Theoretical Evaluation of the Microporosity of Pillared Layered Double Hydroxides

Over the last ten years, the concept of pillaring has frequently been applied on layered double hydroxides (LDHs). Due to the variety of possible anionic pillaring species and the adjustable layer charge density, LDHs offer good perspectives with regard to the creation of porous adsorbents and catalysts. But despite these possibilities, their porosity properties can still not compete with those of industrially applicable materials like zeolites. In this study, theoretical calculations based on geometrical models and performed on both Fe(CN)₆-MgAl-LDHs (A) and [PV₂W¹⁰ O⁴⁰]-ZnAl-LDHs (B) were reported. Properties such as the micropore volume and the interpillar distance were calculated, and compared to experimental data. For a M(II)/M(III) ratio in the layers of 3, the theoretical maximum micropore volumes were 0.3843 cm³/g (A) and 0.1497 cm³/g (B), respectively. By implementing parameters like the stack size, pillars on the outside of the stacks and the possibility of collapse, the model was adjusted in order to create a realistic picture of the microstructure of pillared LDHs. This led to a better understanding of the limiting factors, and gave an explanation for the relatively low micropore volumes of pillared LDHs. For the Fe(CN)₆-MgAl-LDHs, small interpillar distances were responsible for the partial inaccessibility of the interlayer regions by N₂. This effect was the most pronounced for high charge density LDHs. The situation for the [PV₂W¹⁰O⁴⁰]-ZnAl-LDHs is more complex. Probably due to an incomplete pillaring process, the theoretical maximum values are not reached.     

Chemical Defenses Against Fish Predation in Three Brazilian Octocorals: 11β,12β-Epoxypukalide as a Feeding Deterrent in Phyllogorgia dilatata

The feeding-deterrence properties of crude extracts of three Brazilian octocoral species, Neospongodes atlantica Kükenthal (Alcyonacea, Nephtheidae), Plexaurella regia Castro (Gorgonacea, Plexauridae), and Phyllogorgia dilatata Esper (Gorgonacea, Gorgoniidae), were investigated. All the extracts were incorporated into food strips at the concentrations occurring in the living organisms. Crude extract and its ethyl acetate fraction obtained from P. dilatata collected in Armação dos Búzios (Rio de Janeiro State), when incorporated into artificial diets and tested in the habitat of origin, reduced consumption of food strips by fishes, relative to controls. Crude extracts from two octocoral species collected at the National Marine Park of Abrolhos (Bahia State), N. atlantica and P. regia, had no apparent feeding-deterrence properties; in fact, they seemed to stimulate feeding. Bioassay-guided fractionation of the bioactive P. dilatata crude extract revealed that the deterrent property was restricted to a medium polarity fraction. Field palatability experiments with two pure compounds isolated from this fraction revealed that the furanocembranolide 11,12-epoxypukalide is a potent feeding deterrent produced by P. dilatata against fish. Apparently, furanocembranolides are a particular class of compounds with feeding deterrent properties, protecting some octocorals from potential fish predator species in both tropical and temperate environments.     

共混方式对高密度聚乙烯/聚碳酸酯共混体系形态与性能的影响

研究了不同共混方式对高密度聚乙烯（ＨＤＰＥ）／聚碳酸酯（ＰＣ）共混体系形态与性能的影响。将不同组成的ＨＤＰＥ／ＰＣ分别在双螺杆、单螺杆挤出机中共混后注射成型,测试注射样条的力学性能并用扫描电子显微镜（ＳＥＭ）对样条断面进行形态观察。结果发现,共混方式对共混体系拉伸强度影响不大,但对冲击强度和断面形态影响较大。当ＰＣ含量低时,双螺杆的共混效果不如单螺杆;当ＰＣ含量较高时,双螺杆的共混效果优于单螺杆。     

Effect of breast feeding and psychosocial variables upon psychomotor development of 12-month-old infants

This study evaluates the participation of psychosocial variables in the relation between breast feeding (BF) and psychomotor development (PMD) in dyads with different BF duration. We assessed 138 mother-infant dyads, divided in two groups: 86 received BF as unique source of milk feeding for at least 6 months (prolonged BF group) and 52 were weaned before 45 days of age (early weaning group). General information about pregnancy, delivery and feeding was collected in a non experimental prospective design. At 6-7 months of age a milk feeding situation was observed at home, and mother-infant interactional patterns were recorded through a specially designed scale. At 12 months of age the PMD was assessed (Bayley Scales of Infant Development). Infant temperament, home stimulation, mother depression and family stress were also measured. Similar family characteristics were observed in both study groups. Early bonding and first feeding experiences were different, both reported as better in the prolonged BF group. Moreover, dyads of this group showed a higher variety and quality of mother-infant interactional patterns during feeding, with a higher synchrony and reciprocity in the relationship. Mean Mental Development Index (MDI) and Psychomotor Developmental Index (PDI) were similar in both groups. Explicatory variables for MDI and PDI are different in both study groups. Dyads who attained prolonged BF conform from a psychosocial perspective--a different group than the early weaned.     

