WorldWideScience

Sample records for current density limitations

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

    Directory of Open Access Journals (Sweden)

    Jen-Yu Chen

    2014-09-01

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

  2. Charge Exchange Effect on Space-Charge-Limited Current Densities in Ion Diode

    Institute of Scientific and Technical Information of China (English)

    石磊

    2002-01-01

    The article theoretically studied the charge-exchange effects on space charge limited electron and ion current densities of non-relativistic one-dimensional slab ion diode, and compared with those of without charge exchange.

  3. Current limiters

    Energy Technology Data Exchange (ETDEWEB)

    Loescher, D.H. [Sandia National Labs., Albuquerque, NM (United States). Systems Surety Assessment Dept.; Noren, K. [Univ. of Idaho, Moscow, ID (United States). Dept. of Electrical Engineering

    1996-09-01

    The current that flows between the electrical test equipment and the nuclear explosive must be limited to safe levels during electrical tests conducted on nuclear explosives at the DOE Pantex facility. The safest way to limit the current is to use batteries that can provide only acceptably low current into a short circuit; unfortunately this is not always possible. When it is not possible, current limiters, along with other design features, are used to limit the current. Three types of current limiters, the fuse blower, the resistor limiter, and the MOSFET-pass-transistor limiters, are used extensively in Pantex test equipment. Detailed failure mode and effects analyses were conducted on these limiters. Two other types of limiters were also analyzed. It was found that there is no best type of limiter that should be used in all applications. The fuse blower has advantages when many circuits must be monitored, a low insertion voltage drop is important, and size and weight must be kept low. However, this limiter has many failure modes that can lead to the loss of over current protection. The resistor limiter is simple and inexpensive, but is normally usable only on circuits for which the nominal current is less than a few tens of milliamperes. The MOSFET limiter can be used on high current circuits, but it has a number of single point failure modes that can lead to a loss of protective action. Because bad component placement or poor wire routing can defeat any limiter, placement and routing must be designed carefully and documented thoroughly.

  4. Limitations of absolute current densities derived from the Semel & Skumanich method

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Semel and Skumanich proposed a method to obtain the absolute electric current density, |Jz|, without disambiguation of 180° in the transverse field directions. The advantage of the method is that the uncertainty in the determination of the ambiguity in the magnetic azimuth is removed. Here, we investigate the limits of the calculation when applied to a numerical MHD model. We have found that the combination of changes in the magnetic azimuth with vanishing horizontal field component leads to errors, where electric current densities are often strong. Where errors occur, the calculation gives |Jz| too small by factors typically 1.2 - 2.0.

  5. Predicting size effect on diffusion-limited current density of oxygen reduction by copper wire

    Institute of Scientific and Technical Information of China (English)

    LU Yonghong; XU Haibo; WANG Jia; ZHONG Lian

    2011-01-01

    The size effect of copper wire radius (0.04鈥?.82 mm) on the diffusion-limited current density of an oxygen reduction reaction in stagnant simulated seawater (naturally aerated 0.5 mol/L NaCl) is investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) and compared with the results obtained in 0.5 mol/L H2SO4. In the oxygen diffusion-limited range, size effect is found to occur independent of electrolytes, which is attributed to non-linear diffusion. Additionally, to satisfy application in a marine setting, an empirical equation correlating oxygen diffusion-limited current density to copper wire radius is proposed by fitting experimental data.

  6. Limiting current density in bis(trifluoromethylsulfonyl)amide-based ionic liquid for lithium batteries

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jun-Woo; Yoshida, Kazuki; Tachikawa, Naoki; Dokko, Kaoru; Watanabe, Masayoshi [Department of Chemistry and Biotechnology, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan)

    2011-02-15

    The physicochemical and electrochemical properties of the binary ionic liquid (IL), lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) dissolved in N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)amide (DEMETFSA), were investigated. The ionic conductivity of the binary IL decreased with an increase in LiTFSA concentration. The self-diffusion coefficients of Li{sup +}, DEME{sup +}, and TFSA{sup -} dissolved in the IL were measured by using the pulsed-field-gradient spin-echo (PGSE) NMR method. The self-diffusion coefficient of each ionic species was also found to decrease with increasing concentration of LiTFSA. The limiting current density in the IL electrolyte was evaluated by chronoamperometry using symmetric Li vertical stroke IL vertical stroke Li cell. The results suggest that the diffusion process of Li(I) in the IL dominates the limiting current density in the cell. The highest limiting current density is achieved at a concentration of 0.64 mol dm{sup -3} of LiTFSA. (author)

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

    KAUST Repository

    Dacuña, Javier

    2011-11-28

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

  8. Water Dissociation Phenomena on a Bipolar Membrane——Current-voltage Curve in Relation with Ionic Transport and Limiting Current Density

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The water dissociation mechanism on a bipolar membrane under the electrical field was investigated and characterized in terms of ionic transport and limiting current density. It is considered that the depletion layer exists at the junction of a bipolar membrane, which is coincided with the viewpoint of the most literatures, but we also consider that the thickness and conductivity of this layer is not only related with the increase of the applied voltage but also with the limiting current density. Below the limiting current density, the thickness of the depletion layer keeps a constant and the conductivity decreases with the increase of the applied voltage;while above the limiting current density, the depletion thickness will increase with the increase of the applied voltage and the conductivity keeps a very low constant. Based on the data reported in the literatures and independent determinations, the limiting current density was calculated and the experimental curves Ⅰ- Ⅴ in the two directions were compared with the theoretical calculations. It is demonstrated that above the limiting current density, the experimental results,either in the L-H direction or in the H-L direction, are consistent with the theoretical calculations; below the limiting current density, a slight deviation exists between the experimental and the theoretical results, and between the experimental results in the two directions. The change in Donnan potential due to the asymmetry of the mono-layers and the changes of ionic composition in the two directions is possibly responsible for this deviation.

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

    NARCIS (Netherlands)

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

    1998-01-01

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

  10. Theoretical Limit to the Laser Threshold Current Density in an InGaN Quantume Well Laser

    Energy Technology Data Exchange (ETDEWEB)

    Amano, H; Chow, W W; Han, J

    1998-10-09

    This paper describes an investigation of the spontaneous emission limit to the laser threshold current density in an InGaN quantum well laser. The peak gain and spontaneous emission rate as functions of carrier density are com- puted using a microscopic laser theory. From these quantities, the minimum achievable threshold current density is determined for a given threshold gain. The dependence on quantum well width, and the effects of inhomogeneous broadening due to spatial alloy variations are discussed. Also, comparison with experiments is made.

  11. Current Density Limitations in a Fast-Pulsed High-Voltage Diode

    Science.gov (United States)

    1992-06-01

    based on mass x acceleration - charge x E-field) - - -= qT (x)=-e rT(X) (19) dt M c M c where y ,ŕ /•/ 2/c ••V/c; t * time (S) e I electron charge I... Plasmaphysik IPP 4/250, September 1991. 6. Parker, R.K., Explosive Electron Emission and the Characteristics of High-Current Electron Flow, Air Force

  12. Current limiter circuit system

    Energy Technology Data Exchange (ETDEWEB)

    Witcher, Joseph Brandon; Bredemann, Michael V.

    2017-09-05

    An apparatus comprising a steady state sensing circuit, a switching circuit, and a detection circuit. The steady state sensing circuit is connected to a first, a second and a third node. The first node is connected to a first device, the second node is connected to a second device, and the steady state sensing circuit causes a scaled current to flow at the third node. The scaled current is proportional to a voltage difference between the first and second node. The switching circuit limits an amount of current that flows between the first and second device. The detection circuit is connected to the third node and the switching circuit. The detection circuit monitors the scaled current at the third node and controls the switching circuit to limit the amount of the current that flows between the first and second device when the scaled current is greater than a desired level.

  13. The density limit in JET diverted plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, D.J.; Clement, S.; Gottardi, N.; Gowers, C.; Harbour, P.; Loarte, A.; Horton, L.; Lingertat, J.; Lowry, C.G.; Saibene, G.; Stamp, M.; Stork, D. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Monk, R. [Royal Holloway Coll., London (United Kingdom). Dept. of Physics

    1994-07-01

    In JET limiter plasmas the density limit is associated with radiated power fractions of 100% and, in plasmas with carbon limiters, it is invariably disruptive. However, in discharges with solid beryllium limiters the limit is identified with the formation of a MARFE and disruptions are less frequent. In addition, the improved conditioning of the vessel arising from the use of beryllium has significantly improved the density limit scaling, so that the maximum density rises with the square root of the input power. In diverted plasmas several confinement regimes exist, making the characterization of the density limit more complex. While the density limit in L-mode plasmas is generally disruptive, the limit in ELMy and ELM-free H-modes generally prompts a return to the L-mode and a disruption is not inevitable. The density limit does rise with the increasing power, but the L-to-H transition complicates the analysis. Nevertheless, at low plasma currents (<2 MA), densities significantly above the Greenwald limit can be achieved, while at higher currents power handling limitations have constrained the range of density which can be achieved. (authors). 7 refs., 4 figs.

  14. Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb3Sn conductors

    CERN Document Server

    Segal, Christopher; Sung, Zu Hawn; Lee, Peter J; Sailer, Bernd; Thoener, Manfred; Schlenga, Klaud; Ballarino, Amalia; Bottura, Luca; Bordini, Bernardo; Scheuerlein, Christian; Larnalestier, David C

    2016-01-01

    High critical current density ( Jc) Nb3Sn A15 multifilamentary wires require a large volume fraction of small grain (SG), superconducting A15 phase, as well as Cu stabilizer with high Residual Resistance Ratio (RRR) to provide electromagnetic stabilization and protection. In powder-in-tube (PIT) wires the unreacted Nb7.5 wt%Ta outer layer of the tubular filaments acts as a diffusion barrier and protects the interfilamentary Cu stabilizer from Sn contamination. A high RRR requirement generally imposes a restricted A15 reaction heat treatment to prevent localized full reaction of the filament that could allow Sn to reach the Cu. In this study we investigate recent high quality PIT wires that achieve a Jc (12 T, 4.2 K) up to ∼2500 A mm−2 and find that the minimum diffusion barrier thickness decreases as the filament aspect ratio increases from ∼1 in the inner rings of filaments to 1.3 in the outer filament rings. We found that just 2–3 diffusion barrier breaches can degrade RRR from 300 to 150 or less. U...

  15. Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb3Sn conductors

    CERN Document Server

    Segal, Christopher; Sung, Zu Hawn; Lee, Peter J; Sailer, Bernd; Thoener, Manfred; Schlenga, Klaud; Ballarino, Amalia; Bottura, Luca; Bordini, Bernardo; Scheuerlein, Christian; Larnalestier, David C

    2016-01-01

    High critical current density ( Jc) Nb3Sn A15 multifilamentary wires require a large volume fraction of small grain (SG), superconducting A15 phase, as well as Cu stabilizer with high Residual Resistance Ratio (RRR) to provide electromagnetic stabilization and protection. In powder-in-tube (PIT) wires the unreacted Nb7.5 wt%Ta outer layer of the tubular filaments acts as a diffusion barrier and protects the interfilamentary Cu stabilizer from Sn contamination. A high RRR requirement generally imposes a restricted A15 reaction heat treatment to prevent localized full reaction of the filament that could allow Sn to reach the Cu. In this study we investigate recent high quality PIT wires that achieve a Jc (12 T, 4.2 K) up to ∼2500 A mm−2 and find that the minimum diffusion barrier thickness decreases as the filament aspect ratio increases from ∼1 in the inner rings of filaments to 1.3 in the outer filament rings. We found that just 2–3 diffusion barrier breaches can degrade RRR from 300 to 150 or less. U...

  16. Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb3Sn conductors

    Science.gov (United States)

    Segal, Christopher; Tarantini, Chiara; Hawn Sung, Zu; Lee, Peter J.; Sailer, Bernd; Thoener, Manfred; Schlenga, Klaus; Ballarino, Amalia; Bottura, Luca; Bordini, Bernardo; Scheuerlein, Christian; Larbalestier, David C.

    2016-08-01

    High critical current density (J c) Nb3Sn A15 multifilamentary wires require a large volume fraction of small grain (SG), superconducting A15 phase, as well as Cu stabilizer with high Residual Resistance Ratio (RRR) to provide electromagnetic stabilization and protection. In powder-in-tube (PIT) wires the unreacted Nb7.5 wt%Ta outer layer of the tubular filaments acts as a diffusion barrier and protects the interfilamentary Cu stabilizer from Sn contamination. A high RRR requirement generally imposes a restricted A15 reaction heat treatment to prevent localized full reaction of the filament that could allow Sn to reach the Cu. In this study we investigate recent high quality PIT wires that achieve a J c (12 T, 4.2 K) up to ˜2500 A mm-2 and find that the minimum diffusion barrier thickness decreases as the filament aspect ratio increases from ˜1 in the inner rings of filaments to 1.3 in the outer filament rings. We found that just 2-3 diffusion barrier breaches can degrade RRR from 300 to 150 or less. Using progressive etching of the Cu we also found that the RRR degradation is localized near the external filaments where deformation is highest. Consequently minimizing filament distortion during strand fabrication is important for reducing RRR degradation. The additional challenge of developing the highest possible J c must be addressed by forming the maximum fraction of high J c SG A15 and minimizing low J c large-grain (LG) A15 morphologies. In one wire we found that 15% of the filaments had a significantly enhanced SG/LG A15 ratio and no residual A15 in the core, a feature that opens a path to substantial J c improvement.

  17. Density limits investigation and high density operation in EAST tokamak

    Science.gov (United States)

    Zheng, Xingwei; Li, Jiangang; Hu, Jiansheng; Liu, Haiqing; Jie, Yinxian; Wang, Shouxin; Li, Jiahong; Duan, Yanming; Li, Miaohui; Li, Yongchun; Zhang, Ling; Ye, Yang; Yang, Qingquan; Zhang, Tao; Cheng, Yingjie; Xu, Jichan; Wang, Liang; Xu, Liqing; Zhao, Hailin; Wang, Fudi; Lin, Shiyao; Wu, Bin; Lyu, Bo; Xu, Guosheng; Gao, Xiang; Shi, Tonghui; He, Kaiyang; Lan, Heng; Chu, Nan; Cao, Bin; Sun, Zhen; Zuo, Guizhong; Ren, Jun; Zhuang, Huidong; Li, Changzheng; Yuan, Xiaolin; Yu, Yaowei; Wang, Houyin; Chen, Yue; Wu, Jinhua; EAST Team

    2016-05-01

    Increasing the density in a tokamak is limited by the so-called density limit, which is generally performed as an appearance of disruption causing loss of plasma confinement, or a degradation of high confinement mode which could further lead to a H  →  L transition. The L-mode and H-mode density limit has been investigated in EAST tokamak. Experimental results suggest that density limits could be triggered by either edge cooling or excessive central radiation. The L-mode density limit disruption is generally triggered by edge cooling, which leads to the current profile shrinkage and then destabilizes a 2/1 tearing mode, ultimately resulting in a disruption. The L-mode density limit scaling agrees well with the Greenwald limit in EAST. The observed H-mode density limit in EAST is an operational-space limit with a value of 0.8∼ 0.9{{n}\\text{GW}} . High density H-mode heated by neutral beam injection (NBI) and lower hybrid current drive (LHCD) are analyzed, respectively. The constancy of the edge density gradients in H-mode indicates a critical limit caused perhaps by e.g. ballooning induced transport. The maximum density is accessed at the H  →  L transition which is generally caused by the excessive core radiation due to high Z impurities (Fe, Cu). Operating at a high density (>2.8× {{10}19} {{\\text{m}}-3} ) is favorable for suppressing the beam shine through NBI. High density H-mode up to 5.3× {{10}19}{{\\text{m}}-3}~≤ft(∼ 0.8{{n}\\text{GW}}\\right) could be sustained by 2 MW 4.6 GHz LHCD alone, and its current drive efficiency is studied. Statistics show that good control of impurities and recycling facilitate high density operation. With careful control of these factors, high density up to 0.93{{n}\\text{GW}} stable H-mode operation was carried out heated by 1.7 MW LHCD and 1.9 MW ion cyclotron resonance heating with supersonic molecular beam injection fueling.

  18. Minimax Current Density Coil Design

    CERN Document Server

    Poole, Michael; Lopez, Hector Sanchez; Ng, Michael; Crozier, Stuart; 10.1088/0022-3727/43/9/095001

    2010-01-01

    'Coil design' is an inverse problem in which arrangements of wire are designed to generate a prescribed magnetic field when energized with electric current. The design of gradient and shim coils for magnetic resonance imaging (MRI) are important examples of coil design. The magnetic fields that these coils generate are usually required to be both strong and accurate. Other electromagnetic properties of the coils, such as inductance, may be considered in the design process, which becomes an optimization problem. The maximum current density is additionally optimized in this work and the resultant coils are investigated for performance and practicality. Coils with minimax current density were found to exhibit maximally spread wires and may help disperse localized regions of Joule heating. They also produce the highest possible magnetic field strength per unit current for any given surface and wire size. Three different flavours of boundary element method that employ different basis functions (triangular elements...

  19. Active inrush-current limiter

    Science.gov (United States)

    Kichak, R. A.

    1977-01-01

    By stretching turn-on time from approximately 1 to 200 ms, effects of inrush current (and of associated large current spikes) and current rate of rise (dl/dt) are made potentially less severe. Limiter arrangement consists of time-variable impedance connected in series between input dc power source return and power circuit of converter.

  20. Kernel current source density method.

    Science.gov (United States)

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

    2012-02-01

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

  1. On thermodynamic limits of entropy densities

    NARCIS (Netherlands)

    Moriya, H; Van Enter, A

    1998-01-01

    We give some sufficient conditions which guarantee that the entropy density in the thermodynamic limit is equal to the thermodynamic limit of the entropy densities of finite-volume (local) Gibbs states.

  2. Application of fault current limiters

    Energy Technology Data Exchange (ETDEWEB)

    Neumann, A.

    2007-11-30

    This report presents the results of a study commissioned by the Department for Business, Enterprise and Industry (BERR; formerly the Department of Trade and Industry) into the application of fault current limiters in the UK. The study reviewed the current state of fault current limiter (FCL) technology and regulatory position in relation to all types of current limiters. It identified significant research and development work with respect to medium voltage FCLs and a move to high voltage. Appropriate FCL technologies being developed include: solid state breakers; superconducting FCLs (including superconducting transformers); magnetic FCLs; and active network controllers. Commercialisation of these products depends on successful field tests and experience, plus material development in the case of high temperature superconducting FCL technologies. The report describes FCL techniques, the current state of FCL technologies, practical applications and future outlook for FCL technologies, distribution fault level analysis and an outline methodology for assessing the materiality of the fault level problem. A roadmap is presented that provides an 'action agenda' to advance the fault level issues associated with low carbon networks.

  3. Fault current limiters using superconductors

    Science.gov (United States)

    Norris, W. T.; Power, A.

    Fault current limiters on power systems are to reduce damage by heating and electromechanical forces, to alleviate duty on switchgear used to clear the fault, and to mitigate disturbance to unfaulted parts of the system. A basic scheme involves a super-resistor which is a superconductor being driven to high resistance when fault current flows either when current is high during a cycle of a.c. or, if the temperature of the superconductive material rises, for the full cycle. Current may be commuted from superconductor to an impedance in parallel, thus reducing the energy dispersed at low temperature and saving refrigeration. In a super-shorted transformer the ambient temperature primary carries the power system current; the superconductive secondary goes to a resistive condition when excessive currents flow in the primary. A super-transformer has the advantage of not needing current leads from high temperature to low temperature; it behaves as a parallel super-resistor and inductor. The supertransductor with a superconductive d.c. bias winding is large and has small effect on the rate of fall of current at current zero; it does little to alleviate duty on switchgear but does reduce heating and electromechanical forces. It is fully active after a fault has been cleared. Other schemes depend on rapid recooling of the superconductor to achieve this.

  4. DC superconducting fault current limiter

    Science.gov (United States)

    Tixador, P.; Villard, C.; Cointe, Y.

    2006-03-01

    There is a lack of satisfying solutions for fault currents using conventional technologies, especially in DC networks, where a superconducting fault current limiter could play a very important part. DC networks bring a lot of advantages when compared to traditional AC ones, in particular within the context of the liberalization of the electric market. Under normal operation in a DC network, the losses in the superconducting element are nearly zero and only a small, i.e. a low cost, refrigeration system is then required. The absence of zero crossing of a DC fault current favourably accelerates the normal zone propagation. The very high current slope at the time of the short circuit in a DC grid is another favourable parameter. The material used for the experiments is YBCO deposited on Al2O3 as well as YBCO coated conductors. The DC limitation experiments are compared to AC ones at different frequencies (50-2000 Hz). Careful attention is paid to the quench homogenization, which is one of the key issues for an SC FCL. The University of Geneva has proposed constrictions. We have investigated an operating temperature higher than 77 K. As for YBCO bulk, an operation closer to the critical temperature brings a highly improved homogeneity in the electric field development. The material can then absorb large energies without degradation. We present tests at various temperatures. These promising results are to be confirmed over long lengths.

  5. Enhancing critical current density of cuprate superconductors

    Science.gov (United States)

    Chaudhari, Praveen

    2015-06-16

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

  6. Finite Density QCD in the Chiral Limit

    CERN Document Server

    Aloisio, R; Di Carlo, G; Galante, A; Grillo, A F

    1998-01-01

    We present the first results of an exact simulation of full QCD at finite density in the chiral limit. We have used a MFA (Microcanonical Fermionic Average) inspired approach for the reconstruction of the Grand Canonical Partition Function of the theory; using the fugacity expansion of the fermionic determinant we are able to move continuously in the ($\\beta -\\mu$) plane with $m=0$.

  7. High temperature superconducting fault current limiter

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Hinsdale, IL)

    1997-01-01

    A fault current limiter (10) for an electrical circuit (14). The fault current limiter (10) includes a high temperature superconductor (12) in the electrical circuit (14). The high temperature superconductor (12) is cooled below its critical temperature to maintain the superconducting electrical properties during operation as the fault current limiter (10).

  8. Program Calculates Current Densities Of Electronic Designs

    Science.gov (United States)

    Cox, Brian

    1996-01-01

    PDENSITY computer program calculates current densities for use in calculating power densities of electronic designs. Reads parts-list file for given design, file containing current required for each part, and file containing size of each part. For each part in design, program calculates current density in units of milliamperes per square inch. Written by use of AWK utility for Sun4-series computers running SunOS 4.x and IBM PC-series and compatible computers running MS-DOS. Sun version of program (NPO-19588). PC version of program (NPO-19171).

  9. Limiting the current with HTc materials; HTc pour la limitation du courant

    Energy Technology Data Exchange (ETDEWEB)

    Barbut, J.M.; Belmont, O.; Devismes, M.F.; Noudem, J.G.; Porcar, L.; Sanchez, J. [Schneider Electric, Grenoble (France); Tixador, P. [CRTBT, CNRS, Grenoble (France); Bourgault, D.; Tournier, R. [Matformag, CNRS, Grenoble (France)

    1998-01-01

    Superconducting fault current limiter could be used in high voltage network. A most part of existing HTc superconducting materials have been tested in situation to limit fault current. Bulk materials are classified by growing critical current density which correspond to different behaviours. Critical electrical field during transition seems to be about 1 kV/m. (orig.). 7 refs.

  10. Critical current densities in superconducting materials

    Indian Academy of Sciences (India)

    P Chaddah

    2003-02-01

    We discuss recent research in the area of critical current densities $(J_C)$ in superconductors. This shall cover recent work on newly discovered superconductors, as well as on the magnetic-field dependence of $J_C$.

  11. Burnout current density of bismuth nanowires

    Science.gov (United States)

    Cornelius, T. W.; Picht, O.; Müller, S.; Neumann, R.; Völklein, F.; Karim, S.; Duan, J. L.

    2008-05-01

    Single bismuth nanowires with diameters ranging from 100nmto1μm were electrochemically deposited in ion track-etched single-pore polycarbonate membranes. The maximum current density the wires are able to carry was investigated by ramping up the current until failure occurred. It increases by three to four orders of magnitude for nanowires embedded in the template compared to bulk bismuth and rises with diminishing diameter. Simulations show that the wires are heated up electrically to the melting temperature. Since the surface-to-volume ratio rises with diminishing diameter, thinner wires dissipate the heat more efficiently to the surrounding polymer matrix and, thus, can tolerate larger current densities.

  12. Natural Limits for Currents in Charge Separated Pulsar Magnetospheres

    CERN Document Server

    Jessner, A; Kunzl, T A

    2002-01-01

    Rough estimates and upper limits on current and particle densities form the basis of most of the canonical pulsar models. Whereas the surface of the rotating neutron star is capable of supplying sufficient charges to provide a current that, given the polar cap potential, could easily fuel the observed energy loss processes, observational and theoretical constraints provide strict upper limits to the charge densities. The space charge of a current consisting solely of particles having only one sign creates a compensating potential that will make the maximum current dependent on potential and distance. In the non-relativistic case this fact is expressed in the familiar Child-Langmuir law. Its relativistic generalization and subsequent application to the inner pulsar magnetosphere provides clear limits on the strength and radial extension of charged currents originating on the polar cap. Violent Pierce-type oscillations set in, if one attempts to inject more current than the space charge limit into a given volum...

  13. A unified model of density limit in fusion plasmas

    CERN Document Server

    Zanca, P; Escande, D F; Pucella, G; Tudisco, O

    2016-01-01

    A limit for the edge density, ruled by radiation losses from light impurities, is established by a minimal cylindrical magneto-thermal equilibrium model. For ohmic tokamak and reversed field pinch the limit scales linearly with the plasma current, as the empirical Greenwald limit. The auxiliary heating adds a further dependence, scaling with the 0.4 power, in agreement with L-mode tokamak experiments. For a purely externally heated configuration the limit takes on a Sudo-like form, depending mainly on the input power, and is compatible with recent Stellarator scalings.

  14. Fault current limiter using bulk oxides superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Belmont, O.; Ferracci, P.; Porcar, L.; Barbut, J.M. [Schneider Electric, Grenoble (France). Usine A3; Tixador, P.; Noudem, J.G.; Bourgault, D.; Tournier, R

    1998-08-01

    We study the limitation possibilities of bulk Bi high T{sub c} materials. For this we test these materials with AC or DC currents above their critical currents. We study particularly the evolution of the voltage with time or with current. The material, the value of the current and the time duration play important parts. For sintered Bi samples the voltage depends only on the current even for values much larger than the critical current. With textured samples the V(I) curves shows an hysteretic behaviour due to a warming up. The textured materials are more interesting than sintered ones in terms of required volume for the current limitation. In both cases the superconductors are in a dissipative state but not in the normal state. This state is nevertheless reached if the dissipated energy inside the sample is sufficient. We have tried to apply a magnetic field on the samples in order to trigger a more effective limitation. The voltage increases but with a limited effect for currents much higher (3-4 times) than the critical zero field current. We think that the dissipative state is due mainly to the grain boundaries which become resistive above the critical current. (orig.) 11 refs.

  15. Surface current density K: an introduction

    DEFF Research Database (Denmark)

    McAllister, Iain Wilson

    1991-01-01

    The author discusses the vector surface of current density K used in electrical insulation studies. K is related to the vector tangential electric field Kt at the surface of a body by the vector equation K=ΓE t where Γ represents the surface conductivity. The author derives a surface continuity...... equation that represents the boundary condition which the potential distributions in the adjoining media must fulfill. The volume current may be small in comparison to the surface current, and consequently in deriving the potential solutions the first term in this equation can sometimes be neglected....

  16. Computer controlled performance mapping of thermionic converters: effect of collector, guard-ring potential imbalances on the observed collector current-density, voltage characteristics and limited range performance map of an etched-rhenium, niobium planar converter

    Science.gov (United States)

    Manista, E. J.

    1972-01-01

    The effect of collector, guard-ring potential imbalance on the observed collector-current-density J, collector-to-emitter voltage V characteristic was evaluated in a planar, fixed-space, guard-ringed thermionic converter. The J,V characteristic was swept in a period of 15 msec by a variable load. A computerized data acquisition system recorded test parameters. The results indicate minimal distortion of the J,V curve in the power output quadrant for the nominal guard-ring circuit configuration. Considerable distortion, along with a lowering of the ignited-mode striking voltage, was observed for the configuration with the emitter shorted to the guard ring. A limited-range performance map of an etched-rhenium, niobium, planar converter was obtained by using an improved computer program for the data acquisition system.

  17. Superconducting fault current limiter for railway transport

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, L. M., E-mail: LMFisher@niitfa.ru; Alferov, D. F.; Akhmetgareev, M. R.; Budovskii, A. I.; Evsin, D. V.; Voloshin, I. F.; Kalinov, A. V. [National Technical Physics and Automation Research Institute (Russian Federation)

    2015-12-15

    A resistive switching superconducting fault current limiter (SFCL) for DC networks with voltage of 3.5 kV and nominal current of 2 kA is developed. The SFCL consists of two series-connected units: block of superconducting modules and high-speed vacuum breaker with total disconnection time not more than 8 ms. The results of laboratory tests of superconducting SFCL modules in current limiting mode are presented. The recovery time of superconductivity is experimentally determined. The possibility of application of SFCL on traction substations of Russian Railways is considered.

  18. Superconducting toroidal field coil current densities for the TFCX

    Energy Technology Data Exchange (ETDEWEB)

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

    1985-04-01

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

  19. Current Developments in Nuclear Density Functional Methods

    CERN Document Server

    Dobaczewski, J

    2010-01-01

    Density functional theory (DFT) became a universal approach to compute ground-state and excited configurations of many-electron systems held together by an external one-body potential in condensed-matter, atomic, and molecular physics. At present, the DFT strategy is also intensely studied and applied in the area of nuclear structure. The nuclear DFT, a natural extension of the self-consistent mean-field theory, is a tool of choice for computations of ground-state properties and low-lying excitations of medium-mass and heavy nuclei. Over the past thirty-odd years, a lot of experience was accumulated in implementing, adjusting, and using the density-functional methods in nuclei. This research direction is still extremely actively pursued. In particular, current developments concentrate on (i) attempts to improve the performance and precision delivered by the nuclear density-functional methods, (ii) derivations of density functionals from first principles rooted in the low-energy chromodynamics and effective th...

  20. Current limiting remote power control module

    Science.gov (United States)

    Hopkins, Douglas C.

    1990-01-01

    The power source for the Space Station Freedom will be fully utilized nearly all of the time. As such, any loads on the system will need to operate within expected limits. Should any load draw an inordinate amount of power, the bus voltage for the system may sag and disrupt the operation of other loads. To protect the bus and loads some type of power interface between the bus and each load must be provided. This interface is most crucial when load faults occur. A possible system configuration is presented. The proposed interface is the Current Limiting Remote Power Controller (CL-RPC). Such an interface should provide the following power functions: limit overloading and resulting undervoltage; prevent catastrophic failure and still provide for redundancy management within the load; minimize cable heating; and provide accurate current measurement. A functional block diagram of the power processing stage of a CL-RPC is included. There are four functions that drive the circuit design: rate control of current; current sensing; the variable conductance switch (VCS) technology; and the algorithm used for current limiting. Each function is discussed separately.

  1. Superconducting Fault Current Limiter optimized design

    Energy Technology Data Exchange (ETDEWEB)

    Tixador, Pascal, E-mail: Pascal.Tixador@grenoble-inp.fr [Univ. Grenoble Alpes, G2Elab – Institut Néel, F-38000 Grenoble (France); CNRS, G2Elab – Institut Néel, F-38000 Grenoble (France); Badel, Arnaud [CNRS, G2Elab – Institut Néel, F-38000 Grenoble (France)

    2015-11-15

    Highlights: • A low cost design of YBCO Fault Current Limiter. • A high resistance conductor for reduced length. • An asymmetrical YBCO conductor (injection and AC losses). • A thickness suitable for non destructive hot spots. - Abstract: The SuperConducting Fault Current Limiter (SCFCL) appears as one of the most promising SC applications for the electrical grids. Despite its advantages and many successful field experiences the market of SCFCL has difficulties to take off even if the first orders for permanent operation in grids are taken. The analytical design of resistive SCFCL will be discussed with the objective to reduce the quantity of SC conductor (length and section) to be more cost-effective. For that the SC conductor must have a high resistivity in normal state. It can be achieved by using high resistivity alloy for shunt, such as Hastelloy®. One of the most severe constraint is that the SCFCL should operate safely for any faults, especially those with low prospective short-circuit currents. This constraint requires to properly design the thickness of the SC tape in order to limit the hot spot temperature. An operation at 65 K appears as very interesting since it decreases the SC cost at least by a factor 2 with a simple LN2 cryogenics. Taking into account the cost reduction in a near future, the SC conductor cost could be rather low, half a dollar per kV A.

  2. Novel 3-Phase Inductive Fault Current Limiter

    Science.gov (United States)

    Kosa, Janos

    The paper describes the inductive three-phase fault current limiter. In this work I examine the novel arrangements of the perfect closed superconducting loop made of HTS wire. I applied one iron core with 3 limbs and special loops for uniform temperature of the superconducting wire. In this work I present the results of my experiments with this device. I present the static and dynamic measured results of this solution. It has got several advantages e. g. fast switching and less fault power for high-power electric machines. The advantage of the equipment is that in the case of single-phase short circuit the current will decrease in all the three phases. This can be an appropriate solution for high power machines. For example, in the case of high-power electric motor if there is a single-phase breaking or a single phase short circuit, we can decrease the current in the three phases.

  3. Limits on the local dark matter density

    Directory of Open Access Journals (Sweden)

    Read J.I.

    2012-02-01

    Full Text Available We study the systematic problems in determining the local dark matter density ρdm(R☉ from kinematics of stars in the Solar Neighbourhood, using a simulated Milky Way-like galaxy. We introduce a new unbiased method for recovering ρdm(R☉ based on the moments of the Jeans equations, combined with a Monte Carlo Markov Chain (MCMC technique and apply it to real data [1].

  4. Limits on the local dark matter density

    CERN Document Server

    Garbari, Silvia; Lake, George

    2011-01-01

    We revisit systematics in determining the local dark matter density (rho_dm) from the vertical motion of stars in the Solar Neighbourhood. Using a simulation of a Milky Way-like galaxy, we determine the data-quality required to detect the dark matter density at its expected local value. We introduce a new method for recovering rho_dm that uses moments of the Jeans equations, combined with a Monte Carlo Markov Chain technique to marginalise over the unknown parameters. Given sufficiently good data, we show that our method can recover the correct local dark matter density even in the face of disc inhomogeneities, non-isothermal tracers and a non-separable distribution function. We illustrate the power of our technique by applying it to Hipparcos data [Holmberg & Flynn 2000,2004]. We first make the assumption that the A and F star tracer populations are isothermal. This recovers rho_dm=0.003^{+0.009}_{-0.007}Msun/pc^3 (with 90 per cent confidence), consistent with previous determinations. However, the vertic...

  5. Critical current density: Measurements vs. reality

    Science.gov (United States)

    Pan, A. V.; Golovchanskiy, I. A.; Fedoseev, S. A.

    2013-07-01

    Different experimental techniques are employed to evaluate the critical current density (Jc), namely transport current measurements and two different magnetisation measurements forming quasi-equilibrium and dynamic critical states. Our technique-dependent results for superconducting YBa2Cu3O7 (YBCO) film and MgB2 bulk samples show an extremely high sensitivity of Jc and associated interpretations, such as irreversibility fields and Kramer plots, which lose meaning without a universal approach. We propose such approach for YBCO films based on their unique pinning features. This approach allows us to accurately recalculate the magnetic-field-dependent Jc obtained by any technique into the Jc behaviour, which would have been measured by any other method without performing the corresponding experiments. We also discovered low-frequency-dependent phenomena, governing flux dynamics, but contradicting the considered ones in the literature. The understanding of these phenomena, relevant to applications with moving superconductors, can clarify their dramatic impact on the electric-field criterion through flux diffusivity and corresponding measurements.

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

    Science.gov (United States)

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

    2012-01-01

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

  7. Modelling of density limit phenomena in toroidal helical plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, K. [National Inst. for Fusion Science, Toki, Gifu (Japan); Itoh, S.-I. [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Giannone, L. [Max Planck Institut fuer Plasmaphysik, EURATOM-IPP Association, Garching (Germany)

    2000-03-01

    The physics of density limit phenomena in toroidal helical plasmas based on an analytic point model of toroidal plasmas is discussed. The combined mechanism of the transport and radiation loss of energy is analyzed, and the achievable density is derived. A scaling law of the density limit is discussed. The dependence of the critical density on the heating power, magnetic field, plasma size and safety factor in the case of L-mode energy confinement is explained. The dynamic evolution of the plasma energy and radiation loss is discussed. Assuming a simple model of density evolution, of a sudden loss of density if the temperature becomes lower than critical value, then a limit cycle oscillation is shown to occur. A condition that divides the limit cycle oscillation and the complete radiation collapse is discussed. This model seems to explain the density limit oscillation that has been observed on the W7-AS stellarator. (author)

  8. Modelling of density limit phenomena in toroidal helical plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan); Itoh, Sanae-I. [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Giannone, Louis [EURATOM-IPP Association, Max Planck Institut fuer Plasmaphysik, Garching (Germany)

    2001-11-01

    The physics of density limit phenomena in toroidal helical plasmas based on an analytic point model of toroidal plasmas is discussed. The combined mechanism of the transport and radiation loss of energy is analyzed, and the achievable density is derived. A scaling law of the density limit is discussed. The dependence of the critical density on the heating power, magnetic field, plasma size and safety factor in the case of L-mode energy confinement is explained. The dynamic evolution of the plasma energy and radiation loss is discussed. Assuming a simple model of density evolution, of a sudden loss of density if the temperature becomes lower than critical value, then a limit cycle oscillation is shown to occur. A condition that divides the limit cycle oscillation and the complete radiation collapse is discussed. This model seems to explain the density limit oscillation that has been observed on the Wendelstein 7-AS (W7-AS) stellarator. (author)

  9. Limits on the local dark matter density

    Science.gov (United States)

    Garbari, Silvia; Read, Justin I.; Lake, George

    2011-09-01

    We revisit systematics in determining the local dark matter density ρdm from the vertical motion of stars in the solar neighbourhood. Using a simulation of a Milky Way like galaxy, we determine the data quality required to detect ρdm at its expected local value. We introduce a new method for recovering ρdm that uses moments of the Jeans equations, combined with a Markov chain Monte Carlo technique, to marginalize over the unknown parameters. Given sufficiently good data, we show that our method can recover the correct local dark matter density even in the face of disc inhomogeneities, non-isothermal tracers and a non-separable distribution function. We illustrate the power of our technique by applying it to Hipparcos data. We first make the assumption that the A- and F-star tracer populations are isothermal. This recovers ρdm= 0.003+0.009- 0.007 M⊙ pc-3 (ρdm= 0.11+0.34- 0.27 GeV cm-3, with 90 per cent confidence), consistent with previous determinations. However, the vertical dispersion profile of these tracers is poorly known. If we assume instead a non-isothermal profile similar to that of the blue disc stars from SDSS DR-7 recently measured, we obtain a fit with a very similar χ2 value, but with ρdm= 0.033+0.008- 0.009 M⊙ pc-3 (ρdm= 1.25+0.30- 0.34 GeV cm-3 with 90 per cent confidence). This highlights that it is vital to measure the vertical dispersion profile of the tracers to recover an unbiased estimate of ρdm.

  10. Trapped-space-charge-limited currents in organics

    Energy Technology Data Exchange (ETDEWEB)

    Paasch, Gernot [IFW Dresden (Germany); Blom, Paul; Mandoc, Magda; Boer, Bert de [University of Groningen (Netherlands)

    2007-07-01

    The Mott-Gurney law for space charge limited current (SCLC) has been modified early to account for the presence of exponentially distributed traps. This expression has been widely used to analyse transport in organic light emitting diodes. However, the theory fails to describe the rather weak temperature dependence observed for electron transport, for instance in PPV derivatives. There we have shown that the trap-limited SCLC law is essentially modified if the density of transport states is of Gaussian type. Here, we discuss the origin of this modification and present a detailed analysis of the modified law. In addition, we derive further modifications for different combinations of densities of states of both the transport states and the trap distribution. As a result, rather different dependencies of the current on voltage, layer thickness and temperature are possible. Consequently, one has to exercise care in order to obtain reliable trap parameters from SCLC.

  11. Superconducting Fault Current Limiter optimized design

    Science.gov (United States)

    Tixador, Pascal; Badel, Arnaud

    2015-11-01

    The SuperConducting Fault Current Limiter (SCFCL) appears as one of the most promising SC applications for the electrical grids. Despite its advantages and many successful field experiences the market of SCFCL has difficulties to take off even if the first orders for permanent operation in grids are taken. The analytical design of resistive SCFCL will be discussed with the objective to reduce the quantity of SC conductor (length and section) to be more cost-effective. For that the SC conductor must have a high resistivity in normal state. It can be achieved by using high resistivity alloy for shunt, such as Hastelloy®. One of the most severe constraint is that the SCFCL should operate safely for any faults, especially those with low prospective short-circuit currents. This constraint requires to properly design the thickness of the SC tape in order to limit the hot spot temperature. An operation at 65 K appears as very interesting since it decreases the SC cost at least by a factor 2 with a simple LN2 cryogenics. Taking into account the cost reduction in a near future, the SC conductor cost could be rather low, half a dollar per kV A.

  12. Current limiting level-time characteristic of a superconducting fault current limiter

    Science.gov (United States)

    Tang, Y. J.; Yokomizu, Y.; Hayakawa, N.; Matsumura, T.; Okubo, H.; Kito, Y.

    A model superconducting fault current limiter (SE-FCL) has been developed. The adopted superconducting cable is composed of six strands insulated from each other. The current limiting level of the SC-FCL is measured under two types of overcurrent, a sinusoidal and an inrush current. The results show that the current limiting level of the SC-FCL Iq increases with an increase in the rate of rise of the overcurrent. By introducing a new parameter of time-to-quench tf, it is found that Iq increases with decreasing tf. This feature is taken as a current limiting level-time characteristic i.e. the Iq- tf characteristic. The existence of the Iq- tf characteristic found in the SC-FCL is qualitatively explained by measuring current distribution among the six strands. The superconducting cable is driven to the normal state strand by strand. Some delay in time is found from the quench of the first strand to that of the last and this is recognized as an Iq- tf characteristic in its current limiting performance.

  13. Particle Image Velocimetry Study of Density Current Fronts

    Science.gov (United States)

    Martin, Juan Ezequiel

    2009-01-01

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

  14. High current density cathode for electrorefining in molten electrolyte

    Science.gov (United States)

    Li, Shelly X.

    2010-06-29

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

  15. CURRENT-VOLTAGE CURVES FOR TREATING EFFLUENT CONTAINING HEDP: DETERMINATION OF THE LIMITING CURRENT

    Directory of Open Access Journals (Sweden)

    T. Scarazzato

    2015-12-01

    Full Text Available Abstract Membrane separation techniques have been explored for treating industrial effluents to allow water reuse and component recovery. In an electrodialysis system, concentration polarization causes undesirable alterations in the ionic transportation mechanism. The graphic construction of the current voltage curve is proposed for establishing the value of the limiting current density applied to the cell. The aim of this work was to determine the limiting current density in an electrodialysis bench stack, the function of which was the treatment of an electroplating effluent containing HEDP. For this, a system with five compartments was used with a working solution simulating the rinse waters of HEDP-based baths. The results demonstrated correlation between the regions defined by theory and the experimental data.

  16. Fermion N-representability for prescribed density and paramagnetic current density

    OpenAIRE

    Tellgren, Erik I; Kvaal, Simen; Helgaker, Trygve

    2014-01-01

    The $N$-representability problem is the problem of determining whether or not there exists $N$-particle states with some prescribed property. Here we report an affirmative solution to the fermion $N$-representability problem when both the density and paramagnetic current density are prescribed. This problem arises in current-density functional theory and is a generalization of the well-studied corresponding problem (only the density prescribed) in density functional theory. Given any density ...

  17. Inrush-Current Limiter And Bus Isolator

    Science.gov (United States)

    Dolland, Carlisle R.

    1994-01-01

    Electronic circuit protects electrical power bus and source of power against excessive current demands. Circuit intended for use with power-consuming electronic system drawing pulsed currents and including capacitor bank as low-impedance secondary source from which pulsed currents drawn.

  18. Current-voltage curve of a bipolar membrane at high current density

    NARCIS (Netherlands)

    Aritomi, T.; Boomgaard, van den Th.; Strathmann, H.

    1996-01-01

    The potential drop across a bipolar membrane was measured as a function of the applied current density. As a result, an inflection point was observed in the obtained current-voltage curve at high current density. This inflection point indicates that at high current densities water supply from outsid

  19. Current-voltage curve of a bipolar membrane at high current density

    NARCIS (Netherlands)

    Aritomi, T.; van den Boomgaard, Anthonie; Strathmann, H.

    1996-01-01

    The potential drop across a bipolar membrane was measured as a function of the applied current density. As a result, an inflection point was observed in the obtained current-voltage curve at high current density. This inflection point indicates that at high current densities water supply from

  20. Bifurcation of Vortex Density Current in Trapped Bose Condensates

    Institute of Scientific and Technical Information of China (English)

    XU Tao; ZHANG ShengLi

    2002-01-01

    Vortex density current in the Gross-Pitaevskii theory is studied. It is shown that the inner structure of the topological vortices can be classified by Brouwer degrees and Hopf indices of φ-mapping. The dynamical equations of vortex density current have been given. The bifurcation behavior at the critical points of the current is discussed in detail.

  1. Investigation of physical processes limiting plasma density in H-mode on DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    Maingi, R.; Mahdavi, M.A. [General Atomics, San Diego, CA (United States); Jernigan, T.C. [Oak Ridge National Lab., TN (United States)] [and others

    1996-12-01

    A series of experiments was conducted on the DIII-D tokamak to investigate the physical processes which limit density in high confinement mode (H-mode) discharges. The typical H-mode to low confinement mode (L-mode) transition limit at high density near the empirical Greenwald density limit was avoided by divertor pumping, which reduced divertor neutral pressure and prevented formation of a high density, intense radiation zone (MARFE) near the X-point. It was determined that the density decay time after pellet injection was independent of density relative to the Greenwald limit and increased non-linearly with the plasma current. Magnetohydrodynamic (MHD) activity in pellet-fueled plasmas was observed at all power levels, and often caused unacceptable confinement degradation, except when the neutral beam injected (NBI) power was {le} 3 MW. Formation of MARFEs on closed field lines was avoided with low safety factor (q) operation but was observed at high q, qualitatively consistent with theory. By using pellet fueling and optimizing discharge parameters to avoid each of these limits, an operational space was accessed in which density {approximately} 1.5 {times} Greenwald limit was achieved for 600 ms, and good H-mode confinement was maintained for 300 ms of the density flattop. More significantly, the density was successfully increased to the limit where a central radiative collapse was observed, the most fundamental density limit in tokamaks.

  2. Current Source Density Estimation for Single Neurons

    Directory of Open Access Journals (Sweden)

    Dorottya Cserpán

    2014-03-01

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

  3. Equilibrium time correlation functions in the low density limit

    NARCIS (Netherlands)

    Beijeren, H. van; Lanford, O.E.; Lebowitz, J.L.; Spohn, H.

    1980-01-01

    We consider a system of hard spheres in thermal equilibrium. Using Lanford's result about the convergence of the solutions of the BBGKY hierarchy to the solutions of the Boltzmann hierarchy, we show that in the low-density limit (Boltzmann-Grad limit): (i) the total time correlation function is

  4. Medicare Current Beneficiary Survey - Limited Data Set

    Data.gov (United States)

    U.S. Department of Health & Human Services — The Medicare Current Beneficiary Survey (MCBS) is a continuous, multipurpose survey of a representative national sample of the Medicare population. There are two...

  5. Effect of current density on the morphology of Zn electrodeposits

    Institute of Scientific and Technical Information of China (English)

    Ailing Fan; Wenhuai Tian; M. Kurosaki

    2004-01-01

    The effect of current density on the morphology of Zn electrodeposits prepared by a flow-channel cell was investigated by scanning electron microscopy (SEM). It was found that the morphology of Zn electrodeposits evolves from thin-layered hexagonal η-phase crystals to pyramidal η-phase particles with increasing the current density. The morphological evolution at various flow rates was also examined and the results show that the morphological evolution at a lower flow rate is more remarkable than that at a higher flow rate with increasing the current density. To reveal the mechanism of the morphological evolution in detail, the atomic configuration on both (0001)η and { 1100 }η planes under different current densities was investigated, it was noted that a specify current density could provide a good condition for the layered epitaxial growth of hexagonal η-phase.

  6. A unified model of density limit in fusion plasmas

    Science.gov (United States)

    Zanca, P.; Sattin, F.; Escande, D. F.; Pucella, G.; Tudisco, O.

