The Characteristic Parameters of Ni/<Emphasis Type="Italic">n</Emphasis>-6H-SiC Devices Over a Wide Measurement Temperature Range

Ni/n-type 6H-SiC/Ni Schottky barrier diodes (SBDs) have been prepared by the DC magnetron sputtering deposition technique. Their current-voltage characteristics (I-V) have been measured in the measurement temperature range of 40-400 K with steps of 20 K under dark conditions. The barrier height (BH) values from the temperature-dependent forward and reverse bias I-V characteristics by different methods coincide with each other which indicates the elimination of the polarity between the Si and C ions. The ideality factor value remains almost unchanged in the 160-400 K range, and below 160 K, it has the values of 1.57 at 140 K, and 3.82 at 60 K. The BH has the values of 0.79 eV at 400 K, and 0.71 eV at 300 K. The decrease in the BH is due to the fact that the current will preferentially flow through the lowest BH with decreasing temperature due to barrier inhomogeneity. The value of 0.71 eV at 300 K is in close agreement with the values of 0.65 and 0.83 eV reported from the forward bias I-V characteristics for the Ni /n-type 6H-SiC in the literature. Thus, it has been concluded that the reduced barrier devices are promising for applications in devices operating at cryogenic temperatures as infrared detectors, sensors in thermal imaging and small signal zero-bias rectifiers and microwave mixers.     

Nonlinear interactive analysis of cooling tower–foundation–soil interaction under unsymmetrical wind load

This paper deals with physical and material modelling of a cooling tower–foundation–soil system. The physical modelling has been carried out using solid 20-noded isoparametric element to model the cooling tower, annular raft foundation and soil media. The cooling tower–foundation–soil system was analysed under vertical and lateral load generated due to self-weight and wind loads. The soil nonlinearity has been taken into consideration using hyperbolic nonlinear elastic constitutive law. The response of the structure has been investigated with respect to displacement and stresses. Moreover, an attempt has been made to study the effect of the linear and nonlinear interactive analyses compared with conventional analysis. It was seen that the interactive analysis of the cooling tower–foundation–soil media plays a major role in releasing the stresses in the cooling tower, particularly at the bottom ring beam.     

Seasonal variations of disinfection by-product precursors profile and their removal through surface water treatment plants

A sampling program has been undertaken to investigate the variations of disinfection by-products (DBPs) formation and nature and fate of natural organic matter (NOM) through water treatment plants in Istanbul. Specific focus has been given to the effect seasonal changes on the formation of DBPs and organic precursors levels. Water samples were collected from the three reservoirs inlet and within three major water treatment plants of Istanbul, Turkey. Changes in the dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV(254)), specific ultraviolet absorbance (SUVA), trihalomethane formation potential (THMFP), and haloacetic acids formation potential (HAAFP) were measured for both the treated and raw water samples. The variations of THM and HAA concentrations within treatment processes were monitored and also successfully assessed. The reactivity of the organic matter changed throughout the year with the lowest reactivity (THMFP and HAAFP) in winter, increasing in spring and reaching a maximum in fall season. This corresponded to the water being easier to treat in fall and an increase in the proportion of hydrophobic content. Understanding the seasonal changes in organic matter character and their reactivity with treatment chemicals should lead to a better optimization of the treatment processes and a more consistent water quality.     

Analysis of reinforced concrete coupled shear wall structures

The ultimate strength analysis of reinforced concrete coupled shear walls with one or two bands of openings requires a two‐stage approach. In the first stage, the analysis of the coupling beams is carried out. This is followed by the analysis of the complete wall in the second stage. A simple approach based on the ‘total moment concept’ for the analysis of coupled shear walls with one or two bands of openings is presented. Experimental results supporting the predictions of the mode of failure and ultimate strength is also presented. This study updates previous research and enhances further understanding of the behaviour of reinforced concrete shear wall structures at ultimate limit states of loading. Copyright © 1999 John Wiley & Sons, Ltd.     

Evaluation of the performance of a ground-source heat-pump system with series GHE (ground heat exchanger) in the cold climate region

Ground-source heat-pump systems provide a new and clean way of heating buildings in the world. They make use of renewable energy stored in the ground, providing one of the most energy-efficient ways of heating buildings. Consumption costs are lowered through the use of free energy from the environment, and the dependence on fossil fuels simultaneously reduces. The aim of this study is to evaluate the performance of vertical ground-source heat-pump system for climatic condition of Erzurum having cold climate in Turkey. For this purpose, an experimental set-up was constructed. The experimental apparatus consisted of a series GHE (ground heat exchanger), a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement equipments. In this study, the performance of the system was experimentally investigated. The experimental results were obtained from October to May for the months of heating season of 2008–2009. The experimental results indicate that the average heat-pump COP and overall system’s COPS values are approximately 3.0 and 2.6 in the coldest months of heating season. This study also shows that this system could be used for residential heating in the province of Erzurum being a cold climate region of Turkey.     

