垂直入射时无限长分层柱电磁散射的改进算法及应用

结合非均匀球粒子对平面波散射的散射场计算的改进算法,提出了平面波垂直入射无限长分层圆柱散射场快速稳定而有效的改进电磁散射算法。与已有算法相比,改进算法所能计算的无限长非均匀介质圆柱的尺寸参量突破10000,计算层数达到106,并且计算时间很短,最多仅为几秒。该算法可以用于不同的波段以及不同领域的任意无耗或吸收无限长圆柱体散射场的计算。最后将该算法应用于梯度折射率聚合物光纤(GI-POF)散射特性的研究,为非接触、在线测量聚合物光纤折射率分布提供了理论依据。     

Unprecedented coloration of rutile titanium dioxide nanocrystalline thin films

In this communication, TiO2 nanocrystalline thin films synthesized by a room temperature (27 degrees C) chemical dip process. To our knowledge, this is first report of the preparation of nanoscale rutile TiO2 particles from common inorganic salt at such low temperature. Interestingly, unprecedented dynamic color change accompanies with titanium dioxide grain size, which can be seen with the naked eye that generated curiosity in our mind to check UV-vis absorption, where significant changes were observed. The room temperature synthesized thin films of rutile titanium dioxide make it a potential candidate for high-compatibility material, which can be used in artificial heart valves.     

Sensitivity enhancement by exchange mediated magnetization transfer of the xenon biosensor signal

Hyperpolarized xenon associated with ligand derivatized cryptophane-A cages has been developed as a NMR based biosensor. To optimize the detection sensitivity we describe use of xenon exchange between the caged and bulk dissolved xenon as an effective signal amplifier. This approach, somewhat analogous to 'remote detection' described recently, uses the chemical exchange to repeatedly transfer spectroscopic information from caged to bulk xenon, effectively integrating the caged signal. After an optimized integration period, the signal is read out by observation of the bulk magnetization. The spectrum of the caged xenon is reconstructed through use of a variable evolution period before transfer and Fourier analysis of the bulk signal as a function of the evolution time.     

失谐对耗散耦合腔阵列体系超流-绝缘相变的影响

利用平均场理论和微扰论解析求解了失谐存在且环境作用下Jaynes-Cummings-Hubbard模型的哈密顿量,得到了体系序参量的解析表达式,并讨论了失谐对体系超流一绝缘相变的影响,研究结果表明:调节失谐可以改变腔间的有效排斥势和系统的临界隧穿率,实现系统在超流态和绝缘态之间转变,结合耗散耦合腔阵列的输运性质探讨了失谐对序参量取值的影响,结果显示:沿失谐负支随着失谐的增大,序参量会经历先增后减的变化。     

Encapsulation of Photosensitizers and Upconversion Nanocrystals in Lipid Micelles for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising method for cancer therapy. However, it is constrained by limited penetration depth of visible light, hydrophobicity of photosensitizers, and lack of tumor targeting. In this work, the photosensitizer zinc phthalocyanine (ZnPc) and upconversion nanocrystals (UCNs) are encapsulated into OQPGA‐PEG/RGD/TAT lipid micelles. The UCNs acting as a nanotransducer convert deep‐penetrating near‐infrared (NIR) light to visible light for activating the photosensitizer. OQPGA‐PEG/RGD/TAT lipid micelles are used as a carrier for the photosensitizer, with improved biocompatibility and cancer‐targeting ability. The results show that the photosensitizer ZnPc‐ and UCNs‐loaded OQPGA‐PEG/RGD/TAT lipid micelles are nanoparticles with an average size of 25 nm. The lipid micelle nanoparticles are stable in water with low leakage of photosensitizer. The absorption peak of the photosensitizer overlaps with the emission peak of UCNs, so the visible fluorescence emitted from the UCNs upon excitation by the NIR laser at 980 nm can activate the photosensitizer to produce singlet oxygen for PDT. The targeting RGD peptide and cell‐penetrating TAT peptide on the surface help the nanoparticles getting into cancer cells. The OQPGA‐PEG/RGD/TAT lipid micelles encapsulated with both the photosensitizer ZnPc and UCNs could be used for targeted PDT by using deep‐penetrating NIR light as the light source.     

