基于PLC的直流电机控制系统设计

本文提出了一种利用可编程逻辑控制器件(PLC)对他励直流电机进行速度控制的方法。该方法使PLC工作在DC/DC斩波模式,通过将固定直流电压转变为可变直流电压提供给电机电枢。Pang-Pang控制是依据参考速度来导通或关断直流电机的电源。这种方法简单、迅速而且有效,能够在0至100%范围内调整电机转速。该系统能够广泛应用于不同的工业应用场合。     

RF linearity characteristics of SiGe HBTs

Two-tone intermodulation in ultrahigh vacuum/chemical vapor deposition SiGe heterojunction bipolar transistors (HBTs) were analyzed using a Volterra-series-based approach that completely distinguishes individual nonlinearities. Avalanche multiplication and collector-base (CB) capacitance were shown to be the dominant nonlinearities in a single-stage common emitter amplifier. At a given I_c an optimum V_ce exists for a maximum third-order intercept point (IIP3). The IIP3 is limited by the avalanche multiplication nonlinearity at low I_c, and limited by the C_CB nonlinearity at high I_c. The decrease of the avalanche multiplication rate at high I_c is beneficial to linearity in SiGe HBTs. The IIP3 is sensitive to the biasing condition because of strong dependence of the avalanche multiplication current and CB capacitance on I_c and V_ce. The load dependence of linearity was attributed to the feedback through the CB capacitance and the avalanche multiplication in the CB junction. Implications on the optimization of the transistor biasing condition and transistor structure for improved linearity are also discussed     

Multi-Stimuli-Induced Mechanical Bending and Reversible Fluorescence Switching in a Single Organic Crystal

Fluorescent single crystals that respond to multiple external stimuli are of great interest in molecular machines, sensors, and displays. The integration of photo- or acid-induced fluorescence enhancement and bending in one organic crystal, however, has not been reported yet. Herein, we report the interesting plastic photomechanical bending and switching on of the fluorescence of an azine crystal in a single-crystal transformation, due to extended π-conjugation and molecular slippage. Moreover, the fluorescent plastic bending driven by multiple volatile acid vapors was firstly observed, and attributed to the synergistic effect of push–pull electronic structure and hydrogen bonding. The single crystal also shows high elasticity under external force. In addition, reversible fluorescence switching can be triggered by grinding and solvent fuming, as well as by the adsorption and desorption of HCl vapor. The integration of plastic, elastic bending and switch-on fluorescence into one single crystal provides a new strategy for next-generation smart materials.     

乙酰羟酸合成酶突变体对除草剂阔草清抗性的预测研究

本工作测定了商品化除草剂阔草清对大肠杆菌乙酰羟酸合成酶II及其突变体的抑制常数. 利用生物大分子的定量构效关系方法(MB-QSAR)建立了定量、可视的突变体性质与结构关系模型. 实验数据与计算数据之间显示了良好的相关性: MB-QSAR/CoMFA (comparative molecular field analysis)模型的交叉验证系数q²=0.691, 非交叉验证相关性系数r²=0.947, 外部预测能力r²_pred=0.759; MB-QSAR/CoMSIA (comparative molecular similarity indices analysis)模型的相应值分别为0.625, 0.960和0.619. 模型的三维结构-性质关系图为突变体抗性提供了直观阐释, 为抗性规避性农药的设计提供了有价值的信息. 同时, 该模型也在一定程度上显示了除草剂种属选择性的预测能力.     

