The transpiration of water at negative pressures in a synthetic tree

Plant scientists believe that transpiration-the motion of water from the soil, through a vascular plant, and into the air-occurs by a passive, wicking mechanism. This mechanism is described by the cohesion-tension theory: loss of water by evaporation reduces the pressure of the liquid water within the leaf relative to atmospheric pressure; this reduced pressure pulls liquid water out of the soil and up the xylem to maintain hydration. Strikingly, the absolute pressure of the water within the xylem is often negative, such that the liquid is under tension and is thermodynamically metastable with respect to the vapour phase. Qualitatively, this mechanism is the same as that which drives fluid through the synthetic wicks that are key elements in technologies for heat transfer, fuel cells and portable chemical systems. Quantitatively, the differences in pressure generated in plants to drive flow can be more than a hundredfold larger than those generated in synthetic wicks. Here we present the design and operation of a microfluidic system formed in a synthetic hydrogel. This synthetic 'tree' captures the main attributes of transpiration in plants: transduction of subsaturation in the vapour phase of water into negative pressures in the liquid phase, stabilization and flow of liquid water at large negative pressures (-1.0 MPa or lower), continuous heat transfer with the evaporation of liquid water at negative pressure, and continuous extraction of liquid water from subsaturated sources. This development opens the opportunity for technological uses of water under tension and for new experimental studies of the liquid state of water.     

赵家寨矿井充水水源的综合判别分析

本文以赵家寨矿井为研究对象,采集了奥灰岩水样7个,L1-4灰岩水样6个,L7-8灰岩水样25个,砂岩水样2个,第三系水样1个,第四系地下水样1个,老空水样1个。灰岩水样分析结果表明,不同含水层水化学类型有一定差异,如以L7-8灰岩水HCO3-SO4型水为主。以六大离子作为判别因子,经灰色关联度分析、判别分析以及BP神经网络判别模型3种判别方法,对突水水源判别对比,综合选择出适当的水源判别方法。研究表明,该矿井以六大离子作为判别因子时选择BP神经网络分析法进行预测的结果更加可靠。     

模糊综合评价在水污染控制中的应用

应用模糊综合评价在进行水污染防治规划中，使点源总量控制和单元总量控制方案的优化组合上发挥了很好的理论指导意义。在控制断面的污染物排放控制模拟过程中，获得了良好的效果。     

A hybrid model of a subminiature helicopter in horizontal turn

A hybrid model of a subminiature helicopter in horizontal turn is presented. This model is based on a mechanism model and its compensated neural network （NN）. First, the nonlinear dynamics of a sub-miniature helicopter is established. Through the linearization of the nonlinear dynamics on a trim point, the linear time-invariant mechanism model in horizontal turn is obtained. Then a diagonal recursive neural network is used to compensate the model error between the mechanism model and the nonlinear model, thus the hybrid model of a subminiature helicopter in horizontal turn is achieved. Simulation results show that the hybrid model has higher accuracy than the mechanism model and the obtained compensated-NN has good generalization capability.     

引江济太水源地水质及河势可靠性分析

为了模拟计算研究区长江沿岸污染带的污染负荷量,应用有限体积法及通量向量分裂方法(FVS)建立了考虑非点源影响的平面二维水环境数学模型;同时对水源地河床演变和岸线开发利用情况进行了分析.结果表明:研究区岸线污染负荷总量超标,水源地受岸源污染较重;水源地近期萎缩较快,河床处于淤积阶段.     

饮用水生物综合毒性控制技术研究

研究了以发光细菌检测法做为生物毒性快速检测的方法,测定饮用水处理过程中加入的絮凝剂、预氧化剂、活性炭等对水质综合毒性的影响.研究结果表明采用二氧化氯(0.4 mg/L)预氧化+聚合氯化铝(40 mg/L)混凝沉淀+活性炭(2.0 mg/L)吸附+石英砂过滤组合工艺对原水进行处理有比较好的效果.通过上述组合处理工艺原水,...     

复合式MBR处理化学合成类制药废水研究

采用复合式膜生物反应器（CMBR）对化学合成类制药废水的厌氧反应器出水进行处理研究,系统在不同的水力停留时间（HRT）下,各运行了一段时间,以此寻求最短HRT.实验结果表明,当HRT为10 h和5 h时,进水COD质量浓度在915.9-1 937.5 mg/L之间波动,复合式MBR的出水COD分别为62.5-141.7 mg/L和76.2-149.7 mg/L,COD去除率分别为88.7%-96%和85.7%-94.3%,均可以满足达标排放标准要求（150 mg/L）.当HRT为3 h时,出水COD质量浓度为176.2-291.7 mg/L,不能满足达标排放标准要求.复合式MBR处理化学合成类制药废水的最佳HRT应控制在5 h.污泥质量浓度（MLSS）与COD去除的关系表明,为了得到更好的COD去除率,复合式MBR的最佳MLSS应控制在7 000 mg/L左右.     

