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Sample records for air-earth current density

  1. Current interruption by density depression

    International Nuclear Information System (INIS)

    Wagner, J.S.; Tajima, T.; Akasofu, S.I.

    1985-04-01

    Using a one-dimensional electrostatic particle code, we examine processes associated with current interruption in a collisionless plasma when a density depression is present along the current channel. Current interruption due to double layers was suggested by Alfven and Carlqvist (1967) as a cause of solar flares. At a local density depression, plasma instabilities caused by an electron current flow are accentuated, leading to current disruption. Our simulation study encompasses a wide range of the parameters in such a way that under appropriate conditions, both the Alfven and Carlqvist (1967) regime and the Smith and Priest (1972) regime take place. In the latter regime the density depression decays into a stationary structure (''ion-acoustic layer'') which spawns a series of ion-acoustic ''solitons'' and ion phase space holes travelling upstream. A large inductance of the current circuit tends to enhance the plasma instabilities

  2. Critical current densities in superconducting materials

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Critical current density; superconducting materials; magnetic-field ... As current densities are raised to higher than JC the material does not go suddenly from the superconducting state to the normal resistive state, but develops a .... to the superconducting state with liquid nitrogen, but whose commercial exploitation has.

  3. Current density profile evolution in JET

    International Nuclear Information System (INIS)

    Stubberfield, P.M.; Balet, B.; Campbell, D.; Challis, C.D.; Cordey, J.G.; O'Rourke, J.; Hammett, G.; Schmidt, G.L.

    1989-01-01

    Simulation studies have been made of the current density profile evolution in discharges where the bootstrap current is expected to be significant. The changes predicted in the total current profile have been confirmed by comparison with experimental results. (author) 8 refs., 6 figs

  4. Current distribution tomography for determination of internal current density distributions

    International Nuclear Information System (INIS)

    Gailey, P.C.

    1993-01-01

    A method is presented for determination of current densities inside a cylindrical object using measurements of the magnetic fields outside the object. The cross section of the object is discretized with the current assumed constant over each defined region. Magnetic fields outside the object are related to the internal current densities through a geometry matrix which can be inverted to yield a solution for the current densities in terms of the measured fields. The primary limitation of this technique results from singularities in the geometry matrix that arise due to cylindrical symmetry of the problem. Methods for circumventing the singularities to obtain information about the distribution of current densities are discussed. This process of current distribution tomography is designed to determine internal body current densities using measurements of the external magnetic field distribution. It is non-invasive, and relatively simple to implement. Although related to a more general study of magnetic imaging which has been used to investigate endogenous currents in the brain and other parts of the body, it is restricted to currents either applied directly or induced by exposure to an external field. The research is related to public concern about the possibility of health effects resulting from exposure to power frequency electric and magnetic fields

  5. Critical current densities in superconducting materials

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    at this field value, and the net pinning force remains large. The pinning force prevents the motion of vortices until the Lorentz force(J×B)exceeds the pinning force FP . This defines a critical current density JC = FP /B below which transport current is carried without any resistance, and above which flux-flow resistivity sets in.

  6. Critical current densities in superconducting materials

    Indian Academy of Sciences (India)

    We discuss recent research in the area of critical current densities ( J C ) in superconductors. This shall cover recent work on newly discovered superconductors, as well as on the magnetic-field dependence of J C . Author Affiliations. P Chaddah1. Cryogenics and Superconductivity Section, Centre for Advanced Technology ...

  7. Surface current density K: an introduction

    DEFF Research Database (Denmark)

    McAllister, Iain Wilson

    1991-01-01

    The author discusses the vector surface of current density K used in electrical insulation studies. K is related to the vector tangential electric field Kt at the surface of a body by the vector equation K=ΓE t where Γ represents the surface conductivity. The author derives a surface continuity...

  8. Current drive in high density tokamak plasma

    International Nuclear Information System (INIS)

    Sakaguchi, Seiichiro; Jotaki, Eriko; Kawasaki, Shoji; Moriyama, Shin-ichi; Nagao, Akihiro; Nakamura, Kazuo; Nakamura, Yukio; Hiraki, Naoki; Itoh, Satoshi

    1989-01-01

    Current drive in high density tokamak plasma is investigated, with special attention given to mode conversion and proximity conditions that characterize the propagation of electromagnetic waves in the case of current drive by lower hybrid waves. A simple model is used to evaluate the current drive efficiency, and its dependence on various parameters associated with equipment is investigated to provide information required in designing experimental equipment. A strong troidal magnetic field is necessary to produce high density plasma, and incident electromagnetic waves should have a high frequency to prevent the mode conversion, suggesting that a high frequency and a strong troidal field are essential to permit desirable propagation of incident electromagnetic waves. The evaluation of the current drive efficiency shows that the proximity conditions and the power spectrum of the lower hybrid waves entering the plasma are of importance. The average refraction factor in the direction of the troidal field should be larger than but close to that determined from the proximity conditions in order to increase the drive efficiency. As the intensity of the troidal field increases, the refraction factor determined from the proximity conditions decreases, leading to an increase in the drive efficiency. (N.K.)

  9. Current density in radiation stimulated superconductors

    International Nuclear Information System (INIS)

    Wafelbakker, C.K.

    1977-01-01

    Eliashberg's theory of stimulated superconductivity is reviewed and discussed within the BCS-Mattis formalism for impure superconductors. Stimulation by microwaves as well as by acoustical fields is considered. Eliashberg's results are completed by obtaining the nonequilibrium current response to an applied transverse vector potential. The resulting expression may be used to obtain the critical current of small specimens. (Auth.)

  10. Fast wave current drive above the slow wave density limit

    International Nuclear Information System (INIS)

    McWilliams, R.; Sheehan, D.P.; Wolf, N.S.; Edrich, D.

    1989-01-01

    Fast wave and slow wave current drive near the mean gyrofrequency were compared in the Irvine Torus using distinct phased array antennae of similar principal wavelengths, frequencies, and input powers. The slow wave current drive density limit was measured for 50ω ci ≤ω≤500ω ci and found to agree with trends in tokamaks. Fast wave current drive was observed at densities up to the operating limit of the torus, demonstrably above the slow wave density limit

  11. Current Source Density Estimation for Single Neurons

    Directory of Open Access Journals (Sweden)

    Dorottya Cserpán

    2014-03-01

    Full Text Available Recent developments of multielectrode technology made it possible to measure the extracellular potential generated in the neural tissue with spatial precision on the order of tens of micrometers and on submillisecond time scale. Combining such measurements with imaging of single neurons within the studied tissue opens up new experimental possibilities for estimating distribution of current sources along a dendritic tree. In this work we show that if we are able to relate part of the recording of extracellular potential to a specific cell of known morphology we can estimate the spatiotemporal distribution of transmembrane currents along it. We present here an extension of the kernel CSD method (Potworowski et al., 2012 applicable in such case. We test it on several model neurons of progressively complicated morphologies from ball-and-stick to realistic, up to analysis of simulated neuron activity embedded in a substantial working network (Traub et al, 2005. We discuss the caveats and possibilities of this new approach.

  12. Electromagnetic considerations for RF current density imaging [MRI technique].

    Science.gov (United States)

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

    1995-01-01

    Radio frequency current density imaging (RF-CDI) is a recent MRI technique that can image a Larmor frequency current density component parallel to B(0). Because the feasibility of the technique was demonstrated only for homogeneous media, the authors' goal here is to clarify the electromagnetic assumptions and field theory to allow imaging RF currents in heterogeneous media. The complete RF field and current density imaging problem is posed. General solutions are given for measuring lab frame magnetic fields from the rotating frame magnetic field measurements. For the general case of elliptically polarized fields, in which current and magnetic field components are not in phase, one can obtain a modified single rotation approximation. Sufficient information exists to image the amplitude and phase of the RF current density parallel to B(0) if the partial derivative in the B(0) direction of the RF magnetic field (amplitude and phase) parallel to B(0) is much smaller than the corresponding current density component. The heterogeneous extension was verified by imaging conduction and displacement currents in a phantom containing saline and pure water compartments. Finally, the issues required to image eddy currents are presented. Eddy currents within a sample will distort both the transmitter coil reference system, and create measurable rotating frame magnetic fields. However, a three-dimensional electro-magnetic analysis will be required to determine how the reference system distortion affects computed eddy current images.

  13. Determining the Limiting Current Density of Vanadium Redox Flow Batteries

    Directory of Open Access Journals (Sweden)

    Jen-Yu Chen

    2014-09-01

    Full Text Available All-vanadium redox flow batteries (VRFBs are used as energy storage systems for intermittent renewable power sources. The performance of VRFBs depends on materials of key components and operating conditions, such as current density, electrolyte flow rate and electrolyte composition. Mass transfer overpotential is affected by the electrolyte flow rate and electrolyte composition, which is related to the limiting current density. In order to investigate the effect of operating conditions on mass transport overpotential, this study established a relationship between the limiting current density and operating conditions. First, electrolyte solutions with different states of charge were prepared and used for a single cell to obtain discharging polarization curves under various operating conditions. The experimental results were then analyzed and are discussed in this paper. Finally, this paper proposes a limiting current density as a function of operating conditions. The result helps predict the effect of operating condition on the cell performance in a mathematical model.

  14. Solid Oxide Electrolysis Cells: Degradation at High Current Densities

    DEFF Research Database (Denmark)

    Knibbe, Ruth; Traulsen, Marie Lund; Hauch, Anne

    2010-01-01

    The degradation of Ni/yttria-stabilized zirconia (YSZ)-based solid oxide electrolysis cells operated at high current densities was studied. The degradation was examined at 850°C, at current densities of −1.0, −1.5, and −2.0 A/cm2, with a 50:50 (H2O:H2) gas supplied to the Ni/YSZ hydrogen electrode...

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

    NARCIS (Netherlands)

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

    2005-01-01

    This paper describes the working principle of a DC magnetohydrodynamic (MHD) micropump that can be operated at high DC current densities (J) in 75-µm-deep microfluidic channels without introducing gas bubbles into the pumping channel. The main design feature for current generation is a micromachined

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

    NARCIS (Netherlands)

    Homsy, A; Koster, Sander; Eijkel, JCT; van den Berg, A; Lucklum, F; Verpoorte, E; de Rooij, NF

    2005-01-01

    This paper describes the working principle of a DC magnetohydrodynamic (MHD) micropump that can be operated at high DC current densities (J) in 75-mu m-deep microfluidic channels without introducing gas bubbles into the pumping channel. The main design feature for current generation is a

  17. Estimation of current density distribution under electrodes for external defibrillation

    Directory of Open Access Journals (Sweden)

    Papazov Sava P

    2002-12-01

    Full Text Available Abstract Background Transthoracic defibrillation is the most common life-saving technique for the restoration of the heart rhythm of cardiac arrest victims. The procedure requires adequate application of large electrodes on the patient chest, to ensure low-resistance electrical contact. The current density distribution under the electrodes is non-uniform, leading to muscle contraction and pain, or risks of burning. The recent introduction of automatic external defibrillators and even wearable defibrillators, presents new demanding requirements for the structure of electrodes. Method and Results Using the pseudo-elliptic differential equation of Laplace type with appropriate boundary conditions and applying finite element method modeling, electrodes of various shapes and structure were studied. The non-uniformity of the current density distribution was shown to be moderately improved by adding a low resistivity layer between the metal and tissue and by a ring around the electrode perimeter. The inclusion of openings in long-term wearable electrodes additionally disturbs the current density profile. However, a number of small-size perforations may result in acceptable current density distribution. Conclusion The current density distribution non-uniformity of circular electrodes is about 30% less than that of square-shaped electrodes. The use of an interface layer of intermediate resistivity, comparable to that of the underlying tissues, and a high-resistivity perimeter ring, can further improve the distribution. The inclusion of skin aeration openings disturbs the current paths, but an appropriate selection of number and size provides a reasonable compromise.

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

    International Nuclear Information System (INIS)

    Jay L. Hirshfield

    2005-01-01

    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

  19. Superconducting toroidal field coil current densities for the TFCX

    International Nuclear Information System (INIS)

    Kalsi, S.S.; Hooper, R.J.

    1985-04-01

    A major goal of the Tokamak Fusion Core Experiment (TFCX) study was to minimize the size of the device and achieve lowest cost. Two key factors influencing the size of the device employing superconducting magnets are toroidal field (TF) winding current density and its nuclear heat load withstand capability. Lower winding current density requires larger radial build of the winding pack. Likewise, lower allowable nuclear heating in the winding requires larger shield thickness between the plasma and coil. In order to achieve a low-cost device, it is essential to maximize the winding's current density and nuclear heating withhstand capability. To meet the above objective, the TFCX design specification adopted as goals a nominal winding current density of 3500 A/cm 2 with 10-T peak field at the winding and peak nuclear heat load limits of 1 MW/cm 3 for the nominal design and 50 MW/cm 3 for an advanced design. This study developed justification for these current density and nuclear heat load limits

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

    International Nuclear Information System (INIS)

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

    2012-01-01

    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 imaging

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

    Science.gov (United States)

    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. High-current discharge channel contraction in high density gas

    International Nuclear Information System (INIS)

    Rutberg, Ph. G.; Bogomaz, A. A.; Pinchuk, M. E.; Budin, A. V.; Leks, A. G.; Pozubenkov, A. A.

    2011-01-01

    Research results for discharges at current amplitudes of 0.5-1.6 MA and current rise rate of ∼10 10 A/s are presented. The discharge is performed in the hydrogen environment at the initial pressure of 5-35 MPa. Initiation is implemented by a wire explosion. The time length of the first half-period of the discharge current is 70-150 μs. Under such conditions, discharge channel contraction is observed; the contraction is followed by soft x-ray radiation. The phenomena are discussed, which are determined by high density of the gas surrounding the discharge channel. These phenomena are increase of the current critical value, where the channel contraction begins and growth of temperature in the axis region of the channel, where the initial density of the gas increases.

  3. Electron and current density measurements on tokamak plasmas

    International Nuclear Information System (INIS)

    Lammeren, A.C.A.P. van.

    1991-01-01

    The first part of this thesis describes the Thomson-scattering diagnostic as it was present at the TORTUR tokamak. For the first time with this diagnostic a complete tangential scattering spectrum was recorded during one single laser pulse. From this scattering spectrum the local current density was derived. Small deviations from the expected gaussian scattering spectrum were observed indicating the non-Maxwellian character of the electron-velocity distribution. The second part of this thesis describes the multi-channel interferometer/ polarimeter diagnostic which was constructed, build and operated on the Rijnhuizen Tokamak Project (RTP) tokamak. The diagnostic was operated routinely, yielding the development of the density profiles for every discharge. When ECRH (Electron Cyclotron Resonance Heating) is switched on the density profile broadens, the central density decreases and the total density increases, the opposite takes place when ECRH is switched off. The influence of MHD (magnetohydrodynamics) activity on the density was clearly observable. In the central region of the plasma it was measured that in hydrogen discharges the so-called sawtooth collapse is preceded by an m=1 instability which grows rapidly. An increase in radius of this m=1 mode of 1.5 cm just before the crash is observed. In hydrogen discharges the sawtooth induced density pulse shows an asymmetry for the high- and low-field side propagation. This asymmetry disappeared for helium discharges. From the location of the maximum density variations during an m=2 mode the position of the q=2 surface is derived. The density profiles are measured during the energy quench phase of a plasma disruption. A fast flattening and broadening of the density profile is observed. (author). 95 refs.; 66 figs.; 7 tabs

  4. Current density functional theory for optical spectra : A polarization functional

    NARCIS (Netherlands)

    Boeij, P.L. de; Kootstra, F.; Berger, J.A.; Leeuwen, R. van; Snijders, J.G.

    2001-01-01

    In this paper we present a new approach to calculate optical spectra, which for the first time uses a polarization dependent functional within current density functional theory (CDFT), which was proposed by Vignale and Kohn. This polarization dependent functional includes exchange-correlation (xc)

  5. Density currents as a desert dust mobilization mechanism

    Directory of Open Access Journals (Sweden)

    S. Solomos

    2012-11-01

    Full Text Available The formation and propagation of density currents are well studied processes in fluid dynamics with many applications in other science fields. In the atmosphere, density currents are usually meso-β/γ phenomena and are often associated with storm downdrafts. These storms are responsible for the formation of severe dust episodes (haboobs over desert areas. In the present study, the formation of a convective cool pool and the associated dust mobilization are examined for a representative event over the western part of Sahara desert. The physical processes involved in the mobilization of dust are described with the use of the integrated atmospheric-air quality RAMS/ICLAMS model. Dust is effectively produced due to the development of near surface vortices and increased turbulent mixing along the frontal line. Increased dust emissions and recirculation of the elevated particles inside the head of the density current result in the formation of a moving "dust wall". Transport of the dust particles in higher layers – outside of the density current – occurs mainly in three ways: (1 Uplifting of preexisting dust over the frontal line with the aid of the strong updraft (2 Entrainment at the upper part of the density current head due to turbulent mixing (3 Vertical mixing after the dilution of the system. The role of the dust in the associated convective cloud system was found to be limited. Proper representation of convective processes and dust mobilization requires the use of high resolution (cloud resolving model configuration and online parameterization of dust production. Haboob-type dust storms are effective dust sources and should be treated accordingly in dust modeling applications.

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

    DEFF Research Database (Denmark)

    Shore, R. M.; Whaler, K. A.; Macmillan, S.

    2013-01-01

    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...

  7. High current density aluminum stabilized conductor concepts for space applications

    International Nuclear Information System (INIS)

    Huang, X.; Eyssa, Y.M.; Hilal, M.A.

    1989-01-01

    Lightweight conductors are needed for space magnets to achieve values of E/M (energy stored per unit mass) comparable to the or higher than advanced batteries. High purity aluminum stabilized NbTi composite conductors cooled by 1.8 K helium can provide a winding current density up to 15 kA/cm/sup 2/ at fields up to 10 tesla. The conductors are edge cooled with enough surface area to provide recovery following a normalizing disturbance. The conductors are designed so that current diffusion time in the high purity aluminum is smaller than thermal diffusion time in helium. Conductor design, stability and current diffusion are considered in detail

  8. Current density profile inside q=1 on Tore Supra

    International Nuclear Information System (INIS)

    Joffrin, E.; Desgranges, C.; Sabot, R.; Dubois, M.A.

    1995-01-01

    The Tore Supra polarimeter used to measure the poloidal field distribution is described. The current density profiles are computed in two different ways using the interferometric and polarimetric data in conjunction with the magnetic data and the location of the inversion radius determined by the soft X-ray camera. The current density inside the q=1 surface is investigated for normal and monster sawteeth. Its variation are also measured by the polarimeter and compared with that predicted by the current diffusion equation assuming complete reconnection. Finally, the safety factor profile is compared with that obtained with the striation data of the pellet ablation. The results of the evolution of the q profile during sawteeth are in good agreement with those obtained in other devices. (author) 9 refs.; 4 figs

  9. High current density magnets for INTOR and TIBER

    International Nuclear Information System (INIS)

    Miller, J.R.; Henning, C.D.; Kerns, J.A.; Slack, D.S.; Summers, L.T.; Zbasnik, J.P.

    1986-12-01

    The adoption of high current density, high field, superconducting magnets for INTOR and TIBER would prove beneficial. When combined with improved radiation tolerance of the magnets to minimize the inner leg shielding, a substantial reduction in machine dimensions and capital costs can be achieved. Fortunately, cable-in-conduit conductors (CICC) which are capable of the desired enhancements are being developed. Because conductor stability in a CICC depends more on the trapped helium enthalpy, rather than the copper resistivity, higher current densities of the order of 40 A/mm 2 at 12 T are possible. Radiation damage to the copper stabilizer is less important because the growth in resistance is a second-order effect on stability. Such CICC conductors lend themselves naturally to niobium-tin utilization, with the benefits of the high current-sharing temperature of this material being taken to advantage in absorbing radiation heating. When the helium coolant is injected at near the critical pressure, Joule-Thompson expansion in the flow path tends to stabilize the fluid temperature at under 6 K. Thus, higher fields, as well as higher current densities, can be considered for INTOR or TIBER

  10. Numerical Simulation of Density Current Evolution in a Diverging Channel

    Directory of Open Access Journals (Sweden)

    Mitra Javan

    2012-01-01

    Full Text Available When a buoyant inflow of higher density enters a reservoir, it sinks below the ambient water and forms an underflow. Downstream of the plunge point, the flow becomes progressively diluted due to the fluid entrainment. This study seeks to explore the ability of 2D width-averaged unsteady Reynolds-averaged Navier-Stokes (RANS simulation approach for resolving density currents in an inclined diverging channel. 2D width-averaged unsteady RANS equations closed by a buoyancy-modified − turbulence model are integrated in time with a second-order fractional step approach coupled with a direct implicit method and discretized in space on a staggered mesh using a second-order accurate finite volume approach incorporating a high-resolution semi-Lagrangian technique for the convective terms. A series of 2D width-averaged unsteady simulations is carried out for density currents. Comparisons with the experimental measurements and the other numerical simulations show that the predictions of velocity and density field are with reasonable accuracy.

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

    Science.gov (United States)

    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.

  12. Vortex edge barriers and critical current density in granular superconductors

    CERN Document Server

    Belevtsov, L V

    2003-01-01

    Type-II superconductors, even without bulk pinning and in the absence of a macroscopic Bean-Livingston surface barrier for vortex penetration, can exhibit barriers for flux penetration. We investigated some new edge barriers based on the laminar model, that are governed by the anisotropy ratio, grain coupling strength, and grain size. Expressions describing the pinning potential U sub p and critical current density J sub c are derived for magnetic fields near H sub c sub 1. It is shown that edge barrier effects play a substantial role in a realistic description of the critical current density for both MgB sub 2 and high-T sub c superconductors. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

  13. Current density profile measurements in the Proto-Cleo Torsatron

    International Nuclear Information System (INIS)

    Schaeffer, R.C.; Shohet, J.L.

    1979-10-01

    Current density profile measurements were obtained in the Proto-Cleo Torsatron (R = 40 cm, a = 5 cm, l = 3, B/sub T/ = 3 kG, anti n approx. 10 11 cm -3 , T/sub e/ approx. 20 eV) by using a small, back-to-back flat double probe. Three different operating circuits used with this probe are presented, along with experimental results, all showing good agreement. Current is seen to flow only within the separatrix, in channels which follow the magnetic surfaces as they move radially inward with time due to changing vertical magnetic flux

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

    Science.gov (United States)

    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.

  15. Current density monitor for intense relativistic electron beams

    International Nuclear Information System (INIS)

    Fiorito, R.B.; Raleigh, M.; Seltzer, S.M.

    1986-01-01

    We describe a new type of electric probe which is capable of measuring the time-resolved current density profile of a stable, reproducible, high-energy (>4-MeV) high-current (>1-kA) electron beam. The sensing element of this probe is an open-ended but capped-off 50-Ω coaxial line constructed of graphite. The graphite sensor is 4.3 mm in diameter, 6 cm long, and is range thin to the primary beam electrons. The probe produces a signal proportional to the intercepted beam current. When the sensor is scanned radially through the beam during repeated pulses, a curve of signal versus depth of insertion is produced from which the radial current density profile can be determined. Measurements are presented of the profile of the electron beam from the Experimental Test Accelerator (4.5 MeV, 10 kA) at Lawrence Livermore National Laboratory. Good agreement is shown between measurements made with this probe and the beam radius as predicted by transport codes. The advantage of the electric probe lies in its ruggedness, simplicity, inherent fast rise time, and low cost. In contrast to other systems it requires no radiation shielding, water cooling, or auxiliary support equipment to operate in an intense beam environment

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

    Science.gov (United States)

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

    2014-05-01

    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.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

    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

  18. RF Current Density Measurements and Mode Coupling in Helicon Discharges

    Science.gov (United States)

    Madziwa, T. G.; Blackwell, D. D.; Arnush, D.; Chen, F. F.

    1999-10-01

    It has been suggested that the high RF power absorption efficiency in helicon discharges is due to the transfer of energy to electron cyclotron waves called Trivelpiece-Gould (TG) modes.(K. P. Shamrai, V. P. Pavlenko, and V. B. Taranov, Plasma Phys. Control. Fusion 39), 505 (1997). To test this theory, measurements have been performed using magnetic and current density probes to detect TG waves. The experiments are performed in a 10-cm diam chamber with B_circ=25-55 G, n=10^11-10^12 cm-3, p=3 mTorr of argon, and P_rf=0.2-1 kW at 11 MHz. A two-turn m=0 antenna is used to excite the helicon wave plasma. Measurements are compared with a numerical code developed by Arnush and Chen(D. Arnush and F. F. Chen, Phys. Plasmas 5), 1239 (1998). which calculates the wave profiles given the antenna geometry, plasma density profile, and neutral pressure. The results show that, as predicted by theory, the RF current density is strongly influenced by the TG mode, causing broadening and ripples in the profile, while the magnetic field is influenced to a lesser extent.

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

    International Nuclear Information System (INIS)

    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 ∼ 20 T toroidal field magnet with a flat top conductor current of ∼ 300 kA and a sliding electrical joint with a gross current density of ∼ 0.6 kA/cm 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

  20. The dynamics of pyroclastic density currents on Mars

    Science.gov (United States)

    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

  1. Computation of superconductor critical current densities and magnetization curves

    International Nuclear Information System (INIS)

    Hodgdon, M.L.

    1991-01-01

    Using a constitutive law for superconductor hysteresis and the ideas of the critical state model, a system of equations is developed for the critical current density J c , the equilibrium magnetization M e , the upper and lower portions M U and M L of the major hysteresis loop, and their derivatives with respect to the applied field. The constitutive law consists of the differential equation dB/dH=α(H)s(H)[f(H)-B]+g(H) for H≠0, and a rule governing the abrupt changes observed at the turning points of H. For the case presented here in which f, g, and α have analytic forms, the constitutive law yields an easily differentiable expression for the major loop. Hysteresis curves computed from this constitutive law are shown to be in good agreement with experiments. Exponential approximations are given for the critical current densities computed by this method for a polycrystalline sample of YBa 2 Cu 3 O x between 5 and 40 K

  2. Online diagnoses of high current-density beams

    International Nuclear Information System (INIS)

    Gilpatrick, J.D.

    1994-01-01

    Los Alamos National Laboratory has proposed several CW-proton-beam facilities for production of tritium or transmutation of nuclear waste with beam-current densities greater than 5 mA/mm 2 . The primary beam-diagnostics-instrumentation requirement for these facilities is provision of sufficient beam information to understand and minimize beam-loss. To accomplish this task, the beam-diagnostics instrumentation must measure beam parameters such as the centroids and profiles, total integrated current, and particle loss. Noninterceptive techniques must be used for diagnosis of high-intensity CW beam at low energies due to the large quantity of power deposited in an interceptive diagnostic device by the beam. Transverse and longitudinal centroid measurements have been developed for bunched beams by measuring and processing image currents on the accelerator walls. Transverse beam-profile measurement-techniques have also been developed using the interaction of the particle beam with the background gases near the beam region. This paper will discuss these noninterceptive diagnostic Techniques

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

    Science.gov (United States)

    Wang, Qi [Littleton, CO

    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.

  4. Critical current densities in Bi-2223 sinter forgings.

    Energy Technology Data Exchange (ETDEWEB)

    Balachandran, U.; Fisher, B. L.; Goretta, K. C.; Harris, N. C.; Murayama, N.

    1999-07-23

    (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) bars, prepared by sinter forging, exhibited good phase purity and strong textures with the c axes of the Bi-2223 grains parallel to the forging direction. The initial zero-field critical current density (J{sub c}) of the bars was 10{sup 3} A/cm{sup 2}, but because the forged bars were uncoated, this value decreased with repeated thermal cycling. J{sub c} as a function of applied magnetic field magnitude and direction roughly followed the dependencies exhibited by Ag-sheathed Bi-2223 tapes, but the forged bars were more strongly dependent on field strength and less strongly dependent on field angle.

  5. Development of high temperature superconductors having high critical current density

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Gye Wong; Kim, C. J.; Lee, H.G.; Kwon, S. C.; Lee, H. J.; Kim, K. B.; Park, J. Y.; Jung, C. H

    2000-08-01

    Fabrication of high T{sub c} superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm{sup 2} and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation.

  6. A distributed current stimulator ASIC for high density neural stimulation.

    Science.gov (United States)

    Jeong Hoan Park; Chaebin Kim; Seung-Hee Ahn; Tae Mok Gwon; Joonsoo Jeong; Sang Beom Jun; Sung June Kim

    2016-08-01

    This paper presents a novel distributed neural stimulator scheme. Instead of a single stimulator ASIC in the package, multiple ASICs are embedded at each electrode site for stimulation with a high density electrode array. This distributed architecture enables the simplification of wiring between electrodes and stimulator ASIC that otherwise could become too complex as the number of electrode increases. The individual ASIC chip is designed to have a shared data bus that independently controls multiple stimulating channels. Therefore, the number of metal lines is determined by the distributed ASICs, not by the channel number. The function of current steering is also implemented within each ASIC in order to increase the effective number of channels via pseudo channel stimulation. Therefore, the chip area can be used more efficiently. The designed chip was fabricated with area of 0.3 mm2 using 0.18 μm BCDMOS process, and the bench-top test was also conducted to validate chip performance.

  7. Comparison of exact-exchange calculations for solids in current-spin-density- and spin-density-functional theory

    DEFF Research Database (Denmark)

    Sharma, S.; Pittalis, S.; Kurth, S.

    2007-01-01

    The relative merits of current-spin-density- and spin-density-functional theory are investigated for solids treated within the exact-exchange-only approximation. Spin-orbit splittings and orbital magnetic moments are determined at zero external magnetic field. We find that for magnetic (Fe, Co......, and Ni) and nonmagnetic (Si and Ge) solids, the exact-exchange current-spin-density functional approach does not significantly improve the accuracy of the corresponding spin-density functional results....

  8. Orbital functionals in density-matrix- and current-density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Helbig, N.

    2006-05-15

    Density-Functional Theory (DFT), although widely used and very successful in the calculation of several observables, fails to correctly describe strongly correlated materials. In the first part of this work we, therefore, introduce reduced-densitymatrix- functional theory (RDMFT) which is one possible way to treat electron correlation beyond DFT. Within this theory the one-body reduced density matrix (1- RDM) is used as the basic variable. Our main interest is the calculation of the fundamental gap which proves very problematic within DFT. In order to calculate the fundamental gap we generalize RDMFT to fractional particle numbers M by describing the system as an ensemble of an N and an N+1 particle system (with N{<=}M{<=}N+1). For each fixed particle number, M, the total energy is minimized with respect to the natural orbitals and their occupation numbers. This leads to the total energy as a function of M. The derivative of this function with respect to the particle number has a discontinuity at integer particle number which is identical to the gap. In addition, we investigate the necessary and sufficient conditions for the 1- RDM of a system with fractional particle number to be N-representable. Numerical results are presented for alkali atoms, small molecules, and periodic systems. Another problem within DFT is the description of non-relativistic many-electron systems in the presence of magnetic fields. It requires the paramagnetic current density and the spin magnetization to be used as basic variables besides the electron density. However, electron-gas-based functionals of current-spin-density-functional Theory (CSDFT) exhibit derivative discontinuities as a function of the magnetic field whenever a new Landau level is occupied, which makes them difficult to use in practice. Since the appearance of Landau levels is, intrinsically, an orbital effect it is appealing to use orbital-dependent functionals. We have developed a CSDFT version of the optimized

  9. Differential modulation of corticospinal excitability by different current densities of anodal transcranial direct current stimulation.

    Directory of Open Access Journals (Sweden)

    Andisheh Bastani

    Full Text Available 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/cm(2 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 cm(2 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/cm(2 and 0.029 mA/cm(2 (P = 0.003. There were no significant differences between excitability changes for the 0.013 mA/cm(2 and 0.058 mA/cm(2 (P = 0.080 or 0.013 mA/cm(2 and 0.083 mA/cm(2 (P = 0.484 conditions. CONCLUSION: This study found that a-tDCS with a current density of 0.013 mA/cm(2 induces significantly larger corticospinal excitability changes than CDs of 0.029 mA/cm(2. The implication is that might help to avoid applying unwanted amount of current to the cortical areas.

  10. Comparison of current density profiles based on particle orbit-driven current in steady-state plasma on QUEST

    Energy Technology Data Exchange (ETDEWEB)

    Alam, Md Mahbub, E-mail: m.alam@triam.kyushu-u.ac.jp [IGSES, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580 (Japan); Nakamura, Kazuo [RIAM, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580 (Japan); Xia, Fan [CFS, SWIP, P.O. Box 432, 610041 Chengdu (China); Mitarai, Osamu [Tokai University, Kumamoto 862-8652 (Japan); Hasegawa, Makoto; Tokunaga, Kazutoshi; Araki, Kuniaki; Zushi, Hideki; Hanada, Kazuaki; Fujisawa, Akihide; Idei, Hiroshi; Nagashima, Yoshihiko; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki; Nagata, Takahiro [RIAM, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580 (Japan)

    2016-11-01

    Highlights: • Electron cyclotron resonance heating (ECRH) of QUEST. • Particle guiding center orbit calculation. • Orbit-driven current density profile. • Hollow current density. • Equilibrium condition for steady-state operation of QUEST. - Abstract: In the present RF-driven divertor plasma of QUEST, it has been observed that orbit-driven current flows in the open magnetic surfaces outside of the closed magnetic surfaces. To observe this phenomenon and the characteristics of the orbit-driven current, current density profiles have been calculated on two different equilibrium conditions. We calculated current density profiles from particle guiding center orbits both for the fundamental and the second harmonic resonances for the 8.2 GHz electron cyclotron current drive. From this calculation, hollow current density profiles have been obtained with significant characteristics on both conditions. Only positive current distribution has been observed in the open magnetic surfaces outside of the closed magnetic surfaces.

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

    Directory of Open Access Journals (Sweden)

    Stone J. R.

    2015-01-01

    Full Text Available 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.

  12. Valley current characterization of high current density resonant tunnelling diodes for terahertz-wave applications

    Science.gov (United States)

    Jacobs, K. J. P.; Stevens, B. J.; Baba, R.; Wada, O.; Mukai, T.; Hogg, R. A.

    2017-10-01

    We report valley current characterisation of high current density InGaAs/AlAs/InP resonant tunnelling diodes (RTDs) grown by metal-organic vapour phase epitaxy (MOVPE) for THz emission, with a view to investigate the origin of the valley current and optimize device performance. By applying a dual-pass fabrication technique, we are able to measure the RTD I-V characteristic for different perimeter/area ratios, which uniquely allows us to investigate the contribution of leakage current to the valley current and its effect on the PVCR from a single device. Temperature dependent (20 - 300 K) characteristics for a device are critically analysed and the effect of temperature on the maximum extractable power (PMAX) and the negative differential conductance (NDC) of the device is investigated. By performing theoretical modelling, we are able to explore the effect of typical variations in structural composition during the growth process on the tunnelling properties of the device, and hence the device performance.

  13. Current density profile control by programming of gas puffing and plasma current waveform in the JIPPT-II tokamak

    International Nuclear Information System (INIS)

    Toi, K.; Itoh, S.; Kadota, K.; Kawahata, K.; Noda, N.

    1979-03-01

    In the resistive shell tokamak, JIPP T-II, the current density profile control is carried out by pre-programming of both gas puffing and plasma current waveform. The major disruptions are completely suppressed by the method and a high density tokamak plasma with low q(a) is obtained with better MHD stability, where the line-average electron density n sub(e) 13 cm -3 and safety factor at plasma surface q(a) >= 2.2. The control criterion that the current density profile is successfully controlled is derived as a function of the ratio of plasma current to the electron density I sub(p)/n sub(e) in the current rising phase, i.e., 20 x 10 -13 -13 kA.cm 3 . (author)

  14. Evidence for intrinsic critical current density in high Tc superconductors

    International Nuclear Information System (INIS)

    Freltoft, T.; Minnhagen, P.; Jeldtoft Jensen, H.

    1991-01-01

    We present measurements of the voltage-current characteristics of high quality epitaxial YBaCuO films in zero magnetic field. According to the predictions of a current induced vortex pair breaking picture the voltage should follow the functional form V∝I(I-I c ) a-1 . An analysis designed to test this functional behavior is carried out. Consistency is found. (orig.)

  15. Lower hybrid current drive for edge current density modification in DIII-D: Final status report

    Energy Technology Data Exchange (ETDEWEB)

    Fenstermacher, M.E. [Lawrence Livermore National Lab., CA (United States); Porkolab, M. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center

    1993-08-04

    Application of Lower Hybrid (LH) Current Drive (CD) in the DIII-D tokamak has been studied at LLNL, off and on, for several years. The latest effort began in February 1992 in response to a letter from ASDEX indicating that the 2.45 GHz, 3 MW system there was available to be used on another device. An initial assessment of the possible uses for such a system on DIII-D was made and documented in September 1992. Multiple meetings with GA personnel and members of the LH community nationwide have occurred since that time. The work continued through the submission of the 1995 Field Work Proposals in March 1993 and was then put on hold due to budget limitations. The purpose of this document is to record the status of the work in such a way that it could fairly easily be restarted at a future date. This document will take the form of a collection of Appendices giving both background and the latest results from the FY 1993 work, connected by brief descriptive text. Section 2 will describe the final workshop on LHCD in DIII-D held at GA in February 1993. This was an open meeting with attendees from GA, LLNL, MIT and PPPL. Summary documents from the meeting and subsequent papers describing the results will be included in Appendices. Section 3 will describe the status of work on the use of low frequency (2.45 GHZ) LH power and Parametric Decay Instabilities (PDI) for the special case of high dielectric in the edge regions of the DIII-D plasma. This was one of the critical issues identified at the workshop. Other potential issues for LHCD in the DIII-D scenarios are: (1) damping of the waves on fast ions from neutral beam injection, (2) runaway electrons in the low density edge plasma, (3) the validity of the WKB approximation used in the ray-tracing models in the steep edge density gradients.

  16. CdS-metal contact at higher current densities.

    Science.gov (United States)

    Stirn, R. J.; Boeer, K. W.; Dussel, G. A.

    1973-01-01

    An investigation is conducted concerning the mechanisms by which a steady flow of current proceeds through the contact when an external voltage is applied. The main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons. A high-field domain analysis is conducted together with experimental studies. Particular attention is given to the range in which tunneling predominates.

  17. Critical current density for spin transfer torque switching with composite free layer structure

    OpenAIRE

    You, Chun-Yeol

    2009-01-01

    Critical current density of composite free layer (CFL) in magnetic tunneling junction is investigated. CFL consists of two exchange coupled ferromagnetic layers, where the coupling is parallel or anti-parallel. Instability condition of the CFL under the spin transfer torque, which is related with critical current density, is obtained by analytic spin wave excitation model and confirmed by macro-spin Landau-Lifshitz-Gilbert equation. The critical current densities for the coupled two identical...

  18. Effects of electrolyte concentration and current density on the ...

    Indian Academy of Sciences (India)

    The results show that upon increasing the concentration of FeCl 2 , initially the Fe content of the coating increased and then tended to be stable; the deposition rate and microhardness of coating decreased when the cathodic current efficiency ( η ) initially increased and then decreased; and for a FeCl 2 concentration of 3.6 ...

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

    International Nuclear Information System (INIS)

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

    2006-01-01

    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

  20. High current densities in superconducting films from magnetization

    International Nuclear Information System (INIS)

    McGuire, T.R.; Gupta, A.; Koren, G.; Gross, R.

    1990-01-01

    Epitaxial thin films of YBa 2 Cu 3 O 7-x made by laser ablation have the CuO planes parallel to the film surface. In the CuO planes critical currents of J C ∼40 x 10 6 amps/cm 2 are found at 5K in zero field. Multi-layered films with Gd replacing Y each .01μm in thickness have J C nearly 140 x 10 6 amps/cm 2 . This higher value is perhaps due to additional point defects. Perpendicular to the CuO planes magnetization studies indicate strong pinning effects attributed to the CuO planes acting as barriers to flux motion

  1. Density-Driven Currents and Deposition of Fine Materials

    DEFF Research Database (Denmark)

    Saremi, Sina

    . Dredging activities always make changes to the environment, such as alteration of the coastal or river morphology, currents and wave climates, and water quality. Such changes may be considered improving or degrading to the environment. The type of material being dredged, type of the dredging equipment...... and type of sediments change along and into the seabed. Variations in the material entering the hopper have been studied by assuming fluctuating inflow concentrations. The fluctuations impose a mean net change on the overflow concentrations. In the third part of this study, the above described CFD model......Dredging is a key element in river, ports, coastal and offshore development. In general dredging is conducted for excavation at the river,lake or seabed, relocation of the material, maintenance of the navigation channels, mining underwater deposits, land reclamation or cleaning up the environment...

  2. Evaluation of current densities and total contact currents in occupational exposure at 400 kV substations and power lines.

    Science.gov (United States)

    Korpinen, Leena H; Elovaara, Jarmo A; Kuisti, Harri A

    2009-04-01

    This investigation studied the current densities in the neck and total contact currents in occupational exposure at 400 kV substations and power lines. Eight voluntary workers simulated their normal work tasks using the helmet-mask measuring system. In all, 151 work tasks with induced current measurements were made. Work situations were: tasks in 400 kV substations, tasks in 400-110 kV towers and the cutting of vegetation under 400 kV power lines. The average current density in the neck was estimated from the current induced in the helmet. The calculated maximum average current densities in the neck varied from 1.5 to 6.4 mA/m(2) and the maximum total contact currents from 66.8 to 458.4 microA. The study shows that the maximum average current densities and the total contact currents (caused by electric field) in occupational exposure at 400 kV substations and power lines does not exceed the limit and action values (10 mA/m(2) and 1 mA) of the new EU-directive 2004/40/EC (live-line bare-hand works excluded). (c) 2009 Wiley-Liss, Inc.

  3. In vivo mapping of current density distribution in brain tissues during deep brain stimulation (DBS

    Directory of Open Access Journals (Sweden)

    Saurav Z. K. Sajib

    2017-01-01

    Full Text Available New methods for in vivo mapping of brain responses during deep brain stimulation (DBS are indispensable to secure clinical applications. Assessment of current density distribution, induced by internally injected currents, may provide an alternative method for understanding the therapeutic effects of electrical stimulation. The current flow and pathway are affected by internal conductivity, and can be imaged using magnetic resonance-based conductivity imaging methods. Magnetic resonance electrical impedance tomography (MREIT is an imaging method that can enable highly resolved mapping of electromagnetic tissue properties such as current density and conductivity of living tissues. In the current study, we experimentally imaged current density distribution of in vivo canine brains by applying MREIT to electrical stimulation. The current density maps of three canine brains were calculated from the measured magnetic flux density data. The absolute current density values of brain tissues, including gray matter, white matter, and cerebrospinal fluid were compared to assess the active regions during DBS. The resulting current density in different tissue types may provide useful information about current pathways and volume activation for adjusting surgical planning and understanding the therapeutic effects of DBS.

  4. In vivo mapping of current density distribution in brain tissues during deep brain stimulation (DBS)

    Science.gov (United States)

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

    2017-01-01

    New methods for in vivo mapping of brain responses during deep brain stimulation (DBS) are indispensable to secure clinical applications. Assessment of current density distribution, induced by internally injected currents, may provide an alternative method for understanding the therapeutic effects of electrical stimulation. The current flow and pathway are affected by internal conductivity, and can be imaged using magnetic resonance-based conductivity imaging methods. Magnetic resonance electrical impedance tomography (MREIT) is an imaging method that can enable highly resolved mapping of electromagnetic tissue properties such as current density and conductivity of living tissues. In the current study, we experimentally imaged current density distribution of in vivo canine brains by applying MREIT to electrical stimulation. The current density maps of three canine brains were calculated from the measured magnetic flux density data. The absolute current density values of brain tissues, including gray matter, white matter, and cerebrospinal fluid were compared to assess the active regions during DBS. The resulting current density in different tissue types may provide useful information about current pathways and volume activation for adjusting surgical planning and understanding the therapeutic effects of DBS.

  5. Inertial electron instability of current-carrying low-density plasma

    International Nuclear Information System (INIS)

    Basova, S.V.; Varentsova, S.A.; Gordeev, A.V.; Gulin, A.V.; Shuvaev, V.Yu.

    1991-01-01

    Current-carrying low-density plasma instability is investigated taking into account electron inertia at stationary ions. By analytic and numeric methods it is shown that in a constant density plasma the instability occurs under condition that the value H-tilde=H+(m e c/e)dv/dr, where H is the magnetic field, v - electron current velocity, changes the sign as the function of coordinate. Numeric calculations allowed to derive the increments for specific current configurations

  6. Technique of Critical Current Density Measurement of Bulk Superconductor with Linear Extrapolation Method

    International Nuclear Information System (INIS)

    Adi, Wisnu Ari; Sukirman, Engkir; Winatapura, Didin S.

    2000-01-01

    Technique of critical current density measurement (Jc) of HTc bulk ceramic superconductor has been performed by using linear extrapolation with four-point probes method. The measurement of critical current density HTc bulk ceramic superconductor usually causes damage in contact resistance. In order to decrease this damage factor, we introduce extrapolation method. The extrapolating data show that the critical current density Jc for YBCO (123) and BSCCO (2212) at 77 K are 10,85(6) Amp.cm - 2 and 14,46(6) Amp.cm - 2, respectively. This technique is easier, simpler, and the use of the current flow is low, so it will not damage the contact resistance of the sample. We expect that the method can give a better solution for bulk superconductor application. Key words. : superconductor, critical temperature, and critical current density

  7. The actual current density of gas-evolving electrodes—Notes on the bubble coverage

    International Nuclear Information System (INIS)

    Vogt, H.

    2012-01-01

    All investigations of electrochemical reactors with gas-evolving electrodes must take account of the fact that the actual current density controlling cell operation commonly differs substantially from the nominal current density used for practical purposes. Both quantities are interrelated by the fractional bubble coverage. This parameter is shown to be affected by a large number of operational quantities. However, available relationships of the bubble coverage take account only of the nominal current density. A further essential insufficiency is their inconsistency with reality for very large values of the bubble coverage being of relevance for operation conditions leading to anode effects. An improved relationship applicable to the total range is proposed.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kato, S.; Seya, A. [Fuji Electric Co., Ltd., Ichihara-shi (Japan); Asano, A. [Fuji Electric Corporate, Ltd., Yokosuka-shi (Japan)

    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.

  9. Critical current density of domain wall oscillation due to spin-transfer torque

    Energy Technology Data Exchange (ETDEWEB)

    Taniguchi, T; Imamura, H, E-mail: tomohiro-taniguchi@aist.go.jp, E-mail: h-imamura@aist.go.jp [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

    2011-04-01

    The domain wall oscillation due to spin-transfer torque was studied by numerically solving the Landau-Lifshitz-Gilbert (LLG) equation. For a domain wall whose rotation angle {theta}{sub max} is less than 180{sup 0}, we found the existence of the critical current density above which the magnetization dynamics are induced. We studied the dependence of the critical current density on the rotation angle {theta}{sub max} and found that the critical current density is proportional to 180{sup 0} - {theta}{sub max}.

  10. Simulations of current density profile control using lower hybrid current drive in the TdeV tokamak

    International Nuclear Information System (INIS)

    Fuchs, V.; Bonoli, P.T.; Shkarofsky, I.P.; Cote, A.; Demers, Y.; Janicki, C.

    1995-01-01

    The physics basis of a simulation model for lower hybrid current drive (LHCD) is discussed. Issues associated with LH power deposition - wave propagation, mode conversion and cut-offs in toroidal geometry, as well as linear and quasi-linear Landau damping - are analysed. A simulation model (ACCOME) is applied to the LHCD experiment now operating on the Tokamak de Varennes (TdeV). The profiles and values of density and temperature needed as inputs to ACCOME are taken from the experiment. The predictions of current density and loop voltage from ACCOME are then compared with experimental LHCD results. Possible LH current profile control experiments are also analysed for TdeV using composite LH spectra to control the location of RF power deposition. Finally, the relevance of these current profile control results to future devices is discussed and an example is shown for ITER-like parameters. (author). 44 refs, 15 figs, 4 tabs

  11. Effect of coating current density on the wettability of electrodeposited copper thin film on aluminum substrate

    Directory of Open Access Journals (Sweden)

    Arun Augustin

    2016-09-01

    Full Text Available Copper is the only one solid metal registered by the US Environmental Protection Agency as an antimicrobial touch surface. In touch surface applications, wettability of the surface has high significance. The killing rate of the harmful microbes depends on the wetting of pathogenic solution. Compared to the bulk copper, coated one on aluminum has the advantage of economic competitiveness and the possibility of manufacturing complex shapes. In the present work, the copper coating on the aluminum surface has successfully carried out by electrodeposition using non cyanide alkaline bath. To ensure good adhesion strength, the substrate has been pre-zincated prior to copper deposition. The coating current density is one of the important parameters which determine the nucleation density of the copper on the substrate. To understand the effect of current density on wettability, the coating has done at different current densities in the range of 3 A dm−2 to 9 A dm−2 for fixed time interval. The grain size has been measured from TEM micrographs and showed that as current density increases, grain size reduces from 62 nm to 35 nm. Since the grain size reduces, grain boundary volume has increases. As a result the value of strain energy (calculated by Williamson–Hall method has increased. The density of nodular morphology observed in SEM analysis has been increased with coating current density. Further, wettability studies with respect to double distilled water on the electrodeposited copper coatings which are coated at different current densities are carried out. At higher current density the coating is more wettable by water because at these conditions grain size of the coating decreases and morphology of grain changes to a favorable dense nodularity.

  12. Effect of via depth on the TSV filling process for different current densities

    Science.gov (United States)

    Wang, Feng; Zhao, Zhipeng; Nie, Nantian; Wang, Fuliang; Zhu, Wenhui

    2018-04-01

    Through-silicon-via (TSV) filling with optimum electrodeposition parameters is still a challenge in the industry, especially for via with different depths. Herein, the effects of via depth on optimum current density and filling patterns were investigated. It was found that the deeper the via, the lower the optimum current density. At low current density (4 mA cm-2), the via depth only affects the size of the defect, but does not change the filling pattern. However, at medium current density (7 mA cm-2), the filling pattern changes from super-conformal filling to sub-conformal filling with the increase of via depth, the pinch-off position remaining constant at a depth of about 70 µm from the top surface. Simulations of the TSV filling process using COMSOL modeling software revealed that the local concentration of additives, which is affected by the via depth, determine the morphology of the electrodeposition, matching well the experimental results.

  13. Preparation and characterization of high-Tc superconducting thin films with high critical current densities

    International Nuclear Information System (INIS)

    Vase, P.

    1991-08-01

    The project was carried out in relation to possible cable and electronics applications of high-T c materials. Laser ablation was used as the deposition technique because of its stoichiometry conservation. Films were made in the YBa 2 Cu 3 O 7 compound due to its relatively simple stoichiometry compared to other High-T c compounds. Much attention was paid to the critical current density. A very high critical current density was reached. By using texture analysis by X-ray diffraction, it was found that films with high critical current densities were epitaxial, while films with low critical current densities contained several crystalline orientations. Four techniques for patterning the films were used - photo lithography and wet etch, laser ablation lithography, laser writing and electron beam lithography and ion milling. Sub-micron patterning has been demonstrated without degradation of the superconducting properties. The achieved patterning resolution is sufficient for preparation of many superconducting components. (AB)

  14. Dependence of the Spin Transfer Torque Switching Current Density on the Exchange Stiffness Constant

    OpenAIRE

    You, Chun-Yeol

    2012-01-01

    We investigate the dependence of the switching current density on the exchange stiffness constant in the spin transfer torque magnetic tunneling junction structure with micromagnetic simulations. Since the widely accepted analytic expression of the switching current density is based on the macro-spin model, there is no dependence of the exchange stiffness constant. When the switching is occurred, however, the spin configuration forms C-, S-type, or complicated domain structures. Since the spi...

  15. Maximum current density and beam brightness achievable by laser-driven electron sources

    Science.gov (United States)

    Filippetto, D.; Musumeci, P.; Zolotorev, M.; Stupakov, G.

    2014-02-01

    This paper discusses the extension to different electron beam aspect ratio of the Child-Langmuir law for the maximum achievable current density in electron guns. Using a simple model, we derive quantitative formulas in good agreement with simulation codes. The new scaling laws for the peak current density of temporally long and transversely narrow initial beam distributions can be used to estimate the maximum beam brightness and suggest new paths for injector optimization.

  16. Maximum current density and beam brightness achievable by laser-driven electron sources

    Directory of Open Access Journals (Sweden)

    D. Filippetto

    2014-02-01

    Full Text Available This paper discusses the extension to different electron beam aspect ratio of the Child-Langmuir law for the maximum achievable current density in electron guns. Using a simple model, we derive quantitative formulas in good agreement with simulation codes. The new scaling laws for the peak current density of temporally long and transversely narrow initial beam distributions can be used to estimate the maximum beam brightness and suggest new paths for injector optimization.

  17. Expanding the reduced-current approach for thermoelectric generators to achieve higher volumetric power density

    DEFF Research Database (Denmark)

    Wijesooriyage, Waruna Dissanayaka; Rosendahl, Lasse

    2015-01-01

    current approach (RCA) for TE module design, where the same current is induced through the p and n legs of the thermoelectric generator (TEG). The current density of each element is manipulated by changing the area of both legs. This technique leads to a TE module architecture based on the most efficient...... configuration of both p and n legs. In the current paper, we apply an extended version of this technique, to show how a TE module with a higher volumetric power density can be designed, compared to the original RCA. Our studies indicate that for some combinations of p and n material properties, optima yielding...

  18. Software Toolbox for Low-Frequency Conductivity and Current Density Imaging Using MRI.

    Science.gov (United States)

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

    2017-11-01

    Low-frequency conductivity and current density imaging using MRI includes magnetic resonance electrical impedance tomography (MREIT), diffusion tensor MREIT (DT-MREIT), conductivity tensor imaging (CTI), and magnetic resonance current density imaging (MRCDI). MRCDI and MREIT provide current density and isotropic conductivity images, respectively, using current-injection phase MRI techniques. DT-MREIT produces anisotropic conductivity tensor images by incorporating diffusion weighted MRI into MREIT. These current-injection techniques are finding clinical applications in diagnostic imaging and also in transcranial direct current stimulation (tDCS), deep brain stimulation (DBS), and electroporation where treatment currents can function as imaging currents. To avoid adverse effects of nerve and muscle stimulations due to injected currents, conductivity tensor imaging (CTI) utilizes B1 mapping and multi-b diffusion weighted MRI to produce low-frequency anisotropic conductivity tensor images without injecting current. This paper describes numerical implementations of several key mathematical functions for conductivity and current density image reconstructions in MRCDI, MREIT, DT-MREIT, and CTI. To facilitate experimental studies of clinical applications, we developed a software toolbox for these low-frequency conductivity and current density imaging methods. This MR-based conductivity imaging (MRCI) toolbox includes 11 toolbox functions which can be used in the MATLAB environment. The MRCI toolbox is available at http://iirc.khu.ac.kr/software.html . Its functions were tested by using several experimental datasets, which are provided together with the toolbox. Users of the toolbox can focus on experimental designs and interpretations of reconstructed images instead of developing their own image reconstruction softwares. We expect more toolbox functions to be added from future research outcomes. Low-frequency conductivity and current density imaging using MRI includes

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

    Science.gov (United States)

    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.

  20. Current Density Imaging Using Directly Measured Harmonic Bz Data in MREIT

    Directory of Open Access Journals (Sweden)

    Chunjae Park

    2013-01-01

    Full Text Available 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, ∇2Bz, 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 ∇2Bz 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. Anisotropy and intergrain current density in oriented grained bulk YBa2Cu3Ox superconductor

    International Nuclear Information System (INIS)

    Selvamanickam, V.; Salama, K.

    1990-01-01

    The intergrain transport current density and its anisotropy have been studied in oriented grained bulk YBa 2 Cu 3 O x superconductors fabricated by the liquid phase processing method. Current density measurements were performed on oriented grained samples with the transport current aligned at different angles to the a-b plane. In these measurements, the transport current passed through several oriented grain boundaries. The results indicate that the critical current density drops rapidly when the transport current flows at small angles to the a-b plane and then decreases slowly at larger angles. At 77 K and zero magnetic field, an anisotropy ratio of about 25 is observed between J c along a-b plane and that perpendicular to the plane. Further, the critical current density in these samples is found to depend weakly on magnetic field even though the current crosses grain boundaries. These results support the notion that grain boundaries of these superconductors are different in nature from those of solid-state sintered samples.

  2. Formation of ion beam with high current density for micro irradiation techniques

    Energy Technology Data Exchange (ETDEWEB)

    Romanenko, A.V.; Ponomarev, A.G.

    2015-04-01

    The paper describes a study of the ion beam formation for irradiation of microareas of construction materials with individual grains. A numerical simulation of the microbeam formation was performed with profiles of current density distribution close to rectangular to obtain uniform dose. Ion beams with the total current on the target 10–100 nA were considered. An approach for beam focusing with energy variation without moving a sample was considered. The ability to create current density distributions close to uniform in the target plane was experimentally validated.

  3. High current densities enable exoelectrogens to outcompete aerobic heterotrophs for substrate

    KAUST Repository

    Ren, Lijiao

    2014-08-05

    © 2014 Wiley Periodicals, Inc. Chemical oxygen demand (COD) removal rates could be described by first-order kinetics with respect to COD concentration at different current densities, even under open circuit conditions with no current generation. The COD concentration was reduced more quickly with current generation due to the greater consumption of substrate by exoelectrogens, and less substrate was lost to aerobic heterotrophs. Higher current densities enabled exoelectrogens to outcompete aerobic heterotrophs for substrate, allowing for increased coulombic efficiencies with current densities. © 2014 Wiley Periodicals, Inc. In mixed-culture microbial fuel cells (MFCs), exoelectrogens and other microorganisms compete for substrate. It has previously been assumed that substrate losses to other terminal electron acceptors over a fed-batch cycle, such as dissolved oxygen, are constant. However, a constant rate of substrate loss would only explain small increases in coulombic efficiencies (CEs, the fraction of substrate recovered as electrical current) with shorter cycle times, but not the large increases in CE that are usually observed with higher current densities and reduced cycle times. To better understand changes in CEs, COD concentrations were measured over time in fed-batch, single-chamber, air-cathode MFCs at different current densities (external resistances). COD degradation rates were all found to be first-order with respect to COD concentration, even under open circuit conditions with no current generation (first-order rate constant of 0.14±0.01h-1). The rate of COD removal increased when there was current generation, with the highest rate constant (0.33±0.02h-1) obtained at the lowest external resistance (100Ω). Therefore, as the substrate concentration was reduced more quickly due to current generation, the rate of loss of substrate to non-exoelectrogens decreased due to this first-order substrate-concentration dependence. As a result, coulombic

  4. First current density measurements in the ring current region using simultaneous multi-spacecraft CLUSTER-FGM data

    Directory of Open Access Journals (Sweden)

    C. Vallat

    2005-07-01

    Full Text Available The inner magnetosphere's current mapping is one of the key elements for current loop closure inside the entire magnetosphere. A method for directly computing the current is the multi-spacecraft curlometer technique, which is based on the application of Maxwell-Ampère's law. This requires the use of four-point magnetic field high resolution measurements. The FGM experiment on board the four Cluster spacecraft allows, for the first time, an instantaneous calculation of the magnetic field gradients and thus a measurement of the local current density. This technique requires, however, a careful study concerning all the factors that can affect the accuracy of the J estimate, such as the tetrahedral geometry of the four spacecraft, or the size and orientation of the current structure sampled. The first part of this paper is thus providing a detailed analysis of the method accuracy, and points out the limitations of this technique in the region of interest. The second part is an analysis of the ring current region, which reveals, for the first time, the large latitudinal extent of the ring current, for all magnetic activity levels, as well as the latitudinal evolution of the perpendicular (and parallel components of the current along the diffuse auroral zone. Our analysis also points out the sharp transition between two distinct plasma regions, with the existence of high diamagnetic currents at the interface, as well as the filamentation of the current inside the inner plasma sheet. A statistical study over multiple perigee passes of Cluster (at about 4 RE from the Earth reveals the azimuthal extent of the partial ring current. It also reveals that, at these distances and all along the evening sector, there isn't necessarily a strong dependence of the local current density value on the magnetic activity level. This is a direct consequence of the ring current morphology evolution, as well as the relative

  5. First current density measurements in the ring current region using simultaneous multi-spacecraft CLUSTER-FGM data

    Directory of Open Access Journals (Sweden)

    C. Vallat

    2005-07-01

    Full Text Available The inner magnetosphere's current mapping is one of the key elements for current loop closure inside the entire magnetosphere. A method for directly computing the current is the multi-spacecraft curlometer technique, which is based on the application of Maxwell-Ampère's law. This requires the use of four-point magnetic field high resolution measurements. The FGM experiment on board the four Cluster spacecraft allows, for the first time, an instantaneous calculation of the magnetic field gradients and thus a measurement of the local current density. This technique requires, however, a careful study concerning all the factors that can affect the accuracy of the J estimate, such as the tetrahedral geometry of the four spacecraft, or the size and orientation of the current structure sampled. The first part of this paper is thus providing a detailed analysis of the method accuracy, and points out the limitations of this technique in the region of interest. The second part is an analysis of the ring current region, which reveals, for the first time, the large latitudinal extent of the ring current, for all magnetic activity levels, as well as the latitudinal evolution of the perpendicular (and parallel components of the current along the diffuse auroral zone. Our analysis also points out the sharp transition between two distinct plasma regions, with the existence of high diamagnetic currents at the interface, as well as the filamentation of the current inside the inner plasma sheet. A statistical study over multiple perigee passes of Cluster (at about 4 RE from the Earth reveals the azimuthal extent of the partial ring current. It also reveals that, at these distances and all along the evening sector, there isn't necessarily a strong dependence of the local current density value on the magnetic activity level. This is a direct consequence of the ring current morphology evolution, as well as the relative positioning of the spacecraft with respect to

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

    Science.gov (United States)

    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.

  7. Microstructure and critical current density in high-Tc metal oxide superconductors

    International Nuclear Information System (INIS)

    Johnson, S.M.; Gusman, M.I.

