A comparative study for estimating software development effort intervals

Software cost/effort estimation is still an open challenge. Many researchers have proposed various methods that usually focus on point estimates. Until today, software cost estimation has been treated as a regression problem. However, in order to prevent overestimates and underestimates, it is more practical to predict the interval of estimations instead of the exact values. In this paper, we propose an approach that converts cost estimation into a classification problem and that classifies new software projects in one of the effort classes, each of which corresponds to an effort interval. Our approach integrates cluster analysis with classification methods. Cluster analysis is used to determine effort intervals while different classification algorithms are used to find corresponding effort classes. The proposed approach is applied to seven public datasets. Our experimental results show that the hit rate obtained for effort estimation are around 90–100%, which is much higher than that obtained by related studies. Furthermore, in terms of point estimation, our results are comparable to those in the literature although a simple mean/median is used for estimation. Finally, the dynamic generation of effort intervals is the most distinctive part of our study, and it results in time and effort gain for project managers through the removal of human intervention.     

Interpretation of MR images using self-organizing maps and knowledge-based expert systems

A new image segmentation system is presented to automatically segment and label brain magnetic resonance (MR) images to show normal and abnormal brain tissues using self-organizing maps (SOM) and knowledge-based expert systems. Elements of a feature vector are formed by image intensities, first-order features, texture features extracted from gray-level co-occurrence matrix and multiscale features. This feature vector is used as an input to the SOM. SOM is used to over segment images and a knowledge-based expert system is used to join and label the segments. Spatial distributions of segments extracted from the SOM are also considered as well as gray level properties. Segments are labeled as background, skull, white matter, gray matter, cerebrospinal fluid (CSF) and suspicious regions.     

Experiment and simulation investigations for effects of flow channel patterns on the PEMFC performance

Experiments and simulations are presented in this paper to investigate the effects of flow channel patterns on the performance of proton exchange membrane fuel cell (PEMFC). The experiments are conducted in the Fuel Cell Center of Yuan Ze University and the simulations are performed by way of a three‐dimensional full‐cell computational fluid dynamics model. The flow channel patterns adopted in this study include the parallel and serpentine flow channels with the single path of uniform depth and four paths of step‐wise depth, respectively. Experimental measurements show that the performance (i.e. cell voltage) of PEMFC with the serpentine flow channel is superior to that with the parallel flow channel, which is precisely captured by the present simulation model. For the parallel flow channel, different depth patterns of flow channel have a strong influence on the PEMFC performance. However, this effect is insignificant for the serpentine flow channel. In addition, the calculated results obtained by the present model show satisfactory agreement with the experimental data for the PEMFC performance under different flow channel patterns. These validations reveal that this simulation model can supplement the useful and localized information for the PEMFC with confidence, which cannot be obtained from the experimental data. Copyright © 2007 John Wiley & Sons, Ltd.     

Resource allocation in cellular networks based on marketing preferences

As the usage of cellular phones increases wireless subscribers demand many advanced networking capabilities, especially multimedia applications with very high Quality of Service (QoS) requirements. The limited availability of radio spectrum enforces Mobile Network Operators (MNOs) to have efficient resource management strategies. The goal is to offer services that satisfy the QoS requirements of individual users while achieving an efficient utilization of network resources. This paper considers a resource allocation strategy for cellular networks to be applied during call initiation, handoff and allocation of mobile base stations. Long-term customer retention becomes a major challenge for MNOs due to severe competition in the telecommunications industry. Therefore the MNOs need to understand the customer demographics as well as the customer spending behavior in telecommunications market. Our proposed model combines the information about the customer demographics and usage behavior once the call is initiated. Our hypothesis is that using customer information together with call information yields an efficient customer-oriented resource management strategy. We have performed simulations with different real-life scenarios. Our results show that our proposed model performs better in terms of revenue increase when compared to the First-Come First-Serve based approach.     

A study on the integration of micro‐reformer and high‐ temperature PEM fuel cell

This study presented an integration platform for a methanol reformer and high‐temperature proton exchange membrane fuel cell (PEMFC). The methanol micro‐reformer was combined with the catalytic reaction section and reforming section, whereas the catalytic reaction section with Pt catalysis maintained the constant temperature environment for a reforming process. SRM reforming results showed that 74 to 74.9% hydrogen and 23.5 to 25.7% of carbon dioxide in the mixture product, and less than 2% of carbon monoxide, was produced. Using the reforming product of low carbon monoxide concentration and the highest methanol conversion rate, a micro reformer link with a fuel cell integration experiment was performed. Results showed a high temperature PEMFC with 3 to 4 W power output under methanol flow rates of 15 ml/hr. Due to the lower hydrogen pressure supplied from the micro reformer, the fuel cell power output may become unstable. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20322     

Effect of gamma irradiation on the properties of tyre cords

Gamma irradiation of high tenacity Nylon 6.6 (Ny 66) and polyester (PET) tyre cords was investigated. The untreated and treated tyre cords with different twist levels were irradiated at different dose rates in air. The effects of irradiation on both Ny 66 and PET cords were not found to be depending on the twist levels of the cords. The changes in the mechanical and thermal properties with absorbed dose at two different dose rates were measured. The mechanical properties were observed to deteriorate with increasing dose for Ny 66 cords, whereas remained almost unchanged for PET cords both in greige and dipped forms. Hot shrinkage value for the greige Ny 66 cords was found to be improved, i.e. decreased. This decrease was much lower for greige PET than Ny 66 cords. It is concluded that PET cord has higher radiation resistance than Ny 66 cord and the effects of high energy irradiation on tyre cords have to be taken into consideration during tyre design if pre-vulcanization with high energy radiation is to be applied.     

Sedimentation of Permeable Floc

Sedimentation is an essential step to dewatering of wet materials. The present work utilized the computerized axial tomography scanner (CAT scan) to probe the sedimentation behavior of suspension with different initial solid concentrations. Not as assumed by traditional Kynch theory, the solid flux was not only a function of local solid fraction, but also of the settling time and the initial concentrations. Hence, the interior structure of floc was explored by the fluorescence in situ hybridization (FISH) and confocal laser scanning microscope (CLSM). Subsequently, the three-dimensional floc model was built up and intrafloc flow fields numerically solved. The area-weighted average pressure drop in the floc and mean flow rates estimated the floc permeability, based on Darcy's law, which were noted to vary along different principal axes and for different flocs. Local structure determines local flow field, hence determining the settling behavior of floc. Floc of large pores with low tortuosity produced easy flow-through paths, giving fast settling. Use of the average properties, such as porosity, cannot describe the sedimentation behavior of permeable flocs.     

Exergetic performance analysis of a PEM fuel cell

In this paper we investigate the effects of thermodynamic irreversibilities on the exergetic performance of proton exchange membrane (PEM) fuel cells as a function of cell operating temperature, pressures of anode and cathode, current density, and membrane thickness. The practical operating conditions are selected to be 3–5 atm for anode and cathode pressures, and 323–353 K for the cell temperatures, respectively. In addition, the membrane thicknesses are chosen as 0.016, 0.018 and 0.02 cm, respectively. Moreover, the current density range of the PEM fuel cell is selected to be 0.01–2.0 A cm^?2. It is concluded that exergy efficiency of PEM fuel cell decreases with a rise in membrane thickness and current density, and increases with a rise of cell operating pressure and with a decrease of current density for the same membrane thickness. Thus, it can be said that, in order to increase the exergetic performance of PEM fuel cell, the lower membrane thickness, the lower current density and the higher cell operating pressure should be selected in case PEM fuel cell is operated at constant cell temperature. Copyright © 2005 John Wiley & Sons, Ltd.