Phase field modeling of the tetragonal-to-monoclinic phase transformation in zirconia

The allotropic phase transformation in zirconia from the tetragonal to monoclinic double lattices is known to occur by a martensitic twinning mechanism which shows a complex dependence on temperature, stress and environment. This paper is concerned with the development of a phase field model which accounts for the main metallurgical mechanisms governing this martensitic transition. The symmetry reduction and orientation relationship between the parent and product phases were simulated using several non-conserved order parameters representing different transformation paths. Inhomogeneous and anisotropic elastic properties were considered to determine the resultant elastic stresses. Governing equations of the tetragonal-to-monoclinic transformation were solved in a finite element framework under a variety of initial and boundary conditions. It was shown that applying different initial conditions, such as seed embryo or random, did not change the twinning patterns or the final volume fractions of the parent and product phases after the relaxation period. On the other hand, enforcing different boundary conditions resulted in completely different twinning patterns and phase volume fractions. The model was able to predict both the “V” shape morphology of twinning and the surface stress relief with “gable roof” patterns, which were observed by transmission electron microscopy and atomic force microscopy to be characteristic of the tetragonal-to-monoclinic transition.     

Effect of Applying Different Distribution Shapes for Velocities and Pressure on Simulation of Curved Open Channels

Most of the computational models of curved open channel flows use the conventional depth averaged De St. Venant equations. De St. Venant equations assume uniform velocity and hydrostatic pressure distributions. They are thus applicable only to cases of meandering rivers and curved open channels where vertical details are not of importance. The two-dimensional vertically averaged and moment equations model, developed by the writers, is used to study the effect of applying different distribution shapes for velocities and pressure on the simulation of curved open channels. Linear and quadratic distribution shapes are proposed for the horizontal velocity components, while a quadratic distribution shape is considered for the vertical velocity. Linear hydrostatic and quadratic nonhydrostatic distribution shapes are proposed for the pressure. The proposed model is applied to problems involved in curved open channels with different degrees of curvature. The implicit Petrov–Galerkin finite element scheme is applied in this study. Computed values for depth averaged longitudinal and transverse velocities across the channel width and vertical profiles of longitudinal and transverse velocities are compared to the observed experimental data. A fairly good agreement is attained. Predictions of overall flow characteristics suggest that the results are not very sensitive to different approximations of the preassumed applied velocity and pressure distribution shapes.     

Autonomous Schemes for Inter-cell Interference Coordination in the Downlink of LTE Systems

Inter-cell interference (ICI) is one of the key challenges that limit the performance of Long Term Evolution and Long Term Evolution Advanced cellular systems. One approach to deal with ICI is through interference avoidance. Unlike static avoidance techniques where a-priori frequency planning and/or explicit inter-cell coordination is used, dynamic avoidance techniques rely on adapting its frequency planning and allocation based on the current state of the network. However, this improvement in performance comes with the cost of an increased complexity due to the coordination and alignments needed among the base stations (eNB) to manage and allocate channels among the users. Accordingly, autonomous ICI coordination techniques are receiving much interest among the various interference avoidance techniques. In this paper, we propose an autonomous self-adaptive scheme (SA, for short) for radio resource management and interference coordination. We then extend the proposed scheme to become self-adaptive power-aware (SAPA) in order to optimize and reduce the transmission power of the eNBs. A key feature in the proposed schemes is that all computations are independent of the number of users and cells in the network. This allows the proposed schemes to adapt to networks of any size and with an arbitrary number of users. Extensive simulation confirms that the proposed SA scheme ensures efficient frequency reuse patterns that lead to significant performance improvements in the throughput of the edge users without affecting other users. Moreover, the SAPA scheme achieves significant improvement in the power efficiency, while maintaining the throughput enhancements achieved by the SA scheme for both center and edge users.     