    1992-03-01

    Superconductor powders in the U-Ba-Cu-O (YBCO) and Bi-Pb-Sr-Ca-Cu-O (BSCCO) systems were synthesized by freeze-drying. Powders were characterized, and processed into samples for evaluation of superconducting behavior. Freeze-drying is attractive because the powders have high purity, are homogeneous, have a small size and are active. YBCO powders can be sintered to high density at 890 degrees C. Many compositions, processing approaches and heat treatments were explored in an effort to understand relations between microstructure and critical density, and to improve the critical current density. Powders were also formed into sputtering targets for coating preparation at Stanford University. The highest critical current density achieved with the YBCO powders was ∼15,000 A/cm 2 at 4.2K and 0.5T using powders treated to prevent carbon contamination. The BSCCO materials with the highest critical current density, ∼30,000 A/cm 2 at the same conditions were formed by heat treating melted and quenched samples. All critical current density measurements were made by Stanford University, a subcontractor to this effort. Stanford University also prepared coatings by off-axis magnetron sputtering

  8. Current density reversibly alters metabolic spatial structure of exoelectrogenic anode biofilms

    Science.gov (United States)

    Sun, Dan; Cheng, Shaoan; Zhang, Fang; Logan, Bruce E.

    2017-07-01

    Understanding how current densities affect electrogenic biofilm activity is important for wastewater treatment as current densities can substantially decrease at COD concentrations greater than those suitable for discharge to the environment. We examined the biofilm's response, in terms of viability and enzymatic activity, to different current densities using microbial electrolysis cells with a lower (0.7 V) or higher (0.9 V) added voltage to alter current production. Viability was assessed using florescent dyes, with dead cells identified on the basis of dye penetration due to a compromised cell outer-membrane (red), and live cells (intact membrane) fluorescing green. Biofilms operated with 0.7 V produced 2.4 ± 0.2 A m-2, and had an inactive layer near the electrode and a viable layer at the biofilm-solution interface. The lack of cell activity near the electrode surface was confirmed by using an additional dye that fluoresces only with enzymatic activity. Adding 0.9 V increased the current by 61%, and resulted in a single, more homogeneous and active biofilm layer. Switching biofilms between these two voltages produced outcomes associated with the new current rather than the previous biofilm conditions. These findings suggest that maintaining higher current densities will be needed to ensure long-term viability electrogenic biofilms.

  9. Research and development of an aimed magnetic lead current density-magnetic field diagnostic. Final report

    International Nuclear Information System (INIS)

    1985-01-01

    A diagnostics survey was made to provide a clear definition of advanced diagnostic needs and the limitations of current approaches in addressing those needs. Special attention was given to the adequacy with which current diagnostics are interfaced to signal processing/data acquisition devices and systems. Critical evaluations of selected alternative diagnostic techniques for future R and D activities are presented. The conceptual basis of the Aimed Magnetic Lead Gradiometric system as a current density/magnetic field diagnostic is established

  10. Inertial electron instability in low-density current-carrying plasmas

    International Nuclear Information System (INIS)

    Basova, S.V.; Varentsova, S.A.; Gordeev, A.V.; Gulin, A.V.; Shuvaev, V.Yu.

    1991-01-01

    The stability of a low-density current-carrying plasma with finite electron inertia and motionless ions is studied. It is shown analytically and numerically that an instability exists when the quantity H = H + (m e c/e)dv/dr changes sign as a function of position, where H is the magnetic field and v is the current drift velocity of the electrons. The growth rates for specific current configurations are obtained by numerical calculation

  11. Intelligence and EEG current density using low-resolution electromagnetic tomography (LORETA).

    Science.gov (United States)

    Thatcher, R W; North, D; Biver, C

    2007-02-01

    The purpose of this study was to compare EEG current source densities in high IQ subjects vs. low IQ subjects. Resting eyes closed EEG was recorded from 19 scalp locations with a linked ears reference from 442 subjects ages 5 to 52 years. The Wechsler Intelligence Test was administered and subjects were divided into low IQ (90 to or =120) groups. Low-resolution electromagnetic tomographic current densities (LORETA) from 2,394 cortical gray matter voxels were computed from 1-30 Hz based on each subject's EEG. Differences in current densities using t tests, multivariate analyses of covariance, and regression analyses were used to evaluate the relationships between IQ and current density in Brodmann area groupings of cortical gray matter voxels. Frontal, temporal, parietal, and occipital regions of interest (ROIs) consistently exhibited a direct relationship between LORETA current density and IQ. Maximal t test differences were present at 4 Hz, 9 Hz, 13 Hz, 18 Hz, and 30 Hz with different anatomical regions showing different maxima. Linear regression fits from low to high IQ groups were statistically significant (P microstates is hypothesized to explain the results.

  12. Focused current density imaging using internal electrode in magnetic resonance electrical impedance tomography (MREIT).

    Science.gov (United States)

    Jeong, Woo Chul; Sajib, Saurav; Kim, Hyung Joong; Kwon, Oh In

    2014-07-01

    Magnetic resonance electrical impedance tomography (MREIT) is an imaging modality capable of visualizing cross-sectional current density and/or conductivity distributions inside an electrically conducting object. It uses an MRI scanner to measure one component of the magnetic flux density induced by an externally injected current through a pair of surface electrodes. For the cases of deep brain stimulation (DBS), electroporation, and radio frequency (RF) ablation, internal electrodes can be used to improve the quality of the MREIT images. In this paper, we propose a new MREIT imaging method using internal electrodes to visualize a current density distribution within a local region around them. To evaluate its performance, we conducted and analyzed a series of numerical simulations and phantom imaging experiments. We compared the reconstructed current density images using the internal electrodes with the obtained using only the external electrodes. We found that the proposed method using the internal electrodes stably determines the current density in the focused region with better accuracy.

  13. Multishot echo-planar MREIT for fast imaging of conductivity, current density, and electric field distributions.

    Science.gov (United States)

    Chauhan, Munish; Vidya Shankar, Rohini; Ashok Kumar, Neeta; Kodibagkar, Vikram D; Sadleir, Rosalind

    2018-01-01

    Magnetic resonance electrical impedance tomography (MREIT) sequences typically use conventional spin or gradient echo-based acquisition methods for reconstruction of conductivity and current density maps. Use of MREIT in functional and electroporation studies requires higher temporal resolution and faster sequences. Here, single and multishot echo planar imaging (EPI) based MREIT sequences were evaluated to see whether high-quality MREIT phase data could be obtained for rapid reconstruction of current density, conductivity, and electric fields. A gel phantom with an insulating inclusion was used as a test object. Ghost artifact, geometric distortion, and MREIT correction algorithms were applied to the data. The EPI-MREIT-derived phase-projected current density and conductivity images were compared with simulations and spin-echo images as a function of EPI shot number. Good agreement among measures in simulated, spin echo, and EPI data was achieved. Current density errors were stable and below 9% as the shot number decreased from 64 to 2, but increased for single-shot images. Conductivity reconstruction relative contrast ratios were stable as the shot number decreased. The derived electric fields also agreed with the simulated data. The EPI methods can be combined successfully with MREIT reconstruction algorithms to achieve fast imaging of current density, conductivity, and electric field. Magn Reson Med 79:71-82, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  14. LORETA current source density for duration mismatch negativity and neuropsychological assessment in early schizophrenia.

    Directory of Open Access Journals (Sweden)

    Tomohiro Miyanishi

    Full Text Available INTRODUCTION: Patients with schizophrenia elicit cognitive decline from the early phase of the illness. Mismatch negativity (MMN has been shown to be associated with cognitive function. We investigated the current source density of duration mismatch negativity (dMMN, by using low-resolution brain electromagnetic tomography (LORETA, and neuropsychological performance in subjects with early schizophrenia. METHODS: Data were obtained from 20 patients meeting DSM-IV criteria for schizophrenia or schizophreniform disorder, and 20 healthy control (HC subjects. An auditory odd-ball paradigm was used to measure dMMN. Neuropsychological performance was evaluated by the brief assessment of cognition in schizophrenia Japanese version (BACS-J. RESULTS: Patients showed smaller dMMN amplitudes than those in the HC subjects. LORETA current density for dMMN was significantly lower in patients compared to HC subjects, especially in the temporal lobes. dMMN current density in the frontal lobe was positively correlated with working memory performance in patients. CONCLUSIONS: This is the first study to identify brain regions showing smaller dMMN current density in early schizophrenia. Further, poor working memory was associated with decreased dMMN current density in patients. These results are likely to help understand the neural basis for cognitive impairment of schizophrenia.

  15. Two-dimensional electron density characterisation of arc interruption phenomenon in current-zero phase

    Science.gov (United States)

    Inada, Yuki; Kamiya, Tomoki; Matsuoka, Shigeyasu; Kumada, Akiko; Ikeda, Hisatoshi; Hidaka, Kunihiko

    2018-01-01

    Two-dimensional electron density imaging over free burning SF6 arcs and SF6 gas-blast arcs was conducted at current zero using highly sensitive Shack-Hartmann type laser wavefront sensors in order to experimentally characterise electron density distributions for the success and failure of arc interruption in the thermal reignition phase. The experimental results under an interruption probability of 50% showed that free burning SF6 arcs with axially asymmetric electron density profiles were interrupted with a success rate of 88%. On the other hand, the current interruption of SF6 gas-blast arcs was reproducibly achieved under locally reduced electron densities and the interruption success rate was 100%.

  16. Arrays of Synthetic Atoms: Nanocapacitor Batteries with Large Energy Density and Small Leak Currents

    Science.gov (United States)

    2017-11-28

    AFRL-RV-PS- AFRL-RV-PS- TR-2017-0169 TR-2017-0169 ARRAYS OF SYNTHETIC ATOMS : NANOCAPACITOR BATTERIES WITH LARGE ENERGY DENSITY AND SMALL LEAK...1-0247 Arrays of Synthetic Atoms : Nanocapacitor Batteries with Large Energy Density and Small Leak Currents 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...large dielectric strength to a nanoscale rechargeable battery. We fabricated arrays of one-, two- and three-dimensional synthetic atoms and comparison

  17. Eddy current density asymmetric distribution of damper bars in bulb tubular turbine generator

    Directory of Open Access Journals (Sweden)

    Qiu Hongbo

    2017-09-01

    Full Text Available The major reasons that cause the damage of damper bars in the leeward side are found in this paper. It provides a route for the structure optimization design of a hydro generator. Firstly, capacity of a 24 MW bulb tubular turbine generator is taken as an example in this paper. The transient electromagnetic field model is established, and the correctness of the model is verified by the comparison of experimental results and simulation data. Secondly, when the generator is operated at rated condition, the eddy current density distributions of damper bars are studied. And the asymmetric phenomenon of the eddy current density on damper bars is discovered. The change laws of the eddy currents in damper bars are determined through further analysis. Thirdly, through the study of eddy current distributions under different conditions, it is confirmed that the stator slots and armature reaction are the main factors to affect the asymmetric distribution of the eddy current in damper bars. Finally, the studies of the magnetic density distribution and theoretical analysis revealed the asymmetric distribution mechanism of eddy current density.

  18. Ultrathin silicon dioxide layers with a low leakage current density formed by chemical oxidation of Si

    Science.gov (United States)

    Asuha,; Kobayashi, Takuya; Maida, Osamu; Inoue, Morio; Takahashi, Masao; Todokoro, Yoshihiro; Kobayashi, Hikaru

    2002-10-01

    Chemical oxidation of Si by use of azeotrope of nitric acid and water can form 1.4-nm-thick silicon dioxide layers with a leakage current density as low as those of thermally grown SiO2 layers. The capacitance-voltage (C-V) curves for these ultrathin chemical SiO2 layers have been measured due to the low leakage current density. The leakage current density is further decreased to approx1/5 (cf. 0.4 A/cm2 at the forward gate bias of 1 V) by post-metallization annealing at 200 degC in hydrogen. Photoelectron spectroscopy and C-V measurements show that this decrease results from (i) increase in the energy discontinuity at the Si/SiO2 interface, and (ii) elimination of Si/SiO2 interface states and SiO2 gap states.

  19. Current densities in a pregnant woman model induced by simultaneous ELF electric and magnetic field exposure

    International Nuclear Information System (INIS)

    Cech, R; Leitgeb, N; Pediaditis, M

    2008-01-01

    The pregnant woman model SILVY was studied to ascertain to what extent the electric current densities induced by 50 Hz homogeneous electric and magnetic fields increase in the case of simultaneous exposure. By vectorial addition of the electric current densities, it could be shown that under worst case conditions the basic restrictions recommended by ICNIRP (International Commission on Non-Ionizing Radiation Protection) guidelines are exceeded within the central nervous system (CNS) of the mother, whereas in sole field exposure they are not. However, within the foetus the induced current densities do not comply with basic restrictions, either from single reference-level electric fields or from simultaneous exposure to electric and magnetic fields. Basic limits were considerably exceeded

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

    Science.gov (United States)

    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. The study of dynamics of electrons in the presence of large current densities

    International Nuclear Information System (INIS)

    Garcia, G.

    2007-11-01

    The runaway electron effect is considered in different fields: nuclear fusion, or the heating of the solar corona. In this thesis, we are interested in runaway electrons in the ionosphere. We consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a parallel electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. A computational example is given illustrating the approach to equilibrium and the impact of the different terms. Then, a static electric field is applied in a new sample run. In this run, the electrons move in the z direction, parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density up to 20% of the total current density. Nevertheless, we note that the divergence free of the current density is not conserved. We introduce major changes in order to take into account the variation of the different moments of the ion distribution functions. We observe that the electron distribution functions are still non-Maxwellian. Runaway electrons are created and carry the current density. The core distribution stay at rest. As these electrons undergo less collisions, they increase the plasma conductivity. We make a parametric study. We fit the electron distribution function by two Maxwellian. We show that the time to reach the maximal current density is a key point. Thus, when we increase this time, we modify the temperatures. The current density plays a primary role. When the current density increases, all the moments of the distributions increase: electron density and mean velocity of the suprathermal distribution and the electron temperature of the core and

  2. Microstructure characterisation of solid oxide electrolysis cells operated at high current density

    DEFF Research Database (Denmark)

    Bowen, Jacob R.; Bentzen, Janet Jonna; Chen, Ming

    quantified using the mean linear intercept method as a function of current density and correlated to increases in serial resistance. The above structural changes are then compared in terms of electrode degradation observed during the co-electrolysis of steam and CO2 at current densities up to -1.5 A cm-2......High temperature solid oxide cells can be operated either as fuel cells or electrolysis cells for efficient power generation or production of hydrogen from steam or synthesis gas (H2 + CO) from steam and CO2 respectively. When operated under harsh conditions, they often exhibit microstructural...

  3. Multipole lenses with implicit poles and with harmonic distribution of current density in a coil

    International Nuclear Information System (INIS)

    Skachkov, V.S.

    1984-01-01

    General theory of the multipole lense with implicit poles is presented. The thickness of lense coil is finite. Current density distribution in the coil cross section is harmonic in the azimuth direction and arbitrary in the radial one. The calculation of yoke contribution in the lence field is given. Two particular lense variants differing from each other in the method of current density radial distribution are considered and necessary calculated relations for the lense with and without yoke ar presented. A comparative analysis of physical and technological peculiarities of these lenses is performed

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

    International Nuclear Information System (INIS)

    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 parallel B 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

  5. Particle-bearing currents in uniform density and two-layer fluids

    Science.gov (United States)

    Sutherland, Bruce R.; Gingras, Murray K.; Knudson, Calla; Steverango, Luke; Surma, Christopher

    2018-02-01

    Lock-release gravity current experiments are performed to examine the evolution of a particle bearing flow that propagates either in a uniform-density fluid or in a two-layer fluid. In all cases, the current is composed of fresh water plus micrometer-scale particles, the ambient fluid is saline, and the current advances initially either over the surface as a hypopycnal current or at the interface of the two-layer fluid as a mesopycnal current. In most cases the tank is tilted so that the ambient fluid becomes deeper with distance from the lock. For hypopycnal currents advancing in a uniform density fluid, the current typically slows as particles rain out of the current. While the loss of particles alone from the current should increase the current's buoyancy and speed, in practice the current's speed decreases because the particles carry with them interstitial fluid from the current. Meanwhile, rather than settling on the sloping bottom of the tank, the particles form a hyperpycnal (turbidity) current that advances until enough particles rain out that the relatively less dense interstitial fluid returns to the surface, carrying some particles back upward. When a hypopycnal current runs over the surface of a two-layer fluid, the particles that rain out temporarily halt their descent as they reach the interface, eventually passing through it and again forming a hyperpycnal current. Dramatically, a mesopycnal current in a two-layer fluid first advances along the interface and then reverses direction as particles rain out below and fresh interstitial fluid rises above.

  6. Calculation of induced current densities for humans by magnetic fields from electronic article surveillance devices

    Science.gov (United States)

    Gandhi, Om P.; Kang, Gang

    2001-11-01

    This paper illustrates the use of the impedance method to calculate the electric fields and current densities induced in millimetre resolution anatomic models of the human body, namely an adult and 10- and 5-year-old children, for exposure to nonuniform magnetic fields typical of two assumed but representative electronic article surveillance (EAS) devices at 1 and 30 kHz, respectively. The devices assumed for the calculations are a solenoid type magnetic deactivator used at store checkouts and a pass-by panel-type EAS system consisting of two overlapping rectangular current-carrying coils used at entry and exit from a store. The impedance method code is modified to obtain induced current densities averaged over a cross section of 1 cm2 perpendicular to the direction of induced currents. This is done to compare the peak current densities with the limits or the basic restrictions given in the ICNIRP safety guidelines. Because of the stronger magnetic fields at lower heights for both the assumed devices, the peak 1 cm2 area-averaged current densities for the CNS tissues such as the brain and the spinal cord are increasingly larger for smaller models and are the highest for the model of the 5-year-old child. For both the EAS devices, the maximum 1 cm2 area-averaged current densities for the brain of the model of the adult are lower than the ICNIRP safety guideline, but may approach or exceed the ICNIRP basic restrictions for models of 10- and 5-year-old children if sufficiently strong magnetic fields are used.

  7. On the estimation of the current density in space plasmas: Multi- versus single-point techniques

    Science.gov (United States)

    Perri, Silvia; Valentini, Francesco; Sorriso-Valvo, Luca; Reda, Antonio; Malara, Francesco

    2017-06-01

    Thanks to multi-spacecraft mission, it has recently been possible to directly estimate the current density in space plasmas, by using magnetic field time series from four satellites flying in a quasi perfect tetrahedron configuration. The technique developed, commonly called ;curlometer; permits a good estimation of the current density when the magnetic field time series vary linearly in space. This approximation is generally valid for small spacecraft separation. The recent space missions Cluster and Magnetospheric Multiscale (MMS) have provided high resolution measurements with inter-spacecraft separation up to 100 km and 10 km, respectively. The former scale corresponds to the proton gyroradius/ion skin depth in ;typical; solar wind conditions, while the latter to sub-proton scale. However, some works have highlighted an underestimation of the current density via the curlometer technique with respect to the current computed directly from the velocity distribution functions, measured at sub-proton scales resolution with MMS. In this paper we explore the limit of the curlometer technique studying synthetic data sets associated to a cluster of four artificial satellites allowed to fly in a static turbulent field, spanning a wide range of relative separation. This study tries to address the relative importance of measuring plasma moments at very high resolution from a single spacecraft with respect to the multi-spacecraft missions in the current density evaluation.

  8. Crack problem in superconducting cylinder with exponential distribution of critical-current density

    Science.gov (United States)

    Zhao, Yufeng; Xu, Chi; Shi, Liang

    2018-04-01

    The general problem of a center crack in a long cylindrical superconductor with inhomogeneous critical-current distribution is studied based on the extended Bean model for zero-field cooling (ZFC) and field cooling (FC) magnetization processes, in which the inhomogeneous parameter η is introduced for characterizing the critical-current density distribution in inhomogeneous superconductor. The effect of the inhomogeneous parameter η on both the magnetic field distribution and the variations of the normalized stress intensity factors is also obtained based on the plane strain approach and J-integral theory. The numerical results indicate that the exponential distribution of critical-current density will lead a larger trapped field inside the inhomogeneous superconductor and cause the center of the cylinder to fracture more easily. In addition, it is worth pointing out that the nonlinear field distribution is unique to the Bean model by comparing the curve shapes of the magnetization loop with homogeneous and inhomogeneous critical-current distribution.

  9. Effect of electrolysis parameters on the morphologies of copper powder obtained at high current densities

    Directory of Open Access Journals (Sweden)

    Orhan Gökhan

    2012-01-01

    Full Text Available The effects of copper ion concentrations and electrolyte temperature on the morphologies and on the apparent densities of electrolytic copper powders at high current densities under galvanostatic regime were examined. These parameters were evaluated by the current efficiency of hydrogen evolution. In addition, scanning electron microscopy was used for analyzing the morphology of the copper powders. It was found that the morphology was dependent over the copper ion concentration and electrolyte temperature under same current density (CD conditions. At 150 mA cm-2 and the potential of 1000±20 mV (vs. SCE, porous and disperse copper powders were obtained at low concentrations of Cu ions (0.120 M Cu2+ in 0.50 M H2SO4. Under this condition, high rate of hydrogen evolution reaction took place parallel to copper electrodeposition. The morphology was changed from porous, disperse and cauliflower-like to coral-like, shrub-like and stalk-stock like morphology with the increasing of Cu ion concentrations towards 0.120 M, 0.155 M, 0.315 M, 0.475 M and 0.630 M Cu2+ in 0.5 M H2SO4 respectively at the same CD. Similarly, as the temperature was increased, powder morphology and apparent density were observed to be changed. The apparent density values of copper powders were found to be suitable for many of the powder metallurgy applications.

  10. Effect of a superconducting coil as a fault current limiter on current density distribution in BSCCO tape after an over-current pulse

    Science.gov (United States)

    Tallouli, M.; Shyshkin, O.; Yamaguchi, S.

    2017-07-01

    The development of power transmission lines based on long-length high temperature superconducting (HTS) tapes is complicated and technically challenging task. A serious problem for transmission line operation could become HTS power cable damage due to over-current pulse conditions. To avoid the cable damage in any urgent case the superconducting coil technology, i.e. superconductor fault current limiter (SFCL) is required. Comprehensive understanding of the current density characteristics of HTS tapes in both cases, either after pure over-current pulse or after over-current pulse limited by SFCL, is needed to restart or to continue the operation of the power transmission line. Moreover, current density distribution along and across the HTS tape provides us with the sufficient information about the quality of the tape performance in different current feeding regimes. In present paper we examine BSCCO HTS tape under two current feeding regimes. The first one is 100A feeding preceded by 900A over-current pulse. In this case none of tape protection was used. The second scenario is similar to the fist one but SFCL is used to limit an over-current value. For both scenarios after the pulse is gone and the current feeding is set up at 100A we scan magnetic field above the tape by means of Hall probe sensor. Then the feeding is turned of and the magnetic field scanning is repeated. Using the inverse problem numerical solver we calculate the corresponding direct and permanent current density distributions during the feeding and after switch off. It is demonstrated that in the absence of SFCL the current distribution is highly peaked at the tape center. At the same time the current distribution in the experiment with SFCL is similar to that observed under normal current feeding condition. The current peaking in the first case is explained by the effect of an opposite electric field induced at the tape edges during the overcurrent pulse decay, and by degradation of

  11. Effect of a superconducting coil as a fault current limiter on current density distribution in BSCCO tape after an over-current pulse

    International Nuclear Information System (INIS)

    Tallouli, M; Yamaguchi, S.; Shyshkin, O.

    2017-01-01

    The development of power transmission lines based on long-length high temperature superconducting (HTS) tapes is complicated and technically challenging task. A serious problem for transmission line operation could become HTS power cable damage due to over-current pulse conditions. To avoid the cable damage in any urgent case the superconducting coil technology, i.e. superconductor fault current limiter (SFCL) is required. Comprehensive understanding of the current density characteristics of HTS tapes in both cases, either after pure over-current pulse or after over-current pulse limited by SFCL, is needed to restart or to continue the operation of the power transmission line. Moreover, current density distribution along and across the HTS tape provides us with the sufficient information about the quality of the tape performance in different current feeding regimes. In present paper we examine BSCCO HTS tape under two current feeding regimes. The first one is 100A feeding preceded by 900A over-current pulse. In this case none of tape protection was used. The second scenario is similar to the fist one but SFCL is used to limit an over-current value. For both scenarios after the pulse is gone and the current feeding is set up at 100A we scan magnetic field above the tape by means of Hall probe sensor. Then the feeding is turned of and the magnetic field scanning is repeated. Using the inverse problem numerical solver we calculate the corresponding direct and permanent current density distributions during the feeding and after switch off. It is demonstrated that in the absence of SFCL the current distribution is highly peaked at the tape center. At the same time the current distribution in the experiment with SFCL is similar to that observed under normal current feeding condition. The current peaking in the first case is explained by the effect of an opposite electric field induced at the tape edges during the overcurrent pulse decay, and by degradation of

  12. A mathematical model of the current density distribution in electrochemical cells - AUTHORS’ REVIEW

    Directory of Open Access Journals (Sweden)

    PREDRAG M. ŽIVKOVIĆ

    2011-06-01

    Full Text Available An approach based on the equations of electrochemical kinetics for the estimation of the current density distribution in electrochemical cells is presented. This approach was employed for a theoretical explanation of the phenomena of the edge and corner effects. The effects of the geometry of the system, the kinetic parameters of the cathode reactions and the resistivity of the solution are also discussed. A procedure for a complete analysis of the current distribution in electrochemical cells is presented.

  13. Critical current densities in thick yttrium-barium cuprate (1-2-3) films

    International Nuclear Information System (INIS)

    Ryvkina, G.G.; Gorlanov, S.F.; Vedernikov, G.E.; Telegin, A.B.; Ryabin, V.A.; Khodos, M.Ya.

    1993-01-01

    The study of critical current densities j c of oxide superconductors and their thick films is a very important practical task because the value of j c is one of the main criteria for their utilization in modern cryoelectronics. For most devices based on the Josephson effect, the value of j c ∼ 10 2 - 10 3 A/cm 2 is acceptable, which is easily attainable for polycrystalline thick films obtained by stenciling. The study of the current-transport phenomenon involves a number of difficulties, especially for direct current, because both the sample itself and the lead-in contacts are resistance-heated during the measurements, which, in turn, results in lower values of the j c . Measurements with pulsed currents allow one to lower the power that is applied to the sample; the heat that is released in the sample is reduced, in comparison to measurements with direct current, by a factor of the pulsed-current duty cycle. In addition, measurements with direct current detects only the appearance of resistance; it provides no information on the rest of the transition from the normal to the superconductive state, i.e., on the so-called 'tail' of the transition. In this work, the authors studied critical current densities of thick HTSC yttrium-barium cuprate films of the 1-2-3 composition using pulsed current

  14. Measurement of electrical current density distribution in a simple head phantom with magnetic resonance imaging

    Science.gov (United States)

    Gamba, Humberto R.; Bayford, Richard; Holder, David

    1999-01-01

    Knowledge of the influence of the human skull on the electrical current (d.c.) distribution within the brain tissue could prove useful in measuring impedance changes inside the human head. These changes can be related to physiological functions. The studies presented in this paper examine the current density distribution in a simple phantom consisting of a saline filled tank (to simulate scalp and brain) and a ring made of dental grade plaster of Paris (to simulate the human skull). Images of the distribution of the d.c. density of the phantom with and without the plaster of Paris ring were produced using a magnetic resonance imaging technique. These images indicate that the skull is likely to produce a more uniform d.c. density within the brain.

  15. Lower hybrid current drive at ITER-relevant high plasma densities

    International Nuclear Information System (INIS)

    Cesario, R.; Amicucci, L.; Cardinali, A.; Castaldo, C.; Marinucci, M.; Panaccione, L.; Pericoli-Ridolfini, V.; Tuccillo, A. A.; Tudisco, O.; Calabro, G.

    2009-01-01

    Recent experiments indicated that a further non-inductive current, besides bootstrap, should be necessary for developing advanced scenario for ITER. The lower hybrid current drive (LHCD) should provide such tool, but its effectiveness was still not proved in operations with ITER-relevant density of the plasma column periphery. Progress of the LH deposition modelling is presented, performed considering the wave physics of the edge, and different ITER-relevant edge parameters. Operations with relatively high edge electron temperatures are expected to reduce the LH || spectral broadening and, consequently, enabling the LH power to propagate also in high density plasmas ( || is the wavenumber component aligned to the confinement magnetic field). New results of FTU experiments are presented, performed by following the aforementioned modeling: they indicate that, for the first time, the LHCD conditions are established by operating at ITER-relevant high edge densities.

  16. Critical current density measurement of thin films by AC susceptibility based on the penetration parameter h

    DEFF Research Database (Denmark)

    Li, Xiao-Fen; Grivel, Jean-Claude; Abrahamsen, Asger B.

    2012-01-01

    current density Jc of superconducting thin films by AC susceptibility. Compared with the normally used method based on the peak of the imaginary part, our method uses a much larger range of the AC susceptibility curve, thus allowing determination of the temperature (T) dependence of Jc from a normally...

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

    Energy Technology Data Exchange (ETDEWEB)

    Tyagi, P.V., E-mail: tyagipv@ornl.gov [The Graduate University for Advanced Studies, Tsukuba, Ibaraki (Japan); Nishiwaki, M.; Noguchi, T.; Sawabe, M.; Saeki, T.; Hayano, H.; Kato, S. [KEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki (Japan)

    2013-11-15

    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/cm{sup 2}) and low (≈30 mA/cm{sup 2}) 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.

  18. Contributions for the modelling of submarine cables – current density and simplified modelling of wired layers

    DEFF Research Database (Denmark)

    Silva, Filipe Miguel Faria da; Bak, Claus Leth; Ebdrup, Thomas

    2015-01-01

    This article researches two topics relevant for the development of accurate formulae able to estimate the ampacity of HVAC submarine cables. Simplified formulae for estimating the current density distribution, which can be used for theoretical analyses, are developed and compared with the exact...

  19. The Keldysh formalism applied to time-dependent current-density-functional theory

    NARCIS (Netherlands)

    Gidopoulos, NI; Wilson, S

    2003-01-01

    In this work we demonstrate how to derive the Kohn-Sham equations of time-dependent current-density functional theory from a generating action functional defined on a Keldysh time contour. These Kohn-Sham equations contain an exchange-correlation contribution to the vector potential. For this

  20. Particle image velocimetry measurements and numerical modeling of a saline density current

    CSIR Research Space (South Africa)

    Gerber, G

    2011-03-01

    Full Text Available turbulence collapsed. A two-dimensional, unsteady, Reynolds-averaged Navier-Stokes (2DV-URANS) simulation was also performed on this density current. Good agreement was found between the modeled and measured normalized mean flow profiles. A comparison...

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

    International Nuclear Information System (INIS)

    Feng, Y.; Verboncoeur, J. P.

    2006-01-01

    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

  2. Magnetically Filtered Faraday Probe for Measuring the Ion Current Density Profile of a Hall Thruster

    National Research Council Canada - National Science Library

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

    2006-01-01

    .... 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...

  3. Behaviour of bipolar membranes at high current density. Water diffusion limitation

    NARCIS (Netherlands)

    Krol, J.J.; Jansink, M.G.J.; Wessling, Matthias; Strathmann, H.

    1998-01-01

    In this paper the behaviour of bipolar membranes at very high current density is discussed. Current–voltage curves are determined, both for the Tokuyama Soda BP-1 and the WSI Technologies bipolar membrane. The current–voltage curves are characterised by an inflection point at which a drastic

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

    Science.gov (United States)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Bellucci, S. [INFN, Laboratori Nazionali di Frascati, Frascati (Italy); Bezerra de Mello, E.R. [Universidade Federal da Parai ba, Departamento de Fisica, 58.059-970, Joao Pessoa, PB (Brazil); Braganca, E. [INFN, Laboratori Nazionali di Frascati, Frascati (Italy); Universidade Federal da Parai ba, Departamento de Fisica, 58.059-970, Joao Pessoa, PB (Brazil); Saharian, A.A. [Yerevan State University, Department of Physics, Yerevan (Armenia)

    2016-06-15

    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. (orig.)

  6. A study on current density distribution reproduction by bounded-eigenfunction expansion for a tokamak plasma

    International Nuclear Information System (INIS)

    Kurihara, Kenichi

    1997-11-01

    Plasma current density distribution is one of the most important controlled variables to determine plasma performance of energy confinement and stability in a tokamak. However, its reproduction by using magnetic measurements solely is recognized to yield an ill-posed problem. A method to presume the formulas giving profiles of plasma pressure and current has been adopted to regularize the ill-posedness, and hence it has been reported the current density distribution can be reproduced as a solution of Grad-Shafranov equation within a certain accuracy. In order to investigate its strict reproducibility from magnetic measurements in this inverse problem, a new method of 'bounded-eigenfunction expansion' is introduced, and it was found that the reproducibility directly corresponds to the independence of a series of the special function. The results from various investigations in an aspect of applied mathematics concerning this inverse problem are presented in detail. (author)

  7. Measurement of levitation force and critical current density of melt textured YBa2Cu3Ox

    International Nuclear Information System (INIS)

    Lehndorff, B.; Kuerschner, H.G.; Busch, D.; Fischer, B.; Piel, H.

    1993-01-01

    By various Melt Textured Growth (MTG) processes YBa 2 Cu 3 O x (Y-123) samples have been prepared with high critical current densities and high levitation forces. The best value of both have been reported by Murakami et al., who used the melt powder melt growth (MPMG) process with platinum addition. These melt textured samples are applicable to magnetic bearings (3). The goal of this work is to develop technical High Temperature Superconductors (HTSC) for bearings and magnet application. In order to optimize the HTSC material for this purpose, levitation force and critical current measurements were carried out. Within this work samples were prepared by the modified Salama method. Levitation force was measured as a function of the distance between the magnet and the superconductor. The critical current density was determined by an inductive method. (orig.)

  8. 'Anomalous electron transport' with 'Giant Current Density' at room temperature observed with nanogranular materials

    International Nuclear Information System (INIS)

    Koops, Hans W.P.

    2013-01-01

    Focused electron beam induced deposition is a novel bottom up nano-structurization technology. An electron beam of high power density is used to generate nano- structures with dimensions > 20 nm, but being composed from amorphous or nanogranular materials with crystals of 2 to 5 nm diameter embedded in a Fullerene matrix. Those compounds are generated in general by secondary or low energy electrons in layers of inorganic, organic, organometallic compounds absorbed to the sample. Those are converted into nanogranular materials by the electron beam following chemical and physical laws, as given by 'Mother Nature'. Metals and amorphous mixtures of chemical compounds from metals are normal resistors, which can carry a current density J 2 . Nanogranular composites like Au/C or Pt/C with metal nanocrystals embedded in a Fullerene matrix have hopping conduction with 0-dimensional Eigen-value characteristics and show 'anomalous electron transport' and can carry 'Giant Current Densities' with values from > 1 MA/cm 2 to 0.1 GA/cm 2 without destruction of the materials. However the area connecting the nanogranular material with a metal with a 3-dimensional electron gas needs to be designed, that the flowing current is reduced to the current density values which the 3-D metal can support without segregation. The basis for a theoretical explanation of the phenomenon can be geometry quantization for Coulomb blockade, of electron surface orbitals around the nanocrystals, hopping conduction, and the limitation of the density of states for phonons in geometry confined non percolated granular materials with strong difference in mass and orientation. Several applications in electronics, signal generators, light sources, detectors, and solar energy harvesting are suggested. (author)

  9. Human in-vivo brain magnetic resonance current density imaging (MRCDI)

    DEFF Research Database (Denmark)

    Göksu, Cihan; Hanson, Lars G.; Siebner, Hartwig R

    2017-01-01

    Magnetic resonance current density imaging (MRCDI) and MR electrical impedance tomography (MREIT) are two emerging modalities, which combine weak time-varying currents injected via surface electrodes with magnetic resonance imaging (MRI) to acquire information about the current flow and ohmic...... is modulated by these shifts, allowing to determine ΔBz,c for the reconstruction of the current flow and ohmic conductivity. Here, we demonstrate reliable ΔBz,c measurements in-vivo in the human brain based on multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP......-FID measurements, we demonstrate a strong influence of magnetic stray fields on the ΔBz,c images, caused by non-ideal paths of the electrode cables, and validate a correction method. Finally, we perform measurements with two different current injection profiles in five subjects. We demonstrate reliable recordings...

  10. Responsivity Dependent Anodization Current Density of Nanoporous Silicon Based MSM Photodetector

    Directory of Open Access Journals (Sweden)

    Batool Eneaze B. Al-Jumaili

    2016-01-01

    Full Text Available Achieving a cheap and ultrafast metal-semiconductor-metal (MSM photodetector (PD for very high-speed communications is ever-demanding. We report the influence of anodization current density variation on the response of nanoporous silicon (NPSi based MSM PD with platinum (Pt contact electrodes. Such NPSi samples are grown from n-type Si (100 wafer using photoelectrochemical etching with three different anodization current densities. FESEM images of as-prepared samples revealed the existence of discrete pores with spherical and square-like shapes. XRD pattern displayed the growth of nanocrystals with (311 lattice orientation. The nanocrystallite sizes obtained using Scherrer formula are found to be between 20.8 nm and 28.6 nm. The observed rectifying behavior in the I-V characteristics is ascribed to the Pt/PSi/n-Si Schottky barrier formation, where the barrier height at the Pt/PSi interface is estimated to be 0.69 eV. Furthermore, this Pt/PSi/Pt MSM PD achieved maximum responsivity of 0.17 A/W and quantum efficiency as much as 39.3%. The photoresponse of this NPSi based MSM PD demonstrated excellent repeatability, fast response, and enhanced saturation current with increasing anodization current density.

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

    Science.gov (United States)

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

    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 Na2. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Escartín, J. M. [Université de Toulouse, UPS, Laboratoire de Physique Théorique, IRSAMC, F-31062 Toulouse Cedex (France); CNRS, UMR5152, F-31062 Toulouse Cedex (France); Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Vincendon, M.; Dinh, P. M.; Suraud, E. [Université de Toulouse, UPS, Laboratoire de Physique Théorique, IRSAMC, F-31062 Toulouse Cedex (France); CNRS, UMR5152, F-31062 Toulouse Cedex (France); Romaniello, P. [Laboratoire de Physique Théorique, CNRS, IRSAMC, Université Toulouse III - Paul Sabatier and European Theoretical Spectroscopy Facility, 118 Route de Narbonne, 31062 Toulouse Cedex (France); Reinhard, P.-G. [Institut für Theoretische Physik, Universität Erlangen, Staudtstraße 7, D-91058 Erlangen (Germany)

    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.

  13. Time-dependent current-density functional theory for generalized open quantum systems.

    Science.gov (United States)

    Yuen-Zhou, Joel; Rodríguez-Rosario, César; Aspuru-Guzik, Alán

    2009-06-14

    In this article, we prove the one-to-one correspondence between vector potentials and particle and current densities in the context of master equations with arbitrary memory kernels, therefore extending time-dependent current-density functional theory (TD-CDFT) to the domain of generalized many-body open quantum systems (OQS). We also analyse the issue of A-representability for the Kohn-Sham (KS) scheme proposed by D'Agosta and Di Ventra for Markovian OQS [Phys. Rev. Lett. 2007, 98, 226403] and discuss its domain of validity. We suggest ways to expand their scheme, but also propose a novel KS scheme where the auxiliary system is both closed and non-interacting. This scheme is tested numerically with a model system, and several considerations for the future development of functionals are indicated. Our results formalize the possibility of practising TD-CDFT in OQS, hence expanding the applicability of the theory to non-Hamiltonian evolutions.

  14. High current density and low emission field of carbon nanotube array microbundle

    Science.gov (United States)

    Zhang, Quan; Wang, Xi-juan; Meng, Peng; Yue, Hong-xin; Zheng, Rui-ting; Wu, Xiao-ling; Cheng, Guo-an

    2018-01-01

    Field electron emission from carbon nanotubes shows promising application potential in devices. Low adhesive bonding strength between the carbon nanotubes and the substrate presents a practical challenge in environments such as high field emission current density. In this paper, we report on the performance of a carbon nanotube microbundle attached to a tungsten needle by a uniform glue layer. The device is easily fabricated without complex fixture and possesses a complete array structure. After curing the glue in air, the adhesive strength between the carbon nanotubes and the needle is over 2000 N/cm2. Field emission measurements demonstrate that the maximum current density of the emitters is over 20 A/cm2 under a low applied field (X-ray tubes, and lamps.

  15. Distributions of the ion temperature, ion pressure, and electron density over the current sheet surface

    Energy Technology Data Exchange (ETDEWEB)

    Kyrie, N. P., E-mail: kyrie@fpl.gpi.ru; Markov, V. S., E-mail: natalya.kyrie@yandex.ru; Frank, A. G.; Vasilkov, D. G.; Voronova, E. V. [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

    2016-06-15

    The distributions of the ion temperature, ion pressure, and electron density over the width (the major transverse dimension) of the current sheet have been studied for the first time. The current sheets were formed in discharges in argon and helium in 2D and 3D magnetic configurations. It is found that the temperature of argon ions in both 2D and 3D magnetic configurations is almost uniform over the sheet width and that argon ions are accelerated by the Ampère force. In contrast, the distributions of the electron density and the temperature of helium ions are found to be substantially nonuniform. As a result, in the 2D magnetic configuration, the ion pressure gradient across the sheet width makes a significant contribution (comparable with the Ampère force) to the acceleration of helium ions, whereas in the 3D magnetic configuration, the Ampère force is counterbalanced by the pressure gradient.

  16. Large high current density superconducting solenoid for the time projection chamber experiment

    International Nuclear Information System (INIS)

    Green, M.A.; Burns, W.A.; Eberhard, P.H.; Gibson, G.H.; Miller, P.B.; Ross, R.R.; Smits, R.G.; Taylor, J.D.

    1978-06-01

    One of the experiments for the PEP storage rings at the Stanford Linear Accelerator Center uses a superconducting magnet to provide the magnetic field for the Time Projection Chamber detector. This magnet has an inside diameter of 2.04 m and a gap of 3.26 m. The magnet central induction is 1.5 T. This magnetic induction is supplied by a thin high current density superconducting coil which is less than 0.4 radiation lengths thick. The magnet stored energy will be 10.9 MJ; the coil superconductor matrix current density will be about 7.0 x 10 8 Am -2 . The TPC magnet uses a two-phase forced flow tubular cooling system which combines many of the advantages of single-phase supercritical helium cooling with those of boiling helium bath cooling

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

    Energy Technology Data Exchange (ETDEWEB)

    Fadin, V. V., E-mail: fvv@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Aleutdinova, M. I., E-mail: aleut@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Seversk Technological Institute, Branch of State Autonomous Educational Institution of Higher Professional Education “National Research Nuclear University “MEPhI”, Seversk, 636036 (Russian Federation); Rubtsov, V. Ye., E-mail: rvy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Aleutdinova, V. A., E-mail: valery-aleut@yandex.ru [National Research St. Petersburg State Polytechnical University, St. Petersburg, 195251 (Russian Federation)

    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.

  18. Degradation of Solid Oxide Electrolysis Cells Operated at High Current Densities

    DEFF Research Database (Denmark)

    Tao, Youkun; Ebbesen, Sune Dalgaard; Mogensen, Mogens Bjerg

    2014-01-01

    In this work the durability of solid oxide cells for co-electrolysis of steam and carbon dioxide (45 % H2O + 45 % CO2 + 10 % H2) at high current densities was investigated. The tested cells are Ni-YSZ electrode supported, with a YSZ electrolyte and either a LSM-YSZ or LSCF-CGO oxygen electrode....... A current density of -1.5 and -2.0 A/cm2 was applied to the cell and the gas conversion was 45 % and 60 %, respectively. The cells were operated for a period of up to 700 hours. The electrochemical analysis revealed significant performance degradation for the ohmic process, oxygen ion interfacial transfer...

  19. Distribution of the Current Density in Electrolyte of the Pem Fuel Cell

    Directory of Open Access Journals (Sweden)

    Eugeniusz Kurgan

    2004-01-01

    Full Text Available In this paper water management in proton exchange membrane (PEM fuel cell is considered. Firt mass convervation law for water is applied. Next proton transport is described by the Nernst-Planck equation and liqid water convection velocity is eliminated by the Schlogl equation. Electro-osmotic drag coefficient is related to hydrogen index and experimentally determined swelling coefficient. Three partial differential equations for molar water concentration Cw, electric potential ϕ and water pressure Pw are formulated. Current density vector i is derived from proton flux expression. These equations together with adequate boundary conditions were solved using finite element method. The distribution of electric potential and current density in function of geometrical parametres is investigated. At the end some illustrative example is given.

  20. Results of Current Density Distribution Mapping in PEM Fuel Cells Dependent on Operation Parameters

    Directory of Open Access Journals (Sweden)

    Zbigniew A. Styczynski

    2013-07-01

    Full Text Available This paper presents in situ measurements of a newly developed current density measurement system for proton exchange membrane fuel cells (PEMFC. While the functional principle and technical evaluation of the measurement system were presented in a previous paper, this paper analyzes the influence of various operation parameters, including multiple start-stop operation, at the anode, cathode and cooling locations on the distribution and long-term development of the current density. The system was operated for 500 h over two years with long periods of inactivity between measurements. The measurement results are evaluated and provide additional information on how to optimize the operation modes of fuel cells, including the start and stop of such systems as well as the water balance.

  1. Effect of Current Density on Optical Properties of Anisotropic Photoelectrochemical Etched Silicon (110)

    Science.gov (United States)

    Amirhoseiny, M.; Hassan, Z.; Ng, S. S.

    2012-08-01

    Photoelectrochemical etched Si layers were prepared on n-type (110) oriented silicon wafer. The photoluminescence (PL), Fourier transformed infrared (FTIR) absorption and Raman spectroscopies of etched Si (110) at two different current densities were studied. Both samples showed PL peak in the visible spectral range situated from 650 nm to 750 nm. The corresponding changes in Raman spectra at different current density are discussed. The blue shift in the PL and Raman peaks is consequent of the quantum confinement effect and defect states of surface Si nanocrystallites complexes and hydrogen atoms of the photoelectrochemical etched Si (110) samples. The attenuated total reflection (ATR) results show both hydrogen and oxygen related IR modes in the samples which can be used to explain the PL effect.

  2. Attenuation, phase velocity and current density distribution in high critical temperature superconducting planar transmission lines

    Energy Technology Data Exchange (ETDEWEB)

    Cabon, B.; Vu Dinh, T.; Chilo, J. [URA CNRS 833, Grenoble (France). Lab. d`Electromagnetisme

    1995-05-01

    Electromagnetic calculation of propagation parameters for high {Tc} superconductive coplanar and microstrip transmission lines is presented. Calculations are performed by a nodal circuit simulator (SPICE), with possibility of direct interfacing with CAE standards. The results are in good agreement with data obtained with a full-wave analysis and CPU time is much smaller than in standard MW applications. Then, current density distributions are shown.

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

    Science.gov (United States)

    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. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

  4. Contactless estimation of critical current density and its temperature dependence using magnetic measurements

    Czech Academy of Sciences Publication Activity Database

    Youssef, A.; Baničová, L.; Švindrych, Zdeněk; Janů, Zdeněk

    2010-01-01

    Roč. 118, č. 5 (2010), s. 1036-1037 ISSN 0587-4246. [Czech and Slovak Conference on Magnetism /14./. Košice, 06.07.2010-09.07.2010] R&D Projects: GA MŠk(CZ) ME10069 Institutional research plan: CEZ:AV0Z10100520 Keywords : superconductivity * critical state * Bean model * critical current density Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.467, year: 2010

  5. Measurements of current density distribution in shaped e-beam writers

    Czech Academy of Sciences Publication Activity Database

    Bok, Jan; Horáček, Miroslav; Kolařík, Vladimír; Urbánek, Michal; Matějka, Milan; Krzyžánek, Vladislav

    2016-01-01

    Roč. 149, JAN 5 (2016), s. 117-124 ISSN 0167-9317 R&D Projects: GA ČR(CZ) GA14-20012S; GA MŠk(CZ) LO1212; GA MŠk ED0017/01/01 Institutional support: RVO:68081731 Keywords : shaped e-beam writer * electron beam * current density Subject RIV: JB - Sensors, Measurment, Regulation Impact factor: 1.806, year: 2016

  6. Dependence of critical current density on crystalline direction in thin YBCO films

    DEFF Research Database (Denmark)

    Paturi, P.; Peurla, M.; Raittila, J.

    2005-01-01

    The dependence of critical current density (J(c)) on the angle between the current direction and the (100) direction in the ab-plane of thin YBCO films deposited on (001)-SrTiO3 from natiocrystalline and microcrystalline targets is studied using magneto-optical microscopy. In the films made from...... the nanocrystalline target it is found that J(c) does not depend on the angle whereas J(c) decreases with increasing angle in the films made from the microcrystalline target. The films were characterized by detailed X-ray diffraction measurements. The findings are explained in terms of a network of planar defects...

  7. Influence of current density on microstructure and properties of electrodeposited nickel-alumina composite coatings

    International Nuclear Information System (INIS)

    Góral, Anna; Nowak, Marek; Berent, Katarzyna; Kania, Bogusz

    2014-01-01

    Highlights: • Current density of the electrodeposition affects the incorporation of Al 2 O 3 in Ni matrix. • Ni/Al 2 O 3 composite coatings exhibit changes in crystallographic texture. • The pitting corrosion effects were observed in Ni/Al 2 O 3 coatings. • Residual stresses were decreased with increasing current density and coating thickness. - Abstract: Electrodeposition process is a very promising method for producing metal matrix composites reinforced with ceramic particles. In this method insoluble particles suspended in an electrolytic bath are embedded in a growing metal layer. This paper is focused on the investigations of the nickel matrix nanocomposite coatings with hard α-Al 2 O 3 nano-particles, electrochemically deposited from modified Watts-type baths on steel substrates. The influence of various current densities on the microstructure, residual stresses, texture, hardness and corrosion resistance of the deposited nickel/alumina coatings was investigated. The surface morphology, cross sections of the coatings and distribution of the ceramic particles in the metal matrix were examined by scanning electron microscopy. The phase composition, residual stresses and preferred grain orientation of the coatings were characterized using X-ray diffraction techniques. The coating morphology revealed that α-Al 2 O 3 particles show a distinct tendency to form agglomerates, approximately uniformly distributed into the nickel matrix

  8. Reduction in Recombination Current Density in Boron Doped Silicon Using Atomic Hydrogen

    Science.gov (United States)

    Young, Matthew Garett

    The solar industry has grown immensely in recent years and has reached a point where solar energy has now become inexpensive enough that it is starting to emerge as a mainstream electrical generation source. However, recent economic analysis has suggested that for solar to become a truly wide spread source of electricity, the costs still need to plummet by a factor of 8x. This demands new and innovative concepts to help lower such cost. In pursuit of this goal, this dissertation examines the use of atomic hydrogen to lessen the recombination current density in the boron doped region of n-type silicon solar cells. This required the development of a boron diffusion process that maintained the bulk lifetime of n-type silicon such that the recombination current density could be extracted by photoconductance spectroscopy. It is demonstrated that by hydrogenating boron diffusions, the majority carrier concentration can be controlled. By using symmetrically diffused test structures with quinhydrone-methanol surface passivation the recombination current density of a hydrogenated boron profile is shown to be less than that of a standard boron profile, by as much as 30%. This is then applied to a modified industrial silicon solar cell process to demonstrate an efficiency enhancement of 0.4%.

  9. Development of large high current density superconducting solenoid magnets for use in high energy physics experiments

    International Nuclear Information System (INIS)

    Green, M.A.

    1977-05-01

    The development of a unique type of large superconducting solenoid magnet, characterized by very high current density windings and a two-phase helium tubular cooling system is described. The development of the magnet's conceptual design and the construction of two test solenoids are described. The successful test of the superconducting coil and its tubular cooling refrigeration system is presented. The safety, environmental and economic impacts of the test program on future developments in high energy physics are shown. Large solid angle particle detectors for colliding beam physics will analyze both charged and neutral particles. In many cases, these detectors will require neutral particles, such as gamma rays, to pass through the magnet coil with minimum interaction. The magnet coils must be as thin as possible. The use of superconducting windings allows one to minimize radiation thickness, while at the same time maximizing charged particle momentum resolution and saving substantial quantities of electrical energy. The results of the experimental measurements show that large high current density solenoid magnets can be made to operate at high stored energies. The superconducting magnet development described has a positive safety and environmental impact. The use of large high current density thin superconducting solenoids has been proposed in two high energy physics experiments to be conducted at the Stanford Linear Accelerator Center and Cornell University as a result of the successful experiments described

  10. High current density in bulk YBa2Cu3O/sub x/ superconductor

    International Nuclear Information System (INIS)

    Salama, K.; Selvamanickam, V.; Gao, L.; Sun, K.

    1989-01-01

    A liquid phase processing method for the fabrication of bulk YBa 2 Cu 3 O/sub x/ superconductors with large current carrying capacity has been developed. Slow cooling through the peritectic transformation (1030--980 degree C) has been shown to control the microstructure of these superconductors. A cooling rate of 1 degree C/h in this temperature range has yielded a microstructure with long plate type, thick grains oriented over a wide area. Current density up to 18 500 A/cm 2 has been obtained by continuous direct current measurements and in excess of 62 000 A/cm 2 with pulse current of 10 ms duration and 75 000 A/cm 2 using 1 ms pulse. The strong magnetic field dependence observed in sintered bulk 1-2-3 superconductors is also minimized to a large extent where a current density in excess of 37 000 A/cm 2 is obtained in a field of 6000 G

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

    Energy Technology Data Exchange (ETDEWEB)

    Jones, S.E.; Kesner, J.; Luckhardt, S.; Paoletti, F. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center; von Goeler, S.; Bernabei, S.; Kaita, R. [Princeton Univ., NJ (United States). Plasma Physics Lab.; Rimini, F. [JET Joint Undertaking, Abingdon (United Kingdom)

    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.

  12. The effect of current density and saccharin addition on the grain size of nickel coatings

    Energy Technology Data Exchange (ETDEWEB)

    Uhm, Young Rang; Park, Keun Yung; Son, Kwang Jae; Shim, Young Ho; Choi, Sun Ju [KAERI, Daejeon (Korea, Republic of)

    2012-10-15

    Recently, the main advantage of a radioisotope 'fuel' is concentrated, because it is 'burned' at the rate of the isotopes half life. In other words, given a half life of 100 years, a nuclear battery would still produce half of its initial starting power after 100 years. A speck of a radioisotope like nickel 63, for example, contains enough energy to power a nano nuclear battery for decades, and to do so safely. Ni 63, a beta radiation source, is prepared by electrical deposition of radioactive Ni 63 ions on thin non radioactive nickel foil. Ni 63 plating is similar to other electroplating processes that employ soluble metal anodes. It requires the passage of a direct current between two electrodes that are immersed in a conductive, aqueous solution of nickel salts. The charged Ni ions are formed by sulfate, sulfamate, chloride, and a Watts bath. However, the charged Ni 63 ions are formed by dissolving metal Ni 63. To establish the coating condition of Ni 63, non radioactive metal Ni particles were dissolved in an acid solution and electroplated on the Ni sheet. A continuous increase in the grain size versus current density has also been recognized in the direct current electrodeposition of nickel coating. On the other hand, A runa et al. reported that the current density has no significant effect on the grain size of nickel electro deposits. A review of the literature shows that saccharin has often been added to a nickel plating bath since the 1980s to improve the ductility and brightness, and in later periods as a grain refiner agent. In the present paper, not only the preparation of the Ni plating solution prepared by dissolving metal particles but also an optimization of the deposition conditions, such as the influence of current density and saccharin concentration on the grain size, was investigated. The proposed model can also be applied for radioactive Ni 63 electroplating.

  13. Dynamics of low density coronal plasma in low current x-pinches

    International Nuclear Information System (INIS)

    Haas, D; Bott, S C; Vikhrev, V; Eshaq, Y; Ueda, U; Zhang, T; Baranova, E; Krasheninnikov, S I; Beg, F N

    2007-01-01

    Experiments were performed on an x-pinch using a pulsed power current generator capable of producing an 80 kA current with a rise time of 50 ns. Molybdenum wires with and without gold coating were employed to study the effect of high z coating on the low-density ( 18 cm -3 ) coronal plasma dynamics. A comparison of images from XUV frames and optical probing shows that the low density coronal plasma from the wires initially converges at the mid-plane immediately above and below the cross-point. A central jet is formed which moves with a velocity of 6 x 10 4 ms -1 towards both electrodes forming a z-pinch column before the current maximum. A marked change in the low density coronal plasma dynamics was observed when molybdenum wires coated with ∼ 0.09 μm of gold were used. The processes forming the jet structure were delayed relative to bare Mo x-pinches, and the time-resolved x-ray emission also showed differences. An m = 0 instability was observed in the coronal plasma along the x-pinch legs, which were consistent with x-ray PIN diode signals in which x-ray pulses were observed before x-ray spot formation. These early time x-ray pulses were not observed with pure molybdenum x-pinches. These observations indicate that a thin layer of gold coating significantly changes the coronal plasma behaviour. Two dimensional MHD simulations were performed and qualitatively agree with experimental observations of low density coronal plasma

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

    International Nuclear Information System (INIS)

    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 19 - 10 20 m -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 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

  15. Polarization Potential Has No Effect on Maximum Current Density Produced by Halotolerant Bioanodes

    Directory of Open Access Journals (Sweden)

    Muriel González-Muñoz

    2018-03-01

    Full Text Available Halotolerant bioanodes are considered an attractive alternative in microbial electrochemical systems, as they can operate under higher conductive electrolytes, in comparison with traditional wastewater and freshwater bioanodes. The dependency between energetic performance and polarization potential has been addressed in several works; however the vast majority discusses its effect when wastewater or freshwater inocula are employed, and fewer reports focus on inocula from highly-saline environments. Moreover, the effect of the polarization potential on current production is not fully understood. To determine if the polarization potential has a significant effect on current production, eight bioanodes were grown by chronoamperometry at positive and negative potentials relative to the reference electrode (+0.34 V/SHE and −0.16 V/SHE, in a three-electrode set-up employing sediments from a hyperhaline coastal lagoon. The maximum current density obtained was the same, despite the differences in the applied potential. Our findings indicate that even if differences in organic matter removal and coulombic efficiency are obtained, the polarization potential had no statistically significant effect on overall current density production.

  16. Public magnetic field exposure based on internal current density for electric low voltage systems.

    Science.gov (United States)

    Keikko, Tommi; Seesvuori, Reino; Hyvönen, Martti; Valkealahti, Seppo

    2009-04-01

    A measurement concept utilizing a new magnetic field exposure metering system has been developed for indoor substations where voltage is transformed from a medium voltage of 10 or 20 kV to a low voltage of 400 V. The new metering system follows the guidelines published by the International Commission on Non-Ionizing Radiation Protection. It can be used to measure magnetic field values, total harmonic distortion of the magnetic field, magnetic field exposure ratios for public and workers, load current values, and total harmonic distortion of the load current. This paper demonstrates how exposure to non-sinusoidal magnetic fields and magnetic flux density exposure values can be compared directly with limit values for internal current densities in a human body. Further, we present how the magnetic field and magnetic field exposure behaves in the vicinity of magnetic field sources within the indoor substation and in the neighborhood. Measured magnetic fields around the substation components have been used to develop a measurement concept by which long-term measurements in the substations were performed. Long-term measurements revealed interesting and partly unexpected dependencies between the measured quantities, which have been further analyzed. The principle of this paper is to substitute a demanding exposure measurement with measurements of the basic quantities like the 50 Hz fundamental magnetic field component, which can be estimated based on the load currents for certain classes of substation lay-out.

  17. Human in-vivo brain magnetic resonance current density imaging (MRCDI).

    Science.gov (United States)

    Göksu, Cihan; Hanson, Lars G; Siebner, Hartwig R; Ehses, Philipp; Scheffler, Klaus; Thielscher, Axel

    2018-05-01

    Magnetic resonance current density imaging (MRCDI) and MR electrical impedance tomography (MREIT) are two emerging modalities, which combine weak time-varying currents injected via surface electrodes with magnetic resonance imaging (MRI) to acquire information about the current flow and ohmic conductivity distribution at high spatial resolution. The injected current flow creates a magnetic field in the head, and the component of the induced magnetic field ΔB z,c parallel to the main scanner field causes small shifts in the precession frequency of the magnetization. The measured MRI signal is modulated by these shifts, allowing to determine ΔB z,c for the reconstruction of the current flow and ohmic conductivity. Here, we demonstrate reliable ΔB z,c measurements in-vivo in the human brain based on multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP-FID) sequences. In a series of experiments, we optimize their robustness for in-vivo measurements while maintaining a good sensitivity to the current-induced fields. We validate both methods by assessing the linearity of the measured ΔB z,c with respect to the current strength. For the more efficient SSFP-FID measurements, we demonstrate a strong influence of magnetic stray fields on the ΔB z,c images, caused by non-ideal paths of the electrode cables, and validate a correction method. Finally, we perform measurements with two different current injection profiles in five subjects. We demonstrate reliable recordings of ΔB z,c fields as weak as 1 nT, caused by currents of 1 mA strength. Comparison of the ΔB z,c measurements with simulated ΔB z,c images based on FEM calculations and individualized head models reveals significant linear correlations in all subjects, but only for the stray field-corrected data. As final step, we reconstruct current density distributions from the measured and simulated ΔB z,c data. Reconstructions from non-corrected ΔB z,c measurements

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

    Science.gov (United States)

    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).

  19. Reduction of Gas Bubbles and Improved Critical Current Density in Bi-2212 Round Wire by Swaging

    CERN Document Server

    Jiang, J; Huang, Y; Hong, S; Parrell, J; Scheuerlein, C; Di Michiel, M; Ghosh, A; Trociewitz, U; Hellstrom, E; Larbalestier, D

    2013-01-01

    Bi-2212 round wire is made by the powder-in-tube technique. An unavoidable property of powder-in-tube conductors is that there is about 30% void space in the as-drawn wire. We have recently shown that the gas present in the as-drawn Bi-2212 wire agglomerates into large bubbles and that they are presently the most deleterious current limiting mechanism. By densifying short 2212 wires before reaction through cold isostatic pressing (CIPping), the void space was almost removed and the gas bubble density was reduced significantly, resulting in a doubled engineering critical current density (JE) of 810 A/mm2 at 5 T, 4.2 K. Here we report on densifying Bi-2212 wire by swaging, which increased JE (4.2 K, 5 T) from 486 A/mm2 for as-drawn wire to 808 A/mm2 for swaged wire. This result further confirms that enhancing the filament packing density is of great importance for making major JE improvement in this round-wire magnet conductor.

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

    International Nuclear Information System (INIS)

    Chacon-Golcher, E.

