基于变量代换内点法的加权最小绝对值抗差状态估计

传统内点法加权最小绝对值(WLAV)抗差状态估计能够抑制坏数据影响,提高状态估计精度,但该方法模型复杂,计算效率低,限制了其工程应用价值。文中提出一种基于变量代换内点法的电力系统WLAV估计方法,该方法通过添加中间变量,将非线性量测方程分解为两步线性方程和两步非线性变换,并建立两步线性方程的WLAV估计数学模型。与传统内点法WLAV抗差状态估计相比,该方法无须形成海森矩阵,可有效提高迭代方程中系数矩阵的稀疏度,并减小矩阵的阶数,有效提高WLAV状态估计的计算速度。基于美国电气与电子工程师学会(IEEE)标准系统、波兰电网和国内某省网的仿真结果验证了所述方法的有效性,具有良好的工程应用前景。     

双主相合金法制备的(Nd,Ce)-Fe-B永磁合金

利用双主相合金法制备了Ce取代的廉价(Nd,Ce)-Fe-B磁体,研究了Ce取代对永磁体烧结致密化行为、显微结构与磁性能的影响。结果表明,用Ce部分取代Nd能够促进烧结,降低烧结温度;随着Ce取代量的增加,晶粒开始明显长大,磁体晶粒尺寸变得不均匀,晶间富稀土相也开始团聚,磁体各项磁性能逐步降低,在Ce取代量为总稀土的20%时,材料剩磁为1.05T,内禀矫顽力为651.4k A/m(8.18k Oe),最大磁能积为198.4k J/m3(24.92MGOe),仍具有较好的综合磁性能。     

高磁性能SrFe_(12-x)Cr_xO_(19)铁氧体制备和表征

用传统陶瓷工艺制备了M型Sr Fe12-xCrxO19(x=0~0.6)铁氧体,利用X射线衍射、扫描电子显微镜和B-H分析仪对样品的结构与磁性能进行了表征。研究了铬含量、烧结温度和复合添加剂对磁体性能的影响。结果表明,适量的铬取代和复合添加可以提高锶铁氧体的综合磁性能;当x=0.2时,在相对低的温度(1135~1165℃)烧结,其磁性能达到TDK的FB6H性能水平。其中,最佳磁性能可达到Br=401.7m T、Hcb=300.5k A/m、Hcj=353.1k A/m和(BH)max=31.4k J/m3。     

Zn_(0.7)Co_(0.3)(Ti_(1-x)Sn_x)Nb_2O_8陶瓷微波介电性能研究

采用传统固相法制备Zn0.7Co0.3(Ti1-xSnx)Nb2O8(x=0.1,0.15,0.2,0.25,0.3,0.35)微波陶瓷。研究了Sn取代Ti对Zn0.7Co0.3(Ti1-xSnx)Nb2O8微波介质陶瓷的物相结构与介电性能的影响。XRD研究表明,Zn0.7Co0.3(Ti1-xSnx)Nb2O8陶瓷主晶相为ZnTiNb2O8,有极少杂相Zn0.17Ti0.5Nb0.33O2存在;随着Sn含量的增加,陶瓷晶格常数增大,晶胞体积变大,陶瓷密度增大;电子扫描显微镜(SEM)显示随着Sn含量增加陶瓷结构致密;相对介电常数εr逐渐变小,温度系数τf逐渐变小,Q×f值逐渐增大;当Sn含量为0.35时,烧结温度为1 080℃,εr=30.5,Q×f=46 973GHz,τf=-45.4×10-6/℃。     

Zn~(2+)、Sn~(4+)共取代对YIG铁氧体性能的影响

该文通过1 400℃固相烧结制备出Zn2+和Sn4+共取代的Y3Fe5-2xZnxSnxO12(x=0~0.35)铁氧体材料,详细研究了离子取代量对钇铁石榴石铁氧体微观结构及磁性能的影响。研究表明,Zn2+、Sn4+都进入了钇铁石榴石铁氧体的晶格中。随着离子取代量的增加,钇铁石榴石铁氧体的密度与饱和磁化强度先增大后减小;其磁损耗则先减小后增大,在x=0.25时磁损耗取得最小值。该研究进一步说明了Zn2+和Sn4+取代在一定范围内可有效降低材料的磁损耗及控制材料的饱和磁化强度。     

Structural and magnetic properties of strontium substituted NiZn ferrite nanopowders

