大孔PAMPS/PVA半互穿网络型水凝胶的制备及其性能研究

以PEG6000为成孔剂, 合成了大孔聚(2-丙烯酰胺-2-甲基丙磺酸)/聚乙烯醇半互穿网络型(s-IPN)水凝胶. 红外分析表明, PVA与PAMPS之间形成了较强的氢键, 使得PVA分子上的C—O伸缩振动吸收峰移向了低波数处. X射线衍射分析发现, 当PVA用量较高时, 由于部分的PVA结晶, 使得凝胶的半互穿网络结构不均匀. 电镜分析结果表明, 没有使用成孔剂的凝胶表面成褶皱形, 不存在任何孔洞结构; 而以PEG6000为成孔剂的凝胶表面存在相互贯穿的大孔结构. 研究了该水凝胶的溶胀性能, 结果表明, 该水凝胶的平衡溶胀度在116至320之间; 而成孔剂PEG6000的加入能较大幅度提高凝胶的溶胀速率, 凝胶在240 min之内就能达到溶胀平衡. 对凝胶抗压缩性能的研究表明, 当PVA用量为9.1% (w)时, 凝胶的抗压缩强度最大, 可达12.0 MPa; 而成孔剂的加入会在一定程度削弱凝胶的抗压缩强度. 该凝胶具有较好的电场敏感性, 研究发现, 将吸去离子水达到溶胀平衡的凝胶放入施加有电场的0.2 mol•L－1 NaCl溶液中时, 凝胶迅速偏向阳极. 而PVA和成孔剂PGE6000的用量均对凝胶的偏转速度以及最大偏转角存在较大的影响.     

Simultaneous measurement of proline and related compounds in oak leaves by high-performance ligand-exchange chromatography and electrospray ionization mass spectrometry for environmental stress studies

A mass spectrometer was coupled to high-performance ligand-exchange liquid chromatography (HPLEC) for simultaneous analysis of stress associated solutes such as proline, hydroxyproline, methylproline, glycine betaine and trigonelline extracted from leaves of drought stressed oaks and an internal standard namely N-acetylproline. Methanol/chloroform/water extracts were analyzed using an Aminex HPX-87C column and specifically quantified by the positive ion mode of an electrospray ionisation-mass spectrometry (ESI-MS) in single ion monitoring (SIM) mode. The recovery of N-acetyl proline added to oak leaf extracts ranged from 85.2 to 122.1% for an intra-day study. Standard calibration curves showed good linearity in the measured range from 0.3125 to 10 μmol L⁻¹ with the lowest correlation coefficient of 0.99961 for trigonelline. The advantages of this alternative procedure, compared to previously published methods using fluorescence or amperometric detections, are the simultaneous and direct detection of osmoprotectants in a single chromatographic run, a minimal sample preparation, a good specificity and reduced limits of quantification, ranging from 0.1 to 0.6 μmol L⁻¹. Fifty-six days of water deficit exposure resulted in increased foliar free proline levels (2.4-fold, P < 0.001, 155 μmol g⁻¹ FW) and glycine betaine contents (2.5-fold, P < 0.05, 175 μmol g⁻¹ FW) of drought stressed oak compared to control.     

Down syndrome critical region 1 enhances the proteolytic cleavage of calcineurin

Down syndrome critical region 1 (DSCR1), an oxidative stress-response gene, interacts with calcineurin and represses its phosphatase activity. Recently it was shown that hydrogen peroxide inactivates calcineurin by proteolytic cleavage. Based on these facts, we investigated whether oxidative stress affects DSCR1-mediated inactivation of calcineurin. We determined that overexpression of DSCR1 leads to increased proteolytic cleavage of calcineurin. Convertsely, knockdown of DSCR1 abolished calcineurin cleavage upon treatment with hydrogen peroxide. The PXIIXT motif in the COOH-terminus of DSCR1 is responsible for both binding and cleavage of calcineurin. The knockdown of overexpressed DSCR1 in DS fibroblast cells also abrogated calcineurin proteolysis by hydrogen peroxide. These results suggest that DSCR1 has the ability to inactivate calcineurin by inducing proteolytic cleavage of calcineurin upon oxidative stress.     

正交异性双材料的Ⅱ型界面裂纹尖端场

通过引入含16个待定实系数和两个实应力奇异指数的应力函数,再借助边界条件,得到了两个八元非齐次线性方程组.求解该方程组,在双材料工程参数满足适当条件下,确定了两个实应力奇异指数.根据极限唯一性定理,求出了全部系数,得到了应力函数的表示式.代入相应的力学公式,推出了当特征方程组两个判别式都小于0时,每种材料的裂纹尖端应力强度因子、应力场和位移场的理论解.裂纹尖端附近的应力和位移有混合型断裂特征,但没有振荡奇异性和裂纹面相互嵌入现象作为特例,当两种正交异性材料相同时,可以推出正交异性单材料Ⅱ型断裂的应力奇异指数、应力强度因子公式、应力场、位移场表示式.     

