Analysis of steering performance of differential coupling wheelset

In order to improve the curving performance of the conventional wheelset in sharp curves and resolve the steering ability problem of the independently rotating wheel in large radius curves and tangent lines, a differential cou- pling wheelset （DCW） was developed in this work. The DCW was composed of two independently rotating wheels （IRWs） coupled by a clutch-type limited slip differential. The differential contains a static pre-stress clutch, which could lock both sides of IRWs of the DCW to ensure a good steering performance in curves with large radius and tangent track. In contrast, the clutch could unlock the two IRWs of the DCW in a sharp curve to endue it with the characteristic of an IRW, so that the vehicles can go through the tight curve smoothly. To study the dynamic performance of the DCW, a multi-body dynamic model of single bogie with DCWs was established. The self-centering capability, hunting stability, and self-steering performance on a curved track were analyzed and then compared with those of the conventional wheelset and IRW. Finally, the effect of coupling parameters of the DCW on the dynamic performance was investigated.

BER Performance of FSO Communication System with Differential Signaling over Correlated Atmospheric Turbulence Fading

Free space optical(FSO) communication system with differential signaling possesses the advantage of requiring no channel state information and avoiding computational load or link throughput reduction compared to the systems with conventional receivers. In this work, we investigate bit error rate(BER) performance of this system over partially and fully correlated atmospheric turbulence fading. In order to conduct the above analysis, we obtain a probability density functions(PDF) of the channel fading on the differential signals and derive our instantaneous BER using differential signaling scheme. Based on these results, we develop two closed-form mathematical expressions for the average BER under fully correlated and partially correlated fading in the convergent infinite series confirmed by Cauchy’s ratio test. The accuracy of the derived BER expressions is demonstrated by the Monte Carlo simulations, and the analyses for the effects of the system parameters on the BER performance are provided.

Multi-user performance analysis of differential frequency hopping system over Rayleigh-fading channel

A novel non-coherent detection scheme for differential frequency hopping(DFH)system is proposedin asynchronous multi-user environments over Rayleigh-fading channels.The synchronous and asyn-chronous multi-user performances of DFH with the conventional detection scheme and this novel detectionscheme are analyzed,respectively.The performance results are validated with simulation.The results ofanalyses and simulations prove two conclusions.Firstly,the performance of asynchronous multi-user DFHsystem overcomes that of synchronous multi-user DFH system over Rayleigh-fading channel.Secondly,the novel detection scheme can achieve better performance than the conventional non-coherent detectionscheme in asynchronous multi-user environments.

High Performance Bilinear Differential Preamplifier for BESⅢ Time-of-Flight System

A time-of-flight (TOF) detector has been used in the BESIII experiment to provide charged particle identification. In this paper, we present a novel high performance differential amplifier, which has been designed for amplifying the signals from the detectors. The preamplifier can amplify differential signals, which can help to eliminate the common mode pickup, and increase the signal-to-noise ratio (SNR). Bilinear gain is one of the features of this preamplifier, which greatly increases the dynamic range and avoids the dead time of the preamplifier. In order to describe the bilinear gain, a 4-parameter function is developed. And this 4-parameter function can also be used in the calibration of the time walk caused by the amplitude due to the bilinear gain. The preamplifier has a gain about 10V/V with a small signal and about 1.0V/V with a large signal. The rise time of the preamp is less than 2 ns.

A Study on the Effects of Internal Heat Generation on the Thermal Performance of Solid and Porous Fins using Differential Transformation Method

In this study,the impacts of internal heat generation on heat transfer enhancement of porous fin is theoretical investigated using differential transform method.The parametric studies reveal that porosity enhances the fin heat dissipating capacity but the internal heat generation decreases the heat enhancement capacity of extended surface.Also,it is established that when the internal heat parameter increases to some certain values,some negative effects are recorded where the fin stores heat rather than dissipating it.This scenario defeats the prime purpose of the cooling fin.Additionally,it is established in the present study that the limiting value of porosity parameter for thermal stability for the passive device increases as internal heat parameter increases.This shows that although the internal heat parameter can help assist higher range and value of thermal stability of the fin,it produces negative effect which greatly defeats the ultimate purpose of the fin.The results in the work will help in fin design for industrial applications where internal heat generation is involved.

Differentiation-Based Analysis of Environmental Management and Corporate Performance

By building a duopoly model based on product differentiation, both of the clean firm＇s and the dirty firm＇s performances are studied under the assumptions that consumers have different preferences for the product environmental attributes, and that the product cost increases with the environmental attribute. The analysis results show that under either the case with no environmental regulation or that with a tariff levied on the dirty product, the clean firm would always get more profit. In addition, the stricter the regulation is, the more profit the clean finn would obtain. This can verify that from the view of product differentiation, a firm could improve its corporate competitiveness with environmental management.

