Weak-focused acoustic vortex generated by a focused ring array of planar transducers and its application in large-scale rotational object manipulation

Contactless manipulation of multi-scale objects using the acoustic vortex(AV) tweezers offers tremendous perspectives in biomedical applications.However,it is still hindered by the weak acoustic radiation force(ARF) and torque(ART)around the vortex center.By introducing the elevation angle to the planar transducers of an N-element ring array,the weakfocused acoustic vortex(WFAV) composed of a main-AV and N paraxial-AVs is constructed to conduct a large-scale object manipulation.Different from the traditional focused AV(FAV) generated by a ring array of concave spherical transducers,a much larger focal region of the WFAV is generated by the main lobes of the planar transducers with the size inversely associated with the elevation angle.With the pressure simulation of the acoustic field,the capability of the rotational object driving in the focal plane for the WFAV is analyzed using the ARF and the ART exerted on an elastic ball based on acoustic scattering.With the experimental system built in water,the generation of the WFAV is verified by the scanning measurements of the acoustic field and the capability of object manipulation is also analyzed by the rotational trapping of floating particles in the focal plane.The favorable results demonstrate the feasibility of large-scale rotational manipulation of objects with a strengthened ART and a reduced acousto-thermal damage to biological tissues,showing a promising prospect for potential applications in clinical practice.     

基于最小区域的锥束ART算法快速图像重建

针对锥束ART算法重建速度慢的问题,考虑到工业CT重建目标尺寸差异较大的特点,提出了一种基于最小重建区域的快速三维图像重建方法。由不同视角下的锥束投影构建最小区域包络,对最小区域包络进行膨胀处理,以消除重建目标边界附近所出现的伪影,在此基础上,给出了射线穿过最小重建区域的体素索引及权因子的计算。该方法能够根据重建目标的尺寸自适应地确定最小重建区域,从而最大限度地减少了计算量。实验结果表明,该方法不仅大幅度提高了锥束ART算法的重建速度,而且有效地提高了重建质量。     

Synchrotron radiation computed laminography using an inclined detector

Synchrotron radiation computed laminography (SR‐CL) has been in use in three‐dimensional non‐destructive imaging of flat objects for several years. A new set‐up is proposed based on the traditional SR‐CL method but with the detector inclined at the same angle as the sample inclination to collect projections. The results of computer simulations and real‐sample experiments demonstrate that reconstructions acquired using an inclined detector are of better quality compared with those acquired using ordinary detecting methods, especially for the situation of few projections and small difference of attenuation ratio of the sample. This method could be applied to obtain high‐quality images of weak‐contrast samples with short measurement time and mild radiation damage.     

光谱法分析代数迭代重建算法及改进

采用光谱分析技术,系列研究了已有代数迭代重建算法,并进一步研制了改进算法—简单自相关代数迭代重建算法(SSART)。采用数值模拟的方法模拟重建一个含遮挡物场,研究了SSART模拟效果和重建精度。作为对照,分析了已有的传统代数迭代算法同条件下的重建结果,包括基本代数迭代重建算法(ART)、联合代数迭代重建法(SART)和改进的联合代数迭代重建法(MSART)。重建精度用均方误差(MSE),绝对平均误差(AVE)和峰值相对误差(PE)三种误差指数标定。结果发现,SSART重建结果的三种误差指数都明显减小,其中MSE在10-4数量级上比ART的降低了26.6%,PE在10-2数量级降低了77.6%。因此,SSART重建含遮挡物模型场时,重建精度大幅度提高,重建效果明显改善,对传统代数迭代重建算法显著改进。     

简单自相关代数迭代重建算法

创建了简单自相关代数迭代重建算法(simple self-correlative algebraic reconstruction technique, SSCART),分析了其重建效果。采用数值模拟的方法,对代数迭代法(algebraic reconstruction technique, ART)与SSCART两种算法进行了计算机模拟,分析了模拟效果和重建精度。结果发现,SSCART算法的重建精度均方误差(mean square error, MSE)指标在10-4数量级上比ART的降低了65%[(ART的MSE值-SSCART的MSE)/ART的MSE],峰值相对误差(peak error, PE)指标在10-2数量级上降低了99.9%。计算上仅仅比ART多1个除数因子,所以SSCART具有算法简单、易于实现、重建精度高、稳定性好等优点。就作者检索的文献看是目前最优秀的代数迭代法。     

