Multilevel carbon architecture of subnanoscopic silicon for fast‐charging high‐energy‐density lithium‐ion batteries

Silicon(Si)is widely used as a lithium‐ion‐battery anode owing to its high capacity and abundant crustal reserves.However,large volume change upon cycling and poor conductivity of Si cause rapid capacity decay and poor fast‐charging capability limiting its commercial applications.Here,we propose a multilevel carbon architecture with vertical graphene sheets(VGSs)grown on surfaces of subnanoscopically and homogeneously dispersed Si–C composite nanospheres,which are subsequently embedded into a carbon matrix(C/VGSs@Si–C).Subnanoscopic C in the Si–C nanospheres,VGSs,and carbon matrix form a three‐dimensional conductive and robust network,which significantly improves the conductivity and suppresses the volume expansion of Si,thereby boosting charge transport and improving electrode stability.The VGSs with vast exposed edges considerably increase the contact area with the carbon matrix and supply directional transport channels through the entire material,which boosts charge transport.The carbon matrix encapsulates VGSs@Si–C to decrease the specific surface area and increase tap density,thus yielding high first Coulombic efficiency and electrode compaction density.Consequently,C/VGSs@Si–C delivers excellent Li‐ion storage performances under industrial electrode conditions.In particular,the full cells show high energy densities of 603.5 Wh kg^(−1)and 1685.5 Wh L^(−1)at 0.1 C and maintain 80.7%of the energy density at 3 C.

On the Use of Monotonicity-Preserving Interpolatory Techniques in Multilevel Schemes for Balance Laws

Cost-effective multilevel techniques for homogeneous hyperbolic conservation laws are very successful in reducing the computational cost associated to high resolution shock capturing numerical schemes.Because they do not involve any special data structure,and do not induce savings in memory requirements,they are easily implemented on existing codes and are recommended for 1D and 2D simulations when intensive testing is required.The multilevel technique can also be applied to balance laws,but in this case,numerical errors may be induced by the technique.We present a series of numerical tests that point out that the use of monotonicity-preserving interpolatory techniques eliminates the numerical errors observed when using the usual 4-point centered Lagrange interpolation,and leads to a more robust multilevel code for balance laws,while maintaining the efficiency rates observed forhyperbolic conservation laws.

A Comparison of Control Methods for Z-Source Inverter

In recent years, Z-source inverters (ZSI) have been proposed as an replacement power conversion concept which it has both voltage buck and boost abilities. In addition, ZSI doesn’t require dead-time to protection short circuit at two switches any of the same phase leg in the inverter bridge and to achieve optimal harmonic of current, voltage. This paper presents two different control methods (CM) for ZSI. The aim of this study to compare between two modulation methods, there are modi?ed space vector pulse width modulation method (MSVM) and the simple boost control (SBC) about the unique harmonic performance features, the total average and peak switching device power of the inverter system. In addition, this paper also analyzes about the ability exceed modulation index in linear region of two CM using MATLAB/Simulink.

Mechanical response and microscopic damage mechanism of pre-flawed sandstone subjected to monotonic and multilevel cyclic loading:A laboratory-scale investigation

This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how coplanar flaw angle and load type impact the strength and deformation behavior and microscopic damage mechanism.Results indicated that being fluctuated before rising with increasing fissure angle under monotonic loading,the peak strength of the specimen first increased slowly and then steeply under cyclic loading.The effect of multilevel cyclic loading on the mechanical parameters was more significant.For a single fatigue stage,the specimen underwent greater deformation in early cycles,which subsequently stabilized.Similar variation pattern was also reflected by AE count/energy/b-value.Crack behaviors were dominated by the fissure angle and load type and medium-scale crack accounted for 74.83%–86.44%of total crack.Compared with monotonic loading,crack distribution of specimen under cyclic loading was more complicated.Meanwhile,a simple model was proposed to describe the damage evolution of sandstone under cyclic loading.Finally,SEM images revealed that the microstructures at the fracture were mainly composed of intergranular fracture,and percentage of transgranular fracture jumped under cyclic loading due to the rapid release of elastic energy caused by high loading rate.

A Comparative Study of Z-source Inverter and Enhanced Topologies

This paper does some theoretical analysis and simulation studies on the most common topologies of Z-source inverter.As we all know,the traditional Z-source inverter has some problems,such as the voltage of the capacitor which belongs to this topology is higher and there is a startup shock,which caused researchers proposed a variety of improved Z-source topologies to solve these problems.Some of these topologies can increase boost capacity,and some can reduce the capacitor voltage.However,these topologies can improve only part of the problems of the traditional Z-source inverter,which leads to that the users are hard to choose which topologies.Faced with this situation,eleven Z-source topologies are analyzed in terms of boost capacity,inductance start-up current,capacitance stress and economy in this paper.Finally,two kinds of promising topologies were gotten.

