辽西中生代银杏目和茨康目植物生殖器官研究

本文研究了采自辽宁西部下白垩统义县组和上三叠统羊草沟组的三种植物的生殖器官，它们分别属于银杏目 (Ginkgoales) 和茨康目 (Czekanowskiales)。辽宁银杏 (G. liaoningensis Liu, Crane, Li et Wang sp. nov.) 和纤细堆囊穗 (Sorosaccus gracilis Harris 1935 emend. Liu, Hueber, Li et Wang) 是银杏目植物的雄球花，通过将这两种雄球花与现存银杏 (Ginkgo biloba L.) 雄球花的对比研究，讨论了自晚三叠世至今银杏目雄性生殖器官可能的演化途径。蟹形薄果穗 (Leptostrobus cancer Harris 1951 emend. Liu, Li et Wang) 是茨康目植物的雌性生殖器官，我们根据辽西标本对该种的特征集要做了修订，并对薄果穗属 (Leptostrobus Heer 1876) 的种进行了讨论，将三个种归并到蟹形薄果穗薄。主要内容包括： 1. 银杏属植物雄球花——辽宁银杏 采自中国辽宁下白垩统义县组的辽宁银杏，为葇荑花序状，主轴基部有鳞片。小孢子叶螺旋排列在主轴上，小孢子叶上着生3—4个 (少数为2个) 卵形到椭圆形的小孢子囊。小孢子囊下垂，纵状开裂。成熟花粉粒单沟，长椭圆形;而未成熟的花粉粒处在四分体阶段。辽宁银杏的特征和现存银杏十分相似。主要差别在于辽宁银杏的小孢子叶着生3—4个 (少数为2个) 小孢子囊，而现存银杏的小孢子叶绝大多数着生2个小孢子囊。辽宁银杏在大小及小孢子囊数目上区别于其它的银杏属雄球花化石种，如：英国约克郡侏罗纪的胡顿银杏 (Ginkgo huttoni (Sternberg) Heer) 雄球花，加拿大阿尔贝塔晚白垩世一个未定名的银杏属雄球花。辽宁银杏 (化石) 和银杏 (现存) 的比较支持了根据银杏属胚珠器官而提出的缩减假说，因为自早白垩世至今，银杏属雄球花小孢子叶着生的小孢子囊的数目经历了从3—4个到2个的减少。 2. 银杏目植物雄球花——纤细堆囊穗 本文研究的纤细堆囊穗采自中国东北上三叠统羊草沟组。这种雄球花小孢子 叶末端的裂片在形态上差异很大，这是在以前对这种植物的研究中没有发现的重要特征。这些保存精美的化石对于纤细堆囊穗特征的阐明和修订以及种的复原很有帮助。将中国的标本与西伯利亚堆囊穗 (Sorosaccus sibiricus Prynada 1962)、小堆囊穗 (S. minor Harris 1935)、乌马尔堆囊穗 (S. umaltensis Krassilov 1972) 和被定为长叶拜拉 (Baiera longifolia (Pom.) Heer 1876) 的雄球花进行了比较，发现它们与纤细堆囊穗在特征上一致，故将它们处理为纤细堆囊穗的异名。同时，也讨论了堆囊穗属可能的演化意义。它可能是银杏属的远祖，经过小孢子囊数目的减少和小孢子叶长度的缩短而演化到现在的银杏，而辽西早白垩世的辽宁银杏可能代表了堆囊穗和现代银杏在演化上的一个中间阶段。 3. 茨康目雌性生殖器官——蟹形薄果穗 本文研究的蟹形薄果穗采自辽西上三叠统羊草沟组和下白垩统义县组。羊草沟组的材料是蟹形薄果穗属最早的纪录，从而该种的分布在时间上有了新的资料：从晚三叠世到早白垩世。据标本穗轴顶端的完整性，我们修订了蟹形薄果穗的特征集要和提供了它的复原图，并将三种薄果穗归并到蟹形薄果穗。我们也回顾了薄果穗属自1876年建立以来100多年的研究历史，并列出了该属所有材料，还讨论了该属各种的主要特征和建种依据。

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.

In situ formation by laser cladding of a TiC composite coating with a gradient distribution

An in situ method was developed to produce an Ni alloy composite coating reinforced by in situ reacted TiC particles with a gradient distribution, using one-step laser cladding with a pre-placed powder mixture on a 5CrMnMo steel substrate. Dispersed and ultra-fine TIC particles were formed in situ in the coating. Most. of the TiC particles, with a marked gradient distribution, were uniformly distributed within interdendritic regions because of the trapping effect of the advancing solid-liquid interface. In addition, the TiC-gamma-Ni interfaces generated in situ were found to be free from any deleterious surface reaction. Finally, the microhardness also showed a gradient variation, with the highest value of 1250 Hv0.2 and the wear properties of the coating were significantly enhanced.