Cyanate Ester-Based Encapsulation Material for High-Temperature Applications

Cyanate ester resin-based composite materials have been proposed as potential encapsulants for high-temperature applications. The objective of this study is to develop a cyanate ester-based encapsulant, which can also serve as a flip-chip underfill as well as for traditional encapsulation. Two different materials, quartz and alumina fillers, have been studied. The impact of shapes and sizes of the fillers on the overall thermomechanical properties has been investigated. The adhesion strengths of the materials to the ceramic substrate, Kovar lid, and silicon die have also been characterized. The modulus of the resin and the shape of the fillers play a pivotal role in minimizing thermal stress, generated by coefficient of thermal expansion mismatches. Smaller filler particles were found to have better adhesion to the cyanate ester resin. The high-temperature performance of the cyanate ester-based encapsulants was evaluated by thermal aging at 300°C for up to 500 h.     

Intelligent Interactive Tutoring Systemfor Engineering Mechanics

Engineering education has traditionally been imparted through the lecture-tutorial-laboratory paradigm. Education technology in the last few years has tried to make teaching more effective by supplementing the chalkboard teaching with audiovisual aids like overhead∕slide projectors and videos. These are, however, passive teaching tools. Recent advancement in computer multimedia has brought in a new teaching medium. Multimedia education has several advantages; most noticeably, the instructions can be interactive and self-paced to meet the needs of each individual student. The writers have developed an Intelligent Interactive Tutoring System for engineering mechanics for the first-year engineering students at the Nanyang Technological University, Singapore. The main objective of this system was to supplement classroom teaching via intelligent interaction with the computer-based tutoring system. This system is designed to be a self-paced virtual tutor with intelligent, user-friendly interactions. It is intended to be different from the many commercially available computerized textbooks. The prototype system was tried out with about 200 students who had earlier failed the course in the first semester and repeated it in the second semester of academic year 1997–1998. The system received good response from the students. The full version was implemented on the Nanyang Technological University Intranet and the Internet for use by the regular class of more than 1,600 students in both academic years 1998–1999 and 1999–2000.     

Selection of representatives for feedback suppression in reliablemulticast protocols

The representative scheme in which a small set of multicast group members are selected as representatives to represent congested areas and hence suppress feedback from other receivers is an effective way of avoiding feedback implosion. Two algorithms used for selecting group members as representatives are further investigated. It is shown through simulation that the algorithm that selects representatives using the loss probability observed at the receivers is more effective in reducing the feedback returned     

Authentication and correction of digital watermarking images

A novel function for image watermarking is introduced. The proposed function gives a restoration/correction capability to image watermarking as well as the detection and localisation of alterations. The basic idea of the proposed watermarking technique is to adopt conventional error control coding techniques for generating a watermark.     

Transient interstitial fluid flow in brain tumors: Effect on drug delivery

The presence of high interstitial pressure within the tumor's center [Baxter, L.T., Jain, R.K., 1989. Transport of fluid and macromolecules in tumors I role of interstitial pressure and convection. Microvascular Research 37, 77-104] poses severe problems to chemotherapy via systemic administration. Removal of the tumor core by surgery and subsequent insertion of drug-carrying polymers in the resection cavity may improve the treatment [Wang, C.H., Li, J., 1998. Three dimensional simulation of IgG delivery to tumors. Chemical Engineering Science 53 (20), 3579-3600]. The operation establishes a favorable pressure gradient towards the center of the tumor and thus creates flow reversal immediately after the operation. The simulation results of the transient flow field of interstitial fluid in the surgical cavity of a brain tumor are presented. The simulation is carried out using a computational fluid dynamics software, Fluent, with the model geometry constructed from magnetic resonance images (MRI) with reference to the Gliadel^® wafers application [Sampath, P., Brem, H., 1998. Implantable slow-release chemotherapeutic polymers for the treatment of malignant brain tumors. Cancer control. Journal of Molecular and Cellular Cardiology 5 (2), 130-137]. The coupled mass and momentum equations are solved for the steady-state solutions of the pressure and velocity distributions at a cut section of a tumor. The steady-state solution thus obtained is then perturbed to compute the characteristic time scale of the variation in the interstitial fluid pressure and velocity in a surgical cavity immediately after surgery. Simulation results show that the flow field reaches an equilibrium state in less than 3 h. The surgery produces a transient enhancement of the drug delivery but the surgery alone is not capable of removing permanently the unfavorable pressure gradient against the delivery of drug to tumor. The presence of post-surgery edema increases the interstitial pressure and fluid velocity, thus causing higher relative toxicity in the surrounding normal tissues. Simulations employing complete 3D structure show qualitatively similar results with 2D simulation and hence the use of a cut section of the tumor for simplified model calculations is validated.     