Spatial Differentiation and Influencing Factors of Poverty Alleviation Performance Under the Background of Sustainable Development:A Case Study of Contiguous Destitute Areas in Hunan Province,China

Poverty eradication is a realistic requirement for the addressing of the urban-rural development imbalance.It consolidates the achievements of the poverty alleviation,and accelerates the realization of the United Nations Sustainable Development Goals.In research that deals with poverty,qualitative analysis is often used to study the connection between a single influencing factor and poverty reduction,and to solve regional poverty through government measures.However,these studies usually ignore the multidimensional nature of poverty,and the fact that poverty alleviation also needs to be approached from multiple perspectives.By constructing a theoretical framework of poverty alleviation performance from the perspective of sustainable development,this study selects contiguous poverty-stricken areas in the Hunan Province,China as the empirical study area,constructs an evaluation index system from the three dimensions of economic development,infrastructure and people’s livelihood security,and selects influencing factors from three aspects of‘population’,‘land’and‘industry’.The spatial differentiation characteristics and influencing factors of poverty alleviation performance in poverty-stricken areas were studied by using the methods of entropy weight method and geodetector.The results show:firstly,in the concentrated and contiguous poverty-stricken areas of the Hunan Province,the performance of poverty alleviation in the economic development makes little difference,showing a‘high-medium-low’cross-distribution pattern.The poverty alleviation performance of the infrastructure presents a distribution pattern of‘low in the middle and high on both sides.The poverty alleviation performance of people’s livelihood security has significant spatial differentiation characteristics,which all present a reunion distribution.The overall poverty alleviation performance varies greatly,showing a funnel-shaped distribution in space.Secondly,the spatial differentiation of poverty alleviation performance in the concentrated and contiguous poverty-stricken areas of the Hunan Province is the result of the combined effects of multiple factors.‘Population’is the dominant factor affecting the performance of poverty alleviation,‘land’is the basic factor that causes the spatial differentiation of poverty alleviation performance,and‘industry’is the key factor for the improvement of the poverty alleviation ability.

Power supply arm protection scheme of high-speed railway based on wide-area current differential

When fault occurs on cross-coupling autotransformer(AT)power supply traction network,the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity,which leads to an extended power failure.Based on equivalent circuit and Kirchhoff’s current law,the feeder current characteristic in the substation,AT station and sectioning post when T-R fault,F-R fault,and T-F fault occur are analyzed and their expressions are obtained.When the traction power supply system is equipped with wide-area protection measurement and control system,the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed.When a short-circuit fault occurs in the power supply arm,all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations.After data synchronous processing and logic judgment,the fault line of the power supply arm can be identified and isolated quickly.The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions,transition resistances,and fault types.The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit(EMU),and reliability,selectivity,and rapidity of relay protection are all improved.

Relationship Between Differential Gene Expression and Heterosis During Ear Development in Maize (Zea mays L.)

Maize （Zea raays L.） is one of the most important crops because of the remarkable properties of its hybrid, which is responsible for the high commercial value of hybrid maize. The genetic basis of heterosis （hybrid vigor） is not well understood. A differential display technique was performed to identify genes with differential expression across twelve maize inbred lines and thirty-three hybrids during ear development. An incomplete diallel design was used to investigate the relationship between the global framework of differential gene expression and heterosis. It was found that the genes belonging to MONO pattern （i.e., genes expressed in both parental lines and in hybrid） was the highest in percentage among the total five patterns and illustrated that the properties of differentially expressed genes are not entirely responsible for heterosis. Furthermore,a larger number of differentially expressed genes in hybrid, which serves as a major reservoir for generating novel phenotypes that exhibit heterosis of certain agronomic traits during early development and differentiation of maize ear. Moreover, there were some silent genesin hybrids that are responsible for the arrest or abortion of spikelets and for the increase in kernels weight.

NEW TYPE OF LIMITED-SLIP DIFFERENTIAL WITH THREE-PITCH FLUCTUATING SPEED RATIO

A type of three-pitch fluctuating speed ratio limited-slip differential （TPLSD） is presented for the first time, analyzed its working principle, introduced the tooth profile design method of using non-involute tooth profile and separated tooth profile design along the pitch line. Performance comparison between vehicles equipped with three-pitch fluctuating speed ratio limited-slip differential and common open differefitial is finished. The data from experiments prove that three-pitch fluctuating speed ratio limited-slip differential can increase the traction of a vehicle, improve its acceleration performance, decrease braking distance and limit sideslip. The basic structure of new differential is the same of open differential, the only difference is that they have different tooth profile, so the new differential has a high performance price.

