Fiber Bragg grating hydrophone with high sensitivity

A fiber Bragg grating （FBG） hydrophone with high sensitivity was demonstrated. This hydrophone used a rubber diaphragm and a copper hard core as the sensing element. To compensate the hydrostatic pressure, a capillary tube was fixed at the end of the hydrophone. Theoretical analysis of the acoustic pressure sensitivity was given in this letter. Experiments were carried out to test the frequency response of the hydrophone. The result shows that when the Young＇s modulus of the diaphragm is higher, a flatter frequency response will be obtained.     

高质量多孔氧化铝模板的制备

在草酸电解液中研究了阳极氧化法制备多孔氧化铝模板(AAO模板)。采用场发射扫描电子显微镜对多孔模板的形貌进行表征,结果表明:模板孔的分布均匀有序,孔径在40~70 nm;电解液浓度、氧化电压、氧化温度和氧化时间都会影响模板的形态;不经过高温退火及抛光也可以制得规则排布的多孔AAO模板。X射线衍射分析表明:氧化铝膜的主要成分为非晶态Al2O3。     

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。     

外电场辅助化学气相沉积方法制备网格状β-Ga2O3纳米线及其特性研究

利用外电场辅助化学气相沉积（CVD）方法,在蓝宝石衬底上制备出了由三组生长方向构成的网格状β-Ga₂O₃纳米线.研究了不同外加电压大小对β-Ga₂O₃纳米线表面形貌、晶体结构以及光学特性的影响.结果表明：外加电压的大小对样品的表面形貌有着非常大的影响,有外加电场作用时生长的β-Ga₂O₃纳米线取向性开始变好,只出现了由三组不同生长方向构成的网格状β-Ga₂O₃纳米线;并且随着外加电压的增加,纳米线分布变得更加密集、长度明显增长.此外,采用这种外电场辅助的CVD方法可以明显改善样品的结晶和光学质量.     

束流发射度对太赫兹微电真空折叠波导行波管性能的影响

采用理论分析与数值模拟相结合的方法,分别对140,220和345 GHz折叠波导行波管中的束流发射度的影响因素及其对直流导通率的影响进行了分析,总结了发射度随频率、结构参数和电子束参数的变化规律。研究发现,在太赫兹频段束流发射度直接决定着聚焦磁场的选取设计, 是表征太赫兹频段束流品质的一个重要参量。     

高斯光束通过克尔介质的光强分布研究

以亚当姆预测 校正系统数值计算方法为基础,在同时考虑光束通过克尔介质后的相位和光束线型变化的情况下,利用惠更斯 菲涅尔衍射积分公式,对高斯光束通过克尔介质后的近场和远场的横向光强分布进行了研究.结果表明：当高斯光束通过“薄”介质的出射面时,不仅仅相位发生了变化,而且光强线型分布也不再呈理想的高斯分布,而是有一系列丝状的近高斯分布.光束通过克尔介质后,无论是在近场还是远场,其光束总能量分布都被发散了.结果同时表明：光束通过正克尔介质后的远场光强分布主要集中在中心附近,并逐渐向边缘减弱,而光束通过负克尔介质后远场光束能量主要集中在边缘.     

A novel local PCA-based method for detecting activation signals in fMRI.

A novel local principal component analysis (LPCA) technique is presented for activation signal detection in functional magnetic resonance imaging (fMRI) without explicit knowledge about the shape of the model activation signal. Unlike the traditional PCA methods, our LPCA algorithm is based on a measure of separation between two clusters formed by the signal segments in active periods and inactive periods, which is computed in an eigen-subspace. In addition, we only applied PCA to the temporal sequence of each individual voxel instead of applying PCA to the fMRI data set. In our algorithm, we first applied a linear regression procedure to alleviate the baseline drift artifact. Then, the baseline-corrected temporal signals were partitioned into active and inactive segments according to the paradigm used for the fMRI data acquisition. Principal components were computed from all these segments for each voxel by PCA. By projecting the segments of each voxel onto a linear subspace formed by the corresponding most dominant principal components, two separate clusters were formed from active and inactive segments. An activation measure was defined based on the degree of separation between these two clusters in the projection space. We show experimental results on the activation signal detection from various sets of fMRI data with different types of stimulation by using the proposed LPCA algorithm and the standard t-test method for comparison. Our experiments indicate that the LPCA algorithm in general provides substantial signal-to-noise ratio improvement over the t-test method.     

高温退火对蓝宝石基片的表面形貌和对CeO缓冲层以及Tl-2212超导薄膜长的影响

研究了蓝宝石(1102)基片在不同温度和时间下退火时表面形貌和表面相结构的变化,以及它对CeO2缓冲层和T1-2212超导薄膜生长的影响.原子力显微镜(AFM)研究表明,在流动氧环境中1000℃温度下退火,蓝宝石(1102)的表面首先局部区域形成台阶结构,然后表面形成叠层台阶结构,随着退火时间的延长.表面发生了台阶合并现象,表面形貌最终演化为稳定的具有光滑平台的宽台阶结构.XRD测试表明,通过高温热处理可以大幅度提高蓝宝石基片表面结构的完整性.在1000℃温度下热处理20 h的蓝宝石(1102)基片上可以生长出具有面内取向的CeO2(001)缓冲层.在具有缓冲层的蓝宝石基片上可以制作出高质量c轴织构的外延11-2212超导薄膜,其临界转变温度(Tc)为104.7 K,液氮温度下临界电流密度(Jc)达到3.5 MA/cm2,微波表面电阻R(77 K,10 GHz)约为390μΩ.     

Characterization of relativistic electrons generated by a cone guiding laser pulse

We demonstrated the interaction of a gold cone target with a femto second(fs) laser pulse above the relativistic intensity of 1.37×10 18 μm 2 W/cm 2.Relativistic electrons with energy above 2 MeV were observed.A 25%-40% increase of the electron temperature is achieved compared to the case when a plane gold target is used.The electron temperature increase results from the guiding of the laser beam at the tip and the intense quasistatic magnetic field in the cone geometry.The behavior of the relativistic electrons is verified in our 2D-PIC simulations.     

Efficient scheme of quantum SWAP gate and multi-atom cluster state via cavity QED

In this paper, we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms. It is shown that the scheme can also be used to create multi-atom cluster state. During the interaction between atom and cavity, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay. With the help of our scheme it is very simple to prepare the N-atom cluster state with perfect fidelity and probability. The practical feasibility of this method is also discussed.