Dynamics of charge transfer at Au/Si metal-semiconductor nano-interface

An ab initio analysis of the periodic array of Au/Si nanostructure composed of gold clusters linked to silicon quantum dot (QD) co-doped by aluminium and phosphorus along [111] direction is presented in this paper. The density functional theory (DFT) is used to compute the electronic structure of the simulated system. Non-adiabatic coupling implemented in the form of dissipative equation of motion for reduced density matrix is used to study the phonon-induced relaxation in the simulated system. The density of states clearly shows that the formation of Au–Si bonds contributes states to the band gap of the model. Dynamics of selected photo-excitations shows that hole relaxation in energy and in space is much faster than electron relaxation, which is due to the higher density of states of the valence band.     

基于哈希理论和线性近邻传递反馈的乳腺X线图像肿块检索方法

在乳腺X线图像肿块检测中存在较高的假阳性率,通过基于内容的肿块检索,将待判定肿块与已确诊肿块进行相似性分析,可有效降低假阳性率.本文提出了一种结合可区分锚点图哈希和线性近邻传递的乳腺图像肿块检索方法.针对传统锚点图哈希在相似度定义中没有考虑病理相关性的问题,引入病理类别至锚点图哈希图像相似度计算,提出了可区分锚点图哈希以重新表示图像.利用线性近邻传递作为相关反馈技术,基于图像底层特征表达与图像高层语义间的学习机制,实现交互式肿块图像检索.采用北京大学人民医院乳腺中心提供的临床图像作为实验数据,实验结果表明,引入病理类别的可区分锚点图哈希图像表达在肿块相似性分析上优于传统锚点图哈希.相比于现有方法,本文提出的方法在肿块检索性能上得到明显提高.     

Dynamic control of retrieval contrast in a Λ-type atomic system

We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in Λ configuration. The memory procedure consists of write-in, storage, and retrieval phases. By applying a weak microwave field in the storage stage, additional phase-dependent terms are included, and the contrast of the output signal pulses can be dynamically controlled (enhanced or suppressed) through manipulating the relative phase φ between optical and microwave fields. Our numerical analysis shows that the contrast is enhanced to the most extent when φ=1.5π. In addition, the contrast is in proportion to the Rabi frequency of the microwave field with a certain relative phase.     

A type of conserved quantity of Mei symmetry of Nielsen equations for a holonomic system

A type of structural equation and conserved quantity which are directly induced by Mei symmetry of Nielsen equations for a holonomic system are studied.Under the infinitesimal transformation of the groups,from the definition and the criterion of Mei symmetry,a type of structural equation and conserved quantity for the system by proposition 2 are obtained,and the inferences in two special cases are given.Finally,an example is given to illustrate the application of the results.     

掺镱光纤激光器自脉冲与自脉冲内的自锁模研究

采用单端连续抽运方式, 对自由运转的双包层掺镱光纤激光器的输出特性进行了详细的实验研究. 实验中不但观察到了自脉冲, 而且首次在自由运转的光纤激光器中观察到自锁模现象, 对它们产生的物理机理进行了相应的理论分析. 分析表明: 增益光纤的弱(未) 抽运部分对信号光的吸收导致光纤激光器内自脉冲的出现, 轴向模之间的拍频和自相位调制导致自锁模现象的出现, 而受激拉曼散射、 受激布里渊散射等非线性效应使它们进一步增强. 当抽运光功率略高于阈值时, 自脉冲宽度比较宽, 随抽运光功率增加自脉冲的脉宽变窄; 自脉冲包络面内的自锁模脉冲的宽度随抽运光功率增加也变窄, 进一步增加抽运光功率, 自脉冲和自脉冲包络面内的自锁模现象消失. 实验测得自锁模脉冲的间隔为224 ns, 最大(小) 自锁模脉冲的半高全宽约为35.0 ns (6.3 ns); 测得信号光的中心波长为1090 nm, 谱线半高全宽的最大(小) 值约为7.05 nm (2.01 nm).