    2002-01-01

    This dissertation develops diverse research on small (diameter ∼ few mm), high current density (J ∼ several tens of mA/cm 2 ) 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/cm 2 were observed in 2.3 (micro)s 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 (micro)s), high current densities (∼ 100 mA/cm 2 ) and low operating pressures ( e psilon) n (le) 0.006 π mm · mrad) although measured currents differed from the desired ones (I ∼ 5mA) by about a factor of 10

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

    Energy Technology Data Exchange (ETDEWEB)

    Chacon-Golcher, Edwin [Univ. of California, Berkeley, CA (United States)

    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.

  2. High current density Esaki tunnel diodes based on GaSb-InAsSb heterostructure nanowires.

    Science.gov (United States)

    Ganjipour, Bahram; Dey, Anil W; Borg, B Mattias; Ek, Martin; Pistol, Mats-Erik; Dick, Kimberly A; Wernersson, Lars-Erik; Thelander, Claes

    2011-10-12

    We present electrical characterization of broken gap GaSb-InAsSb nanowire heterojunctions. Esaki diode characteristics with maximum reverse current of 1750 kA/cm(2) at 0.50 V, maximum peak current of 67 kA/cm(2) at 0.11 V, and peak-to-valley ratio (PVR) of 2.1 are obtained at room temperature. The reverse current density is comparable to that of state-of-the-art tunnel diodes based on heavily doped p-n junctions. However, the GaSb-InAsSb diodes investigated in this work do not rely on heavy doping, which permits studies of transport mechanisms in simple transistor structures processed with high-κ gate dielectrics and top-gates. Such processing results in devices with improved PVR (3.5) and stability of the electrical properties.

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

    Science.gov (United States)

    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.

  4. Confinement bifurcation by current density profile perturbation in TUMAN-3M tokamak

    International Nuclear Information System (INIS)

    Lebedev, S.V.; Andreiko, M.V.; Askinazi, L.G.

    2001-01-01

    In the recent experiments performed on TUMAN-3M the possibility to switch on/off the H-mode by current density profile perturbations has been shown. The j(r) perturbations were created by fast Current Ramp Up/Down or by Magnetic Compression produced by a fast increase of the toroidal magnetic field. It was found that the Current Ramp Up (CRU) and Magnetic Compression (MC) are useful means for H-mode triggering. The Current Ramp Down (CRD) triggers H-L transition. The difference in the j(r) behavior in these experiments suggests the peripheral current density may not be the critical parameter controlling L-H and H-L transitions. Confinement bifurcation in the above experiments could be explained by the unified mechanism: variation of a turbulent transport resulting from radial electric field emerging near the edge in the conditions of alternating toroidal electric field Ej and different electron and ion collisionalities. According to the suggested model the toroidal field E φ arising in the periphery during the CRU and MC processes amplifies Ware drift, which mainly influences electron component. As a result the favorable for the transition negative (inward directed) E r emerges. In the CRD scenario, when E φ is opposite to the total plasma current direction, the mechanism should generate positive E r , which is thought to be unfavorable for the H-mode. The experimental data on L-H and H-L transitions in various scenarios and the results of the modeling of E r emerging in the CRU experiment are presented in the paper. (author)

  5. Numerical versus analytical Ic(H) patterns in Josephson junctions with periodically alternating critical current density

    International Nuclear Information System (INIS)

    Lazarides, N

    2004-01-01

    An analytical expression for the magnetic-field-dependent critical current I c (H) of Josephson junctions with periodically alternating critical current density J c (x) is derived within the uniform field approximation. Comparison with numerically calculated I c (H) patterns for junctions with identical, thick, periodically arranged defects with the corresponding analytical expression reveals fair agreement for a wide range of parameters, due to increased characteristic length. Based on qualitative arguments, we give the dependence of the new characteristic length on the geometrical parameters of the junction, which is in agreement with self-consistent calculations with the static sine-Gordon equation. The analytical expression captures the observed qualitative features of the I c (H) patterns, while it is practically exact for short junctions or high fields. It also produces the shift of the major peak from the zero-field position of the standard Fraunhofer pattern to another position related to the periodicity of the critical current density in φ-junctions

  6. Effect of Nb3Sn layer structure and morphology on critical current density of multifilamentary superconductors

    Science.gov (United States)

    Deryagina, I. L.; Popova, E. N.; Patrakov, E. I.; Valova-Zaharevskaya, E. G.

    2017-10-01

    The microstructure and morphology of superconducting Nb3Sn layers in multifilamentary composites differing in the fabrication route (bronze technology and internal-tin method), the shape of Nb filaments (continuous, coupled and tubular) and in the mode of Ti doping (doping of bronze matrix or Nb filaments) have been studied. Significant factors determining critical current density of these wires are the average grain sizes and the fraction of equiaxed grains in the superconducting layers. The minimal grain sizes are characteristic of the composites with tubular Nb filaments, whereas the maximal fraction of equiaxed grains is obtained in the internal-tin wires.

  7. Test data on electrical contacts at high surface velocities and high current densities for homopolar generators

    International Nuclear Information System (INIS)

    Brennan, M.; Tolk, K.M.; Weldon, W.F.; Rylander, H.G.; Woodson, H.H.

    1977-01-01

    Test data is presented for one grade of copper graphite brush material, Morganite CMlS, over a wide range of surface velocities, atmospheres, and current densities that are expected for fast discharge (<100 ms) homopolar generators. The brushes were run on a copper coated 7075-T6 aluminum disk at surface speeds up to 277 m/sec. One electroplated copper and three flame sprayed copper coatings were used during the tests. Significant differences in contact voltage drops and surface mechanical properties of the copper coatings were observed

  8. Migrational polarization in high-current density molten salt electrochemical devices

    Energy Technology Data Exchange (ETDEWEB)

    Braunstein, J.; Vallet, C.E.

    1977-01-01

    Electrochemical flux equations based on the thermodynamics of irreversible processes have been derived in terms of experimental transport coefficients for binary molten salt mixtures analogous to those proposed for high temperature batteries and fuel cells. The equations and some numerical solutions indicate steady state composition gradients of significant magnitude. The effects of migrational separation must be considered along with other melt properties in the characterization of electrode behavior, melt composition, operating temperatures and differences of phase stability, wettability and other physicochemical properties at positive and negative electrodes of high current density devices with mixed electrolytes.

  9. Electrodynamic wear of rails in high current density rail gun discharges

    International Nuclear Information System (INIS)

    Edwards, W.T.; Caldwell, S.G.

    1984-01-01

    Significant advances in high current, high speed power sources, has in recent years allowed rail guns to produce very high velocity (> 10 km/sec) macroscopic particles (> 1/10 grams). A continuing problem is the structural integrity of the components under these loadings and in particular, the rail wear due to the high current density plasma contacts. In this investigation a small bore rail gun (6x5 mm) was used with a 10.6 kjoule capacitor energy source to examine the modes of rail damage. The rails were constructed of 110 copper base material. These rails were used in an uncoated condition and also with plasma sprayed coatings of W and W/WC. The resulting surface wear was characterized by standard metallurgical techniques and analyzed for the various coatings

  10. Critical current density of MgB2 thin films and the effect of interface pinning

    International Nuclear Information System (INIS)

    Choi, Eun-Mi; Gupta, S K; Sen, Shashwati; Lee, Hyun-Sook; Kim, Hyun-Jung; Lee, Sung-Ik

    2004-01-01

    Preferentially oriented MgB 2 thin films with c-axis normal to the surface have been prepared and characterized for microstructure and transport properties. The magnetic field dependence of superconducting critical current density J c has been determined from the magnetization hysteresis (M-H) loops at various temperatures using the Bean's critical state model. High J c of these films show their potential for applications. We have also measured the angular dependences of J c . The angular dependence is seen to be in agreement with the anisotropic Ginzburg-Landau model except that at angles close to the ab plane, increased pinning due to film-substrate interaction is observed. The angular range where interface pinning is effective has been determined by measurement of asymmetry in dissipation on reversal of current for fields applied at angles close to the ab plane

  11. Electrical design of a high current density air-core reversed-field pinch ''ZTP''

    International Nuclear Information System (INIS)

    Reass, W.A.; Cribble, R.F.; Melton, J.G.

    1983-01-01

    This paper describes the electrical design of a small, high current density (10 MA/m 2 ) toroidal reversed-field Z-Pinch (RFP) presently being constructed at Los Alamos. Special purpose magnetic field programs were used to calculate self and mutual inductances for the poloidal field windings. The network analysis program MINI-SCEPTRE was then used to predict plasma current, including the interaction between toroidal and poloidal field circuits, as described by the Bessel function model for RFP's. Using these programs, coil geometry was obtained for minimal field errors and the pulse power systems were optimized to minimize equilibrium control power. Results of computer modeling and implementation of the electrical circuits are presented

  12. Density-matrix renormalization-group study of current and activity fluctuations near nonequilibrium phase transitions.

    Science.gov (United States)

    Gorissen, Mieke; Hooyberghs, Jef; Vanderzande, Carlo

    2009-02-01

    Cumulants of a fluctuating current can be obtained from a free-energy-like generating function, which for Markov processes equals the largest eigenvalue of a generalized generator. We determine this eigenvalue with the density-matrix renormalization group for stochastic systems. We calculate the variance of the current in the different phases, and at the phase transitions, of the totally asymmetric exclusion process. Our results can be described in the terms of a scaling ansatz that involves the dynamical exponent z . We also calculate the generating function of the dynamical activity (total number of configuration changes) near the absorbing-state transition of the contact process. Its scaling properties can be expressed in terms of known critical exponents.

  13. Multiphase modeling of channelized pyroclastic density currents and the effect of confinement on mobility and entrainment

    Science.gov (United States)

    Kubo, A. I.; Dufek, J.

    2017-12-01

    Around explosive volcanic centers such as Mount Saint Helens, pyroclastic density currents (PDCs) pose a great risk to life and property. Understanding of the mobility and dynamics of PDCs and other gravity currents is vital to mitigating hazards of future eruptions. Evidence from pyroclastic deposits at Mount Saint Helens and one-dimensional modeling suggest that channelization of flows effectively increases run out distances. Dense flows are thought to scour and erode the bed leading to confinement for subsequent flows and could result in significant changes to predicted runout distance and mobility. Here, we present the results of three-dimensional multiphase models comparing confined and unconfined flows using simplified geometries. We focus on bed stress conditions as a proxy for conditions that could influence subsequent erosion and self-channelization. We also explore the controls on gas entrainment in all scenarios to determine how confinement impacts the particle concentration gradient, granular interactions, and mobility.

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

    Science.gov (United States)

    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.

  15. Frequency spectra from current vs. magnetic flux density measurements for mobile phones and other electrical appliances.

    Science.gov (United States)

    Straume, Aksel; Johnsson, Anders; Oftedal, Gunnhild; Wilén, Jonna

    2007-10-01

    The frequency spectra of electromagnetic fields have to be determined to evaluate human exposure in accordance to ICNIRP guidelines. In the literature, comparisons with magnetic field guidelines have been performed by using the frequency distribution of the current drawn from the battery. In the present study we compared the frequency spectrum in the range 217 Hz to 2.4 kHz of the magnetic flux density measured near the surface of a mobile phone with the frequency spectrum of the supply current. By using the multiple frequency rule, recommended in the ICNIRP guidelines, we estimated the magnetic field exposure in the two cases. Similar measurements and estimations were done for an electric drill, a hair dryer, and a fluorescent desk lamp. All the devices have a basic frequency of 50 Hz, and the frequency spectra were evaluated up to 550 Hz. We also mapped the magnetic field in 3D around three mobile phones. The frequency distributions obtained from the two measurement methods are not equal. The frequency content of the current leads to an overestimation of the magnetic field exposure by a factor up to 2.2 for the mobile phone. For the drill, the hair dryer, and the fluorescent lamp, the supply current signal underestimated the exposure by a factor up to 2.3. In conclusion, an accurate exposure evaluation requires the magnetic flux density spectrum of the device to be measured directly. There was no indication that the devices studied would exceed the reference levels at the working distances normally used.

  16. Current Density Distribution Mapping in PEM Fuel Cells as An Instrument for Operational Measurements

    Directory of Open Access Journals (Sweden)

    Martin Geske

    2010-04-01

    Full Text Available A newly developed measurement system for current density distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFC. Taking into account previously constructed measurement systems, a method based on a multi layer printed circuit board was chosen for the development of the new system. This type of system consists of a sensor, a special electronic device and the control and visualization PC. For the acquisition of the current density distribution values, a sensor device was designed and installed within a multilayer printed circuit board with integrated shunt resistors. Varying shunt values can be taken into consideration with a newly developed and evaluated calibration method. The sensor device was integrated in a PEM fuel cell stack to prove the functionality of the whole measurement system. A software application was implemented to visualize and save the measurement values. Its functionality was verified by operational measurements within a PEMFC system. Measurement accuracy and possible negative reactions of the sensor device during PEMFC operation are discussed in detail in this paper. The developed system enables operational measurements for different operating phases of PEM fuel cells. Additionally, this can be seen as a basis for new opportunities of optimization for fuel cell design and operation modes.

  17. High wall-plug efficiency blue III-nitride LEDs designed for low current density operation.

    Science.gov (United States)

    Kuritzky, Leah Y; Espenlaub, Andrew C; Yonkee, Benjamin P; Pynn, Christopher D; DenBaars, Steven P; Nakamura, Shuji; Weisbuch, Claude; Speck, James S

    2017-11-27

    Commercial LEDs for solid-state lighting are often designed for operation at current densities in the droop regime (~35 A/cm 2 ) to minimize costly chip area; however, many benefits can be realized by operating at low current density (J ≈1 - 5 A/cm 2 ). Along with mitigation of droop losses and reduction of the operating voltage, low J operation of LEDs opens the design space for high light extraction efficiency (LEE). This work presents detailed ray tracing simulations of an LED design for low J operation with LEE ≈94%. The design is realized experimentally resulting in a peak wall-plug efficiency of 78.1% occurring at 3.45 A/cm 2 and producing an output power of 7.2 mW for a 0.1 mm 2 emitting area. At this operation point, the photon voltage V p =hνq exceeds the forward voltage (V), corresponding to a Vp/V = 103%.

  18. Inverse current source density method in two dimensions: inferring neural activation from multielectrode recordings.

    Science.gov (United States)

    Łęski, Szymon; Pettersen, Klas H; Tunstall, Beth; Einevoll, Gaute T; Gigg, John; Wójcik, Daniel K

    2011-12-01

    The recent development of large multielectrode recording arrays has made it affordable for an increasing number of laboratories to record from multiple brain regions simultaneously. The development of analytical tools for array data, however, lags behind these technological advances in hardware. In this paper, we present a method based on forward modeling for estimating current source density from electrophysiological signals recorded on a two-dimensional grid using multi-electrode rectangular arrays. This new method, which we call two-dimensional inverse Current Source Density (iCSD 2D), is based upon and extends our previous one- and three-dimensional techniques. We test several variants of our method, both on surrogate data generated from a collection of Gaussian sources, and on model data from a population of layer 5 neocortical pyramidal neurons. We also apply the method to experimental data from the rat subiculum. The main advantages of the proposed method are the explicit specification of its assumptions, the possibility to include system-specific information as it becomes available, the ability to estimate CSD at the grid boundaries, and lower reconstruction errors when compared to the traditional approach. These features make iCSD 2D a substantial improvement over the approaches used so far and a powerful new tool for the analysis of multielectrode array data. We also provide a free GUI-based MATLAB toolbox to analyze and visualize our test data as well as user datasets.

  19. Current Controlled Magnetization Switching in Cylindrical Nanowires for High-Density 3D Memory Applications

    KAUST Repository

    Mohammed, Hanan

    2018-04-18

    A next-generation memory device utilizing a three-dimensional nanowire system requires the reliable control of domain wall motion. In this letter, domain walls are studied in cylindrical nanowires consisting of alternating segments of cobalt and nickel. The material interfaces acting as domain wall pinning sites, are utilized in combination with current pulses, to control the position of the domain wall, which is monitored using magnetoresistance measurements. Magnetic force microscopy results further confirm the occurrence of current assisted domain wall depinning. Data bits are therefore shifted along the nanowire by sequentially pinning and depinning a domain wall between successive interfaces, a requirement necessary for race-track type memory devices. We demonstrate that the direction, amplitude and duration of the applied current pulses determine the propagation of the domain wall across pinning sites. These results demonstrate a multi-bit cylindrical nanowire device, utilizing current assisted data manipulation. The prospect of sequential pinning and depinning in these nanowires allows the bit density to increase by several Tbs, depending on the number of segments within these nanowires.

  20. Modeling space-charge-limited currents in organic semiconductors: Extracting trap density and mobility

    KAUST Repository

    Dacuña, Javier

    2011-11-28

    We have developed and have applied a mobility edge model that takes drift and diffusion currents to characterize the space-charge-limited current in organic semiconductors into account. The numerical solution of the drift-diffusion equation allows the utilization of asymmetric contacts to describe the built-in potential within the device. The model has been applied to extract information of the distribution of traps from experimental current-voltage measurements of a rubrene single crystal from Krellner showing excellent agreement across several orders of magnitude in the current. Although the two contacts are made of the same metal, an energy offset of 580 meV between them, ascribed to differences in the deposition techniques (lamination vs evaporation) was essential to correctly interpret the shape of the current-voltage characteristics at low voltage. A band mobility of 0.13cm 2V-1s-1 for holes is estimated, which is consistent with transport along the long axis of the orthorhombic unit cell. The total density of traps deeper than 0.1 eV was 2.2×1016cm -3. The sensitivity analysis and error estimation in the obtained parameters show that it is not possible to accurately resolve the shape of the trap distribution for energies deeper than 0.3 eV or shallower than 0.1 eV above the valence-band edge. The total number of traps deeper than 0.3 eV, however, can be estimated. Contact asymmetry and the diffusion component of the current play an important role in the description of the device at low bias and are required to obtain reliable information about the distribution of deep traps. © 2011 American Physical Society.

  1. Effects of volcano profile on dilute pyroclastic density currents: Numerical simulations

    Science.gov (United States)

    Doronzo, D. M.; Valentine, G. A.; Dellino, P.; de Tullio, M. D.

    2012-04-01

    Explosive activity and lava dome collapse at stratovolcanoes can lead to pyroclastic density currents (PDCs; mixtures of volcanic gas, air, and volcanic particles) that produce complex deposits and pose a hazard to surrounding populations. Two-dimensional numerical simulations of dilute PDCs (characterized by a turbulent suspended load and deposition through a bed load) are carried out with the Euler-Lagrange approach of multiphase physics. The fluid phase is modeled as a dusty gas (1.88 kg/m3 dense), and the solid phase is modeled as discrete particles (1 mm, 5 mm, and 10 mm; 1500 kg/m3 dense and irregularly-shaped), which are two-way coupled to the gas, i.e. they affect the fluid turbulence. The initial PDC, which enters a volcano domain 5 km long and 1.9 km high, has the following characteristics: thickness of 200 m, velocity of 20 m/s, temperature of 573 K, turbulence of 5 %, and sediment concentration of 3 % by volume. The actual physics of flow boundary zone is simulated at the PDC base, by monitoring the sediment flux toward the substrate, which acts through the flow boundary zone, and the grain-size distribution. Also, the PDC velocity and dynamic pressure are calculated. The simulations show that PDC transport, deposition, and hazard potential are sensitive to the shape of the volcano slope (profile) down which they flow. In particular, three generic volcano profiles, straight, concave-upward, and convex-upward are focused on. Dilute PDCs that flow down a constant slope gradually decelerate over the simulated run-out distance (5 km in the horizontal direction) due to a combination of sedimentation, which reduces the density of the PDC, and mixing with the atmosphere. However, dilute PDCs down a concave-upward slope accelerate high on the volcano flanks and have less sedimentation until they begin to decelerate over the shallow lower slopes. A convex-upward slope causes dilute PDCs to lose relatively more of their pyroclast load on the upper slopes of a

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

    Science.gov (United States)

    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.

  3. Research of the Ion Current Density Influence on the Glass-Ceramics Surface Defects Forming under Ion-Beam Processing

    Directory of Open Access Journals (Sweden)

    V. G. Pozdnyakov

    2015-01-01

    Full Text Available Development of modern optics is primarily determined by manufacturing accuracy of the working surfaces of optical parts. Therefore, at the last stage of manufacturing optical parts the ion-beam treatment is applied. This method uses spraying the high-energy ions of heavy gases on the surface of a solid body. After an intense ion treatment there are microscopic defects, resembling chips, on the surface of polycrystalline glass. The aim of this work is to study distribution of the surface density of defects by sizes, depending on the density of ion current.Accelerator with an anode layer and a focused ion beam was used as an ion source. The accelerator worked on argon and created ion beam with Gaussian distribution of current density along the radius. The excess positive charge of the ion beam was compensated owing to ionization of residual gas. To eliminate the influence of slow ions with peripheral regions of the ion beam, the etching was performed through a circular aperture with a diameter of 40 mm.Surface treatment of the sample was carried out at the discharge voltage of 3800 V and current of 50 mA for 30 min. The maximum ion current density on the sample surface was 20.2 A/m2 and a power density was of 5.4·104 W/m2 .Distribution of defects by size was measured in three areas of the treated surface corresponding to different densities of ion current, namely: 20.2 A/m2 , 11.3A/m2 , and 3.4 A/m2 . Their number per area unit defines a density of defects.The results show that with increasing ion current density the density of defects on the surface of polycrystalline glass decreases. Thus a view of distribution function of defect density according to size is changed: density of small defects is reduced, and density of large ones increases. Also with increasing ion current density is observed an increase in the size of defects: a 6 times increase of the average size of defects results in 1.6 times increasing ion current density.These data will

  4. Flux pinning and Critical current density in La2-xSrxCuO4+d

    Science.gov (United States)

    Mohottala, Hashini; Wells, B. O.; Budnick, J. I.; Hines, W. A.; Moodenbaugh, A. R.; Chou, F. C.

    2006-03-01

    We have studied the magnetic characteristics of the critical states in a series of samples of the type La2-xSrxCuO4+d that is doped with both Sr and excess O incorporated using electrochemistry. These samples spontaneously phase separate and show both a superconducting phase with TC near 40 K and a magnetic phase with TM near 40 K. Our previous studies established that the superconducting phase is similar to an optimally doped sample while the magnetic phase is consistent with the static spin density wave reported for x=1/8 Sr or Ba doped samples. Magnetization data at various temperatures showed large reversibility in all the samples. The critical current densities JC(0) values were at least an order of magnitude smaller than that of the reported values for YBa2Cu3O7-d and La2-xSrxCuO4. At higher fields JC(H) was smaller indicating the existence of weak flux pinning in the system. Based on our magnetization data we conclude that the vortex lattice pinning is different from non-phase separated cuprates. This work was partially supported by the US-DOE through contract DE-FG02-00ER45801 and the Cottrell Scholar Program of the Research Corporation.

  5. Experimental study on magnetically insulated transmission line electrode surface evolution process under MA/cm current density

    International Nuclear Information System (INIS)

    Zhang, PengFei; Qiu, Aici; Hu, Yang; Yang, HaiLiang; Sun, Jiang; Wang, Liangping; Cong, Peitian

    2016-01-01

    The design of high-current density magnetically insulated transmission line (MITL) is a difficult problem of current large-scale Z-pinch device. In particular, a thorough understanding of the MITL electrode surface evolution process under high current density is lacking. On the “QiangGuang-I” accelerator, the load area possesses a low inductance short-circuit structure with a diameter of 2.85 mm at the cathode, and three reflux columns with a diameter of 3 mm and uniformly distributed circumference at the anode. The length of the high density MITL area is 20 mm. A laser interferometer is used to assess and analyze the state of the MITL cathode and anode gap, and their evolution process under high current density. Experimental results indicate that evident current loss is not observed in the current density area at pulse leading edge, and peak when the surface current density reaches MA/cm. Analysis on electrode surface working conditions indicates that when the current leading edge is at 71.5% of the peak, the total evaporation of MITL cathode structure can be realized by energy deposition caused by ohmic heating. The electrode state changes, and diffusion conditions are reflected in the laser interferometer image. The MITL cathode area mainly exists in metal vapor form. The metal vapor density in the cathode central region is higher than the upper limit of laser penetration density (∼4 × 10 21 /cm 3 ), with an expansion velocity of ∼0.96 km/s. The metal vapor density in the electrode outer area may lead to evident distortion of fringes, and its expansion velocity is faster than that in the center area (1.53 km/s).

  6. Soft x-ray camera for internal shape and current density measurements on a noncircular tokamak

    International Nuclear Information System (INIS)

    Fonck, R.J.; Jaehnig, K.P.; Powell, E.T.; Reusch, M.; Roney, P.; Simon, M.P.

    1988-05-01

    Soft x-ray measurements of the internal plasma flux surface shaped in principle allow a determination of the plasma current density distribution, and provide a necessary monitor of the degree of internal elongation of tokamak plasmas with a noncircular cross section. A two-dimensional, tangentially viewing, soft x-ray pinhole camera has been fabricated to provide internal shape measurements on the PBX-M tokamak. It consists of a scintillator at the focal plane of a foil-filtered pinhole camera, which is, in turn, fiber optically coupled to an intensified framing video camera (/DELTA/t />=/ 3 msec). Automated data acquisition is performed on a stand-alone image-processing system, and data archiving and retrieval takes place on an optical disk video recorder. The entire diagnostic is controlled via a PDP-11/73 microcomputer. The derivation of the polodial emission distribution from the measured image is done by fitting to model profiles. 10 refs., 4 figs

  7. Density dependence of 2p-2h meson-exchange currents

    Science.gov (United States)

    Amaro, J. E.; Barbaro, M. B.; Caballero, J. A.; De Pace, A.; Donnelly, T. W.; Megias, G. D.; Ruiz Simo, I.

    2017-06-01

    We analyze the density dependence of the contribution of meson-exchange currents to the lepton-nucleus inclusive cross section in the two-particle two-hole channel. The model is based on the relativistic Fermi gas, where each nucleus is characterized by its Fermi momentum kF. We find that the 2p-2h nuclear response functions at their peaks scale as A kF2 for Fermi momentum going from 200 to 300 MeV/c and momentum transfer q from 2 kF to 2 GeV /c . This behavior is different from what is found for the quasielastic response, which scales as A /kF . Additionally, the deep scaling region is also discussed and there the usual scaling behavior is found to be preferable.

  8. Study of Chromium Multilayers Properties Obtained by Pulsed Current Density: Residual Stress and Microhardness

    Directory of Open Access Journals (Sweden)

    Julieta TORRES-GONZÁLEZ

    2010-12-01

    Full Text Available Chromium multilayers deposits were obtained from three different bath solutions, they were prepared by switching current density between 10 and 70 Adm-2. Two temperatures were studied, 35°C and 55°C. At 35°C two different microstructures are alternated: columnar obtained at 10 Adm-2 and equiaxial obtained at 70 Adm-2. At 55°C only the columnar type microstructure is present, at 10 and 70 Adm-2, the only difference among the layers is a slight disorientation of grains. The properties of these chromium multilayers were characterized by scanning electron microscopy (SEM and X-ray diffraction (XRD. In general the deposits are microcracked with a high microhardness, high residual stress and a small grain size.

  9. Table 5.1. Exchange current densities and rate constants in aqueous systems

    Science.gov (United States)

    Holze, R.

    This document is part of Volume 9 `Electrochemistry', Subvolume A, of Landolt-Börnstein - Group IV `Physical Chemistry'. This document lists the exchange current densities and the electrode reaction rate constants of the following metallic electrodes in aqueous systems for various electrolyte reactions: silver (Ag), aluminium (Al), gold (Au), bismuth (Bi), carbon (C), cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), copper (Cu), iron (Fe), gallium (Ga), mercury (Hg), indium (In), iridium (Ir), potassium (K), lithium (Li), molybdenum (Mo), natrium (Na), niobium (Nb), nickel (Ni), lead (Pb), palladium (Pd), platinum (Pt), rubidium (Rb), rhodium (Rh), ruthenium (Ru), antimony (Sb), tin (Sn), tantalum (Ta), titanium (Ti), thallium (Tl), vanadium (V), tungsten (W), zinc (Zn). For each electrolyte reaction the electrolyte solution, the educt, product and concentration are specified along with the temperature of determination of the given values.

  10. Higher critical current density achieved in Bi-2223 High-Tc superconductors

    Directory of Open Access Journals (Sweden)

    M.S. Shalaby

    2016-07-01

    Full Text Available Bi2Sr2Ca2Cu3Ox (Bi-2223 were prepared using a solid state reaction method at different sintering times and temperatures. Structural phase identifications have been done using X-Ray analysis and refinement by Reitveld method which proves the coexistence of Bi-2223 and Bi-2212 phases. The critical transition temperature Tc and critical current density Jc values were measured using superconducting quantum interference device magnetometer (SQUID and by the magneto-optics technique. A remarkable rapid decrease to the diamagnetic signal in the magnetization versus temperature M(T at 110 K and Jc around 1.2 × 107 A/m2 at 5 K are confirmed for the Bi-2223 compound.

  11. Large high current density superconducting solenoids for use in high energy physics experiments

    International Nuclear Information System (INIS)

    Green, M.A.; Eberhard, P.H.; Taylor, J.D.

    1976-05-01

    Very often the study of high energy physics in colliding beam storage-rings requires a large magnetic field volume in order to detect and analyze charged particles which are created from the collision of two particle beams. Large superconducting solenoids which are greater than 1 meter in diameter are required for this kind of physics. In many cases, interesting physics can be done outside the magnet coil, and this often requires that the amount of material in the magnet coil be minimized. As a result, these solenoids should have high current density (up to 10 9 A m -2 ) superconducting windings. The methods commonly used to stabilize large superconducting magnets cannot be employed because of this need to minimize the amount of material in the coils. A description is given of the Lawrence Berkeley Laboratory program for building and testing prototype solenoid magnets which are designed to operate at coil current densities in excess of 10 9 A m -2 with magnetic stored energies which are as high as 1.5 Megajoules per meter of solenoid length. The coils use intrinsically stable multifilament Nb--Ti superconductors. Control of the magnetic field quench is achieved by using a low resistance aluminum bore tube which is inductively coupled to the coil. The inner cryostat is replaced by a tubular cooling system which carries two phase liquid helium. The magnet coil, the cooling tubes, and aluminum bore tube are cast in epoxy to form a single unified magnet and cryogenic system which is about 2 centimeters thick. The results of the magnet coil tests are discussed

  12. Modeling the short-circuit current density of polymer solar cells based on P3HT:PCBM blend

    Energy Technology Data Exchange (ETDEWEB)

    Monestier, Florent; Simon, Jean-Jacques; Torchio, Philippe; Escoubas, Ludovic; Flory, Francois [Institut FRESNEL, UMR-CNRS 6133, Domaine Universitaire de St-Jerome, 13397 Marseille Cedex 20 (France); Bailly, Sandrine; de Bettignies, Remi; Guillerez, Stephane [INES CEA/DRT/LITEN/DTS/LCS, BP 332 50, av. du lac Leman 73370, Le Bourget du lac (France); Defranoux, Christophe [SOPRA-SA, Bois Colombes (France)

    2007-03-06

    We have investigated the short-circuit current density of organic solar cells based on poly (3-hexylthiophene)(P3HT)/6,6-phenyl C61-butyric acid methyl ester (PCBM) blend. In order to model charge collection efficiencies with respect to short circuit density in such blends, a full optical modeling of the cell is performed. From the distribution of the electromagnetic field, we compute the rate of exciton generation. This exciton generation rate is used as input in the transport equations of holes and electrons. Charge densities at steady state are obtained as solutions are used for computing short-circuit current densities generated in the cell. The dependence of short-circuit current densities versus the thickness of the blend is analyzed and compared with our experimental data and with data extracted from the literature. (author)

  13. Magmas in motion: Degassing in volcanic conduits and fabrics of pyroclastic density current

    Science.gov (United States)

    Burgisser, Alain

    Volcanoes are caused by the transport of magma batches from the Earth's crust to the surface. These magmas in motion undergo drastic changes of rheologic properties during their journey to the surface and this work explores how these changes affect volcanic eruptions. The first part of this study is devoted to the dynamic aspects of degassing and permeability in magmas with high pressure, high temperature experiments on natural volcanic rocks. Degassing is measured by the influence of decompression rate on the growth of the bubbles present in the magma while permeability is deduced from the temporal evolution of these bubbles. The parameterization of our results in a numerical model of volcanic conduit flow show that previous models based on equilibrium degassing overestimate the acceleration and the decompression rate of the magma. Assessing permeability effects derived form our results show that the transition between explosive and effusive eruptions is a strong function of the magma initial ascent rate. The second part of this work is a unification of two end-members of pyroclastic currents (highly concentrated pyroclastic flows and dilute, turbulent pyroclastic surges) using theoretical scaling arguments based on multiphase physics. Starting from the dynamics of the particle interactions with a fundamental eddy, we consider the full spectrum of eddies generated within a turbulent current. We demonstrate that the presence of particles with various sizes induces a density stratification of the current, leading to its segregation into a basal concentrated part overlain by a dilute cloud. To verify our predictions on the interactions of such a segregated pyroclastic current with its surroundings (hills and sea), we studied the products of the 2050 BP caldera-forming eruption of Okmok Volcano (Alaska). This field study allowed us to reconstruct the eruptive sequence and to validate the main aspects of our theoretical model, such as the superposition of a dense and

  14. Status Epilepticus Induced Spontaneous Dentate Gyrus Spikes: In Vivo Current Source Density Analysis.

    Directory of Open Access Journals (Sweden)

    Sean P Flynn

    Full Text Available 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

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

    Directory of Open Access Journals (Sweden)

    S. D. Parkinson

    2014-09-01

    Full Text Available 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.

  16. Characterization of the Nova Scotia Coastally-Trapped Current and Monitoring of the Associated Density Front Using Underwater Gliders

    Science.gov (United States)

    Dever, M.; Hebert, D.; Greenan, B. J. W.; Sheng, J.

    2016-02-01

    Repeated glider transects across the Scotian Shelf, near Halifax, Nova Scotia, Canada, completed between 2011 and 2015 provide a dataset with high temporal and spatial resolutions. This new dataset is used to characterize the seasonal variability of the Nova Scotia Current (NSC): a southwestward, coastally-trapped, alongshore current flowing from the Gulf of St. Lawrence to the Gulf of Maine. Alongshore currents are estimated by scaling the geostrophic flow, derived from the density field, with the drift experienced by the glider during each dives. The results are compared to concurrent ADCP observations to assess the reliability of the technique and then used to characterize the alongshore circulation across the Halifax Line. It demonstrates that most of the alongshore transport is associated with the density front separating the low-density NSC from denser shelf water. An automated algorithm is then developed to monitor the major characteristics of the density front (e.g. width, frontal depth, density gradient). We find that the persistent summer stratification explains the lag observed between the seasonal pulse of buoyant water coming for the Gulf of St. Lawrence in the fall and the maximum alongshore current in the winter. This reveals that the density gradient is not the only major parameter explaining the seasonal and inter-annual variability of the NSC: the geometry of the density front also plays an important role. This makes wind forcing a potential major driving mechanism of the NSC, as alongshore winds can significantly affect the geometry of the density front via Ekman transport.

  17. Analysis of plasma equilibrium based on orbit-driven current density profile in steady-state plasma on QUEST

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, K., E-mail: nakamura@triam.kyushu-u.ac.jp [RIAM, Kyushu University, Kasuga 816-8580 (Japan); Alam, M.M. [IGSES, Kyushu University, Kasuga 816-8580 (Japan); Jiang, Y.Z. [Tsinghua University, Beijing 100084 (China); Mitarai, O. [Tokai University, Kumamoto 862-8652 (Japan); Kurihara, K.; Kawamata, Y.; Sueoka, M.; Takechi, M. [Japan Atomic Energy Agency, Naka 311-0193 (Japan); Hasegawa, M.; Tokunaga, K.; Araki, K.; Zushi, H.; Hanada, K.; Fujisawa, A.; Idei, H.; Nagashima, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Nagata, T. [RIAM, Kyushu University, Kasuga 816-8580 (Japan); and others

    2016-11-01

    Highlights: • High energy particle guiding center orbit is calculated as a contour plot of conserved variable. • Current density profile is analyzed based on the orbit-driven current. • Plasma equilibrium is reconstructed by considering the hollow current profile. - Abstract: In the present RF-driven (ECCD) steady-state plasma on QUEST (B{sub t} = 0.25 T, R = 0.68 m, a = 0.40 m), plasma current seems to flow in the open magnetic surface outside of the closed magnetic surface in the low-field region according to plasma current fitting (PCF) method. We consider that the current in the open magnetic surface is due to orbit-driven current by high-energy particles in RF-driven plasma. So based on the analysis of current density profile based on the orbit-driven current, plasma equilibrium is to be calculated. We calculated high energy particles guiding center orbits as a contour plot of conserved variable in Hamiltonian formulation and considered particles initial position with different levels of energy and pitch angles that satisfy resonance condition. Then the profile of orbit-driven current is estimated by multiplying the particle density on the resonance surface and the velocity on the orbits. This analysis shows negative current near the magnetic axis and hollow current profile is expected even if pressure driven current is considered. Considering the hollow current profile shifted toward the low-field region, the equilibrium is fitted by J-EFIT coded by MATLAB.

  18. Numerically simulated cardiac exposure to electric current densities induced by TASER X-26 pulses in adult men

    Energy Technology Data Exchange (ETDEWEB)

    Leitgeb, N; Niedermayr, F; Neubauer, R; Loos, G, E-mail: norbert.leitgeb@tugraz.a [Institute of Clinical Engineering with European Notified Body of Medical Devices, Graz University of Technology, Inffeldgasse 18, A-8010 Graz (Austria)

    2010-10-21

    There is still an ongoing debate whether or not electronic stun devices (ESDs) induce cardiac fibrillation. To assess the ventricular fibrillation risk of law enforcing electronic control devices, quantitative estimates of cardiac electric current densities induced by delivered electric pulses are essential. Numerical simulations were performed with the finite integration technique and the anatomical model of a standardized European man (NORMAN) segmented into 2 mm voxels and 35 different tissues. The load-dependent delivery of TASER X-26 pulses has been taken into account. Cardiac exposure to electric current densities of vertically and horizontally aligned dart electrodes was quantified and different hit scenarios compared. Since fibrillation thresholds critically depend on exposed volume, the provided quantitative data are essential for risk assessment. The maximum cardiac rms current densities amounted to 7730 A m{sup -2}. Such high current densities and exposed cardiac volumes do not exclude ventricular fibrillation.

  19. Numerically simulated cardiac exposure to electric current densities induced by TASER X-26 pulses in adult men

    Science.gov (United States)

    Leitgeb, N.; Niedermayr, F.; Neubauer, R.; Loos, G.

    2010-10-01

    There is still an ongoing debate whether or not electronic stun devices (ESDs) induce cardiac fibrillation. To assess the ventricular fibrillation risk of law enforcing electronic control devices, quantitative estimates of cardiac electric current densities induced by delivered electric pulses are essential. Numerical simulations were performed with the finite integration technique and the anatomical model of a standardized European man (NORMAN) segmented into 2 mm voxels and 35 different tissues. The load-dependent delivery of TASER X-26 pulses has been taken into account. Cardiac exposure to electric current densities of vertically and horizontally aligned dart electrodes was quantified and different hit scenarios compared. Since fibrillation thresholds critically depend on exposed volume, the provided quantitative data are essential for risk assessment. The maximum cardiac rms current densities amounted to 7730 A m-2. Such high current densities and exposed cardiac volumes do not exclude ventricular fibrillation.

  20. Investigation into the erosive capacity of pyroclastic density currents at Mount Saint Helens, Washington (USA)

    Science.gov (United States)

    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

  1. First test of BNL electron beam ion source with high current density electron beam

    International Nuclear Information System (INIS)

    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/cm 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

  2. Effects of filament size on critical current density in overpressure processed Bi-2212 round wire.

    Science.gov (United States)

    Jiang, Jianyi; Francis, Ashleigh; Alicea, Ryan; Matras, Maxime; Kametani, Fumitake; Trociewitz, Ulf P; Hellstrom, Eric E; Larbalestier, David C

    2017-06-01

    Bi 2 Sr 2 CaCu 2 O x (Bi-2212) conductor is the only high temperature superconductor manufactured as a round wire and is a very promising conductor for very high field applications. One of the key design parameters of Bi-2212 wire is its filament size, which has been previously reported to affect the critical current density ( J c ) and ac losses. Work with 1 bar heat treatment showed that the optimal filament diameter was about 15 μm but it was not well understood at that time that gas bubbles were the main current limiting mechanism. Here we investigated a recent Bi-2212 wire with a 121×18 filament architecture with varying wire diameter (1.0 to 1.5 mm) using 50 bar overpressure processing. This wire is part of a 1.2 km piece length of 1.0 mm diameter made by Oxford Superconducting Technology. We found that J c is independent of the filament size in the range from 9 to 14 μm, although the n value increased with increasing filament size. A new record J c (4.2 K, 15 T) of 4200 A/mm 2 and J E (4.2 K, 15 T) of 830 A/mm 2 were achieved.

  3. Impact of the storm-time plasma sheet ion composition on the ring current energy density

    Science.gov (United States)

    Mouikis, C.; Kistler, L. M.; Petrinec, S. M.; Fuselier, S. A.; Cohen, I.

    2017-12-01

    The adiabatic inward transport of the night-side near-earth ( 6 Re) hot plasma sheet is the dominant contributor to the ring current pressure during storm times. During storm times, the plasma sheet composition in the 6 - 12 Re tail region changes due to O+ entry from the lobes (from the cusp) and the direct feeding from the night side auroral region. In addition, at substorm onset the plasma sheet O+ ions can be preferentially accelerated. We use MMS and observations during two magnetic storms, 5/8/2016 and 7/16/2017, to monitor the composition changes and energization in the 6 - 12 Re plasma sheet region. For both storms the MMS apogee was in the tail. In addition, we use subsequent Van Allen Probe observations (with apogee in the dawn and dusk respectively) to test if the 6-12 Re plasma sheet, observed by MMS, is a sufficient source of the O+ in the ring current. For this we will compare the phase space density (PSD) of the plasma sheet source population and the PSD of the inner magnetosphere at constant magnetic moment values as used in Kistler et al., [2016].

  4. Pyroclastic density currents at Stromboli volcano (Aeolian Islands, Italy): a case study of the 1930 eruption

    Science.gov (United States)

    Di Roberto, A.; Bertagnini, A.; Pompilio, M.; Bisson, M.

    2014-06-01

    Pyroclastic density currents (PDC) related to paroxysmal eruptions have caused a large number of casualties in the recent history of Stromboli. We combine here a critical review of historical chronicles with detailed stratigraphic, textural, and petrographic analyses of PDC deposits emplaced at Stromboli over the last century to unravel the origin of currents, their flow mechanism and the depositional dynamics. We focus on the 1930 PDC as they are well described in historical accounts and because the 1930 eruption stands as the most voluminous and destructive paroxysm of the last 13 centuries. Stromboli PDC deposits are recognizable from their architecture and the great abundance of fresh, well-preserved juvenile material. General deposit features indicate that Stromboli PDC formed due to the syn-eruptive gravitational collapse of hot pyroclasts rapidly accumulated over steep slopes. Flow channelization within the several small valleys cut on the flanks of the volcano can enhance the mobility of PDC, as well as the production of fine particles by abrasion and comminution of hot juvenile fragments, thereby increasing the degree of fluidization. Textural analyses and historical accounts also indicate that PDC can be fast (15-20 m/s) and relatively hot (360-700 °C). PDC can thus flow right down the slopes of the volcano, representing a major hazard. For this reason, they must be adequately taken into account when compiling risk maps and evaluating volcanic hazard on the Island of Stromboli.

  5. Flexible polyimide microelectrode array for in vivo recordings and current source density analysis.

    Science.gov (United States)

    Cheung, Karen C; Renaud, Philippe; Tanila, Heikki; Djupsund, Kaj

    2007-03-15

    This work presents implantable, flexible polymer-based probes with embedded microelectrodes for acute and chronic neural recordings in vivo, as tested on rodents. Acute recordings using this array were done in mice under urethane anesthesia and compared to those made using silicon-based probes manufactured at the Center for Neural Communication Technology, University of Michigan. The two electrode arrays yielded similar results. Recordings with chronically implanted polymer-based electrodes were performed for 60 days post-surgically in awake, behaving rats. The microelectrodes were used to monitor local field potentials and capture laminar differences in function of cortex and hippocampus, and produced response waveforms of undiminished amplitude and signal-to-noise ratios 8 weeks after chronic implantation. The polymer-based electrodes could also be connected to a lesion current to mark specific locations in the tissue. Current source density (CSD) analysis from the recordings depicted a source - sink-composition. Tissue response was assessed 8 weeks after insertion by immunochemical labeling with glial fibrillary acidic protein (GFAP) to identify astrocytes, and histological analysis showed minimal tissue reaction to the implanted structures.

  6. Current-density functional theory study of the H2 molecule evolving under a strong ultrashort magnetic field

    Science.gov (United States)

    Vikas, Hash(0xb7f6e60)

    2012-01-01

    Hydrogen molecule in a strong ultrashort magnetic field is investigated through a current-density functional theory (CDFT) and quantum fluid dynamics (QFD) based approach employing current-density dependent vector exchange-correlation potential and energy density functional derived with a vorticity variable. The numerical computations through the CDFT based approach are performed for the H2 molecule, starting initially from its field-free ground state, in a parallel internuclear axis and magnetic field-axis configuration with the internuclear separation R ranging from 0.1 a.u. to 14.0 a.u., and the strength of the time-dependent (TD) magnetic field varying between 0-1011 G over a few femtoseconds. The numerical results are compared with that obtained using an approach based on the current-density independent approximation under similar computational constraints but employing only scalar exchange-correlation potential dependent on the electronic charge-density alone. The current-density based approach yields exchange- and correlation energy as well as electronic charge-density of the H2 molecule drastically different from that obtained using current-independent approach, in particular, at TD magnetic field-strengths >109 G during a typical time-period of the field when the magnetic-field had attained maximum applied field-strength and is switched to a decreasing ramp function. This nonadiabatic behavior of the TD electronic charge-density is traced to the TD vorticity-dependent vector exchange-correlation potential of the CDFT based approach. The interesting electron dynamics of the H2 molecule in strong TD magnetic field is further elucidated by treating electronic charge-density as an `electron-fluid'. The present work also reveals interesting real-time dynamics on the attosecond time-scale in the electronic charge-density distribution of the hydrogen molecule.

  7. Change of the dominant luminescent mechanism with increasing current density in molecularly doped organic light-emitting devices

    International Nuclear Information System (INIS)

    Zhou Liang; Zhang Hongjie; Meng Qingguo; Liu Fengyi; Yu Jiangbo; Deng Ruiping; Peng Zeping; Li Zhefeng; Guo Zhiyong

    2007-01-01

    We have fabricated and measured a series of electroluminescent devices with the structure of ITO/TPD/Eu(TTA) 3 phen (x):CBP/BCP/ALQ/LiF/Al, where x is the weight percentage of Eu(TTA) 3 phen (from 0% to 6%). At very low current density, carrier trapping is the dominant luminescent mechanism and the 4% doped device shows the highest electroluminescence (EL) efficiency among all these devices. With increasing current density, Foerster energy transfer participates in EL process. At the current density of 10.0 and 80.0 mA/cm 2 , 2% and 3% doped devices show the highest EL efficiency, respectively. From analysis of the EL spectra and the EL efficiency-current density characteristics, we found that the EL efficiency is manipulated by Foerster energy transfer efficiency at high current density. So we suggest that the dominant luminescent mechanism changes gradually from carrier trapping to Foerster energy transfer with increasing current density. Moreover, the conversion of dominant EL mechanism was suspected to be partly responsible for the EL efficiency roll-off because of the lower EL quantum efficiency of Foerster energy transfer compared with carrier trapping

  8. A novel model for through-silicon via (TSV) filling process simulation considering three additives and current density effect

    Science.gov (United States)

    Wang, Fuliang; Zhao, Zhipeng; Wang, Feng; Wang, Yan; Nie, Nantian

    2017-12-01

    Through-silicon via (TSV) filling by electrochemical deposition is still a challenge for 3D IC packaging, and three-component additive systems (accelerator, suppressor, and leveler) were commonly used in the industry to achieve void-free filling. However, models considering three additive systems and the current density effect have not been fully studied. In this paper, a novel three-component model was developed to study the TSV filling mechanism and process, where the interaction behavior of the three additives (accelerator, suppressor, and leveler) were considered, and the adsorption, desorption, and consumption coefficient of the three additives were changed with the current density. Based on this new model, the three filling types (seam void, ‘V’ shape, and key hole) were simulated under different current density conditions, and the filling results were verified by experiments. The effect of the current density on the copper ion concentration, additives surface coverage, and local current density distribution during the TSV filling process were obtained. Based on the simulation and experimental results, the diffusion–adsorption–desorption–consumption competition behavior between the suppressor, the accelerator, and the leveler were discussed. The filling mechanisms under different current densities were also analyzed.

  9. Topographic control on pyroclastic density currents: the example of Mount St. Helens 1980 blast

    Science.gov (United States)

    Esposti Ongaro, T.; Clarke, A. B.; Voight, B.; Neri, A.; Widiwijayanti, C.

    2012-04-01

    Volcanic lateral blasts are among the most spectacular and devastating of natural phenomena, characterized by the violent release of a relatively low mass of magma producing a remarkably broad area of significant damage. The most known volcanic blast at Mount Saint Helens, on 18 May 1980, devastated an area of 600 squared km in about five minutes, being able to override topographic obstacles of several hundreds of metres. By means of 3D multiphase numerical simulations we demonstrate that Mount St. Helens blast was generated by the rapid expansion (burst) of a pressurized polydisperse mixture of gas and particles and its subsequent gravitational collapse and that the observed front propagation, final runout and damage can be explained by the emplacement of an unsteady, stratified pyroclastic density current (PDC), controlled by gravity and terrain morphology. Numerical results are able to describe the non-equilibrium sedimentation dynamics of volcanic particles during PDC propagation across the rugged topography characterizing the area devastated by the blast. In valleys and topographic lows, pyroclasts accumulate progressively at the base of the flow, after the passage of the flow head, forming a dense basal flow depleted in fines. Blocking and channelling of such basal flow by topographic ridges provides the mechanism for progressive current unloading. On ridges, sedimentation occurs from the upper, dilute wake region, which follows the current head. Although the model formulation and the vertical numerical resolution do not yet allow the direct simulation of the deposit consolidation, present results provide a consistent, quantitative model able to interpret the observed stratigraphic sequence.

  10. He 2++ molecular ion in a strong time-dependent magnetic field: a current-density functional study.

    Science.gov (United States)

    Vikas

    2011-08-01

    The He 2++ molecular ion exposed to a strong ultrashort time-dependent (TD) magnetic field of the order of 10(9) G is investigated through a quantum fluid dynamics (QFD) and current-density functional theory (CDFT) based approach using vector exchange-correlation (XC) potential and energy density functional that depend not only on the electronic charge-density but also on the current density. The TD-QFD-CDFT computations are performed in a parallel internuclear-axis and magnetic field-axis configuration at the field-free equilibrium internuclear separation R = 1.3 au with the field-strength varying between 0 and 10(11) G. The TD behavior of the exchange- and correlation energy of the He 2++ is analyzed and compared with that obtained using a [B-TD-QFD-density functional theory (DFT)] approach based on the conventional TD-DFT under similar computational constraints but using only scalar XC potential and energy density functional dependent on the electronic charge-density alone. The CDFT based approach yields TD exchange- and correlation energy and TD electronic charge-density significantly different from that obtained using the conventional TD-DFT based approach, particularly, at typical magnetic field strengths and during a typical time period of the TD field. This peculiar behavior of the CDFT-based approach is traced to the TD current-density dependent vector XC potential, which can induce nonadiabatic effects causing retardation of the oscillating electronic charge density. Such dissipative electron dynamics of the He 2++ molecular ion is elucidated by treating electronic charge density as an electron-"fluid" in the terminology of QFD. Copyright © 2011 Wiley Periodicals, Inc.

  11. 3-D time-domain induced polarization tomography: a new approach based on a source current density formulation

    Science.gov (United States)

    Soueid Ahmed, A.; Revil, A.

    2018-04-01

    Induced polarization (IP) of porous rocks can be associated with a secondary source current density, which is proportional to both the intrinsic chargeability and the primary (applied) current density. This gives the possibility of reformulating the time domain induced polarization (TDIP) problem as a time-dependent self-potential-type problem. This new approach implies a change of strategy regarding data acquisition and inversion, allowing major time savings for both. For inverting TDIP data, we first retrieve the electrical resistivity distribution. Then, we use this electrical resistivity distribution to reconstruct the primary current density during the injection/retrieval of the (primary) current between the current electrodes A and B. The time-lapse secondary source current density distribution is determined given the primary source current density and a distribution of chargeability (forward modelling step). The inverse problem is linear between the secondary voltages (measured at all the electrodes) and the computed secondary source current density. A kernel matrix relating the secondary observed voltages data to the source current density model is computed once (using the electrical conductivity distribution), and then used throughout the inversion process. This recovered source current density model is in turn used to estimate the time-dependent chargeability (normalized voltages) in each cell of the domain of interest. Assuming a Cole-Cole model for simplicity, we can reconstruct the 3-D distributions of the relaxation time τ and the Cole-Cole exponent c by fitting the intrinsic chargeability decay curve to a Cole-Cole relaxation model for each cell. Two simple cases are studied in details to explain this new approach. In the first case, we estimate the Cole-Cole parameters as well as the source current density field from a synthetic TDIP data set. Our approach is successfully able to reveal the presence of the anomaly and to invert its Cole

  12. Prior knowledge on cortex organization in the reconstruction of source current densities from EEG.

    Science.gov (United States)

    Knösche, Thomas R; Gräser, Markus; Anwander, Alfred

    2013-02-15

    The reconstruction of the generators of electroencephalographic (EEG) signals is important for understanding brain processes. Since the inverse problem has no unique solution, additional knowledge or assumptions are needed. Often, results from other anatomical or functional measurement modalities are difficult to interpret directly in terms of EEG source strengths, but they provide valuable information about the functional similarity between brain regions, for example, in form of parcellations. We propose a novel approach to the incorporation of such parcellations as priors into the reconstruction of distributed source current densities from EEG. Two algorithms are described, based on a surface-constrained LORETA (Low Resolution Electromagnetic TomogrAphy) approach. The first, patchLORETA1, uses both topological neighborhood and prior information to define smoothness, while the second, patchLORETA2, neglects topological neighborhood. Computer simulations, using a smooth reconstruction surface on the brain envelope, reveal important aspects of the algorithms' performance, in particular the influences of noise and incongruence between measurements and prior information. It turns out that patchLORETA1 makes efficient use of the provided prior information and at the same time is quite robust towards faulty priors as well as noise. The algorithms are also tested on the localization of the sources of event-related potentials. Here, both the smooth brain and folded cortical surfaces serve as reconstruction spaces. We find that patchLORETA1 becomes ineffective on the folded cortex, while patchLORETA2 yields plausible results. We also discuss the extension of the proposed algorithms to other types of priors and propose ways to overcome shortcomings of the current implementation. Copyright © 2012 Elsevier Inc. All rights reserved.

  13. Induced current density in the foetus of pregnant workers in high magnetic field environments

    International Nuclear Information System (INIS)

    Xue, C.; Wood, A.W.

    2004-01-01

    Full text: There are moves to limit by legislation the amount of electric and magnetic fields that workers and the general public are exposed to. In work locations near wiring, cables and equipment carrying high electric currents, there are situations in which the proposed magnetic field limits could be exceeded. Since the limits for the general public are more conservative than those for workers and since the foetus or a pregnant worker should be afforded the status of a member of the general public, it is important to assess a worst-case scenario for the purposes of a general code of practice. Three different magnetic field exposures are modelled, which include the worst case - the body of a pregnant woman at a smallest distance of 30 cm to the conductor. All computations were done by using Multiple Multipole Program (MMP), which is based on the Generalized Multipole Technique (GMT) from ETH (Swiss Federal Institute of Technology), Zurich, Switzerland. The torso was modelled as a capped cylinder containing concentric placental and amniotic fluid layers containing a foetus. Appropriate values for conductivity and permittivity were applied to these layers and the Maxwell Equation solver applied for the situations of: cable beneath, alongside perpendicular and alongside parallel to the long axis of the body. Induced current density values were computed for cable distances of 0.3 and 0.5 m from the body and compared to the recommended limit values of 10 and 2 mA/m 2 for Occupational and General Public populations respectively. Regions where these values would be exceeded have been identified in this analysis. In a worst-case scenario the proposed basic restrictions would be exceeded slightly in both maternal and foetal tissue. With appropriate pre-placement assessment, these over-exposures can be avoided. Copyright (2004) Australasian College of Physical Scientists and Engineers in Medicine

  14. Current source density analysis of the potential evoked in hippocampus by perirhinal cortex stimulation.

    Science.gov (United States)

    Liu, P; Bilkey, D K

    1997-01-01

    Previous anatomical research has demonstrated that the perirhinal cortex (PRC) projects to the dorsal hippocampal CA1 field. We have recently presented data (Liu and Bilkey, Hippocampus 1996; 6:125-135) which suggests that this pathway courses via the lateral perforant path (LPP). In the present study, laminar profiles of the average evoked potentials and current source density (CSD) analysis were used to study the input from the perirhinal cortex to the dorsal hippocampus in the urethane-anaesthetized rat. Stimulation of the lateral perforant path activated a current sink in the stratum lacunosum-moleculare of CA1 and the outer molecular layer of the dentate gyrus with an onset latency of 3.5 ms. Stimulation of the perirhinal cortex produced a very similar sink-source pattern with an onset latency of 4.0 ms. Higher-intensity stimulation of lateral entorhinal cortex also produced a similar pattern with an onset latency of 4.5 ms. Electrolytic lesions of PRC conducted 4-5 days prior to testing resulted in a major decrease (58%) in the amplitude of the LPP-elicited potentials and a corresponding reduction across the whole source-sink pattern. A similar result was observed following ibotenic acid lesions of PRC. In contrast, similar-sized electrolytic lesions of lateral entorhinal cortex produced a much smaller (16%) decrease in potential amplitude and little change in the source-sink pattern. These data provide further support for the hypothesis that perirhinal cortex projects to both the dentate gyrus and CA1 regions of the hippocampus via the lateral perforant path.

  15. Enhancement of transport critical current density of epitaxial Nb film by lithography

    Science.gov (United States)

    Yamada, H.; Harada, N.; Kanayama, K.; Nakagawa, S.; Yamasaki, H.; Hamajima, T.

    2005-12-01

    The critical current density, JC, of a superconductor is controlled by the pinning interaction between the flux line lattice and pinning centers. Artificial flux pinning centers are necessary for high- TC superconductors, because JC decreases markedly when a magnetic field of a few Tesla is applied at the temperature of liquid nitrogen. Here, we discuss the effects of groove-shaped artificial pinning centers introduced by microlithography. Superconducting Nb film was deposited epitaxially on Al 2O 3(1 1 0 2) substrates and grooves with a period of 4-μm were introduced. The micro-fabricated film had about 2-fold greater transport JC = 4.1 × 10 9 A/m 2 as compared with the value of JC = 2.1 × 10 9 A/m 2 of the standard film at 4.2 K, 0.1 T. This JC enhancement was observed over a wide temperature range of 4.2-9.0 K.

  16. Development of Ti-sheathed MgB2 wires with high critical current density

    International Nuclear Information System (INIS)

    Liang, G; Fang, H; Hanna, M; Yen, F; Lv, B; Alessandrini, M; Keith, S; Hoyt, C; Tang, Z; Salama, K

    2006-01-01

    Working towards developing lightweight superconducting magnets for future space and other applications, we have successfully fabricated mono-core Ti-sheathed MgB 2 wires by the powder-in-tube method. The wires were characterized by magnetization, electrical resistivity, x-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry measurements. The results indicate that the Ti sheath does not react with the magnesium and boron, and the present wire rolling process can produce MgB 2 wires with a superconducting volume fraction of at least 64% in the core. Using the Bean model, it was found that at 5 K, the magnetic critical current densities, J c , measured in magnetic fields of 0, 5, and 8 T are about 4.2 x 10 5 , 3.6 x 10 4 , and 1.4 x 10 4 A cm -2 , respectively. At 20 K and 0 T, the magnetic J c is about 2.4 x 10 5 A cm -2 . These results show that at zero and low fields, the values of the magnetic J c for Ti-sheathed MgB 2 wires are comparable with the best results available for the Fe-sheathed MgB 2 wires. At high fields, however, the J c for Ti-sheathed MgB 2 wires appears higher than that for the Fe-sheathed MgB 2 wires

  17. Semantic category interference in overt picture naming: sharpening current density localization by PCA.

    Science.gov (United States)

    Maess, Burkhard; Friederici, Angela D; Damian, Markus; Meyer, Antje S; Levelt, Willem J M

    2002-04-01

    The study investigated the neuronal basis of the retrieval of words from the mental lexicon. The semantic category interference effect was used to locate lexical retrieval processes in time and space. This effect reflects the finding that, for overt naming, volunteers are slower when naming pictures out of a sequence of items from the same semantic category than from different categories. Participants named pictures blockwise either in the context of same- or mixed-category items while the brain response was registered using magnetoencephalography (MEG). Fifteen out of 20 participants showed longer response latencies in the same-category compared to the mixed-category condition. Event-related MEG signals for the participants demonstrating the interference effect were submitted to a current source density (CSD) analysis. As a new approach, a principal component analysis was applied to decompose the grand average CSD distribution into spatial subcomponents (factors). The spatial factor indicating left temporal activity revealed significantly different activation for the same-category compared to the mixed-category condition in the time window between 150 and 225 msec post picture onset. These findings indicate a major involvement of the left temporal cortex in the semantic interference effect. As this effect has been shown to take place at the level of lexical selection, the data suggest that the left temporal cortex supports processes of lexical retrieval during production.

  18. Field and temperature scaling of the critical current density in commercial REBCO coated conductors

    CERN Document Server

    Senatore, Carmine; 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 to the others. In the present work we have examined the critical surface for the current density, Jc(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 field 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 = 0deg , 45deg and 90deg , in order to probe the angular anisotropy of Jc. In spite of the large variability of CCs performance, ...

