四种国产野生无髯鸢尾种子休眠与萌发的研究

玉蝉花（Iris ensata）、山鸢尾（Iris setosa）、金脉鸢尾（Iris chrysographes）和西南鸢尾（Iris bulleyana）这四种国产野生无髯鸢尾的种子均存在休眠现象，然而萌发情况各异。通过大田实验、层积处理、离体胚培养、切割胚乳、剥离种皮、切割胚乳不同部位、对种子的珠孔端胚乳进行扫描电子显微镜观察和用Instron 5848微力材料实验机测量刺穿珠孔端结构所需要力，以及把离体胚放在PEG-6000的渗透液中来测试四种鸢尾种子胚的生长势等实验，发现：玉蝉花、山鸢尾、金脉鸢尾和西南鸢尾这四种鸢尾种子存在不同程度的休眠;胚不含萌发抑制剂，已经完成了生理成熟，不是这几种鸢尾休眠的障碍;鸢尾的种皮透水性良好，虽然种皮对萌发有一定的机械抑制作用，然而相对于珠孔端胚乳而言，对胚根伸长的阻力不大，因此不是种子休眠的主要因素。根据实验结果推测，鸢尾种子的胚乳含有萌发抑制剂，然而，珠孔端胚乳的机械束缚可能是鸢尾种子萌发延迟的主要原因。通过进一步的实验发现，玉蝉花和山鸢尾这两种鸢尾胚的生长势高于后两种鸢尾种子，然而，它们的珠孔端结构（胚乳和种皮）对胚伸长的束缚还不及后两者的一半，也就是说，鸢尾种子萌发与否主要取决于珠孔端胚乳对胚根伸长的机械束缚与胚根的生长势的力量的对比，当前者大于后者时，种子不能萌发，当珠孔端胚乳细胞的细胞壁解体或者这一部分被切割之后，珠孔端机械束缚等于或者小于胚的生长势时，种子萌发。

辽西半干旱区褐土机械组成的空间变异性

采用方格网取样，利用经典统计学和地统计学方法，研究了三种不同观测尺度共5个研究区域，总面积为3.12km2褐土耕层土壤机械组成的空间变异性。经典统计特征量表明，不同尺度下褐土耕层土壤机械组成的样本数据存在着不同的差异性。变异函数结构分析显示，土壤机械组成的空间变异在各方向上具有不同变率，但均可通过线性变换而转换为各向同性的统一结构，属于几何各向异性结构；不同观测尺度上有着不同的空间结构特征，对不同空间结构的区域化变量确定了不同的理论模型参数，并绘制克立格图，给出不同观测尺度下满足独立取样的合理取样数目。较清晰地阐明了褐土耕层机械组成在不同尺度上的空间分布规律。为该地区其它土壤性质的空间变异性研究提供理论依据，并为精准农业土壤信息库提供参考。尝试应用地统计学方法对不同尺度进行外推估值，发现在不同观测尺度和不同地形条件下，不同观测变量有着不同的标准差临界值及最大外推估值尺度，外推估值方差随着外推尺度的增大而增大。运用地统计学外推估值可为解决尺度扩展提供一种有效的解决途径。

The effect of formulated molecular weight on temperature resistance and mechanical properties in polyimide based composites

This experimental study examines the role of formulated molecular weight between crosslink sites on the temperature resistance and mechanical properties of composites based on a polyimide containing a diphenyl thioether unit (PTI). The composites are fabricated by in situ polymerization of monomer reactants (PMR) using three monomeric ingredients: bis(3,4-dicarboxyphenyl) sulfide dianhydride (TDPA); 4,4'-methylene dianiline (MDA); and the monomethyl ester of norbornene anhydride (NE). By changing monomeric molar ratio, three formulations are prepared, in which formulated molecular weight between crosslink sites varies from 1487 to 3446 g mol(-1). Unidirectional composite laminates from each formulation and T300 carbon fibres are compression moulded and cut into a series of test specimens. By measuring the glass transition temperature (T-g), Mode I interlaminar fracture toughness (G(IC)) and other mechanical properties at room and elevated temperatures, the influences of formulated molecular weight on the temperature resistance and mechanical properties of PTI-based composites are investigated.

