蚊子是什么?

相信当看到这个问题后,多数读者会带一脸鄙视的表情撇下嘴：“老大,你不会连什么是蚊子都不知道吧？”     

Hydrothermal synthesis of carbonate-free submicron-sized barium titanate from an amorphous precursor: Synthesis and characterization

In this paper, the amorphous barium titanate precursor was prepared by the peroxo-hydroxide method and post-treated by various drying procedures, such as: room temperature drying, room temperature vacuum drying and vacuum drying at 50 °C. The objective in the latter two treatments was to increase the Ti-O-Ba bonds of the precursor. The post-treated precursors were compared with the untreated (i.e., ‘wet’) precursor. Also, a barium titanate precursor was prepared by an alkoxide route. Afterwards, the precursors were hydrothermally treated at 200 °C in a 10 M NaOH solution. Vacuum drying of the precursor seemingly promoted the formation of Ti-O-Ti bonds in the hydrothermal end-product. The low Ba:Ti ratio (0.66) of the alkoxide-route prepared precursor lead to a multi-phase hydrothermal product with BaTiO₃ as the main phase. In contrast, phase pure BaTiO₃, i.e. without BaCO₃ contamination, was obtained for the precursor which was dried at room temperature. Cube-shaped and highly crystalline BaTiO₃ particles were observed by electron microscopy for the hydrothermally treated peroxo-hydroxide-route prepared precursor.     

Benefit of Microscopic Diffusion Measurement for the Characterization of Nanoporous Materials

Detailed knowledge of the transport properties of nanoporous materials is a prerequisite for their complete characterization and optimum technological exploitation. One of the best ways to attain this information is provided by the “microscopic” techniques of diffusion measurement, in particular by the pulsed field gradient technique of NMR and by interference microscopy and IR microscopy. Starting with the measuring principles, the various types of evidence as accessible by these techniques are illustrated. A large variety of host‐guest systems with both ordered and random pore networks have been studied, from microporous up to macroporous materials. The information obtained concerns diffusivities in the various pore domains, extra resistances at the interfaces between them and the associated exchange rates.     

Testing models of school learning: Effects of quality of instruction, motivation, academic coursework, and homework on academic achievement.

Tested the influence of ability, time, quality of instruction, motivation, and academic coursework on students' achievement, controlling for relevant background variables. Structural equation models were analyzed with longitudinal data from a national sample of 25,875 high school students. Intellectual ability and academic coursework had direct effects on achievement, and homework had a smaller direct effect. The indirect effects of quality of instruction and motivation were stronger than their direct effects; quality affected motivation, which affected coursework. Supplemental analyses were consistent with the initial findings. Results support these variables as influences on school learning, and support the theories from which the variables were derived. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New TiO2/MgAl-LDH nanocomposites for the photocatalytic degradation of dyes

In this study we report the synthesis of a series of composite nanostructures comprising LDH and TiO2 phases. The materials characterization showed that the LDH crystallites are encapsulated inside the TiO2 matrix after the anatase seeds are deposited on MgxAl-LDHs. The structure in which LDH phase is embedded into anatase matrix is unique bringing important advantages to the photocatalytic performances of the nanocomposites. The photocatalytic activity of the prepared nanocomposites was tested on the degradation of the methylene blue (MB) in aqueous solution. The photocatalytic activities of the nanocomposites were compared with commercial TiO2 nanoparticles Degussa P25. The nanocomposites exhibited superior photocatalytic activity in basic environment because the negatively charged surface of TiO2 nanoparticles at high pH attracts the positively charged methylene blue species.     

Cuticular Hydrocarbons and Soldier Defense Secretions of <Emphasis Type="Italic">Reticulitermes</Emphasis> in Southern California: A Critical Analysis of the Taxonomy of the Genus in North America

Cuticular hydrocarbons (CHC) and soldier defense secretions (SDS) were characterized for collections of Reticulitermes from six counties (Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Santa Barbara) in southern California. Collection sites included the type locality for R. hesperus, Lake Arrowhead (formerly known as Little Bear Lake) in the San Bernardino Mountains. In southern California, there are two CHC phenotypes, SC-A and SC-B, which are easily distinguished by the presence or absence of 5-methyl pentacosane, 5-methyl heptacosane, 5,17-dimethyl pentacosane, and 5,17-dimethyl heptacosane. These phenotypes are similar, but not identical, to previously designated phenotypes of Reticulitermes from northern California. The SDS of termites collected from southern California were characterized; (—)-germacrene A was abundant in all but the four samples from Lake Arrowhead. Soldiers of phenotype SC-A produced >79% germacrene A. The four samples from Lake Arrowhead produced no germacrene A, but contained >78% γ-cadinene. The SDS from the Lake Arrowhead samples were more similar to those of CA-A/CA-A′ from northern California than to any of the CHC phenotypes from southern California. Soldiers of CHC phenotype SC-B produced germacrene A, with the proportion varying from 16.2 to 98.7%. The SDS of SC-B were more similar to those of SC-A than to any of the phenotypes from northern California. The CHC phenotype SC-A found in southern California likely represents R. hesperus and SC-B appears to be a new, as yet undescribed species. We discuss the state of current taxonomic research on Reticulitermes.

Formation of a Ti-siliceous trimodal material with macroholes, mesopores and zeolitic features via a one-pot templating synthesis

Based on a facile one-pot templating synthesis, using a TS-1 zeolite recipe whereby part of the zeolite structure directing agent is replaced by a mesopore templating agent, a trimodal material is formed. The resulting meso-TSM material combines mesoporosity (Ti-MCM-41) with zeolitic features (TS-1) and a unique sheet-like morphology with uniform macroporous voids (macroholes). Moreover, the macrohole formation, mesoporosity and zeolitic properties of the meso-TSM material can be controlled in a straightforward way by adjusting the length of the hydrothermal treatment. This newly developed material may imply great potential for catalytic redox applications and diffusion limitated processes because of its highly tunable character in all three dimensions (micro-, meso- and macroporous scale).     

SBA-15 mesoporous silica modified with rhodium by MDD method and its catalytic role for N<Subscript>2</Subscript>O decomposition reaction

SBA-15 mesoporous silicas modified with rhodium were studied as catalysts for the N₂O decomposition reaction. Rhodium was deposited on SBA-15 by the Molecular Designed Dispersion (MDD) method using Rh(acac)₃ as a precursor of active phase. The same method was used for the deposition of Cu, Fe, Al and Ti. The SBA-15 support modified with metals were characterized with respect to metal loading (EPMA), structure (XRD), texture (BET), morphology (SEM), Rh dispersion (oxygen chemisorption), surface acidity (pyridine adsorption) and chemical nature of introduced copper and iron species (UV–vis-DRS). The rhodium-containing SBA-15 samples were found to be active catalysts for the N₂O decomposition reaction. Deposition of Al on the Rh-loaded catalyst increased its activity. An opposite effect was observed for the samples modified with Cu and Fe.     

The Complete Analysis of Wood Polysaccharides Using HPLC

The paper describes an analytical method whereby the chemical composition of the polysaccharide fraction of woody materials, including the uronic acids and carbohydrate acid degradation products, can be completely determined. Sealed vessels, termed bombs, are used during the high temperature acid hydrolysis of the materials to retain volatile constituents that would otherwise be lost. High-Performance Liquid Chromatography (HPLC) is used for all of the analyses. The sample preparation procedures are simple and easily adopted into a routine. To demonstrate the reproducibility of the method, triplicate samples of Quaking aspen ( Populus tremuloides ) and White fir ( Abies concolor ) were analyzed. No significant peaks in the chromatograms were left unidentified.