The possibility of increasing the energy supplied to an aluminum metalplasma puff with outer plasma shell by changing the propagation conditions of the arc source plasma in the interelectrode gap has been studied.In the experi ment, the transparency of the cathode grid was varied, onto which the plasma flow of the arc discharge, which is used to form the metalplasma puff, is injected.It was found that when the grid transparency changed from 85% to a solid elec trode, the metalpuff mass increased by ~3 times, and the energy supplied to the liner by ~1.7 times and reached 100 kJ/cm.The decisive influence of the outer plasma shell on the formation of a compact and azimuthally uniform current sheet, which stabilizes the process of metalpuff compression from large diameters in the microsecond regime, is shown.

聚吡咯/MnO 2 纸电极的制备及光热效应增强电容性能

This study compares three conventional electrode arrays in 2D electrical resistivity imaging surveys by applying them to study the sedimentary layers and the hydrological situation in three coastal locations close to the Khor Al-Zubair, southern Iraq. At each location, a 2D imaging line of 1200 m length wasimplemented columnar the Khor Channel, using Dipole-dipole, Wenner and Wenner-Schlumberger arrays at the same line. The inverse models revealed the presence of three major resistivity layers, the uppermost layer has a medium resistivity attributed to the upper aquifer and is affected by the salinegroundwater. The second electrical layer represents the upper aquifer, completely filled with brackish groundwater. The third, very low resistivity layer correlates to the lower aquifer and is filled with saline groundwater. Also, a hard clay bed (aquiclude) is visible on all geophysical lines in the depth range of 20 m-28m. Results indicate that all three electrode arrays can detect the sedimentary layers and the extension of saline groundwater but with a difference in accuracy. The Wenner-Schlumberger array revealed the best results in delineating the resistivity layers, the extension of saline groundwater in the uppermost layer of aquifer and the clayey aquiclude and shows the best horizontal and vertical resolutions. The dipole-dipole array was less accurate in determining this extension of saline groundwater and the aquiclude. The Wenner array results were unsatisfactory in delineating the aquiclude and the lower aquifer. The Wenner-Schlumberger array, as hypothesized, is efficient in determining different resistivity layers, especially in the presence of horizontal and vertical structures or high background noise, and if long survey lines are required.

The participation of high strength steels in marine and offshore structures is increasing, which makes it necessary to develop recommendations for underwater repair welding works. The article presents the results of bead-on-plate welded specimens made of S700MC high strength steel in underwater wet welding conditions by covered elec- trodes. Three specimens with heat input values in the range 0.91-1.05 kJ/mm were made. The specimens were sub- jected to visual, metallographic, macro- and microscopic tests as well as hardness measurements using the Vickers method. It was found that the higher heat input leads to formation of mixed bainite-martensite microstructure in the heat-affected zone (HAZ). Lower heat input value results in presence of martensite in HAZ. It was shown that in the scope of the performed tests, the maximum hardness of HAZ did not exceed the critical value for the material group, and the increase in heat input caused the decrease of hardness by about 25 HV10 to a level 250-260 HV10.

A simplistic and inexpensive electrochemical platform has been fabricated for the simultaneous detection of Dihydroxybenzene Isomers (DHBIs); named- Hydroquinone (HQ), Catechol (CC) and Resorcinol (RS); in aqueous system. Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) were adopted for the detection technique. 2B pencil (Faber Castell) collected from the resident stationary shop was used for fabricating Pencil Graphite Electrode (PGE) used as working electrode. PGE was characterized by SEM and EDX. It was modified electrochemically by ionic liquid, 1-Butyl-3-Methylimidazolium hexafluorophosphate (BIHP). Total analyses were performed in phosphate buffer solution (PBS) at pH 7.0. BIHP-PGE showed good selectivity and robust anti-interference for detection of HQ, CC and RS simultaneously in aqueous media. For HQ, CC and RS, the limit of detection is 9.09 μML -1 , 8.15 μM L -1 and 26.78 μM L -1 respectively and sensitivity is 525.21 μA/mM/cm 2 , 585.68 μA/mM/cm 2 and 178.00 μA/mM/cm 2 respectively at BIHP-PGE in simultaneous detection.

