开环双脉冲液晶自适应光学视网膜成像系统

为了获得高分辨率视网膜图像,利用液晶空间光调制器作为波前校正器建立了一套开环液晶自适应光学视网膜成像系统。与闭环模式相比,采用开环模式后,系统的能量利用率提高了1倍。系统采用双脉冲照明方式,以减少人眼曝光量,保护人眼安全。在照明光学系统中加入了大小视场切换装置使成像视场由之前的0.8°增至1.7°。同时优化了系统的时序控制流程,对人眼像差连续校正的同时快速调节成像相机的前后位置至最佳像面。对于开环模式对动态人眼像差的校正精度进行了测量,实验测得,经开环校正后,残差波面的均方根值约为0.09λ;相应的斯特雷尔(Strehl)比高于0.70,系统分辨率接近光学衍射极限的分辨率。对两名志愿者进行了实验,获得了清晰的眼底视网膜细胞图像。     

平行磨削非轴对称非球面光学元件表面形貌

结合砂轮表面仿真及磨削过程的运动学仿真获得工件表面轮廓、形貌和粗糙度预计,可以作为磨削过程中的理论依据,是精密磨削加工技术中主要的研究内容之一。平行磨削技术是加工非轴对称非球面光学元件的重要手段,而相关的仿真过程报道还很少。提出一种基于平行磨削的精密磨削加工非球面表面生成的仿真方法,该方法主要包含使用高斯方法生成具有不同统计学特征的随机砂轮表面形貌,建立单磨粒运动轨迹方程和圆弧砂轮细分后与工件表面点接触的运动关系,据此给出平行磨削加工表面生成的数值算法,并对不同加工参数下的工件表面形貌进行仿真。仿真结果和测量结果的一致性验证了所给算法的正确性和有效性     

Feeling Inter‐ or Intramolecular Interactions with the Polymer Chain as Probe: Recent Progress in SMFS Studies on Macromolecular Interactions

Single‐molecule force spectroscopy (SMFS) opens new avenues for elucidating the structures and functions of large coiled molecules such as synthetic and biopolymers at the single‐molecule level. In addition, some of the features in the force–extension curves (i.e. force spectra) are closely related to primary/secondary structures of the molecules being stretched. For example, the long force plateau in the DNA stretching curve is related to the double‐helix structure. These features can be regarded as the force fingerprints of individual macromolecules. These force fingerprints can therefore be used as indicators/criteria of single‐molecule manipulation during the measurement of some unknown intra‐ or intermolecular interactions. By comparing the force spectra of a single polymer chain before and after interaction with other molecules, the mode/strength of such molecular interactions can be derived. This Review focuses on recent advances in AFM‐based SMFS studies on molecular interactions in both synthetic and biopolymer systems using a single macromolecular chain as probe, including interactions between nucleic acids and proteins, mechanochemistry of covalent bonds, conformation‐regulated enzymatic reactions, adsorption and desorption of biopolymers on a flat surface or from the nanopore of a carbon nanotube, and polymer interactions in the condensed state.     

Swift heavy-ion irradiated active waveguides in Nd:YAG crystals: fabrication and laser generation

An Nd:YAG planar waveguide laser has been fabricated by ultra-low-fluence (2×10(12) cm(-2)) swift heavy-ion irradiation (60 MeV Ar(4+) ions). The appearance of the buried waveguiding has been associated with an increased refractive index layer as a consequence of the ion-induced electronic damage. Continuous-wave laser oscillations at 1064.2 nm have been observed from the waveguide under 808 nm optical excitation, with the absorbed pump power at threshold and laser slope efficiency close to 26 mW and 5.9%, respectively.     

Recovery type superconvergence and a posteriori error estimates for control problems governed by Stokes equations

In this paper, we derive recovery type superconvergence analysis and a posteriori error estimates for the finite element approximation of the distributed optimal control governed by Stokes equations. We obtain superconvergence results and asymptotically exact a posteriori error estimates by applying two recovery methods, which are the patch recovery technique and the least-squares surface fitting method. Our results are based on some regularity assumption for the Stokes control problems and are applicable to the first order conforming finite element method with regular but nonuniform partitions.     

Finite element methods for optimal control problems governed by integral equations and integro-differential equations

In this paper, we analyze finite-element Galerkin discretizations for a class of constrained optimal control problems that are governed by Fredholm integral or integro-differential equations. The analysis focuses on the derivation of a priori error estimates and a posteriori error estimators for the approximation schemes.Grants, communicated-by lines, or other notes about the article will be placed here between rules. Such notes are optional.     

Colorimetric and bare-eye detection of alkaline earth metal ions based on the aggregation of silver nanoparticles functionalized with thioglycolic acid

We describe a simple and rapid method for colorimetric and bare-eye detection of the alkaline earth metal ions Mg(II), Ca(II), Sr(II) and Ba(II) based on the use of silver nanoparticles (AgNPs) functionalized with thioglycolic acid (TGA). The TGA ligand was self-assembled onto the AgNPs to form a probe that undergoes a color change from yellow to orange or red on exposure to the alkaline earth ions. It is presumed that the color change is a result of the aggregation of the AgNPs caused by the interaction of the bivalent ions with the carboxy groups on the AgNPs. The color change can be used for bare-eye and colorimetric determination of the alkaline earth metal ions, for example to rapidly determine water hardness.

A DFT study on CO oxidation catalyzed by subnanometer AlCu n (n = 1–3) clusters

Through the first-principle density-functional theory (DFT) calculations, we have made an exhaustive study of the mechanism of CO oxidation catalyzed by AlCu _n (n = 1–3) clusters on gas phase. It is shown that mixing two different metals (Al and Cu) can have beneficial effects on the catalytic activity than monometallic Cu _{n + 1} (n = 1–3) cluster toward the reaction of CO oxidation and the alloyed AlCu3 cluster is proposed as the best effective nanocatalysts.     

Thermal decomposition of polypropylene by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

The application of synchrotron vacuum ultraviolet (VUV) photoionization combined with molecular-beam mass spectrometry, also called synchrotron VUV photoionization mass spectrometry (SVUV-PIMS), in the research of the thermal decomposition of polypropylene (PP) was studied, and some main pyrolysis products formed at different photon energies have been identified. Using SVUV-PIMS, some isomers can be distinguished, which are much helpful for further understanding of the thermal decomposition of PP.     

Numerical analysis for the approximation of optimal control problems with pointwise observations

In this paper, we study the numerical methods for optimal control problems governed by elliptic PDEs with pointwise observations of the state. The first order optimality conditions as well as regularities of the solutions are derived. The optimal control and adjoint state have low regularities due to the pointwise observations. For the finite dimensional approximation, we use the standard conforming piecewise linear finite elements to approximate the state and adjoint state variables, whereas variational discretization is applied to the discretization of the control. A priori and a posteriori error estimates for the optimal control, the state and adjoint state are obtained. Numerical experiments are also provided to confirm our theoretical results. Copyright © 2013 John Wiley & Sons, Ltd.