systems remains poorly explored due to the lack of a suitable model. Because the behavior of spins pursuing energy minimization required by physical laws is similar to that of humans chasing payoff maximization studied in game theory, here we combine the Ising model with the market-directed resource-allocation game, yielding an Ising game. Based on the Ising game, we show theoretical, simulative and experimental evidences for a formula, which offers a clear expression of nonequilibrium steady states (NESSs). Interestingly, the formula also reveals a convertible relationship between the external field (exogenous factor) and resource ratio (endogenous factor), and a class of saturation as the external field exceeds certain limits. This work suggests that the Ising game could be a suitable model for studying external-field effects on resource-allocation systems, and it could provide guidance both for seeking more relations between NESSs and equilibrium states and for regulating human systems by choosing NESSs appropriately.
Flavour fields in steady state: stress tensor and free energy
NASA Astrophysics Data System (ADS)
Banerjee, Avik; Kundu, Arnab; Kundu, Sandipan
2016-02-01
The dynamics of a probe brane in a given gravitational background is governed by the Dirac-Born-Infeld action. The corresponding open string metric arises naturally in studying the fluctuations on the probe. In Gauge-String duality, it is known that in the presence of a constant electric field on the worldvolume of the probe, the open string metric acquires an event horizon and therefore the fluctuation modes on the probe experience an effective temperature. In this article, we bring together various properties of such a system to a formal definition and a subsequent narration of the effective thermodynamics and the stress tensor of the corresponding flavour fields, also including a non-vanishing chemical potential. In doing so, we point out a potentially infinitely-degenerate scheme-dependence of regularizing the free energy, which nevertheless yields a universal contribution in certain cases. This universal piece appears as the coefficient of a log-divergence in free energy when a space-filling probe brane is embedded in AdS d+1-background, for d = 2, 4, and is related to conformal anomaly. For the special case of d = 2, the universal factor has a striking resemblance to the well-known heat current formula in (1 + 1)-dimensional conformal field theory in steady-state, which endows a plausible physical interpretation to it. Interestingly, we observe a vanishing conformal anomaly in d = 6.
Models of steady state cooling flows in elliptical galaxies
NASA Technical Reports Server (NTRS)
Vedder, Peter W.; Trester, Jeffrey J.; Canizares, Claude R.
1988-01-01
A comprehensive set of steady state models for spherically symmetric cooling flows in early-type galaxies is presented. It is found that a reduction of the supernova (SN) rate in ellipticals produces a decrease in the X-ray luminosity of galactic cooling flows and a steepening of the surface brightness profile. The mean X-ray temperature of the cooling flow is not affected noticeably by a change in the SN rate. The external pressure around a galaxy does not markedly change the luminosity of the gas within the galaxy but does change the mean temperature of the gas. The presence of a dark matter halo in a galaxy only changes the mean X-ray temperature slightly. The addition of a distribution of mass sinks which remove material from the general accretion flow reduces L(X) very slightly, flattens the surface brightness profile, and reduces the central surface brightness level to values close to those actually observed. A reduction in the stellar mass-loss rate only slightly reduces the X-ray luminosity of the cooling flow and flattens the surface brightness by a small amount.
Optomechanically induced transparency associated with steady-state entanglement
NASA Astrophysics Data System (ADS)
He, Yong
2015-01-01
We theoretically investigate a two-cavity optomechanical system in which a cavity (cavity a ) couples to a mechanical resonator via radiation pressure and to another cavity (cavity c ) via a common waveguide. In the excitation of a strong pump filed to cavity a , the steady-state entanglement between cavity a and c , as a quantum channel, can be generated, which provides an indirect optical pathway to excite cavity c by means of the pump filed. Quantum interference between the direct and indirect optical pathways gives rise to an optomechanically induced transparency appearing in the probe transmission of cavity c . Unlike in a typical optomechanically induced transparency effect, the electromagnetical control of the transmission is implemented by resorting to the quantum channel. Furthermore, the coupling strength of the two cavities is an important factor of the quantum channel, which can influence the width of the transparency window and the bistable behavior of the mean photon number in cavity a . We also illustrate that the electromagnetical control via quantum channel can be exploited to implement the optical switch and the slow light.
Steady-state and dynamic network modes for perceptual expectation.
Choi, Uk-Su; Sung, Yul-Wan; Ogawa, Seiji
2017-01-12
Perceptual expectation can attenuate repetition suppression, the stimulus-induced neuronal response generated by repeated stimulation, suggesting that repetition suppression is a top-down modulatory phenomenon. However, it is still unclear which high-level brain areas are involved and how they interact with low-level brain areas. Further, the temporal range over which perceptual expectation can effectively attenuate repetition suppression effects remains unclear. To elucidate the details of this top-down modulatory process, we used two short and long inter-stimulus intervals for a perceptual expectation paradigm of paired stimulation. We found that top-down modulation enhanced the response to the unexpected stimulus when repetition suppression was weak and that the effect disappeared at 1,000 ms prior to stimulus exposure. The high-level areas involved in this process included the left inferior frontal gyrus (IFG_L) and left parietal lobule (IPL_L). We also found two systems providing modulatory input to the right fusiform face area (FFA_R): one from IFG_L and the other from IPL_L. Most importantly, we identified two states of networks through which perceptual expectation modulates sensory responses: one is a dynamic state and the other is a steady state. Our results provide the first functional magnetic resonance imaging (fMRI) evidence of temporally nested networks in brain processing.
Modeling on the Steady State of Thwaites Glacier
NASA Astrophysics Data System (ADS)
Yu, H.; Rignot, E. J.; Morlighem, M.; Seroussi, H.
2013-12-01
Thwaites Glacier (TWG) is the second largest ice stream in West Antarctica in terms of ice discharge, and the broadest ice stream in Antarctica (120 km wide). Observations and theory suggest that its configuration is inherently unstable in a warming climate. Satellite observations have revealed grounding line retreat, ice thinning, ice stream broadening and in more recent years ice flow acceleration. The most important part of the glacier evolution involves its grounding line dynamics and the impact of ice-ocean interactions. In a region between the grounding line and the limit of the flexure zone, some 10 km downstream, however, the glacier is not in hydrostatic equilibrium. Proper treatment of the grounding line dynamics requires full Stokes solution. Here, we model the grounding line of TWG in 2D, full Stokes, with the goal to examine whether the glacier is in a steady state configuration or not. The model treats ice sheet and ice shelf as two fluids coupled through the ice mass flux (Nowicki, 2008). Water stress is used as a constraint on the ice shelf instead of hydrostatic equilibrium. We use radar interferometry (InSAR) measurements of ice velocity and grounding line position through time, Bedmap2 and IceBridge thickness, and surface mass balance from RACMO to constrain the model. The results are used to conclude on the state of dynamic balance of the glacier. This work is funded by NASA Cryospheric Science Program.
The inductive, steady-state sustainment of stable spheromaks
NASA Astrophysics Data System (ADS)
Hossack, A. C.; Jarboe, T. R.; Morgan, K. D.; Sutherland, D. A.; Hansen, C. J.; Everson, C. J.; Penna, J. M.; Nelson, B. A.
2016-10-01
Inductive helicity injection current drive with imposed perturbations has led to the breakthrough of spheromak sustainment while maintaining stability. Sustained spheromaks show coherent, imposed plasma motion and low plasma-generated mode activity, indicating stability. Additionally, record current gain of 3.9 has been achieved with evidence of pressure confinement. The Helicity Injected Torus - Steady Inductive (HIT-SI) experiment studies efficient, steady-state current drive for magnetic confinement plasmas using a novel experimental method which is ideal for low aspect ratio, toroidal geometries and is compatible with closed flux surfaces. Analysis of surface magnetic probes indicates large n = 0 and 1 toroidal Fourier mode amplitudes and little energy in higher modes. Biorthogonal decomposition shows that almost all of the n = 1 energy is imposed by the injectors, rather than plasma-generated. Ion Doppler spectroscopy (IDS) measurements show coherent, imposed plasma motion of +/-2.5 cm in the region inside r 10 cm (a = 23 cm) and the size of the separate spheromak is consistent with that predicted by Imposed-dynamo Current Drive (IDCD). Coherent motion indicates that the spheromak is stable and a lack of plasma-generated n = 1 energy indicates that the maximum q is maintained below 1 for stability during sustainment.
Dynamic causal models of steady-state responses
Moran, R.J.; Stephan, K.E.; Seidenbecher, T.; Pape, H.-C.; Dolan, R.J.; Friston, K.J.
2009-01-01
In this paper, we describe a dynamic causal model (DCM) of steady-state responses in electrophysiological data that are summarised in terms of their cross-spectral density. These spectral data-features are generated by a biologically plausible, neural-mass model of coupled electromagnetic sources; where each source comprises three sub-populations. Under linearity and stationarity assumptions, the model's biophysical parameters (e.g., post-synaptic receptor density and time constants) prescribe the cross-spectral density of responses measured directly (e.g., local field potentials) or indirectly through some lead-field (e.g., electroencephalographic and magnetoencephalographic data). Inversion of the ensuing DCM provides conditional probabilities on the synaptic parameters of intrinsic and extrinsic connections in the underlying neuronal network. This means we can make inferences about synaptic physiology, as well as changes induced by pharmacological or behavioural manipulations, using the cross-spectral density of invasive or non-invasive electrophysiological recordings. In this paper, we focus on the form of the model, its inversion and validation using synthetic and real data. We conclude with an illustrative application to multi-channel local field potential data acquired during a learning experiment in mice. PMID:19000769
Fault Wear by Damage Evolution During Steady-State Slip
NASA Astrophysics Data System (ADS)
Lyakhovsky, Vladimir; Sagy, Amir; Boneh, Yuval; Reches, Ze'ev
2014-11-01
Slip along faults generates wear products such as gouge layers and cataclasite zones that range in thickness from sub-millimeter to tens of meters. The properties of these zones apparently control fault strength and slip stability. Here we present a new model of wear in a three-body configuration that utilizes the damage rheology approach and considers the process as a microfracturing or damage front propagating from the gouge zone into the solid rock. The derivations for steady-state conditions lead to a scaling relation for the damage front velocity considered as the wear-rate. The model predicts that the wear-rate is a function of the shear-stress and may vanish when the shear-stress drops below the microfracturing strength of the fault host rock. The simulated results successfully fit the measured friction and wear during shear experiments along faults made of carbonate and tonalite. The model is also valid for relatively large confining pressures, small damage-induced change of the bulk modulus and significant degradation of the shear modulus, which are assumed for seismogenic zones of earthquake faults. The presented formulation indicates that wear dynamics in brittle materials in general and in natural faults in particular can be understood by the concept of a "propagating damage front" and the evolution of a third-body layer.
Steady-state and transient results on insulation materials
Graves, R.S.; Yarbrough, D.W.; McElroy, D.L.; Fine, H.A.
1991-01-01
The Unguarded Thin-Heater Apparatus (UTHA, ASTM C 1114) was used to determine the thermal conductivity (k), specific heat (C), and thermal diffusivity ({alpha}) of selected building materials from 24 to 50{degree}C. Steady-state and transient measurements yielded data on four types of material: gypsum wall board containing 0, 15, and 30 wt % wax; calcium silicate insulations with densities ({rho}) of 307, 444, and 605 kg/m{sup 3}; three wood products: southern yellow pine flooring (575 kg/m{sup 3}), Douglas fir plywood (501 kg/m{sup 3}), and white spruce flooring (452 kg/m{sup 3}); and two cellular plastic foams: extruded polystyrene (30 kg/m{sup 3}) blown with HCFC-142b and polyisocyanurate rigid board (30.2 kg/m{sup 3}) blown with CFC-11. The extruded polystyrene was measured several times after production (25 days, 45 days, 74 days, 131 days, and 227 days). The UTHA is an absolute technique that yields k with an uncertainty of less than {plus minus}2% as determined by modeling, by determinate error analyses, and by use of Standard Reference Materials SRM-1450b and SRM-1451. 37 refs., 5 figs., 10 tabs.
Steady-state growth of the marine diatom Thalassiosira pseudonana
Olson, R.J.; SooHoo, J.B.; Kiefer, D.A.
1980-09-01
Seasonal studies of the vertical distribution of nitrate, nitrite, and phytoplankton in the oceans and studies using /sup 15/N as a tracer of nitrate metabolism indicate that the reduction of nitrate by phytoplankton is a source of nitrite in the upper waters of the ocean. To better understand this process, the relationship between nitrate uptake and nitrite production has been examined with continuous cultures of the small marine diatom Thalassiosira pseudonana. In a turbidostat culture, the rates of nitrite production by T. Pseudonana increase with light intensity. This process is only loosely coupled to rates of nitrate assimilation since the ratio of net nitrite production to total nitrate assimilation increases with increased rates of growth. In continuous cultures where steady-state concentrations of nitrate and nitrite were varied, T. pseudonana produced nitrite at rates which increased with increasing concentrations of nitrate. Again, the rates of nitrite production were uncoupled from rates of nitrate assimilation. The study was used to derive a mathematical description of nitrate and nitrite metabolism by T. pseudonana. The validity of this model was supported by the results of a study in which /sup 15/N-labeled nitrite was introduced into the continuous culture, and the model was used to examine patterns in distribution of nitrite in the Antarctic Ocean and the Sargasso Sea.
Steady-state compartmentalization of lipid membranes by active proteins.
Sabra, M C; Mouritsen, O G
1998-01-01
Using a simple microscopic model of lipid-protein interactions, based on the hydrophobic matching principle, we study some generic aspects of lipid-membrane compartmentalization controlled by a dispersion of active integral membrane proteins. The activity of the proteins is simulated by conformational excitations governed by an external drive, and the deexcitation is controlled by interaction of the protein with its lipid surroundings. In response to the flux of energy into the proteins from the environment and the subsequent dissipation of energy into the lipid bilayer, the lipid-protein assembly reorganizes into a steady-state structure with a typical length scale determined by the strength of the external drive. In the specific case of a mixed dimyristoylphosphatidylcholine-distearoylphosphatidylcholine bilayer in the gel-fluid coexistence region, it is shown explicitly by computer simulation that the activity of an integral membrane protein can lead to a compartmentalization of the lipid-bilayer membrane. The compartmentalization is related to the dynamical process of phase separation and lipid domain formation. PMID:9533687
Mimicking Nonequilibrium Steady States with Time-Periodic Driving
NASA Astrophysics Data System (ADS)
Raz, Oren; Subasi, Yigit; Jarzynski, Christopher
Under static conditions, a system satisfying detailed balance generically relaxes to an equilibrium state in which there are no currents: to generate persistent currents, either detailed balance must be broken or the system must be driven in a time-dependent manner. A stationary system that violates detailed balance evolves to a nonequilibrium steady state (NESS) characterized by fixed currents. Conversely, a system that satisfies instantaneous detailed balance but is driven by the time-periodic variation of external parameters - also known as a stochastic pump (SP) - reaches a periodic state with non-vanishing currents. In both cases, these currents are maintained at the cost of entropy production. Are these two paradigmatic scenarios effectively equivalent? For discrete-state systems we establish a mapping between NESS and SP. Given a NESS characterized by a particular set of stationary probabilities, currents and entropy production rates, we show how to construct a SP with exactly the same (time-averaged) values. The mapping works in the opposite direction as well. These results establish a proof of principle: they show that SP are able to mimic the behavior of NESS, and vice-versa, within the theoretical framework of discrete-state stochastic thermodynamics.
Dynamic steady state of periodically driven quantum systems
NASA Astrophysics Data System (ADS)
Yudin, V. I.; Taichenachev, A. V.; Basalaev, M. Yu.
2016-01-01
Using the density matrix formalism, we prove the existence of the periodic steady state for an arbitrary periodically driven system described by linear dynamic equations. This state has the same period as the modulated external influence, and it is realized as an asymptotic solution (t →+∞ ) due to relaxation processes. The presented derivation simultaneously contains a simple and effective computational algorithm (without using either the Floquet or Fourier formalisms), which automatically guarantees a full account of all frequency components. As a particular example, for three-level Λ system we calculate the line shape and field-induced shift of the dark resonance formed by the field with a periodically modulated phase. Also we have analytically solved a basic theoretical problem of the direct frequency comb spectroscopy, when the two-level system is driven by the periodic sequence of rectangular pulses. In this case, the radical dependence of the spectroscopy line shape on pulse area is found. Moreover, the existence of quasiforbidden spectroscopic zones, in which the Ramsey fringes are significantly reduced, is predicted. Our results have a wide area of applications in laser physics, spectroscopy, atomic clocks, and magnetometry. Also they can be useful for any area of quantum physics where periodically driven systems are considered.
Magnetocentrifugal Winds in 3D: Nonaxisymmetric Steady State
Anderson, Jeffrey M.; Li, Zhi-Yun; Krasnopolsky, Ruben; Blandford, Roger D.; /SLAC
2006-11-28
Outflows can be loaded and accelerated to high speeds along rapidly rotating, open magnetic field lines by centrifugal forces. Whether such magnetocentrifugally driven winds are stable is a longstanding theoretical problem. As a step towards addressing this problem, we perform the first large-scale 3D MHD simulations that extend to a distance {approx} 10{sup 2} times beyond the launching region, starting from steady 2D (axisymmetric) solutions. In an attempt to drive the wind unstable, we increase the mass loading on one half of the launching surface by a factor of {radical}10, and reduce it by the same factor on the other half. The evolution of the perturbed wind is followed numerically. We find no evidence for any rapidly growing instability that could disrupt the wind during the launching and initial phase of propagation, even when the magnetic field of the magnetocentrifugal wind is toroidally dominated all the way to the launching surface. The strongly perturbed wind settles into a new steady state, with a highly asymmetric mass distribution. The distribution of magnetic field strength is, in contrast, much more symmetric. We discuss possible reasons for the apparent stability, including stabilization by an axial poloidal magnetic field, which is required to bend field lines away from the vertical direction and produce a magnetocentrifugal wind in the first place.
Classical quasi-steady state reduction-A mathematical characterization
NASA Astrophysics Data System (ADS)
Goeke, Alexandra; Walcher, Sebastian; Zerz, Eva
2017-04-01
We discuss parameter dependent polynomial ordinary differential equations that model chemical reaction networks. By classical quasi-steady state (QSS) reduction we understand the following familiar (heuristically motivated) mathematical procedure: Set the rate of change for certain (a priori chosen) variables equal to zero and use the resulting algebraic equations to obtain a system of smaller dimension for the remaining variables. This procedure will generally be valid only for certain parameter ranges. We start by showing that the reduction is accurate if and only if the corresponding parameter is what we call a QSS parameter value, and that the reduction is approximately accurate if and only if the corresponding parameter is close to a QSS parameter value. The QSS parameter values can be characterized by polynomial equations and inequations, hence parameter ranges for which QSS reduction is valid are accessible in an algorithmic manner. A defining characteristic of a QSS parameter value is that the algebraic variety defined by the QSS relations is invariant for the differential equation. A closer investigation of the associated systems shows the existence of further invariant sets; here singular perturbations enter the picture in a natural manner. We compare QSS reduction and singular perturbation reduction, and show that, while they do not agree in general, they do, up to lowest order in a small parameter, for a quite large and relevant class of examples. This observation, in turn, allows the computation of QSS reductions even in cases where an explicit resolution of the polynomial equations is not possible.
Rasmussen, D.A.; Freeman, R.L.
2001-11-07
The purpose of this Cooperative Research and Development Agreement (CRADA) between UT-Battelle, LLC, (Contractor), and Archimedes Technology Group, (Participant) is to evaluate the design of an RF antenna for a large-bore, high power, steady state plasma processing chamber for material separation. Criteria for optimization will be to maximize the power deposition in the plasma while operating at acceptable voltages and currents in the antenna structure. The project objectives are to evaluate the design of an RF antenna for a large-bore, high power, steady state plasma processing chamber for material separation. Criteria for optimization will be to maximize the power deposition in the plasma while operating at acceptable voltages and currents in the antenna structure.
2012-09-03
use of so-called probability-one methods [22]. The significant advantage of homotopy method to compute steady state solutions is free of Courant ...A homotopy method based on WENO schemes for solving steady state problems of hyperbolic conservation laws Wenrui Hao∗ Jonathan D. Hauenstein† Chi...robustness of the new method . Keywords homotopy continuation, hyperbolic conservation laws, WENO scheme, steady state problems. ∗Department of Applied and
Who will save the tokamak - Harry Potter, Arnold Schwarzenegger, or Shaquille O'Neil?
NASA Astrophysics Data System (ADS)
Freidberg, J.; Mangiarotti, F.; Minervini, J.
2014-10-01
The tokamak is the current leading contender for a fusion power reactor. The reason for the preeminence of the tokamak is its high quality plasma physics performance relative to other concepts. Even so, it is well known that the tokamak must still overcome two basic physics challenges before becoming viable as a DEMO and ultimately a reactor: (1) the achievement of non-inductive steady state operation, and (2) the achievement of robust disruption free operation. These are in addition to the PMI problems faced by all concepts. The work presented here demonstrates by means of a simple but highly credible analytic calculation that a ``standard'' tokamak cannot lead to a reactor - it is just not possible to simultaneously satisfy all the plasma physics plus engineering constraints. Three possible solutions, some more well-known than others, to the problem are analyzed. These visual image generating solutions are defined as (1) the Harry Potter solution, (2) the Arnold Schwarzenegger solution, and (3) the Shaquille O'Neil solution. Each solution will be described both qualitatively and quantitatively at the meeting.
There are no steady state processes in compaction
NASA Astrophysics Data System (ADS)
Dysthe, D. K.
2003-04-01
Compaction of sediments is normally thought to start with grain sliding and cataclastic grain crushing. Then the ductile dissolution-precipitation creep processes take over. Modeling of this process normally neglects all collective rearrangement processes and regard simple packings of grains that slowly deform by steady state pressure solution creep. From simple geometrical reasoning we know, however that imperfect packings of plastic grains must undergo rearrangement during compaction. Such rearrangement will drastically alter the microscopic, or "primitive processes" of compaction. Recent research has questioned the fundamental mechanisms ("primitive processes") of dissolution-precipitation creep. Do grain contacts heal or dissolve? Why is there asymmetric dissolution? Does pressure solution creep in single contacts ever reach steady state? Can transient free face dissolution feed back on pressure solution creep in the contacts? The emerging radical change in our understanding of dissolution-precipitation creep as a dynamic, transient process is driven by new experiments and reevaluation of the fundamental theory. The same change in viewpoint is necessary on all time and length scales. I will present experiments [1-8] and simulations [9-11] of complex compaction behaviour [1], transient primitive processes of pressure solution creep in the contacts [2-4], free face dissolution [5] and crack healing [6]. I will also show that macroscopic observation of compaction shows smooth, universal behaviour [7]. Microscopic observation of compaction shows transient collective behaviour at all scales. Evidence points in the direction that compaction is dominated by transient processes with interacting instabilities. The interaction causes intermittency or switching between processes. A new, more complex theory of compaction is necessary to explain how the cooperative microscopic phenomena contribute to the simple, universal, macroscopic behaviour. 1. Uri, L., et. al., in
Ho, Pang-Yen; Chuang, Guo-Syong; Chao, An-Chong; Li, Hsing-Ya
2005-05-01
The capacity of complex biochemical reaction networks (consisting of 11 coupled non-linear ordinary differential equations) to show multiple steady states, was investigated. The system involved esterification of ethanol and oleic acid by lipase in an isothermal continuous stirred tank reactor (CSTR). The Deficiency One Algorithm and the Subnetwork Analysis were applied to determine the steady state multiplicity. A set of rate constants and two corresponding steady states are computed. The phenomena of bistability, hysteresis and bifurcation are discussed. Moreover, the capacity of steady state multiplicity is extended to the family of the studied reaction networks.
