Nanobubbles in confined solution: Generation, contact angle, and stability.

PubMed

Wei, Jiachen; Zhang, Xianren; Song, Fan; Shao, Yingfeng

2018-02-14

The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.

Nanobubbles in confined solution: Generation, contact angle, and stability

NASA Astrophysics Data System (ADS)

Wei, Jiachen; Zhang, Xianren; Song, Fan; Shao, Yingfeng

2018-02-01

The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.

Electromagnetic Torque in Tokamaks with Toroidal Asymmetries

NASA Astrophysics Data System (ADS)

Logan, Nikolas Christopher

Toroidal rotation and rotation shear strongly influences stability and confinement in tokamaks. Breaking of the toroidal symmetry by fields orders of magnitude smaller than the axisymmetric field can, however, produce electromagnetic torques that significantly affect the plasma rotation, stability and confinement. These electromagnetic torques are the study of this thesis. There are two typical types of electromagnetic torques in tokamaks: 1) "resonant torques" for which a plasma current defined by a single toroidal and single poloidal harmonic interact with external currents and 2) "nonresonant torques" for which the global plasma response to nonaxisymmetric fields is phase shifted by kinetic effects that drive the rotation towards a neoclassical offset. This work describes the diagnostics and analysis necessary to evaluate the torque by measuring the rate of momentum transfer per unit area in the vacuum region between the plasma and external currents using localized magnetic sensors to measure the Maxwell stress. These measurements provide model independent quantification of both the resonant and nonresonant electromagnetic torques, enabling direct verification of theoretical models. Measured values of the nonresonant torque are shown to agree well with the perturbed equilibrium nonambipolar transport (PENT) code calculation of torque from cross field transport in nonaxisymmetric equilibria. A combined neoclassical toroidal viscosity (NTV) theory, valid across a wide range of kinetic regimes, is fully implemented for the first time in general aspect ratio and shaped plasmas. The code captures pitch angle resonances, reproducing previously inaccessible collisionality limits in the model. The complete treatment of the model enables benchmarking to the hybrid kinetic MHD stability codes MARS-K and MISK, confirming the energy-torque equivalency principle in perturbed equilibria. Experimental validations of PENT results confirm the torque applied by nonaxisymmetric coils is often proportional to the energy put into the dominant ideal MHD kink mode. This reduces the control of nonresonant torque to a single mode model, enabling efficient feed forward optimization of applied fields. Initial results including the anisotropic kinetic pressure tensor directly in the plasma eigenmode calculations are presented here, and may eventually provide accurate metrics for multimodal coupling similar to the established single mode metrics.

Ordered and layered structure of liquid nitromethane within a graphene bilayer: toward stabilization of energetic materials through nanoscale confinement.

PubMed

Liu, Yingzhe; Yu, Tao; Lai, Weipeng; Kang, Ying; Ge, Zhongxue

2015-03-01

The structural characteristics involving thermal stabilities of liquid nitromethane (NM)—one of the simplest energetic materials—confined within a graphene (GRA) bilayer were investigated by means of all-atom molecular dynamics simulations and density functional theory calculations. The results show that ordered and layered structures are formed at the confinement of the GRA bilayer induced by the van der Waals attractions of NM with GRA and the dipole-dipole interactions of NM, which is strongly dependent on the confinement size, i.e., the GRA bilayer distance. These unique intermolecular arrangements and preferred orientations of confined NM lead to higher stabilities than bulk NM revealed by bond dissociation energy calculations.

Magnetoelectric confinement and stabilization of Z pinch in a soft-x-ray Ar(+8) laser.

PubMed

Szasz, J; Kiss, M; Santa, I; Szatmari, S; Kukhlevsky, S V

2013-05-03

Magnetoelectric confinement and stabilization of the plasma column in a soft-x-ray Ar(+8) laser, which is excited by a capillary Z pinch, via the combined magnetic and electric fields of the gliding surface discharge is experimentally demonstrated. Unlike soft-x-ray lasers excited by the conventional capillary Z pinches, the magnetoelectric confinement and stabilization of plasma do provide the laser operation without using any external preionization circuit.

Exploratory Research on Bearing Characteristics of Confined Stabilized Soil

NASA Astrophysics Data System (ADS)

Wu, Shuai Shuai; Gao, Zheng Guo; Li, Shi Yang; Cui, Wen Bo; Huang, Xin

2018-06-01

The performance of a new kind of confined stabilized soil (CSS) was investigated which was constructed by filling the stabilized soil, which was made by mixing soil with a binder containing a high content of expansive component, into an engineering plastic pipe. Cube compressive strength of the stabilized soil formed with constraint and axial compression performance of stabilized soil cylinders confined with the constraint pipe were measured. The results indicated that combining the constraint pipe and the binder containing expansion component could achieve such effects: higher production of expansive hydrates could be adopted so as to fill more voids in the stabilized soil and improve its strength; at the same time compressive prestress built on the core stabilized soil, combined of which hoop constraint provided effective radial compressive force on the core stabilized soil. These effects made the CSS acquire plastic failure mode and more than twice bearing capacity of ordinary stabilized soil with the same binder content.

NRMC - A GPU code for N-Reverse Monte Carlo modeling of fluids in confined media

NASA Astrophysics Data System (ADS)

Sánchez-Gil, Vicente; Noya, Eva G.; Lomba, Enrique

2017-08-01

NRMC is a parallel code for performing N-Reverse Monte Carlo modeling of fluids in confined media [V. Sánchez-Gil, E.G. Noya, E. Lomba, J. Chem. Phys. 140 (2014) 024504]. This method is an extension of the usual Reverse Monte Carlo method to obtain structural models of confined fluids compatible with experimental diffraction patterns, specifically designed to overcome the problem of slow diffusion that can appear under conditions of tight confinement. Most of the computational time in N-Reverse Monte Carlo modeling is spent in the evaluation of the structure factor for each trial configuration, a calculation that can be easily parallelized. Implementation of the structure factor evaluation in NVIDIA® CUDA so that the code can be run on GPUs leads to a speed up of up to two orders of magnitude.

Simulating the effects of stellarator geometry on gyrokinetic drift-wave turbulence

NASA Astrophysics Data System (ADS)

Baumgaertel, Jessica Ann

Nuclear fusion is a clean, safe form of energy with abundant fuel. In magnetic fusion energy (MFE) experiments, the plasma fuel is confined by magnetic fields at very high temperatures and densities. One fusion reactor design is the non-axisymmetric, torus-shaped stellarator. Its fully-3D fields have advantages over the simpler, better-understood axisymmetric tokamak, including the ability to optimize magnetic configurations for desired properties, such as lower transport (longer confinement time). Turbulence in the plasma can break MFE confinement. While turbulent transport is known to cause a significant amount of heat loss in tokamaks, it is a new area of research in stellarators. Gyrokinetics is a good mathematical model of the drift-wave instabilities that cause turbulence. Multiple gyrokinetic turbulence codes that had great success comparing to tokamak experiments are being converted for use with stellarator geometry. This thesis describes such adaptations of the gyrokinetic turbulence code, GS2. Herein a new computational grid generator and upgrades to GS2 itself are described, tested, and benchmarked against three other gyrokinetic codes. Using GS2, detailed linear studies using the National Compact Stellarator Experiment (NCSX) geometry were conducted. The first compares stability in two equilibria with different β=(plasma pressure)/(magnetic pressure). Overall, the higher β case was more stable than the lower β case. As high β is important for MFE experiments, this is encouraging. The second compares NCSX linear stability to a tokamak case. NCSX was more stable with a 20% higher critical temperature gradient normalized by the minor radius, suggesting that the fusion power might be enhanced by ˜ 50%. In addition, the first nonlinear, non-axisymmetric GS2 simulations are presented. Finally, linear stability of two locations in a W7-AS plasma were compared. The experimentally-measured parameters used were from a W7-AS shot in which measured heat fluxes match neoclassical theory predictions at inner radii, but are too large for neoclassical predictions at outer radii. Results from GS2 linear simulations show that the outer location has higher gyrokinetic instability growth rates than at the inner one. Mixing-length estimates of the heat flux are within a factor of 3 of the experimental measurements, indicating that gyrokinetic turbulence may be responsible for the higher transport measured by the experiment in the outer regions. Future nonlinear simulations can explore this question in more detail. This work is supported by the Princeton Plasma Physics Laboratory, which is operated by Princeton University for the U.S. Department of Energy under Contract No. DE-AC02-09CH11466, and the SciDAC Center for the Study of Plasma Microturbulence.

Confined Turbulent Swirling Recirculating Flow Predictions. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Abujelala, M. T.

1984-01-01

Turbulent swirling flow, the STARPIC computer code, turbulence modeling of turbulent flows, the k-xi turbulence model and extensions, turbulence parameters deduction from swirling confined flow measurements, extension of the k-xi to confined swirling recirculating flows, and general predictions for confined turbulent swirling flow are discussed.

Edge Stability and Performance of the ELM-Free Quiescent H-Mode and the Quiescent Double Barrier Mode on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, W P; Burrell, K H; Casper, T A

2004-12-03

The quiescent H (QH) mode, an edge localized mode (ELM)-free, high-confinement mode, combines well with an internal transport barrier to form quiescent double barrier (QDB) stationary state, high performance plasmas. The QH-mode edge pedestal pressure is similar to that seen in ELMing phases of the same discharge, with similar global energy confinement. The pedestal density in early ELMing phases of strongly pumped counter injection discharges drops and a transition to QH-mode occurs, leading to lower calculated edge bootstrap current. Plasmas current ramp experiment and ELITE code modeling of edge stability suggest that QH-modes lie near an edge current stability boundary.more » At high triangularity, QH-mode discharges operate at higher pedestal density and pressure, and have achieved ITER level values of {beta}{sub PED} and {nu}*. The QDB achieves performance of {alpha}{sub N}H{sub 89} {approx} 7 in quasi-stationary conditions for a duration of 10 tE, limited by hardware. Recently we demonstrated stationary state QDB discharges with little change in kinetic and q profiles (q{sub 0} > 1) for 2 s, comparable to ELMing ''hybrid scenarios'', yet without the debilitating effects of ELMs. Plasma profile control tools, including electron cyclotron heating and current drive and neutral beam heating, have been demonstrated to control simultaneously the q profile development, the density peaking, impurity accumulation and plasma beta.« less

Stabilizing Effect of Resistivity towards ELM-free H-mode Discharge in Lithium-conditioned NSTX

NASA Astrophysics Data System (ADS)

Banerjee, Debabrata; Zhu, Ping; Maingi, Rajesh

2016-10-01

The stabilizing effect of edge resistivity on the edge localized modes (ELMs) has been recently recovered through analyzing NSTX experimental profiles of Lithium-conditioned ELM-free H-mode discharge. Comparative studies of ELM-free and a reference NSTX ELMy-H mode equilibriums have been performed using both resistive and 2-fluid MHD models implemented in the initial value extended MHD code NIMROD. Our results indicate that in addition to the pedestal profile refinement in electron pressure, the inclusion of enhanced resistivity due to the increase in the effective electric charge number Zeff, which is observed after Lithium-conditioning in experiment, is further required to account for the full stabilization of the low- n edge localized modes. Such a stabilization from the enhanced edge resistivity only becomes effective when the two-fluid diamagnetic and finite-Larmor-radius (FLR) effects are considered in the MHD model. Supported by the National Magnetic Confinement Fusion Program of China under Grant Nos. 2014GB124002 and 2015GB101004, the 100 Talent Program and the President International Fellowship Initiative of the Chinese Academy of Sciences.

Confinement in nanopores can destabilize α-helix folding proteins and stabilize the β structures

NASA Astrophysics Data System (ADS)

Javidpour, Leili; Sahimi, Muhammad

2011-09-01

Protein folding in confined media has attracted wide attention over the past decade due to its importance in both in vivo and in vitro applications. Currently, it is generally believed that protein stability increases by decreasing the size of the confining medium, if its interaction with the confining walls is repulsive, and that the maximum folding temperature in confinement occurs for a pore size only slightly larger than the smallest dimension of the folded state of a protein. Protein stability in pore sizes, very close to the size of the folded state, has not however received the attention that it deserves. Using detailed, 0.3-ms-long molecular dynamics simulations, we show that proteins with an α-helix native state can have an optimal folding temperature in pore sizes that do not affect the folded-state structure. In contradiction to the current theoretical explanations, we find that the maximum folding temperature occurs in larger pores for smaller α-helices. In highly confined pores the free energy surface becomes rough, and a new barrier for protein folding may appear close to the unfolded state. In addition, in small nanopores the protein states that contain the β structures are entropically stabilized, in contrast to the bulk. As a consequence, folding rates decrease notably and the free energy surface becomes rougher. The results shed light on many recent experimental observations that cannot be explained by the current theories, and demonstrate the importance of entropic effects on proteins' misfolded states in highly confined environments. They also support the concept of passive effect of chaperonin GroEL on protein folding by preventing it from aggregation in crowded environment of biological cells, and provide deeper clues to the α → β conformational transition, believed to contribute to Alzheimer's and Parkinson's diseases. The strategy of protein and enzyme stabilization in confined media may also have to be revisited in the case of tight confinement. For in silico studies of protein folding in confined media, use of non-Go potentials may be more appropriate.

Uncertainty propagation in q and current profiles derived from motional Stark effect polarimetry on TFTR (abstract)a)

NASA Astrophysics Data System (ADS)

Batha, S. H.; Levinton, F. M.; Bell, M. G.; Wieland, R. M.; Hirschman, S. P.

1995-01-01

The magnetic-field pitch-angle profile, γp(R)≡arctan(Bpol/Btor), is measured on the TFTR tokamak using a motional Stark effect (MSE) polarimeter. Measured profiles are converted to q profiles with the equilibrium code vmec. Uncertainties in the q profile due to uncertainties in the γp(R), magnetics, and kinetic measurements are quantified. Subsequent uncertainties in the vmec-calculated profiles of current density and shear, both of which are important for stability and transport analyses, are also quantified. Examples of circular plasmas under various confinement modes, including the supershot and L mode, will be given.

Numerical studies of edge localized instabilities in tokamaks

NASA Astrophysics Data System (ADS)

Wilson, H. R.; Snyder, P. B.; Huysmans, G. T. A.; Miller, R. L.

2002-04-01

A new computational tool, edge localized instabilities in tokamaks equilibria (ELITE), has been developed to help our understanding of short wavelength instabilities close to the edge of tokamak plasmas. Such instabilities may be responsible for the edge localized modes observed in high confinement H-mode regimes, which are a serious concern for next step tokamaks because of the high transient power loads which they can impose on divertor target plates. ELITE uses physical insight gained from analytic studies of peeling and ballooning modes to provide an efficient way of calculating the edge ideal magnetohydrodynamic stability properties of tokamaks. This paper describes the theoretical formalism which forms the basis for the code.

Plasma Density Effects on Toroidal Flow Stabilization of Edge Localized Modes

NASA Astrophysics Data System (ADS)

Cheng, Shikui; Zhu, Ping; Banerjee, Debabrata

2016-10-01

Recent EAST experiments have demonstrated mitigation and suppression of edge localized modes (ELMs) with toroidal rotation flow in higher collisionality regime, suggesting potential roles of plasma density. In this work, the effects of plasma density on the toroidal flow stabilization of the high- n edge localized modes have been extensively studied in linear calculations for a circular-shaped limiter H-mode tokamak, using the initial-value extended MHD code NIMROD. In the single MHD model, toroidal flow has a weak stabilizing effects on the high- n modes. Such a stabilization, however, can be significantly enhanced with the increase in plasma density. Furthermore, our calculations show that the enhanced stabilization of high- n modes from toroidal flow with higher edge plasma density persists in the 2-fluid MHD model. These findings may explain the ELM mitigation and suppression by toroidal rotation in higher collisionality regime due to the enhancement of plasma density obtained in EAST experiment. Supported by the National Magnetic Confinement Fusion Program of China under Grant Nos. 2014GB124002 and 2015GB101004, the 100 Talent Program and the President International Fellowship Initiative of Chinese Academy of Sciences.

Development of a Three-Dimensional PSE Code for Compressible Flows: Stability of Three-Dimensional Compressible Boundary Layers

NASA Technical Reports Server (NTRS)

Balakumar, P.; Jeyasingham, Samarasingham

1999-01-01

A program is developed to investigate the linear stability of three-dimensional compressible boundary layer flows over bodies of revolutions. The problem is formulated as a two dimensional (2D) eigenvalue problem incorporating the meanflow variations in the normal and azimuthal directions. Normal mode solutions are sought in the whole plane rather than in a line normal to the wall as is done in the classical one dimensional (1D) stability theory. The stability characteristics of a supersonic boundary layer over a sharp cone with 50 half-angle at 2 degrees angle of attack is investigated. The 1D eigenvalue computations showed that the most amplified disturbances occur around x(sub 2) = 90 degrees and the azimuthal mode number for the most amplified disturbances range between m = -30 to -40. The frequencies of the most amplified waves are smaller in the middle region where the crossflow dominates the instability than the most amplified frequencies near the windward and leeward planes. The 2D eigenvalue computations showed that due to the variations in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the most amplified disturbances are shifted to 120 degrees compared to 90 degrees for the parallel theory. It is also observed that the nonparallel amplification rates are smaller than that is obtained from the parallel theory.

Conservation of prehistoric caves and stability of their inner climate: lessons from Chauvet and other French caves.

PubMed

Bourges, F; Genthon, P; Genty, D; Lorblanchet, M; Mauduit, E; D'Hulst, D

2014-09-15

In the last 150 years, some prehistoric painted caves suffered irreversible degradations due to misperception of conservation issues and subsequent mismanagement. These sites presented naturally an exceptional stability of their internal climate allowing conservation in situ of outstanding fragile remains, some for nearly 40,000 years. This is for a large part due to exchanges of air, CO2, heat and water with the karstic system in which these caves are included. We introduce the concept of underground confinement, based on the stability of the inner cave climate parameters, especially its temperature. Confined caves present the best conservative properties. It is emphasized that this confined state implies slow exchanges with the surrounding karst and that a stable cave cannot be viewed as a closed system. This is illustrated on four case studies of French caves of various confinement states evidenced by long term continuous monitoring and on strategies to improve their conservation properties. The Chauvet cave presents optimal conservation properties. It is wholly confined as shown by the stability of its internal parameters since its discovery in 1994. In Marsoulas cave, archeological works removed the entrance scree and let a strong opening situation of the decorated zone. Remediation is expected by adding a buffer structure at the entrance. In Pech Merle tourist cave, recurrent painting fading was related to natural seasonal drying of walls. Improvement of the cave closure system restored a confined state insuring optimal visibility of the paintings. In Gargas tourist cave, optimization of closures, lighting system and number of visitors, allowed it to gradually reach a semi-confined state that improved the conservation properties. Conclusions are drawn on the characterization of confinement state of caves and on the ways to improve their conservation properties by restoring their initial regulation mechanisms and to avoid threats to their stability. Copyright © 2013 Elsevier B.V. All rights reserved.

Extension of the XGC code for global gyrokinetic simulations in stellarator geometry

NASA Astrophysics Data System (ADS)

Cole, Michael; Moritaka, Toseo; White, Roscoe; Hager, Robert; Ku, Seung-Hoe; Chang, Choong-Seock

2017-10-01

In this work, the total-f, gyrokinetic particle-in-cell code XGC is extended to treat stellarator geometries. Improvements to meshing tools and the code itself have enabled the first physics studies, including single particle tracing and flux surface mapping in the magnetic geometry of the heliotron LHD and quasi-isodynamic stellarator Wendelstein 7-X. These have provided the first successful test cases for our approach. XGC is uniquely placed to model the complex edge physics of stellarators. A roadmap to such a global confinement modeling capability will be presented. Single particle studies will include the physics of energetic particles' global stochastic motions and their effect on confinement. Good confinement of energetic particles is vital for a successful stellarator reactor design. These results can be compared in the core region with those of other codes, such as ORBIT3d. In subsequent work, neoclassical transport and turbulence can then be considered and compared to results from codes such as EUTERPE and GENE. After sufficient verification in the core region, XGC will move into the stellarator edge region including the material wall and neutral particle recycling.

Transport studies in high-performance field reversed configuration plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, S., E-mail: sgupta@trialphaenergy.com; Barnes, D. C.; Dettrick, S. A.

2016-05-15

A significant improvement of field reversed configuration (FRC) lifetime and plasma confinement times in the C-2 plasma, called High Performance FRC regime, has been observed with neutral beam injection (NBI), improved edge stability, and better wall conditioning [Binderbauer et al., Phys. Plasmas 22, 056110 (2015)]. A Quasi-1D (Q1D) fluid transport code has been developed and employed to carry out transport analysis of such C-2 plasma conditions. The Q1D code is coupled to a Monte-Carlo code to incorporate the effect of fast ions, due to NBI, on the background FRC plasma. Numerically, the Q1D transport behavior with enhanced transport coefficients (butmore » with otherwise classical parametric dependencies) such as 5 times classical resistive diffusion, classical thermal ion conductivity, 20 times classical electron thermal conductivity, and classical fast ion behavior fit with the experimentally measured time evolution of the excluded flux radius, line-integrated density, and electron/ion temperature. The numerical study shows near sustainment of poloidal flux for nearly 1 ms in the presence of NBI.« less

System and method of operating toroidal magnetic confinement devices

DOEpatents

Chance, M.S.; Jardin, S.C.; Stix, T.H.; Grimm, R.C.; Manickam, J.; Okabayashi, M.

1984-08-30

This invention pertains to methods and arrangements for attaining high beta values in plasma confinement devices. More specifically, this invention pertains to methods for accessing the second stability region of operation in toroidal magnetic confinement devices.

Nanoscale High Energetic Materials: A Polymeric Nitrogen Chain N8 Confined inside a Carbon Nanotube

NASA Astrophysics Data System (ADS)

Abou-Rachid, Hakima; Hu, Anguang; Timoshevskii, Vladimir; Song, Yanfeng; Lussier, Louis-Simon

2008-05-01

We present a theoretical study of a new hybrid material, nanostructured polymeric nitrogen, where a polymeric nitrogen chain is encapsulated in a carbon nanotube. The electronic and structural properties of the new system are studied by means of ab initio electronic structure and molecular dynamics calculations. Finite temperature simulations demonstrate the stability of this nitrogen phase at ambient pressure and room temperature using carbon nanotube confinement. This nanostructured confinement may open a new path towards stabilizing polynitrogen or polymeric nitrogen at ambient conditions.

A Computational Study of a Circular Interface Richtmyer-Meshkov Instability in MHD

NASA Astrophysics Data System (ADS)

Maxon, William; Black, Wolfgang; Denissen, Nicholas; McFarland, Jacob; Los Alamos National Laboratory Collaboration; University of Missouri Shock Tube Laboratory Team

2017-11-01

The Richtmyer-Meshkov instability (RMI) is a hydrodynamic instability that appears in several high energy density applications such as inertial confinement fusion (ICF). In ICF, as the thermonuclear fuel is being compressed it begins to mix due to fluid instabilities including the RMI. This mixing greatly decreases the energy output. The RMI occurs when two fluids of different densities are impulsively accelerated and the pressure and density gradients are misaligned. In magnetohydrodynamics (MHD), the RMI may be suppressed by introducing a magnetic field in an electrically conducting fluid, such as a plasma. This suppression has been studied as a possible mechanism for improving confinement in ICF targets. In this study,ideal MHD simulations are performed with a circular interface impulsively accelerated by a shock wave in the presence of a magnetic field. These simulations are executed with the research code FLAG, a multiphysics, arbitrary Lagrangian/Eulerian, hydrocode developed and utilized at Los Alamos National Laboratory. The simulation results will be assessed both quantitatively and qualitatively to examine the stabilization mechanism. These simulations will guide ongoing MHD experiments at the University of Missouri Shock Tube Facility.

Effect of the geometry of confining media on the stability and folding rate of α -helix proteins

NASA Astrophysics Data System (ADS)

Wang, Congyue; Piroozan, Nariman; Javidpour, Leili; Sahimi, Muhammad

2018-05-01

Protein folding in confined media has attracted wide attention over the past 15 years due to its importance to both in vivo and in vitro applications. It is generally believed that protein stability increases by decreasing the size of the confining medium, if the medium's walls are repulsive, and that the maximum folding temperature in confinement is in a pore whose size D0 is only slightly larger than the smallest dimension of a protein's folded state. Until recently, the stability of proteins in pores with a size very close to that of the folded state has not received the attention it deserves. In a previous paper [L. Javidpour and M. Sahimi, J. Chem. Phys. 135, 125101 (2011)], we showed that, contrary to the current theoretical predictions, the maximum folding temperature occurs in larger pores for smaller α-helices. Moreover, in very tight pores, the free energy surface becomes rough, giving rise to a new barrier for protein folding close to the unfolded state. In contrast to unbounded domains, in small nanopores proteins with an α-helical native state that contain the β structures are entropically stabilized implying that folding rates decrease notably and that the free energy surface becomes rougher. In view of the potential significance of such results to interpretation of many sets of experimental data that could not be explained by the current theories, particularly the reported anomalously low rates of folding and the importance of entropic effects on proteins' misfolded states in highly confined environments, we address the following question in the present paper: To what extent the geometry of a confined medium affects the stability and folding rates of proteins? Using millisecond-long molecular dynamics simulations, we study the problem in three types of confining media, namely, cylindrical and slit pores and spherical cavities. Most importantly, we find that the prediction of the previous theories that the dependence of the maximum folding temperature Tf on the size D of a confined medium occurs in larger media for larger proteins is correct only in spherical geometry, whereas the opposite is true in the two other geometries that we study. Also studied is the effect of the strength of the interaction between the confined media's walls and the proteins. If the walls are only weakly or moderately attractive, a complex behavior emerges that depends on the size of the confining medium.

System and method of operating toroidal magnetic confinement devices

DOEpatents

Chance, Morrell S.; Jardin, Stephen C.; Stix, Thomas H.; Grimm, deceased, Ray C.; Manickam, Janardhan; Okabayashi, Michio

1987-01-01

For toroidal magnetic confinement devices the second region of stability against ballooning modes can be accessed with controlled operation. Under certain modes of operation, the first and second stability regions may be joined together. Accessing the second region of stability is accomplished by forming a bean-shaped plasma and increasing the indentation until a critical value of indentation is reached. A pusher coil, located at the inner-major-radius side of the device, is engaged to form a bean-shaped poloidal cross-section in the plasma.

One-Dimensional Burn Dynamics of Plasma-Jet Magneto-Inertial Fusion

NASA Astrophysics Data System (ADS)

Santarius, John

2009-11-01

This poster will discuss several issues related to using plasma jets to implode a Magneto-Inertial Fusion (MIF) liner onto a magnetized plasmoid and compress it to fusion-relevant temperatures [1]. The problem of pure plasma jet convergence and compression without a target present will be investigated. Cases with a target present will explore how well the liner's inertia provides transient plasma stability and confinement. The investigation uses UW's 1-D Lagrangian radiation-hydrodynamics code, BUCKY, which solves single-fluid equations of motion with ion-electron interactions, PdV work, table-lookup equations of state, fast-ion energy deposition, and pressure contributions from all species. Extensions to the code include magnetic field evolution as the plasmoid compresses plus dependence of the thermal conductivity and fusion product energy deposition on the magnetic field.[4pt] [1] Y.C. F. Thio, et al.,``Magnetized Target Fusion in a Spheroidal Geometry with Standoff Drivers,'' in Current Trends in International Fusion Research, E. Panarella, ed. (National Research Council of Canada, Ottawa, Canada, 1999), p. 113.

Electromagnetic confinement and movement of thin sheets of molten metal

DOEpatents

Lari, Robert J.; Praeg, Walter F.; Turner, Larry R.

1990-01-01

An apparatus capable of producing a combination of magnetic fields that can retain a metal in liquid form in a region having a smooth vertical boundary including a levitation magnet that produces low frequency magnetic field traveling waves to retain the metal and a stabilization magnet that produces a high frequency magnetic field to produce a smooth vertical boundary. As particularly adapted to the casting of solid metal sheets, a metal in liquid form can be continuously fed into one end of the confinement region produced by the levitation and stabilization magnets and removed in solid form from the other end of confinement region. An additional magnet may be included for support at the edges of the confinement region where eddy currents loop.

Effects of Density and Impurity on Edge Localized Modes in Tokamaks

NASA Astrophysics Data System (ADS)

Zhu, Ping

2017-10-01

Plasma density and impurity concentration are believed to be two of the key elements governing the edge tokamak plasma conditions. Optimal levels of plasma density and impurity concentration in the edge region have been searched for in order to achieve the desired fusion gain and divertor heat/particle load mitigation. However, how plasma density or impurity would affect the edge pedestal stability may have not been well known. Our recent MHD theory modeling and simulations using the NIMROD code have found novel effects of density and impurity on the dynamics of edge-localized modes (ELMs) in tokamaks. First, previous MHD analyses often predict merely a weak stabilizing effect of toroidal flow on ELMs in experimentally relevant regimes. We find that the stabilizing effects on the high- n ELMs from toroidal flow can be significantly enhanced with the increased edge plasma density. Here n denotes the toroidal mode number. Second, the stabilizing effects of the enhanced edge resistivity due to lithium-conditioning on the low- n ELMs in the high confinement (H-mode) discharges in NSTX have been identified. Linear stability analysis of the experimentally constrained equilibrium suggests that the change in the equilibrium plasma density and pressure profiles alone due to lithium-conditioning may not be sufficient for a complete suppression of the low- n ELMs. The enhanced resistivity due to the increased effective electric charge number Zeff after lithium-conditioning provides additional stabilization of the low- n ELMs. These new effects revealed in our theory analyses may help further understand recent ELM experiments and suggest new control schemes for ELM suppression and mitigation in future experiments. They may also pose additional constraints on the optimal levels of plasma density and impurity concentration in the edge region for H-mode tokamak operation. Supported by National Magnetic Confinement Fusion Science Program of China Grants 2014GB124002 and 2015GB101004, the 100 Talent Program of the Chinese Academy of Sciences, and U.S. Department of Energy Grants DE-FG02-86ER53218 and DE-FC02-08ER54975.

Stability of Electrons in the Virtual Cathode Region of an IEC

NASA Astrophysics Data System (ADS)

Kim, Hyng-Jin; Miley, George; Momota, Hiromu

2003-04-01

In the Inertial Electrostatic Confinement (IEC) device, electrons are confined inside a virtual anode that in turn confines ions. Prior stability studies [1, 2] have considered systems in which one species is electrostatically confined by the other, and either or both species are out of local thermal equilibrium. In the present research, electron stability in the virtual cathode region of an ion injected IEC is being studied. The ion density in an IEC is non-uniform due to the radial electrostatic potential, and increases toward the center region. The potential near the virtual cathode is assumed to have a parabolic shape and is determined assuming that the net space charge density is constant in that region. The corresponding ion distribution function is assumed to have the form f = C [sigma] (H W) /L^0.5 and the electron response is taken to be diabatic. Then using a variational principle after linearizing the hydrodynamic equations, stability properties of the electron layer are determined. Results will be presented as a function of injected ion/electron current ratios. 1. L. Chacon and D. C. Barnes, Phys. Plasma 7, 4774 (2000). 2. D. C. Barnes, L. Chacon, and J. M. Finn, Phys. Plasmas 9, 4448 (2002).

PACER -- A fast running computer code for the calculation of short-term containment/confinement loads following coolant boundary failure. Volume 2: User information

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sienicki, J.J.

A fast running and simple computer code has been developed to calculate pressure loadings inside light water reactor containments/confinements under loss-of-coolant accident conditions. PACER was originally developed to calculate containment/confinement pressure and temperature time histories for loss-of-coolant accidents in Soviet-designed VVER reactors and is relevant to the activities of the US International Nuclear Safety Center. The code employs a multicompartment representation of the containment volume and is focused upon application to early time containment phenomena during and immediately following blowdown. PACER has been developed for FORTRAN 77 and earlier versions of FORTRAN. The code has been successfully compiled and executedmore » on SUN SPARC and Hewlett-Packard HP-735 workstations provided that appropriate compiler options are specified. The code incorporates both capabilities built around a hardwired default generic VVER-440 Model V230 design as well as fairly general user-defined input. However, array dimensions are hardwired and must be changed by modifying the source code if the number of compartments/cells differs from the default number of nine. Detailed input instructions are provided as well as a description of outputs. Input files and selected output are presented for two sample problems run on both HP-735 and SUN SPARC workstations.« less

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, A. E., E-mail: whitea@mit.edu; Howard, N. T.; Creely, A. J.

2015-05-15

For the first time, nonlinear gyrokinetic simulations of I-mode plasmas are performed and compared with experiment. I-mode is a high confinement regime, featuring energy confinement similar to H-mode, but without enhanced particle and impurity particle confinement [D. G. Whyte et al., Nucl. Fusion 50, 105005 (2010)]. As a consequence of the separation between heat and particle transport, I-mode exhibits several favorable characteristics compared to H-mode. The nonlinear gyrokinetic code GYRO [J. Candy and R. E. Waltz, J Comput. Phys. 186, 545 (2003)] is used to explore the effects of E × B shear and profile stiffness in I-mode and comparemore » with L-mode. The nonlinear GYRO simulations show that I-mode core ion temperature and electron temperature profiles are more stiff than L-mode core plasmas. Scans of the input E × B shear in GYRO simulations show that E × B shearing of turbulence is a stronger effect in the core of I-mode than L-mode. The nonlinear simulations match the observed reductions in long wavelength density fluctuation levels across the L-I transition but underestimate the reduction of long wavelength electron temperature fluctuation levels. The comparisons between experiment and gyrokinetic simulations for I-mode suggest that increased E × B shearing of turbulence combined with increased profile stiffness are responsible for the reductions in core turbulence observed in the experiment, and that I-mode resembles H-mode plasmas more than L-mode plasmas with regards to marginal stability and temperature profile stiffness.« less

LRFD software for design and actual ultimate capacity of confined rectangular columns.

DOT National Transportation Integrated Search

2013-04-01

The analysis of concrete columns using unconfined concrete models is a well established practice. On the : other hand, prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear : analysis. Modern codes and...

Modeling and control of plasma rotation for NSTX using neoclassical toroidal viscosity and neutral beam injection

NASA Astrophysics Data System (ADS)

Goumiri, I. R.; Rowley, C. W.; Sabbagh, S. A.; Gates, D. A.; Gerhardt, S. P.; Boyer, M. D.; Andre, R.; Kolemen, E.; Taira, K.

2016-03-01

A model-based feedback system is presented to control plasma rotation in a magnetically confined toroidal fusion device, to maintain plasma stability for long-pulse operation. This research uses experimental measurements from the National Spherical Torus Experiment (NSTX) and is aimed at controlling plasma rotation using two different types of actuation: momentum from injected neutral beams and neoclassical toroidal viscosity generated by three-dimensional applied magnetic fields. Based on the data-driven model obtained, a feedback controller is designed, and predictive simulations using the TRANSP plasma transport code show that the controller is able to attain desired plasma rotation profiles given practical constraints on the actuators and the available measurements of rotation.

Modeling and control of plasma rotation for NSTX using neoclassical toroidal viscosity and neutral beam injection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goumiri, I. R.; Rowley, C. W.; Sabbagh, S. A.

2016-02-19

A model-based feedback system is presented to control plasma rotation in a magnetically confined toroidal fusion device, to maintain plasma stability for long-pulse operation. This research uses experimental measurements from the National Spherical Torus Experiment (NSTX) and is aimed at controlling plasma rotation using two different types of actuation: momentum from injected neutral beams and neoclassical toroidal viscosity generated by three-dimensional applied magnetic fields. Based on the data-driven model obtained, a feedback controller is designed, and predictive simulations using the TRANSP plasma transport code show that the controller is able to attain desired plasma rotation profiles given practical constraints onmore » the actuators and the available measurements of rotation.« less

Structural integrity of a confinement vessel for testing nuclear fuels for space propulsion

NASA Astrophysics Data System (ADS)

Bergmann, V. L.

Nuclear propulsion systems for rockets could significantly reduce the travel time to distant destinations in space. However, long before such a concept can become reality, a significant effort must be invested in analysis and ground testing to guide the development of nuclear fuels. Any testing in support of development of nuclear fuels for space propulsion must be safely contained to prevent the release of radioactive materials. This paper describes analyses performed to assess the structural integrity of a test confinement vessel. The confinement structure, a stainless steel pressure vessel with bolted flanges, was designed for operating static pressures in accordance with the ASME Boiler and Pressure Vessel Code. In addition to the static operating pressures, the confinement barrier must withstand static overpressures from off-normal conditions without releasing radioactive material. Results from axisymmetric finite element analyses are used to evaluate the response of the confinement structure under design and accident conditions. For the static design conditions, the stresses computed from the ASME code are compared with the stresses computed by the finite element method.

ELM Suppression and Pedestal Structure in I-Mode Plasmas

NASA Astrophysics Data System (ADS)

Walk, John

2013-10-01

The I-mode regime is characterized by the formation of a temperature pedestal and enhanced energy confinement (H98 up to 1.2), without an accompanying density pedestal or drop in particle transport. Unlike ELMy H-modes, I-mode operation appears to have naturally-occurring suppression of large ELMs in addition to its highly favorable scalings of pedestal structure (and therefore overall performance). Instead, continuous Weakly Coherent Modes help to regulate density. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to the structure and ELM stability of I-mode pedestals. Peeling-ballooning MHD calculations are completed using the ELITE code, showing I-mode pedestals to be generally MHD-stable. Under certain conditions, intermittent ELMs are observed in I-mode at reduced field, typically triggered by sawtooth crashes; modification of the temperature pedestal (and therefore the pressure profile stability) by sawtooth heat pulses is being examined in ELITE. Modeled stability to KBM turbulence in I-mode and ELMy H-mode suggests that typical I-modes are stable against KBM turbulence. Measured I-mode pedestals are significantly wider (more stable) than the width scaling with the square root of poloidal beta characteristic of the KBM-limited pedestals in ELMy H-mode. Finally, we explore scalings of pedestal structure with engineering parameters compared to ELMy H-modes on C-Mod. In particular, we focus on scalings of the pressure pedestal with heating power (and its relation to the favorable scaling of confinement with power in I-mode) and on relationships between heat flux and pedestal temperature gradients. This work is supported by DOE agreement DE-FC02-99ER54512. Theory work at General Atomics is supported by DOE agreement DE-FG02-99ER54309.

Interface stability in a slowly rotating low-gravity tank Theory

NASA Technical Reports Server (NTRS)

Gans, R. F.; Leslie, F. W.

1986-01-01

The equilibrium configuration of a bubble in a rotating liquid confined by flat axial boundaries (baffles) is found. The maximum baffle spacing assuring bubble confinement is bounded from above by the natural length of a bubble in an infinite medium under the same conditions. Effects of nonzero contact angle are minimal. The problem of dynamic stability is posed. It can be solved in the limit of rapid rotation, for which the bubble is a long cylinder. Instability is to axisymmetric perturbations; nonaxisymmetric perturbations are stable. The stability criterion agrees with earlier results.

Numerical Modeling of Three-Dimensional Confined Flows

NASA Technical Reports Server (NTRS)

Greywall, M. S.

1981-01-01

A three dimensional confined flow model is presented. The flow field is computed by calculating velocity and enthalpy along a set of streamlines. The finite difference equations are obtained by applying conservation principles to streamtubes constructed around the chosen streamlines. With appropriate substitutions for the body force terms, the approach computes three dimensional magnetohydrodynamic channel flows. A listing of a computer code, based on this approach is presented in FORTRAN IV language. The code computes three dimensional compressible viscous flow through a rectangular duct, with the duct cross section specified along the axis.

Metallic tin quantum sheets confined in graphene toward high-efficiency carbon dioxide electroreduction

NASA Astrophysics Data System (ADS)

Lei, Fengcai; Liu, Wei; Sun, Yongfu; Xu, Jiaqi; Liu, Katong; Liang, Liang; Yao, Tao; Pan, Bicai; Wei, Shiqiang; Xie, Yi

2016-09-01

Ultrathin metal layers can be highly active carbon dioxide electroreduction catalysts, but may also be prone to oxidation. Here we construct a model of graphene confined ultrathin layers of highly reactive metals, taking the synthetic highly reactive tin quantum sheets confined in graphene as an example. The higher electrochemical active area ensures 9 times larger carbon dioxide adsorption capacity relative to bulk tin, while the highly-conductive graphene favours rate-determining electron transfer from carbon dioxide to its radical anion. The lowered tin-tin coordination numbers, revealed by X-ray absorption fine structure spectroscopy, enable tin quantum sheets confined in graphene to efficiently stabilize the carbon dioxide radical anion, verified by 0.13 volts lowered potential of hydroxyl ion adsorption compared with bulk tin. Hence, the tin quantum sheets confined in graphene show enhanced electrocatalytic activity and stability. This work may provide a promising lead for designing efficient and robust catalysts for electrolytic fuel synthesis.

The A-B transition in superfluid helium-3 under confinement in a thin slab geometry

PubMed Central

Zhelev, N.; Abhilash, T. S.; Smith, E. N.; Bennett, R. G.; Rojas, X.; Levitin, L.; Saunders, J.; Parpia, J. M.

2017-01-01

The influence of confinement on the phases of superfluid helium-3 is studied using the torsional pendulum method. We focus on the transition between the A and B phases, where the A phase is stabilized by confinement and a spatially modulated stripe phase is predicted at the A–B phase boundary. Here we discuss results from superfluid helium-3 contained in a single 1.08-μm-thick nanofluidic cavity incorporated into a high-precision torsion pendulum, and map the phase diagram between 0.1 and 5.6 bar. We observe only small supercooling of the A phase, in comparison to bulk or when confined in aerogel, with evidence for a non-monotonic pressure dependence. This suggests that an intrinsic B-phase nucleation mechanism operates under confinement. Both the phase diagram and the relative superfluid fraction of the A and B phases, show that strong coupling is present at all pressures, with implications for the stability of the stripe phase. PMID:28671184

Effect of confinement potential on exciton diamagnetism in the perspective of constituent carriers in a Quantum Well

NASA Astrophysics Data System (ADS)

Vignesh, G.; Nithiananthi, P.

2018-03-01

Diamagnetic susceptibility of excitons is investigated in the perspective of the electron and hole separation along the lateral (ρ) and normal direction (z) of a GaAs/AlxGa1-xAs quantum well. Using a variational technique, the spatial extensions of these carriers has been observed. The coulomb interaction of the carriers is investigated by subjecting the carriers to three confinement potentials, Square (SQW), Parabolic (PQW) and Triangular Quantum Wells (TQW). The stability of the exciton has been estimated by observing the diamagnetic susceptibility. The hole is very sensitive to confinement potential and has tremendous variations in spatial extension. Among the three confinements, TQW offers more localization and high stability to excitons. The anisotropy of band parameters and the dielectric constants of the well and barrier materials are taken into consideration.

Wavelength stabilized DBR high power diode laser using EBL optical confining grating technology

NASA Astrophysics Data System (ADS)

Paoletti, R.; Codato, S.; Coriasso, C.; Gotta, P.; Meneghini, G.; Morello, G.; De Melchiorre, P.; Riva, E.; Rosso, M.; Stano, A.; Gattiglio, M.

2018-02-01

This paper reports a DBR High Power Diode Laser (DBR-HPDL) realization, emitting up to 10W in the 920 nm range. High spectral purity (90% power in about 0.5 nm), and wavelength stability versus injected current (about 5 times more than standard FP laser) candidates DBR-HPDL as a suitable device for wavelength stabilized pump source, and high brightness applications exploiting Wavelength Division Multiplexing. Key design aspect is a multiple-orders Electron Beam Lithography (EBL) optical confining grating, stabilizing on same wafer multiple wavelengths by a manufacturable and reliable technology. Present paper shows preliminary demonstration of wafer with 3 pitches, generating DBRHPDLs 2.5 nm spaced.

Coupling extended magnetohydrodynamic fluid codes with radiofrequency ray tracing codes for fusion modeling

NASA Astrophysics Data System (ADS)

Jenkins, Thomas G.; Held, Eric D.

2015-09-01

Neoclassical tearing modes are macroscopic (L ∼ 1 m) instabilities in magnetic fusion experiments; if unchecked, these modes degrade plasma performance and may catastrophically destroy plasma confinement by inducing a disruption. Fortunately, the use of properly tuned and directed radiofrequency waves (λ ∼ 1 mm) can eliminate these modes. Numerical modeling of this difficult multiscale problem requires the integration of separate mathematical models for each length and time scale (Jenkins and Kruger, 2012 [21]); the extended MHD model captures macroscopic plasma evolution while the RF model tracks the flow and deposition of injected RF power through the evolving plasma profiles. The scale separation enables use of the eikonal (ray-tracing) approximation to model the RF wave propagation. In this work we demonstrate a technique, based on methods of computational geometry, for mapping the ensuing RF data (associated with discrete ray trajectories) onto the finite-element/pseudospectral grid that is used to model the extended MHD physics. In the new representation, the RF data can then be used to construct source terms in the equations of the extended MHD model, enabling quantitative modeling of RF-induced tearing mode stabilization. Though our specific implementation uses the NIMROD extended MHD (Sovinec et al., 2004 [22]) and GENRAY RF (Smirnov et al., 1994 [23]) codes, the approach presented can be applied more generally to any code coupling requiring the mapping of ray tracing data onto Eulerian grids.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James

2016-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM), strong evidence that drift wave turbulence emerges in RFP plasmas when transport associated with MHD tearing is reduced. Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking. Using inductive control, the tearing modes are reduced and global confinement is increased to values expected for a comparable tokamak plasma. The improved confinement is associated with a large increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have frequencies >50 kHz, wavenumbers k_phi*rho_s<0.14, and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in fluctuations associated with global tearing modes. Their amplitude increases with the local density gradient, and they exhibit a density-gradient threshold at R/L_n 15, higher than in tokamak plasmas by R/a. the GENE code, modified for RFP equilibria, predicts the onset of microinstability for these strong-gradient plasma conditions. The density-gradient-driven TEM is the dominant instability in the region where the measured density fluctuations are largest, and the experimental threshold-gradient is close to the predicted critical gradient for linear stability. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Similar circumstances could occur in the edge region of tokamak plasmas when resonant magnetic perturbations are applied for the control of ELMs. Work supported by US DOE.

First-principles theoretical assessment of catalysis by confinement: NO-O2 reactions within voids of molecular dimensions in siliceous crystalline frameworks.

PubMed

Maestri, Matteo; Iglesia, Enrique

2018-06-01

Density functional theory methods that include dispersive forces are used to show how voids of molecular dimensions enhance reaction rates by the mere confinement of transition states analogous to those involved in homogeneous routes and without requiring specific binding sites or structural defects within confining voids. These van der Waals interactions account for the observed large rate enhancements for NO oxidation in the presence of purely siliceous crystalline frameworks. The minimum free energy paths for NO oxidation within chabazite (CHA) and silicalite (SIL) frameworks involve intermediates similar in stoichiometry, geometry, and kinetic relevance to those involved in the homogeneous route. The termolecular transition state for the kinetically-relevant cis-NOO2NO isomerization to trans-NOO2NO is strongly stabilized by confinement within CHA (by 36.3 kJ mol-1 in enthalpy) and SIL (by 39.2 kJ mol-1); such enthalpic stabilization is compensated, in part, by concomitant entropy losses brought forth by confinement (CHA: 44.9; SIL: 45.3, J mol-1 K-1 at 298 K). These enthalpy and entropy changes upon confinement agree well with those measured and combine to significantly decrease activation free energies and are consistent with the rate enhancements that become larger as temperature decreases because of the more negative apparent activation energies in confined systems compared with homogeneous routes. Calculated free energies of confinement are in quantitative agreement with measured rate enhancements and with their temperature sensitivity. Such quantitative agreements reflect preeminent effects of geometry in determining the van der Waals contributions from contacts between the transition states (TS) and the confining walls and the weak effects of the level of theory on TS geometries. NO oxidation reactions are chosen here to illustrate these remarkable effects of confinement because detailed kinetic analysis of rate data are available, but also because of their critical role in the treatment of combustion effluents and in the synthesis of nitric acid and nitrates. Similar effects are evident from rate enhancements by confinement observed for Diels-Alder and alkyne oligomerization reactions. These reactions also occur in gaseous media at near ambient temperatures, for which enthalpic stabilization upon confinement of their homogeneous transition states becomes the preeminent component of activation free energies.

Confined space facilitates G-quadruplex formation

NASA Astrophysics Data System (ADS)

Shrestha, Prakash; Jonchhe, Sagun; Emura, Tomoko; Hidaka, Kumi; Endo, Masayuki; Sugiyama, Hiroshi; Mao, Hanbin

2017-07-01

Molecular simulations suggest that the stability of a folded macromolecule increases in a confined space due to entropic effects. However, due to the interactions between the confined molecular structure and the walls of the container, clear-cut experimental evidence for this prediction is lacking. Here, using DNA origami nanocages, we show the pure effect of confined space on the property of individual human telomeric DNA G-quadruplexes. We induce targeted mechanical unfolding of the G-quadruplex while leaving the nanocage unperturbed. We find that the mechanical and thermodynamic stabilities of the G-quadruplex inside the nanocage increase with decreasing cage size. Compared to the case of diluted or molecularly crowded buffer solutions, the G-quadruplex inside the nanocage is significantly more stable, showing a 100 times faster folding rate. Our findings suggest the possibility of co-replicational or co-transcriptional folding of G-quadruplex inside the polymerase machinery in cells.

Entropy and enthalpy of interaction between amino acid side chains in nanopores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vaitheeswaran, S., E-mail: vaithee05@gmail.com; Thirumalai, D.; Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742

2014-12-14

Understanding the stabilities of proteins in nanopores requires a quantitative description of confinement induced interactions between amino acid side chains. We use molecular dynamics simulations to study the nature of interactions between the side chain pairs ALA-PHE, SER-ASN, and LYS-GLU in bulk water and in water-filled nanopores. The temperature dependence of the bulk solvent potentials of mean force and the interaction free energies in cylindrical and spherical nanopores is used to identify the corresponding entropic and enthalpic components. The entropically stabilized hydrophobic interaction between ALA and PHE in bulk water is enthalpically dominated upon confinement depending on the relative orientationsmore » between the side chains. In the case of SER-ASN, hydrogen bonded configurations that are similar in bulk water are thermodynamically distinct in a cylindrical pore, thus making rotamer distributions different from those in the bulk. Remarkably, salt bridge formation between LYS-GLU is stabilized by entropy in contrast to the bulk. Implications of our findings for confinement-induced alterations in protein stability are briefly outlined.« less

The accurate particle tracer code

NASA Astrophysics Data System (ADS)

Wang, Yulei; Liu, Jian; Qin, Hong; Yu, Zhi; Yao, Yicun

2017-11-01

The Accurate Particle Tracer (APT) code is designed for systematic large-scale applications of geometric algorithms for particle dynamical simulations. Based on a large variety of advanced geometric algorithms, APT possesses long-term numerical accuracy and stability, which are critical for solving multi-scale and nonlinear problems. To provide a flexible and convenient I/O interface, the libraries of Lua and Hdf5 are used. Following a three-step procedure, users can efficiently extend the libraries of electromagnetic configurations, external non-electromagnetic forces, particle pushers, and initialization approaches by use of the extendible module. APT has been used in simulations of key physical problems, such as runaway electrons in tokamaks and energetic particles in Van Allen belt. As an important realization, the APT-SW version has been successfully distributed on the world's fastest computer, the Sunway TaihuLight supercomputer, by supporting master-slave architecture of Sunway many-core processors. Based on large-scale simulations of a runaway beam under parameters of the ITER tokamak, it is revealed that the magnetic ripple field can disperse the pitch-angle distribution significantly and improve the confinement of energetic runaway beam on the same time.

A note on the effect of fault gouge composition on the stability of frictional sliding

USGS Publications Warehouse

Summers, R.; Byerlee, J.

1977-01-01

The frictional properties of fault gouge have been studied at confining pressures to 6 kbars. If the gouge is composed of strong materials such as crushed granite or quartz sand, the frictional strength is high, and violent stick-slip occurs at confining pressures above approximately 1.5 kbars. If the gouge is composed of minerals such as illite, kaolinite, chlorite, or antigorite, which have weak bonding forces between the structural layers, the frictional strength is slightly lower, but violent stick-slip still occurs under high confining pressure. The expanding clays, montmorillonite and vermiculite, which have free water between their structural layers, slide stably at confining pressures as high as 6.25 kbars and exhibit low friction. A similar stable behavior with lowered strength is observed in water-saturated quartz sand when the water is confined within the fault zone during deformation. The results of this series of experiments support water being the stabilizing influence when it is either (1) trapped within or between rocks of low permeability and can provide a high pore pressure when the rocks are deformed, or (2) loosely bonded in a mineral structure, as in the hydrated clays, where it can produce a pseudo-pore pressure when the clay is compressed. In both these cases, the effective stress can be reduced and the deformation stabilized. ?? 1977.

Dynamic stabilization of Rayleigh-Taylor instability: Experiments with Newtonian fluids as surrogates for ablation fronts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez Prieto, G.; Piriz, A. R.; Lopez Cela, J. J.

2013-01-15

A previous theory on dynamic stabilization of Rayleigh-Taylor instability at interfaces between Newtonian fluids is reformulated in order to make evident the analogy of this problem with the related one on dynamic stabilization of ablation fronts in the framework of inertial confinement fusion. Explicit analytical expressions are obtained for the boundaries of the dynamically stable region which turns out to be completely analogue to the stability charts obtained for the case of ablation fronts. These results allow proposing experiments with Newtonian fluids as surrogates for studying the case of ablation fronts. Experiments with Newtonian fluids are presented which demonstrate themore » validity of the theoretical approach and encourage to pursue experimental research on ablation fronts to settle the feasibility of dynamic stabilization in the inertial confinement fusion scenario.« less

Production and study of high-beta plasma confined by a superconducting dipole magneta)

NASA Astrophysics Data System (ADS)

Garnier, D. T.; Hansen, A.; Mauel, M. E.; Ortiz, E.; Boxer, A. C.; Ellsworth, J.; Karim, I.; Kesner, J.; Mahar, S.; Roach, A.

2006-05-01

The Levitated Dipole Experiment (LDX) [J. Kesner et al., in Fusion Energy 1998, 1165 (1999)] is a new research facility that is exploring the confinement and stability of plasma created within the dipole field produced by a strong superconducting magnet. Unlike other configurations in which stability depends on curvature and magnetic shear, magnetohydrodynamic stability of a dipole derives from plasma compressibility. Theoretically, the dipole magnetic geometry can stabilize a centrally peaked plasma pressure that exceeds the local magnetic pressure (β>1), and the absence of magnetic shear allows particle and energy confinement to decouple. In initial experiments, long-pulse, quasi-steady-state microwave discharges lasting more than 10s have been produced that are consistent with equilibria having peak beta values of 20%. Detailed measurements have been made of discharge evolution, plasma dynamics and instability, and the roles of gas fueling, microwave power deposition profiles, and plasma boundary shape. In these initial experiments, the high-field superconducting floating coil was supported by three thin supports. The plasma is created by multifrequency electron cyclotron resonance heating at 2.45 and 6.4GHz, and a population of energetic electrons, with mean energies above 50keV, dominates the plasma pressure. Creation of high-pressure, high-beta plasma is possible only when intense hot electron interchange instabilities are stabilized by sufficiently high background plasma density. A dramatic transition from a low-density, low-beta regime to a more quiescent, high-beta regime is observed when the plasma fueling rate and confinement time become sufficiently large.

Range shortening, radiation transport, and Rayleigh-Taylor instability phenomena in ion-beam-driven inertial-fusion-reactor-size targets: Implosion, ignition, and burn phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, K.A.; Tahir, N.A.

In this paper we present an analysis of the theory of the energy deposition of ions in cold materials and hot dense plasmas together with numerical calculations for heavy and light ions of interest to ion-beam fusion. We have used the g-smcapso-smcapsr-smcapsg-smcapso-smcapsn-smcaps computer code of Long, Moritz, and Tahir (which is an extension of the code originally written for protons by Nardi, Peleg, and Zinamon) to carry out these calculations. The energy-deposition data calculated in this manner has been used in the design of heavy-ion-beam-driven fusion targets suitable for a reactor, by its inclusion in the m-smcapse-smcapsd-smcapsu-smcapss-smcapsa-smcaps code of Christiansen,more » Ashby, and Roberts as extended by Tahir and Long. A number of other improvements have been made in this code and these are also discussed. Various aspects of the theoretical analysis of such targets are discussed including the calculation of the hydrodynamic stability, the hydrodynamic efficiency, and the gain. Various different target designs have been used, some of them new. In general these targets are driven by Bi/sup +/ ions of energy 8--12 GeV, with an input energy of 4--6.5 MJ, with output energies in the range 600--900 MJ, and with gains in the range 120--180. The peak powers are in the range of 500--750 TW. We present detailed calculations of the ablation, compression, ignition, and burn phases. By the application of a new stability analysis which includes ablation and density-gradient effects we show that these targets appear to implode in a stable manner. Thus the targets designed offer working examples suited for use in a future inertial-confinement fusion reactor.« less

Comparison of hybrid and baseline ELMy H-mode confinement in JET with the carbon wall

NASA Astrophysics Data System (ADS)

Beurskens, M. N. A.; Frassinetti, L.; Challis, C.; Osborne, T.; Snyder, P. B.; Alper, B.; Angioni, C.; Bourdelle, C.; Buratti, P.; Crisanti, F.; Giovannozzi, E.; Giroud, C.; Groebner, R.; Hobirk, J.; Jenkins, I.; Joffrin, E.; Leyland, M. J.; Lomas, P.; Mantica, P.; McDonald, D.; Nunes, I.; Rimini, F.; Saarelma, S.; Voitsekhovitch, I.; de Vries, P.; Zarzoso, D.; Contributors, JET-EFDA

2013-01-01

The confinement in JET baseline type I ELMy H-mode plasmas is compared to that in so-called hybrid H-modes in a database study of 112 plasmas in JET with the carbon fibre composite (CFC) wall. The baseline plasmas typically have βN ˜ 1.5-2, H98 ˜ 1, whereas the hybrid plasmas have βN ˜ 2.5-3, H98 < 1.5. The database study contains both low- (δ ˜ 0.2-0.25) and high-triangularity (δ ˜ 0.4) hybrid and baseline H-mode plasmas from the last JET operational campaigns in the CFC wall from the period 2008-2009. Based on a detailed confinement study of the global as well as the pedestal and core confinement, there is no evidence that the hybrid and baseline plasmas form separate confinement groups; it emerges that the transition between the two scenarios is of a gradual kind rather than demonstrating a bifurcation in the confinement. The elevated confinement enhancement factor H98 in the hybrid plasmas may possibly be explained by the density dependence in the τ98 scaling as n0.41 and the fact that the hybrid plasmas operate at low plasma density compared to the baseline ELMy H-mode plasmas. A separate regression on the confinement data in this study shows a reduction in the density dependence as n0.09±0.08. Furthermore, inclusion of the plasma toroidal rotation in the confinement regression provides a scaling with the toroidal Alfvén Mach number as Mach_A^{0.41+/- 0.07} and again a reduced density dependence as n0.15±0.08. The differences in pedestal confinement can be explained on the basis of linear MHD stability through a coupling of the total and pedestal poloidal pressure and the pedestal performance can be improved through plasma shaping as well as high β operation. This has been confirmed in a comparison with the EPED1 predictive pedestal code which shows a good agreement between the predicted and measured pedestal pressure within 20-30% for a wide range of βN ˜ 1.5-3.5. The core profiles show a strong degree of pressure profile consistency. No beneficial effect of core density peaking on confinement could be identified for the majority of the plasmas presented here as the density peaking is compensated by a temperature de-peaking resulting in no or only a weak variation in the pressure peaking. The core confinement could only be optimized in case the ions and electrons are decoupled, in which case the ion temperature profile peaking can be enhanced, which benefits confinement. In this study, the latter has only been achieved in the low-triangularity hybrid plasmas, and can be attributed to low-density operation. Plasma rotation has been found to reduce core profile stiffness, and can explain an increase in profile peaking at small radius ρtor = 0.3.

A high performance field-reversed configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binderbauer, M. W.; Tajima, T.; Steinhauer, L. C.

2015-05-15

Conventional field-reversed configurations (FRCs), high-beta, prolate compact toroids embedded in poloidal magnetic fields, face notable stability and confinement concerns. These can be ameliorated by various control techniques, such as introducing a significant fast ion population. Indeed, adding neutral beam injection into the FRC over the past half-decade has contributed to striking improvements in confinement and stability. Further, the addition of electrically biased plasma guns at the ends, magnetic end plugs, and advanced surface conditioning led to dramatic reductions in turbulence-driven losses and greatly improved stability. Together, these enabled the build-up of a well-confined and dominant fast-ion population. Under such conditions,more » highly reproducible, macroscopically stable hot FRCs (with total plasma temperature of ∼1 keV) with record lifetimes were achieved. These accomplishments point to the prospect of advanced, beam-driven FRCs as an intriguing path toward fusion reactors. This paper reviews key results and presents context for further interpretation.« less

Stability analysis of confined V-shaped flames in high-velocity streams.

PubMed

El-Rabii, Hazem; Joulin, Guy; Kazakov, Kirill A

2010-06-01

The problem of linear stability of confined V-shaped flames with arbitrary gas expansion is addressed. Using the on-shell description of flame dynamics, a general equation governing propagation of disturbances of an anchored flame is obtained. This equation is solved analytically for V-flames anchored in high-velocity channel streams. It is demonstrated that dynamics of the flame disturbances in this case is controlled by the memory effects associated with vorticity generated by the perturbed flame. The perturbation growth rate spectrum is determined, and explicit analytical expressions for the eigenfunctions are given. It is found that the piecewise linear V structure is unstable for all values of the gas expansion coefficient. Despite the linearity of the basic pattern, however, evolutions of the V-flame disturbances are completely different from those found for freely propagating planar flames or open anchored flames. The obtained results reveal strong influence of the basic flow and the channel walls on the stability properties of confined V-flames.

Non-compliance with the International Code of Marketing of Breast Milk Substitutes is not confined to the infant formula industry.

PubMed

Forsyth, Stewart

2013-06-01

Infant feeding policy and practice continues to be a contentious area of global health care. The infant formula industry is widely considered to be the bête noire with frequent claims that they adopt marketing and sales practices that are not compliant with the WHO Code. However, failure to resolve these issues over three decades suggests that there may be wider systemic failings. Review of published papers, commentaries and reports relating to the implementation and governance of the WHO Code with specific reference to issues of non-compliance. The analysis set out in this paper indicates that there are systemic failings at all levels of the implementation and monitoring process including the failure of WHO to successfully 'urge' governments to implement the Code in its entirety; a lack of political will by Member States to implement and monitor the Code and a lack of formal and transparent governance structures. Non-compliance with the WHO Code is not confined to the infant formula industry and several actions are identified, including the need to address issues of partnership working and the establishment of governance systems that are robust, independent and transparent.

Integrated Scenario Modeling of NSTX Advanced Plasma Configurations

NASA Astrophysics Data System (ADS)

Kessel, Charles; Synakowski, Edward

2003-10-01

The Spherical Torus will provide an attractive fusion energy source if it can demonstrate the following major features: high elongation and triangularity, 100% non-inductive current with a credible path to high bootstrap fractions, non-solenoidal startup and current rampup, high beta with stabilization of RWM instabilities, and sufficiently high energy confinement. NSTX has specific experimental milestones to examine these features, and integrated scenario modeling is helping to understand how these configurations might be produced and what tools are needed to access this operating space. Simulations with the Tokamak Simulation Code (TSC), CURRAY, and JSOLVER/BALMSC/PEST2 have identified fully non-inductively sustained, high beta plasmas that rely on strong plasma shaping accomplished with a PF coil modification, off-axis current drive from Electron Bernstein Waves (EBW), flexible on-axis heating and CD from High Harmonic Fast Wave (HHFW) and Neutral Beam Injection (NBI), and density control. Ideal MHD stability shows that with wall stabilization through plasma rotation and/or RWM feedback coils, a beta of 40% is achievable, with 100% non-inductive current sustained for 4 current diffusion times. Experimental data and theory are combined to produce a best extrapolation to these regimes, which is continuously improved as the discharges approach these parameters, and theoretical/computational methods expand. Further investigations and development for integrated scenario modeling on NSTX is discussed.

Chemical compatibility of some ceramic matrix composite structures with fusion reactor helium coolant at high temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perez, F.J.; Ghoniem, N.M.

The thermodynamic stability of SiC/SiC composite structures proposed for fusion applications is presented in this paper. Minimization of the free energy for reacting species in the temperature range 773-1273 K is achieved by utilizing the NASA-Lewis Chemical Equilibrium Thermodynamics Code (CET). The chemical stability of the matrix (SiC), as well as several potential fiber coatings are studied. Helium coolant is assumed to contain O{sub 2} and water moisture impurities in the range 100-1000 ppm. The work is applied to recent Magnetic and Inertial Confinement Conceptual designs. The present study indicated that the upper useful temperature limit for SiC/SiC composites, frommore » the standpoint of high-temperature corrosion, will be in the neighborhood of 1273 K. Up to this temperature, corrosion of SiC is shown to be negligible. The main mechanism of weight loss will be by evaporation to the plasma side. The presence of a protective SiO{sub 2} condensed phase is discussed, and is shown to result in further reduction of high-temperature corrosion. The thermodynamic stability of C and BN is shown to be very poor under typical fusion reactor conditions. Further development of chemically stable interface materials is required.« less

Surface thermodynamic analysis of fluid confined in a cone and comparison with the sphere-plate and plate-plate geometries.

PubMed

Zargarzadeh, Leila; Elliott, Janet A W

2013-10-22

The behavior of pure fluid confined in a cone is investigated using thermodynamic stability analysis. Four situations are explained on the basis of the initial confined phase (liquid/vapor) and its pressure (above/below the saturation pressure). Thermodynamic stability analysis (a plot of the free energy of the system versus the size of the new potential phase) reveals whether the phase transition is possible and, if so, the number and type (unstable/metastable/stable) of equilibrium states in each of these situations. Moreover we investigated the effect of the equilibrium contact angle and the cone angle (equivalent to the confinement's surface separation distance) on the free energy (potential equilibrium states). The results are then compared to our previous study of pure fluid confined in the gap between a sphere and a flat plate and the gap between two flat plates.1 Confined fluid behavior of the four possible situations (for these three geometries) can be explained in a unified framework under two categories based on only the meniscus shape (concave/convex). For systems with bulk-phase pressure imposed by a reservoir, the stable coexistence of pure liquid and vapor is possible only when the meniscus is concave.

PARVMEC: An Efficient, Scalable Implementation of the Variational Moments Equilibrium Code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seal, Sudip K; Hirshman, Steven Paul; Wingen, Andreas

The ability to sustain magnetically confined plasma in a state of stable equilibrium is crucial for optimal and cost-effective operations of fusion devices like tokamaks and stellarators. The Variational Moments Equilibrium Code (VMEC) is the de-facto serial application used by fusion scientists to compute magnetohydrodynamics (MHD) equilibria and study the physics of three dimensional plasmas in confined configurations. Modern fusion energy experiments have larger system scales with more interactive experimental workflows, both demanding faster analysis turnaround times on computational workloads that are stressing the capabilities of sequential VMEC. In this paper, we present PARVMEC, an efficient, parallel version of itsmore » sequential counterpart, capable of scaling to thousands of processors on distributed memory machines. PARVMEC is a non-linear code, with multiple numerical physics modules, each with its own computational complexity. A detailed speedup analysis supported by scaling results on 1,024 cores of a Cray XC30 supercomputer is presented. Depending on the mode of PARVMEC execution, speedup improvements of one to two orders of magnitude are reported. PARVMEC equips fusion scientists for the first time with a state-of-theart capability for rapid, high fidelity analyses of magnetically confined plasmas at unprecedented scales.« less

Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiaojie; Wang, Cai -Zhuang

Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. Furthermore, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.

