考虑工作点时变特性的并网变流器全工作区间稳定性分析

现有工程运行数据显示,并网变流器(grid-connected converter,GCC)的动态特性与工作点密切相关。受新能源出力波动、负载投切等外部因素的影响,变流器工作点呈现随机时变特性。因此,分析整个工作区间中所有工作点的系统稳定性具有重要意义。传统阻抗/导纳分析方法可以有效分析GCC运行于特定工作点时的稳定性,但考虑系统所有可能工作点时则需重复分析,工作量大且难度较高。为解决这一难题,提出一种考虑工作点变量的多元建模方法。将工作点变量引入导纳模型,通过控制环路重构,建立GCC的多变量单输入单输出(single input single output,SISO)模型。所提模型直接包含工作点变量,因此可以有效分析变流器全工作区间动态特性。此外,综合考虑变流器最大传输限制和动态特性,提出一种基于安全运行域的稳定性分析方法,以实现多维工作区间中系统稳定性的直观表征。仿真和实验验证了所提多变量SISO模型和基于安全运行域的分析方法的正确性。所提模型和方法在分析电力电子装置运行极限、指导变流器设计和辅助功率器件发挥极限性能等工程场景中具有广泛应用潜力。

入院心脏运动康复应用于稳定性慢性心功能不全患者的效果

目的:探讨入院心脏运动康复应用于稳定性慢性心功能不全(CHF)患者的效果。方法:根据随机数字表法将2020年7月—2022年11月收治的121例稳定性慢性心功能不全患者分为传统组(60例)和运动组(61例),其中传统组给予常规护理干预,运动组在传统组的基础上给予入院心脏运动康复,比较两组患者心功能指标、自我管理能力、运动耐力水平。结果:干预3个月后,运动组左心室射血分数(LVEF)高于传统组,6 min步行距离(6MwD)远于传统组,左心室舒张末期内径(LVEDD)小于传统组(P<0.05);两组自我护理能力量表(ESCA)各维度评分显著高于干预前,且运动组高于传统组(P<0.05);两组峰值耗氧量、最大运动功率、代谢当量水平均上升,且运动组高于传统组(P<0.05)。结论:运用入院心脏运动康复能够改善稳定性CHF患者心功能,提高机体自我管理水平及运动耐力水平。

快速稳定性仪评价餐具洗涤产品油污乳化力的研究

采用LUMi Sizer全功能稳定性分析仪研究了不同配方洗洁精-油污乳液的积分透光率变化值,建立了一套能快速评价洗洁精对国标混合油乳化能力的方法。结果表明,当洗洁精溶液含量在0.2%时,该方法与实际去油率实验规律一致,可反映不同配方洗洁精的去污能力。由于该方法具有操作简单,数据重现性好且高效、快捷的优点,可满足研发人员快速筛选配方的需求。由于洗洁精溶液在实际使用过程中浓度范围差异较大,采用该方法可快速评价一定浓度范围内(0.2%~2%)不同配方洗洁精溶液的综合油污乳化能力,从而更为客观、合理地评价不同配方洗洁精的去污力。

Nio-Mora和Glazebrook条件及一类排队网络的稳定性

多级排队网络的稳定性特别是全稳定性一直是随机网络研究的一个热点.Ni o Mora和Glazebrook就多级排队网络的全稳定性给出了一个充分条件,即当每个工作站的峰值流量密度ρ-<1时,该排队网络是全稳定的.通过对该条件的应用得出了此条件成立的必要条件,即当σ(k)≠σ(k+1)时有mk>mk+1.对一类具有两个工作站的重入排队网络证明了若σ(k)≠σ(k+1)时有mk≥mk+1,该排队网络是全稳定的.

