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Summary: DC‐DC converters play a vital role in the integration of renewable energy sources. Modular multilevel converter (MMC) has emerged as a highly promising option for high‐voltage high‐power applications, for DC‐AC and DC‐DC conversion, thanks to its distinctive characteristics. An inherent limitation of using traditional MMC in DC‐DC conversion is the occurrence of arm energy drift, leading to imbalanced voltages across capacitors of submodules (SMs). Many approaches have been presented in the literature to address the energy drift issue during DC‐DC conversion process. In this paper, a novel bidirectional hybrid modular multilevel DC‐DC converter with balanced arm energy has been proposed. The proposed converter consists of one high‐voltage valve and two legs. Each leg is equipped with half‐bridge submodules (HB‐SMs) in the upper arm and full‐bridge submodules (FB‐SMs) in the lower arm. The proposed architecture enables the parallel connection between series‐connected capacitors of the upper arm and series‐connected capacitors of the lower arm during the equalization period. The parallel connectivity enables the energy transfer between the upper and lower arms in the same leg, hence preventing energy drift issues. A detailed illustration of converter operational concept, mathematical analysis, design, and efficiency estimation are presented. The presented simulation and experimental results show the bidirectional power flow ability and the promising behavior of the proposed converter during normal operating conditions with balanced arm energy. Finally, a comparison between the proposed converter and other existing topologies has been made to show the superiority of the proposed converter over the other alternatives. The proposed converter has a lower count of insulated gate bipolar transistors (IGBTs) and eliminates the usage of isolating transformers when compared to the energy equalization modules approach. In addition, unlike the other alternatives, the proposed converter has a DC fault blocking capability. [ABSTRACT FROM AUTHOR]

The development of lightweight and high-strength materials is critical for many industries, including aerospace, automotive, and electronics. Metal matrix composites (MMCs) have shown great promise in meeting these requirements. The structural and physical properties of Al6061 alloy reinforced with hybrid MMCs, including TiB2, SiC, and fly ash (FA), were investigated in this research review. The MMCs investigated were made using the stir-casting process. Their microstructure, structural characteristics, and mechanical features were examined. The inclusion of TiB2 and SiC enhanced the composite’s hardness, tensile strength, and wear resistance, while the addition of FA lowered its density and improved its thermal and corrosion resistance. However, the volume percentage, particle dimension, and arrangement of the reinforcing components all had an effect on the physical characteristics of the composite. Therefore, the optimum combination of the reinforcing materials must be carefully selected to achieve the desired properties. The result of this review provides valuable insights into the development of high-performance MMCs for various industrial applications. [ABSTRACT FROM AUTHOR]

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

AbstractMany commercial modular/pre-cast types of construction do not satisfy seismic ductility requirements and are not aligned with Relevant Good Practice (RGP) in the nuclear regulated sector. Steel-Concrete (SC) composite construction offers potential benefits to significantly reduce the construction period of the site works and allows mechanical attachments and cable trays/pipes to be welded directly to the steel face. However, due to SC’s relative novelty within the nuclear industry, further research is required to determine the advantages and disadvantages when compared to traditional construction forms. This paper investigates the performance of SC construction, including the bespoke Steel Bricks product, against a large commercial aircraft impact threat relevant to nuclear facilities. The research employs state-of-the-art finite element modelling to generate the aircraft impact threat and to apply the associated impact forces and pressures to the structures. The objective of the research is to complete a performance comparison of the SC and Steel Bricks against a traditional RC structure to determine potential benefits. In addition, sensitivity analysis is employed on the SC and Steel Bricks options to provide further information for future assessment and design. [ABSTRACT FROM AUTHOR]

In this paper, the non-destructive assessment of thermo-mechanical characteristics of extremely rigid structures made up of natural composites fibers is conducted. Higher-force dynamic mechanical investigation has allowed for new insights, which is not possible with the regularly employed static and impact test methods. Natural fibers made up of composite sandwich panels with aluminum and aramid honeycomb cores are studied. Various panel cores of equal stiffness and damping capabilities are compared over flight frequencies ranging from 1 to 100 Hz. It was discovered that the exhaustion of the natural fiber sandwich panels depends on both the core material and the applied static load. Additionally, temperature sweeps were carried out, and it was discovered that they can identify variations in the post processing of the natural fiber laminated panels and show the variations in the transition temperature of the matrix material. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research looked at how incorporating carbon quantum dots (C-dots) made from lychee fruit husk (LFH) into a green dielectric made from deionized water changed the machining behavior of AA7075-TiB2 metal matrix composite during an electro-discharge machining (EDM). Waste lychee fruit husk biomass was pyrolyzed at a low temperature of 450 °C at a heating rate of 10 °C/min and surface treated. Greener dielectrics were created using deionized water and C-dots. The 7075-TiB2 metal matrix composites were subjected to EDM processing using a range of dielectric materials. The machinable surfaces were analyzed for their rates of material loss, tool wear, and surface roughness. The results showed that the material removal rate was maximum (10.82 mm3/min) for the dielectric fluid that had been activated by C-dots. Dielectrics that were triggered by C-dots also reduced the rate of tool wear and improved the surface smoothness. C-dot-activated dielectric machined surfaces had better texture, as seen in scanning electron microscopy pictures. It is possible that greener dielectrics with enhanced machining capabilities might be utilized to mill high-strength material with cleaner machining concept. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the impact of input factors, namely spindle speed (Ss), feed rate (Fr), and depth of cut (DOC), on the output response of surface roughness (Ra) and metal removal rate (MRR) during the dry turning process of AA-6061. The material under study, AA-6061, is strengthened with 6% and 8% weight of titanium carbide (TiC) particles, having an average particle size (APS) of 2 microns. To create experimental designs, the Box-Behnken design (BBD) of response surface methodology (RSM) and mathematical models were used. The desirability-function approach of RSM was applied to obtain optimal input factor values. The findings showed that, for 6% TiC composites, Ss had the greatest effect on both Ra and MRR, followed by Fr and DOC. Similarly, for 8% TiC composites, Ss had the most impact on Ra, followed by DOC and Fr, while DOC had the greatest influence on MRR. To validate the accuracy of the proposed models, confirmation tests were conducted. The outcomes of the confirmation test show that the proposed models are valid. The outcome of the study can be applied in manufacturing industries for optimizing machining processes, resulting in increased efficiency and reduced production costs. [ABSTRACT FROM AUTHOR]