对丙型肝炎病毒具有潜在抑制作用的 L-苯丙氨酸衍生物前体的合成

丙型肝炎病毒（HCV ）感染与肝脏病变密切相关,是造成慢性肝炎、肝硬化及肝脏细胞肿瘤的主要原因之一．由于病毒自身的生物学特性,目前仍然没有有效的疫苗和治疗药物,研究开发高效的抗病毒药物具有重要意义．Reddy和他的小组设计合成了一系列 N,N-二取代的苯丙氨酸类似物,并证明了具有该种结构的化合物可对肝炎病毒聚合酶具有很好的抑制作用,以 L-苯丙氨酸为起始原料,经过酯化成氨基酸甲酯、与不同取代基的芳香醛缩合成希夫碱、将亚胺结构还原、酸化脱酯4步反应合成了8种对丙型肝炎病毒具有潜在抑制作用的此类化合物的前体,最高总产率达到77．4％．测定产物熔点,通过核磁氢谱对目标产物的结构进行表征,结果表明实现了目标化合物的合成．     

层次分析法在旅游综合决策中的应用

将层次分析法应用到宁夏旅游业的综合评价和决策中，建立起层次结构模型，并得出了量化分析的结果、     

水煤浆添加剂磺化三聚氰胺-尿素-甲醛树脂的合成

给出了用于水煤浆添加剂复配的水溶性的磺化三聚氰胺-尿素-甲醛树脂的合成过程及影响因素。反应分四步进行羟甲基化、磺化、低pH缩合、高pH重排,反应及树脂产物受pH、温度、时间、料比(氨基/甲醛,氨基/磺化剂)的影响。测定了选择样品羟甲基化物、磺化物和树脂产物的红外波谱。     

南淝河水体中有机磷和菊酯类农药风险评价

文章基于SPE-GC-MS方法,分析了南淝河水体中12种有机磷农药(OPs)和12种菊酯类农药(SPs)的残留,并探讨了敌敌畏和苄氯菊酯的生态风险。结果表明:南淝河水体中OPs和SPs质量浓度分别为(7.02±5.22)ng/L和(5.59±3.83)ng/L,它们最主要成分分别为敌敌畏和苄氯菊酯;与国内外一些其他河流相比较,南淝河水体中OPs质量浓度处于较低水平,并且在我国河流水体中存在北高南低的分布特征;通过物种敏感性分布模型评估,发现南淝河水体中敌敌畏和苄氯菊酯均处于较低的生态风险水平。     

Antibody production to the nucleocapsid and envelope of the hepatitis B virus primed by a single synthetic T cell site

The nucleocapsid (HBcAg) of the hepatitis B virus (HBV) can induce antibody responses via both a T-cell dependent and a T-cell independent pathway and is highly immunogenic during infection. We have examined the T-cell determinants of the antigen and find that HBcAg-specific helper T cells (TH) can help B cells produce antibody against envelope (HBsAg) antigens as well as HBcAg, even though these antigens are found on separate molecules. We have also been able to prime helper T cells with synthetic T-cell epitopes of HBcAg; helper cells primed with a single synthetic epitope can induce B cells to produce antibody that reacts with multiple HBsAg epitopes. One problem with the development of an HBV vaccine is that some vaccinees and patients do not respond to HBsAg directly; our results indicate that this problem can be circumvented using the response to HBcAg.     

Synthesis and optical properties of nanosized CdS prepared in a quaternary CTAB/ nhexanol/n-heptane/water reverse micelle

Quaternary water-in-oil reverse micelles consisting of cetyltrimethylammonium bromide (CTAB), nhexanol, n-heptane and water were prepared and characterized. The optimized reaction conditions were determined, and monodispersed droplets of the reverse micelles were used as microreactors to synthesize CdS nanoparticles. By using transmission electron microscopy (TEM), UV-Vis spectroscopy and fluorescence spectroscopy, the influences of the reverse micelle components on the size, size distribution, morphology, stability and optical properties of CdS nanoparticles were investigated. CdS nanoparticles with narrow size distribution were obtained and the size range is 6–8 nm whenW=24 (W=[water]/[CTAB]), P=5.27 (P=[n-hexanol]/ [CTAB]), [CTAB]=0.2 mol/L, [Cd²⁺] and [S^2-] are 8.45×10⁻⁴ mol/L.     

计算浅水环流的波方程模式

对计算浅水环流的波方程模式进行了研究，指出了波方程模式的解在什么条件下满足质量守恒；并证明了空间离散误差不会影响该模式对非物理短波干扰的衰减，所以波方程模式具有较好的抑制短波振荡的特性。