Stability of magnetohydrodynamic Dean Flow as applied to centrifugally confined plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassam, A.B.

1999-10-01

Dean Flow is the azimuthal flow of fluid between static concentric cylinders. In a magnetized plasma, there may also be radial stratification of the pressure. The ideal magnetohydrodynamic stability of such a flow in the presence of a strong axial magnetic field and an added radial gravitational force is examined. It is shown that both the Kelvin{endash}Helmholtz instability and pressure-gradient-driven interchanges can be stabilized if the flow is driven by a unidirectional external force and if the plasma annulus is sufficiently thin (large aspect ratio). These results find application in schemes using centrifugal confinement of plasma for fusion. {copyright} {italmore » 1999 American Institute of Physics.}« less

Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films

DOE PAGES

Liu, Xiaojie; Wang, Cai -Zhuang

2017-04-03

Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. Furthermore, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.

A conservative MHD scheme on unstructured Lagrangian grids for Z-pinch hydrodynamic simulations

NASA Astrophysics Data System (ADS)

Wu, Fuyuan; Ramis, Rafael; Li, Zhenghong

2018-03-01

A new algorithm to model resistive magnetohydrodynamics (MHD) in Z-pinches has been developed. Two-dimensional axisymmetric geometry with azimuthal magnetic field Bθ is considered. Discretization is carried out using unstructured meshes made up of arbitrarily connected polygons. The algorithm is fully conservative for mass, momentum, and energy. Matter energy and magnetic energy are managed separately. The diffusion of magnetic field is solved using a derivative of the Symmetric-Semi-Implicit scheme, Livne et al. (1985) [23], where unconditional stability is obtained without needing to solve large sparse systems of equations. This MHD package has been integrated into the radiation-hydrodynamics code MULTI-2D, Ramis et al. (2009) [20], that includes hydrodynamics, laser energy deposition, heat conduction, and radiation transport. This setup allows to simulate Z-pinch configurations relevant for Inertial Confinement Fusion.

Investigation of fast ion pressure effects in ASDEX Upgrade by spectral MSE measurements

NASA Astrophysics Data System (ADS)

Reimer, René; Dinklage, Andreas; Wolf, Robert; Dunne, Mike; Geiger, Benedikt; Hobirk, Jörg; Reich, Matthias; ASDEX Upgrade Team; McCarthy, Patrick J.

2017-04-01

High precision measurements of fast ion effects on the magnetic equilibrium in the ASDEX Upgrade tokamak have been conducted in a high-power (10 MW) neutral-beam injection discharge. An improved analysis of the spectral motional Stark effect data based on forward-modeling, including the Zeeman effect, fine-structure and non-statistical sub-level distribution, revealed changes in the order of 1% in |B| . The results were found to be consistent with results from the equilibrium solver CLISTE. The measurements allowed us to derive the fast ion pressure fraction to be Δ {{p}\\text{FI}}/{{p}\\text{mhd}}≈ 10 % and variations of the fast ion pressure are consistent with calculations of the transport code TRANSP. The results advance the understanding of fast ion confinement and magneto-hydrodynamic stability in the presence of fast ions.

Production and Study of High-Beta Plasma Confined by a Superconducting Dipole Magnet

NASA Astrophysics Data System (ADS)

Garnier, Darren

2005-10-01

The Levitated Dipole Experiment (LDX)http://psfcwww2.psfc.mit.edu/ldx/ is a new research facility that is exploring the confinement and stability of plasma created within the dipole field produced by a strong superconducting magnet. Unlike other configurations in which stability depends on curvature and magnetic shear, MHD stability of a dipole derives from plasma compressibility. Theoretically, the dipole magnetic geometry can stabilize a centrally-peaked plasma pressure that exceeds the local magnetic pressure (β> 1), and the absence of magnetic shear allows particle and energy confinement to decouple. In this presentation, the first experiments using the LDX facility are reported. Long-pulse, quasi-steady state microwave discharges lasting up to 12 seconds have been produced that are consistent with equilibria having peak beta values of 10%. Detailed measurements have been made of discharge evolution, plasma dynamics and instability, and the roles of gas fueling, microwave power deposition profiles, and plasma boundary shape. In these initial experiments, the high-field superconducting floating coil was supported by three thin supports and later the coil will be magnetically levitated. The plasma was created by multi- frequency electron cyclotron resonance heating at 2.45 and 6.4 GHz, and a population of energetic electrons, with mean energies above 50 keV, dominated the plasma pressure. Creation of high-pressure, high-beta plasma is only possible when intense hot electron interchange instabilities are stabilized sufficiently by a high background plasma density. A dramatic transition from a low-density, low-beta regime to a more quiescent, high-beta regime is observed when the plasma-fueling rate and confinement times are sufficiently long. External shaping coils are seen to modify the outer plasma boundary and affect the transition.

Chemical reactions confined within carbon nanotubes.

PubMed

Miners, Scott A; Rance, Graham A; Khlobystov, Andrei N

2016-08-22

In this critical review, we survey the wide range of chemical reactions that have been confined within carbon nanotubes, particularly emphasising how the pairwise interactions between the catalysts, reactants, transition states and products of a particular molecular transformation with the host nanotube can be used to control the yields and distributions of products of chemical reactions. We demonstrate that nanoscale confinement within carbon nanotubes enables the control of catalyst activity, morphology and stability, influences the local concentration of reactants and products thus affecting equilibria, rates and selectivity, pre-arranges the reactants for desired reactions and alters the relative stability of isomeric products. We critically evaluate the relative advantages and disadvantages of the confinement of chemical reactions inside carbon nanotubes from a chemical perspective and describe how further developments in the controlled synthesis of carbon nanotubes and the incorporation of multifunctionality are essential for the development of this ever-expanding field, ultimately leading to the effective control of the pathways of chemical reactions through the rational design of multi-functional carbon nanoreactors.

Disjointness of Stabilizer Codes and Limitations on Fault-Tolerant Logical Gates

NASA Astrophysics Data System (ADS)

Jochym-O'Connor, Tomas; Kubica, Aleksander; Yoder, Theodore J.

2018-04-01

Stabilizer codes are among the most successful quantum error-correcting codes, yet they have important limitations on their ability to fault tolerantly compute. Here, we introduce a new quantity, the disjointness of the stabilizer code, which, roughly speaking, is the number of mostly nonoverlapping representations of any given nontrivial logical Pauli operator. The notion of disjointness proves useful in limiting transversal gates on any error-detecting stabilizer code to a finite level of the Clifford hierarchy. For code families, we can similarly restrict logical operators implemented by constant-depth circuits. For instance, we show that it is impossible, with a constant-depth but possibly geometrically nonlocal circuit, to implement a logical non-Clifford gate on the standard two-dimensional surface code.

Centrifugal particle confinement in mirror geometry

NASA Astrophysics Data System (ADS)

White, Roscoe; Hassam, Adil; Brizard, Alain

2018-01-01

The use of supersonic rotation of a plasma in mirror geometry has distinct advantages for thermonuclear fusion. The device is steady state, there are no disruptions, the loss cone is almost closed, sheared rotation stabilizes magnetohydrodynamic instabilities as well as plasma turbulence, there are no runaway electrons, and the coil configuration is simple. In this work, we examine the effect of rotation on mirror confinement using a full cyclotron orbit code. The full cyclotron simulations give a much more complete description of the particle energy distribution and losses than the use of guiding center equations. Both collisionless loss as a function of rotation and the effect of collisions are investigated. Although the cross field diffusion is classical, we find that the local rotating Maxwellian is increased to higher energy, increasing the fusion rate and also enhancing the radial diffusion. We find a loss channel not envisioned with a guiding center treatment, but a design can be chosen that can satisfy the Lawson criterion for ions. Of course, the rotation has a minimal effect on the alpha particle birth distribution, so there is initially loss through the usual loss cone, just as in a mirror with no rotation. However after this loss, the alphas slow down on the electrons with little pitch angle scattering until reaching low energy, so over half of the initial alpha energy is transferred to the electrons. The important problem of energy confinement, with losses primarily through the electron channel, is not addressed in this work. We also discuss the use of rotating mirror geometry to produce an ion thruster.

Segmentation of Hyperacute Cerebral Infarcts Based on Sparse Representation of Diffusion Weighted Imaging.

PubMed

Zhang, Xiaodong; Jing, Shasha; Gao, Peiyi; Xue, Jing; Su, Lu; Li, Weiping; Ren, Lijie; Hu, Qingmao

2016-01-01

Segmentation of infarcts at hyperacute stage is challenging as they exhibit substantial variability which may even be hard for experts to delineate manually. In this paper, a sparse representation based classification method is explored. For each patient, four volumetric data items including three volumes of diffusion weighted imaging and a computed asymmetry map are employed to extract patch features which are then fed to dictionary learning and classification based on sparse representation. Elastic net is adopted to replace the traditional L 0 -norm/ L 1 -norm constraints on sparse representation to stabilize sparse code. To decrease computation cost and to reduce false positives, regions-of-interest are determined to confine candidate infarct voxels. The proposed method has been validated on 98 consecutive patients recruited within 6 hours from onset. It is shown that the proposed method could handle well infarcts with intensity variability and ill-defined edges to yield significantly higher Dice coefficient (0.755 ± 0.118) than the other two methods and their enhanced versions by confining their segmentations within the regions-of-interest (average Dice coefficient less than 0.610). The proposed method could provide a potential tool to quantify infarcts from diffusion weighted imaging at hyperacute stage with accuracy and speed to assist the decision making especially for thrombolytic therapy.

Computer modeling and simulation in inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCrory, R.L.; Verdon, C.P.

1989-03-01

The complex hydrodynamic and transport processes associated with the implosion of an inertial confinement fusion (ICF) pellet place considerable demands on numerical simulation programs. Processes associated with implosion can usually be described using relatively simple models, but their complex interplay requires that programs model most of the relevant physical phenomena accurately. Most hydrodynamic codes used in ICF incorporate a one-fluid, two-temperature model. Electrons and ions are assumed to flow as one fluid (no charge separation). Due to the relatively weak coupling between the ions and electrons, each species is treated separately in terms of its temperature. In this paper wemore » describe some of the major components associated with an ICF hydrodynamics simulation code. To serve as an example we draw heavily on a two-dimensional Lagrangian hydrodynamic code (ORCHID) written at the University of Rochester's Laboratory for Laser Energetics. 46 refs., 19 figs., 1 tab.« less

A plasma rotation control scheme for NSTX and NSTX-U

NASA Astrophysics Data System (ADS)

Goumiri, Imene

2016-10-01

Plasma rotation has been proven to play a key role in stabilizing large scale instabilities and improving plasma confinement by suppressing micro-turbulence. A model-based feedback system which controls the plasma rotation profile on the National Spherical Torus Experiment (NSTX) and its upgrade (NSTX-U) is presented. The first part of this work uses experimental measurements from NSTX as a starting point and models the control of plasma rotation using two different types of actuation: momentum from injected neutral beams and neoclassical toroidal viscosity generated by three-dimensional applied magnetic fields. Whether based on the data-driven model for NSTX or purely predictive modeling for NSTX-U, a reduced order model based feedback controller was designed. Predictive simulations using the TRANSP plasma transport code with the actuator input determined by the controller (controller-in-the-loop) show that the controller drives the plasma's rotation to the desired profiles in less than 100 ms given practical constraints on the actuators and the available real-time rotation measurements. This is the first time that TRANSP has been used as a plasma in simulator in a closed feedback loop test. Another approach to control simultaneously the toroidal rotation profile as well as βN is then shown for NSTX-U. For this case, the neutral beams (actuators) have been augmented in the modeling to match the upgrade version which spread the injection throughout the edge of the plasma. Control robustness in stability and performance has then been tested and used to predict the limits of the resulting controllers when the energy confinement time (τE) and the momentum diffusivity coefficient (χϕ) vary.

Recent breakthroughs on C-2U: Norman’s legacy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binderbauer, M. W.; Tajima, T.; Tuszewski, M.

Conventional field-reversed configurations (FRC) face notable stability and confinement concerns, which can be ameliorated by introducing and maintaining a significant fast ion population in the system. This is the conjecture first introduced by Norman Rostoker multiple decades ago and adopted as the central design tenet in Tri Alpha Energy’s advanced beam driven FRC concept. In fact, studying the physics of such neutral beam (NB) driven FRCs over the past decade, considerable improvements were made in confinement and stability. Next to NB injection, the addition of axially streaming plasma guns, magnetic end plugs, as well as advanced surface conditioning lead tomore » dramatic reductions in turbulence driven losses and greatly improved stability. In turn, fast ion confinement improved significantly and allowed for the build-up of a dominant fast particle population. This recently led to the breakthrough of sustaining an advanced beam driven FRC, thereby demonstrating successful maintenance of trapped magnetic flux, plasma dimensions and total pressure inventory for times much longer than all characteristic system time scales and only limited by hardware and electric supply constraints.« less

Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents [Avoiding Tokamak Disruptions by Magnetically Aligning Locked Modes with Stabilizing Wave-Driven Currents

DOE PAGES

Volpe, F. A.; Hyatt, Alan; La Haye, Robert J.; ...

2015-10-19

The international ITER tokamak has the objective of demonstrating the scientific feasibility of magnetic confinement fusion as a source of energy. A concern towards the achievement of this goal is represented by major disruptions: complete losses of confinement often initiated by a non-rotating ('locked') magnetic island created by magnetic reconnection. During disruptions, energy and particles accumulated in the plasma volume over many seconds are lost in a few milliseconds and released on the plasma-facing materials. In addition, multi-MA level currents flowing in the tokamak plasma for its sustainment and confinement are lost, also in milliseconds, thus terminating the plasma dischargemore » and causing electromagnetic stresses that, if unmitigated, could lead to excessive device wear. Moreover it is shown that magnetic perturbations can be used to avoid disruptions by "guiding" the magnetic island to lock in a position where it is accessible to millimetre wave beams that fully stabilize it.« less

Gyrokinetic simulation of driftwave instability in field-reversed configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulton, D. P., E-mail: dfulton@trialphaenergy.com; University of California, Irvine, California 92697; Lau, C. K.

2016-05-15

Following the recent remarkable progress in magnetohydrodynamic (MHD) stability control in the C-2U advanced beam driven field-reversed configuration (FRC), turbulent transport has become one of the foremost obstacles on the path towards an FRC-based fusion reactor. Significant effort has been made to expand kinetic simulation capabilities in FRC magnetic geometry. The recently upgraded Gyrokinetic Toroidal Code (GTC) now accommodates realistic magnetic geometry from the C-2U experiment at Tri Alpha Energy, Inc. and is optimized to efficiently handle the FRC's magnetic field line orientation. Initial electrostatic GTC simulations find that ion-scale instabilities are linearly stable in the FRC core for realisticmore » pressure gradient drives. Estimated instability thresholds from linear GTC simulations are qualitatively consistent with critical gradients determined from experimental Doppler backscattering fluctuation data, which also find ion scale modes to be depressed in the FRC core. Beyond GTC, A New Code (ANC) has been developed to accurately resolve the magnetic field separatrix and address the interaction between the core and scrape-off layer regions, which ultimately determines global plasma confinement in the FRC. The current status of ANC and future development targets are discussed.« less

Gyrokinetic simulation of driftwave instability in field-reversed configuration

NASA Astrophysics Data System (ADS)

Fulton, D. P.; Lau, C. K.; Schmitz, L.; Holod, I.; Lin, Z.; Tajima, T.; Binderbauer, M. W.

2016-05-01

Following the recent remarkable progress in magnetohydrodynamic (MHD) stability control in the C-2U advanced beam driven field-reversed configuration (FRC), turbulent transport has become one of the foremost obstacles on the path towards an FRC-based fusion reactor. Significant effort has been made to expand kinetic simulation capabilities in FRC magnetic geometry. The recently upgraded Gyrokinetic Toroidal Code (GTC) now accommodates realistic magnetic geometry from the C-2U experiment at Tri Alpha Energy, Inc. and is optimized to efficiently handle the FRC's magnetic field line orientation. Initial electrostatic GTC simulations find that ion-scale instabilities are linearly stable in the FRC core for realistic pressure gradient drives. Estimated instability thresholds from linear GTC simulations are qualitatively consistent with critical gradients determined from experimental Doppler backscattering fluctuation data, which also find ion scale modes to be depressed in the FRC core. Beyond GTC, A New Code (ANC) has been developed to accurately resolve the magnetic field separatrix and address the interaction between the core and scrape-off layer regions, which ultimately determines global plasma confinement in the FRC. The current status of ANC and future development targets are discussed.

The accurate particle tracer code

DOE PAGES

Wang, Yulei; Liu, Jian; Qin, Hong; ...

2017-07-20

The Accurate Particle Tracer (APT) code is designed for systematic large-scale applications of geometric algorithms for particle dynamical simulations. Based on a large variety of advanced geometric algorithms, APT possesses long-term numerical accuracy and stability, which are critical for solving multi-scale and nonlinear problems. To provide a flexible and convenient I/O interface, the libraries of Lua and Hdf5 are used. Following a three-step procedure, users can efficiently extend the libraries of electromagnetic configurations, external non-electromagnetic forces, particle pushers, and initialization approaches by use of the extendible module. APT has been used in simulations of key physical problems, such as runawaymore » electrons in tokamaks and energetic particles in Van Allen belt. As an important realization, the APT-SW version has been successfully distributed on the world’s fastest computer, the Sunway TaihuLight supercomputer, by supporting master–slave architecture of Sunway many-core processors. Here, based on large-scale simulations of a runaway beam under parameters of the ITER tokamak, it is revealed that the magnetic ripple field can disperse the pitch-angle distribution significantly and improve the confinement of energetic runaway beam on the same time.« less

The accurate particle tracer code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yulei; Liu, Jian; Qin, Hong

The Accurate Particle Tracer (APT) code is designed for systematic large-scale applications of geometric algorithms for particle dynamical simulations. Based on a large variety of advanced geometric algorithms, APT possesses long-term numerical accuracy and stability, which are critical for solving multi-scale and nonlinear problems. To provide a flexible and convenient I/O interface, the libraries of Lua and Hdf5 are used. Following a three-step procedure, users can efficiently extend the libraries of electromagnetic configurations, external non-electromagnetic forces, particle pushers, and initialization approaches by use of the extendible module. APT has been used in simulations of key physical problems, such as runawaymore » electrons in tokamaks and energetic particles in Van Allen belt. As an important realization, the APT-SW version has been successfully distributed on the world’s fastest computer, the Sunway TaihuLight supercomputer, by supporting master–slave architecture of Sunway many-core processors. Here, based on large-scale simulations of a runaway beam under parameters of the ITER tokamak, it is revealed that the magnetic ripple field can disperse the pitch-angle distribution significantly and improve the confinement of energetic runaway beam on the same time.« less

Kinetic turbulence simulations at extreme scale on leadership-class systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Bei; Ethier, Stephane; Tang, William

2013-01-01

Reliable predictive simulation capability addressing confinement properties in magnetically confined fusion plasmas is critically-important for ITER, a 20 billion dollar international burning plasma device under construction in France. The complex study of kinetic turbulence, which can severely limit the energy confinement and impact the economic viability of fusion systems, requires simulations at extreme scale for such an unprecedented device size. Our newly optimized, global, ab initio particle-in-cell code solving the nonlinear equations underlying gyrokinetic theory achieves excellent performance with respect to "time to solution" at the full capacity of the IBM Blue Gene/Q on 786,432 cores of Mira at ALCFmore » and recently of the 1,572,864 cores of Sequoia at LLNL. Recent multithreading and domain decomposition optimizations in the new GTC-P code represent critically important software advances for modern, low memory per core systems by enabling routine simulations at unprecedented size (130 million grid points ITER-scale) and resolution (65 billion particles).« less

Stability and Structure of Star-Shape Granules

NASA Astrophysics Data System (ADS)

Zhao, Yuchen; Bares, Jonathan; Liu, Kevin; Zheng, Matthew; Dierichs, Karola; Menges, Achim; Behringer, Robert

Columns made of convex noncohesive grains like sand collapse after being released from a confining container. While various architectures built by concave grains are stable. We explore why these structures are stable, and how stable they can be. We performed experiments by randomly pouring identical star-shape particles into hollow cylinders resting on glass or a roughened base, and then observed how stable these granular columns were after carefully lifting the cylinders. We used particles that are made of acrylics and have six 9 mm arms, which extend symmetrically in xyz directions. We investigated the probability of creating a stable column and other mechanical stability aspects. We define r as the weight fraction of particles that fall out of the column after the confining cylinder is removed. r gradually increases as the column height increases, or the column diameter decreases. We found high column stability when the inter-particle friction was greater. We also explored experiment conditions such as initial vibration of columns when they were confined and loading on the top. In order to understand the inner structure leading to stability, we obtained 3D CT reconstruction data of stable columns. We will discuss coordination number and orientation, etc. We acknowledge supports from W.M.Keck Foundation and Research Triangle MRSEC.

Measurements of confined alphas and tritons in the MHD quiescent core of TFTR plasmas using the pellet charge exchange diagnostic

NASA Astrophysics Data System (ADS)

Medley, S. S.; Budny, R. V.; Mansfield, D. K.; Redi, M. H.; Roquemore, A. L.; Fisher, R. K.; Duong, H. H.; McChesney, J. M.; Parks, P. B.; Petrov, M. P.; Gorelenkov, N. N.

1996-10-01

The energy distributions and radial density profiles of the fast confined trapped alpha particles in DT experiments on TFTR are being measured in the energy range 0.5 - 3.5 MeV using the pellet charge exchange (PCX) diagnostic. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud surrounding an injected impurity pellet as the neutralizer is presented. This paper focuses on alpha and triton measurements in the core of MHD quiescent TFTR discharges where the expected classical slowing-down and pitch angle scattering effects are not complicated by stochastic ripple diffusion and sawtooth activity. In particular, the first measurement of the alpha slowing-down distribution up to the birth energy, obtained using boron pellet injection, is presented. The measurements are compared with predictions using either the TRANSP Monte Carlo code and/or a Fokker - Planck Post-TRANSP processor code, which assumes that the alphas and tritons are well confined and slow down classically. Both the shape of the measured alpha and triton energy distributions and their density ratios are in good agreement with the code calculations. We can conclude that the PCX measurements are consistent with classical thermalization of the fusion-generated alphas and tritons.

8OCB and 8CB Liquid Crystals Confined in Nanoporous Alumina: Effect of Confinement on the Structure and Dynamics.

PubMed

Selevou, Aristoula; Papamokos, George; Steinhart, Martin; Floudas, George

2017-08-03

The effect of oxygen substitution is studied in two homologous compounds of n-cyanobiphenyls with n = 8 in the bulk and under confinement within self-ordered nanoporous alumina (AAO). Oxygen substitution in 8OCB increases the dipole moment and stabilizes the crystalline, smectic, and nematic phases to higher temperatures relative to 8CB. Within their smectic- A (SmA) phase both 8CB and 8OCB behave as weak viscoelastic solids with low shear moduli reflecting the underlying supramolecular defect structure. Dielectric spectroscopy assisted by DFT calculations identified strong dipolar associations within the isotropic phases characterized by a Kirkwood-Fröhlich interaction parameter, g ∼ 0.36. Dielectric spectroscopy further identified a slow process (∼ kHz) of low dielectric strength. The proximity of this process to the rheology time scale suggests as common origin a cooperative relaxation of the defect structure. Confinement alters the phase diagram by stabilizing certain crystalline phases and by reducing the N-I transition temperature in agreement with surface tension effects. However, the N-I transition seems to retain its first order character. Surface treatment with n-decyltrichlorosilane results in destabilization of the SmA phase at the expense of the N phase. This is consistent with a picture of surface anchored LC molecules at the pore walls that stabilize the nematic phase.

Direct measurements of protein-stabilized gold nanoparticle interactions.

PubMed

Eichmann, Shannon L; Bevan, Michael A

2010-09-21

We report integrated video and total internal reflection microscopy measurements of protein stabilized 110 nm Au nanoparticles confined in 280 nm gaps in physiological media. Measured potential energy profiles display quantitative agreement with Brownian dynamic simulations that include hydrodynamic interactions and camera exposure time and noise effects. Our results demonstrate agreement between measured nonspecific van der Waals and adsorbed protein interactions with theoretical potentials. Confined, lateral nanoparticle diffusivity measurements also display excellent agreement with predictions. These findings provide a basis to interrogate specific biomacromolecular interactions in similar experimental configurations and to design future improved measurement methods.

MHD simulation of plasma compression experiments

NASA Astrophysics Data System (ADS)

Reynolds, Meritt; Barsky, Sandra; de Vietien, Peter

2017-10-01

General Fusion (GF) is working to build a magnetized target fusion (MTF) power plant based on compression of magnetically-confined plasma by liquid metal. GF is testing this compression concept by collapsing solid aluminum liners onto plasmas formed by coaxial helicity injection in a series of experiments called PCS (Plasma Compression, Small). We simulate the PCS experiments using the finite-volume MHD code VAC. The single-fluid plasma model includes temperature-dependent resistivity and anisotropic heat transport. The time-dependent curvilinear mesh for MHD simulation is derived from LS-DYNA simulations of actual field tests of liner implosion. We will discuss how 3D simulations reproduced instability observed in the PCS13 experiment and correctly predicted stabilization of PCS14 by ramping the shaft current during compression. We will also present a comparison of simulated Mirnov and x-ray diagnostics with experimental measurements indicating that PCS14 compressed well to a linear compression ratio of 2.5:1.

Damping Rate Measurements of Medium n Alfv'en Eigenmodes in JET

NASA Astrophysics Data System (ADS)

Klein, Alexander; Testa, Duccio; Snipes, Joseph; Fasoli, Ambrogio; Carfantan, Hervé

2007-11-01

Alfv'en Eigenmodes (AE's) with mode numbers 5 < n < 20 are expected to be unstable in burning tokamaks and may lead to loss of fast particle confinement. The active MHD spectroscopy program at JET has already provided a wealth of information about low n (n <= 2) AE's in the past decade, but a recently installed array of four antennas is capable of driving higher mode numbered (n < 100, 30 < f < 350 kHz) perturbations. In the latest JET campaign, the damping rates for several types of AE's were measured parasitically in a wide range of tokamak scenarios. We review the active MHD diagnostic and present the first measurements of medium-n AE stability on JET, then describe future plans for the active MHD spectroscopy project. The data analysis involves a novel method for resolving multiple AE's that exist at identical frequencies, which uses techniques based on the SparSpec code.

Efficient n-type doping of zinc-blende III-V semiconductor nanowires

NASA Astrophysics Data System (ADS)

Besteiro, Lucas V.; Tortajada, Luis; Souto, J.; Gallego, L. J.; Chelikowsky, James R.; Alemany, M. M. G.

2014-03-01

We demonstrate that it is preferable to dope III-V semiconductor nanowires by n-type anion substitution as opposed to cation substitution. Specifically, we show the dopability of zinc-blende nanowires is more efficient when the dopants are placed at the anion site as quantified by formation energies and the stabilization of DX-like defect centers. The comparison with previous work on n - type III-V semiconductor nanocrystals also allows to determine the role of dimensionality and quantum confinement on doping characteristics of materials. Our results are based on first-principles calculations of InP nanowires by using the PARSEC code. Work supported by the Spanish MICINN (FIS2012-33126) and Xunta de Galicia (GPC2013-043) in conjunction with FEDER. JRC acknowledges support from DoE (DE-FG02-06ER46286 and DESC0008877). Computational support was provided in part by CESGA.

Evaluation of the effect of synthetic fibers and non-woven geotextile reinforcement on the stability of heavy clay embankments : technical summary.

DOT National Transportation Integrated Search

2004-07-01

The objectives of this study were to evaluate the effects of soil density, moisture content, fiber content, and confining pressure on the shear strength of the clayey-fiber matrix, and of soil moisture content and confining pressure on the interface ...

Improved mechanical stability of HKUST-1 in confined nanospace.

PubMed

Casco, M E; Fernández-Catalá, J; Martínez-Escandell, M; Rodríguez-Reinoso, F; Ramos-Fernández, E V; Silvestre-Albero, J

2015-09-28

One of the main concerns in the technological application of several metal-organic frameworks (MOFs) relates to their structural instability under pressure (after a conforming step). Here we report for the first time that mechanical instability can be highly improved via nucleation and growth of MOF nanocrystals in the confined nanospace of activated carbons.

Theory-based model for the pedestal, edge stability and ELMs in tokamaks

NASA Astrophysics Data System (ADS)

Pankin, A. Y.; Bateman, G.; Brennan, D. P.; Schnack, D. D.; Snyder, P. B.; Voitsekhovitch, I.; Kritz, A. H.; Janeschitz, G.; Kruger, S.; Onjun, T.; Pacher, G. W.; Pacher, H. D.

2006-04-01

An improved model for triggering edge localized mode (ELM) crashes is developed for use within integrated modelling simulations of the pedestal and ELM cycles at the edge of H-mode tokamak plasmas. The new model is developed by using the BALOO, DCON and ELITE ideal MHD stability codes to derive parametric expressions for the ELM triggering threshold. The whole toroidal mode number spectrum is studied with these codes. The DCON code applies to low mode numbers, while the BALOO code applies to only high mode numbers and the ELITE code applies to intermediate and high mode numbers. The variables used in the parametric stability expressions are the normalized pressure gradient and the parallel current density, which drive ballooning and peeling modes. Two equilibria motivated by DIII-D geometry with different plasma triangularities are studied. It is found that the stable region in the high triangularity discharge covers a much larger region of parameter space than the corresponding stability region in the low triangularity discharge. The new ELM trigger model is used together with a previously developed model for pedestal formation and ELM crashes in the ASTRA integrated modelling code to follow the time evolution of the temperature profiles during ELM cycles. The ELM frequencies obtained in the simulations of low and high triangularity discharges are observed to increase with increasing heating power. There is a transition from second stability to first ballooning mode stability as the heating power is increased in the high triangularity simulations. The results from the ideal MHD stability codes are compared with results from the resistive MHD stability code NIMROD.

Tritium safety study using Caisson Assembly (CATS) at TPL/JAEA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayashi, T.; Kobayashi, K.; Iwai, Y.

Tritium confinement is required as the most important safety Junction for a fusion reactor. In order to demonstrate the confinement performance experimentally, an unique equipment, called CATS: Caisson Assembly for Tritium Safety study, was installed in Tritium Process Laboratory of Japan Atomic Energy Agency and operated for about 10 years. Tritium confinement and migration data in CATS have been accumulated and dynamic simulation code was accumulated using these data. Contamination and decontamination behavior on various materials and new safety equipment functions have been investigated under collaborations with a lot of laboratories and universities. (authors)

Electrostatic-Dipole (ED) Fusion Confinement Studies

NASA Astrophysics Data System (ADS)

Miley, George H.; Shrestha, Prajakti J.; Yang, Yang; Thomas, Robert

2004-11-01

The Electrostatic-Dipole (ED) concept significantly differs from a "pure" dipole confinement device [1] in that the charged particles are preferentially confined to the high-pressure region interior of the dipole coil by the assistance of a surrounding spherical electrostatic grid. In present ED experiments, a current carrying coil is embedded inside the grid of an IEC such as to produce a magnetic dipole field. Charged particles are injected axisymmetrically from an ion gun (or duo-plasmatron) into the center of the ED confinement grid/dipole ring where they oscillate along the magnetic field lines and pass the peak field region at the center of the dipole region. As particles begin accelerating away from the center region towards the outer electrostatic grid region, they encounter a strong electrostatic potential (order of 10's of kilovolts) retarding force. The particles then decelerate, reverse direction and re-enter the dipole field region where again magnetic confinement dominates. This process continues, emulating a complex harmonic oscillator motion. The resulting pressure profile averaged over the field curvature offers good plasma stability in the ED configuration. The basic concept and results from preliminary experiments will be described. [1] M.E. Mauel, et al. "Dipole Equilibrium and Stability," 18th IAEA Conference of Plasma Phys. and Control. Nuclear Fusion, Varenna, Italy 2000, IAEA-F1-CN-70/TH

Development of Integrated Magnetic and Kinetic Control-oriented Transport Model for q-profile Response Prediction in EAST Discharges

NASA Astrophysics Data System (ADS)

Wang, Hexiang; Schuster, Eugenio; Rafiq, Tariq; Kritz, Arnold; Ding, Siye

2016-10-01

Extensive research has been conducted to find high-performance operating scenarios characterized by high fusion gain, good confinement, plasma stability and possible steady-state operation. A key plasma property that is related to both the stability and performance of these advanced plasma scenarios is the safety factor profile. A key component of the EAST research program is the exploration of non-inductively driven steady-state plasmas with the recently upgraded heating and current drive capabilities that include lower hybrid current drive and neutral beam injection. Anticipating the need for tight regulation of the safety factor profile in these plasma scenarios, a first-principles-driven (FPD)control-oriented model is proposed to describe the safety factor profile evolution in EAST in response to the different actuators. The TRANSP simulation code is employed to tailor the FPD model to the EAST tokamak geometry and to convert it into a form suitable for control design. The FPD control-oriented model's prediction capabilities are demonstrated by comparing predictions with experimental data from EAST. Supported by the US DOE under DE-SC0010537,DE-FG02-92ER54141 and DE-SC0013977.

Method and article for primary containment of cesium wastes. [DOE patent application

DOEpatents

Angelini, P.; Lackey, W.J.; Stinton, D.P.; Blanco, R.E.; Bond, W.D.; Arnold, W.D. Jr.

1981-09-03

A method for producing a cesium-retentive waste form, characterized by a high degree of compositional stability and mechanical integrity, is provided by subjecting a cesium-loaded zeolite to heat under conditions suitable for stabilizing the zeolite and immobilizing the cesium, and coating said zeolite for sufficient duration within a suitable environment with at least one dense layer of pyrolytic carbon to seal therein said cesium to produce a final, cesium-bearing waste form. Typically, the zolite is stabilized and the cesium immobilized in less than four hours by confinement within an air environment maintained at about 600/sup 0/C. Coatings are thereafter applied by confining the calcined zeolite within a coating environment comprising inert fluidizing and carbon donor gases maintained at 1000/sup 0/C for a suitable duration.

Method for primary containment of cesium wastes

DOEpatents

Angelini, Peter; Lackey, Walter J.; Stinton, David P.; Blanco, Raymond E.; Bond, Walter D.; Arnold, Jr., Wesley D.

1983-01-01

A method for producing a cesium-retentive waste form, characterized by a high degree of compositional stability and mechanical integrity, is provided by subjecting a cesium-loaded zeolite to heat under conditions suitable for stabilizing the zeolite and immobilizing the cesium, and coating said zeolite for sufficient duration within a suitable environment with at least one dense layer of pyrolytic carbon to seal therein said cesium to produce a final, cesium-bearing waste form. Typically, the zeolite is stabilized and the cesium immobilized in less than four hours by confinement within an air environment maintained at about 600.degree. C. Coatings are thereafter applied by confining the calcined zeolite within a coating environment comprising inert fluidizing and carbon donor gases maintained at 1,000.degree. C. for a suitable duration.

Confinement Stabilizes a Bacterial Suspension into a Spiral Vortex

NASA Astrophysics Data System (ADS)

Wioland, Hugo; Woodhouse, Francis G.; Dunkel, Jörn; Kessler, John O.; Goldstein, Raymond E.

2013-06-01

Confining surfaces play crucial roles in dynamics, transport, and order in many physical systems, but their effects on active matter, a broad class of dynamically self-organizing systems, are poorly understood. We investigate here the influence of global confinement and surface curvature on collective motion by studying the flow and orientational order within small droplets of a dense bacterial suspension. The competition between radial confinement, self-propulsion, steric interactions, and hydrodynamics robustly induces an intriguing steady single-vortex state, in which cells align in inward spiraling patterns accompanied by a thin counterrotating boundary layer. A minimal continuum model is shown to be in good agreement with these observations.

MULTI2D - a computer code for two-dimensional radiation hydrodynamics

NASA Astrophysics Data System (ADS)

Ramis, R.; Meyer-ter-Vehn, J.; Ramírez, J.

2009-06-01

Simulation of radiation hydrodynamics in two spatial dimensions is developed, having in mind, in particular, target design for indirectly driven inertial confinement energy (IFE) and the interpretation of related experiments. Intense radiation pulses by laser or particle beams heat high-Z target configurations of different geometries and lead to a regime which is optically thick in some regions and optically thin in others. A diffusion description is inadequate in this situation. A new numerical code has been developed which describes hydrodynamics in two spatial dimensions (cylindrical R-Z geometry) and radiation transport along rays in three dimensions with the 4 π solid angle discretized in direction. Matter moves on a non-structured mesh composed of trilateral and quadrilateral elements. Radiation flux of a given direction enters on two (one) sides of a triangle and leaves on the opposite side(s) in proportion to the viewing angles depending on the geometry. This scheme allows to propagate sharply edged beams without ray tracing, though at the price of some lateral diffusion. The algorithm treats correctly both the optically thin and optically thick regimes. A symmetric semi-implicit (SSI) method is used to guarantee numerical stability. Program summaryProgram title: MULTI2D Catalogue identifier: AECV_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECV_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 151 098 No. of bytes in distributed program, including test data, etc.: 889 622 Distribution format: tar.gz Programming language: C Computer: PC (32 bits architecture) Operating system: Linux/Unix RAM: 2 Mbytes Word size: 32 bits Classification: 19.7 External routines: X-window standard library (libX11.so) and corresponding heading files (X11/*.h) are required. Nature of problem: In inertial confinement fusion and related experiments with lasers and particle beams, energy transport by thermal radiation becomes important. Under these conditions, the radiation field strongly interacts with the hydrodynamic motion through emission and absorption processes. Solution method: The equations of radiation transfer coupled with Lagrangian hydrodynamics, heat diffusion and beam tracing (laser or ions) are solved, in two-dimensional axial-symmetric geometry ( R-Z coordinates) using a fractional step scheme. Radiation transfer is solved with angular resolution. Matter properties are either interpolated from tables (equations-of-state and opacities) or computed by user routines (conductivities and beam attenuation). Restrictions: The code has been designed for typical conditions prevailing in inertial confinement fusion (ns time scale, matter states close to local thermodynamical equilibrium, negligible radiation pressure, …). Although a wider range of situations can be treated, extrapolations to regions beyond this design range need special care. Unusual features: A special computer language, called r94, is used at top levels of the code. These parts have to be converted to standard C by a translation program (supplied as part of the package). Due to the complexity of code (hydro-code, grid generation, user interface, graphic post-processor, translator program, installation scripts) extensive manuals are supplied as part of the package. Running time: 567 seconds for the example supplied.

Optical properties of voltage sensitive hemicyanine dyes of variable hydrophobicity confined within surfactant micelles

NASA Astrophysics Data System (ADS)

Naeem, Kashif; Naseem, Bushra; Shah, S. S.; Shah, Syed W. H.

2017-11-01

The optical properties of amphiphilic hemicyanine dyes with variable hydrophobicity, confined within anionic micelles of sodium dodecylbenzenesulfonate (NaDDBS) have been studied by UV-visible absorption spectroscopy. The confinement constant, K conf has been determined for each entrapped dye. The ion-pair formation between dye and surfactant causes a decline in electronic transition energy (ΔE T) when dye alkyl chains are smaller due to stabilization of both the ground and excited state. ΔE T values gradually increase with increase in dye hydrophobicity that hampers the electrostatic interaction with dialkylammonium moiety and consequently excited state stabilization is compromised. The average number of dye molecules trapped in a single micelle was also determined. The negative values of Gibbs free energy indicate that the dye entrapment within micelles is energetically favored. These findings have significance for developing functional materials with peculiar luminescent properties, especially for more effective probing of complex biological systems.

H-mode pedestal stability and ELMs in Alcator C-Mod

NASA Astrophysics Data System (ADS)

Mossessian, Dmitri

2002-11-01

For steady state H-mode operation, a relaxation mechanism is required to limit build-up of the edge gradient and impurity accumulation. The major relaxation mechanism seen on most of the existing tokamaks - large type I ELMs - drive high particle and energy fluxes that present a significant power load on the divertor plates. On Alcator C-Mod, however, type I ELMs are not observed. Instead, more benign mechanisms - EDA and small grassy ELMs - appear to drive enhanced particle transport at the edge of H-mode plasmas. Both have good energy confinement, no impurity accumulation, and are steady state. In EDA the edge relaxation mechanism is provided by a quasicoherent electromagnetic mode localized in the outer part of the pedestal. Non-linear gyrofluid and linear gyrokinetic simulations, as well as real geometry fluctuation modeling based on fluid equations show the presence of a coherent mode. Based on those results the observed mode is tentatively identified as resistive ballooning. At higher edge pressure gradient the mode is replaced by broadband fluctuations and small irregular ELMs are observed. Based on ideal MHD calculations that include effects of bootstrap current, these ELMs are identified as medium n coupled ideal peeling/ballooning modes. The stability threshold and modes structure of these modes are studied with recently developed linear MHD stability code ELITE and the results are compared with the observed dependence of the ELMs' character on pedestal parameters and plasma shape.

Quantifying Fusion Born Ion Populations in Magnetically Confined Plasmas using Ion Cyclotron Emission

NASA Astrophysics Data System (ADS)

Carbajal, L.; Dendy, R. O.; Chapman, S. C.; Cook, J. W. S.

2017-03-01

Ion cyclotron emission (ICE) offers a unique promise as a diagnostic of the fusion born alpha-particle population in magnetically confined plasmas. Pioneering observations from JET and TFTR found that ICE intensity PICE scales approximately linearly with the measured neutron flux from fusion reactions, and with the inferred concentration, nα/ni, of fusion born alpha particles confined within the plasma. We present fully nonlinear self-consistent kinetic simulations that reproduce this scaling for the first time. This resolves a long-standing question in the physics of fusion alpha-particle confinement and stability in magnetic confinement fusion plasmas. It confirms the magnetoacoustic cyclotron instability as the likely emission mechanism and greatly strengthens the basis for diagnostic exploitation of ICE in future burning plasmas.

Quantifying Fusion Born Ion Populations in Magnetically Confined Plasmas using Ion Cyclotron Emission.

PubMed

Carbajal, L; Dendy, R O; Chapman, S C; Cook, J W S

2017-03-10

Ion cyclotron emission (ICE) offers a unique promise as a diagnostic of the fusion born alpha-particle population in magnetically confined plasmas. Pioneering observations from JET and TFTR found that ICE intensity P_{ICE} scales approximately linearly with the measured neutron flux from fusion reactions, and with the inferred concentration, n_{α}/n_{i}, of fusion born alpha particles confined within the plasma. We present fully nonlinear self-consistent kinetic simulations that reproduce this scaling for the first time. This resolves a long-standing question in the physics of fusion alpha-particle confinement and stability in magnetic confinement fusion plasmas. It confirms the magnetoacoustic cyclotron instability as the likely emission mechanism and greatly strengthens the basis for diagnostic exploitation of ICE in future burning plasmas.

Stability of a jet in confined pressure-driven biphasic flows at low reynolds numbers.

PubMed

Guillot, Pierre; Colin, Annie; Utada, Andrew S; Ajdari, Armand

2007-09-07

Motivated by its importance for microfluidic applications, we study the stability of jets formed by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes confinement and Poiseuille flow profiles. We experimentally evidence a transition between situations where the flow takes the form of a jet and regimes where drops are produced. We describe this as the transition from convective to absolute instability, within a simple linear analysis using lubrication theory for flows at low Reynolds number, and reach remarkable agreement with the data.

A self-consistent model of an isothermal tokamak

NASA Astrophysics Data System (ADS)

McNamara, Steven; Lilley, Matthew

2014-10-01

Continued progress in liquid lithium coating technologies have made the development of a beam driven tokamak with minimal edge recycling a feasibly possibility. Such devices are characterised by improved confinement due to their inherent stability and the suppression of thermal conduction. Particle and energy confinement become intrinsically linked and the plasma thermal energy content is governed by the injected beam. A self-consistent model of a purely beam fuelled isothermal tokamak is presented, including calculations of the density profile, bulk species temperature ratios and the fusion output. Stability considerations constrain the operating parameters and regions of stable operation are identified and their suitability to potential reactor applications discussed.

Stabilization of the Amorphous Ezetimibe Drug by Confining Its Dimension.

PubMed

Knapik, J; Wojnarowska, Z; Grzybowska, K; Jurkiewicz, K; Stankiewicz, A; Paluch, M

2016-04-04

The purpose of this paper is to investigate the influence of nanoconfinement on the molecular mobility, as well as on the physical stability, of amorphous ezetimibe drug. Two guest/host systems, ezetimibe-Aeroperl 300 and ezetimibe-Neusilin US2, were prepared and studied using various experimental techniques, such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS). Our investigation has shown that the molecular mobility of the examined anticholesterol agent incorporated into nanopore matrices strongly depends on the pore size of the host system. Moreover, it was found that the amorphous ezetimibe confined in 30 nm pores of Aeroperl 300 has a tendency to recrystallize, while the drug incorporated into the smaller--5 nm--pores of Neusilin US2 is not able to crystallize. It has been shown that this significant stabilization of ezetimibe drug can be achieved by an interplay of three factors: changes in molecular dynamics of the confined amorphous drug, the immobilization effect of pore walls on a part of ezetimibe molecules, and the use of host materials with pores that are smaller than the critical size of the drug crystal nuclei.

Extreme Scale Plasma Turbulence Simulations on Top Supercomputers Worldwide

DOE PAGES

Tang, William; Wang, Bei; Ethier, Stephane; ...

2016-11-01

The goal of the extreme scale plasma turbulence studies described in this paper is to expedite the delivery of reliable predictions on confinement physics in large magnetic fusion systems by using world-class supercomputers to carry out simulations with unprecedented resolution and temporal duration. This has involved architecture-dependent optimizations of performance scaling and addressing code portability and energy issues, with the metrics for multi-platform comparisons being 'time-to-solution' and 'energy-to-solution'. Realistic results addressing how confinement losses caused by plasma turbulence scale from present-day devices to the much larger $25 billion international ITER fusion facility have been enabled by innovative advances in themore » GTC-P code including (i) implementation of one-sided communication from MPI 3.0 standard; (ii) creative optimization techniques on Xeon Phi processors; and (iii) development of a novel performance model for the key kernels of the PIC code. Our results show that modeling data movement is sufficient to predict performance on modern supercomputer platforms.« less

Collisional tests and an extension of the TEMPEST continuum gyrokinetic code

NASA Astrophysics Data System (ADS)

Cohen, R. H.; Dorr, M.; Hittinger, J.; Kerbel, G.; Nevins, W. M.; Rognlien, T.; Xiong, Z.; Xu, X. Q.

2006-04-01

An important requirement of a kinetic code for edge plasmas is the ability to accurately treat the effect of colllisions over a broad range of collisionalities. To test the interaction of collisions and parallel streaming, TEMPEST has been compared with published analytic and numerical (Monte Carlo, bounce-averaged Fokker-Planck) results for endloss of particles confined by combined electrostatic and magnetic wells. Good agreement is found over a wide range of collisionality, confining potential and mirror ratio, and the required velocity space resolution is modest. We also describe progress toward extension of (4-dimensional) TEMPEST into a ``kinetic edge transport code'' (a kinetic counterpart of UEDGE). The extension includes averaging of the gyrokinetic equations over fast timescales and approximating the averaged quadratic terms by diffusion terms which respect the boundaries of inaccessable regions in phase space. F. Najmabadi, R.W. Conn and R.H. Cohen, Nucl. Fusion 24, 75 (1984); T.D. Rognlien and T.A. Cutler, Nucl. Fusion 20, 1003 (1980).

Fault-tolerant conversion between adjacent Reed-Muller quantum codes based on gauge fixing

NASA Astrophysics Data System (ADS)

Quan, Dong-Xiao; Zhu, Li-Li; Pei, Chang-Xing; Sanders, Barry C.

2018-03-01

We design forward and backward fault-tolerant conversion circuits, which convert between the Steane code and the 15-qubit Reed-Muller quantum code so as to provide a universal transversal gate set. In our method, only seven out of a total 14 code stabilizers need to be measured, and we further enhance the circuit by simplifying some stabilizers; thus, we need only to measure eight weight-4 stabilizers for one round of forward conversion and seven weight-4 stabilizers for one round of backward conversion. For conversion, we treat random single-qubit errors and their influence on syndromes of gauge operators, and our novel single-step process enables more efficient fault-tolerant conversion between these two codes. We make our method quite general by showing how to convert between any two adjacent Reed-Muller quantum codes \\overline{\\textsf{RM}}(1,m) and \\overline{\\textsf{RM}}≤ft(1,m+1\\right) , for which we need only measure stabilizers whose number scales linearly with m rather than exponentially with m obtained in previous work. We provide the explicit mathematical expression for the necessary stabilizers and the concomitant resources required.

Fault-tolerant logical gates in quantum error-correcting codes

NASA Astrophysics Data System (ADS)

Pastawski, Fernando; Yoshida, Beni

2015-01-01

Recently, S. Bravyi and R. König [Phys. Rev. Lett. 110, 170503 (2013), 10.1103/PhysRevLett.110.170503] have shown that there is a trade-off between fault-tolerantly implementable logical gates and geometric locality of stabilizer codes. They consider locality-preserving operations which are implemented by a constant-depth geometrically local circuit and are thus fault tolerant by construction. In particular, they show that, for local stabilizer codes in D spatial dimensions, locality-preserving gates are restricted to a set of unitary gates known as the D th level of the Clifford hierarchy. In this paper, we explore this idea further by providing several extensions and applications of their characterization to qubit stabilizer and subsystem codes. First, we present a no-go theorem for self-correcting quantum memory. Namely, we prove that a three-dimensional stabilizer Hamiltonian with a locality-preserving implementation of a non-Clifford gate cannot have a macroscopic energy barrier. This result implies that non-Clifford gates do not admit such implementations in Haah's cubic code and Michnicki's welded code. Second, we prove that the code distance of a D -dimensional local stabilizer code with a nontrivial locality-preserving m th -level Clifford logical gate is upper bounded by O (LD +1 -m) . For codes with non-Clifford gates (m >2 ), this improves the previous best bound by S. Bravyi and B. Terhal [New. J. Phys. 11, 043029 (2009), 10.1088/1367-2630/11/4/043029]. Topological color codes, introduced by H. Bombin and M. A. Martin-Delgado [Phys. Rev. Lett. 97, 180501 (2006), 10.1103/PhysRevLett.97.180501; Phys. Rev. Lett. 98, 160502 (2007), 10.1103/PhysRevLett.98.160502; Phys. Rev. B 75, 075103 (2007), 10.1103/PhysRevB.75.075103], saturate the bound for m =D . Third, we prove that the qubit erasure threshold for codes with a nontrivial transversal m th -level Clifford logical gate is upper bounded by 1 /m . This implies that no family of fault-tolerant codes with transversal gates in increasing level of the Clifford hierarchy may exist. This result applies to arbitrary stabilizer and subsystem codes and is not restricted to geometrically local codes. Fourth, we extend the result of Bravyi and König to subsystem codes. Unlike stabilizer codes, the so-called union lemma does not apply to subsystem codes. This problem is avoided by assuming the presence of an error threshold in a subsystem code, and a conclusion analogous to that of Bravyi and König is recovered.

A New Look at the Code of Conduct

DTIC Science & Technology

1974-04-01

often kept apart from the cthers in solitary confinement. Prisoners were fed two meals each day, usually consisting of pumpkin or cab- bage soup, rice...capture, other "early release" prisoners appeared to have been summarily selected, and they surmised that they were re- 163leased for purely political...the routine rigors of confinement or for other purely personal relief. A parole of this nature may be authorized for example, topermit a prisoner to

Laser targets compensate for limitations in inertial confinement fusion drivers

NASA Astrophysics Data System (ADS)

Kilkenny, J. D.; Alexander, N. B.; Nikroo, A.; Steinman, D. A.; Nobile, A.; Bernat, T.; Cook, R.; Letts, S.; Takagi, M.; Harding, D.

2005-10-01

Success in inertial confinement fusion (ICF) requires sophisticated, characterized targets. The increasing fidelity of three-dimensional (3D), radiation hydrodynamic computer codes has made it possible to design targets for ICF which can compensate for limitations in the existing single shot laser and Z pinch ICF drivers. Developments in ICF target fabrication technology allow more esoteric target designs to be fabricated. At present, requirements require new deterministic nano-material fabrication on micro scale.

Investigating inertial confinement fusion target fuel conditions through x-ray spectroscopya)

NASA Astrophysics Data System (ADS)

Hansen, Stephanie B.

2012-05-01

Inertial confinement fusion (ICF) targets are designed to produce hot, dense fuel in a neutron-producing core that is surrounded by a shell of compressing material. The x-rays emitted from ICF plasmas can be analyzed to reveal details of the temperatures, densities, gradients, velocities, and mix characteristics of ICF targets. Such diagnostics are critical to understand the target performance and to improve the predictive power of simulation codes.

Field reversed configuration confinement enhancement through edge biasing and neutral beam injection.

PubMed

Tuszewski, M; Smirnov, A; Thompson, M C; Korepanov, S; Akhmetov, T; Ivanov, A; Voskoboynikov, R; Schmitz, L; Barnes, D; Binderbauer, M W; Brown, R; Bui, D Q; Clary, R; Conroy, K D; Deng, B H; Dettrick, S A; Douglass, J D; Garate, E; Glass, F J; Gota, H; Guo, H Y; Gupta, D; Gupta, S; Kinley, J S; Knapp, K; Longman, A; Hollins, M; Li, X L; Luo, Y; Mendoza, R; Mok, Y; Necas, A; Primavera, S; Ruskov, E; Schroeder, J H; Sevier, L; Sibley, A; Song, Y; Sun, X; Trask, E; Van Drie, A D; Walters, J K; Wyman, M D

2012-06-22

Field reversed configurations (FRCs) with high confinement are obtained in the C-2 device by combining plasma gun edge biasing and neutral beam injection. The plasma gun creates an inward radial electric field that counters the usual FRC spin-up. The n = 2 rotational instability is stabilized without applying quadrupole magnetic fields. The FRCs are nearly axisymmetric, which enables fast ion confinement. The plasma gun also produces E × B shear in the FRC edge layer, which may explain the observed improved particle transport. The FRC confinement times are improved by factors 2 to 4, and the plasma lifetimes are extended from 1 to up to 4 ms.

Addressing the challenges of plasma-surface interactions in NSTX-U*

DOE PAGES

Kaita, Robert; Abrams, Tyler; Jaworski, Michael; ...

2015-04-01

The importance of conditioning plasma-facing components (PFCs) has long been recognized as a critical element in obtaining high-performance plasmas in magnetic confinement devices. Lithium coatings, for example, have been used for decades for conditioning PFCs. Since the initial studies on the Tokamak Fusion Test Reactor, experiments on devices with different aspect ratios and magnetic geometries like the National Spherical Torus Experiment (NSTX) continue to show the relationship between lithium PFCs and good confinement and stability. While such results are promising, their empirical nature do not reflect the detailed relationship between PFCs and the dynamic conditions that occur in the tokamakmore » environment. A first step developing an understanding such complexity will be taken in the upgrade to NSTX (NSTX-U) that is nearing completion. New measurement capabilities include the Materials Analysis and Particle Probe (MAPP) for in situ surface analysis of samples exposed to tokamak plasmas. The OEDGE suite of codes, for example, will provide a new way to model the underlying mechanisms for such material migration in NSTX-U. This will lead to a better understanding of how plasma-facing surfaces evolve during a shot, and how the composition of the plasma facing surface influences the discharge performance we observe. This paper will provide an overview of these capabilities, and highlight their importance for NSTX-U plans to transition from carbon to high-Z PFCs.« less

Recent results from the electron cyclotron heated plasmas in Tokamak à Configuration Variable (TCV)

NASA Astrophysics Data System (ADS)

Henderson, M. A.; Alberti, S.; Angioni, C.; Arnoux, G.; Behn, R.; Blanchard, P.; Bosshard, P.; Camenen, Y.; Coda, S.; Condrea, I.; Goodman, T. P.; Hofmann, F.; Hogge, J.-Ph.; Karpushov, A.; Manini, A.; Martynov, An.; Moret, J.-M.; Nikkola, P.; Nelson-Melby, E.; Pochelon, A.; Porte, L.; Sauter, O.; Ahmed, S. M.; Andrèbe, Y.; Appert, K.; Chavan, R.; Degeling, A.; Duval, B. P.; Etienne, P.; Fasel, D.; Fasoli, A.; Favez, J.-Y.; Furno, I.; Horacek, J.; Isoz, P.; Joye, B.; Klimanov, I.; Lavanchy, P.; Lister, J. B.; Llobet, X.; Magnin, J.-C.; Marlétaz, B.; Marmillod, P.; Martin, Y.; Mayor, J.-M.; Mylnar, J.; Paris, P. J.; Perez, A.; Peysson, Y.; Pitts, R. A.; Raju, D.; Reimerdes, H.; Scarabosio, A.; Scavino, E.; Seo, S. H.; Siravo, U.; Sushkov, A.; Tonetti, G.; Tran, M. Q.; Weisen, H.; Wischmeier, M.; Zabolotsky, A.; Yhuang, G.

2003-05-01

In noninductively driven discharges, 0.9 MW second harmonic (X2) off-axis co-electron cyclotron current drive deposition is combined with 0.45 MW X2 central heating to create an electron internal transport barrier (eITB) in steady plasma conditions resulting in a 1.6-fold increase of the confinement time (τEe) over ITER-98L-mode scaling. The eITB is associated with a reversed shear current profile enhanced by a large bootstrap current fraction (up to 80%) and is sustained for up to 10 current redistribution times. A linear dependence of the confinement improvement on the product of the global shear reversal factor (q0/qmin) and the reversed shear volume (ρq-min2) is shown. In other discharges heated with X2 the sawteeth are destabilized (respectively stabilized) when heating just inside (respectively outside) the q=1 surface. Control of the sawteeth may allow the avoidance of neoclassical tearing modes that can be seeded by the sawtooth instability. Results on H-mode and highly elongated plasmas using the newly completed third harmonic (X3) system and achieving up to 100% absorption are also discussed, along with comparison of experimental results with the TORAY-GA ray tracing code [K. Matsuda, IEEE Trans. Plasma Sci. PS-17, 6 (1989); R. H. Cohen, Phys. Fluids 30, 2442 (1987)].

Stability at high performance in the MAST spherical tokamak

NASA Astrophysics Data System (ADS)

Buttery, R. J.; Akers, R.; Arends, E.; Conway, N. J.; Counsell, G. F.; Cunningham, G.; Gimblett, C. G.; Gryaznevich, M.; Hastie, R. J.; Hole, M. J.; Lehane, I.; Martin, R.; Patel, A.; Pinfold, T.; Sauter, O.; Taylor, D.; Turri, G.; Valovic, M.; Walsh, M. J.; Wilson, H. R.; MAST Team

2004-09-01

The development of reliable H-modes on MAST, together with advances in heating power and a range of high spatial resolution diagnostics, has provided a platform to enable MAST to address some of the most important issues of tokamak stability. In particular the high bgr potential of the spherical tokamak is highlighted with stable operation at bgrN ~ 5-6, bgrT ~ 16% and bgrp up to ~2. Magnetic diagnostic evaluation of the global bgr parameters is independently confirmed by kinetic profile data. Calculations indicate that the bgrN values are in the vicinity of no-wall stability limits. Studies of neoclassical tearing modes (NTMs) have been extended to explore their effects and develop avoidance strategies. Experiments have demonstrated that sawteeth play a strong role in triggering NTMs—by avoiding large sawteeth a much higher bgrN value has been reached. The significance of NTMs is confirmed, with large islands observed using the 300 point Thomson scattering diagnostic, and locking of large n = 1 modes frequently leading to disruptions, which become more rapid at low q95. The role of error fields has been explored. H-mode plasmas are also limited by edge localized modes (ELMs), with confinement degraded as the ELM frequency rises. However, in contrast to the conventional tokamak, the ELMs in high performing regimes on MAST (HIPB98Y2 ~ 1) appear to be type III in nature. Modelling using the ELITE code, which incorporates finite n corrections, identifies instability to peeling modes, consistent with a type III interpretation. It also shows considerable scope to raise pressure gradients before ballooning type modes (perhaps associated with type I ELMs) occur. The calculations show that narrow pedestals can support much stronger pressure gradients than might be expected from simple n = infin ballooning calculations. Finally sawteeth are shown to degrade confinement by ~10-15% in particular cases examined. They are observed not to remove the q = 1 surface in the cases where snakes are present—various physics models of the sawteeth are now being explored. Thus research on MAST is not only demonstrating stable operation at high performance levels and developing methods to control instabilities; it is also providing detailed tests of the stability physics and models applicable to conventional tokamaks, such as ITER.

Polyethylene Glycol Based Graphene Aerogel Confined Phase Change Materials with High Thermal Stability.

PubMed

Fu, Yang; Xiong, Weilai; Wang, Jianying; Li, Jinghua; Mei, Tao; Wang, Xianbao

2018-05-01

Polyethylene glycol (PEG) based graphene aerogel (GA) confined shaped-stabilized phase change materials (PCMs) are simply prepared by a one-step hydrothermal method. Three-dimensional GA inserted by PEG molecule chains, as a supporting material, obtained by reducing graphene oxide sheets, is used to keep their stabilized shape during a phase change process. The volume of GA is obviously expended after adding PEG, and only 9.8 wt% of GA make the composite achieve high energy efficiency without leakage during their phase change because of hydrogen bonding widely existing in the GA/PEG composites (GA-PCMs). The heat storage energy of GA-PCMs is 164.9 J/g, which is 90.2% of the phase change enthalpy of pure PEG. In addition, this composite inherits the natural thermal properties of graphene and thus shows enhanced thermal conductivity compared with pure PEG. This novel study provides an efficient way to fabricate shape-stabilized PCMs with a high content of PEG for thermal energy storage.

ELMO Bumpy Square proposal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dory, R.A.; Uckan, N.A.; Ard, W.B.

The ELMO Bumpy Square (EBS) concept consists of four straight magnetic mirror arrays linked by four high-field corner coils. Extensive calculations show that this configuration offers major improvements over the ELMO Bumpy Torus (EBT) in particle confinement, heating, transport, ring production, and stability. The components of the EBT device at Oak Ridge National Laboratory can be reconfigured into a square arrangement having straight sides composed of EBT coils, with new microwave cavities and high-field corners designed and built for this application. The elimination of neoclassical convection, identified as the dominant mechanism for the limited confinement in EBT, will give themore » EBS device substantially improved confinement and the flexibility to explore the concepts that produce this improvement. The primary goals of the EBS program are twofold: first, to improve the physics of confinement in toroidal systems by developing the concepts of plasma stabilization using the effects of energetic electrons and confinement optimization using magnetic field shaping and electrostatic potential control to limit particle drift, and second, to develop bumpy toroid devices as attractive candidates for fusion reactors. This report presents a brief review of the physics analyses that support the EBS concept, discussions of the design and expected performance of the EBS device, a description of the EBS experimental program, and a review of the reactor potential of bumpy toroid configurations. Detailed information is presented in the appendices.« less

Roothaan's approach to solve the Hartree-Fock equations for atoms confined by soft walls: Basis set with correct asymptotic behavior.

PubMed

Rodriguez-Bautista, Mariano; Díaz-García, Cecilia; Navarrete-López, Alejandra M; Vargas, Rubicelia; Garza, Jorge

2015-07-21

In this report, we use a new basis set for Hartree-Fock calculations related to many-electron atoms confined by soft walls. One- and two-electron integrals were programmed in a code based in parallel programming techniques. The results obtained with this proposal for hydrogen and helium atoms were contrasted with other proposals to study just one and two electron confined atoms, where we have reproduced or improved the results previously reported. Usually, an atom enclosed by hard walls has been used as a model to study confinement effects on orbital energies, the main conclusion reached by this model is that orbital energies always go up when the confinement radius is reduced. However, such an observation is not necessarily valid for atoms confined by penetrable walls. The main reason behind this result is that for atoms with large polarizability, like beryllium or potassium, external orbitals are delocalized when the confinement is imposed and consequently, the internal orbitals behave as if they were in an ionized atom. Naturally, the shell structure of these atoms is modified drastically when they are confined. The delocalization was an argument proposed for atoms confined by hard walls, but it was never verified. In this work, the confinement imposed by soft walls allows to analyze the delocalization concept in many-electron atoms.

Roothaan’s approach to solve the Hartree-Fock equations for atoms confined by soft walls: Basis set with correct asymptotic behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez-Bautista, Mariano; Díaz-García, Cecilia; Navarrete-López, Alejandra M.

2015-07-21

In this report, we use a new basis set for Hartree-Fock calculations related to many-electron atoms confined by soft walls. One- and two-electron integrals were programmed in a code based in parallel programming techniques. The results obtained with this proposal for hydrogen and helium atoms were contrasted with other proposals to study just one and two electron confined atoms, where we have reproduced or improved the results previously reported. Usually, an atom enclosed by hard walls has been used as a model to study confinement effects on orbital energies, the main conclusion reached by this model is that orbital energiesmore » always go up when the confinement radius is reduced. However, such an observation is not necessarily valid for atoms confined by penetrable walls. The main reason behind this result is that for atoms with large polarizability, like beryllium or potassium, external orbitals are delocalized when the confinement is imposed and consequently, the internal orbitals behave as if they were in an ionized atom. Naturally, the shell structure of these atoms is modified drastically when they are confined. The delocalization was an argument proposed for atoms confined by hard walls, but it was never verified. In this work, the confinement imposed by soft walls allows to analyze the delocalization concept in many-electron atoms.« less

Recent Advances in Stellarator Optimization

NASA Astrophysics Data System (ADS)

Gates, David; Brown, T.; Breslau, J.; Landreman, M.; Lazerson, S. A.; Mynick, H.; Neilson, G. H.; Pomphrey, N.

2016-10-01

Computational optimization has revolutionized the field of stellarator design. To date, optimizations have focused primarily on optimization of neoclassical confinement and ideal MHD stability, although limited optimization of other parameters has also been performed. One criticism that has been levelled at this method of design is the complexity of the resultant field coils. Recently, a new coil optimization code, COILOPT + + , was written and included in the STELLOPT suite of codes. The advantage of this method is that it allows the addition of real space constraints on the locations of the coils. As an initial exercise, a constraint that the windings be vertical was placed on large major radius half of the non-planar coils. Further constraints were also imposed that guaranteed that sector blanket modules could be removed from between the coils, enabling a sector maintenance scheme. Results of this exercise will be presented. We have also explored possibilities for generating an experimental database that could check whether the reduction in turbulent transport that is predicted by GENE as a function of local shear would be consistent with experiments. To this end, a series of equilibria that can be made in the now latent QUASAR experiment have been identified. This work was supported by U.S. DoE Contract #DE-AC02-09CH11466.