Subur Makmur Village is an area where the availability of clean water is difficult, especially during the dry season. One of the sources of water that can be used by the villagers is groundwater. However, to obtain groundwater, it is necessary to drill wells and investigate the aquifer layer first. This study aims to obtain an overview of the subsurface layers based on the resistivity properties of the rock, so that the aquifer layer can be identified and can determine the exact location of the drill point in the prospective aquifer position that may be encountered. The geoelectric method is the most efficient method for detecting aquifer layers. It uses two types of configurations, namely, the Wenner and Wenner-Schlumberger configurations where the number of geoelectric paths is one path. The length of the track used is 540 meters, the number of electrodes is 28 with the spacing between the electrodes is 20 meters. The resistivity cross section for both configurations, obtained resistivity values of 11 - 140 Ohm meters. Composed of 2 (two) rock units, namely graywacke sandstone rock units. Consists of graywacke sandstones with claystone inserts. Density value ≥ 40 Ohm meter. Hydraulic properties, small porosity, small permeability, the potential for groundwater in this unit is small. The position of this unit is at a depth of 40 m. In the cross section, the resistivity is yellow - red. The second rock unit comprising this trajectory is the alteration claystone unit consisting of claystone containing bolders of sandstone / igneous rock. Resistivity value ≤ 40 Ohm meter. The position of this unit is on the Surface to a depth of 40 m. Hydraulic properties, large porosity with very small permeability, the potential for groundwater is very small. In the cross section of this unit resistivity are colored dark blue, blue and green. From the resistivity cross section, it can be determined the position of the borehole which is effectively located in the length range of the trajectory between 360 - 420 meters. Keywords: subur makmur, groundwater, wenner, wenner-schlumberger

The role of polymeric binders in water-based lithium-ion battery electrodes

The electrochemical properties of AZ31B Mg alloy is investigated by electrochemical methods in MgSO4-Mg(NO3)2 (0.14 mol/L MgSO4, 1.86 mol/L Mg(NO3)2) electrolyte solution with different Na2SnO3 concentrations. The results suggest that AZ31B Mg alloy has the highest polarization resistance, the shortest delayed time and the lowest voltage drop when Na2SnO3 concentration is of 1 mmol/L. Moreover, the electrochemical impedance, galvanostatic discharge and linear polarization curves are used to research the effect of Mg electrode in the solution with and without Na2SnO3 at different immersion times. It indicates that Na2SnO3 can improve the corrosion resistance and discharge activity of Mg alloy at the same testing time. The surface structure and composition of Mg alloy is characterized by using scanning electron microscopy, and the results show that the improved electrochemical behavior of Mg alloy is related to the change of composition of corrosion products.

This paper comments on a recently published article by Parente et al.

A lot of autonomous power systems have been designed and operated with different power levels and with special requirements for climatic conditions, availability, operation/maintenance cost, fuel consumption, environmental impacts, etc. In this thesis, new methods of designing an autonomous power system are presented by application to the power supply of the shoreline electrode station for HVDC link. This station will be constructed on the small island of Stachtoroi for the new high voltage direct current (HVDC) link of Attica–Crete in Greece. The general guidelines of the International Council on Large Electric Systems (CIGRE) and of the International Electrotechnical Committee (IEC) for the power system of lighting and auxiliary loads for these HVDC stations are supplied from the medium voltage or the low voltage distribution network, whereas they do not take into consideration the criticality of this interconnection, which will practically be the unique power facility of Crete island. Therefore, the respective instructions for the process of designing the electrical supply of shoreline electrode station for HVDC link are reworded, the power needs of the station are evaluated in detail and the optimal design of an autonomous power generation system is carried out in terms of annual equivalent cost of construction, operation and maintenance through exhaustive testing and sensitivity analysis taking into account a number of technical parameters such as battery aging, discharge depth, solar irradiation variance during the day and year, cost of land occupation by the photovoltaic panels etc. Then, the photovoltaic unit is optimally configured for the required power from a set of photovoltaic panels of general use and inverters taking into account technical constraints, installation costs, lifetime, efficiencies, capital recovery rates, etc. and extend the corresponding results of the previous configuration appropriately. Following, the method of optimal design of an autonomous hybrid power generation system with photovoltaic panels, batteries and diesel generators that operate in the optimum operation point is developed, while in addition other parameters are adjusted, such as the charge-discharge range of the battery etc., applying it similar to the case of the autonomous system with photovoltaic panels and batteries. Finally, the proposed autonomous systems are compared with the classic conventional solutions (use of autonomous systems with diesel generators only, connection to the distribution power network) and it turns out that depending on the user requirements the creation of an autonomous system with either general purpose photovoltaic panels and batteries, or with photovoltaic panels for marine applications, batteries and diesel generators for particularly increased reliability requirements are superior to the classic solutions in terms of total annual equivalent construction - operation - maintenance costs for the respective deflated capital recovery rates.

