Science.gov

Sample records for achieve current densities

  1. Electrodialysis simulation to achieve optimum current density

    NASA Technical Reports Server (NTRS)

    Herrmann, Cal C.

    1993-01-01

    Electrodialysis is used to remove salts from waste or other water streams, to yield a concentrated brine and a substatially deionized product water. During the electrodialysis process, the boundary layer adjacent to the ion selective membrane can become depleted of ions, resulting in severe pH changes sometimes accompanied by precipitation, and power losses, by a process known as water splitting. In order to optimize the applied electric current density, to achieve maximum deionization without exceeding the limiting current at any point along the path, a simulation program has been created to plot ion concentrations and fluxes, and cell current densities and voltages along the electrodialysis path. A means for tapering the current density along the path is recommended.

  2. Achieving High Current Density of Perovskite Solar Cells by Modulating the Dominated Facets of Room-Temperature DC Magnetron Sputtered TiO2 Electron Extraction Layer.

    PubMed

    Huang, Aibin; Lei, Lei; Zhu, Jingting; Yu, Yu; Liu, Yan; Yang, Songwang; Bao, Shanhu; Cao, Xun; Jin, Ping

    2017-01-25

    The short circuit current density of perovskite solar cell (PSC) was boosted by modulating the dominated plane facets of TiO2 electron transport layer (ETL). Under optimized condition, TiO2 with dominant {001} facets showed (i) low incident light loss, (ii) highly smooth surface and excellent wettability for precursor solution, (iii) efficient electron extraction, and (iv) high conductivity in perovskite photovoltaic application. A current density of 24.19 mA cm(-2) was achieved as a value near the maximum limit. The power conversion efficiency was improved to 17.25%, which was the record value of PSCs with DC magnetron sputtered carrier transport layer. What is more, the room-temperature process had a great significance for the cost reduction and flexible application of PSCs.

  3. Low-temperature synthesis to achieve high critical current density and avoid a reaction layer in SmFeAsO1-x F x superconducting tapes

    NASA Astrophysics Data System (ADS)

    Zhang, Qianjun; Lin, He; Yuan, Pusheng; Zhang, Xianping; Yao, Chao; Wang, Dongliang; Dong, Chiheng; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo

    2015-10-01

    A low-temperature (300-500 °C) heat treatment process under ambient pressure or uniaxial pressure was performed on Sn-added SmFeAsO1-x F x superconducting tapes fabricated by the ex situ powder-in-tube method. A highest transport critical current density (J c) of 3.95 × 104 A cm-2 (at 4.2 K and self-field) was achieved by this process. The low-temperature process allows tapes to endure much longer heat treatment without J c degradation than the high-temperature method. Microscopic analysis also revealed that this method could obtain a clear boundary without a reaction layer or interdiffusion between a superconducting core and sheath metal.

  4. Achievement of practical level critical current densities in Ba1−xKxFe2As2/Ag tapes by conventional cold mechanical deformation

    PubMed Central

    Gao, Zhaoshun; Togano, Kazumasa; Matsumoto, Akiyoshi; Kumakura, Hiroaki

    2014-01-01

    The recently discovered iron-based superconductors are potential candidates for high-field magnet applications. However, the critical current densities (Jc) of iron-based superconducting wires remain far below the level needed for practical applications. Here, we show that the transport Jc of Ba1−xKxFe2As2/Ag tapes is significantly enhanced by the combination process of cold flat rolling and uniaxial pressing. At 4.2 K, Jc exceeds the practical level of 105 A/cm2 in magnetic fields up to 6 T. The Jc-H curve shows extremely small magnetic field dependence and maintains a high value of 8.6 × 104 A/cm2 in 10 T. These are the highest values reported so far for iron-based superconducting wires. Hardness measurements and microstructure investigations reveal that the superior Jc in our samples is due to the high core density, more textured grains, and a change in the microcrack structure. These results indicate that iron-based superconductors are very promising for high magnetic field applications. PMID:24513646

  5. Kernel current source density method.

    PubMed

    Potworowski, Jan; Jakuczun, Wit; Lȩski, Szymon; Wójcik, Daniel

    2012-02-01

    Local field potentials (LFP), the low-frequency part of extracellular electrical recordings, are a measure of the neural activity reflecting dendritic processing of synaptic inputs to neuronal populations. To localize synaptic dynamics, it is convenient, whenever possible, to estimate the density of transmembrane current sources (CSD) generating the LFP. In this work, we propose a new framework, the kernel current source density method (kCSD), for nonparametric estimation of CSD from LFP recorded from arbitrarily distributed electrodes using kernel methods. We test specific implementations of this framework on model data measured with one-, two-, and three-dimensional multielectrode setups. We compare these methods with the traditional approach through numerical approximation of the Laplacian and with the recently developed inverse current source density methods (iCSD). We show that iCSD is a special case of kCSD. The proposed method opens up new experimental possibilities for CSD analysis from existing or new recordings on arbitrarily distributed electrodes (not necessarily on a grid), which can be obtained in extracellular recordings of single unit activity with multiple electrodes.

  6. Tokamak equilibria with reversed current density.

    PubMed

    Martynov, A A; Medvedev, S Yu; Villard, L

    2003-08-22

    Observations of nearly zero toroidal current in the central region of tokamaks (the "current hole") raises the question of the existence of toroidal equilibria with very low or reversed current in the core. The solutions of the Grad-Shafranov equilibrium equation with hollow toroidal current density profile including negative current density in the plasma center are investigated. Solutions of the corresponding eigenvalue problem provide simple examples of such equilibrium configurations. More realistic equilibria with toroidal current density reversal are computed using a new equilibrium problem formulation and computational algorithm which do not assume nested magnetic surfaces.

  7. Enhancing critical current density of cuprate superconductors

    DOEpatents

    Chaudhari, Praveen

    2015-06-16

    The present invention concerns the enhancement of critical current densities in cuprate superconductors. Such enhancement of critical current densities include using wave function symmetry and restricting movement of Abrikosov (A) vortices, Josephson (J) vortices, or Abrikosov-Josephson (A-J) vortices by using the half integer vortices associated with d-wave symmetry present in the grain boundary.

  8. Maps of current density using density-functional methods

    NASA Astrophysics Data System (ADS)

    Soncini, A.; Teale, A. M.; Helgaker, T.; de Proft, F.; Tozer, D. J.

    2008-08-01

    The performance of several density-functional theory (DFT) methods for the calculation of current densities induced by a uniform magnetic field is examined. Calculations are performed using the BLYP and KT3 generalized-gradient approximations, together with the B3LYP hybrid functional. For the latter, both conventional and optimized effective potential (OEP) approaches are used. Results are also determined from coupled-cluster singles-and-doubles (CCSD) electron densities by a DFT constrained search procedure using the approach of Wu and Yang (WY). The current densities are calculated within the CTOCD-DZ2 distributed origin approach. Comparisons are made with results from Hartree-Fock (HF) theory. Several small molecules for which correlation is known to be especially important in the calculation of magnetic response properties are considered-namely, O3, CO, PN, and H2CO. As examples of aromatic and antiaromatic systems, benzene and planarized cyclooctatetraene molecules are considered, with specific attention paid to the ring current phenomenon and its Kohn-Sham orbital origin. Finally, the o-benzyne molecule is considered as a computationally challenging case. The HF and DFT induced current maps show qualitative differences, while among the DFT methods the maps show a similar qualitative structure. To assess quantitative differences in the calculated current densities with different methods, the maximal moduli of the induced current densities are compared and integration of the current densities to yield shielding constants is performed. In general, the maximal modulus is reduced in moving from HF to B3LYP and BLYP, and further reduced in moving to KT3, OEP(B3LYP), and WY(CCSD). The latter three methods offer the most accurate shielding constants in comparison with both experimental and ab initio data and hence the more reliable route to DFT calculation of induced current density in molecules.

  9. Plasma Medicine: Current Achievements and Future Prospects

    NASA Astrophysics Data System (ADS)

    Laroussi, Mounir

    2012-10-01

    Research on the biomedical applications of low temperature plasmas started with small scale experiments that were simply aimed at discovering what happens to biological cells when exposed to the chemically rich environment of plasma. These early experiments took place in the mid to late 1990s. As interest in this multidisciplinary field dramatically rose, various engineering and physics groups collaborated with biologists and medical experts to investigate the use of plasma technology as a basis for innovative medical approaches to cure various diseases. However, many questions concerning the fundamental mechanisms involved in cell-plasma interaction remained unanswered. As a result various workshops were organized to gather the diverse research community in the field of plasma medicine in order to have a fruitful exchange of ideas regarding the scientific challenges that needed to be surmounted to advance and expand the field's knowledge base. The present GEC workshop continues this important tradition of scientific cooperation since there is still a significant lack of understanding of many of the biochemical and molecular pathways that come into play when biological cells are exposed to plasmas. In this talk, first background information on the various plasma devices developed in our institute will be presented. This will be followed by a summary of our work on the effects of plasmas on prokaryotic and eukaryotic cells. The talk will be concluded by presenting our vision of the future of the field and an outline of the main challenges that need to be overcome if practical medical applications are to be achieved.

  10. Josephson junctions with alternating critical current density

    SciTech Connect

    Mints, R.G.; Kogan, V.G.

    1997-04-01

    The magnetic-field dependence of the critical current I{sub c}(H) is considered for a short Josephson junction with the critical current density j{sub c} alternating along the tunnel contact. Two model cases, periodic and randomly alternating j{sub c}, are treated in detail. Recent experimental data on I{sub c}(H) for grain-boundary Josephson junctions in YBa{sub 2}Cu{sub 3}O{sub x} are discussed. {copyright} {ital 1997} {ital The American Physical Society}

  11. Rotating frame RF current density imaging.

    PubMed

    Scott, G C; Joy, M L; Armstrong, R L; Henkelman, R M

    1995-03-01

    RF current density imaging (RF-CDI) is a new MRI technique for imaging the Larmor frequency current density parallel to B0 in electrolytic media. To extend the use of RF-CDI to biological tissue for generating conductivity contrast, the sensitivity must be increased and the data requirements reduced. A rotating frame approach, in which a large B1 field is applied simultaneously as a rotary echo with RF current, is proposed to meet these requirements. Rotating frame magnetic fields are encoded in the phase of an MRI image. Trials have now been performed with this sequence in a three-compartment cylindrical phantom containing doped water or mineral oil for detecting displacement, conduction and fringe field currents. In a postmortem rat study, 85.56 MHz RF currents injected by implanted electrodes created tissue dependent contrast because of the electrical properties of tissue. A sensitivity and artifact analysis was also performed. The sensitivity of this method is determined by the maximum RF pulse duration. SAR limits pose an upper bound on this time and B1, whereas the avoidance of phase artifacts imposes a lower bound on B1.

  12. Steadiness in Dilute Pyroclastic Density Currents

    NASA Astrophysics Data System (ADS)

    Andrews, B. J.

    2015-12-01

    Pyroclastic density currents (PDCs) are often unsteady, as evidenced by direct observations of dilute lobes or jets emerging from the fronts of larger currents and by deposits that indicate transient transport and depositional regimes. We used scaled experiments to investigate unsteadiness in dilute PDCs. The experimental currents were run in an 8.5x6.1x2.6 m tank and comprised heated or ambient temperature 20-μm talc powder turbulently suspended in air. Experiments were scaled such that densimetric and thermal Richardson numbers, Froude number, and particle Stokes and settling numbers were dynamically similar to natural dilute PDCs. Although the experiment Reynolds numbers are substantially lower than those of natural PDCs, the experiments are fully turbulent. Experiments were observed with video and high-speed cameras and high-frequency thermocouples. Currents were generated with total eruption durations of 100 s. Unsteadiness in source conditions was produced by interrupting supply for intervals, t, with durations of 1, 2.5, 5, and 10 s in the experimental runs at 35 and 70 s. When t<2.5 s, the currents are indistinguishable from currents with steady supply. In runs with t=2.5-5 s, the individual pulses comprising each current are readily apparent near the source, but decay with distance downstream until the currents appear as single (e.g. steady) flows. In experiments with t=10 s, the 3 pulses comprising each run never merge and the currents remain unsteady. Comparison with the integral turbulent timescale, τ, and current velocity, U, show that unsteadiness is persistent when t>3<τ but currents are steady when t<τ. In currents with 3τ>t>τ, unsteadiness decays such that at a distance of ~4Ut, the currents are again steady. Applied to natural dilute PDCs, our results suggest that currents and their resulting deposits, will only show evidence of unsteadiness if they are disrupted for many seconds and those breaks may "heal" over distances of 100s of meters.

  13. Current Density Scaling in Electrochemical Flow Capacitors

    SciTech Connect

    Hoyt, NC; Wainright, JS; Savinell, RF

    2015-02-18

    Electrochemical flow capacitors (EFCs) are a recently developed energy storage technology. One of the principal performance metrics of an EFC is the steady-state electrical current density that it can accept or deliver. Numerical models exist to predict this performance for specific cases, but here we present a study of how the current varies with respect to the applied cell voltage, flow rate, cell dimensions, and slurry properties using scaling laws. The scaling relationships are confirmed by numerical simulations and then subsequently by comparison to results from symmetric cell EFC experiments. This modeling approach permits the delimitation of three distinct operational regimes dependent on the values of two nondimensional combinations of the pertinent variables (specifically, a capacitive Graetz number and a conductivity ratio). Lastly, the models and nondimensional numbers are used to provide design guidance in terms of criteria for proper EFC operation. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.

  14. Elucidation of constant current density molecular plating

    NASA Astrophysics Data System (ADS)

    Vascon, A.; Santi, S.; Isse, A. A.; Reich, T.; Drebert, J.; Christ, H.; Düllmann, Ch. E.; Eberhardt, K.

    2012-12-01

    The production of thin layers by means of constant current or constant voltage electrolysis in organic media is commonly known as molecular plating. Despite the fact that this method has been applied for decades and is known to be among the most efficient ones for obtaining quantitative deposition, a full elucidation of the molecular plating is still lacking. In order to get a general understanding of the process and hence set the basis for further improvements of the method, constant current density electrolysis experiments were carried out in a mixture of isopropanol and isobutanol containing millimolar amounts of HNO3 together with [Nd(NO3)3·6H2O] used as a model electrolyte. The process was investigated by considering the influence of different parameters, namely the electrolyte concentrations (i.e., Nd(NO3)3·6H2O: 0.11, 0.22, 0.44 mM, and HNO3: 0.3, 0.4 mM), the applied current (i.e., 2 mA and 6 mA), and the surface roughness of the deposition substrates (i.e., a few tens to several hundreds of nm). The response of the process to changes of these parameters was monitored recording cell potential curves, which showed to be strongly influenced by the investigated conditions. The produced layers were characterized using γ-ray spectroscopy for the evaluation of Nd deposition yields, X-ray photoelectron spectroscopy for chemical analysis of the surfaces, and atomic force microscopy for surface roughness evaluation. X-ray photoelectron spectroscopy results clearly indicate that Nd is present only as Nd3+ on the cathodic surface after molecular plating. The results obtained from this characterization and some basic features inferred from the study of the cell potential curves were used to interpret the different behaviours of the deposition processes as a consequence of the applied variables.

  15. Extreme hydrogen plasma densities achieved in a linear plasma generator

    SciTech Connect

    Rooij, G. J. van; Veremiyenko, V. P.; Goedheer, W. J.; de Groot, B.; Kleyn, A. W.; Smeets, P. H. M.; Versloot, T. W.; Whyte, D. G.; Engeln, R.; Schram, D. C.; Cardozo, N. J. Lopes

    2007-03-19

    A magnetized hydrogen plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6 T. Its characteristics were measured at a distance of 4 cm from the nozzle: up to a 2 cm beam diameter, 7.5x10{sup 20} m{sup -3} electron density, {approx}2 eV electron and ion temperatures, and 3.5 km/s axial plasma velocity. This gives a 2.6x10{sup 24} H{sup +} m{sup -2} s{sup -1} peak ion flux density, which is unprecedented in linear plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source.

  16. Anode current density distribution in a cusped field thruster

    SciTech Connect

    Wu, Huan Liu, Hui Meng, Yingchao; Zhang, Junyou; Yang, Siyu; Hu, Peng; Chen, Pengbo; Yu, Daren

    2015-12-15

    The cusped field thruster is a new electric propulsion device that is expected to have a non-uniform radial current density at the anode. To further study the anode current density distribution, a multi-annulus anode is designed to directly measure the anode current density for the first time. The anode current density decreases sharply at larger radii; the magnitude of collected current density at the center is far higher compared with the outer annuli. The anode current density non-uniformity does not demonstrate a significant change with varying working conditions.

  17. Anode current density distribution in a cusped field thruster

    NASA Astrophysics Data System (ADS)

    Wu, Huan; Liu, Hui; Meng, Yingchao; Zhang, Junyou; Yang, Siyu; Hu, Peng; Chen, Pengbo; Yu, Daren

    2015-12-01

    The cusped field thruster is a new electric propulsion device that is expected to have a non-uniform radial current density at the anode. To further study the anode current density distribution, a multi-annulus anode is designed to directly measure the anode current density for the first time. The anode current density decreases sharply at larger radii; the magnitude of collected current density at the center is far higher compared with the outer annuli. The anode current density non-uniformity does not demonstrate a significant change with varying working conditions.

  18. Particle Image Velocimetry Study of Density Current Fronts

    ERIC Educational Resources Information Center

    Martin, Juan Ezequiel

    2009-01-01

    Gravity currents are flows that occur when a horizontal density difference causes fluid to move under the action of gravity; density currents are a particular case, for which the scalar causing the density difference is conserved. Flows with a strong effect of the horizontal density difference, even if only partially driven by it--such as the…

  19. High current density cathode for electrorefining in molten electrolyte

    DOEpatents

    Li, Shelly X.

    2010-06-29

    A high current density cathode for electrorefining in a molten electrolyte for the continuous production and collection of loose dendritic or powdery deposits. The high current density cathode eliminates the requirement for mechanical scraping and electrochemical stripping of the deposits from the cathode in an anode/cathode module. The high current density cathode comprises a perforated electrical insulated material coating such that the current density is up to 3 A/cm.sup.2.

  20. Current density partitioning in time-dependent current density functional theory

    SciTech Connect

    Mosquera, Martín A.; Wasserman, Adam

    2014-05-14

    We adapt time-dependent current density functional theory to allow for a fragment-based solution of the many-electron problem of molecules in the presence of time-dependent electric and magnetic fields. Regarding a molecule as a set of non-interacting subsystems that individually evolve under the influence of an auxiliary external electromagnetic vector-scalar potential pair, the partition 4-potential, we show that there are one-to-one mappings between this auxiliary potential, a sharply-defined set of fragment current densities, and the total current density of the system. The partition electromagnetic (EM) 4-potential is expressed in terms of the real EM 4-potential of the system and a gluing EM 4-potential that accounts for exchange-correlation effects and mutual interaction forces between fragments that are required to yield the correct electron dynamics. We prove the zero-force theorem for the fragmented system, establish a variational formulation in terms of action functionals, and provide a simple illustration for a charged particle in a ring.

  1. Ultraclean suspended monolayer graphene achieved by in situ current annealing

    NASA Astrophysics Data System (ADS)

    Wang, Haidong; Zhang, Xing; Takamatsu, Hiroshi

    2017-01-01

    Ultraclean graphene is essential for studying its intrinsic transport properties or fabricating high-performance electronic devices. Unfortunately, the contamination on graphene is unavoidable after microelectromechanical system processing. Here, we report an in situ current-annealing method for achieving ultraclean suspended monolayer graphene. The charge mobility of cleaned graphene reached a surprising 3.8 × 105 cm2 V-1 s-1, one of the highest values ever reported. For the first time, the process of current annealing was recorded under a high-resolution electron scanning microscope. It was demonstrated that temperature was the only dominant factor of the current-annealing process. Meanwhile, the mobility of suspended graphene was found to be highly sensitive to structural defects. The mobility decreased by a factor of over 100 after ion irradiation on graphene. The results revealed the underlying mechanism of current annealing on graphene and provided an effective means of preparing ultraclean graphene membranes.

  2. Current Density and Plasma Displacement Near Perturbed Rational Surface

    SciTech Connect

    A.H. Boozer and N. Pomphrey

    2010-10-10

    The current density in the vicinity of a rational surface of a force-free magnetic field subjected to an ideal perturbation is shown to be the sum of both a smooth and a delta-function distribution, which give comparable currents. The maximum perturbation to the smooth current density is comparable to a typical equilibrium current density and the width of the layer in which the current flows is shown to be proportional to the perturbation amplitude. In the standard linearized theory, the plasma displacement has an unphysical jump across the rational surface, but the full theory gives a continuous displacement.

  3. Theory of tokamak equilibria with central current density reversal.

    PubMed

    Wang, Shaojie

    2004-10-08

    It is found that, with a model current profile, the Grad-Shafranov equation can be reduced to the Helmholtz equation, which can describe a variety of equilibrium configurations. With the eigenvalue problem solved in the toroidal coordinate system, an analytical solution to the Grad-Shafranov equation is found. It is demonstrated that current reversal equilibrium configurations exist with finite radial gradient of plasma pressure and continuous current density, and that current density reversal is accompanied by pressure gradient reversal.

  4. Note: A real-time beam current density meter

    SciTech Connect

    Liu Junliang; Yu Deyang; Ruan Fangfang; Xue Yingli; Wang Wei

    2013-03-15

    We have developed a real-time beam current density meter for charged particle beams. It measures the mean current density by collimating a uniform and large diameter primary beam. The suppression of the secondary electrons and the deflection of the beam were simulated, and it was tested with a 105 keV Ar{sup 7+} ion beam.

  5. Individual differences in transcranial electrical stimulation current density

    PubMed Central

    Russell, Michael J; Goodman, Theodore; Pierson, Ronald; Shepherd, Shane; Wang, Qiang; Groshong, Bennett; Wiley, David F

    2013-01-01

    Transcranial electrical stimulation (TCES) is effective in treating many conditions, but it has not been possible to accurately forecast current density within the complex anatomy of a given subject's head. We sought to predict and verify TCES current densities and determine the variability of these current distributions in patient-specific models based on magnetic resonance imaging (MRI) data. Two experiments were performed. The first experiment estimated conductivity from MRIs and compared the current density results against actual measurements from the scalp surface of 3 subjects. In the second experiment, virtual electrodes were placed on the scalps of 18 subjects to model simulated current densities with 2 mA of virtually applied stimulation. This procedure was repeated for 4 electrode locations. Current densities were then calculated for 75 brain regions. Comparison of modeled and measured external current in experiment 1 yielded a correlation of r = .93. In experiment 2, modeled individual differences were greatest near the electrodes (ten-fold differences were common), but simulated current was found in all regions of the brain. Sites that were distant from the electrodes (e.g. hypothalamus) typically showed two-fold individual differences. MRI-based modeling can effectively predict current densities in individual brains. Significant variation occurs between subjects with the same applied electrode configuration. Individualized MRI-based modeling should be considered in place of the 10-20 system when accurate TCES is needed. PMID:24285948

  6. Current-confinement structure and extremely high current density in organic light-emitting transistors.

    PubMed

    Sawabe, Kosuke; Imakawa, Masaki; Nakano, Masaki; Yamao, Takeshi; Hotta, Shu; Iwasa, Yoshihiro; Takenobu, Taishi

    2012-12-04

    Extremely high current densities are realized in single-crystal ambipolar light-emitting transistors using an electron-injection buffer layer and a current-confinement structure via laser etching. Moreover, a linear increase in the luminance was observed at current densities of up to 1 kA cm(-2) , which is an efficiency-preservation improvement of three orders of magnitude over conventional organic light-emitting diodes (OLEDs) at high current densities.

  7. On bottom density currents on the continental shelves

    NASA Technical Reports Server (NTRS)

    Anuchin, V. N.; Gusev, A. M.; Pyrkin, Y. G.; Khapayev, M. M.

    1975-01-01

    The turbulent characteristics of bottom density currents on the continental shelves and their influence on the vertical profiles of current velocities are studied by considering plane parallel flows of a liquid with one density in a motionless liquid and with lighter density along an inclined plane. The motion of the liquid is a result of gravitational force directed along the parallel plane. Vertical distribution of turbulent stress is determined from a known average velocity profile and is used to obtain the vertical profile of the average current velocity.

  8. Switching current density reduction in perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions

    SciTech Connect

    You, Chun-Yeol

    2014-01-28

    We investigate the switching current density reduction of perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions using micromagnetic simulations. We find that the switching current density can be reduced with elongated lateral shapes of the magnetic tunnel junctions, and additional reduction can be achieved by using a noncollinear polarizer layer. The reduction is closely related to the details of spin configurations during switching processes with the additional in-plane anisotropy.

  9. High current density pulsed cathode experiments at SLAC

    SciTech Connect

    Koontz, R.; Fant, K.; Vlieks, A.

    1990-06-01

    A 1.9 microperveance beam diode has been constructed to test high current density cathodes for use in klystrons. Several standard and specially coated dispenser cathodes are being tested. Results of tests to date show average cathode current densities in excess of 25 amps/cm, and maximum electric field gradients of more than 450 kV/cm for pulses of the order of 1{mu}sec. 3 refs., 11 figs.

  10. A high current density DC magnetohydrodynamic (MHD) micropump.

    PubMed

    Homsy, Alexandra; Koster, Sander; Eijkel, Jan C T; van den Berg, Albert; Lucklum, F; Verpoorte, E; de Rooij, Nico F

    2005-04-01

    This paper describes the working principle of a DC magnetohydrodynamic (MHD) micropump that can be operated at high DC current densities (J) in 75-microm-deep microfluidic channels without introducing gas bubbles into the pumping channel. The main design feature for current generation is a micromachined frit-like structure that connects the pumping channel to side reservoirs, where platinum electrodes are located. Current densities up to 4000 A m(-2) could be obtained without noticeable Joule heating in the system. The pump performance was studied as a function of current density and magnetic field intensity, as well as buffer ionic strength and pH. Bead velocities of up to 1 mm s(-1) (0.5 microL min(-1)) were observed in buffered solutions using a 0.4 T NdFeB permanent magnet, at an applied current density of 4000 A m(-2). This pump is intended for transport of electrolyte solutions having a relatively high ionic strength (0.5-1 M) in a DC magnetic field environment. The application of this pump for the study of biological samples in a miniaturized total analysis system (microTAS) with integrated NMR detection is foreseen. In the 7 T NMR environment, a minimum 16-fold increase in volumetric flow rate for a given applied current density is expected.

  11. The impact of geocoronal density on ring current development

    NASA Astrophysics Data System (ADS)

    Ilie, R.; Skoug, R. M.; Funsten, H. O.; Liemohn, M. W.; Bailey, J. J.; Gruntman, M.

    2013-07-01

    Long-term ring current decay following a magnetic storm is mainly due to charge exchange collisions of ring current ions with geocoronal neutral atoms forming energetic neutral atoms (ENAs) that leave the ring current system. Therefore, the density distribution of these cold and tenuous neutral hydrogen atoms plays a key role in the ring current recovery. TWINS ENA images provide a direct measurement of these ENA losses and therefore insight into the dynamics of the ring current decay through interactions with the geocorona. To assess the influence of geocoronal neutrals on ring current decay, we compare the predicted ENA emission using five different geocoronal models and the HEIDI ring current model to simulate the July 22, 2009 storm. We show that for high energy H+ (≥100 keV), all geocoronal models predict similar decay rates of the ring current ions. However, for low energy ions (≤100 keV), the decay rate varies significantly depending on the geocoronal density model. Comparison with TWINS ENA images shows that the location of the peak ENA enhancements is highly dependent on the distribution of geocoronal hydrogen density. The ring current topology depends greatly on the hydrogen model used, therefore knowing the H-distribution is very important in understanding how the ring current recovers following a magnetic storm.

  12. Casimir effect for scalar current densities in topologically nontrivial spaces

    NASA Astrophysics Data System (ADS)

    Bellucci, S.; Saharian, A. A.; Saharyan, N. A.

    2015-08-01

    We evaluate the Hadamard function and the vacuum expectation value (VEV) of the current density for a charged scalar field, induced by flat boundaries in spacetimes with an arbitrary number of toroidally compactified spatial dimensions. The field operator obeys the Robin conditions on the boundaries and quasiperiodicity conditions with general phases along compact dimensions. In addition, the presence of a constant gauge field is assumed. The latter induces Aharonov-Bohm-type effect on the VEVs. There is a region in the space of the parameters in Robin boundary conditions where the vacuum state becomes unstable. The stability condition depends on the lengths of compact dimensions and is less restrictive than that for background with trivial topology. The vacuum current density is a periodic function of the magnetic flux, enclosed by compact dimensions, with the period equal to the flux quantum. It is explicitly decomposed into the boundary-free and boundary-induced contributions. In sharp contrast to the VEVs of the field squared and the energy-momentum tensor, the current density does not contain surface divergences. Moreover, for Dirichlet condition it vanishes on the boundaries. The normal derivative of the current density on the boundaries vanish for both Dirichlet and Neumann conditions and is nonzero for general Robin conditions. When the separation between the plates is smaller than other length scales, the behavior of the current density is essentially different for non-Neumann and Neumann boundary conditions. In the former case, the total current density in the region between the plates tends to zero. For Neumann boundary condition on both plates, the current density is dominated by the interference part and is inversely proportional to the separation.

  13. Rf Gun with High-Current Density Field Emission Cathode

    SciTech Connect

    Jay L. Hirshfield

    2005-12-19

    High current-density field emission from an array of carbon nanotubes, with field-emission-transistor control, and with secondary electron channel multiplication in a ceramic facing structure, have been combined in a cold cathode for rf guns and diode guns. Electrodynamic and space-charge flow simulations were conducted to specify the cathode configuration and range of emission current density from the field emission cold cathode. Design of this cathode has been made for installation and testing in an existing S-band 2-1/2 cell rf gun. With emission control and modulation, and with current density in the range of 0.1-1 kA/cm2, this cathode could provide performance and long-life not enjoyed by other currently-available cathodes

  14. Magneto-optical imaging of transport current densities in superconductors

    SciTech Connect

    Crabtree, G.W.; Welp, U.; Gunter, D.O.; Zhong, W.; Balachandran, U.; Haldar, P.; Sokolowski, R.S.; Vlasko-Vlasov, V.K.; Nikitenko, V.I.

    1995-12-31

    Direct imaging of the paths of transport currents in superconductors creates many new possibilities for exploring the basic features of vortex pinning mechanisms and for improving the performance of superconducting materials. A technique for imaging the path and magnitude of the transport current density flowing in superconductors is described. Results are given for a 37-filament BSCCO 2223 powder-in-tube wire, showing a highly inhomogeneous current path within the filaments.

  15. Ionospheric midlatitude electric current density inferred from multiple magnetic satellites

    NASA Astrophysics Data System (ADS)

    Shore, R. M.; Whaler, K. A.; Macmillan, S.; Beggan, C.; Olsen, N.; Spain, T.; Aruliah, A.

    2013-09-01

    A method for inferring zonal electric current density in the mid-to-low latitude F region ionosphere is presented. We describe a method of using near-simultaneous overflights of the Ørsted and CHAMP satellites to define a closed circuit for an application of Ampère's integral law to magnetic data. Zonal current density from sources in only the region between the two satellites is estimated for the first time. Six years of mutually available vector magnetic data allows overlaps spanning the full 24 h range of local time twice. Solutions are computed on an event-by-event basis after correcting for estimates of main and crustal magnetic fields. Current density in the range ±0.1 μA/m2 is resolved, with the distribution of electric current largely matching known features such as the Appleton anomaly. The currents appear unmodulated at times of either high-negative Dst or high F10.7, which has implications for any future efforts to model their effects. We resolve persistent current intensifications between geomagnetic latitudes of 30 and 50° in the postmidnight, predawn sector, a region typically thought to be relatively free of electric currents. The cause of these unexpected intensifications remains an open issue. We compare our results with current density predictions made by the Coupled Thermosphere-Ionosphere-Plasmasphere model, a self-consistent, first-principles, three-dimensional numerical dynamic model of ionospheric composition and temperatures. This independent validation of our current density estimates highlights good agreement in the broad spatiotemporal trends we identify, which increases confidence in our results.

  16. Regional absolute conductivity reconstruction using projected current density in MREIT.

    PubMed

    Sajib, Saurav Z K; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2012-09-21

    Magnetic resonance electrical impedance tomography (MREIT) is a non-invasive technique for imaging the internal conductivity distribution in tissue within an MRI scanner, utilizing the magnetic flux density, which is introduced when a current is injected into the tissue from external electrodes. This magnetic flux alters the MRI signal, so that appropriate reconstruction can provide a map of the additional z-component of the magnetic field (B(z)) as well as the internal current density distribution that created it. To extract the internal electrical properties of the subject, including the conductivity and/or the current density distribution, MREIT techniques use the relationship between the external injection current and the z-component of the magnetic flux density B = (B(x), B(y), B(z)). The tissue studied typically contains defective regions, regions with a low MRI signal and/or low MRI signal-to-noise-ratio, due to the low density of nuclear magnetic resonance spins, short T(2) or T*(2) relaxation times, as well as regions with very low electrical conductivity, through which very little current traverses. These defective regions provide noisy B(z) data, which can severely degrade the overall reconstructed conductivity distribution. Injecting two independent currents through surface electrodes, this paper proposes a new direct method to reconstruct a regional absolute isotropic conductivity distribution in a region of interest (ROI) while avoiding the defective regions. First, the proposed method reconstructs the contrast of conductivity using the transversal J-substitution algorithm, which blocks the propagation of severe accumulated noise from the defective region to the ROI. Second, the proposed method reconstructs the regional projected current density using the relationships between the internal current density, which stems from a current injection on the surface, and the measured B(z) data. Combining the contrast conductivity distribution in the entire

  17. High Current Density Scandate Cathodes for Future Vacuum Electronics Applications

    DTIC Science & Technology

    2008-05-30

    braze alloy . The structure was fired in a furnace at 16500 C for 15 minutes. The resultant structure was sectioned to determine if the scandium flowed...Density Cathodes for Future Vacuum Electronics Applications FA9550-07-C-0063 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION...Current Density Scandate Cathodes for Future Vacuum Electronics Applications USAF/AFRL Contract Number FA9550-07-C-0063 Final Report Calabazas Creek

  18. Target current density effects in al-cluster ion emission

    NASA Astrophysics Data System (ADS)

    Ray, N.; Rajasekar, P.; Chakraborty, P.; Dey, S. D.

    1994-04-01

    Target current density effects in secondary emission of positively-charged sputtered clusters from an ion-bombarded polycrystalline aluminium surface have been investigated for various primary Cd+ ion energies. For each cluster type, at medium target current densities (Jp : 0?350 ?A/cm2), apart from the presence of the expected linear term in the I+ s α Jp curves, there is a square law term, depicting that some fraction of the pre-emitted neutral clusters gets ionized in vacuum above the target surface. Thus, a sum of these two terms constitutes the total cluster ion current which shows a non-linear dependence on the target current density. At higher target current densities (350 ?A cm?2?1.05 mA cm?2), in addition to the parabolic effect, a higher order non-linearity comes into play and the net cluster ion current I + s , measured as a function of target current density within the Ip range concerned, can be expressed in terms of our previously proposed semi-empirical formula I+ s = C.Ip + D.I2 p + F.In p , which was earlier found to be applicable in case of single and double charged secondary monomers. A higher power (n > 2) dependence has been observed here for the first time in case of cluster ion emission, suggesting chemical enhancement of secondary clusters. Our present observations seem to support ?direct emission model? even for small metal clusters?a proposition which is in apparent contradiction to the current notion in this field, i.e. vacuum recombination of individual atoms in small cluster formation.

  19. Current drive at plasma densities required for thermonuclear reactors.

    PubMed

    Cesario, R; Amicucci, L; Cardinali, A; Castaldo, C; Marinucci, M; Panaccione, L; Santini, F; Tudisco, O; Apicella, M L; Calabrò, G; Cianfarani, C; Frigione, D; Galli, A; Mazzitelli, G; Mazzotta, C; Pericoli, V; Schettini, G; Tuccillo, A A

    2010-08-10

    Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confined in toroidal tokamak devices requires the development of efficient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing significant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors.

  20. Noise distribution and denoising of current density images.

    PubMed

    Beheshti, Mohammadali; Foomany, Farbod H; Magtibay, Karl; Jaffray, David A; Krishnan, Sridhar; Nanthakumar, Kumaraswamy; Umapathy, Karthikeyan

    2015-04-01

    Current density imaging (CDI) is a magnetic resonance (MR) imaging technique that could be used to study current pathways inside the tissue. The current distribution is measured indirectly as phase changes. The inherent noise in the MR imaging technique degrades the accuracy of phase measurements leading to imprecise current variations. The outcome can be affected significantly, especially at a low signal-to-noise ratio (SNR). We have shown the residual noise distribution of the phase to be Gaussian-like and the noise in CDI images approximated as a Gaussian. This finding matches experimental results. We further investigated this finding by performing comparative analysis with denoising techniques, using two CDI datasets with two different currents (20 and 45 mA). We found that the block-matching and three-dimensional (BM3D) technique outperforms other techniques when applied on current density ([Formula: see text]). The minimum gain in noise power by BM3D applied to [Formula: see text] compared with the next best technique in the analysis was found to be around 2 dB per pixel. We characterize the noise profile in CDI images and provide insights on the performance of different denoising techniques when applied at two different stages of current density reconstruction.

  1. Current Density Measurements of an Annular-Geometry Ion Engine

    NASA Technical Reports Server (NTRS)

    Shastry, Rohit; Patterson, Michael J.; Herman, Daniel A.; Foster, John E.

    2012-01-01

    The concept of the annular-geometry ion engine, or AGI-Engine, has been shown to have many potential benefits when scaling electric propulsion technologies to higher power. However, the necessary asymmetric location of the discharge cathode away from thruster centerline could potentially lead to non-uniformities in the discharge not present in conventional geometry ion thrusters. In an effort to characterize the degree of this potential non-uniformity, a number of current density measurements were taken on a breadboard AGI-Engine. Fourteen button probes were used to measure the ion current density of the discharge along a perforated electrode that replaced the ion optics during conditions of simulated beam extraction. Three Faraday probes spaced apart in the vertical direction were also used in a separate test to interrogate the plume of the AGI-Engine during true beam extraction. It was determined that both the discharge and the plume of the AGI-Engine are highly uniform, with variations under most conditions limited to +/-10% of the average current density in the discharge and +/-5% of the average current density in the plume. Beam flatness parameter measured 30 mm from the ion optics ranged from 0.85 - 0.95, and overall uniformity was shown to generally increase with increasing discharge and beam currents. These measurements indicate that the plasma is highly uniform despite the asymmetric location of the discharge cathode.

  2. Current Density Measurements of an Annular-Geometry Ion Engine

    NASA Technical Reports Server (NTRS)

    Shastry, Rohit; Patterson, Michael J.; Herman, Daniel A.; Foster, John E.

    2012-01-01

    The concept of the annular-geometry ion engine, or AGI-Engine, has been shown to have many potential benefits when scaling electric propulsion technologies to higher power. However, the necessary asymmetric location of the discharge cathode away from thruster centerline could potentially lead to non-uniformities in the discharge not present in conventional geometry ion thrusters. In an effort to characterize the degree of this potential nonuniformity, a number of current density measurements were taken on a breadboard AGI-Engine. Fourteen button probes were used to measure the ion current density of the discharge along a perforated electrode that replaced the ion optics during conditions of simulated beam extraction. Three Faraday probes spaced apart in the vertical direction were also used in a separate test to interrogate the plume of the AGI-Engine during true beam extraction. It was determined that both the discharge and the plume of the AGI-Engine are highly uniform, with variations under most conditions limited to 10% of the average current density in the discharge and 5% of the average current density in the plume. Beam flatness parameter measured 30 mm from the ion optics ranged from 0.85 0.95, and overall uniformity was shown to generally increase with increasing discharge and beam currents. These measurements indicate that the plasma is highly uniform despite the asymmetric location of the discharge cathode.

  3. Amending the uniformity of ion beam current density profile

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaowei; Xu, Dequan; Liu, Ying; Xu, Xiangdong; Fu, Shaojun

    2008-03-01

    The uniformity of ion beam current density profile has been amended by changing the flow of the gas and making a new beam channel. The platform scanned in the horizontal orientation in this experiment, so the horizontal ion beam current distribution had hardly any effect on the etching uniformity and amending the ion beam current density profile in the vertical orientation was sufficient for the purpose of plat etching profile. The ratio of the ion source's working gas inputs has some effect for the uniformity and a ratio of 6.50sccm: 8.00sccm: 9.60sccm of the three gas inputs flow1: flow2: flow3 will lead to a more uniform profile. According to the horizontal distribution and the original vertical ion beam current density distribution measured by Faraday Cup, a new beam channel was made. The uniformity of ion beam current density profile is enhanced from +/-4.31%to +/-1.96% in this experiment.

  4. Three-dimensional structure of dilute pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Andrews, B. J.

    2013-12-01

    Unconfined experimental density currents dynamically similar to pyroclastic density currents (PDCs) suggest that cross-stream motions of the currents and air entrainment through currents' lateral margins strongly affects PDC behavior. Experiments are conducted within an air-filled tank 8.5 m long by 6.1 m wide by 2.6 m tall. Currents are generated by feeding heated powders down a chute into the tank at controlled rates to form dilute, particle-laden, turbulent gravity currents that are fed for 30 to 600 seconds. Powders include 5 μm aluminum oxide, 25 μm talc, 27 μm walnut, 76 μm glass beads and mixtures thereof. Experiments are scaled such that Froude, densimetric and thermal Richardson, particle Stokes and Settling numbers, and thermal to kinetic energy densities are all in agreement with dilute PDCs; experiments have lower Reynolds numbers that natural currents, but the experiments are fully turbulent, thus the large scale structures should be similar. The experiments are illuminated with 3 orthogonal laser sheets (650, 532, and 450 nm wavelengths) and recorded with an array of HD video cameras and a high speed camera (up to 3000 fps); this system provides synchronous observation of a vertical streamwise and cross-stream planes, and a horizontal plane. Ambient temperature currents tend to spread out radially from the source and have long run out distances, whereas warmer currents tend to focus along narrow sectors and have shorter run outs. In addition, when warm currents lift off to form buoyant plumes, lateral spreading ceases. The behavior of short duration currents are dominated by the current head; as eruption duration increases, current transport direction tends to oscillate back and forth (this is particularly true for ambient temperature currents). Turbulent structures in the horizontal plane show air entrainment and advection downstream. Eddies illuminated by the vertical cross-stream laser sheet often show vigorous mixing along the current margins

  5. Electric fields and current densities under small Florida thunderstorms

    NASA Technical Reports Server (NTRS)

    Deaver, Lance E.; Krider, E. P.

    1991-01-01

    Results are presented of measurements of the electric field E and Maxwell current density that were performed simultaneously under and near small Florida thunderstorms. It is shown that the amplitude of JM is of the order of 1 nA/sq cm or less in the absence of precipitation and that there are regular time variations in JM during the intervals between lightning discharges that tend to have the same shapes after different discharges in different storms. It is argued that the major causes of time variations in JM between lightning discharges are currents that flow in the finitely conducting atmosphere in response to the field changes rather than rapid time variations in the strength of cloud current sources. The displacement current densities that are computed from the E records dominate JM except when there is precipitation, when E is large and steady, or when E is unusually noisy.

  6. Role of Resilient Personality on Lower Achieving First Grade Students' Current and Future Achievement

    ERIC Educational Resources Information Center

    Kwok, Oi-man; Hughes, Jan N.; Luo, Wen

    2007-01-01

    This study investigated a measurement model of personality resilience and the contribution of personality resilience to lower achieving first grade students' academic achievement. Participants were 445 ethnically diverse children who at entrance to first grade scored below their school district median on a test of literacy. Participants were…

  7. A method to achieve rapid localised deep heating in a laser irradiated solid density target

    NASA Astrophysics Data System (ADS)

    Schmitz, H.; Robinson, A. P. L.

    2016-09-01

    Rapid heating of small buried regions by laser generated fast electrons may be useful for applications such as extreme ultraviolet (XUV) radiation sources or as drivers for shock experiments. In non-structured targets, the heating profile possesses a global maximum near the front surface. This paper presents a new target design that uses resistive guiding to concentrate the fast electron current density at a finite depth inside the target. The choice of geometry uses principles of non-imaging optics. A global temperature maximum at depths up to 50 μ m into the target is achieved. Although theoretical calculations suggest that small source sizes should perform better than large ones, simulations show that a large angular spread at high intensities results in significant losses of the fast electrons to the sides. A systematic parameter scan suggests an optimal laser intensity. A ratio of 1.6 is demonstrated between the maximum ion temperature and the ion temperature at the front surface.

  8. Path to Efficient Lower Hybrid Current Drive at High Density

    NASA Astrophysics Data System (ADS)

    Baek, S. G.; Bonoli, P. T.; Brunner, D.; Faust, I.; Labombard, B. L.; Parker, R. R.; Shiraiwa, S.; Wallace, G. M.; Wukitch, S.

    2015-11-01

    Recovery of lower hybrid current drive (LHCD) efficiency at high density was demonstrated on Alcator C-Mod by modifying the scrape-off layer (SOL) plasma. RF probe measurements around the C-Mod tokamak indicate that the LH wave amplitude at the high field side wall significantly attenuates with plasma density. This is interpreted as enhanced collisional loss due to the increase in the SOL density and width. By taking advantage of the narrower SOL width by doubling plasma current to 1.1 MA, it is found that the LH wave amplitude maintains its strength, and an effective current drive is extended to above 1x10e20 m-3. An order of magnitude increase in non-thermal Bremsstrahlung emission is consistent with ray-tracing results which take into account the change of SOL profiles with current. In the coming campaign, a further investigation on the role of the SOL plasma is planned by raising plasma current above 1.1 MA. This will be aided with newly developed RF magnetic loop antennas mounted on a radially movable probe head. This system is expected to intercept the LH resonance cone on the first pass, allowing us to measure radial profiles of both the wave amplitude and dominant parallel wavenumber in the SOL for the first time. These data will be compared with the GENRAY ray-tracing code. Work supported by USDoE awards DE-FC02-99ER54512.

  9. MEG forward problem formulation using equivalent surface current densities.

    PubMed

    von Ellenrieder, Nicolás; Muravchik, Carlos H; Nehorai, Arye

    2005-07-01

    We present a formulation for the magnetoencephalography (MEG) forward problem with a layered head model. Traditionally the magnetic field is computed based on the electric potential on the interfaces between the layers. We propose to express the effect of the volumetric currents in terms of an equivalent surface current density on each interface, and obtain the magnetic field based on them. The boundary elements method is used to compute the equivalent current density and the magnetic field for a realistic head geometry. We present numerical results showing that the MEG forward problem is solved correctly with this formulation, and compare it with the performance of the traditional formulation. We conclude that the traditional formulation generally performs better, but still the new formulation is useful in certain situations.

  10. Modeling dilute pyroclastic density currents on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Clarke, A. B.; Brand, B. D.; De'Michieli Vitturi, M.

    2013-12-01

    The surface of Mars has been shaped extensively by volcanic activity, including explosive eruptions that may have been heavily influenced by water- or ice-magma interaction. However, the dynamics of associated pyroclastic density currents (PDCs) under Martian atmospheric conditions and controls on deposition and runout from such currents are poorly understood. This work combines numerical modeling with terrestrial field measurements to explore the dynamics of dilute PDC dynamics on Earth and Mars, especially as they relate to deposit characteristics. We employ two numerical approaches. Model (1) consists of simulation of axi-symmetric flow and sedimentation from a steady-state, depth-averaged density current. Equations for conservation of mass, momentum, and energy are solved simultaneously, and the effects of atmospheric entrainment, particle sedimentation, basal friction, temperature changes, and variations in current thickness and density are explored. The Rouse number and Brunt-Väisälä frequency are used to estimate the wavelength of internal gravity waves in a density-stratified current, which allows us to predict deposit dune wavelengths. The model predicts realistic runout distances and bedform wavelengths for several well-documented field cases on Earth. The model results also suggest that dilute PDCs on Mars would have runout distances up to three times that of equivalent currents on Earth and would produce longer-wavelength bedforms. In both cases results are heavily dependent on source conditions, grain-size characteristics, and entrainment and friction parameters. Model (2) relaxes several key simplifications, resulting in a fully 3D, multiphase, unsteady model that captures more details of propagation, including density stratification, and depositional processes. Using this more complex approach, we focus on the role of unsteady or pulsatory vent conditions typically associated with phreatomagmatic eruptions. Runout distances from Model (2) agree

  11. Transport and sedimentation in unconfined experimental dilute pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Ramirez, G.; Andrews, B. J.; Dennen, R. L.

    2013-12-01

    We present results from experiments conducted in a new facility that permits the study of large, unconfined particle laden density currents that are dynamically similar to natural dilute pyroclastic density currents (PDCs). Experiments were run in a sealed, air-filled tank measuring 8.5 m long by 6.1 m wide by 2.6 m tall. Currents were generated by feeding mixture of heated particles (5 μm aluminum oxide, 25 μm talc, 27 μm walnut shell, 76 μm glass beads) down a chute at controlled rates to produce dilute, turbulent gravity currents. Comparison of experimental currents with natural PDCs shows good agreement between Froude, densimetric and thermal Richardson, and particle Stokes and settling numbers; experimental currents have lower Reynolds numbers than natural PDCs, but are fully turbulent. Currents were illuminated with 3 orthogonal laser sheets (650, 532, and 450 nm wavelengths) and recorded with an array of HD video cameras and a high speed camera (up to 3000 fps). Deposits were mapped using a grid of sedimentation traps. We observe distinct differences between ambient temperature and warm currents: * warm currents have shorter run out distances, narrow map view distributions of currents and deposits, thicken with distance from the source, and lift off to form coignimbrite plumes; * ambient temperature currents typically travel farther, spread out radially, do not thicken greatly with transport distance, and do not form coignimbrite plumes. Long duration currents (600 s compared to 30-100 s) oscillate laterally with time (e.g. transport to the right, then the left, and back); this oscillation happens prior to any interaction with the tank walls. Isopach maps of the deposits show predictable trends in sedimentation versus distance in response to eruption parameters (eruption rate, duration, temperature, and initial current mass), but all sedimentation curves can be fit with 2nd order polynomials (R2>.9). Proximal sedimentation is similar in comparable warm

  12. High dislocation density of tin induced by electric current

    SciTech Connect

    Liao, Yi-Han; Liang, Chien-Lung; Lin, Kwang-Lung; Wu, Albert T.

    2015-12-15

    A dislocation density of as high as 10{sup 17} /m{sup 2} in a tin strip, as revealed by high resolution transmission electron microscope, was induced by current stressing at 6.5 x 10{sup 3} A/ cm{sup 2}. The dislocations exist in terms of dislocation line, dislocation loop, and dislocation aggregates. Electron Backscattered Diffraction images reflect that the high dislocation density induced the formation of low deflection angle subgrains, high deflection angle Widmanstätten grains, and recrystallization. The recrystallization gave rise to grain refining.

  13. Evidence for explosive volcanic density currents on certain Martian volcanoes

    NASA Technical Reports Server (NTRS)

    Reimers, C. E.; Komar, P. D.

    1979-01-01

    The morphologies of certain of the smaller Martian volcanoes are discussed as possible results of explosive volcanic density currents. An examination of newly-photographed flank and caldera features of the Martian volcanoes Ceraunius Tholus, Uranius Tholus, Uranius Patera and Hecates Tholus, including steep slope angles, Krakatoa-type caldera morphologies, erosional features (radial channels and anastamosing gullies) and constructional features (blanketed flanks and possible lava deltas) reveals their similarity to terrestrial cones and composite volcanoes such as Barcena Volcano. Crater age data from the surface of Martian domes and shields indicates that such explosive activity occurred more frequently early in Martian geologic history, consistent with the view that the volcanic density currents were base surges rather than nuees ardentes, with the melting of permafrost supplying the water required in base surge generation.

  14. Enhancement of Current Density by dc Electric Concentrator

    PubMed Central

    Jiang, Wei Xiang; Luo, Chen Yang; Ma, Hui Feng; Mei, Zhong Lei; Cui, Tie Jun

    2012-01-01

    We investigate a dc electric concentrator for steady current fields theoretically and experimentally. Based on the transformation electrostatics, we show that the dc concentrator can focus electric currents into the central concentrated region and enhance the electric field and current density. Outside the concentrator, the current lines are distributed as the same as those in a homogeneous conducting material. Hence, such a dc electric concentrator has no impact on other external devices. Using the analogy between electrically conducting materials and resistor networks, we design, fabricate, and test a dc concentrator using the circuit theory. The measured results agree very well with the theoretical predictions and numerical simulations, demonstrating the perfect concentrating performance. PMID:23233875

  15. Molecular epidemiology of tuberculosis: achievements and challenges to current knowledge.

    PubMed Central

    Murray, Megan; Nardell, Edward

    2002-01-01

    Over the past 10 years, molecular methods have become available with which to strain-type Mycobacterium tuberculosis. They have allowed researchers to study certain important but previously unresolved issues in the epidemiology of tuberculosis (TB). For example, some unsuspected microepidemics have been revealed and it has been shown that the relative contribution of recently acquired disease to the TB burden in many settings is far greater than had been thought. These findings have led to the strengthening of TB control. Other research has demonstrated the existence and described the frequency of exogenous reinfection in areas of high incidence. Much recent work has focused on the phenotypic variation among strains and has evaluated the relative transmissibility, virulence, and immunogenicity of different lineages of the organism. We summarize the recent achievements in TB epidemiology associated with the introduction of DNA fingerprinting techniques, and consider the implications of this technology for the design and analysis of epidemiological studies. PMID:12132006

  16. Composites for Increased Wear Resistance: Current Achievements and Future Prospects

    NASA Technical Reports Server (NTRS)

    Lancaster, J. K.

    1984-01-01

    The various ways in which reductions in wear and/or friction can be achieved by the use of composite materials are reviewed. Reinforced plastics are emphasized and it is shown that fillers and fibers reduce wear via several mechanisms additional to their role of increasing overall mechanical strength, preferential transfer, counter face abrasion, preferential load support, or third-body formation on either the composite or its counterface. Examples are given from recent work on thin layer composites of the type widely used as dry bearings in aircraft flight control mechanisms. Developments in metal based composites and carbon-carbon composites for high energy brakes are discussed. The aspects which could benefit by increased fundamental understanding identified and the types of composites which appear to have greatest potential for further growth are indicated.

  17. Genetic engineering of radish: current achievements and future goals.

    PubMed

    Curtis, Ian S

    2011-05-01

    Radish is a major root crop grown in the Far East and is especially important to some low-income countries where it is consumed on a daily basis. Developments in gene technology systems have helped to accelerate the production of useful germplasms, but progress has been slow, though achieved, via in planta methods and useful traits have been introduced. In the wake of the new Millennium, future goals in terms of improving transformation efficiency and selection of new traits for generating late-flowering radish are described. Furthermore, the techniques available for incorporating pharmaceutical proteins into radish to deliver edible proteins on-site are discussed. Finally, the concerns of releasing transgenic radish to the field in terms of pollen-mediated gene transfer are also reviewed. Such a report identifies key areas of research that is required to allow the crop satisfy the need of poor impoverished countries in the Far East.

  18. Thin-film Josephson junctions with alternating critical current density

    NASA Astrophysics Data System (ADS)

    Moshe, Maayan; Kogan, V. G.; Mints, R. G.

    2009-01-01

    We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions with alternating critical current density. Im(H) is evaluated within nonlocal Josephson electrodynamics taking into account the stray fields that affect the difference of the order-parameter phases across the junction and therefore the tunneling currents. We find that the phase difference along the junction is proportional to the applied field, depends on the junction geometry, but is independent of the Josephson critical current density gc , i.e., it is universal. An explicit form for this universal function is derived for small currents through junctions of the width W≪Λ , the Pearl length. The result is used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant but only in high fields. We find that the spacing between zeros is proportional to 1/W2 . The general approach is applied to calculate Im(H) for a superconducting quantum interference device with two narrow edge-type junctions. If gc changes sign periodically or randomly, as it does in grain boundaries of high- Tc materials and superconductor-ferromagnet-superconductor heterostructures, Im(H) not only acquires the major side peaks, but due to nonlocality the following peaks decay much slower than in bulk junctions.

  19. Magnetic topology and current channels in plasmas with toroidal current density inversions

    SciTech Connect

    Ciro, D.; Caldas, I. L.

    2013-10-15

    The equilibrium magnetic field inside axisymmetric plasmas with inversions on the toroidal current density is considered. Previous works have shown that internal regions with negative current density lead to non-nested magnetic surfaces inside the plasma. Following these results, we derive a general expression relating the positive and negative currents inside the non-nested surfaces. This is done in terms of an anisotropy parameter that is model-independent and is based in very general properties of the magnetic field. We demonstrate that the positive currents in axisymmetric islands screen the negative one in the plasma center by reaching about twice its magnitude. Further, we illustrate these results by developing a family of analytical local solutions for the poloidal magnetic field in a region of interest that contains the inverted current. These local solutions exhibit non-nested magnetic surfaces with a combined current of at least twice the magnitude of the negative one, as prescribed from the topological arguments, and allow to study topological transitions driven by geometrical changes in the current profile. To conclude, we discuss the signatures of internal current density inversions in a confinement device and show that magnetic pitch measurements may be inappropriate to differentiate current reversals and small current holes in plasmas.

  20. Morphology and Density Structure of Post-CME Current Sheets

    NASA Technical Reports Server (NTRS)

    Vrsnak, B.; Poletto, G.; Vujic, E.; Vourlidas, A.

    2009-01-01

    Eruption of a coronal mass ejection (CME) is believed to drag and open the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and field relaxation by magnetic reconnection. This paper analyzes the physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to confirm whether interpreting such phenomena in terms of a reconnecting current sheet is consistent with observations. Methods: The study focuses on UVCS/SOHO and LASCO/SOHO measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of the rays implies that they are produced by Petschek-like reconnection in the large-scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km/s, and are consistent with the narrow opening-angle of rays, which add up to a few degrees. The density of rays is an order of magnitude higher than in the ambient corona. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to higher heights by the reconnection outflow.

  1. Unsteady density-current equations for highly curved terrain

    NASA Technical Reports Server (NTRS)

    Sivakumaran, N. S.; Dressler, R. F.

    1989-01-01

    New nonlinear partial differential equations containing terrain curvature and its rate of change are derived that describe the flow of an atmospheric density current. Unlike the classical hydraulic-type equations for density currents, the new equations are valid for two-dimensional, gradually varied flow over highly curved terrain, hence suitable for computing unsteady (or steady) flows over arbitrary mountain/valley profiles. The model assumes the atmosphere above the density current exerts a known arbitrary variable pressure upon the unknown interface. Later this is specialized to the varying hydrostatic pressure of the atmosphere above. The new equations yield the variable velocity distribution, the interface position, and the pressure distribution that contains a centrifugal component, often significantly larger than its hydrostatic component. These partial differential equations are hyperbolic, and the characteristic equations and characteristic directions are derived. Using these to form a characteristic mesh, a hypothetical unsteady curved-flow problem is calculated, not based upon observed data, merely as an example to illustrate the simplicity of their application to unsteady flows over mountains.

  2. Magnetohydrodynamically stable plasma with supercritical current density at the axis

    SciTech Connect

    Burdakov, A. V.; Postupaev, V. V. Sudnikov, A. V.

    2014-05-15

    In this work, an analysis of magnetic perturbations in the GOL-3 experiment is given. In GOL-3, plasma is collectively heated in a multiple-mirror trap by a high-power electron beam. During the beam injection, the beam-plasma interaction maintains a high-level microturbulence. This provides an unusual radial profile of the net current (that consists of the beam current, current of the preliminary discharge, and the return current). The plasma core carries supercritical current density with the safety factor well below unity, but as a whole, the plasma is stable with q(a) ≈ 4. The net plasma current is counter-directed to the beam current; helicities of the magnetic field in the core and at the edge are of different signs. This forms a system with a strong magnetic shear that stabilizes the plasma core in good confinement regimes. We have found that the most pronounced magnetic perturbation is the well-known n = 1, m = 1 mode for both stable and disruptive regimes.

  3. High current density, cryogenically cooled sliding electrical joint development

    SciTech Connect

    Murray, H.

    1986-09-01

    In the past two years, conceptual designs for fusion energy research devices have focussed on compact, high magnetic field configurations. The concept of sliding electrical joints in the large magnets allows a number of technical advantages including enhanced mechanical integrity, remote maintainability, and reduced project cost. The rationale for sliding electrical joints is presented. The conceptual configuration for this generation of experimental devices is highlghted by an approx. 20 T toroidal field magnet with a flat top conductor current of approx. 300 kA and a sliding electrical joint with a gross current density of approx. 0.6 kA/cm/sup 2/. A numerical model was used to map the conductor current distribution as a function of time and position in the conductor. A series of electrical joint arrangements were produced against the system code envelope constraints for a specific version of the Ignition Studies Project (ISP) which is designated as 1025.

  4. Effect of current density on enhanced transformation of naphthalene.

    PubMed

    Alshawabkeh, Akram N; Sarahney, Hussam

    2005-08-01

    The effect of current density on electrochemically enhanced transformation of naphthalene is evaluated. Electrochemical reactors, composed of an anode and a cathode separated by a Nafion membrane, were used to evaluatethe effect of three current densities (1,9, and 18 mA/ L) on the transformation of naphthalene at two concentration levels (13 and 25 mg/L). Transformation rates varied based on the concentration and current density. Almost 88% of the 13 mg/L naphthalene is degraded after 8 h of treatment under 18.2 mA/L. At the same time, more than 90 h was required to degrade the same amount under 9 mA/ L. The results show that most of the naphthalene degradation occurred in the first 4 h under transformation rates of 2.24 and 1.11 mg/L h under applied currents of 18.2 and 9 mA/L, respectively. Increasing the naphthalene concentration to 25 mg/L produced similar results. Under 18.2 mA/L, the redox potential increased significantly at the anolyte in the first 8 h to about 900 mV. After that, the redox potential continued to increase, but at a lower rate, until it reached 1380 mV at the end of processing. Similar behavior is noted for the anolyte pH, which decreased significantly in the first 8 h to less than 2.5 and continued to decrease until it reached a pH value of 1.86 at the end of testing. Naphthalene transformation can be attributed to electrochemically enhanced oxidation at the anolyte by chlorine gas produced by electrolysis.

  5. Stochastic Time-Dependent Current-Density Functional Theory

    NASA Astrophysics Data System (ADS)

    D'Agosta, Roberto

    2008-03-01

    Static and dynamical density functional methods have been applied with a certain degree of success to a variety of closed quantum mechanical systems, i.e., systems that can be described via a Hamiltonian dynamics. However, the relevance of open quantum systems - those coupled to external environments, e.g., baths or reservoirs - cannot be overestimated. To investigate open quantum systems with DFT methods we have introduced a new theory, we have named Stochastic Time-Dependent Current Density Functional theory (S-TDCDFT) [1]: starting from a suitable description of the system dynamics via a stochastic Schrödinger equation [2], we have proven that given an initial quantum state and the coupling between the system and the environment, there is a one-to-one correspondence between the ensemble-averaged current density and the external vector potential applied to the system.In this talk, I will introduce the stochastic formalism needed for the description of open quantum systems, discuss in details the theorem of Stochastic TD-CDFT, and provide few examples of its applicability like the dissipative dynamics of excited systems, quantum-measurement theory and other applications relevant to charge and energy transport in nanoscale systems.[1] M. Di Ventra and R. D'Agosta, Physical Review Letters 98, 226403 (2007)[2] N.G. van Kampen, Stochastic processes in Physics and Chemistry, (North Holland, 2001), 2nd ed.

  6. Incorporation Of Air Into The Campanian Ignimbrite Pyroclastic Density Current

    NASA Astrophysics Data System (ADS)

    Ort, M. H.; Giordano, G.; Zanella, E.; Isaia, R.

    2015-12-01

    Knowing the temperature of emplacement of an ignimbrite can tell us how much cooling air it incorporated during eruption and transport. Currents that incorporate cool matter (air, water, cold clasts) cool more than those that do not. Lithic fragments record the maximum temperature they reached, up to their maximum unblocking temperature. Studies of large ignimbrites (e.g. Cerro Galan Ignimbrite) emplaced by dense currents show they do not cool very much, with emplacement temperatures often above 580 oC. Smaller currents, such as those from Vesuvius and Colima, lose significant heat in the eruption column, and then lose some, but less, heat as they travel laterally. The amount of atmosphere incorporated by large dilute currents is not known. The ~40 ka Campanian Ignimbrite (CI) erupted from the Campi Flegrei caldera near Naples, Italy, and extends to ~75 km from the caldera. The CI was emplaced from a density-stratified current with a dilute transport system and a denser depositional system that overtopped 1600-m-high ridges, with the depositional system re-forming on the far side. Modeling of dilute currents shows that they can pass over obstacles ~1.5 times their thickness without losing momentum, which implies the CI current was >1 km thick. Much of that dilute current was gas, but how much was atmospheric? Partial thermal demagnetization of lithic clasts allows the identification of the temperature of emplacement. We sampled lithic fragments from the CI in 13 locations from proximal to distal along several azimuths. The current passed over 30-35 km of sea to get to two sites. Partial thermal demagnetization of 10 specimens from each site show that they were heated and deposited above 580 oC, the unblocking temperature of magnetite, implying the temperature of emplacement was at or above this temperature. The CI is poor in lithic clasts (<1% in most places) and evidence of non-magmatic water in the outflow sheet is absent. We suggest the CI current was a large

  7. Emergent loop current order from pair density wave superconductivity

    NASA Astrophysics Data System (ADS)

    Kashyap, Manoj; Melchert, Drew; Agterberg, Daniel

    2015-03-01

    In addition to charge density wave (CDW) order, there is evidence that the pseudogap phase in the cuprates breaks time reversal symmetry. Here we show that pair density wave (PDW) states give rise to a translational invariant non-superconducting order parameter that breaks time reversal and parity symmetries, but preserves their product. This secondary order parameter has a different origin, but shares the same symmetry properties as a magnetoelectric loop current order that has been proposed earlier in the context of the cuprates to explain the appearance of intra-cell magnetic order. We further show that, due to fluctuations, this secondary loop current order, which represents the breaking of discrete symmetries, can preempt PDW order, which breaks both continuous and discrete symmetries. In such a phase, the emergent loop current order coexists with spatial short range CDW and short range superconducting order. Finally, we propose a PDW phase that accounts for intra-cell magnetic order and the Kerr effect, has CDW order consistent with x-ray scattering and nuclear magnetic resonance observations, and quasi-particle properties consistent with angle resolved photoemission scattering. We acknowledge support from NSF Grant No. DMR-1335215

  8. Emergent loop current order from pair density wave superconductivity

    NASA Astrophysics Data System (ADS)

    Agterberg, D. F.; Melchert, Drew S.; Kashyap, M. K.

    2015-02-01

    There is evidence that the pseudogap phase in the cuprates breaks time-reversal symmetry. Here we show that pair density wave (PDW) states give rise to a translational invariant nonsuperconducting order parameter that breaks time-reversal and parity symmetries, but preserves their product. This secondary order parameter has a different origin, but shares the same symmetry properties as a magnetoelectric loop current order that has been proposed earlier in the context of the cuprates to explain the appearance of intracell magnetic order. We further show that, due to fluctuations, this secondary loop current order, which breaks only discrete symmetries, can preempt PDW order, which breaks both continuous and discrete symmetries. In such a phase, the emergent loop current order coexists with spatial short-range superconducting order and possibly short-range charge density wave (CDW) order. Finally, we propose a PDW phase that accounts for intracell magnetic order and the Kerr effect, has CDW order consistent with x-ray scattering and nuclear magnetic resonance observations, and quasiparticle properties consistent with angle-resolved photoemission scattering.

  9. Biophysical assessment of DC iontophoresis and current density on transdermal permeation of methotrexate

    PubMed Central

    Prasad, Rachna; Anand, Sneh; Koul, Veena

    2011-01-01

    Introduction: The effect of DC iontophoresis using low (0.2 mA/cm2) and high current density (0.5 mA/cm2) on transdermal permeation of methotrexate loaded into polyacrylamide hydrogel patch was investigated. Results: Flux of 20.57 ± 1.02 μg/cm2/h and 36.8 ± 2.21 μg/cm2/h was achieved with low and high current density DC iontophoresis, respectively. Attenuated total reflectance-Fourier Transform infrared (ATR-FTIR) spectra and microscopic studies of the treated skin samples supported the permeation results. A greater decrease in the peak height of asymmetric, symmetric C-H stretching vibration and ester peak was noticed with 0.5 mA/cm2 current density as compared to 0.2 mA/cm2 current density samples. Furthermore, an increase in the ratio of amide I and amide II bands from 2.6 to 11 with increase in current density was noticed, thus indicating that hydration levels are associated with iontophoresis and play an important role in increasing the drug permeation. Scanning electron microscopy revealed increase in pore size of the hair follicles. Light microscopy studies of the skin samples treated with low current density DC iontophoresis demonstrated epidermal thinning and focal disruptions, spongiosis and appendageal dilatations. With higher current density, disruption of epidermis in almost half of the sectioned area, loss of appendages and fractured collagen in the dermis was noticed. Moreover, the reversibility studies conducted in vivo on mice revealed that the recovery process had started within 24 h and is complete in 48 h for lower current density treated animals. However, the histological changes associated with 0.5 mA/cm2 current density were not reversible in 48 h and edema, appendageal dilatations along with focal disruption of epidermis persisted. Conclusion: Hence our study suggests that high density current is not well-tolerated by the skin. PMID:23071949

  10. The current density in quantum electrodynamics in external potentials

    SciTech Connect

    Schlemmer, Jan; Zahn, Jochen

    2015-08-15

    We review different definitions of the current density for quantized fermions in the presence of an external electromagnetic field. Several deficiencies in the popular prescription due to Schwinger and the mode sum formula for static external potentials are pointed out. We argue that Dirac’s method, which is the analog of the Hadamard point-splitting employed in quantum field theory in curved space–times, is conceptually the most satisfactory. As a concrete example, we discuss vacuum polarization and the stress–energy tensor for massless fermions in 1+1 dimension. Also a general formula for the vacuum polarization in static external potentials in 3+1 dimensions is derived.