Extended differential geometric guidance law for intercepting maneuvering targets

Without assumptions made on motion states of missile and target, an extended differential geometric guidance law is derived. Through introducing a line of sight rotation coordinate system, the derivation is simplified and has more explicit physical significances. The extended law is theoretically applicable to any engagement scenarios. Then, on basis of the extended law, a modified one is designed without the requirement of target acceleration and an approach is proposed to determining the applied direction of commanded missile acceleration. Qualitative analysis is carried out to study the capture performance and a criterion for capture is given. Simulation results indicate the two laws are effective and make up the deficiency that pure proportional navigation suitable for endoatmospheric interceptions cannot deal with high-speed maneuvering targets. Furthermore, the correctness of the criterion is validated.

Robust Adaptive Attitude Maneuvering and Vibration Reducing Control of Flexible Spacecraft with Prescribed Performance

A robust adaptive control scheme with prescribed performance is proposed for attitude maneuver and vibration suppression of flexible spacecraft,in which the parametric uncertainty,external disturbances and unmeasured elastic vibration are taken into account simultaneously.On the basis of the prescribed performance control(PPC)theory,the prescribed steady state and transient performance for the attitude tracking error can be guaranteed through the stabilization of the transformed system.This controller does not need the knowledge of modal variables.The absence of measurements of these variables is compensated by appropriate dynamics of the controller which supplies their estimates.The method of sliding mode differentiator is introduced to overcome the problem of explosion of complexity inherent in traditional backstepping design.In addition,the requirements of knowing the system parameters and the unknown bound of the lumped uncertainty,including external disturbance and the estimate error of sliding mode differentiator,have been eliminated by using adaptive updating technique.Within the framework of Lyapunov theory,the stability of the transformed system is obtained.Finally,numerical simulations are carried out to verify the effectiveness of the proposed control scheme.

A BALUN-BANDPASS FILTER WITH GOOD IN-BAND PERFORMANCE AND WIDE STOPBAND

A high performance Balun BandPass Filter (BPF) with capacitively loaded multiple coupled lines with very simple structure is proposed in this paper, this structure realizes simultaneous size reduction and superior harmonic response suppression performance in bandpass filtering meanwhile good differential performance of the Balun. The theory of this structure for unbalanced input into balanced output has been studied in this paper and a proper Balun and BPF characteristic by the symmetric feeding and skew symmetric feeding have been obtained to prove the theory. The enter frequency of the fabricated Balun-BPF is operated at 2.45 GHz with 6.93% Fractional Band Width (FBW), and this frequency is used for Bluetooth and some other communication systems. The differences between the two outputs are 180°± 1.92° in phase and within 0.33 dB in magnitude. At f0, the amplitude imbalance and phase difference are within 0.25 dB and 180.86°, respectively. The measured frequency responses agree well with the simulated ones. With the theoretical analyses and practical results, it is shown that the proposed one has the advantages of simple structure, convenient analysis and good performance of both BPF and Balun.

Improvements on Analytical Models for IEEE 802.11e EDCF Differential Services

Zhu introduced typical analytical models to simulate the 802. 11e EDCF channel access protocol. But our analysis indicates that there are some inaccurate derivations in his presentation. This paper intends to improve analytical model with some corrections. Furthermore, for the probability of the channel being busy pb in Zhu＇s model, different points and analysis method are proposed. When the network is under saturation condition, the new results about the probabilities of collision and channel busy, transmission probabilities, successful transmission probabilities, throughput and MAC layer latency are presented.

Effect of Product Differemiation on Business Model Performance in B2B Market

Focusing on B2B market, this paper studies the effect of product differentiation on business model perlbrmance. After interviewing several experts and analyzing numbers of distributing questionnaires. the author discovered that product differentiation has a positive effect on business model performance. Through SEM. it is revealed that product differentiation at each level have positive effect on business model, with different effect weight. The main contributions of this research are summarized as follows： Firstly, the proposed model of the product differentiation on business model performance lays the basis for scientific measurement of product differentiation and its effect on business model performance; Secondly, this research ranks the importance of product differentiation at different level in B2B market; Finally, this research provides a good reference for enterprises to update their product strategy for better business model performance.