Prediction of product quality for catalytic hydrocracking of vacuum gas oil

The main objective of this work is to develop a predictive model for predicting the product quality of vacuum gas oil (VGO) hydrocracking process. Experimental data were obtained using a pilot plant hydrocracking catalytic reactor loaded with the same catalyst type used in a local refinery. Two sets of experimental runs were conducted under various operating conditions. The first one consisted of 18 runs and was used for parameter estimation, while the second set consisted of 29 runs and was used for model validation. Distillation curves of the cracked products were obtained using the simulated distillation (SimDist) test. A distribution model based on probability density function was used to develop the predictive model. The distribution model presents the boiling point as a function of the distilled weight fraction. Model parameters were estimated and related to the specific gravity of the cracked product. Model validation results showed that the proposed model is capable of predicting the distillation curves of the hydrocracked products accurately, especially at high operating severity. Simplicity and accuracy of the developed model makes it suitable for online analysis, to estimate the conversion as well as the product distribution of hydrocracking units in refineries.     

Differential geometry of normalized Stokes vector trajectories in anisotropic media

Trajectory of the normalized Stokes vector on the Poincaré sphere corresponding to light propagation in anisotropic tissues with birefringence and biattenuance is derived. Analytic expressions are determined from the Serret-Frenet formulas and derivatives of arc length for five quantities including the tangent, normal, and binormal vectors with curvature and torsion. Depth variation of curvature and torsion of normalized Stokes vector trajectories corresponding to light propagating in rodent tail tendon are given. Use of analytic expressions for depth variation of curvature and torsion of the normalized Stokes vector trajectories on the Poincaré sphere is discussed for analysis of polarization-sensitive optical coherence tomography data recorded from anisotropic biological tissues with birefringence and biattenuance.     

Feasibility analysis of solar photovoltaic array cladding on commercial towers in Doha,Qatar – a case study

Building-integrated photovoltaic (BIPV) technology has become a major area of research due to environ-mental concerns. This article studies the feasibility of cladding high-rise towers in Doha with solar photovoltaic modules. Specifically, the case of the Qatar Financial Centre (QFC) is discussed. The major aim of the work is to evaluate the technical feasibility, economic impact and environmental effects of using photovoltaic panels on commercial towers in Qatar. Experimental data on solar irradiance and the effect of shading on the QFC Tower are presented. Numerical calculations are done using solar pathfinder software. The studies show that, although there is a significant amount of saving in CO₂ emission by using BIPV on towers in Doha, the payback period is still very long due to the cheaper cost of grid electricity in Qatar and poor conversion efficiency of PV panels. The complete system layout is presented and viable solutions are investigated.     

Optimizing complexity in Benes-type WDM switching networks

In this paper, we propose a new Benes-type wavelength division multiplexing (WDM) optical network with space-wavelength switching capability. Intuitively, adding wavelength switching capability to space Benes networks requires the use of additional hardware components (i.e., wavelength converters). However, in this paper, we show that a Benes network with full-permutation capability in both space and wavelength domains can be designed using a smaller number of hardware components but the same number of stages as that in a space-only Benes network. In addition, wavelength conversion in the proposed network occurs only between two pre-defined wavelengths, eliminating the need for any expensive wide-range wavelength converters. The proposed Benes network is based on the newly proposed concept of wavelength-exchangeable permutation networks. Wavelength-exchangeable networks implement single-step space and wavelength switching and hence reduces the number of hardware components. We show that, such wavelength-exchangeable networks possess some interesting properties that can be used for designing routing algorithms to improve signal quality.

用于声表面波滤波器频响旁瓣抑制的修正汉明窗技术

本文提出了一种新技术,可以提高SAW滤波器频响的旁瓣抑制,同传统的标准加权归一化方法相比有三倍的改善。这一技术可以增加3dB带宽,SAW滤波器的输入叉指换能器（IDT）等值加权,而输出叉指换能器具有修正的汉明窗结构。     

两种提高IEEE802.11b WLAN 物理层数据传输速率的编码技术

本文提出两种将IEEE802.11bWLAN物理层数据速率提高到16.5Mbps的编码和译码方法。这两个方案都继续采用原IEEE802.11b中对于5.5和11Mbps速率所采用的CCK编码方法。两个方案的编码过程变化不大，第一方案的译码还是采用对5.5和11Mbps数据率所使用的快速WALSH变换（FWT），第二个方案的译码被修改成适合16.5Mbps数据率的快速WALSH变换（FWT）。最后通过仿真比较了这两个方案在无多径干扰的AWGN信道上的性能，结果表明第二个方案优于第一个。