基于空间-时间消光图谱技术测定不同稳定剂对西番莲果汁稳定性的影响

为了解决西番莲果汁稳定性差、易沉淀的问题,本研究以西番莲果汁为研究对象,使用基于空间-时间消光图谱技术的全自动稳定性分析仪以沉降速率、积分透射率和透射红外图谱为主要分析指标,判定稳定剂琼脂、羧甲基纤维素钠及这两种稳定剂复配对西番莲果汁稳定性的影响,选出相对适宜的单一稳定剂以及复配稳定剂的添加比例。结果表明:添加单一稳定剂的情况下,羧甲基纤维素钠(CMC-Na)相较琼脂各组的图谱线条更紧凑,线条走向更平稳,其整体稳定效果更好,而添加量为0.30%~0.35%的(CMC-Na)可获得单一稳定剂的最佳稳定效果,其沉降速率最低((0.0209±0.0003)%/s,(0.0181±0.0002)%/s);两种稳定剂复配情况下,随着CMCNa含量的上升以及琼脂含量的降低,图谱中的线条越紧凑和平稳,果汁稳定性增强,最佳的复配添加配比为0.35%CMC-Na+0.15%琼脂和0.30%CMC-Na+0.20%琼脂,其沉降速率最低((0.0231±0.0004)%/s,(0.0209±0.0004)%/s)。上述发现可为西番莲果汁的开发和稳定体系的构建提供一定的科学依据。

全矿渣混凝土的研究及应用

应用矿渣作粗、细骨料制备全矿渣混凝土，通过试验分析，阐述了用高炉重矿渣制备混凝土粗、细集料的工艺、性能、特点以及全矿渣混凝土的应用范围。与普通砂石混凝土相比，全矿渣混凝土平均强度约提高5％、自重减轻1／20～1／30，通过技术、经济分析，混凝土可降低成本21元／m^3左右。

Stability of second order Hopfield neural networks with time delays

Dynamical behaviors of a class of second order Hopfield neural networks with time delays is investigated.The existence of a unique equilibrium point is proved by using Brouwer's fixed point theorem and the counter proof method,and some sufficient conditions for the global asymptotic stability of the equilibrium point are obtained through the combination of a suitable Lyapunov function and an algebraic inequality technique.

卫星天线指向复合控制全物理仿真与试验分析

卫星天线指向复合控制全物理仿真系统是验证多体卫星天线指向复合控制方案的关键设备。首先从力学的角度研究了该系统试验时影响天线指向与定点控制精度的几个不理想因素,并对系统的误差进行了分析和研究,得出了其误差模型,在此基础上设计了自适应控制律并对其进行了稳定性证明。最后对该系统进行了仿真,给出了仿真结果。结果表明该系统可以满足高精度天线指向复合控制要求。为进一步提高卫星天线指向复合控制全物理仿真精度奠定了基础。

微胶囊相变悬浮液物理稳定性实验研究

通过实验研究确定制备稳定的微胶囊相变悬浮液必须采用的最优化表面活性剂添加量和悬浮液pH值。采用全功能稳定性分析仪TURBISCAN LAb研究表面活性剂十二烷基硫酸钠（SDS）添加量和悬浮液pH值对物理稳定性的影响。结果表明,当SDS质量分数太低,即颗粒表面改性不彻底时,稳定性较差;质量分数太高,容易形成表面活性剂胶束沉淀,并同时加速相变微胶囊颗粒上浮,破坏微胶囊相变悬浮液的稳定性,在选定的SDS质量分数范围内,最佳质量分数为0.2%~0.4%;pH值低于7时,溶液颗粒分散性提高不明显,并且出现加快分层现象;pH值过高时,溶液中OH-过多,压缩双电层厚度,减弱颗粒分散性,溶液稳定性提高受到抑制,在选定的pH值范围内,密胺树脂壳材的悬浮液最佳pH值为8。抑制悬浮液的分层和团聚现象对于其在传热和储热中的应用有重要意义,研究结果给制备稳定的悬浮液提供了可靠的依据。

盐酸曲美他嗪治疗冠心病稳定性心绞痛心功能不全及对脑钠肽的影响

目的观察盐酸曲美他嗪对冠心病稳定性心绞痛心功能不全疗效和对脑钠肽(Npro-BNP)的影响。方法选择48例冠心病稳定型心绞痛心功能不全患者,在常规治疗的基础上,给于盐酸曲美他嗪口服,每次20mg,3次/天,疗程3个月。结果治疗3个月后,临床症状,左室射血分数(EF),心排血量(CO),心脏指数(CI),脑钠肽(Npro-BNP)显著改善。治疗前后监测生化指标,每日测血压,心率,观察药物不良反应。结论盐酸曲美他嗪可以显著改善临床症状,改善心功能,减低脑钠肽数值,无严重不良反应,安全有效。

