低温分相法制备高比表面积微/介孔SiOC陶瓷（英文）

以含氢聚硅氧烷(PHMS)、四甲基四乙烯基环四硅氧烷(Dvi4)和铂络合物为原料,采用热交联合成交联体,通过水蒸汽辅助热解促进前驱体低温分相及后续HF对SiOC陶瓷侵蚀基础上,获得高比表面积微/介孔SiOC陶瓷。采用XRD、FT-IR、SEM和BET等测试技术对试样的物相组成、化学键、微观结构、比表面积和孔径分布等进行了表征。实验结果表明,水蒸气能够促进前驱体低温分相,使SiOC陶瓷中生成Si-O-Si键、SiO_2纳米畴和SiO_2纳米晶,这些可以作为造孔剂而被HF侵蚀,从而提高了SiOC陶瓷的比表面积。在热解温度1300℃条件下,微/介孔SiOC陶瓷具有最大比表面积1845.5 m2/g,孔径分布2.0～10 nm。

Experimental Study on the Initial Position Distribution of Taylor Bubbles in Cryogenic Upward Inclined Tubes

An experimental study was carried out to understand the phenomena of the boiling flow of liquid nitrogen in inclined tubes with closed bottom by using the high speed digital camera.The tubes in the experiment are 0.018 m and 0.014 m in inner diameter and 1.0 m in length.The range of the inclination angles is 0-45° from the vertical.The statistical method is employed to analyze the experimental data.The experiment was focused on the effect of the inclination angle on the initial position distribution of Taylor bubbles.The formation criterion of Taylor bubbles was confirmed by analyzing the images of Taylor bubbles.The experimental results show that the initial position of Taylor bubble increased first,and then decreased with the increasing inclination angle,with the maximum at 30°.The standard deviation of the initial position of Taylor bubble in tubes was different with different inner diameters.The lognormal shape was fitted to the measured the initial position distributions of Taylor bubbles in the cryogenic tubes.

Tape casting of borosilicate glass/Al_2O_3 composites for LTCC substrate with various relative molecular masses of PVB

The dispersion, stabilization and rheological properties of the slurry with various relative molecular masses of PVB were studied. The sintering properties, microstructure and dielectric properties of borosilicate glass/Al203 composites were also investigated. The intensities of the typical vibrating bands decrease with the decrease of the relative molecular mass of PVB, which demonstrates that the content of butyral groups in PVB binders decreases correspondingly, leading to a rapid decrease in the viscosity of the mixed slurry. The solid content of samples increases with the decrease of the relative molecular mass of PVB, and this further leads to the increase of tape thickness, bulk density and dried-shrinkage coefficient of tapes. The bulk density, relative density, three-point strength and dielectric constant of sintered samples increase with the increase of the solid content, and the shrinkage and dielectric loss decrease. By contrast, samples for PVB-5s exhibit better properties of a bulk density of 3.10 g/cm3, a relative density of 98.1%, a three-point strength of 208 MPa, aεt value of 8.01, a tanδ value of 7.6× 10^-4 at 10 MHz and a well matching with Ag electrodes.

Occurrence data may provide unreliable thermal preferences and breadth of species

Accurate information on the thermal preference and specialization of species is needed to understand and predict spe- cies geographical range size and vulnerability to climate change. Here we estimate the position and breadth of species within thermal gradients based on the shape of the response curve of species abundance to temperature. The objective of the study is to compare the measurements of this approach based on abundance data with those of the classical approach using species＇ occur- rence data. The relationship between species＇ relative abundance and minimum winter temperature of 106 bird species wintering in the Iberian Peninsula is modeled at 100 Km2 resolution with quadratic logistic regressions. From these models we calculated the preferred temperature of species as the temperature at which the abundance is maximized, and the thermal breadth of species as the relative area under the temperature-abundance curve. We also estimated the thermal preferences and breadth of species as the average temperature and temperature range of the UTM cells in which the species are present. The abundance-temperature response curves reveal that birds prefer higher temperatures to overwinter, and are more thermally selective, than is measured by the classical approach. Moreover, response curves detect a higher inter-specific variability in both thermal preferences and ther- mal breadth of species. As occurrence data gives the same weight to cells with one or many individuals, the average temperature of the cells in which the species is present roughly reflects the average temperature in the region of study and not the environ- mental preferences of species .