    2017-05-01

    In this work we identify by analytical and numerical means the conditions for the existence of a magnetic and thermal equilibrium of a cylindrical plasma, in the presence of Ohmic and/or additional power sources, heat conduction and radiation losses by light impurities. The boundary defining the solutions’ space having realistic temperature profile with small edge value takes mathematically the form of a density limit (DL). Compared to previous similar analyses the present work benefits from dealing with a more accurate set of equations. This refinement is elementary, but decisive, since it discloses a tenuous dependence of the DL on the thermal transport for configurations with an applied electric field. Thanks to this property, the DL scaling law is recovered almost identical for two largely different devices such as the ohmic tokamak and the reversed field pinch. In particular, they have in common a Greenwald scaling, linearly depending on the plasma current, quantitatively consistent with experimental results. In the tokamak case the DL dependence on any additional heating approximately follows a 0.5 power law, which is compatible with L-mode experiments. For a purely externally heated configuration, taken as a cylindrical approximation of the stellarator, the DL dependence on transport is found stronger. By adopting suitable transport models, DL takes on a Sudo-like form, in fair agreement with LHD experiments. Overall, the model provides a good zeroth-order quantitative description of the DL, applicable to widely different configurations.

  7. Cardiac activation mapping using ultrasound current source density imaging (UCSDI).

    Science.gov (United States)

    Olafsson, Ragnar; Witte, Russell S; Jia, Congxian; Huang, Sheng-Wen; Kim, Kang; O'Donnell, Matthew

    2009-03-01

    We describe the first mapping of biological current in a live heart using ultrasound current source density imaging (UCSDI). Ablation procedures that treat severe heart arrhythmias require detailed maps of the cardiac activation wave. The conventional procedure is time-consuming and limited by its poor spatial resolution (5-10 mm). UCSDI can potentially improve on existing mapping procedures. It is based on a pressure-induced change in resistivity known as the acousto-electric (AE) effect, which is spatially confined to the ultrasound focus. Data from 2 experiments are presented. A 540 kHz ultrasonic transducer (f/# = 1, focal length = 90 mm, pulse repetition frequency = 1600 Hz) was scanned over an isolated rabbit heart perfused with an excitation-contraction decoupler to reduce motion significantly while retaining electric function. Tungsten electrodes inserted in the left ventricle recorded simultaneously the AE signal and the low-frequency electrocardiogram (ECG). UCSDI displayed spatial and temporal patterns consistent with the spreading activation wave. The propagation velocity estimated from UCSDI was 0.25 +/- 0.05 mm/ms, comparable to the values obtained with the ECG signals. The maximum AE signal-to-noise ratio after filtering was 18 dB, with an equivalent detection threshold of 0.1 mA/ cm(2). This study demonstrates that UCSDI is a potentially powerful technique for mapping current flow and biopotentials in the heart.

  8. Fault current limitation with HTc superconductors; Limitation de courant a partir de materiaux supraconducteurs HTc

    Energy Technology Data Exchange (ETDEWEB)

    Buzon, D.

    2002-09-15

    This report deals with the possibility of using high critical temperature (HTc) superconductors for current limitation. The transition from a superconductive to a high dissipative state could be used to limit inrush currents. This application of superconductivity is very attractive because it's an innovative device for electrical networks without any conventional equivalence at high voltage. This device would allow to improve the density of connections and the continuity of the electrical distribution. This study can be divided into two fields. The aim of the first one is to analyse the behaviour of different HTc superconductors for current limitation. We carried out experimental measurements to characterise those conductors during a nominal AC rating (measurements of losses) and during a fault setting. Particularly, a description of the transition in bulk textured YBCO samples near Tc was made of inhomogeneous transition of the device and to estimate its losses. Finally, a 1 kV / 100 A demonstrator made of 43 meanders of textured YBCO was tested at 90,5 K. Thermal gradients seem to be responsible of the altering of some of the samples. The other part of this study concerns the dynamic of the transition. Near Tc, our experiments showed that the transition is more homogeneous. Experimental measurements also showed the influence of thermal exchanges with the cryogenic surrounding on the transition. This point can be justified if the dissipated energy is locally concentrated. (author)

  9. High current density nanofilament cathodes for microwave amplifiers

    NARCIS (Netherlands)

    Schnell, J-P.; Minoux, E.; Gangloff, L.; Vincent, P.; Legagneux, P.; Dieumegard, D.; David, J.-F.; Peauger, F.; Hudanski, L.; Teo, K.B.K.; Lacerda, R.; Chhowalla, M.; Hasko, D.G.; Ahmed, H.; Amaratunga, G.A.J.; Milne, W.I.; Vila, L.; Dauginet-De Pra, L.; Demoustier-Champagne, S.; Ferain, E.; Legras, R.; Piraux, L.; Gröening, O.; Raedt, H. De; Michielsen, K.

    2004-01-01

    We study high current density nanofilament cathodes for microwave amplifiers. Two different types of aligned nanofilament array have been studied: first, metallic nanowires grown by electrodeposition into nanoporous templates at very low temperature (T

  10. Density functionals for the strong-interaction limit

    Science.gov (United States)

    Seidl, Michael; Perdew, John P.; Kurth, Stefan

    2000-07-01

    The strong-interaction limit of density-functional (DF) theory is simple and provides information required for an accurate resummation of DF perturbation theory. Here we derive the point-charge-plus-continuum (PC) model for that limit, and its gradient expansion. The exchange-correlation (xc) energy Exc[ρ]≡∫10dαWα[ρ] follows from the xc potential energies Wα at different interaction strengths α>=0 [but at fixed density ρ(r)]. For small α~0, the integrand Wα is obtained accurately from perturbation theory, but the perturbation expansion requires resummation for moderate and large α. For that purpose, we present density functionals for the coefficients in the asymptotic expansion Wα-->W∞+W'∞α-1/2 for α-->∞ in the PC model. WPC∞ arises from strict correlation, and W'PC∞ from zero-point vibration of the electrons around their strictly correlated distributions. The PC values for W∞ and W'∞ agree with those from a self-correlation-free meta-generalized gradient approximation, both for atoms and for atomization energies of molecules. We also (i) explain the difference between the PC cell and the exchange-correlation hole, (ii) present a density-functional measure of correlation strength, (iii) describe the electron localization and spin polarization energy in a highly stretched H2 molecule, and (iv) discuss the soft-plasmon instability of the low-density uniform electron gas.

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

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  12. DISCONTINUOUS FLOW OF TURBID DENSITY CURRENTS Ⅱ. INTERNAL HYDRAULIC JUMP

    Institute of Scientific and Technical Information of China (English)

    Jiahua FAN

    2005-01-01

    Traveling and stationary internal hydraulic jumps in density currents with positive or negative entrainment coefficients were analyzed based on simple assumptions. An expression of internal hydraulic jumps with entrainment coefficients was derived. Experimental data, published in literature, of stationary internal hydraulic jumps in turbid, thermal and saline density currents including measured values of water entrainment were used to compare with theory. Comparison was also made of traveling internal hydraulic jumps between measured data and theory.

  13. Two-dimensional relativistic space charge limited current flow in the drift space

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Y. L.; Chen, S. H., E-mail: chensh@ncu.edu.tw [Department of Physics, National Central University, Jhongli 32001, Taiwan (China); Koh, W. S. [A-STAR Institute of High Performance Computing, Singapore 138632 (Singapore); Ang, L. K. [Engineering Product Development, Singapore University of Technology and Design, Singapore 138682 (Singapore)

    2014-04-15

    Relativistic two-dimensional (2D) electrostatic (ES) formulations have been derived for studying the steady-state space charge limited (SCL) current flow of a finite width W in a drift space with a gap distance D. The theoretical analyses show that the 2D SCL current density in terms of the 1D SCL current density monotonically increases with D/W, and the theory recovers the 1D classical Child-Langmuir law in the drift space under the approximation of uniform charge density in the transverse direction. A 2D static model has also been constructed to study the dynamical behaviors of the current flow with current density exceeding the SCL current density, and the static theory for evaluating the transmitted current fraction and minimum potential position have been verified by using 2D ES particle-in-cell simulation. The results show the 2D SCL current density is mainly determined by the geometrical effects, but the dynamical behaviors of the current flow are mainly determined by the relativistic effect at the current density exceeding the SCL current density.

  14. Influence of Superconductor Fault Current Limiter on Transformers Lifetime

    Directory of Open Access Journals (Sweden)

    2012-07-01

    Full Text Available In this article the impact of the superconducting current limiter and reducing the incidenceof stress single phase short circuit has been analyzed with this method and conventionalmethod of current limiting resistance has been compared. For this purpose a saturated corehigh temperature superconducting current limiter model considered and its effects on networkperformance in different modes has been studied. PSCAD software for simulating thenetwork is used.

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

    NARCIS (Netherlands)

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

    2005-01-01

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

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

    NARCIS (Netherlands)

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

    2005-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Papazov Sava P

    2002-12-01

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

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

    Science.gov (United States)

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

    2015-08-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Jay L. Hirshfield

    2005-12-19

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

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

    Science.gov (United States)

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

    2013-09-01

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

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

    Science.gov (United States)

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

    2010-08-10

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

  2. Scaling rules for critical current density in anisotropic biaxial superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yingxu, E-mail: yingxuli@swjtu.edu.cn [Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Kang, Guozheng [Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Gao, Yuanwen, E-mail: ywgao@lzu.edu.cn [Key Laboratory of Mechanics on Environment and Disaster in Western China, The Ministry of Education of China, Lanzhou, Gansu 730000 (China); Department of Mechanics and Engineering Science, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)

    2016-06-15

    Recent researches highlight the additional anisotropic crystallographic axis within the superconducting plane of high temperature superconductors (HTS), demonstrating the superconducting anisotropy of HTS is better understood in the biaxial frame than the previous uniaxial coordinates within the superconducting layer. To quantitatively evaluate the anisotropy of flux pinning and critical current density in HTS, we extend the scaling rule for single-vortex collective pinning in uniaxial superconductors to account for flux-bundle collective pinning in biaxial superconductors. The scaling results show that in a system of random uncorrected point defects, the field dependence of the critical current density is described by a unified function with the scaled magnetic field of the isotropic superconductor. The obtained angular dependence of the critical current density depicts the main features of experimental observations, considering possible corrections due to the strong-pinning interaction.

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

    Science.gov (United States)

    Stone, J. R.

    2015-05-01

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

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

    Directory of Open Access Journals (Sweden)

    Stone J. R.

    2015-01-01

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

  5. Limit Theorems for Competitive Density Dependent Population Processes

    CERN Document Server

    Parsons, Todd L

    2010-01-01

    Near the beginning of the century, Wright and Fisher devised an elegant, mathematically tractable model of gene reproduction and replacement that laid the foundation for contemporary population genetics. The Wright-Fisher model and its extensions have given biologists powerful tools of statistical inference that enabled the quantification of genetic drift and selection. Given the utility of these tools, we often forget that their model - for mathematical, and not biological reasons - makes assumptions that are violated in most real-world populations. In this paper, I consider an alternative framework that merges P. A. P. Moran's continuous-time Markov chain model of allele frequency with the density dependent models of ecological competition proposed by Gause, Lotka and Volterra, that, unlike Moran's model allow for a stochastically varying -- but bounded -- population size. I require that allele numbers vary according to a density-dependent population process, for which the limiting law of large numbers is a...

  6. High-density turbidity currents: Are they sandy debris flows?

    Energy Technology Data Exchange (ETDEWEB)

    Shanmugam, G. [Mobil Exploration and Producing Technical Center, Dallas, TX (United States)

    1996-01-01

    Conventionally, turbidity currents are considered as fluidal flows in which sediment is supported by fluid turbulence, whereas debris flows are plastic flows in which sediment is supported by matrix strength, dispersive pressure, and buoyant lift. The concept of high-density turbidity current refers to high-concentration, commonly non-turbulent, flows of fluids in which sediment is supported mainly by matrix strength, dispersive pressure, and buoyant lift. The conventional wisdom that traction carpets with entrained turbulent clouds on top represent high-density turbidity currents is a misnomer because traction carpets are neither fluidal nor turbulent. Debris flows may also have entrained turbulent clouds on top. The traction carpet/debris flow and the overriding turbulent clouds are two separate entities in terms of flow rheology and sediment-support mechanism. In experimental and theoretical studies, which has linked massive sands and floating clasts to high-density turbidity currents, the term high-density turbidity current has actually been used for laminar flows. In alleviating this conceptual problem, sandy debris flow is suggested as a substitute for high-density turbidity current. Sandy debris flows represent a continuous spectrum of processes between cohesive and cohesionless debris flows. Commonly they are rheologically plastic. They may occur with or without entrained turbulent clouds on top. Their sediment-support mechanisms include matrix strength, dispersive pressure, and buoyant lift. They are characterized by laminar flow conditions, a moderate to high grain concentration, and a low to moderate mud content. Although flows evolve and transform during the course of transport in density-stratified flows, the preserved features in a deposit are useful to decipher only the final stages of deposition. At present, there are no established criteria to decipher transport mechanism from the depositional record.

  7. Engineering Critical Current Density Improvement in Ag- Bi-2223 Tapes

    DEFF Research Database (Denmark)

    Wang, W. G.; Seifi, Behrouz; Eriksen, Morten;

    2000-01-01

    Ag alloy sheathed Bi-2223 multifilament tapes were produced by the powder-in-tube method. Engineering critical current density improvement has been achieved through both enhancement of critical current density by control of the thermal behavior of oxide powder and by an increase of the filling...... the superconductor composite sustaining large proportional oxide ceramics in the composite during drawing and rolling process. By optimization of the thermal and mechanical process, a Je of 12 kA/cm2 has been achieved in a 0.183.1 mm2 size tape which carried 67 A...

  8. Vacuum Dielectric Recovery Characteristics of a Novel Current Limiting Circuit Breaker Base on Artificial Current Zero

    Institute of Scientific and Technical Information of China (English)

    JIANG Zhuangxian; ZHUANG Jinwu; WANG Chen; WU Jin; LIU Luhui

    2012-01-01

    A novel current limiting circuit breaker employs zero current switching method in cutting off DC current, which gives out a reverse impulsive current towards a high speed vacuum interrupter and force the current down to zero. This kind of breaker is simply in structure and can act in a very short time with high current limiting capability, and therefore it has a long electric life and is extremely suitable to be installed in a DC electrical system as a fault orotection utility.

  9. Current Density Imaging through Acoustically Encoded Magnetometry: A Theoretical Exploration

    CERN Document Server

    Sheltraw, Daniel J

    2014-01-01

    The problem of determining a current density confined to a volume from measurements of the magnetic field it produces exterior to that volume is known to have non-unique solutions. To uniquely determine the current density, or the non-silent components of it, additional spatial encoding of the electric current is needed. In biological systems such as the brain and heart, which generate electric current associated with normal function, a reliable means of generating such additional encoding, on a spatial and temporal scale meaningful to the study of such systems, would be a boon for research. This paper explores a speculative method by which the required additional encoding might be accomplished, on the time scale associated with the propagation of sound across the volume of interest, by means of the application of a radially encoding pulsed acoustic spherical wave.

  10. Space-charge limiting current in spherical cathode diodes

    Institute of Scientific and Technical Information of China (English)

    刘国治; 邵浩

    2003-01-01

    The results of the investigation on the space-charge limiting current for a spherical-cathode diode in the nonrelativistic situation are presented in this paper. The results show that the current enhancement factor equals the square of E-field enhancement factor on the cathode surface. The generated space-charge limiting current is deduced.In the case of a pin-shaped-cathode diode, the space-charge limiting current is also obtained, indicating that the current is independent of the geometric parameters of the diode. Analyses of the shielding effects and the conditions for generation of the uniform space-charge limiting beam show that, for pin-arrayed cathodes, the distance between pins should be in the range from 1.2D to 1.5D, where D is the distance between the two electrodes.

  11. Geometry dependence of 2-dimensional space-charge-limited currents

    CERN Document Server

    De Visschere, Patrick

    2016-01-01

    The space-charge-limited current in a zero thickness planar thin film depends on the geometry of the electrodes. We present a theory which is to a large extent analytical and applicable to many different lay-outs. We show that a space-charge-limited current can only be sustained if the emitting electrode induces a singularity in the field and if the singularity induced by the collecting electrode is not too strong. For those lay-outs where no space-charge-limited current can be sustained for a zero thickness film, the real thickness of the film must be taken into account using a numerical model.

  12. Neutron matter at low density and the unitary limit

    CERN Document Server

    Baldo, M

    2007-01-01

    Neutron matter at low density is studied within the hole-line expansion. Calculations are performed in the range of Fermi momentum $k_F$ between 0.4 and 0.8 fm$^{-1}$. It is found that the Equation of State is determined by the $^1S_0$ channel only, the three-body forces contribution is quite small, the effect of the single particle potential is negligible and the three hole-line contribution is below 5% of the total energy and indeed vanishing small at the lowest densities. Despite the unitary limit is actually never reached, the total energy stays very close to one half of the free gas value throughout the considered density range. A rank one separable representation of the bare NN interaction, which reproduces the physical scattering length and effective range, gives results almost indistinguishable from the full Brueckner G-matrix calculations with a realistic force. The extension of the calculations below $k_F = 0.4$ fm$^{-1}$ does not indicate any pathological behavior of the neutron Equation of State.

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

    Science.gov (United States)

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

    2015-11-01

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

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

    DEFF Research Database (Denmark)

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

    2013-01-01

    A method for inferring zonal electric current density in the mid-to-low latitude F region ionosphere is presented. We describe a method of using near-simultaneous overflights of the Ørsted and CHAMP satellites to define a closed circuit for an application of Ampère's integral law to magnetic data....... Zonal current density from sources in only the region between the two satellites is estimated for the first time. Six years of mutually available vector magnetic data allows overlaps spanning the full 24 h range of local time twice. Solutions are computed on an event-by-event basis after correcting...... for estimates of main and crustal magnetic fields. Current density in the range ±0.1 μA/m2 is resolved, with the distribution of electric current largely matching known features such as the Appleton anomaly. The currents appear unmodulated at times of either high-negative Dst or high F10.7, which has...

  15. The density matrix picture of laser coherent control current

    Institute of Scientific and Technical Information of China (English)

    SHOU Qian; ZHANG Haichao; LIU Luning; LIN Weizhu

    2004-01-01

    The physical substance of the coherent control current and the optical rectification have been analyzed based on density matrix perturbation theory. The analytical results demonstrate that they arise from the real and virtual manifestations of the same nonlinear process associated with diagonal and non-diagonal density matrix.And in terms of polarization, they respectively arise from the intraband and interband polarizations. Both the evolution of the coherent control current exited by ultrafast laser pulse and its dependence on frequency have been studied in time and frequency domains. In order to get an explicit knowledge of intraband polarization and the origination of the coherent control current, we have investigated the initial photo-carriers momentum distribution. The ultrafast decay of the polar momentum population in order of tens of femtosends is given to illustrate its instantaneous optical response.

  16. Fault Current Limitation with Superconducting YBCO Thin Films

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The behavior of YBCO/metal bilayers under transport currents was explored in the framework of fault current limitation (FCL). Properties of the superconducting-normal transition were first studied phenomenologically during sweep current experiments. For current rates higher than 500 A/s, the transition into the normal state was based on non-thermal phenomena and was characterized by a flux creep regime ended by a jump into the normal state. At lower sweep rates, a total diversion of the current in the metallic shunt was observed for temperatures higher than 85 K. In this regime, a partial recovery of the superconducting state took place due to a finite thermal resistance between the superconductingand the metallic films. These two properties of partial diversion into the shunt and of fast switching for a quick rise of the current during a default were exploited for current limitation at 77 K. FCL experiments at 50 Hz show that YBCO/Au bilayers limit the current in about 1 ms at a valueof 2.5Ic by developing electrical fields as high as 3 kV/m. Moreover, a recovery of the zero resistance state could occur under rated mode. A straightforward application of this property would be the transformer connection. Finally, results on DC current limitation and recovery under nominal mode were presented for the first time.

  17. Behavior of the particle transport coefficients near the density limit in MTX

    Energy Technology Data Exchange (ETDEWEB)

    Marinak, M.M.

    1993-04-01

    The perturbed particle transport coefficients were determined for a range of plasma conditions in the Alcator C tokamak, a component of the Microwave Tokamak Experiment (MTX), from analysis of density perturbations created in gas modulation experiments. Density measurements from a 15 chord far-infrared interferometer were sufficiently detailed to allow radial profiles of the transport coefficients to be resolved. Gas modulation experiments were carried out on plasmas over a range of relatively low currents and a wide variety of line-averaged densities, including values near the Greenwald density limit. With this technique the perturbed diffusion coefficient D and the perturbed convection velocity V can be determined simultaneously. Measured profiles of D rise toward the outside of the plasma column in a manner generally similar to those determined previously for {chi}{sub e,HP} from sawtooth heat pulse propagation. Values of D are typically smaller than those of {chi}{sub e,HP} given for the same line-averaged densities by a factor of 2-5. Diffusion coefficients from a series of discharges at constant current showed little variation with density through most of the saturated ohmic confinement regime. At the Greenwald density limit threshold a dramatic increase occurred in both the perturbed convective and diffusive transport coefficients in the outer region of the plasma. The increases were most pronounced at the outermost range of the radii where coefficients were determined (r/a = 0.8), but were apparent over a region which extended well into the plasma interior. Density profiles maintained a similar shape near the density limit, congruous with the similar behavior of the transport coefficients. No dramatic deterioration was evident in the global energy confinement.

  18. High dislocation density of tin induced by electric current

    Energy Technology Data Exchange (ETDEWEB)

    Liao, Yi-Han; Liang, Chien-Lung; Lin, Kwang-Lung, E-mail: matkllin@mail.ncku.edu.tw [Department of Material Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan, R. O. C (China); Wu, Albert T. [Department of Chemical and Material Engineering, National Central University, Jhongli 32001, Taiwan, R. O. C (China)

    2015-12-15

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

  19. Injection-limited current in a polymeric heterojunction

    NARCIS (Netherlands)

    Woudenbergh, T. van; Wildeman, J.; Blom, P.W.M.; Mertens, RP; Claeys, CL

    2004-01-01

    This work describes the current over an interface between two different polymeric semiconductors. The interface barrier amounts to 0.7 to 1.0 eV, which is orders of magnitude larger than the thermal energy. It is demonstrated that the current across the interface is injection limited. Furthermore, i

  20. Testing of 3-meter Prototype Fault Current Limiting Cables

    Energy Technology Data Exchange (ETDEWEB)

    Gouge, Michael J [ORNL; Duckworth, Robert C [ORNL; Demko, Jonathan A [ORNL; Rey, Christopher M [ORNL; Thompson, James R [ORNL; Lindsay, David T [ORNL; Tolbert, Jerry Carlton [ORNL; Willen, Dag [Ultera; Lentge, Heidi [Ultera; Thidemann, Carsten [Ultera; Carter, Bill [AMSC

    2009-01-01

    Two 3-m long, single-phase cables have been fabricated by Ultera from second generation (2G) superconductor supplied by American Superconductor. The first cable was made with two layers of 2G tape conductor and had a critical current of 5,750 A while the second cable had four layers and a critical current of 8,500 A. AC loss was measured for both cables at ac currents of up to 4 kArms. Ultera performed initial fault current studies of both cables in Denmark with limited currents in the range from 9.1 to 44 kA. Results from these tests will provide a basis for a 25-m long, three-phase, prototype cable to be tested at ORNL early next year and a 300-m long, fault current limiting, superconducting cable to be installed in a ConEd substation in New York City.

  1. Using electric current to surpass the microstructure breakup limit

    Science.gov (United States)

    Qin, Rongshan

    2017-01-01

    The elongated droplets and grains can break up into smaller ones. This process is driven by the interfacial free energy minimization, which gives rise to a breakup limit. We demonstrated in this work that the breakup limit can be overpassed drastically by using electric current to interfere. Electric current free energy is dependent on the microstructure configuration. The breakup causes the electric current free energy to reduce in some cases. This compensates the increment of interfacial free energy during breaking up and enables the processing to achieve finer microstructure. With engineering practical electric current parameters, our calculation revealed a significant increment of the obtainable number of particles, showing electric current a powerful microstructure refinement technology. The calculation is validated by our experiments on the breakup of Fe3C-plates in Fe matrix. Furthermore, there is a parameter range that electric current can drive spherical particles to split into smaller ones.

  2. Thermal performance of back-up current-limiting fuses

    Energy Technology Data Exchange (ETDEWEB)

    Torres, E.; Mazon, A.J.; Fernandez, E.; Zamora, I. [Department of Electrical Engineering, University of the Basque Country (UPV/EHU), Alameda de Urquijo, s/n, Bilbao 48013, Bizkaia (Spain); Perez, J.C. [MESA - Schneider Electric, Gatica 48110 (Spain)

    2010-12-15

    The design and development of current-limiting power fuses requires considerable time and expense on testing to verify that the maximum temperature limits under the rated current established in international standards are not exceeded. This paper presents a new methodology that reproduces the thermal behaviour of high voltage current-limiting fuses under currents up to the rated value and so, it reduces the need for testing as prototypes, more similar to the final design, can be obtained. Firstly, the methodology solves the transient heating process of the fuse to obtain the values of the power dissipated and the heat transfer coefficient, corresponding to the steady state condition. Once these values have been calculated, the temperature distribution at the surface of the complete fuse is obtained. The validity of the method proposed has been verified by comparison of the numerical values calculated with those obtained by testing real fuses. (author)

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

    CERN Document Server

    Bellucci, S; Saharyan, N A

    2015-01-01

    We evaluate the Hadamard function and the vacuum expectation value (VEV) of the current density for a charged scalar field, induced by flat boundaries in spacetimes with an arbitrary number of toroidally compactified spatial dimensions. The field operator obeys the Robin conditions on the boundaries and quasiperiodicity conditions with general phases along compact dimensions. In addition, the presence of a constant gauge field is assumed. The latter induces Aharonov-Bohm-type effect on the VEVs. There is a region in the space of the parameters in Robin boundary conditions where the vacuum state becomes unstable. The stability condition depends on the lengths of compact dimensions and is less restrictive than that for background with trivial topology. The vacuum current density is a periodic function of the magnetic flux, enclosed by compact dimensions, with the period equal to the flux quantum. It is explicitly decomposed into the boundary-free and boundary-induced contributions. In sharp contrast to the VEVs...

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

    Directory of Open Access Journals (Sweden)

    Mitra Javan

    2012-01-01

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

  5. Resource Limitation, Controphic Ostracod Density and Larval Mosquito Development.

    Directory of Open Access Journals (Sweden)

    Raylea Rowbottom

    Full Text Available Aquatic environments can be restricted with the amount of available food resources especially with changes to both abiotic and biotic conditions. Mosquito larvae, in particular, are sensitive to changes in food resources. Resource limitation through inter-, and intra-specific competition among mosquitoes are known to affect both their development and survival. However, much less is understood about the effects of non-culicid controphic competitors (species that share the same trophic level. To address this knowledge gap, we investigated and compared mosquito larval development, survival and adult size in two experiments, one with different densities of non-culicid controphic conditions and the other with altered resource conditions. We used Aedes camptorhynchus, a salt marsh breeding mosquito and a prominent vector for Ross River virus in Australia. Aedes camptorhynchus usually has few competitors due to its halo-tolerance and distribution in salt marshes. However, sympatric ostracod micro-crustaceans often co-occur within these salt marshes and can be found in dense populations, with field evidence suggesting exploitative competition for resources. Our experiments demonstrate resource limiting conditions caused significant increases in mosquito developmental times, decreased adult survival and decreased adult size. Overall, non-culicid exploitation experiments showed little effect on larval development and survival, but similar effects on adult size. We suggest that the alterations of adult traits owing to non-culicid controphic competition has potential to extend to vector-borne disease transmission.

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

    Science.gov (United States)

    Ciro, D.; Caldas, I. L.

    2013-10-01

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

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

    Science.gov (United States)

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

    2009-01-01

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

  8. Market potential of superconductor current limiters; Marktpotential von supraleitenden Strombegrenzern

    Energy Technology Data Exchange (ETDEWEB)

    Lakner, M.; Braun, D. [ABB Schweiz AG, Corporate Research, Baden-Daettwil (Switzerland); Schnyder, G.; Mauchle, P. [Schnyder Ingenieure AG, Huenenberg (Switzerland)

    2003-07-01

    This final report for the Swiss Federal Office of Energy describes the two concepts - 'resistive' and 'inductive' - used for Superconducting Fault Current Limiters (SCFCL) that utilise the transition from zero to finite resistance to limit short-circuit currents. The main advantages of SCFCL are compared to other current-limiting technologies: They can limit any type of prospective fault current, operate fail-safe, be self-triggered and self-restoring. Their main disadvantage - the cooling effort necessary - is also discussed. The application possibilities of SCFCL were investigated by simulating the impact on utility and industrial grids. Applications of SCFCL such as the coupling of medium-voltage grids and their use in series with a circuit-breaker on the secondary side of a substation transformer are discussed. It is also shown that, by using fault current limiters, considerable cost savings can be made, especially in connection with new installations or the extension of existing plants.

  9. Fault current limiter with solid-state circuit breakers

    Science.gov (United States)

    Bălan, H.; Neamț, L.; Buzdugan, M. I.; Varodi, T.; Pop, E.

    2016-08-01

    Switching of power circuit breakers is an important technical issue, especially at short circuit, since the fault current cause thermal and dynamic stresses, and the power quality worsens. Recently, the development of distributed renewable electricity induces the short circuit protection problematic because the distributed production of electric energy cause the transport networks to lose their radial character and disturbs the protective relays coordination. The modern technologies for power switching uses static fault current limiters, which offers a viable solution to remove the problems caused by large fault currents in the system. An appropriate design of the current limiting device reduces the thermal and dynamic stress and limits the fault current to a low value. The static switches are based on high power semiconductor devices that offer advantages compared to mechanical switches. Using a fault current limiter that minimizes the effect of distributed generation of electricity in a radial network on the co-ordination of protective relays is a solution to this problem in terms of switching speed and lifespan of power switches.

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

    Energy Technology Data Exchange (ETDEWEB)

    Burdakov, A. V. [Budker Institute of Nuclear Physics, 11 Lavrentjev Avenue, 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 20 Karl Marks Avenue, 630092 Novosibirsk (Russian Federation); Postupaev, V. V., E-mail: V.V.Postupaev@inp.nsk.su; Sudnikov, A. V. [Budker Institute of Nuclear Physics, 11 Lavrentjev Avenue, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 2 Pirogova st., 630090 Novosibirsk (Russian Federation)

    2014-05-15

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

  11. A current limiter with superconducting coil for magnetic field shielding

    Science.gov (United States)

    Kaiho, K.; Yamaguchi, H.; Arai, K.; Umeda, M.; Yamaguchi, M.; Kataoka, T.

    2001-05-01

    The magnetic shield type superconducting fault current limiter have been built and successfully tested in ABB corporate research and so on. The device is essentially a transformer in which the secondary winding is the superconducting tube. However, due to the large AC losses and brittleness of the superconducting bulk tube, they have not yet entered market. A current limiter with superconducting coil for the magnetic field shielding is considered. By using the superconducting coil made by the multi-filamentary high Tc superconductor instead of the superconducting bulk tube, the AC losses can be reduced due to the reduced superconductor thickness and the brittleness of the bulk tube can be avoidable. This paper presents a preliminary consideration of the magnetic shield type superconducting fault current limiter with superconducting coil as secondary winding and their AC losses in comparison to that of superconducting bulk in 50 Hz operation.

  12. Limiting current of intense electron beams in a decelerating gap

    Science.gov (United States)

    Nusinovich, G. S.; Beaudoin, B. L.; Thompson, C.; Karakkad, J. A.; Antonsen, T. M.

    2016-02-01

    For numerous applications, it is desirable to develop electron beam driven efficient sources of electromagnetic radiation that are capable of producing the required power at beam voltages as low as possible. This trend is limited by space charge effects that cause the reduction of electron kinetic energy and can lead to electron reflection. So far, this effect was analyzed for intense beams propagating in uniform metallic pipes. In the present study, the limiting currents of intense electron beams are analyzed for the case of beam propagation in the tubes with gaps. A general treatment is illustrated by an example evaluating the limiting current in a high-power, tunable 1-10 MHz inductive output tube (IOT), which is currently under development for ionospheric modification. Results of the analytical theory are compared to results of numerical simulations. The results obtained allow one to estimate the interaction efficiency of IOTs.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-08-04

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

  14. Quantum theory of space charge limited current in solids

    Energy Technology Data Exchange (ETDEWEB)

    González, Gabriel, E-mail: gabriel.gonzalez@uaslp.mx [Cátedras Conacyt, Universidad Autónoma de San Luis Potosí, San Luis Potosí 78000, Mexico and Coordinación para la Innovación y la Aplicación de la Ciencia y la Tecnología, Universidad Autónoma de San Luis Potosí, San Luis Potosí 78000 (Mexico)

    2015-02-28

    We present a quantum model of space charge limited current transport inside trap-free solids with planar geometry in the mean field approximation. We use a simple transformation which allows us to find the exact analytical solution for the steady state current case. We use our approach to find a Mott-Gurney like behavior and the mobility for single charge carriers in the quantum regime in solids.

  15. Stochastic Time-Dependent Current-Density Functional Theory

    Science.gov (United States)

    D'Agosta, Roberto

    2008-03-01

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

  16. Analysis of the H-mode density limit in the ASDEX upgrade tokamak using bolometry

    Energy Technology Data Exchange (ETDEWEB)

    Bernert, Matthias

    2013-10-23

    The high confinement mode (H-mode) is the operational scenario foreseen for ITER, DEMO and future fusion power plants. At high densities, which are favourable in order to maximize the fusion power, a back transition from the H-mode to the low confinement mode (L-mode) is observed. This H-mode density limit (HDL) occurs at densities on the order of, but below, the Greenwald density. In this thesis, the HDL is revisited in the fully tungsten walled ASDEX Upgrade tokamak (AUG). In AUG discharges, four distinct operational phases were identified in the approach towards the HDL. First, there is a stable H-mode, where the plasma density increases at steady confinement, followed by a degrading H-mode, where the core electron density is fixed and the confinement, expressed as the energy confinement time, reduces. In the third phase, the breakdown of the H-mode and transition to the L-mode, the overall electron density is fixed and the confinement decreases further, leading, finally, to an L-mode, where the density increases again at a steady confinement at typical L-mode values until the disruptive Greenwald limit is reached. These four phases are reproducible, quasi-stable plasma regimes and provide a framework in which the HDL can be further analysed. Radiation losses and several other mechanisms, that were proposed as explanations for the HDL, are ruled out for the current set of AUG experiments with tungsten walls. In addition, a threshold of the radial electric field or of the power flux into the divertor appears to be responsible for the final transition back to L-mode, however, it does not determine the onset of the HDL. The observation of the four phases is explained by the combination of two mechanisms: a fueling limit due to an outward shift of the ionization profile and an additional energy loss channel, which decreases the confinement. The latter is most likely created by an increased radial convective transport at the edge of the plasma. It is shown that the

  17. 47 CFR 25.208 - Power flux density limits.

    Science.gov (United States)

    2010-10-01

    ... Region 2, the single-entry equivalent power-flux density, in the space-to-Earth direction, (EPFDdown), at... in Region 1 and 12.2-12.7 GHz in Region 2, the aggregate equivalent power-flux density, in the space... power flux density levels defined below. (1) In the region of the contiguous United States,...

  18. Superconducting fault-current limiter and inductor design

    Science.gov (United States)

    Rogers, J. D.; Boenig, H. J.; Chowdhuri, P.; Schermer, R. I.; Wollan, J. J.; Weldon, D. M.

    1982-11-01

    A superconducting fault current limiter (SFCL) that uses a biased superconducting inductor in a diode or thyristor bridge circuit was analyzed for transmission systems in 69, 138, and 230 rms kV utility transmission systems. The limiter was evaluated for costs with all components, superconducting coil, diode and/or SCR power electronics, high voltage insulation, high voltage bushings and vapor cooled leads, dewar, and refrigerator, included. A design was undertaken for the superconducting cable and coils for both diode and SCR 69 kV limiter circuits.

  19. Super conducting fault current limiter and inductor design

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, J.; Boenig, H.; Chowdhuri, P.; Schermer, R.; Weldon, D.; Wollan, J.

    1983-05-01

    A superconducting fault current limiter (SFCL) that uses a biased superconducting inductor in a diode or thyristor bridge circuit was analyzed for transmission systems in 69, 138, and 230 rms kV utility transmission systems. The limiter was evaluated for costs with all components--superconducting coil, diode and/or SCR power electronics, high voltage insulation, high voltage bushings and vapor cooled leads, dewar, and refrigerator--included. A design was undertaken for the superconducting cable and coils for both diode and SCR 69 kV limiter circuits.

  20. Superconducting fault-current limiter and inductor design

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, J.D.; Boenig, H.J.; Chowdhuri, P.; Schermer, R.I.; Wollan, J.J.; Weldon, D.M.

    1982-01-01

    A superconducting fault current limiter (SFCL) that uses a biased superconducting inductor in a diode or thyristor bridge circuit was analyzed for transmission systems in 69, 138, and 230 rms kV utility transmission systems. The limiter was evaluated for costs with all components - superconducting coil, diode and/or SCR power electronics, high voltage insulation, high voltage bushings and vapor cooled leads, dewar, and refrigerator - included. A design was undertaken for the superconducting cable and coils for both diode and SCR 69 kV limiter circuits.

  1. High Current Density 2D/3D Esaki Tunnel Diodes

    CERN Document Server

    Krishnamoorthy, Sriram; Lee, Choong Hee; Zhang, Yuewei; McCulloch, William D; Johnson, Jared M; Hwang, Jinwoo; Wu, Yiying; Rajan, Siddharth

    2016-01-01

    The integration of two-dimensional materials such as transition metal dichalcogenides with bulk semiconductors offer interesting opportunities for 2D/3D heterojunction-based novel device structures without any constraints of lattice matching. By exploiting the favorable band alignment at the GaN/MoS2 heterojunction, an Esaki interband tunnel diode is demonstrated by transferring large area, Nb-doped, p-type MoS2 onto heavily n-doped GaN. A peak current density of 446 A/cm2 with repeatable room temperature negative differential resistance, peak to valley current ratio of 1.2, and minimal hysteresis was measured in the MoS2/GaN non-epitaxial tunnel diode. A high current density of 1 kA/cm2 was measured in the Zener mode (reverse bias) at -1 V bias. The GaN/MoS2 tunnel junction was also modeled by treating MoS2 as a bulk semiconductor, and the electrostatics at the 2D/3D interface was found to be crucial in explaining the experimentally observed device characteristics.

  2. Emergent loop current order from pair density wave superconductivity

    Science.gov (United States)

    Kashyap, Manoj; Melchert, Drew; Agterberg, Daniel

    2015-03-01

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

  3. The current density in quantum electrodynamics in external potentials

    Energy Technology Data Exchange (ETDEWEB)

    Schlemmer, Jan, E-mail: jan.schlemmer@univie.ac.at [Fakultät für Physik, Universität Wien, Boltzmanngasse 5, 1090 Wien (Austria); Zahn, Jochen, E-mail: jochen.zahn@itp.uni-leipzig.de [Institut für Theoretische Physik, Universität Leipzig, Brüderstr. 16, 04103 Leipzig (Germany)

    2015-08-15

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

  4. Discretizing Transient Current Densities in the Maxwell Equations

    Energy Technology Data Exchange (ETDEWEB)

    Stowell, M L

    2008-11-25

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

  5. Cooling performance test of the superconducting fault current limiter

    Energy Technology Data Exchange (ETDEWEB)

    Yeom, H.; Hong, Y. J.; Ko, J.; In, S.; Kim, H. B.; Park, S. J. [Korea Institute ofMachinery and Materials, Daejeon (Korea, Republic of); Kim, H.; Kim, H. R. [Korea Electric Power Corporation Research Institute, Daejeon (Korea, Republic of)

    2014-12-15

    The superconducting fault current limiter (SFCL) is an electrical power system device that detects the fault current automatically and limits the magnitude of the current below a certain safety level. The SFCL module does not have any electrical resistance below the critical temperature, which facilitates lossless power transmission in the electric power system. Once given the fault current, however, the superconducting conductor exhibits extremely high electrical resistance, and the magnitude of the current is accordingly limited to a low value. Therefore, SFCL should be maintained at a temperature below the critical temperature, which justifies the cryogenic cooling system as a mandatory component. This report is a study which reported on the cooling system for the 154 kV-class hybrid SFCL owned by Korea Electric Power Corporation (KEPCO). Using the cryocooler, the temperature of liquid nitrogen (LN2) was lowered to 71 K. The cryostat was pressurized to 5 bars to improve the dielectric strength of nitrogen and suppress nitrogen bubble foaming during operation of SFCL. The SFCL module was immersed in the liquid nitrogen of the cryostat to maintain the superconducting state. The performance test results of the key components such as cryocooler, LN2 circulation pump, cold box, and pressure builder are shown in this paper.

  6. Transmission Level High Temperature Superconducting Fault Current Limiter

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, Gary [SuperPower, Inc., Schenectady, NY (United States)

    2016-10-05

    The primary objective of this project was to demonstrate the feasibility and reliability of utilizing high temperature superconducting (HTS) materials in a Transmission Level Superconducting Fault Current Limiter (SFCL) application. During the project, the type of high temperature superconducting material used evolved from 1st generation (1G) BSCCO-2212 melt cast bulk high temperature superconductors to 2nd generation (2G) YBCO based high temperature superconducting tape. The SFCL employed SuperPower's “Matrix” technology that offers modular features to enable scale up to transmission voltage levels. The SFCL consists of individual modules that contain elements and parallel inductors that assist in carrying the current during the fault. A number of these modules are arranged in an m x n array to form the current limiting matrix.

  7. Transmission Level High Temperature Superconducting Fault Current Limiter

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, Gary [SuperPower, Inc., Schenectady, NY (United States)

    2016-10-05

    The primary objective of this project was to demonstrate the feasibility and reliability of utilizing high-temperature superconducting (HTS) materials in a Transmission Level Superconducting Fault Current Limiter (SFCL) application. During the project, the type of high-temperature superconducting material used evolved from 1st generation (1G) BSCCO-2212 melt cast bulk high-temperature superconductors to 2nd generation (2G) YBCO-based high-temperature superconducting tape. The SFCL employed SuperPower's “Matrix” technology, that offers modular features to enable scale up to transmission voltage levels. The SFCL consists of individual modules that contain elements and parallel inductors that assist in carrying the current during the fault. A number of these modules are arranged in an m x n array to form the current-limiting matrix.

  8. On the theory of the electric field and current density in a superconductor carrying transport current

    Energy Technology Data Exchange (ETDEWEB)

    Carr, W.J. [LEI 700 Technology Dr., Pittsburgh, PA 15219 (United States)]. E-mail: wjamescarrjr@att.net

    2005-09-15

    A theory is given to explain the physics behind the flow of low-frequency ac transport current around a closed superconducting circuit, where the circuit consists of two long, straight, parallel, uniform conductors, connected to each other at one end and to an applied emf at the other end. Thus one conductor is the return path for the other. A question of interest is what drives the current at any given point in the circuit. The answer given here is a surface charge, where the purpose of the surface charge is to spread the local emf around the circuit, so that at each point in the conductor it produces, together with the electric field of the vector potential, the electric field necessary for the current to flow. But it is then necessary to explain how the surface charge gets there, which is the central problem of the present analysis. The conclusion is that the total current density consists of the superposition of a large transport current and a very much smaller current system of a different symmetry. The transport current density is defined as a two-dimensional current density with no divergence. It flows uniformly along the conductor length, but can vary over the cross-section. The small additional current density has a much different symmetry, being three-dimensional and diverging at the surface of the conductor. Based on a slightly modified Bean model the transport current is treated as supercurrent having the value {+-}J {sub c}, while the small additional system of current is like normal current, with a density given by the electric field divided by a resistivity. The electric field is computed from the sum of the negative time derivative of the vector potential and the negative gradient of the scalar potential due to the surface charge. It has components parallel and perpendicular to the long axis of the conductor. Thus the small normal current density has a perpendicular component which flows into or out of the surface thereby creating the surface charge

  9. Doubled critical current density in Bi-2212 round wires by reduction of the residual bubble density

    Science.gov (United States)

    Jiang, J.; Starch, W. L.; Hannion, M.; Kametani, F.; Trociewitz, U. P.; Hellstrom, E. E.; Larbalestier, D. C.

    2011-08-01

    We have recently shown that the gas present in the only ~ 70% dense filaments of as-drawn Bi-2212 wire agglomerates into large bubbles that fill the entire filament diameter during the melt phase of the heat treatment. Once formed, these bubbles never disappear, although they can be bridged by 2212 grains formed on cooling. In order to test the effect of these bubbles on the critical current Ic, we increased the density of the filaments after drawing using 2 GPa of cold isostatic pressure, finding that the bubble density and size were greatly reduced and that Ic could be at least doubled. We conclude that enhancement of the filament packing density is of great importance for making major Ic improvements in this very useful, round superconducting wire.

  10. Lower hybrid counter current drive for edge current density modification in DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    Fenstermacher, M.E.; Nevins, W.M. [Lawrence Livermore National Lab., CA (US); Porkolab, M.; Bonoli, P.T. [Massachusetts Inst. of Technology, Cambridge, MA (US). Plasma Fusion Center; Harvey, R.W. [General Atomics, San Diego, CA (US)

    1993-07-01

    Each of the Advanced Tokamak operating modes in DIII-D is thought to have a distinctive current density profile. So far these modes have only been achieved transiently through experiments which ramp the plasma current and shape. Extension of these modes to steady state requires non-inductive current profile control, e.g. with lower hybrid current drive (LHCD). Calculations of LHCD have been done for DIII-D using the ACCOME and CQL3D codes, showing that counter driven current at the plasma edge can cancel some of the undesirable edge bootstrap current and potentially extend the VH-mode. Results are presented for scenarios using 2.45 GHz LH waves launched from both the midplane and off-axis ports. The sensitivity of the results to injected power, n{sub e} and T{sub e}, and launched wave spectrum is also shown.

  11. Tokamak equilibria with strong toroidal current density reversal

    Science.gov (United States)

    Ludwig, G. O.; Rodrigues, Paulo; Bizarro, João P. S.

    2013-05-01

    The equilibrium of large magnetic islands in the core of a tokamak under conditions of strong toroidal current density reversal is investigated by a new method. The method uses distinct spectral representations to describe each simply connected region as well as the containing shell geometry. This ideal conducting shell may substitute for the plasma edge region or take a virtual character representing the external equilibrium field effect. The internal equilibrium of the islands is solved within the framework of the variational moment method. Equivalent surface current densities are defined on the boundaries of the islands and on the thin containing shell, giving a straightforward formulation to the interaction between regions. The equilibrium of the island-shell system is determined by matching moments of the Dirichlet boundary conditions. Finally, the macroscopic stability against a class of tilting displacements is examined by means of an energy principle. It is found out that the up-down symmetric islands are stable to this particular perturbation and geometry but the asymmetric system presents a bifurcation in the equilibrium.

  12. LIMITATIONS OF CURRENT APPROACHES FOR THE TREATMENT OF ACROMEGALY.

    Science.gov (United States)

    Shanik, Michael H

    2016-02-01

    Acromegaly is a rare disease characterized by hypersecretion of growth hormone (GH), typically from a benign pituitary somatotroph adenoma, that leads to subsequent hypersecretion of insulin-like growth factor 1 (IGF-1). Patients with acromegaly have an increased risk of mortality and progressive worsening of comorbidities. Surgery, medical therapy, and radiotherapy are currently available treatment approaches for patients with acromegaly, with overall therapeutic goals of lowering GH levels and achieving normal IGF-1 levels, reducing tumor size, improving comorbidities, and minimizing mortality risk. Although surgery can lead to biochemical remission in some patients with acromegaly, many patients will continue to have uncontrolled disease and require additional treatment. We reviewed recently published reports and present a summary of the safety and efficacy of current treatment modalities for patients with acromegaly. A substantial proportion of patients who receive medical therapy or radiotherapy will have persistently elevated GH and/or IGF-1. Because of the serious health consequences of continued elevation of GH and IGF-1, there is a need to improve therapeutic approaches to optimize biochemical control, particularly in high-need patient populations for whom current treatment options provide limited benefit. This review discusses current treatment options for patients with acromegaly, limitations associated with each treatment approach, and areas within the current treatment algorithm, as well as patient populations for which improved therapeutic options are needed. Novel agents in development were also highlighted, which have the potential to improve management of patients with uncontrolled or persistent acromegaly.

  13. Magnetization of a Current-Carrying Superconducting Disk with B-Dependent Critical Current Density

    Science.gov (United States)

    Sohrabi, Mahdi; Babaei-Brojeny, Ali A.