Study on the chemiluminescence resonance energy transfer between luminol and fluorescent dyes using a linear CCD spectrometer

Chemiluminescence (CL) has been a useful tool for analytical applications. Fluorescein can be used to enhance CL emission of luminol. With three-dimensional (3D) dynamic CL spectrum obtained from a linear CCD (charge-coupled device) flow-injection CL spectrometer, the fluorescein enhanced CL analysis was studied. The enhanced process can be described with chemiluminescence resonance energy transfer (CRET) at certain fluorescein concentrations. In the process of CRET, fluorescein enlarges CL intensity but does not join the CL reaction. Compared with classic luminol-Co²⁺ CL system, the fluorescein-enhanced system exhibits stronger CL signal with the linear range and detection limit for traces of Co²⁺ unchanged.     

代数重建技术在板壳结构断层重建中的应用

针对板壳结构用锥束射线倾斜扫描时数据缺失等问题,利用代数重建技术(ART)进行了断层重建。计算机模拟结果表明,由ART重建出的切片图像质量远好于先前用滤波反投影(FBP)重建出的切片图像质量。对影响ART算法的各种因素进行了调整,即选取适当的初始图像和收敛因子就可获得最佳的图像质量。     

Cathodoluminescence properties of silicon nanocrystallites embedded in silicon oxide thin films

Cathodoluminescence (CL) spectra for the Si nanocrystallites embedded in a matrix of silicon oxide films are measured at room temperature. The CL spectra consist of two principal bands whose peak energies are in a near-infrared (NIR) region (<1.6 eV) and in a blue region (2.6 eV), respectively. The spectral feature of the NIR CL band is similar to the corresponding PL spectra. The strong correlation between the presence of Si nanocrystallites and the formation of the NIR CL band are found as well as the PL spectrum. The peak energy of the blue CL band is slightly lower than that of the luminescence band originating from oxygen vacancies (≡Si–Si≡) in SiO₂. Therefore, the blue CL band is considered to come from Si_n clusters with n3 in the oxide matrix. Under irradiation of electron beams, degradation of the intensity is observed for both the CL bands but the decay characteristics are different.     

基于代数重建算法的有限角度扫描的光声成像

由于滤波反投影重建算法要求对成像区域进行全方位扫描以获取完全投影数据,它需要较长时间采集大量数据,使其在医学上的应用受到限制。研究了在有限角度下采用代数重建算法进行光声成像的方法,实验用的光源为YAG激光器,波长为1064nm,重复频率20Hz,脉宽为6ns,探测器为针状的磺化聚二氟乙烯(PVDF)膜水听器,接收面积的直径为1mm,从仿真和实验结果表明该方法适用于“非完备投影数据”的光声层析成像。从图像重建效果上与滤波反投影算法相比较,该成像算法提高了重建图像的分辨率和对比度。采用代数重建算法的有限角度的光声成像方法,对临床医学的无损伤检测,具有重要的意义。     

Defect detection in semiconductor layers with built-in electric field with the use of cathodoluminescence

Cathodoluminescence (CL) in scanning electron microscopy (SEM) is commonly accepted as revealing local properties of a specimen region illuminated by an electron beam. CL is widely used to visualize defects in semiconductor structures. However, the presence of a strong electric field in, for example, heterojunctions or p–n junctions causes a separation of generated electron–hole (e–h) pairs and suppresses recombination in the specimen region excited by the beam. As a result CL – a radiative recombination – becomes quenched. At the same time, electron beam-induced current (EBIC) flows throughout the structure, which may produce secondary electroluminescence that is registered by the CL detector. Consequently, the CL measurement is distorted and if there are defects in the structure, they remain unrevealed. The current study shows that registration of the CL signal for different values of electron beam current (including high ones) enables true defect detection in semiconductor layers with built-in electric field. Results for a special test structure prepared with focused ion beam on AlGaAs/GaAs laser heterostructures with an 8 nm InGaAs quantum well are presented.     