飞机前轮转弯机构寿命试验测控系统设计

为了测试飞机前起落架机轮转弯机构的寿命和性能,往往需要对其进行重复性的转弯加载试验,针对这一要求,设计了一种专门用于前轮转弯机构寿命试验的测控系统。分别从液压油源系统、加载系统和软硬件系统等方面对整个测控系统的设计过程进行了详细介绍。根据试验加载要求,加载系统采用了一种利用比例溢流阀调节背压的新型加载方式。其中硬件系统以S7 300 PLC为控制核心,上位界面的设计采用VB6.0、通讯软件PRODAVE和组态王为开发软件,很好地实现了试验中要求的数据管理、曲线显示和参数在线整定等功能。该测控系统已经投入使用,证明完全可以满足试验要求。     

Gold nanoclusters as colloidal catalysts for oxidation of long chain aliphatic 1,2-diols in alcohol solvents

Long chain aliphatic 1,2-diols like 1,2-hexanediol and 1,2-octanediol can be converted to the corresponding α-hydroxy-alkanoates with total chemoselectivity, in an oxidation catalyzed by an aqueous gold sol under O₂ atmosphere. The sol is stabilized with poly(vinylalcohol), and the reaction is performed in alcohol solvents. Two methods are proposed for the efficient recycling of the colloidal Au catalyst. Firstly a solvent-resistant membrane filtration can be applied. As the membrane material, poly(dimethylsiloxane) is chosen. Secondly, in appropriate conditions, the reaction proceeds in the liquid biphasic mode, and the aqueous Au sol can be recycled by phase separation. Using either of both approaches, the colloidal stability and catalytic activity can be preserved over several recycles.     

柠檬酸盐法制备Na0.5Bi0.5TiO3陶瓷粉体的工艺研究

本实验采用柠檬酸盐法制备（NaBi）0.5TiO3无铅压电陶瓷粉体,系统研究了柠檬酸浓度、溶液pH值、煅烧温度等工艺条件对制备的影响。经研究分析,当柠檬酸浓度C=9%,溶液pH=7.5时,能形成透明、均匀、稳定的溶胶,且形成时间最短;650℃下煅烧2h能够合成单一的钙钛矿结构的钛酸铋钠晶相,比传统固相反应法煅烧温度降低了200℃。     

Influence of pozzolans and slag on the microstructure of partially carbonated cement paste by means of water vapour and nitrogen sorption experiments and BET calculations

The influence of water-to-binder ratio (0.33 to 0.50) and additions (fly ash, slag, silica fume) on the microstructure of partially carbonated cement pastes was studied by nitrogen sorption and static and dynamic water vapour sorption. The selected technique affects macropore condensation and accessibility of pores, while predrying influences removal of CSH interlayer water. BJH calculations showed the increased amount of capillary pores with higher water-to-cement ratio, and the decrease of micropores (< 2 nm), in pastes with 50% or more fly ash or slag. Paste with 10% SF showed a high amount of gel pores, related to the higher amount of CSH gel, calculated from adsorption at 23% RH. A linear relation was observed between BET specific surface and water-cement ratio. Thermogravimetric analysis illustrated the influence of water-cement ratio and pozzolanic materials on the portlandite content. Introduction of silica fume, increased the specific surface accessible to water, but not to nitrogen molecules.     

Multistability,nonlinear response and wave propagation in self-humidified PEM fuel cells

A simple tanks-in-series model is presented, which allows for the understanding of the basic physics behind complex spatiotemporal behaviors observed in self-humidified polymer electrolyte membrane (PEM) fuel cells. Our approach is focused on how the intrinsically nonlinear dynamics of water formation couples with water transport, leading to multistability, inhomogeneous steady state current profiles through the cell and other nonlinear phenomena. We show in particular how the operating parameters determine the location of high current spots and the subsequent propagation of current waves throughout the cell during the ignition procedure. We also reproduce and explain transient current increases seen during the extinction of the cell and the unusual aspect of the polarization curves. Implications for the efficiency of self-humidified PEM fuel cells are highlighted, and possible ways to improve their performances are discussed on these bases.