Designing cell-compatible hydrogels for biomedical applications

Hydrogels are polymeric materials distinguished by high water content and diverse physical properties. They can be engineered to resemble the extracellular environment of the body's tissues in ways that enable their use in medical implants, biosensors, and drug-delivery devices. Cell-compatible hydrogels are designed by using a strategy of coordinated control over physical properties and bioactivity to influence specific interactions with cellular systems, including spatial and temporal patterns of biochemical and biomechanical cues known to modulate cell behavior. Important new discoveries in stem cell research, cancer biology, and cellular morphogenesis have been realized with model hydrogel systems premised on these designs. Basic and clinical applications for hydrogels in cell therapy, tissue engineering, and biomedical research continue to drive design improvements using performance-based materials engineering paradigms.     

Stretchable and foldable silicon integrated circuits

We have developed a simple approach to high-performance, stretchable, and foldable integrated circuits. The systems integrate inorganic electronic materials, including aligned arrays of nanoribbons of single crystalline silicon, with ultrathin plastic and elastomeric substrates. The designs combine multilayer neutral mechanical plane layouts and "wavy" structural configurations in silicon complementary logic gates, ring oscillators, and differential amplifiers. We performed three-dimensional analytical and computational modeling of the mechanics and the electronic behaviors of these integrated circuits. Collectively, the results represent routes to devices, such as personal health monitors and other biomedical devices, that require extreme mechanical deformations during installation/use and electronic properties approaching those of conventional systems built on brittle semiconductor wafers.     

Reversible switching of hydrogel-actuated nanostructures into complex micropatterns

Responsive behavior, which is intrinsic to natural systems, is becoming a key requirement for advanced artificial materials and devices, presenting a substantial scientific and engineering challenge. We designed dynamic actuation systems by integrating high-aspect-ratio silicon nanocolumns, either free-standing or substrate-attached, with a hydrogel layer. The nanocolumns were put in motion by the "muscle" of the hydrogel, which swells or contracts depending on the humidity level. This actuation resulted in a fast reversible reorientation of the nanocolumns from tilted to perpendicular to the surface. By further controlling the stress field in the hydrogel, the formation of a variety of elaborate reversibly actuated micropatterns was demonstrated. The mechanics of the actuation process have been assessed. Dynamic control over the movement and orientation of surface nanofeatures at the micron and submicron scales may have exciting applications in actuators, microfluidics, or responsive materials.     

工程塑料在农业机械上的应用现状及发展前景

论述了工程塑料的性能、特点及在农业机械上的应用现状，并根据农业机械的发展趋势，展望了工程塑料在农业机械上应用的广阔前景。     

乌拉盖水库工程天然建筑材料调查与评价

水利水电工程一般多因地制宜、就地取材,有的当地天然建筑材料甚至成为决定建筑物类型和工程造价的决定性因素。本文分析了区域地形、地貌、地层、岩性等,通过地质调查、钻探、坑探等勘察手段,在前人工作程度很低的地区寻找到了设计需要的建造土坝的各种材料。同时,使用野外和室内土工实验方法,研究了这些建材的物理、力学性质。在此基础上根据平均厚度法和设计、规范标准对各料场建材进行了计算和评价,其质量和数量均满足要求,为本工程设计和施工提供了可靠的建材依据。     

Laser annealing of ion-implanted semiconductors

The physical and electrical properties of ion-implanted silicon annealed with high-powered laser radiation are described. Particular emphasis is placed on the comparison of materials properties that can be achieved with laser annealing to those which can be achieved by conventional thermal annealing. Applications of these techniques to the fabrication of high-efficiency solar cells, and potential applications of this new technique to other materials areas are discussed.     

X-ray Damage to CF3CO2-Terminated Organic Monolayers on Si/Au: Principal Effect of Electrons

The relative importance of x-rays alone and of x-ray-generated primary and secondary electrons in damaging organic materials was explored by use of self-assembled monolayers (SAMs) on multilayer thin-film supports. The substrates were prepared by the deposit of thin films of silicon (0, 50, 100, and 200 angstroms) on thick layers of gold (2000 angstroms). These systems were supported on chromium-primed silicon wafers. Trifluoroacetoxy-terminated SAMs were assembled on these substrates, and the samples were irradiated with common fluxes of monochromatic aluminum K(alpha) x-rays. The fluxes and energy distributions of the electrons generated by interactions of the x-rays with the various substrates, however, differed. The substrates that emitted a lower flux of electrons exhibited a slower loss of fluorine from the SAMs. This observation indicated that the electrons-and not the x-rays themselves-were largely responsible for the damage to the organic monolayer.     