Hopf and steady state bifurcation analysis in a ratio-dependent predator-prey model
NASA Astrophysics Data System (ADS)
Zhang, Lai; Liu, Jia; Banerjee, Malay
2017-03-01
In this paper, we perform spatiotemporal bifurcation analysis in a ratio-dependent predator-prey model and derive explicit conditions for the existence of non-constant steady states that emerge through steady state bifurcation from related constant steady states. These explicit conditions are numerically verified in details and further compared to those conditions ensuring Turing instability. We find that (1) Turing domain is identical to the parametric domain where there exists only steady state bifurcation, which implies that Turing patterns are stable non-constant steady states, but the opposite is not necessarily true; (2) In non-Turing domain, steady state bifurcation and Hopf bifurcation act in concert to determine the emergent spatial patterns, that is, non-constant steady state emerges through steady state bifurcation but it may be unstable if the destabilising effect of Hopf bifurcation counteracts the stabilising effect of diffusion, leading to non-stationary spatial patterns; (3) Coupling diffusion into an ODE model can significantly enrich population dynamics by inducing alternative non-constant steady states (four different states are observed, two stable and two unstable), in particular when diffusion interacts with different types of bifurcation; (4) Diffusion can promote species coexistence by saving species which otherwise goes to extinction in the absence of diffusion.
Bieri, Oliver
2011-02-01
Conceptually, the only flaw in the standard steady-state free precession theory is the assumption of quasi-instantaneous radio-frequency pulses, and 10-20% signal deviations from theory are observed for common balanced steady-state free precession protocols. This discrepancy in the steady-state signal can be resolved by a simple T(2) substitution taking into account reduced transverse relaxation effects during finite radio-frequency excitation. However, finite radio-frequency effects may also affect the transient phase of balanced steady-state free precession, its contrast or its spin-echo nature and thereby have an adverse effect on common steady-state free precession magnetization preparation methods. As a result, an in-depth understanding of finite radio-frequency effects is not only of fundamental theoretical interest but also has direct practical implications. In this article, an analytical solution for balanced steady-state free precession with finite radio-frequency pulses is derived for the transient phase (under ideal conditions) and in the steady state demonstrating that balanced steady-state free precession key features are preserved but revealing an unexpected dependency of finite radio-frequency effects on relaxation times for the transient decay. Finally, the mathematical framework reveals that finite radio-frequency theory can be understood as a generalization of alternating repetition time and fluctuating equilibrium steady-state free precession sequence schemes.
Phencyclidine Disrupts the Auditory Steady State Response in Rats
Leishman, Emma; O’Donnell, Brian F.; Millward, James B.; Vohs, Jenifer L.; Rass, Olga; Krishnan, Giri P.; Bolbecker, Amanda R.; Morzorati, Sandra L.
2015-01-01
The Auditory Steady-State Response (ASSR) in the electroencephalogram (EEG) is usually reduced in schizophrenia (SZ), particularly to 40 Hz stimulation. The gamma frequency ASSR deficit has been attributed to N-methyl-D-aspartate receptor (NMDAR) hypofunction. We tested whether the NMDAR antagonist, phencyclidine (PCP), produced similar ASSR deficits in rats. EEG was recorded from awake rats via intracranial electrodes overlaying the auditory cortex and at the vertex of the skull. ASSRs to click trains were recorded at 10, 20, 30, 40, 50, and 55 Hz and measured by ASSR Mean Power (MP) and Phase Locking Factor (PLF). In Experiment 1, the effect of different subcutaneous doses of PCP (1.0, 2.5 and 4.0 mg/kg) on the ASSR in 12 rats was assessed. In Experiment 2, ASSRs were compared in PCP treated rats and control rats at baseline, after acute injection (5 mg/kg), following two weeks of subchronic, continuous administration (5 mg/kg/day), and one week after drug cessation. Acute administration of PCP increased PLF and MP at frequencies of stimulation below 50 Hz, and decreased responses at higher frequencies at the auditory cortex site. Acute administration had a less pronounced effect at the vertex site, with a reduction of either PLF or MP observed at frequencies above 20 Hz. Acute effects increased in magnitude with higher doses of PCP. Consistent effects were not observed after subchronic PCP administration. These data indicate that acute administration of PCP, a NMDAR antagonist, produces an increase in ASSR synchrony and power at low frequencies of stimulation and a reduction of high frequency (> 40 Hz) ASSR activity in rats. Subchronic, continuous administration of PCP, on the other hand, has little impact on ASSRs. Thus, while ASSRs are highly sensitive to NMDAR antagonists, their translational utility as a cross-species biomarker for NMDAR hypofunction in SZ and other disorders may be dependent on dose and schedule. PMID:26258486
Steady state growth of E. Coli in low ammonium environment
NASA Astrophysics Data System (ADS)
Kim, Minsu; Deris, Barret; Zhang, Zhongge; Hwa, Terry
2011-03-01
Ammonium is the preferred nitrogen source for many microorganisms. In medium with low ammonium concentrations, enteric bacteria turn on the nitrogen responsive (ntr) genes to assimilate ammonium. Two proteins in E. coli, Glutamine synthetase (GS) and the Ammonium/methylammonium transporter AmtB play crucial roles in this regard. GS is the major ammonium assimilation enzyme below 1mM of NH4 + . AmtB is an inner membrane protein that transports NH4 + across the cell membrane against a concentration gradient. In order to study ammonium uptake at low NH4 + concentration at neutral pH, we developed a microfluidic flow chamber that maintains a homogenous nutrient environment during the course of exponential cell growth, even at very low concentration of nutrients. Cell growth can be accurately monitored using time-lapse microscopy. We followed steady state growth down to micro-molar range of NH4 + for the wild type and Δ amtB strains. The wild type strain is able to maintain the growth rate from 10mM down to a few uM of NH4 + , while the mutant exhibited reduced growth below ~ 20 ~uM of NH4 + . Simultaneous characterization of the expression levels of GS and AmtB using fluorescence reporters reveals that AmtB is turned on already at 1mM, but contributes to function only below ~ 30 ~uM in the wild-type. Down to ~ 20 ~uM of NH4 + , E.~coli can compensate the loss of AmtB by GS alone.
Steady-state and transient electronic dynamics in granular metals
NASA Astrophysics Data System (ADS)
Chen, Wei
In this thesis two very different approaches, steady state and transient, are taken to help understand the electronic dynamics in the nanogranular Cux(SiO2)1-x composite thin films. The electrical conductivity and thermopower are measured from 2 K to room temperature with the Cu volume fraction x varying from 1 down to 0.43. At low temperatures, a T dependence of the electrical conductivity is observed well above the percolation threshold due to the disorder-enhanced electron-electron interaction and as the metal-insulator transition is approached, the electrical conductivity assumes a T1/3 dependence. The thermopower is found to be small and rather insensitive to the degree of disorder in the system. It varies linearly with temperatures at both low and high temperatures. Annealing has considerable influence to the behavior of the electrical conductivity while introducing little changes to the thermopower. Femtosecond pump-probe experiments were performed on a series of Cu x(SiO2)1-x composite films with volume fraction x varying from 0.7 to 1.0 to study the reflectivity change DeltaR/R as a function of composition and temperature. It is discovered that DeltaR/R undergoes drastic changes as the metal content is lowered. Very small amount of SiO 2 inclusions can start to result in qualitatively different Delta R/R behavior from pure Cu. Changes in the dielectric constant of Cu are investigated and possible explanations for the DeltaR/R behaviors in the composite films are discussed.
Experimental Realization of Nearly Steady-State Toroidal Electron Plasmas
NASA Astrophysics Data System (ADS)
Stoneking, M. R.
2008-11-01
Non-neutral plasmas are routinely confined in the uniform magnetic field of a Penning-Malmberg trap for arbitrarily long times and approach thermal equilibrium. Theory predicts that dynamically stable and therefore long-lived equilibria exist for non-neutral plasmas confined in the curved, non-uniform field of a toroidal trap, but that ultimately thermal equilibrium states do not exist. On long timescales, the poloidal ExB rotation through the non-uniform toroidal magnetic field leads to magnetic pumping transport. A new experiment has, for the first time, demonstrated the existence of a stable, long-lived (i.e. nearly steady-state) toroidal equilibrium for pure electron plasmas and is poised to observe the magnetic pumping transport mechanism. Electron plasmas with densities of order 10^6 cm-3 are trapped in the Lawrence Non-neutral Torus II for several seconds. LNT II is a high aspect ratio (Ro/a 10), partially toroidal trap (a 270^o arc with Bo=670 G). The m=1 diocotron mode is launched and detected using isolated segments of a fully-sectored conducting boundary and its frequency is used to determine the total trapped charge as a function of time. The observed confinement time ( 3 s) approaches the theoretical limit ( 6 s) set by the magnetic pumping transport mechanism of Crooks and O'Neil. We also present equilibrium modeling and numerical simulation of the toroidal m=1 mode constrained by experimental data. Future work includes the identification of the dominant transport mechanisms via confinement scaling experiments and measurement of the m=2 mode frequency, and development of a strategy for making a transition to fully toroidal confinement. J.P. Marler and M.R. Stoneking, Phys. Rev. Lett. 100, 155001 (2008). S.M. Crooks and T.M. O'Neil, Phys Plamas 3, 2533 (1996).
Nonequilibrium steady states in a model for prebiotic evolution
NASA Astrophysics Data System (ADS)
Wynveen, A.; Fedorov, I.; Halley, J. W.
2014-02-01
Some statistical features of steady states of a Kauffman-like model for prebiotic evolution are reported from computational studies. We postulate that the interesting "lifelike" states will be characterized by a nonequilibrium distribution of species and a time variable species self-correlation function. Selecting only such states from the population of final states produced by the model yields the probability of the appearance of such states as a function of a parameter p of the model. p is defined as the probability that a possible reaction in the the artificial chemistry actually appears in the network of chemical reactions. Small p corresponds to sparse networks utilizing a small fraction of the available reactions. We find that the probability of the appearance of such lifelike states exhibits a maximum as a function of p: at large p, most final states are in chemical equilibrium and hence are excluded by our criterion. At very small p, the sparseness of the network makes the probability of formation of any nontrivial dynamic final state low, yielding a low probability of production of lifelike states in this limit as well. We also report results on the diversity of the lifelike states (as defined here) that are produced. Repeated starts of the model evolution with different random number seeds in a given reaction network lead to final lifelike states which have a greater than random likelihood of resembling one another. Thus a form of "convergence" is observed. On the other hand, in different reaction networks with the same p, lifelike final states are statistically uncorrelated. In summary, the main results are (1) there is an optimal p or "sparseness" for production of lifelike states in our model—neither very dense nor very sparse networks are optimal—and (2) for a given p or sparseness, the resulting lifelike states can be extremely different. We discuss some possible implications for studies of the origin of life.
Impact of aquifer desaturation on steady-state river seepage
NASA Astrophysics Data System (ADS)
Morel-Seytoux, Hubert J.; Miracapillo, Cinzia; Mehl, Steffen
2016-02-01
Flow exchange between surface and ground water is of great importance be it for beneficial allocation and use of the water resources or for the proper exercise of water rights. That exchange can take place under a saturated or unsaturated flow regime. Which regimes occur depend on conditions in the vicinity of the interactive area. Withdrawals partially sustained by seepage may not bring about desaturation but greater amounts eventually will. The problem considered in this paper deals only with the steady-state case. It is meant as a first step toward a simple, yet accurate and physically based treatment of the transient situation. The primary purpose of the article is to provide simple criteria for determination of the initiation of desaturation in an aquifer originally in saturated hydraulic connection with a river or a recharge area. The extent of the unsaturated zone in the aquifer will increase with increasing withdrawals while at the same time the seepage rate from the river increases. However the seepage increase will stop once infiltration takes place strictly by gravity in the aquifer and is no longer opposed by the capillary rise from the water table below the riverbed. Following desaturation simple criteria are derived and simple analytical formulae provided to estimate the river seepage based on the position of the water table mound below the clogging layer and at some distance away from the river bank. They fully account for the unsaturated flow phenomena, including the existence of a drainage entry pressure. Two secondary objectives were to verify that (1) the assumption of uniform vertical flow through a clogging layer and that (2) the approximation of the water table mound below the seepage area as a flat surface were both reasonably legitimate. This approach will be especially advantageous for the implementation of the methodology in large-scale applications of integrated hydrologic models used for management.
Options for commercial tokamaks
Dabiri, A.E.; Keeton, D.C.; Thomson, S.L.
1986-07-01
Systems studies have been performed at the Fusion Engineering Design Center (FEDC) to assess commercial tokamak options. One study investigates the economics of high-beta operation and determines an optimum operating range of 10 to 20% beta, with a corresponding neutron wall loading of 6 to 8 MW/m/sup 2/. A second study determines conditions under which small, low-power tokamaks can be economically combined into a 1200-MW(electric) multiplex power plant. The results of these studies have directed future efforts at the FEDC toward a high-beta, tokamak design using a modular maintenance configuration.
Turbulence-driven bootstrap current in low-collisionality tokamaks.
McDevitt, C J; Tang, Xian-Zhu; Guo, Zehua
2013-11-15
Neoclassical bootstrap current is expected to provide a significant fraction of the equilibrium plasma current in tokamak reactors. Here we report a novel mechanism through which a bootstrap current may be driven even in a collisionless plasma. In analogy with the neoclassical mechanism, in which the collisional equilibrium established between trapped and passing electrons produces a steady state current, we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons and thus driving a bootstrap current. Employing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions and resonant electron scattering is computed, allowing for the relative strength of these two mechanisms to be quantified as a function of collisionality and fluctuation amplitude.
STARFIRE: a commercial tokamak fusion power plant study
Not Available
1980-09-01
STARFIRE is a 1200 MWe central station fusion electric power plant that utilizes a deuterium-tritium fueled tokamak reactor as a heat source. Emphasis has been placed on developing design features which will provide for simpler assembly and maintenance, and improved safety and environmental characteristics. The major features of STARFIRE include a steady-state operating mode based on continuous rf lower-hybrid current drive and auxiliary heating, solid tritium breeder material, pressurized water cooling, limiter/vacuum system for impurity control and exhaust, high tritium burnup and low vulnerable tritium inventories, superconducting EF coils outside the superconducting TF coils, fully remote maintenance, and a low-activation shield. A comprehensive conceptual design has been developed including reactor features, support facilities and a complete balance of plant. A construction schedule and cost estimate are presented, as well as study conclusions and recommendations.
NASA Astrophysics Data System (ADS)
Chirkov, A. Yu.
2015-09-01
Low gain (Q ~ 1) fusion plasma systems are of interest for concepts of fusion-fission hybrid reactors. Operational regimes of large modern tokamaks are close to Q ≈ 1. Therefore, they can be considered as prototypes of neutron sources for fusion-fission hybrids. Powerful neutral beam injection (NBI) can support the essential population of fast particles compared with the Maxwellial population. In such two-component plasma, fusion reaction rate is higher than for Maxwellian plasma. Increased reaction rate allows the development of relatively small-size and relatively inexpensive neutron sources. Possible operating regimes of the NBI-heated tokamak neutron source are discussed. In a relatively compact device, the predictions of physics of two-component fusion plasma have some volatility that causes taking into account variations of the operational parameters. Consequent parameter ranges are studied. The feasibility of regimes with Q ≈ 1 is shown for the relatively small and low-power system. The effect of NBI fraction in total heating power is analyzed.
The high-β{sub N} hybrid scenario for ITER and FNSF steady-state missions
Turco, F.; Petty, C. C.; Luce, T. C.; Carlstrom, T. N.; Van Zeeland, M. A.; Ferron, J. R.; Heidbrink, W.; Carpanese, F.; Holcomb, C. T.
2015-05-15
New experiments on DIII-D have demonstrated the steady-state potential of the hybrid scenario, with 1 MA of plasma current driven fully non-inductively and β{sub N} up to 3.7 sustained for ∼3 s (∼1.5 current diffusion time, τ{sub R}, in DIII-D), providing the basis for an attractive option for steady-state operation in ITER and FNSF. Excellent confinement is achieved (H{sub 98y2} ∼ 1.6) without performance limiting tearing modes. The hybrid regime overcomes the need for off-axis current drive efficiency, taking advantage of poloidal magnetic flux pumping that is believed to be the result of a saturated 3/2 tearing mode. This allows for efficient current drive close to the axis, without deleterious sawtooth instabilities. In these experiments, the edge surface loop voltage is driven down to zero for >1 τ{sub R} when the poloidal β is increased above 1.9 at a plasma current of 1.0 MA and the ECH power is increased to 3.2 MW. Stationary operation of hybrid plasmas with all on-axis current drive is sustained at pressures slightly above the ideal no-wall limit, while the calculated ideal with-wall MHD limit is β{sub N} ∼ 4–4.5. Off-axis Neutral Beam Injection (NBI) power has been used to broaden the pressure and current profiles in this scenario, seeking to take advantage of higher predicted kink stability limits and lower values of the tearing stability index Δ′, as calculated by the DCON and PEST3 codes. Results based on measured profiles predict ideal limits at β{sub N} > 4.5, 10% higher than the cases with on-axis NBI. A 0-D model, based on the present confinement, β{sub N} and shape values of the DIII-D hybrid scenario, shows that these plasmas are consistent with the ITER 9 MA, Q = 5 mission and the FNSF 6.7 MA scenario with Q = 3.5. With collisionality and edge safety factor values comparable to those envisioned for ITER and FNSF, the high-β{sub N} hybrid represents an attractive high performance option for the steady-state
The high-βN hybrid scenario for ITER and FNSF steady-state missionsa)
NASA Astrophysics Data System (ADS)
Turco, F.; Petty, C. C.; Luce, T. C.; Carlstrom, T. N.; Van Zeeland, M. A.; Heidbrink, W.; Carpanese, F.; Solomon, W.; Holcomb, C. T.; Ferron, J. R.
2015-05-01
New experiments on DIII-D have demonstrated the steady-state potential of the hybrid scenario, with 1 MA of plasma current driven fully non-inductively and βN up to 3.7 sustained for ˜3 s (˜1.5 current diffusion time, τR, in DIII-D), providing the basis for an attractive option for steady-state operation in ITER and FNSF. Excellent confinement is achieved (H98y2 ˜ 1.6) without performance limiting tearing modes. The hybrid regime overcomes the need for off-axis current drive efficiency, taking advantage of poloidal magnetic flux pumping that is believed to be the result of a saturated 3/2 tearing mode. This allows for efficient current drive close to the axis, without deleterious sawtooth instabilities. In these experiments, the edge surface loop voltage is driven down to zero for >1 τR when the poloidal β is increased above 1.9 at a plasma current of 1.0 MA and the ECH power is increased to 3.2 MW. Stationary operation of hybrid plasmas with all on-axis current drive is sustained at pressures slightly above the ideal no-wall limit, while the calculated ideal with-wall MHD limit is βN ˜ 4-4.5. Off-axis Neutral Beam Injection (NBI) power has been used to broaden the pressure and current profiles in this scenario, seeking to take advantage of higher predicted kink stability limits and lower values of the tearing stability index Δ', as calculated by the DCON and PEST3 codes. Results based on measured profiles predict ideal limits at βN > 4.5, 10% higher than the cases with on-axis NBI. A 0-D model, based on the present confinement, βN and shape values of the DIII-D hybrid scenario, shows that these plasmas are consistent with the ITER 9 MA, Q = 5 mission and the FNSF 6.7 MA scenario with Q = 3.5. With collisionality and edge safety factor values comparable to those envisioned for ITER and FNSF, the high-βN hybrid represents an attractive high performance option for the steady-state missions of these devices.
Self-organized stationary states of tokamaks
NASA Astrophysics Data System (ADS)
Jardin, Stephen
2015-11-01
We report here on a nonlinear mechanism that forms and maintains a self-organized stationary (sawtooth free) state in tokamaks. This process was discovered by way of extensive long-time simulations using the M3D-C1 3D extended MHD code in which new physics diagnostics have been added. It is well known that most high-performance modes of tokamak operation undergo ``sawtooth'' cycles, in which the peaking of the toroidal current density triggers a periodic core instability which redistributes the current density. However, certain modes of operation are known, such as the ``hybrid'' mode in DIII-D, ASDEX-U, JT-60U and JET, and the long-lived modes in NSTX and MAST, which do not experience this cycle of instability. Empirically, it is observed that these modes maintain a non-axisymmetric equilibrium which somehow limits the peaking of the toroidal current density. The physical mechanism responsible for this has not previously been understood, but is often referred to as ``flux-pumping,'' in which poloidal flux is redistributed in order to maintain q0 >1. In this talk, we show that in long-time simulations of inductively driven plasmas, a steady-state magnetic equilibrium may be obtained in which the condition q0 >1 is maintained by a dynamo driven by a stationary marginal core interchange mode. This interchange mode, unstable because of the pressure gradient in the ultra-low shear region in the center region, causes a (1,1) perturbation in both the electrostatic potential and the magnetic field, which nonlinearly cause a (0,0) component in the loop voltage that acts to sustain the configuration. This hybrid mode may be a preferred mode of operation for ITER. We present parameter scans that indicate when this sawtooth-free operation can be expected.
NASA Technical Reports Server (NTRS)
Sargent, N. B.
1980-01-01
The steady state test results on a breadboard version of the General Electric Near Term Electric Vehicle (ETV-1) are discussed. The breadboard was built using exact duplicate vehicle propulsion system components with few exceptions. Full instrumentation was provided to measure individual component efficiencies. Tests were conducted on a 50 hp dynamometer in a road load simulator facility. Characterization of the propulsion system over the lower half of the speed-torque operating range has shown the system efficiency to be composed of a predominant motor loss plus a speed dependent transaxle loss. At the lower speeds with normal road loads the armature chopper loss is also a significant factor. At the conditions corresponding to a cycle for which the vehicle system was specifically designed, the efficiencies are near optimum.
Steady-state and dynamic performance of a gas-lubricated seal
NASA Technical Reports Server (NTRS)
Colsher, R.; Shapiro, W.
