Flow and heat transfer in the axisymmetric boundary layer over a circular cylinder

The problem of laminar boundary-layer flow and heat transfer over a long thin cylinder in uniform flow has been analyzed. Solutions are obtained for small as well as large values of the curvature parameter. Solutions valid for small values of curvature are extended to apply to in ermediate values of curvature as well. This is done by casting the expressions into fractions. Finally, these fractions are joined with the asymptotic solution to produce heat-transfer and skin friction results for all values of the curvature parameter. The shapes of the velocity and temperature profiles are given graphically.     

Investigation of cake deposition on various parts of the surface of microfiltration membrane due to fouling

The accumulation of deposited layer on membrane surface in cross-flow microfiltration was investigated. This study provides a basis for elucidation of the membrane segments with superior tendency for cake deposition due to fouling. A commercially available GVWP membrane was fouled with a colored (blue indigo suspension in water) feed. The deposition pattern or fouling tendency was obtained using a digital camera, scanning electron microscope (SEM) and image analysis. The effects of feed concentration, transmembrane pressure and cross-flow velocity on cake deposition were investigated. In the early stages of the filtration trials, cake deposition was increased from the commencement portion (feed inlet) towards the furthermost part (concentrate outlet) of the membrane surface. However, at the completion of filtration, no pronounced difference was realized between cake deposition in the median and end parts of the membrane. Computational fluid dynamics (CFD) modeling of the membrane was carried out to predict the fouling behavior in various segments of the membrane at different operating conditions. The results of CFD modeling are in acceptable agreement with the experimental data. Accomplishment of the membrane sections with higher tendency for accumulation of foulants may provide a basis for manipulation of conditions to diminish the buildup of fouling deposition in the proposed segments. This results in lower cake deposition on vital parts to minimize the overall fouling.     

Low-energy motion estimation architecture using quadrant-based multi-octagon (QBMO) algorithm

The H.264 video-coding standard is a great improvement on its predecessor in that it is able to save 50 % of the bit-rate while maintaining the same quality as MPEG-4. However, its high computational complexity means the standard consumes large amounts of energy to process a video sequence, especially during motion estimation (ME) searches. To overcome this problem, a low-energy ME architecture is proposed in this paper that utilizes a quadrant-based multi-octagon search algorithm as one of its fast-search motion-estimation techniques. The proposed architecture is able to reduce the clock cycle needed to perform the search by 42 % compared to the original conventional algorithm. This clock cycle reduction reduces energy consumption by up to 43 %.     

A triangular MIMO array antenna with a double negative metamaterial superstrate to enhance bandwidth and gain

Multiple‐input‐multiple‐output (MIMO) array antenna integrated with the double negative metamaterial superstrate is presented. The triangular metamaterial unit cell is designed by combining two triangular elements positioned in complementary on the same plane at different sizes. Such design with more gaps is used to excite rooms for more capacitance effects to shift the resonance frequency thus enlarging the bandwidth of the MIMO antenna. The unit cell is arranged in 7 × 7 periodic array created a superstrate metamaterial plane where the C_stray exists in parallel between the two consecutive cells. It is found that the existence of C_stray and gaps for each unit cells significantly influenced the bandwidth of the MIMO antenna. The higher value of the capacitance will lead to the negativity of permittivity. The superstrate plane is then located on top of the 4 × 2 MIMO with a gap of 5 mm. The integration resulted in improving the bandwidth to 12.45% (5.65‐6.4GHz) compared to only 3.49% bandwidth (5.91‐6.12GHz) of the MIMO antenna itself. Moreover, the negative permeability characteristic is created by a strong magnetic field between the complementary unit cells to have 14.05‐dBi peak gain. Besides that, the proposed antenna managed to minimize the mutual coupling and improve the mean effective gain, envelope correlation coefficient, and multiplexing efficiency.     

