In situ polymerization and characterization of polyester‐based polyurethane/nano‐silica composites

Polyester‐based polyurethane/nano‐silica composites were obtained via in situ polymerization and investigated by Fourier‐transform infrared spectroscopy (FTIR), or FTIR coupled with attenuated total reflectance (FTIR‐ATR), Transmission electron microscopy (TEM), atomic force microscopy (AFM), an Instron testing machine, dynamic mechanical analysis (DMA) and ultraviolet‐visible spectrophotometry (UV‐vis). FTIR analysis showed that in situ polymerization provoked some chemical reactions between polyester molecules and nano‐silica particles. FTIR‐ATR, TEM and AFM analyses showed that both surface and interface contained nano‐silica particles. Instron testing and DMA data showed that introducing nano‐silica particles into polyurethane enhanced the hardness, glass temperature and adhesion strength of polyurethane to the substrate, but also increased the resin viscosity. UV‐vis spectrophotometry showed that nano‐silica obtained by the fumed method did not shield UV radiation in polyurethane films. Copyright © 2003 Society of Chemical Industry     

正压冲固基础海洋平台冰激振动动力响应

正压冲固基础海洋平台是一种新型平台桩基结构形式。采用三维有限元的数值分析方法,建立了正压冲固平台的三维有限元模型。基于冰激强迫振动理论提出动冰载荷的计算方法,根据海冰破碎长度和冰速确定冰载周期,冰强度限制的水平冰力作为冰力峰值,得到的动冰载荷用于正压冲固平台的动力响应分析,并依照规范计算了6倍桩径处刚性固定时的动力响应。三维有限元方法计算得到的动力响应大于6倍桩径刚性固定时的计算结果,结构安全性评估偏于安全。     

Boundary knot method for 2D and 3D Helmholtz and convection–diffusion problems under complicated geometry

The boundary knot method (BKM) of very recent origin is an inherently meshless, integration‐free, boundary‐type, radial basis function collocation technique for the numerical discretization of general partial differential equation systems. Unlike the method of fundamental solutions, the use of non‐singular general solution in the BKM avoids the unnecessary requirement of constructing a controversial artificial boundary outside the physical domain. The purpose of this paper is to extend the BKM to solve 2D Helmholtz and convection–diffusion problems under rather complicated irregular geometry. The method is also first applied to 3D problems. Numerical experiments validate that the BKM can produce highly accurate solutions using a relatively small number of knots. For inhomogeneous cases, some inner knots are found necessary to guarantee accuracy and stability. The stability and convergence of the BKM are numerically illustrated and the completeness issue is also discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

Self-Consistent Effects on the Starting Current of Gyrotron Oscillators

Self-consistent effects on the starting current of gyrotron oscillators are examined. Field profiles in the open cavity are shown to be sensitive to the interaction dynamics. This can either significantly raise or lower the oscillation threshold, particularly for the low-Q modes. The transition from resonant-mode oscillations at the low magnetic field to backward-wave oscillations at the high magnetic field is demonstrated.     

Programmable group-delay module using binary polarization switching

We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.     

离子束混合工艺对材料抗蚀性能的影响

本文介绍了离子束混合工艺方法。与直接注入相比较,离子束混合所使用的设备造价低1/4—1/2,而生产效率可提高1—2个数量级,因而使生产成本大幅度降低,这无疑对离子束工艺的实际应用将产生巨大的促进作用。 通过对轴承材料(GCr15和Cr4Mo4V)经Cr、N、Ta不同元素的混合处理后,在0.5M H_2SO_4和0.1M NaCl的缓冲溶液中的阳极极化曲线表明经混合处理后的两种材料试样,其抗蚀能力和抗点蚀能力均大大提高,这与直接注入的试样效果是一致的。 通过俄歇谱仪和透射电镜的分析结果表明混合是成功的,且在一定的条件下,形成非晶组织。 本文的结论是,无论是离子的直接注入还是离子束混合,对提高轴承材料的抗腐蚀性能都是有效的方法,特别是离子束混合技术具有更大的应用前景。     

Effect of precyclic loading on stress-corrosion-cracking initiation in an X-65 pipeline steel exposed to near-neutral pH soil environment

A study was carried out to understand the effect of precyclic loading on stress-corrosion-crack initiation in an X-65 pipeline steel exposed to a near-neutral-pH soil environment. The test specimens were precyclically loaded before corrosion exposure to represent a service history of up to about 20 years, depending on the severity of pressure fluctuation. Microcracks had initiated on the polished surface of the X-65 pipeline steel after long-time exposure at open-circuit potential (OCP) in a near-neutral-pH synthetic soil solution. These microcracks were mostly initiated from pits at metallurgical discontinuities such as grain boundaries, pearlitic colonies, and banded phases in the steel. Strong preferential dissolution was observed along planes of the banded structures in the steel. The selective corrosion attack at these metallurgical discontinuities is attributed to the galvanic nature of those areas to their neighbors. Cyclic loading prior to corrosion exposure had significant effects on microcrack initiation and propagation during subsequent corrosion exposure. Cyclic loading prior to corrosion exposure either reduced or increased the probability of crack initiation and the rate of crack propagation, depending upon the magnitude of the stress cycles. The largest reduction was seen at a peak cyclic stress of about 0.8 of the yield strength. This cyclic-loading-dependent cracking behavior might be related to the alteration of the substructures and the residual stress in the steel as a result of precyclic loading.