MMCs are broadly used in several industrial applications because of their excellent mechanical properties. Hard materials and composites cannot be machined by typical conventional methods. so nonconventional machining methods such as Electrical discharge machining are mostly used. This work focuses to optimize the process variables of EDM of Al5456/SiC/Flyash hybrid composites. The impact of three most significant variables including pulse-off time, current and pulse-on time are examined. Central Composite Design (CCD) based RSM is applied for experimentation. The development model for material removal rate (MRR) and surface roughness (SR) are investigated by using CCD technique. ANOVA is implemented to identify the most significant variables and their output response of MRR and SR. From the validation result, the maximum values of MRR and SR are identified as 0.783 mm3/min and 13.26 μm, whereas minimum values are 0.249 mm3/min and 8.24 μm. ANOVA results show that current and pulse OFF time are highly significant variables to increase MRR and SR. The development of a regression model and 3D/Contour are made to predict and evaluate the Material Removal Surface and Surface roughness. [ABSTRACT FROM AUTHOR]

This study investigates a novel methodology to intricately craft a HAMMC and thoroughly examine its multifaceted mechanical and tribological characteristics. By combining silicon carbide (SiC) and fly ash as reinforcements, a unique identity is bestowed upon this hybrid composite, enhancing its structural integrity and functional attributes. Stir casting is the chosen methodology for fabricating this composite, favored for its economic viability and suitability for large-scale manufacturing. In this research, the emphasis is on developing a cost-effective composite that not only meets stringent economic considerations but also exhibits improved material properties. Within the realm of hybrid metal matrix composites, the well-regarded Al6061 takes on the role of the matrix material, while the synergistic inclusion of fly ash and SiC serves as reinforcing constituents. Three specimens with compostion 90% Al6061 + 5% SiC +5% Fly ash, 90% Al6061 + 10% SiC +6% Fly ash and 90% Al6061 + 15% SiC +7% Fly ash were fabricated. To unravel the intricacies of the fabricated Al6061 metal matrix composite, comprehensive tests are employed. These tests, including the Pin-on Disc test, Scratch test, Rockwell Hardness test, and Charpy Impact test, collectively work to unveil the nuanced tribological and mechanical behaviors encapsulated within this innovative alloy. The results indicated significant improvement in wear resistance in specimen comprising 78% Al6061 + 15% SiC +7% Fly Ash and volumetric loss found to have 0.96 g. Superior hardness characteristics and enhanced abrasion resistance found in 78% Al6061 + 15% SiC +7% Fly Ash than other two specimens. The highest impact strength exhibited in 90% Al 6,061 + 5% SiC +5% Fly ash specimen. [ABSTRACT FROM AUTHOR]

Aluminium silicon carbide (Al-SiC) compounds, highly valued for their outstanding mechanical properties in aerospace, automotive, and structural engineering, were comprehensively examined in this study. The investigation began with the fabrication of Al-SiC composites by stir casting, incorporating various SiC weight fractions (0, 0.18, 0.34, 0.56, 0.69, and 0.96 wt.%) into six labelled samples. The primary focus was to evaluate how these variations affected mechanical performance, notably scrutinizing the distribution of SiC carbide particles through metallurgical microscopy. Various tests were conducted, such as tensile, hardness, and microstructure evaluations, to holistically evaluate mechanical properties. The results revealed notable enhancements in hardness and wear resistance due to the addition of SiC particles, although accompanied by reduced tensile strength. The composite material exhibited a hardness of 123 HV compared to the aluminium hardness of 93.6 HV. Additionally, the tensile stress and strain of aluminium were 261.45 MPa and 0.223 mm/mm, respectively, while those of the composite with highest tensile stress and strain were 198.49 MPa and 0.134 mm/mm, respectively. Microstructure analysis identified sample 5 as exhibiting the most uniform distribution, excelling in tensile tests, while sample 4 exhibited the least favourable characteristics among the samples. These insights offer crucial optimization pathways for Al-SiC compounds in specialized applications, showcasing their potential as high-performance engineering components. This research contributes significantly to understanding these composites, fostering the development of lightweight materials with exceptional mechanical prowess. [ABSTRACT FROM AUTHOR]