PdHx entrapped in covalent triazine framework modulates selectivity in glycerol oxidation [Modulation of palladium activity and stability by a covalent triazine framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chan-Thaw, Carine E.; Villa, Alberto; Wang, Di

The confinement of a Pd nanoparticle within a nitrogen-containing covalent triazine framework (CTF) material was investigated to understand if the highly tunable CTF chemistry mediates the Pd catalytic properties through an ensemble effect with the CTF nitrogen atoms or a confinement effect within the CTF pores. The results surprisingly demonstrate that the CTF stabilizes the formation of 2.6 nm PdHx particles within the pores. These PdHx particles are very active for the liquid phase oxidation of glycerol due to the in situ formation of H2O2 which catalytically promotes the initial C-C cleavage. In addition the confined particles are stable overmore » many catalytic cycles whereas nanoparticles trapped outside of the pores loose activity rapidly. These results indicate that there is the potential to tune the CTF chemistry to significantly modify the chemistry of the catalytic metals.« less

PdHx entrapped in covalent triazine framework modulates selectivity in glycerol oxidation [Modulation of palladium activity and stability by a covalent triazine framework

DOE PAGES

Chan-Thaw, Carine E.; Villa, Alberto; Wang, Di; ...

2015-06-25

The confinement of a Pd nanoparticle within a nitrogen-containing covalent triazine framework (CTF) material was investigated to understand if the highly tunable CTF chemistry mediates the Pd catalytic properties through an ensemble effect with the CTF nitrogen atoms or a confinement effect within the CTF pores. The results surprisingly demonstrate that the CTF stabilizes the formation of 2.6 nm PdHx particles within the pores. These PdHx particles are very active for the liquid phase oxidation of glycerol due to the in situ formation of H2O2 which catalytically promotes the initial C-C cleavage. In addition the confined particles are stable overmore » many catalytic cycles whereas nanoparticles trapped outside of the pores loose activity rapidly. These results indicate that there is the potential to tune the CTF chemistry to significantly modify the chemistry of the catalytic metals.« less

MARTe: A Multiplatform Real-Time Framework

NASA Astrophysics Data System (ADS)

Neto, André C.; Sartori, Filippo; Piccolo, Fabio; Vitelli, Riccardo; De Tommasi, Gianmaria; Zabeo, Luca; Barbalace, Antonio; Fernandes, Horacio; Valcarcel, Daniel F.; Batista, Antonio J. N.

2010-04-01

Development of real-time applications is usually associated with nonportable code targeted at specific real-time operating systems. The boundary between hardware drivers, system services, and user code is commonly not well defined, making the development in the target host significantly difficult. The Multithreaded Application Real-Time executor (MARTe) is a framework built over a multiplatform library that allows the execution of the same code in different operating systems. The framework provides the high-level interfaces with hardware, external configuration programs, and user interfaces, assuring at the same time hard real-time performances. End-users of the framework are required to define and implement algorithms inside a well-defined block of software, named Generic Application Module (GAM), that is executed by the real-time scheduler. Each GAM is reconfigurable with a set of predefined configuration meta-parameters and interchanges information using a set of data pipes that are provided as inputs and required as output. Using these connections, different GAMs can be chained either in series or parallel. GAMs can be developed and debugged in a non-real-time system and, only once the robustness of the code and correctness of the algorithm are verified, deployed to the real-time system. The software also supplies a large set of utilities that greatly ease the interaction and debugging of a running system. Among the most useful are a highly efficient real-time logger, HTTP introspection of real-time objects, and HTTP remote configuration. MARTe is currently being used to successfully drive the plasma vertical stabilization controller on the largest magnetic confinement fusion device in the world, with a control loop cycle of 50 ?s and a jitter under 1 ?s. In this particular project, MARTe is used with the Real-Time Application Interface (RTAI)/Linux operating system exploiting the new ?86 multicore processors technology.

Evolution and stabilization of subnanometric metal species in confined space by in situ TEM

DOE PAGES

Liu, Lichen; Zakharov, Dmitri N.; Arenal, Raul; ...

2018-02-08

Understanding the behavior and dynamic structural transformation of subnanometric metal species under reaction conditions will be helpful for understanding catalytic phenomena and for developing more efficient and stable catalysts based on single atoms and clusters.In this work,the evolution and stabilization of subnanometric Pt species confined in MCM-22 zeolite has been studied by in situ transmission electron microscopy (TEM). By correlating the results from in situ TEM studies and the results obtained in a continuous fix-bed reactor,it has been possible to delimitate the factors that control the dynamic agglomeration and redispersion behavior of metal species under reaction conditions. Here, the dynamicmore » reversible transformation between atomically dispersed Pt species and clusters/nanoparticles during CO oxidation at different temperatures has been elucidated.Ithas also been confirmed that subnanometric Pt clusters can be stabilized in MCM-22 crystallites during NO reduction with CO and H 2.« less

Evolution and stabilization of subnanometric metal species in confined space by in situ TEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lichen; Zakharov, Dmitri N.; Arenal, Raul

Understanding the behavior and dynamic structural transformation of subnanometric metal species under reaction conditions will be helpful for understanding catalytic phenomena and for developing more efficient and stable catalysts based on single atoms and clusters.In this work,the evolution and stabilization of subnanometric Pt species confined in MCM-22 zeolite has been studied by in situ transmission electron microscopy (TEM). By correlating the results from in situ TEM studies and the results obtained in a continuous fix-bed reactor,it has been possible to delimitate the factors that control the dynamic agglomeration and redispersion behavior of metal species under reaction conditions. Here, the dynamicmore » reversible transformation between atomically dispersed Pt species and clusters/nanoparticles during CO oxidation at different temperatures has been elucidated.Ithas also been confirmed that subnanometric Pt clusters can be stabilized in MCM-22 crystallites during NO reduction with CO and H 2.« less

Stabilization of Oxidized Copper Nanoclusters in Confined Spaces

DOE PAGES

Akter, Nusnin; Wang, Mengen; Zhong, Jian-Qiang; ...

2018-01-04

Copper is an important industrial catalyst. The ability to manipulate the oxidation state of copper clusters in a controlled way is critical to understanding structure–reactivity relations of copper catalysts at the molecular level. Experimentally, cupric oxide surfaces or even small domains can only be stabilized at elevated temperatures and in the presence of oxygen, as copper can be easily reduced under reaction conditions. Herein bilayer silica films grown on a metallic substrate are used to trap diluted copper oxide clusters. By combining in situ experiments with first principles calculations, it is found that the confined space created by the silicamore » film leads to an increase in the energy barrier for Cu diffusion. Dispersed copper atoms trapped by the silica film can be easily oxidized by surface oxygen chemisorbed on the metallic substrate, which results in the formation and stabilization of Cu 2+ cations.« less

Increase of electrodeposited catalyst stability via plasma grown vertically oriented graphene nanoparticle movement restriction.

PubMed

Vanrenterghem, Bart; Hodnik, Nejc; Bele, Marjan; Šala, Martin; Amelinckx, Giovanni; Neukermans, Sander; Zaplotnik, Rok; Primc, Gregor; Mozetič, Miran; Breugelmans, Tom

2017-08-17

Beside activity, electrocatalyst stability is gaining in importance. The most common degradation mechanism is the loss of the active surface area due to nanoparticle growth via coalescence/agglomeration. We propose a particle confinement strategy via vertically oriented graphene deposition to overcome degradation of the nanoparticles.

User's manual for the FLORA equilibrium and stability code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freis, R.P.; Cohen, B.I.

1985-04-01

This document provides a user's guide to the content and use of the two-dimensional axisymmetric equilibrium and stability code FLORA. FLORA addresses the low-frequency MHD stability of long-thin axisymmetric tandem mirror systems with finite pressure and finite-larmor-radius effects. FLORA solves an initial-value problem for interchange, rotational, and ballooning stability.

Recent advances in stellarator optimization

DOE PAGES

Gates, D. A.; Boozer, A. H.; Brown, T.; ...

2017-10-27

Computational optimization has revolutionized the field of stellarator design. To date, optimizations have focused primarily on optimization of neoclassical confinement and ideal MHD stability, although limited optimization of other parameters has also been performed. Here, we outline a select set of new concepts for stellarator optimization that, when taken as a group, present a significant step forward in the stellarator concept. One of the criticisms that has been leveled at existing methods of design is the complexity of the resultant field coils. Recently, a new coil optimization code—COILOPT++, which uses a spline instead of a Fourier representation of the coils,—wasmore » written and included in the STELLOPT suite of codes. The advantage of this method is that it allows the addition of real space constraints on the locations of the coils. The code has been tested by generating coil designs for optimized quasi-axisymmetric stellarator plasma configurations of different aspect ratios. As an initial exercise, a constraint that the windings be vertical was placed on large major radius half of the non-planar coils. Further constraints were also imposed that guaranteed that sector blanket modules could be removed from between the coils, enabling a sector maintenance scheme. Results of this exercise will be presented. New ideas on methods for the optimization of turbulent transport have garnered much attention since these methods have led to design concepts that are calculated to have reduced turbulent heat loss. We have explored possibilities for generating an experimental database to test whether the reduction in transport that is predicted is consistent with experimental observations. Thus, a series of equilibria that can be made in the now latent QUASAR experiment have been identified that will test the predicted transport scalings. Fast particle confinement studies aimed at developing a generalized optimization algorithm are also discussed. A new algorithm developed for the design of the scraper element on W7-X is presented along with ideas for automating the optimization approach.« less

Recent advances in stellarator optimization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gates, D. A.; Boozer, A. H.; Brown, T.

Computational optimization has revolutionized the field of stellarator design. To date, optimizations have focused primarily on optimization of neoclassical confinement and ideal MHD stability, although limited optimization of other parameters has also been performed. Here, we outline a select set of new concepts for stellarator optimization that, when taken as a group, present a significant step forward in the stellarator concept. One of the criticisms that has been leveled at existing methods of design is the complexity of the resultant field coils. Recently, a new coil optimization code—COILOPT++, which uses a spline instead of a Fourier representation of the coils,—wasmore » written and included in the STELLOPT suite of codes. The advantage of this method is that it allows the addition of real space constraints on the locations of the coils. The code has been tested by generating coil designs for optimized quasi-axisymmetric stellarator plasma configurations of different aspect ratios. As an initial exercise, a constraint that the windings be vertical was placed on large major radius half of the non-planar coils. Further constraints were also imposed that guaranteed that sector blanket modules could be removed from between the coils, enabling a sector maintenance scheme. Results of this exercise will be presented. New ideas on methods for the optimization of turbulent transport have garnered much attention since these methods have led to design concepts that are calculated to have reduced turbulent heat loss. We have explored possibilities for generating an experimental database to test whether the reduction in transport that is predicted is consistent with experimental observations. Thus, a series of equilibria that can be made in the now latent QUASAR experiment have been identified that will test the predicted transport scalings. Fast particle confinement studies aimed at developing a generalized optimization algorithm are also discussed. A new algorithm developed for the design of the scraper element on W7-X is presented along with ideas for automating the optimization approach.« less

Ionic Liquid Confined in Mesoporous Polymer Membrane with Improved Stability for CO2/N2 Separation

PubMed Central

Tan, Ming; Lu, Jingting; Zhang, Yang; Jiang, Heqing

2017-01-01

Supported ionic liquid membranes (SILMs) have a promising prospect of application in flue gas separation, owing to its high permeability and selectivity of CO2. However, existing SILMs have the disadvantage of poor stability due to the loss of ionic liquid from the large pores of the macroporous support. In this study, a novel SILM with high stability was developed by confining ionic liquid in a mesoporous polymer membrane. First, a mesoporous polymer membrane derived from a soluble, low-molecular-weight phenolic resin precursor was deposited on a porous Al2O3 support, and then 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) was immobilized inside mesopores of phenolic resin, forming the SILM under vacuum. Effects of trans-membrane pressure difference on the SILM separation performance were investigated by measuring the permeances of CO2 and N2. The SILM exhibits a high ideal CO2/N2 selectivity of 40, and an actual selectivity of approximately 25 in a mixed gas (50% CO2 and 50% N2) at a trans-membrane pressure difference of 2.5 bar. Compared to [emim][BF4] supported by polyethersulfone membrane with a pore size of around 0.45 μm, the [emim][BF4] confined in a mesoporous polymer membrane exhibits an improved stability, and its separation performance remained stable for 40 h under a trans-membrane pressure difference of 1.5 bar in a mixed gas before the measurement was intentionally stopped. PMID:28961187

Globally aligned states and hydrodynamic traffic jams in confined suspensions of active asymmetric particles.

PubMed

Lefauve, Adrien; Saintillan, David

2014-02-01

Strongly confined active liquids are subject to unique hydrodynamic interactions due to momentum screening and lubricated friction by the confining walls. Using numerical simulations, we demonstrate that two-dimensional dilute suspensions of fore-aft asymmetric polar swimmers in a Hele-Shaw geometry can exhibit a rich variety of novel phase behaviors depending on particle shape, including coherent polarized density waves with global alignment, persistent counterrotating vortices, density shocks and rarefaction waves. We also explain these phenomena using a linear stability analysis and a nonlinear traffic flow model, both derived from a mean-field kinetic theory.

Combination of cylindrical confinement and spark discharge for signal improvement using laser induced breakdown spectroscopy.

PubMed

Hou, Zongyu; Wang, Zhe; Liu, Jianmin; Ni, Weidou; Li, Zheng

2014-06-02

Spark discharge has been proved to be an effective way to enhance the LIBS signal while moderate cylindrical confinement is able to increase the signal repeatability with limited signal enhancement effects. In the present work, these two methods were combined together not only to improve the pulse-to-pulse signal repeatability but also to simultaneously and significantly enhance the signal as well as SNR. Plasma images showed that the confinement stabilized the morphology of the plasma, especially for the discharge assisted process, which explained the improvement of the signal repeatability.

Determination of broken KAM surfaces for particle orbits in toroidal confinement systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, R. B.

2015-10-05

Here, the destruction of Kolmogorov–Arnold–Moser surfaces in a Hamiltonian system is an important topic in nonlinear dynamics, and in particular in the theory of particle orbits in toroidal magnetic confinement systems. Analytic models for transport due to mode-particle resonances are not sufficiently correct to give the effect of these resonances on transport. In this paper we compare three different methods for the detection of the loss of stability of orbits in the dynamics of charged particles in a toroidal magnetic confinement device in the presence of time dependent magnetic perturbations.

The Role of an Electric Field in the Formation of a Detached Regime in Tokamak Plasma

NASA Astrophysics Data System (ADS)

Senichenkov, I.; Kaveeva, E.; Rozhansky, V.; Sytova, E.; Veselova, I.; Voskoboynikov, S.; Coster, D.

2018-03-01

Modeling of the transition to the detachment of ASDEX Upgrade tokamak plasma with increasing density is performed using the SOLPS-ITER numerical code with a self-consistent account of drifts and currents. Their role in plasma redistribution both in the confinement region and in the scrape-off layer (SOL) is investigated. The mechanism of high field side high-density formation in the SOL in the course of detachment is suggested. In the full detachment regime, when the cold plasma region expands above the X-point and reaches closed magnetic-flux surfaces, plasma perturbation in a confined region may lead to a change in the confinement regime.

Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D [Discovery of stationary operation of quiescent H-mode plasmas with Net-Zero NBI torque and high energy confinement on DIII-D

DOE PAGES

Burrell, Keith H.; Barada, Kshitish; Chen, Xi; ...

2016-03-11

Here, recent experiments in DIII-D have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H 98y2 international tokamak energy confinement scaling (H 98y2=1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggeredmore » in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers ExB rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the ExB shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β N=1.6-1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints. Stationary operation with improved pedestal conditions is highly significant for future burning plasma devices, since operation without ELMs at low rotation and good confinement is key for fusion energy production.« less

Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D [Discovery of stationary operation of quiescent H-mode plasmas with Net-Zero NBI torque and high energy confinement on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burrell, Keith H.; Barada, Kshitish; Chen, Xi

Here, recent experiments in DIII-D have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H 98y2 international tokamak energy confinement scaling (H 98y2=1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggeredmore » in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers ExB rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the ExB shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β N=1.6-1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints. Stationary operation with improved pedestal conditions is highly significant for future burning plasma devices, since operation without ELMs at low rotation and good confinement is key for fusion energy production.« less

Pre-ignition confinement and deflagration violence in LX-10 and PBX 9501

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tringe, J. W., E-mail: tringe2@llnl.gov; Glascoe, E. A.; McClelland, M. A.

In thermal explosions of the nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based explosives LX-10 and PBX-9501, the pre-ignition spatial and temporal heating profile defines the ignition location. The ignition location then determines the extent of inertial confinement and the violence of the resulting deflagration. In this work, we present results of experiments in which ∼23 g cylinders of LX-10 and PBX 9501 in thin-walled aluminum confinement vessels were subjected to identical heating profiles but which presented starkly different energy release signatures. Post-explosion LX-10 containment vessels were completely fragmented, while the PBX 9501 vessels were merely ruptured. Flash x-ray radiography images show that the initiation locationmore » for the LX-10 is a few mm farther from the end caps of the vessel relative to the initiation location of PBX 9501. This difference increases deflagration confinement for LX-10 at the time of ignition and extends the pressurization time during which the deflagration front propagates in the explosive. The variation in the initiation location, in turn, is determined by the thermal boundary conditions, which differ for these two explosives because of the larger coefficient of thermal expansion and greater thermal stability of the Viton binder in LX-10 relative to the estane and bis(2,2-dinitropropyl) acetal/formal binder of the PBX 9501. The thermal profile and initiation location were modeled for LX-10 using the hydrodynamics and structures code ALE3D; results indicate temperatures in the vicinity of the ignition location in excess of 274 °C near the time of ignition. The conductive burn rates for these two explosives, as determined by flash x-ray radiography, are comparable in the range 0.1–0.2 mm/μs, somewhat faster than rates observed by strand burner experiments for explosives in the temperature range 150–180 °C and pressures up to 100 MPa. The thinnest-wall aluminum containment vessels presented here rupture at lower pressures, in the range 10 MPa, suggesting that moderately higher temperatures and pressures are present near the deflagration front. For these explosives, however the most important property for determining deflagration violence is the degree of inertial confinement.« less

Inclusion of pressure and flow in a new 3D MHD equilibrium code

NASA Astrophysics Data System (ADS)

Raburn, Daniel; Fukuyama, Atsushi

2012-10-01

Flow and nonsymmetric effects can play a large role in plasma equilibria and energy confinement. A concept for such a 3D equilibrium code was developed and presented in 2011. The code is called the Kyoto ITerative Equilibrium Solver (KITES) [1], and the concept is based largely on the PIES code [2]. More recently, the work-in-progress KITES code was used to calculate force-free equilibria. Here, progress and results on the inclusion of pressure and flow in the code are presented. [4pt] [1] Daniel Raburn and Atsushi Fukuyama, Plasma and Fusion Research: Regular Articles, 7:240381 (2012).[0pt] [2] H. S. Greenside, A. H. Reiman, and A. Salas, J. Comput. Phys, 81(1):102-136 (1989).

Entropy and the driving force for the filling of carbon nanotubes with water.

PubMed

Pascal, Tod A; Goddard, William A; Jung, Yousung

2011-07-19

The spontaneous filling of hydrophobic carbon nanotubes (CNTs) by water observed both experimentally and from simulations is counterintuitive because confinement is generally expected to decrease both entropy and bonding, and remains largely unexplained. Here we report the entropy, enthalpy, and free energy extracted from molecular dynamics simulations of water confined in CNTs from 0.8 to 2.7-nm diameters. We find for all sizes that water inside the CNTs is more stable than in the bulk, but the nature of the favorable confinement of water changes dramatically with CNT diameter. Thus we find (i) an entropy (both rotational and translational) stabilized, vapor-like phase of water for small CNTs (0.8-1.0 nm), (ii) an enthalpy stabilized, ice-like phase for medium-sized CNTs (1.1-1.2 nm), and (iii) a bulk-like liquid phase for tubes larger than 1.4 nm, stabilized by the increased translational entropy as the waters sample a larger configurational space. Simulations with structureless coarse-grained water models further reveal that the observed free energies and sequence of transitions arise from the tetrahedral structure of liquid water. These results offer a broad theoretical basis for understanding water transport through CNTs and other nanostructures important in nanofluidics, nanofiltrations, and desalination.

Surface Chemistry in Cobalt Phosphide-Stabilized Lithium-Sulfur Batteries.

PubMed

Zhong, Yiren; Yin, Lichang; He, Peng; Liu, Wen; Wu, Zishan; Wang, Hailiang

2018-01-31

Chemistry at the cathode/electrolyte interface plays an important role for lithium-sulfur batteries in which stable cycling of the sulfur cathode requires confinement of the lithium polysulfide intermediates and their fast electrochemical conversion on the electrode surface. While many materials have been found to be effective for confining polysulfides, the underlying chemical interactions remain poorly understood. We report a new and general lithium polysulfide-binding mechanism enabled by surface oxidation layers of transition-metal phosphide and chalcogenide materials. We for the first time find that CoP nanoparticles strongly adsorb polysulfides because their natural oxidation (forming Co-O-P-like species) activates the surface Co sites for binding polysulfides via strong Co-S bonding. With a surface oxidation layer capable of confining polysulfides and an inner core suitable for conducting electrons, the CoP nanoparticles are thus a desirable candidate for stabilizing and improving the performance of sulfur cathodes in lithium-sulfur batteries. We demonstrate that sulfur electrodes that hold a high mass loading of 7 mg cm -2 and a high areal capacity of 5.6 mAh cm -2 can be stably cycled for 200 cycles. We further reveal that this new surface oxidation-induced polysulfide-binding scheme applies to a series of transition-metal phosphide and chalcogenide materials and can explain their stabilizing effects for lithium-sulfur batteries.

Entropy and the driving force for the filling of carbon nanotubes with water

PubMed Central

Pascal, Tod A.; Goddard, William A.; Jung, Yousung

2011-01-01

The spontaneous filling of hydrophobic carbon nanotubes (CNTs) by water observed both experimentally and from simulations is counterintuitive because confinement is generally expected to decrease both entropy and bonding, and remains largely unexplained. Here we report the entropy, enthalpy, and free energy extracted from molecular dynamics simulations of water confined in CNTs from 0.8 to 2.7-nm diameters. We find for all sizes that water inside the CNTs is more stable than in the bulk, but the nature of the favorable confinement of water changes dramatically with CNT diameter. Thus we find (i) an entropy (both rotational and translational) stabilized, vapor-like phase of water for small CNTs (0.8–1.0 nm), (ii) an enthalpy stabilized, ice-like phase for medium-sized CNTs (1.1–1.2 nm), and (iii) a bulk-like liquid phase for tubes larger than 1.4 nm, stabilized by the increased translational entropy as the waters sample a larger configurational space. Simulations with structureless coarse-grained water models further reveal that the observed free energies and sequence of transitions arise from the tetrahedral structure of liquid water. These results offer a broad theoretical basis for understanding water transport through CNTs and other nanostructures important in nanofluidics, nanofiltrations, and desalination. PMID:21709268

Polymer Architecture Effects in Confined Geometry: Molecular Dynamics Simulation Study

NASA Astrophysics Data System (ADS)

Wijesinghe, Sidath; Perahia, Dvora; Grest, Gary

Luminescent rigid polymers confined into nanoparticles, or polydots, are emerging as a promising tool for nano medicine. The constrained architecture of a rigid backbone trapped in nano-dimensions results in photophysics that differs from that of spontaneously assembled rigid polymers. Incorporating ionizable functionalities in the polymers, often required for therapeutics, impacts the polymer conformation in solution. Here we report fully atomistic molecular dynamics simulations on the structure of dialkyl p-phenylene ethynylene confined into polydots. We find that the structure and thermal stability of polydots are sensitive to both the molecular weight n and the carboxylation fraction f. At room temperature , polydots remain confined regardless of n and f . However, as temperature is increased, polydots with lower n or f rearrange whereas polydots with higher n or fremain confined, though no direct clustering of the ionic groups was observed. NSF CHE 1308298 is acknowledged.

Investigation of peeling-ballooning stability prior to transient outbursts accompanying transitions out of H-mode in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldon, David; Boivin, Rejean L.; Groebner, Richard J.

Here, the H-mode transport barrier allows confinement of roughly twice as much energy as in an L-mode plasma. Termination of H-mode necessarily requires release of this energy, and the timescale of that release is of critical importance for the lifetimes of plasma facing components in next step tokamaks such as ITER. H-L transition sequences in modern tokamaks often begin with a transient outburst which appears to be superficially similar to and has sometimes been referred to as a type-I edge localized mode (ELM). Type-I ELMs have been shown to be consistent with ideal peeling ballooning instability and are characterized bymore » significant (up to ~50%) reduction of pedestal height on short (~1 ms) timescales. Knowing whether or not this type of instability is present during H-L back transitions will be important for planning for plasma ramp-down in ITER. This paper presents tests of pre-transition experimental data against ideal peeling-ballooning stability calculations with the ELITE code and supports 2 those results with secondary experiments that together show that the transient associated with the H-L transition is not triggered by the same physics as are type-I ELMs.« less

Investigation of peeling-ballooning stability prior to transient outbursts accompanying transitions out of H-mode in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldon, D., E-mail: deldon@princeton.edu; Princeton University, Princeton, New Jersey 08543; Boivin, R. L.

The H-mode transport barrier allows confinement of roughly twice as much energy as in an L-mode plasma. Termination of H-mode necessarily requires release of this energy, and the timescale of that release is of critical importance for the lifetimes of plasma facing components in next step tokamaks such as ITER. H-L transition sequences in modern tokamaks often begin with a transient outburst which appears to be superficially similar to and has sometimes been referred to as a type-I edge localized mode (ELM). Type-I ELMs have been shown to be consistent with ideal peeling ballooning instability and are characterized by significantmore » (up to ∼50%) reduction of pedestal height on short (∼1 ms) timescales. Knowing whether or not this type of instability is present during H-L back transitions will be important of planning for plasma ramp-down in ITER. This paper presents tests of pre-transition experimental data against ideal peeling-ballooning stability calculations with the ELITE code and supports those results with secondary experiments that together show that the transient associated with the H-L transition is not triggered by the same physics as are type-I ELMs.« less

Investigation of peeling-ballooning stability prior to transient outbursts accompanying transitions out of H-mode in DIII-D

DOE PAGES

Eldon, David; Boivin, Rejean L.; Groebner, Richard J.; ...

2015-05-14

Here, the H-mode transport barrier allows confinement of roughly twice as much energy as in an L-mode plasma. Termination of H-mode necessarily requires release of this energy, and the timescale of that release is of critical importance for the lifetimes of plasma facing components in next step tokamaks such as ITER. H-L transition sequences in modern tokamaks often begin with a transient outburst which appears to be superficially similar to and has sometimes been referred to as a type-I edge localized mode (ELM). Type-I ELMs have been shown to be consistent with ideal peeling ballooning instability and are characterized bymore » significant (up to ~50%) reduction of pedestal height on short (~1 ms) timescales. Knowing whether or not this type of instability is present during H-L back transitions will be important for planning for plasma ramp-down in ITER. This paper presents tests of pre-transition experimental data against ideal peeling-ballooning stability calculations with the ELITE code and supports 2 those results with secondary experiments that together show that the transient associated with the H-L transition is not triggered by the same physics as are type-I ELMs.« less

Cooperative interactions in dense thermal Rb vapour confined in nm-scale cells

NASA Astrophysics Data System (ADS)

Keaveney, James

Gravitational wave detectors are a new class of observatories aiming to detect gravitational waves from cosmic sources. All-reflective interferometer configurations have been proposed for future detectors, replacing transmissive optics with diffractive elements, thereby reducing thermal issues associated with power absorption. However, diffraction gratings introduce additional phase noise, creating more stringent conditions for alignment stability, and further investigations are required into all-reflective interferometers. A suitable mathematical framework using Gaussian modes is required for analysing the alignment stability using diffraction gratings. Such a framework was created, whereby small beam displacements are modelled using a modal technique. It was confirmed that the original modal-based model does not contain the phase changes associated with grating displacements. Experimental tests verified that the phase of a diffracted Gaussian beam is independent of the beam shape. Phase effects were further examined using a rigorous time-domain simulation tool. These findings show that the perceived phase difference is based on an intrinsic change of coordinate system within the modal-based model, and that the extra phase can be added manually to the modal expansion. This thesis provides a well-tested and detailed mathematical framework that can be used to develop simulation codes to model more complex layouts of all-reflective interferometers.

Simulations of Turbulent Momentum and Scalar Transport in Confined Swirling Coaxial Jets

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Liu, Nan-Suey; Moder, Jeffrey P.

2015-01-01

This paper presents the numerical simulations of confined three-dimensional coaxial water jets. The objectives are to validate the newly proposed nonlinear turbulence models of momentum and scalar transport, and to evaluate the newly introduced scalar APDF and DWFDF equation along with its Eulerian implementation in the National Combustion Code(NCC). Simulations conducted include the steady RANS, the unsteady RANS (URANS), and the time-filtered Navier-Stokes (TFNS); both without and with invoking the APDF or DWFDF equation.

Gyroscopic analogy of a rotating stratified flow confined in a tilted spheroid and its implication to stability of a heavy symmetrical top

NASA Astrophysics Data System (ADS)

Fukumoto, Yasuhide; Miyachi, Yuki

2017-11-01

We address the suppression of the gravitational instability of rotating stratified flows in a confined geometry in two ways, continuous and discontinuous stratification. A rotating flow of a stratified fluid confined in an ellipsoid, subject to gravity force, whose velocity and density fields are linear in coordinates, bears an analogy with a mechanical system of finite degrees of freedom, that is, a heavy rigid body. An insight is gained into the mechanism of system rotation for the ability of a lighter fluid of sustaining, on top of it, a heavier fluid when the angular velocity is greater than a critical value. The sleeping top corresponds to such a state. First we show that a rotating stratified flow confined in a tilted spheroid is equivalent to a heavy symmetrical top with the symmetric axis tilted from the top axis. This tilting effect of the symmetric axis on the linear stability of the sleeping top and its bifurcation is investigated in some detail. Second, we explore the incompressible two-layer RTI of a discontinuously stratified fluid confined in the lower-half of an upright spheroid rotating about the axis of symmetry oriented parallel to the vertical direction. The gyroscopic analogy accounts for decrease of the critical rotation rate with oblateness. This work was supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Grant No. 16K05476).

Stability and Structure of Star-Shape Granules

NASA Astrophysics Data System (ADS)

Zhao, Yuchen; Bares, Jonathan; Zheng, Matthew; Dierichs, Karola; Menges, Achim; Behringer, Robert

2015-11-01

Columns are made of convex non-cohesive grains like sand collapse after being released from initial positions. On the other hand, various architectures built by concave grains can maintain stability. We explore why these structures are stable, and how stable they can be. We performed experiments by randomly pouring identical star-shape particles into hollow cylinders left on glass and a rough base, and observed stable granular columns after lifting the cylinders. Particles have six 9 mm arms, which extend symmetrically in the xyz directions. Both the probability of creating a stable column and mechanical stability aspects have been investigated. We define r as the weight fraction of particles that fall out of the column after removing confinement. r gradually increases as the column height increases, or the column diameter decreases. We also explored different experiment conditions such as vibration of columns with confinement, or large basal friction. We also consider different stability measures such as the maximum inclination angle or maximum weight a column can support. In order to understand structure leading to stability, 3D CT scan reconstructions of columns have been done and coordination number and packing density will be discussed. We acknowledge supports from W.M.Keck Foundation and Research Triangle MRSEC.

Effect of α-damage on fission-track annealing in zircon

USGS Publications Warehouse

Kasuya, Masao; Naeser, Charles W.

1988-01-01

The thermal stability of confined fission-track lengths in four zircon samples having different spontaneous track densities (i.e., different amounts of ??-damage) has been studied by one-hour isochronal annealing experiments. The thermal stability of spontaneous track lengths is independent of initial spontaneous track density. The thermal stability of induced track lengths in pre-annealed zircon, however, is significantly higher than that of spontaneous track lengths. The results indicate that the presence of ??-damage lowers the thermal stability of fission-tracks in zircon.

Structural Transitions of Confined Model Proteins: Molecular Dynamics Simulation and Experimental Validation

PubMed Central

Lu, Diannan; Liu, Zheng; Wu, Jianzhong

2006-01-01

Proteins fold in a confined space not only in vivo, i.e., folding assisted by molecular chaperons and chaperonins in a crowded cellular medium, but also in vitro as in production of recombinant proteins. Despite extensive work on protein folding in bulk, little is known about how and to what extent the thermodynamics and kinetics of protein folding are altered by confinement. In this work, we use a Gō-like off-lattice model to investigate the folding and stability of an all β-sheet protein in spherical cages of different sizes and surface hydrophobicity. We find whereas extreme confinement inhibits correct folding, a hydrophilic cage stabilizes the protein due to restriction of the unfolded configurations. In a hydrophobic cage, however, strong attraction from the cage surface destabilizes the confined protein because of competition between self-aggregation and adsorption of hydrophobic residues. We show that the kinetics of protein collapse and folding is strongly correlated with both the cage size and the surface hydrophobicity. It is demonstrated that a cage of moderate size and hydrophobicity optimizes both the folding yield and kinetics of structural transitions. To support the simulation results, we have also investigated the refolding of hen-egg lysozyme in the presence of cetyltrimethylammoniumbromide (CTAB) surfactants that provide an effective confinement of the proteins by micellization. The influence of the surfactant hydrophobicity on the structural and biological activity of the protein is determined with circular dichroism spectrum, fluorescence emission spectrum, and biological activity assay. It is shown that, as predicted by coarse-grained simulations, CTAB micelles facilitate the collapse of denatured lysozyme, whereas the addition of β-cyclodextrin-grafted-PNIPAAm, a weakly hydrophobic stripper, dissociates CTAB micelles and promotes the conformational rearrangement and thereby gives an improved recovery of lysozyme activity. PMID:16461405

Edge-localized mode avoidance and pedestal structure in I-mode plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walk, J. R., E-mail: jrwalk@psfc.mit.edu; Hughes, J. W.; Hubbard, A. E.

I-mode is a high-performance tokamak regime characterized by the formation of a temperature pedestal and enhanced energy confinement, without an accompanying density pedestal or drop in particle and impurity transport. I-mode operation appears to have naturally occurring suppression of large Edge-Localized Modes (ELMs) in addition to its highly favorable scalings of pedestal structure and overall performance. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to themore » structure and ELM stability of I-mode pedestals. Analysis of I-mode discharges prepared with high-resolution pedestal data from the most recent C-Mod campaign reveals favorable pedestal scalings for extrapolation to large machines—pedestal temperature scales strongly with power per particle P{sub net}/n{sup ¯}{sub e}, and likewise pedestal pressure scales as the net heating power (consistent with weak degradation of confinement with heating power). Matched discharges in current, field, and shaping demonstrate the decoupling of energy and particle transport in I-mode, increasing fueling to span nearly a factor of two in density while maintaining matched temperature pedestals with consistent levels of P{sub net}/n{sup ¯}{sub e}. This is consistent with targets for increased performance in I-mode, elevating pedestal β{sub p} and global performance with matched increases in density and heating power. MHD calculations using the ELITE code indicate that I-mode pedestals are strongly stable to edge peeling-ballooning instabilities. Likewise, numerical modeling of the KBM turbulence onset, as well as scalings of the pedestal width with poloidal beta, indicates that I-mode pedestals are not limited by KBM turbulence—both features identified with the trigger for large ELMs, consistent with the observed suppression of large ELMs in I-mode.« less

Improved confinement in highly powered high performance scenarios on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrie, Thomas W.; Osborne, Thomas; Fenstermacher, Max E.

DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q 95 = 6, P IN up to 15 MW, H 98 = 1.4–1.8, and β N = 2.5–4.0. The ion B xmore » $$\\triangledown$$B direction is away from the primary X-point. While plasma conditions at lower to moderate power input (e.g., 11 MW) are shown to be favorable to successful puff-and-pump radiating divertor applications, particularly when using argon seeds, plasma behavior at higher powers (e.g., ≥14 MW) may make successful puff-and-pump operation more problematic. In contrast to lower powered high performance plasmas, both $$\\tau$$ E and β N in the high power cases (≥14 MW) increased and ELM frequency decreased, as density was raised by deuterium gas injection. Improved performance in the higher power plasmas was tied to higher pedestal pressure, which according to peeling-ballooning mode stability analysis using the ELITE code could increase with density along the kink/peeling stability threshold, while the pedestal pressure gradient in the lower power discharges were limited by the ballooning threshold. This resulted in improved fueling efficiency and ≈10% higher $$\\tau$$ E and β N than is normally observed in comparable high performance plasmas on DIII-D. Applying the puff-and-pump radiating divertor approach at moderate versus high power input is shown to result in a much different evolution in core and pedestal plasma behavior. In conclusion, we find that injecting deuterium gas into these highly powered DND plasmas may open up a new avenue for achieving elevated plasma performance, including better fueling, but the resulting higher density may also complicate application of a radiating divertor approach to heat flux reduction in present-day tokamaks, if scenarios involving second-harmonic electron cyclotron heating are used.« less

Improved confinement in highly powered high performance scenarios on DIII-D

DOE PAGES

Petrie, Thomas W.; Osborne, Thomas; Fenstermacher, Max E.; ...

2017-06-09

DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q 95 = 6, P IN up to 15 MW, H 98 = 1.4–1.8, and β N = 2.5–4.0. The ion B xmore » $$\\triangledown$$B direction is away from the primary X-point. While plasma conditions at lower to moderate power input (e.g., 11 MW) are shown to be favorable to successful puff-and-pump radiating divertor applications, particularly when using argon seeds, plasma behavior at higher powers (e.g., ≥14 MW) may make successful puff-and-pump operation more problematic. In contrast to lower powered high performance plasmas, both $$\\tau$$ E and β N in the high power cases (≥14 MW) increased and ELM frequency decreased, as density was raised by deuterium gas injection. Improved performance in the higher power plasmas was tied to higher pedestal pressure, which according to peeling-ballooning mode stability analysis using the ELITE code could increase with density along the kink/peeling stability threshold, while the pedestal pressure gradient in the lower power discharges were limited by the ballooning threshold. This resulted in improved fueling efficiency and ≈10% higher $$\\tau$$ E and β N than is normally observed in comparable high performance plasmas on DIII-D. Applying the puff-and-pump radiating divertor approach at moderate versus high power input is shown to result in a much different evolution in core and pedestal plasma behavior. In conclusion, we find that injecting deuterium gas into these highly powered DND plasmas may open up a new avenue for achieving elevated plasma performance, including better fueling, but the resulting higher density may also complicate application of a radiating divertor approach to heat flux reduction in present-day tokamaks, if scenarios involving second-harmonic electron cyclotron heating are used.« less

Edge-localized mode avoidance and pedestal structure in I-mode plasmasa)

NASA Astrophysics Data System (ADS)

Walk, J. R.; Hughes, J. W.; Hubbard, A. E.; Terry, J. L.; Whyte, D. G.; White, A. E.; Baek, S. G.; Reinke, M. L.; Theiler, C.; Churchill, R. M.; Rice, J. E.; Snyder, P. B.; Osborne, T.; Dominguez, A.; Cziegler, I.

2014-05-01

I-mode is a high-performance tokamak regime characterized by the formation of a temperature pedestal and enhanced energy confinement, without an accompanying density pedestal or drop in particle and impurity transport. I-mode operation appears to have naturally occurring suppression of large Edge-Localized Modes (ELMs) in addition to its highly favorable scalings of pedestal structure and overall performance. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to the structure and ELM stability of I-mode pedestals. Analysis of I-mode discharges prepared with high-resolution pedestal data from the most recent C-Mod campaign reveals favorable pedestal scalings for extrapolation to large machines—pedestal temperature scales strongly with power per particle Pnet/n ¯e, and likewise pedestal pressure scales as the net heating power (consistent with weak degradation of confinement with heating power). Matched discharges in current, field, and shaping demonstrate the decoupling of energy and particle transport in I-mode, increasing fueling to span nearly a factor of two in density while maintaining matched temperature pedestals with consistent levels of Pnet/n ¯e. This is consistent with targets for increased performance in I-mode, elevating pedestal βp and global performance with matched increases in density and heating power. MHD calculations using the ELITE code indicate that I-mode pedestals are strongly stable to edge peeling-ballooning instabilities. Likewise, numerical modeling of the KBM turbulence onset, as well as scalings of the pedestal width with poloidal beta, indicates that I-mode pedestals are not limited by KBM turbulence—both features identified with the trigger for large ELMs, consistent with the observed suppression of large ELMs in I-mode.

PC programs for the prediction of the linear stability behavior of liquid propellant propulsion systems and application to current MSFC rocket engine test programs, volume 1

NASA Technical Reports Server (NTRS)

Doane, George B., III; Armstrong, W. C.

1990-01-01

Research on propulsion stability (chugging and acoustic modes), and propellant valve control was investigated. As part of the activation of the new liquid propulsion test facilities, it is necessary to analyze total propulsion system stability. To accomplish this, several codes were built to run on desktop 386 machines. These codes enable one to analyze the stability question associated with the propellant feed systems. In addition, further work was adapted to this computing environment and furnished along with other codes. This latter inclusion furnishes those interested in high frequency oscillatory combustion behavior (that does not couple to the feed system) a set of codes for study of proposed liquid rocket engines.

Full-f XGC1 gyrokinetic study of improved ion energy confinement from impurity stabilization of ITG turbulence

NASA Astrophysics Data System (ADS)

Kim, Kyuho; Kwon, Jae-Min; Chang, C. S.; Seo, Janghoon; Ku, S.; Choe, W.

2017-06-01

Flux-driven full-f gyrokinetic simulations are performed to study carbon impurity effects on the ion temperature gradient (ITG) turbulence and ion thermal transport in a toroidal geometry. Employing the full-f gyrokinetic code XGC1, both main ions and impurities are evolved self-consistently including turbulence and neoclassical physics. It is found that the carbon impurity profile self-organizes to form an inwardly peaked density profile, which weakens the ITG instabilities and reduces the overall fluctuations and ion thermal transport. A stronger reduction appears in the low frequency components of the fluctuations. The global structure of E × B flow also changes, resulting in the reduction of global avalanche like transport events in the impure plasma. Detailed properties of impurity transport are also studied, and it is revealed that both the inward neoclassical pinch and the outward turbulent transport are equally important in the formation of the steady state impurity profile.

Progress Towards a Rad-Hydro Code for Modern Computing Architectures LA-UR-10-02825

NASA Astrophysics Data System (ADS)

Wohlbier, J. G.; Lowrie, R. B.; Bergen, B.; Calef, M.

2010-11-01

We are entering an era of high performance computing where data movement is the overwhelming bottleneck to scalable performance, as opposed to the speed of floating-point operations per processor. All multi-core hardware paradigms, whether heterogeneous or homogeneous, be it the Cell processor, GPGPU, or multi-core x86, share this common trait. In multi-physics applications such as inertial confinement fusion or astrophysics, one may be solving multi-material hydrodynamics with tabular equation of state data lookups, radiation transport, nuclear reactions, and charged particle transport in a single time cycle. The algorithms are intensely data dependent, e.g., EOS, opacity, nuclear data, and multi-core hardware memory restrictions are forcing code developers to rethink code and algorithm design. For the past two years LANL has been funding a small effort referred to as Multi-Physics on Multi-Core to explore ideas for code design as pertaining to inertial confinement fusion and astrophysics applications. The near term goals of this project are to have a multi-material radiation hydrodynamics capability, with tabular equation of state lookups, on cartesian and curvilinear block structured meshes. In the longer term we plan to add fully implicit multi-group radiation diffusion and material heat conduction, and block structured AMR. We will report on our progress to date.

A high-performance Hg(+) trapped ion frequency standard

NASA Technical Reports Server (NTRS)

Prestage, J. D.; Tjoelker, R. L.; Dick, G. J.; Maleki, L.

1992-01-01

A high-performance frequency standard based on (199)Hg(+) ions confined in a hybrid radio frequency (RF)/dc linear ion trap is demonstrated. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the RF confining fields. A 160-mHz-wide atomic resonance line for the 40.5-GHz clock transition is used to steer the output of a 5-mHz crystal oscillator to obtain a stability of 2 x 10(exp -15) for 24,000-second averaging times. Measurements with a 37-mHz line width for the Hg(+) clock transition demonstrate that the inherent stability for this frequency standard is better than 1 x 10(exp -15) at 10,000-second averaging times.

3D effects on transport and plasma control in the TJ-II stellarator

NASA Astrophysics Data System (ADS)

Castejón, F.; Alegre, D.; Alonso, A.; Alonso, J.; Ascasíbar, E.; Baciero, A.; de Bustos, A.; Baiao, D.; Barcala, J. M.; Blanco, E.; Borchardt, M.; Botija, J.; Cabrera, S.; de la Cal, E.; Calvo, I.; Cappa, A.; Carrasco, R.; Castro, R.; De Castro, A.; Catalán, G.; Chmyga, A. A.; Chamorro, M.; Dinklage, A.; Eliseev, L.; Estrada, T.; Fernández-Marina, F.; Fontdecaba, J. M.; García, L.; García-Cortés, I.; García-Gómez, R.; García-Regaña, J. M.; Guasp, J.; Hatzky, R.; Hernanz, J.; Hernández, J.; Herranz, J.; Hidalgo, C.; Hollmann, E.; Jiménez-Denche, A.; Kirpitchev, I.; Kleiber, R.; Komarov, A. D.; Kozachoek, A. S.; Krupnik, L.; Lapayese, F.; Liniers, M.; Liu, B.; López-Bruna, D.; López-Fraguas, A.; López-Miranda, B.; López-Razola, J.; Losada, U.; de la Luna, E.; Martín de Aguilera, A.; Martín-Díaz, F.; Martínez, M.; Martín-Gómez, G.; Martín-Hernández, F.; Martín-Rojo, A. B.; Martínez-Fernández, J.; McCarthy, K. J.; Medina, F.; Medrano, M.; Melón, L.; Melnikov, A. V.; Méndez, P.; Merino, R.; Miguel, F. J.; van Milligen, B.; Molinero, A.; Momo, B.; Monreal, P.; Moreno, R.; Navarro, M.; Narushima, Y.; Nedzelskiy, I. S.; Ochando, M. A.; Olivares, J.; Oyarzábal, E.; de Pablos, J. L.; Pacios, L.; Panadero, N.; Pastor, I.; Pedrosa, M. A.; de la Peña, A.; Pereira, A.; Petrov, A.; Petrov, S.; Portas, A. B.; Poveda, E.; Rattá, G. A.; Rincón, E.; Ríos, L.; Rodríguez, C.; Rojo, B.; Ros, A.; Sánchez, J.; Sánchez, M.; Sánchez, E.; Sánchez-Sarabia, E.; Sarksian, K.; Satake, S.; Sebastián, J. A.; Silva, C.; Solano, E. R.; Soleto, A.; Sun, B. J.; Tabarés, F. L.; Tafalla, D.; Tallents, S.; Tolkachev, A.; Vega, J.; Velasco, G.; Velasco, J. L.; Wolfers, G.; Yokoyama, M.; Zurro, B.

2017-10-01

The effects of 3D geometry are explored in TJ-II from two relevant points of view: neoclassical transport and modification of stability and dispersion relation of waves. Particle fuelling and impurity transport are studied considering the 3D transport properties, paying attention to both neoclassical transport and other possible mechanisms. The effects of the 3D magnetic topology on stability, confinement and Alfvén Eigenmodes properties are also explored, showing the possibility of controlling Alfvén modes by modifying the configuration; the onset of modes similar to geodesic acoustic modes are driven by fast electrons or fast ions; and the weak effect of magnetic well on confinement. Finally, we show innovative power exhaust scenarios using liquid metals.

Hydrodynamics of confined active fluids.

PubMed

Brotto, Tommaso; Caussin, Jean-Baptiste; Lauga, Eric; Bartolo, Denis

2013-01-18

We theoretically describe the dynamics of swimmer populations in rigidly confined thin liquid films. We first demonstrate that hydrodynamic interactions between confined swimmers depend solely on their shape and are independent of their specific swimming mechanism. We also show that, due to friction with the nearby rigid walls, confined swimmers do not just reorient in flow gradients but also in uniform flows. We then quantify the consequences of these microscopic interaction rules on the large-scale hydrodynamics of isotropic populations. We investigate in detail their stability and the resulting phase behavior, highlighting the differences with conventional active, three-dimensional suspensions. Two classes of polar swimmers are distinguished depending on their geometrical polarity. The first class gives rise to coherent directed motion at all scales, whereas for the second class we predict the spontaneous formation of coherent clusters (swarms).

Linear complexions: Confined chemical and structural states at dislocations

NASA Astrophysics Data System (ADS)

Kuzmina, M.; Herbig, M.; Ponge, D.; Sandlöbes, S.; Raabe, D.

2015-09-01

For 5000 years, metals have been mankind’s most essential materials owing to their ductility and strength. Linear defects called dislocations carry atomic shear steps, enabling their formability. We report chemical and structural states confined at dislocations. In a body-centered cubic Fe-9 atomic percent Mn alloy, we found Mn segregation at dislocation cores during heating, followed by formation of face-centered cubic regions but no further growth. The regions are in equilibrium with the matrix and remain confined to the dislocation cores with coherent interfaces. The phenomenon resembles interface-stabilized structural states called complexions. A cubic meter of strained alloy contains up to a light year of dislocation length, suggesting that linear complexions could provide opportunities to nanostructure alloys via segregation and confined structural states.

Quantifying Fusion Born Ion Populations in Magnetically Confined Plasmas using Ion Cyclotron Emission

DOE PAGES

Carbajal, L.; Warwick Univ., Coventry; Dendy, R. O.; ...

2017-03-07

Ion cyclotron emission (ICE) offers unique promise as a diagnostic of the fusion born alpha-particle population in magnetically confined plasmas. Pioneering observations from JET and TFTR found that ICE intensity P ICE scales approximately linearly with the measured neutron flux from fusion reactions, and with the inferred concentration, n /n i , of fusion-born alpha-particles confined within the plasma. We present fully nonlinear self-consistent kinetic simulations that reproduce this scaling for the first time. This resolves a longstanding question in the physics of fusion alpha particle confinement and stability in MCF plasmas. It confirms the MCI as the likely emissionmore » mechanism and greatly strengthens the basis for diagnostic exploitation of ICE in future burning plasmas.« less

Tearing Mode Stability of Evolving Toroidal Equilibria

NASA Astrophysics Data System (ADS)

Pletzer, A.; McCune, D.; Manickam, J.; Jardin, S. C.

2000-10-01

There are a number of toroidal equilibrium (such as JSOLVER, ESC, EFIT, and VMEC) and transport codes (such as TRANSP, BALDUR, and TSC) in our community that utilize differing equilibrium representations. There are also many heating and current drive (LSC and TORRAY), and stability (PEST1-3, GATO, NOVA, MARS, DCON, M3D) codes that require this equilibrium information. In an effort to provide seamless compatibility between the codes that produce and need these equilibria, we have developed two Fortran 90 modules, MEQ and XPLASMA, that serve as common interfaces between these two classes of codes. XPLASMA provides a common equilibrium representation for the heating and current drive applications while MEQ provides common equilibrium and associated metric information needed by MHD stability codes. We illustrate the utility of this approach by presenting results of PEST-3 tearing stability calculations of an NSTX discharge performed on profiles provided by the TRANSP code. Using the MEQ module, the TRANSP equilibrium data are stored in a Fortran 90 derived type and passed to PEST3 as a subroutine argument. All calculations are performed on the fly, as the profiles evolve.

Connections Underlying Translation and mRNA Stability.

PubMed

Radhakrishnan, Aditya; Green, Rachel

2016-09-11

Gene expression and regulation in organisms minimally depends on transcription by RNA polymerase and on the stability of the RNA product (for both coding and non-coding RNAs). For coding RNAs, gene expression is further influenced by the amount of translation by the ribosome and by the stability of the protein product. The stabilities of these two classes of RNA, non-coding and coding, vary considerably: tRNAs and rRNAs tend to be long lived while mRNAs tend to be more short lived. Even among mRNAs, however, there is a considerable range in stability (ranging from seconds to hours in bacteria and up to days in metazoans), suggesting a significant role for stability in the regulation of gene expression. Here, we review recent experiments from bacteria, yeast and metazoans indicating that the stability of most mRNAs is broadly impacted by the actions of ribosomes that translate them. Ribosomal recognition of defective mRNAs triggers "mRNA surveillance" pathways that target the mRNA for degradation [Shoemaker and Green (2012) ]. More generally, even the stability of perfectly functional mRNAs appears to be dictated by overall rates of translation by the ribosome [Herrick et al. (1990), Presnyak et al. (2015) ]. Given that mRNAs are synthesized for the purpose of being translated into proteins, it is reassuring that such intimate connections between mRNA and the ribosome can drive biological regulation. In closing, we consider the likelihood that these connections between protein synthesis and mRNA stability are widespread or whether other modes of regulation dominate the mRNA stability landscape in higher organisms. Copyright © 2016. Published by Elsevier Ltd.

VERTPAK1. Code Verification Analytic Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golis, M.J.

1983-04-01

VERTPAK1 is a package of analytical solutions used in verification of numerical codes that simulate fluid flow, rock deformation, and solute transport in fractured and unfractured porous media. VERTPAK1 contains the following: BAREN, an analytical solution developed by Barenblatt, Zhelton and Kochina (1960) for describing transient flow to a well penetrating a (double porosity) confined aquifer; GIBMAC, an analytical solution developed by McNamee and Gibson (1960) for describing consolidation of a semi-infinite soil medium subject to a strip (plane strain) or cylindrical (axisymmetric) loading; GRINRH, an analytical solution developed by Gringarten (1971) for describing transient flow to a partially penetratingmore » well in a confined aquifer containing a single horizontal fracture; GRINRV, an analytical solution developed by Gringarten, Ramey, and Raghavan (1974) for describing transient flow to a fully penetrating well in a confined aquifer containing a single vertical fracture; HART, an analytical solution given by Nowacki (1962) and implemented by HART (1981) for describing the elastic behavior of an infinite solid subject to a line heat source; LESTER, an analytical solution presented by Lester, Jansen, and Burkholder (1975) for describing one-dimensional transport of radionuclide chains through an adsorbing medium; STRELT, an analytical solution presented by Streltsova-Adams (1978) for describing transient flow to a fully penetrating well in a (double porosity) confined aquifer; and TANG, an analytical solution developed by Tang, Frind, and Sudicky (1981) for describing solute transport in a porous medium containing a single fracture.« less

Cobalt-doped ZnO nanocrystals: quantum confinement and surface effects from ab initio methods.

PubMed

Schoenhalz, Aline L; Dalpian, Gustavo M

2013-10-14

Cobalt-doped ZnO nanocrystals were studied through ab initio methods based on the Density Functional Theory. Both quantum confinement and surface effects were explicitly taken into account. When only quantum confinement effects are considered, Co atoms interact through a superexchange mechanism, stabilizing an antiferromagnetic ground state. Usually, this is the case for high quality nanoparticles with perfect surface saturation. When the surfaces were considered, a strong hybridization between the Co atoms and surfaces was observed, strongly changing their electronic and magnetic properties. Our results indicated that the surfaces might qualitatively change the properties of impurities in semiconductor nanocrystals.

Observation of the hot electron interchange instability in a high beta dipolar confined plasma

NASA Astrophysics Data System (ADS)

Ortiz, Eugenio Enrique

In this thesis the first study of the high beta, hot electron interchange (HEI) instability in a laboratory, dipolar confined plasma is presented. The Levitated Dipole Experiment (LDX) is a new research facility that explores the confinement and stability of plasma created within the dipole field produced by a strong superconducting magnet. In initial experiments long-pulse, quasi-steady state microwave discharges lasting more than 10 sec have been produced with equilibria having peak beta values of 20%. Creation of high-pressure, high beta plasma is possible only when intense HEI instabilities are stabilized by sufficiently high background plasma density. LDX plasma exist within one of three regimes characterized by its response to heating and fueling. The observed HEI instability depends on the regime and can take one of three forms: as quasiperiodic bursts during the low density, low beta plasma regime, as local high beta relaxation events in the high beta plasma regime, and as global, intense energy relaxation bursts, both in the high beta and afterglow plasma regimes. Measurements of the HEI instability are made using high-impedance, floating potential probes and fast Mirnov coils. Analysis of these signals reveals the extent of the transport during high beta plasmas. During intense high beta HEI instabilities, fluctuations at the edge significantly exceed the magnitude of the equilibrium field generated by the high beta electrons and energetic electron confinement ends in under 100 musec. For heated plasmas, one of the consequences of the observed high beta transport is the presence of hysteresis in the neutral gas fueling required to stabilize and maintain the high beta plasma. Finally, a nonlinear, self-consistent numerical simulation of the growth and saturation of the HEI instability has been adapted for LDX and compared to experimental observations.

Reformulations of the Yang-Mills theory toward quark confinement and mass gap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kondo, Kei-Ichi; Shinohara, Toru; Kato, Seikou

2016-01-22

We propose the reformulations of the SU (N) Yang-Mills theory toward quark confinement and mass gap. In fact, we have given a new framework for reformulating the SU (N) Yang-Mills theory using new field variables. This includes the preceding works given by Cho, Faddeev and Niemi, as a special case called the maximal option in our reformulations. The advantage of our reformulations is that the original non-Abelian gauge field variables can be changed into the new field variables such that one of them called the restricted field gives the dominant contribution to quark confinement in the gauge-independent way. Our reformulationsmore » can be combined with the SU (N) extension of the Diakonov-Petrov version of the non-Abelian Stokes theorem for the Wilson loop operator to give a gauge-invariant definition for the magnetic monopole in the SU (N) Yang-Mills theory without the scalar field. In the so-called minimal option, especially, the restricted field is non-Abelian and involves the non-Abelian magnetic monopole with the stability group U (N− 1). This suggests the non-Abelian dual superconductivity picture for quark confinement. This should be compared with the maximal option: the restricted field is Abelian and involves only the Abelian magnetic monopoles with the stability group U(1){sup N−1}, just like the Abelian projection. We give some applications of this reformulation, e.g., the stability for the homogeneous chromomagnetic condensation of the Savvidy type, the large N treatment for deriving the dimensional transmutation and understanding the mass gap, and also the numerical simulations on a lattice which are given by Dr. Shibata in a subsequent talk.« less

Reformulations of the Yang-Mills theory toward quark confinement and mass gap

NASA Astrophysics Data System (ADS)

Kondo, Kei-Ichi; Kato, Seikou; Shibata, Akihiro; Shinohara, Toru

2016-01-01

We propose the reformulations of the SU (N) Yang-Mills theory toward quark confinement and mass gap. In fact, we have given a new framework for reformulating the SU (N) Yang-Mills theory using new field variables. This includes the preceding works given by Cho, Faddeev and Niemi, as a special case called the maximal option in our reformulations. The advantage of our reformulations is that the original non-Abelian gauge field variables can be changed into the new field variables such that one of them called the restricted field gives the dominant contribution to quark confinement in the gauge-independent way. Our reformulations can be combined with the SU (N) extension of the Diakonov-Petrov version of the non-Abelian Stokes theorem for the Wilson loop operator to give a gauge-invariant definition for the magnetic monopole in the SU (N) Yang-Mills theory without the scalar field. In the so-called minimal option, especially, the restricted field is non-Abelian and involves the non-Abelian magnetic monopole with the stability group U (N- 1). This suggests the non-Abelian dual superconductivity picture for quark confinement. This should be compared with the maximal option: the restricted field is Abelian and involves only the Abelian magnetic monopoles with the stability group U(1)N-1, just like the Abelian projection. We give some applications of this reformulation, e.g., the stability for the homogeneous chromomagnetic condensation of the Savvidy type, the large N treatment for deriving the dimensional transmutation and understanding the mass gap, and also the numerical simulations on a lattice which are given by Dr. Shibata in a subsequent talk.

A novel "signal-on/off" sensing platform for selective detection of thrombin based on target-induced ratiometric electrochemical biosensing and bio-bar-coded nanoprobe amplification strategy.

PubMed

Wang, Lanlan; Ma, Rongna; Jiang, Liushan; Jia, Liping; Jia, Wenli; Wang, Huaisheng

2017-06-15

A novel dual-signal ratiometric electrochemical aptasensor for highly sensitive and selective detection of thrombin has been designed on the basis of signal-on and signal-off strategy. Ferrocene labeled hairpin probe (Fc-HP), thrombin aptamer and methyl blue labeled bio-bar-coded AuNPs (MB-P3-AuNPs) were rationally introduced for the construction of the assay platform, which combined the advantages of the recognition of aptamer, the amplification of bio-bar-coded nanoprobe, and the ratiometric signaling readout. In the presence of thrombin, the interaction between thrombin and the aptamer leads to the departure of MB-P3-AuNPs from the sensing interface, and the conformation of the single stranded Fc-HP to a hairpin structure to take the Fc confined near the electrode surface. Such conformational changes resulted in the oxidation current of Fc increased and that of MB decreased. Therefore, the recognition event of the target can be dual-signal ratiometric electrochemical readout in both the "signal-off" of MB and the "signal-on" of Fc. The proposed strategy showed a wide linear detection range from 0.003 to 30nM with a detection limit of 1.1 pM. Moreover, it exhibits good performance of excellent selectivity, good stability, and acceptable fabrication reproducibility. By changing the recognition probe, this protocol could be easily expanded into the detection of other targets, showing promising potential applications in disease diagnostics and bioanalysis. Copyright © 2016. Published by Elsevier B.V.

Transport and stability analyses supporting disruption prediction in high beta KSTAR plasmas

NASA Astrophysics Data System (ADS)

Ahn, J.-H.; Sabbagh, S. A.; Park, Y. S.; Berkery, J. W.; Jiang, Y.; Riquezes, J.; Lee, H. H.; Terzolo, L.; Scott, S. D.; Wang, Z.; Glasser, A. H.

2017-10-01

KSTAR plasmas have reached high stability parameters in dedicated experiments, with normalized beta βN exceeding 4.3 at relatively low plasma internal inductance li (βN/li>6). Transport and stability analyses have begun on these plasmas to best understand a disruption-free path toward the design target of βN = 5 while aiming to maximize the non-inductive fraction of these plasmas. Initial analysis using the TRANSP code indicates that the non-inductive current fraction in these plasmas has exceeded 50 percent. The advent of KSTAR kinetic equilibrium reconstructions now allows more accurate computation of the MHD stability of these plasmas. Attention is placed on code validation of mode stability using the PEST-3 and resistive DCON codes. Initial evaluation of these analyses for disruption prediction is made using the disruption event characterization and forecasting (DECAF) code. The present global mode kinetic stability model in DECAF developed for low aspect ratio plasmas is evaluated to determine modifications required for successful disruption prediction of KSTAR plasmas. Work supported by U.S. DoE under contract DE-SC0016614.

Numerical Studies of Impurities in Fusion Plasmas

DOE R&D Accomplishments Database

Hulse, R. A.

1982-09-01

The coupled partial differential equations used to describe the behavior of impurity ions in magnetically confined controlled fusion plasmas require numerical solution for cases of practical interest. Computer codes developed for impurity modeling at the Princeton Plasma Physics Laboratory are used as examples of the types of codes employed for this purpose. These codes solve for the impurity ionization state densities and associated radiation rates using atomic physics appropriate for these low-density, high-temperature plasmas. The simpler codes solve local equations in zero spatial dimensions while more complex cases require codes which explicitly include transport of the impurity ions simultaneously with the atomic processes of ionization and recombination. Typical applications are discussed and computational results are presented for selected cases of interest.

Development of Tokamak Transport Solvers for Stiff Confinement Systems

NASA Astrophysics Data System (ADS)

St. John, H. E.; Lao, L. L.; Murakami, M.; Park, J. M.

2006-10-01

Leading transport models such as GLF23 [1] and MM95 [2] describe turbulent plasma energy, momentum and particle flows. In order to accommodate existing transport codes and associated solution methods effective diffusivities have to be derived from these turbulent flow models. This can cause significant problems in predicting unique solutions. We have developed a parallel transport code solver, GCNMP, that can accommodate both flow based and diffusivity based confinement models by solving the discretized nonlinear equations using modern Newton, trust region, steepest descent and homotopy methods. We present our latest development efforts, including multiple dynamic grids, application of two-level parallel schemes, and operator splitting techniques that allow us to combine flow based and diffusivity based models in tokamk simulations. 6pt [1] R.E. Waltz, et al., Phys. Plasmas 4, 7 (1997). [2] G. Bateman, et al., Phys. Plasmas 5, 1793 (1998).

Locality-preserving logical operators in topological stabilizer codes

NASA Astrophysics Data System (ADS)

Webster, Paul; Bartlett, Stephen D.

2018-01-01

Locality-preserving logical operators in topological codes are naturally fault tolerant, since they preserve the correctability of local errors. Using a correspondence between such operators and gapped domain walls, we describe a procedure for finding all locality-preserving logical operators admitted by a large and important class of topological stabilizer codes. In particular, we focus on those equivalent to a stack of a finite number of surface codes of any spatial dimension, where our procedure fully specifies the group of locality-preserving logical operators. We also present examples of how our procedure applies to codes with different boundary conditions, including color codes and toric codes, as well as more general codes such as Abelian quantum double models and codes with fermionic excitations in more than two dimensions.

Langley Stability and Transition Analysis Code (LASTRAC) Version 1.2 User Manual

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan

2004-01-01

LASTRAC is a general-purposed, physics-based transition prediction code released by NASA for Laminar Flow Control studies and transition research. The design and development of the LASTRAC code is aimed at providing an engineering tool that is easy to use and yet capable of dealing with a broad range of transition related issues. It was written from scratch based on the state-of-the-art numerical methods for stability analysis and modern software technologies. At low fidelity, it allows users to perform linear stability analysis and N-factor transition correlation for a broad range of flow regimes and configurations by using either the linear stability theory or linear parabolized stability equations method. At high fidelity, users may use nonlinear PSE to track finite-amplitude disturbances until the skin friction rise. This document describes the governing equations, numerical methods, code development, detailed description of input/output parameters, and case studies for the current release of LASTRAC.

Confining metal-halide perovskites in nanoporous thin films

PubMed Central

Demchyshyn, Stepan; Roemer, Janina Melanie; Groiß, Heiko; Heilbrunner, Herwig; Ulbricht, Christoph; Apaydin, Dogukan; Böhm, Anton; Rütt, Uta; Bertram, Florian; Hesser, Günter; Scharber, Markus Clark; Sariciftci, Niyazi Serdar; Nickel, Bert; Bauer, Siegfried; Głowacki, Eric Daniel; Kaltenbrunner, Martin

2017-01-01

Controlling the size and shape of semiconducting nanocrystals advances nanoelectronics and photonics. Quantum-confined, inexpensive, solution-derived metal halide perovskites offer narrowband, color-pure emitters as integral parts of next-generation displays and optoelectronic devices. We use nanoporous silicon and alumina thin films as templates for the growth of perovskite nanocrystallites directly within device-relevant architectures without the use of colloidal stabilization. We find significantly blue-shifted photoluminescence emission by reducing the pore size; normally infrared-emitting materials become visibly red, and green-emitting materials become cyan and blue. Confining perovskite nanocrystals within porous oxide thin films drastically increases photoluminescence stability because the templates auspiciously serve as encapsulation. We quantify the template-induced size of the perovskite crystals in nanoporous silicon with microfocus high-energy x-ray depth profiling in transmission geometry, verifying the growth of perovskite nanocrystals throughout the entire thickness of the nanoporous films. Low-voltage electroluminescent diodes with narrow, blue-shifted emission fabricated from nanocrystalline perovskites grown in embedded nanoporous alumina thin films substantiate our general concept for next-generation photonic devices. PMID:28798959

FLORA

DOE Office of Scientific and Technical Information (OSTI.GOV)

1985-04-01

FLORA solves, in a 2D domain for the linearized stability of a long-thin (paraxial)axisymmetric equilibrium. This is of interest for determining the magnetohydrodynamic stability of a magnetic mirror plasma confinement system including finite-Larmor radius and rotation effects. An axisymmetric plasma equilibrium is specified by providing pressure profiles, the plasma mass density, the vacuum magnetic fields, and plasma electric potential as functions of (?).

