Assessing Earthquake Forecast Performance Based on b Value in Yunnan Province,China

Many studies have shown that b values tend to decrease prior to large earthquakes. To evaluate the forecast information in b value variations, we conduct a systematic assessment in Yunnan Province, China, where the seismicity is intense and moderate–large earthquakes occur frequently. The catalog in the past two decades is divided into four time periods (January 2000–December 2004, January 2005–December 2009, January 2010–December 2014, and January 2015–December 2019). The spatial b values are calculated for each 5-year span and then are used to forecast moderate-large earthquakes (M ≥ 5.0) in the subsequent period. As the fault systems in Yunnan Province are complex, to avoid possible biases in b value computation caused by different faulting regimes when using the grid search, the hierarchical space–time point-process models (HIST-PPM) proposed by Ogata are utilized to estimate spatial b values in this study. The forecast performance is tested by Molchan error diagram (MED) and the efficiency is quantified by probability gain (PG) and probability difference (PD). It is found that moderate–large earthquakes are more likely to occur in low b regions. The MED analysis shows that there is considerable precursory information in spatial b values and the forecast efficiency increases with magnitude in the Yunnan Province. These results suggest that the b value might be useful in middle- and long-term earthquake forecasts in the study area.     

基于PCA-BP神经网络的光谱消光法颗粒粒径反演算法研究

光谱消光法广泛应用于颗粒粒径测量领域,在利用光谱消光法对颗粒粒径进行反演的过程中,由于颗粒的消光系数存在理论复杂、计算繁琐、收敛速度慢以及求解不稳定等问题,很大程度上影响了整个反演过程的快速性和准确性。且在众多波长的消光数据中,存在较多重复冗余的信息,也很大程度上增加了反演算法的时间。针对光谱消光法粒径反演算法计算繁琐、反演效率低的问题,提出了基于主成分分析（PCA）和BP神经网络的光谱消光颗粒粒径分析方法。基于Mie散射理论对不同粒径、不同波长下的光谱消光值进行了仿真计算,通过对光谱消光数据集的主成分分析及各个波长综合载荷系数的计算,实现了最优特征波长的选取,利用降维后的光谱消光数据训练了PCA-BP神经网络模型,并利用该网络模型计算了粒径颗粒分布。通过仿真计算,比较了PCA-BP神经网络模型与传统的BP神经网络模型的预测精度,并分析了波长数目对两种神经网络模型预测结果的影响。针对训练得到的PCA-BP神经网络模型开展光谱消光法粒径参数反演算法的验证实验,搭建了光谱消光法颗粒粒径参数测量实验系统,测量了粒径范围在0.5～9.7 μm内的6种不同粒径参数的聚苯乙烯标准颗粒。仿真和实验结果表明：基于主成分分析方法可确定各个波长向量之间的相关性,利用综合载荷系数选取最优特征波长对应的消光值对整体的光谱数据具有较好的代表性,可实现光谱数据的降维。相比传统的BP神经网络模型,基于PCA-BP神经网络模型的颗粒粒径分布的分析方法预测精度更高,对于较分散颗粒系的分布参数的预测有更加明显的优势。而且,被选取的波长数较少时,PCA-BP神经网络模型依然有较高的预测精度。利用训练好的PCA-BP神经网络模型对颗粒粒径参数进行实验验证,预测结果可瞬时输出,颗粒粒径分布误差在5%以内,验证了该算法的可行性。     

In-medium pion dispersion relation and medium correction of Nπ■Δ near the threshold energy of pion production

Transport models cannot simultaneously explain very recent data on pion multiplicities and pion charged ratios from central collision of Sn+Sn at 0.27 A GeV.This stimulates further investigations on the pion dispersion relation,in-medium Nπ→Δ cross sections,and Δ→Nπ decay widths near the threshold energy or at subthreshold energy of pion production in isospin asymmetric nuclear matter.In this study,the pion dispersion relation,in-medium Nπ→Δ cross section,and Δ→Nπ decay width near the threshold energy are investigated in isospin asymmetric nuclear matter by using the one-boson-exchange model.With the consideration of the energy conservation effect,the in-medium Nπ→Δ cross sections are enhanced at s1/2 <1.11 GeV in a nuclear medium.The prediction of pion multiplicity and π-/π+ ratios near the threshold energy could be modified if this effect is considered in transport model simulations.     

