From single crystals to supported nanoparticles in experimental and theoretical studies of H2 oxidation over platinum metals (Pt, Pd): Intermediates, surface waves and spillover

The present paper reviews our investigations concerning the mechanism of H₂ + O₂ reaction on the metal surfaces (Pt, Pd) at different structures: single crystals (Pt(1 1 1), Pt(1 0 0), Pd(1 1 0)); microcrystals (Pt tips); and nanoparticles (Pd–Ti³⁺/TiO₂). Field electron microscopy (FEM), field ion microscopy (FIM), high-resolution electron energy loss spectroscopy (HREELS), XPS, UPS, work function (WF), TDS and temperature-programmed reaction (TPR) methods have been applied to study the kinetics of H₂ oxidation on a nanolevel. The adsorption of both O₂ and H₂ and several dissociative products (H_ads, O_ads, OH_ads) was studied by HREELS. Using the DFT technique the equilibrium states and stretching vibrations of H, O, OH, H₂O, adsorbed on the Pt(1 1 1) surface, have been calculated depending on the surrounding of the metal atoms. Sharp tips of Pt, several hundreds angstroms in radius, were used to perform in situ investigations of the dynamic surface processes. The FEM and FIM studies on the Pt-tip surface demonstrate that the self-oscillations and waves propagations are connected with periodic changes in the surface structure of nanoplane (1 0 0)-(hex) ↔ (1 × 1), varying the catalytic property of metal. The role of defects (Ti³⁺-□_O) in the adsorption centers formation, their stabilization by the palladium nanoparticles, and then the defects participation in H₂ + O₂ steady-state reaction over Pd–Ti³⁺/TiO₂ surface have been studied by XPS, UPS and photodesorption techniques (PhDS). This reaction seems to involve the “protonate” hydrogen atoms (H⁺/TiO_x) as a result of spillover effect: diffusion of H_ads atoms from Pd particles on a TiO_x surface. The comprehensive study of H₂, O₂ adsorption and H₂ + O₂ reaction in a row: single crystals → tips → nanoparticles has shown the same nature of active centers over these metal surfaces.     

Flavonoids in Gran Negro berries collected from shoulders and tips within the cluster,and comparison with Brancellao and Mouratón varieties

Galicia (the north-western corner of Spain) is a Spanish region with several old-traditional winegrowing areas. Vitis vinifera L. cv. Mencía is one of the most often used to produce quality red wines but the tendency of the world wine-making market is to reward the production of wines that have particular and differentiated characteristics. In Galicia, there are other red cultivars such as Gran Negro which were not exploited for their potential to produce quality red wines. Dynamics of anthocyanin and flavonol accumulation in Gran Negro berries were studied separately in two different positions within the cluster (tips and shoulders) during 30 days before harvest to assess the existence of different polyphenol quality in both positions and as a consequence, red wines with different qualities. Dynamics of anthocyanins over ripening confirmed that anthocyanins presented upward trends (from 1510 to 1727 mg/kg in tips; and from 1532 to 1728 mg/kg in shoulders) but dynamics of flavonols confirmed that maximum values were reached and stabilised thirty days before harvest (from 45 to 39 mg/kg in tips; and from 49 to 45 mg/kg in shoulders). No differences were observed in anthocyanin and flavonol contents collected from tips and shoulders which indicates that is not necessary to harvest them separately. The results from Gran Negro were compared with those of Brancellao and Mouratón.     

Anthocyanins and flavonols berries from Vitis vinifera L. cv. Brancellao separately collected from two different positions within the cluster

Galicia (N.W. Iberian Peninsula) is a Spanish region with several old-traditional winegrowing areas. Vitis vinifera L. cv. Mencía is one of the most often used to produce quality red wines in the five Galicia Denomination of Origin. However, there are traditional cultivars such as Brancellao, which were not exploited for their potential to produce quality red wines. Dynamics of anthocyanin and flavonol accumulation were studied separately in two different positions within the cluster (tips and shoulders), during 30 days before harvest. The objective of separating berries is to assess the existence of different polyphenol quality in both positions; as a consequence, the selection and harvest of those berries with a higher content of anthocyanins and flavonols could produce red wines with different qualities. Derivatives of five anthocyanins (malvidin, peonidin, petunidin, delphinidin and cyanidin) were detected in skins at both positions within the cluster. Anthocyanin contents stabilized in the 30 days prior to harvest in the berries from the shoulders whereas they continue to increase in those from the tips. Derivatives of six flavonols (quercetin, myricetin, kaempherol, laricitrin, isorhamnetin and syringetin) were detected in skin and flesh at both positions within the cluster. Dynamics of anthocyanins (from 400 to 515 mg/kg in tips; and from 598 to 574 mg/kg in shoulders) and flavonols (from 19 to 29.3 mg/kg in tips; and from 22.7 to 29.4 mg/kg in shoulders) over ripening confirmed that these polyphenols presented upward trends. Therefore, it is not necessary to harvest Brancellao berries separately and a high quality red wine will be obtained with berries from entire clusters regarding these compounds.     