Conventional battery models (e.g., Pseudo-2D model) were developed especially for particle-based battery electrodes and have limitations in addressing the newly-emerging fiber-based ones. This thesis proposes numerical tools for efficient property evaluation of fiber-based electrodes and for multiscale simulation of battery electrochemical behavior. An efficient computational model is first developed to evaluate percolation threshold, effective electronic conductivity, and capacity of fiber-based electrodes. The electrode is composed of conductive and active fibers mixed in an electrolyte matrix. This model rests with generation of randomly-distributed fibers by Monte Carlo method. The connection between conductive fibers is used to determine percolation threshold and electronic conductivity, while the connection between conductive and active fibers defines the active material utilization and capacity. An optimal active-conductive material ratio is identified to maximize the electrode capacity, and the study of fiber orientation effect reveals that the isotropic distribution leads to the highest utilization of active fibers. For more accurate estimation, a FE2 multiscale framework is further proposed to solve physics-based governing equations. The first part extends the conventional FE2 method suited to a one-equation model to transient diffusion in a two-phase medium described by a two-equation model. The new features include the macroscale equations derived by the volume-averaging method and separate treatment of the two phases in terms of information exchange between macro- and micro-scales and boundary conditions of the microscale problem. The differentiation of the two phases results in additional macroscale source terms upscaled from the microscale interfacial flux. Unlike effective material properties, the tangents of the interfacial flux depend on the microscopic length scale. The second part of the FE2 framework addresses the ionic transport in the pore-filling electrolyte of separators, ignoring the interfacial flux between the electrolyte and the active material. The FE2 method features a macroscale constitutive relation numerically obtained, rather than assumed as in Pseudo-2D model and many of the existing models, from microscale simulation results. This unique feature enables the FE2 method to allow for nonlinear (concentration-dependent) transport properties at the microscale and reflect them at the macroscale without postulation. The well-defined microscale problem setting results in effective transport properties expressed in a tensor format that is indispensable for an anisotropic microstructure.

Stroke is the third leading cause of disability worldwide, commonly removing a subject’s independence. However, physical therapy can assist a subject in regaining their lost functionality. Modern physical therapy is incorporating assistive robotic devices, allowing more intensive and repetitive training while reducing therapy cost. The incorporation of surface electromyography (sEMG) into assistive robotics can enable patient-driven intention-based control, leading to increased patient interaction and a more natural, unconscious interface. sEMG is the non-invasive technique of measuring the bio- electrical activity of the skeletal muscle at the skin surface. The bioelectrical signal is bipolar with an amplitude of ≤ 10 mVpk–pk, a frequency spectrum of 0–500 Hz and is typically measured using two recording electrodes and a single reference electrode. However, electrical interference and bioelectrical crosstalk limit the efficacy of bioelectrical feedback for assistive robotic control. In built-up environments, the human body is capacitively coupled to the mains power sup- ply and ground, leading to interference potentials which are a function of the impedance imbalance between recording electrodes. The current methods of reducing electrical interference either removes a portion of the signal of interest; can have limited affect, resulting in large interference potentials; or can be time consuming with the potential to lead to skin irritation. Bioelectrical crosstalk, detected with sEMG, is the phenomenon of one muscle’s signal influencing the recording of another. Crosstalk can lead to misrepresentation of the target signal, increasing the difficulty to provide accurate biofeedback. The tripolar electrode configuration is commonly used to reduce crosstalk. However, using three electrodes increases the possibility of impedance imbalances between recording electrodes. Previous research has focused on balancing the common-mode input impedance of the bioelectrical instrumentation device with the impedance of the electrode-skin interface. The common-mode interference potential was used as an indicator to control the required common-mode input impedance. However, without measuring the electrode-skin impedance, the unique transfer function of each electrode-skin interface will be unknown, reducing the ability to use the frequency spectrum of the bioelectrical signal for biofeed-back. Therefore, there is a need to balance the impedance between electrode-skin interfaces and determine the resulting transfer function between the electrode-skin interface and the bioelectrical instrumentation device. Commercial, research-level sEMG devices do not have an open source signal processing architecture. Therefore, to quantify the impact of balancing the impedance of multiple electrode-skin interfaces, a high quality near-raw signal output sEMG device was developed. The device has a resolution of 298 nV, a baseline noise of less than 5.2 µVrms (when abrasive skin preparation is applied), a signal bandwidth of 21.2–433 Hz, a sampling rate of 1 kHz and built in 1 x 10 mm Ag bar electrodes. Characterising the behaviour of the electrode-skin interface provides quantitative insight into optimising a compensatory system to balance the impedance between multiple electrode- skin interfaces. A method to model the step response of the electrode-skin interface was developed using simulation and physical, passive circuitry, resulting in a mean error per modelled component of 0.076% and 3.49% for simulation and passive circuitry, respectively.

