Self-thinning lines and allometric relation in Chinese fir(Cunninghamia lanceolata) stands

We calculated a self-thinning exponent of 1.05 for tree mass using the 3/2 power equation in 93 Cunninghamia lanceolata plots.According to Weller’s allometric model,the self-thinning exponent for tree mass was calculated as 1.28 from the allometric exponents h and d.The both self-thinning exponents were significantly lower than 3/2.The self-thinning exponent of organs was estimated to be 1.42 for stems,0.93 for branches,0.96 for leaves,1.35 for roots and 1.28 for shoots,respectively.The self-thinning exponent of stem mass was not significantly different from 3/2,whereas thinning exponents of trees,branches,leaves and roots were significantly lower than 3/2.The stand leaf mass and stand branch mass were constant regardless of the stand density.The scaling relations among branch,leaf,stem,root and shoot mass（MB,ML,MS,MR and MA,respectively） showed that MB and ML scaled as the3/4 power of MS,whereas MS or MA scaled isometrically with respect to MR.

Indicator of climate variability:low treeline displacement in arid valleys of mountain areas,China

As climate change intensifies,finding an ecological indicator to quickly and accurately reflect the impact on mountain ecosystems is necessary.The low treeline/timberline,highly sensitive to climate variability and changes significantly within 5–10years,provides a new way to study the response to regional climate variability.This study explored the distribution and vertical displacement patterns of the low treeline in the Upper Minjiang River of China,using SPOT remote sensing images in 1999 and 2013and long-term positional observations.Using the Geodetector model,the study investigated the dominant climatic factors influencing the low treeline displacement.The results showed that the low treeline was located at 1700–3200 m elevation on sunny slopes(southeast,south,southwest,and west slopes)with slopes over 25°.From 1999 to 2013,the low treeline moved downward by 6 m from 2561±264m to 2555±265 m,along with a warm–humid climate tendency.The downward displacement was greater on slopes over 25°and shady slopes(-20 m and-10 m,respectively)than on slopes≤25°and sunny slopes.Additionally,the downward was greater in the warm and humid Zagunao River Basin(-15 m)compared to the arid valley center(-7 m)and the cold Heishui River Basin(-3 m).Meanwhile,the low treeline displacement correlated negatively with precipitation and relative humidity variations at the significance level of 0.05,with correlation coefficients of-0.572and-0.551,respectively.Variations in relative humidity and temperature significantly affected the spatial differentiation of low treeline displacement with influencing power of 0.246(p=0.036<0.05)and 0.183(p=0.032<0.05),respectively.Thus,the low treeline is a moisture-limited line,and its formation and variation are closely related to regional water–heat balance.The study clarifies the indicative value of the low treeline for climate variability in mountain areas and can provide references for ecological restoration in arid valleys.

Establishment and Optimization of Status Assessment Variables for Heavy Haul Railway Line Service Performance

In order to address the issues of complex system structure and variable selection difficulty for the current heavy haul railway line status evaluation system, a three-category and three-layer heavy-haul line status evaluation variable set construction and reduction optimization method is proposed. Firstly, the status of heavy haul railway line is analyzed, and an initial set of evaluation variables affecting the line status is constructed. Then, based on the association rule and the principal component analysis method, key variables are extracted from the initial variable set to establish the evaluation system. Finally, this method is verified with actual data of a line. The results show that the service performance of heavy haul railway line can still be evaluated accurately when the evaluation variables are reduced by 60% in the proposed method.

