High Current Levels Research Articles

Evolution of porous structure with dealloying corrosion on Gasar Cu–Mn alloy

The evolution of nanoporous structure with dealloying condition was investigated, thus, the mechanism of porous structure evolution was uncovered. The Gasar Cu–Mn alloy was dealloyed by room and elevated temperature chemical corrosion, low and high current level electrochemical corrosion, four types of porous structures, including uneven corrosion pits, hybrid porous, haystack type and bicontinuous model were prepared by chemically and electrochemically dealloying the porous Cu–34.6%Mn alloy made by the Gasar process. Then, the surface diffusion coefficient (DS) and the diffusion frequency (kD) of Cu atom, as well as the dissolution frequency (kE) of Mn atom were calculated with dealloying condition. The dealloyed morphologies for room temperature chemical corrosion and low current level electrochemical corrosion were similar due to the same DS. While the dealloyed structures changed from bulk hybrid porous structure to bicontinuous porous film with decreasing kD/kE.

Integrated Starter–Alternator With Sensorless Ringed-Pole PM Synchronous Motor Drive

The so-called integrated starter–alternator (ISA) is a high-efficiency electrical machine that is connected to an internal combustion engine obtaining mild hybrid electric vehicles. The ISA has a twofold task: starting up the engine and generating electrical energy to be stored into a battery. This paper is focused on the first task. Two different motors are investigated: an external rotor surface permanent magnet (SPM) machine and an interior permanent magnet (IPM) machine. For drive control, both motors require knowledge of their rotor position; then, a sensorless technique based on the high-frequency (HF) voltage injection for rotor position detection has been implemented. In order to create an HF anisotropy in the SPM rotor configuration, a ringed-pole solution has been adopted. Experimental tests have highlighted that the first machine has a clear capability of starting up the engine with good speed and position estimation in spite of the particular nonconstant load torque. As regard the IPM machine, the sensorless engine startup appears not possible because the anisotropy disappears at a high current level due to saturation effects.

Performance of the LHCb calorimeters during the period 2010-2012

The calorimeter system of LHCb is subdivided into four sub-detectors which provide its longitudinal segmentation: a Scintillator Pad Detector, followed by a Preshower and, then, an electromagnetic, an hadronic calorimeter. After a description of these detectors, procedures developed to calibrate their response are discussed together with the degradation of response observed due to the harsh conditions (high radiation and current levels). First results on the calorimeter performance over the two most productive years of physics data taking, 2011 and 2012 are given.

Enhanced emission from mid-infrared AlInSb light-emitting diodes with p-type contact grid geometry

We report on the impact of lateral current spreading on light emission from aluminium indium antimonide (AlInSb) mid-infrared p-i-n light-emitting diodes (LEDs) grown by molecular beam epitaxy on a GaAs substrate. Due to the high effective mass of holes in AlxIn1−xSb, the resistivity of p-type material determines the 3-D distribution of current flow in the devices. This work shows that maximum light emission, as measured by electroluminescence, and 3-times wall-plug efficiency improvement were obtained at room temperature from devices with a p-type contact grid geometry with a spacing of twice the current spreading length in the p-type material, which was measured by spatially resolved photocurrent. The LED with the optimal contact geometry exhibits improved performance at high injection current levels thanks to the more uniform carrier distribution across the device area.

Modeling and optimization of Electrical Discharge Machining (EDM) using statistical design

Modeling and optimization of nontraditional machining is still an ongoing area of research. The objective of this work is to optimize Electrical Discharge Machining process parameters of Aluminum-multiwall carbon Nanotube composites (AL-CNT) model. Material Removal Rate (MRR), Wear Electrode Ratio (EWR) and Average Surface Roughness ( Ra ) are primary objectives. The Machining parameters are machining-on time (sec), discharge current (A), voltage (V), total depth of cut (mm), and %wt. CNT added. Mathematical models for all responses as function of significant process parameters are developed using Response Surface Methodology (RSM). Experimental results show optimum levels for material removal rate are %wt. CNT (0%), high level of discharge current (6A) and low level of voltage (50 V) while optimum levels for Electrode wear ratio are %wt. CNT (5%), high level of discharge current (6A) and optimum levels for average surface roughness are %wt. CNT (0%), low level of discharge current (2A) and high level of depth of cut (1 mm). Single-objective optimization is formulated and solved via Genetic Algorithm. Multi-objective optimization model is then formulated for the three responses of interest. This methodology gathers experimental results, builds mathematical models in the domain of interest and optimizes the process models. As such, process analysis, modeling, design and optimization are achieved.

