Generation of subnanosecond electron beams in air at atmospheric pressure

NASA Astrophysics Data System (ADS)

Kostyrya, I. D.; Tarasenko, V. F.; Baksht, E. Kh.; Burachenko, A. G.; Lomaev, M. I.; Rybka, D. V.

2009-11-01

Optimum conditions for the generation of runaway electron beams with maximum current amplitudes and densities in nanosecond pulsed discharges in air at atmospheric pressure are determined. A supershort avalanche electron beam (SAEB) with a current amplitude of ˜30 A, a current density of ˜20 A/cm2, and a pulse full width at half maximum (FWHM) of ˜100 ps has been observed behind the output foil of an air-filled diode. It is shown that the position of the SAEB current maximum relative to the voltage pulse front exhibits a time shift that varies when the small-size collector is moved over the foil surface.

Digital processing with single electrons for arbitrary waveform generation of current

NASA Astrophysics Data System (ADS)

Okazaki, Yuma; Nakamura, Shuji; Onomitsu, Koji; Kaneko, Nobu-Hisa

2018-03-01

We demonstrate arbitrary waveform generation of current using a GaAs-based single-electron pump. In our experiment, a digital processing algorithm known as delta-sigma modulation is incorporated into single-electron pumping to generate a density-modulated single-electron stream, by which we demonstrate the generation of arbitrary waveforms of current including sinusoidal, square, and triangular waves with a peak-to-peak amplitude of approximately 10 pA and an output bandwidth ranging from dc to close to 1 MHz. The developed current generator can be used as the precise and calculable current reference required for measurements of current noise in low-temperature experiments.

Quantum power functional theory for many-body dynamics

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

Schmidt, Matthias, E-mail: Matthias.Schmidt@uni-bayreuth.de

2015-11-07

We construct a one-body variational theory for the time evolution of nonrelativistic quantum many-body systems. The position- and time-dependent one-body density, particle current, and time derivative of the current act as three variational fields. The generating (power rate) functional is minimized by the true current time derivative. The corresponding Euler-Lagrange equation, together with the continuity equation for the density, forms a closed set of one-body equations of motion. Space- and time-nonlocal one-body forces are generated by the superadiabatic contribution to the functional. The theory applies to many-electron systems.

Method to prevent sulfur accumulation in membrane electrode assembly

DOEpatents

Steimke, John L; Steeper, Timothy J; Herman, David T

2014-04-29

A method of operating a hybrid sulfur electrolyzer to generate hydrogen is provided that includes the steps of providing an anolyte with a concentration of sulfur dioxide, and applying a current. During steady state generation of hydrogen a plot of applied current density versus concentration of sulfur dioxide is below a boundary line. The boundary line may be linear and extend through the origin of the graph with a slope of 0.001 in which the current density is measured in mA/cm2 and the concentration of sulfur dioxide is measured in moles of sulfur dioxide per liter of anolyte.

Current-driven dynamics of skyrmions stabilized in MnSi nanowires revealed by topological Hall effect

PubMed Central

Liang, Dong; DeGrave, John P.; Stolt, Matthew J.; Tokura, Yoshinori; Jin, Song

2015-01-01

Skyrmions hold promise for next-generation magnetic storage as their nanoscale dimensions may enable high information storage density and their low threshold for current-driven motion may enable ultra-low energy consumption. Skyrmion-hosting nanowires not only serve as a natural platform for magnetic racetrack memory devices but also stabilize skyrmions. Here we use the topological Hall effect (THE) to study phase stability and current-driven dynamics of skyrmions in MnSi nanowires. THE is observed in an extended magnetic field-temperature window (15–30 K), suggesting stabilization of skyrmions in nanowires compared with the bulk. Furthermore, we show in nanowires that under the high current density of 108–109 A m−2, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field in the extended skyrmion phase region. These results open up the exploration of skyrmions in nanowires for fundamental physics and magnetic storage technologies. PMID:26400204

Magnetic field generator

DOEpatents

Krienin, Frank

1990-01-01

A magnetic field generating device provides a useful magnetic field within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magnetic fields may be generated and contained using superconducting cables to approximate required current surfaces.

Influence of the current density on the electrochemical treatment of concentrated 1-butyl-3-methylimidazolium chloride solutions on diamond electrodes.

PubMed

Marcionilio, Suzana M L de Oliveira; Alves, Gisele M; E Silva, Rachel B Góes; Marques, Pablo J Lima; Maia, Poliana D; Neto, Brenno A D; Linares, José J

2016-10-01

This paper focuses on the influence of the current density treatment of a concentrated 1-butyl-3-methylimidazolium chloride (BMImCl) solution on an electrochemical reactor with a boron-doped diamond (BDD) anode. The decrease in the total organic carbon (TOC) and the BMImCl concentration demonstrate the capability of BDD in oxidizing ionic liquids (ILs) and further mineralizing (to CO2 and NO3 (-)) more rapidly at higher current densities in spite of the reduced current efficiency of the process. Moreover, the presence of Cl(-) led to the formation of oxychlorinated anions (mostly ClO3 (-) and ClO4 (-)) and, in combination with the ammonia generated in the cathode from the nitrate reduction, chloramines, more intensely at higher current density. Finally, the analysis of the intermediates formed revealed no apparent influence of the current density on the BMImCl degradation mechanism. The current density presents therefore a complex influence on the IL treatment process that is discussed throughout this paper.

Fine-Filament MgB2 Superconductor Wire

NASA Technical Reports Server (NTRS)

Cantu, Sherrie

2015-01-01

Hyper Tech Research, Inc., has developed fine-filament magnesium diboride (MgB2) superconductor wire for motors and generators used in turboelectric aircraft propulsion systems. In Phase I of the project, Hyper Tech demonstrated that MgB2 multifilament wires (<10 micrometers) could reduce alternating current (AC) losses that occur due to hysteresis, eddy currents, and coupling losses. The company refined a manufacturing method that incorporates a magnesium-infiltration process and provides a tenfold enhancement in critical current density over wire made by a conventional method involving magnesium-boron powder mixtures. Hyper Tech also improved its wire-drawing capability to fabricate fine multifilament strands. In Phase II, the company developed, manufactured, and tested the wire for superconductor and engineering current density and AC losses. Hyper Tech also fabricated MgB2 rotor coil packs for a superconducting generator. The ultimate goal is to enable low-cost, round, lightweight, low-AC-loss superconductors for motor and generator stator coils operating at 25 K in next-generation turboelectric aircraft propulsion systems.

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

PubMed

Guzmán-Duque, Fernando L; Palma-Goyes, Ricardo E; González, Ignacio; Peñuela, Gustavo; Torres-Palma, Ricardo A

2014-08-15

Taking crystal violet (CV) dye as pollutant model, the electrode, electrolyte and current density (i) relationship for electro-degrading organic molecules is discussed. Boron-doped diamond (BDD) or Iridium dioxide (IrO2) used as anode materials were tested with Na2SO4 or NaCl as electrolytes. CV degradation and generated oxidants showed that degradation pathways and efficiency are strongly linked to the current density-electrode-electrolyte interaction. With BDD, the degradation pathway depends on i: If ii(lim), generated oxidants play a major role in the CV elimination. When IrO2 was used, CV removal was not dependent on i, but on the electrolyte. Pollutant degradation in Na2SO4 on IrO2 seems to occur via IrO3; however, in the presence of NaCl, degradation was dependent on the chlorinated oxidative species generated. In terms of efficiency, the Na2SO4 electrolyte showed better results than NaCl when BDD anodes were employed. On the contrary, NaCl was superior when combined with IrO2. Thus, the IrO2/Cl(-) and BDD/SO4(2-) systems were better at removing the pollutant, being the former the most effective. On the other hand, pollutant degradation with the BDD/SO4(2-) and IrO2/Cl(-) systems is favored at low and high current densities, respectively. Copyright © 2014 Elsevier B.V. All rights reserved.

Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS2 multilayers

NASA Astrophysics Data System (ADS)

Liu, Jun; Goswami, Ankur; Jiang, Keren; Khan, Faheem; Kim, Seokbeom; McGee, Ryan; Li, Zhi; Hu, Zhiyu; Lee, Jungchul; Thundat, Thomas

2018-02-01

The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting1-3. A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification2. Here, we show that continuous direct-current (d.c.) with a maximum density of 106 A m-2 can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS2). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (105-106 V m-2) at the conductive nanoscale tip4. We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.

Interrupting an Imminent Body Current Fault and Restoring Full Power in Milliseconds on a DIII-D National Fusion Facility Gyrotron

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

Ponce, Dan; Brambila, Rigo E.; Cengher, Mirela

The ECH Group at DIII-D has installed in-house engineered, FPGA-based, high voltage reference waveform generators on its gyrotron control systems to enhance the capabilities of the systems and replace obsolete equipment. The new hardware, named D-Wavegen, outputs 16-bit signals every microsecond and can respond to events and anomalies in real-time. These generators have been reliably pausing gyrotron rf output during periods of DIII-D plasma density that exceed the fault density trip level and restarting the rf output if the density falls below the trip level. While tightly monitoring gyrotron body current and internal pressure, D-Wavegen has also been reliably restarting,more » in a little over 10ms, gyrotrons that spontaneously ceased rf generation.« less

Interrupting an Imminent Body Current Fault and Restoring Full Power in Milliseconds on a DIII-D National Fusion Facility Gyrotron

DOE PAGES

Ponce, Dan; Brambila, Rigo E.; Cengher, Mirela; ...

2017-10-19

The ECH Group at DIII-D has installed in-house engineered, FPGA-based, high voltage reference waveform generators on its gyrotron control systems to enhance the capabilities of the systems and replace obsolete equipment. The new hardware, named D-Wavegen, outputs 16-bit signals every microsecond and can respond to events and anomalies in real-time. These generators have been reliably pausing gyrotron rf output during periods of DIII-D plasma density that exceed the fault density trip level and restarting the rf output if the density falls below the trip level. While tightly monitoring gyrotron body current and internal pressure, D-Wavegen has also been reliably restarting,more » in a little over 10ms, gyrotrons that spontaneously ceased rf generation.« less

Bearing failure detection of micro wind turbine via power spectral density analysis for stator current signals spectrum

NASA Astrophysics Data System (ADS)

Mahmood, Faleh H.; Kadhim, Hussein T.; Resen, Ali K.; Shaban, Auday H.

2018-05-01

The failure such as air gap weirdness, rubbing, and scrapping between stator and rotor generator arise unavoidably and may cause extremely terrible results for a wind turbine. Therefore, we should pay more attention to detect and identify its cause-bearing failure in wind turbine to improve the operational reliability. The current paper tends to use of power spectral density analysis method of detecting internal race and external race bearing failure in micro wind turbine by estimation stator current signal of the generator. The failure detector method shows that it is well suited and effective for bearing failure detection.

Non-inductive current generation in fusion plasmas with turbulence

NASA Astrophysics Data System (ADS)

Wang, Weixing; Ethier, S.; Startsev, E.; Chen, J.; Hahm, T. S.; Yoo, M. G.

2017-10-01

It is found that plasma turbulence may strongly influence non-inductive current generation. This may have radical impact on various aspects of tokamak physics. Our simulation study employs a global gyrokinetic model coupling self-consistent neoclassical and turbulent dynamics with focus on electron current. Distinct phases in electron current generation are illustrated in the initial value simulation. In the early phase before turbulence develops, the electron bootstrap current is established in a time scale of a few electron collision times, which closely agrees with the neoclassical prediction. The second phase follows when turbulence begins to saturate, during which turbulent fluctuations are found to strongly affect electron current. The profile structure, amplitude and phase space structure of electron current density are all significantly modified relative to the neoclassical bootstrap current by the presence of turbulence. Both electron parallel acceleration and parallel residual stress drive are shown to play important roles in turbulence-induced current generation. The current density profile is modified in a way that correlates with the fluctuation intensity gradient through its effect on k//-symmetry breaking in fluctuation spectrum. Turbulence is shown to deduct (enhance) plasma self-generated current in low (high) collisionality regime, and the reduction of total electron current relative to the neoclassical bootstrap current increases as collisionality decreases. The implication of this result to the fully non-inductive current operation in steady state burning plasma regime should be investigated. Finally, significant non-inductive current is observed in flat pressure region, which is a nonlocal effect and results from turbulence spreading induced current diffusion. Work supported by U.S. DOE Contract DE-AC02-09-CH11466.

Breaking the current density threshold in spin-orbit-torque magnetic random access memory

NASA Astrophysics Data System (ADS)

Zhang, Yin; Yuan, H. Y.; Wang, X. S.; Wang, X. R.

2018-04-01

Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising technology for the next generation of data storage devices. The main bottleneck of this technology is the high reversal current density threshold. This outstanding problem is now solved by a new strategy in which the magnitude of the driven current density is fixed while the current direction varies with time. The theoretical limit of minimal reversal current density is only a fraction (the Gilbert damping coefficient) of the threshold current density of the conventional strategy. The Euler-Lagrange equation for the fastest magnetization reversal path and the optimal current pulse is derived for an arbitrary magnetic cell and arbitrary spin-orbit torque. The theoretical limit of minimal reversal current density and current density for a GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are, respectively, of the order of 105 A/cm 2 and 106 A/cm 2 far below 107 A/cm 2 and 108 A/cm 2 in the conventional strategy. Furthermore, no external magnetic field is needed for a deterministic reversal in the new strategy.

Anomalous - viscosity current drive

DOEpatents

Stix, Thomas H.; Ono, Masayuki

1988-01-01

An apparatus and method for maintaining a steady-state current in a toroidal magnetically confined plasma. An electric current is generated in an edge region at or near the outermost good magnetic surface of the toroidal plasma. The edge current is generated in a direction parallel to the flow of current in the main plasma and such that its current density is greater than the average density of the main plasma current. The current flow in the edge region is maintained in a direction parallel to the main current for a period of one or two of its characteristic decay times. Current from the edge region will penetrate radially into the plasma and augment the main plasma current through the mechanism of anomalous viscosity. In another aspect of the invention, current flow driven between a cathode and an anode is used to establish a start-up plasma current. The plasma-current channel is magnetically detached from the electrodes, leaving a plasma magnetically insulated from contact with any material obstructions including the cathode and anode.

Guiding supersonic projectiles using optically generated air density channels

NASA Astrophysics Data System (ADS)

Johnson, Luke A.; Sprangle, Phillip

2015-09-01

We investigate the feasibility of using optically generated channels of reduced air density to provide trajectory correction (guiding) for a supersonic projectile. It is shown that the projectile experiences a force perpendicular to its direction of motion as one side of the projectile passes through a channel of reduced air density. A single channel of reduced air density can be generated by the energy deposited from filamentation of an intense laser pulse. We propose changing the laser pulse energy from shot-to-shot to build longer effective channels. Current femtosecond laser systems with multi-millijoule pulses could provide trajectory correction of several meters on 5 km trajectories for sub-kilogram projectiles traveling at Mach 3.

NASA Glenn Research Center Program in High Power Density Motors for Aeropropulsion

NASA Technical Reports Server (NTRS)

Brown, Gerald V.; Kascak, Albert F.; Ebihara, Ben; Johnson, Dexter; Choi, Benjamin; Siebert, Mark; Buccieri, Carl

2005-01-01

Electric drive of transport-sized aircraft propulsors, with electric power generated by fuel cells or turbo-generators, will require electric motors with much higher power density than conventional room-temperature machines. Cryogenic cooling of the motor windings by the liquid hydrogen fuel offers a possible solution, enabling motors with higher power density than turbine engines. Some context on weights of various systems, which is required to assess the problem, is presented. This context includes a survey of turbine engine weights over a considerable size range, a correlation of gear box weights and some examples of conventional and advanced electric motor weights. The NASA Glenn Research Center program for high power density motors is outlined and some technical results to date are presented. These results include current densities of 5,000 A per square centimeter current density achieved in cryogenic coils, finite element predictions compared to measurements of torque production in a switched reluctance motor, and initial tests of a cryogenic switched reluctance motor.

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

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

Branitskii, A. V.; Grabovskii, E. V.; Dzhangobegov, V. V.

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.

3-D capacitance density imaging system

DOEpatents

Fasching, G.E.

1988-03-18

A three-dimensional capacitance density imaging of a gasified bed or the like in a containment vessel is achieved using a plurality of electrodes provided circumferentially about the bed in levels and along the bed in channels. The electrodes are individually and selectively excited electrically at each level to produce a plurality of current flux field patterns generated in the bed at each level. The current flux field patterns are suitably sensed and a density pattern of the bed at each level determined. By combining the determined density patterns at each level, a three-dimensional density image of the bed is achieved. 7 figs.

3-D capacitance density imaging of fluidized bed

DOEpatents

Fasching, George E.

1990-01-01

A three-dimensional capacitance density imaging of a gasified bed or the like in a containment vessel is achieved using a plurality of electrodes provided circumferentially about the bed in levels and along the bed in channels. The electrodes are individually and selectively excited electrically at each level to produce a plurality of current flux field patterns generated in the bed at each level. The current flux field patterns are suitably sensed and a density pattern of the bed at each level determined. By combining the determined density patterns at each level, a three-dimensional density image of the bed is achieved.

Electrochemical disinfection using boron-doped diamond electrode--the synergetic effects of in situ ozone and free chlorine generation.

PubMed

Rajab, Mohamad; Heim, Carolin; Letzel, Thomas; Drewes, Jörg E; Helmreich, Brigitte

2015-02-01

This work investigated the capability of using a boron-doped diamond (BDD) electrode for bacterial disinfection in different water matrices containing varying amounts of chloride. The feed water containing Pseudomonas aeruginosa was electrochemically treated while applying different electrode conditions. Depending on the applied current density and the exposure time, inactivation between 4- and 8-log of the targeted microorganisms could be achieved. The disinfection efficiency was driven by the generation of free chlorine as a function of chloride concentration in the water. A synergetic effect of generating both free chlorine and ozone in situ during the disinfection process resulted in an effective bactericidal impact. The formation of the undesired by-products chlorate and perchlorate depended on the water matrix, the applied current density and the desired target disinfection level. In case of synthetic water with a low chloride concentration (20 mg L(-1)) and an applied current density of 167 mA cm(-2), a 6-log inactivation of Pseudomonas aeruginosa could be achieved after 5 min of exposure. The overall energy consumption ranged between 0.3 and 0.6 kW h m(-3) depending on the applied current density and water chemistry. Electrochemical water disinfection represents a suitable and efficient process for producing pathogen-free water without the use of any chemicals. Copyright © 2014 Elsevier Ltd. All rights reserved.

Characterization of thunderstorm induced Maxwell current densities in the middle atmosphere

NASA Technical Reports Server (NTRS)

Baginski, Michael Edward

1989-01-01

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

Azimuthal swirl in liquid metal electrodes and batteries

NASA Astrophysics Data System (ADS)

Ashour, Rakan; Kelley, Douglas

2016-11-01

Liquid metal batteries consist of two molten metals with different electronegativity separated by molten salt. In these batteries, critical performance related factors such as the limiting current density are governed by fluid mixing in the positive electrode. In this work we present experimental results of a swirling flow in a layer of molten lead-bismuth alloy driven by electrical current. Using in-situ ultrasound velocimetery, we show that poloidal circulation appears at low current density, whereas azimuthal swirl becomes dominant at higher current density. The presence of thermal gradients produces buoyant forces, which are found to compete with those produced by current injection. Taking the ratio of the characteristic electromagnetic to buoyant flow velocity, we are able to predict the current density at which the flow becomes electromagnetically driven. Scaling arguments are also used to show that swirl is generated through self-interaction between the electrical current in the electrode with its own magnetic field.

Abnormalities of P300 cortical current density in unmedicated depressed patients revealed by LORETA analysis of event-related potentials.

PubMed

Kawasaki, Toshihiko; Tanaka, Shin; Wang, Jijun; Hokama, Hiroto; Hiramatsu, Kenichi

2004-02-01

The purpose of the present study was to investigate the neural substrates underlying event-related potential (ERP) abnormalities, with respect to the generators of the ERP components in depressed patients. Using an oddball paradigm, ERP from auditory stimuli were recorded from 22 unmedicated patients with current depressive episodes and compared with those from 22 age- and gender-matched normal controls. Cortical current densities of the N100 and P300 components were analyzed using low-resolution electromagnetic tomography (LORETA). Group differences in cortical current density were mapped on a 3-D cortex model. The results revealed that N100 cortical current densities did not differ between the two groups, while P300 cortical current densities were significantly lower in depressed patients over the bilateral temporal lobes, the left frontal region, and the right temporal-parietal area. Furthermore, the cortical area in which the group difference in P300 current density had been identified was remarkably larger over the right than the left hemisphere, thus supporting the hypothesis of right hemisphere dysfunction in depression.

Validation of neoclassical bootstrap current models in the edge of an H-mode plasma.

PubMed

Wade, M R; Murakami, M; Politzer, P A

2004-06-11

Analysis of the parallel electric field E(parallel) evolution following an L-H transition in the DIII-D tokamak indicates the generation of a large negative pulse near the edge which propagates inward, indicative of the generation of a noninductive edge current. Modeling indicates that the observed E(parallel) evolution is consistent with a narrow current density peak generated in the plasma edge. Very good quantitative agreement is found between the measured E(parallel) evolution and that expected from neoclassical theory predictions of the bootstrap current.

LORETA imaging of P300 in schizophrenia with individual MRI and 128-channel EEG.

PubMed

Pae, Ji Soo; Kwon, Jun Soo; Youn, Tak; Park, Hae-Jeong; Kim, Myung Sun; Lee, Boreom; Park, Kwang Suk

2003-11-01

We investigated the characteristics of P300 generators in schizophrenics by using voxel-based statistical parametric mapping of current density images. P300 generators, produced by a rare target tone of 1500 Hz (15%) under a frequent nontarget tone of 1000 Hz (85%), were measured in 20 right-handed schizophrenics and 21 controls. Low-resolution electromagnetic tomography (LORETA), using a realistic head model of the boundary element method based on individual MRI, was applied to the 128-channel EEG. Three-dimensional current density images were reconstructed from the LORETA intensity maps that covered the whole cortical gray matter. Spatial normalization and intensity normalization of the smoothed current density images were used to reduce anatomical variance and subject-specific global activity and statistical parametric mapping (SPM) was applied for the statistical analysis. We found that the sources of P300 were consistently localized at the left superior parietal area in normal subjects, while those of schizophrenics were diversely distributed. Upon statistical comparison, schizophrenics, with globally reduced current densities, showed a significant P300 current density reduction in the left medial temporal area and in the left inferior parietal area, while both left prefrontal and right orbitofrontal areas were relatively activated. The left parietotemporal area was found to correlate negatively with Positive and Negative Syndrome Scale total scores of schizophrenic patients. In conclusion, the reduced and increased areas of current density in schizophrenic patients suggest that the medial temporal and frontal areas contribute to the pathophysiology of schizophrenia, the frontotemporal circuitry abnormality.

Role of lead in electrochemical reaction of alloy 600, alloy 690, Ni, Cr, and Fe in water

NASA Astrophysics Data System (ADS)

Hwang, Seong Sik; Kim, Joung Soo; Kim, Ju Yup

2003-08-01

It has been reported that lead causes stress corrosion cracking (SCC) in the secondary side of steam generators (SG) in pressurized water reactors (PWR). The materials of SG tubings are alloy 600, alloy 690, or alloy 800, among which the main alloying elements are Ni, Cr, and Fe. The effect of lead on the electrochemical behaviors of alloy 600 and alloy 690 using an anodic polarization technique was evaluated. We also obtained polarization curves of pure Ni, Cr, and Fe in water containing lead. As the amount of lead in the solution increased, critical current densities and passive current densities of alloy 600 and alloy 690 increased, while the breakdown potential of the alloys decreased. Lead increased critical current density and the passive current of Cr in pH 4 and pH 10. The instability of passive film of steam generator tubings in water containing lead might arise from the instability of Cr passivity.

Electrical evaluation of crack generation in SiNx and SiOxNy thin-film encapsulation layers for OLED displays

NASA Astrophysics Data System (ADS)

Park, Eun Kil; Kim, Sungmin; Heo, Jaeyeong; Kim, Hyeong Joon

2016-05-01

By measuring leakage current density, we detected crack generation in silicon nitride (SiNx) and silicon oxynitride (SiOxNy) thin-film encapsulation layers, and correlated with the films' water vapor permeability characteristics. After repeated bending cycles, both the changes in water vapor transmission rate and leakage current density were directly proportional to the crack density. Thick SiNx films had better water vapor barrier characteristics in their pristine state, but cyclic loading led to fast failure. Varying the atomic concentration of the SiOxNy films affected their bending reliability. We attribute these differences to changes in the shape of the crack tip as the oxygen content varies.

Laser beat wave excitation of terahertz radiation in a plasma slab

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

Chauhan, Santosh; Parashar, Jetendra, E-mail: j.p.parashar@gmail.com

2014-10-15

Terahertz (THz) radiation generation by nonlinear mixing of lasers, obliquely incident on a plasma slab is investigated. Two cases are considered: (i) electron density profile is parabolic but density peak is below the critical density corresponding to the beat frequency, (ii) plasma boundaries are sharp and density is uniform. In both cases, nonlinearity arises through the ponderomotive force that gives rise to electron drift at the beat frequency. In the case of inhomogeneous plasma, non zero curl of the nonlinear current density gives rise to electromagnetic THz generation. In case of uniform plasma, the sharp density variation at the plasmamore » boundaries leads to radiation generation. In a slab width of less than a terahertz wavelength, plasma density one fourth of terahertz critical density, laser intensities ∼10{sup 17 }W/cm{sup 2} at 1 μm, one obtains the THz intensity ∼1 GW/cm{sup 2} at 3 THz radiation frequency.« less

Generation of Alfvenic Double Layers, Formation of Auroral Arcs, and Their Impact on Energy and Momentum Transfer in M-I Coupling System

NASA Astrophysics Data System (ADS)

Song, Y.; Lysak, R. L.

2017-12-01

Parallel electrostatic electric fields provide a powerful mechanism to accelerate auroral particles to high energy in the auroral acceleration region (AAR), creating both quasi-static and Alfvenic discrete aurorae. The total field-aligned current can be written as J||total=J||+J||D, where the displacement current is denoted as J||D=(1/4π)(∂E||/∂t), which describes the E||-generation (Song and Lysak, 2006). The generation of the total field-aligned current is related to spatial gradients of the parallel vorticity caused by the axial torque acting on field-aligned flux tubes in M-I coupling system. It should be noticed that parallel electric fields are not produced by the field-aligned current. In fact, the E||-generation is caused by Alfvenic interaction in the M-I coupling system, and is favored by a low plasma density and the enhanced localized azimuthal magnetic flux. We suggest that the nonlinear interaction of incident and reflected Alfven wave packets in the AAR can create reactive stress concentration, and therefore can generate the parallel electrostatic electric fields together with a seed low density cavity. The generated electric fields will quickly deepen the seed low density cavity, which can effectively create even stronger electrostatic electric fields. The electrostatic electric fields nested in a low density cavity and surrounded by enhanced azimuthal magnetic flux constitute Alfvenic electromagnetic plasma structures, such as Alfvenic Double Layers (DLs). The Poynting flux carried by Alfven waves can continuously supply energy from the generator region to the auroral acceleration region, supporting and sustaining Alfvenic DLs with long-lasting electrostatic electric fields which accelerate auroral particles to high energy. The generation of parallel electric fields and the formation of auroral arcs can redistribute perpendicular mechanical and magnetic stresses in auroral flux tubes, decoupling the magnetosphere from ionosphere drag locally. This may enhance the magnetotail earthward shear flows and rapidly buildup stronger parallel electric fields in the auroral acceleration region, leading to a sudden and violent tail energy release, if there is accumulated free magnetic energy in the tail.

Power enhancement of piezoelectric transformers by adding heat transfer equipment.

PubMed

Su, Yu-Hao; Liu, Yuan-Ping; Vasic, Dejan; Wu, Wen-Jong; Costa, François; Lee, Chih-Kung

2012-10-01

It is known that piezoelectric transformers have several inherent advantages compared with conventional electromagnetic transformers. However, the maximum power capacity of piezoelectric transformers is not as large as electromagnetic transformers in practice, especially in the case of high output current. The theoretical power density of piezoelectric transformers calculated by stress boundary can reach 330 W/cm(3), but no piezoelectric transformer has ever reached such a high power density in practice. The power density of piezoelectric transformers is limited to 33 W/cm(3) in practical applications. The underlying reason is that the maximum passing current of the piezoelectric material (mechanical current) is limited by the temperature rise caused by heat generation. To increase this current and the power capacity, we proposed to add a thermal pad to the piezoelectric transformer to dissipate heat. The experimental results showed that the proposed techniques can increase by 3 times the output current of the piezoelectric transformer. A theoretical-phenomenological model which explains the relationship between vibration velocity and generated heat is also established to verify the experimental results.

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

Fertig, Fabian, E-mail: fabian.fertig@ise.fraunhofer.de; Greulich, Johannes; Rein, Stefan

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

Effect of electrode sub-micron surface feature size on current generation of Shewanella oneidensis in microbial fuel cells

NASA Astrophysics Data System (ADS)

Ye, Zhou; Ellis, Michael W.; Nain, Amrinder S.; Behkam, Bahareh

2017-04-01

Microbial fuel cells (MFCs) are envisioned to serve as compact and sustainable sources of energy; however, low current and power density have hindered their widespread use. Introduction of 3D micro/nanostructures on the MFC anode is known to improve its performance by increasing the surface area available for bacteria attachment; however, the role of the feature size remains poorly understood. To delineate the role of feature size from the ensuing surface area increase, nanostructures with feature heights of 115 nm and 300 nm, both at a height to width aspect ratio of 0.3, are fabricated in a grid pattern on glassy carbon electrodes (GCEs). Areal current densities and bacteria attachment densities of the patterned and unpatterned GCEs are compared using Shewanella oneidensis Δbfe in a three-electrode bioreactor. The 115 nm features elicit a remarkable 40% increase in current density and a 78% increase in bacterial attachment density, whereas the GCE with 300 nm pattern does not exhibit significant change in current density or bacterial attachment density. The current density dependency on feature size is maintained over the entire 160 h experiment. Thus, optimally sized surface features have a substantial effect on current production that is independent of their effect on surface area.

Relativistic electron beam generator

DOEpatents

Mooney, L.J.; Hyatt, H.M.

1975-11-11

A relativistic electron beam generator for laser media excitation is described. The device employs a diode type relativistic electron beam source having a cathode shape which provides a rectangular output beam with uniform current density.

Tandem organic light-emitting diodes with buffer-modified C60/pentacene as charge generation layer

NASA Astrophysics Data System (ADS)

Wang, Zhen; Zheng, Xin; Liu, Fei; Wang, Pei; Gan, Lin; Wang, Jing-jing

2017-09-01

Buffer-modified C60/pentacene as charge generation layer (CGL) is investigated to achieve effective performance of charge generation. Undoped green electroluminescent tandem organic light-emitting diodes (OLEDs) with multiple identical emissive units and using buffer-modified C60/pentacene organic semiconductor heterojunction (OHJ) as CGL are demonstrated to exhibit better current density and brightness, compared with conventional single-unit devices. The current density and brightness both can be significantly improved with increasing the thickness of Al. However, excessive thickness of Al seriously decreases the transmittance of films and damages the interface. As a result, the maximum current efficiency of 1.43 cd·A-1 at 30 mA·cm-2 can be achieved for tandem OLEDs with optimal thickness of Al. These results clearly demonstrate that Cs2CO3/Al is an effective buffer for C60/pentacene-based tandem OLEDs.

Cortical inhibition and excitation by bilateral transcranial alternating current stimulation.

PubMed

Cancelli, Andrea; Cottone, Carlo; Zito, Giancarlo; Di Giorgio, Marina; Pasqualetti, Patrizio; Tecchio, Franca

2015-01-01

Transcranial electric stimulations (tES) with amplitude-modulated currents are promising tools to enhance neuromodulation effects. It is essential to select the correct cortical targets and inhibitory/excitatory protocols to reverse changes in specific networks. We aimed at assessing the dependence of cortical excitability changes on the current amplitude of 20 Hz transcranial alternating current stimulation (tACS) over the bilateral primary motor cortex. We chose two amplitude ranges of the stimulations, around 25 μA/cm2 and 63 μA/cm2 from peak to peak, with three values (at steps of about 2.5%) around each, to generate, respectively, inhibitory and excitatory effects of the primary motor cortex. We checked such changes online through transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs). Cortical excitability changes depended upon current density (p = 0.001). Low current densities decreased MEP amplitudes (inhibition) while high current densities increased them (excitation). tACS targeting bilateral homologous cortical areas can induce online inhibition or excitation as a function of the current density.

Insights into the applicability of microbial fuel cells in wastewater treatment plants for a sustainable generation of electricity.

PubMed

Krieg, Thomas; Mayer, Florian; Sell, Dieter; Holtmann, Dirk

2017-11-21

Microbial fuel cells (MFCs) are often discussed as a part of a sustainable generation of electricity for the coming 'energy revolution'. In particular, the application of MFCs in wastewater treatment plants (WWTPs) are often regarded as an attractive alternative to reduce costs while generating electricity. Field surveys are necessary to show the applicability of MFCs in WWTPs considering daily fluctuations and environmental effects such as rain events affecting the MFC performance remarkably. In this study, a MFC system was tested in four municipal WWTPs using different modes of operation. A correlation between current densities and sludge loading (SL) was identified. At low SLs, the activated sludge needs a large amount of the energy derived from the substrate for the maintenance metabolism resulting in quite low current densities of the MFC. At high SLs much more of the energy can be transferred from the activated sludge to the electrode, resulting in higher currents. Furthermore, the effect of environmental conditions on the current densities was evaluated. WWTPs have daily fluctuations depending on the wastewater composition, weather phenomena and population equivalents. Our data show that these daily fluctuations can only be observed in the MFC performance at WWTPs below 50,000 population equivalents.

Neutron generator for BNCT based on high current ECR ion source with gyrotron plasma heating.

PubMed

Skalyga, V; Izotov, I; Golubev, S; Razin, S; Sidorov, A; Maslennikova, A; Volovecky, A; Kalvas, T; Koivisto, H; Tarvainen, O

2015-12-01

BNCT development nowadays is constrained by a progress in neutron sources design. Creation of a cheap and compact intense neutron source would significantly simplify trial treatments avoiding use of expensive and complicated nuclear reactors and accelerators. D-D or D-T neutron generator is one of alternative types of such sources for. A so-called high current quasi-gasdynamic ECR ion source with plasma heating by millimeter wave gyrotron radiation is suggested to be used in a scheme of D-D neutron generator in the present work. Ion source of that type was developed in the Institute of Applied Physics of Russian Academy of Sciences (Nizhny Novgorod, Russia). It can produce deuteron ion beams with current density up to 700-800 mA/cm(2). Generation of the neutron flux with density at the level of 7-8·10(10) s(-1) cm(-2) at the target surface could be obtained in case of TiD2 target bombardment with deuteron beam accelerated to 100 keV. Estimations show that it is enough for formation of epithermal neutron flux with density higher than 10(9) s(-1) cm(-2) suitable for BNCT. Important advantage of described approach is absence of Tritium in the scheme. First experiments performed in pulsed regime with 300 mA, 45 kV deuteron beam directed to D2O target demonstrated 10(9) s(-1) neutron flux. This value corresponds to theoretical estimations and proofs prospects of neutron generator development based on high current quasi-gasdynamic ECR ion source. Copyright © 2015 Elsevier Ltd. All rights reserved.

Gyrotron-driven high current ECR ion source for boron-neutron capture therapy neutron generator

NASA Astrophysics Data System (ADS)

Skalyga, V.; Izotov, I.; Golubev, S.; Razin, S.; Sidorov, A.; Maslennikova, A.; Volovecky, A.; Kalvas, T.; Koivisto, H.; Tarvainen, O.

2014-12-01

Boron-neutron capture therapy (BNCT) is a perspective treatment method for radiation resistant tumors. Unfortunately its development is strongly held back by a several physical and medical problems. Neutron sources for BNCT currently are limited to nuclear reactors and accelerators. For wide spread of BNCT investigations more compact and cheap neutron source would be much more preferable. In present paper an approach for compact D-D neutron generator creation based on a high current ECR ion source is suggested. Results on dense proton beams production are presented. A possibility of ion beams formation with current density up to 600 mA/cm2 is demonstrated. Estimations based on obtained experimental results show that neutron target bombarded by such deuteron beams would theoretically yield a neutron flux density up to 6·1010 cm-2/s. Thus, neutron generator based on a high-current deuteron ECR source with a powerful plasma heating by gyrotron radiation could fulfill the BNCT requirements significantly lower price, smaller size and ease of operation in comparison with existing reactors and accelerators.

Application of hybrid supercapacitor using granule Li4Ti5O12/activated carbon with variation of current density

NASA Astrophysics Data System (ADS)

Lee, Byung-Gwan; Lee, Seung-Hwan

2017-03-01

We report the electrochemical performance of asymmetric hybrid supercapacitors composed of granule Li4Ti5O12 as an anode and activated carbon as a cathode with different current densities. It is demonstrated that the hybrid supercapacitors show good initial discharge capacities were ranged from 39.8 to 46.4 F g-1 in the current densities range of 0.3-1 A g-1. The performance degradation is proportional to the current density due to quick gassing, resulting from H2O and HF formation. In particular, the hybrid supercapacitors show the pretty good cycling stability of 97.4%, even at the high current density of 0.8 A g-1, which are among most important performance in the real application for energy storage devices. Therefore, we believe that hybrid supercapacitors using granule Li4Ti5O12/activated carbon are eligible for the promising next generation energy devices.

Fast electrochemical deposition of Ni(OH)2 precursor involving water electrolysis for fabrication of NiO thin films

NASA Astrophysics Data System (ADS)

Koyama, Miki; Ichimura, Masaya

2018-05-01

Ni(OH)2 precursor films were deposited by galvanostatic electrochemical deposition (ECD), and NiO thin films were fabricated by annealing in air. The effects of the deposition current densities were studied in a range that included current densities high enough to electrolyze water and generate hydrogen bubbles. The films fabricated by ECD involving water electrolysis had higher transparency and smoother surface morphology than those deposited with lower current densities. In addition, the annealed NiO films clearly had preferred (111) orientation when the deposition was accompanied by water electrolysis. p-type conduction was confirmed for the annealed films.

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

NASA Astrophysics Data System (ADS)

Santos, J. J.; Bailly-Grandvaux, M.; Ehret, M.; Arefiev, A. V.; Batani, D.; Beg, F. N.; Calisti, A.; Ferri, S.; Florido, R.; Forestier-Colleoni, P.; Fujioka, S.; Gigosos, M. A.; Giuffrida, L.; Gremillet, L.; Honrubia, J. J.; Kojima, S.; Korneev, Ph.; Law, K. F. F.; Marquès, J.-R.; Morace, A.; Mossé, C.; Peyrusse, O.; Rose, S.; Roth, M.; Sakata, S.; Schaumann, G.; Suzuki-Vidal, F.; Tikhonchuk, V. T.; Toncian, T.; Woolsey, N.; Zhang, Z.

2018-05-01

Powerful nanosecond laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, which describes the evolution of the discharge current, the major control parameter is the laser irradiance Ilasλlas2 . The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport through solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 μm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes, and to laboratory astrophysics.

Large Eddy Simulations of Compositional Density Currents Flowing Over a Mobile Bed

NASA Astrophysics Data System (ADS)

Kyrousi, Foteini; Zordan, Jessica; Leonardi, Alessandro; Juez, Carmelo; Zanello, Francesca; Armenio, Vincenzo; Franca, Mário J.

2017-04-01

Density currents are a ubiquitous phenomenon caused by natural events or anthropogenic activities, and play an important role in the global sediment cycle; they are agents of long distance sediment transport in lakes, seas and oceans. Density gradients induced by salinity, temperature differences, or by the presence of suspended material are all possible triggers of a current. Such flows can travel long distances while eroding or depositing bed materials. This can provoke rapid topological changes, which makes the estimation of their transport capacity of prime interest for environmental engineering. Despite their relevance, field data regarding their dynamics is limited due to density currents scattered and unpredictable occurrence in nature. For this reason, laboratory experiments and numerical simulations have been a preferred way to investigate sediment transport processes associated to density currents. The study of entrainment and deposition processes requires detailed data of velocities spatial and temporal distributions in the boundary layer and bed shear stress, which are troublesome to obtain in laboratory. Motivated by this, we present 3D wall-resolved Large Eddy Simulations (LES) of density currents generated by lock-exchange. The currents travel over a smooth flat bed, which includes a section composed by erodible fine sediment susceptible of eroding. Several sediment sizes and initial density gradients are considered. The grid is set to resolve the velocity field within the boundary layer of the current (a tiny fraction of the total height), which in turn allows to obtain predictions of the bed shear stress. The numerical outcomes are compared with experimental data obtained with an analogous laboratory setting. In laboratory experiments salinity was chosen for generating the initial density gradient in order to facilitate the identification of entrained particles, since salt does not hinder the possibility to track suspended particles. Under these circumstances, it is possible to focus alone on the effect of the dynamics of the current on the particles entrainment. To achieve this, LES-filtered Navier-Stokes equations are coupled with two scalar transport equations: one for salinity and one for sediment concentration. We discuss the use of different sediment pick-up and settling formulations, which are key factors in reproducing the correct erosion and sedimentation mechanisms. The simulations show the emergence of longitudinal bed forms, and highlight the role of turbulent structures in the entrainment pattern for different regions within the current.

Variation of power generation at different buffer types and conductivities in single chamber microbial fuel cells.

PubMed

Nam, Joo-Youn; Kim, Hyun-Woo; Lim, Kyeong-Ho; Shin, Hang-Sik; Logan, Bruce E

2010-01-15

Microbial fuel cells (MFCs) are operated with solutions containing various chemical species required for the growth of electrochemically active microorganisms including nutrients and vitamins, substrates, and chemical buffers. Many different buffers are used in laboratory media, but the effects of these buffers and their inherent electrolyte conductivities have not been examined relative to current generation in MFCs. We investigated the effect of several common buffers (phosphate, MES, HEPES, and PIPES) on power production in single chambered MFCs compared to a non-buffered control. At the same concentrations the buffers produced different solution conductivities which resulted in different ohmic resistances and power densities. Increasing the solution conductivities to the same values using NaCl produced comparable power densities for all buffers. Very large increases in conductivity resulted in a rapid voltage drop at high current densities. Our results suggest that solution conductivity at a specific pH for each buffer is more important in MFC studies than the buffer itself given relatively constant pH conditions. Based on our analysis of internal resistance and a set neutral pH, phosphate and PIPES are the most useful buffers of those examined here because pH was maintained close to the pK(a) of the buffer, maximizing the ability of the buffer to contribute to increase current generation at high power densities. Copyright 2009 Elsevier B.V. All rights reserved.

Starch-fueled microbial fuel cells by two-step and parallel fermentation using Shewanella oneidensis MR-1 and Streptococcus bovis 148.

PubMed

Uno, Megumi; Phansroy, Nichanan; Aso, Yuji; Ohara, Hitomi

2017-08-01

Shewanella oneidensis MR-1 generates electricity from lactic acid, but cannot utilize starch. On the other hand, Streptococcus bovis 148 metabolizes starch and produces lactic acid. Therefore, two methods were trialed for starch-fueled microbial fuel cell (MFC) in this study. In electric generation by two-step fermentation (EGT) method, starch was first converted to lactic acid by S. bovis 148. The S. bovis 148 were then removed by centrifugation, and the fermented broth was preserved for electricity generation by S. oneidensis MR-1. Another method was electric generation by parallel fermentation (EGP) method. In this method, the cultivation and subsequent fermentation processes of S. bovis 148 and S. oneidensis MR-1 were performed simultaneously. After 1, 2, and 3 terms (5-day intervals) of S. oneidensis MR-1 in the EGT fermented broth of S. bovis 148, the maximum currents at each term were 1.8, 2.4, and 2.8 mA, and the maximum current densities at each term were 41.0, 43.6, and 49.9 mW/m 2 , respectively. In the EGP method, starch was also converted into lactic acid with electricity generation. The maximum current density was 140-200 mA/m 2 , and the maximum power density of this method was 12.1 mW/m 2 . Copyright © 2017 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Computational analysis of thresholds for magnetophosphenes

NASA Astrophysics Data System (ADS)

Laakso, Ilkka; Hirata, Akimasa

2012-10-01

In international guidelines, basic restriction limits on the exposure of humans to low-frequency magnetic and electric fields are set with the objective of preventing the generation of phosphenes, visual sensations of flashing light not caused by light. Measured data on magnetophosphenes, i.e. phosphenes caused by a magnetically induced electric field on the retina, are available from volunteer studies. However, there is no simple way for determining the retinal threshold electric field or current density from the measured threshold magnetic flux density. In this study, the experimental field configuration of a previous study, in which phosphenes were generated in volunteers by exposing their heads to a magnetic field between the poles of an electromagnet, is computationally reproduced. The finite-element method is used for determining the induced electric field and current in five different MRI-based anatomical models of the head. The direction of the induced current density on the retina is dominantly radial to the eyeball, and the maximum induced current density is observed at the superior and inferior sides of the retina, which agrees with literature data on the location of magnetophosphenes at the periphery of the visual field. On the basis of computed data, the macroscopic retinal threshold current density for phosphenes at 20 Hz can be estimated as 10 mA m-2 (-20% to  + 30%, depending on the anatomical model); this current density corresponds to an induced eddy current of 14 μA (-20% to  + 10%), and about 20% of this eddy current flows through each eye. The ICNIRP basic restriction limit for the induced electric field in the case of occupational exposure is not exceeded until the magnetic flux density is about two to three times the measured threshold for magnetophosphenes, so the basic restriction limit does not seem to be conservative. However, the reasons for the non-conservativeness are purely technical: removal of the highest 1% of electric field values by taking the 99th percentile as recommended by the ICNIRP leads to the underestimation of the induced electric field, and there are difficulties in applying the basic restriction limit for the retinal electric field.

Effect of thermionic cathode heating current self-magnetic field on gaseous plasma generator characteristics

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

Lopatin, I. V., E-mail: lopatin@opee.hcei.tsc.ru; Akhmadeev, Yu. H.; Koval, N. N.

2015-10-15

The performance capabilities of the PINK, a plasma generator with a thermionic cathode mounted in the cavity of a hollow cathode, depending for its operation on a non-self-sustained low-pressure gas discharge have been investigated. It has been shown that when a single-filament tungsten cathode 2 mm in diameter is used and the peak filament current is equal to or higher than 100 A, the self-magnetic field of the filament current significantly affects the discharge current and voltage waveforms. This effect is due to changes in the time and space distributions of the emission current density from the hot cathode. Whenmore » the electron mean free path is close to the characteristic dimensions of the thermionic cathode, the synthesized plasma density distribution is nonuniform and the cathode is etched nonuniformly. The cathode lifetime in this case is 8–12 h. Using a cathode consisting of several parallel-connected tungsten filaments ∼0.8 mm in diameter moderates the effect of the self-magnetic field of the filament current and nearly doubles the cathode lifetime. The use of this type of cathode together with a discharge igniting electrode reduces the minimum operating pressure in the plasma generator to about one third of that required for the generator operation with a single-filament cathode (to 0.04 Pa)« less

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

NASA Astrophysics Data System (ADS)

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.

Direct current plasma jet at atmospheric pressure operating in nitrogen and air

NASA Astrophysics Data System (ADS)

Deng, X. L.; Nikiforov, A. Yu.; Vanraes, P.; Leys, Ch.

2013-01-01

An atmospheric pressure direct current (DC) plasma jet is investigated in N2 and dry air in terms of plasma properties and generation of active species in the active zone and the afterglow. The influence of working gases and the discharge current on plasma parameters and afterglow properties are studied. The electrical diagnostics show that discharge can be sustained in two different operating modes, depending on the current range: a self-pulsing regime at low current and a glow regime at high current. The gas temperature and the N2 vibrational temperature in the active zone of the jet and in the afterglow are determined by means of emission spectroscopy, based on fitting spectra of N2 second positive system (C3Π-B3Π) and the Boltzmann plot method, respectively. The spectra and temperature differences between the N2 and the air plasma jet are presented and analyzed. Space-resolved ozone and nitric oxide density measurements are carried out in the afterglow of the jet. The density of ozone, which is formed in the afterglow of nitrogen plasma jet, is quantitatively detected by an ozone monitor. The density of nitric oxide, which is generated only in the air plasma jet, is determined by means of mass-spectroscopy techniques.

Ultrahigh–current density anodes with interconnected Li metal reservoir through overlithiation of mesoporous AlF 3 framework

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

Wang, Hansen; Lin, Dingchang; Liu, Yayuan

Lithium (Li) metal is the ultimate solution for next-generation high–energy density batteries but is plagued from commercialization by infinite relative volume change, low Coulombic efficiency due to side reactions, and safety issues caused by dendrite growth. These hazardous issues are further aggravated under high current densities needed by the increasing demand for fast charging/discharging. We report a one-step fabricated Li/Al 4Li 9-LiF nanocomposite (LAFN) through an “overlithiation” process of a mesoporous AlF 3 framework, which can simultaneously mitigate the abovementioned problems. Reaction-produced Al 4Li 9-LiF nanoparticles serve as the ideal skeleton for Li metal infusion, helping to achieve a near-zeromore » volume change during stripping/plating and suppressed dendrite growth. As a result, the LAFN electrode is capable of working properly under an ultrahigh current density of 20 mA cm –2 in symmetric cells and manifests highly improved rate capability with increased Coulombic efficiency in full cells. Here, the simple fabrication process and its remarkable electrochemical performances enable LAFN to be a promising anode candidate for next-generation lithium metal batteries.« less

Ultrahigh–current density anodes with interconnected Li metal reservoir through overlithiation of mesoporous AlF 3 framework

DOE PAGES

Wang, Hansen; Lin, Dingchang; Liu, Yayuan; ...

2017-09-08

Lithium (Li) metal is the ultimate solution for next-generation high–energy density batteries but is plagued from commercialization by infinite relative volume change, low Coulombic efficiency due to side reactions, and safety issues caused by dendrite growth. These hazardous issues are further aggravated under high current densities needed by the increasing demand for fast charging/discharging. We report a one-step fabricated Li/Al 4Li 9-LiF nanocomposite (LAFN) through an “overlithiation” process of a mesoporous AlF 3 framework, which can simultaneously mitigate the abovementioned problems. Reaction-produced Al 4Li 9-LiF nanoparticles serve as the ideal skeleton for Li metal infusion, helping to achieve a near-zeromore » volume change during stripping/plating and suppressed dendrite growth. As a result, the LAFN electrode is capable of working properly under an ultrahigh current density of 20 mA cm –2 in symmetric cells and manifests highly improved rate capability with increased Coulombic efficiency in full cells. Here, the simple fabrication process and its remarkable electrochemical performances enable LAFN to be a promising anode candidate for next-generation lithium metal batteries.« less

Plasma devices to guide and collimate a high density of MeV electrons.

PubMed

Kodama, R; Sentoku, Y; Chen, Z L; Kumar, G R; Hatchett, S P; Toyama, Y; Cowan, T E; Freeman, R R; Fuchs, J; Izawa, Y; Key, M H; Kitagawa, Y; Kondo, K; Matsuoka, T; Nakamura, H; Nakatsutsumi, M; Norreys, P A; Norimatsu, T; Snavely, R A; Stephens, R B; Tampo, M; Tanaka, K A; Yabuuchi, T

2004-12-23

The development of ultra-intense lasers has facilitated new studies in laboratory astrophysics and high-density nuclear science, including laser fusion. Such research relies on the efficient generation of enormous numbers of high-energy charged particles. For example, laser-matter interactions at petawatt (10(15) W) power levels can create pulses of MeV electrons with current densities as large as 10(12) A cm(-2). However, the divergence of these particle beams usually reduces the current density to a few times 10(6) A cm(-2) at distances of the order of centimetres from the source. The invention of devices that can direct such intense, pulsed energetic beams will revolutionize their applications. Here we report high-conductivity devices consisting of transient plasmas that increase the energy density of MeV electrons generated in laser-matter interactions by more than one order of magnitude. A plasma fibre created on a hollow-cone target guides and collimates electrons in a manner akin to the control of light by an optical fibre and collimator. Such plasma devices hold promise for applications using high energy-density particles and should trigger growth in charged particle optics.

Alloy Design Challenge: Development of Low Density Superalloys for Turbine Blade Applications

NASA Technical Reports Server (NTRS)

MacKay, Rebecca A.; Gabb, Timothy P.; Smialek, James L.; Nathal, Michael V.

2009-01-01

New low density single crystal (LDS) alloys have been developed for turbine blade applications, which have the potential for significant improvements in the thrust to weight ratio over current production alloys. An innovative alloying strategy was identified to achieve high temperature creep resistance, alloy density reductions, microstructural stability, and cyclic oxidation resistance. The approach relies on the use of molybdenum (Mo) as a potent solid solution strengthener for the nickel (Ni)-base superalloy; Mo has a density much closer to Ni than other refractory elements, such as rhenium (Re) or tungsten (W). A host of testing and microstructural examinations was conducted on the superalloy single crystals, including creep rupture testing, microstructural stability, cyclic oxidation, and hot corrosion. The paper will provide an overview of the single crystal properties that were generated in this new superalloy design space. The paper will also demonstrate the feasibility of this innovative approach of low density single crystal superalloy design. It will be shown that the best LDS alloy possesses the best attributes of three generations of single crystal alloys: the low density of first-generation single crystal alloys, the excellent oxidation resistance of second-generation single crystal alloys, and a creep strength which exceeds that of second and third generation alloys.

Generation of uniform low-temperature plasma in a pulsed non-self-sustained glow discharge with a large-area hollow cathode

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

Akhmadeev, Yu. H.; Denisov, V. V., E-mail: volodyadenisov@yandex.ru; Koval, N. N.

Generation of plasma in a pulsed non-self-sustained glow discharge with a hollow cathode with an area of ≥2 m{sup 2} at gas pressures of 0.4–1 Pa was studied experimentally. At an auxiliary arc-discharge current of 100 A and a main discharge voltage of 240 V, a pulse-periodic glow discharge with a current amplitude of 370 A, pulse duration of 340 μs, and repetition rate of 1 kHz was obtained. The possibility of creating a uniform gas-discharge plasma with a density of up to 10{sup 12} cm{sup −3} and an electron temperature of 1 eV in a volume of >0.2 m{supmore » 3} was demonstrated. Such plasma can be efficiently used to treat material surfaces and generate pulsed ion beams with a current density of up to 15 mA/cm{sup 2}.« less

Schlieren Technique Applied to Magnetohydrodynamic Generator Plasma Torch

NASA Astrophysics Data System (ADS)

Chopra, Nirbhav; Pearcy, Jacob; Jaworski, Michael

2017-10-01

Magnetohydrodynamic (MHD) generators are a promising augmentation to current hydrocarbon based combustion schemes for creating electrical power. In recent years, interest in MHD generators has been revitalized due to advances in a number of technologies such as superconducting magnets, solid-state power electronics and materials science as well as changing economics associated with carbon capture, utilization, and sequestration. We use a multi-wavelength schlieren imaging system to evaluate electron density independently of gas density in a plasma torch under conditions relevant to MHD generators. The sensitivity and resolution of the optical system are evaluated alongside the development of an automated analysis and calibration program in Python. Preliminary analysis shows spatial resolutions less than 1mm and measures an electron density of ne = 1 ×1016 cm-3 in an atmospheric microwave torch. Work supported by DOE contract DE-AC02-09CH11466.

Two color laser driven THz generation in clustered plasma

NASA Astrophysics Data System (ADS)

Malik, Rakhee; Uma, R.; Kumar, Pawan

2017-07-01

A scheme of terahertz (THz) generation, using nonlinear mixing of two color laser (fundamental ω1 and slightly frequency shifted second harmonic ω2 ) in clustered plasma, is investigated. The lasers exert ponderomotive force on cluster electrons and drive density perturbations at 2 ω1 and ω2-ω1 . The density perturbations beat with the oscillatory velocities to produce nonlinear current at ω2-2 ω1 , generating THz radiation. The radiation is enhanced due to cluster plasmon resonance and by phase matching introduced through a density ripple. The generation involves third order nonlinearity and does not require a magnetic field or inhomogeneity to sustain it. We report THz power conversion efficiency ˜ 10-4 at 1 μm and 0.5 μm wavelengths with intensity ˜ 3 ×1014W/cm 2 .

Harmonic generation in magnetized quantum plasma

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

Kumar, Punit; Singh, Abhisek Kumar; Singh, Shiv

2016-05-06

A study of second harmonic generation by propagation of a linearly polarized electromagnetic wave through homogeneous high density quantum plasma in the presence of transverse magnetic field. The nonlinear current density and dispersion relations for the fundamental and second harmonic frequencies have been obtained using the recently developed quantum hydrodynamic (QHD) model. The effect of quantum Bohm potential, Fermi pressure and the electron spin have been taken into account. The second harmonic is found to be less dispersed than the first.

Electricity Generation in Microbial Fuel Cell (MFC) by Bacterium Isolated from Rice Paddy Field Soil

NASA Astrophysics Data System (ADS)

Fakhirruddin, Fakhriah; Amid, Azura; Salim, Wan Wardatul Amani Wan; Suhaida Azmi, Azlin

2018-03-01

Microbial fuel cell (MFC) is an alternative approach in generating renewable energy by utilising bacteria that will oxidize organic or inorganic substrates, producing electrons yielded as electrical energy. Different species of exoelectrogenic bacteria capable of generating significant amount of electricity in MFC has been identified, using various organic compounds for fuel. Soil sample taken from rice paddy field is proven to contain exoelectrogenic bacteria, thus electricity generation using mixed culture originally found in the soil, and pure culture isolated from the soil is studied. This research will isolate the exoelectrogenic bacterial species in the rice paddy field soil responsible for energy generation. Growth of bacteria isolated from the MFC is observed by measuring the optical density (OD), cell density weight (CDW) and viable cell count. Mixed bacterial species found in paddy field soil generates maximum power of 77.62 μW and 0.70 mA of current. In addition, the research also shows that the pure bacterium in rice paddy field soil can produce maximum power and current at 51.32 μW and 0.28 mA respectively.

Linear calculations of edge current driven kink modes with BOUT++ code

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

Li, G. Q., E-mail: ligq@ipp.ac.cn; Xia, T. Y.; Lawrence Livermore National Laboratory, Livermore, California 94550

This work extends previous BOUT++ work to systematically study the impact of edge current density on edge localized modes, and to benchmark with the GATO and ELITE codes. Using the CORSICA code, a set of equilibria was generated with different edge current densities by keeping total current and pressure profile fixed. Based on these equilibria, the effects of the edge current density on the MHD instabilities were studied with the 3-field BOUT++ code. For the linear calculations, with increasing edge current density, the dominant modes are changed from intermediate-n and high-n ballooning modes to low-n kink modes, and the linearmore » growth rate becomes smaller. The edge current provides stabilizing effects on ballooning modes due to the increase of local shear at the outer mid-plane with the edge current. For edge kink modes, however, the edge current does not always provide a destabilizing effect; with increasing edge current, the linear growth rate first increases, and then decreases. In benchmark calculations for BOUT++ against the linear results with the GATO and ELITE codes, the vacuum model has important effects on the edge kink mode calculations. By setting a realistic density profile and Spitzer resistivity profile in the vacuum region, the resistivity was found to have a destabilizing effect on both the kink mode and on the ballooning mode. With diamagnetic effects included, the intermediate-n and high-n ballooning modes can be totally stabilized for finite edge current density.« less

Cellular generators of the cortical auditory evoked potential initial component.

PubMed

Steinschneider, M; Tenke, C E; Schroeder, C E; Javitt, D C; Simpson, G V; Arezzo, J C; Vaughan, H G

1992-01-01

Cellular generators of the initial cortical auditory evoked potential (AEP) component were determined by analyzing laminar profiles of click-evoked AEPs, current source density, and multiple unit activity (MUA) in primary auditory cortex of awake monkeys. The initial AEP component is a surface-negative wave, N8, that peaks at 8-9 msec and inverts in polarity below lamina 4. N8 is generated by a lamina 4 current sink and a deeper current source. Simultaneous MUA is present from lower lamina 3 to the subjacent white matter. Findings indicate that thalamocortical afferents are a generator of N8 and support a role for lamina 4 stellate cells. Relationships to the human AEP are discussed.

Ion beam deposition system for depositing low defect density extreme ultraviolet mask blanks

NASA Astrophysics Data System (ADS)

Jindal, V.; Kearney, P.; Sohn, J.; Harris-Jones, J.; John, A.; Godwin, M.; Antohe, A.; Teki, R.; Ma, A.; Goodwin, F.; Weaver, A.; Teora, P.

2012-03-01

Extreme ultraviolet lithography (EUVL) is the leading next-generation lithography (NGL) technology to succeed optical lithography at the 22 nm node and beyond. EUVL requires a low defect density reflective mask blank, which is considered to be one of the top two critical technology gaps for commercialization of the technology. At the SEMATECH Mask Blank Development Center (MBDC), research on defect reduction in EUV mask blanks is being pursued using the Veeco Nexus deposition tool. The defect performance of this tool is one of the factors limiting the availability of defect-free EUVL mask blanks. SEMATECH identified the key components in the ion beam deposition system that is currently impeding the reduction of defect density and the yield of EUV mask blanks. SEMATECH's current research is focused on in-house tool components to reduce their contributions to mask blank defects. SEMATECH is also working closely with the supplier to incorporate this learning into a next-generation deposition tool. This paper will describe requirements for the next-generation tool that are essential to realize low defect density EUV mask blanks. The goal of our work is to enable model-based predictions of defect performance and defect improvement for targeted process improvement and component learning to feed into the new deposition tool design. This paper will also highlight the defect reduction resulting from process improvements and the restrictions inherent in the current tool geometry and components that are an impediment to meeting HVM quality EUV mask blanks will be outlined.

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

PubMed Central

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

Control of the recombination time in photoconductive detectors

NASA Astrophysics Data System (ADS)

Pacheco, M. T. T.; Ghizoni, C. C.; Scolari, S. L.

1980-07-01

The current generated at a photoconductive cell depends upon the density of states of the electromagnetic field in the semiconductor film. This density of states is a function of the film geometry and dielectric properties. In this work we demonstrate that, for highly scattering substrate surfaces, which implies in a low density of states, the signal to noise ratio is better than that for smooth surfaces.

Effect of fed-batch vs. continuous mode of operation on microbial fuel cell performance treating biorefinery wastewater

DOE PAGES

Pannell, Tyler C.; Goud, R. Kannaiah; Schell, Daniel J.; ...

2016-05-01

Bioelectrochemical systems have been shown to treat low-value biorefinery streams while recovering energy, however, low current densities and anode conversion efficiencies (ACE) limit their application. A bioanode was developed via enrichment of electroactive biofilm under fed-batch and continuous feeding conditions using corn stover-derived waste stream. The continuously-fed MFC exhibited a current density of 5.8±0.06 A/m 2 and an ACE of 39%±4. The fed-batch MFC achieved a similar current density and an ACE of 19.2%, however, its performance dropped after 36 days of operation to 1.1 A/m 2 and 0.5%, respectively. In comparison, the ACE of the continuously-fed MFC remained stablemore » achieving an ACE of 30% ± 3 after 48 days of operation. An MFC treating a biorefinery stream post fuel separation achieved a current density of 10.7±0.1 A/m 2 and an ACE of 57% ± 9 at an organic loading of 12.5 g COD/L-day. Characterization of the microbial communities indicate higher abundance of Firmicutes and Proteobacteria and lower abundance of Bacteriodetes and a higher level of Geobacter spp. (1.4% vs. 0.2%) in continuously-fed MFC vs. fed-batch MFC. Finally, the results demonstrate that limiting substrate to the equivalent maximum current that the anode can generate, maintains MFC performance over a long term for high strength wastewaters, such as those generated in the biorefinery.« less

Effect of fed-batch vs. continuous mode of operation on microbial fuel cell performance treating biorefinery wastewater

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

Pannell, Tyler C.; Goud, R. Kannaiah; Schell, Daniel J.

Bioelectrochemical systems have been shown to treat low-value biorefinery streams while recovering energy, however, low current densities and anode conversion efficiencies (ACE) limit their application. A bioanode was developed via enrichment of electroactive biofilm under fed-batch and continuous feeding conditions using corn stover-derived waste stream. The continuously-fed MFC exhibited a current density of 5.8±0.06 A/m 2 and an ACE of 39%±4. The fed-batch MFC achieved a similar current density and an ACE of 19.2%, however, its performance dropped after 36 days of operation to 1.1 A/m 2 and 0.5%, respectively. In comparison, the ACE of the continuously-fed MFC remained stablemore » achieving an ACE of 30% ± 3 after 48 days of operation. An MFC treating a biorefinery stream post fuel separation achieved a current density of 10.7±0.1 A/m 2 and an ACE of 57% ± 9 at an organic loading of 12.5 g COD/L-day. Characterization of the microbial communities indicate higher abundance of Firmicutes and Proteobacteria and lower abundance of Bacteriodetes and a higher level of Geobacter spp. (1.4% vs. 0.2%) in continuously-fed MFC vs. fed-batch MFC. Finally, the results demonstrate that limiting substrate to the equivalent maximum current that the anode can generate, maintains MFC performance over a long term for high strength wastewaters, such as those generated in the biorefinery.« less

Charge-exchange plasma generated by an ion thruster

NASA Technical Reports Server (NTRS)

Kaufman, H. R.

