能量选择中子成像技术及其应用

能量选择中子成像技术是利用特定范围波长(能量)的中子进行成像。在热/冷中子范围内(<25meV),能量选择中子成像技术主要基于布拉格边效应和衍射机制,相比常规中子成像技术不但可以显著提高图像对比度,而且能分析应变、应力、织构。在超热中子范围内(>1eV),能量选择中子成像技术主要基于中子共振吸收,中子截面随能量变化是同位素特有的,存在明显的共振吸收峰,因此可以进行同位素的“指纹”识别。能量选择中子成像技术在工程、材料、化学、物理、生物、考古等众多科研领域中有着非常广阔的应用前景。     

A general electron donor–acceptor complex for photoactivation of arenes via thianthrenation

General photoactivation of electron donor–acceptor (EDA) complexes between arylsulfonium salts and 1,4-diazabicyclo[2.2.2]octane with visible light or natural sunlight was discovered. This practical and efficient mode enables the production of aryl radicals under mild conditions, providing an unrealized opportunity for two-step para-selective C–H functionalization of complex arenes. The novel mode for generating aryl radicals via an EDA complex was well supported by UV-vis absorbance measurements, nuclear magnetic resonance titration experiments, and density functional theory (DFT) calculations. The method was applied to the regio- and stereo-selective arylation of various N-heterocycles under mild conditions, yielding an assembly of challengingly linked heteroaryl–(hetero)aryl products. Remarkably, the meaningful couplings of bioactive molecules with structurally complex drugs or agricultural pharmaceuticals were achieved to display favorable in vitro antitumor activities, which will be of great value in academia or industry.

General photoactivation of EDA complexes between arylsulfonium salts and 1,4-diazabicyclo[2.2.2]octane was discovered. This practical mode enables the generation of aryl radicals for C–H functionalization of arenes.     

波束开角对多普勒测频结果的影响*

具有不同波束开角的声学多普勒测速设备未标定的测速结果存在偏差。基于水底椭圆散射模型研究了波束开角对声学多普勒测速结果的影响,对提高声学测速性能具有实际意义。水底椭圆散射模型下,足印上不同方位传播损失和散射强度存在差异,导致频谱不对称,测频结果偏小。利用不对称系数量化频谱不对称程度,若波束开角增大,方位不对称系数随之增大,测频偏差增大,推导了波束开角导致的测频偏差解析式。分析仿真和外场试验数据测频结果可知,不同多普勒频移下测频偏差和理论计算值相符,不同波束开角下实际测频偏差与理论公式计算的测频偏差均随波束开角增大而增大。     

埋地热油管道正常运行的数值模拟研究

对高凝原油管道输送的水力热力问题进行分析研究,掌握管线运行规律,保证管线安全经济运行有着重要意义.本文建立了埋地热油管道正常运行的数学模型,采用非结构化网格和有限容积法对该问题进行了研究,计算结果与实验测量值吻合良好.     

Intelligent Fault Diagnosis of Industrial Robot Based on Multiclass Mahalanobis-Taguchi System for Imbalanced Data

One of the biggest challenges for the fault diagnosis research of industrial robots is that the normal data is far more than the fault data; that is, the data is imbalanced. The traditional diagnosis approaches of industrial robots are more biased toward the majority categories, which makes the diagnosis accuracy of the minority categories decrease. To solve the imbalanced problem, the traditional algorithm is improved by using cost-sensitive learning, single-class learning and other approaches. However, these algorithms also have a series of problems. For instance, it is difficult to estimate the true misclassification cost, overfitting, and long computation time. Therefore, a fault diagnosis approach for industrial robots, based on the Multiclass Mahalanobis-Taguchi system (MMTS), is proposed in this article. It can be classified the categories by measuring the deviation degree from the sample to the reference space, which is more suitable for classifying imbalanced data. The accuracy, G-mean and F-measure are used to verify the effectiveness of the proposed approach on an industrial robot platform. The experimental results show that the proposed approach’s accuracy, F-measure and G-mean improves by an average of 20.74%, 12.85% and 21.68%, compared with the other five traditional approaches when the imbalance ratio is 9. With the increase in the imbalance ratio, the proposed approach has better stability than the traditional algorithms.     