    2010-11-01

    In the frame work of the critical state model (CSM), the magnetic response of a thin type-II superconducting disk that carries a radial transport current and is subjected to an applied magnetic field have been studied. To this end, we have studied the process of the magnetic flux-penetration. For a disk initially containing no magnetic flux but carrying a radial current, when a perpendicular magnetic field is applied, magnetic flux-penetration occurs in three stages: (1) the magnetic flux gradually penetrates from the edges of the disk until an instability occurs, (2) there is a rapid inflow of magnetic flux into the disk’s central region, which becomes resistive, and (3) magnetic flux continues to enter the disk, while persistent azimuthal currents flow in an outer annular region where the net current density is equal to J c . Also the behavior of a current-carrying disk subjected to an AC magnetic field is calculated. The magnetic flux, the current profiles and the magnetization hysteresis loops are calculated for several commonly used J c ( B) dependences. Finally, the results of the applications of the local field-dependent of the critical current density J c ( B) are compared with those obtained from the Bean model.

  14. Defining the safe current limit for opening ID photon shutter

    Energy Technology Data Exchange (ETDEWEB)

    Seletskiy, S. [Brookhaven National Lab. (BNL), Upton, NY (United States). Photon Sciences Dept.

    2015-12-14

    The NSLS-II storage ring is protected from possible damage from insertion devices (IDs) synchrotron radiation by a dedicated active interlock system (AIS). It monitors electron beam position and angle and triggers beam drop if beam orbit exceeds the boundaries of pre-calculated active interlock envelope (AIE). The beamlines (BL) and beamline frontends (FE) are designed under assumption that the electron beam is interlocked within the AIE. For historic reasons the AIS engages the ID active interlock (AI-ID) at any non-zero beam current whenever the ID photon shutter (IDPS) is getting opened. Such arrangement creates major inconveniences for BLs commissioning. Apparently there is some IDPS safe current limit (SCL) under which the IDPS can be opened without interlocking the e-beam. The goal of this paper is to find such limit.

  15. Utility survey of requirements for a HTS fault current limiter

    DEFF Research Database (Denmark)

    Nielsen, Jan Nygaard; Jørgensen, P.; Østergaard, Jacob;

    2000-01-01

    The application of superconducting fault current limiters (SFCL) in the electric utility sector will clearly dependent on to what extent the needs and requirements of electric utilities can be met by the ongoing development of SFCL technology. This paper considers a questionnaire survey of which ...... needs and expectations the Danish electric utilities have to this new technology. A bus-tie application of SFCL in a distribution substation with three parallel-coupled transformers is discussed......The application of superconducting fault current limiters (SFCL) in the electric utility sector will clearly dependent on to what extent the needs and requirements of electric utilities can be met by the ongoing development of SFCL technology. This paper considers a questionnaire survey of which...

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

    Science.gov (United States)

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

    2013-12-01

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

  17. Limiting Current of Oxygen Reduction on Gas-Diffusion Electrodes for Phosphoric Acid Fuel Cells

    DEFF Research Database (Denmark)

    Li, Qingfeng; Gang, Xiao; Hjuler, Hans Aage;

    1994-01-01

    Various models have been devoted to the operation mechanism of porous diffusion electrodes. They are, however, suffering from the lack of accuracy concerning the acid-film thickness on which they are based. In the present paper the limiting current density has been measured for oxygen reduction...... on polytetrafluorine-ethyl bonded gas-diffusion electordes in phosphoric acid with and without fluorinated additives. This provides an alternative to estimate the film thickness by combining it with the acid-adsorption measurements and the porosity analysis of the catalyst layer. It was noticed that the limiting...... expression for the limiting current density. The acid-film thickness estimated this way was found to be of 0.1 mum order of magnitude for the two types of electrodes used in phosphoric acid with and without fluorinated additives at 150-degrees-C....

  18. Design Aspects and Test of an Inductive Fault Current Limiter

    Directory of Open Access Journals (Sweden)

    Arsénio Pedro

    2014-05-01

    Full Text Available Magnetic shielding inductive fault current limiters with high temperature superconducting tapes are considered as emerging devices that provide technology for the advent of modern power grids. The development of such limiters requires magnetic iron cores and leads to several design challenges regarding the constitutive parts of the limiter, namely the primary and secondary windings. Preliminary tests in a laboratory scale prototype have been carried out considering an assembly designed for simplicity in which the optimization of the magnetic coupling between the primary and secondary was not the main focus. This work addresses the design configuration of an inductive current limiter prototype regarding the assembly of the primary and secondary windings in the core. The prototype is based on a closed magnetic core wound by a primary, built from a normal electric conductor, and a short-circuited secondary, built from first generation superconducting tape. Four different design configurations are considered. Through experimental tests, the performance of such prototype is discussed and compared, in terms of normal and fault operation regimes. The results show that all the configurations assure effective magnetic shielding at normal operation regime, however, at fault operation regime, there are differences among configurations.

  19. Superconducting fault current-limiter with variable shunt impedance

    Science.gov (United States)

    Llambes, Juan Carlos H; Xiong, Xuming

    2013-11-19

    A superconducting fault current-limiter is provided, including a superconducting element configured to resistively or inductively limit a fault current, and one or more variable-impedance shunts electrically coupled in parallel with the superconducting element. The variable-impedance shunt(s) is configured to present a first impedance during a superconducting state of the superconducting element and a second impedance during a normal resistive state of the superconducting element. The superconducting element transitions from the superconducting state to the normal resistive state responsive to the fault current, and responsive thereto, the variable-impedance shunt(s) transitions from the first to the second impedance. The second impedance of the variable-impedance shunt(s) is a lower impedance than the first impedance, which facilitates current flow through the variable-impedance shunt(s) during a recovery transition of the superconducting element from the normal resistive state to the superconducting state, and thus, facilitates recovery of the superconducting element under load.

  20. Critical state model with anisotropic critical current density

    CERN Document Server

    Bhagwat, K V; Ravikumar, G

    2003-01-01

    Analytical solutions of Bean's critical state model with critical current density J sub c being anisotropic are obtained for superconducting cylindrical samples of arbitrary cross section in a parallel geometry. We present a method for calculating the flux fronts and magnetization curves. Results are presented for cylinders with elliptical cross section with a specific form of the anisotropy. We find that over a certain range of the anisotropy parameter the flux fronts have shapes similar to those for an isotropic sample. However, in general, the presence of anisotropy significantly modifies the shape of the flux fronts. The field for full flux penetration also depends on the anisotropy parameter. The method is extended to the case of anisotropic J sub c that also depends on the local field B, and magnetization hysteresis curves are presented for typical values of the anisotropy parameter for the case of |J sub c | that decreases exponentially with |B|.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2000-08-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-07-23

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

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

    Science.gov (United States)

    Wang, Qi

    2008-04-22

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

  4. Identifying Distinguishing Characteristics of Secondary Pyroclastic Density Currents

    Science.gov (United States)

    Isom, S. L.; Brand, B. D.

    2014-12-01

    Pyroclastic density currents (PDCs) are ground-hugging mixtures of volcanic particles and gas that travel down the slopes of erupting volcanoes. The combination of high velocities, high bulk densities (due to particles in the current) and high temperatures make PDCs the most dangerous and deadly hazard associated with explosive volcanism. Secondary explosive phenomenon associated with PDCs, such as inland-directed surges (e.g., Montserrat, 2003) and phreatic explosions (e.g., Mt St Helens 1980) can increase the area affected and duration of the hazard. However, little work has been done on distinguishing the deposits of secondary explosive phenomenon from primary phenomenon. Samples have been acquired from the 1980 Mt St Helens phreatic explosion crater deposits and the 2003 eruptive event at Montserrat where a PDC flowed into the ocean, causing an inland-directed surge (Edmonds and Herd, 2005. Geology 33.4:245-248). The samples will be analyzed via depositional characteristics, granulometry, componentry, microscopic analysis and scanning electron microscope imaging. We hypothesize that thermal cracking or vesicle distortion (e.g., compression or hindered expansion) may occur in hot pyroclasts that enter a body of water, leading to a difference between the ash textures of primary PDCs, phreatic surges and inland-directed surge deposits. Analyzing granulometry and componentry from parent flows and secondary flows may also reveal distinguishing characteristics that will allow us to constrain differences in segregation mechanisms of particles for each phenomenon. Determining distinguishing depositional characteristics of these secondary phenomena is important for assessing their occurrence during past eruptions and identifying conditions conducive to the formation of secondary explosions. This will result in the ability to make more accurate hazard maps for volcanoes prone to explosive activity.

  5. Ramp Metering by Limitation of Density and Queue Length

    Science.gov (United States)

    Kamel, Boumediene; Benasser, Amar; Jolly, Daniel

    2009-03-01

    As shown by many works and studies, the control of traffic flow remains the best and the efficient solution of the congestion problems. The ramp metering is a means to reduce congestion effects, it has shown his effectiveness to improve the flow and consequently to reduce the total time spent (TTS) by the vehicles in the network. In Kamel et al. [2008] the concept of flatness-based control was applied to regulate the flow at the mainline section of the road on the traffic flow model LWR. This work was preceded by Abouaïssa et al. [2006]. In this article we have proceeded the same way to set the flat output for a second order model METANET. Unfortunately we were unable to prove that the system is flat and therefore define density as flat output, but we manage to define the control laws in order to respect constraints on density and queue length at the on-ramp. The idea is to express the control variable (the outflow of the on-ramp) according to the output (density or queue length at the on-ramp), then inject it in the system. We use this control method in the ramp metering case. The first aim of the control is to keep the density in the segment where the on-ramp is connected below a density (called the target density YT) for which we have the lowest TTS, and the second aim is to keep the queue length at the on-ramp below a maximum value. In order to evaluate the controller's efficiency and applicability, a comparison is made with traditional ALINEA based controller. We illustrate this approach by comparing the cases 'no control' and 'ramp metering' for a simple network.

  6. Imaging fast calcium currents beyond the limitations of electrode techniques.

    Science.gov (United States)

    Jaafari, Nadia; De Waard, Michel; Canepari, Marco

    2014-09-16

    The current understanding of Ca(2+) channel function is derived from the use of the patch-clamp technique. In particular, the measurement of fast cellular Ca(2+) currents is routinely achieved using whole-cell voltage-clamp recordings. However, this experimental approach is not applicable to the study of local native Ca(2+) channels during physiological changes of membrane potential in complex cells, since the voltage-clamp configuration constrains the membrane potential to a given value. Here, we report for the first time to our knowledge that Ca(2+) currents from individual cells can be quantitatively measured beyond the limitations of the voltage-clamp approach using fast Ca(2+) imaging with low-affinity indicators. The optical measurement of the Ca(2+) current was correlated with the membrane potential, simultaneously measured with a voltage-sensitive dye to investigate the activation of Ca(2+) channels along the apical dendrite of the CA1 hippocampal pyramidal neuron during the back-propagation of an action potential. To validate the method, we analyzed the voltage dependence of high- and low-voltage-gated Ca(2+) channels. In particular, we measured the Ca(2+) current component mediated by T-type channels, and we investigated the mechanisms of recovery from inactivation of these channels. This method is expected to become a reference approach to investigate Ca(2+) channels in their native physiological environment.

  7. Current Status and Research into Overcoming Limitations of Capsule Endoscopy.

    Science.gov (United States)

    Kwack, Won Gun; Lim, Yun Jeong

    2016-01-01

    Endoscopic investigation has a critical role in the diagnosis and treatment of gastrointestinal (GI) diseases. Since 2001, capsule endoscopy (CE) has been available for small-bowel exploration and is under continuous development. During the past decade, CE has achieved impressive improvements in areas such as miniaturization, resolution, and battery life. As a result, CE is currently a first-line tool for the investigation of the small bowel in obscure gastrointestinal bleeding and is a useful alternative to wired enteroscopy. Nevertheless, CE still has several limitations, such as incomplete examination and limited diagnostic and therapeutic capabilities. To resolve these problems, many groups have suggested several models (e.g., controlled CO2 insufflation system, magnetic navigation system, mobile robotic platform, tagging and biopsy equipment, and targeted drug-delivery system), which are in development. In the near future, new technological advances will improve the capabilities of CE and broaden its spectrum of applications not only for the small bowel but also for the colon, stomach, and esophagus. The purpose of this review is to introduce the current status of CE and to review the ongoing development of solutions to address its limitations.

  8. High current density sheet-like electron beam generator

    Science.gov (United States)

    Chow-Miller, Cora; Korevaar, Eric; Schuster, John

    Sheet electron beams are very desirable for coupling to the evanescent waves in small millimeter wave slow-wave circuits to achieve higher powers. In particular, they are critical for operation of the free-electron-laser-like Orotron. The program was a systematic effort to establish a solid technology base for such a sheet-like electron emitter system that will facilitate the detailed studies of beam propagation stability. Specifically, the effort involved the design and test of a novel electron gun using Lanthanum hexaboride (LaB6) as the thermionic cathode material. Three sets of experiments were performed to measure beam propagation as a function of collector current, beam voltage, and heating power. The design demonstrated its reliability by delivering 386.5 hours of operation throughout the weeks of experimentation. In addition, the cathode survived two venting and pump down cycles without being poisoned or losing its emission characteristics. A current density of 10.7 A/sq cm. was measured while operating at 50 W of ohmic heating power. Preliminary results indicate that the nearby presence of a metal plate can stabilize the beam.

  9. High current density contacts for photoconductive semiconductor switches

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-08-01

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

  10. Limitations, improvements and alternatives of the silt density index

    NARCIS (Netherlands)

    Al-Hadidi, A.M.M.; Kemperman, A.J.B.; Schurer, H.; Schippers, J.C.; Wessling, M.; Meer, van der W.G.J.

    2013-01-01

    Reverse osmosis (RO) membrane systems are widely used in the desalination of water. However, flux decline due to fouling phenomena in RO remains a challenge. To minimize fouling, a reliable index is necessary to predict the fouling potential of the RO feed water. The ASTM introduced the silt density

  11. Correcting Acidosis during Hemodialysis: Current Limitations and a Potential Solution.

    Science.gov (United States)

    Tovbin, David; Sherman, Richard A

    2016-01-01

    The deleterious catabolic and pro-inflammatory effects of acidosis in hemodialysis (HD) patients and the importance of its correction for limiting mineral bone disease (MBD) are well known. Although oral base therapy could be a solution for correcting acidosis in HD patients, it increases their already enormous medication load and sodium intake; this approach is not used commonly. Therefore, we need to rely more on correcting acidosis during the HD procedure, which is difficult to achieve, in part, because HD is an intermittent therapy. The currently used fixed dialysate bicarbonate concentrations are associated with pre-HD acidosis and intra-dialytic alkalosis. We suggest that a decreasing dialysate bicarbonate concentration from an initially high concentration be considered as a means of correcting acidosis with limited intra-dialytic alkalosis. Some evidence, as well as theoretical considerations, supports such an approach. © 2015 Wiley Periodicals, Inc.

  12. Pediatric minimally invasive surgery in Africa: limitations and current situation.

    Science.gov (United States)

    Loveland, Jerome; Numanoglu, Alp; Hay, Sameh Abdel

    2012-05-01

    The second largest and most populous continent, with an exploding pediatric population, Africa has an overwhelming burden on its very limited pediatric surgical services. In an international environment of progressively advancing endoscopic and robotic surgical techniques, the authors focus on the current role of endoscopic surgery on the continent and explore the potential reasons for its delayed acceptance and implementation. They proceed to document the spectrum of what is available and, using their "African experience," expand on financially viable models of further rolling out these techniques, including discussion around suitable training models for surgeons and their teams. Copyright © 2012 Elsevier Inc. All rights reserved.

  13. Proposed hybrid superconducting fault current limiter for distribution systems

    Energy Technology Data Exchange (ETDEWEB)

    Elmitwally, A. [Elect. Eng. Dept., Mansoura University, Mansoura 35516 (Egypt)

    2009-11-15

    In this paper, a new hybrid fault current limiter is proposed for primary distribution systems. It incorporates a high temperature superconducting element in parallel with other two branches. The first is an inductive impedance to share the fault current with. The second branch is a gate-turn-off thyristor switch controlled to work in either of two modes. For the main mode, it controls the temperature of the superconducting element and protect it against damaging excessive heating. Instead, it keeps the device applicable without that superconducting element in the auxiliary operation mode. The design, control and operation of the device is addressed. Its performance in 11 kV distribution systems with DG is investigated. The factors affecting the device behavior for different scenarios are explored. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Helbig, N.

    2006-05-15

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

  15. High current density stability of ohmic contacts to silicon carbide

    Science.gov (United States)

    Downey, Brian P.

    The materials properties of SiC, such as wide bandgap, high breakdown electric field, and good thermal conductivity, make it an appealing option for high temperature and high power applications. The replacement of Si devices with SiC components could lead to a reduction in device size, weight, complexity, and cooling requirements along with an increase in device efficiency. One area of concern under high temperature or high current operation is the stability of the ohmic contacts. Ohmic contact degradation can cause an increase in parasitic resistance, which can diminish device performance. While contact studies have primarily focused on the high temperature stability of ohmic contacts to SiC, different failure mechanisms may arise under high current density stressing due to the influence of electromigration. In addition, preferential degradation may occur at the anode or cathode due to the directionality of current flow, known as a polarity effect. The failure mechanisms of ohmic contacts to p-type SiC under high current density stressing are explored. Complementary materials characterization techniques were used to analyze contact degradation, particularly the use of cross-sections prepared by focused ion beam for imaging using field emission scanning electron microscopy and elemental analysis using Auger electron spectroscopy. Initially the degradation of commonly studied Ni and Al-based contacts was investigated under continuous DC current. The contact metallization included a bond pad consisting of a TiW diffusion barrier and thick Au overlayer. The Ni contacts were found to degrade due to the growth of voids within the ohmic contact layer, which were initially produced during the high temperature Ni/SiC ohmic contact anneal. The Al-based contacts degraded due to the movement of Al from the ohmic contact layer to the surface of the Au bond pad, and the movement of Au into the ohmic contact layer from the bond pad. The inequality of Al and Au fluxes generated

  16. Potential and limitations of eddy current lockin-thermography

    Science.gov (United States)

    Riegert, G.; Gleiter, A.; Busse, G.

    2006-04-01

    Eddy current thermography uses an induction coil to induce eddy currents in conductive materials. The involved resistive losses heat the sample. By modulation of the eddy current amplitude, thermal waves are generated which interact with boundaries thereby revealing defects. Conventional eddy current testing has only a limited depth range due to the skin effect of metal samples. In Induction-Lockin-Thermography (ILT) the depth range is extended by the thermal penetration depth. An infrared camera monitors the modulation of the temperature field on the surface as a response to the coded excitation thereby allowing for fast imaging of defects in larger areas without the need of slow point-by-point mapping. This response is decoded by a Fourier analysis at the modulation frequency. So the extracted information is displayed by just two images where one displays local amplitude and the other local phase. ILT has significant advantages as compared to inductive heating with visual inspection of the thermographic sequence: Phase angle images are independent of most artifacts like reflections, variation in emission coefficient, or inhomogeneous heating. Due to the performed Fourier analysis of the temperature image sequence, the signal-to-noise ratio in the amplitude and phase images is significantly better than in single temperature images of the sequence. Induction heating is confined to conductive materials. However, it is applicable not only to metals but also to carbon fiber reinforced laminates (CFRP) or carbon fiber reinforced ceramics (C/C-SiC). The presented examples for applications of ILT illustrate the potential and limitations of this new non-destructive inspection method.

  17. Thermal instability and current-voltage scaling in superconducting fault current limiters

    Energy Technology Data Exchange (ETDEWEB)

    Zeimetz, B [Department of Materials Science and Metallurgy, Cambridge University, Pembroke Street, Cambridge CB1 3QZ (United Kingdom); Tadinada, K [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom); Eves, D E [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom); Coombs, T A [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom); Evetts, J E [Department of Materials Science and Metallurgy, Cambridge University, Pembroke Street, Cambridge CB1 3QZ (United Kingdom); Campbell, A M [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom)

    2004-04-01

    We have developed a computer model for the simulation of resistive superconducting fault current limiters in three dimensions. The program calculates the electromagnetic and thermal response of a superconductor to a time-dependent overload voltage, with different possible cooling conditions for the surfaces, and locally variable superconducting and thermal properties. We find that the cryogen boil-off parameters critically influence the stability of a limiter. The recovery time after a fault increases strongly with thickness. Above a critical thickness, the temperature is unstable even for a small applied AC voltage. The maximum voltage and maximum current during a short fault are correlated by a simple exponential law.

  18. Space-charge-limited leakage current in high dielectric constant and ferroelectric thin films considering the field-dependent permittivity

    Science.gov (United States)

    Sun, J.; Zheng, X. J.; Yin, W.; Tang, M. H.; Li, W.

    2010-12-01

    Distinguishing from the traditional characterization on high-field leakage current density-voltage relationship, the field-dependent permittivity from the polarization derivative is used to solve the space-charge-limited conduction, and the simulated leakage current densities are compared with the previous experimental observations. The influences of the mobility, ferroelectric parameters, and film thickness on the leakage current densities are discussed. The results verify that the high-field quasi-Ohmic region observed experimentally may result from the field-dependent permittivity, and that the leakage current can be influenced by the ferroelectric polarization.

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

    Directory of Open Access Journals (Sweden)

    Andisheh Bastani

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

  20. Correlation of Critical Current Density with Cu3+ Concentration and Density in YBa2Cu3O7-x

    Science.gov (United States)

    Dou, S. X.; Liu, H. K.; Zhou, J. P.; Bourdillon, A. J.; Savvides, N.; Apperley, M.; Gouch, A.; Sorrell, C. C.

    Superconducting YBa2Cu3O7 wires and tapes were fabricated by cold drawing, rolling and extrusion processes. It was found that the critical current density, after O2 equilibration, correlates both with density and Cu3+ concentration. Full density was achieved by using a special heat treatment, but the critical current density was low owing to the low Cu3+ concentration present in this heavily twinned material. The best critical current density results were obtained for material with density of 92-95% of the theoretical value. The low critical current density of the porous specimens is attributed not only to a poor connectivity between grains but also to a low Cu3+ concentration due to the instability of Cu3+ at crystallite surfaces which increase in area with specimen porosity.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-11-01

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

  2. Ion current rectification, limiting and overlimiting conductances in nanopores.

    Directory of Open Access Journals (Sweden)

    Liesbeth van Oeffelen

    Full Text Available Previous reports on Poisson-Nernst-Planck (PNP simulations of solid-state nanopores have focused on steady state behaviour under simplified boundary conditions. These are Neumann boundary conditions for the voltage at the pore walls, and in some cases also Donnan equilibrium boundary conditions for concentrations and voltages at both entrances of the nanopore. In this paper, we report time-dependent and steady state PNP simulations under less restrictive boundary conditions, including Neumann boundary conditions applied throughout the membrane relatively far away from the nanopore. We simulated ion currents through cylindrical and conical nanopores with several surface charge configurations, studying the spatial and temporal dependence of the currents contributed by each ion species. This revealed that, due to slow co-diffusion of oppositely charged ions, steady state is generally not reached in simulations or in practice. Furthermore, it is shown that ion concentration polarization is responsible for the observed limiting conductances and ion current rectification in nanopores with asymmetric surface charges or shapes. Hence, after more than a decade of collective research attempting to understand the nature of ion current rectification in solid-state nanopores, a relatively intuitive model is retrieved. Moreover, we measured and simulated current-voltage characteristics of rectifying silicon nitride nanopores presenting overlimiting conductances. The similarity between measurement and simulation shows that overlimiting conductances can result from the increased conductance of the electric double-layer at the membrane surface at the depletion side due to voltage-induced polarization charges. The MATLAB source code of the simulation software is available via the website http://micr.vub.ac.be.

  3. Ion current rectification, limiting and overlimiting conductances in nanopores.

    Science.gov (United States)

    van Oeffelen, Liesbeth; Van Roy, Willem; Idrissi, Hosni; Charlier, Daniel; Lagae, Liesbet; Borghs, Gustaaf

    2015-01-01

    Previous reports on Poisson-Nernst-Planck (PNP) simulations of solid-state nanopores have focused on steady state behaviour under simplified boundary conditions. These are Neumann boundary conditions for the voltage at the pore walls, and in some cases also Donnan equilibrium boundary conditions for concentrations and voltages at both entrances of the nanopore. In this paper, we report time-dependent and steady state PNP simulations under less restrictive boundary conditions, including Neumann boundary conditions applied throughout the membrane relatively far away from the nanopore. We simulated ion currents through cylindrical and conical nanopores with several surface charge configurations, studying the spatial and temporal dependence of the currents contributed by each ion species. This revealed that, due to slow co-diffusion of oppositely charged ions, steady state is generally not reached in simulations or in practice. Furthermore, it is shown that ion concentration polarization is responsible for the observed limiting conductances and ion current rectification in nanopores with asymmetric surface charges or shapes. Hence, after more than a decade of collective research attempting to understand the nature of ion current rectification in solid-state nanopores, a relatively intuitive model is retrieved. Moreover, we measured and simulated current-voltage characteristics of rectifying silicon nitride nanopores presenting overlimiting conductances. The similarity between measurement and simulation shows that overlimiting conductances can result from the increased conductance of the electric double-layer at the membrane surface at the depletion side due to voltage-induced polarization charges. The MATLAB source code of the simulation software is available via the website http://micr.vub.ac.be.

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

    Science.gov (United States)

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

    2016-07-01

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

  5. Investigation of heavy current discharges with high initial gas density

    Energy Technology Data Exchange (ETDEWEB)

    Budin, A.; Bogomaz, A.; Kolikov, V.; Kuprin, A.; Leontiev, V.; Rutberg, P.; Shirokov, N. [Institute of Problems of Electrophysics of Russian Academy of Sciences, Dvortsovayanab., 18, St. Petersburg, 191065 (Russia)

    1996-05-01

    Piezoelectric pressure transducers, with noise immunity and time resolution of 0,5 {mu}s were used to measure pulse pressures of 430 MPa along the axis of an electrical discharge channel. Initial concentration of He was 2,7{center_dot}10{sup 21}cm{sup {minus}3}, dI/dt=6{center_dot}10{sup 11}A/s, and I{sub max}=560kA. Shock waves with amplitudes exceeding the pressure along the axis, were detected by a pressure transducer on the wall of the discharge chamber. Typical shock velocities were 2{center_dot}4km/s. Average pressure measurements along the discharge axis at different radii were used to estimate the current density distribution along the canal radius. The presence of the shock waves, promoting the additional hydrogen heating in the discharge chamber, has been registered during the discharge in hydrogen for I{sub max}{approximately}1MA and an initial concentration of 10{sup 21}cm{sup {minus}3}. {copyright} {ital 1996 American Institute of Physics.}

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

    Science.gov (United States)

    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

  7. Noise limits of CMOS current interfaces for biosensors: a review.

    Science.gov (United States)

    Crescentini, Marco; Bennati, Marco; Carminati, Marco; Tartagni, Marco

    2014-04-01

    Current sensing readout is one of the most frequent techniques used in biosensing due to the charge-transfer phenomena occurring at solid-liquid interfaces. The development of novel nanodevices for biosensing determines new challenges for electronic interface design based on current sensing, especially when compact and efficient arrays need to be organized, such as in recent trends of rapid label-free electronic detection of DNA synthesis. This paper will review the basic noise limitations of current sensing interfaces with particular emphasis on integrated CMOS technology. Starting from the basic theory, the paper presents, investigates and compares charge-sensitive amplifier architectures used in both continuous-time and discrete-time approaches, along with their design trade-offs involving noise floor, sensitivity to stray capacitance and bandwidth. The ultimate goal of this review is providing analog designers with helpful design rules and analytical tools. Also, in order to present a comprehensive overview of the state-of-the-art, the most relevant papers recently appeared in the literature about this topic are discussed and compared.

  8. Realizing life-scalable experimental pyroclastic density currents

    Science.gov (United States)

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

    2013-12-01

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

  9. Investigation on the relation between edge radial electric field asymmetries in RFX-mod and density limit

    Energy Technology Data Exchange (ETDEWEB)

    Spizzo, Gianluca; Scarin, Paolo; Agostini, Matteo; Alfier, Alberto; Auriemma, Fulvio; Bonfiglio, Daniele; Cappello, Susanna; Fassina, Alessandro; Franz, Paolo; Piron, Lidia; Piovesan, Paolo; Puiatti, Maria Ester; Valisa, Marco; Vianello, Nicola, E-mail: gianluca.spizzo@igi.cnr.i, E-mail: paolo.scarin@igi.cnr.i [Consorzio RFX, Euratom-ENEA Association, Padova (Italy)

    2010-09-15

    In all major confinement devices (tokamaks, stellarators, spheromaks and reversed-field pinches-RFPs), a density limit has been found. Results summarized in a recent work by Puiatti et al (2009 Nucl. Fusion 49 045012) show that in the RFP high density does not cause a disruption, but a sequence of increasingly critical phenomena. First, at intermediate density there is the disappearance of the high-confinement quasisingle helicity/single helical axis regimes. Then, at densities close to the Greenwald limit, toroidally and radially localized density accumulation and radiation condensation are observed, together with a fast resistive decay of the plasma current, which constitutes the real operative limit of the device. In this paper we discuss the effect of the magnetic ripple on test particle motion, showing that the accumulation of electrons in the X-points of the edge m = 0 islands is responsible for a modulation of the radial electric field E{sub r} which is at the core of the density limit mechanism. These results can be also relevant for the explanation of X-point multifaceted asymmetric radiation from the edge formation, observed in L-mode density limit discharges of JET.

  10. Force-free collisionless current sheet models with non-uniform temperature and density profiles

    Science.gov (United States)

    Wilson, F.; Neukirch, T.; Allanson, O.

    2017-09-01

    We present a class of one-dimensional, strictly neutral, Vlasov-Maxwell equilibrium distribution functions for force-free current sheets, with magnetic fields defined in terms of Jacobian elliptic functions, extending the results of Abraham-Shrauner [Phys. Plasmas 20, 102117 (2013)] to allow for non-uniform density and temperature profiles. To achieve this, we use an approach previously applied to the force-free Harris sheet by Kolotkov et al. [Phys. Plasmas 22, 112902 (2015)]. In one limit of the parameters, we recover the model of Kolotkov et al. [Phys. Plasmas 22, 112902 (2015)], while another limit gives a linear force-free field. We discuss conditions on the parameters such that the distribution functions are always positive and give expressions for the pressure, density, temperature, and bulk-flow velocities of the equilibrium, discussing the differences from previous models. We also present some illustrative plots of the distribution function in velocity space.

  11. LIFELONG LEARNING THROUGH SECOND LIFE: CURRENT TRENDS, POTENTIALS AND LIMITATIONS

    Directory of Open Access Journals (Sweden)

    Nil GOKSEL-CANBEK

    2011-08-01

    Full Text Available Lifelong Learning (LLL has been a remarkable response to people-centered educational demand of 21st century. In order to provide effective formal, non-formal, and informal learning, immersive educational activities undertaken throughout life should be aimed to create a learning society in which people can experience individual and collective learning with no constrains of time or location. The concept of lifelong learning within the context of distance immersive education encompasses diverse 3D activities. The three dimensional, Web-based structured activities supported by distance learning technologies can be viewed as interactive tools which foster LLL. In this perspective, Second Life (SL can be regarded as one of the learning simulation milieus that allow learners to participate in various educational LLL activities in individual or group forms. The following paper examines how SL, taking advantage of its simulative nature and the possibility for creative interaction among participants, which are also common in games, allows the learners to participate in immersive constructivist learning activities. The article will also touch on the current uses of SL as a tool for LLL, as well as its potentials for further development according to the current trends in adult education. Further, the authors will discuss its limitations and will make suggestions towards a more complete pedagogical use.

  12. Evolution and current development of Transversal Themes: possibilities and limits

    Directory of Open Access Journals (Sweden)

    Carlos Rosales López

    2015-02-01

    Full Text Available The aim of this study was to determine the characteristics of the evolution and current development of transversal themes in education, considering them basically as important social cuestions with great influence in the overall education of the student. Specifically it seeks to clarify the level of preparation and dedication of teachers and schools to teach them. To do this, legislation used in our country (organics laws and decrees curriculum were analyzed and also the contribution of outstanding educators, institutions and researchers. We analyzed the characteristics of transversal themes in the educational project and the teaching program, its development in the clasroom and its projection out of it through the help of family and community. Conclusions about their current status (possibilities and limitations are derived and future proposals are made on the improvement of initial and ongoing training of teachers, to increase their collegiate or cooperative work of planning, intervention and evaluation, increased media and counseling in use, the need for increased communication and collaboration with families and other community institutions.How to reference this articleRosales López, C. (2015. Evolución y desarrollo actual de los Temas Transversales: posibilidades y límites. Foro de Educación, 13(18, pp. 143-160. doi: http://dx.doi.org/10.14516/fde.2015.013.018.008

  13. Land use, forest density, soil mapping, erosion, drainage, salinity limitations

    Science.gov (United States)

    Yassoglou, N. J. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. The results of analyses show that it is possible to obtain information of practical significance as follows: (1) A quick and accurate estimate of the proper use of the valuable land can be made on the basis of temporal and spectral characteristics of the land features. (2) A rather accurate delineation of the major forest formations in the test areas was achieved on the basis of spatial and spectral characteristics of the studied areas. The forest stands were separated into two density classes; dense forest, and broken forest. On the basis of ERTS-1 data and the existing ground truth information a rather accurate mapping of the major vegetational forms of the mountain ranges can be made. (3) Major soil formations are mapable from ERTS-1 data: recent alluvial soils; soil on quarternary deposits; severely eroded soil and lithosol; and wet soils. (4) An estimation of cost benefits cannot be made accurately at this stage of the investigation. However, a rough estimate of the ratio of the cost for obtaining the same amount information from ERTS-1 data and from conventional operations would be approximately 1:6 to 1:10, in favor of the ERTS-1.

  14. Current distribution and enhancement of the engineering critical current density in multifilament Bi-2223 tapes

    DEFF Research Database (Denmark)

    Wang, W.G.; Jensen, M.B.; Kindl, B.;

    2000-01-01

    The spatial distribution of the critical current density (Jc) and engineering critical current density (Je) along the tape width direction was studied by a cutting technique on Bi-2223 multifilamentary tapes. In general, an increase of Jc towards the centre of the tape was measured. We attribute...... this tendency to the stress-strain experienced in the tape during the rolling process. Jc of 50 kA/cm2 and Jeof 18 kA/cm2 was measured at the centre part (185 μm wide and 200 μm thick) of a tape cut from a 500 meters long tape (average Je of 8 kA/cm2). The low Jc of the edge part is a result of the porous...... microstructure with a great amount of secondary phases. Local variation of Jc was measured within the centre segment of the tape. This indicates the influence of other factors on Jc, such as filament shape, connectivity of the filaments, and sausaging. Enhancement of Je has been pursued in which average Je of 12...

  15. Superconducting matrix fault current limiter with current-driven trigger mechanism

    Science.gov (United States)

    Yuan, Xing

    2008-04-15

    A modular and scalable Matrix-type Fault Current Limiter (MFCL) that functions as a "variable impedance" device in an electric power network, using components made of superconducting and non-superconducting electrically conductive materials. An inductor is connected in series with the trigger superconductor in the trigger matrix and physically surrounds the superconductor. The current surge during a fault will generate a trigger magnetic field in the series inductor to cause fast and uniform quenching of the trigger superconductor to significantly reduce burnout risk due to superconductor material non-uniformity.

  16. Use of catalytic anodes for zinc electrowinning at high current densities from purified electrolytes

    Energy Technology Data Exchange (ETDEWEB)

    Bestetti, M.; Ducati, U. [Polytechnic of Milan, Dept. of Applied Physical Chemistry, Milan (Italy); Kelsall, G.H. [T.H. Huxley School, Imperial College, London (United Kingdom); Li, G. [Cominco Research, Cominco Limited, Trail, British Columbia (Canada); Guerra, E. [Univ. of British Columbia, Dept. of Metals and Materials Engineering, Victoria, British Columbia (Canada)

    2001-07-01

    Substantial energy savings are possible in zinc electrowinning by substituting catalytic oxygen evolution anodes for conventional lead-silver anodes. However, it is well known that the harmful effects of impurities usually present in zinc electrolyte solutions limit the service life of catalytic anodes, though their purification by solvent extraction could obviate such problems. Laboratory-scale zinc deposition experiments, with synthetic electrolytes have been performed to determine the effects of current density, temperature, and electrolyte composition on cell voltages and current efficiencies. These data sets were used in an assessment of the optimum design parameters of the tank house. Zinc electrowinning at high current densities (higher than 2000 A/m{sup 2}) using catalytic anodes and purified solutions (e.g., by solvent extraction), is proposed as an alternative to the conventional process, which is based on lead-silver anodes working at relatively low current densities (ca. 500 A/m{sup 2}). Finally, a system for continuous deposition and stripping of the metal is discussed. (author)

  17. Clast comminution during pyroclastic density current transport: Mt St Helens

    Science.gov (United States)

    Dawson, B.; Brand, B. D.; Dufek, J.

    2011-12-01

    Volcanic clasts within pyroclastic density currents (PDCs) tend to be more rounded than those in fall deposits. This rounding reflects degrees of comminution during transport, which produces an increase in fine-grained ash with distance from source (Manga, M., Patel, A., Dufek., J. 2011. Bull Volcanol 73: 321-333). The amount of ash produced due to comminution can potentially affect runout distance, deposit sorting, the volume of ash lofted into the upper atmosphere, and increase internal pore pressure (e.g., Wohletz, K., Sheridan, M. F., Brown, W.K. 1989. J Geophy Res, 94, 15703-15721). For example, increased pore pressure has been shown to produce longer runout distances than non-comminuted PDC flows (e.g., Dufek, J., and M. Manga, 2008. J. Geophy Res, 113). We build on the work of Manga et al., (2011) by completing a pumice abrasion study for two well-exposed flow units from the May 18th, 1980 eruption of Mt St Helens (MSH). To quantify differences in comminution from source, sampling and the image analysis technique developed in Manga et al., 2010 was completed at distances proximal, medial, and distal from source. Within the units observed, data was taken from the base, middle, and pumice lobes within the outcrops. Our study is unique in that in addition to quantifying the degree of pumice rounding with distance from source, we also determine the possible range of ash sizes produced during comminution by analyzing bubble wall thickness of the pumice through petrographic and SEM analysis. The proportion of this ash size is then measured relative to the grain size of larger ash with distance from source. This allows us to correlate ash production with degree of rounding with distance from source, and determine the fraction of the fine ash produced due to comminution versus vent-fragmentation mechanisms. In addition we test the error in 2D analysis by completing a 3D image analysis of selected pumice samples using a Camsizer. We find that the roundness of PDC

  18. Circulating thyroid cancer biomarkers: Current limitations and future prospects.

    Science.gov (United States)

    Nixon, Alexander M; Provatopoulou, Xeni; Kalogera, Eleni; Zografos, George N; Gounaris, Antonia

    2017-08-01

    Differentiated thyroid cancer (DTC) is the most common malignancy of the endocrine system. There has been a significant increase in its incidence over the past two decades attributable mainly to the use of more sensitive diagnostic modalities. Ultrasound-guided fine needle aspiration cytology is the mainstay of diagnosis of benign disorders and malignancy. However, approximately 20% of lesions cannot be adequately categorized as benign or malignant. In the postoperative setting, monitoring of thyroglobulin (Tg) levels has been employed for the detection of disease recurrence. Unfortunately, Tg antibodies are common and interfere with Tg measurement in this subset of patients. Despite this limitation, Tg remains the sole widely used thyroid cancer biomarker in the clinical setting. In an attempt to bypass antibody interference, research has focused mainly on mRNA targets thought to be exclusively expressed in thyroid cells. Tg and thyroid stimulating hormone receptor (TSHR) mRNA have been extensively studied both for discerning between benign disease and malignancy and in postoperative disease surveillance. However, results among reports have been inconsistent probably reflecting considerable differences in methodology. Recently, microRNA (miRNA) targets are being investigated as potential biomarkers in DTC. MiRNAs are more stable molecules and theoretically are not as vulnerable as mRNA during manipulation. Initial results have been encouraging but large-scale studies are warranted to verify and elucidate their potential application in diagnosis and postoperative surveillance of thyroid cancer. Several other novel targets, primarily mutations and circulating cells, are currently emerging as promising thyroid cancer circulating biomarkers. Although interesting and intriguing, data are limited and derive from small-scale studies in specific patient cohorts. Further research findings demonstrating their value are awaited with anticipation. © 2017 John Wiley & Sons

  19. Current parallel I/O limitations to scalable data analysis.

    Energy Technology Data Exchange (ETDEWEB)

    Mascarenhas, Ajith Arthur; Pebay, Philippe Pierre

    2011-07-01

    This report describes the limitations to parallel scalability which we have encountered when applying our otherwise optimally scalable parallel statistical analysis tool kit to large data sets distributed across the parallel file system of the current premier DOE computational facility. This report describes our study to evaluate the effect of parallel I/O on the overall scalability of a parallel data analysis pipeline using our scalable parallel statistics tool kit [PTBM11]. In this goal, we tested it using the Jaguar-pf DOE/ORNL peta-scale platform on a large combustion simulation data under a variety of process counts and domain decompositions scenarios. In this report we have recalled the foundations of the parallel statistical analysis tool kit which we have designed and implemented, with the specific double intent of reproducing typical data analysis workflows, and achieving optimal design for scalable parallel implementations. We have briefly reviewed those earlier results and publications which allow us to conclude that we have achieved both goals. However, in this report we have further established that, when used in conjuction with a state-of-the-art parallel I/O system, as can be found on the premier DOE peta-scale platform, the scaling properties of the overall analysis pipeline comprising parallel data access routines degrade rapidly. This finding is problematic and must be addressed if peta-scale data analysis is to be made scalable, or even possible. In order to attempt to address these parallel I/O limitations, we will investigate the use the Adaptable IO System (ADIOS) [LZL+10] to improve I/O performance, while maintaining flexibility for a variety of IO options, such MPI IO, POSIX IO. This system is developed at ORNL and other collaborating institutions, and is being tested extensively on Jaguar-pf. Simulation code being developed on these systems will also use ADIOS to output the data thereby making it easier for other systems, such as ours, to

  20. On-chip temperature monitoring of a SiC current limiter

    Energy Technology Data Exchange (ETDEWEB)

    Tournier, D.; Godignon, P.; Millan, J. [Centro Nacional de Microelectronica (CNM), Univ. Autonoma de Barcelona, Bellaterra (Spain); Planson, D.; Chante, J.P. [Centre de Genie Electrique de Lyon (CEGELY) INSA-LYON, UMR 5005 CNRS, Villeurbanne (France); Sarrus, F.; Palma, J.F. de [Ferraz Shawmut, Bonnet de Mure (France)

    2004-07-01

    High voltage and high current potentiality of SiC based devices has been proved, and various devices able to work at high temperature have been reported as well. Nevertheless, packaging is one of the main constrains for high temperature operation of these devices. Up to date, no specific power package has been reported for high temperature operation. Moreover, it is desirable to predict the SiC die temperature to avoid any related failure in order to improve the efficiency of the packaged SiC device. This paper deals with an integrated temperature sensor for SiC current limiting devices. The current limiter is based on a VJFET structure, which capability for dissipating high power density (140 kW/cm{sup 2}), in the limiting state, has been previously demonstrated. Carrier mobility dependence with temperature was extracted from cryogenic measurements. The temperature estimation is based on the measurement of the variation of the electrical resistance (caused by mobility variation) of the sensing device integrated with the current limiter. In this paper we first describe the temperature estimation methodology using various technological solution (from metallic resistor solution to the SiC integrated sensor). Then experimental temperature measurements using an integrated SiC sensor within a packaged current limiting devices will be presented. Electro-thermal measurements on the fabricated devices show that the current limiter is able to work at 205 C under steady state conditions (320 V), without degrading their electrical performances. Finally, perspectives in terms of integration and reliability will be proposed. (orig.)

  1. Current limitations and challenges in nanowaste detection, characterisation and monitoring

    Energy Technology Data Exchange (ETDEWEB)

    Part, Florian; Zecha, Gudrun [Department of Water-Atmosphere-Environment, University of Natural Resources and Life Sciences, Institute of Waste Management, Muthgasse 107, 1190 Vienna (Austria); Causon, Tim [Department of Chemistry, Division of Analytical Chemistry, University of Natural Resources and Life Sciences, Muthgasse 18, 1190 Vienna (Austria); Sinner, Eva-Kathrin [Department of Nanobiotechnology, Institute for Synthetic Bioarchitectures, University of Natural Resources and Life Sciences, Muthgasse 11/II, 1190 Vienna (Austria); Huber-Humer, Marion, E-mail: marion.huber-humer@boku.ac.at [Department of Water-Atmosphere-Environment, University of Natural Resources and Life Sciences, Institute of Waste Management, Muthgasse 107, 1190 Vienna (Austria)

    2015-09-15

    Highlights: • First review on detection of nanomaterials in complex waste samples. • Focus on nanoparticles in solid, liquid and gaseous waste samples. • Summary of current applicable methods for nanowaste detection and characterisation. • Limitations and challenges of characterisation of nanoparticles in waste. - Abstract: Engineered nanomaterials (ENMs) are already extensively used in diverse consumer products. Along the life cycle of a nano-enabled product, ENMs can be released and subsequently accumulate in the environment. Material flow models also indicate that a variety of ENMs may accumulate in waste streams. Therefore, a new type of waste, so-called nanowaste, is generated when end-of-life ENMs and nano-enabled products are disposed of. In terms of the precautionary principle, environmental monitoring of end-of-life ENMs is crucial to allow assessment of the potential impact of nanowaste on our ecosystem. Trace analysis and quantification of nanoparticulate species is very challenging because of the variety of ENM types that are used in products and low concentrations of nanowaste expected in complex environmental media. In the framework of this paper, challenges in nanowaste characterisation and appropriate analytical techniques which can be applied to nanowaste analysis are summarised. Recent case studies focussing on the characterisation of ENMs in waste streams are discussed. Most studies aim to investigate the fate of nanowaste during incineration, particularly considering aerosol measurements; whereas, detailed studies focusing on the potential release of nanowaste during waste recycling processes are currently not available. In terms of suitable analytical methods, separation techniques coupled to spectrometry-based methods are promising tools to detect nanowaste and determine particle size distribution in liquid waste samples. Standardised leaching protocols can be applied to generate soluble fractions stemming from solid wastes, while

  2. Limit currents and value distribution of holomorphic maps

    CERN Document Server

    Buurns, Daniel

    2010-01-01

    We construct $d$-closed and $dd^c$-closed positive currents associated to a holomorphic map $\\phi$ via cluster points of normalized weighted truncated image currents. They are constructed using analogues of the Ahlfors length-area inequality in higher dimensions. Such classes of currents are loosely referred to as Ahlfors currents. We give some applications to equidistribution problems in value distribution theory.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-08-01

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

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

    Science.gov (United States)

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

    2015-02-28

    Time-Dependent Density-Functional Theory (TDDFT) is a well-established theoretical approach to describe and understand irradiation processes in clusters and molecules. However, within the so-called adiabatic local density approximation (ALDA) to the exchange-correlation (xc) potential, TDDFT can show insufficiencies, particularly in violently dynamical processes. This is because within ALDA the xc potential is instantaneous and is a local functional of the density, which means that this approximation neglects memory effects and long-range effects. A way to go beyond ALDA is to use Time-Dependent Current-Density-Functional Theory (TDCDFT), in which the basic quantity is the current density rather than the density as in TDDFT. This has been shown to offer an adequate account of dissipation in the linear domain when the Vignale-Kohn (VK) functional is used. Here, we go beyond the linear regime and we explore this formulation in the time domain. In this case, the equations become very involved making the computation out of reach; we hence propose an approximation to the VK functional which allows us to calculate the dynamics in real time and at the same time to keep most of the physics described by the VK functional. We apply this formulation to the calculation of the time-dependent dipole moment of Ca, Mg and Na2. Our results show trends similar to what was previously observed in model systems or within linear response. In the non-linear domain, our results show that relaxation times do not decrease with increasing deposited excitation energy, which sets some limitations to the practical use of TDCDFT in such a domain of excitations.

  5. High-current-density gun with a LaB6 cathode

    Science.gov (United States)

    Ebihara, K.; Hiramatsu, S.

    1996-08-01

    To develop a high-current electron gun for an induction linac, a prototype of a Pierce-type electron gun using planar 12-mm-diam lanthanum hexaboride (LaB6) is studied as a thermionic emitter at high current densities. The cathode is heated up to temperatures of 1750 °C by electron bombardment and thermal radiation from a tungsten heater. The heater that has the highest temperature in the gun is thermally isolated from the outer vacuum chamber with heat shields. The bombardment voltage of ˜1 kV is typically applied to a gap between the cathode and the heater. The gun has been operated up to voltages of 55 kV, obtaining a maximum current density of 20 A/cm2 with a pulse width of 250 ns at a cathode temperature of 1600 °C. High-voltage pulsing results show that the gun, with applied voltages of over 40 kV, is operated in space-charge-limited region at temperatures of over 1600 °C; also it is operated in a temperature-limited region at temperatures of less than 1500 °C. An effective work function of 2.68 eV is obtained. The cathode, when heated up to 1600 °C, emits over 7 A of electrons with a ˜20% reduction after 850 h of continuous operation. These measurements were made between vacuum pressures of 10-6 and 10-7 Torr.

