光电导及光反射法测量AlGaN薄膜的Al组分

ＡｌＧａＮ／ＧａＮ异质结兰光激光器和发光管近年来得到很大的发展．高速和高功率的ＡｌＧａＮ／ＧａＮ异质结场效应管（ＨＦＥＴ）的研究也得到很大的重视．ＡｌＧａＮ 薄层中的Ａｌ组分是决定此类器件的设计和性能的一个重要参量． 传统的测量组分的方法如ＸＰＳ和Ａｕｇｅｒ等方法需要大型的仪器,而且大多数方法是破坏性的,注意到ＡｌＧａＮ的禁带宽度Ｅｇ和Ａｌ组分有直接的关系,可以通过光学方法先测出Ｅｇ,用下式推算出Ａｌ的组分： Ｅｇ（ＡｌＧａＮ）＝ Ｅｇ（ＧａＮ）（１－ｘ）＋Ｅｇ（ＡｌＮ）ｘ－ｂｘ（１－ｘ）．其中ｘ是…     

有机半导体ADN的DFT理论计算研究

采用密度泛函理论(DFT)方法对9,10-二(2-萘基)蒽(ADN)进行了B3LYP/6-31G水平上的分子结构优化、红外光谱、Raman光谱、紫外-可见光谱、分子前线轨道、Mulliken电荷等理论计算。研究结果表明:理论计算结果与实验数据吻合得较好,对IR、THz、UV-Vis吸收光谱和Raman散射光谱中的特征峰进行了归属,发现ADN在0.1～10 THz波谱范围内有5个明显的吸收峰,分别位于1.08、2.52、4.44、5.64及6.60 THz,其中5.64 THz的吸收是最强的,它是由萘环面外弯曲及蒽环面内摇摆振动产生的。ADN在紫外光波段有三个吸收峰,分别对应于386.34、352.98及352.50nm,其中386.34 nm的紫外吸收峰最强。ADN理论计算能隙值为3.516 eV,比实验值3.2 eV略高。ADN的Mulliken电荷计算表明,所有H原子的Mulliken电荷皆为正电荷,C原子Mulliken电荷与其具体的化学环境相关。     

Study of Low-Temperature Thermocompression Bonding in Ag-In Solder for Packaging Applications

Low-temperature solders have wide applications in integrated circuits and micro-electromechanical systems packaging. In this article, a study on Ag-In solder for chip-to-chip thermocompression bonding was carried out. The resulting joint consists of AgIn₂ and Ag₉In₄ phases, with the latter phase having a melting temperature higher than 400°C. Complete consumption of In solder into a Ag-rich intermetallic compound is achieved by applying a bond pressure of 1.4 MPa at 180°C for 40 min. We also observe that the bonding pressure effect enables a Ag-rich phase to be formed within a shorter bonding duration (10 min) at a higher pressure of 1.6 MPa. Finally, prolonged aging leads to the formation of the final phase of Ag₉In₄ in the bonded joints.     

Polyester composite based on betelnut fibre for tribological applications

A polyester composite based on betelnut fibres was fabricated and its adhesive wear and frictional performance studied using a block on disk machine at different applied loads and sliding distances at 2.8 m/s sliding velocity under dry/wet contact conditions. SEM was used to study worn surface morphology. The results revealed that betelnut fibre reinforced polyester (BFRP) composite had better wear and frictional performance under wet contact condition compared to dry. The wear mechanism of the BFRP composite was predominated by micro and macro-cracks in the polyester regions and debonding of fibres.     

Implementation of Two-Dimensional Polycrystalline Grains in Object Oriented Micromagnetic Framework

In response to the growing need for a more accurate micromagnetic model to understand switching phenomenon in nanoscale magnets, we developed the capability to simulate two-dimensional polycrystalline grains using the Object Oriented Micromagnetic Framework (OOMMF). This addition allows users full flexibility in determining the magnetocrystalline anisotropy and axe in each grain as well as the inter- and intragranular exchange coupling strength.     