STABILIZED PINCH MACHINE

DOEpatents

Anderson, O.A.

1962-04-24

A device for heating and confining a high temperature gas or plasma utilizing the linear pinch effect is described. The pinch discharge produced is the form of an elongated cylinder. The electrical discharge current is returned in parallel along an axial and a concentric conductor whereby the magnetic field of the conductors compresses and stabilizes the pinch discharge against lateral instability. (AEC)

Communication: Relationship between local structure and the stability of water in hydrophobic confinement

NASA Astrophysics Data System (ADS)

Altabet, Y. Elia; Debenedetti, Pablo G.

2017-12-01

Liquid water confined between nanoscale hydrophobic objects can become metastable with respect to its vapor at nanoscale separations. While the separations are only several molecular diameters, macroscopic theories are often invoked to interpret the thermodynamics and kinetics of water under confinement. We perform detailed rate and free energy calculations via molecular simulations in order to assess the dependence of the rate of evaporation, free energy barriers, and free energy differences between confined liquid and vapor upon object separation and compare them to the relevant macroscopic theories. At small enough separations, the rate of evaporation appears to deviate significantly from the predictions of classical nucleation theory, and we attribute such deviations to changes in the structure of the confined liquid film. However, the free energy difference between the confined liquid and vapor phases agrees quantitatively with macroscopic theory, and the free energy barrier to condensation displays qualitative agreement. Overall, the present work suggests that theories attempting to capture the kinetic behavior of nanoscale systems should incorporate structural details rather than treating it as a continuum.

Receptor dimer stabilization by hierarchical plasma membrane microcompartments regulates cytokine signaling

PubMed Central

You, Changjiang; Marquez-Lago, Tatiana T.; Richter, Christian Paolo; Wilmes, Stephan; Moraga, Ignacio; Garcia, K. Christopher; Leier, André; Piehler, Jacob

2016-01-01

The interaction dynamics of signaling complexes is emerging as a key determinant that regulates the specificity of cellular responses. We present a combined experimental and computational study that quantifies the consequences of plasma membrane microcompartmentalization for the dynamics of type I interferon receptor complexes. By using long-term dual-color quantum dot (QD) tracking, we found that the lifetime of individual ligand-induced receptor heterodimers depends on the integrity of the membrane skeleton (MSK), which also proved important for efficient downstream signaling. By pair correlation tracking and localization microscopy as well as by fast QD tracking, we identified a secondary confinement within ~300-nm-sized zones. A quantitative spatial stochastic diffusion-reaction model, entirely parameterized on the basis of experimental data, predicts that transient receptor confinement by the MSK meshwork allows for rapid reassociation of dissociated receptor dimers. Moreover, the experimentally observed apparent stabilization of receptor dimers in the plasma membrane was reproduced by simulations of a refined, hierarchical compartment model. Our simulations further revealed that the two-dimensional association rate constant is a key parameter for controlling the extent of MSK-mediated stabilization of protein complexes, thus ensuring the specificity of this effect. Together, experimental evidence and simulations support the hypothesis that passive receptor confinement by MSK-based microcompartmentalization promotes maintenance of signaling complexes in the plasma membrane. PMID:27957535

Function, structure, and stability of enzymes confined in agarose gels.

PubMed

Kunkel, Jeffrey; Asuri, Prashanth

2014-01-01

Research over the past few decades has attempted to answer how proteins behave in molecularly confined or crowded environments when compared to dilute buffer solutions. This information is vital to understanding in vivo protein behavior, as the average spacing between macromolecules in the cell cytosol is much smaller than the size of the macromolecules themselves. In our study, we attempt to address this question using three structurally and functionally different model enzymes encapsulated in agarose gels of different porosities. Our studies reveal that under standard buffer conditions, the initial reaction rates of the agarose-encapsulated enzymes are lower than that of the solution phase enzymes. However, the encapsulated enzymes retain a higher percentage of their activity in the presence of denaturants. Moreover, the concentration of agarose used for encapsulation had a significant effect on the enzyme functional stability; enzymes encapsulated in higher percentages of agarose were more stable than the enzymes encapsulated in lower percentages of agarose. Similar results were observed through structural measurements of enzyme denaturation using an 8-anilinonaphthalene-1-sulfonic acid fluorescence assay. Our work demonstrates the utility of hydrogels to study protein behavior in highly confined environments similar to those present in vivo; furthermore, the enhanced stability of gel-encapsulated enzymes may find use in the delivery of therapeutic proteins, as well as the design of novel strategies for biohybrid medical devices.

Alpha particle confinement in tandem mirrors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devoto, R.S.; Ohnishi, M.; Kerns, J.

1980-10-10

Mechanisms leading to loss of alpha particles from non-axisymmetric tandem mirrors are considered. Stochastic diffusion due to bounce-drift resonances, which can cause rapid radial losses of high-energy alpha particles, can be suppressed by imposing a 20% rise in axisymmetric fields before the quadrupole transition sections. Alpha particles should then be well-confined until thermal energies when they enter the resonant plateau require. A fast code for computation of drift behavior in reactors is described. Sample calculations are presented for resonant particles in a proposed coil set for the Tandem Mirror Next Step.

The effect of α-damage on fission-track annealing in zircon

USGS Publications Warehouse

Kasuya, M.; Naeser, C.W.

1988-01-01

The thermal stability of confined fission-track lengths in four zircon samples having different spontaneous track densities (i.e. different amounts of ??-damage) has been studied by one hour isochronal annealing experiments. The thermal stability of spontaneous track lengths is independent of initial spontaneous track density. The thermal stability of induced track lengths in pre-annealed zircon, however, is significantly higher than that of spontaneous track lengths. The results indicate that the presence of ??-damage lowers the thermal stability of fission-tracks in zircon. ?? 1988.

Linear complexions: Confined chemical and structural states at dislocations.

PubMed

Kuzmina, M; Herbig, M; Ponge, D; Sandlöbes, S; Raabe, D

2015-09-04

For 5000 years, metals have been mankind's most essential materials owing to their ductility and strength. Linear defects called dislocations carry atomic shear steps, enabling their formability. We report chemical and structural states confined at dislocations. In a body-centered cubic Fe-9 atomic percent Mn alloy, we found Mn segregation at dislocation cores during heating, followed by formation of face-centered cubic regions but no further growth. The regions are in equilibrium with the matrix and remain confined to the dislocation cores with coherent interfaces. The phenomenon resembles interface-stabilized structural states called complexions. A cubic meter of strained alloy contains up to a light year of dislocation length, suggesting that linear complexions could provide opportunities to nanostructure alloys via segregation and confined structural states. Copyright © 2015, American Association for the Advancement of Science.

Vulnerabilities in Bytecode Removed by Analysis, Nuanced Confinement and Diversification (VIBRANCE)

DTIC Science & Technology

2015-06-01

VIBRANCE tool starts with a vulnerable Java application and automatically hardens it against SQL injection, OS command injection, file path traversal...7 2.2 Java Front End...7 2.2.2 Java Byte Code Parser

Ray tracing through a hexahedral mesh in HADES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henderson, G L; Aufderheide, M B

In this paper we describe a new ray tracing method targeted for inclusion in HADES. The algorithm tracks rays through three-dimensional tetrakis hexahedral mesh objects, like those used by the ARES code to model inertial confinement experiments.

Dipole configuration for confinement of positrons and electron-positron plasma

NASA Astrophysics Data System (ADS)

Stenson, E. V.; Saitoh, H.; Horn-Stanja, J.; Hergenhahn, U.; Paschkowski, N.; Sunn Pedersen, T.; Stoneking, M. R.; Dickmann, M.; Singer, M.; Vohburger, S.; Hugenschmidt, C.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.

2016-10-01

Laboratory creation and confinement of electron-positron plasmas, which are expected to exhibit atypical plasma physics characteristics, would enable tests of many theory and simulation predictions (e.g., the stabilization of anomalous transport mechanisms). This is the goal of APEX/PAX (A Positron-Electron eXperiment/Positron Accumulation eXperiment). Following demonstration of efficient (38%) E ×B injection and subsequent confinement (τ = 3-5 ms) of cold positrons in a dipole magnetic field, the system is undergoing upgrades from a supported permanent magnet to a supported HTSC (high-temperature superconductor) coil, then to a levitated HTSC coil suitable for the simultaneous confinement of electrons and positrons. This contribution will report on the design and testing of the new systems and subsystems (e.g., for cooling, excitation, and levitation) and, if available, on results of upcoming experiments using a ``rotating wall'' to generate inward particle flux deeper into the confinement region. on behalf of the APEX/PAX team and collaborators.

Pore Diameter Dependence and Segmental Dynamics of Poly-Z-L-lysine and Poly-L-alanine Confined in 1D Nanocylindrical Geometry

NASA Astrophysics Data System (ADS)

Tuncel, Eylul; Suzuki, Yasuhito; Iossifidis, Agathaggelos; Steinhart, Martin; Butt, Hans-Jurgen; Floudas, George; Duran, Hatice

Structure formation, thermodynamic stability, phase and dynamic behaviors of polypeptides are strongly affected by confinement. Since understanding the changes in these behaviors will allow their rational design as functional devices with tunable properties, herein we investigated Poly-Z-L-lysine (PZLL) and Poly-L-alanine (PAla) homopolypeptides confined in nanoporous alumina containing aligned cylindrical nanopores as a function of pore size by differential scanning calorimetry (DSC), Fourier Transform Infrared Spectroscopy, Solid-state NMR, X-ray diffraction, Dielectric spectroscopy(DS). Bulk PZLL exhibits a glass transition temperature (Tg) at about 301K while PZLL nanorods showed slightly lower Tg (294K). The dynamic investigation by DS also revealed a decrease (4K) in Tg between bulk and PZLL nanorods. DS is a very sensitive probe of the local and global secondary structure relaxation through the large dipole to study effect of confinement. The results revealed that the local segmental dynamics, associated with broken hydrogen bonds, and segmental dynamics speed-up on confinement.

Divergent evolution of part of the involucrin gene in the hominoids: Unique intragenic duplications in the gorilla and human

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teumer, J.; Green, H.

1989-02-01

The gene for involucrin, an epidermal protein, has been remodeled in the higher primates. Most of the coding region of the human gene consists of a modern segment of repeats derived from a 10-codon sequence present in the ancestral segment of the gene. The modern segment can be divided into early, middle, and late regions. The authors report here the nucleotide sequence of three alleles of the gorilla involucrin gene. Each possesses a modern segment homologous to that of the human and consisting of 10-codon repeats. The early and middle regions are similar to the corresponding regions of the humanmore » allele and are nearly identical among the different gorilla alleles. The late region consists of recent duplications whose pattern is unique in each of the gorilla alleles and in the human allele. The early region is located in what is now the 3{prime} third of the modern segment, and the late, polymorphic region is located in what is now the 5{prime} third. Therefore, as the modern segment expanded during evolution, its 3{prime} end became stabilized, and continuing duplications became confined to its 5{prime} end. The expansion of the involucrin coding region, which began long before the separation of the gorilla and human, has continued in both species after their separation.« less

Surfactant-thermal method to synthesize a new Zn(II)-trimesic MOF with confined Ru(bpy){sub 3}{sup 2+} complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Hui; Gao, Junkuo, E-mail: jkgao@zstu.edu.cn; Wang, Jiangpeng

2015-03-15

A surfactant-thermal method was used to prepare a new zinc-1,3,5-benzentricarboxylate-based metal-organic framework (ZJU-100) with confined Ru(bpy){sub 3}{sup 2+} (RuBpy) complex by using surfactant PEG 400 as reaction medium. The RuBpy molecules were encapsulated between the 2-D sheets in ZJU-100. ZJU-100 showed bathochromic shift in the steady-state emission spectrum and increased emission lifetimes relative to RuBpy molecules. The extended lifetime is attributed to the reduced nonradiative decay rate due to the stabilization of RuBpy within the rigid MOF framework. These results represent the first example of MOF with confined complex synthesized by surfactant, indicating that the surfactant-thermal method could offer excitingmore » opportunities for preparing new MOFs host/guest materials with novel structures and interesting luminescent properties. - Graphical abstract: A surfactant-thermal method was used to prepare a new zinc-1,3,5-benzentricarboxylate-based metal-organic framework (ZJU-100) with confined Ru(bpy){sub 3}{sup 2+} (RuBpy) complex by using surfactant PEG 400 as reaction medium. - Highlights: • Surfactant-thermal synthesis of crystalline metal-organic framework host/guest materials. • RuBpy molecules were encapsulated between the 2-D sheets of MOFs. • Extended lifetime is observed due to the stabilization of RuBpy within the rigid MOF framework.« less

ASTROP2 users manual: A program for aeroelastic stability analysis of propfans

NASA Technical Reports Server (NTRS)

Narayanan, G. V.; Kaza, K. R. V.

1991-01-01

A user's manual is presented for the aeroelastic stability and response of propulsion systems computer program called ASTROP2. The ASTROP2 code preforms aeroelastic stability analysis of rotating propfan blades. This analysis uses a two-dimensional, unsteady cascade aerodynamics model and a three-dimensional, normal-mode structural model. Analytical stability results from this code are compared with published experimental results of a rotating composite advanced turboprop model and of nonrotating metallic wing model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carbajal, L.; Warwick Univ., Coventry; Dendy, R. O.

Ion cyclotron emission (ICE) offers unique promise as a diagnostic of the fusion born alpha-particle population in magnetically confined plasmas. Pioneering observations from JET and TFTR found that ICE intensity P ICE scales approximately linearly with the measured neutron flux from fusion reactions, and with the inferred concentration, n /n i , of fusion-born alpha-particles confined within the plasma. We present fully nonlinear self-consistent kinetic simulations that reproduce this scaling for the first time. This resolves a longstanding question in the physics of fusion alpha particle confinement and stability in MCF plasmas. It confirms the MCI as the likely emissionmore » mechanism and greatly strengthens the basis for diagnostic exploitation of ICE in future burning plasmas.« less

Preliminary Tests of a Paul ion Trap as an Ion Source

NASA Astrophysics Data System (ADS)

Sadat Kiai, S. M.; Zirak, A. R.; Elahi, M.; Adlparvar, S.; Mortazavi, B. N.; Safarien, A.; Farhangi, S.; Sheibani, S.; Alhooie, S.; Khalaj, M. M. A.; Dabirzadeh, A. A.; Ruzbehani, M.; Zahedi, F.

2010-10-01

The paper reports on the design and construction of a Paul ion trap as an ion source by using an impact electron ionization technique. Ions are produced in the trap and confined for the specific time which is then extracted and detected by a Faraday cup. Especial electronic configurations are employed between the end caps, ring electrodes, electron gun and a negative voltage for the detector. This configuration allows a constant low level of pure ion source between the pulsed confined ion sources. The present experimental results are based on the production and confinement of Argon ions with good stability and repeatability, but in principle, the technique can be used for various Argon like ions.

Signal quality improvement using cylindrical confinement for laser induced breakdown spectroscopy.

PubMed

Hou, Zongyu; Wang, Zhe; Liu, Jianmin; Ni, Weidou; Li, Zheng

2013-07-01

In our previous work, we found that there was great potential to improve the pulse-to-pulse signal repeatability using a moderate cylindrical cavity confinement. However, the improvement was achieved only with certain experimental parameters; while under other conditions, there was no improvement or even worse repeatability. In the present work, the experimental configuration was redesigned and unexpected uncertainty from the variation of the laser and cavity alignment and the laser ablated aerosols were avoided. With these two improvements, we demonstrated that the cavity can always increase the signal repeatability. In addition, image taken by ICCD verified that the confinement improved the stability of the plasma morphology as expected.

Edge gyrokinetic theory and continuum simulations

NASA Astrophysics Data System (ADS)

Xu, X. Q.; Xiong, Z.; Dorr, M. R.; Hittinger, J. A.; Bodi, K.; Candy, J.; Cohen, B. I.; Cohen, R. H.; Colella, P.; Kerbel, G. D.; Krasheninnikov, S.; Nevins, W. M.; Qin, H.; Rognlien, T. D.; Snyder, P. B.; Umansky, M. V.

2007-08-01

The following results are presented from the development and application of TEMPEST, a fully nonlinear (full-f) five-dimensional (3d2v) gyrokinetic continuum edge-plasma code. (1) As a test of the interaction of collisions and parallel streaming, TEMPEST is compared with published analytic and numerical results for endloss of particles confined by combined electrostatic and magnetic wells. Good agreement is found over a wide range of collisionality, confining potential and mirror ratio, and the required velocity space resolution is modest. (2) In a large-aspect-ratio circular geometry, excellent agreement is found for a neoclassical equilibrium with parallel ion flow in the banana regime with zero temperature gradient and radial electric field. (3) The four-dimensional (2d2v) version of the code produces the first self-consistent simulation results of collisionless damping of geodesic acoustic modes and zonal flow (Rosenbluth-Hinton residual) with Boltzmann electrons using a full-f code. The electric field is also found to agree with the standard neoclassical expression for steep density and ion temperature gradients in the plateau regime. In divertor geometry, it is found that the endloss of particles and energy induces parallel flow stronger than the core neoclassical predictions in the SOL.

Role of Brittle Behaviour of Soft Calcarenites Under Low Confinement: Laboratory Observations and Numerical Investigation

NASA Astrophysics Data System (ADS)

Lollino, Piernicola; Andriani, Gioacchino Francesco

2017-07-01

The strength decay that occurs in the post-peak stage, under low confinement stress, represents a key factor of the stress-strain behaviour of rocks. However, for soft rocks this issue is generally underestimated or even neglected in the solution of boundary value problems, as for example those concerning the stability of underground cavities or rocky cliffs. In these cases, the constitutive models frequently used in limit equilibrium analyses or more sophisticated numerical calculations are, respectively, rigid-plastic or elastic-perfectly plastic. In particular, most of commercial continuum-based numerical codes propose a variety of constitutive models, including elasticity, elasto-plasticity, strain-softening and elasto-viscoplasticity, which are not exhaustive in simulating the progressive failure mechanisms affecting brittle rock materials, these being characterized by material detachment and crack opening and propagation. As a consequence, a numerical coupling with mechanical joint propagation is needed to cope with fracture mechanics. Therefore, continuum-based applications that treat the simulation of the failure processes of intact rock masses at low stress levels may need the adoption of numerical techniques capable of implementing fracture mechanics and rock brittleness concepts, as it is shown in this paper. This work is aimed at highlighting, for some applications of rock mechanics, the essential role of post-peak brittleness of soft rocks by means of the application of a hybrid finite-discrete element method. This method allows for a proper simulation of the brittle rock behaviour and the related mechanism of fracture propagation. In particular, the paper presents two ideal problems, represented by a shallow underground cave and a vertical cliff, for which the evolution of the stability conditions is investigated by comparing the solutions obtained implementing different brittle material responses with those resulting from the assumption of perfectly plastic behaviour. To this purpose, a series of petrophysical and mechanical tests were conducted on samples of soft calcarenite belonging to the Calcarenite di Gravina Fm. (Apulia, Southern Italy), focusing specific attention on the post-peak behaviour of the material under three types of loading (compression, indirect tension and shear). Typical geometrical features representative of real rock engineering problems observed in Southern Italy were assumed in the problems examined. The numerical results indicate the impact of soft rock brittleness in the assessment of stability and highlight the need for the adoption of innovative numerical techniques to analyse these types of problems properly.

Ions lost on their first orbit can impact Alfvén eigenmode stability

DOE PAGES

Heidbrink, William W.; Fu, Guo -Yong; Van Zeeland, Michael A.

2015-08-13

Some neutral-beam ions are deflected onto loss orbits by Alfvén eigenmodes on their first bounce orbit. Here, the resonance condition for these ions differs from the usual resonance condition for a confined fast ion. Estimates indicate that particles on single-pass loss orbits transfer enough energy to the wave to alter mode stability.

Enhancement of Edge Stability with Lithium Wall Coatings in NSTX

NASA Astrophysics Data System (ADS)

Maingi, R.; Bell, R. E.; Leblanc, B. P.; Kaita, R.; Kaye, S. M.; Kugel, H. W.; Mansfield, D. K.; Osborne, T. H.

2008-11-01

ELM reduction or elimination while maintaining high confinement is essential for ITER, which has been designed for H-mode operation. Large ELMs are thought to be triggered by exceeding either edge current density and/or pressure gradient limits (peeling, ballooning modes). Stability calculations show that spherical tori should have access to higher pressure gradients and pedestal heights than higher R/a tokamaks, owing to access to second stability regimes[...1]. An ELM-free regime was recently observed in the NSTX following the application of lithium onto the graphite plasma facing components[......2]. ELMs were eliminated in phases[.....3], with the resulting pressure gradients and pedestal widths increasing substantially. Calculations with TRANSP have shown that the edge bootstrap current increased substantially, consistent with second stability access. These ELM-free discharges have a substantial improvement in energy confinement, up to the global βN˜ 5.5 limit. * Supported by US DOE DE-FG02-04ER54520, DE-AC-76CH03073, and DE-FC02-04ER54698. [.1] P. B. Snyder, et. al., Plasma Phys. Contr. Fusion 46 (2004) A131. [2] H. W. Kugel, et. al., Phys. Plasma 15 (2008) #056118. [3] D. M. Mansfield, et. al., J. Nucl. Materials (2009) submitted.

COSAL: A black-box compressible stability analysis code for transition prediction in three-dimensional boundary layers

NASA Technical Reports Server (NTRS)

Malik, M. R.

1982-01-01

A fast computer code COSAL for transition prediction in three dimensional boundary layers using compressible stability analysis is described. The compressible stability eigenvalue problem is solved using a finite difference method, and the code is a black box in the sense that no guess of the eigenvalue is required from the user. Several optimization procedures were incorporated into COSAL to calculate integrated growth rates (N factor) for transition correlation for swept and tapered laminar flow control wings using the well known e to the Nth power method. A user's guide to the program is provided.

Finite-difference solution of the compressible stability eigenvalue problem

NASA Technical Reports Server (NTRS)

Malik, M. R.

1982-01-01

A compressible stability analysis computer code is developed. The code uses a matrix finite difference method for local eigenvalue solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used initial value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed which may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black box stability code. Sample stability calculations are presented for the boundary layer profiles of a Laminar Flow Control (LFC) swept wing.

Energy evolution mechanism in process of Sandstone failure and energy strength criterion

NASA Astrophysics Data System (ADS)

Wang, Yunfei; Cui, Fang

2018-07-01

To reveal the inherent relation between energy change and confining pressure during the process of sandstone damage, and its characteristics of energy storage and energy dissipation in different deformation stage. Obtaining the mechanical parameters by testing the Sandstone of two1 coal seam roof under uniaxial compression in Zhaogu coalmine, using Particle Flow Code (PFC) and fish program to get the meso-mechanical parameters, studying Sandstone energy evolution mechanism under different confining pressures, and deducing energy strength criterion based on energy principle of rock failure, some main researching results are reached as follows: with the increasing of confining pressure, the Sandstone yield stage and ductility increases, but brittleness decreases; Under higher confining pressure, the elastic strain energy of Sandstone before peak approximately keeps constant in a certain strain range, and rock absorbs all the energy which converts into surface energy required for internal damage development; Under lower confining pressure, Sandstone no longer absorbs energy with increasing strain after peak under lower confining pressure, while it sequentially absorbs energy under higher confining pressure; Under lower confining pressure, the energy Sandstone before peak absorbed mainly converts into elastic strain energy, while under higher confining pressure, dissipation energy significantly increases before peak, which indicates that the degree rock strength loss is higher under higher confining pressure; with the increasing of confining pressure, the limit of elastic strain energy increases and there exists a favourable linear variation relationship; At the peak point, the ratio of elastic strain energy to total energy of Sandstone nonlinearly decreases, while the ratio of dissipation energy to total energy nonlinearly increases with the increasing of confining pressure; According to energy evolution mechanism of rock failure, an energy strength criterion is derived. The criterion equation includes lithology constants and three principal stresses, and its physical meaning is clear. This criterion has an evident advantage than Hoek-Brown and Drucker-Prager criterion in calculation accuracy and can commendably describe rock failure characteristics.

Study of quantum confinement effects in ZnO nanostructures

NASA Astrophysics Data System (ADS)

Movlarooy, Tayebeh

2018-03-01

Motivation to fact that zinc oxide nanowires and nanotubes with successful synthesis and the mechanism of formation, stability and electronic properties have been investigated; in this study the structural, electronic properties and quantum confinement effects of zinc oxide nanotubes and nanowires with different diameters are discussed. The calculations within density functional theory and the pseudo potential approximation are done. The electronic structure and energy gap for Armchair and zigzag ZnO nanotubes with a diameter of about 4 to 55 Angstrom and ZnO nanowires with a diameter range of 4 to 23 Å is calculated. The results revealed that due to the quantum confinement effects, by reducing the diameter of nanowires and nanotubes, the energy gap increases. Zinc oxide semiconductor nanostructures since having direct band gap with size-dependent and quantum confinement effect are recommended as an appropriate candidate for making nanoscale optoelectronic devices.

Towards self-correcting quantum memories

NASA Astrophysics Data System (ADS)

Michnicki, Kamil

This thesis presents a model of self-correcting quantum memories where quantum states are encoded using topological stabilizer codes and error correction is done using local measurements and local dynamics. Quantum noise poses a practical barrier to developing quantum memories. This thesis explores two types of models for suppressing noise. One model suppresses thermalizing noise energetically by engineering a Hamiltonian with a high energy barrier between code states. Thermalizing dynamics are modeled phenomenologically as a Markovian quantum master equation with only local generators. The second model suppresses stochastic noise with a cellular automaton that performs error correction using syndrome measurements and a local update rule. Several ways of visualizing and thinking about stabilizer codes are presented in order to design ones that have a high energy barrier: the non-local Ising model, the quasi-particle graph and the theory of welded stabilizer codes. I develop the theory of welded stabilizer codes and use it to construct a code with the highest known energy barrier in 3-d for spin Hamiltonians: the welded solid code. Although the welded solid code is not fully self correcting, it has some self correcting properties. It has an increased memory lifetime for an increased system size up to a temperature dependent maximum. One strategy for increasing the energy barrier is by mediating an interaction with an external system. I prove a no-go theorem for a class of Hamiltonians where the interaction terms are local, of bounded strength and commute with the stabilizer group. Under these conditions the energy barrier can only be increased by a multiplicative constant. I develop cellular automaton to do error correction on a state encoded using the toric code. The numerical evidence indicates that while there is no threshold, the model can extend the memory lifetime significantly. While of less theoretical importance, this could be practical for real implementations of quantum memories. Numerical evidence also suggests that the cellular automaton could function as a decoder with a soft threshold.

LRFD software for design and actual ultimate capacity of confined rectangular columns : [technical summary].

DOT National Transportation Integrated Search

2013-04-01

Columns are considered the most critical elements in structures. The unconfined analysis for columns is well established in the literature. Structural design codes dictate reduction factors for safety. It wasnt until very recently that design spec...

Accounting for pore water pressure and confined aquifers in assessing the stability of slopes: a Limit Equilibrium analysis carried out through the Minimum Lithostatic Deviation method

NASA Astrophysics Data System (ADS)

Ausilia Paparo, Maria; Tinti, Stefano

2015-04-01

The model we introduce is an implementation of the Minimum Lithostatic Deviation (MLD) method, developed by Tinti and Manucci (Tinti and Manucci 2006; 2008), that makes use of the limit equilibrium (LE) theory to estimate the stability of a slope. The main purpose here is to analyse the role of a confined aquifer on the value of the Safety Factor (F), the parameter that in the LE is used to determine if a slope is stable or unstable. The classical LE methods treat unconfined aquifers by including the water pore pressure in the Mohr-Coulomb failure formula: since the water decreases the friction shear strength, the soil above the sliding surface turns out to be more prone to instability. In case of a confined aquifer, however, due to a presence of impermeable layers, the water is not free to flow into the matrix of the overlying soil. We consider here the assumption of a permeable soil sliding over an impermeable layer, which is an occurrence that is found in several known landslide cases (e.g. Person, 2008; Strout and Tjeltja, 2008; Morgan et al., 2010 for offshore slides; and Palladino and Peck, 1972; Miller and Sias, 1998; Jiao et al. 2005; Paparo et al., 2013 for slopes in proximity of artificial or natural water basins) where clay beds form the potential sliding surface: the water, confined below, pushes along these layers and acts on the sliding body as an external bottom load. We modify the MLD method equations in order to take into account the load due to a confined aquifer and apply the new model to the Vajont case, where many have hypothesised the contribution of a confined aquifer to the failure. Our calculations show that the rain load i) infiltrating directly into the soil body and ii) penetrating into the confined aquifer below the clay layers, in addition with the lowering of the reservoir level, were key factors of destabilization of the Mt Toc flank and caused the disastrous landslide.

HART-II: Prediction of Blade-Vortex Interaction Loading

DTIC Science & Technology

2003-09-01

14:30 (2) Improvement of DLR Rotor Aero- acoustic Code ( APSIM ) and its Valida- tion with Analytic Solution J. Yin, J. Delfs (5...of DLR Rotor Aero- acoustic Code ( APSIM ) and its Valida- tion with Analytic Solution J. Yin, J. Delfs (5) Aeroelastic Stability Analysis of...of DLR Rotor Aero- acoustic Code ( APSIM ) and its Valida- tion with Analytic Solution J. Yin, J. Delfs (5) Aeroelastic Stability Analysis of

Influence of a Confined Methanol Solvent on the Reactivity of Active Sites in UiO-66.

PubMed

Caratelli, Chiara; Hajek, Julianna; Rogge, Sven M J; Vandenbrande, Steven; Meijer, Evert Jan; Waroquier, Michel; Van Speybroeck, Veronique

2018-02-19

UiO-66, composed of Zr-oxide bricks and terephthalate linkers, is currently one of the most studied metal-organic frameworks due to its exceptional stability. Defects can be introduced in the structure, creating undercoordinated Zr atoms which are Lewis acid sites. Here, additional Brønsted sites can be generated by coordinated protic species from the solvent. In this Article, a multilevel modeling approach was applied to unravel the effect of a confined methanol solvent on the active sites in UiO-66. First, active sites were explored with static periodic density functional theory calculations to investigate adsorption of water and methanol. Solvent was then introduced in the pores with grand canonical Monte Carlo simulations, followed by a series of molecular dynamics simulations at operating conditions. A hydrogen-bonded network of methanol molecules is formed, allowing the protons to shuttle between solvent methanol, adsorbed water, and the inorganic brick. Upon deprotonation of an active site, the methanol solvent aids the transfer of protons and stabilizes charged configurations via hydrogen bonding, which could be crucial in stabilizing reactive intermediates. The multilevel modeling approach adopted here sheds light on the important role of a confined solvent on the active sites in the UiO-66 material, introducing dynamic acidity in the system at finite temperatures by which protons may be easily shuttled from various positions at the active sites. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Lawrence Livermore National Laboratories Perspective on Code Development and High Performance Computing Resources in Support of the National HED/ICF Effort

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clouse, C. J.; Edwards, M. J.; McCoy, M. G.

2015-07-07

Through its Advanced Scientific Computing (ASC) and Inertial Confinement Fusion (ICF) code development efforts, Lawrence Livermore National Laboratory (LLNL) provides a world leading numerical simulation capability for the National HED/ICF program in support of the Stockpile Stewardship Program (SSP). In addition the ASC effort provides high performance computing platform capabilities upon which these codes are run. LLNL remains committed to, and will work with, the national HED/ICF program community to help insure numerical simulation needs are met and to make those capabilities available, consistent with programmatic priorities and available resources.

Physical insights of cavity confinement enhancing effect in laser-induced breakdown spectroscopy.

PubMed

Fu, Yangting; Hou, Zongyu; Wang, Zhe

2016-02-08

Using cavity confinement to enhance the plasma emission has been proved to be an effective way in LIBS technique while no direct visual evidence has been made to illustrate the physical mechanism of this enhancing effect. In this work, both laser-induced plasma plume images and shockwave images were obtained and synchronized for both flat surface case and rectangular cavity case. Phenomena of shockwave reflection, plasma compression by the reflected shockwave and merge of the reflected shockwave into plasma were observed. Plasma emission intensities recorded by ICCD in both cases were compared and the enhancement effect in the cavity case was identified in the comparison. The enhancement effect could be explained as reflected shockwave "compressing" effect, that is, the reflected shockwave would compress the plasma and result in a more condensed plasma core area with higher plasma temperature. Reflected shockwave also possibly contributed to plasma core position stabilization, which indicated the potential of better plasma signal reproducibility for the cavity case. Both plasma emission enhancement and plasma core position stabilization only exist within a certain temporal window, which indicates that the delay time of spectra acquisition is essential while using cavity confinement as a way to improve LIBS performance.

Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burrell, K. H.; Chen, X.; Garofalo, A. M.

Recent experiments in DIII-D [J. L. Luxon et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H{sub 98y2} international tokamakmore » energy confinement scaling (H{sub 98y2} = 1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggered in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers E × B rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the E × B shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β{sub N} = 1.6–1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints. Stationary operation with improved pedestal conditions is highly significant for future burning plasma devices, since operation without ELMs at low rotation and good confinement is key for fusion energy production.« less

Method for transition prediction in high-speed boundary layers, phase 2

NASA Astrophysics Data System (ADS)

Herbert, T.; Stuckert, G. K.; Lin, N.

1993-09-01

The parabolized stability equations (PSE) are a new and more reliable approach to analyzing the stability of streamwise varying flows such as boundary layers. This approach has been previously validated for idealized incompressible flows. Here, the PSE are formulated for highly compressible flows in general curvilinear coordinates to permit the analysis of high-speed boundary-layer flows over fairly general bodies. Vigorous numerical studies are carried out to study convergence and accuracy of the linear-stability code LSH and the linear/nonlinear PSE code PSH. Physical interfaces are set up to analyze the M = 8 boundary layer over a blunt cone calculated by using a thin-layer Navier Stokes (TNLS) code and the flow over a sharp cone at angle of attack calculated using the AFWAL parabolized Navier-Stokes (PNS) code. While stability and transition studies at high speeds are far from routine, the method developed here is the best tool available to research the physical processes in high-speed boundary layers.

Unitary reconstruction of secret for stabilizer-based quantum secret sharing

NASA Astrophysics Data System (ADS)

Matsumoto, Ryutaroh

2017-08-01

We propose a unitary procedure to reconstruct quantum secret for a quantum secret sharing scheme constructed from stabilizer quantum error-correcting codes. Erasure correcting procedures for stabilizer codes need to add missing shares for reconstruction of quantum secret, while unitary reconstruction procedures for certain class of quantum secret sharing are known to work without adding missing shares. The proposed procedure also works without adding missing shares.

Preface to Special Topic: Advances in Radio Frequency Physics in Fusion Plasmas

NASA Astrophysics Data System (ADS)

Tuccillo, Angelo A.; Phillips, Cynthia K.; Ceccuzzi, Silvio

2014-06-01

It has long been recognized that auxiliary plasma heating will be required to achieve the high temperature, high density conditions within a magnetically confined plasma in which a fusion "burn" may be sustained by copious fusion reactions. Consequently, the application of radio and microwave frequency electromagnetic waves to magnetically confined plasma, commonly referred to as RF, has been a major part of the program almost since its inception in the 1950s. These RF waves provide heating, current drive, plasma profile control, and Magnetohydrodynamics (MHD) stabilization. Fusion experiments employ electromagnetic radiation in a wide range of frequencies, from tens of MHz to hundreds of GHz. The fusion devices containing the plasma are typically tori, axisymmetric or non, in which the equilibrium magnetic fields are composed of a strong toroidal magnetic field generated by external coils, and a poloidal field created, at least in the symmetric configurations, by currents flowing in the plasma. The waves are excited in the peripheral regions of the plasma, by specially designed launching structures, and subsequently propagate into the core regions, where resonant wave-plasma interactions produce localized heating or other modification of the local equilibrium profiles. Experimental studies coupled with the development of theoretical models and advanced simulation codes over the past 40+ years have led to an unprecedented understanding of the physics of RF heating and current drive in the core of magnetic fusion devices. Nevertheless, there are serious gaps in our knowledge base that continue to have a negative impact on the success of ongoing experiments and that must be resolved as the program progresses to the next generation devices and ultimately to "demo" and "fusion power plant." A serious gap, at least in the ion cyclotron (IC) range of frequencies and partially in the lower hybrid frequency ranges, is the difficulty in coupling large amount of power to the plasma while minimizing the interaction between the plasma and launching structures. These potentially harmful interactions between the plasma and the vessel and launching structures are challenging: (i) significant and variable loss of power in the edge regions of confined plasmas and surrounding vessel structures adversely affect the core plasma performance and lifetime of a device; (ii) the launcher design is partly "trial and error," with the consequence that launchers may have to be reconfigured after initial tests in a given device, at an additional cost. Over the broader frequency range, another serious gap is a quantitative lack of understanding of the combined effects of nonlinear wave-plasma processes, energetic particle interactions and non-axisymmetric equilibrium effects on determining the overall efficiency of plasma equilibrium and stability profile control techniques using RF waves. This is complicated by a corresponding lack of predictive understanding of the time evolution of transport and stability processes in fusion plasmas.

Boundary-Layer Stability Analysis of the Mean Flows Obtained Using Unstructured Grids

NASA Technical Reports Server (NTRS)

Liao, Wei; Malik, Mujeeb R.; Lee-Rausch, Elizabeth M.; Li, Fei; Nielsen, Eric J.; Buning, Pieter G.; Chang, Chau-Lyan; Choudhari, Meelan M.

2012-01-01

Boundary-layer stability analyses of mean flows extracted from unstructured-grid Navier- Stokes solutions have been performed. A procedure has been developed to extract mean flow profiles from the FUN3D unstructured-grid solutions. Extensive code-to-code validations have been performed by comparing the extracted mean ows as well as the corresponding stability characteristics to the predictions based on structured-grid solutions. Comparisons are made on a range of problems from a simple at plate to a full aircraft configuration-a modified Gulfstream-III with a natural laminar flow glove. The future aim of the project is to extend the adjoint-based design capability in FUN3D to include natural laminar flow and laminar flow control by integrating it with boundary-layer stability analysis codes, such as LASTRAC.

Ground state of dipolar hard spheres confined in channels

NASA Astrophysics Data System (ADS)

Deißenbeck, Florian; Löwen, Hartmut; Oǧuz, Erdal C.

2018-05-01

We investigate the ground state of a classical two-dimensional system of hard-sphere dipoles confined between two hard walls. Using lattice sum minimization techniques we reveal that at fixed wall separations, a first-order transition from a vacuum to a straight one-dimensional chain of dipoles occurs upon increasing the density. Further increase in the density yields the stability of an undulated chain as well as nontrivial buckling structures. We explore the close-packed configurations of dipoles in detail, and we find that, in general, the densest packings of dipoles possess complex magnetizations along the principal axis of the slit. Our predictions serve as a guideline for experiments with granular dipolar and magnetic colloidal suspensions confined in slitlike channel geometry.

Control of Screening of a Charged Particle in Electrolytic Aqueous Paul Trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jae Hyun nmn; Krstic, Predrag S

2011-01-01

Individual charged particles could be trapped and confined in the combined radio-frequency and DC quadrupole electric field of an aqueous Paul trap. Viscosity of water improves confinement and extends the range of the trap parameters which characterize the stability of the trap. Electrolyte, if present in aqueous solution, may screen the charged particle and thus partially or fully suppress electrophoretic interaction with the applied filed, possibly reducing it to a generally much weaker dielectrophoretic interaction with an induced dipole. Applying molecular dynamics simulation we show that the quadrupole field has a different affects at the electrolyte ions and at muchmore » heavier charged particle, effectively eliminating the screening effect and reinstating the electrophoretic confinement.« less

Control Of Screening Of A Charged Particle In Electrolytic Aqueous Paul Trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jae Hyun; Krstic, Predrag S.

2011-06-01

Individual charged particles could be trapped and confined by the combined radio-frequency and DC quadrupole electric field of an aqueous Paul trap. Viscosity of water improves confinement and extends the range of the trap parameters which characterize the stability of the trap. Electrolyte, if present in aqueous solution, may screen the charged particle and thus partially or fully suppress electrophoretic interaction with the applied filed, possibly reducing it to a generally much weaker dielectrophoretic interaction with an induced dipole. Applying molecular dynamics simulation we show that the quadrupole field has a different effect at the electrolyte ions and at muchmore » heavier charged particle, effectively eliminating the screening by electrolyte ions and reinstating the electrophoretic confinement.« less

Manufactured solutions for the three-dimensional Euler equations with relevance to Inertial Confinement Fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waltz, J., E-mail: jwaltz@lanl.gov; Canfield, T.R.; Morgan, N.R.

2014-06-15

We present a set of manufactured solutions for the three-dimensional (3D) Euler equations. The purpose of these solutions is to allow for code verification against true 3D flows with physical relevance, as opposed to 3D simulations of lower-dimensional problems or manufactured solutions that lack physical relevance. Of particular interest are solutions with relevance to Inertial Confinement Fusion (ICF) capsules. While ICF capsules are designed for spherical symmetry, they are hypothesized to become highly 3D at late time due to phenomena such as Rayleigh–Taylor instability, drive asymmetry, and vortex decay. ICF capsules also involve highly nonlinear coupling between the fluid dynamicsmore » and other physics, such as radiation transport and thermonuclear fusion. The manufactured solutions we present are specifically designed to test the terms and couplings in the Euler equations that are relevant to these phenomena. Example numerical results generated with a 3D Finite Element hydrodynamics code are presented, including mesh convergence studies.« less

Equilibium and Stability of Spherical Vlasov Systems

NASA Astrophysics Data System (ADS)

Barnes, D. C.; Chacon, L.; Finn, J. M.

2002-04-01

Collisionless systems with inverse square interaction potentials and possible background confining potentials are considered for the case of spherical symmetry and in the Vlasov limit. The equilibrium is the most general, with single-particle distribution function dependence on both total energy E and total angular momentum L. A new formulation of the full integral-equation stability problem is developed. For a general spherical harmonic perturbation potential, the 3D stability problem is reduced to a 2D problem in an arbitrary central plane of motion, then to a small number of coupled 1D problems involving only the radius. Normal modes depend only on the total mode number l, as is shown directly by this new formulation, with all m degenerate. This method has been used for the Coulomb (repulsive) case.[1] An equilibrium family with uniform central (electron) density is found, and the low-frequency response computed to show that these solutions may provide stable confinement of a massive second (ion) species. These methods may be applied to a particle bunch in the beam frame, and some stability results appropriate to this case are presented. Application to the gravitational (attractive) case is also described, and some initial analytic results are presented. [1] D. C. Barnes, L. Chacón, J. M. Finn, “Equilibrium and Low-frequency Stability of a Uniform Density, Collisionless, Spherical Vlasov System,” submitted to Phys. of Plasmas (2002).

Pathways to dewetting in hydrophobic confinement

PubMed Central

Remsing, Richard C.; Xi, Erte; Vembanur, Srivathsan; Sharma, Sumit; Debenedetti, Pablo G.; Garde, Shekhar; Patel, Amish J.

2015-01-01

Liquid water can become metastable with respect to its vapor in hydrophobic confinement. The resulting dewetting transitions are often impeded by large kinetic barriers. According to macroscopic theory, such barriers arise from the free energy required to nucleate a critical vapor tube that spans the region between two hydrophobic surfaces—tubes with smaller radii collapse, whereas larger ones grow to dry the entire confined region. Using extensive molecular simulations of water between two nanoscopic hydrophobic surfaces, in conjunction with advanced sampling techniques, here we show that for intersurface separations that thermodynamically favor dewetting, the barrier to dewetting does not correspond to the formation of a (classical) critical vapor tube. Instead, it corresponds to an abrupt transition from an isolated cavity adjacent to one of the confining surfaces to a gap-spanning vapor tube that is already larger than the critical vapor tube anticipated by macroscopic theory. Correspondingly, the barrier to dewetting is also smaller than the classical expectation. We show that the peculiar nature of water density fluctuations adjacent to extended hydrophobic surfaces—namely, the enhanced likelihood of observing low-density fluctuations relative to Gaussian statistics—facilitates this nonclassical behavior. By stabilizing isolated cavities relative to vapor tubes, enhanced water density fluctuations thus stabilize novel pathways, which circumvent the classical barriers and offer diminished resistance to dewetting. Our results thus suggest a key role for fluctuations in speeding up the kinetics of numerous phenomena ranging from Cassie–Wenzel transitions on superhydrophobic surfaces, to hydrophobically driven biomolecular folding and assembly. PMID:26100866

Pathways to dewetting in hydrophobic confinement.

PubMed

Remsing, Richard C; Xi, Erte; Vembanur, Srivathsan; Sharma, Sumit; Debenedetti, Pablo G; Garde, Shekhar; Patel, Amish J

2015-07-07

Liquid water can become metastable with respect to its vapor in hydrophobic confinement. The resulting dewetting transitions are often impeded by large kinetic barriers. According to macroscopic theory, such barriers arise from the free energy required to nucleate a critical vapor tube that spans the region between two hydrophobic surfaces--tubes with smaller radii collapse, whereas larger ones grow to dry the entire confined region. Using extensive molecular simulations of water between two nanoscopic hydrophobic surfaces, in conjunction with advanced sampling techniques, here we show that for intersurface separations that thermodynamically favor dewetting, the barrier to dewetting does not correspond to the formation of a (classical) critical vapor tube. Instead, it corresponds to an abrupt transition from an isolated cavity adjacent to one of the confining surfaces to a gap-spanning vapor tube that is already larger than the critical vapor tube anticipated by macroscopic theory. Correspondingly, the barrier to dewetting is also smaller than the classical expectation. We show that the peculiar nature of water density fluctuations adjacent to extended hydrophobic surfaces--namely, the enhanced likelihood of observing low-density fluctuations relative to Gaussian statistics--facilitates this nonclassical behavior. By stabilizing isolated cavities relative to vapor tubes, enhanced water density fluctuations thus stabilize novel pathways, which circumvent the classical barriers and offer diminished resistance to dewetting. Our results thus suggest a key role for fluctuations in speeding up the kinetics of numerous phenomena ranging from Cassie-Wenzel transitions on superhydrophobic surfaces, to hydrophobically driven biomolecular folding and assembly.

Confined Water in Layered Silicates: The Origin of Anomalous Thermal Expansion Behavior in Calcium-Silicate-Hydrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishnan, N. M. Anoop; Wang, Bu; Falzone, Gabriel

Water, under conditions of nanoscale confinement, exhibits anomalous dynamics, and enhanced thermal deformations, which may be further enhanced when such water is in contact with hydrophilic surfaces. Such heightened thermal deformations of water could control the volume stability of hydrated materials containing nanoconfined structural water. Understanding and predicting the thermal deformation coefficient (TDC, often referred to as the CTE, coefficient of thermal expansion), which represents volume changes induced in materials under conditions of changing temperature, is of critical importance for hydrated solids including: hydrogels, biological tissues, and calcium silicate hydrates, as changes in their volume can result in stress development,more » and cracking. By pioneering atomistic simulations, we examine the physical origin of thermal expansion in calcium-silicate-hydrates (C–S–H), the binding agent in concrete that is formed by the reaction of cement with water. We report that the TDC of C–S–H shows a sudden increase when the CaO/SiO 2 (molar ratio; abbreviated as Ca/Si) exceeds 1.5. This anomalous behavior arises from a notable increase in the confinement of water contained in the C–S–H’s nanostructure. We identify that confinement is dictated by the topology of the C–S–H’s atomic network. Altogether, the results suggest that thermal deformations of hydrated silicates can be altered by inducing compositional changes, which in turn alter the atomic topology and the resultant volume stability of the solids.« less

External heating and current drive source requirements towards steady-state operation in ITER

NASA Astrophysics Data System (ADS)

Poli, F. M.; Kessel, C. E.; Bonoli, P. T.; Batchelor, D. B.; Harvey, R. W.; Snyder, P. B.

2014-07-01

Steady state scenarios envisaged for ITER aim at optimizing the bootstrap current, while maintaining sufficient confinement and stability to provide the necessary fusion yield. Non-inductive scenarios will need to operate with internal transport barriers (ITBs) in order to reach adequate fusion gain at typical currents of 9 MA. However, the large pressure gradients associated with ITBs in regions of weak or negative magnetic shear can be conducive to ideal MHD instabilities, reducing the no-wall limit. The E × B flow shear from toroidal plasma rotation is expected to be low in ITER, with a major role in the ITB dynamics being played by magnetic geometry. Combinations of heating and current drive (H/CD) sources that sustain reversed magnetic shear profiles throughout the discharge are the focus of this work. Time-dependent transport simulations indicate that a combination of electron cyclotron (EC) and lower hybrid (LH) waves is a promising route towards steady state operation in ITER. The LH forms and sustains expanded barriers and the EC deposition at mid-radius freezes the bootstrap current profile stabilizing the barrier and leading to confinement levels 50% higher than typical H-mode energy confinement times. Using LH spectra with spectrum centred on parallel refractive index of 1.75-1.85, the performance of these plasma scenarios is close to the ITER target of 9 MA non-inductive current, global confinement gain H98 = 1.6 and fusion gain Q = 5.

Observation of Quantum Confinement in Monodisperse Methylammonium Lead Halide Perovskite Nanocrystals Embedded in Mesoporous Silica.

PubMed

Malgras, Victor; Tominaka, Satoshi; Ryan, James W; Henzie, Joel; Takei, Toshiaki; Ohara, Koji; Yamauchi, Yusuke

2016-10-13

Hybrid organic-inorganic metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of bulk metal halide perovskites has been widely studied, the properties of perovskite nanocrystals are less well-understood because synthesizing them is still very challenging, in part because of stability. Here we demonstrate a simple and versatile method to grow monodisperse CH 3 NH 3 PbBr x I x-3 perovskite nanocrystals inside mesoporous silica templates. The size of the nanocrystal is governed by the pore size of the templates (3.3, 3.7, 4.2, 6.2, and 7.1 nm). In-depth structural analysis shows that the nanocrystals maintain the perovskite crystal structure, but it is slightly distorted. Quantum confinement was observed by tuning the size of the particles via the template. This approach provides an additional route to tune the optical bandgap of the nanocrystal. The level of quantum confinement was modeled taking into account the dimensions of the rod-shaped nanocrystals and their close packing inside the channels of the template. Photoluminescence measurements on CH 3 NH 3 PbBr clearly show a shift from green to blue as the pore size is decreased. Synthesizing perovskite nanostructures in templates improves their stability and enables tunable electronic properties via quantum confinement. These structures may be useful as reference materials for comparison with other perovskites, or as functional materials in all solid-state light-emitting diodes.

Confined Water in Layered Silicates: The Origin of Anomalous Thermal Expansion Behavior in Calcium-Silicate-Hydrates.

PubMed

Krishnan, N M Anoop; Wang, Bu; Falzone, Gabriel; Le Pape, Yann; Neithalath, Narayanan; Pilon, Laurent; Bauchy, Mathieu; Sant, Gaurav

2016-12-28

Water, under conditions of nanoscale confinement, exhibits anomalous dynamics, and enhanced thermal deformations, which may be further enhanced when such water is in contact with hydrophilic surfaces. Such heightened thermal deformations of water could control the volume stability of hydrated materials containing nanoconfined structural water. Understanding and predicting the thermal deformation coefficient (TDC, often referred to as the CTE, coefficient of thermal expansion), which represents volume changes induced in materials under conditions of changing temperature, is of critical importance for hydrated solids including: hydrogels, biological tissues, and calcium silicate hydrates, as changes in their volume can result in stress development, and cracking. By pioneering atomistic simulations, we examine the physical origin of thermal expansion in calcium-silicate-hydrates (C-S-H), the binding agent in concrete that is formed by the reaction of cement with water. We report that the TDC of C-S-H shows a sudden increase when the CaO/SiO 2 (molar ratio; abbreviated as Ca/Si) exceeds 1.5. This anomalous behavior arises from a notable increase in the confinement of water contained in the C-S-H's nanostructure. We identify that confinement is dictated by the topology of the C-S-H's atomic network. Taken together, the results suggest that thermal deformations of hydrated silicates can be altered by inducing compositional changes, which in turn alter the atomic topology and the resultant volume stability of the solids.

Confined Water in Layered Silicates: The Origin of Anomalous Thermal Expansion Behavior in Calcium-Silicate-Hydrates

DOE PAGES

Krishnan, N. M. Anoop; Wang, Bu; Falzone, Gabriel; ...

2016-12-06

Water, under conditions of nanoscale confinement, exhibits anomalous dynamics, and enhanced thermal deformations, which may be further enhanced when such water is in contact with hydrophilic surfaces. Such heightened thermal deformations of water could control the volume stability of hydrated materials containing nanoconfined structural water. Understanding and predicting the thermal deformation coefficient (TDC, often referred to as the CTE, coefficient of thermal expansion), which represents volume changes induced in materials under conditions of changing temperature, is of critical importance for hydrated solids including: hydrogels, biological tissues, and calcium silicate hydrates, as changes in their volume can result in stress development,more » and cracking. By pioneering atomistic simulations, we examine the physical origin of thermal expansion in calcium-silicate-hydrates (C–S–H), the binding agent in concrete that is formed by the reaction of cement with water. We report that the TDC of C–S–H shows a sudden increase when the CaO/SiO 2 (molar ratio; abbreviated as Ca/Si) exceeds 1.5. This anomalous behavior arises from a notable increase in the confinement of water contained in the C–S–H’s nanostructure. We identify that confinement is dictated by the topology of the C–S–H’s atomic network. Altogether, the results suggest that thermal deformations of hydrated silicates can be altered by inducing compositional changes, which in turn alter the atomic topology and the resultant volume stability of the solids.« less

Quantum Stabilizer Codes Can Realize Access Structures Impossible by Classical Secret Sharing

NASA Astrophysics Data System (ADS)

Matsumoto, Ryutaroh

We show a simple example of a secret sharing scheme encoding classical secret to quantum shares that can realize an access structure impossible by classical information processing with limitation on the size of each share. The example is based on quantum stabilizer codes.

Fast particle confinement with optimized coil currents in the W7-X stellarator

NASA Astrophysics Data System (ADS)

Drevlak, M.; Geiger, J.; Helander, P.; Turkin, Y.

2014-07-01

One of the principal goals of the W7-X stellarator is to demonstrate good confinement of energetic ions at finite β. This confinement, however, is sensitive to the magnetic field configuration and is thus vulnerable to design modifications of the coil geometry. The collisionless drift orbit losses for 60 keV protons in W7-X are studied using the ANTS code. Particles in this energy range will be produced by the neutral beam injection (NBI) system being constructed for W7-X, and are particularly important because protons at this energy accurately mimick the behaviour of 3.5 MeV α-particles in a HELIAS reactor. To investigate the possibility of improved fast particle confinement, several approaches to adjust the coil currents (5 main field coil currents +2 auxiliary coil currents) were explored. These strategies include simple rules of thumb as well as computational optimization of various properties of the magnetic field. It is shown that significant improvement of collisionless fast particle confinement can be achieved in W7-X for particle populations similar to α particles produced in fusion reactions. Nevertheless, the experimental goal of demonstrating confinement improvement with rising plasma pressure using an NBI-generated population appears to be difficult based on optimization of the coil currents only. The principal reason for this difficulty is that the NBI deposition profile is broader than the region of good fast-ion confinement around the magnetic axis.

On improved confinement in mirror plasmas by a radial electric field

NASA Astrophysics Data System (ADS)

Ågren, O.; Moiseenko, V. E.

2017-11-01

A weak radial electric field can suppress radial excursions of a guiding center from its mean magnetic surface. The physical origin of this effect is the smearing action by a poloidal E × B rotation, which tend to cancel out the inward and outward radial drifts. A use of this phenomenon may provide larger margins for magnetic field shaping with radial confinement of particles maintained in the collision free idealization. Mirror fields, stabilized by a quadrupolar field component, are of particular interest for their MHD stability and the possibility to control the quasi neutral radial electric field by biased potential plates outside the confinement region. Flux surface footprints on the end tank wall have to be traced to avoid short-circuiting between biased plates. Assuming a robust biasing procedure, moderate voltage demands for the biased plates seems adequate to cure even the radial excursions of Yushmanov ions which could be locally trapped near the mirrors. Analytical expressions are obtained for a magnetic quadrupolar mirror configuration which possesses minimal radial magnetic drifts in the central confinement region. By adding a weak controlled radial quasi-neutral electric field, the majority of gyro centers are predicted to be forced to move even closer to their respective mean magnetic surface. The gyro center radial coordinate is in such a case an accurate approximation for a constant of motion. By using this constant of motion, the analysis is in a Vlasov description extended to finite β. A correspondence between that Vlasov system and a fluid description with a scalar pressure and an electric potential is verified. The minimum B criterion is considered and implications for flute mode stability in the considered magnetic field is analyzed. By carrying out a long-thin expansion to a higher order, the validity of the calculations are extended to shorter and more compact device designs.

Topological superfluids confined in a nanoscale slab geometry

NASA Astrophysics Data System (ADS)

Saunders, John

2013-03-01

Nanofluidic samples of superfluid 3He provide a route to explore odd-parity topological superfluids and their surface, edge and defect-bound excitations under well controlled conditions. We have cooled superfluid 3He confined in a precisely defined nano-fabricated cavity to well below 1 mK for the first time. We fingerprint the order parameter by nuclear magnetic resonance, exploiting a SQUID NMR spectrometer of exquisite sensitivity. We demonstrate that dimensional confinement, at length scales comparable to the superfluid Cooper-pair diameter, has a profound influence on the superfluid order of 3He. The chiral A-phase is stabilized at low pressures, in a cavity of height 650 nm. At higher pressures we observe 3He-B with a surface induced planar distortion. 3He-B is a time-reversal invariant topological superfluid, supporting gapless Majorana surface states. In the presence of the small symmetry breaking NMR static magnetic field we observe two possible B-phase states of the order parameter manifold, which can coexist as domains. Non-linear NMR on these states enables a measurement of the surface induced planar distortion, which determines the spectral weight of the surface excitations. The expected structure of the domain walls is such that, at the cavity surface, the line separating the two domains is predicted to host fermion zero modes, protected by symmetry and topology. Increasing confinement should stabilize new p-wave superfluid states of matter, such as the quasi-2D gapped A phase, which breaks time reversal symmetry, has a protected chiral edge mode, and may host half-quantum vortices with a Majorana zero-mode at the core. We discuss experimental progress toward this phase, through measurements on a 100 nm cavity. On the other hand, a cavity height of 1000 nm may stabilize a novel ``striped'' superfluid with spatially modulated order parameter. Supported by EPSRC (UK) GR/J022004/1 and European Microkelvin Consortium, FP7 grant 228464

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanz, J.; Betti, R.

A sharp boundary model for the deceleration phase of imploding capsules in inertial confinement fusion, in both direct and indirect drive, has been developed. The model includes heat conduction, local {alpha}-particle energy deposition, and shell compressibility effects. A differential equation for the temporal evolution of the modal amplitude interface is obtained. It is found that the {alpha}-particle energy has a strong influence on the evolution of the low l modes, via the compressibility of the shell. The modes are damped by vorticity convection, fire polishing, and {alpha}-particle energy deposition. The existence of a cutoff l number arises from the highmore » blow of velocity into the hot region (rocket effect) if density gradient scale length effects are taken into account at the interface. The differential equation for the modal amplitude is used as a postprocessor to the results of 1D-SARA code [J. J. Honrubia, J. Quant. Spectrosc. Radiat. Transfer. 49, 491 (1993)] in a typical capsule for indirect-drive ignition designed on the National Ignition Facility. It is found that modes with l>180 are completely stabilized. The results are in agreement with two-dimensional simulations.« less

Nonlinear Stability and Saturation of Ballooning Modes in Tokamaks*

NASA Astrophysics Data System (ADS)

Ham, C. J.; Cowley, S. C.; Brochard, G.; Wilson, H. R.

2016-06-01

The theory of tokamak stability to nonlinear "ballooning" displacements of elliptical magnetic flux tubes is presented. Above a critical pressure profile the energy stored in the plasma may be lowered by finite (but not infinitesimal) displacements of such tubes (metastability). Above a higher pressure profile, the linear stability boundary, such tubes are linearly and nonlinearly unstable. The predicted saturated flux tube displacement can be of the order of the pressure gradient scale length. Plasma transport from these displaced flux tubes may explain the rapid loss of confinement in some experiments.

Active stabilization of ion trap radiofrequency potentials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, K. G.; Wong-Campos, J. D.; Restelli, A.

2016-05-15

We actively stabilize the harmonic oscillation frequency of a laser-cooled atomic ion confined in a radiofrequency (rf) Paul trap by sampling and rectifying the high voltage rf applied to the trap electrodes. We are able to stabilize the 1 MHz atomic oscillation frequency to be better than 10 Hz or 10 ppm. This represents a suppression of ambient noise on the rf circuit by 34 dB. This technique could impact the sensitivity of ion trap mass spectrometry and the fidelity of quantum operations in ion trap quantum information applications.

A note on the effect of fault gouge thickness on fault stability

USGS Publications Warehouse

Byerlee, J.; Summers, R.

1976-01-01

At low confining pressure, sliding on saw cuts in granite is stable but at high pressure it is unstable. The pressure at which the transition takes place increases if the thickness of the crushed material between the sliding surfaces is increased. This experimental result suggests that on natural faults the stability of sliding may be affected by the width of the fault zone. ?? 1976.

Anisotropic Failure Strength of Shale with Increasing Confinement: Behaviors, Factors and Mechanism.

PubMed

Cheng, Cheng; Li, Xiao; Qian, Haitao

2017-11-15

Some studies reported that the anisotropic failure strength of shale will be weakened by increasing confinement. In this paper, it is found that there are various types of anisotropic strength behaviors. Four types of anisotropic strength ratio ( S A 1 ) behaviors and three types of anisotropic strength difference ( S A 2 ) behaviors have been classified based on laboratory experiments on nine groups of different shale samples. The cohesion c w and friction angle ϕ w of the weak planes are proven to be two dominant factors according to a series of bonded-particle discrete element modelling analyses. It is observed that shale is more prone to a slight increase of S A 1 and significant increase of S A 2 with increasing confinement for higher cohesion c w and lower to medium friction angle ϕ w . This study also investigated the mechanism of the anisotropic strength behaviors with increasing confinement. Owing to different contributions of c w and ϕ w under different confinements, different combinations of c w and ϕ w may have various types of influences on the minimum failure strength with the increasing confinement; therefore, different types of anisotropic behaviors occur for different shale specimens as the confinement increases. These findings are very important to understand the stability of wellbore and underground tunneling in the shale rock mass, and should be helpful for further studies on hydraulic fracture propagations in the shale reservoir.

Anisotropic Failure Strength of Shale with Increasing Confinement: Behaviors, Factors and Mechanism

PubMed Central

Cheng, Cheng; Li, Xiao; Qian, Haitao

2017-01-01

Some studies reported that the anisotropic failure strength of shale will be weakened by increasing confinement. In this paper, it is found that there are various types of anisotropic strength behaviors. Four types of anisotropic strength ratio (SA1) behaviors and three types of anisotropic strength difference (SA2) behaviors have been classified based on laboratory experiments on nine groups of different shale samples. The cohesion cw and friction angle ϕw of the weak planes are proven to be two dominant factors according to a series of bonded-particle discrete element modelling analyses. It is observed that shale is more prone to a slight increase of SA1 and significant increase of SA2 with increasing confinement for higher cohesion cw and lower to medium friction angle ϕw. This study also investigated the mechanism of the anisotropic strength behaviors with increasing confinement. Owing to different contributions of cw and ϕw under different confinements, different combinations of cw and ϕw may have various types of influences on the minimum failure strength with the increasing confinement; therefore, different types of anisotropic behaviors occur for different shale specimens as the confinement increases. These findings are very important to understand the stability of wellbore and underground tunneling in the shale rock mass, and should be helpful for further studies on hydraulic fracture propagations in the shale reservoir. PMID:29140292

INTRODUCTION: Award of the 2004 Hannes Alfvén Prize of the European Physical Society to J W Connor, R J Hastie and J B Taylor

NASA Astrophysics Data System (ADS)

Lister, Jo, Dr

2004-12-01

Jack Connor, Jim Hastie and Bryan Taylor The Hannes Alfvén Prize of the European Physical Society for Outstanding Contributions to Plasma Physics (2004) has been awarded to Jack Connor, Jim Hastie and Bryan Taylor `for their seminal contributions to a wide range of issues of fundamental importance to the success of magnetic confinement fusion, including: the development of gyro-kinetic theory; the prediction of the bootstrap current; dimensionless scaling laws; pressure-limiting instabilities, and micro-stability and transport theory'. Jack Connor, Jim Hastie and Bryan Taylor form one of the most successful teams of theoretical physicists in the history of magnetic confinement fusion. They have made important contributions individually, but their greatest discoveries have mostly been accomplished jointly, either in pairs or as a team involving all three. Their early work, in the 1960s, included the development of the gyro-kinetic theory for fine-scale plasma instabilities, which today forms the basis of the most advanced turbulence simulation codes in tokamak and stellarator research. The theoretical prediction of the bootstrap current, made in 1970-71 was not confirmed experimentally for over a decade but is now regarded as crucial to the success of the tokamak as a steady-state fusion power source. Their work on collisional transport also included the prediction of impurity ion accumulation, which is observed in internal transport barriers and is a key concern for long-pulse tokamak operation. The relativistic threshold for runaway electrons, identified in 1975, forms the basis of the most recent tokamak disruption mitigation schemes. In the late 1970s, the team developed the theory for ballooning instabilities, which provided an important ingredient in the `Troyon-Sykes' β-limit—an expression that is still used as a guide to the performance of tokamaks and in the design of ITER. Ballooning mode theory has also contributed to the understanding of instabilities in space plasmas such as magnetospheres and the solar corona. Finally, coming right up to date, the ballooning mode is thought to be a key ingredient in edge-localized modes (ELMs), which are a main issue for ITER, and ballooning stability is an important feature of modern stellarators. In the late 1970s and through the 1980s, the concept of dimensionless scaling laws was introduced and developed (following work by Kadomtsev), enabling scalings for transport coefficients to be derived without tackling all the details of the plasma turbulence. The same ideas are still used today to provide various constraints on confinement scaling laws, for example, on which the ITER design is largely based. The linear theory of toroidal drift waves was also developed by the team during this period, and into the 1990s. Key results on the role of shear damping in toroidal geometry, the identification of modes with extended radial correlation lengths, and the role of flow shear in reducing these correlation lengths (and hence transport) were deduced. All of these are key ideas that are often components in theoretical models for tokamak confinement and the generation of transport barriers. This laudation can only address a small number of the areas in which this formidable team of theoretical plasma physicists have made great contributions to our understanding of magnetically confined plasmas. It is appropriate and timely that their contributions are recognized as they approach the end of their careers.

