Behaviour of polymeric materials in machining

The machining characteristics of a glassy thermoplastic (Polyvinyl Chloride) and a semi-crystalline thermoplastic (High Density Polyethylene) have been studied. Chip formation mechanisms, cutting forces and surface integrity were found to be dependent, on the cutting conditions and tool geometry. Results were explained by considering the different nature of the microstructure. Segmented and discontinuous chips were produced with PVC, and continuous and segmented chips were produced with HDPE. It was observed that surface damage was closely related to the nature of chip formation in these plastics. Chip formation, surface damage and tool wear mechanisms when machining Glass-Fibre-Reinforced-Plastic (GFRP) were also studied. Cutting tools used were High-Speed-Steel (HSS), cemented carbide (P type and K type) and coated carbide (titanium carbide - and triple-coated). Discontinuous chips were always produced when machining GFRP. Sliding contact is present at the tool/chip and tool/work interface. The principal aspects of surface damage include fibre breakage, resin cracking, resin decomposition and fibre/resin interface debonding. Cutting temperature is not high, but excessive heat generates when the flank wear land develops. Coated carbide tools showed the best performance and HSS tools the poorest. The main wear mechanisms are abrasive wear with HSS tools, attrition wear with cemented carbides, and discrete plastic deformation followed by attrition wear with coated carbides

Indexing and Retrieving Photographic Images Using a Combination of Geo-Location and Content-Based Features

This paper presents a novel method that automatically indexes searches for relevant images using a combination of geo-coded information and content-based visual features. Photographic images are labeled with their corresponding GPS (Global Positioning System) coordinates and UTC time (Coordinated Universal Time) information at the moment of capture, which are then utilized to create spatial and temporal indexes for photograph retrieval. Assessing the performance in terms of average precision and F-score with real-world image collections revealed that the proposed approach significantly improved and enhanced the retrieval process compared to searches based on visual content alone. Combining content and context information thus offers a useful and meaningful new approach to searching and managing large image collections

Adsorption and thermal decomposition characteristics of organic contaminants in coal conversion wastewater

Call number: LD2668 .T4 1984 K55Master of Scienc

Adaptive Pilot Signaling in the Uplink of OFDM-Based Wireless Systems

Orthogonal frequency division multiplexing (OFDM) has been considered as one of key transmission technologies for high-speed wireless communication systems. For channel-adaptive transmission of OFDM signal, base stations transmit a common pilot signal in the downlink, but mobile stations transmit individual pilot signal in the uplink. As a consequence, the uplink may suffer from poorer channel estimation accuracy than the downlink. This problem can be alleviated by increasing the pilot signal density. But this reduces the time and frequency resources for the data transmission, deteriorating the actual transmission throughput. In this paper, we propose an adaptive pilot signaling scheme that adjusts the pilot density in response to the change of channel characteristics. Simulation results show that the proposed scheme can remarkably reduce the pilot overhead without performance degradation, compared to conventional schemes