一种基于功率谱对数变换的联合变换相关器

联合功率谱的高频成份对相关峰识别具有重要作用,实验中记录的联合功率谱随着频率的增加其强度迅速降低。为增强联合功率谱的高频成分,改善其调制程度,可对功率谱进行对数变换,从而有效保留更多的高频成份,压低零级衍射光斑,提高联合变换相关器的识别能力。     

Nonlinear spin current and magnetoresistance of molecular tunnel junctions

We report on a theoretical study of spin-polarized quantum transport through a Ni-bezenedithiol(BDT)-Ni molecular magnetic tunnel junction (MTJ). Our study is based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism, so that microscopic details of the molecular MTJ are taken into account from first principles. A magnetoresistance ratio of approximately 27% is found for the Ni-BDT-Ni MTJ which declines toward zero as bias voltage is increased. The spin currents are nonlinear functions of bias voltage, even changing sign at certain voltages due to specific features of the coupling between molecular states and magnetic leads.     

Dielectron widths of the Gamma(1S,2S,3S) resonances

We determine the dielectron widths of the Gamma(1S), Gamma(2S), and Gamma(3S) resonances with better than 2% precision by integrating the cross section of e+e- -->Gamma over the e+e- center-of-mass energy. Using e+e- energy scans of the Gamma resonances at the Cornell Electron Storage Ring and measuring Gamma production with the CLEO detector, we find dielectron widths of 1.252+/-0.004(sigma(stat))+/-0.019(sigma(syst)) keV, 0.581+/-0.004+/-0.009 keV, and 0.413+/-0.004+/-0.006 keV for the Gamma(1S), Gamma(2S), and Gamma(3S), respectively.     

Generic Bell inequalities for multipartite arbitrary dimensional systems

We present generic Bell inequalities for multipartite arbitrary dimensional systems. The inequalities that any local realistic theory must obey are violated by quantum mechanics for even dimensional systems. A large set of variants are shown to naturally emerge from the generic Bell inequalities. We discuss particular variants of Bell inequalities that are violated for all the systems including odd dimensional systems.     

Ultrafast dynamics of surface plasmon polaritons in plasmonic metamaterials

Using near-field scanning optical microscopy and ultrafast laser spectroscopy, we study the linear optical properties of subwavelength nanoslit and nanohole arrays in metal films, which are prototype structures for novel plasmonic metamaterials. Near-field microscopy provides direct evidence for surface plasmon polariton (SPP) excitation and allows for spatial imaging of the corresponding SPP modes. By employing spectral interferometry with ultrashort 11-fs light pulses, we directly reconstruct the temporal structure of the electric field of these pulses as they are transmitted through the metallic nanostructures. The analysis of these data allows for a quantitative extraction of the plasmonic band structure and the radiative damping of the corresponding SPP modes. Clear evidence for plasmonic band gap formation is given. Our results reveal that the coherent coupling between different SPP modes can result in a pronounced suppression of radiative SPP damping, increasing the SPP lifetime from 30 fs to more than 200 fs. These findings are relevant for optimizing and manipulating the optical properties of novel nano-plasmonic devices. PACS 42.70.Qs; 07.79.Fc; 42.25.-p     

Analysis of the distribution of diffusion coefficients in cat brain at 9.4 T using the inverse Laplace transformation

In this work, the usefulness of the inverse Laplace transformation (ILT) in the characterization of diffusion processes in the brain has been investigated. The method has been implemented on both phantom and in vivo cat brain data acquired at high resolution at 9.4 T. The results were compared with monoexponential and biexponential analyses of the same data. It is shown that in the case of diffusion restricted by white matter axonal tracts, the resulting diffusograms are in good agreement with the biexponential model. In gray matter, however, the non-monoexponential decay does not lead to a bimodal distribution in the ILT, even though the data can be fitted to a biexponential. This finding suggests the possibility of a distribution of diffusion coefficients rather than a discrete biexponential behavior. It is shown that this distribution is sensitive, for example, to experimental parameters such as the diffusion time. Thus, the ILT offers the possibility of implementing a unique tool for the analysis of heterogeneous diffusion, that is, the analysis of the diffusion coefficient distribution, which has the yet unexplored potential of being a valuable parameter in the characterization of tissue structure.     