Strained-layer epitaxy of germanium-silicon alloys

Despite the dominant position of silicon in semiconductor electronics, its use is ultimately limited by its incompatibility with other semiconducting materials. Strained-layer epitaxy overcomes problems of crystallographic compatibility and produces high-quality heterostructures of germanium-silicon layers on silicon. This opens the door to a range of electronic and photonic devices that are based on bandstructure physics.     

甘蔗叶生物力学特性研究理论与分析

甘蔗在中国糖料生产中占重要地位,甘蔗叶是一种储量巨大且亟待开发利用的生物质能源,具有很好的开发利用价值。然而,目前对甘蔗叶生物力学特性方面的研究尚缺乏有效的研究理论与方法。本研究引入新兴的农业生物力学研究理论,结合工程学、生物学、工程力学和工程材料学的基本原理与方法,研究甘蔗叶拉伸力学性能、甘蔗叶剪切力学性能、甘蔗叶力学性能,为研究甘蔗叶的生物力学特性寻找到有效的研究理论与方法,为甘蔗叶粉碎还田、甘蔗叶沼气利用预处理机械,以及甘蔗剥叶、收获等机械的研究开发、优化设计、计算机仿真及智能化提供参考。     

Microbial polysaccharides template assembly of nanocrystal fibers

Biological systems can produce extraordinary inorganic structures and morphologies. The mechanisms of synthesis are poorly understood but are of great interest for engineering novel materials. We use spectromicroscopy to show that microbially generated submicrometer-diameter iron oxyhydroxide (FeOOH) filaments contain polysaccharides, providing an explanation for the formation of akaganeite pseudo-single crystals with aspect ratios of approximately 1000:1. We infer that the cells extrude the polysaccharide strands to localize FeOOH precipitation in proximity to the cell membrane to harness the proton gradient for energy generation. Characterization of organic compounds with high spatial resolution, correlated with mineralogical information, should improve our understanding of biomineralization mechanisms.     

Nanoelectromechanical systems

Nanoelectromechanical systems are evolving, with new scientific studies and technical applications emerging. Mechanical devices are shrinking in thickness and width to reduce mass, increase resonant frequency, and lower the force constants of these systems. Advances in the field include improvements in fabrication processes and new methods for actuating and detecting motion at the nanoscale. Lithographic approaches are capable of creating freestanding objects in silicon and other materials, with thickness and lateral dimensions down to about 20 nanometers. Similar processes can make channels or pores of comparable dimensions, approaching the molecular scale. This allows access to a new experimental regime and suggests new applications in sensing and molecular interactions.     

作物抗虫育种的研究进展

作物的抗虫能力是其本身经过长期进化形成的一套防卫体系，具有潜在的利用价值．我国几十年的抗虫育种实践可以分为形态学抗虫育种、生化抗虫育种和基因工程抗虫育种3个阶段．作物的抗虫性同其它性状一样，是能够遗传的．现代生物技术的发展，为抗虫育种工作的深入提供了技术支持，丰富的植物种质资源为筛选优异的抗虫材料奠定了基础．通过基因工程途径创造抗虫的基因工程植株，并与常规育种相结合，必将培育出性状优良的抗虫新品种，并应用于农业生产．     

从化区农田耕层土壤有效硅空间分布及影响因素

为探究广州市从化区农田土壤有效硅空间分布及影响因素,以期为促进我国粮食主产区水稻产量增长提供科学依据和参考,采用描述性统计、地统计学、相关性分析与GIS （地理信息系统）技术结合的方法对从化区土壤有效硅开展研究。结果表明,研究区土壤有效硅平均含量为60.31 mg·kg^-1,总体偏低,并呈现中度变异;在中心区域、粮食主产区和丘陵地带,土壤有效硅含量较高;有效硅含量与土壤pH、有机质含量、黏粒含量呈正相关,土地利用方式、成土母质对其也有显著影响。研究表明,在所考虑的影响因素中,成土母质对从化区农田土壤有效硅的影响程度居于首位。     