  11. Advances in time-dependent current-density functional theory

    NASA Astrophysics Data System (ADS)

    Berger, Arjan

    In this work we solve the problem of the gauge dependence of molecular magnetic properties (magnetizabilities, circular dichroism) using time-dependent current-density functional theory [1]. We also present a new functional that accurately describes the optical absorption spectra of insulators, semiconductors and metals [2] N. Raimbault, P.L. de Boeij, P. Romaniello, and J.A. Berger Phys. Rev. Lett. 114, 066404 (2015) J.A. Berger, Phys. Rev. Lett. 115, 137402 (2015) This study has been partially supported through the Grant NEXT No. ANR-10-LABX-0037 in the framework of the Programme des Investissements d'Avenir.

  12. Discretizing Transient Current Densities in the Maxwell Equations

    SciTech Connect

    Stowell, M L

    2008-11-25

    We will briefly discuss a technique for applying transient volumetric current sources in full-wave, time-domain electromagnetic simulations which avoids the need for divergence cleaning. The method involves both 'edge-elements' and 'face-elements' in conjunction with a particle-in-cell scheme to track the charge density. Results from a realistic, 6.7 million element, 3D simulation are shown. While the author may have a finite element bias the technique should be applicable to finite difference methods as well.

  13. The dynamics of pyroclastic density currents on Mars

    NASA Astrophysics Data System (ADS)

    Brand, B. D.; Clarke, A. B.

    2010-12-01

    The products of explosive volcanism have long been observed on the surface of Mars, and their corresponding dynamics, associated with phenomenon such as dike propagation, magma fragmentation, and eruption columns under Martian conditions, have been modeled with significant success (e.g., Wilson, L., J. W. Head (1994), Mars- Review and analysis of volcanic eruption theory and relationships to observed landforms, Rev. Geophy, 32, 221-263). However, the dynamics of pyroclastic density currents (PDCs) under Martian conditions is still poorly constrained. Our increasing capability to image the surface at high resolution, both from orbit and from rovers, presents an opportunity for more rigorous deposit observations and descriptions. For example, observations and measurements from Orbiters identify what have been interpreted as extensive aprons of volcanic ash deposits in several volcanic regions, namely those surrounding several southern highland patera, which have been interpreted as the deposits of PDCs. In addition the bedded deposits identified by the Spirit rover at “Home Plate,” an outcrop within the Columbia Hills in Gusev Crater, have been interpreted by many as the deposits of dilute pyroclastic density currents. This demonstrates that the need to understand the role of the Martian atmosphere on flow dynamics and depositional processes is much more important and relevant than it has been in the past. We have developed a quantitative, axi-symmetric model for flow of and sedimentation from a steady-state, vertically uniform dilute density current for application to PDCs on Earth and Mars (following Bursik, M. I., A. W. Woods, 1996, The dynamics and thermodynamics of large ash flows, Bull Volcan, 58, 175-193). The conservation of mass, momentum, and energy are solved simultaneously, and include the effects of atmospheric entrainment, particle sedimentation, basal friction, temperature changes, and variations in current thickness and density. For a given set of

  14. Dynamic Harris current sheet thickness from Cluster current density and plasma measurements

    NASA Technical Reports Server (NTRS)

    Thompson, S. M.; Kivelson, M. G.; Khurana, K. K.; McPherron, R. L.; Weygand, J. M.; Balogh, A.; Reme, H.; Kistler, L. M.

    2005-01-01

    We use the first accurate measurements of current densities in the plasma sheet to calculate the half-thickness and position of the current sheet as a function of time. Our technique assumes a Harris current sheet model, which is parameterized by lobe magnetic field B(o), current sheet half-thickness h, and current sheet position z(sub o). Cluster measurements of magnetic field, current density, and plasma pressure are used to infer the three parameters as a function of time. We find that most long timescale (6-12 hours) current sheet crossings observed by Cluster cannot be described by a static Harris current sheet with a single set of parameters B(sub o), h, and z(sub o). Noting the presence of high-frequency fluctuations that appear to be superimposed on lower frequency variations, we average over running 6-min intervals and use the smoothed data to infer the parameters h(t) and z(sub o)(t), constrained by the pressure balance lobe magnetic field B(sub o)(t). Whereas this approach has been used in previous studies, the spatial gnuhen& now provided by the Cluster magnetometers were unavailable or not well constrained in earlier studies. We place the calculated hdf&cknessa in a magnetospheric context by examining the change in thickness with substorm phase for three case study events and 21 events in a superposed epoch analysis. We find that the inferred half-thickness in many cases reflects the nominal changes experienced by the plasma sheet during substorms (i.e., thinning during growth phase, thickening following substorm onset). We conclude with an analysis of the relative contribution of (Delta)B(sub z)/(Delta)X to the cross-tail current density during substorms. We find that (Delta)B(sub z)/(Delta)X can contribute a significant portion of the cross-tail c m n t around substorm onset.

  15. Critical current density and current distribution in field cooled superconducting disks

    NASA Astrophysics Data System (ADS)

    Bernstein, Pierre; Noudem, Jacques; Dupont, Louis

    2016-07-01

    Applications of bulk superconductors concern superconducting motors and generators, the levitation of vehicles, the generation of high magnetic fields with small size cryo-magnets, the shielding of magnetic fields and other applications. For all of them, it is essential to determine the critical current density, and to understand the effect of the shape and size of the bulks on the properties of interest. In this contribution, we show how the combination of levitation force and trapped field measurements allow one to determine the characteristics and the potential performances of superconducting disks using analytical modeling. As examples of applications we detail the effects of the magnetizing field and of the bulk sheet critical current density on the levitation force. An important result of the reported measurements is that in field-cooled samples, the shielding currents possibly do not flow along the whole thickness of the disks.

  16. Hydraulic jumps within pyroclastic density currents and their sedimentary record

    NASA Astrophysics Data System (ADS)

    Douillet, G.; Mueller, S.; Kueppers, U.; Dingwell, D. B.

    2013-12-01

    This contribution presents a complete and comprehensive formulation of the hydraulic jump phenomenon and reviews sedimentary structures that may be associated with them. Beginning from the general fluid phenomenon, we then focus on examples from pyroclastic density currents in order to infer dynamic parameters on the parent flows. A hydraulic jump is a fluid dynamics phenomenon that corresponds to the sudden increase of the thickness of a flow accompanied by a decrease of its velocity and/or density. A hydraulic jump is the expression of the transition of the flow from two different flow regimes: supercritical to subcritical. This entrains a change in the energy balance between kinetic energy and gravity potential energy. Recently, the terms of 'pneumatic jumps' have been used for similar phenomenon driven within a gas phase, and granular jumps for dense granular flows. It is thought that such strong changes in the flow conditions may leave characteristic structures in the sedimentary record. Indeed, the main variables influencing the sedimentation rate are the flow velocity, particle concentration and turbulence level, all of them strongly affected by a hydraulic jump. Structures deposited by hydraulic/pneumatic jumps have been called cyclic steps and chute and pool structures. Chute and pools represent the record of a single supercritical to subcritical transition, whereas cyclic steps are produced by stable trains of hydraulic jumps and subsequent re-accelerations. Pyroclastic density currents (PDCs) are gas and pyroclasts flows. As such, they can be subjected to granular and pneumatic jumps and their deposit have often been interpreted as containing records of jumps. Steep sided truncations covered by lensoidal layers have been interpreted as the record of internal jumps within density stratified flows. Fines-depleted breccias at breaks in slope are thought to result from the enhanced turbulence at a jump of the entire flow. Sudden increases in thickness of

  17. Ultra-high current density thin-film Si diode

    DOEpatents

    Wang; Qi

    2008-04-22

    A combination of a thin-film .mu.c-Si and a-Si:H containing diode structure characterized by an ultra-high current density that exceeds 1000 A/cm.sup.2, comprising: a substrate; a bottom metal layer disposed on the substrate; an n-layer of .mu.c-Si deposited the bottom metal layer; an i-layer of .mu.c-Si deposited on the n-layer; a buffer layer of a-Si:H deposited on the i-layer, a p-layer of .mu.c-Si deposited on the buffer layer; and a top metal layer deposited on the p-layer.

  18. Sparse imaging of cortical electrical current densities via wavelet transforms

    NASA Astrophysics Data System (ADS)

    Liao, Ke; Zhu, Min; Ding, Lei; Valette, Sébastien; Zhang, Wenbo; Dickens, Deanna

    2012-11-01

    While the cerebral cortex in the human brain is of functional importance, functions defined on this structure are difficult to analyze spatially due to its highly convoluted irregular geometry. This study developed a novel L1-norm regularization method using a newly proposed multi-resolution face-based wavelet method to estimate cortical electrical activities in electroencephalography (EEG) and magnetoencephalography (MEG) inverse problems. The proposed wavelets were developed based on multi-resolution models built from irregular cortical surface meshes, which were realized in this study too. The multi-resolution wavelet analysis was used to seek sparse representation of cortical current densities in transformed domains, which was expected due to the compressibility of wavelets, and evaluated using Monte Carlo simulations. The EEG/MEG inverse problems were solved with the use of the novel L1-norm regularization method exploring the sparseness in the wavelet domain. The inverse solutions obtained from the new method using MEG data were evaluated by Monte Carlo simulations too. The present results indicated that cortical current densities could be efficiently compressed using the proposed face-based wavelet method, which exhibited better performance than the vertex-based wavelet method. In both simulations and auditory experimental data analysis, the proposed L1-norm regularization method showed better source detection accuracy and less estimation errors than other two classic methods, i.e. weighted minimum norm (wMNE) and cortical low-resolution electromagnetic tomography (cLORETA). This study suggests that the L1-norm regularization method with the use of face-based wavelets is a promising tool for studying functional activations of the human brain.

  19. Ion diffusion may introduce spurious current sources in Current-Source Density (CSD) analysis.

    PubMed

    Halnes, Geir; Mäki-Marttunen, Tuomo; Pettersen, Klas H; Andreassen, Ole A; Einevoll, Gaute T

    2017-03-15

    Current-source density (CSD) analysis is a well-established method for analyzing recorded ocal field potentials (LFPs), that is, the low-frequency part of extracellular potentials. Standard CSD theory is based on the assumption that all extracellular currents are purely ohmic, and thus neglects the possible impact from ionic diffusion on recorded potentials. However, it has previously been shown that in physiological conditions with large ion-concentration gradients, diffusive currents can evoke slow shifts in extracellular potentials. Using computer simulations, we here show that diffusion-evoked potential shifts can introduce errors in standard CSD analysis, and can lead to prediction of spurious current sources. Further, we show that the diffusion-evoked prediction errors can be removed by using an improved CSD estimator which accounts for concentration-dependent effects.

  20. High current density contacts for photoconductive semiconductor switches

    SciTech Connect

    Baca, A.G.; Hjalmarson, H.P.; Loubriel, G.M.; McLaughlin, D.L.; Zutavern, F.J.

    1993-08-01

    The current densities implied by current filaments in GaAs photoconductive semiconductor switches (PCSS) are in excess of 1 MA/cm{sup 2}. As the lateral switches are tested repeatedly, damage accumulates at the contacts until electrical breakdown occurs across the surface of the insulating region. In order to improve the switch lifetime, the incorporation of n- and p-type ohmic contacts in lateral switches as well as surface geometry modifications have been investigated. By using p-type AuBe ohmic contacts at the anode and n-type AuGe ohmic contacts at the cathode, contact lifetime improvements of 5--10x were observed compared to switches with n-type contacts at both anode and cathode. Failure analysis on samples operated for 1--1,000 shots show that extensive damage still exists for at least one contact on all switches observed and that temperatures approaching 500{degrees}C are can be reached. However, the n-type AuGe cathode is often found to have no damage observable by scanning electron microscopy (SEM). The observed patterns of contact degradation indicate directions for future contact improvements in lateral switches.

  1. Current densities and total contact currents associated with 400 kV power line tasks.

    PubMed

    Korpinen, Leena; Kuisti, Harri; Elovaara, Jarmo

    2013-12-01

    The aim of the study was to analyze all current values from measured periods while performing tasks on 400 kV power lines. Our aim was also to study the average current densities and average total contact currents caused by electric fields in 400 kV power line tasks. Two workers simulated the following tasks: (A) climbing up a portal tower, (B) climbing up a portal transposing tower, (C) working on the cross-arm of a portal tower, (D) climbing up a portal tube tower, (E) climbing up a Tannenbaum tower on the side of the energized circuit with the other circuit unenergized, (F) climbing up a Tannenbaum tower with both circuits energized, and (G) climbing up a Donau tower. The highest average current density in the neck was 2.5 mA/m(2) (calculated internal electric field 31.5-63.0 mV/m), and the highest average of the contact currents was 240.0 µA. All measured values at 400 kV towers were lower than the limit value of 10 mA/m(2) in the first version of Directive 2004/40/EC and the basic restrictions (0.1 and 0.8 V/m) of the International Commission on Non-ionizing Radiation Protection.

  2. Regional gray matter density is associated with achievement motivation: evidence from voxel-based morphometry.

    PubMed

    Takeuchi, Hikaru; Taki, Yasuyuki; Nouchi, Rui; Sekiguchi, Atsushi; Kotozaki, Yuka; Miyauchi, Carlos Makoto; Yokoyama, Ryoichi; Iizuka, Kunio; Hashizume, Hiroshi; Nakagawa, Seishu; Kunitoki, Keiko; Sassa, Yuko; Kawashima, Ryuta

    2014-01-01

    Achievement motivation can be defined as a recurrent need to improve one's past performance. Despite previous functional imaging studies on motivation-related functional activation, the relationship between regional gray matter (rGM) morphology and achievement motivation has never been investigated. We used voxel-based morphometry and a questionnaire (achievement motivation scale) to measure individual achievement motivation and investigated the association between rGM density (rGMD) and achievement motivation [self-fulfillment achievement motivation (SFAM) and competitive achievement motivation (CAM) across the brain in healthy young adults (age 21.0 ± 1.8 years, men (n = 94), women (n = 91)]. SFAM and rGMD significantly and negatively correlated in the orbitofrontal cortex (OFC). CAM and rGMD significantly and positively correlated in the right putamen, insula, and precuneus. These results suggest that the brain areas that play central roles in externally modulated motivation (OFC and putamen) also contribute to SFAM and CAM, respectively, but in different ways. Furthermore, the brain areas in which rGMD correlated with CAM are related to cognitive processes associated with distressing emotions and social cognition, and these cognitive processes may characterize CAM.

  3. Control of the current density profile with lower hybrid current drive on PBX-M

    SciTech Connect

    Bell, R.E.; Bernabei, S.; Chu, T.K.; Gettelfinger, G.; Greenough, N.; Hatcher, R.; Ignat, D.; Jardin, S.; Kaita, R.; Kaye, S.; Kozub, T.; Kugel, H.; LeBlanc, B.; Okabayashi, M.; Paul, S.; Sauthoff, N.; Sesnic, S.; Sun, Y.; Takahashi, H.; Tighe, W.; Valeo, E.; von Goeler, S.; Blush, L.; Doerner, R.; Schmitz, L.; Tynan, G.; Dunlap, J.; England, A.; Harris, J.; Hirshman, S.; Isler, R.; Lee, D.; Jones, S.; Kesner, J.; Luckhardt, S.; Paoletti, F.; Levinton, F.; Timini, F.

    1993-07-01

    Lower hybrid current drive (LHCD) is being explored as a means to control the current density profile on PBX-M with the goal of raising the central safety factor q(O) to values of 1.5-2 to facilitate access to a full-volume second stable regime. Initial experiments have been conducted with up to 400 kW of 4.6 GHz LH power in circular and indented plasmas with modest parameters. A tangential-viewing two-dimensional hard x-ray imaging diagnostic has been used to observe the bremsstrahlung emission from the suprathermal electrons generated during LHCD. Hollow hard x-ray images have indicated off-axis localization of the driven current. A serious obstacle to the control of the current density profile with LHCD is the concomitant generation of MHD activity, which can seriously degrade the confinement of suprathermal electrons. By combining neutral beam injection with LHCD, an MHD-free condition has been obtained where q(O) is raised above 1.

  4. Radial current density effects on rotating magnetic field current drive in field-reversed configurations

    SciTech Connect

    Clemente, R. A.; Gilli, M.; Farengo, R.

    2008-10-15

    Steady state solutions, suitable for field-reversed configurations (FRCs) sustained by rotating magnetic fields (RMFs) are obtained by properly including three-dimensional effects, in the limit of large FRC elongation, and the radial component of Ohm's law. The steady electrostatic potential, necessary to satisfy Ohm's law, is considered to be a surface function. The problem is analyzed at the midplane of the configuration and it is reduced to the solution of two coupled nonlinear differential equations for the real and imaginary parts of the phasor associated to the longitudinal component of the vector potential. Additional constraints are obtained by requesting that the steady radial current density and poloidal magnetic flux vanish at the plasma boundary which is set at the time-averaged separatrix. The results are presented in terms of the degree of synchronism of the electrons with the RMF and compared with those obtained when radial current effects are neglected. Three important differences are observed when compared with the case without radial current density. First, at low penetration of the RMF into the plasma there is a significant increase in the driven azimuthal current. Second, the RMF amplitude necessary to access the high synchronism regime, starting from low synchronism, is larger and the difference appears to increase as the separatrix to classical skin depth ratio increases. Third, the minimum RMF amplitude necessary to sustain almost full synchronism is reduced.

  5. Differential Modulation of Corticospinal Excitability by Different Current Densities of Anodal Transcranial Direct Current Stimulation

    PubMed Central

    Bastani, Andisheh; Jaberzadeh, Shapour

    2013-01-01

    Background Novel non-invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) have been developed in recent years. TDCS-induced corticospinal excitability changes depend on two important factors current intensity and stimulation duration. Despite clinical success with existing tDCS parameters, optimal protocols are still not entirely set. Objective/hypothesis The current study aimed to investigate the effects of four different anodal tDCS (a-tDCS) current densities on corticospinal excitability. Methods Four current intensities of 0.3, 0.7, 1.4 and 2 mA resulting in current densities (CDs) of 0.013, 0.029, 0.058 and 0.083 mA/cm2 were applied on twelve right-handed (mean age 34.5±10.32 yrs) healthy individuals in different sessions at least 48 hours apart. a-tDCS was applied continuously for 10 minute, with constant active and reference electrode sizes of 24 and 35 cm2 respectively. The corticospinal excitability of the extensor carpi radialis muscle (ECR) was measured before and immediately after the intervention and at 10, 20 and 30 minutes thereafter. Results Post hoc comparisons showed significant differences in corticospinal excitability changes for CDs of 0.013 mA/cm2 and 0.029 mA/cm2 (P = 0.003). There were no significant differences between excitability changes for the 0.013 mA/cm2 and 0.058 mA/cm2 (P = 0.080) or 0.013 mA/cm2 and 0.083 mA/cm2 (P = 0.484) conditions. Conclusion This study found that a-tDCS with a current density of 0.013 mA/cm2 induces significantly larger corticospinal excitability changes than CDs of 0.029 mA/cm2. The implication is that might help to avoid applying unwanted amount of current to the cortical areas. PMID:23991076

  6. Morphological features of the copper surface layer under sliding with high density electric current

    SciTech Connect

    Fadin, V. V.; Aleutdinova, M. I.; Rubtsov, V. Ye.; Aleutdinova, V. A.

    2015-10-27

    Conductivity and wear intensity of copper under the influence of dry friction and electric current with contact density higher 100 A/cm{sup 2} are presented. It is shown that an increase in hardness and heat outflow from a friction zone leads to the reduction of wear intensity and current contact density increase corresponding to the beginning of catastrophic wear. Structural changes, such as the formation of FeO oxide and α-Fe particles in the copper surface layer, have also been found. It is observed that a worn surface is deformed according to a viscous liquid mechanism. Such singularity is explained in terms of appearance of high-excited atomic states in deforming micro-volumes near contact spots that lead to easy stress relaxation by local plastic shears in the vicinity of stress concentrators. In common this effect allows to achieve high wear resistance.

  7. Broadband external cavity tunable quantum dot lasers with low injection current density.

    PubMed

    Lv, X Q; Jin, P; Wang, W Y; Wang, Z G

    2010-04-26

    Broadband grating-coupled external cavity laser, based on InAs/GaAs quantum dots, is achieved. The device has a wavelength tuning range from 1141.6 nm to 1251.7 nm under a low continuous-wave injection current density (458 A/cm(2)). The tunable bandwidth covers consecutively the light emissions from both the ground state and the 1st excited state of quantum dots. The effects of cavity length and antireflection facet coating on device performance are studied. It is shown that antireflection facet coating expands the tuning bandwidth up to ~150 nm, accompanied by an evident increase in threshold current density, which is attributed to the reduced interaction between the light field and the quantum dots in the active region of the device.

  8. Vibration effect on magnetization and critical current density of superconductors

    NASA Astrophysics Data System (ADS)

    Golovchanskiy, Igor A.; Pan, Alexey V.; George, Jonathan; Wells, Frederick S.; Fedoseev, Sergey A.; Rozenfeld, Anatoly

    2016-07-01

    In this work the effect of vibrations on critical current density (J c ) of superconductors has been studied. The vibrations are shown to affect J c of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency (f) and/or amplitude (A) leads to progressive reduction of J c as a function of magnetic field (B a ). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on {J}c({B}a) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending B a is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field ({B}{{irr}}) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of {B}{{irr}} for J c modeling is demonstrated.

  9. High-density matter: current status and future challenges

    NASA Astrophysics Data System (ADS)

    Stone, J. R.

    2015-05-01

    There are many fascinating processes in the Universe which we observe in more and more in detail thanks to increasingly sophisticated technology. One of the most interesting phenomena is the life cycle of stars, their birth, evolution and death. If the stars are massive enough, they end their lives in the core-collapse supernova explosion, the one of the most violent events in the Universe. As the result, the densest objects in the Universe, neutron stars and/or black holes are created. Naturally, the physical basis of these events should be understood in line with observation. The current status of our knowledge of processes in the life of stars is far from adequate for their true understanding. We show that although many models have been constructed their detailed ability to describe observations is limited or non-existent. Furthermore the general failure of all models means that we cannot tell which are heading in the right direction. A possible way forward in modeling of high-density matter is outlined, exemplified by the quark-meson-coupling model (QMC). This model has a natural explanation for the saturation of nuclear forces and depends on very few adjustable parameters, strongly constrained by the underlying physics. Latest QMC results for compact objects and finite nuclei are presented.

  10. Density effect on critical current density and flux pinning properties of polycrystalline SmFeAsO1 - xFx superconductor

    NASA Astrophysics Data System (ADS)

    Ding, Y.; Sun, Y.; Zhuang, J. C.; Cui, L. J.; Shi, Z. X.; Sumption, M. D.; Majoros, M.; Susner, M. A.; Kovacs, C. J.; Li, G. Z.; Collings, E. W.; Ren, Z. A.

    2011-12-01

    A series of polycrystalline SmFeAs1 - xOx bulks was prepared to systematically investigate the influence of sample density on flux pinning properties. Different sample densities were achieved by controlling the pelletizing pressure. The superconducting volume fraction, the critical current densities Jcm and the flux pinning force densities Fp were estimated from the magnetization measurements. Experimental results show that: (1) the superconducting volume fraction increases with the increasing of sample density; (2) the Jcm values have a similar trend except for the sample with very high density due to different connectivity and pinning mechanisms, moreover, the Jcm(B) curve develops a peak effect at approximately the same field at which the high density sample shows a kink; (3) the Fp(B) curve of the high density sample shows a low-field peak and a high-field peak at several temperatures, which can be explained by improved intergranular current, while only one peak can be observed in Fp(B) of the low density samples. Based on the scaling behaviour of flux pinning force densities, the main intragranular pinning is normal point pinning.

  11. Abrasion in pyroclastic density currents: Insights from tumbling experiments

    NASA Astrophysics Data System (ADS)

    Kueppers, Ulrich; Putz, Constanze; Spieler, Oliver; Dingwell, Donald B.

    2012-01-01

    During granular mass movements of any kind, particles may interact with one another. The degree of interaction is a function of several variables including; grain-size distribution, particle concentration, density stratification and degree of fluidisation. The impact of particle interaction is additionally influenced by the relative speed, impact angle and clast temperature. Thus, both source conditions and transport-related processes are expected to influence the flow dynamics of pyroclastic density currents and their subsequent deposition. Here, we use tumbling experiments to shed light on the susceptibility of porous clasts to abrasion. We investigated the abrasion of unaltered volcanic rocks (5.7-80 vol.% porosity) from Unzen (Japan), Bezymianny (Russia) and Santorini (Greece) volcanoes as well as one synthetic analogue material, an insulating material with the trade name Foamglas® (95 vol.% porosity). Each experiment started with angular fragments generated in a jaw crusher from larger clasts. Two experimental series were performed; on samples with narrow and broader grain-size distributions, respectively. The dry samples were subject to rotational movement at constant speed and ambient temperature in a gum rotational tumbler for durations of 15, 30, 45, 60 and 120 min. The amount of volcanic ash (particles <2 mm) generated was evaluated as a function of experimental duration and sample porosity. We term “abrasion” as the ash fraction generated during the experiments. The observed increase of “abrasion” with increasing sample porosity and experimental duration is initially non-linear but becomes linear for experiments of 30 min duration or longer. For any given sample, abrasion appears to be more effective for coarser samples and larger initial mass. The observed range of ash generated in our experiments is between 1 and 35 wt.%. We find that this amount generally increases with increasing initial clast size or increasing breadth of the initial grain

  12. Realizing life-scalable experimental pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Cronin, S. J.; Lube, G.; Breard, E.; Jones, J.; Valentine, G.; Freundt, A.; Hort, M. K.; Bursik, M. I.

    2013-12-01

    Pyroclastic Density Currents (PDCs) - the most deadly threat from volcanoes - are extremely hot, ground-hugging currents of rock fragments and gas that descend slopes at hundreds of kilometers per hour. These hostile flows are impossible to internally measure, thus volcanologists are persistently blocked in efforts to realistically forecast their internal mechanics and hazards. Attempts to fill this gap via laboratory-scale experiments continue to prove difficult, because they usually mismatch the dynamic and kinematic scaling of real-world flows by several orders of magnitude. In a multi-institutional effort, the first large-scale pyroclastic flow generator that can synthesize repeatable hot high-energy gas-particle mixture flows in safety has been commissioned in New Zealand. The final apparatus stands 15 m high, consisting of a tower/elevator system; an instrumented hopper that can hold >6000 kg (or 3.2 m3) of natural volcanic materials, which can be discharged at a range of controlled rates onto an instrumented, variably inclinable (6-25°) glass-sided chute for examining the vertical profiles of PDCs in motion. The use of rhyolitic pyroclastic material from the 1800 AD Taupo Eruption (with its natural grain-size, sorting and shape characteristics) and gas ensures natural coupling between the solids and fluid phases. PDC analogues with runout of >15 meters and flow depths of 1.5-6 meters are created by generating variably heated falling columns of natural volcanic particles (50-1300 kg/s), dispersed and aerated to controlled particle densities between 3 and 60 vol.% at the base of the elevated hopper. The descending columns rapidly generate high-velocity flows (up to 14 m/s) once impacting on the inclined channel, reproducing many features of natural flows, including segregation into dense and dilute regimes, progressive aggradational and en masse deposition of particles and the development of high internal gas-pore-pressures during flow. The PDC starting

  13. determination of current density distribution in an electron beam

    NASA Astrophysics Data System (ADS)

    Kandel, Yudhishthir Prasad

    Electron beams are useful in many applications because they can be focused down to a spot far exceeding the physical limit of focusing visible light or x-rays. Additionally, electron beams are useful in transferring concentrated amounts of energy to a very small well defined region of a target for a fixed duration. This has led to the development of both scanning electron microscopes (SEMs) and electron beam lithography. The goal of this work was to develop a general method that accurately and easily yields the best estimate of the electron current density distribution of a focused electron beam, known as point spread function (PSF). The method developed is fast, easy to use and accurate. Two specific areas of research have been addressed for PSF determination. The first is concerned with the monotonic response of EUV photoresist as a function of electron beam dose. An external metrology is used for mapping the change in thickness that is smaller than the beam spot size. The method developed in this study simultaneously gives the photo-resist thickness change as a function of electron dose and electron beam PSF. A second thrust of this research has been to develop set of PSF characterization approaches that apply to the SEM. Here a knowledge of the PSF offers many benefits including the ability to monitor and optimize SEM performance such as astigmatism control. Perhaps, even more importantly, a knowledge of the PSF combined with a series of well-defined experimental steps has led to the development of new methods for improving the resolution of SEM images through computational means rather than very costly and complex equipment modification.

  14. Interpersonal Relationships, Motivation, Engagement, and Achievement: Yields for Theory, Current Issues, and Educational Practice

    ERIC Educational Resources Information Center

    Martin, Andrew J.; Dowson, Martin

    2009-01-01

    In this review, we scope the role of interpersonal relationships in students' academic motivation, engagement, and achievement. We argue that achievement motivation theory, current issues, and educational practice can be conceptualized in relational terms. Influential theorizing, including attribution theory, expectancy-value theory, goal theory,…

  15. Transport behavior and critical current densities in MgB2 wires

    NASA Astrophysics Data System (ADS)

    Pradhan, A. K.; Feng, Y.; Zhao, Y.; Koshizuka, N.; Zhou, L.; Zhang, P. X.; Liu, X. H.; Ji, P.; Du, S. J.; Liu, C. F.

    2001-09-01

    We report on the transport and magnetization properties of MgB2 wires fabricated by a powder-in-tube (PIT) technique. Temperature and magnetic-field-dependent resistivity displays a high conductivity and upper critical field Hc2 generally observed in dense samples. The electronic mass anisotropy γ≈1.3±0.15 predicts some texturing in the wire. Our data on transition temperature TC, Hc2, and both magnetic and transport critical current density Jc indicate that MgB2 can be manufactured in a wire form using a PIT technique and required engineering Jc can be achieved on further optimization.

  16. Increasing Extracted Beam Current Density in Ion Thrusters through Plasma Potential Modification

    NASA Astrophysics Data System (ADS)

    Arthur, Neil; Foster, John

    2015-09-01

    A gridded ion thruster's maximum extractable beam current is determined by the space charge limit. The classical formulation does not take into account finite ion drift into the acceleration gap. It can be shown that extractable beam current can be increased beyond the conventional Child-Langmuir law if the ions enter the gap at a finite drift speed. In this work, ion drift in a 10 cm thruster is varied by adjusting the plasma potential relative to the potential at the extraction plane. Internal plasma potential variations are achieved using a novel approach involving biasing the magnetic cusps. Ion flow variations are assessed using simulated beam extraction in conjunction with a retarding potential analyzer. Ion beam current density changes at a given total beam voltage in full beam extraction tests are characterized as a function of induced ion drift velocity as well.

  17. High voltage and high current density vertical GaN power diodes

    SciTech Connect

    Fischer, A. J.; Dickerson, J. R.; Armstrong, A. M.; Moseley, M. W.; Crawford, M. H.; King, M. P.; Allerman, A. A.; Kaplar, R. J.; van Heukelom, M. S.; Wierer, J. J.

    2016-01-01

    We report on the realization of a GaN high voltage vertical p-n diode operating at > 3.9 kV breakdown with a specific on-resistance < 0.9 mΩ.cm2. Diodes achieved a forward current of 1 A for on-wafer, DC measurements, corresponding to a current density > 1.4 kA/cm2. An effective critical electric field of 3.9 MV/cm was estimated for the devices from analysis of the forward and reverse current-voltage characteristics. Furthermore this suggests that the fundamental limit to the GaN critical electric field is significantly greater than previously believed.

  18. High voltage and high current density vertical GaN power diodes

    DOE PAGES

    Fischer, A. J.; Dickerson, J. R.; Armstrong, A. M.; ...

    2016-01-01

    We report on the realization of a GaN high voltage vertical p-n diode operating at > 3.9 kV breakdown with a specific on-resistance < 0.9 mΩ.cm2. Diodes achieved a forward current of 1 A for on-wafer, DC measurements, corresponding to a current density > 1.4 kA/cm2. An effective critical electric field of 3.9 MV/cm was estimated for the devices from analysis of the forward and reverse current-voltage characteristics. Furthermore this suggests that the fundamental limit to the GaN critical electric field is significantly greater than previously believed.

  19. High-density lipoprotein cholesterol: current perspective for clinicians.

    PubMed

    Whayne, Thomas F

    2009-01-01

    High-density lipoproteins are regarded as ''good guys'' but not always. Situations involving high-density lipoproteins are discussed and medication results are considered. Clinicians usually consider high-density lipoprotein cholesterol. Nicotinic acid is the best available medication to elevate high-density lipoprotein cholesterol and this appears beneficial for cardiovascular risk. The major problem with nicotinic acid is that many patients do not tolerate the associated flushing. Laropiprant decreases this flushing and has an approval in Europe but not in the United States. The most potent medications for increasing high-density lipoprotein cholesterol are cholesteryl ester transfer protein inhibitors. The initial drug in this class, torcetrapib, was eliminated by excess cardiovascular problems. Two newer cholesteryl ester transfer protein inhibitors, R1658 and anacetrapib, initially appear promising. High-density lipoprotein cholesterol may play an important role in improving cardiovascular risk in the 60% of patients who do not receive cardiovascular mortality/morbidity benefit from low-density lipoproteins reduction by statins.

  20. A new wavelet transform to sparsely represent cortical current densities for EEG/MEG inverse problems.

    PubMed

    Liao, Ke; Zhu, Min; Ding, Lei

    2013-08-01

    The present study investigated the use of transform sparseness of cortical current density on human brain surface to improve electroencephalography/magnetoencephalography (EEG/MEG) inverse solutions. Transform sparseness was assessed by evaluating compressibility of cortical current densities in transform domains. To do that, a structure compression method from computer graphics was first adopted to compress cortical surface structure, either regular or irregular, into hierarchical multi-resolution meshes. Then, a new face-based wavelet method based on generated multi-resolution meshes was proposed to compress current density functions defined on cortical surfaces. Twelve cortical surface models were built by three EEG/MEG softwares and their structural compressibility was evaluated and compared by the proposed method. Monte Carlo simulations were implemented to evaluate the performance of the proposed wavelet method in compressing various cortical current density distributions as compared to other two available vertex-based wavelet methods. The present results indicate that the face-based wavelet method can achieve higher transform sparseness than vertex-based wavelet methods. Furthermore, basis functions from the face-based wavelet method have lower coherence against typical EEG and MEG measurement systems than vertex-based wavelet methods. Both high transform sparseness and low coherent measurements suggest that the proposed face-based wavelet method can improve the performance of L1-norm regularized EEG/MEG inverse solutions, which was further demonstrated in simulations and experimental setups using MEG data. Thus, this new transform on complicated cortical structure is promising to significantly advance EEG/MEG inverse source imaging technologies.

  1. Visualization of cardiac dipole using a current density map: detection of cardiac current undetectable by electrocardiography using magnetocardiography.

    PubMed

    Ikefuji, Hiroyuki; Nomura, Masahiro; Nakaya, Yutaka; Mori, Toshifumi; Kondo, Noriyasu; Ieishi, Kiyoshi; Fujimoto, Sayuri; Ito, Susumu

    2007-02-01

    A close relationship exists between electric current and the magnetic field. However, electricity and magnetism have different physical characteristics, and magnetocardiography (MCG) may provide information on cardiac current that is difficult to obtain by electrocardiography (ECG). In the present study, we investigated the issue of whether the current density map method, in which cardiac current is estimated from the magnetic gradient, facilitates the visualization of cardiac current undetectable by ECG. The subjects were 50 healthy adults (N group), 40 patients with left ventricular overloading (LVO group), 15 patients with right ventricular overloading (RVO group), 10 patients with an old inferior myocardial infarction (OMI group), and 30 patients with diabetes mellitus (DM group). MCGs were recorded with a second derivative superconducting quantum interference device (SQUID) gradiometer using liquid helium. Isopotential maps and current density maps from unipolar precordial ECG leads and MCGs, respectively, were prepared, and the cardiac electric current was examined. The current density map at the ventricular depolarization phase showed one peak of current density in the N group. However, in the OMI group, the current density map showed multiple peaks of current density areas. In the RVO group, two peaks of current densities were detected at the right superior region and left thoracic region and these two diploles appeared to be from the right and left ventricular derived cardiac currents, respectively. Moreover, there was a significant correlation between the magnitude of the current density from the right ventricle and the systolic pulmonary arterial pressure. The current density map at the ventricular repolarization phase in the N group showed only a single current source. However, abnormal current sources in the current density maps were frequently detected even in patients showing no abnormalities on isopotential maps in the LVO, DM, and OMI groups. The

  2. Effects of the current boundary conditions at the plasma-gun gap on density in SSPX

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Roman; Lodestro, L. L.; Meyer, W. H.

    2012-10-01

    The Sustained Spheromak Physics Experiment (SSPX) was a toroidal magnetic-confinement device without toroidal magnetic-field coils or a central transformer but which generated core-plasma currents by dynamo processes driven by coaxial plasma-gun injection into a flux-conserving vessel. Record electron temperatures in a spheromak (Te˜500eV) were achieved, and final results of the SSPX program were reported in [1]. Plasma density, which depended strongly on wall conditions, was an important parameter in SSPX. It was observed that density rises with Igun and that confinement improved as the density was lowered. Shortly after the last experiments, a new feature was added to the Corsica code's solver used to reconstruct SSPX equilibria. Motivated by n=0 fields observed in NIMROD simulations of SSPX, an insulating boundary condition was implemented at the plasma-gun gap. Using this option we will perform new reconstructions of SSPX equilibria and look for correlations between the location of the separatrix (which moves up the gun wall and onto the insulating gap as Igun increases) and plasma density and magnetic-flux amplification [2].[4pt] [1] H. S. McLean, APS, DPP, Dallas, TX, 2008.[0pt] [2] E. B. Hooper et al., Nucl. Fusion 47, 1064 (2007).

  3. Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs.

    PubMed

    Brady, Gerald J; Way, Austin J; Safron, Nathaniel S; Evensen, Harold T; Gopalan, Padma; Arnold, Michael S

    2016-09-01

    Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G 0 = 4e (2)/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G 0. The consequence has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. We report quasi-ballistic CNT array FETs at a density of 47 CNTs μm(-1), fabricated through a combination of CNT purification, solution-based assembly, and CNT treatment. The conductance is as high as 0.46 G 0 per CNT. In parallel, the conductance of the arrays reaches 1.7 mS μm(-1), which is seven times higher than the previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density is as high as 900 μA μm(-1) and is similar to or exceeds that of Si FETs when compared at and equivalent gate oxide thickness and at the same off-state current density. The on-state current density exceeds that of GaAs FETs as well. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies.

  4. Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs

    PubMed Central

    Brady, Gerald J.; Way, Austin J.; Safron, Nathaniel S.; Evensen, Harold T.; Gopalan, Padma; Arnold, Michael S.

    2016-01-01

    Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G0 = 4e2/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G0. The consequence has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. We report quasi-ballistic CNT array FETs at a density of 47 CNTs μm−1, fabricated through a combination of CNT purification, solution-based assembly, and CNT treatment. The conductance is as high as 0.46 G0 per CNT. In parallel, the conductance of the arrays reaches 1.7 mS μm−1, which is seven times higher than the previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density is as high as 900 μA μm−1 and is similar to or exceeds that of Si FETs when compared at and equivalent gate oxide thickness and at the same off-state current density. The on-state current density exceeds that of GaAs FETs as well. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies. PMID:27617293

  5. Studies in High Current Density Ion Sources for Heavy Ion Fusion Applications

    SciTech Connect

    Chacon-Golcher, Edwin

    2002-06-01

    This dissertation develops diverse research on small (diameter ~ few mm), high current density (J ~ several tens of mA/cm2) heavy ion sources. The research has been developed in the context of a programmatic interest within the Heavy Ion Fusion (HIF) Program to explore alternative architectures in the beam injection systems that use the merging of small, bright beams. An ion gun was designed and built for these experiments. Results of average current density yield () at different operating conditions are presented for K+ and Cs+ contact ionization sources and potassium aluminum silicate sources. Maximum values for a K+ beam of ~90 mA/cm2 were observed in 2.3 μs pulses. Measurements of beam intensity profiles and emittances are included. Measurements of neutral particle desorption are presented at different operating conditions which lead to a better understanding of the underlying atomic diffusion processes that determine the lifetime of the emitter. Estimates of diffusion times consistent with measurements are presented, as well as estimates of maximum repetition rates achievable. Diverse studies performed on the composition and preparation of alkali aluminosilicate ion sources are also presented. In addition, this work includes preliminary work carried out exploring the viability of an argon plasma ion source and a bismuth metal vapor vacuum arc (MEVVA) ion source. For the former ion source, fast rise-times (~ 1 μs), high current densities (~ 100 mA/cm+) and low operating pressures (< 2 mtorr) were verified. For the latter, high but acceptable levels of beam emittance were measured (εn ≤ 0.006 π· mm · mrad) although measured currents differed from the desired ones (I ~ 5mA) by about a factor of 10.

  6. Projected current density comparison in tDCS block and smooth FE modeling.

    PubMed

    Indahlastari, Aprinda; Chauhan, Munish; Sadleir, Rosalind J

    2016-08-01

    Current density distribution and projected current density calculation following transcranial direct current stimulation (tDCS) forward model in a human head were compared between two modeling pipelines: block and smooth. Block model was directly constructed from MRI voxel resolution and simulated in C. Smooth models underwent a boundary smoothing process by applying recursive Gaussian filters and simulated in COMSOL. Three smoothing levels were added to determine their effects on current density distribution compared to block models. Median current density percentage differences were calculated in anterior superior temporal gyrus (ASTG), hippocampus (HIP), inferior frontal gyrus (IFG), occipital lobes (OCC) and precentral gyrus (PRC) and normalized against a baseline value. A maximum of + 20% difference in median current density was found for three standard electrode montages: F3-RS, T7-T8 and Cz-Oz. Furthermore, median current density percentage differences in each montage target brain structures were found to be within + 7%. Higher levels of smoothing increased median current density percentage differences in T7-T8 and Cz-Oz target structures. However, while demonstrating similar trends in each montage, additional smoothing levels showed no clear relationship between their smoothing effects and calculated median current density in the five cortical structures. Finally, relative L2 error in reconstructed projected current density was found to be 17% and 21% for block and smooth pipelines, respectively. Overall, a block model workflow may be a more attractive alternative for simulating tDCS stimulation because involves a shorter modeling time and independence from commercial modeling platforms.

  7. Method for determining transport critical current densities and flux penetration depth in bulk superconductors

    NASA Technical Reports Server (NTRS)

    Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)

    1992-01-01

    A contact-less method for determining transport critical current density and flux penetration depth in bulk superconductor material. A compressor having a hollow interior and a plunger for selectively reducing the free space area for distribution of the magnetic flux therein are formed of superconductor material. Analytical relationships, based upon the critical state model, Maxwell's equations and geometrical relationships define transport critical current density and flux penetration depth in terms of the initial trapped magnetic flux density and the ratio between initial and final magnetic flux densities whereby data may be reliably determined by means of the simple test apparatus for evaluating the current density and flux penetration depth.

  8. Quasi-1D van der Waals materials as high current-density local interconnects (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Stolyarov, Maxim; Aytan, Ece; Bloodgood, Matthew; Salguero, Tina T.; Balandin, Alexander A.

    2016-09-01

    The continuous downscaling of interconnect dimensions in combination with the introduction of low-k dielectrics has increased the number of heat dissipation, integration and reliability challenges in modern electronics. As a result, there is a strong need for new materials that have high current-carrying capacity for applications as nanoscale interconnects. In this presentation, we show that quasi-one-dimensional (1D) van der Waals metals such as TaSe3 have excellent breakdown current density exceeding that of 5 MA/cm2. This value is above that currently achievable in conventional copper or aluminum wires. The quasi-1D van der Waals materials are characterized by strong bonds along one dimension and weak van der Waals bonds along two other dimensions. The material for this study was grown by the chemical vapor transport (CVT) method. Both mechanical and chemical exfoliation methods were used to fabricate nanowires with lateral dimensions below 100 nm. The dimensions of the quasi-1D nanowires were verified with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The metal (Ti/Au) contacts for the electrical characterization were deposited using electron beam evaporation (EBE). The measurements were conducted on a number of prototype interconnects with multiple electric contacts to ensure reproducibility. The obtained results suggest that quasi-1D van der Waals metals present a feasible alternative to conventional copper interconnects in terms of the current-carrying capacity and the breakdown current-density. This work was supported, in part, by the SRC and DARPA through STARnet Center for Function Accelerated nanoMaterial Engineering (FAME).

  9. Current Densities in speed analyzer with different symmetries

    SciTech Connect

    Valdeblanquez, E.

    2006-12-04

    A comparative analysis of the currents in speed analyzer of speeds is made with different symmetries. Three kinds of symmetries are considered; plane, cylindrical and spherical. The analyzers considered are formed by threes electrodes, the selector grid, the discriminator and the collector. The selector grid has a negative potential and for the coulombian effect the space charge is formed with the ionic thermal bath. Using kinetic theory a strongly non linear differential equation is obtained which is solved by numerical calculation.

  10. Peltier effect in multilayered nanopillars under high density charge current

    NASA Astrophysics Data System (ADS)

    Gravier, L.; Fukushima, A.; Kubota, H.; Yamamoto, A.; Yuasa, S.

    2006-12-01

    From the basic equations of thermoelectricity, we model the thermal regimes that develop in multilayered nanopillar elements experiencing continuous charge currents. The energy conservation principle was applied to all layer-layer and layer-electrode junctions. The obtained set of equations was solved to derive the temperature of each junction. The contribution of the Peltier effect is included in an effective resistance. This model gives satisfactory fits to experimental data obtained on a series of reference nanopillar elements.

  11. Phase dynamics of low critical current density YBCO Josephson junctions

    NASA Astrophysics Data System (ADS)

    Massarotti, D.; Stornaiuolo, D.; Rotoli, G.; Carillo, F.; Galletti, L.; Longobardi, L.; Beltram, F.; Tafuri, F.

    2014-08-01

    High critical temperature superconductors (HTS) based devices can have impact in the study of the phase dynamics of Josephson junctions (JJs) thanks to the wide range of junction parameters they offer and to their unconventional properties. Measurements of current-voltage characteristics and of switching current distributions constitute a direct way to classify different regimes of the phase dynamics and of the transport, also in nontrivial case of the moderately damped regime (MDR). MDR is going to be more and more common in JJs with advances in nanopatterning superconductors and synthesizing novel hybrid systems. Distinctive signatures of macroscopic quantum tunneling and of thermal activation in presence of different tunable levels of dissipation have been detected in YBCO grain boundary JJs. Experimental data are supported by Monte Carlo simulations of the phase dynamics, in a wide range of temperatures and dissipation levels. This allows us to quantify dissipation in the MDR and partially reconstruct a phase diagram as guideline for a wide range of moderately damped systems.

  12. Low-current-density LED-pumped Nd:YAG laser using a solid cylindrical reflector

    NASA Technical Reports Server (NTRS)

    Farmer, G. I.; Kiang, Y. C.

    1974-01-01

    The dynamic behavior of Nd:YAG lasers is theoretically analyzed. In experiments, an array of twenty GaAlAs diodes was used as the pumping light source for a Nd:YAG laser. An index-matching glass half-cylinder was used instead of the conventional hollow metal reflector. The refractive index of the half-cylinder was 1.8, which matched the refractive index of the Nd:YAG rod. A maximum CW output power of 27 mW at a current density of 207 A/sq cm was achieved using this glass half-cylinder, while 6.7 mW were obtained when a hollow metal reflector was used.

  13. Sparse cortical current density imaging in motor potentials induced by finger movement

    NASA Astrophysics Data System (ADS)

    Ding, Lei; Ni, Ying; Sweeney, John; He, Bin

    2011-06-01

    Predominant components in electro- or magneto-encephalography (EEG/MEG) are scalp projections of synchronized neuronal electrical activity distributed over cortical structures. Reconstruction of cortical sources underlying EEG/MEG can thus be achieved with the use of the cortical current density (CCD) model. We have developed a sparse electromagnetic source imaging method based on the CCD model, named as the variation-based cortical current density (VB-SCCD) algorithm, and have shown that it has much enhanced performance in reconstructing extended cortical sources in simulations (Ding 2009 Phys. Med. Biol. 54 2683-97). The present study aims to evaluate the performance of VB-SCCD, for the first time, using experimental data obtained from six participants. The results indicate that the VB-SCCD algorithm is able to successfully reveal spatially distributed cortical sources behind motor potentials induced by visually cued repetitive finger movements, and their dynamic patterns, with millisecond resolution. These findings of motor sources and cortical systems are supported by the physiological knowledge of motor control and evidence from various neuroimaging studies with similar experiments. Furthermore, our present results indicate the improvement of cortical source resolvability of VB-SCCD, as compared with two other classical algorithms. The proposed solver embedded in VB-SCCD is able to handle large-scale computational problems, which makes the use of high-density CCD models possible and, thus, reduces model misspecifications. The present results suggest that VB-SCCD provides high resolution source reconstruction capability and is a promising tool for studying complicated dynamic systems of brain activity for basic neuroscience and clinical neuropsychiatric research.

  14. Near-surface Density Currents Observed in the Southeast Pacific Stratocumulus-topped Marine Boundary Layer

    SciTech Connect

    Wilbanks, Matt C.; Yuter, S. E.; de Szoeke, S.; Brewer, W. A.; Miller, Matthew A.; Hall, Andrew M.; Burleyson, Casey D.

    2015-09-01

    Density currents (i.e. cold pools or outflows) beneath marine stratocumulus clouds are characterized using a 30-d data set of ship-based observations obtained during the 2008 Variability of American Monsoon Systems (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in the southeast Pacific. An objective method identifies 71 density current fronts using an air density criterion and isolates each density current’s core (peak density) and tail (dissipating) zone. Compared to front and core zones, most density current tails exhibited weaker density gradients and wind anomalies elongated about the axis of the mean wind. The mean cloud-level advection relative to the surface layer wind (1.9 m s-1) nearly matches the mean density current propagation speed (1.8 m s-1). The similarity in speeds allows drizzle cells to deposit tails in their wakes. Based on high-resolution scanning Doppler lidar data, prefrontal updrafts had a mean intensity of 0.91 m s-1, reached an average altitude of 800 m, and were often surmounted by low-lying shelf clouds not connected to the overlying stratocumulus cloud. Nearly 90% of density currents were identified when C-band radar estimated 30-km diameter areal average rain rates exceeded 1 mm d-1. Rather than peaking when rain rates are highest overnight, density current occurrence peaks between 0600 and 0800 local solar time when enhanced local drizzle co-occurs with shallow subcloud dry and stable layers. The dry layers may contribute to density current formation by enhancing subcloud evaporation of drizzle. Density currents preferentially occur in regions of open cells but also occur in regions of closed cells.

  15. Flux avalanche in a superconducting film with non-uniform critical current density

    NASA Astrophysics Data System (ADS)

    Lu, Yurong; Jing, Ze; Yong, Huadong; Zhou, Youhe

    2016-10-01

    The flux avalanche in type-II superconducting thin film is numerically simulated in this paper. We mainly consider the effect of non-uniform critical current density on the thermomagnetic stability. The nonlinear electromagnetic constitutive relation of the superconductor is adopted. Then, Maxwell's equations and heat diffusion equation are numerically solved by the fast Fourier transform technique. We find that the non-uniform critical current density can remarkably affect the behaviour of the flux avalanche. The external magnetic field ramp rate and the environmental temperature have been taken into account. The results are compared with a film with uniform critical current density. The flux avalanche first appears at the interface where the critical current density is discontinuous. Under the same environmental temperature or magnetic field, the flux avalanche occurs more easily for the film with the non-uniform critical current density. The avalanche structure is a finger-like pattern rather than a dendritic structure at low environmental temperatures.

  16. Non-perturbative calculation of molecular magnetic properties within current-density functional theory.

    PubMed

    Tellgren, E I; Teale, A M; Furness, J W; Lange, K K; Ekström, U; Helgaker, T

    2014-01-21

    We present a novel implementation of Kohn-Sham density-functional theory utilizing London atomic orbitals as basis functions. External magnetic fields are treated non-perturbatively, which enable the study of both magnetic response properties and the effects of strong fields, using either standard density functionals or current-density functionals-the implementation is the first fully self-consistent implementation of the latter for molecules. Pilot applications are presented for the finite-field calculation of molecular magnetizabilities, hypermagnetizabilities, and nuclear magnetic resonance shielding constants, focusing on the impact of current-density functionals on the accuracy of the results. Existing current-density functionals based on the gauge-invariant vorticity are tested and found to be sensitive to numerical details of their implementation. Furthermore, when appropriately regularized, the resulting magnetic properties show no improvement over standard density-functional results. An advantage of the present implementation is the ability to apply density-functional theory to molecules in very strong magnetic fields, where the perturbative approach breaks down. Comparison with high accuracy full-configuration-interaction results show that the inadequacies of current-density approximations are exacerbated with increasing magnetic field strength. Standard density-functionals remain well behaved but fail to deliver high accuracy. The need for improved current-dependent density-functionals, and how they may be tested using the presented implementation, is discussed in light of our findings.

  17. 3D Stationary electric current density in a spherical tumor treated with low direct current: an analytical solution.

    PubMed

    Jiménez, Rolando Placeres; Pupo, Ana Elisa Bergues; Cabrales, Jesús Manuel Bergues; Joa, Javier Antonio González; Cabrales, Luis Enrique Bergues; Nava, Juan José Godina; Aguilera, Andrés Ramírez; Mateus, Miguel Angel O'Farril; Jarque, Manuel Verdecia; Brooks, Soraida Candida Acosta

    2011-02-01

    Electrotherapy with direct current delivered through implanted electrodes is used for local control of solid tumors in both preclinical and clinical studies. The aim of this research is to develop a solution method for obtaining a three-dimensional analytical expression for potential and electric current density as functions of direct electric current intensity, differences in conductivities between the tumor and the surrounding healthy tissue, and length, number and polarity of electrodes. The influence of these parameters on electric current density in both media is analyzed. The results show that the electric current density in the tumor is higher than that in the surrounding healthy tissue for any value of these parameters. The conclusion is that the solution method presented in this study is of practical interest because it provides, in a few minutes, a convenient way to visualize in 3D the electric current densities generated by a radial electrode array by means of the adequate selection of direct current intensity, length, number, and polarity of electrodes, and the difference in conductivity between the solid tumor and its surrounding healthy tissue.

  18. Complexities of determining the Field-Aligned current density from LEO satellites.

    NASA Astrophysics Data System (ADS)

    Gjerloev, J. W.; Friel, M. M.; Ohtani, S.; Muhleisen, M.; Gjerloev, A. W.; Martin, P.; Barnes, R. J.

    2015-12-01

    We show results from a study of the field-aligned currents (FAC) as derived from SWARM magnetic field perturbations. We calculate the FAC density using four different techniques and explain why they provide different results. Theoretical work, simulations and data are used to show that widely used techniques can provide current density estimates with errors of 1000%. These errors can be explained by spatial gradients in the currents and temporal variability of the currents as well as a breakdown of other fundamental assumptions. We apply the techniques to auroral crossings with THEMIS ASI coverage and use the SWARM magnetic field observations to calculate the current density. Finally, we show how to estimate the errors in the current density calculations.

  19. Relationship of dislocation density of silicon to solar cell current loss at low temperature.

    NASA Technical Reports Server (NTRS)

    Mandelkorn, J.; Baraona, C. R.; Lamneck, J. H., Jr.

    1972-01-01

    Large decreases in short circuit current of silicon solar cells have been reported to occur as temperature is decreased below -60 C. Experimental results are presented which relate high dislocation density of the silicon bulk material of cells to the large current loss effect. These results reveal a direct relationship between low bulk dislocation density and low current loss at low temperature. Oxygen content does not appear to play a significant role in the low temperature-large current loss effect, since some Czochralski cells did not suffer from this effect whereas some float-zone cells did. Other float-zone silicon cells had only medium current losses at low temperature despite their high bulk dislocation density. It appears that use of low-dislocation-density silicon can eliminate the current loss problem in low temperature cell operation.

  20. Estimation of current density distribution of PAFC by analysis of cell exhaust gas

    SciTech Connect

    Kato, S.; Seya, A.; Asano, A.

    1996-12-31

    To estimate distributions of Current densities, voltages, gas concentrations, etc., in phosphoric acid fuel cell (PAFC) stacks, is very important for getting fuel cells with higher quality. In this work, we leave developed a numerical simulation tool to map out the distribution in a PAFC stack. And especially to Study Current density distribution in the reaction area of the cell, we analyzed gas composition in several positions inside a gas outlet manifold of the PAFC stack. Comparing these measured data with calculated data, the current density distribution in a cell plane calculated by the simulation, was certified.

  1. Method for Determining Local Current Density in 2G HTS Tapes

    NASA Astrophysics Data System (ADS)

    Bludova, A. I.

    Practically important problem is to determine the density and direction of 2G HTS induced currents at each point on the tape in order to examine its local deviations. This problem is resolved indirectly by spatial measurement of generated magnetic field with a scanning Hall sensor at a given height above the tape surface. Current density is subsequently determined by the Biot-Savart law inversion in Fourier domain. Tikhonov regularization is used in order to increase precision. Method is verified with the model current density reconstruction. Optimal calculation parameters and resulting precision are described.

  2. High critical current density and enhanced irreversibility field in superconducting MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Eom, C. B.; Lee, M. K.; Choi, J. H.; Belenky, L. J.; Song, X.; Cooley, L. D.; Naus, M. T.; Patnaik, S.; Jiang, J.; Rikel, M.; Polyanskii, A.; Gurevich, A.; Cai, X. Y.; Bu, S. D.; Babcock, S. E.; Hellstrom, E. E.; Larbalestier, D. C.; Rogado, N.; Regan, K. A.; Hayward, M. A.; He, T.; Slusky, J. S.; Inumaru, K.; Haas, M. K.; Cava, R. J.

    2001-05-01

    The discovery of superconductivity at 39K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7T at liquid helium temperature (4.2K), significantly lower than about 10T for Nb-Ti (ref. 6) and ~20T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2K greater than 14T. In addition, very high critical current densities at 4.2K are achieved: 1MAcm-2 at 1T and 105Acm-2 at 10T. These results demonstrate that MgB2 has potential for high-field superconducting applications.

  3. Relationship of dislocation density of silicon to solar cell current loss at low temperature

    NASA Technical Reports Server (NTRS)

    Mandelkorn, J.; Baraona, C. R.; Lamneck, J. H., Jr.

    1972-01-01

    Large decreases in short circuit current of silicon solar cells have been reported to occur as temperature is decreased below -60 C. Experimental results are presented which relate high dislocation density of the silicon bulk material of cells to the large current loss effect. Solar cells were made by the same processes from a variety of silicon materials, namely low-dislocation-density, high-dislocation-density float-zone, and Czochralski silicon. All cells were etched in a manner which revealed the dislocation density of the cell bulk silicon. It was found that every cell made from any of the various low-dislocation starting materials obtained from three suppliers still had a low-dislocation bulk after cell processing, and that all such cells belonged to category good. Cells made from float-zone materials showed high dislocation densities in their bulk and either fell into category poor, or had intermediate losses of short-circuit current at low temperature.

  4. The Effect of Current Density on CNx Crystal Grain Growth in Electrochemical Deposition

    NASA Astrophysics Data System (ADS)

    Yu, Wei-Feng; Cao, Rong-Gen; Tian, Yu; Wang, Jian-Zhong; Ning, Xi-Jing

    2011-02-01

    The effect of charge current density on the growth of CNx films by electrolysis of a methanol-urea solution is investigated experimentally. It is seen that the C-C3N4 phase grains in the films are about 200-300 nm for a density of 55 mA/cm2 and dendrite growth takes place with grains as large as 7 μm formed when density is about 70 mA/cm2.

  5. Characterizing a December 2005 density current event in the Chicago River, Chicago, Illinois

    USGS Publications Warehouse

    Garcia, C.M.; Jackson, P.R.; Oberg, K.A.; Johnson, K.K.; Garcia, M.H.

    2007-01-01

    During the winter months, the Chicago River in Chicago, Illinois is subject to bi-directional flows, and density currents are thought to be responsible for these flow variations. This paper presents detailed field measurements using three acoustic Doppler current profiler instruments and simultaneous water-quality measurements made during December 2005. Observations indicate that the formation of density currents within the Chicago River and density differences are mostly due to salinity differences between the North Branch and the main stem of the Chicago River, whereas temperature difference does not appreciably affect the creation of density currents. Sources of higher water temperature, conductivity, and salinity values should be addressed in future studies. ?? 2007 ASCE.

  6. 3D current source density imaging based on acoustoelectric effect: a simulation study using unipolar pulses

    PubMed Central

    Yang, Renhuan; Li, Xu; Liu, Jun; He, Bin

    2011-01-01

    It is of importance to image electrical activity and properties of biological tissues. Recently hybrid imaging modality combing ultrasound scanning and source imaging through the acousto-electric (AE) effect has generated considerable interest. Such modality has the potential to provide high spatial resolution current density imaging by utilizing the pressure induced AE resistivity change confined at the ultrasound focus. In this study, we investigate a novel 3-dimensional (3D) ultrasound current source density imaging (UCSDI) approach using unipolar ultrasound pulses. Utilizing specially designed unipolar ultrasound pulses and by combining AE signals associated to the local resistivity changes at the focusing point, we are able to reconstruct the 3D current density distribution with the boundary voltage measurements obtained while performing a 3D ultrasound scan. We have shown in computer simulation that using the present method, it is feasible to image with high spatial resolution an arbitrary 3D current density distribution in an inhomogeneous conductive media. PMID:21628774

  7. Anodic Oxidation of Carbon Steel at High Current Densities and Investigation of Its Corrosion Behavior

    NASA Astrophysics Data System (ADS)

    Fattah-Alhosseini, Arash; Khan, Hamid Yazdani

    2017-02-01

    This work aims at studying the influence of high current densities on the anodization of carbon steel. Anodic protective coatings were prepared on carbon steel at current densities of 100, 125, and 150 A/dm2 followed by a final heat treatment. Coatings microstructures and morphologies were analyzed using X-ray diffraction (XRD) and scanning electron microscope (SEM). The corrosion resistance of the uncoated carbon steel substrate and the anodic coatings were evaluated in 3.5 wt pct NaCl solution through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The results showed that the anodic oxide coatings which were prepared at higher current densities had thicker coatings as a result of a higher anodic forming voltage. Therefore, the anodized coatings showed better anti-corrosion properties compared to those obtained at lower current densities and the base metal.

  8. The increase of the spin-transfer torque threshold current density in coupled vortex domain walls.

    PubMed

    Lepadatu, S; Mihai, A P; Claydon, J S; Maccherozzi, F; Dhesi, S S; Kinane, C J; Langridge, S; Marrows, C H

    2012-01-18

    We have studied the dependence on the domain wall structure of the spin-transfer torque current density threshold for the onset of wall motion in curved, Gd-doped Ni(80)Fe(20) nanowires with no artificial pinning potentials. For single vortex domain walls, for both 10% and 1% Gd-doping concentrations, the threshold current density is inversely proportional to the wire width and significantly lower compared to the threshold current density measured for transverse domain walls. On the other hand for high Gd concentrations and large wire widths, double vortex domain walls are formed which require an increase in the threshold current density compared to single vortex domain walls at the same wire width. We suggest that this is due to the coupling of the vortex cores, which are of opposite chirality, and hence will be acted on by opposing forces arising through the spin-transfer torque effect.

  9. Influence of electropolishing current densities on sulfur generation at niobium surface

    NASA Astrophysics Data System (ADS)

    Tyagi, P. V.; Nishiwaki, M.; Noguchi, T.; Sawabe, M.; Saeki, T.; Hayano, H.; Kato, S.

    2013-11-01

    We report the effect of different current densities on sulfur generation at Nb surface in the electropolishing (EP) with aged electrolyte. In this regard, we conducted a series of electropolishing (EP) experiments in aged EP electrolyte with high (≈50 mA/cm2) and low (≈30 mA/cm2) current densities on Nb surfaces. The experiments were carried out both for laboratory coupons and a real Nb single cell cavity with six witness samples located at three typical positions (equator, iris and beam pipe). Sample's surfaces were investigated by XPS (X-ray photoelectron spectroscopy), SEM (scanning electron microscope) and EDX (energy dispersive X-ray spectroscopy). The surface analysis showed that the EP with a high current density produced a huge amount of sulfate/sulfite particles at Nb surface whereas the EP with a low current density was very helpful to mitigate sulfate/sulfite at Nb surface in both the experiments.

  10. Spatially resolved charge-state and current-density distributions at the extraction of an electron cyclotron resonance ion source

    SciTech Connect

    Panitzsch, Lauri; Peleikis, Thies; Stalder, Michael; Wimmer-Schweingruber, Robert F.

    2011-09-15

    In this paper we present our measurements of charge-state and current-density distributions performed in very close vicinity (15 mm) of the extraction of our hexapole geometry electron cyclotron resonance ion source. We achieved a relatively high spatial resolution reducing the aperture of our 3D-movable extraction (puller) electrode to a diameter of only 0.5 mm. Thus, we are able to limit the source of the extracted ion beam to a very small region of the plasma electrode's hole (O = 4 mm) and therefore to a very small region of the neutral plasma sheath. The information about the charge-state distribution and the current density in the plane of the plasma electrode at each particular position is conserved in the ion beam. We determined the total current density distribution at a fixed coaxial distance of only 15 mm to the plasma electrode by remotely moving the small-aperture puller electrode which contained a dedicated Faraday cup (FC) across the aperture of the plasma electrode. In a second measurement we removed the FC and recorded m/q-spectra for the different positions using a sector magnet. From our results we can deduce that different ion charge-states can be grouped into bloated triangles of different sizes and same orientation at the extraction with the current density peaking at centre. This confirms observations from other groups based on simulations and emittance measurements. We present our measurements in detail and discuss possible systematic errors.

  11. Critical Current Densities for the High Temperature Ceramic Superconductors YBa2Cu3O7 and Bi2Sr2Ca2Cu3O(10 + delta)

    DTIC Science & Technology

    1989-09-01

    in the usual four-probe fashion with a necked determine the entire superconducting /normal phase down section to achieve high current densities. The...intrinsic power dissipated in the sample (and at the current intragrain critical current is greater than 104 A!cm 2 contacts) does not cause measurable...measurements made on the same samples The pulse height, measured across a known series agree with the intrinsic intragrain critical currents resistor, is

  12. Particle pressure and current density in the magnetosphere of Saturn: Origin of the Saturnian ring current

    NASA Astrophysics Data System (ADS)

    Sergis, N.; Krimigis, S. M.; Roelof, E. C.; Mitchell, D. G.; Rymer, A. M.; Arridge, C. S.; Krupp, N.; Thomsen, M. F.; Hamilton, D. C.; McAndrews, H. J.; Coates, A. J.; Wilson, R. J.; Dougherty, M. K.; Young, D. T.

    2009-12-01

    We report initial results on the distribution of the thermal plasma, energetic particle and magnetic field pressure in the equatorial magnetosphere, as measured by the Magnetospheric Imaging Instrument (MIMI), Cassini Plasma Spectrometer (CAPS) and the flux gate magnetometer (MAG) onboard the Cassini spacecraft, currently orbiting Saturn. Data were obtained during 11 passes from September 2005 to May 2006, when the spacecraft was particularly close (±1 Rs) to the nominal magnetic equator in the range 6 to 15 RS. The radial gradient of the total pressure is compared to the inertial body force in order to determine their relative contribution to the Saturnian ring current, and an average radial profile of the azimuthal current intensity is presented. The results can be summarized as follows: (1) The suprathermal (> 3 keV) pressure contribution to the total particle pressure becomes significant outside 8-9 Rs, exceeding 50% for r between 12 and 15 Rs. (2) The plasma beta (particle pressure/magnetic pressure) remains above 1 outside 8 RS, reaching ~3 to ~10 between 11 and 14 Rs. (3) The comparison between the inertial body force and the radial pressure gradient shows that both terms are close at 9-10 Rs, with the pressure gradient becoming dominant outside of 11 Rs. (4) The azimuthal ring current intensity develops a maximum region between approximately 8 and 12 Rs, reaching values of 100-150 pA/m^2. Outside this region, it drops with radial distance faster than the 1/r dependence that a disk current model would suggest.

  13. Direct in Situ Measurements of Current Density Variations in the Ionosphere by Using the Current Density Probe Rogowski Coil Onboard Sych 1M Satellite

    NASA Astrophysics Data System (ADS)

    Krasnoselskikh, V.; Dudok de Wit, T.; Pincon, J.; Lefeuvre, F.; Korepanov, V.; Deferaudy, H.; Chabassiere, M.; Fergeau, P.; Seran, H.; Schekotov, A.; Woolliscroft, L.; Balikhin, M.; Walker, S.; Prado, J.; Kryuchkov, E.

    2006-12-01

    We present the results of the first direct in situ measurements of current density variations to ion and electron whistler waves in the low latitude ionosphere onboard the Ukrainian Sych 1M satellite, in the frame of Variant experiment. These measurements were based on measurements from the Rogowski coil sensor of the Variant experiment onboard the Ukrainian Sych 1M satellite. This instrument, developed at LPCE, Orleans, France, consists of a toroidal coil with a high permeability core and is dedicated to measurements of the variations of the current component perpendicular to the torus. A more detailed description of the principle of measurement and instrument operation can be found in [1, 2]. The scientific objective of the experiment was to study current density variations in the different regions of the upper ionosphere. Due to a technical failure of the third stage of the launcher, only a limited amount of short duration measurements could occasionally be performed in different regions of the ionosphere. In addition to this, the electromagnetic cleanliness of the satellite was far from perfect, causing the measurements to be very noisy. Special care had to be taken to denoise the data of all instruments using multiscale techniques before any interpretation could be carried out. We were eventually able to find simultaneous occurrences of whistlers in the electric and magnetic field data and in current density data, in a frequency band ranging from several tens of Hz up to approximately 1 kHz. The upper limit was given by the cut off frequency of the preamplifier (400 Hz) and the lower limit by the high noise level in the ELF frequency band. The comparison of electromagnetic and current density data associated with the whistlers provides proof of the concepts and techniques used and validates the use of the Rogowski coil for current density variations measurements. 1. Krasnoselskikh, V. V., Natanzon, A. M., Reznikov, A. E., Schyokotov, A. Yu., Klimov, S. I

  14. Wall current probe: A non-invasive in situ plasma diagnostic for space and time resolved current density distribution measurement

    SciTech Connect

    Baude, R.; Gaboriau, F.; Hagelaar, G. J. M.