Sr-substituted NiZn ferrite nanopowders, Ni_0.5-xZn_0.5Sr_xFe_2.0O₄ (0≤x≤0.20), were synthesized by the sol-gel auto-combustion method. The effects of Sr substitution on the structural and magnetic properties have been investigated. Differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements were used to characterize chemical, structural and magnetic properties. The DTA-TG results indicate that there are three steps of combustion process. XRD results indicate that the lattice parameter increases, and the average crystallite size decreases with increasing Sr substitution. The Sr₂FeO₄ and SrFe₁₂O₁₉ impurity phases formed with excess Sr substitution. The saturation magnetization monotonically decreases with the increase of Sr substitution. Meanwhile, the coercivity initially decreases with the increase of Sr substitution when x≤0.15, and increases when x>0.15.     

内型N-Boc-N-去甲托品硫醇的立体控制合成研究

以外型的N-Boc-N-去甲托品醇为原料,经甲磺酰化、S_N2取代反应和水解作用得到内型N-Boc-N-去甲托品硫醇,总收率为49%,结构经~1HNMR和ESI-MS确认。     

Microwave dielectric characteristics of tungsten bronze-type Ba4Nd28/3Ti18-yGa4y/3O54 ceramics with temperature stable and ultra-low loss

A series of high-k Ba₄Nd_28/3Ti_18-yGa_4y/3O₅₄ (0≤y≤2, BNTG) ceramics with temperature stable and ultra-low dielectric loss were synthesized via the conventional solid-state reaction. The main phase of all BNTG ceramics demonstrated an orthorhombic tungsten-bronze structure, but the impurity phase (gallium-rich phase) was found in BNTG (y = 2) ceramic. Partial substitution of Ga³⁺ for Ti⁴⁺ in B-site was a valid method to improve the temperature stability and dielectric loss of BNTG ceramics. The variation of ε_r values of BNTG ceramics was dominated by the ionic polarizability. The ultra-low dielectric loss (ultra-high Q × f values) was associated with grain size, suppression of Ti³⁺ and impurity phase. The decrease of TCF values was highly dependent on the tilting of Ti-O octahedra and impurity phase. Finally, outstanding combination dielectric characteristics were achieved for BNTG microwave ceramics at y = 1.5 (ε_r = 72.8, Q × f = 14,600 GHz, TCF=+4.1 ppm/°C) and at y = 2 (ε_r = 70.3, Q × f = 15,500 GHz, TCF=+3.9 ppm/°C).     

Design of a europium-activated lithium-silicate cyan phosphor via cation substitution

Lithium-containing silicates have been considered as a considerable alternative for luminescent materials. In this study, a novel cyan-emitting phosphor, Na₃LiHf₂Si₃O₁₂: Eu²⁺, was successfully synthesized via cationic substitution with Na₄Hf₂Si₃O₁₂: Eu²⁺ as the initial model. The crystal structure, morphology, and luminescence performance of Na_4-xLi_xHf₂Si₃O₁₂: Eu²⁺ were investigated in detail. The substitution of Li⁺ for Na⁺ site causes a significant blue-shift of the emission band in the range of 550–500 nm and a smaller full width at half maximum. As a result, a cyan phosphor Na₃LiHf₂Si₃O₁₂: Eu²⁺ that can be effectively excited by near-ultraviolet and high-energy beams is obtained. The mechanism of emission regulation was proposed based on the transformation of crystal structure and luminescence performance. In addition, the thermal quenching and cathodoluminescence behaviors were also studied. The results show that cation substitution is an effective method to design new lithium-containing silicate phosphors.     

The Lithiation Reactivity and Selectivity of Differentially Branched Alkyldiphenylphosphine Oxides – A Simple and Versatile Approach to ortho‐Functionalized Arylphosphine Oxides

Alkyldiphenylphosphine oxides typically undergo α‐deprotonation with alkyllithium reagents. Here, the lithiation of differentially branched alkyldiphenylphosphine oxides was investigated and a diverse, but predictable reactivity was found. γ‐Branched derivatives undergo selective directed ortho‐metalation (DoM) using butyllithium and TMEDA as an additive. With decreasing degree of γ‐branching α‐lithiation becomes predominant. The ortho‐phosphinoyllithium intermediates are subject to functionalization and C C bond forming reactions, thus providing a convenient approach to new phosphine oxides and phosphine‐borane complexes, which have a good potential for an approach to new ligands for catalysis.