Joint TDOA, FDOA and differential Doppler rate estimation： Method and its performance analysis

Considering the estimation accuracy reduction of Frequency Difference of Arrival （FDOA） caused by relative Doppler companding, a joint Time Difference of Arrival （TDOA）, FDOA and differential Doppler rate estimation method is proposed and its Cramer-Rao low bound is derived in this paper. Firstly, second-order ambiguity function is utilized to reduce the dimensionality and estimate initial TDOA and differential Doppler rate. Secondly, the TDOA estimation is updated and FDOA is obtained using cross ambiguity function, in which relative Doppler com- panding is compensated by the existing differential Doppler rate. Thirdly, differential Doppler rate estimation is updated using cross estimator. Theoretical analysis on estimation variance and Cramer-Rao low bound shows that the final estimation of TDOA, FDOA and differential Doppler rate performs well at both low and high signal-noise ratio, although the initial estimation accuracy of TDOA and differential Doppler rate is relatively poor under low signal-noise ratio conditions. Simulation results finally verify the theoretical analysis and show that the proposed method can overcome relative Doppler companding problem and performs well for all TDOA, FDOA and differential Doppler rate estimation.

Differential variable speed limits to improve performance and safety of car-truck mixed traffic on freeways

This study develops a differential variable speed limit(DVSL)which assigns different speed limits for car and truck,and varies speed limits based on traffic conditions.The proposed DVSL algorithm changes speed limits in real time based on truck percentage and occupancy immediately upstream of the ramp and the average speed of the control road sections upstream of the ramp.DVSL algorithm also considers spatial coordination of speeds,which gradually changes the speed limits in successive road sections upstream of the ramp when the severe congestion occurs.The study tested the impacts of DVSL and three other speed limit strategies on delay and safety for a section of the Gardiner Expressway in Toronto,Canada using the VISSIM traffic simulation model.The other strategies are 1)uniform speed limit(USL),2)differential speed limit for car and truck(DSL),and 3)USL&DSL(U&D)-i.e.,USL at low truck percentage and DSL at high truck percentage.It was found that DVSL showed the lowest delays for both car and truck among the four strategies.This is mainly because DVSL increased the spacing between vehicles in the right lane upstream of the on-ramp and facilitated vehicles’merging into the mainline freeway.It was also found that DVSL showed the lowest likelihood of rear-end crash between the lead and following vehicles among the four strategies.This study demonstrates that the proposed DVSL algorithm can better control car and truck speeds to reduce delay and improve safety of car-truck mixed traffic flow on freeways.

由规模化到精准化:国家中小学智慧教育平台教师研修的差异化需求及优化策略研究

立足常态化的新发展阶段,国家智慧教育平台教师寒暑假研修如何从规模化走向差异化、精准化,“按需施训”尤为关键。研究以基础教育阶段参训教师的9.06万条、149万余字反馈文本为研究对象,综合运用结构主题模型(STM)及重要性-绩效分析法(IPA),构建了国家中小学智慧教育平台教师研修需求框架,并深入分析其差异、明确基于需求要素的优化方向。研究发现:参训教师需求包含个体发展和系统环境两个层面的五类需求,且均存在显著的区域及城乡差异,针对时间安排及学时认定等研修机制需求仍须优化改进。研究为教师寒暑假研修精准化、差异化发展提供实证依据与决策支持,为优化研修服务提供策略建议。

差异性战略企业社会责任对财务绩效的影响 ——来自精准扶贫的启示

基于2016—2019年A股上市公司精准扶贫项目支出数据,采用Heckman二阶段模型实证考察了差异性战略企业社会责任对财务绩效的影响,并检验了企业能力与企业所有权属性的差异性影响,结果显示:第一,企业社会责任作为一种差异性战略可以促进企业财务绩效的提升;第二,企业能力越强,越能够在差异性战略企业社会责任活动中同时促进社会绩效和财务绩效的提升;第三,相对于国有企业而言,民营企业更善于发挥战略性企业社会责任的战略效果。研究结果表明,企业社会责任可以作为一种差异性战略,使企业获得差异性竞争优势,进而促进财务绩效提升。企业结合不同的战略履行企业社会责任具有一定的现实意义。

无伴随运动2PRU-PRUR并联机构高维多目标优化设计

设计了一种无伴随运动的面对称一移动两转动2PRU-PRUR并联机构,应用旋量理论分析了机构自由度和运动特性。将末端执行器输出轴设置为偏置形式,可提高姿态能力。采用球面姿态角(方位角和倾摆角)描述该输出轴姿态,并推导出机构逆向位置符号解。以旋量理论为数学工具,给出局部和全域传递性能指标的定义和计算方法。在机构性能评价和工作空间分析的基础上,建立了机构尺度参数昂贵约束高维多目标优化模型,并采用多目标进化算法求解该问题。同时,为提高高维多目标优化算法在解决此模型时的性能,提出了一种矢量角高维多目标差分进化(Vector-angle-based many-objective Differential Evolution,VaDE)算法,可综合平衡个体的收敛性和分布性。应用VaDE求解机构高维多目标优化问题,得到多组Pareto备选解。研究结果可为机构尺度综合和实际应用提供参考。