Antifungal effects of cement mortars with two types of organic antifungal agents

This study is concerned with investigating the antifungal effects of cement mortar with an organic antifungal agent on the Aspergilus niger which might be easily discovered in the interiors and exteriors of buildings. Two types of organic antifungal agents: isothiazoline/cabamate and nitrofuran, were used in this study for the purpose of investigating the antifungal effect of cement mortar with antifungal agent on the A. niger of various fungus which can be easily discovered in the interiors and exteriors of building. In addition to the investigation of the antifungal effect, the experiment of basic physical properties, such as compressive and flexural strengths, and flow test was carried out. Cement mortar with the antifungal agent of isothiazoline/cabamate exhibited the outstanding antifungal effects but the antifungal agent of nitrofuran did not give the antifungal effects to cement mortar. Although there is a very slight decrease in the strength, it is almost equal to that of cement mortar without antifungal agents.     

A collaborative wheelchair system.

This paper describes a novel robotic wheelchair, and reports experiments to evaluate its efficiency and understand how human operators use it. The concept at the heart of the collaborative wheelchair assistant (CWA) is to rely on the user's motion planning skills while assisting the maneuvering with flexible path guidance. The user decides where to go and controls the speed (including start and stop), while the system guides the wheelchair along software-defined guide paths. An intuitive path editor allows the user to avoid dangers or obstacles online and to modify the guide paths at will. By using the human sensory and planning systems, no complex sensor processing or artificial decision system is needed, making the system safe, simple, and low-cost. We investigated the performance of the CWA on its interaction with able-bodied subjects and motion efficiency. The results show that path guidance drastically simplifies the control. Using the CWA, the wheelchair user needs little effort from the first trial, while moving efficiently with a conventional wheelchair requires adaptation.     

Fluorination of carbon fibres in atmospheric plasma

Carbon fibres were successfully fluorinated in atmospheric-pressure plasma. By treating carbon fibres in a chlorodifluoromethane containing nitrogen atmospheric-pressure plasma, we were able to introduce fluorine groups to the surface of the carbon fibres. XPS confirms the presence of fluorine moieties on the carbon fibre surfaces. Measured contact angles confirm a significantly increased hydrophobicity of the treated carbon fibres. Zeta-potential measurements showed that acidic character of carbon fibres was increased. Although exposure of the carbon fibres to the atmospheric plasma jet causes surface sputtering; XRD analysis, Raman spectroscopy and conductivity measurements performed on the treated fibres show that atmospheric plasma treatment only modifies the surface of the carbon fibres without affecting the bulk properties.     

Damping margins of interval polynomials

The zero locations of interval polynomials are examined. In particular, it is shown that a family of interval polynomials will have zeros only in the left sector if the real and imaginary parts of four specially constructed complex polynomials have an interlacing real zero property. This is significant for the analysis of uncertain systems, as the computation cost associated with checking the zero locations of interval polynomials will be greatly reduced. The results presented can be readily extended to more general stability regions where the real and imaginary parts of the polar plot are polynomial functions