1977-01-01

The charge exchange plasma generated by an ion thruster was investigated experimentally using both 5 cm and 15 cm thrusters. Results are shown for wide ranges of radial distance from the thruster and angle from the beam direction. Considerations of test environment, as well as distance from the thruster, indicate that a valid simulation of a thruster on a spacecraft was obtained. A calculation procedure and a sample calculation of charge exchange plasma density and saturation electron current density are included.

Current-Driven Dynamics of Skyrmions Stabilized in MnSi Nanowires Revealed by Topological Hall Effect

NASA Astrophysics Data System (ADS)

Liang, Dong; Degrave, John; Stolt, Matthew; Tokura, Yoshinori; Jin, Song

2015-03-01

Skyrmions, novel topologically stable spin vortices, hold promise for next-generation high-density magnetic storage technologies due to their nanoscale domains and ultralow energy consumption. One-dimensional (1D) nanowires are ideal hosts for skyrmions since they not only serve as a natural platform for magnetic racetrack memory devices but also can potentially stabilize skyrmions. We use the topological Hall effect (THE) to study the phase stability and current-driven dynamics of the skyrmions in MnSi nanowires. The THE was observed in an extended magnetic field-temperature window (15 to 30 K), suggesting stabilization of skyrmion phase in nanowires compared with the bulk (27 to 29.5 K). Furthermore, we study skyrmion dynamics in this extended skyrmion phase region and found that under the high current-density of 108-109Am-2 enabled by nanowire geometry, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field. These results open up the exploration of nanowires as an attractive platform for investigating skyrmion physics in 1D systems and exploiting skyrmions in magnetic storage concepts. This work is supported by US National Science Foundation (ECCS-1231916) and JSPS Grant-in-Aid for Scientific Research No. 24224009.

Magnetospheric discontinuities and interfaces as roots of discrete auroral arcs: modeling and comparison with in-situ data

NASA Astrophysics Data System (ADS)

Echim, M.; Maggiolo, R.; de Keyser, J. M.; Roth, M. A.

2009-12-01

We discuss the quasi-stationary coupling between magnetospheric sharp plasma interfaces and discrete auroral arcs. The magnetospheric generator is described by a Vlasov equilibrium similar to the kinetic models of tangential discontinuities. It provides the self-consistent profile of the magnetospheric convergent electric field, Φm. A kinetic current-voltage relationship gives the field-aligned current density flowing into and out of the ionosphere as a function of the potential difference between the magnetospheric generator and the ionospheric load. The electric potential in the ionosphere, Φi, is computed from the current continuity equation taking into account the variation of the Pedersen conductance, ΣP, with the energy flux of the precipitating magnetospheric electrons (ɛem). We discuss results obtained for the interface between the Plasma Sheet Boundary Layer (PSBL) and the lobes and respectively for the inner edge of the Low Latitude Boundary Layer (LLBL). This type of interfaces provides a field-aligned potential drop, ΔΦ=Φi-Φm, of the order of several kilovolts and field-aligned current densities, j||, of the order of tens of μA/m2 . The precipitating particles are confined in thin regions whose thickness is of the order of several kilometers at 200 km altitude. We show that visible auroral arcs form when the velocity shear across the generator magnetospheric plasma interface is above a threshold depending also on the kinetic properties of the generator. Brighter arcs forms for larger velocity shear in the magnetospheric generator. The field-aligned potential drop tends to decrease when the density gradient across the interface increases. Conjugated observations on April 28, 2001 by Cluster and DMSP-F14 give us the opportunity to validate the model with data gathered simultaneously below and above the acceleration region. The magnetospheric module of the coupling model provides a good estimation of the plasma parameters measured by Cluster across the magnetospheric interface: the electric potential, the plasma density and the parallel flux of downgoing electrons and upgoing Oxygen ions. The results of the ionospheric module of the model are in good agreement with the DMSP-F14 measurements of the field-aligned current density, the flux of precipitating energy and the accelerating field-aligned potential drop. A synthetic electron energy spectrum derived from the computed field-aligned potential drop retrieves the spatial scale and spectral width of the inverted-V event observed by DMSP-F14.

Ion source and beam guiding studies for an API neutron generator

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

Sy, A.; Ji, Q.; Persaud, A.

2013-04-19

Recently developed neutron imaging methods require high neutron yields for fast imaging times and small beam widths for good imaging resolution. For ion sources with low current density to be viable for these types of imaging methods, large extraction apertures and beam focusing must be used. We present recent work on the optimization of a Penning-type ion source for neutron generator applications. Two multi-cusp magnet configurations have been tested and are shown to increase the extracted ion current density over operation without multi-cusp magnetic fields. The use of multi-cusp magnetic confinement and gold electrode surfaces have resulted in increased ionmore » current density, up to 2.2 mA/cm{sup 2}. Passive beam focusing using tapered dielectric capillaries has been explored due to its potential for beam compression without the cost and complexity issues associated with active focusing elements. Initial results from first experiments indicate the possibility of beam compression. Further work is required to evaluate the viability of such focusing methods for associated particle imaging (API) systems.« less

Ion beam enhancement in magnetically insulated ion diodes for high-intensity pulsed ion beam generation in non-relativistic mode

NASA Astrophysics Data System (ADS)

Zhu, X. P.; Zhang, Z. C.; Pushkarev, A. I.; Lei, M. K.

2016-01-01

High-intensity pulsed ion beam (HIPIB) with ion current density above Child-Langmuir limit is achieved by extracting ion beam from anode plasma of ion diodes with suppressing electron flow under magnetic field insulation. It was theoretically estimated that with increasing the magnetic field, a maximal value of ion current density may reach nearly 3 times that of Child-Langmuir limit in a non-relativistic mode and close to 6 times in a highly relativistic mode. In this study, the behavior of ion beam enhancement by magnetic insulation is systematically investigated in three types of magnetically insulated ion diodes (MIDs) with passive anode, taking into account the anode plasma generation process on the anode surface. A maximal enhancement factor higher than 6 over the Child-Langmuir limit can be obtained in the non-relativistic mode with accelerating voltage of 200-300 kV. The MIDs differ in two anode plasma formation mechanisms, i.e., surface flashover of a dielectric coating on the anode and explosive emission of electrons from the anode, as well as in two insulation modes of external-magnetic field and self-magnetic field with either non-closed or closed drift of electrons in the anode-cathode (A-K) gap, respectively. Combined with ion current density measurement, energy density characterization is employed to resolve the spatial distribution of energy density before focusing for exploring the ion beam generation process. Consistent results are obtained on three types of MIDs concerning control of neutralizing electron flows for the space charge of ions where the high ion beam enhancement is determined by effective electron neutralization in the A-K gap, while the HIPIB composition of different ion species downstream from the diode may be considerably affected by the ion beam neutralization during propagation.

Giant spin torque in hybrids with anisotropic p-d exchange interaction

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2014-03-01

Control of magnetic domain wall movement by the spin-polarized current looks promising for creation of a new generation of magnetic memory devices. A necessary condition for this is the domain wall shift by a low-density current. Here, I show that a strongly anisotropic exchange interaction between mobile heavy holes and localized magnetic moments enormously increases the current-induced torque on the domain wall as compared to systems with isotropic exchange. This enables one to control the domain wall motion by current density 104 A/cm2 in ferromagnet/semiconductor hybrids. The experimental observation of the anisotropic torque will facilitate the integration of ferromagnetism into semiconductor electronics.

Investigating the origin of efficiency droop by profiling the temperature across the multi-quantum well of an operating light-emitting diode

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

Jung, Euihan; Hwang, Gwangseok; Chung, Jaehun

2015-01-26

Performance degradation resulting from efficiency droop during high-power operation is a critical problem in the development of high-efficiency light-emitting diodes (LEDs). In order to resolve the efficiency droop and increase the external quantum efficiency of LEDs, the droop's origin should be identified first. To experimentally investigate the cause of efficiency droop, we used null-point scanning thermal microscopy to quantitatively profile the temperature distribution on the cross section of the epi-layers of an operating GaN-based vertical LED with nanoscale spatial resolution at four different current densities. The movement of temperature peak towards the p-GaN side as the current density increases suggestsmore » that more heat is generated by leakage current than by Auger recombination. We therefore suspect that at higher current densities, current leakage becomes the dominant cause of the droop problem.« less

Stochastic approach and fluctuation theorem for charge transport in diodes

NASA Astrophysics Data System (ADS)

Gu, Jiayin; Gaspard, Pierre

2018-05-01

A stochastic approach for charge transport in diodes is developed in consistency with the laws of electricity, thermodynamics, and microreversibility. In this approach, the electron and hole densities are ruled by diffusion-reaction stochastic partial differential equations and the electric field generated by the charges is determined with the Poisson equation. These equations are discretized in space for the numerical simulations of the mean density profiles, the mean electric potential, and the current-voltage characteristics. Moreover, the full counting statistics of the carrier current and the measured total current including the contribution of the displacement current are investigated. On the basis of local detailed balance, the fluctuation theorem is shown to hold for both currents.

Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures

NASA Astrophysics Data System (ADS)

Wang, Xi-guang; Chotorlishvili, L.; Guo, Guang-hua; Berakdar, J.

2018-04-01

Conversion of thermal energy into magnonic spin currents and/or effective electric polarization promises new device functionalities. A versatile approach is presented here for generating and controlling open circuit magnonic spin currents and an effective multiferroicity at a uniform temperature with the aid of spatially inhomogeneous, external, static electric fields. This field applied to a ferromagnetic insulator with a Dzyaloshinskii-Moriya type coupling changes locally the magnon dispersion and modifies the density of thermally excited magnons in a region of the scale of the field inhomogeneity. The resulting gradient in the magnon density can be viewed as a gradient in the effective magnon temperature. This effective thermal gradient together with local magnon dispersion result in an open-circuit, electric field controlled magnonic spin current. In fact, for a moderate variation in the external electric field the predicted magnonic spin current is on the scale of the spin (Seebeck) current generated by a comparable external temperature gradient. Analytical methods supported by full-fledge numerics confirm that both, a finite temperature and an inhomogeneous electric field are necessary for this emergent non-equilibrium phenomena. The proposal can be integrated in magnonic and multiferroic circuits, for instance to convert heat into electrically controlled pure spin current using for example nanopatterning, without the need to generate large thermal gradients on the nanoscale.

A contoured gap coaxial plasma gun with injected plasma armature.

PubMed

Witherspoon, F Douglas; Case, Andrew; Messer, Sarah J; Bomgardner, Richard; Phillips, Michael W; Brockington, Samuel; Elton, Raymond

2009-08-01

A new coaxial plasma gun is described. The long term objective is to accelerate 100-200 microg of plasma with density above 10(17) cm(-3) to greater than 200 km/s with a Mach number above 10. Such high velocity dense plasma jets have a number of potential fusion applications, including plasma refueling, magnetized target fusion, injection of angular momentum into centrifugally confined mirrors, high energy density plasmas, and others. The approach uses symmetric injection of high density plasma into a coaxial electromagnetic accelerator having an annular gap geometry tailored to prevent formation of the blow-by instability. The injected plasma is generated by numerous (currently 32) radially oriented capillary discharges arranged uniformly around the circumference of the angled annular injection region of the accelerator. Magnetohydrodynamic modeling identified electrode profiles that can achieve the desired plasma jet parameters. The experimental hardware is described along with initial experimental results in which approximately 200 microg has been accelerated to 100 km/s in a half-scale prototype gun. Initial observations of 64 merging injector jets in a planar cylindrical testing array are presented. Density and velocity are presently limited by available peak current and injection sources. Steps to increase both the drive current and the injected plasma mass are described for next generation experiments.

Cell Seeding Densities in Autologous Chondrocyte Implantation Techniques for Cartilage Repair.

PubMed

Foldager, Casper Bindzus; Gomoll, Andreas H; Lind, Martin; Spector, Myron

2012-04-01

Cartilage repair techniques have been among the most intensively investigated treatments in orthopedics for the past decade, and several different treatment modalities are currently available. Despite the extensive research effort within this field, the generation of hyaline cartilage remains a considerable challenge. There are many parameters attendant to each of the cartilage repair techniques that can affect the amount and types of reparative tissue generated in the cartilage defect, and some of the most fundamental of these parameters have yet to be fully investigated. For procedures in which in vitro-cultured autologous chondrocytes are implanted under a periosteal or synthetic membrane cover, or seeded onto a porous membrane or scaffold, little is known about how the number of cells affects the clinical outcome. Few published clinical studies address the cell seeding density that was employed. The principal objective of this review is to provide an overview of the cell seeding densities used in cell-based treatments currently available in the clinic for cartilage repair. Select preclinical studies that have informed the use of specific cell seeding densities in the clinic are also discussed.

Enhanced THz radiation generation by photo-mixing of tophat lasers in rippled density plasma with a planar magnetostatic wiggler and s-parameter

NASA Astrophysics Data System (ADS)

Abedi-Varaki, M.

2018-02-01

In this paper, the effects of planar magnetostatic wiggler and s-parameter on the terahertz (THz) radiation generation through rippled plasma have been investigated. Efficient THz radiation generation by photo-mixing of tophat lasers for rippled density plasma in the presence of the wiggler field has been presented. Fundamental equations for the analysis of the non-linear current density and THz radiation generation by wiggler magnetostatic field have been derived. It is shown that for the higher order of the tophat lasers, the values of THz amplitude are greater. In fact, the higher order of the tophat lasers has a sharp gradient in the intensity of lasers, which leads to a stronger nonlinear ponderomotive force and, consequently, a stronger current density. In addition, it is seen that by increasing s-parameter, the normalized transverse profile becomes more focused near the axis of y. Furthermore, it is observed that the normalized laser efficiency has a decreasing trend with increasing normalized THz frequency for different values of the wiggler field. Also, it is shown that by employing a greater order of the tophat lasers and a stronger wiggler field, the efficiency of order of 30% can be achieved. Moreover, it is found that we can control focus and intensity of THz radiation emitted in rippled plasma by choosing the appropriate order of the tophat lasers and tuning of the wiggler field.

A Novel and Generalized Lithium-Ion-Battery Configuration utilizing Al Foil as Both Anode and Current Collector for Enhanced Energy Density.

PubMed

Ji, Bifa; Zhang, Fan; Sheng, Maohua; Tong, Xuefeng; Tang, Yongbing

2017-02-01

A novel battery configuration based on an aluminum foil anode and a conventional cathode is developed. The aluminum foil plays a dual role as both the active anode material and the current collector, which enhances the energy density of the packaged battery, and reduces the production cost. This generalized battery configuration has high potential for application in next-generation lithium-ion batteries. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-current fast electron beam propagation in a dielectric target.

PubMed

Klimo, Ondrej; Tikhonchuk, V T; Debayle, A

2007-01-01

Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10(12) A cm(-2). The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.

Combining microbial cultures for efficient production of electricity from butyrate in a microbial electrochemical cell.

PubMed

Miceli, Joseph F; Garcia-Peña, Ines; Parameswaran, Prathap; Torres, César I; Krajmalnik-Brown, Rosa

2014-10-01

Butyrate is an important product of anaerobic fermentation; however, it is not directly used by characterized strains of the highly efficient anode respiring bacteria (ARB) Geobacter sulfurreducens in microbial electrochemical cells. By combining a butyrate-oxidizing community with a Geobacter rich culture, we generated a microbial community which outperformed many naturally derived communities found in the literature for current production from butyrate and rivaled the highest performing natural cultures in terms of current density (∼ 11A/m(2)) and Coulombic efficiency (∼ 70%). Microbial community analyses support the shift in the microbial community from one lacking efficient ARB in the marine hydrothermal vent community to a community consisting of ∼ 80% Geobacter in the anode biofilm. This demonstrates the successful production and adaptation of a novel microbial culture for generating electrical current from butyrate with high current density and high Coulombic efficiency, by combining two mixed microbial cultures containing complementing biochemical pathways. Copyright © 2014 Elsevier Ltd. All rights reserved.

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

DOE PAGES

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide; ...

2017-11-16

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-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-orbitmore » 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.« less

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

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

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-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-orbitmore » 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.« less

Nonlinear MHD simulation of current drive by multi-pulsed coaxial helicity injection in spherical torus

NASA Astrophysics Data System (ADS)

Kanki, Takashi; Nagata, Masayoshi; Kagei, Yasuhiro

2011-10-01

The dynamics of structures of magnetic field, current density, and plasma flow generated during multi-pulsed coaxial helicity injection in spherical torus is investigated by 3-D nonlinear MHD simulations. During the driven phase, the flux and current amplifications occur due to the merging and magnetic reconnection between the preexisting plasma in the confinement region and the ejected plasma from the gun region involving the n = 1 helical kink distortion of the central open flux column (COFC). Interestingly, the diamagnetic poloidal flow which tends toward the gun region is then observed due to the steep pressure gradients of the COFC generated by ohmic heating through an injection current winding around the inboard field lines, resulting in the formation of the strong poloidal flow shear at the interface between the COFC and the core region. This result is consistent with the flow shear observed in the HIST. During the decay phase, the configuration approaches the axisymmetric MHD equilibrium state without flow because of the dissipation of magnetic fluctuation energy to increase the closed flux surfaces, suggesting the generation of ordered magnetic field structure. The parallel current density λ concentrated in the COFC then diffuses to the core region so as to reduce the gradient in λ, relaxing in the direction of the Taylor state.

Using live algae at the anode of a microbial fuel cell to generate electricity.

PubMed

Xu, Chang; Poon, Karen; Choi, Martin M F; Wang, Ruihua

2015-10-01

Live green microalgae Chlorella pyrenoidosa was introduced in the anode of a microbial fuel cell (MFC) to act as an electron donor. By controlling the oxygen content, light intensity, and algal cell density at the anode, microalgae would generate electricity without requiring externally added substrates. Two models of algal microbial fuel cells (MFCs) were constructed with graphite/carbon electrodes and no mediator. Model 1 algal MFC has live microalgae grown at the anode and potassium ferricyanide at the cathode, while model 2 algal MFC had live microalgae in both the anode and cathode in different growth conditions. Results indicated that a higher current produced in model 1 algal MFC was obtained at low light intensity of 2500 lx and algal cell density of 5 × 10(6) cells/ml, in which high algal density would limit the electricity generation, probably by increasing oxygen level and mass transfer problem. The maximum power density per unit anode volume obtained in model 1 algal MFC was relatively high at 6030 mW/m(2), while the maximum power density at 30.15 mW/m(2) was comparable with that of previous reported bacteria-driven MFC with graphite/carbon electrodes. A much smaller power density at 2.5 mW/m(2) was observed in model 2 algal MFC. Increasing the algal cell permeability by 4-nitroaniline would increase the open circuit voltage, while the mitochondrial acting and proton leak promoting agents resveratrol and 2,4-dinitrophenol would increase the electric current production in algal MFC.

Possibility of material cost reduction toward development of low-cost second-generation superconducting wires

NASA Astrophysics Data System (ADS)

Ichinose, Ataru; Horii, Shigeru; Doi, Toshiya

2017-10-01

Two approaches to reducing the material cost of second-generation superconducting wires are proposed in this paper: (1) instead of the electrical stabilizing layers of silver and copper presently used on the superconducting layer, a Nb-doped SrTiO3 conductive buffer layer and cube-textured Cu are proposed as an advanced architecture, and (2) the use of an electromagnetic (EM) steel tape as a metal substrate of coated conductors in a conventional architecture. In structures fabricated without using electrical stabilizing layers on the superconducting layer, the critical current density achieved at 77 K in a self-field was approximately 2.6 MA/cm2. On the other hand, in the case of using EM steel tapes, although the critical current density was far from practical at the current stage, the biaxial alignment of YBa2Cu3O y (YBCO) and buffer layers was realized without oxidation on the metal surface. In this study, the possibility of material cost reduction has been strongly indicated toward the development of low-cost second-generation superconducting wires in the near future.

Boosting current generation in microbial fuel cells by an order of magnitude by coating an ionic liquid polymer on carbon anodes.

PubMed

Yang, Lu; Deng, Wenfang; Zhang, Youming; Tan, Yueming; Ma, Ming; Xie, Qingji

2017-05-15

Microbial fuel cells (MFCs) have attracted great attentions due to their great application potentials, but the relatively low power densities of MFCs still hinder their widespread practical applications. Herein, we report that the current generation in MFCs can be boosted by an order of magnitude, simply by coating a hydrophilic and positively charged ionic liquid polymer (ILP) on carbon cloth (CC) or carbon felt (CF). The ILP coating not only can increase the bacterial loading capacity due to the electrostatic interactions between ILP and bacterial cells, but also can improve the mediated extracellular electron transfer between the electrode and the cytochrome proteins on the outer membrane of Shewanella putrefaciens cells. As a result, the maximum power density of a MFC equipped with the CF-ILP bioanode is as high as 4400±170mWm -2 , which is amongst the highest values reported to date. This work demonstrates a new strategy for greatly boosting the current generation in MFCs. Copyright © 2017 Elsevier B.V. All rights reserved.

Impact of the Hall effect on high-energy-density plasma jets.

PubMed

Gourdain, P-A; Seyler, C E

2013-01-04

Using a 1-MA, 100 ns-rise-time pulsed power generator, radial foil configurations can produce strongly collimated plasma jets. The resulting jets have electron densities on the order of 10(20) cm(-3), temperatures above 50 eV and plasma velocities on the order of 100 km/s, giving Reynolds numbers of the order of 10(3), magnetic Reynolds and Péclet numbers on the order of 1. While Hall physics does not dominate jet dynamics due to the large particle density and flow inside, it strongly impacts flows in the jet periphery where plasma density is low. As a result, Hall physics affects indirectly the geometrical shape of the jet and its density profile. The comparison between experiments and numerical simulations demonstrates that the Hall term enhances the jet density when the plasma current flows away from the jet compared to the case where the plasma current flows towards it.

Return currents in solar flares - Collisionless effects

NASA Technical Reports Server (NTRS)

Rowland, H. L.; Vlahos, L.

1985-01-01

If the primary, precipitating electrons in a solar flare are unstable to beam plasma interactions, it is shown that strong Langmuir turbulence can seriously modify the way in which a return current is carried by the background plasma. In particular, the return (or reverse) current will not be carried by the bulk of the electrons, but by a small number of high velocity electrons. For beam/plasma densities greater than 0.01, this can reduce the effects of collisions on the return current. For higher density beams where the return current could be unstable to current driven instabilities, the effects of strong turbulence anomalous resistivity is shown to prevent the appearance of such instabilities. Again in this regime, how the return current is carried is determined by the beam generated strong turbulence.

Evaluation of local electric fields generated by transcranial direct current stimulation with an extracephalic reference electrode based on realistic 3D body modeling

NASA Astrophysics Data System (ADS)

Im, Chang-Hwan; Park, Ji-Hye; Shim, Miseon; Chang, Won Hyuk; Kim, Yun-Hee

2012-04-01

In this study, local electric field distributions generated by transcranial direct current stimulation (tDCS) with an extracephalic reference electrode were evaluated to address extracephalic tDCS safety issues. To this aim, we generated a numerical model of an adult male human upper body and applied the 3D finite element method to electric current conduction analysis. In our simulations, the active electrode was placed over the left primary motor cortex (M1) and the reference electrode was placed at six different locations: over the right temporal lobe, on the right supraorbital region, on the right deltoid, on the left deltoid, under the chin, and on the right buccinator muscle. The maximum current density and electric field intensity values in the brainstem generated by the extracephalic reference electrodes were comparable to, or even less than, those generated by the cephalic reference electrodes. These results suggest that extracephalic reference electrodes do not lead to unwanted modulation of the brainstem cardio-respiratory and autonomic centers, as indicated by recent experimental studies. The volume energy density was concentrated at the neck area by the use of deltoid reference electrodes, but was still smaller than that around the active electrode locations. In addition, the distributions of elicited cortical electric fields demonstrated that the use of extracephalic reference electrodes might allow for the robust prediction of cortical modulations with little dependence on the reference electrode locations.

Three-dimensional forward solver and its performance analysis for magnetic resonance electrical impedance tomography (MREIT) using recessed electrodes.

PubMed

Lee, Byung Il; Oh, Suk Hoon; Woo, Eung Je; Lee, Soo Yeol; Cho, Min Hyoung; Kwon, Ohin; Seo, Jin Keun; Lee, June-Yub; Baek, Woon Sik

2003-07-07

In magnetic resonance electrical impedance tomography (MREIT), we try to reconstruct a cross-sectional resistivity (or conductivity) image of a subject. When we inject a current through surface electrodes, it generates a magnetic field. Using a magnetic resonance imaging (MRI) scanner, we can obtain the induced magnetic flux density from MR phase images of the subject. We use recessed electrodes to avoid undesirable artefacts near electrodes in measuring magnetic flux densities. An MREIT image reconstruction algorithm produces cross-sectional resistivity images utilizing the measured internal magnetic flux density in addition to boundary voltage data. In order to develop such an image reconstruction algorithm, we need a three-dimensional forward solver. Given injection currents as boundary conditions, the forward solver described in this paper computes voltage and current density distributions using the finite element method (FEM). Then, it calculates the magnetic flux density within the subject using the Biot-Savart law and FEM. The performance of the forward solver is analysed and found to be enough for use in MREIT for resistivity image reconstructions and also experimental designs and validations. The forward solver may find other applications where one needs to compute voltage, current density and magnetic flux density distributions all within a volume conductor.

An information theory approach to the density of the earth

NASA Technical Reports Server (NTRS)

Graber, M. A.

1977-01-01

Information theory can develop a technique which takes experimentally determined numbers and produces a uniquely specified best density model satisfying those numbers. A model was generated using five numerical parameters: the mass of the earth, its moment of inertia, three zero-node torsional normal modes (L = 2, 8, 26). In order to determine the stability of the solution, six additional densities were generated, in each of which the period of one of the three normal modes was increased or decreased by one standard deviation. The superposition of the seven models is shown. It indicates that current knowledge of the torsional modes is sufficient to specify the density in the upper mantle but that the lower mantle and core will require smaller standard deviations before they can be accurately specified.

Scale Sizes of High-Latitude Neutral Mass Density Perturbations

NASA Astrophysics Data System (ADS)

Huang, C. Y.; Huang, Y.; Su, Y. J.; Huang, T.; Sutton, E. K.

2017-12-01

In a statistical study of neutral mass density maxima, we found for a select interval, that 57% of the maxima have correlated field-aligned current (FAC) signatures, indicative of localized Ohmic heating. However the remaining 43% do not, and we suggested that these maxima may be due to gravity waves generated by neutral heating. We follow up on this study by an investigation into the spatial scale sizes of the mass density maxima using high-resolution neutral density and FAC data from CHAMP, when the satellite is in conjunction with DMSP, which provides the corresponding ion drift velocity, particle precipitation and Poynting flux. The study shows the average scale sizes of the perturbations due to J x B heating, as well as the sizes of the waves generated by Joule heating.

A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch

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

Dahlin, J.-E.; Scheffel, J.

2005-06-15

In the advanced reversed-field pinch (RFP), the current density profile is externally controlled to diminish tearing instabilities. Thus the scaling of energy confinement time with plasma current and density is improved substantially as compared to the conventional RFP. This may be numerically simulated by introducing an ad hoc electric field, adjusted to generate a tearing mode stable parallel current density profile. In the present work a current profile control algorithm, based on feedback of the fluctuating electric field in Ohm's law, is introduced into the resistive magnetohydrodynamic code DEBSP [D. D. Schnack and D. C. Baxter, J. Comput. Phys. 55,more » 485 (1984); D. D. Schnack, D. C. Barnes, Z. Mikic, D. S. Marneal, E. J. Caramana, and R. A. Nebel, Comput. Phys. Commun. 43, 17 (1986)]. The resulting radial magnetic field is decreased considerably, causing an increase in energy confinement time and poloidal {beta}. It is found that the parallel current density profile spontaneously becomes hollow, and that a formation, being related to persisting resistive g modes, appears close to the reversal surface.« less

Analysis of the processes occurring in a submicrosecond discharge with a linear current density of up to 3 MA/cm through a thick-wall stainless-steel electrode

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

Branitsky, A. V.; Grabovski, E. V.; Dzhangobegov, V. V.

The state of conductors carrying a megampere current from the generator to the load is studied experimentally. It is found that the plasma produced from cylindrical stainless-steel tubes during the passage of a submicrosecond current pulse with a linear density of 3 MA/cm expands with a velocity of 5.5 km/s. Numerical results on the diffusion of the magnetic field induced by a current with a linear density of 1–3MA/cm into metal electrodes agree with the experimental data on the penetration time of the magnetic field. For a linear current density of 3.1 MA/cm, the experimentally determined electric field strength onmore » the inner surface of the tube is 4 kV/cm. The calculated electric field strength on the inner surface of the tube turns out to be two times higher, which can be explained by plasma production on the outer and inner surfaces of the electrode.« less

Comparison of current distributions in electroconvulsive therapy and transcranial magnetic stimulation

NASA Astrophysics Data System (ADS)

Sekino, Masaki; Ueno, Shoogo

2002-05-01

We compared current density distributions in electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS) by numerical calculations. The model consisted of an air region and three types of tissues with different conductivities representing the brain, the skull, and the scalp. In the ECT model, electric currents were applied through electrodes with a voltage of 100 V. In the TMS model, a figure-eight coil (6 cm diameter per coil) was placed on the vertex of the head model. An alternating current with a peak intensity of 3.0 kA and a frequency of 4.2 kHz was applied to the coil. The maximum current densities inside the brain in ECT (bilateral electrode position) and TMS were 234 and 322 A/m2, respectively. The results indicate that magnetic stimulators can generate comparable current densities to ECT. While the skull significantly affected current distributions in ECT, TMS efficiently induced eddy currents in the brain. In addition, TMS is more beneficial than ECT because the localized current distribution reduces the risk of adverse side effects.

Shot-to-shot reproducibility of a self-magnetically insulated ion diode

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

Pushkarev, A. I.; Isakova, Yu. I.; Khailov, I. P.

In this paper we present the analysis of shot to shot reproducibility of the ion beam which is formed by a self-magnetically insulated ion diode with an explosive emission graphite cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: the first pulse is of negative polarity (300-500 ns, 100-150 kV), and this is followed by a second pulse of positive polarity (150 ns, 250-300 kV). The ion current density was 10-70 A/cm{sup 2} depending on the diode geometry. The beam was composed from carbon ions (80%-85%) and protons. It was found that shot to shotmore » variation in the ion current density was about 35%-40%, whilst the diode voltage and current were comparatively stable with the variation limited to no more than 10%. It was shown that focusing of the ion beam can improve the stability of the ion current generation and reduces the variation to 18%-20%. In order to find out the reason for the shot-to-shot variation in ion current density we examined the statistical correlation between the current density of the accelerated beam and other measured characteristics of the diode, such as the accelerating voltage, total current, and first pulse duration. The correlation between the ion current density measured simultaneously at different positions within the cross-section of the beam was also investigated. It was shown that the shot-to-shot variation in ion current density is mainly attributed to the variation in the density of electrons diffusing from the drift region into the A-K gap.« less

Shot-to-shot reproducibility of a self-magnetically insulated ion diode.

PubMed

Pushkarev, A I; Isakova, Yu I; Khailov, I P

2012-07-01

In this paper we present the analysis of shot to shot reproducibility of the ion beam which is formed by a self-magnetically insulated ion diode with an explosive emission graphite cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: the first pulse is of negative polarity (300-500 ns, 100-150 kV), and this is followed by a second pulse of positive polarity (150 ns, 250-300 kV). The ion current density was 10-70 A/cm(2) depending on the diode geometry. The beam was composed from carbon ions (80%-85%) and protons. It was found that shot to shot variation in the ion current density was about 35%-40%, whilst the diode voltage and current were comparatively stable with the variation limited to no more than 10%. It was shown that focusing of the ion beam can improve the stability of the ion current generation and reduces the variation to 18%-20%. In order to find out the reason for the shot-to-shot variation in ion current density we examined the statistical correlation between the current density of the accelerated beam and other measured characteristics of the diode, such as the accelerating voltage, total current, and first pulse duration. The correlation between the ion current density measured simultaneously at different positions within the cross-section of the beam was also investigated. It was shown that the shot-to-shot variation in ion current density is mainly attributed to the variation in the density of electrons diffusing from the drift region into the A-K gap.

High-voltage electrode optimization towards uniform surface treatment by a pulsed volume discharge

NASA Astrophysics Data System (ADS)

Ponomarev, A. V.; Pedos, M. S.; Scherbinin, S. V.; Mamontov, Y. I.; Ponomarev, S. V.

2015-11-01

In this study, the shape and material of the high-voltage electrode of an atmospheric pressure plasma generation system were optimised. The research was performed with the goal of achieving maximum uniformity of plasma treatment of the surface of the low-voltage electrode with a diameter of 100 mm. In order to generate low-temperature plasma with the volume of roughly 1 cubic decimetre, a pulsed volume discharge was used initiated with a corona discharge. The uniformity of the plasma in the region of the low-voltage electrode was assessed using a system for measuring the distribution of discharge current density. The system's low-voltage electrode - collector - was a disc of 100 mm in diameter, the conducting surface of which was divided into 64 radially located segments of equal surface area. The current at each segment was registered by a high-speed measuring system controlled by an ARM™-based 32-bit microcontroller. To facilitate the interpretation of results obtained, a computer program was developed to visualise the results. The program provides a 3D image of the current density distribution on the surface of the low-voltage electrode. Based on the results obtained an optimum shape for a high-voltage electrode was determined. Uniformity of the distribution of discharge current density in relation to distance between electrodes was studied. It was proven that the level of non-uniformity of current density distribution depends on the size of the gap between electrodes. Experiments indicated that it is advantageous to use graphite felt VGN-6 (Russian abbreviation) as the material of the high-voltage electrode's emitting surface.

Control of malodorous hydrogen sulfide compounds using microbial fuel cell.

PubMed

Eaktasang, Numfon; Min, Hyeong-Sik; Kang, Christina; Kim, Han S

2013-10-01

In this study, a microbial fuel cell (MFC) was used to control malodorous hydrogen sulfide compounds generated from domestic wastewaters. The electricity production demonstrated a distinct pattern of a two-step increase during 170 h of system run: the first maximum current density was 118.6 ± 7.2 mA m⁻² followed by a rebound of current density increase, reaching the second maximum of 176.8 ± 9.4 mA m⁻². The behaviors of the redox potential and the sulfate level in the anode compartment indicated that the microbial production of hydrogen sulfide compounds was suppressed in the first stage, and the hydrogen sulfide compounds generated from the system were removed effectively as a result of their electrochemical oxidation, which contributed to the additional electricity production in the second stage. This was also directly supported by sulfur deposits formed on the anode surface, which was confirmed by analyses on those solids using a scanning electron microscope equipped with energy dispersive X-ray spectroscopy as well as an elemental analyzer. To this end, the overall reduction efficiencies for HS⁻ and H₂S(g) were as high as 67.5 and 96.4 %, respectively. The correlations among current density, redox potential, and sulfate level supported the idea that the electricity signal generated in the MFC can be utilized as a potential indicator of malodor control for the domestic wastewater system.

Improved Electricity Generation by a Microbial Fuel Cell after Pretreatment of Ammonium and Nitrate in Livestock Wastewater with Microbubbles and a Catalyst.

PubMed

Jang, Jae Kyung; Kim, Taeyoung; Kang, Sukwon; Sung, Je Hoon; Kang, Youn Koo; Kim, Young Hwa

2016-11-28

Livestock wastewater containing high concentrations of ammonium and nitrate ions was pretreated with microbubbles and an Fe/MgO catalyst prior to its application in microbial fuel cells because high ion concentrations can interfere with current generation. Therefore, tests were designed to ascertain the effect of pretreatment on current generation. In initial tests, the optimal amount of catalyst was found to be 300 g/l. When 1,000 ml/min O₂ was used as the oxidant, the removal of ammonium- and nitrate-nitrogen was highest. After the operating parameters were optimized, the removal of ammonium and nitrate ions was quantified. The maximum ammonium removal was 32.8%, and nitrate was removed by up to 75.8% at a 500 g/l catalyst concentration over the course of the 2 h reaction time. The current was about 0.5 mA when livestock wastewater was used without pretreatment, whereas the current increased to 2.14 ± 0.08 mA when livestock wastewater was pretreated with the method described above. This finding demonstrates that a 4-fold increase in the current can be achieved when using pretreated livestock wastewater. The maximum power density and current density performance were 10.3 W/m³ and 67.5 A/m³, respectively, during the evaluation of the microbial fuel cells driven by pretreated livestock wastewater.

Numerical analysis of wet separation of particles by density differences

NASA Astrophysics Data System (ADS)

Markauskas, D.; Kruggel-Emden, H.

2017-07-01

Wet particle separation is widely used in mineral processing and plastic recycling to separate mixtures of particulate materials into further usable fractions due to density differences. This work presents efforts aiming to numerically analyze the wet separation of particles with different densities. In the current study the discrete element method (DEM) is used for the solid phase while the smoothed particle hydrodynamics (SPH) is used for modeling of the liquid phase. The two phases are coupled by the use of a volume averaging technique. In the current study, simulations of spherical particle separation were performed. In these simulations, a set of generated particles with two different densities is dropped into a rectangular container filled with liquid. The results of simulations with two different mixtures of particles demonstrated how separation depends on the densities of particles.

Generation and Sustainment of Plasma Rotation by ICRF Heating

NASA Astrophysics Data System (ADS)

Perkins, F. W.

2000-10-01

When tokamak plasmas are heated by the fundamental minority ion-cyclotron process, they are observed to rotate toroidally, even though this heating process introduces negligable angular momentum. This work proposes and evaluates a physics mechanism which resolves this apparent conflict. The argument has two elements. First, it is assumed that angular momentum transport is governed by a diffusion equation with a v_tor = 0 boundary condition at the plasma surface and a torque-density source. When the source consists of separated regions of positive and negative torque density, a finite central rotation velocity results, even though the volume integrated torque density - the angular momentum input - vanishes. Secondly, ions energized by the ICRF process can generate separated regions of positive and negative torque density. Heating increases their banana widths which leads to radial energetic-particle transport that must be balanced by neutralizing radial currents and a j_rB_pR torque density in the bulk plasma. Additional, comparable torque density results from collisional transfer of mechanical angular momentum from energetic particles to the bulk plasma and particle loss through banana particles impacting the wall. Monte-Carlo calculations utilizing the ORBIT code evaluate all sources of torque density and rigorously assure that no net angular momentum is introduced. Two models of ICRF heating, diffusive and instantaneous, give similar results. When the resonance location is on the LFS, the calculated rotation has the magnitude, profile, and co-current sense of Alcator C-Mod observations. For HFS resonance locations, the model predicts counter-current rotation. Scans of rotational profiles vs. resonance location, initial energy, particle loss, pitch, and qm will be presented as will the location of the velocity shear layer its scaling to a reactor.

Anisotropic high-harmonic generation in bulk crystals

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

You, Yong Sing; Reis, David A.; Ghimire, Shambhu

2016-11-21

The microscopic valence electron density determines the optical, electronic, structural and thermal properties of materials. However, current techniques for measuring this electron charge density are limited: for example, scanning tunnelling microscopy is confined to investigations at the surface, and electron diffraction requires very thin samples to avoid multiple scattering. Therefore, an optical method is desirable for measuring the valence charge density of bulk materials. Since the discovery of high-harmonic generation (HHG) in solids, there has been growing interest in using HHG to probe the electronic structure of solids. Here, using single-crystal MgO, we demonstrate that high-harmonic generation in solids ismore » sensitive to interatomic bonding. We find that harmonic efficiency is enhanced (diminished) for semi-classical electron trajectories that connect (avoid) neighbouring atomic sites in the crystal. Finally, these results indicate the possibility of using materials’ own electrons for retrieving the interatomic potential and thus the valence electron density, and perhaps even wavefunctions, in an all-optical setting.« less

431 kA/cm2 peak tunneling current density in GaN/AlN resonant tunneling diodes

NASA Astrophysics Data System (ADS)

Growden, Tyler A.; Zhang, Weidong; Brown, Elliott R.; Storm, David F.; Hansen, Katurah; Fakhimi, Parastou; Meyer, David J.; Berger, Paul R.

2018-01-01

We report on the design and fabrication of high current density GaN/AlN double barrier resonant tunneling diodes grown via plasma assisted molecular-beam epitaxy on bulk GaN substrates. A quantum-transport solver was used to model and optimize designs with high levels of doping and ultra-thin AlN barriers. The devices displayed repeatable room temperature negative differential resistance with peak-to-valley current ratios ranging from 1.20 to 1.60. A maximum peak tunneling current density (Jp) of 431 kA/cm2 was observed. Cross-gap near-UV (370-385 nm) electroluminescence (EL) was observed above +6 V when holes, generated from a polarization induced Zener tunneling effect, recombine with electrons in the emitter region. Analysis of temperature dependent measurements, thermal resistance, and the measured EL spectra revealed the presence of severe self-heating effects.

The trans-generational impact of population density signals on host-parasite interactions.

PubMed

Michel, Jessica; Ebert, Dieter; Hall, Matthew D

2016-11-25

The density of a host population is a key parameter underlying disease transmission, but it also has implications for the expression of disease through its effect on host physiology. In response to higher densities, individuals are predicted to either increase their immune investment in response to the elevated risk of parasitism, or conversely to decrease their immune capacity as a consequence of the stress of a crowded environment. However, an individual's health is shaped by many different factors, including their genetic background, current environmental conditions, and maternal effects. Indeed, population density is often sensed through the presence of info-chemicals in the environment, which may influence a host's interaction with parasites, and also those of its offspring. All of which may alter the expression of disease, and potentially uncouple the presumed link between changes in host density and disease outcomes. In this study, we used the water flea Daphnia magna and its obligate bacterial parasite Pasteuria ramosa, to investigate how signals of high host density impact on host-parasite interactions over two consecutive generations. We found that the chemical signals from crowded treatments induced phenotypic changes in both the parental and offspring generations. In the absence of a pathogen, life-history changes were genotype-specific, but consistent across generations, even when the signal of density was removed. In contrast, the influence of density on infected animals depended on the trait and generation of exposure. When directly exposed to signals of high-density, host genotypes responded differently in how they minimised the severity of disease. Yet, in the subsequent generation, the influence of density was rarely genotype-specific and instead related to ability of the host to minimise the onset of infection. Our findings reveal that population level correlations between host density and infection capture only part of the complex relationship between crowding and the severity of disease. We suggest that besides its role in horizontal transmission, signals of density can influence parasite epidemiology by modifying mechanisms of resistance across multiple generations, and elevating variability via genotype-by-environment interactions. Our results help resolve why some studies are able to find a positive correlation between high density and resistance, while others uncover a negative correlation, or even no direct relationship at all.

High Output Piezo/Triboelectric Hybrid Generator

PubMed Central

Jung, Woo-Suk; Kang, Min-Gyu; Moon, Hi Gyu; Baek, Seung-Hyub; Yoon, Seok-Jin; Wang, Zhong-Lin; Kim, Sang-Woo; Kang, Chong-Yun

2015-01-01

Recently, piezoelectric and triboelectric energy harvesting devices have been developed to convert mechanical energy into electrical energy. Especially, it is well known that triboelectric nanogenerators have a simple structure and a high output voltage. However, whereas nanostructures improve the output of triboelectric generators, its fabrication process is still complicated and unfavorable in term of the large scale and long-time durability of the device. Here, we demonstrate a hybrid generator which does not use nanostructure but generates much higher output power by a small mechanical force and integrates piezoelectric generator into triboelectric generator, derived from the simultaneous use of piezoelectric and triboelectric mechanisms in one press-and-release cycle. This hybrid generator combines high piezoelectric output current and triboelectric output voltage, which produces peak output voltage of ~370 V, current density of ~12 μA·cm−2, and average power density of ~4.44 mW·cm−2. The output power successfully lit up 600 LED bulbs by the application of a 0.2 N mechanical force and it charged a 10 μF capacitor to 10 V in 25 s. Beyond energy harvesting, this work will provide new opportunities for developing a small, built-in power source in self-powered electronics such as mobile electronics. PMID:25791299

3D tomographic reconstruction of the terrestrial exosphere and its time-dependent coupling to the magnetospheric ring current

NASA Astrophysics Data System (ADS)

Waldrop, L.; Cucho-Padin, G.; Ilie, R.

2017-12-01

Charge exchange collisions between ring current ions and hydrogen (H) atoms in the outer exosphere serve to dissipate magnetospheric energy, particularly during the slow recovery phase of geomagnetic storms, through the generation of energetic neutral atoms (ENAs) which escape the system. As a result, knowledge of the spatial distribution and temporal variability of exospheric H density is critical for reliable interpretation of ENA flux measurements as well as for accurate modeling of the ring current. Although numerous theoretical, numerical, and empirical H distributions have been used for such analyses, their reliance on ad hoc or unphysical assumptions, together with their inherently static formulations, is a source of significant uncertainty. Our recent development of a robust tomographic technique for the model-independent estimation of global exospheric H density from optical remote sensing data overcomes the limitations of past analysis and enables an unprecedented investigation of global exospheric and ring current dynamics. Here, we present sample results of our 3D, time-dependent reconstructions of exospheric structure, derived from measurements of resonantly scattered solar Lyman-alpha (121.6 nm) photons acquired by the Lyman-alpha detectors (LADs) onboard NASA's Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission. We use the Hot Electron and Ion Drift Integrator (HEIDI) kinetic model of the ring current to investigate the charge exchange interactions between the resulting H density distribution and ring current ions and generate synthetic images of ENA flux for comparison with those measured by TWINS.

Effect of doping on the forward current-transport mechanisms in a metal-insulator-semiconductor contact to INP:ZN grown by metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Cova, P.; Singh, A.; Medina, A.; Masut, R. A.

1998-04-01

A detailed study of the effect of doping density on current transport was undertaken in Au metal-insulator-semiconductor (MIS) contacts fabricated on Zn-doped InP layers grown by metal organic vapor phase epitaxy. A recently developed method was used for the simultaneous analysis of the current-voltage ( I- V) and capacitance-voltage ( C- V) characteristics in an epitaxial MIS diode which brings out the contributions of different current-transport mechanisms to the total current. I- V and high-frequency C- V measurements were performed on two MIS diodes at different temperatures in the range 220-395 K. The barrier height at zero bias of Au/InP:Zn MIS diodes, φ0 (1.06 V±10%), was independent both of the Zn-doping density and of the surface preparation. The interface state density distribution Nss as well as the thickness of the oxide layer (2.2±15% nm) unintentionally grown before Au deposition were independent of the Zn-doping concentration in the range 10 16< NA<10 17 cm -3; not so the effective potential barrier χ of the insulator layer and the density of the mid-gap traps. χ was much lower for the highly-doped sample. Our results indicate that at high temperatures, independent of the Zn-doping concentration, the interfacial layer-thermionic (ITE) and interfacial layer-diffusion (ID) mechanisms compete with each other to control the current transport. At intermediate temperatures, however, ITE and ID will no longer be the only dominant mechanisms in the MIS diode fabricated on the highly-doped sample. In this case, the assumption of a generation-recombination current permits a better fit to the experimental data. Analysis of the data suggests that the generation-recombination current, observed only in the highly-doped sample, is associated with an increase in the Zn-doping density. From the forward I- V data for this diode we obtained the energy level (0.60 eV from the conduction band) for the most effective recombination centers.

Synthesis of zinc oxide nanostructures on graphene/glass substrate by electrochemical deposition: effects of current density and temperature.

PubMed

Hambali, Nur Ashikyn; Yahaya, Hafizal; Mahmood, Mohamad Rusop; Terasako, Tomoaki; Hashim, Abdul Manaf

2014-01-01

The electrochemical growth of zinc oxide (ZnO) nanostructures on graphene on glass using zinc nitrate hexahydrate was studied. The effects of current densities and temperatures on the morphological, structural, and optical properties of the ZnO structures were studied. Vertically aligned nanorods were obtained at a low temperature of 75°C, and the diameters increased with current density. Growth temperature seems to have a strong effect in generating well-defined hexagonal-shape nanorods with a smooth top edge surface. A film-like structure was observed for high current densities above -1.0 mA/cm(2) and temperatures above 80°C due to the coalescence between the neighboring nanorods with large diameter. The nanorods grown at a temperature of 75°C with a low current density of -0.1 mA/cm(2) exhibited the highest density of 1.45 × 10(9) cm(-2). X-ray diffraction measurements revealed that the grown ZnO crystallites were highly oriented along the c-axis. The intensity ratio of the ultraviolet (UV) region emission to the visible region emission, I UV/I VIS, showed a decrement with the current densities for all grown samples. The samples grown at the current density below -0.5 mA/cm(2) showed high I UV/I VIS values closer to or higher than 1.0, suggesting their fewer structural defects. For all the ZnO/graphene structures, the high transmittance up to 65% was obtained at the light wavelength of 550 nm. Structural and optical properties of the grown ZnO structures seem to be effectively controlled by the current density rather than the growth temperature. ZnO nanorod/graphene hybrid structure on glass is expected to be a promising structure for solar cell which is a conceivable candidate to address the global need for an inexpensive alternative energy source.

High-harmonic generation in amorphous solids

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

You, Yong Sing; Yin, Yanchun; Wu, Yi

High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging. Here we report the observation of high-harmonic generation from amorphous fused silica. We also decouple the role of long-range periodicity by comparingmore » harmonics generated from fused silica and crystalline quartz, which contain the same atomic constituents but differ in long-range periodicity. These results advance current understanding of the strong-field processes leading to high-harmonic generation in solids with implications for the development of robust and compact extreme ultraviolet light sources.« less

High-harmonic generation in amorphous solids

DOE PAGES

You, Yong Sing; Yin, Yanchun; Wu, Yi; ...

2017-09-28

High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging. Here we report the observation of high-harmonic generation from amorphous fused silica. We also decouple the role of long-range periodicity by comparingmore » harmonics generated from fused silica and crystalline quartz, which contain the same atomic constituents but differ in long-range periodicity. These results advance current understanding of the strong-field processes leading to high-harmonic generation in solids with implications for the development of robust and compact extreme ultraviolet light sources.« less

Amyloid-β Production Via Cleavage of Amyloid-β Protein Precursor is Modulated by Cell Density

PubMed Central

Zhang, Can; Browne, Andrew; DiVito, Jason R.; Stevenson, Jesse A.; Romano, Donna; Dong, Yuanlin; Xie, Zhongcong; Tanzi, Rudolph E.

2012-01-01

Mounting evidence suggests that Alzheimer disease (AD) is caused by the accumulation of the small peptide, Aβ, a proteolytic cleavage product of amyloid-β protein precursor (AβPP; or APP). Aβ is generated through a serial cleavage of APP by β- and γ-secretase. Aβ40 and Aβ42 are the two main components of amyloid plaques in AD brains, with Aβ42 being more prone to aggregation. APP can also be processed by α-secretase, which cleaves APP within the Aβ sequence, thereby preventing the generation of Aβ. Little is currently known regarding the effects of cell density on APP processing and Aβ generation. Here we assessed the effects of cell density on APP processing in neuronal and non-neuronal cell lines, as well as mouse primary cortical neurons. We found that decreased cell density significantly increases levels of Aβ40, Aβ42, total Aβ, and the ratio of Aβ42:Aβ40. These results also indicate that cell density is a significant modulator of APP processing. Overall, these findings carry profound implications for both previous and forthcoming studies aiming to assess the effects of various conditions and genetic/chemical factors, e.g. novel drugs on APP processing and Aβ generation in cell-based systems. Moreover, it is interesting to speculate whether cell density changes in vivo may also affect APP processing and Aβ levels in the AD brain. PMID:20847415

High-Density Nanosharp Microstructures Enable Efficient CO2 Electroreduction.

PubMed

Saberi Safaei, Tina; Mepham, Adam; Zheng, Xueli; Pang, Yuanjie; Dinh, Cao-Thang; Liu, Min; Sinton, David; Kelley, Shana O; Sargent, Edward H

2016-11-09

Conversion of CO 2 to CO powered by renewable electricity not only reduces CO 2 pollution but also is a means to store renewable energy via chemical production of fuels from CO. However, the kinetics of this reaction are slow due its large energetic barrier. We have recently reported CO 2 reduction that is considerably enhanced via local electric field concentration at the tips of sharp gold nanostructures. The high local electric field enhances CO 2 concentration at the catalytic active sites, lowering the activation barrier. Here we engineer the nucleation and growth of next-generation Au nanostructures. The electroplating overpotential was manipulated to generate an appreciably increased density of honed nanoneedles. Using this approach, we report the first application of sequential electrodeposition to increase the density of sharp tips in CO 2 electroreduction. Selective regions of the primary nanoneedles are passivated using a thiol SAM (self-assembled monolayer), and then growth is concentrated atop the uncovered high-energy planes, providing new nucleation sites that ultimately lead to an increase in the density of the nanosharp structures. The two-step process leads to a new record in CO 2 to CO reduction, with a geometric current density of 38 mA/cm 2 at -0.4 V (vs reversible hydrogen electrode), and a 15-fold improvement over the best prior reports of electrochemical surface area (ECSA) normalized current density.

Enhanced field emission from hexagonal rhodium nanostructures

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

Sathe, Bhaskar R.; Kakade, Bhalchandra A.; Mulla, Imtiaz S.

2008-06-23

Shape selective synthesis of nanostructured Rh hexagons has been demonstrated with the help of a modified chemical vapor deposition using rhodium acetate. An ultralow threshold field of 0.72 V/{mu}m is observed to generate a field emission current density of 4x10{sup -3} {mu}A/cm{sup 2}. The high enhancement factor (9325) indicates that the origin of electron emission is from nanostructured features. The smaller size of emitting area, excellent current density, and stability over a period of more than 3 h are promising characteristics for the development of electron sources.

Electricity generation and wastewater treatment of oil refinery in microbial fuel cells using Pseudomonas putida.

PubMed

Majumder, Dip; Maity, Jyoti Prakash; Tseng, Min-Jen; Nimje, Vanita Roshan; Chen, Hau-Ren; Chen, Chien-Cheng; Chang, Young-Fo; Yang, Tsui-Chu; Chen, Chen-Yen

2014-09-22

Microbial fuel cells (MFCs) represent a novel platform for treating wastewater and at the same time generating electricity. Using Pseudomonas putida (BCRC 1059), a wild-type bacterium, we demonstrated that the refinery wastewater could be treated and also generate electric current in an air-cathode chamber over four-batch cycles for 63 cumulative days. Our study indicated that the oil refinery wastewater containing 2213 mg/L (ppm) chemical oxygen demand (COD) could be used as a substrate for electricity generation in the reactor of the MFC. A maximum voltage of 355 mV was obtained with the highest power density of 0.005 mW/cm² in the third cycle with a maximum current density of 0.015 mA/cm² in regard to the external resistor of 1000 Ω. A maximum coulombic efficiency of 6 × 10⁻²% was obtained in the fourth cycle. The removal efficiency of the COD reached 30% as a function of time. Electron transfer mechanism was studied using cyclic voltammetry, which indicated the presence of a soluble electron shuttle in the reactor. Our study demonstrated that oil refinery wastewater could be used as a substrate for electricity generation.

Electricity Generation and Wastewater Treatment of Oil Refinery in Microbial Fuel Cells Using Pseudomonas putida

PubMed Central

Majumder, Dip; Maity, Jyoti Prakash; Tseng, Min-Jen; Nimje, Vanita Roshan; Chen, Hau-Ren; Chen, Chien-Cheng; Chang, Young-Fo; Yang, Tsui-Chu; Chen, Chen-Yen

2014-01-01

Microbial fuel cells (MFCs) represent a novel platform for treating wastewater and at the same time generating electricity. Using Pseudomonas putida (BCRC 1059), a wild-type bacterium, we demonstrated that the refinery wastewater could be treated and also generate electric current in an air-cathode chamber over four-batch cycles for 63 cumulative days. Our study indicated that the oil refinery wastewater containing 2213 mg/L (ppm) chemical oxygen demand (COD) could be used as a substrate for electricity generation in the reactor of the MFC. A maximum voltage of 355 mV was obtained with the highest power density of 0.005 mW/cm2 in the third cycle with a maximum current density of 0.015 mA/cm2 in regard to the external resistor of 1000 Ω. A maximum coulombic efficiency of 6 × 10−2% was obtained in the fourth cycle. The removal efficiency of the COD reached 30% as a function of time. Electron transfer mechanism was studied using cyclic voltammetry, which indicated the presence of a soluble electron shuttle in the reactor. Our study demonstrated that oil refinery wastewater could be used as a substrate for electricity generation. PMID:25247576

Artificial cognitive memory—changing from density driven to functionality driven

NASA Astrophysics Data System (ADS)

Shi, L. P.; Yi, K. J.; Ramanathan, K.; Zhao, R.; Ning, N.; Ding, D.; Chong, T. C.

2011-03-01

Increasing density based on bit size reduction is currently a main driving force for the development of data storage technologies. However, it is expected that all of the current available storage technologies might approach their physical limits in around 15 to 20 years due to miniaturization. To further advance the storage technologies, it is required to explore a new development trend that is different from density driven. One possible direction is to derive insights from biological counterparts. Unlike physical memories that have a single function of data storage, human memory is versatile. It contributes to functions of data storage, information processing, and most importantly, cognitive functions such as adaptation, learning, perception, knowledge generation, etc. In this paper, a brief review of current data storage technologies are presented, followed by discussions of future storage technology development trend. We expect that the driving force will evolve from density to functionality, and new memory modules associated with additional functions other than only data storage will appear. As an initial step toward building a future generation memory technology, we propose Artificial Cognitive Memory (ACM), a memory based intelligent system. We also present the characteristics of ACM, new technologies that can be used to develop ACM components such as bioinspired element cells (silicon, memristor, phase change, etc.), and possible methodologies to construct a biologically inspired hierarchical system.

Gaining electricity from in situ oxidation of hydrogen produced by fermentative cellulose degradation.

PubMed

Niessen, J; Schröder, U; Harnisch, F; Scholz, F

2005-01-01

To exploit the fermentative hydrogen generation and direct hydrogen oxidation for the generation of electric current from the degradation of cellulose. Utilizing the metabolic activity of the mesophilic anaerobe Clostridium cellulolyticum and the thermophilic Clostridium thermocellum we show that electricity generation is possible from cellulose fermentation. The current generation is based on an in situ oxidation of microbially synthesized hydrogen at platinum-poly(tetrafluoroaniline) (Pt-PTFA) composite electrodes. Current densities of 130 mA l(-1) (with 3 g cellulose per litre medium) were achieved in poised potential experiments under batch and semi-batch conditions. The presented results show that electricity generation is possible by the in situ oxidation of hydrogen, product of the anaerobic degradation of cellulose by cellulolytic bacteria. For the first time, it is shown that an insoluble complex carbohydrate like cellulose can be used for electricity generation in a microbial fuel cell. The concept represents a first step to the utilization of macromolecular biomass components for microbial electricity generation.

Two dimensional distribution measurement of electric current generated in a polymer electrolyte fuel cell using 49 NMR surface coils.

PubMed

Ogawa, Kuniyasu; Sasaki, Tatsuyoshi; Yoneda, Shigeki; Tsujinaka, Kumiko; Asai, Ritsuko

2018-05-17

In order to increase the current density generated in a PEFC (polymer electrolyte fuel cell), a method for measuring the spatial distribution of both the current and the water content of the MEA (membrane electrode assembly) is necessary. Based on the frequency shifts of NMR (nuclear magnetic resonance) signals acquired from the water contained in the MEA using 49 NMR coils in a 7 × 7 arrangement inserted in the PEFC, a method for measuring the two-dimensional spatial distribution of electric current generated in a unit cell with a power generation area of 140 mm × 160 mm was devised. We also developed an inverse analysis method to determine the two-dimensional electric current distribution that can be applied to actual PEFC connections. Two analytical techniques, namely coarse graining of segments and stepwise search, were used to shorten the calculation time required for inverse analysis of the electric current map. Using this method and techniques, spatial distributions of electric current and water content in the MEA were obtained when the PEFC generated electric power at 100 A. Copyright © 2018 Elsevier Inc. All rights reserved.

High yield neutron generator based on a high-current gasdynamic electron cyclotron resonance ion source

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

Skalyga, V.; Sidorov, A.; Lobachevsky State University of Nizhny Novgorod

2015-09-07

In present paper, an approach for high yield compact D-D neutron generator based on a high current gasdynamic electron cyclotron resonance ion source is suggested. Results on dense pulsed deuteron beam production with current up to 500 mA and current density up to 750 mA/cm{sup 2} are demonstrated. Neutron yield from D{sub 2}O and TiD{sub 2} targets was measured in case of its bombardment by pulsed 300 mA D{sup +} beam with 45 keV energy. Neutron yield density at target surface of 10{sup 9} s{sup −1} cm{sup −2} was detected with a system of two {sup 3}He proportional counters. Estimations based on obtained experimental resultsmore » show that neutron yield from a high quality TiD{sub 2} target bombarded by D{sup +} beam demonstrated in present work accelerated to 100 keV could reach 6 × 10{sup 10} s{sup −1} cm{sup −2}. It is discussed that compact neutron generator with such characteristics could be perspective for a number of applications like boron neutron capture therapy, security systems based on neutron scanning, and neutronography.« less

Effects of the unintentional background concentration, indium composition and defect density on the performance of InGaN p-i-n homojunction solar cells

NASA Astrophysics Data System (ADS)

Wu, Shudong; Cheng, Liwen; Wang, Qiang

2018-07-01

We theoretically investigate the effects of the unintentional background concentration, indium composition and defect density of intrinsic layer (i-layer) on the photovoltaic performance of InGaN p-i-n homojunction solar cells by solving the Poisson and steady-state continuity equations. The built-in electric field and carrier generation rate depend on the position within the i-layer. The collection efficiency, short circuit current density, open circuit voltage, fill factor, and conversion efficiency are found to depend strongly on the background concentration, thickness, indium composition, and defect density of the i-layer. With increasing the background concentration, the maximum thickness of field-bearing i-layer decreases, and the width of depletion region may become even too small to cover the whole i-layer, resulting in a serious decrease of the carrier collection. Some oscillations as a function of indium composition are found in the short circuit current density and conversion efficiency at high indium composition and low defect density due to the interference between the absorbance and the generation rate of carriers. The defect density degrades seriously the overall photovoltaic performance, and its effect on the photovoltaic performance is roughly seven orders of magnitude higher than the previously reported values [Feng et al., J. Appl. Phys. 108 (2010) 093118]. As a result, the high crystalline quality InGaN with high indium composition is a key factor in the device performance of III-nitride based solar cells.

Electric energy production by particle thermionic-thermoelectric power generators

NASA Technical Reports Server (NTRS)

Oettinger, P. E.

1980-01-01

Thermionic-thermoelectric power generators, composed of a thin layer of porous, low work function material separating a heated emitter electrode and a cooler collector electrode, have extremely large Seebeck coefficients of over 2 mV/K and can provide significant output power. Preliminary experiments with 20-micron thick (Ba Sr Ca)O coatings, limited by evaporative loss to temperatures below 1400 K, have yielded short circuit current densities of 500 mA/sq cm and power densities of 60 mW/ sq cm. Substantially more output is expected with cesium-coated refractory oxide particle coatings operating at higher temperatures. Practical generators will have thermal-to-electrical efficiencies of 10 to 20%. Further increases can be gained by cascading these high-temperature devices with lower temperature conventional thermoelectric generators.

Electrodeless RF Plasma Thruster Using m = 0 Coil

NASA Astrophysics Data System (ADS)

Nishimura, Shuichi; Arai, Daisuke; Kuwahara, Daisuke; Shinohara, Shunjiro

2016-10-01

In order to realize a deep space exploration in the future, we have been developing a next generation electrodeless electric propulsion system by electromagnetic acceleration of high-density helicon plasma. A new proposed method by m = 0 coil plasma acceleration (m is an azimuthal mode number) is based on the Lorentz force: a product of the induced azimuthal current by supplying an AC current to the m = 0 coil and the radial component of the externally applied magnetic field (divergent field configuration). Here, we have investigated the dependences of an ion velocity and an electron density on the external parameters, leading to optimized conditions, using the SHD device. By increasing AC current on the order of 100 A, we could see the increase of ion velocity and electron density by a factor of 2.5 and 3, respectively.

The equivalent magnetizing method applied to the design of gradient coils for MRI.

PubMed

Lopez, Hector Sanchez; Liu, Feng; Crozier, Stuart

2008-01-01

This paper presents a new method for the design of gradient coils for Magnetic Resonance Imaging systems. The method is based on the equivalence between a magnetized volume surrounded by a conducting surface and its equivalent representation in surface current/charge density. We demonstrate that the curl of the vertical magnetization induces a surface current density whose stream line defines the coil current pattern. This method can be applied for coils wounds on arbitrary surface shapes. A single layer unshielded transverse gradient coil is designed and compared, with the designs obtained using two conventional methods. Through the presented example we demonstrate that the generated unconventional current patterns obtained using the magnetizing current method produces a superior gradient coil performance than coils designed by applying conventional methods.

