全息校正GRIN透镜像差

梯度折射率(GRIN)透镜的像差会导致像面弥散斑增大从而降低透镜的聚焦性能。基于激光全息成像理论,利用全息技术来校正GRIN透镜的像差,从而改善其聚焦性能。通过对GRIN透镜全息校正系统的仿真,计算了全息记录时通过GRIN透镜的物光波在全息图上的相位分布,得到其波像差为0.34λ;分析了全息再现时全息干版的轴向位移对像面弥散斑成像质量的影响,提出一种通过引入轴上点像差平衡轴外点像差的方法并进一步提高了聚焦性能。结果表明:应用该方法在1.5°视场内,弥散斑均方根半径值由14.1μm减小到7.2μm。在3°全视场内,弥散斑均方根半径值均在衍射极限范围内,能够满足GRIN透镜在重叠复眼成像系统中的聚焦要求。     

Enhancing the Stability of Perovskite Quantum Dots by Encapsulation in Crosslinked Polystyrene Beads via a Swelling–Shrinking Strategy toward Superior Water Resistance

Organic/inorganic hybrid lead halide perovskites are promising optoelectronic materials due to their unique structure, excellent properties, and fascinating potential applications in lighting, photovoltaic, etc. However, perovskite materials are very sensitive to moisture and polar solvent, which greatly hinders their practical applications. Here, highly luminescent perovskite–polystyrene composite beads with uniform morphology are prepared via a simple swelling–shrinking strategy. This process is carried out only in nonpolar toluene and hexane without the addition of any polar reagents. As a result, the as‐prepared composite beads not only retain high luminescence but also exhibit superior water‐resistant property. The composites emit strong luminescence after being immersed into water over nine months. Moreover, even in some harsh environments such as acid/alkali aqueous solution, phosphate buffer solution, and Dulbecco's modified eagle medium biological buffers, they still preserve high luminescence. The applications in light‐emitting diodes and cellular labeling agents are also carried out to demonstrate their ultrastability.     

Real‐Time Probing Nanopore‐in‐Nanogap Plasmonic Coupling Effect on Silver Supercrystals with Surface‐Enhanced Raman Spectroscopy

Nanopore structures have displayed attractive prospects in diverse important applications such as nanopore‐based biosensors and enhanced spectroscopy. However, on the one hand, the fabrication techniques to obtain sub‐10 nm sized nanopores so far is very limited. On the other hand, the electromagnetic enhancement of nanopores is still relatively low. In this work, using a facile chemical etching strategy on 2D plasmonic Ag nanoparticle supercrystals, fine nanopore arrays with sub‐10 nm pore size have been successfully fabricated and a “nanopore‐in‐nanogap” hybrid plasmon mode has been investigated. An in situ etching and surface‐enhanced Raman spectroscopy (SERS) detection indicate that novel hybrid plasmon structure may create an enhanced electromagnetic coupling and increase SERS signal at ≈10× magnification. The breaking of plasmon bonding dipolar mode and generation of antibonding‐like plasmon mode contribute to this enhanced electromagnetic coupling. The facile etching strategy, as a common approach, may open the doors for the fabrication of nanopores in various compositions for numerous applications.     

Novel Iron/Cobalt‐Containing Polypyrrole Hydrogel‐Derived Trifunctional Electrocatalyst for Self‐Powered Overall Water Splitting

Development of efficient, low‐cost, and durable electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is of significant importance for many electrochemical devices, such as rechargeable metal–air batteries, fuel cells, and water electrolyzers. Here, a novel approach for the synthesis of a trifunctional electrocatalyst derived from iron/cobalt‐containing polypyrrole (PPy) hydrogel is reported. This strategy relies on the formation of a supramolecularly cross‐linked PPy hydrogel that allows for efficient and homogeneous incorporation of highly active Fe/Co–N–C species. Meanwhile, Co nanoparticles are also formed and embedded into the carbon scaffold during the pyrolysis process, further promoting electrochemical activities. The resultant electrocatalyst exhibits prominent catalytic activities for ORR, OER, and HER, surpassing previously reported trifunctional electrocatalysts. Finally, it is demonstrated that the as‐obtained trifunctional electrocatalyst can be used for electrocatalytic overall water splitting in a self‐powered manner under ambient conditions. This work offers new prospects in developing highly active, nonprecious‐metal‐based electrocatalysts in electrochemical energy devices.     

