低聚壳聚糖几何结构和物理化学属性的理论研究

运用密度泛函B3LYP/6-31G+(d)方法对gg构象的低聚壳聚糖进行了结构优化、频率计算和电子结构,并用更高精度的WB97XD/6-311+G(d,p)方法计算了平均结合能及零点能校正,分析了热力学性质.结果表明,由于低聚壳聚糖中的氢键作用,使其形成螺旋结构;聚合度的增加,使平均结合能随之下降,结构的稳定性增强;在降解过程中,均为放热反应,验证了利用降温来提高降解产率的实验的可行性;此外,聚合度的增加,使能隙减小且快速收敛于聚合度为7的6.99 eV,稳定的反应活性与实验相符;HOMO、LUMO的电子密度分布表明,化学活性集中在C2位的氨基、C6位的羟基以及链的两端位置.该结果对低聚壳聚糖模型的建立和低聚壳聚糖降解过程、活性位置以及物理化学属性的尺寸依赖等现象的研究有着指导意义.     

任意相位差条纹信号细分方法的研究

为消除传统细分方法中由于两路条纹信号不正交引入的细分误差，提出了一种可对任意相位差条纹信号直接细分的新方法。根据两路条纹信号的极性和幅值大小，把一个信号周期分成8个区段。高速采集两路条纹信号，通过判断信号采样点所处的区段是否跳变对信号幅值交点进行动态跟踪。对不足一个周期的条纹移动，当测量出起点与终点的幅值，计算出其所在的区段及位置后，结合两路信号的交点，可实现对任意相位差条纹信号的细分。实验结果表明，该方法突破了传统细分方法必须信号正交的限制，可对任意相位差信号进行准确地细分，降低了条纹测量中器件安装与调试的难度，具有更强的环境适应性和抗干扰能力。     

采用可见/近红外光谱检测大麦叶片过氧化氢酶与过氧化物酶含量的研究

采用可见/近红外光谱对丙酯草醚胁迫下大麦叶片过氧化氢酶(catalase, CAT)与过氧化物酶(peroxidase, POD)含量预测进行研究。对500～900 nm光谱采用移动平均法(moving average, MA)11点平滑方法进行预处理。采用蒙特卡罗-偏最小二乘法(monte carlo-partial least squares, MCPLS)方法分别对于CAT与POD的含量预测剔除7个与8个异常样本。基于全部光谱建立了CAT与POD含量预测的PLS,最小二乘支持向量机(least-squares support vector machine, LS-SVM)与极限学习机(extreme learning machine, ELM)模型,ELM模型对CAT含量预测效果最好,建模集相关系数(correlation coefficient of calibration, R_c)为0.916,预测集相关系数R_p为0.786;PLS模型对POD含量预测效果最佳,R_c为0.984,R_p为0.876。采用连续投影算法(successive projections algorithm, SPA)算法分别为CAT与POD预测选择了8个与19个特征波长,基于特征波长建立的PLS,LS-SVM与ELM模型中,ELM模型对CAT与POD含量预测效果均最佳,CAT含量预测的相关系数为R_c=0.928,R_p=0.790;POD含量预测的相关系数R_c=0.965,R_p=0.941。基于全谱与基于特征波长的回归分析模型预测效果相当,且对POD含量的预测效果优于对CAT含量的预测效果,而这需要进一步研究以得到精度和稳定性更高的预测模型。研究结果表明,采用可见/近红外光谱结合化学计量学方法可以实现对除草剂胁迫下大麦叶片CAT与POD含量的预测。     

Influence of the illumination on the subband structure and?occupation in AlxGa1?xN/GaN heterostructures

The subband structure and occupation in the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces have been investigated by means of temperature dependent Shubnikov–de Haas (SdH) measurements at low temperatures and high magnetic fields under illumination. After the illumination of the heterostructures, the total two-dimensional electron gas concentration increases, and the SdH oscillation amplitudes are enhanced when there is no additional subband occupation. It is also found that the energy separation between the subbands decreases after the illumination. We suggest that the illumination decreases the electric field and thus weakens the quantum confinement of the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces. The GaN layer is thought to be the primary contributor of the excited electrons by the illumination.     