  19. High critical current density YBCO films and fabrication of dc-SQUIDs

    CERN Document Server

    Kuriki, S; Kawaguchi, Y; Matsuda, M; Otowa, T

    2002-01-01

    In order to improve the sensitivity of SQUID magnetometers made of high-T sub c films, we have studied the conditions of pulsed-laser deposition of YBCO films. Among the different deposition parameters examined, extensive degassing of the vacuum chamber before and precise control of the substrate temperature during the film deposition were found effective for obtaining high critical temperature T sub c and high critical current density J sub c. It was also found that the residual-resistance ratio has a clear correlation with J sub c , indicating that it can be a good, and easy to measure, index of the film quality. Films having T sub c approx 89-90 K and J sub c >= 5x10 sup 6 A cm sup - sup 2 at 77 K were used to fabricate SQUIDs without a pickup loop. Grain-boundary junctions formed on bicrystal substrates with a 30 deg. misorientation angle exhibited I sub c R sub n values of more than 100 mu V at 77 K. The well-known scaling behaviour of the relation I sub c R sub n propor to (J sup G sup B sub c) sup 1 su...

  20. A dense voltage-mode Josephson memory cell insensitive to systematic variations in critical current density

    International Nuclear Information System (INIS)

    Bradley, P.; Van Duzer, T.

    1985-01-01

    A destructive read-out (DRO) memory cell using three Josephson junctions has been devised whose operation depends only on the ratio of critical currents and application of the proper read/write voltages. The effects of run-to-run and across-thewafer variations in I /SUB c/ are minimized since all three junctions for a given cell are quite close to each other. Additional advantages are: immunity from flux trapping, high circuit density, and fast switching. Since destructive read-out is generally undesirable, a self-rewriting scheme is necessary. Rows and columns of cells with drivers and sense circuits, as well as small memory arrays and decoders have been simulated on SPICE. Power dissipation of cells and bias circuits for a 1K-bit RAM is estimated at about 2 mW. Inclusion of peripheral circuitry raises this by as much as a factor of five depending on the driving scheme and speed desired. Estimated access time is appreciably less than a nanosecond. Preliminary experimental investigations are reported

  1. Photoelectrolysis of water at high current density - Use of ultraviolet laser excitation

    Science.gov (United States)

    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.

  2. Physiology of the entorhinal and perirhinal projections to the hippocampus studied by current source density analysis.

    Science.gov (United States)

    Canning, K J; Wu, K; Peloquin, P; Kloosterman, F; Leung, L S

    2000-06-01

    Evoked field potentials and current-source-density analysis were used to study the olfactory, entorhinal, and perirhinal projections to the hippocampus. In urethane-anesthetized rats, various structures were electrically stimulated, and evoked potentials were mapped using glass micropipettes or multichannel silicon probes. Stimulation of the olfactory bulb, lateral olfactory tract, piriform cortex, amygdala-entorhinal transition, lateral entorhinal cortex, or lateral perforant path (LPP) evoked an outer molecular layer sink (inferred distal dendritic excitation) in the dentate gyrus, with progressively decreasing onset latency. Medial perforant path (MPP) stimulation evoked a middle molecular layer sink (mid-dendritic excitation) in the dentate gyrus. LPP and MPP were also inferred to monosynaptically excite the distal dendrites of CA3, often resulting in a population spike in CA3. CA3 spiking, in turn, was often followed by excitation at the inner molecular layer of the dentate gyrus. LPP and MPP evoked distal dendritic sinks but no population spikes in CA1. Stimulation of the perirhinal cortex activated a sink in the subiculum/CA1 border without activating the dentate gyrus. In addition, reverberatory activity through a hippocampal-entorhinal-hippocampal pathway may be activated by MPP or CA3 stimulation. It is suggested that the parallel projections of the entorhinal and perirhinal inputs to the distal dendrites of hippocampal principal neurons enhance local and distributed processing as characterized by CA3 to dentate gyrus feedback, and hippocampal-entorhinal reverberation.

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

    Science.gov (United States)

    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 (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 35 kPa can be expected within 3 km from source, ensuring complete destruction of the area; Pdyn > 15 kPa up to 5 km from source, resulting in heavy structural damage to most buildings and near destruction of weaker buildings; and Pdyn <10 kPa at ~6 km from source, resulting in severe damage to weaker structures at least up to this distance. This exercise illustrates our ability to combine field measurements with numerical techniques to explore controlling parameters of dilute PDC dynamics. These tools can be used to understand and estimate the damage potential and

  4. Investigation of electrodes under flow of a submicrosecond current pulse with linear density up to 3 MA/cm

    International Nuclear Information System (INIS)

    Branitskii, A. V.; Grabovskii, E. V.; Dzhangobegov, V. V.; Laukhin, Ya. N.; Mitrofanov, K. N.; Oleinik, G. M.; Sasorov, P. V.; Tkachenko, S. I.; Frolov, I. N.

    2016-01-01

    The states of current-carrying elements at the transmission of megaampere current into load are studied. It is determined that the expansion velocity of plasma generated at the outer surface of cylindrical tubes produced of stainless steel, at flowing through them of submicrosecond current pulses with linear density of 3 MA/cm is 5.5 km/s. The evolution of various modes of instability is analyzed.

  5. Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis bumpy torus plasma

    Science.gov (United States)

    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.

  6. Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis Bumpy Torus plasma

    Science.gov (United States)

    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.

  7. Early effect of NEURAPAS® balance on current source density (CSD of human EEG

    Directory of Open Access Journals (Sweden)

    Koch Klaus

    2011-08-01

    Full Text Available Abstract Psychiatric patients often suffer from stress, anxiety and depression. Various plant extracts are known to fight stress (valerian, anxiety (passion flower or depression (St. John's wort. NEURAPAS® balance is a mixture of these three extracts and has been designed to cover this complex of psychiatric conditions. The study was initiated to quantitatively assess the effect of this combination on brain electric activity. Method Quantitative electroencephalogram (EEG current source density (CSD recording from 16 healthy male and female human volunteers (average age 49 years was used in a randomized, placebo-controlled cross over study. Recordings were performed 0. 5, 1. 5, 3 and 4 hours after administration of the preparations under the conditions of 6 min eyes open and 5 min d2 concentration test, mathematical calculation test and memory test, respectively. All variables (electric power within 6 frequency ranges at 17 electrode positions were fed into a linear discriminant analysis (eyes open condition. In the presence of mental load these variables were used to construct brain maps of frequency changes. Results Under the condition of mental load, centro-parietal spectral power remained statistically significantly lower within alpha1, alpha2 and beta1 frequencies in the presence of verum in comparison to placebo. Discriminant analysis revealed a difference to placebo 3 and 4 hours after intake of 6 tablets of NEURAPAS® balance. Data location within the polydimensional space was projected into the area of the effects of sedative and anti-depressive reference drugs tested earlier under identical conditions. Results appeared closer to the effects of fluoxetine than to St. John's wort. Conclusions Analysis of the neurophysiological changes following the intake of NEURAPAS® balance revealed a similarity of frequency changes to those of calming and anti-depressive drugs on the EEG without impairment of cognition. Trial registration Clinical

  8. Geomagnetic paleointensity in historical pyroclastic density currents: Testing the effects of emplacement temperature and postemplacement alteration

    Science.gov (United States)

    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.

  9. The effect of aging on the critical current density in superconducting Nb-Ti-Zr alloys

    International Nuclear Information System (INIS)

    Ishida, Fumihiko; Doi, Toshio

    1979-01-01

    The effect of aging temperature, cold-reduction prior to aging, O 2 content and composition on the variation in the critical current density, J sub(c), by isothermal aging was investigated in heavily cold-worked Nb-Ti-Zr alloys on the Nb-Ti side. The results are summarized as follows: (1) When these alloys are aged isothermally at temperatures from 350 to 500 0 C, J sub(c) increases initially, reaches a maximum value and then decreases. Increase in J sub(c) of three orders of magnitude is possible as a result of aging. (2) The maximum value of J sub(c) on the isothermal aging curve becomes higher at a lower aging temperature, at a less cold-reduction prior to aging or with a higher O 2 content. (3) The J sub(c) of aged alloy becomes a maximum in composition containing 35 at%Nb, 60 to 65 at%Ti and less than 5 at%Zr. (4) The maximum value of J sub(c) was obtained for Nb-60.0 at%Ti-5.0 at%Zr alloy containing 1200 wt ppm O 2 , aged at 350 0 C for 330 h after 98.44% cold-reduction. The values of J sub(c) at 4.2 K were 2.4 x 10 9 A/m 2 at 5.0 T, 1.1 x 10 9 A/m 2 at 7.0 T and 3.0 x 10 8 A/m 2 at 9.0 T, respectively. The upper critical field of this specimen was 11.3 T at 4.2 K and its critical temperature was 8.6 K. (author)

  10. Calculations on the current density and the voltage-current relation under a.c. conditions of filaments

    NARCIS (Netherlands)

    Hartmann, R.A.; Dijkstra, D.; van Beckum, F.P.H.; van de Klundert, L.J.M.

    1989-01-01

    Technical applications of multifilamentary wires indicate that filaments are used in complex magnetic fields (a combination of non-parallel a.c./d.c. transverse and rotating fields) carrying an a.c./d.c. transport current of various frequency. Furthermore, due to technical manufacturing processes

  11. On the toroidal current density flowing across a poloidal-magnetic-field null in an axisymmetric plasma

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Paulo; Bizarro, Joao P. S. [Associacao Euratom-IST, Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, 1049-001 Lisboa (Portugal)

    2013-04-15

    The axisymmetry condition and two of Maxwell's equations are used to show that, in general, there are no nested magnetic surfaces around a poloidal-magnetic-field null for a sufficiently small value of the toroidal current density flowing there. Hence, the toroidal current density at the axis of a magnetic configuration with extreme shear reversal cannot continuously approach zero unless nested surfaces are first broken or particular values are assigned to boundary conditions and other plasma parameters. The threshold of the toroidal current-density at which the topology changes is shown to be set by such parameters, and some examples of the predicted topology transition are presented using analytical solutions of the Grad-Shafranov equation.

  12. Structural and phase transformations in zinc and brass wires under heating with high-density current pulse

    Energy Technology Data Exchange (ETDEWEB)

    Pervikov, A. V. [Laboratory of Physical Chemistry of Ultrafine Materials, Institute of Strength Physics and Materials Science, 2/4, pr. Akademicheskii, 634021 Tomsk, Russia and Department of High Voltage Electrophysics and High Current Electronics, Tomsk Polytechnic University, 30 Lenin Avenue, 634050 Tomsk (Russian Federation)

    2016-06-15

    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 × 10{sup 7} A/cm{sup 2} 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.

  13. Optimization of a ribbon diode with magnetic insulation for increasing the current density in a high-current relativistic electron beam

    Science.gov (United States)

    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.

  14. Separation Test Method for Investigation of Current Density Effects on Bond Wires of SiC Power MOSFET Modules

    DEFF Research Database (Denmark)

    Luo, Haoze; Iannuzzo, Francesco; Blaabjerg, Frede

    2017-01-01

    In this paper, a separation test method for eliminating the effects of different current densities on the bond wires is proposed. The separation test method makes it possible to study the effect of different current density on the fatigue damage of bond wires without changing the temperature swing...... and average temperature during the test. By analyzing the output characteristics of the linear region of MOSFET, the constraint relations among the gate voltage, on-state voltage drop and junction temperature are revealed in this paper. The one-to-one correspondence between gate voltage and conduction power...

  15. Influence of Electrolyte Modulus on the Local Current Density at a Dendrite Tip on a Lithium Metal Electrode

    Energy Technology Data Exchange (ETDEWEB)

    Harry, KJ; Higa, K; Srinivasan, V; Balsara, NP

    2016-08-10

    Understanding and controlling the electrochemical deposition of lithium is imperative for the safe use of rechargeable batteries with a lithium metal anode. Solid block copolymer electrolyte membranes are known to enhance the stability of lithium metal anodes by mechanically suppressing the formation of lithium protrusions during battery charging. Time-resolved hard X-ray microtomography was used to monitor the internal structure of a symmetric lithium-polymer cell during galvanostatic polarization. The microtomography images were used to determine the local rate of lithium deposition, i.e. local current density, in the vicinity of a lithium globule growing through the electrolyte. Measurements of electrolyte displacement enabled estimation of local stresses in the electrolyte. At early times, the current density was maximized at the globule tip, as expected from simple current distribution arguments. At later times, the current density was maximized at the globule perimeter. We show that this phenomenon is related to the local stress fields that arise as the electrolyte is deformed. The local current density, normalized for the radius of curvature, decreases with increasing compressive stresses at the lithium-polymer interface. To our knowledge, our study provides the first direct measurement showing the influence of local mechanical stresses on the deposition kinetics at lithium metal electrodes.

  16. Critical current densities amd pinning mechanisms of high-Tc films on single crystalline and technologically relevant substrates. Final report

    International Nuclear Information System (INIS)

    Adrian, H.

    1995-12-01

    The report deals with six project tasks: (1) Effects of impurity additions at atomic level on the pinning behaviour and the critical current densities, examined in epitactic YBA 2 (Cu 1-x Ni x ) 3 O 7 films. It could be proven that the Ni atoms increase the activation energy for flux movement and the critical current density in a concentration range of 0 2 Sr 2 Ca n-1 Cu n O 2n+4+δ films (n = 2 and 3) with good crystalline properties, high critical currents, and high current densities were prepared. Thin YBa 2 Cu 3 O 7 films of high quality could be grown on saphire substrates, both by the MO-CVD process and by MBE. The aim of depositing biaxially textured YBa 2 Cu 3 O 7 films with high critical current densities on polycrystalline, metallic substrates was achieved by the IBAD process combined with MBE. The buffer layer was YSZ. Heterostructures of the layer sequence YBa 2 Cu 3 O 7 /CeO 2 /Y 0.3 Pr 0.7 Ba 2 Cu 3 O 7 /YBa 2 Cu 3 O 7 and YBa 2 Cu 3 O 7 /CeO 2 /Au were prepared by laser ablation and sputtering processes, in order to examine Josephson ramp contacts and superconducting field-effect transistors. (orig./MM) [de

  17. The Merapi 2010 eruption: An interdisciplinary impact assessment methodology for studying pyroclastic density current dynamics

    Science.gov (United States)

    Jenkins, S.; Komorowski, J.-C.; Baxter, P. J.; Spence, R.; Picquout, A.; Lavigne, F.; Surono

    2013-07-01

    The large explosive eruption of Merapi volcano, Indonesia, in 2010 presented a key, and rare, opportunity to study the impacts of a major explosive eruption in a densely populated area. Pyroclastic density currents (PDCs) produced throughout the 2010 eruption were unusually destructive, causing near complete devastation across a 22 km2 swath of the densely populated southern flanks and casualties to the end of their runout at 15.5 km from the volcano. The majority (> 120) of the more than 200 fatalities occurred more than 12 km from the volcano, where many people were caught in PDCs as they were evacuating. The 2010 eruption (VEI 4) exhibited a range of PDC behaviour in a complex multi-stage event that marked a change in eruption behaviour at Merapi, being the first eruption of this magnitude and style since 1872. This shift in style may mark a change in regime, and so understanding the potential impact of such large explosive eruptions is essential for future risk-assessment at Merapi. We describe a new impact assessment methodology that allowed us to collect important empirical geological, damage and casualty information and reconstruct impact dynamics associated with the PDCs. In contrast to previous PDC impact studies, we combined remote, field, laboratory and GIS assessments and were able to enter the affected areas safely and before their disturbance by rains or human activity. By integrating the results of our geological, damage and medical studies, we could reconstruct the spatial and temporal dynamics of the PDCs and their main hazard characteristics. Our interdisciplinary methods and preliminary findings are discussed here. In the areas damaged by PDCs, we used empirical damage data and calculations of material and structural resistance to lateral force to estimate approximate dynamic pressures. Dynamic pressures associated with the 5 November paroxysm exceeded 15 kPa more than 6 km from source and rapidly attenuated over a distance of less than 1 km at

  18. Functional interconnections between CA3 and the dentate gyrus revealed by current source density analysis.

    Science.gov (United States)

    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 (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 infer that CA3 provides an early excitatory feedback path to DG through recurrent collaterals or

  19. Ultrasound Current Source Density Imaging in live rabbit hearts using clinical intracardiac catheter

    Science.gov (United States)

    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

  20. Negative-ion current density dependence of the surface potential of insulated electrode during negative-ion implantation

    International Nuclear Information System (INIS)

    Tsuji, Hiroshi; Okayama, Yoshio; Toyota, Yoshitaka; Gotoh, Yasuhito; Ishikawa, Junzo; Sakai, Shigeki; Tanjyo, Masayasu; Matsuda, Kouji.

    1994-01-01

    Positive ion implantation has been utilized as the method of impurity injection in ultra-LSI production, but the problem of substrate charging cannot be resolved by conventional charge compensation method. It was forecast that by negative ion implantation, this charging problem can be resolved. Recently the experiment on the negative ion implantation into insulated electrodes was carried out, and the effect of negative ion implantation to this problem was proved. However, the dependence of charged potential on the increase of negative ion current at the time of negative ion implantation is a serious problem in large current negative ion implantation hereafter. The charged potential of insulated conductor substrates was measured by the negative ion implantation using the current up to several mA/cm 2 . The experimental method is explained. Medium current density and high current density negative ion implantation and charged potential are reported. Accordingly in negative ion implantation, if current density is optimized, the negative ion implantation without charging can be realized. (K.I.)

  1. Influences of the current density on the performances of the chrome-plated layer in deterministic electroplating repair

    Science.gov (United States)

    Xia, H.; Shen, X. M.; Yang, X. C.; Xiong, Y.; Jiang, G. L.

    2018-01-01

    Deterministic electroplating repair is a novel method for rapidly repairing the attrited parts. By the qualitative contrast and quantitative comparison, influences of the current density on performances of the chrome-plated layer were concluded in this study. The chrome-plated layers were fabricated under different current densities when the other parameters were kept constant. Hardnesses, thicknesses and components, surface morphologies and roughnesses, and wearability of the chrome-plated layers were detected by the Vickers hardness tester, scanning electron microscope / energy dispersive X-ray detector, digital microscope in the 3D imaging mode, and the ball-milling instrument with profilograph, respectively. In order to scientifically evaluate each factor, the experimental data was normalized. A comprehensive evaluation model was founded to quantitative analyse influence of the current density based on analytic hierarchy process method and the weighted evaluation method. The calculated comprehensive evaluation indexes corresponding to current density of 40A/dm2, 45A/dm2, 50A/dm2, 55A/dm2, 60A/dm2, and 65A/dm2 were 0.2246, 0.4850, 0.4799, 0.4922, 0.8672, and 0.1381, respectively. Experimental results indicate that final optimal option was 60A/dm2, and the priority orders were 60A/dm2, 55A/dm2, 45A/dm2, 50A/dm2, 40A/dm2, and 65A/dm2.

  2. Effect of preionization, fluorine concentration, and current density on the discharge uniformity in F2 excimer laser gas mixtures

    NARCIS (Netherlands)

    Mathew, D.; Bastiaens, Hubertus M.J.; Boller, Klaus J.; Peters, P.J.M.

    2007-01-01

    The discharge homogeneity in F2-based excimer laser gas mixtures and its dependence on various key parameters, such as the degree of preionization, preionization delay time, F2 concentration and current density, is investigated in a small x-ray preionized discharge chamber. The spatial and temporal

  3. The role of relativity in the optical response of gold within the time-dependent current-density-functional theory

    NARCIS (Netherlands)

    Romaniello, P; de Boeij, PL

    2005-01-01

    We included relativistic effects in the formulation of the time-dependent current-density-functional theory for the calculation of linear response properties of metals [P. Romaniello and P. L. de Boeij, Phys. Rev. B (to be published)]. We treat the dominant scalar-relativistic effects using the

  4. Charge and current density profiles of a degenerate magnetized free-electron gas near a hard wall

    NARCIS (Netherlands)

    Kettenis, M.M.; Suttorp, L.G.

    1998-01-01

    The charge and current densities of a completely degenerate free-electron gas in a uniform magnetic field are found to have a damped oscillatory spatial dependence near a wall that is parallel to the magnetic field. For large distances from the wall the behaviour of the associated profile functions

  5. Experimental investigation of the effect of titanium dioxide and barium titanate additives on DC transient currents in low density polyethylene

    DEFF Research Database (Denmark)

    Khalil, M.S; Henk, Peter O; Henriksen, Mogens

    1988-01-01

    The effect of titanium dioxide as a semiconductive additive and barium titanate as a highly polar additive on the DC transient currents in low-density polyethylene is investigated. Experiments were made using thick specimens under a high electric field (>25×106 V/m) and a constant temperature of 40...

  6. Improved critical current densities of bulk MgB.sub.2./sub. using carbon-coated amorphous boron

    Czech Academy of Sciences Publication Activity Database

    Muralidhar, M.; Higuchi, M.; Jirsa, Miloš; Diko, P.; Kokal, I.; Murakami, M.

    2017-01-01

    Roč. 27, č. 4 (2017), s. 1-4, č. článku 6201104. ISSN 1051-8223 Institutional support: RVO:68378271 Keywords : carbon-encapsulated boron * critical current density * flux pinning * micro-structure Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.092, year: 2015

  7. Effect of current density on the microstructure and corrosion resistance of microarc oxidized ZK60 magnesium alloy.

    Science.gov (United States)

    You, Qiongya; Yu, Huijun; Wang, Hui; Pan, Yaokun; Chen, Chuanzhong

    2014-09-01

    The application of magnesium alloys as biomaterials is limited by their poor corrosion behavior. Microarc oxidation (MAO) treatment was used to prepare ceramic coatings on ZK60 magnesium alloys in order to overcome the poor corrosion resistance. The process was conducted at different current densities (3.5 and 9.0 A/dm(2)), and the effect of current density on the process was studied. The microstructure, elemental distribution, and phase composition of the MAO coatings were characterized by scanning electron microscopy, energy-dispersive x-ray spectrometry, and x-ray diffraction, respectively. The increment of current density contributes to the increase of thickness. A new phase Mg2SiO4 was detected as the current density increased to 9.0 A/dm(2). A homogeneous distribution of micropores could be observed in the coating produced at 3.5 A/dm(2), while the surface morphology of the coating formed at 9.0 A/dm(2) was more rough and apparent microcracks could be observed. The coating obtained at 3.5 A/dm(2) possessed a better anticorrosion behavior.

  8. Evaluation of a Magnetically-Filtered Faraday Probe for Measuring the ion Current Density Profile of a Hall Thruster

    National Research Council Canada - National Science Library

    Rovey, Joshua L; Walker, Micthell L; Gallimore, Alec D; Peterson, Peter Y

    2004-01-01

    .... In this study, a MFFP, boxed Faraday probe (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operated over the range of 300-500 V and 5-10 mg...

  9. High Current, High Density Arc Plasma as a New Source for WiPAL

    Science.gov (United States)

    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.

  10. Calculation of induced current densities and specific absorption rates (SAR) for pregnant women exposed to hand-held metal detectors

    Science.gov (United States)

    Kainz, Wolfgang; Chan, Dulciana D.; Casamento, Jon P.; Bassen, Howard I.

    2003-08-01

    The finite difference time domain (FDTD) method in combination with a well established frequency scaling method was used to calculate the internal fields and current densities induced in a simple model of a pregnant woman and her foetus, when exposed to hand-held metal detectors. The pregnant woman and foetus were modelled using a simple semi-heterogeneous model in 10 mm resolution, consisting of three different types of tissue. The model is based on the scanned shape of a pregnant woman in the 34th gestational week. Nine different representative models of hand-held metal detectors operating in the frequency range from 8 kHz to 2 MHz were evaluated. The metal detectors were placed directly on the abdomen of the computational model with a spacing of 1 cm. Both the induced current density and the specific absorption rate (SAR) are well below the recommended limits for exposure of the general public published in the ICNIRP Guidelines and the IEEE C95.1 Standard. The highest current density is 8.3 mA m-2 and the highest SAR is 26.5 µW kg-1. Compared to the limits for the induced current density recommended in the ICNIRP Guidelines, a minimum safety factor of 3 exists. Compared to the IEEE C95.1 Standard, a safety factor of 60 000 for the specific absorption rate was found. Based on the very low specific absorption rate and an induced current density below the recommended exposure limits, significant temperature rise or nerve stimulation in the pregnant woman or in the foetus can be excluded.

  11. Calculation of induced current densities and specific absorption rates (SAR) for pregnant women exposed to hand-held metal detectors

    International Nuclear Information System (INIS)

    Kainz, Wolfgang; Chan, Dulciana D; Casamento, Jon P; Bassen, Howard I

    2003-01-01

    The finite difference time domain (FDTD) method in combination with a well established frequency scaling method was used to calculate the internal fields and current densities induced in a simple model of a pregnant woman and her foetus, when exposed to hand-held metal detectors. The pregnant woman and foetus were modelled using a simple semi-heterogeneous model in 10 mm resolution, consisting of three different types of tissue. The model is based on the scanned shape of a pregnant woman in the 34th gestational week. Nine different representative models of hand-held metal detectors operating in the frequency range from 8 kHz to 2 MHz were evaluated. The metal detectors were placed directly on the abdomen of the computational model with a spacing of 1 cm. Both the induced current density and the specific absorption rate (SAR) are well below the recommended limits for exposure of the general public published in the ICNIRP Guidelines and the IEEE C95.1 Standard. The highest current density is 8.3 mA m -2 and the highest SAR is 26.5 μW kg -1 . Compared to the limits for the induced current density recommended in the ICNIRP Guidelines, a minimum safety factor of 3 exists. Compared to the IEEE C95.1 Standard, a safety factor of 60,000 for the specific absorption rate was found. Based on the very low specific absorption rate and an induced current density below the recommended exposure limits, significant temperature rise or nerve stimulation in the pregnant woman or in the foetus can be excluded

  12. Calculation of induced current densities and specific absorption rates (SAR) for pregnant women exposed to hand-held metal detectors

    Energy Technology Data Exchange (ETDEWEB)

    Kainz, Wolfgang; Chan, Dulciana D; Casamento, Jon P; Bassen, Howard I [Food and Drug Administration, Center for Devices and Radiological Health (CDRH), 12725 Twinbrook Parkway, Rockville, MD 20852 (United States)

    2003-08-07

    The finite difference time domain (FDTD) method in combination with a well established frequency scaling method was used to calculate the internal fields and current densities induced in a simple model of a pregnant woman and her foetus, when exposed to hand-held metal detectors. The pregnant woman and foetus were modelled using a simple semi-heterogeneous model in 10 mm resolution, consisting of three different types of tissue. The model is based on the scanned shape of a pregnant woman in the 34th gestational week. Nine different representative models of hand-held metal detectors operating in the frequency range from 8 kHz to 2 MHz were evaluated. The metal detectors were placed directly on the abdomen of the computational model with a spacing of 1 cm. Both the induced current density and the specific absorption rate (SAR) are well below the recommended limits for exposure of the general public published in the ICNIRP Guidelines and the IEEE C95.1 Standard. The highest current density is 8.3 mA m{sup -2} and the highest SAR is 26.5 {mu}W kg{sup -1}. Compared to the limits for the induced current density recommended in the ICNIRP Guidelines, a minimum safety factor of 3 exists. Compared to the IEEE C95.1 Standard, a safety factor of 60,000 for the specific absorption rate was found. Based on the very low specific absorption rate and an induced current density below the recommended exposure limits, significant temperature rise or nerve stimulation in the pregnant woman or in the foetus can be excluded.

  13. Review of the critical current densities and magnetic irreversibilities in high T_c superconductors

    Science.gov (United States)

    Senoussi, S.

    1992-07-01

    This review article is concerned with critical current density (J) and magnetic irreversibilities in high-T_c superconductors (HTSC). The apparent J derived from different experimental techniques (transport, hysteresis cycle, ac-susceptibility) are compared. The influence of time (relaxation effects) as well as the macroscopic size of the sample on the criteria defining J are discussed. The dependences of the critical current on grain boundaries (“weaks-links”), texturing and other physical and chemical defects are examined in detail. The role of self fields is clarified. The critical current is strongly influenced by the anisotropy of the layered structure practically whatever the experimental conditions. Intrinsic pinning is lowered by defects. Demagnetizing effects and surface pinnings are reviewed. The usual critical state and flux creep models are recalled emphasizing the physical aspects most specific to HTSC. A theoretical model which takes into account the equilibrium magnetization and sample granularity is developed. It reproduces most of the characteristic features of both the hysteresis cycle and ac-susceptibility. A number of new formulae are introduced. They generalize the Bean model and show how to correct for the dimensions of the grains (granular materials), the macroscopic radius of the sample, anisotropy and demagnetization effects in certain situations. Several limits beyond which the usual critical state breaks down are discussed: (1) the quasi elastic limit where the variable field is too weak to depin the vortices, (2) H≈ H_C1 so that the interaction between vortex lines is exponentially weak and (3) T and H close to the “irreversibility line” where the influence of viscous forces are strong. (4) Hgg H_C1 so that J is governed by collective pinning. Ce papier de revue est consacré aux courant critiques (J) et aux irréversibilités magnétiques dans les nouveaux matériaux supraconducteurs (HTSC). Nous y comparons les densités des

  14. Cooling of Water in a Flask: Convection Currents in a Fluid with a Density Maximum

    Science.gov (United States)

    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…

  15. Effect of electrodeposition current density on the microstructure and the degradation of electroformed iron for degradable stents

    Energy Technology Data Exchange (ETDEWEB)

    Moravej, Maryam [Laboratory for Biomaterials and Bioengineering, Department of Mining, Metallurgy and Materials Engineering and University Hospital Research Center, Universite Laval, Quebec City, Que. G1V 0A6 (Canada); Department of Mining, Metallurgy and Materials Engineering, Pavillon Adrien-Pouliot, 1065 avenue de la Medecine, Local 1745-E, Universite Laval, Quebec City, Que. G1V 0A6 (Canada); Amira, Sofiene [Aluminium Technology Centre, Industrial Materials Institute, National Research Council Canada, 501, boul. de l' Universite Est, Saguenay, Que. G7H 8C3 (Canada); Prima, Frederic [Laboratory for Physical Metallurgy, Ecole Nationale Superieure de Chimie de Paris, Universite Pierre et Marie Curie, Paris 6 (France); Rahem, Ahmed [Aluminium Technology Centre, Industrial Materials Institute, National Research Council Canada, 501, boul. de l' Universite Est, Saguenay, Que. G7H 8C3 (Canada); Fiset, Michel [Department of Mining, Metallurgy and Materials Engineering, Pavillon Adrien-Pouliot, 1065 avenue de la Medecine, Local 1745-E, Universite Laval, Quebec City, Que. G1V 0A6 (Canada); and others

    2011-12-15

    Pure iron has become one of the most interesting candidate materials for degradable metallic stents due to its high mechanical properties and moderate degradation. In this work we studied the effect of electrodeposition current density on microstructure and degradation of pure iron films electrodeposited on Ti alloy substrate for degradable metallic stent application. Iron sheets were produced by electrodeposition using four different current densities 1, 2, 5 and 10 A dm{sup -2}. The films were then studied by SEM (scanning electron microscope) and EBSD (electron backscatter diffraction) to observe the surface morphology, grain size and orientation. Potentiodynamic polarization and static immersion tests were used to determine the corrosion rate and to study the degradation behavior of iron films, respectively. The current density was found to significantly influence the texture, the grain size and the grain shape of the electrodeposited iron. At current densities of 1, 5 and 10 A dm{sup -2}, weak textures corresponding to Left-Pointing-Angle-Bracket 1 0 1 Right-Pointing-Angle-Bracket , Left-Pointing-Angle-Bracket 1 1 1 Right-Pointing-Angle-Bracket and Left-Pointing-Angle-Bracket 1 1 2 Right-Pointing-Angle-Bracket in the normal (electrodeposition) direction were obtained, respectively. At these current densities, average grain sizes smaller than 3 {mu}m were also obtained. However, at 2 A dm{sup -2}, a strong Left-Pointing-Angle-Bracket 1 1 1 Right-Pointing-Angle-Bracket //ND texture with density of 7.4 MUD was obtained with larger average grain size of 4.4 {mu}m. The microstructure of iron samples changed after annealing at 550 Degree-Sign C because of the induced recrystallization. Different corrosion rates were obtained from potentiodynamic polarization curves of iron films deposited at different current densities because of their microstructures. Fe-2 showed the lowest corrosion rate due to its larger grains size and its texture. The corrosion rates of all

  16. ac loss and dc critical current densities of Nb3Sn tapes by the solid state diffusion process

    International Nuclear Information System (INIS)

    Suenaga, M.; Klamut, C.; Bussiere, J.F.

    1976-01-01

    The effects of metallurgical processing on 60 Hz ac losses and dc critical currents in Nb 3 Sn tapes fabricated by the solid state diffusion technique were investigated. An addition of Al to the Cu--Sn alloy for the matrix resulted in large reduction in the ac losses of Nb 3 Sn tapes, but the highest linear critical current densities were observed in Nb 3 Sn tapes produced with a Nb-1 wt percent Zr core in a Cu-13 wt percent Sn matrix. Values of the losses and the critical currents in these tapes can meet the present requirements for the ac superconducting power cables

  17. Effect of Magnetic Flux Density and Applied Current on Temperature, Velocity and Entropy Generation Distributions in MHD Pumps

    Directory of Open Access Journals (Sweden)

    M. Kiyasatfar

    2011-01-01

    Full Text Available In the present study, simulation of steady state, incompressible and fully developed laminar flow has been conducted in a magneto hydrodynamic (MHD pump. The governing equations are solved numerically by finite-difference method. The effect of the magnetic flux density and current on the flow and temperature distributions in a MHD pump is investigated. The obtained results showed that controlling the flow and the temperature is possible through the controlling of the applied current and the magnetic flux. Furthermore, the effects of the magnetic flux density and current on entropy generation in MHD pump are considered. Our presented numerical results are in good agreement with the experimental data showed in literature.

  18. Microstructural and crystallographic imperfections of MgB2 superconducting wire and their correlation with the critical current density

    Science.gov (United States)

    Shahabuddin, Mohammed; Alzayed, Nasser S.; Oh, Sangjun; Choi, Seyong; Maeda, Minoru; Hata, Satoshi; Shimada, Yusuke; Hossain, Md Shahriar Al; Kim, Jung Ho

    2014-01-01

    A comprehensive study of the effects of structural imperfections in MgB2 superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB2 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 MgB2, 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 MgB2, however, even at low sintering temperature, and thus block current transport paths.

  19. Effects of heat and water transport on the performance of polymer electrolyte membrane fuel cell under high current density operation

    International Nuclear Information System (INIS)

    Tabuchi, Yuichiro; Shiomi, Takeshi; Aoki, Osamu; Kubo, Norio; Shinohara, Kazuhiko

    2010-01-01

    Key challenges to the acceptance of polymer electrolyte membrane fuel cells (PEMFCs) for automobiles are the cost reduction and improvement in its power density for compactness. In order to get the solution, the further improvement in a fuel cell performance is required. In particular, under higher current density operation, water and heat transport in PEMFCs has considerable effects on the cell performance. In this study, the impact of heat and water transport on the cell performance under high current density was investigated by experimental evaluation of liquid water distribution and numerical validation. Liquid water distribution in MEA between rib and channel area is evaluated by neutron radiography. In order to neglect the effect of liquid water in gas channels and reactant species concentration distribution in the flow direction, the differential cell was used in this study. Experimental results suggested that liquid water under the channel was dramatically changed with rib/channel width. From the numerical study, it is found that the change of liquid water distribution was significantly affected by temperature distribution in MEA between rib and channel area. In addition, not only heat transport but also water transport through the membrane also significantly affected the cell performance under high current density operation.

  20. High-current-density electrodeposition using pulsed and constant currents to produce thick CoPt magnetic films on silicon substrates

    Science.gov (United States)

    Ewing, Jacob; Wang, Yuzheng; Arnold, David P.

    2018-05-01

    This paper investigates methods for electroplating thick (>20 μm), high-coercivity CoPt films using high current densities (up to 1 A/cm2) and elevated bath temperatures (70 °C). Correlations are made tying current-density and temperature process parameters with plating rate, elemental ratio and magnetic properties of the deposited CoPt films. It also investigates how pulsed currents can increase the plating rate and film to substrate adhesion. Using 500 mA/cm2 and constant current, high-quality, dense CoPt films were successfully electroplated up to 20 μm thick in 1 hr on silicon substrates (0.35 μm/min plating rate). After standard thermal treatment (675°C, 30 min) to achieve the ordered L10 crystalline phase, strong magnetic properties were measured: coercivities up 850 kA/m, remanences >0.5 T, and maximum energy products up to 46 kJ/m3.

  1. Effects of Duty Cycle, Current Frequency, and Current Density on Corrosion Behavior of the Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Artificial Seawater

    Science.gov (United States)

    Vakili-Azghandi, Mojtaba; Fattah-alhosseini, Arash

    2017-10-01

    In this study, the effects of duty cycle, current frequency, and current density on corrosion behavior of the plasma electrolytic oxidation (PEO) coatings on 6061 Al alloy in artificial seawater (3.5 wt pct NaCl solution) were investigated. To serve this purpose, the electrical parameters of a unipolar pulsed current were applied during the PEO process on 6061 Al alloy in alkaline silicate electrolyte with and without Al2O3 nanoparticles. The coating morphology and microstructure were characterized by the scanning electron microscopy. The corrosion behavior and electrochemical response of the specimens treated by plasma electrolytic oxidation were analyzed by the electrochemical impedance spectroscopy and the potentiodynamic polarization in artificial seawater. It was found that PEO coatings formed in the presence of Al2O3 nanoparticle had lower porosity and exhibited better corrosion behavior compared with the coatings formed in the absence of Al2O3 nanoparticle in the structure. This can be attributed to the nanoparticles' incorporation and penetration through the PEO coatings. On the other hand, the decrease in the current density and increases in the duty cycle and frequency lead to further reduction of the nanoparticles' incorporation and distribution on the coating surface.

  2. Comparison of ring currents evaluated consistently at density functional and Hartree-Fock levels

    NARCIS (Netherlands)

    Havenith, Remco W. A.; Meijer, Anthony J. H. M.; Irving, Benjamin J.; Fowler, Patrick W.

    2009-01-01

    Ring-current maps give an immediate visualisation of aromaticity on the magnetic criterion-by which a cyclic system that supports diatropic (paratropic) current induced by a perpendicular magnetic field is aromatic (anti-aromatic). Calculations of maps with the ipsocentric choice of origin are made

  3. Spin transfer torques in MnSi at ultralow current densities

    NARCIS (Netherlands)

    Jonietz, F.; Mühlbauer, S.; Pfleiderer, C.; Neubauer, A.; Münzer, W.; Bauer, A.; Adams, T.; Georgii, R.; Böni, P.; Duine, R.A.|info:eu-repo/dai/nl/304830127; Everschor, K.; Garst, M.; Rosch, A.

    2010-01-01

    Spin manipulation using electric currents is one of the most promising directions in the field of spintronics. We used neutron scattering to observe the influence of an electric current on the magnetic structure in a bulk material. In the skyrmion lattice of manganese silicon, where the spins form a

  4. Spin transfer torques in MnSi at ultralow current densities.

    Science.gov (United States)

    Jonietz, F; Mühlbauer, S; Pfleiderer, C; Neubauer, A; Münzer, W; Bauer, A; Adams, T; Georgii, R; Böni, P; Duine, R A; Everschor, K; Garst, M; Rosch, A

    2010-12-17

    Spin manipulation using electric currents is one of the most promising directions in the field of spintronics. We used neutron scattering to observe the influence of an electric current on the magnetic structure in a bulk material. In the skyrmion lattice of manganese silicon, where the spins form a lattice of magnetic vortices similar to the vortex lattice in type II superconductors, we observe the rotation of the diffraction pattern in response to currents that are over five orders of magnitude smaller than those typically applied in experimental studies on current-driven magnetization dynamics in nanostructures. We attribute our observations to an extremely efficient coupling of inhomogeneous spin currents to topologically stable knots in spin structures.

  5. Study of the origin and structure of a nocturnal atmospheric density current from observations and numerical simulations

    Science.gov (United States)

    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

  6. Correlations of current parameters with flash density from winter thunderstorms in Japan

    DEFF Research Database (Denmark)

    Vogel, Stephan; Ishii, M.; Saito, M.

    2017-01-01

    In this work, Lightning Location System (LLS) data from theJapanese Lightning Detection Network (JLDN) are correlated with lightning current measurements from the New Energy and Industrial Technology Development Organization (NEDO) project which conducted lightning measurements on wind turbines...

  7. Transport studies in FTU with decoupled temperature and current density profiles

    International Nuclear Information System (INIS)

    Bracco, G.; Buratti, P.; Micozzi, P.; Tudisco, O.

    1994-01-01

    Electron temperature profiles in tokamaks are subject to global constraints that can be attributed either to their link with current profiles, i.e. to MHD stability conditions, a clear example being sawtooth activity, or to other mechanisms like marginal stability. Also a direct effect on transport coefficients was attributed to the current profile. Fast current ramps in FTU ohmic pulses have been used to study the effect of current profile variations on the energy confinement time. The global profile constraint was transiently removed in these pulses, and variations in the shape of temperature profiles could be observed. Modified profiles were also observed in pulses with a strong central radiative sink; in this case the modification was not transient. Finally, the transport properties in the central region have been studied by the analysis of temperature evolution between crashes of very long period sawteeth; very small electron heat transport was found. (author) 6 refs., 5 figs

  8. Determination of Charge-Carrier Mobility in Disordered Thin-Film Solar Cells as a Function of Current Density

    Science.gov (United States)

    Mäckel, Helmut; MacKenzie, Roderick C. I.

    2018-03-01

    Charge-carrier mobility is a fundamental material parameter, which plays an important role in determining solar-cell efficiency. The higher the mobility, the less time a charge carrier will spend in a device and the less likely it is that it will be lost to recombination. Despite the importance of this physical property, it is notoriously difficult to measure accurately in disordered thin-film solar cells under operating conditions. We, therefore, investigate a method previously proposed in the literature for the determination of mobility as a function of current density. The method is based on a simple analytical model that relates the mobility to carrier density and transport resistance. By revising the theoretical background of the method, we clearly demonstrate what type of mobility can be extracted (constant mobility or effective mobility of electrons and holes). We generalize the method to any combination of measurements that is able to determine the mean electron and hole carrier density, and the transport resistance at a given current density. We explore the robustness of the method by simulating typical organic solar-cell structures with a variety of physical properties, including unbalanced mobilities, unbalanced carrier densities, and for high or low carrier trapping rates. The simulations reveal that near VOC and JSC , the method fails due to the limitation of determining the transport resistance. However, away from these regions (and, importantly, around the maximum power point), the method can accurately determine charge-carrier mobility. In the presence of strong carrier trapping, the method overestimates the effective mobility due to an underestimation of the carrier density.

  9. A theoretical analysis of the electromigration-induced void morphological evolution under high current density

    Science.gov (United States)

    Wang, Yuexing; Yao, Yao

    2017-10-01

    In this work, analysis of electromigration-induced void morphological evolution in solder interconnects is performed based on mass diffusion theory. The analysis is conducted for three typical experimentally observed void shapes: circular, ellipse, and cardioid. Void morphological evolution is governed by the competition between the electric field and surface capillary force. In the developed model, both the electric field and capillary force on the void's surface are solved analytically. Based on the mass conversation principle, the normal velocity on the void surface during diffusion is obtained. The void morphological evolution behavior is investigated, and a physical model is developed to predict void collapse to a crack or to split into sub-voids under electric current. It is noted that when the electric current is being applied from the horizontal direction, a circular void may either move stably along the electric current direction or collapse to a finger shape, depending on the relative magnitude of the electric current and surface capillary force. However, the elliptical-shaped void will elongate along the electric current direction and finally collapse to the finger shape. On the other hand, the cardioid-shaped void could bifurcate into two sub-voids when the electric current reaches a critical value. The theoretical predictions agree well with the experimental observations.

  10. Interacting effects of age, density, and weather on survival and current reproduction for a large mammal.

    Science.gov (United States)

    Richard, Emmanuelle; Simpson, Steven E; Medill, Sarah A; McLoughlin, Philip D

    2014-10-01

    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 [[Formula: see text] ± 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.

  11. Critical current density improvements in MgB2 superconducting bulk samples by K2CO3 additions  

    DEFF Research Database (Denmark)

    Grivel, J.-C.

    2018-01-01

    reaction. The critical current density of MgB2 was improved both in self field and under applied magnetic field for T ≤ 30 K, with optimum results for 1 mol% K2CO3 addition. The normalized flux pinning force (f(b)) shows that the flux pinning mechanism at low field is similar for all samples, following...... the predictions of the point pinning model. In contrast the behavior of f(b) is significantly altered at reduced fields (b) larger than unity by K2CO3 additions, tending towards surface pinning. Besides providing carbon, another effect of K2CO3 may originate from the presence of a transient liquid phase...... that appears to improve the crystallinity and thus the critical current density at low field....

  12. Enhancement of critical current density of in situ processed MgB sub 2 tapes by WB addition

    CERN Document Server

    Fujii, H; Kumakura, H

    2003-01-01

    The effect of tungsten boride (WB) addition on the microstructure and superconducting properties of Fe-sheathed MgB sub 2 tapes has been investigated. The microstructure was not influenced appreciably by the addition, whereas the superconducting properties changed. Even by a 5 mol% addition, the critical temperature (T sub c) decreased by about 0.5 K. However, the field dependence of the inductive critical current density (J sub c sub i) became smaller with the increase in the amount of addition, suggesting that pinning centres effective in a high-field region were possibly introduced. The transport critical current density (J sub c sub t) at 4.2 K increased about twice by the 5 mol% addition and reached 15 and 5 kA cm sup - sup 2 at 8 and 10 T, respectively.

  13. In-situ electric field and current density in Japanese male and female models for uniform magnetic field exposures

    International Nuclear Information System (INIS)

    Hirata, A.; Wake, K.; Watanabe, S.; Taki, M.

    2009-01-01

    The present study quantified the in situ electric field and induced current density in anatomically based numeric Japanese male and female models for exposure to extremely low-frequency magnetic fields. A quasi-static FDTD method was applied to analyse this problem. The computational results obtained herein reveal that the 99. percentile value of the in situ electric field in the nerve tissue and the current density averaged over an area of 1 cm 2 of the nerve tissue (excluding non-nerve tissues in the averaging region) in the female models were less than 35 and 25%, respectively. These induced quantities in the Japanese models were smaller than those for European models reported in a previous study, which is mainly due to the difference in cross-sectional area of the body. (authors)

  14. Sleepwalking episodes are preceded by arousal-related activation in the cingulate motor area: EEG current density imaging.

    Science.gov (United States)

    Januszko, Piotr; Niemcewicz, Szymon; Gajda, Tomasz; Wołyńczyk-Gmaj, Dorota; Piotrowska, Anna Justyna; Gmaj, Bartłomiej; Piotrowski, Tadeusz; Szelenberger, Waldemar

    2016-01-01

    To investigate local arousal fluctuations in adults who received ICSD-2 diagnosis of somnambulism. EEG neuroimaging (eLORETA) was utilized to compare current density distribution for 4s epochs immediately preceding sleepwalking episode (from -4.0 s to 0 s) to the distribution during earlier 4s epochs (from -8.0 s to -4.0 s) in 20 EEG segments from 15 patients. Comparisons between eLORETA images revealed significant (t>4.52; psleepwalking, with greater current density within beta 3 frequency range (24-30 Hz) in Brodmann areas 33 and 24. Sleepwalking motor events are associated with arousal-related activation of cingulate motor area. These results support the notion of blurred boundaries between wakefulness and NREM sleep in sleepwalking. Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

  15. Measurement of Magnetic Field From an Induction Heating Hob and Estimation of Induced Current Density in Human Body

    Science.gov (United States)

    Suzuki, Yukihisa; Taki, Masao

    Magnetic fields around induction heating hobs are measured and evaluated with regard to the compliance with safety guidelines of human exposure. The magnetic flux density distributions are highly inhomogeneous and the maximum can exceed the reference levels of the guideline at the very proximity to the device. The induced current densities in human body exposed to these magnetic fields are estimated by numerical calculations by means of impedance method with an anatomical human model. The results indicate that induced currents are sufficiently lower than the basic restriction of the ICNIRP guideline. It is shown that the spatially peak incident field does not provide a relevant reference to compare with the reference level of guideline because it is too conservative but spatially averaged incident magnetic field provides much more relevant reference.

  16. Visualizing the mechanism that determines the critical current density in polycrystalline superconductors using time-dependent Ginzburg-Landau theory.

    OpenAIRE

    Carty, G. J.; Hampshire, D. P.

    2008-01-01

    In polycrystalline superconducting materials optimized for high critical current density (JC) in high magnetic fields, the mechanism that determines JC has long remained uncertain because of the complicated manner in which the fluxon-fluxon and fluxon-microstructure forces combine. In this work, the time-dependent Ginzburg-Landau equations are used to produce visualizations of fluxons at JC that show the disorder in the pinned part of the flux-line lattice and the motion of those fluxons alon...

  17. Achieving the Widest Range of Syngas Proportions at High Current Density over Cadmium Sulfoselenide Nanorods in CO2Electroreduction.

    Science.gov (United States)

    He, Rong; Zhang, An; Ding, Yilun; Kong, Taoyi; Xiao, Qing; Li, Hongliang; Liu, Yan; Zeng, Jie

    2018-02-01

    Electroreduction of CO 2 is a sustainable approach to produce syngas with controllable ratios, which are required as specific reactants for the optimization of different industrial processes. However, it is challenging to achieve tunable syngas production with a wide ratio of CO/H 2 , while maintaining a high current density. Herein, cadmium sulfoselenide (CdS x Se 1- x ) alloyed nanorods are developed, which enable the widest range of syngas proportions ever reported at the current density above 10 mA cm -2 in CO 2 electroreduction. Among CdS x Se 1- x nanorods, CdS nanorods exhibit the highest Faradaic efficiency (FE) of 81% for CO production with a current density of 27.1 mA cm -2 at -1.2 V vs. reversible hydrogen electrode. With the increase of Se content in CdS x Se 1- x nanorods, the FE for H 2 production increases. At -1.2 V vs. RHE, the ratios of CO/H 2 in products vary from 4:1 to 1:4 on CdS x Se 1- x nanorods (x from 1 to 0). Notably, all proportions of syngas are achieved with current density higher than ≈25 mA cm -2 . Mechanistic study reveals that the increased Se content in CdS x Se 1- x nanorods strengthens the binding of H atoms, resulting in the increased coverage of H* and thus the enhanced selectivity for H 2 production in CO 2 electroreduction. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    Science.gov (United States)

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

    2015-01-01

    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. PMID:26548444

  19. Microstructure and Properties of Ni and Ni/Al2O3 Coatings Electrodeposited at Various Current Densities

    Directory of Open Access Journals (Sweden)

    Góral A.

    2016-03-01

    Full Text Available The study presents investigations of an influence of various direct current densities on microstructure, residual stresses, texture, microhardness and corrosion resistance of the nickel coatings electrodeposited from modified Watt’s baths. The properties of obtained coatings were compared to the nano-crystalline composite Ni/Al2O3 coatings prepared under the same plating conditions. The similarities and differences of the obtained coatings microstructures visible on both their surfaces and cross sections and determined properties were presented. The differences in the growth character of the Ni matrix and in the microstructural properties were observed. All electrodeposited Ni and Ni/Al2O3 coatings were compact and well adhering to the steel substrates. The thickness and the microhardness of the Ni and Ni/Al2O3 deposits increased significantly with the current density in the range 2 - 6 A/dm2. Residual stresses are tensile and they reduced as the current density increased. The composite coatings revealed better protection from the corrosion of steel substrate than pure nickel in solution 1 M NaCl.

  20. Comparison of SAR and induced current densities in adults and children exposed to electromagnetic fields from electronic article surveillance devices

    Science.gov (United States)

    Martínez-Búrdalo, M.; Sanchis, A.; Martín, A.; Villar, R.

    2010-02-01

    Electronic article surveillance (EAS) devices are widely used in most stores as anti-theft systems. In this work, the compliance with international guidelines in the human exposure to these devices is analysed by using the finite-difference time-domain (FDTD) method. Two sets of high resolution numerical phantoms of different size (REMCOM/Hershey and Virtual Family), simulating adult and child bodies, are exposed to a 10 MHz pass-by panel-type EAS consisting of two overlapping current-carrying coils. Two different relative positions between the EAS and the body (frontal and lateral exposures), which imply the exposure of different parts of the body at different distances, have been considered. In all cases, induced current densities in tissues of the central nervous system and specific absorption rates (SARs) are calculated to be compared with the limits from the guidelines. Results show that induced current densities are lower in the case of adult models as compared with those of children in both lateral and frontal exposures. Maximum SAR values calculated in lateral exposure are significantly lower than those calculated in frontal exposure, where the EAS-body distance is shorter. Nevertheless, in all studied cases, with an EAS driving current of 4 A rms, maximum induced current and SAR values are below basic restrictions.

  1. Comparison of SAR and induced current densities in adults and children exposed to electromagnetic fields from electronic article surveillance devices

    International Nuclear Information System (INIS)

    Martinez-Burdalo, M; Sanchis, A; Martin, A; Villar, R

    2010-01-01

    Electronic article surveillance (EAS) devices are widely used in most stores as anti-theft systems. In this work, the compliance with international guidelines in the human exposure to these devices is analysed by using the finite-difference time-domain (FDTD) method. Two sets of high resolution numerical phantoms of different size (REMCOM/Hershey and Virtual Family), simulating adult and child bodies, are exposed to a 10 MHz pass-by panel-type EAS consisting of two overlapping current-carrying coils. Two different relative positions between the EAS and the body (frontal and lateral exposures), which imply the exposure of different parts of the body at different distances, have been considered. In all cases, induced current densities in tissues of the central nervous system and specific absorption rates (SARs) are calculated to be compared with the limits from the guidelines. Results show that induced current densities are lower in the case of adult models as compared with those of children in both lateral and frontal exposures. Maximum SAR values calculated in lateral exposure are significantly lower than those calculated in frontal exposure, where the EAS-body distance is shorter. Nevertheless, in all studied cases, with an EAS driving current of 4 A rms, maximum induced current and SAR values are below basic restrictions.

  2. High Current Density InAsSb/GaSb Tunnel Field Effect Transistors

    OpenAIRE

    Dey, Anil; Borg, Mattias; Ganjipour, Bahram; Ek, Martin; Dick Thelander, Kimberly; Lind, Erik; Nilsson, Peter; Thelander, Claes; Wernersson, Lars-Erik

    2012-01-01

    Steep-slope devices, such as tunnel field-effect transistors (TFETs), have recently gained interest due to their potential for low power operation at room temperature. The devices are based on inter-band tunneling which could limit the on-current since the charge carriers must tunnel through a barrier to traverse the device. The InAs/GaSb heterostructure forms a broken type II band alignment which enables inter-band tunneling without a barrier, allowing high on-currents. We ha...

  3. Density-matrix simulation of small surface codes under current and projected experimental noise

    Science.gov (United States)

    O'Brien, T. E.; Tarasinski, B.; DiCarlo, L.

    2017-09-01

    We present a density-matrix simulation of the quantum memory and computing performance of the distance-3 logical qubit Surface-17, following a recently proposed quantum circuit and using experimental error parameters for transmon qubits in a planar circuit QED architecture. We use this simulation to optimize components of the QEC scheme (e.g., trading off stabilizer measurement infidelity for reduced cycle time) and to investigate the benefits of feedback harnessing the fundamental asymmetry of relaxation-dominated error in the constituent transmons. A lower-order approximate calculation extends these predictions to the distance-5 Surface-49. These results clearly indicate error rates below the fault-tolerance threshold of the surface code, and the potential for Surface-17 to perform beyond the break-even point of quantum memory. However, Surface-49 is required to surpass the break-even point of computation at state-of-the-art qubit relaxation times and readout speeds.

  4. Relationship between anode material, supporting electrolyte and current density during electrochemical degradation of organic compounds in water

    Energy Technology Data Exchange (ETDEWEB)

    Guzmán-Duque, Fernando L. [Grupo de diagnóstico y control de la contaminación, Facultad de ingeniería, Universidad de Antioquia, A.A. 1226, Medellín (Colombia); Palma-Goyes, Ricardo E. [Grupo de Investigación en Remediación Ambiental y Biocatálisis, Instituto de Química, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquía Udea, A.A. 1226, Medellín (Colombia); González, Ignacio [Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Química, Av. San Rafael Atlixco No 186, C.P 09340, México D.F (Mexico); Peñuela, Gustavo [Grupo de diagnóstico y control de la contaminación, Facultad de ingeniería, Universidad de Antioquia, A.A. 1226, Medellín (Colombia); Torres-Palma, Ricardo A., E-mail: rtorres@matematicas.udea.edu.co [Grupo de Investigación en Remediación Ambiental y Biocatálisis, Instituto de Química, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquía Udea, A.A. 1226, Medellín (Colombia)

    2014-08-15

    Highlights: • Pathway and efficiency are linked to the current-electrode–electrolyte interaction. • Unlike BDD, IrO{sub 2} route was independent of current but dependent on the electrolyte. • IrO{sub 2}/SO{sub 4}{sup 2−} and IrO{sub 2}/Cl{sup −} routes were via IrO{sub 3} and chlorine species, respectively. • BDD/SO{sub 4}{sup 2−} and IrO{sub 2}/Cl{sup −} systems were favored at low and high currents, respectively. - Abstract: 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 (IrO{sub 2}) used as anode materials were tested with Na{sub 2}SO{sub 4} 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 i < the limiting current density (i{sub lim}), CV is mainly degraded by ·OH radicals, whereas if i > i{sub lim}, generated oxidants play a major role in the CV elimination. When IrO{sub 2} was used, CV removal was not dependent on i, but on the electrolyte. Pollutant degradation in Na{sub 2}SO{sub 4} on IrO{sub 2} seems to occur via IrO{sub 3}; however, in the presence of NaCl, degradation was dependent on the chlorinated oxidative species generated. In terms of efficiency, the Na{sub 2}SO{sub 4} electrolyte showed better results than NaCl when BDD anodes were employed. On the contrary, NaCl was superior when combined with IrO{sub 2}. Thus, the IrO{sub 2}/Cl{sup −} and BDD/SO{sub 4}{sup 2−} systems were better at removing the pollutant, being the former the most effective. On the other hand, pollutant degradation with the BDD/SO{sub 4}{sup 2−} and IrO{sub 2}/Cl{sup −} systems is favored at low and high current densities, respectively.

  5. Sedimentology and geomorphology of the deposits from the August 2006 pyroclastic density currents at Tungurahua volcano, Ecuador.

    Science.gov (United States)

    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

  6. Brain Surface Current Density Mapping in Pianists and Non-Pianists

    Science.gov (United States)

    2001-10-25

    while listening to piano pieces. Keywords - Inverse problems, Biomagnetism I. INTRODUCTION In magnetoencephalography (MEG), one of the common...Number Author(s) Project Number Task Number Work Unit Number Performing Organization Name(s) and Address(es) Biomagnetic Center Friedrich-Schiller...Haueisen, H. Nowak, and H. Brauer, “Equivalent Ellipsoid as an interpretation tool of extended current distributions in biomagnetic inverse problems,” IEEE Trans. Mag., vol. 36, pp. 1692 – 1695, 2000

  7. THE INVESTIGATION OF DENSITY CURRENTS AND RATE OF OUTFLOW FROM A SEPTIC TANK

    Directory of Open Access Journals (Sweden)

    Maciej Pawlak

    2015-09-01

    Full Text Available The aim of the study was to verify the possibility of the existence of preferential flow paths in a septic tank and the effect of using various types of inlet and outlet in this context. Two of the most unfavourable variants of favoured flow paths for different types of inlet and outlet were analysed. The first variant was related to the occurrence of the privileged flow path below the water surface level directly to the outlet and the second variant – to the so-called boiling phenomenon in a septic tank. During the study, the intensity of outflow from the septic tank was measured. The time between successive doses also was measured. These studies were carried out using several inlet and outlet structures combinations. It was observed that by introducing a suitable outlet it is possible to limit and in the case of the particular type of filtering basket – to eliminate the unwanted phenomenon of preferential flow paths after hot water introduction. The phenomenon of boiling in the septic tank may occur due to the introduction of wastewater of higher density containing a higher concentration of the suspension. The effect of cooler water introduction on this phenomenon was not observed. The limitation of the maximum intensity of outflow from the septic tank can be achieved by filtering basket using at the outlet, which increases the flow resistance thanks to the low porosity.

  8. The role of relativity in the optical response of gold within the time-dependent current-density-functional theory.

    Science.gov (United States)

    Romaniello, P; de Boeij, P L

    2005-04-22

    We included relativistic effects in the formulation of the time-dependent current-density-functional theory for the calculation of linear response properties of metals [P. Romaniello and P. L. de Boeij, Phys. Rev. B (to be published)]. We treat the dominant scalar-relativistic effects using the zeroth-order regular approximation in the ground-state density-functional theory calculations, as well as in the time-dependent response calculations. The results for the dielectric function of gold calculated in the spectral range of 0-10 eV are compared with experimental data reported in literature and recent ellipsometric measurements. As well known, relativistic effects strongly influence the color of gold. We find that the onset of interband transitions is shifted from around 3.5 eV, obtained in a nonrelativistic calculation, to around 1.9 eV when relativity is included. With the inclusion of the scalar-relativistic effects there is an overall improvement of both real and imaginary parts of the dielectric function over the nonrelativistic ones. Nevertheless some important features in the absorption spectrum are not well reproduced, but can be explained in terms of spin-orbit coupling effects. The remaining deviations are attributed to the underestimation of the interband gap (5d-6sp band gap) in the local-density approximation and to the use of the adiabatic local-density approximation in the response calculation.

  9. Water-induced charge transport in tablets of microcrystalline cellulose of varying density: dielectric spectroscopy and transient current measurements

    International Nuclear Information System (INIS)

    Nilsson, Martin; Alderborn, Goeran; Stroemme, Maria

    2003-01-01

    Room temperature dielectric frequency response data taken over 13 decades in frequency on microcrystalline cellulose (MCC) tablets of varying density are presented. The frequency response shows on three different processes: the first one is a high-frequency relaxation process whose magnitude increases and reaches a plateau as the tablet density increases. This process is associated with orientational motions of local chain segments via glycosidic bonds. The second relaxation process, related to the presence of water in the MCC matrix, is insensitive to changes in tablet density. At lower frequencies, dc-like imperfect charge transport dominates the dielectric spectrum. The dc conductivity was found to decrease with increasing tablet density and increase exponentially with increasing humidity. Transient current measurements indicated that two different ionic species, protons and OH - ions, lied behind the observed conductivity. At ambient humidity of 22%, only one in a billion of the water molecules present in the tablet matrix participated in long range dc conduction. The diffusion coefficient of the protons and OH - ions were found to be of the order of 10 -9 cm 2 /s, which is the same as for small salt building ions in MCC. This shows that ionic drugs leaving a tablet matrix may diffuse in the same manner as the constituent ions of water and, thus, elucidates the necessity to understand the water transport properties of excipient materials to be able to tailor the drug release process from pharmaceutical tablets

  10. The dependence of critical current density of GdFeCo layer on composition of thermally assisted STT-RAM

    Science.gov (United States)

    Dai, B.; Zhu, J.; Liu, K.; Yang, L.; Han, J.

