An evaluation of the DAWN-B light scattering unit from wyatt technology: Suggested calibration,normalization, and clarification procedures

Proper normalization, calibration, and sample clarification procedures for use with the Wyatt Technology DAWN-B laser light scattering photometer are described. The utility of the proposed methods is confirmed by comparing results obtained on the solution properties of polystyrene standards in three different solvents (toluene, tetrahydrofuran, and methyl ethyl ketone) with results from the literature and generated using a Chromatix KMX-6 low-angle light scattering photometer. © 1993 John Wiley & Sons, Inc.     

Long endurance fatigue performance of bonded structural joints

Resin bonded joints are being used for a variety of applications in highway bridges. Such uses involve operation under different combinations of dead and live loading plus weathering. This paper is concerned with the fatigue performance of steel-to-steel lap joints for endurances of up to 10⁸ cycles. The effects on fatigue performance of curing temperature and operating temperature have been examined and work in progress to investigate effects of weathering is described. Special attention is given to performances at long endurances and low stresses relevant to traffic loading during service.     

Robustness of connectionist swimming controllers against random variation in neural connections

The ability to achieve high swimming speed and efficiency is very important to both the real lamprey and its robotic implementation. In previous studies, we used evolutionary algorithms to evolve biologically plausible connectionist swimming controllers for a simulated lamprey. This letter investigates the robustness and optimality of the best-evolved controllers as well as the biological controller hand-crafted by Ekeberg. Comparing cases of random variation in intrasegmental or intersegmental weights against each controller allows estimates of robustness to be made. We conduct experiments on the controllers' robustness at the excitation level, which corresponds to either the maximum swimming speed or efficiency by randomly varying the segmental connection weights and on some occasions also the intersegmental couplings, through varying noise ranges. Interestingly, although the swimming performance (in terms of maximum speed and efficiency) of the Ekeberg biological controller is not as good as that of the artificially evolved controllers, it is relatively robust against noise in the neural networks. This suggests that the natural evolutions have evolved a swimming controller that is good enough to survive in the real world. Our findings could inspire neurobiologists to conduct real physiological experiments to gain a better understanding on how neural connectivity affects behavior. The results can also be applied to control an artificial lamprey in simulation and possibly also a robotic one.     

Quantitative Characterization of the Fracture Surface of Si Single Crystals by Confocal Microscopy

Experiments are conducted to study the dislocation nucleation conditions at the crack tip in {110}〈110〉 oriented Si single crystals. Specimens with surface cracks are first statically loaded at elevated temperatures for a prolonged period of time to initiate and move dislocations away from the crack tip, then cooled down to room temperature and loaded to fracture to measure the fracture toughness. Fractographic analysis of the fracture surfaces is performed. Distinct wavy patterns on the fracture surface at the initial cleavage crack front are observed, which is attributed to the existence of local mixed mode I/mode III stresses resulting from the inhomogeneous dislocation activity. Confocal microscopy is employed to quantify the fracture surface roughness. The results show that the increase of fracture toughness is directly associated with the increased area of the rough surface, which is characterized by the roughness number or the fractal dimension increment. Our results also demonstrate that dislocation nucleation can occur only at discrete sites. The spacing between these dislocation nucleation sources is of the order of 1 μm. A simple model is developed for the relationship between the fracture toughness and the surface roughness parameters, which is in good agreement with the experimental results.     

Sustainability Assessment of Urban Water Distribution Systems

A methodology is presented for determining sustainability indices for pressure and water age in water distribution systems (WDSs). These sustainability indices are based upon performance criteria including reliability, resiliency, and vulnerability. Pressure and water age are determined for a WDS as a function of operation time using the U.S. Environmental Protection Agency EPANET model. The values of pressure and water age are used to determine reliability, resiliency, and vulnerability performance criteria, which are then combined into the nodal sustainability indices for water age and pressure. In addition, the sustainability index (SI) computations are performed for zones to define the SI for water age and SI for pressure. A combined SI calculation is performed to produce an overall sustainability score for the entire zone in the water distribution network. The proposed methodology can be used to monitor the sustainability of existing WDSs and to help define alternative solutions including changes in pump operation and modifications to WDS to increase the sustainability.     

Graphene/Strontium Titanate: Approaching Single Crystal–Like Charge Transport in Polycrystalline Oxide Perovskite Nanocomposites through Grain Boundary Engineering

Grain boundaries critically limit the electronic performance of oxide perovskites. These interfaces lower the carrier mobilities of polycrystalline materials by several orders of magnitude compared to single crystals. Despite extensive effort, improving the mobility of polycrystalline materials (to meet the performance of single crystals) is still a severe challenge. In this work, the grain boundary effect is eliminated in perovskite strontium titanate (STO) by incorporating graphene into the polycrystalline microstructure. An effective mass model provides strong evidence that polycrystalline graphene/strontium titanate (G/STO) nanocomposites approach single crystal‐like charge transport. This phenomenological model reduces the complexity of analyzing charge transport properties so that a quantitative comparison can be made between the nanocomposites and STO single crystals. In other related works, graphene composites also optimize the thermal transport properties of thermoelectric materials. Therefore, decorating grain boundaries with graphene appears to be a robust strategy to achieve “phonon glass–electron crystal” behavior in oxide perovskites.     

超细钛酸锶系列功能材料的制备技术及进展

钛酸锶(SrTiO3)陶瓷是一种新兴的多功能电子陶瓷材料，由于其优异的电学性能而在很多领域有着广泛的应用。综述了SrTiO3粉体的主要制备技术及新进展，并对其加以比较。指出液相化学合成法是现阶段制备SrTiO3的主要方法，而作为液相法之一的直接沉淀法由于具有设备简单、操作方便、粉体粒径小、粒度分布窄、易于掺杂等优点有着诱人的工业应用前景。