平凉市模数整体过渡转换发展状况

我国将于2008年全面推广地面数字电视,2015年关闭模拟电视。平凉同全国兄弟省、市一样,不甘落后,积极努力创造条件,争取早日过渡加速发展,为尽早加入广播电视数字化行列构建平台。     

Frontiers in Circularly Polarized Phosphorescent Materials

Circularly polarized luminescence (CPL) materials have received increasing attention in recent years. Amongst various CPL materials, circularly polarized phosphorescence (CPP) materials featuring long life-time represent a novel research frontier and exhibit promising applications in various fields. Herein, the state-of-the-art advances of CPP materials are systematically summarized, as classified into transition metal complexes, organic small molecules, polymers, and organic/inorganic hybrid materials. Besides, the recent applications of CPP materials in organic light-emitting diodes and encryption display are also summarized. Furthermore, the current challenges and future perspectives are put forward. It is expected that this review will offer more inspirations for the future rational design of advanced CPP materials, thus further promoting their future practical applications.     

Collective Surface Enabling an Ultralong Life of LiCoO2 at High Voltage and Elevated Temperature

Rapidly increasing demand for energy density in consumer electronics is eager for developing high-voltage LiCoO₂ (LCO). However, some great challenges such as severe phase transition and surface instability negate the cycle life of LCO operated at high-voltages (≥4.6 V). Herein, a chemical reconstruction strategy is proposed to form a collective surface of LCO through an interdiffusion reaction of MgHPO₄·3H₂O (MP) so as to extend the cycle life of high-voltage LCO. The collective surface renders a three-layer configuration that demonstrates an amorphous Li₃PO₄ outmost layer, a spinel-like layer beneath, and a Mg diffusion layer within LCO bulk. MP with relatively low hardness enables the uniform precoating via mechanical mixing, followed by a sintering process to undergo an interdiffusion reaction. Li₃PO₄ is an intrinsic electrochemical stabilizer against interfacial side reactions. The spinel-like compounds build a high-voltage-stable surface against irreversible O₂ release. In addition, Mg diffuses into the bulk lattice to suppress irreversible phase transition during the deep delithiation of LCO. Therefore, such modified LCO with a collective surface exhibits ultralong life with capacity retention of 82% after 1000 cycles at 1 C within 3.0–4.6 V and stable operating at 4.7 V or elevated temperature (45 °C).     

Magneto-polaron induced intersubband optical transition in a wide band gap II–VI semiconductor quantum dot

Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a Cd_0.8Zn_0.2Se/ZnSe quantum dot in the presence of magnetic field strength. The magneto-polaron induced hydrogenic binding energy as a function of dot radius in the wide band gap quantum dot is calculated. The oscillator strength and the spontaneous lifetime are studied taking into account the spatial confinement, magnetic field strength and the phonon contribution. Numerical calculations are carried out using variational formulism within the single band effective mass approximation. The optical properties are computed with the compact density matrix method. The magneto-polaron induced optical gain as a function of photon energy is observed. The results show that the optical telecommunication wavelength in the fiber optic communications can be achieved using CdSe/ZnSe semiconductors and it can be tuned with the proper applications of external perturbations.     

First principles study of structural,electronic and optical properties of AgSbS2

In this work, we study the structural, electronic and optical properties of AgSbS₂, using full-potential linearized augmented plane wave and the pseudopotential plane wave scheme in the frame of generalized gradient approximation. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. Our results suggest a phase transition from AF-IIb phase to rocksalt (B1) phase under high pressure. The calculated band structure and density of states show that the material under load has an indirect energy band gap X→(LГ) for AF-IIb phase (semiconductor) and a negative band gap W→(ГX) for B1 phase (semimetal). The optical properties are analyzed and the origin of some peaks in the spectra is discussed. Besides, the dielectric function, refractive index and extinction coefficient for radiation up to 14 eV have also been reported and discussed.     

质心干扰与切割效应探讨

针对无源质心干扰反导作战过程中箔条云和舰艇作为面目标考虑的情况,根据波束线宽变化确定的质心效应规律对其进行了定量分析,探讨了一种被称为切割效应的质心转移过程,通过计算舰艇和箔条云对导弹视场角、距离的变化,判断了目标和箔条云的切割程度及先后顺序,可推断出质心干扰成功或失败,同时为舰艇指挥员正确使用质心干扰防御反舰导弹提供了理论依据。     

Lithiation-Induced Defect Engineering to Promote Oxygen Evolution Reaction

Exploring efficient electrocatalysts for oxygen evolution reaction (OER) is an urgent need to advance the development of sustainable energy conversion. Though defect engineering is considered an effective strategy to regulate catalyst activity for enhanced OER performance, the controllable synthesis of defective oxides electrocatalysts remains challenging. Here, oxygen defects are introduced into NiCo₂O₄ nanorods by an electrochemical lithiation strategy. By tuning in situ lithiation potentials, the concentration of oxygen defects and the corresponding catalytic activity can be feasibly regulated. In addition, the relationship between the changes in the defect density and electronic structure and the lithiation cut-off voltages is revealed. The results show that NiCo₂O₄ nanorods undertook intercalation and two-step conversion reaction, in which the lithiation-induced conversion reaction gives rise to a CoO@NiO-based structure with higher defect density and lower oxidation states. As a result, the defective CoO@NiO-based catalyst exhibits exceptional OER activity with an overpotential of 270 mV at 10 mA cm⁻², which is about 74 mV below the pristine nanomaterials. This research proposes a novel strategy to explore high-performance catalysts with structural stability and defect control.     

毫米波LTCC组件中的波导-微带转换

介绍了Ka波段LTCC(低温共烧陶瓷)组件中矩形波导-微带的一种新型转换结构。这种转换结构通过波导和微带间的开槽耦合以及在LTCC多层布线基板中用金属填充通孔阵列等效替换波导壁而实现。此类型波导到微带的转换无需将安装在波导内的LTCC基板加工成特殊形状,便于加工,而且转换对LTCC基板和波导的机械安装公差要求较低。     

电镜能谱仪中过渡金属元素的化学价态分析

本文利用电子探针－能谱仪（ EPMA-EDS）对试样微米区域内过渡金属元素的化学价态进行了分析。研究结果表明,过渡金属元素的化学价态可以通过特征X射线Lα／Kβ强度比值结果进行区分,但试样形状、组成成分和化学结构等都可能影响化学价态的判断。此外,本文结合电子－离子碰撞的相关理论对实验结果进行了合理的解释,并将此方法应用到未知样品元素价态的判断中。研究结果对样品内部过渡金属元素化学价态的判断具有重要参考价值。     

应用于OTDR测试的光纤光栅反射器

本文阐述了反射器在PON的OTDR测试诊断系统中的作用及其必要性,探讨了光纤光栅反射器方案的应用特点、与介质薄膜滤波器对比的优势及在国际市场上的应用情况,并介绍了目前光纤光栅反射器在成本方面的突破。