Metal-based anode for high performance bioelectrochemical systems through photo-electrochemical interaction

NASA Astrophysics Data System (ADS)

Liang, Yuxiang; Feng, Huajun; Shen, Dongsheng; Long, Yuyang; Li, Na; Zhou, Yuyang; Ying, Xianbin; Gu, Yuan; Wang, Yanfeng

2016-08-01

This paper introduces a novel composite anode that uses light to enhance current generation and accelerate biofilm formation in bioelectrochemical systems. The composite anode is composed of 316L stainless steel substrate and a nanostructured α-Fe2O3 photocatalyst (PSS). The electrode properties, current generation, and biofilm properties of the anode are investigated. In terms of photocurrent, the optimal deposition and heat-treatment times are found to be 30 min and 2 min, respectively, which result in a maximum photocurrent of 0.6 A m-2. The start-up time of the PSS is 1.2 days and the maximum current density is 2.8 A m-2, twice and 25 times that of unmodified anode, respectively. The current density of the PSS remains stable during 20 days of illumination. Confocal laser scanning microscope images show that the PSS could benefit biofilm formation, while electrochemical impedance spectroscopy indicates that the PSS reduce the charge-transfer resistance of the anode. Our findings show that photo-electrochemical interaction is a promising way to enhance the biocompatibility of metal anodes for bioelectrochemical systems.

Ion beam enhancement in magnetically insulated ion diodes for high-intensity pulsed ion beam generation in non-relativistic mode

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

Zhu, X. P.; Surface Engineering Laboratory, School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024; Zhang, Z. C.

High-intensity pulsed ion beam (HIPIB) with ion current density above Child-Langmuir limit is achieved by extracting ion beam from anode plasma of ion diodes with suppressing electron flow under magnetic field insulation. It was theoretically estimated that with increasing the magnetic field, a maximal value of ion current density may reach nearly 3 times that of Child-Langmuir limit in a non-relativistic mode and close to 6 times in a highly relativistic mode. In this study, the behavior of ion beam enhancement by magnetic insulation is systematically investigated in three types of magnetically insulated ion diodes (MIDs) with passive anode, takingmore » into account the anode plasma generation process on the anode surface. A maximal enhancement factor higher than 6 over the Child-Langmuir limit can be obtained in the non-relativistic mode with accelerating voltage of 200–300 kV. The MIDs differ in two anode plasma formation mechanisms, i.e., surface flashover of a dielectric coating on the anode and explosive emission of electrons from the anode, as well as in two insulation modes of external-magnetic field and self-magnetic field with either non-closed or closed drift of electrons in the anode-cathode (A-K) gap, respectively. Combined with ion current density measurement, energy density characterization is employed to resolve the spatial distribution of energy density before focusing for exploring the ion beam generation process. Consistent results are obtained on three types of MIDs concerning control of neutralizing electron flows for the space charge of ions where the high ion beam enhancement is determined by effective electron neutralization in the A-K gap, while the HIPIB composition of different ion species downstream from the diode may be considerably affected by the ion beam neutralization during propagation.« less

Experimental Investigation of Pseudospark generated electron beam

NASA Astrophysics Data System (ADS)

Kumar, Niraj; Verma, D. K.; Prajapati, J.; Kumar, M.; Meena, B. L.; Tyagi, M. S.; Srivastava, V.; Pal, U. N.

2012-11-01

The pseudospark (PS) discharge is, however, more recently recognized as a different type of discharge which is capable of generating electron beams with the highest combined current density and brightness of any known type of electron source. PS discharge is a specific type of gas discharge, which operates on the left-hand side of the hollow cathode analogy to the Paschen curve with axially symmetric parallel electrodes and central holes on the electrodes. The PS discharge generated electron beam has tremendous applications in plasma filled microwave sources where normal material cathode cannot be used. Analysis of the electron beam profile has been carried out experimentally for different applied voltages. The investigation has been done at different axial and radial location inside the drift tube in argon atmosphere. This paper represents experimentally derived axial and radial variation of the beam current inside the plasma filled drift tube of PS discharge based plasma cathode electron (PCE) gun. With the help of current density estimation the focusing and defocusing point of electron beam in axial direction can be analyzed. It has been further confirmed the successful propagation of electron beam in confined manner without any assistance of external magnetic field.

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

Fertig, Fabian, E-mail: fabian.fertig@ise.fraunhofer.de; Greulich, Johannes; Rein, Stefan

Spatially resolved determination of solar cell parameters is beneficial for loss analysis and optimization of conversion efficiency. One key parameter that has been challenging to access by an imaging technique on solar cell level is short-circuit current density. This work discusses the robustness of a recently suggested approach to determine short-circuit current density spatially resolved based on a series of lock-in thermography images and options for a simplified image acquisition procedure. For an accurate result, one or two emissivity-corrected illuminated lock-in thermography images and one dark lock-in thermography image have to be recorded. The dark lock-in thermography image can bemore » omitted if local shunts are negligible. Furthermore, it is shown that omitting the correction of lock-in thermography images for local emissivity variations only leads to minor distortions for standard silicon solar cells. Hence, adequate acquisition of one image only is sufficient to generate a meaningful map of short-circuit current density. Beyond that, this work illustrates the underlying physics of the recently proposed method and demonstrates its robustness concerning varying excitation conditions and locally increased series resistance. Experimentally gained short-circuit current density images are validated for monochromatic illumination in comparison to the reference method of light-beam induced current.« less

The TELEC - A plasma type of direct energy converter. [Thermo-Electronic Laser Energy Converter for electric power generation

NASA Technical Reports Server (NTRS)

Britt, E. J.

1978-01-01

The Thermo-Electronic Laser Energy Converter (TELEC) is a high-power density plasma device designed to convert a 10.6-micron CO2 laser beam into electric power. Electromagnetic radiation is absorbed in plasma electrons, creating a high-electron temperature. Energetic electrons diffuse from the plasma and strike two electrodes having different areas. The larger electrode collects more electrons and there is a net transport of current. An electromagnetic field is generated in the external circuit. A computer program has been designed to analyze TELEC performance allowing parametric variation for optimization. Values are presented for TELEC performance as a function of cesium pressure and for current density and efficiency as a function of output voltage. Efficiency is shown to increase with pressure, reaching a maximum over 45%.

Ozone and dinitrogen monoxide production in atmospheric pressure air dielectric barrier discharge plasma effluent generated by nanosecond pulse superimposed alternating current voltage

NASA Astrophysics Data System (ADS)

Takashima, Keisuke; Kaneko, Toshiro

2017-06-01

The effects of nanosecond pulse superposition to alternating current voltage (NS + AC) on the generation of an air dielectric barrier discharge (DBD) plasma and reactive species are experimentally studied, along with measurements of ozone (O3) and dinitrogen monoxide (N2O) in the exhausted gas through the air DBD plasma (air plasma effluent). The charge-voltage cycle measurement indicates that the role of nanosecond pulse superposition is to induce electrical charge transport and excess charge accumulation on the dielectric surface following the nanosecond pulses. The densities of O3 and N2O in NS + AC DBD are found to be significantly increased in the plasma effluent, compared to the sum of those densities generated in NS DBD and AC DBD operated individually. The production of O3 and N2O is modulated significantly by the phase in which the nanosecond pulse is superimposed. The density increase and modulation effects by the nanosecond pulse are found to correspond with the electrical charge transport and the excess electrical charge accumulation induced by the nanosecond pulse. It is suggested that the electrical charge transport by the nanosecond pulse might result in the enhancement of the nanosecond pulse current, which may lead to more efficient molecular dissociation, and the excess electrical charge accumulation induced by the nanosecond pulse increases the discharge coupling power which would enhance molecular dissociation.

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

NASA Astrophysics Data System (ADS)

Santos, Joao

2017-10-01

Powerful laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in the kTesla range. The B-fields are measured by proton-deflectometry and high-frequency bandwidth B-dot probes. According to our modeling, the quasi-static currents are provided from hot electron ejection from the laser-irradiated surface, accounting for the space charge neutralization and the plasma magnetization. The major control parameter is the laser irradiance Iλ2 . The B-fields ns-scale is long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport into solid dielectric targets, yielding an unprecedented enhancement of a factor 5 on the energy-density flux at 60 µm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes and to laboratory astrophysics. We acknowledge funding from French National Agency for Research (ANR), Grant TERRE ANR-2011-BS04-014, and from EUROfusion Consortium, European Union's Horizon 2020 research and innovation programme, Grant 633053.

Biosolar energy generation and harvesting from biomolecule-copolymer hybrid systems

NASA Astrophysics Data System (ADS)

Chu, Bong-Chieh Benjamin

Alternative energy sources have become an increasingly important topic as energy needs outpace supply. Furthermore, as the world moves into the digital age of portable electronics, highly efficient and lightweight energy sources will need to be developed. Current technology, such as lithium ion batteries, provide enough power to run portable electronics for hours or days, but can still allow for improvement in their power density (W/kg). Utilizing energy-transducing membrane proteins, which are by nature highly efficient, it is possible to engineer biological-based energy sources with energy densities far greater than any solid-state systems. Furthermore, solar powered membrane proteins have the added benefit of a virtually unlimited supply of energy. This work has developed protein-polymer hybrid films and nanoscale vesicles for a variety of applications from fuel-cell technology to biological-based photovoltaics. Bacteriorhodopsin (BR), a light-activated proton pump, and Cytochrome C Oxidase (COX), a protein involved in the electron transport chain in mitochondria, were reconstituted into biomimetic triblock copolymer membranes. Block copolymer membranes mimic the amphiphilic nature of a natural lipid bilayer but exhibit greater mechanical stability due to UV-polymerizable endgroups. In BR/COX functionalized nanovesicles, proton gradients generated by the light-activated proton pumping of BR are used to drive COX in reverse to generate electrons, providing a hybrid biologically-active polymer to convert solar energy to chemical energy, and finally to electrical energy. This work has found protein activity in planar membranes through the photoelectric current generation by BR and the proton pumping activity of BR-functionalized polymer membranes deposited onto proton exchange membranes, as well as the coupled functionality of BR and COX through current generation in cyclic voltammetry and direct current measurements. Current switching between light and dark environments of composite BR/COX polymer vesicles show a light-dependent current generation with current changes as high as 10muA. Furthermore, electrode modifications were made using polymer and polymer/carbon nanotube (CNT) coatings as anti-absorbent and conductive anti-absorbent layers for the purpose of a more robust electrode. These findings have shown that biological functionality can be engineered into synthetic polymers to make hybrid devices.

Strong terahertz emission by optical rectification of shaped laser pulse in transversely magnetized plasma

NASA Astrophysics Data System (ADS)

Singh, Ram Kishor; Singh, Monika; Rajouria, Satish Kumar; Sharma, R. P.

2017-07-01

This communication presents a theoretical model for efficient terahertz (THz) radiation generation by the optical rectification of shaped laser pulse in transversely magnetised ripple density plasma. The laser beam imparts a nonlinear ponderomotive force to the electron and this force exerts a nonlinear velocity component in both transverse and axial directions which have spectral components in the THz range. These velocity components couple with the pre-existing density ripple and give rise to a strong nonlinear current density which drives the THz wave in the plasma. The THz yield increases with the increasing strength of the background magnetic field and the sensitivity depends on the ripple wave number. The emitted power is directly proportional to the square of the amplitude of the density ripple. For exact phase matching condition, the normalised power of the generated THz wave can be achieved of the order of 10-4.

Large Area Crop Inventory Experiment (LACIE). Second-generation sampling strategy evaluation report. [Kansas, North Dakota, and U.S.S.R.

NASA Technical Reports Server (NTRS)

Basu, J. P. (Principal Investigator); Dragich, S. M.; Mcguigan, D. P.

1978-01-01

The author has identified the following significant results. The stratification procedure in the new sampling strategy for LACIE included: (1) correlation test results indicating that an agrophysical stratum may be homogeneous with respect to agricultural density, but not with respect to wheat density; and (2) agrophysical unit homogeneity test results indicating that with respect to agricultural density many agrophysical units are not homogeneous, but removal of one or more refined strata from any such current agrophysical unit can make the strata homogeneous. The apportioning procedure results indicated that the current procedure is not performing well and that the apportioned estimates of refined strata wheat area are often unreliable.

Bernstein wave aided laser third harmonic generation in a plasma

NASA Astrophysics Data System (ADS)

Tyagi, Yachna; Tripathi, Deepak; Kumar, Ashok

2016-09-01

The process of Bernstein wave aided resonant third harmonic generation of laser in a magnetized plasma is investigated. The extra-ordinary mode (X-mode) laser of frequency ω 0 and wave number k → 0 , travelling across the magnetic field in a plasma, exerts a second harmonic ponderomotive force on the electrons imparting them an oscillatory velocity v → 2 ω0 , 2 k → 0 . This velocity beats with the density perturbation due to the Bernstein wave to produce a density perturbation at cyclotron frequency shifted second harmonic. The density perturbation couples with the oscillatory velocity v → ω0 , k → 0 of X-mode of the laser to produce the cyclotron frequency shifted third harmonic current density leading to harmonic radiation. The phase matching condition for the up shifted frequency is satisfied when the Bernstein wave is nearly counter-propagating to the laser. As the transverse wave number of the Bernstein wave is large, it is effective in the phase matched third harmonic generation, when the laser frequency is not too far from the upper hybrid frequency.

Helicon plasma generator-assisted surface conversion ion source for the production of H- ion beams at the Los Alamos Neutron Science Centera)

NASA Astrophysics Data System (ADS)

Tarvainen, O.; Rouleau, G.; Keller, R.; Geros, E.; Stelzer, J.; Ferris, J.

2008-02-01

The converter-type negative ion source currently employed at the Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H- ion beams in a filament-driven discharge. In this kind of an ion source the extracted H- beam current is limited by the achievable plasma density which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which deposits on the H- converter surface and degrades its performance. Therefore, we have started an ion source development project focused on replacing these thermionic cathodes (filaments) of the converter source by a helicon plasma generator capable of producing high-density hydrogen plasmas with low electron energy. In our studies which have so far shown that the plasma density of the surface conversion source can be increased significantly by exciting a helicon wave in the plasma, and we expect to improve the performance of the surface converter H- ion source in terms of beam brightness and time between services. The design of this new source and preliminary results are presented, along with a discussion of physical processes relevant for H- ion beam production with this novel design. Ultimately, we perceive this approach as an interim step towards our long-term goal, combining a helicon plasma generator with an SNS-type main discharge chamber, which will allow us to individually optimize the plasma properties of the plasma cathode (helicon) and H- production (main discharge) in order to further improve the brightness of extracted H- ion beams.

Helicon plasma generator-assisted surface conversion ion source for the production of H(-) ion beams at the Los Alamos Neutron Science Center.

PubMed

Tarvainen, O; Rouleau, G; Keller, R; Geros, E; Stelzer, J; Ferris, J

2008-02-01

The converter-type negative ion source currently employed at the Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H(-) ion beams in a filament-driven discharge. In this kind of an ion source the extracted H(-) beam current is limited by the achievable plasma density which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which deposits on the H(-) converter surface and degrades its performance. Therefore, we have started an ion source development project focused on replacing these thermionic cathodes (filaments) of the converter source by a helicon plasma generator capable of producing high-density hydrogen plasmas with low electron energy. In our studies which have so far shown that the plasma density of the surface conversion source can be increased significantly by exciting a helicon wave in the plasma, and we expect to improve the performance of the surface converter H(-) ion source in terms of beam brightness and time between services. The design of this new source and preliminary results are presented, along with a discussion of physical processes relevant for H(-) ion beam production with this novel design. Ultimately, we perceive this approach as an interim step towards our long-term goal, combining a helicon plasma generator with an SNS-type main discharge chamber, which will allow us to individually optimize the plasma properties of the plasma cathode (helicon) and H(-) production (main discharge) in order to further improve the brightness of extracted H(-) ion beams.

Amyloid-β production via cleavage of amyloid-β protein precursor is modulated by cell density.

PubMed

Zhang, Can; Browne, Andrew; Divito, Jason R; Stevenson, Jesse A; Romano, Donna; Dong, Yuanlin; Xie, Zhongcong; Tanzi, Rudolph E

2010-01-01

Mounting evidence suggests that Alzheimer's disease (AD) is caused by the accumulation of the small peptide, amyloid-β (Aβ), a proteolytic cleavage product of amyloid-β protein precursor (AβPP). Aβ is generated through a serial cleavage of AβPP by β- and γ-secretase. Aβ40 and Aβ42 are the two main components of amyloid plaques in AD brains, with Aβ42 being more prone to aggregation. AβPP can also be processed by α-secretase, which cleaves AβPP within the Aβ sequence, thereby preventing the generation of Aβ. Little is currently known regarding the effects of cell density on AβPP processing and Aβ generation. Here we assessed the effects of cell density on AβPP processing in neuronal and non-neuronal cell lines, as well as mouse primary cortical neurons. We found that decreased cell density significantly increases levels of Aβ40, Aβ42, total Aβ, and the ratio of Aβ42: Aβ40. These results also indicate that cell density is a significant modulator of AβPP processing. Overall, these findings carry profound implications for both previous and forthcoming studies aiming to assess the effects of various conditions and genetic/chemical factors, e.g., novel drugs on AβPP processing and Aβ generation in cell-based systems. Moreover, it is interesting to speculate whether cell density changes in vivo may also affect AβPP processing and Aβ levels in the AD brain.

A simulation study of interactions of space-shuttle generated electron beams with ambient plasma and neutral gas

NASA Technical Reports Server (NTRS)

Winglee, Robert M.

1991-01-01

The objective was to conduct large scale simulations of electron beams injected into space. The study of the active injection of electron beams from spacecraft is important, as it provides valuable insight into the plasma beam interactions and the development of current systems in the ionosphere. However, the beam injection itself is not simple, being constrained by the ability of the spacecraft to draw current from the ambient plasma. The generation of these return currents is dependent on several factors, including the density of the ambient plasma relative to the beam density, the presence of neutrals around the spacecraft, the configuration of the spacecraft, and the motion of the spacecraft through the plasma. Two dimensional (three velocity) particle simulations with collisional processes included are used to show how these different and often coupled processes can be used to enhance beam propagation from the spacecraft. To understand the radial expansion mechanism of an electron beam injected from a highly charged spacecraft, two dimensional particle-in-cell simulations were conducted for a high density electron beam injected parallel to magnetic fields from an isolated equipotential conductor into a cold background plasma. The simulations indicate that charge build-up at the beam stagnation point causes the beam to expand radially to the beam electron gyroradius.

A simulation study of interactions of Space-Shuttle generated electron beams with ambient plasma and neutral gas

NASA Technical Reports Server (NTRS)

1991-01-01

The object was to conduct large scale simulations of electron beams injected into space. The study of active injection of electron beams from spacecraft is important since it provides valuable insight into beam-plasma interactions and the development of current systems in the ionosphere. However, the beam injection itself is not simple, being constrained by the ability of the spacecraft to draw return current from the ambient plasma. The generation of these return currents is dependent on several factors, including the density of the ambient plasma relative to the beam density, the presence of neutrals around the spacecraft, the configuration of the spacecraft, and the motion of the spacecraft through the plasma. Two dimensional particle simulations with collisional processes included are used to show how these different and often coupled processes can be utilized to enhance beam propagation from the spacecraft. To understand the radical expansion of mechanism of an electron beam from a highly charged spacecraft, two dimensional particle in cell simulations were conducted for a high density electron beam injected parallel to magnetic fields from an isolated equipotential conductor into a cold background plasma. The simulations indicate that charge buildup at the beam stagnation point causes the beam to expand radially to the beam electron gyroradius.

Magnetic nano-oscillator driven by pure spin current.

PubMed

Demidov, Vladislav E; Urazhdin, Sergei; Ulrichs, Henning; Tiberkevich, Vasyl; Slavin, Andrei; Baither, Dietmar; Schmitz, Guido; Demokritov, Sergej O

2012-12-01

With the advent of pure-spin-current sources, spin-based electronic (spintronic) devices no longer require electrical charge transfer, opening new possibilities for both conducting and insulating spintronic systems. Pure spin currents have been used to suppress noise caused by thermal fluctuations in magnetic nanodevices, amplify propagating magnetization waves, and to reduce the dynamic damping in magnetic films. However, generation of coherent auto-oscillations by pure spin currents has not been achieved so far. Here we demonstrate the generation of single-mode coherent auto-oscillations in a device that combines local injection of a pure spin current with enhanced spin-wave radiation losses. Counterintuitively, radiation losses enable excitation of auto-oscillation, suppressing the nonlinear processes that prevent auto-oscillation by redistributing the energy between different modes. Our devices exhibit auto-oscillations at moderate current densities, at a microwave frequency tunable over a wide range. These findings suggest a new route for the implementation of nanoscale microwave sources for next-generation integrated electronics.

Porous graphene current collectors filled with silicon as high-performance lithium battery anode

NASA Astrophysics Data System (ADS)

Ababtain, Khalid; Babu, Ganguli; Susarla, Sandhya; Gullapalli, Hemtej; Masurkar, Nirul; Ajayan, Pulickel M.; Mohana Reddy Arava, Leela

2018-01-01

Despite the massive success for high energy density, the charge-discharge current rate performance of the lithium-ion batteries are still a major concern owing to inherent sluggish Li-ion kinetics. Herein, we demonstrate three-dimensional porous electrodes engineered on highly conductive graphene current collectors to enhance the Li-ion conductivity, thereby c-rate performance. Such high-quality graphene provides surface area for loading a large amount of electrochemically active material and strong adhesion with the electrode. The synergism of porous structure and conductive current collector enables us to realize high-performance new-generation silicon anodes with a high energy density of 1.8 mAh cm-2. Further, silicon electrodes revealed with excellent current rates up to 5C with a capacity of 0.37 mAh cm-2 for 500 nm planar thickness.

Magnetic field line reconnection experiments. V - Current disruptions and double layers

NASA Technical Reports Server (NTRS)

Stenzel, R. L.; Gekelman, W.; Wild, N.

1983-01-01

An investigation is conducted of the stability of a large laboratory plasma current sheet, which has been generated in the process of magnetic field line reconnection, with respect to local current increases. Magnetic flux variations in regions remote from the current sheet generate an inductive voltage in the current loop that drops off inside the plasma in the form of a potential double layer, leading to particle acceleration with velocities much larger than those expected from the steady state electric fields in the plasma. A model for the mechanism of the current disruptions is formulated in which the potential structure leads to ion expulsion, creating a localized density drop. The associated current drop in an inductive circuit drives the potential structure, providing feedback for the disruptive instability. Similarities to, and differences from, magnetospheric substorm phenomena are noted.

Effects of electrode gap and electric current on chlorine generation of electrolyzed deep ocean water.

PubMed

Hsu, Guoo-Shyng Wang; Hsu, Shun-Yao

2018-04-01

Electrolyzed water is a sustainable disinfectant, which can comply with food safety regulations and is environmental friendly. A two-factor central composite design was adopted for studying the effects of electrode gap and electric current on chlorine generation efficiency of electrolyzed deep ocean water. Deep ocean water was electrolyzed in a glass electrolyzing cell equipped with platinum-plated titanium anode and cathode in a constant-current operation mode. Results showed that current density, chlorine concentration, and electrolyte temperature increased with electric current, while electric efficiency decreased with electric current and electrode gap. An electrode gap of less than 11.7 mm, and a low electric current appeared to be a more energy efficient design and operation condition for the electrolysis system. Copyright © 2017. Published by Elsevier B.V.

Alkaline-Acid Zn-H2 O Fuel Cell for the Simultaneous Generation of Hydrogen and Electricity.

PubMed

Cai, Pingwei; Li, Yan; Wang, Genxiang; Wen, Zhenhai

2018-04-03

An alkaline-acid Zn-H 2 O fuel cell is proposed for the simultaneous generation of electricity with an open circuit voltage of about 1.25 V and production of H 2 with almost 100 % Faradic efficiency. We demonstrate that, as a result of harvesting energy from both electrochemical neutralization and electrochemical Zn oxidation, the as-developed hybrid cell can deliver a power density of up to 80 mW cm -2 and an energy density of 934 Wh kg -1 and maintain long-term stability for H 2 production with an output voltage of 1.16 V at a current density of 10 mA cm -2 . © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Large-Area Permanent-Magnet ECR Plasma Source

NASA Technical Reports Server (NTRS)

Foster, John E.

2007-01-01

A 40-cm-diameter plasma device has been developed as a source of ions for material-processing and ion-thruster applications. Like the device described in the immediately preceding article, this device utilizes electron cyclotron resonance (ECR) excited by microwave power in a magnetic field to generate a plasma in an electrodeless (noncontact) manner and without need for an electrically insulating, microwave-transmissive window at the source. Hence, this device offers the same advantages of electrodeless, windowless design - low contamination and long operational life. The device generates a uniform, high-density plasma capable of sustaining uniform ion-current densities at its exit plane while operating at low pressure [<10(exp -4) torr (less than about 1.3 10(exp -2) Pa)] and input power <200 W at a frequency of 2.45 GHz. Though the prototype model operates at 2.45 GHz, operation at higher frequencies can be achieved by straightforward modification to the input microwave waveguide. Higher frequency operation may be desirable in those applications that require even higher background plasma densities. In the design of this ECR plasma source, there are no cumbersome, power-hungry electromagnets. The magnetic field in this device is generated by a permanent-magnet circuit that is optimized to generate resonance surfaces. The microwave power is injected on the centerline of the device. The resulting discharge plasma jumps into a "high mode" when the input power rises above 150 W. This mode is associated with elevated plasma density and high uniformity. The large area and uniformity of the plasma and the low operating pressure are well suited for such material-processing applications as etching and deposition on large silicon wafers. The high exit-plane ion-current density makes it possible to attain a high rate of etching or deposition. The plasma potential is <3 V low enough that there is little likelihood of sputtering, which, in plasma processing, is undesired because it is associated with erosion and contamination. The electron temperature is low and does not vary appreciably with power.

Interaction of high voltage surfaces with the space plasma. [solar arrays

NASA Technical Reports Server (NTRS)

Kaufman, H. R.; Robinson, R. S.

1979-01-01

Tests were conducted using plasma densities of approximately 10 to the 5th power - 10 to the 6th power/cu cm. Insulating materials tested were polyimide (Dapton), mica and glass. Surface-area effects were found to be substantially reduced from those previously reported at lower plasma densities. The difference in typical plasma density was felt to be the major cause of this change, although a saturation effect may also be involved. At the 10 to the 5th power/cu cm plasma density range, surface effects on collection current appear limited to roughly 1 cm from the hole. A factor of several reduction of collected current was obtained with both surface scribing and a 2 x 2 cm conducting mesh. It appears possible that the effects of surface treatment might be more significant at lower plasma densities. Effects of repeated tests were also noted, with current collection decreasing with successive tests. Depending on the materials involved, the effect appeared due to either the smoothing of the inside of the insulator hole or the sputtering of insulator on the exposed conductor. A general conclusion was made from a variety of observations, that the generation of vapor is a major factor in the enhancement of collected current.

Collisionless effects on beam-return current systems in solar flares

NASA Technical Reports Server (NTRS)

Vlahos, L.; Rowland, H. L.

1985-01-01

A theoretical study of the beam-return current system (BRCS) in solar flares shows that the precipitating electrons modify the way in which the return current (RC) is carried by the background plasma. In particular it is found that the RC is not carried by the bulk of the electrons but by a small number of high-velocity electrons. For beam/plasma densities exceeding approximately 0.001, this can reduce the effects of collisions and heating by the RC. For higher-density beams, where the RC could be unstable to current-driven instabilities, the effects of strong turbulence anomalous resistivity prevent the appearance of such instabilities. The main conclusion is that the BRCS is interconnected, and that the beam-generated strong turbulence determines how the RC is carried.

State diagram of magnetostatic coupling phase-locked spin-torque oscillators

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

Zhang, Mengwei; Wang, Longze; Wei, Dan, E-mail: weidan@mail.tsinghua.edu.cn

2015-05-07

The state diagram of magnetostatic coupling phase-locked spin torque oscillator (STO) with perpendicular reference layer and planar field generation layer (FGL) is studied by the macrospin model and the micromagnetic model. The state diagrams of current densities are calculated under various external fields. The simulation shows that there are two phase-lock current density regions. In the phase-locked STOs in low current region I, the spin configuration of FGL is uniform; in high current region II, the spin configuration of FGL is highly nonuniform. In addition, the results with different STOs separation L{sub s} are compared, and the coupling between twomore » STOs is largely decreased when L{sub s} is increased from 40 nm to 60 nm.« less

Current density distributions, field distributions and impedance analysis of segmented deep brain stimulation electrodes

NASA Astrophysics Data System (ADS)

Wei, Xuefeng F.; Grill, Warren M.

2005-12-01

Deep brain stimulation (DBS) electrodes are designed to stimulate specific areas of the brain. The most widely used DBS electrode has a linear array of 4 cylindrical contacts that can be selectively turned on depending on the placement of the electrode and the specific area of the brain to be stimulated. The efficacy of DBS therapy can be improved by localizing the current delivery into specific populations of neurons and by increasing the power efficiency through a suitable choice of electrode geometrical characteristics. We investigated segmented electrode designs created by sectioning each cylindrical contact into multiple rings. Prototypes of these designs, made with different materials and larger dimensions than those of clinical DBS electrodes, were evaluated in vitro and in simulation. A finite element model was developed to study the effects of varying the electrode characteristics on the current density and field distributions in an idealized electrolytic medium and in vitro experiments were conducted to measure the electrode impedance. The current density over the electrode surface increased towards the edges of the electrode, and multiple edges increased the non-uniformity of the current density profile. The edge effects were more pronounced over the end segments than over the central segments. Segmented electrodes generated larger magnitudes of the second spatial difference of the extracellular potentials, and thus required lower stimulation intensities to achieve the same level of neuronal activation as solid electrodes. For a fixed electrode conductive area, increasing the number of segments (edges) decreased the impedance compared to a single solid electrode, because the average current density over the segments increased. Edge effects played a critical role in determining the current density distributions, neuronal excitation patterns, and impedance of cylindrical electrodes, and segmented electrodes provide a means to increase the efficiency of DBS.

Effect of partially ionized impurities and radiation on the effective critical electric field for runaway generation

NASA Astrophysics Data System (ADS)

Hesslow, L.; Embréus, O.; Wilkie, G. J.; Papp, G.; Fülöp, T.

2018-07-01

We derive a formula for the effective critical electric field for runaway generation and decay that accounts for the presence of partially ionized impurities in combination with synchrotron and bremsstrahlung radiation losses. We show that the effective critical field is drastically larger than the classical Connor–Hastie field, and even exceeds the value obtained by replacing the free electron density by the total electron density (including both free and bound electrons). Using a kinetic equation solver with an inductive electric field, we show that the runaway current decay after an impurity injection is expected to be linear in time and proportional to the effective critical electric field in highly inductive tokamak devices. This is relevant for the efficacy of mitigation strategies for runaway electrons since it reduces the required amount of injected impurities to achieve a certain current decay rate.

Ignition and extinction phenomena in helium micro hollow cathode discharges

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

Kulsreshath, M. K.; Schwaederle, L.; Dufour, T.

Micro hollow cathode discharges (MHCD) were produced using 250 μm thick dielectric layer of alumina sandwiched between two nickel electrodes of 8 μm thickness. A through cavity at the center of the chip was formed by laser drilling technique. MHCD with a diameter of few hundreds of micrometers allowed us to generate direct current discharges in helium at up to atmospheric pressure. A slowly varying ramped voltage generator was used to study the ignition and the extinction periods of the microdischarges. The analysis was performed by using electrical characterisation of the V-I behaviour and the measurement of He*({sup 3}S{sub 1}) metastable atomsmore » density by tunable diode laser spectroscopy. At the ignition of the microdischarges, 2 μs long current peak as high as 24 mA was observed, sometimes followed by low amplitude damped oscillations. At helium pressure above 400 Torr, an oscillatory behaviour of the discharge current was observed just before the extinction of the microdischarges. The same type of instability in the extinction period at high pressure also appeared on the density of He*({sup 3}S{sub 1}) metastable atoms, but delayed by a few μs relative to the current oscillations. Metastable atoms thus cannot be at the origin of the generation of the observed instabilities.« less

Skyrmion-based high-frequency signal generator

NASA Astrophysics Data System (ADS)

Luo, Shijiang; Zhang, Yue; Shen, Maokang; Ou-Yang, Jun; Yan, Baiqian; Yang, Xiaofei; Chen, Shi; Zhu, Benpeng; You, Long

2017-03-01

Many concepts for skyrmion-based devices have been proposed, and most of their possible applications are based on the motion of skyrmions driven by a dc current in an area with a constricted geometry. However, skyrmion motion driven by a pulsed current has not been investigated so far. In this work, we propose a skyrmion-based high-frequency signal generator based on the pulsed-current-driven circular motion of skyrmions in a square-shaped film by micromagnetic simulation. The results indicate that skyrmions can move in a closed curve with central symmetry. The trajectory and cycle period can be adjusted by tuning the size of the film, the current density, the Dzyaloshinskii-Moriya interaction constant, and the local in-plane magnetic anisotropy. The period can be tuned from several nanoseconds to tens of nanoseconds, which offers the possibility to prepare high-frequency signal generator based on skyrmions.

Current collection by high voltage anodes in near ionospheric conditions

NASA Technical Reports Server (NTRS)

Antoniades, John A.; Greaves, Rod G.; Boyd, D. A.; Ellis, R.

1990-01-01

The authors experimentally identified three distinct regimes with large differences in current collection in the presence of neutrals and weak magnetic fields. In magnetic field/anode voltage space the three regions are separated by very sharp transition boundaries. The authors performed a series of laboratory experiments to study the dependence of the region boundaries on several parameters, such as the ambient neutral density, plasma density, magnetic field strength, applied anode voltage, voltage pulsewidth, chamber material, chamber size and anode radius. The three observed regimes are: classical magnetic field limited collection; stable medium current toroidal discharge; and large scale, high current space glow discharge. There is as much as several orders of magnitude of difference in the amount of collected current upon any boundary crossing, particularly if one enters the space glow regime. They measured some of the properties of the plasma generated by the breakdown that is present in regimes II and III in the vicinity of the anode including the sheath modified electrostatic potential, I-V characteristics at high voltage as well as the local plasma density.

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

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

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

1996-10-01

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

Efficient Suppression of Defects and Charge Trapping in High Density In-Sn-Zn-O Thin Film Transistor Prepared using Microwave-Assisted Sputter.

PubMed

Goh, Youngin; Ahn, Jaehan; Lee, Jeong Rak; Park, Wan Woo; Ko Park, Sang-Hee; Jeon, Sanghun

2017-10-25

Amorphous oxide semiconductor-based thin film transistors (TFTs) have been considered as excellent switching elements for driving active-matrix organic light-emitting diodes (AMOLED) owing to their high mobility and process compatibility. However, oxide semiconductors have inherent defects, causing fast transient charge trapping and device instability. For the next-generation displays such as flexible, wearable, or transparent displays, an active semiconductor layer with ultrahigh mobility and high reliability at low deposition temperature is required. Therefore, we introduced high density plasma microwave-assisted (MWA) sputtering method as a promising deposition tool for the formation of high density and high-performance oxide semiconductor films. In this paper, we present the effect of the MWA sputtering method on the defects and fast charge trapping in In-Sn-Zn-O (ITZO) TFTs using various AC device characterization methodologies including fast I-V, pulsed I-V, transient current, low frequency noise, and discharge current analysis. Using these methods, we were able to analyze the charge trapping mechanism and intrinsic electrical characteristics, and extract the subgap density of the states of oxide TFTs quantitatively. In comparison to conventional sputtered ITZO, high density plasma MWA-sputtered ITZO exhibits outstanding electrical performance, negligible charge trapping characteristics and low subgap density of states. High-density plasma MWA sputtering method has high deposition rate even at low working pressure and control the ion bombardment energy, resulting in forming low defect generation in ITZO and presenting high performance ITZO TFT. We expect the proposed high density plasma sputtering method to be applicable to a wide range of oxide semiconductor device applications.

Influence of diligent disintegration on anaerobic biomass and performance of microbial fuel cell.

PubMed

Divyalakshmi, Palanisamy; Murugan, Devaraj; Rai, Chockalingam Lajapathi

2017-12-01

To enhance the performance of microbial fuel cells (MFC) by increasing the surface area of cathode and diligent mechanical disintegration of anaerobic biomass. Tannery effluent and anaerobic biomass were used. The increase in surface area of the cathode resulted in 78% COD removal, with the potential, current density, power density and coulombic efficiency of 675 mV, 147 mA m -2 , 33 mW m -2 and 3.5%, respectively. The work coupled with increased surface area of the cathode with diligent mechanical disintegration of the biomass, led to a further increase in COD removal of 82% with the potential, current density, power density and coulombic efficiency of 748 mV, 229 mA m -2 , 78 mW m -2 and 6% respectively. Mechanical disintegration of the biomass along with increased surface area of cathode enhances power generation in vertical MFC reactors using tannery effluent as fuel.

Magnetron sputtering system for coatings deposition with activation of working gas mixture by low-energy high-current electron beam

NASA Astrophysics Data System (ADS)

Gavrilov, N. V.; Kamenetskikh, A. S.; Men'shakov, A. I.; Bureyev, O. A.

2015-11-01

For the purposes of efficient decomposition and ionization of the gaseous mixtures in a system for coatings deposition using reactive magnetron sputtering, a low-energy (100-200 eV) high-current electron beam is generated by a grid-stabilized plasma electron source. The electron source utilizes both continuous (up to 20 A) and pulse-periodic mode of discharge with a self-heated hollow cathode (10-100 A; 0.2 ms; 10-1000 Hz). The conditions for initiation and stable burning of the high-current pulse discharge are studied along with the stable generation of a low-energy electron beam within the gas pressure range of 0.01 - 1 Pa. It is shown that the use of the electron beam with controllable parameters results in reduction of the threshold values both for the pressure of gaseous mixture and for the fluxes of molecular gases. Using such a beam also provides a wide range (0.1-10) of the flux density ratios of ions and sputtered atoms over the coating surface, enables an increase in the maximum pulse density of ion current from plasma up to 0.1 A, ensures an excellent adhesion, optimizes the coating structure, and imparts improved properties to the superhard nanocomposite coatings of (Ti,Al)N/a-Si3N4 and TiC/-a-C:H. Mass-spectrometric measurements of the beam-generated plasma composition proved to demonstrate a twofold increase in the average concentration of N+ ions in the Ar-N2 plasma generated by the high-current (100 A) pulsed electron beam, as compared to the dc electron beam.

Aging characteristics of blue InGaN micro-light emitting diodes at an extremely high current density of 3.5 kA cm-2

NASA Astrophysics Data System (ADS)

Tian, Pengfei; Althumali, Ahmad; Gu, Erdan; Watson, Ian M.; Dawson, Martin D.; Liu, Ran

2016-04-01

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.

Treatment of solutions containing nonylphenol ethoxylate by photoelectrooxidation.

PubMed

da Silva, Salatiel Wohlmuth; Bordignon, Gustavo Lanferdini; Viegas, Cheila; Rodrigues, Marco Antônio Siqueira; Arenzon, Alexandre; Bernardes, Andréa Moura

2015-01-01

In this work the photoelectrooxidation (PEO) was applied in the treatment of a solution containing nonylphenol ethoxylate surfactant (NP4EO). The use of different lamps (125 and 250 W), current density (5 and 10 mA cm(-2)) and treatment time (0, 60, 120, 180 and 240 min) were investigated. The samples were characterized by UV/Vis, total organic carbon (TOC), gas chromatography associated to mass spectroscopy (GC/MS) and ecotoxicity. The reaction kinetics were calculated and the light flux and pH were measured. The results of analysis by UV/Vis show that there is degradation of nonylphenol ethoxylated in the treatment time of 240 min for all configurations, and the configurations that used a 250 W lamp and a current density of 10 mA cm(-2) obtained better results, with a reduction of 83% in TOC, indicating a high mineralization of the surfactant. It was further found in the GC/MS that the configurations that used the 125 W lamp promoted a smaller incident light flux on the solution, and, regardless of the applied current density, it was generated the reaction intermediate nonylphenol, more toxic than the parent compound. The opposite can be observed when a 250 W lamp was used, which produced a higher incident light flux. Based on the degradation products detected, a simplified mechanism for degradation of nonylphenol ethoxylate was proposed. Although a treatment time of 240 min with photoelectrooxidation with different configurations was not effective in the complete mineralization of the compound, a promising process was developed with the treatment using a lamp of 250 W and a current density of 10 mA cm(-2), which generated a solution with less toxicity than the original one. Copyright © 2014 Elsevier Ltd. All rights reserved.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes.

PubMed

Kumar, Niraj; Pal, Dharmendra Kumar; Jadon, Arvind Singh; Pal, Udit Narayan; Rahaman, Hasibur; Prakash, Ram

2016-03-01

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes

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

Kumar, Niraj; Pal, Udit Narayan; Prakash, Ram

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electronmore » beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.« less

Power Generation from a Radiative Thermal Source Using a Large-Area Infrared Rectenna

NASA Astrophysics Data System (ADS)

Shank, Joshua; Kadlec, Emil A.; Jarecki, Robert L.; Starbuck, Andrew; Howell, Stephen; Peters, David W.; Davids, Paul S.

2018-05-01

Electrical power generation from a moderate-temperature thermal source by means of direct conversion of infrared radiation is important and highly desirable for energy harvesting from waste heat and micropower applications. Here, we demonstrate direct rectified power generation from an unbiased large-area nanoantenna-coupled tunnel diode rectifier called a rectenna. Using a vacuum radiometric measurement technique with irradiation from a temperature-stabilized thermal source, a generated power density of 8 nW /cm2 is observed at a source temperature of 450 °C for the unbiased rectenna across an optimized load resistance. The optimized load resistance for the peak power generation for each temperature coincides with the tunnel diode resistance at zero bias and corresponds to the impedance matching condition for a rectifying antenna. Current-voltage measurements of a thermally illuminated large-area rectenna show current zero crossing shifts into the second quadrant indicating rectification. Photon-assisted tunneling in the unbiased rectenna is modeled as the mechanism for the large short-circuit photocurrents observed where the photon energy serves as an effective bias across the tunnel junction. The measured current and voltage across the load resistor as a function of the thermal source temperature represents direct current electrical power generation.

Spinstand demonstration of areal density enhancement using two-dimensional magnetic recording (invited)

NASA Astrophysics Data System (ADS)

Lippman, Thomas; Brockie, Richard; Coker, Jon; Contreras, John; Galbraith, Rick; Garzon, Samir; Hanson, Weldon; Leong, Tom; Marley, Arley; Wood, Roger; Zakai, Rehan; Zolla, Howard; Duquette, Paul; Petrizzi, Joe

2015-05-01

Exponential growth of the areal density has driven the magnetic recording industry for almost sixty years. But now areal density growth is slowing down, suggesting that current technologies are reaching their fundamental limit. The next generation of recording technologies, namely, energy-assisted writing and bit-patterned media, remains just over the horizon. Two-Dimensional Magnetic Recording (TDMR) is a promising new approach, enabling continued areal density growth with only modest changes to the heads and recording electronics. We demonstrate a first generation implementation of TDMR by using a dual-element read sensor to improve the recovery of data encoded by a conventional low-density parity-check (LDPC) channel. The signals are combined with a 2D equalizer into a single modified waveform that is decoded by a standard LDPC channel. Our detection hardware can perform simultaneous measurement of the pre- and post-combined error rate information, allowing one set of measurements to assess the absolute areal density capability of the TDMR system as well as the gain over a conventional shingled magnetic recording system with identical components. We discuss areal density measurements using this hardware and demonstrate gains exceeding five percent based on experimental dual reader components.

Propagation of a turbidity current in confined geometries

NASA Astrophysics Data System (ADS)

Silvestre, Nuno; Salgueiro, Dora; Franca, Mário J.; Ferreira, Rui M. L.

2017-04-01

Sedimentation in reservoirs due to turbidity currents originates problems of loss of storage capacity as well as clogging of outlets/intakes. These currents are driven by the difference in specific weight between the current itself and the surrounding fluid, due to the presence of particles in suspension. As a gravity current, the main properties of these phenomena has been investigated by several authors since the 1970´s. Despite driven by a simple mechanism, the propagation of these currents can become more complex owing to the influence of factors such as geometry, bed roughness and other non-uniform elements. However, the majority of conducted studies has been focused in characterising only the influence of density imbalance. The propagation of a density current in confined geometries and the influence of bed roughness is herein investigated, through laboratory experiments carried out at the Laboratory of Hydraulics and Environment of Instituto Superior Técnico, Lisbon. The density currents were generated with brine to allow for visualization and velocity measurement. The laboratory experiments comprised point and continuous release of a dense NaCl mixture with a tracer (Rhodamine WT), with a density equal to 1028 g/L, into a tank with resting freshwater (1000 g/L). The transport and the mixing processes were recorded with high-speed video. The mass distribution was obtained through a photometric methodology and the Particle Image Velocimetry (PIV) technique was used to measure the instantaneous flow velocity fields and the depth of the density current. Both methodologies were used to measure different plan views of the phenomena, including profile and top views, for different regions, near-field and far-field. Different bed roughness were studied, including smooth and rough bed. The facility was designed with the objective to generate a complex 2D flow with an advancing wave front but also shocks reflected from the walls. As the image analysis technique provided high-resolution images, the front velocity in the far field was tracked with an algorithm that captured its geometry with great accuracy (including, for instance, the lobe and cleft formation). The temporal analysis of the velocity signal revealed great "oscillations" that are beyond the scale/influence of the irregularity of lobes and clefts. This sloshing effect is assessed and discussed. The results obtained provide data with high spatial and temporal resolution that can lead to a better understanding of the mechanisms involved in such flows. Thus, these results can be used for a proper modelling and the development of mitigation measures against the adverse effects of density currents. This research was partially supported by Portuguese and European funds, within programs COMPETE2020 and PORL-FEDER, through project PTDC/ECM-HID/6387/2014 granted by the National Foundation for Science and Technology (FCT).

Current induced domain wall motion and tilting in Pt/Co/Ta structures with perpendicular magnetic anisotropy in the presence of the Dyzaloshinskii–Moriya interaction

NASA Astrophysics Data System (ADS)

Yun, Jijun; Li, Dong; Cui, Baoshan; Guo, Xiaobin; Wu, Kai; Zhang, Xu; Wang, Yupei; Mao, Jian; Zuo, Yalu; Xi, Li

2018-04-01

Current induced domain wall motion (CIDWM) was studied in Pt/Co/Ta structures with perpendicular magnetic anisotropy and the Dyzaloshinskii–Moriya interaction (DMI) by the spin-orbit torque (SOT). We measured the strength of DMI and SOT efficiency in Pt/Co/Ta with the variation of the thickness of Ta using a current induced hysteresis loop shift method. The results indicate that the DMI stabilizes a chiral Néel-type domain wall (DW), and the DW motion can be driven by the enhanced large SOT generated from Pt and Ta with opposite signs of spin Hall angle in Pt/Co/Ta stacks. The CIDWM velocity, which is 104 times larger than the field driven DW velocity, obeys a creep law, and reaches around tens of meters per second with current density of ~106 A cm‑2. We also found that the Joule heating accompanied with current also accelerates the DW motion. Meanwhile, a domain wall tilting was observed, which increases with current density increasing. These results can be explained by the spin Hall effect generated from both heavy metals Pt and Ta, inherent DMI, and the current accompanying Joule heating effect. Our results could provide some new designing prospects to move multiple DWs by SOT for achieving racetrack memories.

Alfven resonance mode conversion in the Phaedrus-T current drive experiments: Modelling and density fluctuations measurements

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

Vukovic, M.; Harper, M.; Breun, R.

1995-12-31

Current drive experiments on the Phaedrus-T tokamak performed with a low field side two-strap fast wave antenna at frequencies below {omega}{sub cH} show loop volt drops of up to 30% with strap phasing (0, {pi}/2). RF induced density fluctuations in the plasma core have also been observed with a microwave reflectometer. It is believed that they are caused by kinetic Alfven waves generated by mode conversion of fast waves at the Alfven resonance. Correlation of the observed density fluctuations with the magnitude of the {Delta}V{sub loop} suggest that the {Delta}V{sub loop} is attributable to current drive/heating due to mode convertedmore » kinetic Alfven waves. The toroidal cold plasma wave code LION is used to model the Alfven resonance mode conversion surfaces in the experiments while the cylindrical hot plasma kinetic wave code ISMENE is used to model the behavior of kinetic Alfven waves at the Alfven resonance location. Initial results obtained from limited density, magnetic field, antenna phase, and impurity scans show good agreement between the RF induced density fluctuations and the predicted behavior of the kinetic Alfven waves. Detailed comparisons between the density fluctuations and the code predictions are presented.« less

Oxygen suppresses light-driven anodic current generation by a mixed phototrophic culture.

PubMed

Darus, Libertus; Ledezma, Pablo; Keller, Jürg; Freguia, Stefano

2014-12-02

This paper describes the detrimental effect of photosynthetically evolved oxygen on anodic current generation in the presence of riboflavin upon illumination of a mixed phototrophic culture enriched from a freshwater pond at +0.6 V vs standard hydrogen electrode. In the presence of riboflavin, the phototrophic biomass in the anodic compartment produced an electrical current in response to light/dark cycles (12 h/12 h) over 12 months of operation, generating a maximum current density of 17.5 mA x m(-2) during the dark phase, whereas a much lower current of approximately 2 mA x m(-2) was generated during illumination. We found that the low current generation under light exposure was caused by high rates of reoxidation of reduced riboflavin by oxygen produced during photosynthesis. Quantification of biomass by fluorescence in situ hybridization images suggested that green algae were predominant in both the anode-based biofilm (55.1%) and the anolyte suspension (87.9%) with the remaining biovolume accounted for by bacteria. Genus-level sequencing analysis revealed that bacteria were dominated by cyanobacterium Leptolyngbia (∼35%), while the prevailing algae were Dictyosphaerium, Coelastrum, and Auxenochlorella. This study offers a key comprehension of mediator sensitivity to reoxidation by dissolved oxygen for improvement of microbial solar cell performance.

Generation and detection of pure valley current by electrically induced Berry curvature in bilayer graphene

NASA Astrophysics Data System (ADS)

Shimazaki, Y.; Yamamoto, M.; Borzenets, I. V.; Watanabe, K.; Taniguchi, T.; Tarucha, S.

2015-12-01

The field of `Valleytronics’ has recently been attracting growing interest as a promising concept for the next generation electronics, because non-dissipative pure valley currents with no accompanying net charge flow can be manipulated for computational use, akin to pure spin currents. Valley is a quantum number defined in an electronic system whose energy bands contain energetically degenerate but non-equivalent local minima (conduction band) or maxima (valence band) due to a certain crystal structure. Specifically, spatial inversion symmetry broken two-dimensional honeycomb lattice systems exhibiting Berry curvature is a subset of possible systems that enable optical, magnetic and electrical control of the valley degree of freedom. Here we use dual-gated bilayer graphene to electrically induce and control broken inversion symmetry (or Berry curvature) as well as the carrier density for generating and detecting the pure valley current. In the insulating regime, at zero-magnetic field, we observe a large nonlocal resistance that scales cubically with the local resistivity, which is evidence of pure valley current.

An exact analysis of a rectangular plate piezoelectric generator.

PubMed

Yang, Jiashi; Chen, Ziguang; Hu, Yuantai

2007-01-01

We study thickness-twist vibration of a finite, piezoelectric plate of polarized ceramics or 6-mm crystals driven by surface mechanical loads. An exact solution from the three-dimensional equations of piezoelectricity is obtained. The plate is properly electroded and connected to a circuit such that an electric output is generated. The structure analyzed represents a piezoelectric generator for converting mechanical energy to electrical energy. Analytical expressions for the output voltage, current, power, efficiency, and power density are given. The basic behaviors of the generator are shown by numerical results.

Improving the aluminum-air battery system for use in electrical vehicles

NASA Astrophysics Data System (ADS)

Yang, Shaohua

The objectives of this study include improvement of the efficiency of the aluminum/air battery system and demonstration of its ability for vehicle applications. The aluminum/air battery system can generate enough energy and power for driving ranges and acceleration similar to that of gasoline powered cars. Therefore has the potential to be a power source for electrical vehicles. Aluminum/air battery vehicle life cycle analysis was conducted and compared to that of lead/acid and nickel-metal hydride vehicles. Only the aluminum/air vehicles can be projected to have a travel range comparable to that of internal combustion engine vehicles (ICE). From this analysis, an aluminum/air vehicle is a promising candidate compared to ICE vehicles in terms of travel range, purchase price, fuel cost, and life cycle cost. We have chosen two grades of Al alloys (Al alloy 1350, 99.5% and Al alloy 1199, 99.99%) in our study. Only Al 1199 was studied extensively using Na 2SnO3 as an electrolyte additive. We then varied concentration and temperature, and determined the effects on the parasitic (corrosion) current density and open circuit potential. We also determined cell performance and selectivity curves. To optimize the performance of the cell based on our experiments, the recommended operating conditions are: 3--4 N NaOH, about 55°C, and a current density of 150--300 mA/cm2. We have modeled the cell performance using the equations we developed. The model prediction of cell performance shows good agreement with experimental data. For better cell performance, our model studies suggest use of higher electrolyte flow rate, smaller cell gap, higher conductivity and lower parasitic current density. We have analyzed the secondary current density distributions in a two plane, parallel Al/air cell and a wedge-type Al/air cell. The activity of the cathode has a large effect on the local current density. With increases in the cell gap, the local current density increases, but the increase is not as significant as the increase in the current density away from the entrance. By extending the cathode below the anode, the high local current density can be reduced.

Exfoliated YBCO filaments for second-generation superconducting cable

NASA Astrophysics Data System (ADS)

Solovyov, Vyacheslav; Farrell, Paul

2017-01-01

The second-generation high temperature superconductor (2G HTS) wire is the most promising conductor for high-field magnets such as accelerator dipoles and compact fusion devices. The key element of the wire is a thin Y1Ba2Cu3O7 (YBCO) layer deposited on a flexible metal substrate. The substrate, which becomes incorporated in the 2G conductor, reduces the electrical and mechanical performance of the wire. This is a process that exfoliates the YBCO layer from the substrate while retaining the critical current density of the superconductor. Ten-centimeter long coupons of exfoliated YBCO layers were manufactured, and detailed structural, electrical, and mechanical characterization were reported. After exfoliation, the YBCO layer was supported by a 75 μm thick stainless steel foil, which makes for a compact, mechanically stronger, and inexpensive conductor. The critical current density of the filaments was measured at both 77 K and 4.2 K. The exfoliated YBCO retained 90% of the original critical current. Similarly, tests in an external magnetic field at 4.2 K confirmed that the pinning strength of the YBCO layer was also retained following exfoliation.

Electrochemical current noise on aluminum microelectrodes

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

Isaac, J.W.; Hebert, K.R.

1999-02-01

Aluminum disk microelectrodes were used to investigate electrochemical current noise in pH 8.8 borate buffer. The current noise spectra, expressed in terms of the current spectral density, had a characteristic two-plateau structure in the experimental bandwidth of 0.05--50 Hz, were potential-independent, and increased proportionally to electrode area. Injection of NaCl solution near the electrode surface, at potentials below that of the onset of pitting corrosion, caused 0.1--1 Hz current fluctuations to appear. From the frequency and area dependence of the current spectral density in the chloride-free solution, it was concluded that the noise arose from a number of discrete, approximatelymore » evenly distributed voltage noise sources positioned electrically in series with the inner barrier layer of the oxide film. A mathematical model for the current noise was developed which described a physical mechanism for noise production based on fluctuations in the widths of cracks or pores in the outer part of the surface film. The model was consistent with the observed area and frequency dependence of the current spectral density, suggesting that the physical process it described is a possible mechanism of noise generation. It could not be determined whether the noise sources were isolated defects or flaws, or pores in an outer precipitated portion of the oxide film.« less

Process Research of Polycrystalline Silicon Material (PROPSM)

NASA Technical Reports Server (NTRS)

Culik, J. S.

1984-01-01

An investigation was begun into the usefulness of molecular hydrogen annealing on polycrystalline solar cells. No improvement was realized even after twenty hours of hydrogenation. Thus, samples were chosen on the basis of: (1) low open circuit voltage; (2) low shunt conductance; and (3) high light generated current. These cells were hydrogenated in molecular hydrogen at 300 C. The differences between the before and after hydrogenation values are so slight as to be negligible. These cells have light generated current densities that indicate long minority carrier diffusion lengths. The open circuit voltage appears to be degraded, and quasi-neutral recombination current enhanced. Therefore, molecular hydrogen is not usful for passivating electrically active defects.

Strong second harmonic generation in two-dimensional ferroelectric IV-monochalcogenides

NASA Astrophysics Data System (ADS)

Panday, Suman Raj; Fregoso, Benjamin M.

2017-11-01

The two-dimensional ferroelectrics GeS, GeSe, SnS and SnSe are expected to have large spontaneous in-plane electric polarization and enhanced shift-current response. Using density functional methods, we show that these materials also exhibit the largest effective second harmonic generation reported so far. It can reach magnitudes up to 10~nm~V-1 which is about an order of magnitude larger than that of prototypical GaAs. To rationalize this result we model the optical response with a simple one-dimensional two-band model along the spontaneous polarization direction. Within this model the second-harmonic generation tensor is proportional to the shift-current response tensor. The large shift current and second harmonic responses of GeS, GeSe, SnS and SnSe make them promising non-linear materials for optoelectronic applications.

Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

DOE PAGES

Gao, Lan; Ji, Hantao; Fiksel, Gennady; ...

2016-04-15

Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ~ 1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ~ 3 x 10 16 W/cm 2. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ~ 40-50 T magnetic fields at the center of the coil ~ 3-4 ns after laser irradiation. In conclusion, themore » experiments provide significant insight for future target designs that aim to develop a powerful source of external magnetic fields for various applications in high-energy-density science.« less

Advances on Sensitive Electron-injection based Cameras for Low-Flux, Short-Wave-Infrared Applications

NASA Astrophysics Data System (ADS)

Fathipour, Vala; Bonakdar, Alireza; Mohseni, Hooman

2016-08-01

Short-wave infrared (SWIR) photon detection has become an essential technology in the modern world. Sensitive SWIR detector arrays with high pixel density, low noise levels and high signal-to-noise-ratios are highly desirable for a variety of applications including biophotonics, light detection and ranging, optical tomography, and astronomical imaging. As such many efforts in infrared detector research are directed towards improving the performance of the photon detectors operating in this wavelength range. We review the history, principle of operation, present status and possible future developments of a sensitive SWIR detector technology, which has demonstrated to be one of the most promising paths to high pixel density focal plane arrays for low flux applications. The so-called electron-injection (EI) detector was demonstrated for the first time (in 2007). It offers an overall system-level sensitivity enhancement compared to the p-i-n diode due to a stable internal avalanche-free gain. The amplification method is inherently low noise, and devices exhibit an excess noise of unity. The detector operates in linear-mode and requires only bias voltage of a few volts. The stable detector characteristics, makes formation of high yield large-format, and high pixel density focal plane arrays less challenging compared to other detector technologies such as avalanche photodetectors. Detector is based on the mature InP material system (InP/InAlAs/GaAsSb/InGaAs), and has a cutoff wavelength of 1700 nm. It takes advantage of a unique three-dimensional geometry and combines the efficiency of a large absorbing volume with the sensitivity of a low-dimensional switch (injector) to sense and amplify signals. Current devices provide high-speed response ~ 5 ns rise time, and low jitter ~ 12 ps at room temperature. The internal dark current density is ~ 1 μA/cm2 at room temperature decreasing to 0.1 nA/cm2 at 160 K. EI detectors have been designed, fabricated, and tested during two generations of development and optimization cycles. We review our imager results using the first-generation detectors. In the second-generation devices, the dark current is reduced by two orders of magnitude, and bandwidth is improved by 4 orders of magnitude. The dark current density of the EI detector is shown to outperform the state-of-the-art technology, the

Design Study: Rocket Based MHD Generator

NASA Technical Reports Server (NTRS)

1997-01-01

This report addresses the technical feasibility and design of a rocket based MHD generator using a sub-scale LOx/RP rocket motor. The design study was constrained by assuming the generator must function within the performance and structural limits of an existing magnet and by assuming realistic limits on (1) the axial electric field, (2) the Hall parameter, (3) current density, and (4) heat flux (given the criteria of heat sink operation). The major results of the work are summarized as follows: (1) A Faraday type of generator with rectangular cross section is designed to operate with a combustor pressure of 300 psi. Based on a magnetic field strength of 1.5 Tesla, the electrical power output from this generator is estimated to be 54.2 KW with potassium seed (weight fraction 3.74%) and 92 KW with cesium seed (weight fraction 9.66%). The former corresponds to a enthalpy extraction ratio of 2.36% while that for the latter is 4.16%; (2) A conceptual design of the Faraday MHD channel is proposed, based on a maximum operating time of 10 to 15 seconds. This concept utilizes a phenolic back wall for inserting the electrodes and inter-electrode insulators. Copper electrode and aluminum oxide insulator are suggested for this channel; and (3) A testing configuration for the sub-scale rocket based MHD system is proposed. An estimate of performance of an ideal rocket based MHD accelerator is performed. With a current density constraint of 5 Amps/cm(exp 2) and a conductivity of 30 Siemens/m, the push power density can be 250, 431, and 750 MW/m(sup 3) when the induced voltage uB have values of 5, 10, and 15 KV/m, respectively.

PEDOT as a Flexible Organic Electrode for a Thin Film Acoustic Energy Harvester.

PubMed

Kim, Younghoon; Na, Jongbeom; Park, Chihyun; Shin, Haijin; Kim, Eunkyoung

2015-08-05

An efficient thin film acoustic energy harvester was explored using flexible poly(3,4-ethylene dioxythiophene) (PEDOT) films as electrodes in an all-organic triboelectric generator (AO-TEG). A thin film AO-TEG structured as PEDOT/Kapton//PET/PEDOT was prepared by the solution casting polymerization(SCP) on the dielectric polymer films. As-prepared AO-TEG showed high flexibility and durability due to the strong adhesion between the electrodes and the dielectric polymer. The short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum power density (Pw) reached 50 mA/m(2), 700 V, and 12.9 W/m(2) respectively. The output current density decreased with the increase in the electrode resistance (Re), but the energy loss in the organic electrodes was negligible. The AO-TEG could light up 180 LEDs instantaneously upon touching of the AO-TEG with a palm (∼120 N). With the flexible structure, the AO-TEG was worn as clothes and generated electricity to light LEDs upon regular human movement. Furthermore, the AO-TEG was applicable as a thin film acoustic energy harvester, which used music to generate electricity enough for powering of 5 LEDs. An AO-TEG with a PEDOT electrode (Re = 200 Ω) showed instantaneous peak-to-peak voltage generation of 11 V under a sound pressure level (SPL) of 90-100 dB. The harvested acoustic energy through the AO-TEG was 350 μJ from the 4 min playing of the same single song. This is the first demonstration of a flexible triboelectric generator (TEG) using an organic electrode for harvesting acoustic energy from ambient environment.

Effect of reabsorbed recombination radiation on the saturation current of direct gap p-n junctions

NASA Technical Reports Server (NTRS)

Von Roos, O.; Mavromatis, H.

1984-01-01

The application of the radiative transfer theory for semiconductors to p-n homojunctions subject to low level injection conditions is discussed. By virtue of the interaction of the radiation field with free carriers across the depletion layer, the saturation current density in Shockley's expression for the diode current is reduced at high doping levels. The reduction, due to self-induced photon generation, is noticeable for n-type material owing to the small electron effective mass in direct band-gap III-V compounds. The effect is insignificant in p-type material. At an equilibrium electron concentration of 2 x 10 to the 18th/cu cm in GaAs, a reduction of the saturation current density by 15 percent is predicted. It is concluded that realistic GaAs p-n junctions possess a finite thickness.

Predictions for the drive capabilities of the RancheroS Flux Compression Generator into various load inductances using the Eulerian AMR Code Roxane

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

Watt, Robert Gregory

The Ranchero Magnetic Flux Compression Generator (FCG) has been used to create current pulses in the 10-­100 MA range for driving both “static” low inductance (0.5 nH) loads1 for generator demonstration purposes and high inductance (10-­20 nH) imploding liner loads2 for ultimate use in physics experiments at very high energy density. Simulations of the standard Ranchero generator have recently shown that it had a design issue that could lead to flux trapping in the generator, and a non-­ robust predictability in its use in high energy density experiments. A re-­examination of the design concept for the standard Ranchero generator, promptedmore » by the possible appearance of an aneurism at the output glide plane, has led to a new generation of Ranchero generators designated the RancheroS (for swooped). This generator has removed the problematic output glide plane and replaced it with a region of constantly increasing diameter in the output end of the FCG cavity in which the armature is driven outward under the influence of an additional HE load not present in the original Ranchero. The resultant RancheroS generator, to be tested in LA43S-­L13, probably in early FY17, has a significantly increased initial inductance and may be able to drive a somewhat higher load inductance than the standard Ranchero. This report will use the Eulerian AMR code Roxane to study the ability of the new design to drive static loads, with a goal of providing a database corresponding to the load inductances for which the generator might be used and the anticipated peak currents such loads might produce in physics experiments. Such a database, combined with a simple analytic model of an ideal generator, where d(LI)/dt = 0, and supplemented by earlier estimates of losses in actual use of the standard Ranchero, scaled to estimate the increase in losses due to the longer current carrying perimeter in the RancheroS, can then be used to bound the expectations for the current drive one may apply to any load assembly in future experiments.« less

Study of the Generation of Intense Pulsed Electron Beams Using Glow Discharges

DTIC Science & Technology

1988-02-01

de Investigaciones Opticas, Rep. Argentina. (2) On leave from PROFET (UNCPBA) Programa de Fisica Experimental Tandil, Rep. Argentina. (3) Edwards... de Investigaciones Opticas, (CIC-BA) Rep. Argentina. Section III-D. Measurements of the plasma density andB. T. Szapiro is on leave from Programa de ...discussed. The radial profiles Szapiro was supported by a fellowship from the Universidad Nacional de show the presence of a high-current-density

Diffusion of Conserved Charges in Relativistic Heavy Ion Collisions

NASA Astrophysics Data System (ADS)

Greif, Moritz; Fotakis, Jan. A.; Denicol, Gabriel S.; Greiner, Carsten

2018-06-01

We demonstrate that the diffusion currents do not depend only on gradients of their corresponding charge density, but that the different diffusion charge currents are coupled. This happens in such a way that it is possible for density gradients of a given charge to generate dissipative currents of another charge. Within this scheme, the charge diffusion coefficient is best viewed as a matrix, in which the diagonal terms correspond to the usual charge diffusion coefficients, while the off-diagonal terms describe the coupling between the different currents. In this Letter, we calculate for the first time the complete diffusion matrix for hot and dense nuclear matter, including baryon, electric, and strangeness charges. We find that the baryon diffusion current is strongly affected by baryon charge gradients but also by its coupling to gradients in strangeness. The electric charge diffusion current is found to be strongly affected by electric and strangeness gradients, whereas strangeness currents depend mostly on strange and baryon gradients.

