Short-circuit Connection Research Articles

An Energy-Efficient Start-Up Strategy for Large Variable Speed Hydro Pump Turbine Equipped with Doubly Fed Asynchronous Machine

The use of a Doubly Fed Asynchronous Machine (DFAM) provides attractive characteristics and offers operational flexibility in many variable speed generation applications, such as in a hydroelectric pumped storage plant. In a variable speed hydroelectric pumped storage plant, the start-up process of DFAM is identical to the conventional singly fed asynchronous machine, wherein a significant amount of energy is wasted. This paper introduces an energy-efficient start-up strategy in DFAM based hydroelectric pump-turbine. The back-to-back voltage source converter connected to the rotor side is amenable for speed control (real power), braking (regenerative/dynamic), and starting the unit. Further, in this starting technique, the stator circuit of the machine is injected with a low voltage DC supply at starting instead of short-circuiting the windings. This DC injection reduces the slip losses and cuts down the magnetizing current requirement. The magnitude of the required DC supply is estimated based on the machine’s reactive power requirement. Also, the switching of stator winding between the short circuit connection, DC injection, and grid supply is carried out using a changeover switch and determined by the speed of the rotor. The proposed starting strategy is investigated with 250 MW DFAM in Matlab/Simulink environment and experimented with a 2.2 kW DFAM prototype. Test results show that the proposed starting method can conserve more than 26.1 percent of electrical energy in the example application compared to the conventional V/f start-up strategy.

Enhanced gradient learning for deep neural networks

Deep neural networks have achieved great success in both computer vision and natural language processing tasks. How to improve the gradient flows is crucial in training very deep neural networks. To address this challenge, a gradient enhancement approach is proposed through constructing the short circuit neural connections. The proposed short circuit is a unidirectional neural connection that back propagates the sensitivities rather than gradients in neural networks from the deep layers to the shallow layers. Moreover, the short circuit is further formulated as a gradient truncation operation in its connecting layers, which can be plugged into the backbone models without introducing extra training parameters. Extensive experiments demonstrate that the deep neural networks, with the help of short circuit connection, gain a large margin of improvement over the baselines on both computer vision and natural language processing tasks. The work provides the promising solution to the low-resource scenarios, such as, intelligence transport systems of computer vision, question answering of natural language processing.

Control of electron acceleration process during merging start-up of spherical tokamak

The axial plasma merging method is one of the start-up schemes to form spherical tokamak (ST) plasma without use of a center-solenoid coil. It involves a magnetic reconnection process in the presence of high toroidal magnetic field parallel to the reconnection electric field and has the potential to accelerate electrons directly along the magnetic field lines. In the paper, the role of boundary conditions of the reconnection downstream region was investigated in the UTST experiment. Self-generated axial electric field in the reconnection downstream region was observed to grow up to 20–30 times as large as the toroidal electric field where the MHD condition holds, but was largely suppressed inside the area where the magnetic field lines are contacted to the inboard limiter conductors equipped on the center stack. This suppression effect was attributed to the short circuit connection of the magnetic field lines to hinder the axial charge separation and then a significant part of the parallel electric field remained. These experimental results suggest that the merging start-up method has the capability to enhance electron acceleration efficiency by magnetic reconnection and may have the potential to produce high electron temperature ST plasma applicable for additional heating and current drive techniques.

Spinal cord vascular diseases

Spinal vascular malformations include various entities, including spinal dural arteriovenous (AV) fistulas, acquired malformations and cavernous hemangiomas, and spinal arteriovenous malformations. AV fistula refers to aspinal cord vascular malformation in which there is a short-circuit connection between adural artery and aperimedullary vein superficial to the myelon. The condition is relatively rare, initial clinical symptoms are often misinterpreted, and adefinitive diagnosis is often delayed by 12months or more. However, early diagnosis is important to prevent progression of clinical symptoms, which may include paraplegia. Early magnetic resonance imaging (MRI) is helpful, showing intramedullary edema in the T2-weighted sequences and superficial, markedly dilated veins. Treatment consists of ligation of the AV fistula, either surgically or by embolization. Cavernous hemangiomas, consisting of alarge number of closely located immature blood vessels, are also relatively rare and have alow risk of bleeding (approximately 0.2-0.5%). Venous hemorrhage may also occur, resulting in clinical symptoms (including paraplegia).

Case Study of an Electric Vehicle Battery Thermal Runaway and Online Internal Short-Circuit Detection

A thermal runaway happened in a battery cell of an electric vehicle during driving, and the fire spreads to other batteries in a few minutes. Based on the recorded battery operation data, this letter analyzes the battery thermal runaway process, and identifies the critical time points of fault signals like cell voltages and temperatures, etc., which depict the start and spread of thermal runaway in the battery pack. By tracing back the clues, it is concluded that the cause of the fire is battery internal short circuit (ISC), and battery overcharge is a potential cause of ISC. Then, three different patterns of battery cell voltage abnormalities are compared, including battery external short circuit, ISC, and poor-signal wire connection. A cell voltage difference-based method is proposed to diagnose ISC online, which is simple and reliable to implement in engineering.