    2013-08-15

    In the context of low temperature plasma research, we propose a wall current probe to determine the local charged particle fluxes flowing to the chamber walls. This non-intrusive planar probe consists of an array of electrode elements which can be individually biased and for which the current can be measured separately. We detail the probe properties and present the ability of the diagnostic to be used as a space and time resolved measurement of the ion and electron current density at the chamber walls. This diagnostic will be relevant to study the electron transport in magnetized low-pressure plasmas.

  15. Wall current probe: a non-invasive in situ plasma diagnostic for space and time resolved current density distribution measurement.

    PubMed

    Baude, R; Gaboriau, F; Hagelaar, G J M

    2013-08-01

    In the context of low temperature plasma research, we propose a wall current probe to determine the local charged particle fluxes flowing to the chamber walls. This non-intrusive planar probe consists of an array of electrode elements which can be individually biased and for which the current can be measured separately. We detail the probe properties and present the ability of the diagnostic to be used as a space and time resolved measurement of the ion and electron current density at the chamber walls. This diagnostic will be relevant to study the electron transport in magnetized low-pressure plasmas.

  16. Interaction of pyroclastic density currents with human settlements: Evidence from ancient Pompeii

    NASA Astrophysics Data System (ADS)

    Gurioli, Lucia; Pareschi, M. Teresa; Zanella, Elena; Lanza, Roberto; Deluca, Enrico; Bisson, Marina

    2005-06-01

    Integrating field observations and rock-magnetic measurements, we report how a turbulent pyroclastic density current interacted with and moved through an urban area. The data are from the most energetic, turbulent pyroclastic density current of the A.D. 79 eruption of Vesuvius, Italy, which partially destroyed the Roman city of Pompeii. Our results show that the urban fabric was able to divide the lower portion of the current into several streams that followed the city walls and the intracity roads. Vortices, revealed by upstream particle orientations and decreases in deposit temperature, formed downflow of obstacles or inside cavities. Although these perturbations affected only the lower part of the current and were localized, they could represent, in certain cases, cooler zones within which chances of human survival are increased. Our integrated field data for pyroclastic density current temperature and flow direction, collected for the first time across an urban environment, enable verification of coupled thermodynamic numerical models and their hazard simulation abilities.

  17. Effect of an axial magnetic field and arc current on the anode current density in diffuse vacuum arcs

    NASA Astrophysics Data System (ADS)

    Ma, Hui; Geng, Yingsan; Liu, Zhiyuan; Wang, Jianhua; Wang, Zhenxing; Zhang, Zaiqin

    2016-09-01

    The objective of this paper is to measure the effect of an axial magnetic field (AMF) BAMF and arc current on the anode current density in diffuse vacuum arcs. The experimental geometry included a split anode and a butt-type cathode, both with a diameter of 60 mm. The anode surface was divided into a central area and three symmetrically disposed peripheral annular areas. The central area of the split anode had a diameter of 20 mm. The contact material was CuCr25 (25% Cr). The arc current IARC ranged from 4 to 14 kA (rms) at 50 Hz. The opening velocity was 2.4 m/s. The currents of the four areas on the anode contact were measured using four Rogowski coils situated outside the vacuum chamber. An external uniform AMF BAMF ranging from 0 to 110 mT was applied during the experiment. The observed arc modes were recorded by a high-speed charge-coupled device video camera. The experimental results quantitatively reveal that the current density distribution on the anode surface in the diffuse arc mode was not uniform but concentrated in the central area. The current density in the central anode area at the current peak JPeakArea I decreased with increasing BAMF following a power law. For BAMF of 0-110 mT and IARC of 4-14 kA, JPeakArea I = (2.2 IARC + 0.069 IARC2) BAMF-0.22, where JPeakArea I is in A/mm2, BAMF is in mT, and IARC is in kA. Moreover, the current distribution was uneven in the three peripheral areas.

  18. Investigations of LHW-plasma coupling and current drive at high density related to H-mode experiments in EAST

    NASA Astrophysics Data System (ADS)

    Ding, B. J.; Li, Y. C.; Zhang, L.; Li, M. H.; Wei, W.; Kong, E. H.; Wang, M.; Xu, H. D.; Wang, S. L.; Xu, G. S.; Zhao, L. M.; Hu, H. C.; Jia, H.; Cheng, M.; Yang, Y.; Liu, L.; Zhao, H. L.; Peysson, Y.; Decker, J.; Goniche, M.; Amicucci, L.; Cesario, R.; Tuccillo, A. A.; Baek, S. G.; Parker, R.; Bonoli, P. T.; Paoletti, F.; Yang, C.; Shan, J. F.; Liu, F. K.; Zhao, Y. P.; Gong, X. Z.; Hu, L. Q.; Gao, X.; Wan, B. N.; Li, J. G.; the EAST Team

    2015-09-01

    Two important issues in achieving lower hybrid current drive (LHCD) high confinement plasma in EAST are to improve lower hybrid wave (LHW)-plasma coupling and to drive the plasma current at a high density. Studies in different configurations with different directions of toroidal magnetic field (Bt) show that the density near the antenna is affected by both the radial electric field induced by plasma without a LHW (Er_plasma) in the scrape off layer (SOL), and the radial electric field induced by LHW power (Er_LH) near the grill. Investigations indicate that Er  ×  Bt in the SOL leads to a different effect of configuration on the LHW-plasma coupling and Er_LH  ×  Bt accounts for the asymmetric density behaviour in the SOL observed in the experiments, where Er is the total radial electric field in the SOL. Modelling of parametric instability (PI), collisional absorption (CA) and scattering from density fluctuations (SDF) in the edge region, performed considering the parameters of high density LHCD experiments in EAST, has shown that these mechanisms could be responsible for the low current drive (CD) efficiency at high density. Radiofrequency probe spectra, useful for documenting PI occurrence, show sidebands whose amplitude in the case of the lithiated vacuum chamber is smaller than in the case of poor lithiation, consistently with growth rates from PI modeling of the respective reference discharges. Since strong lithiation is also expected to diminish the parasitic effect on the LHCD of the remaining possible mechanisms, this appears to be a useful method for improving LHCD efficiency at a high density.

  19. Faraday-Effect Polarimeter-Interferometer System for current density measurement on EAST

    NASA Astrophysics Data System (ADS)

    Liu, Haiqing; Jie, Yinxian; Ding, Weixing; Brower, David Lyn; Zou, Zhiyong; Qian, Jinping; Li, Weiming; Zeng, Long; Zhang, Shoubiao; Hu, Liqun; Wan, Baonian

    2015-11-01

    An eleven-channel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique has been implemented for current density and electron density profile measurements in the EAST tokamak. Both polarimetric and interferometric measurement are obtained in a long pulse (~ 52s) discharge. The electron line-integrated density resolution of POINT is less than 5 × 1016 m-2 (~ 2°), and the Faraday rotation angle rms phase noise is <0.1°. With the high temporal (~ 1 μsec) and phase resolution (<0.1°), density perturbations associated with the sawteeth cycle and tearing mode activities have been observed. It is evident that tearing modes are well correlated to dynamics of equilibrium current profile (or q-profile). Faraday rotation angle shows clear variation with low hybrid current drive while line-integrated density remains little changed, implying the current drive in the core. A Digital Phase Detector with 250 kHz bandwidth provides real-time Faraday rotation angle and density phase shift output, which will be integrated into current profile control system in a long pulse discharge in future. This work is supported by the National Magnetic Confinement Fusion Program of China with contract No. 2012GB101002 and partly supported by the US D.O.E. contract DESC0010469.

  20. Current density imaging using directly measured harmonic Bz data in MREIT.

    PubMed

    Park, Chunjae; Kwon, Oh In

    2013-01-01

    Magnetic resonance electrical impedance tomography (MREIT) measures magnetic flux density signals through the use of a magnetic resonance imaging (MRI) in order to visualize the internal conductivity and/or current density. Understanding the reconstruction procedure for the internal current density, we directly measure the second derivative of Bz data from the measured k-space data, from which we can avoid a tedious phase unwrapping to obtain the phase signal of Bz . We determine optimal weighting factors to combine the derivatives of magnetic flux density data, [Symbol: see text](2) Bz , measured using the multi-echo train. The proposed method reconstructs the internal current density using the relationships between the induced internal current and the measured [Symbol: see text](2) Bz data. Results from a phantom experiment demonstrate that the proposed method reduces the scanning time and provides the internal current density, while suppressing the background field inhomogeneity. To implement the real experiment, we use a phantom with a saline solution including a balloon, which excludes other artifacts by any concentration gradient in the phantom.

  1. A new model for marine density-turbidity currents with criteria for ignition

    NASA Astrophysics Data System (ADS)

    Salusti, E.

    We discuss the hydrodynamic stability properties of a one-dimensional quasi-steady marine current, driven by a density excess caused by low temperature or high salinity, and flowing over a regular slope, taking bottom-erosion phenomena into consideration. The term density-turbidity current is used here for a thermohaline density current, with that density increased by entrained sediment. Thermohaline currents are of fundamental importance with regard to the Earth's climate, and the same must apply to density-turbidity currents. To simplify this complex problem, we schematize the flow as a thin turbulent quasisteady current, with gravitational and frictional forces in approximate equilibrium; the effects of small-scale perturbations, and of interaction with the bottom sediment, are then schematised by assuming a heuristic model of sediment evolution. Indeed, as in recent work by Caserta et al. (1990), we postulate that density variation due to bottom erosion or deposition is a function only of the shear stress exerted on the sea bottom by the current. Using these assumptions, we arrive at a complex nonlinear equation which considers both time and space variability for a realistic two-layer model of these density-turbidity currents. This finally gives a nonlinear heat equation that displays both diffusive behaviour and a peculiar type of time-delayed nonlinear behaviour, a previously-unrecognised effect governed by a criterion which defines explosive perturbations. It is of interest that this criterion is not related to energy considerations, like other criteria discussed in the literature, but is based on hydrodynamic instability considerations. The above model can also be applied to classical turbidity currents, i.e. those in which the interstitial fluid has the same density as the ambient fluid. However, the way in which the initial turbid water is generated is of paramount importance; mechanisms include submarine slumping, underflows from large flooded rivers

  2. An adaptive finite element approach to modelling sediment laden density currents

    NASA Astrophysics Data System (ADS)

    Parkinson, S.; Hill, J.; Allison, P. A.; Piggott, M. D.

    2012-04-01

    Modelling sediment-laden density currents at real-world scales is a challenging task. Here we present Fluidity, which uses dynamic adaptive re-meshing to reduce computational costs whilst maintaining sufficient resolution where and when it is required. This allows small-scale processes to be captured in large scale simulations. Density currents, also known as gravity or buoyancy currents, occur wherever two fluids with different densities meet. They can occur at scales of up to hundred kilometres in the ocean when continental shelves collapse. This process releases large quantities of sediment into the ocean which increase the bulk density of the fluid to form a density current. These currents can carry sediment hundreds of kilometres, at speeds of up to a hundred kilometres per hour, over the sea bed. They can be tsunamigenic and they have the potential to cause significant damage to submarine infrastructure, such as submarine telecommunications cables or oil and gas infrastructure. They are also a key process for movement of organic material into the depths of the ocean. Due to this, they play an important role in the global carbon cycle on the Earth, forming a significant component of the stratigraphic record, and their deposits can form useful sources of important hydrocarbons. Modelling large scale sediment laden density currents is a very challenging problem. Particles within the current are suspended by turbulence that occurs at length scales that are several orders of magnitude smaller than the size of the current. Models that resolve the vertical structure of the flow require a very large, highly resolved mesh, and substantial computing power to solve. Here, we verify our adaptive model by comparison with a set of laboratory experiments by Gladstone et al. [1998] on the propagation and sediment deposition of bidisperse gravity currents. Comparisons are also made with fixed mesh solutions, and it is shown that accuracy can be maintained with fewer elements

  3. Calculations of current densities for neutral and doubly charged persubstituted benzenes using effective core potentials.

    PubMed

    Rauhalahti, Markus; Taubert, Stefan; Sundholm, Dage; Liégeois, Vincent

    2017-03-08

    Magnetically induced current density susceptibilities and ring-current strengths have been calculated for neutral and doubly charged persubstituted benzenes C6X6 and C6X6(2+) with X = F, Cl, Br, I, At, SeH, SeMe, TeH, TeMe, and SbH2. The current densities have been calculated using the gauge-including magnetically induced current (GIMIC) method, which has been interfaced to the Gaussian electronic structure code rendering current density calculations using effective core potentials (ECP) feasible. Relativistic effects on the ring-current strengths have been assessed by employing ECP calculations of the current densities. Comparison of the ring-current strengths obtained in calculations on C6At6 and C6At6(2+) using relativistic and non-relativistic ECPs show that scalar relativistic effects have only a small influence on the ring-current strengths. Comparisons of the ring-current strengths and ring-current profiles show that the C6I6(2+), C6At6(2+), C6(SeH)6(2+), C6(SeMe)6(2+), C6(TeH)6(2+), C6(TeMe)6(2+), and C6(SbH2)6(2+) dications are doubly aromatic sustaining spatially separated ring currents in the carbon ring and in the exterior of the molecule. The C6I6(+) radical cation is also found to be doubly aromatic with a weaker ring current than obtained for the dication.

  4. Current status and recent research achievements in SiC/SiC composites

    NASA Astrophysics Data System (ADS)

    Katoh, Y.; Snead, L. L.; Henager, C. H.; Nozawa, T.; Hinoki, T.; Iveković, A.; Novak, S.; Gonzalez de Vicente, S. M.

    2014-12-01

    The silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite system for fusion applications has seen a continual evolution from development a fundamental understanding of the material system and its behavior in a hostile irradiation environment to the current effort which is directed at a broad-based program of technology maturation program. In essence, over the past few decades this material system has steadily moved from a laboratory curiosity to an engineering material, both for fusion structural applications and other high performance application such as aerospace. This paper outlines the recent international scientific and technological achievements towards the development of SiC/SiC composite material technologies for fusion application and discusses future research directions. It also reviews the materials system in the larger context of progress to maturity as an engineering material for both the larger nuclear community and broader engineering applications.

  5. Alcohol liver disease: A review of current therapeutic approaches to achieve long-term abstinence

    PubMed Central

    García, María Luisa Gutiérrez; Blasco-Algora, Sara; Fernández-Rodríguez, Conrado M

    2015-01-01

    Harmful alcohol drinking may lead to significant damage on any organ or system of the body. Alcoholic liver disease (ALD) is the most prevalent cause of advanced liver disease in Europe. In ALD, only alcohol abstinence was associated with a better long-term survival. Therefore, current effective therapeutic strategy should be oriented towards achieving alcohol abstinence or a significant reduction in alcohol consumption. Screening all primary care patients to detect those cases with alcohol abuse has been proposed as population-wide preventive intervention in primary care. It has been suggested that in patients with mild alcohol use disorder the best approach is brief intervention in the primary care setting with the ultimate goal being abstinence, whereas patients with moderate-to-severe alcohol use disorder must be referred to specialized care where detoxification and medical treatment of alcohol dependence must be undertaken. PMID:26229395

  6. Current Status and Recent Research Achievements in SiC/SiC Composites

    SciTech Connect

    Katoh, Yutai; Snead, Lance L.; Henager, Charles H.; Nozawa, T.; Hinoki, Tetsuya; Ivekovic, Aljaz; Novak, Sasa; Gonzalez de Vicente, Sehila M.

    2014-12-01

    The development and maturation of the silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite system for fusion applications has seen the evolution from fundamental development and understanding of the material system and its behavior in a hostile irradiation environment to the current effort which essentially is a broad-based program of technology, directed at moving this material class from a laboratory curiosity to an engineering material. This paper lays out the recent international scientific and technological achievements in the development of SiC/SiC composite material technologies for fusion application and will discuss future research directions. It also reviews the materials system in the larger context of progress to maturity as an engineering material for both the larger nuclear community and for general engineering applications.

  7. Incorporation of Ca and P on anodized titanium surface: Effect of high current density.

    PubMed

    Laurindo, Carlos A H; Torres, Ricardo D; Mali, Sachin A; Gilbert, Jeremy L; Soares, Paulo

    2014-04-01

    This study systematically evaluated the surface and corrosion characteristics of commercially pure titanium (grade 2) modified by plasma electrolytic oxidation (PEO) with high current density. The anodization process was carried out galvanostatically (constant current density) using a solution containing calcium glycerophosphate (0.02mol/L) and calcium acetate (0.15mol/L). The current densities applied were 400, 700, 1000 and 1200mA/cm(2) for a period of 15s. Composition, crystalline structure, morphology, roughness, wettability and "in-vitro" bioactivity test in SBF of the anodized layer were evaluated by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, profilometry and contact angle measurements. Corrosion properties were evaluated by open circuit potential, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The results show that the TiO2 oxide layers present an increase of thickness, porosity, roughness, wettability, Ca/P ratio, and bioactivity, with the applied current density up to 1000mA/cm(2). Corrosion resistance also increases with applied current density. It is observed that for 1200mA/cm(2), there is a degradation of the oxide layer. In general, the results suggest that the anodized TiO2 layer with better properties is formed with an applied current of 1000mA/cm(2).

  8. Gauge-Origin Independent Calculations of the Anisotropy of the Magnetically Induced Current Densities.

    PubMed

    Fliegl, Heike; Jusélius, Jonas; Sundholm, Dage

    2016-07-21

    Gauge-origin independent current density susceptibility tensors have been computed using the gauge-including magnetically induced current (GIMIC) method. The anisotropy of the magnetically induced current density (ACID) functions constructed from the current density susceptibility tensors are therefore gauge-origin independent. The ability of the gauge-origin independent ACID function to provide quantitative information about the current flow along chemical bonds has been assessed by integrating the cross-section area of the ACID function in the middle of chemical bonds. Analogously, the current strength susceptibility passing a given plane through the molecule is obtained by numerical integration of the current flow parallel to the normal vector of the integration plane. The cross-section area of the ACID function is found to be strongly dependent on the exact location of the integration plane, which is in sheer contrast to the calculated ring-current strength susceptibilities that are practically independent of the chosen position of the integration plane. The gauge-origin independent ACID functions plotted for different isosurface values show that a visual assessment of the current flow and degree of aromaticity depends on the chosen isosurface. The present study shows that ACID functions are not an unambiguous means to estimate the degree of molecular aromaticity according to the magnetic criterion and to determine the current pathway of complex molecular rings.

  9. Selective regulation of current densities underlies spontaneous changes in the activity of cultured neurons.

    PubMed

    Turrigiano, G; LeMasson, G; Marder, E

    1995-05-01

    We study the electrical activity patterns and the expression of conductances in adult stomatogastric ganglion (STG) neurons as a function of time in primary cell culture. When first plated in culture, these neurons had few active properties. After 1 d in culture they produced small action potentials that rapidly inactivated during maintained depolarization. After 2 d in culture they fired large action potentials tonically when depolarized, and their properties resembled very closely the properties of STG neurons pharmacologically isolated in the ganglion. After 3-4 d in culture, however, their electrical properties changed and they fired in bursts when depolarized. We characterized the currents expressed by these neurons in culture. They included two TTX-sensitive sodium currents, a calcium current, a delayed-rectifier-like current, a calcium-dependent potassium current, and two A-type currents. The changes in firing properties with time in culture were accompanied by an increase in inward and decrease in outward current densities. A single-compartment conductance-based model of an STG neuron was constructed by fitting the currents measured in the biological neurons. When the current densities in the model neuron were matched to those measured for the biological neurons in each activity state, the model neuron closely reproduced each state, indicating that the changes in current densities are sufficient to account for the changes in intrinsic properties. These data indicate that STG neurons isolated in culture change their intrinsic electrical properties by selectively adjusting the magnitudes of their ionic conductances.

  10. Probability Density Function of the Output Current of Cascaded Multiplexer/Demultiplexers in Transparent Optical Networks

    NASA Astrophysics Data System (ADS)

    Rebola, João L.; Cartaxo, Adolfo V. T.

    The influence of the concatenation of arbitrary optical multiplexers/demultiplexers (MUX/DEMUXs) on the probability density function (PDF) of the output current of a transparent optical network is assessed. All PDF results obtained analytically are compared with estimates from Monte Carlo simulation and an excellent agreement is achieved. The non-Gaussian behavior of the PDFs, previously reported by other authors for square-law detectors, is significantly enhanced with the number of nodes increase due to the noise accumulation along the cascade of MUX/DEMUXs. The increase of the MUX/DEMUXs bandwidth and detuning also enhances the PDFs non-Gaussian behavior. The PDF shape variation with the detuning depends strongly on the number of nodes. Explanations for the Gaussian approximation (GA) accuracy on the assessment of the performance of a concatenation of optical MUX/DEMUXs are also provided. For infinite extinction ratio and tuned MUX/DEMUXs, the GA error probabilities are, in general, pessimistic, due to the inaccurate estimation of the error probability for both bits. For low extinction ratio, the GA is very accurate due to a balance between the error probabilities estimated for the bits "1" and "0." With the detuning increase, the GA estimates can become optimistic.

  11. Simulation study of the critical current density of YBa2Cu3O7 ceramics

    NASA Astrophysics Data System (ADS)

    Cai, Zhi-Xiong; Welch, David O.

    1992-02-01

    A two-dimensional Josephson-junction-array model is used to study the effect of grain boundaries on the critical current density of YBa2Cu3O7 superconducting ceramics. The model represents a network of superconducting grains with a distribution of tilt angles θ. Each grain boundary has a critical current density Jc(θ) and normal-state resistance R(θ). The current-voltage characteristics are calculated numerically for different tilt-angle distributions. The scaling law and statistics of extremes, introduced by Duxbury, Beale, and Leath for general breakdown behavior, based on the most critical defect (normal region) in the network, are tested and found to be accurate for the predicted critical-current distribution of random samples. When the applied current is larger than but close to its critical value, there is a periodic V(t) with discrete power spectra. When the applied current gets larger, chaotic behavior appears with nearly continuous power spectra.

  12. High baryon densities achievable in the fragmentation regions at RHIC and LHC

    NASA Astrophysics Data System (ADS)

    Kapusta, Joseph; Li, Ming

    2017-01-01

    We use the McLerran-Venugopalan model of the glasma energy-momentum tensor to compute the rapidity loss and excitation energy of the colliding nuclei in the fragmentation regions followed by a space-time picture to obtain their energy and baryon densities. At the top RHIC energy we find baryon densities up to 3 baryons/fm3, which is 20 times that of atomic nuclei. Assuming the formation of quark-gluon plasma, we find initial temperatures of 200 to 300 MeV and baryon chemical potentials of order 1 GeV. Assuming a roughly adiabatic expansion it would imply trajectories in the T ‑ μ plane which would straddle a possible critical point.

  13. Induced fermionic charge and current densities in two-dimensional rings

    NASA Astrophysics Data System (ADS)

    Bellucci, S.; Saharian, A. A.; Grigoryan, A. Kh.

    2016-11-01

    For a massive quantum fermionic field, we investigate the vacuum expectation values (VEVs) of the charge and current densities induced by an external magnetic flux in a two-dimensional circular ring. Both the irreducible representations of the Clifford algebra are considered. On the ring edges the bag (infinite mass) boundary conditions are imposed for the field operator. This leads to the Casimir type effect on the vacuum characteristics. The radial current vanishes. The charge and the azimuthal current are decomposed into the boundary-free and boundary-induced contributions. Both these contributions are odd periodic functions of the magnetic flux with the period equal to the flux quantum. An important feature that distinguishes the VEVs of the charge and current densities from the VEV of the energy density is their finiteness on the ring edges. The current density is equal to the charge density for the outer edge and has the opposite sign on the inner edge. The VEVs are peaked near the inner edge and, as functions of the field mass, exhibit quite different features for two inequivalent representations of the Clifford algebra. We show that, unlike the VEVs in the boundary-free geometry, the vacuum charge and the current in the ring are continuous functions of the magnetic flux and vanish for half-odd integer values of the flux in units of the flux quantum. Combining the results for two irreducible representations, we also investigate the induced charge and current in parity and time-reversal symmetric models. The corresponding results are applied to graphene rings with the electronic subsystem described in terms of the effective Dirac theory with the energy gap. If the energy gaps for two valleys of the graphene hexagonal lattice are the same, the charge densities corresponding to the separate valleys cancel each other, whereas the azimuthal current is doubled.

  14. Coupling of turbulent and non-turbulent flow regimes within pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Breard, Eric C. P.; Lube, Gert; Jones, Jim R.; Dufek, Josef; Cronin, Shane J.; Valentine, Greg A.; Moebis, Anja

    2016-10-01

    Volcanic eruptions are at their most deadly when pyroclastic density currents sweep across landscapes to devastate everything in their path. The internal dynamics underpinning these hazards cannot be directly observed. Here we present a quantitative view inside pyroclastic density currents by synthesizing their natural flow behaviour in large-scale experiments. The experiments trace flow dynamics from initiation to deposition, and can explain the sequence and evolution of real-world deposits. We show that, inside pyroclastic density currents, the long-hypothesized non-turbulent underflow and fully turbulent ash-cloud regions are linked through a hitherto unrecognized middle zone of intermediate turbulence and concentration. Bounded by abrupt jumps in turbulence, the middle zone couples underflow and ash-cloud regions kinematically. Inside this zone, strong feedback between gas and particle phases leads to the formation of mesoscale turbulence clusters. These extremely fast-settling dendritic structures dictate the internal stratification and evolution of pyroclastic density currents and allow the underflows to grow significantly during runout. Our experiments reveal how the underflow and ash-cloud regions are dynamically related--insights that are relevant to the forecasting of pyroclastic density current behaviour in volcanic hazard models.

  15. Stabilizing Effects of Edge Current Density on Peeling-Ballooning Instability

    NASA Astrophysics Data System (ADS)

    Zhu, P.; Hegna, C. C.; Sovinec, C. R.

    2011-10-01

    Resistive MHD computations using the NIMROD code find a strong dependence of low- n edge instabilities on the edge parallel current density distribution. Here n is the toroidal mode number. The low- n edge-localized-modes can be driven unstable by increasing the edge current density across the peeling-ballooning stability boundary. When edge peak current density is sufficiently large, the corresponding safety factor q profile obtains an edge region with zero or reversed magnetic shear, and the low- n edge instabilities are partially or fully stabilized. These results are consistent with previous analytic theory on peeling modes which indicates that zero or reversed magnetic shear can be stabilizing. Nonlinear simulations indicate that the stabilizing effects of edge current density on the low- n peeling-dominant modes through zero and reversed shear can persist throughout the nonlinear exponential growth phase. Near the end of this nonlinear phase, the radial extent of the filament exceeds the pedestal width, and disconnected blob-like substructures start to develop within the filaments. Relative pedestal energy loss from these radially extending filaments can reach 20 - 30 % . Both filament size and pedestal energy loss from the nonlinear low- n peeling-dominant instabilities can be reduced and regulated by the equilibrium edge current density distribution. Supported by Grants DE-FG02-86ER53218 and DE-FC02-08ER54975.

  16. Current densities and total contact currents for 110 and 220 kV power line tasks.

    PubMed

    Korpinen, Leena; Kuisti, Harri; Elovaara, Jarmo

    2014-10-01

    The aim of this study was to analyze all values of electric current from measured periods while performing tasks on 110 and 220 kV power lines. Additionally, the objective was to study the average current densities and average total contact currents caused by electric fields in 110 and 220 kV power line tasks. One worker simulated the following tasks: (A) tested insulation voltage at a 110 kV portal tower, (B) checked the wooden towers for rot at a 110 kV portal tower, (C) tested insulation voltage at a 220 kV portal tower, and (D) checked the wooden towers for rot at a 220 kV portal tower. The highest average current density in the neck was 2.0 mA/m(2) (calculated internal electric field was 19.0-38.0 mV/m), and the highest average contact current was 234 µA. All measured values at 110 and 220 kV towers were lower than the basic restrictions (0.1 and 0.8 V/m) of the International Commission on Non-ionizing Radiation Protection.

  17. Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping

    NASA Technical Reports Server (NTRS)

    Bhattacharya, P. K.; Dhar, S.; Berger, P.; Juang, F.-Y.

    1986-01-01

    A study has been made of the effects of adding small amounts of In (0.2-1.2 pct) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by Briones and Collins (1982) and Skromme et al. (1985).

  18. Estimation of nighttime dip-equatorial E-region current density using measurements and models

    NASA Astrophysics Data System (ADS)

    Pandey, Kuldeep; Sekar, R.; Anandarao, B. G.; Gupta, S. P.; Chakrabarty, D.

    2016-08-01

    The existence of the possible ionospheric current during nighttime over low-equatorial latitudes is one of the unresolved issues in ionospheric physics and geomagnetism. A detailed investigation is carried out to estimate the same over Indian longitudes using in situ measurements from Thumba (8.5 ° N, 76.9 ° E), empirical plasma drift model (Fejer et al., 2008) and equatorial electrojet model developed by Anandarao (1976). This investigation reveals that the nighttime E-region current densities vary from ∼0.3 to ∼0.7 A/km2 during pre-midnight to early morning hours on geomagnetically quiet conditions. The nighttime current densities over the dip equator are estimated using three different methods (discussed in methodology section) and are found to be consistent with one another within the uncertainty limits. Altitude structures in the E-region current densities are also noticed which are shown to be associated with altitudinal structures in the electron densities. The horizontal component of the magnetic field induced by these nighttime ionospheric currents is estimated to vary between ∼2 and ∼6 nT during geomagnetically quiet periods. This investigation confirms the existence of nighttime ionospheric current and opens up a possibility of estimating base line value for geomagnetic field fluctuations as observed by ground-based magnetometer.

  19. What limits the achievable areal densities of large aperture space telescopes?

    NASA Astrophysics Data System (ADS)

    Peterson, Lee D.; Hinkle, Jason D.

    2005-08-01

    This paper examines requirements trades involving areal density for large space telescope mirrors. A segmented mirror architecture is used to define a quantitative example that leads to relevant insight about the trades. In this architecture, the mirror consists of segments of non-structural optical elements held in place by a structural truss that rests behind the segments. An analysis is presented of the driving design requirements for typical on-orbit loads and ground-test loads. It is shown that the driving on-orbit load would be the resonance of the lowest mode of the mirror by a reaction wheel static unbalance. The driving ground-test load would be dynamics due to ground-induced random vibration. Two general conclusions are derived from these results. First, the areal density that can be allocated to the segments depends on the depth allocated to the structure. More depth in the structure allows the allocation of more mass to the segments. This, however, leads to large structural depth that might be a significant development challenge. Second, the requirement for ground-test-ability results in an order of magnitude or more depth in the structure than is required by the on-orbit loads. This leads to the proposition that avoiding ground test as a driving requirement should be a fundamental technology on par with the provision of deployable depth. Both are important structural challenges for these future systems.

  20. Towards the definition of AMS facies in the deposits of pyroclastic density currents

    USGS Publications Warehouse

    Ort, M.H.; Newkirk, T.T.; Vilas, J.F.; Vazquez, J.A.; Ort, M.H.; Porreca, Massimiliano; Geissman, J.W.

    2014-01-01

    Anisotropy of magnetic susceptibility (AMS) provides a statistically robust technique to characterize the fabrics of deposits of pyroclastic density currents (PDCs). AMS fabrics in two types of pyroclastic deposits (small-volume phreatomagmatic currents in the Hopi Buttes volcanic field, Arizona, USA, and large-volume caldera-forming currents, Caviahue Caldera, Neuquén, Argentina) show similar patterns. Near the vent and in areas of high topographical roughness, AMS depositional fabrics are poorly grouped, with weak lineations and foliations. In a densely welded proximal ignimbrite, this fabric is overprinted by a foliation formed as the rock compacted and deformed. Medial deposits have moderate–strong AMS lineations and foliations. The most distal deposits have strong foliations but weak lineations. Based on these facies and existing models for pyroclastic density currents, deposition in the medial areas occurs from the strongly sheared, high-particle-concentration base of a density-stratified current. In proximal areas and where topography mixes this denser base upwards into the current, deposition occurs rapidly from a current with little uniformity to the shear, in which particles fall and collide in a chaotic fashion. Distal deposits are emplaced by a slowing or stalled current so that the dominant particle motion is vertical, leading to weak lineation and strong foliation.

  1. Characterization of thunderstorm induced Maxwell current densities in the middle atmosphere

    NASA Technical Reports Server (NTRS)

    Baginski, Michael Edward

    1989-01-01

    Middle atmospheric transient Maxwell current densities generated by lightning induced charge perturbations are investigated via a simulation of Maxwell's equations. A time domain finite element analysis is employed for the simulations. The atmosphere is modeled as a region contained within a right circular cylinder with a height of 110 km and radius of 80 km. A composite conductivity profile based on measured data is used when charge perturbations are centered about the vertical axis at altitudes of 6 and 10 km. The simulations indicate that the temporal structure of the Maxwell current density is relatively insensitive to altitude variation within the region considered. It is also shown that the electric field and Maxwell current density are not generally aligned.

  2. Simultaneous Observations of Electric Fields, Current Density, Plasma Density, and Neutral Winds During Two Sounding Rocket Experiments Launched from Wallops Island into Strong Daytime Dynamo Currents

    NASA Astrophysics Data System (ADS)

    Pfaff, R. F., Jr.; Rowland, D. E.; Klenzing, J.; Freudenreich, H. T.; Martin, S. C.; Abe, T.; Habu, H.; Yamamoto, M. Y.; Watanabe, S.; Yamamoto, M.; Yokoyama, T.; Kakinami, Y.; Yamazaki, Y.; Larsen, M. F.; Hurd, L.; Clemmons, J. H.; Bishop, R. L.; Walterscheid, R. L.; Fish, C. S.; Bullett, T. W.; Mabie, J. J.; Murphy, N.; Angelopoulos, V.; Leinweber, H. K.; Bernal, I.; Chi, P. J.

    2015-12-01

    To investigate the ion-neutral coupling that creates the global electrical daytime "dynamo" currents in the mid-latitude, lower ionosphere, NASA carried out two multiple sounding rocket experiments from Wallops Island, VA on July 10, 2011 (14:00 UT, 10:00 LT) and July 4, 2013 (14:31 UT, 10:31 LT). The rockets were launched in the presence of well-defined, westward Hall currents observed on the ground with ΔH values of ­-25 nT and -30 nT, respectively, as well as a well-defined, daytime ionospheric density observed by the VIPIR ionosonde at Wallops. During the 2011 experiment, a narrow, intense sporadic-E layer was observed near 102 km. Each experiment consisted of a pair of rockets launched 15 sec apart. The first rocket of each pair carried instruments to measure DC electric and magnetic fields, as well as the ambient plasma and neutral gases and attained apogees of 158 km and 135 km in the 2011 and 2013 experiments, respectively. The second rocket of each pair carried canisters which released a lithium vapor trail along the upleg to illuminate neutral winds in the upper atmosphere. This daytime vapor trail technology was developed jointly by researchers at JAXA and Clemson University. In the second experiment, the lithium release was clearly visible in cameras with infrared filters operated by US and Japanese researchers in a NASA airplane at 9.6 km altitude. The observed wind profiles reached speeds of 100 m/s with strong shears with respect to altitude and were consistent with an independent derivation of the wind from the ionization gauge sensor suite on the instrumented rocket. The "vapor trail" rockets, which also included a falling sphere, attained apogees of 150 km and 143 km in the 2011 and 2013 experiments, respectively. By measuring the current density, conductivity, DC electric fields, and neutral winds, we solve the dynamo equation as a function of altitude, revealing the different contributions to the lower E-region currents. We find that the DC

  3. Climatology of convective density currents in the southern foothills of the Atlas Mountains

    NASA Astrophysics Data System (ADS)

    Emmel, C.; Knippertz, P.; Schulz, O.

    2010-06-01

    Density currents fed by evaporationally cooled air are an important dust storm-generating feature and can constitute a source of moisture in arid regions. Recently, the existence of such systems has been demonstrated for the area between the High Atlas Mountains and the Sahara desert in southern Morocco on the basis of case studies. Here, a climatological analysis is presented that uses data from the dense climate station network of the IMPETUS project (An Integrated Approach to the Efficient Management of Scarce Water Resources in West Africa) for the 5 year period 2002-2006. Objective criteria mainly based upon abrupt changes in wind and dew point temperature are defined to identify possible density current situations. The preselected events are then subjectively evaluated with the help of satellite imagery and surface observations to exclude causes for air mass changes other than moist convective cold pool formation. On average, 11 ± 4 density currents per year are detected with the main season lasting from April to September. Density currents occur mainly in the afternoon and evening due to the diurnal cycle of moist convection. Mean changes at the leading edge are increases in 2 m dew point temperature and wind speed by 5.4°C and 8.2 m s-1, respectively, and a decrease in 2 m air temperature of 2.3°C. The High Atlas and Jebel Saghro are found to be the most important source regions, while only a few systems originate over the Saharan lowlands. Labilization of the atmosphere due to upper-level troughs over northwest Africa and an enhanced moisture content favor density current formation. In addition, detailed case studies representative of different density current types are presented.

  4. Corrosion current density prediction in reinforced concrete by imperialist competitive algorithm.

    PubMed

    Sadowski, Lukasz; Nikoo, Mehdi

    2014-01-01

    This study attempted to predict corrosion current density in concrete using artificial neural networks (ANN) combined with imperialist competitive algorithm (ICA) used to optimize weights of ANN. For that reason, temperature, AC resistivity over the steel bar, AC resistivity remote from the steel bar, and the DC resistivity over the steel bar are considered as input parameters and corrosion current density as output parameter. The ICA-ANN model has been compared with the genetic algorithm to evaluate its accuracy in three phases of training, testing, and prediction. The results showed that the ICA-ANN model enjoys more ability, flexibility, and accuracy.

  5. Postprocessing of 3-D current density reconstruction results with equivalent ellipsoids.

    PubMed

    Ziolkowski, Marek; Haueisen, Jens; Leder, Uwe

    2002-11-01

    A method of postprocessing and visualizing three-dimensional vector fields, such as current density reconstruction results, is presented. This method is based on equivalent ellipsoids fitted to the vector fields. The technique has been tested with simulated data and current density reconstructions based on bioelectromagnetic data obtained from a physical thorax phantom. Three different approaches based on: 1) longest distance; 2) dominant direction; and 3) principal component analysis, for fitting the equivalent ellipsoids are proposed. Multiple foci in vector fields are extracted by multiple ellipsoids which are fitted iteratively. The method enables statistical postprocessing for the sake of comparisons of different source reconstructions algorithms or comparisons of groups of patients or volunteers.

  6. Modelling of Current Density Redistribution in Hollow Needle to Plate Electrical Discharge Designed for Ozone Generation

    NASA Astrophysics Data System (ADS)

    Kriha, Vitezslav

    2003-10-01

    Non-thermal plasma of atmospheric pressure electrical discharges in flowing air can be used to generation of ozone. We have been observed two modes of discharge burning in a hollow needle to plane electrodes configuration studied in the ozone generation experiments: A low current diffuse mode is characterized by increasing of the ozone production with the discharge current; a high current filamentary mode is disadvantageous for the ozone generation(the ozone production decreases when the discharge current increases). A possible interpretation of this effect is following: The filamentary mode discharge current density is redistributed and high current densities in filaments cores lead to degradation of the ozone generation. Local fields in the discharge can be modified by charged metallic and/or dielectric components (passive modulators) in the discharge space. An interactive numerical model has been developed for this purpose. This model is based on Ferguson's polynomial objects for both the discharge chamber scene modelling and the discharge fields analyzing. This approach allows intuitive modifications of modulators shapes and positions in 3D scene followed by quantitative comparison of the current density distribution with previous configurations.

  7. Measurements of Current Densities and Skin Effects in Current Carrying Conductors Using Electro-optic and Magneto-optic Sensors

    NASA Astrophysics Data System (ADS)

    Garzarella, Anthony; Wu, Dong Ho

    2015-03-01

    In this presentation, we will describe experiments involving all-dielectric electromagnetic field sensors based on electro-optic (EO) and magneto-optic (MO) crystals. EO sensors measure electric fields through the Pockels Effect, while MO sensors measure magnetic fields through the Faraday Effect. These sensors have been attached to optical fibers and calibrated in a variety of radio frequency, pulsed power and microwaves sources ranging in frequencies from dc to 20 GHz and ranging in power from 10-4 to 106 Watts. In this talk, we will focus on recent experimental measurements of electric and magnetic fields generated by current carrying conductors. Our EO and MO sensor data, when combined, allows us to determine current densities and current distributions within a conductor cross section. Additionally, skin effects, which are a major source of Joule heating and resistive wear, can be characterized in detail.

  8. Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe.

    PubMed

    Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A; Vasiliev, Alexander N; Park, Tuson

    2015-11-09

    We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors.

  9. On the Need for Rethinking Current Practice that Highlights Goal Achievement Risk in an Enterprise Context.

    PubMed

    Aven, Eyvind; Aven, Terje

    2015-09-01

    This article addresses the issue of how performance and risk management can complement each other in order to enhance the management of an enterprise. Often, we see that risk management focuses on goal achievements and not the enterprise risk related to its activities in the value chain. The statement "no goal, no risk" is a common misconception. The main aim of the article is to present a normative model for describing the links between performance and risk, and to use this model to give recommendations on how to best structure and plan the management of an enterprise in situations involving risk and uncertainties. The model, which has several novel features, is based on the interaction between different types of risk management (enterprise risk management, task risk management, and personal risk management) and a structure where the enterprise risk management overrules both the task and personal risk management. To illustrate the model we use the metaphor of a ship, where the ship is loaded with cash-generating activities and has a direction over time determined by the overall strategic objectives. Compared to the current enterprise risk management practice, the model and related analysis are founded on a new perspective on risk, highlighting knowledge and uncertainties beyond probabilities.

  10. [Evolving 5-Fluorouracil Therapy to Achieve Enhanced Efficacy-Past and Current Efforts of Researchers].

    PubMed

    Maehara, Yoshihiko; Oki, Eiji; Saeki, Hiroshi; Tokunaga, Eriko; Kitao, Hiroyuki; Iimori, Makoto; Niimi, Shinichiro; Kataoka, Yuki; Emi, Yasunori; Kakeji, Yoshihiro; Baba, Hideo; Shirasaka, Tetsuhiko

    2016-07-01

    5-fluorouracil(5-FU)therapy has advanced greatly over the past 50 years, achieving enhanced therapeutic effects and reduced adverse effects. By taking advantage of the metabolism of 5-FU, researchers have made efforts to develop prodrugs, combination drug products, and combination therapy regimens via biochemical modulation(BCM)with alteration of the drug metabolism. Examples include the advent of the prodrug tegafur(FT), followed by tegafur-uracil(UFT)and tegafurgimeracil- potassium oxonate(S-1)as combined products based on BCM. In the current standard treatment for gastrointestinal cancers, anticancer 5-FU derivatives serve as a platform for combination regimens with other cytotoxic agents or molecular- targeted drugs. To provide further improvements in anticancer therapy outcomes, novel molecular-targeted agents, immune checkpoint inhibitors, and other drugs are being developed, but 5-FU remains an attractive target that shows further potential for increased efficacy. In the future, the evolution of anticancer therapy with 5-FU derivatives is expected to continue via a variety of approaches.

  11. Small Barriers Trigger Liftoff of Unconfined Dilute Heated Laboratory Density Currents

    NASA Astrophysics Data System (ADS)

    Fauria, K.; Andrews, B. J.; Manga, M.

    2015-12-01

    Dilute pyroclastic density currents (PDCs) are hot, turbulent, particle-laden flows that propagate because they are denser than air. PDCs can traverse tens to hundreds of kilometers and surmount ridges 100s of m tall, yet the effects of complex topography on PDC liftoff and runout distance are uncertain. Here we used scaled laboratory experiments to explore how barriers affect dilute density current dynamics and the occurrence of liftoff. We created dilute density currents by heating and suspending 20 μm diameter talc in air in an 8.5 x 6.1 x 2.6 m tank. We scaled the currents with respect to Froude, densimetric and thermal Richardson, particle Stokes and Settling numbers such that they were dynamically similar to natural PDCs. While currents were fully turbulent, their Reynolds numbers were not as high as those for natural PDCs. We performed the first set of experiments in a laterally unconfined volume, used laser sheets to illuminate the currents, measured bulk sedimentation rates down the current centerlines, and positioned four to twenty-four cm tall ridge-like barriers in the path of the currents. We found that relatively small barriers (~ half the current height) caused PDC liftoff. By comparison, conservation of kinetic and potential energy predicts that incompressible density currents are able to surmount barriers twice their height. Furthermore, we observed increased sedimentation immediately upstream of barriers and conclude that small barriers initiated buoyancy reversal through a combination of increased air entrainment and sedimentation. We conducted a second set of experiments with the same thermal scaling and mass flux rates but where the currents were laterally confined within a 0.6 m wide channel. We found that small barriers also triggered liftoff of confined currents, but that the body of these currents reattached after liftoff. Those results suggest that lateral confinement inhibits buoyancy reversal by limiting the surface area of the current

  12. Effects of intracellular calcium on sodium current density in cultured neonatal rat cardiac myocytes.

    PubMed Central

    Chiamvimonvat, N; Kargacin, M E; Clark, R B; Duff, H J

    1995-01-01

    1. Na+ channel mRNA levels in the heart can be modulated by changes in intracellular Ca2+ ([Ca2+]i). We have investigated whether this regulation of Na+ channel biosynthesis by cytosolic Ca2+ translates into functional Na+ channels that can be detected electrophysiologically. 2. Whole-cell Na+ currents (INa) were recorded using patch-clamp techniques from single ventricular myocytes isolated from neonatal rats and maintained in tissue culture for 24 h. Na+ current density, measured at a membrane potential of -10 mV, was significantly decreased in the cells which were exposed for 24 h to culture medium containing 10 mM of both external Ca2+ and K+ in order to raise [Ca2+]i compared with control cells which were maintained in culture medium containing 2 and 5 mM of Ca2+ and K+, respectively. In contrast, Na+ current density (at -10 mV) was significantly increased in cells exposed for 24 h to 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetraacetoxymethyl ester (BAPTA AM; a cell membrane-permeable Ca2+ chelator) which lowered the average [Ca2+]i compared with control. 3. Changes in current density were not associated with changes in the voltage dependence of activation and inactivation of INa. There were no changes in single-channel conductances. 4. It is concluded that Na+ current density in neonatal rat cardiac myocytes is modulated by [Ca2+]i. The findings suggest that the differences in current density are attributable to a change in Na+ channel numbers rather than to changes in single-channel conductance or gating. These changes are consistent with the previously documented modulation of Na+ channel biosynthesis by cytosolic Ca2+. PMID:7650605

  13. Down-regulation of endogenous KLHL1 decreases voltage-gated calcium current density.

    PubMed

    Perissinotti, Paula P; Ethington, Elizabeth G; Cribbs, Leanne; Koob, Michael D; Martin, Jody; Piedras-Rentería, Erika S

    2014-05-01

    The actin-binding protein Kelch-like 1 (KLHL1) can modulate voltage-gated calcium channels in vitro. KLHL1 interacts with actin and with the pore-forming subunits of Cav2.1 and CaV3.2 calcium channels, resulting in up-regulation of P/Q and T-type current density. Here we tested whether endogenous KLHL1 modulates voltage gated calcium currents in cultured hippocampal neurons by down-regulating the expression of KLHL1 via adenoviral delivery of shRNA targeted against KLHL1 (shKLHL1). Control adenoviruses did not affect any of the neuronal properties measured, yet down-regulation of KLHL1 resulted in HVA current densities ~68% smaller and LVA current densities 44% smaller than uninfected controls, with a concomitant reduction in α(1A) and α(1H) protein levels. Biophysical analysis and western blot experiments suggest Ca(V)3.1 and 3.3 currents are also present in shKLHL1-infected neurons. Synapsin I levels, miniature postsynaptic current frequency, and excitatory and inhibitory synapse number were reduced in KLHL1 knockdown. This study corroborates the physiological role of KLHL1 as a calcium channel modulator and demonstrates a novel, presynaptic role.

  14. Achieving universal health care coverage: Current debates in Ghana on covering those outside the formal sector

    PubMed Central

    2012-01-01

    Background Globally, extending financial protection and equitable access to health services to those outside the formal sector employment is a major challenge for achieving universal coverage. While some favour contributory schemes, others have embraced tax-funded health service cover for those outside the formal sector. This paper critically examines the issue of how to cover those outside the formal sector through the lens of stakeholder views on the proposed one-time premium payment (OTPP) policy in Ghana. Discussion Ghana in 2004 implemented a National Health Insurance Scheme, based on a contributory model where service benefits are restricted to those who contribute (with some groups exempted from contributing), as the policy direction for moving towards universal coverage. In 2008, the OTPP system was proposed as an alternative way of ensuring coverage for those outside formal sector employment. There are divergent stakeholder views with regard to the meaning of the one-time premium and how it will be financed and sustained. Our stakeholder interviews indicate that the underlying issue being debated is whether the current contributory NHIS model for those outside the formal employment sector should be maintained or whether services for this group should be tax funded. However, the advantages and disadvantages of these alternatives are not being explored in an explicit or systematic way and are obscured by the considerable confusion about the likely design of the OTPP policy. We attempt to contribute to the broader debate about how best to fund coverage for those outside the formal sector by unpacking some of these issues and pointing to the empirical evidence needed to shed even further light on appropriate funding mechanisms for universal health systems. Summary The Ghanaian debate on OTPP is related to one of the most important challenges facing low- and middle-income countries seeking to achieve a universal health care system. It is critical that there is

  15. Dissipative particle dynamics simulation for the density currents of polymer fluids

    NASA Astrophysics Data System (ADS)

    Li, Yanggui; Geng, Xingguo; Liu, Zhijun; Liu, Qingsheng; Ouyang, Jie

    2016-11-01

    In this work, the two-dimensional lock-exchange density currents of polymer fluids are numerically investigated using dissipative particle dynamics (DPD) at the mesoscale particle level. A modified finitely extensible nonlinear elastic (FENE) chain model is chosen to describe the polymer system, which perfectly depicts not only the elastic tension but also the elastic repulsion between the adjacent beads with bond length as the equilibrium length of one segment. Through the model and numerical simulation, we analyze the dynamics behavior of the density currents of polymer fluids. A comparison with its Newtonian counterpart suggests that the interface between two polymer fluids is more smoothed, and the front structure is different from the Newtonian case because the Kelvin-Helmholtz instability and cleft instability are suppressed by the polymer. Besides, we also probe the influences of polymer volume concentration, chain length and extensibility on the density currents. These simulation results show that increasing any of the parameters, concentration, chain length, and extensibility, the inhibiting effect of polymer on the density currents becomes more significant.

  16. Interpretation of very low frequency electromagnetic measurements in terms of normalized current density over variable topography

    NASA Astrophysics Data System (ADS)

    Singh, Anand; Sharma, S. P.

    2016-10-01

    A 2D inversion approach is developed to interpret VLF electromagnetic measurement recorded over variable topography. To depict the variable topography accurately, an octree mesh discretization is incorporated. Subsurface structure is modeled in terms of apparent current density distribution and compared with the inversion results for actual resistivity distribution obtained using numerical techniques. The study demonstrates that the results obtained using both approaches (current density and resistivity distribution) are comparable, but due to analytical expression, current density imaging is faster. The conjugate gradient method is used to reduce the computation time and storage space when solving the matrix equations, resulting in feasible and practical imaging inversion of VLF data. The preconditioned matrix, which is determined by the distances between the blocks and observation points, has an important function in improving the resolution. In case of flat earth, preconditioned conjugate gradient inversion of data results in images that are comparable to those obtained using resistivity inversion. We also test whether topography variation in the order of skin depth is significant to incorporate topography in the modeling. The example of a topographical field VLF data inversion shows the efficacy of the presented approach to appraise the subsurface structure in terms of current density.

  17. Transition from Fowler-Nordheim field emission to space charge limited current density

    NASA Astrophysics Data System (ADS)

    Feng, Y.; Verboncoeur, J. P.

    2006-07-01

    The Fowler-Nordheim law gives the current density extracted from a surface under strong fields, by treating the emission of electrons from a metal-vacuum interface in the presence of an electric field normal to the surface as a quantum mechanical tunneling process. Child's law predicts the maximum transmitted current density by considering the space charge effect. When the electric field becomes high enough, the emitted current density will be limited by Child's law. This work analyzes the transition of the transmitted current density from the Fowler-Nordheim law to Child's law space charge limit using a one-dimensional particle-in-cell code. Also studied is the response of the emission model to strong electric fields near the transition point. We find the transition without geometrical effort is smooth and much slower than reported previously [J. P. Barbour, W. W. Dolan, J. K. Trolan, E. E. Martin, and W. P. Dyke, Phys. Rev. 92, 45 (1953)]. We analyze the effects of geometric field enhancement and work function on the transition. Using our previous model for effective field enhancement [Y. Feng and J. P. Verboncoeur, Phys. Plasmas 12, 103301 (2005)], we find the geometric effect dominates, and enhancement β >10 can accelerate the approach to the space charge limit at practical electric field. A damped oscillation near the local plasma frequency is observed in the transient system response.

  18. Transition from Fowler-Nordheim field emission to space charge limited current density

    SciTech Connect

    Feng, Y.; Verboncoeur, J. P.

    2006-07-15

    The Fowler-Nordheim law gives the current density extracted from a surface under strong fields, by treating the emission of electrons from a metal-vacuum interface in the presence of an electric field normal to the surface as a quantum mechanical tunneling process. Child's law predicts the maximum transmitted current density by considering the space charge effect. When the electric field becomes high enough, the emitted current density will be limited by Child's law. This work analyzes the transition of the transmitted current density from the Fowler-Nordheim law to Child's law space charge limit using a one-dimensional particle-in-cell code. Also studied is the response of the emission model to strong electric fields near the transition point. We find the transition without geometrical effort is smooth and much slower than reported previously [J. P. Barbour, W. W. Dolan, J. K. Trolan, E. E. Martin, and W. P. Dyke, Phys. Rev. 92, 45 (1953)]. We analyze the effects of geometric field enhancement and work function on the transition. Using our previous model for effective field enhancement [Y. Feng and J. P. Verboncoeur, Phys. Plasmas 12, 103301 (2005)], we find the geometric effect dominates, and enhancement {beta}>10 can accelerate the approach to the space charge limit at practical electric field. A damped oscillation near the local plasma frequency is observed in the transient system response.

  19. Role of fluid density in shaping eruption currents driven by frontal particle blow-out

    NASA Astrophysics Data System (ADS)

    Carroll, C. S.; Turnbull, B.; Louge, M. Y.

    2012-06-01

    We study the role of suspension density in eruption currents, a regime of gravity-driven flow that is sustained by massive, localized blow-out of particles acting as a steady source of heavier fluid injected into a uniform flow at high Reynolds number. Inspired by the potential flow solution of Saffman and Yuen ["Finite-amplitude interfacial waves in the presence of a current," J. Fluid Mech. 123, 459-476 (1982), 10.1017/S0022112082003152], we show that the relative density difference between the two fluids swells the size of the current's head without changing its shape, while inducing a velocity jump at the interface. We test this inviscid theory against inviscid and large-eddy-simulations. We also conduct experiments in a water flume, where a line source of fluorescent brines of various densities is injected in a cross-stream and visualized with a narrow sheet of light. Simulations and experiments reveal that, with isotropic velocity distribution on a finite source, eruption currents expand further and develop interface oscillations, but the inviscid theory still captures relative swelling induced by density. We compare predictions to the static pressure data of McElwaine and Turnbull ["Air pressure data from the Vallee de la Sionne avalanches of 2004," J. Geophys. Res. 110, F03010, doi:, 10.1029/2004JF000237 (2005)] in powder snow avalanches.

  20. Model Predictive Control with Integral Action for Current Density Profile Tracking in NSTX-U

    NASA Astrophysics Data System (ADS)

    Ilhan, Z. O.; Wehner, W. P.; Schuster, E.; Boyer, M. D.

    2016-10-01

    Active control of the toroidal current density profile may play a critical role in non-inductively sustained long-pulse, high-beta scenarios in a spherical torus (ST) configuration, which is among the missions of the NSTX-U facility. In this work, a previously developed physics-based control-oriented model is embedded in a feedback control scheme based on a model predictive control (MPC) strategy to track a desired current density profile evolution specified indirectly by a desired rotational transform profile. An integrator is embedded into the standard MPC formulation to reject various modeling uncertainties and external disturbances. Neutral beam powers, electron density, and total plasma current are used as actuators. The proposed MPC strategy incorporates various state and actuator constraints directly into the control design process by solving a constrained optimization problem in real-time to determine the optimal actuator requests. The effectiveness of the proposed controller in regulating the current density profile in NSTX-U is demonstrated in closed-loop nonlinear simulations. Supported by the US DOE under DE-AC02-09CH11466.

  1. Model-based Optimization and Feedback Control of the Current Density Profile Evolution in NSTX-U

    NASA Astrophysics Data System (ADS)

    Ilhan, Zeki Okan

    Nuclear fusion research is a highly challenging, multidisciplinary field seeking contributions from both plasma physics and multiple engineering areas. As an application of plasma control engineering, this dissertation mainly explores methods to control the current density profile evolution within the National Spherical Torus eXperiment-Upgrade (NSTX-U), which is a substantial upgrade based on the NSTX device, which is located in Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ. Active control of the toroidal current density profile is among those plasma control milestones that the NSTX-U program must achieve to realize its next-step operational goals, which are characterized by high-performance, long-pulse, MHD-stable plasma operation with neutral beam heating. Therefore, the aim of this work is to develop model-based, feedforward and feedback controllers that can enable time regulation of the current density profile in NSTX-U by actuating the total plasma current, electron density, and the powers of the individual neutral beam injectors. Motivated by the coupled, nonlinear, multivariable, distributed-parameter plasma dynamics, the first step towards control design is the development of a physics-based, control-oriented model for the current profile evolution in NSTX-U in response to non-inductive current drives and heating systems. Numerical simulations of the proposed control-oriented model show qualitative agreement with the high-fidelity physics code TRANSP. The next step is to utilize the proposed control-oriented model to design an open-loop actuator trajectory optimizer. Given a desired operating state, the optimizer produces the actuator trajectories that can steer the plasma to such state. The objective of the feedforward control design is to provide a more systematic approach to advanced scenario planning in NSTX-U since the development of such scenarios is conventionally carried out experimentally by modifying the tokamak's actuator

  2. The Impact of Cathode Material and Shape on Current Density in an Aluminum Electrolysis Cell

    NASA Astrophysics Data System (ADS)

    Song, Yang; Peng, Jianping; Di, Yuezhong; Wang, Yaowu; Li, Baokuan; Feng, Naixiang

    2016-02-01

    A finite element model was developed to determine the impact of cathode material and shape on current density in an aluminum electrolysis cell. For the cathode material, results show that increased electrical resistivity leads to a higher cathode voltage drop; however, the horizontal current is reduced in the metal. The horizontal current magnitude for six different cathode materials in decreasing order is graphitized, semi-graphitized, full graphitic, 50% anthracite (50% artificial graphite), 70% anthracite (30% artificial graphite), 100% anthracite. The modified cathode shapes with an inclined cathode surface, higher collector bar and cylindrical protrusions are intended to improve horizontal current and flow resistance. Compared to a traditional cathode, modified collector bar sizes of 70 mm × 230 mm and 80 mm × 270 mm can reduce horizontal current density component Jx by 10% and 19%, respectively, due to better conductivity of the steel. The horizontal current in the metal decreases with increase of cathode inclination. The peak value of Jx can be approximately reduced by 20% for a 2° change in inclination. Cylindrical protrusions lead to local horizontal current increase on their tops, but the average current is less affected and the molten metal is effectively slowed down.

  3. Faraday-effect polarimeter-interferometer system for current density measurement on EAST

    NASA Astrophysics Data System (ADS)

    Liu, H. Q.; Jie, Y. X.; Ding, W. X.; Brower, D. L.; Zou, Z. Y.; Li, W. M.; Wang, Z. X.; Qian, J. P.; Yang, Y.; Zeng, L.; Lan, T.; Wei, X. C.; Li, G. S.; Hu, L. Q.; Wan, B. N.

    2014-11-01

    A multichannel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retro-reflectors are mounted in the inside wall for the double-pass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. Initial calibration indicates the electron line-integrated density resolution is less than 5 × 1016 m-2 (˜2°), and the Faraday rotation angle rms phase noise is <0.1°.

  4. Faraday-effect polarimeter-interferometer system for current density measurement on EAST.

    PubMed

    Liu, H Q; Jie, Y X; Ding, W X; Brower, D L; Zou, Z Y; Li, W M; Wang, Z X; Qian, J P; Yang, Y; Zeng, L; Lan, T; Wei, X C; Li, G S; Hu, L Q; Wan, B N

    2014-11-01

    A multichannel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retro-reflectors are mounted in the inside wall for the double-pass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. Initial calibration indicates the electron line-integrated density resolution is less than 5 × 10(16) m(-2) (∼2°), and the Faraday rotation angle rms phase noise is <0.1°.

  5. Faraday-effect polarimeter-interferometer system for current density measurement on EAST

    SciTech Connect

    Liu, H. Q.; Jie, Y. X. Zou, Z. Y.; Li, W. M.; Wang, Z. X.; Qian, J. P.; Yang, Y.; Zeng, L.; Wei, X. C.; Hu, L. Q.; Wan, B. N.; Ding, W. X.; Brower, D. L.; Lan, T.; Li, G. S.

    2014-11-15

    A multichannel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retro-reflectors are mounted in the inside wall for the double-pass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. Initial calibration indicates the electron line-integrated density resolution is less than 5 × 10{sup 16} m{sup −2} (∼2°), and the Faraday rotation angle rms phase noise is <0.1°.

  6. Improvement of the noise level of the Split Langmuir Probe - a spatial current density meter

    NASA Astrophysics Data System (ADS)

    Marusenkov, Andriy; Dudkin, Fedor; Shuvalov, Valentyn

    2013-04-01

    One of the main tasks at the experimental investigations of the wave processes in space plasma is the determination of the dispersion relations between their wave vector and frequency. The frequency analysis of the magnetic field fluctuations and the electric current density in plasma is very efficient in this case. It had been shown that the simultaneous measurements of the magnetic field orthogonal components and the spatial current density fluctuations can give the wave vector k values for the plane wave spectra, by which a wave field in a plasma reference frame can be represented. The measurements of the magnetic field fluctuations usually are made by a variety of magnetometers using well developed methods. Unfortunately, up to the moment the methods and instruments for the reliable measurements of the space current density are not so good developed as the magnetic ones. There are three independent techniques to study the spatial current density in plasma: the contactless Rogovsky coil, the Faraday cap and the Split Langmuir Probe (SLP). The attempt to compare the different approaches and instruments was carried out during the experiment "Variant" onboard Ukrainian remote sensing satellite SICH-1M launched 2004. The clear advantages of the SLP over other instruments were revealed and proved. Using whistler as a test signal the very good consistency between the magnetic and electric fields and the spatial electric current density was obtained. However, the signal-to-noise ratio of the current density meters has to be further improved. In this report we analyze the sources of the SLP noises and propose the ways to decrease it. The computer simulation of the improved current density meter reveals that the introduced changes have almost no influence on the sensor matching with the space plasma and, as a result, the minor changes of the transformation factor in operation frequency band are expected. The modernized version of the SLP was successfully tested in the

  7. Current densities and total contact currents during forest clearing tasks under 400 kV power lines

    PubMed Central

    Kuisti, Harri; Elovaara, Jarmo

    2016-01-01

    The aim of the study was to analyze all values of electric currents from measured periods while performing tasks in forest clearing. The objective was also to choose and analyze measurement cases, where current measurements successfully lasted the entire work period (about 30 min). Two forestry workers volunteered to perform four forest clearing tasks under 400 kV power lines. The sampling frequency of the current measurements was 1 sample/s. The maximum values of the current densities were 1.0–1.2 mA/m2 (calculated internal EFs 5.0–12.0 mV/m), and the average values were 0.2–0.4 mA/m2. The highest contact current was 167.4 μA. All measured values during forest clearing tasks were lower than basic restrictions (0.1 V/m and 0.8 V/m) of the International Commission on Non‐Ionizing Radiation Protection. Bioelectromagnetics. 37:423–428, 2016. © 2016 The Authors. Bioelectromagnetics published by Wiley Periodicals, Inc. PMID:27192179

  8. Finite temperature fermion condensate, charge and current densities in a (2+1)-dimensional conical space

    NASA Astrophysics Data System (ADS)

    Bellucci, S.; Bezerra de Mello, E. R.; Bragança, E.; Saharian, A. A.

    2016-06-01

    We evaluate the fermion condensate and the expectation values of the charge and current densities for a massive fermionic field in (2+1)-dimensional conical spacetime with a magnetic flux located at the cone apex. The consideration is done for both irreducible representations of the Clifford algebra. The expectation values are decomposed into the vacuum expectation values and contributions coming from particles and antiparticles. All these contributions are periodic functions of the magnetic flux with the period equal to the flux quantum. Related to the non-invariance of the model under the parity and time-reversal transformations, the fermion condensate and the charge density have indefinite parity with respect to the change of the signs of the magnetic flux and chemical potential. The expectation value of the radial current density vanishes. The azimuthal current density is the same for both the irreducible representations of the Clifford algebra. It is an odd function of the magnetic flux and an even function of the chemical potential. The behavior of the expectation values in various asymptotic regions of the parameters are discussed in detail. In particular, we show that for points near the cone apex the vacuum parts dominate. For a massless field with zero chemical potential the fermion condensate and charge density vanish. Simple expressions are derived for the part in the total charge induced by the planar angle deficit and magnetic flux. Combining the results for separate irreducible representations, we also consider the fermion condensate, charge and current densities in parity and time-reversal symmetric models. Possible applications to graphitic nanocones are discussed.

  9. Remarks on time-dependent [current]-density functional theory for open quantum systems.

    PubMed

    Yuen-Zhou, Joel; Aspuru-Guzik, Alán

    2013-08-14

    Time-dependent [current]-density functional theory for open quantum systems (OQS) has emerged as a formalism that can incorporate dissipative effects in the dynamics of many-body quantum systems. Here, we review and clarify some formal aspects of these theories that have been recently questioned in the literature. In particular, we provide theoretical support for the following conclusions: (1) contrary to what we and others had stated before, within the master equation framework, there is in fact a one-to-one mapping between vector potentials and current densities for fixed initial state, particle-particle interaction, and memory kernel; (2) regardless of the first conclusion, all of our recently suggested Kohn-Sham (KS) schemes to reproduce the current and particle densities of the original OQS, and in particular, the use of a KS closed driven system, remains formally valid; (3) the Lindblad master equation maintains the positivity of the density matrix regardless of the time-dependence of the Hamiltonian or the dissipation operators; (4) within the stochastic Schrödinger equation picture, a one-to-one mapping from stochastic vector potential to stochastic current density for individual trajectories has not been proven so far, except in the case where the vector potential is the same for every member of the ensemble, in which case, it reduces to the Lindblad master equation picture; (5) master equations may violate certain desired properties of the density matrix, such as positivity, but they remain as one of the most useful constructs to study OQS when the environment is not easily incorporated explicitly in the calculation. The conclusions support our previous work as formally rigorous, offer new insights into it, and provide a common ground to discuss related theories.

  10. Conductivity and current density image reconstruction using harmonic Bz algorithm in magnetic resonance electrical impedance tomography.

    PubMed

    Oh, Suk Hoon; Lee, Byung Il; Woo, Eung Je; Lee, Soo Yeol; Cho, Min Hyoung; Kwon, Ohin; Seo, Jin Keun

    2003-10-07

    Magnetic resonance electrical impedance tomography (MREIT) is to provide cross-sectional images of the conductivity distribution sigma of a subject. While injecting current into the subject, we measure one component Bz of the induced magnetic flux density B = (Bx, By, Bz) using an MRI scanner. Based on the relation between (inverted delta)2 Bz and inverted delta sigma, the harmonic Bz algorithm reconstructs an image of sigma using the measured Bz data from multiple imaging slices. After we obtain sigma, we can reconstruct images of current density distributions for any given current injection method. Following the description of the harmonic Bz algorithm, this paper presents reconstructed conductivity and current density images from computer simulations and phantom experiments using four recessed electrodes injecting six different currents of 26 mA. For experimental results, we used a three-dimensional saline phantom with two polyacrylamide objects inside. We used our 0.3 T (tesla) experimental MRI scanner to measure the induced Bz. Using the harmonic Bz algorithm, we could reconstruct conductivity and current density images with 82 x 82 pixels. The pixel size was 0.6 x 0.6 mm2. The relative L2 errors of the reconstructed images were between 13.8 and 21.5% when the signal-to-noise ratio (SNR) of the corresponding MR magnitude images was about 30. The results suggest that in vitro and in vivo experimental studies with animal subjects are feasible. Further studies are requested to reduce the amount of injection current down to less than 1 mA for human subjects.

  11. Laboratory study of magnetic reconnection with a density asymmetry across the current sheet.

    PubMed

    Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Jara-Almonte, Jonathan; Myers, Clayton E; Chen, Li-Jen

    2014-08-29

    The effects of a density asymmetry across the current sheet on anti-parallel magnetic reconnection are studied systematically in a laboratory plasma. Despite a significant density ratio of up to 10, the in-plane magnetic field profile is not significantly changed. On the other hand, the out-of-plane Hall magnetic field profile is considerably modified; it is almost bipolar in structure with the density asymmetry, as compared to quadrupolar in structure with the symmetric configuration. Moreover, the ion stagnation point is shifted to the low-density side, and the electrostatic potential profile also becomes asymmetric with a deeper potential well on the low-density side. Nonclassical bulk electron heating together with electromagnetic fluctuations in the lower hybrid frequency range is observed near the low-density-side separatrix. The dependence of the ion outflow and reconnection electric field on the density asymmetry is measured and compared with theoretical expectations. The measured ion outflow speeds are about 40% of the theoretical values.