Evaluation of Two Momentum Control Variable Schemes and Their Impact on the Variational Assimilation of Radar Wind Data:Case Study of a Squall Line

Different choices of control variables in variational assimilation can bring about different influences on the analyzed atmospheric state. Based on the WRF model＇s three-dimensional variational assimilation system, this study compares the be- havior of two momentum control variable options-streamfunction velocity potential （ψ-χ） and horizontal wind components （U-V）-in radar wind data assimilation for a squall line case that occurred in Jiangsu Province on 24 August 2014. The wind increment from the single observation test shows that the ψ-χ control variable scheme produces negative increments in the neighborhood around the observation point because streamfunction and velocity potential preserve integrals of velocity. On the contrary, the U-V control variable scheme objectively reflects the information of the observation itself. Furthermore, radial velocity data from 17 Doppler radars in eastern China are assimilated. As compared to the impact of conventional observation, the assimilation of radar radial velocity based on the U-V control variable scheme significantly improves the mesoscale dynamic field in the initial condition. The enhanced low-level jet stream, water vapor convergence and low-level wind shear result in better squall line forecasting. However, the ψ-χ control variable scheme generates a discontinuous wind field and unrealistic convergence/divergence in the analyzed field, which lead to a degraded precipitation forecast.

On-line measurement of electrical variables of the transducer during ultrasonic welding and cutting

A measurement system for high power electrical variables with ultrasonic frequency was established. It can measure the effective values of the voltage and the current, the active power, the phase difference of voltage and current, the frequency of the transducer during ultrasonic welding and cutting. In sampling circuits of the system, the measured current is sensed by using a no capacitance and no inductance precision resistor and is treated with a difference amplifier, the measured voltage is processed by using a proportional amplifier. For achieving good amplitude frequency characteristics and rapid measurement of high frequency signals, the resistors, capacitors and amplifiers used in the system are rationally selected. Calibrating experiments show that relative errors are less than 1% for voltage and current effective values and less than 2.5% for active power, and absolute errors are ±1 Hz for frequency and ±1.7° for phase difference of voltage and current in the range of 17～23 kHz .

Simulation of the emission lines radiated from cataclysmic variables

Cataclysmic variables are special celestial bodies because they have particular light curves and spectra.The mechanisms for generating emission lines radiated from dwarf novae in their quiescent phases are studied.We assume that the incident radiation field which is emitted by a hot source（white dwarf and boundary layer）irradiates the gaseous layer evaporated from the accretion disk,and the emission lines are radiated from the gas.We model the fluxes of emission lines by using the photoionization code CLOUDY.Using this method,we input some reasonable parameters and get a series of simulated spectra.In order to find a simulated spectrum which is the best fit to an observed spectrum,we use a cross-correlation method to match them.After the calculation,we use the approximation that the parameters of the simulated spectrum can simulate the observed spectrum.Finally,we learn more about the physical conditions of the system.

Comprehensive Study on the Basis of Eye Blink, Suggesting Length of Text Line, Considering Typographical Variables the Way How to Improve Reading from Computer Screen

The advent and extensive use of computer and increasing development of different technologies it is important to increase the awareness of issues related to the electronic text or text presentation on computer screen. The usage of web shows the importance of usability and readability of the web applications or sources provide by the web and web textual contents. Web application fails to encounter the user’s requirements in effective manner specially related to textual information, because the designers are unaware from some of the important factors effecting readability, reading from the screen. In this regard, this study is the continuation of the previous work that has been done for the improvement of readability, to handle the readability issues on the basis of Eye Blink for male participants and female participants. To achieve general recommendations for suitable or optimum length of text line for all type of users on the bases of eye blink. Basically during reading from the computer screen focus losses at two positions, when eye blink in the middle of text line and when text line ends. The study specifies suitable length of text line on the basis of Eye Blink, assuming three typographical variables i.e. font style, font color, font size, and with white background, which improve the overall readability or reading from computer screen. The study also shows two important things the degree of understandability and the degree of attractive appearance of different combination.

Binary Oriented Feature Selection for Valid Product Derivation in Software Product Line

