Moessbauer spectra of MnFe2-2x Al2xO4 （0 ≤x≤ 0.4） ferrites

The effect of non-magnetic Al³⁺ ion doping on the magnetic properties of MnFe_2−2x Al_2x O₄ (0≼x≼0.4) spinel ferrites was studied using M?ssbauer spectroscopy measurements at room temperature. From the M?ssbauer study, it is observed that the resolved hyperfine sextets are due to the distribution of Fe ions on the two sublattices of the spinel ferrites. The value of the isomer shift obtained from the fitting of the M?ssbauer spectra indicates that Fe ions are in +3 state. A paramagnetic doublet is observed at degree of inversion x=0.4, superimposed on the hyperfine sextets, indicating that the super-exchange interaction A–B decreases due to the dilution of sublattice by Al³⁺ ions. The hyperfine magnetic field decreases at both interstitial sites of tetrahedral (A) and octahedral (B) with the increase in Al concentration.     

Sylow子群的秩≤2的有限群

本文对Ｓｙｌｏｗ子群的秩≤２的有限群结构进行讨论，得到了关于这类群的一系列很好的性质。     

Phase and Structure in the System Gd_(2-x)Eu_xZr_2O_7 (0.0≤x≤2.0)

Pyrochlore Gd2Zr2O7 are considered as an excellent candidate for treatment of radioactive waste forms, because of its superior physical, chemical and anti-irradiation properties. To investigate the phase and structure of pyrochlore Gd2Zr2O7 used for immobilizing Pu(Ⅲ), trivalent europium was used as the simulacrum for plutonium with trivalence. The compounds of stoichiometry Gd2-xEuxZr2O7(0.0x2.0) synthesized by high temperature solid state reaction method, were analyzed with the help of XRD and Rietveld structural refinement method. The results indicated that the phases of compounds continuously kept the phase of pyrochlore under our experimental condition. The linear relation between a andxwas discovered in the system of Gd2-xEuxZr2O7(0.0≤x≤2.0) at 1 773 K, which accorded with a=10.538 41+0.008 95 x, V=1 170.373 32+2.985 97 x.     

(1-x)SrZnP_2O_7-xSr_2P_2O_7(0.2≤x≤0.8)陶瓷微波介电性能研究!

采用固相反应法制备了复相体系(1-x)SrZnP2O7-xSr2P2O7陶瓷,研究了该体系的相组成、晶体结构对微波介电性能的影响。研究结果表明,在比例系数x从0.2到0.8的范围内所获得的材料只含有SrZnP2O7和Sr2P2O7两种晶体相,并且当烧结温度合适时所有复相比例的材料均可获得较高的烧结密度。烧结温度的升高会使材料的相对密度和介电常数均有所上升;而随着x值的增大,体系中的Sr2P2O7相含量也逐渐升高,在同样的烧结温度下则伴随着品质因子Q×f值的下降和频率温度系数τf值的上升。在复合比x=0.6时,上述材料具有较优良的微波介电性能:ε=7.44,Q×f=10200GHz,τf=-28.6×10-6/℃。上述结果表明,复合Sr2P2O7相可以有效地使SrZnP2O7材料的负的频率温度系数τf值得到补偿。     

Mssbauer spectra of MnFe_(2-2x)Al_(2x)O_4(0≤x≤0.4) ferrites

The effect of non-magnetic Al3+ ion doping on the magnetic properties of MnFe2-2xAl2xO4(0≤x≤0.4) spinel ferrites was studied using Mssbauer spectroscopy measurements at room temperature.From the Mssbauer study,it is observed that the resolved hyperfine sextets are due to the distribution of Fe ions on the two sublattices of the spinel ferrites.The value of the isomer shift obtained from the fitting of the Mssbauer spectra indicates that Fe ions are in +3 state.A paramagnetic doublet is observed at degree of inversion x=0.4,superimposed on the hyperfine sextets,indicating that the super-exchange interaction A-B decreases due to the dilution of sublattice by Al3+ ions.The hyperfine magnetic field decreases at both interstitial sites of tetrahedral(A) and octahedral(B) with the increase in Al concentration.     

Impedance spectroscopy study on Mn_(1+x)Fe_(2-2x)Ti_xO_4(0≤x≤0.5) ferrites

The complex impedance spectroscopy and surface morphology of Mn1+xFe2-2xTixO4(0≤x≤0.5) system,prepared using a conventional solid state reaction technique,were investigated.The impedance spectroscopy measurements were carried out at room temperature in the frequency range of 42-5 MHz.The electrical processes in the samples were modeled in the form of an equivalent circuit made up of a combination of two parallel RC circuits attributed to grain and grain boundaries.The DC conductivity obtained by extrapolation of AC data using impedance spectroscopy and four-probe method increases at 10% doping of Ti ions.The energy-dispersive X-ray(EDX) pattern confirmed the homogeneous mixing of the Mn,Fe,Ti and O atoms in pure and doped ferrite samples.     