    2017-07-01

    Amorphous rare earth-transitional metal (RETM) GdFeCo memory layer with RE- and TM-rich compositions was fabricated in stacks of GdFeCo (10 nm)/Cu (3 nm)/[Co(0.2 nm)/Pd(0.4 nm)]6. Their magnetic properties and spin transfer torque (STT) switching of magnetization were investigated. The maximum magneto-resistance (MR) was around 0.24% for the TM-rich Gd21.4 (Fe90Co10)78.6 memory layer and was -0.03% for the RE-rich Gd29.0 (Fe90Co10)71.0 memory layer. The critical current densities Jc to switch the GdFeCo memory layers are in the range of 1.4 × 107 A/cm2-4.5 × 107 A/cm2. The dependence of critical current density Jc and effective anisotropy constant Keff on Gd composition were also investigated. Both Jc and Keff have maximum values in the Gd composition range from 21-29 at.%, suitable for thermally assisted STT-RAM for storage density exceeding Gb/inch2.

  11. Ni/YSZ electrode degradation studied by impedance spectroscopy: Effects of gas cleaning and current density

    DEFF Research Database (Denmark)

    Hauch, Anne; Mogensen, Mogens Bjerg

    2010-01-01

    on the anode degradation, tests were set-up both with and without gas cleaning. Gas cleaning was done by passing the H2 over porous nickel at room temperature. It was found that cleaning of the inlet H2 gas more than halved the anode degradation under current load. For tests at OCV the increase in the Ni...... at OCV prior to fuel cell testing provided fuel cell tests with minimal/negligible anode degradation compared to tests where fuel cell testing was started immediately after initial characterization of the cells....

  12. Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

    Science.gov (United States)

    Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.

    2017-11-01

    The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.

  13. Current density and polarization curves for radial flow field patterns applied to PEMFCs (Proton Exchange Membrane Fuel Cells)

    International Nuclear Information System (INIS)

    Cano-Andrade, S.; Hernandez-Guerrero, A.; Spakovsky, M.R. von; Damian-Ascencio, C.E.; Rubio-Arana, J.C.

    2010-01-01

    A numerical solution of the current density and velocity fields of a 3-D PEM radial configuration fuel cell is presented. The energy, momentum and electrochemical equations are solved using a computational fluid dynamics (CFD) code based on a finite volume scheme. There are three cases of principal interest for this radial model: four channels, eight channels and twelve channels placed in a symmetrical path over the flow field plate. The figures for the current-voltage curves for the three models proposed are presented, and the main factors that affect the behavior of each of the curves are discussed. Velocity contours are presented for the three different models, showing how the fuel cell behavior is affected by the velocity variations in the radial configuration. All these results are presented for the case of high relative humidity. The favorable results obtained for this unconventional geometry seems to indicate that this geometry could replace the conventional commercial geometries currently in use.

  14. Metallic amorphous electrodeposited molybdenum coating from aqueous electrolyte: Structural, electrical and morphological properties under current density

    Energy Technology Data Exchange (ETDEWEB)

    Nemla, Fatima [LEPCM, Department of Physics, University of Batna (Algeria); Cherrad, Djellal, E-mail: cherradphisic@yahoo.fr [Laboratory for Developing New Materials and Their Characterizations, University of Setif (Algeria)

    2016-07-01

    Graphical abstract: - Highlights: • Although difficulties related to electrodeposition of Mo films, we have successfully coated onto a cooper substrate. • A good formation of bcc Mo phase and lattice parameter was very accurate. • It seems that electrical properties of our samples are good and suitable as back contact for thin film solar cells. • It seems that grain size, microstrain and dislocation density are all managed and correlated to retain the resistivity to a considerable minimum value. - Abstract: Molybdenum coatings are extensively utilized as back contact for CIGS-based solar cells. However, their electrodeposition from aqueous electrolyte still sophisticates, since long time, owing to the high reactivity with oxygen. In this study, we present a successful 30 min electrodeposition experiment of somewhat thick (∼0.98–2.9 μm) and of moderate surface roughness RMS (∼47–58 nm), metallic bright Mo coating from aqueous electrolyte containing molybdate ions. XRD analysis and Hall Effect measurements have been used to confirm the presence of Mo. The crystal structure of deposits was slightly amorphous in nature to body centred cubic structure (bcc) Mo (110), (211) and (220) face. Lattice parameters exhibit some weak fluctuated tensile stress when compared to the reference lattice parameter. Additionally, our calculated lattice parameters are in good agreement with some previous works from literature. Discussions on the grain growth prove that they are constrained by grain boundary energy not the thickness effect. Further discussions were made on the electrical resistivity and surface morphology. Resonance scattering of Fermi electrons are expected to contribute towards the variation in the film resistivity through the carrier mobility limitation. However, studied samples might be qualified as candidates for solar cell application.

  15. Alternating steady state free precession for estimation of current-induced magnetic flux density: A feasibility study.

    Science.gov (United States)

    Lee, Hyunyeol; Jeong, Woo Chul; Kim, Hyung Joong; Woo, Eung Je; Park, Jaeseok

    2016-05-01

    To develop a novel, current-controlled alternating steady-state free precession (SSFP)-based conductivity imaging method and corresponding MR signal models to estimate current-induced magnetic flux density (Bz ) and conductivity distribution. In the proposed method, an SSFP pulse sequence, which is in sync with alternating current pulses, produces dual oscillating steady states while yielding nonlinear relation between signal phase and Bz . A ratiometric signal model between the states was analytically derived using the Bloch equation, wherein Bz was estimated by solving a nonlinear inverse problem for conductivity estimation. A theoretical analysis on the signal-to-noise ratio of Bz was given. Numerical and experimental studies were performed using SSFP-FID and SSFP-ECHO with current pulses positioned either before or after signal encoding to investigate the feasibility of the proposed method in conductivity estimation. Given all SSFP variants herein, SSFP-FID with alternating current pulses applied before signal encoding exhibits the highest Bz signal-to-noise ratio and conductivity contrast. Additionally, compared with conventional conductivity imaging, the proposed method benefits from rapid SSFP acquisition without apparent loss of conductivity contrast. We successfully demonstrated the feasibility of the proposed method in estimating current-induced Bz and conductivity distribution. It can be a promising, rapid imaging strategy for quantitative conductivity imaging. © 2015 Wiley Periodicals, Inc.

  16. A process study of the interaction of tidal currents, tidal mixing and density gradients in a region of freshwater influence

    Science.gov (United States)

    Xing, Jiuxing; Chen, Shengli

    2017-08-01

    A three dimensional unstructured grid model of the west coast of Britain is used to study the process of the interaction of tidal currents, tidal mixing and density gradient in the Liverpool Bay region. Calculations with M2 tidal forcing and omitting freshwater discharge show that tidal currents in the region are strong (of order 1 ms- 1), with tidal current ellipses essentially rectilinear in the surface and bottom. In the absence of tidal forcing, the freshwater is confined to a thin surface layer. With the inclusion of tidal mixing the surface layer thickens, and in the shallow water area mixed layer occupies the whole water depth. This has a significant effect of reducing its lateral spread. A detailed study of time series of velocity, salinity and turbulence reveals that at flood tide, more saline water is advected into the coastal region and rapid vertical mixing occurs, whereas at ebb tide, fresher water is advected over more saline water. The induced strong pycnocline uncouples surface and bottom layers leading to more circular tidal ellipses which rotate in opposite directions in the vertical, as found in observations. The three dimensional nature of the model reveals that this process involves both horizontal and vertical density gradients, and shows significant horizontal variability in the Liverpool Bay region.

  17. Intracranial current density (LORETA) differences in QEEG frequency bands between depressed and non-depressed alcoholic patients.

    Science.gov (United States)

    Coutin-Churchman, Pedro; Moreno, Rocío

    2008-04-01

    To assess possible differences in intracranial source distribution of surface QEEG power between depressed and non-depressed alcoholic patients in order to find any symptom-related topographic features of physiopathologic relevance. Low-Resolution Electromagnetic Tomography (LORETA) for the delta, theta, alpha and beta bands of EEG spectra was estimated from 38 alcoholic patients, 20 with and 18 without clinical depression, in which QEEG showed decreased slow and increased beta activity diffusely. Statistical non-parametric mapping was used to compare depressed and non-depressed groups. Measures of intracranial current density in individual patients at areas of significant differences were correlated with BDI scores. Patients with clinical depression showed areas of significantly lower current density than non-depressed patients in delta band at left anterior temporal, left midtemporal (including amygdala and hippocampus), and both frontopolar cortices mostly on the right; and in theta band at bilateral parietal lobe, anterior cingulate and medial frontal cortex. No differences were found at alpha and beta band. Intracranial current density in delta band at left parahippocampal, left midfrontal cortex and right frontopolar cortex was negatively correlated with BDI score. Theta band also showed negative correlations with BDI at sites of significant differences. Diffusely decreased delta and theta activity in the surface QEEG of alcoholic patients has a different intracranial distribution linked to the presence or not of clinical depression that seems to reveal a dysfunctional neuronal state at several specific limbic and other cortical locations that have been related to a specific clinical disorder such as depression. These results provided further evidence on the effects of depression in the context of alcohol dependence, in this case decreased slow activity as a possible marker of neuronal damage secondary to alcohol toxicity, clinically expressed as depressive

  18. Quench Analysis of High Current Density Nb3Sn Conductors in Racetrack Coil Configuration

    CERN Document Server

    Bajas, H; Bordini, B; Bottura, L; Izquierdo Bermudez, S; Feuvrier, J; Chiuchiolo, A; Perez, J C; Willering, G

    2015-01-01

    The luminosity upgrade of the Large Hadron Collider (HL-LHC) requires the development of new type of superconducting cables based on advanced Nb3Sn strands. In the framework of the FP7 European project EUCARD the cables foreseen for the HL-LHC project have been tested recently in a simplified racetrack coil configuration, the so-called Short Model Coil (SMC). In 2013 to 2014, two SMCs wound with 40-strand (RRP 108/127) cables, with different heat treatment processes, reached during training at 1.9 K a current and peak magnetic field of 15.9 kA, 13.9T,and 14.3 kA, 12.7 Trespectively. Using the measured signals from the voltage taps, the behavior of the quenches is analyzed in terms of transverse and longitudinal propagation velocity and hot spot temperature. These measurements are compared with both analytical and numerical calculations from adiabatic models.The coherence of the results from the presented independent methods helps in estimating the relevance of the material properties and the adiabatic assump...

  19. Visualizing the mechanism that determines the critical current density in polycrystalline superconductors using time-dependent Ginzburg-Landau theory

    Science.gov (United States)

    Carty, George J.; Hampshire, Damian P.

    2008-05-01

    In polycrystalline superconducting materials optimized for high critical current density (JC) in high magnetic fields, the mechanism that determines JC has long remained uncertain because of the complicated manner in which the fluxon-fluxon and fluxon-microstructure forces combine. In this work, the time-dependent Ginzburg-Landau equations are used to produce visualizations of fluxons at JC that show the disorder in the pinned part of the flux-line lattice and the motion of those fluxons along grain boundaries that cause dissipation. Calculated values of JC are consistent with experimental data.

  20. Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in polymer solar cells

    Energy Technology Data Exchange (ETDEWEB)

    He, Zhicai; Zhong, Chengmei; Wu, Hongbin; Su, Shijian; Cao, Yong [Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China); Huang, Xun; Chen, Liwei [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou Industrial Park, Suzhou 215123 (China); Wong, Wai-Yeung [Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee, Hong Kong) and Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Hong Kong (China)

    2011-10-25

    Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in highly efficient polymer solar cells by incorporating an alcohol/water-soluble conjugated polymer as cathode interlayer is domonstrated. When combined with a low-bandgap polymer PTB7 as the electron donor material, the power efficiency of the devices is improved to certified 8.370%. Due to drastic improvement in efficiency and easy utilization, this method opens new opportunities for PSCs from various material systems to improve towards 10% efficiency. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Fermion condensate and vacuum current density induced by homogeneous and inhomogeneous magnetic fields in (2+1) dimensions

    International Nuclear Information System (INIS)

    Raya, Alfredo; Reyes, Edward

    2010-01-01

    We calculate the condensate and the vacuum current density induced by external static magnetic fields in (2+1) dimensions. At the perturbative level, we consider an exponentially decaying magnetic field along one Cartesian coordinate. Nonperturbatively, we obtain the fermion propagator in the presence of a uniform magnetic field by solving the Schwinger-Dyson equation in the rainbow-ladder approximation. In the large flux limit, we observe that both these quantities, either perturbative (inhomogeneous) and nonperturbative (homogeneous), are proportional to the external field, in agreement with early expectations.

  2. Measurements of Pfirsch-Schlueter current and pressure profile for the high density ECH plasmas in Heliotron DR

    International Nuclear Information System (INIS)

    Morimoto, S.; Yanagi, N.; Nakasuga, M.; Obiki, T.; Iiyoshi, A.; Uo, K.

    1988-01-01

    The Pfirsch-Schlueter current and pressure profiles are estimated from magnetic measurements for high density electron cyclotron heating (ECH) plasmas (n-bar e =(2-3)x10 13 cm -3 , T e0 =200-400 eV, (β) 0 (1-(r/a) 2 ) s , is about two in macroscopically stable plasmas. A fast loss of plasma energy from the centre to the periphery is observed during the onset of the MHD instability. This method of measuring the pressure profile shape is simple and useful for heliotron type devices. (author). 20 refs, 8 figs, 1 tab

  3. Enhancement of short-circuit current density in polymer bulk heterojunction solar cells comprising plasmonic silver nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Yuzhao; Lin, Xiaofeng; Ou, Jiemei; Chen, Xudong, E-mail: cescxd@mail.sysu.edu.cn, E-mail: stszx@mail.sysu.edu.cn, E-mail: chenyj69@mail.sysu.edu.cn [Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education of China, Sun Yat-sen University, Guangzhou 510275 (China); Qing, Jian; Zhong, Zhenfeng; Zhou, Xiang, E-mail: cescxd@mail.sysu.edu.cn, E-mail: stszx@mail.sysu.edu.cn, E-mail: chenyj69@mail.sysu.edu.cn; Chen, Yujie, E-mail: cescxd@mail.sysu.edu.cn, E-mail: stszx@mail.sysu.edu.cn, E-mail: chenyj69@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Hu, Chenglong [Key Laboratory of Optoelectronic Chemical Materials and Devices of Ministry of Education, Jianghan University, Wuhan 430056 (China)

    2014-03-24

    We demonstrate that the influence of plasmonic effects based on silver nanowires (Ag NWs) on the characteristics of polymer solar cells (PSCs). The solution-processed Ag NWs are situated at the interface of anode buffer layer and active layer, which could enhance the performance especially the photocurrent of PSCs by scattering, localized surface plasmon resonance, and surface plasmon polaritons. Plasmonic effects are confirmed by the enhancement of extinction spectra, external quantum efficiency, and steady state photoluminescence. Consequently, the short-circuit current density (J{sub sc}) and power conversion efficiency enhance about 24% and 18%, respectively, under AM1.5 illumination when Ag NWs plasmonic nanostructure incorporated into PSCs.

  4. Co-current Doping Effect of Nanoscale Carbon and Aluminum Nitride on Critical Current Density and Flux Pinning Properties of Bulk MgB2 Superconductors

    Science.gov (United States)

    Tripathi, D.; Dey, T. K.

    2018-01-01

    The effect of nanoscale aluminum nitride (n-AlN) and carbon (n-C) co-doping on superconducting properties of polycrystalline bulk MgB2 superconductor has been investigated. Polycrystalline pellets of MgB2 , MgB2 + 0.5 wt% AlN (nano), MgB_{1.99}C_{0.01} and MgB_{1.99}C_{0.01} + 0.5 wt% AlN (nano) have been synthesized by a solid reaction process under inert atmosphere. The transition temperature (TC) estimated from resistivity measurement indicates only a small decrease for C (nano) and co-doped MgB2 samples. The magnetic field response of investigated samples has been measured at 4, 10, and 20 K in the field range ± 6 T. MgB2 pellets co-doped with 0.5 wt% n-AlN and 1 wt% n-C display appreciable enhancement in critical current density (J_C ) of MgB2 in both low (≥ 3 times), as well as, high-field region (≥ 15 times). J_C versus H behavior of both pristine and doped MgB2 pellets is well explained in the light of the collective pinning model. Further, the normalized pinning force density f_p(= F_p/F_{pmax}) displays a fair correspondence with the scaling procedure proposed by Eisterer et al. Moreover, the scaled data of the pinning force density (i.e., f_p{-}h data) of the investigated pellets at different temperature are well interpreted by a modified Dew-Hughes expression reported by Sandu and Chee.

  5. Suppression of external quantum efficiency roll-off of nanopatterned organic-light emitting diodes at high current densities

    Energy Technology Data Exchange (ETDEWEB)

    Kuwae, Hiroyuki; Kasahara, Takashi [Nano-Science and Nano-Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan); JST, ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Nitta, Atsushi; Yoshida, Kou; Inoue, Munetomo [Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Matsushima, Toshinori; Adachi, Chihaya, E-mail: adachi@cstf.kyushu-u.ac.jp [JST, ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Shoji, Shuichi [Nano-Science and Nano-Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan); Mizuno, Jun [JST, ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Research Organization for Nano and Life Innovation, Waseda University, 513 Waseda Tsurumaki-cho, Shinjuku, Tokyo 162-0041 (Japan)

    2015-10-21

    We developed organic light-emitting diodes (OLEDs) with nanopatterned current flow regions using electron-beam lithography with the aim of suppressing singlet–polaron annihilation (SPA). Nanopatterns composed of lines and circles were used in the current flow regions of nano-line and nano-dot OLEDs, respectively. Excitons partially escape from the current flow regions where SPA takes place. As such, current densities where external quantum efficiencies were half of their initial values (J{sub 0}) increased as line width and circle diameter were decreased to close to the exciton diffusion length. Circles were more efficient at enhancing exciton escape and increasing J{sub 0} than lines. The J{sub 0} increase in the nano-dot OLEDs containing nanopatterned circles with a diameter of 50 nm was approximately 41-fold that of a conventional OLED with a current flow region of 4 mm{sup 2}. The dependence of J{sub 0} on the size and shape of the nanopatterns was well explained by an SPA model that considered exciton diffusion. Nanopatterning of OLEDs is a feasible method of obtaining large J{sub 0}.

  6. V-I curves and plasma parameters in a high density DC glow discharge generated by a current-source

    International Nuclear Information System (INIS)

    Granda-Gutierrez, E E; Lopez-Callejas, R; Piedad-Beneitez, A de la; BenItez-Read, J S; Pacheco-Sotelo, J O; Pena-Eguiluz, R; A, R Valencia; Mercado-Cabrera, A; Barocio, S R

    2008-01-01

    Nitrogen DC glow discharges, conducted in a cylindrical geometry, have been characterized using a new current-source able to provide 10 -3 - 3 A for the sustainment of the discharge, instead of a conventional voltage-source. The V-I characteristic curves obtained from these discharges were found to fit the general form i(v) = A(p)v k(p) , whereby the plasma itself can be modeled as a voltage-controlled current-source. We conclude that the fitting parameters A and k, which mainly depend on the gas pressure p, are strongly related to the plasma characteristics, so much so that they can indicate the pressure interval in which the maximum plasma density is located, with values in the order of 10 16 m -3 at reduced discharge potential (300-600 V) and low working pressure (10 -1 - 10 1 Pa)

  7. Topographic controls on pyroclastic density current dynamics: Insight from 18 May 1980 deposits at Mount St. Helens, Washington (USA)

    Science.gov (United States)

    Brand, Brittany D.; Bendaña, Sylvana; Self, Stephen; Pollock, Nicholas

    2016-07-01

    Our ability to interpret the deposits of pyroclastic density currents (PDCs) is critical for understanding the transport and depositional processes that control PDC dynamics. This paper focuses on the influence of slope on flow dynamics and criticality as recorded in PDC deposits from the 18 May 1980 eruption of Mt. St. Helens (USA). PDC deposits are found along the steep flanks (10°-30°) and across the pumice plain ( 5°) up to 8 km north of the volcano. Granulometry, componentry and descriptions of depositional characteristics (e.g., bedform morphology) are recorded with distance from source. The pumice plain deposits are primarily thick (3-12 m), massive and poorly-sorted, and represent deposition from a series of concentrated PDCs. By contrast, the steep flank deposits are stratified to cross-stratified, suggesting deposition from PDCs where turbulence strongly influenced transport and depositional processes. We propose that acceleration of the concentrated PDCs along the steep flanks resulted in thinning of the concentrated, basal region of the current(s). Enhanced entrainment of ambient air, and autofluidization from upward fluxes of air from substrate interstices and plunging breakers across rugged, irregular topography further inflated the currents to the point that the overriding turbulent region strongly influenced transport and depositional mechanisms. Acceleration in combination with partial confinement in slot canyons and high surface roughness would also increase basal shear stress, further promoting shear and traction transport in the basal region of the current. Conditions along the steep flank resulted in supercritical flow, as recorded by regressive bedforms, which gradually transitioned to subcritical flow downstream as the concentrated basal region thickness increased as a function of decreasing slope and flow energy. We also find that (1) PDCs were erosive into the underlying granular substrate along high slopes (> 25°) where currents were

  8. A high critical current density MOCVD coated conductor with strong vortex pinning centers suitable for very high field use

    International Nuclear Information System (INIS)

    Chen, Z; Kametani, F; Larbalestier, D C; Chen, Y; Xie, Y; Selvamanickam, V

    2009-01-01

    We have made extensive low temperature and high field evaluations of a recent 2.1 μm thick coated conductor (CC) grown by metal-organic chemical vapor deposition (MOCVD) with a view to its use for high field magnet applications, for which its very strong Hastelloy substrate makes it very suitable. This conductor contains dense three-dimensional (Y,Sm) 2 O 3 nanoprecipitates, which are self-aligned in planes tilted ∼7 deg. from the tape plane. Very strong vortex pinning is evidenced by high critical current density J c values of ∼3.1 MA cm -2 at 77 K and ∼43 MA cm -2 at 4.2 K, and by a strongly enhanced irreversibility field H irr , which reaches that of Nb 3 Sn (∼28 T at 1.5 K) at 60 K, even in the inferior direction of H parallel c axis. At 4.2 K, J c values are ∼15% of the depairing current density J d , much the highest of any superconductor suitable for magnet construction.

  9. A high critical current density MOCVD coated conductor with strong vortex pinning centers suitable for very high field use

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Z; Kametani, F; Larbalestier, D C [National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310 (United States); Chen, Y; Xie, Y; Selvamanickam, V [SuperPower Incorporated, Schenectady, NY 12304 (United States)], E-mail: zhijun@asc.magnet.fsu.edu

    2009-05-15

    We have made extensive low temperature and high field evaluations of a recent 2.1 {mu}m thick coated conductor (CC) grown by metal-organic chemical vapor deposition (MOCVD) with a view to its use for high field magnet applications, for which its very strong Hastelloy substrate makes it very suitable. This conductor contains dense three-dimensional (Y,Sm){sub 2}O{sub 3} nanoprecipitates, which are self-aligned in planes tilted {approx}7 deg. from the tape plane. Very strong vortex pinning is evidenced by high critical current density J{sub c} values of {approx}3.1 MA cm{sup -2} at 77 K and {approx}43 MA cm{sup -2} at 4.2 K, and by a strongly enhanced irreversibility field H{sub irr}, which reaches that of Nb{sub 3}Sn ({approx}28 T at 1.5 K) at 60 K, even in the inferior direction of H parallel c axis. At 4.2 K, J{sub c} values are {approx}15% of the depairing current density J{sub d}, much the highest of any superconductor suitable for magnet construction.

  10. Microstructural analysis of mass transport phenomena in gas diffusion media for high current density operation in PEM fuel cells

    Science.gov (United States)

    Kotaka, Toshikazu; Tabuchi, Yuichiro; Mukherjee, Partha P.

    2015-04-01

    Cost reduction is a key issue for commercialization of fuel cell electric vehicles (FCEV). High current density operation is a solution pathway. In order to realize high current density operation, it is necessary to reduce mass transport resistance in the gas diffusion media commonly consisted of gas diffusion layer (GDL) and micro porous layer (MPL). However, fundamental understanding of the underlying mass transport phenomena in the porous components is not only critical but also not fully understood yet due to the inherent microstructural complexity. In this study, a comprehensive analysis of electron and oxygen transport in the GDL and MPL is conducted experimentally and numerically with three-dimensional (3D) microstructural data to reveal the structure-transport relationship. The results reveal that the mass transport in the GDL is strongly dependent on the local microstructural variations, such as local pore/solid volume fractions and connectivity. However, especially in the case of the electrical conductivity of MPL, the contact resistance between carbon particles is the dominant factor. This suggests that reducing the contact resistance between carbon particles and/or the number of contact points along the transport pathway can improve the electrical conductivity of MPL.

  11. Magnetic properties and critical current density of bulk MgB2 polycrystalline with Bi-2212 addition

    International Nuclear Information System (INIS)

    Shen, T M; Li, G; Zhu, X T; Cheng, C H; Zhao, Y

    2005-01-01

    Bulk samples of MgB 2 were prepared with 0, 3, 5, and 10 wt% Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) particles, added using a simple solid-state reaction route in order to investigate the effect of inclusions of a material with higher T c than the superconducting matrix. The density, diamagnetic signal, and critical current density, J c , of the samples change significantly with the doping level. It is found that J c is significantly enhanced by the Bi-2212 addition. Microstructural analysis indicates that a small amount of Bi-2212 is decomposed into Cu 2 O and other impurity phases while a significant amount of unreacted Bi-2212 particles remains in MgB 2 matrix, and these act as effective pinning centres for vortices. The enhanced pinning force is mainly attributable to these highly dispersed inclusions inserted in the MgB 2 grains. Despite the effectiveness of the high-T c inclusions in increasing superconducting critical currents in our experiment, our results seem to demonstrate the superiority of attractive centres over repulsive ones. A pinning mechanism is proposed to account for the contribution of this type of pinning centre in MgB 2 superconductors. (rapid communication)

  12. Study on lower hybrid current drive efficiency at high density towards long-pulse regimes in Experimental Advanced Superconducting Tokamak

    International Nuclear Information System (INIS)

    Li, M. H.; Ding, B. J.; Zhang, J. Z.; Gan, K. F.; Wang, H. Q.; Zhang, L.; Wei, W.; Li, Y. C.; Wu, Z. G.; Ma, W. D.; Jia, H.; Chen, M.; Yang, Y.; Feng, J. Q.; Wang, M.; Xu, H. D.; Shan, J. F.; Liu, F. K.; Peysson, Y.

    2014-01-01

    Significant progress on both L- and H-mode long-pulse discharges has been made recently in Experimental Advanced Superconducting Tokamak (EAST) with lower hybrid current drive (LHCD) [J. Li et al., Nature Phys. 9, 817 (2013) And B. N. Wan et al., Nucl. Fusion 53, 104006 (2013).]. In this paper, LHCD experiments at high density in L-mode plasmas have been investigated in order to explore possible methods of improving current drive (CD) efficiency, thus to extend the operational space in long-pulse and high performance plasma regime. It is observed that the normalized bremsstrahlung emission falls much more steeply than 1/n e-av (line-averaged density) above n e-av  = 2.2 × 10 19  m −3 indicating anomalous loss of CD efficiency. A large broadening of the operating line frequency (f = 2.45 GHz), measured by a radio frequency (RF) probe located outside the EAST vacuum vessel, is generally observed during high density cases, which is found to be one of the physical mechanisms resulting in the unfavorable CD efficiency. Collisional absorption of lower hybrid wave in the scrape off layer (SOL) may be another cause, but this assertion needs more experimental evidence and numerical analysis. It is found that plasmas with strong lithiation can improve CD efficiency largely, which should be benefited from the changes of edge parameters. In addition, several possible methods are proposed to recover good efficiency in future experiments for EAST

  13. Current source density of sustained potential shifts associated with electrographic seizures and with spreading depression in rat hippocampus.

    Science.gov (United States)

    Wadman, W J; Juta, A J; Kamphuis, W; Somjen, G G

    1992-01-20

    The membrane currents responsible for the sustained potential shifts associated with electrographic seizures and with spreading depression in hippocampus were studied in the anesthetized rat. Probes incorporating 16 sensors in a straight line, spaced at 150-microns distances, were recording the potential changes with DC-coupled amplifiers in CA1 and dentate gyrus (DG) of one hemisphere. Seizures and spreading depression were provoked by repetitive stimulation of different afferent pathways. Seizures always began in DG before CA1, regardless of the pathway stimulated. Tonic seizures were associated with a sustained negative potential shift that was largest in the cell body layers. Current source density was computed from these recordings and confirmed the presence of a current sink limited to the cell body layer throughout the duration of electrographic seizures. Spreading depression was associated with a very large sink located in the layer of apical dendrites, maximal among the proximal segment of dendrites, to which the cell body layer served as a source. We conclude that seizures are associated with an inward current in neuron cell bodies, probably flowing through membrane channels of as yet no know physiological function.

  14. Microelectrode array analysis of hippocampal network dynamics following theta-burst stimulation via current source density reconstruction by Gaussian interpolation.

    Science.gov (United States)

    Kim, Hyun-Bum; Oh, Tong-In; Swanberg, Kelley M; Lee, Mun-Bae; Kim, Tae-Woo; Woo, Eung-Je; Park, Ji-Ho; Kwon, Oh-In

    2016-05-01

    Multielectrode arrays (MEAs) have been used to understand electrophysiological network dynamics by recording real-time activity in groups of cells. The extent to which the collection of such data enables hypothesis testing on the level of circuits and networks depends largely on the sophistication of the analyses applied. We studied the systemic temporal variations of endogenous signaling within an organotypic hippocampal network following theta-burst stimulation (TBS) to the Schaffer collateral-commissural pathways. The recovered current source density (CSD) information from the raw grid of extracellular potentials by using a Gaussian interpolation method increases spatial resolution and avoids border artifacts by numerical differentials. We compared total sink and source currents in DG, CA3, and CA1; calculated accumulated correlation coefficients to compare pre- with post-stimulation CSD dynamics in each region; and reconstructed functional connectivity maps for regional cross-correlations with respect to temporal CSD variations. The functional connectivity maps for potential correlations pre- and post-TBS were compared to investigate the neural network as a whole, revealing differences post-TBS. Previous MEA work on plasticity in hippocampal evoked potentials has focused on synchronicity across the hippocampus within isolated subregions. Such analyses ignore the complex relationships among diverse components of the hippocampal circuitry, thus failing to capture network-level behaviors integral to understanding hippocampal function. The proposed method of recovering current source density to examine whole-hippocampal function is sensitive to experimental manipulation and is worth further examination in the context of network-level analyses of neural signaling. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. The ground layer of the Campanian Ignimbrite: an example of deposition from a dilute pyroclastic density current

    Science.gov (United States)

    Scarpati, Claudio; Sparice, Domenico; Perrotta, Annamaria

    2015-11-01

    A thin, fines-poor, and lithic- and crystal-rich layer locally present, from proximal to distal areas, at the base of the pyroclastic density current deposits of the Campanian Ignimbrite eruption (39 ka), sourced from Campi Flegrei (Italy), is interpreted as a ground layer (GL). It has an average lithic and crystal content of 57 and 25 wt%, respectively. The GL rests on a paleosol or an early fall deposit and is capped by a stratified ash deposit. It is bounded by erosion surfaces and its thickness does not change systematically from the source. The occurrences of GL in places separated from the source by a stretch of sea and the angular to sub-angular shape of the lithic clasts are consistent with deposition from a dilute current. The presence of the GL up to 971 m above sea level and beyond 1400-1500-m-high mountain ridges, allows estimation of the thickness of the PDC as having been at least 1.5 km. To investigate the parameters influencing the transport and emplacement mechanisms that produced the GL, we use field and sedimentological data (grain size and componentry), from samples collected between 30 and 70 km from the source. The progressive decrease in maximum lithic clast and median grain-size with distance from the vent and increasing altitude corresponds to lateral and vertical grading of lithic clasts within the current. The coarser clasts moved toward the basal part of the current, settling in more proximal areas and at low altitude. Farther from the vent (45-50 km), the lower part of the pyroclastic current impacted against the reliefs surrounding the Campanian Plain, causing the emplacement of coarser and more poorly sorted deposits on slopes oriented toward the source.

  16. Generator localization by current source density (CSD): Implications of volume conduction and field closure at intracranial and scalp resolutions

    Science.gov (United States)

    Tenke, Craig E.; Kayser, Jürgen

    2012-01-01

    The topographic ambiguity and reference-dependency that has plagued EEG/ERP research throughout its history are largely attributable to volume conduction, which may be concisely described by a vector form of Ohm’s Law. This biophysical relationship is common to popular algorithms that infer neuronal generators via inverse solutions. It may be further simplified as Poisson’s source equation, which identifies underlying current generators from estimates of the second spatial derivative of the field potential (Laplacian transformation). Intracranial current source density (CSD) studies have dissected the “cortical dipole” into intracortical sources and sinks, corresponding to physiologically-meaningful patterns of neuronal activity at a sublaminar resolution, much of which is locally cancelled (i.e., closed field). By virtue of the macroscopic scale of the scalp-recorded EEG, a surface Laplacian reflects the radial projections of these underlying currents, representing a unique, unambiguous measure of neuronal activity at scalp. Although the surface Laplacian requires minimal assumptions compared to complex, model-sensitive inverses, the resulting waveform topographies faithfully summarize and simplify essential constraints that must be placed on putative generators of a scalp potential topography, even if they arise from deep or partially-closed fields. CSD methods thereby provide a global empirical and biophysical context for generator localization, spanning scales from intracortical to scalp recordings. PMID:22796039

  17. Influence of thermal, morphological and measuring variables on the thermal runaway of superconducting films under high current densities

    International Nuclear Information System (INIS)

    Ferro, G; Maza, J; Ramallo, M V; Veira, J A; Vidal, F

    2009-01-01

    We study the abrupt jump in voltage seen in the current-voltage characteristics of high-T c films at current densities, J*, around 2-3 times the critical one, and for perturbations with characteristic times in the millisecond range. Customarily, even for these long characteristic times, the voltage jump has been ascribed to an electrodynamic vortex instability. Recent results based on finite-element analyses show quantitatively that smooth, i.e., jumpfree isothermal curves may show up themselves as the jumping, i.e., discontinuous curves experimentalists observe, once the nonlinearity, thermal feedback and measurement rate are properly accounted for. The thermal nature of the transition to a highly dissipative state in high-T c superconductors at zero magnetic field makes the control of the instability transition easier in that there are more parameters available to experimentalists that may be tuned to tailor the phenomenon. This is specially relevant for devices working on their superconducting borderline as current-limiters or even magnets. Here we explore through finite-element analysis the role of film geometry, measurement rate and substrate thermal conductivity in the triggering of the thermal runaway.

  18. Bone density loss on computed tomography at 3-year follow-up in current compared to former male smokers

    International Nuclear Information System (INIS)

    Pompe, E.; Bartstra, J.; Verhaar, H.J.; Koning, H.J. de; Aalst, C.M. van der; Oudkerk, M.; Vliegenthart, R.; Lammers, J.-W.J.; Jong, P.A. de; Mohamed Hoesein, F.A.A.

    2017-01-01

    Objectives: Cigarette smoking negatively affects bone quality and increases fracture risk. Little is known on the effect of smoking cessation and computed tomography (CT)-derived bone mineral density (BMD) decline in the spine. We evaluated the association of current and former smoking with BMD decline after 3-year follow-up. Methods: Male current and former smokers participating in a lung cancer screening trial who underwent baseline and 3-year follow-up CT were included. BMD was measured by manual placement of a region of interest in the first lumbar vertebra and expressed in Hounsfield Unit (HU). Multiple linear regression analysis was used to evaluate the association between pack years smoked and smoking status with BMD decline. Results: 408 participants were included with median (25th–75th percentile) age of 59.4 (55.9–63.5) years. At the start of the study, 197 (48.3%) participants were current smokers and 211 (51.7%) were former smokers and had a similar amount of pack years. Current smokers had quit smoking for 6 (4–8) years prior to inclusion. There was no difference in BMD between current and former smokers at baseline (109 ± 34 HU vs. 108 ± 32 HU, p = 0.96). At 3-year follow-up, current smokers had a mean BMD decline of −3 ± 13 HU (p = 0.001), while BMD in former smokers did not change as compared to baseline (1 ± 13 HU, p = 0.34). After adjustment for BMD at baseline and body mass index, current smoking was independently associated with BMD decline (−3.8 HU, p = 0.003). Age, pack years, and the presence of a fracture at baseline did not associate with BMD decline. Conclusions: Current smokers showed a more rapid BMD decline over a 3-year period compared to former smokers. This information might be important to identify subjects at risk for osteoporosis and emphasizes the importance of smoking cessation in light of BMD decline.

  19. Bone density loss on computed tomography at 3-year follow-up in current compared to former male smokers

    Energy Technology Data Exchange (ETDEWEB)

    Pompe, E., E-mail: e.pompe@umcutrecht.nl [Department of Pulmonology, University Medical Center Utrecht, Utrecht (Netherlands); Bartstra, J. [Department of Radiology, University Medical Center Utrecht, Utrecht (Netherlands); Verhaar, H.J. [Department of Geriatric Medicine, University Medical Center Utrecht, Utrecht (Netherlands); Koning, H.J. de; Aalst, C.M. van der [Department of Public Health, Erasmus MC − University Medical Center Rotterdam, Rotterdam (Netherlands); Oudkerk, M. [University of Groningen, University Medical Center Groningen, Groningen, Department of Radiology (Netherlands); Vliegenthart, R. [University of Groningen, University Medical Center Groningen, Groningen, Department of Radiology (Netherlands); University of Groningen, University Medical Center Groningen, Center for Medical Imaging-North East Netherlands, Groningen (Netherlands); Lammers, J.-W.J. [Department of Pulmonology, University Medical Center Utrecht, Utrecht (Netherlands); Jong, P.A. de; Mohamed Hoesein, F.A.A. [Department of Radiology, University Medical Center Utrecht, Utrecht (Netherlands)

    2017-04-15

    Objectives: Cigarette smoking negatively affects bone quality and increases fracture risk. Little is known on the effect of smoking cessation and computed tomography (CT)-derived bone mineral density (BMD) decline in the spine. We evaluated the association of current and former smoking with BMD decline after 3-year follow-up. Methods: Male current and former smokers participating in a lung cancer screening trial who underwent baseline and 3-year follow-up CT were included. BMD was measured by manual placement of a region of interest in the first lumbar vertebra and expressed in Hounsfield Unit (HU). Multiple linear regression analysis was used to evaluate the association between pack years smoked and smoking status with BMD decline. Results: 408 participants were included with median (25th–75th percentile) age of 59.4 (55.9–63.5) years. At the start of the study, 197 (48.3%) participants were current smokers and 211 (51.7%) were former smokers and had a similar amount of pack years. Current smokers had quit smoking for 6 (4–8) years prior to inclusion. There was no difference in BMD between current and former smokers at baseline (109 ± 34 HU vs. 108 ± 32 HU, p = 0.96). At 3-year follow-up, current smokers had a mean BMD decline of −3 ± 13 HU (p = 0.001), while BMD in former smokers did not change as compared to baseline (1 ± 13 HU, p = 0.34). After adjustment for BMD at baseline and body mass index, current smoking was independently associated with BMD decline (−3.8 HU, p = 0.003). Age, pack years, and the presence of a fracture at baseline did not associate with BMD decline. Conclusions: Current smokers showed a more rapid BMD decline over a 3-year period compared to former smokers. This information might be important to identify subjects at risk for osteoporosis and emphasizes the importance of smoking cessation in light of BMD decline.

  20. Entorhinal inputs to hippocampal CA1 and dentate gyrus in the rat: a current-source-density study.

    Science.gov (United States)

    Leung, L S; Roth, L; Canning, K J

    1995-06-01

    1. Laminar profiles of the average evoked potentials and current-source-density analysis were used to study the input provided by the medial perforant path (PP) to the hippocampus in the urethan-anesthetized rat. 2. Stimulation of the PP activated an early latency sink in the middle molecular layer of the dentate gyrus (DG) and in the stratum lacunosum-moleculare in CA1. The DG current sink was generated by excitatory synaptic currents activated by the PP on dentate granule cells. In the normal rat, the peak current sink in the DG was typically five times greater than that of CA1. However, the CA1 sink could be distinguished from the DG sink in several ways: 1) it peaked when the DG sink was subsiding; 2) it showed paired-pulse facilitation, whereas the DG sink did not; and 3) in rats in which the DG was lesioned by local colchicine injection, the DG sink was reduced much more than the CA1 sink. 3. The PP afferents to CA1 required a slightly higher stimulus threshold (> 100 microA) for activation than those projecting to the DG granule cells (sink (2.5 +/- 0.2 ms, mean +/- SE) was also slightly longer than that of the DG sink (1.7 +/- 0.1 ms), suggesting that the axons of entorhinal layer III cells that project to CA1 have a slightly lower conduction velocity than the axons of the layer II cells that project to the DG. 4. The short-latency current sink activated by the PP in the distal dendritic layers of CA1 was likely provided by excitatory currents at the distal apical dendrites of CA1 pyramidal cells. The accompanying current source was mainly confined to stratum radiatum and appeared not to involve the cell body layer. Thus the electrotonic current spread may not be effective enough to depolarize the cell body or axon hillock. Contribution of interneurons to the above source-sink profile is possible, with the provision that these interneurons must have dendritic processes that span strata radiatum and lacunosum moleculare. 5. Extracellular field recordings

  1. The role of interfacial defects in enhancing the critical current density of YBa2Cu3O7-delta coatings

    Energy Technology Data Exchange (ETDEWEB)

    Foltyn, Stephen R [Los Alamos National Laboratory; Wang, Haiyan [Los Alamos National Laboratory; Civale, Leonardo [Los Alamos National Laboratory; Maiorov, Boris A [Los Alamos National Laboratory; Jia, Quanxi [Los Alamos National Laboratory

    2009-01-01

    The critical current density (J{sub c}) of YBa{sub 2}Cu{sub 3}0{sub 7-{delta}} (YBCO) films can approach 10 MA/cm{sup 2} at 77 K in self field , but only for very thin films. We have shown previously that strong thickness dependence results if J{sub c} is enhanced near the film-substrate interface. In the present work we investigate interfacial enhancement using laser-deposited YBCO films on NdGaO{sub 3} substrates, and find that we can adjust deposition conditions to switch the enhancement on and off. Interestingly, we find that the 'on' state is accompanied by interfacial misfit dislocations, establishing an unambiguous correlation between enhanced J{sub c} and dislocations at the film-substrate interface.

  2. CONTROL SYSTEM FOR THE LITHIUM BEAM EDGE PLASMA CURRENT DENSITY DIAGNOSTIC ON THE DIII-D TOKAMAK

    International Nuclear Information System (INIS)

    PEAVY, J.J.; CARY, W.P; THOMAS, D.M; KELLMAN, D.H.; HOYT, D.M; DELAWARE, S.W.; PRONKO, S.G.E.; HARRIS, T.E.

    2004-03-01

    OAK-B135 An edge plasma current density diagnostic employing a neutralized lithium ion beam system has been installed on the DIII-D tokamak. The lithium beam control system is designed around a GE Fanuc 90-30 series PLC and Cimplicity(reg s ign) HMI (Human Machine Interface) software. The control system operates and supervises a collection of commercial and in-house designed high voltage power supplies for beam acceleration and focusing, filament and bias power supplies for ion creation, neutralization, vacuum, triggering, and safety interlocks. This paper provides an overview of the control system, while highlighting innovative aspects including its remote operation, pulsed source heating and pulsed neutralizer heating, optimizing beam regulation, and beam ramping, ending with a discussion of its performance

  3. Enhanced vortex pinning and critical current density in proton-irradiated YBa2Cu3O7-δ thin films

    International Nuclear Information System (INIS)

    Venturini, E.L.; Siegal, M.P.; White, A.E.; Hou, S.Y.; Phillips, J.M.

    1993-01-01

    The appropriate fluence of 2.0 MeV H + ions has been shown previously to enhance the critical current density J c by a factor of two at a magnetic field of 0.9 tesla in 1,000 angstrom thick epitaxial films of YBa 2 Cu 3 O 7-δ grown by the ex situ BaF 2 process. The as-grown films exhibit single crystal-like behavior in both atomic ordering and J c versus temperature and magnetic field. TRIM simulations suggest that H + irradiation generates mainly point defects throughout the crystal structure. The authors show here that such defects result in an even greater enhancement of J c for fields above 1 tesla plus a significant increase in the apparent vortex pinning potential deduced from magnetization relaxation data

  4. Enhanced vortex pinning and critical current density in proton-irradiated YBa2Cu3O7-δ thin films

    International Nuclear Information System (INIS)

    Venturini, E.L.; Siegal, M.P.; White, A.E.; Hou, S.Y.; Phillips, J.M.

    1992-01-01

    The appropriate fluence of 2.0 MeV H + ions has been shown previously to enhance the critical current density J c by a factor of two at a magnetic field of 0.9 tesla in 1000 Angstrom thick epitaxial films of YBa 2 Cu 3 O 7-δ grown by the ex situ BaF 2 process. The as-grown films exhibit single crystal-like behavior in both atomic ordering and J c versus temperature and magnetic field. TRIM simulations suggest that H + irradiation generates mainly point defects throughout the crystal structure. We show here that such defects produce both a large enhancement of J c for fields above 1 tesla and a significant increase in the apparent vortex pinning potential deduced from magnetization relaxation data

  5. Enhanced vortex pinning and critical current density in proton-irradiated YBa2Cu3O(7-delta) thin films

    Science.gov (United States)

    Venturini, E. L.; Siegal, M. P.; White, A. E.; Hou, S. Y.; Phillips, J. M.

    1992-11-01

    The appropriate fluence of 2.0 MeV H(sup +) ions has been shown previously to enhance the critical current density J(sub c) by a factor of two at a magnetic field of 0.9 tesla in 1000 (Angstrom) thick epitaxial films of YBa(2)Cu(3)O(7-delta) grown by the ex situ BaF2 process. The as-grown films exhibit single crystal-like behavior in both atomic ordering and J(sub c) versus temperature and magnetic field. TRIM simulations suggest that H(sup +) irradiation generates mainly point defects throughout the crystal structure. We show here that such defects produce both a large enhancement of J(sub c) for fields above 1 tesla and a significant increase in the apparent vortex pinning potential deduced from magnetization relaxation data.

  6. Critical current density versus normal-state resistivity in granular high-temperature superconductors with different average grain size

    International Nuclear Information System (INIS)

    Curras, S.R.; Veira, J.A.; Maza, J.; Vidal, Felix

    2000-01-01

    The resistivity, ρ, and the critical current density at zero applied magnetic field, J c , of ceramic Y 1 Ba 2 Cu 3 O 7-δ samples with different average grain size, a (from 5 to 14 μm), are reported. These results show that at a given temperature J c depends only on the specific contact resistance of the average grain boundary junction, ρ□, so that the product J c ρ□ is sample independent. The relevance of ρ□ and not of a on J c has been further tested on a subset of samples having very different average grain size but similar ρ□ for which negligible variations of J c are observed. (author)

  7. The enhancement of critical current density on the bulk of BPSCCO-system superconductor with silver additions

    International Nuclear Information System (INIS)

    Engkir Sukirman; Wisnu Ari Adi; Puji Sulisworo dan W Prasuad

    1999-01-01

    The influence of silver additions on the critical current density (Jc) of BPSCCO-bulk superconductor was investigated, with the aim of getting an increase of its Jc and trying to find out a correlation of Jc and structures of BPSCCO-silver composites. The BPSCCO-system superconductors with nominal composition Bi 1.84 Pb 0.34 Sr 2.00 Ca 2.03 Cu 3.06 O x (2223-phase) were synthesized by using solid state reaction method. The silver added was in the powder-AgO form varied from 0 to 30 wt % AgO. The critical current density, crystal structure, and micro-structure of BPSCCO-silver composites were characterized by means of four-point probe, x-ray diffractometer, and scanning electron microscope that is equipped with a link system energy dispersive spectrometer. It was found that silver additions to BPSCCO cause a reasonable improvement in Jc from 120 to 215 A/cm 2 , and a slight increase in Tc from 92 to 108 K, and lattice parameters of the 2223-phase from a 3.811(3) to 3.820(2) A, and from c = 37.08(3) to 37.15(2) A, with the optimum value occurs at 20 wt % AgO. The AgO powders added to the BPSCCO specimens were converted to Ag 2 O and metallic Ag during the annealing process at 827degC for 96 h in air. The addition of AgO to BPSCCO system does not necessarily lead to decomposition of the 2223-phase. The AgO reacts with and suppresses the 2201-phase. (author)

  8. Behavior of Lithium Metal Anodes under Various Capacity Utilization and High Current Density in Lithium Metal Batteries

    Energy Technology Data Exchange (ETDEWEB)

    Jiao, Shuhong; Zheng, Jianming; Li, Qiuyan; Li, Xing; Engelhard, Mark H.; Cao, Ruiguo; Zhang, Ji-Guang; Xu, Wu

    2018-01-01

    Lithium (Li) metal batteries (LMBs) are regarded as the most promising power sources for electric vehicles. Besides the Li dendrite growth and low Li Coulombic efficiency, how to well match Li metal anode with a high loading (normally over 3.0 mAh cm-2) cathode is another key challenge to achieve the real high energy density battery. In this work, we systematically investigate the effects of the Li metal capacity usage in each cycle, manipulated by varying the cathode areal loading, on the stability of Li metal anode and the cycling performance of LMBs using the LiNi1/3Mn1/3Co1/3O2 (NMC) cathode and an additive-containing dual-salt/carbonate-solvent electrolyte. It is demonstrated that the Li||NMC cells show decent long-term cycling performance even with NMC areal capacity loading up to ca. 4.0 mAh cm-2 and at a charge current density of 1.0 mA cm-2. The increase of the Li capacity usage in each cycle causes variation in the components of the solid electrolyte interphase (SEI) layer on Li metal anode and generates more ionic conductive species from this electrolyte. Further study reveals for the first time that the degradation of Li metal anode and the thickness of SEI layer on Li anode show linear relationship with the areal capacity of NMC cathode. Meanwhile, the expansion rate of consumed Li and the ratio of SEI thickness to NMC areal loading are kept almost the same value with increasing cathode loading, respectively. These fundamental findings provide new perspectives on the rational evaluation of Li metal anode stability for the development of rechargeable LMBs.

  9. Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field

    Science.gov (United States)

    Vikas, Hash(0x125f4490)

    2011-02-01

    Evolution of the helium atom in a strong time-dependent (TD) magnetic field ( B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrödinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs "dynamically" from the CDFT based approach under similar computational constraints.

  10. Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field

    International Nuclear Information System (INIS)

    Vikas

    2011-01-01

    Evolution of the helium atom in a strong time-dependent (TD) magnetic field (B) of strength up to 10 11 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schroedinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >10 9 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >10 9 G, the conventional TD-DFT based approach differs 'dynamically' from the CDFT based approach under similar computational constraints. (author)

  11. Current and future pharmacologic options for the management of patients unable to achieve low-density lipoprotein-cholesterol goals with statins

    NARCIS (Netherlands)

    El Harchaoui, Karim; Akdim, Fatima; Stroes, Erik S. G.; Trip, Mieke D.; Kastelein, John J. P.

    2008-01-01

    Low-density lipoprotein-cholesterol (LDL-C) lowering is the mainstay of the current treatment guidelines in the management of cardiovascular risk. HMG-CoA reductase inhibitors (statins) are Currently the most effective LDL-C-lowering drugs. However, a substantial number of patients do not reach

  12. Enhancement in the critical current density of C-doped MgB2 wire using a polyacrylic acid dopant.

    Science.gov (United States)

    Lee, Seung Muk; Hwang, Soo Min; Lee, Chang Min; Kim, Won; Joo, Jinho; Lim, Jun Hyung; Kim, Chan-Joong; Hong, Gye-Won

    2012-02-01

    C-doped MgB2 wires were fabricated from a polyacrylic acid (PAA) using a conventional in-situ PIT technique. The effects of the PAA content on the lattice parameter, microstructure, critical temperature (Tc) and critical current density (Jc) were examined. With increasing PAA content, the amount of MgO in the sample increased but the crystallinity, a-axis lattice parameter, and Tc of MgB2 wires decreased, indicating that the C that decomposed from PAA during heat treatment had substituted for B. All doped samples exhibited a higher Jc than the undoped sample at high magnetic field, and the Jc(B) property improved with increasing PAA content: for the 7 wt% doped sample, the Jc was approximately 3-times higher than that of the pristine sample (1.28 kA/cm2 vs. 3.43 kA/cm2) at 5 K and 6.6 T. The improved Jc(B) of the doped sample was attributed to the decreased grain size, enlarged lattice distortion and increased C doping level.

  13. Degradation of solid oxide cells during co-electrolysis of steam and carbon dioxide at high current densities

    DEFF Research Database (Denmark)

    Tao, Youkun; Ebbesen, Sune Dalgaard; Mogensen, Mogens Bjerg

    2016-01-01

    In this work, the durability of Ni–YSZ based solid oxide cells was investigated during co-electrolysis of steam and carbon dioxide (45% H2O + 45% CO2 + 10% H2) at current density of −1.5 or −2.0 A cm−2. The cell consists of ∼300 μm Ni–YSZ support, ∼10 μm Ni–YSZ electrode, ∼10 μm YSZ electrolyte...... and ∼15 μm LSM–YSZ oxygen electrode. The gas conversion was 45% at −1.5 A cm−2 and 60% at −2.0 A cm−2, and the operating durations were up to 700 h. The detailed electrochemical analysis revealed significant increase of the ohmic resistance, oxide ion transport resistance in the Ni–YSZ composite...... electrodes and the electrochemical reaction resistance at the Ni–YSZ triple-phase boundaries. The performance degradation is mainly ascribed to the microstructural change in the Ni–YSZ electrode close to the YSZ electrolyte, including the percolation loss of Ni, the contact loss between Ni and YSZ...

  14. Analytical description of generation of the residual current density in the plasma produced by a few-cycle laser pulse

    Energy Technology Data Exchange (ETDEWEB)

    Silaev, A. A., E-mail: silaev@appl.sci-nnov.ru; Vvedenskii, N. V., E-mail: vved@appl.sci-nnov.ru [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950 (Russian Federation); University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation)

    2015-05-15

    When a gas is ionized by a few-cycle laser pulse, some residual current density (RCD) of free electrons remains in the produced plasma after the passage of the laser pulse. This quasi-dc RCD is an initial impetus to plasma polarization and excitation of the plasma oscillations which can radiate terahertz (THz) waves. In this work, the analytical model for calculation of RCD excited by a few-cycle laser pulse is developed for the first time. The dependences of the RCD on the carrier-envelope phase (CEP), wavelength, duration, and intensity of the laser pulse are derived. It is shown that maximum RCD corresponding to optimal CEP increases with the laser pulse wavelength, which indicates the prospects of using mid-infrared few-cycle laser pulses in the schemes of generation of high-power THz pulses. Analytical formulas for optimal pulse intensity and maximum efficiency of excitation of the RCD are obtained. Basing on numerical solution of the 3D time-dependent Schrödinger equation for hydrogen atoms, RCD dependence on CEP is calculated in a wide range of wavelengths. High accuracy of analytical formulas is demonstrated at the laser pulse parameters which correspond to the tunneling regime of ionization.

  15. Algorithms for Computing the Magnetic Field, Vector Potential, and Field Derivatives for a Thin Solenoid with Uniform Current Density

    Energy Technology Data Exchange (ETDEWEB)

    Walstrom, Peter Lowell [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-08-07

    A numerical algorithm for computing the field components Br and Bz and their r and z derivatives with open boundaries in cylindrical coordinates for radially thin solenoids with uniform current density is described in this note. An algorithm for computing the vector potential Aθ is also described. For the convenience of the reader, derivations of the final expressions from their defining integrals are given in detail, since their derivations are not all easily found in textbooks. Numerical calculations are based on evaluation of complete elliptic integrals using the Bulirsch algorithm cel. The (apparently) new feature of the algorithms described in this note applies to cases where the field point is outside of the bore of the solenoid and the field-point radius approaches the solenoid radius. Since the elliptic integrals of the third kind normally used in computing Bz and Aθ become infinite in this region of parameter space, fields for points with the axial coordinate z outside of the ends of the solenoid and near the solenoid radius are treated by use of elliptic integrals of the third kind of modified argument, derived by use of an addition theorem. Also, the algorithms also avoid the numerical difficulties the textbook solutions have for points near the axis arising from explicit factors of 1/r or 1/r2 in the some of the expressions.

  16. Simulation of Field Dependence of Critical Current Densities of Bulk High Tc Superconducting Materials regarding Thermally Activated Flux Motion

    Science.gov (United States)

    Santosh, M.; Naik, S. Pavan Kumar; Koblischka, M. R.

    2017-07-01

    In the upcoming generation, bulk high temperature superconductors (HTS) will play a crucial and a promising role in numerous industrial applications ranging from Maglev trains to magnetic resonance imaging, etc. Especially, the bulk HTS as permanent magnets are suitable due to the fact that they can trap magnetic fields being several orders of magnitude higher than those of the best hard ferromagnets. The bulk HTS LREBa2Cu3O7-δ (LREBCO or LRE-123, LRE: Y, Gd, etc.,) materials could obtain very powerful compact superconducting super-magnets, which can be operated at the cheaper liquid nitrogen temperature or below due to higher critical temperatures (i.e., ∼90 K). As a result, the new advanced technology can be utilized in a more attractive manner for a variety of technological and medical applications which have the capacity to revolutionize the field. An understanding of the magnetic field dependence of the critical current density (J c(H)) is important to develop better adapted materials. To achieve this goal, a variety of Jc (H) behaviours of bulk LREBCO samples were modelled regarding thermally activated flux motion. In essence, the Jc (H) curves follows a certain criterion where an exponential model is applied. However, to fit the complete Jc (H) curve of the LRE-123 samples an unique model is necessary to explain the behavior at low and high fields. The modelling of the various superconducting materials could be understood in terms of the pinning mechanisms.

  17. Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb3Sn conductors

    CERN Document Server

    Segal, Christopher; Sung, Zu Hawn; Lee, Peter J; Sailer, Bernd; Thoener, Manfred; Schlenga, Klaud; Ballarino, Amalia; Bottura, Luca; Bordini, Bernardo; Scheuerlein, Christian; Larnalestier, David C

    2016-01-01

    High critical current density ( Jc) 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 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. U...

  18. An overview of the software architecture of the plasma position, current and density realtime controller of the FTU

    Energy Technology Data Exchange (ETDEWEB)

    Boncagni, Luca, E-mail: luca.boncagni@enea.it [EURATOM - ENEA Fusion Association, Frascati Research Centre, Division of Fusion Physics, Frascati, Rome (Italy); Vitelli, Riccardo; Carnevale, Daniele [Department of Computer Science, Systems and Production, University of Rome Tor Vergata, Rome (Italy); Galperti, Cristian, E-mail: galperti@ifp.cnr.it [EURATOM - ENEA - CNR Fusion Association, CNR-IFP via R. Cozzi 53, 20125 Milan (Italy); Artaserse, Giovanni [EURATOM - ENEA Fusion Association, Frascati Research Centre, Division of Fusion Physics, Frascati, Rome (Italy); Pucci, Daniele [Dipartimento Antonio Ruberti, Universit degli Studi di Roma La Sapienza, Rome (Italy)

    2014-03-15

    Highlights: • We implement the FTU PPCDC system using the MARTe Framework. • We describe how it is logically divided and how it works. • We show experimental examples to describe how it works. - Abstract: Experimental fusion devices requires flexible control systems with a modern architecture, which allows the controller to be distributed and modular. The aforementioned requirements are all fulfilled by MARTe, a multi-platform framework for the development of low-latency hard-real-time control system already used with success in many European machine, it was decided to adopt it as the basis of the new FTU Plasma Position Current Density Control (PPCDC) system and the other coupled realtime systems. The main rationale to revamp the FTU control system was to use new technologies and to easily test different control solutions. MARTe has been proved effective from both the points of view, being platform independent, and having a modular architecture which completely separate the control algorithms from the rest of the infrastructure. We report on the new controller deployed at FTU. In particular, after a brief introduction on the machine, we illustrate the structure of the feedback system, together with a detailed analysis and appropriate experimental examples, of the various GAMs (modules) which make up the controller.

  19. Transport current density at temperatures up to 25 K of Cu/Ag composite sheathed 122-type tapes and wires

    Science.gov (United States)

    Liu, Shifa; Lin, Kaili; Yao, Chao; Zhang, Xianping; Dong, Chiheng; Wang, Dongliang; Awaji, Satoshi; Kumakura, Hiroaki; Ma, Yanwei

    2017-11-01

    The fabrication of iron-based superconductors with high transport critical current density (J c) and low cost is a crucial determinant of whether they can be used for practical applications. In this paper, Cu/Ag composite sheathed Sr0.6K0.4Fe2As2 (Sr122) tapes and Ba0.6K0.4Fe2As2 (Ba122) round wires were fabricated via an ex situ powder-in-tube method and heat-treated by the hot pressing and hot isostatic pressing process respectively. In order to thoroughly reveal the application potential of Cu/Ag composite sheathed ‘122’ iron pnictide superconductors, transport J c of tapes and wires in high fields at temperatures up to 25 K was measured. High transport J c of 4.4 × 104 A cm-2 at 4.2 K and 3.6 × 103 A cm-2 at 20 K in 10 T was achieved in Cu/Ag composite sheathed Sr122 tapes. Transport J c of Ba122 wires is 9.4 × 103 A cm-2 at 4.2 K and 1.9 × 103 A cm-2 at 20 K in 10 T. These results demonstrate the great potential of Cu/Ag composite sheathed ‘122’ iron pnictide superconducting tapes and wires for high-field applications at intermediate temperatures around 20 K, which can be easily obtained by using cryocoolers.