A popularity-based query scheme in P2P networks using adaptive gossip sampling

As P2P networks, such as many forms of social networking have been rapidly growing, numerous efforts have been made to improve the efficiency of the search operation especially in terms of response time and hit ratio. To this end, popularity-based schemes have recently attracted attention aimed at increasing search efficiency using content popularity ranking; however, these methods suffer from high cost and overhead, or inappropriate level of accuracy in specifying the popularity. In this paper, we propose an adaptive sampling scheme to make a tradeoff between cost and accuracy. This scheme relies on exchanging File Index Table (FIT) between peers in a local neighborhood using a Gossip Exchange Method (GEM). The proposed Hybrid Adaptive Search According to Gossip Exchange Method (HAS-A-GEM) is based on smart unstructured peer to peer overlays. We apply a hybrid overlay that efficiently combines topology-aware and interest-based links instead of random or DHT invoked connections. An analytical model as well as a simulation framework is developed to illustrate the performance of this scheme. The effectiveness of the proposed scheme is demonstrated under various conditions. Simulation results reveal that HAS-A-GEM performs well for large-scale networks, exploiting local content popularity when each local area contains enough number of peers.     

Crack incubation in shot peened AA7050 and mechanism for fatigue enhancement

Shot peening is a dynamic cold‐working process involving the impingement of peening media onto a substrate surface. Shot peening is commonly used as a surface treatment technique within the aerospace industry during manufacturing to improve fatigue performance of structural components. The compressive residual stress induced during shot peening results in fatigue crack growth retardation, improving the performance of shot‐peened components. However, shot peening is a compromise between the benefit of inducing a compressive residual stress and causing detrimental surface damage. Because of the relatively soft nature of AA7050‐T7451, shot peening can result in cracking of the constituent precipitate particles, creating an initial damage state. The aim of this paper is to understand the balance and fundamentals of these competing phenomena through a comparative study throughout the fatigue lifecycle of baseline versus shot‐peened AA7050‐T7451. Microstructure and surface topology characterization and comparison of the baseline and shot‐peened AA7050‐T7451 has been performed using scanning electron microscopy, electron backscatter diffraction, energy dispersive spectroscopy, and optical profilometry techniques. A residual stress analysis through interrupted fatigue of the baseline and shot‐peened AA7050‐T7451 was completed using a combination of X‐ray diffraction and nanoindentation. The fatigue life performance of the baseline versus shot‐peened material has been evaluated, including crack initiation and propagation. Subsurface particles crack upon shot peening but did not incubate into the matrix during fatigue loading, presumably due to the compressive residual stress field. In the baseline samples, the particles were initially intact, but upon fatigue loading, crack nucleation was observed in the particles, and these cracks incubated into the matrix. In damage tolerant analysis, an initial defect size is needed for lifetime assessment, which is often difficult to determine, leading to overly conservative evaluations. This work provides a critical assessment of the mechanism for shot peening enhancement for fatigue performance and quantifies how incubation of a short crack is inhibited from an initially cracked particle into the matrix within a residual stress field.     

Review of technologies for oil and gas produced water treatment

Produced water is the largest waste stream generated in oil and gas industries. It is a mixture of different organic and inorganic compounds. Due to the increasing volume of waste all over the world in the current decade, the outcome and effect of discharging produced water on the environment has lately become a significant issue of environmental concern. Produced water is conventionally treated through different physical, chemical, and biological methods. In offshore platforms because of space constraints, compact physical and chemical systems are used. However, current technologies cannot remove small-suspended oil particles and dissolved elements. Besides, many chemical treatments, whose initial and/or running cost are high and produce hazardous sludge. In onshore facilities, biological pretreatment of oily wastewater can be a cost-effective and environmental friendly method. As high salt concentration and variations of influent characteristics have direct influence on the turbidity of the effluent, it is appropriate to incorporate a physical treatment, e.g., membrane to refine the final effluent. For these reasons, major research efforts in the future could focus on the optimization of current technologies and use of combined physico-chemical and/or biological treatment of produced water in order to comply with reuse and discharge limits.     

反应磁控溅射沉积纳米多孔BiVO4薄膜光催化剂:总压力和基底的影响

使用脉冲直流电源、金属Bi和V靶材,在氩气和氧气气氛保护下,通过反应磁控溅射法在不同基板上沉积纳米多孔BiVO4薄膜,然后在空气中进行后退火处理,形成具有光敏性的单斜白钨矿晶体.研究总压力和基底对薄膜晶体结构、形貌、显微组织、光学和光催化性能的影响.结果表明,在石英玻璃基底上沉积的单斜白钨矿结构于250℃开始结晶,薄膜...