土壤传热特性的实验研究(Experimental Study of Soil Heat Diffusivity)

发展了测定实验室土样热扩散率的方法,介绍了研制的实验装置和建议的操作程序。给出的实验结果表明土壤热扩散率随土壤空隙率、含水量和温度等许多参数而变化。

Wave-soil-pipe coupling effect on submarine pipeline on-bottom stability

Wave-soil-pipe coupling effect on the untrenched pipeline stability on sands is for the first time investigated experimentally. Tests are conducted in the U-shaped water tunnel, which generates an oscillatory how, simulating the water particle movements with periodically changing direction under the wave action. Characteristic times and phases during the instability process are revealed. Linear relationship between Froude number and non-dimensional pipe weight is obtained. Effects of initial embedment and loading history are observed. Test results between the wavesoil-pipe interaction and pipe-soil interaction under cyclic mechanical loading are compared. The mechanism is briefly discussed. For applying in the practical design, more extensive and systematic investigations are needed.

Stochastic Structural Model of Rock and Soil Aggregates by Continuum-Based Discrete Element Method

This paper first presents a stochastic structural model to describe the random geometrical features of rock and soil aggregates. The stochastic structural model uses mixture ratio, rock size and rock shape to construct the microstructures of aggregates,and introduces two types of structural elements (block element and jointed element) and three types of material elements (rock element, soil element, and weaker jointed element)for this microstructure. Then, continuum-based discrete element method is used to study the deformation and failure mechanism of rock and soil aggregate through a series of loading tests. It is found that the stress-strain curve of rock and soil aggregates is nonlinear, and the failure is usually initialized from weaker jointed elements. Finally, some factors such as mixture ratio, rock size and rock shape are studied in detail. The numerical results are in good agreement with in situ test. Therefore, current model is effective for simulating the mechanical behaviors of rock and soil aggregates.

Microstructure and mechanical properties at TiCp/Ni-alloy interfaces in laser-synthesized coatings

Titanium carbide particle (TiCp) reinforced Ni alloy composite coatings were synthesized by laser cladding using a cw 3 kW CO2 laser. Two kinds of coatings were present in terms of TiCp origins, i.e. undissolved and in situ reacted TiCp, respectively. The former came from the TiCp pre-coated on the sample, whereas the latter from in situ reaction between titanium and graphite in the molten pool during laser irradiation. Conventional and high-resolution transmission electron microscope observations showed the epitaxial growth of TiC, the precipitation of CrB, and the chemical reaction between Ti and B elements around phase interfaces of undissolved TiCp. The hardness, H, and elastic modulus, E, were measured by nanoindentation of the matrix near the TiCp interface. For undissolved TiCp, the loading curve revealed pop-in phenomena caused by the plastic deformation of the crack formation or debounding of TiCp from the matrix. As for in situ generated TiCp, no pop-in mark appears. On the other hand, in situ reacted TiCp led to much higher hardness and modulus than that in the case of undissolved TiCp. The coating reinforced by in situ generated TiCp displayed the highest impact wear resistance at both low and high impact conditions, as compared with coatings with undissolved TiCp and without TiCp. The impact wear resistance of the coating reinforced by undissolved TiCp increases at a low impact work but decreases at a high impact work, as compared with the single Ni alloy coating. The degree of wear for the composite coating depends primarily on the debonding removal of TiCp.

The Effects of Grain Size Distribution and Structure on Mechanical Behavior of Silt

Abstract: In order to investigate the effects of the grain size distribution and the micro-structure of soils on the mechani- cal characteristics, some static triaxial compression tests were carried out, and then the relationship of stress-strain and the strength behavior of silty sand were compared among undisturbed samples with different grain size distribution, undis- turbed and remolded samples with the same grain size distribution, and reconstituted samples (or called mixed samples) with different grain size distribution. The effects of grain size distribution and structure on the mechanic behavior of silty sands were mainly analyzed. It is shown that the obvious differences of the mechanical characteristics between undis- turbed soils and remolded soils are caused by the differences of soil structures. Although the grain size distribution are different between two soil samples, their mechanical characteristics may be close to each other, or may have obvious differences because of the effects of micro-structure.