Software Product Line(SPL)is a group of software-intensive systems that share common and variable resources for developing a particular system.The feature model is a tree-type structure used to manage SPL’s common and variable features with their different relations and problem of Crosstree Constraints(CTC).CTC problems exist in groups of common and variable features among the sub-tree of feature models more diverse in Internet of Things(IoT)devices because different Internet devices and protocols are communicated.Therefore,managing the CTC problem to achieve valid product configuration in IoT-based SPL is more complex,time-consuming,and hard.However,the CTC problem needs to be considered in previously proposed approaches such as Commonality VariabilityModeling of Features(COVAMOF)andGenarch+tool;therefore,invalid products are generated.This research has proposed a novel approach Binary Oriented Feature Selection Crosstree Constraints(BOFS-CTC),to find all possible valid products by selecting the features according to cardinality constraints and cross-tree constraint problems in the featuremodel of SPL.BOFS-CTC removes the invalid products at the early stage of feature selection for the product configuration.Furthermore,this research developed the BOFS-CTC algorithm and applied it to,IoT-based feature models.The findings of this research are that no relationship constraints and CTC violations occur and drive the valid feature product configurations for the application development by removing the invalid product configurations.The accuracy of BOFS-CTC is measured by the integration sampling technique,where different valid product configurations are compared with the product configurations derived by BOFS-CTC and found 100%correct.Using BOFS-CTC eliminates the testing cost and development effort of invalid SPL products.

基于自适应窗口与压缩幅值的瞬时转频估计

针对变转速工况下轴承信号的时频分布能量发散、噪声和谐波干扰强导致其转频难以获取的问题,提出一种基于自适应窗口和压缩幅值的瞬时转频估计方法。首先,通过自适应窗口在频率轴方向搜索出脊线窗口避免噪声和谐波的干扰;其次,在脊线窗口内用压缩幅值方法集中发散的脊线能量;然后,用惩罚函数法提取脊线,实现转频的精确估计;最后,根据采用轴承实验台收集的数据验证了所提出方法的有效性和鲁棒性。结果表明,相比于传统方法,采用所提方法估计瞬时转动频率使误差降低约8%。

局部外形参数对高速飞行器的RCS影响

为了降低高速飞行器的雷达散射截面(radar cross section,RCS),采用多层快速多极子算法和物理光学法研究局部外形参数对飞行器雷达散射特性的影响。在此基础上,提出一种变半径弧形的边缘钝化形式,以提高飞行器仰视对抗能力。所提出的变半径弧形钝化外形具有良好的RCS减缩能力,与传统圆弧钝化外形相比,在前向重点角域内,RCS对数均值降低了22.88%;随着仰角的增大,变半径弧形钝化形式还具备全向RCS减缩能力,在全向角域内RCS对数均值降低了13.37%。最后,研究所提出的变半径弧形钝化方式在不同雷达波频段下的RCS特性,结果表明这种钝化方式对于频率较高时仰视对抗能力更好。

工位数固定的U型拆卸线部分拆卸平衡问题

为提高工位数固定的U型拆卸线拆卸效率,减少有害部件对操作人员的潜在威胁,针对高价值零部件和有害零部件的拆卸需求,本文提出了工位数固定的U型拆卸线部分拆卸平衡问题,建立了以最小化节拍时间、高危工位数目和负载均衡为目标的优化模型,并设计了改进的变邻域搜索算法进行求解.在编码过程中提出一种基于零部件释放位置的选择策略,以减少前继零部件拆卸顺序对编码的影响;提出最小偏差二分法,有效减少解码的迭代次数;提出瓶颈挤压局部搜索策略,用以优化节拍时间和均衡负载指标.通过与其他算法对比,结果表明改进的变邻域搜索算法求解具有优越性,并且可实现对工位数固定的U型拆卸线部分拆卸平衡问题的高效求解.

非圆形隧洞衬砌支护下应力与位移的新解法

以往在利用平面弹性复变函数方法进行衬砌支护作用下非圆形隧洞的力学分析时,一般将洞室外域保角映射到象平面的单位圆外域,并认为可以利用同一个映射函数将衬砌截面映射到象平面的圆环域内。当衬砌厚度很薄时,这种方法是可行的,而当衬砌相对较厚时,利用同一映射函数所得到的衬砌截面形状发生严重失真。为解决此问题,本文引入两套映射函数,分别将洞室外域映射到象平面的单位圆的圆外域,衬砌截面映射到圆环域。这种方法可以适应于不同的衬砌厚度,利用这种方式获得的衬砌截面,在衬砌较厚时仍能保证衬砌厚度相对均匀。在求解解析函数过程中不再采用传统的幂级数解法,而是使用边界配点法,将两套映射函数结合,获得了该问题的应力解和位移解。本文以马蹄形隧洞为例,求解结果与ANSYS软件所得数值解吻合很好,分析了衬砌厚度对隧洞应力和位移的影响。根据本文解答可以方便、快捷地进行相近条件下隧道的初步设计。