The Control Technology Research of the Z-source Three-phase Four-bridge Arm Inverter

Z-source inverter can boost the voltage of the DC-side, allow the two switches of the same bridge arm conducting at the same time and it has some other advantages. The zero-sequence current flows through the fourth leg of the three-phase four-leg inverter so the three-phase four-leg inverter can work with unbalanced load. This paper presents a Z-source three-phase four-leg inverter which combines a Z-source network with three-phase four-leg inverter. The circuit uses simple SPWM modulation technique and the fourth bridge arm uses fully compensated control method. The inverter can maintain a symmetrical output voltage when the proposed scheme under the unbalanced load.

A Review on Industrial Applications of Z-Source Inverter

Nowadays, Z-source inverters (ZSI) are one of the most emerging topologies in field of power electronics. This paper deals with brief review of Z-source inverter, comprehensive study of its various topologies and significance of ZSI in modern industry. Different PWM techniques are used to obtain wider modulation range and easier real time implementation. This paper provides a systematic reference for future scientists for further development and advancement of ZSI.

A New Switching Scheme for Z-source Inverter to Minimize Ripples in the Z-source Elements

This paper presents a modification in pulse width modulation （PWM） scheme with unequal shoot-through distribution for the Z-source inverter （ZSI） which can minimize ripples in the current through the Z-source inductors as well as the voltage across the Z-source capacitors. For the same system parameters, the proposed control technique provides better voltage boost across the Z-source capacitor, DC-link, and also the AC output voltage than the traditional PWM. The ripples in the Z-network elements are found to be reduced by 75 % in the proposed modulation scheme with optimum harmonic profile in the AC output. Since the Zqnetwork requirement will be based on the ripple profile of the elements, the Z-network requirements can be greatly reduced. The effectiveness of the proposed modulation scheme has been simulated in Matlab/Simulink software and the results are validated by the experiment in the laboratory.

Practical Implementation of Embedded Controlled Reduced Switch Z-Source Inverter-Fed Induction Motor Drive

A cost-effective component minimized embedded controlled Z-source inverter for induction motor drive is presented. The proposed topology combines the advantages of a traditional four-switch three-phase inverter with the advantages of the z impedance network (two inductors in series and two X connected capacitors). This new topology, besides the self-boost property, has low switch count and it can operate as a buck-boost inverter. As a result, the new embedded controlled reduced switch Z-source inverter system provides ride through capability during voltage sags, reduces line harmonics, improves power factor, reliability and extends output voltage range. Analysis, simulation and experiment result will be presented to demonstrate these new features.

Control of Z-Source Inverter Connected to a Single-Phase AC Utility System

This paper presents a single-phase Z-source inverter as a power conditioning system for a single phase utility connected system. Z-source inverter is a single-stage topology that has buck-boost feature, which is possible because of additional shoot through state introduced in zero state of the conventional inverter pulse width modulation and provides desired output AC voltage. Small distributed generation （DG） system with alternate energy sources requires power conditioning units with low cost, high efficiency and tolerance to wide range of input voltage variation and has to perform various functions such as dc-ac conversion, system control and achieve power quality norms. To meet some of these requirements a two-loop control strategy for ac side control with grid current feedback with PI control and inner filter capacitor current feedback with proportional control and on dc side PID control for Z-source capacitor voltage regulation are employed, which gives good transient response also suppress load and source disturbances effectively. Theoretical analysis of proposed scheme is established and then simulation results are presented to validate proposed control strategy.

Enforcing a Source-end Cooperative Multilevel Defense Mechanism to Counter Flooding Attack

The exponential advancement in telecommunication embeds the Internet in every aspect of communication.Interconnections of networks all over the world impose monumental risks on the Internet.A Flooding Attack(FA)is one of the major intimidating risks on the Internet where legitimate users are prevented from accessing network services.Irrespective of the protective measures incorporated in the communication infrastructure,FA still persists due to the lack of global cooperation.Most of the existing mitigation is set up either at the traffic starting point or at the traffic ending point.Providing mitigation at one or the other end may not be a complete solution.To insist on better protection againstflooding attacks,this work proposes a cooperative multilevel defense mechanism.The proposed cooperative multilevel defense mechanism consists of two-level of mitigation.In thefirst level,it is proposed to design a Threshold-based rate-limiting with a Spoofing Resistant Tag(TSRT),as a source end countermeasure for High-Rate Flooding Attacks(HRFA)and spoofing attacks.In the second level,the accent is to discriminate normal traffic after Distributed Denial of Service(DDoS)traffic and drop the DDoS traffic at the destination end.Flow Congruence-based Selective Pushback(FCSP),as a destination-initiated countermeasure for the Low Rate Flooding Attack(LRFA).The source and the destination cooperate to identify and block the attack.A key advantage of this cooperative mechanism is that it can distinguish and channel down the attack traffic nearer to the starting point of the attack.The presentation of the agreeable cooperative multilevel safeguard mechanism is approved through broad recreation in NS-2.The investigation and the exploratory outcomes show that the proposed plan can effectively identify and shield from the attack.