Effects of heavy metals on plants and resistance mechanisms

Goal, Scope and Background. As one of the consequences of heavy metal pollution in soil, water and air, plants are contaminated by heavy metals in some parts of China. To understand the effects of heavy metals upon plants and the resistance mechanisms, would make it possible to use plants for cleaning and remediating heavy metal-polluted sites. Methods. The research results on the effects of heavy metals on plants and resistant mechanisms are compiled from Chinese publications from scientific journals and university journals, mostly published during the last decade. Results and Discussion. Effects of heavy metals on plants result in growth inhibition, structure damage, a decline of physiological and biochemical activities as well as of the function of plants. The effects and bioavailability of heavy metals depend on many factors, such as environmental conditions, pH, species of element, organic substances of the media and fertilization, plant species. But, there are also studies on plant resistance mechanisms to protect plants against the toxic effects of heavy metals such as combining heavy metals by proteins and expressing of detoxifying enzyme and nucleic acid, these mechanisms are integrated to protect the plants against injury by heavy metals. Conclusions. There are two aspects on the interaction of plants and heavy metals. On one hand, heavy metals show negative effects on plants. On the other hand, plants have their own resistance mechanisms against toxic effects and for detoxifying heavy metal pollution. Recommendations and Outlook. To study the effects of heavy metals on plants and mechanisms of resistance, one must select crop cultivars and/or plants for removing heavy metals from soil and water. More highly resistant plants can be selected especially for a remediation of the pollution site. The molecular mechanisms of resistance of plants to heavy metals should be studied further to develop the actual resistance of these plants to heavy metals. Understanding the bioavailability of heavy metals is advantageous for plant cultivation and phytoremediation. Decrease in the bioavailability to farmlands would reduce the accumulation of heavy metals in food. Alternatively, one could increase the bioavailability of plants to extract more heavy metals.

Influence factors on wear resistance of two alumina matrix composites

We measured the wear resistances of alumina, alumina/silicon carbide composite and alumina/mullite composite by abrasive wear. And we studied the influence of fracture mode and worn surface pullout on wear resistance. The results are as follows: the main wear mechanisms of alumina and alumina/silicon carbide were fracture wear and plastic wear respectively, and for alumina/mullite composite, fracture wear and plastic wear mechanisms worked together. The wear resistance of the alumina/silicon carbide composite and the alumina/mullite composite was better by a factor of 1 similar to 3 than that of the monolithic alumina. There were two main reasons for the better wear resistance, i.e., the improved mechanical properties and the more smooth worn surfaces. However, The primary reason was the reduction of area fraction of pullout on the worn surfaces induced by fracture mode transition. (C) 2007 Published by Elsevier B.V.

Wear resistance of reaction sintered alumina/mullite composites

Alumina and alumina/mullite composites with mullite content of 0.96-8.72 vol.% were subjected to an abrasive wear test under loads of 0.1-2.0 N with a ball-on-disc apparatus. The wear rate and area fraction of pullout f(po) on the worn surfaces were measured. The wear resistances of the alumina/mullite composites were better by a factor of 1-2 than that of pure alumina. The main wear mechanism of alumina is fracture wear, and for alumina/mullite composites, fracture wear and plastic wear mechanisms work together. The influence of mechanical properties on wear resistance was estimated by Evans' method. It was found that the wear rate depends on f(po), and the primary reason for the better wear resistance of alumina/mullite composites is the reduction off, induced by fracture mode transition. (c) 2007 Elsevier B.V. All rights reserved.

Stress Resistance and Disease Resistance in Seaweeds:The Role of Reactive Oxygen Metabolism

It has become clear that the last 15-20 years that the immediate effect of a wide range of environmental stresses,and of infection,on vascular plants is to increase the information of reactive oxygen species(ROS) and to impose oxidative stress on the cells.Since 1994,sufficient examples similar responses in a broad range of marine macroalgae have been decribed to show that reactive oxygen metabolism also underlies the mechanisms by which seaweeds respond(and become resistant) to stress and infection.Desiccation,freezing,low temperatures,high light,ultraviolet radiation,and heavy metals all tend to result in a gradual and continued buildup of ROS because photosynthesis is inhibited and excess energy results in the formation of singlet oxygen.The response to other stresses (infection or oligosaccharides which signal that infection is occurring,mechanical stress,hyperosmotic shock) is quite different-a more rapid and intence,but short-lived production of ROS ,discribed as an "oxidative burst"-which is attributed to activation of NADPHoxidases in the plasma membrane.Seaweed species that are able to survive such stresses or resist infection have the capacity to remove the ROS through a high cellular content of antioxidant compounds,or a high activity of antioxidant enzymes.

The microstructure and mechanical properties of Mg-3Al-3RE alloys

The Mg-3Al-3RE alloys (RE, the cerium-rich or the yttrium-rich misch metal) were smelted in a resistance furnace under the protective flux from the Mg-RE master alloys and pure magnesium ingots. The microstructure and mechanical properties of samples prepared by steel mould casting method were investigated.