Informatica

The paper analyses the problem of aggregation of internal quality characteristics of an information system specification language. It surveys main categories of aggregation operators, their mathematical and behavioural properties and proposes how to aggregate quality characteristics taking into account measurements of all lowest-level characteristics in a proper way. The paper shows that four different kinds of dependencies can occur among characteristics of internal quality and discusses in detail what aggregation techniques are reasonable for each case. It also describes a heuristic for minimisation of possible deviations of measurement results obtained after using a number of different metrics or because of the inaccuracy of used measurement techniques.

Recently, e-commerce becomes widespread; hence electronic department stores come into being. As a result, Chan and Chang proposed a scheme for digital gift certificates in 2002. Because it is hard to estimate the number of the clients of the electronic department stores, reducing the computation complexity of the electronic department stores becomes an important issue. Due to the need, we propose two schemes for digital gift certificates. Our proposed schemes are very practical since the computation load is light. So the schemes can be applied to the terminals with low computation power.

To offer high quality services, when users are increasingly demanding and competition more and more hard, is now a major problem that transportation companies are faced with. So, ensuring a regular traffic needs to identify the randomly occurring disturbances that affect the transportation system and to eliminate or reduce their impacts on the traffic.

Efficient computation of the modular exponentiations is very important and useful for public-key cryptosystems. In this paper, an efficient parallel binary exponentiation algorithm is proposed which based on the Montgomery multiplication algorithm, the signed-digit-folding (SDF) and common-multiplicand-multiplicand (CMM) techniques. By using the CMM technique of computing the common part from two modular multiplications, the same common part in two modular multiplications can be computed once rather twice, we can thus improve the efficiency of the binary exponentiation algorithm by decreasing the number of modular multiplications. By dividing the bit pattern of the minimal-signed-digit recoding exponent into three equal length parts and using the technique of recording the common parts in the folded substrings, the proposed SDF-CMM algorithm can improve the efficiency of the binary algorithm, thus can further decrease the computational complexity of modular exponentiation. Furthermore, by using the proposed parallel SDF-CMM Montgomery binary exponentiation algorithm, on average the total number of single-precision multiplications can be reduced by about 61.3% and 74.1% as compared with Chang-Kuo-Lin's CMM modular exponentiation algorithm and Ha-Moon's CMM Montgomery modular exponentiation algorithm, respectively.

In this paper, we study the fault diagnosis problem for distributed discrete event systems. The model assumes that the system is composed of distributed components that are modeled in labeled Petri nets and interact with each other via sets of common resources (places). Further, a component's own access to a common resource is an observable event. Based on the diagnoser approach proposed by Sampath et al, a distributed fault diagnosis algorithm with communication is presented. The distributed algorithm assumes that the local diagnosis process can exchange messages upon the occurrence of observable events. We prove the distribute diagnosis algorithm is correct in the sense that it recovers the same diagnostic information as the centralized diagnosis algorithm. And then, the OBDD (Ordered Binary Decision Diagrams) is introduced to manage the state explosion problem in state estimation of the system.

Most recent papers about visual cryptography for halftone images are dedicated to get a higher contrast decoded image. However, the hidden visual pattern often blends into the background image and leads to a confused image. In this paper, we propose an improved method for halftone image hiding. By using the proposed method, the background image can be eliminated and the hidden visual pattern can be revealed precisely. Experimental results show that the decoded visual patterns could reveal good visual quality under various kinds of input patterns. Furthermore, better visual quality can be obtained when more halftone images are overlaid.

The paper offers a new way of presenting the structure of a sentence. None of the two widely known methods of representation the syntactic structure of a sentence can be of any avail when applied to the Lithuanian language. Neither the tree, based on the phrase structure principle, nor the tree, suggested by the dependency grammar, do reflect all the syntactic information, which a Lithuanian sentence contains.

This paper relates properties of operators with the well-known concepts of positive realness and passivity properties in dynamic systems and their associate transfer functions. Those concepts together with very close related ones are first examined from a physical point of view. Then, they are related with hyperstability and properties of transfer functions while the hyperstability theorem is revisited and interpreted. Finally, the above concepts are compared to the mathematical concepts of positivity and closely related ones in operator theory in Hilbert spaces.

A modernization of signature scheme published in (Sakalauskas, 2004) is presented. This scheme differs from the prototype by its structure and uses a more general algebraic systems. It has a higher security and shorter key length and is also more computationally effective.

The problem of system input selection, dubbed in the literature as Type I Structure Identification problem, is addressed in this paper using an effective novel method. More specifically, the fuzzy curve technique, introduced by Lin and Cunningham (1995), is extended to an advantageous fuzzy surface technique; the latter is used for fast building a coarse model of the system from a subset of the initial candidate inputs. A simple genetic algorithm, enhanced with a local search operator, is used for finding an optimal subset of necessary and sufficient inputs by considering jointly more than one inputs. Extensive simulation results on both artificial data and real world data have demonstrated comparatively the advantages of the proposed method.