Effect of Superimposed Pulsating Flow on Liquid‐Solid Mass Transfer in Fixed Beds

The liquid‐solid mass transfer behaviour of a fixed bed of cylinders has been studied using the dissolution of copper in acidified dichromate solution under pulsating flow conditions. The bed diameter was 100 mm. The depth of the working section was 95 mm and the length and diameter of the cylinders were 19.1 mm. Variables studied were steady flow superficial liquid velocity, and oscillation amplitude and frequency. Data have been correlated as the Sherwood number in terms of Schmidt number and the cylinder Reynolds numbers for steady and oscillatory flow. The form of the correlation permits comparison with literature data for the limiting cases where either of these Reynolds numbers is zero.     

A design model for circular porous air bearings using the 1D generalized flow method

Although the working principles of porous air bearings have been known for many years, most calculation procedures still involve specialized 3D CFD techniques which are not very useful to design engineers who initially require first-order engineering models for feasibility studies. This paper presents a simple design model for a circular porous air bearing based on well-established 1D generalized flow theory. Understanding porous air bearing mechanics is relatively easy with the proposed design model because it captures the essential physical phenomena governing the airflow. Moreover, the 1D model has a very simple architecture that allows easy design synthesis and requires minimal computational requirements. Comparison with experimental data shows accuracy comparable to specialized 3D techniques.     

Analysis of assisted coupled solar stills

The potential of coupled solar stills as a mean for improving solar distillation yield is investigated. A model for a simple solar still assisted by an external solar collector is presented. The governing coupled heat and momentum balance equations are solved for a quasi-steady-state condition with temperature dependent physical properties. The results show that for coupled stills the fresh water productivity increases as the solar collector area of the assisting device increases. For an ideal system, neglecting the thermal inertia, the yield is linearly dependent upon the solar insolation. The thermal inertia causes a significant drop in the system yield and deviation from linearity. The net efficiency of the coupled system is higher than that of a similar simple still by a value that depends mainly upon the system configuration and independent of the meteorological conditions. Comparison of the analysis with experimental data is satisfactory.     

Design of a negative conductance dielectric resonator oscillator for X-band applications

An X-band tunable microwave low-phase noise planar oscillator employing a novel-fed dielectric resonator (DR) with a single transistor has been investigated and realized. A ZrSnTi oxide composite ceramic-based DR with dielectric permittivity of 95 enclosed in a metallic cavity with an unloaded Q factor of 5,000 at 10 GHz is proposed. The resonant frequency affinity with respect to geometric parameters is established by using the compensation technique based on dual negative conductance feedback, the outputs of which are combined via a Wilkinson power divider (WPD). The feedback parallel-coupled DR oscillator is incorporated into a laminate microwave board using the photolithographic technique. The oscillator includes a pseudomorphic low noise amplifier based on a high-electron-mobility transistor. Hence, the proposed oscillator with mechanic tuning is measured, and the results show that DR resonates at TE _01δ mode with frequency of 10 GHz. The measured phase noise of the oscillator is –81.03 dBc/Hz at a 100 kHz offset.     

A survey and comparative study of QoS aware broadcasting techniques in VANET

Mobile operators currently encounter numerous challenges caused by the centralized architecture of mobile networks. A single mobility anchor placed at the network core maintains the entire mobility and data traffic forwarding in the existing centralized mobility management (CMM) solutions. The CMM approach confronts several issues in scalability, reliability, signaling overhead, and non-optimal routing due to the increasing number of mobile devices and the volume of data traffic. To overcome these issues, a new architectural paradigm called distributed mobility management (DMM) is proposed to flatten the network architecture by moving mobility anchors closer to users and separating the control and data planes at the network edge. Two DMM solutions are developed: partially distributed mobility management (partial-DMM) in which only the data plane is distributed and fully distributed mobility management (full-DMM) where both control and data planes are distributed, which can be potentially applied for future mobile networks. This paper presents a network-based full-DMM scheme that was developed and implemented using NS2 network simulator by removing any dedicated centralized mobility anchor from the architecture. Extensive simulations were conducted to evaluate and compare the performance of the full-DMM model with that of the traditional CMM model. The simulation results show that the full-DMM provides lower end-to-end delay performance than CMM. However, the full-DMM generates higher handover latency and packet loss than CMM at high MN speeds. Moreover, simulation results clearly show the benefits of dynamic mobility activation in the full-DMM model.     

Microwave synthesis of zeolites from Egyptian kaolin: Evaluation of heavy metals removal

Zeolite A and analcime were prepared using microwave method and fully characterized. Both zeolites had high surface area and sharp peak. Both zeolite types were introduced for removal of 100 mg/L of 5 metal ions. The operating conditions were optimized. Adsorption followed pseudo-first-order kinetics and fits for Langmuir, Freundlich, Dubinin–Kaganer–Radushkevich, and Temkin models. Adsorption capacities were in the order Co > V > As > Pb > Ni. Zeolite A was more efficient in metal removal than analcime due to its higher surface area. Zeolite types can be used in efficient metals removal up to more than eight cycles.     

配方对富燃复合推进剂力学性能影响的实验研究（英）

为实验研究推进剂配方对基于端羟基聚丁二烯粘结剂(HTPB)/过氯酸铵氧化剂(AP)/铝粉燃料(Al)的富燃复合推进剂力学性能的影响。综合混合、浇铸和固化影响因素,制备了11种不同推进剂试样10 kg,并在25 ℃下采用Zwick试验机以50 mm·min^-1的速率对标准JANNAF试件进行了测试。结果表明,当粘结剂的含量从74.5%减小到34.5%、以AP和Al替代时,推进剂的应变减小,抗拉强度、杨氏模量和硬度增大。AP的颗粒尺寸和含量对推进剂的力学性能有影响,AP细颗粒可充当了活性的填充物并增强复合推进剂的力学性能,当AP颗粒的平均直径从55.9 μm减小到9 μm时,推进剂的抗拉强度、杨氏模量和硬度增大,应变减小,表明该类富燃复合推进剂力学性能主要受到粘结剂和AP平均颗粒尺寸的影响。     

Transmission behavior improvement of electro‐optic modulators for integrated photonic systems in the present communication technology

This paper has presented the transmission performance evaluation of different electro‐optic modulators (EOM) for ultra high switching speed operations and applications. As well as the optimization design parameters for different EOMs have been investigated, where the effective refractive index plays an essential role in the evaluation of the bandwidth structure. The effects of the operating parameters on the switching, modulating voltage, device performance index, and optical bandwidth are also investigated for different material‐based EOMs, where the transmission bit rate is evaluated by using non‐return‐to‐zero coding transmission technique. As well as lithium niobate, gallium arsenide, and poly methyl metha acrylate polymer EOMs have been developed for extensive use in high speed and high transmission performance optical fiber transmission systems. Copyright © 2013 John Wiley & Sons, Ltd.