High voltage direct current （HVDC） transmission based on modular multilevel converter （MMC） is widely used in large-scale renewable energy delivery. However， the lagged inertia of MMC controllers may undermine the small-signal stability. Firstly， the mechanical inertia of synchronous generators is analyzed， and a second-order unified expression of inertia applicable to MMC controller is proposed. Secondly， based on the dynamic and inertial delay of MMC closed-loop controller， a small-signal stability criterion for MMC controller connected to weak power grid is presented. Finally， through simulation analysis of a double-side MMC grid-connected system， the correctness of the proposed stability criterion is validated.

Currently, research on the small-signal stability of grid-forming converters under two control modes, grid-following and grid-forming, mainly focuses on low-level converters. However, studies on the differences between grid-following modular multilevel converters (MMC) and grid-forming MMC are limited. A comprehensive analysis of the wideband oscillation risk differences in MMC-HVDC systems under these two control modes from the perspective of impedance characteristics is necessary. Therefore, based on the harmonic state-space (HSS) modeling theory, this article establishes wideband sequence impedance models for grid-forming and grid-following MMC. Subsequently, this article identifies key control parameters affecting the impedance characteristics of MMC under two control modes. The wideband oscillation risks of MMC-HVDC systems under both control modes are compared. The study indicates that when the grid strength weakens, grid-following MMC faces instability risks, while grid-forming MMC can maintain stability. In instances where high-frequency resonance peaks exist in the impedance of the grid, both control modes of MMC may face instability risks. Furthermore, by adjusting the obtained key control parameters of MMC, this article effectively suppresses the oscillation risk discussed above. Finally, the analysis results are verified through an electromagnetic transient simulation. [ABSTRACT FROM AUTHOR]

Nowadays, advanced engineering materials are gradually becoming more attractive to the industries because of their high fatigue strength, hardness, thermal shock resistance, attractive strength to weight ratio, etc. Aluminium metal matrix composites (MMCs) have such properties and good electrical conductivity. Therefore, wire electrical discharge machining (WEDM) was found to be a suitable process for machining of such materials. The open gap voltage, pulse-on-time, pulse-off-time, peak current, wire feed rate and wire tension were considered as input process parameters, and experiments were carried out on fabricated hybrid Al/(SiC+ZrO2+ NiTi)-MMC. Taguchi method-based L18 (21x37) mixed orthogonal array was employed for planning of experiments. The process parameters were optimised for material removal rate (MRR) and surface roughness (SR) heights. Confirmation results reveals 61.88%, −28.75% and −20.25% improvement in MRR, Ra and Rt respectively, over initial setting. From analysis of variance (ANOVA), open gap voltage and pulse-on-time were found significant parameters for MRR and SR. The mathematical models for MRR and SR were developed and confirmation test reveals good agreement of it with experimental results. Scanning electron microscopy images reveal that the recast layer thickness was 8.569 µm at optimal MRR setting and 6.113 µm at optimal surface roughness (Ra) setting. [ABSTRACT FROM AUTHOR]

Background: The pigtail was used to create an opening at the lower punctal site in grade 0 stenosis with insertion of self-retaining tube and Mitomycin C (MMC). Methods: The patients with acquired lower punctal stenosis (grade 0) were divided randomly into equal groups, Group A: were treated with pigtail and MMC 0.02% and Group B: were treated with pigtail alone. The pigtail was inserted through the upper punctum until its tip reached the occluded punctum, this site was incised with a scalpel (No. 11). A self-retaining bicanalicular tube was then placed. Results: Results of 36 eyes from 26 patients were included. No differences were observed between both groups regarding epiphora score, FDD test and punctal size preoperatively. The postoperative epiphora score, there were significant differences at 1 month (P = 0.035), 3 months (P = 0.005), and 6 months after removal (P < 0.001). The FDD test, there were significant differences at 6 months (P = 0.045), 1 month (P = 0.021), 3 months (P = 0.012), and 6 months post tube removal (P = 0.005). The punctal size, both groups differed at 1 month (P = 0.045), 3 months (P = 0.03), and 6 months post tube removal (P = 0.005). Only one case (5.5%) at each group showed extrusion of the tube. Conclusion: The pigtail probe, bicanalicular stent and MMC can be an effective method in treatment of severe punctal stenosis. [ABSTRACT FROM AUTHOR]