跳过程的不变分布

设(E,ε)是状态空间,(q(x),q(x,dy))为保守的q对,即 q(x,E)=q(x),x∈E,π是一严格正的概率测度,满足 π(ΩIA)=0,A∈ε.问何时存在q-过程使得π是它的不变分布?本文对q对为全稳定情形,解决了该问题。

Exponential stability and existence of periodic solutions for a class of recurrent neural networks with delays

Both the global exponential stability and the existence of periodic solutions for a class of recurrent neural networks with continuously distributed delays （RNNs） are studied. By employing the inequality α∏k=1^m bk^qk≤1/r ∑qkbk^r＋1/rα^r（α≥0,bk≥0,qk〉0,with ∑k=1^m qk=r-1,r≥1, constructing suitable Lyapunov r k=l k=l functions and applying the homeomorphism theory, a family of simple and new sufficient conditions are given ensuring the global exponential stability and the existence of periodic solutions of RNNs. The results extend and improve the results of earlier publications.

Periodic Solution and Global Stability of a Kind of Nonlinear Differential Equation

In this paper, it is discussed the model of a kind of nonlinear differential, equation d s d t=1-s-x 1s 0δQ 2(m 1s 0sk 1+s 0s-k) d x 1 d t=x 1Q(m 1s 0sk 1+s 0s-k)-x 1-x 2m 2x 1/Qk 2+x 1/Q d x 2 d t=x 2Q m 2x 1/Qk 2+x 1/Q-x 2.It is proved that the system is exist at least one stable periodic solution on under the following condition:m 2x * 2(k 1δ+s 0δ-Qλ 2-x * 2) 2】m 1δk 1(k 2+Q 2λ 2) 2.Furthermore, ifm 2x * 2(k 1δ+s 0δ-Qλ 2-x * 2) 2【m 1δk 1(k 2-Q 2λ 2) 2mold true them equilibrium point (s *,x * 1,x * 2)∈ set Ω is global asymptotic stable.

Asymptotic Stability in the Large of Zero Solution of Second Order Nonlinear Differential Equation

There are many works on the asymptotic stability of second dimensional nonlinear differential equation. In particular, these results only concern with the system which includes one or two terms, whereas few works concern with system which includes more than two terms. In this paper, system which includes four nonlinear terms are studies. We obtain the global asymptotic stability of zero solution, and discard the condition which require the Liapunov function trends to infinity, and only require that the positive orbit is bounded.

Research on Stability of Desert Climate of Minqin County in Gansu Province

In order to study the stability of desert climate, the instability of climate in Minqin desert in response to global warming during 1961-2013 was analyzed by sliding standard deviation and a linear trend line. The results show that the instabili- ty of average temperature in January and April increased, and the isothermal date in February was 10.36 d earlier from 1961 to 2013. The instability of extreme maxi- mum temperature in December and January improved. The instability of extreme minimum temperature in July instability also increased. The coefficient of variation of extreme minimum temperature in May was up to 287.3%. It is concluded that the instability of desert climate of Minqin County increased with global warming. The stability of climate is more worthy of attention.

催化裂化油浆水洗脱固的研究

利用加入破乳剂水洗的方法脱除催化裂化油浆中的固体颗粒,选用性质相近的模型油对其机理进行探讨发现,50℃条件下,加入100 mg/L破乳剂时,油水界面张力由37.5 m N/m降低至26 m N/m,即破乳剂显著降低了油水界面张力。同时由全功能稳定性分析可知,破乳剂的加入加速了背散射光的降低,加速了乳状液颗粒之间的聚并。通过红外、核磁共振光谱和凝胶色谱对破乳剂分子的结构进行了表征。同时将此破乳剂用在油浆中,在去离子水质量分数为16%,破乳剂质量浓度为50 mg/L时,脱水率即可达到90%以上,并且油浆灰分质量分数也由原来的0.26%降到了0.02%,取得很好效果。

Stability of finite difference numerical simulations of acoustic logging-while-drilling with different perfectly matched layer schemes

