显花植物器官形成激素调控的分子机理研究

本论文以显花植物水稻和拟南芥为对象，研究植物器官形成激素调控的分子机理。发现拟南芥干细胞决定基因WUS和ABA信号关键调节因子ABI3间存在相互调节关系，它们对质体和根毛发育等具有调控作用；运用细胞学手段对OsAGAP和OsRMC调控根发育的机理进行了研究。这些结果为了解ABA、生长素和JA等激素对分生组织或根等器官的形成的调控机理提供了新资料。 拟南芥WUS基因是一个重要的干细胞决定基因。在茎尖分生组织和花分生组织的动态平衡调节中各存在一个反馈调节环：WUS促进CLV3的表达，而CLV3 反馈抑制WUS表达，它们共同决定干细胞的数目；在WUS+LFY 和AG之间也存在一个类似的反馈环，负责花器官的正常启动和终止。本工作发现在外源ABA 存在下，拟南芥WUS功能获得突变体sef (stem ectopic flowers)子叶黄化过程受到抑制，即sef突变体对ABA 的敏感性降低，而且在sef突变体中ABI3转录水平下调，说明WUS 抑制ABI3的表达。另一方面，在abi3突变体中WUS转录水平下降，启动子分析发现WUS是ABI3所在的B3结构域家族基因的靶基因，酵母单杂交实验表明B3家族蛋白FUS3可以与WUS调控区结合；外源ABA 处理pWUS::GUS植株发现ABA可使WUS异位表达，暗示受ABA信号诱导的B3类转录因子可与WUS调控区结合，从而促进WUS的表达。这些结果支持ABI3/WUS间的反馈调节机理，该调节环可能参与调控拟南芥质体和根毛发育等过程。 双子叶和单子叶植物的发育和器官形成高度依赖生长素极性运输（PAT）， 生长素输入和输出载体的准确定位对于极性运输的正常进行是必要的。在双子叶模式植物拟南芥中，生长素输出载体PIN1的转运和定位受小G蛋白ARF鸟苷酸转换因子GNOM介导。本实验室克隆到一个水稻ARF GAPase激活蛋白OsAGAP， 其超表达引起PAT改变且干扰主根和侧根的发生及发育。前期生理实验显示超表达植株侧根的表型可被膜渗透性生长素NAA恢复，但不能被载体依赖型生长素IAA和2, 4-D恢复。为了解释OsAGAP过表达引起根系发育受到抑制的表型，本工作主要从细胞学角度继续深入分析OsAGAP介导生长素运输的机理。实验发现，OsAGAP超表达植株中AUX1在细胞中分布改变；生长素输出载体PIN1和PIN2的定位不受影响；该基因的超表达使囊泡聚集，形成类似囊泡运输抑制剂BFA处理后的结构；OsAGAP与细胞转运系统中的高尔基体存在部分共定位。以上结果表明OsAGAP调节小G蛋白Arf的活性，参与调控生长素极性运输过程，进而调控根系发育。通过对JA诱导的OsRMC蛋白的膜定位分析及转基因植株根中JA合成水平的测定，为研究此蛋白参与JA信号、调控根系发育提供了直接证据。 此外，论文还对拟南芥STAR2基因的功能进行了一定的初探。

Computer simulation of human iodothyronine deiodinase single-chain antibody

Iodothyronine plays a major role in growth, basic metabolism and organ formation. It has an extremely limited source in the body. In this thesis, we designed iodothyronine(T4) as hapten. Then a single chain antibody displayed on phange was obtained from a human phage displaying a single chain antibody library. The specific genes of E3 was subcloned in P-5E vector. According to its amino acid sequences, we simulate its three dimention structure by computer. It has never been reported in PDB.

Flow pattern in chandler loop - the artificial thrombus formation

In this paper a hydrodynamic approach is used to analyse carefully the flow field inChandler loop--the artificial thrombus formation. The results obtained show that near thelower meniscus where the thrombus is formed, there is a back flow accompanied with asecondary flow and its mainflow is toward the meniscus, thus providing a favourable condi-tion for corpuscle aggregation. Our finding is valuable for studying the mechanism ofthrombus formation in artificial organ and in vivo.

