LED在自感现象演示实验中的应用

利用发光二极管对自感现象演示实验进行了改进,明显地提高了实验效果,加深了对自感现象的认识。     

Photocatalytic degradation of methyl orange by nano-TiO_2 thin films prepared by RF magnetron sputtering

Nano-TiO2 thin films are deposited by radio frequency （RF） magnetron sputtering using TiO2 ceramic target and characterized by X-ray diffractometer, atomic force microscope, and ultraviolet-visible spectrophotometer. The photocatalytic activity is evaluated by light-induced degradation of methyl orange solutions （5, 10, and 20 ppm） using a high pressure mercury lamp as the light source. The film is amorphous, and its energy gap is 3.02 eV. The photocatalytic degradation of methyl orange solution is the first-order reaction and the apparent reaction rate constants are 0.00369, 0.0024, and 0.00151 for the methyl orange solution concentrations of 5, 10, and 20 ppm, respectively.     

Two-dimensional model of elastically coupled molecular motors

A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins.Extensive Langevin simulations of the model are performed.We discuss the dependences of motion and efficiency on the model parameters,including the external force and the temperature.A good qualitative agreement with the expected behavior is observed.     

Experimental observation of classical subwavelength interference with a pseudothermal light source

We report the experimental observation of classical subwavelength double slit interference with a pseudothermal light source. The experimental results are in good agreement with the theoretical simulation using the second order correlation function for the thermal light.     

A new subdivision method for grating-based displacement sensor using imaging array

A new subdivision method for grating-based displacement sensor was proposed in the present study, which takes advantages of imaging array's high resolution and pixels’ good uniformity in the space. In this method, the magnified grating image is received by imaging array and grating pitch is directly subdivided by pixels, which is quite different from that moiré fringe is subdivided by complex subsequent circuits in moiré-type displacement sensor. The displacement is statistically calculated by using the whole grating image, which greatly eliminates the errors arising from illumination, electrical signals’ fluctuation, grating defect, and so on. Therefore, the subdivision method is easy to obtain signal with high signal-to-noise ratio, insensitive to some external factors, and able to attain high measurement precision with low cost. In this paper, the principle of subdivision method was illuminated, the systemic resolution was theoretically discussed, the measurement precision was experimentally checked, and the uncertainty of measurement was analyzed. The subdivision system consisted of the grating with 20-μm pitch and the CMOS image sensor with the pixels of 1280×1024 had the resolution of 0.04 μm, and the maximum displacement error was less than 0.4 μm, which has been tested in the Abbe comparator platform.     

研究堆慢正电子源构建中的关键机理问题

研究堆慢正电子源是获得高强度慢正电子束流的有效方式,国际上己建成多座装置并获得广泛应用.与常规同位素慢正电子源相比,研究堆慢正电子源的物理过程复杂,影响末端束流强度的因素众多,对其进行深入研究与合理建模是未来在中国绵阳研究堆(CMRR)上构建慢正电子源的基础.本文厘清了研究堆慢正电子产生的关键过程与物理机理,建立了预测末端正电子束流强度的理论模型,找到了影响其末端强度的主要物理量:快正电子体产生率、慢化体有效表面积、慢化体扩散距离、慢正电子从表面被提取到靶环末端的效率、及束流系统提取效率.用多种实验结果对模型进行校验,包括多个同位素慢正电子源的效率测量值,以及PULSTAR研究堆慢正电子源测量结果,充分验证了模型正确性.根据模型对各物理量的影响因素进行了分析,找到了需着重关注的影响因素,对未来源/靶结构的设计给出建议.     

Direct numerical simulation methods of hypersonic flat-plate boundary layer in thermally perfect gas

High-temperature effects alter the physical and transport properties of air such as vibrational excitation in a thermally perfect gas,and this factor should be considered in order to compute the flow field correctly.Herein,for the thermally perfect gas,a simple method of direct numerical simulation on flat-plat boundary layer is put forward,using the equivalent specific heat ratio instead of constant specific heat ratio in the N-S equations and flux splitting form of a calorically perfect gas.The results calculated by the new method are consistent with that by solving the N-S equations of a thermally perfect gas directly.The mean flow has the similarity,and consistent to the corresponding Blasius solution,which confirms that satisfactory results can be obtained basing on the Blasius solution as the mean flow directly in stability analysis.The amplitude growth curve of small disturbance is introduced at the inlet by using direct numerical simulation,which is consistent with that obtained by linear stability theory.It verified that the equation established and the simulation method is correct.     

Evaluation of an oral carrier system in rats: bioavailability and gastrointestinal absorption properties of curcumin encapsulated PBCA nanoparticles

A new oral delivery system, polybutylcyanoacrylate nanoparticles (PBCNs), was introduced to improve the oral bioavailability of curcumin (CUR), a poorly soluble drug. The formulation was optimized by orthogonal design and the optimal PBCNs loading CUR exhibited a spherical shape under transmission electron microscopy with a range of 40?C400?nm. Physicochemical state of CUR in PBCN was investigated by X-ray diffraction and the possible structure changes occurring in CUR after conjugating with polybutylcyanoacrylate were studied with FTIR. The results indicated that CUR in PBCN was in a non-crystalline state and CUR was encapsulated in PBCN without chemical reaction. The oral pharmacokinetic study was conducted in rats and the relative bioavailability of CUR encapsulated PBCNs to the crude CUR was more than 800%. The in situ absorption experiment in rat intestine indicated the absorption was first order with passive diffusion mechanism. The absorption results in various segments of intestine showed that the main absorption sites were ileum and colon. It can be concluded that PBCNs as an oral carrier can significantly improve the oral absorption of a poorly soluble drug.     

Half baudrate electrical clock based demultiplexing scheme for OTDM-DQPSK signal using SOA and optical filter

A demultiplexing scheme based on semiconductor optical amplifier(SOA)and optical filter for optical time division multiplexing differential quadrature phase shift keying(OTDM-DQPSK)system is proposed and investigated experimentally.With only a common half baudrate electrical clock modulated 33%duty cycle return-to-zero(RZ-33)optical clock signal as pump,this scheme is cost-effective,energy-efficient,and integration-potential.A proof-of-concept experiment is carried out for the demultiplexing of a 2×40-GBd OTDM-DQPSK signal.Error-free performance is demonstrated,and the average power penalty for both channels is about 3 dB.     

基于压扩变换的60GHz正交频分复用光载无线通信系统实验研究

提出并实验研究了在60GHz正交频分复用(OFDM)-光载无线通信(ROF)系统中采用压扩变换技术降低OFDM信号峰值平均功率比(PAPR),并提高系统的接收灵敏度。实验结果表明,携带基于压扩变换的2.5Gb/s60GHz的OFDM-ROF信号经标准单模光纤传输50km后,在无色散补偿和误码率为10-3的条件下,当入纤功率为12dBm时,系统接收灵敏度提高约2.3dB,并且当互补累积分布函数(CCDF)为10-4时,OFDM信号的PAPR下降约3dB。