Surface Modification of Reinforcement Fibers for Composites by Acid Treatments

In this study, we investigated the surface modification of reinforcement fibers for composites by acid treatments, including PBO fiber, Kevlar fiber and carbon fiber. The corresponding changes in the surface free energy components were carefully evaluated using a Cahn dynamic contact angle analysis system. In addition, the fiber's surface elemental composition and topography were studied using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that the surface nitrogen-to-carbon (N/C) and oxygen-to-carbon (O/C) ratios were significantly increased after the treatments. The surface free energy of PBO fiber was increased from 43.3 mJ/m² to 58.5 mJ/m² or by 35% with 60 wt% methanesulfonic acid solution treatment for 36 h. However, the increase with 60 wt% nitric acid solution was only by 14% (to 49.5 mJ/m²) for the same treatment time.     

Odour emission ability (OEA) and its application in assessing odour removal efficiency

Odourous emissions from sewer networks and wastewater treatment plants (WWTPs) can significantly impact a local population. Sampling techniques such as wind tunnels and flux hood chambers are traditionally used to collect area source samples for subsequent quantification of odour emission rates using dilution olfactometry, however these methods are unsuitable for assessing liquid samples from point sources due to the large liquid volumes required. To overcome this limitation, a gas phase sample preparation method was developed for assessing the total Odour Emission Ability (OEA) from a liquid sample. The method was validated using two volatile organic sulphur compounds (VOSCs), dimethyl-trisulphide (DMTS) and bismethylthiomethane (BMTM) that are frequently detected from sewers and WWTPs and are relatively stable compared with common VOSCs like mercaptan or methyl mercaptan. The recovery rates of DMTS and BMTM were quantified by injecting a known volume of a standard liquid sample into Tedlar bags using a static injection and a dynamic injection methodology. It was confirmed that both dynamic and static injection methods at ambient condition achieved high recovery rates with no need to consider increasing evaporation by elevating the temperature. This method can also be used to assess odour removal effectiveness of liquids by comparing the OEA before and after the treatment tests. Two application examples were presented.     

Effects of the heterogeneity of game complexity and user population in learning performance of business simulation games

Previous studies on business simulation games (BSGs) have concluded that improved performance may not be the primary benefit of using BSGs, due to mixed results between student performance and perceptions. Two relevant and insightful issues attract our attention, namely, the impacts of the heterogeneous student population and the different complexity levels of BSG software. To address these issues, the present study aims to understand the relationship between student profile/characteristics and performance in the classroom with BSG-facilitated learning. An in-depth case study is conducted on a general college course designed to teach three different complexities of BSGs to students enrolled in different majors. Four student profile factors are individually tested for differences in performance scores as evaluated by the teacher. Additionally, the influences of 11 student characteristics are assessed with regard their self-reported perceived learning performances. Regression analysis and ANOVA are used to investigate the impacts of heterogeneous users and game complexity on student performance. Based on the regression analyses of the data collected from 43 respondents who participated in the general course, the study concludes that knowledge and skill may influence the heterogeneous student population; moreover, student participation and tacit learning preference improve performance, and students with an auditory learning preference or high learning motivation may not perform well in classroom BSG learning. However, the low value of adjusted R square implies that more dimensions or variables are needed to increase the explaining power of the performance scores in the regression analyses. In contrast, heterogeneous BSG software with different complexity levels present different results. The current research contributes practical and incremental knowledge on the complexity of heterogeneous BSG software on performance scores and the perceived learning performance of heterogeneous student populations. With the research limitations acknowledged, a series of suggestions for teachers pertaining to appropriate applications of BSGs in classes is offered as well as recommendations to BSG providers. Nevertheless, in-depth analyses are required, preferably with larger student population samples, to further explore the insignificant relationship between student perceptions and attitude under nonlinear extended complexity.     

Numerical analysis of coronary artery bypass grafts: An over view

Arterial bypass grafts tend to fail after some years due to the development of intimal thickening (restenosis). Non-uniform hemodynamics following a bypass operation contributes to restenosis and bypass failure can occur due to the focal development of anastomotic intimal hyperplasia. Additionally, surgical injury aggravated by compliance mismatch between the graft and artery has been suggested as an initiating factor for progress of wall thickening along the suture line Vascular grafts that are small in diameter tend to occlude rapidly. Computational fluid dynamics (CFD) methods have been effectively used to simulate the physical and geometrical parameters characterizing the hemodynamics of various arteries and bypass configurations. The effects of such changes on the pressure and flow characteristics as well as the wall shear stress during a cardiac cycle can be simulated. Recently, utilization of fluid and structure interactions have been used to determine fluid flow parameters and structure forces including stress and strains relationships under steady and transient conditions. In parallel to this, experimental diagnostics techniques such as Laser Doppler Anemometry, Particle Image Velocimetry, Doppler Guide wire and Magnetic Resonance Imaging have been used to provide essential information and to validate the numerical results. Moreover, clinical imaging techniques such as magnetic resonance or computed tomography have assisted considerably in gaining a detailed patient-specific picture of the blood flow and structure dynamics. This paper gives a review of recent numerical investigations of various configurations of coronary artery bypass grafts (CABG). In addition, the paper ends with a summary of the findings and the future directions.     

