Linewidth Analysis of Spin Labels in Liquids: II. Experimental

This work demonstrates that homogeneous linewidths can be extracted from continuous wave electron paramagnetic resonance spectra and that they quantitatively agree with the predictions of existing relaxation theory. We suggest that relaxation theory can be used to predict experimental lineshapes provided that the simulations properly include sources of broadening. We have found that the rotational correlation times for spin labels in different percentages of glycerol/water mixtures are best modeled by a power law treatment for the viscosity, similar to that for translational diffusion. The translational diffusion coefficients themselves also have a power law dependence on the viscosity for glycerol/water mixtures. The linewidths were linearly dependent upon both the oxygen and the spin label concentration. The hyperfine splittings of all nuclei were observed to decrease linearly with increasing spin label concentration, completely at odds with existing theory which predicts a quadratic dependence upon concentration. The linear dependence was independent of hyperfine splitting until the magnitude of the hyperfine splitting was less than the homogeneous linewidth.     

Quantum algorithm for total least squares data fitting

The total least squares (TLS) method is widely used in data-fitting. Compared with the least squares fitting method, the TLS fitting takes into account not only observation errors, but also errors from the measurement matrix of the variables. In this work, the TLS problem is transformed to finding the ground state of a Hamiltonian matrix. We propose quantum algorithms for solving this problem based on quantum simulation of resonant transitions. Our algorithms can achieve at least polynomial speedup over the known classical algorithms.     

Triplet-state spin labels for highly sensitive pulsed dipolar spectroscopy

ABSTRACT

Pulsed dipolar spectroscopic methods allow nanometer distance measurements between pairs of spin labels. We have proposed a new spin labelling approach, based on the population of a chromophore triplet under light excitation, testing it on a peptide-based spectroscopic ruler and a photosynthetic protein. We have applied a modified Pulsed Electron DOuble Resonance (PELDOR) sequence where the photogeneration of the triplet spin precedes the conventional 4-pulse PELDOR sequence. In this experiment, the triplet-state serves as detection spin while the stable nitroxide is the pump spin. Alternatively, a new method, Laser-Induced Magnetic Dipole spectroscopy (LaserIMD), has been proposed: the nitroxide signal is detected while a time varying laser pulse acts as a pump to generate the triplet state [C. Hintze, D. Bücker, S. Domingo Köhler, G. Jeschke and M. Drescher, J. Phys. Chem. Lett. 7 (12), 2204 (2016)]. For the first time, in this work, we compare the two dipolar techniques performing X-band experiments in the same experimental conditions and deriving analytical expressions for the echo modulation by the density matrix formalism.     

Spin treatment-based approach for electronic transport in paramagnetic liquid transition metals

A novel concept is proposed to calculate both the electrical resistivity and thermoelectric power (TEP) of liquid transition metals (Mn, Fe, Co and Ni) characterized by a paramagnetic state in the liquid phase. By contrast to a previous work (PRB64, 094202 (2001)), where the resistivity was calculated by treating separately the interactions between spin up and spin down using the Matthiessen rule, our current approach is based on two types of muffin tin potentials in the t-matrix, namely spin up and spin down. The resistivity is treated as the result of the interference of the two kinds of spin states of electrons including a cross-contribution. The calculated resistivity values agree reasonably well with the available experimental ones for all the metals considered. Moreover, the calculated TEP, as deduced from the slope of resistivity vs. energy, has been found to be positive for Mn and Fe but negative for Co and Ni. Besides that, this formalism for resistivity calculation may be generalized to a system that may exist in different atomic states. It is worth mentioning that this concept is analogous to the one used in the process of neutron scattering on a metal composed of multiple isotopes.     