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

    Science.gov (United States)

    Sadhu, Tridib; Derrida, Bernard

    2016-11-01

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

  7. Density and current profiles in Uq (A2(1)) zero range process

    Science.gov (United States)

    Kuniba, A.; Mangazeev, V. V.

    2017-09-01

    The stochastic R matrix for Uq (An(1)) introduced recently gives rise to an integrable zero range process of n classes of particles in one dimension. For n = 2 we investigate how finitely many first class particles fixed as defects influence the grand canonical ensemble of the second class particles. By using the matrix product stationary probabilities involving infinite products of q-bosons, exact formulas are derived for the local density and current of the second class particles in the large volume limit.

  8. An Assessment of Reservoir Density Currents and Inflow Processes

    Science.gov (United States)

    1983-07-01

    are defined once where used in the main text and appendices and, for convience , are listed and redefined in Appendix D. Unless specifically stated...techniques are described hereafter and sample applications are presented in Appendix B. Overflows 118. Overflows occur when the inflowing water density is

  9. Fourier transform magnetic resonance current density imaging (FT-MRCDI) from one component of magnetic flux density.

    Science.gov (United States)

    Ider, Yusuf Ziya; Birgul, Ozlem; Oran, Omer Faruk; Arikan, Orhan; Hamamura, Mark J; Muftuler, L Tugan

    2010-06-01

    Fourier transform (FT)-based algorithms for magnetic resonance current density imaging (MRCDI) from one component of magnetic flux density have been developed for 2D and 3D problems. For 2D problems, where current is confined to the xy-plane and z-component of the magnetic flux density is measured also on the xy-plane inside the object, an iterative FT-MRCDI algorithm is developed by which both the current distribution inside the object and the z-component of the magnetic flux density on the xy-plane outside the object are reconstructed. The method is applied to simulated as well as actual data from phantoms. The effect of measurement error on the spatial resolution of the current density reconstruction is also investigated. For 3D objects an iterative FT-based algorithm is developed whereby the projected current is reconstructed on any slice using as data the Laplacian of the z-component of magnetic flux density measured for that slice. In an injected current MRCDI scenario, the current is not divergence free on the boundary of the object. The method developed in this study also handles this situation.

  10. Reconstruction of conductivity and current density images using only one component of magnetic field measurements.

    Science.gov (United States)

    Seo, Jin Keun; Yoon, Jeong-Rock; Woo, Eung Je; Kwon, Ohin

    2003-09-01

    Magnetic resonance current density imaging (MRCDI) is to provide current density images of a subject using a magnetic resonance imaging (MRI) scanner with a current injection apparatus. The injection current generates a magnetic field that we can measure from MR phase images. We obtain internal current density images from the measured magnetic flux densities via Ampere's law. However, we must rotate the subject to acquire all of the three components of the induced magnetic flux density. This subject rotation is impractical in clinical MRI scanners when the subject is a human body. In this paper, we propose a way to eliminate the requirement of subject rotation by careful mathematical analysis of the MRCDI problem. In our new MRCDI technique, we need to measure only one component of the induced magnetic flux density and reconstruct both cross-sectional conductivity and current density images without any subject rotation.

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

    DEFF Research Database (Denmark)

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

    2007-01-01

    The relative merits of current-spin-density- and spin-density-functional theory are investigated for solids treated within the exact-exchange-only approximation. Spin-orbit splittings and orbital magnetic moments are determined at zero external magnetic field. We find that for magnetic (Fe, Co...

  12. Theoretical Modeling of Internal Hydraulic Jump in Density Currents

    CERN Document Server

    Firoozabadi, Bahar; Aryanfar, Asghar; Afshin, Hossein

    2013-01-01

    In this paper, we propose an analytical framework for internal hydraulic jumps. Density jumps or internal hydraulic jumps occur when a supper critical flow of water discharges into a stagnant layer of water with slightly different density. The approach used here is control volume method which is also used to analyze ordinary hydraulic jumps. The important difference here is that entrainment is taken into account. Using conservation equations with the aid of some simplifying assumptions we come to an equation that gives jump downstream height as function of jump upstream characteristics and the entrainment. To determine the magnitude of downstream height we use an experimental equation for calculating the entrainment. Finally we verify our framework by comparing the height that we gain from the derived equation with some experimental data.

  13. Analysis of recoverable current from one component of magnetic flux density in MREIT and MRCDI.

    Science.gov (United States)

    Park, Chunjae; Lee, Byung Il; Kwon, Oh In

    2007-06-01

    Magnetic resonance current density imaging (MRCDI) provides a current density image by measuring the induced magnetic flux density within the subject with a magnetic resonance imaging (MRI) scanner. Magnetic resonance electrical impedance tomography (MREIT) has been focused on extracting some useful information of the current density and conductivity distribution in the subject Omega using measured B(z), one component of the magnetic flux density B. In this paper, we analyze the map Tau from current density vector field J to one component of magnetic flux density B(z) without any assumption on the conductivity. The map Tau provides an orthogonal decomposition J = J(P) + J(N) of the current J where J(N) belongs to the null space of the map Tau. We explicitly describe the projected current density J(P) from measured B(z). Based on the decomposition, we prove that B(z) data due to one injection current guarantee a unique determination of the isotropic conductivity under assumptions that the current is two-dimensional and the conductivity value on the surface is known. For a two-dimensional dominating current case, the projected current density J(P) provides a good approximation of the true current J without accumulating noise effects. Numerical simulations show that J(P) from measured B(z) is quite similar to the target J. Biological tissue phantom experiments compare J(P) with the reconstructed J via the reconstructed isotropic conductivity using the harmonic B(z) algorithm.

  14. On Dynamic Range Limitations of CMOS Current Conveyors

    DEFF Research Database (Denmark)

    Bruun, Erik

    1999-01-01

    This paper is concerned with the dynamic range of continuous time CMOS current mode circuits. As a representative current mode device a class AB current conveyor is examined. First, the voltage input range of the high impedance Y input is investigated. Next, the current input range of the low...... frequency band and for the situation where the conveyor is used over the full bandwidth achievable. Finally, the optimisation of the current input range is related to the distortion characteristics and it is pointed out that to a first order approximation the distortion is independent of the current range....... impedance X input is investigated. It is compared to the thermal noise in the X to Z signal path in order to evaluate the dynamic range, and the dependencies of the dynamic range on the supply voltage and the transistor lay-out is derived, both for the situation where the conveyor is used over a narrow...

  15. DISCONTINUOUS FLOW OF TURBID DENSITY CURRENTS I. CHANNEL EXPANSION AND CONTRACTION

    Institute of Scientific and Technical Information of China (English)

    Jiahua FAN

    2005-01-01

    Laboratory experiments on turbid density currents were conducted to observe the flow features of these currents with abrupt contracted and expanded reaches. Experimental data were used to determine water entrainment coefficients for both channel expansion and contraction. Expressions for turbid density currents with water entrainment coefficients in abrupt contracted and expanded reaches were derived,and compared with experimental data.

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

    Science.gov (United States)

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

    2016-08-01

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

  17. Electrochemical Characterization of PEMECs Operating at Various Current Densities

    DEFF Research Database (Denmark)

    Elsøe, Katrine; G.-Madsen, Laila; Scherer, Guenther G.

    2016-01-01

    be applied to gain insight into the relative magnitudes of resistance contributions from the two electrodes, the electrolyte and of mass transfer limitations and can help identifying the time scale of the respective processes. The gained knowledge may facilitate further development of the PEMECs....

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-03-28

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

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

    Science.gov (United States)

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

    2016-01-01

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

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

    Science.gov (United States)

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

    1992-01-01

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

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

    Science.gov (United States)

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

    2017-03-08

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

  3. Novel Topology of Saturated-core Fault Current Limiter

    NARCIS (Netherlands)

    Cvoric, D.

    2010-01-01

    Increasing levels of fault currents in utility grids are expected to result in mechanical and thermal overstresses of different power system components. To cope with these increased levels, expensive upgrades and replacements of currently employed Circuit Breakers might be required in the near futur

  4. Dependence of the critical current density on the first matching field density

    Energy Technology Data Exchange (ETDEWEB)

    Obaidat, I.M. [Department of Physics, United Arab Emirates University, Al-Ain 17551 (United Arab Emirates)], E-mail: iobaidat@uaeu.ac.ae; Benkraouda, M.; Khawaja, U. Al [Department of Physics, United Arab Emirates University, Al-Ain 17551 (United Arab Emirates)

    2008-10-01

    Molecular dynamic simulations were carried out to investigate the properties of the critical depinning force in high temperature superconductors at several vortex densities at the first matching field. The study was conducted on samples with periodic square arrays of vortices and pinning sites. The variables in the simulations were the vortex density, the pinning sites density, the temperature, the pinning strength, the size of pinning sites. The critical depinning force is found to decrease with temperature for all first matching field densities. The rate of this decrease was found to be slower as the pinning strength and size of pinning site gets larger. At low temperatures and for large pinning strengths, the critical depinning force was found to decrease with increasing the first matching field density. But very interesting results were obtained at moderate temperatures where the critical depinning force was found to increase as the first matching field density increases. The same behavior of the critical depinning force was found at low temperatures, for small pinning strengths. These unexpected results were attributed to a vortex structural phase transition from a disordered state to an ordered state.

  5. Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

    Institute of Scientific and Technical Information of China (English)

    WANG Lijun; JIA Shenli; SHI Zongqian

    2008-01-01

    In this study, the influence of the initial jet angles (IJAs) and ion number densities (INDs) at the cathode side on the low current vacuum arc (LCVA) characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.

  6. Engineering Critical Current Density Improvement in Ag- Bi-2223 Tapes

    DEFF Research Database (Denmark)

    Wang, W. G.; Seifi, Behrouz; Eriksen, Morten

    2000-01-01

    round wire as a preform prior to the flat rolling that achieved more homogenous filament distribution. Filament geometry and density were simulated by Finite Element Modeling. The tapes with large filling factor up to 45 % have been produced with a hard metal outer sheath, which facilitates...... the superconductor composite sustaining large proportional oxide ceramics in the composite during drawing and rolling process. By optimization of the thermal and mechanical process, a Je of 12 kA/cm2 has been achieved in a 0.183.1 mm2 size tape which carried 67 A...... factor of the tapes. Phase evolution at initial sintering stage has been studied by a quench experiment in Ag-Bi-2223 tapes. The content, texture, and microstructure of various phases were determined by XRD and SEM. A novel process approach has been invented in which square wire was chosen rather than...

  7. A Novel Explanation of the Greenwald Density Limit-Thermal-Resistive Tearing Mode

    Science.gov (United States)

    Teng, Qian; Brennan, Dylan; Delgado-Aparicio, Luis; Gates, David; Swerdlow, Josh; White, Roscoe

    2015-11-01

    R.B. White et. al. showed that the asymmetry of a magnetic island created by a tearing mode is crucial to understand its evolution. An island is thermally isolated, the internal temperature given by the balance of radiation loss and Ohmic heating. When radiation loss from the island dominates, the cooling of the island, coupled to the asymmetry, can cause rapid growth, leading to a potential mechanism to explain the Greenwald density limit. In this work we successfully reproduced the density limit with experiment-relevant parameters using this model. Using simple equilibrium profiles and assuming internal inductance evolution with density, we simulated the equilibrium evolution as a function of density. The modeling of internal inductance is motivated by D.A. Gates and L. Delgado-Aparicio's finding that the density limit is accompanied with internal inductance increasing. Given reasonable numbers for geometric size, electric and magnetic field, we calculated power balance inside island. The simulation showed local power balance criterion agrees with the density limit within 2%. The very sharp limit is determined by the strong dependence of radiative loss on density. Next work is to use a toroidal model and experimentally obtained equilibria to compare with experiments directly.

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

    Science.gov (United States)

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

    2006-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Gravier, L [Institut de Physique des Nanostructures, Ecole Polytechnique Federale de Lausanne (EPFL), EPFL-SB-IPN station 3, 1015 Lausanne (Switzerland); Fukushima, A [National Institute of Advances Industrial Science and Technology (AIST) 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Kubota, H [National Institute of Advances Industrial Science and Technology (AIST) 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Yamamoto, A [National Institute of Advances Industrial Science and Technology (AIST) 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Yuasa, S [National Institute of Advances Industrial Science and Technology (AIST) 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

    2006-12-21

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

  10. Equilibria and Stability of JET Discharges with Zero Core Current Density

    Energy Technology Data Exchange (ETDEWEB)

    B.C. Stratton; N.C. Hawkes; G.T.A. Huysmans; J.A. Breslau; L.E. Zakharov; B. Alper; R.V. Budny; C.D. Challis; R. Deangelis; V. Drozdov; C. Fenzi; C. Giroud; T.C. Hender; J. Hobirk; S.C. Jardin; E. Joffrin; P.J. Lomas; P. Lotte; J. Mailloux; W. Park; E. Rachlew; S. Reyes-Cortes; E. Solano; T. Tala; K-D. Zastrow; JET-EFDA Contributors

    2002-10-15

    Injection of Lower Hybrid Heating and Current Drive (LHCD) into the current ramp-up phase of JET [Joint European Torus] discharges can produce extremely reversed q-profiles characterized by a core region of near zero current density (within Motional Stark Effect diagnostic measurement errors). Non-inductive, off-axis co-current drive induces a back electromotive force inside the non-inductive current radius that drives a negative current in the plasma core. The core current density does not go negative, although current diffusion calculations indicate that there is sufficient LHCD to cause this. The clamping of the core current density near zero is consistent with n=0 reconnection events redistributing the core current soon after it goes negative. This is seen in reduced MHD simulations and in nonlinear resistive MHD simulations which predict that these discharges undergo n=0 reconnection events that clamp the core current near zero.

  11. Current limitation in low-voltage grids; Strombegrenzung fuer Niederspannungsnetze

    Energy Technology Data Exchange (ETDEWEB)

    Verstraate, F. [Schneider Electric GmbH, Ratingen (Germany)

    1997-12-31

    The electricity supply grids operated by public utilities, industrial enterprises etc. are faced with a further significant increase of their delivery capacity. In view of the high power density that is already available, this means a further increase of power plant capacities and additional meshing of network structures. (orig.) [Deutsch] Die elektrischen Netze von Industrie, EVUs usw. stehen in den naechsten Jahren vor einer weiteren erheblichen Steigerung ihrer Abgabeleistung. Bei der bereits vorhandenen hohen Leistungsdichte ergibt sich daraus die Notwendigkeit, sowohl die Kraftwerkskapazitaeten zu erhoehen als auch eine zusaetzliche Vermaschung der Netzstruktur vorzunehmen. (orig.)

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

    Science.gov (United States)

    Akande, Akinlolu; Sanvito, Stefano

    2016-11-01

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

  13. Density-Driven Currents and Deposition of Fine Materials

    DEFF Research Database (Denmark)

    Saremi, Sina

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

  14. Assessment of the impact of HTSCs on superconducting fault-current limiters

    Energy Technology Data Exchange (ETDEWEB)

    Giese, R.F. [Argonne National Lab., IL (United States); Runde, M. [Energiforsyningens Forskningsinstitutt A/S, Trondheim (Norway)

    1993-03-01

    The possible impact of nitrogen-cooled superconductors on the desip and cost of superconducting fault-current limiters is assessed by considering the technical specifications such devices must meet and by comparing material properties of 77-K and 4-K superconductors. The main advantages of operating superconductors at 77 K are that the refrigeration operating cost is reduced by a factor of up to 25 and the refrigeration capital cost is reduced by a factor of up to 10. The heat capacity is several orders of magnitude Larger at 77 K and at 4 K. This phenomenon increases conductor stability against flux jumps but makes switching from the superconducting to the normal state slow and difficult. Therefore, a high critical current density, probably at least 10{sup 5} A/cm{sup 2}, is required.

  15. Proceedings of the 1979 workshop on beam current limitations in storage rings, July 16-27, 1979

    Energy Technology Data Exchange (ETDEWEB)

    Pellegrini, C. (ed.)

    1979-01-01

    The Workshop on Beam Current Limitations in Storage Rings was held at Brookhaven National Laboratory from July 16 to 27, 1979. The purpose of this Workshop was to discuss the physical mechanisms limiting the beam current or current density in accelerators or storage rings. Many of these machines are now being built or planned for a variety of applications, such as colliding beam experiments, synchrotron light production, heavy ion beams. This diversity was reflected in the Workshop and in the papers which have been contributed to these Proceedings. The twenty-one papers from the workshop were incorporated individually in the data base. (GHT)

  16. The non-thermal origin of the tokamak low-density stability limit

    Science.gov (United States)

    Paz-Soldan, C.; La Haye, R. J.; Shiraki, D.; Buttery, R. J.; Eidietis, N. W.; Hollmann, E. M.; Moyer, R. A.; Boom, J. E.; Chapman, I. T.; Contributors, JET

    2016-05-01

    DIII-D plasmas at very low density exhibit the onset of n  =  1 error field (EF) penetration (the ‘low-density locked mode’) not at a critical density or EF, but instead at a critical level of runaway electron (RE) intensity. Raising the density during a discharge does not avoid EF penetration, so long as RE growth proceeds to the critical level. Penetration is preceded by non-thermalization of the electron cyclotron emission, anisotropization of the total pressure, synchrotron emission shape changes, as well as decreases in the loop voltage and bulk thermal electron temperature. The same phenomena occur despite various types of optimal EF correction, and in some cases modes are born rotating. Similar phenomena are also found at the low-density limit in JET. These results stand in contrast to the conventional interpretation of the low-density stability limit as being due to residual EFs and demonstrate a new pathway to EF penetration instability due to REs. Existing scaling laws for penetration project to increasing EF sensitivity as bulk temperatures decrease, though other possible mechanisms include classical tearing instability, thermo-resistive instability, and pressure-anisotropy driven instability. Regardless of the first-principles mechanism, known scaling laws for Ohmic energy confinement combined with theoretical RE production rates allow rough extrapolation of the RE criticality condition, and thus the low-density limit, to other tokamaks. The extrapolated low-density limit by this pathway decreases with increasing machine size and is considerably below expected operating conditions for ITER. While likely unimportant for ITER, this effect can explain the low-density limit of existing tokamaks operating with small residual EFs.

  17. The density dilemma: limitations on juvenile production in threatened salmon populations

    Science.gov (United States)

    Walters, Annika W.; Copeland, Timothy; Venditti, David A.

    2013-01-01

    Density-dependent processes have repeatedly been shown to have a central role in salmonid population dynamics, but are often assumed to be negligible for populations at low abundances relative to historical records. Density dependence has been observed in overall spring/summer Snake River Chinook salmon Oncorhynchus tshawytscha production, but it is not clear how patterns observed at the aggregate level relate to individual populations within the basin. We used a Bayesian hierarchical modelling approach to explore the degree of density dependence in juvenile production for nine Idaho populations. Our results indicate that density dependence is ubiquitous, although its strength varies between populations. We also investigated the processes driving the population-level pattern and found density-dependent growth and mortality present for both common life-history strategies, but no evidence of density-dependent movement. Overwinter mortality, spatial clustering of redds and limited resource availability were identified as potentially important limiting factors contributing to density dependence. The ubiquity of density dependence for these threatened populations is alarming as stability at present low abundance levels suggests recovery may be difficult without major changes. We conclude that density dependence at the population level is common and must be considered in demographic analysis and management.

  18. Limitations of eddy current testing in a fast reactor environment

    Science.gov (United States)

    Wu, Tao; Bowler, John R.

    2016-02-01

    The feasibility of using eddy current probes for detecting flaws in fast nuclear reactor structures has been investigated with the aim of detecting defects immersed in electrically conductive coolant including under liquid sodium during standby. For the inspections to be viable, there is a need to use an encapsulated sensor system that can be move into position with the aid of visualization tools. The initial objective being to locate the surface to be investigated using, for example, a combination of electromagnetic sensors and sonar. Here we focus on one feature of the task in which eddy current probe impedance variations due to interaction with the external surface of a tube are evaluated in order to monitor the probe location and orientation during inspection.

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

    Science.gov (United States)

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

    2014-01-21

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Tellgren, E. I., E-mail: erik.tellgren@kjemi.uio.no; Lange, K. K.; Ekström, U.; Helgaker, T. [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); Teale, A. M., E-mail: andrew.teale@nottingham.ac.uk [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Furness, J. W. [School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)

    2014-01-21

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

  1. Variation of Eddy Current Density Distribution and its Effect on Crack Signal in Eddy Current Non-Destructive of Testing

    Directory of Open Access Journals (Sweden)

    Ladislav Janousek

    2006-01-01

    Full Text Available The paper deals with variation of eddy current density distribution along material depth and investigates an effect of the variation on a crack signal in eddy current non-destructive testing. Four coaxial rectangular tangential coils are used to induce eddy currents in a tested conductive object. The exciting coils are driven independently by phase-shifted AC currents; a ratio of amplitudes of the exciting currents is continuously changed to vary the distribution of eddy current density along material depth under a circular pick-up coil positioned in centre between the exciting coils. Dependences of a crack signal amplitude and its phase on the ratio are evaluated and special features are extracted. It is revealed that the dependences are strongly influenced by depth of a crack, and thus the extracted features can enhance evaluation of a detected crack.

  2. Current status of nuclear medicine in chronic airflow limitation

    Energy Technology Data Exchange (ETDEWEB)

    Clarke, S.W.; Agnew, J.E.

    1987-06-01

    Radionuclide imaging, quite apart from its role in the diagnosis of pulmonary embolism, offers information about the distribution of ventilatory and perfusion abnormalities within the lung. The extent of ventilatory abnormality seen can be related to the severity of airways obstruction as assessed spirometrically, whilst abnormalities in the matching of perfusion to ventilation can be related to the severity of hypoxaemia in patients with chronic airflow limitation. Clearance of mucus from the lungs of patients with chronic mucus hypersection may be assessed by following the clearance rate of insoluble radioaerosol particles; by such means the relative contributions of mucociliary transport and of cough to the overall clearance can be observed. Clearance is often severely impaired in patients with airways obstruction; the radioaerosol technique can be used to determine the effects of drug or physiotherapy treatment. Chronic airflow limitation leading to hypoxaemia can be associated with pulmonary artery hypertension and right ventricular hypertrophy - this may be investigated noninvasively by a radionuclide test of right ventricular ejection fraction.

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

    Science.gov (United States)

    Bovery, Caitlin M; Wyneken, Jeanette

    2015-01-01

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

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

    Science.gov (United States)

    Bovery, Caitlin M.; Wyneken, Jeanette

    2015-01-01

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

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

    Science.gov (United States)

    Palma, John; Mil'shtein, Samson

    2011-12-01

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

  6. Density limit of H-mode plasmas on JET-ILW

    Energy Technology Data Exchange (ETDEWEB)

    Huber, A., E-mail: a.huber@fz-juelich.de [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, Trilateral Euregio Cluster, 52425 Jülich (Germany); Brezinsek, S.; Sergienko, G. [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, Trilateral Euregio Cluster, 52425 Jülich (Germany); Groth, M. [Aalto University, Otakaari 4, 02015 Espoo (Finland); Vries, P.C. de [ITER Organisation, 13115 St Paul Lez Durance (France); Aho-Mantila, L. [VTT Technical Research Centre of Finland, 02044 VTT (Finland); Arnoux, G. [Culham Centre for Fusion Energy, Abingdon OX14 3DB (United Kingdom); Bernert, M. [Max-Planck-Institut für Plasmaphysik, D-85748 Garching (Germany); Beurskens, M.N.A. [Culham Centre for Fusion Energy, Abingdon OX14 3DB (United Kingdom); Calabro, G. [ENEA, Via Enrico Ferri 46, I-0044 Frascati (Italy); Clever, M.; Esser, H.G. [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, Trilateral Euregio Cluster, 52425 Jülich (Germany); Guillemaut, C. [CEA, IRFM, 13108 St Paul lez Durance (France); Jachmich, S. [Laboratory for Plasma Physics, ERM/KMS, B-1000 Brussels (Belgium); Järvinen, A. [Aalto University, Otakaari 4, 02015 Espoo (Finland); Linsmeier, Ch. [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, Trilateral Euregio Cluster, 52425 Jülich (Germany); Matthews, G.F.; Meigs, A.G. [Culham Centre for Fusion Energy, Abingdon OX14 3DB (United Kingdom); and others

    2015-08-15

    High-density discharges on JET with ITER-like Wall (ILW) have been analysed with the aim of establishing a mechanism for the H-mode density limit (DL) and compared with experiments in the JET carbon material configuration. The density limit is up to 20% higher in the JET-ILW than in the JET-C machine. The observed H-mode density limit is found close to the Greenwald limit. It is sensitive to the main plasma shape and is almost independent of the heating power. It has been observed that the transition from H-mode to L-mode is not always an abrupt event but may exhibit a series of H–L–H transitions, the so-called “dithering H-mode”. It was observed that detachment, as well as the X-point MARFE itself, does not trigger the H–L transition and thus does not present a limit on the plasma density and that it is the plasma confinement which is ultimately responsible for the H-mode DL.

  7. PRA: A PERSPECTIVE ON STRENGTHS, CURRENT LIMITATIONS, AND POSSIBLE IMPROVEMENTS

    Directory of Open Access Journals (Sweden)

    ALI MOSLEH

    2014-02-01

    Full Text Available Probabilistic risk assessment (PRA has been used in various technological fields to assist regulatory agencies, managerial decision makers, and systems designers in assessing and mitigating the risks inherent in these complex arrangements. Has PRA delivered on its promise? How do we gage PRA performance? Are our expectations about value of PRA realistic? Are there disparities between what we get and what we think we are getting form PRA and its various derivatives? Do current PRAs reflect the knowledge gained from actual events? How do we address potential gaps? These are some of the questions that have been raised over the years since the inception of the field more than forty years ago. This paper offers a brief assessment of PRA as a technical discipline in theory and practice, its key strengths and weaknesses, and suggestions on ways to address real and perceived shortcomings.

  8. On the phase diagram of the extended Hubbard model with intersite density-density interactions in the atomic limit

    Science.gov (United States)

    Kapcia, Konrad Jerzy; Robaszkiewicz, Stanisław

    2016-11-01

    The charge ordering is a phenomenon associated with inhomogeneous distribution of electron density occurring mostly in strongly correlated materials such as transition metal oxides or organic conductors. The extended Hubbard model (EHM) is one of the simplest model for description of this phenomenon. The full phase diagram of the EHM with intersite density-density interactions W1 and W2 (nearest- and next-nearest-neighbour, respectively) in the atomic limit as a function of the chemical potential has been derived in the variational approach, which treats the on-site interaction exactly and the intersite interactions within mean-field approximation. The results for arbitrary values of model parameters (in the two-sublattice assumption) reveal that the diagram has very complex structure including various (multi-)critical points. A variety of the transitions between different phases, in particular with long-range charge-order, has been found to occur on the diagram. The results presented are rigorous ones in the high-dimension limit for any W1 and W2 ≤ 0.

  9. Fighting Sharka in Peach: Current Limitations and Future Perspectives

    Science.gov (United States)

    Cirilli, Marco; Geuna, Filippo; Babini, Anna R.; Bozhkova, Valentina; Catalano, Luigi; Cavagna, Beniamino; Dallot, Sylvie; Decroocq, Véronique; Dondini, Luca; Foschi, Stefano; Ilardi, Vincenza; Liverani, Alessandro; Mezzetti, Bruno; Minafra, Angelantonio; Pancaldi, Marco; Pandolfini, Tiziana; Pascal, Thierry; Savino, Vito N.; Scorza, Ralph; Verde, Ignazio; Bassi, Daniele

    2016-01-01

    Sharka, caused by Plum Pox Virus (PPV), is by far the most important infectious disease of peach [P. persica (L.) Batsch] and other Prunus species. The progressive spread of the virus in many important growing areas throughout Europe poses serious issues to the economic sustainability of stone fruit crops, peach in particular. The adoption of internationally agreed-upon rules for diagnostic tests, strain-specific monitoring schemes and spatial–temporal modeling of virus spread, are all essential for a more effective sharka containment. The EU regulations on nursery activity should be modified based on the zone delimitation of PPV presence, limiting open-field production of propagation materials only to virus-free areas. Increasing the efficiency of preventive measures should be augmented by the short-term development of resistant cultivars. Putative sources of resistance/tolerance have been recently identified in peach germplasm, although the majority of novel resistant sources to PPV-M have been found in almond. However, the complexity of introgression from related-species imposes the search for alternative strategies. The use of genetic engineering, particularly RNA interference (RNAi)-based approaches, appears as one of the most promising perspectives to introduce a durable resistance to PPV in peach germplasm, notwithstanding the well-known difficulties of in vitro plant regeneration in this species. In this regard, rootstock transformation to induce RNAi-mediated systemic resistance would avoid the transformation of numerous commercial cultivars, and may alleviate consumer resistance to the use of GM plants. PMID:27625664

  10. Fighting Sharka in Peach: Current Limitations and Future Perspectives

    Directory of Open Access Journals (Sweden)

    Marco Cirilli

    2016-08-01

    Full Text Available Sharka, caused by Plum Pox Virus (PPV, is by far the most important infectious disease of peach [P. persica (L. Batsch] and other Prunus species. The progressive spread of the virus in many important growing areas throughout Europe poses serious issues to the economic sustainability of stone fruit crops, peach in particular. The adoption of internationally agreed-upon rules for diagnostic tests, strain-specific monitoring schemes and spatial-temporal modeling of virus spread, are all essential for a more effective sharka containment. The EU regulations on nursery activity should be modified based on the zone delimitation of PPV presence, limiting open-field production of propagation materials only to virus-free areas. Increasing the efficiency of preventive measures should be augmented by the short-term development of resistant cultivars. Putative sources of resistance/tolerance have been recently identified in peach germplasm, although the majority of novel resistant sources to PPV-M have been found in almond. However, the complexity of introgression from related-species imposes the search for alternative strategies. The use of genetic engineering, particularly RNAi-based approaches, appears as one of the most promising perspectives to introduce a durable resistance to PPV in peach germplasm, notwithstanding the well-known difficulties of in vitro plant regeneration in this species. In this regard, rootstock transformation to induce RNAi-mediated systemic resistance to PPV would avoid the transformation of numerous commercial cultivars, and may alleviate consumer resistance to the use of GM plants.

  11. High Current Density and Low Thermal Conductivity of Atomically Thin Semimetallic WTe2.

    Science.gov (United States)

    Mleczko, Michal J; Xu, Runjie Lily; Okabe, Kye; Kuo, Hsueh-Hui; Fisher, Ian R; Wong, H-S Philip; Nishi, Yoshio; Pop, Eric

    2016-08-23

    Two-dimensional (2D) semimetals beyond graphene have been relatively unexplored in the atomically thin limit. Here, we introduce a facile growth mechanism for semimetallic WTe2 crystals and then fabricate few-layer test structures while carefully avoiding degradation from exposure to air. Low-field electrical measurements of 80 nm to 2 μm long devices allow us to separate intrinsic and contact resistance, revealing metallic response in the thinnest encapsulated and stable WTe2 devices studied to date (3-20 layers thick). High-field electrical measurements and electrothermal modeling demonstrate that ultrathin WTe2 can carry remarkably high current density (approaching 50 MA/cm(2), higher than most common interconnect metals) despite a very low thermal conductivity (of the order ∼3 Wm(-1) K(-1)). These results suggest several pathways for air-stable technological viability of this layered semimetal.

  12. The Effect of Ion Current Density on Target Etching in Radio Frequency-Magnetron Sputtering Process

    Institute of Scientific and Technical Information of China (English)

    王庆; 王永富; 巴德纯; 岳向吉

    2012-01-01

    The effect of ion current density of argon plasma on target sputtering in magnetron sputtering process was investigated. Using home-made ion probe with computer-based data acquisition system, the ion current density as functions of discharge power, gas pressure and positions was measured. A double-hump shape was found in ion current density curve after the analysis of the effects of power and pressure. The data demonstrate that ion current density increases with the increase in gas pressure in spite of slightly at the double-hump site, sharply at wave-trough and side positions. Simultaneously, the ion current density increases upon increase in power. Es- pecially, the ion current density steeply increases at the double-hump site. The highest energy of the secondary electrons arising from Larmor precession was found at the double-hump position, which results in high ion density. The target was etched seriously at the double-hump position due to the high ion density there. The data indicates that the increase in power can lead to a high sputtering speed rate.

  13. Charged impurity scattering limited low temperature resistivity of low density silicon inversion layers

    OpenAIRE

    Sarma, S. Das; Hwang, E. H.

    1998-01-01

    We calculate within the Boltzmann equation approach the charged impurity scattering limited low temperature electronic resistivity of low density $n$-type inversion layers in Si MOSFET structures. We find a rather sharp quantum to classical crossover in the transport behavior in the $0 - 5$K temperature range, with the low density, low temperature mobility showing a strikingly strong non-monotonic temperature dependence, which may qualitatively explain the recently observed anomalously strong...

  14. Role of edge turbulence and shear flows in density limit on HL-2A tokamak

    Science.gov (United States)

    Hong, Rongjie; Tynan, George; Xu, Min; Nie, Lin; Guo, Dong; Ke, Rui; Long, Ting; Wu, Yifang; Yuan, Boda

    2016-10-01

    The tokamak density limit has long been suspected as a consequence of the enhanced turbulent transport in edge plasmas. In this study, evolutions of the turbulence and shear flows were investigated at different normalized density ne /nG in the plasma boundary region of HL-2A tokamak using Langmuir probes. As the density limit was approached, the equilibrium profile of density was flattened in the Scrape-Off Layer (SOL) and steepened inside the separatrix, while the edge cooling was observed from the electron temperature profile. The turbulent cross-field transport also increased substantially with the ne /nG and the collisionality. In addition, the amplitude of the poloidal phase velocity decreased at higher densities. This destruction of the shear layer was associated with the collapse of the Reynolds stress and thus the reduction in the nonlinear energy transfer from high-frequency fluctuations to low-frequency shear flows. These observations indicate an important role of the edge turbulence and the turbulence-driven shear flow in the underlying physics of tokamak density limit. Thank the HL-2A team for machine operation. Partly supported by DOE Grant No. DE-SC0008378.

  15. Vortex-lattice pinning and critical current density in anisotropic high-temperature superconductors

    Science.gov (United States)

    Li, Yingxu; Li, Xiangyu; Kang, Guozheng; Gao, Yuanwen

    2016-10-01

    The anisotropy of critical current density is an impressive manifestation in the physics of high-temperature superconductors. We develop an analytical characterization of anisotropic flux-lattice pinning and critical current density in a system of random point defects. The effect of superconducting anisotropy on the pinning force and critical current density is formulated. The in-plane/out-of-plane anisotropy and microscopic characteristic lengths are incorporated in the field and angular dependence of the critical current density. This is helpful in understanding the physical essence of the scaling behavior in the experiments for critical current anisotropy. We discuss the role of strong and weak point defects in the anisotropic flux-lattice pinning. Relevance of the theory to the critical-state model is dictated as well.

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

    Science.gov (United States)

    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

  17. Influence of High-Current-Density Impulses on the Compression Behavior: Experiments with Iron and a Nickel-Based Alloy

    Science.gov (United States)

    Demler, E.; Gerstein, G.; Dalinger, A.; Epishin, A.; Rodman, D.; Nürnberger, F.

    2017-01-01

    Difficulties of processing of high strength and/or brittle materials by plastic deformation, e.g., by forging, require to develop new industrial technologies. In particular, the feasible deformation rates are limited for low-ductile metallic materials. For this reason, processes were investigated to improve the deformability in which electrical impulses are to be applied to lower the yield strength. However, owing to the impulse duration and low current densities, concomitant effects always occur, e.g., as a result of Joule heating. Current developments in power electronics allow now to transmit high currents as short pulses. By reducing the impulse duration and increasing the current density, the plasticity of metallic materials can be correspondingly increased. Using the examples of polycrystalline iron and a single-crystal, nickel-based alloy (PWA 1480), current advances in the development of methods for forming materials by means of high-current-density impulses are demonstrated. For this purpose, appropriate specimens were loaded in compression and, using novel testing equipment, subjected to a current strength of 10 kA with an impulse duration of 2 ms. For a pre-defined strain, the test results show a significant decrease in the compressive stress during the compression test and a significant change in the dislocation distribution following the current impulse treatment.

  18. Influence of High-Current-Density Impulses on the Compression Behavior: Experiments with Iron and a Nickel-Based Alloy

    Science.gov (United States)

    Demler, E.; Gerstein, G.; Dalinger, A.; Epishin, A.; Rodman, D.; Nürnberger, F.

    2016-12-01

    Difficulties of processing of high strength and/or brittle materials by plastic deformation, e.g., by forging, require to develop new industrial technologies. In particular, the feasible deformation rates are limited for low-ductile metallic materials. For this reason, processes were investigated to improve the deformability in which electrical impulses are to be applied to lower the yield strength. However, owing to the impulse duration and low current densities, concomitant effects always occur, e.g., as a result of Joule heating. Current developments in power electronics allow now to transmit high currents as short pulses. By reducing the impulse duration and increasing the current density, the plasticity of metallic materials can be correspondingly increased. Using the examples of polycrystalline iron and a single-crystal, nickel-based alloy (PWA 1480), current advances in the development of methods for forming materials by means of high-current-density impulses are demonstrated. For this purpose, appropriate specimens were loaded in compression and, using novel testing equipment, subjected to a current strength of 10 kA with an impulse duration of 2 ms. For a pre-defined strain, the test results show a significant decrease in the compressive stress during the compression test and a significant change in the dislocation distribution following the current impulse treatment.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-12-31

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

  20. Current density and conductivity through modified gravity in the graphene with defects

    CERN Document Server

    Sepehri, Alireza; Bamba, Kazuharu; Capozziello, Salvatore; Saridakis, Emmanuel N

    2016-01-01

    We propose a model describing the evolution of the free electron current density in graphene. Based on the concept of Mp-branes, we perform the analysis using the difference between curvatures of parallel and antiparallel spins. In such a framework an effective graviton emerges in the form of gauge field exchange between electrons. In a plain graphene system, the curvatures produced by both kinds of spins neutralize each other. However, in the presence of defects, the inequality between curvatures leads to the emergence of current density, modified gravity and conductivity. Depending on the type of the defects, the resulting current density can be negative or positive.

  1. Depairing current density through a low-angle grain boundary in a superconducting film

    Directory of Open Access Journals (Sweden)

    Feng Xue

    2016-05-01

    Full Text Available In this paper, the effect of a grain boundary (GB on the depairing current density of a high-temperature superconducting film is investigated. The modified effective free energy is proposed by considering the interaction of the superconducting condensate with the deformation of the superconductor due to the dislocations which constitute a grain boundary. After the elastic strain field of the dislocation is obtained, we analyzed the depress effect of the GB on the depairing current density of a superconducting film. The results are qualitatively agreement with the classic exponential relationship with the misorientation angles of the critical current density of high-temperature superconductors.

  2. Effects of Electron Flow Current Density on Flow Impedance of Magnetically Insulated Transmission Lines

    Institute of Scientific and Technical Information of China (English)

    HE Yong; ZOU Wen-Kang; SONG Sheng-Yi

    2011-01-01

    @@ In modern pulsed power systems, magnetically insulated transmission lines (MITLs) are used to couple power between the driver and the load.The circuit parameters of MITLs are well understood by employing the concept of Sow impedance derived from Maxwell's equations and pressure balance across the flow.However, the electron density in an MITL is always taken as constant in the application of flow impedance.Thus effects of electron flow current density (product of electron density and drift velocity) in an MITL are neglected.We calculate the flow impedances of an MITL and compare them under three classical MITL theories, in which the electron density profile and electron flow current density are different from each other.It is found that the assumption of constant electron density profile in the calculation of the Sow impedance is not always valid.The electron density profile and the electron flow current density have significant effects on flow impedance of the MITL.The details of the electron flow current density and its effects on the operation impedance of the MITL should be addressed more explicitly experiments and theories in the future.

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

    Science.gov (United States)

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

    2012-01-01

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

  4. Steady-state probability density function in wave turbulence under large volume limit

    Institute of Scientific and Technical Information of China (English)

    Yeontaek Choia; Sang Gyu Job

    2011-01-01

    We investigate the possibility for two-mode probability density function (PDF) to have a non-zero flux steady state solution. We take the large volume limit so that the space of modes becomes continuous. It is shown that in this limit all the steady-state two- or higher-mode PDFs are the product of one-mode PDFs. The flux of this steady-state solution turns out to be zero for any finite mode PDF.

  5. Electromigration in Sn–Ag solder thin films under high current density

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, X. [School of Computing and Mathematical Sciences, University of Greenwich, 30 Park Row, London SE10 9LS (United Kingdom); Kotadia, H. [Physics Department, School of Natural and Mathematical Sciences, King' s College London, Strand, London WC2R 2LS (United Kingdom); Xu, S. [Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kow-loon Tong, Hong Kong (China); Lu, H. [School of Computing and Mathematical Sciences, University of Greenwich, 30 Park Row, London SE10 9LS (United Kingdom); Mannan, S.H. [Physics Department, School of Natural and Mathematical Sciences, King' s College London, Strand, London WC2R 2LS (United Kingdom); Bailey, C. [School of Computing and Mathematical Sciences, University of Greenwich, 30 Park Row, London SE10 9LS (United Kingdom); Chan, Y.C. [Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kow-loon Tong, Hong Kong (China)

    2014-08-28

    The electro-migration behavior of a Sn–Ag solder thin film stripe that is deposited on a glass substrate has been investigated under a high current density in the absence ofthermo-migration. The distribution of voids and hillocks at current densities of 4.4–6.0 × 10{sup 4} A/cm{sup 2} has been analyzed optically and using electron microscopy. The voids mainly formed at the cathode side of the stripe where maximum current density was predicted but voids also formed along a line that crosses the stripe. This was explained in terms of the initial voids forming at locations of maximum current density concentration, altering these locations, and then expanding into them. The movement of the maximum current density location is caused by redistribution of current as the voids form. An atomic migration model has been developed and used in this work. It was found that if thermal gradients were completely neglected, the model was unable to account for the divergence of atomic flux density which is necessary for void nucleation. However, the temperature dependence of the diffusivity of atoms is sufficient to account for void nucleation within the timescale of the experiments. - Highlights: • Experimental and computational study of electron migration in a SnAg film • The calculated atomic flux divergence has been used to predict void formation. • Voids caused by electromigration observed at current crowding sites and in other regions.

  6. Definition of current density in the presence of a non-local potential.

    Science.gov (United States)

    Li, Changsheng; Wan, Langhui; Wei, Yadong; Wang, Jian

    2008-04-16

    In the presence of a non-local potential arising from electron-electron interaction, the conventional definition of current density J(c) = (e/2m)([(p-eA)ψ](*)ψ-ψ(*)[(p-eA)ψ]) cannot satisfy the condition of current conservation, i.e., [Formula: see text] in the steady state. In order to solve this problem, we give a new definition of current density including the contribution due to the non-local potential. We show that the current calculated based on the new definition of current density conserves the current and is the same as that obtained from the Landauer-Büttiker formula. Examples are given to demonstrate our results.

  7. Ion density and dielectric breakdown in the afterglow of a high-current arc discharge

    Energy Technology Data Exchange (ETDEWEB)

    Rutgers, W.R.; Verhagen, F.C.M.; De Zeeuw, W.A.

    1984-01-01

    The ion density in the afterglow of a high-current atmospheric arc-discharge and electrical breakdown have been investigated in atomic (argon), molecular (nitrogen) and electronegative (carbon dioxide) media. From the decay with time of the ion density, effective recombination coefficients can be calculated. When the ion density is reduced to values below 2 x 10/sup 17/m/sup -3/, the afterglow plasma changes from a resistive into a dielectric medium. (J.C.R.)

  8. Melt textured YBaCuO transport current capability. Application to current limitation; Capacite de transport et de limitation du courant des materiaux YBaCuO textures

    Energy Technology Data Exchange (ETDEWEB)

    Porcar, L.; Belmont, O.; Noudem, J.G.; Barbut, J.M.; Barrault, M. [Schneider Electric S.A., Grenoble (France); Bourgault, D.; Chaud, X.; Tournier, R. [CNRS-EPM/Matformag, Grenoble (France); Tixador, P. [CNRS-CRTBT/LEG, Grenoble (France)

    1998-01-01

    Pulsed and permanent sinusoidal transport current have been applied to melt textured Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} in order to estimate its current limitation capability. High pulsed transport currents reaching 9000A (23000 A/cm{sup 2}) crossed a 4 cm long sample. In permanent sinusoidal current, 3000 A (7800 A/cm{sup 2}) crossed the sample without showing any resistive losses. Above the critical current, the transition from the superconducting to the normal state is strongly abrupt. (orig.). 8 refs.

  9. A Galvanostatic Modeling for Preparation of Electrodeposited Nanocrystalline Coatings by Control of Current Density

    Institute of Scientific and Technical Information of China (English)

    Ali Mohammad Rashidi

    2012-01-01

    The correlation between the grain size of electrodeposited coatings and the current densities was modeled by considering galvanostatic conditions. In order to test the model by experimental results, nanocrystalline (NC) nickel samples were deposited at different current densities using a Watts bath. The grain size of the deposits was evaluated by X-ray diffraction (XRD) technique. Model predictions were validated by finding a curve being the best-fit to the experimental results which were gathered from literature for different NC coatings in addition to those data measured in this research for NC nickel coatings. According to our model, the variation of grain size with the reciprocal of the current density follows a power law. A good agreement between the experimental results and model predictions was observed which indicated that the derived analytical model is applicable for producting the nanocrystalline electrodeposits with the desired grain size by controling current density.

  10. Flux quantum tunneling effect and its influence on the experimental critical current density

    Institute of Scientific and Technical Information of China (English)

    闻海虎; 赵忠贤; GriessenR.

    1995-01-01

    By using magnetic sweeping method, the temperature and magnetic field dependencies of the experimental current density and the normalized relaxation rate have been obtained. The true critical current density corresponding to the zero activation energy has been carried out based on the collective-pinning and the thermally-activated flux motion models, and therefore the influences of the quantum tunneling effect and the thermal activation effect on the experimental critical current density are distinguished. It is found that, with temperature lower than 10 K, the relaxation rate will not drop to zero when T approaches zero K because of the occurrence of the flux quantum tunneling. This additional flux motion further reduces the experimental critical current density j making it saturated with lowering temperature.

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

    Science.gov (United States)

    Fattah-Alhosseini, Arash; Khan, Hamid Yazdani

    2017-02-01

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

  12. Fresh water-salt water density currents, a major cause of siltation in estuaries

    National Research Council Canada - National Science Library

    Schultz, E.A; Simmons, H.B

    1957-01-01

    ... the effects of changing the upland discharge into estuaries, rivers, and harbours where the fresh water-salt water density currents are present in some degree, and in some cases are the major cause of siltation; and 4...

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

    Directory of Open Access Journals (Sweden)

    Arun Augustin

    2016-09-01

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

  14. Use density, visitor experience, and limiting recreational use in wilderness: progress to date and research needs

    Science.gov (United States)

    Wayne A. Freimund; David N. Cole

    2001-01-01

    Recent increases in demand have revitalized interest and controversy surrounding use limits and the effect of visitor density on wilderness experiences. A workshop held in Missoula, Montana, in June of 2000 addressed the potential for social science to contribute to understanding and managing increasingly populated wilderness conditions. Scientists identified progress...

  15. 4-Component relativistic calculation of the magnetically induced current density in the group 15 heteroaromatic compounds

    Energy Technology Data Exchange (ETDEWEB)

    Bast, Radovan; Juselius, Jonas [Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Tromso, N-9037 Tromso (Norway); Saue, Trond [Institut de Chimie de Strasbourg, CNRS et Universite Louis Pasteur, Laboratoire de Chimie Quantique, 4, rue Blaise Pascal, BP 1032, F-67070 Strasbourg (France)], E-mail: tsaue@chimie.u-strasbg.fr

    2009-02-17

    We present a 4-component relativistic implementation for calculating the magnetically induced current density within Hartree-Fock and Kohn-Sham linear response theory using a common gauge origin. We demonstrate how the current density can be decomposed into paramagnetic and diamagnetic contributions by calculating separately the contributions from rotations between positive-energy orbitals and contributions from rotations between the occupied positive-energy orbitals and the virtual negative-energy orbitals, respectively. This methodology is applied to the study of the magnetically induced current density in benzene and the group 15 heteroaromatic compounds C{sub 5}H{sub 5}E (E = N, P, As, Sb, Bi). Quantitative values for the magnetically induced ring currents are obtained by numerical integration over the current flow. We have found that the diatropic ring current is sustained for the entire series of the group 15 heteroaromatic compounds-the induced ring current susceptibility of bismabenzene being 76% of the benzene result. Having employed two hybrid and two nonhybrid generalized gradient approximation functionals, the results are found to be rather insensitive to the choice of the density functional approximation. The relativistic effect is relatively small, reaching its maximum of 8% for bismabenzene. The presented 4-component relativistic methodology opens up the possibility to visualize magnetically induced current densities of aromatic heavy-element systems with both scalar relativistic and spin-orbit effects included.