利用微悬臂梁表面应力研究聚N-异丙基丙烯酰胺分子的构象转变

提出了一种基于微悬臂梁传感技术研究大分子折叠/构象转变的新方法.通过分子自组装的方法将热敏性的聚N-异丙基丙烯酰胺(PNIPAM)分子链修饰到微悬臂梁的单侧表面,用光杠杆技术检测温度在20-40 ℃之间变化时由于微悬臂梁上的PNIPAM分子在水中的构象转变所引起的微悬臂梁变形.实验结果显示:在升温过程中,微悬臂梁的表面应力发生了变化并且导致微悬臂梁产生了弯曲变形,这个过程对应着微悬臂梁上的PNIPAM分子从无规线团构象到塌缩小球构象的构象转变.在降温过程中,微悬臂梁发生了反方向的弯曲变形,这对应着PNIPAM分子从塌缩小球构象向无规线团构象的构象转变.整个温度变化过程中构象转变是连续进行的,而在低临界溶解温度(约32 ℃)附近转变幅度较大,这与自由水溶液中PNIPAM分子的无规线团-塌缩小球构象转变相对应.实验结果还显示:由于PNIPAM分子在塌缩过程中氢键的形成和链段间可能的缠结效应,整个温度循环过程中微悬臂梁的变形是不可逆的且有明显的迟滞效应.     

(111)取向(Pb,La)TiO3铁电薄膜中90°纳米带状畴与热释电性能的研究

采用射频磁控溅射技术在Pt/Ti/SiO2/Si(100)衬底上生长了掺镧钛酸铅(PLT)铁电薄膜.用X射线衍射技术(XRD)研究了PLT薄膜结晶性能,结果表明PLT薄膜为(111)择优取向钙钛矿相织构.使用原子力显微镜(AFM)和压电响应力显微镜(PFM)分别观察了PLT薄膜的表面形貌和对应区域的电畴结构.PFM观察显示PLT薄膜中存在90°纳米带状畴,电畴的极化为首尾相接的低能量的排列方式,带状畴的宽度为20-60nm.研究了PLT10铁电薄膜的制备条件与性能之间的关系.发现在优化条件下制备的PLT10铁电薄膜的介电常数εr为365、介电损耗tgδ为0.02,热释电系数γ为2.18×10-8C·(cm2·K)-1,可以满足制备非制冷红外探测器的需要.     

Ultrafast laser ablation of indium tin oxide thin films for organic light-emitting diode application

Ultrafast laser ablation of ITO thin film coated on the glass has been investigated as a function of laser fluence as well as the number of laser pulses. The ablation threshold of ITO thin film was found to be 0.07 J/cm² that is much lower than that of glass substrate (about 1.2–1.6 J/cm²), which leads to a selective ablation of ITO film without damage on glass substrate. The changes in the electrical resistance and morphology of ablated trench of ITO electrode were found to be strongly dependent on the processing conditions. We present the performance of organic light-emitting diodes (OLED) fabricated with ITO electrode patterned by ultrafast laser ablation.     

Single-exposure optical sectioning by color structured illumination microscopy

Structured illumination microscopy (SIM) is a wide-field technique that rivals confocal microscopy in optical sectioning ability at a small fraction of the acquisition time. For standard detectors such as a CCD camera, SIM requires a minimum of three sequential frame captures, limiting its usefulness to static objects. By using a color grid and camera, we surpass this limit and achieve optical sectioning with just a single image acquisition. The extended method is now applicable to moving objects and improves the speed of three-dimensional imaging of static objects by at least a factor of three.