Effect of Al addition on microstructure of AZ91D

Casting is a net shape or near net shape forming process so work-hardening will not be applicable for improving properties of magnesium cast alloys. Grain refinement, solid-solution strengthening, precipitation hardening and specially designed heat treatment are the techniques used to enhance the properties of these alloys. This research focusses on grain refinement of magnesium alloy AZ91D, which is a widely used commercial cast alloy. Recently, Al-B based master alloys have shown potential in grain refining AZ91D. A comparative study of the grain refinement of AZ91D by addition of 0.02wt%B, 0.04wt%B, 0.1wt%B, 0.5wt%B and 1.0wt%B of A1-5B master alloy and equivalent amount of solute element aluminium is described in this paper. Hardness profile of AZ91D alloyed with boron and aluminium is compared

Semi-blind CFO, channel estimation and data detection for ofdm systems over doubly selective channels

Proceedings of the IEEE International Symposium on Circuits and Systems, 2010, p. 1887-1890Semi-blind joint CFO, channel estimation and data detection for OFDM systems over doubly selective channels (DSCs) is investigated in this work. A joint iterative algorithm is developed based on the maximum a posteriori expectation-maximization (MAP-EM) algorithm. In addition, a novel algorithm is also proposed to obtain the initial estimates of CFO and channels. Simulation results show that the performance of the proposed CFO and channel estimators approaches to that of the estimators with full training at high SNRs. Moreover, after convergence, the performance of data detection is close to the ideal case with perfect CFO and channel state information. ©2010 IEEE.published_or_final_versionThe IEEE International Symposium on Circuits and Systems (ISCAS), Paris, France, 30 May-2 June 2010. In Proceedings of ISCAS, 2010, p. 1887-189

A reorganized innovation approach to linear estimation

2004-2005 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Joint channel estimation and data detection for OFDM systems over doubly selective channels

In this paper, a joint channel estimation and data detection algorithm is proposed for OFDM systems under doubly selective channels (DSCs). After representing the DSC using Karhunen-Loève basis expansion model (K-L BEM), the proposed algorithm is developed based on the expectationmaximization (EM) algorithm. Basically, it is an iterative algorithm including two steps at each iteration. In the first step, the unknown coefficients in K-L BEM are first integrated out to obtain a function which only depends on data, and meanwhile, a maximum a posteriori (MAP) channel estimator is obtained. In the second step, data are directly detected by a novel approach based on the function obtained in the first step. Moreover, a Bayesian Cramer-Rao Lower Bound (BCRB) which is valid for any channel estimator is also derived to evaluate the performance of the proposed channel estimator. The effectiveness of the proposed algorithm is finally corroborated by simulation results. ©2009 IEEE.published_or_final_versionThe 20th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2009), Tokyo, Japan. 13-16 September 2009. In Proceedings of the 20th PIMRC, 2009, p. 446-45

Fully-distributed joint clock synchronization and ranging in wireless sensor networks under exponential delays

In this paper, we study the global clock synchro- nization and ranging problem for wireless sensor networks in the presence of unknown exponential delays using the two- way message exchange mechanism. Based on the Alternating Direction Method of Multipliers (ADMM), we propose a fully- distributed synchronization and ranging algorithm which has low communication overhead and computation cost. Simulation results show that the proposed algorithm achieves better accuracy than consensus algorithm, and can always converge to the centralized optimal solution.published_or_final_versio

Superimposed training-based channel estimation and data detection for OFDM amplify-and-forward cooperative systems under high mobility

In this paper, joint channel estimation and data detection in orthogonal frequency division multiplexing (OFDM) amplify-and-forward (AF) cooperative systems under high mobility is investigated. Unlike previous works on cooperative systems in which a number of subcarriers are solely occupied by pilots, partial data-dependent superimposed training (PDDST) is considered here, thus preserving the spectral efficiency. First, a closed-form channel estimator is developed based on the least squares (LS) method with Tikhonov regularization and a corresponding data detection algorithm is proposed using the linear minimum mean square error (LMMSE) criterion. In the derived channel estimator, the unknown data is treated as part of the noise and the resulting data detection may not meet the required performance. To address this issue, an iterative method based on the variational inference approach is derived to improve performance. Simulation results show that the data detection performance of the proposed iterative algorithm initialized by the LMMSE data detector is close to the ideal case with perfect channel state information. © 2006 IEEE.published_or_final_versio

為城市環境設計之微型風力發電機系統

風力發電擁有巨大潛力，可廣泛在許多國家發展以減少化石燃料之使用。傳統的三葉片風力發電機常用於風能密度高的地方，小型風力發電機則專為風量低的地點而設計，例如市區及面積較小的平地等。本項研究專為風速通常較低的都市環境開發一部創新的微型風力發電機。傳統的風力發電機可直接連接到輸電網，這個系統則可連接到小型發電機和蓄電池並主要在設置系统的地方使用。微型風力發電機的優點包括低成本和低切入風速，並可靈活調節大小。這項研究進行了計算流體動力學（CFD）的模擬分析和實驗，以幫助評估設有不同配置的個別微型風力發電機的性能，以及多個微型風力發電機系統的發電特性。關鍵詞：發電，空氣動力學，功率係數。published_or_final_versio

IQ imbalance compensation: A semi-blind method for OFDM systems in fast fading channels

Proceedings of the IEEE Asia-Pacific Conference on Circuits and Systems, 2010, p. 362-365In this paper, an orthogonal frequency division multiplexing (OFDM) system operating in a fast fading environment modeled by a doubly selective channel (DSC) is considered. The paper first reformulates a commonly adopted system model using the generalized complex exponential basis expansion technique. The resulting model enables the IQ imbalance and DSC to be estimated in the time domain with a small number of scattered pilots within an OFDM symbol. A joint estimation and compensation scheme is then proposed which compensates all the inter-carrier interference terms. Simulation results show that the proposed compensation method achieves better symbol error rate performance than previous proposed methods. © 2010 IEEE.published_or_final_versionThe IEEE Asia Pacific Conference on Circuits and Systems (APCCAS'2010), Kuala Lumpur, Malaysia, 6-9 December 2010. in Proceedings of APCCAS'2010, 2010, p. 362-36

Recent development of VUV-based processes for air pollutant degradation

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Micro-wind turbine system in urban environment

Wind power is identified to be of great potential for extensive development in many countries to reduce the fossil fuel based power generation. Conventional three blades wind turbines are commonly used in locations with high wind energy density, while small wind turbines are developed for less windy locations such as urban areas and flat lands. An innovative micro wind turbine was developed to generate power in urban environment where wind speed is usually low. Differing from the traditional wind turbine that can be connected directly to the grid, this system is linked to a small generator and batteries, and mainly used for local applications. The advantage of the micro wind turbine is that, apart from its low cost, it can be propelled by a very low wind speed. Computation fluid dynamics (CFD) simulations have been conducted to help evaluate the performance of a single micro wind turbine.published_or_final_versio