Ferrocene-Promoted Long-Cycle Lithium-Sulfur Batteries.

PubMed

Mi, Yingying; Liu, Wen; Yang, Ke R; Jiang, Jianbing; Fan, Qi; Weng, Zhe; Zhong, Yiren; Wu, Zishan; Brudvig, Gary W; Batista, Victor S; Zhou, Henghui; Wang, Hailiang

2016-11-14

Confining lithium polysulfide intermediates is one of the most effective ways to alleviate the capacity fade of sulfur-cathode materials in lithium-sulfur (Li-S) batteries. To develop long-cycle Li-S batteries, there is an urgent need for material structures with effective polysulfide binding capability and well-defined surface sites; thereby improving cycling stability and allowing study of molecular-level interactions. This challenge was addressed by introducing an organometallic molecular compound, ferrocene, as a new polysulfide-confining agent. With ferrocene molecules covalently anchored on graphene oxide, sulfur electrode materials with capacity decay as low as 0.014 % per cycle were realized, among the best of cycling stabilities reported to date. With combined spectroscopic studies and theoretical calculations, it was determined that effective polysulfide binding originates from favorable cation-π interactions between Li + of lithium polysulfides and the negatively charged cyclopentadienyl ligands of ferrocene. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design of high-perveance confined-flow guns for periodic-permanent-magnet-focused tubes

NASA Technical Reports Server (NTRS)

Stankiewicz, N.

1979-01-01

An approach to the design of high perveance, low compression guns is described in which confinement is used to stabilize the beam for subsequent periodic-permanent-magnet focusing. The computed results for two cases are presented. A magnetic boundary value problem was solved for the scalar potential from which the axial magnetic field was computed. A solution was found by iterating between Poisson's equation and the electron trajectory calculations. Magnetic field values were varied in magnitude until a laminar beam with minimum scalloping was produced.

Aspects on HTS applications in confined power grids

NASA Astrophysics Data System (ADS)

Arndt, T.; Grundmann, J.; Kuhnert, A.; Kummeth, P.; Nick, W.; Oomen, M.; Schacherer, C.; Schmidt, W.

2014-12-01

In an increasing number of electric power grids the share of distributed energy generation is also increasing. The grids have to cope with a considerable change of power flow, which has an impact on the optimum topology of the grids and sub-grids (high-voltage, medium-voltage and low-voltage sub-grids) and the size of quasi-autonomous grid sections. Furthermore the stability of grids is influenced by its size. Thus special benefits of HTS applications in the power grid might become most visible in confined power grids.

The high-βN hybrid scenario for ITER and FNSF steady-state missions

DOE PAGES

Turco, Francesca; Petty, Clinton C.; Luce, Timothy C.; ...

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 βN up to 3.7 sustained for ~3 s (~1.5 current diffusion time, τ R, in DIII-D), providing the basis for an attractive option for steady-state operation in ITER and FNSF. Excellent confinement is achieved (H 98y2~1.6) without performance limiting tearing modes. Furthermore, 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 efficientmore » 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 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 N~4-4.5. Off-axis 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. Our results are based on measured profiles that 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.« less

Overview of recent and current research on the TCV tokamak

NASA Astrophysics Data System (ADS)

S. Codathe TCV Team

2013-10-01

Through a diverse research programme, the Tokamak à Configuration Variable (TCV) addresses physics issues and develops tools for ITER and for the longer term goals of nuclear fusion, relying especially on its extreme plasma shaping and electron cyclotron resonance heating (ECRH) launching flexibility and preparing for an ECRH and NBI power upgrade. Localized edge heating was unexpectedly found to decrease the period and relative energy loss of edge localized modes (ELMs). Successful ELM pacing has been demonstrated by following individual ELM detection with an ECRH power cut before turning the power back up to trigger the next ELM, the duration of the cut determining the ELM period. Negative triangularity was also seen to reduce the ELM energy release. H-mode studies have focused on the L-H threshold dependence on the main ion species and on the divertor leg length. Both L- and H-modes have been explored in the snowflake configuration with emphasis on edge measurements, revealing that the heat flux to the strike points on the secondary separatrix increases as the X-points approach each other, well before they coalesce. In L-mode, a systematic scan of the auxiliary power deposition profile, with no effect on confinement, has ruled it out as the cause of confinement degradation. An ECRH power absorption observer based on transmitted stray radiation was validated for eventual polarization control. A new profile control methodology was introduced, relying on real-time modelling to supplement diagnostic information; the RAPTOR current transport code in particular has been employed for joint control of the internal inductance and central temperature. An internal inductance controller using the ohmic transformer has also been demonstrated. Fundamental investigations of neoclassical tearing mode (NTM) seed island formation by sawtooth crashes and of NTM destabilization in the absence of a sawtooth trigger were carried out. Both stabilizing and destabilizing agents (electron cyclotron current drive on or inside the q = 1 surface, respectively) were used to pace sawtooth oscillations, permitting precise control of their period. Locking of the sawtooth period to a pre-defined ECRH modulation period was also demonstrated. Sawtooth control has permitted nearly failsafe NTM prevention when combined with backup NTM stabilization by ECRH.

Vector processing efficiency of plasma MHD codes by use of the FACOM 230-75 APU

NASA Astrophysics Data System (ADS)

Matsuura, T.; Tanaka, Y.; Naraoka, K.; Takizuka, T.; Tsunematsu, T.; Tokuda, S.; Azumi, M.; Kurita, G.; Takeda, T.

1982-06-01

In the framework of pipelined vector architecture, the efficiency of vector processing is assessed with respect to plasma MHD codes in nuclear fusion research. By using a vector processor, the FACOM 230-75 APU, the limit of the enhancement factor due to parallelism of current vector machines is examined for three numerical codes based on a fluid model. Reasonable speed-up factors of approximately 6,6 and 4 times faster than the highly optimized scalar version are obtained for ERATO (linear stability code), AEOLUS-R1 (nonlinear stability code) and APOLLO (1-1/2D transport code), respectively. Problems of the pipelined vector processors are discussed from the viewpoint of restructuring, optimization and choice of algorithms. In conclusion, the important concept of "concurrency within pipelined parallelism" is emphasized.

PROGRESS IN THE PEELING-BALLOONING MODEL OF ELMS: TOROIDAL ROTATION AND 3D NONLINEAR DYNAMICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

SNYDER,P.B; WILSON,H.R; XU,X.Q

2004-06-01

Understanding the physics of the H-Mode pedestal and edge localized modes (ELMs) is very important to next-step fusion devices for two primary reasons: (1) The pressure at the top of the edge barrier (''pedestal height'') strongly impacts global confinement and fusion performance, and (2) large ELMs lead to localized transient heat loads on material surfaces that may constrain component lifetimes. The development of the peeling-ballooning model has shed light on these issues by positing a mechanism for ELM onset and constraints on the pedestal height. The mechanism involves instability of ideal coupled ''peeling-ballooning'' modes driven by the sharp pressure gradientmore » and consequent large bootstrap current in the H-mode edge. It was first investigated in the local, high-n limit [1], and later quantified for non-local, finite-n modes in general toroidal geometry [2,3]. Important aspects are that a range of wavelengths may potentially be unstable, with intermediate n's (n {approx} 3-30) generally limiting in high performance regimes, and that stability bounds are strongly sensitive to shape [Fig l(a)], and to collisionality (i.e. temperature and density) [4] through the bootstrap current. The development of efficient MHD stability codes such as ELITE [3,2] and MISHKA [5] has allowed detailed quantification of peeling-ballooning stability bounds (e.g. [6]) and extensive and largely successful comparisons with observation (e.g. [2,6-9]). These previous calculations are ideal, static, and linear. Here we extend this work to incorporate the impact of sheared toroidal rotation, and the non-ideal, nonlinear dynamics which must be studied to quantify ELM size and heat deposition on material surfaces.« less

Structures of Neural Correlation and How They Favor Coding

PubMed Central

Franke, Felix; Fiscella, Michele; Sevelev, Maksim; Roska, Botond; Hierlemann, Andreas; da Silveira, Rava Azeredo

2017-01-01

Summary The neural representation of information suffers from “noise”—the trial-to-trial variability in the response of neurons. The impact of correlated noise upon population coding has been debated, but a direct connection between theory and experiment remains tenuous. Here, we substantiate this connection and propose a refined theoretical picture. Using simultaneous recordings from a population of direction-selective retinal ganglion cells, we demonstrate that coding benefits from noise correlations. The effect is appreciable already in small populations, yet it is a collective phenomenon. Furthermore, the stimulus-dependent structure of correlation is key. We develop simple functional models that capture the stimulus-dependent statistics. We then use them to quantify the performance of population coding, which depends upon interplays of feature sensitivities and noise correlations in the population. Because favorable structures of correlation emerge robustly in circuits with noisy, nonlinear elements, they will arise and benefit coding beyond the confines of retina. PMID:26796692

Nucleotide sequence determination of guinea-pig casein B mRNA reveals homology with bovine and rat alpha s1 caseins and conservation of the non-coding regions of the mRNA.

PubMed Central

Hall, L; Laird, J E; Craig, R K

1984-01-01

Nucleotide sequence analysis of cloned guinea-pig casein B cDNA sequences has identified two casein B variants related to the bovine and rat alpha s1 caseins. Amino acid homology was largely confined to the known bovine or predicted rat phosphorylation sites and within the 'signal' precursor sequence. Comparison of the deduced nucleotide sequence of the guinea-pig and rat alpha s1 casein mRNA species showed greater sequence conservation in the non-coding than in the coding regions, suggesting a functional and possibly regulatory role for the non-coding regions of casein mRNA. The results provide insight into the evolution of the casein genes, and raise questions as to the role of conserved nucleotide sequences within the non-coding regions of mRNA species. Images Fig. 1. PMID:6548375

Comparing Turbulence Simulation with Experiment in DIII-D

NASA Astrophysics Data System (ADS)

Ross, D. W.; Bravenec, R. V.; Dorland, W.; Beer, M. A.; Hammett, G. W.; McKee, G. R.; Murakami, M.; Jackson, G. L.

2000-10-01

Gyrofluid simulations of DIII-D discharges with the GRYFFIN code(D. W. Ross et al.), Transport Task Force Workshop, Burlington, VT, (2000). are compared with transport and fluctuation measurements. The evolution of confinement-improved discharges(G. R. McKee et al.), Phys. Plasmas 7, 1870 (200) is studied at early times following impurity injection, when EXB rotational shear plays a small role. The ion thermal transport predicted by the code is consistent with the experimental values. Experimentally, changes in density profiles resulting from the injection of neon, lead to reduction in fluctuation levels and transport following the injection. This triggers subsequent changes in the shearing rate that further reduce the turbulence.(M. Murakami et al.), European Physical Society, Budapest (2000); M. Murakami et al., this meeting. Estimated uncertainties in the plasma profiles, however, make it difficult to simulate these reductions with the code. These cases will also be studied with the GS2 gyrokinetic code.

Modeling anomalous radial transport in kinetic transport codes

NASA Astrophysics Data System (ADS)

Bodi, K.; Krasheninnikov, S. I.; Cohen, R. H.; Rognlien, T. D.

2009-11-01

Anomalous transport is typically the dominant component of the radial transport in magnetically confined plasmas, where the physical origin of this transport is believed to be plasma turbulence. A model is presented for anomalous transport that can be used in continuum kinetic edge codes like TEMPEST, NEO and the next-generation code being developed by the Edge Simulation Laboratory. The model can also be adapted to particle-based codes. It is demonstrated that the model with a velocity-dependent diffusion and convection terms can match a diagonal gradient-driven transport matrix as found in contemporary fluid codes, but can also include off-diagonal effects. The anomalous transport model is also combined with particle drifts and a particle/energy-conserving Krook collision operator to study possible synergistic effects with neoclassical transport. For the latter study, a velocity-independent anomalous diffusion coefficient is used to mimic the effect of long-wavelength ExB turbulence.

A velocity-dependent anomalous radial transport model for (2-D, 2-V) kinetic transport codes

NASA Astrophysics Data System (ADS)

Bodi, Kowsik; Krasheninnikov, Sergei; Cohen, Ron; Rognlien, Tom

2008-11-01

Plasma turbulence constitutes a significant part of radial plasma transport in magnetically confined plasmas. This turbulent transport is modeled in the form of anomalous convection and diffusion coefficients in fluid transport codes. There is a need to model the same in continuum kinetic edge codes [such as the (2-D, 2-V) transport version of TEMPEST, NEO, and the code being developed by the Edge Simulation Laboratory] with non-Maxwellian distributions. We present an anomalous transport model with velocity-dependent convection and diffusion coefficients leading to a diagonal transport matrix similar to that used in contemporary fluid transport models (e.g., UEDGE). Also presented are results of simulations corresponding to radial transport due to long-wavelength ExB turbulence using a velocity-independent diffusion coefficient. A BGK collision model is used to enable comparison with fluid transport codes.

Study of Evaporation Rate of Water in Hydrophobic Confinement using Forward Flux Sampling

NASA Astrophysics Data System (ADS)

Sharma, Sumit; Debenedetti, Pablo G.

2012-02-01

Drying of hydrophobic cavities is of interest in understanding biological self assembly, protein stability and opening and closing of ion channels. Liquid-to-vapor transition of water in confinement is associated with large kinetic barriers which preclude its study using conventional simulation techniques. Using forward flux sampling to study the kinetics of the transition between two hydrophobic surfaces, we show that a) the free energy barriers to evaporation scale linearly with the distance between the two surfaces, d; b) the evaporation rates increase as the lateral size of the surfaces, L increases, and c) the transition state to evaporation for sufficiently large L is a cylindrical vapor cavity connecting the two hydrophobic surfaces. Finally, we decouple the effects of confinement geometry and surface chemistry on the evaporation rates.

On fully three-dimensional resistive wall mode and feedback stabilization computationsa)

NASA Astrophysics Data System (ADS)

Strumberger, E.; Merkel, P.; Sempf, M.; Günter, S.

2008-05-01

Resistive walls, located close to the plasma boundary, reduce the growth rates of external kink modes to resistive time scales. For such slowly growing resistive wall modes, the stabilization by an active feedback system becomes feasible. The fully three-dimensional stability code STARWALL, and the feedback optimization code OPTIM have been developed [P. Merkel and M. Sempf, 21st IAEA Fusion Energy Conference 2006, Chengdu, China (International Atomic Energy Agency, Vienna, 2006, paper TH/P3-8] to compute the growth rates of resistive wall modes in the presence of nonaxisymmetric, multiply connected wall structures and to model the active feedback stabilization of these modes. In order to demonstrate the capabilities of the codes and to study the effect of the toroidal mode coupling caused by multiply connected wall structures, the codes are applied to test equilibria using the resistive wall structures currently under debate for ITER [M. Shimada et al., Nucl. Fusion 47, S1 (2007)] and ASDEX Upgrade [W. Köppendörfer et al., Proceedings of the 16th Symposium on Fusion Technology, London, 1990 (Elsevier, Amsterdam, 1991), Vol. 1, p. 208].

On fully three-dimensional resistive wall mode and feedback stabilization computations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strumberger, E.; Merkel, P.; Sempf, M.

2008-05-15

Resistive walls, located close to the plasma boundary, reduce the growth rates of external kink modes to resistive time scales. For such slowly growing resistive wall modes, the stabilization by an active feedback system becomes feasible. The fully three-dimensional stability code STARWALL, and the feedback optimization code OPTIM have been developed [P. Merkel and M. Sempf, 21st IAEA Fusion Energy Conference 2006, Chengdu, China (International Atomic Energy Agency, Vienna, 2006, paper TH/P3-8] to compute the growth rates of resistive wall modes in the presence of nonaxisymmetric, multiply connected wall structures and to model the active feedback stabilization of these modes.more » In order to demonstrate the capabilities of the codes and to study the effect of the toroidal mode coupling caused by multiply connected wall structures, the codes are applied to test equilibria using the resistive wall structures currently under debate for ITER [M. Shimada et al., Nucl. Fusion 47, S1 (2007)] and ASDEX Upgrade [W. Koeppendoerfer et al., Proceedings of the 16th Symposium on Fusion Technology, London, 1990 (Elsevier, Amsterdam, 1991), Vol. 1, p. 208].« less

Effects of geometry on blast-induced loadings

NASA Astrophysics Data System (ADS)

Moore, Christopher Dyer

Simulations of blasts in an urban environment were performed using Loci/BLAST, a full-featured fluid dynamics simulation code, and analyzed. A two-structure urban environment blast case was used to perform a mesh refinement study. Results show that mesh spacing on and around the structure must be 12.5 cm or less to resolve fluid dynamic features sufficiently to yield accurate results. The effects of confinement were illustrated by analyzing a blast initiated from the same location with and without the presence of a neighboring structure. Analysis of extreme pressures and impulses on structures showed that confinement can increase blast loading by more than 200 percent.

Field Validation of the Stability Limit of a Multi MW Turbine

NASA Astrophysics Data System (ADS)

Kallesøe, Bjarne S.; Kragh, Knud A.

2016-09-01

Long slender blades of modern multi-megawatt turbines exhibit a flutter like instability at rotor speeds above a critical rotor speed. Knowing the critical rotor speed is crucial to a safe turbine design. The flutter like instability can only be estimated using geometrically non-linear aeroelastic codes. In this study, the estimated rotor speed stability limit of a 7 MW state of the art wind turbine is validated experimentally. The stability limit is estimated using Siemens Wind Powers in-house aeroelastic code, and the results show that the predicted stability limit is within 5% of the experimentally observed limit.

Turbulent edge transport in the Princeton Beta Experiment-Modified high confinement mode

NASA Astrophysics Data System (ADS)

Tynan, G. R.; Schmitz, L.; Blush, L.; Boedo, J. A.; Conn, R. W.; Doerner, R.; Lehmer, R.; Moyer, R.; Kugel, H.; Bell, R.; Kaye, S.; Okabayashi, M.; Sesnic, S.; Sun, Y.

1994-10-01

The first probe measurements of edge turbulence and transport in a neutral beam induced high confinement mode (H-mode) are reported. A strong negative radial electric field is directly observed in H-mode. A transient suppression of normalized ion saturation and floating potential fluctuation levels occurs at the low confinement mode to high confinement mode (L-H) transition, followed by a recovery to near low mode (L-mode) levels. The average poloidal wave number and the poloidal wave-number spectral width are decreased, and the correlation between fluctuating density and potential is reduced. A large-amplitude coherent oscillation, localized to the strong radial electric field region, is observed in H-mode but does not cause transport. In H-mode the effective turbulent diffusion coefficient is reduced by an order of magnitude inside the last closed flux surface and in the scrape-off layer. The results are compared with a heuristic model of turbulence suppression by velocity-shear stabilization.

Self-Assembly of Diblock Molecular Polymer Brushes in the Spherical Confinement of Nanoemulsion Droplets.

PubMed

Steinhaus, Andrea; Pelras, Théophile; Chakroun, Ramzi; Gröschel, André H; Müllner, Markus

2018-05-02

Understanding the self-assembly behavior of polymers of various topologies is key to a reliable design of functional polymer materials. Self-assembly under confinement conditions emerges as a versatile avenue to design polymer particles with complex internal morphologies while simultaneously facilitating scale-up. However, only linear block copolymers have been studied to date, despite the increasing control over macromolecule composition and architecture available. This study extends the investigation of polymer self-assembly in confinement from regular diblock copolymers to diblock molecular polymer brushes (MPBs). Block-type MPBs with polystyrene (PS) and polylactide (PLA) compartments of different sizes are incorporated into surfactant-stabilized oil-in-water (chloroform/water) emulsions. The increasing confinement in the nanoemulsion droplets during solvent evaporation directs the MPBs to form solid nano/microparticles. Microscopy studies reveal an intricate internal particle structure, including interpenetrating networks and axially stacked lamellae of PS and PLA, depending on the PS/PLA ratio of the brushes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Crystallization in Micellar Cores: confinement effects and dynamics

NASA Astrophysics Data System (ADS)

Lund, Reidar; Zinn, Thomas; Willner, Lutz; Department of Chemistry, University of Oslo Team; Forschungszentrum Jülich Collaboration

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Here we demonstrate that n-alkanes forming 2-3 nm small micellar cores are considerably affected by confinement in analogue with hard confined systems. We study micelles form by self-assembly of a series of well-defined n-Alkyl-PEO polymers in aqueous solutions. By using small-angle X-ray scattering (SAXS), densiometry and differential scanning calorimetry (DSC), we show that n-alkane exhibit a first-order phase transition i.e. melting. Correlating the structural and thermodynamic data, we find that a melting depression can be accurately described by the Gibbs-Thomson equation. ∖f1 The effect of core crystallinity on the molecular exchange kinetics is investigated using time-resolved small-angle neutron scattering (TR-SANS). We show that there are considerable entropic and enthalpic contributions from the chain packing that affect the kinetic stability of micelles. ∖pard

Investigation of air cleaning system response to accident conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrae, R.W.; Bolstad, J.W.; Foster, R.D.

1980-01-01

Air cleaning system response to the stress of accident conditions are being investigated. A program overview and hghlight recent results of our investigation are presented. The program includes both analytical and experimental investigations. Computer codes for predicting effects of tornados, explosions, fires, and material transport are described. The test facilities used to obtain supportive experimental data to define structural integrity and confinement effectiveness of ventilation system components are described. Examples of experimental results for code verification, blower response to tornado transients, and filter response to tornado and explosion transients are reported.

Transport properties of NSTX-U L- and H-mode plasmas

NASA Astrophysics Data System (ADS)

Kaye, Stanley; Guttenfelder, Walter; Bell, Ron; Diallo, Ahmed; Leblanc, Ben; Podesta, Mario

2016-10-01

The confinement and transport properties of L- and H-mode plasmas in NSTX-U has been studied using the TRANSP code. A dedicated series of L-mode discharges was obtained to study the dependence of confinement and transport on power level and beam aiming angle. The latter is made possible by having two beamlines with 3 sources each, capable of injecting with tangency radii from Rtan = 50 to 130 cm (Rgeo = 92 cm). L-mode plasmas typically have confinement enhancement factors with H98y,2 =0.6 to 0.65, exhibiting a 25% decrease in confinement time as the beam power is raised from 1 to 3 MW. Associated with this is an increase in the electron thermal diffusivity in the core of the plasma from 3.5 to 10 m2/s. Electron thermal transport is the dominant energy loss channel in these plasmas. H-mode plasmas exhibit improved confinement, with H98y,2 =1 or above, and core electron thermal diffusivity values <1 m2/s. Details of these studies will be presented, along with the results of the beam tangency radius scan in L-mode plasmas. This research was supported by the U.S. Department of Energy contract # DE-AC02-09CH11466.

Stability of a Plasma Column. Free-Particle Model; STABILITE D'UNE COLONNE DE PLASMA. MODELE DES PARTICULES LIBRES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Troyon, F.

1963-12-01

The stability of a field-free homogeneous column of plasma confined to an axial static field and the sum of an alternating and static B/sub tt/ field is considered in the freeparticle model. Conditions for the existence of a positive average restoring force are derived, and it is shown that for small deformations the column is stable for sufficientiy high frequency. (auth)

Longitudinal structure of MHD perturbations at the boundary of convective stability in the Kruskal-Oberman model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arsenin, V. V.

2010-10-15

It is shown that, in contrast to the MHD model, a perturbation at the boundary of convective stability of a finite-pressure plasma in confinement systems without an averaged minB in the Kruskal-Oberman model is not generally a purely flute one. The reasons for this discrepancy are clarified. The analysis is carried out for axisymmetric configurations formed by a poloidal magnetic field.

High-beta steady-state research with integrated modeling in the JT-60 Upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ozeki, T.

2007-05-15

Improvement of high-beta performance and its long sustainment was obtained with ferritic steel tiles in the JT-60 Upgrade (JT-60U) [T. Fujita et al., Phys. Plasmas 50, 104 (2005)], which were installed inside the vacuum vessel to reduce fast ion loss by decreasing the toroidal field ripple. When a separation between the plasma surface and the wall was small, high-beta plasmas reached the ideal wall stability limit, i.e., the ideal magnetohydrodynamics stability limit with the wall stabilization. A small rotation velocity of 0.3% of the Alfven velocity was found to be effective for suppressing the resistive wall mode. Sustainment of themore » high normalized beta value of {beta}{sub N}=2.3 has been extended to 28.6 s ({approx}15 times the current diffusion time) by improvement of the confinement and increase in the net heating power. Based on the research in JT-60U experiments and first-principle simulations, integrated models of core, edge-pedestal, and scrape-off-layer (SOL) divertors were developed, and they clarified complex features of reactor-relevant plasmas. The integrated core plasma model indicated that the small amount of electron cyclotron (EC) current density of about half the bootstrap current density could effectively stabilize the neoclassical tearing mode by the localized EC current accurately aligned to the magnetic island center. The integrated edge-pedestal model clarified that the collisionality dependence of energy loss due to the edge-localized mode was caused by the change in the width of the unstable mode and the SOL transport. The integrated SOL-divertor model clarified the effect of the exhaust slot on the pumping efficiency and the cause of enhanced radiation near the X-point multifaceted asymmetric radiation from edge. Success in these consistent analyses using the integrated code indicates that it is an effective means to investigate complex plasmas and to control the integrated performance.« less

Benchmarking kinetic calculations of resistive wall mode stability

NASA Astrophysics Data System (ADS)

Berkery, J. W.; Liu, Y. Q.; Wang, Z. R.; Sabbagh, S. A.; Logan, N. C.; Park, J.-K.; Manickam, J.; Betti, R.

2014-05-01

Validating the calculations of kinetic resistive wall mode (RWM) stability is important for confidently predicting RWM stable operating regions in ITER and other high performance tokamaks for disruption avoidance. Benchmarking the calculations of the Magnetohydrodynamic Resistive Spectrum—Kinetic (MARS-K) [Y. Liu et al., Phys. Plasmas 15, 112503 (2008)], Modification to Ideal Stability by Kinetic effects (MISK) [B. Hu et al., Phys. Plasmas 12, 057301 (2005)], and Perturbed Equilibrium Nonambipolar Transport PENT) [N. Logan et al., Phys. Plasmas 20, 122507 (2013)] codes for two Solov'ev analytical equilibria and a projected ITER equilibrium has demonstrated good agreement between the codes. The important particle frequencies, the frequency resonance energy integral in which they are used, the marginally stable eigenfunctions, perturbed Lagrangians, and fluid growth rates are all generally consistent between the codes. The most important kinetic effect at low rotation is the resonance between the mode rotation and the trapped thermal particle's precession drift, and MARS-K, MISK, and PENT show good agreement in this term. The different ways the rational surface contribution was treated historically in the codes is identified as a source of disagreement in the bounce and transit resonance terms at higher plasma rotation. Calculations from all of the codes support the present understanding that RWM stability can be increased by kinetic effects at low rotation through precession drift resonance and at high rotation by bounce and transit resonances, while intermediate rotation can remain susceptible to instability. The applicability of benchmarked kinetic stability calculations to experimental results is demonstrated by the prediction of MISK calculations of near marginal growth rates for experimental marginal stability points from the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)].

Impact of neoclassical tearing mode–turbulence multi-scale interaction in global confinement degradation and magnetic island stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bardoczi, Lazlo; Carter, Troy A.; La Haye, Robert J.

Recent measurements of turbulent density (more » $$\\tilde{n}$$) and electron-temperature ($$\\tilde{T}$$ e) fluctuations have reported turbulence modifications by Neoclassical Tearing Mode (NTM) islands: turbulence decreases (increases) inside (outside) the island region when the island width (W) exceeds a threshold (W T), in qualitative agreement with gyrokinetic simulations. As the cross-field transport in tokamaks is dominantly driven by turbulence, these observations call into question the conventional understanding of confinement degradation by NTMs and magnetic island stability physics. The experimental data presented here support the following points: (i) When profiles flatten at the O-point and gradients increase outside of the island, $$\\tilde{n}$$ decreases (increases) inside (outside) the island. Along with the parallel transport resulting in increased fluxes inside the island, the increase of $$\\tilde{n}$$ outside of the island offers an explanation for the temporal increase of fluxes in that region. As the plasma stored energy (WMHD) gradually decreases in synchronization with the island growth and saturation, gradients, $$\\tilde{n}$$ and fluxes also decrease outside the island until they become about the same as before NTM onset. These fluxes balance the constant sources, and the plasma comes to a steady state at lower W MHD. (ii) Turbulence reduction in the O-point region has a destabilizing effect on the island. This effect is, however, nearly compensated by the reduced confinement. In conclusion, these observations suggest that driving turbulence in the island region could lead to smaller saturated islands offering a path toward better confinement and safer operation of reactor-scale fusion devices.« less

Impact of neoclassical tearing mode–turbulence multi-scale interaction in global confinement degradation and magnetic island stability

DOE PAGES

Bardoczi, Lazlo; Carter, Troy A.; La Haye, Robert J.; ...

2017-12-08

Recent measurements of turbulent density (more » $$\\tilde{n}$$) and electron-temperature ($$\\tilde{T}$$ e) fluctuations have reported turbulence modifications by Neoclassical Tearing Mode (NTM) islands: turbulence decreases (increases) inside (outside) the island region when the island width (W) exceeds a threshold (W T), in qualitative agreement with gyrokinetic simulations. As the cross-field transport in tokamaks is dominantly driven by turbulence, these observations call into question the conventional understanding of confinement degradation by NTMs and magnetic island stability physics. The experimental data presented here support the following points: (i) When profiles flatten at the O-point and gradients increase outside of the island, $$\\tilde{n}$$ decreases (increases) inside (outside) the island. Along with the parallel transport resulting in increased fluxes inside the island, the increase of $$\\tilde{n}$$ outside of the island offers an explanation for the temporal increase of fluxes in that region. As the plasma stored energy (WMHD) gradually decreases in synchronization with the island growth and saturation, gradients, $$\\tilde{n}$$ and fluxes also decrease outside the island until they become about the same as before NTM onset. These fluxes balance the constant sources, and the plasma comes to a steady state at lower W MHD. (ii) Turbulence reduction in the O-point region has a destabilizing effect on the island. This effect is, however, nearly compensated by the reduced confinement. In conclusion, these observations suggest that driving turbulence in the island region could lead to smaller saturated islands offering a path toward better confinement and safer operation of reactor-scale fusion devices.« less

Electronic Structure of Helium Atom in a Quantum Dot

NASA Astrophysics Data System (ADS)

Saha, Jayanta K.; Bhattacharyya, S.; Mukherjee, T. K.

2016-03-01

Bound and resonance states of helium atom have been investigated inside a quantum dot by using explicitly correlated Hylleraas type basis set within the framework of stabilization method. To be specific, precise energy eigenvalues of bound 1sns (1Se) (n = 1-6) states and the resonance parameters i.e. positions and widths of 1Se states due to 2sns (n = 2-5) and 2pnp (n = 2-5) configurations of confined helium below N = 2 ionization threshold of He+ have been estimated. The two-parameter (Depth and Width) finite oscillator potential is used to represent the confining potential due to the quantum dot. It has been explicitly demonstrated that the electronic structural properties become sensitive functions of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within a quantum dot may be manipulated by varying the confinement parameters. A possibility of controlling the autoionization lifetime of doubly excited states of two-electron ions by tuning the width of the quantum cavity is also discussed here. TKM Gratefully Acknowledges Financial Support under Grant No. 37(3)/14/27/2014-BRNS from the Department of Atomic Energy, BRNS, Government of India. SB Acknowledges Financial Support under Grant No. PSW-160/14-15(ERO) from University Grants Commission, Government of India

Confined Rayleigh-Bénard, Rotating Rayleigh-Bénard, and Double Diffusive Convection: A Unifying View on Turbulent Transport Enhancement through Coherent Structure Manipulation

NASA Astrophysics Data System (ADS)

Chong, Kai Leong; Yang, Yantao; Huang, Shi-Di; Zhong, Jin-Qiang; Stevens, Richard J. A. M.; Verzicco, Roberto; Lohse, Detlef; Xia, Ke-Qing

2017-08-01

Many natural and engineering systems are simultaneously subjected to a driving force and a stabilizing force. The interplay between the two forces, especially for highly nonlinear systems such as fluid flow, often results in surprising features. Here we reveal such features in three different types of Rayleigh-Bénard (RB) convection, i.e., buoyancy-driven flow with the fluid density being affected by a scalar field. In the three cases different stabilizing forces are considered, namely (i) horizontal confinement, (ii) rotation around a vertical axis, and (iii) a second stabilizing scalar field. Despite the very different nature of the stabilizing forces and the corresponding equations of motion, at moderate strength we counterintuitively but consistently observe an enhancement in the flux, even though the flow motion is weaker than the original RB flow. The flux enhancement occurs in an intermediate regime in which the stabilizing force is strong enough to alter the flow structures in the bulk to a more organized morphology, yet not too strong to severely suppress the flow motions. Near the optimal transport enhancements all three systems exhibit a transition from a state in which the thermal boundary layer (BL) is nested inside the momentum BL to the one with the thermal BL being thicker than the momentum BL. The observed optimal transport enhancement is explained through an optimal coupling between the suction of hot or fresh fluid and the corresponding scalar fluctuations.

Surface-confined fluorescence enhancement of Au nanoclusters anchoring to a two-dimensional ultrathin nanosheet toward bioimaging

NASA Astrophysics Data System (ADS)

Tian, Rui; Yan, Dongpeng; Li, Chunyang; Xu, Simin; Liang, Ruizheng; Guo, Lingyan; Wei, Min; Evans, David G.; Duan, Xue

2016-05-01

Gold nanoclusters (Au NCs) as ultrasmall fluorescent nanomaterials possess discrete electronic energy and unique physicochemical properties, but suffer from relatively low quantum yield (QY) which severely affects their application in displays and imaging. To solve this conundrum and obtain highly-efficient fluorescent emission, 2D exfoliated layered double hydroxide (ELDH) nanosheets were employed to localize Au NCs with a density as high as 5.44 × 1013 cm-2, by virtue of the surface confinement effect of ELDH. Both experimental studies and computational simulations testify that the excited electrons of Au NCs are strongly confined by MgAl-ELDH nanosheets, which results in a largely promoted QY as well as prolonged fluorescence lifetime (both ~7 times enhancement). In addition, the as-fabricated Au NC/ELDH hybrid material exhibits excellent imaging properties with good stability and biocompatibility in the intracellular environment. Therefore, this work provides a facile strategy to achieve highly luminescent Au NCs via surface-confined emission enhancement imposed by ultrathin inorganic nanosheets, which can be potentially used in bio-imaging and cell labelling.Gold nanoclusters (Au NCs) as ultrasmall fluorescent nanomaterials possess discrete electronic energy and unique physicochemical properties, but suffer from relatively low quantum yield (QY) which severely affects their application in displays and imaging. To solve this conundrum and obtain highly-efficient fluorescent emission, 2D exfoliated layered double hydroxide (ELDH) nanosheets were employed to localize Au NCs with a density as high as 5.44 × 1013 cm-2, by virtue of the surface confinement effect of ELDH. Both experimental studies and computational simulations testify that the excited electrons of Au NCs are strongly confined by MgAl-ELDH nanosheets, which results in a largely promoted QY as well as prolonged fluorescence lifetime (both ~7 times enhancement). In addition, the as-fabricated Au NC/ELDH hybrid material exhibits excellent imaging properties with good stability and biocompatibility in the intracellular environment. Therefore, this work provides a facile strategy to achieve highly luminescent Au NCs via surface-confined emission enhancement imposed by ultrathin inorganic nanosheets, which can be potentially used in bio-imaging and cell labelling. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01624c

Documentation of a numerical code for the simulation of variable density ground-water flow in three dimensions

USGS Publications Warehouse

Kuiper, L.K.

1985-01-01

A numerical code is documented for the simulation of variable density time dependent groundwater flow in three dimensions. The groundwater density, although variable with distance, is assumed to be constant in time. The Integrated Finite Difference grid elements in the code follow the geologic strata in the modeled area. If appropriate, the determination of hydraulic head in confining beds can be deleted to decrease computation time. The strongly implicit procedure (SIP), successive over-relaxation (SOR), and eight different preconditioned conjugate gradient (PCG) methods are used to solve the approximating equations. The use of the computer program that performs the calculations in the numerical code is emphasized. Detailed instructions are given for using the computer program, including input data formats. An example simulation and the Fortran listing of the program are included. (USGS)

A nonlocal electron conduction model for multidimensional radiation hydrodynamics codes

NASA Astrophysics Data System (ADS)

Schurtz, G. P.; Nicolaï, Ph. D.; Busquet, M.

2000-10-01

Numerical simulation of laser driven Inertial Confinement Fusion (ICF) related experiments require the use of large multidimensional hydro codes. Though these codes include detailed physics for numerous phenomena, they deal poorly with electron conduction, which is the leading energy transport mechanism of these systems. Electron heat flow is known, since the work of Luciani, Mora, and Virmont (LMV) [Phys. Rev. Lett. 51, 1664 (1983)], to be a nonlocal process, which the local Spitzer-Harm theory, even flux limited, is unable to account for. The present work aims at extending the original formula of LMV to two or three dimensions of space. This multidimensional extension leads to an equivalent transport equation suitable for easy implementation in a two-dimensional radiation-hydrodynamic code. Simulations are presented and compared to Fokker-Planck simulations in one and two dimensions of space.

MHD Stability of Axisymmetric Plasmas In Closed Line Magnetic Fields

NASA Astrophysics Data System (ADS)

Simakov, Andrei N.; Catto, Peter J.; Ramos, Jesus J.; Hastie, R. J.

2003-04-01

The stability of axisymmetric plasmas confined by closed poloidal magnetic field lines is considered. The results are relevant to plasmas in the dipolar fields of stars and planets, as well as the Levitated Dipole Experiment, multipoles, Z pinches and field reversed configurations. The ideal MHD energy principle is employed to study stability of pressure driven Alfvén modes. A point dipole is considered in detail to demonstrate that equilibria exist, which are MHD stable for arbitrary beta. Effects of sound waves and plasma resistivity are investigated next for point dipole equilibria by means of resistive MHD theory.

What Gives an Insulin Hexamer Its Unique Shape and Stability? Role of Ten Confined Water Molecules.

PubMed

Mukherjee, Saumyak; Mondal, Sayantan; Deshmukh, Ashish Anilrao; Gopal, Balasubramanian; Bagchi, Biman

2018-02-08

Self-assembly of proteins often gives rise to interesting quasi-stable structures that serve important biological purposes. Insulin hexamer is such an assembly. While monomer is the biologically active form of insulin, hexamer serves as the storehouse of the hormone. The hexamer also prevents the formation of higher order aggregates. While several studies explored the role of bivalent metal ions like Zn 2+ , Ca 2+ , etc., in the stabilization of the hexameric form, the role of water molecules has been ignored. We combine molecular dynamics simulations, quantum calculations, and X-ray analyses to discover that a team of approximately 10 water molecules confined inside a barrel-shaped nanocavity at the center of insulin hexamer is one of the major causes that account for the unusual stability of the biomolecular assembly. These cavity water molecules exhibit interesting dynamical features like intermittent escape and reentrance. We find that these water molecules are dynamically slower than the bulk and weave an intricate hydrogen bond network among themselves and with neighboring protein residues to generate a robust backbone at the center of the hexamer that holds the association strongly from inside and maintains the barrel shape.

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.

Computerized Support of the Pretrial Confinement Decision-Making Process in the Marine Corps.

DTIC Science & Technology

1988-03-01

Books Inc., Blue Ridge Summit, Pennsylvania, 1986. 7. Pressman , R.S., Software Engineering: A Practitioner’s Approach, Second Edition, McGraw-Hill Book...Lieutenant Commander Barry Frew, Code 54Fw 2 Naval Postgraduate School Monterey, California 93943-500 150 NIN U1 W 40 I U n

Effects of residual kinetic energy on yield degradation and ion temperature asymmetries in inertial confinement fusion implosions

NASA Astrophysics Data System (ADS)

Woo, K. M.; Betti, R.; Shvarts, D.; Bose, A.; Patel, D.; Yan, R.; Chang, P.-Y.; Mannion, O. M.; Epstein, R.; Delettrez, J. A.; Charissis, M.; Anderson, K. S.; Radha, P. B.; Shvydky, A.; Igumenshchev, I. V.; Gopalaswamy, V.; Christopherson, A. R.; Sanz, J.; Aluie, H.

2018-05-01

The study of Rayleigh-Taylor instability in the deceleration phase of inertial confinement fusion implosions is carried out using the three-dimensional (3-D) radiation-hydrodynamic Eulerian parallel code DEC3D. We show that the yield-over-clean is a strong function of the residual kinetic energy (RKE) for low modes. Our analytical models indicate that the behavior of larger hot-spot volumes observed in low modes and the consequential pressure degradation can be explained in terms of increasing the RKE. These results are derived using a simple adiabatic implosion model of the deceleration phase as well as through an extensive set of 3-D single-mode simulations using the code DEC3D. The effect of the bulk velocity broadening on ion temperature asymmetries is analyzed for different mode numbers ℓ=1 -12. The jet observed in low mode ℓ=1 is shown to cause the largest ion temperature variation in the mode spectrum. The vortices of high modes within the cold bubbles are shown to cause lower ion temperature variations than low modes.

Edge Mechanisms for Power Excursion Control in Burning Plasmas

NASA Astrophysics Data System (ADS)

Hill, M. D.; Stacey, W. M.

2017-10-01

ITER must have active and preferably also passive control mechanisms that will limit inadvertent plasma power excursions which could trigger runaway fusion heating. We are identifying and investigating the potential of ion-orbit loss, impurity seeding, and various divertor ``choking'' phenomena to control or limit sudden increases in plasma density or temperature by reducing energy confinement, increasing radiation loss, etc., with the idea that such mechanisms could be tested on DIII-D and other existing tokamaks. We are assembling an edge-divertor code (GTEDGE-2) with a neutral transport model and a burn dynamics code, for this purpose. One potential control mechanism is the enhanced ion orbit loss from the thermalized ion distribution that would result from heating of the thermalized plasma ion distribution. Another possibility is impurity seeding with ions whose emissivity would increase sharply if the edge temperature increased. Enhanced radiative losses should also reduce the thermal energy flux across the separatrix, perhaps dropping the plasma into the poorer L-mode confinement regime. We will present some initial calculations to quantify these ideas. Work supported by US DOE under DE-FC02-04ER54698.

A numerical study on the thermal initiation of a confined explosive in 2-D geometry.

PubMed

Aydemir, Erdoğan; Ulas, Abdullah

2011-02-15

Insensitive munitions design against thermal stimuli like slow or fast cook-off has become a significant requirement for today's munitions. In order to achieve insensitive munitions characteristics, the response of the energetic material needs to be predicted against heating stimuli. In this study, a 2D numerical code was developed to simulate the slow and fast cook-off heating conditions of confined munitions and to obtain the response of the energetic materials. Computations were performed in order to predict the transient temperature distribution, the ignition time, and the location of ignition in the munitions. These predictions enable the designers to have an idea of when and at which location the energetic material ignites under certain adverse surrounding conditions. In the paper, the development of the code is explained and the numerical results are compared with available experimental and numerical data in the literature. Additionally, a parametric study was performed showing the effect of dimensional scaling of munitions and the heating rate on the ignition characteristics. Copyright © 2010 Elsevier B.V. All rights reserved.

Modeling of Resistive Wall Modes in Tokamak and Reversed Field Pinch Configurations of KTX

NASA Astrophysics Data System (ADS)

Han, Rui; Zhu, Ping; Bai, Wei; Lan, Tao; Liu, Wandong

2016-10-01

Resistive wall mode is believed to be one of the leading causes for macroscopic degradation of plasma confinement in tokamaks and reversed field pinches (RFP). In this study, we evaluate the linear RWM instability of Keda Torus eXperiment (KTX) in both tokamak and RFP configurations. For the tokamak configuration, the extended MHD code NIMROD is employed for calculating the dependence of the RWM growth rate on the position and conductivity of the vacuum wall for a model tokamak equilibrium of KTX in the large aspect-ratio approximation. For the RFP configuration, the standard formulation of dispersion relation for RWM based on the MHD energy principle has been evaluated for a cylindrical α- Θ model of KTX plasma equilibrium, in an effort to investigate the effects of thin wall on the RWM in KTX. Full MHD calculations of RWM in the RFP configuration of KTX using the NIMROD code are also being developed. Supported by National Magnetic Confinement Fusion Science Program of China Grant Nos. 2014GB124002, 2015GB101004, 2011GB106000, and 2011GB106003.

Energetic particle transport and alpha driven instabilities in advanced confinement DT plasmas on TFTR

NASA Astrophysics Data System (ADS)

Stratton, B. C.; Budny, R. V.; Darrow, D. S.; Fisher, R. K.; Fredrickson, E. D.; Fu, G. Y.; Medley, S. S.; Nazikian, R.; Petrov, M. P.; Redi, M. H.; Ruskov, E.; Taylor, G.; White, R. B.; Zweben, S. J.; TFTR Group

1999-09-01

The article reviews the physics of fusion alpha particles and energetic neutral beam ions studied in the final phase of TFTR operation, with an emphasis on observations in reversed magnetic shear (RS) and enhanced reversed shear (ERS) DT plasmas. Energy resolved measurements of the radial profiles of confined, trapped alphas in RS plasmas exhibit reduced core alpha density with increasing alpha energy, in contrast to plasmas with normal monotonic shear. The measured profiles are consistent with predictions of increased alpha loss due to stochastic ripple diffusion and increased first orbit loss in RS plasmas. In experiments in which a short tritium beam pulse is injected into a deuterium RS plasma, the measured DT neutron emission is lower than standard predictions assuming first orbit loss and stochastic ripple diffusion of the beam ions. A microwave reflectometer measured the spatial localization of low toroidal mode number (n), alpha driven toroidal Alfvén eigenmodes (TAEs) in DT RS discharges. Although the observed ballooning character of the n = 4 mode is consistent with predictions of a kinetic MHD stability code, the observed antiballooning nature of the n = 2 mode is not. Furthermore, the modelling does not show the observed strong dependence of mode frequency on n. These alpha driven TAEs do not cause measurable alpha loss in TFTR. Other Alfvén frequency modes with n = 2-4 seen in both DT and DD ERS and RS discharges are localized to the weak magnetic shear region near qmin. In 10-20% of DT discharges, normal low n MHD activity causes alpha loss at levels above the first orbit loss rate.

Tailoring nanoscopic confines to maximize catalytic activity of hydronium ions

NASA Astrophysics Data System (ADS)

Shi, Hui; Eckstein, Sebastian; Vjunov, Aleksei; Camaioni, Donald M.; Lercher, Johannes A.

2017-05-01

Acid catalysis by hydronium ions is ubiquitous in aqueous-phase organic reactions. Here we show that hydronium ion catalysis, exemplified by intramolecular dehydration of cyclohexanol, is markedly influenced by steric constraints, yielding turnover rates that increase by up to two orders of magnitude in tight confines relative to an aqueous solution of a Brønsted acid. The higher activities in zeolites BEA and FAU than in water are caused by more positive activation entropies that more than offset higher activation enthalpies. The higher activity in zeolite MFI with pores smaller than BEA and FAU is caused by a lower activation enthalpy in the tighter confines that more than offsets a less positive activation entropy. Molecularly sized pores significantly enhance the association between hydronium ions and alcohols in a steric environment resembling the constraints in pockets of enzymes stabilizing active sites.

Motifs for molecular recognition exploiting hydrophobic enclosure in protein-ligand binding.

PubMed

Young, Tom; Abel, Robert; Kim, Byungchan; Berne, Bruce J; Friesner, Richard A

2007-01-16

The thermodynamic properties and phase behavior of water in confined regions can vary significantly from that observed in the bulk. This is particularly true for systems in which the confinement is on the molecular-length scale. In this study, we use molecular dynamics simulations and a powerful solvent analysis technique based on inhomogenous solvation theory to investigate the properties of water molecules that solvate the confined regions of protein active sites. Our simulations and analysis indicate that the solvation of protein active sites that are characterized by hydrophobic enclosure and correlated hydrogen bonds induce atypical entropic and enthalpic penalties of hydration. These penalties apparently stabilize the protein-ligand complex with respect to the independently solvated ligand and protein, which leads to enhanced binding affinities. Our analysis elucidates several challenging cases, including the super affinity of the streptavidin-biotin system.

The kinetic stabilizer: a route to simpler tandem mirror systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Post, R F

2001-02-02

As we enter the new millennium there is a growing urgency to address the issue of finding long-range solutions to the world's energy needs. Fusion offers such a solution, provided economically viable means can be found to extract useful energy from fusion reactions. While the magnetic confinement approach to fusion has a long and productive history, to date the mainline approaches to magnetic confinement, namely closed systems such as the tokamak, appear to many as being too large and complex to be acceptable economically, despite the impressive progress that has made toward the achievement of fusion-relevant confinement parameters. Thus theremore » is a growing feeling that it is imperative to search for new and simpler approaches to magnetic fusion, ones that might lead to smaller and more economically attractive fusion power plants.« less

Turbulent Flame Stabilization Methods Using Confinement, Diluents, and High-Potential Electric Fields

DTIC Science & Technology

2014-08-03

the corona discharge was optimal for flame stabilization when it was located where fuel/air mixtures were within flammability limits locally...field [56]. This ionic wind is also known as the “ corona wind” [57] due to the corona discharge that develops at the sharp edge of the charged... Corona Discharge ,” Transactions of the American Institute of Electrical Engineers, Part I: Communication and Electronics, vol. 80, no. 2, pp. 143-150

Self-organization and self-limitation in high power impulse magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anders, Andre

The plasma over the racetrack in high power impulse magnetron sputtering develops in traveling ionization zones. Power densities can locally reach 10{sup 9} W/m{sup 2}, which is much higher than usually reported. Ionization zones move because ions are 'evacuated' by the electric field, exposing neutrals to magnetically confined, drifting electrons. Drifting secondary electrons amplify ionization of the same ionization zone where the primary ions came from, while sputtered and outgassing atoms are supplied to the following zone(s). Strong density gradients parallel to the target disrupt electron confinement: a negative feedback mechanism that stabilizes ionization runaway.

Rayleigh-Taylor-instability evolution in colliding-plasma-jet experiments with magnetic and viscous stabilization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Colin Stuart

The Rayleigh-Taylor instability causes mixing in plasmas throughout the universe, from micron-scale plasmas in inertial confinement fusion implosions to parsec-scale supernova remnants. The evolution of this interchange instability in a plasma is influenced by the presence of viscosity and magnetic fields, both of which have the potential to stabilize short-wavelength modes. Very few experimental observations of Rayleigh-Taylor growth in plasmas with stabilizing mechanisms are reported in the literature, and those that are reported are in sub-millimeter scale plasmas that are difficult to diagnose. Experimental observations in well-characterized plasmas are important for validation of computational models used to make design predictionsmore » for inertial confinement fusion efforts. This dissertation presents observations of instability growth during the interaction between a high Mach-number, initially un-magnetized plasma jet and a stagnated, magnetized plasma. A multi-frame fast camera captures Rayleigh-Taylor-instability growth while interferometry, spectroscopy, photodiode, and magnetic probe diagnostics are employed to estimate plasma parameters in the vicinity of the collision. As the instability grows, an evolution to longer mode wavelength is observed. Comparisons of experimental data with idealized magnetohydrodynamic simulations including a physical viscosity model suggest that the observed instability evolution is consistent with both magnetic and viscous stabilization. These data provide the opportunity to benchmark computational models used in astrophysics and fusion research.« less

2D Perovskites with Short Interlayer Distance for High-Performance Solar Cell Application.

PubMed

Ma, Chunqing; Shen, Dong; Ng, Tsz-Wai; Lo, Ming-Fai; Lee, Chun-Sing

2018-05-01

2D perovskites have emerged as one of the most promising photovoltaic materials owing to their excellent stability compared with their 3D counterparts. However, in typical 2D perovskites, the highly conductive inorganic layers are isolated by large organic cations leading to quantum confinement and thus inferior electrical conductivity across layers. To address this issue, the large organic cations are replaced with small propane-1,3-diammonium (PDA) cations to reduce distance between the inorganic perovskite layers. As shown by optical characterizations, quantum confinement is no longer dominating in the PDA-based 2D perovskites. This leads to considerable enhancement of charge transport as confirmed with electrochemical impedance spectroscopy, time-resolved photoluminescence, and mobility measurements. The improved electric properties of the interlayer-engineered 2D perovskites yield a power conversion efficiency of 13.0%. Furthermore, environmental stabilities of the PDA-based 2D perovskites are improved. PDA-based 2D perovskite solar cells (PSCs) with encapsulation can retain over 90% of their efficiency upon storage for over 1000 h, and PSCs without encapsulation can maintain their initial efficiency at 70 °C for over 100 h, which exhibit promising stabilities. These results reveal excellent optoelectronic properties and intrinsic stabilities of the layered perovskites with reduced interlayer distance. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Uncertainty Quantification For Physical and Numerical Diffusion Models In Inertial Confinement Fusion Simulations

NASA Astrophysics Data System (ADS)

Rana, Verinder S.

This thesis concerns simulations of Inertial Confinement Fusion. Inertial confinement is carried out in a large scale facility at National Ignition Facility. The experiments have failed to reproduce design calculations, and so uncertainty quantification of calculations is an important asset. Uncertainties can be classified as aleatoric or epistemic. This thesis is concerned with aleatoric uncertainty quantification. Among the many uncertain aspects that affect the simulations, we have narrowed our study of possible uncertainties. The first source of uncertainty we present is the amount of pre-heating of the fuel done by hot electrons. The second source of uncertainty we consider is the effect of the algorithmic and physical transport diffusion and their effect on the hot spot thermodynamics. Physical transport mechanisms play an important role for the entire duration of the ICF capsule, so modeling them correctly becomes extremely vital. In addition, codes that simulate material mixing introduce numerical (algorithmically) generated transport across the material interfaces. This adds another layer of uncertainty in the solution through the artificially added diffusion. The third source of uncertainty we consider is physical model uncertainty. The fourth source of uncertainty we focus on a single localized surface perturbation (a divot) which creates a perturbation to the solution that can potentially enter the hot spot to diminish the thermonuclear environment. Jets of ablator material are hypothesized to enter the hot spot and cool the core, contributing to the observed lower reactions than predicted levels. A plasma transport package, Transport for Inertial Confinement Fusion (TICF) has been implemented into the Radiation Hydrodynamics code FLASH, from the University of Chicago. TICF has thermal, viscous and mass diffusion models that span the entire ICF implosion regime. We introduced a Quantum Molecular Dynamics calibrated thermal conduction model due to Hu for thermal transport. The numerical approximation uncertainties are introduced by the choice of a hydrodynamic solver for a particular flow. Solvers tend to be diffusive at material interfaces and the Front Tracking (FT) algorithm, which is an already available software code in the form of an API, helps to ameliorate such effects. The FT algorithm has also been implemented in FLASH and we use this to study the effect that divots can have on the hot spot properties.

Benchmarking atomic physics models for magnetically confined fusion plasma physics experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

May, M.J.; Finkenthal, M.; Soukhanovskii, V.

In present magnetically confined fusion devices, high and intermediate {ital Z} impurities are either puffed into the plasma for divertor radiative cooling experiments or are sputtered from the high {ital Z} plasma facing armor. The beneficial cooling of the edge as well as the detrimental radiative losses from the core of these impurities can be properly understood only if the atomic physics used in the modeling of the cooling curves is very accurate. To this end, a comprehensive experimental and theoretical analysis of some relevant impurities is undertaken. Gases (Ne, Ar, Kr, and Xe) are puffed and nongases are introducedmore » through laser ablation into the FTU tokamak plasma. The charge state distributions and total density of these impurities are determined from spatial scans of several photometrically calibrated vacuum ultraviolet and x-ray spectrographs (3{endash}1600 {Angstrom}), the multiple ionization state transport code transport code (MIST) and a collisional radiative model. The radiative power losses are measured with bolometery, and the emissivity profiles were measured by a visible bremsstrahlung array. The ionization balance, excitation physics, and the radiative cooling curves are computed from the Hebrew University Lawrence Livermore atomic code (HULLAC) and are benchmarked by these experiments. (Supported by U.S. DOE Grant No. DE-FG02-86ER53214 at JHU and Contract No. W-7405-ENG-48 at LLNL.) {copyright} {ital 1999 American Institute of Physics.}« less

Continuum Edge Gyrokinetic Theory and Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, X Q; Xiong, Z; Dorr, M R

The following results are presented from the development and application of TEMPEST, a fully nonlinear (full-f) five dimensional (3d2v) gyrokinetic continuum edge-plasma code. (1) As a test of the interaction of collisions and parallel streaming, TEMPEST is compared with published analytic and numerical results for endloss of particles confined by combined electrostatic and magnetic wells. Good agreement is found over a wide range of collisionality, confining potential, and mirror ratio; and the required velocity space resolution is modest. (2) In a large-aspect-ratio circular geometry, excellent agreement is found for a neoclassical equilibrium with parallel ion flow in the banana regimemore » with zero temperature gradient and radial electric field. (3) The four-dimensional (2d2v) version of the code produces the first self-consistent simulation results of collisionless damping of geodesic acoustic modes and zonal flow (Rosenbluth-Hinton residual) with Boltzmann electrons using a full-f code. The electric field is also found to agree with the standard neoclassical expression for steep density and ion temperature gradients in the banana regime. In divertor geometry, it is found that the endloss of particles and energy induces parallel flow stronger than the core neoclassical predictions in the SOL. (5) Our 5D gyrokinetic formulation yields a set of nonlinear electrostatic gyrokinetic equations that are for both neoclassical and turbulence simulations.« less

A qualitative content analysis of global health engagements in Peacekeeping and Stability Operations Institute's stability operations lessons learned and information management system.

PubMed

Nang, Roberto N; Monahan, Felicia; Diehl, Glendon B; French, Daniel

2015-04-01

Many institutions collect reports in databases to make important lessons-learned available to their members. The Uniformed Services University of the Health Sciences collaborated with the Peacekeeping and Stability Operations Institute to conduct a descriptive and qualitative analysis of global health engagements (GHEs) contained in the Stability Operations Lessons Learned and Information Management System (SOLLIMS). This study used a summative qualitative content analysis approach involving six steps: (1) a comprehensive search; (2) two-stage reading and screening process to identify first-hand, health-related records; (3) qualitative and quantitative data analysis using MAXQDA, a software program; (4) a word cloud to illustrate word frequencies and interrelationships; (5) coding of individual themes and validation of the coding scheme; and (6) identification of relationships in the data and overarching lessons-learned. The individual codes with the most number of text segments coded included: planning, personnel, interorganizational coordination, communication/information sharing, and resources/supplies. When compared to the Department of Defense's (DoD's) evolving GHE principles and capabilities, the SOLLIMS coding scheme appeared to align well with the list of GHE capabilities developed by the Department of Defense Global Health Working Group. The results of this study will inform practitioners of global health and encourage additional qualitative analysis of other lessons-learned databases. Reprint & Copyright © 2015 Association of Military Surgeons of the U.S.

Helium Catalyzed D-D Fusion in a Levitated Dipole

NASA Astrophysics Data System (ADS)

Kesner, J.; Bromberg, L.; Garnier, D. T.; Hansen, A.; Mauel, M. E.

2003-10-01

Fusion research has focused on the goal of deuterium and tritium (D-T) fusion power because the reaction rate is large compared with the other fusion fuels: D-D or D-He3. Furthermore, the D-D cycle is difficult in traditional confinement devices, such as tokamaks, because good energy confinement is accompanied by good particle confinement which leads to an accumulation of ash. Fusion reactors based on the D-D reaction would be advantageous to D-T based reactors since they do not require the breeding of tritium and can reduce the flux of energetic neutrons that cause material damage. We propose a fusion power source based on the levitated dipole fusion concept that uses a "helium catalyzed D-D" fuel cycle, where rapid circulation of plasma allows the removal of tritium and the re-injection of the He3 decay product, eliminating the need for a massive blanket and shield. Stable dipole confinement derives from plasma compressibility instead of the magnetic shear and average good curvature. As a result, a dipole magnetic field can stabilize plasma at high beta while allowing large-scale adiabatic particle circulation. These properties may make the levitated dipole uniquely capable of achieving good energy confinement with low particle confinement. We find that a dipole based D-D power source can provide better utilization of magnetic field energy with a comparable mass power density to a D-T based tokamak power source.

Two-Dimensional MoS2 Confined Co(OH)2 Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes.

PubMed

Luo, Yuting; Li, Xu; Cai, Xingke; Zou, Xiaolong; Kang, Feiyu; Cheng, Hui-Ming; Liu, Bilu

2018-05-22

The development of abundant and cheap electrocatalysts for the hydrogen evolution reaction (HER) has attracted increasing attention over recent years. However, to achieve low-cost HER electrocatalysis, especially in alkaline media, is still a big challenge due to the sluggish water dissociation kinetics as well as the poor long-term stability of catalysts. In this paper we report the design and synthesis of a two-dimensional (2D) MoS 2 confined Co(OH) 2 nanoparticle electrocatalyst, which accelerates water dissociation and exhibits good durability in alkaline solutions, leading to significant improvement in HER performance. A two-step method was used to synthesize the electrocatalyst, starting with the lithium intercalation of exfoliated MoS 2 nanosheets followed by Co 2+ exchange in alkaline media to form MoS 2 intercalated with Co(OH) 2 nanoparticles (denoted Co-Ex-MoS 2 ), which was fully characterized by spectroscopic studies. Electrochemical tests indicated that the electrocatalyst exhibits superior HER activity and excellent stability, with an onset overpotential and Tafel slope as low as 15 mV and 53 mV dec -1 , respectively, which are among the best values reported so far for the Pt-free HER in alkaline media. Furthermore, density functional theory calculations show that the cojoint roles of Co(OH) 2 nanoparticles and MoS 2 nanosheets result in the excellent activity of the Co-Ex-MoS 2 electrocatalyst, and the good stability is attributed to the confinement of the Co(OH) 2 nanoparticles. This work provides an imporant strategy for designing HER electrocatalysts in alkaline solutions, and can, in principle, be expanded to other materials besides the Co(OH) 2 and MoS 2 used here.

Investigations into the behaviour of Plasma surrounding Pulsars: DYMPHNA3D

NASA Astrophysics Data System (ADS)

Rochford, Ronan; Mc Donald, John; Shearer, Andy

2011-08-01

We report on a new 3D fully relativistic, modular, parallel and scalable Particle-In-Cell (PIC) code currently being developed at the Computational Astrophysics Laboratory in the National University of Ireland, Galway and its initial test applications to the plasma distribution in the vicinity of a rapidly rotating neutron star. We find that Plasma remains confined by trapping surfaces close to the star as opposed to propagating to a significant portion of the light-cylinder distance as predicted in this early work. We discuss planned future modifications and applications of the developed code.

Joint DIII-D/EAST Experiments Toward Steady State AT Demonstration

NASA Astrophysics Data System (ADS)

Garofalo, A. M.; Meneghini, O.; Staebler, G. M.; van Zeeland, M. A.; Gong, X.; Ding, S.; Qian, J.; Ren, Q.; Xu, G.; Grierson, B. A.; Solomon, W. M.; Holcomb, C. T.

2015-11-01

Joint DIII-D/EAST experiments on fully noninductive operation at high poloidal beta have demonstrated several attractive features of this regime for a steady-state fusion reactor. Very large bootstrap fraction (>80 %) is desirable because it reduces the demands on external noninductive current drive. High bootstrap fraction with an H-mode edge results in a broad current profile and internal transport barriers (ITBs) at large minor radius, leading to high normalized energy confinement and high MHD stability limits. The ITB radius expands with higher normalized beta, further improving both stability and confinement. Electron density ITB and large Shafranov shift lead to low AE activity in the plasma core and low anomalous fast ion losses. Both the ITB and the current profile show remarkable robustness against perturbations, without external control. Supported by US DOE under DE-FC02-04ER54698, DE-AC02-09CH11466 & DE-AC52-07NA27344 & by NMCFSP under contracts 2015GB102000 and 2015GB110001.

A Sugar-Derived Room-Temperature Sodium Sulfur Battery with Long Term Cycling Stability.

PubMed

Carter, Rachel; Oakes, Landon; Douglas, Anna; Muralidharan, Nitin; Cohn, Adam P; Pint, Cary L

2017-03-08

We demonstrate a room-temperature sodium sulfur battery based on a confining microporous carbon template derived from sucrose that delivers a reversible capacity over 700 mAh/g S at 0.1C rates, maintaining 370 mAh/g S at 10 times higher rates of 1C. Cycling at 1C rates reveals retention of over 300 mAh/g S capacity across 1500 cycles with Coulombic efficiency >98% due to microporous sulfur confinement and stability of the sodium metal anode in a glyme-based electrolyte. We show sucrose to be an ideal platform to develop microporous carbon capable of mitigating electrode-electrolyte reactivity and loss of soluble intermediate discharge products. In a manner parallel to the low-cost materials of the traditional sodium beta battery, our work demonstrates the combination of table sugar, sulfur, and sodium, all of which are cheap and earth abundant, for a high-performance stable room-temperature sodium sulfur battery.

Thermal stability and formation barrier of a high-energetic material N8 polymer nitrogen encapsulated in (5,5) carbon nanotube

NASA Astrophysics Data System (ADS)

Ji, Wei; Timoshevskii, V.; Guo, H.; Abou-Rachid, Hakima; Lussier, Louis-Simon

2009-07-01

We report the density functional theory total energy calculations of thermal stability and formation barrier of polymer nitrogen confined in carbon nanotubes (CNT). The analysis suggests that N8 polymer nitrogen encapsulated in (5,5) carbon nanotube [N8@CNT(5,5)] is thermally (meta)stable at a finite temperature up to energy scale of at least 5000 K, similar to nitrogen molecule gas phase confined in CNT [N2@CNT(5,5)]. The energetic difference between these two phases of N does not significantly change with temperature. A barrier of 1.07 eV was found for the formation of N8@CNT(5,5) from N2@CNT(5,5), while the dissociation barrier was found to be 0.2 eV. Snapshots of the reaction pathway show that the transition state is composed by a N2 and a N6 inside a CNT(5,5).

Progress toward magnetic confinement of a positron-electron plasma: nearly 100% positron injection efficiency into a dipole trap

NASA Astrophysics Data System (ADS)

Stoneking, Matthew

2017-10-01

The hydrogen atom provides the simplest system and in some cases the most precise one for comparing theory and experiment in atomics physics. The field of plasma physics lacks an experimental counterpart, but there are efforts underway to produce a magnetically confined positron-electron plasma that promises to represent the simplest plasma system. The mass symmetry of positron-electron plasma makes it particularly tractable from a theoretical standpoint and many theory papers have been published predicting modified wave and stability properties in these systems. Our approach is to utilize techniques from the non-neutral plasma community to trap and accumulate electrons and positrons prior to mixing in a magnetic trap with good confinement properties. Ultimately we aim to use a levitated superconducting dipole configuration fueled by positrons from a reactor-based positron source and buffer-gas trap. To date we have conducted experiments to characterize and optimize the positron beam and test strategies for injecting positrons into the field of a supported permanent magnet by use of ExB drifts and tailored static and dynamic potentials applied to boundary electrodes and to the magnet itself. Nearly 100% injection efficiency has been achieved under certain conditions and some fraction of the injected positrons are confined for as long as 400 ms. These results are promising for the next step in the project which is to use an inductively energized high Tc superconducting coil to produce the dipole field, initially in a supported configuration, but ultimately levitated using feedback stabilization. Work performed with the support of the German Research Foundation (DFG), JSPS KAKENHI, NIFS Collaboration Research Program, and the UCSD Foundation.

