关于货币市场结构转换利率期限结构的实证研究

基本的利率期限结构模型均未能将结构转换效应考虑进来,因此为了探讨结构转换架构下利率期限结构模型的特性,本文在中国货币市场利率数据的基础上对基本利率期限结构模型和结构转换利率期限结构模型进行了比较研究,结果发现中国货币市场利率动态中存在明显的结构转换效应,且在结构转换效应中其本身也存在着不稳定性,这充分反映了中国货币市场在发展过程中的不成熟特征.     

Experimental characterization and numerical analysis of the 4H-SiC p-i-n diodes static and transient behaviour

Steady-state and turn-off switching characteristics of aluminium-implanted 4H-SiC p-i-n diodes designed for high-current density operation, are investigated experimentally and by mean of numerical simulations in the 298-523 K temperature range. The diodes present circular structure with a diameter of 350 μm and employ an anode region with an aluminium depth profile peaking at 6×10¹⁹ cm⁻³ at the surface. The profile edge and the junction depth are located at 0.2 and 1.35 μm, respectively. At room temperature the measured forward current density is close to 370 A/cm² at 5 V with an ideality factor always less than 2 before high-current injection or device-series resistance became dominant. The transient analysis reveals a strong potential of this diodes for use in high-speed, high-power applications, especially at high temperature, with a very low turn-off recovery time (<80 ns) in the whole range of test conditions. The simulated results match the experimental data, showing that the switching performance is mainly due to the poor minority charge carrier lifetime estimated to be 15 ns for these implanted devices.     

星载光谱仪光路切换组件振动特性仿真分析

为研究星载设备在复杂力学环境下的振动响应特性, 利用有限元分析软件对光谱仪光路切换组件进行仿真分 析。首先根据星上载荷的力学环境试验条件, 通过谱形参数计算方法建立星上载荷输入谱密度激励曲线图。随后, 对 光路切换组件进行模态分析和随机振动分析, 得到激励谱条件下组件的振动响应结果和最大等效应力。强度校核计 算结果显示组件安全裕度为 1.57, 满足刚度和强度要求。最后, 对整机振动进行试验验证, 验证结果显示组件结构完 好, 且光学性能比照试验结果显示振动前后, 三个通道的卤素灯图像的成像范围、光谱强度特性等基本一致, 光路切 换组件无异常变化, 验证了仿真分析的可靠性。     

A 4H-SiC trench MOSFET structure with wrap N-type pillar for low oxide field and enhanced switching performance

An optimized silicon carbide (SiC) trench metal-oxide-semiconductor field-effect transistor (MOSFET) structure with side-wall p-type pillar (p-pillar) and wrap n-type pillar (n-pillar) in the n-drain was investigated by utilizing Silvaco TCAD simulations. The optimized structure mainly includes a p$+$ buried region, a light n-type current spreading layer (CSL), a p-type pillar region, and a wrapping n-type pillar region at the right and bottom of the p-pillar. The improved structure is named as SNPPT-MOS. The side-wall p-pillar region could better relieve the high electric field around the p$+$ shielding region and the gate oxide in the off-state mode. The wrapping n-pillar region and CSL can also effectively reduce the specific on-resistance ($R_{\rm on,sp}$). As a result, the SNPPT-MOS structure exhibits that the figure of merit (FoM) related to the breakdown voltage ($V_{\rm BR}$) and $R_{\rm on,sp}$ ($V_{\rm BR}^{2}R_{\rm on,sp}$) of the SNPPT-MOS is improved by 44.5%, in comparison to that of the conventional trench gate SJ MOSFET (full-SJ-MOS). In addition, the SNPPT-MOS structure achieves a much faster-witching speed than the full-SJ-MOS, and the result indicates an appreciable reduction in the switching energy loss.     

Optimal harvesting policy of an inland fishery resource under incomplete information

A new mathematical model for finding the optimal harvesting policy of an inland fishery resource under incomplete information is proposed in this paper. The model is based on a stochastic control formalism in a regime‐switching environment. The incompleteness of information is due to uncertainties involved in the body growth rate of the fishery resource: a key biological parameter. Finding the most cost‐effective harvesting policy of the fishery resource ultimately reduces to solving a terminal and boundary value problem of a Hamilton‐Jacobi‐Bellman equation: a nonlinear and degenerate parabolic partial differential equation. A simple finite difference scheme for solving the equation is then presented, which turns out to be convergent and generates numerical solutions that comply with certain theoretical upper and lower bounds. The model is finally applied to the management of Plecoglossus altivelis, a major inland fishery resource in Japan. The regime switching in this case is due to the temporal dynamics of benthic algae, the main food of the fish. Model parameter values are identified from field measurement results in 2017. Our computational results clearly show the dependence of the optimal harvesting policy on the river environmental and biological conditions. The proposed model would serve as a mathematical tool for fishery resource management under uncertainties.     