Lie symmetry analysis and numerical solutions for thermosolutal chemically reacting radiative micropolar flow from an inclined porous surface

Steady, laminar, incompressible thermosolutal natural convection flow of micropolar fluid from an inclined perforated surface with convective boundary conditions is studied. Thermal radiative flux and chemical reaction effects are included to represent phenomena encountered in high-temperature materials synthesis operations. Rosseland's diffusion approximation is used to describe the radiative heat flux in the energy equation. A Lie scaling group transformation is implemented to derive a self-similar form of the partial differential conservation equations. The resulting coupled nonlinear boundary value problem is solved with Runge-Kutta fourth order numerical quadrature (shooting technique). Validation of solutions with an optimized Adomian decomposition method algorithm is included. Verification of the accuracy of shooting is also conducted as a particular case of nonreactive micropolar flow from a vertical permeable surface. The evolution of velocity, angular velocity (microrotation component), temperature, and concentration are examined for a variety of parameters including coupling number, plate inclination angle, suction/injection parameter, radiation-conduction parameter, Biot number, and reaction parameter. Numerical results for steady-state skin friction coefficient, couple stress coefficient, Nusselt number, and Sherwood number are tabulated and discussed. Interesting features of the hydrodynamic, heat and mass transfer characteristics are examined.     

The evaluation of a direct injection diesel engine operating with waste cooking oil biodiesel in point of the environmental and enviroeconomic aspects

In this study, the environmental and enviroeconomic analyzes were implemented to the single-cylinder, four-stroke, direct-injection diesel engine operating with diesel fuel, waste cooking oil biodiesel and their blends (B5, B10, B20, and B30) under different fuel injection pressures (170–220 bars) and engine speeds (1000–3200 rpm) and at full load conditions. The environmental and enviroeconomic analyzes results showed that B20 was the worst fuel at the other fuel injection pressures, while diesel fuel was the worst fuel at the original fuel injection pressure. It was determined that B100 gave the best results among the other fuels the entire engine operating conditions.     

基于超混沌Lorenz系统的自适应异步抗噪声保密通信方案

针对非实时通信对安全性要求高且信道中存在噪声的问题,提出了基于超混沌掩盖调制的自适应异步抗噪声保密通信方案。通信原理是由超混沌Lorenz系统生成四个状态变量的伪随机向量,并通过信号增益将它们调整到同一区间;再由分段线性混沌映射（PWLCM）生成两个向量,用于在四个状态变量之间随机切换选取和确定动态时滞步长,以生成载体信号;然后将预编码后的二进制信息成对掩盖到载体信号中,添加高斯噪声后发送出去。实验结果分析发现最小信号增益和噪声系数的比值稳定在一个小区间[0.08,0.11]内,如果把该比值设置成某个大于该区间上限的值,则比特误码率可达到零,因此接收端可在噪声信道中接收并完美恢复出被掩盖信号。该方案利用超混沌系统的非线性动力学特性,能够在噪声信道中自适应实现异步保密通信,数值仿真验证了其有效性。     

Polydopamine as an intermediate layer for silver and hydroxyapatite immobilisation on metallic biomaterials surface

Hydroxyapatite (HA) coated implant is more susceptible to bacterial infection as the micro-structure surface which is beneficial for osseointegration, could also become a reservoir for bacterial colonisation. The aim of this study was to introduce the antibacterial effect of silver (Ag) to the biomineralised HA by utilising a polydopamine film as an intermediate layer for Ag and HA immobilisation. Sufficient catechol groups in polydopamine were required to bind chemically stainless steel 316 L, Ag and HA elements. Different amounts of Ag nanoparticles were metallised on the polydopamine grafted stainless steel by varying the immersion time in silver nitrate solution from 12 to 24 h. Another polydopamine layer was then formed on the metallised film, followed by surface biomineralisation in 1.5 Simulated Body Fluid (SBF) solution for 3 days. Several characterisation techniques including X-Ray Photoelectron Spectroscopy, Atomic Force Microscopy, Scanning Electron Microscopy and Contact Angle showed that Ag nanoparticles and HA agglomerations were successfully immobilised on the polydopamine film through an element reduction process. The Ag metallisation at 24 h has killed the viable bacteria with 97.88% of bactericidal ratio. The Ag was ionised up to 7 days which is crucial to prevent bacterial infection during the first stage of implant restoration. The aged functionalised films were considered stable due to less alteration of its chemical composition, surface roughness and wettability properties. The ability of the functionalised film to coat complex and micro scale metal make it suitable for dental and orthopaedic implants application.     

Substrate Temperature Dependent Surface Morphology and Photoluminescence of Germanium Quantum Dots Grown by Radio Frequency Magnetron Sputtering

The visible luminescence from Ge nanoparticles and nanocrystallites has generated interest due to the feasibility of tuning band gap by controlling the sizes. Germanium (Ge) quantum dots (QDs) with average diameter ~16 to 8 nm are synthesized by radio frequency magnetron sputtering under different growth conditions. These QDs with narrow size distribution and high density, characterized using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) are obtained under the optimal growth conditions of 400 °C substrate temperature, 100 W radio frequency powers and 10 Sccm Argon flow. The possibility of surface passivation and configuration of these dots are confirmed by elemental energy dispersive X-ray (EDX) analysis. The room temperature strong visible photoluminescence (PL) from such QDs suggests their potential application in optoelectronics. The sample grown at 400 °C in particular, shows three PL peaks at around ~2.95 eV, 3.34 eV and 4.36 eV attributed to the interaction between Ge, GeO_x manifesting the possibility of the formation of core-shell structures. A red shift of ~0.11 eV in the PL peak is observed with decreasing substrate temperature. We assert that our easy and economic method is suitable for the large-scale production of Ge QDs useful in optoelectronic devices.