Direct Currents Research Articles

On stable quantum currents

We study the transport properties of discrete quantum dynamical systems on the lattice, in particular, coined quantum walks and the Chalker–Coddington model. We prove the existence of a non-trivial charge transport implying that the absolutely continuous spectrum covers the whole unit circle under mild assumptions. We discuss anomalous quantum charge transport. For quantum walks, we exhibit the explicit constructions of coins that imply the existence of stable directed quantum currents along classical curves. The results are of topological nature and independent of the details of the model.

Electric Currents through J-shaped and Non-J-shaped Flare Ribbons

Abstract Increasing attention has recently been paid to solar flares exhibiting double-J-shaped ribbons in the lower solar atmosphere, in the context of extending the two-dimensional standard flare model to three dimensions, as motivated by the spatial correlation between photospheric current channels and flare ribbons. Here, we study the electric currents through the photospheric area swept by flare ribbons (termed the synthesized ribbon area (SRA)), with a sample of 71 two-ribbon flares, of which 36 are J-shaped. Electric currents flowing through one ribbon are highly correlated with those flowing through the other, and they therefore belong to the same current system. The nonneutrality factor of this current system is independent of the flare magnitude, implying that both direct and return currents participate in flares. J-shaped flares are distinct from non-J-shaped flares in the following ways: (1) electric-current densities within the J-shaped SRA are significantly smaller than those within the non-J-shaped SRA, but the J-shaped SRA and its associated magnetic flux is also significantly larger. (2) Electric currents through the SRA are positively correlated with the flare magnitude, but J-shaped flares show a stronger correlation than non-J-shaped flares. (3) The majority (75%) of J-shaped flares are eruptive, while the majority (86%) of non-J-shaped flares are confined; accordingly, hosting active regions of J-shaped flares are more likely to be sigmoidal than non-J-shaped flares. Thus, J-shaped flares constitute a distinct subset of two-ribbon flares, probably representative of eruptive ones. Further, we found that combining the SRA and its associated magnetic flux has the potential to differentiate eruptive from confined flares.

OBSTETRIC GYNECOLOGICAL SOCIETY IN BERLIN
 Meeting December 11, 1891

Brse demonstrated a new vaginal electrode that he made for such electrical applications where one wishes to take advantage of the pole-to-pole current. The electrode consists of a clay cylinder with a circumference of 9 cm, which is inserted into the vagina in exactly the same way as a tubular mirror. In this clay cylinder is placed a metal cylinder, equipped with numerous holes, which has a screw at its outer end to strengthen the conductor. After the introduction of the clay cylinder, a metal cylinder is inserted into the vagina, and the clay tube is filled with warm water. The wet clay cylinder is an excellent conductor of current and replaces the skin electrode made from a sponge. If this cylinder is inserted into the vagina for a length of 8-10 cm, then with a circumference of 9 cm, it will correspond to a flat electrode of 72-90 sq. Cm. This electrode is intended for use where one wants to concentrate the current density in more than one place of the vagina. but evenly distribute the current over the pelvic organs. It is used more where, when using strong galvanic currents, they want to avoid the cauterizing effect on the vaginal mucosa, which easily occurs when spherical electrodes are used, despite being wrapped in cotton wool. Finally, it is used where one wants to obtain an interpolar (so-called catalytic) effect. The patient, when using this electrode, tolerates perfectly well currents of 80-100 MA, while cauterization of the vaginal mucosa is not obtained.

Variations of galvanic currents and corrosion forms of 2024/Q235/304 tri-metallic couple with multivariable cathode/anode area ratios: Experiments and modeling

Tri-metallic galvanic corrosion is inevitable in practical applications, but relevant investigations are far from sufficient. In this study, a mathematical model based on the Butler-Volmer equation and a finite element model (FEM) of tri-metallic galvanic corrosion were built and validated, which can reasonably predict galvanic corrosion of tri-metallic couples. Simulation and experimental results indicate that galvanic current density and galvanic potential of the tri-metallic couple of 2024 aluminum alloy/Q235 carbon steel/304 stainless steel change with the cathode/anode area ratios in a power function relationship and logarithmic relationship, respectively in 3.5 wt% NaCl. Besides, galvanic corrosion not only accelerates the dissolution of 2024 Al alloy but also transforms its corrosion form. The uncoupled 2024 Al alloy presents pitting corrosion, but the coupled 2024 Al alloy shows typical intergranular corrosion (IGC) morphology.