Prospects for measurement‐based quantum computing with solid state spins

This article aims to review the developments, both theoretical and experimental, that have in the past decade laid the ground for a new approach to solid state quantum computing. Measurement‐based quantum computing (MBQC) requires neither direct interaction between qubits nor even what would be considered controlled generation of entanglement. Rather it can be achieved using entanglement that is generated probabilistically by the collapse of quantum states upon measurement. Single electronic spins in solids make suitable qubits for such an approach, offering long coherence times and well defined routes to optical measurement. We will review the theoretical basis of MBQC and experimental data for two frontrunner candidate qubits – nitrogen‐vacancy (NV) centres in diamond and semiconductor quantum dots – and discuss the prospects and challenges that lie ahead in realising MBQC in the solid state.     

高精度高次非球面最接近球面计算方法

分析了高次非球面与其加工用最接近球面之间的几何关系特点,提出了一种基于1维搜索的高精度高次非球面最接近球面计算方法。该算法可以计算二次或高次凹（凸）非球面的加工用最接近球面半径、球心位置及非球面度。通过计算实例与现有计算最接近球面的方法相比,该算法在计算高次非球面时将最大非球面度从500.8 m减小到30.0 m,在计算二次非球面时计算结果与精确公式法得到的结果一致。计算实例表明该方法计算高次非球面时得到的最接近球面更优、计算精度更高,且适用于任意次非球面最接近球面的精确计算。     

A fast algorithm for simulating vesicle flows in three dimensions

Vesicles are locally-inextensible fluid membranes that can sustain bending. In this paper, we extend the study of Veerapaneni et al. [S.K. Veerapaneni, D. Gueyffier, G. Biros, D. Zorin, A numerical method for simulating the dynamics of 3D axisymmetric vesicles suspended in viscous flows, Journal of Computational Physics 228 (19) (2009) 7233–7249] to general non-axisymmetric vesicle flows in three dimensions.     

Implementation and comparative study of random sequences for nonlinear least square data fitting

A numerical study of nonlinear least square data fitting using random numbers from the congruential generator and several quasi-random generators is presented. The results indicate that at least up to five dimensions some of the quasi-random sequences yield better accuracy than the congruential pseudo-random sequence. Some recommendations for selecting the generators of quasi-random sequences are also given.     

基于Savitzky-Golay加权拟合的红外图像非均匀性条带校正方法

针对红外成像探测器单元响应不一致等因素导致的图像非均匀性条带问题, 提出了基于直方图加权和Savitzky-Golay拟合的非均匀性条带校正方法。首先, 计算每列的归一化直方图函数并将其作为权值对图像进行加权运算;然后, 利用Savitzky-Golay滤波器对加权后的图像列均值和列方差进行拟合, 并将结果带入校正公式, 通过可调参数的迭代完成校正。实验结果表明:该方法能有效地去除非均匀性条带, 保留图像的光谱辐射信息和纹理细节, 各项评价指标均提高10%。     

基于张量网络算法的自旋梯子系统的弦序参量的研究

通过基于矩阵乘积态(MPS)的强关联电子量子自旋梯子格点系统的张量网络(TN)算法,摸索研究自旋梯子量子多体系统的弦序参量,探测系统的量子相变点,刻画系统的量子临界现象,获取系统的量子相图,这为我们提供了一个研究自旋梯子系统的量子多体物理性质强有力的工具和方法:在不知道系统是否缺乏Landau对称性破缺序或者系统是否存在相关的拓扑弦序的情况下,可以先得到系统的基态波函数,如果基态缺乏Landau对称性破缺序,或可以通过其它方式找出系统存在若干非局域的弦序参量,来完整地描述一些拓扑量子相变点,获得系统的量子相图,从而丰富和发展了传统的Landau对称性破缺的相变理论.     