Sensitivity to microstimulation of somatosensory cortex distributed over multiple electrodes.

Meaningful and repeatable tactile sensations can be evoked by electrically stimulating primary somatosensory cortex. Intracortical microstimulation (ICMS) may thus be a viable approach to restore the sense of touch in individuals who have lost it, for example tetraplegic patients. One of the potential limitations of this approach, however, is that high levels of current can damage the neuronal tissue if the resulting current densities are too high. The limited range of safe ICMS amplitudes thus limits the dynamic range of ICMS-evoked sensations. One way to get around this limitation would be to distribute the ICMS over multiple electrodes in the hopes of intensifying the resulting percept without increasing the current density experienced by the neuronal tissue. Here, we test whether stimulating through multiple electrodes is a viable solution to increase the dynamic range of ICMS-elicited sensations without increasing the peak current density. To this end, we compare the ability of non-human primates to detect ICMS delivered through one vs. multiple electrodes. We also compare their ability to discriminate pulse trains differing in amplitude when these are delivered through one or more electrodes. We find that increasing the number of electrodes through which ICMS is delivered only has a marginal effect on detectability or discriminability despite the fact that 2–4 times more current is delivered overall. Furthermore, the impact of multielectrode stimulation (or lack thereof) is found whether pulses are delivered synchronously or asynchronously, whether the leading phase of the pulses is cathodic or anodic, and regardless of the spatial configuration of the electrode groups.

Stable and efficient colour enrichment powders of nonpolar nanocrystals in LiCl.

In this work, we propose and develop the inorganic salt encapsulation of semiconductor nanocrystal (NC) dispersion in a nonpolar phase to make a highly stable and highly efficient colour converting powder for colour enrichment in light-emitting diode backlighting. Here the wrapping of the as-synthesized green-emitting CdSe/CdZnSeS/ZnS nanocrystals into a salt matrix without ligand exchange is uniquely enabled by using a LiCl ionic host dissolved in tetrahydrofuran (THF), which simultaneously disperses these nonpolar nanocrystals. We studied the emission stability of the solid films prepared using NCs with and without LiCl encapsulation on blue LEDs driven at high current levels. The encapsulated NC powder in epoxy preserved 95.5% of the initial emission intensity and stabilized at this level while the emission intensity of NCs without salt encapsulation continuously decreased to 34.7% of its initial value after 96 h of operation. In addition, we investigated the effect of ionic salt encapsulation on the quantum efficiency of nonpolar NCs and found the quantum efficiency of the NCs-in-LiCl to be 75.1% while that of the NCs in dispersion was 73.0% and that in a film without LiCl encapsulation was 67.9%. We believe that such ionic salt encapsulated powders of nonpolar NCs presented here will find ubiquitous use for colour enrichment in display backlighting.

基于混合型量子阱的GaN基垂直结构发光二极管性能

In order to solve the problem that Ga N-based vertical structure LEDs( VS-LEDs) suffer from efficiency droop under high current injection level,hybrid quantum wells( HQWs) with coupled quantum wells( CQWs) and normal quantum wells( NQWs) were employed. Compared to VSLEDs with NQWs,VS-LEDs with HQWs had better properties,wherein forward voltage reduced by0. 68 V and light-output power increased by 53. 0% at a forward current of 350 m A. Meanwhile,the relative external quantum efficiencies of VS-LEDs with NQWs and VS-LEDs with HQWs reduced to37. 7% and 67. 5% of their maximum,respectively. The results reveal that the efficiency droop of LEDs can become less severe by exploiting HQWs.