Direct detection of spin Nernst effect in platinum

NASA Astrophysics Data System (ADS)

Bose, A.; Bhuktare, S.; Singh, H.; Dutta, S.; Achanta, V. G.; Tulapurkar, A. A.

2018-04-01

Generation of spin current lies at the heart of spintronic research. The spin Hall effect and the spin Seebeck effect have drawn considerable attention in the last few years to create pure spin current by heavy metals and ferromagnets, respectively. In this work, we show the direct evidence of heat current to spin current conversion in non-magnetic Platinum by the spin Nernst effect (SNE) at room temperature. This is the thermal analogue of the spin Hall effect in non-magnets. We have shown that the 8 K/μm thermal gradient in Pt can lead to the generation of pure spin current density of the order of 108 A/m2 by virtue of SNE. This opens up an additional possibility to couple the relativistic spin-orbit interaction with the thermal gradient for spintronic applications.

Effect of high current density to defect generation of blue LED and its characterization with transmission electron microscope

NASA Astrophysics Data System (ADS)

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.

Effect of surface bilayer charges on the magnetic field around ionic channels

NASA Astrophysics Data System (ADS)

Gomes Soares, Marília Amável; Cortez, Celia Martins; Oliveira Cruz, Frederico Alan de; Silva, Dilson

2017-01-01

In this work, we present a physic-mathematical model for representing the ion transport through membrane channels, in special Na+ and K+-channels, and discuss the influence of surface bilayer charges on the magnetic field behavior around the ionic current. The model was composed of a set of equations, including: a nonlinear differential Poisson-Boltzmann equation which usually allows to estimate the surface potentials and electric potential profile across membrane; equations for the ionic flux through channel and the ionic current density based on Armstrong's model for Na+ and K+ permeability and other Physics concepts; and a magnetic field expression derived from the classical Ampère equation. Results from computational simulations using the finite element method suggest that the ionic permeability is strongly dependent of surface bilayer charges, the current density through a K+-channel is very less sensible to temperature changes than the current density through a Na+- channel, active Na+-channels do not directly interfere with the K+-channels around, and vice-versa, since the magnetic perturbation generated by an active channel is of short-range.

Rarefied flow diagnostics using pulsed high-current electron beams

NASA Technical Reports Server (NTRS)

Wojcik, Radoslaw M.; Schilling, John H.; Erwin, Daniel A.

1990-01-01

The use of high-current short-pulse electron beams in low-density gas flow diagnostics is introduced. Efficient beam propagation is demonstrated for pressure up to 300 microns. The beams, generated by low-pressure pseudospark discharges in helium, provide extremely high fluorescence levels, allowing time-resolved visualization in high-background environments. The fluorescence signal frequency is species-dependent, allowing instantaneous visualization of mixing flowfields.

Bipolar membrane electrodialysis for generation of hydrochloric acid and ammonia from simulated ammonium chloride wastewater.

PubMed

Li, Ya; Shi, Shaoyuan; Cao, Hongbin; Wu, Xinmin; Zhao, Zhijuan; Wang, Liying

2016-02-01

Simulated ammonium chloride wastewater was treated by a lab-scale bipolar membrane electrodialysis for the generation of HCl and NH3·H2O and desalination. The influence of initial concentration of NH4Cl, current density, salt solution volume, initial concentration of acid and base and membrane stack structure on the yields of HCl and NH3·H2O was investigated. The current efficiency and energy consumption were also examined under different conditions. The results showed that, at the current density of 48 mA/cm(2), the highest concentration of HCl and NH3·H2O with initial concentration of 110 g/L NH4Cl was 57.67 g/L and 45.85 g/L, respectively. Higher initial concentration of NH4Cl was favor to reduce unit energy consumption and increase current efficiency of the BMED system. The membrane stack voltage of BMED increased quickly under constant current when the concentration of NH4Cl contained in the solution of salt compartment was depleted below the "inflection point concentration" about 8000 mg/L. It means that the concentration of NH4Cl below 8000 mg/L was no longer suitable for BMED because of higher energy consumption. The HCl and NH3·H2O concentration increased more quickly following the increase of current density. When increasing the volume of NH4Cl, the concentration of HCl and NH3·H2O also increased. The high initial concentration of acid and base could improve the final concentration of them, while the growth rate was decreased. Compared with the BMED system with three compartments, the growth rate of HCl concentration with the two compartments was higher and its unit energy consumption was lower. It meant that the performance of the BMED system could be improved by optimizing operation conditions. The application feasibility of the generation of HCl and NH3·H2O and desalination of ammonium chloride wastewater by BMED was proved. Copyright © 2015 Elsevier Ltd. All rights reserved.

Characteristics of a RF-Driven Ion Source for a Neutron Generator Used for Associated Particle Imaging

NASA Astrophysics Data System (ADS)

Wu, Ying; Hurley, John P.; Ji, Qing; Kwan, Joe; Leung, Ka-Ngo

2009-03-01

We present recent work on a prototype compact neutron generator for associated particle imaging (API). API uses alpha particles that are produced simultaneously with neutrons in the deuterium-tritium (2D(3T,n)4α) fusion reaction to determine the direction of the neutrons upon exiting the reaction. This method determines the spatial position of each neutron interaction and requires the neutrons to be generated from a small spot in order to achieve high spatial resolution. The ion source for API is designed to produce a focused ion beam with a beam spot diameter of 1-mm or less on the target. We use an axial type neutron generator with a predicted neutron yield of 108 n/s for a 50 μA D/T ion beam current accelerated to 80 kV. The generator utilizes an RF planar spiral antenna at 13.56 MHz to create a highly efficient inductively coupled plasma at the ion source. Experimental results show that beams with an atomic ion fraction of over 80% can be obtained while utilizing only 100 watts of RF power in the ion source. A single acceleration gap with a secondary electron suppression electrode is used in the tube. Experimental results from ion source testing, such as the current density, atomic ion fraction, electron temperature, and electron density will be discussed.

High Energy Density Physics and Exotic Acceleration Schemes

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

Cowan, T.; /General Atomics, San Diego; Colby, E.

2005-09-27

The High Energy Density and Exotic Acceleration working group took as our goal to reach beyond the community of plasma accelerator research with its applications to high energy physics, to promote exchange with other disciplines which are challenged by related and demanding beam physics issues. The scope of the group was to cover particle acceleration and beam transport that, unlike other groups at AAC, are not mediated by plasmas or by electromagnetic structures. At this Workshop, we saw an impressive advancement from years past in the area of Vacuum Acceleration, for example with the LEAP experiment at Stanford. And wemore » saw an influx of exciting new beam physics topics involving particle propagation inside of solid-density plasmas or at extremely high charge density, particularly in the areas of laser acceleration of ions, and extreme beams for fusion energy research, including Heavy-ion Inertial Fusion beam physics. One example of the importance and extreme nature of beam physics in HED research is the requirement in the Fast Ignitor scheme of inertial fusion to heat a compressed DT fusion pellet to keV temperatures by injection of laser-driven electron or ion beams of giga-Amp current. Even in modest experiments presently being performed on the laser-acceleration of ions from solids, mega-amp currents of MeV electrons must be transported through solid foils, requiring almost complete return current neutralization, and giving rise to a wide variety of beam-plasma instabilities. As keynote talks our group promoted Ion Acceleration (plenary talk by A. MacKinnon), which historically has grown out of inertial fusion research, and HIF Accelerator Research (invited talk by A. Friedman), which will require impressive advancements in space-charge-limited ion beam physics and in understanding the generation and transport of neutralized ion beams. A unifying aspect of High Energy Density applications was the physics of particle beams inside of solids, which is proving to be a very important field for diverse applications such as muon cooling, fusion energy research, and ultra-bright particle and radiation generation with high intensity lasers. We had several talks on these and other subjects, and many joint sessions with the Computational group, the EM Structures group, and the Beam Generation group. We summarize our groups' work in the following categories: vacuum acceleration schemes; ion acceleration; particle transport in solids; and applications to high energy density phenomena.« less

Wind Power Generation Design Considerations.

DTIC Science & Technology

1984-12-01

DISTRIBUTION 4 I o ....................................... . . . e . * * TABLES Number Page I Wind Turbine Characteristics II 0- 2 Maximum Economic Life II 3...Ratio of Blade Tip Speed to Wind Speed 10 4 Interference with Microwave and TV Reception by Wind Turbines 13 5 Typical Flow Patterns Over Two...18 * 12 Annual Mean Wind Power Density 21 5 FIGURES (Cont’d) Number Page 13 Wind - Turbine /Generator Types Currently Being Tested on Utility Sites 22 14

Organic pollutant removal from edible oil process wastewater using electrocoagulation

NASA Astrophysics Data System (ADS)

Sharma, S.; Can, O. T.; Hammed, M.; Nawarathna, D.; Simsek, H.

2018-03-01

Wastewaters generated from vegetable oil industries contain a high concentration of organic pollutants that are detrimental to the aquatic ecosystem. Electrochemical processes are gaining importance in the treatment of inorganic and resistant organic pollutants in wastewaters. In this study, electrocoagulation (EC) was applied to remove organic pollutants and oil and grease from canola oil wastewater using aluminum (Al) and iron (Fe) electrodes. The application of EC in the wastewater achieved more than 80% removal of organic carbon and nearly 100% removal of suspended solids (SS). The effectiveness of EC is influenced mainly by current density, pH, electrolyte (NaCl), electrode contact time and electrode type. It was observed that Al electrode combination yielded better removal at a lesser time compared to that of Fe electrodes. However, varying current densities had its significance in terms of coagulation time only. Increase in current density achieved decrease in coagulation time. Both Al and Fe could remove between 52-59% of oil and grease from canola oil wastewater

High efficiency silicon solar cell based on asymmetric nanowire.

PubMed

Ko, Myung-Dong; Rim, Taiuk; Kim, Kihyun; Meyyappan, M; Baek, Chang-Ki

2015-07-08

Improving the efficiency of solar cells through novel materials and devices is critical to realize the full potential of solar energy to meet the growing worldwide energy demands. We present here a highly efficient radial p-n junction silicon solar cell using an asymmetric nanowire structure with a shorter bottom core diameter than at the top. A maximum short circuit current density of 27.5 mA/cm(2) and an efficiency of 7.53% were realized without anti-reflection coating. Changing the silicon nanowire (SiNW) structure from conventional symmetric to asymmetric nature improves the efficiency due to increased short circuit current density. From numerical simulation and measurement of the optical characteristics, the total reflection on the sidewalls is seen to increase the light trapping path and charge carrier generation in the radial junction of the asymmetric SiNW, yielding high external quantum efficiency and short circuit current density. The proposed asymmetric structure has great potential to effectively improve the efficiency of the SiNW solar cells.

Highly efficient tandem organic light-emitting devices employing an easily fabricated charge generation unit

NASA Astrophysics Data System (ADS)

Yang, Huishan; Yu, Yaoyao; Wu, Lishuang; Qu, Biao; Lin, Wenyan; Yu, Ye; Wu, Zhijun; Xie, Wenfa

2018-02-01

We have realized highly efficient tandem organic light-emitting devices (OLEDs) employing an easily fabricated charge generation unit (CGU) combining 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile with ultrathin bilayers of CsN3 and Al. The charge generation and separation processes of the CGU have been demonstrated by studying the differences in the current density-voltage characteristics of external-carrier-excluding devices. At high luminances of 1000 and 10000 cd/m2, the current efficiencies of the phosphorescent tandem device are about 2.2- and 2.3-fold those of the corresponding single-unit device, respectively. Simultaneously, an efficient tandem white OLED exhibiting high color stability and warm white emission has also been fabricated.

Particle simulation of ion heating in the ring current

NASA Technical Reports Server (NTRS)

Qian, S.; Hudson, M. K.; Roth, I.

1990-01-01

Heating of heavy ions has been observed in the equatorial magnetosphere in GEOS 1 and 2 and ATS 6 data due to ion cyclotron waves generated by anisotropic hot ring current ions. A one-dimensional hybrid-Darwin code has been developed to study ion heating in the ring current. Here, a strong instability and heating of thermal ions is investigated in a plasma with a los cone distribution of hot ions. The linear growth rate calculation and particle simulations are conducted for cases with different loss cones and relative ion densities. The linear instability of the waves, the quasi-linear heating of cold ions and dependence on the thermal H(+)/He(+) density ratio are analyzed, as well as nonlinear parallel heating of thermal ions. Effects of thermal oxygen and hot oxygen are also studied.

Electrodynamic Tether Operations beyond the Ionosphere in the Low-Density Magnetosphere

NASA Technical Reports Server (NTRS)

Stone, Nobie H.

2007-01-01

In the classical concept for the operation of electrodynamic tethers in space, a voltage is generated across the tether, either by the tether's orbital motion through the earth's planetary magnetic field or by a power supply; electrons are then collected from the ionospheric plasma at the positive pole; actively emitted back into space at the negative pole; and the circuit is closed by currents driven through the ambient conducting ionosphere. This concept has been proven to work in space by the Tethered Satellite System TSS-1 and TSS-1R Space Shuttle missions; and the Plasma Motor-Generator (PMG) tether flight experiment. However, it limits electrodynamic tether operations to the F-region of the ionosphere where the plasma density is sufficient to conduct the required currents--in other words, between altitudes of approximately 200 to 1000 km in sunlight. In the earth's shadow, the ionospheric density drops precipitously and tether operations, using the above approach, are not effective--even within this altitude range. There are numerous missions that require in-space propulsion in the Earth's shadow and/or outside of the above altitude range. This paper will, therefore, present the fundamentals of a concept that would allow electrodynamic tethers to operate almost anywhere within the magnetosphere, the region of space containing the earth's planetary magnetic field. In other words, because operations would be virtually independent of any ambient plasma, the range of electrodynamic operations would be extended into the earth's shadow and out to synchronous orbit--forty times the present operational range. The key to this concept is the active generation of plasma at each pole of the tether so that current generation ,does not depend on the conductivity of the ambient ionosphere. Arguments will be presented, based on ,existing flight data, which shed light on the behavior of charge emissions in space and show the plausibility of the concept.

Production of high transient heat and particle fluxes in a linear plasma device

NASA Astrophysics Data System (ADS)

De Temmerman, G.; Zielinski, J. J.; van der Meiden, H.; Melissen, W.; Rapp, J.

2010-08-01

We report on the generation of high transient heat and particle fluxes in a linear plasma device by pulsed operation of the plasma source. A capacitor bank is discharged into the source to transiently increase the discharge current up to 1.7 kA, allowing peak densities and temperature of 70×1020 m-3 and 6 eV corresponding to a surface power density of about 400 MW m-2.

Flame oxidation of stainless steel felt enhances anodic biofilm formation and current output in bioelectrochemical systems.

PubMed

Guo, Kun; Donose, Bogdan C; Soeriyadi, Alexander H; Prévoteau, Antonin; Patil, Sunil A; Freguia, Stefano; Gooding, J Justin; Rabaey, Korneel

2014-06-17

Stainless steel (SS) can be an attractive material to create large electrodes for microbial bioelectrochemical systems (BESs), due to its low cost and high conductivity. However, poor biocompatibility limits its successful application today. Here we report a simple and effective method to make SS electrodes biocompatible by means of flame oxidation. Physicochemical characterization of electrode surface indicated that iron oxide nanoparticles (IONPs) were generated in situ on an SS felt surface by flame oxidation. IONPs-coating dramatically enhanced the biocompatibility of SS felt and consequently resulted in a robust electroactive biofilm formation at its surface in BESs. The maximum current densities reached at IONPs-coated SS felt electrodes were 16.5 times and 4.8 times higher than the untreated SS felts and carbon felts, respectively. Furthermore, the maximum current density achieved with the IONPs-coated SS felt (1.92 mA/cm(2), 27.42 mA/cm(3)) is one of the highest current densities reported thus far. These results demonstrate for the first time that flame oxidized SS felts could be a good alternative to carbon-based electrodes for achieving high current densities in BESs. Most importantly, high conductivity, excellent mechanical strength, strong chemical stability, large specific surface area, and comparatively low cost of flame oxidized SS felts offer exciting opportunities for scaling-up of the anodes for BESs.

Polymer electrolyte membrane water electrolysis: Restraining degradation in the presence of fluctuating power

NASA Astrophysics Data System (ADS)

Rakousky, Christoph; Reimer, Uwe; Wippermann, Klaus; Kuhri, Susanne; Carmo, Marcelo; Lueke, Wiebke; Stolten, Detlef

2017-02-01

Polymer electrolyte membrane (PEM) water electrolysis generates 'green' hydrogen when conducted with electricity from renewable - but fluctuating - sources like wind or solar photovoltaic. Unfortunately, the long-term stability of the electrolyzer performance is still not fully understood under these input power profiles. In this study, we contrast the degradation behavior of our PEM water electrolysis single cells that occurs under operation with constant and intermittent power and derive preferable operating states. For this purpose, five different current density profiles are used, of which two were constant and three dynamic. Cells operated at 1 A cm-2 show no degradation. However, degradation was observed for the remaining four profiles, all of which underwent periods of high current density (2 A cm-2). Hereby, constant operation at 2 A cm-2 led to the highest degradation rate (194 μV h-1). Degradation can be greatly reduced when the cells are operated with an intermittent profile. Current density switching has a positive effect on durability, as it causes reversible parts of degradation to recover and results in a substantially reduced degradation per mole of hydrogen produced. Two general degradation phenomena were identified, a decreased anode exchange current density and an increased contact resistance at the titanium porous transport layer (Ti-PTL).

In situ hydrostatic pressure induced improvement of critical current density and suppression of magnetic relaxation in Y(Dy0.5)Ba2Cu3O7‑δ coated conductors

NASA Astrophysics Data System (ADS)

Sang, Lina; Gutiérrez, Joffre; Cai, Chuanbing; Dou, Shixue; Wang, Xiaolin

2018-07-01

We report on the effect of in situ hydrostatic pressure on the enhancement of the in-magnetic-field critical current density parallel to the crystallographic c-axis and vortex pinning in epitaxial Y(Dy0.5)Ba2Cu3O7‑δ coated conductors prepared by metal organic deposition. Our results show that in situ hydrostatic pressure greatly enhances the critical current density at high fields and high temperatures. At 80 K and 5 T we observe a ten-fold increase in the critical current density under the pressure of 1.2 GPa, and the irreversibility line is shifted to higher fields without changing the critical temperature. The normalized magnetic relaxation rate shows that vortex creep rates are strongly suppressed due to applied pressure, and the pinning energy is significantly increased based on the collective creep theory. After releasing the pressure, we recover the original superconducting properties. Therefore, we speculate that the in situ hydrostatic pressure exerted on the coated conductor enhances the pinning of existing extended defects. This is totally different from what has been observed in REBa2Cu3O7‑δ melt-textured crystals, where the effect of pressure generates point-like defects.

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

NASA Astrophysics Data System (ADS)

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%.

Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

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

Gao, Lan; Ji, Hantao; Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543

2016-04-15

Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ∼1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ∼3 × 10{sup 16 }W/cm{sup 2}. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ∼40–50 T magnetic fields at the center of the coil ∼3–4 ns after laser irradiation. The experiments provide significant insight for future target designs that aim tomore » develop a powerful source of external magnetic fields for various applications in high-energy-density science.« less

Design of Ultra-High-Power-Density Machine Optimized for Future Aircraft

NASA Technical Reports Server (NTRS)

Choi, Benjamin B.

2004-01-01

The NASA Glenn Research Center's Structural Mechanics and Dynamics Branch is developing a compact, nonpolluting, bearingless electric machine with electric power supplied by fuel cells for future "more-electric" aircraft with specific power in the projected range of 50 hp/lb, whereas conventional electric machines generate usually 0.2 hp/lb. The use of such electric drives for propulsive fans or propellers depends on the successful development of ultra-high-power-density machines. One possible candidate for such ultra-high-power-density machines, a round-rotor synchronous machine with an engineering current density as high as 20,000 A/sq cm, was selected to investigate how much torque and power can be produced.

Comparative simulation of switching regimes of magnetic explosion generators by copper and aluminum magnetodynamic current breakers taking into account elastoplastic properties of materials

NASA Astrophysics Data System (ADS)

Bazanov, A. A.; Ivanovskii, A. V.; Panov, A. I.; Samodolov, A. V.; Sokolov, S. S.; Shaidullin, V. Sh.

2017-06-01

We report on the results of the computer simulation of the operation of magnetodynamic break switches used as the second stage of current pulse formation in magnetic explosion generators. The simulation was carried out under the conditions when the magnetic field energy density on the surface of the switching conductor as a function of the current through it was close to but still did not exceed the critical value typical of the beginning of electric explosion. In the computational model, we used the parameters of experimentally tested sample of a coil magnetic explosion generator that can store energy of up to 2.7 MJ in the inductive storage circuit and equipped with a primary explosion stage of the current pulse formation. It has been shown that the choice of the switching conductor material, as well as its elastoplastic properties, considerably affects the breaker speed. Comparative results of computer simulation for copper and aluminum have been considered.

Evaluation of Lightning Incidence to Elements of a Complex Structure: A Monte Carlo Approach

NASA Technical Reports Server (NTRS)

Mata, Carlos T.; Rakov, V. A.

2008-01-01

There are complex structures for which the installation and positioning of the lightning protection system (LPS) cannot be done using the lightning protection standard guidelines. As a result, there are some "unprotected" or "exposed" areas. In an effort to quantify the lightning threat to these areas, a Monte Carlo statistical tool has been developed. This statistical tool uses two random number generators: a uniform distribution to generate origins of downward propagating leaders and a lognormal distribution to generate returns stroke peak currents. Downward leaders propagate vertically downward and their striking distances are defined by the polarity and peak current. Following the electrogeometrical concept, we assume that the leader attaches to the closest object within its striking distance. The statistical analysis is run for 10,000 years with an assumed ground flash density and peak current distributions, and the output of the program is the probability of direct attachment to objects of interest with its corresponding peak current distribution.

Multi-line triggering and interdigitated electrode structure for photoconductive semiconductor switches

DOEpatents

Mar, Alan [Albuquerque, NM; Zutavern, Fred J [Albuquerque, NM; Loubriel, Guillermo [Albuquerque, NM

2007-02-06

An improved photoconductive semiconductor switch comprises multiple-line optical triggering of multiple, high-current parallel filaments between the switch electrodes. The switch can also have a multi-gap, interdigitated electrode for the generation of additional parallel filaments. Multi-line triggering can increase the switch lifetime at high currents by increasing the number of current filaments and reducing the current density at the contact electrodes in a controlled manner. Furthermore, the improved switch can mitigate the degradation of switching conditions with increased number of firings of the switch.

Current induced domain wall motion in antiferromagnetically coupled (Co70Fe30/Pd) multilayer nanowires

NASA Astrophysics Data System (ADS)

Meng, Zhaoliang; He, Shikun; Huang, Lisen; Qiu, Jinjun; Zhou, Tiejun; Panagopoulos, Christos; Han, Guchang; Teo, Kie-Leong

2016-10-01

We investigate the current induced domain wall (DW) motion in the ultrathin CoFe/Pd multilayer based synthetically antiferromagnetic (SAF) structure nanowires by anomalous Hall effect measurement. The threshold current density (Jth) for the DW displacement decreases and the DW velocity (v) increases accordingly with the exchange coupling Jex between the top and bottom ferromagnetic CoFe/Pd multilayers. The lowest Jth = 9.3 × 1010 A/m2 and a maximum v = 150 m/s with J = 1.5 × 1012 A/m2 are achieved due to the exchange coupling torque (ECT) generated in the SAF structure. The strength of ECT is dependent on both of Jex and the strong spin-orbit torque mainly generated by Ta layer.

Generation of mechanical vibrations in metal samples by the use of the pinch effect

NASA Astrophysics Data System (ADS)

Troitskiy, O. A.; Skvortsov, O. B.; Stashenko, V. I.

2017-07-01

The article presents the recent research in electrodynamic processes for metal samples exposed to current pulses. The pinch effect and the skin effect cause the vibration of the metal rods. The results of these studies show how current and magnetic field interact with material samples of gold, silver and copper. The analysis allowed establishing the dependences of peak acceleration on current density and conductor diameter. The dependencies can be used in metal workings and for nondestructive testing.

Parallel, staged opening switch power conditioning techniques for flux compression generator applications

NASA Astrophysics Data System (ADS)

Reinovsky, R. E.; Levi, P. S.; Bueck, J. C.; Goforth, J. H.

The Air Force Weapons Laboratory, working jointly with Los Alamos National Laboratory, has conducted a series of experiments directed at exploring composite, or staged, switching techniques for use in opening switches in applications which require the conduction of very high currents (or current densities) with very low losses for relatively long times (several tens of microseconds), and the interruption of these currents in much shorter times (ultimately a few hundred nanoseconds). The results of those experiments are reported.

Development of a new generation of high-temperature composite materials

NASA Technical Reports Server (NTRS)

Brindley, Pamela K.

1987-01-01

There are ever-increasing demands to develop low-density materials that maintain high strength and stiffness properties at elevated temperatures. Such materials are essential if the requirements for advanced aircraft, space power generation, and space station plans are to be realized. Metal matrix composites and intermetallic matrix composites are currently being investigated at NASA Lewis for such applications because they offer potential increases in strength, stiffness, and use temperature at a lower density than the most advanced single-crystal superalloys presently available. Today's discussion centers around the intermetallic matrix composites proposed by Lewis for meeting advanced aeropropulsion requirements. The fabrication process currently being used at Lewis to produce intermetallic matrix composites will be reviewed, and the properties of one such composite, SiC/Ti3Al+Nb, will be presented. In addition, the direction of future research will be outlined, including plans for enhanced fabrication of aluminide composites by the arc spray technique and fiber development by the floating-zone process.

Plasmonic excitation-assisted optical and electric enhancement in ultra-thin solar cells: the influence of nano-strip cross section

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

Sabaeian, Mohammad, E-mail: sabaiean@scu.ac.ir; Heydari, Mehdi; Ajamgard, Narges

The effects of Ag nano-strips with triangle, rectangular and trapezoid cross sections on the optical absorption, generation rate, and short-circuit current density of ultra-thin solar cells were investigated. By putting the nano-strips as a grating structure on the top of the solar cells, the waveguide, surface plasmon polariton (SPP), and localized surface plasmon (LSP) modes, which are excited with the assistance of nano-strips, were evaluated in TE and TM polarizations. The results show, firstly, the TM modes are more influential than TE modes in optical and electrical properties enhancement of solar cell, because of plasmonic excitations in TM mode. Secondly,more » the trapezoid nano-strips reveal noticeable impact on the optical absorption, generation rate, and short-circuit current density enhancement than triangle and rectangular ones. In particular, the absorption of long wavelengths which is a challenge in ultra-thin solar cells is significantly improved by using Ag trapezoid nano-strips.« less

Magnetic Effects in a Moderate-Temperature, High-Beta, Toroidal Plasma Device

NASA Astrophysics Data System (ADS)

Edwards, W. F.; Singh, A. K.; Held, E. D.

2011-10-01

A small toroidal machine (STOR-1M; minor radius 4.5 cm), on loan from the University of Saskatchewan, has been modified to operate at hydrogen ionization levels ~0.1%, beta values between 0.1 and 1, electron number density ~5x1016/m3, temperature ~5 eV, and applied toroidal magnetic field ~20 gauss. Plasma is generated using magnetron-produced microwaves. Langmuir and Hall probes determine radial profiles of electron number density, temperature, and magnetic field. For most values of the externally-applied magnetic field, the internal field is the same with or without plasma, however, in a narrow window of B, diamagnetism and other effects are present. The effect is observed with no externally induced current; plasma currents are self generated through some sort of relaxation process. Beta and radius conditions correlate well with similar magnetic structures in the laboratory (eg., plasma focus, Z pinch) and in space (eg., Venus flux ropes, solar coronal loops).

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

NASA Astrophysics Data System (ADS)

Gomez, M. R.; Gilgenbach, R. M.; Cuneo, M. E.; Jennings, C. A.; McBride, R. D.; Waisman, E. M.; Hutsel, B. T.; Stygar, W. A.; Rose, D. V.; Maron, Y.

2017-01-01

The Z pulsed-power generator at Sandia National Laboratories drives high energy density physics experiments with load currents of up to 26 MA. Z utilizes a double post-hole convolute to combine the current from four parallel magnetically insulated transmission lines into a single transmission line just upstream of the load. Current loss is observed in most experiments and is traditionally attributed to inefficient convolute performance. The apparent loss current varies substantially for z-pinch loads with different inductance histories; however, a similar convolute impedance history is observed for all load types. This paper details direct spectroscopic measurements of plasma density, temperature, and apparent and actual plasma closure velocities within the convolute. Spectral measurements indicate a correlation between impedance collapse and plasma formation in the convolute. Absorption features in the spectra show the convolute plasma consists primarily of hydrogen, which likely forms from desorbed electrode contaminant species such as H2O , H2 , and hydrocarbons. Plasma densities increase from 1 ×1016 cm-3 (level of detectability) just before peak current to over 1 ×1017 cm-3 at stagnation (tens of ns later). The density seems to be highest near the cathode surface, with an apparent cathode to anode plasma velocity in the range of 35 - 50 cm /μ s . Similar plasma conditions and convolute impedance histories are observed in experiments with high and low losses, suggesting that losses are driven largely by load dynamics, which determine the voltage on the convolute.

Development of a plasma generator for a long pulse ion source for neutral beam injectors.

PubMed

Watanabe, K; Dairaku, M; Tobari, H; Kashiwagi, M; Inoue, T; Hanada, M; Jeong, S H; Chang, D H; Kim, T S; Kim, B R; Seo, C S; Jin, J T; Lee, K W; In, S R; Oh, B H; Kim, J; Bae, Y S

2011-06-01

A plasma generator for a long pulse H(+)/D(+) ion source has been developed. The plasma generator was designed to produce 65 A H(+)/D(+) beams at an energy of 120 keV from an ion extraction area of 12 cm in width and 45 cm in length. Configuration of the plasma generator is a multi-cusp bucket type with SmCo permanent magnets. Dimension of a plasma chamber is 25 cm in width, 59 cm in length, and 32.5 cm in depth. The plasma generator was designed and fabricated at Japan Atomic Energy Agency. Source plasma generation and beam extraction tests for hydrogen coupling with an accelerator of the KSTAR ion source have been performed at the KSTAR neutral beam test stand under the agreement of Japan-Korea collaborative experiment. Spatial uniformity of the source plasma at the extraction region was measured using Langmuir probes and ±7% of the deviation from an averaged ion saturation current density was obtained. A long pulse test of the plasma generation up to 200 s with an arc discharge power of 70 kW has been successfully demonstrated. The arc discharge power satisfies the requirement of the beam production for the KSTAR NBI. A 70 keV, 41 A, 5 s hydrogen ion beam has been extracted with a high arc efficiency of 0.9 -1.1 A/kW at a beam extraction experiment. A deuteron yield of 77% was measured even at a low beam current density of 73 mA/cm(2). © 2011 American Institute of Physics

Spatial and Time Dynamics of Non-Linear Vortices in Plasma Lens for High-Current Ion Beam Focusing

NASA Astrophysics Data System (ADS)

Goncharov, Alexei A.; Maslov, Vasyl I.; Onishchenko, Ivan N.; Tretyakov, Vitalij N.

2002-11-01

It is known from numerical simulation (see, for example, [1]) and from experiments (see, for example, [2]), that an electron density bunches as discrete vortices are long - living structures in vacuum. However, in laboratory experiments [2] it has been shown that the vortices are changed faster, when they are submersed in electrons, distributed around them. The charged plasma lens intended for a focussing of high-current ion beams, has the same crossed configuration of a radial electrical and longitudinal magnetic field [3], as only electron plasma. In this lens the vortical turbulence is excited [3]. The vortex - bunch and vortex - hole are rotated in the inverse directions in system of their rest. The instability development in initially homogeneous plasma causes that the vortices are excited by pairs. Namely, if the vortex - bunch of electrons is generated, near the vortex - hole of electrons is also generated. It is shown, that in nonuniform plasma the vortices behave is various in time. Namely, the vortex - bunch goes to area of larger electron density, and the vortex - hole goes to area of smaller electron density. The speed of the vortex - hole is less than speed of the vortex - bunch. It is shown, that the electron vortices, generated in the plasma lens, can result in to formation of spiral distribution of electron density. The physical mechanism of coalescence of electron vortices - bunches is proposed. 1.Driscoll C.F. et al. Plasma Phys. Contr. Fus. Res. 3 (1989) 507. 2.Kiwamoto Y. et al. Non-neutral plasma physics. Princeton. 1999. P. 99-105. 3.Goncharov A. et al. Plasma Phys. Rep. 20 (1994) 499.

Currents between tethered electrodes in a magnetized laboratory plasma

NASA Technical Reports Server (NTRS)

Stenzel, R. L.; Urrutia, J. M.

1989-01-01

Laboratory experiments on important plasma physics issues of electrodynamic tethers were performed. These included current propagation, formation of wave wings, limits of current collection, nonlinear effects and instabilities, charging phenomena, and characteristics of transmission lines in plasmas. The experiments were conducted in a large afterglow plasma. The current system was established with a small electron-emitting hot cathode tethered to an electron-collecting anode, both movable across the magnetic field and energized by potential difference up to V approx.=100 T(sub e). The total current density in space and time was obtained from complete measurements of the perturbed magnetic field. The fast spacecraft motion was reproduced in the laboratory by moving the tethered electrodes in small increments, applying delayed current pulses, and reconstructing the net field by a linear superposition of locally emitted wavelets. With this technique, the small-amplitude dc current pattern is shown to form whistler wings at each electrode instead of the generally accepted Alfven wings. For the beam electrode, the whistler wing separates from the field-aligned beam which carries no net current. Large amplitude return currents to a stationary anode generate current-driven microinstabilities, parallel electric fields, ion depletions, current disruptions and time-varying electrode charging. At appropriately high potentials and neutral densities, excess neutrals are ionized near the anode. The anode sheath emits high-frequency electron transit-time oscillations at the sheath-plasma resonance. The beam generates Langmuir turbulence, ion sound turbulence, electron heating, space charge fields, and Hall currents. An insulated, perfectly conducting transmission line embedded in the plasma becomes lossy due to excitation of whistler waves and magnetic field diffusion effects. The implications of the laboratory observations on electrodynamic tethers in space are discussed.

Anode catalysts for direct ethanol fuel cells utilizing directly solar light illumination.

PubMed

Chu, Daobao; Wang, Shuxi; Zheng, Peng; Wang, Jian; Zha, Longwu; Hou, Yuanyuan; He, Jianguo; Xiao, Ying; Lin, Huashui; Tian, Zhaowu

2009-01-01

Shine a light: A PtNiRu/TiO(2) anode catalyst for direct ethanol fuel cells shows photocatalytic activity. The peak current density for ethanol oxidation under solar light illumination is 2-3 times greater than that in the absence of solar light. Ethanol is oxidized by light-generated holes, and the electrons are collected by the TiO(2) support to generate the oxidation current.Novel PtNiRu/TiO(2) anode catalysts for direct ethanol fuel cells (DEFCs) were prepared from PtNiRu nanoparticles (1:1:1 atomic ratios) and a nanoporous TiO(2) film by a sol-gel and electrodeposition method. The performances of the catalysts for ethanol oxidation were investigated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results indicate a remarkable enhancement of activity for ethanol oxidation under solar light illumination. Under solar light illumination, the generated oxidation peak current density is 24.6 mA cm(-2), which is about 2.5 times higher than that observed without solar light (9.9 mA cm(-2)). The high catalytic activity of the PtNiRu/TiO(2) complex catalyst for the electrooxidation of ethanol may be attributed to the modified metal/nanoporous TiO(2) film, and the enhanced electrooxidation of ethanol under solar light may be due to the photogeneration of holes in the modified nanoporous TiO(2) film.

Hybrid friction stir welding for dissimilar materials through electro-plastic effect

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

Liu, Xun; Lan, Shuhuai; Ni, Jun

A hybrid Friction Stir Welding approach and device for dissimilar materials joining employing Electro-Plastic Effect. The approach and device include an introduction of high density, short period current pulses into traditional friction stir welding process, which therefore can generate a localized softened zone in the workpiece during plastic stirring without significant additional temperature increase. This material softened zone is created by high density current pulses based on Electro-Plastic Effect and will move along with the friction stir welding tool. Smaller downward force, larger processing window and better joint quality for dissimilar materials are expected to be achieved through this hybridmore » welding technique.« less

High current ion source

DOEpatents

Brown, Ian G.; MacGill, Robert A.; Galvin, James E.

1990-01-01

An ion source utilizing a cathode and anode for producing an electric arc therebetween. The arc is sufficient to vaporize a portion of the cathode to form a plasma. The plasma leaves the generation region and expands through another regon. The density profile of the plasma may be flattened using a magnetic field formed within a vacuum chamber. Ions are extracted from the plasma to produce a high current broad on beam.

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

PubMed

Liao, Ke; Zhu, Min; Ding, Lei

2013-08-01

The present study investigated the use of transform sparseness of cortical current density on human brain surface to improve electroencephalography/magnetoencephalography (EEG/MEG) inverse solutions. Transform sparseness was assessed by evaluating compressibility of cortical current densities in transform domains. To do that, a structure compression method from computer graphics was first adopted to compress cortical surface structure, either regular or irregular, into hierarchical multi-resolution meshes. Then, a new face-based wavelet method based on generated multi-resolution meshes was proposed to compress current density functions defined on cortical surfaces. Twelve cortical surface models were built by three EEG/MEG softwares and their structural compressibility was evaluated and compared by the proposed method. Monte Carlo simulations were implemented to evaluate the performance of the proposed wavelet method in compressing various cortical current density distributions as compared to other two available vertex-based wavelet methods. The present results indicate that the face-based wavelet method can achieve higher transform sparseness than vertex-based wavelet methods. Furthermore, basis functions from the face-based wavelet method have lower coherence against typical EEG and MEG measurement systems than vertex-based wavelet methods. Both high transform sparseness and low coherent measurements suggest that the proposed face-based wavelet method can improve the performance of L1-norm regularized EEG/MEG inverse solutions, which was further demonstrated in simulations and experimental setups using MEG data. Thus, this new transform on complicated cortical structure is promising to significantly advance EEG/MEG inverse source imaging technologies. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Method and apparatus for the formation of a spheromak plasma

DOEpatents

Jardin, Stephen C.; Yamada, Masaaki; Furth, Harold P.; Okabayashi, Mitcheo

1984-01-01

An inductive method and apparatus for forming detached spheromak plasma using a thin-walled metal toroidal ring, with external current leads and internal poloidal and toroidal field coils located inside a vacuum chamber filled with low density hydrogen gas and an external axial field generating coil. The presence of a current in the poloidal field coils, and an externally generated axial field sets up the initial poloidal field configuration in which the field is strongest toward the major axis of the toroid. The internal toroidal-field-generating coil is then pulsed on, ionizing the gas and inducing poloidal current and toroidal magnetic field into the plasma region in the sleeve exterior to and adjacent to the ring and causing the plasma to expand away from the ring and toward the major axis. Next the current in the poloidal field coils in the ring is reversed. This induces toroidal current into the plasma and causes the poloidal magnetic field lines to reconnect. The reconnection continues until substantially all of the plasma is formed in a separated spheromak configuration held in equilibrium by the initial external field.

Magnetic-field-dependent shear modulus of a magnetorheological elastomer based on natural rubber

NASA Astrophysics Data System (ADS)

Yang, In-Hyung; Yoon, Ji-Hyun; Jeong, Jae-Eun; Jeong, Un-Chang; Kim, Jin-Su; Chung, Kyung Ho; Oh, Jae-Eung

2013-01-01

A magnetorheological elastomer (MRE) is a smart material that has a reversible and variable modulus in a magnetic field. Natural rubber, which has better physical properties than silicone matrices, was used as a matrix in the fabrication of the MREs used in this study. Carbonyl iron powder (CIP), which has a rapid magnetic reaction, was selected as a magnetic material to generate the magnetic-field-dependent modulus in the MREs. The MRE specimens were cured in an anisotropic mold, which could be used to induce a uniaxial magnetic field via permanent magnets, to control the orientation of the CIP, and the shear modulus of the MREs was evaluated under a magnetic field induced by using a magnetic flux generator (MFG). Because the use of a conventional evaluation system to determine the magnetic-field-dependent shear modulus of the MREs was difficult, an evaluation system based on single degree-of-freedom vibration and electromagnetics that included an MFG, which is a device that generates a magnetic field via a variable induced current, was designed. An electromagnetic finite element method (FEM) analysis and design of experiments (DoE) techniques were employed to optimize the magnetic flux density generated by the MFG. The optimized system was verified over the range to determine the magnetic flux density generated by the MFG in order to use a magnetic circuit analysis to identify the existence of magnetic saturation. A variation in the shear modulus was observed with increasing CIP volume fraction and induced current. The experimental results revealed that the maximum variation in the shear modulus was 76.3% for 40 vol% CIP at an induced current of 4 A. With these results, the appropriate CIP volume fraction, induced current, and design procedure of the MFG can be proposed as guidelines for applications of MREs based on natural rubber.

Generation of Low-Energy High-Current Electron Beams in Plasma-Anode Electron Guns

NASA Astrophysics Data System (ADS)

Ozur, G. E.; Proskurovsky, D. I.

2018-01-01

This paper is a review of studies on the generation of low-energy high-current electron beams in electron guns with a plasma anode and an explosive-emission cathode. The problems related to the initiation of explosive electron emission under plasma and the formation and transport of high-current electron beams in plasma-filled systems are discussed consecutively. Considerable attention is given to the nonstationary effects that occur in the space charge layers of plasma. Emphasis is also placed on the problem of providing a uniform energy density distribution over the beam cross section, which is of critical importance in using electron beams of this type for surface treatment of materials. Examples of facilities based on low-energy high-current electron beam sources are presented and their applications in materials science and practice are discussed.

Modifying Current Collectors to Produce High Volumetric Energy Density and Power Density Storage Devices.

PubMed

Khani, Hadi; Dowell, Timothy J; Wipf, David O

2018-06-27

We develop zirconium-templated NiO/NiOOH nanosheets on nickel foam and polypyrrole-embedded in exfoliated carbon fiber cloth as complementary electrodes for an asymmetric battery-type supercapacitor device. We achieve high volumetric energy and power density by the modification of commercially available current collectors (CCs). The modified CCs provide the source of active material, actively participate in the charge storage process, provide a larger surface area for active material loading, need no additional binders or conductive additives, and retain the ability to act as the CC. Nickel foam (NF) CCs are modified by use of a soft-templating/solvothermal treatment to generate NiO/NiOOH nanosheets, where the NF is the source of Ni for the synthesis. Carbon-fiber cloth (CFC) CCs are modified by an electrochemical oxidation/reduction process to generate exfoliated core-shell structures (ECFC). Electropolymerization of pyrrole into the shell structure produces polypyrrole embedded in exfoliated core-shell material (PPy@rECFC). Battery-type supercapacitor devices are produced with NiO/NiOOH@NF and PPy@rECFC as positive and negative electrodes, respectively, to demonstrate the utility of this approach. Volumetric energy densities for the full-cell device are in the range of 2.60-4.12 mWh cm -3 with corresponding power densities in the range of 9.17-425.58 mW cm -3 . This is comparable to thin-film lithium-ion batteries (0.3-10 mWh cm -3 ) and better than some commercial supercapacitors (<1 mWh cm -3 ). 1 The energy and power density is impressive considering that it was calculated using the entire cell volume (active materials, separator, and both CCs). The full-cell device is highly stable, retaining 96% and 88% of capacity after 2000 and 5000 cycles, respectively. These results demonstrate the utility of directly modifying the CCs and suggest a new method to produce high volumetric energy density and power density storage devices.

Meta-proteomic analysis of protein expression distinctive to electricity-generating biofilm communities in air-cathode microbial fuel cells.

PubMed

Chignell, Jeremy F; De Long, Susan K; Reardon, Kenneth F

2018-01-01

Bioelectrochemical systems (BESs) harness electrons from microbial respiration to generate power or chemical products from a variety of organic feedstocks, including lignocellulosic biomass, fermentation byproducts, and wastewater sludge. In some BESs, such as microbial fuel cells (MFCs), bacteria living in a biofilm use the anode as an electron acceptor for electrons harvested from organic materials such as lignocellulosic biomass or waste byproducts, generating energy that may be used by humans. Many BES applications use bacterial biofilm communities, but no studies have investigated protein expression by the anode biofilm community as a whole. To discover functional protein expression during current generation that may be useful for MFC optimization, a label-free meta-proteomics approach was used to compare protein expression in acetate-fed anode biofilms before and after the onset of robust electricity generation. Meta-proteomic comparisons were integrated with 16S rRNA gene-based community analysis at four developmental stages. The community composition shifted from dominance by aerobic Gammaproteobacteria (90.9 ± 3.3%) during initial biofilm formation to dominance by Deltaproteobacteria , particularly Geobacter (68.7 ± 3.6%) in mature, electricity-generating anodes. Community diversity in the intermediate stage, just after robust current generation began, was double that at the early stage and nearly double that of mature anode communities. Maximum current densities at the intermediate stage, however, were relatively similar (~ 83%) to those achieved by mature-stage biofilms. Meta-proteomic analysis, correlated with population changes, revealed significant enrichment of categories specific to membrane and transport functions among proteins from electricity-producing biofilms. Proteins detected only in electricity-producing biofilms were associated with gluconeogenesis, the glyoxylate cycle, and fatty acid β-oxidation, as well as with denitrification and competitive inhibition. The results demonstrate that it is possible for an MFC microbial community to generate robust current densities while exhibiting high taxonomic diversity. Moreover, these data provide evidence to suggest that startup growth of air-cathode MFCs under conditions that promote the establishment of aerobic-anaerobic syntrophy may decrease startup times. This study represents the first investigation into protein expression of a complex BES anode biofilm community as a whole. The findings contribute to understanding of the molecular mechanisms at work during BES startup and suggest options for improvement of BES generation of bioelectricity from renewable biomass.

Replacing critical rare earth materials in high energy density magnets

NASA Astrophysics Data System (ADS)

McCallum, R. William

2012-02-01

High energy density permanent magnets are crucial to the design of internal permanent magnet motors (IPM) for hybride and electric vehicles and direct drive wind generators. Current motor designs use rare earth permanent magnets which easily meet the performance goals, however, the rising concerns over cost and foreign control of the current supply of rare earth resources has motivated a search for non-rare earth based permanent magnets alloys with performance metrics which allow the design of permanent magnet motors and generators without rare earth magnets. This talk will discuss the state of non-rare-earth permanent magnets and efforts to both improve the current materials and find new materials. These efforts combine first principles calculations and meso-scale magnetic modeling with advance characterization and synthesis techniques in order to advance the state of the art in non rare earth permanent magnets. The use of genetic algorithms in first principle structural calculations, combinatorial synthesis in the experimental search for materials, atom probe microscopy to characterize grain boundaries on the atomic level, and other state of the art techniques will be discussed. In addition the possibility of replacing critical rare earth elements with the most abundant rare earth Ce will be discussed.

A comparative study of radiofrequency antennas for Helicon plasma sources

NASA Astrophysics Data System (ADS)

Melazzi, D.; Lancellotti, V.

2015-04-01

Since Helicon plasma sources can efficiently couple power and generate high-density plasma, they have received interest also as spacecraft propulsive devices, among other applications. In order to maximize the power deposited into the plasma, it is necessary to assess the performance of the radiofrequency (RF) antenna that drives the discharge, as typical plasma parameters (e.g. the density) are varied. For this reason, we have conducted a comparative analysis of three Helicon sources which feature different RF antennas, namely, the single-loop, the Nagoya type-III and the fractional helix. These antennas are compared in terms of input impedance and induced current density; in particular, the real part of the impedance constitutes a measure of the antenna ability to couple power into the plasma. The results presented in this work have been obtained through a full-wave approach which (being hinged on the numerical solution of a system of integral equations) allows computing the antenna current and impedance self-consistently. Our findings indicate that certain combinations of plasma parameters can indeed maximize the real part of the input impedance and, thus, the deposited power, and that one of the three antennas analyzed performs best for a given plasma. Furthermore, unlike other strategies which rely on approximate antenna models, our approach enables us to reveal that the antenna current density is not spatially uniform, and that a correlation exists between the plasma parameters and the spatial distribution of the current density.

Toroidal momentum pinch velocity due to the coriolis drift effect on small scale instabilities in a toroidal plasma.

PubMed

Peeters, A G; Angioni, C; Strintzi, D

2007-06-29

In this Letter, the influence of the "Coriolis drift" on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments.

Toroidal Momentum Pinch Velocity due to the Coriolis Drift Effect on Small Scale Instabilities in a Toroidal Plasma

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

Peeters, A. G.; Angioni, C.; Strintzi, D.

In this Letter, the influence of the ''Coriolis drift'' on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torquemore » on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiment000.« less

Removal of organic matter and electricity generation of sediments from Progreso, Yucatan, Mexico, in a sediment microbial fuel cell.

PubMed

González-Gamboa, Nancy Karina; Valdés-Lozano, David Sergio; Barahona-Pérez, Luis Felipe; Alzate-Gaviria, Liliana; Domínguez-Maldonado, Jorge Arturo

2017-02-01

Sediment microbial fuel cells (SMFCs) are devices that generate electrical energy through sediments rich in organic matter (OM). The present study assessed the potential of sediments collected at two sites in Yucatan, Mexico, (the swamp of Progreso port and Yucalpetén dock) to be used in these electrochemical devices. Sediments were collected during the rainy and winter seasons and were monitored in the SMFC for 120 days through electrochemical and physicochemical characterization. OM removal in the SMFC ranged from 8.1-18.01%, generating a maximum current density of 232.46 mA/cm 2 and power density of 95.85 mW/cm 2 . SUVA analysis indicated that with a young soil, the ratio E4/E6 presented evidence directly related to the degradation of aromatic and aliphatic compound formation, implying humification and, therefore, sediment enrichment.

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

NASA Astrophysics Data System (ADS)

Ander Arrillaga, Jon; Yagüe, Carlos; Román-Cascón, Carlos; Sastre, Mariano

2016-04-01

Density currents are flows generated when a dense fluid passes through a less dense surrounding, under the influence of gravity. They usually appear as a consequence of sea-breeze circulations, thunderstorm outflows or katabatic flows. Density currents acquire a particular relevance during nocturnal stable situations, as their onset causes a significant turbulence increase (both from buoyancy and shear) and they occasionally produce turbulence intermittency through the formation of gravity waves. In this work, the arrival of a density current on 23 September 2015 is analysed in the CIBA site (Spain), which is located in the Spanish Northern Plateau, approximately 200 km away from the sea and 100 km away from the closest mountain ranges. Previous studies at this location associated similar nocturnal events with daytime sea breeze in the eastern Cantabrian coast [1]. Micrometeorological measurements from sonic anemometers and different sensors at multiple levels up to 100 m agl provide a solid database. In this specific case, the outbreak of the density current occurs 2 hours after sunset, causing an abrupt increase of the wind speed and a significant weakening of the surface-based thermal inversion. Besides, turbulent parameters and fluxes such as the friction velocity, the sensible heat flux and the Turbulent Kinetic Energy (TKE) are sharply altered with its arrival. The latter, indeed, increases by two orders of magnitude and the Multi Resolution Flux Decomposition (MRFD) of this and other turbulent variables gives the approximate size of the contributing eddies. Furthermore, simulations with the WRF model, which is tested for different Planetary Boundary Layer (PBL) schemes and the topo_wind option for complex topography [2], give meaningful information about the vertical structure and origin of this density current. [1] Udina, M., Soler, M.R., Viana, S. & Yagüe, C. (2013). Model simulation of gravity waves triggered by a density current. Q J R Meteorol Soc, 139, 701-714. [2] Jiménez, P.A., Dudhia, J., González-Rouco, J.F., Navarro, J., Montávez, J.P., García-Bustamante, E. (2012). A revised scheme for the wrf surface layer formulation. Mon Weather Rev, 140, 898-918.

Electron beam emission from a diamond-amplifier cathode.

PubMed

Chang, Xiangyun; Wu, Qiong; Ben-Zvi, Ilan; Burrill, Andrew; Kewisch, Jorg; Rao, Triveni; Smedley, John; Wang, Erdong; Muller, Erik M; Busby, Richard; Dimitrov, Dimitre

2010-10-15

The diamond amplifier (DA) is a new device for generating high-current, high-brightness electron beams. Our transmission-mode tests show that, with single-crystal, high-purity diamonds, the peak current density is greater than 400  mA/mm², while its average density can be more than 100  mA/mm². The gain of the primary electrons easily exceeds 200, and is independent of their density within the practical range of DA applications. We observed the electron emission. The maximum emission gain measured was 40, and the bunch charge was 50  pC/0.5  mm². There was a 35% probability of the emission of an electron from the hydrogenated surface in our tests. We identified a mechanism of slow charging of the diamond due to thermal ionization of surface states that cancels the applied field within it. We also demonstrated that a hydrogenated diamond is extremely robust.

Morphological Study on Porous Silicon Carbide Membrane Fabricated by Double-Step Electrochemical Etching

NASA Astrophysics Data System (ADS)

Omiya, Takuma; Tanaka, Akira; Shimomura, Masaru

2012-07-01

The structure of porous silicon carbide membranes that peeled off spontaneously during electrochemical etching was studied. They were fabricated from n-type 6H SiC(0001) wafers by a double-step electrochemical etching process in a hydrofluoric electrolyte. Nanoporous membranes were obtained after double-step etching with current densities of 10-20 and 60-100 mA/cm2 in the first and second steps, respectively. Microporous membranes were also fabricated after double-step etching with current densities of 100 and 200 mA/cm2. It was found that the pore diameter is influenced by the etching current in step 1, and that a higher current is required in step 2 when the current in step 1 is increased. During the etching processes in steps 1 and 2, vertical nanopore and lateral crack formations proceed, respectively. The influx pathway of hydrofluoric solution, expansion of generated gases, and transfer limitation of positive holes to the pore surface are the key factors in the peeling-off mechanism of the membrane.

Currents Induced by Injected Charge in Junction Detectors

PubMed Central

Gaubas, Eugenijus; Ceponis, Tomas; Kalesinskas, Vidas

2013-01-01

The problem of drifting charge-induced currents is considered in order to predict the pulsed operational characteristics in photo- and particle-detectors with a junction controlled active area. The direct analysis of the field changes induced by drifting charge in the abrupt junction devices with a plane-parallel geometry of finite area electrodes is presented. The problem is solved using the one-dimensional approach. The models of the formation of the induced pulsed currents have been analyzed for the regimes of partial and full depletion. The obtained solutions for the current density contain expressions of a velocity field dependence on the applied voltage, location of the injected surface charge domain and carrier capture parameters. The drift component of this current coincides with Ramo's expression. It has been illustrated, that the synchronous action of carrier drift, trapping, generation and diffusion can lead to a vast variety of possible current pulse waveforms. Experimental illustrations of the current pulse variations determined by either the rather small or large carrier density within the photo-injected charge domain are presented, based on a study of Si detectors. PMID:24036586

Basaltic ignimbrites in monogenetic volcanism: the example of La Garrotxa volcanic field

NASA Astrophysics Data System (ADS)

Martí, J.; Planagumà, L. l.; Geyer, A.; Aguirre-Díaz, G.; Pedrazzi, D.; Bolós, X.

2017-05-01

Ignimbrites are pyroclastic density current deposits common in explosive volcanism involving intermediate and silicic magmas and in less abundance in eruptions of basaltic central and shield volcanoes. However, they are not widely described in association with monogenetic volcanism, where typical products include lava flows, scoria and lapilli fall deposits, as well as various kinds of pyroclastic density current deposits and explosion breccias. In La Garrotxa basaltic monogenetic volcanic field, part of the Neogene-Quaternary European rift system located in the northeast of the Iberian Peninsula, we have identified a particular group of pyroclastic density current deposits that show similar textural characteristics to silicic ignimbrites, indicating an overlap in transport and depositional processes. These deposits can be clearly distinguished from other pyroclastic density current deposits generated during phreatomagmatic phases that typically correspond to thinly laminated units with planar-to-cross-bedded stratification. The monogenetic ignimbrite deposits correspond to a few meters to several tens of meters thick units rich in lithic- and lapilli scoria fragments, with an abundant ash matrix, and internally massive structure, emplaced along valleys and gullies, with run-out distances up to 6 km and individual volumes ranging from 106 to 1.5 × 107 m3. The presence of flattened scoria and columnar jointing in some of these deposits suggests relatively high emplacement temperatures, coinciding with available paleomagnetic data that suggests an emplacement temperature around 450-500 °C. In this work, we describe the main characteristics of these pyroclastic deposits that were generated by a number of phreatomagmatic episodes. Comparison with similar deposits from silicic eruptions and previous examples of ignimbrites associated with basaltic volcanism allows us to classify them as `basaltic ignimbrites'. The recognition in monogenetic volcanism of such pyroclastic products, which may extend several kilometres from source, has an important consequence for hazard assessment in these volcanic fields, which previously have been considered to present only minor hazards and risks.

Silent calcium channels in skeletal muscle fibers of the crustacean Atya lanipes.

PubMed

Monterrubio, J; Lizardi, L; Zuazaga, C

2000-01-01

The superficial (tonic) abdominal flexor muscles of Atya lanipes do not generate Ca(2+) action potentials when depolarized and have no detectable inward Ca(2+) current. These fibers, however, are strictly dependent on Ca(2+) influx for contraction, suggesting that they depend on Ca(2+)-induced Ca(2+) release for contractile activation. The nature of the communication between Ca(2+) channels in the sarcolemmal/tubular membrane and Ca(2+) release channels in the sarcoplasmic reticulum in this crustacean muscle was investigated. The effects of dihydropyridines on tension generation and the passive electrical response were examined in current-clamped fibers: Bay K 8644 enhanced tension about 100% but did not alter the passive electrical response; nifedipine inhibited tension by about 70%. Sr(2+) and Ba(2+) action potentials could be elicited in Ca(2+)-free solutions. The spikes generated by these divalent cations were abolished by nifedipine. As the Sr(2+) or Ba(2+) concentrations were increased, the amplitudes of the action potentials and their maximum rate of rise, V(max), increased and tended towards saturation. Three-microelectrode voltage-clamp experiments showed that even at high (138 mm) extracellular Ca(2+) concentration the channels were silent, i.e., no inward Ca(2+) current was detected. In Ca(2+)-free solutions, inward currents carried by 138 mm Sr(2+) or Ba(2+) were observed. The currents activated at voltages above -40 mV and peaked at about 0 mV. This voltage-activation profile and the sensitivity of the channels to dihydropyridines indicate that they resemble L-type Ca(2+) channels. Peak inward current density values were low, ca. -33 microA/cm(2) for Sr(2+) and -14 microA/cm(2) for Ba(2+), suggesting that Ca(2+) channels are present at a very low density. It is concluded that Ca(2+)-induced Ca(2+) release in this crustacean muscle operates with an unusually high gain: Ca(2+) influx through the silent Ca(2+) channels is too low to generate a macroscopic inward current, but increases sufficiently the local concentration of Ca(2+) in the immediate vicinity of the sarcoplasmic reticulum Ca(2+) release channels to trigger the highly amplified release of Ca(2+) required for tension generation.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

Characterization of Pulse Reverses Electroforming on Hard Gold Coating.

PubMed

Byoun, Young-Min; Noh, Young-Tai; Kim, Young-Geun; Ma, Seung-Hwan; Kim, Gwan-Hoon

2018-03-01

Effect of pulse reverse current (PRC) method on brass coatings electroplated from gold solution was investigated by various plating parameters such as plating duration, the anodic duty cycle, the anodic current density and the cathodic current density. The reversed current results in a significant change in the morphology of electrodeposits, improvement of the overall current efficiency and reduction of deposit porosity. With longer pulses, hemispherical surface features are generated, while larger grains result from shorter pulse widths. The porosity of the plated samples is found to decrease compared with results at the same time-average plating rate obtained from DC or Pulse plating. A major impediment to reducing gold later thickness is the corrosion of the underlying substrate, which is affected by the porosity of the gold layer. Both the morphology and the hydrogen evolution reaction have significant impact on porosity. PRC plating affect hydrogen gold and may oxidize hydrogen produced during the cathodic portion of the waveform. Whether the dissolution of gold and oxidation of hydrogen occur depends on the type of plating bath and the plating conditions adapted. In reversed pulse plating, the amount of excess near-surface cyanide is changed after the cathodic current is applied, and the oxidation of gold under these conditions has not been fully addressed. The effects of the current density, pulse-reverse ratio and brightener concentration of the electroplating process were investigated and optimized for suitable performance.

Formation of Ion Beam from High Density Plasma of ECR Discharge

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

Izotov, I.; Razin, S.; Sidorov, A.

2005-03-15

One of the most promising directions of ECR multicharged ion sources evolution is related with increase in frequency of microwave pumping. During last years microwave generators of millimeter wave range - gyrotrons have been used more frequently. Creation of plasma with density 1013 cm-3 with medium charged ions and ion flux density through a plug of a magnetic trap along magnetic field lines on level of a few A/cm2 is possible under pumping by powerful millimeter wave radiation and quasigasdynamic (collisional) regime of plasma confinement in the magnetic trap. Such plasma has great prospects for application in plasma based ionmore » implantation systems for processing of surfaces with complicated and petit relief. Use it for ion beam formation seams to be difficult because of too high ion current density. This paper continues investigations described elsewhere and shows possibility to arrange ion extraction in zone of plasma expansion from the magnetic trap along axis of system and magnetic field lines.Plasma was created at ECR gas discharge by means of millimeter wave radiation of a gyrotron with frequency 37.5 GHz, maximum power 100 kW, pulse duration 1.5 ms. Two and three electrode quasi-Pierce extraction systems were used for ion beam formation.It is demonstrated that there is no changes in ion charge state distribution along expansion routing of plasma under collisional confinement. Also ion flux density decreases with distance from plug of the trap, it allows to control extracting ion current density. Multicharged ion beam of Nitrogen with total current up to 2.5 mA at diameter of extracting hole 1 mm, that corresponds current density 320 mA/cm2, was obtained. Magnitude of total ion current was limited due to extracting voltage (60 kV). Under such conditions characteristic transversal dimension of plasma equaled 4 cm, magnetic field value in extracting zone was about 0.1 T at axisymmetrical configuration.« less

Particle in cell simulation of peaking switch for breakdown evaluation

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

Umbarkar, Sachin B.; Bindu, S.; Mangalvedekar, H.A.

2014-07-01

Marx generator connected to peaking capacitor and peaking switch can generate Ultra-Wideband (UWB) radiation. A new peaking switch is designed for converting the existing nanosecond Marx generator to a UWB source. The paper explains the particle in cell (PIC) simulation for this peaking switch, using MAGIC 3D software. This peaking switch electrode is made up of copper tungsten material and is fixed inside the hermitically sealed derlin material. The switch can withstand a gas pressure up to 13.5 kg/cm{sup 2}. The lower electrode of the switch is connected to the last stage of the Marx generator. Initially Marx generator (withoutmore » peaking stage) in air; gives the output pulse with peak amplitude of 113.75 kV and pulse rise time of 25 ns. Thus, we design a new peaking switch to improve the rise time of output pulse and to pressurize this peaking switch separately (i.e. Marx and peaking switch is at different pressure). The PIC simulation gives the particle charge density, current density, E counter plot, emitted electron current, and particle energy along the axis of gap between electrodes. The charge injection and electric field dependence on ionic dissociation phenomenon are briefly analyzed using this simulation. The model is simulated with different gases (N{sub 2}, H{sub 2}, and Air) under different pressure (2 kg/cm{sup 2}, 5 kg/cm{sup 2}, 10 kg/cm{sup 2}). (author)« less

Assessment of the magnetic field exposure due to the battery current of digital mobile phones.