Reconstruction of emission coefficients for a non-axisymmetric coupling arc by algebraic reconstruction technique

A preliminary investigation of tomographic reconstruction of an asymmetric arc plasma has been carried out. The objective of this work aims at reconstructing emission coefficients of a non-axisymmetric coupling arc from measured intensities by means of an algebraic reconstruction technique (ART). In order to define the optimal experimental scheme for good quality with limited views, the dependence of the reconstruction quality on three configurations (four, eight, ten projection angles) are presented and discussed via a displaced Gaussian model. Then, the emission coefficients of a free burning arc are reconstructed by the ART with the ten-view configuration and an Abel inversion, respectively, and good agreement is obtained. Finally, the emission coefficient profiles of the coupling arc are successfully achieved with the ten-view configuration. The results show that the distribution of emission coefficient for the coupling arc is different from centrosymmetric shape. The ART is perfectly suitable for reconstructing emission coefficients of the coupling arc with the ten-view configuration, proving the feasibility and utility of the ART to characterize an asymmetric arc.     

基于压缩传感和代数重建法的CT图像重建

代数重建法(ART)是一种重要的CT图像重建方法,适合于不完全投影数据的图像重建,其缺点是重建速度慢。为提高图像重建的质量和速度,利用压缩传感理论提出了一种基于ART的高质量图像重建算法。该算法将CT图像的梯度稀疏性结合到ART图像重建中,在每次迭代中的投影操作结束后用梯度下降法调整全变差,减小图像梯度的l1范数。实验结果验证了该算法的有效性。     

有机化合物对Luminol-KIO4-H2O2体系化学发光的抑制和增强

研究了36种有机化合物对鲁米诺-高碘酸钾-过氧化氢(luminol-KIO₄-H₂O₂)体系化学发光的影响,发现其大部分能抑制或增强体系化学发光强度,并且抑制或增强化学发光强度的能力与化学发光体系的pH值以及有机化合物分子结构中芳香环上功能基(—OH和—NH₂)的数目、位置,取代基的电子效应、空间效应等有关。讨论了化学发光强度抑制或增强的机理。基于24种有机化合物对体系化学发光的抑制或增强考察了其分析应用的可能性,发现数个化合物的检测限可达ng·mL^-1水平。     

Temporal integration of the contralateral acoustic-reflex threshold and its age-related changes

Although numerous studies have investigated temporal integration of the acoustic-reflex threshold (ART), research is lacking on the effect of age on temporal integration of the ART. Therefore the effect of age on temporal integration of the ART was investigated for a broad-band noise (BBN) activator. Subjects consisted of two groups of adults with normal-hearing sensitivity: one group of 20 young adults (ten males and ten females, ages 18-29 years, with a mean age of 24 years) and one group of 20 older adults (ten males and ten females, ages 59-75 years, with a mean age of 67.5 years). Activating stimulus durations were 12, 25, 50, 100, 200, 300, 500, and 1000 ms. Significant main effects for duration and age were obtained. That is, as the duration increased, the acoustic reflex threshold for BBN decreased. The interactions of duration x age group and duration x hearing level were not significant. The result of pair-wise analysis indicated statistically significant differences between the two age groups at durations of 20 ms and longer. The observed age effect on temporal integration of the ART for the BBN activator is interpreted in relation to senescent changes in the auditory system.     

ZnSe量子点增敏鲁米诺-铁氰化钾化学发光测定牛奶中的己烯雌酚

碱性介质中,ZnSe量子点能够增强鲁米诺-铁氰化钾体系的化学发光,己烯雌酚对该体系的化学发光有很强的抑制作用,据此建立了测定己烯雌酚的新方法,并对可能的反应机理进行了探讨。结果表明,在优化实验条件下,己烯雌酚在6.0×10^-9~4.0×10^-5 mol／L的浓度范围内与发光强度呈良好的线性关系,检出限为2.0×10^-9 mol/L(信噪比S／N=3)。对于浓度为4.0×10^-6 mol／L的己烯雌酚,测定11次的相对标准偏差为1.4％。将该体系用于牛奶中己烯雌酚的测定,回收率为94.47％~107.61％。     

