退火温度对La0.75Mg0.25Ni3.5Co0.2贮氢电极合金的结构及电化学性能的影响

为了改善La-Mg-Ni系合金电极的循环稳定性,对铸态合金La0.75Mg0.25Ni3.5Co0.2在0.3 MPa压力氩气保护下进行不同温度的退火（1123,1223和1323 K）,保温时间均为10 h。系统研究了退火温度对合金的微观结构及电化学性能的影响。X射线衍射（XRD）和扫描电镜（SEM）研究结果表明,合金具有多相结构,当铸态及1123 K温度退火后合金主要由LaNi5,（La,Mg）2（Ni,Co）7相以及少量的LaNi2相组成。当退火温度为1223和1323 K时,合金中LaNi2相消失,合金主要由LaNi5,（La,Mg）2（Ni,Co）7及（La,Mg）（Ni,Co）3相组成。随退火温度提高,合金最大放电容量单调下降,但合金的循环稳定性得到改善。退火处理改善合金循环稳定性的原因在于退火后合金组织均匀,晶粒增大,在KOH电解质溶液中增强合金电极抗氧化腐蚀能力,抑制合金颗粒粉化。     

分类先验特征选择算法在代谢组学数据变量筛选中的应用

该文提出了基于无监督判别投影特征选择的支持向量机方法（UDPFS－SVM）用于标志物筛选。UDPFS－SVM首先通过无监督判别投影算法（UDPFS）引入分类先验信息、添加正则化与惩罚函数等约束自适应地获得具有稀疏性的判别投影矩阵,然后根据获得的矩阵求得相应低维代谢矩阵,最后建立支持向量机（SVM）分类模型寻找生物标志物。所提出的方法能够同时进行模糊学习与稀疏学习,并可合理利用变量之间的依赖关系。通过UDPFS－SVM与偏最小二乘判别分析（PLS－DA）方法对高脂血症大鼠血浆代谢组学数据进行变量筛选,并采用方差分析、ROC曲线、线性判别分析（LDA）对筛选得到的生物标志物进行评价。结果表明,两种方法均发现8个生物标志物。方差分析显示UDPFS－SVM方法获得的生物标志物均具有显著性差异,且显著性差异值均大于PLS－DA;ROC结果显示UDPFS－SVM结果为1.00,比PLS－DA结果高0.05;LDA显示UDPFS－SVM获得的生物标志物在高脂血症样本中可以更好地消除组内代谢差异,区分组间代谢差异,说明UDPFS－SVM方法在高脂血症生物标志物发现上优于PLS－DA,为生物标志物的发现提供了一种新思路。     

Accelerated Path-Following Iterative Shrinkage Thresholding Algorithm With Application to Semiparametric Graph Estimation

We propose an accelerated path-following iterative shrinkage thresholding algorithm (APISTA) for solving high-dimensional sparse nonconvex learning problems. The main difference between APISTA and the path-following iterative shrinkage thresholding algorithm (PISTA) is that APISTA exploits an additional coordinate descent subroutine to boost the computational performance. Such a modification, though simple, has profound impact: APISTA not only enjoys the same theoretical guarantee as that of PISTA, that is, APISTA attains a linear rate of convergence to a unique sparse local optimum with good statistical properties, but also significantly outperforms PISTA in empirical benchmarks. As an application, we apply APISTA to solve a family of nonconvex optimization problems motivated by estimating sparse semiparametric graphical models. APISTA allows us to obtain new statistical recovery results that do not exist in the existing literature. Thorough numerical results are provided to back up our theory.     

Synergistic Cocatalytic Effect of Carbon Nanodots and Co3O4 Nanoclusters for the Photoelectrochemical Water Oxidation on Hematite

Cocatalysis plays an important role in enhancing the activity of semiconductor photocatalysts for solar water splitting. Compared to a single cocatalyst configuration, a cocatalytic system consisting of multiple components with different functions may realize outstanding enhancement through their interactions, yet limited research has been reported. Herein we describe the synergistic cocatalytic effect between carbon nanodots (CDots) and Co₃O₄, which promotes the photoelectrochemical water oxidation activity of the Fe₂O₃ photoanode with a 60 mV cathodically shifted onset potential. The C/Co₃O₄‐Fe₂O₃ photoanode exhibits a photocurrent density of 1.48 mA cm^?2 at 1.23 V (vs. reversible hydrogen electrode), 78 % higher than that of the bare Fe₂O₃ photoanode. The slow reaction process on the single Co^III‐OH site of the Co₃O₄ cocatalyst, oxidizing H₂O to H₂O₂ with two photogenerated holes, could be accelerated by the timely H₂O₂ oxidation to O₂ catalyzed on CDots.     