用于复杂光谱数据压缩的自适应小波算法

对于超短脉冲激光与气体相互作用产生的复杂光谱，提出了基于递归最小方差方法的自适应小波算法，实现了对该类光谱数据的高效压缩. 在对三种气体，共计27组光谱数据进行压缩后，数据由最初的3968个点被压缩成124个点，压缩比为32∶1. 选择其中13组作为样本送入支持向量机神经网络进行训练，用剩下的14组进行检验，正确率为100%. 关键词： 非线性荧光光谱 小波分析 递归最小方差算法 线性神经网络     

New reconstruction and forecasting algorithm for TEC data

To reconstruct the missing data of the total electron content(TEC) observations, a new method is proposed, which is based on the empirical orthogonal functions(EOF) decomposition and the value of eigenvalue itself. It is a self-adaptive EOF decomposition without any prior information needed, and the error of reconstructed data can be estimated. The interval quartering algorithm and cross-validation algorithm are used to compute the optimal number of EOFs for reconstruction.The interval quartering algorithm can reduce the computation time. The application of the data interpolating empirical orthogonal functions(DINEOF) method to the real data have demonstrated that the method can reconstruct the TEC map with high accuracy, which can be employed on the real-time system in the future work.     

Fast and accurate algorithm for the simulation of NMR spectra of large spin systems

The computational cost for the simulation of NMR spectra grows exponentially with the number of nuclei. Today, the memory available to store the Hamiltonian limits the size of the system that can be studied. Modern computers enable to tackle systems containing up to 13 spins [1], which obviously does not allow to study most molecules of interest in research. This issue can be addressed by identifying groups of spins or fragments that are not or only weakly interacting together, i.e., that only share weakly coupled spin pairs. Such a fragmentation is only permitted in the weak coupling regime, i.e., when the coupling interaction is weak compared to the difference in chemical shift of the coupled spins. Here, we propose a procedure that removes weak coupling interactions in order to split the spin system efficiently and to correct a posteriori for the effect of the neglected couplings. This approach yields accurate spectra when the adequate interactions are removed, i.e., between spins only involved in weak coupling interactions, but fails otherwise. As a result, the computational time for the simulation of 1D spectra grows linearly with the size of the spin system.     

基于小波变换和高斯拟合的在线谱图综合处理方法

微小型移动式现场在线检测技术是分析仪器发展的新领域。针对复杂工作环境中谱图存在强噪声干扰、谱峰重叠、不规则峰形等严重影响仪器的定性和定量准确度的瓶颈技术,提出了一种基于小波变换和高斯拟合相结合的谱图在线综合处理方法,用自研的仪器对甲苯和全氟三丁胺两种典型化合物的谱图进行了处理,并与实验室分析仪器普遍应用的算法进行了对比分析。结果表明,综合方法能够有效解决强噪声干扰、谱峰重叠、不规则峰形问题,提高仪器的定性和定量准确性,同时能够实现数据压缩,满足仪器的在线实时检测要求。综合方法处理甲苯特征峰的平均信噪比(SNR)较移动平滑方法提高了1.3倍,峰位误差ΔM降低了3.6倍,处理全氟三丁胺谱图的数据压缩比为197∶1。     

Development and exploration of a new methodology for the fitting and analysis of XAS data

A new data analysis methodology for X‐ray absorption near‐edge spectroscopy (XANES) is introduced and tested using several examples. The methodology has been implemented within the context of a new Matlab‐based program discussed in a companion related article [Delgado‐Jaime et al. (2010), J. Synchrotron Rad. 17 , 132–137]. The approach makes use of a Monte Carlo search method to seek appropriate starting points for a fit model, allowing for the generation of a large number of independent fits with minimal user‐induced bias. The applicability of this methodology is tested using various data sets on the Cl K‐edge XAS data for tetragonal CuCl₄^2?, a common reference compound used for calibration and covalency estimation in M—Cl bonds. A new background model function that effectively blends together background profiles with spectral features is an important component of the discussed methodology. The development of a robust evaluation function to fit multiple‐edge data is discussed and the implications regarding standard approaches to data analysis are discussed and explored within these examples.     