Coupled field effects in BWR stability simulations using SIMULATE-3K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borkowski, J.; Smith, K.; Hagrman, D.

1996-12-31

The SIMULATE-3K code is the transient analysis version of the Studsvik advanced nodal reactor analysis code, SIMULATE-3. Recent developments have focused on further broadening the range of transient applications by refinement of core thermal-hydraulic models and on comparison with boiling water reactor (BWR) stability measurements performed at Ringhals unit 1, during the startups of cycles 14 through 17.

GBS: Global 3D simulation of tokamak edge region

NASA Astrophysics Data System (ADS)

Zhu, Ben; Fisher, Dustin; Rogers, Barrett; Ricci, Paolo

2012-10-01

A 3D two-fluid global code, namely Global Braginskii Solver (GBS), is being developed to explore the physics of turbulent transport, confinement, self-consistent profile formation, pedestal scaling and related phenomena in the edge region of tokamaks. Aimed at solving drift-reduced Braginskii equations [1] in complex magnetic geometry, the GBS is used for turbulence simulation in SOL region. In the recent upgrade, the simulation domain is expanded into close flux region with twist-shift boundary conditions. Hence, the new GBS code is able to explore global transport physics in an annular full-torus domain from the top of the pedestal into the far SOL. We are in the process of identifying and analyzing the linear and nonlinear instabilities in the system using the new GBS code. Preliminary results will be presented and compared with other codes if possible.[4pt] [1] A. Zeiler, J. F. Drake and B. Rogers, Phys. Plasmas 4, 2134 (1997)

Ultrathin Coating of Confined Pt Nanocatalysts by Atomic Layer Deposition for Enhanced Catalytic Performance in Hydrogenation Reactions.

PubMed

Wang, Meihua; Gao, Zhe; Zhang, Bin; Yang, Huimin; Qiao, Yan; Chen, Shuai; Ge, Huibin; Zhang, Jiankang; Qin, Yong

2016-06-13

Metal-support interfaces play a prominent role in heterogeneous catalysis. However, tailoring the metal-support interfaces to realize full utilization remains a major challenge. In this work, we propose a graceful strategy to maximize the metal-oxide interfaces by coating confined nanoparticles with an ultrathin oxide layer. This is achieved by sequential deposition of ultrathin Al2 O3 coats, Pt, and a thick Al2 O3 layer on carbon nanocoils templates by atomic layer deposition (ALD), followed by removal of the templates. Compared with the Pt catalysts confined in Al2 O3 nanotubes without the ultrathin coats, the ultrathin coated samples have larger Pt-Al2 O3 interfaces. The maximized interfaces significantly improve the activity and the protecting Al2 O3 nanotubes retain the stability for hydrogenation reactions of 4-nitrophenol. We believe that applying ALD ultrathin coats on confined catalysts is a promising way to achieve enhanced performance for other catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Markov-state model for CO2 binding with carbonic anhydrase under confinement

NASA Astrophysics Data System (ADS)

Chen, Gong; Xu, Weina; Lu, Diannan; Wu, Jianzhong; Liu, Zheng

2018-01-01

Enzyme immobilization with a nanostructure material can enhance its stability and facilitate reusability. However, the apparent activity is often compromised due to additional diffusion barriers and complex interactions with the substrates and solvent molecules. The present study elucidates the effects of the surface hydrophobicity of nano-confinement on CO2 diffusion to the active site of human carbonic anhydrase II (CA), an enzyme that is able to catalyze CO2 hydration at extremely high turnover rates. Using the Markov-state model in combination with coarse-grained molecular dynamics simulations, we demonstrate that a hydrophobic cage increases CO2 local density but hinders its diffusion towards the active site of CA under confinement. By contrast, a hydrophilic cage hinders CO2 adsorption but promotes its binding with CA. An optimal surface hydrophobicity can be identified to maximize both the CO2 occupation probability and the diffusion rate. The simulation results offer insight into understanding enzyme performance under nano-confinement and help us to advance broader applications of CA for CO2 absorption and recovery.

Superstable Ultrathin Water Film Confined in a Hydrophilized Carbon Nanotube.

PubMed

Tomo, Yoko; Askounis, Alexandros; Ikuta, Tatsuya; Takata, Yasuyuki; Sefiane, Khellil; Takahashi, Koji

2018-03-14

Fluids confined in a nanoscale space behave differently than in the bulk due to strong interactions between fluid molecules and solid atoms. Here, we observed water confined inside "open" hydrophilized carbon nanotubes (CNT), with diameter of tens of nanometers, using transmission electron microscopy (TEM). A 1-7 nm water film adhering to most of the inner wall surface was observed and remained stable in the high vacuum (order of 10 -5 Pa) of the TEM. The superstability of this film was attributed to a combination of curvature, nanoroughness, and confinement resulting in a lower vapor pressure for water and hence inhibiting its vaporization. Occasional, suspended ultrathin water film with thickness of 3-20 nm were found and remained stable inside the CNT. This film thickness is 1 order of magnitude smaller than the critical film thickness (about 40 nm) reported by the Derjaguin-Landau-Verwey-Overbeek theory and previous experimental investigations. The stability of the suspended ultrathin water film is attributed to the additional molecular interactions due to the extended water meniscus, which balances the rest of the disjoining pressures.

Brain Tumor Genetic Modification Yields Increased Resistance to Paclitaxel in Physical Confinement

PubMed Central

Bui, Loan; Hendricks, Alissa; Wright, Jamie; Chuong, Cheng-Jen; Davé, Digant; Bachoo, Robert; Kim, Young-tae

2016-01-01

Brain tumor cells remain highly resistant to radiation and chemotherapy, particularly malignant and secondary cancers. In this study, we utilized microchannel devices to examine the effect of a confined environment on the viability and drug resistance of the following brain cancer cell lines: primary cancers (glioblastoma multiforme and neuroblastoma), human brain cancer cell lines (D54 and D54-EGFRvIII), and genetically modified mouse astrocytes (wild type, p53−/−, p53−/− PTEN−/−, p53−/− Braf, and p53−/− PTEN−/− Braf). We found that loss of PTEN combined with Braf activation resulted in higher viability in narrow microchannels. In addition, Braf conferred increased resistance to the microtubule-stabilizing drug Taxol in narrow confinement. Similarly, survival of D54-EGFRvIII cells was unaffected following treatment with Taxol, whereas the viability of D54 cells was reduced by 75% under these conditions. Taken together, our data suggests key targets for anticancer drugs based on cellular genotypes and their specific survival phenotypes during confined migration. PMID:27184621

Confined Ultrathin Pd-Ce Nanowires with Outstanding Moisture and SO2 Tolerance in Methane Combustion.

PubMed

Peng, Honggen; Rao, Cheng; Zhang, Ning; Wang, Xiang; Liu, Wenming; Mao, Wenting; Han, Lu; Zhang, Pengfei; Dai, Sheng

2018-05-22

An efficient strategy (enhanced metal oxide interaction and core-shell confinement to inhibit the sintering of noble metal) is presented confined ultrathin Pd-CeO x nanowire (2.4 nm) catalysts for methane combustion, which enable CH 4 total oxidation at a low temperature of 350 °C, much lower than that of a commercial Pd/Al 2 O 3 catalyst (425 °C). Importantly, unexpected stability was observed even under harsh conditions (800 °C, water vapor, and SO 2 ), owing to the confinement and shielding effect of the porous silica shell together with the promotion of CeO 2 . Pd-CeO x solid solution nanowires (Pd-Ce NW) as cores and porous silica as shells (Pd-CeNW@SiO 2 ) were rationally prepared by a facile and direct self-assembly strategy for the first time. This strategy is expected to inspire more active and stable catalysts for use under severe conditions (vehicle emissions control, reforming, and water-gas shift reaction). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two-dimensional implosion simulations with a kinetic particle code [2D implosion simulations with a kinetic particle code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagert, Irina; Even, Wesley Paul; Strother, Terrance Timothy

Here, we perform two-dimensional implosion simulations using a Monte Carlo kinetic particle code. The application of a kinetic transport code is motivated, in part, by the occurrence of nonequilibrium effects in inertial confinement fusion capsule implosions, which cannot be fully captured by hydrodynamic simulations. Kinetic methods, on the other hand, are able to describe both continuum and rarefied flows. We perform simple two-dimensional disk implosion simulations using one-particle species and compare the results to simulations with the hydrodynamics code rage. The impact of the particle mean free path on the implosion is also explored. In a second study, we focusmore » on the formation of fluid instabilities from induced perturbations. We find good agreement with hydrodynamic studies regarding the location of the shock and the implosion dynamics. Differences are found in the evolution of fluid instabilities, originating from the higher resolution of rage and statistical noise in the kinetic studies.« less

Two-dimensional implosion simulations with a kinetic particle code [2D implosion simulations with a kinetic particle code

DOE PAGES

Sagert, Irina; Even, Wesley Paul; Strother, Terrance Timothy

2017-05-17

Here, we perform two-dimensional implosion simulations using a Monte Carlo kinetic particle code. The application of a kinetic transport code is motivated, in part, by the occurrence of nonequilibrium effects in inertial confinement fusion capsule implosions, which cannot be fully captured by hydrodynamic simulations. Kinetic methods, on the other hand, are able to describe both continuum and rarefied flows. We perform simple two-dimensional disk implosion simulations using one-particle species and compare the results to simulations with the hydrodynamics code rage. The impact of the particle mean free path on the implosion is also explored. In a second study, we focusmore » on the formation of fluid instabilities from induced perturbations. We find good agreement with hydrodynamic studies regarding the location of the shock and the implosion dynamics. Differences are found in the evolution of fluid instabilities, originating from the higher resolution of rage and statistical noise in the kinetic studies.« less

Response surface method in geotechnical/structural analysis, phase 1

NASA Astrophysics Data System (ADS)

Wong, F. S.

1981-02-01

In the response surface approach, an approximating function is fit to a long running computer code based on a limited number of code calculations. The approximating function, called the response surface, is then used to replace the code in subsequent repetitive computations required in a statistical analysis. The procedure of the response surface development and feasibility of the method are shown using a sample problem in slop stability which is based on data from centrifuge experiments of model soil slopes and involves five random soil parameters. It is shown that a response surface can be constructed based on as few as four code calculations and that the response surface is computationally extremely efficient compared to the code calculation. Potential applications of this research include probabilistic analysis of dynamic, complex, nonlinear soil/structure systems such as slope stability, liquefaction, and nuclear reactor safety.

On entanglement-assisted quantum codes achieving the entanglement-assisted Griesmer bound

NASA Astrophysics Data System (ADS)

Li, Ruihu; Li, Xueliang; Guo, Luobin

2015-12-01

The theory of entanglement-assisted quantum error-correcting codes (EAQECCs) is a generalization of the standard stabilizer formalism. Any quaternary (or binary) linear code can be used to construct EAQECCs under the entanglement-assisted (EA) formalism. We derive an EA-Griesmer bound for linear EAQECCs, which is a quantum analog of the Griesmer bound for classical codes. This EA-Griesmer bound is tighter than known bounds for EAQECCs in the literature. For a given quaternary linear code {C}, we show that the parameters of the EAQECC that EA-stabilized by the dual of {C} can be determined by a zero radical quaternary code induced from {C}, and a necessary condition under which a linear EAQECC may achieve the EA-Griesmer bound is also presented. We construct four families of optimal EAQECCs and then show the necessary condition for existence of EAQECCs is also sufficient for some low-dimensional linear EAQECCs. The four families of optimal EAQECCs are degenerate codes and go beyond earlier constructions. What is more, except four codes, our [[n,k,d_{ea};c

Observation of finite-. beta. MHD phenomena in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGuire, K.M.

1984-09-01

Stable high-beta plasmas are required for the tokamak to attain an economical fusion reactor. Recently, intense neutral beam heating experiments in tokamaks have shown new effects on plasma stability and confinement associated with high beta plasmas. The observed spectrum of MHD fluctuations at high beta is clearly dominated by the n = 1 mode when the q = 1 surface is in the plasma. The m/n = 1/1 mode drives other n = 1 modes through toroidal coupling and n > 1 modes through nonlinear coupling. On PDX, with near perpendicular injection, a resonant interaction between the n = 1more » internal kink and the trapped fast ions results in loss of beam particles and heating power. Key parameters in the theory are the value of q/sub 0/ and the injection angle. High frequency broadband magnetic fluctuations have been observed on ISX-B and D-III and a correlation with the deterioration of plasma confinement was reported. During enhanced confinement (H-mode) discharges in divertor plasmas, two new edge instabilities were observed, both localized radially near the separatrix. By assembling results from the different tokamak experiments, it is found that the simple theoretical ideal MHD beta limit has not been exceeded. Whether this represents an ultimate tokamak limit or if beta optimized configurations (Dee- or bean-shaped plasmas) can exceed this limit and perhaps enter a second regime of stability remains to be clarified.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garofalo, Andrea M.; Burrell, Keith H.; Eldon, David

For the first time, DIII-D experiments have achieved stationary quiescent H-mode (QH-mode) operation for many energy confinement times at simultaneous ITER-relevant values of beta, confinement, and safety factor, in an ITER similar shape. QH-mode provides excellent energy confinement, even at very low plasma rotation, while operating without edge localized modes (ELMs) and with strong impurity transport via the benign edge harmonic oscillation (EHO). By tailoring the plasma shape to improve the edge stability, the QH-mode operating space has also been extended to densities exceeding 80% of the Greenwald limit, overcoming the long-standing low-density limit of QH-mode operation. In the theory,more » the density range over which the plasma encounters the kink-peeling boundary widens as the plasma cross-section shaping is increased, thus increasing the QH-mode density threshold. Here, the DIII-D results are in excellent agreement with these predictions, and nonlinear MHD analysis of reconstructed QH-mode equilibria shows unstable low n kink-peeling modes growing to a saturated level, consistent with the theoretical picture of the EHO. Furthermore, high density operation in the QH-mode regime has opened a path to a new, previously predicted region of parameter space, named “Super H-mode” because it is characterized by very high pedestals that can be more than a factor of two above the peeling-ballooning stability limit for similar ELMing H-mode discharges at the same density.« less

Confined turbulent swirling recirculating flow predictions. Ph.D. Thesis. Final Report

NASA Technical Reports Server (NTRS)

Abujelala, M. T.; Lilley, D. G.

1985-01-01

The capability and the accuracy of the STARPIC computer code in predicting confined turbulent swirling recirculating flows is presented. Inlet flow boundary conditions were demonstrated to be extremely important in simulating a flowfield via numerical calculations. The degree of swirl strength and expansion ratio have strong effects on the characteristics of swirling flow. In a nonswirling flow, a large corner recirculation zone exists in the flowfield with an expansion ratio greater than one. However, as the degree of inlet swirl increases, the size of this zone decreases and a central recirculation zone appears near the inlet. Generally, the size of the central zone increased with swirl strength and expansion ratio. Neither the standard k-epsilon turbulence mode nor its previous extensions show effective capability for predicting confined turbulent swirling recirculating flows. However, either reduced optimum values of three parameters in the mode or the empirical C sub mu formulation obtained via careful analysis of available turbulence measurements, can provide more acceptable accuracy in the prediction of these swirling flows.

The possible crossover effects of NaNO3 confined in porous media: From bulk to clusters

NASA Astrophysics Data System (ADS)

Mu, R.; Jin, F.; Morgan, S. H.; Henderson, D. O.; Silberman, E.

1994-05-01

Differential scanning calorimetry (DSC) and Raman spectra are reported for NaNO3 bulk and for NaNO3 confined in porous silica with pore radii, rp=2.5, 5, 10, 20 nm. Raman spectra are also given for a 6 M solution of NaNO3. The melting transition for the confined NaNO3 exhibits a 1/rp dependence where rp is the pore radius for rp≳5 nm. No melting transition is observed for NaNO3 confined in 2.5 nm pores. Above this pore size, their appears to be a deviation in the melting transition dependence on rp. The internal modes observed in the Raman spectra for the confined material are in agreement with those of the bulk solid except for a feature observed on the low frequency side of the ν1 band. The external TO mode observed at 100 cm-1 and the librational mode at 175 cm-1 for NaNO3 both decrease in intensity and broaden as rp decreases and both bands disappear at rp=2.5 nm. An additional peak at 70 cm-1 not observed in the solution or bulk NaNO3 spectra appears in the spectra of confined NaNO3 and increases in intensity as rp decreases. We assign this band to a new phase of NaNO3 which is stabilized by the surface hydroxyl groups of the porous silica. For NaNO3 confined in pores, rp≤2.5 nm, we suggest that NaNO3 exists as disordered aggregates.

The impact of collisionality, FLR, and parallel closure effects on instabilities in the tokamak pedestal: Numerical studies with the NIMROD code

DOE PAGES

King, J. R.; Pankin, A. Y.; Kruger, S. E.; ...

2016-06-24

The extended-MHD NIMROD code [C. R. Sovinec and J. R. King, J. Comput. Phys. 229, 5803 (2010)] is verified against the ideal-MHD ELITE code [H. R. Wilson et al., Phys. Plasmas 9, 1277 (2002)] on a diverted tokamak discharge. When the NIMROD model complexity is increased incrementally, resistive and first-order finite-Larmour radius effects are destabilizing and stabilizing, respectively. Lastly, the full result is compared to local analytic calculations which are found to overpredict both the resistive destabilization and drift stabilization in comparison to the NIMROD computations.

The impact of collisionality, FLR, and parallel closure effects on instabilities in the tokamak pedestal: Numerical studies with the NIMROD code

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, J. R.; Pankin, A. Y.; Kruger, S. E.

The extended-MHD NIMROD code [C. R. Sovinec and J. R. King, J. Comput. Phys. 229, 5803 (2010)] is verified against the ideal-MHD ELITE code [H. R. Wilson et al., Phys. Plasmas 9, 1277 (2002)] on a diverted tokamak discharge. When the NIMROD model complexity is increased incrementally, resistive and first-order finite-Larmour radius effects are destabilizing and stabilizing, respectively. The full result is compared to local analytic calculations which are found to overpredict both the resistive destabilization and drift stabilization in comparison to the NIMROD computations.

The impact of collisionality, FLR, and parallel closure effects on instabilities in the tokamak pedestal: Numerical studies with the NIMROD code

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, J. R.; Pankin, A. Y.; Kruger, S. E.

The extended-MHD NIMROD code [C. R. Sovinec and J. R. King, J. Comput. Phys. 229, 5803 (2010)] is verified against the ideal-MHD ELITE code [H. R. Wilson et al., Phys. Plasmas 9, 1277 (2002)] on a diverted tokamak discharge. When the NIMROD model complexity is increased incrementally, resistive and first-order finite-Larmour radius effects are destabilizing and stabilizing, respectively. Lastly, the full result is compared to local analytic calculations which are found to overpredict both the resistive destabilization and drift stabilization in comparison to the NIMROD computations.

Stability of an aqueous quadrupole micro-trap

DOE PAGES

Park, Jae Hyun; Krstić, Predrag S.

2012-03-30

Recently demonstrated functionality of an aqueous quadrupole micro- or nano-trap opens a new avenue for applications of the Paul traps, like is confinement of a charged biomolecule which requires water environment for its chemical stability. Besides strong viscosity forces, motion of a charged particle in the aqueous trap is subject to dielectrophoretic and electrophoretic forces. In this study, we describe the general conditions for stability of a charged particle in an aqueous quadrupole trap. We find that for the typical micro-trap parameters, effects of both dielectrophoresis and electrophoresis significantly influence the trap stability. In particular, the aqueous quadrupole trap couldmore » play of a role of a synthetic virtual nanopore for the 3rd generation of DNA sequencing technology.« less

Transport simulation of EAST long-pulse H-mode discharge with integrated modeling

NASA Astrophysics Data System (ADS)

Wu, M. Q.; Li, G. Q.; Chen, J. L.; Du, H. F.; Gao, X.; Ren, Q. L.; Li, K.; Chan, Vincent; Pan, C. K.; Ding, S. Y.; Jian, X.; Zhu, X.; Lian, H.; Qian, J. P.; Gong, X. Z.; Zang, Q.; Duan, Y. M.; Liu, H. Q.; Lyu, B.

2018-04-01

In the 2017 EAST experimental campaign, a steady-state long-pulse H-mode discharge lasting longer than 100 s has been obtained using only radio frequency heating and current drive, and the confinement quality is slightly better than standard H-mode, H98y2 ~ 1.1, with stationary peaked electron temperature profiles. Integrated modeling of one long-pulse H-mode discharge in the 2016 EAST experimental campaign has been performed with equilibrium code EFIT, and transport codes TGYRO and ONETWO under integrated modeling framework OMFIT. The plasma current is fully-noninductively driven with a combination of ~2.2 MW LHW, ~0.3 MW ECH and ~1.1 MW ICRF. Time evolution of the predicted electron and ion temperature profiles through integrated modeling agree closely with that from measurements. The plasma current (I p ~ 0.45 MA) and electron density are kept constantly. A steady-state is achieved using integrated modeling, and the bootstrap current fraction is ~28%, the RF drive current fraction is ~72%. The predicted current density profile matches the experimental one well. Analysis shows that electron cyclotron heating (ECH) makes large contribution to the plasma confinement when heating in the core region while heating in large radius does smaller improvement, also a more peaked LHW driven current profile is got when heating in the core. Linear analysis shows that the high-k modes instability (electron temperature gradient driven modes) is suppressed in the core region where exists weak electron internal transport barriers. The trapped electron modes dominates in the low-k region, which is mainly responsible for driving the electron energy flux. It is found that the ECH heating effect is very local and not the main cause to sustained the good confinement, the peaked current density profile has the most important effect on plasma confinement improvement. Transport analysis of the long-pulse H-mode experiments on EAST will be helpful to build future experiments.

High-resolution modeling of indirectly driven high-convergence layered inertial confinement fusion capsule implosions

DOE PAGES

Haines, Brian M.; Aldrich, C. H.; Campbell, J. M.; ...

2017-04-24

In this study, we present the results of high-resolution simulations of the implosion of high-convergence layered indirect-drive inertial confinement fusion capsules of the type fielded on the National Ignition Facility using the xRAGE radiation-hydrodynamics code. In order to evaluate the suitability of xRAGE to model such experiments, we benchmark simulation results against available experimental data, including shock-timing, shock-velocity, and shell trajectory data, as well as hydrodynamic instability growth rates. We discuss the code improvements that were necessary in order to achieve favorable comparisons with these data. Due to its use of adaptive mesh refinement and Eulerian hydrodynamics, xRAGE is particularlymore » well suited for high-resolution study of multi-scale engineering features such as the capsule support tent and fill tube, which are known to impact the performance of high-convergence capsule implosions. High-resolution two-dimensional (2D) simulations including accurate and well-resolved models for the capsule fill tube, support tent, drive asymmetry, and capsule surface roughness are presented. These asymmetry seeds are isolated in order to study their relative importance and the resolution of the simulations enables the observation of details that have not been previously reported. We analyze simulation results to determine how the different asymmetries affect hotspot reactivity, confinement, and confinement time and how these combine to degrade yield. Yield degradation associated with the tent occurs largely through decreased reactivity due to the escape of hot fuel mass from the hotspot. Drive asymmetries and the fill tube, however, degrade yield primarily via burn truncation, as associated instability growth accelerates the disassembly of the hotspot. Finally, modeling all of these asymmetries together in 2D leads to improved agreement with experiment but falls short of explaining the experimentally observed yield degradation, consistent with previous 2D simulations of such capsules.« less

Interface confined hydrogen evolution reaction in zero valent metal nanoparticles-intercalated molybdenum disulfide

PubMed Central

Chen, Zhongxin; Leng, Kai; Zhao, Xiaoxu; Malkhandi, Souradip; Tang, Wei; Tian, Bingbing; Dong, Lei; Zheng, Lirong; Lin, Ming; Yeo, Boon Siang; Loh, Kian Ping

2017-01-01

Interface confined reactions, which can modulate the bonding of reactants with catalytic centres and influence the rate of the mass transport from bulk solution, have emerged as a viable strategy for achieving highly stable and selective catalysis. Here we demonstrate that 1T′-enriched lithiated molybdenum disulfide is a highly powerful reducing agent, which can be exploited for the in-situ reduction of metal ions within the inner planes of lithiated molybdenum disulfide to form a zero valent metal-intercalated molybdenum disulfide. The confinement of platinum nanoparticles within the molybdenum disulfide layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support. In particular, the inner platinum surface is accessible to charged species like proton and metal ions, while blocking poisoning by larger sized pollutants or neutral molecules. This points a way forward for using bulk intercalated compounds for energy related applications. PMID:28230105

Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis.

PubMed

Fang, Xinzuo; Shang, Qichao; Wang, Yu; Jiao, Long; Yao, Tao; Li, Yafei; Zhang, Qun; Luo, Yi; Jiang, Hai-Long

2018-02-01

It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h -1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H 2 production activity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In-situ confined formation of NiFe layered double hydroxide quantum dots in expanded graphite for active electrocatalytic oxygen evolution

NASA Astrophysics Data System (ADS)

Guo, Jinxue; Li, Xiaoyan; Sun, Yanfang; Liu, Qingyun; Quan, Zhenlan; Zhang, Xiao

2018-06-01

Development of noble-metal-free catalysts towards highly efficient electrochemical oxygen evolution reaction (OER) is critical but challenging in the renewable energy area. Herein, we firstly embed NiFe LDHs quantum dots (QDs) into expanded graphite (NiFe LDHs/EG) via in-situ confined formation process. The interlayer spacing of EG layers acts as nanoreactors for spatially confined formation of NiFe LDHs QDs. The QDs supply huge catalytic sites for OER. The in-situ decoration endows the strong affinity between QDs with EG, thus inducing fast charge transfer. Based on the aforementioned benefits, the designed catalyst exhibits outstanding OER properties, in terms of small overpotential (220 mV required to generate 10 mA cm-2), low Tafel slope, and good durable stability, making it a promising candidate for inexpensive OER catalyst.

Comparison of confinement in resistive-shell reversed-field pinch devices with two different magnetic shell penetration times

NASA Astrophysics Data System (ADS)

Gravestijn, R. M.; Drake, J. R.; Hedqvist, A.; Rachlew, E.

2004-01-01

A loop voltage is required to sustain the reversed-field pinch (RFP) equilibrium. The configuration is characterized by redistribution of magnetic helicity but with the condition that the total helicity is maintained constant. The magnetic field shell penetration time, tgrs, has a critical role in the stability and performance of the RFP. Confinement in the EXTRAP device has been studied with two values of tgrs, first (EXTRAP-T2) with tgrs of the order of the typical relaxation cycle timescale and then (EXTRAP-T2R) with tgrs much longer than the relaxation cycle timescale, but still much shorter than the pulse length. Plasma parameters show significant improvements in confinement in EXTRAP-T2R. The typical loop voltage required to sustain comparable electron poloidal beta values is a factor of 3 lower in the EXTRAP-T2R device. The improvement is attributed to reduced magnetic turbulence.

Methane Hydrate in Confined Spaces: An Alternative Storage System.

PubMed

Borchardt, Lars; Casco, Mirian Elizabeth; Silvestre-Albero, Joaquin

2018-06-05

Methane hydrate inheres the great potential to be a nature-inspired alternative for chemical energy storage, as it allows to store large amounts of methane in a dense solid phase. The embedment of methane hydrate in the confined environment of porous materials can be capitalized for potential applications as its physicochemical properties, such as the formation kinetics or pressure and temperature stability, are significantly changed compared to the bulk system. We review this topic from a materials scientific perspective by considering porous carbons, silica, clays, zeolites, and polymers as host structures for methane hydrate formation. We discuss the contribution of advanced characterization techniques and theoretical simulations towards the elucidation of the methane hydrate formation and dissociation process within the confined space. We outline the scientific challenges this system is currently facing and look on possible future applications for this technology. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Special Issue on the 20th Workshop on MHD Stability Control

DOE PAGES

Park, Jong -Kyu

2016-11-08

The 20th workshop on magnetohydrodynamic (MHD) stability control took place November 22–24, 2015, in Princeton Plasma Physics Laboratory (PPPL), following the American Physical Society—Division of Plasma Physics annual meeting on November 16–20 in Savannah, GA. The purpose of this workshop is to stimulate in depth discussion and motivate future research in the areas of MHD stability physics and control of magnetically confined plasmas. Furthermore, the workshop was organized jointly by Auburn University, Columbia University, General Atomics, Princeton Plasma Physics Laboratory, University of Wisconsin-Madison, and the Los Alamos National Laboratory, and under the auspices of the US/Japan Collaboration.

Ion temperature gradient driven transport in tokamaks with square shaping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joiner, N.; Dorland, W.

2010-06-15

Advanced tokamak schemes which may offer significant improvement to plasma confinement on the usual large aspect ratio Dee-shaped flux surface configuration are of great interest to the fusion community. One possibility is to introduce square shaping to the flux surfaces. The gyrokinetic code GS2[Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1996)] is used to study linear stability and the resulting nonlinear thermal transport of the ion temperature gradient driven (ITG) mode in tokamak equilibria with square shaping. The maximum linear growth rate of ITG modes is increased by negative squareness (diamond shaping) and reduced by positive values (square shaping).more » The dependence of thermal transport produced by saturated ITG instabilities on squareness is not as clear. The overall trend follows that of the linear instability, heat and particle fluxes increase with negative squareness and decrease with positive squareness. This is contradictory to recent experimental results [Holcomb et al., Phys. Plasmas 16, 056116 (2009)] which show a reduction in transport with negative squareness. This may be reconciled as a reduction in transport (consistent with the experiment) is observed at small negative values of the squareness parameter.« less

Turbulent Simulations of Divertor Detachment Based On BOUT + + Framework

NASA Astrophysics Data System (ADS)

Chen, Bin; Xu, Xueqiao; Xia, Tianyang; Ye, Minyou

2015-11-01

China Fusion Engineering Testing Reactor is under conceptual design, acting as a bridge between ITER and DEMO. The detached divertor operation offers great promise for a reduction of heat flux onto divertor target plates for acceptable erosion. Therefore, a density scan is performed via an increase of D2 gas puffing rates in the range of 0 . 0 ~ 5 . 0 ×1023s-1 by using the B2-Eirene/SOLPS 5.0 code package to study the heat flux control and impurity screening property. As the density increases, it shows a gradually change of the divertor operation status, from low-recycling regime to high-recycling regime and finally to detachment. Significant radiation loss inside the confined plasma in the divertor region during detachment leads to strong parallel density and temperature gradients. Based on the SOLPS simulations, BOUT + + simulations will be presented to investigate the stability and turbulent transport under divertor plasma detachment, particularly the strong parallel gradient driven instabilities and enhanced plasma turbulence to spread heat flux over larger surface areas. The correlation between outer mid-plane and divertor turbulence and the related transport will be analyzed. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-675075.

MHD stability analysis and global mode identification preparing for high beta operation in KSTAR

NASA Astrophysics Data System (ADS)

Park, Y. S.; Sabbagh, S. A.; Berkery, J. W.; Jiang, Y.; Ahn, J. H.; Han, H. S.; Bak, J. G.; Park, B. H.; Jeon, Y. M.; Kim, J.; Hahn, S. H.; Lee, J. H.; Ko, J. S.; in, Y. K.; Yoon, S. W.; Oh, Y. K.; Wang, Z.; Glasser, A. H.

2017-10-01

H-mode plasma operation in KSTAR has surpassed the computed n = 1 ideal no-wall stability limit in discharges exceeding several seconds in duration. The achieved high normalized beta plasmas are presently limited by resistive tearing instabilities rather than global kink/ballooning or RWMs. The ideal and resistive stability of these plasmas is examined by using different physics models. The observed m/ n = 2/1 tearing stability is computed by using the M3D-C1 code, and by the resistive DCON code. The global MHD stability modified by kinetic effects is examined using the MISK code. Results from the analysis explain the stabilization of the plasma above the ideal MHD no-wall limit. Equilibrium reconstructions used include the measured kinetic profiles and MSE data. In preparation for plasma operation at higher beta utilizing the planned second NBI system, three sets of 3D magnetic field sensors have been installed and will be used for RWM active feedback control. To accurately determine the dominant n-component produced by low frequency unstable RWMs, an algorithm has been developed that includes magnetic sensor compensation of the prompt applied field and the field from the induced current on the passive conductors. Supported by US DOE Contracts DE-FG02-99ER54524 and DE-SC0016614.

Structural characteristics of liquid nitromethane at the nanoscale confinement in carbon nanotubes.

PubMed

Liu, Yingzhe; Lai, Weipeng; Yu, Tao; Ge, Zhongxue; Kang, Ying

2014-10-01

The stability of energetic materials confined in the carbon nanotubes can be improved at ambient pressure and room temperature, leading to potential energy storage and controlled energy release. However, the microscopic structure of confined energetic materials and the role played by the confinement size are still fragmentary. In this study, molecular dynamics simulations have been performed to explore the structural characteristics of liquid nitromethane (NM), one of the simplest energetic materials, confined in a series of armchair single-walled carbon nanotubes (SWNTs) changing from (5,5) to (16,16) at ambient conditions. The simulation results show that the size-dependent ordered structures of NM with preferred orientations are formed inside the tubular cavities driven by the van der Waals attractions between NM and SWNT together with the dipole-dipole interactions of NM, giving rise to a higher local mass density than that of bulk NM. The NM dipoles prefer to align parallel along the SWNT axis in an end-to-end fashion inside all the nanotubes except the (7,7) SWNT where a unique staggered orientation of NM dipoles perpendicular to the SWNT axis is observed. As the SWNT radius increases, the structural arrangements and dipole orientations of NM become disordered as a result of the weakening of van der Waals interactions between NM and SWNT.

Numerical Investigations On The Seismic Behaviour Of Confined Masonry Walls

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calderini, Chiara; Cattari, Serena; Lagomarsino, Sergio

2008-07-08

In the last century, severe earthquakes highlighted the seismic vulnerability of unreinforced masonry buildings. Many technological innovations have been introduced in time in order to improve resistance, ductility, and dissipation properties of this type of constructions. The most widely diffused are reinforced masonry and confined masonry. Damage observation of recent earthquakes demonstrated the effectiveness of the response of confined masonry structures to seismic actions. In general, in this type of structures, reinforced concrete beams and columns are not main structural elements, however, they have the following functions: to confine masonry in order to increase its ductility; to bear tensile stressesmore » derived from bending; to contrast the out-of-plane overturning of masonry panels. It is well evident that these functions are as much effectively performed as the connection between masonry and reinforced concrete elements is good (for example by mean of local interlocking or reinforcements). Confined masonry structures have been extensively studied in the last decades both from a theoretical point of view and by experimental tests Aims of this paper is to give a contribution to the understanding of the seismic behaviour of confined masonry walls by means of numerical parametrical analyses. There latter are performed by mean of the finite element method; a nonlinear anisotropic constitutive law recently developed for masonry is adopted. Comparison with available experimental results are carried out in order to validate the results. A comparison between the resistance obtained from the numerical analyses and the prevision provided by simplified resistance criteria proposed in literature and in codes is finally provided.« less

How to Recharge a Confined Aquifer: An Exploration of Geologic Controls on Groundwater Storage.

NASA Astrophysics Data System (ADS)

Maples, S.; Fogg, G. E.; Maxwell, R. M.; Liu, Y.

2017-12-01

Decreased snowpack storage and groundwater overdraft in California has increased interest in managed aquifer recharge (MAR) of excess winter runoff to the Central Valley aquifer system, which has unused storage capacity that far exceeds the state's surface reservoirs. Recharge to the productive, confined aquifer system remains a challenge due to the presence of nearly-ubiquitous, multiple silt and clay confining units that limit recharge pathways. However, previous studies have identified interconnected networks of sand and gravel deposits that bypass the confining units and accommodate rapid, high-volume recharge to the confined aquifer system in select locations. We use the variably-saturated, fully-integrated groundwater/surface-water flow code, ParFlow, in combination with a high-resolution, transition probability Markov-chain geostatistical model of the subsurface geologic heterogeneity of the east side of the Sacramento Valley, CA, to characterize recharge potential across a landscape that includes these geologic features. Multiple 180-day MAR simulations show that recharge potential is highly dependent on subsurface geologic structure, with a several order-of-magnitude range of recharge rates and volumes across the landscape. Where there are recharge pathways to the productive confined-aquifer system, pressure propagation in the confined system is widespread and rapid, with multi-kilometer lateral pressure propagation. Although widespread pressure propagation occurs in the confined system, only a small fraction of recharge volume is accommodated there. Instead, the majority of recharge occurs by filling unsaturated pore spaces. Where they outcrop at land surface, high-K recharge pathways fill rapidly, accommodating the majority of recharge during early time. However, these features become saturated quickly, and somewhat counterintuitively, the low-K silt and clay facies accommodate the majority of recharge volume during most of the simulation. These findings (1) highlight the large variability of MAR potential across the landscape, wherein the recharge capacity in select areas far exceeds recharge potential over most of the landscape, and (2) elucidate important physical processes that control MAR potential in alluvial aquifer systems.

Scalar collapse in AdS with an OpenCL open source code

NASA Astrophysics Data System (ADS)

Liebling, Steven L.; Khanna, Gaurav

2017-10-01

We study the spherically symmetric collapse of a scalar field in anti-de Sitter spacetime using a newly constructed, open-source code which parallelizes over heterogeneous architectures using the open standard OpenCL. An open question for this scenario concerns how to tell, a priori, whether some form of initial data will be stable or will instead develop under the turbulent instability into a black hole in the limit of vanishing amplitude. Previous work suggested the existence of islands of stability around quasi-periodic solutions, and we use this new code to examine the stability properties of approximately quasi-periodic solutions which balance energy transfer to higher modes with energy transfer to lower modes. The evolutions provide some evidence, though not conclusively, for stability of initial data sufficiently close to quasiperiodic solutions.

Evaluation of the use of shredded tires around buried pipes : technical assistance report.

DOT National Transportation Integrated Search

1999-05-01

The objective of this project was to assess the potential of placement and compaction of shredded tire chips and soil-tire mix in confined trenches around buried pipes and to evaluate the stability and deformation of metal pipes in such systems. The ...

Plasma confinement theory and transport simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ross, D.W.

The objectives are: (1) to advance the transport studies of tokamaks, including development and maintenance of the Magnetic Fusion Energy Database, and (2) to provide theoretical interpretation, modeling and equilibrium and stability studies for TEXT-Upgrade. Recent reports, publications, and conference presentations of the Fusion Research Center are listed.

TRACE/PARCS analysis of the OECD/NEA Oskarshamn-2 BWR stability benchmark

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlowski, T.; Downar, T.; Xu, Y.

2012-07-01

On February 25, 1999, the Oskarshamn-2 NPP experienced a stability event which culminated in diverging power oscillations with a decay ratio of about 1.4. The event was successfully modeled by the TRACE/PARCS coupled code system, and further analysis of the event is described in this paper. The results show very good agreement with the plant data, capturing the entire behavior of the transient including the onset of instability, growth of the oscillations (decay ratio) and oscillation frequency. This provides confidence in the prediction of other parameters which are not available from the plant records. The event provides coupled code validationmore » for a challenging BWR stability event, which involves the accurate simulation of neutron kinetics (NK), thermal-hydraulics (TH), and TH/NK. coupling. The success of this work has demonstrated the ability of the 3-D coupled systems code TRACE/PARCS to capture the complex behavior of BWR stability events. The problem was released as an international OECD/NEA benchmark, and it is the first benchmark based on measured plant data for a stability event with a DR greater than one. Interested participants are invited to contact authors for more information. (authors)« less

A scheme for reducing deceleration-phase Rayleigh-Taylor growth in inertial confinement fusion implosions

NASA Astrophysics Data System (ADS)

Wang, L. F.; Ye, W. H.; Wu, J. F.; Liu, Jie; Zhang, W. Y.; He, X. T.

2016-05-01

It is demonstrated that the growth of acceleration-phase instabilities in inertial confinement fusion implosions can be controlled, especially in the high-foot implosions [O. A. Hurricane et al., Phys. Plasmas 21, 056314 (2014)] on the National Ignition Facility. However, the excessive growth of the deceleration-phase instabilities can still destroy the hot spot ignition. A scheme is proposed to retard the deceleration-phase Rayleigh-Taylor instability growth by shock collision near the waist of the inner shell surface. Two-dimensional radiation hydrodynamic simulations confirm the improved deceleration-phase hot spot stability properties without sacrificing the fuel compression.

Binary mixtures of condensates in generic confining potentials

NASA Astrophysics Data System (ADS)

Facchi, P.; Florio, G.; Pascazio, S.; Pepe, F. V.

2011-12-01

We study a binary mixture of Bose-Einstein condensates, confined in a generic potential, in the Thomas-Fermi approximation. We search for the zero-temperature ground state of the system, both in the case of fixed numbers of particles and fixed chemical potentials. For generic potentials, we analyze the transition from mixed to separated ground-state configurations as the inter-species interaction increases. We derive a simple formula that enables one to determine the location of the domain walls. Finally, we find criteria for the energetic stability of separated configurations, depending on the number and the position of the domain walls separating the two species.

A scheme for reducing deceleration-phase Rayleigh–Taylor growth in inertial confinement fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, L. F., E-mail: wang-lifeng@iapcm.ac.cn; Ye, W. H.; Liu, Jie

It is demonstrated that the growth of acceleration-phase instabilities in inertial confinement fusion implosions can be controlled, especially in the high-foot implosions [O. A. Hurricane et al., Phys. Plasmas 21, 056314 (2014)] on the National Ignition Facility. However, the excessive growth of the deceleration-phase instabilities can still destroy the hot spot ignition. A scheme is proposed to retard the deceleration-phase Rayleigh–Taylor instability growth by shock collision near the waist of the inner shell surface. Two-dimensional radiation hydrodynamic simulations confirm the improved deceleration-phase hot spot stability properties without sacrificing the fuel compression.

Development of comprehensive numerical schemes for predicting evaporating gas-droplets flow processes of a liquid-fueled combustor

NASA Technical Reports Server (NTRS)

Chen, C. P.

1990-01-01

An existing Computational Fluid Dynamics code for simulating complex turbulent flows inside a liquid rocket combustion chamber was validated and further developed. The Advanced Rocket Injector/Combustor Code (ARICC) is simplified and validated against benchmark flow situations for laminar and turbulent flows. The numerical method used in ARICC Code is re-examined for incompressible flow calculations. For turbulent flows, both the subgrid and the two equation k-epsilon turbulence models are studied. Cases tested include idealized Burger's equation in complex geometries and boundaries, a laminar pipe flow, a high Reynolds number turbulent flow, and a confined coaxial jet with recirculations. The accuracy of the algorithm is examined by comparing the numerical results with the analytical solutions as well as experimented data with different grid sizes.

Extended capability of the integrated transport analysis suite, TASK3D-a, for LHD experiment

NASA Astrophysics Data System (ADS)

Yokoyama, M.; Seki, R.; Suzuki, C.; Sato, M.; Emoto, M.; Murakami, S.; Osakabe, M.; Tsujimura, T. Ii.; Yoshimura, Y.; Ido, T.; Ogawa, K.; Satake, S.; Suzuki, Y.; Goto, T.; Ida, K.; Pablant, N.; Gates, D.; Warmer, F.; Vincenzi, P.; Simulation Reactor Research Project, Numerical; LHD Experiment Group

2017-12-01

The integrated transport analysis suite, TASK3D-a (Analysis), has been developed to be capable for routine whole-discharge analyses of plasmas confined in three-dimensional (3D) magnetic configurations such as the LHD. The routine dynamic energy balance analysis for NBI-heated plasmas was made possible in the first version released in September 2012. The suite has been further extended through implementing additional modules for neoclassical transport and ECH deposition for 3D configurations. A module has also been added for creating systematic data for the International Stellarator-Heliotron Confinement and Profile Database. Improvement of neutral beam injection modules for multiple-ion species plasmas and loose coupling with a large-simulation code are also highlights of recent developments.

Modelling of radiation impact on ITER Beryllium wall

NASA Astrophysics Data System (ADS)

Landman, I. S.; Janeschitz, G.

2009-04-01

In the ITER H-Mode confinement regime, edge localized instabilities (ELMs) will perturb the discharge. Plasma lost after each ELM moves along magnetic field lines and impacts on divertor armour, causing plasma contamination by back propagating eroded carbon or tungsten. These impurities produce enhanced radiation flux distributed mainly over the beryllium main chamber wall. The simulation of the complicated processes involved are subject of the integrated tokamak code TOKES that is currently under development. This work describes the new TOKES model for radiation transport through confined plasma. Equations for level populations of the multi-fluid plasma species and the propagation of different kinds of radiation (resonance, recombination and bremsstrahlung photons) are implemented. First simulation results without account of resonance lines are presented.

Advances in petascale kinetic plasma simulation with VPIC and Roadrunner

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowers, Kevin J; Albright, Brian J; Yin, Lin

2009-01-01

VPIC, a first-principles 3d electromagnetic charge-conserving relativistic kinetic particle-in-cell (PIC) code, was recently adapted to run on Los Alamos's Roadrunner, the first supercomputer to break a petaflop (10{sup 15} floating point operations per second) in the TOP500 supercomputer performance rankings. They give a brief overview of the modeling capabilities and optimization techniques used in VPIC and the computational characteristics of petascale supercomputers like Roadrunner. They then discuss three applications enabled by VPIC's unprecedented performance on Roadrunner: modeling laser plasma interaction in upcoming inertial confinement fusion experiments at the National Ignition Facility (NIF), modeling short pulse laser GeV ion acceleration andmore » modeling reconnection in magnetic confinement fusion experiments.« less

Self-Mutilating Adolescents in Secure Confinement: A Nationwide Survey of Institutional Response Systems.

ERIC Educational Resources Information Center

Traver, Michael D.; Rule, Warren R.

1996-01-01

Reviews the types of treatment facilities being utilized by youth facilities nationwide and their practices regarding self-mutilating residents. Results indicate varied frequencies of self-harming behavior. Findings suggest that departments that chose to take responsibility for stabilizing mutilating adolescents as a distinct group express greater…

Effects of residual kinetic energy on yield degradation and ion temperature asymmetries in inertial confinement fusion implosions

DOE PAGES

Woo, K. M.; Betti, R.; Shvarts, D.; ...

2018-05-09

Tmore » he study of Rayleigh–aylor instability in the deceleration phase of inertial confinement fusion implosions is carried out using the three-dimensional (3-D) radiation-hydrodynamic Eulerian parallel code DEC3D. In this paper, we show that the yield-over-clean is a strong function of the residual kinetic energy (RKE) for low modes. Our analytical models indicate that the behavior of larger hot-spot volumes observed in low modes and the consequential pressure degradation can be explained in terms of increasing the RKE. hese results are derived using a simple adiabatic implosion model of the deceleration phase as well as through an extensive set of 3-D single-mode simulations using the code DEC3D. he effect of the bulk velocity broadening on ion temperature asymmetries is analyzed for different mode numbers ℓ = 1 -12. he jet observed in low mode ℓ = 1 is shown to cause the largest ion temperature variation in the mode spectrum. Finally, the vortices of high modes within the cold bubbles are shown to cause lower ion temperature variations than low modes.« less

Effects of residual kinetic energy on yield degradation and ion temperature asymmetries in inertial confinement fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woo, K. M.; Betti, R.; Shvarts, D.

Tmore » he study of Rayleigh–aylor instability in the deceleration phase of inertial confinement fusion implosions is carried out using the three-dimensional (3-D) radiation-hydrodynamic Eulerian parallel code DEC3D. In this paper, we show that the yield-over-clean is a strong function of the residual kinetic energy (RKE) for low modes. Our analytical models indicate that the behavior of larger hot-spot volumes observed in low modes and the consequential pressure degradation can be explained in terms of increasing the RKE. hese results are derived using a simple adiabatic implosion model of the deceleration phase as well as through an extensive set of 3-D single-mode simulations using the code DEC3D. he effect of the bulk velocity broadening on ion temperature asymmetries is analyzed for different mode numbers ℓ = 1 -12. he jet observed in low mode ℓ = 1 is shown to cause the largest ion temperature variation in the mode spectrum. Finally, the vortices of high modes within the cold bubbles are shown to cause lower ion temperature variations than low modes.« less

The effects of resonant magnetic perturbations on fast ion confinement in the Mega Amp Spherical Tokamak

NASA Astrophysics Data System (ADS)

McClements, K. G.; Akers, R. J.; Boeglin, W. U.; Cecconello, M.; Keeling, D.; Jones, O. M.; Kirk, A.; Klimek, I.; Perez, R. V.; Shinohara, K.; Tani, K.

2015-07-01

The effects of resonant magnetic perturbations (RMPs) on the confinement of energetic (neutral beam) ions in the Mega Amp Spherical Tokamak (MAST) are assessed experimentally using measurements of neutrons, fusion protons and fast ion Dα (FIDA) light emission. In single null-diverted (SND) MAST pulses with relatively low plasma current (400 kA), the total neutron emission dropped by approximately a factor of two when RMPs with toroidal mode number n = 3 were applied. The measured neutron rate during RMPs was much lower than that calculated using the TRANSP plasma simulation code, even when non-classical (but axisymmetric) ad hoc fast ion transport was taken into account in the latter. Sharp drops in spatially-resolved neutron rates, fusion proton rates and FIDA emission were also observed. First principles-based simulations of RMP-induced fast ion transport in MAST, using the F3D-OFMC code, show similar losses for two alternative representations of the MAST first wall, with and without full orbit effects taken into account; for n = 6 RMPs in a 600 kA plasma, the additional loss of beam power due to the RMPs was found in the simulations to be approximately 11%.

MATLAB Stability and Control Toolbox Trim and Static Stability Module

NASA Technical Reports Server (NTRS)

Kenny, Sean P.; Crespo, Luis

2012-01-01

MATLAB Stability and Control Toolbox (MASCOT) utilizes geometric, aerodynamic, and inertial inputs to calculate air vehicle stability in a variety of critical flight conditions. The code is based on fundamental, non-linear equations of motion and is able to translate results into a qualitative, graphical scale useful to the non-expert. MASCOT was created to provide the conceptual aircraft designer accurate predictions of air vehicle stability and control characteristics. The code takes as input mass property data in the form of an inertia tensor, aerodynamic loading data, and propulsion (i.e. thrust) loading data. Using fundamental nonlinear equations of motion, MASCOT then calculates vehicle trim and static stability data for the desired flight condition(s). Available flight conditions include six horizontal and six landing rotation conditions with varying options for engine out, crosswind, and sideslip, plus three take-off rotation conditions. Results are displayed through a unique graphical interface developed to provide the non-stability and control expert conceptual design engineer a qualitative scale indicating whether the vehicle has acceptable, marginal, or unacceptable static stability characteristics. If desired, the user can also examine the detailed, quantitative results.

Computer code for the prediction of nozzle admittance

NASA Technical Reports Server (NTRS)

Nguyen, Thong V.

1988-01-01

A procedure which can accurately characterize injector designs for large thrust (0.5 to 1.5 million pounds), high pressure (500 to 3000 psia) LOX/hydrocarbon engines is currently under development. In this procedure, a rectangular cross-sectional combustion chamber is to be used to simulate the lower traverse frequency modes of the large scale chamber. The chamber will be sized so that the first width mode of the rectangular chamber corresponds to the first tangential mode of the full-scale chamber. Test data to be obtained from the rectangular chamber will be used to assess the full scale engine stability. This requires the development of combustion stability models for rectangular chambers. As part of the combustion stability model development, a computer code, NOAD based on existing theory was developed to calculate the nozzle admittances for both rectangular and axisymmetric nozzles. This code is detailed.

Efficient preparation of large-block-code ancilla states for fault-tolerant quantum computation

NASA Astrophysics Data System (ADS)

Zheng, Yi-Cong; Lai, Ching-Yi; Brun, Todd A.

2018-03-01

Fault-tolerant quantum computation (FTQC) schemes that use multiqubit large block codes can potentially reduce the resource overhead to a great extent. A major obstacle is the requirement for a large number of clean ancilla states of different types without correlated errors inside each block. These ancilla states are usually logical stabilizer states of the data-code blocks, which are generally difficult to prepare if the code size is large. Previously, we have proposed an ancilla distillation protocol for Calderbank-Shor-Steane (CSS) codes by classical error-correcting codes. It was assumed that the quantum gates in the distillation circuit were perfect; however, in reality, noisy quantum gates may introduce correlated errors that are not treatable by the protocol. In this paper, we show that additional postselection by another classical error-detecting code can be applied to remove almost all correlated errors. Consequently, the revised protocol is fully fault tolerant and capable of preparing a large set of stabilizer states sufficient for FTQC using large block codes. At the same time, the yield rate can be boosted from O (t-2) to O (1 ) in practice for an [[n ,k ,d =2 t +1

Study on an azimuthal line cusp ion source for the KSTAR neutral beam injector.

PubMed

Jeong, Seung Ho; Chang, Doo-Hee; In, Sang Ryul; Lee, Kwang Won; Oh, Byung-Hoon; Yoon, Byung-Joo; Song, Woo Sob; Kim, Jinchoon; Kim, Tae Seong

2008-02-01

In this study it is found that the cusp magnetic field configuration of an anode bucket influences the primary electron behavior. An electron orbit code (ELEORBIT code) showed that an azimuthal line cusp (cusp lines run azimuthally with respect to the beam extraction direction) provides a longer primary electron confinement time than an axial line cusp configuration. Experimentally higher plasma densities were obtained under the same arc power when the azimuthal cusp chamber was used. The newly designed azimuthal cusp bucket has been investigated in an effort to increase the plasma density in its plasma generator per arc power.

The high-β{sub N} hybrid scenario for ITER and FNSF steady-state missions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turco, F.; Petty, C. C.; Luce, T. C.

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 currentmore » 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 missions of these devices.« less

Control of External Kink Instability

NASA Astrophysics Data System (ADS)

Navratil, Gerald

2004-11-01

A fundamental pressure and current limiting phenomenon in magnetically confined plasmas for fusion energy is the long wavelength ideal-MHD kink mode. These modes have been extensively studied in tokamak and reversed field pinch (RFP) devices. They are characterized by significant amplitude on the boundary of the confined plasma and can therefore be controlled by manipulation of the external boundary conditions. In the past ten years, the theoretically predicted stabilizing effect of a nearby conducting wall has been documented in experiments, which opens the possibility of a significant increase in maximum stable plasma pressure. While these modes are predicted to remain unstable when the stabilizing wall is resistive, their growth rates are greatly reduced from the hydrodynamic time scale to the time scale of magnetic diffusion through the resistive wall. These resistive wall slowed kink modes have been identified as limiting phenomena in tokamak (DIII-D, PBX-M, HBT-EP, JT-60U, JET, NSTX) and RFP (HBTX, Extrap, T2R) devices. The theoretical prediction of stabilization to nearly the ideal wall pressure limit by toroidal plasma rotation and/or active feedback control using coils has recently been realized experimentally. Sustained, stable operation at double the no-wall pressure limit has been achieved. Discovery of the phenomenon of resonant field amplification by marginally stable kink modes and its role in the momentum balance of rotationally stabilized plasmas has emerged as a key feature. A theoretical framework, based on an extension of the very successful treatment of the n=0 axisymmetric mode developed in the early 1990's, to understand the stabilization mechanisms and model the performance of active feedback control systems is now established. This allows design of kink control systems for burning plasma experiments like ITER.

Accuracy enhancement of laser induced breakdown spectra using permittivity and size optimized plasma confinement rings.

PubMed

Li, An; Guo, Shuai; Wazir, Nasrullah; Chai, Ke; Liang, Liang; Zhang, Min; Hao, Yan; Nan, Pengfei; Liu, Ruibin

2017-10-30

The inevitable problems in laser induced breakdown spectroscopy are matrix effect and statistical fluctuation of the spectral signal, which can be partly avoided by utilizing a proper confined unit. The dependences of spectral signal enhancement on relative permittivity were studied by varying materials to confine the plasma, which include polytetrafluoroethylene(PTFE), nylon/dacron, silicagel, and nitrile-butadiene rubber (NBR) with the relative permittivity 2.2, ~3.3, 3.6, 8~13, 15~22. We found that higher relative permittivity rings induce stronger enhancement ability, which restricts the energy dissipation of plasma better and due to the reflected electromagnetic wave from the wall of different materials, the electromagnetic field of plasma can be well confined and makes the distribution of plasma more orderly. The spectral intensities of the characteristic lines Si I 243.5 nm and Si I 263.1 nm increased approximately 2 times with relative permittivity values from 2.2 to ~20. The size dependent enhancement of PTFE was further checked and the maximum gain was realized by using a confinement ring with a diameter size of 5 mm and a height of 3 mm (D5mmH3mm), and the rings with D2mmH1mm and D3mmH2mm also show higher enhancement factor. In view of peak shift, peak lost and accidental peaks in the obtained spectra were properly treated in data progressing; the spectral fluctuation decreased drastically for various materials with different relative permittivities as confined units, which means the core of plasma is stabilized, attributing to the confinement effect. Furthermore, the quantitative analysis in coal shows wonderful results-the prediction fitting coefficient R 2 reaches 0.98 for ash and 0.99 for both volatile and carbon.

Immobilization of Cr6+ in an urban and industrial soil from Mexico

NASA Astrophysics Data System (ADS)

Jordán, Manuel Miguel; Ballesteros, Sergio; María Rincón, Jesus; Rincón-Mora, Beatriz; Pardo, Francisco; Bech, Jaume

2017-04-01

In Mexico, some areas are highly contaminated by heavy metals. Currently, there are more than 75,000 tons of untreated residues in the form of slags and sludges containing high concentrations of hexavalent chromium, Cr6+, in densely populated zones very near Mexico City. Capillary migration of Cr6+ and its concentration towards the surface at landfill or confinement sites is variable due to the presence of slowly soluble chromium salts and changes in meteorological conditions. Due to these phenomena, concentrations a few centimeters from the ground surface can vary from just a few parts per million to percentage levels that are many times greater than the concentration at the very confinement site. At these sites, chromate enrichment is evident at the subsoil surface or confinement areas as outcrops in the form of greenish-yellow stains extending along constructed walls and confinement installations or processing areas. This research describes the characteristics, formation mechanisms, and leaching of Cr6+ wastes that are contaminating a Mexican urban soil (Ballesteros et al, 2016). By means of a vitrification process, a method has been proposed that transforms Cr6+ to Cr3+ and achieves effective immobilization of this highly toxic industrial waste affecting an urban area. By various physicochemical techniques, such as XRD, DTA, and SEM/EDS, carrying out complete characterization of these new materials was possible. The final vitrified or glassy products of silicate composition lead to a glass ceramic material that is environmentally very stable, showing high chemical and mechanical stability where all Cr6+ was reduced to Cr3+ in the residual glass network, as well as other chromium oxidation states confined in the crystalline phases formed in the final glass-ceramic. The leaching tests on samples stabilized by vitrification have shown that the release of ions from the structure of these new materials was negligible, yielding values less than 0.5 mg/l with respect to current international and domestic environmental regulations. References Ballesteros; S, Rincón, J.Ma; Rincón-Mora, B.; Jordán, M.M. (2016). Vitrification of Urban Soil Contamination by Hexavalent Chromium. Journal of Geochemical Exploration. In press.

A Spreadsheet for the Mixing of a Row of Jets with a Confined Crossflow

NASA Technical Reports Server (NTRS)

Holderman, J. D.; Smith, T. D.; Clisset, J. R.; Lear, W. E.

2005-01-01

An interactive computer code, written with a readily available software program, Microsoft Excel (Microsoft Corporation, Redmond, WA) is presented which displays 3 D oblique plots of a conserved scalar distribution downstream of jets mixing with a confined crossflow, for a single row, double rows, or opposed rows of jets with or without flow area convergence and/or a non-uniform crossflow scalar distribution. This project used a previously developed empirical model of jets mixing in a confined crossflow to create an Microsoft Excel spreadsheet that can output the profiles of a conserved scalar for jets injected into a confined crossflow given several input variables. The program uses multiple spreadsheets in a single Microsoft Excel notebook to carry out the modeling. The first sheet contains the main program, controls for the type of problem to be solved, and convergence criteria. The first sheet also provides for input of the specific geometry and flow conditions. The second sheet presents the results calculated with this routine to show the effects on the mixing of varying flow and geometric parameters. Comparisons are also made between results from the version of the empirical correlations implemented in the spreadsheet and the versions originally written in Applesoft BASIC (Apple Computer, Cupertino, CA) in the 1980's.

A Spreadsheet for the Mixing of a Row of Jets with a Confined Crossflow. Supplement

NASA Technical Reports Server (NTRS)

Holderman, J. D.; Smith, T. D.; Clisset, J. R.; Lear, W. E.

2005-01-01

An interactive computer code, written with a readily available software program, Microsoft Excel (Microsoft Corporation, Redmond, WA) is presented which displays 3 D oblique plots of a conserved scalar distribution downstream of jets mixing with a confined crossflow, for a single row, double rows, or opposed rows of jets with or without flow area convergence and/or a non-uniform crossflow scalar distribution. This project used a previously developed empirical model of jets mixing in a confined crossflow to create an Microsoft Excel spreadsheet that can output the profiles of a conserved scalar for jets injected into a confined crossflow given several input variables. The program uses multiple spreadsheets in a single Microsoft Excel notebook to carry out the modeling. The first sheet contains the main program, controls for the type of problem to be solved, and convergence criteria. The first sheet also provides for input of the specific geometry and flow conditions. The second sheet presents the results calculated with this routine to show the effects on the mixing of varying flow and geometric parameters. Comparisons are also made between results from the version of the empirical correlations implemented in the spreadsheet and the versions originally written in Applesoft BASIC (Apple Computer, Cupertino, CA) in the 1980's.

Static-stress analysis of dual-axis confinement vessel

NASA Astrophysics Data System (ADS)

Bultman, D. H.

1992-11-01

This study evaluates the static-pressure containment capability of a 6-ft-diameter, spherical vessel, made of HSLA-100 steel, to be used for high-explosive (HE) containment. The confinement vessel is designed for use with the Dual-Axis Radiographic Hydrotest Facility (DARHT) being developed at Los Alamos National Laboratory. Two sets of openings in the vessel are covered with x-ray transparent covers to allow radiographic imaging of an explosion as it occurs inside the vessel. The confinement vessel is analyzed as a pressure vessel based on the ASME Boiler and Pressure Vessel Code, Section 8, Division 1, and the Welding Research Council Bulletin, WRC-107. Combined stresses resulting from internal pressure and external loads on nozzles are calculated and compared with the allowable stresses for HSLA-100 steel. Results confirm that the shell and nozzles of the confinement vessel are adequately designed to safely contain the maximum residual pressure of 1675 psi that would result from an HE charge of 24.2 kg detonated in a vacuum. Shell stresses at the shell-to-nozzle interface, produced from external loads on the nozzles, were less than 400 psi. The maximum combined stress resulting from the internal pressure plus external loads was 16,070 psi, which is less than half the allowable stress of 42,375 psi for HSLA-100 steel.

Flow shear stabilization of rotating plasmas due to the Coriolis effect.

PubMed

Haverkort, J W; de Blank, H J

2012-07-01

A radially decreasing toroidal rotation frequency can have a stabilizing effect on nonaxisymmetric magnetohydrodynamic (MHD) instabilities. We show that this is a consequence of the Coriolis effect that induces a restoring pressure gradient force when plasma is perturbed radially. In a rotating cylindrical plasma, this Coriolis-pressure effect is canceled by the centrifugal effect responsible for the magnetorotational instability. In a magnetically confined toroidal plasma, a large aspect ratio expansion shows that only half of the effect is canceled. This analytical result is confirmed by numerical computations. When the plasma rotates faster toroidally in the core than near the edge, the effect can contribute to the formation of transport barriers by stabilizing MHD instabilities.

Optimization of Kink Stability in High-Beta Quasi-axisymmetric Stellarators

NASA Astrophysics Data System (ADS)

Fu, G. Y.; Ku, L.-P.; Manickam, J.; Cooper, W. A.

1998-11-01

A key issue for design of Quasi-axisymmetric stellarators( A. Reiman et al, this conference.) (QAS) is the stability of external kink modes driven by pressure-induced bootstrap current. In this work, the 3D MHD stability code TERPSICHORE(W.A. Cooper, Phys. Plasmas 3), 275(1996). is used to calculate the stability of low-n external kink modes in a high-beta QAS. The kink stability is optimized by adjusting plasma boundary shape (i.e., external coil configuration) as well as plasma pressure and current profiles. For this purpose, the TERPSICHORE code has been implemented successfully in an optimizer which maximizes kink stability as well as quasi-symmetry. A key factor for kink stability is rotational transform profile. It is found that the edge magnetic shear is strongly stabilizing. The amount of the shear needed for complete stabilization increases with edge transform. It is also found that the plasma boundary shape plays an important role in the kink stability besides transform profile. The physics mechanisms for the kink stability are being studied by examining the contributions of individual terms in δ W of the energy principle: the field line bending term, the current-driven term, the pressure-driven term, and the vacuum term. Detailed results will be reported.

Fabrication of hierarchical porous N-doping carbon membrane by using ;confined nanospace deposition; method for supercapacitor

NASA Astrophysics Data System (ADS)

Wang, Guoxu; Liu, Meng; Du, Juan; Liu, Lei; Yu, Yifeng; Sha, Jitong; Chen, Aibing

2018-03-01

The membrane carbon materials with hierarchical porous architecture are attractive because they can provide more channels for ion transport and shorten the ions transport path. Herein, we develop a facile way based on "confined nanospace deposition" to fabricate N-dopi-ng three dimensional hierarchical porous membrane carbon material (N-THPMC) via coating the nickel nitrate, silicate oligomers and triblock copolymer P123 on the branches of commercial polyamide membrane (PAM). During high temperature treatment, the mesoporous silica layer and Ni species serve as a "confined nanospace" and catalyst respectively, which are indispensable elements for formation of carbon framework, and the gas-phase carbon precursors which derive from the decomposition of PAM are deposited into the "confined nanospace" forming carbon framework. The N-THPMC with hierarchical macro/meso/microporous structure, N-doping (2.9%) and large specific surface area (994m2 g-1) well inherits the membrane morphology and hierarchical porous structure of PAM. The N-THPMC as electrode without binder exhibits a specific capacitance of 252 F g-1 at the current density of 1 A g-1 in 6 M KOH electrolyte and excellent cycling stability of 92.7% even after 5000 cycles.

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

Dephasing dynamics in confined myoglobin

NASA Astrophysics Data System (ADS)

Goj, Anne; Loring, Roger F.

2007-11-01

Confinement of a solution can slow solvent dynamics and in turn influence the reactivity and structure of the solute. Encapsulating a protein in an aqueous pore affects its binding properties, stability to degradation, interconversion between conformational states, and energy relaxation. We perform molecular dynamics simulations of H64V-CO mutant myoglobin solvated by varying amounts of liquid water, and in turn enclosed by a matrix of immobilized solvent, to mimic differing degrees of confinement of H64V-CO in a glass. We calculate the three-pulse vibrational echo signal of the CO ligand from the autocorrelation function of fluctuations in the CO vibrational frequency. When the first solvation layer alone is free to relax, the correlation function displays only fast relaxation reminiscent of the case of a protein in a fixed, immobilized solvent matrix. However the vibrational echo signal in this case decays significantly more rapidly than for a static solvent. With two solvation layers mobile, the correlation function displays long time relaxation characteristic of the unconfined protein and the echo signal decays rapidly. The echo signal of the protein with two mobile solvation layers is nearly identical to that of the unconfined protein, despite the substantially constrained solvent dynamics in the confined case.