Metal matrix composites (MMC) introduced special features such as resistance to wear and high strength to weight ratio and these characteristics categorized them as difficult-to-cut materials in the field of machining. In the current paper, a novel study on the cutting fluid emulsion 5% role in the machinability of a magnesium-based metal matrix composite reinforced by silicon carbide (SiC) particles is presented. AZ91 magnesium alloy, with nominal composition Mg-9Al-1Zn, composites were made using stir casting method. Then, the composite samples were machined and the cutting parameters such as cutting speed, feed rate and side cutting edge angle were varied to assess their effects on the wear and surface roughness. To measure and analyze the wear, optical and scanning electron microscope (SEM) were used. Also, elemental analysis through energy-dispersive X-ray spectroscopy (EDS) was accomplished. Surface roughness of machined samples were measured by a profilometer and 3D surface topography. Results of SEM and EDS images indicated that SiC particles included in the composites act as grinders and remove the surface of tool even in a short time because of the severe abrasion. Additionally, surface of machined MMCs contains some defects such as cracks, broken SiC, and unwanted deformations. Using cutting fluid emulsion 5% enhanced the tool life as well as the surface quality remarkably for different cutting speeds, feed rates and cutting edge angles although finished surface of the samples were oxidized. Also, the cutting fluid considerably reduced the amount of adhered materials on the flank face. [ABSTRACT FROM AUTHOR]

With the ever-growing emphasis on global decarbonization and rapid increases in the power densities of electronics equipment in recent years, new methods and lightweight materials have been developed to manage heat load as well as interfacial stresses associated with coefficient of thermal expansion (CTE) mismatches between components. The Al–Si system provides an attractive combination of CTE performance and high thermal conductivity whilst being a very lightweight option. Such materials are of interest to industries where thermal management is a key design criterion, such as the aerospace, automotive, consumer electronics, defense, EV, and space sectors. This paper will describe the development and manufacture of a family of high-performance hypereutectic Al–Si alloys (AyontEX™) by a powder metallurgy method. These alloys are of particular interest for structural heat sink applications that require high reliability under thermal cycling (CTE of 17 μm/(m·°C)), as well as reflective optics and instrument assemblies that require good thermal and mechanical stability (CTE of 13 μm/(m·°C)). Critical performance relationships are presented, coupled with the microstructural, physical, and mechanical properties of these Al–Si alloys. [ABSTRACT FROM AUTHOR]

To solve the problem of high heat flux heat dissipation in microelectronic devices, a manifold micro-channel heat sink with corrugated bottom (CB-MMC) is proposed on the basis of the manifold microchannel heat sink (MMC). The flow and heat transfer characteristics of HFE-7100 in MMC and CB-MMC are investigated numerically. The results show that CB-MMC reduces the pressure loss and enhances the heat transfer performance in single-phase flow. The orthogonal test method is used to obtain structural design solutions with optimal thermal performance. It is observed that the temperature reduction is always at the expense of the increase of the pressure drop. In addition, the optimization parameters combination obtained through comprehensive evaluation of temperature and pressure drop through weight matrix - optimized solution 19 (wavelength A = 800 µm, amplitude B = 40 µm, channel depth C = 180 µm, outlet width D = 300 µm, channel width E = 25 µm). Its Tave has decreased by 6.89 °C, ΔP decreased by 10.27 kPa. Moreover, the subcooled boiling flow and heat transfer performance in MMC and CB-MMC are comparatively studied. The results demonstrate that the dynamic behavior of vapor bubbles causes large pressure fluctuations, which further leads to small temperature fluctuations, and thus reduces the stability of the flow and boiling heat transfer. Compared with MMC, CB-MMC exhibits more stable two-phase flow and better boiling heat transfer. [ABSTRACT FROM AUTHOR]

In MMC, the variations in capacitor voltage of sub-modules produce the circulating current. This research work presented intends to develop the MMC-HVDC using an the most effective 3 H-infinity regulator for solar energy systems. Initially, the unstable currents are observed using the new sensor and are compared to the current controller, which produces an erroneous current flowing. The current controller is set to zero. Since variations amongst error circulating current adds reference mistakes was expressed as a non-linear meaningful purpose, it is thought to be the primary factor in lowering the total harmonic distortion (THD). Using the Self-Adaptive Cuckoo search algorithm (SA-CS) for signal control, the gain is maximised in the H-infinity controller. Regulate evaluation, conversion performance monitoring, and battery voltage analysis are also used in the performance calculation of the proposed model in addition to THD and circulating current analysis. The results of the simulation show how well the proposed control strategy operates. [ABSTRACT FROM AUTHOR]

This paper presents the control strategies and performance analysis of doubly fed induction generator (DFIG) for grid-connected wind energy conversion system (WECS). The wind power produces environmentally sustainable electricity and helps to meet national energy demand as the amounts of non-renewable resources are declining. The development of the WECS can be seen with development in power electronics technology. Currently, two types of major generator used in WECS these are DFIG and the permanent magnet synchronous generator (PMSG). Both variable oprational speed are used in wind turbine. Because its high performance, reliability, controllability and high-power and voltage capabilities, multilevel converters have become a popular option for multi-MW WECSs. This paper focuses on the application of back-to-back modular multilevel converters in a DFIG and PMSG-based WECS. A comparative performance analysis of the two systems based on power quality, active, reactive power, and modular multilevel converter dynamics is presented. The comparison is based on simulation results created in MATLAB/Simulink software. [ABSTRACT FROM AUTHOR]