Rational Design of Pt−Pd−Ni Trimetallic Nanocatalysts for Room-Temperature Benzaldehyde and Styrene Hydrogenation

Nanostructures of the multimetallic catalysts offer great scope for fine tuning of heterogeneous catalysis, but clear understanding of the surface chemistry and structures is important to enhance their selectivity and efficiency. Focussing on a typical Pt−Pd−Ni trimetallic system, we comparatively examined the Ni/C, Pt/Ni/C, Pd/Ni/C and Pt−Pd/Ni/C catalysts synthesized by impregnation and galvanic replacement reaction. To clarify surface chemical/structural effect, the Pt−Pd/Ni/C catalyst was thermally treated at X=200, 400 or 600 °C in a H₂ reducing atmosphere, respectively termed as Pt−Pd/Ni/C−X. The as-prepared catalysts were characterized complementarily by XRD, XPS, TEM, HRTEM, HS-LEIS and STEM-EDS elemental mapping and line-scanning. All the catalysts were comparatively evaluated for benzaldehyde and styrene hydrogenation. It is shown that the “PtPd alloy nanoclusters on Ni nanoparticles” (PtPd/Ni) and the synergistic effect of the trimetallic Pt−Pd−Ni, lead to much improved catalytic performance, compared with the mono- or bi- metallic counterparts. However, with the increase of the treatment temperature of the Pt−Pd/Ni/C, the catalytic performance was gradually degraded, which was likely due to that the favourable nanostructure of fine “PtPd/Ni” was gradually transformed to relatively large “PtPdNi alloy on Ni” (PtPdNi/Ni) particles, thus decreasing the number of noble metal (Pt and Pd) active sites on the surface of the catalyst. The optimum trimetallic structure is thus the as synthesised Pt−Pd/Ni/C. This work provides a novel strategy for the design and development of highly efficient and low-cost multimetallic catalysts, e. g. for hydrogenation reactions.     

基质辅助激光解吸电离飞行时间串联质谱法分析人乳β-酪蛋白新生儿体外消化模型多肽组

通过体外模拟新生儿消化道条件,用基质辅助激光解吸离子化飞行时间串联质谱法(MALDI-TOF/TOF)探究人乳β-酪蛋白消化后的多肽组.在离子源加速电压为20 kV,激光波长337 nm,激光频率200 Hz,离子延迟提取时间330 ns,质谱信号单次扫描累加2000次条件下,扫描质量范围m/z 500 ～ 5000的肽段.结果表明,消化后得到26个肽段,分子量集中在1000～4000Da.与已知功能的肽段序列进行对比,人乳β-酪蛋白在新生儿体外模型消化后未产生与已知功能的活性肽序列匹配的肽段,但发现9个肽前体,其中含4个血管紧张素转化酶(ACE)抑制肽前体,2个酪蛋白磷酸肽(CPP)前体,2个抗氧化肽前体,1个免疫活性肽前体,由酶切位点推测分析,肽前体可以继续在蛋白酶作用下转化为生物活性肽.     

Palladium(II)/Brønsted Acid‐Catalyzed Enantioselective Oxidative Carbocyclization–Borylation of Enallenes

An enantioselective oxidative carbocyclization–borylation of enallenes that is catalyzed by palladium(II) and a Brønsted acid was developed. Biphenol‐type chiral phosphoric acids were superior co‐catalysts for inducing the enantioselective cyclization. A number of chiral borylated carbocycles were synthesized in high enantiomeric excess.     

电感耦合等离子体-原子发射光谱法测定镍基高温合金中的硅、锰、铁、铬、钼、钴和钨

建立了电感耦合等离子体-原子发射光谱法测定试样中硅、锰、铁、铬、钼、钴和钨含量的新方法.研究了溶样方法、基体影响和分析谱线对测定的影响.在优化的实验条件下,测定结果的相对标准偏差(RSD,n=5)在0.41 ％-2.02％,回收率在94.0％-104.0％之间.