On-line血液透析滤过对维持性血液透析患者心率变异性的影响

目的探讨On-line血液透析滤过技术对维持性血液透析患者心率变异性(HRV)的影响。方法 50例维持性血液透析(MHD)患者随机分为常规血液透析治疗组(HD组)和On-line血液透析滤过治疗组(OL-HDF组),每组各25例。患者每周行3次、每次4 h的血液透析治疗或OL-HDF,治疗24个月。比较两组常规的实验室检查和24h动态心电图监测结果。结果治疗24个月后,OL-HDF组的β2-微球蛋白(β2-MG)由基线值30.1±7.2 mg/dl降至21.7±6.1 mg/dl(P<0.05),HD组的β2-MG则无明显下降。OL-HDF组HRV的时域性和频域性指标均值高于基线值(P<0.05),HD组的HRV指标则无显著性变化(P>0.05)。结论与普通血液透析比较,OL-HDF能更好地改善MHD患者的HRV,改善自主神经功能。

基于改进谱线增强的光电编码器γ辐射噪声滤波算法研究

针对核辐射环境下光电编码器因受γ辐射总剂量效应影响而导致输出信号质量劣化的问题,提出了一种兼顾精度和效率的改进谱线增强算法(Improved Adaptive Line Enhancer Method,IALEM)。该算法引入Softsign函数建立误差与步长之间的非线性关系,通过在步长更新公式中引入前一时刻步长值,达到收敛速度快且稳态误差小的目的。分别在算法收敛速度、稳态误差、低信噪比输入、计算量4个方面与同类算法进行比较。结果表明,该算法在拥有较低计算量的同时,其收敛速度更快、稳态误差更小,并且对于低信噪比信号具有更好的滤波效果。最后,在光电编码器上对本文所提算法进行了现场可编程门阵列(Field Programmable Gate Array,FPGA)硬件实现;并在60Co γ辐射环境中对算法的滤波效果进行了实验测试。实验结果表明:所提出的算法可有效滤除光电编码器因γ辐射产生的噪声,提高光电编码器输出信号的质量。

基于优先权与双可变时间窗的大型热轧生产线机会维护建模

为解决大型热轧生产线日常动态维护和支撑辊定期更换带来的维护需求差异问题,综合考虑长距离条件下的维护资源及停机时间限制,引入维护优先权规则识别部件的组合维护判断次序,构建双可变时间窗规则辨别部件是否维护并区分维护需求,进而建立系统整体动态机会维护模型.实例分析表明,该模型可有效解决维护资源和停机时间限制下大型热轧生产线的差异化维护调度问题,且比传统基于时间窗的模型更具成本优势.

Study on damage characteristics of iron ore under variable line density charge structure blasting

Blasting test research was conducted on iron ore specimens with variable line density charging structures.Computer tomography(CT),digital image processing,and three-dimensional model reconstruction techniques were used to analyze the damage characteristics of iron ore specimens after blasting based on the calculated number of box dimensions.The results show that increasing the variable line density section charge uncoupling coefficient reduces the overall damage to the specimen by up to 1.73%,indicating that the overall damage size negatively correlates with the size of the variable line density section charge uncoupling coefficient.The damage characteristics of iron ore specimens from different layers(uncoupled charging section,transition section,coupled charging section)have some variability;when the uncoupling coefficient of the uncoupled charging section was reduced,the uncoupled section of the center of the damaged layer increased and then reduced.In contrast,the transition section shows a trend of increase,and the coupled section shows a minor difference,fully demonstrating the change in the variable line density section of the uncoupling coefficient of the specimen blasting damage effects.This study concludes that in the actual blasting project,choosing a reasonable variable line charge density structure can make the release of explosive blast energy more uniform to efficiently and thoroughly use explosive power to improve the iron ore crushing effect.