  12. Investigation of current-density modification during magnetic reconnection by analysis of hydrogen-pellet deflection.

    PubMed

    Waller, V; Pégourié, B; Giruzzi, G; Huysmans, G T A; Garzotti, L; Géraud, A

    2003-11-14

    A pellet penetrating the inner region of a tokamak discharge, where the safety factor drops below unity, triggers an instability analogous to a sawtooth crash. Because of the simultaneity of the crash and pellet crossing, the latter is an appropriate probe for investigating the current distribution during reconnection. In this Letter, pellet deflection is used to characterize the associated electron distribution function. The perturbation compatible with the observed trajectory requires a negative current layer on the q=1 magnetic surface between 3 and 12 times the equilibrium current density and an expulsion of high energy electrons from the plasma core.

  13. Development of internal magnetic probe for current density profile measurement in Versatile Experiment Spherical Torus

    NASA Astrophysics Data System (ADS)

    Yang, J.; Lee, J. W.; Jung, B. K.; Chung, K. J.; Hwang, Y. S.

    2014-11-01

    An internal magnetic probe using Hall sensors to measure a current density profile directly with perturbation of less than 10% to the plasma current is successfully operated for the first time in Versatile Experiment Spherical Torus (VEST). An appropriate Hall sensor is chosen to produce sufficient signals for VEST magnetic field while maintaining the small size of 10 mm in outer diameter. Temperature around the Hall sensor in a typical VEST plasma is regulated by blown air of 2 bars. First measurement of 60 kA VEST ohmic discharge shows a reasonable agreement with the total plasma current measured by Rogowski coil in VEST.

  14. Development of internal magnetic probe for current density profile measurement in Versatile Experiment Spherical Torus.

    PubMed

    Yang, J; Lee, J W; Jung, B K; Chung, K J; Hwang, Y S

    2014-11-01

    An internal magnetic probe using Hall sensors to measure a current density profile directly with perturbation of less than 10% to the plasma current is successfully operated for the first time in Versatile Experiment Spherical Torus (VEST). An appropriate Hall sensor is chosen to produce sufficient signals for VEST magnetic field while maintaining the small size of 10 mm in outer diameter. Temperature around the Hall sensor in a typical VEST plasma is regulated by blown air of 2 bars. First measurement of 60 kA VEST ohmic discharge shows a reasonable agreement with the total plasma current measured by Rogowski coil in VEST.

  15. Nanoscale Imaging of Current Density with a Single-Spin Magnetometer.

    PubMed

    Chang, K; Eichler, A; Rhensius, J; Lorenzelli, L; Degen, C L

    2017-03-24

    Charge transport in nanostructures and thin films is fundamental to many phenomena and processes in science and technology, ranging from quantum effects and electronic correlations in mesoscopic physics, to integrated charge- or spin-based electronic circuits, to photoactive layers in energy research. Direct visualization of the charge flow in such structures is challenging due to their nanometer size and the itinerant nature of currents. In this work, we demonstrate noninvasive magnetic imaging of current density in two-dimensional conductor networks including metallic nanowires and carbon nanotubes. Our sensor is the electronic spin of a diamond nitrogen-vacancy center attached to a scanning tip and operated under ambient conditions. Using a differential measurement technique, we detect DC currents down to a few μA with a current density noise floor of ∼2 × 10(4) A/cm(2). Reconstructed images have a spatial resolution of typically 50 nm, with a best-effort value of 22 nm. Current density imaging offers a new route for studying electronic transport and conductance variations in two-dimensional materials and devices, with many exciting applications in condensed matter physics and materials science.

  16. High temperature and current density induced degradation of multi-layer graphene

    SciTech Connect

    Wang, Baoming; Haque, M. A.; Mag-isa, Alexander E.; Kim, Jae-Hyun; Lee, Hak-Joo

    2015-10-19

    We present evidence of moderate current density, when accompanied with high temperature, promoting migration of foreign atoms on the surface of multi-layer graphene. Our in situ transmission electron microscope experiments show migration of silicon atoms at temperatures above 800 °C and current density around 4.2 × 10{sup 7} A/cm{sup 2}. Originating from the micro-machined silicon structures that clamp the freestanding specimen, the atoms are observed to react with the carbon atoms in the multi-layer graphene to produce silicon carbide at temperatures of 900–1000 °C. In the absence of electrical current, there is no migration of silicon and only pyrolysis of polymeric residue is observed.

  17. Transport, deposition, and liftoff in laboratory density currents composed of hot particles in air

    NASA Astrophysics Data System (ADS)

    Andrews, B. J.; Manga, M.

    2010-12-01

    Understanding the dynamics of transport, deposition, and air entrainment in pyroclastic density currents (PDCs) is required for accurate predictions of future current behaviors and interpretations of ancient deposits, but directly observing the interiors of natural PDCs is effectively impossible. We model PDCs with scaled, hot, particle-laden density currents generated in a 6 m long, 0.6 m wide, 1.8 m tall air-filled tank. Comparison of relevant scaling between our experiments and natural PDCs indicates that we are accurately capturing much of the dynamics of dilute PDCs: * Reynolds numbers of our experiments are lower than natural currents, 10^3 compared to 10^6, but still fully turbulent; * Densimetric and Thermal Richardson numbers are of O(1) in both natural and modeled currents; * Stokes and settling numbers for particles in the experiments fall within the expected range for natural PDCs. Conditions within the tank are monitored with temperature and humidity probes. Experiments are illuminated with sheet lighting, and recorded with high-definition video cameras. In general, currents have average velocities of 10-20 cm/s, initial thicknesses of 10-20 cm (although thickness greatly increases as currents entrain and expand air), and run out or lift off distances of 3-5 m. Large Kelvin-Helmholtz type eddies usually form along the top of the current immediately behind the head; these vortices are similar in size to the total current thickness. In currents that lift off, the distal current end typically retreats with time. Preliminary results suggest that lift off distance decreases with increasing thermal Richardson number. Analysis of turbulent structures indicates that the current heads are dominated by large coherent structures with length scales, L, comparable to the current thickness. Within 5-10 L of the current fronts, sequences of similar large eddies often occur. At greater distances behind the current fronts, turbulent structures become smaller and less

  18. Role of head of turbulent 3-D density currents in mixing during slumping regime

    NASA Astrophysics Data System (ADS)

    Bhaganagar, Kiran

    2017-02-01

    A fundamental study was conducted to shed light on entrainment and mixing in buoyancy-driven Boussinesq density currents. Large-eddy simulation was performed on lock-exchange (LE) release density currents—an idealized test bed to generate density currents. As dense fluid was released over a sloping surface into an ambient lighter fluid, the dense fluid slumps to the bottom and forms a characteristic head of the current. The dynamics of the head dictated the mixing processes in LE currents. The key contribution of this study is to resolve an ongoing debate on mixing: We demonstrate that substantial mixing occurs in the early stages of evolution in an LE experiment and that entrainment is highly inhomogeneous and unsteady during the slumping regime. Guided by the flow physics, entrainment is calculated using two different but related perspectives. In the first approach, the entrainment parameter (E) is defined as the fraction of ambient fluid displaced by the head that entrains into the current. It is an indicator of the efficiency in which ambient fluid is displaced into the current and it serves as an important metric to compare the entrainment of dense currents over different types of surfaces, e.g., roughness configuration. In the second approach, E measures the net entrainment in the current at an instantaneous time t over the length of the current. Net entrainment coefficient is a metric to compare the effects of flow dynamical conditions, i.e., lock-aspect ratio that dictates the fraction of buoyancy entering the head, and also the effect of the sloping angle. Together, the entrainment coefficient and the net entrainment coefficient provide an insight into the entrainment process. The "active" head of the current acts as an engine that mixes the ambient fluid with the existing dense fluid, the 3-D lobes and clefts on the frontal end of the current causes recirculation of the ambient fluid into the current, and Kelvin-Helmholtz rolls are the mixers that

  19. Spectral broadening of parametric instability in lower hybrid current drive at a high density

    NASA Astrophysics Data System (ADS)

    Cesario, R.; Amicucci, L.; Cardinali, A.; Castaldo, C.; Marinucci, M.; Napoli, F.; Paoletti, F.; De Arcangelis, D.; Ferrari, M.; Galli, A.; Gallo, G.; Pullara, E.; Schettini, G.; Tuccillo, A. A.

    2014-04-01

    The important goal of adding to the bootstrap current a more flexible tool, capable of producing and controlling steady-state profiles with a high fraction of non-inductive plasma current, could be reached using the lower hybrid current drive (LHCD) effect. Experiments performed on FTU (Frascati Tokamak Upgrade) demonstrated that LHCD can occur at reactor-graded high plasma density, provided that the parametric instability (PI)-produced broadening of the spectrum launched by the antenna is reduced under proper operating conditions, capable of producing relatively high temperature in the outer region of plasma column. This condition was produced by operations that reduce particle recycling from the vessel walls, and enhance the gas fuelling in the core by means of fast pellet. New results of FTU experiments are presented documenting that the useful effect of temperature at the periphery, which reduces the LH spectral broadening and enhances the LH-induced hard-x ray emission level, occurs in a broader range of plasma parameters than in previous work. Modelling results show that a further tool for helping LHCD at a high density would be provided by electron cyclotron resonant heating of plasma periphery. New information is provided on the modelling, able determining frequencies, growth rates and LH spectral broadening produced by PI, which allowed assessing the new method for enabling LHCD at high densities. Further robustness is provided to theoretical and experimental fundaments of the method for LHCD at a high density.

  20. THEMIS two-point measurements of the cross-tail current density: A thick bifurcated current sheet in the near-Earth plasma sheet.

    PubMed

    Saito, Miho

    2015-08-01

    The basic properties of the near-Earth current sheet from 8 RE to 12 RE were determined based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations from 2007 to 2013. Ampere's law was used to estimate the current density when the locations of two spacecraft were suitable for the calculation. A total of 3838 current density observations were obtained to study the vertical profile. For typical solar wind conditions, the current density near (off) the central plane of the current sheet ranged from 1 to 2 nA/m(2) (1 to 8 nA/m(2)). All the high current densities appeared off the central plane of the current sheet, indicating the formation of a bifurcated current sheet structure when the current density increased above 2 nA/m(2). The median profile also showed a bifurcated structure, in which the half thickness was about 3 RE . The distance between the peak of the current density and the central plane of the current sheet was 0.5 to 1 RE . High current densities above 4 nA/m(2) were observed in some cases that occurred preferentially during substorms, but they also occurred in quiet times. In contrast to the commonly accepted picture, these high current densities can form without a high solar wind dynamic pressure. In addition, these high current densities can appear in two magnetic configurations: tail-like and dipolar structures. At least two mechanisms, magnetic flux depletion and new current system formation during the expansion phase, other than plasma sheet compression are responsible for the formation of the bifurcated current sheets.

  1. THEMIS two‐point measurements of the cross‐tail current density: A thick bifurcated current sheet in the near‐Earth plasma sheet

    PubMed Central

    2015-01-01

    Abstract The basic properties of the near‐Earth current sheet from 8 RE to 12 RE were determined based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations from 2007 to 2013. Ampere's law was used to estimate the current density when the locations of two spacecraft were suitable for the calculation. A total of 3838 current density observations were obtained to study the vertical profile. For typical solar wind conditions, the current density near (off) the central plane of the current sheet ranged from 1 to 2 nA/m2 (1 to 8 nA/m2). All the high current densities appeared off the central plane of the current sheet, indicating the formation of a bifurcated current sheet structure when the current density increased above 2 nA/m2. The median profile also showed a bifurcated structure, in which the half thickness was about 3 RE. The distance between the peak of the current density and the central plane of the current sheet was 0.5 to 1 RE. High current densities above 4 nA/m2 were observed in some cases that occurred preferentially during substorms, but they also occurred in quiet times. In contrast to the commonly accepted picture, these high current densities can form without a high solar wind dynamic pressure. In addition, these high current densities can appear in two magnetic configurations: tail‐like and dipolar structures. At least two mechanisms, magnetic flux depletion and new current system formation during the expansion phase, other than plasma sheet compression are responsible for the formation of the bifurcated current sheets. PMID:27722039

  2. Comparison between the magnetic and transport critical current densities in high critical current density melt-textured yttrium barium copper-oxide

    NASA Technical Reports Server (NTRS)

    Gao, L.; Meng, R. L.; Xue, Y. Y.; Hor, P. H.; Chu, C. W.

    1991-01-01

    Using a recently developed pulsed critical current density (Jc) measuring system, the Jc of the high-Jc melt-textured YBa2Cu3O(7-delta) (Y123) bulk samples has been determined. I-V curves with a voltage resolution of 0.5 microV were obtained, and transport Jc's along the a-b plane as high as 7.2 x 10 to the 4th A/sq cm were extracted. These results are comparable to the values obtained magnetically. On the other hand, transport Jc along the c axis were found to be two orders of magnitude smaller, even though the magnetic Jc along the c axis is only about five times smaller than Jc along the a-b plane. It is suggested that for the high-temperature superconducting materials which are highly anisotropic, caution should be taken when using the nontransport magnetic methods to determine Jc.

  3. Non-equilibrium steady states: fluctuations and large deviations of the density and of the current

    NASA Astrophysics Data System (ADS)

    Derrida, Bernard

    2007-07-01

    These lecture notes give a short review of methods such as the matrix ansatz, the additivity principle or the macroscopic fluctuation theory, developed recently in the theory of non-equilibrium phenomena. They show how these methods allow us to calculate the fluctuations and large deviations of the density and the current in non-equilibrium steady states of systems like exclusion processes. The properties of these fluctuations and large deviation functions in non-equilibrium steady states (for example, non-Gaussian fluctuations of density or non-convexity of the large deviation function which generalizes the notion of free energy) are compared with those of systems at equilibrium.

  4. Effects of Neutral Density on Energetic Ions Produced Near High-Current Hollow Cathodes

    NASA Technical Reports Server (NTRS)

    Kameyama, Ikuya

    1997-01-01

    Energy distributions of ion current from high-current, xenon hollow cathodes, which are essential information to understand erosion phenomena observed in high-power ion thrusters, were obtained using an electrostatic energy analyzer (ESA). The effects of ambient pressure and external flow rate introduced immediately downstream of hollow cathode on ion currents with energies greater than that associated with the cathode-to-anode potential difference were investigated. The results were analyzed to determine the changes in the magnitudes of ion currents to the ESA at various energies. Either increasing the ambient pressure or adding external flow induces an increase in the distribution of ion currents with moderate energies (epsilon less than 25 to 35 eV) and a decrease in the distribution for high energies (epsilon greater than 25 to 35 eV). The magnitude of the current distribution increase in the moderate energy range is greater for a cathode equipped with a toroidal keeper than for one without a keeper, but the distribution in the high energy range does not seem to be affected by a keeper. An MHD model, which has been proposed to describe energetic-ion production mechanism in hollow cathode at high discharge currents, was developed to describe these effects. The results show, however, that this model involves no mechanism by which a significant increase of ion current could occur at any energy. It was found, on the other hand, that the potential-hill model of energetic ion production, which assumes existence of a local maximum of plasma potential, could explain combined increases in the currents of ions with moderate energies and decreases in high energy ions due to increased neutral atom density using a charge-exchange mechanism. The existing, simplified version of the potential-hill model, however, shows poor quantitative agreement with measured ion-current-energy-distribution changes induced by neutral density changes.

  5. Thermal history of pyroclastic density currents and pyroclasts at Tungurahua, Ecuador

    NASA Astrophysics Data System (ADS)

    Benage, M. C.; Dufek, J.

    2014-12-01

    The associated hazards and opaqueness of pyroclastic density currents (PDCs) make it impossible for in-situ thermal or concentration measurements within the currents that would provide critical information on the dynamics of PDCs. The entrainment of ambient air into these currents significantly impacts their runout distance and thermal history. The most efficient mechanism to cool a PDC is through the entrainment of colder, denser ambient air through Kelvin-Helmholtz and lobe-and-cleft instabilities, which are dependent on density stratification in the current and topographic-current interactions. The combination of high-resolution multiphase numerical models in concert with field measurements of PDC deposits allows us to better understand the evolving concentration gradients, instabilities, entrainment of air, and temperatures of PDCs. We employ a three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model, high-resolution topography, and field data to understand the PDCs that traveled down the Juive Grande quebrada during the 2006 eruption of Tungurahua volcano. The multiphase model allows us to examine PDC dynamics such as particle concentrations, velocities, thermal heterogeneities, and ambient air entrainment. As the PDC propagates, the entrainment coefficient decreases due to enhanced density stratification. The interaction of the current with rugged topography increases the entrainment coefficient. We also calculate the temperature of deposition and breadcrust bomb rind thickness for individual pyroclasts. The individual pyroclasts are tracked as Lagrangian particles in the multiphase model and we employ the breadcrust bomb model (Benage et al., 2014) to calculate the deposition temperature and the formation of the non-vesicular to low vesicularity rinds. The model results are compared to paleomagnetic data and field measurements of rind thickness, respectively. This allows the deposited pyroclasts to be natural thermometers that help constrain the

  6. Density currents in the Chicago River: Characterization, effects on water quality, and potential sources

    USGS Publications Warehouse

    Jackson, P. Ryan; Garcia, Carlos M.; Oberg, Kevin A.; Johnson, Kevin K.; Garcia, Marcelo H.

    2008-01-01

    Bidirectional flows in a river system can occur under stratified flow conditions and in addition to creating significant errors in discharge estimates, the upstream propagating currents are capable of transporting contaminants and affecting water quality. Detailed field observations of bidirectional flows were made in the Chicago River in Chicago, Illinois in the winter of 2005-06. Using multiple acoustic Doppler current profilers simultaneously with a water-quality profiler, the formation of upstream propagating density currents within the Chicago River both as an underflow and an overflow was observed on three occasions. Density differences driving the flow primarily arise from salinity differences between intersecting branches of the Chicago River, whereas water temperature is secondary in the creation of these currents. Deicing salts appear to be the primary source of salinity in the North Branch of the Chicago River, entering the waterway through direct runoff and effluent from a wastewater-treatment plant in a large metropolitan area primarily served by combined sewers. Water-quality assessments of the Chicago River may underestimate (or overestimate) the impairment of the river because standard water-quality monitoring practices do not account for density-driven underflows (or overflows). Chloride concentrations near the riverbed can significantly exceed concentrations at the river surface during underflows indicating that full-depth parameter profiles are necessary for accurate water-quality assessments in urban environments where application of deicing salt is common.

  7. Current density filaments measured by electrostatic, magnetic and optical diagnostics in RFX-mod

    NASA Astrophysics Data System (ADS)

    Vianello, N.; Spolaore, M.; Agostini, M.; Antoni, V.; Cavazzana, R.; Martines, E.; Serianni, G.; Scarin, P.; Spada, E.; Zuin, M.

    2008-11-01

    Edge turbulence is ubiquitous in fusion devices and characterized by the formation of coherent structures which are believed to play a relevant role in driving particle losses. These structures have been observed also in the edge region of the RFX-mod Reversed Field Pinch device. In order to gain insight into their origin and features an original probe system has been used measuring both magnetic and electrostatic fluctuations simultaneously and on the same location with a high time resolution. This insertable probe head allows the direct measurements of several plasma parameters including local vorticity patterns and current density fluctuations. An array of toroidally distributed sensors allows following the structures along the main flow direction. It is found that in the cross-field plane bursts correspond to pressure structures and are related to current density filaments mainly oriented along the magnetic field. These results are compared with those provided by the measured relationship between structures on HeI emitted radiation observed by the Gas Puffing Imaging system and magnetic fluctuations. The presence and features of the current density filaments are assessed at different plasma current regimes.

  8. Irreversibility line in superconductor as line of constant shielding current density

    SciTech Connect

    Goemoery, F.; Takacs, S.; Holubar, T.

    1997-06-01

    The irreversibility of magnetic properties of superconductors is due to the existence of macroscopic shielding currents persisting for some period of time. The same currents offer nearly lossless electricity transport. Thus, the extent of magnetic irreversibility is directly proportional to the current-carrying capacity of a superconductor. Because the current-carrying capacity is an intrinsic property of the material, various experimental techniques should give the same irreversibility line corresponding to the same macroscopic shielding current density. Following this approach, the authors compared the irreversibility lines obtained from AC susceptibility measurement with those determined from quasistatic magnetization loops recorded with the help of a SQUID susceptometer. An additional parameter which has to be comparable is the electrical field characterizing the rate of change of the magnetic field. Fulfilling these conditions of equivalency, the authors found that it is possible to explain the irreversibility lines obtained by various techniques and at different conditions by the same physical model. They demonstrate that for the data, taken within two orders of magnitude for the current density and more than seven orders of magnitude for the electrical field, a consistent picture expressing all the observed features by the same model can be found. Measurements are presented from YBCO samples.

  9. Assessing Current State Science Teaching and Learning Standards for Ability to Achieve Climate Science Literacy

    NASA Astrophysics Data System (ADS)

    Busch, K. C.

    2012-12-01

    addressed. Least covered were number 6 "Human activities are impacting the climate system" and number 7 "Climate change will have consequences for the Earth system and human lives." Most references, either direct or indirect, occurred in the high school standards for earth science, a class not required for graduation in either state. This research points to the gaps between what the 7 Essential Principles of Climate Literacy defines as essential knowledge and what students may learn in their K-12 science classes. Thus, the formal system does not seem to offer an experience which can potentially develop a more knowledgeable citizenry who will be able to make wise personal and policy decisions about climate change, falling short of the ultimate goal of achieving widespread climate literacy. Especially troubling was the sparse attention to the principles addressing the human connection to the climate - principles number 6 and 7. If climate literate citizens are to make "wise personal and policy decisions" (USGCRP, 2009), these two principles especially are vital. This research, therefore, has been valuable for identifying current shortcomings in state standards.

  10. Magnetically filtered Faraday probe for measuring the ion current density profile of a Hall thruster

    SciTech Connect

    Rovey, Joshua L.; Walker, Mitchell L.R.; Gallimore, Alec D.; Peterson, Peter Y.

    2006-01-15

    The ability of a magnetically filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operating over the range of 300-500 V and 5-10 mg/s. The probes are evaluated on a xenon propellant Hall thruster in the University of Michigan Large Vacuum Test Facility at operating pressures within the range of 4.4x10{sup -4} Pa Xe (3.3x10{sup -6} Torr Xe) to 1.1x10{sup -3} Pa Xe (8.4x10{sup -6} Torr Xe) in order to study the ability of the Faraday probe designs to filter out CEX ions. Detailed examination of the results shows that the nude probe measures a greater ion current density profile than both the MFFP and BFP over the range of angular positions investigated for each operating condition. The differences between the current density profiles obtained by each probe are attributed to the ion filtering systems employed. Analysis of the results shows that the MFFP, operating at a +5 A solenoid current, provides the best agreement with flight-test data and across operating pressures.

  11. Experimental investigations of LHW-plasma coupling and current drive related to achieving H-mode plasmas in EAST

    NASA Astrophysics Data System (ADS)

    Ding, B. J.; Kong, E. H.; Li, M. H.; Zhang, Lei; Wei, W.; Wang, M.; Xu, H. D.; Li, Y. C.; Ling, B. L.; Zang, Q.; Xu, G. S.; Han, X. F.; Zhao, H. L.; Zhang, Ling; Zhao, L. M.; Hu, H. C.; Yang, Y.; Liu, L.; Ekedahl, A.; Goniche, M.; Cesario, R.; Peysson, Y.; Decker, J.; Basiuk, V.; Huynh, P.; Artaud, J.; Imbeaux, F.; Shan, J. F.; Liu, F. K.; Zhao, Y. P.; Gong, X. Z.; Hu, L. Q.; Gao, X.; Guo, H. Y.; Wan, B. N.; Li, J. G.; the EAST Team

    2013-11-01

    Aimed at high-confinement (H-mode) plasmas in the Experimental Advanced Superconducting Tokamak (EAST), the effect of local gas puffing from electron and ion sides of a lower hybrid wave (LHW) antenna on LHW-plasma coupling and high-density experiments with lower hybrid current drive (LHCD) are investigated in EAST. Experimental results show that gas puffing from the electron side is more favourable to improve coupling compared with gas puffing from the ion side. Investigations indicate that LHW-plasma coupling without gas puffing is affected by the density near the LHW grill (grill density), hence leading to multi-transition of low-high-low (L-H-L) confinement, with a correspondingly periodic characteristic behaviour in the plasma radiation. High-density experiments with LHCD suggest that strong lithiation gives a significant improvement on current drive efficiency in the higher density region than 2 × 1019 m-3. Studies indicate that the sharp decrease in current drive efficiency is mainly correlated with parametric decay instability. Using lithium coating and gas puffing from the electron side of the LHW antenna, an H-mode plasma is obtained by LHCD in a wide range of parameters, whether LHW is deposited inside the half-minor radius or not, implying that a central and large driven current is not a necessary condition for the H-mode plasma. H-mode is investigated with CRONOS.

  12. Clinical Outcomes according to the Achievement of Target Low Density Lipoprotein-Cholesterol in Patients with Acute Myocardial Infarction

    PubMed Central

    Ahn, Taehoon; Lee, Kyounghoon; Kang, Woong Chol; Han, Seung Hwan; Ahn, Youngkeun; Jeong, Myung Ho

    2017-01-01

    Background and Objectives The clinical outcome of patient with an acute myocardial infarction (AMI) undergoing percutaneous coronary intervention (PCI), with or without achievement of target low density lipoprotein-cholesterol (LDL-C), has little known information. This study investigated if target LDL-C level (below 70 mg/dL) achievements in patients with AMI showed better clinical outcomes or not. Subjects and Methods Between May 2008 and September 2012, this study enrolled 13473 AMI patients in a large-scale, prospective, multicenter Korean Myocardial Infarction (KorMI) registry. 12720 patients survived and 6746 patients completed a 1-year clinical follow up. Among them 3315 patients received serial lipid profile follow-ups. Propensity score matching was applied to adjust for differences in clinical baseline and angiographic characteristics, producing a total of 1292 patients (646 target LDL-C achievers vs. 646 non-achievers). The primary end point was the composite of a 1-year major adverse cardiac event (MACE) including cardiac death, recurrent myocardial infarction (MI), target lesion revascularization (TLR) and coronary artery bypass grafting. Results After propensity score matching, baseline clinical and angiographic characteristics were similar between the two groups. Clinical outcomes of the propensity score matched patients who showed no significant differences in cardiac death (0.5% vs. 0.5%, p=1.000), recurrent MI (1.1% vs. 0.8%, p=0.562), TLR (5.0% vs. 4.5%, p=0.649), MACEs (6.5% vs. 5.9%, p=0.644) and stent thrombosis (2.5% vs. 1.9%, p=0.560). Conclusion In this propensity-matched comparison, AMI patients undergoing PCI with a target LDL-C (below 70 mg/dL) achievement did not show better clinical outcomes. PMID:28154588

  13. Achieving High-Energy-High-Power Density in a Flexible Quasi-Solid-State Sodium Ion Capacitor.

    PubMed

    Li, Hongsen; Peng, Lele; Zhu, Yue; Zhang, Xiaogang; Yu, Guihua

    2016-09-14

    Simultaneous integration of high-energy output with high-power delivery is a major challenge for electrochemical energy storage systems, limiting dual fine attributes on a device. We introduce a quasi-solid-state sodium ion capacitor (NIC) based on a battery type urchin-like Na2Ti3O7 anode and a capacitor type peanut shell derived carbon cathode, using a sodium ion conducting gel polymer as electrolyte, achieving high-energy-high-power characteristics in solid state. Energy densities can reach 111.2 Wh kg(-1) at power density of 800 W kg(-1), and 33.2 Wh kg(-1) at power density of 11200 W kg(-1), which are among the best reported state-of-the-art NICs. The designed device also exhibits long-term cycling stability over 3000 cycles with capacity retention ∼86%. Furthermore, we demonstrate the assembly of a highly flexible quasi-solid-state NIC and it shows no obvious capacity loss under different bending conditions.

  14. Towards time-dependent current-density-functional theory in the non-linear regime

    SciTech Connect

    Escartín, J. M.; Vincendon, M.; Dinh, P. M.; Suraud, E.; Romaniello, P.; Reinhard, P.-G.

    2015-02-28

    Time-Dependent Density-Functional Theory (TDDFT) is a well-established theoretical approach to describe and understand irradiation processes in clusters and molecules. However, within the so-called adiabatic local density approximation (ALDA) to the exchange-correlation (xc) potential, TDDFT can show insufficiencies, particularly in violently dynamical processes. This is because within ALDA the xc potential is instantaneous and is a local functional of the density, which means that this approximation neglects memory effects and long-range effects. A way to go beyond ALDA is to use Time-Dependent Current-Density-Functional Theory (TDCDFT), in which the basic quantity is the current density rather than the density as in TDDFT. This has been shown to offer an adequate account of dissipation in the linear domain when the Vignale-Kohn (VK) functional is used. Here, we go beyond the linear regime and we explore this formulation in the time domain. In this case, the equations become very involved making the computation out of reach; we hence propose an approximation to the VK functional which allows us to calculate the dynamics in real time and at the same time to keep most of the physics described by the VK functional. We apply this formulation to the calculation of the time-dependent dipole moment of Ca, Mg and Na{sub 2}. Our results show trends similar to what was previously observed in model systems or within linear response. In the non-linear domain, our results show that relaxation times do not decrease with increasing deposited excitation energy, which sets some limitations to the practical use of TDCDFT in such a domain of excitations.

  15. Cluster electric current density measurements within a magnetic flux rope in the plasma sheet

    NASA Technical Reports Server (NTRS)

    Slavin, J. A.; Lepping, R. P.; Gjerloev, J.; Goldstein, M. L.; Fairfield, D. H.; Acuna, M. H.; Balogh, A.; Dunlop, M.; Kivelson, M. G.; Khurana, K.

    2003-01-01

    On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

  16. Influences of urban fabric on pyroclastic density currents at Pompeii (Italy): 1. Flow direction and deposition

    NASA Astrophysics Data System (ADS)

    Gurioli, L.; Zanella, E.; Pareschi, M. T.; Lanza, R.

    2007-05-01

    To assess ways in which the products of explosive eruptions interact with human settlements, we performed volcanological and rock magnetic analyses on the deposits of the A.D. 79 eruption at the Pompeii excavations (Italy). During this eruption the Roman town of Pompeii was covered by 2.5 m of fallout pumice and then partially destroyed by pyroclastic density currents (PDCs). Anisotropy of magnetic susceptibility measurements performed on the fine matrix of the deposits allowed the quantification of the variations in flow direction and emplacement mechanisms of the parental PDCs that entered the town. These results, integrated with volcanological field investigations, revealed that the presence of buildings, still protruding through the fallout deposits, strongly affected the distribution and accumulation of the erupted products. All of the PDCs that entered the town, even the most dilute ones, were density stratified currents in which interaction with the urban fabric occurred in the lower part of the current. The degree of interaction varied mainly as a function of obstacle height and density stratification within the current. For examples, the lower part of the EU4pf current left deposits up to 3 m thick and was able to interact with 2- to 4-m-high obstacles. However, a decrease in thickness and grain size of the deposits across the town indicates that even though the upper portion of the current was able to decouple from the lower portion, enabling it to flow over the town, it was not able to fully restore the sediment supply to the lower portion in order to maintain the deposition observed upon entry into the town.

  17. X-ray diagnostic for current density profiling relativistic electron beams in vacuum and gas

    SciTech Connect

    Slaughter, D.; Koppel, L.; Smith, J.

    1986-02-15

    An x-ray imaging technique has been studied for the purpose of observing the current density profile in a high-current relativistic electron beam (50 MeV, 10 kA). Calculations and measurements of energy spectra and intensities are in good agreement. Results indicate sufficient photon yield for pinhole imaging when the beam deposits a small part of its energy in high-Z gas or a thin high-Z foil. Characteristic L and K x-ray emission is not found not be a reliable technique due to strong L and K shell fluorescence in the presence of intense bremsstrahlung radiation. It is also found that at pressures on the order of one atmosphere, the density of energy deposition in a gas cell is too small to generate sufficient photon yield for time-resolved measurements.

  18. High current density and low turn-on field from aligned Cd(OH)2 nanosheets

    NASA Astrophysics Data System (ADS)

    Bagal, Vivekanand S.; Patil, Girish P.; Deore, Amol B.; Baviskar, Prashant K.; Suryawanshi, Sachin R.; More, Mahendra A.; Chavan, Padmakar G.

    2016-04-01

    High current density of 9.8 mA/cm2 was drawn at an applied field of 4.1 V/μm from aligned Cd(OH)2 nanosheets and low turn-on field of 1.4 V/μm was found for the emission current density of 10 μA/cm2. The aligned Cd(OH)2 nanosheets were synthesized by CBD technique on Cadmium foil. To the best of our knowledge this is the first report on the field emission studies of Cd(OH)2 nanosheets. Simple synthesis route coupled with superior field emission properties indicate the possible use of Cd(OH)2 nanosheets for micro/nanoelectronic devices.

  19. Two-dimensional simulations of temperature and current-density distribution in electromigrated structures

    NASA Astrophysics Data System (ADS)

    Kießig, Birgit; Schäfer, Roland; von Löhneysen, Hilbert

    2014-01-01

    We report on the application of a feedback-controlled electromigration technique for the formation of nanometre-sized gaps in mesoscopic gold wires and rings. The effect of current density and temperature, linked via Joule heating, on the resulting gap size is investigated. Our experiments include in situ measurements of the evolution of the electrical resistance and of the structure of the device during electromigration. Experimentally, a good thermal coupling to the substrate turned out to be crucial to reach electrode spacings below 10 nm and to avoid overall melting of the nanostructures. This finding is supported by numerical calculations of the current-density and temperature profiles for structure layouts subjected to electromigration. The numerical method can be used for optimizing the layout so as to predetermine the location where electromigration leads to the formation of a gap.

  20. Simulating the frontal instability of lock-exchange density currents with dissipative particle dynamics

    NASA Astrophysics Data System (ADS)

    Li, Yanggui; Geng, Xingguo; Wang, Heping; Zhuang, Xin; Ouyang, Jie

    2016-06-01

    The frontal instability of lock-exchange density currents is numerically investigated using dissipative particle dynamics (DPD) at the mesoscopic particle level. For modeling two-phase flow, the “color” repulsion model is adopted to describe binary fluids according to Rothman-Keller method. The present DPD simulation can reproduce the flow phenomena of lock-exchange density currents, including the lobe-and-cleft instability that appears at the head, as well as the formation of coherent billow structures at the interface behind the head due to the growth of Kelvin-Helmholtz instability. Furthermore, through the DPD simulation, some small-scale characteristics can be observed, which are difficult to be captured in macroscopic simulation and experiment.

  1. Effect of particle entrainment on the runout of pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Fauria, Kristen E.; Manga, Michael; Chamberlain, Michael

    2016-09-01

    Pyroclastic density currents (PDCs) can erode soil and bedrock, yet we currently lack a mechanistic understanding of particle entrainment that can be incorporated into models and used to understand how PDC bulking affects runout. Here we quantify how particle splash, the ejection of particles due to impact by a projectile, entrains particles into dilute PDCs. We use scaled laboratory experiments to measure the mass of sand ejected by impacts of pumice, wood, and nylon spheres. We then derive an expression for particle splash that we validate with our experimental results as well as results from seven other studies. We find that the number of ejected particles scales with the kinetic energy of the impactor and the depth of the crater generated by the impactor. Last, we use a one-dimensional model of a dilute, compressible density current—where runout distance is controlled by air entrainment and particle exchange with the substrate—to examine how particle entrainment by splash affects PDC density and runout. Splash-driven particle entrainment can increase the runout distance of dilute PDCs by an order of magnitude. Furthermore, the temperature of entrained particles greatly affects runout and PDCs that entrain ambient temperature particles runout farther than those that entrain hot particles. Particle entrainment by splash therefore not only increases the runout of dilute PDCs but demonstrates that the temperature and composition of the lower boundary have consequences for PDC density, temperature, runout, hazards and depositional record.

  2. Current density and poloidal magnetic field for toroidal elliptic plasmas with triangularity

    SciTech Connect

    Martin, P.; Haines, M.G.; Castro, E.

    2005-08-15

    Changes in the poloidal magnetic field around a tokamak magnetic surface due to different values of triangularity and ellipticity are analyzed in this paper. The treatment here presented allows the determination of the poloidal magnetic field from knowledge of the toroidal current density. Different profiles of these currents are studied. Improvements in the analytic forms of the magnetic surfaces have also been found. The treatment has been performed using a recent published system of coordinates. Suitable analytic equations have been used for the elliptic magnetic surfaces with triangularity and Shafranov shift.

  3. Magnetic resonance electrical impedance tomography (MREIT): conductivity and current density imaging

    NASA Astrophysics Data System (ADS)

    Seo, Jin Keun; Kwon, Ohin; Woo, Eung Je

    2005-01-01

    This paper reviews the latest impedance imaging technique called Magnetic Resonance Electrical Impedance Tomography (MREIT) providing information on electrical conductivity and current density distributions inside an electrically conducting domain such as the human body. The motivation for this research is explained by discussing conductivity changes related with physiological and pathological events, electromagnetic source imaging and electromagnetic stimulations. We briefly summarize the related technique of Electrical Impedance Tomography (EIT) that deals with cross-sectional image reconstructions of conductivity distributions from boundary measurements of current-voltage data. Noting that EIT suffers from the ill-posed nature of the corresponding inverse problem, we introduce MREIT as a new conductivity imaging modality providing images with better spatial resolution and accuracy. MREIT utilizes internal information on the induced magnetic field in addition to the boundary current-voltage measurements to produce three-dimensional images of conductivity and current density distributions. Mathematical theory, algorithms, and experimental methods of current MREIT research are described. With numerous potential applications in mind, future research directions in MREIT are proposed.

  4. Fast electron current density profile and diffusion studies during LHCD in PBX-M

    SciTech Connect

    Jones, S.E.; Kesner, J.; Luckhardt, S.; Paoletti, F.; von Goeler, S.; Bernabei, S.; Kaita, R.; Rimini, F.

    1993-08-01

    Successful current profile control experiments using lower hybrid current drive (LCHD) clearly require knowledge of (1) the location of the driven fast electrons and (2) the ability to maintain that location from spreading due to radial diffusion. These issues can be addressed by examining the data from the hard x-ray camera on PBX-M, a unique diagnostic producing two-dimensional, time resolved tangential images of fast electron bremsstrahlung. Using modeling, these line-of-sight images are inverted to extract a radial fast electron current density profile. We note that ``hollow`` profiles have been observed, indicative of off-axis current drive. These profiles can then be used to calculate an upper bound for an effective fast electron diffusion constant: assuming an extremely radially narrow lower hybrid absorption profile and a transport model based on Rax and Moreau, a model fast electron current density profile is calculated and compared to the experimentally derived profile. The model diffusion constant is adjusted until a good match is found. Applied to steady-state quiescent modes on PBX-M, we obtain an upper limit for an effective diffusion constant of about D*=1.1 m{sup 2}/sec.

  5. Structural transitions in electron beam deposited Co-carbonyl suspended nanowires at high electrical current densities.

    PubMed

    Gazzadi, Gian Carlo; Frabboni, Stefano

    2015-01-01

    Suspended nanowires (SNWs) have been deposited from Co-carbonyl precursor (Co2(CO)8) by focused electron beam induced deposition (FEBID). The SNWs dimensions are about 30-50 nm in diameter and 600-850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC) and hexagonal close-packed (HCP) Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM) analysis and by energy-dispersive X-ray (EDX) spectroscopy, respectively. Current (I)-voltage (V) measurements with current densities up to 10(7) A/cm(2) determine different structural transitions in the SNWs, depending on the I-V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 10(7) A/cm(2). The role played by resistive heating and electromigration in these transitions is discussed.

  6. Microstructure dependence of the c-axis critical current density in second generation YBCO tapes

    SciTech Connect

    Jia, Y. Welp, U. Crabtree, G.W.; Kwok, W.K.; Malozemoff, A.P.; Rupich, M.W.; Fleshler, S.; Clem, J.R.

    2011-10-31

    C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density J{sub c}{sup c} has been recently found to be orders of magnitude lower than the ab-plane critical current density J{sub c}{sup ab}. Here we report on J{sub c}{sup c} (77 K, sf) values of various YBa{sub 2}Cu{sub 3}O{sub 7}-based (YBCO) tapes with different microstructures. Our results show that the value of J{sub c}{sup c} (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy {gamma} = J{sub c}{sup ab}/J{sub c}{sup c} can reach values as high as 2070, implying that in the highest-anisotropy tape, {approx}20% of the tape width carries c-axis current in a helically wound power cable.

  7. Microstructure dependence of the c-axis critical current density in second-generation YBCO tapes.

    SciTech Connect

    Jia, Y.; Welp, U.; Crabtree, G. W.; Kwok, W. K.; Malozemoff, A. P.; Rupich, M. W.; Fleshler, S.; Clem, J. R.

    2011-10-01

    C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density J{sub c}{sup c} has been recently found to be orders of magnitude lower than the ab-plane critical current density J{sub c}{sup ab}. Here we report on J{sub c}{sup c} (77 K, sf) values of various YBa{sub 2}Cu{sub 3}O{sub 7}-based (YBCO) tapes with different microstructures. Our results show that the value of J{sub c}{sup c} (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy {gamma} = J{sub c}{sup ab}/J{sub c}{sup c} can reach values as high as 2070, implying that in the highest-anisotropy tape, {approx}20% of the tape width carries c-axis current in a helically wound power cable.

  8. Microwave field frequency and current density modulated skyrmion-chain in nanotrack

    PubMed Central

    Ma, Fusheng; Ezawa, Motohiko; Zhou, Yan

    2015-01-01

    Magnetic skyrmions are promising candidates as information carriers for the next-generation spintronic devices because of their small size, facile current-driven motion and topological stability. The controllable nucleation and motion of skyrmions in magnetic nanostructures will be essential in future skyrmionic devices. Here, we present the microwave assisted nucleation and motion of skyrmion-chains in magnetic nanotrack by micromagnetic simulation. A skyrmion-chain is a one-dimensional cluster of equally spaced skyrmions. A skyrmion-chain conveys an integer bit n when it consists of n skyrmions. A series of skyrmion-chains with various lengths is generated and moved in the nanotrack driven by spin-polarized current. The period, length and spacing of the skyrmion-chains can be dynamically manipulated by controlling either the frequency of the microwave field or the time dependent spin-polarized current density. A skyrmion-chain behaves as a massless particle, where it stops without delay when the current is stopped. Their velocity is found to be linearly dependent on the current density and insensitive to the frequency and amplitude of the excitation microwave field. Uniform motion of trains of skyrmion-chains in nanotrack offers a promising approach for spintronic multi-bit memories containing series of skyrmion-chains to represent data stream. PMID:26468929

  9. Generalized theory for current-source-density analysis in brain tissue

    NASA Astrophysics Data System (ADS)

    Bédard, Claude; Destexhe, Alain

    2011-10-01

    The current-source density (CSD) analysis is a widely used method in brain electrophysiology, but this method rests on a series of assumptions, namely that the surrounding extracellular medium is resistive and uniform, and in some versions of the theory, that the current sources are exclusively made by dipoles. Because of these assumptions, this standard model does not correctly describe the contributions of monopolar sources or of nonresistive aspects of the extracellular medium. We propose here a general framework to model electric fields and potentials resulting from current source densities, without relying on the above assumptions. We develop a mean-field formalism that is a generalization of the standard model and that can directly incorporate nonresistive (nonohmic) properties of the extracellular medium, such as ionic diffusion effects. This formalism recovers the classic results of the standard model such as the CSD analysis, but in addition, we provide expressions to generalize the CSD approach to situations with nonresistive media and arbitrarily complex multipolar configurations of current sources. We found that the power spectrum of the signal contains the signature of the nature of current sources and extracellular medium, which provides a direct way to estimate those properties from experimental data and, in particular, estimate the possible contribution of electric monopoles.

  10. Enhanced current and power density of micro-scale microbial fuel cells with ultramicroelectrode anodes

    NASA Astrophysics Data System (ADS)

    Ren, Hao; Rangaswami, Sriram; Lee, Hyung-Sool; Chae, Junseok

    2016-09-01

    We present a micro-scale microbial fuel cell (MFC) with an ultramicroelectrode (UME) anode, with the aim of creating a miniaturized high-current/power-density converter using carbon-neutral and renewable energy sources. Micro-scale MFCs have been studied for more than a decade, yet their current and power densities are still an order of magnitude lower than those of their macro-scale counterparts. In order to enhance the current/power densities, we engineer a concentric ring-shaped UME, with a width of 20 μm, to facilitate the diffusion of ions in the vicinity of the micro-organisms that form biofilm on the UME. The biofilm extends approximately 15 μm from the edge of the UME, suggesting the effective biofilm area increases. Measured current/power densities per the effective area and the original anode area are 7.08  ±  0.01 A m-2 & 3.09  ±  0.04 W m-2 and 17.7  ±  0.03 A m-2 & 7.72  ±  0.09 W m-2, respectively. This is substantially higher than any prior work in micro-scale MFCs, and very close, or even higher, to that of macro-scale MFCs. A Coulombic efficiency, a measure of how efficiently an MFC harvests electrons from donor substrate, of 70%, and an energy conversion efficiency of 17% are marked, highlighting the micro-scale MFC as an attractive alternative within the existing energy conversion portfolio.

  11. Electrical transport properties and current density - voltage characteristic of PVA-Ag nanocomposite film

    NASA Astrophysics Data System (ADS)

    Das, A. K.; Dutta, B.; Sinha, S.; Mukherjee, A.; Basu, S.; Meikap, A. K.

    2016-05-01

    Silver (Ag) nanoparticle and Polyvinyl alcohol (PVA) - Silver (Ag) composite have been prepared and its dielectric constant, ac conductivity, and current density-voltage characteristics have been studied, at and above room temperature. Here correlated barrier hopping found to be the dominant charge transport mechanism with maximum barrier height of 0.11 eV. The sample, under ±5 V applied voltage, show back to back Schottky diode behaviour.

  12. Resistance of 4H-SiC Schottky barriers at high forward-current densities

    SciTech Connect

    Ivanov, P. A. Samsonova, T. P.; Il’inskaya, N. D.; Serebrennikova, O. Yu.; Kon’kov, O. I.; Potapov, A. S.

    2015-07-15

    The resistance of Schottky barriers based on 4H-SiC is experimentally determined at high forward-current densities. The measured resistance is found to be significantly higher than the resistance predicted by classical mechanisms of electron transport in Schottky contacts. An assumption concerning the crucial contribution of the tunnel-transparent intermediate oxide layer between the metal and semiconductor to the barrier resistance is proposed and partially justified.

  13. What's All the Talc About? Air Entrainment in Dilute Pyroclastic Density Currents

    NASA Astrophysics Data System (ADS)

    Marshall, B. J.; Andrews, B. J.; Fauria, K.

    2015-12-01

    A quantitative understanding of air entrainment is critical to predicting the behaviors of dilute Pyroclastic Density Currents (PDCs), including runout distance, liftoff, and mass fractionation into co-PDC plumes. We performed experiments in an 8.5x6x2.6 meter tank using 20 micron talc powder over a range of conditions to describe air entrainment as a function of temperature, duration and mass flux. The experiments are reproducible and are scaled with respect to the densimetric and thermal Richardson numbers (Ri and RiT), Froude number, thermal to kinetic energy density ratio (TEb/KE), Stokes number, and Settling number, such that they are dynamically similar to natural dilute PDCs. Experiments are illuminated with a swept laser sheet and imaged at 1000 Hz to create 3D reconstructions of the currents, with ~1-2 cm resolution, at up to 1.5 Hz. An array of 30 high-frequency thermocouples record the precise temperature in the currents at 3 Hz. Bulk entrainment rates are calculated based on measured current volumes, surface areas, temperatures and velocities. Entrainment rates vary from ~0-0.9 and do not show simple variation with TEb/KE, Ri, or RiT. Entrainment does, however, increase with decreasing eruption duration and increasing mass flux. Our results suggest that current heads entrain air more efficiently than current bodies (>0.5 compared to ~0.1). Because shorter duration currents have proportionally larger heads, their bulk entrainment rates are controlled by those heads, whereas longer duration currents are dominated by their bodies. Our experiments demonstrate that air entrainment, which exerts a fundamental control on PDC runout and liftoff, varies spatially and temporally within PDCs.

  14. Crystallization of Ti33Cu67 metallic glass under high-current density electrical pulses

    PubMed Central

    2011-01-01

    We have studied the phase and structure evolution of the Ti33Cu67 amorphous alloy subjected to electrical pulses of high current density. By varying the pulse parameters, different stages of crystallization could be observed in the samples. Partial polymorphic nanocrystallization resulting in the formation of 5- to 8-nm crystallites of the TiCu2 intermetallic in the residual amorphous matrix occurred when the maximum current density reached 9.7·108 A m-2 and the pulse duration was 140 μs, though the calculated temperature increase due to Joule heating was not enough to reach the crystallization temperature of the alloy. Samples subjected to higher current densities and higher values of the evolved Joule heat per unit mass fully crystallized and contained the Ti2Cu3 and TiCu3 phases. A common feature of the crystallized ribbons was their non-uniform microstructure with regions that experienced local melting and rapid solidification. PACS: 81; 81.05.Bx; 81.05.Kf. PMID:21871070

  15. Measurement of current density fluctuations and ambipolar particle flux due to magnetic fluctuations in MST

    SciTech Connect

    Shen, Weimin.

    1992-08-01

    Studies of magnetic fluctuation induced particle transport on Reversed Field Pinch plasmas were done on the Madison Symmetric Torus. Plasma current density and current density fluctuations were measured using a multi-coil magnetic probes. The low frequency (f<50 kHz) current density fluctuations are consistent with the global resistive tearing instabilities predicted by 3-D MHD simulations. At frequencies above 50 kHz, the magnetic fluctuations were detected to be localized with a radial correlation length of about 1--2 cm. These modes are locally resonant modes since the measured dominant mode number spectra match the local safety factor q. The net charged particle flux induced by magnetic fluctuations was obtained by measuring the correlation term <{tilde j}{sub {parallel}} {tilde B}{sub r}>. The result of zero net charged particle loss was obtained, meaning the flux is ambipolar. The ambipolarity of low frequency global tearing modes is satisfied through the phase relations determined by tearing instabilities. The ambipolarity of high frequency localized modes could be partially explained by the simple model of Waltz based on the radial average of small scale turbulence.

  16. Injection-insensitive lateral divergence in broad-area diode lasers achieved by spatial current modulation

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Tong, Cunzhu; Wang, Lijie; Zeng, Yugang; Tian, Sicong; Shu, Shili; Zhang, Jian; Wang, Lijun

    2016-11-01

    High-power broad-area (BA) diode lasers often suffer from low beam quality, broad linewidth, and a widened slow-axis far field with increasing current. In this paper, a two-dimensional current-modulated structure is proposed and it is demonstrated that it can reduce not only the far-field sensitivity to the injection current but also the linewidth of the lasing spectra. Injection-insensitive lateral divergence was realized, and the beam parameter product (BPP) was improved by 36.5%. At the same time, the linewidth was decreased by about 45% without significant degradations of emission power and conversion efficiency.

  17. Effect of a pinning field on the critical current density for current-induced domain wall motion in perpendicular magnetic anisotropy nanowires.

    PubMed

    Ooba, Ayaka; Fujimura, Yuma; Takahashi, Kota; Komine, Takashi; Sugita, Ryuji

    2012-09-01

    In this study, the effect of a pinning field on the critical current density for current-induced domain wall motion in nanowires with perpendicular magnetic anisotropy was investigated using micromagnetic simulations. In order to estimate the pinning field in notched nanowires, we conducted wall energy calculations for nanowires with various saturation magnetizations. The pinning field increased as the notch size increased. The pinning field decreased as the saturation magnetization decreased. As a result, the decreased in the pinning field causes the reduction of the critical current density. Therefore, a significant reduction of the critical current density can be obtained by decreasing the saturation magnetization, even if wall pinning occurs.

  18. Amplification of current density modulation in a FEL with an infinite electron beam

    SciTech Connect

    Wang, G.; Litvinenko, V.N.; Webb, S.D.

    2011-03-28

    We show that the paraxial field equation for a free electron laser (FEL) in an infinitely wide electron beam with {kappa}-2 energy distribution can be reduced to a fourth ordinary differential equation (ODE). Its solution for arbitrary initial phase space density modulation has been derived in the wave-vector domain. For initial current modulation with Gaussian profile, close form solutions are obtained in space-time domain. In developing an analytical model for a FEL-based coherent electron cooling system, an infinite electron beam has been assumed for the modulation and correction processes. While the assumption has its limitation, it allows for an analytical close form solution to be obtained, which is essential for investigating the underlying scaling law, benchmarking the simulation codes and understanding the fundamental physics. 1D theory was previously applied to model a CeC FEL amplifier. However, the theory ignores diffraction effects and does not provide the transverse profile of the amplified electron density modulation. On the other hand, 3D theories developed for a finite electron beam usually have solutions expanded over infinite number of modes determined by the specific transverse boundary conditions. Unless the mode with the largest growth rate substantially dominates other modes, both evaluation and extracting scaling laws can be complicated. Furthermore, it is also preferable to have an analytical FEL model with assumptions consistent with the other two sections of a CeC system. Recently, we developed the FEL theory in an infinitely wide electron beam with {kappa}-1 (Lorentzian) energy distribution. Close form solutions have been obtained for the amplified current modulation initiated by an external electric field with various spatial-profiles. In this work, we extend the theory into {kappa}-2 energy distribution and study the evolution of current density induced by an initial density modulation.

  19. Impurities, temperature, and density in a miniature electrostatic plasma and current source

    SciTech Connect

    Den Hartog, D.J.; Craig, D.J.; Fiksel, G.; Sarff, J.S.

    1996-10-01

    We have spectroscopically investigated the Sterling Scientific miniature electrostatic plasma source-a plasma gun. This gun is a clean source of high density (10{sup 19} - 10{sup 20} m{sup -3}), low temperature (5 - 15 eV) plasma. A key result of our investigation is that molybdenum from the gun electrodes is largely trapped in the internal gun discharge; only a small amount escapes in the plasma flowing out of the gun. In addition, the gun plasma parameters actually improve (even lower impurity contamination and higher ion temperature) when up to 1 kA of electron current is extracted from the gun via the application of an external bias. This improvement occurs because the internal gun anode no longer acts as the current return for the internal gun discharge. The gun plasma is a virtual plasma electrode capable of sourcing an electron emission current density of 1 kA/cm{sup 2}. The high emission current, small size (3 - 4 cm diameter), and low impurity generation make this gun attractive for a variety of fusion and plasma technology applications.

  20. Relation between electric current densities and X-ray emissions from particles accelerated during solar flares

    NASA Astrophysics Data System (ADS)

    Musset, Sophie; Vilmer, Nicole; Bommier, Veronique

    The energy released during solar flares is believed to be stored in non-potential magnetic fields associated with electric currents. This energy is partially transferred to particle acceleration. We studied for several X-class flares located near the solar disk center the relation between the location of the X-ray emissions produced by energetic electrons accelerated in the corona and the magnetic field and vertical component of the electric current density in the photosphere. The study is based on X-ray images with data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and magnetic field maps and current density maps calculated with the UNNOFIT inversion and Metcalf disambiguation codes from the spectropolarimetric measurements of the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). A comparison between X-ray and Extreme Ultraviolet (EUV) images from the SDO Atmospheric Imaging Assembly (AIA) complete the study. We shall present preliminary conclusions on the link between particle acceleration and the presence of electric currents in the active region.

  1. Lab Experiments Probe Interactions Between Dilute Pyroclastic Density Currents and 3D Barriers

    NASA Astrophysics Data System (ADS)

    Fauria, K.; Andrews, B. J.; Manga, M.

    2014-12-01

    We conducted scaled laboratory experiments of unconfined dilute pyroclastic density currents (PDCs) to examine interactions between three - dimensional obstacles and dilute PDCs. While it is known that PDCs can surmount barriers by converting kinetic energy into potential energy, the signature of topography on PDC dynamics is unclear. To examine the interplay between PDCs and topography, we turbulently suspended heated and ambient-temperature 20 μm talc powder in air within an 8.5 x 6.1 x 2.6 m tank. Experimental parameters (Froude number, densimetric and thermal Richardson number, particle Stokes and Settling numbers) were scaled such that the experimental currents were dynamically similar to natural PCS. The Reynolds number, however, is much smaller than in natural currents, but still large enough for the flows to be turbulent. We placed cylindrical and ridge-like objects in the path of the currents, illuminated the currents with orthogonal laser sheets, and recorded each experiment with high definition cameras. We observed currents surmounting ridge-like barriers (barrier height = current height). Slanted ridges redirected the currents upward and parallel to the upstream face of the ridges (~45° from horizontal). Down stream of the slanted ridges, ambient-temperature currents reattached to the floor. By comparison, hot currents reversed buoyancy and lifted off. These observations suggest that obstacles enhance air entrainment, a process key to affecting runout distance and the depletion of fine particles in ignimbrites. Moreover, we observed vortex shedding in the wake of cylinders. Our experiments demonstrate that barriers of various shapes affect PDC dynamics and can shorten PDC runout distances. Understanding the effects of topography on PDCs is required for interpreting many deposits because processes such as vortex shedding and topographically-induced changes in turbulent length scales and entrainment likely leave depositional signatures.

  2. Persistent current and Drude weight of one-dimensional interacting fermions on imperfect ring from current lattice density functional theory

    NASA Astrophysics Data System (ADS)

    Akande, Akinlolu; Sanvito, Stefano

    2016-11-01

    We perform a numerical study of interacting one-dimensional Hubbard rings with a single impurity potential and pierced by a magnetic flux. Our calculations are carried out at the level of current lattice density functional theory (CLDFT) for the Hubbard model and compared to known results obtained in the thermodynamical limit from the Bethe ansatz. In particular, we investigate the effects of disorder and Coulomb interaction on the persistent current (PC) and the Drude weight. It is found that CLDFT is able to accurately describe qualitative and quantitative features of these ground state properties in the presence of disorder and electronic interaction. When the impurity potential is switched off, the CLDFT approach describes well the velocity of the Luttinger liquid excitations as a function of both interaction strength and electron filling. Then, when the impurity scattering potential is finite, we find the PC to vanish as {{L}-{{α\\text{B}}-1}} for large L and independent on the strength of the scattering potential, in good agreement with Luttinger liquid theory.

  3. Pyroclastic density currents and local topography as seen with the conveyer model

    NASA Astrophysics Data System (ADS)

    Doronzo, Domenico M.; Dellino, Pierfrancesco

    2014-05-01

    Pyroclastic density currents (PDCs) are multiphase flows generated during explosive volcanic eruptions, and they move down the volcano, and over the surrounding topography. The flow-topography interaction can play a fundamental role in the sedimentary processes, and in the resulting deposit facies architecture, as well as can play a dramatic role in the flow behavior, and in the associated volcanic hazard. This paper aims at discussing the PDC-topography interaction theme from the viewpoint of both deposits and flow structure, by accounting for appropriate literature, and revising the concepts in light of the theoretical conveyer model of Doronzo and Dellino (2013) on sedimentation and deposition in particulate density currents. First the effects, then the causes of the flow-topography interaction are discussed, in order to follow the historical development of theme concepts. The discussion is relative in terms of inertial and forced currents, which are defined on the basis of a dimensionless quantity (SD) representing the conservation of mass. Momentum equation relating depositional unit thickness, flow shear velocity, and density contrast shows that the flow is the cause of PDC motion, whereas the density contrast sustains the momentum, and the deposits are the process effect. In particular, the flow structure is described into three parts, flow-substrate boundary zone, boundary layer (lower part), and wake region (upper part) of the current. The facies architecture of PDC deposits, and the volcanic hazard depend on fluid dynamic and hydraulic behavior represented, in light of the conveyer model, by the balance of sedimentation and deposition rates through transport and erosion (“sedimentation-deposition” ratio, SD). This balance acts between flow-substrate boundary zone and boundary layer. The paper discussion mainly applies to small-to-intermediate volume eruptions. Field and modeling examples of Vulcano tuff cone and Colli Albani maar (Italy) constrain the

  4. Current initiation in low-density foam z-pinch plasmas

    SciTech Connect

    Derzon, M.; Nash, T.; Allshouse, G.

    1996-07-01

    Low density agar and aerogel foams were tested as z-pinch loads on the SATURN accelerator. In these first experiments, we studied the initial plasma conditions by measuring the visible emission at early times with a framing camera and 1-D imaging. At later time, near the stagnation when the plasma is hotter, x-ray imaging and spectral diagnostics were used to characterize the plasma. Filamentation and arcing at the current contacts was observed. None of the implosions were uniform along the z-axis. The prime causes of these problems are believed to be the electrode contacts and the current return configuration and these are solvable. Periodic phenomena consistent with the formation of instabilities were observed on one shot, not on others, implying that there may be a way of controlling instabilities in the pinch. Many of the issues involving current initiation may be solvable. Solutions are discussed.

  5. Micromagnetic model for studies on Magnetic Tunnel Junction switching dynamics, including local current density

    NASA Astrophysics Data System (ADS)

    Frankowski, Marek; Czapkiewicz, Maciej; Skowroński, Witold; Stobiecki, Tomasz

    2014-02-01

    We present a model introducing the Landau-Lifshitz-Gilbert equation with a Slonczewski's Spin-Transfer-Torque (STT) component in order to take into account spin polarized current influence on the magnetization dynamics, which was developed as an Object Oriented MicroMagnetic Framework extension. We implement the following computations: magnetoresistance of vertical channels is calculated from the local spin arrangement, local current density is used to calculate the in-plane and perpendicular STT components as well as the Oersted field, which is caused by the vertical current flow. The model allows for an analysis of all listed components separately, therefore, the contribution of each physical phenomenon in dynamic behavior of Magnetic Tunnel Junction (MTJ) magnetization is discussed. The simulated switching voltage is compared with the experimental data measured in MTJ nanopillars.

  6. Nature and velocity of pyroclastic density currents inferred from models of entrainment of substrate lithic clasts

    NASA Astrophysics Data System (ADS)

    Roche, Olivier

    2015-05-01

    Deposits of pyroclastic density currents (PDCs) often contain accidental lithic clasts of typical size of 0.1-1 m captured from an underlying substrate by the parent flows at distances up to several tens of kilometers from the eruptive vent. In order to gain insights into the nature of PDCs, this study investigates the conditions required for entrainment of particles from a granular substrate by a gas-particle density current, with special emphasis to ignimbrite-forming currents whose dynamics are controversial. The two types of physics of emplacement of PDCs proposed in literature are considered. The first model deals with a hydraulically rough, dilute turbulent PDC of bulk density of ∼1-10 kg/m3 and considers that entrainment through both traction and saltation is controlled by a Shield criterion at high (>104) particle Reynolds number. The second model considers entrainment by a PDC consisting of a dense basal flow of bulk density of the order of 103 kg /m3 and with high interstitial gas pore pressure. This model involves uplift of substrate particles, caused by an upward pressure gradient at the flow-substrate interface, and then transport and deposition on the aggrading basal deposit of the flow as demonstrated by recent laboratory experiments. Results show that a dilute PDC can entrain blocks of maximum size of ∼10-15 cm (for a block density of 2000-3000 kg/m3) if maximum current velocities up to ∼100 m/s are taken into account. This, in turn, suggests that larger (heavier) blocks found in deposits were captured by PDCs if these had a dense basal flow. The dense flow model predicts that PDCs have the potential to entrain metric blocks, whose maximum size (up to ∼2-5 m) decreases with decreasing atmospheric pressure (i.e. increasing altitude). Application of the model considering published data on the characteristics of accidental blocks in several well-studied ignimbrites indicates that the velocity of the parent dense PDCs was up to ∼25-30 m/s.

  7. Lower hybrid current drive in FTU high density shear reversed discharges

    NASA Astrophysics Data System (ADS)

    Tuccillo, A. A.; Barbato, E.; Crisanti, F.; Panaccione, L.; Pericoli, V.; Podda, S.; Cirant, S.; Acitelli, L.; Alladio, F.; Amadeo, P.; Angelini, B.; Apicella, M. L.; Apruzzese, G.; Bertocchi, A.; Borra, M.; Bracco, G.; Bruschi, A.; Buceti, G.; Buratti, P.; Cardinali, A.; Centioli, C.; Cesario, R.; Ciattaglia, S.; Ciotti, M.; Cocilovo, V.; De Angelis, R.; De Marco, F.; Esposito, B.; Frigione, D.; Gabellieri, L.; Gatti, G.; Giovannozzi, E.; Gourlan, C.; Granucci, G.; Grolli, M.; Imparato, A.; Kroegler, H.; Leigheb, M.; Lovisetto, L.; Maddaluno, G.; Maffia, G.; Mancuso, A.; Marinucci, M.; Mazzitelli, G.; Micozzi, P.; Mirizzi, F.; Orsitto, P.; Pacella, D.; Panella, M.; Pieroni, L.; Righetti, G. B.; Romanelli, F.; Santini, F.; Simonetto, A.; Sozzi, C.; Sternini, S.; Tudisco, O.; Valente, F.; Vitale, V.; Vlad, G.; Zanza, V.; Zerbini, M.

    1997-04-01

    Results are reported of the 8 GHz Lower Hybrid experiments on FTU after the installation of the new toroidal limiter. A figure of merit of the Current Drive efficiency ηCD≈0.11ṡ1020 A/Wm2 is estimated for plasma density n¯e=1020 m-3 and no appreciable broadening of the launched frequency is detected. In low density experiments sawteeth are stabilised and m=1 activity is present in the plasma. Shear reversed discharges with large reversal radius, rs/a≈0.5, are obtained at higher density, lower temperature, BT=4 T, qa≈5.5, by off-axis LH CD. The reversed configurations exhibit high central temperature coexisting with regular m=2, n=1 relaxations of large amplitude and are maintained up to LH switch off. At higher magnetic field, B=5.2 T, qa≈7, irregular DTM crashes are present during the whole LH pulse. Confinement time of radiofrequency heated discharges (PLH=0.5÷2ṡPOH) exhibits the same behaviour of FTU ohmic discharges following the ITER89-P scaling. Preliminary results of central 140 GHz Electron Cyclotron Resonant Heating (ECRH) during the plasma current ramp-up, aimed at obtaining shear reversed configurations are also reported.

  8. Critical Current Density and Bulk Pinning Force in RHQT-Processed Niobium-Aluminum Superconductors

    NASA Astrophysics Data System (ADS)

    Buta, F.; Sumption, M. D.; Collings, E. W.

    2004-06-01

    Transformation heat treatments with short excursions (1-10 min) to 1000°C preceding the conventional 800°C/10h were applied to jelly-roll Nb-Al samples that had been rapidly heated and quenched (RHQ) in bcc phase from high temperatures. The critical current density dependence on magnetic field at 4.2K in magnetic fields ranging from 0 to 8.5T was determined from magnetization measurements performed by Vibrating Sample Magnetometry. It was found that in this range of magnetic fields the highest critical current densities are not necessarily obtained for the samples with the highest initial heating rate of the transformation heat treatment as it is the case at magnetic fields in the vicinity of 20T. The highest pinning force density is present in samples that were transformed by rapid insertion in a furnace preheated to 1000°C and not in samples that were ohmically heated to 1000°C (the fastest heating rate employed).

  9. Faraday-Effect Polarimeter-Interferometer System for current density measurement on EAST

    NASA Astrophysics Data System (ADS)

    Liu, Haiqing; Jie, Yinxian; Ding, Weixing; Brower, David Lyn; Zou, Zhiyong; Li, Weiming; Qian, Jinping; Yang, Yao; Zeng, Long; Lan, Ting; Li, Gongshun; Hu, Liqun; Wan, Baonian

    2014-10-01

    A multichannel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retro-reflectors are mounted in the inside wall for the double-pass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. System time response (~1 microsecond) and phase resolution (<0.1°) allows resolution of fast equilibrium changes associated with MHD events. Initial calibration indicates the electron line-integrated density resolution is less than 5 × 1016 m-2 (~2°), and the Faraday rotation angle rms phase noise is <0.1°. Initial results of POINT system will be presented. This work is supported by the National Magnetic Confinement Fusion Program of China Contract No. 2012GB101002. This work is partly supported by the US D.O.E. Contract DESC0010469.

  10. Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene.

    PubMed

    Pallon, Love K H; Nilsson, Fritjof; Yu, Shun; Liu, Dongming; Diaz, Ana; Holler, Mirko; Chen, Xiangrong R; Gubanski, Stanislaw; Hedenqvist, Mikael S; Olsson, Richard T; Gedde, Ulf W

    2017-03-08

    Electrical trees are one reason for the breakdown of insulating materials in electrical power systems. An understanding of the growth of electrical trees plays a crucial role in the development of reliable high voltage direct current (HVDC) power grid systems with transmission voltages up to 1 MV. A section that contained an electrical tree in low-density polyethylene (LDPE) has been visualized in three dimensions (3D) with a resolution of 92 nm by X-ray ptychographic tomography. The 3D imaging revealed prechannel-formations with a lower density with the width of a couple of hundred nanometers formed around the main branch of the electrical tree. The prechannel structures were partially connected with the main tree via paths through material with a lower density, proving that the tree had grown in a step-by-step manner via the prestep structures formed in front of the main channels. All the prechannel structures had a size well below the limit of the Paschen law and were thus not formed by partial discharges. Instead, it is suggested that the prechannel structures were formed by electro-mechanical stress and impact ionization, where the former was confirmed by simulations to be a potential explanation with electro-mechanical stress tensors being almost of the same order of magnitude as the short-term modulus of low-density polyethylene.

