Ageing studies of pineapple leaf fiber–reinforced polyester composites

This experimental study evaluated the water absorption characteristics of pineapple leaf fiber (PALF)–polyester composites of different fiber content. The degree of water absorption was found to increase with fiber loading. The mechanism of diffusion was analyzed and the effect of fiber loading on the sorption kinetics was studied. The diffusion coefficient was calculated and found to increase with fiber content. Studies were also made to correlate water absorption with the cross‐sectional areas of the specimens. The effects of ageing on the tensile properties and dimensional stability of PALF polyester composites were studied under two different ageing conditions. Ageing studies showed a decrease in tensile strength of the composites. The composite specimens subjected to thermal ageing showed only a slight deterioration in strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 503–510, 2004     

Hop count optimal position-based packet routing algorithms for ad hoc wireless networks with a realistic physical Layer

Existing routing and broadcasting protocols for ad hoc networks assume an ideal physical layer model. We apply the log-normal shadow fading model to represent a realistic physical layer and use the probability p(x) for receiving a packet successfully as a function of distance x between two nodes. We define the transmission radius R as the distance at which p(R)=0.5. We propose a medium access control layer protocol, where receiver node acknowledges packet to sender node u times, where u*p(x)/spl ap/1. We derived an approximation for p(x) to reduce computation time. It can be used as the weight in the optimal shortest hop count routing scheme. We then study the optimal packet forwarding distance to minimize the hop count, and show that it is approximately 0.73R (for power attenuation degree 2). A hop count optimal, greedy, localized routing algorithm [referred as ideal hop count routing (IHCR)] for ad hoc wireless networks is then presented. We present another algorithm called expected progress routing with acknowledgment (referred as aEPR) for ad hoc wireless networks. Two variants of aEPR algorithm, namely, aEPR-1 and aEPR-u are also presented. Next, we propose projection progress scheme, and its two variants, 1-Projection and u-Projection. Iterative versions of aEPR and projection progress attempt to improve their performance. We then propose tR-greedy routing scheme, where packet is forwarded to neighbor closest to destination, among neighbors that are within distance tR. All described schemes are implemented, and their performances are evaluated and compared.     

Design guidelines for routing protocols in ad hoc and sensor networks with a realistic physical layer

We present guidelines on how to design network layer protocols when the unit disk graph (UDG) model is replaced by a more realistic physical layer model. Instead of merely using the transmission radius in the UDG model, physical, MAC, and network layers share the information about a bit and/or packet reception probability as a function of distance between nodes. We assume that all nodes use the same transmission power for sending messages, and that a packet is received when all its bits are correctly received. The MAC layer reacts to this probabilistic reception information by adjusting the number of acknowledgments and/or retransmissions. We observe that an optimal route discovery protocol cannot be based on a single retransmission by each node, because such a search may fail to reach the destination or find the optimal path. Next, we discuss that gaining neighbor knowledge information with "hello" packets is not a trivial protocol. We describe localized position-based routing protocols that aim to minimize the expected hop count (in case of hop-by-hop acknowledgments and fixed bit rate) or maximize the probability of delivery (when acknowledgments are not sent). We propose a guideline for the design of greedy position-based routing protocols with known destination locations. The node currently holding the message forwards it to a neighbor (closer to the destination than itself) that minimizes the ratio of cost over progress, where the cost measure depends on the assumptions and metrics used, while the progress measures the difference in distances to the destination. We consider two basic medium access layer approaches, with fixed and variable packet lengths. This article serves as a preliminary contribution toward the development of network layer protocols that match the assumptions and criteria already used in simulators and ultimately in real equipment.     

A pixel-based approach for classification of cardiac single photon emission computed tomography images

In this work, a computer-based algorithm is proposed for the initial interpretation of human cardiac images. Reconstructed single photon emission computed tomography images are used to differentiate between subjects with normal value and abnormal value of ejection fraction. The method analyses pixel intensities that correspond to blood flow in the left ventricular region. The algorithm proceeds through three main stages: the initial stage does a pre-processing task to reduce noise as well as blur in the image. The second stage extracts features from the images. Classification is done in the final stage. The pre-processing stage consists of a de-noising part and a de-blurring part. Novel features are used for classification. Features are extracted as three different sets based on: the pixel intensity distribution in different regions, spatial relationship of pixels and multi-scale image information. Two supervised algorithms are proposed for classification: one algorithm is based on a threshold value computed from the features extracted from the training images and the other algorithm is based on sequential minimal optimization-based support vector machine approach. Experimental studies were performed on real cardiac SPECT images obtained from hospital. The result of classification has been verified by an expert nuclear medicine physician and by the ejection fraction value obtained from quantitative gated SPECT, the most widely used software package for quantifying gated SPECT images.     

PARAMETRIC INFLUENCE AND OPTIMIZATION OF WIRE EDM OF HOT DIE STEEL

Wire-cut Electro Discharge Machining (WEDM) is a special form of conventional EDM process in which the electrode is a continuously moving conductive wire. The present study aims at determining parametric influence and optimum process parameters of Wire-EDM using Taguchi's technique and a Genetic algorithm. The variation of the performance parameters with machining parameters was mathematically modeled by Regression analysis method. The objective functions are defined as Dimensional Error (DE), Surface Roughness (SR) and Volumetric Material Removal Rate (VMRR). Experiments were designed as per Taguchi's L₁₆ Orthogonal Array (OA) wherein Pulse-on duration, Current, Pulse-off duration, Bed-speed and Flushing rate have been considered as the important input parameters. The matrix experiments were conducted for the material Hot Die Steel (HDS) having the thickness of 40 mm. The Heat Affected Zone (HAZ) characteristics of the eroded materials were assessed by Scanning Electron Microscope (SEM) and the microhardness of the material was tested using Vickers microhardness tester. The results of the study reveal that among the machining parameters, it is preferable to go for smaller pulse-off duration for achieving overall good performance. Regarding pulse-on duration, higher values are recommended for error constrained machining with higher MRR and constrained/limited values for attaining good surface texture. Smaller current is suggested for better surface finish/texture control, medium range for error control and high value for MRR. Finally, the validation exercise was performed with the optimum levels of the process parameters. The results confirm the efficiency of the approach employed for optimization of process parameters in this study.     

Reproducibility and validity of oral visual inspection by trained health workers in the detection of oral precancer and cancer

A randomized intervention trial is in progress in Kerala, India, to evaluate the effectiveness of oral visual inspection by trained health workers (HWs) in the prevention of oral cancer. Fourteen health workers with college graduation as the basic qualification were trained in oral visual inspection to identify oral cancers and precancers among the participants of the screening trial and to refer them for further confirmation and management. The aim of the present study was to evaluate the reproducibility and validity of the screening test provided by the health worker against the reference oral visual findings of three physicians. A total of 2069 subjects who had already been examined were re-examined by the health workers and physicians. The sensitivity and the specificity of the oral visual inspection were 94.3% and 99.3% respectively. There was moderate agreement between the findings of the initial and the repeat mouth examinations carried out by the health workers, which were on average 6 months apart. There was almost perfect agreement (kappa = 0.85) between the findings of the health workers and the physicians in identifying the different types of oral precancerous lesions. The findings of our study indicate that it is possible to train resource persons to perform the oral cancer screening test as accurately as doctors, although experience appears to be a crucial component of health workers' accuracy. The efficacy of such an approach to reduce the incidence of and mortality from oral cancer, however, remains to be proven.