Microwave dielectric and magnetic properties of superparamagnetic 8-nm Fe3O4 nanoparticles

The superparamagnetic 8-nm Fe₃O₄ nanoparticles were successfully prepared by chemical oxidation process. For the complex permittivity, the dual dielectric relaxation processes have been proved by two overlapped Cole–Cole semicircles, and the natural resonance frequency is 3.03 GHz for the complex permeability. The maximum reflection loss value reaches −55.5 dB at 6.11 GHz with 3.85 mm in the thickness of the absorbers for the superparamagnetic 8-nm Fe₃O₄ nanoparticles which is better than that of 150 nm and 30 nm Fe₃O₄ nanoparticles. It is believed that the superparamagnetic 8-nm Fe₃O₄ nanoparticles can be used as a kind of candidate for microwave absorber.     

Michelson干涉仪式光纤空气声传感器

介绍了一种用于直升机等低空目标探测的光纤空气声传感器.该传感器基于光纤Michelson干涉仪的原理,结合弹性盘片的应力应变理论分析和光纤粘接的工艺设计,采用相位载波解调技术进行信号解调.对比实验测试验证了这种声音探测技术可行性.传感器理论灵敏度为2.38 rad/Pa,实测灵敏度为1.5 rad/Pa,采用PGC相位解调理论最小可探测的最小声信号为6.7 μPa,即9.5 dB.传感器在20～300 Hz范围内响应基本平坦.结合声音传播规律分析并肯定其在实用中的可行性.     

基于木材化学组分的银杏系统进化问题研究

采用傅里叶变换红外光谱(FTIR)法测定了银杏、苏铁、毛白杨等22个针阔树种木材的红外光谱,分析了指纹区内吸收峰数目差异以及纤维素、木质素两种物质的特征吸收峰位置和相对强度的变化规律,进而探讨了银杏的系统进化问题。结果表明：银杏的红外光谱与苏铁差异较大,与松杉类等针叶树种比较相似,说明银杏在木材的化学组成上较苏铁更为进化,与松杉类等针叶树有较近的亲缘关系;银杏木材木质素的含量较一般针叶树高,这可能是一种遗留下来的古老性状;银杏木材中含有较多的紫丁香基木质素,表明银杏有向阔叶树进化的趋势。     

基于Stark展宽的TIG焊接电弧三维电子密度测量研究

焊接电弧三维电子密度的测量对于焊接质量控制具有重要意义,通过光谱仪采集电弧弦方向特征谱线轮廓,利用多项式拟合对径向采集数据进行降噪及平滑处理,通过Abel逆变换法重新构建径向光谱发射系数谱线轮廓,采用傅里叶变换从重建光谱轮廓中分离出Lorentz线形,获得Stark展宽,最终计算了TIG焊电弧等离子体电子密度的三维空间分布。     

集成成像三维显示系统显示性能的研究进展

集成成像三维显示技术是利用透镜阵列获取和显示立体图像的一种三维显示技术。本文首先综述了集成成像三维显示系统的特点,考虑其系统性能主要受分辨率、景深和观看视场角的限制,对近年来集成成像三维显示系统在增大分辨率、景深和观看视场角方面的研究进展做了综合论述,比较分析了各种改进方法的优劣。最后,对我国集成成像三维显示技术的研究现状进行了总结,并简述了本研究小组在该领域取得的若干研究成果。     

Simultaneous chromatic dispersion monitoring,extinction ratio enhancement and wavelength conversion using four-wave mixing

This paper presents a multi-functional all-optical device performs simultaneous chromatic dispersion (CD) monitoring, extinction ratio (ER) improvement and tunable wavelength conversion using four-wave mixing (FWM) in a single piece of highly nonlinear optical fiber (HNLF). The multi-functional ability arises from the nonlinear power transfer function (PTF) between the input signal and the output idler wave, which not only maps the CD information of the signal onto the average power of idler wave, but also transfers the data information to the idler wave with ER enhancement, making the device compact and cost effective. Furthermore within the wavelength tuning range the monitoring sensitivity and output ER can be much higher compared to all optical monitors and regenerators proposed before. Numerical simulations are then used to demonstrate the efficiency of this method.     

Quasi-fractional Talbot effect of resonant diffraction grating

The Fresnel diffraction of resonant diffraction grating is studied on the basis of the modal method, and it shows that the conventional fractional Talbot effect can still occur by choosing appropriate parameters. The Fresnel diffraction distributions of the resonant diffraction gratings with periods between λ and 4λ are analyzed, and the diffraction fields exhibit periodicity in both grating direction and the propagating direction. The experiment is carried out to verify the simulation results of the quasi-fractional Talbot effect of the resonant diffraction grating. This effect has potential application in lithography for high-resolution patterning.     

非马尔可夫环境下经典场驱动Jaynes-Cummings模型中原子的熵压缩

运用非马尔可夫量子理论与熵压缩理论,研究了非马尔可夫环境下经典场驱动Jaynes-Cummings模型中原子的熵压缩,考察了非马尔可夫效应、经典场驱动、体系失谐量对原子熵压缩的影响.用非马尔可夫过程的记忆效应解释了原子熵压缩的动力学行为.结果表明:非马尔可夫效应和经典场驱动的共同作用有利于原子熵压缩的产生与维持.在非马尔可夫环境下,通过选择适当的系统参数,可以产生压缩度大、压缩持续时间长的原子熵压缩态.研究结果为利用光场-原子相互作用制备压缩度大、压缩持续时间长的最佳原子压缩态提供了可能途径.     

Observation of D+(s)K- and evidence for D+(s)pi- final states in neutral B decays

We report the first observation of a B meson decay that is not accessible by a direct spectator process. The channel B(0)-->D(+)(s)K- is found in a sample of 85 x 10(6) BB; events, collected with the Belle detector at KEKB, with a branching fraction B(B(0)-->D(+)(s)K-)=(4.6(+1.2)(-1.1)+/-1.3) x 10(-5). We also obtain evidence for the B0-->D(+)(s)pi(-) decay with branching fraction B(B0-->D(+)(s)pi(-))=(2.4(+1.0)(-0.8)+/-0.7) x 10(-5). This value may be used to extract a model-dependent value of |V(ub)|.     

Temporal electronic structure of non-resonant Raman excited virtual state of P-nitroaniline by 514 nm excitation via bond polarisabilities

We have studied the temporal bond polarisabilities of para-nitroaniline from the Raman intensities by the algorithm proposed by Wu et al.in 1987 (Tian B,Wu G,Liu G 1987 J.Chem.Phys.87 7300).The bond polarisabilities provide much information concerning the electronic structure of the non-resonant Raman excited virtual state.At the initial moment by the 514.5 nm excitation,the tendency of the excited electrons (mapped out by the bond polarisabilities) is to spread to the molecular periphery,and the electronic structure of the Raman virtual state is close to the pseudo-quinonoidic state.When the final stage of relaxation is approached,the bond polarisabilities of those peripheral bonds relax faster than those closer to the molecular core,the phenyl ring.The molecule is in the benzenoidic form as demonstrated by the bond polarisabilities after relaxation.