In acoustic logging-while-drilling （ALWD） finite difference in time domain （FDTD） simulations, large drill collar occupies, most of the fluid-filled borehole and divides the borehole fluid into two thin fluid columns （radius -27 mm）. Fine grids and large computational models are required to model the thin fluid region between the tool and the formation. As a result, small time step and more iterations are needed, which increases the cumulative numerical error. Furthermore, due to high impedance contrast between the drill collar and fluid in the borehole （the difference is 〉30 times）, the stability and efficiency of the perfectly matched layer （PML） scheme is critical to simulate complicated wave modes accurately. In this paper, we compared four different PML implementations in a staggered grid finite difference in time domain （FDTD） in the ALWD simulation, including field-splitting PML （SPML）, multiaxial PML（M- PML）, non-splitting PML （NPML）, and complex frequency-shifted PML （CFS-PML）. The comparison indicated that NPML and CFS-PML can absorb the guided wave reflection from the computational boundaries more efficiently than SPML and M-PML. For large simulation time, SPML, M-PML, and NPML are numerically unstable. However, the stability of M-PML can be improved further to some extent. Based on the analysis, we proposed that the CFS-PML method is used in FDTD to eliminate the numerical instability and to improve the efficiency of absorption in the PML layers for LWD modeling. The optimal values of CFS-PML parameters in the LWD simulation were investigated based on thousands of 3D simulations. For typical LWD cases, the best maximum value of the quadratic damping profile was obtained using one do. The optimal parameter space for the maximum value of the linear frequency-shifted factor （a0） and the scaling factor （β0） depended on the thickness of the PML layer. For typical formations, if the PML thickness is 10 grid points, the global error can be reduced to 〈1% using the optimal PML parameters, and the error will decrease as the PML thickness increases.

Stability of long trench in soft soils by bentonite-water slurry

A series of centrifuge model tests exploring the effects of different types of slurry on long-trench stability in soft clay were conducted. The influence of groundwater conditions relative to trench stability was examined by constructing long trenches using different slurries. The soil deformation and surface settlement induced by the excavation of the trench are found to be closely related to slurry type and excavation depth of the long trench. Increasing the bentonite concentration of the slurry has beneficial effects on stability: 1) larger particles can improve local and global stability in cases where filter cakes do not form, and 2) larger viscosity can promote filter cake formation on the walls of long trenches excavated in soft clay and enhance their stability.

Green large-scale production of N/O-dual doping hard carbon derived from bagasse as high-performance anodes for sodium-ion batteries

Sodium-ion batteries are considered as a promising candidate for lithium-ion batteries due to abundant sodium resources and similar intercalation chemistry.Hard carbon derived from biomass with the virtue of abundance and renewability is a cost-effective anode material.Herein,hard carbon is derived from renewable bagasse through a simple two-step method combining mechanical ball milling with carbonization.The hard carbon electrodes exhibit superior electrochemical performance with a high reversible capacity of 315 mA∙h/g.Furthermore,the initial capacity of the full cell,HC//NaMn0.4Ni0.4Ti0.1Mg0.1O2,is 253 mA∙h/g and its capacity retention rate is 77%after 80 cycles,which further verifies its practical application.The simple and low-cost preparation process,as well as excellent electrochemical properties,demonstrates that hard carbon derived from bagasse is a promising anode for sodium-ion batteries.

Developments and prospects of microseismic monitoring technology in underground metal mines in China

Microseismic monitoring technology has become an important technique to assess stability of rock mass in metal mines.Due to the special characteristics of underground metal mines in China,including the high tectonic stress,irregular shape and existence of ore body,and complex mining methods,the application of microseismic technology is more diverse in China compared to other countries,and is more challenging than in other underground structures such as tunnels,hydropower stations and coal mines.Apart from assessing rock mass stability and ground pressure hazards induced by mining process,blasting,water inrush and large scale goaf,microseismic technology is also used to monitor illegal mining,and track personnel location during rescue work.Moreover,microseismic data have been used to optimize mining parameters in some metal mines.The technology is increasingly used to investigate cracking mechanism in the design of rock mass supports.In this paper,the application,research development and related achievements of microseismic technology in underground metal mines in China are summarized.By considering underground mines from the perspective of informatization,automation and intelligentization,future studies should focus on intelligent microseismic data processing method,e.g.,signal identification of microseismic and precise location algorithm,and on the research and development of microseismic equipment.In addition,integrated monitoring and collaborative analysis for rock mass response caused by mining disturbance will have good prospects for future development.