This work describes the preparation of an Al2O3 electrode material for a performing and stable supercapacitor. The electrode was prepared by a DC thermal plasma plant installed at ENEA Research Centre of Portici. The structures and morphologies of samples were characterized by SEM, XRD, TG, and FT-IR. Al2O3 electrode electrochemical characteristics were performed in a sulphuric acid solution electrolyte. Cyclic Voltammetry (CV) technique was carried out. The results show that Al2O3 exhibits a good specific capacitance. Furthermore, after 10000 cycles, 98% of the initial capacitance was maintained.

Supercapacitors (SCs) are energy storage devices with a growing interest thanks to their high-power charge and discharge process and long-cycle life. Their main drawback, when compared to more common devices such as batteries, consists in a low energy density. The performances of SCs can however be improved with the coupling of additives to the main active material, which usually is an Activated Carbon. The most common additive is instead Carbon Black (CB), while more recently also Graphene-derived materials have been successfully exploited for this purpose, as the reduced Graphene Oxide (rGO). However, besides raw materials choice, details related to the manufacturing have a leading importance in the attempt to obtain novel active materials with an industrial-ready process which also looks toward the needs of more environmental friendly and economically convenient solutions. In this work, a physical-chemical analysis is performed to show temperature effects on CB, GO and on a CB/GO water-based slurry with helpful results about GO reduction and CB/GO nanocomposite formation.

Cyclic Voltammetry Simulations on Batteries with Porous Electrodes

The polyaniline nanowire/self-supported graphene (PANI/SGr) composite was synthesized by one-step electrochemical exfoliation and electrodeposition method using graphite paper. The directional migration of electrolyte ions and the electropolymerization of aniline monomers through the electrical field simultaneously occurred in the mixed solution including Na2SO4, HCl and aniline (An) monomers. The stability of the PANI/SGr composite is enhanced by the combination of the new-born SGr with high activity and PANI. The uniform distribution of the nanowire-like PANI is achieved on the surface of the SGr. The PANI nanowires lead to the formation of the three-dimensional network architecture, where the existence of pores facilitates the diffusion of electrolyte ions into the internal structure of the PANI/SGr composite. The electrochemical tests of the PANI/SGr composite were conducted as a supercapacitor electrode material. The specific capacitance of 453 F·g−1 at a scan rate of 2 mV·s−1 is achieved. The rate capability of the PANI/SGr composite at the current densities of 0.5-10 A·g−1 is up to 73.1%. The cycling stability of the PANI/SGr composite is as high as 87.3% after 10000 discharge-charge cycles at the current density of 1 A·g−1. All of these results indicate that the PANI/SGr composite possesses good capacitive performance and excellent cycling stability. The PANI/SGr composite is promising for supercapacitor electrode materials.

Here the performance in 4-Nitrophenol (4-NP) detection of magnetite-few layer graphene-based electrode was reported. The prepared nanocomposite, synthesized according to a “wet chemistry” approach, was broadly characterized: SEM and TEM images and XRD spectra indicate the formation of nanoparticles with a few nanometers size dispersed on graphene layers. The sample was tested as an electrochemical sensor for the detection of small traces of 4-NP in aqueous solutions with a limit of detection (LOD) of 4 µM. The sensor was tested also for 1 month, showing proper operation and excellent stability.

