Composites reinforced in three dimensions by using low magnetic fields

The orientation and distribution of reinforcing particles in artificial composites are key to enable effective reinforcement of the material in mechanically loaded directions, but remain poor if compared to the distinctive architectures present in natural structural composites such as teeth, bone, and seashells. We show that micrometer-sized reinforcing particles coated with minimal concentrations of superparamagnetic nanoparticles (0.01 to 1 volume percent) can be controlled by using ultralow magnetic fields (1 to 10 milliteslas) to produce synthetic composites with tuned three-dimensional orientation and distribution of reinforcements. A variety of structures can be achieved with this simple method, leading to composites with tailored local reinforcement, wear resistance, and shape memory effects.     

Embedded nanostructures revealed in three dimensions

Nanotechnology creates a new challenge for materials characterization because device properties now depend on size and shape as much as they depend on the traditional parameters of structure and composition. Here we show that Z-contrast tomography in the scanning transmission electron microscope has been developed to determine the complete three-dimensional size and shape of embedded structures with a resolution of approximately 1 cubic nanometer. The results from a tin/silicon quantum dot system show that the positions of the quantum dots and their size, shape, structure, and formation mechanism can be determined directly. These methods are applicable to any system, providing a unique and versatile three-dimensional visualization tool.     

Scroll-shaped waves of chemical activity in three dimensions

Ferric ions catalyze the oxidation of malonate by bromate in acid solution, sometimes at a spatially uniform, steady rate, but sometimes in a self-regenerating three-dimensional wave which resembles a rotating scroll, often with its axis closed in a ring. In cross section perpendicular to the axis, one sees an involute spiral emerging from a thin cylindrical core. This "dissipative structure" organizes reaction stages periodically in space and time everywhere except along its rotation axis, which may therefore be a thermodynamically unique locus.     

Forming supramolecular networks from nanoscale rods in binary, phase-separating mixtures

Simulations show that when low-volume fractions of nanoscale rods are immersed in a binary, phase-separating blend, the rods self-assemble into needle-like, percolating networks. The interconnected network arises through the dynamic interplay of phase-separation between the fluids, through preferential adsorption of the minority component onto the mobile rods, and through rod-rod repulsion. Such cooperative effects provide a means of manipulating the motion of nanoscopic objects and directing their association into supramolecular structures. Increasing the rod concentration beyond the effective percolation threshold drives the system to self-assemble into a lamellar morphology, with layers of wetted rods alternating with layers of the majority-component fluid. This approach can potentially yield organic/inorganic composites that are ordered on nanometer scales and exhibit electrical or structural integrity.     

论罗杰斯人本主义教育思想的三重维度

罗杰斯人本主义教育思想以全新的视角阐述了一种新型教育方式。在新时代,重温罗 杰斯人本主义教育思想对高校思想政治教育工作仍具有时代价值。     

Hierarchical self-assembly of F-actin and cationic lipid complexes: stacked three-layer tubule networks

We describe a distinct type of spontaneous hierarchical self-assembly of cytoskeletal filamentous actin (F-actin), a highly charged polyelectrolyte, and cationic lipid membranes. On the mesoscopic length scale, confocal microscopy reveals ribbonlike tubule structures that connect to form a network of tubules on the macroscopic scale (more than 100 micrometers). Within the tubules, on the 0.5- to 50-nanometer length scale, x-ray diffraction reveals an unusual structure consisting of osmotically swollen stacks of composite membranes with no direct analog in simple amphiphilic systems. The composite membrane is composed of three layers, a lipid bilayer sandwiched between two layers of actin, and is reminiscent of multilayered bacterial cell walls that exist far from equilibrium. Electron microscopy reveals that the actin layer consists of laterally locked F-actin filaments forming an anisotropic two-dimensional tethered crystal that appears to be the origin of the tubule formation.     

The goldfish ear codes the axis of acoustic particle motion in three dimensions

Auditory and vestibular nerve fibers of the goldfish are strongly directionally sensitive to whole-body acceleration at audio frequencies. The three-dimensional pattern of sensitivity shows that input from a receptor ensemble (hair cells) is essentially equivalent to that expected from a single hair cell having a given three-dimensional orientation of best sensitivity. Fibers from the sacculus, lagena, and utriculus differ with respect to distributions of directional orientation, but are similar in best threshold (less than 1 nanometer, root mean square, at 140 hertz). In combination with other mechanisms for detection of sound pressure, this directionality is a likely basis for directional hearing in fishes, and it could allow the determination of underwater acoustic intensity.     

Single crystals of single-walled carbon nanotubes formed by self-assembly

We report the self-assembly of single crystals of single-walled carbon nanotubes (SWCNTs) using thermolysis of nano-patterned precursors. The synthesis of these perfectly ordered, single crystals of SWCNTs results in extended structures with dimension on the micrometer scale. Each crystal is composed of an ordered array of tubes with identical diameters and chirality, although these properties vary between crystals. The results show that SWCNTs can be produced as a perfect bulk material on the micrometer scale and point toward the synthesis of bulk macroscopic crystalline material.     

三网融合对图书馆信息资源的影响

针对电信。网络和有线电视三网融合趋势的现状,介绍了三网融合的意义和基本知识,阐述了三网融合对图书馆数字资源的影响,并提出了图书馆在现代信息社会中应作出的对策,从而加强新时期图书馆对信息资源的利用。