Photo‐Induced Charge‐Variable Conjugated Polyelectrolyte Brushes Encapsulating Upconversion Nanoparticles for Promoted siRNA Release and Collaborative Photodynamic Therapy under NIR Light Irradiation

Combination of photodynamic therapy (PDT) with small interfering RNA (siRNA) therapy has become a major strategy in cancer treatment for enhancing anticancer efficacy. However, developing nanoplatform that can promote siRNA release and collaborate with efficient PDT under NIR light irradiation is still a big challenge. Photo‐induced charge‐variable conjugated polyelectrolyte brushes encapsulating upconversion nanoparticles (UCNP@CCPEB) as an efficient nanoplatform are reported. Cationic conjugated polyelectrolyte brush (CCPEB) is synthesized through quaternary ammoniation of N‐functionalized polyfluorene brush by photodegradable 2‐nitrobenzyl‐2‐bromoacetate. CCPEB with abundant positive charges and intrinsic photosensitizer (PS) performance is good for integrating siRNA carrier and PS into one molecule. The obtained CCPEB next encapsulates upconversion nanoparticle for realizing its NIR light excitation. Agarose gel electrophoresis experiments show that UCNP@CCPEB present good stability and excellent siRNA‐loading capacity (1 mol UCNP@CCPEB to at least 32.5 mol siRNA). Under 980 nm light irradiation, UCNP@CCPEB exhibit efficient single oxygen production for PDT. Concurrently, the photoresponsive cationic side‐chain of CCPEB turns into zwitterionic chain and thus accelerates its siRNA release to 80%. In vitro and in vivo experiments show that the successful A549 tumor suppression is achieved by UCNP@CCPEB/siPlk1 complex under 980 irradiation. It is envisioned that UCNP@CCPEB can serve as an efficient platform for combining various phototherapies together.     

一种小型化宽阻带窄带通滤波器研究

为实现滤波器设计小型化,降低带通滤波器的高次谐波干扰,本文结合传统的1/4波长谐振器结构,采用在谐振器微带线上添加开路线的方法,降低高次谐振频点处的插入损耗,消减谐波影响。相比半波谐振器,1/4波长谐振器能有效地减小滤波器尺寸,此外开路线的添加除具有消减高次谐波作用,同时还能降低基频谐振点,促进设计小型化。通过仿真软件对该方案的验证及网络分析仪的实物测试表明,此方案具有良好效果,能广泛应用于窄带通滤波器小型化及谐波抑制。     

Compressed sensing of complex-valued data

Compressed sensing (CS) is a recently proposed technique that allows the reconstruction of a signal sampled in violation of the traditional Nyquist criterion. It has immediate applications in reduction of acquisition time for measurements, simplification of hardware, reduction of memory space required for data storage, etc. CS has been applied usually by considering real-valued data. However, complex-valued data are very common in practice, such as terahertz (THz) imaging, synthetic aperture radar and sonar, holography, etc. In such cases CS is applied by decoupling real and imaginary parts or using amplitude constraints. Recently, it was shown in the literature that the quality of reconstruction for THz imaging can be improved by applying smoothness constraint on phase as well as amplitude. In this paper, we propose a general l_p minimization recovery algorithm for CS, which can deal with complex data and smooth the amplitude and phase of the data at the same time as well has the additional feature of using a separate sparsity promoting basis such as wavelets. Thus, objects can be better detected from limited noisy measurements, which are useful for surveillance systems.     

一个动态门限的基于属性签密方案

签密能同时实现加密与签名,并且代价小于传统的先签名再加密。该文在Li等人(2010)签名方案的基础上提出了一个动态门限的基于属性签密方案,除具有一般签密方案的保密性和认证性外,还同时具有签密者属性隐私安全性和多接收者特性。在随机预言机模型下,利用判定双线性Diffie-Hellman (DBDH)问题和计算Diffie- Hellman (CDH)问题的困难性,证明了该方案满足在适应性选择密文攻击下的不可区分性及适应性选择消息下的不可伪造性。     

A multiplicative iterative algorithm for box-constrained penalized likelihood image restoration

Image restoration is a computationally intensive problem as a large number of pixel values have to be determined. Since the pixel values of digital images can attain only a finite number of values (e.g., 8-bit images can have only 256 gray levels), one would like to recover an image within some dynamic range. This leads to the imposition of box constraints on the pixel values. The traditional gradient projection methods for constrained optimization can be used to impose box constraints, but they may suffer from either slow convergence or repeated searching for active sets in each iteration. In this paper, we develop a new box-constrained multiplicative iterative (BCMI) algorithm for box-constrained image restoration. The BCMI algorithm just requires pixelwise updates in each iteration, and there is no need to invert any matrices. We give the convergence proof of this algorithm and apply it to total variation image restoration problems, where the observed blurry images contain Poisson, Gaussian, or salt-and-pepper noises.     

基于自旋图的三维自动目标识别

将三维表面匹配领域的自旋图(spin-images)方法运用于扫描激光雷达自动目标识别中,基于自旋图特征,提出了平均最大相似性度量、候选对应关系数目、几何一致性筛选后对应关系数目、分组筛选后最大组的对应关系数目这4个识别指标,并将其组合构成组合识别准则,从而进行三维目标识别。同时针对实际应用需求,进一步研究了点云空间分辨率、激光雷达测距误差以及遮挡对目标识别率的影响,为激光雷达三维目标识别系统的设计提供了参考。