Deep Multilabel Multilingual Document Learning for Cross-Lingual Document Retrieval

Cross-lingual document retrieval, which aims to take a query in one language to retrieve relevant documents in another, has attracted strong research interest in the last decades. Most studies on this task start with cross-lingual comparisons at the word level and then represent documents via word embeddings, which leads to insufficient structure information. In this work, the cross-lingual comparison at the document level is achieved through the cross-lingual semantic space. Our method, MDL (deep multilabel multilingual document learning), leverages a six-layer fully connected network to project cross-lingual documents into a shared semantic space. The semantic distances can be calculated when the cross-lingual documents are transformed into embeddings in semantic space. The supervision signals are automatically extracted from the data and then used to construct the semantic space via a linear classifier. The ambiguity of manual labels could be avoided and the multilabel supervision signals can be acquired instead of a single label. The representation of the semantic space is enriched by multilabel supervision signals, which improves the discriminative ability of the embeddings. The MDL is easy to extend to other fields since it does not depend on specific data. Furthermore, MDL is more efficient than the models training all languages jointly, since each language is trained individually. Experiments on Wikipedia data showed that the proposed method outperforms the state-of-the-art cross-lingual document retrieval methods.     

Optical bistability based on surface plasmon coupled between two noble metal films involving Kerr materials

We successfully investigate an optical bistability phenomenon in a layered structure consisting of Kretschmann configuration involving the Kerr-type nonlinear and the silver film. Pure theoretical approaches are employed to investigate that the surface plasmon could easily be coupled and both the reflection and transmission curves versus the incident intensity forms optical bistability. The transmission curves are greatly influenced by the thickness of the second silver film. These results may be useful for designing novel surface plasmon-based optical devices and will be essential for future classical and quantum information processes.     

A new electronically deficient atropisomeric diphosphine ligand (S)-CF3O-BiPhep and its application in asymmetric hydrogenation

A new electronically deficient atropisomeric diphosphine ligand (S)-CF₃O-BiPhep was synthesized from 1-bromo-3-(trifluoromethoxy)benzene in high yield. The key steps included oxidative coupling with anhydrous ferric chloride and optical resolution by (+)-DMTA. The ligand afforded high performance for Ir-catalyzed asymmetric hydrogenation of quinolines with ee up to 92% and TON up to 25,000. It was also successfully applied to the Pd-catalyzed asymmetric hydrogenation of simple indoles with ee up to 87% and Rh-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone with 97% ee.     

Why calcium inhibits magnesium-dependent enzyme phosphoserine phosphatase? A theoretical study

Mechanisms for the formation of the Schiff base from acetaldehyde and butylamine, glycine and phosphatidylethanolamine based on Dmol3/DFT calculations were realized. For the case of phosphatidylethanolamine, calculations were done under periodic boundary conditions, in an amine-phospholipid monolayer model with two molecules of phosphatidylethanolamine by cell. All models contained explicit aqueous solvent. In the three cases, a neutral amino group is used to model the nucleophilic attack on the carbonyl group of acetaldehyde, and water molecules form hydrogen bond networks. These networks were involved in the reactions by performing as proton-transfer carriers, important in some steps of reactions, and stabilizing reaction intermediates. In all the studied reactions, they take place in two steps, namely: (1) formation of a carbinolamine and (2) its dehydration to the Schiff base, being the dehydration the rate-determining step of the process, consistent with available experimental evidence for similar reactions. The main difference between the studied reactions is found in the value for relative free energy for the intermediates and transition states in the second step; these values are lower in the cases of glycine and phosphatidylethanolamine in comparison with butylamine, due the influence of their molecular environments. Based on the results, the aminophospholipid surface environment and carboxylic group of glycine may boost Schiff base formation via a neighboring catalyst effect.