Band 5, Heft 1

Self-organizing maps are extremely useful in the field of pattern recognition. They become less useful, however, when neurons fail to activate during training. This phenomenon occurs when neurons are initialized in areas of non-input and are far enough away from the input data to never move toward the input. These neurons effectively misrepresent the data set. This results in, among other things, patterns becoming unrecognizable.We introduce an algorithm called No Neuron Left Behind to solve this problem.We show that our algorithm produces a more accurate topological representation of the input space.We also show that no neuron clusters form in areas of noninput and that mapping quality of the SOM increases drastically when our algorithm is implemented. Finally, the running time of NNLB is better or comparable to classic SOM without it.

This paper presents a novel variance of subregions and discrete cosine transform based image-coding scheme. The proposed encoder divides the input image into a number of non-overlapping blocks. The coefficients in each block are then transformed into their spatial frequencies using a discrete cosine transform. Coefficients with the same spatial frequency index at different blocks are put together generating a number of matrices, where each matrix contains coefficients of a particular spatial frequency index. The matrix containing DC coefficients is losslessly coded to preserve its visually important information. Matrices containing high frequency coefficients are coded using a variance of sub-regions based encoding algorithm proposed in this paper. Perceptual weights are used to regulate the threshold value required in the coding process of the high frequency matrices. An extension of the system to the progressive image transmission is also developed. The proposed coding scheme, JPEG and JPEG2000were applied to a number of test images. Results show that the proposed coding scheme outperforms JPEG and JPEG2000 subjectively and objectively at low compression ratios. Results also indicate that the proposed codec decoded images exhibit superior subjective quality at high compression ratios compared to that of JPEG, while offering satisfactory results to that of JPEG2000.

We propose several new heuristics for the twopage book crossing problem, which are based on recent algorithms for the corresponding one-page problem. Especially, the neural network model for edge allocation is combined for the first time with various one-page algorithms. We investigate the performance of the new heuristics by testing them on various benchmark test suites. It is found out that the new heuristics outperform the previously known heuristics and produce good approximations of the planar crossing number for severalwell-known graph families. We conjecture that the optimal two-page drawing of a graph represents the planar drawing of the graph.

Integrating heterogeneous data in distributed databases has been a research issue for many years. In this paper, we discuss some of these problems and propose a solution using a semantic model. This semantic model is built upon the semantic relationships between existing data. Applying these semantics enables us to take into account different dimensions of user queries and find the best possible answer for them. The proposed approach leads us to introducing "a common language that is understandable for all databases". We use such a common language in order to return an effective response to the user’s query, as well as reducing the problems of integration.

The paper presents the exemplary industrial system models from the event-driven simulator up to Approximate network analytical performance evaluation system tool (Anapest). The basic approximations assumed in Anapest are roughly discussed together with the basic network configuration for which the tool was developed. The two basic ways of Anapest validation, i.e. the internal network measuring tool Sitwa and event-driven simulation are depicted. In addition, the major network performance evaluation projects run till now described, together with the basic outcome from Anapest.

Wireless vehicular communication is used to enhance traffic safety and to minimize congestion, thereby leading to increased driving efficiency. A malicious node can transmit an inaccurate message to trigger inevitable situations by pretending to be multiple (other) vehicles. Therefore, it is critical to identify malicious nodes as well as fake messages generated by such nodes, and discard such messages quickly. In a Sybil attack, an attacker participates in the network with multiple forged identities in order to disrupt the fundamental operations of VANET. Sybil attacks are particularly easy to launch in VANETs due to the open and broadcast nature of communication medium. In this paper, we present the implementation of simulated Sybil attack scenario in VANET and its consequences on the performance of the network. We also propose a lightweight, scalable and distributed detection approach based on the difference in movement patterns of Sybil nodes and legitimate nodes. In our approach, each Road Side Unit (RSU) computes, stores and verifies various parameter values including RSS, distance, angle of passing-by vehicles through passive overhearing process to detect Sybil attackers. The combination of different parameters makes our detection approach highly accurate. We validate our results on realistic traces obtained from a multi-agent microscopic traffic simulator (MMTS). Simulation results show the effectiveness of the proposed approach to locate Sybil nodes with a different number of network parameters.

Application composition is an approach to create applications by using software components as building blocks. Applications can be composed ofWeb Services and resources associated with mobile devices, displays and various augmented everyday objects. In this article, we focus on ubiquitous applicationswhich aim at supporting users’ needs and everyday activities. Application composition is particularly suitable for these applications as it proposes to compose ubiquitous applications by choosing the appropriate set of services and resources and their configuration as required by users, their needs and other contexts. This article gives an overview and classifies interactive application composition approaches. These approaches provide the necessary user tools and various user interfaces to enable users themselves to specify their needs and achieve their goals with composed applications. The approaches in this article are analyzed according to the user support provided during the application life-cycle and user involvement during the application composition and execution phases. Furthermore,we look inside the design of user interfaces for visual and non-visual user tools and discuss their advantages and disadvantages. In addition to giving an overview of this research field, our aim is to provide means for describing, classifying and comparing different composition approaches.