Predicting new solids and superconductors

It is now possible to start with a simple model of a solid composed of atomic cores and itinerant valence electrons and compute the total energy for a given structural arrangement of atoms with enough precision to predict the existence of new solids and their properties. The application of the model based on the pseudopotential method is described with silicon chosen as a prototype material. With only information about the constituent atoms, the electronic, structural, vibrational, and even superconducting properties of solids can be calculated from first principles. The successful predictions of superconductivity in highly condensed hexagonal silicon and the existence of new high-pressure semiconductor phases are highlighted. A discussion is presented of the use of the method to discover new stable or metastable solids at high pressures.     

Silicon isotope evidence against an enstatite chondrite Earth

The compositions of Earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems. Although this suggests that Earth largely accreted from enstatite chondrites, definitive proof of this model has been lacking. By comparing the silicon (Si) isotope signatures of several extraterrestrial materials with terrestrial samples, we show that they cannot be explained by core-formation scenarios involving a bulk Earth of enstatite chondrite composition. Si isotope similarities between the bulk silicate Earth and the Moon preclude the existence of a hidden reservoir in the lower mantle, a necessary condition of the enstatite chondrite model, and require an equilibrium process after the Moon-forming impact. A three-end-member chondritic mixing model for Earth reconciles the Si isotope similarities between enstatite chondrites and Earth.     

New magnetic alloys

Three notable new developments in magnetic alloys are highlighted. These include rare earth-cobalt permanent magnets with maximum energy products up to 240 kilojoules per cubic meter; chromium-cobalt-iron permanent magnets that have magnetic properties similar to those of the Alnicos, but contain only about half as much cobalt and are sufficiently ductile to be cold-formable; and high-induction grain-oriented silicon steels that exhibit 20 percent less core loss as transformer core materials than conventional oriented grades.     

Toxic potential of materials at the nanolevel

Nanomaterials are engineered structures with at least one dimension of 100 nanometers or less. These materials are increasingly being used for commercial purposes such as fillers, opacifiers, catalysts, semiconductors, cosmetics, microelectronics, and drug carriers. Materials in this size range may approach the length scale at which some specific physical or chemical interactions with their environment can occur. As a result, their properties differ substantially from those bulk materials of the same composition, allowing them to perform exceptional feats of conductivity, reactivity, and optical sensitivity. Possible undesirable results of these capabilities are harmful interactions with biological systems and the environment, with the potential to generate toxicity. The establishment of principles and test procedures to ensure safe manufacture and use of nanomaterials in the marketplace is urgently required and achievable.     

元模型在工程数据仓库中的作用

工程数据的组织管理分散、模式复杂且随时间变化,这就要求工程数据管理系统不仅可以统一管理数据,而且支持客户化工作、可扩展。这种系统的设计必须依赖数据模型的灵活性和自描述性。本文在分析工程数据的特点及其管理现状基础上,描述了工程数据仓库的体系结构和多层元模型;重点刻画了利用元对象技术实现工程数据管理的设计实现;最后描述了一个现实的利用元对象管理仓库中工程数据的系统-FTEDWS,证明了本方案和元模型的有效性。这种采用元模型的方法提供了一个灵活、可互交换的环境,用以支持系统演化和重用。     

土地利用对土壤性质影响的区域差异研究

 【目的】研究探讨土地利用对土壤性质影响的区域差异性。【方法】选择4类土地利用方式（天然林、人工林、灌丛和耕地），分别在山西寿阳县和四川丹棱县野外采集土壤样方进行测定，利用统计分析法研究土地利用对土壤性质影响的区域差异。【结果】不同土地利用方式对土壤性质的影响差异显著。人类活动干扰小的土地利用方式的土壤有机质、全氮含量和含盐量等普遍高于人类影响较强的土地利用方式。相同的土地利用方式对土壤性质的影响具有空间差异。即便在相同的土地利用方式下，不同的耕作制度和田间管理措施（灌溉、施肥、农药等）也会造成土壤特性的区域异质性。【结论】不同土地利用方式对土壤性质影响的区域差异揭示了人类活动对环境变化影响的区域差异，可以在一定程度上解释“人-地”的复杂性关系，研究结果可为国家在区域土地规划、作物栽培布局和水土保持政策制订等提供科学依据。