  16. Evaluation of Ferrite Chip Beads as Surge Current Limiters in Circuits with Tantalum Capacitors

    Science.gov (United States)

    Teverovsky, Alexander

    2014-01-01

    Limiting resistors are currently required to be connected in series with tantalum capacitors to reduce the risk of surge current failures. However, application of limiting resistors decreases substantially the efficiency of the power supply systems. An ideal surge current limiting device should have a negligible resistance for DC currents and high resistance at frequencies corresponding to transients in tantalum capacitors. This work evaluates the possibility of using chip ferrite beads (FB) as such devices. Twelve types of small size FBs from three manufacturers were used to evaluate their robustness under soldering stresses and at high surge current spikes associated with transients in tantalum capacitors. Results show that FBs are capable to withstand current pulses that are substantially greater than the specified current limits. However, due to a sharp decrease of impedance with current, FBs do not reduce surge currents to the required level that can be achieved with regular resistors.

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

    Energy Technology Data Exchange (ETDEWEB)

    You, Chun-Yeol [Department of Physics, Inha University, Incheon 402-751 (Korea, Republic of)

    2014-01-28

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

  18. Progress in American Superconductor's HTS wire and optimization for fault current limiting systems

    Science.gov (United States)

    Malozemoff, Alexis P.

    2016-11-01

    American Superconductor has developed composite coated conductor tape-shaped wires using high temperature superconductor (HTS) on a flexible substrate with laminated metal stabilizer. Such wires enable many applications, each requiring specific optimization. For example, coils for HTS rotating machinery require increased current density J at 25-50 K. A collaboration with Argonne, Brookhaven and Los Alamos National Laboratories and several universities has increased J using an optimized combination of precipitates and ion irradiation defects in the HTS. Major commercial opportunities also exist to enhance electric power grid resiliency by linking substations with distribution-voltage HTS power cables [10]. Such links provide alternative power sources if one substation's transmission-voltage power is compromised. But they must also limit fault currents which would otherwise be increased by such distribution-level links. This can be done in an HTS cable, exploiting the superconductor-to-resistive transition when current exceeds the wires' critical J. A key insight is that such transitions are usually nonuniform; so the wire must be designed to prevent localized hot spots from damaging the wire or even generating gas bubbles in the cable causing dielectric breakdown. Analysis shows that local heating can be minimized by increasing the composite tape's total thickness, decreasing its total resistance in the normal state and decreasing its critical J. This conflicts with other desirable wire characteristics. Optimization of these conflicting requirements is discussed.

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

    Science.gov (United States)

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

    2016-11-01

    gravity. When the box model is opportunely calibrated with the numerical simulation results, the prediction of the flow runout is fairly accurate and the model predicts a rapid, non-linear decay of the flow kinetic energy (or dynamic pressure) with the distance from the source. The capability of PDC to overcome topographic obstacles can thus be analysed in the framework of the energy-conoid approach, in which the predicted kinetic energy of the flow front is compared with the potential energy jump associated with the elevated topography to derive a condition for blocking. Model results show that, although preferable to the energy-cone, the energy-conoid approach still has some serious limitations, mostly associated with the behaviour of the flow head. Implications of these outcomes are discussed in the context of probabilistic hazard assessment studies, in which a calibrated box model can be used as a fast pyroclastic density current emulator for Monte Carlo simulations.

  20. Influence of current density on microstructure of pulse electrodeposited tin coatings

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Ashutosh; Bhattacharya, Sumit; Sen, Ranjan; Reddy, B.S.B. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology-Kharagpur, Kharagpur-721302 (India); Fecht, H.-J. [Institut fuer Mikro- und Nanomaterialien, Universitaet Ulm, D-89081 Ulm (Germany); Das, Karabi, E-mail: karabi@metal.iitkgp.ernet.in [Department of Metallurgical and Materials Engineering, Indian Institute of Technology-Kharagpur, Kharagpur-721302 (India); Das, Siddhartha [Department of Metallurgical and Materials Engineering, Indian Institute of Technology-Kharagpur, Kharagpur-721302 (India)

    2012-06-15

    Pulse electrodeposited tin coatings on copper substrate have been synthesized from an aqueous solution containing sodium stannate (Na{sub 2}SnO{sub 3}.3H{sub 2}O) and sodium hydroxide (NaOH). The effect of current density on surface morphology of the deposits has been investigated. As deposited coatings are characterized by X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, and line profile analysis. The X-ray diffraction analysis shows that the deposits consist of tetragonal ({beta}-Sn) structure with microcrystalline grains. The deposits plated at lower current density exhibit (110) texture which decreases with increasing current densities. The effects of current density on Cu-Sn diffusion and whisker growth of the electrodeposited tin coatings are also reported here. - Highlights: Black-Right-Pointing-Pointer Pulse electrodeposition of Sn from aqueous alkaline solution without adding any organic additive. Black-Right-Pointing-Pointer Effect of current density on morphology and whisker growth in tin coatings aged for 1 year. Black-Right-Pointing-Pointer Solution bath is stable and can be operated over a wide range of current density.

  1. Experimental study of the velocity of density currents in convergent and divergent channels

    Institute of Scientific and Technical Information of China (English)

    Hasan Torabi POUDEH; Samad EMAMGHOLIZADEH; Manoocher Fathi-MOGHADAM

    2014-01-01

    The head velocity of the density current in the convergent and divergent channel is a key parameter for evaluating the extent to which suspended material travels, and for determining the type and distribution of sediment in the water body. This study experimentally evaluated the effects of the reach degree of convergence and divergence on the head velocity of the density current. Experiments were conducted in the flume with 6.0 m long, 0.72 m width and 0.6 m height. The head velocity was measured at three convergent degrees (-8o;-12o;-26o), at three divergent degrees (8o; 12o; 26o) and two slopes (0.009, 0.016) for various discharges. The measured head velocity of the density current is compared with the head velocity of the density current in the constant cross section channel. Based on non-dimensional and statistical analysis, relations as linear multiple regression are offered for predicting head velocity of the density current in the convergent, divergent and constant cross section channel. Also the results of this research show that for the same slope and discharge, the head velocity of the density current in the convergent and divergent channel are greater and less than the head velocity of the constant cross section, respectively.

  2. Numerical Simulation of Current Density Distribution in Keyhole Double-Sided Arc Welding

    Institute of Scientific and Technical Information of China (English)

    Junsheng SUN; Chuansong WU; Min ZHANG; Houxiao WANG

    2004-01-01

    In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process.Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.

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

    Science.gov (United States)

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

    2005-06-01

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

  4. A Solid-State Fault Current Limiting Device for VSC-HVDC Systems

    Science.gov (United States)

    Larruskain, D. Marene; Zamora, Inmaculada; Abarrategui, , Oihane; Iturregi, Araitz

    2013-08-01

    Faults in the DC circuit constitute one of the main limitations of voltage source converter VSC-HVDC systems, as the high fault currents can damage seriously the converters. In this article, a new design for a fault current limiter (FCL) is proposed, which is capable of limiting the fault current as well as interrupting it, isolating the DC grid. The operation of the proposed FCL is analysed and verified with the most usual faults that can occur in overhead lines.

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

    Science.gov (United States)

    Flynn, Sean P; Barriere, Sylvain; Barrier, Sylvain; Scott, Rod C; Lenck-Santini, Pierre-Pascal; Holmes, Gregory L

    2015-01-01

    The dentate gyrus is considered to function as an inhibitory gate limiting excitatory input to the hippocampus. Following status epilepticus (SE), this gating function is reduced and granule cells become hyper-excitable. Dentate spikes (DS) are large amplitude potentials observed in the dentate gyrus (DG) of normal animals. DS are associated with membrane depolarization of granule cells, increased activity of hilar interneurons and suppression of CA3 and CA1 pyramidal cell firing. Therefore, DS could act as an anti-excitatory mechanism. Because of the altered gating function of the dentate gyrus following SE, we sought to investigate how DS are affected following pilocarpine-induced SE. Two weeks following lithium-pilocarpine SE induction, hippocampal EEG was recorded in male Sprague-Dawley rats with 16-channel silicon probes under urethane anesthesia. Probes were placed dorso-ventrally to encompass either CA1-CA3 or CA1-DG layers. Large amplitude spikes were detected from EEG recordings and subject to current source density analysis. Probe placement was verified histologically to evaluate the anatomical localization of current sinks and the origin of DS. In 9 of 11 pilocarpine-treated animals and two controls, DS were confirmed with large current sinks in the molecular layer of the dentate gyrus. DS frequency was significantly increased in pilocarpine-treated animals compared to controls. Additionally, in pilocarpine-treated animals, DS displayed current sinks in the outer, middle and/or inner molecular layers. However, there was no difference in the frequency of events when comparing between layers. This suggests that following SE, DS can be generated by input from medial and lateral entorhinal cortex, or within the dentate gyrus. DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1. These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the

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

    Directory of Open Access Journals (Sweden)

    Sean P Flynn

    Full Text Available The dentate gyrus is considered to function as an inhibitory gate limiting excitatory input to the hippocampus. Following status epilepticus (SE, this gating function is reduced and granule cells become hyper-excitable. Dentate spikes (DS are large amplitude potentials observed in the dentate gyrus (DG of normal animals. DS are associated with membrane depolarization of granule cells, increased activity of hilar interneurons and suppression of CA3 and CA1 pyramidal cell firing. Therefore, DS could act as an anti-excitatory mechanism. Because of the altered gating function of the dentate gyrus following SE, we sought to investigate how DS are affected following pilocarpine-induced SE. Two weeks following lithium-pilocarpine SE induction, hippocampal EEG was recorded in male Sprague-Dawley rats with 16-channel silicon probes under urethane anesthesia. Probes were placed dorso-ventrally to encompass either CA1-CA3 or CA1-DG layers. Large amplitude spikes were detected from EEG recordings and subject to current source density analysis. Probe placement was verified histologically to evaluate the anatomical localization of current sinks and the origin of DS. In 9 of 11 pilocarpine-treated animals and two controls, DS were confirmed with large current sinks in the molecular layer of the dentate gyrus. DS frequency was significantly increased in pilocarpine-treated animals compared to controls. Additionally, in pilocarpine-treated animals, DS displayed current sinks in the outer, middle and/or inner molecular layers. However, there was no difference in the frequency of events when comparing between layers. This suggests that following SE, DS can be generated by input from medial and lateral entorhinal cortex, or within the dentate gyrus. DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1. These results suggest that following SE there is an increase in DS activity, potentially arising from

  7. A carbon nanotube field emission cathode with high current density and long-term stability

    Science.gov (United States)

    Calderón-Colón, Xiomara; Geng, Huaizhi; Gao, Bo; An, Lei; Cao, Guohua; Zhou, Otto

    2009-08-01

    Carbon nanotube (CNT) field emitters are now being evaluated for a wide range of vacuum electronic applications. However, problems including short lifetime at high current density, instability under high voltage, poor emission uniformity, and pixel-to-pixel inconsistency are still major obstacles for device applications. We developed an electrophoretic process to fabricate composite CNT films with controlled nanotube orientation and surface density, and enhanced adhesion. The cathodes have significantly enhanced macroscopic field emission current density and long-term stability under high operating voltages. The application of this CNT electron source for high-resolution x-ray imaging is demonstrated.

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

    Science.gov (United States)

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

    2001-05-31

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

  9. Physical and Mechanical Characterization of Electrodeposited Nickel Nanowires -- Influence of Current Density and External Magnetic Field

    Science.gov (United States)

    Samykano, Mahendran

    Magnetic 1-D nanostructures have received great interest due to their various applications including high-density magnetic storage, sensors, drug delivery, and NEMS/MEMS systems. Among different 1-D nanostructures, magnetic nickel (Ni) nanowires with their ferromagnetic properties are of interest in such applications due to their lower cost, and they can be consistently synthesized via electrodeposition. While physical properties are influenced by processing parameters during electrodeposition of Ni nanowires, understanding of their influence on the mechanical properties is still not available. This is primarily due to the following challenges: tediousness involved in experimental techniques for mechanical characterization at nanoscale; sophisticated and careful experimentation required to be performed with advanced microscopy systems (SEM, AFM); robust nanoscale manipulators needed to place a single nanowire within the device; and difficulty in correctly loading and obtaining data for stress-strain within high powered microscopy environments. All of these factors pose significant challenges, limiting the current state of the art in mechanical characterization to its infancy, with wide differences in characterization curves and reported properties in this field. The present research and dissertation focuses on: 1. Experimental synthesis of electrodeposited Ni nanowires at different current densities and external magnetic fields, 2. Physical properties characterization of the synthesized nanowires to understand their morphology, structural and crystallographic properties, 3. Mechanical properties characterization of synthesized Ni nanowires through careful experiments within scanning electron microscope (SEM) based on uni-axial MEMS tensile loading device, 4. Data analysis to understand the process, physical and mechanical property interrelationship and to obtain insights on tensile deformation and failure modes observed in the Ni nanowires studied. Key research

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

    Science.gov (United States)

    Park, Chunjae; Kwon, Oh In

    2013-01-01

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

  11. Some current problems in perovskite nano-ferroelectrics and multiferroics: kinetically-limited systems of finite lateral size

    Science.gov (United States)

    Scott, James F.; Schilling, Alina; Rowley, S. E.; Gregg, J. Marty

    2015-06-01

    We describe some unsolved problems of current interest; these involve quantum critical points in ferroelectrics and problems which are not amenable to the usual density functional theory, nor to classical Landau free energy approaches (they are kinetically limited), nor even to the Landau-Kittel relationship for domain size (they do not satisfy the assumption of infinite lateral diameter) because they are dominated by finite aperiodic boundary conditions.

  12. Electronic Zero-Point Oscillations in the Strong-Interaction Limit of Density Functional Theory.

    Science.gov (United States)

    Gori-Giorgi, Paola; Vignale, Giovanni; Seidl, Michael

    2009-04-14

    The exchange-correlation energy in Kohn-Sham density functional theory can be expressed exactly in terms of the change in the expectation of the electron-electron repulsion operator when, in the many-electron Hamiltonian, this same operator is multiplied by a real parameter λ varying between 0 (Kohn-Sham system) and 1 (physical system). In this process, usually called adiabatic connection, the one-electron density is kept fixed by a suitable local one-body potential. The strong-interaction limit of density functional theory, defined as the limit λ→∞, turns out to be like the opposite noninteracting Kohn-Sham limit (λ→0) mathematically simpler than the physical (λ = 1) case and can be used to build an approximate interpolation formula between λ→0 and λ→∞ for the exchange-correlation energy. Here we extend the systematic treatment of the λ→∞ limit [Phys. Rev. A 2007, 75, 042511] to the next leading term, describing zero-point oscillations of strictly correlated electrons, with numerical examples for small spherical atoms. We also propose an improved approximate functional for the zero-point term and a revised interpolation formula for the exchange-correlation energy satisfying more exact constraints.

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

    Science.gov (United States)

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

    2012-04-01

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

  14. Measurement of induced magnetic flux density using injection current nonlinear encoding (ICNE) in MREIT.

    Science.gov (United States)

    Park, Chunjae; Lee, Byung Il; Kwon, Ohin; Woo, Eung Je

    2007-02-01

    Magnetic resonance electrical impedance tomography (MREIT) measures induced magnetic flux densities subject to externally injected currents in order to visualize conductivity distributions inside an electrically conducting object. Injection currents induce magnetic flux densities that appear in phase parts of acquired MR image data. In the conventional current injection method, we inject currents during the time segment between the end of the first RF pulse and the beginning of the reading gradient in order to ensure the gradient linearity. Noting that longer current injections can accumulate more phase changes, we propose a new pulse sequence called injection current nonlinear encoding (ICNE) where the duration of the injection current pulse is extended until the end of the reading gradient. Since the current injection during the reading gradient disturbs the gradient linearity, we first analyze the MR signal produced by the ICNE pulse sequence and suggest a novel algorithm to extract the induced magnetic flux density from the acquired MR signal. Numerical simulations and phantom experiments show that the new method is clearly advantageous in terms of the reduced noise level in measured magnetic flux density data. The amount of noise reduction depends on the choice of the data acquisition time and it was about 24% when we used a prolonged data acquisition time of 10.8 ms. The ICNE method will enhance the clinical applicability of the MREIT technique when it is combined with an appropriate phase artefact minimization method.

  15. Can the current density map topology be extracted from the nucleus independent chemical shifts?

    NARCIS (Netherlands)

    Van Damme, Sofie; Acke, Guillaume; Havenith, Remco W. A.; Bultinck, Patrick

    2016-01-01

    Aromatic compounds are characterised by the presence of a ring current when in a magnetic field. As a consequence, current density maps are used to assess (the degree of) aromaticity of a compound. However, often a more discrete set of so-called Nucleus Independent Chemical Shift (NICS) values is us

  16. Remote forcing of subsurface currents and temperatures near the northern limit of the California Current System

    Science.gov (United States)

    Engida, Zelalem; Monahan, Adam; Ianson, Debby; Thomson, Richard E.

    2016-10-01

    Local and remote wind forcing of upwelling along continental shelves of coastal upwelling regions play key roles in driving biogeochemical fluxes, including vertical net fluxes of carbon and nutrients. These fluxes are responsible for high primary productivity, which in turn supports a lucrative fishery in these regions. However, the relative contributions of local versus remote wind forcing are not well quantified or understood. We present results of coherence analyses between currents at a single mooring site (48.5°N, 126°W) in the northern portion of the California Current System (CalCS) from 1989 to 2008 and coincident time series of North America Regional Reanalysis (NARR) 10 m wind stress within the CalCS (36-54°N, 120-132°W). The two-decade-long current records from the three shallowest depths (35, 100, and 175 m) show a remote response to winds from south as far as 36°N. In contrast, only temperatures at the deepest depth (400 m) show strong coherences with remote winds. Weaker local wind influence is observed in both the currents and 400 m temperatures but is mostly due to the large spatial coherence within the wind field itself. Lack of coherence between distal winds and the 400 m currents suggests that the temperature variations at that depth are driven by vertical motion resulting from poleward travelling coastal trapped waves (CTWs). Understanding the effects of remote forcing in coastal upwelling regions is necessary for determining the occurrence and timing of extreme conditions in coastal oceans, and their subsequent impact on marine ecosystems.

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

    Science.gov (United States)

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

    2017-03-08

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

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

    KAUST Repository

    Ren, Lijiao

    2014-08-05

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

  19. Effect of the current density on electrodepositing alpha-lead dioxide coating on aluminum substrate

    Institute of Scientific and Technical Information of China (English)

    Burning CHEN; Zhongcheng GUO; Hui HUANG; Xianwan YANG; Yuandong CAO

    2009-01-01

    The α-PbO_2 electrodes are prepared by anodic electrodeposition on Al/conductive coating electrode from alkaline plumbite solutions in order to investigate the effect of the different current densities on the properties of α-PbO_2 electrodes. The physic-ochemical properties of the α-PbO_2 electrodes are analyzed by using SEM, EDS, XRD, Tafel plot, linear sweep voltammetry (LSV) and A.C. Impedance. A compact and uniform layer of lead dioxide was obtained at the current density of 3 mA-cm~(-2) . A further increase in current density results in smaller particles with high porosity. EDS and XRD analyses have shown that the PbO_2 deposited in alkaline conditions is highly non stoichiometric, and the PbO impurities are formed on the surface layer besides the α-PbO_2. The corrosion resistance of α-PbO_2 at the low current density is superior to that of the high current density. It can be attributed to a porous layer of deposited films at high current densities. When used as anodes for oxygen evolution in aqueous Zn~(2+) 50 g·L~(-1), H_2SO_4 150 g·L~(-1), the Al/conductive coating/α-PbO_2 exhibits lower potential compared to Pb electrode. Al/conductive coating/α-PbO_2 electrode with the best electrocatalytic activity was obtained at current density of 1 mA·cm~(-2). The lowest roughness factor was obtained at 1 mA·cm~(-2).

  20. Transport critical-current density of superconducting films with hysteretic ferromagnetic dots

    Directory of Open Access Journals (Sweden)

    Nuria Del-Valle

    2012-06-01

    Full Text Available Superconductor-ferromagnet hybrids present a rich and complex phenomenology. Particularly, a hysteretic behavior on the transport critical-current density, as a function of a uniform perpendicular applied field, has been experimentally found in superconducting films with some embedded ferromagnets. Here we analyze the interaction superconductor-ferromagnets by means of an iterative model based on the critical-state model with field-dependent internal critical-current density and compare the results with actual transport measurements. By using arguments of field compensation, we show how the change in the magnetization of the ferromagnetic inclusions is responsible for the observed hysteresis on the transport critical current.

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

    Science.gov (United States)

    Turrigiano, G; LeMasson, G; Marder, E

    1995-05-01

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

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

    Science.gov (United States)

    Fliegl, Heike; Jusélius, Jonas; Sundholm, Dage

    2016-07-21

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

  3. Direct mapping of local redox current density on a monolith electrode by laser scanning.

    Science.gov (United States)

    Lee, Seung-Woo; Lopez, Jeffrey; Saraf, Ravi F

    2013-09-15

    An optical method of mapping local redox reaction over a monolith electrode using simple laser scanning is described. As the optical signal is linearly proportional to the maximum redox current that is measured concomitantly by voltammetry, the optical signal quantitatively maps the local redox current density distribution. The method is demonstrated on two types of reactions: (1) a reversible reaction where the redox moieties are ionic, and (2) an irreversible reaction on two different types of enzymes immobilized on the electrode where the reaction moieties are nonionic. To demonstrate the scanning capability, the local redox behavior on a "V-shaped" electrode is studied where the local length scale and, hence, the local current density, is nonuniform. The ability to measure the current density distribution by this method will pave the way for multianalyte analysis on a monolith electrode using a standard three-electrode configuration. The method is called Scanning Electrometer for Electrical Double-layer (SEED).

  4. Measurement of local current density of all-vanadium redox flow batteries

    Science.gov (United States)

    Hsieh, Wen-Yen; Leu, Chih-Hsing; Wu, Chun-Hsing; Chen, Yong-Song

    2014-12-01

    This article presents a preliminary study of the measurement of local current density in all-vanadium redox flow batteries. Two batteries are designed and manufactured in this study, and the experimental results are compared. In the first cell, the current collector is divided into 25 segments, and the flow field plate is not segmented, whereas in the other cell, the flow field plate is segmented. The effects of the electrolyte flow rate on the battery efficiencies and the local current density variation are investigated. The experimental results show that the current density near the outlet significantly decreases when the discharge capacity approaches zero. In addition, the battery has a larger discharge depth at a higher electrolyte flow rate.

  5. Pure density functional for strong correlation and the thermodynamic limit from machine learning

    Science.gov (United States)

    Li, Li; Baker, Thomas E.; White, Steven R.; Burke, Kieron

    2016-12-01

    We use the density-matrix renormalization group, applied to a one-dimensional model of continuum Hamiltonians, to accurately solve chains of hydrogen atoms of various separations and numbers of atoms. We train and test a machine-learned approximation to F [n ] , the universal part of the electronic density functional, to within quantum chemical accuracy. We also develop a data-driven, atom-centered basis set for densities which greatly reduces the computational cost and accurately represents the physical information in the machine-learning calculation. Our calculation (a) bypasses the standard Kohn-Sham approach, avoiding the need to find orbitals, (b) includes the strong correlation of highly stretched bonds without any specific difficulty (unlike all standard DFT approximations), and (c) is so accurate that it can be used to find the energy in the thermodynamic limit to quantum chemical accuracy.

  6. A novel hybrid FEM-BEM method for 3D eddy current field calculation using current density J

    Institute of Scientific and Technical Information of China (English)

    LIU; Zhizhen(刘志珍); WANG; Yanzhang(王衍章); JIA; Zhiping(贾智平); SUN; Yingming(孙英明)

    2003-01-01

    This paper introduces a novel hybrid FEM-BEM method for calculating 3D eddy current field. In the eddy current region, the eddy current density J is solved by the finite element method (FEM) which is discretized by brick finite element mesh, while in the eddy current free region, the magnetic field intensity H is solved by the boundary element method (BEM) which is discretized by rectangular boundary element mesh. Under the boundary conditions, an algebraic equation group is obtained that only includes J by eliminating H. This method has many advantages over traditional ones, such as fewer variables, more convenient coupling between the FEM and the BEM and wider application to multiply-connected regions. The calculated values of two models are in good agreement with experimental results. This shows the validity of our method.

  7. Limit Distribution Theory for Maximum Likelihood Estimation of a Log-Concave Density.

    Science.gov (United States)

    Balabdaoui, Fadoua; Rufibach, Kaspar; Wellner, Jon A

    2009-06-01

    We find limiting distributions of the nonparametric maximum likelihood estimator (MLE) of a log-concave density, i.e. a density of the form f(0) = exp varphi(0) where varphi(0) is a concave function on R. Existence, form, characterizations and uniform rates of convergence of the MLE are given by Rufibach (2006) and Dümbgen and Rufibach (2007). The characterization of the log-concave MLE in terms of distribution functions is the same (up to sign) as the characterization of the least squares estimator of a convex density on [0, infinity) as studied by Groeneboom, Jongbloed and Wellner (2001b). We use this connection to show that the limiting distributions of the MLE and its derivative are, under comparable smoothness assumptions, the same (up to sign) as in the convex density estimation problem. In particular, changing the smoothness assumptions of Groeneboom, Jongbloed and Wellner (2001b) slightly by allowing some higher derivatives to vanish at the point of interest, we find that the pointwise limiting distributions depend on the second and third derivatives at 0 of H(k), the "lower invelope" of an integrated Brownian motion process minus a drift term depending on the number of vanishing derivatives of varphi(0) = log f(0) at the point of interest. We also establish the limiting distribution of the resulting estimator of the mode M(f(0)) and establish a new local asymptotic minimax lower bound which shows the optimality of our mode estimator in terms of both rate of convergence and dependence of constants on population values.

  8. The Shear Viscosity to Entropy Density Ratio of Trapped Fermions in the Unitarity Limit

    CERN Document Server

    Schaefer, Thomas

    2007-01-01

    We extract the shear viscosity to entropy density ratio \\eta/s of cold fermionic atoms in the unitarity limit from experimental data on the damping of collective excitations. We find that near the critical temperature \\eta/s is roughly equal to 1/2 in units of \\hbar/k_B. With the possible exception of the quark gluon plasma, this value is closer to the conjectured lower bound 1/(4\\pi) than any other known liquid.

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

    Directory of Open Access Journals (Sweden)

    Tomohiro Miyanishi

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

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

    CERN Document Server

    Bellucci, S; Grigoryan, A Kh

    2016-01-01

    For a massive quantum fermionic field, we investigate the vacuum expectation values (VEVs) of the charge and current densities induced by an external magnetic flux in a two-dimensional circular ring. Both the irreducible representations of the Clifford algebra are considered. On the ring edges the bag (infinite mass) boundary conditions are imposed for the field operator. This leads to the Casimir type effect on the vacuum characteristics. The radial current vanishes. The charge and the azimuthal current are decomposed into the boundary-free and boundary-induced contributions. Both these contributions are odd periodic functions of the magnetic flux with the period equal to the flux quantum. An important feature that distinguishes the VEVs of the charge and current densities from the VEV of the energy density, is their finiteness on the ring edges. The current density is equal to the charge density for the outer edge and has the opposite sign on the inner edge. The VEVs are peaked near the inner edge and, as f...

  11. High Field Emission Current Density from Patterned Carbon Nanotube Field Emitter Arrays with Random Growth.

    Science.gov (United States)

    Khaneja, Mamta; Ghosh, Santanu; Gautam, Seema; Kumar, Prashant; Rawat, J S; Chaudhury, P K; Vankar, V D; Kumar, Vikram

    2015-05-01

    High field emission (FE) current density from carbon nanotube (CNT) arrays grown on lithographically patterned silicon substrates is reported. A typical patterned field emitter array consists of bundles of nanotubes separated by a fixed gap and spread over the entire emission area. Emission performance from such an array having randomly oriented nanotube growth within each bundle is reported for different bundle sizes and separations. One typical sample with aligned CNTs within the bundle is also examined for comparison. It is seen that the current density from an array having random nanotube growth within the bundles is appreciably higher as compared to its aligned counterpart. The influence of structure on FE current densities as revealed by Raman spectroscopy is also seen. It is also observed that current density depends on edge length and increases with the same for all samples under study. Highest current density of -100 mA cm(-2) at an applied field of 5 V/μm is achieved from the random growth patterned sample with a bundle size of 2 μm and spacing of 4 μm between the bundles.

  12. Effect of Applied Current Density on Morphological and Structural Properties of Electrodeposited Fe-Cu Films

    Institute of Scientific and Technical Information of China (English)

    Umut Sarac; M. Celalettin Baykul

    2012-01-01

    A detailed study has been carried out to investigate the effect of applied current density on the composition, crystallographic structure, grain size, and surface morphology of Fe-Cu films. X-ray diffraction (XRD) results show that the films consist of a mixture of face-centered cubic (fcc) Cu and body centered cubic (bcc) ~-Fe phases. The average crystalline size of both Fe and Cu particles decreases as the applied current density becomes more negative. Compositional analysis of Fe-Cu films indicates that the Fe content within the films increases with decreasing current density towards more negative values. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to investigate the surface morphology of Fe-Cu films. It is observed that the surface morphology of the films changes from dendritic structure to a cauliflower structure as the applied current density becomes more negative. The surface roughness and grain size of the Fe-Cu films decrease with decreasing applied current density towards more negative values.

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

    Science.gov (United States)

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

    2014-01-01

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

  14. Effects of discharge current and voltage on the high density of metastable helium atoms

    Institute of Scientific and Technical Information of China (English)

    FengXian-Ping; DAndruczyk; BWJames; KTakiyama; SNamba; TOda

    2003-01-01

    Both hollow-cathode and Penning-type discharges were adopted toexcite helium atoms to a metastable state. Experimental data indicate that Penning discharge is more suitable for generating high fractions of metastables in a low-density helium hean for laser-induced fluorescence technique in measuring electric fields at the edge of a plasma. The metastable density increases with increasing helium gas pressure in the range of 1.33×10-2-66.7Pa. The highest metastable density of 3.8×1016m-3 is observed at a static gas pressure of 66.7Pa. An approximately linear relationship between the density of metastable helium atoms and the plasma discharge current is observed. Magnetic field plays a very important role in producing a high density of metastable atoms in Penning discharge.

  15. Effects of discharge current and voltage on the high density of metastable helium atoms

    Institute of Scientific and Technical Information of China (English)

    Feng Xian-Ping(冯贤平); D Andruczyk; B W James; K Takiyama; S Namba; T Oda

    2003-01-01

    Both hollow-cathode and Penning-type discharges were adopted to excite helium atoms to a metastable state.Experimental data indicate that Penning discharge is more suitable for generating high fractions of metastables in a low-density helium beam for laser-induced fluorescence technique in measuring electric fields at the edge of a plasma.The metastable density increases with increasing helium gas pressure in the range of 1.33× 10-2-66.7Pa. The highest metastable density of 3.8 × 1016m-3 is observed at a static gas pressure of 66.7Pa. An approximately linear relationship between the density of metastable helium atoms and the plasma discharge current is observed. Magnetic field plays a very important role in producing a high density of metastable atoms in Penning discharge.

  16. Effects of Current Density on Microstructure of Titania Coatings by Micro-arc Oxidation

    Institute of Scientific and Technical Information of China (English)

    Yue Yang; Hua Wu

    2012-01-01

    In the present study, titania coatings were prepared under different current density conditions in micro-arc oxidation (MAO) process on titanium alloy in NaAlO2 solution. The aim of this work was to study the effects of current density on the microstructure of titania coatings. The morphology and phase composition of the coatings were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectra. The thickness and surface roughness of the coatings were characterized by confocal laser Scanning Microscopy (CLSM). The results showed that the coatings were composed of crystalline anatase and rutile phases of TiO2, and contain a network of evenly distributed small pores. It has also shown that an increase in current density leads to an increase in rutile content.

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

    DEFF Research Database (Denmark)

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

    High temperature solid oxide cells can be operated either as fuel cells or electrolysis cells for efficient power generation or production of hydrogen from steam or synthesis gas (H2 + CO) from steam and CO2 respectively. When operated under harsh conditions, they often exhibit microstructural......, microstructure evolution of the Ni-yttria stabilized zirconia (YSZ) is followed as a function of galvanostatic steam electrolysis testing at current densities between -0.5 and -1.0 A cm-2 for periods of up to 750 hours at 800 °C. The volume fraction and size of the percolating Ni particles was statistically...... quantified using the mean linear intercept method as a function of current density and correlated to increases in serial resistance. The above structural changes are then compared in terms of electrode degradation observed during the co-electrolysis of steam and CO2 at current densities up to -1.5 A cm-2...

  18. SOL plasma measurements during high density and long duration current drive on TRIAM-1M

    Energy Technology Data Exchange (ETDEWEB)

    Takemura, Takeharu; Kawasaki, Shoji; Jotaki, Eriko; Makino, Ken-ichi; Sakamoto, Mizuki; Nakamura, Kazuo; Nakamura, Yukio; Itoh, Sanae; Itoh, Satoshi [Kyushu Univ., Kasuga, Fukuoka (Japan). Research Inst. for Applied Mechanics

    1997-02-01

    In the superconducting, strong magnetic field tokamak, TRIAM-1M, for the purpose of maintaining high density plasma for long time, the current drive experiment using 8.2 GHz lower hybrid wave has been carried out. For maintaining high density plasma for long time, it is indispensable to control gas puff and recycling from wall, as these are closely related to the structure and characteristics of boundary plasma including scrape-off layer (SOL). In this study, in the high density, long time current drive using 8.2 GHz lower hybrid wave, the electron density and electron temperature of SOL plasma were measured by using double probe, and the z-direction distribution and the toroidal magnetic field dependence of the electron density and electron temperature of SOL plasma were examined and compared with OH discharge. Also the dependence of the electron density of SOL plasma on the phase difference in a adjoining waveguide tubes was examined. The experimental setup and the double probe theory are explained. The experimental results of the change with time lapse, the z-direction distribution and the magnetic field dependence of the electron density and electron temperature of SOL plasma are reported. (K.I.)

  19. The importance of current contributions to shielding constants in density-functional theory.

    Science.gov (United States)

    Reimann, Sarah; Ekström, Ulf; Stopkowicz, Stella; Teale, Andrew M; Borgoo, Alex; Helgaker, Trygve

    2015-07-28

    The sources of error in the calculation of nuclear-magnetic-resonance shielding constants determined by density-functional theory are examined. Highly accurate Kohn-Sham wave functions are obtained from coupled-cluster electron density functions and used to define accurate-but current independent-density-functional shielding constants. These new reference values, in tandem with high-accuracy coupled-cluster shielding constants, provide a benchmark for the assessment of errors in common density-functional approximations. In particular the role of errors arising in the diamagnetic and paramagnetic terms is investigated, with particular emphasis on the role of current-dependence in the latter. For carbon and nitrogen the current correction is found to be, in some cases, larger than 10 ppm. This indicates that the absence of this correction in general purpose exchange-correlation functionals is one of the main sources of error in shielding calculations using density functional theory. It is shown that the current correction improves the shielding performance of many popular approximate DFT functionals.

  20. Ion Current Density Calculation of the Inductive Radio Frequency Ion Source

    Directory of Open Access Journals (Sweden)

    V.I. Voznyi

    2012-10-01

    Full Text Available A radio-frequency (RF inductive ion source at 27.12 MHz is investigated. With a global model of the argon discharge, plasma density, electron temperature and ion current density of the ion source is calculated in relation to absorbed RF power and gas pressure as a discharge chamber size changes. It is found that ion beam current density grows as the discharge chamber size decreases. Calculations show that in the RF source with a discharge chamber 30 mm in diameter and 35 mm long the ion current density is 40 mA/cm2 at 100 W of absorbed RF power and 7 mTorr of pressure, and agrees well with experimentally measured value of 43 mA/cm2. With decreasing discharge chamber diameter to 15 mm ion current density can reach 85 mA/cm2 at absorbed RF power of 100 W.

  1. Series transformer based diode-bridge-type solid state fault current limiter

    Institute of Scientific and Technical Information of China (English)

    Amir HEIDARY; Hamid RADMANESH; Seyed Hamid FATHI; G B GHAREHPETIAN

    2015-01-01

    We propose a novel series transformer based diode-bridge-type solid state fault current limiter (SSFCL). To control the fault current, a series RLC branch is connected to the secondary side of an isolation series transformer. Based on this RLC branch, two current limiting modes are created. In the first mode, R and C are bypassed via a paralleled power electronic switch (insulated-gate bipolar transistor, IGBT) and L remains connected to the secondary side of the transformer as a DC reactor. In the second mode, the series reactor impedance is not enough to limit the fault current. In this case, the fault current can be con-trolled by selecting a proper on-off duration of the parallel IGBT, across the series damping resistor (R) and capacitor, which inserts high impedance into the line to limit the fault current. Then, by controlling the magnitude of the DC reactor current, the fault current is reduced and the voltage of the point of common coupling (PCC) is kept at an acceptable level. In addition, in the new SSFCL, the series RC branch, connected in parallel with the IGBT, serves as a snubber circuit for decreasing the transient recovery voltage (TRV) of the IGBT during on-off states. Therefore, the power quality indices can be improved. The measure-ment results of a built prototype are presented to support the simulation and theoretical studies. The proposed SSFCL can limit the fault current without any delay and successfully smooth the fault current waveform.

  2. Limited Angle Torque Motors Having High Torque Density, Used in Accurate Drive Systems

    Directory of Open Access Journals (Sweden)

    R. Obreja

    2011-01-01

    Full Text Available A torque motor is a special electric motor that is able to develop the highest possible torque in a certain volume. A torque motor usually has a pancake configuration, and is directly jointed to a drive system (without a gear box. A limited angle torque motor is a torque motor that has no rotary electromagnetic field — in certain papers it is referred to as a linear electromagnet. The main intention of the authors for this paper is to present a means for analyzing and designing a limited angle torque motor only through the finite element method. Users nowadays require very high-performance limited angle torque motors with high density torque. It is therefore necessary to develop the highest possible torque in a relatively small volume. A way to design such motors is by using numerical methods based on the finite element method.

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

    Science.gov (United States)

    Sadowski, Lukasz; Nikoo, Mehdi

    2014-01-01

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

  4. A double-stage start-up structure to limit the inrush current used in current mode charge pump

    Science.gov (United States)

    Cong, Liu; Xinquan, Lai; Hanxiao, Du; Yuan, Chi

    2016-06-01

    A double-stage start-up structure to limit the inrush current used in current-mode charge pump with wide input range, fixed output and multimode operation is presented in this paper. As a widely utilized power source implement, a Li-battery is always used as the power supply for chips. Due to the internal resistance, a potential drop will be generated at the input terminal of the chip with an input current. A false shut down with a low supply voltage will happen if the input current is too large, leading to the degradation of the Li-battery's service life. To solve this problem, the inrush current is limited by introducing a new start-up state. All of the circuits have been implemented with the NUVOTON 0.6 μm CMOS process. The measurement results show that the inrush current can be limited below 1 A within all input supply ranges, and the power efficiency is higher than the conventional structure. Project supported by the National Natural Science Foundation of China (No. 61106026).

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

    Science.gov (United States)

    Kriha, Vitezslav

    2003-10-01

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

  6. Probabilistic volcanic hazard assessments of Pyroclastic Density Currents: ongoing practices and future perspectives

    Science.gov (United States)

    Tierz, Pablo; Sandri, Laura; Ramona Stefanescu, Elena; Patra, Abani; Marzocchi, Warner; Costa, Antonio; Sulpizio, Roberto

    2014-05-01

    Explosive volcanoes and, especially, Pyroclastic Density Currents (PDCs) pose an enormous threat to populations living in the surroundings of volcanic areas. Difficulties in the modeling of PDCs are related to (i) very complex and stochastic physical processes, intrinsic to their occurrence, and (ii) to a lack of knowledge about how these processes actually form and evolve. This means that there are deep uncertainties (namely, of aleatory nature due to point (i) above, and of epistemic nature due to point (ii) above) associated to the study and forecast of PDCs. Consequently, the assessment of their hazard is better described in terms of probabilistic approaches rather than by deterministic ones. What is actually done to assess probabilistic hazard from PDCs is to couple deterministic simulators with statistical techniques that can, eventually, supply probabilities and inform about the uncertainties involved. In this work, some examples of both PDC numerical simulators (Energy Cone and TITAN2D) and uncertainty quantification techniques (Monte Carlo sampling -MC-, Polynomial Chaos Quadrature -PCQ- and Bayesian Linear Emulation -BLE-) are presented, and their advantages, limitations and future potential are underlined. The key point in choosing a specific method leans on the balance between its related computational cost, the physical reliability of the simulator and the pursued target of the hazard analysis (type of PDCs considered, time-scale selected for the analysis, particular guidelines received from decision-making agencies, etc.). Although current numerical and statistical techniques have brought important advances in probabilistic volcanic hazard assessment from PDCs, some of them may be further applicable to more sophisticated simulators. In addition, forthcoming improvements could be focused on three main multidisciplinary directions: 1) Validate the simulators frequently used (through comparison with PDC deposits and other simulators), 2) Decrease

  7. The electrical current density vector in the inner penumbra of a Sunspot

    CERN Document Server

    Puschmann, K G; Pillet, V Martínez

    2010-01-01

    We determine the entire electrical current density vector in a geometrical 3D volume of the inner penumbra of a sunspot from an inversion of spectropolarimetric data obtained with Hinode/SP. Significant currents are seen to wrap around the hotter, more elevated regions with lower and more horizontal magnetic field that harbor strong upflows and radial outflows (the intraspines). The horizontal component of the current density vector is 3-4 times larger than the vertical; nearly all previous studies only obtain the vertical component and thus strongly underestimate the current density. The current density and the magnetic field vectors form an angle of about 20 degrees. The plasma beta at the 0 km level is larger than 1 in the intraspines and is one order of magnitude lower in the background component of the penumbra (spines). At the 200 km level, the plasma beta is below 0.3 nearly everywhere. The plasma beta surface as well as the surface optical depth unity are very corrugated. At the borders of intraspines...

  8. Feasibility and limitations of bulk density assignment in MRI for head and neck IMRT treatment planning.

    Science.gov (United States)

    Chin, Alexander L; Lin, Alexander; Anamalayil, Shibu; Teo, Boon-Keng Kevin

    2014-01-01

    Head and neck cancers centered at the base of skull are better visualized on MRI than on CT. The purpose of this investigation was to investigate the accuracy of bulk density assignment in head and neck intensity-modulated radiation therapy (IMRT) treatment plan optimization. Our study investigates dose calculation differences between density-assigned MRI and CT, and identifies potential limitations related to dental implants and MRI geometrical distortion in the framework of MRI-only-based treatment planning. Bulk density assignment was performed and applied onto MRI to generate three MRI image sets with increasing levels of heterogeneity for seven patients: 1) MRIW: all water-equivalent; 2) MRIW+B: included bone with density of 1.53 g/cm3; and 3) MRIW+B+A: included bone and air. Using identical planning and optimization parameters, MRI-based IMRT plans were generated and compared to corresponding, forward-calculated, CT-based plans on the basis of target coverage, isodose distributions, and dose-volume histograms (DVHs). Phantom studies were performed to assess the magnitude and spatial dependence of MRI geometrical distortion. MRIW-based dose calculations overestimated target coverage by 16.1%. Segmentation of bone reduced differences to within 2% of the coverage area on the CT-based plan. Further segmentation of air improved conformity near air-tissue interfaces. Dental artifacts caused substantial target coverage overestimation even on MRIW+B+A. Geometrical distortion was less than 1 mm in an imaging volume 20 × 20 × 20 cm3 around scanner isocenter, but up to 4 mm at 17 cm lateral to isocenter. Bulk density assignment in the framework of MRI-only IMRT head and neck treatment planning is a feasible method with certain limitations. Bone and teeth account for the majority of density heterogeneity effects. While soft tissue is well visualized on MRI compared to CT, dental implants may not be visible on MRI and must be identified by other means and assigned

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

    DEFF Research Database (Denmark)

    Wijesooriyage, Waruna Dissanayaka; Rosendahl, Lasse

    2015-01-01

    Thermoelectrics are candidate niche electrical generator devices for energy management. At present, scientists are more focused on thermoelectric (TE) material development, but the TE module design procedure is still in a relatively virgin state. One of the most well-known methods is the reduced...... current approach (RCA) for TE module design, where the same current is induced through the p and n legs of the thermoelectric generator (TEG). The current density of each element is manipulated by changing the area of both legs. This technique leads to a TE module architecture based on the most efficient...... configuration of both p and n legs. In the current paper, we apply an extended version of this technique, to show how a TE module with a higher volumetric power density can be designed, compared to the original RCA. Our studies indicate that for some combinations of p and n material properties, optima yielding...

  10. Effect of current density on distribution coefficient of solute at solid-liquid interface

    Institute of Scientific and Technical Information of China (English)

    常国威; 王自东; 吴春京; 胡汉起

    2003-01-01

    When current passes through the solid-liquid interface, the growth rate of crystal, solid-liquid interfaceenergy and radius of curvature at dendritic tip will change. Based on this fact, the theoretical relation between thedistribution of solute at solid-liquid interface and current density was established, and the effect of current on thedistribution coefficient of solute through effecting the rate of crystal growth, the solid-liquid interface energy and theradius of curvature at the dendritic tip was discussed. The results show that as the current density increases, thedistribution coefficient of solute tends to rise in a whole, and when the former is larger than about 400 A/cm2 , thelatter varies significantly.

  11. [Heart current density as the most important biological parameter of electrocution in the bathtub].

    Science.gov (United States)

    Fechner, G; Brinkmann, B; Heckmann, M

    1990-01-01

    The most important factor during electrocution in a bathtub is the amount of current flowing through a body, not the amount of voltage. A method of measurement is introduced which--under simulation of various electrical situations--provides the possibility to measure the current flowing through the heart and to determine it's direction and density in the tissue. Hereby a ranking of the different factors influencing electrocution can be set up.

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

    DEFF Research Database (Denmark)

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

    2005-01-01

    The dependence of critical current density (J(c)) on the angle between the current direction and the (100) direction in the ab-plane of thin YBCO films deposited on (001)-SrTiO3 from natiocrystalline and microcrystalline targets is studied using magneto-optical microscopy. In the films made from ...... indicating that in addition to linear defects also the twin boundaries are very important flux pinning sites. (c) 2005 Elsevier B.V. All rights reserved....

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

    Directory of Open Access Journals (Sweden)

    PREDRAG M. ŽIVKOVIĆ

    2011-06-01

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

  14. Pure density functional for strong correlations and the thermodynamic limit from machine learning

    CERN Document Server

    Li, Li; White, Steven R; Burke, Kieron

    2016-01-01

    We use density-matrix renormalization group, applied to a one-dimensional model of continuum Hamiltonians, to accurately solve chains of hydrogen atoms of various separations and numbers of atoms. We train and test a machine-learned approximation to $F[n]$, the universal part of the electronic density functional, to within quantum chemical accuracy. Our calculation (a) bypasses the standard Kohn-Sham approach, avoiding the need to find orbitals, (b) includes the strong correlation of highly-stretched bonds without any specific difficulty (unlike all standard DFT approximations) and (c) is so accurate that it can be used to find the energy in the thermodynamic limit to quantum chemical accuracy.

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

    Directory of Open Access Journals (Sweden)

    Orhan Gökhan

    2012-01-01

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

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

    Science.gov (United States)

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

    2014-05-01

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

  17. A micro-power LDO with piecewise voltage foldback current limit protection

    Institute of Scientific and Technical Information of China (English)

    Wei Hailong; Liu Youbao; Guo Zhongjie; Liao Xue

    2012-01-01

    To achieve a constant current limit,low power consumption and high driving capability,a micro-power LDO with a piecewise voltage-foldback current-limit circuit is presented.The current-limit threshold is dynamically adjusted to achieve a maximum driving capability and lower quiescent current of only 300 nA.To increase the loop stability of the proposed LDO,a high impedance transconductance buffer under a micro quiescent current is designed for splitting the pole that exists at the gate of the pass transistor to the dominant pole,and a zero is designed for the purpose of the second pole phase compensation.The proposed LDO is fabricated in a BiCMOS process.The measurement results show that the short-circuit current of the LDO is 190 mA,the constant limit current under a high drop-out voltage is 440 mA,and the maximum load current under a low drop-out voltage is up to 800 mA.In addition,the quiescent current of the LDO is only 7 μA,the load regulation is about 0.56% on full scale,the line regulation is about 0.012%/V,the PSRR at 120 Hz is 58 dB and the drop-out voltage is only 70 mV when the load current is 250 mA.