Parallel Connection of 1200 V/100 A SiC MOSFET Half-bridge Modules

Silicon (Si) insulated-gate bipolar transistors (IGBTs) are widely used in power converters. Silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speed. The first SiC-metal-oxide-semiconductor field-effect transistor (MOSFET) half-bridge modules (SiC HBM) are now commercially available and look promising. Although they are still limited in breakdown voltage, these components should, for instance, improve traction-chain efficiencies. In particular, a significant reduction in switching losses is to be expected which should lead to improvements in power-to-weight ratios-of particular interest for rolling-stock. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these modules is critical. In this paper, the authors investigate the parallel connection of SiC HBM with a focus on traction equipment. The key points are underlined and an original approach is proposed to design the bus-bar and the gate-drive circuit. Experimental results performed on an opposition method test bench, valid the correct operation of three SiC modules in parallel.

IC 보호회로를 갖는 저면적 Dual mode DC-DC Buck Converter

본 논문에서는 DT-CMOS(Dynamic Threshold voltage Complementary MOSFET) 스위칭 소자를 사용한 DC-DC Buck 컨버터를 제안하였다. 높은 효율을 얻기 위하여 PWM 제어방식을 사용하였으며, 낮은 온 저항을 갖는 DT-CMOS 스위치 소자를 설계하여 도통 손실을 감소시켰다. 제안한 Buck 컨버터는 밴드갭 기준 전압 회로, 삼각파 발생기, 오차 증폭기, 비교기, 보상 회로, PWM 제어 블록으로 구성되어 있다. 삼각파 발생기는 전원전압(3.3V)부터 접지까지 출력 진폭의 범위를 갖는 1.2MHz의 주파수를 생성하며, 비교기는 2단 증폭기로 설계되었다. 그리고 오차 증폭기는 70dB의 이득과 <TEX>$64^{\circ}$</TEX>의 위상여유를 갖도록 설계하였다. 또한 제안한 Buck 컨버터는 current-mode PWM 제어회로와 낮은 온 저항을 갖는 스위치를 사용하여 100mA의 출력 전류에서 최대 95%의 효율을 구현하였으며, 1mA 이하의 대기모드에도 높은 효율을 구현하기 위하여 LDO 레귤레이터를 설계하였으며, 또한 2개의 IC 보호 회로를 내장하여 신뢰성을 확보하였다. In this paper, high efficiency power management IC(PMIC) with DT-CMOS(Dynamic threshold voltage Complementary MOSFET) switching device is presented. PMIC is controlled PWM control method in order to have high power efficiency at high current level. The DT-CMOS switch with low on-resistance is designed to decrease conduction loss. The control parts in Buck converter, that is, PWM control circuit consist of a saw-tooth generator, a band-gap reference(BGR) circuit, an error amplifier, comparator circuit, compensation circuit, and control block. The saw-tooth generator is made to have 1.2MHz oscillation frequency and full range of output swing from supply voltage(3.3V) to ground. The comparator is designed with two stage OP amplifier. And the error amplifier has 70dB DC gain and <TEX>$64^{\circ}$</TEX> phase margin. DC-DC converter, based on current mode PWM control circuits and low on-resistance switching device, achieved the high efficiency nearly 96% at 100mA output current. And Buck converter is designed along LDO in standby mode which fewer than 1mA for high efficiency. Also, this paper proposes two protection circuit in order to ensure the reliability.

In Situ Observation of Degradation by Ligand Substitution in Small-Molecule Phosphorescent Organic Light-Emitting Diodes

Solutions of facial-tris(1-phenylpyrazole)Ir(III) (fac-Ir(ppz)3), when dissolved in either tert-butyl isocyanide or in solid films of 2-naphthylisocyanide, undergo replacement of a ppz ligand by the isocyanide molecules after irradiation with UV light as demonstrated by liquid chromatograph mass spectrometer analysis. Similarly, solutions of Ir(ppz)3 and bathophenanthroline (BPhen) in CH2Cl2 or acetone-d6 form a brightly emissive species, [Ir(ppz)2(Bphen)]+ when irradiated with UV light as established by optical, mass, and 1H nuclear magnetic resonance spectroscopy. Electroluminescent data from blocked organic light-emitting diode (OLED) devices demonstrate that both mer- and fac-(Ir(ppz)3) dissociate a ligand and coordinate a neighboring BPhen molecule when the device is operated at moderate to high current levels. These experiments offer direct evidence of the dissociation of a metal–ligand bond and subsequent ligand substitution as a degradation pathway in active OLED devices during operation and provi...