  20. An overview of the software architecture of the plasma position, current and density realtime controller of the FTU

    International Nuclear Information System (INIS)

    Boncagni, Luca; Vitelli, Riccardo; Carnevale, Daniele; Galperti, Cristian; Artaserse, Giovanni; Pucci, Daniele

    2014-01-01

    Highlights: • We implement the FTU PPCDC system using the MARTe Framework. • We describe how it is logically divided and how it works. • We show experimental examples to describe how it works. - Abstract: Experimental fusion devices requires flexible control systems with a modern architecture, which allows the controller to be distributed and modular. The aforementioned requirements are all fulfilled by MARTe, a multi-platform framework for the development of low-latency hard-real-time control system already used with success in many European machine, it was decided to adopt it as the basis of the new FTU Plasma Position Current Density Control (PPCDC) system and the other coupled realtime systems. The main rationale to revamp the FTU control system was to use new technologies and to easily test different control solutions. MARTe has been proved effective from both the points of view, being platform independent, and having a modular architecture which completely separate the control algorithms from the rest of the infrastructure. We report on the new controller deployed at FTU. In particular, after a brief introduction on the machine, we illustrate the structure of the feedback system, together with a detailed analysis and appropriate experimental examples, of the various GAMs (modules) which make up the controller

  1. Bilocal current densities and mean trajectories in a Young interferometer with two Gaussian slits and two detectors

    Energy Technology Data Exchange (ETDEWEB)

    Withers, L. P., E-mail: lpwithers@mitre.org [School of Physics, Astronomy, and Computational Science, George Mason University, Fairfax, Virginia 22030-4444 (United States); Narducci, F. A., E-mail: francesco.narducci@navy.mil [Naval Air Systems Command, Patuxent River, Maryland 20670 (United States)

    2015-06-15

    The recent single-photon double-slit experiment of Steinberg et al., based on a weak measurement method proposed by Wiseman, showed that, by encoding the photon’s transverse momentum behind the slits into its polarization state, the momentum profile can subsequently be measured on average, from a difference of the separated fringe intensities for the two circular polarization components. They then integrated the measured average velocity field, to obtain the average trajectories of the photons enroute to the detector array. In this paper, we propose a modification of their experiment, to demonstrate that the average particle velocities and trajectories change when the mode of detection changes. The proposed experiment replaces a single detector by a pair of detectors with a given spacing between them. The pair of detectors is configured so that it is impossible to distinguish which detector received the particle. The pair of detectors is then analogous to the simple pair of slits, in that it is impossible to distinguish which slit the particle passed through. To establish the paradoxical outcome of the modified experiment, the theory and explicit three-dimensional formulas are developed for the bilocal probability and current densities, and for the average velocity field and trajectories as the particle wavefunction propagates in the volume of space behind the Gaussian slits. Examples of these predicted results are plotted. Implementation details of the proposed experiment are discussed.

  2. Density-dependent intraspecific competition in the larval stage of Aedes aegypti (Diptera: Culicidae): revisiting the current paradigm.

    Science.gov (United States)

    Legros, Mathieu; Lloyd, Alun L; Huang, Yunxin; Gould, Fred

    2009-05-01

    Density-dependent intraspecific competition has been considered an important determinant of the dynamics of larval stages of Aedes aegypti. A model was published in 1984 providing a mathematical description of this density dependence, based on field data, that has since been widely used. This description, however, is based on the strong assumption that all mortality is density-dependent. We re-examine the data without this premise and find a reduced importance of density dependence, as well as a different functional form. Based on these discrepancies, we emphasize that the characterization of density dependence in the larval stages of Ae. aegypti should be based on a more complete dataset, and we use artificially generated data to explore how such additional information could help developing a better description of this density dependence. We review other empirical studies on larval competition, discuss the need for further dedicated studies, and provide a few simple guidelines for the design of such studies.

  3. Improved critical current densities in bulk FeSe superconductor using ball milled powders and high temperature sintering

    Energy Technology Data Exchange (ETDEWEB)

    Muralidhar, M.; Furutani, K.; Murakami, M. [Graduate School of Science and Engineering, Superconducting Materials Laboratory, Shibaura Institute of Technology, Tokyo (Japan); Kumar, Dinesh; Rao, M.S. Ramachandra [Department of Physics, Nano Functional Materials Technology Centre and Materials Science Research Centre, Indian Institute of Technology Madras, Chennai (India); Koblischka, M.R. [Institute of Experimental Physics, Saarland University, Saarbruecken (Germany)

    2016-12-15

    The present study is investigating the effect of high temperature sintering combined with ball milled powders for the preparation of FeSe material via solid state sintering technique. The commercial powders of Fe (99.9% purity) and Se (99.9% purity) were mixed in a nominal ratio Fe:Se = 1:1 and thoroughly ground and ball-milled in a glove box during 6 h. Then, the powder mixture was pressed into pellets of 5 mm in diameter and 2 mm thickness using an uniaxial pressure of 100 MPa. The samples were sealed in quartz tubes and sintered at 600 C for 24 h. Then, the pellets were again thoroughly ground and ball-milled in the glove box and pressed into pellets, and the final sintering was performed at two different temperatures, namely at 900 C for 24 h and at 950 C for 24 h. X-ray diffraction results confirmed that both samples showed mainly of the β-FeSe with tetragonal structure. The temperature dependence of magnetization (M-T) curves revealed a sharp superconducting transition T{sub c,} {sub onset} = 8.16 K for the sample sintered at 900 C. Further, scanning electron microscopy observations proved that samples sintered at 900 C show a platelike grain structure with high density. As a result, improved irreversibility fields around 5 T and the critical current density (J{sub c}) values of 6252 A cm{sup -2} at 5 K and self-field are obtained. Furthermore, the normalized volume pinning force versus the reduced field plots indicated a peak position at 0.4 for the sample sintered at 900 C. Improved flux pinning and the high J{sub c} values are attributed to the textured microstructure of the material, produced by a combination of high temperature sintering and ball milling. (copyright 2016 The Authors. Phys. Status Solidi A published by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Controlling Blend Morphology for Ultra-High Current Density in Non-Fullerene Acceptor Based Organic Solar Cells

    KAUST Repository

    Song, Xin

    2018-01-23

    Due to the high absorption coefficient and modulated band gap of non-fullerene small molecule acceptors (NFAs), photons can be utilized more efficiently in near-infrared (NIR) range. In this report, we highlight a system with a well-known polymer donor (PTB7-Th) blended with a narrow bandgap non-fullerene acceptor (IEICO-4F) as active layer and 1-chloronaphthalene (CN) as the solvent additive. The optimization of the photoactive layer nanomorphology yields short-circuit current density value (Jsc) of 27.3 mA/cm2, one of the highest value in OSCs reported to date, which competes with other types of solution processed solar cells such as perovskite or quantum dot devices. Along with decent open-circuit voltage (0.71V) and fill factor values (66%), a power conversion efficiency of 12.8% is achieved for the champion devices. Grazing incidence wide-angle X-ray scattering (GIWAXS) patterns and resonant soft X-ray scattering (R-SoXS) elucidate that the origin of this high photocurrent is mainly due to increased π-π coherence length of the acceptor, the domain spacing as well as the mean-square composition variation of the blend. Optoelectronic measurements confirm a balanced hole and electron mobility and reduced trap-assisted recombination for the best devices. These findings unveil the relevant solvent processing-nanostructure-electronic properties correlation in low band gap non-fullerene based solar cells, which provide a helpful guide for maximizing photocurrent that can pave the way for high efficiency organic solar cells.

  5. Saturation Ion Current Densities in Inductively Coupled Hydrogen Plasma Produced by Large-Power Radio Frequency Generator

    Science.gov (United States)

    Wang, Songbai; Lei, Guangjiu; Bi, Zhenhua; Ghomi, H.; Yang, Size; Liu, Dongping

    2016-09-01

    An experimental investigation of the saturation ion current densities (Jions) in hydrogen inductively coupled plasma (ICP) produced by a large-power (2-32 kW) radio frequency (RF) generator is reported, then some reasonable explanations are given out. With the increase of RF power, the experimental results show three stages: in the first stage (2-14 kW), the electron temperature will rise with the increase of RF power in the ICP, thus, the Jions increases continually as the electron temperature rises in the ICP. In the second stage (14-20 kW), as some H- ions lead to the mutual neutralization (MN), the slope of Jions variation firstly decreases then increases. In the third stage (20-32 kW), both the electronic detachment (ED) and the associative detachment (AD) in the ICP result in the destruction of H- ions, therefore, the increased amplitude of the Jions in the third stage is weaker than the one in the first stage. In addition, with the equivalent transformer model, we successfully explain that the Jions at different radial locations in ICP has the same rule. Finally, it is found that the Jions has nothing to do with the outer/inner puffing gas pressure ratio, which is attributed to the high-speed movement of hydrogen molecules. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2011GB108011 and 2010GB103001), the Major International (Regional) Project Cooperation and Exchanges of China (No. 11320101005) and the Startup Fund from Fuzhou University (No. 510071)

  6. Correlations between critical current density, jc, critical temperature, Tc, and structural quality of Y1B2Cu3O7-x thin superconducting films

    International Nuclear Information System (INIS)

    Chrzanowski, J.; Xing, W.B.; Atlan, D.

    1994-01-01

    Correlations between critical current density (j c ) critical temperature (T c ) and the density of edge dislocations and nonuniform strain have been observed in YBCO thin films deposited by pulsed laser ablation on (001) LaAlO 3 single crystals. Distinct maxima in j c as a function of the linewidths of the (00 ell) Bragg reflections and as a function of the mosaic spread have been found in the epitaxial films. These maxima in j c indicate that the magnetic flux lines, in films of structural quality approaching that of single crystals, are insufficiently pinned which results in a decreased critical current density. T c increased monotonically with improving crystalline quality and approached a value characteristic of a pure single crystal. A strong correlation between j c and the density of edge dislocations N D was found. At the maximum of the critical current density the density of edge dislocations was estimated to be N D ∼1-2 x 10 9 /cm 2

  7. Maximum field emission current density of CuO nanowires: theoretical study using a defect-related semiconductor field emission model and in situ measurements.

    Science.gov (United States)

    Lin, Zufang; Zhao, Peng; Ye, Peng; Chen, Yicong; Gan, Haibo; She, Juncong; Deng, Shaozhi; Xu, Ningsheng; Chen, Jun

    2018-02-01

    In this study, we proposed a theoretical model for one-dimensional semiconductor nanowires (NWs), taking account of the defect-related electrical transport process. The maximum emission current density was calculated by considering the influence of Joule heating, using a one-dimensional heat equation. The field emission properties of individual CuO NWs with different electrical properties were studied using an in situ experimental technique. The experimental results for maximum emission current density agreed well with the theoretical predictions and suggested that multiple conduction mechanisms were active. These may be induced by the concentration of defects in the CuO NW. The concentration of defects and the transport mechanisms were found to be key factors influencing the maximum field emission current density of the semiconductor NW. As is limited by the change of resistivity with temperature, only thermal runaway can trigger breakdown in CuO NWs.

  8. Electrodialytic remediation of harbour sediment in suspension - Evaluation of effects induced by changes in stirring velocity and current density on heavy metal removal and pH

    DEFF Research Database (Denmark)

    Kirkelund, Gunvor Marie; Ottosen, Lisbeth M.; Villumsen, Arne

    2009-01-01

    Electrodialytic remediation was used to remove heavy metals from a suspension of dredged harbour sediment. The studied metals Cu, Pb, Zn and Cd are normally strongly bound in anoxic sediment. Six electrodialytic laboratory remediation experiments were made, lasting 14 days and under oxic conditions....... The influence on the metal removal was investigated by changing current densities and stirring velocity of the sediment suspension. Using a current density of 1.0 mA/cm2 gave the highest metal removal. The sediment suspension was partly oxidised when mixed into a suspension for the electrodialytic remediation...... experiments and was further oxidised during the experiments. Even at low stirring velocities, oxic conditions were obtained. The metal removal was dependent on the achieved pH in the sediment and the highest metal removal and corresponding low pH was obtained by using a current density of 1.0 mA/cm2...

  9. The study of dynamics of electrons in the presence of large current densities; Etude de la dynamique des electrons en presence de fortes densites de courant

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, G

    2007-11-15

    The runaway electron effect is considered in different fields: nuclear fusion, or the heating of the solar corona. In this thesis, we are interested in runaway electrons in the ionosphere. We consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a parallel electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. A computational example is given illustrating the approach to equilibrium and the impact of the different terms. Then, a static electric field is applied in a new sample run. In this run, the electrons move in the z direction, parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density up to 20% of the total current density. Nevertheless, we note that the divergence free of the current density is not conserved. We introduce major changes in order to take into account the variation of the different moments of the ion distribution functions. We observe that the electron distribution functions are still non-Maxwellian. Runaway electrons are created and carry the current density. The core distribution stay at rest. As these electrons undergo less collisions, they increase the plasma conductivity. We make a parametric study. We fit the electron distribution function by two Maxwellian. We show that the time to reach the maximal current density is a key point. Thus, when we increase this time, we modify the temperatures. The current density plays a primary role. When the current density increases, all the moments of the distributions increase: electron density and mean velocity of the suprathermal distribution and the electron temperature of the core and

  10. Field, temperature, and angle dependent critical current density Jc(H,T,θ) in coated conductors obtained via contact-free methods

    International Nuclear Information System (INIS)

    Thompson, J R; Christen, D K; Zhang Yifei; Zuev, Y L; Cantoni, C; Sinclair, J W; Chen Yimin; Selvamanickam, V

    2010-01-01

    Applications of coated conductors based on high- T c superconductors often require detailed knowledge of their critical current density J c as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods for obtaining the angularly dependent J c using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

  11. Field, temperature, and angle dependent critical current density Jc(H,T, ) in coated conductors obtained via contact-free methods

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, James R [ORNL; Sinclair IV, John W [ORNL; Christen, David K [ORNL; Zhang, Yifei [ORNL; Zuev, Yuri L [ORNL; Cantoni, Claudia [ORNL; Chen, Y [SuperPower Incorporated, Schenectady, New York; Selvamanickam, V. [SuperPower Incorporated, Schenectady, New York

    2010-01-01

    Applications of coated conductors based on high-Tc superconductors often require detailed knowledge of their critical current density Jc as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods to obtain the angularly dependent Jc using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

  12. Field, temperature, and angle dependent critical current density J{sub c}(H,T,{theta}) in coated conductors obtained via contact-free methods

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, J R; Christen, D K; Zhang Yifei; Zuev, Y L; Cantoni, C [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6092 (United States); Sinclair, J W [Department of Physics, University of Tennessee, Knoxville, TN 37996-1200 (United States); Chen Yimin; Selvamanickam, V [SuperPower, Incorporated, 450 Duane Avenue, Schenectady, NY 12304 (United States)

    2010-01-15

    Applications of coated conductors based on high- T{sub c} superconductors often require detailed knowledge of their critical current density J{sub c} as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods for obtaining the angularly dependent J{sub c} using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

  13. Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Vikas [Quantum Chemistry Group, Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, 160014 Chandigrah (India)

    2011-02-15

    Evolution of the helium atom in a strong time-dependent (TD) magnetic field (B) of strength up to 10{sup 11} G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schroedinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >10{sup 9} G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >10{sup 9} G, the conventional TD-DFT based approach differs 'dynamically' from the CDFT based approach under similar computational constraints. (author)

  14. An analysis of the gradient-induced electric fields and current densities in human models when situated in a hybrid MRI-LINAC system

    Science.gov (United States)

    Liu, Limei; Trakic, Adnan; Sanchez-Lopez, Hector; Liu, Feng; Crozier, Stuart

    2014-01-01

    MRI-LINAC is a new image-guided radiotherapy treatment system that combines magnetic resonance imaging (MRI) with a linear accelerator (LINAC) in a single unit. One drawback is that the pulsing of the split gradient coils of the system induces an electric field and currents in the patient which need to be predicted and evaluated for patient safety. In this novel numerical study the in situ electric fields and associated current densities were evaluated inside tissue-accurate male and female human voxel models when a number of different split-geometry gradient coils were operated. The body models were located in the MRI-LINAC system along the axial and radial directions in three different body positions. Each model had a region of interest (ROI) suitable for image-guided radiotherapy. The simulation results show that the amplitudes and distributions of the field and current density induced by different split x-gradient coils were similar with one another in the ROI of the body model, but varied outside of the region. The fields and current densities induced by a split classic coil with the surface unconnected showed the largest deviation from those given by the conventional non-split coils. Another finding indicated that the distributions of the peak current densities varied when the body position, orientation or gender changed, while the peak electric fields mainly occurred in the skin and fat tissues.

  15. Two-dimensional probability density analysis of single channel currents from reconstituted acetylcholine receptors and sodium channels.

    Science.gov (United States)

    Keller, B U; Montal, M S; Hartshorne, R P; Montal, M

    1990-01-01

    Two-dimensional probability density analysis of single channel current recordings was applied to two purified channel proteins reconstituted in planar lipid bilayers: Torpedo acetylcholine receptors and voltage-sensitive sodium channels from rat brain. The information contained in the dynamic history of the gating process, i.e., the time sequence of opening and closing events was extracted from two-dimensional distributions of transitions between identifiable states. This approach allows one to identify kinetic models consistent with the observables. Gating of acetylcholine receptors expresses "memory" of the transition history: the receptor has two channel open (O) states; the residence time in each of them strongly depends on both the preceding open time and the intervening closed interval. Correspondingly, the residence time in the closed (C) states depends on both the preceding open time and the preceding closed time. This result confirms the scheme that considers, at least, two transition pathways between the open and closed states and extends the details of the model in that it defines that the short-lived open state is primarily entered from long-lived closed states while the long-lived open state is accessed mainly through short-lived closed states. Since ligand binding to the acetylcholine-binding sites is a reaction with channel closed states, we infer that the longest closed state (approximately 19 ms) is unliganded, the intermediate closed state (approximately 2 ms) is singly liganded and makes transitions to the short open state (approximately 0.5 ms) and the shortest closed state (approximately 0.4 ms) is doubly liganded and isomerizes to long open states (approximately 5 ms). This is the simplest interpretation consistent with available data. In contrast, sodium channels modified with batrachotoxin to eliminate inactivation show no correlation in the sequence of channel opening and closing events, i.e., have no memory of the transition history. This

  16. Critical current density, irreversibility line, and flux creep activation energy in silver-sheathed Bi2Sr2Ca2Cu3Ox superconducting tapes

    International Nuclear Information System (INIS)

    Shi, D.; Wang, Z.; Sengupta, S.; Smith, M.; Goodrich, L.F.; Dou, S.X.; Liu, H.K.; Guo, Y.C.

    1992-08-01

    Transport data, magnetic hysteresis and flux creep activation energy experimental results are presented for silver-sheathed high-T c Bi 2 Sr 2 Ca 2 Cu 3 O x superconducting tapes. The 110 K superconducting phase was formed by lead doping in a Bi-Sr-Ca-Cu-0 system. The transport critical current density was measured at 4.0 K to be 0.7 x 10 5 A/cm 2 (the corresponding critical current is 74 A) at zero field and 1.6 x 10 4 A/cm 2 at 12 T for H parallel ab. Excellent grain alignment in the a-b plane was achieved by a short-melting method, which considerably improved the critical current density and irreversibility line. Flux creep activation energy as a function of current is obtained based on the magnetic relaxation measurements

  17. The anatomy of a pyroclastic density current: the 10 July 2015 event at Volcán de Colima (Mexico)

    Science.gov (United States)

    Capra, L.; Sulpizio, R.; Márquez-Ramirez, V. H.; Coviello, V.; Doronzo, D. M.; Arambula-Mendoza, R.; Cruz, S.

    2018-04-01

    Pyroclastic density currents (PDCs) represent one of the most dangerous phenomena occurring in explosive volcanic eruptions, and any advance in the physical understanding of their transport and sedimentation processes can contribute to improving their hazard assessment. The 10-11 July 2015 eruption at Volcán de Colima provided a unique opportunity to better understand the internal behaviour of PDCs based on seismic monitoring data. On 10 July 2015, the summit dome collapsed, producing concentrated PDCs that filled the main channel of the Montegrande ravine. A lahar monitoring station installed 6 km from the volcano summit recorded a PDC before being completely destroyed. Real-time data acquisition from a camcorder and a geophone that were part of the station, along with field observations and grain-size data of the pyroclastic deposits, are used here to interpret the internal flow structure and time-variant transport dynamics of low-volume, valley-confined concentrated PDCs. The PDC that reached the monitoring station moved at a velocity of 7 m/s and filled a 12-m-deep channel. The outcrops show massive, block-and-ash flow deposits with trains of coarse clasts in the middle and towards the top of the depositional units. The seismic record gathered with the geophone was analysed for the time window when the flow travelled past the sensor. The geophone record was also compared with the recordings of a broadband seismic station located nearby. Two main frequency ranges were recognised which could be correlated with the basal frictional forces exerted by the flow on the channel bed (10-20 Hz) and a collisional regime (20-40 Hz) interpreted to be associated with a clast segregation process (i.e. kinematic squeezing). This latter regime promoted the upward migration of large blocks, which subsequently deviated towards the margin of the flow where they interacted with the sidewall of the main channel. The energy calculated for both seismic components shows that the

  18. Boiling-over dense pyroclastic density currents during the formation of the 100 km3 Huichapan ignimbrite in Central Mexico: Stratigraphic and lithofacies analysis

    Science.gov (United States)

    Pacheco-Hoyos, Jaime G.; Aguirre-Díaz, Gerardo J.; Dávila-Harris, Pablo

    2018-01-01

    A lithofacies analysis of the Huichapan ignimbrite has been undertaken to evaluate its depositional history from large pyroclastic density currents. The Huichapan ignimbrite is a massive ignimbrite sheet with a maximum runout of at least 55 km and thickness variations between 6 and 80 m. The lower portion of the Huichapan ignimbrite consists of a large plateau [ 100 km3; 69 km3 as dense-rock equivalent (DRE)] of massive ignimbrites with welding variations from densely welded to partly welded, devitrification, and high-temperature vapor-phase alteration. The lower part grades laterally to moderately welded and non-devitrified ignimbrites. These variations are interpreted as the sedimentation of density-stratified pyroclastic density currents erupted as boiling-over pulses from the Huichapan-Donguinyó caldera complex at a continuous rate, supporting deposition by quasi-steady progressive aggradation of sustained and hot currents. To the north of the caldera, the lower portion of the ignimbrite consists of a small plateau (< 10 km3) in which the densely welded and devitrified lithofacies are absent. Our interpretation is that the pyroclastic density currents flowed late to the north of the caldera and formed a smaller ignimbrite plateau with respect to the western one. This northern ignimbrite plateau cooled faster than the western ignimbrite plateau. Deposition-induced topographic modifications suggest that topographic obstacles, such as remnants of older volcanoes, may have promoted the deviation of the density currents to the north. The upper portion of the ignimbrite is composed of extensive, massive, coarse clast-rich, non-devitrified, and non-welded ignimbrites with abundant fines-poor pipes. This upper part was deposited from largely sustained and rapidly aggrading high-concentration currents in a near end-member, fluid escape-dominated flow boundary zone. The absence of welding in the upper portion may record pyroclastic density currents cooling during the

  19. Synthesis and Biochemical effects of magnetite nanoparticle by surfactant-free electrochemical method in an aqueous system:the current density effect

    Directory of Open Access Journals (Sweden)

    Mousa Aliahmad

    2016-07-01

    Full Text Available Obejective(s: In this research, magnetite nanoparticles with an average size of 23-36 nm were successfully synthesized via surfactant-free electrochemical method using iron as the anode and water as the electrolyte in a closed aqueous system in the presence of NaOH at room temperature. Methods: The effect of the current density on product formation and particle size was investigated. Particle size was controlled by adjusting the current density. It was found that particle size decreases by decreasing the current density. In addition, the effect of current density  on the structural and optical properties of nanostructures were studied by X-ray diffraction, Field emission scanning electron microscopy, Fourier transformed infrared, and vibrating sample magnetometer techniques.  Results: The results obtained from the magnetization property study of samples at room temperature showed coactivity and saturation manetization of 0-100 Oe and 27.2- 40.5 emu. g-1, respectively. Finally, the results of biological activity study of nanoparticles on liver and kidney function in male wistar rats demonstrated that oral administration of NPs caused significant alterations to the levels of aspartate transaminase, alanine transaminase, and alkaline phosphatase in serum. Conclusions: No significant changes were detected in the groups treated with 10 and 100 ppm/ day nanostructure (P>0.05. There was a significant increase in the serum level of creatinine and blood urea nitrogen level (p

  20. User's guide for SLWDN9, a code for calculating flux-surfaced-averaging of alpha densities, currents, and heating in non-circular tokamaks

    International Nuclear Information System (INIS)

    Hively, L.M.; Miley, G.M.

    1980-03-01

    The code calculates flux-surfaced-averaged values of alpha density, current, and electron/ion heating profiles in realistic, non-circular tokamak plasmas. The code is written in FORTRAN and execute on the CRAY-1 machine at the Magnetic Fusion Energy Computer Center

  1. Electrolytic deposition of calcium phosphate/cithosan coating on titanium alloy: growth kinetics and influence of current density, acetic acid, and cithosan.

    NARCIS (Netherlands)

    Wang, J.; van Apeldoorn, Aart A.; de Groot, K.

    2006-01-01

    Electrolytically deposited calcium phosphate/chitosan coating demonstrated good bone marrow stromal cell attachment. The aim of this study was to understand the coating's growth kinetics as well as the effects of current density, acetic acid, and chitosan on the coating's formation. The scanning

  2. Foraminiferal area density as a proxy for ocean acidification over the last 200 years in the California Current System

    Science.gov (United States)

    Osborne, E.; Thunell, R.

    2013-12-01

    Anthropogenic activities have resulted in an increase in atmospheric CO2 from 280 ppm to 400 ppm over the last 250 years. It is estimated that approximately one-third of this anthropogenically produced CO2 is sequestered in the global ocean, increasing the inventory of bicarbonate (HCO3-) and hydrogen ions (H+) and consuming carbonate (CO32-) as a result of carbonate buffering reactions. This increase in [H+] lowers seawater pH, the phenomenon known as ocean acidification (OA). Estimates indicate that mean seawater pH has already decreased by 0.1 pH units since 1750 and IPCC reports indicate it is likely that CO2 concentrations will reach 790 ppm by 2100 further reducing pH by 0.3 units. Marine calcifiers, such as foraminifera, utilize CO32- dissolved in seawater during calcification, a process that is highly sensitive to changes in pH due to the chemical reactions described above. The reduction in surface ocean carbonate ion concentration ([CO32-]) caused by OA has impaired calcification of planktonic foraminifera and other marine calcifiers. It has been proposed that planktonic foraminiferal shell weight or shell thickness is positively correlated with ambient [CO32-] and has been used as proxy to reconstruct past changes in the surface ocean carbonate system. An ideal location for the application of this proxy is the California Current System (CSS), an Eastern Boundary Upwelling System (EBUS), which is characterized as having naturally lower pH. Upwelling introduces CO2-enriched bottom waters to the surface ocean, intensifying the effects of increasing dissolved CO2 as a result of anthropogenic activities. Upwelling produces a wide range of surface water [CO32-] making the Santa Barbara Basin (SBB) an ideal site to carry out a foraminiferal shell weight calibration study. Area density (ρA) is a new method for collecting size-normalized shell weights that will be used in this study. Species-specific calibrations have been derived for two symbiont

  3. Design and development of a low cost, high current density power supply for streamer free atmospheric pressure DBD plasma generation in air

    Science.gov (United States)

    Jain, Vishal; Visani, Anand; Srinivasan, R.; Agarwal, Vivek

    2018-03-01

    This paper presents a new power supply architecture for generating a uniform dielectric barrier discharge (DBD) plasma in air medium at atmospheric pressure. It is quite a challenge to generate atmospheric pressure uniform glow discharge plasma, especially in air. This is because air plasma needs very high voltage for initiation of discharge. If the high voltage is used along with high current density, it leads to the formation of streamers, which is undesirable for most applications like textile treatment, etc. Researchers have tried to generate high-density plasma using a RF source, nanosecond pulsed DC source, and medium frequency AC source. However, these solutions suffer from low current discharge and low efficiency due to the addition of an external resistor to control the discharge current. Moreover, they are relatively costly and bulky. This paper presents a new power supply configuration which is very compact and generates high average density (˜0.28 W/cm2) uniform glow DBD plasma in air at atmospheric pressure. The efficiency is also higher as no external resistor is required to control the discharge current. An inherent feature of this topology is that it can drive higher current oscillations (˜50 A peak and 2-3 MHz frequency) into the plasma that damp out due to the plasma dissipation only. A newly proposed model has been used with experimental validation in this paper. Simulations and experimental validation of the proposed topology are included. Also, the application of the generated plasma for polymer film treatment is demonstrated.

  4. Universal correlation between critical current density and normal-state resistivity in porous YBa2Cu3O7-x thin films

    International Nuclear Information System (INIS)

    Bartolome, E; Goemory, F; Granados, X; Puig, T; Obradors, X

    2007-01-01

    We have simulated the inductive critical currents and transport currents in the dissipative state of superconducting thin films with an increasing amount of porosity by using a Bean model-based programme (Trazacorrientes(registered) ) and finite-element software. Simulations allowed us to find a quantitative, quasi-universal relationship between the overall critical current density and the normal-state resistivity via the sample porosity. This theoretical curve served to fit the experimental data found for a large number (∼150) of epitaxial YBa 2 Cu 3 O 7-x thin films grown by the trifluoracetate route

  5. Voltage and oxide thickness dependent tunneling current density and tunnel resistivity model: Application to high-k material HfO2 based MOS devices

    Science.gov (United States)

    Maity, N. P.; Maity, Reshmi; Baishya, Srimanta

    2017-11-01

    In this paper presents a straightforward efficient investigation of tunneling current density for ultra thin oxide layer based metal-oxide-semiconductor (MOS) devices to realization the gate current as a function of applied potential and oxide thickness. Solutions to the Schrödinger's wave equation are evolved for the different potential energy regions of the MOS device considering appropriate effective mass for each region. For finding approximate mathematical solutions to linear differential equations using spatially changeable coefficients the Wentzel-Kramers-Brillouin (WKB) approximation technique is considered. A p-substrate based n-channel MOS device has been analyzed consisting of SiO2 material as the oxide dielectric along with high-k material HfO2. The tunnel resistivity is correspondingly assessed employing this tunneling current density model. Synopsys Technology Computer Aided Design (TCAD) tool results are employed to validate the analytical model. Tremendous agreements among the results are observed.

  6. Electrochemical evaluation of sulfur poisoning in a methane-fuelled solid oxide fuel cell: Effect of current density and sulfur concentration

    DEFF Research Database (Denmark)

    Hagen, Anke; Johnson, Gregory B.; Hjalmarsson, Per

    2014-01-01

    , the effect of sulfur was less pronounced on mass transfer/fuel reforming processes but quite significant on the charge transfer/TPB processes. Overall, sulfur related performance loss was more severe at the highest current density (1 A cm−2), due to the deactivation of catalytic fuel reforming reactions......A Ni/ScYSZ based SOFC was tested at 1, 0.5, 0.25, and 0 (OCV) A cm−2 in methane fuel containing 0–100 ppm H2S. Analysis of cell voltage loss during short-term H2S poisoning showed that SOFC performance loss was generally larger at higher current loads. Separating the effect of H2S on catalytic...... reforming and electrochemical activity by evaluating the relevant area specific resistances and charge transfer processes based on impedance spectroscopy revealed that the poisoning of electrochemical activity was not dependent on current density. Two major anode processes were significantly affected...

  7. GaAsP/InGaP HBTs grown epitaxially on Si substrates: Effect of dislocation density on DC current gain

    Science.gov (United States)

    Heidelberger, Christopher; Fitzgerald, Eugene A.

    2018-04-01

    Heterojunction bipolar transistors (HBTs) with GaAs0.825P0.175 bases and collectors and In0.40Ga0.60P emitters were integrated monolithically onto Si substrates. The HBT structures were grown epitaxially on Si via metalorganic chemical vapor deposition, using SiGe compositionally graded buffers to accommodate the lattice mismatch while maintaining threading dislocation density at an acceptable level (˜3 × 106 cm-2). GaAs0.825P0.175 is used as an active material instead of GaAs because of its higher bandgap (increased breakdown voltage) and closer lattice constant to Si. Misfit dislocation density in the active device layers, measured by electron-beam-induced current, was reduced by making iterative changes to the epitaxial structure. This optimized process culminated in a GaAs0.825P0.175/In0.40Ga0.60P HBT grown on Si with a DC current gain of 156. By considering the various GaAsP/InGaP HBTs grown on Si substrates alongside several control devices grown on GaAs substrates, a wide range of threading dislocation densities and misfit dislocation densities in the active layers could be correlated with HBT current gain. The effect of threading dislocations on current gain was moderated by the reduction in minority carrier lifetime in the base region, in agreement with existing models for GaAs light-emitting diodes and photovoltaic cells. Current gain was shown to be extremely sensitive to misfit dislocations in the active layers of the HBT—much more sensitive than to threading dislocations. We develop a model for this relationship where increased base current is mediated by Fermi level pinning near misfit dislocations.

  8. Thick YBa2Cu3O7-x BaSnO3 Films with Enhanced Critical Current Density at High Magnetic Fields

    Science.gov (United States)

    2008-10-01

    contains color. 14. ABSTRACT The thickness dependence was studied for the critical current density (Jc) of YBa2Cu3O7-x (YBCO)+ BaSnO3 (BSO...TELEPHONE NUMBER (Include Area Code) N/A Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18 Thick YBa2Cu3O7−x+ BaSnO3 films with...density Jc of YBa2Cu3O7−xYBCO+ BaSnO3 BSO nanocomposite films. These films showed a significantly reduced decline of the Jc with thickness, especially

  9. Effect of high current density to defect generation of blue LED and its characterization with transmission electron microscope

    Science.gov (United States)

    Gunawan, R.; Sugiarti, E.; Isnaeni; Purawiardi, R. I.; Widodo, H.; Muslimin, A. N.; Yuliasari; Ronaldus, C. E.; Prastomo, N.; Hastuty, S.

    2018-03-01

    The optical, electrical and structural characteristics of InGaN-based blue light-emitting diodes (LEDs) were investigated to identify the degradation of LED before and after current injection. The sample was injected by high current of 200 A/cm2 for 5 and 20 minutes. It was observed that injection of current shifts light intensity and wavelength characteristics that indicated defect generation. Transmission Electron Microscopy (TEM) characterization was carried out in order to clarify the structure degradation caused by defect in active layer which consisted of 14 quantum well with thickness of about 5 nm and confined with barrier layer with thickness of about 12 nm. TEM results showed pre-existing defect in LED before injection with high current. Furthermore, discontinue and edge defect was found in dark spot region of LED after injection with high current.

  10. The September 14, 2015 phreatomagmatic eruption of Nakadake first crater, Aso Volcano, Japan: Eruption sequence inferred from ballistic, pyroclastic density current and fallout deposits

    Science.gov (United States)

    Miyabuchi, Yasuo; Iizuka, Yoshiyuki; Hara, Chihoko; Yokoo, Akihiko; Ohkura, Takahiro

    2018-02-01

    An explosive eruption occurred at Nakadake first crater, Aso Volcano in central Kyushu, southwestern Japan, on September 14, 2015. The sequence and causes of the eruption were reconstructed from the distribution, textures, grain-size, component and chemical characteristics of the related deposits, and video record. The eruptive deposits are divided into ballistics, pyroclastic density current and ash-fall deposits. A large number of ballistic clasts (mostly < 10 cm in diameter; maximum size 1.6 m) are scattered within about 500 m from the center of the crater. Almost half of the ballistics appear as fresh and unaltered basaltic andesite rocks interpreted to be derived from a fresh batch of magma, while the rest is weakly to highly altered clasts. A relatively thin ash derived from pyroclastic density currents covered an area of 2.3 km2 with the SE-trending main axis and two minor axes to the NE and NW. The pyroclastic density current deposit (maximum thickness < 10 cm even at the crater rim) is wholly fine grained, containing no block-sized clasts. Based on the isopach map, the mass of the pyroclastic density current deposit was estimated at ca. 5.2 × 104 tons. The ash-fall deposit is finer grained and clearly distributed to about 8 km west of the source crater. The mass of the ash-fall deposit was calculated at about 2.7 × 104 tons. Adding the mass of the pyroclastic density current deposit, the total discharged mass of the September 14, 2015 eruption was 7.9 × 104 tons. The September 14 pyroclastic density current and ash-fall deposits consist of glass shards (ca. 30%), crystals (20-30%) and lithic (40-50%) grains. Most glass shards are unaltered poorly crystallized pale brown glasses which probably resulted from quenching of juvenile magma. This suggests that the September 14, 2015 event at the Nakadake first crater was a phreatomagmatic eruption. Similar phreatomagmatic eruptions occurred at the same crater on September 6, 1979 and April 20, 1990 whose

  11. Calculation of magnetic field-induced current densities for humans from EAS countertop activation/deactivation devices that use ferromagnetic cores

    Science.gov (United States)

    Li, Qingxiang; Gandhi, Om P.

    2005-01-01

    Compliance testing of electronic article surveillance (EAS) devices requires that induced current densities in central nervous system (CNS) tissues, i.e. brain and the spinal cord, be less than the prescribed safety limits. Even though ferromagnetic cores are mostly used for activation/deactivation of embedded magnetic tags, assumed equivalent air-core coils with guessed increased number of ampere turns have always been used to calculate the magnetic fields for the proximal region to which a customer is exposed. We show that at low frequencies up to several kilohertz, duality of electric and magnetic circuits may be exploited such that the shaped high reluctance core is modelled as though it was a higher conductivity electric circuit of the corresponding shape. The proposed procedure is tested by examples of two magnetic cores typical of countertop activation/deactivation devices. The equivalent exposure magnetic fields obtained from the dual electric fields are shown to be in excellent agreement (within ±5%) with those measured for these ferromagnetic EAS devices. The previously proposed impedance method is then used to calculate the induced current densities for a 1.974 × 1.974 × 2.93 mm resolution anatomic model of a human. For the two considered EAS systems using excitation currents of 5000 A turns at 200 Hz, the maximum 1 cm2 area-averaged induced current densities in the CNS tissues are calculated and found to be less than the ICNIRP safety limits.

  12. Fundamental transverse mode selection and self-stabilization in large optical cavity diode lasers under high injection current densities

    Science.gov (United States)

    Avrutin, Eugene A.; Ryvkin, Boris S.; Payusov, Alexey S.; Serin, Artem A.; Gordeev, Nikita Yu

    2015-11-01

    It is shown that in high-power, large optical cavity laser diodes at high injection currents, the optical losses due to nonuniform carrier accumulation in the optical confinement layer can ensure the laser operation in the fundamental transverse mode. An experimental demonstration of switching from second order mode to fundamental mode in large optical cavity lasers with current and/or temperature increase is reported and explained, with the calculated values for the switching current and temperature in good agreement with the measurements. The results experimentally prove the nonuniform nature of carrier accumulation in the confinement layer and may aid laser design for optimizing the output.

  13. Large critical current densities in YBa2Cu3O7- x thin films formed by plasma-enhanced metalorganic chemical vapor deposition at reduced temperature

    Science.gov (United States)

    Zhao, J.; Li, Y. Q.; Chern, C. S.; Huang, W.; Norris, P.; Gallois, B.; Kear, B.; Lu, P.; Cosandey, F.

    1991-04-01

    YBa2Cu3O7- x (YBCO) superconducting thin films with a critical current density exceeding 1 x 106 A/cm2 at 77.7 K were prepared by a plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) process. The thin films (130 nm thick) were formed in-situ on LaAlO3 substrates at a temperature of 670‡ C in 2 Torr partial pressure of activated N2O. Resistivity and magnetic susceptibility measurements of the as-deposited films show a sharp superconducting transition temperature of 89.8 K. Critical current densities were measured by the dc transport method with a patterned bridge of 120 × 40 Μm. Both x-ray diffraction and high resolution electron microscopy measurements indicate that films grew epitaxially with the c-axis perpendicular to the surface of the substrate.

  14. Enhancement of the critical current density in FeO-coated MgB2 thin films at high magnetic fields

    Directory of Open Access Journals (Sweden)

    Andrei E. Surdu

    2011-12-01

    Full Text Available The effect of depositing FeO nanoparticles with a diameter of 10 nm onto the surface of MgB2 thin films on the critical current density was studied in comparison with the case of uncoated MgB2 thin films. We calculated the superconducting critical current densities (Jc from the magnetization hysteresis (M–H curves for both sets of samples and found that the Jc value of FeO-coated films is higher at all fields and temperatures than the Jc value for uncoated films, and that it decreases to ~105 A/cm2 at B = 1 T and T = 20 K and remains approximately constant at higher fields up to 7 T.

  15. Temperature, pressure, and density of electron, atom and ion, in the breaking arc of silver-cadmium contacts used in medium current region

    International Nuclear Information System (INIS)

    Aida, Teizo

    1979-01-01

    Wear of silver-cadmium contacts at the time of breaking was studied. The materials of the contacts were silver-cadmium alloy and silver-cadmium oxide sinter. The spectra of arc discharge generated at the time of breaking contact were analyzed with a monochromator photo multiplier. The ratio of the densities of cadmium and silver atoms in the arc can be estimated from the observed intensities of spectrum lines. The electron density is obtained from the arc current density. The proportion of the cadmium atoms in the arc was about 30 percent. The densities of silver atoms and cadmium atoms can be estimated by the principle of thermal ionization equilibrium. The ion densities were also estimated. The partial pressures of silver and cadmium atoms in the arc can be obtained from the Boyle-Charles' law. A formula which gives the number of atoms liberated from the surfaces of contacts at the time of breaking was given by Boddy et al. (Kato, T.)

  16. Generation of High-Density, Uniform Plasmas by Low-Frequency RF Currents: Key Concepts, Experiments and Applications

    International Nuclear Information System (INIS)

    Xu, S.; Tsakadze, Z.L.; Tsakadze, E.L.; Ostrikov, K.

    2003-01-01

    The results on generation and technological applications of high-density and highly uniform low-frequency (∼460-500 kHz) inductively coupled plasmas (LF ICP) are reviewed. The ICP source is capable of sustaining stable discharges in electrostatic (E) or electromagnetic (H) regimes. In the H operation mode, plasma densities as high as 8 x 1012 cm-3 are achievable with moderate (∼1 kW) Rf powers at low and intermediate pressures (10-100 mTorr). The ICP also features high degree of uniformity over large processing volumes and surfaces. It is shown that the plasma source has a great potential for a number of industrial applications. As an example, the efficiency of the LF ICP for synthesis of silicon nitride (Si3N4) on Si(111) substrate in low-pressure discharges of Ar+N2 gas mixtures, is demonstrated. The main mechanism involved in the process is the extensive nitrogen ion implantation combined with plasma enhanced thermal diffusion. The crystalline structure, bonding states and chemical composition of the silicon nitride film are studied

  17. Increased bronchial density of CD25+Foxp3+ regulatory T cells in occupational asthma: relationship to current smoking.

    Science.gov (United States)

    Sjåheim, T B; Bjørtuft, Ø; Drabløs, P A; Kongerud, J; Halstensen, T S

    2013-05-01

    To identify activated T cell subset in the asthmatic bronchia, we developed a triple-colour immunohistofluorescence labelling technique on cryo-section to discriminate activated CD4+CD25+ T cells, (effector T cells) from Foxp3+ regulatory T cells (Treg). Additional coexpression of activation and proliferation markers was also examined in situ. Bronchial biopsies were taken from 20 aluminium potroom workers (12 smokers) with asthma (>12% reversibility), 15 non-asthmatic potroom workers (7 smokers) and 10 non-smoking, non-exposed controls. Non-smoking asthmatics had significantly higher subepithelial density of both Tregs, effector T cells, activated (HLA-DR+) CD8+ and activated CD4+ T cells. Moreover, both Tregs, effector T cells and CD8+ T cells proliferated in the non-smoking asthmatics, only. Although smoking asthmatics had no asthma-associated increase in bronchial T cell, both had a significantly increase in effector T cell to Treg ratios. The significantly increased bronchial density of Tregs, effector T cells, proliferative T cells and activated CD8+ T cells in non-smoking asthmatics clearly showed that both the effector T cells and the inhibitory Treg system were activated in asthma. © 2013 The Authors. Scandinavian Journal of Immunology © 2013 Blackwell Publishing Ltd.

  18. Extension of the source-sink potential approach to Hartree-Fock and density functional theory: A new tool to visualize the ballistic current through molecules

    Science.gov (United States)

    Fias, Stijn; Stuyver, Thijs

    2017-11-01

    The recent source and sink potential approach by Pickup et al. [J. Chem. Phys. 143, 194105 (2015)] is extended to Hartree-Fock and density functional theory, allowing the calculation of the transmission and the visualization of ballistic currents through molecules at these levels of theory. This visualization allows the study of the transmission process in real-space, providing an important tool to better understand the conduction process.

  19. Finite element model predicts current density distribution for clinical applications of tDCS and tACS

    Directory of Open Access Journals (Sweden)

    Toralf eNeuling

    2012-09-01

    Full Text Available Transcranial direct current stimulation (tDCS has been applied in numerous scientific studies over the past decade. However, the possibility to apply tDCS in therapy of neuropsychiatric disorders is still debated. While transcranial magnetic stimulation (TMS has been approved for treatment of major depression in the United States by the Food and Drug Administration (FDA, tDCS is not as widely accepted. One of the criticisms against tDCS is the lack of spatial specificity. Focality is limited by the electrode size (35 cm2 are commonly used and the bipolar arrangement. However, a current flow through the head directly from anode to cathode is an outdated view. Finite element (FE models have recently been used to predict the exact current flow during tDCS. These simulations have demonstrated that the current flow depends on tissue shape and conductivity. Toface the challenge to predict the location, magnitude and direction of the current flow induced by tDCS and transcranial alternating current stimulation (tACS, we used a refined realistic FE modeling approach. With respect to the literature on clinical tDCS and tACS, we analyzed two common setups for the location of the stimulation electrodes which target the frontal lobe and the occipital lobe, respectively. We compared lateral and medial electrode configuration with regard to theirusability. We were able to demonstrate that the lateral configurations yielded more focused stimulation areas as well as higher current intensities in the target areas. The high resolution of our simulation allows one to combine the modeled current flow with the knowledge of neuronal orientation to predict the consequences of tDCS and tACS. Our results not only offer a basis for a deeper understanding of the stimulation sites currently in use for clinical applications but also offer a better interpretation of observed effects.

  20. Analysis of the current density characteristics in through-mask electrochemical micromachining (TMEMM for fabrication of micro-hole arrays on invar alloy film

    Directory of Open Access Journals (Sweden)

    Da-som JIN

    2017-06-01

    Full Text Available Invar alloy consisting of 64% iron and 36% nickel has been widely used for the production of shadow masks for organic light emitting diodes (OLEDs because of its low thermal expansion coefficient (1.86 × 10−6 cm/°C. To fabricate micro-hole arrays on 30 μm invar alloy film, through-mask electrochemical micromachining (TMEMM was developed and combined with a portion of the photolithography etching process. For precise hole shapes, patterned photoresist (PR film was applied as an insulating mask. To investigate the relationship between the current density and the material removal rate, the principle of the electrochemical machining was studied with a focus on the equation. The finite element method (FEM was used to verify the influence of each parameter on the current density on the invar alloy film surface. The parameters considered were the thickness of the PR mask, inter-electrode gap (IEG, and electrolyte concentration. Design of experiments (DOE was used to figure out the contribution of each parameter. A simulation was conducted with varying parameters to figure out their relationships with the current density. Optimization was conducted to select the suitable conditions. An experiment was carried out to verify the simulation results. It was possible to fabricate micro-hole arrays on invar alloy film using TMEMM, which is a promising method that can be applied to fabrications of OLEDs shadow masks.

  1. Influence of Y2BaCuO5 precipitates on the current density of melt processed YBa2Cu3Ox superconductor

    International Nuclear Information System (INIS)

    Salama, K.; Selvamanickam, V.

    1992-01-01

    YBa 2 Cu 3 O x superconductors fabricated by melt processing methods have been shown to exhibit current density around 10 5 A/cm 2 at 77 K. Since YBa 2 Cu 3 O x decomposes peritectically above 1000 C, more than 50 vol. % of Y 2 BaCuO 5 (211) precipitates are formed during the incongruent melting. Even under stringent slow cooling conditions, a significant amount of these precipitates remain unreacted with the liquid and are left embedded in the long 123 grains. The potential of these precipitates as flux pinning sites has been investigated extensively, but remains controversial. In this study, we have performed transport current density measurements on melt processed YBa 2 Cu 3 O x superconductor prepared with varying amount of 211 precipitates. The current density measurements were performed in magnetic fields up to 1.5 T at 77 K with the field aligned at different angles to the a-b plane. The results provided in this paper show that Jc decreases monotonically with increasing amount of 211, irrespective of the angle between the field and the a-b plane indicating the absence of significant pinning by 211 precipitates in melt processed YBa 2 Cu 3 O x superconductor

  2. Degradation of solid oxide cells during co-electrolysis of H2O and CO2: Carbon deposition under high current densities

    DEFF Research Database (Denmark)

    Tao, Youkun; Ebbesen, Sune Dalgaard; Mogensen, Mogens Bjerg

    2012-01-01

    During co-electrolysis of H2O and CO2 using solid oxide cells (SOCs) the risk of carbon deposition in the Ni-YSZ electrode under high current densities (∼ 2.0 A/cm2) was studied in this work. Five galvanostatic tests were performed at current density between 1.5 and 2.25 A/cm2 and the average...... conversions of the reactants were no more than 66.8 %. Ni-YSZ electrode delamination and carbon nano-fibers could be observed after test at the Ni-YSZ | YSZ electrolyte interface for two of the cells. Thermodynamic calculation shows that the reactant conversion needed for carbon formation is above 99 %, far...... above the experimental conversions. The observed carbon formation may be caused by the gas diffusion limitations at high current densities. Carbon nano-fibers were only observed close to the YSZ electrolyte indicating a large overpotential gradient at the TPBs close to the electrolyte...

  3. Simultaneous use of a crossflow filtration membrane as microbial fuel cell anode - Permeate flow leads to 4-fold increased current densities.

    Science.gov (United States)

    Madjarov, Joana; Götze, Arne; Zengerle, Roland; Kerzenmacher, Sven

    2018-06-01

    A new concept for the combination of membrane bioreactors and microbial fuel cells is introduced, that aims at the production of electricity for reducing the overall energy consumption of wastewater treatment. In contrast to previous approaches, the anode is integrated as microfiltration membrane in sidestream crossflow configuration. Using a stainless steel filtration membrane with G. sulfurreducens and an acetate-based synthetic medium, up to 4-fold higher current densities are achieved. In a standard setup without filtration, a membrane of filter grade 1 µm shows current densities of 5.8 A m -2  ± 0.5 A m -2 compared to >11 A m -2 when it is used simultaneously as membrane filter. With smaller pore sizes of filter grade 0.5 µm, 4.4 A m -2  ± 0.5 A m -2 in a standard setup and >15 A m -2 in a filtration setup are achieved. The permeate flow was identified as the main parameter leading to increased current densities. Copyright © 2018 Elsevier Ltd. All rights reserved.

  4. Aging characteristics of blue InGaN micro-light emitting diodes at an extremely high current density of 3.5 kA cm−2

    International Nuclear Information System (INIS)

    Tian, Pengfei; Liu, Ran; Althumali, Ahmad; Gu, Erdan; Watson, Ian M; Dawson, Martin D

    2016-01-01

    The aging characteristics of blue InGaN micro-light emitting diodes (micro-LEDs) with different sizes have been studied at an extremely high current density 3.5 kA cm −2 for emerging micro-LED applications including visible light communication (VLC), micro-LED pumped organic lasers and optogenetics. The light output power of micro-LEDs first increases and then decreases due to the competition of Mg activation in p-GaN layer and defect generation in the active region. The smaller micro-LEDs show less light output power degradation compared with larger micro-LEDs, which is attributed to the lower junction temperature of smaller micro-LEDs. It is found that the high current density without additional junction temperature cannot induce significant micro-LED degradation at room temperature but the combination of the high current density and high junction temperature leads to strong degradation. Furthermore, the cluster LEDs, composed of a micro-LED array, have been developed with both high light output power and less light output degradation for micro-LED applications in solid state lighting and VLC. (paper)

  5. Study of critical current density from ac susceptibility measurements in (La1-xYx)2Ba2CaCu5O2 superconductors

    International Nuclear Information System (INIS)

    Nayak, P.K.; Ravi, S. . sravi@iitg.ernet.in

    2008-01-01

    We have prepared a series of compounds (La 1-x Y x ) 2 Ba 2 CaCu 5 O 2 for x = 0 to 0.5 by adding a CaCuO 2 layer to the parent compound La 2 Ba 2 Cu 4 O 2 and by doping Y in place of La. These materials are also prepared by adding 5 wt% of Ag to enhance the intergranular coupling and critical current density. X-ray diffraction measurements show that all the samples are essentially in single phase form and the patterns could be refined using P4/mmm space group in tetragonal cell. The typical lattice parameters are found to be a = b 3.856 A, c = 11.576 A for x = 0.5 sample. Temperature variations of dc electrical resistivity measured on the above samples show that they exhibit superconductivity with T c ranging from 60 to 75 K. Temperature and ac field amplitude variation of ac susceptibility have been measured on the above samples. The field variation of ac susceptibility data has been analyzed by using Bean critical state model. Using both temperature and field variations of ac susceptibility data, the material dependent parameters, such as critical current density as a function of temperature and effective volume fraction grains have been estimated. The Ag doped samples show relatively large critical current density compared to pure samples due to improved intergranular coupling. (author)

  6. Effects of cold-working on pinning behaviour and critical current densities in NbTi-based superconductors

    International Nuclear Information System (INIS)

    Yamada, Y.; Murase, S.; Wada, H.; Tachikawa, K.

    1985-01-01

    The effects of cold-working on high-field pinning behaviour at 1.8 K and 4.2 K have been studied for multifilamentary NbTi, NbTiHf and NbTiTa superconductors, which were subjected to cold-working, heat treatment and cold-working, in sequence. It is found that the cold-working, either before or after heat treatment, shifts the peak in pinning force density to a higher field, while the maximum pinning force value is first increased with increasing amount of cold-working, and then decreased. This result can not be predicted by existing pinning theories, and we conclude that for pinning behaviour induced by cold-working, not only the introduction of pinning centres but also their size and spacing must be taken into account. (author)

  7. Transport phenomena in intrinsic semiconductors and insulators at high current densities: Suppression of the broken neutrality drift

    Energy Technology Data Exchange (ETDEWEB)

    Mnatsakanov, T. T.; Tandoev, A. G.; Yurkov, S. N. [All-Russia Electrotechnical Institute, Krasnokazarmennaya 12, 111250 Moscow (Russian Federation); Levinshtein, M. E. [The Ioffe Physico-Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg (Russian Federation)

    2013-08-14

    It is shown that, in addition to the diffusion and broken neutrality drift (BND) modes well-known for insulators and very lightly doped semiconductors, the quasineutral drift (QND) mode is possible. The transition from the BND to QND mode is accompanied by the appearance of a portion with a very sharp current rise in the current-voltage characteristic. This effect is observed in a new type of semiconductor detectors (CIDs, Current Injected Detectors) of high-intensity neutron and proton radiation, suggested, in particular, for Large Hadron Collider. The effect is unambiguously attributed now to the presence of radiation-induced deep centers in a semiconductor. It is shown, however, in this paper that the effect of a very sharp rise in current upon a slight increase in voltage is even possible when there are no deep centers. An equation adequately describing the possible transport modes in intrinsic semiconductors and insulators is derived. The results of an analytical study are confirmed by an adequate simulation.

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

    Czech Academy of Sciences Publication Activity Database

    Vandas, Marek; Romashets, E.

    2016-01-01

    Roč. 34, č. 12 (2016), s. 1165-1173 ISSN 0992-7689 R&D Projects: GA ČR(CZ) GA14-19376S Institutional support: RVO:67985815 Keywords : magnetospheric physics * scale birkeland currents * charged particles Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.610, year: 2016

  9. A Low-Power Current-Reuse Analog Front-End for High-Density Neural Recording Implants.

    Science.gov (United States)

    Rezaei, Masoud; Maghsoudloo, Esmaeel; Bories, Cyril; De Koninck, Yves; Gosselin, Benoit

    2018-04-01

    Studying brain activity in vivo requires collecting bioelectrical signals from several microelectrodes simultaneously in order to capture neuron interactions. In this work, we present a new current-reuse analog front-end (AFE), which is scalable to very large numbers of recording channels, thanks to its small implementation silicon area and its low-power consumption. This current-reuse AFE, which is including a low-noise amplifier (LNA) and a programmable gain amplifier (PGA), employs a new fully differential current-mirror topology using fewer transistors, and improving several design parameters, such as power consumption and noise, over previous current-reuse amplifier circuit implementations. We show that the proposed current-reuse amplifier can provide a theoretical noise efficiency factor (NEF) as low as 1.01, which is the lowest reported theoretical NEF provided by an LNA topology. A foue-channel current-reuse AFE implemented in a CMOS 0.18-μm technology is presented as a proof-of-concept. T-network capacitive circuits are used to decrease the size of input capacitors and to increase the gain accuracy in the AFE. The measured performance of the whole AFE is presented. The total power consumption per channel, including the LNA and the PGA stage, is 9 μW (4.5 μW for LNA and 4.5 μW for PGA), for an input referred noise of 3.2 μV rms , achieving a measured NEF of 1.94. The entire AFE presents three selectable gains of 35.04, 43.1, and 49.5 dB, and occupies a die area of 0.072 mm 2 per channel. The implemented circuit has a measured inter-channel rejection ratio of 54 dB. In vivo recording results obtained with the proposed AFE are reported. It successfully allows collecting low-amplitude extracellular action potential signals from a tungsten wire microelectrode implanted in the hippocampus of a laboratory mouse.

  10. Real-space distribution of the Hall current densities and their spin polarization in nonmagnetic zine-blende semiconductors

    Czech Academy of Sciences Publication Activity Database

    Středa, Pavel; Drchal, Václav

    2012-01-01

    Roč. 86, č. 19 (2012), "195204-1"-"195204-8" ISSN 1098-0121 R&D Projects: GA ČR(CZ) GAP204/11/1228 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10100520 Keywords : nonmagnetic semiconductors * spin Hall currents Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.767, year: 2012

  11. Well-posedness of the conductivity reconstruction from an interior current density in terms of Schauder theory

    KAUST Repository

    Kim, Yong-Jung

    2015-06-23

    We show the well-posedness of the conductivity image reconstruction problem with a single set of interior electrical current data and boundary conductivity data. Isotropic conductivity is considered in two space dimensions. Uniqueness for similar conductivity reconstruction problems has been known for several cases. However, the existence and the stability are obtained in this paper for the first time. The main tool of the proof is the method of characteristics of a related curl equation.

  12. Effect of discharge current and deposition temperature on roughness and density of NbC films fabricated by ion beam sputtering technique

    Science.gov (United States)

    Dhawan, Rajnish; Rai, Sanjay; Lodha, G. S.

    2014-04-01

    NbC films were prepared using Ion beam sputtering system at various discharges current from 0.4 amps to 1.2 amps at room temperature. Effect of temperature on NbC films were also studied by depositing NbC films at various temperatures from room temperature to 200,300,400 and 600°C. X-ray reflectivity (XRR) study shows that surface roughness of the film decreases with decrease in discharge current. The optimum lowest roughness 3.2´̊A having density 92% of bulk was achieved at discharge current 0.6 amps at 3.0 cm3/min Ar gas flow. X-ray study also shows that film roughness decreases with increase in temperature of the film and after a certain temperature it increases with increase in temperature. The lowest surface roughness 2.1´̊A was achieved at 300°C with density 83% of bulk NbC at constant discharge current 0.6 amps.

  13. High performance of mixed halide perovskite solar cells: Role of halogen atom and plasmonic nanoparticles on the ideal current density of cell

    Science.gov (United States)

    Mohebpour, Mohammad Ali; Saffari, Mohaddeseh; Soleimani, Hamid Rahimpour; Tagani, Meysam Bagheri

    2018-03-01

    To be able to increase the efficiency of perovskite solar cells which is one of the most substantial challenges ahead in photovoltaic industry, the structural and optical properties of perovskite CH3NH3PbI3-xBrx for values x = 1-3 have been studied employing density functional theory (DFT). Using the optical constants extracted from DFT calculations, the amount of light reflectance and ideal current density of a simulated single-junction perovskite solar cell have been investigated. The results of DFT calculations indicate that adding halogen bromide to CH3NH3PbI3 compound causes the relocation of energy bands in band structure which its consequence is increasing the bandgap. In addition, the effect of increasing Br in this structure can be seen as a reduction in lattice constant, refractive index, extinction and absorption coefficient. As well, results of the simulation suggest a significant current density enhancement as much as 22% can be achieved by an optimized array of Platinum nanoparticles that is remarkable. This plan is able to be a prelude for accomplishment of solar cells with higher energy conversion efficiency.

  14. A Method to Increase Current Density in a Mono Element Internal Tin Processed Superconductor Utilizing Zr Oxide to Refine Grain Size

    Energy Technology Data Exchange (ETDEWEB)

    Bruce A. Zeitlin, Eric Gregory

    2008-04-07

    The effect of Oxygen on (Nb1Zr)3Sn multifilament conductors manufactured by the Mono Element Internal Tin (MEIT) process was explored to improve the current density by refining the grain size. This followed work first done by General Electric on the Nb3Sn tape process. Techniques to fabricate the more difficult Nb1Zr composites are described and allowed fabrication of long lengths of .254 mm diameter wire from an 88.9 mm diameter billet. Oxygen was incorporated through the use of SnO2 mixed with tin powder and incorporated into the core. These were compared to samples with Ti+Sn and Cu+Sn cores. Heat treatments covered the range of 700 C to 1000 C. Current density vs. H, grain size, and reaction percentages are provided for the materials tested. The Oxygen gave superior results in the temperature range of 815-1000 C. It also stabilized the filament geometry of the array in comparison to the other additions at the higher temperatures. At 815 C a peak in layer Jc yielded values of 2537 A/mm2 at 12 T and 1353 A/mm2 at 15T, 8-22% and 30-73% greater respectively than 700 C values. Results with Oxygen at high temperature show the possibility of high speed continuous reaction of the composite versus the current batch or react in place methods. In general the Ti additions gave superior results at the lower reaction temperature. Future work is suggested to determine if the 815 C reaction temperature can lead to higher current density in high tin (Nb1Zr+Ox)3Sn conductors. A second technique incorporated oxygen directly into the Nb1Zr rods through heat treatment with Nb2O5 at 1100 C for 100 hours in vacuum prior to extrusion. The majority of the filaments reduced properly in the composite but some local variations in hardness led to breakage at smaller diameters.