1972-01-01
Steady-state and dynamic performance of a gas-lubricated, self-acting face seal was determined using numerical methods based on a variable grid, finite-difference, time-transient procedure. Results were obtained for a gas turbine main shaft seal operating at 206.9 newton per square centimeter (300 psi) sealed air pressure and 152.4 meters per second (500 ft/sec) sliding velocity. Analysis of the seal dynamics revealed that the response of the seal nosepiece to runout of the seat face is markedly affected by secondary seal friction and by nosepiece inertia. The nosepiece response was determined for various levels of secondary seal friction and seat face runout magnitudes.
Hashiguchi, Kimiaki; Morioka, Takato; Samura, Kazuhiro; Yoshida, Fumiaki; Miyagi, Yasushi; Nagata, Shinji; Kokubo, Takayuki; Yoshiura, Takashi; Sasaki, Tomio
2008-01-01
We report an operated case with terminal myelocystocele and holocord hydrosyringomyelia (syrinx). The patient exhibited a subcutaneous mass at the right lumbosacral region with multiple anomalies including scoliosis and hyperdactylia of the right foot and systemic disease such as hydronephroureter. Neurological examination revealed palsy of the left diaphragm, and left upper and right lower limbs. Constructive interference in steady-state (CISS) images demonstrated a terminal myelocystocele with a huge syrinx extending to the medulla. The curvilinear reconstruction of the CISS sequence depicted continuous cystocele and whole syrinx. At day 37, sac excision and untethering of the spinal cord were performed. The caudal part of the central canal was opened to the subarachnoid space (terminal ventriculostomy), resulting in a slight improvement of limb palsy and shrinkage of the holocord syrinx. CISS imaging is useful to detect the complicated pathology, and terminal ventriculostomy should be performed to improve associated syrinx.
Steady-State Characterization of Bacteriorhodopsin-D85N Photocycle
NASA Technical Reports Server (NTRS)
Timucin, Dogan A.; Downie, John D.; Norvig, Peter (Technical Monitor)
1999-01-01
An operational characterization of the photocycle of the genetic mutant D85N of bacteriorhodopsin, BR-D85N, is presented. Steady-state bleach spectra and pump-probe absorbance data are obtained with thick hydrated films containing BR-D85N embedded in a gelatin host. Simple two- and three-state models are used to analyze the photocycle dynamics and extract relevant information such as pure-state absorption spectra, photochemical-transition quantum efficiencies, and thermal lifetimes of dominant states appearing in the photocycle, the knowledge of which should aid in the analysis of optical recording and retrieval of data in films incorporating this photochromic material. The remarkable characteristics of this material and their implications from the viewpoint of optical data storage and processing are discussed.
NASA Technical Reports Server (NTRS)
Horn, Thomas J.; Abdelmessih, Amanie N.
2000-01-01
A blackbody calibration furnace at the NASA Dryden Flight Research Center is used to calibrate heat flux gages. These gages are for measuring the aerodynamic heat flux on hypersonic flight vehicle surfaces. The blackbody is a graphite tube with a midplane partition which divides the tube into two compartments (dual cavities). Electrical resistance heating is used to heat the graphite tube. This heating and the boundary conditions imposed on the graphite tube result in temperature gradients along the walls of the blackbody cavity. This paper describes measurements made during steady-state operation and development of finite-difference thermal models of the blockbody furnace at 1100 C. Two configurations were studied, one with the blackbody outer surface insulated and the other without insulation. The dominant modes of heat transfer were identified for each configuration and the effect of variations in material properties and electric current that was passed through the blackbody were quantified.
Steady State Analysis Of The Variable Speed Switched Reluctance Motor Drive
NASA Astrophysics Data System (ADS)
Materu, P.; Krishnan, R.; Farzanehfard, H.
1987-10-01
The switched reluctance motor (SRM) drive has recently received attention mainly because of its simple motor construction and unidirectional converter requirement. The principle of operation of the motor drive demands that the motor and converter be treated as one unit. Little has been done to develop a complete analysis of this motor-converter combination 1'2. This paper presents an approach to the steady state analysis of the SRM drive including the effects of stator winding resistance, input filter dynamics and snubber circuits which are often neglected. The analysis yields phase current waveforms providing guidelines to the optimal design of the converter and motor. A novel single-switch-per phase converter developed by one of the authors is used. The approach can be used for any other motor-converter combination.
NASA Technical Reports Server (NTRS)
Alkasab, K. A.; Abdul-Aziz, A.
1991-01-01
The influence of thermophysical properties and flow rate on the steady-state temperature distribution in a phosphoric-acid fuel cell electrode plate was experimentally investigated. An experimental setup that simulates the operating conditions prevailing in a phosphoric-acid fuel cell stack was used. The fuel cell cooling system utilized three types of coolants to remove excess heat generated in the cell electrode and to maintain a reasonably uniform temperature distribution in the electrode plate. The coolants used were water, engine oil, and air. These coolants were circulated at Reynolds number ranging from 1165 to 6165 for water; 3070 to 6864 for air; and 15 to 79 for oil. Experimental results are presented.
COMSOL Simulations for Steady State Thermal Hydraulics Analyses of ORNL s High Flux Isotope Reactor
Khane, Vaibhav B; Jain, Prashant K; Freels, James D
2012-01-01
Simulation models for steady state thermal hydraulics analyses of Oak Ridge National Laboratory s High Flux Isotope Reactor (HFIR) have been developed using the COMSOL Multiphysics simulation software. A single fuel plate and coolant channel of each type of HFIR fuel element was modeled in three dimensions; coupling to adjacent plates and channels was accounted for by using periodic boundary conditions. The standard k- turbulence model was used in simulating turbulent flow with conjugate heat transfer. The COMSOL models were developed to be fully parameterized to allow assessing impacts of fuel fabrication tolerances and uncertainties related to low enriched uranium (LEU) fuel design and reactor operating parameters. Heat source input for the simulations was obtained from separate Monte Carlo N Particle calculations for the axially non-contoured LEU fuel designs at the beginning of the reactor cycle. Mesh refinement studies have been performed to calibrate the models against the pressure drop measured across the HFIR core.
Mirnov, S. V.; Azizov, E. A.; Lazarev, V. B.; Evtikhin, V. A.; Lyublinski, I. E.; Vertkov, A. V.; Prokhorov, D. Yu.; Soboleva, T. K.
2006-12-04
The idea of use the Capillary-Pore System (CPS) as material of tokamak limiter is discussed. The results of CPS Li limiter tests in T-11M tokamak have shown that the Li erosion in temperature interval 200 -700 deg. C can not be a serious obstacle for tokamak operations. The sorption of deuterium ions by Li wall can be excluded by its heating up to 400-500 deg. C. The idea of combined lithium limiter with thin (1-0,6mm) Li CPS coating as a solution of heat removal problem was realized. The quasi steady state tokamak regime with duration up to 0.2-0.3s and clean (Zeff{approx_equal}1) deuterium plasma has been achieved. The measurements of plasma radiation showed up to 90 % of total non-coronal radiation losses located in a relatively thin (5cm) boundary layer. A version of Li CPS limiter of DEMO reactor and Li CPS limiter experiment in ITER are suggested. The concept of 'emitter-collector' tokamak limiter is discussed.
Profile control of advanced tokamak plasmas in view of continuous operation
NASA Astrophysics Data System (ADS)
Mazon, D.
2015-07-01
The concept of the tokamak is a very good candidate to lead to a fusion reactor. In fact, certain regimes of functioning allow today the tokamaks to attain performances close to those requested by a reactor. Among the various scenarios of functioning nowadays considered for the reactor option, certain named 'advanced scenarios' are characterized by an improvement of the stability and confinement in the plasma core, as well as by a modification of the current profile, notably thank to an auto-generated 'bootstrap' current. The general frame of this paper treats the perspective of a real-time control of advanced regimes. Concrete examples will underline the impact of diagnostics on the identification of plasma models, from which the control algorithms are constructed. Several preliminary attempts will be described.
Rod Bundle Heat Transfer: Steady-State Steam Cooling Experiments
Spring, J.P.; McLaughlin, D.M.
2006-07-01
Through the joint efforts of the Pennsylvania State University and the United States Nuclear Regulatory Commission, an experimental rod bundle heat transfer (RBHT) facility was designed and built. The rod bundle consists of a 7 x 7 square pitch array with spacer grids and geometry similar to that found in a modern pressurized water reactor. From this facility, a series of steady-state steam cooling experiments were performed. The bundle inlet Reynolds number was varied from 1 400 to 30 000 over a pressure range from 1.36 to 4 bars (20 to 60 psia). The bundle inlet steam temperature was controlled to be at saturation for the specified pressure and the fluid exit temperature exceeded 550 deg. C in the highest power tests. One important quantity of interest is the local convective heat transfer coefficient defined in terms of the local bulk mean temperature of the flow, local wall temperature, and heat flux. Steam temperatures were measured at the center of selected subchannels along the length of the bundle by traversing miniaturized thermocouples. Using an analogy between momentum and energy transport, a method was developed for relating the local subchannel centerline temperature measurement to the local bulk mean temperature. Wall temperatures were measured using internal thermocouples strategically placed along the length of each rod and the local wall heat flux was obtained from an inverse conduction program. The local heat transfer coefficient was calculated from the data at each rod thermocouple location. The local heat transfer coefficients calculated for locations where the flow was fully developed were compared against several published correlations. The Weisman and El-Genk correlations were found to agree best with the RBHT steam cooling data, especially over the range of turbulent Reynolds numbers. The effect of spacer grids on the heat transfer enhancement was also determined from instrumentation placed downstream of the spacer grid locations. The local
Critical particle circulation caused by high-performance steady-state plasma discharge
NASA Astrophysics Data System (ADS)
Kasahara, Hiroshi
2015-11-01
Steady-state operation focused on the fusion reactor has been investigated in magnetic confined fusion devices, and plasma performance and duration time are steadily extended by the improvement of the quality of plasma heating and sophisticating plasma operation using the understanding of long-pulse plasma experiments. When higher-performance helium steady-state plasma discharges with duration time over 40 min, electron density of 1.2x1019 m-3, ion and electron temperatures over 2 keV and heating power of 1.2MW were repeatedly achieved in LHD, time-evolution of the wall-pumping and increasing frequency of impurity contaminations around the plasma edge clearly occurred. These are strongly related to the increasing mixed-material layer caused by continuous divertor erosion around geometrical dense divertor plates, which consists of carbon (> 90%) and iron (< a few %) with amorphous structure, that can retain the helium particles and affect the particle balance in long-pulse discharges. The mixed-material layer is easily exfoliated by the thermal stress and helium explosion in the layer, and small pieces of exfoliation enter the plasma edge in all toroidal sections. Uncontrolled flake contamination was one of the causes of plasma termination in long-pulse experiments. Increased plasma performance using higher heating power (~ 3.3 MW) with high quality makes robust plasma against impurity contaminations, and then a small amount of contamination of mixed-material does not terminate the helium plasma. Carbon impurity was circulated from the divertor plates and around the plates to the plasma edge in long-pulse plasma discharges, and the circulation was increased by the plasma duration and performance. The eroded material plays an important role in degrading the plasma performance as an impurity source and in the controllability of particle fueling in long-pulse discharges.
Transient and steady State Patterns in Gravel Bars Following Sediment Supply Increases
NASA Astrophysics Data System (ADS)
Podolak, C.; Wilcock, P.
2011-12-01
Bedforms in a gravel-bed river respond to a combination of water discharge, sediment supply, and valley-scale geometry. The bed configuration can also vary between transient and steady-state conditions. Field and flume observations of gravel bedform responses to changes in sediment supply have focused primarily on decreased sediment supply, and those that have dealt with increased sediment supply have found cases of both increasing relief and decreasing relief. We present gravel bedform configurations under conditions of increased sediment supply in both field and laboratory conditions. The field study tracked the response of the Sandy River, Oregon after an increase in sediment flux due to the 2007 Marmot Dam removal in which nearly 750,000 m3 of impounded sediment which was made available for transport and resulted in a several-fold increase in annual sediment flux. The flume experiments introduced perturbation in a planar gravel bed (gravel D50 = 10mm, 15% sand) prompting alternate bar formation. Sediment was then manually added to the recirculating flume (in essence operating it as a feed flume) increasing flux rates by 50%. Upon reaching a steady state, the upstream flux was then augmented again to double the steady state rate. In response to the increased sediment supply the bed topography steepened to transport the imposed sediment flux. In both flume and field, the final bed response to increased sediment supply was deposition of a sediment wedge, steeping the channel slope with little change in bar morphology. Although the location and morphology of the bedforms were similar as the bed configuration stabilized, the transient response showed different patterns of deposition across the stream. A pattern of decreasing relief both from bar tops eroding and pools filling was observed as well as the migration of smaller wavelength high-celerity gravel bars as the bed decreased in relief. To explore the transient response we modeled both cases with a 2-D depth
40 CFR 92.130 - Determination of steady-state concentrations.
Code of Federal Regulations, 2013 CFR
2013-07-01
... concentrations. 92.130 Section 92.130 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR....130 Determination of steady-state concentrations. (a)(1) For HC and NOX emissions, a steady-state concentration measurement, measured after 300 seconds (or 840 seconds for notch 8) of testing shall be...
40 CFR 92.130 - Determination of steady-state concentrations.
Code of Federal Regulations, 2010 CFR
2010-07-01
... concentrations. 92.130 Section 92.130 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR....130 Determination of steady-state concentrations. (a)(1) For HC and NOX emissions, a steady-state concentration measurement, measured after 300 seconds (or 840 seconds for notch 8) of testing shall be...
40 CFR 92.130 - Determination of steady-state concentrations.
Code of Federal Regulations, 2011 CFR
2011-07-01
... concentrations. 92.130 Section 92.130 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR....130 Determination of steady-state concentrations. (a)(1) For HC and NOX emissions, a steady-state concentration measurement, measured after 300 seconds (or 840 seconds for notch 8) of testing shall be...
40 CFR 92.130 - Determination of steady-state concentrations.
Code of Federal Regulations, 2012 CFR
2012-07-01
... concentrations. 92.130 Section 92.130 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR....130 Determination of steady-state concentrations. (a)(1) For HC and NOX emissions, a steady-state concentration measurement, measured after 300 seconds (or 840 seconds for notch 8) of testing shall be...
40 CFR 92.130 - Determination of steady-state concentrations.
Code of Federal Regulations, 2014 CFR
2014-07-01
... concentrations. 92.130 Section 92.130 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR....130 Determination of steady-state concentrations. (a)(1) For HC and NOX emissions, a steady-state concentration measurement, measured after 300 seconds (or 840 seconds for notch 8) of testing shall be...
Constructive interference in steady-state/FIESTA-C clinical applications in neuroimaging.
Kulkarni, Makarand; Kulkami, Makarand
2011-04-01
High spatial resolution is one of the major problems in neuroimaging, particularly in cranial and spinal nerve imaging. Constructive interference in steady-state/fast imaging employing steady-state acquisition with phase cycling is a robust sequence in imaging the cranial and spinal nerve pathologies. This pictorial review is a concise article about the applications of this sequence in neuroimaging with clinical examples.
40 CFR 85.2230 - Steady state test dynamometer-EPA 91.
Code of Federal Regulations, 2010 CFR
2010-07-01
... 40 Protection of Environment 18 2010-07-01 2010-07-01 false Steady state test dynamometer-EPA 91. 85.2230 Section 85.2230 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... Warranty Short Tests § 85.2230 Steady state test dynamometer—EPA 91. (a) Special calendar and model...
Phased Array Ghost Elimination (PAGE) for Segmented SSFP Imaging With Interrupted Steady-State
Kellman, Peter; Guttman, Michael A.; Herzka, Daniel A.; McVeigh, Elliot R.
2007-01-01
Steady-state free precession (SSFP) has recently proven to be valuable for cardiac imaging due to its high signal-to-noise ratio and blood-myocardium contrast. Data acquired using ECG-triggered, segmented sequences during the approach to steady-state, or return to steady-state after interruption, may have ghost artifacts due to periodic k-space distortion. Schemes involving several preparatory RF pulses have been proposed to restore steady-state, but these consume imaging time during early systole. Alternatively, the phased-array ghost elimination (PAGE) method may be used to remove ghost artifacts from the first several frames. PAGE was demonstrated for cardiac cine SSFP imaging with interrupted steady-state using a simple alpha/2 magnetization preparation and storage scheme and a spatial tagging preparation. PMID:12465121
LONG PULSE ADVANCED TOKAMAK DISCHARGES IN THE DIII-D TOKAMAK
P.I. PETERSEN
2002-06-01
One of the main goals for the DIII-D research program is to establish an advanced tokamak plasma with high bootstrap current fraction that can be sustained in-principle steady-state. Substantial progress has been made in several areas during the last year. The resistive wall mode stabilization has been done with spinning plasmas in which the plasma pressure has been extended well above the no-wall beta limit. The 3/2 neoclassical tearing mode has been stabilized by the injection of ECH into the magnetic islands, which drives current to substitute the missing bootstrap current. In these experiments either the plasma was moved or the toroidal field was changed to overlap the ECCD resonance with the location of the NTMs. Effective disruption mitigation has been obtained by massive noble gas injection into shots where disruptions were deliberately triggered. The massive gas puff causes a fast and clean current quench with essentially all the plasma energy radiated fairly uniformly to the vessel walls. The run-away electrons that are normally seen accompanying disruptions are suppressed by the large density of electrons still bound on the impurity nuclei. Major elements required to establish integrated, long-pulse, advanced tokamak operations have been achieved in DIII-D: {beta}{sub T} = 4.2%, {beta}{sub p} = 2, f{sub BS} = 65%, and {beta}{sub N}H{sub 89} = 10 for 600 ms ({approx} 4{tau}{sub E}). The next challenge is to integrate the different elements, which will be the goal for the next five years when additional control will be available. Twelve resistive wall mode coils are scheduled to be installed in DIII-D during the summer of 2003. The future plans include upgrading the tokamak pulse length capability and increasing the ECH power, to control the current profile evolution.
Steady- and non-steady-state carbonate-silicate controls on atmospheric CO2
Sundquist, E.T.
1991-01-01
Two contrasting hypotheses have recently been proposed for the past long-term relation between atmospheric CO2 and the carbonate-silicate geochemical cycle. One approach (Berner, 1990) suggests that CO2 levels have varied in a manner that has maintained chemical weathering and carbonate sedimentation at a steady state with respect to tectonically controlled decarbonation reactions. A second approach (Raymo et al., 1988), applied specificlly to the late Cenozoic, suggests a decrease in CO2 caused by an uplift-induced increase in chemical weathering, without regard to the rate of decarbonation. According to the steady-state (first) hypothesis, increased weathering and carbonate sedimentation are generally associated with increasing atmospheric CO2, whereas the uplift (second) hypothesis implies decreasing CO2 under the same conditions. An ocean-atmosphere-sediment model has been used to assess the response of atmospheric CO2 and carbonate sedimentation to global perturbations in chemical weathering and decarbonation reactions. Although this assessment is theoretical and cannot yet be related to the geologic record, the model simulations compare steady-state and non-steady-state carbonate-silicate cycle response. The e-fold response time of the 'CO2-weathering' feedback mechanism is between 300 and 400 ka. The response of carbonate sedimentation is much more rapid. These response times provide a measure of the strength of steady-state assumptions, and imply that certain systematic relations are sustained throughout steady-state and non-steady-state scenarios for the carbonate-silicate cycle. The simulations suggest that feedbacks can maintain the system near a steady state, but that non-steady-state effects may contribute to long-term trends. The steady-state and uplift hypotheses are not necessarily incompatible over time scales of a few million years. ?? 1991.
On the use of steady-state signal equations for 2D TrueFISP imaging.
Coolen, Bram F; Heijman, Edwin; Nicolay, Klaas; Strijkers, Gustav J
2009-07-01
To explain the signal behavior in 2D-TrueFISP imaging, a slice excitation profile should be considered that describes a variation of effective flip angles and magnetization phases after excitation. These parameters can be incorporated into steady-state equations to predict the final signal within a pixel. The use of steady-state equations assumes that excitation occurs instantaneously, although in reality this is a nonlinear process. In addition, often the flip angle variation within the slice excitation profile is solely considered when using steady-state equations, while TrueFISP is especially known for its sensitivity to phase variations. The purpose of this study was therefore to evaluate the precision of steady-state equations in calculating signal intensities in 2D TrueFISP imaging. To that end, steady-state slice profiles and corresponding signal intensities were calculated as function of flip angle, RF phase advance and pulse shape. More complex Bloch simulations were considered as a gold standard, which described every excitation within the sequence until steady state was reached. They were used to analyze two different methods based on steady-state equations. In addition, measurements on phantoms were done with corresponding imaging parameters. Although the Bloch simulations described the steady-state slice profile formation better than methods based on steady-state equations, the latter performed well in predicting the steady-state signal resulting from it. In certain cases the phase variation within the slice excitation profile did not even have to be taken into account.
de la Cruz, Roberto; Guerrero, Pilar; Spill, Fabian; Alarcón, Tomás
2015-08-21
We analyse the effect of intrinsic fluctuations on the properties of bistable stochastic systems with time scale separation operating under quasi-steady state conditions. We first formulate a stochastic generalisation of the quasi-steady state approximation based on the semi-classical approximation of the partial differential equation for the generating function associated with the chemical master equation. Such approximation proceeds by optimising an action functional whose associated set of Euler-Lagrange (Hamilton) equations provides the most likely fluctuation path. We show that, under appropriate conditions granting time scale separation, the Hamiltonian can be re-scaled so that the set of Hamilton equations splits up into slow and fast variables, whereby the quasi-steady state approximation can be applied. We analyse two particular examples of systems whose mean-field limit has been shown to exhibit bi-stability: an enzyme-catalysed system of two mutually inhibitory proteins and a gene regulatory circuit with self-activation. Our theory establishes that the number of molecules of the conserved species is order parameters whose variation regulates bistable behaviour in the associated systems beyond the predictions of the mean-field theory. This prediction is fully confirmed by direct numerical simulations using the stochastic simulation algorithm. This result allows us to propose strategies whereby, by varying the number of molecules of the three conserved chemical species, cell properties associated to bistable behaviour (phenotype, cell-cycle status, etc.) can be controlled.
Cruz, Roberto; Alarcón, Tomás de la; Guerrero, Pilar; Spill, Fabian
2015-08-21
We analyse the effect of intrinsic fluctuations on the properties of bistable stochastic systems with time scale separation operating under quasi-steady state conditions. We first formulate a stochastic generalisation of the quasi-steady state approximation based on the semi-classical approximation of the partial differential equation for the generating function associated with the chemical master equation. Such approximation proceeds by optimising an action functional whose associated set of Euler-Lagrange (Hamilton) equations provides the most likely fluctuation path. We show that, under appropriate conditions granting time scale separation, the Hamiltonian can be re-scaled so that the set of Hamilton equations splits up into slow and fast variables, whereby the quasi-steady state approximation can be applied. We analyse two particular examples of systems whose mean-field limit has been shown to exhibit bi-stability: an enzyme-catalysed system of two mutually inhibitory proteins and a gene regulatory circuit with self-activation. Our theory establishes that the number of molecules of the conserved species is order parameters whose variation regulates bistable behaviour in the associated systems beyond the predictions of the mean-field theory. This prediction is fully confirmed by direct numerical simulations using the stochastic simulation algorithm. This result allows us to propose strategies whereby, by varying the number of molecules of the three conserved chemical species, cell properties associated to bistable behaviour (phenotype, cell-cycle status, etc.) can be controlled.