Use of Fluorescence Probes for Detection of Reactive Nitrogen Species: A Review

The biological and toxicological effects that have been attributed to reactive nitrogen species (RNS) are increasingly stirring the scientific inquisitiveness about the molecular mechanisms involved. However, RNS present some characteristics that complicate their detection, namely their short lifetime and the normal presence of a variety of endogenous compounds capable of reacting with these reactive species, when the studies are performed in biological matrices. The development of methodologies capable of circumvent these difficulties is thus of fundamental importance. Fluorescence probes are particularly important due to their high sensibility and usefulness in temporal and spatial monitoring of RNS, particularly in microanalysis conditions in biological media akin to cells or tissues. In the present review is given an account of the fluorescence probes that have been used for detection of nitric oxide (^⋅NO), peroxynitrite anion (ONOO⁻), as well as of some of its derivatives in biological and nonbiological media.     

Fracture of a biopolymer gel as a viscoplastic disentanglement process

We present an extensive experimental study of mode-I, steady, slow crack dynamics in gelatin gels. Taking advantage of the sensitivity of the elastic stiffness to gel composition and history we confirm and extend the model for fracture of physical hydrogels which we proposed in a previous paper (Nature Mater. 5, 552 (2006)), which attributes decohesion to the viscoplastic pull-out of the network-constituting chains. So, we propose that, in contrast with chemically cross-linked ones, reversible gels fracture without chain scission.     

静脉壁的力学特性及负压失稳问题

应用一类超弹性应变能函数,通过非线性弹性理论,研究了静脉壁在跨壁压及轴向拉伸联合作用下的变形和应力分布等力学特性,并分析了静脉壁的负压失稳问题．首先利用超弹性材料薄壁圆筒模型,得到了静脉壁在跨壁压及轴向拉伸联合作用下的变形方程,给出了正常静脉压下静脉壁的变形曲线和应力分布曲线,讨论了静脉壁的变形和应力分布规律．然后给出了负跨壁压下静脉壁的变形曲线,并由能量比较讨论了静脉壁的负压失稳问题．     

杂交元零能模式抑制的正交基本变形模式方法

通过杂交元位移场直接推导了单元基本变形模式,并且采用联合正交条件提出一种新的正交化方法,所得到的正交基本变形模式不仅具有简单的变形特征而且和材料参数无关,可以方便有效地考察单元性能,为评价不同杂交元提供了一个统一的参考标准．在此基础上利用柔度矩阵正定性给出一种简单有效的零能模式识别方法,并进一步利用基本变形模式和初始应力模式之间耦合关系,提出一种抑制杂交元零能模式的假设应力场方法,同时指出基本变形模式正交性是抑制单元零能模式的充分必要条件．2D-4节点和3D-8节点单元的数值算例说明了该文基本变形模式方法的有效性．     

激光快速烧结合成A(WO4)2(A=Zr2+,Hf2+)的特性研究

利用二氧化碳激光快速凝固技术合成了负热膨胀材料ZrW2O8和HfW2 O8,Raman光谱和X射线衍射分析表明激光烧结合成的ZrW2 O8为正交相,压应力的大小估计在0.4～0.5 GPa之间,激光烧结合成的HfW2 O8,主要为立方晶系,含有极少量的正交系,压应力的大小估计在0.6 GPa左右,这是由于样品在快速凝固的过程中受到了压应力造成的.由于压应力的影响,二氧化碳激光快速凝固技术更适合HfW2O8的制备和合成.     

大涡模拟研究展向旋转槽道湍流流动

本文用大涡模拟预测了以不同转速做展向旋转的槽道湍流流动,统计平均的流向速度型在壁面附近与已有实验数据符合很好,在通道中部的预测差异也能给出合理解释,对比不同转速的计算结果,表明展向旋转通道的湍流应力和壁面摩擦力在压力面附近提高、在吸力面附近降低,这些高阶湍流统计量的变化规律可以结合湍流应力输运方程加以解释,漩涡识别技术显示了近壁条带结构,其形态和猝发率受旋转附加力的影响发生改变,进而影响壁面摩擦速度的数值和分布,进一步考察垂直流动方向的截面内速度分布,发现旋转引起了垂直壁面方向的流动,形成正负相间排列的流向涡对,并随着转速的增加向压力面靠近。