Aluminum-based composites provide tribological performance and thermophysical properties that, combined with being lightweight, are suitable for their application in automotive brake discs. Aluminum alloys allow the use of secondary materials to produce composites, with the drawback of several elements, impurities, and oxides that can harm the mechanical and thermophysical properties. This preliminary study explored the mechanical and thermophysical performance of a composite material produced with a secondary matrix alloy. Overall, the results are promising, with a minimal decrease in mechanical and thermophysical properties despite clustered silicon carbide particles in the composite with the secondary matrix. The challenges in effectively dispersing carbides in the melt seem linked to aluminum oxides, and future microstructural investigations will aim to clarify this aspect. [ABSTRACT FROM AUTHOR]

Thermal control of semiconductor devices in the submodules (SMs) is a key factor for the safe and reliable operation of modular multilevel converters (MMCs). During normal operation, significant thermal differences can arise among SMs due to the manufacturing tolerance and aging effect of capacitors, which can affect the lifespan of semiconductor devices and even lead to equipment failure. To address the problem, this paper presents a method for achieving thermal balancing among SMs with different capacitances by adjusting their switching principle. Firstly, the relationship between the degree of capacitance degradation and the junction temperature difference among SMs is revealed. Then, by setting data windows to capture the dynamic losses of power devices, which can reflect the trend of junction temperature. The switching principle of thermal balance among SMs is studied based on the trend of junction temperature in power devices. The thermal balancing method has advantages including not requiring high-precision temperature sensors and eliminating the reliance on capacitance monitoring technology. Finally, the simulation and experimentation results demonstrate that the proposed method can effectively achieve balanced junction temperatures of power devices among different SMs.

In this paper, the non-destructive assessment of thermo-mechanical characteristics of extremely rigid structures made up of natural composites fibers is conducted. Higher-force dynamic mechanical investigation has allowed for new insights, which is not possible with the regularly employed static and impact test methods. Natural fibers made up of composite sandwich panels with aluminum and aramid honeycomb cores are studied. Various panel cores of equal stiffness and damping capabilities are compared over flight frequencies ranging from 1 to 100 Hz. It was discovered that the exhaustion of the natural fiber sandwich panels depends on both the core material and the applied static load. Additionally, temperature sweeps were carried out, and it was discovered that they can identify variations in the post processing of the natural fiber laminated panels and show the variations in the transition temperature of the matrix material.

The existing fault current analysis in distribution networks tend to ignore the impact of the control dynamics arising from AC/DC converters. In response to the abovementioned challenge, this paper introduces a novel fault current estimation calculation approach tailored for AC/DC distribution networks, specifically considering the control dynamics of Modular Multilevel Converters (MMC). The methodology commences with the simplified model of the AC/DC distribution networks. Subsequently, on the basis of the analysis for the control structure of MMC, the impact of various control dynamics on fault current is quantified. Then, the branch currents and node voltages are obtained through a set of voltage-current differential equations. To validate the proposed method, simulation verification is conducted using PSCAD/EMTDC. The calculation results of main branch currents demonstrate that the accuracy of the improved method is about 90%, which shows the effectiveness of the proposed method. Furthermore, the robustness of the presented method against the variations of voltage level, breaker delay, and transition resistance is validated, where its accuracy is over 80%.

In this study, a novel AA7075-TiO2 metal matrix composite was machined utilizing a biosilica mixed EDM technique and the surface roughness and material removal rate are optimized. The biosilica particles are produced from waste maize cobs and then silane-treated. The optimization of process variables wasperformed using Taguchi grey relational approach with a process variable of peak current, gap voltage and pulse-on time. Results revealed that the gap voltage is the most important process variable, since it has a larger max-min difference of 0.25. In order to create a high MRR of 11.6mm3/min and a surface roughness of 2.25 m, the maximum GRG of 0.79 for Trial 1 (A2B1C3) represents the most ideal process variable group. The best results appear to be obtained with a peak current of 10 A, a gap voltage of 20V, and a pulse-on time of 140μs. The new GRG, however, is around 2.51% better than the anticipated optimized process variables of A2B1C3 with an old GRG of 0.79, according to the confirmation research. The new MRR of 11.89mm3/min and the surface roughness of 2.30s with a GRG of 0.81 are based on the optimized new process variables (A1B1C3). [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effect of aqueous and acetone extracts from Artemisia vulgaris L. (AV) and Artemisia alba Turra (AA), and two major polyphenols compounds (3,5-dihydroxybenzoic acid and quercetin-3-O-glucopyranoside) presented in both extracts of the plants against mitomycin C (MMC)-induced genomic instability. Genomic instability was measured using cytokinesis block micronucleus (MN) assay in human peripheral blood lymphocytes (PBLs) in vitro by analyzing two biomarkers – MN and nuclear division index (NDI). Extracts were tested in a concentration-dependent manner (10–250 µg/mL), while 3,5-dihydroxybenzoic acid and quercetin-3-O-glucopyranoside were tested in three different concentrations, in combination with 0.5 µg/mL of MMC. Aqueous and acetone extracts obtained from both plants significantly reduced MMC-induced MN frequency in PBLs, compared to positive control cells (p < 0.05). Extracts from AV did not affect NDI, whereas the concentrations of 10–100 μg/mL of aqueous and acetone AA extracts significantly elevated MMC-decreased NDI values in comparison to positive control cells (p < 0.05). Combined treatment of 3,5-dihydroxybenzoic acid and MMC showed a significant reduction of MMC-induced MN frequency, while quercetin-3-O-glucopyranoside increased MN frequency compared to positive control cells (p < 0.05). Both compounds decreased NDI values but only at the highest tested concentration of quercetin-3-O-glucopyranoside it was of greater significance. In conclusion, all extracts from AV and AA and 3,5-dihydroxybenzoic acid showed protective effect, whereby aqueous AA demonstrated the highest protective effect on MMC- induced genomic instability, while quercetin-3-O-glucopyranoside showed co-mutagen effect. [ABSTRACT FROM AUTHOR]