The partial solutions consideration based self-adaptive evolutionary algorithm: A learning structure of neuro-fuzzy networks

Evolutionary computation has become a popular research field due to its global searching ability. Therefore, it raises a challenge to develop an efficient and robustness evolutionary algorithm to not only reduce the evolution process but also increase the chances to meet the global solution. To this end, this study aims to provide a novel evolutionary algorithm named the partial solutions consideration based self-adaptive evolutionary algorithm (PSC-SEA) to address this issue; the proposed algorithm is applied to adjust the parameters of the neuro-fuzzy networks. More specifically, different from the existing evolution algorithms, the partial solutions consideration (PSC) tends to consider both the specializations and complementary relationships of the partial solutions from the complete solution to prevent converging to suboptimal solution. Moreover, a self-adaptive evolutionary algorithm (SEA) is proposed to dynamically adjust the searching space according to the performance. By doing so, the proposed evolutionary algorithm can consider the influence of partial solutions and provide a suitable searching space to increase the chances to meet the global solution. As shown in the results, the proposed evolutionary algorithm obtains better performance and smoother learning curves than other existing evolutionary algorithms. In other words, the proposed evolutionary algorithm can efficient tune the parameters of the neuro-fuzzy networks to meet the global solution. Base on the results, a framework is proposed to build a benchmark for developing the evolutionary algorithms that can not only consider the influence of partial solutions but also provide a suitable searching space.     

Metal-defined polymeric variable optical attenuator

A variable optical attenuator (VOA) based on a metal-defined polymeric optical waveguide has been demonstrated for the first time. The metal film stressor deposited on top of the upper cladding layer not only produces the refractive index change within the core layer, but also acts as a thin-film heater allowing thermal tuning of the optical power within a metal-defined optical waveguide. Fabricated devices exhibit greater than 25 dB of optical attenuation with an applied electrical current of /spl sim/40 mA at 1550-nm wavelength. The switching speed of the VOA exhibits 800 /spl mu/s of rising and 720 /spl mu/s of falling time.     

Comprehensive Study of Emitter-Ledge Thickness of InGaP/GaAs HBTs

A comprehensive study of emitter-ledge thickness of InGaP/GaAs heterojunction bipolar transistors (HBTs) has been undertaken. It is shown that the recombination rate and electron densities are drastically increased near the exposed base surface between the base contact and the emitter ledge. In contrast, the corresponding hole densities are decreased. If the emitter ledge is too thick, current will flow through the undepleted ledge, which increases the emitter-size effect. In contrast, if the emitter ledge is too thin, it may not effectively passivate the surface. Therefore, the thickness of the emitter ledge is a crucial issue and should be carefully considered. It is shown that, from simulated and experimental results, the optimum emitter-ledge thickness of InGaP/GaAs HBT is 100-200 Aring     

A Novel Pt/In0.52Al0.48As Schottky Diode-Type Hydrogen Sensor

On the basis of a Pt/In_0.52Al_0.48As metal-semiconductor structure, a novel hydrogen sensor is fabricated and demonstrated. The studied Pt/In_0.52Al_0.48As Schottky diode-type hydrogen sensor exhibits significant sensing performance including high relative sensitivity ratio of about 2600% (under the 1% H₂/air gas and V_R=-0.5 V at 30 degC), large current variation of 310 muA (under the 1% H₂/air gas and V_R=-5 V at 200 degC), widespread reverse-voltage regime (0~-5 V), stable hydrogen-sensing current-voltage (I-V) curves, and fast transient response time of 1.5 s. The calculated Schottky barrier-height change and series-resistance variation, from the thermionic-emission model and Norde method, are 87.0 meV and 288 Omega, respectively (under the 1% H₂/air gas at 30 degC). The hydrogen concentrations and operating temperatures tested in this letter are in the range of 15 ppm-1% H₂/air and 30 degC-250 degC, respectively. Based on the excellent integration compatibility with InP-based electronic devices, the studied device provides the potentiality in high-performance sensor-array applications     

溅射沉积Cu膜生长的Monte Carlo模拟

在本文中,我们建立了一个较完整的基于动力学晶格蒙特卡罗方法的模拟薄膜生长的三维模型,利用该模型我们研究了溅射沉积条件下粒子的沉积角度、沉积速率以及入射能量对Cu膜生长的影响.模拟结果表明Cu膜表面粗糙度会随沉积角度和沉积速率的增大而增大,而相对密度随之减小.模拟的薄膜的三维形貌显示,在薄膜的表面存在着柱状结构,这与实验是相符的.