  15. Design of a Probe for Strain Sensitivity Studies of Critical Current Densities in SC Wires and Tapes

    Energy Technology Data Exchange (ETDEWEB)

    Dhanaraj, N.; Barzi, E.; Turrioni, D.; Rusy, A.; Lombardo, V.; /Fermilab

    2011-07-01

    The design of a variable-temperature probe used to perform strain sensitivity measurements on LTS wires and HTS wires and tapes is described. The measurements are intended to be performed at liquid helium temperatures (4.2 K). The wire or tape to be measured is wound and soldered on to a helical spring device, which is fixed at one end and subjected to a torque at the free end. The design goal is to be able to achieve {+-} 0.8 % strain in the wire and tape. The probe is designed to carry a current of 2000A.

  16. Role of silver addition in the synthesis of high critical current density MgB sub 2 bulk superconductors

    CERN Document Server

    Kumar, D; Narayan, J B; Wang, H; Tiwari, A

    2003-01-01

    Ag-doped MgB sub 2 bulk superconductors have been prepared using a standard solid state processing. The addition of Ag to MgB sub 2 powders during the sintering process has been found to result in an important advantage, namely, the prevention/reduction of loss of Mg, a problem most commonly observed in the sintering of MgB sub 2 bulk samples at elevated temperature and ambient pressures. The Ag-doped MgB sub 2 sample has a distinct superconducting transition temperature around 39 K, while the undoped MgB sub 2 undergoes only a very feeble transition to a diamagnetic superconducting state at around 39 K. The normal conducting silver regions in the MgB sub 2 matrix act as pinning centres resulting in the realization of high critical currents in the presence of magnetic fields.

  17. Photoelectrolysis of water at high current density - Use of laser light excitation of semiconductor-based photoelectrochemical cells

    Science.gov (United States)

    Wrighton, M. S.; Bocarsley, A. B.; Bolts, J. M.

    1978-01-01

    In the present paper, some results are given for UV laser light irradiation of the photoanode (SnO2, SrTiO3, or TiO2) in a cell for the light-driven electrolysis of H2O, at radiation intensities of up to 380 W/sq cm. The properties of the anode material are found to be independent of light intensity. Conversion of UV light to stored chemical energy in the form of 2H2/O2 from H2O was driven at a rate of up to 30 W/sq cm. High O2 evolution rates at the irradiated anodes without changes in the current-voltage curves are attributed to the excess oxidizing power associated with photogenerated holes. A test for this sort of hypothesis for H2 evolution at p-type materials is proposed.

  18. Determination of the ReA Electron Beam Ion Trap electron beam radius and current density with an X-ray pinhole camera

    Energy Technology Data Exchange (ETDEWEB)

    Baumann, Thomas M., E-mail: baumannt@nscl.msu.edu; Lapierre, Alain, E-mail: lapierre@nscl.msu.edu; Kittimanapun, Kritsada; Schwarz, Stefan; Leitner, Daniela; Bollen, Georg [National Superconducting Cyclotron Laboratory (NSCL), Michigan State University (MSU), 640 S. Shaw Lane, East Lansing, Michigan, 48824 (United States)

    2014-07-15

    The Electron Beam Ion Trap (EBIT) of the National Superconducting Cyclotron Laboratory at Michigan State University is used as a charge booster and injector for the currently commissioned rare isotope re-accelerator facility ReA. This EBIT charge breeder is equipped with a unique superconducting magnet configuration, a combination of a solenoid and a pair of Helmholtz coils, allowing for a direct observation of the ion cloud while maintaining the advantages of a long ion trapping region. The current density of its electron beam is a key factor for efficient capture and fast charge breeding of continuously injected, short-lived isotope beams. It depends on the radius of the magnetically compressed electron beam. This radius is measured by imaging the highly charged ion cloud trapped within the electron beam with a pinhole camera, which is sensitive to X-rays emitted by the ions with photon energies between 2 keV and 10 keV. The 80%-radius of a cylindrical 800 mA electron beam with an energy of 15 keV is determined to be r{sub 80%}=(212±19)μm in a 4 T magnetic field. From this, a current density of j = (454 ± 83)A/cm{sup 2} is derived. These results are in good agreement with electron beam trajectory simulations performed with TriComp and serve as a test for future electron gun design developments.

  19. Surface Morphology Study of Nanostructured Lead-Free Solder Alloy Sn-Ag-Cu Developed by Electrodeposition: Effect of Current Density Investigation

    Directory of Open Access Journals (Sweden)

    Sakinah Mohd Yusof

    2013-10-01

    Full Text Available Normal 0 false false false IN X-NONE X-NONE MicrosoftInternetExplorer4 Nanostructured lead-free solder Sn-Ag-Cu (SAC was developed by electrodeposition method at room temperature. Electrolite bath which comprised of the predetermined quantity of tin methane sulfonate, copper sulfate and silver sulfate were added sequentially to MSA solution. The methane sulphonic acid (MSA based ternary Sn-Ag-Cu bath was developed by using tin methane sulfonate as a source of Sn ions while the Cu+ and Ag+ ions were obtained from their respective sulfate salts. The rate of the electrodeposition was controlled by variation of current density. The addition of the buffer, comprising of sodium and ammonium acetate helped in raising the pH solution. During the experimental procedure, the pH of solution, composition of the electrolite bath, and the electrodeposition time were kept constant. The electrodeposited rate, deposit composition and microstructure were investigated as the effect of current density. The electrodeposited solder alloy was characterized for their morphology using Field Emission Scanning Electron Microscope (FESEM. In conclusion, vary of current density will play significant role in the surface morphology of nanostructured lead-free solder SAC developed. Normal 0 false false false IN X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New

  20. Impact zone dynamics of dilute mono- and polydisperse jets and their implications for the initial conditions of pyroclastic density currents

    Science.gov (United States)

    Sweeney, Matthew R.; Valentine, Greg A.

    2017-09-01

    The fluid dynamics at the impact zone of an impinging jet dictate the initial conditions for the resulting downstream flow. Current understanding of this impact zone is limited to small scale, single phase, or monodisperse impinging jet experiments with a focus on industrial and engineering applications. Here, we present multifield numerical modeling results of mono- and polydisperse impinging jets with length scales and physical parameters relevant to large explosive volcanic eruptions. Our modeling shows that particle behavior is sensitive to whether a jet is monodisperse or polydisperse. For a monodisperse jet, the downstream flow behavior can be predicted by the coupling between the particles and gas, which we characterize by a form of the Stokes number (Stimp) where the time scale of changes in fluid motion is defined by the length scale and velocity change associated with vertical deceleration as a mixture approaches an impact surface. We find that the length scale of deceleration is sensitive to the mixture Mach number, as high Mach number flows produce standing shocks upstream of the impact site. For low Stimp monodisperse cases, the particles make the transition from axial to radial flow easily, and the flow continues downstream relatively unimpeded and well mixed. In contrast, in situations where the monodisperse particles are sufficiently poorly coupled (high Stimp), the particles rebound and/or concentrate at the impact zone, which results in a radial acceleration of gas as it is expelled from the concentrating mixture. In polydisperse jets, larger particles become better coupled to the gas in the free jet zone when in the presence of smaller, well-coupled particles due to particle-particle drag. However, the larger particles still lose significant momentum in the impact zone, which results in a lag effect where the smaller particles and gas are expelled and advance radially at a greater velocity. Although the simulations are simplified compared with

  1. PYFLOW_2.0: a computer program for calculating flow properties and impact parameters of past dilute pyroclastic density currents based on field data

    Science.gov (United States)

    Dioguardi, Fabio; Mele, Daniela

    2018-03-01

    This paper presents PYFLOW_2.0, a hazard tool for the calculation of the impact parameters of dilute pyroclastic density currents (DPDCs). DPDCs represent the dilute turbulent type of gravity flows that occur during explosive volcanic eruptions; their hazard is the result of their mobility and the capability to laterally impact buildings and infrastructures and to transport variable amounts of volcanic ash along the path. Starting from data coming from the analysis of deposits formed by DPDCs, PYFLOW_2.0 calculates the flow properties (e.g., velocity, bulk density, thickness) and impact parameters (dynamic pressure, deposition time) at the location of the sampled outcrop. Given the inherent uncertainties related to sampling, laboratory analyses, and modeling assumptions, the program provides ranges of variations and probability density functions of the impact parameters rather than single specific values; from these functions, the user can interrogate the program to obtain the value of the computed impact parameter at any specified exceedance probability. In this paper, the sedimentological models implemented in PYFLOW_2.0 are presented, program functionalities are briefly introduced, and two application examples are discussed so as to show the capabilities of the software in quantifying the impact of the analyzed DPDCs in terms of dynamic pressure, volcanic ash concentration, and residence time in the atmosphere. The software and user's manual are made available as a downloadable electronic supplement.

  2. Epitaxial YBa2Cu3O7 on biaxially textured (001) Ni: An approach to high critical current density superconducting tapes

    International Nuclear Information System (INIS)

    Norton, D.P.; Goyal, A.; Budai, J.D.

    1997-01-01

    In-plane aligned, c-axis oriented YBa 2 Cu 3 O 7 (YBCO) films with superconducting critical current densities, J c , as high as 700,000 amperes per square centimeter at 77 kelvin have been grown on thermo-mechanically, rolled-textured (001) Ni tapes using pulsed-laser deposition. Epitaxial growth of oxide buffer layers directly on biaxially textured Ni, formed by recrystallization of cold-rolled pure Ni, enables the growth of 1.5 micrometer-thick YBCO films with superconducting properties that are comparable to those observed for epitaxial films on single crystal oxide substrates. This result represents a viable approach for producing long-length superconducting tapes for high current, high field applications at 77 kelvin

  3. Matching field effects at tesla-level magnetic fields in critical current density in high-Tc superconductors containing self-assembled columnar defects

    Energy Technology Data Exchange (ETDEWEB)

    Sinclair, J. [University of Tennessee, Knoxville (UTK); Zuev, Yuri L [ORNL; Cantoni, Claudia [ORNL; Wee, Sung Hun [ORNL; Varanasi, C. V. [University of Dayton Research Institute; Thompson, James R [ORNL; Christen, David K [ORNL

    2012-01-01

    We have investigated the superconductive transport properties of YBa2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC.H/ data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC.H/. The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.

  4. Volcanic Lightning, Pyroclastic Density Currents, Ballistic Fall, Vent Tremor, and One Very Loud Blast: Acoustic Analysis of the 14 July 2013 Vulcanian Eruption at Tungurahua, Ecuador.

    Science.gov (United States)

    Anderson, J.; Johnson, J. B.; Steele, A. L.; Anzieta, J. C.; Ortiz, H. D.; Hall, M. L.; Ruiz, M. C.

    2014-12-01

    Acoustic recordings reveal a variety of volcanic activities during an exceptionally loud vulcanian eruption at Tungurahua. A period of several months of mild surface activity came to an abrupt end with the emission of a powerful blast wave heard at least 180 km away. Sensors 2080 m from the vent recorded a stepped rise to its maximum overpressure of 1220 Pa (corresponding to a sound pressure level of 156 dB) and its unusually long dominant period of 5.6 s. We discuss source processes that produced the blast wave, considering that wave propagation could be nonlinear near the vent because of high overpressures. More than an hour of acoustic activity was recorded after the blast wave, including sound from falling ballistics, reflections of the blast wave from nearby mountains, pyroclastic density currents, and acoustic tremor at the vent. Glitches in the acoustic records related to plume lightning were also serendipitously observed, although thunder could not be unambiguously identified. We discuss acoustic signatures of falling ballistics and pyroclastic density currents and how array-style deployments and analytic methods can be used to reveal them. Placement of sensors high on the volcano's slopes facilitated resolving these distinct processes. This study demonstrates that near-vent, array-style acoustic installations can be used to monitor various types of volcanic activity.

  5. MoS2/Ni3S4 composite nanosheets on interconnected carbon shells as an excellent supercapacitor electrode architecture for long term cycling at high current densities

    Science.gov (United States)

    Qin, Shengchun; Yao, Tinghui; Guo, Xin; Chen, Qiang; Liu, Dequan; Liu, Qiming; Li, Yali; Li, Junshuai; He, Deyan

    2018-05-01

    In this paper, we report an electrode architecture of molybdenum disulfide (MoS2)/nickel sulfide (Ni3S4) composite nanosheets anchored on interconnected carbon (C) shells (C@MoS2/Ni3S4). Electrochemical measurements indicate that the C@MoS2/Ni3S4 structure possesses excellent supercapacitive properties especially for long term cycling at high current densities. A specific capacitance as high as ∼640.7 F g-1 can still be delivered even after 10,000 cycles at a high current density of 20 A g-1. From comparison of microstructures and electrochemical properties of the related materials/structures, the improved performance of C@MoS2/Ni3S4 can be attributed to the relatively dispersedly distributed nanosheet-shaped MoS2/Ni3S4 that provides efficient contact with electrolyte and effectively buffers the volume change during charge/discharge processes, enhanced cycling stability by MoS2, and reduced equivalent series resistance by the interconnected C shells.

  6. Larger late sodium current density as well as greater sensitivities to ATX II and ranolazine in rabbit left atrial than left ventricular myocytes.

    Science.gov (United States)

    Luo, Antao; Ma, Jihua; Song, Yejia; Qian, Chunping; Wu, Ying; Zhang, Peihua; Wang, Leilei; Fu, Chen; Cao, Zhenzhen; Shryock, John C

    2014-02-01

    An increase of cardiac late sodium current (INa.L) is arrhythmogenic in atrial and ventricular tissues, but the densities of INa.L and thus the potential relative contributions of this current to sodium ion (Na(+)) influx and arrhythmogenesis in atria and ventricles are unclear. In this study, whole-cell and cell-attached patch-clamp techniques were used to measure INa.L in rabbit left atrial and ventricular myocytes under identical conditions. The density of INa.L was 67% greater in left atrial (0.50 ± 0.09 pA/pF, n = 20) than in left ventricular cells (0.30 ± 0.07 pA/pF, n = 27, P ATX II) increased INa.L with an EC50 value of 14 ± 2 nM and a Hill slope of 1.4 ± 0.1 (n = 9) in atrial myocytes and with an EC50 of 21 ± 5 nM and a Hill slope of 1.2 ± 0.1 (n = 12) in ventricular myocytes. Na(+) channel open probability (but not mean open time) was greater in atrial than in ventricular cells in the absence and presence of ATX II. The INa.L inhibitor ranolazine (3, 6, and 9 μM) reduced INa.L more in atrial than ventricular myocytes in the presence of 40 nM ATX II. In summary, rabbit left atrial myocytes have a greater density of INa.L and higher sensitivities to ATX II and ranolazine than rabbit left ventricular myocytes.

  7. PYFLOW 2.0. A new open-source software for quantifying the impact and depositional properties of dilute pyroclastic density currents

    Science.gov (United States)

    Dioguardi, Fabio; Dellino, Pierfrancesco

    2017-04-01

    Dilute pyroclastic density currents (DPDC) are ground-hugging turbulent gas-particle flows that move down volcano slopes under the combined action of density contrast and gravity. DPDCs are dangerous for human lives and infrastructures both because they exert a dynamic pressure in their direction of motion and transport volcanic ash particles, which remain in the atmosphere during the waning stage and after the passage of a DPDC. Deposits formed by the passage of a DPDC show peculiar characteristics that can be linked to flow field variables with sedimentological models. Here we present PYFLOW_2.0, a significantly improved version of the code of Dioguardi and Dellino (2014) that was already extensively used for the hazard assessment of DPDCs at Campi Flegrei and Vesuvius (Italy). In the latest new version the code structure, the computation times and the data input method have been updated and improved. A set of shape-dependent drag laws have been implemented as to better estimate the aerodynamic drag of particles transported and deposited by the flow. A depositional model for calculating the deposition time and rate of the ash and lapilli layer formed by the pyroclastic flow has also been included. This model links deposit (e.g. componentry, grainsize) to flow characteristics (e.g. flow average density and shear velocity), the latter either calculated by the code itself or given in input by the user. The deposition rate is calculated by summing the contributions of each grainsize class of all components constituting the deposit (e.g. juvenile particles, crystals, etc.), which are in turn computed as a function of particle density, terminal velocity, concentration and deposition probability. Here we apply the concept of deposition probability, previously introduced for estimating the deposition rates of turbidity currents (Stow and Bowen, 1980), to DPDCs, although with a different approach, i.e. starting from what is observed in the deposit (e.g. the weight

  8. High-transport current density up to 30 T in bulk YBa2Cu3O7 and the critical angle effect

    International Nuclear Information System (INIS)

    Ekin, J.W.; Salama, K.; Selvamanickam, V.

    1991-01-01

    Measurements of the dc transport critical current of oriented-grained YBa 2 Cu 3 O 7 have been made using high quality Ag contacts and a high-current sample mount. The critical- current density J c at 77 K for mutually perpendicular current and magnetic field B in the a,b plane is 8 kA/cm 2 at 8 T, decreasing gradually to 3.7 kA/cm 2 at 20 T, and remaining over 1 kA/cm 2 out to 30 T. High magnetic field measurements of J c as a function of the angle θ of B with respect to the c axis are also reported. In contrast to earlier results at lower fields ( c vs θ curve with a head-and-shoulders shape, consisting of a sharp peak (''head'') 2 planes, and a wide (30 degree at 9 T, for example) shoulder region on either side of B perpendicular c, where the transport J c remains high and constant. Beyond the shoulder region, however, the transport J c decreases sharply, giving rise to the concept of a critical field angle for application design, defined by the minima in d 2 J c /dθ 2 at the edge of the shoulders

  9. Hall voltage drives pulsing counter-currents of the sliding charge density wave and of quantized normal carriers at self-filled Landau levels

    Science.gov (United States)

    Orlov, Andrey P.; Sinchenko, Aleksander A.; Monceau, Pierre; Brazovskii, Serguei; Latyshev, Yuri I.

    2017-11-01

    Remnant pockets of carriers left over after formation of a charge density wave (CDW) were brought, by virtue of transverse electric and magnetic fields, to a current-carrying state at quantized Landau Levels. The generated Hall voltage polarizes and puts to sliding the flexible CDW background. The screening from the CDW allows for a so strong redistribution of normal electrons density under the action of the Lorentz force alone, that an integer filling of the lowest Landau level might be reached at one edge at the expense of the full depletion at another edge of the Hall bar. With the Hall field exceeding the sliding threshold, the regime of exactly compensated collective and normal counter-currents develops in the open-circuit direction across the bar. The annihilation of the two currents proceeds via a regular sequence of phase slips which are the space-time vortices of the CDW phase around the enforced amplitude nodes. The resulting spontaneous generation of coherent high ( GHz) frequency signals was detected by observations of multiple Shapiro steps. This picture results from studies of micron-sized Hall bars in crystals of NbSe3 prepared by means of focused ion beams. The interpretation is confirmed and illustrated by a numerical solution of the derived equations. The depinning pulse propagates from edges to the bulk and the sliding sets in, accompanied by the generation of periodic phase slips near the Hall bar edge where the CDW phase is advanced in steps of 2π at expense of the CDW amplitude passing through zero.

  10. Microstructure and Critical Current Density of YBa2Cu3O7-x + BaSnO3 Thick Films Grown with Pre-Mixed Pulsed Laser Ablation Target (Postprint)

    Science.gov (United States)

    2010-01-01

    AFRL-RZ-WP-TP-2012-0149 MICROSTRUCTURE AND CRITICAL CURRENT DENSITY OF YBa2Cu3O7-x + BaSnO3 THICK FILMS GROWN WITH PRE-MIXED PULSED LASER...CURRENT DENSITY OF YBa2Cu3O7-x + BaSnO3 THICK FILMS GROWN WITH PRE-MIXED PULSED LASER ABLATION TARGET (POSTPRINT) 5a. CONTRACT NUMBER In-house 5b...YBa2Cu3O7-x (YBCO) + BaSnO3 (BSO) thin films with BSO nanocolumns have been shown to have improved critical current density (Jc) in applied magnetic fields

  11. Efficiency roll-off suppression in organic light-emitting diodes using size-tunable bimetallic bowtie nanoantennas at high current densities

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Yukun [Key Laboratory of Physical Electronics and Devices of Ministry of Education and Shaanxi Provincial Key Laboratory of Photonics & Information Technology, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Solid-State Lighting Engineering Research Center, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ (United Kingdom); Yun, Feng, E-mail: fyun2010@mail.xjtu.edu.cn; Li, Yufeng; Feng, Lungang; Ding, Wen [Key Laboratory of Physical Electronics and Devices of Ministry of Education and Shaanxi Provincial Key Laboratory of Photonics & Information Technology, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Solid-State Lighting Engineering Research Center, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Huang, Yi [Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ (United Kingdom); Wu, Zhaoxin; Jiao, Bo; Li, Sanfeng [Key Laboratory of Physical Electronics and Devices of Ministry of Education and Shaanxi Provincial Key Laboratory of Photonics & Information Technology, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Zhang, Ye [Solid-State Lighting Engineering Research Center, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China)

    2016-07-04

    Size-tunable bimetallic bowtie nanoantennas have been utilized to suppress the efficiency roll-off characteristics in organic light-emitting diodes (OLEDs) using both the numerical and experimental approaches. The resonant range can be widened by the strong dual-atomic couplings in bimetallic bowtie nanoantennas. Compared with the green OLED with conventional bowtie nanoantennas at a high current density of 800 mA/cm{sup 2}, the measured efficiency roll-off ratio of the OLED with size-modulated bowtie nanoantennas is decreased from 53.2% to 41.8%, and the measured current efficiency is enhanced by 29.9%. When the size-modulated bowtie nanoantennas are utilized in blue phosphorescent OLEDs, the experimental roll-off ratio is suppressed from 43.6% to 25.9% at 250 mA/cm{sup 2}, and the measured current efficiency is also enhanced significantly. It is proposed that the efficiency roll-off suppression is mainly related to the enhanced localized surface plasmon effect, which leads to a shorter radiative lifetime.

  12. Study of Electric Explosion of Flat Micron-Thick Foils at Current Densities of (5-50)×108 A/cm2

    Science.gov (United States)

    Shelkovenko, T. A.; Pikuz, S. A.; Tilikin, I. N.; Mingaleev, A. R.; Atoyan, L.; Hammer, D. A.

    2018-02-01

    Electric explosions of flat Al, Ti, Ni, Cu, and Ta foils with thicknesses of 1-16 μm, widths of 1-8 mm, and lengths of 5-11 mm were studied experimentally on the BIN, XP, and COBRA high-current generators at currents of 40-1000 kA and current densities of (5-50) × 108 A/cm2. The images of the exploded foils were taken at different angles to the foil surface by using point projection radiography with an X-pinch hot spot as the radiation source, the spatial resolution and exposure time being 3 μm and 50 ps, respectively, as well by the laser probing method with a spatial resolution of 20 μm and an exposure time of 180 ps. In the course of foil explosion, rapidly expanding objects resembling the core and corona of an exploded wire were observed. It is shown that the core of the exploded foil has a complicated time-varying structure.

  13. Bubble Formation within Filaments of Melt-Processed Bi2212 wires and its strongly negative effect on the Critical Current Density

    CERN Document Server

    Kametani, F; Jiang, J; Scheuerlein, C; Malagoli, A; Di Michiel, M; Huang, Y; Miao, H; Parrell, J A; Hellstrom, E E; Larbalestier, D C

    2011-01-01

    Most studies of Bi2Sr2CaCu2Ox (Bi2212) show that the critical current density Jc is limited by the connectivity of the filaments, but what determines the connectivity is still elusive. Here we report on the role played by filament porosity in limiting Jc. By a microstructural investigation of wires quenched from the melt state, we find that porosity in the unreacted wire agglomerates into bubbles that segment the Bi2212 melt within the filaments into discrete sections. These bubbles do not disappear during subsequent processing because they are only partially filled by Bi2212 grains as the Bi2212 forms on cooling. Correlating the microstructure of quenched wires to their final, fully processed Jc values shows an inverse relation between Jc and bubble density. Bubbles are variable between conductors and perhaps from sample to sample, but they occur frequently and almost completely fill the filament diameter, so they exert a strongly variable but always negative effect on Jc. Bubbles reduce the continuous Bi221...

  14. Influence of B4C-doping and high-energy ball milling on phase formation and critical current density of (Bi,Pb)-2223 HTS

    Science.gov (United States)

    Margiani, N. G.; Mumladze, G. A.; Adamia, Z. A.; Kuzanyan, A. S.; Zhghamadze, V. V.

    2018-05-01

    In this paper, the combined effects of B4C-doping and planetary ball milling on the phase evolution, microstructure and transport properties of Bi1.7Pb0.3Sr2Ca2Cu3Oy(B4C)x HTS with x = 0 ÷ 0.125 were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), resistivity and critical current density measurements. Obtained results have shown that B4C additive leads to the strong acceleration of high-Tc phase formation and substantial enhancement in Jc. High-energy ball milling seems to produce a more homogeneous distribution of refined doped particles in the (Bi,Pb)-2223 HTS which results in an improved intergranular flux pinning and better self-field Jc performance.

  15. Critical current density of strained multilayer thin films of Nd1.83Ce0.17CuOx/YBa2Cu3O7-δ

    International Nuclear Information System (INIS)

    Gross, R.; Gupta, A.; Olsson, E.; Segmueller, A.; Koren, G.

    1990-01-01

    The superconducting transport properties of strained multilayer thin films of YBa 2 Cu 3 O 7-δ / Nd 1.83 Ce 0.17 CuO x , grown heteroepitaxially by laser ablation deposition, are reported. For individual layer thicknesses below a critical layer thickness of about 250 A, coherency strain removes the orthorhombic distortion in the YBa 2 Cu 3 O 7-δ layers and makes them twin-free. Zero-field critical current densities as high as 1.1x10 7 A/cm 2 at 77 K have been measured for the YBa 2 Cu 3 O 7-δ layers. Flux pinning energies at zero temperature and zero magnetic field in the range of 80--140 meV have been found

  16. Development of the female voxel phantom, NAOMI, and its application to calculations of induced current densities and electric fields from applied low frequency magnetic and electric fields

    International Nuclear Information System (INIS)

    Dimbylow, Peter

    2005-01-01

    This paper outlines the development of a 2 mm resolution voxel model, NAOMI (aNAtOMIcal model), designed to be representative of the average adult female. The primary medical imaging data were derived from a high-resolution MRI scan of a 1.65 m tall, 23 year old female subject with a mass of 58 kg. The model was rescaled to a height of 1.63 m and a mass of 60 kg, the dimensions of the International Commission on Radiological Protection reference adult female. There are 41 tissue types in the model. The application of NAOMI to the calculations of induced current densities and electric fields from applied low frequency magnetic and electric fields is described. Comparisons are made with values from the male voxel model, NORMAN. The calculations were extended from 50 Hz up to 10 MHz. External field reference levels are compared with the ICNIRP guidelines

  17. Improvement of Short-Circuit Current Density in Dye-Sensitized Solar Cells Using Sputtered Nanocolumnar TiO2 Compact Layer

    Directory of Open Access Journals (Sweden)

    Lung-Chien Chen

    2010-01-01

    Full Text Available The effect of a nanocolumnar TiO2 compact layer in dye-sensitized solar cells (DSSCs was examined. Such a compact layer was sputtered on a glass substrate with an indium tin oxide (ITO film using TiO2 powder as the raw material, with a thickness of ~100 nm. The compact layer improved the short-circuit current density and the efficiency of conversion of solar energy to electricity by the DSSC by 53.37% and 59.34%, yielding values of 27.33 mA/cm2 and 9.21%, respectively. The performance was attributed to the effective electron pathways in the TiO2 compact layer, which reduced the back reaction by preventing direct contact between the redox electrolyte and the conductive substrate.

  18. High-superconducting critical current densities in YBa2Cu3O7/PrBa2Cu3O7 superlattices

    International Nuclear Information System (INIS)

    Jakob, G.; Przyslupski, P.; Stoelzel, C.; Tome-Rosa, C.; Walkenhorst, A.; Schmitt, M.; Adrian, H.

    1991-01-01

    Well-ordered [(YBa 2 Cu 3 O 7 ) nY /(PrBa 2 Cu 3 O 7 ) nPr ] m superlattices with high superconducting critical temperatures were prepared by sequential reactive dc sputtering. The superconducting critical current density at 4.5 K reaches values as high as 1.1x10 7 A/cm 2 for a sample with n Y = 2 and n Pr = 1 and 3.8x10 6 A/cm 2 for n Y = 1 and n Pr = 3, indicating that the coupling of the CuO 2 layers is not necessary for high-j c values. The angular dependence j c (var-phi) is determined by the component of the magnetic field perpendicular to the a-b planes and shows that these superlattices are two-dimensional systems

  19. Achieving 12.8% Efficiency by Simultaneously Improving Open-Circuit Voltage and Short-Circuit Current Density in Tandem Organic Solar Cells.

    Science.gov (United States)

    Qin, Yunpeng; Chen, Yu; Cui, Yong; Zhang, Shaoqing; Yao, Huifeng; Huang, Jiang; Li, Wanning; Zheng, Zhong; Hou, Jianhui

    2017-06-01

    Tandem organic solar cells (TOSCs), which integrate multiple organic photovoltaic layers with complementary absorption in series, have been proved to be a strong contender in organic photovoltaic depending on their advantages in harvesting a greater part of the solar spectrum and more efficient photon utilization than traditional single-junction organic solar cells. However, simultaneously improving open circuit voltage (V oc ) and short current density (J sc ) is a still particularly tricky issue for highly efficient TOSCs. In this work, by employing the low-bandgap nonfullerene acceptor, IEICO, into the rear cell to extend absorption, and meanwhile introducing PBDD4T-2F into the front cell for improving V oc , an impressive efficiency of 12.8% has been achieved in well-designed TOSC. This result is also one of the highest efficiencies reported in state-of-the-art organic solar cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Improvement of Short-Circuit Current Density in p-Ni1−xO:Li/n-Si Heterojunction Solar Cells by Wet Chemical Etching

    Directory of Open Access Journals (Sweden)

    Feng-Hao Hsu

    2014-01-01

    Full Text Available This study confirms that the surface texturation of window layer (Al-Y codoped ZnO etched by diluted HCl effectively increases conversion efficiency of p-Ni1−xO:Li/n-Si heterojunction solar cells. The results show that the short circuit current density (Jsc of cell etched at 10 s increases about 8.5% compared to unetched cell, which also corresponds to the increase of efficient photoelectric conversion in NIR region as shown in external quantum efficiency spectra. It is attributed to the increase of light transmittance of AZOY thin films in the NIR region and the effective light path of the NIR wavelength, which results in increasing of light absorption in the base layer.

  1. Comparison between nano-diamond and carbon nanotube doping effects on critical current density and flux pinning in MgB2

    International Nuclear Information System (INIS)

    Cheng, C H; Yang, Y; Munroe, P; Zhao, Y

    2007-01-01

    Doping effects of nano-diamond and carbon nanotubes (CNTs) on critical current density of bulk MgB 2 have been studied. CNTs are found prone to be doped into the MgB 2 lattice whereas nano-diamond tends to form second-phase inclusions in the MgB 2 matrix, leading to a more significant improvement of J c (H) by doping by nano-diamond than by CNTs in MgB 2 . TEM reveals tightly packed MgB 2 nanograins (50-100 nm) with a dense distribution of diamond nanoparticles (10-20 nm) inside MgB 2 grains in nano-diamond-doped samples. Such a unique microstructure leads to a flux pinning behaviour different from that in CNTs-doped MgB 2

  2. An experimental study on the cathode humidification and evaporative cooling of polymer electrolyte membrane fuel cells using direct water injection method at high current densities

    International Nuclear Information System (INIS)

    Hwang, Seong Hoon; Kim, Min Soo

    2016-01-01

    Highlights: • Proposal of a cathode humidification and evaporative cooling system for PEM fuel cells. • An external-mixing air-assist atomizer is used to produce a very fine water spray. • The system is effective in both cathode humidification and stack cooling. • Increased water flow rate improves stack performance and evaporative cooling capacity. • At a given water flow rate, lower stack temperatures cause greater humidification effect. - Abstract: Humidification and cooling are critical issues in enhancing the efficiency and durability of polymer electrolyte membrane fuel cells (PEMFCs). However, existing humidifiers and cooling systems have the disadvantage that they must be quite large to achieve adequate PEMFC performance. In this study, to eliminate the need for a bulky humidifier and to lighten the cooling load of PEMFCs, a cathode humidification and evaporative cooling system using an external-mixing air-assist atomizer was developed and its performance was investigated. The atomization performance of the nozzle was analyzed experimentally under various operating conditions with minimal changes in the system design. Experiments with a five-cell PEMFC stack with an active area of 250 cm 2 were carried out to analyze the effects of various parameters (such as the operating temperature, current density, and water injection flow rate) on the evaporation of injected water for humidification and cooling performances. The experimental results demonstrate that the direct water injection method proposed in this study is quite effective in cathode humidification and stack cooling in PEM fuel cells at high current densities. The stack performance was improved by humidification effect and the coolant temperature at the stack outlet decreased by evaporative cooling effect.

  3. Mechanisms Responsible for the Trophic Effect of Beta-Adrenoceptors on the Ito Current Density in Type 1 Diabetic Rat Cardiomyocytes

    Directory of Open Access Journals (Sweden)

    Raúl Setién

    2013-01-01

    Full Text Available Background/Aims: In diabetic ventricular myocytes, transient outward potassium current (Ito amplitude is severely reduced because of the impaired catecholamine release that characterizes diabetic autonomic neuropathy. Sympathetic nervous system exhibits a trophic effect on Ito since incubation of myocytes with noradrenaline restores current amplitude via beta-adrenoceptor (βAR stimulation. Here, we investigate the intracellular signalling pathway though which incubation of diabetic cardiomyocytes with the βAR agonist isoproterenol recovers Ito amplitude to normal values. Methods: Experiments were performed in ventricular myocytes isolated from streptozotocin-diabetic rats. Ito current was recorded by using the patch-clamp technique. Kv4 channel expression was determined by immunofluorescence. Protein-protein interaction was determined by coimmunoprecipitation. Results: Stimulation of βAR activates first a Gαs protein, adenylyl cyclase and Protein Kinase A. PKA-phosphorylated receptor then switches to the Gαi protein. This leads to the activation of the βAR-Kinase-1 and further receptor phosphorylation and arrestin dependent internalization. The internalized receptor-arrestin complex recruits and activates cSrc and the MAPK cascade, where Ras, c-Raf1 and finally ERK1/2 mediate the increase in Kv4.2 and Kv4.3 protein abundance in the plasma membrane. Conclusion: β2AR stimulation activates a Gαs and Gαi protein dependent pathway where the ERK1/2 modulates the Ito current amplitude and the density of the Kv4.2 and Kv4.2 channels in the plasma membrane upon sympathetic stimulation in diabetic heart.

  4. A combined field and numerical approach to understanding dilute pyroclastic density current dynamics and hazard potential: Auckland Volcanic Field, New Zealand

    Science.gov (United States)

    Brand, Brittany D.; Gravley, Darren M.; Clarke, Amanda B.; Lindsay, Jan M.; Bloomberg, Simon H.; Agustin-Flores, Javier; Németh, Károly

    2014-04-01

    The most dangerous and deadly hazards associated with phreatomagmatic eruptions in the Auckland Volcanic Field (AVF; Auckland, New Zealand) are those related to volcanic base surges - dilute, ground-hugging, particle laden currents with dynamic pressures capable of severe to complete structural damage. We use the well-exposed base surge deposits of the Maungataketake tuff ring (Manukau coast, Auckland), to reconstruct flow dynamics and destructive potential of base surges produced during the eruption. The initial base surge(s) snapped trees up to 0.5 m in diameter near their base as far as 0.7-0.9 km from the vent. Beyond this distance the trees were encapsulated and buried by the surge in growth position. Using the tree diameter and yield strength of the wood we calculate that dynamic pressures (Pdyn) in excess of 12-35 kPa are necessary to cause the observed damage. Next we develop a quantitative model for flow of and sedimentation from a radially-spreading, dilute pyroclastic density currents (PDCs) to determine the damage potential of the base surges produced during the early phases of the eruption and explore the implications of this potential on future eruptions in the region. We find that initial conditions with velocities on the order of 65 m s- 1, bulk density of 38 kg m- 3 and initial, near-vent current thicknesses of 60 m reproduce the field-based Pdyn estimates and runout distances. A sensitivity analysis revealed that lower initial bulk densities result in shorter run-out distances, more rapid deceleration of the current and lower dynamic pressures. Initial velocity does not have a strong influence on run-out distance, although higher initial velocity and slope slightly decrease runout distance due to higher rates of atmospheric entrainment. Using this model we determine that for base surges with runout distances of up to 4 km, complete destruction can be expected within 0.5 km from the vent, moderate destruction can be expected up to 2 km, but much

  5. Improving the current density Jsc and efficiency enhancement of polymer solar cells P3HT:PCBM via nanorods ZnO

    Directory of Open Access Journals (Sweden)

    lida ahmadkhani

    2017-09-01

    Full Text Available Hybrid solar cells combine organic and inorganic materials with the aim of utilizing the low cost cell production of organic photovoltaics (OPV as well as obtaining other advantages, such as tuneable absorption spectra, from the inorganic component. Whilst hybrid solar cells have the potential to achieve high power conversion efficiencies (PCE, currently obtained efficiencies are quite low. The design of the inorganic material used as the electron acceptor in hybrid solar cells, particularly the electronic structure, is crucial to the performance of the device. Hence, this paper, nanorods ZnO have been synthesized by using zinc acetate dihydrate and polyvinylpyrrolidone (PVP as starting materials. The calcined powders in air at 600 oC for 1 hour have been characterized by XRD, TEM and SEM. So, with nanorods ZnO as electrode in inverted polymer solar cells,the average performance of devices with open circuit voltage ,short circuit current density, fill factor,and power conversion efficiency are measured are measured as 0.61V, 8.7 mA/cm2, 0.58 and 3.01%, respectively. The results indicate that the structure of ZnO nanorod can effectively serve as an electrode for inverted polymer solar cells.

  6. Dynamics of 120 and 20 kV plasma focus devices with respect to density and current distribution, and neutron and X-ray emission

    International Nuclear Information System (INIS)

    Decker, G.; Nahrath, B.; Oppenlaender, T.; Pross, G.; Rueckle, B.; Schmidt, H.; Shakhatre, M.; Trunk, M.

    1977-01-01

    The experiments had two goals: (1) Better understanding of the dynamics and neutron production of the focus phase and (2) improved scaling of the neutron yield by operating a high-voltage focus. For the first goal, experiments with a 30-kJ/16-kV plasma focus of the Mather type (NESSI) were performed. The simultaneously applied diagnostics include interferometry, X-ray photography with channel plates, magnetic probes and scintillator/photomultiplier detectors for measuring hard X-ray and neutron emission. In the established chronology one can distinguish five phases in the development of the plasma focus: A compression phase is followed by a short (8 ns) very dense phase, where the density peaks at a minimum radius (t=0, authors' chronology). The plasma cylinder expands to a relatively long-lasting (30 to 70 ns) quiescent phase before instabilities occur. This short unstable phase is followed by a decay phase during which the neutron emission peaks. Important correlations between the plasma parameters and the neutron emission are discussed. Secondly, on the assumption that the neutron yield scales with a high power of the current, it was concluded that a high-voltage focus could result in higher neutron yield as compared with a lower voltage device of the same energy. The proper adjustments of the discharge parameters necessary due to the very short current risetime were investigated. (author)

  7. Dynamics of 120 and 20 kV plasma focus devices with respect to density and current distribution, neutron and X-ray emission

    International Nuclear Information System (INIS)

    Decker, G.; Nahrath, B.; Oppenlaender, T.; Pross, G.; Rueckle, B.; Schmidt, H.; Shakhatre, M.; Trunk, M.

    1976-01-01

    Our experiments have aimed at two goals: 1) better understanding of the dynamics and neutron production of the focus phase and 2) improved scaling of the neutron yield by operating a high voltage focus. 1) For the first goal, experiments with a 30 kJ/ 16 kV plasma focus of the Mather type (NESSI) were performed. The simultaneously applied diagnostics include interferometry, X-ray photography with channel plates, magnetic probes and neutron emission. In the established chronology we can distinguish 5 phases in the development of the plasma focus: a compression phase is followed by a short (8 ns) very dense phase, where the density peaks at a minimum radius (t = 0 in our chronology). The plasma cylinder expands to a relatively long lasting (30 to 70 ns) quiescent phase before instabilities occur. This short unstable phase is followed by a decay phase during which the neutron emission peaks. Important correlations between the plasma parameters and the neutron emission are discussed. 2) Under the assumption that the neutron yield scales with a high power of the current, we concluded that a high voltage focus could result in higher neutron yield as compared with a lower voltage device of the same energy. The proper adjustments of the discharge parameters necessary due to the very short current risetime have been investigated. (orig.) [de

  8. Cooperative doping effects of Ti and nano-SiC on transport critical current density and grain connectivity of in situ MgB{sub 2} tapes

    Energy Technology Data Exchange (ETDEWEB)

    Pan, X.F., E-mail: PAN.Xifeng@nims.go.jp [National Institute for Materials Science, Superconducting Materials Research Center, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047 (Japan)] [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Southwest Jiaotong University, Chengdu 610031 (China); Matsumoto, A.; Kumakura, H. [National Institute for Materials Science, Superconducting Materials Research Center, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Cheng, C.H.; Zhao, Y. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Southwest Jiaotong University, Chengdu 610031 (China)] [School of Materials Science and Engineering, University of New South Wales, Sydney 2052, NSW (Australia)

    2011-11-15

    We studied the cooperative doping effects of Ti and nano-SiC on transport J{sub c} and grain connectivity of MgB{sub 2} tape. Ti doping significantly weakens the current dependence of T{sub c} of MgB{sub 2} tapes at self-field, and does not change T{sub c} or slightly increases T{sub c}. Further Ti adding can enhance in-field J{sub c} performance of SiC doped MgB{sub 2} tapes by a factor of 50-100% at 4.2 K and 10 T. Ti addition improves the J{sub c} performance of undoped and SiC doped MgB{sub 2} by modifying their grains connection. By now, nano-SiC powder (20-30 nm) is still the most effective additive for improving upper critical field and critical current density of MgB{sub 2}-based superconducting materials. However, some decomposed carbon aggregates at grain boundaries and results in serious weak-links of MgB{sub 2} grains, and these weak-links limit the further improvement of critical current density, J{sub c} of MgB{sub 2}, especially at lower fields. Ti doping is reported to increase the compactness of MgB{sub 2}, and modify its intergranular coupling by forming ultrathin TiB{sub 2} layer at grain boundaries. In this work, we studied the cooperative doping effects of Ti and nano-SiC on transport J{sub c} and grain connectivity of MgB{sub 2} and the possibility to improve transport J{sub c} of SiC doped MgB{sub 2} by introducing Ti additive. The results suggest the Ti addition can obviously improve J{sub c} of MgB{sub 2} at lower fields and also enhance the J{sub c} of SiC doped MgB{sub 2} by improving their grain connectivity which shows serious intergranular weak-links.

  9. Measurement of critical current density of YBCO film by a mutual inductive method using a drive coil with a sharp iron core

    International Nuclear Information System (INIS)

    Yamada, H.; Bitoh, A.; Mitsuno, Y.; Imai, I.; Nomura, K.; Kanayama, K.; Nakagawa, S.; Mawatari, Y.; Yamasaki, H.

    2005-01-01

    Recent developments in high-temperature superconductors have facilitated the production of high critical current and large-area films by the PLD method or MOD method. Nondestructive measurement techniques for high quality films are of great importance to estimate superconducting properties, such as the critical current density, J C . The inductive method using the third-harmonic voltage component, V 3 , is a promising technique for the measurement of the properties of J C . On inductive determination of J C for high-J C thin films and thicker films (thickness d ≥ 0.1 mm), the drive coil must generate a magnetic field sufficiently large to break the complete field shielding of the film. Therefore, we investigated a mutual inductance technique using a drive coil with a sharp ferromagnetic core for investigation of the J C of the PLD-YBCO film. As a result, an abrupt nonlinear increase in the voltage across the pick-up coil was detected after magnetic full penetration of the film, and the threshold of the drive current I th was suppressed to 0.23-0.28 times as compared with that measured by the inductive method using the third-harmonic voltage, V 3 . FEM analysis indicated the diameter of the excitation field region to be 0.6 mm in the case of a 0.4 mm φ iron core. The E-J characters measured by the mutual inductive method as a function of frequency agreed well with those measured by the inductive method using V 3

  10. Modeling plant density and ponding water effects on flooded rice evapotranspiration and crop coefficients: critical discussion about the concepts used in current methods

    Science.gov (United States)

    Aschonitis, Vassilis; Diamantopoulou, Maria; Papamichail, Dimitris

    2018-05-01

    The aim of the study is to propose new modeling approaches for daily estimations of crop coefficient K c for flooded rice ( Oryza sativa L., ssp. indica) under various plant densities. Non-linear regression (NLR) and artificial neural networks (ANN) were used to predict K c based on leaf area index LAI, crop height, wind speed, water albedo, and ponding water depth. Two years of evapotranspiration ET c measurements from lysimeters located in a Mediterranean environment were used in this study. The NLR approach combines bootstrapping and Bayesian sensitivity analysis based on a semi-empirical formula. This approach provided significant information about the hidden role of the same predictor variables in the Levenberg-Marquardt ANN approach, which improved K c predictions. Relationships of production versus ET c were also built and verified by data obtained from Australia. The results of the study showed that the daily K c values, under extremely high plant densities (e.g., for LAI max > 10), can reach extremely high values ( K c > 3) during the reproductive stage. Justifications given in the discussion question both the K c values given by FAO and the energy budget approaches, which assume that ET c cannot exceed a specific threshold defined by the net radiation. These approaches can no longer explain the continuous increase of global rice yields (currently are more than double in comparison to the 1960s) due to the improvement of cultivars and agriculture intensification. The study suggests that the safest method to verify predefined or modeled K c values is through preconstructed relationships of production versus ET c using field measurements.

  11. Visualization of the current density in Josephson junctions with 0- and {pi}-facets; Visualisierung der Stromverteilung in Josephsonkontakten mit 0- und {pi}-Facetten

    Energy Technology Data Exchange (ETDEWEB)

    Guerlich, Christian

    2010-05-11

    With Low-Temperature-Electron-Microscopy (LTSEM) it is possible to analyse the transport properties of solids at low temperatures. In particular it is possible to image the supercurrent density j{sub s} in Josephson junctions. This was demonstrated by comparing TTREM-images with calculated values for j{sub s}. In this thesis ramp-type Nd{sub 2-x}Ce{sub x}CuO{sub 4-y}/Nb-Josephson-junctions (NCCO/Nb) and Josephson junctions with a ferromagnetic interlayer Nb/Al-Al{sub 2}O{sub 3}/NiCu/Nb, so-called SIFS (superconductor-insulator-ferromagnet-superconductor) Josephson junctions were studied.It was demonstrated that LTSEM provides direct imaging of the sign change of the order parameter in superconductors with d{sub x{sup 2}-y{sup 2}}-symmetry. This was a controversial issue over the last decade. A step like variation in the thickness of the F-layer allows the fabrication of linear and annular Josephson junctions with different numbers of 0 and {pi} facets. With the LTSEM 0-, {pi}-, 0-{pi}-, 0-{pi}-0-, 0/2-{pi}-0/2-, 20 x (0-{pi})- as well as square-shaped-, circular- and annular-Josephson-junctions were studied. It was demonstrated, that these junctions are of good quality and have critical current densities up to 42 A/cm{sup 2} at T=4.2 K, which is a record value for SIFS junctions with a NiCu F-layer so far. By comparing the measurements with simulations a first indication of a semifluxon at the 0-{pi}-boundary was found. (orig.)

  12. Large critical current densities and pinning forces in CSD-grown superconducting GdBa2Cu3O7-x -BaHfO3 nanocomposite films

    Science.gov (United States)

    Cayado, Pablo; Erbe, Manuela; Kauffmann-Weiss, Sandra; Bühler, Carl; Jung, Alexandra; Hänisch, Jens; Holzapfel, Bernhard

    2017-09-01

    GdBa2Cu3O7-x -BaHfO3 (GdBCO-BHO) nanocomposite (NC) films containing 12 mol% BHO nanoparticles were prepared by chemical solution deposition (CSD) following the TFA route on SrTiO3 (STO) single crystals and buffered metallic tapes supplied by two different companies: Deutsche Nanoschicht GmbH and SuperOx. We optimized the preparation of our GdBCO-BHO solutions with acetylacetone making the film synthesis very robust and reproducible, and obtained 220 nm films with excellent superconducting properties. We show the structural, morphological and superconducting properties of the films after a careful optimization of the processing parameters (growth temperature, oxygen partial pressure and heating ramp). The films reach critical temperatures (T c) of ˜94 K, self-field critical current densities (J c) of >7 MA cm- 2 and maximum pinning force densities (F p) of ˜16 GN m- 3 at 77 K on STO and T c of ˜94.5 K and J c > 1.5 MA cm- 2 on buffered metallic tapes. The transport properties under applied magnetic fields are significantly improved with respect to the pristine GdBCO films. The GdBCO-BHO NC films on STO present epitaxial c-axis orientation with excellent out-of-plane and in-plane texture. The films are, in general, very dense with a low amount of pores and only superficial indentations. On the other hand, we present, for the first time, a systematic study of CSD-grown GdBCO-BHO NC films on buffered metallic tapes. We have used the optimized growth conditions for STO as a reference and identified some limitations on the film synthesis that should be overcome for further improvement of the films’ superconducting properties.

  13. Totally solution-processed CuInS2 solar cells based on chloride inks: reduced metastable phases and improved current density

    Science.gov (United States)

    Dehghani, Mehdi; Behjat, Abbas; Tajabadi, Fariba; Taghavinia, Nima

    2015-03-01

    Planar superstrate CuInS2 (CIS) solar cell devices are fabricated using totally solution-processed deposition methods. These Cd-free devices are structured by FTO/TiO2/In2S3/CIS/carbon, where TiO2 and In2S3 are deposited by spray pyrolysis, and a CIS film is deposited using spin-coating followed by annealing at 250 °C. The pasted carbon layer is utilized as the anode. No further sulfurization or selenization is employed. The Cu/In ratio in the ink is found as a critical factor affecting the morphology and crystallinity of the film as well as the photovoltaic performance of the device. An optimum Cu/In = 1.05 results in large-grain films with sharp diffraction peaks and, subsequently, optimal series resistance and shunt conductance. It is also found that the chloride-based ink results in CIS films with considerably reduced metastable phases, compared to the conventional acetate-based inks. A current density of 23.6 mA cm-2 is obtained for the best devices, leading to a conversion efficiency of 4.1%.

  14. Heat treatment control of Bi-2212 coils: I. Unravelling the complex dependence of the critical current density of Bi-2212 wires on heat treatment

    Science.gov (United States)

    Shen, Tengming; Li, Pei; Ye, Liyang

    2018-01-01

    A robust and reliable heat treatment is crucial for developing superconducting magnets from several superconductors especially Bi-2212. An improper heat treatment may significantly reduce the critical current density Jc of a Bi-2212 superconducting coil, even to zero, since the Jc of Bi-2212 wires is sensitive to parameters of its heat treatment (partial melt processing). To provide an essential database for heat treating Bi-2212 coils, the dependence of Jc on heat treatment is studied systematically in 11 industrial Bi-2212 wires, revealing several common traits shared between these wires and outlier behaviors. The dependence of the Jc of Bi-2212 on heat treatment is rather complex, with many processing parameters affecting Jc, including the peak processing temperature Tp, the time at the peak temperature tp, the time in the melt tmelt, the rate at which Bi-2212 melt is initially cooled CR1, the rate at which the solidification of Bi-2212 melt occurs CR2, and the temperature Tq at which the cooling rate switches from CR1 to CR2. The role of these parameters is analyzed and clarified, in the perspective of heat treating a coil. Practical advices on heat treatment design are given. The ability of a Bi-2212 coil to follow the prescribed recipe decreases with increasing coil sizes. The size of a coil that can be properly heat treated is determined.

  15. Negative effects of crystalline-SiC doping on the critical current density in Ti-sheathed MgB2(SiC)y superconducting wires

    International Nuclear Information System (INIS)

    Liang, G; Fang, H; Luo, Z P; Hoyt, C; Yen, F; Guchhait, S; Lv, B; Markert, J T

    2007-01-01

    Ti-sheathed MgB 2 wires doped with nanosize crystalline-SiC up to a concentration of 15 wt% SiC have been fabricated, and the effects of the SiC doping on the critical current density (J c ) and other superconducting properties studied. In contrast with the previously reported results that nano-SiC doping with a doping range below 16 wt% usually enhances J c , particularly at higher fields, our measurements show that SiC doping decreases J c over almost the whole field range from 0 to 7.3 T at all temperatures. Furthermore, it is found that the degradation of J c becomes stronger at higher SiC doping levels, which is also in sharp contrast with the reported results that J c is usually optimized at doping levels near 10 wt% SiC. Our results indicate that these negative effects on J c could be attributed to the absence of significant effective pinning centres (mainly Mg 2 Si) due to the high chemical stability of the crystalline-SiC particles

  16. Effects of clamping force on the water transport and performance of a PEM (proton electrolyte membrane) fuel cell with relative humidity and current density

    International Nuclear Information System (INIS)

    Cha, Dowon; Ahn, Jae Hwan; Kim, Hyung Soon; Kim, Yongchan

    2015-01-01

    The clamping force should be applied to a proton electrolyte membrane (PEM) fuel cell due to its structural characteristics. The clamping force affects the ohmic and mass transport resistances in the PEM fuel cell. In this study, the effects of the clamping force on the water transport and performance characteristics of a PEM fuel cell are experimentally investigated with variations in the relative humidity and current density. The water transport characteristics were analyzed by calculating the net drag coefficient. The ohmic resistance decreased with the increase in the clamping force due to the reduced contact resistance and more even membrane hydration. However, the mass transport resistance increased with the increase in the clamping force due to the gas diffusion layer compression. The net drag coefficient decreased with the increase in the clamping force due to high water back-diffusion. Additionally, the relationship between the total resistance and the net drag coefficient was investigated. - Highlights: • Effects of clamping force on the performance of a PEM fuel cell are investigated. • Water transport characteristics are analyzed using net drag coefficient. • Ohmic resistance decreased with clamping force, but mass transport resistance increased. • Net drag coefficient decreased with the increase in clamping force. • Total resistance was significantly degraded for a net drag coefficient below 0.2.

  17. High current density GaAs/Si rectifying heterojunction by defect free Epitaxial Lateral overgrowth on Tunnel Oxide from nano-seed.

    Science.gov (United States)

    Renard, Charles; Molière, Timothée; Cherkashin, Nikolay; Alvarez, José; Vincent, Laetitia; Jaffré, Alexandre; Hallais, Géraldine; Connolly, James Patrick; Mencaraglia, Denis; Bouchier, Daniel

    2016-05-04

    Interest in the heteroepitaxy of GaAs on Si has never failed in the last years due to the potential for monolithic integration of GaAs-based devices with Si integrated circuits. But in spite of this effort, devices fabricated from them still use homo-epitaxy only. Here we present an epitaxial technique based on the epitaxial lateral overgrowth of micrometer scale GaAs crystals on a thin SiO2 layer from nanoscale Si seeds. This method permits the integration of high quality and defect-free crystalline GaAs on Si substrate and provides active GaAs/Si heterojunctions with efficient carrier transport through the thin SiO2 layer. The nucleation from small width openings avoids the emission of misfit dislocations and the formation of antiphase domains. With this method, we have experimentally demonstrated for the first time a monolithically integrated GaAs/Si diode with high current densities of 10 kA.cm(-2) for a forward bias of 3.7 V. This epitaxial technique paves the way to hybrid III-V/Si devices that are free from lattice-matching restrictions, and where silicon not only behaves as a substrate but also as an active medium.

  18. Lateral critical current density distributions degraded near edges of coated conductors through cutting processes and their influence on ac loss characteristics of power transmission cables

    International Nuclear Information System (INIS)

    Amemiya, N.; Li, Q.; Nishino, R.; Takeuchi, K.; Nakamura, T.; Ohmatsu, K.; Ohya, M.; Maruyama, O.; Okuma, T.; Izumi, T.

    2011-01-01

    A wide coated conductor is often cut into narrow ones in fabrication process. We measured the lateral J c distributions of coated conductors cut by a mechanical slitter or a laser. The J c is degraded at 0.15-0.25 mm from the edges of coated conductors through cutting process. The ac losses of superconducting cables are affected by the degraded J c near the edges of coated conductors. It is more marked in cables with fewer layers or carrying larger I t /I c . The critical current density (J c ) near the edges of coated conductor could impact the ac loss characteristics of the cables comprising coated conductors. A wide coated conductor is often cut into narrower coated conductors in fabrication processes, and the J c might degrade near the edges of coated conductors through the cutting process. This possible degradation of J c could depend on cutting technology. Lateral J c distributions of coated conductors cut by using a mechanical slitter as well as a laser were measured by the magnetic knife method. The measured coated conductors are fabricated by PLD process on clad type textured-metal substrates with reduced magnetism. Based on the degradation of J c near the edges of coated conductors which was determined experimentally, ac losses of multi-layer cables as well as mono-layer cables were calculated numerically to evaluate the impact of the J c degradation near the edges of coated conductors on the their ac loss characteristics.

  19. Direct observation of in-plane anisotropy of the superconducting critical current density in Ba (Fe1-xCox) 2As2 crystals

    Science.gov (United States)

    Hecher, J.; Ishida, S.; Song, D.; Ogino, H.; Iyo, A.; Eisaki, H.; Nakajima, M.; Kagerbauer, D.; Eisterer, M.

    2018-01-01

    The phase diagram of iron-based superconductors exhibits structural transitions, electronic nematicity, and magnetic ordering, which are often accompanied by an electronic in-plane anisotropy and a sharp maximum of the superconducting critical current density (Jc) near the phase boundary of the tetragonal and the antiferromagnetic-orthorhombic phase. We utilized scanning Hall-probe microscopy to visualize the Jc of twinned and detwinned Ba (Fe1-xCox) 2As2 (x =5 %-8 % ) crystals to compare the electronic normal state properties with superconducting properties. We find that the electronic in-plane anisotropy continues into the superconducting state. The observed correlation between the electronic and the Jc anisotropy agrees qualitatively with basic models, however, the Jc anisotropy is larger than predicted from the resistivity data. Furthermore, our measurements show that the maximum of Jc at the phase boundary does not vanish when the crystals are detwinned. This shows that twin boundaries are not responsible for the large Jc, suggesting an exotic pinning mechanism.

  20. Is multidetector CT-based bone mineral density and quantitative bone microstructure assessment at the spine still feasible using ultra-low tube current and sparse sampling?

    Energy Technology Data Exchange (ETDEWEB)

    Mei, Kai; Kopp, Felix K.; Schwaiger, Benedikt J.; Gersing, Alexandra S.; Sauter, Andreas; Muenzel, Daniela; Rummeny, Ernst J. [Klinikum rechts der Isar, Technische Universitaet Muenchen, Department of Diagnostic and Interventional Radiology, Munich (Germany); Bippus, Rolf [Research Laboratories, Philips GmbH Innovative Technologies, Hamburg (Germany); Koehler, Thomas [Research Laboratories, Philips GmbH Innovative Technologies, Hamburg (Germany); Technische Universitaet Muenchen, TUM Institute for Advanced Studies, Garching (Germany); Fehringer, Andreas [Technische Universitaet Muenchen, Lehrstuhl fuer Biomedizinische Physik, Garching (Germany); Pfeiffer, Franz [Klinikum rechts der Isar, Technische Universitaet Muenchen, Department of Diagnostic and Interventional Radiology, Munich (Germany); Technische Universitaet Muenchen, TUM Institute for Advanced Studies, Garching (Germany); Technische Universitaet Muenchen, Lehrstuhl fuer Biomedizinische Physik, Garching (Germany); Kirschke, Jan S. [Klinikum rechts der Isar, Technische Universitaet Muenchen, Section of Diagnostic and Interventional Neuroradiology, Munich (Germany); Noel, Peter B. [Klinikum rechts der Isar, Technische Universitaet Muenchen, Department of Diagnostic and Interventional Radiology, Munich (Germany); Technische Universitaet Muenchen, Lehrstuhl fuer Biomedizinische Physik, Garching (Germany); Baum, Thomas [Klinikum rechts der Isar, Technische Universitaet Muenchen, Department of Diagnostic and Interventional Radiology, Munich (Germany); Klinikum rechts der Isar, Technische Universitaet Muenchen, Section of Diagnostic and Interventional Neuroradiology, Munich (Germany)

    2017-12-15

    Osteoporosis diagnosis using multidetector CT (MDCT) is limited to relatively high radiation exposure. We investigated the effect of simulated ultra-low-dose protocols on in-vivo bone mineral density (BMD) and quantitative trabecular bone assessment. Institutional review board approval was obtained. Twelve subjects with osteoporotic vertebral fractures and 12 age- and gender-matched controls undergoing routine thoracic and abdominal MDCT were included (average effective dose: 10 mSv). Ultra-low radiation examinations were achieved by simulating lower tube currents and sparse samplings at 50%, 25% and 10% of the original dose. BMD and trabecular bone parameters were extracted in T10-L5. Except for BMD measurements in sparse sampling data, absolute values of all parameters derived from ultra-low-dose data were significantly different from those derived from original dose images (p<0.05). BMD, apparent bone fraction and trabecular thickness were still consistently lower in subjects with than in those without fractures (p<0.05). In ultra-low-dose scans, BMD and microstructure parameters were able to differentiate subjects with and without vertebral fractures, suggesting osteoporosis diagnosis is feasible. However, absolute values differed from original values. BMD from sparse sampling appeared to be more robust. This dose-dependency of parameters should be considered for future clinical use. (orig.)

  1. Lateral entorhinal, perirhinal, and amygdala-entorhinal transition projections to hippocampal CA1 and dentate gyrus in the rat: a current source density study.