This article demonstrates the electro erosion milling process in Al-SiC metal matrix composites. Material Erosion Rate (MER) and Tool Erosion Rate (TER) are measured which depict the productivity aspect of the process. Depth and width of the slots, surface roughness (Ra) is used to indicate the geometrical accuracy. Maximum MER (0.1097 mm3/min) is obtained at 5A. Maximum TER (0.65 µm/min) is obtained at 2.15A. Minimum Ra (2.13 µm) is obtained at 2.15A. Maximum MER (0.1194 mm3/min) is obtained at 100µs. Lowest TER (0.73µm/min) is obtained at 10µs. Lowest Ra (7.66µm) is obtained at Ton of 100µs. Jaya algorithm is used to optimize and create Pareto front from which the results are extracted and reported. Material removal mechanism has been detailed which includes melting / evaporating of matrix material, electrochemical dislodging of SiC grains. Better surfaces have crater diameters ranging from 40–50µm and the bigger craters are in the range of 100–150µm. [ABSTRACT FROM AUTHOR]

Mechanical properties of metal matrix nanocomposites mainly depend on the distribution, size, and inter-particle spacing of nanoparticles in the matrix. AZ91 alloy nanocomposites are fabricated by adding 0%, 0.5%, 1%, and 3% by weight of 50 nm size Al2O3 particles assisted by ultrasonic solidification technique. The grain size and particle distribution of nanocomposites are quantitatively studied using optical and scanning electron microscopy. Less agglomeration and better distribution of nano-sized particles are observed even up to 3 wt% addition. Indentation creep tests are performed on the as-cast base alloy and prepared nanocomposites at a temperature of 498 K using three different applied stresses of 222 MPa, 305 MPa and 388 MPa. Better distribution of alumina nanoparticles resulted in significant increase in the tensile strength and creep resistance of nanocomposites over that of the as-cast alloy. AZ91/3 wt% alumina composite exhibited the highest creep resistance. [ABSTRACT FROM AUTHOR]

Generally, circulating current is generated in a Modular Multilevel Converter (MMC) by fluctuations in the capacitor voltage of sub-modules. Therefore, this research work seeks to build the Photo Voltaic (PV) integrated MMC-High-Voltage Direct Current (HVDC) systems with optimal H-infinity controller which is appropriate for 3-phase system. To verify the unstable voltages of sub-modules, the reference current is initially set to zero, as well as the unstable currents in each phase are monitored with a current sensor as well as contrasted to the reference current, resulting in the generation of an incorrect circulating current. The main contribution is to reduce the error among the reference current as well as the actual circulating current. In the H-infinity controller, the gains are optimally tuned via a new hybrid algorithm referred as Jaya Optimization Insisted Explored Chimp (JOI-EC) algorithm, which is the hybridized version of the Jaya Optimization Algorithm (JOA) and the Chimp Optimization Algorithm (ChOA). Moreover, the performance of the proposed model is examined through control analysis, converter performance analysis, as well as capacitor voltage analysis in addition to the circulating current. The result of simulation shows the robust performance of the proposed controller with respect to minimum circulating current, voltage, and stability analysis. [ABSTRACT FROM AUTHOR]

The friction consolidation method successfully reinforced aluminum 7075 alloy (AA7075) with high-volume fractions (12 and 24 vol%) of titanium diboride (TiB2) by high pressure and severe plastic deformation at elevated temperatures. The consolidated AMCs have a uniform dispersion of submicron- and micron-sized TiB2 particles in the AA7075 matrix, with significant refinement of the matrix grain size and the particles. The addition of TiB2 significantly increases hardness by up to 50 %, Young’s modulus by up to 62 %, and ultimate tensile strength by up to 28 % to 672 MPa, while reducing ductility by 80 %. Wear resistance of 7075/24 vol% TiB2 improves seven-fold compared to baseline, making it comparable to that of carburized steels. Microstructure-based finite element modeling provided a theoretical strength limit of ∼730 MPa for the composites and indicated that high triaxiality in conjunction with severe equivalent plastic strain in a narrow area between the TiB2 particles led to early fracture initiations, limiting the ductility.