Closed Loop Control of Bi-Directional Soft Switched Quasi Z-Source DC-DC Converter

Quasi Z-source converter is a single stage soft switched power converter derived from Z-source converter topology, employing an impedance network coupling the source with the converter. The quasi Z-source source converter can buck or boost the voltage and current flow is bidirectional. The duty cycle of the switch can be adjusted to maintain constant voltage during load change. To obtain constant output voltage, proper controller design is a must. This paper presents closed loop control of quasi Z-source converter using PI controller where controller parameters are estimated using the small signal model of the entire system. The transfer function of the system with AC sweep is used to obtain appropriate proportional and integral gain constants to reduce transient dynamics and to reduce steady state error.

Salp Swarm Algorithm with Multilevel Thresholding Based Brain Tumor Segmentation Model

Biomedical image processing acts as an essential part of severalmedical applications in supporting computer aided disease diagnosis. MagneticResonance Image (MRI) is a commonly utilized imaging tool used tosave glioma for clinical examination. Biomedical image segmentation plays avital role in healthcare decision making process which also helps to identifythe affected regions in the MRI. Though numerous segmentation models areavailable in the literature, it is still needed to develop effective segmentationmodels for BT. This study develops a salp swarm algorithm with multi-levelthresholding based brain tumor segmentation (SSAMLT-BTS) model. Thepresented SSAMLT-BTS model initially employs bilateral filtering based onnoise removal and skull stripping as a pre-processing phase. In addition,Otsu thresholding approach is applied to segment the biomedical imagesand the optimum threshold values are chosen by the use of SSA. Finally,active contour (AC) technique is used to identify the suspicious regions in themedical image. A comprehensive experimental analysis of the SSAMLT-BTSmodel is performed using benchmark dataset and the outcomes are inspectedin many aspects. The simulation outcomes reported the improved outcomesof the SSAMLT-BTS model over recent approaches with maximum accuracyof 95.95%.

Ride through Strategy for a Three-Level Dual Z-Source Inverter Using TRIAC

A new ride through strategy is introduced in a three-level dual Z-source inverter, for isolation under semiconductor switching failure condition. Here the output will have no significant decrease in the amplitude and quality. Instead of diodes, the triacs are added to the inverter source ends, as it can perform a bidirectional power transfer also it can operate well in both low and high voltage operating conditions. The faulted part can be isolated by simply altering the firing pulses for turning on/off the triacs using the carrier based SPWM technique and resulting in a boosting output with zero common mode voltage. Consequently, it forms a common floating point or null point with a zero common mode voltage. It is experimentally verified by using MATLAB, and digital oscilloscope.

A Multilevel Hierarchical Parallel Algorithm for Large-Scale Finite Element Modal Analysis

The strict and high-standard requirements for the safety and stability ofmajor engineering systems make it a tough challenge for large-scale finite element modal analysis.At the same time,realizing the systematic analysis of the entire large structure of these engineering systems is extremely meaningful in practice.This article proposes a multilevel hierarchical parallel algorithm for large-scale finite element modal analysis to reduce the parallel computational efficiency loss when using heterogeneous multicore distributed storage computers in solving large-scale finite element modal analysis.Based on two-level partitioning and four-transformation strategies,the proposed algorithm not only improves the memory access rate through the sparsely distributed storage of a large amount of data but also reduces the solution time by reducing the scale of the generalized characteristic equation(GCEs).Moreover,a multilevel hierarchical parallelization approach is introduced during the computational procedure to enable the separation of the communication of inter-nodes,intra-nodes,heterogeneous core groups(HCGs),and inside HCGs through mapping computing tasks to various hardware layers.This method can efficiently achieve load balancing at different layers and significantly improve the communication rate through hierarchical communication.Therefore,it can enhance the efficiency of parallel computing of large-scale finite element modal analysis by fully exploiting the architecture characteristics of heterogeneous multicore clusters.Finally,typical numerical experiments were used to validate the correctness and efficiency of the proposedmethod.Then a parallel modal analysis example of the cross-river tunnel with over ten million degrees of freedom(DOFs)was performed,and ten-thousand core processors were applied to verify the feasibility of the algorithm.