  18. Setting an observational upper limit to the number density of interstellar objects with Pan-STARRS

    Science.gov (United States)

    Engelhardt, T.; Vereš, P.; Jedicke, R.; Denneau, L.; Beshore, E.

    2014-07-01

    Since the theory of a spherical reservoir of comets far beyond the planetary orbits (Oort, 1950) and subsequent work on origin and evolution of planets and small bodies (Charnoz and Morbidelli, 2003) it has been suggested that countless comets have left the Solar System shortly after its formation. Hence, it is likely that the other planetary systems ejected comets into interstellar space as well. However, the interstellar object (ISO) on a hyperbolic orbit with respect to the Sun has not been observed yet. In our work we derive the number density of ISO based on observational data from the Catalina Sky Survey (2005-2012) and Pan-STARRS1 survey (2010-2013). In the simulation we created 10,000,000 synthetic ISO based on velocity distribution by Grav et al. (2011) and used synthetics in the simulated survey study by using MOPS (Denneau et al., 2013). The number density of ISO was elaborated through the Poisson statistics of a non-detection with the 90 % confidence limit (C.L.) and detection efficiency of observed fields with known limiting magnitudes and survey characteristics. The number density was derived as a function of the absolute magnitude H and size-frequency distribution slope α by taking the cometary activity of long-period comets into account. We found that at 90 % C.L. the density of inert ISO population is 5.4×10^{-2} au^{-3} and 1.6×10^{-3} au^{-3} for the active population for objects larger than H>19 and with α=0.5.

  19. OLEDs under high current densities. Transient electroluminescence turn-on peaks and singlet-triplet quenching

    Energy Technology Data Exchange (ETDEWEB)

    Kasemann, Daniel

    2012-02-27

    This work focuses on a better understanding of the behavior of organic light emitting devices (OLEDs) under intense electrical excitation. Attaining high exciton densities in organic semiconductors by electrical excitation is of special interest for the field of organic semiconductor lasers (OSLs). In these devices, the high singlet exciton density needed in the active layer to obtain population inversion is easily created by pulsed optical pumping, but direct electrical pumping has not been achieved yet. First, the steps necessary to achieve stable high current densities in organic semiconductors are discussed. After determining the optimal excitation scheme using single p-doped transport layers, the device complexity is increased up to full p-i-n OLEDs with their power dependent emission spectra. For this purpose, two exemplary emitter systems are chosen: the fluorescent laser dye 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) doped into Aluminum(III)bis (2-methyl-8-quinolinato)-4-phenylphenolate (Alq{sub 3}) and the efficient phosphorescent emitter system N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine (alpha-NPD) doped by Iridium(III) bis(2-methyl-dibenzo[f,h]quinoxaline)(acetylacetonate) (Ir(MDQ){sub 2}(acac)). For pulsed excitation using 50 ns pulses and a repetition rate of 1 kHz, single 100 nm thin p- and n-doped transport layers sustain current densities of over 6 kA/cm{sup 2}. While the maximum current density decreases with increasing device thickness, the full OLEDs still sustain current densities beyond 800 A/cm{sup 2} and exhibit a continuously increasing emission intensity with increasing input power. Next, the time-resolved emission behavior of the singlet and triplet emitter device at high excitation densities is analyzed on the nanosecond scale. Here, the peak emission intensity of the phosphorescent emitter system is found to be more than eight times lower than for the singlet emitter system at comparable current

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

    Science.gov (United States)

    Singh, Anand; Sharma, S. P.

    2016-10-01

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

  1. Time-dependent current-density-functional theory for the metallic response of solids

    NARCIS (Netherlands)

    Romaniello, P; de Boeij, PL

    2005-01-01

    We extend the formulation of time-dependent current-density-functional theory for the linear response properties of dielectric and semi-metallic solids [Kootstra , J. Chem. Phys. 112, 6517 (2000)] to treat metals as well. To achieve this, the Kohn-Sham response functions have to include both interba

  2. Time-dependent current-density-functional theory for the metallic response of solids

    NARCIS (Netherlands)

    Romaniello, P; de Boeij, PL

    We extend the formulation of time-dependent current-density-functional theory for the linear response properties of dielectric and semi-metallic solids [Kootstra , J. Chem. Phys. 112, 6517 (2000)] to treat metals as well. To achieve this, the Kohn-Sham response functions have to include both

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

    NARCIS (Netherlands)

    Gidopoulos, NI; Wilson, S

    2003-01-01

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

  4. Reliability of quantitative EEG (qEEG) measures and LORETA current source density at 30 days.

    Science.gov (United States)

    Cannon, Rex L; Baldwin, Debora R; Shaw, Tiffany L; Diloreto, Dominic J; Phillips, Sherman M; Scruggs, Annie M; Riehl, Timothy C

    2012-06-14

    There is a growing interest for using quantitative EEG and LORETA current source density in clinical and research settings. Importantly, if these indices are to be employed in clinical settings then the reliability of these measures is of great concern. Neuroguide (Applied Neurosciences) is sophisticated software developed for the analyses of power, and connectivity measures of the EEG as well as LORETA current source density. To date there are relatively few data evaluating topographical EEG reliability contrasts for all 19 channels and no studies have evaluated reliability for LORETA calculations. We obtained 4 min eyes-closed and eyes-opened EEG recordings at 30-day intervals. The EEG was analyzed in Neuroguide and FFT power, coherence and phase was computed for traditional frequency bands (delta, theta, alpha and beta) and LORETA current source density was calculated in 1 Hz increments and summed for total power in eight regions of interest (ROI). In order to obtain a robust measure of reliability we utilized a random effects model with an absolute agreement definition. The results show very good reproducibility for total absolute power and coherence. Phase shows lower reliability coefficients. LORETA current source density shows very good reliability with an average 0.81 for ECB and 0.82 for EOB. Similarly, the eight regions of interest show good to very good agreement across time. Implications for future directions and use of qEEG and LORETA in clinical populations are discussed.

  5. Advanced Tokamak current density profiles for non-inductive Tore Supra operation

    Energy Technology Data Exchange (ETDEWEB)

    Kazarian-Vibert, F.; Litaudon, X.; Arslanbekov, R.; Bibet, P.; Froissard, P.; Goniche, M.; Hoang, G.T.; Joffrin, E.; Moreau, D.; Peysson, Y.; Rey, G. [Association Euratom-CEA, Centre d`Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee

    1995-12-31

    This document deals with the advanced Tokamak concept concerning self consistent hollow current density profiles. Several Lower Hybrid experiments performed on Tore Supra are presented: the feasibility of the constant-flux operation mode is demonstrated and a new improved confinement regime with a reversed shear has been obtained. (TEC). 12 refs., 5 figs.

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    In this work the durability of solid oxide cells for co-electrolysis of steam and carbon dioxide (45 % H2O + 45 % CO2 + 10 % H2) at high current densities was investigated. The tested cells are Ni-YSZ electrode supported, with a YSZ electrolyte and either a LSM-YSZ or LSCF-CGO oxygen electrode...

  7. High current density in light-emitting transistors of organic single crystals

    NARCIS (Netherlands)

    Takenobu, Taishi; Bisri, Satria Zulkarnaen; Takahashi, Tetsuo; Yahiro, Masayuki; Adachi, Chihaya; Iwasa, Yoshihiro

    2008-01-01

    We measured the external electroluminescence quantum efficiency (eta(ext)) in light-emitting field-effect transistors (LETs) made of organic single crystals and found that, in the ambipolar transport region, eta(ext) is not degraded up to several hundreds A/cm(2) current-density range, which is 2 or

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

    CSIR Research Space (South Africa)

    Gerber, G

    2011-03-01

    Full Text Available Particle image velocimetry scalar measurements were carried out on the body of a stably stratified density current with an inlet Reynolds number of 2,300 and bulk Richardson number of 0.1. These measurements allowed the mass and momentum transport...

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

    Science.gov (United States)

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

    2016-10-01

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

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

    Science.gov (United States)

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

    2016-11-01

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

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

    DEFF Research Database (Denmark)

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

    2015-01-01

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

  12. Investigation of the Critical Current Density of YBaCuO high-temperature Superconductor Ceramic

    OpenAIRE

    METSKHVARISHVILI, I. R.; KEKELIDZE, N. P.; METSKHVARISHVILI, M. R.

    2002-01-01

    The method of high harmonics is used to investigate penetration of low magnetic fields within the Y1Ba2Cu3O7 high-temperature superconductor ceramic. Given experimental results are explained by the modal dependencies between the value of critical current density and the magnetic induction B: jc(B) = jc(0){\\frac{{B02}} {{B02 + B2}}}.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-11-15

    We report the effect of different current densities on sulfur generation at Nb surface in the electropolishing (EP) with aged electrolyte. In this regard, we conducted a series of electropolishing (EP) experiments in aged EP electrolyte with high (≈50 mA/cm{sup 2}) and low (≈30 mA/cm{sup 2}) current densities on Nb surfaces. The experiments were carried out both for laboratory coupons and a real Nb single cell cavity with six witness samples located at three typical positions (equator, iris and beam pipe). Sample's surfaces were investigated by XPS (X-ray photoelectron spectroscopy), SEM (scanning electron microscope) and EDX (energy dispersive X-ray spectroscopy). The surface analysis showed that the EP with a high current density produced a huge amount of sulfate/sulfite particles at Nb surface whereas the EP with a low current density was very helpful to mitigate sulfate/sulfite at Nb surface in both the experiments.

  14. Electrical safety in spinal cord stimulation: current density analysis by computer modeling

    NARCIS (Netherlands)

    Wesselink, W.A.; Holsheimer, J.

    1995-01-01

    The possibility of tissue damage in spinal cord stimulation was investigated in a computer modeling study. A decrease of the electrode area in monopolar stimulation resulted in an increase of the current density at the electrode surface. When comparing the modeling results with experimental data

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

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Tianni [State key Laboratory for Mechanical Behavior of Materials of Xi' an Jiaotong University, Xi' an 710014 (China); SMRC, Northwest Institute for Nonferrous Metal Research, Xi' an 710016 (China); Zhang, Cuiping [SMRC, Northwest Institute for Nonferrous Metal Research, Xi' an 710016 (China); Guo, Shengwu [State key Laboratory for Mechanical Behavior of Materials of Xi' an Jiaotong University, Xi' an 710014 (China); Wu, Yifang [State key Laboratory for Mechanical Behavior of Materials of Xi' an Jiaotong University, Xi' an 710014 (China); SMRC, Northwest Institute for Nonferrous Metal Research, Xi' an 710016 (China); Li, Chengshan, E-mail: csli368@126.com [SMRC, Northwest Institute for Nonferrous Metal Research, Xi' an 710016 (China); Zhou, Lian [State key Laboratory for Mechanical Behavior of Materials of Xi' an Jiaotong University, Xi' an 710014 (China); SMRC, Northwest Institute for Nonferrous Metal Research, Xi' an 710016 (China)

    2015-12-15

    Highlights: • Ca substituting Yb element in Bi-2212 single crystal. • The critical current density of this sample is the highest without the optimal Tc value. • The Cu–O{sub 2} and Ca–O layers in pure and doping samples are observed using HRTEM. • The optimal defect density is calculated. - Abstract: Bi{sub 2}Sr{sub 2}Ca{sub 1−x}Yb{sub x}Cu{sub 2}O{sub 8+δ} (Bi-2212) single crystals with x = 0.000, 0.005, 0.010 and 0.020 have been prepared by self-flux method. The influences of Yb doping on the formation of the dislocations in the lattice structures, as well as the related current carrying capability are investigated. Due to the SQUID measurement and the Bean model calculation, the maximum critical current density (Jc) is obtained when the Yb doping content is x = 0.010, though the Tc and the carrier concentration are not in the optimal region. Based on the HRTEM analyses of the Ca–O and Cu–O{sub 2} layers, the optimal dislocation density in the Cu–O{sub 2} layers is deduced according to the number of the dislocations per unit area. Besides, the sizes of the dislocations also prove the effectiveness of Yb substitution on the enhancement of the current carrying capability in Bi-2212 single crystals.

  16. Electrochemical impedance spectroscopy analysis of porous silicon prepared by photo-electrochemical etching: current density effect

    Science.gov (United States)

    Husairi, F. S.; Rouhi, J.; Eswar, K. A.; Zainurul, A. Z.; Rusop, M.; Abdullah, S.

    2014-09-01

    Electrical impedance characteristics of porous silicon nanostructures (PSiNs) in frequency function were studied. PSiNs were prepared through photo-electrochemical etching method at various current densities (15-40 mA/cm2) and constant etching time. The atomic force microscope images of PSiNs show that pore diameter and roughness increase when current density increases to 35 mA/cm2. The surface roughness subsequently decreases because of continuous etching of pillars, and a second etching process occurs. Photoluminescence spectra show blue and red shift with increasing applied current density that is attributed to PSiNs size. Variations of electrical resistance and capacitance values of PSiNs were measured using electrochemical impedance spectroscopy analysis. These results indicate that PSiNs prepared at 20 mA/cm2 current density have uniform porous structures with a large number of pillars. Furthermore, this PSiNs structure influences large values of charge transfer resistance and double layer capacitance, indicating potential application in sensors.

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

    Science.gov (United States)

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

    2014-11-01

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

  18. Superconducting technology for overcurrent limiting in a 25 kA current injection system

    Science.gov (United States)

    Heydari, Hossein; Faghihi, Faramarz; Sharifi, Reza; Poursoltanmohammadi, Amir Hossein

    2008-09-01

    Current injection transformer (CIT) systems are within the major group of the standard type test of high current equipment in the electrical industry, so their performance becomes very important. When designing high current systems, there are many factors to be considered from which their overcurrent protection must be ensured. The output of a CIT is wholly dependent on the impedance of the equipment under test (EUT). Therefore current flow beyond the allowable limit can occur. The present state of the art provides an important guide to developing current limiters not only for the grid application but also in industrial equipment. This paper reports the state of the art in the technology available that could be developed into an application of superconductivity for high current equipment (CIT) protection with no test disruption. This will result in a greater market choice and lower costs for equipment protection solutions, reduced costs and improved system reliability. The paper will also push the state of the art by using two distinctive circuits, closed-core and open-core, for overcurrent protection of a 25 kA CIT system, based on a flux-lock-type superconducting fault current limiter (SFCL) and magnetic properties of high temperature superconducting (HTS) elements. An appropriate location of the HTS element will enhance the rate of limitation with the help of the magnetic field generated by the CIT output busbars. The calculation of the HTS parameters for overcurrent limiting is also performed to suit the required current levels of the CIT.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-06-15

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

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

    Science.gov (United States)

    Yuen-Zhou, Joel; Aspuru-Guzik, Alán

    2013-08-14

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

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

    Science.gov (United States)

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

    2014-08-29

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

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

    Science.gov (United States)

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

    2003-10-07

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

  3. Current limiting characteristics of transformer type SFCL with coupled secondary windings according to its winding direction

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Sung Hun [Dept. of Electrical Engineering, Soongsil University, Seoul (Korea, Republic of); Han, Tae Hee [Dept. of Aero Materials Engineering, Jungwon University, Goesan (Korea, Republic of)

    2017-06-15

    In this paper, the current limiting characteristics of the transformer type superconducting fault current limiter (SFCL) with the two coupled secondary windings due to its winding direction were analyzed. To analyze the dependence of transient fault current limiting characteristics on the winding direction of the additional secondary winding, the fault current limiting tests of the SFCL with an additional secondary winding, wound as subtractive polarity winding and additive polarity winding, were carried out. The time interval of quench occurrence between two superconducting elements comprising the transformer type SFCL with the additional secondary winding was confirmed to be affected by the winding direction of the additional secondary winding. In case of the subtractive polarity winding of the additional secondary winding, the time interval of the quench occurrence in two superconducting elements was shorter than the case of the additive polarity winding.

  4. Estimating Heat and Mass Transfer Processes in Green Roof Systems: Current Modeling Capabilities and Limitations (Presentation)

    Energy Technology Data Exchange (ETDEWEB)

    Tabares Velasco, P. C.

    2011-04-01

    This presentation discusses estimating heat and mass transfer processes in green roof systems: current modeling capabilities and limitations. Green roofs are 'specialized roofing systems that support vegetation growth on rooftops.'

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

    Science.gov (United States)

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

    2010-02-01

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

  6. Link community detection through global optimization and the inverse resolution limit of partition density

    CERN Document Server

    Lee, Juyong; Lee, Jooyoung; Brooks, Bernard R; Ahn, Yong-Yeol

    2016-01-01

    We investigate the possibility of global optimization-based overlapping community detection, using link community framework. We first show that partition density, the original quality function used in link community detection method, is not suitable as a quality function for global optimization because it prefers breaking communities into triangles except in highly limited conditions. We analytically derive those conditions and confirm it with computational results on direct optimization of various synthetic and real-world networks. To overcome this limitation, we propose alternative approaches combining the weighted line graph transformation and existing quality functions for node-based communities. We suggest a new line graph weighting scheme, a normalized Jaccard index. Computational results show that community detection using the weighted line graphs generated with the normalized Jaccard index leads to a more accurate community structure.

  7. Limiting Short-term Noise versus Optical Density in a Direct Absorption Spectrometer for Trace Gas Detection

    Science.gov (United States)

    Jervis, D.

    2016-12-01

    Field-deployable trace gas monitors are important for understanding a multitude of atmospheric processes: from forest photosynthesis and respiration [1], to fugitive methane emissions [2] and satellite measurement validation [3]. Consequently, a detailed knowledge of the performance limitations of these instruments is essential in order to establish reliable datasets. We present the short-term ( >1 Hz) performance of a long-pass direct absorption spectrometer as a function of the optical density of the absorption transition being probed. In particular, we identify fluctuations in the laser intensity as limiting the optical density uncertainty to 4x10-6/√Hz for weak transitions, and noise in the laser drive current as limiting the fractional noise in the optical density to 4x10-5/√Hz for deep transitions. We provide numerical and analytical predictions for both effects, as well as using the understanding of this phenomena to estimate how noise on neighboring strong and weak transitions couple to each other. All measurements were performed using the Aerodyne Research TILDAS Monitor, but are general to any instrument that uses direct absorption spectroscopy as a detection method. Wehr, R., et al. "Seasonality of temperate forest photosynthesis and daytime respiration." Nature 534.7609 (2016): 680-683. Conley, S., et al. "Methane emissions from the 2015 Aliso Canyon blowout in Los Angeles, CA." Science 351.6279 (2016): 1317-1320. Emmons, L. K., et al. "Validation of Measurements of Pollution in the Troposphere (MOPITT) CO retrievals with aircraft in situ profiles." Journal of Geophysical Research: Atmospheres 109.D3 (2004).

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

    Science.gov (United States)

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

    2017-03-24

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

  9. Thickness scaling of the space-charge-limited current in poly(p-phenylene vinylene)

    NARCIS (Netherlands)

    Blom, PWM; Tanase, C; de Leeuw, DM; Coehoorn, R

    2005-01-01

    Charge transport in light-emitting diodes (LEDs) based on a polyp-phenylene vinylene) (PPV) derivative is investigated as a function of sample thickness. Via the thickness dependence, the contributions from the electric field and charge carrier density to the mobility in space-charge-limited (SCL) d

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

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Baoming; Haque, M. A., E-mail: mah37@psu.edu [Mechanical and Nuclear Engineering, The Pennsylvania State University, 314, Leonhard Building, University Park, Pennsylvania 16802 (United States); Mag-isa, Alexander E.; Kim, Jae-Hyun [Korea Institute of Machinery and Materials, 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of); Lee, Hak-Joo [Korea Institute of Machinery and Materials, 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of); Center for Advanced Meta-Materials (CAMM), 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of)

    2015-10-19

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

  11. Effects of current density on preparation of grainy electrolytic manganese dioxide

    Institute of Scientific and Technical Information of China (English)

    GUO Hua-jun; ZHU Bing-quan; LI Xin-hai; ZHANG Xin-ming; WANG Zhi-xing; PENG Wen-jie; LIU Lu-ping

    2005-01-01

    Grainy electrolytic manganese dioxide was prepared by electrodeposition in a 0.9 mol/L MnSO4 and 2.5 mol/L H2SO4 solution. The structure, particle size and appearance of the grainy electrolytic manganese dioxide were determined by powder X-ray diffraction, laser particle size analysis and scanning electron micrographs measurements. Current density has important effects on cell voltage, anodic current efficiency and particle size of the grainy electrolytic manganese dioxide, and the optimum current density is 30 A/dm 2. The grainy electrolytic manganese dioxide electrodeposited under the optimum conditions consists of γ-MnO2 with an orthorhombic lattice structure; the grainy electrolytic manganese dioxide has a spherical or sphere-like appearance and a narrow particle size distribution with an average particle diameter of 7.237 μm.

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

    Science.gov (United States)

    Andrews, B. J.; Manga, M.

    2010-12-01

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

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    Li, Qian

    Ultrasound Current Source Density Imaging (UCSDI) is a noninvasive modality for mapping electrical activities in the body (brain and heart) in 4-dimensions (space + time). Conventional cardiac mapping technologies for guiding the radiofrequency ablation procedure for treatment of cardiac arrhythmias have certain limitations. UCSDI can potentially overcome these limitations and enhance the electrophysiology mapping of the heart. UCSDI exploits the acoustoelectric (AE) effect, an interaction between ultrasound pressure and electrical resistivity. When an ultrasound beam intersects a current path in a material, the local resistivity of the material is modulated by the ultrasonic pressure, and a change in voltage signal can be detected based on Ohm's Law. The degree of modulation is determined by the AE interaction constant K. K is a fundamental property of any type of material, and directly affects the amplitude of the AE signal detected in UCSDI. UCSDI requires detecting a small AE signal associated with electrocardiogram. So sensitivity becomes a major challenge for transferring UCSDI to the clinic. This dissertation will determine the limits of sensitivity and resolution for UCSDI, balancing the tradeoff between them by finding the optimal parameters for electrical cardiac mapping, and finally test the optimized system in a realistic setting. This work begins by describing a technique for measuring K, the AE interaction constant, in ionic solution and biological tissue, and reporting the value of K in excised rabbit cardiac tissue for the first time. K was found to be strongly dependent on concentration for the divalent salt CuSO4, but not for the monovalent salt NaCl, consistent with their different chemical properties. In the rabbit heart tissue, K was determined to be 0.041 +/- 0.012 %/MPa, similar to the measurement of K in physiologic saline: 0.034 +/- 0.003 %/MPa. Next, this dissertation investigates the sensitivity limit of UCSDI by quantifying the relation

  15. Mapping the density of scattering centers limiting the electron mean free path in graphene.

    Science.gov (United States)

    Giannazzo, Filippo; Sonde, Sushant; Nigro, Raffaella Lo; Rimini, Emanuele; Raineri, Vito

    2011-11-09

    Recently, giant carrier mobility μ (>10(5) cm(2) V(-1) s(-1)) and micrometer electron mean free path (l) have been measured in suspended graphene or in graphene encapsulated between inert and ultraflat BN layers. Much lower μ values (10000-20000 cm(2) V(-1) s(-1)) are typically reported in graphene on common substrates (SiO(2), SiC) used for device fabrication. The debate on the factors limiting graphene electron mean free path is still open with charged impurities (CI) and resonant scatterers (RS) indicated as the most probable candidates. As a matter of fact, the inhomogeneous distribution of such scattering sources in graphene is responsible of nanoscale lateral inhomogeneities in the electronic properties, which could affect the behavior of graphene nanodevices. Hence, high resolution two-dimensional (2D) mapping of their density is very important. Here, we used scanning capacitance microscopy/spectroscopy to obtain 2D maps of l in graphene on substrates with different dielectric permittivities, that is, SiO(2) (κ(SiO2) = 3.9), 4H-SiC (0001) (κ(SiC) = 9.7) and the very-high-κ perovskite strontium titanate, SrTiO(3) (001), briefly STO (κ(STO) = 330). After measuring l versus the gate bias V(g) on an array of points on graphene, maps of the CI density (N(CI)) have been determined by the neutrality point shift from V(g) = 0 V in each curve, whereas maps of the RS density (N(RS)) have been extracted by fitting the dependence of l on the carrier density (n). Laterally inhomogeneous densities of CI and RS have been found. The RS distribution exhibits an average value ∼3 × 10(10) cm(-2) independently on the substrate. For the first time, a clear correlation between the minima in the l map and the maxima in the N(CI) map is obtained for graphene on SiO(2) and 4H-SiC, indicating that CI are the main source of the lateral inhomogeneity of l. On the contrary, the l and N(CI) maps are uncorrelated in graphene on STO, while a clear correlation is found between l

  16. Density of Saturated Nuclear Matter at Large $N_{c}$ and Heavy Quark Mass Limits

    CERN Document Server

    Adhikari, Prabal; Datta, Ishaun

    2013-01-01

    We exhibit the existence of stable, saturated nuclear matter in the large $N_{c}$ and heavy quark mass limits of QCD. In this limit, baryons (with the same spin flavor structure) interact at leading order in $N_{c}$ via a repulsive interaction due to the Pauli exclusion principle and at subleading order in $1/N_c$ via the exchange of glueballs. Assuming that the lightest glueball is a scalar, which implies that the subleading baryon interaction is attractive, we find that nuclear matter saturates since the subleading attractive interaction is longer ranged than the leading order repulsive one. We find that the saturated matter is in the form of a crystal with either a face-centered cubic or a hexagonal-close-packed symmetry with baryon densities of $\\mathcal{O}((\\, \\tilde{\\alpha}_{s} m_q (\\ln (N_{c}m_{q}\\Lambda_{\\textrm{QCD}}^{-1}))^{-1})^3 )$. Remarkably, the leading order expression for the density of saturated nuclear matter is independent of the lighest glueball mass and scalar-glueball-baryon coupling in...

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

    Science.gov (United States)

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

    1991-01-01

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

  18. Diabetes Mellitus and Cardiovascular Prevention: The Role and the Limitations of Currently Available Antiplatelet Drugs

    Directory of Open Access Journals (Sweden)

    A. Tufano

    2011-01-01

    This paper reviews the role of currently available antiplatelet drugs in primary and secondary prevention of vascular events in diabetic patients and the limitations of these drugs, and it discusses the role of novel and more potent antiplatelets and of new agents currently under clinical development.

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

    Science.gov (United States)

    Derrida, Bernard

    2007-07-01

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

  20. InP Gunn Diodes with Current Limiting Contact for High Efficiency Gunn Oscillators

    Science.gov (United States)

    Kim, Mi-Ra; Rhee, Jin-Koo; Lee, Chang-Woo; Chae, Yeon-Sik; Choi, Jae-Hyun; Kim, Wan-Joo

    We fabricated and examined current limiting effect for InP Gunn diodes with stable depletion layer mode operation of diodes for high efficiency Gunn oscillators. Current limiting at the cathode was achieved by a shallow Schottky barrier at the interface. We discussed fabrication procedure, the results for negative differential resistance and rf tests for InP Gunn diodes. It was shown that the fabricated Gunn diodes have the output power of 10.22dBm at a frequency of 90.13GHz. Its input voltage and corresponding current were 8.55V and 252mA, respectively.

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

    Directory of Open Access Journals (Sweden)

    Batool Eneaze B. Al-Jumaili

    2016-01-01

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

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

    Science.gov (United States)

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

    2008-01-01

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

  3. Over-limiting Current and Control of Dendritic Growth by Surface Conduction in Nanopores

    CERN Document Server

    Han, Ji-Hyung; Bai, Peng; Bazant, Martin Z

    2014-01-01

    Understanding over-limiting current (faster than diffusion) is a long-standing challenge in electrochemistry with applications in desalination and energy storage. Known mechanisms involve either chemical or hydrodynamic instabilities in unconfined electrolytes. Here, it is shown that over-limiting current can be sustained by surface conduction in nano pores, without any such instabilities, and used to control dendritic growth during electrodeposition. Copper electrode posits are grown in anodized aluminum oxide membranes with polyelectrolyte coatings to modify the surface charge. At low currents, uniform electroplating occurs, unaffected by surface modification due to thin electric double layers, but the morphology changes dramatically above the limiting current. With negative surface charge, growth is enhanced along the nanopore surfaces, forming surface dendrites and nanotubes behind a deionization shock. With positive surface charge, dendrites avoid the surfaces and are either guided along the nanopore cen...

  4. A superconducting direct-current limiter with a power of up to 8 MVA

    Science.gov (United States)

    Fisher, L. M.; Alferov, D. F.; Akhmetgareev, M. R.; Budovskii, A. I.; Evsin, D. V.; Voloshin, I. F.; Kalinov, A. V.

    2016-12-01

    A resistive switching superconducting fault current limiter (SFCL) for DC networks with a nominal voltage of 3.5 kV and a nominal current of 2 kA was developed, produced, and tested. The SFCL has two main units—an assembly of superconducting modules and a high-speed vacuum circuit breaker. The assembly of superconducting modules consists of nine (3 × 3) parallel-series connected modules. Each module contains four parallel-connected 2G high-temperature superconducting (HTS) tapes. The results of SFCL tests in the short-circuit emulation mode with a maximum current rise rate of 1300 A/ms are presented. The SFCL is capable of limiting the current at a level of 7 kA and break it 8 ms after the current-limiting mode begins. The average temperature of HTS tapes during the current-limiting mode increases to 210 K. After the current is interrupted, the superconductivity recovery time does not exceed 1 s.

  5. AVERAGE GEOMETRICAL FEATURES OF THE ELECTRON WAVE PACKAGES DISTRIBUTION IN METALLIC CONDUCTORS WITH PULSED AXIAL CURRENT OF HIGH DENSITY

    Directory of Open Access Journals (Sweden)

    M. I. Baranov

    2016-11-01

    Full Text Available Purpose. Calculation and experimental determination of average geometrical features of distributing of macroscopic electron wave packages (EWP in round cylindrical metallic conductors with the pulsed axial current of high density. Methodology. Theoretical bases of the electrical engineering, bases of atomic and quantum physics, electrophysics bases of technique of high voltage and high pulsed currents. Results. The results of the conducted calculation and experimental researches are resulted on close determination of average geometrical features of distribution of longitudinal and radial EWP of macroscopic sizes in the indicated conductors. These descriptions are included by the average widths of «hot» and «cold» longitudinal and radial areas of conductor, and also average steps of division into the periods of similar areas. Results of the executed calculations and high temperature experiments for average geometrical features of longitudinal EWP in the zincked steel wire of diameter of 1.6 mm and length of 320 mm with the aperiodic impulse of current of temporal form 9 ms/160 ms and by amplitude 745 A coincide within the limits of 19 %. Originality. First with the use of methods of atomic and quantum physics the features of the stochastic distributing and mean values of basic geometrical sizes are analysed macroscopic longitudinal and radial EWP in round cylindrical metallic conductors with the pulsed axial current of high density. Practical value. Drawing on the got results in practice will allow more reliably to forecast geometrical sizes and places of localization of arising up in the probed metallic conductors with pulsed axial current of high density longitudinal and radial EWP.

  6. First experimental results with the Current Limit Avoidance System at the JET tokamak

    Energy Technology Data Exchange (ETDEWEB)

    De Tommasi, G. [Associazione EURATOM-ENEA-CREATE, Università di Napoli Federico II, Via Claudio 21, 80125 Napoli (Italy); Galeani, S. [Dipartimento di Informatica, Sistemi e Produzione, Università di Roma, Tor Vergata, Rome (Italy); Jachmich, S. [Association EURATOM-Belgian State, Koninklijke Militaire School - Ecole Royale Militaire, B-1000 Brussels (Belgium); Joffrin, E. [IRFM-CEA, Centre de Cadarache, 13108 Saint-paul-lez-Durance (France); Lennholm, M. [EFDA Close Support Unit, Culham Science Centre, OX14 3DB Abingdon (United Kingdom); European Commission, B-1049 Brussels (Belgium); Lomas, P.J. [Euratom-CCFE, Culham Science Centre, OX14 3DB Abingdon (United Kingdom); Neto, A.C. [Associazione EURATOM-IST, Instituto de Plasmas e Fusao Nuclear, IST, 1049-001 Lisboa (Portugal); Maviglia, F. [Associazione EURATOM-ENEA-CREATE, Via Claudio 21, 80125 Napoli (Italy); McCullen, P. [Euratom-CCFE, Culham Science Centre, OX14 3DB Abingdon (United Kingdom); Pironti, A. [Associazione EURATOM-ENEA-CREATE, Università di Napoli Federico II, Via Claudio 21, 80125 Napoli (Italy); Rimini, F.G. [Euratom-CCFE, Culham Science Centre, OX14 3DB Abingdon (United Kingdom); Sips, A.C.C. [European Commission, B-1049 Brussels (Belgium); Varano, G.; Vitelli, R. [Dipartimento di Informatica, Sistemi e Produzione, Università di Roma, Tor Vergata, Rome (Italy); Zaccarian, L. [CNRS, LAAS, 7 Avenue du Colonel Roche, F-31400 Toulouse (France); Universitè de Toulouse, LAAS, F-31400 Toulouse (France)

    2013-06-15

    The Current Limit Avoidance System (CLA) has been recently deployed at the JET tokamak to avoid current saturations in the poloidal field (PF) coils when the eXtreme Shape Controller is used to control the plasma shape. In order to cope with the current saturation limits, the CLA exploits the redundancy of the PF coils system to automatically obtain almost the same plasma shape using a different combination of currents in the PF coils. In the presence of disturbances it tries to avoid the current saturations by relaxing the constraints on the plasma shape control. The CLA system has been successfully implemented on the JET tokamak and fully commissioned in 2011. This paper presents the first experimental results achieved in 2011–2012 during the restart and the ITER-like wall campaigns at JET.

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

    Science.gov (United States)

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

    2007-05-01

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

  8. The current density in quantum electrodynamics in time-dependent external potentials and the Schwinger effect

    CERN Document Server

    Zahn, Jochen

    2015-01-01

    In the framework of quantum electrodynamics (QED) in external potentials, we introduce a method to compute the time-dependence of the expectation value of the current density for time-dependent homogeneous external electric fields. We apply it to the so-called Sauter pulse. For late times, our results agree with the asymptotic value due to electron-positron pair production. For sub-critical peak field strengths, or results agree very well with the general expression derived by Serber for the linearization in the external field. In particular, the expectation value of the current density at intermediate times can be much greater than at asymptotic times. We comment on consequences of these findings for recent proposals to test the Schwinger effect with high intensity lasers using processes at intermediate times.

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

    Science.gov (United States)

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

    2014-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Eugeniusz Kurgan

    2004-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Zbigniew A. Styczynski

    2013-07-01

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

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

    Science.gov (United States)

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

    2016-06-01

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

  13. Current densities of thin filament MgB2/Ti/GlidCop® wire

    Science.gov (United States)

    Kováč, P.; Hušek, I.; Melišek, T.; Kopera, L.

    2011-10-01

    Fine-filamentary MgB2/Ti/GlidCop wire has been produced by an in situ process. Hydrostatic extrusion, drawing and two-axis rolling were used for wire deformation up to the size of 0.2 × 0.2 mm2. An averaged filament size of 7.6-14 µm was obtained for two-axis rolled wire and tape, which are the smallest MgB2 filaments known so far. Very short annealing periods (3-7 min) were used for the thinnest filaments, resulting in a critical current density of ≈12 000 A cm - 2 at 8 T and 4.2 K. The results presented demonstrate the ability to prepare uniform ≈10 µm size and high current density filamentary MgB2 wires in nonmagnetic sheaths, which can be applied for DC and AC coils.

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

    Science.gov (United States)

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

    2009-06-14

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

  15. Strong critical current density enhancement in NiCu/NbN superconducting nanostripes for optical detection

    Science.gov (United States)

    Marrocco, N.; Pepe, G. P.; Capretti, A.; Parlato, L.; Pagliarulo, V.; Peluso, G.; Barone, A.; Cristiano, R.; Ejrnaes, M.; Casaburi, A.; Kashiwazaki, N.; Taino, T.; Myoren, H.; Sobolewski, Roman

    2010-08-01

    We present measurements of ferromagnet/superconductor (NiCu/NbN) and plain superconducting (NbN) nanostripes with the linewidth ranging from 150 to 300 nm. The NiCu (3 nm)/NbN (8 nm) bilayers, as compared to NbN (8 nm), showed a up to six times increase in their critical current density, reaching at 4.2 K the values of 5.5 MA/cm2 for a 150 nm wide nanostripe meander and 12.1 MA/cm2 for a 300 nm one. We also observed six-time sensitivity enhancement when the 150 nm wide NiCu/NbN nanostripe was used as an optical detector. The strong critical current enhancement is explained by the vortex pinning strength and density increase in NiCu/NbN bilayers and confirmed by approximately tenfold increase in the vortex polarizability factor.

  16. Real-time identification of the current density profile in the JET Tokamak: method and validation

    CERN Document Server

    Mazon, Didier; Boulbe, Cédric; Faugeras, Blaise; Boboc, A; Brix, M; De Vries, P; Sharapov, S; Zabeo, L

    2009-01-01

    The real-time reconstruction of the plasma magnetic equilibrium in a Tokamak is a key point to access high performance regimes. Indeed, the shape of the plasma current density profile is a direct output of the reconstruction and has a leading effect for reaching a steady-state high performance regime of operation. In this paper we present the methodology followed to identify numerically the plasma current density in a Tokamak and its equilibrium. In order to meet the real-time requirements a C++ software has been developed using the combination of a finite element method, a nonlinear fixed point algorithm associated to a least square optimization procedure. The experimental measurements that enable the identification are the magnetics on the vacuum vessel, the interferometric and polarimetric measurements on several chords and the motional Stark effect. Details are given about the validation of the reconstruction on the JET tokamak, either by comparison with ?off-line' equilibrium codes or real time software ...

  17. Current progress in high cell density yeast bioprocesses for bioethanol production.

    Science.gov (United States)

    Westman, Johan O; Franzén, Carl Johan

    2015-08-01

    High capital costs and low reaction rates are major challenges for establishment of fermentation-based production systems in the bioeconomy. Using high cell density cultures is an efficient way to increase the volumetric productivity of fermentation processes, thereby enabling faster and more robust processes and use of smaller reactors. In this review, we summarize recent progress in the application of high cell density yeast bioprocesses for first and second generation bioethanol production. High biomass concentrations obtained by retention of yeast cells in the reactor enables easier cell reuse, simplified product recovery and higher dilution rates in continuous processes. High local cell density cultures, in the form of encapsulated or strongly flocculating yeast, furthermore obtain increased tolerance to convertible fermentation inhibitors and utilize glucose and other sugars simultaneously, thereby overcoming two additional hurdles for second generation bioethanol production. These effects are caused by local concentration gradients due to diffusion limitations and conversion of inhibitors and sugars by the cells, which lead to low local concentrations of inhibitors and glucose. Quorum sensing may also contribute to the increased stress tolerance. Recent developments indicate that high cell density methodology, with emphasis on high local cell density, offers significant advantages for sustainable second generation bioethanol production.

  18. Current Density Functional Theory Using Meta-Generalized Gradient Exchange-Correlation Functionals.

    Science.gov (United States)

    Furness, James W; Verbeke, Joachim; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M

    2015-09-08

    We present the self-consistent implementation of current-dependent (hybrid) meta-generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn-Sham current density functional theory (KS-CDFT). A unique feature of the nonperturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 au (∼235 kT) in strength. CDFT functionals based on the TPSS and B98 forms are investigated, and their performance is assessed by comparison with accurate coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) data. In the weak field regime, magnetic properties such as magnetizabilities and nuclear magnetic resonance shielding constants show modest but systematic improvements over generalized gradient approximations (GGA). However, in the strong field regime, the mGGA-based forms lead to a significantly improved description of the recently proposed perpendicular paramagnetic bonding mechanism, comparing well with CCSD(T) data. In contrast to functionals based on the vorticity, these forms are found to be numerically stable, and their accuracy at high field suggests that the extension of mGGAs to CDFT via the generalized kinetic energy density should provide a useful starting point for further development of CDFT approximations.

  19. New theorem of classical electromagnetism: equilibrium magnetic field and current density are zero inside ideal conductors

    CERN Document Server

    Fiolhais, Miguel C N; Providencia, C; Nordmark, Arne B

    2010-01-01

    We prove a theorem on the magnetic energy minimum in a system of perfect, or ideal, conductors. It is analogous to Thomson's theorem on the equilibrium electric field and charge distribution in a system of conductors. We first prove Thomson's theorem using a variational principle. Our new theorem is then derived by similar methods. We find that magnetic energy is minimized when the current distribution is a surface current density with zero interior magnetic field; perfect conductors are perfectly diamagnetic. The results agree with currents in superconductors being confined near the surface. The theorem implies a generalized force that expels current and magnetic field from the interior of a conductor that loses its resistivity. Examples of solutions that obey the theorem are presented.

  20. Influence of Fast Neutron Irradiation on Critical Current Densities of Bi-2223/Ag Tape

    Institute of Scientific and Technical Information of China (English)

    Duan Zhenzhong

    2004-01-01

    Experimental results on the magnetic field behavior of the critical current in silver sheathed Bi-2223 tapes are presented. The experiments consist of transport and magnetic measurements in a wide temperature range and in external magnetic field up to 6 T. Significant enhancement of the intragrain critical current densities Jc are observed after irradiation with fast neutron. This is attributed to an improvement of flux pinning capability by the neutron induced defects, but the weak link structure is somewhat damaged as evidenced by the small degradation of transport critical current at low field. According to the measurement of remanent magnetic moment before and after irradiation with fast neutron, the connectivity in Bi-2223 tapes is reduced by 50% after irradiated to a fluence of 2 × 1021 m-2, which resulted in the critical currents degradated by a factor of 10%.

  1. Accurate Prediction of Transimpedances and Equivalent Input Noise Current Densities of Tuned Optical Receiver Front Ends

    DEFF Research Database (Denmark)

    Liu, Qing Zhong

    1991-01-01

    Novel analytical expressions have been derived for calculating transimpedances and equivalent input noise current densities of five tuned optical receiver front ends based on PIN diode and MESFETs or HEMTs. Miller's capacitance, which has been omitted in previous studies, has been taken into acco...... into account. The accuracy of the expressions has been verified by using Touchstone simulator. The agreement between the calculated and simulated front end performances is very good....

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

    Science.gov (United States)

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

    2016-09-01

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

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

    OpenAIRE

    Derrida, B.

    2007-01-01

    These lecture notes give a short review of methods such as the matrix ansatz, the additivity principle or the macroscopic fluctuation theory, developed recently in the theory of non-equilibrium phenomena. They show how these methods allow to calculate the fluctuations and large deviations of the density and of the current in non-equilibrium steady states of systems like exclusion processes. The properties of these fluctuations and large deviation functions in non-equilibrium steady states (fo...

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

    Science.gov (United States)

    Liao, Ke; Zhu, Min; Ding, Lei

    2013-08-01

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

  5. Divergence of the axial current and fermion density in Gross-Neveu models

    CERN Document Server

    Karbstein, Felix

    2007-01-01

    The divergence of the axial current is used to relate the spatial derivative of the fermion density to the bare fermion mass and scalar/pseudoscalar condensates in 1+1 dimensional Gross-Neveu models. This serves as a novel test of known results, to explain simple features of the continuous chiral model and to resolve a conflict concerning the assignment of baryon number to certain multi-fermion bound states.

  6. Multi-Soft gluon limits and extended current algebras at null-infinity

    CERN Document Server

    McLoughlin, Tristan

    2016-01-01

    In this note we consider aspects of the current algebra interpretation of multi-soft limits of tree-level gluon scattering amplitudes in four dimensions. Building on the relation between a positive helicity gluon soft-limit and the Ward identity for a level-zero Kac-Moody current, we use the double-soft limit to define the Sugawara energy-momentum tensor and, by using the triple- and quadruple-soft limits, show that it satisfies the correct OPEs for a CFT. We study the resulting Knizhnik-Zamolodchikov equations and show that they hold for positive helicity gluons in MHV amplitudes. Turning to the sub-leading soft-terms we define a one-parameter family of currents whose Ward identities correspond to the universal tree-level sub-leading soft-behaviour. We compute the algebra of these currents formed with the leading currents and amongst themselves. Finally, by parameterising the ambiguity in the double-soft limit for mixed helicities, we introduce a non-trivial OPE between the holomorphic and anti-holomorphic c...

  7. Influence of the anodic etching current density on the morphology of the porous SiC layer

    Directory of Open Access Journals (Sweden)

    Anh Tuan Cao

    2014-03-01

    Full Text Available In this report, we fabricated a porous layer in amorphous SiC thin films by using constant-current anodic etching in an electrolyte of aqueous diluted hydrofluoric acid. The morphology of the porous amorphous SiC layer changed as the anodic current density changed: At low current density, the porous layer had a low pore density and consisted of small pores that branched downward. At moderate current density, the pore size and depth increased, and the pores grew perpendicular to the surface, creating a columnar pore structure. At high current density, the porous structure remained perpendicular, the pore size increased, and the pore depth decreased. We explained the changes in pore size and depth at high current density by the growth of a silicon oxide layer during etching at the tips of the pores.

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

    Science.gov (United States)

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

    2005-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Gian Carlo Gazzadi

    2015-06-01

    Full Text Available Suspended nanowires (SNWs have been deposited from Co–carbonyl precursor (Co2(CO8 by focused electron beam induced deposition (FEBID. The SNWs dimensions are about 30–50 nm in diameter and 600–850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC and hexagonal close-packed (HCP Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM analysis and by energy-dispersive X-ray (EDX spectroscopy, respectively. Current (I–voltage (V measurements with current densities up to 107 A/cm2 determine different structural transitions in the SNWs, depending on the I–V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 107 A/cm2. The role played by resistive heating and electromigration in these transitions is discussed.

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

    Science.gov (United States)

    Gazzadi, Gian Carlo; Frabboni, Stefano

    2015-01-01

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

  11. Energy transportation via MITL by the linear current flow density up to 7 MA/cm

    Science.gov (United States)

    Korolev, V. D.; Bakshaev, Yu. L.; Bartov, A. V.; Blinov, P. I.; Bryzgunov, V. A.; Chernenko, A. S.; Dan'ko, S. A.; Kalinin, Yu. G.; Kingsep, A. S.; Kazakov, E. D.; Smirnov, V. P.; Smirnova, E. A.; Ustroev, G. I.

    2006-10-01

    The transmission properties of the magnetically self-insulated vacuum transporting line (MITL) were studied on the S-300 pulsed power machine (3 MA, 100 ns) at the high linear current flow density up to dI/db = 7 MA/cm. Experiments were carried out with the short line sections with 10 ÷ 15 mm length and 3 ÷ 5 mm vacuum gap. For measuring of the plasma parameters, the frame ICT photography with the nanosecond temporal resolution in the SXR range and ICT (Image Converter Tube) chronography in visible range were used. The X-ray radiation in various ranges was recorded by the XRD with thin filters (SXR) and by the semiconductor detectors (HXR). The information about current transmission efficiency was obtained by means of magnetic loops and low-inductance shunt. It was determined that dense plasma arose on both anode and cathode when the linear current flow density was low enough, dI/db ≤ 1 MA/cm. A dense plasma moves across the vacuum gap with the velocity (1 ÷ 2) × 106 cm/s. By recording the current and hard X-ray radiation it was found that electron losses in the current front did not exceed 10 ÷ 100 kA. Under strong magnetization of electrons r H = mvc/eB Conceptual Project of fusion reactor on the base of fast Z-pinch has been brought about.

  12. Improving Transient Recovery voltage of circuit breaker using Fault Current Limiter

    Directory of Open Access Journals (Sweden)

    Amir Heidary

    2012-12-01

    Full Text Available This study investigates influence of Fault Current Limiter (FCL on short-circuits current level of substation bus bar splitter circuit breaker and its TRV. An approach for TRV evaluation is developed and applied for proposed power system as shown in this study. FCL circuit is connected to the power system in order to limit TRV. The limiter circuit consists of two equal windings which are turned around unique magnetic core. One of the windings is connected in series with the power system network and the other is connected to the network via series capacitor and power electronic switches. During normal operating condition, both tyristors are in on state and current of the primary and secondary windings are equal. This causes zero impedance of the limiter. During fault, faults current cause the power electronic switch to turn off which increases the limiter impedance. By increasing the limiter impedance, amplitude of TRV decreases substantially. The novel method presented in this study is a cheap and successful scheme.