  11. Simulation of the distribution of current density in the brain of slaughter pigs with the finite element method.

    PubMed

    Eike, H; Koch, R; Feldhusen, F; Seifert, H

    2005-04-01

    The current density in the brain of a slaughter pig during electric stunning was calculated and visualised with an finite element method computer model. The anatomic model of the pig's head was constructed with the computer programme Ansys. Ansys offers the possibility of calculating the current density between electrodes in any position using the mathematical "finite element method" model. After calculation the current density distribution can be visualised in planes in any direction through the pig's head. Our simulation confirmed the common practice of positioning the electrodes for electric stunning either eye to eye or eye to ear, because the highest current density through the brain was calculated for these positions. Setting the electrodes further caudally reduced the current density remarkably and, stunning is therefore not guaranteed. Additionally, this model showed for the first time that, due to their lower resistance, the nervus opticus and blood vessels conduct the current like wires into the brain.

  12. Enhancement of critical current densities in (Ba,K)Fe2As2 wires and tapes using HIP technique

    NASA Astrophysics Data System (ADS)

    Pyon, Sunseng; Suwa, Takahiro; Park, Akiyoshi; Kajitani, Hideki; Koizumi, Norikiyo; Tsuchiya, Yuji; Awaji, Satoshi; Watanabe, Kazuo; Tamegai, Tsuyoshi

    2016-11-01

    (Ba,K)Fe2As2 superconducting wires and tapes are fabricated by using hot isostatic pressing (HIP) technique, and their superconducting properties are studied. In the HIP round wire, transport critical current density (J c) at 4.2 K has achieved record-high value of 175 kA cm-2 at zero field, and exceeds 20 kA cm-2 even at 100 kOe. Improvement of polycrystalline powder synthesis may play a key role for the enhancement of J c. In the HIP tape, even larger transport J c of 380 kA cm-2 is realized at zero field. Based on magnetization and magneto-optical measurements, possible further enhancement of J c is discussed.

  13. Impact of Te and ne on edge current density profiles in ELM mitigated regimes on ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Dunne, M. G.; Rathgeber, S.; Burckhart, A.; Fischer, R.; Giannone, L.; McCarthy, P. J.; Schneider, P. A.; Wolfrum, E.; the ASDEX Upgrade Team

    2015-01-01

    ELM resolved edge current density profiles are reconstructed using the CLISTE equilibrium code. As input, highly spatially and temporally resolved edge electron temperature and density profiles are used in addition to data from the extensive set of external poloidal field measurements available at ASDEX Upgrade, flux loop difference measurements, and current measurements in the scrape-off layer. Both the local and flux surface averaged current density profiles are analysed for several ELM mitigation regimes. The focus throughout is on the impact of altered temperature and density profiles on the current density. In particular, many ELM mitigation regimes rely on operation at high density. Two reference plasmas with type-I ELMs are analysed, one with a deuterium gas puff and one without, in order to provide a reference for the behaviour in type-II ELMy regimes and high density ELM mitigation with external magnetic perturbations at ASDEX Upgrade. For type-II ELMs it is found that while a similar pedestal top pressure is sustained at the higher density, the temperature gradient decreases in the pedestal. This results in lower local and flux surface averaged current densities in these phases, which reduces the drive for the peeling mode. No significant differences between the current density measured in the type-I phase and ELM mitigated phase is seen when external perturbations are applied, though the pedestal top density was increased. Finally, ELMs during the nitrogen seeded phase of a high performance discharge are analysed and compared to ELMs in the reference phase. An increased pedestal pressure gradient, which is the source of confinement improvement in impurity seeded discharges, causes a local current density increase. However, the increased Zeff in the pedestal acts to reduce the flux surface averaged current density. This dichotomy, which is not observed in other mitigation regimes, could act to stabilize both the ballooning mode and the peeling mode at the

  14. Surface Current Density Mapping for Identification of Gastric Slow Wave Propagation

    PubMed Central

    Bradshaw, L. A.; Cheng, L. K.; Richards, W. O.; Pullan, A. J.

    2009-01-01

    The magnetogastrogram records clinically relevant parameters of the electrical slow wave of the stomach noninvasively. Besides slow wave frequency, gastric slow wave propagation velocity is a potentially useful clinical indicator of the state of health of gastric tissue, but it is a difficult parameter to determine from noninvasive bioelectric or biomagnetic measurements. We present a method for computing the surface current density (SCD) from multichannel magnetogastrogram recordings that allows computation of the propagation velocity of the gastric slow wave. A moving dipole source model with hypothetical as well as realistic biomagnetometer parameters demonstrates that while a relatively sparse array of magnetometer sensors is sufficient to compute a single average propagation velocity, more detailed information about spatial variations in propagation velocity requires higher density magnetometer arrays. Finally, the method is validated with simultaneous MGG and serosal EMG measurements in a porcine subject. PMID:19403355

  15. The influence of critical current density of Bi-2212 superconductors by defects after Yb-doping

    NASA Astrophysics Data System (ADS)

    Lu, Tianni; Zhang, Cuiping; Guo, Shengwu; Wu, Yifang; Li, Chengshan; Zhou, Lian

    2015-12-01

    Bi2Sr2Ca1-xYbxCu2O8+δ (Bi-2212) single crystals with x = 0.000, 0.005, 0.010 and 0.020 have been prepared by self-flux method. The influences of Yb doping on the formation of the dislocations in the lattice structures, as well as the related current carrying capability are investigated. Due to the SQUID measurement and the Bean model calculation, the maximum critical current density (Jc) is obtained when the Yb doping content is x = 0.010, though the Tc and the carrier concentration are not in the optimal region. Based on the HRTEM analyses of the Ca-O and Cu-O2 layers, the optimal dislocation density in the Cu-O2 layers is deduced according to the number of the dislocations per unit area. Besides, the sizes of the dislocations also prove the effectiveness of Yb substitution on the enhancement of the current carrying capability in Bi-2212 single crystals.

  16. Transport critical current density of Fe sheath MgB 2 tapes sintered at different temperatures

    NASA Astrophysics Data System (ADS)

    Ruan, K. Q.; Li, H. L.; Yu, Y.; Wang, C. Y.; Cao, L. Z.; Liu, C. F.; Du, S. J.; Yan, G.; Feng, Y.; Wu, X.; Wang, J. R.; Liu, X. H.; Zhang, P. X.; Wu, X. Z.; Zhou, L.

    2003-04-01

    Fe sheath MgB 2 tapes sintered at 650, 750, 850 and 950 °C, respectively, for 2 h in a high purity argon gas were prepared using the powder-in-tube method. Transport critical current densities of tapes were measured in the fields up to 10 T from 4 to 30 K. Both tapes sintered at 850 and 950 °C completely lost the capacity of carrying superconducting current over the temperature range from 4 to 30 K. Compared to a tape sintered at 650 °C, an improvement in the in-field critical current density Jc and irreversibility field μ0H*( T) was observed in a tape sintered at 750 °C. At 20 K, the Jc value was ∼1.32×10 5 A/cm 2 in self-field and the μ0H* value 4.2 T for the tape sintered at 750 °C, whereas the Jc in self-field and μ0H* values were ∼5.9×10 4 A/cm 2 and 2.8 T for that sintered at 650 °C.

  17. Characterisation of high current density resonant tunneling diodes for THz emission using photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Jacobs, Kristof J. P.; Baba, Razvan; Stevens, Benjamin J.; Mukai, Toshikazu; Ohnishi, Dai; Hogg, Richard A.

    2016-03-01

    Resonant tunneling diodes (RTDs) provide high speed current oscillation which is applicable to THz generation when coupled to a suitably designed antenna. For this purpose, the InGaAs/AlAs/InP materials have been used, as this system offers high electron mobility, suitable band-offsets, and low resistance contacts. However for high current density operation (~MA/cm2) the epitaxial structure is challenging to characterize using conventional techniques as it consists of a single, very thin AlAs/InGaAs quantum well (QW). Here, we present a detailed low temperature photoluminescence spectroscopic study of high current density RTDs that allow the non-destructive mapping of a range of critical parameters for the device. We show how the doping level of the emitter/collector and contact layers in the RTD structure can be measured using the Moss-Burstein effect. For the full device structure, we show how emission from the QW may be identified, and detail how the emission changes with differing indium composition and well widths. We show that by studying nominally identical, un-doped structures, a type-II QW emission is observed, and explain the origin of the type-I emission in doped devices. This observation opens the way for a new characterization scheme where a "dummy" RTD active element is incorporated below the real RTD structure. This structure allows significantly greater control in the epitaxial process.

  18. Current products and practices: curriculum development in orthodontic specialist registrar training: can orthodontics achieve constructive alignment?

    PubMed

    Chadwick, S M

    2004-09-01

    This paper aims to encourage a debate on the learning outcomes that have been developed for orthodontic specialist education. In outcome-based education the learning outcomes are clearly defined. They determine curriculum content and its organization, the teaching and learning approaches, the assessment techniques and hope to focus the minds of the students on ensuring all the learning outcomes are met. In Orthodontic Specialist Registrar training, whether constructive alignment can be achieved depends on the relationship between these aspects of the education process and the various bodies responsible for their delivery in the UK.

  19. Invariance in current dipole moment density across brain structures and species: physiological constraint for neuroimaging.

    PubMed

    Murakami, Shingo; Okada, Yoshio

    2015-05-01

    Although anatomical constraints have been shown to be effective for MEG and EEG inverse solutions, there are still no effective physiological constraints. Strength of the current generator is normally described by the moment of an equivalent current dipole Q. This value is quite variable since it depends on size of active tissue. In contrast, the current dipole moment density q, defined as Q per surface area of active cortex, is independent of size of active tissue. Here we studied whether the value of q has a maximum in physiological conditions across brain structures and species. We determined the value due to the primary neuronal current (q primary) alone, correcting for distortions due to measurement conditions and secondary current sources at boundaries separating regions of differing electrical conductivities. The values were in the same range for turtle cerebellum (0.56-1.48 nAm/mm(2)), guinea pig hippocampus (0.30-1.34 nAm/mm(2)), and swine neocortex (0.18-1.63 nAm/mm(2)), rat neocortex (~2.2 nAm/mm(2)), monkey neocortex (~0.40 nAm/mm(2)) and human neocortex (0.16-0.77 nAm/mm(2)). Thus, there appears to be a maximum value across the brain structures and species (1-2 nAm/mm(2)). The empirical values closely matched the theoretical values obtained with our independently validated neural network model (1.6-2.8 nAm/mm(2) for initial spike and 0.7-3.1 nAm/mm(2) for burst), indicating that the apparent invariance is not coincidental. Our model study shows that a single maximum value may exist across a wide range of brain structures and species, varying in neuron density, due to fundamental electrical properties of neurons. The maximum value of q primary may serve as an effective physiological constraint for MEG/EEG inverse solutions.

  20. Structural, optical and electrical characterization of nanostructured porous silicon: Effect of current density

    NASA Astrophysics Data System (ADS)

    Kulathuraan, K.; Mohanraj, K.; Natarajan, B.

    2016-01-01

    In this work, an attempt has been made to fabricate porous silicon (PS) from p-type crystalline silicon (c-Si) wafers by using the electrochemical etching process at six different current densities (40, 60, 75, 100, 125 and 150 mA/cm2) with constant time (30 min). The influence of varying current density on morphological, structural, optical and electrical properties of PS samples were analyzed by using SEM, AFM, XRD, FT-IR, PL and electrical (I-V) techniques, respectively. Microstructural images clearly showed that the average pore diameter and thickness increase with increase current densities up to 100 mA/cm2 and decrease for 125 mA/cm2. It could be related to breaking of pore walls and exposing to the next layer of c-Si. Further increase the current density about 150 mA/cm2, the average pore diameter increase as in the case of first layer (40-100 mA/cm2) of c-Si wafer. The result is reflected in PL emission band (at 708 nm) and the intensity of the emission band shifted towards red region. The X-ray diffraction pattern confirm the formation of porous silicon as appeared as a broad peak at 2θ = 69.3° belongs to (4 0 0) reflection. The FTIR study supports the X-ray diffraction analysis that shows the vibrational bands of S-H2 and Si-O-Si at 2109 cm-1, 915 cm-1 and 615 cm-1 and 1107 cm-1, respectively. The I-V characteristic of PS exhibited rectifying behavior with different values of ideality factor (η) and barrier height (ϕb). It is concluded from the experimental results that the formed pores developed up to 100 mA/cm2 in the top layer of c-Si and the formed pores exposed to the next layer of c-Si when increase the high electrochemical etching process (above 100 mA/cm2).

  1. Ac Permeability Measurement for Inter- and Intragrain Critical Current Densities in Oxide Superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, Teruo; Ni, Baorong

    1989-03-01

    A simple measuring method to discriminate between inter- and intragrain current densities in oxide superconductors under given magnetic fields and temperatures is proposed. This is a measurement of the imaginary part of the ac permeability or susceptibility as a function of the ac field amplitude. In this method, the analysis used to derive the penetration depth of the ac field in Campbell’s method or the waveform analysis method is not necessary. This method is useful when the value of the penetration field into the grains and that into the bulk specimen are remarkably different.

  2. System and method for magnetic current density imaging at ultra low magnetic fields

    SciTech Connect

    Espy, Michelle A.; George, John Stevens; Kraus, Robert Henry; Magnelind, Per; Matlashov, Andrei Nikolaevich; Tucker, Don; Turovets, Sergei; Volegov, Petr Lvovich

    2016-02-09

    Preferred systems can include an electrical impedance tomography apparatus electrically connectable to an object; an ultra low field magnetic resonance imaging apparatus including a plurality of field directions and disposable about the object; a controller connected to the ultra low field magnetic resonance imaging apparatus and configured to implement a sequencing of one or more ultra low magnetic fields substantially along one or more of the plurality of field directions; and a display connected to the controller, and wherein the controller is further configured to reconstruct a displayable image of an electrical current density in the object. Preferred methods, apparatuses, and computer program products are also disclosed.

  3. Correlations of the density and of the current in non-equilibrium diffusive systems

    NASA Astrophysics Data System (ADS)

    Sadhu, Tridib; Derrida, Bernard

    2016-11-01

    We use fluctuating hydrodynamics to analyze the dynamical properties in the non-equilibrium steady state of a diffusive system coupled with reservoirs. We derive the two-time correlations of the density and of the current in the hydrodynamic limit in terms of the diffusivity and the mobility. Within this hydrodynamic framework we discuss a generalization of the fluctuation dissipation relation in a non-equilibrium steady state where the response function is expressed in terms of the two-time correlations. We compare our results to an exact solution of the symmetric exclusion process. This exact solution also allows one to directly verify the fluctuating hydrodynamics equation.

  4. A significant improvement of luminance vs current density efficiency of a BioLED

    NASA Astrophysics Data System (ADS)

    Grykien, Remigiusz; Luszczynska, Beata; Glowacki, Ireneusz; Ulanski, Jacek; Kajzar, Francois; Zgarian, Roxana; Rau, Ileana

    2014-04-01

    We report on fabrication and characterization of an organic light emitting diode by incorporating a pure DNA as electron blocking layer. As emission layer a thin film of phosphorescent Ir(ppy)3 luminophore, embedded in the poly(N-vinylcarbazole) (PVK)/2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) is used. The BioLED shows a good stability and its luminance efficiency vs current density is improved by ca 40% in comparison with the case without EBL.

  5. Electron density profile measurements at a self-focusing ion beam with high current density and low energy extracted through concave electrodes

    SciTech Connect

    Fujiwara, Y. Nakamiya, A.; Sakakita, H.; Hirano, Y.; Kiyama, S.; Koguchi, H.

    2014-02-15

    The self-focusing phenomenon has been observed in a high current density and low energy ion beam. In order to study the mechanism of this phenomenon, a special designed double probe to measure the electron density and temperature is installed into the chamber where the high current density ion beam is injected. Electron density profile is successfully measured without the influence of the ion beam components. Estimated electron temperature and density are ∼0.9 eV and ∼8 × 10{sup 8} cm{sup −3} at the center of ion beam cross section, respectively. It was found that a large amount of electrons are spontaneously accumulated in the ion beam line in the case of self-forcing state.

  6. A finite element analysis of the effect of electrode area and inter-electrode distance on the spatial distribution of the current density in tDCS

    NASA Astrophysics Data System (ADS)

    Faria, Paula; Hallett, Mark; Cavaleiro Miranda, Pedro

    2011-12-01

    We investigated the effect of electrode area and inter-electrode distance on the spatial distribution of the current density in transcranial direct current stimulation (tDCS). For this purpose, we used the finite element method to compute the distribution of the current density in a four-layered spherical head model using various electrode montages, corresponding to a range of electrode sizes and inter-electrode distances. We found that smaller electrodes required slightly less current to achieve a constant value of the current density at a reference point on the brain surface located directly under the electrode center. Under these conditions, smaller electrodes also produced a more focal current density distribution in the brain, i.e. the magnitude of the current density fell more rapidly with distance from the reference point. The combination of two electrodes with different areas produced an asymmetric current distribution that could lead to more effective and localized neural modulation under the smaller electrode than under the larger one. Focality improved rapidly with decreasing electrode size when the larger electrode sizes were considered but the improvement was less marked for the smaller electrode sizes. Also, focality was not affected significantly by inter-electrode distance unless two large electrodes were placed close together. Increasing the inter-electrode distance resulted in decreased shunting of the current through the scalp and the cerebrospinal fluid, and decreasing electrode area resulted in increased current density on the scalp under the edges of the electrode. Our calculations suggest that when working with conventional electrodes (25-35 cm2), one of the electrodes should be placed just 'behind' the target relative to the other electrode, for maximum current density on the target. Also electrodes with areas in the range 3.5-12 cm2 may provide a better compromise between focality and current density in the scalp than the traditional

  7. Growth and characterization of high current density, high-speed InAs/AlSb resonant tunneling diodes

    NASA Technical Reports Server (NTRS)

    Soderstrom, J. R.; Brown, E. R.; Parker, C. D.; Mahoney, L. J.; Yao, J. Y.

    1991-01-01

    InAs/AlSb double-barrier resonant tunneling diodes with peak current densities up to 370,000 A/sq cm and high peak-to-valley current ratios of 3.2 at room temperature have been fabricated. The peak current density is well-explained by a stationary-state transport model with the two-band envelope function approximation. The valley current density predicted by this model is less than the experimental value by a factor that is typical of the discrepancy found in other double-barrier structures. It is concluded that threading dislocations are largely inactive in the resonant tunneling process.

  8. Truncation planes from a dilute pyroclastic density current: field data and analogue experiments.

    NASA Astrophysics Data System (ADS)

    Douillet, Guilhem Amin; Gegg, Lukas; Mato, Celia; Kueppers, Ulrich; Dingwell, Donald B.

    2016-04-01

    Pyroclastic density currents (PDCs) are a catastrophic transport mode of ground hugging gas-particle mixtures associated with explosive volcanic eruptions. The extremely high sedimentation rates and turbulence levels of these particulate density currents can freeze and preserve dynamic phenomena that happen but are not recorded in other sedimentary environments. Several intriguing and unanticipated features have been identified in outcrops and reproduced via analogue experiments, with the potential to change our views on morphodynamics and particle motion. Three types of small-scale (ca. 10 cm) erosion structures were observed on the stoss side of dune bedforms in the field: 1) vertical erosion planes covered with stoss-aggrading, vertical lamination, 2) overturned laminations at the preserved limit of erosion planes and 3) loss of stratification at erosion planes. These features are interpreted to indicate rapidly evolving velocities, undeveloped boundary layers, and a diffuse zone rather than a sharp border defining the flow-bed interface. Most experimental work on particle motion and erosion from the literature has been accomplished under constant conditions and with planar particle beds. Here, in order to reproduce the field observations, short-lived air-jets generated with a compressor-gun were shot into stratified beds of coarse particles (300 μm) of low density (1000 kg/m3). These "eroding jets" were filmed with a high speed camera and the deposits were sectioned after the experiments. The three natural types of erosion characteristics were experimentally generated. Vertical erosion planes are produced by small-scale, relatively sustained jets. Overturned laminations are due to a fluidization-like behavior at the erosion front of short-lived, strong jets, demonstrating that the fluid's velocity profile penetrates into the deposit. Loss of lamination seems related to the nature of erosion onset in packages. Rather than providing simple answers, the dataset

  9. High-field, high-current-density, stable superconducting magnets for fusion machines

    SciTech Connect

    Lue, J.W.; Dresner, L.; Lubell, M.S.

    1989-01-01

    Designs for large fusion machines require high-performance superconducting magnets to reduce cost or increase machine performance. By employing force-flow cooling, cable-in-conduit conductor configuration, and NbTi superconductor, it is now possible to design superconducting magnets that operate a high fields (8-12 T) with high current densities (5-15 kA/cm/sup 2/ over the winding pack) in a stable manner. High current density leads to smaller, lighter, and thus less expensive coils. The force-flow cooling provides confined helium, full conductor insulation, and a rigid winding pack for better load distribution. The cable-in-conduit conductor configuration ensures a high stability margin for the magnet. The NbTi superconductor has reached a good engineering material standard. Its strain-insensitive critical parameters are particularly suitable for complex coil windings of a stellarator machine. The optimization procedure for such a conductor design, developed over the past decade, is summarized here. If desired a magnet built on the principles outlines in this paper can be extended to a field higher than the design value without degrading its stability by simply lowering the operating temperature below 4.2 K. 11 refs., 3 figs.

  10. Relaxation and dissipation in time-dependent current-density functional theory

    NASA Astrophysics Data System (ADS)

    D'Agosta, Roberto

    2005-03-01

    In a typical relaxation problem a many-particle system evolves from an initial excited state under the action of its own hamiltonian plus a ``thermal bath", until equilibrium (or the ground-state at T=0) is reached. Due to the presence of the thermal bath the time evolution of the system is not unitary, and an initially pure state will evolve into a statistical mixture of states. Here we show that the time-dependent current density functional theory^1 allows a hamiltonian description of the relaxation process, whereby the quantum state of the system undergoes a unitary time evolution without becoming entangled with a thermal bath. The essential feature that causes the system to eventually settle into a stationary state of the ground-state Kohn-Sham hamiltonian is the presence of an effective electric field, which is determined by the instantaneous values of the current and the density. Our theory is consistent with recent numerical results by Wijewardane and Ullrich^ 2.1. G. Vignale, C. A. Ullrich, and S. Conti, PRL 79, 4878 (1997)2. H. O. Wijewardane and C. A. Ullrich, cond-mat/0411157

  11. Seasonal variation in sea turtle density and abundance in the southeast Florida current and surrounding waters

    DOE PAGES

    Bovery, Caitlin M.; Wyneken, Jeanette

    2015-12-30

    Assessment and management of sea turtle populations is often limited by a lack of available data pertaining to at-sea distributions at appropriate spatial and temporal resolutions. Assessing the spatial and temporal distributions of marine turtles in an open system poses both observational and analytical challenges due to the turtles’ highly migratory nature. Surface counts of marine turtles in waters along the southern part of Florida’s east coast were made in and adjacent to the southeast portion of the Florida Current using standard aerial surveys during 2011 and 2012 to assess their seasonal presence. This area is of particular concern formore » sea turtles as interest increases in offshore energy developments, specifically harnessing the power of the Florida Current. While it is understood that marine turtles use these waters, here we evaluate seasonal variation in sea turtle abundance and density over two years. Density of sea turtles observed within the study area ranged from 0.003 turtles km-2 in the winter of 2011 to 0.064 turtles km-2 in the spring of 2012. As a result, this assessment of marine turtles in the waters off southeast Florida quantifies their in-water abundance across seasons in this area to establish baselines and inform future management strategies of these protected species.« less

  12. A study of low-current-density microsecond electron beam diodes

    NASA Astrophysics Data System (ADS)

    Ramirez, J. J.; Cook, D. L.

    1980-09-01

    The performances of various field emitters and plasma-injected diodes for the generation of low-current-density microsecond electron beams to be used in gas laser excitation are investigated and compared. The output from a microsecond high-voltage pulse-forming network was fed to a large-area vacuum diode containing metal-oxide matrix and carbon fiber field emitters and to diodes filled with plasma and containing preformed plasma on the cathode surface. Of the field emitters, a brush cathode made with 10-micron carbon filaments is found to give the best performance, with emission at fields as low as 10 kV/cm, space charge-limited flow established in 60 nsec and apparent gap closure velocities of 1.5 cm/sec. Although substantial control of the diode impedance was obtained when the plasma was allowed to fill the anode-cathode volume, the constraining of the plasma to the cathode surface is found to improve the uniformity and reproducibility of anode current density, with apparent gap closure velocities as low as 2 cm/sec.

  13. Seasonal variation in sea turtle density and abundance in the southeast Florida current and surrounding waters

    SciTech Connect

    Bovery, Caitlin M.; Wyneken, Jeanette

    2015-12-30

    Assessment and management of sea turtle populations is often limited by a lack of available data pertaining to at-sea distributions at appropriate spatial and temporal resolutions. Assessing the spatial and temporal distributions of marine turtles in an open system poses both observational and analytical challenges due to the turtles’ highly migratory nature. Surface counts of marine turtles in waters along the southern part of Florida’s east coast were made in and adjacent to the southeast portion of the Florida Current using standard aerial surveys during 2011 and 2012 to assess their seasonal presence. This area is of particular concern for sea turtles as interest increases in offshore energy developments, specifically harnessing the power of the Florida Current. While it is understood that marine turtles use these waters, here we evaluate seasonal variation in sea turtle abundance and density over two years. Density of sea turtles observed within the study area ranged from 0.003 turtles km-2 in the winter of 2011 to 0.064 turtles km-2 in the spring of 2012. As a result, this assessment of marine turtles in the waters off southeast Florida quantifies their in-water abundance across seasons in this area to establish baselines and inform future management strategies of these protected species.

  14. Pyroclastic density current volume estimation after the 2010 Merapi volcano eruption using X-band SAR

    NASA Astrophysics Data System (ADS)

    Bignami, Christian; Ruch, Joel; Chini, Marco; Neri, Marco; Buongiorno, Maria Fabrizia; Hidayati, Sri; Sayudi, Dewi Sri; Surono

    2013-07-01

    Pyroclastic density current deposits remobilized by water during periods of heavy rainfall trigger lahars (volcanic mudflows) that affect inhabited areas at considerable distance from volcanoes, even years after an eruption. Here we present an innovative approach to detect and estimate the thickness and volume of pyroclastic density current (PDC) deposits as well as erosional versus depositional environments. We use SAR interferometry to compare an airborne digital surface model (DSM) acquired in 2004 to a post eruption 2010 DSM created using COSMO-SkyMed satellite data to estimate the volume of 2010 Merapi eruption PDC deposits along the Gendol river (Kali Gendol, KG). Results show PDC thicknesses of up to 75 m in canyons and a volume of about 40 × 106 m3, mainly along KG, and at distances of up to 16 km from the volcano summit. This volume estimate corresponds mainly to the 2010 pyroclastic deposits along the KG - material that is potentially available to produce lahars. Our volume estimate is approximately twice that estimated by field studies, a difference we consider acceptable given the uncertainties involved in both satellite- and field-based methods. Our technique can be used to rapidly evaluate volumes of PDC deposits at active volcanoes, in remote settings and where continuous activity may prevent field observations.

  15. Seasonal Variation in Sea Turtle Density and Abundance in the Southeast Florida Current and Surrounding Waters.

    PubMed

    Bovery, Caitlin M; Wyneken, Jeanette

    2015-01-01

    Assessment and management of sea turtle populations is often limited by a lack of available data pertaining to at-sea distributions at appropriate spatial and temporal resolutions. Assessing the spatial and temporal distributions of marine turtles in an open system poses both observational and analytical challenges due to the turtles' highly migratory nature. Surface counts of marine turtles in waters along the southern part of Florida's east coast were made in and adjacent to the southeast portion of the Florida Current using standard aerial surveys during 2011 and 2012 to assess their seasonal presence. This area is of particular concern for sea turtles as interest increases in offshore energy developments, specifically harnessing the power of the Florida Current. While it is understood that marine turtles use these waters, here we evaluate seasonal variation in sea turtle abundance and density over two years. Density of sea turtles observed within the study area ranged from 0.003 turtles km-2 in the winter of 2011 to 0.064 turtles km-2 in the spring of 2012. This assessment of marine turtles in the waters off southeast Florida quantifies their in-water abundance across seasons in this area to establish baselines and inform future management strategies of these protected species.

  16. Evaluation of ion current density distribution on an extraction electrode of a radio frequency ion thruster

    NASA Astrophysics Data System (ADS)

    Masherov, P.; Riaby, V.; Abgaryan, V.

    2017-01-01

    The radial distributions of ion current density on an ion extracting electrode of a radio frequency (RF) ion thruster (RIT) with an inductive plasma source were obtained using probe diagnostics of the RF xenon plasma. Measurements were carried out using a plane wall probe simulator and the VGPS-12 Probe System of Plasma Sensors Co. At xenon flow rate q  =  2 sccm plasma pressure was 2 · 10-3 Torr, incident RF generator power varied in the range P g  =  50-250 W with RF power absorbed by plasma up to P p  =  220 W. Ion current densities were determined using semi- and double-logarithmic probe characteristics by linear extrapolations of their ion branches to probe floating potentials. The same parameters were also measured in undisturbed plasma by a classic cylindrical probe. They exceeded plane probe data by more than two times, showing the effectiveness of plasma sheath reproduction of the RIT ion extracting electrode by the plane wall probe simulator. Slight non-uniformity of the resulting plasma distributions and simplified RIT model design showed that the studied device with flat antenna coil and ferrite core could be considered as a promising prospect for RITs of new generation.

  17. Seasonal Variation in Sea Turtle Density and Abundance in the Southeast Florida Current and Surrounding Waters

    PubMed Central

    Bovery, Caitlin M.; Wyneken, Jeanette

    2015-01-01

    Assessment and management of sea turtle populations is often limited by a lack of available data pertaining to at-sea distributions at appropriate spatial and temporal resolutions. Assessing the spatial and temporal distributions of marine turtles in an open system poses both observational and analytical challenges due to the turtles’ highly migratory nature. Surface counts of marine turtles in waters along the southern part of Florida’s east coast were made in and adjacent to the southeast portion of the Florida Current using standard aerial surveys during 2011 and 2012 to assess their seasonal presence. This area is of particular concern for sea turtles as interest increases in offshore energy developments, specifically harnessing the power of the Florida Current. While it is understood that marine turtles use these waters, here we evaluate seasonal variation in sea turtle abundance and density over two years. Density of sea turtles observed within the study area ranged from 0.003 turtles km-2 in the winter of 2011 to 0.064 turtles km-2 in the spring of 2012. This assessment of marine turtles in the waters off southeast Florida quantifies their in-water abundance across seasons in this area to establish baselines and inform future management strategies of these protected species. PMID:26717520

  18. Classification of motor imagery by means of cortical current density estimation and Von Neumann entropy.

    PubMed

    Kamousi, Baharan; Amini, Ali Nasiri; He, Bin

    2007-06-01

    The goal of the present study is to employ the source imaging methods such as cortical current density estimation for the classification of left- and right-hand motor imagery tasks, which may be used for brain-computer interface (BCI) applications. The scalp recorded EEG was first preprocessed by surface Laplacian filtering, time-frequency filtering, noise normalization and independent component analysis. Then the cortical imaging technique was used to solve the EEG inverse problem. Cortical current density distributions of left and right trials were classified from each other by exploiting the concept of Von Neumann entropy. The proposed method was tested on three human subjects (180 trials each) and a maximum accuracy of 91.5% and an average accuracy of 88% were obtained. The present results confirm the hypothesis that source analysis methods may improve accuracy for classification of motor imagery tasks. The present promising results using source analysis for classification of motor imagery enhances our ability of performing source analysis from single trial EEG data recorded on the scalp, and may have applications to improved BCI systems.

  19. Reduced event-related current density in the anterior cingulate cortex in schizophrenia.

    PubMed

    Mulert, C; Gallinat, J; Pascual-Marqui, R; Dorn, H; Frick, K; Schlattmann, P; Mientus, S; Herrmann, W M; Winterer, G

    2001-04-01

    There is good evidence from neuroanatomic postmortem and functional imaging studies that dysfunction of the anterior cingulate cortex plays a prominent role in the pathophysiology of schizophrenia. So far, no electrophysiological localization study has been performed to investigate this deficit. We investigated 18 drug-free schizophrenic patients and 25 normal subjects with an auditory choice reaction task and measured event-related activity with 19 electrodes. Estimation of the current source density distribution in Talairach space was performed with low-resolution electromagnetic tomography (LORETA). In normals, we could differentiate between an early event-related potential peak of the N1 (90-100 ms) and a later N1 peak (120-130 ms). Subsequent current-density LORETA analysis in Talairach space showed increased activity in the auditory cortex area during the first N1 peak and increased activity in the anterior cingulate gyrus during the second N1 peak. No activation difference was observed in the auditory cortex between normals and patients with schizophrenia. However, schizophrenics showed significantly less anterior cingulate gyrus activation and slowed reaction times. Our results confirm previous findings of an electrical source in the anterior cingulate and an anterior cingulate dysfunction in schizophrenics. Our data also suggest that anterior cingulate function in schizophrenics is disturbed at a relatively early time point in the information-processing stream (100-140 ms poststimulus).

  20. Reconstructing cortical current density by exploring sparseness in the transform domain.

    PubMed

    Ding, Lei

    2009-05-07

    In the present study, we have developed a novel electromagnetic source imaging approach to reconstruct extended cortical sources by means of cortical current density (CCD) modeling and a novel EEG imaging algorithm which explores sparseness in cortical source representations through the use of L1-norm in objective functions. The new sparse cortical current density (SCCD) imaging algorithm is unique since it reconstructs cortical sources by attaining sparseness in a transform domain (the variation map of cortical source distributions). While large variations are expected to occur along boundaries (sparseness) between active and inactive cortical regions, cortical sources can be reconstructed and their spatial extents can be estimated by locating these boundaries. We studied the SCCD algorithm using numerous simulations to investigate its capability in reconstructing cortical sources with different extents and in reconstructing multiple cortical sources with different extent contrasts. The SCCD algorithm was compared with two L2-norm solutions, i.e. weighted minimum norm estimate (wMNE) and cortical LORETA. Our simulation data from the comparison study show that the proposed sparse source imaging algorithm is able to accurately and efficiently recover extended cortical sources and is promising to provide high-accuracy estimation of cortical source extents.

  1. Spatially resolved determination of the short-circuit current density of silicon solar cells via lock-in thermography

    SciTech Connect

    Fertig, Fabian Greulich, Johannes; Rein, Stefan

    2014-05-19

    We present a spatially resolved method to determine the short-circuit current density of crystalline silicon solar cells by means of lock-in thermography. The method utilizes the property of crystalline silicon solar cells that the short-circuit current does not differ significantly from the illuminated current under moderate reverse bias. Since lock-in thermography images locally dissipated power density, this information is exploited to extract values of spatially resolved current density under short-circuit conditions. In order to obtain an accurate result, one or two illuminated lock-in thermography images and one dark lock-in thermography image need to be recorded. The method can be simplified in a way that only one image is required to generate a meaningful short-circuit current density map. The proposed method is theoretically motivated, and experimentally validated for monochromatic illumination in comparison to the reference method of light-beam induced current.

  2. Determination of Defect Densities in High Electron Mobility Transistors Using Current Transient DLTS

    NASA Astrophysics Data System (ADS)

    Palma, John; Mil'shtein, Samson

    2011-12-01

    Since its introduction, Deep Level Transient Spectroscopy (DLTS) has become the preferred tool for investigating semiconductor defects. The limitations of measuring the small changes in gate capacitance in transistors led to the advent of current transient DLTS where the defects manifest themselves as a small change in drain current. However, this method was introduced at a time when heterostructure devices, such as High Electron Mobility Transistors (HEMTs), were non-existent and fails in determining defect concentrations in these modern devices. This study establishes a method by which defect concentrations can be determined in HEMT structures using current transient DLTS. First, the relationship between the change in the trap charge and the transistor drain current is established. Then, a computer aided technique is described which determines the volume within the device where the Fermi level crosses the trap energy. The result is that trap densities and their locations can be determined. DLTS measurements revealed two traps with ET = 0.43 and Nt = 1.1×1017cm-3, and ET = 0.19 and Nt = 3.1×1017 cm-3 for a tested HEMT.

  3. Discriminating hand gesture motor imagery tasks using cortical current density estimation.

    PubMed

    Edelman, Bradley; Baxter, Bryan; He, Bin

    2014-01-01

    Current EEG based brain computer interface (BCI) systems have achieved successful control in up to 3 dimensions; however the current paradigm may be unnatural for many rehabilitative and recreational applications. Therefore there is a great need to find motor imagination (MI) tasks that are realistic for output device control. In this paper we present our results on classifying hand gesture MI tasks, including right hand flexion, extension, supination and pronation using a novel EEG inverse imaging approach. By using both temporal and spatial specificity in the source domain we were able to separate MI tasks with up to 95% accuracy for binary classification of any two tasks compared to a maximum of only 79% in the sensor domain.

  4. Achieving glycemic control in elderly patients with type 2 diabetes: a critical comparison of current options

    PubMed Central

    Du, Ye-Fong; Ou, Horng-Yih; Beverly, Elizabeth A; Chiu, Ching-Ju

    2014-01-01

    The prevalence of type 2 diabetes mellitus (T2DM) is increasing in the elderly. Because of the unique characteristics of elderly people with T2DM, therapeutic strategy and focus should be tailored to suit this population. This article reviews the guidelines and studies related to older people with T2DM worldwide. A few important themes are generalized: 1) the functional and cognitive status is critical for older people with T2DM considering their life expectancy compared to younger counterparts; 2) both severe hypoglycemia and persistent hyperglycemia are deleterious to older adults with T2DM, and both conditions should be avoided when determining therapeutic goals; 3) recently developed guidelines emphasize the avoidance of hypoglycemic episodes in older people, even in the absence of symptoms. In addition, we raise the concern of glycemic variability, and discuss the rationale for the selection of current options in managing this patient population. PMID:25429208

  5. Current challenges and future achievements of blood transfusion service in Afghanistan.

    PubMed

    Cheraghali, A M; Sanei Moghaddam, E; Masoud, A; Faisal, H

    2012-10-01

    Afghanistan is a country with population of over 28 million. The long term conflicts have devastated country's qualified resources including human resources. ANBSTS was established by MoPH as the country national blood service. Currently in addition to central and regional blood centers of ANBSTS many other hospitals have their own transfusion services. Blood donation in Afghanistan mainly depends on replacement donors. Donor selection and donor interview are not very efficient. Most of the blood in Afghanistan is administered as fresh whole blood. Although blood transfusion services in Afghanistan require more efforts to be fully efficient, based on recent improvements in working procedures of ANBSTS a promising future for blood transfusion services in Afghanistan is predicted.

  6. Achieving donor repetition and motivation by block leaders among current blood donors.

    PubMed

    Martín-Santana, Josefa D; Beerli-Palacio, Asunción

    2012-12-01

    This paper presents an explicative model on the recommendation of donating blood made to relatives and friends by current donors. This model establishes satisfaction and intention to return as direct antecedents, and the quality perceived in the donation process and the existence of inhibitors as indirect antecedents. The results show that (1) the perceived quality has a positive influence on satisfaction and intention to return; (2) the intention to donate again depends positively on satisfaction, but negatively on the existence of internal and external inhibitors; and lastly (3) the recommendation to donate depends on donor satisfaction and their intention to return to donate, this being the most influential factor. At the same time, we contrasted how the model does not vary, whether it is a first-time donor or a repeat donor.

  7. Laboratory study of magnetic reconnection with a guide field and density asymmetry across the current sheet

    NASA Astrophysics Data System (ADS)

    Zhu, Hongxuan; Yoo, J.; Ji, H.; Jara-Almonte, J.; Fox, W.; Yamada, M.

    2016-10-01

    It has been known that the diamagnetic drift can stabilize the tearing mode, which is used to explain incomplete reconnection during sawtooth oscillations in Tokamaks. Swisdak et al. propose that reconnection with a strong guide field and pressure asymmetry is suppressed when the relative drift speed between ions and electrons along the outflow direction exceeds the upstream Alfvén speed. Swisdak's argument has been supported by space observations, but the exact mechanism of suppression has not been conclusively verified. We will conduct experiments in MRX to study suppression of reconnection with a strong guide field and density asymmetry. We will apply a guide field strength of about 2-3 times of the reconnecting field and achieve a density ratio up to 10. By systematically changing the guide field strength, we will investigate how the electron diamagnetic drift can affect profiles of the magnetic/electric field and patterns of the ion/electron flow. Finally, we will study how these modified field profiles and flow patterns contribute to reduction of the reconnection rate. This work is supported by DOE Contract No. DE-AC0209CH11466.

  8. Current guidelines for nut consumption are achievable and sustainable: a hazelnut intervention.

    PubMed

    Tey, S L; Brown, R; Chisholm, A; Gray, A; Williams, S; Delahunty, C

    2011-05-01

    Nuts are known for their hypocholesterolaemic properties; however, to achieve optimal health benefits, nuts must be consumed regularly and in sufficient quantity. It is therefore important to assess the acceptability of regular consumption of nuts. The present study examined the long-term effects of hazelnut consumption in three different forms on 'desire to consume' and 'overall liking'. A total of forty-eight participants took part in this randomised cross-over study with three dietary phases of 4 weeks: 30 g/d of whole, sliced and ground hazelnuts. 'Overall liking' was measured in a three-stage design: a pre- and post-exposure tasting session and daily evaluation over the exposure period. 'Desire to consume' hazelnuts was measured during the exposure period only. Ratings were measured on a 150 mm visual analogue scale. Mean ratings of 'desire to consume' were 92 (SD 35) mm for ground, 108 (SD 33) mm for sliced and 116 (SD 30) mm for whole hazelnuts. For 'overall liking', the mean ratings were 101 (SD 29) mm for ground, 110 (SD 32) mm for sliced and 118 (SD 30) mm for whole hazelnuts. Ground hazelnuts had significantly lower ratings than both sliced (P ≤ 0·034) and whole hazelnuts (P < 0·001), with no difference in ratings between sliced and whole hazelnuts (P ≥ 0·125). For each form of nut, ratings of 'overall liking' and 'desire to consume' were stable over the exposure period, indicating that not only did the participants like the nuts, but also they wished to continue eating them. Therefore, the guideline to consume nuts on a regular basis appears to be a sustainable behaviour to reduce CVD.

  9. Room-temperature ferromagnetism in Cr-doped Si achieved by controlling atomic structure, Cr concentration, and carrier densities: A first-principles study

    SciTech Connect

    Wei, Xin-Yuan; Yang, Zhong-Qin; Zhu, Yan; Li, Yun

    2015-04-28

    By using first-principles calculations, we investigated how to achieve a strong ferromagnetism in Cr-doped Si by controlling the atomic structure and Cr concentration as well as carrier densities. We found that the configuration in which the Cr atom occupies the tetrahedral interstitial site can exist stably and the Cr atom has a large magnetic moment. Using this doping configuration, room-temperature ferromagnetism can be achieved in both n-type and p-type Si by tuning Cr concentration and carrier densities. The results indicate that the carrier density plays a crucial role in realizing strong ferromagnetism in diluted magnetic semiconductors.

  10. A fast, calibrated model for pyroclastic density currents kinematics and hazard

    NASA Astrophysics Data System (ADS)

    Esposti Ongaro, Tomaso; Orsucci, Simone; Cornolti, Fulvio

    2016-11-01

    Multiphase flow models represent valuable tools for the study of the complex, non-equilibrium dynamics of pyroclastic density currents. Particle sedimentation, flow stratification and rheological changes, depending on the flow regime, interaction with topographic obstacles, turbulent air entrainment, buoyancy reversal, and other complex features of pyroclastic currents can be simulated in two and three dimensions, by exploiting efficient numerical solvers and the improved computational capability of modern supercomputers. However, numerical simulations of polydisperse gas-particle mixtures are quite computationally expensive, so that their use in hazard assessment studies (where there is the need of evaluating the probability of hazardous actions over hundreds of possible scenarios) is still challenging. To this aim, a simplified integral (box) model can be used, under the appropriate hypotheses, to describe the kinematics of pyroclastic density currents over a flat topography, their scaling properties and their depositional features. In this work, multiphase flow simulations are used to evaluate integral model approximations, to calibrate its free parameters and to assess the influence of the input data on the results. Two-dimensional numerical simulations describe the generation and decoupling of a dense, basal layer (formed by progressive particle sedimentation) from the dilute transport system. In the Boussinesq regime (i.e., for solid mass fractions below about 0.1), the current Froude number (i.e., the ratio between the current inertia and buoyancy) does not strongly depend on initial conditions and it is consistent to that measured in laboratory experiments (i.e., between 1.05 and 1.2). For higher density ratios (solid mass fraction in the range 0.1-0.9) but still in a relatively dilute regime (particle volume fraction lower than 0.01), numerical simulations demonstrate that the box model is still applicable, but the Froude number depends on the reduced

  11. Ion Current Density Study of the NASA-300M and NASA-457Mv2 Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Huang, Wensheng; Shastry, Rohit; Herman, Daniel A.; Soulas, George C.; Kamhawi, Hani

    2012-01-01

    NASA Glenn Research Center is developing a Hall thruster in the 15-50 kW range to support future NASA missions. As a part of the process, the performance and plume characteristics of the NASA-300M, a 20-kW Hall thruster, and the NASA-457Mv2, a 50-kW Hall thruster, were evaluated. The collected data will be used to improve the fidelity of the JPL modeling tool, Hall2De, which will then be used to aid the design of the 15-50 kW Hall thruster. This paper gives a detailed overview of the Faraday probe portion of the plume characterization study. The Faraday probe in this study is a near-field probe swept radially at many axial locations downstream of the thruster exit plane. Threshold-based integration limits with threshold values of 1/e, 1/e2, and 1/e3 times the local peak current density are tried for the purpose of ion current integration and divergence angle calculation. The NASA-300M is operated at 7 conditions and the NASA-457Mv2 at 14 conditions. These conditions span discharge voltages of 200 to 500 V and discharge power of 10 to 50 kW. The ion current density profiles of the near-field plume originating from the discharge channel are discovered to strongly resemble Gaussian distributions. A novel analysis approach involving a form of ray tracing is used to determine an effective point of origin for the near-field plume. In the process of performing this analysis, definitive evidence is discovered that showed the near-field plume is bending towards the thruster centerline.

  12. Ion Current Density Study of the NASA-300M and NASA-457Mv2 Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Huang, Wensheng; Shastry, Rohit; Herman, Daniel A.; Soulas, George C.; Kamhawi, Hani

    2012-01-01

    NASA Glenn Research Center is developing a Hall thruster in the 15-50 kW range to support future NASA missions. As a part of the process, the performance and plume characteristics of the NASA-300M, a 20-kW Hall thruster, and the NASA-457Mv2, a 50-kW Hall thruster, were evaluated. The collected data will be used to improve the fidelity of the JPL modeling tool, Hall2De, which will then be used to aid the design of the 15-50 kW Hall thruster. This paper gives a detailed overview of the Faraday probe portion of the plume characterization study. The Faraday probe in this study is a near-field probe swept radially at many axial locations downstream of the thruster exit plane. Threshold-based integration limits with threshold values of 1/e, 1/e(sup 2), and 1/e(sup 3) times the local peak current density are tried for the purpose of ion current integration and divergence angle calculation. The NASA-300M is operated at 7 conditions and the NASA-457Mv2 at 14 conditions. These conditions span discharge voltages of 200 to 500 V and discharge power of 10 to 50 kW. The ion current density profiles of the near-field plume originating from the discharge channel are discovered to strongly resemble Gaussian distributions. A novel analysis approach involving a form of ray tracing is used to determine an effective point of origin for the near-field plume. In the process of performing this analysis, definitive evidence is discovered that showed the near-field plume is bending towards the thruster centerline.

  13. At the Crossroads of Nanotoxicology in vitro: Past Achievements and Current Challenges.

    PubMed

    Hussain, Saber M; Warheit, David B; Ng, Sheung P; Comfort, Kristen K; Grabinski, Christin M; Braydich-Stolle, Laura K

    2015-09-01

    The exponential growth in the employment of nanomaterials (NMs) has given rise to the field of nanotoxicology; which evaluates the safety of engineered NMs. Initial nanotoxicological studies were limited by a lack of both available materials and accurate biodispersion characterization tools. However, the years that followed were marked by the development of enhanced synthesis techniques and characterization technologies; which are now standard practice for nanotoxicological evaluation. Paralleling advances in characterization, significant progress was made in correlating specific physical parameters, such as size, morphology, or coating, to resultant physiological responses. Although great strides have been made to advance the field, nanotoxicology is currently at a crossroads and faces a number of obstacles and technical limitations not associated with traditional toxicology. Some of the most pressing and influential challenges include establishing full characterization requirements, standardization of dosimetry, evaluating kinetic rates of ionic dissolution, improving in vitro to in vivo predictive efficiencies, and establishing safety exposure limits. This Review will discuss both the progress and future directions of nanotoxicology: highlighting key previous research successes and exploring challenges plaguing the field today.

  14. Topics in Current Science Research: Closing the Achievement Gap for Under Resourced Students of Color

    NASA Astrophysics Data System (ADS)

    Loya Villalpando, Alvaro; Daal, Miguel; Phipps, Arran; Speller, Danielle; Sadoulet, Bernard; Winheld, Rachel; Cryogenic Dark Matter Search Collaboration

    2015-04-01

    Topics in Current Science Research (TCSR) is a five-week summer course offered at the University of California, Berkeley through a collaboration between the Level Playing Field Institute's Summer Math and Science Honors Academy (SMASH) Program and the Cryogenic Dark Matter Search (CDMS) group at UC Berkeley. SMASH is an academic enrichment program geared towards under-resourced, high school students of color. The goals of the course are to expand the students' conception of STEM, to teach the students that science is a method of inquiry and not just a collection of facts that are taught in school, and to expose the scholars to critical thinking within a scientific setting. The course's curriculum engages the scholars in hands-on scientific research, project proposal writing, and presentation of their scientific work to their peers as well as to a panel of UC Berkeley scientists. In this talk, we describe the course and the impact it has had on previous scholars, we discuss how the course's pedagogy has evolved over the past 10 years to enhance students' perception and understanding of science, and we present previous participants' reflections and feedback about the course and its success in providing high school students a genuine research experience at the university level.

  15. Modelling of the reactive sputtering process with non-uniform discharge current density and different temperature conditions

    NASA Astrophysics Data System (ADS)

    Vašina, P; Hytková, T; Eliáš, M

    2009-05-01

    The majority of current models of the reactive magnetron sputtering assume a uniform shape of the discharge current density and the same temperature near the target and the substrate. However, in the real experimental set-up, the presence of the magnetic field causes high density plasma to form in front of the cathode in the shape of a toroid. Consequently, the discharge current density is laterally non-uniform. In addition to this, the heating of the background gas by sputtered particles, which is usually referred to as the gas rarefaction, plays an important role. This paper presents an extended model of the reactive magnetron sputtering that assumes the non-uniform discharge current density and which accommodates the gas rarefaction effect. It is devoted mainly to the study of the behaviour of the reactive sputtering rather that to the prediction of the coating properties. Outputs of this model are compared with those that assume uniform discharge current density and uniform temperature profile in the deposition chamber. Particular attention is paid to the modelling of the radial variation of the target composition near transitions from the metallic to the compound mode and vice versa. A study of the target utilization in the metallic and compound mode is performed for two different discharge current density profiles corresponding to typical two pole and multipole magnetics available on the market now. Different shapes of the discharge current density were tested. Finally, hysteresis curves are plotted for various temperature conditions in the reactor.

  16. A HIgh Current Density Low Cost Niobium 3 Tin Titanium Doped Conductor Utilizing A Novel Internal Tin Process

    SciTech Connect

    Bruce A Zeitlin

    2005-02-23

    An internal tin conductor has been developed using a Mono Element Internal Tin (MEIT) with an integral Nb barrier surrounding the Nb filaments. High current densities of 3000 A/mm2+ at 12 T and 1800 A/mm2 at 15 T have been achieved in conductors as small as 0.152 mm with the use of Nb7.5Ta filaments and Ti in the Sn core. In contrast, conductors with pure Nb and Ti in the Sn achieved 2700 A/mm2 at 12 T. Two internal fins, developed and patented on the project, were introduced into the filament array and reduced the effective filament diameter (Deff) by 38%. Additional fins will further reduce Deff The conductor was produced from 152.4 mm diameter billets to produce wire as small as 0.152 mm. The process promises be scaleable to 304 mm diameter billets yielding wire of 0.304 mm diameter. The MEIT process wire was easy to draw with relatively few breaks. The cost of this conductor in large production quantities based on the cost model presented could meet the 1.5 $/kilo amp meter(KAM) target of the HEP community

  17. Current Status and Future Prospects to Achieve Foot-and-Mouth Disease Eradication in South America.

    PubMed

    Clavijo, A; Sanchez-Vazquez, M J; Buzanovsky, L P; Martini, M; Pompei, J C; Cosivi, O

    2017-02-01

    South America has a favourable position with respect to foot-and-mouth disease (FMD) compared with other FMD-affected regions due to the elimination of endemic clinical presentation of the disease. South America has reached the final stage of control and aims to eradicate the disease in the region under the provisions of the Hemispheric Program for the Eradication of FMD 2011-2020 (PHEFA). This programme aims at bringing eradication to completion, thereby eliminating the pool of foot-and-mouth disease genotypes active in South America. This plan includes a regional political agreement that provides strategies and technical guidelines for the eradication of foot-and-mouth disease from South America. It incorporates knowledge and experience regarding the disease's history and its connection with the different production systems, animal movement and trade. The Pan American Foot and Mouth Disease Center has led the control and eradication programmes, providing the framework for designing national and subregional programmes that have led to significant progress in controlling the disease in South America. The current situation is the result of several factors, including the proper implementation of a national control programmes, good veterinary infrastructure in most countries and public-private participation in the process of eradicating the disease. Notwithstanding the favourable health status, there are significant challenges for the goal of eradication. At this stage, South American countries should enhance their surveillance strategies particularly through the use of target or risk-based surveys that contribute to increase the degree of sensitivity in the search for viral circulation in the context of absence of clinical occurrence of FMD.

  18. Direct numerical simulations of particle-laden density currents with adaptive, discontinuous finite elements

    NASA Astrophysics Data System (ADS)

    Parkinson, S. D.; Hill, J.; Piggott, M. D.; Allison, P. A.

    2014-05-01

    High resolution direct numerical simulations (DNS) are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier-Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE) DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two, and three-dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring mesh performance in capturing the range of dynamics. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. Use of discontinuous discretisations and adaptive unstructured meshing technologies, which reduce the required element count by approximately two orders of magnitude, results in high resolution DNS models of turbidity currents at a fraction of the cost of traditional FE models. The benefits of this technique will enable simulation of turbidity currents in complex and large domains where DNS modelling was previously unachievable.

  19. Current density and heating patterns in organic solar cells: modelling and imaging experiments (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Oettking, Rolf; Fluhr, Daniel; Rösch, Roland; Muhsin, Burhan; Hoppe, Harald

    2016-09-01

    We developed finite element models of organic solar cells in order to investigate current pathways and dissipative losses under different geometries. The models are of purely resistive nature, as this is sufficient to describe the effects under consideration. The overall behaviour of the current mostly steers the resistive behaviour of the device and is a delicate consequence of the interplay between the individual layer properties, namely the resistivities and layer thicknesses in combination. The model calculations solely based on external material parameters, i.e. without fitting, yield the spatial distribution of the current densities, potentials and the according resistive losses. In particular, the current pathways are spread out from the entire length of the top contact towards the entire width of the ground contact, running along the electric potential gradient. On the other hand, current crowding appears at the foremost part of the top electrode, resulting in a respective concentration of the resistive loss in this vicinity. The resistive loss in turn is the origin of the heat pattern, which is visible in DLIT/ILIT experiments. The comparison between experiment and simulation shows remarkable agreement. Having established the description of defect free solar cells, defects were simulated. We utilized the micro-diode-model as another established simulation method to model shunt or blocking contact defects in combination with electro luminescence imaging methods. The respective heat patterns were calculated in FEM. Nice agreement is found between the various experimental and simulation methods. The respective heat patterns then allow identifying several classes of defects such as shunt defects or blocking contact defects in accordance with their patterns from various imaging measurements, bridging the gap between theory and experiment to further the detailed analysis of organic solar cells.

  20. Pyroclastic Density Current Hazards in the Auckland Volcanic Field, New Zealand

    NASA Astrophysics Data System (ADS)

    Brand, B. D.; Gravley, D.; Clarke, A. B.; Bloomberg, S. H.

    2012-12-01

    The most dangerous phenomena associated with phreatomagmatic eruptions are dilute pyroclastic density currents (PDCs). These are turbulent, ground-hugging sediment gravity currents that travel radially away from the explosive center at up to 100 m/s. The Auckland Volcanic Field (AVF), New Zealand, consists of approximately 50 eruptive centers, at least 39 of which have had explosive phreatomagmatic behaviour. A primary concern for future AVF eruptions is the impact of dilute PDCs in and around the Auckland area. We combine field observations from the Maungataketake tuff ring, which has one of the best exposures of dilute PDC deposits in the AVF, with a quantitative model for flow of and sedimentation from a radially-spreading, steady-state, depth-averaged dilute PDC (modified from Bursik and Woods, 1996 Bull Volcanol 58:175-193). The model allows us to explore the depositional mechanisms, macroscale current dynamics, and potential impact on societal infrastructure of dilute PDCs from a future AVF eruption. The lower portion of the Maungataketake tuff ring pyroclastic deposits contains trunks, limbs and fragments of Podocarp trees (<1 m in diameter) that were blown down by dilute PDCs up to 0.7-0.9 km from the vent. Beyond this trees were encapsulated and buried in growth position up to the total runout distance of 1.6-1.8 km. This observation suggests that the dynamic pressure of the current quickly dropped as it travelled away from source. Using the tree diameter and yield strength of the wood, we calculate that dynamic pressures (Pdyn) of 10-75 kPa are necessary to topple trees of this size and composition. Thus the two main criteria for model success based on the field evidence include (a) Pdyn must be >10 kPa nearer than 0.9 km to the vent, and <10 kPa beyond 0.9 km, and (b) the total run-out distance must be between 1.6 and 1.8 km. Model results suggest the two main forces controlling the runout distance and Pdyn over the extent of the current are

  1. Invariance in current dipole moment density across brain structures and species: Physiological constraint for neuroimaging

    PubMed Central

    Murakami, Shingo; Okada, Yoshio

    2015-01-01

    Although anatomical constraints have been shown to be effective for MEG and EEG inverse solutions, there are still no effective physiological constraints. Strength of the current generator is normally described by the moment of an equivalent current dipole Q. This value is quite variable since it depends on size of active tissue. In contrast, the current dipole moment density q, defined as Q per surface area of active cortex, is independent of size of active tissue. Here we studied whether the value of q has a maximum in physiological conditions across brain structures and species. We determined the value due to the primary neuronal current (qprimary) alone, correcting for distortions due to measurement conditions and secondary current sources at boundaries separating regions of differing electrical conductivity. The values were in the same range for turtle cerebellum (0.56–1.48 nAm/mm2), guinea pig hippocampus (0.30–1.34 nAm/mm2), and swine neocortex (0.18–1.63 nAm/mm2), rat neocortex (~2.2 nAm/mm2), monkey neocortex (~0.40 nAm/mm2) and human neocortex (0.16–0.77 nAm/mm2). Thus, there appears to be a maximum value across the brain structures and species (1–2 nAm/mm2). The empirical values closely matched the theoretical values obtained with our independently validated neural network model (1.6–2.8 nAm/mm2 for initial spike and 0.7–3.1 nAm/mm2 for burst), indicating that the apparent invariance is not coincidental. Our model study shows that a single maximum value may exist across a wide range of brain structures and species, varying in neuron density, due to fundamental electrical properties of neurons. The maximum value of qprimary may serve as an effective physiological constraint for MEG/EEG inverse solutions. PMID:25680520

  2. Observations of currents and density structure across a buoyant plume front

    USGS Publications Warehouse

    Gelfenbaum, G.; Stumpf, R.P.

    1993-01-01

    Observations of the Mobile Bay, Alabama, plume during a flood event in April 1991 reveal significant differences in the current field on either side of a front associated with the buoyant plume. During a strong southeasterly wind, turbid, low salinity water from Mobile Bay was pushed through an opening in the west side of the ebb-tidal delta and moved parallel to the coast. A stable front developed between the low salinity water of the buoyant plume (11???) and the high salinity coastal water (>23???) that was being forced landward by the prevailing winds. Despite the shallow water depth of 6 m, measurements of currents, temperature, and salinity show large shears and density gradients in both the vertical and the horizontal directions. At a station outside of the buoyant plume, currents at 0.5 m and 1.5 m below the surface were in the same direction as the wind. Inside the plume, however, currents at 0.5 m below the surface were parallel to the coast, 45??, off the direction of the wind and the magnitude was 45% larger than the magnitude of the surface currents outside the plume. Beneath the level of the plume, the currents were identical to the wind-driven currents in the ambient water south of the front. Our observations suggest that the wind-driven surface currents of the ambient water converged with the buoyant plume at the front and were subducted beneath the plume. The motion of the ambient coastal surface water was in the direction of the local wind stress, however, the motion of the plume had no northerly component of motion. The plume also did not show any flow toward the front, suggesting a balance between the northerly component of wind stress and the southerly component of buoyant spreading. In addition, the motion of the plume did not appear to affect the motion of the underlying ambient water, suggesting a lack of mixing between the two waters. ?? 1993 Estuarine Research Federation.

  3. Erosion and entrainment of snow and ice by pyroclastic density currents: some outstanding questions (Invited)

    NASA Astrophysics Data System (ADS)

    Walder, J. S.

    2010-12-01

    A pyroclastic density current moving over snow is likely to transform to a lahar if the pyroclasts incorporate enough (melting) snow and meltwater to bring the bulk water content of the mixture to about 35% by volume. However, the processes by which such a mixture forms are still not well understood. Walder (Bull. Volcanol., v. 62, 2000) showed experimentally the existence of an erosion mechanism that functions even in the absence of relative shear motion between pyroclasts and snow substrate: a portion of the snow melted by a blanket of pyroclasts is vaporized; the flux of water vapor upward through the pyroclasts may be enough to fluidize the pyroclasts, which then convect, rapidly scour the snow substrate and transform into a slurry. But these experiments do not tell us how moving pyroclasts would erode snow, and simply releasing a hot grain flow over a snow surface in the lab gives misleading results owing to improper scaling of τ/σ , the ratio of the shear stress τ exerted by the pyroclastic flow to the shear strength σ of snow. There seems to be no way around this problem for experiments with actual snow. However, it may be possible to circumvent the scaling problem by replacing the snow substrate by a gas-fluidized particle bed: by varying the gas flux, the apparent shear strength of the particle bed can be varied. Such an investigation of erosional processes could be done at room temperature. Snow-avalanche studies (for example, Gauer and Issler, Ann. Glaciol. v. 38, 2003) may provide some insight into snow erosion by a pyroclastic density current. Snow is eroded at the base of a dense snow avalanche by abrasion, particle impacts, and—at the avalanche head—by plowing and a “blasting” mechanism associated with compression of the snowpack and expulsion of pore fluid (air). Erosion at the avalanche head seems to be particularly important. Similar processes are likely to occur when the over-riding flow comprises hot grains. The laboratory release of

  4. Euler potentials for two layers with non-constant current densities in the ambient magnetic field aligned to the layers

    NASA Astrophysics Data System (ADS)

    Vandas, Marek; Romashets, Eugene P.

    2016-12-01

    The Euler potentials for two current layers aligned to an ambient homogeneous magnetic field are found. Previous treatment of such a system assumed constant current density in the layers. However, the magnetic field becomes infinite at the edges. The new approach eliminates this inconsistency by introducing an inhomogeneous current density. Euler potentials are constructed semi-analytically for such a system. Charged-particle motion and trapping in it are examined by this representation. Using Euler potentials, the influence of current sheets of zero and non-zero thicknesses on energetic-particle fluxes is investigated, and characteristic flux variations near the sheets are presented. The results can be applied to Birkeland currents.

  5. An exponential scaling law for the strain dependence of the Nb3Sn critical current density

    NASA Astrophysics Data System (ADS)

    Bordini, B.; Alknes, P.; Bottura, L.; Rossi, L.; Valentinis, D.

    2013-07-01

    The critical current density of the Nb3Sn superconductor is strongly dependent on the strain applied to the material. In order to investigate this dependence, it is a common practice to measure the critical current of Nb3Sn strands for different values of applied axial strain. In the literature, several models have been proposed to describe these experimental data in the reversible strain region. All these models are capable of fitting the measurement results in the strain region where data are collected, but tend to predict unphysical trends outside the range of data, and especially for large strain values. In this paper we present a model of a new strain function, together with the results obtained by applying the new scaling law on relevant datasets. The data analyzed consisted of the critical current measurements at 4.2 K that were carried out under applied axial strain at Durham University and the University of Geneva on different strand types. With respect to the previous models proposed, the new scaling function does not present problems at large strain values, has a lower number of fitting parameters (only two instead of three or four), and is very stable, so that, starting from few experimental points, it can estimate quite accurately the strand behavior in a strain region where there are no data. A relationship is shown between the proposed strain function and the elastic strain energy, and an analogy is drawn with the exponential form of the McMillan equation for the critical temperature.

  6. Thermal instability induced by high current densities in high-Tc coated conductors

    NASA Astrophysics Data System (ADS)

    Maza, J.; Ferro, G.; Veira, J. A.; Vidal, F.

    2013-10-01

    By using a 1 ms pulse technique, the current-voltage curves (CVC) under zero-applied magnetic field have been measured in practical high-Tc superconducting wires based on coated (RE)BCO. The measurements extend up to the so-called supercritical current intensity, I*, at which superconductivity disappears accompanied by an abrupt jump in the voltage. The resulting CVC, including the temperature dependence of I*, were analysed at a quantitative level in terms of a thermal instability model proposed recently. An attractive aspect of our thermal instability approach is that in spite of the complexity of the coated layered structure, in its simpler formulation all the geometric and thermal variables are encapsulated into a single characteristic parameter r with units of thermal resistance. All the experimental results for I* from 76 to 86 K are quantitatively, within 2%, accounted for by the thermal instability analysis. Furthermore, the best-fit value of r is found to be quite consistent with the inner geometry and composition of the wires. Another remarkable result of our analysis is that the temperature T* reached by the wire at I*, i.e., the temperature triggering the thermal runaway, is less than one kelvin above the bath temperature. These results further support the universality of the thermal instability mechanism of superconductivity quenching by high current densities.

  7. Air Entrainment and Thermal Evolution of Pyroclastic Density Currents at Tungurahua, Ecuador

    NASA Astrophysics Data System (ADS)

    Benage, M. C.; Dufek, J.; Mothes, P. A.

    2015-12-01

    The entrainment of air into pyroclastic density currents (PDCs) impacts the thermal profile and evolution of the current. However, the associated hazards and opaqueness of PDCs make it difficult to discern internal dynamics and entrainment through direct observations. In this work, we use a three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model, deposit descriptions, and pyroclast field data, such as paleomagnetic and rind thickness, to study the entrainment efficiency and thus the thermal history of PDCs down the Juive Grande quebrada during the August 16-17th 2006 eruption of Tungurahua volcano. We conclude that 1) the efficient entrainment of ambient air cools the nose and upper portion of the PDCs by 30-60% of the original temperature, 2) PDCs with an initial temperature of 727 °C are on average more efficient at entraining ambient air than PDCs with an initial temperature of 327 °C, 3) the channelized PDCs develop a particle concentration gradient with a concentrated bed load region and suspended load region that leads to a large vertical temperature gradient, and 4) observations and pyroclast temperatures and textures suggest that the PDCs had temperatures greater than 327 °C in the bed load region while the upper, exterior portion of the currents cooled down to temperatures less than 100 °C. By combining field data and numerical models, the structure and dynamics of a PDC can be deduced for these relatively common small volume PDCs.

  8. Magnetic field dependence of shielding current density in Y-Ba-Cu-O rings at 77 K

    SciTech Connect

    Polak, M.; Majoros, M.; Hanic, F.; Pitel, J.; Kedrova, M.; Kottman, P.; Talapa, J.; Vencel, L. )

    1989-06-01

    A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current density J{sub cs} and the intergranular transport current density J{sub ct} are identical if the measurement conditions are similar. A degradation of J{sub cs} measured in the external field with AC ripple has been observed.

  9. Comparison between the vorticity expansion approximation and the local density approximation of the current-density functional theory from the viewpoint of sum rules.

    PubMed

    Higuchi, K; Higuchi, M

    2007-09-12

    We compare the vorticity expansion approximation (VEA) with the local density approximation (LDA) of the current-density functional theory from the viewpoint of sum rules. The VEA formulae satisfy all sum rules which are derived from uniform and nonuniform coordinate scaling properties, while the LDA formulae do not satisfy at least about a third of the sum rules. The validity of the VEA formula is thus confirmed successfully.

  10. Time-dependent current-density-functional theory for the linear response of weakly disordered systems

    NASA Astrophysics Data System (ADS)

    Ullrich, C. A.; Vignale, G.

    2002-05-01

    Time-dependent density-functional theory (TDFT) provides a way of calculating, in principle exactly, the linear response of interacting many-electron systems, and thus allows one to obtain their excitation energies. For extended systems, there exist excitations of a collective nature, such as bulk and surface plasmons in metals or intersubband plasmons in doped semiconductor quantum wells. This paper develops a quantitatively accurate first-principles description for the frequency and the linewidth of such excitations in inhomogeneous weakly disordered systems. A finite linewidth in general has intrinsic and extrinsic sources. At low temperatures and outside the region where electron-phonon interaction occurs, the only intrinsic damping mechanism is provided by electron-electron interaction. This kind of intrinsic damping can be described within TDFT, but one needs to go beyond the adiabatic approximation and include retardation effects. It has been shown [G. Vignale, C. A. Ullrich, and S. Conti, Phys. Rev. Lett. 79, 4878 (1997)] that a density-functional response theory that is local in space but nonlocal in time has to be constructed in terms of the currents, rather than the density. This theory will be reviewed in the first part of this paper. For quantitatively accurate linewidths, extrinsic dissipation mechanisms, such as impurities or disorder, have to be included in the response theory. In the second part of this paper, we discuss how extrinsic dissipation can be described within the so-called memory-function formalism. This formalism will first be introduced and reviewed for homogeneous systems. We will then present a synthesis of TDFT with the memory function formalism for inhomogeneous systems, which allows one to simultaneously account for intrinsic and extrinsic damping of collective excitations. As an example where both sources of dissipation are important and where high-quality experimental data are available for comparison, we discuss intersubband

  11. [Focal evoked potentials in the rabbit visual cortex: density analysis of current sources].