A Sensor-less Surface Mounted PMSM for Electronic Speed Control in Multilevel Inverter

Recent advancements in power electronics technology evolves inverter fed electric motors.Speed signals and rotor position are essential for controlling an electric motor accurately.In this paper,the sensorless speed control of surface-mounted permanent magnet synchronous motor(SPMSM)has been attempted.SPMSM wants a digital inverter for its precise working.Hence,this study incor-poratesfifteen level inverter to the SPMSM.A sliding mode observer(SMO)based sensorless speed control scheme is projected to determine rotor spot and speed of the multilevel inverter(MLI)fed SPMSM.MLI has been operated using a multi carrier pulse width modulation(MCPWM)strategy for generation offif-teen level voltages.The simulation works are executed with MATLAB/SIMU-LINK software.The steadiness and the heftiness of the projected model have been investigated under no loaded and loaded situations of SPMSM.Furthermore,the projected method can be adapted for electric vehicles.

Multilevel optoelectronic hybrid memory based on N-doped Ge_(2)Sb_(2)Te_(5)film with low resistance drift and ultrafast speed

Multilevel phase-change memory is an attractive technology to increase storage capacity and density owing to its high-speed,scalable and non-volatile characteristics.However,the contradiction between thermal stability and operation speed is one of key factors to restrain the development of phase-change memory.Here,N-doped Ge_(2)Sb_(2)Te_(5)-based optoelectronic hybrid memory is proposed to simultaneously implement high thermal stability and ultrafast operation speed.The picosecond laser is adopted to write/erase information based on reversible phase transition characteristics whereas the resistance is detected to perform information readout.Results show that when N content is 27.4 at.%,N-doped Ge_(2)Sb_(2)Te_(5)film possesses high ten-year data retention temperature of 175℃and low resistance drift coefficient of 0.00024 at 85℃,0.00170 at 120℃,and 0.00249 at 150℃,respectively,owing to the formation of Ge–N,Sb–N,and Te–N bonds.The SET/RESET operation speeds of the film reach 520 ps/13 ps.In parallel,the reversible switching cycle of the corresponding device is realized with the resistance ratio of three orders of magnitude.Four-level reversible resistance states induced by various crystallization degrees are also obtained together with low resistance drift coefficients.Therefore,the N-doped Ge_(2)Sb_(2)Te_(5)thin film is a promising phase-change material for ultrafast multilevel optoelectronic hybrid storage.

基于多层次模块化的金工实习教学改革与实践

金工实习是培养高校大学生工程能力与素养的重要实践环节之一,其课程内容的丰富性、课程体系的完善性、教学方法的先进性一直是当代高校极为重视的授课要素。该文围绕“以常规技能训练为主的基础训练平台,以学科技术训练为主的拓展训练平台,以学生能力发展为主的综合训练平台,以创新能力培养为主的创新训练平台”进行课程体系和实训项目的设计和执行。通过“基础-拓展-综合-创新”四个阶段,实施多层次模块化金工实习教学模式的改革与实践,为金工实习教学改革与实践研究提供借鉴和支持。

多层次领导力发展模型的构建及其有效性检验——基于扎根理论的探索性研究

领导力发展对企业人力资源开发和领导者培养至关重要,而关于领导力发展的具体内容和如何验证发展结果的有效性,一直存有争议。采用扎根理论的研究方法,对正在进行领导力发展计划的A企业进行深度访谈和现场研究,构建了一个多层次视角的领导力发展模型。该模型基于发展自我、发展团队、发展组织的多层次视角,提出了领导力的发展内容包括做人、做事、发展下属、凝聚团队、组织管理、业绩管理六个核心要素。进一步将该模型与“方向-协作-承诺”模型(DAC模型)做对比分析,研究结果表明“发展自我”激发承诺,“发展团队”产生方向、协作和承诺,“发展组织”促进方向和协作,从而验证了该领导力发展模型的有效性。

部分接入电池储能系统的模块化多电平换流器控制方法

部分接入电池储能系统的模块化多电平换流器(MMC with partly integrated BESS,MMCPBESS)可以在接入储能的同时节约建造成本,但其控制更加复杂。针对下桥臂接入储能电池的MMC-PBESS拓扑,建立数学模型及等效电路。在此基础上给出电容电压均衡策略,提出了上/下桥臂分控的控制策略,并分析了其运行边界。在MATLAB/Simulink平台搭建仿真模型,仿真了不同交直流功率比例的运行工况,所提控制策略可以在维持电容电压平衡的同时实现对电池充电的功能。该策略无需额外的环流计算,上下桥臂控制解耦,简单灵活。