PubMed

Jokela, Kari; Puranen, Lauri; Sihvonen, Ari-Pekka

2004-01-01

Hand-held digital mobile phones generate pulsed magnetic fields associated with the battery current. The peak value and the waveform of the battery current were measured for seven different models of digital mobile phones, and the results were applied to compute approximately the magnetic flux density and induced currents in the phone-user's head. A simple circular loop model was used for the magnetic field source and a homogeneous sphere consisting of average brain tissue equivalent material simulated the head. The broadband magnetic flux density and the maximal induced current density were compared with the guidelines of ICNIRP using two various approaches. In the first approach the relative exposure was determined separately at each frequency and the exposure ratios were summed to obtain the total exposure (multiple-frequency rule). In the second approach the waveform was weighted in the time domain with a simple low-pass RC filter and the peak value was divided by a peak limit, both derived from the guidelines (weighted peak approach). With the maximum transmitting power (2 W) the measured peak current varied from 1 to 2.7 A. The ICNIRP exposure ratio based on the current density varied from 0.04 to 0.14 for the weighted peak approach and from 0.08 to 0.27 for the multiple-frequency rule. The latter values are considerably greater than the corresponding exposure ratios 0.005 (min) to 0.013 (max) obtained by applying the evaluation based on frequency components presented by the new IEEE standard. Hence, the exposure does not seem to exceed the guidelines. The computed peak magnetic flux density exceeded substantially the derived peak reference level of ICNIRP, but it should be noted that in a near-field exposure the external field strengths are not valid indicators of exposure. Currently, no biological data exist to give a reason for concern about the health effects of magnetic field pulses from mobile phones.

ELF exposure from mobile and cordless phones for the epidemiological MOBI-Kids study.

PubMed

Calderón, Carolina; Ichikawa, Hiroki; Taki, Masao; Wake, Kanako; Addison, Darren; Mee, Terry; Maslanyj, Myron; Kromhout, Hans; Lee, Ae-Kyoung; Sim, Malcolm R; Wiart, Joe; Cardis, Elisabeth

2017-04-01

This paper describes measurements and computational modelling carried out in the MOBI-Kids case-control study to assess the extremely low frequency (ELF) exposure of the brain from use of mobile and cordless phones. Four different communication systems were investigated: Global System for Mobile (GSM), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT) and Wi-Fi Voice over Internet Protocol (VoIP). The magnetic fields produced by the phones during transmission were measured under controlled laboratory conditions, and an equivalent loop was fitted to the data to produce three-dimensional extrapolations of the field. Computational modelling was then used to calculate the induced current density and electric field strength in the brain resulting from exposure to these magnetic fields. Human voxel phantoms of four different ages were used: 8, 11, 14 and adult. The results indicate that the current densities induced in the brain during DECT calls are likely to be an order of magnitude lower than those generated during GSM calls but over twice that during UMTS calls. The average current density during Wi-Fi VoIP calls was found to be lower than for UMTS by 30%, but the variability across the samples investigated was high. Spectral contributions were important to consider in relation to current density, particularly for DECT phones. This study suggests that the spatial distribution of the ELF induced current densities in brain tissues is determined by the physical characteristics of the phone (in particular battery position) while the amplitude is mainly dependent on communication system, thus providing a feasible basis for assessing ELF exposure in the epidemiological study. The number of phantoms was not large enough to provide definitive evidence of an increase of induced current density with age, but the data that are available suggest that, if present, the effect is likely to be very small. Copyright © 2017 Elsevier Ltd. All rights reserved.

Inductively generated streaming plasma ion source

DOEpatents

Glidden, Steven C.; Sanders, Howard D.; Greenly, John B.

2006-07-25

A novel pulsed, neutralized ion beam source is provided. The source uses pulsed inductive breakdown of neutral gas, and magnetic acceleration and control of the resulting plasma, to form a beam. The beam supplies ions for applications requiring excellent control of ion species, low remittance, high current density, and spatial uniformity.

Cell density-dependent differential proliferation of neural stem cells on omnidirectional nanopore-arrayed surface.

PubMed

Cha, Kyoung Je; Kong, Sun-Young; Lee, Ji Soo; Kim, Hyung Woo; Shin, Jae-Yeon; La, Moonwoo; Han, Byung Woo; Kim, Dong Sung; Kim, Hyun-Jung

2017-10-12

Recently, the importance of surface nanotopography in the determination of stem cell fate and behavior has been revealed. In the current study, we generated polystyrene cell-culture dishes with an omnidirectional nanopore arrayed surface (ONAS) (diameter: 200 nm, depth: 500 nm, center-to-center distance: 500 nm) and investigated the effects of nanotopography on rat neural stem cells (NSCs). NSCs cultured on ONAS proliferated better than those on the flat surface when cell density was low and showed less spontaneous differentiation during proliferation in the presence of mitogens. Interestingly, NSCs cultured on ONAS at clonal density demonstrated a propensity to generate neurospheres, whereas those on the flat surface migrated out, proliferated as individuals, and spread out to attach to the surface. However, the differential patterns of proliferation were cell density-dependent since the distinct phenomena were lost when cell density was increased. ONAS modulated cytoskeletal reorganization and inhibited formation of focal adhesion, which is generally observed in NSCs grown on flat surfaces. ONAS appeared to reinforce NSC-NSC interaction, restricted individual cell migration and prohibited NSC attachment to the nanopore surface. These data demonstrate that ONAS maintains NSCs as undifferentiated while retaining multipotency and is a better topography for culturing low density NSCs.

A symmetric supercapacitor/biofuel cell hybrid device based on enzyme-modified nanoporous gold: An autonomous pulse generator.

PubMed

Xiao, Xinxin; Conghaile, Peter Ó; Leech, Dónal; Ludwig, Roland; Magner, Edmond

2017-04-15

The integration of supercapacitors with enzymatic biofuel cells (BFCs) can be used to prepare hybrid devices in order to harvest significantly higher power output. In this study, a supercapacitor/biofuel cell hybrid device was prepared by the immobilisation of redox enzymes with electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) and the redox polymer [Os(2,2'-bipyridine) 2 (polyvinylimidazole) 10 Cl] +/2+ (Os(bpy) 2 PVI) on dealloyed nanoporous gold. The thickness of the deposition layer can be easily controlled by tuning the deposition conditions. Once charged by the internal BFC, the device can be discharged as a supercapacitor at a current density of 2mAcm -2 providing a maximum power density of 608.8μWcm -2 , an increase of a factor of 468 when compared to the power output from the BFC itself. The hybrid device exhibited good operational stability for 50 charge/discharge cycles and ca. 7h at a discharge current density of 0.2mAcm -2 . The device could be used as a pulse generator, mimicking a cardiac pacemaker delivering pulses of 10μA for 0.5ms at a frequency of 0.2Hz. Copyright © 2016 Elsevier B.V. All rights reserved.

Energetic Combustion Devices for Aerospace Propulsion and Power

NASA Technical Reports Server (NTRS)

Litchford, Ron J.

2000-01-01

Chemical reactions have long been the mainstay thermal energy source for aerospace propulsion and power. Although it is widely recognized that the intrinsic energy density limitations of chemical bonds place severe constraints on maximum realizable performance, it will likely be several years before systems based on high energy density nuclear fuels can be placed into routine service. In the mean time, efforts to develop high energy density chemicals and advanced combustion devices which can utilize such energetic fuels may yield worthwhile returns in overall system performance and cost. Current efforts in this vein are being carried out at NASA MSFC under the direction of the author in the areas of pulse detonation engine technology development and light metals combustion devices. Pulse detonation engines are touted as a low cost alternative to gas turbine engines and to conventional rocket engines, but actual performance and cost benefits have yet to be convincingly demonstrated. Light metal fueled engines also offer potential benefits in certain niche applications such as aluminum/CO2 fueled engines for endo-atmospheric Martian propulsion. Light metal fueled MHD generators also present promising opportunities with respect to electric power generation for electromagnetic launch assist. This presentation will discuss the applications potential of these concepts with respect to aero ace propulsion and power and will review the current status of the development efforts.

Langmuir Probe Analysis of Maser-Driven Alfven Waves Using New LaB6 Cathode in LaPD

NASA Astrophysics Data System (ADS)

Clark, Mary; Dorfman, Seth; Zhu, Ziyan; Rossi, Giovanni; Carter, Troy

2015-11-01

Previous research in the Large Plasma Device shows that specific conditions on the magnetic field and cathode discharge voltage allow an Alfven wave to develop in the cathode-anode region. When the speed of bulk electrons (dependent on discharge voltage) entering the region exceeds the Alfven speed, the electrons can excite a wave. This phenomenon mimics one proposed to exist in the Earth's ionosphere. Previous experiments used a cathode coated with Barium Oxide, and this project uses a new cathode coated with Lanthanum Hexaboride (LaB6). The experiment seeks to characterize the behavior of plasmas generated with the LaB6 source, as well as understand properties of the driven wave when using the new cathode. Langmuir probes are used to find electron temperature, ion saturation current, and plasma density. These parameters determine characteristics of the wave. Preliminary analysis implies that density increases with LaB6 discharge voltage until 170 V, where it levels off. A linear increase in density is expected; the plateau implies cathode power does not ionize the plasma after 170 V. It is possible the power is carried out by the generated Alfven wave, or heats the plasma or cathode. This ``missing'' power is currently under investigation. Work funded by DOE and NSF.

Current Flow and Pair Creation at Low Altitude in Rotation-Powered Pulsars' Force-Free Magnetospheres: Space Charge Limited Flow

NASA Technical Reports Server (NTRS)

Timokhin, A. N.; Arons, J.

2013-01-01

We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs.We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 < j/j(sub GJ) < 1), space charge limited acceleration of the current carrying beam is mild, with the full Goldreich-Julian charge density comprising the charge densities of the beam and a cloud of electrically trapped particles with the same sign of charge as the beam. The voltage drops are of the order of mc(sup 2)/e, and pair creation is absent. (b) When the current density exceeds the Goldreich-Julian value (j/j(sub GJ) > 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/j(sub GJ) < 0, the system develops similar bursts of pair creation. These discharges are similar to those encountered in previous calculations by Timokhin of pair creation when the surface has a high work function and cannot freely emit charge. In cases (b) and (c), the intermittently generated pairs allow the system to simultaneously carry the magnetospherically prescribed currents and adjust the charge density and average electric field to force-free conditions. We also elucidate the conditions for pair creating beam flow to be steady (stationary with small fluctuations in the rotating frame), finding that such steady flows can occupy only a small fraction of the current density parameter space exhibited by the force-free magnetospheric model. The generic polar flow dynamics and pair creation are strongly time dependent. The model has an essential difference from almost all previous quantitative studies, in that we sought the accelerating voltage (with pair creation, when the voltage drops are sufficiently large; without, when they are small) as a function of the applied current.

Experimental Design of a Magnetic Flux Compression Experiment

NASA Astrophysics Data System (ADS)

Fuelling, Stephan; Awe, Thomas J.; Bauer, Bruno S.; Goodrich, Tasha; Lindemuth, Irvin R.; Makhin, Volodymyr; Siemon, Richard E.; Atchison, Walter L.; Reinovsky, Robert E.; Salazar, Mike A.; Scudder, David W.; Turchi, Peter J.; Degnan, James H.; Ruden, Edward L.

2007-06-01

Generation of ultrahigh magnetic fields is an interesting topic of high-energy-density physics, and an essential aspect of Magnetized Target Fusion (MTF). To examine plasma formation from conductors impinged upon by ultrahigh magnetic fields, in a geometry similar to that of the MAGO experiments, an experiment is under design to compress magnetic flux in a toroidal cavity, using the Shiva Star or Atlas generator. An initial toroidal bias magnetic field is provided by a current on a central conductor. The central current is generated by diverting a fraction of the liner current using an innovative inductive current divider, thus avoiding the need for an auxiliary power supply. A 50-mm-radius cylindrical aluminum liner implodes along glide planes with velocity of about 5 km/s. Inward liner motion causes electrical closure of the toroidal chamber, after which flux in the chamber is conserved and compressed, yielding magnetic fields of 2-3 MG. Plasma is generated on the liner and central rod surfaces by Ohmic heating. Diagnostics include B-dot probes, Faraday rotation, radiography, filtered photodiodes, and VUV spectroscopy. Optical access to the chamber is provided through small holes in the walls.

Terahertz radiation from accelerating charge carriers in graphene under ultrafast photoexcitation

NASA Astrophysics Data System (ADS)

Rustagi, Avinash; Stanton, C. J.

2016-11-01

We study the generation of terahertz (THz) radiation from the acceleration of ultrafast photoexcited charge carriers in graphene in the presence of a dc electric field. Our model is based on calculating the transient current density from the time-dependent distribution function which is determined using the Boltzmann transport equation (BTE) within a relaxation time approximation. We include the time-dependent generation of carriers by the pump pulse by solving for the carrier generation rate using the optical Bloch equations in the rotating wave approximation (RWA). The linearly polarized pump pulse generates an anisotropic distribution of photoexcited carriers in the kx-ky plane. The collision integral in the Boltzmann equation includes a term that leads to the thermalization of carriers via carrier-carrier scattering to an effective temperature above the lattice temperature, as well as a cooling term, which leads to energy relaxation via inelastic carrier-phonon scattering. The radiated signal is proportional to the time derivative of the transient current density. In spite of the fact that the magnitude of the velocity is the same for all the carriers in graphene, there is still emitted radiation from the photoexcited charge carriers with frequency components in the THz range due to a change in the direction of velocity of the photoexcited carriers in the external electric field as well as cooling of the photoexcited carriers on a subpicosecond time scale.

Two color interferometric electron density measurement in an axially blown arc

NASA Astrophysics Data System (ADS)

Stoller, Patrick; Carstensen, Jan; Galletti, Bernardo; Doiron, Charles; Sokolov, Alexey; Salzmann, René; Simon, Sandor; Jabs, Philipp

2016-09-01

High voltage circuit breakers protect the power grid by interrupting the current in case of a short circuit. To do so an arc is ignited between two contacts as they separate; transonic gas flow is used to cool and ultimately extinguish the arc at a current-zero crossing of the alternating current. A detailed understanding of the arc interruption process is needed to improve circuit breaker design. The conductivity of the partially ionized gas remaining after the current-zero crossing, a key parameter in determining whether the arc will be interrupted or not, is a function of the electron density. The electron density, in turn, is a function of the detailed dynamics of the arc cooling process, which does not necessarily occur under local thermodynamic equilibrium (LTE) conditions. In this work, we measure the spatially resolved line-integrated index of refraction in a near-current-zero arc stabilized in an axial flow of synthetic air with two nanosecond pulsed lasers at wavelengths of 532 nm and 671 nm. Generating a stable, cylindrically symmetric arc enables us to determine the three-dimensional index of refraction distribution using Abel inversion. Due to the wavelength dependence of the component of the index of refraction related to the free electrons, the information at two different wavelengths can be used to determine the electron density. This information allows us to determine how important it is to take into account non-equilibrium effects for accurate modeling of the physics of decaying arcs.

ELECTRIC CURRENT FILAMENTATION AT A NON-POTENTIAL MAGNETIC NULL-POINT DUE TO PRESSURE PERTURBATION

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

Jelínek, P.; Karlický, M.; Murawski, K., E-mail: pjelinek@prf.jcu.cz

2015-10-20

An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with amore » plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh–Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares.« less

Striate cortical contribution to the transcorneal electrically evoked response of the visual system.

PubMed

Shimazu, K; Miyake, Y; Fukatsu, Y; Watanabe, S

1996-01-01

Analyses of current-source-density (CSD) and multiple unit activity (MUA) in area 17 of the cat were performed to determine the sources of the cortical transcorneal electrically evoked response. Cortical field potential, CSD and MUA profiles were obtained with multi-electrodes. CSD findings include: current sinks (inward cell membrane current) within 20 ms latency, in layers 4 and 6 of the striate cortex; current sinks corresponding to N3 (negative component of the EER; latency, 35 ms) in layer 4 and lower layer 3 with current sources (outward cell membrane current) for N3 in the supragranular layers; current sinks with latency over 40 ms in the supragranular layers. In the layers 4 and 6, simultaneous MUA was seen. When the stimulus frequency was increased or with dual stimulation, the N3 current sinks were decreased. This indicates that N1 (latency, 9 ms) and N2 (latency, 20 ms) reflect near-field potentials in layers 4 and 6, generated by geniculocortical afferents, and that N3 is a post- and polysynaptic component. It is also suggested that dipoles composed of cell bodies and the apical dendrites of pyramidal cells of layer 3, generated by satellite cells in layer 4, play a major role in generating N3.

Nonequilibrium Tuning of the Thermal Casimir Effect.

PubMed

Dean, David S; Lu, Bing-Sui; Maggs, A C; Podgornik, Rudolf

2016-06-17

In net-neutral systems correlations between charge fluctuations generate strong attractive thermal Casimir forces and engineering these forces to optimize nanodevice performance is an important challenge. We show how the normal and lateral thermal Casimir forces between two plates containing Brownian charges can be modulated by decorrelating the system through the application of an electric field, which generates a nonequilibrium steady state with a constant current in one or both plates, reducing the ensuing fluctuation-generated normal force while at the same time generating a lateral drag force. This hypothesis is confirmed by detailed numerical simulations as well as an analytical approach based on stochastic density functional theory.

Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse

NASA Astrophysics Data System (ADS)

Grishkov, V. E.; Uryupin, S. A.

2017-03-01

Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse is analyzed within the kinetic approach. It is shown that the most efficient source of plasma waves is the nonlinear current arising due to the gradient of the energy density of the high-frequency field. Generation of plasma waves by the drag current is usually less efficient but not negligibly small at relatively high frequencies of electron-ion collisions. The influence of electron collisions on the excitation of plasma waves by pulses of different duration is described quantitatively.

Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse

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

Grishkov, V. E.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru

Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse is analyzed within the kinetic approach. It is shown that the most efficient source of plasma waves is the nonlinear current arising due to the gradient of the energy density of the high-frequency field. Generation of plasma waves by the drag current is usually less efficient but not negligibly small at relatively high frequencies of electron–ion collisions. The influence of electron collisions on the excitation of plasma waves by pulses of different duration is described quantitatively.

Ion current in a magnetic neutral region - Generation of an incipient magnetopause

NASA Technical Reports Server (NTRS)

Whipple, E. C.; Silevitch, M. B.

1982-01-01

The current contributed by ions trapped in the vicinity of a magnetic X line is calculated. The three dimensional configuration of the neutral region is found to be critical in determining the current in that the escape mechanism and trapping times depend on the three-dimensional aspects. A trapping criterion is defined. In the neutral region the ions can gain substantial kinetic energy, and the current will change the X line configuration in such a way that there will be a positive feedback effect, rapidly forming an extended magnetopauselike structure for even very small incident plasma densities.

Effect of Propellant Flowrate and Purity on Carbon Deposition in LO2/Methane Gas Generators

NASA Technical Reports Server (NTRS)

Bossard, J. A.; Burkhardt, W. M.; Niiya, K. Y.; Braam, F.

1989-01-01

The generation and deposition of carbon was studied in the Carbon Deposition Program using subscale hardware with LO2/Liquid Natural Gas (LNG) and LO2/Methane propellants at low mixture ratios. The purpose of the testing was to evaluate the effect of methane purity and full scale injection density on carbon deposition. The LO2/LNG gas generator/preburner testing was performed at mixture ratios between 0.24 and 0.58 and chamber pressures from 5.8 to 9.4 MPa (840 to 1370 psia). A total of seven 200 second duration tests were performed. The LNG testing occurred at low injection densities, similar to the previous LO2/RP-1, LO2/propane, and LO2/methane testing performed on the carbon deposition program. The current LO2/methane test series occurred at an injection density factor of approximately 10 times higher than the previous testing. The high injection density LO2/methane testing was performed at mixture ratios between from 0.23 to 0.81 and chamber pressures from 6.4 to 15.2 MPa (925 to 2210 psia). A total of nine high injection density tests were performed. The testing performed demonstrated that low purity methane (LNG) did not produce any detectable change in carbon deposition when compared to pure methane. In addition, the C* performance and the combustion gas temperatures measured were similar to those obtained for pure methane. Similar results were obtained testing pure methane at higher propellant injection densities with coarse injector elements.

Enhanced diamagnetic perturbations and electric currents observed downstream of the high power helicon

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

Roberson, B. Race; Winglee, Robert; Prager, James

2011-05-15

The high power helicon (HPH) is capable of producing a high density plasma (10{sup 17}-10{sup 18} m{sup -3}) and directed ion energies greater than 20 eV that continue to increase tens of centimeters downstream of the thruster. In order to understand the coupling mechanism between the helicon antenna and the plasma outside the immediate source region, measurements were made in the plasma plume downstream from the thruster of the propagating wave magnetic field and the perturbation of the axial bulk field using a type 'R' helicon antenna. This magnetic field perturbation ({Delta}B) peaks at more than 15 G in strengthmore » downstream of the plasma source, and is 3-5 times larger than those previously reported from HPH. Taking the curl of this measured magnetic perturbation and assuming azimuthal symmetry suggests that this magnetic field is generated by a (predominantly) azimuthal current ring with a current density on the order of tens of kA m{sup -2}. At this current density the diamagnetic field is intense enough to cancel out the B{sub 0} axial magnetic field near the source region. The presence of the diamagnetic current is important as it demonstrates modification of the vacuum fields well beyond the source region and signifies the presence of a high density, collimated plasma stream. This diamagnetic current also modifies the propagation of the helicon wave, which facilitates a better understanding of coupling between the helicon wave and the resultant plasma acceleration.« less

Nanoscale discharge electrode for minimizing ozone emission from indoor corona devices.

PubMed

Bo, Zheng; Yu, Kehan; Lu, Ganhua; Mao, Shun; Chen, Junhong; Fan, Fa-Gung

2010-08-15

Ground-level ozone emitted from indoor corona devices poses serious health risks to the human respiratory system and the lung function. Federal regulations call for effective techniques to minimize the indoor ozone production. In this work, stable atmospheric corona discharges from nanomaterials are demonstrated using horizontally suspended carbon nanotubes (CNTs) as the discharge electrode. Compared with the conventional discharges employing micro- or macroscale electrodes, the corona discharge from CNTs could initiate and operate at a much lower voltage due to the small electrode diameter, and is thus energy-efficient. Most importantly, the reported discharge is environmentally friendly since no ozone (below the detection limit of 0.5 ppb) was detected for area current densities up to 0.744 A/m(2) due to the significantly reduced number of electrons and plasma volume generated by CNT discharges. The resulting discharge current density depends on the CNT loading. Contrary to the conventional wisdom, negative CNT discharges should be used to enhance the current density owing to the efficient field emission of electrons from the CNT surface.

Electrolyte additive enabled fast charging and stable cycling lithium metal batteries

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

Zheng, Jianming; Engelhard, Mark H.; Mei, Donghai

2017-03-01

Batteries using lithium (Li) metal as anodes are considered promising energy storage systems because of their high energy densities. However, safety concerns associated with dendrite growth along with limited cycle life, especially at high charge current densities, hinder their practical uses. Here we report that an optimal amount (0.05 M) of LiPF6 as an additive in LiTFSI-LiBOB dual-salt/carbonate-solvent-based electrolytes significantly enhances the charging capability and cycling stability of Li metal batteries. In a Li metal battery using a 4-V Li-ion cathode at a moderately high loading of 1.75mAh cm(-2), a cyclability of 97.1% capacity retention after 500 cycles along withmore » very limited increase in electrode overpotential is accomplished at a charge/discharge current density up to 1.75 mA cm(-2). The fast charging and stable cycling performances are ascribed to the generation of a robust and conductive solid electrolyte interphase at the Li metal surface and stabilization of the Al cathode current collector.« less

Wiggler magnetic field assisted third harmonic generation in expanding clusters

NASA Astrophysics Data System (ADS)

Vij, Shivani

2018-04-01

A simple theoretical model is constructed to study the wiggler magnetic field assisted third harmonic generation of intense short pulse laser in a cluster in its expanding phase. The ponderomotive force of laser causes density perturbations in cluster electron density which couples with wiggler magnetic field to produce a nonlinear current that generates transverse third harmonic. An intense short pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls via tunnel ionization. Initially, the electron plasma frequency inside the clusters ω pe > \\sqrt{3}{ω }1 (with ω 1 being the frequency of the laser). As the cluster expands under Coulomb force and hydrodynamic pressure, ω pe decreases to \\sqrt{3}{ω }1. At this time, there is resonant enhancement in the efficiency of the third harmonic generation. The efficiency of third harmonic generation is enhanced due to cluster plasmon resonance and by phase matching due to wiggler magnetic field. The effect of cluster size on the expansion rate is studied to observe that the clusters of different radii would expand differently. The impact of laser intensity and wiggler magnetic field on the efficiency of third harmonic generation is also explored.

Minimized open-circuit voltage reduction in GaAs/InGaAs quantum well solar cells with bandgap-engineered graded quantum well depths

NASA Astrophysics Data System (ADS)

Li, Xiaohan; Dasika, Vaishno D.; Li, Ping-Chun; Ji, Li; Bank, Seth R.; Yu, Edward T.

2014-09-01

The use of InGaAs quantum wells with composition graded across the intrinsic region to increase open-circuit voltage in p-i-n GaAs/InGaAs quantum well solar cells is demonstrated and analyzed. By engineering the band-edge energy profile to reduce photo-generated carrier concentration in the quantum wells at high forward bias, simultaneous increases in both open-circuit voltage and short-circuit current density are achieved, compared to those for a structure with the same average In concentration, but constant rather than graded quantum well composition across the intrinsic region. This approach is combined with light trapping to further increase short-circuit current density.

Electrochemical Treatment of Textile Dye Wastewater by Mild Steel Anode.

PubMed

Bhavya, J G; Rekha, H B; Murthy, Usha N

2014-04-01

This paper presents the results of the treatment of textile dye wastewater generated from a textile processing industry by electrochemical method. Experiments were conducted at current densities of 12, 24 and 48 A/m2 using mild steel as anode and cathode. During the various stages of electrolysis, parameters such as COD, color and BOD5 were determined in order to know the feasibility of electrochemical treatment. It was observed that increasing the electrolysis time and increased current density bring down the concentration of pollutants. Also COD removal rate and energy consumption during the electrolysis were calculated and presented in this paper. The present study proves the effectiveness of electrochemical treatment using MS as anode for TDW oxidation.

Synchronization Tomography: Modeling and Exploring Complex Brain Dynamics

NASA Astrophysics Data System (ADS)

Fieseler, Thomas

2002-03-01

Phase synchronization (PS) plays an important role both under physiological and pathological conditions. With standard averaging techniques of MEG data, it is difficult to reliably detect cortico-cortical and cortico-muscular PS processes that are not time-locked to an external stimulus. For this reason, novel synchronization analysis techniques were developed and directly applied to MEG signals. Of course, due to the lack of an inverse modeling (i.e. source localization), the spatial resolution of this approach was limited. To detect and localize cerebral PS, we here present the synchronization tomography (ST): For this, we first estimate the cerebral current source density by means of the magnetic field tomography (MFT). We then apply the single-run PS analysis to the current source density in each voxel of the reconstruction space. In this way we study simulated PS, voxel by voxel in order to determine the spatio-temporal resolution of the ST. To this end different generators of ongoing rhythmic cerebral activity are simulated by current dipoles at different locations and directions, which are modeled by slightly detuned chaotic oscillators. MEG signals for these generators are simulated for a spherical head model and a whole-head MEG system. MFT current density solutions are calculated from these simulated signals within a hemispherical source space. We compare the spatial resolution of the ST with that of the MFT. Our results show that adjacent sources which are indistinguishable for the MFT, can nevertheless be separated with the ST, provided they are not strongly phase synchronized. This clearly demonstrates the potential of combining spatial information (i.e. source localization) with temporal information for the anatomical localization of phase synchronization in the human brain.

Observation of a stationary, current-free double layer in a plasma

NASA Technical Reports Server (NTRS)

Hairapetian, G.; Stenzel, R. L.

1990-01-01

A stationary, current-free, potential double layer is formed in a two-electron-population plasma due to self-consistent separation of the two electron species. The position and amplitude of the double layer are controlled by the relative densities of the two electron populations. The steady-state double layer traps the colder electrons on the high potential side, and generates a neutralized, monoenergetic ion beam on the low potential side. The field-aligned double layer is annihilated when an electron current is drawn through the plasma.

Turbidity Currents In The Ocean; Are They Stably Stratified?

NASA Astrophysics Data System (ADS)

Kneller, B. C.; Nasr-Azadani, M.; Meiburg, E. H.

2013-12-01

A large proportion of the sediment generated by erosion of the continents is ultimately delivered to the deep ocean to form submarine fans, being carried to the margins of these fans by turbidity currents that flow through submarine channels that may be hundreds or even thousands of kilometers long. The persistence of these flows over extremely long distances with gradients that may be 10-4 or less, while maintaining sediment as coarse as fine-grained sand in suspension, is enigmatic, given the drag that one would expect to be experienced by such flows, and the effects of progressive dilution by entrainment of ambient seawater. The commonly-held view of the flow structure of turbidity currents, based on many laboratory and numerical simulations and rare observations in the ocean, is that of a vertical profile of time-averaged horizontal velocity with a maximum value close the bed, largely due to much higher drag on the upper boundary than on the lower. This upper boundary drag is related to Kelvin-Helmholtz (K-H) instabilities generated by shear between the current and the ambient seawater. K-H instabilities result when fluid shear dominates over density stratification within the turbidity current; the dimensionless ratio of these two influences is the gradient Richardson number. When this exceeds a value of 0.25 the stratification is stable, and no K-H instabilities will form, eliminating much of the drag and entrainment. The majority of the entrainment of ambient seawater into the turbidity current also occurs via the K-H instabilities. Analysis by Birman et al. (2009) suggests that there may be little or no entrainment of ambient fluid in turbidity currents flowing over low gradients, implying that K-H instabilities may be absent under these conditions. We examine the case of flows on the extremely low gradients of the ocean floor, and suggest some conditions that may lead to stably-stratified currents, with dramatically reduced drag, and a fundamentally different mean and turbulent velocity structure. We report preliminary results of direct numerical simulations that may help to constrain the conditions under which such currents may form. In order to model accurately the potentially stabilizing effect of significant density gradients within such currents, it may be useful to abandon the Boussinesq approximation (under which density variations appear only in the buoyancy term), and explicitly model the influence of density variations. Experiments reported by Sequeiros at al. (2010) show the type of velocity profiles expected in flows without K-H instabilities, which they relate to Froude-subcritical flow. We suggest that the presence of stable density stratification is far more representative of the structure of turbidity currents in long fan channels than are the more familiar profiles commonly reported. Birman, V.K., Meiburg, E. & Kneller, B., 2009. J. Fluid Mech., 619, 367-376. Sequeiros, O. E.; Spinewine, B., Beaubouef, R.T., Sun, T. García, M.H. & Parker, G. 2010. J. Hydr. Eng, 136, 412-433

Strong terahertz radiation from relativistic laser interaction with solid density plasmas

NASA Astrophysics Data System (ADS)

Li, Y. T.; Li, C.; Zhou, M. L.; Wang, W. M.; Du, F.; Ding, W. J.; Lin, X. X.; Liu, F.; Sheng, Z. M.; Peng, X. Y.; Chen, L. M.; Ma, J. L.; Lu, X.; Wang, Z. H.; Wei, Z. Y.; Zhang, J.

2012-06-01

We report a plasma-based strong THz source generated in intense laser-solid interactions at relativistic intensities >1018 W/cm2. Energies up to 50 μJ/sr per THz pulse is observed when the laser pulses are incident onto a copper foil at 67.5°. The temporal properties of the THz radiation are measured by a single shot, electro-optic sampling method with a chirped laser pulse. The THz radiation is attributed to the self-organized transient fast electron currents formed along the target surface. Such a source allows potential applications in THz nonlinear physics and provides a diagnostic of transient currents generated in intense laser-solid interactions.

Single-friction-surface triboelectric generator with human body conduit

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

Meng, Bo; Cheng, Xiaoliang; Zhang, Xiaosheng

2014-03-10

We present a transparent single-friction-surface triboelectric generator (STEG) employing human body as the conduit, making the applications of STEG in portable electronics much more practical and leading to a significant output improvement. The STEG with micro-patterned polydimethylsiloxane surface achieved an output voltage of over 200 V with a current density of 4.7 μA/cm{sup 2}. With human body conduit, the output current increased by 39% and the amount of charge that transferred increased by 34% compared to the results with grounded electrode. A larger increment of 210% and 81% was obtained in the case of STEG with a large-size flat polyethylenemore » terephthalate surface.« less

Charge generation layers for solution processed tandem organic light emitting diodes with regular device architecture.

PubMed

Höfle, Stefan; Bernhard, Christoph; Bruns, Michael; Kübel, Christian; Scherer, Torsten; Lemmer, Uli; Colsmann, Alexander

2015-04-22

Tandem organic light emitting diodes (OLEDs) utilizing fluorescent polymers in both sub-OLEDs and a regular device architecture were fabricated from solution, and their structure and performance characterized. The charge carrier generation layer comprised a zinc oxide layer, modified by a polyethylenimine interface dipole, for electron injection and either MoO3, WO3, or VOx for hole injection into the adjacent sub-OLEDs. ToF-SIMS investigations and STEM-EDX mapping verified the distinct functional layers throughout the layer stack. At a given device current density, the current efficiencies of both sub-OLEDs add up to a maximum of 25 cd/A, indicating a properly working tandem OLED.

Thermoelectric Generation Using Counter-Flows of Ideal Fluids

NASA Astrophysics Data System (ADS)

Meng, Xiangning; Lu, Baiyi; Zhu, Miaoyong; Suzuki, Ryosuke O.

2017-08-01

Thermoelectric (TE) performance of a three-dimensional (3-D) TE module is examined by exposing it between a pair of counter-flows of ideal fluids. The ideal fluids are thermal sources of TE module flow in the opposite direction at the same flow rate and generate temperature differences on the hot and cold surfaces due to their different temperatures at the channel inlet. TE performance caused by different inlet temperatures of thermal fluids are numerically analyzed by using the finite-volume method on 3-D meshed physical models and then compared with those using a constant boundary temperature. The results show that voltage and current of the TE module increase gradually from a beginning moment to a steady flow and reach a stable value. The stable values increase with inlet temperature of the hot fluid when the inlet temperature of cold fluid is fixed. However, the time to get to the stable values is almost consistent for all the temperature differences. Moreover, the trend of TE performance using a fluid flow boundary is similar to that of using a constant boundary temperature. Furthermore, 3-D contours of fluid pressure, temperature, enthalpy, electromotive force, current density and heat flux are exhibited in order to clarify the influence of counter-flows of ideal fluids on TE generation. The current density and heat flux homogeneously distribute on an entire TE module, thus indicating that the counter-flows of thermal fluids have high potential to bring about fine performance for TE modules.

Increase in Ca2+ current by sustained cAMP levels enhances proliferation rate in GH3 cells.

PubMed

Rodrigues, Andréia Laura; Brescia, Marcella; Koschinski, Andreas; Moreira, Thaís Helena; Cameron, Ryan T; Baillie, George; Beirão, Paulo S L; Zaccolo, Manuela; Cruz, Jader S

2018-01-01

Ca 2+ and cAMP are important intracellular modulators. In order to generate intracellular signals with various amplitudes, as well as different temporal and spatial properties, a tightly and precise control of these modulators in intracellular compartments is necessary. The aim of this study was to evaluate the effects of elevated and sustained cAMP levels on voltage-dependent Ca 2+ currents and proliferation in pituitary tumor GH3 cells. Effect of long-term exposure to forskolin and dibutyryl-cyclic AMP (dbcAMP) on Ca 2+ current density and cell proliferation rate were determined by using the whole-cell patch-clamp technique and real time cell monitoring system. The cAMP levels were assayed, after exposing transfected GH3 cells with the EPAC-1 cAMP sensor to forskolin and dbcAMP, by FRET analysis. Sustained forskolin treatment (24 and 48h) induced a significant increase in total Ca 2+ current density in GH3 cells. Accordingly, dibutyryl-cAMP incubation (dbcAMP) also elicited increase in Ca 2+ current density. However, the maximum effect of dbcAMP occurred only after 72h incubation, whereas forskolin showed maximal effect at 48h. FRET-experiments confirmed that the time-course to elevate intracellular cAMP was distinct between forskolin and dbcAMP. Mibefradil inhibited the fast inactivating current component selectively, indicating the recruitment of T-type Ca 2+ channels. A significant increase on cell proliferation rate, which could be related to the elevated and sustained intracellular levels of cAMP was observed. We conclude that maintaining high levels of intracellular cAMP will cause an increase in Ca 2+ current density and this phenomenon impacts proliferation rate in GH3 cells. Copyright © 2017 Elsevier Inc. All rights reserved.

Long life electrodes for large-area x-ray generators

NASA Technical Reports Server (NTRS)

Rothe, Dietmar E. (Inventor)

1991-01-01

This invention is directed to rugged, reliable, and long-life electrodes for use in large-area, high-current-density electron gun and x-ray generators which are employed as contamination-free preionizers for high-energy pulsed gas lasers. The electron source at the cathode is a corona plasma formed at the interface between a conductor, or semiconductor, and a high-permittivity dielectric. Detailed descriptions are provided of a reliable cold plasma cathode, as well as an efficient liquid-cooled electron beam target (anode) and x-ray generator which concentrates the x-ray flux in the direction of an x-ray window.

Self-Assembled Array of Tethered Manganese Oxide Nanoparticles for the Next Generation of Energy Storage

PubMed Central

Stevens, Tyler E.; Pearce, Charles J.; Whitten, Caleah N.; Grant, Richard P.; Monson, Todd C.

2017-01-01

Many challenges must be overcome in order to create reliable electrochemical energy storage devices with not only high energy but also high power densities. Gaps exist in both battery and supercapacitor technologies, with neither one satisfying the need for both large power and energy densities in a single device. To begin addressing these challenges (and others), we report a process to create a self-assembled array of electrochemically active nanoparticles bound directly to a current collector using extremely short (2 nm or less) conductive tethers. The tethered array of nanoparticles, MnO in this case, bound directly to a gold current collector via short conducting linkages eliminates the need for fillers, resulting in a material which achieves 99.9% active material by mass (excluding the current collector). This strategy is expected to be both scalable as well as effective for alternative tethers and metal oxide nanoparticles. PMID:28287183

Application of the monolithic solid oxide fuel cell to space power systems

NASA Astrophysics Data System (ADS)

Myles, Kevin M.; Bhattacharyya, Samit K.

1991-01-01

The monolithic solid-oxide fuel cell (MSOFC) is a promising electrochemical power generation device that is currently under development at Argonne National Laboratory. The extremely high power density of the MSOFC leads to MSOFC systems that have sufficiently high energy densities that they are excellent candidates for a number of space missions. The fuel cell can also be operated in reverse, if it can be coupled to an external power source, to regenerate the fuel and oxidant from the water product. This feature further enhances the potential mission applications of the MSOFC. In this paper, the current status of the fuel cell development is presented—the focus being on fabrication and currently achievable performance. In addition, a specific example of a space power system, featuring a liquid metal cooled fast spectrum nuclear reactor and a monolithic solid oxide fuel cell, is presented to demonstrate the features of an integrated system.

Origin of nonsaturating linear magnetoresistivity

NASA Astrophysics Data System (ADS)

Kisslinger, Ferdinand; Ott, Christian; Weber, Heiko B.

2017-01-01

The observation of nonsaturating classical linear magnetoresistivity has been an enigmatic phenomenon in solid-state physics. We present a study of a two-dimensional ohmic conductor, including local Hall effect and a self-consistent consideration of the environment. An equivalent-circuit scheme delivers a simple and convincing argument why the magnetoresistivity is linear in strong magnetic field, provided that current and biasing electric field are misaligned by a nonlocal mechanism. A finite-element model of a two-dimensional conductor is suited to display the situations that create such deviating currents. Besides edge effects next to electrodes, charge carrier density fluctuations are efficiently generating this effect. However, mobility fluctuations that have frequently been related to linear magnetoresistivity are barely relevant. Despite its rare observation, linear magnetoresitivity is rather the rule than the exception in a regime of low charge carrier densities, misaligned current pathways and strong magnetic field.

Experimental research of different plasma cathodes for generation of high-current electron beams

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

Shafir, G.; Kreif, M.; Gleizer, J. Z.

2015-11-21

The results of experimental studies of different types of cathodes—carbon-epoxy rods, carbon-epoxy capillary, edged graphite, and metal-dielectric—under the application of high-voltage pulses with an amplitude of several hundreds of kV and pulse duration of several nanoseconds are presented. The best diode performance was achieved with the edged graphite and carbon-epoxy-based cathodes characterized by uniform and fast (<1 ns) formation of explosive emission plasma spots and quasi-constant diode impedance. This result was achieved for both annular cathodes in a strong magnetic field and planar cathodes of a similar diameter (∼2 cm) with no external magnetic field. The cathodes based on carbon-epoxy rods andmore » carbon-epoxy capillaries operating with an average current density up to 1 kA/cm{sup 2} showed insignificant erosion along 10{sup 6} pulses of the generator and the generated electron beam current showed excellent reproducibility in terms of the amplitude and waveform.« less

Evaluation of Lightning Incidence to Elements of a Complex Structure: A Monte Carlo Approach

NASA Technical Reports Server (NTRS)

Mata, Carlos T.; Rakov, V. A.

2008-01-01

There are complex structures for which the installation and positioning of the lightning protection system (LPS) cannot be done using the lightning protection standard guidelines. As a result, there are some "unprotected" or "exposed" areas. In an effort to quantify the lightning threat to these areas, a Monte Carlo statistical tool has been developed. This statistical tool uses two random number generators: a uniform distribution to generate the origin of downward propagating leaders and a lognormal distribution to generate the corresponding returns stroke peak currents. Downward leaders propagate vertically downward and their striking distances are defined by the polarity and peak current. Following the electrogeometrical concept, we assume that the leader attaches to the closest object within its striking distance. The statistical analysis is run for N number of years with an assumed ground flash density and the output of the program is the probability of direct attachment to objects of interest with its corresponding peak current distribution.

Influence of supporting electrolyte in electricity generation and degradation of organic pollutants in photocatalytic fuel cell.

PubMed

Khalik, Wan Fadhilah; Ong, Soon-An; Ho, Li-Ngee; Wong, Yee-Shian; Voon, Chun-Hong; Yusuf, Sara Yasina; Yusoff, Nik Athirah; Lee, Sin-Li

2016-08-01

This study investigated the effect of different supporting electrolyte (Na2SO4, MgSO4, NaCl) in degradation of Reactive Black 5 (RB5) and generation of electricity. Zinc oxide (ZnO) was immobilized onto carbon felt acted as photoanode, while Pt-coated carbon paper as photocathode was placed in a single chamber photocatalytic fuel cell, which then irradiated by UV lamp for 24 h. The degradation and mineralization of RB5 with 0.1 M NaCl rapidly decreased after 24-h irradiation time, followed by MgSO4, Na2SO4 and without electrolyte. The voltage outputs for Na2SO4, MgSO4 and NaCl were 908, 628 and 523 mV, respectively, after 24-h irradiation time; meanwhile, their short-circuit current density, J SC, was 1.3, 1.2 and 1.05 mA cm(-2), respectively. The power densities for Na2SO4, MgSO4 and NaCl were 0.335, 0.256 and 0.245 mW cm(-2), respectively. On the other hand, for without supporting electrolyte, the voltage output and short-circuit current density was 271.6 mV and 0.055 mA cm(-2), respectively. The supporting electrolyte NaCl showed greater performance in degradation of RB5 and generation of electricity due to the formation of superoxide radical anions which enhance the degradation of dye. The mineralization of RB5 with different supporting electrolyte was measured through spectrum analysis and reduction in COD concentration.

Evaluation and characterization of fetal exposures to low frequency magnetic fields generated by laptop computers.

PubMed

Zoppetti, Nicola; Andreuccetti, Daniele; Bellieni, Carlo; Bogi, Andrea; Pinto, Iole

2011-12-01

Portable - or "laptop" - computers (LCs) are widely and increasingly used all over the world. Since LCs are often used in tight contact with the body even by pregnant women, fetal exposures to low frequency magnetic fields generated by these units can occur. LC emissions are usually characterized by complex waveforms and are often generated by the main AC power supply (when connected) and by the display power supply sub-system. In the present study, low frequency magnetic field emissions were measured for a set of five models of portable computers. For each of them, the magnetic flux density was characterized in terms not just of field amplitude, but also of the so called "weighted peak" (WP) index, introduced in the 2003 ICNIRP Statement on complex waveforms and confirmed in the 2010 ICNIRP Guidelines for low frequency fields. For the model of LC presenting the higher emission, a deeper analysis was also carried out, using numerical dosimetry techniques to calculate internal quantities (current density and in-situ electric field) with reference to a digital body model of a pregnant woman. Since internal quantities have complex waveforms too, the concept of WP index was extended to them, considering the ICNIRP basic restrictions defined in the 1998 Guidelines for the current density and in the 2010 Guidelines for the in-situ electric field. Induced quantities and WP indexes were computed using an appropriate original formulation of the well known Scalar Potential Finite Difference (SPFD) numerical method for electromagnetic dosimetry in quasi-static conditions. Copyright © 2011 Elsevier Ltd. All rights reserved.

Characterization of Exoelectrogenic Bacteria Enterobacter Strains Isolated from a Microbial Fuel Cell Exposed to Copper Shock Load

PubMed Central

Feng, Cuijie; Li, Jiangwei; Qin, Dan; Chen, Lixiang; Zhao, Feng; Chen, Shaohua; Hu, Hongbo; Yu, Chang-Ping

2014-01-01

Microorganisms capable of generating electricity in microbial fuel cells (MFCs) have gained increasing interest. Here fourteen exoelectrogenic bacterial strains were isolated from the anodic biofilm in an MFC before and after copper (Cu) shock load by Hungate roll-tube technique with solid ferric (III) oxide as an electron acceptor and acetate as an electron donor. Phylogenetic analysis of the 16S rRNA gene sequences revealed that they were all closely related to Enterobacter ludwigii DSM 16688T within the Enterobacteriaceae family, although these isolated bacteria showed slightly different morphology before and after Cu shock load. Two representative strains R2B1 (before Cu shock load) and B4B2 (after Cu shock load) were chosen for further analysis. B4B2 is resistant to 200 mg L−1 of Cu(II) while R2B1 is not, which indicated the potential selection of the Cu shock load. Raman analysis revealed that both R2B1 and B4B2 contained c-type cytochromes. Cyclic voltammetry measurements revealed that strain R2B1 had the capacity to transfer electrons to electrodes. The experimental results demonstrated that strain R2B1 was capable of utilizing a wide range of substrates, including Luria-Bertani (LB) broth, cellulose, acetate, citrate, glucose, sucrose, glycerol and lactose to generate electricity, with the highest current density of 440 mA·m−2 generated from LB-fed MFC. Further experiments indicated that the bacterial cell density had potential correlation with the current density. PMID:25412475

Turbulent mixing and fluid transport within Florida Bay seagrass meadows

NASA Astrophysics Data System (ADS)

Hansen, Jennifer C. R.; Reidenbach, Matthew A.

2017-10-01

Seagrasses serve an important function in the ecology of Florida Bay, providing critical nursery habitat and a food source for a variety of organisms. They also create significant benthic structure that induces drag, altering local hydrodynamics that can influence mixing and nutrient dynamics. Thalassia testudinum seagrass meadows were investigated to determine how shoot density and morphometrics alter local wave conditions, the generation of turbulence, and fluid exchange above and within the canopy. Sparsely vegetated and densely vegetated meadows were monitored, with shoot densities of 259 ± 26 and 484 ± 78 shoots m-2, respectively. The temporal and spatial structure of velocity and turbulence were measured using acoustic Doppler velocimeters and an in situ particle image velocimetry (PIV) system positioned both above and within the seagrass canopy. The retention of fluid within the canopy was determined by examining e-folding times calculated from the concentration curves of dye plumes released within the seagrass canopy. Results show that a shear layer with an inflection point develops at the top of the seagrass canopy, which generates instabilities that impart turbulence into the seagrass meadow. Compared to the overlying water column, turbulence was enhanced within the sparse canopy due to flow interaction with the seagrass blades, but reduced within the dense canopy. Wave generated oscillatory motion penetrated deeper into the canopy than unidirectional currents, enhancing fluid exchange. Both shoot density and the relative magnitude of wave- versus current-driven flow conditions were found to be important controls on turbulent exchange of water masses across the canopy-water interface.

Modelling the electric field and the current density generated by cerebellar transcranial DC stimulation in humans.

PubMed

Parazzini, Marta; Rossi, Elena; Ferrucci, Roberta; Liorni, Ilaria; Priori, Alberto; Ravazzani, Paolo

2014-03-01

Transcranial Direct Current Stimulation (tDCS) over the cerebellum (or cerebellar tDCS) modulates working memory, changes cerebello-brain interaction, and affects locomotion in humans. Also, the use of tDCS has been proposed for the treatment of disorders characterized by cerebellar dysfunction. Nonetheless, the electric field (E) and current density (J) spatial distributions generated by cerebellar tDCS are unknown. This work aimed to estimate E and J distributions during cerebellar tDCS. Computational electromagnetics techniques were applied in three human realistic models of different ages and gender. The stronger E and J occurred mainly in the cerebellar cortex, with some spread (up to 4%) toward the occipital cortex. Also, changes by ±1cm in the position of the active electrode resulted in a small effect (up to 4%) in the E and J spatial distribution in the cerebellum. Finally, the E and J spreads to the brainstem and the heart were negligible, thus further supporting the safety of this technique. Despite inter-individual differences, our modeling study confirms that the cerebellum is the structure mainly involved by cerebellar tDCS. Modeling approach reveals that during cerebellar tDCS the current spread to other structures outside the cerebellum is unlike to produce functional effects. Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Experimental investigation and numerical modelling of positive corona discharge: ozone generation

NASA Astrophysics Data System (ADS)

Yanallah, K; Pontiga, F; Fernández-Rueda, A; Castellanos, A

2009-03-01

The spatial distribution of the species generated in a wire-cylinder positive corona discharge in pure oxygen has been computed using a plasma chemistry model that includes the most significant reactions between electrons, ions, atoms and molecules. The plasma chemistry model is included in the continuity equations of each species, which are coupled with Poisson's equation for the electric field and the energy conservation equation for the gas temperature. The current-voltage characteristic measured in the experiments has been used as an input data to the numerical simulation. The numerical model is able to reproduce the basic structure of the positive corona discharge and highlights the importance of Joule heating on ozone generation. The average ozone density has been computed as a function of current intensity and compared with the experimental measurements of ozone concentration determined by UV absorption spectroscopy.

Giga-seal formation alters properties of sodium channels of human myoballs.

PubMed

Fahlke, C; Rüdel, R

1992-03-01

The influence of giga-seal formation on the properties of the Na+ channels within the covered membrane patch was investigated with a whole-cell pipette and a patch pipette applied to the same cell. Current kinetics, current/voltage relation and channel densities were determined in three combinations: (i) voltage-clamping and current recording with the whole-cell pipette, (ii) voltage-clamping with the whole-cell pipette and current recording with the patch pipette and, (iii) voltage-clamping and current recording with the patch pipette. The Hodgkin-Huxley (1952) parameters tau m and tau h were smaller for the patch currents than for the whole cell, and the h infinity curve was shifted in the negative direction. The channel density was of the order of 10 times smaller. All effects were independent of the extracellular Ca2+ concentration. The capacitive current generated in the patch by the whole-cell Na+ current and its effect on the transmembrane voltage of the patch were evaluated. The kinetic parameters of the Na+ channels in the patch did not depend on whether the voltage was clamped with the whole-cell pipette or the patch pipette. Thus, the results are not due to spurious voltage.

Current source density correlates of cerebellar Golgi and Purkinje cell responses to tactile input

PubMed Central

Tahon, Koen; Wijnants, Mike; De Schutter, Erik

2011-01-01

The overall circuitry of the cerebellar cortex has been known for over a century, but the function of many synaptic connections remains poorly characterized in vivo. We used a one-dimensional multielectrode probe to estimate the current source density (CSD) of Crus IIa in response to perioral tactile stimuli in anesthetized rats and to correlate current sinks and sources to changes in the spike rate of corecorded Golgi and Purkinje cells. The punctate stimuli evoked two distinct early waves of excitation (at <10 and ∼20 ms) associated with current sinks in the granular layer. The second wave was putatively of corticopontine origin, and its associated sink was located higher in the granular layer than the first trigeminal sink. The distinctive patterns of granular-layer sinks correlated with the spike responses of corecorded Golgi cells. In general, Golgi cell spike responses could be linearly reconstructed from the CSD profile. A dip in simple-spike activity of coregistered Purkinje cells correlated with a current source deep in the molecular layer, probably generated by basket cell synapses, interspersed between sparse early sinks presumably generated by synapses from granule cells. The late (>30 ms) enhancement of simple-spike activity in Purkinje cells was characterized by the absence of simultaneous sinks in the granular layer and by the suppression of corecorded Golgi cell activity, pointing at inhibition of Golgi cells by Purkinje axon collaterals as a likely mechanism of late Purkinje cell excitation. PMID:21228303

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

Polat, Ozgur; Ertugrul, Memhet; Thompson, James R

To obtain an engineered surface for deposition of high-Tc superconductors, nanoscale modulations of the surface of the underlying LaMnO3 (LMO) cap layer is a potential source for generating microstructural defects in YBa2Cu3O7- (YBCO) films. These defects may improve the flux-pinning and consequently increase the critical current density, Jc. To provide such nanoscale modulation via a practical and scalable process, tantalum (Ta) and palladium (Pd) nano-islands were deposited using dc-magnetron sputtering on the surface of the cap layer of commercial metal tape templates for second-generation wires. The size and density of these nano-islands can be controlled by changing sputtering conditions suchmore » as the power and deposition time. Compared to the reference sample grown on an untreated LMO cap layer, the YBCO films grown on the LMO cap layers with Ta or Pd nano-islands exhibited improved in-field Jc performance. Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) were used to assess the evolving size and density of the nano-islands.« less

Tunable High-Intensity Electron Bunch Train Production Based on Nonlinear Longitudinal Space Charge Oscillation

NASA Astrophysics Data System (ADS)

Zhang, Zhen; Yan, Lixin; Du, Yingchao; Zhou, Zheng; Su, Xiaolu; Zheng, Lianmin; Wang, Dong; Tian, Qili; Wang, Wei; Shi, Jiaru; Chen, Huaibi; Huang, Wenhui; Gai, Wei; Tang, Chuanxiang

2016-05-01

High-intensity trains of electron bunches with tunable picosecond spacing are produced and measured experimentally with the goal of generating terahertz (THz) radiation. By imposing an initial density modulation on a relativistic electron beam and controlling the charge density over the beam propagation, density spikes of several-hundred-ampere peak current in the temporal profile, which are several times higher than the initial amplitudes, have been observed for the first time. We also demonstrate that the periodic spacing of the bunch train can be varied continuously either by tuning launching phase of a radio-frequency gun or by tuning the compression of a downstream magnetic chicane. Narrow-band coherent THz radiation from the bunch train was also measured with μ J -level energies and tunable central frequency of the spectrum in the range of ˜0.5 to 1.6 THz. Our results pave the way towards generating mJ-level narrow-band coherent THz radiation and driving high-gradient wakefield-based acceleration.

Tunable High-Intensity Electron Bunch Train Production Based on Nonlinear Longitudinal Space Charge Oscillation

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

Zhang, Zhen; Yan, Lixin; Du, Yingchao

2016-05-05

High-intensity trains of electron bunches with tunable picosecond spacing are produced and measured experimentally with the goal of generating terahertz (THz) radiation. By imposing an initial density modulation on a relativistic electron beam and controlling the charge density over the beam propagation, density spikes of several-hundred-ampere peak current in the temporal profile, which are several times higher than the initial amplitudes, have been observed for the first time. We also demonstrate that the periodic spacing of the bunch train can be varied continuously either by tuning launching phase of a radiofrequency gun or by tuning the compression of a downstreammore » magnetic chicane. Narrow-band coherent THz radiation from the bunch train was also measured with μJ-level energies and tunable central frequency of the spectrum in the range of ~0.5 to 1.6 THz. Our results pave the way towards generating mJ-level narrow-band coherent THz radiation and driving high-gradient wakefield-based acceleration.« less

Trains of electron micro-bunches in plasma wake-field acceleration

NASA Astrophysics Data System (ADS)

Lécz, Zsolt; Andreev, Alexander; Konoplev, Ivan; Seryi, Andrei; Smith, Jonathan

2018-07-01

Plasma-based charged particle accelerators have been intensively investigated in the past three decades due to their capability to open up new horizons in accelerator science and particle physics yielding electric field accelerating gradient more than three orders of magnitudes higher than in conventional devices. At the current stage the most advanced and reliable mechanism for accelerating electrons is based on the propagation of an intense laser pulse or a relativistic electron beam in a low density gaseous target. In this paper we concentrate on the electron beam-driven plasma wake-field acceleration and demonstrate using 3D PiC simulations that a train of electron micro-bunches with ∼10 fs period can be generated behind the driving beam propagating in a density down-ramp. We will discuss the conditions and properties of the micro-bunches generated aiming at understanding and study of multi-bunch mechanism of injection. It is show that the periodicity and duration of micro-bunches can be controlled by adjusting the plasma density gradient and driving beam charge.

Photo-electrochemical communication between cyanobacteria (Leptolyngbia sp.) and osmium redox polymer modified electrodes.

PubMed

Hasan, Kamrul; Bekir Yildiz, Huseyin; Sperling, Eva; Conghaile, Peter Ó; Packer, Michael A; Leech, Dónal; Hägerhäll, Cecilia; Gorton, Lo

2014-12-07

Photosynthetic microbial fuel cells (PMFCs) are an emerging technology for renewable solar energy conversion. Major efforts have been made to explore the electrogenic activity of cyanobacteria, mostly using practically unsustainable reagents. Here we report on photocurrent generation (≈8.64 μA cm(-2)) from cyanobacteria immobilized on electrodes modified with an efficient electron mediator, an Os(2+/3+) redox polymer. Upon addition of ferricyanide to the electrolyte, cyanobacteria generate the maximum current density of ≈48.2 μA cm(-2).

The high voltage homopolar generator

NASA Astrophysics Data System (ADS)

Price, J. H.; Gully, J. H.; Driga, M. D.

1986-11-01

System and component design features of proposed high voltage homopolar generator (HVHPG) are described. The system is to have an open circuit voltage of 500 V, a peak output current of 500 kA, 3.25 MJ of stored inertial energy and possess an average magnetic-flux density of 5 T. Stator assembly components are discussed, including the stator, mount structure, hydrostatic bearings, main and motoring brushgears and rotor. Planned operational procedures such as monitoring the rotor to full speed and operation with a superconducting field coil are delineated.

Static feed water electrolysis module

NASA Technical Reports Server (NTRS)

Powell, J. D.; Schubert, F. H.; Jensen, F. C.

1974-01-01

An advanced static feed water electrolysis module (SFWEM) and associated instrumentation for generating breathable O2 was developed. The system also generates a H2 byproduct for use in an air revitalization system for O2 recovery from metabolic CO2. Special attention was given to: (1) eliminating water feed compartment degassing, (2) eliminating need for zero gravity condenser/separators, (3) increasing current density capability, and (4) providing a self contained module so that operation is independent of laboratory instrumentation and complicated startup/shutdown procedures.

Can amorphization take place in nanoscale interconnects?

PubMed

Kumar, S; Joshi, K L; van Duin, A C T; Haque, M A

2012-03-09

The trend of miniaturization has highlighted the problems of heat dissipation and electromigration in nanoelectronic device interconnects, but not amorphization. While amorphization is known to be a high pressure and/or temperature phenomenon, we argue that defect density is the key factor, while temperature and pressure are only the means. For nanoscale interconnects carrying modest current density, large vacancy concentrations may be generated without the necessity of high temperature or pressure due to the large fraction of grain boundaries and triple points. To investigate this hypothesis, we performed in situ transmission electron microscope (TEM) experiments on 200 nm thick (80 nm average grain size) aluminum specimens. Electron diffraction patterns indicate partial amorphization at modest current density of about 10(5) A cm(-2), which is too low to trigger electromigration. Since amorphization results in drastic decrease in mechanical ductility as well as electrical and thermal conductivity, further increase in current density to about 7 × 10(5) A cm(-2) resulted in brittle fracture failure. Our molecular dynamics (MD) simulations predict the formation of amorphous regions in response to large mechanical stresses (due to nanoscale grain size) and excess vacancies at the cathode side of the thin films. The findings of this study suggest that amorphization can precede electromigration and thereby play a vital role in the reliability of micro/nanoelectronic devices.

Lower Hybrid Wave Induced SOL Emissivity Variation at High Density on the Alcator C-Mod Tokamak

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

Faust, I.; Terry, J. L.; Reinke, M. L.

Lower Hybrid Current Drive (LHCD) in the Alcator C-Mod tokamak provides current profile control for the generation of Advanced Tokamak (AT) plasmas. Non-thermal electron bremsstrahlung emission decreases dramatically at n-bar{sub e}>1{center_dot}10{sup 20}[m{sup -3}] for diverted discharges, indicating low current drive efficiency. It is suggested that Scrape-Off-Layer (SOL) collisional absorption of LH waves is the cause for the absence of non-thermal electrons at high density. VUV and visible spectroscopy in the SOL provide direct information on collision excitation processes. Deuterium Balmer-, Lyman- and He-I transition emission measurements were used for initial characterization of SOL electron-neutral collisional absorption. Data from Helium andmore » Deuterium LHCD discharges were characterized by an overall increase in the emissivity as well as an outward radial shift in the emissivity profile with increasing plasma density and applied LHCD power. High-temperature, high-field (T{sub e} = 5keV,B{sub t} = 8T) helium discharges at high density display increased non-thermal signatures as well as reduced SOL emissivity. Variations in emissivity due to LHCD were seen in SOL regions not magnetically connected to the LH Launcher, indicating global SOL effects due to LHCD.« less

The effect of chemical vapor deposition temperature on the performance of binder-free sewage sludge-derived anodes in microbial fuel cells.

PubMed

Feng, Huajun; Jia, Yufeng; Shen, Dongsheng; Zhou, Yuyang; Chen, Ting; Chen, Wei; Ge, Zhipeng; Zheng, Shuting; Wang, Meizhen

2018-04-13

Conversion of sewage sludge (SS) into value-added material has garnered increasing attention due to its potential applications. In this study, we propose a new application of the sewage sludge-derived carbon (SSC) as an electrode without binder in microbial fuel cells (MFCs). SS was firstly converted into SSC monoliths by methane chemical vapor method at different temperature (600, 800, 1000 or 1200°C). Scanning electron microscopy images showed that carbon micro-wires were present on the surfaces of the samples prepared at 1000 and 1200°C. The results showed that it was beneficial for converting sludge into a highly conductive electrode and increasing carbon content of the electrode at higher temperatures, thereby improving the current generation. The conductivity results show that a higher temperature favors the conversion of sludge into a highly conductive electrode. The MFC using an SSC anode processed at 1200°C generated the maximum power density of 2228mWm -2 and the maximum current density of 14.2Am -2 . This value was 5 times greater than that generated by an MFC equipped with a graphite anode. These results present a promising means of converting SS into electrode materials. Copyright © 2018 Elsevier B.V. All rights reserved.

Comparison of growth texture in round Bi2212 and flat Bi2223 wires and its relation to high critical current density development

DOE PAGES

Kametani, F.; Jiang, J.; Matras, M.; ...

2015-02-10

Why Bi₂Sr₂CaCu₂O x (Bi2212) allows high critical current density J c in round wires rather than only in the anisotropic tape form demanded by all other high temperature superconductors is important for future magnet applications. Here we compare the local texture of state-of-the-art Bi2212 and Bi2223 ((Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀), finding that round wire Bi2212 generates a dominant a-axis growth texture that also enforces a local biaxial texture (FWHM <15°) while simultaneously allowing the c-axes of its polycrystals to rotate azimuthally along and about the filament axis so as to generate macroscopically isotropic behavior. By contrast Bi2223 shows only a uniaxial (FWHM <15°)more » c-axis texture perpendicular to the tape plane without any in-plane texture. Consistent with these observations, a marked, field-increasing, field-decreasing J c(H) hysteresis characteristic of weak-linked systems appears in Bi2223 but is absent in Bi2212 round wire. Growth-induced texture on cooling from the melt step of the Bi2212 J c optimization process appears to be the key step in generating this highly desirable microstructure.« less

A self-powered glucose biosensing system.

PubMed

Slaughter, Gymama; Kulkarni, Tanmay

2016-04-15

A self-powered glucose biosensor (SPGS) system is fabricated and in vitro characterization of the power generation and charging frequency characteristics in glucose analyte are described. The bioelectrodes consist of compressed network of three-dimensional multi-walled carbon nanotubes with redox enzymes, pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) and laccase functioning as the anodic and cathodic catalyst, respectively. When operated in 45 mM glucose, the biofuel cell exhibited an open circuit voltage and power density of 681.8 mV and 67.86 µW/cm(2) at 335 mV, respectively, with a current density of 202.2 µA/cm(2). Moreover, at physiological glucose concentration (5mM), the biofuel cell exhibits open circuit voltage and power density of 302.1 mV and 15.98 µW/cm(2) at 166.3 mV, respectively, with a current density of 100 µA/cm(2). The biofuel cell assembly produced a linear dynamic range of 0.5-45 mM glucose. These findings show that glucose biofuel cells can be further investigated in the development of a self-powered glucose biosensor by using a capacitor as the transducer element. By monitoring the capacitor charging frequencies, which are influenced by the concentration of the glucose analyte, a linear dynamic range of 0.5-35 mM glucose is observed. The operational stability of SPGS is monitored over a period of 63 days and is found to be stable with 15.38% and 11.76% drop in power density under continuous discharge in 10mM and 20mM glucose, respectively. These results demonstrate that SPGSs can simultaneously generate bioelectricity to power ultra-low powered devices and sense glucose. Copyright © 2015 Elsevier B.V. All rights reserved.

