Mean–semivariance portfolio selection under probability distortion

We formulate and study a mean–semivariance portfolio selection problem in continuous time when the probability is distorted by a nonlinear transformation. We give necessary and sufficient conditions for the feasibility and the existence of optimal strategies, respectively, and present the general form of optimal solutions when they exist. In sharp contrast with the previously established result that the infimum of the problem is not attainable when there is no probability distortion, we show that the infimum can be achieved with proper probability distortions. Finally, for a number of interesting cases we derive the optimal solutions in closed forms whenever they exist.     

Removal of J-coupling peak distortion in PGSE experiments

Peak distortion caused by homonuclear J-coupling is a major problem that limits the utility of the pulsed-field gradient spin–echo (PGSE) method for studying translational diffusion. This unwanted effect can be removed by incorporation of anti-phase magnetization purging pulse elements at the end of the spin–echo sequence. Three methods, namely, trim-pulse, homospoil pulse gradient and chirp based z-filter were evaluated as potential candidates for an improved NMR diffusion method that is less sensitive to J-coupling peak distortion. The chirp based z-filter was found to be excellent in suppressing anti-phase magnetization while leaving the in-phase magnetization basically intact in spin–echo and stimulated-echo based experiments. The incorporation of chirp based z-filter into PGSE could allow diffusion analysis that would otherwise be impossible by conventional means.     

autoDIAS: a python tool for an automated distortion/interaction activation strain analysis

The distortion/interaction activation strain (DIAS) analysis is a powerful tool for the investigation of energy barriers. However, setup and data analysis of such a calculation can be cumbersome and requires lengthy intervention of the user. We present autoDIAS, a python tool for the automated setup, performance, and data extraction of the DIAS analysis, including automated detection of fragments and relevant geometric parameters. © 2019 Wiley Periodicals, Inc.     

The high-resolution infrared spectrum of pyrrole between 900 and 1500 cm revisited

The Fourier transform gas-phase infrared spectrum of pyrrole, C₄H₅N, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 900-1500 cm⁻¹ spectral region. Four fundamental bands, ν₈(A₁; 1016.9 cm⁻¹), ν₂₃(B₂; 1049.1 cm⁻¹), ν₇(A₁; 1074.6 cm⁻¹), ν₂₀(B₂; 1424.4 cm⁻¹) and the overtone band 2ν₁₆(A₁; 962.7 cm⁻¹) have been analysed using the Watson model. The ν₈ and 2ν₁₆ bands are unperturbed; the ν₇ and ν₂₃ bands are locally perturbed, while the ν₂₀ band is globally perturbed by weak c-Coriolis resonance. Upper state vibrational term values, and rotational and centrifugal distortion constants, have been obtained from fits using S-reduction and I^r-representation as well as A-reduction and III^r-representation. A set of ground state rotational and centrifugal distortion constants using A-reduction was obtained from a simultaneous fit of ground state combination differences from all five bands and previous microwave and millimetre-wave data.     

Study of closed orbit response to magnet vibrations at the SSRF storage ring

This paper presents the analytical and simulation responses of the closed orbit distortion in the SSRF storage ring to random and plane wave like magnet vibrations respectively. It is shown that the use of girder is very beneficial in the view of suppressing this response function. Effect of the independently supported gradient bending magnets to the closed orbit response is given. An analytic formula is written to give a rough estimate of the closed orbit distortion due to ground motion, taking into account the closed orbit response function and girder transfer function. As an example, the result of SSRF case is given.     

Concurrent correction of geometric distortion and motion using the map-slice-to-volume method in echo-planar imaging

The accuracy of measuring voxel intensity changes between stimulus and rest images in fMRI echo-planar imaging (EPI) data is severely degraded in the presence of head motion. In addition, EPI is sensitive to susceptibility-induced geometric distortions. Head motion causes image shifts and associated field map changes that induce different geometric distortion at different time points. Conventionally, geometric distortion is "corrected" with a static field map independently of image registration. That approach ignores all field map changes induced by head motion. This work evaluates the improved motion correction capability of mapping slice to volume with concurrent iterative field corrected reconstruction using updated field maps derived from an initial static field map that has been spatially transformed and resampled. It accounts for motion-induced field map changes for translational and in-plane rotation motion. The results from simulated EPI time series data, in which motion, image intensity and activation ground truths are available, show improved accuracy in image registration, field corrected image reconstruction and activation detection.     

瞄准精度对中子半影成像的影响

在Monte Carlo方法模拟中子半影成像的基础上,对视场内点的空间线性不变性进行了研究.在视场范围内,离轴点产生了与离轴距离成正比的展宽现象,但点的积分强度保持了很好一致性,证明系统满足线性不变性假设.利用这一结果,分析了瞄准精度对成像系统的影响.结果表明：靶心在物面上的径向偏差应控制在50μm之内;物距误差控制应在300μm以内;编码孔旋转弧度须小于0.1mrad. 关键词： 空间线性不变性 瞄准精度 展宽效应 图像畸变     

CCD摄像系统镜头的畸变测量

从畸变定义出发,讨论了畸变数学模型,介绍了精密测角法与比长法综合测量畸变的原理。通过放大率法标定出CCD探测器的像素距离当量,通过质心法求出点目标的质心,质心与原点的像素距离乘以像素距离当量得到精确长度。利用正切函数求出绝对畸变值,用最小二乘法解多组数据超定方程,求出拟和公式的系数。实际计算和数据处理结果表明：畸变数学模型在中视场范围内拟合效果很好。     

小视场长焦距镜头畸变高精度测量研究

利用由精密测角仪、显微摄像测量系统、微型双光栅平面干涉仪、平行光管以及星点组成畸变测量系统,对小视场长焦距的镜头进行畸变测量。在计算镜头畸变中,利用中心视场区域内畸变设计无穷小,采用三次多项式拟和的方法,计算镜头理论焦距;在边视场采用像高高次方和视场角正弦高次方加权平均的方法对测量偏差角进行修正,得到各视场的相对和绝对畸变。通过实际测量和计算验证,镜头全视场畸变测量精度可达到0.02%。     

Ni单原子催化剂表面CO2电还原动力学的电化学谱学解析

针对Ni单原子催化剂表面的CO₂电还原反应(CO₂RR), 提出了以Ni为活性位点的“单中心”机理以及同时借助Ni位点还原和碳氮锚定位水解的“双功能”机理. 依据稳态极化的实验结果, 开展了CO₂RR的动力学解析与模型参数的敏感性分析; 借助暂态模型方程, 分别获取可表达CO₂RR线性与非线性频响特征的电化学阻抗谱(EIS)与总谐波失真(THD)谱. 研究结果表明, CO₂的溶解分压对CO₂RR活性影响最显著. 若CO₂RR遵循“单中心”机理, Ni位点COOH_ads的形成为速率控制步骤; 但若为“双功能”机理, 碳氮锚定位的水解与Ni位点的CO_2,ads还原同为速率控制步骤. EIS理论上可用于区分CO₂RR的“单中心”机理与“双功能”机理; 与之相比, THD谱在CO₂RR的机理识别中并无优势.