Operation of bolometer system using Pt foil on SiN substrate detector for EAST tokamak.
Duan, Y M; Mao, S T; Hu, L Q; Xu, P; Xu, L Q; Zhang, J Z; Lin, S Y
2016-11-01
The foil resistive bolometer diagnostic on experimental advanced superconducting tokamak has been upgraded partly with a new generation of detectors. The new detectors have faster response time. However, the microwave interference is still a serious issue for the bolometer system. The system response to microwave is tested, and the test results show that the closed Wheatstone bridge circuit in the detector is the most sensitive component to high power microwave field. Simulation results of microwave transmission by the high frequency structure simulator software and shielding design are also presented.
Efficient Steady-State Solution Techniques for Variably Saturated Groundwater Flow
NASA Astrophysics Data System (ADS)
Farthing, M. W.; Kees, C. E.; Coffey, T. S.; Kelley, C. T.; Miller, C. T.
2002-12-01
We consider the simulation of steady-state variably saturated groundwater flow using Richards' equation. The difficulties associated with solving Richards' equation numerically are well known. Most discretization approaches for Richards' equation lead to nonlinear systems that are large and difficult to solve. The solution of nonlinear systems for steady-state problems can be particularly challenging, since a good initial guess for the steady-state solution is often hard to obtain, and the resulting linear systems may be poorly scaled. Common approaches like modified Picard iteration or variations of Newton's method have their advantages but perform poorly with standard globalization techniques under certain conditions. Pseudo-transient continuation has been used in computational fluid dynamics for some time to obtain steady-state solutions for problems in which Newton's method with standard line-search strategies fails. It combines aspects of backward Euler time integration and Newton's method to select intermediate estimates of the steady-state solution. In this work, we examine the use of pseudo-transient continuation methods for Richards' equation. We evaluate their performance for steady-state problems in heterogeneous domains by comparing them with Newton's method using standard globalization techniques. We investigate the methods' performance with both direct and preconditioned Krylov iterative linear solvers. We then make recommendations for robust and efficient approaches to obtain steady-state solutions for Richards' equation under a variety of conditions.
Transient getter scheme for the Tokamak Fusion Test Reactor
Cecchi, J.L.; Cohen, S.A.; Sredniawski, J.J.
1980-01-01
The ability of the Tokamak Fusion Test Reactor (TFTR) to attain the largest fusion power gain depends critically on minimizing plasma contamination and controlling the densities of the reacting deuterium and tritium. Experiments on a number of tokamaks have demonstrated that gettering over an appreciable surface area (greater than or equal to 10%) of the vacuum vessel greatly facilitates both of these objectives. One particular problem in implementing a surface pumping system in TFTR, however, is a restriction on the maximum allowable tritium content of the getter. This restriction could require regeneration of the absorbed tritium after as few as 50 machine pulses. We have developed a scheme utilizing SAES Zr/Al getter modules which obviates the need for such frequent interruptions of machine operation by taking advantage of the pulsed operation of TFTR. With the Zr/Al getter at temperatures between 500/sup 0/C to 600/sup 0/C it is possible to achieve a quasi-steady state in the tritium loading where the quantity of tritium desorbed between pulses is equal to the quantity which is absorbed during a pulse. Since frequent thermal cycling is not required, this scheme also reduces the possibility of Zr/Al getter material fatigue.
Tokamak power system studies at ANL
Baker, C.C.; Ehst, D.A.; Brooks, J.N.; Evans, K. Jr.
1986-06-01
The following features, in particular, have been examined: (a) large aspect ratio (A approx. = 6), which may ease maintenance; (b) high beta (..beta.. greater than or equal to 0.20) without indentation, which brings the maximum toroidal field down to about 6 to 7 T; (c) low toroidal current (I approx. = 4MA), which reduces the cost of the current drive and equilibrium field system; and (d) steady state operation with current density control via fast and slow wave current drive. The key to high beta operation with low toroidal current lies in utilizing second stability regime equilibria with the required current distributions produced by an appropriate selection of wave driver frequencies and power spectra. The ray tracing and current drive calculation is self-consistent with the actual magnetic fields they produce in the plasma. The impurity control activities in TPSS have emphasized the self-pumping concept as applied to using the entire first wall or ''slot'' limiters. The blanket design effort has emphasized liquid metal and Flibe concepts. The reference concept is a liquid lithium/vanadium, self-cooled configuration. Overall, there exists a number of major design improvements which will substantially improve the attractiveness of tokamak reactors.
The condensation of ampholytes in steady state moving boundaries - Analysis by computer simulation
NASA Technical Reports Server (NTRS)
Mosher, Richard A.; Thormann, Wolfgang
1986-01-01
A digital simulation of the behavior of amphoteric sample components in moving steady state boundaries is presented. Complete computer simulation data, including profiles of concentration, conductivity and pH as functions of time, are given for both cationic and anionic electrolyte configurations which incorporate one amphoteric sample constituent. The condensation of ampholytes in steady state moving boundaries is shown to proceed via an isotachophoretic mechanism and not by isoelectric focusing. Mobility (velocity) relationships necessary for sample components to form steady state zones are discussed.
NASA Astrophysics Data System (ADS)
Whyte, D. G.; Bonoli, P.; Barnard, H.; Haakonsen, C.; Hartwig, Z.; Kasten, C.; Palmer, T.; Sung, C.; Sutherland, D.; Bromberg, L.; Mangiarotti, F.; Goh, J.; Sorbom, B.; Sierchio, J.; Ball, J.; Greenwald, M.; Olynyk, G.; Minervini, J.
2012-10-01
Two of the greatest challenges to tokamak reactors are 1) large single-unit cost of each reactor's construction and 2) their susceptibility to disruptions from operation at or above operational limits. We present an attractive tokamak reactor design that substantially lessens these issues by exploiting recent advancements in superconductor (SC) tapes allowing peak field on SC coil > 20 Tesla. A R˜3.3 m, B˜9.2 T, ˜ 500 MW fusion power tokamak provides high fusion gain while avoiding all disruptive operating boundaries (no-wall beta, kink, and density limits). Robust steady-state core scenarios are obtained by exploiting the synergy of high field, compact size and ideal efficiency current drive using high-field side launch of Lower Hybrid waves. The design features a completely modular replacement of internal solid components enabled by the demountability of the coils/tapes and the use of an immersion liquid blanket. This modularity opens up the possibility of using the device as a nuclear component test facility.
Steady-state fuel behavior modeling of nitride fuels in FRAPCON-EP
NASA Astrophysics Data System (ADS)
Feng, Bo; Karahan, Aydın; Kazimi, Mujid S.
2012-08-01
Fuel material properties and mechanistic fission gas models in FRAPCON-EP were updated to model the steady-state behavior of high-porosity nitride fuel operating at temperatures below half of the melting point. The fuel thermal conductivity and fuel thermal expansion models were updated with correlations for UN and (U,Pu)N fuels. Hot-pressing of the as-fabricated porosity was modeled as a function of the hydrostatic pressure and creep rate. The solid fission product swelling was assumed to increase linearly with burnup. Fission gas swelling constitutive models were updated to appropriately capture the intragranular gas bubble evolution in nitride fuel. Intergranular gas swelling was neglected due to the assumed high porosity of the fuel. The fission gas release behavior was modeled by fitting the fission gas diffusion coefficient in UN to FRAPCON's default fission gas release model. This fitted gas diffusion coefficient reflects the effects of porosity, burnup, operating temperature, fission rate, and bubble sink strength. Fission gas release and fuel swelling benchmarks against irradiation data were performed. The updated code was applied to UN fuel in typical PWR geometry and operating conditions, with an extended cycle length of 24 months. The results show that swelling of the nitride fuel up to 60 MWd/kg burnup did not lead to excessive straining of the cladding. Furthermore, this study showed that a porous (>15% porosity) nitride fuel pellet could achieve a much higher margin to failure from the cladding collapse and grid-to-rod fretting.
Liu, Lin; Gao, Da-Wen; Liang, Hong
2012-01-01
We have investigated the effect of sludge discharge location on the steady-state aerobic granules in sequencing batch reactors (SBRs). Two SBRs were operated concurrently with the same sludge retention time using sludge discharge ports at: (a) the reactor bottom in R1; and (b) the reactor middle-lower level in R2. Results indicate that both reactors could maintain sludge granulation and stable operation, but the two different sludge discharge methods resulted in significantly different aerobic granule characteristics. Over 30 days, the chemical oxygen demand (COD) removal of the two reactors was maintained at similar levels (above 96%), and typical bioflocs were not observed. The average aerobic granule size in R2 was twice that in R1, as settling velocity increased in proportion to size increment. Meanwhile, the production yields of polysaccharide and protein content in R2 were always higher than those in R1. However, due to mass transfer limitations and the presence of anaerobes in the aerobic granule cores, larger granules had a tendency to disintegrate in R2. Thus, we conclude that a sludge discharge port situated at the reactor bottom is beneficial for aerobic granule stability, and enhances the potential for long-term aerobic granule SBR operation.
Entropy and Nonlinear Nonequilibrium Thermodynamic Relation for Heat Conducting Steady States
NASA Astrophysics Data System (ADS)
Komatsu, Teruhisa S.; Nakagawa, Naoko; Sasa, Shin-Ichi; Tasaki, Hal
2011-01-01
Among various possible routes to extend entropy and thermodynamics to nonequilibrium steady states (NESS), we take the one which is guided by operational thermodynamics and the Clausius relation. In our previous study, we derived the extended Clausius relation for NESS, where the heat in the original relation is replaced by its "renormalized" counterpart called the excess heat, and the Gibbs-Shannon expression for the entropy by a new symmetrized Gibbs-Shannon-like expression. Here we concentrate on Markov processes describing heat conducting systems, and develop a new method for deriving thermodynamic relations. We first present a new simpler derivation of the extended Clausius relation, and clarify its close relation with the linear response theory. We then derive a new improved extended Clausius relation with a "nonlinear nonequilibrium" contribution which is written as a correlation between work and heat. We argue that the "nonlinear nonequilibrium" contribution is unavoidable, and is determined uniquely once we accept the (very natural) definition of the excess heat. Moreover it turns out that to operationally determine the difference in the nonequilibrium entropy to the second order in the temperature difference, one may only use the previous Clausius relation without a nonlinear term or must use the new relation, depending on the operation (i.e., the path in the parameter space). This peculiar "twist" may be a clue to a better understanding of thermodynamics and statistical mechanics of NESS.
Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System.
Roder, H M; Perkins, R A; Laesecke, A; Nieto de Castro, C A
2000-01-01
A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy.
Spin-locked balanced steady-state free-precession (slSSFP).
Witschey, Walter R T; Borthakur, Ari; Elliott, Mark A; Magland, Jeremy; McArdle, Erin L; Wheaton, Andrew; Reddy, Ravinder
2009-10-01
A spin-locked balanced steady-state free-precession (slSSFP) pulse sequence is described that combines a balanced gradient-echo acquisition with an off-resonance spin-lock pulse for fast MRI. The transient and steady-state magnetization trajectory was solved numerically using the Bloch equations and was shown to be similar to balanced steady-state free-precession (bSSFP) for a range of T(2)/T(1) and flip angles, although the slSSFP steady-state could be maintained with considerably lower radio frequency (RF) power. In both simulations and brain scans performed at 7T, slSSFP was shown to exhibit similar contrast and signal-to-noise ratio (SNR) efficiency to bSSFP, but with significantly lower power.
On the theory of steady-state crystallization with a non-equilibrium mushy layer
NASA Astrophysics Data System (ADS)
Alexandrov, D. V.; Alexandrova, I. V.; Ivanov, A. A.
2016-12-01
Complete analytical solutions of nonlinear equations describing the steady-state directional crystallization of binary melts with a nonequilibrium mushy layer, where the processes of nucleation and growth of crystals occur, are constructed.
Quasi steady-state aerodynamic model development for race vehicle simulations
NASA Astrophysics Data System (ADS)
Mohrfeld-Halterman, J. A.; Uddin, M.
2016-01-01
Presented in this paper is a procedure to develop a high fidelity quasi steady-state aerodynamic model for use in race car vehicle dynamic simulations. Developed to fit quasi steady-state wind tunnel data, the aerodynamic model is regressed against three independent variables: front ground clearance, rear ride height, and yaw angle. An initial dual range model is presented and then further refined to reduce the model complexity while maintaining a high level of predictive accuracy. The model complexity reduction decreases the required amount of wind tunnel data thereby reducing wind tunnel testing time and cost. The quasi steady-state aerodynamic model for the pitch moment degree of freedom is systematically developed in this paper. This same procedure can be extended to the other five aerodynamic degrees of freedom to develop a complete six degree of freedom quasi steady-state aerodynamic model for any vehicle.
Decoding of the sound frequency from the steady-state neural activities in rat auditory cortex.
Shiramatsu, Tomoyo I; Noda, Takahiro; Kanzaki, Ryohei; Takahashi, Hirokazu
2013-01-01
In the auditory cortex, onset activities have been extensively investigated as a cortical representation of sound information such as sound frequency. Yet, less attention has been paid to date to steady-state activities following the onset activities. In this study, we used machine learning to investigate whether steady-state activities in the presence of continuous sounds represent the sound frequency. Sparse Logistic Regression (SLR) decoded the sound frequency from band specific power or phase locking value (PLV) of local field potentials (LFP) from the fourth layer of the auditory cortex of anesthetized rats. Consequently, we found that SLR was able to decode the sound frequency from steady-state neural activities as well as onset activities. This result demonstrates that the steady-state activities contain information about the sound such as sound frequency.
Steady-state existence of passive vector fields under the Kraichnan model.
Arponen, Heikki
2010-03-01
The steady-state existence problem for Kraichnan advected passive vector models is considered for isotropic and anisotropic initial values in arbitrary dimension. The models include the magnetohydrodynamic (MHD) equations, linear pressure model, and linearized Navier-Stokes (LNS) equations. In addition to reproducing the previously known results for the MHD model, we obtain the values of the Kraichnan model roughness parameter xi for which the LNS steady state exists.
Steady-state ab initio laser theory for N-level lasers.
Cerjan, Alexander; Chong, Yidong; Ge, Li; Stone, A Douglas
2012-01-02
We show that Steady-state Ab initio Laser Theory (SALT) can be applied to find the stationary multimode lasing properties of an N-level laser. This is achieved by mapping the N-level rate equations to an effective two-level model of the type solved by the SALT algorithm. This mapping yields excellent agreement with more computationally demanding N-level time domain solutions for the steady state.
Bifurcation analysis of steady-state flows in the lid-driven cavity
NASA Astrophysics Data System (ADS)
Nuriev, A. N.; Egorov, A. G.; Zaitseva, O. N.
2016-12-01
The paper is devoted to the study of the non-uniqueness issues of a steady-state flow in the square lid-driven cavity. A range 0\\lt {Re} \\lt 20000 of Reynolds numbers is considered in which a numerical bifurcation analysis is carried out. The analysis allows us to localize several branches of the steady-state solution and also to investigate their stability.
Rosenblatt, Marcus; Timmer, Jens; Kaschek, Daniel
2016-01-01
Ordinary differential equation models have become a wide-spread approach to analyze dynamical systems and understand underlying mechanisms. Model parameters are often unknown and have to be estimated from experimental data, e.g., by maximum-likelihood estimation. In particular, models of biological systems contain a large number of parameters. To reduce the dimensionality of the parameter space, steady-state information is incorporated in the parameter estimation process. For non-linear models, analytical steady-state calculation typically leads to higher-order polynomial equations for which no closed-form solutions can be obtained. This can be circumvented by solving the steady-state equations for kinetic parameters, which results in a linear equation system with comparatively simple solutions. At the same time multiplicity of steady-state solutions is avoided, which otherwise is problematic for optimization. When solved for kinetic parameters, however, steady-state constraints tend to become negative for particular model specifications, thus, generating new types of optimization problems. Here, we present an algorithm based on graph theory that derives non-negative, analytical steady-state expressions by stepwise removal of cyclic dependencies between dynamical variables. The algorithm avoids multiple steady-state solutions by construction. We show that our method is applicable to most common classes of biochemical reaction networks containing inhibition terms, mass-action and Hill-type kinetic equations. Comparing the performance of parameter estimation for different analytical and numerical methods of incorporating steady-state information, we show that our approach is especially well-tailored to guarantee a high success rate of optimization.
Steady-state entanglement of a Bose-Einstein condensate and a nanomechanical resonator
Asjad, Muhammad; Saif, Farhan
2011-09-15
We analyze the steady-state entanglement between Bose-Einstein condensate trapped inside an optical cavity with a moving end mirror (nanomechanical resonator) driven by a single mode laser. The quantized laser field mediates the interaction between the Bose-Einstein condensate and nanomechanical resonator. In particular, we study the influence of temperature on the entanglement of the coupled system, and note that the steady-state entanglement is fragile with respect to temperature.
Steady-state 2. pi. pulses under conditions of passive locking of laser modes
Komarov, K.P.; Ugozhaev, V.D.
1984-06-01
A theoretical study is made of laser mode locking in the regime of self-induced transparency of a passive filter. It is shown that there is a solution in the form of ultrashort steady-state 2..pi.. pulses. The range of stability of this regime and its characteristics are determined. By way of example, estimates are obtained of parameters of a steady-state pulse emitted by an alexandrite laser with a potassium absorption cell.
The effect of oxygen on denitrification during steady-state growth of Paracoccus halodenitrificans
NASA Technical Reports Server (NTRS)
Hochstein, L. I.; Betlach, M.; Kritikos, G.
1984-01-01
Steady-state cultures of Paracoccus halodenitrificans were grown anaerobically prior to establishing steady states at different concentrations of oxygen. In the absence of oxygen, nitrate-limited cultures produced dinitrogen, and as the oxygen supply increased, these cultures produced nitrous oxide, then nitrite. These changes reflected two phenomena: the inactivation of nitrous oxide reductase by oxygen and the diversion of electrons from nitrite to oxygen.
Rosenblatt, Marcus; Timmer, Jens; Kaschek, Daniel
2016-01-01
Ordinary differential equation models have become a wide-spread approach to analyze dynamical systems and understand underlying mechanisms. Model parameters are often unknown and have to be estimated from experimental data, e.g., by maximum-likelihood estimation. In particular, models of biological systems contain a large number of parameters. To reduce the dimensionality of the parameter space, steady-state information is incorporated in the parameter estimation process. For non-linear models, analytical steady-state calculation typically leads to higher-order polynomial equations for which no closed-form solutions can be obtained. This can be circumvented by solving the steady-state equations for kinetic parameters, which results in a linear equation system with comparatively simple solutions. At the same time multiplicity of steady-state solutions is avoided, which otherwise is problematic for optimization. When solved for kinetic parameters, however, steady-state constraints tend to become negative for particular model specifications, thus, generating new types of optimization problems. Here, we present an algorithm based on graph theory that derives non-negative, analytical steady-state expressions by stepwise removal of cyclic dependencies between dynamical variables. The algorithm avoids multiple steady-state solutions by construction. We show that our method is applicable to most common classes of biochemical reaction networks containing inhibition terms, mass-action and Hill-type kinetic equations. Comparing the performance of parameter estimation for different analytical and numerical methods of incorporating steady-state information, we show that our approach is especially well-tailored to guarantee a high success rate of optimization. PMID:27243005
Simonen, T.C.; Baker, D.
1993-01-01
The DIII-D tokamak research program is carried out by General Atomics for the U.S. Department of Energy. The DIII-D is the most flexible and best diagnosed tokamak in the world and the second largest tokamak in the U.S. The primary goal of the DIII-D tokamak research program is to provide data needed by ITER and to develop a conceptual physics blueprint for a commercially attractive electrical demonstration plant (DEMO) that would open a path to fusion power commercialization. Specific DIII-D objectives include the steady-state sustainment of plasma current as well as demonstrating techniques for microwave heating, divertor heat removal, fuel exhaust and tokamak plasma control. The DIII-D program is addressing these objectives in an integrated fashion with high beta and with good confinement. The DIII-D long-range plan is organized into two major thrusts; the development of advanced divertor and the development of advanced tokamak concepts. These two thrusts have a common goal: an improved DEMO reactor with lower cost and smaller size than the present DEMO which can be extrapolated from the conventional ITER operational scenario. In order to prepare for the long-range program, in FY92 the DIII-D research program concentrated in three major areas: Tokamak Physics, Divertor and Boundary Physics, and Advanced Tokamak Studies.
Steady state effects in a two-pulse diffusion-weighted sequence
Zubkov, Mikhail; Stait-Gardner, Timothy; Price, William S.; Stilbs, Peter
2015-04-21
In conventional nuclear magnetic resonance (NMR) diffusion measurements a significant amount of experimental time is used up by magnetization recovery, serving to prevent the formation of the steady state, as in the latter case the manifestation of diffusion is modulated by multiple applications of the pulse sequence and conventional diffusion coefficient inference procedures are generally not applicable. Here, an analytical expression for diffusion-related effects in a two-pulse NMR experiment (e.g., pulsed-gradient spin echo) in the steady state mode (with repetition times less than the longitudinal relaxation time of the sample) is derived by employing a Fourier series expansion within the solution of the Bloch-Torrey equations. Considerations are given for the transition conditions between the full relaxation and the steady state experiment description. The diffusion coefficient of a polymer solution (polyethylene glycol) is measured by a two-pulse sequence in the full relaxation mode and for a range of repetition times, approaching the rapid steady state experiment. The precision of the fitting employing the presented steady state solution by far exceeds that of the conventional fitting. Additionally, numerical simulations are performed yielding results strongly supporting the proposed description of the NMR diffusion measurements in the steady state.
Efficient steady-state solution techniques for variably saturated groundwater flow
NASA Astrophysics Data System (ADS)
Farthing, Matthew W.; Kees, Christopher E.; Coffey, Todd S.; Kelley, C. T.; Miller, Cass T.
We consider the simulation of steady-state variably saturated groundwater flow using Richards' equation (RE). The difficulties associated with solving RE numerically are well known. Most discretization approaches for RE lead to nonlinear systems that are large and difficult to solve. The solution of nonlinear systems for steady-state problems can be particularly challenging, since a good initial guess for the steady-state solution is often hard to obtain, and the resulting linear systems may be poorly scaled. Common approaches like Picard iteration or variations of Newton's method have their advantages but perform poorly with standard globalization techniques under certain conditions. Pseudo-transient continuation has been used in computational fluid dynamics for some time to obtain steady-state solutions for problems in which Newton's method with standard line-search strategies fails. Here, we examine the use of pseudo-transient continuation as well as Newton's method combined with standard globalization techniques for steady-state problems in heterogeneous domains. We investigate the methods' performance with direct and preconditioned Krylov iterative linear solvers. We then make recommendations for robust and efficient approaches to obtain steady-state solutions for RE under a range of conditions.