Confinement and controlling the effective compressive stiffness of carbyne

NASA Astrophysics Data System (ADS)

Kocsis, Ashley J.; Aditya Reddy Yedama, Neta; Cranford, Steven W.

2014-08-01

Carbyne is a one-dimensional chain of carbon atoms, consisting of repeating sp-hybridized groups, thereby representing a minimalist molecular rod or chain. While exhibiting exemplary mechanical properties in tension (a 1D modulus on the order of 313 nN and a strength on the order of 11 nN), its use as a structural component at the molecular scale is limited due to its relative weakness in compression and the immediate onset of buckling under load. To circumvent this effect, here, we probe the effect of confinement to enhance the mechanical behavior of carbyne chains in compression. Through full atomistic molecular dynamics, we characterize the mechanical properties of a free (unconfined chain) and explore the effect of confinement radius (R), free chain length (L) and temperature (T) on the effective compressive stiffness of carbyne chains and demonstrate that the stiffness can be tuned over an order of magnitude (from approximately 0.54 kcal mol-1 Å2 to 46 kcal mol-1 Å2) by geometric control. Confinement may inherently stabilize the chains, potentially providing a platform for the synthesis of extraordinarily long chains (tens of nanometers) with variable compressive response.

Failure Behavior of Granite Affected by Confinement and Water Pressure and Its Influence on the Seepage Behavior by Laboratory Experiments.

PubMed

Cheng, Cheng; Li, Xiao; Li, Shouding; Zheng, Bo

2017-07-14

Failure behavior of granite material is paramount for host rock stability of geological repositories for high-level waste (HLW) disposal. Failure behavior also affects the seepage behavior related to transportation of radionuclide. Few of the published studies gave a consistent analysis on how confinement and water pressure affect the failure behavior, which in turn influences the seepage behavior of the rock during the damage process. Based on a series of laboratory experiments on NRG01 granite samples cored from Alxa area, a candidate area for China's HLW disposal, this paper presents some detailed observations and analyses for a better understanding on the failure mechanism and seepage behavior of the samples under different confinements and water pressure. The main findings of this study are as follows: (1) Strength reduction properties were found for the granite under water pressure. Besides, the complete axial stress-strain curves show more obvious yielding process in the pre-peak region and a more gradual stress drop in the post-peak region; (2) Shear fracturing pattern is more likely to form in the granite samples with the effect of water pressure, even under much lower confinements, than the predictions from the conventional triaxial compressive results; (3) Four stages of inflow rate curves are divided and the seepage behaviors are found to depend on the failure behavior affected by the confinement and water pressure.

Enzymatic reactivity of glucose oxidase confined in nanochannels.

PubMed

Yu, Jiachao; Zhang, Yuanjian; Liu, Songqin

2014-05-15

The construction of nanodevices coupled with an integrated real-time detection system for evaluation of the function of biomolecules in biological processes, and enzymatic reaction kinetics occurring at the confined space or interface is a significant challenge. In this work, a nanochannel-enzyme system in which the enzymatic reaction could be investigated with an electrochemical method was constructed. The model system was established by covalently linking glucose oxidase (GOD) onto the inner wall of the nanochannels of the porous anodic alumina (PAA) membrane. An Au disc was attached at the end of the nanochannels of the PAA membrane as the working electrode for detection of H2O2 product of enzymatic reaction. The effects of ionic strength, amount of immobilized enzyme and pore diameter of the nanochannels on the enzymatic reaction kinetics were illustrated. The GOD confined in nanochannels showed high stability and reactivity. Upon addition of glucose to the nanochannel-enzyme system, the current response had a calibration range span from 0.005 to 2 mM of glucose concentration. The apparent Michaelis-Menten constant (K(m)(app)) of GOD confined in nanochannel was 0.4 mM. The presented work provided a platform for real-time monitoring of the enzyme reaction kinetics confined in nanospaces. Such a nanochannel-enzyme system could also help design future biosensors and enzyme reactors with high sensitivity and efficiency. Copyright © 2013 Elsevier B.V. All rights reserved.

A GDT-based fusion neutron source for academic and industrial applications

NASA Astrophysics Data System (ADS)

Anderson, J. K.; Forest, C. B.; Mirnov, V. V.; Peterson, E. E.; Waleffe, R.; Wallace, J.; Harvey, R. W.

2017-10-01

The design of a fusion neutron source based on the gas dynamic trap (GDT) configuration is underway. The motivation is both the ends and the means. There are immediate applications for neutrons including medical isotope production and actinide burners. Taking the next step in the magnetic mirror path will leverage advances in high-temperature superconducting magnets and additive manufacturing in confining a fusion plasma, and both the technological and physics bases exist. Recent breakthrough results at the GDT facility in Russia demonstrate stable confinement of a beta 60% mirror plasma at high Te ( 1 keV). These scale readily to a fusion neutron source with an increase in magnetic field, mirror ratio, and ion energy. Studies of a next-step compact device focus on calculations of MHD equilibrium and stability, and Fokker-Planck modeling to optimize the heating scenario. The conceptualized device uses off-the-shelf MRI magnets for a 1 T central field, REBCO superconducting mirror coils (which can currently produce fields in excess of 30T), and existing 75 keV NBI and 140 GHz ECRH. High harmonic fast wave injection is damped on beam ions, dramatically increasing the fusion reactivity for an incremental bump in input power. MHD stability is achieved with the vortex confinement scheme, where a biasing profile imposes optimal ExB rotation of the plasma. Liquid metal divertors are being considered in the end cells. Work supported by the Wisconsin Alumni Research Foundation.

Fully-kinetic Ion Simulation of Global Electrostatic Turbulent Transport in C-2U

NASA Astrophysics Data System (ADS)

Fulton, Daniel; Lau, Calvin; Bao, Jian; Lin, Zhihong; Tajima, Toshiki; TAE Team

2017-10-01

Understanding the nature of particle and energy transport in field-reversed configuration (FRC) plasmas is a crucial step towards an FRC-based fusion reactor. The C-2U device at Tri Alpha Energy (TAE) achieved macroscopically stable plasmas and electron energy confinement time which scaled favorably with electron temperature. This success led to experimental and theoretical investigation of turbulence in C-2U, including gyrokinetic ion simulations with the Gyrokinetic Toroidal Code (GTC). A primary objective of TAE's new C-2W device is to explore transport scaling in an extended parameter regime. In concert with the C-2W experimental campaign, numerical efforts have also been extended in A New Code (ANC) to use fully-kinetic (FK) ions and a Vlasov-Poisson field solver. Global FK ion simulations are presented. Future code development is also discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lao, Lang L.; St John, Holger; Staebler, Gary M.

This report describes the work done under U.S. Department of Energy grant number DE-FG02-07ER54935 for the period ending July 31, 2010. The goal of this project was to provide predictive transport analysis to the PTRANSP code. Our contribution to this effort consisted of three parts: (a) a predictive solver suitable for use with highly non-linear transport models and installation of the turbulent confinement models GLF23 and TGLF, (b) an interface of this solver with the PTRANSP code, and (c) initial development of an EPED1 edge pedestal model interface with PTRANSP. PTRANSP has been installed locally on this cluster by importingmore » a complete PTRANSP build environment that always contains the proper version of the libraries and other object files that PTRANSP requires. The GCNMP package and its interface code have been added to the SVN repository at PPPL.« less

NASA-VOF3D: A three-dimensional computer program for incompressible flows with free surfaces

NASA Astrophysics Data System (ADS)

Torrey, M. D.; Mjolsness, R. C.; Stein, L. R.

1987-07-01

Presented is the NASA-VOF3D three-dimensional, transient, free-surface hydrodynamics program. This three-dimensional extension of NASA-VOF2D will, in principle, permit treatment in full three-dimensional generality of the wide variety of applications that could be treated by NASA-VOF2D only within the two-dimensional idealization. In particular, it, like NASA-VOF2D, is specifically designed to calculate confined flows in a low g environment. The code is presently restricted to cylindrical geometry. The code is based on the fractional volume-of-fluid method and allows multiple free surfaces with surface tension and wall adhesion. It also has a partial cell treatment that allows curved boundaries and internal obstacles. This report provides a brief discussion of the numerical method, a code listing, and some sample problems.

Experimental studies related to the origin of the genetic code and the process of protein synthesis - A review

NASA Technical Reports Server (NTRS)

Lacey, J. C., Jr.; Mullins, D. W., Jr.

1983-01-01

A survey is presented of the literature on the experimental evidence for the genetic code assignments and the chemical reactions involved in the process of protein synthesis. In view of the enormous number of theoretical models that have been advanced to explain the origin of the genetic code, attention is confined to experimental studies. Since genetic coding has significance only within the context of protein synthesis, it is believed that the problem of the origin of the code must be dealt with in terms of the origin of the process of protein synthesis. It is contended that the answers must lie in the nature of the molecules, amino acids and nucleotides, the affinities they might have for one another, and the effect that those affinities must have on the chemical reactions that are related to primitive protein synthesis. The survey establishes that for the bulk of amino acids, there is a direct and significant correlation between the hydrophobicity rank of the amino acids and the hydrophobicity rank of their anticodonic dinucleotides.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Batchelor, D.B.; Carreras, B.A.; Hirshman, S.P.

Significant progress has been made in the development of new modest-size compact stellarator devices that could test optimization principles for the design of a more attractive reactor. These are 3 and 4 field period low-aspect-ratio quasi-omnigenous (QO) stellarators based on an optimization method that targets improved confinement, stability, ease of coil design, low-aspect-ratio, and low bootstrap current.

Hydrodynamic Capture of Particles by Micro-swimmers under Hele-Shaw Flows

NASA Astrophysics Data System (ADS)

Mishler, Grant; Tsang, Alan Cheng Hou; Pak, On Shun

2017-11-01

We explore a hydrodynamic capture mechanism of a driven particle by a micro-swimmer in confined microfluidic environments with an idealized model. The capture is mediated by the hydrodynamic interactions between the micro-swimmer, the driven particle, and the background flow. This capture mechanism relies on the existence of attractive stable equilibrium configurations between the driven particle and the micro-swimmer, which occurs when the background flow is larger than a certain critical threshold. Dynamics and stability of capture and non-capture events will be discussed. This study may have potential applications in the study of capture and delivery of therapeutic payloads by micro-swimmers as well as particle self-assembly under confinements.

Mechanics and stability of vesicles and droplets in confined spaces

PubMed Central

Benet, Eduard; Vernerey, Franck J.

2017-01-01

The permeation and trapping of soft colloidal particles in the confined space of porous media are of critical importance in cell migration studies, design of drug delivery vehicles, and colloid separation devices. Our current understanding of these processes is however limited by the lack of quantitative models that can relate how the elasticity, size, and adhesion properties of the vesicle-pore complex affect colloid transport. We address this shortcoming by introducing a semianalytical model that predicts the equilibrium shapes of a soft vesicle driven by pressure in a narrow pore. Using this approach, the problem is recast in terms of pressure and energy diagrams that characterize the vesicle stability and permeation pressures in different conditions. We particularly show that the critical permeation pressure for a vesicle arises from a compromise between the critical entry pressure and exit pressure, both of which are sensitive to geometrical features, mechanics, and adhesion. We further find that these results can be leveraged to rationally design microfluidic devices and diodes that can help characterize, select, and separate colloids based on physical properties. PMID:28085314

Experimental study of the stability and flow characteristics of floating liquid columns confined between rotating disks

NASA Technical Reports Server (NTRS)

Fowle, A. A.; Soto, L.; Strong, P. F.; Wang, C. A.

1980-01-01

A low Bond number simulation technique was used to establish the stability limits of cylindrical and conical floating liquid columns under conditions of isorotation, equal counter rotation, rotation of one end only, and parallel axis offset. The conditions for resonance in cylindrical liquid columns perturbed by axial, sinusoidal vibration of one end face are also reported. All tests were carried out under isothermal conditions with water and silicone fluids of various viscosities. A technique for the quantitative measurement of stream velocity within a floating, isothermal, liquid column confined between rotatable disks was developed. In the measurement, small, light scattering particles were used as streamline markers in common arrangement, but the capability of the measurement was extended by use of stereopair photography system to provide quantitative data. Results of velocity measurements made under a few selected conditions, which established the precision and accuracy of the technique, are given. The general qualitative features of the isothermal flow patterns under various conditions of end face rotation resulting from both still photography and motion pictures are presented.

Portable rotating discharge plasma device

NASA Astrophysics Data System (ADS)

Dwyer, B. L.; Brooks, N. H.; Lee, R. L.

2011-10-01

We constructed two devices for the purpose of educational demonstration: a rotating tube containing media of two densities to demonstrate axial confinement and a similar device that uses pressure variation to convert a long plasma glow discharge into a long straight arc. In the first device, the buoyant force is countered by the centripetal force, which confines less dense materials to the center of the column. Similarly, a plasma arc heats the gas through which it passes, creating a hot gaseous bubble that is less dense than the surrounding medium. Rotating its containment envelope stabilizes this gas bubble in an analogous manner to an air bubble in a rotating tube of water. In addition to stabilization, the rotating discharge also exhibits a decrease in buoyancy-driven convection currents. This limits the power loss to the walls, which decreases the field strength requirement for maintaining the arc. These devices demonstrate principles of electrodynamics, plasma physics, and fluid mechanics. They are portable and safe for classroom use. Work supported by US DOE under DE-FC02-04ER54698 and the National Undergraduate Fellowship in Fusion Science and Engineering.

Composite operator and condensate in the S U (N ) Yang-Mills theory with U (N -1 ) stability group

NASA Astrophysics Data System (ADS)

Warschinke, Matthias; Matsudo, Ryutaro; Nishino, Shogo; Shinohara, Toru; Kondo, Kei-Ichi

2018-02-01

Recently, some reformulations of the Yang-Mills theory inspired by the Cho-Faddeev-Niemi decomposition have been developed in order to understand confinement from the viewpoint of the dual superconductivity. In this paper we focus on the reformulated S U (N ) Yang-Mills theory in the minimal option with U (N -1 ) stability group. Despite existing numerical simulations on the lattice we perform the perturbative analysis to one-loop level as a first step towards the nonperturbative analytical treatment. First, we give the Feynman rules and calculate all renormalization factors to obtain the standard renormalization group functions to one-loop level in light of the renormalizability of this theory. Then we introduce a mixed gluon-ghost composite operator of mass dimension 2 and show the Bechi-Rouet-Stora-Tyutin invariance and the multiplicative renormalizability. Armed with these results, we argue the existence of the mixed gluon-ghost condensate by means of the so-called local composite operator formalism, which leads to various interesting implications for confinement as shown in preceding works.

Edge Currents and Stability in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, D M; Fenstermacher, M E; Finkenthal, D K

2004-12-01

Understanding the stability physics of the H-mode pedestal in tokamak devices requires an accurate measurement of plasma current in the pedestal region with good spatial resolution. Theoretically, the high pressure gradients achieved in the edge of H-mode plasmas should lead to generation of a significant edge current density peak through bootstrap and Pfirsh-Schl{umlt u}ter effects. This edge current is important for the achievement of second stability in the context of coupled magneto hydrodynamic (MHD) modes which are both pressure (ballooning) and current (peeling) driven. Many aspects of edge localized mode (ELM) behavior can be accounted for in terms of anmore » edge current density peak, with the identification of Type 1 ELMs as intermediate-n toroidal mode number MHD modes being a natural feature of this model. The development of a edge localized instabilities in tokamak experiments code (ELITE) based on this model allows one to efficiently calculate the stability and growth of the relevant modes for a broad range of plasma parameters and thus provides a framework for understanding the limits on pedestal height. This however requires an accurate assessment of the edge current. While estimates of j{sub edge} can be made based on specific bootstrap models, their validity may be limited in the edge (gradient scalelengths comparable to orbit size, large changes in collisionality, etc.). Therefore it is highly desirable to have an actual measurement. Such measurements have been made on the DIII-D tokamak using combined polarimetry and spectroscopy of an injected lithium beam. By analyzing one of the Zeeman-split 2S-2P lithium resonance line components, one can obtain direct information on the local magnetic field components. These values allow one to infer details of the edge current density. Because of the negligible Stark mixing of the relevant atomic levels in lithium, this method of determining j(r) is insensitive to the large local electric fields typically found in enhanced confinement (H-mode) edges, and thus avoids an ambiguity common to MSE measurements of B{sub pol}.« less

Edge Currents and Stability in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, D M; Fenstermacher, M E; Finkenthal, D K

2005-05-05

Understanding the stability physics of the H-mode pedestal in tokamak devices requires an accurate measurement of plasma current in the pedestal region with good spatial resolution. Theoretically, the high pressure gradients achieved in the edge of H-mode plasmas should lead to generation of a significant edge current density peak through bootstrap and Pfirsh-Schlueter effects. This edge current is important for the achievement of second stability in the context of coupled magneto hydrodynamic (MHD) modes which are both pressure (ballooning) and current (peeling) driven [1]. Many aspects of edge localized mode (ELM) behavior can be accounted for in terms of anmore » edge current density peak, with the identification of Type 1 ELMs as intermediate-n toroidal mode number MHD modes being a natural feature of this model [2]. The development of a edge localized instabilities in tokamak experiments code (ELITE) based on this model allows one to efficiently calculate the stability and growth of the relevant modes for a broad range of plasma parameters [3,4] and thus provides a framework for understanding the limits on pedestal height. This however requires an accurate assessment of the edge current. While estimates of j{sub edge} can be made based on specific bootstrap models, their validity may be limited in the edge (gradient scale lengths comparable to orbit size, large changes in collisionality, etc.). Therefore it is highly desirable to have an actual measurement. Such measurements have been made on the DIII-D tokamak using combined polarimetry and spectroscopy of an injected lithium beam. [5,6]. By analyzing one of the Zeeman-split 2S-2P lithium resonance line components, one can obtain direct information on the local magnetic field components. These values allow one to infer details of the edge current density. Because of the negligible Stark mixing of the relevant atomic levels in lithium, this method of determining j(r) is insensitive to the large local electric fields typically found in enhanced confinement (H-mode) edges, and thus avoids an ambiguity common to MSE measurements of B{sub pol}.« less

End-of-life decisions in Malaysia: Adequacies of ethical codes and developing legal standards.

PubMed

Kassim, Puteri Nemie Jahn; Alias, Fadhlina

2015-06-01

End-of-life decision-making is an area of medical practice in which ethical dilemmas and legal interventions have become increasingly prevalent. Decisions are no longer confined to clinical assessments; rather, they involve wider considerations such as a patient's religious and cultural beliefs, financial constraints, and the wishes and needs of family members. These decisions affect everyone concerned, including members of the community as a whole. Therefore it is imperative that clear ethical codes and legal standards are developed to help guide the medical profession on the best possible course of action for patients. This article considers the relevant ethical, codes and legal provisions in Malaysia governing certain aspects of end-of-life decision-making. It highlights the lack of judicial decisions in this area as well as the limitations with the Malaysian regulatory system. The article recommends the development of comprehensive ethical codes and legal standards to guide end-of-life decision-making in Malaysia.

Optical spectroscopy to study confined and semi-closed explosions of homogeneous and composite charges

NASA Astrophysics Data System (ADS)

Maiz, Lotfi; Trzciński, Waldemar A.; Paszula, Józef

2017-01-01

Confined and semi-closed explosions of new class of energetic composites as well as TNT and RDX charges were investigated using optical spectroscopy. These composites are considered as thermobarics when used in layered charges or enhanced blast explosives when pressed. Two methods to estimate fireball temperature histories of both homogeneous and metallized explosives from the spectroscopic data are also presented, compared and analyzed. Fireball temperature results of the charges detonated in a small explosion chamber under air and argon atmospheres, and detonated in a semi-closed bunker are presented and compared with theoretical ones calculated by a thermochemical code. Important conclusions about the fireball temperatures and the physical and chemical phenomena occurring after the detonation of homogeneous explosives and composite formulations are deduced.

Winds of Massive Magnetic Stars: Interacting Fields and Flow

NASA Astrophysics Data System (ADS)

Daley-Yates, S.; Stevens, I. R.

2018-01-01

We present results of 3D numerical simulations of magnetically confined, radiatively driven stellar winds of massive stars, conducted using the astrophysical MHD code Pluto, with a focus on understanding the rotational variability of radio and sub-mm emission. Radiative driving is implemented according to the Castor, Abbott and Klein theory of radiatively driven winds. Many magnetic massive stars posses a magnetic axis which is inclined with respect to the rotational axis. This misalignment leads to a complex wind structure as magnetic confinement, centrifugal acceleration and radiative driving act to channel the circumstellar plasma into a warped disk whose observable properties should be apparent in multiple wavelengths. This structure is analysed to calculate free-free thermal radio emission and determine the characteristic intensity maps and radio light curves.

The fracture characteristic of three collinear cracks under true triaxial compression.

PubMed

Liu, Jianjun; Zhu, Zheming; Wang, Bo

2014-01-01

The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses.

Two-Plasmon Decay Mitigation in Direct-Drive Inertial-Confinement-Fusion Experiments Using Multilayer Targets.

PubMed

Follett, R K; Delettrez, J A; Edgell, D H; Goncharov, V N; Henchen, R J; Katz, J; Michel, D T; Myatt, J F; Shaw, J; Solodov, A A; Stoeckl, C; Yaakobi, B; Froula, D H

2016-04-15

Multilayer direct-drive inertial-confinement-fusion targets are shown to significantly reduce two-plasmon decay (TPD) driven hot-electron production while maintaining high hydrodynamic efficiency. Implosion experiments on the OMEGA laser used targets with silicon layered between an inner beryllium and outer silicon-doped plastic ablator. A factor-of-5 reduction in hot-electron generation (>50  keV) was observed in the multilayer targets relative to pure CH targets. Three-dimensional simulations of the TPD-driven hot-electron production using a laser-plasma interaction code (lpse) that includes nonlinear and kinetic effects show good agreement with the measurements. The simulations suggest that the reduction in hot-electron production observed in the multilayer targets is primarily caused by increased electron-ion collisional damping.

The Fracture Characteristic of Three Collinear Cracks under True Triaxial Compression

PubMed Central

Liu, Jianjun; Zhu, Zheming; Wang, Bo

2014-01-01

The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses. PMID:24790569

A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahlin, J.-E.; Scheffel, J.

2005-06-15

In the advanced reversed-field pinch (RFP), the current density profile is externally controlled to diminish tearing instabilities. Thus the scaling of energy confinement time with plasma current and density is improved substantially as compared to the conventional RFP. This may be numerically simulated by introducing an ad hoc electric field, adjusted to generate a tearing mode stable parallel current density profile. In the present work a current profile control algorithm, based on feedback of the fluctuating electric field in Ohm's law, is introduced into the resistive magnetohydrodynamic code DEBSP [D. D. Schnack and D. C. Baxter, J. Comput. Phys. 55,more » 485 (1984); D. D. Schnack, D. C. Barnes, Z. Mikic, D. S. Marneal, E. J. Caramana, and R. A. Nebel, Comput. Phys. Commun. 43, 17 (1986)]. The resulting radial magnetic field is decreased considerably, causing an increase in energy confinement time and poloidal {beta}. It is found that the parallel current density profile spontaneously becomes hollow, and that a formation, being related to persisting resistive g modes, appears close to the reversal surface.« less

Comparison of various contact algorithms for poroelastic tissues.

PubMed

Galbusera, Fabio; Bashkuev, Maxim; Wilke, Hans-Joachim; Shirazi-Adl, Aboulfazl; Schmidt, Hendrik

2014-01-01

Capabilities of the commercial finite element package ABAQUS in simulating frictionless contact between two saturated porous structures were evaluated and compared with those of an open source code, FEBio. In ABAQUS, both the default contact implementation and another algorithm based on an iterative approach requiring script programming were considered. Test simulations included a patch test of two cylindrical slabs in a gapless contact and confined compression conditions; a confined compression test of a porous cylindrical slab with a spherical porous indenter; and finally two unconfined compression tests of soft tissues mimicking diarthrodial joints. The patch test showed almost identical results for all algorithms. On the contrary, the confined and unconfined compression tests demonstrated large differences related to distinct physical and boundary conditions considered in each of the three contact algorithms investigated in this study. In general, contact with non-uniform gaps between fluid-filled porous structures could be effectively simulated with either ABAQUS or FEBio. The user should be aware of the parameter definitions, assumptions and limitations in each case, and take into consideration the physics and boundary conditions of the problem of interest when searching for the most appropriate model.

Joint DIII-D/EAST research on the development of a high poloidal beta scenario for the steady state missions of ITER and CFETR

NASA Astrophysics Data System (ADS)

Garofalo, A. M.; Gong, X. Z.; Ding, S. Y.; Huang, J.; McClenaghan, J.; Pan, C. K.; Qian, J.; Ren, Q. L.; Staebler, G. M.; Chen, J.; Cui, L.; Grierson, B. A.; Hanson, J. M.; Holcomb, C. T.; Jian, X.; Li, G.; Li, M.; Pankin, A. Y.; Peysson, Y.; Zhai, X.; Bonoli, P.; Brower, D.; Ding, W. X.; Ferron, J. R.; Guo, W.; Lao, L. L.; Li, K.; Liu, H.; Lyv, B.; Xu, G.; Zang, Q.

2018-01-01

Experimental and modeling investigations on the DIII-D and EAST tokamaks show the attractive transport and stability properties of fully noninductive, high poloidal-beta (β P ) plasmas, and their suitability for steady-state operating scenarios in ITER and CFETR. A key feature of the high-β P regime is the large-radius (ρ > 0.6) internal transport barrier (ITB), often observed in all channels (ne, Te, Ti, rotation), and responsible for both excellent energy confinement quality and excellent stability properties. Experiments on DIII-D have shown that, with a large-radius ITB, very high β N and β P values (both ≥ 4) can be reached by taking advantage of the stabilizing effect of a nearby conducting wall. Synergistically, higher plasma pressure provides turbulence suppression by Shafranov shift, leading to ITB sustainment independent of the plasma rotation. Experiments on EAST have been used to assess the long pulse potential of the high-β P regime. Using RF-only heating and current drive, EAST achieved minute-long fully noninductive steady state H-mode operation with strike points on an ITER-like tungsten divertor. Improved confinement (relative to standard H-mode) and steady state ITB features are observed with a monotonic q-profile with q min ˜ 1.5. Separately, experiments have shown that increasing the density in plasmas driven by lower hybrid wave broadens the q-profile, a technique that could enable a large radius ITB. These experimental results have been used to validate MHD, current drive, and turbulent transport models, and to project the high-β P regime to a burning plasma. These projections suggest the Shafranov shift alone will not suffice to provide improved confinement (over standard H-mode) without rotation and rotation shear. However, increasing the negative magnetic shear (higher q on axis) provides a similar turbulence suppression mechanism to Shafranov shift, and can help devices such as ITER and CFETR achieve their steady-state fusion goals.

ASTROP2-LE: A Mistuned Aeroelastic Analysis System Based on a Two Dimensional Linearized Euler Solver

NASA Technical Reports Server (NTRS)

Reddy, T. S. R.; Srivastava, R.; Mehmed, Oral

2002-01-01

An aeroelastic analysis system for flutter and forced response analysis of turbomachines based on a two-dimensional linearized unsteady Euler solver has been developed. The ASTROP2 code, an aeroelastic stability analysis program for turbomachinery, was used as a basis for this development. The ASTROP2 code uses strip theory to couple a two dimensional aerodynamic model with a three dimensional structural model. The code was modified to include forced response capability. The formulation was also modified to include aeroelastic analysis with mistuning. A linearized unsteady Euler solver, LINFLX2D is added to model the unsteady aerodynamics in ASTROP2. By calculating the unsteady aerodynamic loads using LINFLX2D, it is possible to include the effects of transonic flow on flutter and forced response in the analysis. The stability is inferred from an eigenvalue analysis. The revised code, ASTROP2-LE for ASTROP2 code using Linearized Euler aerodynamics, is validated by comparing the predictions with those obtained using linear unsteady aerodynamic solutions.

Stability of bound species during alkene reactions on solid acids

NASA Astrophysics Data System (ADS)

Sarazen, Michele L.; Iglesia, Enrique

2017-05-01

This study reports the thermodynamics of bound species derived from ethene, propene, n-butene, and isobutene on solid acids with diverse strength and confining voids. Density functional theory (DFT) and kinetic data indicate that covalently bound alkoxides form C-C bonds in the kinetically relevant step for dimerization turnovers on protons within TON (0.57 nm) and MOR (0.67 nm) zeolitic channels and on stronger acids HPW (polyoxometalate clusters on silica). Turnover rates for mixed alkenes give relative alkoxide stabilities; the respective adsorption constants are obtained from in situ infrared spectra. Tertiary alkoxides (from isobutene) within larger voids (MOR, HPW) are more stable than less substituted isomers but are destabilized within smaller concave environments (TON) because framework distortions are required to avoid steric repulsion. Adsorption constants are similar on MOR and HPW for each alkoxide, indicating that binding is insensitive to acid strength for covalently bound species. DFT-derived formation free energies for alkoxides with different framework attachments and backbone length/structure agree with measurements when dispersion forces, which mediate stabilization by confinement in host-guest systems, are considered. Theory reveals previously unrecognized framework distortions that balance the C-O bond lengths required for covalency with host-guest distances that maximize van der Waals contacts. These distortions, reported here as changes in O-atom locations and dihedral angles, become stronger for larger, more substituted alkoxides. The thermodynamic properties reported here for alkoxides and acid hosts differing in size and conjugate-anion stability are benchmarked against DFT-derived free energies; their details are essential to design host-guest pairs that direct alkoxide species toward specific products.

Strength and deformation behaviors of veined marble specimens after vacuum heat treatment under conventional triaxial compression

NASA Astrophysics Data System (ADS)

Su, Haijian; Jing, Hongwen; Yin, Qian; Yu, Liyuan; Wang, Yingchao; Wu, Xingjie

2017-10-01

The mechanical behaviors of rocks affected by high temperature and stress are generally believed to be significant for the stability of certain projects involving rocks, such as nuclear waste storage and geothermal resource exploitation. In this paper, veined marble specimens were treated to high temperature treatment and then used in conventional triaxial compression tests to investigate the effect of temperature, confining pressure, and vein angle on strength and deformation behaviors. The results show that the strength and deformation parameters of the veined marble specimens changed with the temperature, presenting a critical temperature of 600 °C. The triaxial compression strength of a horizontal vein (β = 90°) is obviously larger than that of a vertical vein (β = 0°). The triaxial compression strength, elasticity modulus, and secant modulus have an approximately linear relation to the confining pressure. Finally, Mohr-Coulomb and Hoek-Brown criteria were respectively used to analyze the effect of confining pressure on triaxial compression strength.

Chemistry in Confinement: Copper and Palladium Catalyzed Ecofriendly Organic Transformations within Porous Frameworks.

PubMed

Kumar, Basuvaraj Suresh; Pitchumani, Kasi

2018-05-01

A concise account on the use of transition metals copper (Cu) and palladium (Pd), as their cations as well as nanoparticles exchanged/immobilized onto porous frameworks such as zeolites, metal organic frameworks (MOFs), covalent organic polymers (COPs) and hollow nanostructures, functioning as catalysts in organic synthesis is presented. This biomimetic account, "focusing on catalytic systems in confinement" within zero-dimensional microenvironments and second sphere coordination covers primarily results from our group on N-sulfonylketenimine mediated cycloaddition, hydrogenation and C-C bond forming reactions, thus providing an interesting insight into the versatility and utility of these Cu and Pd catalysts. Other significant advantages and green credentials of confinement such as stability, selectivity, reusability, promotion of multicomponent reactions, use of green solvents, atom economy, and use of ambient conditions are highlighted at appropriate places. In the final section, our views on the current achievements and the future prospects in this area are summarized. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Installation of the National Transport Code Collaboration Data Server at the ITPA International Multi-tokamak Confinement Profile Database

NASA Astrophysics Data System (ADS)

Roach, Colin; Carlsson, Johan; Cary, John R.; Alexander, David A.

2002-11-01

The National Transport Code Collaboration (NTCC) has developed an array of software, including a data client/server. The data server, which is written in C++, serves local data (in the ITER Profile Database format) as well as remote data (by accessing one or several MDS+ servers). The client, a web-invocable Java applet, provides a uniform, intuitive, user-friendly, graphical interface to the data server. The uniformity of the interface relieves the user from the trouble of mastering the differences between different data formats and lets him/her focus on the essentials: plotting and viewing the data. The user runs the client by visiting a web page using any Java capable Web browser. The client is automatically downloaded and run by the browser. A reference to the data server is then retrieved via the standard Web protocol (HTTP). The communication between the client and the server is then handled by the mature, industry-standard CORBA middleware. CORBA has bindings for all common languages and many high-quality implementations are available (both Open Source and commercial). The NTCC data server has been installed at the ITPA International Multi-tokamak Confinement Profile Database, which is hosted by the UKAEA at Culham Science Centre. The installation of the data server is protected by an Internet firewall. To make it accessible to clients outside the firewall some modifications of the server were required. The working version of the ITPA confinement profile database is not open to the public. Authentification of legitimate users is done utilizing built-in Java security features to demand a password to download the client. We present an overview of the NTCC data client/server and some details of how the CORBA firewall-traversal issues were resolved and how the user authentification is implemented.

CORSICA modelling of ITER hybrid operation scenarios

NASA Astrophysics Data System (ADS)

Kim, S. H.; Bulmer, R. H.; Campbell, D. J.; Casper, T. A.; LoDestro, L. L.; Meyer, W. H.; Pearlstein, L. D.; Snipes, J. A.

2016-12-01

The hybrid operating mode observed in several tokamaks is characterized by further enhancement over the high plasma confinement (H-mode) associated with reduced magneto-hydro-dynamic (MHD) instabilities linked to a stationary flat safety factor (q ) profile in the core region. The proposed ITER hybrid operation is currently aiming at operating for a long burn duration (>1000 s) with a moderate fusion power multiplication factor, Q , of at least 5. This paper presents candidate ITER hybrid operation scenarios developed using a free-boundary transport modelling code, CORSICA, taking all relevant physics and engineering constraints into account. The ITER hybrid operation scenarios have been developed by tailoring the 15 MA baseline ITER inductive H-mode scenario. Accessible operation conditions for ITER hybrid operation and achievable range of plasma parameters have been investigated considering uncertainties on the plasma confinement and transport. ITER operation capability for avoiding the poloidal field coil current, field and force limits has been examined by applying different current ramp rates, flat-top plasma currents and densities, and pre-magnetization of the poloidal field coils. Various combinations of heating and current drive (H&CD) schemes have been applied to study several physics issues, such as the plasma current density profile tailoring, enhancement of the plasma energy confinement and fusion power generation. A parameterized edge pedestal model based on EPED1 added to the CORSICA code has been applied to hybrid operation scenarios. Finally, fully self-consistent free-boundary transport simulations have been performed to provide information on the poloidal field coil voltage demands and to study the controllability with the ITER controllers. Extended from Proc. 24th Int. Conf. on Fusion Energy (San Diego, 2012) IT/P1-13.

SciDAC GSEP: Gyrokinetic Simulation of Energetic Particle Turbulence and Transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Zhihong

Energetic particle (EP) confinement is a key physics issue for burning plasma experiment ITER, the crucial next step in the quest for clean and abundant energy, since ignition relies on self-heating by energetic fusion products (α-particles). Due to the strong coupling of EP with burning thermal plasmas, plasma confinement property in the ignition regime is one of the most uncertain factors when extrapolating from existing fusion devices to the ITER tokamak. EP population in current tokamaks are mostly produced by auxiliary heating such as neutral beam injection (NBI) and radio frequency (RF) heating. Remarkable progress in developing comprehensive EP simulationmore » codes and understanding basic EP physics has been made by two concurrent SciDAC EP projects GSEP funded by the Department of Energy (DOE) Office of Fusion Energy Science (OFES), which have successfully established gyrokinetic turbulence simulation as a necessary paradigm shift for studying the EP confinement in burning plasmas. Verification and validation have rapidly advanced through close collaborations between simulation, theory, and experiment. Furthermore, productive collaborations with computational scientists have enabled EP simulation codes to effectively utilize current petascale computers and emerging exascale computers. We review here key physics progress in the GSEP projects regarding verification and validation of gyrokinetic simulations, nonlinear EP physics, EP coupling with thermal plasmas, and reduced EP transport models. Advances in high performance computing through collaborations with computational scientists that enable these large scale electromagnetic simulations are also highlighted. These results have been widely disseminated in numerous peer-reviewed publications including many Phys. Rev. Lett. papers and many invited presentations at prominent fusion conferences such as the biennial International Atomic Energy Agency (IAEA) Fusion Energy Conference and the annual meeting of the American Physics Society, Division of Plasma Physics (APS-DPP).« less

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Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-17

... Antimicrobial Pesticides (NAICS code 32561); Producers of Nitrogen Stabilizers (NAICS code 32531); and Producers... Food, Drug, and Cosmetic Act (FFDCA), which requires endocrine screening of all pesticide chemicals and...

High speed transition prediction

NASA Technical Reports Server (NTRS)

Gasperas, Gediminis

1993-01-01

The main objective of this work period was to develop, maintain and exercise state-of-the-art methods for transition prediction in supersonic flow fields. Basic state and stability codes, acquired during the last work period, were exercised and applied to calculate the properties of various flowfields. The development of a code for the prediction of transition location using a currently novel method (the PSE or Parabolized Stability Equation method), initiated during the last work period and continued during the present work period, was cancelled at mid-year for budgetary reasons. Other activities during this period included the presentation of a paper at the APS meeting in Tallahassee, Florida entitled 'Stability of Two-Dimensional Compressible Boundary Layers', as well as the initiation of a paper co-authored with H. Reed of the Arizona State University entitled 'Stability of Boundary Layers'.

REVIEW ARTICLE: Major results from the stellarator Wendelstein 7-AS

NASA Astrophysics Data System (ADS)

Hirsch, M.; Baldzuhn, J.; Beidler, C.; Brakel, R.; Burhenn, R.; Dinklage, A.; Ehmler, H.; Endler, M.; Erckmann, V.; Feng, Y.; Geiger, J.; Giannone, L.; Grieger, G.; Grigull, P.; Hartfuß, H.-J.; Hartmann, D.; Jaenicke, R.; König, R.; Laqua, H. P.; Maaßberg, H.; McCormick, K.; Sardei, F.; Speth, E.; Stroth, U.; Wagner, F.; Weller, A.; Werner, A.; Wobig, H.; Zoletnik, S.; W7-AS Team

2008-05-01

Wendelstein 7-AS was the first modular stellarator device to test some basic elements of stellarator optimization: a reduced Shafranov shift and improved stability properties resulted in β-values up to 3.4% (at 0.9 T). This operational limit was determined by power balance and impurity radiation without noticeable degradation of stability or a violent collapse. The partial reduction of neoclassical transport could be verified in agreement with calculations indicating the feasibility of the concept of drift optimization. A full neoclassical optimization, in particular a minimization of the bootstrap current was beyond the scope of this project. A variety of non-ohmic heating and current drive scenarios by ICRH, NBI and in particular, ECRH were tested and compared successfully with their theoretical predictions. Besides, new heating schemes of overdense plasmas were developed such as RF mode conversion heating—Ordinary mode, Extraordinary mode, Bernstein-wave (OXB) heating—or 2nd harmonic O-mode (O2) heating. The energy confinement was about a factor of 2 above ISS95 without degradation near operational boundaries. A number of improved confinement regimes such as core electron-root confinement with central Te <= 7 keV and regimes with strongly sheared radial electric field at the plasma edge resulting in Ti <= 1.7 keV were obtained. As the first non-tokamak device, W7-AS achieved the H-mode and moreover developed a high density H-mode regime (HDH) with strongly reduced impurity confinement that allowed quasi-steady-state operation (τ ≈ 65 · τE) at densities \\bar {n}_{\\rme} \\cong 4 \\times 10^{20}\\,\\mbox{m}^{-3} (at 2.5 T). The first island divertor was tested successfully and operated with stable partial detachment in agreement with numerical simulations. With these results W7-AS laid the physics background for operation of an optimized low-shear steady-state stellarator.

Quantum Kronecker sum-product low-density parity-check codes with finite rate

NASA Astrophysics Data System (ADS)

Kovalev, Alexey A.; Pryadko, Leonid P.

2013-07-01

We introduce an ansatz for quantum codes which gives the hypergraph-product (generalized toric) codes by Tillich and Zémor and generalized bicycle codes by MacKay as limiting cases. The construction allows for both the lower and the upper bounds on the minimum distance; they scale as a square root of the block length. Many thus defined codes have a finite rate and limited-weight stabilizer generators, an analog of classical low-density parity-check (LDPC) codes. Compared to the hypergraph-product codes, hyperbicycle codes generally have a wider range of parameters; in particular, they can have a higher rate while preserving the estimated error threshold.

Transport modeling of L- and H-mode discharges with LHCD on EAST

NASA Astrophysics Data System (ADS)

Li, M. H.; Ding, B. J.; Imbeaux, F.; Decker, J.; Zhang, X. J.; Kong, E. H.; Zhang, L.; Wei, W.; Shan, J. F.; Liu, F. K.; Wang, M.; Xu, H. D.; Yang, Y.; Peysson, Y.; Basiuk, V.; Artaud, J.-F.; Yuynh, P.; Wan, B. N.

2013-04-01

High-confinement (H-mode) discharges with lower hybrid current drive (LHCD) as the only heating source are obtained on EAST. In this paper, an empirical transport model of mixed Bohm/gyro-Bohm for electron and ion heat transport was first calibrated against a database of 3 L-mode shots on EAST. The electron and ion temperature profiles are well reproduced in the predictive modeling with the calibrated model coupled to the suite of codes CRONOS. CRONOS calculations with experimental profiles are also performed for electron power balance analysis. In addition, the time evolutions of LHCD are calculated by the C3PO/LUKE code involving current diffusion, and the results are compared with experimental observations.

A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

NASA Astrophysics Data System (ADS)

Ku, S.; Chang, C. S.; Hager, R.; Churchill, R. M.; Tynan, G. R.; Cziegler, I.; Greenwald, M.; Hughes, J.; Parker, S. E.; Adams, M. F.; D'Azevedo, E.; Worley, P.

2018-05-01

A fast edge turbulence suppression event has been simulated in the electrostatic version of the gyrokinetic particle-in-cell code XGC1 in a realistic diverted tokamak edge geometry under neutral particle recycling. The results show that the sequence of turbulent Reynolds stress followed by neoclassical ion orbit-loss driven together conspire to form the sustaining radial electric field shear and to quench turbulent transport just inside the last closed magnetic flux surface. The main suppression action is located in a thin radial layer around ψN≃0.96 -0.98 , where ψN is the normalized poloidal flux, with the time scale ˜0.1 ms.

Center for Extended Magnetohydrodynamics Modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramos, Jesus

This researcher participated in the DOE-funded Center for Extended Magnetohydrodynamics Modeling (CEMM), a multi-institutional collaboration led by the Princeton Plasma Physics Laboratory with Dr. Stephen Jardin as the overall Principal Investigator. This project developed advanced simulation tools to study the non-linear macroscopic dynamics of magnetically confined plasmas. The collaborative effort focused on the development of two large numerical simulation codes, M3D-C1 and NIMROD, and their application to a wide variety of problems. Dr. Ramos was responsible for theoretical aspects of the project, deriving consistent sets of model equations applicable to weakly collisional plasmas and devising test problems for verification ofmore » the numerical codes. This activity was funded for twelve years.« less

Effect of Isotope Mass in Simulations of JET H-mode Discharges

NASA Astrophysics Data System (ADS)

Snyder, S. E.; Onjun, T.; Kritz, A. H.; Bateman, G.; Parail, V.

2004-11-01

In JET type-I ELMy H-mode discharges, it is found that the height of the pressure pedestal increases and the frequency of the ELMs decreases with increasing isotope mass. These experimentally observed trends are obtained in these simulations only if the pedestal width increases with isotope mass. Simulations are carried out using the JETTO integrated modeling code with a dynamic model for the H-mode pedestal and the ELMs.(T. Onjun et al, Phys. Plasmas 11 (2004) 1469 and 3006.) The HELENA and MISHKA stability codes are applied to calibrate the stability criteria used to trigger ELM crashes in the JETTO code and to explore possible access to second stability in the pedestal. In the simulations, transport in the pedestal is given by the ion thermal neoclassical diffusivity, which increases with isotope mass. Consequently, as the isotope mass is increased, the pressure gradient and the bootstrap current in the pedestal rebuild more slowly after each ELM crash. Several models are explored in which the pedestal width increases with isotope mass.

Study of neoclassical effects on the pedestal structure in ELMy H-mode plasmas

NASA Astrophysics Data System (ADS)

Pankin, A. Y.; Bateman, G.; Kritz, A. H.; Rafiq, T.; Park, G. Y.; Ku, S.; Chang, C. S.; Snyder, P. B.

2009-11-01

The neoclassical effects on the H-mode pedestal structure are investigated in this study. First principles' kinetic simulations of the neoclassical pedestal dynamics are combined with the MHD stability conditions for triggering ELM crashes that limit the pedestal width and height in H-mode plasmas. The neoclassical kinetic XGC0 code [1] is used to produce systematic scans over plasma parameters including plasma current, elongation, and triangularity. As plasma profiles evolve, the MHD stability limits of these profiles are analyzed with the ideal MHD stability ELITE code [2]. The scalings of the pedestal width and height are presented as a function of the scanned plasma parameters. Simulations with the XGC0 code, which include coupled ion-electron dynamics, yield predictions for both ion and electron pedestal profiles. Differences in the electron and ion pedestal scalings are investigated. [1] C.S. Chang et al, Phys. Plasmas 11 (2004) 2649. [2] P.B. Snyder et al, Phys. Plasmas, 9 (2002) 2037.

The long non-coding RNA LSINCT5 promotes malignancy in non-small cell lung cancer by stabilizing HMGA2.

PubMed

Tian, Yuheng; Zhang, Lina; Chen, Shuwen; Ma, Yuan; Liu, Yanyan

2018-06-08

Long non-coding RNAs (lncRNAs) can actively participate in tumorigenesis in various cancers. However, the involvement of lncRNA long stress induced non-coding transcripts 5 (LSINCT5) in non-small cell lung cancer (NSCLC) remains largely unknown. Here we showed a novel lncRNA signature in NSCLC through lncRNA profiling. Increased LSINCT5 expression positively correlates with malignant clinicopathological features and poor survival. LSINCT5 can promote migration and viability of various NSCLC cells in vitro and also enhance lung cancer progression in vivo. RNA immunoprecipitation followed by mass spectrometry has identified that LSINCT5 interacts with HMGA2. This physical interaction can increase the stability of HMGA2 by inhibiting proteasome-mediated degradation. Therefore, LSINCT5 may possibly contribute to NSCLC tumorigenesis by stabilizing the oncogenic factor of HMGA2. This novel LSINCT5/HMGA2 axis can modulate lung cancer progression and might be a promising target for pharmacological intervention.

MMPI--2 Code-Type Congruence of Injured Workers

ERIC Educational Resources Information Center

Livingston, Ronald B.; Jennings, Earl; Colotla, Victor A.; Reynolds, Cecil R.; Shercliffe, Regan J.

2006-01-01

In this study, the authors examined the stability of Minnesota Multiphasic Personality Inventory--2 (J. N. Butcher, W. G. Dahlstrom, J. R. Graham, A. Tellegen, & B. Kaemmer, 1989) code types in a sample of 94 injured workers with a mean test-retest interval of 21.3 months (SD = 14.1). Congruence rates for undefined code types were 34% for…

Are partons confined tachyons?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noyes, H.P.

1996-03-01

The author notes that if hadrons are gravitationally stabilized ``black holes``, as discrete physics suggests, it is possible that partons, and in particular quarks, could be modeled as tachyons, i.e. particles having v{sup 2} > c{sup 2}, without conflict with the observational fact that neither quarks nor tachyons have appeared as ``free particles``. Some consequences of this model are explored.

Plasma confinement theory and transport simulation. Technical progress report, May 1, 1991--April 30, 1992

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ross, D.W.

The objectives are: (1) to advance the transport studies of tokamaks, including development and maintenance of the Magnetic Fusion Energy Database, and (2) to provide theoretical interpretation, modeling and equilibrium and stability studies for TEXT-Upgrade. Recent reports, publications, and conference presentations of the Fusion Research Center are listed.

Laser Blow-Off Impurity Injection Experiments at the HSX Stellarator

NASA Astrophysics Data System (ADS)

Castillo, J. F.; Bader, A.; Likin, K. M.; Anderson, D. T.; Anderson, F. S. B.; Kumar, S. T. A.; Talmadge, J. N.

2017-10-01

Results from the HSX laser blow-off experiment are presented and compared to a synthetic diagnostic implemented in the STRAHL impurity transport modeling code in order to measure the impurity transport diffusivity and convective velocity. A laser blow-off impurity injection system is used to rapidly deposit a small, controlled quantity of aluminum into the confinement volume. Five AXUV photodiode arrays are used to take time-resolved measurements of the impurity radiation. The spatially one-dimensional impurity transport code STRAHL is used to calculate a time-dependent plasma emissivity profile. Modeled intensity signals calculated from a synthetic diagnostic code provide direct comparison between plasma simulation and experimental results. An optimization algorithm with impurity transport coefficients acting as free parameters is used to fit the model to experimental data. This work is supported by US DOE Grant DE-FG02-93ER54222.

Tailoring Magnetic Skyrmions by Geometric Confinement of Magnetic Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Steven S.-L.; Phatak, C.; Petford-Long, A K

Nanoscale magnetic skyrmions have interesting static and transport properties that make them candidates for future spintronic devices. Control and manipulation of the size and behavior of skyrmions is thus of crucial importance. Here, using a Ginzburg-Landau approach, we show theoretically that skyrmions and skyrmion lattices can be stabilized by a spatial modulation of the uniaxial magnetic anisotropy in a thin film of a centro-symmetric ferromagnet. Remarkably, the skyrmion size is determined by the ratio of the exchange length and the period of the spatial modulation of the anisotropy, at variance with conventional skyrmions stabilized by dipolar and Dzyaloshinskii–Moriya interactions.

Oxygen stabilized zirconium-vanadium-iron alloy

DOEpatents

Mendelsohn, Marshall H.; Gruen, Dieter M.

1982-01-01

An oxygen stabilized intermetallic compound having the formula (Zr.sub.1-x Ti.sub.x).sub.2-u (V.sub.1-y Fe.sub.y)O.sub.z where x=0.0 to 0.9, y=0.01 to 0.9, z=0.25 to 0.5 and u=0 to 1. The compound is capable of reversibly sorbing hydrogen at temperatures from -196.degree. C. to 200.degree. C. at pressures down to 10.sup.-6 torr. The compound is suitable for use as a hydrogen getter in low pressure, high temperature applications such as magnetic confinement fusion devices.

Bimeron nanoconfined design

NASA Astrophysics Data System (ADS)

Iakovlev, I. A.; Sotnikov, O. M.; Mazurenko, V. V.

2018-05-01

We report on the stabilization of the topological bimeron structures in confined geometries. The Monte Carlo simulations for a ferromagnet with a strong Dzyaloshinskii-Moriya interaction revealed the formation of a mixed skyrmion-bimeron phase at finite temperatures. The vacancy grid created in the spin lattice drastically changes the picture of the observed spin configurations and allows one to choose between the formation of a pure bimeron and skyrmion lattice. We found that the rhombic plaquette provides a natural environment for stabilization of the bimeron structures. Such a rhombic geometry can protect the topological state even in the absence of the magnetic field.

Tailoring Magnetic Skyrmions by Geometric Confinement of Magnetic Structures

DOE PAGES

Zhang, Steven S.-L.; Phatak, C.; Petford-Long, A K; ...

2017-12-12

Nanoscale magnetic skyrmions have interesting static and transport properties that make them candidates for future spintronic devices. Control and manipulation of the size and behavior of skyrmions is thus of crucial importance. Here, using a Ginzburg-Landau approach, we show theoretically that skyrmions and skyrmion lattices can be stabilized by a spatial modulation of the uniaxial magnetic anisotropy in a thin film of a centro-symmetric ferromagnet. Remarkably, the skyrmion size is determined by the ratio of the exchange length and the period of the spatial modulation of the anisotropy, at variance with conventional skyrmions stabilized by dipolar and Dzyaloshinskii–Moriya interactions.

Oxygen-stabilized zirconium-vanadium-iron alloy

DOEpatents

Mendelsohn, M.H.; Gruen, D.M.

1981-06-16

An oxygen stabilized intermetallic compound is described which has the formula (Zr/sub 1-x/Ti/sub x/)/sub 2-u/(V/sub 1-y/Fe/sub y/)O/sub z/ where x = 0.0 to 0.9, y = 0.01 to 0.9, z = 0.25 to 0.5 and u = 0 to 1. The compound is capable of reversibly sorbing hydrogen at temperatures from -196/sup 0/C to 200/sup 0/C at pressures down to 10/sup -6/ torr. The compound is suitable for use as a hydrogen getter in low pressure, high temperature applications such as magnetic confinement fusion devices.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jong -Kyu

The 20th workshop on magnetohydrodynamic (MHD) stability control took place November 22–24, 2015, in Princeton Plasma Physics Laboratory (PPPL), following the American Physical Society—Division of Plasma Physics annual meeting on November 16–20 in Savannah, GA. The purpose of this workshop is to stimulate in depth discussion and motivate future research in the areas of MHD stability physics and control of magnetically confined plasmas. Furthermore, the workshop was organized jointly by Auburn University, Columbia University, General Atomics, Princeton Plasma Physics Laboratory, University of Wisconsin-Madison, and the Los Alamos National Laboratory, and under the auspices of the US/Japan Collaboration.

Predicting Catastrophic BGP Routing Instabilities

DTIC Science & Technology

2004-03-01

predict a BGP routing instability confine their focus to either macro- or micro -level metrics, but not to both. The inherent limitations of each of...Level and Micro -Level Metrics Correlation; Worm Attack Studies; 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT Unclassified 18. SECURITY... micro -level metrics, but not to both. The inherent limitations of each of these forms of metric gives rise to an excessive rate of spurious alerts

Small-amplitude magnetic Rayleigh-Taylor instability growth in cylindrical liners and Z-pinches imploded in an axial magnetic field

NASA Astrophysics Data System (ADS)

Velikovich, A. L.; Giuliani, J. L.; Clark, R. W.; Mikitchuk, D.; Kroupp, E.; Maron, Y.; Fisher, A.; Schmit, P. F.

2014-10-01

Recent progress in developing the MagLIF approach to pulsed-power driven inertial confinement fusion has stimulated the interest in observation and mitigation of the magnetic Rayleigh-Taylor instability (MRTI) of liners and Z-pinches imploded in an axial magnetic field. Theoretical analysis of these issues is particularly important because direct numerical simulation of the MRTI development is challenging due to intrinsically 3D helical structure of the fastest-growing modes. We review the analytical small-amplitude theory of the MRTI perturbation development and the weakly nonlinear theory of MRTI mode interaction, emphasizing basic physics, opportunity for 3D code verification against exact analytical solutions, and stabilization criteria. The theory is compared to the experimental results obtained at Weizmann Institute with gas-puff Z pinches and on the Z facility at Sandia with solid liners imploded in an axial magnetic field. Work supported by the US DOE/NNSA, and by the US-Israel Binational Science Foundation. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

Simulations of Low-q Disruptions in the Compact Toroidal Hybrid Experiment

NASA Astrophysics Data System (ADS)

Howell, E. C.; Hanson, J. D.; Ennis, D. A.; Hartwell, G. J.; Maurer, D. A.

2017-10-01

Resistive MHD simulations of low-q disruptions in the Compact Toroidal Hybrid Device (CTH) are performed using the NIMROD code. CTH is a current-carrying stellarator used to study the effects of 3D shaping on MHD stability. Experimentally, it is observed that the application of 3D vacuum fields allows CTH to operate with edge safety factor less than 2.0. However, these low-q discharges often disrupt after peak current if the applied 3D fields are too weak. Nonlinear simulations are initialized using model VMEC equilibria representative of low-q discharges with weak vacuum transform. Initially a series of symmetry preserving island chains are excited at the q=6/5, 7/5, 8/5, and 9/5 rational surfaces. These island chains act as transport barriers preventing stochastic magnetic fields in the edge from penetrating into the core. As the simulation progresses, predominately m/n=3/2 and 4/3 instabilities are destabilized. As these instabilities grow to large amplitude they destroy the symmetry preserving islands leading to large regions of stochastic fields. A current spike and loss of core thermal confinement occurs when the innermost island chain (6/5) is destroyed. Work Supported by US-DOE Grant #DE-FG02-03ER54692.

Experiment-theory comparison for low frequency BAE modes in the strongly shaped H-1NF stellarator

DOE PAGES

Haskey, S. R.; Blackwell, B. D.; Nuhrenberg, C.; ...

2015-08-12

Here, recent advances in the modeling, analysis, and measurement of fluctuations have significantly improved the diagnosis and understanding of Alfvén eigenmodes in the strongly shaped H-1NF helical axis stellarator. Experimental measurements, including 3D tomographic inversions of high resolution visible light images, are in close agreement with beta-induced Alfvén eigenmodes (BAEs) calculated using the compressible ideal MHD code, CAS3D. This is despite the low β in H-1NF, providing experimental evidence that these modes can exist due to compression that is induced by the strong shaping in stellarators, in addition to high β, as is the case in tokamaks. This is confirmedmore » using the CONTI and CAS3D codes, which show significant gap structures at lower frequencies which contain BAE and beta-acoustic Alfvén eigenmodes (BAAEs). The BAEs are excited in the absence of a well confined energetic particle source, further confirming previous studies that thermal particles, electrons, or even radiation fluctuations can drive these modes. Datamining of magnetic probe data shows the experimentally measured frequency of these modes has a clear dependence on the rotational transform profile, which is consistent with a frequency dependency due to postulated confinement related temperature variations.« less

Numerical stability of the error diffusion concept

NASA Astrophysics Data System (ADS)

Weissbach, Severin; Wyrowski, Frank

1992-10-01

The error diffusion algorithm is an easy implementable mean to handle nonlinearities in signal processing, e.g. in picture binarization and coding of diffractive elements. The numerical stability of the algorithm depends on the choice of the diffusion weights. A criterion for the stability of the algorithm is presented and evaluated for some examples.

Self-pinched transport for ion-driven inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Welch, D.R.; Olson, C.L.

Efficient transport of intense ion beams is necessary for ion-driven inertial confinement fusion (ICF). The self-pinched transport scheme involves the focusing of an ion beam to a radius of about 1 cm or less. At this radius, using the beam`s self-magnetic field for confinement, the ion beam propagates through the reactor chamber to an ICF target. A promising regime for self-pinched transport involves the injection of a high current beam into an initially neutral gas at about 200 mTorr less. A simple equilibrium theory of a beam with a temporally pinching radial envelope predicts that large confining magnetic fields aremore » possible with net currents of more than 50% of the beam current. The magnitude of these fields is strongly dependent on the rate of ionization of the given ion species. The authors have simulated ion-beam propagation, using the hybrid code IPROP, which self-consistently calculates the gas breakdown and electromagnetic fields. In agreement, with the theory, a propagation window of 20-200 mTorr of argon is calculated for a 50 kA, 5 MeV proton beam similar to the parameters of the SABRE accelerator at Sandia National Laboratories. The authors present simulations of the focusing and propagation of the SABRE beam, with the purpose of designing a self-pinch experiment.« less

Local non-Calderbank-Shor-Steane quantum error-correcting code on a three-dimensional lattice

NASA Astrophysics Data System (ADS)

Kim, Isaac H.

2011-05-01

We present a family of non-Calderbank-Shor-Steane quantum error-correcting code consisting of geometrically local stabilizer generators on a 3D lattice. We study the Hamiltonian constructed from ferromagnetic interaction of overcomplete set of local stabilizer generators. The degenerate ground state of the system is characterized by a quantum error-correcting code whose number of encoded qubits are equal to the second Betti number of the manifold. These models (i) have solely local interactions; (ii) admit a strong-weak duality relation with an Ising model on a dual lattice; (iii) have topological order in the ground state, some of which survive at finite temperature; and (iv) behave as classical memory at finite temperature.

Failure Behavior of Granite Affected by Confinement and Water Pressure and Its Influence on the Seepage Behavior by Laboratory Experiments

PubMed Central

Cheng, Cheng; Li, Xiao; Li, Shouding; Zheng, Bo

2017-01-01

Failure behavior of granite material is paramount for host rock stability of geological repositories for high-level waste (HLW) disposal. Failure behavior also affects the seepage behavior related to transportation of radionuclide. Few of the published studies gave a consistent analysis on how confinement and water pressure affect the failure behavior, which in turn influences the seepage behavior of the rock during the damage process. Based on a series of laboratory experiments on NRG01 granite samples cored from Alxa area, a candidate area for China’s HLW disposal, this paper presents some detailed observations and analyses for a better understanding on the failure mechanism and seepage behavior of the samples under different confinements and water pressure. The main findings of this study are as follows: (1) Strength reduction properties were found for the granite under water pressure. Besides, the complete axial stress–strain curves show more obvious yielding process in the pre-peak region and a more gradual stress drop in the post-peak region; (2) Shear fracturing pattern is more likely to form in the granite samples with the effect of water pressure, even under much lower confinements, than the predictions from the conventional triaxial compressive results; (3) Four stages of inflow rate curves are divided and the seepage behaviors are found to depend on the failure behavior affected by the confinement and water pressure. PMID:28773157

Effect of material flexibility on the thermodynamics and kinetics of hydrophobically induced evaporation of water.

PubMed

Altabet, Y Elia; Haji-Akbari, Amir; Debenedetti, Pablo G

2017-03-28

The evaporation of water induced by confinement between hydrophobic surfaces has received much attention due to its suggested functional role in numerous biophysical phenomena and its importance as a general mechanism of hydrophobic self-assembly. Although much progress has been made in understanding the basic physics of hydrophobically induced evaporation, a comprehensive understanding of the substrate material features (e.g., geometry, chemistry, and mechanical properties) that promote or inhibit such transitions remains lacking. In particular, comparatively little research has explored the relationship between water's phase behavior in hydrophobic confinement and the mechanical properties of the confining material. Here, we report the results of extensive molecular simulations characterizing the rates, free energy barriers, and mechanism of water evaporation when confined between model hydrophobic materials with tunable flexibility. A single-order-of-magnitude reduction in the material's modulus results in up to a nine-orders-of-magnitude increase in the evaporation rate, with the corresponding characteristic time decreasing from tens of seconds to tens of nanoseconds. Such a modulus reduction results in a 24-orders-of-magnitude decrease in the reverse rate of condensation, with time scales increasing from nanoseconds to tens of millions of years. Free energy calculations provide the barriers to evaporation and confirm our previous theoretical predictions that making the material more flexible stabilizes the confined vapor with respect to liquid. The mechanism of evaporation involves surface bubbles growing/coalescing to form a subcritical gap-spanning tube, which then must grow to cross the barrier.

Transition from eruptive to confined flares in the same active region

NASA Astrophysics Data System (ADS)

Zuccarello, F. P.; Chandra, R.; Schmieder, B.; Aulanier, G.; Joshi, R.

2017-05-01

Context. Solar flares are sudden and violent releases of magnetic energy in the solar atmosphere that can be divided into two classes: eruptive flares, where plasma is ejected from the solar atmosphere resulting in a coronal mass ejection (CME), and confined flares, where no CME is associated with the flare. Aims: We present a case study showing the evolution of key topological structures, such as spines and fans, which may determine the eruptive versus non-eruptive behavior of the series of eruptive flares followed by confined flares, which all originate from the same site. Methods: To study the connectivity of the different flux domains and their evolution, we compute a potential magnetic field model of the active region. Quasi-separatrix layers are retrieved from the magnetic field extrapolation. Results: The change in behavior of the flares from one day to the next - from eruptive to confined - can be attributed to the change in orientation of the magnetic field below the fan with respect to the orientation of the overlaying spine rather than an overall change in the stability of the large-scale field. Conclusions: Flares tend to be more confined when the field that supports the filament and the overlying field gradually becomes less anti-parallel as a direct result of changes in the photospheric flux distribution, being themselves driven by continuous shearing motions of the different magnetic flux concentrations. Movies associated to Figs. 2, 3, and 5 are available at http://www.aanda.org

Role of the electron blocking layer in the graded-index separate confinement heterostructure nitride laser diodes

NASA Astrophysics Data System (ADS)

Bojarska, Agata; Goss, Jakub; Stanczyk, Szymon; Makarowa, Irina; Schiavon, Dario; Czernecki, Robert; Suski, Tadeusz; Perlin, Piotr

2018-04-01

In this work, we investigate the role of the electron blocking layer (EBL) in laser diodes based on a graded index separate confinement heterostructure. We compare two sets of devices with very different EBL aluminum composition (3% and 12%) and design (graded and superlattice). The results of electro-optical characterization of these laser diodes reveal surprisingly modest role of electron blocking layer composition in determination of the threshold current and the differential efficiency values. However, EBL structure influences the operating voltage, which is decreased for devices with lower EBL and superlattice EBL. We observe also the differences in the thermal stability of devices - characteristic temperature is lower for lasers with 3% Al in EBL.

Bimetallic NiFe2O4 synthesized via confined carburization in NiFe-MOFs for efficient oxygen evolution reaction

NASA Astrophysics Data System (ADS)

Fang, Zhiqiang; Hao, Zhaomin; Dong, Qingsong; Cui, Yong

2018-04-01

Transition metal oxides that derived from metal-organic framework (MOF) precursor have intensively received attention because of their numerous electrochemical applications. Bimetallic Ni-Fe oxides have been rarely reported on the basis of MOF-related strategy. Herein, a bimetallic NiFe2O4 was successfully synthesized via confined carburization in NiFe-MOF precursors and characterized by XRD, XPS, SEM, and TEM. After conducting an investigation of oxygen evolution reaction (OER), the as-synthesized NiFe2O4 material exhibited good catalytic efficiency and high stability and durability in alkaline media. The as-synthesized NiFe2O4 material would promote the development of MOFs in non-noble-metal OER catalyst.

Dancing droplets: Contact angle, drag, and confinement

NASA Astrophysics Data System (ADS)

Benusiglio, Adrien; Cira, Nate; Prakash, Manu

2015-11-01

When deposited on a clean glass slide, a mixture of water and propylene glycol forms a droplet of given contact angle, when both pure liquids spread. (Cira, Benusiglio, Prakash: Nature, 2015). The droplet is stabilized by a gradient of surface tension due to evaporation that induces a Marangoni flow from the border to the apex of the droplets. The apparent contact angle of the droplets depends on both their composition and the external humidity as captured by simple models. These droplets present remarkable properties such as lack of a large pinning force. We discuss the drag on these droplets as a function of various parameters. We show theoretical and experimental results of how various confinement geometries change the vapor gradient and the dynamics of droplet attraction.