Reduced field-of-view DTI segmentation of cervical spine tissue

The number of diffusion tensor imaging (DTI) studies regarding the human spine has considerably increased and it is challenging because of the spine’s small size and artifacts associated with the most commonly used clinical imaging method. A novel segmentation method based on the reduced field-of-view (rFOV) DTI dataset is presented in cervical spinal canal cerebrospinal fluid, spinal cord grey matter and white matter classification in both healthy volunteers and patients with neuromyelitis optica (NMO) and multiple sclerosis (MS). Due to each channel based on high resolution rFOV DTI images providing complementary information on spinal tissue segmentation, we want to choose a different contribution map from multiple channel images. Via principal component analysis (PCA) and a hybrid diffusion filter with a continuous switch applied on fourteen channel features, eigen maps can be obtained and used for tissue segmentation based on the Bayesian discrimination method. Relative to segmentation by a pair of expert readers, all of the automated segmentation results in the experiment fall in the good segmentation area and performed well, giving an average segmentation accuracy of about 0.852 for cervical spinal cord grey matter in terms of volume overlap. Furthermore, this has important applications in defining more accurate human spinal cord tissue maps when fusing structural data with diffusion data. rFOV DTI and the proposed automatic segmentation outperform traditional manual segmentation methods in classifying MR cervical spinal images and might be potentially helpful for detecting cervical spine diseases in NMO and MS.     

Semipolar (11\bar 2\bar 2) ZnO thin films grown on LaAlO3‐buffered LSAT (112) single crystals by pulsed laser deposition

Semipolar (11\bar 2 \bar 2) ZnO was successfully grown on (112) LaAlO₃/(LaAlO₃)_0.29(Sr₂AlTaO₆)_0.35 substrate by pulsed laser deposition. The epitaxial relationship is [11\bar 23]_{\rm ZnO} // [11\bar 1]_{\rm LAO/LSAT} with the polar axis of [000\bar 1]_{\rm ZnO} pointing to the surface. For ZnO films with thickness of 1.6 μm, the threading dislocation density is ～1 × 10⁹ cm^–2, and the density of basal stacking faults is below 1 × 10⁴ cm^–1. The (11\bar 2 \bar 2) ZnO exhibits strong D⁰X emissions with a FWHM of 9 meV and very few green–yellow emissions in the low‐temperature (10 K) and room‐temperature photoluminescence spectra, respectively.

     

ZnAl2O4：Tb3+荧光粉的合成、结构及其光学性能研究

通过溶胶-凝胶法制备出不同Tb³⁺掺杂浓度和不同二次煅烧温度下的ZnAl₂O₄:Tb³⁺荧光粉, 并利用X射线衍射(XRD)和荧光光谱等对样品进行了表征。由XRD结果可知,当Tb³⁺掺杂的摩尔分数不大于9%,二次煅烧温度在600℃以上时,所得粉体为结晶性良好的尖晶石相。在紫外光激发下,ZnAl₂O₄:Tb³⁺荧光粉的发射光谱由位于488 nm(⁵D₄→⁷F₆)、542 nm(⁵D₄→⁷F₅)、587 nm(⁵D₄→⁷F₄ )和621.5 nm(⁵D₄→⁷F₃)的4个发射峰组成。研究发现,Tb³⁺的掺杂浓度和二次煅烧温度对样品发光强度有着重要影响,当Tb³⁺的摩尔分数为5%,二次煅烧温度为900℃时,ZnAl₂O₄:Tb³⁺荧光粉的发光最强,继续增加Tb³⁺掺杂浓度或提高煅烧温度,分别会出现浓度猝灭和温度猝灭现象。     