Vortex generator installation studies on steady state and dynamic inlet distortion
NASA Technical Reports Server (NTRS)
Anderson, Bernhard H.; Gibb, James
1996-01-01
The theoretical and experimental work carried out under the NASA/MOD Joint Aeronautical Program has shown that CFD vortex generator installations designs successfully managed inlet duct flow distortion and that significant benefits in flow unsteadiness at the engine face were also present. The main conclusions to date from the collaborative effort between NASA/Lewis and DRA/Bedford are as follows: (1) vortex generator installations can be designed to be effective over a wide range of inlet operating conditions using Computational Fluid Dynamics and formal optimization procedures, (2) reductions in steady state engine face distortion of up to 80% have been measured in the M2129 inlet S-duct using CFD designed vortex generator installations, (3) reductions in flow unsteadiness of up to 80% have been measured in the W129 inlet S-duct using CFD designed vortex generator installations, and (4) the Reduced Navier-Stokes code RNS3D is a useful tool to design vortex generator installations to manage engine face distortions over a wide range of inlet operating conditions.
Theoretical research of helium pulsating heat pipe under steady state conditions
NASA Astrophysics Data System (ADS)
Xu, D.; Liu, H. M.; Li, L. F.; Huang, R. J.; Wang, W.
2015-12-01
As a new-type heat pipe, pulsating heat pipe (PHP) has several outstanding features, such as great heat transport ability, strong adjustability, small size and simple construction. PHP is a complex two-phase flow system associated with many physical subjects and parameters, which utilizes the pressure and temperature changes in volume expansion and contraction during phase changes to excite the pulsation motion of liquid plugs and vapor bubbles in the capillary tube between the evaporator and the condenser. At present time, some experimental investigation of helium PHP have been done. However, theoretical research of helium PHP is rare. In this paper, the physical and mathematical models of operating mechanism for helium PHP under steady state are established based on the conservation of mass, momentum, and energy. Several important parameters are correlated and solved, including the liquid filling ratio, flow velocity, heat power, temperature, etc. Based on the results, the operational driving force and flow resistances of helium PHP are analysed, and the flow and heat transfer is further studied.
Starting and steady-state characteristics of dc motors powered by solar cell generators
NASA Astrophysics Data System (ADS)
Appelbaum, J.
1986-03-01
The performance of dc motors (series, separately-excited, and shunt motors) powered by a solar cell generator and loaded by two different types of loads, one a constant load and one a ventilator load, were analyzed with respect to the transient (starting) and steady state operation. Direct current motors are employed in photovoltaic water pumping systems; therefore, the understanding of the system operation and the matching of the system components (solar cells, dc motor type, and load type) are important factors of the system design. Since the solar cell generator in a nonlinear and time-dependent power supply with an output that varies with the insolation (hourly and daily), the performance characteristics of the dc motor are different when supplied by a solar cell generator than when supplied by a conventional constant voltage source. The transient solution was obtained by using an available computer program - SUPER SCEPTRE. The separately-excited (or permanent magnet) motor with a ventilator load was found to be the most suitable for the solar cell generator. The series motor is quite acceptable, but the shunt motor gives poor performance. In all cases the ventilator load is more compatible with the solar cell generator than with the constant load.
Two-dimensional steady-state analysis of an electrically heated thermionic fuel element
Huimin Xue; El-Genk, M.S.; Paramonov, D. )
1993-01-20
A two-dimensional transient model of a single cell, long Thermionic Fuel Element (TFE) is developed and its predictions are compared with published calculations and experimental data on steady-state operation of electrically heated, TOPAZ-II type TFEs. The operation parameters of the TFE, such as axial distributions of the emitter temperature, emission current density, and the electrode voltage are calculated and discussed. Results show that despite the excellent agreement between the model predictions of the axial distribution of the emitter temperature, its predictions of the maximum emission current density was lower by about 17%. This difference is attributed primarily to the J-V characteristics in the model, which could be different than those of the TOPAZ-II TFE, hence additional data on the latter is needed. When compared with experimental data, the model predictions of the electric power output are in excellent agreement with the data at thermal power input of 3.5 kW or higher, but within 10% of the data at lower thermal power.
NASA Astrophysics Data System (ADS)
Yanhong, Ma; Zhichao, Liang; Hong, Wang; Dayi, Zhang; Jie, Hong
2013-10-01
An Air Film Damper (AFD) made with a highly damping material called Metal Rubber (MR) as the outer ring is a novel damping structure that aims to reduce the remarkable vibrations produced by a flexible rotor system. The mechanism of an AFD is firstly put forward and the mechanical model describing the fluid structure interaction is constructed. Taking into consideration the complex whirl of the rotor and the precession of the floating ring, the Reynolds equation of AFDs is derived and the air film pressure is obtained. Based on these calculations, the selection of MR stiffness is introduced and the adaptive properties of AFD are analyzed. Then the effects of AFD on the rotordynamics are studied based on the characterization of the parameters of a rotor system in the steady state. The mechanism and the effects of AFD on a rotor system are verified through rotating experimental tests. The theoretical and experimental results both show that AFD can adjust the air film clearance adaptively according to the vibration of the rotor; this can not only decrease the friction between the journal and the floating ring, but can also provide additional stiffness and damping to the rotor system, thus yielding additional vibration control. The mechanism of an AFD is obtained by theoretical and experimental investigations. Due to the elastic MR serving as the outer ring, an AFD can adjust the air film clearance adaptively according to the vibration of the rotor; this not only decreases the friction between the journal and the floating ring, but also provides additional stiffness and damping to the rotor system, as a function of vibration control. Taking into consideration the complex whirl of the rotor and the precession of the floating ring, the Reynolds equation of an AFD is derived and the mechanical model is established, based on the fluid structure interaction. Moreover, based on the maximum radial displacement during the entire operational process and the minimum thickness of
Feasibility study of a fission-suppressed tokamak fusion breeder
Moir, R.W.; Lee, J.D.; Neef, W.S.; Berwald, D.H.; Garner, J.K.; Whitley, R.H.; Ghoniem, N.; Wong, C.P.C.; Maya, I.; Schultz, K.R.
1984-12-01
The preliminary conceptual design of a tokamak fissile fuel producer is described. The blanket technology is based on the fission suppressed breeding concept where neutron multiplication occurs in a bed of 2 cm diameter beryllium pebbles which are cooled by helium at 50 atmospheres pressure. Uranium-233 is bred in thorium metal fuel elements which are in the form of snap rings attached to each beryllium pebble. Tritium is bred in lithium bearing material contained in tubes immersed in the pebble bed and is recovered by a purge flow of helium. The neutron wall load is 3 MW/m/sup 2/ and the blanket material is ferritic steel. The net fissile breeding ratio is 0.54 +- 30% per fusion reaction. This results in the production of 4900 kg of /sup 233/U per year from 3000 MW of fusion power. This quantity of fuel will provide makeup fuel for about 12 LWRs of equal thermal power or about 18 1 GW/sub e/ LWRs. The calculated cost of the produced uranium-233 is between $23/g and $53/g or equivalent to $10/kg to $90/kg of U/sub 3/O/sub 8/ depending on government financing or utility financing assumptions. Additional topics discussed in the report include the tokamak operating mode (both steady state and long pulse considered), the design and breeding implications of using a poloidal divertor for impurity control, reactor safety, the choice of a tritium breeder, and fuel management.
Tokamak Physics Experiment (TPX) power supply design and development
Neumeyer, C.; Bronner, G.; Lu, E.; Ramakrishnan, S.
1995-04-01
The Tokamak Physics Experiment (TPX) is an advanced tokamak project aimed at the production of quasi-steady state plasmas with advanced shape, heating, and particle control. TPX is to be built at the Princeton Plasma Physics Laboratory (PPPL) using many of the facilities from the Tokamak Fusion Test Reactor (TFTR). TPX will be the first tokamak to utilize superconducting (SC) magnets in both the toroidal field (TF) and poloidal field (PF) systems. This new feature requires a departure from the traditional tokamak power supply schemes. This paper describes the plan for the adaptation of the PPPL/FTR power system facilities to supply TPX. Five major areas are addressed, namely the AC power system, the TF, PF and Fast Plasma Position Control (FPPC) power supplies, and quench protection for the TF and PF systems. Special emphasis is placed on the development of new power supply and protection schemes.
Using bioprocess stoichiometry to build a plant-wide mass balance based steady-state WWTP model.
Ekama, G A
2009-05-01
Steady-state models are useful for design of wastewater treatment plants (WWTPs) because they allow reactor sizes and interconnecting flows to be simply determined from explicit equations in terms of unit operation performance criteria. Once the overall WWTP scheme is established and the main system defining parameters of the individual unit operations estimated, dynamic models can be applied to the connected unit operations to refine their design and evaluate their performance under dynamic flow and load conditions. To model anaerobic digestion (AD) within plant-wide WWTP models, not only COD and nitrogen (N) but also carbon (C) fluxes entering the AD need to be defined. Current plant-wide models, like benchmark simulation model No 2 (BSM2), impose a C flux at the AD influent. In this paper, the COD and N mass balance steady-state models of activated sludge (AS) organics degradation, nitrification and denitrification (ND) and anaerobic (AD) and aerobic (AerD) digestion of wastewater sludge are extended and linked with bioprocess transformation stoichiometry to form C, H, O, N, chemical oxygen demand (COD) and charge mass balance based models so that also C (and H and O) can be tracked through the whole WWTP. By assigning a stoichiometric composition (x, y, z and a in C(x)H(y)O(z)N(a)) to each of the five main influent wastewater organic fractions and ammonia, these, and the products generated from them via the biological processes, are tracked through the WWTP. The model is applied to two theoretical case study WWTPs treating the same raw wastewater (WW) to the same final sludge residual biodegradable COD. It is demonstrated that much useful information can be generated with the relatively simple steady-state models to aid WWTP layout design and track the different products exiting the WWTP via the solid, liquid and gas streams, such as aerobic versus anaerobic digestion of waste activated sludge, N loads in recycle streams, methane production for energy recovery
Nunz, G.J.
1993-10-01
A dimensionless group, called a Pressure Loss Modulus (N{sub PL}), is introduced which, in conjunction with an appropriately defined Reynolds number, is of considerable engineering utility in correlating steady-state {Delta}P vs. flow calibration data and subsequently as a predictor, using the same or a different fluid, in uniformly distributed pressure loss devices. It is particularly useful under operation in the transition regime. Applications of this simple bivariate correlation to three diverse devices of particular interest for small liquid rocket engine fluid systems are discussed: large L/D capillary tube restrictors; packed granular catalyst beds; and stacked vortex-loss disc restrictors.
Divertor design for the Tokamak Physics Experiment
Hill, D.N.; Braams, B.; Brooks, J.N.
1994-05-01
In this paper we discuss the present divertor design for the planned TPX tokamak, which will explore the physics and technology of steady-state (1000s pulses) heat and particle removal in high confinement (2--4{times} L-mode), high beta ({beta}{sub N} {ge} 3) divertor plasmas sustained by non-inductive current drive. The TPX device will operate in the double-null divertor configuration, with actively cooled graphite targets forming a deep (0.5 m) slot at the outer strike point. The peak heat flux on, the highly tilted (74{degrees} from normal) re-entrant (to recycle ions back toward the separatrix) will be in the range of 4--6 MW/m{sup 2} with 18 MW of neutral beams and RF heating power. The combination of active pumping and gas puffing (deuterium plus impurities), along with higher heating power (45 MW maximum) will allow testing of radiative divertor concepts at ITER-like power densities.
Experimental investigation of steady state high power MPD thrusters
NASA Astrophysics Data System (ADS)
Wegmann, Thomas; Auweter-Kurtz, Monika; Habiger, Harald A.; Kurtz, Helmut L.; Schrade, Herbert O.
1992-07-01
MPD thrusters with different geometries, nozzle type and cylindrical, were compared under various operating parameters. The effects of mass flow rate and power input on the operating conditions were explored, and plasma parameters were determined with both probe measurements and optical diagnostics. Besides water-cooled plasma accelerators, tests with a hot anode thruster having a radiation-cooled anode were performed. They showed the feasibility of large radiating tungsten anodes and a lower voltage level than water-cooled devices. A systematic study of the various instabilities of the arc and the plasma flow occurring at high power levels was begun. The cathode erosion and its mechanisms were examined with purified propellant gases.
Electrode erosion in steady-state electric propulsion engines
NASA Technical Reports Server (NTRS)
Pivirotto, Thomas J.; Deininger, William D.
1988-01-01
The anode and cathode of a 30 kW class arcjet engine were sectioned and analyzed. This arcjet was operated for a total time of 573 hr at power levels between 25 and 30 kW with ammonia at flow rates of 0.25 and 0.27 gm/s. The accumulated run time was sufficient to clearly establish erosion patterns and their causes. The type of electron emission from various parts of the cathode surface was made clear by scanning electron microscope analysis. A scanning electron microscope was used to study recrystallization on the hot anode surface. These electrodes were made of 2 percent thoriated tungsten and the surface thorium content and gradient perpendicular to the surfaces was determined by quantitative microprobe analysis. The results of this material analysis on the electrodes and recommendations for improving electrode operational life time are presented.
ERIC Educational Resources Information Center
Kosman, Daniel J.
2009-01-01
The steady-state is a fundamental aspect of biochemical pathways in cells; indeed, the concept of steady-state is a definition of life itself. In a simple enzyme kinetic scheme, the steady-state condition is easy to define analytically but experimentally often difficult to capture because of its evanescent quality; the initial, constant velocity…
Progress toward steady-state, high-efficiency vircators
Poulsen, P.; Pincosy, P.A.; Morrison, J.J.
1990-12-05
The resonance at which high-efficiency operation of virtual cathode oscillators is obtained occurs when the beam frequency equals the reflex frequency to within 2%. This tolerance limit in the frequency ratio implies that cathode closure in the anode-cathode gap is not acceptable. We have developed and tested a 6-cm{sup 2} cathode that will operate longer than 1 {mu}s at 300 A/cm{sup 2} without significant closure. As yet, the full-scale (>80-cm{sup 2}) cathode has not worked quite as well. In many tests, the cathode will operate in the emission-limited temperature/field (T/F) mode for approximately 300 ns, and then transition into explosive emission with a relatively slow ({approximately}0.5 cm/{mu}s) closure rate. The current density was 45 to 90 A/cm{sup 2}. We have not run high-power rf-emission tests under conditions where the diode stays open and in resonance for the duration of the rf pulse at a current density of 250 A/cm{sup 2}, which is required for 3-GHz operation; that test remains the focus of our continuing research. We have obtained long (600-ns) duration rf pulses at low power. We have also extended the data base on microwave generation at lower power and have shown that high-efficiency resonances will occur when a multiple of the reflex frequency equals the beam frequency. This allows greater flexibility in the design and scaling of the microwave device. 6 refs., 14 figs.
Helicity content and tokamak applications of helicity
Boozer, A.H.
1986-05-01
Magnetic helicity is approximately conserved by the turbulence associated with resistive instabilities of plasmas. To generalize the application of the concept of helicity, the helicity content of an arbitrary bounded region of space will be defined. The definition has the virtues that both the helicity content and its time derivative have simple expressions in terms of the poloidal and toroidal magnetic fluxes, the average toroidal loop voltage and the electric potential on the bounding surface, and the volume integral of E-B. The application of the helicity concept to tokamak plasmas is illustrated by a discussion of so-called MHD current drive, an example of a stable tokamak q profile with q less than one in the center, and a discussion of the possibility of a natural steady-state tokamak due to the bootstrap current coupling to tearing instabilities.
Dynamic optimization of open-loop input signals for ramp-up current profiles in tokamak plasmas
NASA Astrophysics Data System (ADS)
Ren, Zhigang; Xu, Chao; Lin, Qun; Loxton, Ryan; Teo, Kok Lay
2016-03-01
Establishing a good current spatial profile in tokamak fusion reactors is crucial to effective steady-state operation. The evolution of the current spatial profile is related to the evolution of the poloidal magnetic flux, which can be modeled in the normalized cylindrical coordinates using a parabolic partial differential equation (PDE) called the magnetic diffusion equation. In this paper, we consider the dynamic optimization problem of attaining the best possible current spatial profile during the ramp-up phase of the tokamak. We first use the Galerkin method to obtain a finite-dimensional ordinary differential equation (ODE) model based on the original magnetic diffusion PDE. Then, we combine the control parameterization method with a novel time-scaling transformation to obtain an approximate optimal parameter selection problem, which can be solved using gradient-based optimization techniques such as sequential quadratic programming (SQP). This control parameterization approach involves approximating the tokamak input signals by piecewise-linear functions whose slopes and break-points are decision variables to be optimized. We show that the gradient of the objective function with respect to the decision variables can be computed by solving an auxiliary dynamic system governing the state sensitivity matrix. Finally, we conclude the paper with simulation results for an example problem based on experimental data from the DIII-D tokamak in San Diego, California.
Steady state, erosional continuity, and the topography of landscapes developed in layered rocks
NASA Astrophysics Data System (ADS)
Perne, Matija; Covington, Matthew D.; Thaler, Evan A.; Myre, Joseph M.
2017-01-01
The concept of topographic steady state has substantially informed our understanding of the relationships between landscapes, tectonics, climate, and lithology. In topographic steady state, erosion rates are equal everywhere, and steepness adjusts to enable equal erosion rates in rocks of different strengths. This conceptual model makes an implicit assumption of vertical contacts between different rock types. Here we hypothesize that landscapes in layered rocks will be driven toward a state of erosional continuity, where retreat rates on either side of a contact are equal in a direction parallel to the contact rather than in the vertical direction. For vertical contacts, erosional continuity is the same as topographic steady state, whereas for horizontal contacts it is equivalent to equal rates of horizontal retreat on either side of a rock contact. Using analytical solutions and numerical simulations, we show that erosional continuity predicts the form of flux steady-state landscapes that develop in simulations with horizontally layered rocks. For stream power erosion, the nature of continuity steady state depends on the exponent, n, in the erosion model. For n = 1, the landscape cannot maintain continuity. For cases where n ≠ 1, continuity is maintained, and steepness is a function of erodibility that is predicted by the theory. The landscape in continuity steady state can be quite different from that predicted by topographic steady state. For n < 1 continuity predicts that channels incising subhorizontal layers will be steeper in the weaker rock layers. For subhorizontal layered rocks with different erodibilities, continuity also predicts larger slope contrasts than in topographic steady state. Therefore, the relationship between steepness and erodibility within a sequence of layered rocks is a function of contact dip. For the subhorizontal limit, the history of layers exposed at base level also influences the steepness-erodibility relationship. If uplift rate
Two-phase bioconversion product recovery by microfiltration I. Steady state studies.
Conrad, P B; Lee, S S
1998-03-20
Recovery of an aqueous bioconversion product from complex, two-phase Pseudomonas putida broths containing 20% (v/v) soybean oil presents a significant challenge for downstream processing. Although not used before in multiple-phase separation for complex biotech products, crossflow filtration employing ceramic filters is one of the most attractive options which allow the design of integrated, continuous bioconversion processes. As a first attempt, we studied multichannel, monolithic ceramic membranes of different nominal pore sizes and lumen diameters under steady-state conditions. The best performance was obtained with 0.2-microm-pore/3-mm-lumen membrane, which completely rejected both cells and oil droplets from the permeate, creating a clear aqueous product stream. Although the same separation was achieved, the 50K molecular weight cut-off (MWCO) ultrafilter showed greater irreversible but similar reversible resistance, in addition to an order-of-magnitude higher membrane resistance. Larger nominal pore microfilters, such as 0.45 and 1.0 microm, experienced both cell and oil leakage even at low transmembrane pressure (10 psig). Attributed to greater shear at the same recirculation rate, smaller lumen filters did provide greater permeate flux. However, for practical purposes, the 0. 2-microm-pore/4-mm-lumen ceramic membrane was chosen for further evaluation. Transmembrane pressures up to 50 psig provided only marginal gains in filtration performance, whereas increasing shear rate resulted in linear increases in steady-state flux, presumably due to formation of shear-sensitive, complex gel/oil/cell layer near the membrane surface. A nominal shear rate of 9200 s-1 and 20 psig transmembrane pressure were chosen as optimal operating conditions. Additional studies in a clean system revealed that as low as 5% (v/v) soybean oil in deionized (DI) water resulted in an order-of-magnitude decline in steady-state permeate flux. Breakthrough of oil droplets occurred at 35 psig
Differences in Transient and Steady State Isobaric Counterdiffusion.
1982-07-19
tubes to act ns insulators. (3) Food and water are provided and can be locked in with a gravity feed system during an experiment. D’Aoust: 7 (4...pneumatically operated large diameter ball valve. This arrangement was strain-relieved to the same frame/stanchion set-up which restrained the animal (see...drain for saliva , (2) a monitor of nmsk pressure during exhalation and inhalation. This was recorded with two sensitive "NaMaehalic" gsages shn on the
THE DEBRIS DISK OF VEGA: A STEADY-STATE COLLISIONAL CASCADE, NATURALLY
Mueller, S.; Loehne, T.; Krivov, A. V.
2010-01-10
The archetypical debris disk around Vega has been observed intensively over the past 25 years. It has been argued that the resulting photometric data and images may be in contradiction with a standard, steady-state collisional scenario of the disk evolution. In particular, the emission in the mid-infrared (mid-IR) appears to be in excess of what is expected from a 'Kuiper belt' at approx100 AU, which is evident in the submillimeter images and inferred from the majority of photometric points. Here we re-address the question of whether or not the Vega disk observations are compatible with a continuous dust production through a collisional cascade. Instead of seeking a size and spatial distribution of dust that provide the best fit to observations, our approach involves physical modeling of the debris disk 'from the sources'. We assume that dust is maintained by a belt of parent planetesimals, and employ our collisional and radiative transfer codes to consistently model the size and radial distribution of the disk material and then thermal emission of dust. In doing so, we vary a broad set of parameters, including the stellar properties, the exact location, extension, and dynamical excitation of the planetesimal belt, chemical composition of solids, and the collisional prescription. We are able to reproduce the spectral energy distribution in the entire wavelength range from the near-IR to millimeter, as well as the mid-IR and submillimeter radial brightness profiles of the Vega disk. Thus, our results suggest that the Vega disk observations are not in contradiction with a steady-state collisional dust production, and we put important constraints on the disk parameters and physical processes that sustain it. The total disk mass in approx<100 km-sized bodies is estimated to be approx10 Earth masses. Provided that collisional cascade has been operating over much of the Vega age of approx350 Myr, the disk must have lost a few Earth masses of solids during that time. We
Hsiang, J.-T.; Hu, B.L.