This study investigates a novel methodology to intricately craft a HAMMC and thoroughly examine its multifaceted mechanical and tribological characteristics. By combining silicon carbide (SiC) and fly ash as reinforcements, a unique identity is bestowed upon this hybrid composite, enhancing its structural integrity and functional attributes. Stir casting is the chosen methodology for fabricating this composite, favored for its economic viability and suitability for large-scale manufacturing. In this research, the emphasis is on developing a cost-effective composite that not only meets stringent economic considerations but also exhibits improved material properties. Within the realm of hybrid metal matrix composites, the well-regarded Al6061 takes on the role of the matrix material, while the synergistic inclusion of fly ash and SiC serves as reinforcing constituents. Three specimens with compostion 90% Al6061 + 5% SiC +5% Fly ash, 90% Al6061 + 10% SiC +6% Fly ash and 90% Al6061 + 15% SiC +7% Fly ash were fabricated. To unravel the intricacies of the fabricated Al6061 metal matrix composite, comprehensive tests are employed. These tests, including the Pin-on Disc test, Scratch test, Rockwell Hardness test, and Charpy Impact test, collectively work to unveil the nuanced tribological and mechanical behaviors encapsulated within this innovative alloy. The results indicated significant improvement in wear resistance in specimen comprising 78% Al6061 + 15% SiC +7% Fly Ash and volumetric loss found to have 0.96 g. Superior hardness characteristics and enhanced abrasion resistance found in 78% Al6061 + 15% SiC +7% Fly Ash than other two specimens. The highest impact strength exhibited in 90% Al 6,061 + 5% SiC +5% Fly ash specimen.

The voltage source converter (VSC) based HVDC (high voltage direct current system) offers the possibility to integrate other renewable energy sources (RES) into the electrical grid, and allows power flow reversal capability. These appealing features of VSC technology led to the further development of multi-terminal direct current (MTDC) systems. MTDC grids provide the possibility of interconnection between conventional power systems and other large-scale offshore sources like wind and solar systems. The modular multilevel converter (MMC) has become a popular technology in the development of the VSC-MTDC system due to its salient features such as modularity and scalability. Although, the employment of MMC converter in the MTDC system improves the overall system performance. However, there are some technical challenges related to its operation, control, modeling and protection that need to be addressed. This paper mainly provides a comprehensive review and investigation of the control and protection of the MMC-based MTDC system. In addition, the issues and challenges associated with the development of the MMC-MTDC system have been discussed in this paper. It majorly covers the control schemes that provide the AC system support and state-of-the-art relaying algorithm/ dc fault detection and location algorithms. Different types of dc fault detection and location algorithms presented in the literature have been reviewed, such as local measurement-based, communication-based, traveling wave-based and artificial intelligence-based. Characteristics of the protection techniques are compared and analyzed in terms of various scenarios such as implementation in CBs, system configuration, selectivity, and robustness. Finally, future challenges and issues regarding the development of the MTDC system have been discussed in detail.

The integration of renewable energy sources in Medium-/High-voltage DC grids has called up continuous research to develop DC-DC conversion systems. This paper presents a hybrid modular multilevel DC-DC converter topology which successfully overcomes the issue of capacitors voltage imbalance during DC-DC conversion. In the proposed topology, single MMC leg is employed with half-bridge submodules in the upper arm and full-bridge submodules in the lower arm along with soft-switched high-voltage valves. The proposed hybrid modular multilevel converter has inherited arm energy equalization with the help of the parallel connectivity of involved arms’ capacitors. During the equalization period, the series-connected upper arm capacitors are connected in parallel to the series-connected lower arm capacitors to transfer the energy between the involved arms which results in operating with balanced capacitors voltages. The proposed modular DC-DC converter is a bidirectional converter which allows power flow from high-voltage side to low-voltage side and vice versa, i.e., it can be operated successfully as a DC transformer. The operational concept of the proposed configuration, control strategy, and parameters design are presented. Simulation results are presented along with experimental results of a scaled-down prototype to validate the proposed approach. Simulation and experimental results show the viability of the suggested approach.

South Africa's 2016 medical male circumcision (MMC) guidelines ("the guidelines") provide direction for the MMC programme's implementation in South Africa. The aim of our document analysis was to assess the guidelines, particularly in lieu of changing guidance from WHO and PEPFAR. We then assessed how the guidelines might be applied to infant and child male circumcision (ICMC). The analysis was performed by reviewing South Africa's guidelines, along with international documents used in developing those guidelines, to identify the historical development of the guidelines, as well as the implications for MMC and ICMC decision-making within the South African context. The following principles were analysed within the context of South Africa's guidelines: (1) quality and safety; (2) informed consent; (3) confidentiality; (4) human rights; and (5) accessibility of services. Tthe document analysis also identified ambiguities that exist in the guidelines, particularly regarding consent, recognising religious or cultural exemptions, and guaranteeing the best interests of the child. South Africa's MMC guidelines could benefit from incorporating common definitions to assist with interpretation and understanding, thus preventing confusion and controversy among programme planners, parents and boys. The guidelines were made available in 2016 and recommendations for circumcision have evolved as new research and information has become available. South Africa's National Department of Health should review and update these guidelines, with a focus on both MMC and ICMC issues, so that they reflect the most up-to-date, accurate information available, to avoid inconsistent practices, risks, and litigation in the management of the programme. This study was situated within a qualitative paradigm and applied a social choice theory perspective to make sense of the MMC guidelines. The study concludes that future policy revisions should develop a broader understanding of the complex medical male circumcision decision-making process, particularly faced by parents. [ABSTRACT FROM AUTHOR]