Electrochemical Immunosensor for the Sensitive Detection of Alzheimer's Biomarker Amyloid-β (1–42) Using the Heme-amyloid-β (1–42) Complex as the Signal Source

The amyloid-β peptide (1–42) (Aβ₄₂) can provide high diagnostic accuracy for the early diagnosis of Alzheimer's disease (AD). In this study, an immunosensor based on the peroxidase-like activity of heme-Aβ₄₂ was designed for Aβ₄₂ detection. The glassy carbon electrode (GCE) was electrodeposited Au particles (GCE/Au). The GCE/Au was modified using polythionine-methylene blue (PTH−MB), AuNPs, monoclonal antibody (anti-Aβ₄₂), and bovine serum albumin (BSA), successively. The GCE/Au/PTH−MB/AuNPs/anti-Aβ₄₂/BSA could competitively recognize Aβ₄₂ and heme-Aβ₄₂. The anchored heme-Aβ₄₂ showed strong electrocatalytic activity between H₂O₂ and ferrocenemethanol. Under optimum conditions, we determined detection limits of 17.3 pM in PBS pH 7, 25.2 pM in serum, and 23.8 pM in saliva. The recovery ranged from 71.0 % to 117.8 %.     

Bi0·5K0·5TiO3-based lead-free relaxor ferroelectric with high energy storage performances via the grain size and bandgap engineering

Dielectric capacitors with high energy storage performance show a huge competitive advantage for use in vehicles and power electronics. Here, the (1-x) (0.75Bi_0·5K_0·5TiO₃?0.25BiFeO₃) – xSr_0.7Bi_0·2TiO₃ (BKT-BF-xSBT) materials were designed based on the dual optimization strategy of grain size and bandgap. The optimal performance was obtained in the BKT-BF-0.4SBT sample, achieving high energy storage density W_rec of 5.21 J/cm³ and high energy storage efficiency η of 90.87% at 360 kV/cm. The addition of SBT optimized the microstructure and relaxation behavior of BKT-BF ceramic, giving rise to the formation of polar nanoregions (PNRs), small grain size (G), compact grain boundaries, and wide bandgap (E_g) synchronously. Encouragingly, prominent stabilities against temperature, frequency, and cycle numbers, and favorable charge/discharge performance (power density P_D ≈ 64.5 MW/cm³, τ_0.9 ≈ 90 ns) are also accomplished in designed BKT-based ceramics. These findings indicate that the BKT-BF-xSBT ceramic system has excellent potential in the dielectric energy storage field and also provides a viable prospect for engineering design of high-efficiency lead-free dielectrics via bandgap and grain size.     

有机电致发光器件的磁电导效应研究进展

有机电致发光器件的磁电导效应,是指在恒定外加偏压下,对于不含有任何磁性材料功能层的有机电致发光器件,通过器件的电流发生变化的现象。由于器件对外磁场很敏感,通过给器件施加偏压,如果有外磁场的存在,器件的电流会有较显著地改变,通过与事先测定好的B-I 特性曲线对比,便能测定外加磁场的大小。因此利用这种效应可以制成磁场传感器等新型实用器件。有机电致发光器件中存在复杂的激发态及自旋弛豫过程,充分了解这些复杂的物理机制有助于开发更加高效的器件,而磁场会对以上物理过程产生作用,因此是一种很好的研究有机电致发光机制的工具。故这种研究具有较大的科学价值和社会应用前景。文中将从有机电致发光器件磁电导效应的研究背景、发展现状及存在问题等几个方面做详细的论述,并探讨磁电导效应产生的可能微观机制,并对未来的研究方向做进一步的展望。     

基于梯度相位和显著性约束的Hausdorff 距离模板匹配方法

针对复杂背景下形状不规则、高度较低的平面目标自动识别问题,提出了一种基于Hausdorff距离的模板匹配方法。在完成平面目标前视模板制备后,文中首先定义了基于边缘位置、梯度相位和边缘点显著性约束的相似性度量方法,模板与实时图中对应两个边缘点位置越近、梯度相位差越小及实时图边缘点越显著,这两点的匹配就越好;然后融合三种度量结果,设计了一种基于边缘相位和显著性约束的Hausdorff 距离模板匹配方法,实现了平面目标轮廓的准确匹配。实测数据处理结果表明,该方法能够实现复杂地面场景中任意形状的平面目标轮廓的匹配定位,并且定位精度高、鲁棒性好、适用范围广