2015-11-15
The existence and uniqueness of a steady state for nonequilibrium systems (NESS) is a fundamental subject and a main theme of research in statistical mechanics for decades. For Gaussian systems, such as a chain of classical harmonic oscillators connected at each end to a heat bath, and for classical anharmonic oscillators under specified conditions, definitive answers exist in the form of proven theorems. Answering this question for quantum many-body systems poses a challenge for the present. In this work we address this issue by deriving the stochastic equations for the reduced system with self-consistent backaction from the two baths, calculating the energy flow from one bath to the chain to the other bath, and exhibiting a power balance relation in the total (chain + baths) system which testifies to the existence of a NESS in this system at late times. Its insensitivity to the initial conditions of the chain corroborates to its uniqueness. The functional method we adopt here entails the use of the influence functional, the coarse-grained and stochastic effective actions, from which one can derive the stochastic equations and calculate the average values of physical variables in open quantum systems. This involves both taking the expectation values of quantum operators of the system and the distributional averages of stochastic variables stemming from the coarse-grained environment. This method though formal in appearance is compact and complete. It can also easily accommodate perturbative techniques and diagrammatic methods from field theory. Taken all together it provides a solid platform for carrying out systematic investigations into the nonequilibrium dynamics of open quantum systems and quantum thermodynamics. -- Highlights: •Nonequilibrium steady state (NESS) for interacting quantum many-body systems. •Derivation of stochastic equations for quantum oscillator chain with two heat baths. •Explicit calculation of the energy flow from one bath to the
Measurement and Characterization of Helicopter Noise in Steady-State and Maneuvering Flight
NASA Technical Reports Server (NTRS)
Schmitz, Fredric H.; Greenwood, Eric; Sickenberger, Richard D.; Gopalan, Gaurav; Sim, Ben Well-C; Conner, David; Moralez, Ernesto; Decker, William A.
2007-01-01
A special acoustic flight test program was performed on the Bell 206B helicopter outfitted with an in-flight microphone boom/array attached to the helicopter while simultaneous acoustic measurements were made using a linear ground array of microphones arranged to be perpendicular to the flight path. Air and ground noise measurements were made in steady-state longitudinal and steady turning flight, and during selected dynamic maneuvers. Special instrumentation, including direct measurement of the helicopter s longitudinal tip-path-plane (TPP) angle, Differential Global Positioning System (DGPS) and Inertial Navigation Unit (INU) measurements, and a pursuit guidance display were used to measure important noise controlling parameters and to make the task of flying precise operating conditions and flight track easier for the pilot. Special care was also made to test only in very low winds. The resulting acoustic data is of relatively high quality and shows the value of carefully monitoring and controlling the helicopter s performance state. This paper has shown experimentally, that microphones close to the helicopter can be used to estimate the specific noise sources that radiate to the far field, if the microphones are positioned correctly relative to the noise source. Directivity patterns for steady, turning flight were also developed, for the first time, and connected to the turning performance of the helicopter. Some of the acoustic benefits of combining normally separated flight segments (i.e. an accelerated segment and a descending segment) were also demonstrated.
Modeling of steady-state convective cooling of cylindrical Li-ion cells
NASA Astrophysics Data System (ADS)
Shah, K.; Drake, S. J.; Wetz, D. A.; Ostanek, J. K.; Miller, S. P.; Heinzel, J. M.; Jain, A.
2014-07-01
While Lithium-ion batteries have the potential to serve as an excellent means of energy storage, they suffer from several operational safety concerns. Temperature excursion beyond a specified limit for a Lithium-ion battery triggers a sequence of decomposition and release, which can preclude thermal runaway events and catastrophic failure. To optimize liquid or air-based convective cooling approaches, it is important to accurately model the thermal response of Lithium-ion cells to convective cooling, particularly in high-rate discharge applications where significant heat generation is expected. This paper presents closed-form analytical solutions for the steady-state temperature profile in a convectively cooled cylindrical Lithium-ion cell. These models account for the strongly anisotropic thermal conductivity of cylindrical Lithium-ion batteries due to the spirally wound electrode assembly. Model results are in excellent agreement with experimentally measured temperature rise in a thermal test cell. Results indicate that improvements in radial thermal conductivity and axial convective heat transfer coefficient may result in significant peak temperature reduction. Battery sizing optimization using the analytical model is discussed, indicating the dependence of thermal performance of the cell on its size and aspect ratio. Results presented in this paper may aid in accurate thermal design and thermal management of Lithium-ion batteries.
Field study of subsurface heterogeneity with steady-state hydraulic tomography.
Berg, Steven J; Illman, Walter A
2013-01-01
Remediation of subsurface contamination requires an understanding of the contaminant (history, source location, plume extent and concentration, etc.), and, knowledge of the spatial distribution of hydraulic conductivity (K) that governs groundwater flow and solute transport. Many methods exist for characterizing K heterogeneity, but most if not all methods require the collection of a large number of small-scale data and its interpolation. In this study, we conduct a hydraulic tomography survey at a highly heterogeneous glaciofluvial deposit at the North Campus Research Site (NCRS) located at the University of Waterloo, Waterloo, Ontario, Canada to sequentially interpret four pumping tests using the steady-state form of the Sequential Successive Linear Estimator (SSLE) (Yeh and Liu 2000). The resulting three-dimensional (3D) K distribution (or K-tomogram) is compared against: (1) K distributions obtained through the inverse modeling of individual pumping tests using SSLE, and (2) effective hydraulic conductivity (K(eff) ) estimates obtained by automatically calibrating a groundwater flow model while treating the medium to be homogeneous. Such a K(eff) is often used for designing remediation operations, and thus is used as the basis for comparison with the K-tomogram. Our results clearly show that hydraulic tomography is superior to the inversions of single pumping tests or K(eff) estimates. This is particularly significant for contaminated sites where an accurate representation of the flow field is critical for simulating contaminant transport and injection of chemical and biological agents used for active remediation of contaminant source zones and plumes.
NASA Astrophysics Data System (ADS)
Wang, Fei; Nie, Wei; Feng, Xunli; Oh, C. H.
2016-07-01
The correlated emission lasing (CEL) is experimentally demonstrated in harmonic oscillators coupled via a single three-level artificial atom [Phys. Rev. Lett. 115, 223603 (2015), 10.1103/PhysRevLett.115.223603] in which two-mode entanglement only exists in a certain time period when the harmonic oscillators are resonant with the atomic transitions. Here we examine this system and show that it is possible to obtain the steady-state entanglement when the two harmonic oscillators are resonant with Rabi sidebands. Applying dressed atomic states and Bogoliubov-mode transformation, we obtain the analytical results of the variance sum of a pair of Einstein-Podolsky-Rosen (EPR)-like operators. The stable entanglement originates from the dissipation process of the Bogoliubov modes because the atomic system can act as a reservoir in dressed state representation. We also show that the entanglement is robust against the dephasing rates of the superconducing atom, which is expected to have important applications in quantum information processing.
Evaluation of boundary lubricants using steady-state wear and friction
NASA Technical Reports Server (NTRS)
Loomis, W. R.; Jones, W. R., Jr.
1981-01-01
A friction and wear study was made at 20 C to establish operating limits and procedures for obtaining improved reproducibility and reliability in boundary lubrication testing. Ester base and C-other base fluids were used to lubricate a pure iron rider in sliding contact with a rotating M-50 steel disk in a pin-on-disk apparatus. Results of a parametric study with varying loads and speeds slowed that satisfactory test conditions for studying the direction and wear characteristics in the boundary lubrication regime with this test device were found to be 1 kilogram load; 7 to 9 meters-per-minute (50 rpm) surface speed; dry air test atmosphere (less than 100 ppm H2O); and use of a time stepwise procedure for measuring wear. Highly reproducible steady-state wear rates resulted from the two fluid studies which had a linearity of about 99 percent after initially higher wear rates and friction coefficients during run-in periods of 20 to 40 minutes.
Steady-state computer design model for air-to-air heat pumps
NASA Astrophysics Data System (ADS)
Fischer, S. K.; Rice, C. K.
1981-12-01
A FORTRAN-4 computer program to predict the steady-state performance of conventional, vapor compression, electrically-driven, air-to-air heat pumps in both heating and cooling modes is described. This model is intended to serve as an analytical design tool for use by heat pump manufacturers, consulting engineers, research institutions, and universities in studies directed toward the improvement of heat pump performance. The heat pump design model allows the user to specify: system operating conditions, compressor characteristics, refrigerant flow control devices, fin-and-tube heat exchanger parameters, fan and indoor duct characteristics, and any of ten refrigerants. The model will compute: system capacity and COP (or EER), compressor and fan motor power consumptions, coil outlet air dry- and wet-bulb temperatures, air- and refrigerant-side pressure drops, a summary of the refrigerant-side states throughout the cycle, and overall compressor efficiencies and heat exchanger effectiveness. Documentation of how to use and/or modify the model is provided.
Hong, Changki; Hwang, Jeewon; Cho, Kwang-Hyun; Shin, Insik
2015-01-01
Boolean networks have been widely used to model biological processes lacking detailed kinetic information. Despite their simplicity, Boolean network dynamics can still capture some important features of biological systems such as stable cell phenotypes represented by steady states. For small models, steady states can be determined through exhaustive enumeration of all state transitions. As the number of nodes increases, however, the state space grows exponentially thus making it difficult to find steady states. Over the last several decades, many studies have addressed how to handle such a state space explosion. Recently, increasing attention has been paid to a satisfiability solving algorithm due to its potential scalability to handle large networks. Meanwhile, there still lies a problem in the case of large models with high maximum node connectivity where the satisfiability solving algorithm is known to be computationally intractable. To address the problem, this paper presents a new partitioning-based method that breaks down a given network into smaller subnetworks. Steady states of each subnetworks are identified by independently applying the satisfiability solving algorithm. Then, they are combined to construct the steady states of the overall network. To efficiently apply the satisfiability solving algorithm to each subnetwork, it is crucial to find the best partition of the network. In this paper, we propose a method that divides each subnetwork to be smallest in size and lowest in maximum node connectivity. This minimizes the total cost of finding all steady states in entire subnetworks. The proposed algorithm is compared with others for steady states identification through a number of simulations on both published small models and randomly generated large models with differing maximum node connectivities. The simulation results show that our method can scale up to several hundreds of nodes even for Boolean networks with high maximum node connectivity. The
Hong, Changki; Hwang, Jeewon; Cho, Kwang-Hyun; Shin, Insik
2015-01-01
Boolean networks have been widely used to model biological processes lacking detailed kinetic information. Despite their simplicity, Boolean network dynamics can still capture some important features of biological systems such as stable cell phenotypes represented by steady states. For small models, steady states can be determined through exhaustive enumeration of all state transitions. As the number of nodes increases, however, the state space grows exponentially thus making it difficult to find steady states. Over the last several decades, many studies have addressed how to handle such a state space explosion. Recently, increasing attention has been paid to a satisfiability solving algorithm due to its potential scalability to handle large networks. Meanwhile, there still lies a problem in the case of large models with high maximum node connectivity where the satisfiability solving algorithm is known to be computationally intractable. To address the problem, this paper presents a new partitioning-based method that breaks down a given network into smaller subnetworks. Steady states of each subnetworks are identified by independently applying the satisfiability solving algorithm. Then, they are combined to construct the steady states of the overall network. To efficiently apply the satisfiability solving algorithm to each subnetwork, it is crucial to find the best partition of the network. In this paper, we propose a method that divides each subnetwork to be smallest in size and lowest in maximum node connectivity. This minimizes the total cost of finding all steady states in entire subnetworks. The proposed algorithm is compared with others for steady states identification through a number of simulations on both published small models and randomly generated large models with differing maximum node connectivities. The simulation results show that our method can scale up to several hundreds of nodes even for Boolean networks with high maximum node connectivity. The
2014-01-01
Background A key problem in the analysis of mathematical models of molecular networks is the determination of their steady states. The present paper addresses this problem for Boolean network models, an increasingly popular modeling paradigm for networks lacking detailed kinetic information. For small models, the problem can be solved by exhaustive enumeration of all state transitions. But for larger models this is not feasible, since the size of the phase space grows exponentially with the dimension of the network. The dimension of published models is growing to over 100, so that efficient methods for steady state determination are essential. Several methods have been proposed for large networks, some of them heuristic. While these methods represent a substantial improvement in scalability over exhaustive enumeration, the problem for large networks is still unsolved in general. Results This paper presents an algorithm that consists of two main parts. The first is a graph theoretic reduction of the wiring diagram of the network, while preserving all information about steady states. The second part formulates the determination of all steady states of a Boolean network as a problem of finding all solutions to a system of polynomial equations over the finite number system with two elements. This problem can be solved with existing computer algebra software. This algorithm compares favorably with several existing algorithms for steady state determination. One advantage is that it is not heuristic or reliant on sampling, but rather determines algorithmically and exactly all steady states of a Boolean network. The code for the algorithm, as well as the test suite of benchmark networks, is available upon request from the corresponding author. Conclusions The algorithm presented in this paper reliably determines all steady states of sparse Boolean networks with up to 1000 nodes. The algorithm is effective at analyzing virtually all published models even those of moderate
Steady-State Thermal-Hydraulics Analyses for the Conversion of the BR2 Reactor to LEU
Licht, J. R.; Bergeron, A.; Dionne, B.; Van den Branden, G.; Kalcheva, S; Sikik, E; Koonen, E
2016-09-01
BR2 is a research reactor used for radioisotope production and materials testing. It’s a tank-in-pool type reactor cooled by light water and moderated by beryllium and light water. The reactor core consists of a beryllium moderator forming a matrix of 79 hexagonal prisms in a hyperboloid configuration; each having a central bore that can contain a variety of different components such as a fuel assembly, a control or regulating rod, an experimental device, or a beryllium or aluminum plug. Based on a series of tests, the BR2 operation is currently limited to a maximum allowable heat flux of 470 W/cm^{2} to ensure fuel plate integrity during steady-state operation and after a loss-of-flow/loss-of-pressure accident. A feasibility study for the conversion of the BR2 reactor from highly-enriched uranium (HEU) to low-enriched uranium (LEU) fuel was previously performed to verify it can operate safely at the same maximum nominal steady-state heat flux. An assessment was also performed to quantify the heat fluxes at which the onset of flow instability and critical heat flux occur for each fuel type. This document updates and expands these results for the current representative core configuration (assuming a fresh beryllium matrix) by evaluating the onset of nucleate boiling (ONB), onset of fully developed nucleate boiling (FDNB), onset of flow instability (OFI) and critical heat flux (CHF).
Development of Burning Plasma and Advanced Scenarios in the DIII-D Tokamak
Luce, T C
2004-12-01
Significant progress in the development of burning plasma scenarios, steady-state scenarios at high fusion performance, and basic tokamak physics has been made by the DIII-D Team. Discharges similar to the ITER baseline scenario have demonstrated normalized fusion performance nearly 50% higher than required for Q = 10 in ITER, under stationary conditions. Discharges that extrapolate to Q {approx} 10 for longer than one hour in ITER at reduced current have also been demonstrated in DIII-D under stationary conditions. Proof of high fusion performance with full noninductive operation has been obtained. Underlying this work are studies validating approaches to confinement extrapolation, disruption avoidance and mitigation, tritium retention, ELM avoidance, and operation above the no-wall pressure limit. In addition, the unique capabilities of the DIII-D facility have advanced studies of the sawtooth instability with unprecedented time and space resolution, threshold behavior in the electron heat transport, and rotation in plasmas in the absence of external torque.
Development of Burning Plasma and Advanced Scenarios in the DIII-D Tokamak
Luce, T C
2004-10-18
Significant progress in the development of burning plasma scenarios, steady-state scenarios at high fusion performance, and basic tokamak physics has been made by the DIII-D Team. Discharges similar to the ITER baseline scenario have demonstrated normalized fusion performance nearly 50% higher than required for Q = 10 in ITER, under stationary conditions. Discharges that extrapolate to Q {approx} 10 for longer than one hour in ITER at reduced current have also been demonstrated in DIII-D under stationary conditions. Proof of high fusion performance with full noninductive operation has been obtained. Underlying this work are studies validating approaches to confinement extrapolation, disruption avoidance and mitigation, tritium retention, ELM avoidance, and operation above the no-wall pressure limit. In addition, the unique capabilities of the DIII-D facility have advanced studies of the sawtooth instability with unprecedented time and space resolution, threshold behavior in the electron heat transport, and rotation in plasmas in the absence of external torque.
Baumgartner, S.; Bieli, R.; Bergmann, U. C.
2012-07-01
An overview is given of existing CPR design criteria and the methods used in BWR reload analysis to evaluate the impact of channel bow on CPR margins. Potential weaknesses in today's methodologies are discussed. Westinghouse in collaboration with KKL and Axpo - operator and owner of the Leibstadt NPP - has developed an optimized CPR methodology based on a new criterion to protect against dryout during normal operation and with a more rigorous treatment of channel bow. The new steady-state criterion is expressed in terms of an upper limit of 0.01 for the dryout failure probability per year. This is considered a meaningful and appropriate criterion that can be directly related to the probabilistic criteria set-up for the analyses of Anticipated Operation Occurrences (AOOs) and accidents. In the Monte Carlo approach a statistical modeling of channel bow and an accurate evaluation of CPR response functions allow the associated CPR penalties to be included directly in the plant SLMCPR and OLMCPR in a best-estimate manner. In this way, the treatment of channel bow is equivalent to all other uncertainties affecting CPR. Emphasis is put on quantifying the statistical distribution of channel bow throughout the core using measurement data. The optimized CPR methodology has been implemented in the Westinghouse Monte Carlo code, McSLAP. The methodology improves the quality of dryout safety assessments by supplying more valuable information and better control of conservatisms in establishing operational limits for CPR. The methodology is demonstrated with application examples from the introduction at KKL. (authors)
Steady state security assessment in deregulated power systems
NASA Astrophysics Data System (ADS)
Manjure, Durgesh Padmakar
Power system operations are undergoing changes, brought about primarily due to deregulation and subsequent restructuring of the power industry. The primary intention of the introduction of deregulation in power systems was to bring about competition and improved customer focus. The underlying motive was increased economic benefit. Present day power system analysis is much different than what it was earlier, essentially due to the transformation of the power industry from being cost-based to one that is price-based and due to open access of transmission networks to the various market participants. Power is now treated as a commodity and is traded in an open market. The resultant interdependence of the technical criteria and the economic considerations has only accentuated the need for accurate analysis in power systems. The main impetus in security analysis studies is on efficient assessment of the post-contingency status of the system, accuracy being of secondary consideration. In most cases, given the time frame involved, it is not feasible to run a complete AC load flow for determining the post-contingency state of the system. Quite often, it is not warranted as well, as an indication of the state of the system is desired rather than the exact quantification of the various state variables. With the inception of deregulation, transmission networks are subjected to a host of multilateral transactions, which would influence physical system quantities like real power flows, security margins and voltage levels. For efficient asset utilization and maximization of the revenue, more often than not, transmission networks are operated under stressed conditions, close to security limits. Therefore, a quantitative assessment of the extent to which each transaction adversely affects the transmission network is required. This needs to be done accurately as the feasibility of the power transactions and subsequent decisions (execution, curtailment, pricing) would depend upon the
NASA Astrophysics Data System (ADS)
Froio, A.; Bonifetto, R.; Carli, S.; Quartararo, A.; Savoldi, L.; Zanino, R.
2016-09-01
In superconducting tokamaks, the cryoplant provides the helium needed to cool different clients, among which by far the most important one is the superconducting magnet system. The evaluation of the transient heat load from the magnets to the cryoplant is fundamental for the design of the latter and the assessment of suitable strategies to smooth the heat load pulses, induced by the intrinsically pulsed plasma scenarios characteristic of today's tokamaks, is crucial for both suitable sizing and stable operation of the cryoplant. For that evaluation, accurate but expensive system-level models, as implemented in e.g. the validated state-of-the-art 4C code, were developed in the past, including both the magnets and the respective external cryogenic cooling circuits. Here we show how these models can be successfully substituted with cheaper ones, where the magnets are described by suitably trained Artificial Neural Networks (ANNs) for the evaluation of the heat load to the cryoplant. First, two simplified thermal-hydraulic models for an ITER Toroidal Field (TF) magnet and for the ITER Central Solenoid (CS) are developed, based on ANNs, and a detailed analysis of the chosen networks' topology and parameters is presented and discussed. The ANNs are then inserted into the 4C model of the ITER TF and CS cooling circuits, which also includes active controls to achieve a smoothing of the variation of the heat load to the cryoplant. The training of the ANNs is achieved using the results of full 4C simulations (including detailed models of the magnets) for conventional sigmoid-like waveforms of the drivers and the predictive capabilities of the ANN-based models in the case of actual ITER operating scenarios are demonstrated by comparison with the results of full 4C runs, both with and without active smoothing, in terms of both accuracy and computational time. Exploiting the low computational effort requested by the ANN-based models, a demonstrative optimization study has been
Froio, A.; Bonifetto, R.; Carli, S.; Quartararo, A.; Savoldi, L. Zanino, R.
2016-09-15
In superconducting tokamaks, the cryoplant provides the helium needed to cool different clients, among which by far the most important one is the superconducting magnet system. The evaluation of the transient heat load from the magnets to the cryoplant is fundamental for the design of the latter and the assessment of suitable strategies to smooth the heat load pulses, induced by the intrinsically pulsed plasma scenarios characteristic of today's tokamaks, is crucial for both suitable sizing and stable operation of the cryoplant. For that evaluation, accurate but expensive system-level models, as implemented in e.g. the validated state-of-the-art 4C code, were developed in the past, including both the magnets and the respective external cryogenic cooling circuits. Here we show how these models can be successfully substituted with cheaper ones, where the magnets are described by suitably trained Artificial Neural Networks (ANNs) for the evaluation of the heat load to the cryoplant. First, two simplified thermal-hydraulic models for an ITER Toroidal Field (TF) magnet and for the ITER Central Solenoid (CS) are developed, based on ANNs, and a detailed analysis of the chosen networks' topology and parameters is presented and discussed. The ANNs are then inserted into the 4C model of the ITER TF and CS cooling circuits, which also includes active controls to achieve a smoothing of the variation of the heat load to the cryoplant. The training of the ANNs is achieved using the results of full 4C simulations (including detailed models of the magnets) for conventional sigmoid-like waveforms of the drivers and the predictive capabilities of the ANN-based models in the case of actual ITER operating scenarios are demonstrated by comparison with the results of full 4C runs, both with and without active smoothing, in terms of both accuracy and computational time. Exploiting the low computational effort requested by the ANN-based models, a demonstrative optimization study has been
Simulation of a steady-state integrated human thermal system.
NASA Technical Reports Server (NTRS)
Hsu, F. T.; Fan, L. T.; Hwang, C. L.
1972-01-01
The mathematical model of an integrated human thermal system is formulated. The system consists of an external thermal regulation device on the human body. The purpose of the device (a network of cooling tubes held in contact with the surface of the skin) is to maintain the human body in a state of thermoneutrality. The device is controlled by varying the inlet coolant temperature and coolant mass flow rate. The differential equations of the model are approximated by a set of algebraic equations which result from the application of the explicit forward finite difference method to the differential equations. The integrated human thermal system is simulated for a variety of combinations of the inlet coolant temperature, coolant mass flow rate, and metabolic rates. Two specific cases are considered: (1) the external thermal regulation device is placed only on the head and (2) the devices are placed on the head and the torso. The results of the simulation indicate that when the human body is exposed to hot environment, thermoneutrality can be attained by localized cooling if the operating variables of the external regulation device(s) are properly controlled.