What's the Best Course? Evidence From Alumni on the Value of Business Presentations Preparation

Developing effective presentation skills is a core competence skill for business communicators. Self-report data from a survey of 1,610 2- to 12-year business alumni show that 37.1% present monthly and 27.9% present weekly in their current positions. Alumni who completed a general public speaking course, or both managerial communication and a public speaking course, reported higher current levels of confidence across 12 aspects of business presentations than alumni who took only a managerial communication course or who relied on embedded presentation assignments in disciplinary courses. Gains were reported for content skills since graduation, with less confidence handling nervousness and delivery.

Carrier-transport mechanism of Er-silicide Schottky contacts to strained-silicon-on-insulator and silicon-on-insulator.

The current-voltage characteristics and the carrier-transport mechanism of the Er-silicide (ErSi1.7) Schottky contacts to strained-silicon-on-insulator (sSOI) and silicon-on-insulator (SOI) were investigated. Barrier heights of 0.74 eV and 0.82 eV were obtained for the sSOI and SOI structures, respectively. The barrier height of the sSOI structure was observed to be lower than that of the SoI structure despite the formation of a Schottky contact using the same metal silicide. The sSOI structure exhibited better rectification and higher current level than the SOI structure, which could be associated with a reduction in the band gap of Si caused by strain. The generation-recombination mechanism was found to be dominant in the forward bias for both structures. Carrier generation along with the Poole-Frenkel mechanism dominated the reverse-biased current in the SOI structure. The saturation tendency of the reverse leakage current in the sSOI structure could be attributed to strain-induced defects at the interface in non-lattice-matched structures.

Overcurrent Protection Coordination in a Power Distribution Network With the Active Superconductive Fault Current Limiter

The active saturated iron-core superconducting fault current limiter (SISFCL) is one of the best solutions to coping with high fault current levels and may be helpful in building future smart distribution networks. The application of an SISFCL in a distribution system can reduce the fault current to an acceptable level when a short-circuit fault occurs at different positions. The operational principle and the current-limiting characteristic of an active SISFCL are briefly introduced in this paper. The influence of an active SISFCL on the conventional inverse and definite time-delay overcurrent protective relays is discussed. In order to maintain reliable operation of the distribution system with an SISFCL, the protection coordination and setting solution is proposed. A model of a real 35-kV distribution system with an active SISFCL was built and simulated with the Electro-Magnetic Transients Program including DC software. Simulation tests have demonstrated the correctness and validity of theoretical analyses.

세라믹 멤브레인 활용 직접 에탄올 연료전지

>> Direct ethanol fuel cell has been fabricated with ceramic membrane. A porous silicon carbide (SiC) membrane having approximately 30% porosity has been applied for a direct ethanol proton exchange membrane (DE-PEM) fuel cell. A horizontal type cell having Pt (18mg/cm) catalyst layer on both side of the ceramic membrane was used for the demonstration test. The ethanol oxidation based-fuel cell stack showed very high voltage (1.289V) and measurable current level (68mA) even though at room temperature.

The Mtr Pathway of Shewanella oneidensis MR‐1 Couples Substrate Utilization to Current Production in Escherichia coli

AbstractIntroducing an electronic interface into Escherichia coli will allow its enormous synthetic biology toolkit to be leveraged in bioelectrochemical applications. While E. coli expressing the Mtr pathway of Shewanella oneidensis MR‐1 transfer electrons to an anode, it has remained unclear if this current production alters the intracellular state of E. coli, which is a critical requirement for bioelectronic technologies. Here we address this by characterizing current production in Mtr‐expressing E. coli and its effects on cellular viability, substrate consumption, and product generation. We found that cymA‐mtr E. coli sustained ∼8‐fold higher current levels than a control strain. This increased current production did not change E. coli viability or substrate consumption, but it did alter metabolic fluxes. A shift to more oxidized products strongly suggests that the Mtr pathway improves redox balance in E. coli. By demonstrating the Mtr module couples current production to intracellular state, this work establishes Mtr‐expressing E. coli as a platform for accelerated development of bioelectronic technologies.

