Blumlein双极脉冲形成线

为了提高超宽带系统的辐射因子,对超宽带脉冲整形技术进行了深入研究,介绍了采用Blumlein线产生双极脉冲的高功率双极脉冲产生技术。对采用Blumlein线产生双极脉冲的原理进行了讨论,通过数值模拟分析了影响双极脉冲形成的主要因素。设计了一套Blumlein高功率双极脉冲形成线,在800 kV脉冲源上开展了高压实验研究,分析了开关及形成线长度对形双极脉冲的影响。在输入单极脉冲电压为652.0 kV、脉宽为2.1 ns的情况下,Blumlein双极脉冲形成线可以产生负峰电压为571.9 kV、正峰电压为550.4 kV、半周期为740 ps的双极脉冲,峰-峰值电压是入射脉冲峰值电压的1.72倍,辐射因子为4.54 MV。     

基于Shape Context和尺度不变特征变换的多模图像自动配准方法

提出了基于修正的尺度不变特征变换（SIFT）特征提取和Shape Context特征描述算子相结合的多模图像自动配准算法,该算法利用修正的SIFT算法提取多模图像中的特征点,然后采用Shape Context算子描述特征点,利用特征点周围区域边缘点的梯度方向形成特征向量。采用欧氏距离作为匹配标准对多模图像中特征点进行初始匹配,然后通过RANSAC算法消除误匹配的特征点对,并采用最小二乘法计算仿射变换参数,最后通过仿射变换和双线性插值实现图像配准。对红外图像和可见光图像的配准实验结果表明了本算法的有效性和稳定性。     

Metabolomics reveals hippocampal metabolic fluctuations of postoperative fatigue syndrome and anti‐fatigue effect of Carthamus tinctorius L. extract in rat model

Postoperative fatigue syndrome (POFS) is a common clinical complication following almost every major abdominal surgery. There is not a full explanation of the etiology of POFS, especially its central mechanism. Carthamus tinctorius L. is a classic traditional Chinese medicine (TCM) which could exert ananti‐fatigue effect on POFS. However, its mechanism is still lacking. Here, ultra‐high performance liquid chromatography coupled with a quadrupole time‐of‐flight mass spectrometry (UHPLC‐Q‐TOFMS) based metabonomic approach was used to characterize hippocampal metabolic fluctuations of POFS in a rat model induced by partial hepatectomy, and to evaluate the anti‐fatigue effect of C. tinctorius L. extract (CTLE). With partial least‐squares discriminant analysis for classification and selection of biomarkers, 15 hippocampal metabolites related to POFS were identified, primarily involving alanine, aspartate and glutamate metabolism, valine, leucine and isoleucine degradation, purine metabolism, phenylalanine metabolism, tryptophan metabolism, phospholipid metabolism and fatty acid metabolism. With these altered metabolic pathways as possible drug targets, we systematically analyzed the protective effect of CTLE, which showed that CTLE could provide an anti‐fatigue effect on POFS through partially regulating the perturbed metabolic pathways. This study indicated that UHPLC‐Q‐TOFMS‐based metabolomics provided a powerful tool to reveal hippocampal metabolic fluctuations of POFS and study the mechanism of TCM. Copyright © 2015 John Wiley & Sons, Ltd.     

Seed‐Mediated Synthesis of Gold Tetrahedra in High Purity and with Tunable,Well‐Controlled Sizes

We report a facile synthesis of Au tetrahedra in high purity and with tunable, well‐controlled sizes via seed‐mediated growth. The success of this synthesis relies on the use of single‐crystal, spherical Au nanocrystals as the seeds and manipulation of the reaction kinetics to induce an unsymmetrical growth pattern for the seeds. In particular, the dropwise addition of a precursor solution with a syringe pump, assisted by cetyltrimethylammonium chloride and bromide at appropriate concentrations, was found to be critical to the formation of Au tetrahedra in high purity. Their sizes could be readily tuned in the range of 30–60 nm by simply varying the amount of precursor added to the reaction solution. The current strategy not only enables the synthesis of Au tetrahedra with tunable and controlled sizes but also provides a facile and versatile approach to reducing the symmetry of nanocrystals made of a face‐centered cubic lattice.     

Fluorescence resonance energy transfer between cerium ion(III) and levofloxacin in micellar solution and its analytical application to the determination of levofloxacin

Fluorescence resonance energy transfer between cerium ion(III) and levofloxacin is studied in a micellar solution of cetyltrimethyl ammonium bromide. A non-fluorescent 1:2 complex was formed between excited cerium ion(III) and ground state levofloxacin. The fluorescence of cerium ion(III) is quenched by levofloxacin with the quenching in accordance with the Stern–Volmer relation. The analytical relationship was established between the ratio of the fluorescence of levofloxacin present and absent cerium ion (III) and the concentration of levofloxacin, which helped to estimate the content of levofloxacin directly.     

A study of fluorescence properties of citrinin in β-cyclodextrin aqueous solution and different solvents

Citrinin (CIT) is a nephrotoxic mycotoxin initially isolated from filamentous fungus Penicilliu citrinum. It was later isolated from several other species, such as Aspergillus and Monascus. It has a conjugated, planar structure that gives it a natural fluorescence ability, which can be used to develop sensitive methods for detecting CIT in food. In this paper, we used the spectro?uorescence technique to study the effects of pH value, β-cyclodextrin (β-CD) and organic solvents on the CIT fluorescence intensity. The results show that lower pH value, aceitc acid, β-CD and acetonitrile can induce a higher fluorescence intensity of CIT, but methanol or H₂O has a decreasing effect on the fluorescence intensity of CIT. Findings in this study provide a theoretical basis for development of a high sensitivity fluorescence-based trace analysis for CIT detection.     

Gamma radiation effects on physical properties of parchment documents: Assessment of Dmax

Parchments are important documents that give testimony for History; therefore these materials should be respected and preserved. Considering incremental biodeterioration problems that have to be faced daily, the Archive of the University of Coimbra (AUC) is involved in different scientific projects in order to evaluate and determine new methods for document decontamination and preservation.The aim of this study was to evaluate gamma radiation effects on the colour and texture of the AUC parchment documents. The assessment of these effects was used to estimate the maximum gamma radiation dose (D_max) that could guarantee parchment documents′ decontamination treatment, without significant alteration of their physical properties. Parchment samples were exposed to gamma radiation doses ranging from 10 to 30 kGy. The texture and colour of samples were assessed before and after the irradiation procedure, using a texture analyser and an electronic colorimeter. Hardness and springiness were determined based on texture spectra. Lightness (L?), Chroma (C), greenness vs. redness (a*) and yellowness vs. blueness (b*) values were obtained from colorimetric measures. Results indicate no significant effects of gamma radiation on the texture and colour of parchment for the studied doses.