A Novel Multi-Branch Channel Expansion Network for Garbage Image Classification

Due to the lack of data available for training, deep learning hardly performed well in the field of garbage image classification. We choose the TrashNet data set which is widely used in the field of garbage image classification, and try to overcome data deficiencies in this field by optimizing the network structure. In this article, it is found that the deeper network and short-circuit connection, which are generally accepted in the field of deep learning, will not work well on the TrashNet data set. By analyzing and modifying the network structure, we propose an effective method to improve the network performance on TrashNet data set. This method widens the network by expanding branches, and then uses add layers to realize the fusion of feature information. It can make full use of feature information at slight additional computational cost. Using this method to replace the core structure of the Xception network, the performance of the improved network has been improved greatly. Finally, the M-b Xception network proposed by us achieves 94.34% classification accuracy on the TrashNet data set, and has certain advantages over some state-of-the-art methods on multiple indicators. The python code can be download from https://github.com/scp19801980/Trash-classify-M_b-Xception.

Electrical characterization, crosstalk compensation and experimental examination of AlN-based piezoelectric micro resonators

Aluminum nitride based micro resonators are fabricated and measured with an all-electrical excitation and detection method in this paper. Low resistivity single crystal silicon is used as resonating element, serving simultaneously as bottom electrode for the piezoelectric layer. The elimination of the bottom metal electrodes reduces the number of stacked layers and stress in the cantilever; however, the short circuit connection between drive and sense port silicon grounds induces serious feedthrough capacitance effect. Electrical measurement results indicate that, the resonator output is a superposition of mechanical resonance behavior and electrical crosstalk from feedthrough capacitance. A general equivalent circuit model is derived to analyze the resonator’s electromechanical performance. To eliminate the electrical crosstalk, a compensation solution has been developed, by applying an inverted adjustable voltage to the common bottom electrode. Further experimental investigations of the device under different controlled pressures show that, the output amplitude after compensation is precisely symmetric around the resonance peak, and phase shift of -90° occurs at resonance, indicating that the feedthrough has been adequently cancelled out.

Reservoir Water-Level Drawdowns Accelerate and Amplify Methane Emission.

Water-level fluctuations due to reservoir management could substantially affect the timing and magnitude of reservoir methane (CH4) fluxes to the atmosphere. However, effects of such fluctuations on CH4 emissions have received limited attention. Here we examine CH4 emission dynamics in six Pacific Northwest U.S. reservoirs of varying trophic status, morphometry, and management regimes. In these systems, we show that water-level drawdowns can, at least temporarily, greatly increase per-area reservoir CH4 fluxes to the atmosphere, and can account for more than 90% of annual reservoir CH4 flux in a period of just a few weeks. Reservoirs with higher epilimnetic [chlorophyll a] experienced larger increases in CH4 emission in response to drawdown (R2 = 0.84, p < 0.01), suggesting that eutrophication magnifies the effect of drawdown on CH4 emission. We show that drawdowns as small as 0.5 m can stimulate ebullition events. Given that drawdown events of this magnitude are quite common in reservoirs, our results suggest that this process must be considered in sampling strategies designed to characterize total CH4 fluxes from reservoirs. The extent to which (and the mechanisms by which) drawdowns short-circuit connections between methanogenesis and methanotrophy, thereby increasing net CH4 fluxes to the atmosphere, should be a focus of future work.

Interventional treatment of arterio-venous malformations

BackgroundDue to their hemodynamic effects and tendency to progress, the majority of congenital arterio-venous malformations (AVM) require treatment. AVM are classified according to clinical severity (Schobinger classification, stages I–V) and angiographic appearance (types I–IV).TreatmentEndovascular embolization is the treatment of choice. However, because complications such as necrosis and neuropathy occur in up to 15% of cases, treatment is challenging and is dependent on the angiographic appearance. Critical for treatment success is elimination of the so-called nidus, which is the location of the short circuit connection between the artery and the often extended aneurysm-like drainage vein. Embolization of only the feeding artery without the actual nidus or the incomplete elimination of drainage veins should be avoided. Absolute 96 % alcohol in addition to coiling of the nidus has been established as the most effective technique.ConclusionUnlike other embolic agents, alcohol leads to a definitive destruction of the vessel wall. Recanalization and recurrence are excluded due to adequate elimination of the nidus.

Atomic Force Microscopy Detection of Electronic Short-Circuits in Solid Polymer Electrolytes Fuel Cell Membranes after Accelerated Degradation

In this work we investigated Nafion® 211 polymer electrolyte membranes after 1600 h operation at open circuit voltage. With scanning electron microscopy (SEM) platinum deposition was identified inside the membrane. By investigation of cross sections with Atomic Force Microscopy (AFM) numerous platinum particles and micrometer large two-dimensional sheets of platinum particles were found across the membrane. Conductive AFM was performed to measure the electronic current across the membrane. To avoid additional ionic current contributions the measurements were performed at dry membranes in argon atmosphere with a noncatalytic gold coated AFM tip. At a few sites a steady state electronic current measured through the half cell membranes was detected that had an ohmic current-voltage polarization curve. These electric short-circuit connections, formed by platinum deposition inside the membrane, can be considered as a failure mechanisms for the fuel cell and by enhancement of radical formation may lead to formation of pin-holes.