Through-mask electrochemical micromachining of micro pillar arrays on aluminum

Surface textures, such as micro pillar arrays, greatly promote the developments of many advanced fields. As many methods have been applied to fabricate the micro pillar arrays on silicon and polymer substrates, it is a still challenge to fabricate micro pillar arrays on metals. In this paper, through-mask electrochemical micromachining (TMEMM) was employed to fabricate micro pillar arrays on aluminum (Al) substrate. The effects of the direct and pulsed currents on surface morphology of the micro pillar arrays were investigated, and the ordered micro pillar arrays with different top diameters were obtained at the pulsed currents. Then, the influences of the current densities on the morphology of the micro pillar arrays were studied, and the largest etching anisotropy factor (EF) was obtained at a current density of 1 A/cm2. Finally, the wettability of the as-prepared micro pillar arrays with low surface energy modification was investigated. When the top diameters were 50– 90 μm and the heights were larger than 35 μm, all the micro pillar arrays obtained at different current densities showed superhydrophobicity with water contact angle larger than 150°.

Electrochemical methods for on‐site corrosion detection

AbstractThe corrosion mechanism is of electrochemical nature and then, electrochemical techniques are the most adequate to measure the process and quantify it. In present paper are briefly described the most applied on site: corrosion potential, resistivity, galvanic current, and polarization resistance. In general, due to the difficulty to measure quasi‐infinite in size reinforcement, the measurements are made on probes embedded in the cover attached to the bars. From the techniques used, only linear polarization is quantitative. Corrosion potential provides information about the corrosion risk, and resistivity is directly related with the concrete water content. The galvanic current is misleading if real size of anode and cathode are unknown. Although, frequently mistaken, galvanic current is not equal to corrosion rate and reference to areas involved is needed. Two examples are described on the monitoring of these methods.

Application of the Gibbs Magnetodynamic Principle to Calculation of the Distribution of Direct Currents in Solid Bodies

The thermodynamic hypothesis of Gibbs allowing to solve a problem by means of the magnetic principle of virtual works is applied to finding of equilibrium distribution of superficial and volume stationary currents in a continuous body. The variation of magnetic energy is considered with the additional conditions defining constancy of currents, two of which having a differential appearance are necessary and sufficient for the solution of a task in case of a one-coherent body. If the considered body two-coherent (torus, a thick ring) appears one more condition is necessary. In work it is shown what this condition which is also providing uniqueness of the decision can be or constancy of the current proceeding through cross section a torus, or a task of a constant stream of magnetic induction through an opening a torus. At problem definition the first option as more evident was chosen. The problem is solved with the help of a method of Lagrange multipliers. The main received result is that circumstance that induction of magnetic field and volume current in volume address in zero. Thus, magnetic field together with currents is squeezed out on a surface. Communication of the received results with Meissner --- Ochsenfeld effect and the London’s equation applied in the theory of superconductivity and also a problem of communication of molecular currents and currents of conductivity are discussed

Two-stages electrodeposition for the synthesis of anticorrosive Ni–W-Co coating from a deactivated nickel bath

This study used a deactivated bath from the electroplating industry to compose an electrolyte. Two-stages of direct currents were applied in the electrodeposition process using a full factorial design to evaluate the influences of temperature and electric current density on deposition efficiencies, which achieved a value of nearly 87%. The alloys were predominant nanocrystalline, with a high Ni content in the final composition. Using two currents generated a significant effect on surface morphology, preventing crack according to the micrographs and, consequently, increased corrosion resistance. The electrodeposition at 100 °C with a current density of 55 mA cm−2 followed by 10 mA cm−2, resulted in a coating without cracks, with a high polarization resistance (159.446 kΩ cm2).

Meta-heuristic optimization algorithms based direct current and DC link voltage controllers for three-phase grid connected photovoltaic inverter

This paper deals with improving the effectiveness of the control system for the DC/AC grid connected photovoltaic (PV) inverter. The three-phase DC/AC grid connected PV inverter control system consists of two main control loops: (i) external loop to control the DC link voltage. (ii) An internal control loop for regulating the inverter current by controlling both direct and quadrature currents (Id, Iq) that are provided by the inverter phase-locked loop (PLL). The main component of each control loop is the proportional-integral (PI) controller, whose optimal gains are challenging tasks. The optimal PI controller gains should be selected to achieve multi-objectives such as increasing inverter efficiency, stability and power factor while decreasing the total harmonic distortion (THD) in the inverter output current as well as voltage. For this purpose, various meta-heuristic techniques (MHTs) are suggested with a comprehensive comparative study such as: (i) Whales Optimization Algorithm (WOA), (ii) Grey Wolf Optimization (GWO) algorithm, (iii) Antlions Optimization algorithm (ALO) and (iv) Moth Flame Optimization (MFO) algorithm. The numerical results attained through MatlabTM-Simulink reveal that the WOA technique is more superior than the three others studied MHTs in enhancing the inverter efficiency, stability and power factor with minimum THD.