Formation and structure of composite coating of HDA and micro-plasma oxidation on A3 steel

Composite coatings were obtained on A3 steel by hot dipping aluminum(HDA) at 720 ℃ for 6 min and micro-plasma oxidation(MPO) in alkali electrolyte. The surface morphology, element distribution and interface structure of composite coatings were studied by means of XRD, SEM and EDS. The results show that the composite coatings obtained through HDA/MPO on A3 steel consist of four layers. From the surface to the substrate, the layer is loose Al2O3 ceramic, compact Al2O3 ceramic, Al and FeAl intermetallic compound layer in turn. The adhesions among all the layers are strengthened because the ceramic layer formed at the Al surface originally, FeAl intermetallic compound layer and substrate are combined in metallurgical form through mutual diffusion during HDA process.Initial experiment results disclose that the anti-corrosion performance and wear resistance of composite coating are obviously improved through HDA/MPO treatment.

Formation of Fivefold Deformation Twins in Nanocrystalline Face-Centered-Cubic Copper Based on Molecular Dynamics Simulations

Fivefold deformation twins were reported recently to be observed in the experiment of the nanocrystalline face-centered-cubic metals and alloys. However, they were not predicted previously based on the molecular dynamics (MD) simulations and the reason was thought to be a uniaxial tension considered in the simulations. In the present investigation, through introducing pretwins in grain regions, using the MD simulations, the authors predict out the fivefold deformation twins in the grain regions of the nanocrystal grain cell, which undergoes a uniaxial tension. It is shown in their simulation results that series of Shockley partial dislocations emitted from grain boundaries provide sequential twining mechanism, which results in fivefold deformation twins. (c) 2006 American Institute of Physics.

Numerical Simulation of Nox Formation in Coal Combustion with Inlet Natural Gas Burning

A full two-fluid model of reacting gas-particle flows and coal combustion is used to simulate coal combustion with and without inlet natural gas added in the inlet. The simulation results for the case without natural gas burning is in fair agreement with the experimental results reported in references. The simulation results of different natural gas adding positions indicate that the natural gas burning can form lean oxygen combustion enviroment at the combustor inlet region and the NOz concentration is reduced. The same result can be obtained from chemical equilibrium analysis.

Twinning and Stacking Fault Formation during Tensile Deformation of Nanocrystalline Ni

Deformation twins and stacking faults have been observed in nanocrystal line Ni, for the first time under uniaxial tensile test conditions. These partial dislocation mediated deformation mechanisms are enhanced at cryogenic test temperatures. Our observations highlight the effects of deformation conditions, temperature in particular, on deformation mechanisms in nanograins.

Formation, Thermal Stability and Deformation Behavior of Graphite-Flakes Reinforced Cu-based Bulk Metallic Glass Matrix Composites

Graphite-flake reinforced Cu47Ti34Zr11 Ni-8 bulk metallic glass matrix composite was fabricated by water-cooled copper mould cast. Most of the graphite flakes still keep unreacted and distribute uniformly in the amorphous matrix except that some reactive wetting occurs by the formation of TiC particles around the flakes. It reveals that the presence of graphite flakes does not affect the onset of the glass transition temperature, crystallization reaction and liquidus of the metallic glass. The resulting material shows obvious serrated flow and higher fracture strength under room temperature compressive load, comparing with the monolithic bulk metallic glass (BMG). Three types of interaction between the shear bands and graphite flakes, namely, shear band termination, shear bands branching and new shear bands formation near the graphite flakes can be observed by quasi-static uniaxial compression test and bonded interface technique through Vickers indentation.

Effect of Particle Size on the Formation of Adiabatic Shear Band In Particle Reinforced Metal Matrix Composites

In this paper, the effect of particle size on the formation of adiabatic shear band in 2024 All matrix composites reinforced with 15% volume fraction of 3.5, 10 and 20 mum SiC particles was investigated by making use of split Hopkinson pressure bar (SHPB). The results have demonstrated that the onset of adiabatic shear banding in the composites strongly depends on the particle size and adiabatic shear banding is more readily observed in the composite reinforced with small particles than that in the composite with large particles. This size dependency phenomenon can be characterized by the strain gradient effect. Instability analysis reveals that high strain gradient is a strong driving force for the formation of adiabatic shear banding in particle reinforced metal matrix composites (MMCp).