Development of a current collection loss management system for SDI homopolar power supplies

NASA Astrophysics Data System (ADS)

Brown, D. W.

1991-04-01

High speed, high power density current collection systems have been identified as an enabling technology required to construct homopolar power supplies to meet SDI missions. This work is part of a three-year effort directed towards the analysis, experimental verification, and prototype construction of a current collection system designed to operate continuously at 2 kA/sq cm, at a rubbing speed of 200 m/s, and with acceptable losses in a space environment. To date, no system has achieved these conditions simultaneously. This is the final report covering the three year period of performance on DOE contract AC03-86SF-16518. Major areas covered include design, construction and operation of a cryogenically cooled brush test rig, design and construction of a high speed brush test rig, optimization study for homopolar machines, loss analysis of the current collection system, and an application study which defines the air-core homopolar construction necessary to achieve the goal of 80 kW/kg generator power density.

Electromagnetic characteristics of eccentric figure-eight coils for transcranial magnetic stimulation: A numerical study

NASA Astrophysics Data System (ADS)

Kato, Takuya; Sekino, Masaki; Matsuzaki, Taiga; Nishikawa, Atsushi; Saitoh, Youichi; Ohsaki, Hiroyuki

2012-04-01

Repetitive transcranial magnetic stimulation (rTMS) is effective for treatment of several neurological and psychiatric diseases. We proposed an eccentric figure-eight coil, which induces strong eddy currents in the target brain tissue. In this study, numerical analyses were carried out to obtain magnetic field distribution of the eccentric figure-eight coil and eddy current in the brain. The analyses were performed with various coil design parameters, such as the outer and inner diameters and number of turns, to investigate the influence of these parameters on the coil characteristics. Increases in the inner diameter, outer diameter, and number of turns caused increases in the maximum eddy current densities. Coil inductance, working voltage, and heat generation also became higher with the increases in these design parameters. In order to develop a compact stimulator system for use at home, we need to obtain strong eddy current density, keeping the working voltage as low as possible. Our results show that it is effective to enlarge the outer diameter.

Study of Electric Explosion of Flat Micron-Thick Foils at Current Densities of (5-50)×108 A/cm2

NASA Astrophysics Data System (ADS)

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.

Social Demand of New Generation Information Network: Introduction to High Spectral Density Optical Communication Technology

NASA Astrophysics Data System (ADS)

Kamiya, Takeshi; Miyazaki, Tetsuya; Kubota, Fumito

In this section, first, current situation of traffic growth and penetration of broadband services are described. Then social demand, technical issues, and research trend for future information network in the United States, Europe, and Japan are described. Finally, a detailed construction of this book is introduced.

Workshop on Plasma Experiments in the Laboratory and in Space. Abstracts

DTIC Science & Technology

1991-01-01

The AMPTE IRM satellite revealed in the region of overlap between plasmaspheric and ring current plasmas a gra- dual decrease of cold plasna density...names UMKD generator, "Alive wine , or 4unipolar Inductor’ For space physics, the breakdown of this tid picture is a( Interest because it results in the

In situ fabrication of green reduced graphene-based biocompatible anode for efficient energy recycle.

PubMed

Cheng, Ying; Mallavarapu, Megharaj; Naidu, Ravi; Chen, Zuliang

2018-02-01

Improving the anode configuration to enhance biocompatibility and accelerate electron shuttling is critical for efficient energy recovery in microbial fuel cells (MFCs). In this paper, green reduced graphene nanocomposite was successfully coated using layer-by-layer assembly technique onto carbon brush anode. The modified anode achieved a 3.2-fold higher power density of 33.7 W m -3 at a current density of 69.4 A m -3 with a 75% shorter start period. As revealed in the characterization, the green synthesized nanocomposite film affords larger surface roughness for microbial colonization. Besides, gold nanoparticles, which anchored on graphene sheets, promise the relatively high electroactive sites and facilitate electron transfer from electricigens to the anode. The reduction-oxidation peaks in cyclic voltammograms indicated the mechanism of surface cytochromes facilitated current generation while the electrochemical impedance spectroscopy confirmed the enhanced electron transfer from surface cytochrome to electrode. The green synthesis process has the potential to generate a high performing anode in further applications of MFCs. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effect of the electrical currents generated by the intestinal smooth muscle layers on pancreatic enzyme activity: an in vitro study.

PubMed

Dabek, Marta; Podgurniak, Paweł; Piedra, Jose L Valverde; Szymańczyk, Sylwia; Filip, Rafał; Wojtasz-Pajak, Anna; Werpachowska, Eliza; Podgurniak, Malgorzata; Pierzynowski, Stefan G

2007-05-01

Gut enzymes in the small intestine are exposed to extremely low electrical currents (ELEC) generated by the smooth muscle. In the present study, the in vitro tests were undertaken to evaluate the effect of these electric currents on the activity of the proteolytic pancreatic digestive enzymes. A simulator generating the typical electrical activity of pig gut was used for these studies. The electric current emitted by the simulator was transmitted to the samples, containing enzyme and its substrate, using platinum plate electrodes. All samples were incubated at 37 degrees C for 1 h. The changes in optical density, corresponding to enzyme activity, in samples stimulated for 1 h with ELEC was compared with that not exposed to ELEC. The obtained results show that the electrical current with the characteristics of the myoelectrical migrating complex (MMC) has an influence on pancreatic enzyme activity. Increased endopeptidase and reduced exopeptidase activity was noticed in samples treated with ELEC. This observation can be of important as analyzed factors which can alter enzymatic activity of the gut, can thus also affect feed/food digestibility. (c) 2007 Wiley-Liss, Inc.

Numerical study of the inductive plasma coupling to ramp up the plasma density for the Linac4 H- ion source

NASA Astrophysics Data System (ADS)

Ohta, M.; Mattei, S.; Yasumoto, M.; Hatayama, A.; Lettry, J.

2014-02-01

In the Linac4 H- ion source, the plasma is generated by an RF antenna operated at 2 MHz. In order to investigate the conditions necessary for ramping up the plasma density of the Linac4 H- ion source in the low plasma density, a numerical study has been performed for a wide range of parameter space of RF coil current and initial pressure from H2 gas injection. We have employed an Electromagnetic Particle in Cell model, in which the collision processes have been calculated by a Monte Carlo method. The results have shown that the range of initial gas pressure from 2 to 3 Pa is suitable for ramping up plasma density via inductive coupling.

Application of active quenching of second generation wire for current limiting

DOE PAGES

Solovyov, Vyacheslav F.; Li, Qiang

2015-10-19

Superconducting fault current limiters (SFCL's) are increasingly implemented in the power grid as a protection of substation equipment from fault currents. Resistive SFCL's are compact and light, however they are passively triggered and thus may not be sufficiently sensitive to respond to faults in the distribution grid. Here, we explore the prospect of adding an active management feature to a traditional resistive SFCL. A flexible radio-frequency coil, which is an integral part of the switching structure, acts as a triggering device. We show that the application of a short, 10 ms, burst of ac magnetic field during the fault triggersmore » a uniform quench of the wire and significantly reduces the reaction time of the wire at low currents. The ac field burst generates a high density of normal zones, which merge into a continuous resistive region at a rate much faster than that of sparse normal zones created by the transport current alone.« less

A β-Ta system for current induced magnetic switching in the absence of external magnetic field

NASA Astrophysics Data System (ADS)

Chen, Wenzhe; Qian, Lijuan; Xiao, Gang

2018-05-01

Magnetic switching via Giant Spin Hall Effect (GSHE) has received great interest for its role in developing future spintronics logic or memory devices. In this work, a new material system (i.e. a transition metal sandwiched between two ferromagnetic layers) with interlayer exchange coupling is introduced to realize the deterministic field-free perpendicular magnetic switching. This system uses β-Ta, as the GSHE agent to generate a spin current and as the interlayer exchange coupling medium to generate an internal field. The critical switching current density at zero field is on the order of 106 A/cm2 due to the large spin Hall angle of β-Ta. The internal field, along with switching efficiency, depends strongly on the orthogonal magnetization states of two ferromagnetic coupling layers in this system.

A 1 MA, variable risetime pulse generator for high energy density plasma research

NASA Astrophysics Data System (ADS)

Greenly, J. B.; Douglas, J. D.; Hammer, D. A.; Kusse, B. R.; Glidden, S. C.; Sanders, H. D.

2008-07-01

COBRA is a 0.5Ω pulse generator driving loads of order 10nH inductance to >1MA current. The design is based on independently timed, laser-triggered switching of four water pulse-forming lines whose outputs are added in parallel to drive the load current pulse. The detailed design and operation of the switching to give a wide variety of current pulse shapes and rise times from 95to230ns is described. The design and operation of a simple inductive load voltage monitor are described which allows good accounting of load impedance and energy dissipation. A method of eliminating gas bubbles on the underside of nearly horizontal insulator surfaces in water was required for reliable operation of COBRA; a novel and effective solution to this problem is described.

On the energy deposition into the plasma for an inverted fireball geometry

NASA Astrophysics Data System (ADS)

Levko, Dmitry; Gruenwald, Johannes

2017-10-01

Energy deposition into a plasma for an inverted fireball geometry is studied using a self-consistent two-dimensional Particle-in-Cell Monte Carlo collision model. In this model, the cathode is a pin which injects the fixed electron current and the anode is a hollow metal tube covered with the metal grid. We obtain an almost constant ratio between the densities of plasmas generated in the cathode-grid gap and inside the hollow anode. The results of the simulations show that there is no energy exchange between the beam and plasma electrons at low emission currents. For increasing current, however, we observe the increasing coupling between the electron beam and the thermal plasma electrons. This leads to the heating of plasma electrons and the generation of the so-called supra-thermal electrons.

Applying a new mammographic imaging marker to predict breast cancer risk

NASA Astrophysics Data System (ADS)

Aghaei, Faranak; Danala, Gopichandh; Hollingsworth, Alan B.; Stoug, Rebecca G.; Pearce, Melanie; Liu, Hong; Zheng, Bin

2018-02-01

Identifying and developing new mammographic imaging markers to assist prediction of breast cancer risk has been attracting extensive research interest recently. Although mammographic density is considered an important breast cancer risk, its discriminatory power is lower for predicting short-term breast cancer risk, which is a prerequisite to establish a more effective personalized breast cancer screening paradigm. In this study, we presented a new interactive computer-aided detection (CAD) scheme to generate a new quantitative mammographic imaging marker based on the bilateral mammographic tissue density asymmetry to predict risk of cancer detection in the next subsequent mammography screening. An image database involving 1,397 women was retrospectively assembled and tested. Each woman had two digital mammography screenings namely, the "current" and "prior" screenings with a time interval from 365 to 600 days. All "prior" images were originally interpreted negative. In "current" screenings, these cases were divided into 3 groups, which include 402 positive, 643 negative, and 352 biopsy-proved benign cases, respectively. There is no significant difference of BIRADS based mammographic density ratings between 3 case groups (p < 0.6). When applying the CAD-generated imaging marker or risk model to classify between 402 positive and 643 negative cases using "prior" negative mammograms, the area under a ROC curve is 0.70+/-0.02 and the adjusted odds ratios show an increasing trend from 1.0 to 8.13 to predict the risk of cancer detection in the "current" screening. Study demonstrated that this new imaging marker had potential to yield significantly higher discriminatory power to predict short-term breast cancer risk.

Exceptional Lithium Storage in a Co(OH) 2 Anode: Hydride Formation

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

Kim, Hyunchul; Choi, Woon Ih; Jang, Yoonjung

Current lithium ion battery technology is tied in with conventional reaction mechanisms such as insertion, conversion, and alloying reactions even though most future applications like EVs demand much higher energy densities than current ones. Exploring the exceptional reaction mechanism and related electrode materials can be critical for pushing current battery technology to a next level. Here, we introduce an exceptional reaction with a Co(OH)(2) material which exhibits an initial charge capacity of 1112 mAh g(-1), about twice its theoretical value based on known conventional conversion reaction, and retains its first cycle capacity after 30 cycles. The combined results of synchrotronmore » X-ray diffraction and X-ray absorption spectroscopy indicate that nanosized Co metal particles and LiOH are generated by conversion reaction at high voltages, and CoxHy, Li2O, and LiH are subsequently formed by hydride reaction between Co metal, LiOH, and other lithium species at low voltages, resulting in a anomalously high capacity beyond the theoretical capacity of Co(OH)(2). This is further corroborated by AIMD simulations, localized STEM, and XPS. These findings will provide not only further understanding of exceptional lithium storage of recent nanostructured materials but also valuable guidance to develop advanced electrode materials with high energy density for next-generation batteries.« less

[Electricity generation from corn steepwater using microbial fuel cell technology].

PubMed

Lu, Na; Zhou, Shun-Gui; Zhang, Jin-Tao; Ni, Jin-Ren

2009-02-15

Corn steepwater containing 49,732.2 mg/L of chemical oxygen demand (COD) was used as fuel for a membrane electrode assembly microbial fuel cell (MEA-MFC), which could generate electricity and treat the wastewater at the same time. During a batch experiment of 94 days with a fixed 1,000 Omega external resistance, the maximum voltage output of 525.0 mV and power density of 169.6 mW/m2 were obtained after 17 days, corresponding to the current density, internal resistance and open voltage of 440.2 mA/m2, 350 Omega and 619.5 mV, respectively. However, data showed that the coulombic efficiency was only 1.6%, suggesting very limited COD was utilized for electricity generation. At the conclusion of the test, the removals of COD and ammonia-nitrogen were achieved 51.6% and 25.8%, respectively. This study demonstrates that corn steepwater can be used for power generation in MFC with simultaneous accomplishments of wastewater treatment, providing a novel approach for the safe disposal and recycle of corn steepwater.

Hydrogen production profiles using furans in microbial electrolysis cells.

PubMed

Catal, Tunc; Gover, Tansu; Yaman, Bugra; Droguetti, Jessica; Yilancioglu, Kaan

2017-06-01

Microbial electrochemical cells including microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are novel biotechnological tools that can convert organic substances in wastewater or biomass into electricity or hydrogen. Electroactive microbial biofilms used in this technology have ability to transfer electrons from organic compounds to anodes. Evaluation of biofilm formation on anode is crucial for enhancing our understanding of hydrogen generation in terms of substrate utilization by microorganisms. In this study, furfural and hydroxymethylfurfural (HMF) were analyzed for hydrogen generation using single chamber membrane-free MECs (17 mL), and anode biofilms were also examined. MECs were inoculated with mixed bacterial culture enriched using chloroethane sulphonate. Hydrogen was succesfully produced in the presence of HMF, but not furfural. MECs generated similar current densities (5.9 and 6 mA/cm 2 furfural and HMF, respectively). Biofilm samples obtained on the 24th and 40th day of cultivation using aromatic compounds were evaluated by using epi-fluorescent microscope. Our results show a correlation between biofilm density and hydrogen generation in single chamber MECs.

Hydrogen production by geobacter species and a mixed consortium in a microbial electrolysis cell.

PubMed

Call, Douglas F; Wagner, Rachel C; Logan, Bruce E

2009-12-01

A hydrogen utilizing exoelectrogenic bacterium (Geobacter sulfurreducens) was compared to both a nonhydrogen oxidizer (Geobacter metallireducens) and a mixed consortium in order to compare the hydrogen production rates and hydrogen recoveries of pure and mixed cultures in microbial electrolysis cells (MECs). At an applied voltage of 0.7 V, both G. sulfurreducens and the mixed culture generated similar current densities (ca. 160 A/m3), resulting in hydrogen production rates of ca. 1.9 m(3) H2/m3/day, whereas G. metallireducens exhibited lower current densities and production rates of 110 +/- 7 A/m3 and 1.3 +/- 0.1 m3 H2/m3/day, respectively. Before methane was detected in the mixed-culture MEC, the mixed consortium achieved the highest overall energy recovery (relative to both electricity and substrate energy inputs) of 82% +/- 8% compared to G. sulfurreducens (77% +/- 2%) and G. metallireducens (78% +/- 5%), due to the higher coulombic efficiency of the mixed consortium. At an applied voltage of 0.4 V, methane production increased in the mixed-culture MEC and, as a result, the hydrogen recovery decreased and the overall energy recovery dropped to 38% +/- 16% compared to 80% +/- 5% for G. sulfurreducens and 76% +/- 0% for G. metallireducens. Internal hydrogen recycling was confirmed since the mixed culture generated a stable current density of 31 +/- 0 A/m3 when fed hydrogen gas, whereas G. sulfurreducens exhibited a steady decrease in current production. Community analysis suggested that G. sulfurreducens was predominant in the mixed-culture MEC (72% of clones) despite its relative absence in the mixed-culture inoculum obtained from a microbial fuel cell reactor (2% of clones). These results demonstrate that Geobacter species are capable of obtaining similar hydrogen production rates and energy recoveries as mixed cultures in an MEC and that high coulombic efficiencies in mixed culture MECs can be attributed in part to the recycling of hydrogen into current.

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

NASA Astrophysics Data System (ADS)

Bhaganagar, Kiran

2017-02-01

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

Novel model of stator design to reduce the mass of superconducting generators

NASA Astrophysics Data System (ADS)

Kails, Kevin; Li, Quan; Mueller, Markus

2018-05-01

High temperature superconductors (HTS), with much higher current density than conventional copper wires, make it feasible to develop very powerful and compact power generators. Thus, they are considered as one promising solution for large (10 + MW) direct-drive offshore wind turbines due to their low tower head mass. However, most HTS generator designs are based on a radial topology, which requires an excessive amount of HTS material and suffers from cooling and reliability issues. Axial flux machines on the other hand offer higher torque/volume ratios than the radial machines, which makes them an attractive option where space and transportation becomes an issue. However, their disadvantage is heavy structural mass. In this paper a novel stator design is introduced for HTS axial flux machines which enables a reduction in their structural mass. The stator is for the first time designed with a 45° angle that deviates the air gap closing forces into the vertical direction reducing the axial forces. The reduced axial forces improve the structural stability and consequently simplify their structural design. The novel methodology was then validated through an existing design of the HTS axial flux machine achieving a ∼10% mass reduction from 126 tonnes down to 115 tonnes. In addition, the air gap flux density increases due to the new claw pole shapes improving its power density from 53.19 to 61.90 W kg‑1. It is expected that the HTS axial flux machines designed with the new methodology offer a competitive advantage over other proposed superconducting generator designs in terms of cost, reliability and power density.

Generating short-term probabilistic wind power scenarios via nonparametric forecast error density estimators: Generating short-term probabilistic wind power scenarios via nonparametric forecast error density estimators

DOE PAGES

Staid, Andrea; Watson, Jean -Paul; Wets, Roger J. -B.; ...

2017-07-11

Forecasts of available wind power are critical in key electric power systems operations planning problems, including economic dispatch and unit commitment. Such forecasts are necessarily uncertain, limiting the reliability and cost effectiveness of operations planning models based on a single deterministic or “point” forecast. A common approach to address this limitation involves the use of a number of probabilistic scenarios, each specifying a possible trajectory of wind power production, with associated probability. We present and analyze a novel method for generating probabilistic wind power scenarios, leveraging available historical information in the form of forecasted and corresponding observed wind power timemore » series. We estimate non-parametric forecast error densities, specifically using epi-spline basis functions, allowing us to capture the skewed and non-parametric nature of error densities observed in real-world data. We then describe a method to generate probabilistic scenarios from these basis functions that allows users to control for the degree to which extreme errors are captured.We compare the performance of our approach to the current state-of-the-art considering publicly available data associated with the Bonneville Power Administration, analyzing aggregate production of a number of wind farms over a large geographic region. Finally, we discuss the advantages of our approach in the context of specific power systems operations planning problems: stochastic unit commitment and economic dispatch. Here, our methodology is embodied in the joint Sandia – University of California Davis Prescient software package for assessing and analyzing stochastic operations strategies.« less

Generating short-term probabilistic wind power scenarios via nonparametric forecast error density estimators: Generating short-term probabilistic wind power scenarios via nonparametric forecast error density estimators

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

Staid, Andrea; Watson, Jean -Paul; Wets, Roger J. -B.

Forecasts of available wind power are critical in key electric power systems operations planning problems, including economic dispatch and unit commitment. Such forecasts are necessarily uncertain, limiting the reliability and cost effectiveness of operations planning models based on a single deterministic or “point” forecast. A common approach to address this limitation involves the use of a number of probabilistic scenarios, each specifying a possible trajectory of wind power production, with associated probability. We present and analyze a novel method for generating probabilistic wind power scenarios, leveraging available historical information in the form of forecasted and corresponding observed wind power timemore » series. We estimate non-parametric forecast error densities, specifically using epi-spline basis functions, allowing us to capture the skewed and non-parametric nature of error densities observed in real-world data. We then describe a method to generate probabilistic scenarios from these basis functions that allows users to control for the degree to which extreme errors are captured.We compare the performance of our approach to the current state-of-the-art considering publicly available data associated with the Bonneville Power Administration, analyzing aggregate production of a number of wind farms over a large geographic region. Finally, we discuss the advantages of our approach in the context of specific power systems operations planning problems: stochastic unit commitment and economic dispatch. Here, our methodology is embodied in the joint Sandia – University of California Davis Prescient software package for assessing and analyzing stochastic operations strategies.« less

Bacterial Community Analysis, New Exoelectrogen Isolation and Enhanced Performance of Microbial Electrochemical Systems Using Nano-Decorated Anodes

NASA Astrophysics Data System (ADS)

Xu, Shoutao

Microbial electrochemical systems (MESs) have attracted much research attention in recent years due to their promising applications in renewable energy generation, bioremediation, and wastewater treatment. In a MES, microorganisms interact with electrodes via electrons, catalyzing oxidation and reduction reactions at the anode and the cathode. The bacterial community of a high power mixed consortium MESs (maximum power density is 6.5W/m2) was analyzed by using denature gradient gel electrophoresis (DGGE) and 16S DNA clone library methods. The bacterial DGGE profiles were relatively complex (more than 10 bands) but only three brightly dominant bands in DGGE results. These results indicated there are three dominant bacterial species in mixed consortium MFCs. The 16S DNA clone library method results revealed that the predominant bacterial species in mixed culture is Geobacter sp (66%), Arcobacter sp and Citrobacter sp. These three bacterial species reached to 88% of total bacterial species. This result is consistent with the DGGE result which showed that three bright bands represented three dominant bacterial species. Exoelectrogenic bacterial strain SX-1 was isolated from a mediator-less microbial fuel cell by conventional plating techniques with ferric citrate as electron acceptor under anaerobic conditions. Phylogenetic analysis of the 16S rDNA sequence revealed that it was related to the members of Citrobacter genus with Citrobacter sp. sdy-48 being the most closely related species. The bacterial strain SX-1 produced electricity from citrate, acetate, glucose, sucrose, glycerol, and lactose in MFCs with the highest current density of 205 mA/m2 generated from citrate. Cyclic voltammetry analysis indicated that membrane associated proteins may play an important role in facilitating electron transfer from the bacteria to the electrode. This is the first study that demonstrates that Citrobacter species can transfer electrons to extracellular electron acceptors. Citrobacter strain SX-1 is capable of generating electricity from a wide range of substrates in MFCs. This finding increases the known diversity of power generating exoelectrogens and provids a new strain to explore the mechanisms of extracellular electron transfer from bacteria to electrode. The wide range of substrate utilization by SX-1 increases the application potential of MFCs in renewable energy generation and waste treatment. Anode properties are critical for the performance of microbial electrolysis cells (MECs). Inexpensive Fe nanoparticle modified graphite disks were used as anodes to preliminarily investigate the effects of nanoparticles on the performance of Shewanella oneidensis MR-1 in MECs. Results demonstrated that average current densities produced with Fe nanoparticle decorated anodes were up to 5.9-fold higher than plain graphite anodes. Whole genome microarray analysis of the gene expression showed that genes encoding biofilm formation were significantly up-regulated as a response to nanoparticle decorated anodes. Increased expression of genes related to nanowires, flavins and c-type cytochromes indicate that enhanced mechanisms of electron transfer to the anode may also have contributed to the observed increases in current density. The majority of the remaining differentially expressed genes were associated with electron transport and anaerobic metabolism demonstrating a systemic response to increased power loads. The carbon nanotube (CNT) is another form of nano materials. Carbon nanotube (CNT) modified graphite disks were used as anodes to investigate the effects of nanostructures on the performance S. oneidensis MR-1 in microbial electrolysis cells (MECs). The current densities produced with CNT decorated anodes were up to 5.6-fold higher than plain graphite anodes. Global transcriptome analysis showed that cytochrome c genes associated with extracellular electron transfer are up-expressed by CNT decorated anodes, which is the leading factor to contribute current increase in CNT decorated anode MECs. The up regulated genes encoded to flavin also contribute to current enhancement in CNT decorated anode MECs.

4th Generation ECR Ion Sources

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

Lyneis, Claude M.; Leitner, D.; Todd, D.S.

2008-12-01

The concepts and technical challenges related to developing a 4th generation ECR ion source with an RF frequency greater than 40 GHz and magnetic confinement fields greater than twice Becr will be explored in this paper. Based on the semi-empirical frequency scaling of ECR plasma density with the square of operating frequency, there should be significant gains in performance over current 3rd generation ECR ion sources, which operate at RF frequencies between 20 and 30 GHz. While the 3rd generation ECR ion sources use NbTi superconducting solenoid and sextupole coils, the new sources will need to use different superconducting materialsmore » such as Nb3Sn to reach the required magnetic confinement, which scales linearly with RF frequency. Additional technical challenges include increased bremsstrahlung production, which may increase faster than the plasma density, bremsstrahlung heating of the cold mass and the availability of high power continuous wave microwave sources at these frequencies. With each generation of ECR ion sources, there are new challenges to be mastered, but the potential for higher performance and reduced cost of the associated accelerator continue to make this a promising avenue for development.« less

Magnetic Recording Media Technology for the Tb/in2 Era"

ScienceCinema

Bertero, Gerardo [Western Digital

2017-12-09

Magnetic recording has been the technology of choice of massive storage of information. The hard-disk drive industry has recently undergone a major technological transition from longitudinal magnetic recording (LMR) to perpendicular magnetic recording (PMR). However, convention perpendicular recording can only support a few new product generations before facing insurmountable physical limits. In order to support sustained recording areal density growth, new technological paradigms, such as energy-assisted recording and bit-patterined media recording are being contemplated and planned. In this talk, we will briefly discuss the LMR-to-PMR transition, the extendibility of current PMR recording, and the nature and merits of new enabling technologies. We will also discuss a technology roadmap toward recording densities approaching 10 Tv/in2, approximately 40 times higher than in current disk drives.

Calculations of electric currents in Europa

NASA Technical Reports Server (NTRS)

Colburn, D. S.; Reynolds, R. T.

1986-01-01

Electrical currents should flow in the Galilean satellite, Europa, because it is located in Jupiter's corotating magnetosphere. The possible magnitudes of these currents are calculated by assuming that Europa is a differentiated body consisting of an outer H2O layer and a silicate core. Two types of models are considered here: one in which the water is completely frozen and a second in which there is an intermediate liquid layer. For the transverse electric mode (eddy currents), the calculated current density in a liquid layer is approximately 10 to the -5/Am. For the transverse magnetic mode (unipolar generator), the calculated current density in the liquid is severely constrained by the ice layer to a range of only 10 to the -10 to -11th power/ Am, for a total H2O thickness of 100 km, provided that neither layer is less than 4 km thick. The current density is less for a completely frozen H2O layer. If transient cracks were to appear in the ice layer, thereby exposing liquid, the calculated current density could rise to a range of 10 to the -6 to 10 to the -5/Am, depending on layer thicknesses, which would require an exposed area of 10 to the -9 to 10 to the -8 of the Europa surface. The corresponding total current of 2.3x10 to the 5th power A could in 1 yr. electrolyze 7x10 to the 5th power kg of water (and more if the cells were in series), and thereby store up to 10 the 8th power J of energy, but it is not clear how electrolysis can take place in the absence of suitable electrodes. Electrical heating would be significant only if the ice-layer thickness were on the order of 1 m, such as might occur if an exposed liquid surface were to freeze over; the heating under this condition could hinder the thickening of the ice layer.

A miniaturized human-motion energy harvester using flux-guided magnet stacks

NASA Astrophysics Data System (ADS)

Halim, M. A.; Park, J. Y.

2016-11-01

We present a miniaturized electromagnetic energy harvester (EMEH) using two flux-guided magnet stacks to harvest energy from human-generated vibration such as handshaking. Each flux-guided magnet stack increases (40%) the magnetic flux density by guiding the flux lines through a soft magnetic material. The EMEH has been designed to up-convert the applied human-motion vibration to a high-frequency oscillation by mechanical impact of a spring-less structure. The high-frequency oscillator consists of the analyzed 2-magnet stack and a customized helical compression spring. A standard AAA battery sized prototype (3.9 cm3) can generate maximum 203 μW average power from human hand-shaking vibration. It has a maximum average power density of 52 μWcm-3 which is significantly higher than the current state-of-the-art devices. A 6-stage multiplier and rectifier circuit interfaces the harvester with a wearable electronic load (wrist watch) to demonstrate its capability of powering small- scale electronic systems from human-generated vibration.

TiO2 nanocrystals decorated Z-schemed core-shell CdS-CdO nanorod arrays as high efficiency anodes for photoelectrochemical hydrogen generation.

PubMed

Li, Chia-Hsun; Hsu, Chan-Wei; Lu, Shih-Yuan

2018-07-01

TiO 2 nanocrystals decorated core-shell CdS-CdO nanorod arrays, TiO 2 @CdO/CdS NR, were fabricated as high efficiency anodes for photoelctrochemical hydrogen generation. The novel sandwich heterostructure was constructed from first growth of CdS nanorod arrays on a fluorine doped tin oxide (FTO) substrate with a hydrothermal process, followed by in situ generation of CdO thin films of single digit nanometers from the CdS nanorod surfaces through thermal oxidation, and final decoration of TiO 2 nanocrystals of 10-20 nm via a successive ionic layer absorption and reaction process. The core-shell CdS-CdO heterostructure possesses a Z-scheme band structure to enhance interfacial charge transfer, facilitating effective charge separation to suppress electron-hole recombination within CdS for much improved current density generation. The final decoration of TiO 2 nanocrystals passivates surface defects and trap states of CdO, further suppressing surface charge recombination for even higher photovoltaic conversion efficiencies. The photoelectrochemical performances of the plain CdS nanorod array were significantly improved with the formation of the sandwich heterostructure, achieving a photo current density of 3.2 mA/cm 2 at 1.23 V (vs. RHE), a 141% improvement over the plain CdS nanorod array and a 32% improvement over the CdO/CdS nanorod array. Copyright © 2018 Elsevier Inc. All rights reserved.

Positron Radiography of Ignition-Relevant ICF Capsules

NASA Astrophysics Data System (ADS)

Williams, Jackson; Chen, Hui; Field, John; Landen, Nino; Strozzi, David

2017-10-01

X-ray and neutron radiography are currently used to infer residual ICF shell and fuel asymmetries and areal density non-uniformities near and at peak compression that can impede ignition. Charged particles offer an alternative probe source that, in principle, are capable of radiographing the shell shape and areal density at arbitrary times, even in the presence of large x-ray self-emission. Laser-generated positrons are evaluated as a source to radiograph ICF capsules where current ultraintense laser facilities are capable of producing 2 ×1012 relativistic positrons in a narrow energy bandwidth and short duration. Monte Carlo simulations suggest that both the areal density and shell radius can be reconstructed for ignition-relevant capsules conditions between 0.002-2 g/cm2, and that this technique might be better suited to direct-drive. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the LDRD Program under project tracking code 17-ERD-010.

TEMPy: a Python library for assessment of three-dimensional electron microscopy density fits.

PubMed

Farabella, Irene; Vasishtan, Daven; Joseph, Agnel Praveen; Pandurangan, Arun Prasad; Sahota, Harpal; Topf, Maya

2015-08-01

Three-dimensional electron microscopy is currently one of the most promising techniques used to study macromolecular assemblies. Rigid and flexible fitting of atomic models into density maps is often essential to gain further insights into the assemblies they represent. Currently, tools that facilitate the assessment of fitted atomic models and maps are needed. TEMPy (template and electron microscopy comparison using Python) is a toolkit designed for this purpose. The library includes a set of methods to assess density fits in intermediate-to-low resolution maps, both globally and locally. It also provides procedures for single-fit assessment, ensemble generation of fits, clustering, and multiple and consensus scoring, as well as plots and output files for visualization purposes to help the user in analysing rigid and flexible fits. The modular nature of TEMPy helps the integration of scoring and assessment of fits into large pipelines, making it a tool suitable for both novice and expert structural biologists.

Capacitance-level/density monitor for fluidized-bed combustor

DOEpatents

Fasching, George E.; Utt, Carroll E.

1982-01-01

A multiple segment three-terminal type capacitance probe with segment selection, capacitance detection and compensation circuitry and read-out control for level/density measurements in a fluidized-bed vessel is provided. The probe is driven at a high excitation frequency of up to 50 kHz to sense quadrature (capacitive) current related to probe/vessel capacitance while being relatively insensitive to the resistance current component. Compensation circuitry is provided for generating a negative current of equal magnitude to cancel out only the resistive component current. Clock-operated control circuitry separately selects the probe segments in a predetermined order for detecting and storing this capacitance measurement. The selected segment acts as a guarded electrode and is connected to the read-out circuitry while all unselected segments are connected to the probe body, which together form the probe guard electrode. The selected probe segment capacitance component signal is directed to a corresponding segment channel sample and hold circuit dedicated to that segment to store the signal derived from that segment. This provides parallel outputs for display, computer input, etc., for the detected capacitance values. The rate of segment sampling may be varied to either monitor the dynamic density profile of the bed (high sampling rate) or monitor average bed characteristics (slower sampling rate).

Electroformed Nickel Mirrors for the Next Generation Space Telescope

NASA Technical Reports Server (NTRS)

Redmon, John W.; Engelhaupt, Darrel

1998-01-01

This paper summarizes the work to date on a novel mirror fabrication technique being developed at the Marshall Space Flight Center for potential use on the Next Generation Space Telescope (NGST). This technique involves forming an extremely lightweight mirror by electroplating nickel and nickel based alloys onto a highly polished precision mandrel. The resulting mirror shell can then be backed up with or attached to a lightweight structure to produce a mirror element that is on the order of 15 kg/sq m areal density. Since the mirrors are fabricated from a mandrel (or master), subsequent mirrors can be made with very high economy; this technique is particularly suited to segmented mirrors schemes whereby large apertures are achieved through the deployment of smaller segments. Control of the electroplating process is the key element for producing high quality optics; bath chemistry and real time control of the plating current density yields uniform grained electroforms with zero residual stress. To accomplish this, a special electronic sensor was developed whereby the residual stress can be monitored as the nickel is electrolytically deposited. This information is used in a feedback loop to modulate current density which, in turn, directly governs the residual stress. Details pertaining to this and other aspects of the fabrication of a half meter mirror will be published along with test results and metrology data.

Effect of particle entrainment on the runout of pyroclastic density currents

NASA Astrophysics Data System (ADS)

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

2016-09-01

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

Mesoporous composite nickel cobalt oxide/graphene oxide synthesized via a template-assistant co-precipitation route as electrode material for supercapacitors

NASA Astrophysics Data System (ADS)

Xu, Yanjie; Wang, Lincai; Cao, Peiqi; Cai, Chuanlin; Fu, Yanbao; Ma, Xiaohua

2016-02-01

A simple co-precipitation method utilizing SDS (sodium dodecyl sulfate) as template and ammonia as precipitant is successfully employed to synthesize nickel cobalt oxide/graphene oxide (NiCo2O4/GO) composite. The as-prepared composite (NCG-10) exhibits a high capacitance of 1211.25 F g-1, 687 F g-1 at the current density of 1 A g-1, 10 A g-1 and good cycling ability which renders NCG-10 as promising electrode material for supercapacitors. An asymmetric supercapacitor (ASC) (full button cell) has been constructed with NCG-10 as positive electrode and lab-made reduced graphene oxide (rGO) as negative electrode. The fabricated NCG-10//rGO with an extended stable operational voltage of 1.6 V can deliver a high specific capacitance of 144.45 F g-1 at a current density of 1 A g-1. The as-prepared NCG-10//rGO demonstrates remarkable energy density (51.36 W h kg-1 at 1 A g-1), high power density (50 kW kg-1 at 20 A g-1). The retention of capacitance is 88.6% at the current density of 8 A g-1 after 2000 cycles. The enhanced capacitive performance can be attributed to the improved specific surface area and 3D open area of NCG-10 generated by the pores and channels with the substantial function of SDS.

Formation and termination of runaway beams in ITER disruptions

NASA Astrophysics Data System (ADS)

Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

2017-06-01

A self-consistent analysis of the relevant physics regarding the formation and termination of runaway beams during mitigated disruptions by Ar and Ne injection is presented for selected ITER scenarios with the aim of improving our understanding of the physics underlying the runaway heat loads onto the plasma facing components (PFCs) and identifying open issues for developing and accessing disruption mitigation schemes for ITER. This is carried out by means of simplified models, but still retaining sufficient details of the key physical processes, including: (a) the expected dominant runaway generation mechanisms (avalanche and primary runaway seeds: Dreicer and hot tail runaway generation, tritium decay and Compton scattering of γ rays emitted by the activated wall), (b) effects associated with the plasma and runaway current density profile shape, and (c) corrections to the runaway dynamics to account for the collisions of the runaways with the partially stripped impurity ions, which are found to have strong effects leading to low runaway current generation and low energy conversion during current termination for mitigated disruptions by noble gas injection (particularly for Ne injection) for the shortest current quench times compatible with acceptable forces on the ITER vessel and in-vessel components ({τ\\text{res}}∼ 22~\\text{ms} ). For the case of long current quench times ({τ\\text{res}}∼ 66~\\text{ms} ), runaway beams up to  ∼10 MA can be generated during the disruption current quench and, if the termination of the runaway current is slow enough, the generation of runaways by the avalanche mechanism can play an important role, increasing substantially the energy deposited by the runaways onto the PFCs up to a few hundreds of MJs. Mixed impurity (Ar or Ne) plus deuterium injection proves to be effective in controlling the formation of the runaway current during the current quench, even for the longest current quench times, as well as in decreasing the energy deposited on the runaway electrons during current termination.

Characteristics of electricity generation and biodegradation in tidal river sludge-used microbial fuel cells.

PubMed

Touch, Narong; Hibino, Tadashi; Nagatsu, Yoshiyuki; Tachiuchi, Kouhei

2014-04-01

The electricity generation behavior of microbial fuel cell (MFC) using the sludge collected from the riverbank of a tidal river, and the biodegradation of the sludge by the electricity generation are evaluated. Although the maximum current density (150-300 mA/m(2)) was higher than that of MFC using freshwater sediment (30 mA/m(2)), the output current was greatly restricted by the mass transfer limitation. However, our results also indicate that placing the anode in different locations in the sludge could reduce the mass transfer limitation. After approximately 3 months, the removal efficiency of organic carbon was approximately 10%, demonstrated that MFC could also enhance the biodegradation of the sludge by nearly 10-fold comparing with the natural biodegradation. We also found that the biodegradation could be identified by the behavior of oxygen consumption of the sludge. Importantly, the oxygen consumption of the sludge became higher along with the electricity generation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Microbial fuel cells operating on mixed fatty acids.

PubMed

Freguia, Stefano; Teh, Ee Hoi; Boon, Nico; Leung, Kar Man; Keller, Jurg; Rabaey, Korneel

2010-02-01

Strategies are being developed to harvest the energy content of the wasted sludge generated from the treatment of domestic wastewater. Sludge can be hydrolysed and fermented, giving a mixture of volatile fatty acids (VFAs). Based on the composition of such a fermented stream, synthetic media were created and tested for VFA conversion in microbial fuel cells (MFCs). Mainly acetate and propionate were preferred as electron donors in the mixed VFA system, which generated a power density of 49+/-1 mW L(NAC)(-1). The other VFAs (butyrates/valerates/caproic acid) were also removed, albeit at lower rates. In single VFA tests, each VFA could be removed, but particularly i-butyrate did not provide significant current generation. PCR-DGGE indicated that the microbial community structure was highly determined by the fed VFA, rather than by the initial inoculum. The communities were dominated by Proteobacteria such as Geobacter, Comamonas, Pseudomonas and Pelobacter species. This study demonstrated the feasibility of using fatty acids, as present in fermented sludge hydrolysates, for current generation.

An innovative demonstration of high power density in a compact MDH (magnetohydrodynamic) generator

NASA Astrophysics Data System (ADS)

Schmidt, H. J.; Lineberry, J. T.; Chapman, J. N.

1990-06-01

The present program was conducted by the University of Tennessee Space Institute (UTSI). It was by its nature a high risk experimental program to demonstrate the feasibility of high power density operation in a laboratory scale combustion driven MHD generator. Maximization of specific energy was not a consideration for the present program, but the results have implications in this regard by virtue of high energy fuel used. The power density is the ratio of the electrical energy output to the internal volume of the generator channel. The MHD process is a volumetric process and the power density is therefore a direct measure of the compactness of the system. Specific energy, is the ratio of the electrical energy output to consumable energy used for its production. The two parameters are conceptually interrelated. To achieve high power density and implied commensurate low system volume and weight, it was necessary to use an energetic fuel. The high energy fuel of choice was a mixture of powdered aluminum and carbon seeded with potassium carbonate and burned with gaseous oxygen. The solid fuel was burned in a hybrid combustion scheme wherein the fuel was cast within a cylindrical combustor in analogy with a solid propellant rocket motor. Experimental data is limited to gross channel output current and voltage, magnetic field strength, fuel and oxidizer flow rates, flow train external temperatures and combustor pressure. Similarly, while instantaneous oxidizer flow rates were measured, only average fuel consumption based on pre and post test component weights and dimensions was possible.

Development of a compact, rf-driven, pulsed ion source for neutron generation

NASA Astrophysics Data System (ADS)

Perkins, L. T.; Celata, C.; Lee, Y.; Leung, K. N.; Picard, D. S.; Vilaithong, R.; Williams, M. D.; Wutte, D.

1997-02-01

Lawrence Berkeley National Laboratory is currently developing a compact, sealed-accelerator-tube neutron generator capable of producing a neutron flux in the range of 109 to 1010 D-T neutrons per second. The ion source, a miniaturized variation of earlier radio-frequency (rf)-driven multicusp ion sources, is designed to fit within a ˜5 cm diameter borehole. Typical operating parameters include repetition rates up to 100 pps, with pulse widths between 10 and 80 μs (limited only by the available rf power supply) and source pressures as low as ˜5 mTorr. In this configuration, peak extractable hydrogen current densities exceeding 1180 mA/cm2 with H1+ yields over 94% having been achieved.

Status and applicability of solid polymer electrolyte technology to electrolytic hydrogen and oxygen production

NASA Technical Reports Server (NTRS)

Titterington, W. A.

1973-01-01

The solid polymer electrolyte (SPE) water electrolysis technology is presented as a potential energy conversion method for wind driven generator systems. Electrolysis life and performance data are presented from laboratory sized single cells (7.2 sq in active area) with high cell current density selected (1000 ASF) for normal operation.

Electricity generation by Pyrococcus furiosus in microbial fuel cells operated at 90°C.

PubMed

Sekar, Narendran; Wu, Chang-Hao; Adams, Michael W W; Ramasamy, Ramaraja P

2017-07-01

Hyperthermophiles are microorganisms that thrive in extremely hot environments with temperatures near and even above 100°C. They are the most deeply rooted microorganisms on phylogenetic trees suggesting they may have evolved to survive in the early hostile earth. The simple respiratory systems of some of these hyperthermophiles make them potential candidates to develop microbial fuel cells (MFC) that can generate power at temperatures approaching the boiling point. We explored extracellular electron transfer in the hyperthermophilic archaeon Pyrococcus furiosus (Pf) by studying its ability to generate electricity in a two-chamber MFC. Pf growing in defined medium functioned as an anolyte in a MFC operated at 90°C, generating a maximum current density of 2 A m -2 and a peak power density of 225 mW m -2 without the addition of any external redox mediator. Electron microscopy and electrochemical impedance spectroscopy of the anode with the attached Pf biofilm demonstrated bio-electrochemical behavior that led to electricity generation in the MFC via direct electron transfer. This proof of concept study reveals for the first time that a hyperthermophile such as Pf can generate electricity in MFC at extreme temperatures. Biotechnol. Bioeng. 2017;114: 1419-1427. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

The Role of Nongyrotropy in Balancing the Reconnection Diffusion Region

NASA Astrophysics Data System (ADS)

Hesse, M.; Liu, Y. H.; Chen, L. J.; Bessho, N.; Wang, S.; Burch, J. L.; Moretto, T.; Genestreti, K.; Phan, T.; Tenfjord, P.

2017-12-01

The structure of the reconnection diffusion region is, to a large degree, determined by the requirement to balance both the current flow and its dissipation processes, and the forces exerted onto the current layer by the inflow magnetic pressure. These balances are critical: without resupply processes, the transport of accelerated and current-carrying particles away from the diffusion region would generate a current density depletion, which, in principle, could lead to a mismatch with the curl of the magnetic field. Similarly, without heating processes, the convection of hot plasma away from the diffusion region would generate a force imbalance with the ambient magnetic field. The fact that neither of these imbalances occur is a consequence of the reconnection electric field, which is therefore not only required to facilitate magnetic flux transport, but also to provide the energization required to maintain balance in the diffusion region. In this presentation, we will use particle-in-cell simulations to analyze these balance conditions. We will furthermore show that nongyrotropic particle dynamics plays a key role both as current dissipation mechanism, and as overall heating mechanism in the diffusion region current layer.

Chiral current generation in QED by longitudinal photons

NASA Astrophysics Data System (ADS)

Acosta Avalo, J. L.; Pérez Rojas, H.

2016-08-01

We report the generation of a pseudovector electric current having imbalanced chirality in an electron-positron strongly magnetized gas in QED. It propagates along the external applied magnetic field B as a chiral magnetic effect in QED. It is triggered by a perturbative electric field parallel to B, associated to a pseudovector longitudinal mode propagating along B. An electromagnetic chemical potential was introduced, but our results remain valid even when it vanishes. A nonzero fermion mass was assumed, which is usually considered vanishing in the literature. In the quantum field theory formalism at finite temperature and density, an anomaly relation for the axial current was found for a medium of massive fermions. It bears some analogy to the Adler-Bell-Jackiw anomaly. From the expression for the chiral current in terms of the photon self-energy tensor in a medium, it is obtained that electrons and positrons scattered by longitudinal photons (inside the light cone) contribute to the chiral current, as well as the to pair creation due to longitudinal photons (out of light cone). In the static limit, an electric pseudovector current is obtained in the lowest Landau level.

Conceptual Design of a 100kW Energy Integrated Type Bi-Directional Tidal Current Turbine

NASA Astrophysics Data System (ADS)

Kim, Ki Pyoung; Ahmed, M. Rafiuddin; Lee, Young Ho

2010-06-01

The development of a tidal current turbine that can extract maximum energy from the tidal current will be extremely beneficial for supplying continuous electric power. The present paper presents a conceptual design of a 100kW energy integrated type tidal current turbine for tidal power generation. The instantaneous power density of a flowing fluid incident on an underwater turbine is proportional to the cubic power of current velocity which is approximately 2.5m/s. A cross-flow turbine, provided with a nozzle and a diffuser, is designed and analyzed. The potential advantages of ducted and diffuser-augmented turbines were taken into consideration in order to achieve higher output at a relatively low speed. This study looks at a cross-flow turbine system which is placed in an augmentation channel to generate electricity bi-directionally. The compatibility of this turbine system is verified using a commercial CFD code, ANSYSCFX. This paper presents the results of the numerical analysis in terms of pressure, streaklines, velocity vectors and performance curves for energy integrated type bi-directional tidal current turbine (BDT) with augmentation.

Tissue Engineering of the Corneal Endothelium: A Review of Carrier Materials

PubMed Central

Teichmann, Juliane; Valtink, Monika; Nitschke, Mirko; Gramm, Stefan; Funk, Richard H.W.; Engelmann, Katrin; Werner, Carsten

2013-01-01

Functional impairment of the human corneal endothelium can lead to corneal blindness. In order to meet the high demand for transplants with an appropriate human corneal endothelial cell density as a prerequisite for corneal function, several tissue engineering techniques have been developed to generate transplantable endothelial cell sheets. These approaches range from the use of natural membranes, biological polymers and biosynthetic material compositions, to completely synthetic materials as matrices for corneal endothelial cell sheet generation. This review gives an overview about currently used materials for the generation of transplantable corneal endothelial cell sheets with a special focus on thermo-responsive polymer coatings. PMID:24956190

High rate copper and energy recovery in microbial fuel cells

PubMed Central

Rodenas Motos, Pau; ter Heijne, Annemiek; van der Weijden, Renata; Saakes, Michel; Buisman, Cees J. N.; Sleutels, Tom H. J. A.

2015-01-01

Bioelectrochemical systems (BESs) are a novel, promising technology for the recovery of metals. The prerequisite for upscaling from laboratory to industrial size is that high current and high power densities can be produced. In this study we report the recovery of copper from a copper sulfate stream (2 g L-1 Cu2+) using a laboratory scale BES at high rate. To achieve this, we used a novel cell configuration to reduce the internal voltage losses of the system. At the anode, electroactive microorganisms produce electrons at the surface of an electrode, which generates a stable cell voltage of 485 mV when combined with a cathode where copper is reduced. In this system, a maximum current density of 23 A m-2 in combination with a power density of 5.5 W m-2 was produced. XRD analysis confirmed 99% purity in copper of copper deposited onto cathode surface. Analysis of voltage losses showed that at the highest current, most voltage losses occurred at the cathode, and membrane, while anode losses had the lowest contribution to the total voltage loss. These results encourage further development of BESs for bioelectrochemical metal recovery. PMID:26150802

AC Loss Analysis of MgB2-Based Fully Superconducting Machines

NASA Astrophysics Data System (ADS)

Feddersen, M.; Haran, K. S.; Berg, F.

2017-12-01

Superconducting electric machines have shown potential for significant increase in power density, making them attractive for size and weight sensitive applications such as offshore wind generation, marine propulsion, and hybrid-electric aircraft propulsion. Superconductors exhibit no loss under dc conditions, though ac current and field produce considerable losses due to hysteresis, eddy currents, and coupling mechanisms. For this reason, many present machines are designed to be partially superconducting, meaning that the dc field components are superconducting while the ac armature coils are conventional conductors. Fully superconducting designs can provide increases in power density with significantly higher armature current; however, a good estimate of ac losses is required to determine the feasibility under the machines intended operating conditions. This paper aims to characterize the expected losses in a fully superconducting machine targeted towards aircraft, based on an actively-shielded, partially superconducting machine from prior work. Various factors are examined such as magnet strength, operating frequency, and machine load to produce a model for the loss in the superconducting components of the machine. This model is then used to optimize the design of the machine for minimal ac loss while maximizing power density. Important observations from the study are discussed.

Using high haze (> 90%) light-trapping film to enhance the efficiency of a-Si:H solar cells

NASA Astrophysics Data System (ADS)

Chu, Wei-Ping; Lin, Jian-Shian; Lin, Tien-Chai; Tsai, Yu-Sheng; Kuo, Chen-Wei; Chung, Ming-Hua; Hsieh, Tsung-Eong; Liu, Lung-Chang; Juang, Fuh-Shyang; Chen, Nien-Po

2012-07-01

The high haze light-trapping (LT) film offers enhanced scattering of light and is applied to a-Si:H solar cells. UV glue was spin coated on glass, and then the LT pattern was imprinted. Finally, a UV lamp was used to cure the UV glue on the glass. The LT film effectively increased the Haze ratio of glass and decreased the reflectance of a-Si:H solar cells. Therefore, the photon path length was increased to obtain maximum absorption by the absorber layer. High Haze LT film is able to enhance short circuit current density and efficiency of the device, as partial composite film generates broader scattering light, thereby causing shorter wave length light to be absorbed by the P layer so that the short circuit current density decreases. In case of lab-made a-Si:H thin film solar cells with v-shaped LT films, superior optoelectronic performances have been found (Voc = 0.74 V, Jsc = 15.62 mA/cm2, F.F. = 70%, and η = 8.09%). We observed ~ 35% enhancement of the short-circuit current density and ~ 31% enhancement of the conversion efficiency.

Threshold-voltage modulated phase change heterojunction for application of high density memory

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

Yan, Baihan; Tong, Hao, E-mail: tonghao@hust.edu.cn; Qian, Hang

2015-09-28

Phase change random access memory is one of the most important candidates for the next generation non-volatile memory technology. However, the ability to reduce its memory size is compromised by the fundamental limitations inherent in the CMOS technology. While 0T1R configuration without any additional access transistor shows great advantages in improving the storage density, the leakage current and small operation window limit its application in large-scale arrays. In this work, phase change heterojunction based on GeTe and n-Si is fabricated to address those problems. The relationship between threshold voltage and doping concentration is investigated, and energy band diagrams and X-raymore » photoelectron spectroscopy measurements are provided to explain the results. The threshold voltage is modulated to provide a large operational window based on this relationship. The switching performance of the heterojunction is also tested, showing a good reverse characteristic, which could effectively decrease the leakage current. Furthermore, a reliable read-write-erase function is achieved during the tests. Phase change heterojunction is proposed for high-density memory, showing some notable advantages, such as modulated threshold voltage, large operational window, and low leakage current.« less

Device and method for relativistic electron beam heating of a high-density plasma to drive fast liners

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner which is generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner.

Runaway electron generation as possible trigger for enhancement of magnetohydrodynamic plasma activity and fast changes in runaway beam behavior

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

Pankratov, I. M., E-mail: pankratov@kipt.kharkov.ua, E-mail: rjzhou@ipp.ac.cn; Zhou, R. J., E-mail: pankratov@kipt.kharkov.ua, E-mail: rjzhou@ipp.ac.cn; Hu, L. Q.

2015-07-15

Peculiar phenomena were observed during experiments with runaway electrons: rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the electron cyclotron emission (ECE) signal (cyclotron radiation of suprathermal electrons). These phenomena were initially observed in TEXTOR (Tokamak Experiment for Technology Oriented Research), where these events only occurred in the current decay phase or in discharges with thin stable runaway beams at a q = 1 drift surface. These rapid changes in the synchrotron spot were interpreted by the TEXTOR team as a fast pitch angle scattering event. Recently, similar rapid changes in the synchrotron spot andmore » its intensity that coincided with stepwise increases in the non-thermal ECE signal were observed in the EAST (Experimental Advanced Superconducting Tokamak) runaway discharge. Runaway electrons were located around the q = 2 rational magnetic surface (ring-like runaway electron beam). During the EAST runaway discharge, stepwise ECE signal increases coincided with enhanced magnetohydrodynamic (MHD) activity. This behavior was peculiar to this shot. In this paper, we show that these non-thermal ECE step-like jumps were related to the abrupt growth of suprathermal electrons induced by bursting electric fields at reconnection events during this MHD plasma activity. Enhancement of the secondary runaway electron generation also occurred simultaneously. Local changes in the current-density gradient appeared because of local enhancement of the runaway electron generation process. These current-density gradient changes are considered to be a possible trigger for enhancement of the MHD plasma activity and the rapid changes in runaway beam behavior.« less

Runaway electron generation as possible trigger for enhancement of magnetohydrodynamic plasma activity and fast changes in runaway beam behavior

NASA Astrophysics Data System (ADS)

Pankratov, I. M.; Zhou, R. J.; Hu, L. Q.

2015-07-01

Peculiar phenomena were observed during experiments with runaway electrons: rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the electron cyclotron emission (ECE) signal (cyclotron radiation of suprathermal electrons). These phenomena were initially observed in TEXTOR (Tokamak Experiment for Technology Oriented Research), where these events only occurred in the current decay phase or in discharges with thin stable runaway beams at a q = 1 drift surface. These rapid changes in the synchrotron spot were interpreted by the TEXTOR team as a fast pitch angle scattering event. Recently, similar rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the non-thermal ECE signal were observed in the EAST (Experimental Advanced Superconducting Tokamak) runaway discharge. Runaway electrons were located around the q = 2 rational magnetic surface (ring-like runaway electron beam). During the EAST runaway discharge, stepwise ECE signal increases coincided with enhanced magnetohydrodynamic (MHD) activity. This behavior was peculiar to this shot. In this paper, we show that these non-thermal ECE step-like jumps were related to the abrupt growth of suprathermal electrons induced by bursting electric fields at reconnection events during this MHD plasma activity. Enhancement of the secondary runaway electron generation also occurred simultaneously. Local changes in the current-density gradient appeared because of local enhancement of the runaway electron generation process. These current-density gradient changes are considered to be a possible trigger for enhancement of the MHD plasma activity and the rapid changes in runaway beam behavior.

Cosmological magnetic fields from inflation in extended electromagnetism

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

Beltran Jimenez, Jose; Maroto, Antonio L.

2011-01-15

In this work we consider an extended electromagnetic theory in which the scalar state which is usually eliminated by means of the Lorenz condition is allowed to propagate. This state has been shown to generate a small cosmological constant in the context of standard inflationary cosmology. Here we show that the usual Lorenz gauge-breaking term now plays the role of an effective electromagnetic current. Such a current is generated during inflation from quantum fluctuations and gives rise to a stochastic effective charge density distribution. Because of the high electric conductivity of the cosmic plasma after inflation, the electric charge densitymore » generates currents which give rise to both vorticity and magnetic fields on sub-Hubble scales. Present upper limits on vorticity coming from temperature anisotropies of the CMB are translated into lower limits on the present value of cosmic magnetic fields. We find that, for a nearly scale invariant vorticity spectrum, magnetic fields B{sub {lambda}>}10{sup -12} G are typically generated with coherence lengths ranging from subgalactic scales up to the present Hubble radius. Those fields could act as seeds for a galactic dynamo or even account for observations just by collapse and differential rotation of the protogalactic cloud.« less

Electrochemical treatment of pharmaceutical wastewater by combining anodic oxidation with ozonation.

PubMed

Menapace, Hannes M; Diaz, Nicolas; Weiss, Stefan

2008-07-01

Wastewater effluents from sewage treatment plants (STP) are important point sources for residues of pharmaceuticals and complexing agents in the aquatic environment. For this reason a research project, which started in December 2006, was established to eliminate pharmaceutical substances and complexing agents found in wastewater as micropollutants. For the treatment process a combination of anodic oxidation by boron-doped diamond (BDD) electrodes and ozonation is examined and presented. For the ozone production a non-conventional, separate reactor was used, in which ozone was generated by electrolysis with diamond electrodes For the determination of the achievable remediation rates four complexing agents (e.g., EDTA, NTA) and eight pharmaceutical substances (e.g., diazepam, carbamazepin) were analyzed in several test runs under different conditions (varied flux, varied current density for the diamond electrode and the ozone producing electrode of the ozone generator, different packing materials for the column in the ozone injection system). The flowrates of the treated water samples were varied from 3 L/h up to 26 L/h. For the anodic oxidation the influence of the current density was examined in the range between 22.7 and 45.5 mA/cm(2), for the ozone producing reactor two densities (1.8 a/cm(2) and 2.0 A/cm(2)) were tested. Matrix effects were investigated by test runs with samples from the effluent of an STP and synthetic waste water. Therefore the impact of the organic material in the samples could be determined by the comparison of the redox potential and the achievable elimination rates of the investigated substances. Comparing both technologies anodic oxidation seems to be superior to ozonation in each investigated area. With the used technology of anodic oxidation elimination rates up to 99% were reached for the investigated pharmaceutical substances at a current density of 45.5 mA/cm(2) and a maximum sample flux of 26 L/h.

Anisotropic thermoelectric behavior in armchair and zigzag mono- and fewlayer MoS2 in thermoelectric generator applications

PubMed Central

Arab, Abbas; Li, Qiliang

2015-01-01

In this work, we have studied thermoelectric properties of monolayer and fewlayer MoS2 in both armchair and zigzag orientations. Density functional theory (DFT) using non-equilibrium Green’s function (NEGF) method has been implemented to calculate the transmission spectra of mono- and fewlayer MoS2 in armchair and zigzag directions. Phonon transmission spectra are calculated based on parameterization of Stillinger-Weber potential. Thermoelectric figure of merit, ZT, is calculated using these electronic and phonon transmission spectra. In general, a thermoelectric generator is composed of thermocouples made of both n-type and p-type legs. Based on our calculations, monolayer MoS2 in armchair orientation is found to have the highest ZT value for both p-type and n-type legs compared to all other armchair and zigzag structures. We have proposed a thermoelectric generator based on monolayer MoS2 in armchair orientation. Moreover, we have studied the effect of various dopant species on thermoelectric current of our proposed generator. Further, we have compared output current of our proposed generator with those of Silicon thin films. Results indicate that thermoelectric current of MoS2 armchair monolayer is several orders of magnitude higher than that of Silicon thin films. PMID:26333948

Anisotropic thermoelectric behavior in armchair and zigzag mono- and fewlayer MoS2 in thermoelectric generator applications.

PubMed

Arab, Abbas; Li, Qiliang

2015-09-03

In this work, we have studied thermoelectric properties of monolayer and fewlayer MoS2 in both armchair and zigzag orientations. Density functional theory (DFT) using non-equilibrium Green's function (NEGF) method has been implemented to calculate the transmission spectra of mono- and fewlayer MoS2 in armchair and zigzag directions. Phonon transmission spectra are calculated based on parameterization of Stillinger-Weber potential. Thermoelectric figure of merit, ZT, is calculated using these electronic and phonon transmission spectra. In general, a thermoelectric generator is composed of thermocouples made of both n-type and p-type legs. Based on our calculations, monolayer MoS2 in armchair orientation is found to have the highest ZT value for both p-type and n-type legs compared to all other armchair and zigzag structures. We have proposed a thermoelectric generator based on monolayer MoS2 in armchair orientation. Moreover, we have studied the effect of various dopant species on thermoelectric current of our proposed generator. Further, we have compared output current of our proposed generator with those of Silicon thin films. Results indicate that thermoelectric current of MoS2 armchair monolayer is several orders of magnitude higher than that of Silicon thin films.

A current drive by using the fast wave in frequency range higher than two timeslower hybrid resonance frequency on tokamaks

NASA Astrophysics Data System (ADS)

Kim, Sun Ho; Hwang, Yong Seok; Jeong, Seung Ho; Wang, Son Jong; Kwak, Jong Gu

2017-10-01

An efficient current drive scheme in central or off-axis region is required for the steady state operation of tokamak fusion reactors. The current drive by using the fast wave in frequency range higher than two times lower hybrid resonance (w>2wlh) could be such a scheme in high density, high temperature reactor-grade tokamak plasmas. First, it has relatively higher parallel electric field to the magnetic field favorable to the current generation, compared to fast waves in other frequency range. Second, it can deeply penetrate into high density plasmas compared to the slow wave in the same frequency range. Third, parasitic coupling to the slow wave can contribute also to the current drive avoiding parametric instability, thermal mode conversion and ion heating occured in the frequency range w<2wlh. In this study, the propagation boundary, accessibility, and the energy flow of the fast wave are given via cold dispersion relation and group velocity. The power absorption and current drive efficiency are discussed qualitatively through the hot dispersion relation and the polarization. Finally, those characteristics are confirmed with ray tracing code GENRAY for the KSTAR plasmas.

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

NASA Astrophysics Data System (ADS)

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

2012-10-01

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

Mathematical physics approaches to lightning discharge problems

NASA Technical Reports Server (NTRS)

Kyrala, A.

1985-01-01

Mathematical physics arguments useful for lightning discharge and generation problems are pursued. A soliton Ansatz for the lightning stroke is treated including a charge generation term which is the ultimate source for the phenomena. Equations are established for a partially ionized plasma inding the effects of pressure, magnetic field, electric field, gravitation, viscosity, and temperature. From these equations is then derived the non-stationary generalized Ohm's Law essential for describing field/current density relationships in the horizon channel of the lightning stroke. The discharge initiation problem is discussed. It is argued that the ionization rate drives both the convective current and electric displacement current to increase exponentially. The statistical distributions of charge in the thundercloud preceding a lightning dischage are considered. The stability of the pre-lightning charge distributions and the use of Boltzmann relaxational equations to determine them are discussed along with a covered impedance path provided by the aircraft.

Production of atmospheric-pressure glow discharge in nitrogen using needle-array electrode

NASA Astrophysics Data System (ADS)

Takaki, K.; Hosokawa, M.; Sasaki, T.; Mukaigawa, S.; Fujiwara, T.

2005-04-01

An atmospheric pressure glow discharge was generated using a needle-array electrode in nitrogen, and the voltage-current characteristics of the glow discharge were obtained in a range from 1 mA to 60 A. A pulsed high voltage with short rise time under 10 ns was employed to generate streamer discharges simultaneously at all needle tips. The large number of streamer discharges prevented the glow-to-arc transition caused by inhomogeneous thermalization. Semiconductor opening switch diodes were employed as an opening switch to shorten the rise time. The glow voltage was almost constant until the discharge current became 0.3 A, whereas the voltage increased with the current higher than 0.3 A. Electron density and temperature in a positive column of the glow discharge at 60 A were obtained to 1.4×1012cm-3 and 1.3 eV from calculation based on nitrogen swarm data.