Dynamic Var Reserve Assessment in Multi-Infeed LCC-HVDC Networks

Recently, multi-infeed line-commutated converter-based high-voltage direct currents (LCC-HVDCs) represent one of the most attractive ways to accommodate large-scale power transfer in main load centers. However, this approach deteriorates the dynamic var reserve (DVR) in the receiving-end power grid, especially in scenarios with heavy loads. If the system does not reserve sufficient dynamic var in advance, a severe voltage dip may occur and further lead to consecutive commutation failures, ultimately resulting in DC blocking and voltage collapse. To address the voltage/var control challenges, a robust DVR assessment method is proposed in this paper. This method is used to determine both the inductive and capacitive DVR and prevent cascading failures. First, continuous dynamic algebraic equations are formulated using a piecewise functional block approximation method for efficient application of second-order trajectory sensitivity analysis (SOTSA). Next, a robust DVR assessment model is formulated, and the corresponding computational strategy is introduced to effectively and accurately solve the large-scale problem. Finally, in numerical simulations, the computational efficiency and accuracy of the proposed method are verified using a simple system and operational data from a real system in the Eastern China Power Grid.

Empirical study on influences of electromagnetic field on Hall Effect sensor for analysing oil lubricant deterioration

This study aims to present the procedure developed for detecting deterioration of oil lubricant under variation of electromagnetic field which was generated by a ferrite-core solenoid coil. The overall diameter of coil was 18.5 mm and the inductance was 22.421 mH from direct current stimulation. The results were then compared to those from frequency stimulation. The optimal efficiency of measurement systems was then assessed by real-time analyzing the metal particle contamination of 3 oil lubricants categorized by grade namely ISO 32, ISO 46 and ISO 68 as well as the viscosity under specific conditions which were flow rate and temperature ranging from 25 °C to 100 °C. The analysis was performed to compare the results from experiments of unused and used (approximately 6 months) oil lubricants. From experiments, the viscosity of oil lubricant was reduced when the temperature exceeded 50 °C. However, the stimulation of coil using 0.9 A direct current could clearly distinguish the difference between the unused and used oil lubricants with metal particle contamination comparing to other values of direct currents applied with 0.42 % of error. Also, the 0.5 kHz of frequency would be the most appropriate value for frequency stimulation with 0.38 % of error.

Electrochemical removal of brilliant green dye from wastewater

Dyes are one of the most widely used materials in many industrial fields as coloring agents such as textile, wood, and food manufacturing. As these dyes end up in a water source, this high rate of dyes use represents one of the severe risks to the environment and health organizations. Most of the dyes are considered as highly toxic compounds and dangerous to the environment and human health as it consists of heavy metals, carcinogenic elements, oxygen – absorbing chemicals, and other toxic compounds that need to be well treated before discharge them back to environment. As a result, federal legislations have directed that all industrials that waste dyes-containing effluents to ensure a full dyes removal before discharging their effluents back to water bodies. Industries have applied many different treatment methods including physical, chemical, and biological methods in order to meet the required legislations. In recent years, many industries started to use electrocoagulation as the main treatment method. This study is focusing on using electrocoagulation (EC) method to remediate artificial colored effluents from coloring agents (brilliant green dye (BG dye) as a model). Electrocoagulation reactor, uses aluminum electrodes, was employed to remove this dye under different initial pH (40-10.0), direct currents (DC) (244-732 mA), and spaces between electrodes (SBE) (4-12 mm). According to the findings obtained, EC was highly efficient in treatment of colored effluents; 95.3% of BG dye was removed at treatment time, SBE, DC and pH of 30 minutes, 4 mm, 488 mA and 7.0, respectively.

