Mass transfer kinetics of neodymium(III) extraction by calix[4]arene carboxylic acid using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamics and kinetics data are both important to explain the extraction property. In order to develop a novel separation technology superior to current extraction systems, many promising extractants have been developed including calixarene carboxylic acids. The extraction thermodynamics behavior of calix[4]arene carboxylic acids has been reported extensively. In this study, the mass transfer kinetics of neodymium(III) and the interfacial behavior of calix[4]arene carboxylic acid were investigated. RESULTS: The rate constant (K_ao) becomes constant when the stirring speed was controlled between 250 rpm and 400 rpm. The activation energy (E_a) was calculated to be 21·41 kJ mol^?1 or 88·17 kJ mol^?1 (dependent on temperature) from the slope of log K_ao against 1000/T. The linear relationship between the specific area and the extraction rate is the characteristic of an interfacial reaction control. The minimum bulk concentration of the extractant necessary to saturate the interface (C_min) is lower than 4·19 × 10^?4 mol L^?1. CONCLUSION: The effect of stirring speed, temperature, and species concentration on the extraction rate demonstrates that the extraction regime depends on the extraction conditions. The chemical reaction control governs the extraction regime at temperatures below 303 K and a mixed control regime occurs when the temperature is between 303 K and 318 K. The probable locale for the chemical reaction is at the liquid–liquid interface and the rate equation is deduced to be: ? d[Nd³⁺]_(a)/dt = k_f[Nd³⁺]_(a)[H₄A]_(o)^0·727[H⁺]_(a)^?0·978. The rate‐controlling step was suggested by the analysis of the experimental results. Copyright © 2008 Society of Chemical Industry     

电信服务营销渠道转型的必要性

分析了电信企业服务营销渠道的特点、旧有的服务营销渠道模式和存在的问题以及今后电信业和市场等方面发展的新需求，对电信服务营销渠道转型的必要性进行了探讨和研究,同时提供了一个可供参考的服务营销渠道价值评估体系架构,从量化服务营销渠道对电信企业贡献价值的角度论述了服务营销渠道转型的必要性。     

Effect of exponentially graded base doping on the performance ofGaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5×10¹⁹ cm^-3 at the emitter edge to 5×10¹⁸ cm^-3 at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1×10¹⁹ cm^-3 , the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%     

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.     

Low cycle fatigue and creep behavior of recrystallized Molybdenum near room termperature

The deformation behavior of pure recrystallized molybdenum under cyclic and static loads was investigated in the temperature range between 30°C and 10O°C, for stress amplitudes between 100 MPa and 250 MPa and for static loads up to 200 MPa. The results show that in spite of the low test temperatures and stress levels the Mo material exhibits considerable plastic strains which depend sensitively on frequenez and small changes in temperature.The activation energy deduced for the static and dynamic deformation is less than 0.98 eV which indicates thermally activated processes, to be explained by a dislocation kink model as described in the literature. The low-temperature fatigue behavior appears strongly influenced by creep-fatigue interaction phenomena.     

分割电极片状压电致动器——(二)位移特性及狭缝宽度对其影响的实验研究

研究了悬臂梁式分割电极片状压电致动器的位移特性。理论分析表明，分割电极狭缝宽度会减小致动器自由端的位移输出，但当狭缝宽度小于致动器电极宽度的１０％时，可忽略狭缝宽度的影响。致动器端部位移的测试结果大于理论计算值。与现有磁头悬浮臂尺寸相近的致动器，在２０Ｖ～５０Ｖ的电压驱动下均可获得１μｍ～２μｍ的致动位移。对９８５０道／厘米的密度磁盘，该位移能覆盖至少一个磁道宽度，满足磁头定位两级伺服系统对第二级致动器位移的基本要求。     

铁磁偶合的Gd（Ⅲ）Cu（Ⅱ）配合物──组装分子基铁磁体的一种重要元件

铁磁偶合的Ｇｄ（Ⅲ）Ｃｕ（Ⅱ）配合物──组装分子基铁磁体的一种重要元件缪明明，廖代正，王耕霖（南开大学化学系天津３０００７１）摘要分子基磁体的设计是自然界向化学家挑战的一个热点课题。铁磁偶合的Ｇｄ（Ⅲ）Ｃｕ（Ⅱ）配合物是组装分子基磁体的一种重要元件。...     

Two bit correlation-an adaptive time delay estimation

Time delay estimation is a very important operation in ultrasound time-domain flow mapping and correction of phase aberration of an array transducer. As the interest increases in the application of one and a half-dimensional (1.5-D) and two-dimensional (2-D) array transducers to improving image quality and three-dimensional (3-D) imaging, the need of simple, fast, and sufficiently accurate algorithms for real-time time delay estimation becomes exceedingly crucial. In this paper, we present an adaptive time-delay estimation algorithm which minimizes the problem of noise sensitivity associated with the one bit correlation while retaining simplicity in implementation. This algorithm converts each sample datum into a two bit representation including the sign of the sample and an adaptively selected threshold. A bit pattern correlation operation is applied to find the time delay between two engaged signals. By using the criterion of misregistration as an indicator, we are able to show that the proposed algorithm is better than one bit correlation in susceptibility to noise level. Analytical results show that the improvement in reducing misregistration of the two bit correlation over its counterpart is consistent over a wide range of noise level. This is achieved by an adaptive adjustment of the threshold to accommodate signal corruption due to noise. The analytical results are corroborated by results from simulating the blood as a random distribution of red blood cells. Finally, we also present a memory-based architecture to implement the two bit correlation algorithm whose computation time does not depend upon the time delay of the signals to be correlated