    PubMed

    Supin, A Ia

    1981-01-01

    Focal evoked potentials were elicited in the rabbit visual cortex by punctiform light stimuli and analyzed by the current source density technique. They contained two main components. The first component was generated by local sink at depths form 0.6 to 1.0 mm (layer IV) with 30 ms latency and peak time about 50 ms. The second one was generated by less local sink at depths form 0.2-0.3 to 1.3-1.5 mm (layers III-VI) with peak time 90-100 ms. These two sinks are considered as active and indicating the localization of depolarizing synapses. Passive sources are dissipated around the zone of the active sinks.

  12. Effect of Adding on the Critical Current Density and Lateral Levitation Force of Bulk

    NASA Astrophysics Data System (ADS)

    Savaşkan, B.; Koparan, E. Taylan; Güner, S. B.; Çelik, Ş.; Öztürk, K.; Yanmaz, E.

    2015-10-01

    We fabricated malic acid -added bulks by wet mixing and "Two-step solid state reaction method". The effects of adding malic acid on , behaviour and lateral levitation force features of bulk have been investigated. A systematic decrease in the critical temperature with increasing adding level confirms the substitution of C at the B site of . While the 4 wt% sample showed the best of at 4 T and 5 K, 15 wt% sample showed uncompetitive lower critical current density , which ascribes the poor connectivity due to the excessive unsubstituted C distribution at grain boundaries and the presence of high MgO amount. At 24 and 28 K, the 4 and 6 wt% malic-acid-added samples exhibit a higher lateral force than pure sample. Based on the observed values of M- H, ( H) and lateral levitation force , it can be concluded that the 4 wt% malic-acid-added sample is the best of the studied samples.

  13. Current density in generalized Fibonacci superlattices under a uniform electric field.

    PubMed

    Panchadhyayee, P; Biswas, R; Khan, Arif; Mahapatra, P K

    2008-07-09

    We present an exhaustive study on tunneling and electrical conduction in an electrically biased GaAs-Al(y)Ga(1-y)As generalized Fibonacci superlattice. The study is based on transfer matrix formalism using an Airy function approach and provides an exact calculation of the current density in the case of quasi-periodic multibarrier systems. The results suggest the use of such quasi-periodic systems in perfect band-pass or band-eliminator (of extremely low width) circuitry. We have clearly demonstrated the resonance-type peaks and negative differential conductivity regimes in such systems. It has also been found that quasi-periodicity favors sharp negative differential conductivity peaks compared to those in periodic superlattices and thus have profound importance in device applications.

  14. Current source density estimation and interpolation based on the spherical harmonic Fourier expansion.

    PubMed

    Pascual-Marqui, R D; Gonzalez-Andino, S L; Valdes-Sosa, P A; Biscay-Lirio, R

    1988-12-01

    A method for the spatial analysis of EEG and EP data, based on the spherical harmonic Fourier expansion (SHE) of scalp potential measurements, is described. This model provides efficient and accurate formulas for: (1) the computation of the surface Laplacian and (2) the interpolation of electrical potentials, current source densities, test statistics and other derived variables. Physiologically based simulation experiments show that the SHE method gives better estimates of the surface Laplacian than the commonly used finite difference method. Cross-validation studies for the objective comparison of different interpolation methods demonstrate the superiority of the SHE over the commonly used methods based on the weighted (inverse distance) average of the nearest three and four neighbor values.

  15. Current-source density analysis of slow brain potentials during time estimation.

    PubMed

    Gibbons, Henning; Rammsayer, Thomas H

    2004-11-01

    Two event-related potential studies were conducted to investigate differential brain correlates of temporal processing of intervals below and above 3-4 s. In the first experiment, 24 participants were presented with auditorily marked target durations of 2, 4, and 6 s that had to be reproduced. Timing accuracy was similar for all three target durations. As revealed by current-source density analysis, slow-wave components during both presentation and reproduction were independent of target duration. Experiment 2 examined potential modulating effects of type of interval (filled and empty) and presentation mode (randomized and blocked presentation of target durations). Behavioral and slow-wave findings were consistent with those of Experiment 1. Thus, the present findings support the notion of a general timing mechanism irrespective of interval duration as proposed by scalar timing theory and pacemaker-counter models of time estimation.

  16. Spatio-temporal current density reconstruction (stCDR) from EEG/MEG-data.

    PubMed

    Darvas, F; Schmitt, U; Louis, A K; Fuchs, M; Knoll, G; Buchner, H

    2001-01-01

    Among the different approaches to the bioelectromagnetic inverse problem, the current-density reconstruction methods (CDR) provide the most general solutions. Since the inverse problem does not have a unique solution, model assumptions have to be taken into account. Multi-channel measurements contain not only spatial, but also temporal information about the sources, so a naturally extension to existing methods leads to spatio-temporal model constraints. Spatio-temporal CDR's (stCDR) have been tested in simplified volume conductor models, assuming different spatial model constraints and a smooth temporal activation model. Comparison to existing spatial model constraints showed a significant improvement of spatial and temporal resolution of the reconstructed sources for the spatio-temporal models especial in noisy data.

  17. Effects of rotation and sloping terrain on the fronts of density currents

    NASA Astrophysics Data System (ADS)

    Hunt, J. C. R.; Pacheco, J. R.; Mahalov, A.; Fernando, H. J. S.

    2005-08-01

    The initial stage of the adjustment of a gravity current to the effects of rotation with angular velocity f/2 is analysed using a short time analysis where Coriolis forces are initiated in an inviscid von Kármán Benjamin gravity current front at t_F {=} 0. It is shown how, on a time-scale of order 1/f, as a result of ageostrophic dynamics, the slope and front speed U_F are much reduced from their initial values, while the transverse anticyclonic velocity parallel to the front increases from zero to O(N H_0), where N {=} sqrt{g'/H_0} is the buoyancy frequency, and g' {=} g Delta rho /rho_0 is the reduced acceleration due to gravity. Here rho_0 is the density and Delta rho and H_0 are the density difference and initial height of the current. Extending the steady-state theory to account for the effect of the slope sigma on the bottom boundary shows that, without rotation, U_{F} has a maximum value for sigma {=} upi/6, while with rotation, U_{F} tends to zero on any slope. For the asymptotic stage when ft_F {≫} 1, the theory of unsteady waves on the current is reviewed using nonlinear shallow-water equations and the van der Pol averaging method. Their motions naturally split into a ‘balanced’ component satisfying the Margules geostrophic relation and an equally large ‘unbalanced’ component, in which there is horizontal divergence and ageostrophic vorticity. The latter is responsible for nonlinear oscillations in the current on a time scale f(-1) , which have been observed in the atmosphere and field experiments. Their magnitude is mainly determined by the initial potential energy in relation to that of the current and is proportional to the ratio sqrtBu {=} L_R/R_0, where L_R {=} N H_0/f is the Rossby deformation radius and R_0 is the initial radius. The effect of slope friction also prevents the formation of a steady front. From the analysis it is concluded that a weak mean radial flow must be driven by the ageostrophic oscillations, preventing the mean

  18. Surface Lattice Resonances for Enhanced and Directional Electroluminescence at High Current Densities.

    PubMed

    Zakharko, Yuriy; Held, Martin; Graf, Arko; Rödlmeier, Tobias; Eckstein, Ralph; Hernandez-Sosa, Gerardo; Hähnlein, Bernd; Pezoldt, Jörg; Zaumseil, Jana

    2016-12-21

    Hybrid photonic-plasmonic modes in periodic arrays of metallic nanostructures offer a promising trade-off between high-quality cavities and subdiffraction mode confinement. However, their application in electrically driven light-emitting devices is hindered by their sensitivity to the surrounding environment and to charge injecting metallic electrodes in particular. Here, we demonstrate that the planar structure of light-emitting field-effect transistor (LEFET) ensures undisturbed operation of the characteristic modes. We incorporate a square array of gold nanodisks into the charge transporting and emissive layer of a polymer LEFET in order to tailor directionality and emission efficiency via the Purcell effect and variation of the fractional local density of states in particular. Angle- and polarization-resolved spectra confirm that the enhanced electroluminescence correlates with the dispersion curves of the surface lattice resonances supported by these structures. These LEFETs reach current densities on the order of 10 kA/cm(2), which may pave the way toward practical optoelectronic devices with tailored emission patterns and potentially electrically pumped plasmonic lasers.

  19. Surface Lattice Resonances for Enhanced and Directional Electroluminescence at High Current Densities

    PubMed Central

    2016-01-01

    Hybrid photonic-plasmonic modes in periodic arrays of metallic nanostructures offer a promising trade-off between high-quality cavities and subdiffraction mode confinement. However, their application in electrically driven light-emitting devices is hindered by their sensitivity to the surrounding environment and to charge injecting metallic electrodes in particular. Here, we demonstrate that the planar structure of light-emitting field-effect transistor (LEFET) ensures undisturbed operation of the characteristic modes. We incorporate a square array of gold nanodisks into the charge transporting and emissive layer of a polymer LEFET in order to tailor directionality and emission efficiency via the Purcell effect and variation of the fractional local density of states in particular. Angle- and polarization-resolved spectra confirm that the enhanced electroluminescence correlates with the dispersion curves of the surface lattice resonances supported by these structures. These LEFETs reach current densities on the order of 10 kA/cm2, which may pave the way toward practical optoelectronic devices with tailored emission patterns and potentially electrically pumped plasmonic lasers. PMID:28042593

  20. Microstructure, critical current density and trapped field experiments in IG-processed Y-123

    NASA Astrophysics Data System (ADS)

    Muralidhar, M.; Ide, N.; Koblischka, M. R.; Diko, P.; Inoue, K.; Murakami, M.

    2016-05-01

    In this paper, we adapted the top-seeded infiltration growth ‘IG’ technique and produced several YBa2Cu3O y ‘Y-123’ samples with an addition of Y2BaCuO5 ‘Y-211’ secondary phase particles with varying sizes by the sintering process and the ball milling technique. For the first set of samples, Y-211 disks were sintered at temperatures ranging between 900 °C and 1100 °C and were used for the production of Y-123 material by the IG process. Magnetization measurements showed a sharp superconducting transition with an onset T c at around 92 K, irrespective of the sintering temperature. However, the trapped field and critical current density (J c) values were dependent on the sintering temperature and it was found that the best temperature is around 925 °C. Further, the trapped field distribution measurements at 77 K indicated that all samples are of single grain nature. The highest trapped field was recorded around 0.31 T at 77 K for the Y-123 sample with 20 mm in diameter and 5 mm thickness produced by Y-211 pre-from around 925 °C. On the other hand, a second set of samples Y-211 were controlled by ball milling technique combined with an optimized slow cooling process. As a result, the critical current density (J c) at 77 K and zero field was determined to be 225 kA cm-2. The improved performance of the Y-123 material can be understood in terms of homogeneous distribution of fine secondary phase particles which is demonstrated by AFM micrographs.

  1. Scaling laws for the critical current density of NbN films in high magnetic fields

    SciTech Connect

    Hampshire, D.P. . Dept. of Physics); Gray, K.E.; Kampwirth, R.T. )

    1992-08-01

    We have measured the critical current density (Jc) of two NbN films (500 {Angstrom} and 1550 {Angstrom} thick) as a function of temperature in magnetic fields up to 25 Tesla using transport measurements. In both films, the functional form of the volume pinning force F{sub p} obeys the Fietz - Webb scaling law throughout the entire magnetic field and temperature range such that: F{sub p}=J{sub c} {times} B= {alpha}B{sub c2}{sup m}(T)b{sup {1/2}} (1-b){sup 2} = {alpha}*(1-T/T{sub c}){sup m}b{sup {1/2}}(1-b){sup 2} where {alpha} and {alpha}* are constants dependent on the film, B{sub c2}(T) is the upper critical field, b = B/B{sub c2}(T) is the reduced magnetic field, {Tc} is the critical temperature and we find m = 2.7 {plus minus} 0.1. Over a limited range of magnetic fields close to B{sub c2}(T), we can approximate this functional form by: F{sub p} = {Beta}B{sub c2}{sup M}(T)b(1-b){sup 2}={Beta}*(1-T/{Tc}){sup M}b(1-b){sup 2} where {Beta} and {Beta}* are constants and we find M = 2.6{plus minus}0.2. Values of J{sub c} derived from D.C. magnetisation data obtained using Bean's model show qualitative agreement with the transport measurements throughout the superconducting phase. Despite the marked granularity in the microstructure of these films, we interpret our results as evidence that a flux pinning mechanism determines the transport current density in NbN films in high magnetic fields.

  2. Scaling laws for the critical current density of NbN films in high magnetic fields

    SciTech Connect

    Hampshire, D.P.; Gray, K.E.; Kampwirth, R.T.

    1992-08-01

    We have measured the critical current density (Jc) of two NbN films (500 {Angstrom} and 1550 {Angstrom} thick) as a function of temperature in magnetic fields up to 25 Tesla using transport measurements. In both films, the functional form of the volume pinning force F{sub p} obeys the Fietz - Webb scaling law throughout the entire magnetic field and temperature range such that: F{sub p}=J{sub c} {times} B= {alpha}B{sub c2}{sup m}(T)b{sup {1/2}} (1-b){sup 2} = {alpha}*(1-T/T{sub c}){sup m}b{sup {1/2}}(1-b){sup 2} where {alpha} and {alpha}* are constants dependent on the film, B{sub c2}(T) is the upper critical field, b = B/B{sub c2}(T) is the reduced magnetic field, {Tc} is the critical temperature and we find m = 2.7 {plus_minus} 0.1. Over a limited range of magnetic fields close to B{sub c2}(T), we can approximate this functional form by: F{sub p} = {Beta}B{sub c2}{sup M}(T)b(1-b){sup 2}={Beta}*(1-T/{Tc}){sup M}b(1-b){sup 2} where {Beta} and {Beta}* are constants and we find M = 2.6{plus_minus}0.2. Values of J{sub c} derived from D.C. magnetisation data obtained using Bean`s model show qualitative agreement with the transport measurements throughout the superconducting phase. Despite the marked granularity in the microstructure of these films, we interpret our results as evidence that a flux pinning mechanism determines the transport current density in NbN films in high magnetic fields.

  3. Status Epilepticus Induced Spontaneous Dentate Gyrus Spikes: In Vivo Current Source Density Analysis

    PubMed Central

    Flynn, Sean P.; Barrier, Sylvain; Scott, Rod C.; Lenck- Santini, Pierre-Pascal; Holmes, Gregory L.

    2015-01-01

    The dentate gyrus is considered to function as an inhibitory gate limiting excitatory input to the hippocampus. Following status epilepticus (SE), this gating function is reduced and granule cells become hyper-excitable. Dentate spikes (DS) are large amplitude potentials observed in the dentate gyrus (DG) of normal animals. DS are associated with membrane depolarization of granule cells, increased activity of hilar interneurons and suppression of CA3 and CA1 pyramidal cell firing. Therefore, DS could act as an anti-excitatory mechanism. Because of the altered gating function of the dentate gyrus following SE, we sought to investigate how DS are affected following pilocarpine-induced SE. Two weeks following lithium-pilocarpine SE induction, hippocampal EEG was recorded in male Sprague-Dawley rats with 16-channel silicon probes under urethane anesthesia. Probes were placed dorso-ventrally to encompass either CA1-CA3 or CA1-DG layers. Large amplitude spikes were detected from EEG recordings and subject to current source density analysis. Probe placement was verified histologically to evaluate the anatomical localization of current sinks and the origin of DS. In 9 of 11 pilocarpine-treated animals and two controls, DS were confirmed with large current sinks in the molecular layer of the dentate gyrus. DS frequency was significantly increased in pilocarpine-treated animals compared to controls. Additionally, in pilocarpine-treated animals, DS displayed current sinks in the outer, middle and/or inner molecular layers. However, there was no difference in the frequency of events when comparing between layers. This suggests that following SE, DS can be generated by input from medial and lateral entorhinal cortex, or within the dentate gyrus. DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1. These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the

  4. Dynamics of Braided Channels, Bars, and Associated Deposits Under Experimental Density Currents

    NASA Astrophysics Data System (ADS)

    Limaye, A. B. S.; Jean-Louis, G.; Paola, C.

    2015-12-01

    Turbidity currents are the principal agents that transfer clastic sediment from continental margins to the deep ocean. The extensive sedimentary deposits that result can record influences from fluvial transport, ocean currents, and seafloor bathymetry; decoding these controls is key to understanding long-term continental denudation and the formation of hydrocarbon reservoirs. Experimental turbidity currents often use pre-formed, single-thread channels, but more recent experiments and seafloor observations suggest that braided channels also develop in submarine environments. Yet controls on the formation of submarine braided channels and relationships between these channels and stratigraphic evolution remain largely untested. We have conducted a series of experiments to determine the conditions conducive to forming braided submarine channels, and to relate channel geometry and kinematics to deposit architecture. Dissolved salt supplies the excess density of the experimental turbidity currents, which transport plastic, sand-sized sediment as bedload across a test section two meters long and one meter wide. Our experiments indicate that braided channels can form as constructional features without prior erosion for a range of input water and sediment fluxes. Channel migration, avulsion, and aggradation construct sedimentary deposits with bars at a variety of scales. Bar geometry and channel kinematics are qualitatively similar under subaerial and subaqueous experiments with other parameters fixed. We will present quantitative analyses of the relationships between channel geometry and mobility and deposit architecture, at scales from individual bars to the entire deposit, and compare these results to control experiments with subaerial braiding. These experimental results suggest parallels between subaerial and subaqueous braiding, and help to constrain forward models for stratigraphic evolution and inverse methods for estimating flow conditions from turbidites.

  5. Direct numerical simulations of particle-laden density currents with adaptive, discontinuous finite elements

    NASA Astrophysics Data System (ADS)

    Parkinson, S. D.; Hill, J.; Piggott, M. D.; Allison, P. A.

    2014-09-01

    High-resolution direct numerical simulations (DNSs) are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier-Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE) DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two and three dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring model performance in capturing the range of dynamics on a range of meshes. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. The use of adaptive mesh optimisation is shown to reduce the required element count by approximately two orders of magnitude in comparison with fixed, uniform mesh simulations. This leads to a substantial reduction in computational cost. The computational savings and flexibility afforded by adaptivity along with the flexibility of FE methods make this model well suited to simulating turbidity currents in complex domains.

  6. The influence of current speed and vegetation density on flow structure in two macrotidal eelgrass canopies

    USGS Publications Warehouse

    Lacy, Jessica R.; Wyllie-Echeverria, Sandy

    2011-01-01

    The influence of eelgrass (Zostera marina) on near-bed currents, turbulence, and drag was investigated at three sites in two eelgrass canopies of differing density and at one unvegetated site in the San Juan archipelago of Puget Sound, Washington, USA. Eelgrass blade length exceeded 1 m. Velocity profiles up to 1.5 m above the sea floor were collected over a spring-neap tidal cycle with a downward-looking pulse-coherent acoustic Doppler profiler above the canopies and two acoustic Doppler velocimeters within the canopies. The eelgrass attenuated currents by a minimum of 40%, and by more than 70% at the most densely vegetated site. Attenuation decreased with increasing current speed. The data were compared to the shear-layer model of vegetated flows and the displaced logarithmic model. Velocity profiles outside the meadows were logarithmic. Within the canopies, most profiles were consistent with the shear-layer model, with a logarithmic layer above the canopy. However, at the less-dense sites, when currents were strong, shear at the sea floor and above the canopy was significant relative to shear at the top of the canopy, and the velocity profiles more closely resembled those in a rough-wall boundary layer. Turbulence was strong at the canopy top and decreased with height. Friction velocity at the canopy top was 1.5–2 times greater than at the unvegetated, sandy site. The coefficient of drag CD on the overlying flow derived from the logarithmic velocity profile above the canopy, was 3–8 times greater than at the unvegetated site (0.01–0.023 vs. 2.9 × 10−3).

  7. A promising tool to achieve chemical accuracy for density functional theory calculations on Y-NO homolysis bond dissociation energies.

    PubMed

    Li, Hong Zhi; Hu, Li Hong; Tao, Wei; Gao, Ting; Li, Hui; Lu, Ying Hua; Su, Zhong Min

    2012-01-01

    A DFT-SOFM-RBFNN method is proposed to improve the accuracy of DFT calculations on Y-NO (Y = C, N, O, S) homolysis bond dissociation energies (BDE) by combining density functional theory (DFT) and artificial intelligence/machine learning methods, which consist of self-organizing feature mapping neural networks (SOFMNN) and radial basis function neural networks (RBFNN). A descriptor refinement step including SOFMNN clustering analysis and correlation analysis is implemented. The SOFMNN clustering analysis is applied to classify descriptors, and the representative descriptors in the groups are selected as neural network inputs according to their closeness to the experimental values through correlation analysis. Redundant descriptors and intuitively biased choices of descriptors can be avoided by this newly introduced step. Using RBFNN calculation with the selected descriptors, chemical accuracy (≤1 kcal·mol(-1)) is achieved for all 92 calculated organic Y-NO homolysis BDE calculated by DFT-B3LYP, and the mean absolute deviations (MADs) of the B3LYP/6-31G(d) and B3LYP/STO-3G methods are reduced from 4.45 and 10.53 kcal·mol(-1) to 0.15 and 0.18 kcal·mol(-1), respectively. The improved results for the minimal basis set STO-3G reach the same accuracy as those of 6-31G(d), and thus B3LYP calculation with the minimal basis set is recommended to be used for minimizing the computational cost and to expand the applications to large molecular systems. Further extrapolation tests are performed with six molecules (two containing Si-NO bonds and two containing fluorine), and the accuracy of the tests was within 1 kcal·mol(-1). This study shows that DFT-SOFM-RBFNN is an efficient and highly accurate method for Y-NO homolysis BDE. The method may be used as a tool to design new NO carrier molecules.

  8. Effects of Current Density and Frequency on Microstructure and Mechanical Properties of Ni Stencil Masks Fabricated by Pulse Electroforming

    NASA Astrophysics Data System (ADS)

    Park, Geun Chul; Choi, Jun Hyuk; Kim, Ji Cheol; Kim, Tae Woong; Song, Keun; Lim, Jun Hyung; Joo, Jinho

    2012-09-01

    We fabricated Ni stencil masks using a pulse electroforming and investigated the effects of current density and frequency on the microstructure and mechanical property. In the electroforming process, the current densities were 2.5 and 5 A/dm2 and the frequency varied from 0 (DC) to 1000 Hz at a duty cycle of 50%. Texture, microstructure, and mechanical properties varied with the current density and frequency. The preferred orientation of (220) at 2.5 A/dm2 changed to (200) as the current density increased to 5 A/dm2. Grain size decreased with decreasing current density or increasing frequency, probably due to a sufficient supply of Ni ions and the presence of inhibitor species. This decrease in grain size resulted in increase of hardness and wear resistance. However, with increase in current density and frequency (5 A/dm2 and 1000 Hz), the grain size became large, as a result of faradic current during the off-time.

  9. Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

    SciTech Connect

    Kinjo, Hidekazu Machida, Kenji; Aoshima, Ken-ichi; Kato, Daisuke; Kuga, Kiyoshi; Kikuchi, Hiroshi; Shimidzu, Naoki; Matsui, Koichi

    2014-05-28

    Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

  10. Propagation and deposition mechanisms of dense pyroclastic density currents: insights from analogue laboratory experiments. (Invited)

    NASA Astrophysics Data System (ADS)

    Roche, O.; Montserrat, S.; Niño, Y.; Tamburrino, A.

    2010-12-01

    Analogue laboratory experiments on air-particle flows represent a useful tool to investigate the mechanisms of propagation and deposition of dense (or the dense part of) pyroclastic density currents. In this context, we carried out experiments in the dam-break configuration and studied the emplacement processes of analogue biphasic currents generated from the quasi-instantaneous release of fluidized columns of fine (80 µm) particles. The low permeability of the granular material permitted relatively slow diffusion of the initial pore pressure within the flows until they came to halt. Analysis of the flow kinematics and comparison with flows of water in the same apparatus revealed that the air-particle currents propagated in two distinct stages. They behaved as their inertial water counterparts for most their emplacement, as both types of flows had the same morphology and propagated at constant front velocity U~√(2gh), h being the initial height of the granular column. This occurred as long as the height of the collapsing fluidized columns was higher than the that of the resultant flows, thus generating a driving pressure gradient. This fluid-inertial behavior suggested that the pore fluid pressure was high during propagation of the mixture. In order to check this hypothesis, we carried out non invasive measurements of the pore fluid pressure at the base of the air-particle flows and made correlation of the pressure signal with the flow structure from analyses of high speed videos. The flow structure consisted of a sliding head that caused underpressure relative to ambient conditions and whose magnitude correlated with the flow velocity. The flow head was followed by a body that generated overpressure and at the base of which a deposit aggraded at a nearly constant rate. Both the flow head and body were sheared pervasively as the internal velocity increased upwards. The combination of pressure advection from the source and relatively slow pressure diffusion

  11. Investigation into the erosive capacity of pyroclastic density currents at Mount Saint Helens, Washington (USA)

    NASA Astrophysics Data System (ADS)

    Pollock, N. M.; Brand, B. D.

    2012-12-01

    Two fundamental aspects of PDC dynamics that remain poorly understood are the primary control(s) on substrate erosion and the effect of erosion on downstream flow dynamics. The gap in understanding reflects the lack of sufficient field exposures with evidence for these processes. In the 32 years since the May 18th, 1980 eruption of Mount St Helens (MSH), kilometers of new outcrops have been exposed throughout the PDC and debris avalanche hummock deposits that provide substantial evidence of substrate erosion and entrainment by the PDCs produced throughout the afternoon of the eruption. Field observations include a reappearance of large lithics (>1 m) in PDC deposits at distances of 4-5 km from the vent, suggesting that these lithics were entrained locally. For this study, detailed componentry and roundness analyses are utilized to determine the source of lithics in PDC deposits and to quantify the erosive capacity of the PDCs at MSH. Comparison of componentry data from the PDC deposits with debris avalanche deposits ~200 m upstream indicate that >50% of the lithics were locally entrained. The entrainment of these lithics appears to have significantly altered the dynamics of the current as contacts between flow units change from purely depositional upstream from the hummocks to erosive and scouring following the entrainment of dense lithics. This evidence suggests that the capacity of a PDC to behave erosively could be a self-perpetuating process; entrainment of dense lithics at the base of the current results in an increased density gradient, which in turn enhances a current's ability to continue to erode. In addition, the presence of locally entrained lithics at various heights within a single flow unit and within close proximity to the source of the lithics suggests both a progressive entrainment of the substrate as well as a progressive aggradation of the deposits, depending on localized flow conditions. While erosion may have initially occurred due to the

  12. Emplacement temperatures of boiling-over pyroclastic density currents from Tungurahua and Cotopaxi volcanoes, Ecuador

    NASA Astrophysics Data System (ADS)

    Rader, E. L.; Geist, D.; Geissman, J. W.; Harpp, K. S.; Dufek, J.

    2011-12-01

    Pyroclastic density currents (PDC) can be sourced by collapsing columns, dome collapse, and boiling-over fountains. Although there are innumerable studies of the deposits produced by the first 2 mechanisms, pyroclastic deposits from boiling-over have not been well characterized. We are studying several pyroclastic flow deposits from two boiling over eruptions in Ecuador, Tungurahua, 2006 and Cotopaxi, 1877. These eruptions produced abundant cauliflower-textured, large (up to 1 m in diameter), fragile scoria clasts. Some evidence points to relatively low temperatures during transport. For example, some flows at Cotopaxi are unusually long and sinuous and probably influenced by melt water from the glacier that caps the cone. Additionally, un-charred vegetation and eyewitness reports of un-melted plastic in the path of pyroclastic flows at Tungurahua also support cool emplacement temperatures. On the other hand, some scoria clasts were ductile when deposited as evidenced by draped clasts. We cut 5 to 9 cm transects from rim to core of 36 lithic and juvenile samples, which were then thermally demagnetized and measured. Lithic samples from Tungurahua indicate only one flow was fully remagnetized above ~580°C, while another flow was only partially remagnetized below 210°C. All other lithics from both volcanoes were never heated to above 90°C. Juvenile clasts from Cotopaxi indicate three types of flows: currents that begin hot (above 580°C) but cool quickly (juveniles emplaced hot, but lithics emplaced cold); currents that deposit at ~330°C (two components of magnetization that intersect at 330°C in the juvenile clasts), and cold currents such as lahars. The majority of currents from Tungurahua are of the 2nd type, having emplacement temperatures of ~380°C-280°C, with the deformable juvenile clasts being hotter than the rest of the flow. Despite the intact nature of the fragile bombs, emplacement temperatures indicate that the majority of flow deposits at

  13. Influence of Critical Current Density on Magnetic Force of Htsc Bulk above Pmr with 3D-MODELING Numerical Solutions

    NASA Astrophysics Data System (ADS)

    Lu, Yiyun; Lu, Bingjuan; Ge, Yunwang; Chen, Wenqing

    Numerical electromagnetic field simulations of high-temperature superconductors (HTSC) bulk were carried out to calculate the magnetic force between the HTSC bulk and the permanent magnet railway (PMR). A 3D-modeling numerical calculation method is proposed using the finite element method. The model is formulated with the magnetic field vector (H-method). The resulting code was written with FORTRAN language. The electric field intensity E and the current density J constitutive relation of HTSC were described with E-J power law. The Kim macro-model is used to describe critical current density Jc of HTSC bulk. Two virtual HTSC bulks were used to solve the critical current density Jc anisotropic properties of HTSC materials. A superconducting levitation system composed of one HTSC bulk and PMR is successfully investigated using the proposed method. By this method, the influence of critical current density on magnetic levitation force of the superconducting levitation system is mathematically studied.

  14. Application of hybrid supercapacitor using granule Li4Ti5O12/activated carbon with variation of current density

    NASA Astrophysics Data System (ADS)

    Lee, Byung-Gwan; Lee, Seung-Hwan

    2017-03-01

    We report the electrochemical performance of asymmetric hybrid supercapacitors composed of granule Li4Ti5O12 as an anode and activated carbon as a cathode with different current densities. It is demonstrated that the hybrid supercapacitors show good initial discharge capacities were ranged from 39.8 to 46.4 F g-1 in the current densities range of 0.3-1 A g-1. The performance degradation is proportional to the current density due to quick gassing, resulting from H2O and HF formation. In particular, the hybrid supercapacitors show the pretty good cycling stability of 97.4%, even at the high current density of 0.8 A g-1, which are among most important performance in the real application for energy storage devices. Therefore, we believe that hybrid supercapacitors using granule Li4Ti5O12/activated carbon are eligible for the promising next generation energy devices.

  15. Influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium

    SciTech Connect

    Ostrovskaya, G. V.; Markov, V. S.; Frank, A. G.

    2016-01-15

    The influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium plasma in 2D and 3D magnetic configurations with X-type singular lines is studied by the methods of holographic interferometry and magnetic measurements. Significant differences in the structures of plasma and current sheets formed at close parameters of the initial plasma and similar configurations of the initial magnetic fields are revealed.

  16. Characterizing the Li–Li7La3Zr2O12 interface stability and kinetics as a function of temperature and current density

    DOE PAGES

    Sharafi, Asma; Meyer, Harry M.; Nanda, Jagjit; ...

    2015-10-27

    The stability and kinetics of the Li–Li7La3Zr2O12 (LLZO) interface were characterized as a function of temperature and current density. Polycrystalline LLZO was densified using a rapid hot-pressing technique achieving 97 ± 1% relative density, and <10% grain boundary resistance; effectively consisting of an ensemble of single LLZO crystals. It was determined that by heating to 175 °C, the room temperature Li-LLZO interface resistance decreases dramatically from 5822 (as-assembled) to 514 Ω cm2; a > 10-fold decrease. In characterizing the maximum sustainable current density (or critical current density – CCD) of the Li-LLZO interface, several signs of degradation were observed. Inmore » DC cycling tests, significant deviation from Ohmic behavior was observed. In post-cycling tests, regions of metallic Li were observed; propagating parallel to the ionic current. For the cells cycled at 30, 70, 100, 130 and 160 °C, the CCD was determined to be 50, 200, 800, 3500, and 20000 μA cm–2, respectively. As a result, the relationships and phenomena observed in this work can be used to better understand the Li-LLZO interface stability, enabling the use of batteries employing Li metal anodes.« less

  17. First test of BNL electron beam ion source with high current density electron beam

    SciTech Connect

    Pikin, Alexander Alessi, James G. Beebe, Edward N.; Shornikov, Andrey; Mertzig, Robert; Wenander, Fredrik; Scrivens, Richard

    2015-01-09

    A new electron gun with electrostatic compression has been installed at the Electron Beam Ion Source (EBIS) Test Stand at BNL. This is a collaborative effort by BNL and CERN teams with a common goal to study an EBIS with electron beam current up to 10 A, current density up to 10,000 A/cm{sup 2} and energy more than 50 keV. Intensive and pure beams of heavy highly charged ions with mass-to-charge ratio < 4.5 are requested by many heavy ion research facilities including NASA Space Radiation Laboratory (NSRL) at BNL and HIE-ISOLDE at CERN. With a multiampere electron gun, the EBIS should be capable of delivering highly charged ions for both RHIC facility applications at BNL and for ISOLDE experiments at CERN. Details of the electron gun simulations and design, and the Test EBIS electrostatic and magnetostatic structures with the new electron gun are presented. The experimental results of the electron beam transmission are given.

  18. Critical current density and microstructural state of an internal tin multifilamentary superconducting wire

    NASA Astrophysics Data System (ADS)

    Dietderich, D. R.; Glazer, J.; Lea, C.; Hassenzahl, W. V.; Morris, J. W., Jr.

    1984-09-01

    The critical current density (J sub c) of internal tin wires is increased when low-temperature diffusion heat treatments are performed prior to a high temperature reaction. To determine the variation of J sub c with prereaction heat treatments a copper-stabilized IGC internal tin wire with an outside diameter of 0.267mm was studied. The wire has 2 to 2.5 micron diameter filameters, and within the Ta barrier, the area ratio of the copper matrix and Sn core to Nb is about 2.2. Due to the character of the Cu-Sn phase diagram, heat treatments at a series of temperatures below the Nb3Sn reaction temperature affect the local Sn concentration in the matrix about the Nb filaments. The variation in J sub c resulting from these heat treatments is a consequence of the microstructural state of the conductor and the morphology of the Nb3Sn layer produced. The results of this work show that the internal tin and bronze-processed wires have different J sub c (H) characteristics. The two processes have comparable critical currents at high fields, suggesting the same H sub c2, while at low fields the internal tin wire is superior, suggesting a better grain morphology.

  19. Metal based gas diffusion layers for enhanced fuel cell performance at high current densities

    NASA Astrophysics Data System (ADS)

    Hussain, Nabeel; Van Steen, Eric; Tanaka, Shiro; Levecque, Pieter

    2017-01-01

    The gas diffusion layer strongly influences the performance and durability of polymer electrolyte fuel cells. A major drawback of current carbon fiber based GDLs is the non-controlled variation in porosity resulting in a random micro-structure. Moreover, when subjected to compression these materials show significant reduction in porosity and permeability leading to water management problems and mass transfer losses within the fuel cell. This study investigated the use of uniform perforated metal sheets as GDLs in conjunction with microchannel flowfields. A metal sheet design with a pitch of 110 μm and a hole diameter of 60 μm in combination with an MPL showed superior performance in the high current density region compared to a commercially available carbon paper based GDL in a single cell environment. Fuel cell testing with different oxidants (air, heliox and oxygen) indicate that the metal sheet offers both superior diffusion and reduced flooding in comparison to the carbon based GDL. The presence of the MPL has been found to be critical to the functionality of the metal sheet suggesting that the MPL design may represent an important optimisation parameter for further improvements in performance.

  20. High transport critical current density in Cu-clad multifilament MgB2 tape

    NASA Astrophysics Data System (ADS)

    Liu, C. F.; Du, S. J.; Yan, G.; Fu, B. Q.; Feng, Y.; Ji, P.; Wang, J. R.; Liu, X. H.; Zhang, P. X.; Wu, X. Z.; Zhou, L.; Cao, L. Z.; Ruan, K. Q.; Wang, C. Y.; Li, X. G.; Zhou, G. E.; Zhang, Y. H.

    2002-05-01

    Cu-clad multifilament MgB2 tapes with Ta or NbZr buffer have been fabricated by using a powder-in-tube (PIT). Mg+2B mixture powder was used as the central conductor core in single filament with Cu sheath and Ta or NbZr buffer wall. The composite tapes with 18 filaments were heat-treated in pure Ar atmosphere at 600-1000 °C for 1-10 h, and reacted in-situ to form MgB2. The phase composition and microstructure in the samples were examined by using X-ray diffraction and optical microscopy. Transport critical current was measured by a standard four-probe technique at different magnetic fields and temperatures. The sample with 18 filaments and NbZr buffer shows a high transport critical current density of 8×104 A/cm2 (10 K, 0 T) and 1.36×104 A/cm2 (10 K, 1 T).

  1. Critical current density and grain connectivity of Bi-2223 added MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2014-04-01

    Polycrystalline MgB2 with addition of 0, 1, 3, and 5 wt. % of Bi-2223(Bi1.8Pb0.26Sr2Ca2Cu3O10+x) powder has been synthesized by solid reaction process. The effect of Bi-2223 addition on current transport and superconducting properties of polycrystalline MgB2 superconductor is discussed. Four probe DC resistivity measurement shows that low level of Bi-2223 addition hardly affects the superconducting transition temperature, Tc of MgB2. The modified Bloch- Gruneisen (B-G) analysis of normal state resistivity data reveals a decrease in intergrain connectivity and increase in intragrain connectivity of MgB2 by Bi-2223 addition. The critical current density of present set of samples is estimated from M- H hysteresis loop in the light of Bean's model. MgB2 added with 1 wt. % of Bi- 2223 added gives the best performance (˜ 2 times enhancement in Jc) amongst the studied samples.

  2. Ultrasound Current Source Density Imaging of the Cardiac Activation Wave Using a Clinical Cardiac Catheter

    PubMed Central

    Qin, Yexian; Li, Qian; Ingram, Pier; Barber, Christy; Liu, Zhonglin

    2015-01-01

    Ultrasound current source density imaging (UCSDI), based on the acoustoelectric (AE) effect, is a noninvasive method for mapping electrical current in 4-D (space + time). This technique potentially overcomes limitations with conventional electrical mapping procedures typically used during treatment of sustained arrhythmias. However, the weak AE signal associated with the electrocardiogram is a major challenge for advancing this technology. In this study, we examined the effects of the electrode configuration and ultrasound frequency on the magnitude of the AE signal and quality of UCSDI using a rabbit Langendorff heart preparation. The AE signal was much stronger at 0.5 MHz (2.99 μV/MPa) than 1.0 MHz (0.42 μV/MPa). Also, a clinical lasso catheter placed on the epicardium exhibited excellent sensitivity without penetrating the tissue. We also present, for the first time, 3-D cardiac activation maps of the live rabbit heart using only one pair of recording electrodes. Activation maps were used to calculate the cardiac conduction velocity for atrial (1.31 m/s) and apical (0.67 m/s) pacing. This study demonstrated that UCSDI is potentially capable of real-time 3-D cardiac activation wave mapping, which would greatly facilitate ablation procedures for treatment of arrhythmias. PMID:25122512

  3. High current density PQQ-dependent alcohol and aldehyde dehydrogenase bioanodes.

    PubMed

    Aquino Neto, Sidney; Hickey, David P; Milton, Ross D; De Andrade, Adalgisa R; Minteer, Shelley D

    2015-10-15

    In this paper, we explore the bioelectrooxidation of ethanol using pyrroloquinoline quinone (PQQ)-dependent alcohol and aldehyde dehydrogenase (ADH and AldDH) enzymes for biofuel cell applications. The bioanode architectures were designed with both direct electron transfer (DET) and mediated electron transfer (MET) mechanisms employing high surface area materials such as multi-walled carbon nanotubes (MWCNTs) and MWCNT-decorated gold nanoparticles, along with different immobilization techniques. Three different polymeric matrices were tested (tetrabutyl ammonium bromide (TBAB)-modified Nafion; octyl-modified linear polyethyleneimine (C8-LPEI); and cellulose) in the DET studies. The modified Nafion membrane provided the best electrical communication between enzymes and the electrode surface, with catalytic currents as high as 16.8 ± 2.1 µA cm(-2). Then, a series of ferrocene redox polymers were evaluated for MET. The redox polymer 1,1'-dimethylferrocene-modified linear polyethyleneimine (FcMe2-C3-LPEI) provided the best electrochemical response. Using this polymer, the electrochemical assays conducted in the presence of MWCNTs and MWCNTs-Au indicated a Jmax of 781 ± 59 µA cm(-2) and 925 ± 68 µA cm(-2), respectively. Overall, from the results obtained here, DET using the PQQ-dependent ADH and AldDH still lacks high current density, while the bioanodes that operate via MET employing ferrocene-modified LPEI redox polymers show efficient energy conversion capability in ethanol/air biofuel cells.

  4. An organic-heterojunction diode current equation including random site trap density

    NASA Astrophysics Data System (ADS)

    Kim, SeongMin; Ha, Jaewook; Kim, Jin-Baek

    2016-08-01

    The current-voltage characteristics of an organic heterojunction (HJ), where random site trap density at the donor-acceptor (D-A) interface is included, is numerically investigated based on the polaron-pair (PP) model (Phys. Rev. B. 82, 155305 (2010)). To derive the analytic equation, the electric field FI at the D-A interface, which is included in the field parameter b, is first approximated to estimate the polaron-pair dissociation rate, k_{ppd}. It is then assumed that the quasi-Fermi level E_{Fp/n} at the donor/acceptor lies in the trap energy level ( E_{trap}) at random sites without a direct dependence on applied bias ( Va), but on a HOMO/LUMO with Va dependence. As a result, the low diode current (DC) at forward bias is attributed to the E_{trap}, which is lower than the LUMO at acceptors, and is higher than the HOMO at donors. This implies that the pattern of DC is at forward biases depending upon the position of E_{trap}.

  5. First test of BNL electron beam ion source with high current density electron beam

    NASA Astrophysics Data System (ADS)

    Pikin, Alexander; Alessi, James G.; Beebe, Edward N.; Shornikov, Andrey; Mertzig, Robert; Wenander, Fredrik; Scrivens, Richard

    2015-01-01

    A new electron gun with electrostatic compression has been installed at the Electron Beam Ion Source (EBIS) Test Stand at BNL. This is a collaborative effort by BNL and CERN teams with a common goal to study an EBIS with electron beam current up to 10 A, current density up to 10,000 A/cm2 and energy more than 50 keV. Intensive and pure beams of heavy highly charged ions with mass-to-charge ratio < 4.5 are requested by many heavy ion research facilities including NASA Space Radiation Laboratory (NSRL) at BNL and HIE-ISOLDE at CERN. With a multiampere electron gun, the EBIS should be capable of delivering highly charged ions for both RHIC facility applications at BNL and for ISOLDE experiments at CERN. Details of the electron gun simulations and design, and the Test EBIS electrostatic and magnetostatic structures with the new electron gun are presented. The experimental results of the electron beam transmission are given.

  6. Simulation-based validation for four- dimensional multi-channel ultrasound current source density imaging.

    PubMed

    Wang, Zhaohui; Witte, Russell S

    2014-03-01

    Ultrasound current source density imaging (UCSDI), which has application to the heart and brain, exploits the acoustoelectric (AE) effect and Ohm's law to detect and map an electrical current distribution. In this study, we describe 4-D UCSDI simulations of a dipole field for comparison and validation with bench-top experiments. The simulations consider the properties of the ultrasound pulse as it passes through a conductive medium, the electric field of the injected dipole, and the lead field of the detectors. In the simulation, the lead fields of detectors and electric field of the dipole were calculated by the finite element (FE) method, and the convolution and correlation in the computation of the detected AE voltage signal were accelerated using 3-D fast Fourier transforms. In the bench-top experiment, an electric dipole was produced in a bath of 0.9% NaCl solution containing two electrodes, which injected an ac pulse (200 Hz, 3 cycles) ranging from 0 to 140 mA. Stimulating and recording electrodes were placed in a custom electrode chamber made on a rapid prototype printer. Each electrode could be positioned anywhere on an x-y grid (5 mm spacing) and individually adjusted in the depth direction for precise control of the geometry of the current sources and detecting electrodes. A 1-MHz ultrasound beam was pulsed and focused through a plastic film to modulate the current distribution inside the saline-filled tank. AE signals were simultaneously detected at a sampling frequency of 15 MHz on multiple recording electrodes. A single recording electrode is sufficient to form volume images of the current flow and electric potentials. The AE potential is sensitive to the distance from the dipole, but is less sensitive to the angle between the detector and the dipole. Multi-channel UCSDI potentially improves 4-D mapping of bioelectric sources in the body at high spatial resolution, which is especially important for diagnosing and guiding treatment of cardiac and

  7. Effect of surface charge density and electro-osmotic flow on ionic current in a bipolar nanopore fluidic diode

    NASA Astrophysics Data System (ADS)

    Pal Singh, Kunwar; Kumar, Manoj

    2011-10-01

    We have simulated bipolar nanopore fluidic diodes for different values of surface charge densities, electrolyte concentrations, and thickness of transition zone. Nanopore enrichment leads to increased nanopore conductivity with the surface charge density at low electrolyte concentrations. Potential drop across the nanopore and electric field inside the nanopore decreases. Forward current and ionic current rectification peaks for a specific value of surface charge density. Even though the electro-osmotic current component remains small as compared to other components, its non-inclusion in the modeling leads to serious errors in the solutions. Significant ion current rectification can be obtained even if transition zone between oppositely charged zones is not narrow. The effect of the surface charge is screened by counterions at higher electrolyte concentrations, which leads to reduced electrolyte polarization and a decrease in the ion current rectification.

  8. A hydrodynamical model of shear flow over semi-infinite barriers with application to density currents

    SciTech Connect

    Shapiro, A. )

    1992-12-01

    Vertically sheared airflow over semi-infinite barriers is investigated with a simple hydrodynamical model. The idealized flow is steady, two-dimensional, neutrally buoyant, and inviscid, bounded on the bottom by a semi-infinite impermeable barrier and on the top by a rigid tropopause lid. With attention further restricted to an exponentially decreasing wind shear, the equations of motion (Euler's equations) reduce, without approximation, to a modified Poisson equation for a pseudo streamfunction and a formula for the Exner function. The free parameters characterizing the model's environment are the tropopause height, the density scale height, the wind speed at ground level, and the wind speed at tropopause level. Additional parameters characterize the barrier geometry. Exact solutions of the equations of motion are obtained for semi-infinite plateau barriers and for a barrier qualitatively resembling the shallow density current associated with some thunderstorm outflows. These solutions are noteworthy in that the reduction of a certain nondimensional shear parameter (through negative values) results in greater vertical parcel displacements over the barrier despite a corresponding reduction in the vertical velocity. This steepening tendency culminates in overturning motions associated with both upstream and down-stream steering levels. In this latter case the low-level inflow impinging on the barrier participates in a mixed jump and overturning updraft reminiscent of updrafts simulated in numerical convective models. Conversely, for large values of the nondimensional shear parameter, parcels undergo small vertical parcel displacements over the barrier despite large vertical velocities. This latter behavior may account for the finding that strong convergence along the leading edge of storm outflows does not always trigger deep convection even in unstable environments.

  9. Kinetic theory of current and density drift instabilities with weak charged-neutral collisions. [in space plasmas

    NASA Technical Reports Server (NTRS)

    Gary, S. P.

    1984-01-01

    This paper describes the linear kinetic theory of electrostatic instabilities driven by a density gradient drift and a magnetic-field-aligned current in a plasma with weak charged neutral collisions. The configuration is that of a uniform magnetic field B, a weak, uniform density gradient in the x direction and a weak, uniform electric field in the z direction. Collisions are represented by the BGK model. The transition from the (kinetic) universal density drift instability to the (fluidlike) current convective instability is studied in detail, and the short wavelength properties of the latter mode are investigated.

  10. Effects of the vortex line shape on the critical current density in high Tc superconducting film with nanorod pinning centers

    NASA Astrophysics Data System (ADS)

    Jung, Y.; Kwak, K.; Lee, W.; Rhee, J.; Youm, D.; Yoo, J.; Han, Y. H.; Park, B. J.

    2012-06-01

    We studied the critical current density distribution in a coated conductor comprised of (Gd,Y)1Ba2Cu3O7-δ-BaZrO3 film. Transmission electron microscopy measurements showed that nanorod pinning centers tilt by ˜13° from the c-axis. Magneto-optical image (MOI) measurements showed interesting asymmetric distributions of magnetic flux density. From MOIs we calculated the asymmetric distributions of the critical current density, which is associated with the properties of vortex pinning. We were able to explain these results through the geometrical relationship of the tilted rod pinning centers and the curved vortex lines.

  11. Effectiveness of an eel curriculum on student achievement for the California earth science standard on ocean currents A comparative analysis

    NASA Astrophysics Data System (ADS)

    Eisenberg, David A.

    With the intent oftransitioning a traditional secondary physical science course into a more Earth science focused course, the CalEP A Education and the Environment (EEl) Curriculum was substituted in place of an existing curriculum on ocean currents. For one week students were presented a complete unit covering California State Earth Science Standard 5.d regarding ocean currents. Student sections were separated into two groups, one using previous instructional materials and one using the EEl curriculum to determine if there was a significant difference in student achievement between the two curriculums. The independent t-test between the two groups did not show a significant difference in student posttest scores when the EEl curriculum was used in substitution of the predecessor curriculum. An analysis of student work revealed some advantages to the substituted EEl curriculum in the quality of student responses and increased student engagement.

  12. Maximum surface charge density for triboelectric nanogenerators achieved by ionized-air injection: methodology and theoretical understanding.

    PubMed

    Wang, Sihong; Xie, Yannan; Niu, Simiao; Lin, Long; Liu, Chang; Zhou, Yu Sheng; Wang, Zhong Lin

    2014-10-22

    For the maximization of the surface charge density in triboelectric nanogenerators, a new method of injecting single-polarity ions onto surfaces is introduced for the generation of surface charges. The triboelectric nanogenerator's output power gets greatly enhanced and its maximum surface charge density is systematically studied, which shows a huge room for the improvement of the output of triboelectric nanogenerators by surface modification.

  13. The roles of CHPD: superior critical current density and n-value obtained in binary in situ MgB2 cables

    NASA Astrophysics Data System (ADS)

    Hossain, M. S. A.; Motaman, A.; Barua, S.; Patel, D.; Mustapic, M.; Kim, J. H.; Maeda, M.; Rindfleisch, M.; Tomsic, M.; Cicek, O.; Melisek, T.; Kopera, L.; Kario, A.; Ringsdorf, B.; Runtsch, B.; Jung, A.; Dou, S. X.; Goldacker, W.; Kovac, P.

    2014-09-01

    A binary magnesium diboride (MgB2) cable has been assembled by braiding six Nb/Monel sheathed monofilament strands around a central copper stabilizer for improving the operational environment. The total critical current (Ic) of the braided cable is obtained by multiplying the Ic of six single wires, without any dissipation. In this work, various mechanical deformations, i.e., swaging, two-axial rolling, groove rolling, and cold high-pressure densification (CHPD) at 1.8 GPa have been applied to the 6-stranded cable to obtain additional densification. The highest critical current density at both 4.2 and 20 K has been achieved in this work through the CHPD treated cable due to higher filament mass density. The present results are promising in view of the cable, particularly in power applications at industrial lengths that pave the way to seeking an optimal protocol to meet a practical functionality.

  14. Continuous-wave InAs/GaAs quantum-dot laser diodes monolithically grown on Si substrate with low threshold current densities.

    PubMed

    Lee, Andrew; Jiang, Qi; Tang, Mingchu; Seeds, Alwyn; Liu, Huiyun

    2012-09-24

    We report the first room-temperature continuous-wave operation of III-V quantum-dot laser diodes monolithically grown on a Si substrate. Long-wavelength InAs/GaAs quantum-dot structures were fabricated on Ge-on-Si substrates. Room-temperature lasing at a wavelength of 1.28 μm has been achieved with threshold current densities of 163 A/cm(2) and 64.3 A/cm(2) under continuous-wave and pulsed conditions for ridge-waveguide lasers with as cleaved facets, respectively. The value of 64.3 A/cm(2) represents the lowest room-temperature threshold current density for any kind of laser on Si to date.

  15. Evidences on eddy variability and density currents in the deep flow of the Strait of Otranto

    NASA Astrophysics Data System (ADS)

    Kovacevic, Vedrana; Ursella, Laura; Gacic, Miroslav

    2010-05-01

    The Strait of Otranto is 70 km wide channel connecting the Adriatic and the Ionian Seas (Mediterranean) over the 800 m deep sill. On average, a northward/southward inflow/outflow takes place along the eastern/western coast of the channel. In particular, the outflow of the Adriatic Dense Water (AdDW) occurs as a density-driven current in the bottom layer pressed against the western continental margin. In the framework of the Italian national project VECTOR ("VulnErabilità delle Coste e degli ecosistemi marini italiani ai cambiamenti climaTici e loro ruolO nei cicli del caRbonio mediterraneo") the vein of the AdDW was monitored in the period Nov2006-Apr2007. Three moorings (V2, V3 and V4), about 13 km apart, were deployed in the bottom layer along the E-W section at the southernmost and deepest end of the strait. They were equipped with RDI upward-looking ADCPs (Acoustic Doppler Current Profiler), bottom RCM current-meters and SBE-CT (Conductivity and Temperature) instruments. The current-meter at the deepest mooring (V4) mounted also a turbidity sensor. Rotational events at the ten-day time scale are observed in the current records. In particular, two strong events are evident on the 8-11 and on the 20-24 December 2006. Cross-correlation and rotary spectral analysis of current time-series at the outermost and central mooring reveal the concomitant occurrence of the rotation in the opposite sense. These rotational events have been explained in terms of the passage of mesoscale eddies (diameter of few tens of kilometers and velocity propagation of 15 cm/s toward south). The assumption is that the eddy formation mechanism is due to the stretching of the high potential vorticity water column over the Strait sill to the north. The footprint of mesoscale eddies is also clearly evident both in CT and turbidity records. A detailed look into the two December events, when the eddy passage is assumed, shows a number of coincidences: temperature and salinity drop at V3 and V4

  16. Current density distributions and sputter marks in electron cyclotron resonance ion sources

    SciTech Connect

    Panitzsch, Lauri; Peleikis, Thies; Boettcher, Stephan; Stalder, Michael; Wimmer-Schweingruber, Robert F.

    2013-01-15

    Most electron cyclotron resonance ion sources use hexapolar magnetic fields for the radial confinement of the plasma. The geometry of this magnetic structure is then-induced by charged particles-mapped onto the inner side of the plasma electrode via sputtering and deposition. The resulting structures usually show two different patterns: a sharp triangular one in the central region which in some cases is even sputtered deep into the material (referred to as thin groove or sharp structure), and a blurred but still triangular-like one in the surroundings (referred to as broad halo). Therefore, both patterns seem to have different sources. To investigate their origins we replaced the standard plasma electrode by a custom-built plasma electrode acting as a planar, multi-segment current-detector. For different biased disc voltages, detector positions, and source biases (referred to the detector) we measured the electrical current density distributions in the plane of the plasma electrode. The results show a strong and sharply confined electron population with triangular shape surrounded by less intense and spatially less confined ions. Observed sputter- and deposition marks are related to the analysis of the results. Our measurements suggest that the two different patterns (thin and broad) indeed originate from different particle populations. The thin structures seem to be caused by the hot electron population while the broad marks seem to stem from the medium to highly charged ions. In this paper we present our measurements together with theoretical considerations and substantiate the conclusions drawn above. The validity of these results is also discussed.

  17. Probabilistic volcanic hazard assessments of Pyroclastic Density Currents: ongoing practices and future perspectives

    NASA Astrophysics Data System (ADS)

    Tierz, Pablo; Sandri, Laura; Ramona Stefanescu, Elena; Patra, Abani; Marzocchi, Warner; Costa, Antonio; Sulpizio, Roberto

    2014-05-01

    Explosive volcanoes and, especially, Pyroclastic Density Currents (PDCs) pose an enormous threat to populations living in the surroundings of volcanic areas. Difficulties in the modeling of PDCs are related to (i) very complex and stochastic physical processes, intrinsic to their occurrence, and (ii) to a lack of knowledge about how these processes actually form and evolve. This means that there are deep uncertainties (namely, of aleatory nature due to point (i) above, and of epistemic nature due to point (ii) above) associated to the study and forecast of PDCs. Consequently, the assessment of their hazard is better described in terms of probabilistic approaches rather than by deterministic ones. What is actually done to assess probabilistic hazard from PDCs is to couple deterministic simulators with statistical techniques that can, eventually, supply probabilities and inform about the uncertainties involved. In this work, some examples of both PDC numerical simulators (Energy Cone and TITAN2D) and uncertainty quantification techniques (Monte Carlo sampling -MC-, Polynomial Chaos Quadrature -PCQ- and Bayesian Linear Emulation -BLE-) are presented, and their advantages, limitations and future potential are underlined. The key point in choosing a specific method leans on the balance between its related computational cost, the physical reliability of the simulator and the pursued target of the hazard analysis (type of PDCs considered, time-scale selected for the analysis, particular guidelines received from decision-making agencies, etc.). Although current numerical and statistical techniques have brought important advances in probabilistic volcanic hazard assessment from PDCs, some of them may be further applicable to more sophisticated simulators. In addition, forthcoming improvements could be focused on three main multidisciplinary directions: 1) Validate the simulators frequently used (through comparison with PDC deposits and other simulators), 2) Decrease

  18. Spatial profiles of interelectrode electron density in direct current superposed dual-frequency capacitively coupled plasmas

    NASA Astrophysics Data System (ADS)

    Ohya, Yoshinobu; Ishikawa, Kenji; Komuro, Tatsuya; Yamaguchi, Tsuyoshi; Takeda, Keigo; Kondo, Hiroki; Sekine, Makoto; Hori, Masaru

    2017-04-01

    We present experimentally determined spatial profiles of the interelectrode electron density (n e) in dual-frequency capacitively coupled plasmas in which the negative direct current (dc) bias voltage (V dc) is superposed; in the experiment, 13 MHz (P low) was applied to the lower electrode and 60 MHz (P high) to the upper electrode. The bulk n e increased substantially with increases in the external power, P high, P low, and with increases in V dc. When P low was insufficient, the bulk n e decreased as the V dc bias increased. The bulk n e increased due to its dependence on V dc, especially for |V dc|  >  500 V. This may correspond to the sheath voltages (V s) of the lower electrode. The n e values in front of the upper electrode were coupled with the V dc: the V dc dependence first decreased and then increased. The dc currents (I dc) of the upper electrode were collected when a large P low was applied. The value of I dc at the threshold value of V dc  ≈  V s (e.g.  ‑500 V) increased with an increase in n e. When |V dc| exceeded the threshold, the spatial n e profile and the I dc dependence were changed relative to the electrical characteristics of the dc superposition; this led to a change in the location of the maximum n e, the width of the area of n e depletion in front of the electrodes, and a transition in the electron heating modes.

  19. Current density distributions and sputter marks in electron cyclotron resonance ion sources.

    PubMed

    Panitzsch, Lauri; Peleikis, Thies; Böttcher, Stephan; Stalder, Michael; Wimmer-Schweingruber, Robert F

    2013-01-01

    Most electron cyclotron resonance ion sources use hexapolar magnetic fields for the radial confinement of the plasma. The geometry of this magnetic structure is then--induced by charged particles--mapped onto the inner side of the plasma electrode via sputtering and deposition. The resulting structures usually show two different patterns: a sharp triangular one in the central region which in some cases is even sputtered deep into the material (referred to as thin groove or sharp structure), and a blurred but still triangular-like one in the surroundings (referred to as broad halo). Therefore, both patterns seem to have different sources. To investigate their origins we replaced the standard plasma electrode by a custom-built plasma electrode acting as a planar, multi-segment current-detector. For different biased disc voltages, detector positions, and source biases (referred to the detector) we measured the electrical current density distributions in the plane of the plasma electrode. The results show a strong and sharply confined electron population with triangular shape surrounded by less intense and spatially less confined ions. Observed sputter- and deposition marks are related to the analysis of the results. Our measurements suggest that the two different patterns (thin and broad) indeed originate from different particle populations. The thin structures seem to be caused by the hot electron population while the broad marks seem to stem from the medium to highly charged ions. In this paper we present our measurements together with theoretical considerations and substantiate the conclusions drawn above. The validity of these results is also discussed.

  20. Influence of the current density on the electrochemical treatment of concentrated 1-butyl-3-methylimidazolium chloride solutions on diamond electrodes.

    PubMed

    Marcionilio, Suzana M L de Oliveira; Alves, Gisele M; E Silva, Rachel B Góes; Marques, Pablo J Lima; Maia, Poliana D; Neto, Brenno A D; Linares, José J

    2016-10-01

    This paper focuses on the influence of the current density treatment of a concentrated 1-butyl-3-methylimidazolium chloride (BMImCl) solution on an electrochemical reactor with a boron-doped diamond (BDD) anode. The decrease in the total organic carbon (TOC) and the BMImCl concentration demonstrate the capability of BDD in oxidizing ionic liquids (ILs) and further mineralizing (to CO2 and NO3 (-)) more rapidly at higher current densities in spite of the reduced current efficiency of the process. Moreover, the presence of Cl(-) led to the formation of oxychlorinated anions (mostly ClO3 (-) and ClO4 (-)) and, in combination with the ammonia generated in the cathode from the nitrate reduction, chloramines, more intensely at higher current density. Finally, the analysis of the intermediates formed revealed no apparent influence of the current density on the BMImCl degradation mechanism. The current density presents therefore a complex influence on the IL treatment process that is discussed throughout this paper.

  1. Influences of current density on tribological characteristics of ceramic coatings on ZK60 Mg alloy by plasma electrolytic oxidation.

    PubMed

    Wu, Xiaohong; Su, Peibo; Jiang, Zhaohua; Meng, Song

    2010-03-01

    Current density is a key factor of plasma electrolytic oxidation process. Its influences on structure, mechanical, and tribological characteristics of ceramic coatings on ZK60 Mg alloy by pulsed bipolar microplasma oxidation in Na(3)PO(4) solution were studied in this paper. Thickness, structure, composition, mechanical property, and tribological characteristics of the coatings were studied by eddy current coating thickness gauge, scanning electron microscope (SEM), X-ray diffraction (XRD), nanoindentation measurements, and ball-on-disk friction testing. The results show that all the coatings prepared under different current densities are composed of MgO phase. The amount of MgO phase, thickness and friction coefficient of the coatings increased with the increasing current density. Among three ceramic coatings produced under three current densities, the coating produced under the current density of 7 A/dm(2) got the highest nanohardness and lowest wear rate with the value of 1.7 GPa and 1.27 x 10(-5) mm(3)/Nm.

  2. A 3-D reconstruction solution to current density imaging based on acoustoelectric effect by deconvolution: a simulation study.

    PubMed

    Yang, Renhuan; Li, Xu; Song, Aiguo; He, Bin; Yan, Ruqiang

    2013-05-01

    Hybrid imaging modality combining ultrasound scanning and electrical current density imaging through the acoustoelectric (AE) effect may potentially provide solutions to imaging electrical activities and properties of biological tissues with high spatial resolution. In this study, a 3-D reconstruction solution to ultrasound current source density imaging (UCSDI) by means of Wiener deconvolution is proposed and evaluated through computer simulations. As compared to previous 2-D UCSDI problem, in a 3-D volume conductor with broadly distributed current density field, the AE signal becomes a 3-D convolution between the electric field and the acoustic field, and effective 3-D reconstruction algorithm has not been developed so far. In the proposed method, a 3-D ultrasound scanning is performed while the corresponding AE signals are collected from multiple electrode pairs attached on the surface of the imaging object. From the collected AE signals, the acoustic field and electric field were first decoupled by Wiener deconvolution. Then, the current density distribution was reconstructed by inverse projection. Our simulations using artificial current fields in homogeneous phantoms suggest that the proposed method is feasible and robust against noise. It is also shown that using the proposed method, it is feasible to reconstruct 3-D current density distribution in an inhomogeneous conductive medium.

  3. High Current Density, Long Life Cathodes for High Power RF Sources

    SciTech Connect

    Ives, Robert Lawrence; Collins, George; Falce, Lou; Schwartzkopf, Steve; Busbaher, Daniel

    2014-01-22

    This program was tasked with improving the quality and expanding applications for Controlled Porosity Reservoir (CPR) cathodes. Calabazas Creek Research, Inc. (CCR) initially developed CPR cathodes on a DOE-funded SBIR program to improve cathodes for magnetron injection guns. Subsequent funding was received from the Defense Advanced Research Projects Agency. The program developed design requirements for implementation of the technology into high current density cathodes for high frequency applications. During Phase I of this program, CCR was awarded the prestigious 2011 R&D100 award for this technology. Subsequently, the technology was presented at numerous technical conferences. A patent was issued for the technology in 2009. These cathodes are now marketed by Semicon Associates, Inc. in Lexington, KY. They are the world’s largest producer of cathodes for vacuum electron devices. During this program, CCR teamed with Semicon Associates, Inc. and Ron Witherspoon, Inc. to improve the fabrication processes and expand applications for the cathodes. Specific fabrications issues included the quality of the wire winding that provides the basic structure and the sintering to bond the wires into a robust, cohesive structure. The program also developed improved techniques for integrating the resulting material into cathodes for electron guns.

  4. Paleomagnetic study of juvenile basaltic-andesite clasts from Andean pyroclastic density current deposits

    NASA Astrophysics Data System (ADS)

    Roperch, Pierrick; Chauvin, Annick; Le Pennec, Jean-Luc; Lara, Luis E.

    2014-02-01

    Additional paleomagnetic data are necessary to improve geomagnetic models of secular variation during the Holocene, especially from the southern hemisphere. In most of the Andean volcanoes from Ecuador to the Chilean central volcanic zone, very well dated lava flows are rare. In contrast, andesitic to basaltic pyroclastic density current (PDC) deposits commonly contain charcoal, facilitating their age determination with 14C. In this study we present the magnetic properties and the paleomagnetic results obtained from three PDC deposits of basaltic to andesitic composition. One is the 2006 PDC deposit from the Ecuadorian Tungurahua volcano and the two others are well-dated PDC deposits from Chilean volcanoes Osorno and Villarica. Although most paleomagnetic studies in pyroclastic rocks deal with the estimation of emplacement temperatures from bulk deposits or accessory and accidental (non-juvenile) clasts, we show that juvenile clasts embedded in PDC deposits provide well-grouped paleomagnetic directions indicating post-emplacement in situ cooling below Curie points. Moreover, the rapid cooling of the juvenile clasts yields an abundance of single domain titanomagnetite grains providing low unblocking temperatures and a reliable material for paleointensity determination.

  5. Catalysts for ultrahigh current density oxygen cathodes for space fuel cell applications

    NASA Technical Reports Server (NTRS)

    Tryk, D.; Yeager, E.; Shingler, M.; Aldred, W.; Wang, C.

    1990-01-01

    The objective of this research was to identify promising electrocatalyst/support systems for the oxygen cathode in alkaline fuel cells operating at relatively high temperatures, O2 pressures and current densities. A number of materials were prepared, including Pb-Ru and Pb-Ir pyrochlores, RuO2 and Pt-doped RuO2, and lithiated NiO. Several of these were prepared using techniques that had not been previously used to prepare them. Particularly interesting is the use of the alkaline solution technique to prepare the Pt-doped Pb-Ru pyrochlore in high area form. Well-crystallized Pb(2)Ru(2)O(7-y) was used to fabricate high performance O2 cathodes with relatively good stability in room temperature KOH. This material was also found to be stable over a useful potential range at approximately 140 C in concentrated KOH. Other pyrochlores were found to be either unstable (amorphous samples) or the fabrication of the gas-fed electrodes could not be fully optimized during this project period. Future work may be directed at this problem. High area platinum supported on conductive metal oxide supports produced mixed results: small improvements in O2 reduction performance for Pb(2)Ru(2)O(7-y) but a large improvement for Li-doped NiO at room temperature. Nearly reversible behavior was observed for the O2/OH couple for Li-doped NiO at approximately 200 C.

  6. Photoelectrolysis of water at high current density - Use of ultraviolet laser excitation

    NASA Technical Reports Server (NTRS)

    Bocarsly, A. B.; Bolts, J. M.; Cummins, P. G.; Wrighton, M. S.

    1977-01-01

    The behavior of TiO2 and SrTiO3 photoanodes in cells for the photoelectrolysis of H2O has been investigated for high-intensity 351-,364-nm excitation from an Ar ion laser. Intensities up to 380 W/sq cm have been used. For TiO2 a small amount of surface decomposition is found after irradiation at high intensity, whereas SrTiO3 undergoes no detectable changes. Current-voltage properties for both electrodes are essentially independent of light intensity up to the level of 380 W/sq cm, and there is little if any change in quantum efficiency for electron flow. Photocurrent densities have been shown to exceed 5 A/sq cm for O2 evolution. Data show that the energy storage rate associated with the SrTiO3 photoelectrolysis can exceed 30 W/sq cm; this represents the highest demonstrated rate of sustained optical-to-chemical energy conversion.

  7. Catalysts for ultrahigh current density oxygen cathodes for space fuel cell applications

    NASA Astrophysics Data System (ADS)

    Tryk, D.; Yeager, E.; Shingler, M.; Aldred, W.; Wang, C.