Investigations of Pulse‐Plasma‐Polymer Coating on TiO2 Nanoparticles and Their Dispersion

An amorphous acrylic acid (AA) polymer coating was generated on TiO₂ nanoparticles through pulse radio frequency (RF) plasma polymerization. The AA plasma synthesis mechanism was studied by its optical emission spectrum. The chemical structures of AA–plasma‐polymer were carefully investigated by Fourier transform infrared spectroscopy (FTIR). The dispersion behaviors of AA‐coated and uncoated TiO₂ nanoparticles in glycol solution were characterized by ultraviolet absorbency and particle size distribution measurements. The results showed that the aggregation of TiO₂ nanoparticles in glycol solution was effectively lowered and the dispersion was improved a lot after AA–plasma‐polymer coating. The pulse plasma coating parameters played an important role in the dispersion enhancement of TiO₂ nanoparticles. By properly regulating the pulse discharge parameters, the system could gain the highest radical–monomer reactions rate, the most compatible functional groups on the nanoparticles, and the best dispersion in the background media.     

A Novel Pyrene Fluorescent Sensor Based on the π–π Interaction Between Pyrene and Graphene of Graphene–Cadmium Telluride Quantum Dot Nanocomposites

In this article, water-soluble graphene–cadmium telluride quantum dot nanocomposites were fabricated through the synthesis of cadmium telluride quantum dots in the presence of graphene aqueous dispersion. It was found that pyrene could remarkably quench fluorescence of graphene–cadmium telluride quantum dot nanocomposites. On this basis, a novel method for the determination of pyrene was developed. Factors affecting the pyrene detection were investigated, and the optimum conditions were determined. Under the optimum conditions, a linear relationship could be established between the quenching of fluorescence intensity of graphene–cadmium telluride quantum dot nanocomposites and the pyrene concentration in the range of 6.00 × 10^?8–2.00 × 10^?6 mol L^?1 with a correlation coefficient of 0.9959. The detection limit was 4.02 × 10^?8 mol L^?1. Furthermore, the nanocomposites were applied to practical determination of pyrene in different water samples with satisfactory results.     

Green ultrasound-assisted extraction of carotenoids based on the bio-refinery concept using sunflower oil as an alternative solvent

A green, inexpensive and easy-to-use method for carotenoids extraction from fresh carrots assisted by ultrasound was designed in this work. Sunflower oil was applied as a substitute to organic solvents in this green ultrasound-assisted extraction (UAE): a process which is in line with green extraction and bio-refinery concepts. The processing procedure of this original UAE was first compared with conventional solvent extraction (CSE) using hexane as solvent. Moreover, the UAE optimal conditions for the subsequent comparison were optimized using response surface methodology (RSM) and ultra performance liquid chromatography – diode array detector – mass spectroscopy (UPLC–DAD–MS). The results showed that the UAE using sunflower as solvent has obtained its highest β-carotene yield (334.75 mg/l) in 20 min only, while CSE using hexane as solvent obtained a similar yield (321.35 mg/l) in 60 min. The green UAE performed under optimal extraction conditions (carrot to oil ratio of 2:10, ultrasonic intensity of 22.5 W cm^?2, temperature of 40 °C and sonication time of 20 min) gave the best yield of β-carotene.     

Spectral Database Systems: A Review

Abstract: Spectroscopy has been demonstrated to be an important method of analysis and detection. A spectral database system (SDBS) can not only satisfy the traditional requirements for spectral management but also provides several new functions, including spectra sharing on the website and web-based and real-time analysis and detection. Chemists and spectroscopists could analyze and detect pure materials and some mixtures rapidly with the help of standard SDBS, and now they are trying to improve these systems to fulfill rapid analysis for complex mixtures, even those as complex as agro-products. Overall, SDBS make it possible to analyze and detect unknown samples rapidly and nondestructively. This article focuses on significant progress in research on infrared (IR), near-infrared (NIR), and Raman SDBSs. Additionally, the drawbacks and obstacles of SDBSs are summarized and trends are discussed.