Contactless galvano-magnetics transducers of monitoring and control systems in agricultural energy

The paper provides information on the state of the use of direct current energy in the electric power industry of agriculture and water resource, hydraulic engineering, industry and metallurgy, irrigation, and land reclamation. Identified the need for contactless non-destructive testing of large constant currents in high-power electrical installations in irrigation, land reclamation, and hydraulic engineering. The basic requirements for contactless transducers and meters of large direct currents in circuits without breaking them are shown. Identified priority areas in the development of these transducers. The general principles of constructing contactless ferromagnetic transducers of large direct currents also the basic requirements for them and the results of the development of one of the options for the development of effective innovative galvano-magnetic contactless transducers of large direct currents with an expanded range of monitoring and control systems for powerful pumping stations in water supply and land reclamation are presented. To increase the sensitivity of galvanomagnetic contactless transducers of large direct currents, Hall transducers have supplied with short-term rectangular current pulses from a special generator. When measuring the amplitude values of the rectified current, in this case of galvanomagnetic contactless transducers, the supply of pulses of the control current of the Hall transducers with the converted current in the bus synchronization is provided. This is achieved by supplying galvano-magnetic contactless transducers of large direct currents with a magnetically controlled contact located near the bus with the converted current and included in the circuit of the current electrodes of the Hall transducers.A static characteristic of the developed galvano-magnetic contactless transducer of high currents obtained and its main technical characteristics and parameters are given. It is shown that the developed transducer, unlike the known ones, has increased accuracy and sensitivity, a technological design, and low weight and dimensions at low material consumption and cost. It can be widely used in electrical systems in land reclamation and irrigation, in water supply, industry, rail transport, science, technology, and for checking electric meters at the installation site.

Thermoelectric effects induced dendrite branching dynamics in pure substances: An insight from morphological theory.

Insights on the mechanical behavior in materials highly depend upon sufficiently characterizing microstructure details at the relevant length scales. In this study, the side-branching dynamics of dendritic structures formation in pure substances is studied upon the phase-field simulations of crystallization with applied direct currents. The effect of heat diffusion (including thermoelectric effect and undercooling) on the dendritic development is investigated, and the characteristics of the primary arms and side-branches are identified by implementing the image recognition technique. Results indicate that increasing the latent heat release would firstly enhance the side-branching and then cause the side-branches re-melting with large heat extraction form the solid. The side-branching could be tailored by rationally controlling the applied electric filed as well the heat treatment, which could be a potential way to improve the mechanical properties in metallic materials via optimizing the microstructure.

Multidiscription wide-range non-contact converters of control systems

The paper presents data on the features of the non-contact conversion of large direct currents. It substantiates the need for the development of non-contact monitoring tools. The general principles of the construction of geoinformational non-contact ferromagnetic converters of large direct currents and the basic requirements for them are considered. It also presents the results of the development of one of the variants of the proposed universal multi-profile contactless magnetomodulating converters of large direct currents with an extended range. The converters can be widely used in the control and management systems of renewable energy sources, laser systems, as well as in industry, agriculture, and water management. Their difference is an extended controlled range with small dimensions and weight and increased accuracy and sensitivity. The converters have simple and technologically advanced designs with low material consumption and cost. They can contactless control large both direct and alternating currents. The work provides elements of a theory, a static characteristic, and basic technical data and parameters of one of the developed converters. Moreover, the developed converters can be widely used in any geographical point of Uzbekistan, even in mountainous and desert areas in GIS - technology, and, in particular, in digital coatings and database visualization. They can be used in hydraulic engineering, industry, agriculture, and water management, as well as for checking electricity meters at the place of their installation.

HTS CroCo - a Strand for High Direct Current Applications

High temperature superconductors (HTS) are discussed as energy-efficient solutions for applications needing high direct currents beyond 10 kA e.g. for large high-field magnets or bus bar systems in industrial electrolysis plants. A number of high-current cable concepts based on REBCO tapes were developed such as the Roebel cable, co-axially wound tapes and several stacked-tape arrangements, among them the HTS CrossConductor (HTS CroCo), a stacked-tape conductor with high current density developed at KIT. In this manuscript, the experimental test of a high DC demonstrator, termed Supra-DC-Cable, made from twelve HTS CroCo strands is presented. The demonstrator was tested successfully at T = 77 K, reaching the expected critical current of 33 kA at 77 K and even for a constant-current operation at 36 kA for more than 30 minutes limited by the copper connections, not the superconducting cable. Currents and voltages were measured in all twelve strands individually during the parallel operation in the cable. These measured data allow the experimental validation of the modelled current distribution, based on the individual characterization of the twelve strands.