Number of Negative Entries in A2≤0

Let A be a real matrix or a sign pattern of order n. N_ (A) denotes the number of negative entries in A. In 1972 R DeMarr and A Steger conjectured: If A is a real matrix of order n such that A^2≤0, then N- (A^2)≤( n - 1)^2 1. Now the conjecture is proved to be true when A is reducible or a matrix of order n≤3 and some sufficient conditions for N- (A^2)≤(n - 1)^2 1 are given. It is also proved that N_ (A^2)≤n^2 -4n 5 when A is a reducible combinatorially symmetric sign pattern such that A^2≤0, and the extreme sign patterns are characterized.     

Influence of Ti^4＋ doping on hyperfine field parameters of Mg0.95Mn0.05Fe2-2xTizxO4 （0 ≤x ≤ 0.7）

The mixed spinel ferrite system Mg_0.95Mn_0.05Fe_2−2x Ti_2x O₄ (0⩽x⩽0.7) was synthesized by the conventional solid-state reaction technique. The effect of Ti⁴⁺ doping was studied by using the M?ssbauer spectroscopy measurements at room temperature. From the analysis of the M?ssbauer spectra, it is observed that s-electron density, electric field gradient (EFG), quadrupole coupling constant (QCC) and the net hyperfine magnetic fields acting on the M?ssbauer nuclei-Fe_A ³⁺ and Fe_B ³⁺ change with the increase of Ti⁴⁺ doping in Mg_0.95Mn_0.05Fe₂O₄. The hyperfine magnetic field decreases with the increase of Ti⁴⁺ doping.     

n≤2d-4的本原有向图的本原指数的上界

设ｄ为ｎ阶本原有向图Ｄ的直径，本文证明了：当时，γ（Ｄ）≤ｄ２＋１．     

空间1←pq(0《p≤1≤q《+∞)及其完备性

二重序列空间l←pq(0＜p≤1≤q＜+∞)是完备的赋P-范序列空间,它具有与通常的Banach序列空间lp(0＜P＜1)不同的性质和包含关系.本文引入这样一类赋P-范二重序列空间并证明了它的完备性,讨论了这类空间的包含关系.     

空间l"非汉字符号"(0

郑杰 《辽东学院学报(自然科学版)》2003,(4)

Influence of Ti~(4+) doping on hyperfine field parameters of Mg_(0.95)Mn_(0.05)Fe_(2-2x)Ti_(2x)O_4(0≤x≤0.7)

The mixed spinel ferrite system Mg0.95Mn0.05Fe2-2xTi2xO4(0≤x≤0.7) was synthesized by the conventional solid-state reaction technique.The effect of Ti4+ doping was studied by using the Mssbauer spectroscopy measurements at room temperature.From the analysis of the Mssbauer spectra,it is observed that s-electron density,electric field gradient(EFG),quadrupole coupling constant(QCC) and the net hyperfine magnetic fields acting on the M-ssbauer nuclei-FeA3+ and FeB3+ change with the increase of Ti4+ doping in Mg0.95Mn0.05Fe2O4.The hyperfine magnetic field decreases with the increase of Ti4+ doping.     

分数阶为2 < α≤3的微分方程两点边值问题解的存在性

利用schauder不动点定理及Green函数的性质得到了分数阶为2<α≤3的微分方程两点边值问题\left\\beginarraylD_0+ ^\alpha u(t)=f\left(t, u(t), ^c D_0+ ^\beta u(t)\right), 0 \leqslant t \leqslant 1 \ u(0)=u(1)=u(0)=0, 2<\alpha \leqslant 3, 0<\beta \leqslant 1\endarray\right., 解的存在性。其中, D₀₊α为Riemann-Liouville分数阶导数, cD₀₊β为caputo's分数阶导数。       

Dy0.65Tb0.25Pr0.1Fex合金的显微组织和磁致伸缩（1.70≤x≤…

采用金相、Ｘ射线衍射、电子探针显微分析、交流初始磁化率和标准应变测试技术研究了Ｄｙ０．６５Ｔｂ０．２５Ｐｒ０．１Ｆｅｘ合金的显微组织、居里温度和磁致伸缩。