低密度气凝胶的高温结构变化及其耐温性研究

以正硅酸乙酯为原料,采用二步法制备了密度为30 kg/m³的二氧化硅低密度气凝胶块体材料。将低密度气凝胶分别在100、400、600、700、800、900、1 000 ℃下处理后,使用扫描电子显微镜（SEM）、氮吸附等手段表征高温下低密度气凝胶微观结构变化趋势,并与同等条件下处理的密度为100 kg/m³气凝胶的比表面积进行对比。结果表明：在处理温度超过700 ℃后,低密度气凝胶比表面积出现明显下降,纳米多孔结构出现收缩和坍塌,因此其高温耐受温度为700 ℃。虽然密度为30 kg/m³的二氧化硅气凝胶材料具有更为纤细的网络结构和更高表面活性的纳米组成颗粒,但是由于高温下纳米颗粒反应收缩程度大于纳米颗粒尺寸效应,其表现出与100 kg/m³密度的气凝胶材料相同的耐温性。     

Non-commutativity in the brain.

In non-commutative algebra, order makes a difference to multiplication, so that a x b not equal to b x a. This feature is necessary for computing rotary motion, because order makes a difference to the combined effect of two rotations. It has therefore been proposed that there are non-commutative operators in the brain circuits that deal with rotations, including motor circuits that steer the eyes, head and limbs, and sensory circuits that handle spatial information. This idea is controversial: studies of eye and head control have revealed behaviours that are consistent with non-commutativity in the brain, but none that clearly rules out all commutative models. Here we demonstrate non-commutative computation in the vestibulo-ocular reflex. We show that subjects rotated in darkness can hold their gaze points stable in space, correctly computing different final eye-position commands when put through the same two rotations in different orders, in a way that is unattainable by any commutative system.     

Crystallization and preliminary X-ray diffraction analysis of FKBP12 complexed with a new neurotrophic ligand

Thetherapyofnerveinjuryandneurode generativediseasessuchasAlzheimer’sdiseaseandParkinson’sdiseaseisadifficultprojectforscientiststosurmount.Manydrugsandtherapeuticapproacheshavebeenusedtotreatthesediseases ,buttheresultisunsatisfactory[1] .Inrecent years ,neurotrophinsincludingnervegrowthfactor (NGF) ,neurotrophin3(NT3) ,neurotrophin 4 / 5 (NT4 / 5 )andbrain de rivedneurotrophicfactor (BDNF)werestudiedex tensivelyandfoundtoaffectthesurvival,growth ,and/ordifferentiationofneuronsandsever…     

Identification of two related pentapeptides from the brain with potent opiate agonist activity.

Enkephalin, a natural ligand for opiate receptors is composed of the pentapepides H-Tyr-Gly-Gly-Phe-Met-OH and H-Tyr-Gly-Gly-Phe-Leu-OH. The evidence is based on the determination of the amino acid sequence of natural enkephalin by the dansyl-Edman procedure and by mass spectrometry followed by synthesis and comparison of the natural and synthetic peptides.     

不同密度人工水草对氮、磷去除效果研究

污水处理厂出水作为城市公园景观用水,已成为我国北方缺水城市的通遍做法。由于污水处理厂出水中氮、磷含量相对较高,景观水体极易发生富营养化。本实验利用碳纤维人工水草作为生态基形成生物膜,对景观水体进行脱氮除磷处理效果进行研究。试验共布设2株/m~2、4株/m~2、10株/m~2、16株/m~2、20株/m~2 5种水草密度,通过SPSS进行方差分析,结果显示不同密度人工水草对氮,磷去除效果存在差异,明4株/m~2、10株/m~2,20株/m~2对总氮、氨氮、溶解性磷酸盐具有显著去除效果,对总磷去除效果不明显。叶绿素a浓度与氮、磷去除率呈正相关,表明在流动水体中藻类优势群落的形成对微生物膜快速形成以及污染物的去除有重要影响。     

集料复配情况下沥青混合料小梁弯曲试验研究

为考察不同来源集料进行配合比设计时,由于密度差异导致的矿料级配组成与设计级配组成不一致对混合料性能的影响,首先提出了完整的密度修正办法,用于不同密度集料混掺使用时采用修正质量称量以确保设计体积百分比符合要求.然后,以UTM小梁低温弯曲试验对密度修正过程进行了验证,考察了集料密度修正、粉胶比、不同集料来源、轮碾次数和加载速率对小梁弯拉应变的影响.结果表明:混合料集料复配时若不进行密度影响修正,则会改变混合料中矿料的体积百分率,尤其是填料的百分比,继而影响粉胶比和混合料低温性能.进行密度修正后,质量称量在保证达到设计体积百分率的情况下,集料岩性不影响混合料低温性能.粗级配相较中值级配和细级配,具有良好的低温性能.压实次数能较大程度影响混合料的抗弯拉变形能力.加载速率能极大影响测试弯拉应变值,试验时须谨慎设定.     

低光强时丹参叶片的光合速率与光强的关系

本文用一个新的植物叶片的光响应模型详细讨论了植物在低光强时光合速率与光强之间的关系。并用新的植物叶片的光响应模型重新拟合了丹参的光合响应数据。拟合结果显示新模型拟合的结果与实验测量值符合得很好。认为在自然条件下，在低光强时植物丹参的光合速率对光强的响应不是线性。