The performance of a Half Bridge (HB) Modular Multilevel Converter (MMC) for D-STATCOM application is studied in this article. For the control of MMC switches, the Carrier-Based (CB) Pulse Width Modulation (PWM) scheme has been selected as the appropriate method. There are two types of CB PWM schemes such as phase shift and level shift. Phase Disposition (PD), Phase Opposition Disposition (POD), and Alternate Phase Opposite Disposition (APOD) are the three different types of PWM that are used in level shifts. The PD CB PWM is projected in this work due to its simplicity and accuracy. The conventional PI Controller (PIC) has its disadvantages, including that it is time-consuming and comes with complexity in the estimation of gain values. Hence, the Cuttlefish Optimization Scheme (COS) is proposed for the online tuning of the PI gain values. The verification of performance parameters, including active power, reactive power, DC voltage balance, and Total Harmonic Distortion (THD), is effectively conducted using the COS method and subsequently compared with the conventional PIC. The suggested research is executed using the Matlab/Simulink software package. [ABSTRACT FROM AUTHOR]

The integration of renewable energy sources in Medium-/High-voltage DC grids has called up continuous research to develop DC-DC conversion systems. This paper presents a hybrid modular multilevel DC-DC converter topology which successfully overcomes the issue of capacitors voltage imbalance during DC-DC conversion. In the proposed topology, single MMC leg is employed with half-bridge submodules in the upper arm and full-bridge submodules in the lower arm along with soft-switched high-voltage valves. The proposed hybrid modular multilevel converter has inherited arm energy equalization with the help of the parallel connectivity of involved arms' capacitors. During the equalization period, the series-connected upper arm capacitors are connected in parallel to the series-connected lower arm capacitors to transfer the energy between the involved arms which results in operating with balanced capacitors voltages. The proposed modular DC-DC converter is a bidirectional converter which allows power flow from high-voltage side to low-voltage side and vice versa, i.e., it can be operated successfully as a DC transformer. The operational concept of the proposed configuration, control strategy, and parameters design are presented. Simulation results are presented along with experimental results of a scaled-down prototype to validate the proposed approach. Simulation and experimental results show the viability of the suggested approach. [ABSTRACT FROM AUTHOR]

This study presents a performance analysis of a half-bridge commutation cell using MATLAB/Simulink simulations. The behavior of IGBTs as semiconductor switches is examined under diverse load conditions, and the power losses, including conduction and switching losses, of two IGBT models, IXGH25N120 and IRG7IA19UPbF, are evaluated. A simulation-based design methodology is proposed for selecting suitable IGBTs for the half-bridge commutation cell. The comparative analysis reveals that the IXGH25N120 IGBT is well-suited for high-performance applications, while the IRG7IA19UPbF IGBT is optimized for energy recovery circuits. Furthermore, it is observed that IGBT1 (IXGH25N120) exhibits higher power losses due to its significant conduction losses compared to IGBT2 (IRG7IA19UPbF). The IGBT2 exhibits low conduction losses but has dominant switching losses due to high switching frequency. The utilization of a simulation-based approach provides valuable insights into the influence of IGBT characteristics on the responses of the half-bridge commutation cell, enabling an enhanced understanding for the design and performance analysis of the cell within the context of MMC. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the long-term efficacy and safety of the novel method sutureless trabeculectomy with topical administration of bevacizumab. Materials/Methods: Primary open-angle glaucoma patients with intraocular pressure (IOP) > 21 mmHg despite maximum tolerated medication were included in a single-blind prospective interventional clinical trial. Group 1 underwent sutureless scleral tunnel trabeculectomy with intraoperative topical administration of bevacizumab (1.25 mg) applied on the scleral incision for 1 min. Group 2 underwent sutureless trabeculectomy alone and group 3 (control group) underwent conventional trabeculectomy with mitomycin C (MMC). Outcome measures were surgical success, IOP, number of needed anti-glaucoma medications, and complications. Patients were followed for two years. Results: Finally, 50 eyes from group 1, 46 from group 2, and 47 from group 3 were analyzed. At the end of 24 months, 52% (n = 26) of group 1, 34.8% (n = 16) of group 2, and 57.4% (n = 27) of group 3 had complete success (IOP < 18 mmHg without medication). The difference was only significant between groups 2 and 3 (p = 0.003). 94% (n = 47) of group 1, 89.1% (n = 41) of group 2, and 91.5% (n = 43) of group 3 had qualified success (IOP < 18 mmHg with ≤ 2 anti-glaucoma medications) (p = 0.69). There was a significant difference in the overall IOP mean between the three groups (p < 0.0001). There was no significant difference between the three groups in complication rates and the number of needed anti-glaucoma medications for IOP control. Conclusion: Sutureless trabeculectomy with topical application of bevacizumab showed comparable surgical success rates with conventional trabeculectomy and MMC in long-term follow-up. Additionally, adjuvant use of topical bevacizumab had a significant positive impact on long-term IOP control. [ABSTRACT FROM AUTHOR]