Material flow and core/multi-shell structures in a friction stir welded aluminum alloy with embedded copper markers

The objective of this study was to reveal the material flow and temperature distribution in a thick aluminum plate during friction stir welding and examine the subsequent microstructural change with particular attention to the reaction between copper marker and aluminum matrix. It is shown that the material adjacent to the threaded pin was transported from the top to bottom non-symmetrically, and then was forced to move upwards at a small distance from the pin due to the constraint of an extrusion-die-like configuration. The interaction between the copper marker and aluminum matrix led to the formation of (i) a unique core/multi-shell microstructure consisting of copper core, inner shell of AlCu and outer shell of Al₂Cu, and (ii) a composite band containing uniformly-distributed Al₂Cu particles with refined grains due to the lower stacking fault energy of copper and the pinning role of Al₂Cu particles.     

The influence of ingredients of silica suspensions and laser exposure on UV curing behavior of aqueous ceramic suspensions in stereolithography

This paper focused on the influence of ingredients of silica suspensions and laser exposure on curing behavior of the highly concentrated aqueous silica suspensions. As a basic building unit, single cured lines were regarded as research objects to characterize the curing behavior of aqueous ceramic suspensions. The cured width and depth were characteristic parameters of single cured lines and measured with a digital optical microscope. The relationships between two characteristic parameters and ingredients of highly concentrated aqueous ceramic suspensions and laser exposure were investigated. The cured depth and width of single cured lines increased with the ceramic mean diameter and monomer concentrations. The cured width of single cured lines decreased with the solid content, but the cured depth increased with the solid content for silica suspensions. The cured depth and width of the single cured line all decreased with the laser scanning speed. The experimental results show that the ingredients of ceramic suspensions and laser exposure all have great influence on curing behavior of the highly concentrated silica suspensions, which indicates that the formula is an intrinsic factor on the curing behavior of ceramic suspensions and laser exposure is an exterior factor.     

Job cycle time estimation in a wafer fabrication factory with a bi-directional classifying fuzzy-neural approach

Estimating the cycle time for every job in a factory is a critical task. It was recently reported that job classification noticeably enhanced the accuracy of job cycle time estimation. In pre-classifying approaches, whether the pre-classification approach combined with the subsequent estimation approach is suitable for the data is questionable. Conversely, the difficulty in classifying a job according to only the estimation error not the various attributes is a problem to post-classifying approaches. To tackle these problems, a bi-directional classifying fuzzy-neural approach is proposed in this study. In the proposed methodology, jobs are not only pre-classified but also post-classified. The results of pre-classification and post-classification are aggregated into a suitability index for each job. A job is then assigned to the category to which its suitability index is the highest. A radial basis function network is also constructed to predict the suitability index of a job according to the various attributes. To evaluate the effectiveness of the proposed methodology, a practical example was used in this study. According to experimental results, the estimation accuracy of the proposed methodology was significantly better than those of many existing approaches.     

Shaping the interdisciplinary knowledge network of China: a network analysis based on citation data from 1981 to 2010

This study builds the interdisciplinary knowledge network of China, which is used to catch the knowledge exchange structure of disciplines, and investigates the evolution process from 1981 to 2010. A network analysis was performed to examine the special structure and we compare state of the networks in different periods to determine how the network has got such properties. The dataset are get from the reference relationship in literature on important Chinese academic journals from 1980 to 2010. The analytical results reveal the hidden network structure of interdisciplinary knowledge flows in China and demonstrate that the network is highly connected and has a homogeneous link structure and heterogeneous weight distribution. Through comparing of the network in three periods, that is 1981–1990, 1991–2000 and 2001–2010, we find that the special evolution process, which is limited by the number of nodes, play an important influence on interdisciplinary knowledge flows.     

High-sensitivity and wide-directivity ultrasound detection using high Q polymer microring resonators

Small size ultrahigh Q polymer microrings working at near visible wavelength have been experimentally demonstrated as ultralow noise ultrasound detectors with wide directivity at high frequencies (>20 MHz). By combining a resist reflow and a low bias continuous etching and passivation process in mold fabrication, imprinted polymer microrings with drastically improved sidewall smoothness were obtained. An ultralow noise-equivalent pressure of 21.4 Pa over 1-75 MHz range has been achieved using a fabricated detector of 60 μm diameter. The device's wide acceptance angle with high sensitivity considerably benefits ultrasound-related imaging.     

Thermal conductivity measurement of the epoxies and composite material for low temperature superconducting magnet design

The thermal conductivities of solid materials were measured by a G-M cryo-cooler based apparatus in the temperature range of 2.6–21.0 K. The performance of this apparatus was verified by measuring the thermal conductivity of 304-stainless steel, and good reproducibility as well as accuracy was shown when compared with the certified values. The thermal conductivities of EC1017 and Stycast2850FT and a composite material were measured. Similar behavior to amorphous materials was shown for EC1017 and Stycast2850FT in that there was an apparent plateau, which could be ascribed to a very lower crystallinity of epoxy. An equivalent model was proposed to predict the thermal conductivity of the composite material.     

Spray-drying of alumina powder for APS: effect of slurry properties and drying conditions upon particle size and morphology of feedstock

In this paper, effects of variables concerning slurry properties and drying conditions on the particle size and morphology of feedstock were discussed. The results indicated that, the increase of powder loading increased D ₅₀ and volume content but reduced recovery rate slightly. Other variables, such as inlet temperature, showed a maximum on the desired property. The particle size of resulting feedstock increased with the rise of feeding rate of slurry, however, decreased with the increase of atomization pressure based on the premise that atomization pressure was enough to force slurry to form the liquid membrane. For preparation of spherical feedstock, optimized variables were as follows: 60 wt.% powder in slurry, 2 wt.% PVA in slurry, inlet temperature of 60°C, atomization pressure of 13 × 10³ KPa and feeding rate of 12 ml min^?1. The volume content of feedstocks with 10–45 μm was above 65% and for D ₅₀ it was 15·42 μm. In addition, according to the heat and mass transfer equation, the drying mechanism was established, which was well in agreement with the experimental results.     

Interface-dependent resistance switching in Nd<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> ceramics

Interface-dependent electric-pulse-induced resistance switching effect (EPIR) in Nd_0.7Sr_0.3MnO₃ ceramics was studied. The results reveal that the EPIR effect originates from the interface between the electrodes and the bulk, and the EPIR ratio as well as the high and low resistance states can be strongly influenced by applying a large electrical field on the sample for different intervals. Also, the pulse parameters have great effect on the stability of EPIR and the optimal pulse width, pulse amplitude and read bias are obtained. Based on the space charge limited current mechanism together with the theory of interfacial charge-trapped state, the interface-dependent resistance switching effect is discussed.