剪切力模式近场扫描光学显微镜的恒幅反馈控制方法研究

剪切力模式近场扫描光学显微镜(Near-field Scanning Optical Microscopy,NSOM) 的音叉探针间距控制系统中,用相位反馈控制和检测剪切力,同时采用比例＋积分（PI）技术实现对音叉探针振幅的反馈控制,使探针振幅在扫描过程中保持为恒定值.用相位信号作为探针与样品间距控制信号,分别在无振幅反馈和有振幅反馈两种情况下,以不同速率扫描得到标准CD_RW光盘光栅的两组图像,并进行了比较分析.实验表明,恒振幅反馈电路的引入有助于提高探针系统的响应速度和灵敏度,改善所得图像的质量及分辨率.     

Time‐resolved coherent anti‐Stokes Raman spectroscopy impulsively excited by supercontinuum

Time‐resolved coherent anti‐Stokes Raman scattering (CARS) impulsively excited by a supercontinuum (SC) is investigated. We show that it is critical to optimize the temporal overlapping of the constituent solitons of a SC in order to impulsively excite vibrational modes over a broad frequency range. The cross‐correlation frequency‐resolved optical gating technique is utilized to retrieve the optical response function of molecules under SC impulsive excitation, and background‐free CARS with spectral resolution significantly better than the bandwidth of the probe pulses is achieved. Copyright © 2011 John Wiley & Sons, Ltd.     

Absorption and resonance Raman spectroscopy of the 1Bu state of trans‐1,3,5‐hexatriene including vibronic coupling

The vibronic coupling between the first excited S₁ (2¹A_g) and the second excited S₂ (1¹B_u) singlet electronic states in spectroscopy of trans‐1,3,5‐hexatriene molecule is investigated on the basis of a model consisting of two electronic states coupled by two vibrational modes. Employing a perturbation theory that treats the intramolecular couplings in a perturbative manner, the absorption and resonance Raman cross sections and excitation profiles of this molecule are calculated using the time‐correlation function formalism. The non‐Condon corrections are included in evaluation of cross sections. The multidimensional time‐domain integrals that arise in these calculations have been evaluated for the case in which S₀ (1¹A_g) S₂ (1¹B_u) electronic transition takes place between displaced and distorted harmonic potential energy surfaces. The calculated spectra are in good agreement with the experimental ones. Copyright © 2011 John Wiley & Sons, Ltd.     

Origin of the Raman mode at 379 cm−1 observed in ZnO thin films grown on sapphire

In this work, we present a detailed Raman scattering study to clarify the origin of the mode at 379 cm⁻¹ which is observed in Raman spectra of the ZnO films grown on c‐sapphire substrates and generally attributed to the A₁‐transverse optical (A₁‐TO) mode of ZnO. The studied ZnO films were deposited by metal‐organic chemical vapor deposition on c‐sapphire and (0001) ZnO substrates. In the z(−,−)z̄ backscattering configuration, the A₁‐TO mode is forbidden, while the 379 cm⁻¹ peak is still observed in the as‐deposited film grown on sapphire substrate. However, this mode is not observed in Raman spectra of the as deposited film grown on ZnO substrate. We suggest that the peak at 379 cm⁻¹ is the E_1g mode of the sapphire substrate which is allowed in z(−,−)z̄ backscattering configuration. The effects of annealing, the substrate and the collection cross‐section on Raman active modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

Study of blood collection and sample preparation for analysis of vitamin D and its metabolites by liquid chromatography–tandem mass spectrometry

The analysis of vitamin D status, with special emphasis on 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, is gaining interest in clinical studies due to the classical and non-classical effects attributed to this prohormone. In this research, the influence of the two steps preceding determination (viz. sample collection and preparation) on the quantitative analysis of vitamin D and its more important metabolites has been studied. Two preparation approaches, deproteination and solid-phase extraction (SPE), have been evaluated in terms of sensitivity to delimit their application, thus establishing that detection of 1,25-dihydroxyvitamin D cannot be addressed by protein precipitation. Concerning sample collection, serum and plasma reported high accuracy (above 83.3%) for vitamin D and metabolites, while precision, expressed as relative standard deviation, was below 12.9% for all analytes in both samples. Statistical analysis revealed that serum and plasma provided similar physiological levels for vitamin D₃, 24,25-dihydroxyvitamin D₃ and 25-hydroxyvitamin D₃, while significantly different levels were obtained for 1,25-dihydroxyvitamin D₃, always higher in plasma than in serum. Sample collection and treatment have proved to be significant in the analysis of vitamin D and its relevant metabolites.     

Stochastic sensitivity analysis of coupled acoustic-structural systems under non-stationary random excitations

This paper presents a new sensitivity analysis method for coupled acoustic–structural systems subjected to non-stationary random excitations. The integral of the response power spectrum density (PSD) of the coupled system is taken as the objective function. The thickness of each structural element is used as a design variable. A time-domain algorithm integrating the pseudo excitation method (PEM), direct differentiation method (DDM) and high precision direct (HPD) integration method is proposed for the sensitivity analysis of the objective function with respect to design variables. Firstly, the PEM is adopted to transform the sensitivity analysis under non-stationary random excitations into the sensitivity analysis under pseudo transient excitations. Then, the sensitivity analysis equation of the coupled system under pseudo transient excitations is derived based on the DDM. Moreover, the HPD integration method is used to efficiently solve the sensitivity analysis equation under pseudo transient excitations in a reduced-order modal space. Numerical examples are presented to demonstrate the validity of the proposed method.     

Sliding mode control for a diffuse interface tumor growth model coupling a Cahn–Hilliard equation with a reaction–diffusion equation

We consider the sliding mode control (SMC) problem for a diffuse interface tumor growth model coupling a Cahn–Hilliard equation with a reaction–diffusion equation perturbed by a maximal monotone nonlinearity. We prove existence and regularity of strong solutions and, under further assumptions, a uniqueness result. Then, we show that the chosen SMC law forces the system to reach within finite time a sliding manifold that we chose in order that the tumor phase remains constant in time.     

线上线下混合式实验教学模式的改革与探索

大学化学实验课程是培养材料、化学、化工等专业人才应用基本操作和理论解决实际问题的综合性实践训练环节。文章探讨了当前大学化学实验发展由于受到仪器设备大型化、专业化、成本大、更新快等因素限制出现瓶颈,设计了线上线下混合实验教学模式,进行相应的软硬件建设,并开展线上线下混合式实验教学模式的改革与探索。该教学模式具有良好的教学效果,并且可复制可推广,为创新人才的培养和实验教学的创新提供了有益的借鉴。     

宽体液腔Janus-Helmholtz换能器

本文使用有限元方法对宽体液腔Janus-Helmholtz(JH)换能器进行了仿真分析,得出了壳体宽度拓展增量对JH换能器工作性能的影响规律。使用三维建模的方式,分析了连接部分对换能器性能的影响及宽体壳体的的模态,证明了三维建模的必要性。依据仿真优化结构设计了一款宽体液腔JH换能器并进行了湖上测试。最终测试结果与仿真结果有很好的一致性,相较直筒JH换能器其谐振频率降低300Hz,发射电压响应最高可达144dB。