    1990-06-01

    The objective of this research was to identify promising electrocatalyst/support systems for the oxygen cathode in alkaline fuel cells operating at relatively high temperatures, O2 pressures and current densities. A number of materials were prepared, including Pb-Ru and Pb-Ir pyrochlores, RuO2 and Pt-doped RuO2, and lithiated NiO. Several of these were prepared using techniques that had not been previously used to prepare them. Particularly interesting is the use of the alkaline solution technique to prepare the Pt-doped Pb-Ru pyrochlore in high area form. Well-crystallized Pb(2)Ru(2)O(7-y) was used to fabricate high performance O2 cathodes with relatively good stability in room temperature KOH. This material was also found to be stable over a useful potential range at approximately 140 C in concentrated KOH. Other pyrochlores were found to be either unstable (amorphous samples) or the fabrication of the gas-fed electrodes could not be fully optimized during this project period. Future work may be directed at this problem. High area platinum supported on conductive metal oxide supports produced mixed results: small improvements in O2 reduction performance for Pb(2)Ru(2)O(7-y) but a large improvement for Li-doped NiO at room temperature. Nearly reversible behavior was observed for the O2/OH couple for Li-doped NiO at approximately 200 C.

  8. Pyroclastic density current dynamics and associated hazards at ice-covered volcanoes

    NASA Astrophysics Data System (ADS)

    Dufek, J.; Cowlyn, J.; Kennedy, B.; McAdams, J.

    2015-12-01

    Understanding the processes by which pyroclastic density currents (PDCs) are emplaced is crucial for volcanic hazard prediction and assessment. Snow and ice can facilitate PDC generation by lowering the coefficient of friction and by causing secondary hydrovolcanic explosions, promoting remobilisation of proximally deposited material. Where PDCs travel over snow or ice, the reduction in surface roughness and addition of steam and meltwater signficantly changes the flow dynamics, affecting PDC velocities and runout distances. Additionally, meltwater generated during transit and after the flow has come to rest presents an immediate secondary lahar hazard that can impact areas many tens of kilometers beyond the intial PDC. This, together with the fact that deposits emplaced on ice are rarely preserved means that PDCs over ice have been little studied despite the prevalence of summit ice at many tall stratovolcanoes. At Ruapehu volcano in the North Island of New Zealand, a monolithologic welded PDC deposit with unusually rounded clasts provides textural evidence for having been transported over glacial ice. Here, we present the results of high-resolution multiphase numerical PDC modeling coupled with experimentaly determined rates of water and steam production for the Ruapehu deposits in order to assess the effect of ice on the Ruapehu PDC. The results suggest that the presence of ice significantly modified the PDC dynamics, with implications for assessing the PDC and associated lahar hazards at Ruapehu and other glaciated volcanoes worldwide.

  9. Minimax current density gradient coils: analysis of coil performance and heating.

    PubMed

    Poole, Michael S; While, Peter T; Lopez, Hector Sanchez; Crozier, Stuart

    2012-08-01

    Standard gradient coils are designed by minimizing the inductance or resistance for an acceptable level of gradient field nonlinearity. Recently, a new method was proposed to minimize the maximum value of the current density in a coil additionally. The stated aim of that method was to increase the minimum wire spacing and to reduce the peak temperature in a coil for fixed efficiency. These claims are tested in this study with experimental measurements of magnetic field and temperature as well as simulations of the performance of many coils. Experimental results show a 90% increase in minimum wire spacing and 40% reduction in peak temperature for equal coil efficiency and field linearity. Simulations of many more coils indicate increase in minimum wire spacing of between 50 and 340% for the coils studied here. This method is shown to be able to increase coil efficiency when constrained by minimum wire spacing rather than switching times or total power dissipation. This increase in efficiency could be used to increase gradient strength, duty cycle, or buildability.

  10. Evaporation of metals by high-density (107 A · cm-2) electrical currents

    NASA Astrophysics Data System (ADS)

    Rakhel, A. D.

    1996-09-01

    In the present work, the problem of time evolution of pressure and temperature profiles across a wire through which an electrical current with a density of the order of 107 A · cm-2 flows is solved. The correct boundary conditions for a metal surface are obtained for the case when this metal is rapidly evaporated as a result of high-power Joule heating. The pressure profile appears under these conditions due to pinch-effect and inertia of thermal expansion of the metal; the temperature profile arises because of intensive evaporation from the surface of the wire. The conditions under which a liquid metal is superheated are formulated. On the basis of the analysis of the experimental results on exploding wires, the conclusion is drawn that decay of the metastable state takes place near the binodal. It is shown that the distribution of fine dispersed vapor bubbles is strongly nonuniform across the wire and the process of expansion of the two-phase mixture is very similar to the motion of a wave.

  11. Relationship between intrinsic surface resistance and critical current density of YBCO thin films with various thickness

    NASA Astrophysics Data System (ADS)

    Nakagawa, K.; Nakayama, S.; Saito, A.; Ono, S.; Kai, H.; Mukaida, M.; Honma, T.; Ohshima, S.

    2010-11-01

    We investigated the relationship between the intrinsic surface resistance (Rsint) and critical current density (Jc) of YBa2Cu3Oy (YBCO) film thinner than the penetration depth (λL). The measured YBCO films were deposited on CeO2-buffered r-cut Al2O3 substrates by the pulsed laser deposition method. The thicknesses of these films were 300, 200, and 100 nm, respectively. The Rsint means the surface resistance of YBCO film removing the loss by the impedance of the substrates. The effective surface resistance (Rseff) including the impedance of the substrate and the Jc of each YBCO film were measured using the dielectric resonator method at 21.8 GHz and the inductive method. We calculated Rsint by using phenomenological expressions and the Rseff value. The Rsint values of each YBCO film were almost the same in the measured temperature region. As a result, we found that Rsint was in inverse proportion to the Jc of YBCO film thinner than λL.

  12. Antarctic density stratification and the strength of the circumpolar current during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, Jean; Ito, Takamitsu; Michel, Elisabeth

    2016-05-01

    The interaction between ocean circulation and biological processes in the Southern Ocean is thought to be a major control on atmospheric carbon dioxide content over glacial cycles. A better understanding of stratification and circulation in the Southern Ocean during the Last Glacial Maximum (LGM) provides information that will help us to assess these scenarios. First, we evaluate the link between Southern Ocean stratification and circulation states in a suite of climate model simulations. While simulated Antarctic Circumpolar Current (ACC) transport varies widely (80-350 Sverdrup (Sv)), it co-varies with horizontal and vertical stratification and the formation of the southern deep water. We then test the LGM simulations against available data from paleoceanographic proxies, which can be used to assess the density stratification and ACC transport south of Australia. The paleoceanographic data suggest a moderate increase in the Southern Ocean stratification and the ACC strength during the LGM. Even with the relatively large uncertainty in the proxy-based estimates, extreme scenarios exhibited by some climate models with ACC transports of greater than 250 Sv and highly saline Antarctic Bottom Water are highly unlikely.

  13. Na+ current densities and voltage dependence in human intercostal muscle fibres.

    PubMed Central

    Ruff, R L; Whittlesey, D

    1992-01-01

    1. Voltage-clamp Na+ currents (INa) were studied in human intercostal muscle fibres using the loose-patch-clamp technique. 2. The fibres could be divided into two groups based upon the properties of INa. The two groups of fibres were called type 1 and type 2. 3. Both type 1 and type 2 fibres demonstrated fast and slow inactivation of INa. 4. Type 1 fibres had lower INa on the endplate border and extrajunctional membrane than type 2 fibres and required larger membrane depolarizations to inactivate Na+ channels by fast or slow inactivation of INa. 5. Type 2 fibres had a higher ratio of INa at the endplate border compared to extrajunctional membrane than Type 1 fibres. 6. Measurement of membrane capacitance suggested that the increase in INa at the endplate border was due to increased Na+ channel density. 7. Histochemical staining of some fibres suggested that type 1 fibres were slow twitch and type 2 fibres were fast twitch. 8. Differences in the properties of Na+ channels between fast- and slow-twitch fibres may contribute to the ability of fast-twitch fibres to operate at high firing frequencies and slow-twitch fibres to be tonically active. PMID:1338797

  14. Exponential dependence of the vortex pinning potential on current density in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Yan, H.; Abdelhadi, M. M.; Jung, J. A.; Willemsen, B. A.; Kihlstrom, K. E.

    2005-08-01

    We investigated the dependence of the vortex pinning potential on current density Ueff(J) in Tl2Ba2CaCu2Oy , Tl2Ba2Ca2Cu3Oy , and YBa2Cu3Oy thin films and single crystals, measured by us and other research groups. In all these cases Ueff(J) was calculated from the magnetic relaxation data using Maley’s procedure [Phys. Rev. B 42, 2639 (1990)]. We explored the exponential dependence of Ueff(J) , first introduced by Thompson [Phys. Rev. B 44, 456 (1991).] to explain long-term nonlogarithmic magnetic relaxations in high-temperature superconductors (HTSC), as an alternative to power-law and logarithmic forms of Ueff(J) . The results revealed that for J larger than approximately 0.4Jc , the energy barrier can be expressed in the following form: Ueff(J)=aIco(1-T/T*)3/2exp(-bJ/Jco) , where the constant b is the same for all samples investigated. This result is independent of the anisotropy (the interplanar coupling). The experimental results were analyzed taking into account the spatial dependence of the pinning potential, proposed by Qin [J. Appl. Phys. 77, 2618 (1995)]. We suggested that the exponential form of Ueff(J) could represent vortex pinning and motion in the a-b planes due to a nanoscopic variation of the order parameter, in agreement with the growing experimental evidence for the presence of nanostructures, stripes (filaments) in HTSC.

  15. Field and temperature scaling of the critical current density in commercial REBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Senatore, Carmine; Barth, Christian; Bonura, Marco; Kulich, Miloslav; Mondonico, Giorgio

    2016-01-01

    Scaling relations describing the electromagnetic behaviour of coated conductors (CCs) greatly simplify the design of REBCO-based devices. The performance of REBCO CCs is strongly influenced by fabrication route, conductor architecture and materials, and these parameters vary from one manufacturer another. In the present work we have examined the critical surface for the current density, J c(T, B, θ), of coated conductors from six different manufacturers: American Superconductor Co. (US), Bruker HTS GmbH (Germany), Fujikura Ltd (Japan), SuNAM Co. Ltd (Korea), SuperOx ZAO (Russia) and SuperPower Inc. (US). Electrical transport and magnetic measurements were performed at temperatures between 4.2 K and 77 K and in magnetic fields of up to 19 T. Experiments were conducted at three different orientations of the field with respect to the crystallographic c-axis of the REBCO layer, θ = 0°, 45° and 90°, in order to probe the angular anisotropy of J c. In spite of the large variability of the CCs’ performance, we show here that field and temperature dependences of J c at a given angle can be reproduced over wide ranges using a scaling relation based only on three parameters. Furthermore, we present and validate a new approach combining magnetic and transport measurements for the determination of the scaling parameters with minimal experimental effort.

  16. Magnetic petrofabric of igneous rocks: Lessons from pyroclastic density current deposits and obsidians

    NASA Astrophysics Data System (ADS)

    Cañón-Tapia, E.; Mendoza-Borunda, R.

    2014-12-01

    Measurement of the anisotropy of magnetic susceptibility (AMS) of igneous rocks can provide clues concerning their mechanism of formation and in particular are very helpful as flow direction indicators. Unlike other igneous rocks, however, pyroclastic density current deposits (PDCDs) present a challenge in the interpretation of AMS measurements due to the complexity of their mechanism of emplacement. In this paper we review the most common assumptions made in the interpretation of the AMS of PDCD, taking advantage of key lessons obtained from obsidians. Despite the complexities on the mechanism of formation of PDCDs, it is shown that a key element for the fruitful interpretation of AMS is to give proper attention to the various components likely to be involved in controlling their general petrofabric. The anisotropies of ferromagnetic crystals (whether as free phases or embedded within clasts or shards), and those of paramagnetic minerals (mainly ferrosilicates) need to be taken into consideration when interpreting the AMS measurements of PDCDs. Variations of the deposition regime both as a function of position and of time also need to be considered on the interpretations. Nevertheless, if a suitable sampling strategy is adopted, the potential of the AMS method as a petrofabric indicator is maximized.

  17. Estimation of population firing rates and current source densities from laminar electrode recordings.

    PubMed

    Pettersen, Klas H; Hagen, Espen; Einevoll, Gaute T

    2008-06-01

    This model study investigates the validity of methods used to interpret linear (laminar) multielectrode recordings. In computer experiments extracellular potentials from a synaptically activated population of about 1,000 pyramidal neurons are calculated using biologically realistic compartmental neuron models combined with electrostatic forward modeling. The somas of the pyramidal neurons are located in a 0.4 mm high and wide columnar cylinder, mimicking a stimulus-evoked layer-5 population in a neocortical column. Current-source density (CSD) analysis of the low-frequency part (<500 Hz) of the calculated potentials (local field potentials, LFP) based on the 'inverse' CSD method is, in contrast to the 'standard' CSD method, seen to give excellent estimates of the true underlying CSD. The high-frequency part (>750 Hz) of the potentials (multi-unit activity, MUA) is found to scale approximately as the population firing rate to the power 3/4 and to give excellent estimates of the underlying population firing rate for trial-averaged data. The MUA signal is found to decay much more sharply outside the columnar populations than the LFP.

  18. Improvement of critical current density of bronze processed Nb{sub 3}Sn superconducting wire

    SciTech Connect

    Miyazaki, T.; Fukumoto, Y.; Matsukura, N.

    1997-06-01

    Effects of tantalum addition to niobium filaments and tin contents in bronze matrix on the critical current density (J{sub c}) of Nb{sub 3}Sn superconducting wires manufactured by the bronze process were investigated in order to improve the J{sub c} in the high magnetic fields. In the results using the bronze composition of Cu-13wt.%Sn-0.3wt.%Ti, the J{sub c} shows a peak for 1 wt.% of tantalum content in the niobium filament. On the other hand, J{sub c} of samples with Cu-14wt.%Sn-0.3wt.%Ti is almost 1.7 times higher than that with Cu-13wt.%Sn-0.3wt.%Ti. From these findings, the authors manufactured a multifilamentary prototype (Nb,Ti,Ta){sub 3}Sn conductor made of Nb-1.0wt.%Ta and Cu-14wt.%Sn.0.3wt.%Ti. The non Cu J{sub c} of the conductor was 701 A/mm{sup 2} at 12 T and 51 A/mm{sup 2} at 21 T for the heat treatment temperature of 650{degrees} C.

  19. Reduction of ocular artefacts in source current density brain mappings by ARX2 filtering.

    PubMed

    Filligoi, G C; Capitanio, L; Babiloni, F; Fattorini, L; Urbano, A; Cerutti, S

    1995-06-01

    Sweep by sweep analysis of event-related potentials (ERP) of the human scalp represents a reliable tool for both the diagnosis of neurologic diseases and the study of the central nervous system during cognitive tasks. The off-line procedure based on stochastic parametric identification and filtering herewith described, allows an accurate analysis of single-sweep ERP and a drastic reduction of ocular artefacts variously propagating through the skull. Moreover, the spatial distribution of the recorded ERP in bidimensional form was enhanced by using the Laplacian operator in order to get an estimate of the source current density (SCD) flow from the skull into the scalp. Complete single-trial signals were filtered according to an autoregressive model of signal generation with 2 exogenous inputs (ARX2). The ARX2 procedure models the recorded signal as the sum of three signals: (a) the background EEG activity, modelled as an autoregressive process driven by a white noise; (b) a filtered version of a reference signal carrying the average information contained in each sweep; (c) a signal due to the ocular artefact propagation. The evaluation of the effect of artefact suppression on those channels close to the eyes was compared with standard ordinary least squares method (OLS) based on a linear model of the influence of EOG on ERP. Finally, the better results obtainable through ARX filtering on sweep-by-sweep brain mappings are also presented.

  20. In vitro biological response to the oxide layer in pure titanium formed at different current densities by plasma electrolytic oxidation

    NASA Astrophysics Data System (ADS)

    Shin, Ki Ryong; Kim, Yeon Sung; Yang, Hae Woong; Ko, Young Gun; Shin, Dong Hyuk

    2014-09-01

    This study examined the influence of the current density on the surface characteristics and biological response of titanium oxide layers produced by a plasma electrolytic oxidation process. For this purpose, the present processes were carried out under alternating current conditions in a phosphate electrolyte for 300 s at current densities of 100, 150, 200, and 250 mA/cm2. The pore size decreased with decreasing the current density, whereas the mean surface roughness and amount of anatase phase increased. This tendency is considered suitable for the formation of biomimetic apatite and the proliferation of osteoblast cells. The in vitro examinations showed that the formation of biomimetic apatite and the proliferation of osteoblasts on the titanium oxide layer produced at 100 mA/cm2 were highest among the samples evaluated.

  1. The antidune question for bedforms in deposits of dilute pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Amin Douillet, Guilhem; Kueppers, Ulrich; Dingwell, Donald B.

    2014-05-01

    Dilute pyroclastic density currents (PDCs) are mixture of volcanic particles and gas that can be produced during explosive volcanic eruptions. Like turbidites, they travel on the ground driven by their higher density compared to the ambient fluid, which is due to the load of suspended particles. Dilute PDCs have a low enough particle concentration so that their deposit can contain cross stratification, but high enough so that they do not lift off as ash clouds. Since the 1970's most dune bedform cross stratifications found within dilute PDC deposits have been interpreted as antidunes, mainly due to the fact that they can exhibit more aggradation on the stoss than on the lee side. However, several studies have challenged this interpretation in the last few years (stepwise aggradation, differential draping, flow reversal, near-bed load blocking). In order to decipher which are the valuable arguments to confirm or infirm the antidune interpretation, we document deposits from different eruptions: Tungurahua (Ecuador), Laacher See (Germany), Purrumbete (Australia), Ubehebe (USA), Stromboli (Italy), Yasur (Vanuatu). We consider fluid dynamics arguments on the formation of gravity waves within the shallow water approximation and for internal gravity waves within a stratified medium. Indeed, antidunes are by definition sedimentary prints of stationary gravity waves. We also consider the possibility of cyclic steps as a parental phenomenon for the formation of dilute PDC bedforms. Finally, results of wind tunnel experiments for boundary layer conditions give another independent set of data to interpret cross stratifications within dilute PDC deposits. Whereas we cannot rule out an interpretation as antidunes for some bedforms (lensoidal stoss-depositional structures, low aspect ratio bedforms in train), others can clearly be disregarded based on geometrical considerations. Overall, the interpretation as antidune cannot be simply based on stoss-deposition, and needs to take

  2. Laboratory Study Of Magnetic Reconnection With A Density Asymmetry Across The Current Sheet

    SciTech Connect

    Yoo, Joseph; Yamada, Massaaki; Ji, Hantao; Meyers,, Clayton E.; Jara-Almonte,; Chen, Li-Jen

    2014-04-18

    The effects of an upstream density asymmetry on magnetic reconnection are studied systematically in a laboratory plasma. Despite a significant upstream density asymmetry of up to 10, the reconnecting magnetic field pro file is not signifi cantly changed. On the other hand, the out-of-plane magnetic field profile is considerably modified; it is almost bipolar in structure with the density asymmetry, as compared to the quadrupolar structure in the symmetric configuration. The in-plane ion flow pattern and the electrostatic potential pro file are also affected by the density asymmetry. Strong bulk electron heating is observed near the low-density-side separatrix together with electromagnetic fluctuations in the lower hybrid frequency range. The dependence of the ion outflow and reconnection electric field on the density asymmetry is measured and compared with theoretical expectations.

  3. Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis bumpy torus plasma

    NASA Technical Reports Server (NTRS)

    Roth, J. R.

    1976-01-01

    Parametric variation of independent variables which may affect the characteristics of bumpy torus plasma have identified those which have a significant effect on the plasma current, ion kinetic temperature, and plasma number density, and those which do not. Empirical power law correlations of the plasma current, and the ion kinetic temperature and number density were obtained as functions of potential applied to the midplane electrode rings, the background neutral gas pressure, and the magnetic field strength. Additional parameters studied included the type of gas, the polarity of the midplane electrode rings, the mode of plasma operation, and the method of measuring the plasma number density. No significant departures from the scaling laws appear to occur at the highest ion kinetic temperatures or number densities obtained to date.

  4. Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis Bumpy Torus plasma

    NASA Technical Reports Server (NTRS)

    Roth, J. R.

    1976-01-01

    Parametric variation of independent variables which may affect the characteristics of the NASA Lewis Bumpy Torus plasma have identified those which have a significant effect on the plasma current, ion kinetic temperature, and plasma number density, and those which do not. Empirical power-law correlations of the plasma current, and the ion kinetic temperature and number density were obtained as functions of the potential applied to the midplane electrode rings, the background neutral gas pressure, and the magnetic field strength. Additional parameters studied include the type of gas, the polarity of the midplane electrode rings (and hence the direction of the radial electric field), the mode of plasma operation, and the method of measuring the plasma number density. No significant departures from the scaling laws appear to occur at the highest ion kinetic temperatures or number densities obtained to date.

  5. Functional interconnections between CA3 and the dentate gyrus revealed by current source density analysis.

    PubMed

    Wu, K; Canning, K J; Leung, L S

    1998-01-01

    The physiological interactions between the dentate gyrus (DG) and CA3 were studied in urethane-anesthetized rats by using field potential recording and current source density (CSD) analysis. Stimulation of CA3b resulted in a short-latency (<2.5-ms onset latency) antidromic population spike in both the DG and CA3c. An excitation (current sink) at the middle molecular layer (MML) was observed at 3-ms latency, possibly mediated by the backfiring of perforant path fibers that projected to both DG and CA3. CA3 stimulation also resulted in a sink at the dendritic layers of CA3c, which was likely mediated by excitatory CA3 recurrent collaterals. It was inferred that the DG was excited at the inner molecular layer (IML) after stimulation near the CA3b/CA3c border. This IML excitation (sink) probably resulted from orthodromic CA3 or hilar projections to the IML and not from mossy fiber backfiring. The IML and the CA3c dendritic sinks were blocked by an intracerebroventricular injection of a non-N-methyl-D-aspartate receptor antagonist, 6-cyano-7-nitroquinoxaline-2, 3-dione, but not by a gamma-aminobutyric acid type A (GABA(A)) receptor antagonist, bicuculline. CA3b stimulation evoked population spike bursts (3-7-ms latency) in both DG and CA3c when GABA(A) inhibition was suppressed by bicuculline, thus confirming that the excitatory afferents project from CA3b to DG and CA3c. A CA3 conditioning stimulus pulse given 30-200 ms before a perforant-path test pulse increased the amplitude of the perforant-path-evoked DG population spike (as compared with the test response without conditioning). After a moderate-intensity stimulation of CA3, a late (<20-ms latency) excitation of the MML of the DG was found. The late DG excitation was blocked by procaine injection at the medial perforant path, suggesting its origin from the medial entorhinal cortex. In conclusion, rich interactions between CA3 and other hippocampal structures were studied quantitatively by CSD analysis in vivo. We

  6. Geomagnetic paleointensity in historical pyroclastic density currents: Testing the effects of emplacement temperature and postemplacement alteration

    NASA Astrophysics Data System (ADS)

    Bowles, Julie A.; Gee, Jeffrey S.; Jackson, Mike J.; Avery, Margaret S.

    2015-10-01

    Thellier-type paleointensity experiments were conducted on welded ash matrix or pumice from the 1912 Novarupta (NV) and 1980 Mt. St. Helens (MSH) pyroclastic density currents (PDCs) with the intention of evaluating their suitability for geomagnetic paleointensity studies. PDCs are common worldwide, but can have complicated thermal and alteration histories. We attempt to address the role that emplacement temperature and postemplacement hydrothermal alteration may play in nonideal paleointensity behavior of PDCs. Results demonstrate two types of nonideal behavior: unstable remanence in multidomain (MD) titanomagnetite, and nonideal behavior linked to fumarolic and vapor phase alteration. Emplacement temperature indirectly influences MSH results by controlling the fraction of homogenous MD versus oxyexsolved pseudo-single domain titanomagnetite. NV samples are more directly influenced by vapor phase alteration. The majority of NV samples show distinct two-slope behavior in the natural remanent magnetization—partial thermal remanent magnetization plots. We interpret this to arise from a (thermo)chemical remanent magnetization associated with vapor phase alteration, and samples with high water content (>0.75% loss on ignition) generate paleointensities that deviate most strongly from the true value. We find that PDCs can be productively used for paleointensity, but that—as with all paleointensity studies—care should be taken in identifying potential postemplacement alteration below the Curie temperature, and that large, welded flows may be more alteration-prone. One advantage in using PDCs is that they typically have greater areal (spatial) exposure than a basalt flow, allowing for more extensive sampling and better assessment of errors and uncertainty.

  7. Effect of La doping on microstructure and critical current density of MgB2

    NASA Astrophysics Data System (ADS)

    Shekhar, Chandra; Giri, Rajiv; Tiwari, R. S.; Rana, D. S.; Malik, S. K.; Srivastava, O. N.

    2005-09-01

    In the present study, La-doped MgB2 superconductors with different doping levels (Mg1-xLaxB2; x = 0.00, 0.01, 0.03 and 0.05) have been synthesized by the solid-state reaction route at ambient pressure. Effects of La doping have been investigated in relation to microstructural characteristics and superconducting properties, particularly intragrain critical current density (Jc). The microstructural characteristics of the as-synthesized Mg(La)B2 compounds were studied employing the transmission electron microscopic (TEM) technique. The TEM investigations reveal inclusion of LaB6 nanoparticles within the MgB2 grains, which provide effective flux pinning centres. The evaluation of intragrain Jc through magnetic measurements on the fine powdered version of the as-synthesized samples reveal that Jc values of the samples change significantly with the doping level. The optimum result on Jc is obtained for Mg0.97La0.03B2 at 5 K Jc reaches ~1.4 × 107 A cm-2 in self-field, ~2.1 × 106 A cm-2 at 1 T, ~2.5 × 105 A cm-2 at 2.5 T and ~1.8 × 104 A cm-2 at 4.5 T. The highest value of intragrain Jc in the Mg0.97La0.03B2 superconductor has been attributed to the inclusion of LaB6 nanoparticles, which are capable of providing effective flux pinning centres.

  8. Volcán de Colima dome collapse of July, 2015 and associated pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Reyes-Dávila, Gabriel A.; Arámbula-Mendoza, Raúl; Espinasa-Pereña, Ramón; Pankhurst, Matthew J.; Navarro-Ochoa, Carlos; Savov, Ivan; Vargas-Bracamontes, Dulce M.; Cortés-Cortés, Abel; Gutiérrez-Martínez, Carlos; Valdés-González, Carlos; Domínguez-Reyes, Tonatiuh; González-Amezcua, Miguel; Martínez-Fierros, Alejandro; Ramírez-Vázquez, Carlos Ariel; Cárdenas-González, Lucio; Castañeda-Bastida, Elizabeth; Vázquez Espinoza de los Monteros, Diana M.; Nieto-Torres, Amiel; Campion, Robin; Courtois, Loic; Lee, Peter D.

    2016-06-01

    During July 10th-11th 2015, Volcán de Colima, Mexico, underwent its most intense eruptive phase since its Subplinian-Plinian 1913 AD eruption. Production of scoria coincident with elevated fumarolic activity and SO2 flux indicate a significant switch of upper-conduit dynamics compared with the preceding decades of dome building and vulcanian explosions. A marked increase in rockfall events and degassing activity was observed on the 8th and 9th of July. On the 10th at 20:16 h (Local time = UTM - 6 h) a partial collapse of the dome generated a series of pyroclastic density currents (PDCs) that lasted 52 min and reached 9.1 km to the south of the volcano. The PDCs were mostly channelized by the Montegrande and San Antonio ravines, and produced a deposit with an estimated volume of 2.4 × 106 m3. Nearly 16 h after the first collapse, a second and larger collapse occurred which lasted 1 h 47 min. This second collapse produced a series of PDCs along the same ravines, reaching a distance of 10.3 km. The total volume calculated for the PDCs of the second event is 8.0 × 106 m3. Including associated ashfall deposits, the two episodes produced a total of 14.2 × 106 m3 of fragmentary material. The collapses formed an amphitheater-shaped crater open towards the south. We propose that the dome collapse was triggered by arrival of gas-rich magma to the upper conduit, which then boiled-over and sustained the PDCs. A juvenile scoria sample selected from the second partial dome collapse contains hornblende, yet at an order of magnitude less abundant (0.2%) than that of 1913, and exhibits reaction rims, whereas the 1913 hornblende is unreacted. At present there is no compelling petrologic evidence for imminent end-cycle activity observed at Volcán de Colima.

  9. Three-dimensional turbulent bottom density currents from a high-order nonhydrostatic spectral element model.

    SciTech Connect

    Ozgokmen, T.; Fischer, P.; Duan, J.; Iliescu, T.; Mathematics and Computer Science; Univ. of Miami; IIT; Virginia Polytechnic Inst. and State Univ.

    2004-09-01

    Overflows are bottom gravity currents that supply dense water masses generated in high-latitude and marginal seas into the general circulation. Oceanic observations have revealed that mixing of overflows with ambient water masses takes place over small spatial and time scales. Studies with ocean general circulation models indicate that the strength of the thermohaline circulation is strongly sensitive to representation of overflows in these models. In light of these results, overflow-induced mixing emerges as one of the prominent oceanic processes. In this study, as a continuation of an effort to develop appropriate process models for overflows, nonhydrostatic 3D simulations of bottom gravity are carried out that would complement analysis of dedicated observations and large-scale ocean modeling. A parallel high-order spectral-element Navier-Stokes solver is used as the basis of the simulations. Numerical experiments are conducted in an idealized setting focusing on the startup phase of a dense water mass released at the top of a sloping wedge. Results from 3D experiments are compared with results from 2D experiments and laboratory experiments, based on propagation speed of the density front, growth rate of the characteristic head at the leading edge, turbulent overturning length scales, and entrainment parameters. Results from 3D experiments are found to be in general agreement with those from laboratory tank experiments. In 2D simulations, the propagation speed is approximately 20% slower than that of the 3D experiments and the head growth rate is 3 times as large, Thorpe scales are 1.3-1.5 times as large, and the entrainment parameter is up to 2 times as large as those in the 3D experiments. The differences between 2D and 3D simulations are entirely due to internal factors associated with the truncation of the Navier-Stokes equations for 2D approximation.

  10. Reduced Na⁺ current density underlies impaired propagation in the diabetic rabbit ventricle.

    PubMed

    Stables, Catherine L; Musa, Hassan; Mitra, Aditi; Bhushal, Sandesh; Deo, Makarand; Guerrero-Serna, Guadalupe; Mironov, Sergey; Zarzoso, Manuel; Vikstrom, Karen L; Cawthorn, William; Pandit, Sandeep V

    2014-04-01

    Diabetes is associated with an increased risk of sudden cardiac death, but the underlying mechanisms remain unclear. Our goal was to investigate changes occurring in the action potential duration (APD) and conduction velocity (CV) in the diabetic rabbit ventricle, and delineate the principal ionic determinants. A rabbit model of alloxan-induced diabetes was utilized. Optical imaging was used to record electrical activity in isolated Langendorff-perfused hearts in normo-, hypo- and hyper-kalemia ([K(+)]o=4, 2, 12 mM respectively). Patch clamp experiments were conducted to record Na(+) current (I(Na)) in isolated ventricular myocytes. The mRNA/protein expression levels for Nav1.5 (the α-subunit of I(Na)) and connexin-43 (Cx43), as well as fibrosis levels were examined. Computer simulations were performed to interpret experimental data. We found that the APD was not different, but the CV was significantly reduced in diabetic hearts in normo-, hypo-, and, hyper-kalemic conditions (13%, 17% and 33% reduction in diabetic vs. control, respectively). The cell capacitance (Cm) was increased (by ~14%), and the density of INa was reduced by ~32% in diabetic compared to control hearts, but the other biophysical properties of I(Na) were unaltered. The mRNA/protein expression levels for Cx43 were unaltered. For Nav1.5, the mRNA expression was not changed, and though the protein level tended to be less in diabetic hearts, this reduction was not statistically significant. Staining showed no difference in fibrosis levels between the control and diabetic ventricles. Computer simulations showed that the reduced magnitude of I(Na) was a key determinant of impaired propagation in the diabetic ventricle, which may have important implications for arrhythmogenesis.

  11. New insights into aromatic pathways of carbachlorins and carbaporphyrins based on calculations of magnetically induced current densities.

    PubMed

    Benkyi, Isaac; Fliegl, Heike; Valiev, Rashid R; Sundholm, Dage

    2016-04-28

    Magnetically induced current densities have been calculated and analyzed for a number of synthesized carbachlorins and carbaporphyrins using density functional theory and the gauge including magnetically induced current (GIMIC) method. Aromatic properties have been determined by using accurate numerical integration of the current flow yielding reliable current strengths and pathways that are related to the degree of aromaticity and the aromatic character of the studied molecules. All investigated compounds are found to be aromatic. However, the obtained aromatic pathways differ from those previously deduced from spectroscopic data and magnetic shielding calculations. For all studied compounds, the ring current divides into an outer and an inner branch at each pyrrolic subring, showing that all π-electrons of the pyrrolic rings take part in the delocalization pathway. The calculations do not support the common notion that the main share of the current takes the inner route at the pyrrolic rings without an inner hydrogen and follows an 18π aromatic pathway. The aromatic pathways of the investigated carbaporphyrins and carbachlorins are very similar, since the current strength via the Cβ[double bond, length as m-dash]Cβ' bond of the cyclopentadienyl ring of the carbaporphyrins is almost as weak as the current density passing the corresponding saturated Cβ-Cβ' bond of the carbachlorins.

  12. Influence of High-Current-Density Impulses on the Compression Behavior: Experiments with Iron and a Nickel-Based Alloy

    NASA Astrophysics Data System (ADS)

    Demler, E.; Gerstein, G.; Dalinger, A.; Epishin, A.; Rodman, D.; Nürnberger, F.

    2016-12-01

    Difficulties of processing of high strength and/or brittle materials by plastic deformation, e.g., by forging, require to develop new industrial technologies. In particular, the feasible deformation rates are limited for low-ductile metallic materials. For this reason, processes were investigated to improve the deformability in which electrical impulses are to be applied to lower the yield strength. However, owing to the impulse duration and low current densities, concomitant effects always occur, e.g., as a result of Joule heating. Current developments in power electronics allow now to transmit high currents as short pulses. By reducing the impulse duration and increasing the current density, the plasticity of metallic materials can be correspondingly increased. Using the examples of polycrystalline iron and a single-crystal, nickel-based alloy (PWA 1480), current advances in the development of methods for forming materials by means of high-current-density impulses are demonstrated. For this purpose, appropriate specimens were loaded in compression and, using novel testing equipment, subjected to a current strength of 10 kA with an impulse duration of 2 ms. For a pre-defined strain, the test results show a significant decrease in the compressive stress during the compression test and a significant change in the dislocation distribution following the current impulse treatment.

  13. Influence of High-Current-Density Impulses on the Compression Behavior: Experiments with Iron and a Nickel-Based Alloy

    NASA Astrophysics Data System (ADS)

    Demler, E.; Gerstein, G.; Dalinger, A.; Epishin, A.; Rodman, D.; Nürnberger, F.

    2017-01-01

    Difficulties of processing of high strength and/or brittle materials by plastic deformation, e.g., by forging, require to develop new industrial technologies. In particular, the feasible deformation rates are limited for low-ductile metallic materials. For this reason, processes were investigated to improve the deformability in which electrical impulses are to be applied to lower the yield strength. However, owing to the impulse duration and low current densities, concomitant effects always occur, e.g., as a result of Joule heating. Current developments in power electronics allow now to transmit high currents as short pulses. By reducing the impulse duration and increasing the current density, the plasticity of metallic materials can be correspondingly increased. Using the examples of polycrystalline iron and a single-crystal, nickel-based alloy (PWA 1480), current advances in the development of methods for forming materials by means of high-current-density impulses are demonstrated. For this purpose, appropriate specimens were loaded in compression and, using novel testing equipment, subjected to a current strength of 10 kA with an impulse duration of 2 ms. For a pre-defined strain, the test results show a significant decrease in the compressive stress during the compression test and a significant change in the dislocation distribution following the current impulse treatment.

  14. The influence of post-growth thermal treatments on the critical current density of TSMG YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Diko, P.; Antal, V.; Zmorayová, K.; Šefčiková, M.; Chaud, X.; Kováč, J.; Yao, X.; Chen, I.; Eisterer, M.; Weber, H. W.

    2010-12-01

    Oxygenation and thermochemical post-growth treatments of top seeded melt-growth (TSMG) YBCO bulk superconductors can significantly influence critical current density. It is shown that, depending on oxygenation conditions and the size of 211 particles, different reductions of intrinsic critical current density values can be obtained due to the reduction in the sample cross-section caused by the presence of a/b-microcracks induced by 211 particles, and a/b- and a/c-cracks induced by oxygenation. The possibility of eliminating oxygenation cracks by high pressure oxygenation and consequently significantly increasing the macroscopic critical current density is demonstrated. An effective dopant concentration for chemical pinning is proposed and possible clustering of substitutions in the Y123 lattice by thermochemical treatments is shown.

  15. Structural and phase transformations in zinc and brass wires under heating with high-density current pulse

    NASA Astrophysics Data System (ADS)

    Pervikov, A. V.

    2016-06-01

    The work is focused on revealing the mechanism of structure and phase transformations in the metal wires under heating with a high-density current pulse (the electric explosion of wires, EEWs). It has been demonstrated on the example of brass and zinc wires that the transition of a current pulse with the density of j ≈ 3.3 × 107 A/cm2 results in homogeneous heating of the crystalline structure of the metal/alloy. It has been determined that under heating with a pulse of high-density current pulse, the electric resistance of the liquid phases of zinc and brass decreases as the temperature increases. The results obtained allow for a conclusion that the presence of the particles of the condensed phase in the expanding products of EEW is the result of overheating instabilities in the liquid metal.

  16. Analysis of the magnetically induced current density of molecules consisting of annelated aromatic and antiaromatic hydrocarbon rings.

    PubMed

    Sundholm, Dage; Berger, Raphael J F; Fliegl, Heike

    2016-06-21

    Magnetically induced current susceptibilities and current pathways have been calculated for molecules consisting of two pentalene groups annelated with a benzene (1) or naphthalene (2) moiety. Current strength susceptibilities have been obtained by numerically integrating separately the diatropic and paratropic contributions to the current flow passing planes through chosen bonds of the molecules. The current density calculations provide novel and unambiguous current pathways for the unusual molecules with annelated aromatic and antiaromatic hydrocarbon moieties. The calculations show that the benzene and naphthalene moieties annelated with two pentalene units as in molecules 1 and 2, respectively, are unexpectedly antiaromatic sustaining only a local paratropic ring current around the ring, whereas a weak diatropic current flows around the C-H moiety of the benzene ring. For 1 and 2, the individual five-membered rings of the pentalenes are antiaromatic and a slightly weaker semilocal paratropic current flows around the two pentalene rings. Molecules 1 and 2 do not sustain any net global ring current. The naphthalene moiety of the molecule consisting of a naphthalene annelated with two pentalene units (3) does not sustain any strong ring current that is typical for naphthalene. Instead, half of the diatropic current passing the naphthalene moiety forms a zig-zag pattern along the C-C bonds of the naphthalene moiety that are not shared with the pentalene moieties and one third of the current continues around the whole molecule partially cancelling the very strong paratropic semilocal ring current of the pentalenes. For molecule 3, the pentalene moieties and the individual five-membered rings of the pentalenes are more antiaromatic than for 1 and 2. The calculated current patterns elucidate why the compounds with formally [4n + 2] π-electrons have unusual aromatic properties violating the Hückel π-electron count rule. The current density calculations also provide

  17. Optimization of a ribbon diode with magnetic insulation for increasing the current density in a high-current relativistic electron beam

    NASA Astrophysics Data System (ADS)

    Astrelin, V. T.; Arzhannikov, A. V.; Burdakov, A. V.; Sinitskii, S. L.; Stepanov, V. D.

    2009-05-01

    The geometry of the ribbon diode of the U-2 accelerator is optimized to increase both the current density and the total current of the relativistic electron beam for its subsequent injection into the plasma of a multimirror GOL-3 trap. Beam simulation in the diode was performed using the POISSON-2 applied software modified on the basis of the results obtained using the theory of a planar diode in an inclined magnetic field. As a result of the optimization, the diode geometry and the magnetic field configuration were found that should provide a factor of 1.5-2 increase in the current density in experiments with a small angular divergence of electron velocities.

  18. Critical current density behaviors across a grain boundary inclined to current with different angles in YBa2Cu3O7-δ bicrystal junctions

    NASA Astrophysics Data System (ADS)

    Tao, Hua; Wei-Wei, Xu; Zheng-Ming, Ji; Da-Yuan, Guo; Qing-Yun, Wang; Xiang-Rong, Ma; Rui-Yu, Liang

    2016-06-01

    The critical current density behaviors across a bicrystal grain boundary (GB) inclined to the current direction with different angles in YBa2Cu3O7-δ bicrystal junctions in magnetic fields are investigated. There are two main reasons for the difference in critical current density in junctions at different GB inclined angles in the same magnetic field: (i) the GB plane area determines the current carrying cross section; (ii) the vortex motion dynamics at the GB affects the critical current value when the vortex starts to move along the GB by Lorentz force. Furthermore, the vortex motion in a bicrystal GB is studied by investigating transverse (Hall) and longitudinal current-voltage characteristics (I-V xx and I-V xy ). It is found that the I-V xx curve diverges from linearity at a high driving current, while the I-V xy curve keeps nearly linear, which indicates the vortices inside the GB break out of the GB by Lorentz force. Project supported by the National Natural Science Foundation of China (Grant Nos. 61501222, 61371036, and 61571219) and the School Scientific Research Fund of Nanjing Institute of Technology, China (Grant Nos. YKJ201418).

  19. Surface layer structure of AISI 1020 steel at different stages of dry sliding under electric current of high density

    NASA Astrophysics Data System (ADS)

    Aleutdinov, K. A.; Rubtsov, V. Ye; Fadin, V. V.; Aleutdinova, M. I.

    2016-02-01

    Wear intensity of the sliding electric contact steel 1020/steel 1045 depending on sliding time is presented at the contact current density higher than 100 A/cm2 without lubricant. It is shown that wear intensity of 1020 steel decreases at increasing of sliding time. Wear intensity is stabilized after some sliding time. This time (burn-in time) decreases at reduction of current density. Structural changes are realized in surface layer. Signs of liquid phase are observed on sliding surface. This liquid isn't a result of melting. It is established using Auger spectrometry that the contact layer contains up to 50 at.% of oxygen.

  20. Theory of electron current filamentation instability and ion density filamentation in the early development of a DPF discharge

    SciTech Connect

    Guillory, J.; Rose, D. V.; Lerner, E. J.

    2009-01-21

    Two-dimensional simulations of the initial stages of plasma formation in a dense plasma focus show the formation, in a few tens of nanoseconds, of a dense layer of plasma (n{sub e}{approx}10{sup 18} cm{sup -3},T{sub e}{approx}3 eV) in a thin layer surrounding the insulator-covered central anode of the focus device, and carrying axially-directed current at rather high current density.Earlier work on the filamentation of dense cathode plasma in high-power diodes seems to indicate that the anode plasma current layer in a dense plasma focus (DPF) device could be subject to the same instability, creating a growth of axially-directed filaments in the current density. The growth rate for resistive-thermal-driven filamentation, e.g. at 30 torr and {approx}3 eV electron temperature, exceeds the that due to non-thermal current (JxB) driving, and is determined by electron dynamics, so its evolution is quicker than the response-time of the ions.Nonetheless, with such a growing current-density perturbation as a seed and its increasing rippling of the azimuthal magnetic field as a driver, the ions will eventually take part in the azimuthal bunching, forming filaments in the ion density as well. The resistive-thermal-driven filamentation fields thus serve to 'hurry-up' the development of ion density filamentation, as shown approximately in the work presented here. This theory predicts, for light ions, a relatively early ({<=}250 ns) development of visible filaments along the anode, perhaps even before the main rundown phase of the focus plasma motion, and these filaments may persist during the 'liftoff' phase of the current layer to form the rundown phase of the plasma front. This work is supported by Larwenceville Plasma Physics.

  1. Formation of Mosaic Silicon Oxide Structure during Metal-Assisted Electrochemical Etching of Silicon at High Current Density

    NASA Astrophysics Data System (ADS)

    Cao, Dao Tran; Anh, Cao Tuan; Ngan, Luong Truc Quynh

    2016-05-01

    We have used constant-current, metal-assisted electrochemical etching of silicon in HF/H2O2/ethanol electrolyte to fabricate porous silicon. We found that, at large enough current density, the sponge-like porous silicon structure is replaced by a mosaic structure, which includes islands of various shapes emerging between trenches that have been etched downward. Energy-dispersive x-ray analysis showed that the surface of the mosaic pieces was covered with silicon oxide, while little silicon oxide developed on the surface of trenches. We suggest that the appearance of the mosaic structure can be explained by the increase in the oxidation rate of silicon when the anodic current density increases, combined with no change in the dissolution rate of silicon oxide into the solution. Consequently, above a certain value of anodic current density, there is sufficient residual silicon oxide on the etched surface to create a continuous thin film. However, if the silicon oxide layer is too thick (e.g., due to too high anodic current density or too long etching time), it will become cracked (formation of mosaic pieces), likely due to differences in thermal expansion coefficient between the amorphous silicon oxide layer and crystalline silicon substrate. The oxide is cracked at locations with many defects, and the cracks reveal the silicon substrate. Therefore, at the locations where cracks occur, etching will go sideways and downward, creating trenches.

  2. Short-circuit current density imaging of crystalline silicon solar cells via lock-in thermography: Robustness and simplifications

    SciTech Connect

    Fertig, Fabian Greulich, Johannes; Rein, Stefan

    2014-11-14

    Spatially resolved determination of solar cell parameters is beneficial for loss analysis and optimization of conversion efficiency. One key parameter that has been challenging to access by an imaging technique on solar cell level is short-circuit current density. This work discusses the robustness of a recently suggested approach to determine short-circuit current density spatially resolved based on a series of lock-in thermography images and options for a simplified image acquisition procedure. For an accurate result, one or two emissivity-corrected illuminated lock-in thermography images and one dark lock-in thermography image have to be recorded. The dark lock-in thermography image can be omitted if local shunts are negligible. Furthermore, it is shown that omitting the correction of lock-in thermography images for local emissivity variations only leads to minor distortions for standard silicon solar cells. Hence, adequate acquisition of one image only is sufficient to generate a meaningful map of short-circuit current density. Beyond that, this work illustrates the underlying physics of the recently proposed method and demonstrates its robustness concerning varying excitation conditions and locally increased series resistance. Experimentally gained short-circuit current density images are validated for monochromatic illumination in comparison to the reference method of light-beam induced current.

  3. Transient 3D numerical simulations of column collapse and pyroclastic density current scenarios at Vesuvius

    NASA Astrophysics Data System (ADS)

    Esposti Ongaro, T.; Neri, A.; Menconi, G.; de'Michieli Vitturi, M.; Marianelli, P.; Cavazzoni, C.; Erbacci, G.; Baxter, P. J.

    2008-12-01

    Numerical simulations of column collapse and pyroclastic density current (PDC) scenarios at Vesuvius were carried out using a transient 3D flow model based on multiphase transport laws. The model describes the dynamics of the collapse as well as the effects of the 3D topography of the volcano on PDC propagation. Source conditions refer to a medium-scale sub-Plinian event and consider a pressure-balanced jet. Simulation results provide new insights into the complex dynamics of these phenomena. In particular: 1) column collapse can be characterized by different regimes, from incipient collapse to partial or nearly total collapse, thus confirming the possibility of a transitional field of behaviour of the column characterized by the contemporaneous and/or intermittent occurrence of ash fallout and PDCs; 2) the collapse regime can be characterized by its fraction of eruptive mass reaching the ground and generating PDCs; 3) within the range of the investigated source conditions, the propagation and hazard potential of PDCs appear to be directly correlated with the flow-rate of the mass collapsing to the ground, rather than to the collapse height of the column (this finding is in contrast with predictions based on the energy-line concept, which simply correlates the PDC runout and kinetic energy with the collapse height of the column); 4) first-order values of hazard variables associated with PDCs (i.e., dynamic pressure, temperature, airborne ash concentration) can be derived from simulation results, thereby providing initial estimates for the quantification of damage scenarios; 5) for scenarios assuming a location of the central vent coinciding with that of the present Gran Cono, Mount Somma significantly influences the propagation of PDCs, largely reducing their propagation in the northern sector, and diverting mass toward the west and southeast, accentuating runouts and hazard variables for these sectors; 6) the 2D modelling approximation can force an artificial

  4. Catalysts for ultrahigh current density oxygen cathodes for space fuel cell applications

    NASA Technical Reports Server (NTRS)

    Tryk, Donald A.; Yeager, E.

    1992-01-01

    The objective was to identify promising electrocatalyst/support systems for oxygen cathodes capable of operating at ultrahigh current densities in alkaline fuel cells. Such cells will require operation at relatively high temperatures and O2 pressures. A number of materials were prepared, including Pb-Ru and Pb-Ir pyrochlores, RuO2 and Pt-doped RuO2, lithiated NiO and La-Ni perovskites. Several of these materials were prepared using techniques that had not been previously used to prepare them. Particularly interesting was the use of the alkaline solution technique to prepare Pt-doped and Pb-Ru pyrochlores in high area form. Also interesting was the use of the fusion (melt) method for preparing the Pb-Ru pyrochlore. Several of the materials were also deposited with platinum. Well-crystallized Pb2Ru2O(7-y) was used to fabricate very high performance O2 cathodes with good stability in room temperature KOH. This material was also found to be stable over a useful potential range at approx. 140 C in concentrated KOH. For some of the samples, fabrication of the gas-fed electrodes could not be fully optimized during this project period. Future work may be directed at this problem. Pyrochlores that were not well-crystallized were found to be unstable in alkaline solution. Very good O2 reduction performance and stability were observed with Pb2RuO(7-y) in a carbon-based gas-fed electrode with an anion-conducting membrane placed on the electrolyte side of the electrode. The performance came within a factor of about two of that observed without carbon. High area platinum and gold supported on several conductive metal oxide supports were examined. Only small improvements in O2 reduction performance at room temperature were observed for Pb2Ru2O(7-y) as a support because of the high intrinsic activity of the pyrochlore. In contrast, a large improvement was observed for Li-doped NiO as a support for Pt. Very poor performance was observed for Au deposited on Li-NiO at approx. 150 C

  5. Comparing Pyroclastic Density Current (PDC) deposits at Colima (Mexico) and Tungurahua (Ecuador) volcanoes

    NASA Astrophysics Data System (ADS)

    Goldstein, Fabian; Varley, Nick; Bustillos, Jorge; Kueppers, Ulrich; Lavallee, Yan; Dingwell, Donald B.

    2010-05-01

    Sudden transitions from effusive to explosive eruptive behaviour have been observed at several volcanoes. As a result of explosive activity, pyroclastic density currents represent a major threat to life and infrastructure, mostly due to their unpredictability, mass, and velocity. Difficulties in direct observation force us to deduce crucial information from their deposits. Here, we present data from field work performed in 2009 on primary deposits from recent explosive episodes at Volcán de Colima (Mexico) and Tungurahua (Ecuador). Volcán de Colima, located 40km away from the Capital city Colima with 300,000 inhabitants, has been active since 1999. Activity has been primarily characterized by the slow effusion of lava dome with the daily occurrence of episodic gas (and sometimes ash) explosion events. During a period of peak activity in 2005, explosive eruptions repeatedly destroyed the dome and column collapse resulted in several PDCs that travelled down the W, S, and SE flanks. Tungurahua looms over the 20,000 inhabitants of the city of Baños, located 5km away, and is considered one of the most active volcanoes in Ecuador. The most recent eruptive cycle began in 1999 and climaxed in July and August of 2006 with the eruptions of several PDCs that traveled down the western flanks, controlled by the hydrological network. During two field campaigns, we collected an extensive data set of porosity and grain size distribution on PDCs at both volcanoes. The deposits have been mapped in detail and the porosity distribution of clasts across the surface of the deposits has been measured at more than 30 sites (> 3.000 samples). Our porosity distribution data (mean porosity values range between 17 and 24%) suggests an influence of run out distance and lateral position. Preliminary results of grain size analysis of ash and lapilli (< 5mm) has been performed at approximately 50 sites at varying longitudinal, lateral and vertical positions, and show a correlation with run

  6. A new look at mobility metrics for pyroclastic density currents: collection, interpretation, and use

    NASA Astrophysics Data System (ADS)

    Ogburn, S. E.; Lopes, D.; Calder, E. S.

    2012-12-01

    Mitigation of risk associated with pyroclastic density currents (PDCs) depends upon accurate forecasting of possible flow paths, often using empirical models that rely on mobility metrics or the stochastic application of computational flow models. Mobility metrics often inform computational models, sometimes as direct model inputs (e.g. energy cone model), or as estimates for input parameters (e.g. basal friction parameter in TITAN2D). These mobility metrics are often compiled from PDCs at many volcanoes, generalized to reveal empirical constants, or sampled for use in probabilistic models. In practice, however, there are often inconsistencies in how mobility metrics have been collected, reported, and used. For instance, the runout of PDCs often varies depending on the method used (e.g. manually measured from a paper map, automated using GIS software); and the distance traveled by the center of mass of PDCs is rarely reported due to the difficulty in locating it. This work reexamines the way we measure, report, and analyze PDC mobility metrics. Several metrics, such as the Heim coefficient (height dropped/runout, H/L) and the proportionality of inundated area to volume (A∝V2/3) have been used successfully with PDC data (Sparks 1976; Nairn and Self 1977; Sheridan 1979; Hayashi and Self 1992; Calder et al. 1999; Widiwijayanti et al. 2008) in addition to the non-volcanic flows they were originally developed for. Other mobility metrics have been investigated by the debris avalanche community but have not yet been extensively applied to pyroclastic flows (e.g. the initial aspect ratio of collapsing pile). We investigate the relative merits and suitability of contrasting mobility metrics for different types of PDCs (e.g. dome-collapse pyroclastic flows, ash-cloud surges, pumice flows), and indicate certain circumstances under which each model performs optimally. We show that these metrics can be used (with varying success) to predict the runout of a PDC of given volume

  7. Immobilization of bilirubin oxidase on graphene oxide flakes with different negative charge density for oxygen reduction. The effect of GO charge density on enzyme coverage, electron transfer rate and current density.

    PubMed

    Filip, Jaroslav; Andicsová-Eckstein, Anita; Vikartovská, Alica; Tkac, Jan

    2017-03-15

    Previously we showed that an effective bilirubin oxidase (BOD)-based biocathode using graphene oxide (GO) could be prepared in 2 steps: 1. electrostatic adsorption of BOD on GO; 2. electrochemical reduction of the BOD-GO composite to form a BOD-ErGO (electrochemically reduced GO) film on the electrode. In order to identify an optimal charge density of GO for BOD-ErGO composite preparation, several GO fractions differing in an average flake size and ζ-potential were prepared using centrifugation and consequently employed for BOD-ErGO biocathode preparation. A simple way to express surface charge density of these particular GO nanosheets was developed. The values obtained were then correlated with biocatalytic and electrochemical parameters of the prepared biocathodes, i.e. electrocatalytically active BOD surface coverage (Γ), heterogeneous electron transfer rate (kS) and a maximum biocatalytic current density. The highest bioelectrocatalytic current density of (597±25)μAcm(-2) and the highest Γ of (23.6±0.9)pmolcm(-2) were obtained on BOD-GO composite having the same moderate negative charge density, but the highest kS of (79.4±4.6)s(-1) was observed on BOD-GO composite having different negative charge density. This study is a solid foundation for others to consider the influence of a charge density of GO on direct bioelectrochemistry/bioelectrocatalysis of other redox enzymes applicable for construction of biosensors, bioanodes, biocathodes or biofuel cells.

  8. Achieving cholesterol targets by individualizing starting doses of statin according to baseline low-density lipoprotein cholesterol and coronary artery disease risk category: The CANadians Achieve Cholesterol Targets Fast with Atorvastatin Stratified Titration (CanACTFAST) study

    PubMed Central

    Ur, Ehud; Langer, Anatoly; Rabkin, Simon W; Calciu, Cristina-Dana; Leiter, Lawrence A

    2010-01-01

    BACKGROUND: Despite an increasing body of evidence on the benefit of lowering elevated levels of low-density lipoprotein cholesterol (LDL-C), there is still considerable concern that patients are not achieving target LDL-C levels. OBJECTIVE: The CANadians Achieve Cholesterol Targets Fast with Atorvastatin Stratified Titration (CanACTFAST) trial tested whether an algorithm-based statin dosing approach would enable patients to achieve LDL-C and total cholesterol/high-density lipoprotein cholesterol (TC/HDL-C) ratio targets quickly. METHODS: Subjects requiring statin therapy, but with an LDL-C level of 5.7 mmol/L or lower, and triglycerides of 6.8 mmol/L or lower at screening participated in the 12-week study, which had two open-label, six-week phases: a treatment period during which patients received 10 mg, 20 mg, 40 mg or 80 mg of atorvastatin based on an algorithm incorporating baseline LDL-C value and cardiovascular risk; and patients who achieved both LDL-C and TC/HDL-C ratio targets at six weeks continued on the same atorvastatin dose. Patients who did not achieve both targets received dose uptitration using a single-step titration regimen. The primary efficacy outcome was the proportion of patients achieving target LDL-C levels after 12 weeks. RESULTS: Of 2016 subjects screened at 88 Canadian sites, 1258 were assigned to a study drug (1101 were statin-free and 157 were statin-treated at baseline). The proportion of subjects who achieved LDL-C targets after 12 weeks of treatment was 86% (95% CI 84% to 88%) for statin-free patients and 54% (95% CI 46% to 61%) for statin-treated patients. Overall, 1003 subjects (80%; 95% CI 78% to 82%) achieved both lipid targets. CONCLUSIONS: Algorithm-based statin dosing enables patients to achieve LDL-C and TC/HDL-C ratio targets quickly, with either no titration or a single titration. PMID:20151053

  9. Ultrasound Current Source Density Imaging in live rabbit hearts using clinical intracardiac catheter

    NASA Astrophysics Data System (ADS)

    Li, Qian

    Ultrasound Current Source Density Imaging (UCSDI) is a noninvasive modality for mapping electrical activities in the body (brain and heart) in 4-dimensions (space + time). Conventional cardiac mapping technologies for guiding the radiofrequency ablation procedure for treatment of cardiac arrhythmias have certain limitations. UCSDI can potentially overcome these limitations and enhance the electrophysiology mapping of the heart. UCSDI exploits the acoustoelectric (AE) effect, an interaction between ultrasound pressure and electrical resistivity. When an ultrasound beam intersects a current path in a material, the local resistivity of the material is modulated by the ultrasonic pressure, and a change in voltage signal can be detected based on Ohm's Law. The degree of modulation is determined by the AE interaction constant K. K is a fundamental property of any type of material, and directly affects the amplitude of the AE signal detected in UCSDI. UCSDI requires detecting a small AE signal associated with electrocardiogram. So sensitivity becomes a major challenge for transferring UCSDI to the clinic. This dissertation will determine the limits of sensitivity and resolution for UCSDI, balancing the tradeoff between them by finding the optimal parameters for electrical cardiac mapping, and finally test the optimized system in a realistic setting. This work begins by describing a technique for measuring K, the AE interaction constant, in ionic solution and biological tissue, and reporting the value of K in excised rabbit cardiac tissue for the first time. K was found to be strongly dependent on concentration for the divalent salt CuSO4, but not for the monovalent salt NaCl, consistent with their different chemical properties. In the rabbit heart tissue, K was determined to be 0.041 +/- 0.012 %/MPa, similar to the measurement of K in physiologic saline: 0.034 +/- 0.003 %/MPa. Next, this dissertation investigates the sensitivity limit of UCSDI by quantifying the relation

  10. Theoretical design of gradient coils with minimum power dissipation: Accounting for the discretization of current density into coil windings

    NASA Astrophysics Data System (ADS)

    While, Peter T.; Korvink, Jan G.; Shah, N. Jon; Poole, Michael S.

    2013-10-01

    Gradient coil windings are typically constructed from either variable width copper tracks or fixed width wires. Excessive power dissipation within these windings during gradient coil operation limits the maximum drive current or duty cycle of the coil. It is common to design gradient coils in terms of a continuous minimum power current density and to perform a discretization to obtain the locations of the coil tracks or wires. However, the existence of finite gaps between these conductors and a maximum conductor width leads to an underestimation of coil resistance when calculated using the continuous current density. Put equivalently, the actual current density within the tracks or wires is higher than that used in the optimization and this departure results in suboptimal coil designs. In this work, a mapping to an effective current density is proposed to account for these effects and provide the correct contribution to the power dissipation. This enables the design of gradient coils that are genuinely optimal in terms of power minimization, post-discretization. The method was applied to the theoretical design of a variety of small x- and z-gradient coils for use in small animal imaging and coils for human head imaging. Computer-driven comparisons were made between coils designed with and without the current density mapping, in terms of simulated power dissipation. For coils to be built using variable width tracks, the method provides slight reductions in power dissipation in most cases and substantial gains only in cases where the minimum separation between track centre-lines is less than twice the gap size. However, for coils to be built using fixed width wires, very considerable reductions in dissipated power are consistently attainable (up to 60%) when compared to standard approaches of coil optimization.

  11. Studies of challenge in lower hybrid current drive capability at high density regime in experimental advanced superconducting tokamak

    NASA Astrophysics Data System (ADS)

    Ding, B. J.; Li, M. H.; Li, Y. C.; Wang, M.; Liu, F. K.; Shan, J. F.; Li, J. G.; Wan, B. N.; Wan

    2017-02-01

    Aiming at a fusion reactor, two issues must be solved for the lower hybrid current drive (LHCD), namely good lower hybrid wave (LHW)-plasma coupling and effective current drive at high density. For this goal, efforts have been made to improve LHW-plasma coupling and current drive capability at high density in experimental advanced superconducting tokamak (EAST). LHW-plasma coupling is improved by means of local gas puffing and gas puffing from the electron side is taken as a routine way for EAST to operate with LHCD. Studies of high density experiments suggest that low recycling and high lower hybrid (LH) frequency are preferred for LHCD experiments at high density, consistent with previous results in other machines. With the combination of 2.45 GHz and 4.6 GHz LH waves, a repeatable high confinement mode plasma with maximum density up to 19~\\text{m}-3$ was obtained by LHCD in EAST. In addition, in the first stage of LHCD cyclic operation, an alternative candidate for more economical fusion reactors has been demonstrated in EAST and further work will be continued.

  12. Estimation of critical current density and grain connectivity in superconducting MgB 2 bulk using Campbell’s method

    NASA Astrophysics Data System (ADS)

    Ni, B.; Morita, Y.; Liu, Z.; Liu, C.; Himeki, K.; Otabe, E. S.; Kiuchi, M.; Matsushita, T.

    2008-09-01

    Many recent reports on the critical current density ( Jc) in superconducting MgB 2 bulks indicated that improving the grain connectivity is important, since the obtained Jc values were generally much lower than those in other metallic superconductors and it was ascribed to the poor connectivity between grains in polycrystalline MgB 2. In this study, we focused on the estimation of the global critical current density, super-current path, grain connectivity and their relationships with the faults volume fraction in the MgB 2 bulks prepared by a modified PIT (powder in tube) method. Campbell’s method was applied for the purpose of obtaining the penetrating AC flux profile and the characteristic of AC magnetic field vs. penetration depth from the sample’s surface. A computer simulation on the penetrating AC flux profile in MgB 2 bulks with randomly distributed voids, oxidized grains and other faults was also carried out. Jc obtained by Campbell’s method turned out to be smaller than that obtained from the SQUID measurement, implying that the global super-current was reduced by the existence of various faults and the lack of the electrical connectivity. It was verified that the relationship between the global critical current characteristics and the faults contained in MgB 2 samples can be quantitatively clarified by comparing the simulated critical current densities and other factors with the experimental results.

  13. Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb3Sn conductors

    NASA Astrophysics Data System (ADS)

    Segal, Christopher; Tarantini, Chiara; Hawn Sung, Zu; Lee, Peter J.; Sailer, Bernd; Thoener, Manfred; Schlenga, Klaus; Ballarino, Amalia; Bottura, Luca; Bordini, Bernardo; Scheuerlein, Christian; Larbalestier, David C.

    2016-08-01

    High critical current density (J c) Nb3Sn A15 multifilamentary wires require a large volume fraction of small grain (SG), superconducting A15 phase, as well as Cu stabilizer with high Residual Resistance Ratio (RRR) to provide electromagnetic stabilization and protection. In powder-in-tube (PIT) wires the unreacted Nb7.5 wt%Ta outer layer of the tubular filaments acts as a diffusion barrier and protects the interfilamentary Cu stabilizer from Sn contamination. A high RRR requirement generally imposes a restricted A15 reaction heat treatment to prevent localized full reaction of the filament that could allow Sn to reach the Cu. In this study we investigate recent high quality PIT wires that achieve a J c (12 T, 4.2 K) up to ˜2500 A mm-2 and find that the minimum diffusion barrier thickness decreases as the filament aspect ratio increases from ˜1 in the inner rings of filaments to 1.3 in the outer filament rings. We found that just 2-3 diffusion barrier breaches can degrade RRR from 300 to 150 or less. Using progressive etching of the Cu we also found that the RRR degradation is localized near the external filaments where deformation is highest. Consequently minimizing filament distortion during strand fabrication is important for reducing RRR degradation. The additional challenge of developing the highest possible J c must be addressed by forming the maximum fraction of high J c SG A15 and minimizing low J c large-grain (LG) A15 morphologies. In one wire we found that 15% of the filaments had a significantly enhanced SG/LG A15 ratio and no residual A15 in the core, a feature that opens a path to substantial J c improvement.

  14. Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb3Sn conductors

    DOE PAGES

    Segal, Christopher; Tarantini, Chiara; Sung, Zu Hawn; ...

    2016-06-10

    High critical current density (Jc) Nb3Sn A15 multifilamentary wires require a large volume fraction of small grain, superconducting A15 phase, as well as Cu stabilizer with high Residual Resistance Ratio (RRR) to provide electromagnetic stabilization and protection. In Powder-in-Tube (PIT) wires the unreacted Nb7.5wt.%Ta outer layer of the tubular filaments acts as a diffusion barrier and protects the interfilamentary Cu stabilizer from Sn contamination. A high RRR requirement generally imposes a restricted A15 reaction heat treatment (HT) to prevent localized full reaction of the filament that could allow Sn to reach the Cu. In this paper we investigate recent highmore » quality PIT wires that achieve a Jc(12 T, 4.2 K) up to ~2500 A/mm-2 and find that the minimum diffusion barrier thickness decreases as the filament aspect ratio increases from ~1 in the inner rings of filaments to 1.3 in the outer filament rings. We found that just 2-3 diffusion barrier breaches can degrade RRR from 300 to 150 or less. Using progressive etching of the Cu we also found that the RRR degradation is localized near the external filaments where deformation is highest. Consequently minimizing filament distortion during strand fabrication is important for reducing RRR degradation. The additional challenge of developing the highest possible Jc must be addressed by forming the maximum fraction of high Jc small-grain (SG) A15 and minimizing low Jc large-grain (LG) A15 morphologies. Finally, in one wire we found that 15% of the filaments had a significantly enhanced SG/LG A15 ratio and no residual A15 in the core, a feature that opens a path to substantial Jc improvement.« less

  15. Huge Critical Current Density and Tailored Superconducting Anisotropy in SmFeAsO(0.8)F(0.15) by Low Density Columnar-Defect Incorporation

    NASA Astrophysics Data System (ADS)

    Welp, U.; Fang, L.; Jia, Y.; Mishra, V.; Chaparro, C.; Vlasko-Vlasov, V. K.; Koshelev, A. E.; Crabtree, G. W.; Zhu, S. F.; Zhigadlo, N. D.; Katrych, S.; Karpinski, J.; Kwok, W. K.

    2014-03-01

    SmFeAsO(0.8)F(0.15) is of great interest because it has the highest transition temperature of all the iron-based superconductors. We find that the introduction of a low density of correlated nano-scale defects enhances the critical current density up to 2 × 107A/cm2 at 5 K without any suppression in the high superconducting transition temperature of 50 K and amounting to 20 % of the theoretical depairing current density. We also observed a surprising reduction in the thermodynamic superconducting anisotropy from 8 to 4 upon irradiation. A model based on anisotropic electron scattering predicts that the superconducting anisotropy can be tailored via correlated defects in semi-metallic, fully gapped type II superconductors. - We acknowledge support by the Center for Emergent Superconductivity, an EFRC funded by the US DOE, Office of Basic Energy Sciences (LF, YJ, VM, AEK, WKK, GWC), by the DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 (CC, VKV, UW), by the EC Research Council project SuperIron (JK, SK), and by the Swiss National Science Foundation and the National Center of Competence in Research MaNEP (NDZ).

  16. Extracted ion current density in close-coupling multi-antenna type radio frequency driven ion source: CC-MATIS

    SciTech Connect

    Oka, Y. E-mail: oka@LHD.nifs.ac.jp; Shoji, T.

    2014-02-15

    Positive ions are extracted by using a small extractor from the Close-Coupling Multi-Antenna Type radio frequency driven Ion Source. Two types of RF antenna are used. The maximum extracted ion current density reaches 0.106 A/cm{sup 2}. The RF net power efficiency of the extracted ion current density under standard condition is 11.6 mA/cm{sup 2}/kW. The efficiency corresponds to the level of previous beam experiments on elementary designs of multi-antenna sources, and also to the efficiency level of a plasma driven by a filament in the same chamber. The multi-antenna type RF plasma source is promising for all metal high density ion sources in a large volume chamber.