Evaluation of the Cumulative Formation of High-Speed Liquid Jets

This paper describes the generation of pulsed, high-speed liquid jets using the cumulation method. This work mainly includes (1) the design of the nozzle assembly, (2) the measurement of the jet velocity and (3) flow visualization of the injection sequences. The cumulation method can be briefly described as the liquid being accelerated first by the impact of a moving projectile and then further after it enters a converging section. The experimental results show that the cumulation method is useful in obtaining a liquid jet with high velocity. The flow visualization shows the roles of the Rayleigh-Taylor and Kelvin-Helmholtz instabilities in the breakup of the liquid depend on the jet diameter and the downstream distance. When the liquid jet front is far downstream from the nozzle exit, the jet is decelerated by air drag. Meanwhile, large coherent vortex structures are formed surrounding the jet. The liquid will break up totally by the action of these vortices. Experimental results showing the effect of the liquid volume on the jet velocity are also included in this paper. Finally, a method for measuring the jet velocity by cutting two carbon rods is examined.

Formation Mechanism of Cracks in Saturated Sand

The formation mechanism of “water film” (or crack) in saturated sand is analyzed theoretically and numerically. The theoretical analysis shows that there will be no stable “water film” in the saturated sand if the strength of the skeleton is zero and no positions are choked. It is shown by numerical simulation that stable water films initiate and grow if the choking state keeps unchanged once the fluid velocities decrease to zero in the liquefied sand column. The developments of “water film” based on the model presented in this paper are compared with experimental results.

Electrochemical, spectroscopic and SPM evidence for the controlled formation of self-assembled monolayers and organised multilayers of ferrocenyl alkyl thiols on Au(111)

Organised multilayers were formed from the controlled self-assembly of ferrocene alkyl thiols on Au(111) surfaces. The control was accomplished by increasing the concentration of the thiol solutions used for the assembly. Cyclic voltammetry, ellipsometry, scanning probe microscopy (STM and AFM) and in situ FTIR spectroscopy were used to probe the differences between mono- and multilayers of the same compounds. Electrochemical desorption studies confirmed that the multilayer structure is attached to the surface via one monolayer. The electrochemical behaviour of the multilayers indicated the presence of more than one controlling factor during the oxidation step, whereas the reduction was kinetically controlled which contrasts with the behaviour of monolayers, which exhibit kinetic control for the oxidation and reduction steps. Conventional and imaging ellipsometry confirmed that multilayers with well-defined increments in thickness could be produced. However, STM indicated that at the monolayer stage, the thiols used promote the mobility of Au atoms on the surface. It is very likely that the multilayer structure is held together through hydrogen bonding. To the best of out knowledge, this is the first example of a controlled one-step growth of multilayers of ferrocenyl alkyl thiols using self-assembly techniques.

On the mechanism of the formation of horizontal cracks in a vertical column of saturated sand

Extended horizontal cracks have! been observed experimentally in a vertical column of saturated sand when a flow of water is forced to percolate upward through it. This paper provides a theory for this phenomenon. It will be shown that the presence of inhomogeneity in permeability along the length of the column is essential for such cracks to develop. It will also be shown that small initial inhomogeneity may be magnified through the transport of the finer component of the sand by percolation. Under certain conditions liquefaction takes place at a section of the sand column causing a crack to initiate and grow there. This theory is found to be in good qualitative agreement with the experimental findings.

On the Formation of Periodic Segmentation Cracks in a Coating Plated on a Substrate with Periodic Subsurface Inclusions

The mechanism of the formation of periodic segmentation cracks of a coating plated on a substrate with periodic subsurface inclusions (PSI) is investigated. The internal stress in coating and subsequently the strain energy release rate (SERR) of the segmentation cracks are computed with finite element method (FEM). And the effect of the geometrical parameters of the PSI is studied. The results indicate that the ratio of the width of the inclusion to the period of the repeated structure has an optimum value, at which the maximum internal tensile stress and SERR arise. On the other hand, the ratio of the max-thickness of the inclusion to the thickness of the coating has a threshold value, above which the further increase of this ratio should seldom influence the internal stress or the SERR.