    Science.gov (United States)

    Canning, K J; Leung, L S

    1997-01-01

    In urethane-anesthetized rats, cortical regions which provide distal dendritic excitation of the dentate gyrus and CA1 of the dorsal hippocampus were studied using current source density analysis. Electrical stimulation of the lateral perforant path (LPP) in the lateral angular bundle, lateral entorhinal cortex (LEC), and amygdala-entorhinal transition (TR) resulted in a current sink in the outer molecular layer of the dentate gyrus accompanied by proximal sources; this sink-source pattern is distinctly different from the source-sink-source pattern evoked by medial perforant path stimulation. The progressive decrease of the sink latency following stimulation of the TR, LEC, and LPP (11.6, 7.8, and 3.6 ms, respectively, at the dorsal blade of the dentate gyrus) suggests a possible sequence of orthodromic activation of these structures. Stimulation of the LEC or TR (collectively termed cortical stimulation) differed from LPP (fiber) stimulation. A low threshold and small chronaxie were characteristic of fiber rather than cortical stimulation. In addition, cortical stimulation, possibly through excitation of intracortical circuits, evoked larger paired-pulse facilitation of the excitatory postsynaptic currents in dentate gyrus and more symmetric excitation of the dorsal and ventral blades of the dentate gyrus as compared to fiber stimulation. Stimulation of the perirhinal cortex (PRh) evoked a short-latency sink in the outer molecular layer of the dentate gyrus with no paired-pulse facilitation, similar to fiber stimulation. A distal dendritic CA1 sink was observed after LPP but not after PRh stimulation. An ibotenic acid injection that lesioned almost all the cells in the perirhinal cortex confirmed the hypothesis that PRh stimulation activated fibers of passage, perhaps in the rostral ventrolateral angular bundle. We conclude that the PRh does not provide a significant excitatory input to the DG or CA1. We have found distinct dendritic excitation of the dentate

  2. From hot rocks to glowing avalanches: Numerical modelling of gravity-induced pyroclastic density currents and hazard maps at the Stromboli volcano (Italy)

    Science.gov (United States)

    Salvatici, Teresa; Di Roberto, Alessio; Di Traglia, Federico; Bisson, Marina; Morelli, Stefano; Fidolini, Francesco; Bertagnini, Antonella; Pompilio, Massimo; Hungr, Oldrich; Casagli, Nicola

    2016-11-01

    Gravity-induced pyroclastic density currents (PDCs) can be produced by the collapse of volcanic crater rims or due to the gravitational instability of materials deposited in proximal areas during explosive activity. These types of PDCs, which are also known as ;glowing avalanches;, have been directly observed, and their deposits have been widely identified on the flanks of several volcanoes that are fed by mafic to intermediate magmas. In this research, the suitability of landslide numerical models for simulating gravity-induced PDCs to provide hazard assessments was tested. This work also presents the results of a back-analysis of three events that occurred in 1906, 1930 and 1944 at the Stromboli volcano by applying a depth-averaged 3D numerical code named DAN-3D. The model assumes a frictional internal rheology and a variable basal rheology (i.e., frictional, Voellmy and plastic). The numerical modelling was able to reproduce the gravity-induced PDCs' extension and deposit thicknesses to an order of magnitude of that reported in the literature. The best results when compared with field data were obtained using a Voellmy model with a frictional coefficient of f = 0.19 and a turbulence parameter ξ = 1000 m s- 1. The results highlight the suitability of this numerical code, which is generally used for landslides, to reproduce the destructive potential of these events in volcanic environments and to obtain information on hazards connected with explosive-related, mass-wasting phenomena in Stromboli Island and at volcanic systems characterized by similar phenomena.

  3. Experimental densities and surface tension and models generating the best-current-knowledge values of them for members of 1-Cn-3-methylimidazolium bromide homologous series

    Czech Academy of Sciences Publication Activity Database

    Klomfar, Jaroslav; Součková, Monika; Pátek, Jaroslav

    2018-01-01

    Roč. 118, March (2018), s. 225-234 ISSN 0021-9614 R&D Projects: GA ČR GA13-00145S Institutional support: RVO:61388998 Keywords : 1-Alkyl-3-methylimidazolium-based cation * bromide anion * density- temperature relation * density- temperature relation * recommended property values Subject RIV: BJ - Thermodynamics OBOR OECD: Thermodynamics Impact factor: 2.726, year: 2016

  4. Thermal interactions of the AD79 Vesuvius pyroclastic density currents and their deposits at Villa dei Papiri (Herculaneum archaeological site, Italy)

    Science.gov (United States)

    Giordano, G.; Zanella, E.; Trolese, M.; Baffioni, C.; Vona, A.; Caricchi, C.; De Benedetti, A. A.; Corrado, S.; Romano, C.; Sulpizio, R.; Geshi, N.

    2018-05-01

    Pyroclastic density currents (PDCs) can have devastating impacts on urban settlements, due to their dynamic pressure and high temperatures. Our degree of understanding of the interplay between these hot currents and the affected infrastructures is thus fundamental not only to implement our strategies for risk reduction, but also to better understand PDC dynamics. We studied the temperature of emplacement of PDC deposits that destroyed and buried the Villa dei Papiri, an aristocratic Roman edifice located just outside the Herculaneum city, during the AD79 plinian eruption of Mt Vesuvius (Italy) by using the thermal remanent magnetization of embedded lithic clasts. The PDC deposits around and inside the Villa show substantial internal thermal disequilibrium. In areas affected by convective mixing with surface water or with collapsed walls, temperatures average at around 270 °C (min 190 °C, max 300 °C). Where the deposits show no evidence of mixing with external material, the temperature is much higher, averaging at 350 °C (min 300 °C; max 440 °C). Numerical simulations and comparison with temperatures retrieved at the very same sites from the reflectance of charcoal fragments indicate that such thermal disequilibrium can be maintained inside the PDC deposit for time-scales well over 24 hours, i.e. the acquisition time of deposit temperatures for common proxies. We reconstructed in detail the history of the progressive destruction and burial of Villa dei Papiri and infer that the rather homogeneous highest deposit temperatures (average 350 °C) were carried by the ash-sized fraction in thermal equilibrium with the fluid phase of the incoming PDCs. These temperatures can be lowered on short time- (less than hours) and length-scales (meters to tens of meters) only where convective mixing with external materials or fluids occurs. By contrast, where the Villa walls remained standing the thermal exchange was only conductive and very slow, i.e. negligible at 50 cm

  5. Three-Dimensional Grain Shape-Fabric from Unconsolidated Pyroclastic Density Current Deposits: Implications for Extracting Flow Direction and Insights on Rheology

    Science.gov (United States)

    Hawkins, T. T.; Brand, B. D.; Sarrochi, D.; Pollock, N.

    2016-12-01

    One of the greatest challenges volcanologists face is the ability to extrapolate information about eruption dynamics and emplacement conditions from deposits. Pyroclastic density current (PDC) deposits are particularly challenging given the wide range of initial current conditions, (e.g., granular, fluidized, concentrated, dilute), and rapid flow transformations due to interaction with evolving topography. Analysis of particle shape-fabric can be used to determine flow direction, and may help to understand the rheological characteristics of the flows. However, extracting shape-fabric information from outcrop (2D) apparent fabric is limited, especially when outcrop exposure is incomplete or lacks context. To better understand and quantify the complex flow dynamics reflected in PDC deposits, we study the complete shape-fabric data in 3D using oriented samples. In the field, the prospective sample is carved from the unconsolidated deposit in blocks, the dimensions of which depend on the average clast size in the sample. The sample is saturated in situ with a water-based sodium silicate solution, then wrapped in plaster-soaked gauze to form a protective cast. The orientation of the sample is recorded on the block faces. The samples dry for five days and are then extracted in intact blocks. In the lab, the sample is vacuum impregnated with sodium silicate and cured in an oven. The fully lithified sample is first cut along the plan view to identify orientations of the long axes of the grains (flow direction), and then cut in the two plains perpendicular to grain elongation. 3D fabric analysis is performed using high resolution images of the cut-faces using computer assisted image analysis software devoted to shape-fabric analysis. Here we present the results of samples taken from the 18 May 1980 PDC deposit facies, including massive, diffuse-stratified and cross-stratified lapilli tuff. We show a relationship between the strength of iso-orientation of the elongated

  6. Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): forest disturbances, deposits, and dynamics

    Science.gov (United States)

    Major, Jon J.; Pierson, Thomas C.; Hoblitt, Richard P.; Moreno, Hugo

    2013-01-01

    Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km from the caldera rim. Felled trees pointing in the down-current direction dominate the disturbance zones. The PDC on the north flank of Chaitén left a decimeters-thick, bipartite deposit having a basal layer of poorly sorted, fines-depleted pumice-and-lithic coarse ash and lapilli, which transitions abruptly to fines-enriched pumice-and-lithic coarse ash. The deposit contains fragments of mostly uncharred organics near its base; vegetation protruding above the deposit is uncharred. The nature of the forest disturbance and deposit characteristics suggest the PDC was dilute, of relatively low temperature (-1. It was formed by directionally focused explosions throughout the volcano's prehistoric, intracaldera lava dome. Dilute, low-temperature PDCs that exited the caldera over a low point on the east-southeast caldera rim deposited meters-thick fill of stratified beds of pumice-and-lithic coarse ash and lapilli. They did not fell large trees more than a few hundred of meters from the caldera rim and were thus less energetic than those on the north and northeast flanks. They likely formed by partial collapses of the margins of vertical eruption columns. In the Chaitén River valley south of the volcano, several-meter-thick deposits of two block-and-ash flow (BAF) PDCs are preserved. Both have a coarse ash matrix that supports blocks and lapilli predominantly of lithic rhyolite dome rock, minor obsidian, and local bedrock. One deposit was emplaced by a BAF that traveled an undetermined distance downvalley between June and November 2008, apparently triggered by partial collapse of a newly effused lava dome on that started growing on 12 May. A second, and larger, BAF related

  7. A simple method of extracting the polarization charge density in the AlGaN/GaN heterostructure from current-voltage and capacitance-voltage characteristics

    International Nuclear Information System (INIS)

    Lü Yuan-Jie; Lin Zhao-Jun; Yu Ying-Xia; Meng Ling-Guo; Cao Zhi-Fang; Luan Chong-Biao; Wang Zhan-Guo

    2012-01-01

    An Ni Schottky contact on the AlGaN/GaN heterostructure is fabricated. The flat-band voltage for the Schottky contact on the AlGaN/GaN heterostructure is obtained from the forward current—voltage characteristics. With the measured capacitance—voltage curve and the flat-band voltage, the polarization charge density in the AlGaN/GaN heterostructure is investigated, and a simple formula for calculating the polarization charge density is obtained and analyzed. With the approach described in this paper, the obtained polarization charge density agrees well with the one calculated by self-consistently solving Schrodinger's and Poisson's equations

  8. Teaching of the subject "density difference caused by salinity", one of the reasons that plays role in the occurrence of currents in straits, seas and oceans by the use of a teaching material

    Science.gov (United States)

    Gumussoy, Verim

    2015-04-01

    Large masses of moving water in seas and oceans are called currents. Root causes of currents are steady winds that occur due to the global atmospheric system and the density differences caused by different heat and salinity levels of water masses. Different feeding and evaporation characteristics of seas and oceans result in salinity and density levels. As a result, subsurface currents occur in straits where seas with different salinity and density levels meet and in the nearby seas. The Bosporus in Istanbul where I live and the school I am working at is has these subsurface currents. In the Black Sea where the rivers the Danube, Dnieper, Don, Yesilirmak, Kizilirmak and Sakarya flow into and the evaporation level is less due to the latitude effect, salinity level is less compared to Marmara and Aegean Seas. As Marmara Sea has higher salt amount than Black Sea, there is a great density difference between these two seas. Marmara Sea has a higher concentration of salt and therefore a higher density than Black Sea. And this leads to occurrence of subsurface currents in the Bosporus. I get my students to carry out a small demonstration to help them understand the occurrence of ocean currents and currents in the seas and the Bosporus by the use of a material. We need very simple materials to carry out this demonstration. These are an aquarium, a bowl, water, salt, dye and a mixer. The demonstration is carried out as follows: we put water, salt and dye in the bowl and mix it well. The salt will increase the density of the water and the dye will help distinguish the salty water. Then we put tap water half way to the aquarium and pour the mixture in the bowl to the aquarium slowly. As a result, the colored salty water sinks down due to its higher density, setting an example of a subsurface current. Natural events occur in very long periods by great dynamic systems, making understanding of them difficult. It is important to use different kinds of materials that address to

  9. Innovative High Energy Density Storage in Nano Vacuum Tubes (NVTs) designed for Small Leakage Current with Enhanced Coulomb Blockade in Nano Gaps, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — NASA's various Space Mission Directorate seek to develop technology to fulfill the technology gap and to enable missions with the unique high energy density charge...

  10. Five-minute grid of marine bird density off central California - Davidson Current seasons, 1980-2001 (CDAS data set Da0_dens.shp)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Da0_dens is a polygon shapefile representing 5 minute x 5 minute latitude x longitude cells that contain the overall, combined densities (birds/sq km), of 76 species...

  11. Five-minute grid of marine bird biomass density surveyed off central California - Davidson Current season, 1980-2001 (CDAS data set Da0_mass.shp)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Da0_MASS is a polygon shapefile representing 5 minute x 5 minute latitude x longitude cells that house the overall total biomass densities (kg/sq.km.) of 76 species...

  12. Field-trip guide to Mount St. Helens, Washington - An overview of the eruptive history and petrology, tephra deposits, 1980 pyroclastic density current deposits, and the crater

    Science.gov (United States)

    Pallister, John S.; Clynne, Michael A.; Wright, Heather M.; Van Eaton, Alexa R.; Vallance, James W.; Sherrod, David R.; Kokelaar, B. Peter

    2017-08-02

    master teacher.” The 1980 eruption and studies both before and after 1980 played a major role in the establishment of the modern U.S. Geological Survey Volcano Hazards Program and our understanding of flank collapses, debris avalanches, cryptodomes, blasts, pyroclastic density currents, and lahars, as well as the dynamics of magma ascent and eruption.

  13. Field-trip guide for exploring pyroclastic density current deposits from the May 18, 1980, eruption of Mount St. Helens, Washington

    Science.gov (United States)

    Brand, Brittany D.; Pollock, Nicholas; Sarocchi, Damiano; Dufek, Josef; Clynne, Michael A.

    2017-07-05

    Pyroclastic density currents (PDCs) are one of the most dangerous phenomena associated with explosive volcanism. To help constrain damage potential, a combination of field studies, laboratory experiments, and numerical modeling are used to establish conditions that influence PDC dynamics and depositional processes, including runout distance. The objective of this field trip is to explore field relations that may constrain PDCs at the time of emplacement.The PDC deposits from the May 18, 1980, eruption of Mount St. Helens are well exposed along the steep flanks (10–30° slopes) and across the pumice plain (5–12° slopes) as far as 8 km north of the volcano. The pumice plain deposits represent deposition from a series of concentrated PDCs and are primarily thick (3–12 m), massive, and poorly sorted. In contrast, the steep east-flank deposits are stratified to cross-stratified, suggesting deposition from PDCs where turbulence strongly influenced transport and depositional processes.The PDCs that descended the west flank were largely nondepositional; they maintained a higher flow energy and carrying capacity than PDCs funneled through the main breach, as evidenced by the higher concentration of large blocks in their deposits. The PDC from the west flank collided with PDCs funneled through the breach at various points along the pumice plain. Evidence for flow collision will be explored and debated throughout the field trip.Evidence for substrate erosion and entrainment is found (1) along the steep eastern flank of the volcano, which has a higher degree of rough, irregular topography relative to the west flanks where PDCs were likely nonerosive, (2) where PDCs encountered debris-avalanche hummocks across the pumice plain, and (3) where PDCs eroded and entrained material deposited by PDCs produced during earlier phases of the eruption. Two features interpreted as large-scale (tens of meters wide) levees and a large (~200 m wide) channel scour-and-fill feature

  14. Connectivity and critical current density of in-situ processed MgB{sub 2} superconductors: Effect of excess Mg and non-carbon based additives

    Energy Technology Data Exchange (ETDEWEB)

    Bhadauria, P. P. S.; Gupta, Anurag, E-mail: anurag@nplindia.org; Kishan, Hari [National Physical Laboratory (CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Narlikar, A. V. [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017, MP (India)

    2014-05-14

    In a sequel to our previous paper (J. Appl. Phys. 113, 036908 (2013)), where we reported comprehensive analysis of inter-grain connectivity (A{sub F}), pinning, percolation threshold (P{sub c}), and anisotropy (γ) in a series of ex-situ processed MgB{sub 2}, we address the same issues in in-situ processed samples. MgB{sub 2} samples with stoichiometric composition, excess Mg (5 wt. %) and further 3 wt. % addition of various non-carbon based additives like nano-Ag, nano-Ni, and YBCO are synthesised by the in-situ route. Detailed investigations of X-ray diffraction, magnetization (M), and resistivity (ρ) as a function of temperature (T) and field (B) in the range 5–300 K and 0–8 T are carried out in all the samples. The resistive superconducting onset T{sub con} ∼ 38.6 ± 0.3 K and offset (where ρ goes to zero) T{sub c0} ∼ 38.1 ± 0.3 K of the samples stay nearly unchanged. The inter-grain connectivity (A{sub F}) of the samples varies between 11%–20%. All the additives result in a critical current density (J{sub c}) higher than the stoichiometric MgB{sub 2} sample, where the highest values (e.g., J{sub c}(1 T, 5 K) ∼ 1.2 × 10{sup 9} A/m{sup 2}) are observed for the sample with 5 wt. % excess Mg. The major findings based on quantitative analysis of ρ (T, B) and J{sub c} (B, T) data in all the samples are: (1) along with previously studied ex-situ samples, the J{sub c}(A{sub F}) shows a significant increase at A{sub F} ∼ 7%; (2) the irreversibility lines lie lower than the characteristic T{sub c0}(B) lines in the B-T phase diagram; (3) a universal core pinning (δl- and/or δT{sub c}- type) mechanism is revealed in the entire T range 5–30 K; and (4) typical values of P{sub c} ∼ 0.57 ± 0.04 is indicative of weak link networks.

  15. Ground penetrating radar and terrestrial laser scanner surveys on deposits of dilute pyroclastic density current deposits: insights for dune bedform genesis

    Science.gov (United States)

    Rémi Dujardin, Jean; Amin Douillet, Guilhem; Abolghasem, Amir; Cordonnier, Benoit; Kueppers, Ulrich; Bano, Maksim; Dingwell, Donald B.

    2014-05-01

    Dune bedforms formed by dilute pyroclastic density currents (PDC) are often described or interpreted as antidunes and chute and pools. However, the interpretation remains essentially speculative and is not well understood. This is largely due to the seeming impossibility of in-situ measurements and experimental scaling, as well as the lack of recent, 3D exposures. Indeed, most dune bedform cross-stratifications from the dilute PDC record outcrop in 2D sections. The 2006 eruption of Tungurahua has produced well-developed bedforms that are well-exposed on the surface of the deposits with easy access. We performed a survey of these deposits combining ground penetrating radar (GPR) profiling with terrestrial laser scanning of the surface. The GPR survey was carried in dense arrays (from 10 to 25 cm spacing between profiles) over ca. 10 m long bedforms. GPR profiles were corrected for topography from photogrammetry data. An in-house software, RadLab (written in matlab), was used for common processing of individual profiles and 2D & 3D topographic migration. Each topography-corrected profile was then loaded into a seismic interpretation software, OpenDtect, for 3D visualization and interpretation. Most bedforms show high lateral stability that is independent of the cross-stratification pattern (that varies between stoss-aggrading bedsets, stoss-erosive bedsets and stoss-depositional lensoidal layers). Anecdotic bedforms have their profiles that evolve laterally (i.e. in a direction perpendicular to the flow direction). Cannibalization of two dune bedforms into a single one on one end of the profile can evolve into growth of a single bedform at the other lateral end. Also, lateral variation in the migration direction occurs, i.e. a single bedform can show upstream aggradation at one lateral end of the bedform, but show downstream migration at the other end. Some bedforms have great variations in their internal structure. Several episodes of growth and erosion can be

  16. Nuclear Level Densities

    International Nuclear Information System (INIS)

    Grimes, S.M.

    2005-01-01

    Recent research in the area of nuclear level densities is reviewed. The current interest in nuclear astrophysics and in structure of nuclei off of the line of stability has led to the development of radioactive beam facilities with larger machines currently being planned. Nuclear level densities for the systems used to produce the radioactive beams influence substantially the production rates of these beams. The modification of level-density parameters near the drip lines would also affect nucleosynthesis rates and abundances

  17. Determination of a Fit Function for the Critical Current Density for NbTi Cables used in LHC Main Bending Magnets Student Research Project

    CERN Document Server

    Schwerg, N

    2005-01-01

    For the construction of the LHC at CERN the main dipoles and the superconducting cables are produced in industry. As part of the quality control the field quality of the magnets is measured both at warm and at cold conditions at CERN. In superconducting accelerator magnets field errors are mainly created by the positioning of the conductors, but also by so-called persistent currents. These currents are linked to the superconductor magnetization and they are an inevitable property of type II superconducting materials. The superconductor magnetization behavior of each strand used for the LHC main dipoles is tested at CERN and the cable has to be approved before use. It has been observed that the dependency of the superconductor magnetization on the applied magnetic induction is different for the different manufacturers. Based on the magnetization measurements and the critical state model the persistent current effects can be calculated by means of a model for superconducting filaments. For this thesis the inter...

  18. High improvement in trap level density and direct current breakdown strength of block polypropylene by doping with a β-nucleating agent

    Science.gov (United States)

    Zhang, Chong; Zha, Jun-Wei; Yan, Hong-Da; Li, Wei-Kang; Dang, Zhi-Min

    2018-02-01

    Polypropylene is one kind of eco-friendly insulating material, which has attracted more attention for use in high voltage direct current (HVDC) insulation due to the long-distance transmission, low loss, and recyclability. In this work, the morphology and thermal and electrical properties of the block polypropylene with various β-nucleating agent (β-NA) contents were investigated. The relative fraction of the β-crystal can reach 64.7% after adding 0.05 wt. % β-NA. The β-NA also greatly reduced the melting point and improved the crystallization temperature. The electrical property results showed that the alternating and direct current breakdown strength and conduction current were obviously improved. In addition, space charge accumulation was significantly suppressed by introducing the β-NA. This work provides an attractive strategy of design and fabrication of polypropylene for HVDC application.

  19. Different Densities of Na-Ca Exchange Current in T-Tubular and Surface Membranes and Their Impact on Cellular Activity in a Model of Rat Ventricular Cardiomyocyte

    Czech Academy of Sciences Publication Activity Database

    Pásek, Michal; Šimurda, J.; Christé, G.

    2017-01-01

    Roč. 2017, č. 2017 (2017), č. článku 6343821. ISSN 2314-6133 Institutional support: RVO:61388998 Keywords : rat ventricular cell * mathematical model * Na-Ca current * t-tubules Subject RIV: BO - Biophysics OBOR OECD: Biophysics Impact factor: 2.476, year: 2016

  20. Reconstruction of Cell Surface Densities of Ion Pumps, Exchangers, and Channels from mRNA Expression, Conductance Kinetics, Whole-Cell Calcium, and Current-Clamp Voltage Recordings, with an Application to Human Uterine Smooth Muscle Cells.

    Directory of Open Access Journals (Sweden)

    Jolene Atia

    2016-04-01

    Full Text Available Uterine smooth muscle cells remain quiescent throughout most of gestation, only generating spontaneous action potentials immediately prior to, and during, labor. This study presents a method that combines transcriptomics with biophysical recordings to characterise the conductance repertoire of these cells, the 'conductance repertoire' being the total complement of ion channels and transporters expressed by an electrically active cell. Transcriptomic analysis provides a set of potential electrogenic entities, of which the conductance repertoire is a subset. Each entity within the conductance repertoire was modeled independently and its gating parameter values were fixed using the available biophysical data. The only remaining free parameters were the surface densities for each entity. We characterise the space of combinations of surface densities (density vectors consistent with experimentally observed membrane potential and calcium waveforms. This yields insights on the functional redundancy of the system as well as its behavioral versatility. Our approach couples high-throughput transcriptomic data with physiological behaviors in health and disease, and provides a formal method to link genotype to phenotype in excitable systems. We accurately predict current densities and chart functional redundancy. For example, we find that to evoke the observed voltage waveform, the BK channel is functionally redundant whereas hERG is essential. Furthermore, our analysis suggests that activation of calcium-activated chloride conductances by intracellular calcium release is the key factor underlying spontaneous depolarisations.

  1. High current density and nonlinearity combination of selection device based on TaO(x)/TiO2/TaO(x) structure for one selector-one resistor arrays.

    Science.gov (United States)

    Lee, Wootae; Park, Jubong; Kim, Seonghyun; Woo, Jiyong; Shin, Jungho; Choi, Godeuni; Park, Sangsu; Lee, Daeseok; Cha, Euijun; Lee, Byoung Hun; Hwang, Hyunsang

    2012-09-25

    We demonstrate a high-performance selection device by utilizing the concept of crested oxide barrier to suppress the sneak current in bipolar resistive memory arrays. Using a TaO(x)/TiO(2)/TaO(x) structure, high current density over 10(7) A cm(-2) and excellent nonlinear characteristics up to 10(4) were successfully demonstrated. On the basis of the defect chemistry and SIMS depth profile result, we found that some Ta atoms gradually diffused into TiO(2) film, and consequently, the energy band of the TiO(2) film was symmetrically bent at the top and bottom TaO(x)/TiO(2) interfaces and modified as a crested oxide barrier. Furthermore, the one selector-one resistor device exhibited significant suppression of the leakage current, indicating excellent selector characteristics.

  2. Assessing the Driver’s Current Level of Working Memory Load with High Density Functional Near-infrared Spectroscopy: A Realistic Driving Simulator Study

    Directory of Open Access Journals (Sweden)

    Anirudh Unni

    2017-04-01

    Full Text Available Cognitive overload or underload results in a decrease in human performance which may result in fatal incidents while driving. We envision that driver assistive systems which adapt their functionality to the driver’s cognitive state could be a promising approach to reduce road accidents due to human errors. This research attempts to predict variations of cognitive working memory load levels in a natural driving scenario with multiple parallel tasks and to reveal predictive brain areas. We used a modified version of the n-back task to induce five different working memory load levels (from 0-back up to 4-back forcing the participants to continuously update, memorize, and recall the previous ‘n’ speed sequences and adjust their speed accordingly while they drove for approximately 60 min on a highway with concurrent traffic in a virtual reality driving simulator. We measured brain activation using multichannel whole head, high density functional near-infrared spectroscopy (fNIRS and predicted working memory load level from the fNIRS data by combining multivariate lasso regression and cross-validation. This allowed us to predict variations in working memory load in a continuous time-resolved manner with mean Pearson correlations between induced and predicted working memory load over 15 participants of 0.61 [standard error (SE 0.04] and a maximum of 0.8. Restricting the analysis to prefrontal sensors placed over the forehead reduced the mean correlation to 0.38 (SE 0.04, indicating additional information gained through whole head coverage. Moreover, working memory load predictions derived from peripheral heart rate parameters achieved much lower correlations (mean 0.21, SE 0.1. Importantly, whole head fNIRS sampling revealed increasing brain activation in bilateral inferior frontal and bilateral temporo-occipital brain areas with increasing working memory load levels suggesting that these areas are specifically involved in workload

  3. Effects of graphite doping on critical current density and microstructure of MgB{sub 2} bulks by an improved Mg-diffusion method

    Energy Technology Data Exchange (ETDEWEB)

    Pan, X.F. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhao, Y. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); School of Materials Science and Engineering, University of New South Wales, Sydney 2052, NSW (Australia)], E-mail: yshao@home.swjtu.edu.cn; Feng, Y. [Northwest Institute for Nonferrous Metal Research, P.O. Box 51, Xi' an, Shaanxi 710016 (China); Western Superconductivity Technology Company, Xi' an (China); Yang, Y. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Cheng, C.H. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); School of Materials Science and Engineering, University of New South Wales, Sydney 2052, NSW (Australia)

    2008-09-15

    abstract: A series of graphite-doped MgB{sub 2} bulks with high density have been successfully prepared by an improved Mg-diffusion method in ambient pressure. The effects of graphite doping on lattice parameters, T{sub c}, J{sub c} and microstructure of MgB{sub 2} have been investigated. The results show that compared to the nano-C-doped or CNTs-doped MgB{sub 2}, C is not easy to substitute B in graphite-doped MgB{sub 2}. However, at the same C content, the graphite-doped MgB{sub 2} has a higher J{sub c}. At 10 K and self-field, the J{sub c} for MgB{sub 1.985}C{sub 0.015} reaches 0.58 MA/cm{sup 2}. For the MgB{sub 1.945}C{sub 0.055}, at 5 K, 7 T and 10 K, 6 T the J{sub c} achieves 10,000 A/cm{sup 2} which is two orders of magnitude higher than that for the undoped sample. In addition to improving electron scattering and intergranular connectivity, the unreacted graphite in the graphite-doped MgB{sub 2} is proposed to be responsible to the excellent J{sub c} properties of MgB{sub 2} in high fields, due to depressed grain growth and enhanced grain boundary flux pinning.

  4. Enhancement and Angular Dependence of Transport Critical Current Density in Pulsed Laser Deposited YBa2Cu3O7-x+BaSnO3 Films in Applied Magnetic Fields (Postprint)

    Science.gov (United States)

    2007-09-25

    BaSnO3 FILMS IN APPLIED MAGNETIC FIELDS (POSTPRINT) C.V. Varanasi, J. Burke, and L. Brunke University of Dayton Research Institute H. Wang...SUBTITLE ENHANCEMENT AND ANGULAR DEPENDENCE OF TRANSPORT CRITICAL CURRENT DENSITY IN PULSED LASER DEPOSITED YBa2Cu3O7−x+ BaSnO3 FILMS IN APPLIED...nanoparticles of BaSnO3 (BSO) were processed using pulsed laser ablation of a special target made with dual phase sectors of YBCO and BSO. Transport critical

  5. Critical Current Density and Microstructure Variations in YBa2Cu3O7-x + BaSnO3 Films with Different Concentrations of BaSnO3 (Postprint)

    Science.gov (United States)

    2008-12-01

    AFRL-RZ-WP-TP-2012-0147 CRITICAL CURRENT DENSITY AND MICROSTRUCTURE VARIATIONS IN YBa2Cu3O7−x + BaSnO3 FILMS WITH DIFFERENT CONCENTRATIONS...OF BaSnO3 (POSTPRINT) C.V. Varanasi, J. Burke, and L. Brunke University of Dayton Research Institute H. Wang and J.H. Lee Texas A&M...VARIATIONS IN YBa2Cu3O7−x + BaSnO3 FILMS WITH DIFFERENT CONCENTRATIONS OF BaSnO3 (POSTPRINT) 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c

  6. Bond length and electric current oscillation of long linear carbon chains: Density functional theory, MpB model, and quantum spin transport studies

    International Nuclear Information System (INIS)

    Oeiras, R. Y.; Silva, E. Z. da

    2014-01-01

    Carbon linear atomic chains attached to graphene have experimentally been produced. Motivated by these results, we study the nature of the carbon bonds in these nanowires and how it affects their electrical properties. In the present study we investigate chains with different numbers of atoms and we observe that nanowires with odd number of atoms present a distinct behavior than the ones with even numbers. Using graphene nanoribbons as leads, we identify differences in the quantum transport of the chains with the consequence that even and odd numbered chains have low and high electrical conduction, respectively. We also noted a dependence of current with the wire size. We study this unexpected behavior using a combination of first principles calculations and simple models based on chemical bond theory. From our studies, the electrons of carbon nanowires present a quasi-free electron behavior and this explains qualitatively the high electrical conduction and the bond lengths with unexpected values for the case of odd nanowires. Our study also allows the understanding of the electric conduction dependence with the number of atoms and their parity in the chain. In the case of odd number chains a proposed π-bond (MpB) model describes unsaturated carbons that introduce a mobile π-bond that changes dramatically the structure and transport properties of these wires. Our results indicate that the nature of bonds plays the main role in the oscillation of quantum electrical conduction for chains with even and odd number of atoms and also that nanowires bonded to graphene nanoribbons behave as a quasi-free electron system, suggesting that this behavior is general and it could also remain if the chains are bonded to other materials

  7. Road density

    Data.gov (United States)

    U.S. Environmental Protection Agency — Road density is generally highly correlated with amount of developed land cover. High road densities usually indicate high levels of ecological disturbance. More...

  8. Lung density

    DEFF Research Database (Denmark)

    Garnett, E S; Webber, C E; Coates, G

    1977-01-01

    The density of a defined volume of the human lung can be measured in vivo by a new noninvasive technique. A beam of gamma-rays is directed at the lung and, by measuring the scattered gamma-rays, lung density is calculated. The density in the lower lobe of the right lung in normal man during quiet...

  9. Probing the self-heating effects in the transition to the normal state induced in YBa2Cu3O7-δ thin films by high current density ramps in the millisecond range

    International Nuclear Information System (INIS)

    Ruibal, Mauricio; Ferro, Gonzalo; Blanch, Montserrat; Veira, Jose A.; Maza, Jesus; Vidal, Felix

    2007-01-01

    Some preliminary current-voltage curves measured in YBa 2 Cu 3 O 7-δ thin film microbridges for widths between 5 and 100 μm and for 70 K ≤ T ≤ T c are summarized here, together with some generalities about the synthesis of these microbridges. These results suggest that in the non critical dissipative regime the flux-flow resistivity does not depend on the microbridge width whereas the current density at which the quenching occurs decreases as the microbridge width increases. First qualitative analysis of our results in terms of a simple model suggest that our results might be explained in terms of self-heating driven by conventional (non singular) flux-flow effects

  10. The effect of magnetic substorms on near-ground atmospheric current

    Directory of Open Access Journals (Sweden)

    E. Belova

    2000-12-01

    Full Text Available Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between "substorm" and "quiet" atmospheric currents decreases. The amplitude of this "substorm" variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms.Key words: Ionosphere (electric fields and currents · Magnetospheric physics (storms and substorms · Meteorology and atmospheric dynamics (atmospheric electricity

  11. Current Density and Continuity in Discretized Models

    Science.gov (United States)

    Boykin, Timothy B.; Luisier, Mathieu; Klimeck, Gerhard

    2010-01-01

    Discrete approaches have long been used in numerical modelling of physical systems in both research and teaching. Discrete versions of the Schrodinger equation employing either one or several basis functions per mesh point are often used by senior undergraduates and beginning graduate students in computational physics projects. In studying…

  12. Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet

    International Nuclear Information System (INIS)

    Sunwong, P.; Higgins, J. S.; Hampshire, D. P.

    2014-01-01

    We present the designs of probes for making critical current density (J c ) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ∼0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make J c measurements, made by uniformly ramping the current up to a maximum current (I max ) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b ′ ), and the maximum safe temperature for the critical-current leads (T max ). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI max /A=[1.46D −0.18 L 0.4 (T max −300) 0.25D −0.09 +750(b ′ /I max )D 10 −3 I max −2.87b ′ ]× 10 6 A m −1 where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm 2 is obtained when I max = 1000 A, T max = 400 K, D = 0.2, b ′ = 0.3 l h −1 and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h −1 . When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I max  ≈ (1.35 × 10 −3 )D 0.41 l h ‑1  A −1 . A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in

  13. Effect of current density and pH in obtaining the Ni-Fe alloy by electrodeposition; Efeito da densidade de corrente e pH na obtencao da liga Ni-Fe por eletrodeposicao

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Jose Anderson Machado; Raulino, Anamelia de Medeiros Dantas; Raulino, Jose Leonardo Costa; Campos, Ana Regina Nascimento; Prasad, Shiva; Santana, Renato Alexandre Costa de, E-mail: jmo.anderson@gmail.com, E-mail: anameliadantas@yahoo.com.br, E-mail: leonardo.jcr@hotmail.com, E-mail: arncampos@yahoo.com.br, E-mail: prasad@deq.ufcg.edu.br, E-mail: renatoacs@ufcg.edu.br [Universidade Federal de Campina Grande (UFCG), Cuite, PB (Brazil). Lab. de Eletroquimica e Corrosao

    2017-01-15

    Metallic coatings can be applied for different purposes, for example to improve the mechanical, catalytic, anti corrosive properties or simply to improve the decorative appearance. In the work the Fe-Ni alloys have been obtained by electrodeposition process using a simple electrolytic bath containing the reagents, nickel sulfate, iron sulfate and sodium tartrate. A complete experimental design 2{sup 2} , associated with the response surface methodology (RSM) technique was used as optimization tool. Chemical composition, current efficiency, surface morphology and electrochemical corrosion measures were performed. It was observed that a decrease in the pH favored an increase in iron and decrease in nickel contents in the alloy. The iron content influenced the alloy morphology. The best experiment showed an average corrosion resistance 5471.5 Ω.cm² and a corrosion current density 4.814x10{sup -6} A/cm². This experiment presented a composition of 70 wt% Ni and 30 wt% Fe in the alloy and an average deposition current efficiency of 58.7%. (author)

  14. Critical current density of strained multilayer thin films of Nd sub 1. 83 Ce sub 0. 17 CuO sub x /YBa sub 2 Cu sub 3 O sub 7 minus. delta

    Energy Technology Data Exchange (ETDEWEB)

    Gross, R.; Gupta, A.; Olsson, E.; Segmueller, A.; Koren, G. (IBM T. J. Watson Research Center, P.O. Box 218, Yorktown Heights, New York 10598 (USA))

    1990-07-09

    The superconducting transport properties of strained multilayer thin films of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}/ Nd{sub 1.83}Ce{sub 0.17}CuO{sub {ital x}}, grown heteroepitaxially by laser ablation deposition, are reported. For individual layer thicknesses below a critical layer thickness of about 250 A, coherency strain removes the orthorhombic distortion in the YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} layers and makes them twin-free. Zero-field critical current densities as high as 1.1{times}10{sup 7} A/cm{sup 2} at 77 K have been measured for the YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} layers. Flux pinning energies at zero temperature and zero magnetic field in the range of 80--140 meV have been found.

  15. LaNiO3 buffer layers for high critical current density YBa2Cu3O7-δ and Tl2Ba2CaCu2O8-δ films

    International Nuclear Information System (INIS)

    Carlson, C.M.; Parilla, P.A.; Siegal, M.P.; Ginley, D.S.; Wang, Y.; Blaugher, R.D.; Price, J.C.; Overmyer, D.L.; Venturini, E.L.

    1999-01-01

    We demonstrate high critical current density superconducting films of YBa 2 Cu 3 O 7-δ (YBCO) and Tl 2 Ba 2 CaCu 2 O 8-δ (Tl-2212) using LaNiO 3 (LNO) buffer layers. YBCO films grown on an LNO buffer layer have only a slightly lower J c (5 K, H=0) than films grown directly on a bare LaAlO 3 substrate. YBCO films grown on LNO buffer layers exhibit minor microstructural disorder and enhanced flux pinning. LNO-buffered Tl-2212 samples show large reductions in J c at all temperatures and fields compared to those grown on bare LaAlO 3 , correlating to both a-axis grain and nonsuperconducting phase formation. LNO could be a promising buffer layer for both YBCO and Tl-based superconducting films in coated conductor applications. copyright 1999 American Institute of Physics

  16. LaNiO3 Buffer Layers for High Critical Current Density YBa2Cu3O7δ and Tl2Ba2CaCu2O8δ Films

    International Nuclear Information System (INIS)

    Carlson, C.M.; Parilla, P.A.; Siegal, M.P.; Ginley, D.S.; Wang, Y.-T.; Blaugher, R.D.; Price, J.C.; Overmyer, D.L.; Venturini, E.L.

    1999-01-01

    We demonstrate high critical current density superconducting films of YBa 2 Cu 3 O 7-δ (YBCO) and Tl 2 Ba 2 CaCu 2 O 8-δ (Tl-2212) using LaNiO 3 (LNO) buffer layers. YBCO films grown on an LNO buffer layer have only a slightly lower J c (5K, H=0) than films grown directly on a bare LaAlO 3 substrate. It is noteworthy that YBCO films grown on LNO buffer layers exhibit minor microstructural disorder and enhanced flux pinning. LNO-buffered Tl-2212 samples show large reductions in J c at all temperatures and fields compared to those grown on bare LaAlO 3 , correlating to both a-axis grain and nonsuperconducting phase formation. With additional optimization, LNO could be a promising buffer layer for both YBCO and Tl-based superconducting films, perhaps ideally suited for coated conductor applications

  17. A spin transfer torque magnetoresistance random access memory-based high-density and ultralow-power associative memory for fully data-adaptive nearest neighbor search with current-mode similarity evaluation and time-domain minimum searching

    Science.gov (United States)

    Ma, Yitao; Miura, Sadahiko; Honjo, Hiroaki; Ikeda, Shoji; Hanyu, Takahiro; Ohno, Hideo; Endoh, Tetsuo

    2017-04-01

    A high-density nonvolatile associative memory (NV-AM) based on spin transfer torque magnetoresistive random access memory (STT-MRAM), which achieves highly concurrent and ultralow-power nearest neighbor search with full adaptivity of the template data format, has been proposed and fabricated using the 90 nm CMOS/70 nm perpendicular-magnetic-tunnel-junction hybrid process. A truly compact current-mode circuitry is developed to realize flexibly controllable and high-parallel similarity evaluation, which makes the NV-AM adaptable to any dimensionality and component-bit of template data. A compact dual-stage time-domain minimum searching circuit is also developed, which can freely extend the system for more template data by connecting multiple NM-AM cores without additional circuits for integrated processing. Both the embedded STT-MRAM module and the computing circuit modules in this NV-AM chip are synchronously power-gated to completely eliminate standby power and maximally reduce operation power by only activating the currently accessed circuit blocks. The operations of a prototype chip at 40 MHz are demonstrated by measurement. The average operation power is only 130 µW, and the circuit density is less than 11 µm2/bit. Compared with the latest conventional works in both volatile and nonvolatile approaches, more than 31.3% circuit area reductions and 99.2% power improvements are achieved, respectively. Further power performance analyses are discussed, which verify the special superiority of the proposed NV-AM in low-power and large-memory-based VLSIs.

  18. Population Density Modeling Tool

    Science.gov (United States)

    2012-06-26

    194 POPULATION DENSITY MODELING TOOL by Davy Andrew Michael Knott David Burke 26 June 2012 Distribution...MARYLAND NAWCADPAX/TR-2012/194 26 June 2012 POPULATION DENSITY MODELING TOOL by Davy Andrew Michael Knott David Burke...information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE 26

  19. Air shower density spectrum

    Science.gov (United States)

    Porter, M. R.; Foster, J. M.; Hodson, A. L.; Hazen, W. E.; Hendel, A. Z.; Bull, R. M.

    Results are presented of a measurement of the differential local density spectrum of extensive air showers at sea level using 1 sq m current-limited spark chambers. The 2 cm gap, Ne/He-filled discharge chambers with 6 mm thick 'Georgia-wired' glass faces, were mounted directly on the underside of a light, uniform, sandwich-panel roof. Separate runs with different trigger requirements were made. Low density spectra according to different counting criteria are presented in a graph. Another graph shows a differential local density spectrum. The results of the measurements are compared with previous measurements

  20. Low Bone Density

    Science.gov (United States)

    ... Bone Density Exam/Testing › Low Bone Density Low Bone Density Low bone density is when your bone ... to people with normal bone density. Detecting Low Bone Density A bone density test will determine whether ...

  1. LaNiO(3) Buffer Layers for High Critical Current Density YBa(2)Cu(3)O(7-delta) and Tl(2)Ba(2)CaCu(2)O(8-delta) Films

    Energy Technology Data Exchange (ETDEWEB)

    Carlson, C.M.; Parilla, P.A.; Siegal, M.P.; Ginley, D.S.; Wang, Y.-T.; Blaugher, R.D.; Price, J.C.; Overmyer, D.L.; Venturini, E.L.

    1999-08-24

    We demonstrate high critical current density superconducting films of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) and Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8{minus}{delta}} (Tl-2212) using LaNiO{sub 3} (LNO) buffer layers. YBCO films grown on an LNO buffer layer have only a slightly lower J{sub c} (5K, H=0) than films grown directly on a bare LaAlO{sub 3} substrate. It is noteworthy that YBCO films grown on LNO buffer layers exhibit minor microstructural disorder and enhanced flux pinning. LNO-buffered Tl-2212 samples show large reductions in J{sub c} at all temperatures and fields compared to those grown on bare LaAlO{sub 3}, correlating to both a-axis grain and nonsuperconducting phase formation. With additional optimization, LNO could be a promising buffer layer for both YBCO and Tl-based superconducting films, perhaps ideally suited for coated conductor applications.

  2. Fabrication and critical current density analysis of YBa2Cu3O7+(BaSnO3)‧/YBa2Cu3O7+(BaSnO3)″ multilayer films

    Science.gov (United States)

    Horide, Tomoya; Sakamoto, Nobuhiro; Ichinose, Ataru; Matsumoto, Kaname

    2016-08-01

    Multilayers (MLs) comprising of YBa2Cu3O7(YBCO)+BaSnO3(BSO) layers with different BSO content were fabricated, and their critical current density (J c) was measured to understand influence of ML structure on vortex pinning. Elongated and segmented nanorods were observed in the MLs, and ab-plane aligned nanoparticles appeared depending on BSO content. When BSO formed only elongated and segmented nanorods in MLs, J c exhibited a linear relationship between J c in the single layer films. On the other hand, when MLs contained ab-plane aligned nanoparticles in addition to nanorods, J c decreased with lower-J c-layer fraction more rapidly. These results suggest that J c was degraded due to easy vortex flow along the lower-J c-layers, and that the acceleration of vortex motion depended on the type of lower-J c-layers. Vortex behavior which is not observed in conventional systems such as single layer films and bulk samples is strongly expected in MLs, since fine tuning of pinning center structure is possible.

  3. Holographic magnetisation density waves

    Energy Technology Data Exchange (ETDEWEB)

    Donos, Aristomenis [Centre for Particle Theory and Department of Mathematical Sciences, Durham University,Stockton Road, Durham, DH1 3LE (United Kingdom); Pantelidou, Christiana [Departament de Fisica Quantica i Astrofisica & Institut de Ciencies del Cosmos (ICC),Universitat de Barcelona,Marti i Franques 1, 08028 Barcelona (Spain)

    2016-10-10

    We numerically construct asymptotically AdS black brane solutions of D=4 Einstein theory coupled to a scalar and two U(1) gauge fields. The solutions are holographically dual to d=3 CFTs in a constant external magnetic field along one of the U(1)’s. Below a critical temperature the system’s magnetisation density becomes inhomogeneous, leading to spontaneous formation of current density waves. We find that the transition can be of second order and that the solutions which minimise the free energy locally in the parameter space of solutions have averaged stressed tensor of a perfect fluid.

  4. Effect of combined addition of nano-SiC and nano-Ho2O3 on the in-field critical current density of MgB2 superconductor

    Science.gov (United States)

    Varghese, Neson; Vinod, K.; Chattopadhyay, M. K.; Roy, S. B.; Syamaprasad, U.

    2010-01-01

    MgB2 superconducting samples added with nano-Ho2O3 (n-Ho2O3) and/or nano-SiC (n-SiC) have been prepared by an in situ solid state reaction method to investigate and compare the combined and individual effects of n-SiC and n-Ho2O3 on a crystal structure, critical temperature (TC), and critical current density (JC) of MgB2. All the doped samples exhibit significantly enhanced in-field JC and the codoped sample with 2.5 wt % n-Ho2O3 and 5 wt % n-SiC gives the best performance in in-field JC, and the enhancement is around 100 times and 2 times greater than the undoped and monodoped n-SiC samples, respectively, at 5 K and 8 T. For the n-SiC added sample, lattice distortions due to C substitution on the B site and the formation of reacted phase Mg2Si as flux pinners cause enhanced JC up to the maximum field studied (8 T). While in the n-Ho2O3 added sample, a reacted phase HoB4 having a strong magnetic moment forms, without any substitution at the Mg or B site, which acts as a flux pinner in order to enhance the in-field JC. Accordingly the best codoped sample exhibits these combined benefits of n-SiC and n-Ho2O3 in MgB2 superconductor.

  5. Density games.

    Science.gov (United States)

    Novak, Sebastian; Chatterjee, Krishnendu; Nowak, Martin A

    2013-10-07

    The basic idea of evolutionary game theory is that payoff determines reproductive rate. Successful individuals have a higher payoff and produce more offspring. But in evolutionary and ecological situations there is not only reproductive rate but also carrying capacity. Individuals may differ in their exposure to density limiting effects. Here we explore an alternative approach to evolutionary game theory by assuming that the payoff from the game determines the carrying capacity of individual phenotypes. Successful strategies are less affected by density limitation (crowding) and reach higher equilibrium abundance. We demonstrate similarities and differences between our framework and the standard replicator equation. Our equation is defined on the positive orthant, instead of the simplex, but has the same equilibrium points as the replicator equation. Linear stability analysis produces the classical conditions for asymptotic stability of pure strategies, but the stability properties of internal equilibria can differ in the two frameworks. For example, in a two-strategy game with an internal equilibrium that is always stable under the replicator equation, the corresponding equilibrium can be unstable in the new framework resulting in a limit cycle. Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.

  6. Effect of Hf addition on critical current density of (Y,Eu)Ba{sub 2}Cu{sub 3.6}O{sub 7-δ} thin films prepared by trifluoroacetate metal organic deposition

    Energy Technology Data Exchange (ETDEWEB)

    Li, M.Y., E-mail: limengyaorz@163.com [Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, 99 Shangda Road, Shanghai University, Shanghai 200444 (China); Liu, Z.Y. [Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, 99 Shangda Road, Shanghai University, Shanghai 200444 (China); Shanghai Creative Superconductor Technologies Co. Ltd., Shanghai 201401 (China); Fang, Q. [Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, 99 Shangda Road, Shanghai University, Shanghai 200444 (China); Guo, Y.Q.; Lu, Y.M.; Bai, C.Y. [Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, 99 Shangda Road, Shanghai University, Shanghai 200444 (China); Shanghai Creative Superconductor Technologies Co. Ltd., Shanghai 201401 (China); Cai, C.B., E-mail: cbcai@t.shu.edu.cn [Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, 99 Shangda Road, Shanghai University, Shanghai 200444 (China); Shanghai Creative Superconductor Technologies Co. Ltd., Shanghai 201401 (China)

    2016-12-15

    Highlights: • This work firstly introduce the Eu and Hf co-doping effect on the performance of YBa{sub 2}Cu{sub 3.6}O{sub 7-δ} thin films, prepared on oxide buffered metallic substrates by trifluoroacetate metal organic deposition (TFA-MOD). • (Y, Eu)Ba{sub 2}Cu{sub 3.6}O{sub 7-δ} film showed a very different surface morphology, smooth and regular, compared to YBa{sub 2}Cu{sub 3.6}O{sub 7-δ} thin film, which has never been reported before. • The J{sub c} value under self-field of (Y, Eu)Ba{sub 2}Cu{sub 3.6}O{sub 7-δ} thin film was obviously improved compared to YBa{sub 2}Cu{sub 3.6}O{sub 7-δ} thin film. • (Y, Eu)Ba{sub 2}Cu{sub 3.6}O{sub 7-δ} thin film with Hf addition exhibited enhancement of J{sub c} value under magnetic fields. - Abstract: The critical current density (J{sub c}) performance of YBCO coated conductors (CCs) under magnetic field has become a considerable limitation for its commercial application in recent years. It is well known that the proper amount of element doping into the CCs is a convenient method to increase flux pinning and then to enhance the J{sub c}. In the present work, we firstly introduce the co-doping of Eu and Hf and study the effect on the performance of YBa{sub 2}Cu{sub 3.6}O{sub 7-δ} thin films. Three types of high temperature superconducting thin films, i.e., YBa{sub 2}Cu{sub 3.6}O{sub 7-δ}, (Y,Eu)Ba{sub 2}Cu{sub 3.6}O{sub 7-δ} and Hf doped (Y,Eu)Ba{sub 2}Cu{sub 3.6}O{sub 7-δ} were prepared on the oxide buffered metallic substrates by using trifluoroacetate metal organic deposition (TFA-MOD). The component and structure of the as-prepared samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and atomic force microscopy (AFM). Superconducting properties were measured with a SQUID magnetometer. It was revealed that the (Y,Eu)Ba{sub 2}Cu{sub 3.6}O{sub 7-δ} thin films exhibit better out-plane and in-plane texture compared with the pure YBa{sub 2}Cu{sub 3.6}O{sub 7-δ} thin

  7. Quantal density functional theory

    CERN Document Server

    Sahni, Viraht

    2016-01-01

    This book deals with quantal density functional theory (QDFT) which is a time-dependent local effective potential theory of the electronic structure of matter. The treated time-independent QDFT constitutes a special case. In the 2nd edition, the theory is extended to include the presence of external magnetostatic fields. The theory is a description of matter based on the ‘quantal Newtonian’ first and second laws which is in terms of “classical” fields that pervade all space, and their quantal sources. The fields, which are explicitly defined, are separately representative of electron correlations due to the Pauli exclusion principle, Coulomb repulsion, correlation-kinetic, correlation-current-density, and correlation-magnetic effects. The book further describes Schrödinger theory from the new physical perspective of fields and quantal sources. It also describes traditional Hohenberg-Kohn-Sham DFT, and explains via QDFT the physics underlying the various energy functionals and functional derivatives o...

  8. Spatial and temporal distribution of ionospheric currents-4: altitude ...

    African Journals Online (AJOL)

    (a) The continuous distribution of current density model reproduces the altitude distribution parameters of EEJ current density very well, (b) the altitude distribution parameters of EEJ current density in India and Peru are not significantly different and (c) The altitude distribution parameters of EEJ current density from rockets ...

  9. Amplification of the discharge current density of lithium-ion batteries with spinel phase Li(PtAu)0.02Mn1.98O4 nano-materials

    CSIR Research Space (South Africa)

    Ross, N

    2014-05-01

    Full Text Available capacity retention of 99% after 50 cycles. Faster charge transportation at high current rates proved to prevent the pronounced pile-up of Li(sup+) ions and undesired Mn(sup3+) ions on the surfaces. The electrochemical impedance spectroscopy (EIS) results...

  10. Evidence that the reversible strain effect on critical current density and flux pinning in Bi2Sr2Ca2Cu3Ox tapes is caused entirely by the pressure dependence of the critical temperature

    NARCIS (Netherlands)

    van der Laan, D. C.; Douglas, J. F.; Clickner, C. C.; Stauffer, T. C.; Goodrich, L. F.; van Eck, H. J. N.

    2011-01-01

    It is well known that the critical temperature of cuprate-and iron-based high-temperature superconductors changes with pressure. YBa2Cu3O7-delta coated conductors, as well as Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox tapes and wires, show a clear reversible effect of strain on their current-carrying

  11. Weak currents

    International Nuclear Information System (INIS)

    Leite Lopes, J.

    1976-01-01

    A survey of the fundamental ideas on weak currents such as CVC and PCAC and a presentation of the Cabibbo current and the neutral weak currents according to the Salam-Weinberg model and the Glashow-Iliopoulos-Miami model are given [fr

  12. Spin current

    CERN Document Server

    Valenzuela, Sergio O; Saitoh, Eiji; Kimura, Takashi

    2012-01-01

    In a new branch of physics and technology called spin-electronics or spintronics, the flow of electrical charge (usual current) as well as the flow of electron spin, the so-called 'spin current', are manipulated and controlled together. This book provides an introduction and guide to the new physics and application of spin current.

  13. Laboratory Density Functionals

    OpenAIRE

    Giraud, B. G.

    2007-01-01

    We compare several definitions of the density of a self-bound system, such as a nucleus, in relation with its center-of-mass zero-point motion. A trivial deconvolution relates the internal density to the density defined in the laboratory frame. This result is useful for the practical definition of density functionals.

  14. Doping dependence of the upper critical field, superconducting current density and thermally activated flux flow activation energy in polycrystalline CeFeAsO1-xFx superconductors

    Science.gov (United States)

    Chong, S. V.; Williams, G. V. M.; Sambale, S.; Kadowaki, K.

    2014-12-01

    We report the results from resistivity and magnetic measurements on polycrystalline Ce oxypnictide (CeFeAsO1-xFx) samples where x spans from 0.13 to 0.25. We find that the orbital limiting field is as high as 150 T and it systematically decreases with increasing doping. The Maki parameter is greater than one across the phase diagram and the large Maki parameter suggests that orbital and Pauli limiting effects contribute to the upper critical field. The broadening of the superconducting transition in the resistivity data was interpreted using the thermally activated flux flow (TAFF) model where we find that the TAFF activation energy, U0(B), is proportional to B-γ from 1 T to high fields, and γ does not significantly change with doping. However, U0 and the superconducting critical current, Jc, are peaked in the mid-doping region (x = 0.15-0.20), and not in the low (x 0.20) regions. Furthermore, U0 is correlated with Jc and follows the two fluid model for granular samples.

  15. Current cosmology

    International Nuclear Information System (INIS)

    Zeldovich, Ya.

    1984-01-01

    The knowledge is summed up of contemporary cosmology on the universe and its development resulting from a great number of highly sensitive observations and the application of contemporary physical theories to the entire universe. The questions are assessed of mass density in the universe, the structure and origin of the universe, its baryon asymmetry and the quantum explanation of the origin of the universe. Physical problems are presented which should be resolved for the future development of cosmology. (Ha)

  16. The impact of triggering mechanism on flow dynamics and depositional geometry: results from an experimental study of non-conservative density currents; Influencia do mecanismo de iniciacao na dinamica dos fluxos e na geometria dos depositos gerados: observacoes obtidas a partir de estudo experimental de correntes de densidade nao-conservativas

    Energy Technology Data Exchange (ETDEWEB)

    Manica, Rafael [Rio Grande do Sul Univ., Porto Alegre (Brazil). Inst. de Pesquisas Hidraulicas. Nucleo de Estudos de Correntes de Densidade]. E-mail: rmanica@portoweb.com.br; Del Rey, Antonio Cosme; Maestri, Rogerio Dornelles; Borges, Ana Luiza de Oliveira; Viana, Adriano Roessler

    2005-05-01

    This study presents 28 physical simulations of non-conservative density currents used to evaluate their depositional patterns. Two different triggering mechanisms were used: lock gate and fluid injection. The impact of specific gravity, material type and grain size on the mixture were also checked. Dynamic and geometric features, such as head velocity and head/body height, were recorded. Results show flow velocity increase as concentration grows; deposition volumes present a general tendency to exponential decline with distance; the grain size range of the deposits decreases towards the distal portion of the channel. The results obtained have showed the efficiency of physical modeling in the study of turbidites in allowing correlations to be defined between currents and deposition patterns. (author)

  17. Metastable atom probe for measuring electron beam density profiles

    Science.gov (United States)

    Lockhart, J. M.; Zorn, J. C.

    1972-01-01

    Metastable atom probe was developed for measuring current density in electron beam as function of two arbitrary coordinates, with spatial resolution better than 0.5 mm. Probe shows effects of space charge, magnetic fields, and other factors which influence electron current density, but operates with such low beam densities that introduced perturbation is very small.

  18. Individualized volume CT dose index determined by cross-sectional area and mean density of the body to achieve uniform image noise of contrast-enhanced pediatric chest CT obtained at variable kV levels and with combined tube current modulation

    Energy Technology Data Exchange (ETDEWEB)

    Goo, Hyun Woo [University of Ulsan College of Medicine, Department of Radiology and Research Institute of Radiology, Asan Medical Center, Seoul (Korea, Republic of)

    2011-07-15

    A practical body-size adaptive protocol providing uniform image noise at various kV levels is not available for pediatric CT. To develop a practical contrast-enhanced pediatric chest CT protocol providing uniform image noise by using an individualized volume CT dose index (CTDIvol) determined by the cross-sectional area and density of the body at variable kV levels and with combined tube current modulation. A total of 137 patients (mean age, 7.6 years) underwent contrast-enhanced pediatric chest CT based on body weight. From the CTDIvol, image noise, and area and mean density of the cross-section at the lung base in the weight-based group, the best fit equation was estimated with a very high correlation coefficient ({gamma}{sup 2} = 0.86, P < 0.001). For the next study, 177 patients (mean age, 7.9 years; the CTDIvol group) underwent contrast-enhanced pediatric chest CT with the CTDIvol determined individually by the best fit equation. CTDIvol values on the dose report after CT scanning, noise differences from the target noise, areas, and mean densities were compared between these two groups. The CTDIvol values (mean{+-}standard deviation, 1.6 {+-} 0.7 mGy) and the noise differences from the target noise (1.1 {+-} 0.9 HU) of the CTDIvol group were significantly lower than those of the weight-based group (2.0 {+-} 1.0 mGy, 1.8 {+-} 1.4 HU) (P < 0.001). In contrast, no statistically significant difference was found in area (317.0 {+-} 136.8 cm{sup 2} vs. 326.3 {+-} 124.8 cm{sup 2}), mean density (-212.9 {+-} 53.1 HU vs. -221.1 {+-} 56.3 HU), and image noise (13.8 {+-} 2.3 vs. 13.6 {+-} 1.7 HU) between the weight-based and the CTDIvol groups (P > 0.05). Contrast-enhanced pediatric chest CT with the CTDIvol determined individually by the cross-sectional area and density of the body provides more uniform noise and better dose adaptation to body habitus than does weight-based CT at variable kV levels and with combined tube current modulation. (orig.)

  19. Stability analysis of direct current control in current source rectifier

    DEFF Research Database (Denmark)

    Lu, Dapeng; Wang, Xiongfei; Blaabjerg, Frede

    2017-01-01

    Current source rectifier with high switching frequency has a great potential for improving the power efficiency and power density in ac-dc power conversion. This paper analyzes the stability of direct current control based on the time delay effect. Small signal model including dynamic behaviors...

  20. Current limiters

    Energy Technology Data Exchange (ETDEWEB)

    Loescher, D.H. [Sandia National Labs., Albuquerque, NM (United States). Systems Surety Assessment Dept.; Noren, K. [Univ. of Idaho, Moscow, ID (United States). Dept. of Electrical Engineering

    1996-09-01

    The current that flows between the electrical test equipment and the nuclear explosive must be limited to safe levels during electrical tests conducted on nuclear explosives at the DOE Pantex facility. The safest way to limit the current is to use batteries that can provide only acceptably low current into a short circuit; unfortunately this is not always possible. When it is not possible, current limiters, along with other design features, are used to limit the current. Three types of current limiters, the fuse blower, the resistor limiter, and the MOSFET-pass-transistor limiters, are used extensively in Pantex test equipment. Detailed failure mode and effects analyses were conducted on these limiters. Two other types of limiters were also analyzed. It was found that there is no best type of limiter that should be used in all applications. The fuse blower has advantages when many circuits must be monitored, a low insertion voltage drop is important, and size and weight must be kept low. However, this limiter has many failure modes that can lead to the loss of over current protection. The resistor limiter is simple and inexpensive, but is normally usable only on circuits for which the nominal current is less than a few tens of milliamperes. The MOSFET limiter can be used on high current circuits, but it has a number of single point failure modes that can lead to a loss of protective action. Because bad component placement or poor wire routing can defeat any limiter, placement and routing must be designed carefully and documented thoroughly.