高斯光束经圆形光阑衍射的远场发散特性

线偏振高斯光束经圆形光阑衍射后,其远场可表示成互相正交的横电(TE)项和横磁(TM)项之和。利用TE项和TM项的远场能流分布,导出了高斯衍射光束的TE项和TM项远场功率的解析表达式,由此可度量TE项和TM项在远场占总功率的比例。基于能流二阶矩的定义,给出了高斯衍射光束、TE项和TM项远场发散角的解析式以及三者远场发散角间的关系通式,重点分析了f参数和截取参数对远场发散角的影响。结果表明:随着f参数的增大,远场发散角先增大后趋向于各自的饱和值。截取参数对远场发散角的影响与f参数相关,当f参数较大时,截取参数对远场发散角的影响不明显;当f参数适中时,随着截取参数的增大,远场发散角先减小后趋向于各自的最小值;但当f参数较小时,高斯衍射光束和TM项二者的远场发散角出现一定的波动性。     

Manganese doping effects on interband electronic transitions,lattice vibrations,and dielectric functions of perovskite-type Ba<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>TiO<Subscript>3</Subscript> ferroelectric ceramics

The Ba_0.4Sr_0.6−x Mn _x TiO₃ (BSMT) ceramics with different Mn composition (from 1% to 10%) have been prepared via the conventional solid-state reaction sintering. The X-ray diffraction analysis shows that the ceramics are polycrystalline with the single perovskite phase. The lattice vibrations and optical properties have been investigated using Raman scattering, spectroscopic ellipsometry (SE), and infrared reflectance spectra. It was found that the optical bandgap for the BSMT ceramics is varied between 3.40 and 3.65 eV. The three first-order Raman-active phonon modes can be observed, and the frequency of the A ₁(LO₃)/E(LO) mode shows a blue shift of 8 cm⁻¹ with the Mn composition, which can be attributed to the distortion of the TiO₆ octahedron. With increasing Mn composition, the frequency of the infrared-active TO₄ mode decreases from 532 to 520 cm⁻¹, owing to the local variation of the lattice constant induced by the Mn incorporation. Moreover, the optical functions of the ceramics from the far-infrared to ultraviolet region are obtained based on the SE and reflectance spectra, which is useful for the potential applications in ferroelectric-based optoelectronic devices.     

Compact and efficient coupler to interface hybrid dielectric-loaded plasmonic waveguide with silicon photonic slab waveguide

A coupler is proposed to interface a hybrid dielectric-loaded plasmonic waveguide (HDLPW) with a silicon photonic slab waveguide. The HDLPW is firstly designed and optimized to attain the best tradeoff between the mode confinement and the propagation distance. The designed coupler is inspired from the taper configuration and numerically modeled through finite-difference time-domain (FDTD) simulation. The results demonstrate that a high confinement and low loss of the energy is achieved from a silicon photonic slab waveguide into the dielectric slot of area 50×200 nm² in the HDLPW. The transmission attained through the coupler with a compact size of 400 nm is found to be as high as 80% (1 dB). Further, the planar nature of taper configuration makes the coupler easy to fabricate using the state-of-the-art CMOS facilities. The proposed coupler is useful in enabling the integration between photonic and hybrid plasmonic waveguides and thus realizing on-chip hybrid integrated circuits.     

Infrared and Raman investigation of the charge–density-wave state in rare-earth tri-telluride compounds

We summarize our recent efforts in investigating the charge–density-wave (CDW) state of the rare-earth tri-tellurides RTe₃ by means of infrared and Raman techniques. We identify the CDW gap, as order parameter of the broken-symmetry ground state, as well as the collective mode of the CDW condensate.     

Domain,dielectric and optical studies in antiferroelectric (Pb,La) (Zr,Sn, Ti)O3 single crystals

Antiferroelectric (Pb, La) (Zr, Sn, Ti)O₃ (PLZST) single crystals have been successfully grown by flux method using PbO–PbF₂–B₂O₃ as the flux. The obtained crystals are pale yellow in color and translucent. Domain structures, dielectric constants and optical transmission measurements have been performed on the 〈001〉-oriented PLZST single crystals. Two types of domains, namely, 90° and 180° domains, are observed. The extinction of 90° domains at P/A: 0° reveals a tetragonal structure in the crystal. The sequence of phase transitions from antiferroelectric to ferroelectric and then paraelectric has been established with increasing temperature. According to the modified Curie–Weiss relationship, the PLZST crystal is in an intermediate state between normal and relaxor antiferroelectrics. The broad optical transparent region (from 0.4 to 7.0 μm) and high optical transmittance (up to 65%) indicate that PLZST crystals are promising for optical uses.     

有限气相反应速率条件下MFF模型应用方法的研究

本文使用CO相对燃烧速率的概念和通用的有效影响参数转化方程,将带有气相反应速率无穷快假设的移动火焰锋面(MFF)模型成功地扩展应用到有限气相反应速率条件的计算中。对于多组不同有限气相反应速率、以及不同粒径的碳粒燃烧计算,MFF模型扩展应用的预报结果都与严格连续膜模型符合较好,碳粒着火温度的预报也更为准确。