Local electrochemical characteristics of pure iron under a saline droplet I: Effect of droplet size on electrochemical distribution

Despite historically being the focus of much research and measurement development, atmospheric corrosion under saline droplets and its underlying mechanisms continues to require more accurate investigations. Toward this goal, the electrochemical distributions of pure iron under different volumes of 3.5% NaCl droplets at different elapsed times were investigated using newly developed concentric three-electrode array measurements. The results showed that the electrochemical distribution under a droplet was directly affected by the droplet size. Distributions of corrosion potential and galvanic current on the CTEA under a 110 μL droplet were circumferentially symmetric; whereas, the electrochemical distribution under a 25 μL droplet was characterized by a neighboring peak-valley pair, and that of a 340 μL droplet exhibited multiple adjacent peaks and valleys. The asymmetric electrochemical distributions under droplets with volumes of 25 μL and 340 μL can be attributed to the difference between the droplet sizes and the effective influencing distance of the corrosion couple, which is determined by the corrosion potential difference between the anode and cathode, the galvanic current, and the anodic and cathodic polarizabilities. The standard deviations of galvanic current trend indicated a greater tendency towards localized corrosion under the 110 μL droplet after a coupling period of 60 min. The results suggested that a droplet with the proper size and electrochemical distribution symmetry is more likely to initiate and develop local atmospheric corrosion.

TDCS Anodal tDCS increases bilateral corticospinal excitability irrespective of hemispheric dominance

Background: Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that utilizes weak direct currents to induce polarity-dependent modulation of corticospinal excitability. Although tDCS exerts a modulatory effect over the stimulation region, several studies have also demonstrated that distal areas of the brain connected to the region of stimulation may also be affected, as well as the contralateral hemisphere. Objective: We examined the effect of a single session of anodal tDCS on corticospinal excitability and inhibition of both the stimulated and non-stimulated hemisphere and examined the influence of these responses by the brain-derived neurotrophic factor (BDNF) polymorphism. Methods: In a randomized cross-over design, changes in corticospinal excitability and inhibition of the stimulated and non-stimulated hemispheres were analysed in 13 participants in both the dominant and non-dominant primary motor cortex (M1). Participants were exposed to 20 min of anodal and sham tDCS and also undertook a blood sample for BDNF genotyping. Results: TMS revealed a bilateral increase in corticospinal excitability irrespective of which hemisphere (dominant vs non-dominant) was stimulated (all P < 0.05). Furthermore, the induction of corticospinal excitability was influenced by the BDNF polymorphism. Conclusion: This finding shows that anodal tDCS induces bilateral effects in corticospinal excitability irrespective of hemispheric dominance. This finding provides scientists and medical practitioners with a greater understanding as to how this technique may be used as a therapeutic tool for clinical populations.

Changes in pH as a result of galvanic currents used in percutaneous needle electrolysis

Abstract Aim To determine whether sodium chloride electrolysis causes a change in the pH of tissues. Methods The effects of a 3 mA galvanic current has been evaluated, applied for 3 seconds and 3 repetitions (3:3:3). In vitro pH changes were evaluated in three experiments: 1) Eppendorf® tubes filled with Ringer's solution; 2) a very small volume of Ringer's solution (100µl); 3) Eppendorf® tubes filled with saline solution (NaCl 0.9%). The pH changes in the gastrocnemius of mice were evaluated, using the left limb as a control and the right limb for the intervention. The gastrocnemius muscles were ground up and the pH of each group was determined. Results In the in vitro experiments 1 and 2, no variation was observed in the pH of either the cathode in the Ringer's solution or the anode in the Ringer's solution (the variation did not exceed 16% in either of the cases, p> 0.05). In the third in vitro study, the pH after galvanic current application increased by 70% in the saline solution of the cathode and the anode pH decreased by 34% (p < 0.05 in both cases). In the in vivo experiments, no change in pH was obtained (% variation: 0.00 ± 0.00). Conclusions The galvanic current used in percutaneous needle electrolysis applying the 3:3:3 parameters generates very small changes in the pH, in the area near the needle, which the body is able to rapidly compensate for.

Information universal non-contact transducers of control and management systems

In contact and communication devices, power equipment, relay protection and automation terminals, and in the electric power industry of smart cities and houses, microprocessor-based devices for relay protection and automation, distributed generation installations, including renewable energy sources, and energy storage devices, as well as “smart” ones, are beginning to be used automated information-measuring systems. They widely use non-contact transducers of direct and alternating currents of control and management systems. Their disadvantages are a narrow range of controlled currents, large dimensions and weight. Therefore, their elimination is important. The paper considers the general principles of building information non-contact transducers of large direct currents, the basic requirements for them. The paper shows the results of the development of one of the options proposed by us, universal non-contact magnetomodulating transducers of large direct currents with an extended range for various monitoring and control systems in the electric power industry of solar power plants, renewable energy sources, laser and solar installations, in industry, science and technology, in rural and water management, as well as in farming and in everyday life. The developed non-contact transducer can be widely used in industry, in agriculture, as well as in the electric power industry of smart cities.