THREE-DIMENSIONAL NUMERICAL MODELING OF HEAT AND MASS TRANSFER IN A CERAMIC OXYGEN GENERATOR (COG)

A three-dimensional numerical model has been developed to simulate the conjugate heat transfer and the separation of oxygen from air in a single-cell ceramic oxygen generator (COG). Attention is focussed on the temperature distribution in the brittle ceramic electrolyte as a result of heat generated from electrochemical reactions and the resistance to current flow. Investigations conducted to determine the influence on the thermal behaviour of the electrolyte with the presence of metallic current collectors and gas distributors in the model will also be summarised.     

Analysis of Echoes in Single-Image Random-Dot-Stereograms

Three-dimensional depth information of a surface can be encoded in a two-dimensional image called autostereograms. The encoded surface can be reconstructed from an autostereogram by using the correspondences between pixels in human brains or computer algorithms. However, in some cases, the reconstructed surface is not unique because of echoes. In the presence of echoes, reconstruction of the original surface from the autostereogram cannot be guaranteed since no cue of the original surface is available in autostereograms. In this paper, the causes of echoes are investigated and conditions for echo-free reconstruction are derived. Based on these conditions, autostereogram generation algorithm is revised to guarantee echo-free autostereograms. Besides, the surface reconstruction algorithm is modified such that original surfaces encoded are always reconstructed from echo-free autostereograms.     

Design of a RFID case-based resource management system for warehouse operations

In the past, the selection of resources to execute various warehouse operation services was done solely by experts. In this paper, a RFID-based Resource Management System (RFID-RMS) is designed to help users to select the most suitable resource usage packages for handling warehouse operation orders by retrieving and analysing useful knowledge from a case-based data warehouse for solutions in both time saving and cost effective manner. In addition, a pure integral-linear programming model using a branch and bound algorithm to define the optimum travel distance of forklifts is also developed and embedded in the proposed system. The proposed system, which is suitable for usage in a warehouse operation environment, enhances the effectiveness in formulating resource usage package and managing resource operation by integrating the Radio Frequency Identification (RFID), case-based reasoning (CBR) technologies and the programming model for forklift route optimization. Through applying RFID-RMS in the GENCO Distribution System, a multinational logistics company, the utilization of warehouse resources is expected to be maximized while work efficiency will be greatly enhanced.     

Automatic generation of artistic chinese calligraphy

Chinese calligraphy is among the finest and most important of all Chinese art forms and an inseparable part of Chinese history. Its delicate aesthetic effects are generally considered to be unique among all calligraphic arts. Its subtle power is integral to traditional Chinese painting. A novel intelligent system uses a constraint-based analogous-reasoning process to automatically generate original Chinese calligraphy that meets visually aesthetic requirements. We propose an intelligent system that can automatically create novel, aesthetically appealing Chinese calligraphy from a few training examples of existing calligraphic styles. To demonstrate the proposed methodology's feasibility, we have implemented a prototype system that automatically generates new Chinese calligraphic art from a small training set.     

Low complexity Byzantine-resilient consensus

The application of the tolerance paradigm to security - intrusion tolerance - has been raising a reasonable amount of attention in the dependability and security communities. In this paper we present a novel approach to intrusion tolerance. The idea is to use privileged components - generically designated by wormholes - to support the execution of intrusion-tolerant protocols, often called Byzantine-resilient in the literature.The paper introduces the design of wormhole-aware intrusion-tolerant protocols using a classical distributed systems problem: consensus. The system where the consensus protocol runs is mostly asynchronous and can fail in an arbitrary way, except for the wormhole, which is secure and synchronous. Using the wormhole to execute a few critical steps, the protocol manages to have a low time complexity: in the best case, it runs in two rounds, even if some processes are malicious. The protocol also shows how often theoretical partial synchrony assumptions can be substantiated in practical distributed systems. The paper shows the significance of the TTCB as an engineering paradigm, since the protocol manages to be simple when compared with other protocols in the literature.Published online: 29 October 2004This work was partially supported by the EC, through project IST-1999-11583 (MAFTIA), and by the FCT, through the Large-Scale Informatic Systems Laboratory (LASIGE) and projects POSI/1999/CHS/33996 (DEFEATS) and POSI/CHS/39815/2001 (COPE).