Robust manifold learning with CycleCut

Many manifold learning algorithms utilise graphs of local neighbourhoods to estimate manifold topology. When neighbourhood connections short-circuit between geodesically distant regions of the manifold, poor results are obtained due to the compromises that the manifold learner must make to satisfy the erroneous criteria. Also, existing manifold learning algorithms have difficulty in unfolding manifolds with toroidal intrinsic variables without introducing significant distortions to local neighbourhoods. An algorithm called CycleCut is presented, which prepares data for manifold learning by removing short-circuit connections and by severing toroidal connections in a manifold.

Discontinuous lymph node metastases ("skipping") in malignant lung tumors

In 50 lung cancers (25 small cell lung cancers, 17 squamous cell carcinomas, 8 adenocarcinomas) pulmonary, mediastinal and cervical lymph node-metastases were analyzed. Lymph-node "skipping" was demonstrated in 46% of the investigated tumors. In seven of these cases the lymph nodes were skipped, which showed complete hyalinization as a consequence of preexisting anthracosilicosis. In 5 other tumors additional lymph nodes with preserved structure were skipped by the metastatic process. Fibrosis of lymphatic tissue after tuberculosis or exposure to ionizing radiation were further reasons for lymph-node skipping. The skipping of intact lymph nodes can be explained by anatomically demonstrable intra- and perinodal short circuit connections. Apart from that, preexisting lymph node changes (silicosis, fibrosis) play an important part.

Determination of scattering parameters of junctions associated with electromagnetic topology

This paper is dedicated to the determination of topological S parameters in the transmission line networks. We are especially interested in ideal junctions which consist of short circuit connections. For this type of junctions, it is impossible to deduce the S parameters from the usual impedance or admittance matrices which are not defined in this case. We suggest a method allowing a direct calculation of S. This procedure is described and then carried out for a two wire fork. At last, an experimental application is given for this model.

Soil electromagnetic parameters as functions of frequency, soil density, and soil moisture

Measurements are made to determine the conductivity and dielectric constants of a gray clay loam and a reddish-brown clay loam. The measurements are made as a function of soil density (from 1.2 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 1.8 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), soil moisture (from 0 percent to 20 percent of the dry soil weight), and excitation frequency (from 30 MHz to 4 GHz), using standard transmission line techniques. A correction term is presented to allow the effective open-circuit and short-circuit connections to be placed at any convenient location with respect to the soil-air interface.

Transitional Delay Fault Test Generation Using AGenetic Algorithm

With the continuous technological advancements in digital electronic circuit technology devices are becoming even more complex, it is essential that a high level of operational reliability is maintained which is why there is always a requirement for new and improved test methodologies. A fault condition in a digital circuit may be the result of a manufacturing problem causing physical imperfection in the device, this imperfection may be open circuit or short circuit connections, or a flaw that changes other characteristics of the device. The propagation of a gate may be affected introducing a delay defect into the circuit, often creating timing problems, which have always proved difficult to detect. This paper presents a new approach to the generation of test patterns that detect gross delay defects in combinational VLSI circuits. In O'Dare and Arslan [1] the authors presented a technique that implemented a genetic algorithm (GA) for the generation of test patterns to detect single stuck-at-faults in combinational VLSI circuits. In order to generate a test for delay faults it is necessary to create a transition in logical state at the fault site within the circuit, the only way to achieve this is by generating pairs of test patterns . The first test pattern initialises the state of all nodes within the circuit, the second test pattern is then used to force the required transition at the designated test node. The problem of test generation for delay faults is considerably more complex than that of test pattern generation for single stuck-at-faults presented in O'Dare and Arslan [1], with an increase in search space size from 2 n to 2 2n for an n input circuit. The problem is further augmented by the necessity of applying the two test patterns in a strict ordered sequence to create the required transition. The authors have therefore developed a new genetic test technique to overcome the problem, using chromosomes-pairs to represent the test patterns. The GAs primary component is a dynamically evolving Global Record Table (GRT), which is used to guide the search towards optimal test pairs in an otherwise complex solution space, producing a compact and efficient set of test pattern-pairs as the GA evolves. The experimental results presented in this paper are compared with other research results for well known combinational benchmark circuits.

Dispositif analogique automatique pour la determination du potentiel dans les elements a effet hall

The analogue study of an element with Hall effect in which the induction field is normal to the current lines has been carried out using a network of identical resistances, thus permitting the use of the Laplace equation ΔV=0. The current input contacts in the element are represented by short-circuit connections between certain nodes and the limiting conditions corresponding to the geometrical shape of the element are implemented by means of transistorized operational amplifiers. The value of the Hall angle is shown by means of graduated precision potentiometers. Thus the required conditions are met without the use of complementary adjustment or iteration. An automatic measuring device ensures the readings of potentials at the nodes of the network. The system whose stability has been theoretically and practically proved has been applied to determine the potential in a parallelepiped-shaped sample; its use can be extended to areas of any other shape.