V-cluster algorithm: A new algorithm for clustering molecules based upon numeric data

Summary Clustering molecules based on numeric data such as, gene-expression data, physiochemical properties, or theoretical data is very important in drug discovery and other life sciences. Most approaches use hierarchical clustering algorithms, non-hierarchical algorithms (for examples, K-mean and K-nearest neighbor), and other similar methods (for examples, the Self-Organization Mapping (SOM) and the Support Vector Machine (SVM)). These approaches are non-robust (results are not consistent) and, computationally expensive. This paper will report a new, non-hierarchical algorithm called the V-Cluster (V stands for vector) Algorithm. This algorithm produces rational, robust results while reducing computing complexity. Similarity measurement and data normalization rules are also discussed along with case studies. When molecules are represented in a set of numeric vectors, the V-Cluster Algorithm clusters the molecules in three steps: (1) ranking the vectors based upon their overall intensity levels, (2) computing cluster centers based upon neighboring density, and (3) assigning molecules to their nearest cluster center. The program is written in C/C++ language, and runs on Window95/NT and UNIX platforms. With the V-Cluster program, the user can quickly complete the clustering process and, easily examine the results by use of thumbnail graphs, superimposed intensity curves of vectors, and spreadsheets. Multi-functional query tools have also been implemented.     

在传统的数值拟合中物理数据的误差来源于哪里?

应用传统的最小二乘法和作者基于微扰理论建立的代数方法(AM),本文研究并比较了双原子分子NaK的部分电子态的振动能谱和离解能.从而得出了这两种方法所得不同结果的主要原因,并建议了对于需要从实验物理数据中提取正确物理量的数学工作,人们不仅要使用恰当的数学方法,同时也应使用那些能从实验数据中挑选出包含完整物理信息的一组最佳实验数据的物理判据,从而由挑选出的这组最佳实验数据获得描述这些数据所代表的真实物理规律或物理信息的正确物理表象.     

靶场外弹道数据处理中的实时野值剔除算法

针对靶场外弹道数据处理过程中数据实时预处理的需要,在对最小二乘估计野值剔除算法分析的基础上,提出一种计算量小,满足实时性要求,且对雷达、光电经纬仪等大型测试设备数据预处理具有通用性的自适应野值剔除算法。该算法把连续5个实测数据的标准差的3倍作为阈值,以此判定下一个数据点是否为野值,最终完成整个弹道的实时野值剔除。通过Matlab仿真验证及实测数据分析表明,该算法对孤立野值点的剔除率可以达到100%,适用于靶场外弹道数据的实时预处理。     

A universal algorithm for calculating the backscattering factor in Auger-electron spectroscopy

We describe a universal Monte Carlo algorithm that can be used for the efficient calculation of backscattering factors (BFs) for quantitative Auger-electron spectroscopy (AES). This algorithm makes use of the continuous slowing-down approximation and the electron stopping power instead of simulation of individual inelastic-scattering events. This approach is attractive because it can be applied to any material with an empirical formula for the stopping power, available data for differential elastic-scattering cross sections, and an empirical formula for inner-shell ionization cross sections. We report BFs for the Si KL₂₃L₂₃, Cu L₃M₄₅M₄₅, Ag M₅N₄₅N₄₅, and Au M₅N₆₇N₆₇ Auger transitions in the corresponding elemental solids. These BFs were calculated for normal incidence of the primary beam, primary energies from near threshold for ionization of the relevant core levels to 20 keV, and Auger-electron emission angles of 10°, 60°, and 80°. We found satisfactory agreement between these BFs and values obtained from a more accurate algorithm in which individual inelastic-scattering events were simulated. Percentage deviations between BFs from the two algorithms were <2% for Au, <5% for Ag, <7% for Cu, and <10% for Si for primary energies likely to be used in practical AES. These deviations arise mainly from our use of stopping powers from the empirical formula rather than more reliable values calculated from experimental optical data.