Aroma potential of Brancellao grapes from different cluster positions

In this study the presence of aroma compounds in grapes of Brancellao (Vitis vinifera L.) was investigated in order to obtain its aroma potential fingerprint. It is well known that differences exist in aromatic compounds amongst grapevine varieties at ripening stages. Within the framework of an increasingly competitive market, the chance of obtaining different wines from vines of the same variety grown at the same vineyard is becoming of increasing importance. This can be done through the managing of the vineyard, but also some wineries have assayed the separation of the tip and shoulder berries of the clusters of a specific variety with this objective. In this work it is evaluated that, in the final stages of maturation, differences exist in the probable alcoholic degree, total acidity of the must, as well as in the aromatic composition of skin and flesh of berries coming from the tips and shoulders of the clusters. Gas chromatography coupled to mass spectrometry (GC-MS) was used to determine the aromatic composition, in the skin and flesh of each sample, either tip or shoulder berries from the clusters. The obtained results showed that there was not variability for the probable alcoholic degree and total acidity between the shoulders and tips, whereas there was variability for their aromatic composition. For the berries from the tips of the clusters most of volatiles were found in the flesh (except aldehydes) and spicy and floral nuances (with the only exception of β-ionone) were in higher proportions. For the berries from the shoulders of the clusters, most of volatiles were found in the skin (monoterpenes, norisoprenoids, aldehydes, and C₆ alcohols), where the flesh was slightly richer in aromatic alcohols, volatile phenols and pantolactone; β-ionone and herbaceous nuances were in higher proportions. These results are promising for those wineries that are considering the chance of separating berries from tips and shoulders of the clusters for the elaboration of different quality wines.     

一种高效、简便原子力显微镜液体中原位实验方法

原子力显微镜从1986年发明以来,由于其在显微成像术中的独特优势,受到愈来愈多的来自各个学科领域研究人员的高度注视。目前所报道的有关原子力显微镜原位动态观察的方法在实际操作中需要较高的技巧性。本文介绍一种原子力显微镜的原位成像方法,能够做到在液体中高效、简便观察生物样品。     

Active odorants in Mouratón grapes from shoulders and tips into the bunch

The opportunity for obtaining different wines from the same variety cultivated in the same vineyard is becoming of increasing importance. This is why some wine cellars have started to assay the separation of the tips and shoulders berries of the clusters of a specific variety with this objective. In this work, the study is focused on berries of Mouratón (Vitis vinifera L.) to investigate if, in the latter stages of ripening, differences exist in the probable alcoholic degree, total acidity of the must, as well as in the aromatic composition of skin and flesh of berries coming from the tips and shoulders of the clusters. Gas chromatography coupled to mass spectrometry (GC–MS) was used to determine the aromatic composition. The obtained results showed that there was not variability for the probable alcoholic degree and total acidity between the tips and shoulders, whereas there was variability for their aromatic composition during ripening. These results are promising for those wine cellars that are considering the separation of berries from tips and shoulders of the clusters for the elaboration of different quality wines.     

钢管热镀锌用160t电阻加热炉的生产实践

介绍了钢管热镀锌用160t电阻加热炉的特点,主要设计参数和如何选择锌锅材质、壁厚等。简要说明了炉温的控制方法及炉体存在的不足之处。多年生产实践证明,由于锌锅锅体尺寸和材质及壁厚选择比较合理,锌液的温度均匀,从而延长了锌锅的使用寿命。     

微电极针尖的制备方法

针尖工艺是针型微电极制造的关键技术.利用电生理实验室常用设备搭建了加工平台,采用阴极圆环营造出一个渐变电场,通过一组正交试验,研究了电解液浓度、腐蚀电压、通电时间等对针尖质量的影响,得到了最佳加工参数:NaCl溶液浓度为3.0g/L,腐蚀电压为5.0V,通电时间为30s,制备出符合电刺激实验要求的高质量针尖.该方法操作简单、制备时间短、成本低,适用于电生理实验中微电极尖端形态的改进.     

烘烤期间带茎采收的烤烟顶部叶某些生理生化特性变化

为进一步探讨烤烟顶部叶带茎采收烘烤的生理生化机制,对烤烟顶部叶带茎采收烘烤和不带茎采收烘烤的色素含量、淀粉酶、多酚氧化酶(PPO)、超氧化物歧化酶(SOD)、过氧化物酶(POD)活性及丙二醛(MDA)含量进行了测定。结果表明,烤烟顶部叶带茎采收烘烤在变黄12~24h时的叶绿素降解速度快于不带茎采收烘烤,到定色末期时带茎采收烘烤和不带茎采收烘烤的顶部叶叶绿素含量基本相同;带茎采收烘烤与不带茎采收烘烤的顶部叶类胡萝卜素与叶绿素的比值变化趋势基本一致,但带茎采收烘烤比不带茎采收烘烤的类胡萝卜素的降解量大。带茎采收烘烤和不带茎采收烘烤的顶部叶淀粉酶活性变化规律差异较大。带茎采收烘烤的PPO活性总体上低于不带茎采收烘烤,SOD活性高于不带茎采收烘烤,POD活性和MDA含量低于不带茎采收烘烤。综合分析,烤烟顶部叶带茎采收烘烤的生理生化变化对烤后烟叶的质量形成是有利的。     

竖立在晶态金表面上的短单壁碳纳米管

合成和提纯了单壁碳纳米管(SWCNTs),用胶体将其竖直地组装在金薄膜表面上。用此组装技术制造了扫描隧道显微镜(STM)的针尖,成功地观测到了金晶粒的形貌像和高定向石墨的原子像。SWCNTs竖立在金表面上对于电学特性测量,制造场发射电子源,组装纳米电子器件,制作扫描探针显微镜(SPM)针尖等有重要意义。