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

    Energy Technology Data Exchange (ETDEWEB)

    Góral, Anna, E-mail: a.goral@imim.pl [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow (Poland); Nowak, Marek [Institute of Non-Ferrous Metals Gliwice, Light Metals Division Skawina, 19 Pilsudskiego St., 32-050 Skawina (Poland); Berent, Katarzyna; Kania, Bogusz [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow (Poland)

    2014-12-05

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

  14. On the study of phase formation and critical current density in superconducting MgB2

    Indian Academy of Sciences (India)

    Suchitra Rajput; Sujeet Chaudhary; Subhash C Kashyap; Pankaj Srivastava

    2006-06-01

    Superconducting bulk MgB2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic ratios of Mg : B, as against the nominally required Mg : B = 1 : 2 ratio, we have obtained superconducting MgB2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation, transition temperature (C) and critical current density (C) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron spectroscopic analyses of MgB2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established that MgB2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2 : 2 ratio, at temperatures around 790°C. Critical current density has been found to vary systematically with processing temperature.

  15. Modeling Bubble Flow and Current Density Distribution in an Alkaline Electrolysis Cell

    Directory of Open Access Journals (Sweden)

    Ravichandra S. Jupudi

    2009-12-01

    Full Text Available The effect of bubbles on the current density distribution over the electrodes of an alkaline electrolyzer cell is studied using a two-dimensional computational fluid dynamics model. Model includes Eulerian-Eulerian two-phase flow methodology to model the multiphase flow of Hydrogen and Oxygen with water and the behavior of each phase is accounted for using first principle. Hydrogen/Oxygen evolution, flow field and current density distribution are incorporated in the model to account for the complicated physics involved in the process. Fluent 6.2 is used to solve two-phase flow and electrochemistry is incorporated using UDF (User Defined Function feature of Fluent. Model is validated with mesh refinement study and by comparison with experimental measurements. Model is found to replicate the effect of cell voltage and inter-electrode gap (distance between the electrodes on current density accurately. Further, model is found to capture the existence of optimum cell height. The validated model is expected to be a very useful tool in the design and optimization of alkaline electrolyzer cells.

  16. Iontophoretic Permeation of Lisinopril at Different Current Densities and Drug Concentrations

    Directory of Open Access Journals (Sweden)

    Ashish Jain

    2012-08-01

    Full Text Available Purpose: The purpose of the present work was to assess iontophoretic permeation of Lisinopril at different current densities and concentrations for development of patient-controlled active transdermal system. Methods: In vitro iontophoretic transdermal delivery of Lisinopril across the pigskin was investigated at three different drug concentrations and three different current densities (0.25- 0.75 mA/cm2 in the donor cell of the diffusion apparatus, using cathodal iontophoresis along with the passive controls. Results: For passive permeation, the steady state flux significantly increased with the increasing of donor drug concentration. At all concentration levels, iontophoresis considerably increased the permeation rate compared to passive controls. Iontophoretic transport of Lisinopril was to be found increase with current densities. Flux enhancement was highest at the lowest drug load and lowest at the highest drug load. Conclusion: The obtained results indicate that permeation rate of Lisinopril across the pigskin can be considerably enhanced, controlled or optimized by the use of Iontophoresis technique.

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

    Directory of Open Access Journals (Sweden)

    Mali Vyacheslav

    2011-01-01

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

  18. Tin Oxide Nanoparticles: Synthesis, Characterization and Study their Particle Size at Different Current Density

    Directory of Open Access Journals (Sweden)

    Karzan A. Omar

    2013-11-01

    Full Text Available Tin oxide nanoparticles are prepared by electrochemical reduction method using tetrapropylammonium bromide (TPAB and tetrabutylammonium bromide (TBAB as structure directing agent in an organic medium viz. tetrahydrofuran (THF and acetonitrile (ACN in 4:1 ratio by optimizing current density and molar concentration of the ligand. The reduction process takes place under an inert atmosphere of nitrogen over a period of 2 h. Such nanoparticles are prepared by using a simple electrolysis cell in which the sacrificial anode as a commercially available in tin metal sheet and platinum (inert sheet act as a cathode. The parameters such as current density, solvent polarity, distance between electrodes and concentration of stabilizers are used to control the size of nanoparticles. The synthesized tin oxide nanoparticles are characterized by using UV–Visible, FT-IR and SEM–EDS analysis techniques. UV-Visible spectroscopy has revealed the optical band gap to be 4.13, 4.16 and 4.24 ev for (8, 10 and 12 mA/cm2 and the effect of current density on theirs particle size, respectively.

  19. J-resolved He I emission predictions in the low-density limit

    CERN Document Server

    Bauman, R P; Ferland, G J; MacAdam, K B

    2005-01-01

    Determinations of the primordial helium abundance are used in precision cosmological tests. These require highly accurate He I recombination rate coefficients. Here we reconsider the formation of He I recombination lines in the low-density limit. This is the simplest case and it forms the basis for the more complex situation where collisions are important. The formation of a recombination line is a two-step process, beginning with the capture of a continuum electron into a bound state and followed by radiative cascade to ground. The rate coefficient for capture from the continuum is obtained from photoionization cross sections and detailed balancing, while radiative transition probabilities determine the cascades. We have made every effort to use today's best atomic data. Radiative decay rates are from Drake's variational calculations, which include QED, fine structure, and singlet-triplet mixing. Certain high-$L$ fine-structure levels do not have a singlet-triplet distinction and the singlets and triplets ar...

  20. Proposal of rectifier type superconducting fault current limiter with non-inductive reactor (SFCL)

    Science.gov (United States)

    Mohammad Salim, Khosru; Muta, Itsuya; Hoshino, Tsutomu; Nakamura, Taketsune; Yamada, Masato

    2004-03-01

    A rectifier type superconducting fault current limiter (SFCL) with non-inductive reactor has been proposed. The concept behind this SFCL is the appearance of high impedance during non-superconducting state of the coil. In a hybrid bridge circuit, two superconducting coils connected in anti-parallel: a trigger coil and a limiting coil. Both the coils are magnetically coupled with each other and have same number of turns. There is almost zero flux inside the core and therefore the total inductance is small during normal operation. At fault time when the trigger coil current reaches to a certain level, the trigger coil changes from superconducting state to normal state. This super-to-normal transition of the trigger coil changes the current ratio of the coils and therefore the flux inside the reactor is no longer zero. So, the equivalent impedance of both the coils increased thus limits the fault current. We have carried out computer simulation using EMTDC and observed the results. A preliminary experiment has already been performed using copper wired reactor with simulated super-to-normal transition resistance and magnetic switches. Both the simulation and preliminary experiment shows good results. The advantage of using hybrid bridge circuit is that the SFCL can also be used as circuit breaker. Two separate bridge circuit can be used for both trigger coil and the limiter coil. In such a case, the trigger coil can be shutdown immediately after the fault to reduce heat and thus reduce the recovery time. Again, at the end of fault when the SFCL needs to re-enter to the grid, turning off the trigger circuit in the two-bridge configuration the inrush current can be reduced. This is because the current only flows through the limiting coil. Another advantage of this type of SFCL is that no voltage sag will appear during load increasing time as long as the load current stays below the trigger current level.

  1. Blue duiker Philantomba monticola densities in the Tsitsikamma National Park and probable factors limiting these populations

    Directory of Open Access Journals (Sweden)

    N. Hanekom

    1991-09-01

    Full Text Available Numbers of blue duikers recorded on 157 and 28 variable width transect counts, done over a two year period in the Tsitsikamma Coastal National Park (TCNP and Tsitsikamma Forest National Park (TFNP respectively, did not differ significantly {P > 0,10 with seasons (summer v. winter. Population density estimates from transects were similar to those from game drives (0,18 v. 0,19 duikers/ha (TCNP and 0,13 v. 0,17 duikers/ha (TFNP; P >0,10, higher than from faecal pellet counts (P < 0,10 and at least three times lower than estimates from the Kenneth Stainbank Nature Reserve and Umdoni Park in Natal. Factors contributing to the low population densities in the Tsitsikamma national parks were investigated. Twentyseven and seven percent of leopard (25 and caracal (12 scats respectively analyzed contained blue duiker remains, but predator numbers appear to be low. Forest characteristics were investigated, and results from this and other studies suggest that undergrowth cover does not markedly influence blue duiker densities in the southern Cape forests. Field and stomach analysis indicate that blue duikers feed primarily on freshly fallen leaves and fruit, and are selective foragers. In the Tsitsikamma national parks (TNPs the frequency of occurrence of trees known to be palatable to duikers are low, while less than 45 percent of the dominant tree species fruit fully annually. This apparent scarcity of food, the low numbers of antelope species and individuals in these forests and results from duiker research in Zaire, suggest that habitat rather than predation is limiting duiker numbers in the Tsitsikamma national parks.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-08-15

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

  3. The Γ-Limit of the Two-Dimensional Ohta-Kawasaki Energy. I. Droplet Density

    Science.gov (United States)

    Goldman, Dorian; Muratov, Cyrill B.; Serfaty, Sylvia

    2013-11-01

    This is the first in a series of two papers in which we derive a Γ-expansion for a two-dimensional non-local Ginzburg-Landau energy with Coulomb repulsion, also known as the Ohta-Kawasaki model, in connection with diblock copolymer systems. In that model, two phases appear, which interact via a nonlocal Coulomb type energy. We focus on the regime where one of the phases has very small volume fraction, thus creating small "droplets" of the minority phase in a "sea" of the majority phase. In this paper we show that an appropriate setting for Γ-convergence in the considered parameter regime is via weak convergence of the suitably normalized charge density in the sense of measures. We prove that, after a suitable rescaling, the Ohta-Kawasaki energy functional Γ-converges to a quadratic energy functional of the limit charge density generated by the screened Coulomb kernel. A consequence of our results is that minimizers (or almost minimizers) of the energy have droplets which are almost all asymptotically round, have the same radius and are uniformly distributed in the domain. The proof relies mainly on the analysis of the sharp interface version of the energy, with the connection to the original diffuse interface model obtained via matching upper and lower bounds for the energy. We thus also obtain an asymptotic characterization of the energy minimizers in the diffuse interface model.

  4. Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating Primordial Black Holes

    CERN Document Server

    Abdo, A A; Alfaro, R; Allen, B T; Alvarez, C; Álvarez, J D; Arceo, R; Arteaga-Velázquez, J C; Aune, T; Solares, H A Ayala; Barber, A S; Baughman, B M; Bautista-Elivar, N; Gonzalez, J Becerra; Belmont, E; BenZvi, S Y; Berley, D; Rosales, M Bonilla; Braun, J; Caballero-Lopez, R A; Caballero-Mora, K S; Carramiñana, A; Castillo, M; Chen, C; Christopher, G E; Cotti, U; Cotzomi, J; de la Fuente, E; De León, C; DeYoung, T; Hernandez, R Diaz; Diaz-Cruz, L; Díaz-Vélez, J C; Dingus, B L; DuVernois, M A; Ellsworth, R W; Fiorino, D W; Fraija, N; Galindo, A; Garfias, F; González, M M; Goodman, J A; Grabski, V; Gussert, M; Hampel-Arias, Z; Harding, J P; Hays, E; Hoffman, C M; Hui, C M; Hüntemeyer, P; Imran, A; Iriarte, A; Karn, P; Kieda, D; Kolterman, B E; Kunde, G J; Lara, A; Lauer, R J; Lee, W H; Lennarz, D; Vargas, H León; Linares, E C; Linnemann, J T; Longo, M; Luna-GarcIa, R; MacGibbon, J H; Marinelli, A; Marinelli, S S; Martinez, H; Martinez, O; Martínez-Castro, J; Matthews, J A J; McEnery, J; Torres, E Mendoza; Mincer, A I; Miranda-Romagnoli, P; Moreno, E; Morgan, T; Mostafá, M; Nellen, L; Nemethy, P; Newbold, M; Noriega-Papaqui, R; Oceguera-Becerra, T; Patricelli, B; Pelayo, R; Pérez-Pérez, E G; Pretz, J; Rivière, C; Rosa-González, D; Ruiz-Velasco, E; Ryan, J; Salazar, H; Salesa, F; Sandoval, A; Parkinson, P M Saz; Schneider, M; Shoup, A; Silich, S; Sinnis, G; Smith, A J; Stump, D; Woodle, K Sparks; Springer, R W; Taboada, I; Toale, P A; Tollefson, K; Torres, I; Ukwatta, T N; Vasileiou, V; Villaseñor, L; Walker, G P; Weisgarber, T; Westerhoff, S; Williams, D A; Wisher, I G; Wood, J; Yodh, G B; Younk, P W; Zaborov, D; Zepeda, A; Zhou, H

    2014-01-01

    Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and can emit all species of fundamental particles thermally. PBHs with initial masses of ~5.0 x 10^14 g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV - TeV energy range, making them candidate Gamma-ray Burst (GRB) progenitors. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma-rays, the Milagro observatory is well suited for a direct search of PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a...

  5. Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating Primordial Black Holes

    Science.gov (United States)

    Abdo, A. A.; Abeysekara, A. U.; Alfaro, R.; Allen, B. T.; Alvarez, C.; Alvarez, J. D.; Arceo, R.; Arteaga-Velazquez, J. C.; Aune, T.; Ayala Solares, H. A.; Barber, A. S.; Baughman, B. M.; Bautista-Elivar, N.; Becerra Gonzalez, J.; Belmont, E.; BenZvi, S. Y.; Berley, D.; Rosales, M. Bonilla; Braun, J.; Hays, E.

    2014-01-01

    Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally. PBHs with initial masses of approx.5.0 x 10(exp 14) g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV-TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a range of PBH observation times. In addition, we report the sensitivity of the Milagro successor, the High Altitude Water Cherenkov (HAWC) observatory, to PBH evaporation events.

  6. Milagro limits and HAWC sensitivity for the rate-density of evaporating Primordial Black Holes

    Science.gov (United States)

    Abdo, A. A.; Abeysekara, A. U.; Alfaro, R.; Allen, B. T.; Alvarez, C.; Álvarez, J. D.; Arceo, R.; Arteaga-Velázquez, J. C.; Aune, T.; Ayala Solares, H. A.; Barber, A. S.; Baughman, B. M.; Bautista-Elivar, N.; Becerra Gonzalez, J.; Belmont, E.; BenZvi, S. Y.; Berley, D.; Bonilla Rosales, M.; Braun, J.; Caballero-Lopez, R. A.; Caballero-Mora, K. S.; Carramiñana, A.; Castillo, M.; Christopher, G. E.; Cotti, U.; Cotzomi, J.; de la Fuente, E.; De León, C.; DeYoung, T.; Diaz Hernandez, R.; Diaz-Cruz, L.; Díaz-Vélez, J. C.; Dingus, B. L.; DuVernois, M. A.; Ellsworth, R. W.; Fiorino, D. W.; Fraija, N.; Galindo, A.; Garfias, F.; González, M. M.; Goodman, J. A.; Grabski, V.; Gussert, M.; Hampel-Arias, Z.; Harding, J. P.; Hays, E.; Hoffman, C. M.; Hui, C. M.; Hüntemeyer, P.; Imran, A.; Iriarte, A.; Karn, P.; Kieda, D.; Kolterman, B. E.; Kunde, G. J.; Lara, A.; Lauer, R. J.; Lee, W. H.; Lennarz, D.; León Vargas, H.; Linares, E. C.; Linnemann, J. T.; Longo, M.; Luna-GarcIa, R.; MacGibbon, J. H.; Marinelli, A.; Marinelli, S. S.; Martinez, H.; Martinez, O.; Martínez-Castro, J.; Matthews, J. A. J.; McEnery, J.; Mendoza Torres, E.; Mincer, A. I.; Miranda-Romagnoli, P.; Moreno, E.; Morgan, T.; Mostafá, M.; Nellen, L.; Nemethy, P.; Newbold, M.; Noriega-Papaqui, R.; Oceguera-Becerra, T.; Patricelli, B.; Pelayo, R.; Pérez-Pérez, E. G.; Pretz, J.; Rivière, C.; Rosa-González, D.; Ruiz-Velasco, E.; Ryan, J.; Salazar, H.; Salesa, F.; Sandoval, A.; Saz Parkinson, P. M.; Schneider, M.; Silich, S.; Sinnis, G.; Smith, A. J.; Stump, D.; Sparks Woodle, K.; Springer, R. W.; Taboada, I.; Toale, P. A.; Tollefson, K.; Torres, I.; Ukwatta, T. N.; Vasileiou, V.; Villaseñor, L.; Weisgarber, T.; Westerhoff, S.; Williams, D. A.; Wisher, I. G.; Wood, J.; Yodh, G. B.; Younk, P. W.; Zaborov, D.; Zepeda, A.; Zhou, H.

    2015-04-01

    Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally. PBHs with initial masses of ∼5.0 × 1014 g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV-TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a range of PBH observation times. In addition, we report the sensitivity of the Milagro successor, the High Altitude Water Cherenkov (HAWC) observatory, to PBH evaporation events.

  7. Cluster model for the ionic product of water: accuracy and limitations of common density functional methods.

    Science.gov (United States)

    Svozil, Daniel; Jungwirth, Pavel

    2006-07-27

    In the present study, the performance of six popular density functionals (B3LYP, PBE0, BLYP, BP86, PBE, and SVWN) for the description of the autoionization process in the water octamer was studied. As a benchmark, MP2 energies with complete basis sets limit extrapolation and CCSD(T) correction were used. At this level, the autoionized structure lies 28.5 kcal.mol(-1) above the neutral water octamer. Accounting for zero-point energy lowers this value by 3.0 kcal.mol(-1). The transition state of the proton transfer reaction, lying only 0.7 kcal.mol(-1) above the energy of the ionized system, was identified at the MP2/aug-cc-pVDZ level of theory. Different density functionals describe the reactant and product with varying accuracy, while they all fail to characterize the transition state. We find improved results with hybrid functionals compared to the gradient-corrected ones. In particular, B3LYP describes the reaction energetics within 2.5 kcal.mol(-1) of the benchmark value. Therefore, this functional is suggested to be preferably used both for Carr-Parinello molecular dynamics and for quantum mechanics/molecular mechanics (QM/MM) simulations of autoionization of water.

  8. Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating Primordial Black Holes

    Science.gov (United States)

    Abdo, A. A.; Abeysekara, A. U.; Alfaro, R.; Allen, B. T.; Alvarez, C.; Alvarez, J. D.; Arceo, R.; Arteaga-Velazquez, J. C.; Aune, T.; Ayala Solares, H. A.; hide

    2014-01-01

    Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally. PBHs with initial masses of approx.5.0 x 10(exp 14) g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV-TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a range of PBH observation times. In addition, we report the sensitivity of the Milagro successor, the High Altitude Water Cherenkov (HAWC) observatory, to PBH evaporation events.

  9. Does nest site availability limit the density of hole nesting birds in small woodland patches?

    Directory of Open Access Journals (Sweden)

    J. Loman

    2006-11-01

    Full Text Available By providing nest boxes, previous studies have shown that nest sites are in short supply and limit the populations of several small passerines, including the Great Tit Parus major, the Blue Tit P. caeruleus, and the Pied Flycatcher Ficedula hypoleuca. Can this influence their distribution over a range of small woodland patch sizes in a heterogeneous landscape? To investigate this, a study was conducted in a heterogeneous agricultural landscape, with a mixture of wooded patches and cropped fields, in southern Sweden. The descriptive part of the study involved mapping territories of the three species in 135 patches. These species avoided small (<1 ha, Pied Flycatcher or very small (<0.2 ha, the two tit species forest patches in this landscape. In an experimental part, a subset of 34 patches, 0.01 to 24 ha in size was used. Territories were mapped in a first year as a control. In a second year, patches were matched by size and vegetation and nest-boxes were provided in one patch of each pair. Territories were again mapped. Providing nestboxes increased the density of breeding Great Tits in patches of all sizes and expanded their use of very small patches. The nest-boxes increased the density of Pied Flycatchers in large patches but not in small patches. So, is the lack of territories in small patches due to shortage of nest sites? The outcome of the experiment suggests nest site limitation as a cause of the observed Great Tit discrimination against very small habitat patches. The lack of Pied Flycatchers in small patches must however have another basis than lack of nest sites. The effect of providing nest-boxes on Blue Tit distribution was inconclusive.

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

    Science.gov (United States)

    Douillet, Guilhem Amin; Tsang-Hin-Sun, Ève; Kueppers, Ulrich; Letort, Jean; Pacheco, Daniel Alejandro; Goldstein, Fabian; Von Aulock, Felix; Lavallée, Yan; Hanson, Jonathan Bruce; Bustillos, Jorge; Robin, Claude; Ramón, Patricio; Hall, Minard; Dingwell, Donald B

    The deposits of the pyroclastic density currents from the August 2006 eruption of Tungurahua show three facies associations depending on the topographic setting: the massive, proximal cross-stratified, and distal cross-stratified facies. (1) The massive facies is confined to valleys on the slopes of the volcano. It contains clasts of >1 m diameter to fine ash material, is massive, and interpreted as deposited from dense pyroclastic flows. Its surface can exhibit lobes and levees covered with disk-shaped and vesicular large clasts. These fragile large clasts must have rafted at the surface of the flows all along the path in order to be preserved, and thus imply a sharp density boundary near the surface of these flows. (2) The proximal cross-stratified facies is exposed on valley overbanks on the upper part of the volcano and contains both massive coarse-grained layers and cross-stratified ash and lapilli bedsets. It is interpreted as deposited from (a) dense pyroclastic flows that overflowed the gentle ridges of valleys of the upper part of the volcano and (b) dilute pyroclastic density currents created from the dense flows by the entrainment of air on the steep upper flanks. (3) The distal cross-stratified facies outcrops as spatially limited, isolated, and wedge-shaped bodies of cross-stratified ash deposits located downstream of cliffs on valleys overbanks. It contains numerous aggrading dune bedforms, whose crest orientations reveal parental flow directions. A downstream decrease in the size of the dune bedforms, together with a downstream fining trend in the grain size distribution are observed on a 100-m scale. This facies is interpreted to have been deposited from dilute pyroclastic density currents with basal tractional boundary layers. We suggest that the parental flows were produced from the dense flows by entrainment of air at cliffs, and that these diluted currents might rapidly deposit through "pneumatic jumps". Three modes are present in the grain

  11. Analysis and design of over-current limit control strategies applied in aeronautical power supplies

    Institute of Scientific and Technical Information of China (English)

    WANG Lin-bing; HE Xiang-ning

    2007-01-01

    Some Over-Current Limit Control strategies are analyzed and designed to meet the demands of high reliability and rapid dynamic response in the aeronautical power supply applications. The control schemes are both effective in DC-DC converters and DC-AC converters. Controller models are set up, and the over-current limit operation principles of analogy and digital control are analyzed too. An 800VA aeronautical power supply has been constructed to verify the performance of the proposed control strategy in various cases such as the sudden load change and the constant load. The analysis and experiments confirm the advantages of the proposed over-current limit strategies as follows: simple,effective and reliable.

  12. Current self-limitation in a transverse nanosecond discharge with a slotted cathode

    Science.gov (United States)

    N, A. ASHURBEKOV; K, O. IMINOV; O, A. POPOV; G, S. SHAKHSINOV

    2017-03-01

    A high-voltage transverse pulsed nanosecond discharge with a slotted hollow cathode was found to be a source of high-energy (few kV) ribbon electron beams. Conditions for the formation and extinction of electron beams were experimentally studied in discharges in helium at pressures of 1–100 Torr. It was found that interaction of fast electrons with a non-uniform electric field near the slotted cathode led to limitation of the magnitude of the discharge current. A physical model was developed to describe the discharge current self-limitation that was in satisfactory agreement with the experimental results. Some technical solutions that are expected to increase the upper current limits in transverse nanosecond discharge are discussed.

  13. A Consideration on Increasing Current Density in Normal Conducting Toroidal Field Coil for Spherical Tokamak Power Plant

    Institute of Scientific and Technical Information of China (English)

    Song Yuntao; Satoshi NISHIO

    2005-01-01

    The center post is the most critical component as an inboard part of the toroidal field coil for the low aspect ratio tokamak. During the discharge it endures not only a tremendous ohmic heating owing to its carrying a rather high current but also a large nuclear heating and irradiation owing to the plasma operation. All the severe operating conditions, including the structure stress intensity and the stability of the structure, largely limit the maximum allowable current density. But in order to contain a very high dense plasma, it is hoped that the fusion power plant system can operate with a much high maximum magnetic field BT ≥12 T~15 T in the center post. A new method is presented in this paper to improve the maximum magnetic field up to 17 T and to investigate the possibility of the normal conducting center post to be used in the future fusion tokamak power plant.

  14. Influence of current density on surface morphology and properties of pulse plated tin films from citrate electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Ashutosh; Bhattacharya, Sumit; Das, Siddhartha; Das, Karabi, E-mail: karabi@metal.iitkgp.ernet.in

    2014-01-30

    Bulk polycrystalline tin films have been processed by pulse electrodeposition technique from a simple solution containing triammonium citrate and stannous chloride. The cathodic investigations have been carried out by galvanostatic methods. As deposited samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD analysis of the deposited films shows microcrystalline grains having β-Sn form. The surface morphology is very rough at lower current density, but becomes smooth at higher current density, and exhibits pyramid type morphology at all the current densities. The effect of current density on microhardness, melting behavior, and electrical resistivity are also reported here.

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

    Science.gov (United States)

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

    2012-09-01

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

  16. Runout distance and dynamic pressure of pyroclastic density currents: Evidence from 18 May 1980 blast surge of Mount St. Helens

    Science.gov (United States)

    Gardner, J. E.; Andrews, B. J.

    2016-12-01

    Pyroclastic density currents (flows and surges) are one of the most deadly hazards associated with volcanic eruptions. Understanding what controls how far such currents will travel, and how their dynamic pressure evolves, could help mitigate their hazards. The distance a ground hugging, pyroclastic density current travels is partly limited by when it reverses buoyancy and lifts off into the atmosphere. The 1980 blast surge of Mount St. Helens offers an example of a current seen to lift off. Before lofting, it had traveled up to 20 km and leveled more than 600 km3 of thick forest (the blowdown zone). The outer edge of the devastated area - where burned trees that were left standing (the singe zone) - is where the surge is thought to have lifted off. We recently examined deposits in the outer parts of the blowdown and in the singe zone at 32 sites. The important finding is that the laterally moving surge travelled into the singe zone, and hence the change in tree damage does not mark the run out distance of the ground hugging surge. Eyewitness accounts and impacts on trees and vehicles reveal that the surge consisted of a fast, dilute "overcurrent" and a slower "undercurrent", where most of the mass (and heat) was retained. Reasonable estimates for flow density and velocity show that dynamic pressure of the surge (i.e., its ability to topple trees) peaked near the base of the overcurrent. We propose that when the overcurrent began to lift off, the height of peak dynamic pressure rose above the trees and stopped toppling them. The slower undercurrent continued forward, burning trees but it lacked the dynamic pressure needed to topple them. Grain-size variations argue that it slowed from 30 m/s when it entered the singe zone to 3 m/s at the far end. Buoyancy reversal and liftoff are thus not preserved in the deposits where the surge lofted upwards.

  17. Power lateral pnp transistor operating with high current density in irradiated voltage regulator

    Directory of Open Access Journals (Sweden)

    Vukić Vladimir Đ.

    2013-01-01

    Full Text Available The operation of power lateral pnp transistors in gamma radiation field was examined by detection of the minimum dropout voltage on heavily loaded low-dropout voltage regulators LM2940CT5, clearly demonstrating their low radiation hardness, with unacceptably low values of output voltage and collector-emitter voltage volatility. In conjunction with previous results on base current and forward emitter current gain of serial transistors, it was possible to determine the positive influence of high load current on a slight improvement of voltage regulator LM2940CT5 radiation hardness. The high-current flow through the wide emitter aluminum contact of the serial transistor above the isolation oxide caused intensive annealing of the positive oxide-trapped charge, leading to decrease of the lateral pnp transistor's current gain, but also a more intensive recovery of the small-signal npn transistors in the control circuit. The high current density in the base area of the lateral pnp transistor immediately below the isolation oxide decreased the concentration of negative interface traps. Consequently, the positive influence of the reduced concentration of the oxide-trapped charge on the negative feedback reaction circuit, together with the favourable effect of reduced interface traps concentration, exceeded negative influence of the annealed oxide-trapped charge on the serial pnp transistor's forward emitter current gain.

  18. Modeling the Non Linear Behavior of a Magnetic Fault Current Limiter

    Directory of Open Access Journals (Sweden)

    P. R. Wilson

    2015-11-01

    Full Text Available Fault Current Limiters are used in a wide array of applications from small circuit protection at low power levels to large scale high power applications which require superconductors and complex control circuitry. One advantage of  passive fault current limiters (FCL is the automatic behavior that is dependent on the intrinsic properties of the circuit elements rather than on a complex feedback control scheme making this approach attractive for low cost applications and also where reliability is critical. This paper describes the behavioral modeling of a passive Magnetic FCL and its potential application in practical circuits.

  19. Analysis of nanosecond breaking of a high-density current in SOS diodes

    Science.gov (United States)

    Grekhov, I. V.; Lyublinskii, A. G.; Smirnova, I. A.

    2015-11-01

    Effect of a sharp (nanosecond) breaking of the reverse current with a density on the order of 103-104 A/cm2 in a silicon diode upon switching from direct to reverse bias voltage (so-called silicon opening switch, or SOS effect) is widely used in nanosecond technologies of gigawatt powers. For detailed analysis of the SOS effect, we constructed a special setup with small stray inductance, which makes it possible to test single SOS diodes with a working area of 1-2 mm2 in a wide range of current densities. Our experiments show, in particular, that the numerical model of the SOS effect developed at the Institute of Electrophysics, Ural Branch, Russian Academy of Sciences successfully described the experimental results. It is also shown that the charge extracted from the diode structure by the reverse current exceeds the charge introduced by a direct current pulse by not more than 10%, indicating a relatively small role of ionization processes. The possibility to carry out experiments on single samples with a small surface area allows us to study the SOS effect and considerably facilitates investigations aimed at the perfection of the design of SOS diodes.

  20. The Keck+Magellan Survey for Lyman Limit Absorption III: Sample Definition and Column Density Measurements

    CERN Document Server

    Prochaska, J Xavier; Fumagalli, Michele; Bernstein, Rebecca A; Burles, Scott M

    2015-01-01

    We present an absorption-line survey of optically thick gas clouds -- Lyman Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39 restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3, nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5-10) that may have super-solar abundances. High Si^+/Fe^+ ratios suggest an alpha-enhanced medium whereas ...

  1. Regge limit of R-current correlators in AdS supergravity

    Energy Technology Data Exchange (ETDEWEB)

    Bartels, J.; Kotanski, J.; Mischler, A.M. [II. Inst. fuer Theoretische Physik, Univ. Hamburg (Germany); Schomerus, V. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2009-08-15

    Four-point functions of R-currents are discussed within Anti-de Sitter supergravity. In particular, we compute Witten diagrams with graviton and gauge boson exchange in the high energy Regge limit. Assuming validity of the AdS/CFT correspondence, our results apply to R-current four-point functions of N=4 super Yang-Mills theory at strong coupling. (orig.)

  2. Surveillance of fetal arrhythmias in the outpatient setting: current limitations and call for action.

    Science.gov (United States)

    Freire, Grace

    2015-12-01

    Surveillance of fetal arrhythmias in the outpatient setting remains limited by lack of monitoring modalities. Despite technological advances made in the field of obstetrics, existing devices are not currently suitable to monitor fetal arrhythmias. In this report, the author describes the current and developing fetal heart rate monitoring technologies including the recent introduction of hand-held Doppler monitors for outpatient surveillance of fetal arrhythmias.

  3. Virtual Impedance Based Fault Current Limiters for Inverter Dominated AC Microgrids

    DEFF Research Database (Denmark)

    Lu, Xiaonan; Wang, Jianhui; Guerrero, Josep M.

    2017-01-01

    In this paper, a virtual impedance based fault current limiter (VI-FCL) is proposed for islanded microgrids comprised of multiple inverter interfaced distributed generators (DGs). Considering the increased fault current capability induced by high penetration of renewable energy sources (RESs), FC......, and the stability analysis in consideration of VI-FCLs is thereby studied. MATLAB/Simulink model comprised of three inverter-interfaced DGs is implemented to verify the feasibility of the proposed method....

  4. Simple voltage-controlled current source for wideband electrical bioimpedance spectroscopy: circuit dependences and limitations

    Science.gov (United States)

    Seoane, F.; Macías, R.; Bragós, R.; Lindecrantz, K.

    2011-11-01

    In this work, the single Op-Amp with load-in-the-loop topology as a current source is revisited. This circuit topology was already used as a voltage-controlled current source (VCCS) in the 1960s but was left unused when the requirements for higher frequency arose among the applications of electrical bioimpedance (EBI). The aim of the authors is not only limited to show that with the currently available electronic devices it is perfectly viable to use this simple VCCS topology as a working current source for wideband spectroscopy applications of EBI, but also to identify the limitations and the role of each of the circuit components in the most important parameter of a current for wideband applications: the output impedance. The study includes the eventual presence of a stray capacitance and also an original enhancement, driving with current the VCCS. Based on the theoretical analysis and experimental measurements, an accurate model of the output impedance is provided, explaining the role of the main constitutive elements of the circuit in the source's output impedance. Using the topologies presented in this work and the proposed model, any electronic designer can easily implement a simple and efficient current source for wideband EBI spectroscopy applications, e.g. in this study, values above 150 kΩ at 1 MHz have been obtained, which to the knowledge of the authors are the largest values experimentally measured and reported for a current source in EBI at this frequency.

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

    Energy Technology Data Exchange (ETDEWEB)

    Frankowski, Marek, E-mail: mfrankow@agh.edu.pl; Czapkiewicz, Maciej; Skowronski, Witold; Stobiecki, Tomasz

    2014-02-15

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

  6. Superhydrophobic SAM Modified Electrodes for Enhanced Current Limiting Properties in Intrinsic Conducting Polymer Surge Protection Devices.

    Science.gov (United States)

    Jabarullah, Noor H; Verrelli, Emanuele; Mauldin, Clayton; Navarro, Luis A; Golden, Josh H; Madianos, Leonidas M; Kemp, Neil T

    2015-06-09

    Surface interface engineering using superhydrophobic gold electrodes made with 1-dodecanethiol self-assembled monolayer (SAM) has been used to enhance the current limiting properties of novel surge protection devices based on the intrinsic conducting polymer, polyaniline doped with methanesulfonic acid. The resulting devices show significantly enhanced current limiting characteristics, including current saturation, foldback, and negative differential effects. We show how SAM modification changes the morphology of the polymer film directly adjacent to the electrodes, leading to the formation of an interfacial compact thin film that lowers the contact resistance at the Au-polymer interface. We attribute the enhanced current limiting properties of the devices to a combination of lower contact resistance and increased Joule heating within this interface region which during a current surge produces a current blocking resistive barrier due to a thermally induced dedoping effect caused by the rapid diffusion of moisture away from this region. The effect is exacerbated at higher applied voltages as the higher temperature leads to stronger depletion of charge carriers in this region, resulting in a negative differential resistance effect.

  7. Cdc45 limits replicon usage from a low density of preRCs in mammalian cells.

    Science.gov (United States)

    Wong, Philip G; Winter, Sherry L; Zaika, Elena; Cao, Thinh V; Oguz, Umut; Koomen, John M; Hamlin, Joyce L; Alexandrow, Mark G

    2011-03-01

    Little is known about mammalian preRC stoichiometry, the number of preRCs on chromosomes, and how this relates to replicon size and usage. We show here that, on average, each 100-kb of the mammalian genome contains a preRC composed of approximately one ORC hexamer, 4-5 MCM hexamers, and 2 Cdc6. Relative to these subunits, ∼0.35 total molecules of the pre-Initiation Complex factor Cdc45 are present. Thus, based on ORC availability, somatic cells contain ∼70,000 preRCs of this average total stoichiometry, although subunits may not be juxtaposed with each other. Except for ORC, the chromatin-bound complement of preRC subunits is even lower. Cdc45 is present at very low levels relative to the preRC subunits, but is highly stable, and the same limited number of stable Cdc45 molecules are present from the beginning of S-phase to its completion. Efforts to artificially increase Cdc45 levels through ectopic expression block cell growth. However, microinjection of excess purified Cdc45 into S-phase nuclei activates additional replication foci by three-fold, indicating that Cdc45 functions to activate dormant preRCs and is rate-limiting for somatic replicon usage. Paradoxically, although Cdc45 colocalizes in vivo with some MCM sites and is rate-limiting for DNA replication to occur, neither Cdc45 nor MCMs colocalize with active replication sites. Embryonic metazoan chromatin consists of small replicons that are used efficiently via an excess of preRC subunits. In contrast, somatic mammalian cells contain a low density of preRCs, each containing only a few MCMs that compete for limiting amounts of Cdc45. This provides a molecular explanation why, relative to embryonic replicon dynamics, somatic replicons are, on average, larger and origin efficiency tends to be lower. The stable, continuous, and rate-limiting nature of Cdc45 suggests that Cdc45 contributes to the staggering of replicon usage throughout S-phase, and that replicon activation requires reutilization of

  8. Changes of IK,ATP current density and allosteric modulation during chronic atrial fibrillation

    Institute of Scientific and Technical Information of China (English)

    WU Gang; HUANG Cong-xin; TANG Yan-hong; JIANG Hong; WAN Jun; CHEN Hui; XIE Qiang; HUANG Zheng-rong

    2005-01-01

    Background Atrial fibrillation (AF) is the most common supraventricular arrhythmia in clinical practice. Chronic atrial fibrillation (CAF) is associated with ionic remodeling. However, little is known about the activity of ATP-sensitive potassium current (IK,ATP) during CAF. So we studied the changes of IK,ATP density and allosteric modulation of ATP-sensitivity by intracellular pH during CAF.Methods Myocardium samples were obtained from the right auricular appendage of patients with rheumatic heart disease complicated with valvular disease in sinus rhythm (SR) or CAF. There were 14 patients in SR group and 9 patients in CAF group. Single atrial cells were isolated using an enzyme dispersion technique. IK,ATP was recorded using the whole-cell and inside-out configuration of voltage-clamp techniques. In whole-cell model, myocytes of SR and CAF groups were perfused with simulated ischemic solution to elicit IK,ATP. In inside-out configuration, the internal patch membranes were exposed to different ATP concentrations in pH 7.4 and 6.8.Results Under simulated ischemia, IK,ATP current density of CAF group was significantly higher than in SR group [(83.5±10.8) vs. (58.7±8.4) pA/pF, P<0.01]. IK,ATP of the two groups showed ATP concentration-dependent inhibition. The ATP concentration for 50% current inhibition (IC50) for the SR group was significantly different in pH 7.4 and pH 6.8 (24 vs. 74 μmol/L, P<0.01). The IC50 did not change significantly in CAF group when the pH decreased from 7.4 to 6.8.Conclusions During CAF, IK,ATP current density was increased and its allosteric modulation of ATP-sensitivity by intracellular pH was diminished.

  9. Current Density-Functional Theory using meta-Generalized Gradient Exchange--Correlation Functionals

    CERN Document Server

    Furness, James W; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M

    2015-01-01

    We present the self-consistent implementation of current-dependent (hybrid) meta generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn--Sham current density-functional theory (KS-CDFT). A unique feature of the non-perturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 a.u. ($\\sim 235000$T) in strength. CDFT functionals based on the TPSS and B98 forms are investigated and their performance is assessed by comparison with accurate CCSD(T) data. In the weak field regime magnetic properties such as magnetizabilities and NMR shielding constants show modest but systematic improvements over GGA functionals. However, in strong field regime the mGGA based forms lead to a significantly improved description of the recently proposed perpendicular paramagnetic bonding mechanism, comparing well with CCSD(T...

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

    Science.gov (United States)

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

    2012-10-01

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

  11. Assessment of the impact of HTSCs on superconducting fault-current limiters. [High Temperature SuperConductors (HTSCs)

    Energy Technology Data Exchange (ETDEWEB)

    Giese, R.F. (Argonne National Lab., IL (United States)); Runde, M. (Energiforsyningens Forskningsinstitutt A/S, Trondheim (Norway))

    1993-01-01

    The possible impact of nitrogen-cooled superconductors on the desip and cost of superconducting fault-current limiters is assessed by considering the technical specifications such devices must meet and by comparing material properties of 77-K and 4-K superconductors. The main advantages of operating superconductors at 77 K are that the refrigeration operating cost is reduced by a factor of up to 25 and the refrigeration capital cost is reduced by a factor of up to 10. The heat capacity is several orders of magnitude Larger at 77 K and at 4 K. This phenomenon increases conductor stability against flux jumps but makes switching from the superconducting to the normal state slow and difficult. Therefore, a high critical current density, probably at least 10[sup 5] A/cm[sup 2], is required.

  12. InGaAs-InP avalanche photodiodes with dark current limited by generation-recombination.

    Science.gov (United States)

    Zhao, Yanli; Zhang, Dongdong; Qin, Long; Tang, Qi; Wu, Rui Hua; Liu, Jianjun; Zhang, Youping; Zhang, Hong; Yuan, Xiuhua; Liu, Wen

    2011-04-25

    Separate absorption grading charge multiplication avalanche photodiodes (SAGCM APDs) are widely accepted in photon starved optical communication systems due to the presence of large photocurrent gain. In this work, we present a detailed analysis of dark currents of planar-type SAGCM InGaAs-InP APDs with different thicknesses of multiplication layer. The effect of the diffusion process, the generation-recombination process, the tunneling process and the multiplication process on the total leakage current is discussed. A new empirical formula has been established to predict the optimal multiplication layer thickness of SAGCM APDs with dark current limited by generation-recombination at multiplication gain of 8.

  13. Obtaining the Probability Vector Current Density in Canonical Quantum Mechanics by Linear Superposition

    CERN Document Server

    Kauffmann, Steven Kenneth

    2013-01-01

    The quantum mechanics status of the probability vector current density has long seemed to be marginal. On one hand no systematic prescription for its construction is provided, and the special examples of it that are obtained for particular types of Hamiltonian operator could conceivably be attributed to happenstance. On the other hand this concept's key physical interpretation as local average particle flux, which flows from the equation of continuity that it is supposed to satisfy in conjunction with the probability scalar density, has been claimed to breach the uncertainty principle. Given the dispiriting impact of that claim, we straightaway point out that the subtle directional nature of the uncertainty principle makes it consistent with the measurement of local average particle flux. We next focus on the fact that the unique closed-form linear-superposition quantization of any classical Hamiltonian function yields in tandem the corresponding unique linear-superposition closed-form divergence of the proba...

  14. One-dimensional transport of interacting particles: currents, density profiles, phase diagrams, and symmetries.

    Science.gov (United States)

    Dierl, Marcel; Einax, Mario; Maass, Philipp

    2013-06-01

    Driven lattice gases serve as canonical models for investigating collective transport phenomena and properties of nonequilibrium steady states. Here we study one-dimensional transport with nearest-neighbor interactions both in closed bulk systems and in open channels coupled to two particle reservoirs at the ends of the channel. For the widely employed Glauber rates we derive an exact current-density relation in the bulk for unidirectional hopping. An approach based on time-dependent density functional theory provides a good description of the kinetics. For open systems, the system-reservoir couplings are shown to have a striking influence on boundary-induced phase diagrams. The role of particle-hole symmetry is discussed, and its consequence for the topology of the phase diagrams. It is furthermore demonstrated that systems with weak bias can be mapped onto systems with unidirectional hopping.

  15. Implementation of superconducting fault current limiter for flexible operation in the power substation

    Energy Technology Data Exchange (ETDEWEB)

    Song, Chong Suk, E-mail: chong_suk@korea.ac.kr [School of Electrical Engineering, Korea University, Anam dong, Seonbukgu, Seoul 136-713 (Korea, Republic of); Lee, Hansang [School of Railway and Electrical Engineering, Kyungil University, Hayang-eup, Gyeongsan-si, Gyeongsangbuk-do 712-701 (Korea, Republic of); Cho, Yoon-sung [Department of Electric and Energy Engineering, Catholic University of Daegu, Hayang-eup, Gyeongsan-si, Gyeongsangbuk-do 712-702 (Korea, Republic of); Suh, Jaewan [School of Electrical Engineering, Korea University, Anam dong, Seonbukgu, Seoul 136-713 (Korea, Republic of); Jang, Gilsoo, E-mail: gjang@korea.ac.kr [School of Electrical Engineering, Korea University, Anam dong, Seonbukgu, Seoul 136-713 (Korea, Republic of)

    2014-09-15

    Highlights: • The power load concentrated in load centers results in high levels of fault current. • This paper introduces a fault current reduction scheme using SFCLs in substations. • The SFCL is connected in parallel to the bus tie between the two busbars. • The fault current mitigation using SFCLs is verified through PSS/e simulations. - Abstract: The concentration of large-scale power loads located in the metropolitan areas have resulted in high fault current levels during a fault thereby requiring the substation to operate in the double busbar configuration mode. However, the double busbar configuration mode results in deterioration of power system reliability and unbalanced power flow in the adjacent transmission lines which may result in issues such as overloading of lines. This paper proposes the implementation of the superconducting fault current limiter (SFCL) to be installed between the two substation busbars for a more efficient and flexible operation of the substation enabling both single and double busbar configurations depending on the system conditions for guaranteeing power system reliability as well as fault current limitations. Case studies are being performed for the effectiveness of the SFCL installation and results are compared for the cases where the substation is operating in single and double busbar mode and with and without the installation of the SFCL for fault current mitigation.

  16. THE MATHEMATIC MODEL OF POTENTIAL RELAXATION IN COULOSTATIC CONDITIONS FOR LIMITING DIFFUSION CURRENT CASE

    Directory of Open Access Journals (Sweden)

    O. H. Kapitonov

    2010-05-01

    Full Text Available A mathematical model of coulostatic relaxation of the potential for solid metallic electrode was presented. The solution in the case of limiting diffusion current was obtained. On the basis of this model the technique of concentration measurements for heavy metal ions in diluted solutions was suggested. The model adequacy was proved by experimental data.

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

    Science.gov (United States)

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

    2011-12-01

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

  18. Ultrahigh-current-density metal-ion implantation and diamondlike-hydrocarbon films for tribological applications

    Science.gov (United States)

    Wilbur, P. J.

    1993-09-01

    The metal-ion-implantation system used to implant metals into substrates are described. The metal vapor required for operation is supplied by drawing sufficient electron current from the plasma discharge to an anode-potential crucible so a solid, pure metal placed in the crucible will be heated to the point of vaporization. The ion-producing, plasma discharge is initiated within a graphite-ion-source body, which operates at high temperature, by using an argon flow that is turned off once the metal vapor is present. Extraction of ion beams several cm in diameter at current densities ranging to several hundred micro-A/sq cm on a target 50 cm downstream of the ion source were demonstrated using Mg, Ag, Cr, Cu, Si, Ti, V, B, and Zr. These metals were implanted into over 100 substrates (discs, pins, flats, wires). A model describing thermal stresses induced in materials (e.g. ceramic plates) during high-current-density implantation is presented. Tribological and microstructural characteristics of iron and 304-stainless-steel samples implanted with Ti or B are examined. Diamondlike-hydrocarbon coatings were applied to steel surfaces and found to exhibit good tribological performance.

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

    Science.gov (United States)

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

    2015-12-01

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

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Science.gov (United States)

    Murakami, Shingo; Okada, Yoshio

    2015-05-01

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

  2. Analysis of the effects of asymmetric faults in three-phase superconducting inductive fault current limiters

    Science.gov (United States)

    Ferreira, R.; Pina, J. M.; Vilhena, N.; Arsénio, P.; Pronto, A. G.; Martins, J.

    2014-05-01

    Inductive fault current limiters of magnetic shielding type can be described in terms of the excursion in the plane defined by flux linked with primary and line current, and this methodology has been previously applied to single-phase devices. Practical applications, however, require three-phase limiters, which, for the sake of compactness, may be built by three legged cores, instead of three single phase units. This has the advantage of using well established methods of power transformers industry, but the performance of the devices depends on the type of fault, e.g. phase to ground or phase to phase. For instance, in a three legged core, a phase to ground fault affects healthy phases, and these are the most frequent faults in distribution grids, where such systems are envisaged. The effects of asymmetric faults are analysed in this paper, by means of measured excursions in the linked flux-current plane.

  3. Planar gradient coil design by scaling the spatial frequencies of minimum-inductance current density.

    Science.gov (United States)

    Lee, S Y; Park, B S; Yi, J H; Yi, W

    1997-11-01

    Gradient coil inductance has been remarkably reduced by the minimum-inductance design technique, which minimizes the magnetic energy stored by the gradient coil. The planar gradient coil designed by this technique, however, often has poor magnetic field linearity. Scaling the spatial frequencies of the current density function derived by this method, the magnetic field linearity of the planar gradient coil can be greatly improved with a small sacrifice of gradient coil inductance. A figure of merit of the planar gradient coil has been found to be improved by scaling the spatial frequencies.

  4. A class of vector identities relevant to the representation of the electric current density

    CERN Document Server

    Bornatici, M

    2007-01-01

    A rigorous mathematical proof is given of a class of vector identities that provide a way to separate an arbitrary vector field (over a linear space) into the sum of a radial (i.e., pointing toward the radial unit vector) vector field, minus the divergence of a tensor plus the curl of an axial vector. Such a separation is applied to the representation of electric current densities yielding a specific form of the effective polarization and magnetization fields which is also discussed in some details.