  17. Extracted ion current density in close-coupling multi-antenna type radio frequency driven ion source: CC-MATIS.

    PubMed

    Oka, Y; Shoji, T

    2014-02-01

    Positive ions are extracted by using a small extractor from the Close-Coupling Multi-Antenna Type radio frequency driven Ion Source. Two types of RF antenna are used. The maximum extracted ion current density reaches 0.106 A/cm(2). The RF net power efficiency of the extracted ion current density under standard condition is 11.6 mA/cm(2)/kW. The efficiency corresponds to the level of previous beam experiments on elementary designs of multi-antenna sources, and also to the efficiency level of a plasma driven by a filament in the same chamber. The multi-antenna type RF plasma source is promising for all metal high density ion sources in a large volume chamber.

  18. Determination of the intragrain critical current density of the Bi(2223) phase inside Ag-sheathed tapes

    NASA Astrophysics Data System (ADS)

    Cimberle, M. R.; Ferdeghini, C.; Grasso, G.; Rizzuto, C.; Siri, A. S.; Flükiger, R.; Marti, F.

    1998-09-01

    Multifilamentary Ag-sheathed 0953-2048/11/9/003/img10 tapes, prepared by the powder-in-tube method, have been characterized by both transport and magnetic techniques at temperatures T between 4.5 K and 85 K in a magnetic field 0953-2048/11/9/003/img11 up to 15 T, with the aim of studying the residual presence of a granular behaviour over this wide H-T range. From a comparison between these measurements we have determined a domain of the H-T plane where the current density is still limited by the quality of the boundaries between adjacent grains and the polycrystalline superconductor behaves as a granular one and, on the contrary, the temperature region where it behaves like a strongly connected body. Finally, the temperature behaviour of the intrinsic Bi(2223) current density has been evaluated. At temperatures below 30 K in zero applied field, the intragrain current density is at least an order of magnitude higher than the transport current density.

  19. Syntrophic interactions between H2-scavenging and anode-respiring bacteria can improve current density in microbial electrochemical cells

    EPA Science Inventory

    High current density of 10.0-14.6 A/m2 and COD removal up to 96% were obtained in a microbial electrochemical cell (MEC) fed with digestate at hydraulic retention time (HRT) of 4d and 8d. Volatile fatty acids became undetectable in MEC effluent (HRT 8d), except for trivial acetat...

  20. The Evolution of Ring Current Energy Density and Energy Content during Geomagnetic Storms Based on Van Allen Probes Measurements

    NASA Astrophysics Data System (ADS)

    Zhao, H.; Li, X.; Baker, D. N.; Claudepierre, S. G.; Fennell, J. F.; Blake, J. B.; Larsen, B.; Skoug, R. M.; Funsten, H. O.; Freidel, R. H. W.; Reeves, G. D.; Spence, H. E.; Mitchell, D. G.; Lanzerotti, L. J.; Rodriguez, J. V.

    2015-12-01

    Enabled by the comprehensive measurements from the MagEIS, HOPE, and RBSPICE instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of particles with different energies and species to the ring current energy density and their dependence on the geomagnetic storms and storm phases are quantified. During the main phases of moderate storms (with minimum Dst between -50 nT and -100 nT), ions of energies < 50 keV and electrons of energies of <35 keV contribute more significantly to the ring current energy than those of higher energies. During the recovery phase and quiet times higher energy protons dominate the ring current energy content. For the March 29, 2013 moderate storm, the contribution from O+ is ~25% of the ring current energy content during the main phase, and the majority of that comes from < 50 keV O+. This indicates that even during moderate geomagnetic storms the ionosphere is still an important contributor to the ring current ions and low energy O+ plays an important role in ring current dynamics. The contribution of electrons to the ring current energy content is up to ~7% during this moderate storm and the magnetic local time dependence of electron energy density is also investigated. However, the ring current energy partitions for different species and energy ranges are very different during the great storm of 17 March 2015 (with minimum Dst<-210 nT).

  1. High critical current densities of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} thin films on buffered technical substrates

    SciTech Connect

    Knierim, A.; Auer, R.; Geerk, J.; Linker, G.; Meyer, O.; Reiner, H.; Schneider, R.

    1997-02-01

    C-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) thin films were deposited on polycrystalline metallic tapes buffered with yttria stabilized zirconia (YSZ). The in-plane alignment of the YSZ layers achieved by simultaneous ion bombardment of the growing film (ion beam assisted deposition) and of the postdeposited YBCO thin films was studied by x-ray diffraction as a function of the buffer layer thickness. A significant improvement of the in-plane texture, achieved for buffer layers exceeding a thickness of about 1.5 {mu}m, resulted in high critical current densities above 10{sup 6} A/cm{sup 2} of the YBCO films. {copyright} {ital 1997 American Institute of Physics.}

  2. Current progress in high cell density yeast bioprocesses for bioethanol production.

    PubMed

    Westman, Johan O; Franzén, Carl Johan

    2015-08-01

    High capital costs and low reaction rates are major challenges for establishment of fermentation-based production systems in the bioeconomy. Using high cell density cultures is an efficient way to increase the volumetric productivity of fermentation processes, thereby enabling faster and more robust processes and use of smaller reactors. In this review, we summarize recent progress in the application of high cell density yeast bioprocesses for first and second generation bioethanol production. High biomass concentrations obtained by retention of yeast cells in the reactor enables easier cell reuse, simplified product recovery and higher dilution rates in continuous processes. High local cell density cultures, in the form of encapsulated or strongly flocculating yeast, furthermore obtain increased tolerance to convertible fermentation inhibitors and utilize glucose and other sugars simultaneously, thereby overcoming two additional hurdles for second generation bioethanol production. These effects are caused by local concentration gradients due to diffusion limitations and conversion of inhibitors and sugars by the cells, which lead to low local concentrations of inhibitors and glucose. Quorum sensing may also contribute to the increased stress tolerance. Recent developments indicate that high cell density methodology, with emphasis on high local cell density, offers significant advantages for sustainable second generation bioethanol production.

  3. The use of segmented cathodes to determine the spoke current density distribution in high power impulse magnetron sputtering plasmas

    SciTech Connect

    Poolcharuansin, Phitsanu; Estrin, Francis Lockwood; Bradley, James W.

    2015-04-28

    The localized target current density associated with quasi-periodic ionization zones (spokes) has been measured in a high power impulse magnetron sputtering (HiPIMS) discharge using an array of azimuthally separated and electrical isolated probes incorporated into a circular aluminum target. For a particular range of operating conditions (pulse energies up to 2.2 J and argon pressures from 0.2 to 1.9 Pa), strong oscillations in the probe current density are seen with amplitudes up to 52% above a base value. These perturbations, identified as spokes, travel around the discharge above the target in the E×B direction. Using phase information from the angularly separated probes, the spoke drift speeds, angular frequencies, and mode number have been determined. Generally, at low HiPIMS pulse energies E{sub p} < 0.8 J, spokes appear to be chaotic in nature (with random arrival times), however as E{sub p} increases, coherent spokes are observed with velocities between 6.5 and 10 km s{sup −1} and mode numbers m = 3 or above. At E{sub p} > 1.8 J, the plasma becomes spoke-free. The boundaries between chaotic, coherent, and no-spoke regions are weakly dependent on pressure. During each HiPIMS pulse, the spoke velocities increase by about 50%. Such an observation is explained by considering spoke velocities to be determined by the critical ionization velocity, which changes as the plasma composition changes during the pulse. From the shape of individual current density oscillations, it appears that the leading edge of the spoke is associated with a slow increase in local current density to the target and the rear with a more rapid decrease. The measurements show that the discharge current density associated with individual spokes is broadly spread over a wide region of the target.

  4. 3D model of small-scale density cavities in the auroral magnetosphere with field-aligned current

    NASA Astrophysics Data System (ADS)

    Bespalov, P. A.; Misonova, V. G.; Savina, O. N.

    2016-09-01

    We propose a 3D model of small-scale density cavities stimulated by an auroral field-aligned current and an oscillating field-aligned current of kinetic Alfvén waves. It is shown that when the field-aligned current increases so that the electron drift velocity exceeds a value of the order of the electron thermal velocity, the plasma becomes unstable to the formation of cavities with low density and strong electric field. The condition of instability is associated with the value of the background magnetic field. In the case of a relatively weak magnetic field (where the electron gyro-radius is greater than the ion acoustic wavelength), the current instability can lead to the formation of one-dimensional cavities along the magnetic field. In the case of a stronger magnetic field (where the ion acoustic wavelength is greater than the electron gyro-radius, but still is less than the ion gyro-radius), the instability can lead to the formation of 3D density cavities. In this case, the spatial scales of the cavity, both along and across the background magnetic field, can be comparable, and at the earlier stage of the cavity formation they are of the order of the ion acoustic wavelength. Rarefactions of the cavity density are accompanied by an increase in the electric field and are limited by the pressure of bipolar electric fields that occur within them. The estimates of typical density cavity characteristics and the results of numerical solutions agree with known experimental data: small-scale structures with a sufficiently strong electric field are observed in the auroral regions with strong field-aligned current.

  5. High Current, High Density Arc Plasma as a New Source for WiPAL

    NASA Astrophysics Data System (ADS)

    Waleffe, Roger; Endrizzi, Doug; Myers, Rachel; Wallace, John; Clark, Mike; Forest, Cary; WiPAL Team

    2016-10-01

    The Wisconsin Plasma Astrophysics Lab (WiPAL) has installed a new array of nineteen plasma sources (plasma guns) on its 3 m diameter, spherical vacuum vessel. Each gun is a cylindrical, molybdenum, washer-stabilized, arc plasma source. During discharge, the guns are maintained at 1.2 kA across 100 V for 10 ms by the gun power supply establishing a high density plasma. Each plasma source is fired independently allowing for adjustable plasma parameters, with densities varying between 1018 -1019 m-3 and electron temperatures of 5-15 eV. Measurements were characterized using a 16 tip Langmuir probe. The plasma source will be used as a background plasma for the magnetized coaxial plasma gun (MCPG), the Terrestrial Reconnection Experiment (TREX), and as the plasma source for a magnetic mirror experiment. Temperature, density, and confinement results will be presented. This work is supported by the DoE and the NSF.

  6. Fabrication of high critical current density superconducting tapes by epitaxial deposition of YBCO thick films on biaxially textured metal substrates

    SciTech Connect

    Goyal, A.; Norton, D.P.; Paranthaman, M.

    1996-12-31

    High critical current density YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) tapes were fabricated by epitaxial deposition on rolling- assisted-biaxially-textured-substrates (RABiTS). The RABiTS technique uses well established, industrially scaleable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers to yield chemically and structurally compatible surfaces. Epitaxial YBCO films grown on such substrates have critical current densities approaching 10{sup 6} A/cm{sup 2} at 77K in zero field and have field dependences similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for fabricating long lengths of high J{sub c} wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

  7. Spin-orbit effects on magnetically induced current densities in the M42- (M = B, Al, Ga, In, Tl) clusters

    NASA Astrophysics Data System (ADS)

    Alvarez-Thon, Luis; Caimanque-Aguilar, Wilson

    2017-03-01

    We report about the spin-orbit effects on the aromaticity of the B42-, Al42-, Ga42-, In42-, and Tl42-, clusters via the magnetically-induced current density method. All-electron density functional theory (DFT) calculations were carried out using the four-component Dirac-Coulomb (DC) Hamiltonian, including scalar and spin-orbit relativistic effects. The relativistic values for ring current strengths were obtained by numerical integration over the current flow. These values were compared to the scalar relativistic and non-relativistic values, in order to assess the corresponding contributions to aromaticity. It was found that in the heavy cluster, Tl42-, , there is a significant influence of both scalar and spin-orbit relativistic effects.

  8. Microstructural and crystallographic imperfections of MgB{sub 2} superconducting wire and their correlation with the critical current density

    SciTech Connect

    Shahabuddin, Mohammed; Alzayed, Nasser S.; Oh, Sangjun; Choi, Seyong; Maeda, Minoru; Hata, Satoshi; Shimada, Yusuke; Hossain, Md Shahriar Al; Kim, Jung Ho

    2014-01-15

    A comprehensive study of the effects of structural imperfections in MgB{sub 2} superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB{sub 2} material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB{sub 2}, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB{sub 2}, however, even at low sintering temperature, and thus block current transport paths.

  9. An experimental investigation of the dynamics of submarine leveed channel initiation as sediment-laden density currents experience sudden unconfinement

    SciTech Connect

    Rowland, Joel C; Hilley, George E; Fildani, Andrea

    2009-01-01

    Leveed submarine channels play a critical role in the transfer of sediment from the upper continental slopes to interslope basins and ultimately deepwater settings. Despite a reasonable understanding of how these channels grow once established, how such channels initiate on previously unchannelized portions of the seafloor remains poorly understood. We conducted a series of experiments that elucidate the influence of excess density relative to flow velocity on the dynamics of, and depositional morphologies arising from, density currents undergoing sudden unconfinement across a sloped bed. Experimental currents transported only suspended sediment across a non-erodible substrate. Under flow conditions ranging from supercritical to subcritical (bulk Richardson numbers of 0.02 to 1.2) our experiments failed to produce deposits resembling or exhibiting the potential to evolve into self-formed leveed channels. In the absence of excess density, a submerged sediment-laden flow produced sharp crested lateral deposits bounding the margins of the flow for approximately a distance of two outlet widths down basin. These lateral deposits terminated in a centerline deposit that greatly exceeded marginal deposits in thickness. As excess density increased relative to the outlet velocity, the rate of lateral spreading of the flow increased relative to the downstream propagation of the density current, transitioning from a narrow flow aligned with the channel outlet to a broad radially expanding flow. Coincident with these changes in flow dynamics, the bounding lateral deposits extended for shorter distances, had lower, more poorly defined crests that were increasingly wider in separation than the initial outlet, and progressively became more oblong rather than linear. Based on our results, we conclude that leveed channels cannot initiate from sediment-laden density currents under strictly depositional conditions. Partial confinement of these currents appears to be necessary to

  10. Density- and viscosity-stratified gravity currents: Insight from laboratory experiments and implications for submarine flow deposits

    NASA Astrophysics Data System (ADS)

    Amy, L. A.; Peakall, J.; Talling, P. J.

    2005-08-01

    Vertical stratification of particle concentration is a common if not ubiquitous feature of submarine particulate gravity flows. To investigate the control of stratification on current behaviour, analogue stratified flows were studied using laboratory experiments. Stratified density currents were generated by releasing two-layer glycerol solutions into a tank of water. Flows were sustained for periods of tens of seconds and their velocity and concentration measured. In a set of experiments the strength of the initial density and viscosity stratification was increased by progressively varying the lower-layer concentration, CL. Two types of current were observed indicating two regimes of behaviour. Currents with a faster-moving high-concentration basal region that outran the upper layer were produced if CL < 75%. Above this critical value of CL, currents were formed with a relatively slow, high-concentration base that lagged behind the flow front. The observed transition in behaviour is interpreted to indicate a change from inertia- to viscosity-dominated flow with increasing concentration. The reduction in lower-layer velocity at high concentrations is explained by enhanced drag at low Reynolds numbers. Results show that vertical stratification produces longitudinal stratification in the currents. Furthermore, different vertical and temporal velocity and concentration profiles characterise the observed flow types. Implications for the deposit character of particle-laden currents are discussed and illustrated using examples from ancient turbidite systems.

  11. Cooling of Water in a Flask: Convection Currents in a Fluid with a Density Maximum

    ERIC Educational Resources Information Center

    Velasco, S.; White, J. A.; Roman, F. L.

    2010-01-01

    The effect of density inversion on the convective flow of water in a spherical glass flask cooled with the help of an ice-water bath is shown. The experiment was carried out by temperature measurements (cooling curves) taken at three different heights along the vertical diameter of the flask. Flows inside the flask are visualized by seeding the…

  12. Alfven resonance mode conversion in the Phaedrus-T current drive experiments: Modelling and density fluctuations measurements

    SciTech Connect

    Vukovic, M.; Harper, M.; Breun, R.; Wukitch, S.

    1995-12-31

    Current drive experiments on the Phaedrus-T tokamak performed with a low field side two-strap fast wave antenna at frequencies below {omega}{sub cH} show loop volt drops of up to 30% with strap phasing (0, {pi}/2). RF induced density fluctuations in the plasma core have also been observed with a microwave reflectometer. It is believed that they are caused by kinetic Alfven waves generated by mode conversion of fast waves at the Alfven resonance. Correlation of the observed density fluctuations with the magnitude of the {Delta}V{sub loop} suggest that the {Delta}V{sub loop} is attributable to current drive/heating due to mode converted kinetic Alfven waves. The toroidal cold plasma wave code LION is used to model the Alfven resonance mode conversion surfaces in the experiments while the cylindrical hot plasma kinetic wave code ISMENE is used to model the behavior of kinetic Alfven waves at the Alfven resonance location. Initial results obtained from limited density, magnetic field, antenna phase, and impurity scans show good agreement between the RF induced density fluctuations and the predicted behavior of the kinetic Alfven waves. Detailed comparisons between the density fluctuations and the code predictions are presented.

  13. Density banding in corals: barcodes of past and current climate change

    NASA Astrophysics Data System (ADS)

    Brachert, T. C.; Reuter, M.; Krüger, S.; Böcker, A.; Lohmann, H.; Mertz-Kraus, R.; Fassoulas, C.

    2013-12-01

    The predicted sea surface temperature (SST) rise over the next decades is likely hazardous to coral health because precipitation of the calcareous skeleton depends primarily on SST. Temperature modulates vertical growth and density of the skeleton with seasonal SST changes resulting in an alternation of high-density and low-density bands (HDB and LDB). Notably, growth rates and the timing of the HDBs and LDBs relative to the seasons differ on a global scale within geographic regions. In this contribution, we use combined information of skeletal density and seasonally resolved oxygen isotope SST estimates from massive Porites from a Late Miocene (9 Ma) reef in the eastern Mediterranean Sea (Crete, Greece) to understand reef vulnerability over short and geological periods of time. Three types of HDB-SST relationships have been found: (1) coincidence of HDB with summer, (2) winter or (3) autumn and spring. The latter doubles HDBs in a year and implies maximum calcification is coupled to the taxon-specific optimum SST during the transitional seasons and reduced at its respective critical winter and summer SSTs. Modeling with a nonlinear temperature-calcification relationship reproduces the climate barcode of density bands. The model should be relevant for other poikilothermic carbonate producers in reefs and platforms and has implications for judging geographic distributions and causes of extinctions of corals, benthic carbonate communities and entire carbonate systems. With regard to the causes underlying expansion and demise of carbonate platforms and reefs in geological history, we expect the model predictions to help for a deeper understanding of biotic responses during hyperthermals or coolings and possibly also for identifying regions in the modern ocean where corals are endangered or taking advantage of global warming.

  14. Current density distribution in cylindrical Li-Ion cells during impedance measurements

    NASA Astrophysics Data System (ADS)

    Osswald, P. J.; Erhard, S. V.; Noel, A.; Keil, P.; Kindermann, F. M.; Hoster, H.; Jossen, A.

    2016-05-01

    In this work, modified commercial cylindrical lithium-ion cells with multiple separate current tabs are used to analyze the influence of tab pattern, frequency and temperature on electrochemical impedance spectroscopy. In a first step, the effect of different current tab arrangements on the impedance spectra is analyzed and possible electrochemical causes are discussed. In a second step, one terminal is used to apply a sinusoidal current while the other terminals are used to monitor the local potential distribution at different positions along the electrodes of the cell. It is observed that the characteristic decay of the voltage amplitude along the electrode changes non-linearly with frequency, where high-frequent currents experience a stronger attenuation along the current collector than low-frequent currents. In further experiments, the decay characteristic is controlled by the cell temperature, driven by the increasing resistance of the current collector and the enhanced kinetic and transport properties of the active material and electrolyte. Measurements indicate that the ac current distribution depends strongly on the frequency and the temperature. In this context, the challenges for electrochemical impedance spectroscopy as cell diagnostic technique for commercial cells are discussed.

  15. Current density in a model of a human body with a conductive implant exposed to ELF electric and magnetic fields.

    PubMed

    Valic, Blaz; Gajsek, Peter; Miklavcic, Damijan

    2009-10-01

    A numerical model of a human body with an intramedullary nail in the femur was built to evaluate the effects of the implant on the current density distribution in extremely low frequency electric and magnetic fields. The intramedullary nail was chosen because it is one of the longest high conductive implants used in the human body. As such it is expected to alter the electric and magnetic fields significantly. The exposure was a simultaneous combination of inferior to superior electric field and posterior to anterior magnetic field both alternating at 50 Hz with the values corresponding to the ICNIRP reference levels: 5000 V m(-1) for electric field and 100 microT for magnetic flux density. The calculated current density distribution inside the model was compared to the ICNIRP basic restrictions for general public (2 mA m(-2)). The results show that the implant significantly increases the current density up to 9.5 mA m(-2) in the region where it is in contact with soft tissue in the model with the implant in comparison to 0.9 mA m(-2) in the model without the implant. As demonstrated the ICNIRP basic restrictions are exceeded in a limited volume of the tissue in spite of the compliance with the ICNIRP reference levels for general public, meaning that the existing safety limits do not necessarily protect implanted persons to the same extent as they protect people without implants.

  16. Farfield Ion Current Density Measurements before and after the NASA HiVHAc EDU2 Vibration Test

    NASA Technical Reports Server (NTRS)

    Huang, Wensheng; Kamhawi, Hani; Shastry, Rohit

    2012-01-01

    There is an increasing need to characterize the plasma plume of the NASA HiVHAc thruster in order to better understand the plasma physics and to obtain data for spacecraft interaction studies. To address this need, the HiVHAc research team is in the process of developing a number of plume diagnostic systems. This paper presents the initial results of the farfield current density probe diagnostic system. Farfield current density measurements were carried out before and after a vibration test of the HiVHAc engineering development unit 2 that simulate typical launch conditions. The main purposes of the current density measurements were to evaluate the thruster plume divergence and to investigate any changes in the plasma plume that may occur as a result of the vibration test. Radial sweeps, as opposed to the traditional polar sweeps, were performed during these tests. The charged-weighted divergence angles were found to vary from 16 to 28 degrees. Charge density profiles measured pre- and post-vibration-test were found to be in excellent agreement. This result, alongside thrust measurements reported in a companion paper, confirm that the operation of the HiVHAc engineering development unit 2 were not altered by full-level/random vibration testing.

  17. Ionic liquid gating on atomic layer deposition passivated GaN: Ultra-high electron density induced high drain current and low contact resistance

    NASA Astrophysics Data System (ADS)

    Zhou, Hong; Du, Yuchen; Ye, Peide D.

    2016-05-01

    Herein, we report on achieving ultra-high electron density (exceeding 1014 cm-2) in a GaN bulk material device by ionic liquid gating, through the application of atomic layer deposition (ALD) of Al2O3 to passivate the GaN surface. Output characteristics demonstrate a maximum drain current of 1.47 A/mm, the highest reported among all bulk GaN field-effect transistors, with an on/off ratio of 105 at room temperature. An ultra-high electron density exceeding 1014 cm-2 accumulated at the surface is confirmed via Hall-effect measurement and transfer length measurement. In addition to the ultra-high electron density, we also observe a reduction of the contact resistance due to the narrowing of the Schottky barrier width on the contacts. Taking advantage of the ALD surface passivation and ionic liquid gating technique, this work provides a route to study the field-effect and carrier transport properties of conventional semiconductors in unprecedented ultra-high charge density regions.

  18. Experimental study of the maximum resolution and packing density achievable in sintered and non-sintered binder-jet 3D printed steel microchannels

    SciTech Connect

    Elliott, Amy M; Mehdizadeh Momen, Ayyoub; Benedict, Michael; Kiggans Jr, James O

    2015-01-01

    Developing high resolution 3D printed metallic microchannels is a challenge especially when there is an essential need for high packing density of the primary material. While high packing density could be achieved by heating the structure to the sintering temperature, some heat sensitive applications require other strategies to improve the packing density of primary materials. In this study the goal is to develop high green or pack densities microchannels on the scale of 2-300 microns which have a robust mechanical structure. Binder-jet 3D printing is an additive manufacturing process in which droplets of binder are deposited via inkjet into a bed of powder. By repeatedly spreading thin layers of powder and depositing binder into the appropriate 2D profiles, complex 3D objects can be created one layer at time. Microchannels with features on the order of 500 microns were fabricated via binder jetting of steel powder and then sintered and/or infiltrated with a secondary material. The average particle size of the steel powder was varied along with the droplet volume of the inkjet-deposited binder. The resolution of the process, packing density of the primary material, the subsequent features sizes of the microchannels, and the overall microchannel quality were characterized as a function of particle size distribution, droplet sizes and heat treatment temperatures.

  19. Magnetization behavior and critical current density along the c-axis in melt-grown YBCO fiber crystal

    NASA Astrophysics Data System (ADS)

    Ishii, H.; Hara, T.; Hirano, S.; Figueredo, A. M.; Cima, M. J.

    1994-05-01

    The magnetic-hysteresis behavior of single-crystal YBCO fibers was investigated below 1 T and in the temperature range 40 to 88 K. The sample was prepared by the laser-heated floating zone method. The magnetization curves exhibited a fairly large asymmetry with respect to the field axis, especially at elevated temperatures. This behavior may be attributed to the surface Meissner current contribution. It was demonstrated for the temperature range examined that the magnetic hysteresis width, Δ M, versus external-field curves were well described by assuming that the critical current density in the c-axis direction Jcc obeys the critical-state model of the form Jc( B)= JcO[1+( B/ B0) n]-1. Then, in turn, the field dependence of the critical current density along the c-axis at field temperatures was deduced using parameters obtained by fitting the Δ M vs. field curves. It was shown that the critical current density in the direction of the c-axis in our sample was over 10 4 A/cm 2 at 77.3 K below 0.3 T. The field and temperature variations of Jcc were discussed in relation to the previous studies on some melt-processed YBCO.

  20. Study of the origin and structure of a nocturnal atmospheric density current from observations and numerical simulations

    NASA Astrophysics Data System (ADS)

    Ander Arrillaga, Jon; Yagüe, Carlos; Román-Cascón, Carlos; Sastre, Mariano

    2016-04-01

    Density currents are flows generated when a dense fluid passes through a less dense surrounding, under the influence of gravity. They usually appear as a consequence of sea-breeze circulations, thunderstorm outflows or katabatic flows. Density currents acquire a particular relevance during nocturnal stable situations, as their onset causes a significant turbulence increase (both from buoyancy and shear) and they occasionally produce turbulence intermittency through the formation of gravity waves. In this work, the arrival of a density current on 23 September 2015 is analysed in the CIBA site (Spain), which is located in the Spanish Northern Plateau, approximately 200 km away from the sea and 100 km away from the closest mountain ranges. Previous studies at this location associated similar nocturnal events with daytime sea breeze in the eastern Cantabrian coast [1]. Micrometeorological measurements from sonic anemometers and different sensors at multiple levels up to 100 m agl provide a solid database. In this specific case, the outbreak of the density current occurs 2 hours after sunset, causing an abrupt increase of the wind speed and a significant weakening of the surface-based thermal inversion. Besides, turbulent parameters and fluxes such as the friction velocity, the sensible heat flux and the Turbulent Kinetic Energy (TKE) are sharply altered with its arrival. The latter, indeed, increases by two orders of magnitude and the Multi Resolution Flux Decomposition (MRFD) of this and other turbulent variables gives the approximate size of the contributing eddies. Furthermore, simulations with the WRF model, which is tested for different Planetary Boundary Layer (PBL) schemes and the topo_wind option for complex topography [2], give meaningful information about the vertical structure and origin of this density current. [1] Udina, M., Soler, M.R., Viana, S. & Yagüe, C. (2013). Model simulation of gravity waves triggered by a density current. Q J R Meteorol Soc, 139

  1. Methods for passivating silicon devices at low temperature to achieve low interface state density and low recombination velocity while preserving carrier lifetime

    DOEpatents

    Chen, Zhizhang; Rohatgi, Ajeet

    1995-01-01

    A new process has been developed to achieve a very low SiO.sub.x /Si interface state density D.sub.it, low recombination velocity S (<2 cm/s), and high effective carrier lifetime T.sub.eff (>5 ms) for oxides deposited on silicon substrates at low temperature. The technique involves direct plasma-enhanced chemical vapor deposition (PECVD), with appropriate growth conditions, followed by a photo-assisted rapid thermal annealing (RTA) process. Approximately 500-A-thick SiO.sub.x layers are deposited on Si by PECVD at 250.degree. C. with 0.02 W/cm.sup.-2 rf power, then covered with SiN or an evaporated thin aluminum layer, and subjected to a photo-assisted anneal in forming gas ambient at 350.degree. C., resulting in an interface state density D.sub.it in the range of about 1-4.times.10.sup.10 cm.sup.-2 eV.sup.-1, which sets a record for the lowest interface state density D.sub.it for PECVD oxides fabricated to date. Detailed analysis shows that the PECVD deposition conditions, photo-assisted anneal, forming gas ambient, and the presence of an aluminum layer on top of the oxides during the anneal, all contributed to this low value of interface state density D.sub.it. Detailed metal-oxide semiconductor analysis and model calculations show that such a low recombination velocity S is the result of moderately high positive oxide charge (5.times.10.sup.11 -1.times.10.sup.12 cm.sup.-2) and relatively low midgap interface state density (1.times.10.sup.10 -4.times.10.sup.10 cm.sup.-2 eV.sup.-1). Photo-assisted anneal was found to be superior to furnace annealing, and a forming gas ambient was better than a nitrogen ambient for achieving a very low surface recombination velocity S.

  2. Critical current densities and irreversibility fields of MgB 2 bulks

    NASA Astrophysics Data System (ADS)

    Kumakura, H.; Takano, Y.; Fujii, H.; Togano, K.; Kito, H.; Ihara, H.

    2001-11-01

    We prepared two MgB 2 bulks by applying conventional sintering and high-pressure sintering methods, and compared the current carrying properties. Jc obtained by the resistive method was larger than that obtained by the magnetic method. Jc- B curves obtained by the resistive method showed no history effect. These results indicate that most of the superconducting currents flowing in the MgB 2 bulks were intergrain (transport) currents and intragrain currents were negligibly small. The high-pressure sintered sample with smaller grain size showed smaller field dependence of Jc and higher Birr than the conventionally sintered sample with larger grain size. This behavior can be explained by the grain boundary flux pinning.

  3. High-Current-Density Thermionic Cathodes and the Generation of High-Voltage Electron Beams

    DTIC Science & Technology

    1989-04-30

    pulsing results, up to 140 kV was applied across this length of boron nitride without surface flashover . The anode face plate is made of stainless steel...current distribution over the cathode surface and correlation with thermionic-emission theory , 3. sign and testing of an electron-gun diode with an...aperture across the cathode surface by moving the anode transversely. The arrangement is shown in Figure 5. The sampled cathode current (0.16 percent of

  4. The enhancement of antibody concentration and achievement of high cell density CHO cell cultivation by adding nucleoside.

    PubMed

    Takagi, Yasuhiro; Kikuchi, Takuya; Wada, Ryuta; Omasa, Takeshi

    2017-03-02

    Recently, with the dramatic increase in demand for therapeutic antibodies, Chinese hamster ovary (CHO) cell culture systems have made significant progress in recombinant antibody production. Over the past two decades, recombinant antibody productivity has been improved by more than 100-fold. Medium optimization has been identified as an important key approach for increasing product concentrations. In this study, we evaluated the effects of deoxyuridine addition to fed-batch cultures of antibody-expressing CHO cell lines. Furthermore, we investigated the effects of combined addition of deoxyuridine, thymidine, and deoxycytidine. Our results suggest that addition of these pyrimidine nucleosides can increase CHO cell growth, with no significant change in the specific production rate. As a result of the increased cell growth, the antibody concentration was elevated and we were able to achieve more than 9 g/L during 16 days of culture. Similar effects of nucleoside addition were observed in fed-batch cultures of a Fab fragment-expressing CHO cell line, and the final Fab fragment concentration was more than 4 g/L. This nucleoside addition strategy could be a powerful platform for efficient antibody production.

  5. Syntrophic interactions between H2-scavenging and anode-respiring bacteria can improve current density in microbial electrochemical cells.

    PubMed

    Gao, Yaohuan; Ryu, Hodon; Santo Domingo, Jorge W; Lee, Hyung-Sool

    2014-02-01

    High current density of 10.0-14.6A/m(2) and COD removal up to 96% were obtained in a microbial electrochemical cell (MEC) fed with digestate at hydraulic retention time (HRT) of 4d and 8d. Volatile fatty acids became undetectable in MEC effluent (HRT 8d), except for trivial acetate (4.16±1.86mgCOD/L). Accumulated methane only accounted for 3.42% of ΔCOD. Pyrosequencing analyses showed abundant fermenters (Kosmotoga spp.) and homoacetogens (Treponema spp.) in anolytes. In anode biofilm, propionate fermenters (Kosmotoga, and Syntrophobacter spp.), homoacetogens (Treponema spp.), and anode-respiring bacteria (ARB) (Geobacter spp. and Dysgonomonas spp.) were dominant. These results imply that syntrophic interactions among fermenters, homoacetogens and ARB would allow MECs to maintain high current density and coulombic efficiency.

  6. Surface layer structure and average contact temperature of copper-containing materials under dry sliding with high electric current density

    NASA Astrophysics Data System (ADS)

    Fadin, V. V.; Aleutdinova, M. I.; Rubtsov, V. Ye.; Aleutdinov, K. A.

    2016-11-01

    Dry sliding of copper and powder composites of Cu-Fe and Cu-Fe-graphite compositions against 1045 steel under electric current of contact density higher than 250 A/cm2 has been studied, which demonstrated the change in surface layer structure and formation of tribolayer consisting of iron, copper and FeO oxide. Signs of quasi-viscous flow of worn surface were observed. It was noted that the thin contact layer containing about 40 at % of oxygen and 40% of Fe was the main factor decreasing the adhesion interaction. It was affirmed that the introduction of graphite into the primary structure of the composite leads to rather low content of FeO oxide and to the increased tendency of surface layer to catastrophic deterioration under sliding with contact current density of about 300 A/cm2. The temperature of contact did not exceed 400°C.

  7. A new latch-free LIGBT on SOI with very high current density and low drive voltage

    NASA Astrophysics Data System (ADS)

    Olsson, J.; Vestling, L.; Eklund, K.-H.

    2016-01-01

    A new latch-free LIGBT on SOI is presented. The new device combines advantages from both LDMOS as well as LIGBT technologies; high breakdown voltage, high drive current density, low control voltages, at the same time eliminating latch-up problems. The new LIGBT has the unique property of independent scaling of the input control device, i.e. LDMOS, and the output part of the device, i.e. the p-n-p part. This allows for additional freedom in designing and optimizing the device properties. Breakdown voltage of over 200 V, on-state current density over 3 A/mm, specific on-resistance below 190 mΩ mm2, and latch-free operation is demonstrated.

  8. Polarization curve measurements combined with potential probe sensing for determining current density distribution in vanadium redox-flow batteries

    NASA Astrophysics Data System (ADS)

    Becker, Maik; Bredemeyer, Niels; Tenhumberg, Nils; Turek, Thomas

    2016-03-01

    Potential probes are applied to vanadium redox-flow batteries for determination of effective felt resistance and current density distribution. During the measurement of polarization curves in 100 cm2 cells with different carbon felt compression rates, alternating potential steps at cell voltages between 0.6 V and 2.0 V are applied. Polarization curves are recorded at different flow rates and states of charge of the battery. Increasing compression rates lead to lower effective felt resistances and a more uniform resistance distribution. Low flow rates at high or low state of charge result in non-linear current density distribution with high gradients, while high flow rates give rise to a nearly linear behavior.

  9. Fabrication and characterization of high current-density, submicron, NbN/MgO/NbN tunnel junctions

    NASA Technical Reports Server (NTRS)

    Stern, J. A.; Leduc, Henry G.; Judas, A. J.

    1992-01-01

    At near-millimeter wavelengths, heterodyne receivers based on SIS tunnel junctions are the most sensitive available. However, in order to scale these results to submillimeter wavelengths, certain device properties should be scaled. The tunnel-junction's current density should be increased to reduce the RC product. The device's area should be reduced to efficiently couple power from the antenna to the mixer. Finally, the superconductor used should have a large energy gap to minimize RF losses. Most SIS mixers use Nb or Pb-alloy tunnel junctions; the gap frequency for these materials is approximately 725 GHz. Above the gap frequency, these materials exhibit losses similar to those in a normal metal. The gap frequency in NbN films is as-large-as 1440 GHz. Therefore, we have developed a process to fabricate small area (down to 0.13 sq microns), high current density, NbN/MgO/NbN tunnel junctions.

  10. Interacting effects of age, density, and weather on survival and current reproduction for a large mammal

    PubMed Central

    Richard, Emmanuelle; Simpson, Steven E; Medill, Sarah A; McLoughlin, Philip D

    2014-01-01

    Individual-based study of natural populations allows for accurate and precise estimation of fitness components and the extent to which they might vary with ecological conditions. By tracking the fates of all 701 horses known to have lived on Sable Island, Canada, from 2009 to 2013 (where there is no predation, human interference, or interspecific competition for food), we present a detailed analysis of structured population dynamics with focus on interacting effects of intraspecific competition and weather on reproduction and survival. Annual survival of adult females (0.866 ± 0.107 [ ± SE]) was lower than that of 3-year-olds (0.955 ± 0.051), although annual fecundity (producing a foal in a year that was observed during our census) was higher in adults (0.616 ± 0.023) compared to 3-year-olds (0.402 ± 0.054). Milder winters and lower densities during gestation increased fecundity. Density negatively impacted survival for all age and sex categories; however, highest adult female survival was observed during high-density years coupled with a harsh winter, the result expected if pregnancy loss during winter or loss of foals in spring improved survival. Three-year-old females, which reproduced at lower rates, experienced higher survival than adults. Our results contrast with a previous study of feral horses that suggested recently feral ungulates might be artificially selected to reproduce even when costs to survival are high. In part, this may be because of the comparably long history of feralization (250 years; at least 25 generations) for Sable Island horses. PMID:25614799

  11. Angular dependence of critical current density and magnetoresistance of sputtered high-T{sub c}-films

    SciTech Connect

    Geerkens, A.; Frenck, H.J.; Ewert, S.

    1994-12-31

    The angular dependence of the critical current density and the magnetoresistance of high-T{sub c}-films in high and low magnetic fields and for different temperatures were measured to investigate the flux pinning and the superconducting properties. A comparison of the results for the different superconductors shows their increasing dependence on the angle {Theta} between the magnetic field and the c-axis of the film due to the anisotropy of the chosen superconductor. Furthermore the influence of the current direction to the {Theta}-rotation plane is discussed.

  12. Angular dependence of critical current density and magnetoresistance of sputtered high-T(sub c)-films

    NASA Technical Reports Server (NTRS)

    Geerkens, A.; Meven, M.; Frenck, H.-J.; Ewert, S.

    1995-01-01

    The angular dependence of the critical current density and the magnetoresistance of high-T(sub c)-films in high and low magnetic fields and for different temperatures were measured to investigate the flux pinning and the superconducting properties. A comparison of the results for the different superconductors shows their increasing dependence on the angle Theta between the magnetic field and the c-axis of the film due to the anisotropy of the chosen superconductor. Furthermore the influence of the current direction to the Theta-rotation plane is discussed.

  13. Quenched dynamics in interacting one-dimensional systems: Appearance of current carrying steady states from initial domain wall density profiles

    NASA Astrophysics Data System (ADS)

    Lancaster, Jarrett; Gull, Emanuel; Mitra, Aditi

    2011-03-01

    Dynamics arising after an interaction quench in the quantum sine-Gordon model is studied for the case of a system initially prepared in a spatially inhomogeneous domain wall state. The time-evolution of the density, current and equal time correlation functions are studied using the truncated Wigner approximation (TWA) to which quantum corrections are added in order to set the limits on its validity. For weak to moderate strengths of the back-scattering interaction, the domain wall is found to spread out ballistically with the system within the light cone reaching a non-equilibrium steady-state characterized by a net current flow. A steady state current is also found to exist for a quench at the exactly solvable Luther-Emery point. The magnitude of the current decreases with increasing strength of the back-scattering interaction. The two-point correlation function of the variable canonically conjugate to the density reaches a steady state which is spatially oscillating at a wavelength which is inversely related to the current. This was was supported by NSF-DMR (Award no. 1004589).

  14. Temperature and Magnetic Field Dependence of Critical Current Density of YBCO with Varying Flux Pinning Additions (POSTPRINT)

    DTIC Science & Technology

    2010-03-01

    coverage corresponding to M phase 1 nm thickness was found to be necessary to increase compared to YBCO . The op- timal layer thickness for each M phase was...kept constant in this experiment: , Y211 0.8 nm , and [17]. Using the optimal M phase thickness, the YBCO layer was also systematically varied for...AFRL-RZ-WP-TP-2010-2083 TEMPERATURE AND MAGNETIC FIELD DEPENDENCE OF CRITICAL CURRENT DENSITY OF YBCO WITH VARYING FLUX PINNING ADDITIONS

  15. Effects of grain size and grain boundary on critical current density of high T(sub c) superconducting oxides

    NASA Technical Reports Server (NTRS)

    Zhao, Y.; Zhang, Q. R.; Zhang, H.

    1990-01-01

    By means of adding impurity elements in high T sub c oxides, the effects were studied of grain size and grain boundary on the critical current density of the following systems: YBa2Cu3O(7-y) and Bi-Pr-Sr-Ca-Cu-O. In order to only change the microstructure instead of the superconductivity of the grains in the samples, the impurity elements were added into the systems in terms of the methods like this: (1) substituting Y with the lanthanide except Pr, Ce, and Tb in YBa2Cu3O(7-y) system to finning down grains in the samples, therefore, the effect can be investigated of the grain size on the critical current density of 1:2:3 compounds; (2) mixing the high T sub c oxides with the metal elements, such as Ag, according to the composition of (high T sub c oxide)1-xAgx to metallize the grain boundaries in the samples, studying the effect of the electric conductivity of the grain boundaries on the critical current density; (3) adding SiO2, PbO2, and SnO2 into the high T sub c oxide to form impurity phases in the grain boundaries, trying to find out the effects of the impurity phases or metalloid grain boundaries on the critical current density of the high T sub c superconductors. The experimental results indicate that in the case of of the presence of the metalloid grain boundaries finning down grains fails to enhance the j sub c, but restrains it strongly, the granular high T sub c superconductors with the small size grains coupled weakly is always the low j sub c system.

  16. Relationship between anode material, supporting electrolyte and current density during electrochemical degradation of organic compounds in water.

    PubMed

    Guzmán-Duque, Fernando L; Palma-Goyes, Ricardo E; González, Ignacio; Peñuela, Gustavo; Torres-Palma, Ricardo A

    2014-08-15

    Taking crystal violet (CV) dye as pollutant model, the electrode, electrolyte and current density (i) relationship for electro-degrading organic molecules is discussed. Boron-doped diamond (BDD) or Iridium dioxide (IrO2) used as anode materials were tested with Na2SO4 or NaCl as electrolytes. CV degradation and generated oxidants showed that degradation pathways and efficiency are strongly linked to the current density-electrode-electrolyte interaction. With BDD, the degradation pathway depends on i: If icurrent density (i(lim)), CV is mainly degraded by OH radicals, whereas if i>i(lim), generated oxidants play a major role in the CV elimination. When IrO2 was used, CV removal was not dependent on i, but on the electrolyte. Pollutant degradation in Na2SO4 on IrO2 seems to occur via IrO3; however, in the presence of NaCl, degradation was dependent on the chlorinated oxidative species generated. In terms of efficiency, the Na2SO4 electrolyte showed better results than NaCl when BDD anodes were employed. On the contrary, NaCl was superior when combined with IrO2. Thus, the IrO2/Cl(-) and BDD/SO4(2-) systems were better at removing the pollutant, being the former the most effective. On the other hand, pollutant degradation with the BDD/SO4(2-) and IrO2/Cl(-) systems is favored at low and high current densities, respectively.

  17. High current density ion beam obtained by a transition to a highly focused state in extremely low-energy region

    SciTech Connect

    Hirano, Y. E-mail: hirano.yoichi@phys.cst.nihon-u.ac.jp; Kiyama, S.; Koguchi, H.; Fujiwara, Y.; Sakakita, H.

    2015-11-15

    A high current density (≈3 mA/cm{sup 2}) hydrogen ion beam source operating in an extremely low-energy region (E{sub ib} ≈ 150–200 eV) has been realized by using a transition to a highly focused state, where the beam is extracted from the ion source chamber through three concave electrodes with nominal focal lengths of ≈350 mm. The transition occurs when the beam energy exceeds a threshold value between 145 and 170 eV. Low-level hysteresis is observed in the transition when E{sub ib} is being reduced. The radial profiles of the ion beam current density and the low temperature ion current density can be obtained separately using a Faraday cup with a grid in front. The measured profiles confirm that more than a half of the extracted beam ions reaches the target plate with a good focusing profile with a full width at half maximum of ≈3 cm. Estimation of the particle balances in beam ions, the slow ions, and the electrons indicates the possibility that the secondary electron emission from the target plate and electron impact ionization of hydrogen may play roles as particle sources in this extremely low-energy beam after the compensation of beam ion space charge.

  18. High current density ion beam obtained by a transition to a highly focused state in extremely low-energy region.

    PubMed

    Hirano, Y; Kiyama, S; Fujiwara, Y; Koguchi, H; Sakakita, H

    2015-11-01

    A high current density (≈3 mA/cm(2)) hydrogen ion beam source operating in an extremely low-energy region (E(ib) ≈ 150-200 eV) has been realized by using a transition to a highly focused state, where the beam is extracted from the ion source chamber through three concave electrodes with nominal focal lengths of ≈350 mm. The transition occurs when the beam energy exceeds a threshold value between 145 and 170 eV. Low-level hysteresis is observed in the transition when E(ib) is being reduced. The radial profiles of the ion beam current density and the low temperature ion current density can be obtained separately using a Faraday cup with a grid in front. The measured profiles confirm that more than a half of the extracted beam ions reaches the target plate with a good focusing profile with a full width at half maximum of ≈3 cm. Estimation of the particle balances in beam ions, the slow ions, and the electrons indicates the possibility that the secondary electron emission from the target plate and electron impact ionization of hydrogen may play roles as particle sources in this extremely low-energy beam after the compensation of beam ion space charge.

  19. Obtaining source current density related to irregularly structured electromagnetic target field inside human body using hybrid inverse/FDTD method.

    PubMed

    Han, Jijun; Yang, Deqiang; Sun, Houjun; Xin, Sherman Xuegang

    2017-01-01

    Inverse method is inherently suitable for calculating the distribution of source current density related with an irregularly structured electromagnetic target field. However, the present form of inverse method cannot calculate complex field-tissue interactions. A novel hybrid inverse/finite-difference time domain (FDTD) method that can calculate the complex field-tissue interactions for the inverse design of source current density related with an irregularly structured electromagnetic target field is proposed. A Huygens' equivalent surface is established as a bridge to combine the inverse and FDTD method. Distribution of the radiofrequency (RF) magnetic field on the Huygens' equivalent surface is obtained using the FDTD method by considering the complex field-tissue interactions within the human body model. The obtained magnetic field distributed on the Huygens' equivalent surface is regarded as the next target. The current density on the designated source surface is derived using the inverse method. The homogeneity of target magnetic field and specific energy absorption rate are calculated to verify the proposed method.

  20. Dust mobilization due to density currents in the Atlas region: Observations from the Saharan Mineral Dust Experiment 2006 field campaign

    NASA Astrophysics Data System (ADS)

    Knippertz, P.; Deutscher, C.; Kandler, K.; Müller, T.; Schulz, O.; Schütz, L.

    2007-11-01

    Evaporation of precipitation is a ubiquitous feature of dry and hot desert environments. The resulting cooling often generates density currents with strong turbulent winds along their leading edges, which can mobilize large amounts of dust. Mountains support this process by triggering convection, by downslope acceleration of the cool air, and by fostering the accumulation of fine-grained sediments along their foothills through the action of water. For the Sahara, the world's largest dust source, this mechanism has been little studied because of the lack of sufficiently high resolution observational data. The present study demonstrates the frequent occurrence of density currents along the Sahara side of the Atlas Mountain chain in southern Morocco using the unique data set collected during the Saharan Mineral Dust Experiment (SAMUM) field campaign in May/June 2006. The density currents are related to convection over the mountains in the afternoon hours and have lifetimes on the order of 10 h. The passage of the sharp leading edge that sometimes reaches several hundred kilometers in length is usually associated with a marked increase in dew point and wind speed, a change in wind direction, and a decrease in temperature and visibility due to suspended dust. It is conceivable that this mechanism is relevant for other mountainous regions in northern Africa during the warm season. This would imply that simulations of the dust cycle with numerical models need a reliable representation of moist convective processes in order to generate realistic dust emissions from the Sahara.

  1. The effect of ion current density amplification in a diode with passive anode in magnetic self-isolation mode

    SciTech Connect

    Pushkarev, Alexander I.; Isakova, Yulia I.; Vakhrushev, Dmitry V.

    2010-12-15

    The results of a study on gigawatt power pulsed ion beam parameters are presented here. The pulsed ion beam is formed by a diode with an explosive-emission potential electrode, in magnetic self-isolation mode [A. I. Pushkarev, J. I. Isakova, M. S. Saltimakov et al., Phys. Plasmas 17, 013104 (2010)]. The ion current density is 20-40 A/cm{sup 2}, the energy of the ions is 200-250 keV, and the beam composition is of protons and carbon ions. Experiments have been performed on the TEMP-4M accelerator, set in double-pulse formation mode. To measure the beam parameters, we used a time-of-flight diagnosis. It is shown that the carbon ion current density, formed in a planar diode with graphite potential electrode, is five to seven times higher than the values calculated from the Child-Langmuir ratio. A model of ion current density amplification in a diode with magnetic self-isolation is proposed. The motion of electrons in the anode-cathode gap is simulated using the program CST PARTICLE STUDIO.

  2. Fast super-resolution imaging with ultra-high labeling density achieved by joint tagging super-resolution optical fluctuation imaging.

    PubMed

    Zeng, Zhiping; Chen, Xuanze; Wang, Hening; Huang, Ning; Shan, Chunyan; Zhang, Hao; Teng, Junlin; Xi, Peng

    2015-02-10

    Previous stochastic localization-based super-resolution techniques are largely limited by the labeling density and the fidelity to the morphology of specimen. We report on an optical super-resolution imaging scheme implementing joint tagging using multiple fluorescent blinking dyes associated with super-resolution optical fluctuation imaging (JT-SOFI), achieving ultra-high labeling density super-resolution imaging. To demonstrate the feasibility of JT-SOFI, quantum dots with different emission spectra were jointly labeled to the tubulin in COS7 cells, creating ultra-high density labeling. After analyzing and combining the fluorescence intermittency images emanating from spectrally resolved quantum dots, the microtubule networks are capable of being investigated with high fidelity and remarkably enhanced contrast at sub-diffraction resolution. The spectral separation also significantly decreased the frame number required for SOFI, enabling fast super-resolution microscopy through simultaneous data acquisition. As the joint-tagging scheme can decrease the labeling density in each spectral channel, thereby bring it closer to single-molecule state, we can faithfully reconstruct the continuous microtubule structure with high resolution through collection of only 100 frames per channel. The improved continuity of the microtubule structure is quantitatively validated with image skeletonization, thus demonstrating the advantage of JT-SOFI over other localization-based super-resolution methods.

  3. Achieving high power factor and output power density in p-type half-Heuslers Nb1-xTixFeSb.

    PubMed

    He, Ran; Kraemer, Daniel; Mao, Jun; Zeng, Lingping; Jie, Qing; Lan, Yucheng; Li, Chunhua; Shuai, Jing; Kim, Hee Seok; Liu, Yuan; Broido, David; Chu, Ching-Wu; Chen, Gang; Ren, Zhifeng

    2016-11-29

    Improvements in thermoelectric material performance over the past two decades have largely been based on decreasing the phonon thermal conductivity. Enhancing the power factor has been less successful in comparison. In this work, a peak power factor of ∼106 μW⋅cm(-1)⋅K(-2) is achieved by increasing the hot pressing temperature up to 1,373 K in the p-type half-Heusler Nb0.95Ti0.05FeSb. The high power factor subsequently yields a record output power density of ∼22 W⋅cm(-2) based on a single-leg device operating at between 293 K and 868 K. Such a high-output power density can be beneficial for large-scale power generation applications.

  4. Current Fluctuations in One Dimensional Diffusive Systems with a Step Initial Density Profile

    NASA Astrophysics Data System (ADS)

    Derrida, Bernard; Gerschenfeld, Antoine

    2009-12-01

    We show how to apply the macroscopic fluctuation theory (MFT) of Bertini, De Sole, Gabrielli, Jona-Lasinio, and Landim to study the current fluctuations of diffusive systems with a step initial condition. We argue that one has to distinguish between two ways of averaging (the annealed and the quenched cases) depending on whether we let the initial condition fluctuate or not. Although the initial condition is not a steady state, the distribution of the current satisfies a symmetry very reminiscent of the fluctuation theorem. We show how the equations of the MFT can be solved in the case of non-interacting particles. The symmetry of these equations can be used to deduce the distribution of the current for several other models, from its knowledge (Derrida and Gerschenfeld in J. Stat. Phys. 136, 1-15, 2009) for the symmetric simple exclusion process. In the range where the integrated current Qt˜sqrt{t} , we show that the non-Gaussian decay exp [- Q {/t 3}/ t] of the distribution of Q t is generic.

  5. Critical current density in wire drawn and hydrostatically extruded Nb-Ti superconductors

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Woollam, J. A.; Collings, E. W.

    1979-01-01

    Critical current studies have been made on copper-clad Nb-Ti composite wire prepared under area reductions of 100:1 and 10,000:1 by hydrostatic extrusion (HE), wire drawing and HE plus drawing. Comparative evaluation of the thermomechanical processing equivalent of HE was performed.

  6. Low field critical current density of titanium sheathed magnesium diboride wires

    NASA Astrophysics Data System (ADS)

    Rostila, L.; Grasso, G.; Demenčík, E.; Tumino, A.; Brisigotti, S.; Kováč, P.

    2010-06-01

    Magnesium diboride (MgB2) is replacing some of the conventional superconductors due to its low cost and availability in kilometer lengths. MgB2 has also been considered for AC applications. In order to model the AC losses and the critical currents of the applications, intrinsic Jc(B)-dependence is an important factor also at low fields. In this work Jc(B)-dependence of an MgB2 sample is extracted from the standard in field voltage-current measurements. The proposed method is applied to a non magnetic titanium sheathed sample at 16 and 20 K and a simple formula for Jc(B) aligns with the measurements. In the fitting process, the critical current distribution inside the wire is numerically simulated in order to take the self field of the sample into account. Moreover, the same formula aligns with measurements of a different sample. These critical current measurements, performed at 4.2 K, were based on magnetization. In the self field computations, the superconducting cross section must be determined accurately. Therefore, we tailored an image processing tool for MgB2 wires to obtain the geometry from a photograph.

  7. Low high-density lipoprotein cholesterol is a residual risk factor associated with long-term clinical outcomes in diabetic patients with stable coronary artery disease who achieve optimal control of low-density lipoprotein cholesterol.

    PubMed

    Ogita, Manabu; Miyauchi, Katsumi; Miyazaki, Tadashi; Naito, Ryo; Konishi, Hirokazu; Tsuboi, Shuta; Dohi, Tomotaka; Kasai, Takatoshi; Yokoyama, Takayuki; Okazaki, Shinya; Kurata, Takeshi; Daida, Hiroyuki

    2014-01-01

    Diabetes mellitus is recognized an independent risk factor for coronary artery disease (CAD) and mortality. Clinical trials have shown that statins significantly reduce cardiovascular events in diabetic patients. However, residual cardiovascular risk persists despite the achievement of target low-density lipoprotein cholesterol (LDL-C) levels with statin. High-density lipoprotein cholesterol (HDL-C) is an established coronary risk factor that is independent of LDL-C levels. We evaluated the impact of HDL-C on long-term mortality in diabetic patients with stable CAD who achieved optimal LDL-C. We enrolled 438 consecutive diabetic patients who were scheduled for percutaneous coronary intervention between 2004 and 2007 at our institution. We identified 165 patients who achieved target LDL-C <100 mg/dl. Patients were stratified into two groups according to HDL-C levels (low HDL-C group, baseline HDL-C <40 mg/dl; high HDL-C group, ≥40 mg/dl). Major adverse cardiac events (MACE) that included all-cause death, acute coronary syndrome, and target lesion revascularization were evaluated between the two groups. The median follow-up period was 946 days. The rate of MACE was significantly higher in diabetic patients with low-HDL-C who achieved optimal LDL-C (6.9 vs 17.9 %, log-rank P = 0.030). Multivariate Cox regression analysis showed that HDL-C is significantly associated with clinical outcomes (adjusted hazard ratio for MACE 1.33, 95 % confidence interval 1.01-1.75, P = 0.042). Low HDL-C is a residual risk factor that is significantly associated with long-term clinical outcomes among diabetic patients with stable CAD who achieve optimal LDL-C levels.

  8. Formation of the space charge region in diffusion p- n junctions under high-density current interruption

    NASA Astrophysics Data System (ADS)

    Grekhov, I. V.; Kyuregyan, A. S.

    2005-07-01

    The recovery of diodes with diffusion p- n junctions in the case of high reverse current density j is analyzed. A condition for quasi-neutrality breaking in the diffusion layers with allowance for the dependence of charge carrier mobility μ on electric field strength E is obtained that is valid for a wide range of j. The problem of formation of the space charge region in a circuit with inductance L and resistance R is reduced to a system of two ordinary differential equations. Approximation of a numerical solution to this system makes it possible to derive crude analytical relationships between interrupted current density {ie88-1}, circuit parameters, diode parameters, and parameters of a forming voltage pulse (with amplitude V m and pulse rise time t p). The limiting parameters of a pulser with an inductive energy storage and current interrupter based on diffusion diodes are studied. The critical density of interrupted current {ie88-2} is determined at which the field in the space charge region near the anode reaches breakdown value E b and intense impact ionization by holes begins. The impact ionization decreases the rates of current decay and voltage increase in the space charge region. As a result, at {ie88-3}, t p starts increasing and the overvoltage factor of the pulser decreases. The value of V m corresponding to {ie88-4} is roughly given by {ie88-5}, where m is the number of diodes in the interrupter, ɛ is the permittivity of the semiconductor, {ie88-6} is the saturated drift velocity of holes, and l p is the depth of the p- n junction (diffusion depth). Theoretical predictions are confirmed by exact numerical simulation of the recovery process and qualitatively agree with the available experimental data.

  9. Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03 As single crystals under hydrostatic pressure

    PubMed Central

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S. R.; Wang, A. F.; Dou, Shixue; Chen, X. H.

    2015-01-01

    Tremendous efforts towards improvement in the critical current density “Jc” of iron based superconductors (FeSCs), especially at relatively low temperatures and magnetic fields, have been made so far through different methods, resulting in real progress. Jc at high temperatures in high fields still needs to be further improved, however, in order to meet the requirements of practical applications. Here, we demonstrate a simple approach to achieve this. Hydrostatic pressure can significantly enhance Jc in NaFe0.97Co0.03As single crystals by at least tenfold at low field and more than a hundredfold at high fields. Significant enhancement in the in-field performance of NaFe0.97Co0.03As single crystal in terms of pinning force density (Fp) is found at high pressures. At high fields, the Fp is over 20 and 80 times higher than under ambient pressure at12 K and 14 K, respectively, at P = 1 GPa. We believe that the Co-doped NaFeAs compounds are very exciting and deserve to be more intensively investigated. Finally, it is worthwhile to say that by using hydrostatic pressure, we can achieve more milestones in terms of high Jc values in tapes, wires or films of other Fe-based superconductors. PMID:26030085

  10. Sedimentology and geomorphology of the deposits from the August 2006 pyroclastic density currents at Tungurahua volcano, Ecuador.

    PubMed

    Douillet, Guilhem Amin; Tsang-Hin-Sun, Ève; Kueppers, Ulrich; Letort, Jean; Pacheco, Daniel Alejandro; Goldstein, Fabian; Von Aulock, Felix; Lavallée, Yan; Hanson, Jonathan Bruce; Bustillos, Jorge; Robin, Claude; Ramón, Patricio; Hall, Minard; Dingwell, Donald B

    The deposits of the pyroclastic density currents from the August 2006 eruption of Tungurahua show three facies associations depending on the topographic setting: the massive, proximal cross-stratified, and distal cross-stratified facies. (1) The massive facies is confined to valleys on the slopes of the volcano. It contains clasts of >1 m diameter to fine ash material, is massive, and interpreted as deposited from dense pyroclastic flows. Its surface can exhibit lobes and levees covered with disk-shaped and vesicular large clasts. These fragile large clasts must have rafted at the surface of the flows all along the path in order to be preserved, and thus imply a sharp density boundary near the surface of these flows. (2) The proximal cross-stratified facies is exposed on valley overbanks on the upper part of the volcano and contains both massive coarse-grained layers and cross-stratified ash and lapilli bedsets. It is interpreted as deposited from (a) dense pyroclastic flows that overflowed the gentle ridges of valleys of the upper part of the volcano and (b) dilute pyroclastic density currents created from the dense flows by the entrainment of air on the steep upper flanks. (3) The distal cross-stratified facies outcrops as spatially limited, isolated, and wedge-shaped bodies of cross-stratified ash deposits located downstream of cliffs on valleys overbanks. It contains numerous aggrading dune bedforms, whose crest orientations reveal parental flow directions. A downstream decrease in the size of the dune bedforms, together with a downstream fining trend in the grain size distribution are observed on a 100-m scale. This facies is interpreted to have been deposited from dilute pyroclastic density currents with basal tractional boundary layers. We suggest that the parental flows were produced from the dense flows by entrainment of air at cliffs, and that these diluted currents might rapidly deposit through "pneumatic jumps". Three modes are present in the grain

  11. Current evolution and plasma density space distribution in the reflex discharge with ring cathodes

    NASA Astrophysics Data System (ADS)

    Samokhin, A. A.; Liziakin, G. D.; Gavrikov, A. V.; Usmanov, R. A.; Smirnov, V. P.

    2016-11-01

    In this paper the numerical model of direct current gas discharge in drift-diffusion approximation is considered. For two-component plasma the processes of the gas discharge development in the reflex geometry with ring cathodes at a helium pressure of 35 mTorr are studied. We investigate the influence of: (a) the boundary conditions on the dielectric, (b) the electron temperature and (c) the coefficient of the secondary ion-electron emission on the I-U curve of the discharge. In a magnetic field of 50 Gauss the impact of the discharge voltage U = 300-700 V on the evolutionary process of the discharge is examined. The effect of diffusion on maintaining steady state discharge is researched. The parameters of the existence of a high-current (tens of μA) and low voltage (tens of mA) discharge modes are defined.

  12. Current Density Limitations in a Fast-Pulsed High-Voltage Diode

    DTIC Science & Technology

    1992-06-01

    based on mass x acceleration - charge x E-field) - - -= qT (x)=-e rT(X) (19) dt M c M c where y ,ŕ /•/ 2/c ••V/c; t * time (S) e I electron charge I... Plasmaphysik IPP 4/250, September 1991. 6. Parker, R.K., Explosive Electron Emission and the Characteristics of High-Current Electron Flow, Air Force

  13. Evaluation of Plume Divergence and Facility Effects on Far-Field Faraday Probe Current Density Profiles

    DTIC Science & Technology

    2009-09-01

    elevated background pressure, compared nude Faraday probe designs, and evaluated design modifications to minimize uncertainty due to charge exchange...evaluated Faraday probe design and facility background pressure on collected ion current. A comparison of two nude Faraday probe designs concluded...140.5 Plasma potential in the region surrounding a nude Faraday probe has been measured to study the possibility of probe bias voltage acting as a

  14. Particle pressure, inertial force and ring current density in the magnetosphere of Saturn

    NASA Astrophysics Data System (ADS)

    Sergis, Nick; Krimigis, Stamatios; Arridge, Christopher; Roelof, Edmond; Rymer, Abigail; Mitchell, Donald; Thomsen, Michelle; Kivelson, Margaret; Ramer, Kate; Hamilton, Douglas; Krupp, Norbert; Dougherty, Michele; Coates, Andrew; Young, David

    2010-05-01

    We present the most recent radial profiles for the thermal plasma, energetic particle and magnetic field pressures in the equatorial magnetosphere of Saturn, as measured by the MIMI, CAPS and MAG instruments of Cassini, currently orbiting Saturn. Data were obtained between September 2005 and May 2006, when the spacecraft was particularly close (±0.5 RS) to the nominal magnetic equator in the range 6 to 15 RS. The radial gradient of the total pressure is compared to the inertial body force and an average radial profile of the azimuthal current intensity is presented. The results show that: (1) The suprathermal (keV) pressure contribution to the total particle pressure becomes significant outside 8-9 RS, exceeding 50% for r>12 RS. (2) The plasma beta remains above 1 outside 8 RS, reaching ~3 to ~10 between 11 and 14 RS. (3) The inertial body force and the radial pressure gradient are similar at 9-10 RS, with the pressure gradient prevailing beyond 11 RS. (4) The ring current develops a maximum between ~8 and 12 RS, reaching values of 100-150 pA/m2, and is primarily inertial inside of 8.5 RS but increasingly pressure gradient-driven in its maximum region and beyond. Farther away, it drops with radial distance much faster than the 1/r rate that several disk current models assume. The distribution of various plasma and energetic particle parameters in SLS phase is also examined in connection with the observed periodicity in the radial and azimuthal components of the magnetic field.

  15. Non-invasive probe diagnostic method for electron temperature and ion current density in atmospheric pressure plasma jet source

    SciTech Connect

    Kim, Young-Cheol; Kim, Yu-Sin; Lee, Hyo-Chang; Moon, Jun-Hyeon; Chung, Chin-Wook; Kim, Yunjung; Cho, Guangsup

    2015-08-15

    The electrical probe diagnostics are very hard to be applied to atmospheric plasmas due to severe perturbation by the electrical probes. To overcome this, the probe for measuring electron temperature and ion current density is indirectly contacted with an atmospheric jet source. The plasma parameters are obtained by using floating harmonic analysis. The probe is mounted on the quartz tube that surrounds plasma. When a sinusoidal voltage is applied to a probe contacting on a quartz tube, the electrons near the sheath at dielectric tube are collected and the probe current has harmonic components due to probe sheath nonlinearity. From the relation of the harmonic currents and amplitude of the sheath voltage, the electron temperature near the wall can be obtained with collisional sheath model. The electron temperatures and ion current densities measured at the discharge region are in the ranges of 2.7–3.4 eV and 1.7–5.2 mA/cm{sup 2} at various flow rates and input powers.

  16. Microstructure refinement and enhanced critical current density in binary doped SmFeAsO superconductor

    SciTech Connect

    Anooja, J. B.; Aswathy, P. M.; Varghese, Neson; Syamaprasad, U.; Aloysius, R. P.

    2014-04-24

    The iron-pnictide Sm{sub 1−x}Ca{sub x}FeAsO{sub 1−2x}F{sub 2x} superconductor was prepared and the combined effect of electron and hole doping was studied in detail. It is observed that the binary doping using CaF{sub 2} improves the microstructure tremendously with a preferred orientation of the (00l) planes. Moreover, a maximum T{sub C} of 53.8 K and a transport J{sub C} of 880 A/cm{sup 2} (12 K), which is double to that of the F-doped sample, are achieved. The dopant CaF{sub 2} seems to be a potential candidate for solving the grain-connectivity concerns in iron-pnictides paving the way towards conductor development.

  17. Microstructure refinement and enhanced critical current density in binary doped SmFeAsO superconductor

    NASA Astrophysics Data System (ADS)

    Anooja, J. B.; Aswathy, P. M.; Varghese, Neson; Aloysius, R. P.; Syamaprasad, U.

    2014-04-01

    The iron-pnictide Sm1-xCaxFeAsO1-2xF2x superconductor was prepared and the combined effect of electron and hole doping was studied in detail. It is observed that the binary doping using CaF2 improves the microstructure tremendously with a preferred orientation of the (00l) planes. Moreover, a maximum TC of 53.8 K and a transport JC of 880 A/cm2 (12 K), which is double to that of the F-doped sample, are achieved. The dopant CaF2 seems to be a potential candidate for solving the grain-connectivity concerns in iron-pnictides paving the way towards conductor development.

  18. InAs-based interband-cascade-lasers emitting around 7 μm with threshold current densities below 1 kA/cm{sup 2} at room temperature

    SciTech Connect

    Dallner, Matthias; Hau, Florian; Kamp, Martin; Höfling, Sven

    2015-01-26

    Interband cascade lasers (ICLs) grown on InAs substrates with threshold current densities below 1 kA/cm{sup 2} are presented. Two cascade designs with different lengths of the electron injector were investigated. Using a cascade design with 3 InAs quantum wells (QWs) in the electron injector, a device incorporating 22 stages in the active region exhibited a threshold current density of 940 A/cm{sup 2} at a record wavelength of 7 μm for ICLs operating in pulsed mode at room temperature. By investigating the influence of the number of stages on the device performance for a cascade design with 2 QWs in the electron injector, a further reduction of the threshold current density to 800 A/cm{sup 2} was achieved for a 30 stage device.

  19. Quantifying entrainment in pyroclastic density currents from the Tungurahua eruption, Ecuador: Integrating field proxies with numerical simulations

    NASA Astrophysics Data System (ADS)

    Benage, M. C.; Dufek, J.; Mothes, P. A.

    2016-07-01

    The entrainment of air into pyroclastic density currents (PDCs) impacts the dynamics and thermal history of these highly mobile currents. However, direct measurement of entrainment in PDCs is hampered due to hazardous conditions and opaqueness of these flows. We combine three-dimensional multiphase Eulerian-Eulerian-Lagrangian calculations with proxies of thermal conditions preserved in deposits to quantify air entrainment in PDCs at Tungurahua volcano, Ecuador. We conclude that small-volume PDCs develop a particle concentration gradient that results in disparate thermal characteristics for the concentrated bed load (>600 to ~800 K) and the overlying dilute suspended load (~300-600 K). The dilute suspended load has effective entrainment coefficients 2-3 times larger than the bed load. This investigation reveals a dich