Overview of NSTX Upgrade initial results and modelling highlights

NASA Astrophysics Data System (ADS)

Menard, J. E.; Allain, J. P.; Battaglia, D. J.; Bedoya, F.; Bell, R. E.; Belova, E.; Berkery, J. W.; Boyer, M. D.; Crocker, N.; Diallo, A.; Ebrahimi, F.; Ferraro, N.; Fredrickson, E.; Frerichs, H.; Gerhardt, S.; Gorelenkov, N.; Guttenfelder, W.; Heidbrink, W.; Kaita, R.; Kaye, S. M.; Kriete, D. M.; Kubota, S.; LeBlanc, B. P.; Liu, D.; Lunsford, R.; Mueller, D.; Myers, C. E.; Ono, M.; Park, J.-K.; Podesta, M.; Raman, R.; Reinke, M.; Ren, Y.; Sabbagh, S. A.; Schmitz, O.; Scotti, F.; Sechrest, Y.; Skinner, C. H.; Smith, D. R.; Soukhanovskii, V.; Stoltzfus-Dueck, T.; Yuh, H.; Wang, Z.; Waters, I.; Ahn, J.-W.; Andre, R.; Barchfeld, R.; Beiersdorfer, P.; Bertelli, N.; Bhattacharjee, A.; Brennan, D.; Buttery, R.; Capece, A.; Canal, G.; Canik, J.; Chang, C. S.; Darrow, D.; Delgado-Aparicio, L.; Domier, C.; Ethier, S.; Evans, T.; Ferron, J.; Finkenthal, M.; Fonck, R.; Gan, K.; Gates, D.; Goumiri, I.; Gray, T.; Hosea, J.; Humphreys, D.; Jarboe, T.; Jardin, S.; Jaworski, M. A.; Koel, B.; Kolemen, E.; Ku, S.; La Haye, R. J.; Levinton, F.; Luhmann, N.; Maingi, R.; Maqueda, R.; McKee, G.; Meier, E.; Myra, J.; Perkins, R.; Poli, F.; Rhodes, T.; Riquezes, J.; Rowley, C.; Russell, D.; Schuster, E.; Stratton, B.; Stutman, D.; Taylor, G.; Tritz, K.; Wang, W.; Wirth, B.; Zweben, S. J.

2017-10-01

The National Spherical Torus Experiment (NSTX) has undergone a major upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in the summer of 2015. NSTX-U first plasma was subsequently achieved, diagnostic and control systems have been commissioned, the H-mode accessed, magnetic error fields identified and mitigated, and the first physics research campaign carried out. During ten run weeks of operation, NSTX-U surpassed NSTX record pulse-durations and toroidal fields (TF), and high-performance ~1 MA H-mode plasmas comparable to the best of NSTX have been sustained near and slightly above the n  =  1 no-wall stability limit and with H-mode confinement multiplier H98y,2 above 1. Transport and turbulence studies in L-mode plasmas have identified the coexistence of at least two ion-gyro-scale turbulent micro-instabilities near the same radial location but propagating in opposite (i.e. ion and electron diamagnetic) directions. These modes have the characteristics of ion-temperature gradient and micro-tearing modes, respectively, and the role of these modes in contributing to thermal transport is under active investigation. The new second more tangential neutral beam injection was observed to significantly modify the stability of two types of Alfven eigenmodes. Improvements in offline disruption forecasting were made in the areas of identification of rotating MHD modes and other macroscopic instabilities using the disruption event characterization and forecasting code. Lastly, the materials analysis and particle probe was utilized on NSTX-U for the first time and enabled assessments of the correlation between boronized wall conditions and plasma performance. These and other highlights from the first run campaign of NSTX-U are described.

Overview of NSTX Upgrade Initial Results and Modelling Highlights

DOE Data Explorer

Menard, J.E. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000312923286); Allain, J.P.; Battaglia, D.J. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000188979740); Bedoya, F.; Bell, R.E. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:000000019544498X); Belova, E. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000215251027); Berkery, J.W. [Columbia University, New York, NY, United States of America; Boyer, M.D. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000268459155); Crocker, N.; Diallo, A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:000000020706060X); Ebrahimi, F. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000331095367); Ferraro, N. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000263487827); Fredrickson, E. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Frerichs, H.; Gerhardt, S. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000225462194); Gorelenkov, N. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Guttenfelder, W. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:000000018181058X); Heidbrink, W.; Kaita, R. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000285159824); Kaye, S.M. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Kriete, D.M.; Kubota, S.; LeBlanc, B.P. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000314550129); Liu, D. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000191747078); Lunsford, R. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000335886801); Mueller, D. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000224563356); Myers, C.E.; Ono, M. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Park, J-K. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000324198667); Podesta, M. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000349750585); Raman, R. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000220273271); Reinke, M.; Ren, Y. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000198316035); Sabbagh, S.A.; Schmitz, O.; Scotti, F. [Lawrence Livermore National Laboratory, Livermore, CA, United States of America; Sechrest, Y.; Skinner, C.H. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Smith, D.R. [University of Wisconsin, Madison, WI, United States of America; Soukhanovskii, V.; Stoltzfus-Dueck, T. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000325876298); Yuh, H.; Wang, Z. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Waters, I.; Ahn, J-W.; Andre, R.; Barchfield, R.; Beiersdorfer, P.; Bertelli, N. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000293267585); Bhattacharjee, A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000164110178); Boyle, D. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000180918169); Brennan, D.; Buttery, R.; Capece, A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000341477174); Canal, G.; Canik, J.; Chang, C.S. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000233465731); Darrow, D. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Delgado-Aparicio, L. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000167394380); Domier, C.; Ethier, S. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Evans, T.; Ferron, J.; Finkenthal, M.; Fonck, R.; Gan, K.; Gates, D. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000156793124); Goumiri, I. [University of Wisconsin, Madison, WI, United States of America; Gray, T.; Hosea, J. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Humphreys, D.; Jarboe, T.; Jardin, S. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000163906908); Jaworski, M.A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Koel, B.; Kolemen, E. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000342123247); Ku, S. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000299641208); LaHaye, R.J.; Levinton, F.; Luhmann Jr., N.; Maingi, R. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000312388121); Maqueda, R. [X Science LLC, Plainsboro, NJ, United States of America; McKee, G.; Meier, E.; Myra, J.; Perkins, R. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000272160201); Poli, F. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000339594371); Rhodes, T.; Riquezes, J.; Rowley, C. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000290995739); Russell, D.; Schuster, E.; Stratton, B. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Stutman, D.; Taylor, G. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000258487152); Tritz, K. [Johns Hopkins University, Baltimore, MD, United States of America; Wang, W. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Wirth, B.; Zweben, S.J. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000217380586)

2017-01-01

The National Spherical Torus Experiment (NSTX) has undergone a major upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in the summer of 2015. NSTX-U first plasma was subsequently achieved, diagnostic and control systems have been commissioned, H-Mode accessed, magnetic error fields identified and mitigated, and the first physics research campaign carried out. During 10 run weeks of operation, NSTX-U surpassed NSTX-record pulse-durations and toroidal fields, and high-performance ~1MA H-mode plasmas comparable to the best of NSTX have been sustained near and slightly above the n=1 no-wall stability limit and with H-mode confinement multiplier H98y2 above 1. Transport and turbulence studies in L-mode plasmas have identified the coexistence of at least two ion-gyro-scale turbulent micro-instabilities near the same radial location but propagating in opposite (i.e. ion and electron diamagnetic) directions. These modes have the characteristics of ion-temperature gradient and micro-tearing modes, respectively, and the role of these modes in contributing to thermal transport is under active investigation. The new second more tangential neutral beam injection was observed to significantly modify the stability of two types of Alfven Eigenmodes. Improvements in offline disruption forecasting were made in the areas of identification of rotating MHD modes and other macroscopic instabilities using the Disruption Event Characterization and Forecasting (DECAF) code. Lastly, the Materials Analysis and Particle Probe (MAPP) was utilized on NSTX-U for the first time and enabled assessments of the correlation between boronized wall conditions and plasma performance. These and other highlights from the first run campaign of NSTX-U are described.

Overview of NSTX Upgrade initial results and modelling highlights

DOE PAGES

Menard, J. E.; Allain, J. P.; Battaglia, D. J.; ...

2017-06-20

The National Spherical Torus Experiment (NSTX) has undergone a major upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in the summer of 2015. NSTX-U first plasma was subsequently achieved, diagnostic and control systems have been commissioned, the H-mode accessed, magnetic error fields identified and mitigated, and the first physics research campaign carried out. During ten run weeks of operation, NSTX-U surpassed NSTX record pulse-durations and toroidal fields (TF), and high-performance ~1 MA H-mode plasmas comparable to the best of NSTX have been sustained near and slightly above the n = 1 no-wall stability limit and with H-mode confinement multipliermore » H 98y,2 above 1. Transport and turbulence studies in L-mode plasmas have identified the coexistence of at least two ion-gyro-scale turbulent micro-instabilities near the same radial location but propagating in opposite (i.e. ion and electron diamagnetic) directions. These modes have the characteristics of ion-temperature gradient and micro-tearing modes, respectively, and the role of these modes in contributing to thermal transport is under active investigation. The new second more tangential neutral beam injection was observed to significantly modify the stability of two types of Alfven eigenmodes. Improvements in offline disruption forecasting were made in the areas of identification of rotating MHD modes and other macroscopic instabilities using the disruption event characterization and forecasting code. Finally, the materials analysis and particle probe was utilized on NSTX-U for the first time and enabled assessments of the correlation between boronized wall conditions and plasma performance. These and other highlights from the first run campaign of NSTX-U are described.« less

The quiescent H-mode regime for high performance edge localized mode-stable operation in future burning plasmas [The quiescent H-mode regime for high performance ELM-stable operation in future burning plasmas

DOE PAGES

Garofalo, Andrea M.; Burrell, Keith H.; Eldon, David; ...

2015-05-26

For the first time, DIII-D experiments have achieved stationary quiescent H-mode (QH-mode) operation for many energy confinement times at simultaneous ITER-relevant values of beta, confinement, and safety factor, in an ITER similar shape. QH-mode provides excellent energy confinement, even at very low plasma rotation, while operating without edge localized modes (ELMs) and with strong impurity transport via the benign edge harmonic oscillation (EHO). By tailoring the plasma shape to improve the edge stability, the QH-mode operating space has also been extended to densities exceeding 80% of the Greenwald limit, overcoming the long-standing low-density limit of QH-mode operation. In the theory,more » the density range over which the plasma encounters the kink-peeling boundary widens as the plasma cross-section shaping is increased, thus increasing the QH-mode density threshold. Here, the DIII-D results are in excellent agreement with these predictions, and nonlinear MHD analysis of reconstructed QH-mode equilibria shows unstable low n kink-peeling modes growing to a saturated level, consistent with the theoretical picture of the EHO. Furthermore, high density operation in the QH-mode regime has opened a path to a new, previously predicted region of parameter space, named “Super H-mode” because it is characterized by very high pedestals that can be more than a factor of two above the peeling-ballooning stability limit for similar ELMing H-mode discharges at the same density.« less

Dynamic Confinement of ITER Plasma by O-Mode Driver at Electron Cyclotron Frequency Range

NASA Astrophysics Data System (ADS)

Stefan, V. Alexander

2009-05-01

A low B-field side launched electron cyclotron O-Mode driver leads to the dynamic rf confinement, in addition to rf turbulent heating, of ITER plasma. The scaling law for the local energy confinement time τE is evaluated (τE ˜ 3neTe/2Q, where (3/2) neTe is the local plasma thermal energy density and Q is the local rf turbulent heating rate). The dynamics of unstable dissipative trapped particle modes (DTPM) strongly coupled to Trivelpiece-Gould (T-G) modes is studied for gyrotron frequency 170GHz; power˜24 MW CW; and on-axis B-field ˜ 10T. In the case of dynamic stabilization of DTPM turbulence and for the heavily damped T-G modes, the energy confinement time scales as τE˜(I0)-2, whereby I0(W/m^2) is the O-Mode driver irradiance. R. Prater et. al., Nucl. Fusion 48, No 3 (March 2008). E. P. Velikhov, History of the Russian Tokamak and the Tokamak Thermonuclear Fusion Research Worldwide That Led to ITER (Documentary movie; Stefan Studios Int'l, La Jolla, CA, 2008; E. P. Velikhov, V. Stefan.) M N Rosenbluth, Phys. Scr. T2A 104-109 1982 B. B. Kadomtsev and O. P. Pogutse, Nucl. Fusion 11, 67 (1971).

System and method for embedding emotion in logic systems

NASA Technical Reports Server (NTRS)

Curtis, Steven A. (Inventor)

2012-01-01

A system, method, and computer readable-media for creating a stable synthetic neural system. The method includes training an intellectual choice-driven synthetic neural system (SNS), training an emotional rule-driven SNS by generating emotions from rules, incorporating the rule-driven SNS into the choice-driven SNS through an evolvable interface, and balancing the emotional SNS and the intellectual SNS to achieve stability in a nontrivial autonomous environment with a Stability Algorithm for Neural Entities (SANE). Generating emotions from rules can include coding the rules into the rule-driven SNS in a self-consistent way. Training the emotional rule-driven SNS can occur during a training stage in parallel with training the choice-driven SNS. The training stage can include a self assessment loop which measures performance characteristics of the rule-driven SNS against core genetic code. The method uses a stability threshold to measure stability of the incorporated rule-driven SNS and choice-driven SNS using SANE.

Molecular Dynamics of Hot Dense Plasmas: New Horizons

NASA Astrophysics Data System (ADS)

Graziani, Frank

2011-10-01

We describe the status of a new time-dependent simulation capability for hot dense plasmas. The backbone of this multi-institutional computational and experimental effort--the Cimarron Project--is the massively parallel molecular dynamics (MD) code ``ddcMD''. The project's focus is material conditions such as exist in inertial confinement fusion experiments, and in many stellar interiors: high temperatures, high densities, significant electromagnetic fields, mixtures of high- and low- Zelements, and non-Maxwellian particle distributions. Of particular importance is our ability to incorporate into this classical MD code key atomic, radiative, and nuclear processes, so that their interacting effects under non-ideal plasma conditions can be investigated. This talk summarizes progress in computational methodology, discusses strengths and weaknesses of quantum statistical potentials as effective interactions for MD, explains the model used for quantum events possibly occurring in a collision and highlights some significant results obtained to date. We describe the status of a new time-dependent simulation capability for hot dense plasmas. The backbone of this multi-institutional computational and experimental effort--the Cimarron Project--is the massively parallel molecular dynamics (MD) code ``ddcMD''. The project's focus is material conditions such as exist in inertial confinement fusion experiments, and in many stellar interiors: high temperatures, high densities, significant electromagnetic fields, mixtures of high- and low- Zelements, and non-Maxwellian particle distributions. Of particular importance is our ability to incorporate into this classical MD code key atomic, radiative, and nuclear processes, so that their interacting effects under non-ideal plasma conditions can be investigated. This talk summarizes progress in computational methodology, discusses strengths and weaknesses of quantum statistical potentials as effective interactions for MD, explains the model used for quantum events possibly occurring in a collision and highlights some significant results obtained to date. This work is performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Simulations of Turbulent Momentum and Scalar Transport in Confined Swirling Coaxial Jets

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Liu, Nan-Suey

2014-01-01

This paper presents the numerical simulations of confined three dimensional coaxial water jets. The objectives are to validate the newly proposed nonlinear turbulence models of momentum and scalar transport, and to evaluate the newly introduced scalar APDF and DWFDF equation along with its Eulerian implementation in the National Combustion Code (NCC). Simulations conducted include the steady RANS, the unsteady RANS (URANS), and the time-filtered Navier-Stokes (TFNS) with and without invoking the APDF or DWFDF equation. When the APDF or DWFDF equation is invoked, the simulations are of a hybrid nature, i.e., the transport equations of energy and species are replaced by the APDF or DWFDF equation. Results of simulations are compared with the available experimental data. Some positive impacts of the nonlinear turbulence models and the Eulerian scalar APDF and DWFDF approach are observed.

Two-plasmon decay mitigation in direct-drive inertial-confinement-fusion experiments using multilayer targets

DOE PAGES

Follett, R. K.; Delettrez, J. A.; Edgell, D. H.; ...

2016-04-15

Multilayer direct-drive inertial-confinement-fusion (ICF) targets are shown to significantly reduce two-plasmon-decay (TPD) driven hot-electron production while maintaining high hydrodynamic efficiency. Implosion experiments on the OMEGA Laser used targets with silicon layered between an inner beryllium and outer silicon-doped plastic ablator. A factor of five reduction in hot-electron generation (> 50 keV) was observed in the multilayer targets relative to pure CH targets. Three-dimensional simulations of the TPD driven hot-electron production using a laser-plasma interaction code (LPSE) that includes nonlinear and kinetic effects show excellent agreement with the measurements. As a result, the simulations suggest that the reduction in hot-electron productionmore » observed in the multilayer targets is primarily due to increased electron-ion collisional damping.« less

Computational Methods for Dynamic Stability and Control Derivatives

NASA Technical Reports Server (NTRS)

Green, Lawrence L.; Spence, Angela M.; Murphy, Patrick C.

2003-01-01

Force and moment measurements from an F-16XL during forced pitch oscillation tests result in dynamic stability derivatives, which are measured in combinations. Initial computational simulations of the motions and combined derivatives are attempted via a low-order, time-dependent panel method computational fluid dynamics code. The code dynamics are shown to be highly questionable for this application and the chosen configuration. However, three methods to computationally separate such combined dynamic stability derivatives are proposed. One of the separation techniques is demonstrated on the measured forced pitch oscillation data. Extensions of the separation techniques to yawing and rolling motions are discussed. In addition, the possibility of considering the angles of attack and sideslip state vector elements as distributed quantities, rather than point quantities, is introduced.

Computational Methods for Dynamic Stability and Control Derivatives

NASA Technical Reports Server (NTRS)

Green, Lawrence L.; Spence, Angela M.; Murphy, Patrick C.

2004-01-01

Force and moment measurements from an F-16XL during forced pitch oscillation tests result in dynamic stability derivatives, which are measured in combinations. Initial computational simulations of the motions and combined derivatives are attempted via a low-order, time-dependent panel method computational fluid dynamics code. The code dynamics are shown to be highly questionable for this application and the chosen configuration. However, three methods to computationally separate such combined dynamic stability derivatives are proposed. One of the separation techniques is demonstrated on the measured forced pitch oscillation data. Extensions of the separation techniques to yawing and rolling motions are discussed. In addition, the possibility of considering the angles of attack and sideslip state vector elements as distributed quantities, rather than point quantities, is introduced.

A network of autism linked genes stabilizes two pools of synaptic GABAA receptors

PubMed Central

Tong, Xia-Jing; Hu, Zhitao; Liu, Yu; Anderson, Dorian; Kaplan, Joshua M

2015-01-01

Changing receptor abundance at synapses is an important mechanism for regulating synaptic strength. Synapses contain two pools of receptors, immobilized and diffusing receptors, both of which are confined to post-synaptic elements. Here we show that immobile and diffusing GABAA receptors are stabilized by distinct synaptic scaffolds at C. elegans neuromuscular junctions. Immobilized GABAA receptors are stabilized by binding to FRM-3/EPB4.1 and LIN-2A/CASK. Diffusing GABAA receptors are stabilized by the synaptic adhesion molecules Neurexin and Neuroligin. Inhibitory post-synaptic currents are eliminated in double mutants lacking both scaffolds. Neurexin, Neuroligin, and CASK mutations are all linked to Autism Spectrum Disorders (ASD). Our results suggest that these mutations may directly alter inhibitory transmission, which could contribute to the developmental and cognitive deficits observed in ASD. DOI: http://dx.doi.org/10.7554/eLife.09648.001 PMID:26575289

Feasibility of self-correcting quantum memory and thermal stability of topological order

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshida, Beni, E-mail: rouge@mit.edu

2011-10-15

Recently, it has become apparent that the thermal stability of topologically ordered systems at finite temperature, as discussed in condensed matter physics, can be studied by addressing the feasibility of self-correcting quantum memory, as discussed in quantum information science. Here, with this correspondence in mind, we propose a model of quantum codes that may cover a large class of physically realizable quantum memory. The model is supported by a certain class of gapped spin Hamiltonians, called stabilizer Hamiltonians, with translation symmetries and a small number of ground states that does not grow with the system size. We show that themore » model does not work as self-correcting quantum memory due to a certain topological constraint on geometric shapes of its logical operators. This quantum coding theoretical result implies that systems covered or approximated by the model cannot have thermally stable topological order, meaning that systems cannot be stable against both thermal fluctuations and local perturbations simultaneously in two and three spatial dimensions. - Highlights: > We define a class of physically realizable quantum codes. > We determine their coding and physical properties completely. > We establish the connection between topological order and self-correcting memory. > We find they do not work as self-correcting quantum memory. > We find they do not have thermally stable topological order.« less

46 CFR 160.051-7 - Design and performance of Coastal Service inflatable liferafts.

Code of Federal Regulations, 2012 CFR

2012-10-01

... diameter of the buoyancy chambers is greater than 500 mm (19.5 in). (g) Stability (IMO LSA Code, chapter IV/4.2.5). Each Coastal Service inflatable liferaft must either meet the stability criteria in § 160.151-17(a) or be fitted with water-containing stability pockets meeting the following requirements: (1...

Formation and Stabilization of Vertical Hierarchies among Adolescents: Towards a Quantitative Ethology of Dominance among Humans

ERIC Educational Resources Information Center

Martin, John Levi

2009-01-01

Social psychological investigations of hierarchy formation have been almost entirely confined to the case of task-oriented groups and hence have produced theories that turn on the existence of such a task. But other forms of vertical hierarchy may emerge in non-task groups. One form, orderings of dominance, has been studied among animals using…

Design of polymer conjugated 3-helix micelles as nanocarriers with tunable shapes.

PubMed

Ma, Dan; DeBenedictis, Elizabeth P; Lund, Reidar; Keten, Sinan

2016-11-24

Amphiphilic peptide-polymer conjugates have the ability to form stable nanoscale micelles, which show great promise for drug delivery and other applications. A recent design has utilized the end-conjugation of alkyl chains to 3-helix coiled coils to achieve amphiphilicity, combined with the side-chain conjugation of polyethylene glycol (PEG) to tune micelle size through entropic confinement forces. Here we investigate this phenomenon in depth, using coarse-grained dissipative particle dynamics (DPD) simulations in an explicit solvent and micelle theory. We analyze the conformations of PEG chains conjugated to three different positions on 3-helix bundle peptides to ascertain the degree of confinement upon assembly, as well as the ordering of the subunits making up the micelle. We discover that the micelle size and stability is dictated by a competition between the entropy of PEG chain conformations in the assembled state, as well as intermolecular cross-interactions among PEG chains that promote cohesion between neighboring conjugates. Our analyses build on the role of PEG molecular weight and conjugation site and lead to computational phase diagrams that can be used to design 3-helix micelles. This work opens pathways for the design of multifunctional micelles with tunable size, shape and stability.

Benefits of Moderate-Z Ablators for Direct-Drive Inertial Confinement Fusion

NASA Astrophysics Data System (ADS)

Lafon, M.; Betti, R.; Anderson, K. S.; Collins, T. J. B.; Skupsky, S.; McKenty, P. W.

2014-10-01

Control of hydrodynamic instabilities and DT-fuel preheating by hot electrons produced by laser-plasma interaction is crucial in inertial confinement fusion. Moderate- Z ablators have been shown to reduce the laser imprinting on target and suppress the generation of hot electrons from the two-plasmon-decay instability. These results have motivated the use of ablators of higher- Z than pure plastic in direct-drive-ignition target designs for the National Ignition Facility (NIF). Two-dimensional radiation-hydrodynamic simulations assess the robustness of these ignition designs to laser imprint and capsule nonuniformities. The complex behavior of the hydrodynamic stability of mid- Z ablators is investigated through single and multimode simulations. A polar-drive configuration is developed within the NIF Laser System specifications for each ablator material. The use of multilayer ablators is also investigated to enhance the hydrodynamic stability. Results indicate that ignition target designs using mid- Z ablators exhibit good hydrodynamic properties, leading to high target gain for direct-drive implosions on the NIF. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and the Office of Fusion Energy Sciences Number DE-FG02-04ER54786.

Direct observation of growth and collapse of a Bose-Einstein condensate with attractive interactions

NASA Astrophysics Data System (ADS)

Gerton, Jordan M.; Strekalov, Dmitry; Prodan, Ionut; Hulet, Randall G.

2000-12-01

Quantum theory predicts that Bose-Einstein condensation of a spatially homogeneous gas with attractive interactions is precluded by a conventional phase transition into either a liquid or solid. When confined to a trap, however, such a condensate can form, provided that its occupation number does not exceed a limiting value. The stability limit is determined by a balance between the self-attractive forces and a repulsion that arises from position-momentum uncertainty under conditions of spatial confinement. Near the stability limit, self-attraction can overwhelm the repulsion, causing the condensate to collapse. Growth of the condensate is therefore punctuated by intermittent collapses that are triggered by either macroscopic quantum tunnelling or thermal fluctuation. Previous observations of growth and collapse dynamics have been hampered by the stochastic nature of these mechanisms. Here we report direct observations of the growth and subsequent collapse of a 7Li condensate with attractive interactions, using phase-contrast imaging. The success of the measurement lies in our ability to reduce the stochasticity in the dynamics by controlling the initial number of condensate atoms using a two-photon transition to a diatomic molecular state.

Kinetically Stabilized Axisymmetric Tandem Mirrors: Summary of Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Post, R F

2005-02-08

The path to practical fusion power through plasma confinement in magnetic fields, if it is solely based on the present front-runner, the tokamak, is clearly long, expensive, and arduous. The root causes for this situation lie in the effects of endemic plasma turbulence and in the complexity the tokamak's ''closed'' field geometry. The studies carried out in the investigations described in the attached reports are aimed at finding an approach that does not suffer from these problems. This goal is to be achieved by employing an axisymmetric ''open'' magnetic field geometry, i.e. one generated by a linear array of circularmore » magnet coils, and employing the magnetic mirror effect in accomplishing the plugging of end leakage. More specifically, the studies were aimed at utilizing the tandem-mirror concept in an axisymmetric configuration to achieve performance superior to the tokamak, and in a far simpler system, one for which the cost and development time could be much lower than that for the tokamak, as exemplified by ITER and its follow-ons. An important stimulus for investigating axisymmetric versions of the tandem mirror is the fact that, beginning from early days in fusion research there have been examples of axisymmetric mirror experiments where the plasma exhibited crossfield transport far below the turbulence-enhanced rates characteristic of tokamaks, in specific cases approaching the ''classical'' rate. From the standpoint of theory, axisymmetric mirror-based systems have special characteristics that help explain the low levels of turbulence that have been observed. Among these are the facts that there are no parallel currents in the equilibrium state, and that the drift surfaces of all of the trapped particles are closed surfaces, as shown early on by Teller and Northrop. In addition, in such systems it is possible to arrange that the radial boundary of the confined plasma terminates without contact with the chamber wall. This possibility reduces the probability of so-called ''temperature-gradient'' instabilities, known to be endemic to closed systems. Finally, the open-ended nature of the field readily allows the control of the radial potential distribution, a circumstance that has been shown, for example in the Gamma 10 tandem-mirror experiment at Tsukuba Japan, to suppress drift-type instability modes. Standing against all of these attractive properties of axisymmetric mirror-based systems is the fact, shown early on, that such systems are prone to MHD ''interchange'' instabilities, one in which the plasma column drifts transversely, at a rate far above classical transport. Observed early on, the ''cure'' that was universally adopted, as first demonstrated in the famous ''Ioffe experiment'', was to abandon axisymmetry and employ so-called ''magnetic-well'' fields, ones in which the field increases radially and axially from its interior, strongly suppressing the MHD interchange mode, up to plasma ''beta'' values approaching unity, observed in the 2X2B experiment. When the tandem mirror concept was introduced in 1976 every experiment that was constructed employed various combinations of non-axisymmetric coil configurations (''Baseball,'' and ''Yin-Yang'' coils) to create the magnetic fields. But it came at a heavy price: non-axisymmetric fields gave rise to new non-classical loss channels, and the complexity of the fields introduced difficult engineering problems. It was well recognized at the time that it would be highly advantageous to preserve axisymmetry of the tandem mirror coils, but there was no apparent way to stabilize the ubiquitous MHD interchange mode. A decade later a way to accomplish this end was analyzed theoretically, and, a few years later successfully demonstrated experimentally, in the Gas Dynamic Trap (GDT) experiment at Novosibirsk. The concept: the presence of a sufficient amount of plasma on the expanding field lines outside the end mirrors of a mirror machine can act as an ''anchor,'' MHD stabilizing the interior, confined, plasma. Moreover, Ryutov's theory showed that the pressure of this anchor plasma could be orders of magnitude smaller than that of the confined plasma, and still be able to stabilize it. In the GDT, which operates in a collision-dominated region (as opposed to the near-collisionless mode of a tandem mirror), the effluent plasma, though much lower in density than that of the confined plasma, is sufficient to stabilize the central plasma, up to plasma beta values of 40 percent. Furthermore, once MHD stabilized, the confined plasma in the GDT exhibited no signs of plasma turbulence or enhanced cross-field transport, even in the presence of a substantial population of high energy ions produced by neutral-beam injection.« less

When in London, It's a Burger and Neapolitan Ice Cream for You: Rejoinder to "Identifying Research Topic Development in Business and Management Education Research Using Legitimation Code Theory"

ERIC Educational Resources Information Center

Kenworthy, Amy L.; Hrivnak, George A.

2016-01-01

In this rejoinder, Kenworthy and Hrivnak, recognized as thought leaders in the tertiary education domain, report their greatest concern with Arbaugh et al.'s (2016) work is its inherently narrow and restrictive nature. In their rejoinder they report, first, the search terms use to identify the BME top 100 are confined to business education.…

Estimating DoD Transportation Spending: Analyses of Contract and Payment Transactions

DTIC Science & Technology

2007-01-01

the Defense Logistics Agency (DLA) and of expenditures by shipment material and volume (or cube). The analysis of DLA expenditures appears in Appendix...Defense Logistics Agency (DLA) not completely captured in DD350 data. Limited implementation outside the United States confines inferences that can be...Defense Information Systems Agency DLA Defense Logistics Agency DoD U.S. Department of Defense DoDAAC U.S. Department of Defense Activity Address Code

Electrostatics at the oil–water interface, stability, and order in emulsions and colloids

PubMed Central

Leunissen, Mirjam E.; van Blaaderen, Alfons; Hollingsworth, Andrew D.; Sullivan, Matthew T.; Chaikin, Paul M.

2007-01-01

Oil–water mixtures are ubiquitous in nature and are particularly important in biology and industry. Usually additives are used to prevent the liquid droplets from coalescing. Here, we show that stabilization can also be obtained from electrostatics, because of the well known remarkable properties of water. Preferential ion uptake leads to a tunable droplet charge and surprisingly stable, additive-free, water-in-oil emulsions that can crystallize. For particle-stabilized (“Pickering”) emulsions we find that even extremely hydrophobic, nonwetting particles can be strongly bound to (like-charged) oil–water interfaces because of image charge effects. These basic insights are important for emulsion production, encapsulation, and (self-)assembly, as we demonstrate by fabricating a diversity of structures in bulk, on surfaces, and in confined geometries. PMID:17307876

Cross-verification of the GENE and XGC codes in preparation for their coupling

NASA Astrophysics Data System (ADS)

Jenko, Frank; Merlo, Gabriele; Bhattacharjee, Amitava; Chang, Cs; Dominski, Julien; Ku, Seunghoe; Parker, Scott; Lanti, Emmanuel

2017-10-01

A high-fidelity Whole Device Model (WDM) of a magnetically confined plasma is a crucial tool for planning and optimizing the design of future fusion reactors, including ITER. Aiming at building such a tool, in the framework of the Exascale Computing Project (ECP) the two existing gyrokinetic codes GENE (Eulerian delta-f) and XGC (PIC full-f) will be coupled, thus enabling to carry out first principle kinetic WDM simulations. In preparation for this ultimate goal, a benchmark between the two codes is carried out looking at ITG modes in the adiabatic electron limit. This verification exercise is also joined by the global Lagrangian PIC code ORB5. Linear and nonlinear comparisons have been carried out, neglecting for simplicity collisions and sources. A very good agreement is recovered on frequency, growth rate and mode structure of linear modes. A similarly excellent agreement is also observed comparing the evolution of the heat flux and of the background temperature profile during nonlinear simulations. Work supported by the US DOE under the Exascale Computing Project (17-SC-20-SC).

Stabilization of Tokamak Plasmas by the Addition of Nonaxisymmetric Coils

NASA Astrophysics Data System (ADS)

Reiman, Allan

2008-11-01

It has been recognized since the early days of the fusion program that stellarator coils can be used to stabilize current carrying, toroidal, magnetically confined plasmas.[1] More recently, it has been shown that the vertical mode in a tokamak can be stabilized by a relatively simple set of parallelogram-shaped, localized, nonaxisymmetric coils.[2] We show that by superposing sets of these parallelogram-shaped, nonaxisymmetric coils at different locations, it is possible to reproduce the coil current patterns for conventional stellarator coils as well as those for Furth-Hartman coils[3]. This allows us to gain insight into the physics of stabilization produced by various sets of nonaxisymmetric coils by analysis of the effect on stability of localized coils at differing locations. In particular, the relationship between the stabilization effect and the rotational transform generated by the nonaxisymmetric coils is clarified. [1] J. L. Johnson, C. R. Oberman, R. M. Kulsrud, and E. A. Frieman, Phys. Fluids 1, 281 (1958) [2] A. Reiman, Phys. Rev. Lett. 99, 135007, (2007). [3] H.P. Furth and C.W. Hartman, Phys. Fluids 11, 408 (1968).

A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

DOE PAGES

Ku, S.; Chang, C. S.; Hager, R.; ...

2018-04-18

Here, a fast edge turbulence suppression event has been simulated in the electrostatic version of the gyrokinetic particle-in-cell code XGC1 in a realistic diverted tokamak edge geometry under neutral particle recycling. The results show that the sequence of turbulent Reynolds stress followed by neoclassical ion orbit-loss driven together conspire to form the sustaining radial electric field shear and to quench turbulent transport just inside the last closed magnetic flux surface. As a result, the main suppression action is located in a thin radial layer around ψ N≃0.96–0.98, where ψ N is the normalized poloidal flux, with the time scale ~0.1more » ms.« less

Validation of extended magnetohydrodynamic simulations of the HIT-SI3 experiment using the NIMROD code

NASA Astrophysics Data System (ADS)

Morgan, K. D.; Jarboe, T. R.; Hossack, A. C.; Chandra, R. N.; Everson, C. J.

2017-12-01

The HIT-SI3 experiment uses a set of inductively driven helicity injectors to apply a non-axisymmetric current drive on the edge of the plasma, driving an axisymmetric spheromak equilibrium in a central confinement volume. These helicity injectors drive a non-axisymmetric perturbation that oscillates in time, with relative temporal phasing of the injectors modifying the mode structure of the applied perturbation. A set of three experimental discharges with different perturbation spectra are modelled using the NIMROD extended magnetohydrodynamics code, and comparisons are made to both magnetic and fluid measurements. These models successfully capture the bulk dynamics of both the perturbation and the equilibrium, though disagreements related to the pressure gradients experimentally measured exist.

Theoretical Issues for Plasma Regimes to be Explored by the Ignitor Experiment

NASA Astrophysics Data System (ADS)

Cardinali, A.; Coppi, B.; Sonnino, G.

2014-10-01

At present, the Ignitor experiment is the only one designed and planned to approach and explore ignition regimes under controlled DT burning conditions. The machine parameters have been established on the basis of existing knowledge of the confinement properties of high density plasmas. A variety of improved confinement regimes are expected to be accessible by means of the available ICRH heating power in addition to the prevalent programmable Ohmic heating power and relying on the injection of high velocity pellets for density profile control. The relevance of the various known confinement regimes to the objectives of Ignitor is discussed. Among other theoretical efforts, a non-linear thermal energy balance equation is investigated to study the onset of thermonuclear instability in the plasmas expected to be produced in Ignitor. The equation for the temperature profile in the equilibrium state is solved with the resulting profiles in agreement with those obtained by a full transport code and commonly adopted scalings for them. The evolution of the thermonuclear instability that relies on the solution of the time dependent energy balance equation is obtained. Sponsored in part by the U.S. DOE.

Effects of routine handling and tagging procedures on physiological stress responses in juvenile chinook salmon

USGS Publications Warehouse

Sharpe, C.S.; Thompson, D.A.; Blankenship, H.L.; Schreck, C.B.

1998-01-01

Juvenile chinook salmon Oncorhynchus tshawytscha were subjected to handling and tagging protocols typical of normal hatchery operations and monitored for their physiological response to stress. Treatments included coded-wire-tagging, counting, ventral fin clipping, adipose fin clipping, and a procedure simulating a pond split. Treatment fish were also subjected to a standardized stress challenge (1 h confinement) to evaluate their ability to deal with disturbances subsequent to a handling or tagging procedure. Circulating levels of cortisol and glucose were used as indicators of stress. Each of the treatments elicited very similar responses among treatment groups. Cortisol increased from resting levels of about 20 ng/mL to about 90 ng/mL by 1 h poststress and returned to near resting levels by 8 h poststress. Glucose levels increased from 50 mg/dL to about 80 mg/dL by 1 h poststress and remained elevated for much of the experiment. The cortisol and glucose responses to the confinement stress did not differ over time or among treatments. However, the confinement stress results do suggest a small but significant cumulative response, indicating small residual effects of the original handling protocols. No deaths were noted among treatment groups.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James; Sarff, John; Ding, Weixing; Brower, David; Parke, Eli; Chapman, Brett; Terry, Paul; Pueschel, M. J.; Williams, Zach

2017-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM). Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking, which are suppressed via inductive control for this work. The improved confinement is associated with an increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have f 50 kHz, kϕρs < 0.14 , and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in global tearing mode associated fluctuations, their amplitude increases with local density gradient, and they exhibit a density-gradient threshold at R /Ln 15 . The GENE code, modified for the RFP, predicts the onset of density-gradient-driven TEM for these strong-gradient plasma conditions. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations, comparable to experimental magnetic fluctuations, causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Work supported by US DOE.

Simple agarose micro-confinement array and machine-learning-based classification for analyzing the patterned differentiation of mesenchymal stem cells

PubMed Central

Sato, Asako; Vogel, Viola; Tanaka, Yo

2017-01-01

The geometrical confinement of small cell colonies gives differential cues to cells sitting at the periphery versus the core. To utilize this effect, for example to create spatially graded differentiation patterns of human mesenchymal stem cells (hMSCs) in vitro or to investigate underpinning mechanisms, the confinement needs to be robust for extended time periods. To create highly repeatable micro-fabricated structures for cellular patterning and high-throughput data mining, we employed here a simple casting method to fabricate more than 800 adhesive patches confined by agarose micro-walls. In addition, a machine learning based image processing software was developed (open code) to detect the differentiation patterns of the population of hMSCs automatically. Utilizing the agarose walls, the circular patterns of hMSCs were successfully maintained throughout 15 days of cell culture. After staining lipid droplets and alkaline phosphatase as the markers of adipogenic and osteogenic differentiation, respectively, the mega-pixels of RGB color images of hMSCs were processed by the software on a laptop PC within several minutes. The image analysis successfully showed that hMSCs sitting on the more central versus peripheral sections of the adhesive circles showed adipogenic versus osteogenic differentiation as reported previously, indicating the compatibility of patterned agarose walls to conventional microcontact printing. In addition, we found a considerable fraction of undifferentiated cells which are preferentially located at the peripheral part of the adhesive circles, even in differentiation-inducing culture media. In this study, we thus successfully demonstrated a simple framework for analyzing the patterned differentiation of hMSCs in confined microenvironments, which has a range of applications in biology, including stem cell biology. PMID:28380036

The hybrid reactor project based on the straight field line mirror concept

NASA Astrophysics Data System (ADS)

Ågren, O.; Noack, K.; Moiseenko, V. E.; Hagnestâl, A.; Källne, J.; Anglart, H.

2012-06-01

The straight field line mirror (SFLM) concept is aiming towards a steady-state compact fusion neutron source. Besides the possibility for steady state operation for a year or more, the geometry is chosen to avoid high loads on materials and plasma facing components. A comparatively small fusion hybrid device with "semi-poor" plasma confinement (with a low fusion Q factor) may be developed for industrial transmutation and energy production from spent nuclear fuel. This opportunity arises from a large fission to fusion energy multiplication ratio, Qr = Pfis/Pfus>>1. The upper bound on Qr is primarily determined by geometry and reactor safety. For the SFLM, the upper bound is Qr≈150, corresponding to a neutron multiplicity of keff=0.97. Power production in a mirror hybrid is predicted for a substantially lower electron temperature than the requirement Te≈10 keV for a fusion reactor. Power production in the SFLM seems possible with Q≈0.15, which is 10 times lower than typically anticipated for hybrids (and 100 times smaller than required for a fusion reactor). This relaxes plasma confinement demands, and broadens the range for use of plasmas with supra-thermal ions in hybrid reactors. The SFLM concept is based on a mirror machine stabilized by qudrupolar magnetic fields and large expander tanks beyond the confinement region. The purpose of the expander tanks is to distribute axial plasma loss flow over a sufficiently large area so that the receiving plates can withstand the heat. Plasma stability is not relying on a plasma flow into the expander regions. With a suppressed plasma flow into the expander tanks, a possibility arise for higher electron temperature. A brief presentation will be given on basic theory for the SFLM with plasma stability and electron temperature issues, RF heating computations with sloshing ion formation, neutron transport computations with reactor safety margins and material load estimates, magnetic coil designs as well as a discussion on the implications of the geometry for possible diagnostics. Reactor safety issues are addressed and a vertical orientation of the device could assist passive coolant circulation. Specific attention is put to a device with a 25 m long confinement region and 40 cm plasma radius in the mid-plane. In an optimal case (keff = 0.97) with a fusion power of only 10 MW, such a device may be capable of producing a power of 1.5 GWth.

Towards Realistic Implementations of a Majorana Surface Code.

PubMed

Landau, L A; Plugge, S; Sela, E; Altland, A; Albrecht, S M; Egger, R

2016-02-05

Surface codes have emerged as promising candidates for quantum information processing. Building on the previous idea to realize the physical qubits of such systems in terms of Majorana bound states supported by topological semiconductor nanowires, we show that the basic code operations, namely projective stabilizer measurements and qubit manipulations, can be implemented by conventional tunnel conductance probes and charge pumping via single-electron transistors, respectively. The simplicity of the access scheme suggests that a functional code might be in close experimental reach.

Neural Decoder for Topological Codes

NASA Astrophysics Data System (ADS)

Torlai, Giacomo; Melko, Roger G.

2017-07-01

We present an algorithm for error correction in topological codes that exploits modern machine learning techniques. Our decoder is constructed from a stochastic neural network called a Boltzmann machine, of the type extensively used in deep learning. We provide a general prescription for the training of the network and a decoding strategy that is applicable to a wide variety of stabilizer codes with very little specialization. We demonstrate the neural decoder numerically on the well-known two-dimensional toric code with phase-flip errors.

Entangled cloning of stabilizer codes and free fermions

NASA Astrophysics Data System (ADS)

Hsieh, Timothy H.

2016-10-01

Though the no-cloning theorem [Wooters and Zurek, Nature (London) 299, 802 (1982), 10.1038/299802a0] prohibits exact replication of arbitrary quantum states, there are many instances in quantum information processing and entanglement measurement in which a weaker form of cloning may be useful. Here, I provide a construction for generating an "entangled clone" for a particular but rather expansive and rich class of states. Given a stabilizer code or free fermion Hamiltonian, this construction generates an exact entangled clone of the original ground state, in the sense that the entanglement between the original and the exact copy can be tuned to be arbitrarily small but finite, or large, and the relation between the original and the copy can also be modified to some extent. For example, this Rapid Communication focuses on generating time-reversed copies of stabilizer codes and particle-hole transformed ground states of free fermion systems, although untransformed clones can also be generated. The protocol leverages entanglement to simulate a transformed copy of the Hamiltonian without having to physically implement it and can potentially be realized in superconducting qubits or ultracold atomic systems.

M3D-K Simulations of Beam-Driven Alfven Eigenmodes in ASDEX-U

NASA Astrophysics Data System (ADS)

Wang, Ge; Fu, Guoyong; Lauber, Philipp; Schneller, Mirjam

2013-10-01

Core-localized Alfven eigenmodes are often observed in neutral beam-heated plasma in ASDEX-U tokamak. In this work, hybrid simulations with the global kinetic/MHD hybrid code M3D-K have been carried out to investigate the linear stability and nonlinear dynamics of beam-driven Alfven eigenmodes using experimental parameters and profiles of an ASDEX-U discharge. The safety factor q profile is weakly reversed with minimum q value about qmin = 3.0. The simulation results show that the n = 3 mode transits from a reversed shear Alfven eigenmode (RSAE) to a core-localized toroidal Alfven eigenmode (TAE) as qmin drops from 3.0 to 2.79, consistent with results from the stability code NOVA as well as the experimental measurement. The M3D-K results are being compared with those of the linear gyrokinetic stability code LIGKA for benchmark. The simulation results will also be compared with the measured mode frequency and mode structure. This work was funded by the Max-Planck/Princeton Center for Plasma Physics.

Tapping-mode AFM study of tip-induced polymer deformation under geometrical confinement.

PubMed

Zhang, Hong; Honda, Yukio; Takeoka, Shinji

2013-02-05

The morphological stability of polymer films is critically important to their application as functional materials. The deformation of polymer surfaces on the nanoscale may be significantly influenced by geometrical confinement. Herein, we constructed a mechanically heterogeneous polymer surface by phase separation in a thin polymer film and investigated the deformation behavior of its nanostructure (∼30 nm thickness and ∼100 nm average diameter) with tapping-mode atomic force microscopy. By changing different scan parameters, we could induce deformation localized to the nanostructure in a controllable manner. A quantity called the deformation index is defined and shown to be correlated to energy dissipation by tip-sample interaction. We clarified that the plastic deformation of a polymer on the nanoscale is energy-dependent and is related to the glass-to-rubber transition. The mobility of polymer chains beneath the tapping tip is enhanced, and in the corresponding region a rubberlike deformation with the lateral motion of the tip is performed. The method we developed can provide insight into the geometrical confinement effects on polymer behavior.

Electrohydrodynamic controlled assembly and fracturing of thin colloidal particle films confined at drop interfaces

NASA Astrophysics Data System (ADS)

Rozynek, Z.; Dommersnes, P.; Mikkelsen, A.; Michels, L.; Fossum, J. O.

2014-09-01

Particles can adsorb strongly at liquid interfaces due to capillary forces, which in practice can confine the particles to the interface. Here we investigate the electrohydrodynamic flow driven packing and deformation of colloidal particle layers confined at the surface of liquid drops. The electrohydrodynamic flow has a stagnation point at the drop equator, leading to assembly of particles in a ribbon shaped film. The flow is entirely controlled by the electric field, and we demonstrate that AC fields can be used to induce hydrodynamic "shaking" of the colloidal particle film. We find that the mechanical properties of the film is highly dependent on the particles: monodisperse polystyrene beads form packed granular monolayers which "liquefies" upon shaking, whereas clay mineral particles form cohesive films that fracture upon shaking. The results are expected to be relevant for understanding the mechanics and rheology of particle stabilized emulsions. Supplementary material in the form of a pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjst/e2014-02231-x

Modelling of Field-Reversed Configuration Experiment with Large Safety Factor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinhauer, L; Guo, H; Hoffman, A

2005-11-28

The Translation-Confinement-Sustainment facility has been operated in the 'translation-formation' mode in which a plasma is ejected at high-speed from a {theta}-pinch-like source into a confinement chamber where it settles into a field-reversed-configuration state. Measurements of the poloidal and toroidal field have been the basis of modeling to infer the safety factor. It is found that the edge safety factor exceeds two, and that there is strong forward magnetic shear. The high-q arises because the large elongation compensates for the modest ratio of toroidal-to-poloidal field in the plasma. This is the first known instance of a very high-{beta} plasma with amore » safety factor greater than unity. Two-fluid modeling of the measurements also indicate several other significant features: a broad 'transition layer' at the plasma boundary with probable line-tying effects, complex high-speed flows, and the appearance of a two-fluid minimum-energy state in the plasma core. All these features may contribute to both the stability and good confinement of the plasma.« less

Euler Technology Assessment - SPLITFLOW Code Applications for Stability and Control Analysis on an Advanced Fighter Model Employing Innovative Control Concepts

NASA Technical Reports Server (NTRS)

Jordan, Keith J.

1998-01-01

This report documents results from the NASA-Langley sponsored Euler Technology Assessment Study conducted by Lockheed-Martin Tactical Aircraft Systems (LMTAS). The purpose of the study was to evaluate the ability of the SPLITFLOW code using viscous and inviscid flow models to predict aerodynamic stability and control of an advanced fighter model. The inviscid flow model was found to perform well at incidence angles below approximately 15 deg, but not as well at higher angles of attack. The results using a turbulent, viscous flow model matched the trends of the wind tunnel data, but did not show significant improvement over the Euler solutions. Overall, the predictions were found to be useful for stability and control design purposes.

Control of plasma profiles and stability through localised Electron Cyclotron Current Drive

NASA Astrophysics Data System (ADS)

Merkulov, Oleksiy

2006-06-01

The work presented in this thesis addresses several topics from the physics of the magnetically confined plasma inside a tokamak. At the moment, the tokamak is the most successful concept for becoming a future thermonuclear reactor. However, there are plenty of physics and engineering problems to surpass before the prototype can become an economically and environmentally feasible device. The plasma in the tokamak experiences periodic oscillations of the central temperature and density when the safety factor, q, drops below unity on-axis. These oscillations are called the sawtooth instability and are the subject of the first part of this thesis. The sawtooth oscillations are characterised by the relatively slow rise phase, when the central temperature increases, and a following crash phase, when the central temperature drops. The energy, particles and plasma current are redistributed during the sawtooth crash. Obviously, this leads to a confinement degradation and moreover, the sawtooth instability can trigger potentially other more dangerous instabilities, such as a neoclassical tearing mode. The sawtooth period control is realised on the basis of the sawtooth trigger model, derived by Porcelli. The main idea of this model is that the sawtooth crash is triggered when the magnetic shear at the q=1 surface, s1, reaches a critical value which depends on the local plasma parameters. The magnetic shear, s, is a measure for the rate of change in the direction of the field line as a function of the position in the plasma. The sawtooth period can be changed by affecting the evolution of s1. The effects of the electron cyclotron current drive (ECCD) on the shear evolution are studied with a simple model for the poloidal field evolution. The results of the model are summarised in a form of a criterion for the amount of the non-inductive current drive required for sawtooth period control. The effects of the ECCD have been studied in the TEXTOR tokamak in order to confirm the outcome of the model. The observations are complicated by the unavoidable presence of concurrent heating, which also affects the sawtooth period. The effects of additional heating have been separated from the effects of current drive by normalising the sawtooth period, as a function of the power deposition radius, to a case with heating only. The results are in qualitative agreement with the predictions of the theory and confirm that the shear around the q=1 surface determines the moment of the sawtooth crash. The next topic addresses the current diffusion in the presence of the ECCD. It is known that the synergy between non-inductively driven current and the ohmic current can affect the current penetration. However, the standard method of calculations, which assumes neoclassical plasma resistivity, cannot describe the synergistic effects. We propose a model which combines a Fokker-Planck code and magnetic diffusion calculation in a self-consistent manner; where the plasma resistivity is approximated from the Fokker-Planck code at every time step. In this way the parallel electric field is no longer a constant input profile for the Fokker-Planck code, but is a result of calculations of the magnetic diffusion. This model allowed us to identify situations where the synergy between the driven and the ohmic currents becomes significant and affects the current penetration. Both the ECCD power and the electron density have been varied over a wide range of parameters, thus changing the well known non-linearity criterion for ECCD after Harvey. This criterion indicates the non-linear behaviour of the current drive efficiency and also appears to be a good predictor for the synergistic effects. The results are compared with the standard method of calculations which were supplied by the ASTRA transport code. The standard method and the Fokker-Planck code with the self-consistent electric field show similar results in the absence of the synergy and therefore for low values of the Harvey parameter. For co-ECCD and high values of the Harvey parameter substantial synergy between ECCD and the ohmic current is observed and leads to the generation of a large population of suprathermal electrons and slows down the current penetration. The synergy between counter-ECCD and the inductive current results in a decrease of the total driven current and a much smaller population of suprathermal electrons. Another plasma stability problem has been studied during the current ramp-up phase. Quiet and MHD free current ramp-up is a necessary requirement for a long and efficient flat-top phase. The current penetration in the plasma scenarios with various plasma ramp-up rates has been modelled with the ASTRA transport code. It is shown that in the absence of MHD activity the predictions of the ASTRA code are in a agreement with the experimental results.

BLSTA: A boundary layer code for stability analysis

NASA Technical Reports Server (NTRS)

Wie, Yong-Sun

1992-01-01

A computer program is developed to solve the compressible, laminar boundary-layer equations for two-dimensional flow, axisymmetric flow, and quasi-three-dimensional flows including the flow along the plane of symmetry, flow along the leading-edge attachment line, and swept-wing flows with a conical flow approximation. The finite-difference numerical procedure used to solve the governing equations is second-order accurate. The flow over a wide range of speed, from subsonic to hypersonic speed with perfect gas assumption, can be calculated. Various wall boundary conditions, such as wall suction or blowing and hot or cold walls, can be applied. The results indicate that this boundary-layer code gives velocity and temperature profiles which are accurate, smooth, and continuous through the first and second normal derivatives. The code presented herein can be coupled with a stability analysis code and used to predict the onset of the boundary-layer transition which enables the assessment of the laminar flow control techniques. A user's manual is also included.

Physics Based Model for Cryogenic Chilldown and Loading. Part IV: Code Structure

NASA Technical Reports Server (NTRS)

Luchinsky, D. G.; Smelyanskiy, V. N.; Brown, B.

2014-01-01

This is the fourth report in a series of technical reports that describe separated two-phase flow model application to the cryogenic loading operation. In this report we present the structure of the code. The code consists of five major modules: (1) geometry module; (2) solver; (3) material properties; (4) correlations; and finally (5) stability control module. The two key modules - solver and correlations - are further divided into a number of submodules. Most of the physics and knowledge databases related to the properties of cryogenic two-phase flow are included into the cryogenic correlations module. The functional form of those correlations is not well established and is a subject of extensive research. Multiple parametric forms for various correlations are currently available. Some of them are included into correlations module as will be described in details in a separate technical report. Here we describe the overall structure of the code and focus on the details of the solver and stability control modules.

Dynamic Stability Experiment of Maglev Systems,

DTIC Science & Technology

1995-04-01

This report summarizes the research performed on maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also... maglev system, it is important to consider this phenomenon in the development of all maglev systems. This report presents dynamic stability experiments...on maglev systems and compares their numerical simulation with predictions calculated by a nonlinear dynamic computer code. Instabilities of an

Observation of magnetic fluctuations and rapid density decay of magnetospheric plasma in Ring Trap 1

NASA Astrophysics Data System (ADS)

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Mikami, H.; Kasaoka, N.; Sakamoto, W.

2012-06-01

The Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet, has created high-β (local β ˜ 70%) plasma by using electron cyclotron resonance heating (ECH). When a large population of energetic electrons is generated at low neutral gas pressure operation, high frequency magnetic fluctuations are observed. When the fluctuations are strongly excited, rapid loss of plasma was simultaneously observed especially in a quiet decay phase after the ECH microwave power is turned off. Although the plasma is confined in a strongly inhomogeneous dipole field configuration, the frequency spectra of the fluctuations have sharp frequency peaks, implying spatially localized sources of the fluctuations. The fluctuations are stabilized by decreasing the hot electron component below approximately 40%, realizing stable high-β confinement.

Initial experimental test of a helicon plasma based mass filter

NASA Astrophysics Data System (ADS)

Gueroult, R.; Evans, E. S.; Zweben, S. J.; Fisch, N. J.; Levinton, F.

2016-06-01

High throughput plasma mass separation requires rotation control in a high density multi-species plasmas. A preliminary mass separation device based on a helicon plasma operating in gas mixtures and featuring concentric biasable ring electrodes is introduced. Plasma profile shows strong response to electrode biasing. In light of floating potential measurements, the density response is interpreted as the consequence of a reshaping of the radial electric field in the plasma. This field can be made confining or de-confining depending on the imposed potential at the electrodes, in a way which is consistent with single particle orbit radial stability. Concurrent spatially resolved spectroscopic measurements suggest ion separation, with heavy to light ion emission line ratio increasing with radius when a specific potential gradient is applied to the electrodes.

Biomimetic enzyme nanocomplexes and their use as antidotes and preventive measures for alcohol intoxication

NASA Astrophysics Data System (ADS)

Liu, Yang; Du, Juanjuan; Yan, Ming; Lau, Mo Yin; Hu, Jay; Han, Hui; Yang, Otto O.; Liang, Sheng; Wei, Wei; Wang, Hui; Li, Jianmin; Zhu, Xinyuan; Shi, Linqi; Chen, Wei; Ji, Cheng; Lu, Yunfeng

2013-03-01

Organisms have sophisticated subcellular compartments containing enzymes that function in tandem. These confined compartments ensure effective chemical transformation and transport of molecules, and the elimination of toxic metabolic wastes. Creating functional enzyme complexes that are confined in a similar way remains challenging. Here we show that two or more enzymes with complementary functions can be assembled and encapsulated within a thin polymer shell to form enzyme nanocomplexes. These nanocomplexes exhibit improved catalytic efficiency and enhanced stability when compared with free enzymes. Furthermore, the co-localized enzymes display complementary functions, whereby toxic intermediates generated by one enzyme can be promptly eliminated by another enzyme. We show that nanocomplexes containing alcohol oxidase and catalase could reduce blood alcohol levels in intoxicated mice, offering an alternative antidote and prophylactic for alcohol intoxication.

Effects of wall suction/blowing on two-dimensional flow past a confined square cylinder.

PubMed

Zhang, Wei; Jiang, Yanqun; Li, Lang; Chen, Guoping

2016-01-01

A numerical simulation is conducted to study the laminar flow past a square cylinder confined in a channel (the ratio of side length of the square to channel width is fixed at 1/4) subjected to a locally uniform blowing/suction speed placed at the top and bottom channel walls. Governing equations with boundary conditions are resolved using a finite volume method in pressure-velocity formulation. The flow patterns relevant to the critical spacing values are investigated. Numerical results show that wall blowing has a stabilizing effect on the flow, and the corresponding critical Reynolds number increases monotonically with increasing blowing velocity. Remarkably, steady asymmetric solutions and hysteretic mode transitions exist in a certain range of parameters (Reynolds number and suction speed) in the case of suction.

Effect of material flexibility on the thermodynamics and kinetics of hydrophobically induced evaporation of water

PubMed Central

Altabet, Y. Elia; Haji-Akbari, Amir; Debenedetti, Pablo G.

2017-01-01

The evaporation of water induced by confinement between hydrophobic surfaces has received much attention due to its suggested functional role in numerous biophysical phenomena and its importance as a general mechanism of hydrophobic self-assembly. Although much progress has been made in understanding the basic physics of hydrophobically induced evaporation, a comprehensive understanding of the substrate material features (e.g., geometry, chemistry, and mechanical properties) that promote or inhibit such transitions remains lacking. In particular, comparatively little research has explored the relationship between water’s phase behavior in hydrophobic confinement and the mechanical properties of the confining material. Here, we report the results of extensive molecular simulations characterizing the rates, free energy barriers, and mechanism of water evaporation when confined between model hydrophobic materials with tunable flexibility. A single-order-of-magnitude reduction in the material’s modulus results in up to a nine-orders-of-magnitude increase in the evaporation rate, with the corresponding characteristic time decreasing from tens of seconds to tens of nanoseconds. Such a modulus reduction results in a 24-orders-of-magnitude decrease in the reverse rate of condensation, with time scales increasing from nanoseconds to tens of millions of years. Free energy calculations provide the barriers to evaporation and confirm our previous theoretical predictions that making the material more flexible stabilizes the confined vapor with respect to liquid. The mechanism of evaporation involves surface bubbles growing/coalescing to form a subcritical gap-spanning tube, which then must grow to cross the barrier. PMID:28289194

Confinement and Structural Changes in Vertically Aligned Dust Structures

NASA Astrophysics Data System (ADS)

Hyde, Truell

2013-10-01

In physics, confinement is known to influence collective system behavior. Examples include coulomb crystal variants such as those formed from ions or dust particles (classical), electrons in quantum dots (quantum) and the structural changes observed in vertically aligned dust particle systems formed within a glass box placed on the lower electrode of a Gaseous Electronics Conference (GEC) rf reference cell. Recent experimental studies have expanded the above to include the biological domain by showing that the stability and dynamics of proteins confined through encapsulation and enzyme molecules placed in inorganic cavities such as those found in biosensors are also directly influenced by their confinement. In this paper, the self-assembly and subsequent collective behavior of structures formed from n, charged dust particles interacting with one another and located within a glass box placed on the lower, powered electrode of a GEC rf reference cell is discussed. Self-organized formation of vertically aligned one-dimensional chains, two-dimensional zigzag structures, and three-dimensional helical structures of triangular, quadrangular, pentagonal, hexagonal, and heptagonal symmetries are shown to occur. System evolution is shown to progress from one-dimensional chain structures, through a zigzag transition to a two-dimensional, spindle like structures, and then to various three-dimensional, helical structures exhibiting various symmetries. Stable configurations are shown to be strongly dependent upon system confinement. The critical conditions for structural transitions as well as the basic symmetry exhibited by the one-, two-, and three-dimensional structures that subsequently develop will be shown to be in good agreement with molecular dynamics simulations.

Convergence acceleration of the Proteus computer code with multigrid methods

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Ibraheem, S. O.

1992-01-01

Presented here is the first part of a study to implement convergence acceleration techniques based on the multigrid concept in the Proteus computer code. A review is given of previous studies on the implementation of multigrid methods in computer codes for compressible flow analysis. Also presented is a detailed stability analysis of upwind and central-difference based numerical schemes for solving the Euler and Navier-Stokes equations. Results are given of a convergence study of the Proteus code on computational grids of different sizes. The results presented here form the foundation for the implementation of multigrid methods in the Proteus code.

VERTPAK1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golis, M.J.

1983-04-01

VERTPAK1 is a package of analytical solutions used in verification of numerical codes that simulate fluid flow, rock deformation, and solute transport in fractured and unfractured porous media. VERTPAK1 contains the following: BAREN, an analytical solution developed by Barenblatt, Zhelton and Kochina (1960) for describing transient flow to a well penetrating a (double porosity) confined aquifer; GIBMAC, an analytical solution developed by McNamee and Gibson (1960) for describing consolidation of a semi-infinite soil medium subject to a strip (plane strain) or cylindrical (axisymmetric) loading; GRINRH, an analytical solution developed by Gringarten (1971) for describing transient flow to a partially penetratingmore » well in a confined aquifer containing a single horizontal fracture; GRINRV, an analytical solution developed by Gringarten, Ramey, and Raghavan (1974) for describing transient flow to a fully penetrating well in a confined aquifer containing a single vertical fracture; HART, an analytical solution given by Nowacki (1962) and implemented by HART (1981) for describing the elastic behavior of an infinite solid subject to a line heat source; LESTER, an analytical solution presented by Lester, Jansen, and Burkholder (1975) for describing one-dimensional transport of radionuclide chains through an adsorbing medium; STRELT, an analytical solution presented by Streltsova-Adams (1978) for describing transient flow to a fully penetrating well in a (double porosity) confined aquifer; and TANG, an analytical solution developed by Tang, Frind, and Sudicky (1981) for describing solute transport in a porous medium containing a single fracture.« less

Observation of Trapped-Electron Mode Microturbulence in Improved Confinement Reversed-Field Pinch Plasmas

NASA Astrophysics Data System (ADS)

Duff, James R.

This is a dissertation for the completion of a Doctorate of Philosophy in Physics degree granted at the University of Wisconsin-Madison. Density fluctuations in the large-density-gradient region of improved confinement Madison Sym- metric Torus (MST) RFP plasmas exhibit multiple features that are characteristic of the trapped- electron mode (TEM). In fusion relevant plasmas, thermal transport is a key avenue of research in order to achieve a burning plasma. In the reversed field pinch (RFP) magnetic geometry, the dy- namics of conventional plasma discharges are primarily governed by magnetic stochasticity stem- ming from multiple long-wavelength tearing modes, that sustain the RFP discharge but have an adverse effect on the plasma confinement. Using inductive current profile control, these tearing modes are reduced, and global confinement is increased to that expected for comparable tokamak plasma. Under these conditions with certain plasma equilibria, new short-wavelength fluctuations distinct from global tearing modes appear in the spectrum at frequencies f 50 kHz that have normalized perpendicular wavenumbers k⊥rhos ≤ 0.2, and propagate in the electron diamagnetic drift direction. By adjusting the plasma current or the inductive suppression, there are observable variations in the spectral features. They exhibit a critical-gradient threshold, and the fluctuation amplitude increases with a local density gradient dependent parameter. These characteristics are consistent with the predictions of unstable TEMs based on gyrokinetic analysis using the GENE code. This thesis represents the first observation and description of TEM-like instabilities in the RFP geometry.

Fast Ion Effects During Test Blanket Module Simulation Experiments in DIII-D

NASA Astrophysics Data System (ADS)

Kramer, G. J.; Budny, R.; Nazikian, R.; Heidbrink, W. W.; Kurki-Suonio, T.; Salmi, A.; Schaffer, M. J.; van Zeeland, M. A.; Shinohara, K.; Snipes, J. A.; Spong, D.

2010-11-01

The fast beam-ion confinement in the presence of a scaled mock-up of two Test Blanket Modules (TBM) for ITER was studied in DIII-D. The TBM on DIII-D has four vertically arranged protective carbon tiles with thermocouples placed at the back of each tile. Temperature increases of up to 200^oC were measured for the two tiles closest to the midplane when the TBM fields were present. These measurements agree qualitatively with results from the full orbit-following beam-ion code, SPIRAL, that predict beam-ion losses to be localized on the central two carbon tiles when the TBM fields present. Within the experimental uncertainties no significant change in the fast-ion population was found in the core of these plasmas which is consistent with SPIRAL analysis. These experiments indicate that the TBM fields do not affect the fast-ion confinement in a harmful way which is good news for ITER.

Molecular dynamics and Monte Carlo simulations resolve apparent diffusion rate differences for proteins confined in nanochannels

DOE PAGES

Tringe, J. W.; Ileri, N.; Levie, H. W.; ...

2015-08-01

We use Molecular Dynamics and Monte Carlo simulations to examine molecular transport phenomena in nanochannels, explaining four orders of magnitude difference in wheat germ agglutinin (WGA) protein diffusion rates observed by fluorescence correlation spectroscopy (FCS) and by direct imaging of fluorescently-labeled proteins. We first use the ESPResSo Molecular Dynamics code to estimate the surface transport distance for neutral and charged proteins. We then employ a Monte Carlo model to calculate the paths of protein molecules on surfaces and in the bulk liquid transport medium. Our results show that the transport characteristics depend strongly on the degree of molecular surface coverage.more » Atomic force microscope characterization of surfaces exposed to WGA proteins for 1000 s show large protein aggregates consistent with the predicted coverage. These calculations and experiments provide useful insight into the details of molecular motion in confined geometries.« less