  5. Temperature-dependence of Threshold Current Density-Length Product in Metallization Lines: A Revisit

    Science.gov (United States)

    Saptono Duryat, Rahmat; Kim, Choong-Un

    2016-04-01

    One of the important phenomena in Electromigration (EM) is Blech Effect. The existence of Threshold Current Density-Length Product or EM Threshold has such fundamental and technological consequences in the design, manufacture, and testing of electronics. Temperature-dependence of Blech Product had been thermodynamically established and the real behavior of such interconnect materials have been extensively studied. The present paper reviewed the temperature-dependence of EM threshold in metallization lines of different materials and structure as found in relevant published articles. It is expected that the reader can see a big picture from the compiled data, which might be overlooked when it was examined in pieces.

  6. Analysis of reliability metrics and quality enhancement measures in current density imaging.

    Science.gov (United States)

    Foomany, F H; Beheshti, M; Magtibay, K; Masse, S; Foltz, W; Sevaptsidis, E; Lai, P; Jaffray, D A; Krishnan, S; Nanthakumar, K; Umapathy, K

    2013-01-01

    Low frequency current density imaging (LFCDI) is a magnetic resonance imaging (MRI) technique which enables calculation of current pathways within the medium of study. The induced current produces a magnetic flux which presents itself in phase images obtained through MRI scanning. A class of LFCDI challenges arises from the subject rotation requirement, which calls for reliability analysis metrics and specific image registration techniques. In this study these challenges are formulated and in light of proposed discussions, the reliability analysis of calculation of current pathways in a designed phantom and a pig heart is presented. The current passed is measured with less than 5% error for phantom, using CDI method. It is shown that Gauss's law for magnetism can be treated as reliability metric in matching the images in two orientations. For the phantom and pig heart the usefulness of image registration for mitigation of rotation errors is demonstrated. The reliability metric provides a good representation of the degree of correspondence between images in two orientations for phantom and pig heart. In our CDI experiments this metric produced values of 95% and 26%, for phantom, and 88% and 75% for pig heart, for mismatch rotations of 0 and 20 degrees respectively.

  7. Airflow limitation as a risk factor for low bone mineral density and hip fracture

    Science.gov (United States)

    Herland, Trine; Apalset, Ellen M; Eide, Geir Egil; Tell, Grethe S; Lehmann, Sverre

    2016-01-01

    Aim To investigate whether airflow limitation is associated with bone mineral density (BMD) and risk of hip fractures. Methods A community sample of 5,100 subjects 47–48 and 71–73 years old and living in Bergen was invited. Participants filled in questionnaires and performed a post-bronchodilator spirometry measuring forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC). All attendants were invited to have a BMD measurement of the hip. During 10 years of follow-up, information on death was collected from the Norwegian Cause of Death Registry, and incident hip fractures were registered from regional hospital records of discharge diagnoses and surgical procedure codes. Results The attendance rate was 69% (n=3,506). The prevalence of chronic obstructive pulmonary disease (COPD) (FEV1/FVC<0.7) was 9%. In multiple logistic regression, the lowest quartile of BMD versus the three upper was significantly predicted by FEV1/FVC<0.7 and FEV1% predicted (odds ratio [OR]: 1.58, 95% confidence interval [CI]: 1.11 to 2.25, and OR per increase of 10%: 0.92, 95% CI: 0.86 to 0.99, respectively). Hip fracture occurred in 126 (4%) participants. In a Cox regression analysis, FEV1% predicted was associated with a lowered risk of hip fracture (hazard ratio per increase of 10%: 0.89, 95% CI: 0.79 to 0.997). Conclusion Airflow limitation is positively associated with low BMD and risk of hip fracture in middle-aged and elderly. PMID:27733234

  8. Effects on magnetic reconnection of a density asymmetry across the current sheet

    Directory of Open Access Journals (Sweden)

    K. G. Tanaka

    2008-08-01

    Full Text Available The magnetopause (MP reconnection is characterized by a density asymmetry across the current sheet. The asymmetry is expected to produce characteristic features in the reconnection layer. Here we present a comparison between the Cluster MP crossing reported by Retinò et al. (2006 and virtual observations in two-dimensional particle-in-cell simulation results. The simulation, which includes the density asymmetry but has zero guide field in the initial condition, has reproduced well the observed features as follows: (1 The prominent density dip region is detected at the separatrix region (SR on the magnetospheric (MSP side of the MP. (2 The intense electric field normal to the MP is pointing to the center of the MP at the location where the density dip is detected. (3 The ion bulk outflow due to the magnetic reconnection is seen to be biased towards the MSP side. (4 The out-of-plane magnetic field (the Hall magnetic field has bipolar rather than quadrupolar structure, the latter of which is seen for a density symmetric case. The simulation also showed rich electron dynamics (formation of field-aligned beams in the proximity of the separatrices, which was not fully resolved in the observations. Stepping beyond the simulation-observation comparison, we have also analyzed the electron acceleration and the field line structure in the simulation results. It is found that the bipolar Hall magnetic field structure is produced by the substantial drift of the reconnected field lines at the MSP SR due to the enhanced normal electric field. The field-aligned electrons at the same MSP SR are identified as the gun smokes of the electron acceleration in the close proximity of the X-line. We have also analyzed the X-line structure obtained in the simulation to find that the density asymmetry leads to a steep density gradient in the in-flow region, which may lead to a non-stationary behavior of the X-line when three-dimensional freedom is taken into account.

  9. Inrush Current Limitation in Wind Generators by SCR Based Soft-starter during grid connection

    Directory of Open Access Journals (Sweden)

    Sanjay Mishra

    2013-10-01

    Full Text Available High Inrush current & harmonics is a generic problem wind generators during grid connection.The designed SCR based soft-starter successfully limits the high inrush current during the connection of the wind-turbine system to the grid. The proposed SCR based soft starter using will be simulating in PSCAD on a three-phase induction generator. Expected results will show a significant reduction in high inrush current and smooth connection of the three phase induction generator to the grid with small impact on the power quality. A small-scale wind turbine coupled three phase induction generator is an attractive choice for an isolated grid hybrid power system in remote areas because of its low cost, compactness, ruggedness, high reliability, low inertia and ease in control. In this work, a SCR based soft starter for limiting the high inrush current during the connection of the small-scale wind turbine coupled three phase induction generator to an isolated weak grid has been proposed. Soft-starter is designed to reduce inrush current or surge in current while achieving a proper synchronism between the generator and the grid.

  10. Scanning Hall-probe microscopy system for two-dimensional imaging of critical current density in RE-123 coated conductors

    Energy Technology Data Exchange (ETDEWEB)

    Higashikawa, K., E-mail: kohei@super.ees.kyushu-u.ac.jp [Department of Electrical Engineering, Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Inoue, M.; Kawaguchi, T.; Shiohara, K.; Imamura, K.; Kiss, T. [Department of Electrical Engineering, Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Iijima, Y.; Kakimoto, K.; Saitoh, T. [Material Technology Laboratory, Fujikura, 1-5-1, Kiba, Koto-ku, Tokyo 135-8512 (Japan); Izumi, T. [Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062 (Japan)

    2011-11-15

    Nondestructive characterization method of in-plane distribution of critical current density for coated conductors. Current distribution in a coated conductor compared with that from theoretical analysis. Relationship between local critical current density and local magnetic field. We have developed a characterization method for two-dimensional imaging of critical current density in coated conductors (CCs) based on scanning Hall-probe microscopy (SHPM). The distributions of the magnetic field around a sample were measured for several different conditions of external magnetic fields, and then were converted to those of the sheet current density which flowed to shield the external magnetic field or to trap the penetrated magnetic field. As a result, it was found that the amplitude of the sheet current density corresponded to that of critical current density almost in all the area of the sample except for the region where current direction changed. This indicates that we could obtain an in-plane distribution of the critical current density with a spatial resolution of around 100 {mu}m in non-destructive manner by this method. We believe that this measurement will be a multifunctional and comprehensive characterization method for coated conductors.

  11. Milagro Limits and HAWC Sensitivity for the Rate Density of Evaporating Primordial Black Holes

    Science.gov (United States)

    Marinelli, Samuel; HAWC Collaboration; Milagro Collaboration

    2015-04-01

    Primordial black holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and will emit all energetically allowed species of fundamental particles thermally. PBHs with initial masses of order 5 . 0 ×1010 g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV - TeV energy range. The Milagro high-energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field of view, more than 90% duty cycle, and sensitivity up to 100-TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. A search of five years of Milagro data yielded no detections at 5 σ and set a local (parsec-scale) upper limit of 3 . 6 ×104 PBH bursts/year/pc3. In addition, we will report the sensitivity of the Milagro successor, the High-Altitude Water-Cherenkov (HAWC) observatory, to PBH evaporation events. This work was supported by the National Science Foundation.

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

    Science.gov (United States)

    Pikin, Alexander; Alessi, James G.; Beebe, Edward N.; Shornikov, Andrey; Mertzig, Robert; Wenander, Fredrik; Scrivens, Richard

    2015-01-01

    A new electron gun with electrostatic compression has been installed at the Electron Beam Ion Source (EBIS) Test Stand at BNL. This is a collaborative effort by BNL and CERN teams with a common goal to study an EBIS with electron beam current up to 10 A, current density up to 10,000 A/cm2 and energy more than 50 keV. Intensive and pure beams of heavy highly charged ions with mass-to-charge ratio heavy ion research facilities including NASA Space Radiation Laboratory (NSRL) at BNL and HIE-ISOLDE at CERN. With a multiampere electron gun, the EBIS should be capable of delivering highly charged ions for both RHIC facility applications at BNL and for ISOLDE experiments at CERN. Details of the electron gun simulations and design, and the Test EBIS electrostatic and magnetostatic structures with the new electron gun are presented. The experimental results of the electron beam transmission are given.

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

    Science.gov (United States)

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

    1991-01-01

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

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

    Science.gov (United States)

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

    2007-10-01

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

  15. Enhancement of transient stability using fault current limiter and braking resistor

    Energy Technology Data Exchange (ETDEWEB)

    Yagami, M.; Hiratsuka, Y. [Hokkaido Inst. of Technology, Sapporo, Hokkaido (Japan); Tamura, J. [Kitami Inst. of Technology, Kitami, Hokkaido (Japan)

    2006-07-01

    Replacement of aging substation equipment is needed in order to maintain the stability of electric power systems which are becoming increasingly interconnected. This paper addressed the issue of using fault current limiters (FCLs) as a means of limiting fault currents and enhancing the transient stability of a power system. FCL limits the fault current by generating an impedance when a fault occurs. The limiting impedance helps to increase generator output degraded by a fault, thus providing stabilization. However, FCLs installed in series with transmission lines can only be operated during the period from the fault occurrence to the fault clearing. Therefore, they cannot control the generator disturbances after the clearing of a fault. However, in the event of power failures, thyristor controlled braking resistors (TCBRs) can quickly control generator disturbances. Therefore, the authors proposed the use of both FCL and TCBR devices to enhance transient stability and damp the turbine shaft torsional oscillations. The effectiveness of both devices on suppression of the turbine shaft torsional oscillations was illustrated through simulations performed in EMTP/ATP considering three-lines-to-ground fault. It was shown that if both devices operate at the same bus, the stabilization control scheme can be carried out continuously and with flexibility from the fault occurrence instance, thereby effectively improving transient stability. 7 refs., 2 tabs., 10 figs.

  16. Mapping the ECG in the live rabbit heart using Ultrasound Current Source Density Imaging with coded excitation.

    Science.gov (United States)

    Qin, Yexian; Li, Qian; Ingram, Pier; Witte, Russell S

    2012-10-01

    Ultrasound current source density imaging (UCSDI) is a noninvasive technique for mapping electric current fields in 4D (space + time) with the resolution of ultrasound imaging. This approach can potentially overcome limitations of conventional electrical mapping procedures often used during treatment of cardiac arrhythmia or epilepsy. However, at physiologic currents, the detected acoustoelectric (AE) interaction signal in tissue is very weak. In this work, we evaluated coded ultrasound excitation (chirps) for improving the sensitivity of UCSDI for mapping the electrocardiogram (ECG) in a live rabbit heart preparation. Results confirmed that chirps improved detection of the AE signal by as much as 6.1 dB compared to a square pulse. We further demonstrated mapping the ECG using a clinical intracardiac catheter, 1 MHz ultrasound transducer and coded excitation. B-mode pulse echo and UCSDI revealed regions of high current flow in the heart wall during the peak of the ECG. These improvements to UCSDI are important steps towards translation of this new technology to the clinic for rapidly mapping the cardiac activation wave.

  17. Current Limitations and Recommendations to Improve Testing for the Environmental Assessment of Endocrine Active Substances

    DEFF Research Database (Denmark)

    Coady, Katherine K; Biever, Ronald C; Denslow, Nancy D

    2016-01-01

    evaluate whether a chemical possesses endocrine activity and whether this activity can result in adverse outcomes either to humans or the environment. Current test systems include in silico, in vitro and in vivo techniques focused on detecting potential endocrine activity, and in vivo tests that collect...... apical data to detect possible adverse effects. These test systems are currently designed to robustly assess endocrine activity and/or adverse effects in the estrogen, androgen, and thyroid hormone signaling pathways; however, there are some limitations of current test systems for evaluating endocrine...... methods currently do not exist, and addressing key endocrine pathways of possible concern in addition to those associated with estrogen, androgen and thyroid signaling. This article is protected by copyright. All rights reserved....

  18. Review on Superconducting Fault Current Limiters%超导限流器综述

    Institute of Scientific and Technical Information of China (English)

    信赢

    2015-01-01

    This paper briefly recalls the scientific origin and R&D history of superconducting fault current limiters. The working princi-ple, generic structure, and equivalent circuitry of resistive type, saturated iron-core type, magnetic shield type, and bridge type super-conducting fault current limiters are introduced. The functional characteristics, technical advantages and disadvantages of resistive type and saturated iron-core type superconducting fault current limiters are analyzed and compared in detail. Real grid application examples of these two types of devices are presented. Discussing the application scope and prospect of superconducting fault current limiters, the paper points out that besides conventional fault current limiting functions, superconducting fault current limiters may become an indis-pensable device in grid integration of distributed renewable generations, and they will play an important role in upgrading power grids by reducing transmission loss and enhancing efficiency in the future.%概述了超导限流器的科学基础和发展历史,介绍了电阻型、饱和铁心型、磁屏蔽性和电桥型超导限流器的技术原理、基本结构和等效电路,详细分析和比较了电阻型和饱和铁心型超导限流器的性能特征、优点和缺点,以及其在实际电网挂网运行的案例。展望了超导限流器可能的应用范围及前景,指出除了传统观念上的短路故障限流作用之外,超导限流器未来可能成为可再生能源分布式发电并网的必要设备,在降低输电损耗和提高输送效率方面发挥重要作用。

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

    Science.gov (United States)

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

    2007-06-01

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

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

    Science.gov (United States)

    Ding, Lei

    2009-05-07

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

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

    Science.gov (United States)

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

    2001-04-01

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

  2. Current density distribution mapping in PEM fuel cells as an instrument for operational measurements

    Energy Technology Data Exchange (ETDEWEB)

    Geske, M.; Heuer, M.; Heideck, G.; Styczynski, Z. A. [Otto-von-Guericke University Magdeburg, Chair Electric Power Networks and Renewable Energy Sources, Magdeburg (Germany)

    2010-07-01

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

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Li Xiaofen, E-mail: xiaofenli@gmail.com [Materials Research Division, Riso National Laboratory for Sustainable Energy, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde (Denmark); Grivel, Jean-Claude; Abrahamsen, Asger B.; Andersen, Niels H. [Materials Research Division, Riso National Laboratory for Sustainable Energy, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde (Denmark)

    2012-07-15

    We have numerically proved that the dependence of AC susceptibility {chi} of a E(J) power law superconducting thin disc on many parameters can be reduced to one penetration parameter h, with E the electric field and J the current density. Based on this result, we propose a way of measuring the critical current density J{sub c} of superconducting thin films by AC susceptibility. Compared with the normally used method based on the peak of the imaginary part, our method uses a much larger range of the AC susceptibility curve, thus allowing determination of the temperature (T) dependence of J{sub c} from a normally applied {chi}(T) measurement. A fitting equation J{sub c} = 1.9H{sub a} Divides {chi} Prime Divides {sup 0.69}/d, -0.4 < {chi} Prime < -0.001 derived from the critical state case (Bean model) can be used in most situations, where H{sub a} is the amplitude of the applied AC field, {chi} Prime is the real part of the normalized susceptibility and d is the thickness of the film. The method is valid for the cases where the film is fully penetrated. We also discuss how the finite London penetration depth affects the susceptibility when the film is screened. Measurements with varying T, H{sub a} and DC background field H{sub dc} are performed to support the arguments.

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

    Science.gov (United States)

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

    2012-07-01

    We have numerically proved that the dependence of AC susceptibility χ of a E(J) power law superconducting thin disc on many parameters can be reduced to one penetration parameter h, with E the electric field and J the current density. Based on this result, we propose a way of measuring the critical current density Jc of superconducting thin films by AC susceptibility. Compared with the normally used method based on the peak of the imaginary part, our method uses a much larger range of the AC susceptibility curve, thus allowing determination of the temperature (T) dependence of Jc from a normally applied χ(T) measurement. A fitting equation Jc = 1.9Ha∣χ‧∣0.69/d, -0.4 Bean model) can be used in most situations, where Ha is the amplitude of the applied AC field, χ‧ is the real part of the normalized susceptibility and d is the thickness of the film. The method is valid for the cases where the film is fully penetrated. We also discuss how the finite London penetration depth affects the susceptibility when the film is screened. Measurements with varying T, Ha and DC background field Hdc are performed to support the arguments.

  6. A new method for estimating the critical current density of a superconductor from its hysteresis loop

    Energy Technology Data Exchange (ETDEWEB)

    Lal, Ratan, E-mail: rlal_npl_3543@yahoo.i [Superconductivity Division, National Physical Laboratory, Council of Scientific and Industrial Research, Dr. K.S. Krishnan Road, New Delhi 110012 (India)

    2010-02-15

    The critical current density J{sub c} of some of the superconducting samples, calculated on the basis of the Bean's model, shows negative curvature for low magnetic field with a downward bending near H = 0. To avoid this problem Kim's expression of the critical current density, J{sub c} = k/(H{sub 0} + H), where J{sub c} has positive curvature for all H, has been employed by connecting the positive constants k and H{sub 0} with the features of the hysteresis loop of a superconductor. A relation between the full penetration field H{sub p} and the magnetic field H{sub min}, at which the magnetization is minimum, is obtained from the Kim's theory. Taking the value of J{sub c} at H = H{sub p} according to the actual loop width, as in the Bean's theory, and at H = 0 according to an enhanced loop width due to the local internal field, values of k and H{sub 0} are obtained in terms of the magnetization values M{sup +}(-H{sub min}), M{sup -}(H{sub min}), M{sup +}(H{sub p}) and M{sup -}(H{sub p}). The resulting method of estimating J{sub c} from the hysteresis loop turns out to be as simple as the Bean's method.

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

    Directory of Open Access Journals (Sweden)

    Martin Geske

    2010-04-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Fertig, Fabian, E-mail: fabian.fertig@ise.fraunhofer.de; Greulich, Johannes; Rein, Stefan [Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstr. 2, D-79110 Freiburg (Germany)

    2014-05-19

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

  9. Research on a Fast-Closing Switch Based Fault Current Limiter with Series Compensation

    Institute of Scientific and Technical Information of China (English)

    CHEN Jin-xiang; ZOU Ji-yan; DONG En-yuan; SHI Jing

    2002-01-01

    A new type of fault current limiter (FCL) with series compensation based fast-closing switch is proposed. It is composed of a capacitor bank and a reactor in series.The main control component is a fast-closing switch connected in parallel with the capacitors, which is driven by the electromagnetic repulsion force. When fault occurs, the switch closes and bypasses the capacitors,and the fault is limited by the reactor then. Simulated analysis and experiments show that it is feasible to develop the FCL with low cost and high reliability. The effectiveness of transient stability for power system is evaluated by digital simulation.

  10. Impact and Limitations Deriving from Basel II within the Context of the Current Financial Crisis

    Directory of Open Access Journals (Sweden)

    Oana Miruna DĂNILĂ

    2012-06-01

    Full Text Available The Banking sector risk management framework, geared towards maintaining a solid capital adequacy level, has witnessed a permanent evolution, determined by the global economic and financial reality.Basel II has brought an improvement of the risk management framework by adding minimum capital levels corresponding to market and operational risk and by the introduction of internal rating models. However the current crisis has brought forward some adverse effects as well as limitations.This paper analyses the evolution of prudential rules and regulations introduced by Basel II and their impact on the banking system together with outlining certain limitations.

  11. Improved critical current density of MgB2--carbon nanotubes composite.

    Science.gov (United States)

    Shekhar, Chandra; Giri, Rajiv; Malik, S K; Srivastav, O N

    2007-06-01

    In the present study, we report a systematic study of doping/admixing of carbon nanotubes (CNTs) in different concentrations in MgB2. The composite material corresponding to MgB2-x at.% CNTs (35 at.% > or = x > or = 0 at.%) have been prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/microstructural characterization employing XRD, Scanning electron microscopic (SEM), and Transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by Physical property measurement system (PPMS) and electrical transport measurements have been done by the four-probe technique. The microstructural investigations reveal the formation of MgB2-carbon nanotube composites. A CNT connecting the MgB2 grains may enhance critical current density due to its size (approximately 5-20 nm diameter) compatible with coherence length of MgB2 (approximately 5-6 nm) and ballistic transport current carrying capability along the tube axis. The transport critical current density (Jct) of MgB2 samples with varying CNTs concentration have been found to vary significantly e.g., Jct of the MgB2 sample with 10 at.% CNT addition is approximately 2.3 x 10(3) A/cm2 and its value for MgB2 sample without CNT addition is approximately 7.2 x 102 A/cm2 at 20 K. In order to study the flux pinning effect of CNTs doping/ admixing in MgB2, the evaluation of intragrain critical current density (JJ) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on Jc is obtained for 10 at.% CNTs admixed MgB2 sample at 5 K, the Jc reaches approximately 5.2 x 10(6) A/cm2 in self field, -1.6 x 10(6) A/cm2 at 1 T, approximately 2.9 x 10(5) A/cm2 at 2.6 T, and approximately 3.9 x 10(4) A/cm2 at 4 T. The high value of intragrain Jc in 10 at.% CNTs admixed MgB2 superconductor has been attributed to the incorporation of CNTs into the crystal matrix of

  12. Evaluation of Yield and Yield Components of Black Cumin (Nigella sativa L. under different Plant Density and Limited Irrigation Condition

    Directory of Open Access Journals (Sweden)

    Sh Rezvan Beidokhti

    2012-10-01

    Full Text Available Research on crop response to deficit irrigation is important to reduce agriculture water use in areas where water is limited resource. Using drought resistant landraces with irrigation scheduling based on phenological stages in semi-arid and arid regions may provide an opportunity to optimize irrigation efficiency and water savings in these regions. In order to evaluate of yield and yield components of black cumin under different plant density and limited irrigation condition an experiment was conducted in Research Farm of Islamic Azad University of Damghan during growing season of 2007-2008. The experimental treatments were arranged in split plots based on a complete randomized block design with three replications. The limited irrigation (based on phenological stages treatments were included: cutting irrigation at blooming (folded flowers, cutting irrigation at flowering stage, cutting irrigation at seed formation and normal weekly irrigation (control were allocated to the main plots and different plant density: 100, 150, 200 and 250 plant per square meter (m2 were allocated to sub plots. The results showed that the effect of limited irrigation, plant density and their interaction on plant height, number of follicle, follicle weight, number of seed, 1000 seed weight, seed yield, biological yield and harvest index Black Cumin. The highest yield and yield components was obtained in normal irrigation (control and 200 plant density and the lowest yield were obtained when irrigation cut at the blooming stage and 250 plant density. There was a significant correlation between seed yield and number (r=0.90, 1000 seed weight (r=0.95 and biological yield (r=0.97. Optimum plant density of black cumin was decreased under limited irrigation treatments. Under normal (control and limited irrigation, optimum plant density was 200 and 150 plant per (m2 respectively.

  13. Predicting the behavioural impact of transcranial direct current stimulation: issues and limitations

    Directory of Open Access Journals (Sweden)

    Archy Otto De Berker

    2013-10-01

    Full Text Available The transcranial application of weak currents to the human brain has enjoyed a decade of success, providing a simple and powerful tool for non-invasively altering human brain function. However, our understanding of current delivery and its impact upon neural circuitry leaves much to be desired. We argue that the credibility of conclusions drawn with tDCS is contingent upon realistic explanations of how tDCS works, and that our present understanding of tDCS limits the technique’s use to localize function in the human brain. We outline two central issues where progress is required: the localization of currents, and predicting their functional consequence. We encourage experimenters to eschew simplistic explanations of mechanisms of transcranial current stimulation. We suggest the use of individualized current modelling, together with computational neurostimulation to inform mechanistic frameworks in which to interpret the physiological impact of tDCS. We hope that through mechanistically richer descriptions of current flow and action, insight into the biological processes by which transcranial currents influence behaviour can be gained, leading to more effective stimulation protocols and empowering conclusions drawn with tDCS.

  14. Durability of the Solid Oxide Cells for Co-Electrolysis of Steam and Carbon Dioxide under High Current Densities

    DEFF Research Database (Denmark)

    Tao, Youkun

    Production of hydrogen and syngas (CO + H2) using solid oxide electrolysis cells (SOECs) has become increasingly attractive due to high oil price, the capability for conversion and storage of intermittent energy from renewable sources and the general interest in hydrogen energy and carbon......-neutral energy sources. Long-term stability of SOECs for high fuel productivity is crucial for the application of this technology. In this work, a series of galvanostatic durability tests were performed at high current densities (|i| = 1.5 or 2.0 A/cm2), 850 oC for up to about 700 hours for co-electrolysis...... occurred during co-electrolysis of steam and CO2 at |i| ≥ 2.0 A/cm2. Gas diffusion limitations contribute to the dramatic increase of cell voltage and a very reducing atmosphere at the interface....

  15. A dulal-functional medium voltage level DVR to limit downstream fault currents

    DEFF Research Database (Denmark)

    Li, Yun Wei; Vilathgamuwa, D. Mahinda; Loh, Poh Chiang

    2007-01-01

    , the DVR will therefore be tasked to mitigate even more faults involving downstream loads. Large fault currents would flow through the DVR during a downstream fault before the opening of a circuit breaker. This will cause the voltage at point of common coupling (PCC) to drop, which would affect the loads...... on the other parallel feeders connected to PCC. Furthermore, if not controlled properly, the DVR might also contribute to this PCC voltage sag in the process of compensating the missing voltage, thus further worsening the fault situation. To limit the flow of large line currents, and therefore restore the PCC...... voltage as well as protect the DVR system components, a downstream fault limiting function is proposed and integrated in the DVR operation. A flux-charge-model feedback algorithm is implemented so that the DVR would act as a large virtual inductance in series with the distribution feeder in fault...

  16. Study of the Fast—Closing Switch Used for Fault Current Limiters in Power System

    Institute of Scientific and Technical Information of China (English)

    邹积岩; 陈金祥; 等

    2002-01-01

    This paper presents a new type of fault current limiter(FCL) based on fast-closing switch,which is composed of a capacitor bank and a reactor in series.The main control component is a fast-closing switch connected in parallel with the capactitors,which is drien by the electromagnetic repulsion force.It can response the order within 1 ms.When fault occurs,the switch closes and the capacitors are bypassed.and the fault current is limited by the reactor,Simulation analysis and experiment show that the electromagnetic repulsion force actuator can meet the demand of fast-closing switch,it is feasible to develop the FCL with low cost and high reliability.

  17. High short-circuit current density CdTe solar cells using all-electrodeposited semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Echendu, O.K., E-mail: oechendu@yahoo.com; Fauzi, F.; Weerasinghe, A.R.; Dharmadasa, I.M.

    2014-04-01

    CdS/CdTe and ZnS/CdTe n–n heterojunction solar cells have been fabricated using all-electrodeposited semiconductors. The best devices show remarkable high short-circuit current densities of 38.5 mAcm{sup −2} and 47.8 mAcm{sup −2}, open-circuit voltages of 630 mV and 646 mV and conversion efficiencies of 8.0% and 12.0% respectively. The major strength of these device structures lies in the combination of n–n heterojunction with a large Schottky barrier at the n-CdTe/metal back contact which provides the required band bending for the separation of photo-generated charge carriers. This is in addition to the use of a high quality n-type CdTe absorber layer with high electron mobility. The potential barrier heights estimated for these devices from the current–voltage characteristics exceed 1.09 eV and 1.13 eV for CdS/CdTe and ZnS/CdTe cells respectively. The diode rectification factors of both devices are in excess of four orders of magnitude with reverse saturation current densities of 1.0 × 10{sup −7} Acm{sup −2} and 4.0 × 10{sup −7} Acm{sup −2} respectively. These all-electrodeposited solar cell device structures are currently being studied and developed as an alternative to the well-known p–n junction structures which utilise chemical bath-deposited CdS. The preliminary material growth, device fabrication and assessment results are presented in this paper. - Highlights: • Two-electrode deposition. • High J{sub sc} Schottky barrier solar cells. • CdCl{sub 2} + CdF{sub 2} treatment.

  18. Current-limiting reactor based on high-T sub c superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Bashkirov, Y.A.; Fleishman, L.S.; Patsayeve, T.Y.; Sobolev, A.N.P; Vdovin, A.B. (Krzhizhanovsky Power Engineering Inst., Leninsky prospect, 19, Moscow 117927 (SU))

    1991-03-01

    This paper deals with one of the possible applications of high-temperature superconductors in power devices with superconducting shields. The behavior was analyzed of a current-limiting reactor combining a high-T{sub c} shield and an iron core in an a.c. circuit. The model of the device was built comprising a stack of yttrium ceramic rings. The experiments with such a reactor confirmed the presence of nonlinear characteristics with transition from low to high impedance.

  19. Transformation of current limiting effect into varistor effect in tin dioxide based ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Bondarchuk, A N; Glot, A B [Universidad Tecnologica de la Mixteca, Huajuapan de Leon, Oaxaca, C.P. 69000 (Mexico)], E-mail: alexbond@mixteco.utm.mx

    2008-09-07

    The current limiting effect and its transformation into the varistor effect were found in SnO{sub 2}-Co{sub 3}O{sub 4}-Nb{sub 2}O{sub 5}-Cr{sub 2}O{sub 3} ceramics sintered at relatively low temperatures 1100-1200 {sup 0}C. Results of electrical measurements in oxidizing and inert atmosphere are explained in terms of the modified barrier model.

  20. Limiting current technique in the research of mass/heat transfer in nanofluid

    Science.gov (United States)

    Wilk, J.; Grosicki, S.

    2016-09-01

    In the paper the authors focused on the application of the electrochemical limiting diffusion current technique to the study of mass transfer in nanofluid flow. As mass and heat transfer are analogical phenomena, analysing mass transfer helps understand heat transfer processes in nanofluids. The paper begins with a short review of the available literature on the subject followed by the authors' results of mass transfer coefficient measurements and the conclusions concerning mass/heat transfer enhancement in nanofluids.

  1. Current meter data from moored current meter casts in the Northeast Pacific (limit - 180) from 12 June 1992 - 20 June 1994 (NODC Accession 9700237)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current meter data were collected using moored current meter casts in the Northeast Pacific (limit - 180) from June 12, 1992 to June 20, 1994. Data were submitted by...

  2. Current components data from current meters from the NE Pacific (limit-180) from 01 June 1954 to 01 June 1970 (NODC Accession 7601441)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current components data were collected from current meters in the NE Pacific (limit-180). Data were collected by the Japanese Hydrographic Office from 01 June 1954...

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

    Science.gov (United States)

    Vašina, P; Hytková, T; Eliáš, M

    2009-05-01

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

  4. Modeling and analysis of the three-dimensional current density in sandwich-type single-carrier devices of disordered organic semiconductors

    Science.gov (United States)

    van der Holst, J. J. M.; Uijttewaal, M. A.; Balasubramanian, R.; Coehoorn, R.; Bobbert, P. A.; de Wijs, G. A.; de Groot, R. A.

    2009-02-01

    We present the results of a modeling study of the three-dimensional current density in single-carrier sandwich-type devices of disordered organic semiconductors. The calculations are based on a master-equation approach, assuming a Gaussian distribution of site energies without spatial correlations. The injection-barrier lowering due to the image potential is taken into account, so that the model provides a comprehensive treatment of the space-charge-limited current as well as the injection-limited current (ILC) regimes. We show that the current distribution can be highly filamentary for voltages, layer thicknesses, and disorder strengths that are realistic for organic light-emitting diodes and, that, as a result, the current density in both regimes can be significantly larger than as obtained from a one-dimensional continuum drift-diffusion device model. For devices with large injection barriers and strong disorder, in the ILC transport regime, good agreement is obtained with the average current density predicted from a model assuming injection and transport via one-dimensional filaments [A. L. Burin and M. A. Ratner, J. Chem. Phys. 113, 3941 (2000)].

  5. Plasma Shape and Current Density Profile Control in Advanced Tokamak Operating Scenarios

    Science.gov (United States)

    Shi, Wenyu

    The need for new sources of energy is expected to become a critical problem within the next few decades. Nuclear fusion has sufficient energy density to potentially supply the world population with its increasing energy demands. The tokamak is a magnetic confinement device used to achieve controlled fusion reactions. Experimental fusion technology has now reached a level where tokamaks are able to produce about as much energy as is expended in heating the fusion fuel. The next step towards the realization of a nuclear fusion tokamak power plant is ITER, which will be capable of exploring advanced tokamak (AT) modes, characterized by a high fusion gain and plasma stability. The extreme requirements of the advanced modes motivates researchers to improve the modeling of the plasma response as well as the design of feedback controllers. This dissertation focuses on several magnetic and kinetic control problems, including the plasma current, position and shape control, and data-driven and first-principles-driven modeling and control of plasma current density profile and the normalized plasma pressure ratio betaN. The plasma is confined within the vacuum vessel by an external electromagnetic field, produced primarily by toroidal and poloidal field coils. The outermost closed plasma surface or plasma boundary is referred to as the shape of the plasma. A central characteristic of AT plasma regimes is an extreme elongated shape. The equilibrium among the electromagnetic forces acting on an elongated plasma is unstable. Moreover, the tokamak performance is improved if the plasma is located in close proximity to the torus wall, which guarantees an efficient use of available volume. As a consequence, feedback control of the plasma position and shape is necessary. In this dissertation, an Hinfinity-based, multi-input-multi-output (MIMO) controller for the National Spherical Torus Experiment (NSTX) is developed, which is used to control the plasma position, shape, and X

  6. Dynamics of pyroclastic density currents: Conditions that promote substrate erosion and self-channelization - Mount St Helens, Washington (USA)

    Science.gov (United States)

    Brand, Brittany D.; Mackaman-Lofland, Chelsea; Pollock, Nicholas M.; Bendaña, Sylvana; Dawson, Blaine; Wichgers, Pamela

    2014-04-01

    features but typically has a basal lithic-rich region, is variably fines-depleted and contains pumice lobes, suggesting density segregation in a less concentrated current relative to Unit III. Deep, erosive channels cut by the Unit III current and thick lithic levee deposits within Unit IV occur in an area where debris avalanche relief is limited, suggesting self-channelization developed as a function of internal flow dynamics. An increase in the proportion and size of lithic blocks is found (1) downstream of debris avalanche hummocks, suggesting the PDCs were energetic enough to locally entrain accidental lithics from the hummocks and transport them tens of meters downstream, and (2) within large channels cut by later PDCs into earlier PDC deposits, suggesting self-channelization of the flows increased the carrying capacity of the subsequent channelized currents. Finally, the combination of thick, massive deposits with a high percentage of fine ash within Unit III and in the medial-distal depositional regions of Units II-IV suggests that the PDCs developed and maintained a high internal pore pressure during transport and deposition. The most important results include our ability to understand the role of internal pore pressure on current mobility, the influence of self-channelization on carrying capacity of the currents and the influence of surface roughness on substrate erosion. These observations have critical consequences for understanding the flow dynamics and hazard potential of PDCs.

  7. Functional limitations linked to high body mass index, age and current pain in obese women.

    Science.gov (United States)

    Evers Larsson, U; Mattsson, E

    2001-06-01

    To describe functional limitations in obese women. Comparisons of functional limitations in obese women and in a normal-weight reference group regarding mobility, balance and housework transport. A large room with a corridor and staircase nearby. Fifty-seven consecutively selected obese female outpatients, mean age 44 y, body mass index (BMI) 37 kg.m(-2), and 22 voluntary references, mean age 49 y, BMI 22 kg.m(-2). Pain questionnaire (for background data); a new valid and reliable test protocol measuring activities of daily life (ADL), pain and exertion, heart rate, balance and speed. The patients had problems in performing 13 of 16 actions compared with the references (P-values between 0.05 and 0.001). They moved more slowly and had difficulties and /or pain and exertion in flexibility tasks, balancing, activities at floor level (bending and kneeling), climbing stairs and carrying groceries. BMI (P=0.002), age (P=0.02) and current pain (P=0.02) from the lower body predicted functional limitation. The functional test reflected functional limitations in obese women, revealing difficulties and perceived pain in ADL. The test protocol can be used to evaluate the effects of training or dieting. For clinical use we recommend considering BMI, age and current pain for use when individualizing advice on training.

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

    Directory of Open Access Journals (Sweden)

    S. D. Parkinson

    2014-05-01

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

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

    Science.gov (United States)

    Walder, J. S.

    2010-12-01

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

  10. Flow Transformation in Pyroclastic Density Currents: Entrainment and Granular Dynamics during the 2006 eruption of Tungurahua

    Science.gov (United States)

    Dufek, J.; Benage, M. C.; Geist, D.; Harpp, K. S.

    2013-12-01

    Pyroclastic density currents are ground hugging flows composed of hot gases, fragments of juvenile magmatic material, and entrained clasts from the conduit or the edifice over which the flows have traveled. The interior of these flows are opaque to observation due to their large ash content, but recent investigations have highlighted that there are likely strong gradients in particle concentration and segregation of particle sizes in these particle-laden gravity currents. Pyroclastic density currents refer to a broad range of phenomena from dense flows in which the dynamics are dominated by frictional interaction between particles (dense granular flows), to gas fluidized flows, to dilute flows dominated by particle-gas turbulent interaction. However, abrupt flow transformation (e.g. from dense to dilute pyroclastic density currents) can arise due to energy exchange across multiple length scales and phases, and understanding these flow transformations is important in delineating the entrainment and erosion history of these flows, interpretations of their deposits, and in better understanding the hazards they present. During the 2006 eruption of Tungurahua, Ecuador numerous, dense pyroclastic density currents descended the volcano as result of boiling-over or low column collapse eruptions. The deposits of these flows typically have pronounced snouts and levees, and are often dominated by large, clasts (meter scale in some locations). There is an exceptional observational record of these flows and their deposits, permitting detailed field constraints of their dynamics. A particularly interesting set of flows occurred on Aug. 17, 2006 during the paroxysmal phase of the eruption that descended the slope of the volcano, filled in the river channel of the Chambo river, removing much of the larger clasts from the flow, and resulting in a dilute ';surge' that transported finer material across the channel and uphill forming dune features on the opposite bank of the river. We

  11. Distribution characteristics of coronal electric current density as an indicator for the occurrence of a solar flare

    Science.gov (United States)

    Kang, Jihye; Magara, Tetsuya; Inoue, Satoshi; Kubo, Yuki; Nishizuka, Naoto

    2016-10-01

    In this paper we investigate the distribution characteristics of the coronal electric current density in a flare-producing active region (AR12158; SOL2014-09-10) by reconstructing nonlinear force-free (NLFF) fields from photospheric magnetic field data. A time series of NLFF fields shows the spatial distribution and its temporal development of coronal current density in this active region. A fractal dimensional analysis shows that a concentrated coronal current forms a structure of fractal spatiality. Furthermore, the distribution function of coronal current density is featured with a double power-law profile, and the value of electric current density at the breaking point of a double power-law fitting function shows a noticeable time variation toward the onset of an X-class flare. We discuss that this quantity will be a useful indicator for the occurrence of a flare.

  12. Distribution characteristics of coronal electric current density as an indicator for the occurrence of a solar flare

    Science.gov (United States)

    Kang, Jihye; Magara, Tetsuya; Inoue, Satoshi; Kubo, Yuki; Nishizuka, Naoto

    2016-12-01

    In this paper we investigate the distribution characteristics of the coronal electric current density in a flare-producing active region (AR12158; SOL2014-09-10) by reconstructing nonlinear force-free (NLFF) fields from photospheric magnetic field data. A time series of NLFF fields shows the spatial distribution and its temporal development of coronal current density in this active region. A fractal dimensional analysis shows that a concentrated coronal current forms a structure of fractal spatiality. Furthermore, the distribution function of coronal current density is featured with a double power-law profile, and the value of electric current density at the breaking point of a double power-law fitting function shows a noticeable time variation toward the onset of an X-class flare. We discuss that this quantity will be a useful indicator for the occurrence of a flare.

  13. Operation Tests for SN Transition Superconducting Fault Current Limiter in the Power System Simulator

    Science.gov (United States)

    Kameda, Hideyuki; Torii, Shinji; Kumano, Teruhisa; Sakaki, Hisayoshi; Kubota, Hiroshi; Yasuda, Kenji

    One of important problems to be solved in Japanese trunk transmission systems is the reduction of short circuit capacity. As this countermeasure, double buses are split into two buses in some substations. In recent years, dispersed generators are introduced in lower voltage classes due to the introduction of the electricity deregulation. In such a distribution system as many dispersed generators are introduced, it is a possibility that the fault current becomes beyond the breaking capacity at the occurrence of short circuit. Introduction of superconducting fault current limiters into a power system is very effective as one of the means to solve the above-mentioned problem, and we have studied on the effective introduction method of them and setting method of their parameters. This paper describes the results of the operation tests for SN transition type of a superconducting fault current limiter using 3 phases of FCL modules against various kinds of system faults or inrush current in the Power System Simulator installed at CRIEPI.

  14. Excessive magnetic field flux density distribution from overhead isolated powerline conductors due to neutral line current.

    Science.gov (United States)

    Netzer, Moshe

    2013-06-01

    Overhead isolated powerline conductors (hereinafter: "OIPLC") are the most compact form for distributing low voltage currents. From the known physics of magnetic field emission from 3-phase power lines, it is expected that excellent symmetry of the 120° shifted phase currents and where compact configuration of the 3-phase+neutral line exist, the phase current vectorial summation of the magnetic field flux density (MFFD) is expected to be extremely low. However, despite this estimation, an unexpectedly very high MFFD was found in at least three towns in Israel. This paper explains the reasons leading to high MFFD emissions from compact OIPLC and the proper technique to fix it. Analysis and measurement results had led to the failure hypothsis of neutral line poor connection design and poor grounding design of the HV-LV utility transformers. The paper elaborates on the low MFFD exposure level setup by the Israeli Environmental Protection Office which adopted a rather conservative precaution principal exposure level (2 mG averaged over 24 h).

  15. Extracting functional components of neural dynamics with Independent Component Analysis and inverse Current Source Density.

    Science.gov (United States)

    Lęski, Szymon; Kublik, Ewa; Swiejkowski, Daniel A; Wróbel, Andrzej; Wójcik, Daniel K

    2010-12-01

    Local field potentials have good temporal resolution but are blurred due to the slow spatial decay of the electric field. For simultaneous recordings on regular grids one can reconstruct efficiently the current sources (CSD) using the inverse Current Source Density method (iCSD). It is possible to decompose the resultant spatiotemporal information about the current dynamics into functional components using Independent Component Analysis (ICA). We show on test data modeling recordings of evoked potentials on a grid of 4 × 5 × 7 points that meaningful results are obtained with spatial ICA decomposition of reconstructed CSD. The components obtained through decomposition of CSD are better defined and allow easier physiological interpretation than the results of similar analysis of corresponding evoked potentials in the thalamus. We show that spatiotemporal ICA decompositions can perform better for certain types of sources but it does not seem to be the case for the experimental data studied. Having found the appropriate approach to decomposing neural dynamics into functional components we use the technique to study the somatosensory evoked potentials recorded on a grid spanning a large part of the forebrain. We discuss two example components associated with the first waves of activation of the somatosensory thalamus. We show that the proposed method brings up new, more detailed information on the time and spatial location of specific activity conveyed through various parts of the somatosensory thalamus in the rat.

  16. Large critical current density improvement in Bi-2212 wires through the groove-rolling process

    Science.gov (United States)

    Malagoli, A.; Bernini, C.; Braccini, V.; Romano, G.; Putti, M.; Chaud, X.; Debray, F.

    2013-04-01

    Recently there has been a growing interest in Bi-2212 superconductor round wire for high magnetic field use despite the fact that an increase of the critical current is still needed to boost its successful use in such applications. Recent studies have demonstrated that the main obstacle to current flow, especially in long wires, is the residual porosity inside these powder-in-tube processed conductors that develops from bubble agglomeration when the Bi-2212 melts. In this work we tried to overcome this issue affecting the wire densification by changing the deformation process. Here we show the effects of groove rolling versus the drawing process on the critical current density JC and on the microstructure. In particular, groove-rolled multifilamentary wires show a JC increased by a factor of about 3 with respect to drawn wires prepared with the same Bi-2212 powder and architecture. We think that this approach in the deformation process is able to produce the required improvements both because the superconducting properties are enhanced and because it makes the fabrication process faster and cheaper.

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

    Science.gov (United States)

    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.

  18. Critical current densities estimated from AC susceptibilities in proximity-induced superconducting matrix of multifilamentary wire

    Science.gov (United States)

    Akune, Tadahiro; Sakamoto, Nobuyoshi

    2009-03-01

    In a multifilamentary wire proximity-currents between filaments show a close resemblance with the inter-grain current in a high-Tc superconductor. The critical current densities of the proximity-induced superconducting matrix Jcm can be estimated from measured twist-pitch dependence of magnetization and have been shown to follow the well-known scaling law of the pinning strength. The grained Bean model is applied on the multifilamentary wire to obtain Jcm, where the filaments are immersed in the proximity-induced superconducting matrix. Difference of the superconducting characteristics of the filament, the matrix and the filament content factor give a variety of deformation on the AC susceptibility curves. The computed AC susceptibility curves of multifilamentary wires using the grained Bean model are favorably compared with the experimental results. The values of Jcm estimated from the susceptibilities using the grained Bean model are comparable to those estimated from measured twist-pitch dependence of magnetization. The applicability of the grained Bean model on the multifilamentary wire is discussed in detail.

  19. Critical current densities estimated from AC susceptibilities in proximity-induced superconducting matrix of multifilamentary wire

    Energy Technology Data Exchange (ETDEWEB)

    Akune, Tadahiro; Sakamoto, Nobuyoshi, E-mail: akune@te.kyusan-u.ac.j [Department of Electrical Engineering and Information Technology, Kyushu Sangyo University, 2-3-1 Matsukadai, Fukuoka 813-8503 (Japan)

    2009-03-01

    In a multifilamentary wire proximity-currents between filaments show a close resemblance with the inter-grain current in a high-T{sub c} superconductor. The critical current densities of the proximity-induced superconducting matrix J{sub cm} can be estimated from measured twist-pitch dependence of magnetization and have been shown to follow the well-known scaling law of the pinning strength. The grained Bean model is applied on the multifilamentary wire to obtain J{sub cm}, where the filaments are immersed in the proximity-induced superconducting matrix. Difference of the superconducting characteristics of the filament, the matrix and the filament content factor give a variety of deformation on the AC susceptibility curves. The computed AC susceptibility curves of multifilamentary wires using the grained Bean model are favorably compared with the experimental results. The values of J{sub cm} estimated from the susceptibilities using the grained Bean model are comparable to those estimated from measured twist-pitch dependence of magnetization. The applicability of the grained Bean model on the multifilamentary wire is discussed in detail.

  20. Limitations Of The Current State Space Modelling Approach In Multistage Machining Processes Due To Operation Variations

    Science.gov (United States)

    Abellán-Nebot, J. V.; Liu, J.; Romero, F.

    2009-11-01

    The State Space modelling approach has been recently proposed as an engineering-driven technique for part quality prediction in Multistage Machining Processes (MMP). Current State Space models incorporate fixture and datum variations in the multi-stage variation propagation, without explicitly considering common operation variations such as machine-tool thermal distortions, cutting-tool wear, cutting-tool deflections, etc. This paper shows the limitations of the current State Space model through an experimental case study where the effect of the spindle thermal expansion, cutting-tool flank wear and locator errors are introduced. The paper also discusses the extension of the current State Space model to include operation variations and its potential benefits.