可变重心线路巡检机器人摆振分析及抑制

针对野外输电线巡检机器人(power transmission line inspection robot,PTLIR)受自然风影响出现的机身摆动问题,提出一种在机器人的可变重心箱体中加装摆式动力吸振器(dynamic vibration absorber,DVA)的摆振抑制策略。描述了输电线系统与巡检机器人加装摆式动力吸振器的结构特点。基于Davenport风速谱与输电线系统的特点建立了风扰动模型。分析了机器人行走对输电线的影响,建立了简化后风扰动影响下机器人摆动的动力学模型,仿真了抑振前机器人在风扰动影响下的风振响应;基于拉格朗日方程建立了加装动力吸振器优化后的巡检机器人动力学模型,并完成了吸振器的参数设计。通过仿真不同风速下机器人的风振响应,验证所提出的振动抑制策略的有效性。基于改进结构下的巡检机器人样机,开展了室内风扰动试验。结果表明,所提出的吸振器抑振策略可在一定程度上抑制机器人的机身摆动,提高工作稳定性。该研究过程对其他摆式结构设备的振动抑制具有一定的参考价值。

一种Boost PFC电路改进VOT控制策略研究

为了解决恒定导通时间(COT)控制策略下负向谐振电流和输入滤波电容引起功率因数(PF)和总谐波失真(THD)性能变差的问题,提出一种改进变导通时间(VOT)的控制策略。通过自适应增加导通时间以抵消负向谐振电流,减小相位差,使电感平均电流在工频周期内接近正弦波,并分析其工作原理与控制过程。结合主电路设计关键参数,研制1台额定功率320 W的样机,进行COT控制策略和改进VOT控制策略的对比实验。计算机仿真和实验结果表明,改进VOT控制策略在265 V高电压输入20%负载工作时,PF值由0.726提升至0.801,THD由27.92%降低至18.4%;在40%~100%负载时满足PF>0.9、THD<15%的要求,验证所提控制策略的有效性。

基于变步长匹配追踪的G3-PLC系统信道估计算法

为合理利用电力线信道的稀疏特性,提高G3-PLC系统通信的可靠性,基于压缩感知(compressed sensing,CS)理论,提出一种稀疏度自适应的变步长前向后向匹配追踪(sparsity adaptive variable step size forward-backward pursuit,SA-VSSFBP)算法。该算法在前向后向匹配追踪算法(forward-backward pursuit,FBP)的基础上引入变步长自适应的思想,于迭代初期选择大步长以减小迭代次数,迭代后期使用小步长获得精确估计。同时利用原子匹配度测试进行稀疏度预估计,确保逼近真实稀疏度的前提下,加快迭代速度,减少算法运行的时间。仿真实验结果表明,对比传统的信道估计方式,压缩感知信道估计方式具有更优越的性能,且相较于正交匹配追踪算法(orthogonal matching pursuit,OMP)与FBP的压缩感知信道估计算法,文章提出的算法能够在保证精度与步长为1的FBP相当的情况下算法效率分别能够提升24.14%和47.2%。

双碳与新型电力系统背景下半波长可控调谐技术研究

面向“碳达峰、碳中和”目标,发展半波长输电技术可为构建以新能源为主体的新型电力系统提供能源保障。半波长技术因其输电距离远、经济性好等独特优势,在“西电东送”能源战略中有较好的应用前景。针对输电线路自然长度不足工频半波长现象以及固定调谐的不足,文章提出一种变阻抗型可控调谐方法,基于可控串补(thyristor controlled series compensator,TCSC)阻抗控制策略构造可微调的调谐电感,基于电容三级投切策略构造可分级的调谐电容。对可控调谐可行性、故障过电压特征以及串补过压抑制进行仿真分析。结果表明,可控调谐能够消除电气长度误差,使线路保持半波长特性,线路补偿效果与可控调谐长度相关。