阴极荧光在表面等离激元研究领域的应用

表面等离激元以其独特的光学性质广泛应用于纳米尺度的局域电磁场增强、超高分辨成像及微弱光电探测.阴极荧光是电子与物质相互作用而产生的光学响应,利用电子束激发金属纳米结构能够实现局域等离激元共振,并在亚波长尺度实现对共振模式的调控,具有超高空间分辨的成像特点.阴极荧光探测通常结合扫描电子显微镜或透射电子显微镜而实现,目前己被应用于表面等离激元的探测及共振模式的分析.本文从阴极荧光物理机理出发,综述了单一金属纳米结构和金属耦合结构的等离激元共振模式阴极荧光研究进展,并总结了阴极荧光与角分辨、时间分辨以及电子能量损失谱等关键技术相结合的应用,进一步分析了其面临的关键问题,最后展望了阴极荧光等离激元研究方向.     

异丙醇-ClO——H2O2化学发光新体系研究

本文首次报道异丙醇-ClO--H2O2新体系的化学发光,对影响该化学发光反应的因素进行了研究,并探讨了该发光新体系的分析应用和反应机理。     

流动注射化学发光法对安乃近进行选择性定量测定

通过对药物中安乃近的选择性定量测定 ,提出一种新的化学发光分析法。当安乃近溶液与酸性的聚乙二醇 4 0 0及罗丹明 6G混合溶液相遇时 ,会产生强烈的化学发光信号 ,根据光信号的大小即可定量测定安乃近的含量。反应中无任何氧化剂使用 ,因此 ,很难解释光信号产生的原因 ,该反应发光机理仍在探讨之中。这种测定方法具有极高的选择性 ,无论被测物是否含有磺酸基团 ,实验中未发现任何其他药物或化学物质会产生有意义的光信号 ,所以 ,不会象其他化学发光体系存在其他物质干扰问题。另外 ,此反应具有高度的灵敏性 ,其工作曲线线性范围为 0 0 1～ 1 0 0 μg·mL-1 ,检出限为 0 0 0 3μg·mL-1 ,此为目前安乃近的所有化学发光测定法中最低的检出限值。该测定方法已成功用于针剂及片剂药物中乃安近的定量测定     

一种基于光谱库的雪粒径及形状参数反演新方法

雪粒径的形状因素对积雪的反射光谱曲线影响较大,如何有效地刻画雪粒径的形状参数成为研究的热点。渐进辐射传输模型被广泛地应用于雪粒径反演,其对雪粒径形状的描述只采用了2个值(3.62对应于片状雪粒径,4.53为球形雪粒径),较难描述积雪的形状参数,同时为了反演积雪的雪粒径,这两个形状参数必须被提前固定,这大大降低了雪粒径的反演精度,为此提出了一种基于光谱库的雪粒径及形状参数反演算法(LUTMA)。首先利用渐进辐射传输模型建立不同粒径,不同形状参数的光谱库,然后采用光谱角指标进行匹配,最终获取积雪的粒径与形状参数。实验表明,基于光谱库的雪粒径及形状参数反演新方法与实测数据较为吻合。     

Thermal instability of a reconnecting current layer as a trigger for solar flares

The stability of small perturbations of a reconnecting current layer (CL) in a plasma with a strong magnetic field has been investigated in the approximation of dissipative magnetohydrodynamics. The case where the wavevector of the perturbations is parallel to the electric current in the CL has been considered. The suppression of plasma heat conduction by a magnetic field perturbation inside the CL is shown to be responsible for the instability. At the linear stage of instability development, the perturbations grow with the characteristic radiative plasma cooling time calculated in the approximation of an optically thin plasma with cosmic abundances of elements. The formation of a periodic structure of cold and hot magnetic flux tubes, viz., filaments, located across the direction of the electric current, should be expected at the nonlinear stage of the instability in the CL. The proposed mechanism of the thermal CL instability can explain the sequential brightening (ignition) in the arcades of magnetic loops in solar flares.