Exact general relativistic disks with magnetic fields

NASA Astrophysics Data System (ADS)

Letelier, Patricio S.

1999-11-01

The well-known ``displace, cut, and reflect'' method used to generate cold disks from given solutions of Einstein equations is extended to solutions of Einstein-Maxwell equations. Four exact solutions of the these last equations are used to construct models of hot disks with surface density, azimuthal pressure, and azimuthal current. The solutions are closely related to Kerr, Taub-NUT, Lynden-Bell-Pinault, and to a one-soliton solution. We find that the presence of the magnetic field can change in a nontrivial way the different properties of the disks. In particular, the pure general relativistic instability studied by Bic̆ák, Lynden-Bell, and Katz [Phys. Rev. D 47, 4334 (1993)] can be enhanced or cured by different distributions of currents inside the disk. These currents, outside the disk, generate a variety of axial symmetric magnetic fields. As far as we know these are the first models of hot disks studied in the context of general relativity.

Self-propulsion of a planar electric or magnetic microbot immersed in a polar viscous fluid

NASA Astrophysics Data System (ADS)

Felderhof, B. U.

2011-05-01

A planar sheet immersed in an electrically polar liquid like water can propel itself by means of a plane wave charge density propagating in the sheet. The corresponding running electric wave polarizes the fluid and causes an electrical torque density to act on the fluid. The sheet is convected by the fluid motion resulting from the conversion of rotational particle motion, generated by the torque density, into translational fluid motion by the mechanism of friction and spin diffusion. Similarly, a planar sheet immersed in a magnetic ferrofluid can propel itself by means of a plane wave current density in the sheet and the torque density acting on the fluid corresponding to the running wave magnetic field and magnetization. The effect is studied on the basis of the micropolar fluid equations of motion and Maxwell’s equations of electrostatics or magnetostatics, respectively. An analytic expression is derived for the velocity of the sheet by perturbation theory to second order in powers of the amplitude of the driving charge or current density. Under the assumption that the equilibrium magnetic equation of state may be used in linearized form and that higher harmonics than the first may be neglected, a set of self-consistent integral equations is derived which can be solved numerically by iteration. In typical situations the second-order perturbation theory turns out to be quite accurate.

Automatically Generated Vegetation Density Maps with LiDAR Survey for Orienteering Purpose

NASA Astrophysics Data System (ADS)

Petrovič, Dušan

2018-05-01

The focus of our research was to automatically generate the most adequate vegetation density maps for orienteering purpose. Application Karttapullatuin was used for automated generation of vegetation density maps, which requires LiDAR data to process an automatically generated map. A part of the orienteering map in the area of Kazlje-Tomaj was used to compare the graphical display of vegetation density. With different settings of parameters in the Karttapullautin application we changed the way how vegetation density of automatically generated map was presented, and tried to match it as much as possible with the orienteering map of Kazlje-Tomaj. Comparing more created maps of vegetation density the most suitable parameter settings to automatically generate maps on other areas were proposed, too.

THERMOCHEMICAL CONVERSION OF FERMENTATION-DERIVED OXYGENATES TO FUELS

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

Ramasamy, Karthikeyan K.; Wang, Yong

2013-06-01

At present ethanol generated from renewable resources through fermentation process is the dominant biofuel. But ethanol suffers from undesirable fuel properties such as low energy density and high water solubility. The production capacity of fermentation derived oxygenates are projected to rise in near future beyond the current needs. The conversion of oxygenates to hydrocarbon compounds that are similar to gasoline, diesel and jet fuel is considered as one of the viable option. In this chapter the thermo catalytic conversion of oxygenates generated through fermentation to fuel range hydrocarbons will be discussed.

Three-dimensional structure of dilute pyroclastic density currents

NASA Astrophysics Data System (ADS)

Andrews, B. J.

2013-12-01

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

New Model for Ionospheric Irregularities at Mars

NASA Astrophysics Data System (ADS)

Keskinen, M. J.

2018-03-01

A new model for ionospheric irregularities at Mars is presented. It is shown that wind-driven currents in the dynamo region of the Martian ionosphere can be unstable to the electromagnetic gradient drift instability. This plasma instability can generate ionospheric density and magnetic field irregularities with scale sizes of approximately 15-20 km down to a few kilometers. We show that the instability-driven magnetic field fluctuation amplitudes relative to background are correlated with the ionospheric density fluctuation amplitudes relative to background. Our results can explain recent observations made by the Mars Atmosphere and Volatile EvolutioN spacecraft in the Martian ionosphere dynamo region.

Fractal-Based Oscillation of Macular Arteriogenesis and Dropout During Progressive Diabetic Retinopathy

NASA Technical Reports Server (NTRS)

Radharkrishnan, Krishnan; Kaiser, Peter K.

2011-01-01

By both fractal (D1) and branching (Lv) analysis, macular arterial density oscillated with progression from mild NPDR to PDR. Results are consistent with out study reported recently for the entire arterial and venous branching trees within 50 degree FAs by VESGEN generational branching analysis. Current and previous results are important for advances in early-stage regenerative DR therapies, for which reversal of DR progression to a normal vessel density may be possible. For example, potential use of regenerative angiogenesis stimulators to reverse vascular dropout during mild and severe NPDR is not indicated for treatment of moderate NPDR.

Experimental study of atmospheric-pressure micro-plasmas for the ambient sampling of conductive materials

NASA Astrophysics Data System (ADS)

Duan, Zhengchao; He, Feng; Si, Xinlu; Bradley, James W.; Ouyang, Jiting

2018-02-01

Conductive solid material sampling by micro-plasma under ambient atmosphere was studied experimentally. A high-voltage pulse generator was utilized to drive discharge between a tungsten needle and metal samples. The effects of pulse width on discharge, micro-plasma and sampling were investigated. The electrical results show that two discharge current pulses can be formed in one voltage pulse. The duration of the first current pulse is of the order of 100 ns. The duration of the second current pulse depends on the width of the voltage pulse. The electrical results also show that arc micro-plasma was generated during both current pulses. The results of the emission spectra of different sampled materials indicate that the relative emission intensity of elemental metal ions will increase with pulse width. The excitation temperature and electron density of the arc micro-plasmas increase with the voltage pulse width, which contributes to the increase of relative emission intensity of metal ions. The optical images and energy dispersive spectroscopy results of the sampling spots on metal surfaces indicate that discharge with a short voltage pulse can generate a small sputtering crater.

Breakover mechanism of GaAs photoconductive switch triggering spark gap for high power applications

NASA Astrophysics Data System (ADS)

Tian, Liqiang; Shi, Wei; Feng, Qingqing

2011-11-01

A spark gap (SG) triggered by a semi-insulating GaAs photoconductive semiconductor switch (PCSS) is presented. Currents as high as 5.6 kA have been generated using the combined switch, which is excited by a laser pulse with energy of 1.8 mJ and under a bias of 4 kV. Based on the transferred-electron effect and gas streamer theory, the breakover characteristics of the combined switch are analyzed. The photoexcited carrier density in the PCSS is calculated. The calculation and analysis indicate that the PCSS breakover is caused by nucleation of the photoactivated avalanching charge domain. It is shown that the high output current is generated by the discharge of a high-energy gas streamer induced by the strong local electric field distortion or by overvoltage of the SG resulting from quenching of the avalanching domain, and periodic oscillation of the current is caused by interaction between the gas streamer and the charge domain. The cycle of the current oscillation is determined by the rise time of the triggering electric pulse generated by the PCSS, the pulse transmission time between the PCSS and the SG, and the streamer transit time in the SG.

Superconducting light generator for large offshore wind turbines

NASA Astrophysics Data System (ADS)

Sanz, S.; Arlaban, T.; Manzanas, R.; Tropeano, M.; Funke, R.; Kováč, P.; Yang, Y.; Neumann, H.; Mondesert, B.

2014-05-01

Offshore wind market demands higher power rate and reliable turbines in order to optimize capital and operational cost. These requests are difficult to overcome with conventional generator technologies due to a significant weight and cost increase with the scaling up. Thus superconducting materials appears as a prominent solution for wind generators, based on their capacity to held high current densities with very small losses, which permits to efficiently replace copper conductors mainly in the rotor field coils. However the state-of-the-art superconducting generator concepts still seem to be expensive and technically challenging for the marine environment. This paper describes a 10 MW class novel direct drive superconducting generator, based on MgB2 wires and a modular cryogen free cooling system, which has been specifically designed for the offshore wind industry needs.

Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams.

PubMed

Liu, Lie; Li, Limin; Wen, Jianchun; Wan, Hong

2009-02-01

This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a approximately 450 kV, approximately 400 ns pulse. It was found that 300-400 MW, approximately 250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.

Analytical solution for the effect of the permittivity of coating layer on eddy current generated in an aluminum sample by EMAT

NASA Astrophysics Data System (ADS)

Sun, Feiran; Sun, Zhenguo; Chen, Qiang

2016-02-01

In order to improve the ultrasonic wave amplitude excited by electromagnetic acoustic transducers (EMATs), many researchers have proposed models. But they always ignored displacement current or the effect of the permittivity of the air or the metal sample during modeling, due to its low permittivity. However, more durable dielectric materials are replacing or coating with metals in many applications which have a much higher permittivity than air or metal sample so that the effect of permittivity cannot be ignored. Based on an analytical model, the effect of the permittivity of coating layer on the eddy current generated in an aluminum sample by EMAT has been studied. The analytical analysis indicates that the eddy current density excited by the spiral coil of EMAT slowly increases in the beginning and then decreases rapidly while the permittivity increases, and it has much relation to the thickness of the coating layer and the exciting frequency, which is verified by the simulation result.

Utilizing upper hybrid resonance for high density plasma production and negative ion generation in a downstream region

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

Sahu, Debaprasad; Bhattacharjee, Sudeep

2012-09-15

Localized wave-induced resonances are created by microwaves launched directly into a multicusp (MC) plasma device in the k Up-Tack B mode, where k is the wave vector and B is the static magnetic field. The resonance zone is identified as upper hybrid resonance (UHR), and lies r = {approx}22 mm away from the MC boundary. Measurement of radial wave electric field intensity confirms the right hand cutoff of the wave (r = 22.5-32.1 mm) located near the UHR zone. A sharp rise in the corresponding electron temperature in the resonance region by {approx}13 eV from its value away from resonancemore » at r = 0, is favorable for the generation of vibrationally excited molecules of hydrogen. A transverse magnetic filter allows cold electrons ({approx}1-2 eV) to pass into the downstream region where they generate negative ions by dissociative attachment. Measurements of electron energy distribution function (EEDF) support the viewpoint. H{sup -} current density of {approx}0.26 mA/cm{sup 2} is obtained at a wave power density of {approx}3 W/cm{sup 2} at 2.0 mTorr pressure, which agrees reasonably well with results obtained from a steady state model using particle balance equations.« less

A Multiple Z-Pinch Configuration for the Generation of High-Density, Magnetized Plasmas

NASA Astrophysics Data System (ADS)

Tarditi, Alfonso G.

2015-11-01

The z-pinch is arguably the most straightforward and economical approach for the generation and confinement of hot plasmas, with a long history of theoretical investigations and experimental developments. While most of the past studies were focused on countering the natural tendency of z-pinches to develop instabilities, this study attempts to take advantage of those unstable regimes to form a quasi-stable plasma, with higher density and temperature, possibly of interest for a fusion reactor concept. For this purpose, a configuration with four z-pinch discharges, with axis parallel to each other and symmetrically positioned, is considered. Electrodes for the generation of the discharges and magnetic coils are arranged to favor the formation of concave discharge patterns. The mutual attraction from the co-streaming discharge currents enhances this pattern, leading to bent plasma streams, all nearing towards the axis. This configuration is intended to excite and sustain a ``kink'' unstable mode for each z-pinch, eventually producing either plasmoid structures, detached from each discharge, or sustained kink patterns: both these cases appear to lead to plasmas merging in the central region. The feasibility of this approach in creating a higher density, hotter, meta-stable plasma regime is investigated computationally, addressing both the kink excitation phase and the dynamics of the converging plasma columns.

Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness

NASA Astrophysics Data System (ADS)

Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E.; Huang, Yu

2012-01-01

Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications.Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications. Electronic supplementary information (ESI) available: Supplementary TEM, EELS, EDS, Electro-chemical measurement data can be found. See DOI: 10.1039/c1nr11374g

Current source density analysis of the hippocampal theta rhythm: associated sustained potentials and candidate synaptic generators.

PubMed

Brankack, J; Stewart, M; Fox, S E

1993-07-02

Single-electrode depth profiles of the hippocampal EEG were made in urethane-anesthetized rats and rats trained in an alternating running/drinking task. Current source density (CSD) was computed from the voltage as a function of depth. A problem inherent to AC-coupled profiles was eliminated by incorporating sustained potential components of the EEG. 'AC' profiles force phasic current sinks to alternate with current sources at each lamina, changing the magnitude and even the sign of the computed membrane current. It was possible to include DC potentials in the profiles from anesthetized rats by using glass micropipettes for recording. A method of 'subtracting' profiles of the non-theta EEG from theta profiles was developed as an approach to including sustained potentials in recordings from freely-moving animals implanted with platinum electrodes. 'DC' profiles are superior to 'AC' profiles for analysis of EEG activity because 'DC'-CSD values can be considered correct in sign and more closely represent the actual membrane current magnitudes. Since hippocampal inputs are laminated, CSD analysis leads to straightforward predictions of the afferents involved. Theta-related activity in afferents from entorhinal neurons, hippocampal interneurons and ipsi- and contralateral hippocampal pyramids all appear to contribute to sources and sinks in CA1 and the dentate area. The largest theta-related generator was a sink at the fissure, having both phasic and tonic components. This sink may reflect activity in afferents from the lateral entorhinal cortex. The phase of the dentate mid-molecular sink suggests that medial entorhinal afferents drive the theta-related granule and pyramidal cell firing. The sustained components may be simply due to different average rates of firing during theta rhythm than during non-theta EEG in afferents whose firing rates are also phasically modulated.

Electrolytic treatment of Standard Malaysian Rubber process wastewater.

PubMed

Vijayaraghavan, Krishnan; Ahmad, Desa; Yazid, Ahmad Yuzri Ahmad

2008-01-31

A new method of Standard Malaysian Rubber (SMR) process wastewater treatment was developed based on in situ hypochlorous acid generation. The hypochlorous acid was generated in an undivided electrolytic cell consisting of two sets of graphite as anode and stainless sheets as cathode. The generated hypochlorous acid served as an oxidizing agent to destroy the organic matter present in the SMR wastewater. For an influent COD concentration of 2960 mg/L at an initial pH 4.5+/-0.1, current density 74.5 mA/cm(2), sodium chloride content 3% and electrolysis period of 75 min, resulted in the following residual values pH 7.5, COD 87 mg/L, BOD(5) 60 mg/L, TOC 65 mg/L, total chlorine 146 mg/L, turbidity 7 NTU and temperature 48 degrees C, respectively. In the case of 2% sodium chloride as an electrolyte for the above said operating condition resulted in the following values namely: pH 7.2, COD 165 mg/L, BOD(5) 105 mg/L, TOC 120 mg/L, total chlorine 120 mg/L, turbidity 27 NTU and temperature 53 degrees C, respectively. The energy requirement were found to be 30 and 46 Wh/L, while treating 24 L of SMR wastewater at 2 and 3% sodium chloride concentration at a current density 74.5 mA/cm(2). The observed energy difference was due to the improved conductivity at high sodium chloride content.

Coupled thermal, electrical, and fluid flow analyses of AMTEC multitube cell with adiabatic side wall

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

Schock, A.; Or, C.; Noravian, H.

1997-01-01

The paper describes a novel OSC-generated methodology for analyzing the performance of multitube AMTEC (Alkali Metal Thermal-to-Electrical Conversion) cells, which are under development by AMPS (Advanced Modular Power Systems, Inc.) for the Air Force Phillips Laboratory (AFPL) and NASA{close_quote}s Jet Propulsion Laboratory (JPL), for possible application to the Pluto Express and other space missions. The OSC study was supported by the Department of Energy (DOE), and was strongly encouraged by JPL, AFPL, and AMPS. It resulted in an iterative procedure for the coupled solution of the interdependent thermal, electrical, and fluid flow differential and integral equations governing the performance ofmore » AMTEC cells and generators. The paper clarifies the OSC procedure by presenting detailed results of its application to an illustrative example of a converter cell with an adiabatic side wall, including the non-linear axial variation of temperature, pressure, open-circuit voltage, interelectrode voltage, current density, axial current, sodium mass flow, and power density. The next paper in these proceedings describes parametric results obtained by applying the same procedure to variations of the baseline adiabatic converter design, culminating in an OSC-recommended revised cell design. A subsequent paper in these proceedings extends the procedure to analyze a variety of OSC-designed radioisotope-heated generators employing non-adiabatic multitube AMTEC cells. {copyright} {ital 1997 American Institute of Physics.}« less

A mini-type hydrogen generator from aluminum for proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Wang, Er-Dong; Shi, Peng-Fei; Du, Chun-Yu; Wang, Xiao-Rui

A safe and simple hydrogen generator, which produced hydrogen by chemical reaction of aluminum and sodium hydroxide solution, was proposed for proton exchange membrane fuel cells. The effects of concentration, dropping rate and initial temperature of sodium hydroxide solution on hydrogen generation rate were investigated. The results showed that about 38 ml min -1 of hydrogen generation rate was obtained with 25 wt.% concentration and 0.01 ml s -1 dropping rate of sodium hydroxide solution. The cell fueled by hydrogen from the generator exhibited performance improvement at low current densities, which was mainly due to the humidified hydrogen reduced the protonic resistivity of the proton exchange membrane. The hydrogen generator could stably operate a single cell under 500 mA for nearly 5 h with about 77% hydrogen utilization ratio.

Review of electric discharge microplasmas generated in highly fluctuating fluids: Characteristics and application to nanomaterials synthesis

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

Stauss, Sven, E-mail: sven.stauss@plasma.k.u-tokyo.ac.jp; Terashima, Kazuo, E-mail: kazuo@plasma.k.u-tokyo.ac.jp; Muneoka, Hitoshi

2015-05-15

Plasma-based fabrication of novel nanomaterials and nanostructures is indispensible for the development of next-generation electronic devices and for green energy applications. In particular, controlling the interactions between plasmas and materials interfaces, and the plasma fluctuations, is crucial for further development of plasma-based processes and bottom-up growth of nanomaterials. Electric discharge microplasmas generated in supercritical fluids represent a special class of high-pressure plasmas, where fluctuations on the molecular scale influence the discharge properties and the possible bottom-up growth of nanomaterials. This review discusses an anomaly observed for direct current microplasmas generated near the critical point, a local decrease in the breakdownmore » voltage. This anomalous behavior is suggested to be caused by the concomitant decrease of the ionization potential due to the formation of clusters near the critical point, and the formation of extended electron mean free paths caused by the high-density fluctuation near the critical point. It is also shown that in the case of dielectric barrier microdischarges generated close to the critical point, the high-density fluctuation of the supercritical fluid persists. The final part of the review discusses the application of discharges generated in supercritical fluids to synthesis of nanomaterials, in particular, molecular diamond—so-called diamondoids—by microplasmas generated inside conventional batch-type and continuous flow microreactors.« less

Hall-MHD and PIC Modeling of the Conduction-to-Opening Transition in a Plasma Opening Switch

NASA Astrophysics Data System (ADS)

Schumer, J. W.; SwanekampDdagger, S. B.; Ottinger, P. F.; Commisso, R. J.; Weber, B. V.

1998-11-01

Utilizing the fast opening characteristics of a plasma opening switch (POS), inductive energy storage devices can generate short-duration high-power pulses (<0.1 μ s, >1 TW) with current rise-times on the order of 10 ns. Plasma redistribution and thinning during the POS conduction phase can be modeled adequately with MHD methods. By including the Hall term in Ohm's Law, MHD methods can simulate plasmas with density gradient scale lengths between c/ω_pe < Ln < c/ω_pi. However, the neglect of electron inertia (c/ω_pe) and space-charge separation (λ_De) by single-fluid theory eventually becomes invalid in small gap regions that form during POS opening. PIC methods are well-suited for low-density plasmas, but are numerically taxed by high-density POS regions. An interface converts MHD (Mach2) output into PIC (Magic) input suitable for validating various transition criteria through comparison of current and density distributions from both methods. We will discuss recent progress in interfacing Hall-MHD and PIC simulations. Work supported by Defense Special Weapons Agency. ^ NRL-NRC Research Associate. hspace0.25in ^ JAYCOR, Vienna, VA 22102.

An eFTD-VP framework for efficiently generating patient-specific anatomically detailed facial soft tissue FE mesh for craniomaxillofacial surgery simulation

PubMed Central

Zhang, Xiaoyan; Kim, Daeseung; Shen, Shunyao; Yuan, Peng; Liu, Siting; Tang, Zhen; Zhang, Guangming; Zhou, Xiaobo; Gateno, Jaime

2017-01-01

Accurate surgical planning and prediction of craniomaxillofacial surgery outcome requires simulation of soft tissue changes following osteotomy. This can only be achieved by using an anatomically detailed facial soft tissue model. The current state-of-the-art of model generation is not appropriate to clinical applications due to the time-intensive nature of manual segmentation and volumetric mesh generation. The conventional patient-specific finite element (FE) mesh generation methods are to deform a template FE mesh to match the shape of a patient based on registration. However, these methods commonly produce element distortion. Additionally, the mesh density for patients depends on that of the template model. It could not be adjusted to conduct mesh density sensitivity analysis. In this study, we propose a new framework of patient-specific facial soft tissue FE mesh generation. The goal of the developed method is to efficiently generate a high-quality patient-specific hexahedral FE mesh with adjustable mesh density while preserving the accuracy in anatomical structure correspondence. Our FE mesh is generated by eFace template deformation followed by volumetric parametrization. First, the patient-specific anatomically detailed facial soft tissue model (including skin, mucosa, and muscles) is generated by deforming an eFace template model. The adaptation of the eFace template model is achieved by using a hybrid landmark-based morphing and dense surface fitting approach followed by a thin-plate spline interpolation. Then, high-quality hexahedral mesh is constructed by using volumetric parameterization. The user can control the resolution of hexahedron mesh to best reflect clinicians’ need. Our approach was validated using 30 patient models and 4 visible human datasets. The generated patient-specific FE mesh showed high surface matching accuracy, element quality, and internal structure matching accuracy. They can be directly and effectively used for clinical simulation of facial soft tissue change. PMID:29027022

An eFTD-VP framework for efficiently generating patient-specific anatomically detailed facial soft tissue FE mesh for craniomaxillofacial surgery simulation.

PubMed

Zhang, Xiaoyan; Kim, Daeseung; Shen, Shunyao; Yuan, Peng; Liu, Siting; Tang, Zhen; Zhang, Guangming; Zhou, Xiaobo; Gateno, Jaime; Liebschner, Michael A K; Xia, James J

2018-04-01

Accurate surgical planning and prediction of craniomaxillofacial surgery outcome requires simulation of soft tissue changes following osteotomy. This can only be achieved by using an anatomically detailed facial soft tissue model. The current state-of-the-art of model generation is not appropriate to clinical applications due to the time-intensive nature of manual segmentation and volumetric mesh generation. The conventional patient-specific finite element (FE) mesh generation methods are to deform a template FE mesh to match the shape of a patient based on registration. However, these methods commonly produce element distortion. Additionally, the mesh density for patients depends on that of the template model. It could not be adjusted to conduct mesh density sensitivity analysis. In this study, we propose a new framework of patient-specific facial soft tissue FE mesh generation. The goal of the developed method is to efficiently generate a high-quality patient-specific hexahedral FE mesh with adjustable mesh density while preserving the accuracy in anatomical structure correspondence. Our FE mesh is generated by eFace template deformation followed by volumetric parametrization. First, the patient-specific anatomically detailed facial soft tissue model (including skin, mucosa, and muscles) is generated by deforming an eFace template model. The adaptation of the eFace template model is achieved by using a hybrid landmark-based morphing and dense surface fitting approach followed by a thin-plate spline interpolation. Then, high-quality hexahedral mesh is constructed by using volumetric parameterization. The user can control the resolution of hexahedron mesh to best reflect clinicians' need. Our approach was validated using 30 patient models and 4 visible human datasets. The generated patient-specific FE mesh showed high surface matching accuracy, element quality, and internal structure matching accuracy. They can be directly and effectively used for clinical simulation of facial soft tissue change.

Analysis of factors that affect the potential of star fruit (Averhoa Bilimbi) and cactus (Gymnocalycium Hossei) extracts as alternative battery

NASA Astrophysics Data System (ADS)

Rahmawati, Sitti; Agnesstacia

2014-03-01

This research analyzes the factors that affect the work of the battery from the star fruit extract and the cactus extract. The value voltage and current generated are measure the work of the battery. Voltage measurement based on the electrode distance function, and electrode surface area. Voltage as a surface area electrode function and electrode distance function determined the current density and the voltage generated. From the experimental results obtained that the battery voltage is large enough, it is about 1.8 V for the extract of star fruit, and 1.7 V for the extract of cactus, which means that the juice extract from star fruit and the juice extract of cactus can become an alternative as battery replacement. The measurements with different electrode surface area on the star fruit and cactus extract which has the depth of the electrode 0.5 cm to 4 cm causes a decrease in the electric current generated from 12.5 mA to 1.0 mA, but obtained the same voltage.

Measurements of beam current density and proton fraction of a permanent-magnet microwave ion source.

PubMed

Waldmann, Ole; Ludewigt, Bernhard

2011-11-01

A permanent-magnet microwave ion source has been built for use in a high-yield, compact neutron generator. The source has been designed to produce up to 100 mA of deuterium and tritium ions. The electron-cyclotron resonance condition is met at a microwave frequency of 2.45 GHz and a magnetic field strength of 87.5 mT. The source operates at a low hydrogen gas pressure of about 0.15 Pa. Hydrogen beams with a current density of 40 mA/cm(2) have been extracted at a microwave power of 450 W. The dependence of the extracted proton beam fraction on wall materials and operating parameters was measured and found to vary from 45% for steel to 95% for boron nitride as a wall liner material. © 2011 American Institute of Physics

Influence of the electrode gap separation on the pseudospark-sourced electron beam generation

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

Zhao, J., E-mail: junping.zhao@qq.com; State Key Laboratory of Electrical Insulation and Power Equipment, West Xianning Road, Xi'an 710049; Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG Scotland

Pseudospark-sourced electron beam is a self-focused intense electron beam which can propagate without any external focusing magnetic field. This electron beam can drive a beam-wave interaction directly or after being post-accelerated. It is especially suitable for terahertz radiation generation due to the ability of a pseudospark discharge to produce small size in the micron range and very high current density and bright electron beams. In this paper, a single-gap pseudospark discharge chamber has been built and tested with several electrode gap separations to explore the dependence of the pseudospark-sourced electron beam current on the discharge voltage and the electrode gapmore » separation. Experimental results show that the beam pulses have similar pulse width and delay time from the distinct drop of the applied voltage for smaller electrode gap separations but longer delay time for the largest gap separation used in the experiment. It has been found that the electron beam only starts to occur when the charging voltage is above a certain value, which is defined as the starting voltage of the electron beam. The starting voltage is different for different electrode gap separations and decreases with increasing electrode gap separation in our pseudospark discharge configuration. The electron beam current increases with the increasing discharge voltage following two tendencies. Under the same discharge voltage, the configuration with the larger electrode gap separation will generate higher electron beam current. When the discharge voltage is higher than 10 kV, the beam current generated at the electrode gap separation of 17.0 mm, is much higher than that generated at smaller gap separations. The ionization of the neutral gas in the main gap is inferred to contribute more to the current increase with increasing electrode gap separation.« less

Cadmium recovery by coupling double microbial fuel cells.

PubMed

Choi, Chansoo; Hu, Naixu; Lim, Bongsu

2014-10-01

Cr(VI)-MFC of the double microbial fuel cell (d-MFC) arrangement could successfully complement the insufficient voltage and power needed to recover cadmium metal from Cd(II)-MFC, which operated as a redox-flow battery. It was also possible to drain electrical energy from the d-MFC by an additional passage. The highest maximum utilization power density (22.5Wm(-2)) of Cr(VI)-MFC, with the cathode optimized with sulfate buffer, was 11.3times higher than the highest power density directly supplied to Cd(II)-MFC (2.0Wm(-2)). Cr(VI)-MFC could generate 3times higher power with the additional passage than without it; and the current density for the former was 4.2times higher than the latter at the same maximum power point (38.0Am(-2) vs. 9.0Am(-2)). This boosting phenomenon could be explained by the Le Chatelier's principle, which addresses the rate of electron-hole pair formation that can be accelerated by quickly removing electrons generated by microorganisms. Copyright © 2014 Elsevier Ltd. All rights reserved.

Substrate removal and electricity generation in a membrane-less microbial fuel cell for biological treatment of wastewater.

PubMed

Wang, Haiping; Jiang, Sunny C; Wang, Yun; Xiao, Bo

2013-06-01

Microbial fuel cells have gained popularity in recent years due to its promise in converting organic wastewater into renewable electrical energy. In this study, a membrane-less MFC with a biocathode was developed to evaluate its performance in electricity generation while simultaneously treating wastewater. The MFC fed with a continuous flow of 2g/day acetate produced a power density of 30 mW/m(2) and current density of 245 mA/m(2). A substrate degradation efficiency (SDE) of 75.9% was achieved with 48.7% attributed to the anaerobic process and 27.2% to the aerobic process. Sequencing analysis of the microbial consortia using 16S rDNA pryosequencing showed the predominance of Bacteroidia in the anode after one month of operation, while the microbial community in the cathode chamber was dominated by Gamma-proteobacteria and Beta-proteobacteria. Coulombic efficiencies varied from 19.8% to 58.1% using different acetate concentrations, indicating power density can be further improved through the accumulation of electron-transferring bacteria. Copyright © 2013 Elsevier Ltd. All rights reserved.

The effect of the electric wind on the spatial distribution of chemical species in the positive corona discharge

NASA Astrophysics Data System (ADS)

Yanallah, K.; Pontiga, F.; Bouazza, M. R.; Chen, J. H.

2017-08-01

The electrohydrodynamic air flow generated by a positive corona discharge, and its effect on the spatial distribution of chemical species within a wire-plate corona reactor, have been numerically simulated. The computational model is based on the solutions of the Navier-Stokes equation and the continuity equation of each chemical species generated by the electrical discharge. A simplified analytical expression of the electric force density, which only requires the current density as the input parameter, has been used in the Navier-Stokes equation to obtain the velocity field. For the solution of the continuity equations, a plasma chemistry model that includes the most important reactions between electrons, atoms and molecules in air has been used. Similar to the electric force, the electron density distribution has been approximated by using a semi-analytical expression appropriate for the electrode geometry. The results of the study show that the spatial distribution of chemical species can be very different, and depends on the interplay between the electrohydrodynamic flow, the chemical kinetics of the species and its characteristic lifetime.

Alfvenic Generation of Field-Aligned Currents and Displacement Currents in the M-I Coupling System and the Formation of Discrete Auroral Arcs

NASA Astrophysics Data System (ADS)

Song, Y.; Lysak, R. L.

2016-12-01

In previous theories (e.g., Hasegawa and Sato, 1979; Sato and Iijima, 1979; Vasyliunas, 1984), field-aligned current (FAC) generation is derived from current continuity assumption plus the force balance between the Lorentz force and other forces in the MHD momentum equation. These theories suggest that the FAC is generated by other forces, such as the inertia and/or pressure gradients. In fact, the FAC cannot be generated by these forces. From Maxwell's equations, FAC generation is associated with enhanced sheared magnetic fields and free magnetic energy where a dynamo action and Alfven waves are needed to generate and transport free magnetic energy. It is obvious that the mechanism of FAC generation cannot be given by analyzing a local force balance. We propose that FACs are generated by Alfvenic interactions in the M-I coupling driven system. From a full set of the dynamical equations, we have found that the generation of the total FAC (J||total ) is associated with spatial gradients of the parallel vorticity, where J||total=J||+J||D, and J||D=(1/4∏)(∂E||/∂t) is the displacement current, which describes E|| generation (Song and Lysak, 2006). The J||total generation is a dynamo process associated with the increase of the azimuthal magnetic flux caused by the axial torque acting on FAC flux tubes. Although the magnitude of the J||D is often very small relative to J||, neglecting this term, we cannot find the mechanism of the E|| generation. When the plasma density is low J||D becomes important relative to the current. We will demonstrate how the generation of E|| and the formation of auroral arcs can redistribute perpendicular mechanical and magnetic stresses which can cause a sudden and violent tail energy release and enhance the total FAC leading to the substorm auroral poleward expansion. We will also show how the nonlinear interaction of incident and reflected Alfven wave packets in the auroral acceleration region can produce quasi-stationary non-propagating electromagnetic plasma structures, such as Alfvenic double layers. These structures will sustain the J||D and can constitute powerful high energy particle accelerators, where electromagnetic energy can be efficiently converted to the particle energy.

Study of Electric Explosion of Flat Micron-Thick Foils at Current Densities of (5-50)×10 8A/cm 2

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

Shelkovenko, T. A.; Pikuz, S. A.; Tilikin, I. N.

Electric explosions of flat Al, Тi, Ni, Cu, and Та 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) × 10 8 A/cm 2. 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 methodmore » 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.« less

Study of Electric Explosion of Flat Micron-Thick Foils at Current Densities of (5-50)×10 8A/cm 2

DOE PAGES

Shelkovenko, T. A.; Pikuz, S. A.; Tilikin, I. N.; ...

2018-01-01

Electric explosions of flat Al, Тi, Ni, Cu, and Та 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) × 10 8 A/cm 2. 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 methodmore » 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.« less

Development of a current collection loss management system for SDI homopolar power supplies

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

Brown, D.W.

1989-01-01

High speed, high power density current collection systems have been identified as an enabling technology required to construct homopolar power supplies to meet SDI missions. This work is part of a three-year effort directed towards the analysis, experimental verification, and prototype construction of a current collection system designed to operate continuously at 2 kA/cm{sup 2}, at a rubbing speed of 200 m/s, and with acceptable losses in a space environment. To data, no system has achieved these conditions simultaneously. This is the annual report covering the second year period of performance on DOE contract DE-AC03-86SF16518. Major areas covered include design,more » construction and operation of a cryogenically cooled brush test rig, design and construction of a high speed brush test rig, optimization study for homopolar machines, loss analysis of the current collection system, and an application study which defines the air-core homopolar construction necessary to achieve the goal of 80--90 kW/kg generator power density. 17 figs., 2 tabs.« less

Simulation of turbid underflows generated by the plunging of a river

NASA Astrophysics Data System (ADS)

Kassem, Ahmed; Imran, Jasim

2001-07-01

When the density of sediment-laden river water exceeds that of the lake or ocean into which it discharges, the river plunges to the bottom of the receiving water body and continues to flow as a hyperpycnal flow. These particle-laden underflows, also known as turbidity currents, can travel remarkable distances and profoundly influence the seabed morphology from shoreline to abyss by depositing, eroding, and dispersing large quantities of sediment particles. Here we present a new approach to investigating the transformation of a plunging river flow into a turbidity current. Unlike previous workers using experimental and numerical treatments, we consider the evolution of a turbidity current from a river as different stages of a single flow process. From initial commotion to final stabilization, the transformation of a river (open channel flow) into a density-driven current (hyperpycnal flow) is captured in its entirety by a numerical model. Successful implementation of the model in laboratory and field cases has revealed the dynamics of a complex geophysical flow that is extremely difficult to observe in the field or model in the laboratory.

Nano-solenoid: helicoid carbon-boron nitride hetero-nanotube

NASA Astrophysics Data System (ADS)

Zhang, Zi-Yue; Miao, Chunyang; Guo, Wanlin

2013-11-01

As a fundamental element of a nanoscale passive circuit, a nano-inductor is proposed based on a hetero-nanotube consisting of a spiral carbon strip and a spiral boron nitride strip. It is shown by density functional theory associated with nonequilibrium Green function calculations that the nanotube exhibits attractive transport properties tunable by tube chirality, diameter, component proportion and connection manner between the two strips, with excellent `OFF' state performance and high current on the order of 10-100 μA. All the hetero-nanotubes show negative differential resistance. The transmission peaks of current are absolutely derived from the helicoid carbon strips or C-BN boundaries, giving rise to a spiral current analogous with an energized nano-solenoid. According to Ampere's Law, the energized nano-solenoid can generate a uniform and tremendous magnetic field of more than 1 tesla, closing to that generated by the main magnet of medical nuclear magnetic resonance. Moreover, the magnitude of magnetic field can be easily modulated by bias voltage, providing great promise for a nano-inductor to realize electromagnetic conversion at the nanoscale.As a fundamental element of a nanoscale passive circuit, a nano-inductor is proposed based on a hetero-nanotube consisting of a spiral carbon strip and a spiral boron nitride strip. It is shown by density functional theory associated with nonequilibrium Green function calculations that the nanotube exhibits attractive transport properties tunable by tube chirality, diameter, component proportion and connection manner between the two strips, with excellent `OFF' state performance and high current on the order of 10-100 μA. All the hetero-nanotubes show negative differential resistance. The transmission peaks of current are absolutely derived from the helicoid carbon strips or C-BN boundaries, giving rise to a spiral current analogous with an energized nano-solenoid. According to Ampere's Law, the energized nano-solenoid can generate a uniform and tremendous magnetic field of more than 1 tesla, closing to that generated by the main magnet of medical nuclear magnetic resonance. Moreover, the magnitude of magnetic field can be easily modulated by bias voltage, providing great promise for a nano-inductor to realize electromagnetic conversion at the nanoscale. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02914j

Doubling of the Critical Current Density of 2G-YBCO Coated Conductors through proton irradiation

NASA Astrophysics Data System (ADS)

Welp, Ulrich; Jia, Ying; Kwok, Wai-Kwong; Rupich, Marty; Fleshler, Steven; Kayani, Asfghar

2013-03-01

We report on magnetization and transport measurements of the critical current density of commercial 2G YBCO coated conductors before and after proton irradiation. The samples were irradiated along the c-axis with 4 MeV protons to a fluence of 1.5x1016 p/cm2. We find that at temperatures below 50 K, proton irradiation increases Jc by a factor of 2 in low fields and increases up to 2.5 in fields of 7 T. At 77 K, proton irradiation is less effective in enhancing the critical current. Doubling of Jc in fields of several Tesla and at temperatures below 50 K will be highly beneficial for applications of coated conductors in rotating machinery, generators and magnet coils. - Work supported by the US DoE-BES funded Energy Frontier Research Center (YJ), and by Department of Energy, Office of Science, Office of Basic Energy Sciences (UW, WKK), under Contract No. DE-AC02-06CH11357.

Self-Assembled Array of Tethered Manganese Oxide Nanoparticles for the Next Generation of Energy Storage

DOE PAGES

Stevens, Tyler E.; Pearce, Charles J.; Whitten, Caleah N.; ...

2017-03-13

There are many challenges to overcome in order to create reliable electrochemical energy storage devices with not only high energy but also high power densities. Gaps exist in both battery and supercapacitor technologies, with neither one satisfying the need for both large power and energy densities in a single device. We report a process to create a self-assembled array of electrochemically active nanoparticles bound directly to a current collector using extremely short (2 nm or less) conductive tethers, in order to begin addressing these challenges (and others). The tethered array of nanoparticles, MnO in this case, bound directly to amore » gold current collector via short conducting linkages eliminates the need for fillers, resulting in a material which achieves 99.9% active material by mass (excluding the current collector). Our strategy is expected to be both scalable as well as effective for alternative tethers and metal oxide nanoparticles.« less

Superconducting Generators for Airborne Applications and YBCO-Coated Conductors (Preprint)

DTIC Science & Technology

2008-10-01

Maiorov, M. E. Hawley , M. P. Maley, D. E. Peterson, “Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3...ed., New York: Taylor and Francis, 2001. [17] S. P. Ashworth, M. Maley, M. Suenaga, S. R. Foltyn, and J. O. Willis , J. Appl. Phys., vol. 88, p

Incorporating YBCO Coated Conductors in High-speed Superconducting Generators

DTIC Science & Technology

2008-07-01

Maiorov, M. E. Hawley , M. P. Maley, D. E. Peterson, ―Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3...2nd ed., New York: Taylor and Francis, 2001. [23] S. P. Ashworth, M. Maley, M. Suenaga, S. R. Foltyn, and J. O. Willis , J. Appl. Phys., vol. 88

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

Larbalestier, David C.; Lee, Peter J.; Tarantini, Chiara

All present circular accelerators use superconducting magnets to bend and to focus the particle beams. The most powerful of these machines is the large hadron collider (LHC) at CERN. The main ring dipole magnets of the LHC are made from Nb-Ti but, as the machine is upgraded to higher luminosity, more powerful magnets made of Nb 3Sn will be required. Our work addresses how to make the Nb 3Sn conductors more effective and more suitable for use in the LHC. The most important property of the superconducting conductor used for an accelerator magnet is that it must have very highmore » critical current density, the property that allows the generation of high magnetic fields in small spaces. Nb 3Sn is the original high field superconductor, the material which was discovered in 1960 to allow a high current density in the field of about 9 T. For the high luminosity upgrade of the LHC, much higher current densities in fields of about 12 Tesla will be required. The critical value of the current density is of order 2600 A/mm 2 in a field of 12 Tesla. But there are very important secondary factors that complicate the attainment of this critical current density. The first is that the effective filament diameter must be no larger than about 40 µm. The second factor is that 50% of the cross-section of the Nb 3Sn conductor that is pure copper must be protected from any poisoning by any Sn leakage through the diffusion barrier that protects the package of niobium and tin from which the Nb 3Sn is formed by a high temperature reaction. These three, somewhat conflicting requirements, mean that optimization of the conductor is complex. The work described in this contract report addresses these conflicting requirements. They show that very sophisticated characterizations can uncover the way to satisfy all 3 requirements and they also suggest that the ultimate optimization of Nb 3Sn is still not yet in sight« less

Power production and wastewater treatment simultaneously by dual-chamber microbial fuel cell technique.

PubMed

Izadi, Paniz; Rahimnejad, Mostafa; Ghoreyshi, Ali

2015-01-01

Microbial fuel cell (MFC) is a novel technology that is able to convert the chemical energy of organic and inorganic substrates to electrical energy directly. The use of fossil fuels and recent energy crisis bring increasing attention to this technology. Besides electricity generation, wastewater treatment is another application of MFCs. Sulfide is a hazardous ion that is common in wastes. In this article, dual-chamber MFC was fabricated and a mixed culture of microorganisms was used as an active biocatalyst in an anaerobic anodic chamber to convert substrate to electricity. The obtained experimental results indicate that this MFC can successfully alter sulfide to elementary sulfur and power generation. The initial concentration of sulfide in wastewater was 1.5 g L(-1) , and it was removed after 10 days of MFC operation. Maximum produced power and current density were 48.68 mW⋅m(-2) and 231.47 mA⋅m(-2) , respectively. Besides, the influences of a biocathode were investigated and accordingly the data obtained for power and current density were increased to 372.27 mW⋅m(-2) and 1,665.15 mA⋅m(-2) , respectively. © 2015 International Union of Biochemistry and Molecular Biology, Inc.

[Objective Assessment of Emotion Processing. Forensic Case Report].

PubMed

Reyes, Ana Calzada; Gutiérrez Manso, Ana Teresa; González, Mariloly Acosta

2014-03-01

The main objective of the emotions is to ensure the homeostasis, the survival and the well-being of the organism. To demonstrate the usefulness of performing neurophysiological and neuropsychological assessments in patients, in order to demonstrate the significant role of the emotions in the execution of certain behaviours. A forensic psychiatric interview was conducted. EEG in vigil state was registered, the generators of current density to theta band were calculated, and the emotions recognition test was performed. The results of the psychiatric interview demonstrated that fear was an important element in acting impulsively, and lack of foresight of the accused. A substantial decrease was demonstrated in the ability to understand the scope of the acts and the direction of the behaviour during the time the crime occurred. The EEG showed alterations in frontal regions, and the generators of current density were located in frontal-temporal regions and occipital associative areas. It is recommended to associate these studies with the forensic psychiatric assessment, in order to increase the objectivity of the diagnoses formulated by medical experts. Copyright © 2014 Asociación Colombiana de Psiquiatría. Publicado por Elsevier España. All rights reserved.

Thermal limitations in a rapid-fire multirail launcher powered by a pulsed magnetodhydrodynamic generator

NASA Astrophysics Data System (ADS)

Stankevich, S. V.; Shvetsov, G. A.; Butov, V. G.; Sinyaev, S. V.

2017-09-01

The operation of rapid burst firing multirail electromagnetic launchers of solids is numerically simulated using unsteady two-dimensional and three-dimensional models. In the calculations, the launchers are powered by a Sakhalin pulsed magnetohydrodynamic generator. Launchers with three and five pairs of parallel rails connected in a series electrical circuit are considered. Firing sequences of different numbers of solid projectiles of different masses is modeled. It is established that the heating of the rails is one of the main factors limiting the performance of launchers under such conditions. It is shown that the rate of heating of the rails is determined by the nonuniformity of the current density distribution over the rail cross-section due to the unsteady diffusion of the magnetic field into the rails. Calculations taking into account the unsteady current density distribution in the rails of a multirail launcher show that with an appropriate of the mass of the projectiles (up to 800 g), their number in the sequence, and the material of the rails, it is possible to attain launching velocities of 1.8-2.5 km/s with moderate heating of the rails.

Polymer-based protein engineering grown ferrocene-containing redox polymers improve current generation in an enzymatic biofuel cell.

PubMed

Campbell, Alan S; Murata, Hironobu; Carmali, Sheiliza; Matyjaszewski, Krzysztof; Islam, Mohammad F; Russell, Alan J

2016-12-15

Enzymatic biofuel cells (EBFCs) are capable of generating electricity from physiologically present fuels making them promising power sources for the future of implantable devices. The potential application of such systems is limited, however, by inefficient current generation. Polymer-based protein engineering (PBPE) offers a unique method to tailor enzyme function through tunable modification of the enzyme surface with functional polymers. In this study, we report on the modification of glucose oxidase (GOX) with ferrocene-containing redox polymers to increase current generation efficiency in an enzyme-modified anode. Poly(N-(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide) (pFcAc) was grown from covalently attached, water-soluble initiator molecules on the surface of GOX in a "grafting-from" approach using atom transfer radical polymerization (ATRP). The covalently-coupled ferrocene-containing polymers on the enzyme surface promoted the effective "wiring" of the GOX active site to an external electrode. The resulting GOX-pFcAc conjugates generated over an order of magnitude increase in current generation efficiency and a 4-fold increase in maximum EBFC power density (≈1.7µWcm(-2)) with similar open circuit voltage (0.27V) compared to native GOX when physically adsorbed onto paddle-shaped electrodes made up of electrospun polyacrylonitrile fibers coated with gold nanoparticles and multi-wall carbon nanotubes. The formation of electroactive enzyme-redox polymer conjugates using PBPE represents a powerful new tool for the improvement of mediated enzyme-based bioelectronics without the need for free redox mediators or anode/cathode compartmentalization. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

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

Analysis of magnetically immersed electron guns with non-adiabatic fields

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

Pikin, Alexander; Alessi, James G.; Beebe, Edward N.

Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode. The relatively high magnetic compression of the electron beam achieved by this method is important for producing electron beams withmore » high current density. A similar result can be obtained by inducing a strong variation of the magnetic field in a cathode-anode gap. It was observed that creating a dip in the axial magnetic field in the cathode-anode gap of an adiabatic electron gun has an optical effect similar to guns with strong variation of radial electric field. By analyzing the electron trajectories angles and presenting the results in a gun performance map different geometries of magnetically immersed electron guns with non-adiabatic fields are compared with each other and with a more traditional adiabatic electron gun. Some advantages and limitations of guns with non-adiabatic fields are outlined. In conclusion, the tests results of non-adiabatic electron gun with modified magnetic field are presented.« less

Analysis of magnetically immersed electron guns with non-adiabatic fields

DOE PAGES

Pikin, Alexander; Alessi, James G.; Beebe, Edward N.; ...

2016-11-08

Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode. The relatively high magnetic compression of the electron beam achieved by this method is important for producing electron beams withmore » high current density. A similar result can be obtained by inducing a strong variation of the magnetic field in a cathode-anode gap. It was observed that creating a dip in the axial magnetic field in the cathode-anode gap of an adiabatic electron gun has an optical effect similar to guns with strong variation of radial electric field. By analyzing the electron trajectories angles and presenting the results in a gun performance map different geometries of magnetically immersed electron guns with non-adiabatic fields are compared with each other and with a more traditional adiabatic electron gun. Some advantages and limitations of guns with non-adiabatic fields are outlined. In conclusion, the tests results of non-adiabatic electron gun with modified magnetic field are presented.« less

Analysis of magnetically immersed electron guns with non-adiabatic fields.

PubMed

Pikin, Alexander; Alessi, James G; Beebe, Edward N; Raparia, Deepak; Ritter, John

2016-11-01

Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode. The relatively high magnetic compression of the electron beam achieved by this method is important for producing electron beams with high current density. A similar result can be obtained by inducing a strong variation of the magnetic field in a cathode-anode gap. It was observed that creating a dip in the axial magnetic field in the cathode-anode gap of an adiabatic electron gun has an optical effect similar to guns with strong variation of radial electric field. By analyzing the electron trajectories angles and presenting the results in a gun performance map, different geometries of magnetically immersed electron guns with non-adiabatic fields are compared with each other and with a more traditional adiabatic electron gun. Some advantages and limitations of guns with non-adiabatic fields are outlined. The tests' results of a non-adiabatic electron gun with modified magnetic field are presented.

Domestic wastewater treatment and power generation in continuous flow air-cathode stacked microbial fuel cell: Effect of series and parallel configuration.

PubMed

Estrada-Arriaga, Edson Baltazar; Hernández-Romano, Jesús; García-Sánchez, Liliana; Guillén Garcés, Rosa Angélica; Bahena-Bahena, Erick Obed; Guadarrama-Pérez, Oscar; Moeller Chavez, Gabriela Eleonora

2018-05-15

In this study, a continuous flow stack consisting of 40 individual air-cathode MFC units was used to determine the performance of stacked MFC during domestic wastewater treatment operated with unconnected individual MFC and in series and parallel configuration. The voltages obtained from individual MFC units were of 0.08-1.1 V at open circuit voltage, while in series connection, the maximum power and current density were 2500 mW/m 2 and 500 mA/m 2 (4.9 V), respectively. In parallel connection, the maximum power and current density was 5.8 mW/m 2 and 24 mA/m 2 , respectively. When the cells were not connected to each other MFC unit, the main bacterial species found in the anode biofilms were Bacillus and Lysinibacillus. After switching from unconnected to series and parallel connections, the most abundant species in the stacked MFC were Pseudomonas aeruginosa, followed by different Bacilli classes. This study demonstrated that when the stacked MFC was switched from unconnected to series and parallel connections, the pollutants removal, performance electricity and microbial community changed significantly. Voltages drops were observed in the stacked MFC, which was mainly limited by the cathodes. These voltages loss indicated high resistances within the stacked MFC, generating a parasitic cross current. Copyright © 2018 Elsevier Ltd. All rights reserved.

Device and method for imploding a microsphere with a fast liner

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner to drive the fast liner to implode a microsphere.

Generating high-current monoenergetic proton beams by a circularly polarized laser pulse in the phase-stable acceleration regime.

PubMed

Yan, X Q; Lin, C; Sheng, Z M; Guo, Z Y; Liu, B C; Lu, Y R; Fang, J X; Chen, J E

2008-04-04

A new ion acceleration method, namely, phase-stable acceleration, using circularly-polarized laser pulses is proposed. When the initial target density n(0) and thickness D satisfy a(L) approximately (n(0)/n(c))D/lambda(L) and D>l(s) with a(L), lambda(L), l(s), and n(c) the normalized laser amplitude, the laser wavelength in vacuum, the plasma skin depth, and the critical density of the incident laser pulse, respectively, a quasiequilibrium for the electrons is established by the light pressure and the space charge electrostatic field at the interacting front of the laser pulse. The ions within the skin depth of the laser pulse are synchronously accelerated and bunched by the electrostatic field, and thereby a high-intensity monoenergetic proton beam can be generated. The proton dynamics is investigated analytically and the results are verified by one- and two-dimensional particle-in-cell simulations.

Enhanced power generation and energy conversion of sewage sludge by CEA-microbial fuel cells.

PubMed

Abourached, Carole; Lesnik, Keaton Larson; Liu, Hong

2014-08-01

The production of methane from sewage sludge through the use of anaerobic digestion has been able to effectively offset energy costs for wastewater treatment. However, significant energy reserves are left unrecovered and effluent standards are not met necessitating secondary processes such as aeration. In the current study a novel cloth-electrode assembly microbial fuel cell (CEA-MFC) was used to generate electricity from sewage sludge. Fermentation pretreatment of the sludge effectively increased the COD of the supernatant and improved reactor performance. Using the CEA-MFC design, a maximum power density of 1200 mW m(-2) was reached after a fermentation pre-treatment time of 96 h. This power density represents a 275% increase over those previously observed in MFC systems. Results indicate continued improvements are possible and MFCs may be a viable modification to existing wastewater treatment infrastructure. Copyright © 2014 Elsevier Ltd. All rights reserved.

Simulation of a cascaded longitudinal space charge amplifier for coherent radiation generation

DOE PAGES

Halavanau, A.; Piot, P.

2016-03-03

Longitudinal space charge (LSC) effects are generally considered as harmful in free-electron lasers as they can seed unfavorable energy modulations that can result in density modulations with associated emittance dilution. It was pointed out, however, that such \\micro-bunching instabilities" could be potentially useful to support the generation of broadband coherent radiation. Therefore there has been an increasing interest in devising accelerator beam lines capable of controlling LSC induced density modulations. In the present paper we augment these previous investigations by combining a grid-less space charge algorithm with the popular particle-tracking program elegant. This high-fidelity model of the space charge ismore » used to benchmark conventional LSC models. We then employ the developed model to optimize the performance of a cascaded longitudinal space charge amplifier using beam parameters comparable to the ones achievable at Fermilab Accelerator Science & Technology (FAST) facility currently under commissioning at Fermilab.« less

The electrochemical generation of useful chemical species from lunar materials

NASA Technical Reports Server (NTRS)

Tsai, Kan J.; Kuchynka, Daniel J.; Sammells, Anthony F.

1990-01-01

Electrochemical cells have been fabricated for the simultaneous generation of oxygen and lithium from a Li2O-containing molten salt (Li2O-LiCl-LiF). The cell utilizes an oxygen vacancy conducting solid electrolyte, yttria-stabilized zirconia (YSZ), to effect separation between oxygen evolving and lithium reduction half-cell reactions. The cell, which operates at 700-850 C, possesses rapid electrode kinetics at the lithium-alloy electrode with exchange current density values being greater than 60 mA/sq cm. When used in the electrolytic mode, lithium produced at the negative electrode would be continuously removed from the cell for later use (under lunar conditions) as an easily storable reducing agent for the chemical refining of lunar ores. Because of the high reversibility of this electrochemical system, it has also formed the basis for the lithium-oxygen secondary battery system which possesses the highest theoretical energy density yet investigated.

The electrochemical generation of useful chemical species from lunar materials

NASA Astrophysics Data System (ADS)

Tsai, Kan J.; Kuchynka, Daniel J.; Sammells, Anthony F.

Electrochemical cells have been fabricated for the simultaneous generation of oxygen and lithium from a Li2O-containing molten salt (Li2O-LiCl-LiF). The cell utilizes an oxygen vacancy conducting solid electrolyte, yttria-stabilized zirconia (YSZ), to effect separation between oxygen evolving and lithium reduction half-cell reactions. The cell, which operates at 700-850 C, possesses rapid electrode kinetics at the lithium-alloy electrode with exchange current density values being greater than 60 mA/sq cm. When used in the electrolytic mode, lithium produced at the negative electrode would be continuously removed from the cell for later use (under lunar conditions) as an easily storable reducing agent for the chemical refining of lunar ores. Because of the high reversibility of this electrochemical system, it has also formed the basis for the lithium-oxygen secondary battery system which possesses the highest theoretical energy density yet investigated.

Generation of electrical power under human skin by subdermal solar cell arrays for implantable bioelectronic devices.

PubMed

Song, Kwangsun; Han, Jung Hyun; Yang, Hyung Chae; Nam, Kwang Il; Lee, Jongho

2017-06-15

Medical electronic implants can significantly improve people's health and quality of life. These implants are typically powered by batteries, which usually have a finite lifetime and therefore must be replaced periodically using surgical procedures. Recently, subdermal solar cells that can generate electricity by absorbing light transmitted through skin have been proposed as a sustainable electricity source to power medical electronic implants in bodies. However, the results to date have been obtained with animal models. To apply the technology to human beings, electrical performance should be characterized using human skin covering the subdermal solar cells. In this paper, we present electrical performance results (up to 9.05mW/cm 2 ) of the implantable solar cell array under 59 human skin samples isolated from 10 cadavers. The results indicate that the power densities depend on the thickness and tone of the human skin, e.g., higher power was generated under thinner and brighter skin. The generated power density is high enough to operate currently available medical electronic implants such as pacemakers that require tens of microwatt. Copyright © 2016 Elsevier B.V. All rights reserved.

Design and analysis of a flux intensifying permanent magnet embedded salient pole wind generator

NASA Astrophysics Data System (ADS)

Guo, Yujing; Jin, Ping; Lin, Heyun; Yang, Hui; Lyu, Shukang

2018-05-01

This paper presents an improved flux intensifying permanent magnet embedded salient pole wind generator (FI-PMESPWG) with mirror symmetrical magnetizing directions permanent magnet (PM) for improving generator's performances. The air-gap flux densities, the output voltage, the cogging torque and the d- and q-axis inductances of FI-PMESPWG are all calculated and analyzed by using the finite element method (FEM). To highlight the advantages of the proposed FI-PMESPWG, an original permanent magnet embedded salient pole wind generator (PMESPWG) model is adopted for comparison under the same operating conditions. The calculating results show that the air-gap flux densities of FI-PMESPWG are intensified with the same magnet amounts because the PMs are set in a form of V shape in each pole. The difference between d-axis inductance and q-axis inductance of the proposed FI-PMESPWG is reduced. Thus, the output power of the proposed FI-PMESPWG reaches a higher value than that of the original PMESPWG at the same current phase angle. The cogging torque is diminished because the flux path is changed. All the analysis results indicate that the electromagnetic characteristics of the proposed FI-PMESPWG are significantly better than that of the original PMESPWG.

Boosting mediated electron transfer in bioelectrochemical systems with tailored defined microbial cocultures.

PubMed

Schmitz, Simone; Rosenbaum, Miriam A

2018-05-19

Bioelectrochemical systems (BES) hold great promise for sustainable energy generation via a microbial catalyst from organic matter, for example, from wastewater. To improve current generation in BES, understanding the underlying microbiology of the electrode community is essential. Electron mediator producing microorganism like Pseudomonas aeruginosa play an essential role in efficient electricity generation in BES. These microbes enable even nonelectroactive microorganism like Enterobacter aerogenes to contribute to current production. Together they form a synergistic coculture, where both contribute to community welfare. To use microbial co-operation in BES, the physical and chemical environments provided in the natural habitats of the coculture play a crucial role. Here, we show that synergistic effects in defined cocultures of P. aeruginosa and E. aerogenes can be strongly enhanced toward high current production by adapting process parameters, like pH, temperature, oxygen demand, and substrate requirements. Especially, oxygen was identified as a major factor influencing coculture behavior and optimization of its supply could enhance electric current production over 400%. Furthermore, operating the coculture in fed-batch mode enabled us to obtain very high current densities and to harvest electrical energy for 1 month. In this optimized condition, the coulombic efficiency of the process was boosted to 20%, which is outstanding for mediator-based electron transfer. This study lays the foundation for a rationally designed utilization of cocultures in BES for bioenergy generation from specific wastewaters or for bioprocess sensing and for benefiting from their synergistic effects under controlled bioprocess condition. © 2018 Wiley Periodicals, Inc.

Structure of the Magnetotail Current Sheet

NASA Technical Reports Server (NTRS)

Larson, Douglas J.; Kaufmann, Richard L.

1996-01-01

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(sub E) less than x less than - 14 R(sub E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

Structure of the Magnetotail Current Sheet

NASA Technical Reports Server (NTRS)

Larson, Douglas J.; Kaufmann, Richard L.

1996-01-01

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(E) less than x less than -14 R(E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

The effect of pH and buffer concentration on anode biofilms of Thermincola ferriacetica.

PubMed

Lusk, Bradley G; Parameswaran, Prathap; Popat, Sudeep C; Rittmann, Bruce E; Torres, Cesar I

2016-12-01

We assessed the effects of pH and buffer concentration on current production and growth of biofilms of Thermincola ferriacetica - a thermophilic, Gram-positive, anode-respiring bacterium (ARB) - grown on anodes poised at a potential of -0.06V vs. SHE in microbial electrolysis cells (MECs) at 60°C. T. ferriacetica generated current in the pH range of 5.2 to 8.3 with acetate as the electron donor and 50mM bicarbonate buffer. Maximum current density was reduced by ~80% at pH5.2 and ~14% at 7.0 compared to pH8.3. Increasing bicarbonate buffer concentrations from 10mM to 100mM resulted in an increase in the current density by 40±6%, from 6.8±1.1 to 11.2±2.7Am(-2), supporting that more buffer alleviated pH depression within T. ferriacetica biofilms. Confocal laser scanning microscopy (CLSM) images indicated that higher bicarbonate buffer concentrations resulted in larger live biofilm thicknesses: from 68±20μm at 10mM bicarbonate to >150μm at 100mM, supporting that buffer availability was a strong influence on biofilm thickness. In comparison to mesophilic Geobacter sulfurreducens biofilms, the faster transport rates at higher temperature and the ability to grow at relatively lower pH allowed T. ferriacetica to produce higher current densities with lower buffer concentrations. Published by Elsevier B.V.

Submesoscale currents in the ocean

PubMed Central

2016-01-01

This article is a perspective on the recently discovered realm of submesoscale currents in the ocean. They are intermediate-scale flow structures in the form of density fronts and filaments, topographic wakes and persistent coherent vortices at the surface and throughout the interior. They are created from mesoscale eddies and strong currents, and they provide a dynamical conduit for energy transfer towards microscale dissipation and diapycnal mixing. Consideration is given to their generation mechanisms, instabilities, life cycles, disruption of approximately diagnostic force balance (e.g. geostrophy), turbulent cascades, internal-wave interactions, and transport and dispersion of materials. At a fundamental level, more questions remain than answers, implicating a programme for further research. PMID:27279778

A kinetic Monte Carlo model with improved charge injection model for the photocurrent characteristics of organic solar cells

NASA Astrophysics Data System (ADS)

Kipp, Dylan; Ganesan, Venkat

2013-06-01

We develop a kinetic Monte Carlo model for photocurrent generation in organic solar cells that demonstrates improved agreement with experimental illuminated and dark current-voltage curves. In our model, we introduce a charge injection rate prefactor to correct for the electrode grid-size and electrode charge density biases apparent in the coarse-grained approximation of the electrode as a grid of single occupancy, charge-injecting reservoirs. We use the charge injection rate prefactor to control the portion of dark current attributed to each of four kinds of charge injection. By shifting the dark current between electrode-polymer pairs, we align the injection timescales and expand the applicability of the method to accommodate ohmic energy barriers. We consider the device characteristics of the ITO/PEDOT/PSS:PPDI:PBTT:Al system and demonstrate the manner in which our model captures the device charge densities unique to systems with small injection energy barriers. To elucidate the defining characteristics of our model, we first demonstrate the manner in which charge accumulation and band bending affect the shape and placement of the various current-voltage regimes. We then discuss the influence of various model parameters upon the current-voltage characteristics.

Characterization and Performance of a High-Current-Density Ion Implanter with Magnetized Hollow-Cathode Plasma Source

NASA Astrophysics Data System (ADS)

Falkenstein, Zoran; Rej, Donald; Gavrilov, Nikolai

1998-10-01

In a collaboration between the Institute of Electrophysics (IEP) and the Los Alamos National Laboratory (LANL), the IEP has developed an industrial scalable, high-power, large-area ion source for the surface modification of materials. The plasma source of the ion beam source can be described as a pulsed glow discharge with a cold, hollow-cathode in a weak magnetic field. Extraction and focusing of positive ions by an acceleration and ion-optical plate system renders the generation of a homogeneous, large-area ion beam with an averaged total ion current of up to 50 mA at acceleration voltages of up to 50 kV. The principle set-up of the ion beam source as well as some electrical characteristics (gas discharge current and the extracted ion beam current) are presented for a lab-scale prototype. Measurements of the radial ion current density profiles within the ion beam for various discharge parameters, as well as results on surface modification by ion implantation of nitrogen into aluminum and chromium are presented. Finally, a comparison of the applied ion dose with the retained ion doses is given.

Recent charge-breeding developments with EBIS/T devices (invited).