Metal-Organic Frameworks as Hosts for Fluorinated Azobenzenes: A Path towards Quantitative Photoswitching with Visible Light

Fifteen new photochromic hybrid materials were synthesized by gas phase loading of fluorinated azobenzenes, namely ortho-tetrafluoroazobenzene (tF-AZB), 4H,4H′-octafluoroazobenzene (oF-AZB), and perfluoroazobenzene (pF-AZB), into the pores of the well-known metal-organic frameworks MOF-5, MIL-53(Al), MIL-53(Ga), MIL-68(Ga), and MIL-68(In). Their composition was analysed by elemental (CHNS) and DSC/TGA. For pF-AZB_0.34@MIL-53(Al), a structural model based on high-resolution synchrotron powder diffraction data was developed and the host-guest and guest-guest interactions were elucidated from this model. These interactions of O−H⋅⋅⋅F and π⋅⋅⋅π type were confirmed by significant shifts of the O−H frequencies in loaded and unloaded MOFs of the MIL-53 and MIL-68 series. Most remarkably, all of the synthesized F-AZB@MOF systems can be switched with visible light, and some of them show almost quantitative (>95 %) photo-isomerization between its E and Z forms with no significant fatigue after repeated switching cycles.     

Fabrication of a Cu‐Cone‐Shaped Cation Source Inserted Conductive Bridge Random Access Memory and Its Improved Switching Reliability

Conductive bridge random access memory (CBRAM) has been regarded as a promising candidate for the next‐generation nonvolatile memory technology. Even with the great performance of CBRAM, the global generation and overinjection of cations after much repetitive switching cannot be prevented. The overinjection of cations into an electrolyte layer causes high‐resistance‐state resistance (R_HRS) degradation, on/off ratio reduction, and eventual switching failure. It also degrades the switching uniformity. In this work, a Cu‐cone‐structure‐embedded TiN/TiO₂/Cu cone/TiN device is fabricated to alleviate the problems of Cu‐based CBRAM, mentioned above. The fabrication method of the device, which is useful for laboratory scale experiment, is developed, and its superior switching performance and reliability compared with the conventional planar device. The insertion of the Cu cone structure allows the placement of only a limited amount of cation source in each cell, and the embedded conical structure also concentrates the applied electric field, which enables filament growth control. Furthermore, the concentrated field localizes the resistive switching on the tip area of the cone structure, which makes the effective switching area about tens of nanometers even for the much larger area of the entire electrode (several µm²).     

Reversible Crystal-to-Crystal Phase Transitions with High-Contrast Luminescent Alterations for a Thermally Activated Delayed Fluorescence Emitter

Merging thermally activated delayed fluorescence (TADF) and mechanochromic luminescence (MCL) into one single molecule is a promising strategy for developing multifunctional organic materials. Herein, a unique multifunctional molecule TPA-DQP, comprising a large π-conjugated diquinoxalino[2,3-a:2′,3′-c]phenazine (DQP) as the acceptor and triphenylamine (TPA) as the donor, is designed and synthesized. TPA-DQP possesses polymorphism, efficient TADF emission as well as MCL property with high-contrast in emission colors from 576 to 706 nm. Reversible crystal-to-crystal phase transitions in response to external stimuli such as vapor fuming and heating are realized on the basis of the two polymorphs of TPA-DQP. The distinct crystal-to-crystal phase transition is attributed ultimately to the change of packing arrangements and intermolecular interactions of the two polymorphs under stimuli. Furthermore, TPA-DQP-based organic light emitting diode (OLED) device achieves external quantum efficiency as high as 18.3% at 676 nm, which represents the best performance for deep-red OLEDs based on MCL-active TADF emitters. This study reports a novel MCL-active TADF material that exhibits crystal-to-crystal phase transition and brings insight into the underlying relationship between molecular packing modes and the photoluminescent behavior.