NASA Astrophysics Data System (ADS)
Gedeon, M.; Mallants, D.
2012-04-01
Radionuclide concentration predictions in aquifers play an important role in estimating impact of planned surface disposal of radioactive waste in Belgium, developed by the Belgian Agency for Radioactive Waste and Enriched Fissile Materials (ONDRAF), who also coordinates and leads the corresponding research. Long-term concentration predictions are based on a steady-state flow solution obtained by a cascade of multi-scale models from the catchment to the detailed (site) scale performed in MODFLOW. To test the concept and accuracy of the groundwater flow solution and conservativeness of the concentration predictions obtained therewith, a transient model, considered more realistic, was set up in a sub-domain of the intermediate scale steady-state model. Besides the modelling domain reduction, the transient model was and exact copy of the steady-state model, having the infiltration as the only time-varying parameter. The transient model was run for a twenty-year period, whereas the results were compared to the steady-state results based on infiltration value and observations averaged over the same period. The comparison of the steady-state and transient flow solutions includes the analyses of the goodness of fit, the parameter sensitivities, relative importance of the individual observations and one-percent sensitivity maps. The steady-state and transient flow solutions were subsequently translated into a site-scale transport model, used to predict the radionuclide concentrations in a hypothetical well in the aquifers. The translation of the flow solutions between the models of distinct scales was performed using the Local grid refinement method available in MODFLOW. In the site-scale models, MT3DMS transport simulations were performed to obtain respective concentration predictions in a hypothetical well, situated at 70 meters from the disposal tumuli. The equilibrium concentrations based on a constant source flux achieved using a steady-state solution were then
Archelas, Alain; Zhao, Wei; Faure, Bruno; Iacazio, Gilles; Kotik, Michael
2016-02-01
A detailed kinetic study based on steady-state and pre-steady-state measurements is described for the highly enantioselective epoxide hydrolase Kau2. The enzyme, which is a member of the α/β-hydrolase fold family, preferentially reacts with the (S,S)-enantiomer of trans-stilbene oxide (TSO) with an E value of ∼200. The enzyme follows a classical two-step catalytic mechanism with formation of an alkyl-enzyme intermediate in the first step and hydrolysis of this intermediate in a rate-limiting second step. Tryptophan fluorescence quenching during TSO conversion appears to correlate with alkylation of the enzyme. The steady-state data are consistent with (S,S) and (R,R)-TSO being two competing substrates with marked differences in k(cat) and K(M) values. The high enantiopreference of the epoxide hydrolase is best explained by pronounced differences in the second-order alkylation rate constant (k2/K(S)) and the alkyl-enzyme hydrolysis rate k3 between the (S,S) and (R,R)-enantiomers of TSO. Our data suggest that during conversion of (S,S)-TSO the two active site tyrosines, Tyr(157) and Tyr(259), serve mainly as electrophilic catalysts in the alkylation half-reaction, polarizing the oxirane oxygen of the bound epoxide through hydrogen bond formation, however, without fully donating their hydrogens to the forming alkyl-enzyme intermediate.
Estimation of the current driven by residual loop voltage in LHCD plasma on EAST Tokamak
NASA Astrophysics Data System (ADS)
Zhang, X. M.; Yu, L. M.; Wan, B. N.; Xue, E. B.; Fang, Y.; Shi, K. Y.; EAST Team
2016-02-01
The lower hybrid wave current drive (LHCD) is one of the efficient methods of driving the non-inductive current required for Tokamak operating in steady-state. Residual loop voltage exists in Tokamak when the non-inductive current is not fully driven. Residual loop voltage also accelerates the fast electrons generated by the lower hybrid wave (LHW), which can drive extra current and combine with the current driven by the LHW. It is generally difficult to separate these two different components of driven current in the experiment. In this paper, the currents driven by LHCD and residual loop voltage are separated directly by solving the Fokker-Plank equation numerically. The fraction of the current driven by residual loop voltage compared to the current driven by LHW is evaluated on the experimental advanced superconducting tokamak (EAST). The current driven by residual loop voltage is several percent of the currents driven by the LHCD when the residual loop voltage is small, but it increases with the residual loop voltage up to 25% when the residual loop voltage is about 2 V. The hot electrical conductivity is deduced from the net current driven by the residual loop voltage. Its distribution profile is related to the fast electron distribution driven by LHW.
Synchronous machine steady-state stability analysis using an artificial neural network
Chen, C.R.; Hsu, Y.Y. . Dept. of Electrical Engineering)
1991-03-01
A new type of artificial neural network is proposed for the steady-state stability analysis of a synchronous generator. In the developed artificial neutral network, those system variables which play an important role in steady-state stability such as generator outputs and power system stabilizer parameters are employed as the inputs. The output of the neural net provides the information on steady-state stability. Once the connection weights of the neural network have been learned using a set of training data derived off-line, the neural net can be applied to analyze the steady-state stability of the system time. To demonstrate the effectiveness of the proposed neural net, steady-state stability analysis is performed on a synchronous generator connected to a large power system. It is found that the proposed neural net requires much less training time than the multilayer feedforward network with backpropagation-momentum learning algorithm. It is also concluded from the test results that correct stability assessment can be achieved by the neural network.
Perception of steady-state vowels and vowelless syllables by adults and children
NASA Astrophysics Data System (ADS)
Nittrouer, Susan
2005-04-01
Vowels can be produced as long, isolated, and steady-state, but that is not how they are found in natural speech. Instead natural speech consists of almost continuously changing (i.e., dynamic) acoustic forms from which mature listeners recover underlying phonetic form. Some theories suggest that children need steady-state information to recognize vowels (and so learn vowel systems), even though that information is sparse in natural speech. The current study examined whether young children can recover vowel targets from dynamic forms, or whether they need steady-state information. Vowel recognition was measured for adults and children (3, 5, and 7 years) for natural productions of /dæd/, /dUd/ /æ/, /U/ edited to make six stimulus sets: three dynamic (whole syllables; syllables with middle 50-percent replaced by cough; syllables with all but the first and last three pitch periods replaced by cough), and three steady-state (natural, isolated vowels; reiterated pitch periods from those vowels; reiterated pitch periods from the syllables). Adults scored nearly perfectly on all but first/last three pitch period stimuli. Children performed nearly perfectly only when the entire syllable was heard, and performed similarly (near 80%) for all other stimuli. Consequently, children need dynamic forms to perceive vowels; steady-state forms are not preferred.
Halász, Adám M; Lai, Hong-Jian; McCabe Pryor, Meghan; Radhakrishnan, Krishnan; Edwards, Jeremy S
2013-01-01
True steady states are a rare occurrence in living organisms, yet their knowledge is essential for quasi-steady-state approximations, multistability analysis, and other important tools in the investigation of chemical reaction networks (CRN) used to describe molecular processes on the cellular level. Here, we present an approach that can provide closed form steady-state solutions to complex systems, resulting from CRN with binary reactions and mass-action rate laws. We map the nonlinear algebraic problem of finding steady states onto a linear problem in a higher-dimensional space. We show that the linearized version of the steady-state equations obeys the linear conservation laws of the original CRN. We identify two classes of problems for which complete, minimally parameterized solutions may be obtained using only the machinery of linear systems and a judicious choice of the variables used as free parameters. We exemplify our method, providing explicit formulae, on CRN describing signal initiation of two important types of RTK receptor-ligand systems, VEGF and EGF-ErbB1.
Analytical Solution of Steady State Equations for Chemical Reaction Networks with Bilinear Rate Laws
Halász, Ádám M.; Lai, Hong-Jian; McCabe, Meghan M.; Radhakrishnan, Krishnan; Edwards, Jeremy S.
2014-01-01
True steady states are a rare occurrence in living organisms, yet their knowledge is essential for quasi-steady state approximations, multistability analysis, and other important tools in the investigation of chemical reaction networks (CRN) used to describe molecular processes on the cellular level. Here we present an approach that can provide closed form steady-state solutions to complex systems, resulting from CRN with binary reactions and mass-action rate laws. We map the nonlinear algebraic problem of finding steady states onto a linear problem in a higher dimensional space. We show that the linearized version of the steady state equations obeys the linear conservation laws of the original CRN. We identify two classes of problems for which complete, minimally parameterized solutions may be obtained using only the machinery of linear systems and a judicious choice of the variables used as free parameters. We exemplify our method, providing explicit formulae, on CRN describing signal initiation of two important types of RTK receptor-ligand systems, VEGF and EGF-ErbB1. PMID:24334389
Steady state scenario development with elevated minimum safety factor on DIII-D
Holcomb, C. T.; Ferron, J. R.; Luce, T. C.; ...
2014-08-15
On DIII-D (Luxon 2005 Fusion Sci. Technol. 48 828), a high β scenario with minimum safety factor (qmin) near 1.4 has been optimized with new tools and shown to be a favourable candidate for long pulse or steady state operation in future devices. Furthermore, the new capability to redirect up to 5 MW of neutral beam injection (NBI) from on- to off-axis improves the ability to sustain elevated qmin with a less peaked pressure profile. The observed changes increase the ideal magnetohydrodynamics (MHD) n = 1 mode βN limit thus providing a path forward for increasing the noninductive current drivemore » fraction by operating at high βN. Quasi-stationary discharges free of tearing modes have been sustained at βN = 3.5 and βT = 3.6% for two current profile diffusion timescales (about 3 s) limited by neutral beam duration. The discharge performance has normalized fusion performance expected to give fusion gain Q ≈ 5 in a device the size of ITER. Analysis of the poloidal flux evolution and current drive balance show that the loop voltage profile is almost relaxed even with 25% of the current driven inductively, and qmin remains elevated near 1.4. Our observations increase confidence that the current profile will not evolve to one unstable to a tearing mode. In preliminary tests a divertor heat flux reduction technique based on producing a radiating mantle with neon injection appears compatible with this operating scenario. 0D model extrapolations suggest it may be possible to push this scenario up to 100% noninductive current drive by raising βN. Similar discharges with qmin = 1.5–2 were susceptible to tearing modes and off-axis fishbones, and with qmin > 2 lower normalized global energy confinement time is observed.« less
NASA Technical Reports Server (NTRS)
Wasynczuk, O.; Krause, P. C.; Biess, J. J.; Kapustka, R.
1990-01-01
A detailed computer simulation was used to illustrate the steady-state and dynamic operating characteristics of a 20-kHz resonant spacecraft power system. The simulated system consists of a parallel-connected set of DC-inductor resonant inverters (drivers), a 440-V cable, a node transformer, a 220-V cable, and a transformer-rectifier-filter (TRF) AC-to-DC receiver load. Also included in the system are a 1-kW 0.8-pf RL load and a double-LC filter connected at the receiving end of the 20-kHz AC system. The detailed computer simulation was used to illustrate the normal steady-state operating characteristics and the dynamic system performance following, for example, TRF startup. It is shown that without any filtering the given system exhibits harmonic resonances due to an interaction between the switching of the source and/or load converters and the AC system. However, the double-LC filter at the receiving-end of the AC system and harmonic traps connected in series with each of the drivers significantly reduce the harmonic distortion of the 20-kHz bus voltage. Significant additional improvement in the waveform quality can be achieved by including a double-LC filter with each driver.
NASA Astrophysics Data System (ADS)
Jena, Ajay Kumar; Kulkarni, Ashish; Ikegami, Masashi; Miyasaka, Tsutomu
2016-03-01
Hysteresis in current-voltage curves of perovskite solar cells is a serious concern as it creates confusions about actual cell performance and raises questions on its reliability. Although a lot of effort has been made to understand the origin of hysteresis, knowing whether hysteresis affects the cell performance while they are in practical use (operated constantly at maximum power point) is not yet examined. In the present study, we investigate steady state performance and performance stability of perovskite solar cells (planar architecture with varying perovskite film thickness and TiO2 mesoscopic structure with different TiO2 compact layer thickness exhibiting hysteresis of different magnitudes) operating across an external load in relation to hysteresis. The planar cells with larger hysteresis exhibit a steady state current that closely matches the value determined on forward voltage scan. Cyclic photocurrent-dark current measurements on cells with hysteresis of different magnitudes reveal that photo-induced electrical instability (not material degradation), which might be originated from ion migration or photo-induced traps formation, is not related to hysteresis. Performance of the cells is recovered partially or fully, depending on the device structure, on storage in dark. TiO2 meso-structure cells tend to show complete recovery while the planar cells recover partially.
Number of microstates and configurational entropy for steady-state two-phase flows in pore networks
NASA Astrophysics Data System (ADS)
Daras, T.; Valavanides, M. S.
2015-01-01
Steady-state two-phase flow in porous media is a process whereby a wetting phase displaces a non-wetting phase within a pore network. It is a stationary, off equilibrium process -in the sense that it is maintained in dynamic equilibrium on the expense of energy supplied to the system. The efficiency of the process depends on its spontaneity, measurable by the rate of global entropy production. The latter has been proposed to comprise two components: the rate of mechanical energy dissipation at constant temperature (a thermal entropy component, Q/T, in the continuum mechanics scale) and a configurational entropy production component (a Boltzmann-type statistical-entropy component, klnW), due to the existence of a canonical ensemble of flow configurations, physically admissible to the externally imposed macrostate stationary conditions. Here, the number of microstates, lnW, in steady-state two-phase flows in pore networks is estimated in three stages: Combinatorics are implemented to evaluate the number of identified microstates per physically admissible internal flow arrangement compatible with the imposed stationary flow conditions. Then, "Stirling's approximation limiting procedure" is applied to downscale the computational effort associated with the operations between large factorial numbers. Finally, the number of microstates is estimated by contriving a limiting procedure over the canonical ensemble of the physically admissible flow configurations. Counting the microstates is a prerequisite for estimating the process configurational entropy in order to implement the Maximum Entropy Production principle and justify the existence of optimum operating conditions.
Wootton, A.J.
1993-04-01
This progress report covers the period from November 1, 1990 to April 30, 1993. During that period, TEXT was operated as a circular tokamak with a material limiter. It was devoted to the study of basic plasma physics, in particular to study of fluctuations, turbulence, and transport. The purpose is to operate and maintain TEXT Upgrade as a complete facility for applied tokamak physics, specifically to conduct a research program under the following main headings: (1) to elucidate the mechanisms of working gas, impurity, and thermal transport in tokamaks, in particular to understand the role of turbulence; (2) to study physics of the edge plasma, in particular the turbulence; (3) to study the physics or resonant magnetic fields (ergodic magnetic divertors, intra island pumping); and (4) to study the physics of electron cyclotron heating (ECRH). Results of studies in each of these areas are reported.
Joseph, David; Schobelock, Michael J; Riesenberg, Robert R; Vince, Bradley D; Webster, Lynn R; Adeniji, Abidemi; Elgadi, Mabrouk; Huang, Fenglei
2015-01-01
The effects of steady-state faldaprevir on the safety, pharmacokinetics, and pharmacodynamics of steady-state methadone and buprenorphine-naloxone were assessed in 34 healthy male and female subjects receiving stable addiction management therapy. Subjects continued receiving a stable oral dose of either methadone (up to a maximum dose of 180 mg per day) or buprenorphine-naloxone (up to a maximum dose of 24 mg-6 mg per day) and also received oral faldaprevir (240 mg) once daily (QD) for 8 days following a 480-mg loading dose. Serial blood samples were taken for pharmacokinetic analysis. The pharmacodynamics of the opioid maintenance regimens were evaluated by the objective and subjective opioid withdrawal scales. Coadministration of faldaprevir with methadone or buprenorphine-naloxone resulted in geometric mean ratios for the steady-state area under the concentration-time curve from 0 to 24 h (AUC(0-24,ss)), the steady-state maximum concentration of the drug in plasma (C(max,ss)), and the steady-state concentration of the drug in plasma at 24 h (C(24,ss)) of 0.92 to 1.18 for (R)-methadone, (S)-methadone, buprenorphine, norbuprenorphine, and naloxone, with 90% confidence intervals including, or very close to including, 1.00 (no effect), suggesting a limited overall effect of faldaprevir. Although individual data showed moderate variability in the exposures between subjects and treatments, there was no evidence of symptoms of opiate overdose or withdrawal either during the coadministration of faldaprevir with methadone or buprenorphine-naloxone or after faldaprevir dosing was stopped. Similar faldaprevir exposures were observed in the methadone- and buprenorphine-naloxone-treated subjects. In conclusion, faldaprevir at 240 mg QD can be coadministered with methadone or buprenorphine-naloxone without dose adjustment, although given the relatively narrow therapeutic windows of these agents, monitoring for opiate overdose and withdrawal may still be appropriate. (This
Wang, Qian; Li, Bincheng
2015-09-28
Spatially resolved steady-state photocarrier radiometric (PCR) imaging technique is developed to characterize the electronic transport properties of silicon wafers. Based on a nonlinear PCR theory, simulations are performed to investigate the effects of electronic transport parameters (the carrier lifetime, the carrier diffusion coefficient, and the front surface recombination velocity) on the steady-state PCR intensity profiles. The electronic transport parameters of an n-type silicon wafer are simultaneously determined by fitting the measured steady-state PCR intensity profiles to the three-dimensional nonlinear PCR model. The determined transport parameters are in good agreement with the results obtained by the conventional modulated PCR technique with multiple pump beam radii.
The steady-state visual evoked potential in vision research: A review
Norcia, Anthony M.; Appelbaum, L. Gregory; Ales, Justin M.; Cottereau, Benoit R.; Rossion, Bruno
2015-01-01
Periodic visual stimulation and analysis of the resulting steady-state visual evoked potentials were first introduced over 80 years ago as a means to study visual sensation and perception. From the first single-channel recording of responses to modulated light to the present use of sophisticated digital displays composed of complex visual stimuli and high-density recording arrays, steady-state methods have been applied in a broad range of scientific and applied settings.The purpose of this article is to describe the fundamental stimulation paradigms for steady-state visual evoked potentials and to illustrate these principles through research findings across a range of applications in vision science. PMID:26024451
Mechanism of Non-Steady State Dissolution of Goethite in the Presence of Siderophores
NASA Astrophysics Data System (ADS)
Reichard, P. U.; Kretzschmar, R.; Kraemer, S. M.
2003-12-01
Iron is an essential micronutrient for almost all known organisms. Bacteria, fungi, and graminaceous plants are capable of exuding siderophores as part of an iron acquisition strategy. The production of these strong iron chelating ligands is induced by iron limited conditions. Grasses under iron stress, for example, exude phytosiderophores into the rhizosphere in a special diurnal rhythm (Roemheld and Marschner 1986). A few hours after sunrise the exudation starts, culminates around noon and is shut down again until about 4 hours after noon. The phytosiderophores diffuse into the rhizosphere (Marschner et al. 1986) and are passively back transported to the plants by advective flow induced by high transpiration around noon. Despite a fairly short residence time of the phytosiderophores in the rhizosphere, it is a very effective strategy for iron acquisition. To investigate the effect of such pulse inputs of siderophores on iron acquisition, we studied the dissolution mechanism of goethite (alpha-FeOOH), a mineral phase common in soils, under non-steady state conditions. In consideration of the chemical complexity of the rhizosphere, we also investigated the effect of other organic ligands commonly found in the rhizosphere (e. g. oxalate) on the dissolution kinetics. The dissolution experiments were conducted in batch reactors with a constant goethite solids concentration of 2.5 g/l, an ionic strength of 0.01 M, a pH of 6 and 100 microM oxalate. To induce non-steady state conditions, 3 mM phytosiderophores were added to a batch after the goethite-oxalate suspension reacted for a certain time period. Before the siderophore was added to the goethite-oxalate suspension, no dissolution of iron was observed. But, with the addition of the siderophore, a high rate was observed for the iron mobilization under these non-steady state conditions that subsequently was followed by a slow steady state dissolution rate. The results of these non-steady state experiments are very
NASA Astrophysics Data System (ADS)
Jazaei, Farhad; Simpson, Matthew J.; Clement, T. Prabhakar
2017-01-01
The diffusion equation is one of the most commonly used models for describing environmental problems involving heat, solute, and water transport. A diffusive system can be either transient or steady state. When a system is transient, the dependent variable (e.g., temperature, concentration, or hydraulic head) varies with time; whereas at steady state, the temporal variations are negligible. Here we consider an intermediate state, called steady shape, corresponding to the situation where temporal variations in diffusive fluxes are negligible but the dependent variable may remain transient. We present a general theoretical framework for identifying steady shape conditions and propose a novel method for evaluating the time scale needed for a diffusive system to approach both steady shape and steady state conditions.
Exact steady state manifold of a boundary driven spin-1 Lai-Sutherland chain
NASA Astrophysics Data System (ADS)
Ilievski, Enej; Prosen, Tomaž
2014-05-01
We present an explicit construction of a family of steady state density matrices for an open integrable spin-1 chain with bilinear and biquadratic interactions, also known as the Lai-Sutherland model, driven far from equilibrium by means of two oppositely polarizing Markovian dissipation channels localized at the boundary. The steady state solution exhibits n+1 fold degeneracy, for a chain of length n, due to existence of (strong) Liouvillian U(1) symmetry. The latter can be exploited to introduce a chemical potential and define a grand canonical nonequilibrium steady state ensemble. The matrix product form of the solution entails an infinitely-dimensional representation of a non-trivial Lie algebra (semidirect product of sl2 and a non-nilpotent radical) and hints to a novel Yang-Baxter integrability structure.
Sickle cell disease painful crisis and steady state differentiation by proton magnetic resonance.
Fernández, Adolfo A; Cabal, Carlos A; Lores, Manuel A; Losada, Jorge; Pérez, Enrique R
2009-01-01
The delay time of the Hb S polymerization process was investigated in 63 patients with sickle cell disease during steady state and 10 during painful crisis starting from spin-spin proton magnetic resonance (PMR) time behavior measured at 36 degrees C and during spontaneous deoxygenation. We found a significant decrease of delay time as a result of the crisis (36 +/- 10%) and two well-differentiated ranges of values for each state: 273-354 min for steady state and 166-229 min for crisis with an uncertainty region of 15%. It is possible to use PMR as an objective and quantitative method in order to differentiate both clinical conditions of the sickle cell patient, but a more clear differentiation can be established comparing the delay time (td) value of one patient during crisis with his own td value during steady state.
Kitazumi, Yuki; Hamamoto, Katsumi; Noda, Tatsuo; Shirai, Osamu; Kano, Kenji
2015-01-01
The fabrication of ultrathin-ring electrodes with a diameter of 2 mm and a thickness of 100 nm is established. The ultrathin-ring electrodes provide a large density of pseudo-steady-state currents, and realize pseudo-steady-state amperometry under quiescent conditions without a Faraday cage. Under the limiting current conditions, the current response at the ultrathin-ring electrode can be well explained by the theory of the microband electrode response. Cyclic voltammograms at the ultrathin-ring electrode show sigmoidal characteristics with some hysteresis. Numerical simulation reveals that the hysteresis can be ascribed to the time-dependence of pseudo-steady-state current. The performance of amperometry with the ultrathin-ring electrode has been verified in its application to redox enzyme kinetic measurements.