PubMed

Schwarz, S; Lapierre, A

2016-02-01

Short breeding times, narrow charge state distributions, low background, high efficiency, and the flexible time structure of the ejected low-emittance ion pulses are among the most attractive features of electron beam ion source or trap (EBIS/T) based charge breeders. Significant progress has been made to further improve these properties: Several groups are working to increase current densities towards 10(3) or even 10(4) A/cm(2). These current densities will become necessary to deliver high charge states of heavy nuclei in a short time and/or provide sufficient space-charge capacity to handle high-current ion beams in next-generation rare-isotope beam (RIB) facilities. Efficient capture of continuous beams, attractive because of its potential of handling highest-current ion beams, has become possible with the development of high-density electron beams of >1 A. Requests for the time structure of the charge bred ion pulse range from ultra-short pulses to quasi-continuous beams. Progress is being made on both ends of this spectrum, by either dividing the extracted charge in many pulse-lets, adjusting the extraction potential for a near-uniform long pulse, or adding dedicated devices to spread the ion bunches delivered from the EBIS/T in time. Advances in EBIS/T charge state breeding are summarized, including recent results with NSCL's ReA EBIS/T charge breeder.

Recent charge-breeding developments with EBIS/T devices (invited)

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

Schwarz, S., E-mail: schwarz@nscl.msu.edu; Lapierre, A.

Short breeding times, narrow charge state distributions, low background, high efficiency, and the flexible time structure of the ejected low-emittance ion pulses are among the most attractive features of electron beam ion source or trap (EBIS/T) based charge breeders. Significant progress has been made to further improve these properties: Several groups are working to increase current densities towards 10{sup 3} or even 10{sup 4} A/cm{sup 2}. These current densities will become necessary to deliver high charge states of heavy nuclei in a short time and/or provide sufficient space-charge capacity to handle high-current ion beams in next-generation rare-isotope beam (RIB) facilities.more » Efficient capture of continuous beams, attractive because of its potential of handling highest-current ion beams, has become possible with the development of high-density electron beams of >1 A. Requests for the time structure of the charge bred ion pulse range from ultra-short pulses to quasi-continuous beams. Progress is being made on both ends of this spectrum, by either dividing the extracted charge in many pulse-lets, adjusting the extraction potential for a near-uniform long pulse, or adding dedicated devices to spread the ion bunches delivered from the EBIS/T in time. Advances in EBIS/T charge state breeding are summarized, including recent results with NSCL’s ReA EBIS/T charge breeder.« less

Comparative study on extinction process of gas-blasted air and CO2 arc discharge using two-dimensional electron density imaging sensor

NASA Astrophysics Data System (ADS)

Inada, Yuki; Kumada, Akiko; Ikeda, Hisatoshi; Hidaka, Kunihiko; Nakano, Tomoyuki; Murai, Kosuke; Tanaka, Yasunori; Shinkai, Takeshi

2017-05-01

Shack-Hartmann type laser wavefront sensors were applied to gas-blasted arc discharges under current-zero phases, generated in a 50 mm-long interelectrode gap confined by a gas flow nozzle, in order to conduct a systematic comparison of electron density decaying processes for two kinds of arc-quenching gas media: air and \\text{C}{{\\text{O}}2} . The experimental results for the air and \\text{C}{{\\text{O}}2} arc plasmas showed that the electron densities and arc diameters became thinner toward the nozzle-throat inlet due to a stronger convection loss in the arc radial direction. In addition, \\text{C}{{\\text{O}}2} had a shorter electron density decaying time constant than air, which could be caused by convection loss and turbulent flow of \\text{C}{{\\text{O}}2} stronger than air.

Raman imaging of carrier distribution in the channel of an ionic liquid-gated transistor fabricated with regioregular poly(3-hexylthiophene)

NASA Astrophysics Data System (ADS)

Wada, Y.; Enokida, I.; Yamamoto, J.; Furukawa, Y.

2018-05-01

Raman images of carriers (positive polarons) at the channel of an ionic liquid-gated transistor (ILGT) fabricated with regioregular poly(3-hexylthiophene) (P3HT) have been measured with excitation at 785 nm. The observed spectra indicate that carriers generated are positive polarons. The intensities of the 1415 cm-1 band attributed to polarons in the P3HT channel were plotted as Raman images; they showed the carrier density distribution. When the source-drain voltage VD is lower than the source-gate voltage VG (linear region), the carrier density was uniform. When VD is nearly equal to VG (saturation region), a negative carrier density gradient from the source electrode towards the drain electrode was observed. This carrier density distribution is associated with the observed current-voltage characteristics, which is not consistent with the "pinch-off" theory of inorganic semiconductor transistors.

Extreme plasma states in laser-governed vacuum breakdown.

PubMed

Efimenko, Evgeny S; Bashinov, Aleksei V; Bastrakov, Sergei I; Gonoskov, Arkady A; Muraviev, Alexander A; Meyerov, Iosif B; Kim, Arkady V; Sergeev, Alexander M

2018-02-05

Triggering vacuum breakdown at laser facility is expected to provide rapid electron-positron pair production for studies in laboratory astrophysics and fundamental physics. However, the density of the produced plasma may cease to increase at a relativistic critical density, when the plasma becomes opaque. Here, we identify the opportunity of breaking this limit using optimal beam configuration of petawatt-class lasers. Tightly focused laser fields allow generating plasma in a small focal volume much less than λ 3 and creating extreme plasma states in terms of density and produced currents. These states can be regarded to be a new object of nonlinear plasma physics. Using 3D QED-PIC simulations we demonstrate a possibility of reaching densities over 10 25  cm -3 , which is an order of magnitude higher than expected earlier. Controlling the process via initial target parameters provides an opportunity to reach the discovered plasma states at the upcoming laser facilities.

Characteristics of the three-half-turn-antenna-driven RF discharge in the Uragan-3M torsatron

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

Grigor’eva, L. I.; Chechkin, V. V., E-mail: chechkin@ipp.kharkov.ua; Moiseenko, V. E.

In the ℓ = 3 Uragan-3M torsatron hydrogen plasma is produced by RF fields in the Alfvén range of frequencies (ω ≤ ω{sub ci}). The initial (target) plasma with the line-averaged density of units 10{sup 12} cm{sup −3} is produced by a frame antenna with a broad spectrum of generated parallel wavenumbers. After this, to heat the plasma and bring its density to ∼10{sup 13} cm{sup –3}, another, shorter wavelength three-half-turn antenna with large transverse currents is used. The behavior of the density, electron temperature, and loss of the plasma supported by the three-half-turn antenna is studied depending on themore » RF power fed to the antenna and initial values of the density and electron temperature supplied by the frame antenna.« less

LDPC product coding scheme with extrinsic information for bit patterned media recoding

NASA Astrophysics Data System (ADS)

Jeong, Seongkwon; Lee, Jaejin

2017-05-01

Since the density limit of the current perpendicular magnetic storage system will soon be reached, bit patterned media recording (BPMR) is a promising candidate for the next generation storage system to achieve an areal density beyond 1 Tb/in2. Each recording bit is stored in a fabricated magnetic island and the space between the magnetic islands is nonmagnetic in BPMR. To approach recording densities of 1 Tb/in2, the spacing of the magnetic islands must be less than 25 nm. Consequently, severe inter-symbol interference (ISI) and inter-track interference (ITI) occur. ITI and ISI degrade the performance of BPMR. In this paper, we propose a low-density parity check (LDPC) product coding scheme that exploits extrinsic information for BPMR. This scheme shows an improved bit error rate performance compared to that in which one LDPC code is used.

Honeycomblike large area LaB6 plasma source for Multi-Purpose Plasma facility

NASA Astrophysics Data System (ADS)

Woo, Hyun-Jong; Chung, Kyu-Sun; You, Hyun-Jong; Lee, Myoung-Jae; Lho, Taihyeop; Choh, Kwon Kook; Yoon, Jung-Sik; Jung, Yong Ho; Lee, Bongju; Yoo, Suk Jae; Kwon, Myeon

2007-10-01

A Multi-Purpose Plasma (MP2) facility has been renovated from Hanbit mirror device [Kwon et al., Nucl. Fusion 43, 686 (2003)] by adopting the same philosophy of diversified plasma simulator (DiPS) [Chung et al., Contrib. Plasma Phys. 46, 354 (2006)] by installing two plasma sources: LaB6 (dc) and helicon (rf) plasma sources; and making three distinct simulators: divertor plasma simulator, space propulsion simulator, and astrophysics simulator. During the first renovation stage, a honeycomblike large area LaB6 (HLA-LaB6) cathode was developed for the divertor plasma simulator to improve the resistance against the thermal shock fragility for large and high density plasma generation. A HLA-LaB6 cathode is composed of the one inner cathode with 4in. diameter and the six outer cathodes with 2in. diameter along with separate graphite heaters. The first plasma is generated with Ar gas and its properties are measured by the electric probes with various discharge currents and magnetic field configurations. Plasma density at the middle of central cell reaches up to 2.6×1012 cm-3, while the electron temperature remains around 3-3.5eV at the low discharge current of less than 45A, and the magnetic field intensity of 870G. Unique features of electric property of heaters, plasma density profiles, is explained comparing with those of single LaB6 cathode with 4in. diameter in DiPS.

Scaling of Energy Deposition in Fast Ignition Targets

NASA Astrophysics Data System (ADS)

Campbell, R. B.; Welch, Dale

2005-10-01

We examine the scaling to ignition of the energy deposition of laser generated electrons in compressed fast ignition cores. Relevant cores have densities of several hundred g/cm^3, with a few keV initial temperature. As the laser intensities increase approaching ignition systems, on the order of a few 10^21W/cm^2, the hot electron energies expected to approach 100MeV[1]. Most certainly anomalous processes must play a role in the energy transfer, but the exact nature of these processes, as well as a practical way to model them, remain open issues. Traditional PIC explicit methods are limited to low densities on current and anticipated computing platforms, so the study of relevant parameter ranges has received so far little attention. We use LSP[2] to examine a relativistic electron beam (presumed generated from a laser plasma interaction) of legislated energy and angular distribution is injected into a 3D block of compressed DT. Collective effects will determine the stopping, most likely driven by magnetic field filamentation. The scaling of the stopping as a function of block density and temperature, as well as hot electron current and laser intensity is presented. Sub-grid models may be profitably used and degenerate effects included in the solution of this problem. Sandia is operated by Sandia Corporation, for the USDOE. [1] A. Pukhov, et. al., Phys. Plas. 6, p2847 (1999) [2] D. R. Welch et al., Comput. Phys.Commun. 164, p183 (2004).

Honeycomblike large area LaB6 plasma source for Multi-Purpose Plasma facility.

PubMed

Woo, Hyun-Jong; Chung, Kyu-Sun; You, Hyun-Jong; Lee, Myoung-Jae; Lho, Taihyeop; Choh, Kwon Kook; Yoon, Jung-Sik; Jung, Yong Ho; Lee, Bongju; Yoo, Suk Jae; Kwon, Myeon

2007-10-01

A Multi-Purpose Plasma (MP(2)) facility has been renovated from Hanbit mirror device [Kwon et al., Nucl. Fusion 43, 686 (2003)] by adopting the same philosophy of diversified plasma simulator (DiPS) [Chung et al., Contrib. Plasma Phys. 46, 354 (2006)] by installing two plasma sources: LaB(6) (dc) and helicon (rf) plasma sources; and making three distinct simulators: divertor plasma simulator, space propulsion simulator, and astrophysics simulator. During the first renovation stage, a honeycomblike large area LaB(6) (HLA-LaB(6)) cathode was developed for the divertor plasma simulator to improve the resistance against the thermal shock fragility for large and high density plasma generation. A HLA-LaB(6) cathode is composed of the one inner cathode with 4 in. diameter and the six outer cathodes with 2 in. diameter along with separate graphite heaters. The first plasma is generated with Ar gas and its properties are measured by the electric probes with various discharge currents and magnetic field configurations. Plasma density at the middle of central cell reaches up to 2.6 x 10(12) cm(-3), while the electron temperature remains around 3-3.5 eV at the low discharge current of less than 45 A, and the magnetic field intensity of 870 G. Unique features of electric property of heaters, plasma density profiles, is explained comparing with those of single LaB(6) cathode with 4 in. diameter in DiPS.

A novel pilot-scale stacked microbial fuel cell for efficient electricity generation and wastewater treatment.

PubMed

Wu, Shijia; Li, Hui; Zhou, Xuechen; Liang, Peng; Zhang, Xiaoyuan; Jiang, Yong; Huang, Xia

2016-07-01

A novel stacked microbial fuel cell (MFC) which had a total volume of 72 L with granular activated carbon (GAC) packed bed electrodes was constructed and verified to present remarkable power generation and COD removal performance due to its advantageous design of stack and electrode configuration. During the fed-batch operation period, a power density of 50.9 ± 1.7 W/m(3) and a COD removal efficiency of 97% were achieved within 48 h. Because of the differences among MFC modules in the stack, reversal current occurred in parallel circuit connection with high external resistances (>100 Ω). This reversal current consequently reduced the electrochemical performance of some MFC modules and led to a lower power density in parallel circuit connection than that in independent circuit connection. While increasing the influent COD concentrations from 200 to 800 mg/L at hydraulic retention time of 1.25 h in continuous operation mode, the power density of stacked MFC increased from 25.6 ± 2.5 to 42.1 ± 1.2 W/m(3) and the COD removal rates increased from 1.3 to 5.2 kg COD/(m(3) d). This study demonstrated that this novel MFC stack configuration coupling with GAC packed bed electrode could be a feasible strategy to effectively scale up MFC systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

Current flow and pair creation at low altitude in rotation-powered pulsars' force-free magnetospheres: space charge limited flow

NASA Astrophysics Data System (ADS)

Timokhin, A. N.; Arons, J.

2013-02-01

We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs. We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 < j/jGJ < 1), space charge limited acceleration of the current carrying beam is mild, with the full Goldreich-Julian charge density comprising the charge densities of the beam and a cloud of electrically trapped particles with the same sign of charge as the beam. The voltage drops are of the order of mc2/e, and pair creation is absent. (b) When the current density exceeds the Goldreich-Julian value (j/jGJ > 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/jGJ < 0, the system develops similar bursts of pair creation. These discharges are similar to those encountered in previous calculations by Timokhin of pair creation when the surface has a high work function and cannot freely emit charge. In cases (b) and (c), the intermittently generated pairs allow the system to simultaneously carry the magnetospherically prescribed currents and adjust the charge density and average electric field to force-free conditions. We also elucidate the conditions for pair creating beam flow to be steady (stationary with small fluctuations in the rotating frame), finding that such steady flows can occupy only a small fraction of the current density parameter space exhibited by the force-free magnetospheric model. The generic polar flow dynamics and pair creation are strongly time dependent. The model has an essential difference from almost all previous quantitative studies, in that we sought the accelerating voltage (with pair creation, when the voltage drops are sufficiently large; without, when they are small) as a function of the applied current. The 1D results described here characterize the dependence of acceleration and pair creation on the magnitude and sign of current. The dependence on the spatial distribution of the current is a multi-dimensional problem, possibly exhibiting more chaotic behaviour. We briefly outline possible relations of the electric field fluctuations observed in the polar flows (both with and without pair creation discharges) to direct emission of radio waves, as well as revive the possible relation of the observed limit cycle behaviour to microstructure in the radio emission. Actually modelling these effects requires the multi-dimensional treatment, to be reported in a later paper.

Pulsed metallic-plasma generators.

NASA Technical Reports Server (NTRS)

Gilmour, A. S., Jr.; Lockwood, D. L.

1972-01-01

A pulsed metallic-plasma generator is described which utilizes a vacuum arc as the plasma source. The arc is initiated on the surface of a consumable cathode which can be any electrically conductive material. Ignition is accomplished by using a current pulse to vaporize a portion of a conductive film on the surface of an insulator separating the cathode from the ignition electrode. The film is regenerated during the ensuing arc. Over 100 million ignition cycles have been accomplished by using four 0.125-in. diameter zinc cathodes operating in parallel and high-density aluminum-oxide insulators. Among the applications being investigated for the generator are metal deposition, vacuum pumping, electric propulsion, and high-power dc arc interruption.

Dynamic Statistical Models for Pyroclastic Density Current Generation at Soufrière Hills Volcano

NASA Astrophysics Data System (ADS)

Wolpert, Robert L.; Spiller, Elaine T.; Calder, Eliza S.

2018-05-01

To mitigate volcanic hazards from pyroclastic density currents, volcanologists generate hazard maps that provide long-term forecasts of areas of potential impact. Several recent efforts in the field develop new statistical methods for application of flow models to generate fully probabilistic hazard maps that both account for, and quantify, uncertainty. However a limitation to the use of most statistical hazard models, and a key source of uncertainty within them, is the time-averaged nature of the datasets by which the volcanic activity is statistically characterized. Where the level, or directionality, of volcanic activity frequently changes, e.g. during protracted eruptive episodes, or at volcanoes that are classified as persistently active, it is not appropriate to make short term forecasts based on longer time-averaged metrics of the activity. Thus, here we build, fit and explore dynamic statistical models for the generation of pyroclastic density current from Soufrière Hills Volcano (SHV) on Montserrat including their respective collapse direction and flow volumes based on 1996-2008 flow datasets. The development of this approach allows for short-term behavioral changes to be taken into account in probabilistic volcanic hazard assessments. We show that collapses from the SHV lava dome follow a clear pattern, and that a series of smaller flows in a given direction often culminate in a larger collapse and thereafter directionality of the flows change. Such models enable short term forecasting (weeks to months) that can reflect evolving conditions such as dome and crater morphology changes and non-stationary eruptive behavior such as extrusion rate variations. For example, the probability of inundation of the Belham Valley in the first 180 days of a forecast period is about twice as high for lava domes facing Northwest toward that valley as it is for domes pointing East toward the Tar River Valley. As rich multi-parametric volcano monitoring dataset become increasingly available, eruption forecasting is becoming an increasingly viable and important research field. We demonstrate an approach to utilize such data in order to appropriately 'tune' probabilistic hazard assessments for pyroclastic flows. Our broader objective with development of this method is to help advance time-dependent volcanic hazard assessment, by bridging the

Nonparametric Density Estimation Based on Self-Organizing Incremental Neural Network for Large Noisy Data.

PubMed

Nakamura, Yoshihiro; Hasegawa, Osamu

2017-01-01

With the ongoing development and expansion of communication networks and sensors, massive amounts of data are continuously generated in real time from real environments. Beforehand, prediction of a distribution underlying such data is difficult; furthermore, the data include substantial amounts of noise. These factors make it difficult to estimate probability densities. To handle these issues and massive amounts of data, we propose a nonparametric density estimator that rapidly learns data online and has high robustness. Our approach is an extension of both kernel density estimation (KDE) and a self-organizing incremental neural network (SOINN); therefore, we call our approach KDESOINN. An SOINN provides a clustering method that learns about the given data as networks of prototype of data; more specifically, an SOINN can learn the distribution underlying the given data. Using this information, KDESOINN estimates the probability density function. The results of our experiments show that KDESOINN outperforms or achieves performance comparable to the current state-of-the-art approaches in terms of robustness, learning time, and accuracy.

Electron dynamics in high energy density plasma bunch generation driven by intense picosecond laser pulse

NASA Astrophysics Data System (ADS)

Li, M.; Yuan, T.; Xu, Y. X.; Luo, S. N.

2018-05-01

When an intense picosecond laser pulse is loaded upon a dense plasma, a high energy density plasma bunch, including electron bunch and ion bunch, can be generated in the target. We simulate this process through one-dimensional particle-in-cell simulation and find that the electron bunch generation is mainly due to a local high energy density electron sphere originated in the plasma skin layer. Once generated the sphere rapidly expands to compress the surrounding electrons and induce high density electron layer, coupled with that, hot electrons are efficiently triggered in the local sphere and traveling in the whole target. Under the compressions of light pressure, forward-running and backward-running hot electrons, a high energy density electron bunch generates. The bunch energy density is as high as TJ/m3 order of magnitude in our conditions, which is significant in laser driven dynamic high pressure generation and may find applications in high energy density physics.

Research on Plasma Synthetic Jet Actuator

NASA Astrophysics Data System (ADS)

Che, X. K.; Nie, W. S.; Hou, Z. Y.

2011-09-01

Circular dielectric barrier surface discharge (DBDs) actuator is a new concept of zero mass synthetic jet actuator. The characteristic of discharge and flow control effect of annular-circular plasma synthetic jet actuator has been studied by means of of numerical simulation and experiment. The discharge current density, electron density, electrostatic body force density and flowfield have been obtained. The results show annular-circular actuator can produce normal jet whose velocity will be greater than 2.0 m/s. The jet will excite circumfluence. In order to insure the discharge is generated in the exposed electrode annular and produce centripetal and normal electrostatic body force, the width and annular diameter of exposed electrode must be big enough, or an opposite phase drove voltage potential should be applied between the two electrodes.

Anode current density distribution in a cusped field thruster

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

Wu, Huan, E-mail: wuhuan58@qq.com; Liu, Hui, E-mail: hlying@gmail.com; Meng, Yingchao

2015-12-15

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

Intense Pulsed Heavy Ion Beam Technology

NASA Astrophysics Data System (ADS)

Masugata, Katsumi; Ito, Hiroaki

Development of intense pulsed heavy ion beam accelerator technology is described for the application of materials processing. Gas puff plasma gun and vacuum arc discharge plasma gun were developed as an active ion source for magnetically insulated pulsed ion diode. Source plasma of nitrogen and aluminum were successfully produced with the gas puff plasma gun and the vacuum arc plasma gun, respectively. The ion diode was successfully operated with gas puff plasma gun at diode voltage 190 kV, diode current 2.2 kA and nitrogen ion beam of ion current density 27 A/cm2 was obtained. The ion composition was evaluated by a Thomson parabola spectrometer and the purity of the nitrogen ion beam was estimated to be 86%. The diode also operated with aluminum ion source of vacuum arc plasma gun. The ion diode was operated at 200 kV, 12 kA, and aluminum ion beam of current density 230 A/cm2 was obtained. The beam consists of aluminum ions (Al(1-3)+) of energy 60-400 keV, and protons (90-130 keV), and the purity was estimated to be 89 %. The development of the bipolar pulse accelerator (BPA) was reported. A double coaxial type bipolar pulse generator was developed as the power supply of the BPA. The generator was tested with dummy load of 7.5 ohm, bipolar pulses of -138 kV, 72 ns (1st pulse) and +130 kV, 70 ns (2nd pulse) were succesively generated. By applying the bipolar pulse to the drift tube of the BPA, nitrogen ion beam of 2 A/cm2 was observed in the cathode, which suggests the bipolar pulse acceleration.

Dark energy, non-minimal couplings and the origin of cosmic magnetic fields

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

Jiménez, Jose Beltrán; Maroto, Antonio L., E-mail: jobeltra@fis.ucm.es, E-mail: maroto@fis.ucm.es

2010-12-01

In this work we consider the most general electromagnetic theory in curved space-time leading to linear second order differential equations, including non-minimal couplings to the space-time curvature. We assume the presence of a temporal electromagnetic background whose energy density plays the role of dark energy, as has been recently suggested. Imposing the consistency of the theory in the weak-field limit, we show that it reduces to standard electromagnetism in the presence of an effective electromagnetic current which is generated by the momentum density of the matter/energy distribution, even for neutral sources. This implies that in the presence of dark energy,more » the motion of large-scale structures generates magnetic fields. Estimates of the present amplitude of the generated seed fields for typical spiral galaxies could reach 10{sup −9} G without any amplification. In the case of compact rotating objects, the theory predicts their magnetic moments to be related to their angular momenta in the way suggested by the so called Schuster-Blackett conjecture.« less

Lithium-coated polymeric matrix as a minimum volume-change and dendrite-free lithium metal anode

PubMed Central

Liu, Yayuan; Lin, Dingchang; Liang, Zheng; Zhao, Jie; Yan, Kai; Cui, Yi

2016-01-01

Lithium metal is the ideal anode for the next generation of high-energy-density batteries. Nevertheless, dendrite growth, side reactions and infinite relative volume change have prevented it from practical applications. Here, we demonstrate a promising metallic lithium anode design by infusing molten lithium into a polymeric matrix. The electrospun polyimide employed is stable against highly reactive molten lithium and, via a conformal layer of zinc oxide coating to render the surface lithiophilic, molten lithium can be drawn into the matrix, affording a nano-porous lithium electrode. Importantly, the polymeric backbone enables uniform lithium stripping/plating, which successfully confines lithium within the matrix, realizing minimum volume change and effective dendrite suppression. The porous electrode reduces the effective current density; thus, flat voltage profiles and stable cycling of more than 100 cycles is achieved even at a high current density of 5 mA cm−2 in both carbonate and ether electrolyte. The advantages of the porous, polymeric matrix provide important insights into the design principles of lithium metal anodes. PMID:26987481

Lithium-coated polymeric matrix as a minimum volume-change and dendrite-free lithium metal anode

DOE PAGES

Liu, Yayuan; Lin, Dingchang; Liang, Zheng; ...

2016-03-18

Lithium metal is the ideal anode for the next generation of high-energy-density batteries. Nevertheless, dendrite growth, side reactions and infinite relative volume change have prevented it from practical applications. Here, we demonstrate a promising metallic lithium anode design by infusing molten lithium into a polymeric matrix. The electrospun polyimide employed is stable against highly reactive molten lithium and, via a conformal layer of zinc oxide coating to render the surface lithiophilic, molten lithium can be drawn into the matrix, affording a nano-porous lithium electrode. Importantly, the polymeric backbone enables uniform lithium stripping/plating, which successfully confines lithium within the matrix, realizingmore » minimum volume change and effective dendrite suppression. The porous electrode reduces the effective current density; thus, flat voltage profiles and stable cycling of more than 100 cycles is achieved even at a high current density of 5 mA cm -2 in both carbonate and ether electrolyte. Furthermore, the advantages of the porous, polymeric matrix provide important insights into the design principles of lithium metal anodes.« less

Lithium-coated polymeric matrix as a minimum volume-change and dendrite-free lithium metal anode

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

Liu, Yayuan; Lin, Dingchang; Liang, Zheng

Lithium metal is the ideal anode for the next generation of high-energy-density batteries. Nevertheless, dendrite growth, side reactions and infinite relative volume change have prevented it from practical applications. Here, we demonstrate a promising metallic lithium anode design by infusing molten lithium into a polymeric matrix. The electrospun polyimide employed is stable against highly reactive molten lithium and, via a conformal layer of zinc oxide coating to render the surface lithiophilic, molten lithium can be drawn into the matrix, affording a nano-porous lithium electrode. Importantly, the polymeric backbone enables uniform lithium stripping/plating, which successfully confines lithium within the matrix, realizingmore » minimum volume change and effective dendrite suppression. The porous electrode reduces the effective current density; thus, flat voltage profiles and stable cycling of more than 100 cycles is achieved even at a high current density of 5 mA cm -2 in both carbonate and ether electrolyte. Furthermore, the advantages of the porous, polymeric matrix provide important insights into the design principles of lithium metal anodes.« less

Enhancing light absorption within the carrier transport length in quantum junction solar cells.

PubMed

Fu, Yulan; Hara, Yukihiro; Miller, Christopher W; Lopez, Rene

2015-09-10

Colloidal quantum dot (CQD) solar cells have attracted tremendous attention because of their tunable absorption spectrum window and potentially low processing cost. Recently reported quantum junction solar cells represent a promising approach to building a rectifying photovoltaic device that employs CQD layers on each side of the p-n junction. However, the ultimate efficiency of CQD solar cells is still highly limited by their high trap state density in both p- and n-type CQDs. By modeling photonic structures to enhance the light absorption within the carrier transport length and by ensuring that the carrier generation and collection efficiencies were both augmented, our work shows that overall device current density could be improved. We utilized a two-dimensional numerical model to calculate the characteristics of patterned CQD solar cells based on a simple grating structure. Our calculation predicts a short circuit current density as high as 31  mA/cm², a value nearly 1.5 times larger than that of the conventional flat design, showing the great potential value of patterned quantum junction solar cells.

Continuous development of current sheets near and away from magnetic nulls

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

Kumar, Sanjay; Bhattacharyya, R.

2016-04-15

The presented computations compare the strength of current sheets which develop near and away from the magnetic nulls. To ensure the spontaneous generation of current sheets, the computations are performed congruently with Parker's magnetostatic theorem. The simulations evince current sheets near two dimensional and three dimensional magnetic nulls as well as away from them. An important finding of this work is in the demonstration of comparative scaling of peak current density with numerical resolution, for these different types of current sheets. The results document current sheets near two dimensional magnetic nulls to have larger strength while exhibiting a stronger scalingmore » than the current sheets close to three dimensional magnetic nulls or away from any magnetic null. The comparative scaling points to a scenario where the magnetic topology near a developing current sheet is important for energetics of the subsequent reconnection.« less

ADCP measurements of gravity currents in the Chicago River, Illinois

USGS Publications Warehouse

Garcia, C.M.; Oberg, K.; Garcia, M.H.

2007-01-01

A unique set of observations of stratified flow phenomena in the Chicago River was made using an upward-looking acoustic Doppler current profiler (ADCP) during the period November 20, 2003 to February 1, 2004. Water density differences between the Chicago River and its North Branch (NB) seem to be responsible for the development of gravity currents. With the objective of characterizing the occurrence, frequency, and evolution of such currents, the ADCP was configured to continuously collect high-resolution water velocity and echo intensity profiles in the Chicago River at Columbus Drive. During the observation period, 28 gravity current events were identified, lasting a total of 77% of the time. Sixteen of these events were generated by underflows from the NB and 12 of these events were generated by overflows from the NB. On average, the duration of the underflow and overflow events was 52.3 and 42.1 h, respectively. A detailed analysis of one underflow event, which started on January 7, 2004, and lasted about 65h, was performed. This is the first time that ADCP technology has been used to continuously monitor gravity currents in a river. ?? 2007 ASCE.

Diamond Thin-Film Thermionic Generator

NASA Astrophysics Data System (ADS)

Clewell, J. M.; Ordonez, C. A.; Perez, J. M.

1997-03-01

Since the eighteen-hundreds scientists have sought to develop the highest thermal efficiency in heat engines such as thermionic generators. Modern research in the emerging diamond film industry has indicated the work functions of diamond thin-films can be much less than one electron volt, compelling fresh investigation into their capacity as thermionic generators and inviting new methodology for determining that efficiency. Our objective is to predict the efficiency of a low-work-function, degenerate semiconductor (diamond film) thermionic generator operated as a heat engine between two constant-temperature thermal reservoirs. Our presentation will focus on a theoretical model which predicts the efficiency of the system by employing a Monte Carlo computational technique from which we report results for the thermal efficiency and the thermionic current densities of diamond thin-films.

Characteristics of electromagnetic interference generated by arc discharges. [in spacecraft

NASA Technical Reports Server (NTRS)

Leung, Philip

1986-01-01

Electromagnetic interference (EMI) signatures resulting from arc discharges are characterized, and the effects of electrostatic discharges (ESDs) on the design of spacecraft systems are investigated. EMI characterization experiments were performed on Mylar, Teflon, Kapton, fused silica, and fiberglass in a vacuum chamber with acrylic walls; the experimental design and procedures are described. Discharge current pulses and RF spectra generated by the sample materials are examined. The relation between the magnitude of EMI generated during an ESD event and the material, environment, and geometry is studied. The solar-array/plasma interaction is analyzed; particular attention is given to the rate of discharge as a function of plasma density. The physical mechanisms of ESD-generated EMI are discussed. The data reveal that ESD parameters are dependent on the test environment.

LORETA analysis of three-dimensional distribution of δ band activity in schizophrenia: relation to negative symptoms.

PubMed

Itoh, Toru; Sumiyoshi, Tomiki; Higuchi, Yuko; Suzuki, Michio; Kawasaki, Yasuhiro

2011-08-01

We sought to determine if altered electroencephalography (EEG) activities, such as delta band activity, in specific brain regions are associated with psychotic symptoms. Data were obtained from 17 neuroleptic-naive patients with schizophrenia and age- and sex-matched 17 healthy control subjects. Low Resolution Brain Electromagnetic Tomography (LORETA) was used to generate current source density images of delta, theta, alpha, and beta activities. Localization of the difference in EEG activity between the two groups was assessed by voxel-by-voxel non-paired t-test of the LORETA images. Spearman's correlation coefficient was obtained to relate LORETA values of EEG current density in brain regions showing a significant between-group difference and psychopathology scores. Delta band activity, represented by LORETA current density, was greater for patients in the following areas; the left inferior temporal gyrus, right middle frontal gyrus, right superior frontal gyrus, right inferior frontal gyrus, and right parahippocampal gyrus. LORETA values for delta band activity in the above five brain regions were negatively correlated with negative, but not positive symptoms. The results of this study suggest the role for electrophysiological changes in some of the brain regions, e.g. prefrontal cortex, in the manifestation of negative symptoms. Copyright © 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

Field characteristics of deposits from spatter-rich pyroclastic density currents at Summer Coon volcano, Colorado

NASA Astrophysics Data System (ADS)

Valentine, G. A.; Perry, F. V.; WoldeGabriel, G.

2000-12-01

The Oligocene, deeply eroded Summer Coon composite volcano contains mafic andesite deposits that are massive to poorly bedded, have abundant flattened and deformed spatter clasts, have varying proportions of dense lithic clasts, and are supported mostly by a coarse-ash matrix. Although superficially these deposits resemble typical facies from Strombolian eruptions (emplaced ballistically, by fallout, and by rolling and local grain-avalanches down steep cone slopes), there are several lines of evidence that lead to an interpretation that the deposits were emplaced by pyroclastic density currents. These include local coarse-tail grading, deformation of spatter clasts in a down-flow direction, incorporation of matrix ash and lapilli into flattened spatter clasts, imbrication of large clasts, plastering of spatter on stoss sides of large lithic blocks and lenses of lithic-rich material on lee sides, deposition on angles less than the angle of repose, and a paucity of clast shapes associated with Strombolian mechanisms. The deposit characteristics are consistent with rapid sedimentation from a low-particle-concentration, turbulent flow onto an aggrading bed. We infer two potential mechanisms for generating these density currents: (1) explosive magma-water interaction involving lithic debris and relatively unfragmented melt; and (2) collapse of oversteepened upper cone slopes due to rapid accumulation of spatter from voluminous Strombolian eruptions.

Ohmic resistance affects microbial community and ...

EPA Pesticide Factsheets

Multi-anode microbial electrochemical cells (MXCs) are considered as one of the most promising configurations for scale-up of MXCs, but fundamental understanding of anode kinetics governing current density is limited in the MXCs. In this study we first assessed microbial community and electrochemical kinetic parameters for biofilms on individual anodes in a multi-anode MXC to better comprehend anode fundamentals. Microbial community analysis using 16S rRNA illumine sequencing showed that Geobactor genus, one of the most kinetically efficient anode-respiring bacteria (ARB), was abundant (87%) only on the biofilm anode closest to a reference electrode in which current density was the highest among four anodes. In comparison, Geobacter populations were less than 11% for other three anodes more distant from the reference electrode, generating small current density. Half-saturation anode potential (EKA) was the lowest at -0.251 to -0.242 V (vs. standard hydrogen electrode) for the closest anode, while EKA was as high as -0.134 V for the farthest anode. Our study clearly proves that ohmic resistance changes anode potential which mainly causes different biofilm communities on individual anodes and consequently influences anode kinetics. This study explored the use of multiple anodes in microelectrochemical cells and the microbial community on these anodes, as a function of the efficiency in producing hydrogen peroxide.

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

Al-Robaee, M.S.; Krishna, M.G.; Rao, K.N.

Single layer films of CeO{sub 2} have been deposited both by conventional electron beam evaporation and ion assisted deposition with oxygen and argon ions. A broad beam Kaufman ion source (3 cm diam) has been used to generate the ions. A systematic study has been made on optical properties such as refractive index, extinction coefficient and inhomogeneity of the films as a function of: (1) oxygen partial pressure in the range 1{times}10{sup {minus}4} to 1{times}10{sup {minus}5} mbar. (2) Incidence of oxygen ions with energy in the range 300--700 eV and current density in the range 50--220 {mu}A/cm{sup 2}. (3) Incidencemore » of mixed argon and oxygen ions of different ratios. The refractive index of the films deposited under the influence of ion bombardment showed higher indices than the conventionally evaporated films. The maximum index obtained with an oxygen ion bombardment was 2.3 at an ion energy of 600 eV and current density of 220 {mu}A/cm{sup 2}. The bombardment of the films with a mixed argon--oxygen (25% Ar) ion beam of the same energy and current density was found to further increase the refractive index. The extinction coefficient in both cases was negligible.« less

Microcrack healing in non-ferrous metal tubes through eddy current pulse treatment.

PubMed

Xu, Wenchen; Yang, Chuan; Yu, Haiping; Jin, Xueze; Guo, Bin; Shan, Debin

2018-04-16

This study proposed a novel method to heal microcrack within Mg alloy tubes using high density eddy current pulse treatment (ECPT). Through electromagnetic induction inside a copper coil connected with a high density pulse power source supply, the high density (greater than 5 × 10 9  A/m 2 ) and short duration eddy current was generated in tube specimens of Mg alloy. The results show that the microcracks in tube specimens was healed evidently and the mechanical properties of the tubes subjected to ECPT were improved simultaneously. The crack healing during ECPT was ascribed to not only the thermal stress around the microcrack tips and the softening or melting of metals in the vicinity of microcrack tips, but also the squeezing action acted by the Lorentz force. In the inward-discharging scheme, both the compressive radial stress and tangential stress induced by the Lorentz force contributed to more sufficient crack healing and thus better mechanical properties of tube specimens after the ECPT experiment, compared to the outward-discharging scheme. The ECPT can heal microcracks automatically without directly contacting tubular specimens and is not limited by the length of tubular workpieces, exhibiting great potential for crack healing in non-ferrous alloy tubes.

"Fan-Tip-Drive" High-Power-Density, Permanent Magnet Electric Motor and Test Rig Designed for a Nonpolluting Aircraft Propulsion Program

NASA Technical Reports Server (NTRS)

Brown, Gerald V.; Kascak, Albert F.

2004-01-01

A scaled blade-tip-drive test rig was designed at the NASA Glenn Research Center. The rig is a scaled version of a direct-current brushless motor that would be located in the shroud of a thrust fan. This geometry is very attractive since the allowable speed of the armature is approximately the speed of the blade tips (Mach 1 or 1100 ft/s). The magnetic pressure generated in the motor acts over a large area and, thus, produces a large force or torque. This large force multiplied by the large velocity results in a high-power-density motor.

High Density Thermal Energy Storage with Supercritical Fluids

NASA Technical Reports Server (NTRS)

Ganapathi, Gani B.; Wirz, Richard

2012-01-01

A novel approach to storing thermal energy with supercritical fluids is being investigated, which if successful, promises to transform the way thermal energy is captured and utilized. The use of supercritical fluids allows cost-affordable high-density storage with a combination of latent heat and sensible heat in the two-phase as well as the supercritical state. This technology will enhance penetration of several thermal power generation applications and high temperature water for commercial use if the overall cost of the technology can be demonstrated to be lower than the current state-of-the-art molten salt using sodium nitrate and potassium nitrate eutectic mixtures.

Design, modeling, and diagnostics of microplasma generation at microwave frequency

NASA Astrophysics Data System (ADS)

Miura, Naoto

Plasmas are partially ionized gases that find wide utility in the processing of materials, especially in integrated circuit fabrication. Most industrial applications of plasma occur in near-vacuum where the electrons are hot (>10,000 K) but the gas remains near room temperature. Typical atmospheric plasmas, such as arcs, are hot and destructive to sensitive materials. Recently the emerging field of microplasmas has demonstrated that atmospheric ionization of cold gases is possible if the plasma is microscopic. This dissertation investigates the fundamental physical properties of two classes of microplasma, both driven by microwave electric fields. The extension of point-source microplasmas into a line-shaped plasma is also described. The line-shape plasma is important for atmospheric processing of materials using roll-coating. Microplasma generators driven near 1 GHz were designed using microstrip transmission lines and characterized using argon near atmospheric pressure. The electrical characteristics of the microplasma including the discharge voltage, current and resistance were estimated by comparing the experimental power reflection coefficient to that of an electromagnetic simulation. The gas temperature, argon metastable density and electron density were obtained by optical absorption and emission spectroscopy. The microscopic internal plasma structure was probed using spatially-resolved diode laser absorption spectroscopy of excited argon states. The spatially resolved diagnostics revealed that argon metastable atoms were depleted within the 200mum core of the microplasma where the electron density was maximum. Two microplasma generators, the split-ring resonator (SRR) and the transmission line (T-line) generator, were compared. The SRR ran efficiently with a high impedance plasma (>1000 O) and was stabilized by the self-limiting of absorbed power (<1W) as a lower impedance plasma caused an impedance mismatch. Gas temperatures were <1000 K and electron densities were ~1020 m-3, conditions which are favorable for treatment of delicate materials. The T-line generator ran most efficiently with an intense, low impedance plasma that matched the impedance of the T-line (35 O). With the T-line generator, the absorbed power could exceed 20W, which created an electron density of 1021 m-3, but the gas temperature exceeded 2000 K. Finally, line-shaped microplasmas based on resonant and non-resonant configurations were developed, tested, and analyzed.

Notepad-like triboelectric generator for efficiently harvesting low-velocity motion energy by interconversion between kinetic energy and elastic potential energy.

PubMed

Liu, Guanlin; Leng, Qiang; Lian, Jiawei; Guo, Hengyu; Yi, Xi; Hu, Chenguo

2015-01-21

Great attention has been paid to nanogenerators that harvest energy from ambient environments lately. In order to give considerable output current, most nanogenerators require high-velocity motion that in most cases can hardly be provided in our daily life. Here we report a notepad-like triboelectric generator (NTEG), which uses simple notepad-like structure to generate elastic deformation so as to turn a low-velocity kinetic energy into high-velocity kinetic energy through the conversion of elastic potential energy. Therefore, the NTEG can achieve high current output under low-velocity motion, which completely distinguishes it from tribogenerators previously reported. The factors that may affect the output performance are explored, including the number of slices, active length of slice, press speed, and vertical displacement. In addition, the working mechanism is systematically studied, indicating that the efficiency of the generator can be greatly enhanced by interconversion between kinetic energy and elastic potential energy. The short-circuit current, the open-circuit voltage, and power density are 205 μA and 470 V and 9.86 W/m(2), respectively, which is powerful enough to light up hundreds of light-emitting diodes (LEDs) and charge a commercial capacitor. Besides, NTEGs have been successfully applied to a self-powered door monitor.

A facile synthesis of reduced holey graphene oxide for supercapacitors.

PubMed

Hu, Xinjun; Bai, Dongchen; Wu, Yiqi; Chen, Songbo; Ma, Yu; Lu, Yue; Chao, Yuanzhi; Bai, Yongxiao

2017-12-12

Hydroxyl radicals (˙OH) generated from a UV/O 3 solution reaction is used to efficiently etch graphene oxide nanosheets under moderate conditions. Reduced holey graphene oxide is directly used as a supercapacitor electrode material and exhibits high specific capacitance (224 F g -1 at a current density of 1 A g -1 ) and high volumetric capacitance (up to 206 F cm -3 ).

Electrically conductive polycrystalline diamond and particulate metal based electrodes

DOEpatents

Swain, Greg M.; Wang, Jian

2005-04-26

An electrically conducting and dimensionally stable diamond (12, 14) and metal particle (13) electrode produced by electrodepositing the metal on the diamond is described. The electrode is particularly useful in harsh chemical environments and at high current densities and potentials. The electrode is particularly useful for generating hydrogen, and for reducing oxygen and oxidizing methanol in reactions which are of importance in fuel cells.

System and method for generating steady state confining current for a toroidal plasma fusion reactor

DOEpatents

Fisch, Nathaniel J.

1981-01-01

A system for generating steady state confining current for a toroidal plasma fusion reactor providing steady-state generation of the thermonuclear power. A dense, hot toroidal plasma is initially prepared with a confining magnetic field with toroidal and poloidal components. Continuous wave RF energy is injected into said plasma to establish a spectrum of traveling waves in the plasma, where the traveling waves have momentum components substantially either all parallel, or all anti-parallel to the confining magnetic field. The injected RF energy is phased to couple to said traveling waves with both a phase velocity component and a wave momentum component in the direction of the plasma traveling wave components. The injected RF energy has a predetermined spectrum selected so that said traveling waves couple to plasma electrons having velocities in a predetermined range .DELTA.. The velocities in the range are substantially greater than the thermal electron velocity of the plasma. In addition, the range is sufficiently broad to produce a raised plateau having width .DELTA. in the plasma electron velocity distribution so that the plateau electrons provide steady-state current to generate a poloidal magnetic field component sufficient for confining the plasma. In steady state operation of the fusion reactor, the fusion power density in the plasma exceeds the power dissipated in the plasma.

System and method for generating steady state confining current for a toroidal plasma fusion reactor

DOEpatents

Bers, Abraham

1981-01-01

A system for generating steady state confining current for a toroidal plasma fusion reactor providing steady-state generation of the thermonuclear power. A dense, hot toroidal plasma is initially prepared with a confining magnetic field with toroidal and poloidal components. Continuous wave RF energy is injected into said plasma to estalish a spectrum of traveling waves in the plasma, where the traveling waves have momentum components substantially either all parallel, or all anti-parallel to the confining magnetic field. The injected RF energy is phased to couple to said traveling waves with both a phase velocity component and a wave momentum component in the direction of the plasma traveling wave components. The injected RF energy has a predetermined spectrum selected so that said traveling waves couple to plasma electrons having velocities in a predetermined range .DELTA.. The velocities in the range are substantially greater than the thermal electron velocity of the plasma. In addition, the range is sufficiently broad to produce a raised plateau having width .DELTA. in the plasma electron velocity distribution so that the plateau electrons provide steady-state current to generate a poloidal magnetic field component sufficient for confining the plasma. In steady state operation of the fusion reactor, the fusion power density in the plasma exceeds the power dissipated inthe plasma.

Hydrogen Production by Geobacter Species and a Mixed Consortium in a Microbial Electrolysis Cell▿

PubMed Central

Call, Douglas F.; Wagner, Rachel C.; Logan, Bruce E.

2009-01-01

A hydrogen utilizing exoelectrogenic bacterium (Geobacter sulfurreducens) was compared to both a nonhydrogen oxidizer (Geobacter metallireducens) and a mixed consortium in order to compare the hydrogen production rates and hydrogen recoveries of pure and mixed cultures in microbial electrolysis cells (MECs). At an applied voltage of 0.7 V, both G. sulfurreducens and the mixed culture generated similar current densities (ca. 160 A/m3), resulting in hydrogen production rates of ca. 1.9 m3 H2/m3/day, whereas G. metallireducens exhibited lower current densities and production rates of 110 ± 7 A/m3 and 1.3 ± 0.1 m3 H2/m3/day, respectively. Before methane was detected in the mixed-culture MEC, the mixed consortium achieved the highest overall energy recovery (relative to both electricity and substrate energy inputs) of 82% ± 8% compared to G. sulfurreducens (77% ± 2%) and G. metallireducens (78% ± 5%), due to the higher coulombic efficiency of the mixed consortium. At an applied voltage of 0.4 V, methane production increased in the mixed-culture MEC and, as a result, the hydrogen recovery decreased and the overall energy recovery dropped to 38% ± 16% compared to 80% ± 5% for G. sulfurreducens and 76% ± 0% for G. metallireducens. Internal hydrogen recycling was confirmed since the mixed culture generated a stable current density of 31 ± 0 A/m3 when fed hydrogen gas, whereas G. sulfurreducens exhibited a steady decrease in current production. Community analysis suggested that G. sulfurreducens was predominant in the mixed-culture MEC (72% of clones) despite its relative absence in the mixed-culture inoculum obtained from a microbial fuel cell reactor (2% of clones). These results demonstrate that Geobacter species are capable of obtaining similar hydrogen production rates and energy recoveries as mixed cultures in an MEC and that high coulombic efficiencies in mixed culture MECs can be attributed in part to the recycling of hydrogen into current. PMID:19820150

Turbulent structures in cylindrical density currents in a rotating frame of reference

NASA Astrophysics Data System (ADS)

Salinas, Jorge S.; Cantero, Mariano I.; Dari, Enzo A.; Bonometti, Thomas

2018-06-01

Gravity currents are flows generated by the action of gravity on fluids with different densities. In some geophysical applications, modeling such flows makes it necessary to account for rotating effects, modifying the dynamics of the flow. While previous works on rotating stratified flows focused on currents of large Coriolis number, the present work focuses on flows with small Coriolis numbers (i.e. moderate-to-large Rossby numbers). In this work, cylindrical rotating gravity currents are investigated by means of highly resolved simulations. A brief analysis of the mean flow evolution to the final state is presented to provide a complete picture of the flow dynamics. The numerical results, showing the well-known oscillatory behavior of the flow (inertial waves) and a final state lens shape (geostrophic adjustment), are in good agreement with experimental observations and theoretical models. The turbulent structures in the flow are visualized and described using, among others, a stereoscopic visualization and videos as supplementary material. In particular, the structure of the lobes and clefts at the front of the current is presented in association to local turbulent structures. In rotating gravity currents, the vortices observed at the lobes front are not of hairpin type but are rather of Kelvin-Helmholtz type.

Simulation of Electromigration Based on Resistor Networks

NASA Astrophysics Data System (ADS)

Patrinos, Anthony John

A two dimensional computer simulation of electromigration based on resistor networks was designed and implemented. The model utilizes a realistic grain structure generated by the Monte Carlo method and takes specific account of the local effects through which electromigration damage progresses. The dynamic evolution of the simulated thin film is governed by the local current and temperature distributions. The current distribution is calculated by superimposing a two dimensional electrical network on the lattice whose nodes correspond to the particles in the lattice and the branches to interparticle bonds. Current is assumed to flow from site to site via nearest neighbor bonds. The current distribution problem is solved by applying Kirchhoff's rules on the resulting electrical network. The calculation of the temperature distribution in the lattice proceeds by discretizing the partial differential equation for heat conduction, with appropriate material parameters chosen for the lattice and its defects. SEReNe (for Simulation of Electromigration using Resistor Networks) was tested by applying it to common situations arising in experiments with real films with satisfactory results. Specifically, the model successfully reproduces the expected grain size, line width and bamboo effects, the lognormal failure time distribution and the relationship between current density exponent and current density. It has also been modified to simulate temperature ramp experiments but with mixed, in this case, results.

Globally optimal superconducting magnets part II: symmetric MSE coil arrangement.

PubMed

Tieng, Quang M; Vegh, Viktor; Brereton, Ian M

2009-01-01

A globally optimal superconducting magnet coil design procedure based on the Minimum Stored Energy (MSE) current density map is outlined. The method has the ability to arrange coils in a manner that generates a strong and homogeneous axial magnetic field over a predefined region, and ensures the stray field external to the assembly and peak magnetic field at the wires are in acceptable ranges. The outlined strategy of allocating coils within a given domain suggests that coils should be placed around the perimeter of the domain with adjacent coils possessing alternating winding directions for optimum performance. The underlying current density maps from which the coils themselves are derived are unique, and optimized to possess minimal stored energy. Therefore, the method produces magnet designs with the lowest possible overall stored energy. Optimal coil layouts are provided for unshielded and shielded short bore symmetric superconducting magnets.

Treatment of automotive industry oily wastewater by electrocoagulation: statistical optimization of the operational parameters.

PubMed

GilPavas, Edison; Molina-Tirado, Kevin; Gómez-García, Miguel Angel

2009-01-01

An electrocoagulation process was used for the treatment of oily wastewater generated from an automotive industry in Medellín (Colombia). An electrochemical cell consisting of four parallel electrodes (Fe and Al) in bipolar configuration was implemented. A multifactorial experimental design was used for evaluating the influence of several parameters including: type and arrangement of electrodes, pH, and current density. Oil and grease removal was defined as the response variable for the statistical analysis. Additionally, the BOD(5), COD, and TOC were monitored during the treatment process. According to the results, at the optimum parameter values (current density = 4.3 mA/cm(2), distance between electrodes = 1.5 cm, Fe as anode, and pH = 12) it was possible to reach a c.a. 95% oils removal, COD and mineralization of 87.4% and 70.6%, respectively. A final biodegradability (BOD(5)/COD) of 0.54 was reached.

Fractional Josephson vortices in two-gap superconductor long Josephson junctions

NASA Astrophysics Data System (ADS)

Kim, Ju

2014-03-01

We investigated the phase dynamics of long Josephson junctions (LJJ) with two-gap superconductors in the broken time reversal symmetry state. In this LJJ, spatial phase textures (i-solitons) can be excited due to the presence of two condensates and the interband Joesphson effect between them. The presence of a spatial phase texture in each superconductor layer leads to a spatial variation of the critical current density between the superconductor layers. We find that this spatial dependence of the crtitical current density can self-generate magnetic flux in the insulator layer, resulting in Josephson vortices with fractional flux quanta. Similar to the situation in a YBa2 Cu3O7 - x superconductor film grain boundary, the fractionalization of a Josephson vortex arises as a response to either periodic or random excitation of i-solitions. This suggests that magnetic flux measurements may be used to probe i-soliton excitations in multi-gap superconductor LJJs.

Design of experiments with four-factors for a PEM fuel cell optimization

NASA Astrophysics Data System (ADS)

Olteanu, V.; Pǎtularu, L.; Popescu, C. L.; Popescu, M. O.; Crǎciunescu, A.

2017-07-01

Nowadays, many research efforts are allocated for the development of fuel cells, since they constitute a carbon-free electrical energy generator which can be used for stationary, mobile and portable applications. The maximum value of the delivered power of a fuel cell depends on many factors as: the height of plates' channels, the stoichiometry level of the air flow, the air pressure for the cathode, and of the actual operating electric current density. In this paper, two levels, full four-factors factorial experiment has been designed in order to obtain the appropriate response surface which approximates the maximum delivered power dependence of the above-mentioned factors. The optimum set of the fuel-cell factors which determine the maximum value of the delivered power was determined and a comparison between simulated and measured optimal Power versus Current Density characteristics is given.

Vertically grown multiwalled carbon nanotube anode and nickel silicide integrated high performance microsized (1.25 μL) microbial fuel cell.

PubMed

Mink, Justine E; Rojas, Jhonathan P; Logan, Bruce E; Hussain, Muhammad M

2012-02-08

Microbial fuel cells (MFCs) are an environmentally friendly method for water purification and self-sustained electricity generation using microorganisms. Microsized MFCs can also be a useful power source for lab-on-a-chip and similar integrated devices. We fabricated a 1.25 μL microsized MFC containing an anode of vertically aligned, forest type multiwalled carbon nanotubes (MWCNTs) with a nickel silicide (NiSi) contact area that produced 197 mA/m(2) of current density and 392 mW/m(3) of power density. The MWCNTs increased the anode surface-to-volume ratio, which improved the ability of the microorganisms to couple and transfer electrons to the anode. The use of nickel silicide also helped to boost the output current by providing a low resistance contact area to more efficiently shuttle electrons from the anode out of the device. © 2012 American Chemical Society

Simulation of superconducting tapes and coils with convex quadratic programming method

NASA Astrophysics Data System (ADS)

Zhang, Yan; Song, Yuntao; Wang, Lei; Liu, Xufeng

2015-08-01

Second-generation (2G) high-temperature superconducting coated conductors are playing an increasingly important role in power applications due to their large current density under high magnetic fields. In this paper, we conclude and explore the ability and possible potential of J formulation from the mathematical modeling point of view. An equivalent matrix form of J formulation has been presented and a relation between electromagnetic quantities and Karush-Kuhn-Tucker (KKT) conditions in optimization theory has been discovered. The use of the latest formulae to calculate inductance in a coil system and the primal-dual interior-point method algorithm is a trial to make the process of modeling stylized and build a bridge to commercial optimization solvers. Two different dependences of the critical current density on the magnetic field have been used in order to make a comparison with those published papers.

Nanosecond repetitively pulsed discharges in air at atmospheric pressure—the spark regime

NASA Astrophysics Data System (ADS)

Pai, David Z.; Lacoste, Deanna A.; Laux, Christophe O.

2010-12-01

Nanosecond repetitively pulsed (NRP) spark discharges have been studied in atmospheric pressure air preheated to 1000 K. Measurements of spark initiation and stability, plasma dynamics, gas temperature and current-voltage characteristics of the spark regime are presented. Using 10 ns pulses applied repetitively at 30 kHz, we find that 2-400 pulses are required to initiate the spark, depending on the applied voltage. Furthermore, about 30-50 pulses are required for the spark discharge to reach steady state, following initiation. Based on space- and time-resolved optical emission spectroscopy, the spark discharge in steady state is found to ignite homogeneously in the discharge gap, without evidence of an initial streamer. Using measured emission from the N2 (C-B) 0-0 band, it is found that the gas temperature rises by several thousand Kelvin in the span of about 30 ns following the application of the high-voltage pulse. Current-voltage measurements show that up to 20-40 A of conduction current is generated, which corresponds to an electron number density of up to 1015 cm-3 towards the end of the high-voltage pulse. The discharge dynamics, gas temperature and electron number density are consistent with a streamer-less spark that develops homogeneously through avalanche ionization in volume. This occurs because the pre-ionization electron number density of about 1011 cm-3 produced by the high frequency train of pulses is above the critical density for streamer-less discharge development, which is shown to be about 108 cm-3.

Proton acceleration by multi-terawatt interaction with a near-critical density hydrogen jet

NASA Astrophysics Data System (ADS)

Goers, Andy; Feder, Linus; Hine, George; Salehi, Fatholah; Woodbury, Daniel; Su, J. J.; Papadopoulos, Dennis; Zigler, Arie; Milchberg, Howard

2016-10-01

We investigate the high intensity laser interaction with thin, near critical density plasmas as a means of efficient acceleration of MeV protons. A promising mechanism is magnetic vortex acceleration, where the ponderomotive force of a tightly focused laser pulse drives a relativistic electron current which generates a strong azimuthal magnetic field. The rapid expansion of this azimuthal magnetic field at the back side of the target can accelerate plasma ions to MeV scale energies. Compared to typical ion acceleration experiments utilizing a laser- thin solid foil interaction, magnetic vortex acceleration in near critical density plasma may be realized in a high density gas jet, making it attractive for applications requiring high repetition rates. We present preliminary experiments studying laser-plasma interaction and proton acceleration in a thin (< 200 μm) near-critical density hydrogen gas jet delivering electron densities 1020 -1021 cm-3 . This research was funded by the United States Department of Energy and the Defense Advanced Research Projects Agency (DARPA) under Contract Number W911-NF-15-C-0217, issued by the Army Research Office.

Dynamics and density estimation of hydroxyl radicals in a pulsed corona discharge

NASA Astrophysics Data System (ADS)

Ono, Ryo; Oda, Tetsuji

2002-09-01

Hydroxyl radicals generated by a pulsed corona discharge are measured by laser-induced fluorescence (LIF) with a tunable KrF excimer laser. The discharge with 35 kV voltage and 100 ns pulse current occurs between needle and plate electrodes in H2O/O2/N2 mixture at atmospheric pressure. The density and decay profile of OH radicals are studied. OH radicals decay with time after the discharge with a time constant of about 30-60 µs. The OH density is estimated to be about 7×1014 cm-3 in H2O(2.4%)/N2 mixture 10 µs after the discharge. The OH density is approximately proportional to the energy dissipated in the discharge. The O2 content influences the OH production. When the O2 content is varied in H2O(2.4%)/O2/N2 mixture, the OH density is maximum at an O2 content of 2%. The spatial distribution of OH density shows that OH radicals are produced in the streamers under positive discharge.

Effect of salt concentration and mediators in salt bridge microbial fuel cell for electricity generation from synthetic wastewater.

PubMed

Sevda, Surajbhan; Sreekrishnan, T R

2012-01-01

The aim of this study was to investigate the feasibility of using agar salt bridges for proton transport in Microbial Fuel Cells (MFC). It also tries to elucidate and effect of mediators on electricity production from wastewaters through experimentation using a simulated wastewater. In order to offset the very high cost of proton exchange membrane, salt bridges have been used in dual chamber MFCs. When the concentration of salt was varied in agar salt bridges from 1% to 10%, the volumetric power density changed from 1.71 to 84.99 mW/m(3) with a concomitant variation in power density from 0.32 to 16.02 mW/m(2). The maximum power density was observed at 5% salt concentration with 10% agar, which was accompanied by 88.41% COD reduction. In the case of methylene blue (0.01 mM) as the electron mediator, the voltage and current generation were 0.551 V and 0.47 mA, respectively. A maximum open circuit voltage of 0.718 V was seen at 0.08 mM methylene blue concentration, whereas maximum power densities of 17.59 mW/m(2) and 89.22 mW/m(3) were obtained. Different concentrations of neutral red were also tried out as mediators. A maximum open circuit voltage of 0.730 V was seen at 0.01 mM neutral red, corresponding to a power density of 12.02 mW/m(2) (volumetric power density of 60.97 mW/m(3)). Biofilm formation on the electrode surface was not observed in the presence of mediators, but was present in the absence of mediators. The results clearly demonstrated the feasibility to use agar salt bridge for proton transport and role of mediators in MFCs to generate electricity.

Formation and dissipation of runaway current by MGI on J-TEXT

NASA Astrophysics Data System (ADS)

Wei, Yunong; Chen, Zhongyong; Huang, Duwei; Tong, Ruihai; Zhang, Xiaolong

2017-10-01

Plasma disruptions are one of the major concern for ITER. A large fraction of runaway current may be formed due to the avalanche generation of runaway electrons (REs) during disruptions and ruin the device structure. Experiments of runaway current formation and dissipation have been done on J-TEXT. Two massive gas injection (MGI) valves are used to form and dissipate the runaway current. Hot tail RE generation caused by the fast thermal quench leads to an abnormal formation of runaway current when the pre-TQ electron density increases in a range of 0.5-2-10 19m-3. 1020-22 quantities of He, Ne, Ar or Kr impurities are injected by MGI2 to dissipate the runaway current. He injection shows no obvious effect on runaway current dissipation in the experiments and Kr injection shows the best. The kinetic energy of REs and the magnetic energy of RE beam will affect the dissipation efficiency to a certain extent. Runaway current decay rate is found increasing quickly with the increase of the gas injection when the quantity is moderate, and then reaches to a saturation value with large quantity injection. A possible reason to explain the saturation of dissipation effect is the saturation of gas assimilation efficiency.

Selection rules for harmonic generation in solids

NASA Astrophysics Data System (ADS)

Moiseyev, Nimrod

2015-05-01

High-order harmonic generation (HHG) in a bulk crystal was first observed in 2011 [S. Ghimire, A. D. DiChiara, E. Sistrunk, P. Agostini, L. F. DiMauro, and D. A. Reis, Nat. Phys. 7, 138 (2011), 10.1038/nphys1847]. Only odd-order harmonics were observed as expected on the basis of the selection rules in solids, which were derived when only the interband currents were taken into consideration. Here we study HHG in solids when the intraband currents are taken into consideration as well. We show that the dynamical selection rules are broken in solids and the possibility of generation of even-order harmonics cannot be excluded on the basis of the dynamical symmetry analysis. However, a simple analysis of the expression we obtained for the amplitude of the emitted high-order harmonics shows, without the need to carry out numerical calculations, that the even-order harmonics are suppressed due to the localization of the field-free one-electron density probability on the atoms in the solids.

Corrosion Performance of New Generation Aluminum-Lithium Alloys for Aerospace Applications

NASA Astrophysics Data System (ADS)

Moran, James P.; Bovard, Francine S.; Chrzan, James D.; Vandenburgh, Peter

Over the past several years, a new generation of aluminum-lithium alloys has been developed. These alloys are characterized by excellent strength, low density, and high modulus of elasticity and are therefore of interest for lightweight structural materials applications particularly for construction of current and future aircraft. These new alloys have also demonstrated significant improvements in corrosion resistance when compared with the legacy and incumbent alloys. This paper documents the superior corrosion resistance of the current commercial tempers of these materials and also discusses the corrosion performance as a function of the degree of artificial aging. Results from laboratory corrosion tests are compared with results from exposures in a seacoast atmosphere to assess the predictive capability of the laboratory tests. The correlations that have been developed between the laboratory tests and the seacoast exposures provide confidence that a set of available methods can provide an accurate assessment of the corrosion performance of this new generation of alloys.

Electron-irradiated n+-Si as hole injection tunable anode of organic light-emitting diode

NASA Astrophysics Data System (ADS)

Li, Y. Z.; Wang, Z. L.; Wang, Y. Z.; Luo, H.; Xu, W. J.; Ran, G. Z.; Qin, G. G.

2013-01-01

Traditionally, n-type silicon is not regarded as a good anode of organic light emitting diode (OLED) due to the extremely low hole concentration in it; however, when doped with Au element which acts as carrier generation centers, it can be, as shown in our previous work. In this study, we demonstrate a new kind of carrier generation centers in n+-type silicon, which are the defects produced by 5 MeV electron irradiation. The density of carrier generation centers in the irradiated n+-Si anode can be controlled by tuning the electron irradiation time, and thus hole injection current in the OLEDs with the irradiated n+-Si anode can be optimized, leading to their much higher maximum efficiencies than those of the OLEDs with non-irradiated n+-Si anode. For a green phosphorescent OLED with the irradiated n+-Si anode, the current efficiency and power efficiency reach up to 12.1 cd/A and 4.2 lm/W, respectively.