Generation of chip based microelectrochemical cell arrays for long-term and high-resolution recording of ionic currents through ion channel proteins

High throughput and a long life-time of the devices are two crucial challenges in planar chip technology for electrophysiological measurements of ionic current recording through ion channel proteins. In this paper, we present a wafer-scale process for the generation of novel arrays of microelectrochemical cells for long-term and high-resolution current recording. At the bottom of each of the cells, which have typically diameters of around 60μm and volumes of around 30pL, a nanocrystalline silver/silver chloride secondary electrode is generated for ionic current recording. The top of the cell is closed by a lid containing a small (6–16μm) opening which connects liquid in the chamber to a contacting liquid on the outside. The processes necessary for manufacturing such a chip through photolithography and wafer-scale bonding have been developed, the resulting structures were characterized and the procedures were optimized. Combining a large surface area of the electrode with a – in relation to the cell size – relatively large amount of silver/silver chloride allows for the recording of DC ionic currents for prolonged periods of time. First measurements were performed where the electrochemical cells were closed by model membranes containing single ion channel proteins. The currents generated by ions passing through these ion channels are reported. These measurements demonstrate the usefulness of the microelectrochemical cell array for long time ionic current recordings at – for these type of measurements – relatively high current levels.

Safe Operating Area and Long-Term Reliability of 9-kV Silicon Carbide PNPN Super Gate Turn-Off Thyristors

One of the major requirements for adoption of new silicon carbide (SiC) super gate turn-off thyristors (SGTOs) into high-energy applications is to verify the safe operating area and long-term reliability capabilities of these devices. In this letter, we have developed a unique high-energy testing system that can evaluate the performance limitations with respect to lifetime capabilities of the 9 kV, 1 cm 2 , SGTOs at ultrahigh pulsed current levels from 1 to 3.5 kA. The test system produces square current pulses with a user specified current amplitude and a 100-μs pulsewidth at a maximum repetition rate of 1 shot/s (>0.1% duty cycle). A lifetime safe operating area with respect to maximum pulsed current was then established that these 1 cm 2 , 9 kV, SiC SGTOs can perform reliably without significant degradation at pulsed current levels up to 2.0 kA. At current levels above 2.0 kA shifts in the on-state voltage are observed probably due to device over-heating at such high current levels and having not enough time to fully dissipate the heat between any two shots, which results in the device rapidly deteriorating due to increased on-state losses ultimately leading to premature failure.

Shedding light on the appropriateness of the (high) gasoline tax level in Germany

Germany imposes an energy tax of 0.65€/l on gasoline which is one of the highest tax rates across countries. The effective tax is even higher when accounting for the consumption tax levied on top of the energy tax. Answers to the question whether such a high tax level is justified on efficiency grounds would add precious arguments to policy discussion debating the appropriate level of a car driver׳s tax burden. This paper sheds light on that issue by calculating the optimal gasoline tax in Germany using an optimal tax approach that accounts for gasoline/diesel car substitution and interactions of the gasoline tax with the broader fiscal system. According to the baseline calculation the optimal gasoline tax is 0.96€/l, thus, exceeding the (already high) current tax level by 48%. The corrective tax component exclusively reflecting the externalities associated with car driving contributes 0.64€/l to that optimal level while the positive net effect of the interaction of the gasoline tax with the other distortive taxes in the economy adds another 0.32€/l. Sensitivity analyses reveal that the optimal tax is very unlikely to fall below its current level. Even quite the contrary, the optimal tax rises dramatically (to approximately two times the current rate) when account is taken of the medium/long term EU fuel economy regulation legislation aiming at tightening CO2 emission standards of passenger vehicles. All in all, the present analyses suggest that there is no reasoning on efficiency grounds for adjusting the current gasoline tax downwards given the present practice of mainly levying fuel taxes rather than charging individual car drivers on a distance related basis.

Off-state breakdown and leakage current transport analysis of AlGaN/GaN high electron mobility transistors

Off-state breakdown characteristics of AlGaN/GaN high-electron-mobility transistors have been studied based on drain current injection method. It is found that at low drain current injection level, the observed premature breakdown is caused by excess gate-to-drain leakage current. Nevertheless, at high drain injection current level, buffer-leakage-dominated breakdown proceeds gate-leakage-dominated breakdown as the gate bias increases from pinch-off voltage to deep-depletion voltage. In both breakdown regions, the breakdown voltages show negative temperature coefficients. The buffer-leakage-induced breakdown should be defect-related, which is confirmed by temperature-dependent buffer leakage measurements.