Steady-state solutions of a diffusive energy-balance climate model and their stability
NASA Technical Reports Server (NTRS)
Ghil, M.
1975-01-01
A diffusive energy-balance climate model, governed by a nonlinear parabolic partial differential equation, was studied. Three positive steady-state solutions of this equation are found; they correspond to three possible climates of our planet: an interglacial (nearly identical to the present climate), a glacial, and a completely ice-covered earth. Models similar to the main one are considered, and the number of their steady states was determined. All the models have albedo continuously varying with latitude and temperature, and entirely diffusive horizontal heat transfer. The stability under small perturbations of the main model's climates was investigated. A stability criterion is derived, and its application shows that the present climate and the deep freeze are stable, whereas the model's glacial is unstable. The dependence was examined of the number of steady states and of their stability on the average solar radiation.
Foster, Carl; Farland, Courtney V.; Guidotti, Flavia; Harbin, Michelle; Roberts, Brianna; Schuette, Jeff; Tuuri, Andrew; Doberstein, Scott T.; Porcari, John P.
2015-01-01
High intensity interval training (HIIT) has become an increasingly popular form of exercise due to its potentially large effects on exercise capacity and small time requirement. This study compared the effects of two HIIT protocols vs steady-state training on aerobic and anaerobic capacity following 8-weeks of training. Fifty-five untrained college-aged subjects were randomly assigned to three training groups (3x weekly). Steady-state (n = 19) exercised (cycle ergometer) 20 minutes at 90% of ventilatory threshold (VT). Tabata (n = 21) completed eight intervals of 20s at 170% VO2max/10s rest. Meyer (n = 15) completed 13 sets of 30s (20 min) @ 100% PVO2 max/ 60s recovery, average PO = 90% VT. Each subject did 24 training sessions during 8 weeks. Results: There were significant (p < 0.05) increases in VO2max (+19, +18 and +18%) and PPO (+17, +24 and +14%) for each training group, as well as significant increases in peak (+8, + 9 and +5%) & mean (+4, +7 and +6%) power during Wingate testing, but no significant differences between groups. Measures of the enjoyment of the training program indicated that the Tabata protocol was significantly less enjoyable (p < 0.05) than the steady state and Meyer protocols, and that the enjoyment of all protocols declined (p < 0.05) across the duration of the study. The results suggest that although HIIT protocols are time efficient, they are not superior to conventional exercise training in sedentary young adults. Key points Steady state training equivalent to HIIT in untrained students Mild interval training presents very similar physiologic challenge compared to steady state training HIIT (particularly very high intensity variants were less enjoyable than steady state or mild interval training Enjoyment of training decreases across the course of an 8 week experimental training program PMID:26664271
Mass transport in salt repositories: Steady-state transport through interbeds
Hwang, Y.; Lee, W.W.-L.; Chambre, P.L.; Pigford, T.H. . Dept. of Nuclear Engineering)
1989-03-01
Salt has long been a candidate for geologic disposal of nuclear waste. Because salt is extremely soluble in water, the existence of rock salt in the ground atest to the long-term stability of the salt. Both bedded salt and salt domes have been considered for nuclear waste disposal in the United States and Europe. While the salt is known to be quite pure in salt domes, bedded salt is interlaced with beds of sediments. Traditionally rock salt has not been considered water-conducting, but sediments layers would be classical porous media, capable of conducting water. Therefore there is interest in determining whether interbeds in bedded salt constitute pathway for radionuclide migration. In this report we consider steady-state migration of radionuclides from a single waste cylinder into a single interbed. Two approaches are used. In 1982 Neretnieks proposed an approach for calculating the steady-state transport of oxidants to a copper container. We have adapted that approach for calculating steady-state radionuclide migration away from the waste package, as a first approximation. We have also analyzed the problem of time-dependent radionuclide diffusion from a container through a backfill layer into a fracture, and we used the steady-state solution from that problem for comparison. Section 2 gives a brief summary of the geology of interbeds in bedded salt. Section 3 presents the mass transfer resistances approach of Neretnieks, summarizing the formulation and giving numerical illustrations of the steady-state two-dimensional diffusion analysis. Section 4 gives a brief statement of the steady-state result from a related analysis. Conclusions are stated in Section 5. 13 refs., 5 figs., 2 tabs.
Robust control of long-pulse, high performance plasmas in KSTAR tokamak
NASA Astrophysics Data System (ADS)
Jeon, Youngmu; Hahn, S. H.; Han, H. S.; Woo, M. H.; Joung, M.; Kim, Jayhyun; Bae, Y. S.; Kim, H.-S.; Yoon, S. W.; Oh, Y. K.; Na, Y. S.; Eidietis, N. W.; Walker, M. L.; Lanctot, M. J.; Hyatt, A. W.; Mueller, D. A.; Kstar Team
2016-10-01
The goal of KSTAR is to achieve and demonstrate high performance, steady state tokamak operations in long pulse up to 300 s. In recent years, we made significant progresses on plasma control and performance for this advanced tokamak (AT) operation. First of all, the plasma equilibrium magnetic control has been substantially improved by applying fully decoupled multi-input-multi-output (MIMO) isoflux shape controllers [1]. The MIMO shape controllers were designed using a newly developed design method by taking the plasma equilibrium response into account self-consistently. More than eight shape control variables including plasma currents are controlled independently on each other with high accuracy (less than 1cm error on average) and with wide variations of plasma shape. By virtue of this robust control, various long pulse H-mode discharges have been operated up to 60 s, which was the maximum pulse length allowable in current KSTAR system. Also, plasma performance has been improved accordingly. A fully non-inductive H-mode operation [1] was achieved for the first time in KSTAR, through the so-called `high betap' operation with betap 3.0. In addition, various experimental attempts for advanced scenario development have been conducted such as the `hybrid' [2] and `high li' scenarios[3].
NASA Astrophysics Data System (ADS)
Kostoglou, M.; Karapantsios, T. D.; Buffone, C.; Glushchuk, A.; Iorio, C.
2016-10-01
The present work attempts to model the case of combined gravitational and capillary motion of condensate for an axisymmetric fin under steady and transient fin operation conditions. The focus here is to examine the structure of the mathematical problem and to develop suitable numerical techniques rather than yield information on the macroscopic condensate flow rate and fin efficiency. The problem is formulated starting from general conditions and is simplified step by step by introducing corresponding assumptions. The particular fin shape of a paraboloid from revolution is chosen and the equations are properly non-dimensionalized. A vast reduction of the number of problem parameters is achieved in this way. The cases of isothermal fin, steady state operation and dynamic operation are treated separately using specialized numerical solution techniques developed for each case in order to improve computational efficiency and accuracy. Typical results of fin temperature and condensate film thickness are presented and discussed.
S3C: EBT Steady-State Shooting code description and user's guide
Downum, W.B.
1983-09-01
The Oak Ridge National Laboratory (ORNL) one-dimensional (1-D) Steady-State Shooting code (S3C) for ELMO Bumpy Torus (EBT) plasmas is described. Benchmark calculations finding the steady-state density and electron and ion temperature profiles for a known neutral density profile and known external energy sources are carried out. Good agreement is obtained with results from the ORNL Radially Resolved Time Dependent 1-D Transport code for an EBT-Q type reactor. The program logic is described, along with the physics models in each code block and the variable names used. Sample input and output files are listed, along with the main code.
A quaternionic map for the steady states of the Heisenberg spin-chain
NASA Astrophysics Data System (ADS)
Mehta, Mitaxi P.; Dutta, Souvik; Tiwari, Shubhanshu
2014-01-01
We show that the steady states of the classical Heisenberg XXX spin-chain in an external magnetic field can be found by iterations of a quaternionic map. A restricted model, e.g., the xy spin-chain is known to have spatially chaotic steady states and the phase space occupied by these chaotic states is known to go through discrete changes as the field strength is varied. The same phenomenon is studied for the xxx spin-chain. It is seen that in this model the phase space volume varies smoothly with the external field.
Mass-Radius Spirals for Steady State Families of the Vlasov-Poisson System
NASA Astrophysics Data System (ADS)
Ramming, Tobias; Rein, Gerhard
2017-02-01
We consider spherically symmetric steady states of the Vlasov-Poisson system, which describe equilibrium configurations of galaxies or globular clusters. If the microscopic equation of state, i.e., the dependence of the steady state on the particle energy (and angular momentum) is fixed, a one-parameter family of such states is obtained. In the polytropic case the mass of the state along such a one-parameter family is a monotone function of its radius. We prove that for the King, Woolley-Dickens, and related models this mass-radius relation takes the form of a spiral.
Three-state, steady-state Ising systems: Monte Carlo and Bragg-Williams treatments
Hill, Terrell L.; Chen, Yi-Der
1981-01-01
In two earlier papers, the steady-state critical and phase-transition properties of a lattice of three-state enzyme molecules were studied by using the “closed” Bragg-Williams (BW), or mean field, approximation. The “open” BW and Monte Carlo methods are applied to the same problem in this paper by using finite lattices. The open BW treatment provides a way of locating the cut across a van der Waals type of loop encountered in a phase transition in the closed BW system. Thermodynamic-like methods cannot be used for this purpose as they can with two-state, steady-state systems. PMID:16592956
Non-equilibrium steady states: fluctuations and large deviations of the density and of the current
NASA Astrophysics Data System (ADS)
Derrida, Bernard
2007-07-01
These lecture notes give a short review of methods such as the matrix ansatz, the additivity principle or the macroscopic fluctuation theory, developed recently in the theory of non-equilibrium phenomena. They show how these methods allow us to calculate the fluctuations and large deviations of the density and the current in non-equilibrium steady states of systems like exclusion processes. The properties of these fluctuations and large deviation functions in non-equilibrium steady states (for example, non-Gaussian fluctuations of density or non-convexity of the large deviation function which generalizes the notion of free energy) are compared with those of systems at equilibrium.
Ng, P K
1980-07-01
This paper describes the use of a programmable calculator (HP-97) to determine the individualized Michaelis-Menten parameters of phenytoin by utilising the linear regression technique in fitting data of multiple doses and corresponding steady-state concentrations to a linear-transformed Michaelis-Menten equation and solving for the Michaelis-Menten parameters. In addition, the calculator program can predict the corresponding steady-state concentration of phenytoin for any given dose used in an individual by employing the derived Michaelis-Menten parameters and the Michaelis-Menten equation.
Spectral characteristics of steady-state Lévy flights in confinement potential profiles
NASA Astrophysics Data System (ADS)
Kharcheva, A. A.; Dubkov, A. A.; Dybiec, B.; Spagnolo, B.; Valenti, D.
2016-05-01
The steady-state correlation characteristics of superdiffusion in the form of Lévy flights in one-dimensional confinement potential profiles are investigated both theoretically and numerically. Specifically, for Cauchy stable noise we calculate the steady-state probability density function for an infinitely deep rectangular potential well and for a symmetric steep potential well of the type U(x)\\propto {{x}2m} . For these potential profiles and arbitrary Lévy index α, we obtain the asymptotic expression of the spectral power density.
Transient and steady-state velocity of domain walls for a complete range of drive fields
NASA Technical Reports Server (NTRS)
Bourne, H. C., Jr.; Bartran, D. S.
1974-01-01
Approximate analytic solutions for transient and steady-state 180 deg domain wall motion in bulk magnetic material are obtained from the dynamic torque equations with a Gilbert damping term. The results for the Walker region in which the transient solution approaches the familiar Walker steady-state solution are presented in a slightly new form for completeness. An analytic solution corresponding to larger drive fields predicts an oscillatory motion with an average value which decreases with drive field for reasonable values of the damping parameter. These results agree with those obtained by a computer solution of the torque equation and those obtained with the assumption of a very large anisotropy field.
Characterization of polyester films used in capacitors. 1: Transient and steady-state conductivity
NASA Astrophysics Data System (ADS)
Thielen, A.; Niezette, J.; Feyder, G.; Vanderschueren, J.
1994-10-01
Charging and discharging currents flowing through polyethylene terephthalate (PET) ultrathin films (1.5 - 12 micrometers) were measured by the use of a two-electrode configuration involving opposite lateral contacts. A study of the influence of electrification time, applied electric field, film thickness, nature of electrodes, and water content was carried out on both transient and steady-state conduction. The transient behavior can be interpreted in terms of dipolar orientation and relaxation processes while steady-state conductivity can be mainly accounted for in terms of Schottky emission. A comparison between PET and polyethylene naphthalate films is also reported.
NASA Astrophysics Data System (ADS)
Crane, D. T.
2011-05-01
High-power-density, segmented, thermoelectric (TE) elements have been intimately integrated into heat exchangers, eliminating many of the loss mechanisms of conventional TE assemblies, including the ceramic electrical isolation layer. Numerical models comprising simultaneously solved, nonlinear, energy balance equations have been created to simulate these novel architectures. Both steady-state and transient models have been created in a MATLAB/Simulink environment. The models predict data from experiments in various configurations and applications over a broad range of temperature, flow, and current conditions for power produced, efficiency, and a variety of other important outputs. Using the validated models, devices and systems are optimized using advanced multiparameter optimization techniques. Devices optimized for particular steady-state operating conditions can then be dynamically simulated in a transient operating model. The transient model can simulate a variety of operating conditions including automotive and truck drive cycles.
DIII-D research operations. Annual report, October 1, 1992--September 30, 1993
La Haye, R.J.
1994-05-01
The DIII-D tokamak research program is carried out by General Atomics (GA) for the U.S. Department of Energy (DOE). The DIII-D is the most flexible tokamak in the world. The primary goal of the DIII-D tokamak research program is to provide data to develop a conceptual physics blueprint for a commercially attractive electrical demonstration plant (DEMO) that would open a path to fusion power commercialization. In doing so, the DIII-D program provides physics and technology R&D outputs to aid the Tokamak Physics Experiment (TPX) and the International Thermonuclear Experimental Reactor (ITER). Specific DIII-D objectives include the steady-state sustainment of plasma current as well as demonstrating techniques for microwave heating, divertor heat removal, fuel exhaust and tokamak plasma control. The DIII-D program is addressing these objectives in an integrated fashion with high beta and with good confinement. The long-range plan is organized into two major thrusts; the development of an advanced divertor and the development of advanced tokamak concepts. These two thrusts have a common goal: an improved DEMO reactor with lower cost and smaller size than the present DEMO which can be extrapolated from the conventional ITER operational scenario. In order to prepare for the long-range program, in FY93 the DIII-D research program concentrated on three major areas: Divertor and Boundary Physics, Advanced Tokamak Studies, and Tokamak Physics. The major goals of the Divertor and Boundary Physics studies are the control of impurities, efficient heat removal and understanding the strong role that the edge plasma plays in the global energy confinement of the plasma. The advanced tokamak studies initiated the investigation into new techniques for improving energy confinement, controlling particle fueling and increasing plasma beta. The major goal of the Tokamak Physics Studies is the understanding of energy and particle transport in a reactor relevant plasma.
Are type III-IV muscle afferents required for a normal steady-state exercise hyperpnoea in humans?
Dempsey, Jerome A; Blain, Grégory M; Amann, Markus
2014-02-01
When tested in isolation, stimuli associated with respiratory CO2 exchange, feedforward central command and type III-IV muscle afferent feedback have each been shown to be capable of eliciting exercise-like cardio-ventilatory responses, but their relative contributions in a setting of physiological exercise remains controversial. We reasoned that in order to determine whether any of these regulators are obligatory to the exercise hyperpnoea each needs to be removed or significantly diminished in a setting of physiological steady-state exercise, during which all recognized stimuli (and other potential modulators) are normally operative. In the past few years we and others have used intrathecal fentanyl, a μ-opiate receptor agonist, in humans to reduce the input from type III-IV opiate-sensitive muscle afferents. During various types of intensities and durations of exercise a sustained hypoventilation, as well as reduced systemic pressure and cardioacceleration, were consistently observed with this blockade. These data provide the basis for the hypothesis that type III-IV muscle afferents are obligatory to the hyperpnoea of mild to moderate intensity rhythmic, large muscle, steady-state exercise. We discuss the limitations of these studies, the reasons for their disagreement with previous negative findings, the nature of the muscle afferent feedback stimulus and the need for future investigations.
Advanced commercial tokamak study
Thomson, S.L.; Dabiri, A.E.; Keeton, D.C.; Brown, T.G.; Bussell, G.T.
1985-12-01
Advanced commercial tokamak studies were performed by the Fusion Engineering Design Center (FEDC) as a participant in the Tokamak Power Systems Studies (TPSS) project coordinated by the Office of Fusion Energy. The FEDC studies addressed the issues of tokamak reactor cost, size, and complexity. A scoping study model was developed to determine the effect of beta on tokamak economics, and it was found that a competitive cost of electricity could be achieved at a beta of 10 to 15%. The implications of operating at a beta of up to 25% were also addressed. It was found that the economics of fusion, like those of fission, improve as unit size increases. However, small units were found to be competitive as elements of a multiplex plant, provided that unit cost and maintenance time reductions are realized for the small units. The modular tokamak configuration combined several new approaches to develop a less complex and lower cost reactor. The modular design combines the toroidal field coil with the reactor structure, locates the primary vacuum boundary at the reactor cell wall, and uses a vertical assembly and maintenance approach. 12 refs., 19 figs.
Baker, D.
1993-05-01
The DIII-D tokamak research program is carried out by, General Atomics (GA) for the U.S. Department of Energy (DOE). The DIII-D is the most flexible tokamak in the world. The primary goal of the DIII-D tokamak research program is to provide data needed by International Thermonuclear Experimental Reactor (ITER) and to develop a conceptual physics blueprint for a commercially attractive electrical demonstration plant (DEMO) that would open a path to fusion power commercialization. Specific DIII-D objectives include the steady-state sustainment of plasma current as well as demonstrating techniques for microwave heating, divertor heat removal, fuel exhaust and tokamak plasma control. The DIII-D program is addressing these objectives in an integrated fashion with high beta and with good confinement. The DIII-D long-range plan is organized into two major thrusts; the development of an advanced divertor and the development of advanced tokamak concepts. These two thrusts have a common goal: an improved DEMO reactor with lower cost and smaller size than the present DEMO which can be extrapolated from the conventional ITER operational scenario. In order to prepare for the long-range program, in FY92 the DIII-D research program concentrated on three major areas: Divertor and Boundary Physics, Advanced Tokamak Studies, and Tokamak Physics.
Experimental verification of subcooled flow boiling for tokamak pump limiter designs
Koski, J.A.; Beattie, A.G.; Whitley, J.B.; Croessmann, C.D.
1987-01-01
In fusion energy research devices such as tokamaks, limiters are used to define the plasma boundary, and may serve the additional functions of plasma density and impurity control by removing neutralized particles from the plasma edge region. Because the devices must operate in the plasma edge, they are subject to high heat fluxes. In this paper, experimental studies conducted in support of a pump limiter design currently under development are discussed. Subcooled flow boiling of water and twisted tape flow enhancement are combined to enable heat removal of highly peaked local heat fluxes at the tube-water boundary in the 40 to 50 MW/m/sup 2/ range. Critical heat flux and heat removal experiments were conducted on copper tube targets with the use of a rastered 30 kV electron beam apparatus capable of producing the desired steady state heat flux levels.
Observation of anomalous momentum transport in tokamak plasmas with no momentum input.
Lee, W D; Rice, J E; Marmar, E S; Greenwald, M J; Hutchinson, I H; Snipes, J A
2003-11-14
Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas through analysis of the time evolution of core impurity toroidal rotation velocity profiles. Following the L-mode to EDA (enhanced D(alpha)) H-mode transition, the ensuing cocurrent toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core. The steady state toroidal rotation velocity profiles are relatively flat and the momentum transport can be simulated with a simple diffusion model. Velocity profiles during edge localized mode free (ELM-free) H-modes are centrally peaked, which suggests the addition of inward momentum convection. In all operating regimes the observed momentum diffusivities are much larger than the neoclassical values.
STEADY STATE MODELING OF THE MINIMUM CRITICAL CORE OF THE TRANSIENT REACTOR TEST FACILITY
Anthony L. Alberti; Todd S. Palmer; Javier Ortensi; Mark D. DeHart
2016-05-01
With the advent of next generation reactor systems and new fuel designs, the U.S. Department of Energy (DOE) has identified the need for the resumption of transient testing of nuclear fuels. The DOE has decided that the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory (INL) is best suited for future testing. TREAT is a thermal neutron spectrum, air-cooled, nuclear test facility that is designed to test nuclear fuels in transient scenarios. These specific scenarios range from simple temperature transients to full fuel melt accidents. DOE has expressed a desire to develop a simulation capability that will accurately model the experiments before they are irradiated at the facility. It is the aim for this capability to have an emphasis on effective and safe operation while minimizing experimental time and cost. The multi physics platform MOOSE has been selected as the framework for this project. The goals for this work are to identify the fundamental neutronics properties of TREAT and to develop an accurate steady state model for future multiphysics transient simulations. In order to minimize computational cost, the effect of spatial homogenization and angular discretization are investigated. It was found that significant anisotropy is present in TREAT assemblies and to capture this effect, explicit modeling of cooling channels and inter-element gaps is necessary. For this modeling scheme, single element calculations at 293 K gave power distributions with a root mean square difference of 0.076% from those of reference SERPENT calculations. The minimum critical core configuration with identical gap and channel treatment at 293 K resulted in a root mean square, total core, radial power distribution 2.423% different than those of reference SERPENT solutions.
Transient and steady state photoelectronic analysis in TlInSe{sub 2} crystals
Qasrawi, A.F.; Gasanly, N.M.
2011-08-15
Highlights: {yields} The steady state and time dependent photoconductivity kinetics of the TlInSe{sub 2} crystals are investigated in the temperature region of 100-350 K. {yields} The photocurrent of the sample exhibited linear, sublinear, and supralinear recombination mechanisms, at, above and below 160 K, respectively. {yields} Steady state photoconductivity revealed two recombination centres located at 234 and 94 meV. {yields} The transient photoconductivity is limited by a trapping center located at 173 meV. {yields} The capture coefficient of the trap for holes was determined as 3.11 x 10{sup -22} cm{sup -2}. -- Abstract: The temperature and illumination effects on the transient and steady state photoconductivities of TlInSe{sub 2} crystals have been studied. Namely, two recombination centres located at 234 and at 94 meV and one trap center located at 173 meV were determined from the temperature-dependent steady state and transient photoconductivities, respectively. The illumination dependence of photoconductivity indicated the domination of sublinear and supralinear recombination mechanisms above and below 160 K, respectively. The change in the recombination mechanism is attributed to the exchange of roles between the linear recombination at the surface and trapping centres in the crystal, which become dominant as temperature decreases. The transient photoconductivity measurement allowed the determination of the capture coefficient of traps for holes as 3.11 x 10{sup -22} cm{sup -2}.