BUILDING USER TASK SPACE BY MINING TEMPORALLY PROXIMATE DESKTOP ACTIONS

Awareness of the user's current context, that is, the task the user resides in, can allow for various ways of supporting their work. In this article we present a novel approach for mining user's regular tasks on the basis of temporal proximity of users’ desktop actions without user intervention in a completely automatic, unobtrusive, and unsupervised manner. The proposed method is based on time-based clustering of a user's desktop actions and, in contrast to previous approaches, it does not enforce fixed time constraints on the mined actions, and typical transition times, when they exist, emerge from the logged activity data for that specific user. The performance of our technique was evaluated on a large data set of 724 days of desktop work by five knowledge workers. The results showed that our approach performed very well and was able to cluster those temporally proximate user actions that commonly used fix time window techniques fail to deal with. Notably, the main improvement is in the recall of the tasks, where our approach recalled 10.18% more actions than the predefined time window technique.     

Improving the performance of Crumb Rubber bitumen by means of Poly Phosphoric Acid (PPA) and Vestenamer additives

Paralleled to the numerous researches on Crumb Rubber (CR) modified bitumen, some limited work-studies have also been implemented on the effects of specific chemical modifiers, such as Poly Phosphoric Acid (PPA) and Vestenamer, on the performance of bitumen. The main difference between present research and previous ones is simultaneous evaluation of these additives on bitumen performance grade. In this research, five samples of modified bitumen were prepared using PG58-22, PPA, Vestenamer, and various CR percentages. The samples were classified according to the superpave performance grading system. The results indicate that these modifiers have significantly improved the performance of bitumen.     

In vitro bioactivity and biocompatibility of lithium substituted 45S5 bioglass

In this study, different concentrations of Li₂O (0–12 wt.%) were substituted for Na₂O in 45S5 bioglass® and the effect of these substitutions on both in vitro apatite formation ability and osteoblastic cell responses was studied. For these purposes, the structural and topographical properties of the glasses were studied using, XRD, FTIR, SEM/EDXA and AFM techniques, before and after storing in simulated body fluid for different time intervals. Additionally, the proliferation rate and activity of newborn rat calvaria-derived osteoblastic cells on different samples were examined by using dimethylthiazol diphenyl tetrazolium bromide (MTT) and alkaline phosphatase (ALP) assessment methods. From XRD and FTIR data, it was found that poor crystalline carbonated nanoapatite phase was formed on the surface of glasses with maximum concentration of Li or without Li, while at low substitutions an inhibition of apatite formation was observed. The apatite layer formed on the surfaces of the glasses had similar morphology, flakes which tightly entangled to others. All samples had the same surface roughness before soaking but different values after that. It was found that both proliferation rate and alkaline phosphatase activity of the cells cultured on Li-substituted glasses were higher than those of Li-free sample in a dose-dependent manner. The results suggest that lithia-modified glasses may be successfully used as bone defect filler even with more effectiveness than 45S5 bioglass®.     

Range-only measurements based target following for wheeled mobile robots

We consider the problem of navigation and guidance of a wheeled mobile robot towards a maneuvering target based on the measurements concerning only the distance from the robot to the target. We propose a sliding mode controller that drives the robot to the predefined distance from the target and makes the robot follow the target at this distance. Mathematically rigorous proof of convergence and stability of the proposed guidance law is presented. Simulation results confirm the applicability and performance of the proposed guidance approach.     

Tool point dynamics prediction by a three-component model utilizing distributed joint interfaces

In machine dynamics the tool point frequency response functions (FRFs) are employed to predict the stable machining conditions. In this paper, a combined analytical–experimental substructuring procedure is proposed to determine the tool point FRFs for different holder–tool configurations. The method employs the measured spindle-machine FRFs and analytical models of the tool and the holder to predict the tool tip FRFs for different sets of tools and holders mounted on the machine spindle without the need for repeated experimental measurements. Distributed joint interfaces are used to couple the three-component model of the machine. The machine tool tip FRFs with different tool–holder combinations are obtained assuming the clamping conditions at joint interfaces remain unchanged. An experimental case study is provided to demonstrate the applicability of the proposed method in dynamic modeling of machine tool.     

Tuning fuzzy PD and PI controllers using reinforcement learning

In this paper, we propose a new auto-tuning fuzzy PD and PI controllers using reinforcement Q-learning (QL) algorithm for SISO (single-input single-output) and TITO (two-input two-output) systems. We first, investigate the design parameters and settings of a typical class of Fuzzy PD (FPD) and Fuzzy PI (FPI) controllers: zero-order Takagi–Sugeno controllers with equidistant triangular membership functions for inputs, equidistant singleton membership functions for output, Larsen’s implication method, and average sum defuzzification method. Secondly, the analytical structures of these typical fuzzy PD and PI controllers are compared to their classical counterpart PD and PI controllers. Finally, the effectiveness of the proposed method is proven through simulation examples.     

Towards the performance evaluation of 4th generation wireless communication standards: LTE versus Mobile WiMAX

Advances in wireless communication protocols and networking toward support of the next generation of mobile and radio broadband technologies have contributed to a strong competition among various telecommunication standards in particular Long Term Evolution (LTE) and Mobile Worldwide Interoperability for Microwave Access (WiMAX). In this paper, we provide an in‐depth comparison analysis of LTE and Mobile WiMAX at the physical (PHY) layer by studying the most similar PHY configuration scenarios for these two technologies. Our study includes a throughput analysis of downlink (DL) and uplink (UL) transmissions in time division duplex with the least overhead possible and different antenna schemes as well as modulation and code rates. This study also performs an overhead analysis in both protocols to provide a more in‐depth understanding of the PHY layer capacity in various PHY layer configurations. Our simulation results generally show higher performance for LTE in both DL and UL transmission with 7 Mbps in DL and 5 Mbps in UL, when using one antenna port. However, by increasing the number of antennas for multiple‐input/multiple‐output configurations, the results illustrate a reduction in the performance of LTE compared to Mobile WiMAX. This arises from the increase in reference signal overhead in LTE from 4.7% in single‐input/single‐output (SISO) to 14.28% in 4 × 4 multiple‐input/multiple‐output (MIMO). Copyright © 2013 John Wiley & Sons, Ltd.