The Sn-based materials have been a focus as promising high-capacity electrode materials of lithium-ion battery. However, its poor cycling performance has severely restricted the large-scale practical applications. The Sn quantum dot/graphene (SnQds/rGO) composite electrode material was synthesized by chemical reduction method, using graphene oxide as the carrier. The Sn quantum dots with <10 nm were uniformly loaded on the surface of graphene. The experimental results show that the SnQds/rGO composite with Sn mass fraction of 90wt% has good comprehensive electrochemical performance. The first discharge capacity and Coulomb efficiency of the SnQds/rGO composite are 939 mAh/g and 66.6%, respectively. It’s discapacity can reach 621 mAh/g after 200 cycles and the capacity retention rate is 66.1%. The structure stability of SnQds/rGO composite is improve, meanwhile its impedance reduce, owing to the commposite of small size Sn quantum dots and graphenethe. As a result, the cycle performance and rate performance of the SnQds/rGO composite have been significantly improved. However, the initial Coulomb efficiency of SnQds/rGO composite decreases.

Batteries gained a lot of attention due to a raising demand for energy storage, as required for renewable energy generation systems, portable electronics and transport applications. For the development of new battery materials understanding of fundamental processes is essential, which often relies on the development of new characterisation techniques and tools that enable to study the underlying electrochemical processes at the relevant length scales, i.e. from an atomistic to a macroscopic level. Future batteries should be able to store more energy (per unit mass and or volume) and should be safer. Battery material solutions to achieve this are in principle known, where this thesis focusses on: (1) Si being one of the most promising negative electrode based on its large Li storage capacity (ten times higher than current graphite) and (2) solid electrolytes, replacing liquid electrolytes, which would practically annihilate safety concerns of Li batteries. However, for these new battery materials the challenge is to achieve a long cycle life by slowing down, or even preventing degradation reactions at the interfaces between the electrode and the electrolyte. This is the binding theme, and the topic of the main research questions of this thesis are thus: What are these degradation mechanisms and what is the impact of strategies to prevent it and achieve a long cycle life. The focus in this thesis is on Si negative electrodes in combination with liquid electrolytes in general, and for solid electrolytes in particular

In the context of the present diploma thesis, the flow field of an electrically conducting fluid was experimentally examined, employing the 2D-PIV technique, under the presence of an electric and a magnetic field. The examined fluid was a sodium chloridewater solution, with a concentration of 15% by weight. The fluid tank was made of Plexiglas with a cross-section 45 mm x 55 mm, 6 mm deep, with a free surface. Two vertical aluminum plates at a distance of 45 mm were connected to a direct elecric current source, generating a current through the fluid, up to 1.2A and a maximum voltage of 14V. A number of permanent magents were intalled under the tank with a magnetic flux of 50 mT at a distance of 6 mm from their surface generating a spatially varying vertical magnetic field. A toroidal magnet was also used. Due to the electromagnetic Lorentz forces, the fluid was set into motion. The basic feature of the flow field, which was measured 3 mm far from the tank bottom, was the presence of vortices, the number, place and circulation of which were varying in time. The basic conclusions are as follows: a) In the 4 magnet configuration, the flow field initially consists of 8 vortices, with their centers being along two parallel lines, perpendicular to the electric current but eventually there are reduced to 4 big vortices. When the electric current increases, the fluid velocities and fluctuations increase as well, reaching values like 50 mm/s and 25 mm/s, respectively, for a voltage of 14V. The mean kinetic energy of the flow field increases initially wih a fast rate, but later it tends to a certain value athough fluctuating. b) In the 10 magnet configuration, the flow field initially consists of 4 vortices, with their centers being along a line normal to the electric current. Later, the vortices are reduced to two of the same sign of circulation with their centers being on a line which forms a small angle with respect to the electrodes planes. The fluid velocities are greater, compared to the 4 magnet case, the unsteadiness of the flow is more pronounced and the mean kinetic energy of the flow field takes more than two times higher values. c) In the case of the toroidal magnet, the flow field consists of 4 vortices with their centers being close to the four edges of the tank and two of them are stronger than the other. The number of the vortices does not seem to be reduced with time. Only in case that the elecrodes were disconnected from the current source, the four vortices were transformed to one vortex, before the fluid comes to a rest.