Journal:Informatica
Volume 17, Issue 2 (2006), pp. 199–206
Abstract
This paper presents an iterative autoregressive system parameter estimation algorithm in the presence of white observation noise. The algorithm is based on the parameter estimation bias correction approach. We use high order Yule–Walker equations, sequentially estimate the noise variance, and exploit these estimated variances for the bias correction. The improved performance of the proposed algorithm in the presence of white noise is demonstrated via Monte Carlo experiments.
Journal:Informatica
Volume 17, Issue 2 (2006), pp. 187–198
Abstract
In this paper, a digital watermarking algorithm for copyright protection based on the concept of embed digital watermark and modifying frequency coefficients in discrete wavelet transform (DWT) domain is presented. We embed the watermark into the detail wavelet coefficients of the original image with the use of a key. This key is randomly generated and is used to select the exact locations in the wavelet domain in which to embed the watermark. The corresponding watermark detection algorithm is presented. A new metric that measure the objective quality of the image based on the detected watermark bit is introduced, which the original unmarked image is not required for watermark extraction. The performance of the proposed watermarking algorithm is robust to variety of signal distortions, such a JPEG, image cropping, geometric transformations and noises.
Journal:Informatica
Volume 17, Issue 2 (2006), pp. 177–186
Abstract
This paper presents identity based serial and parallel multisignature schemes using bilinear pairings. Our serial multisignature scheme requires a forced verification at every level to avoid the overlooking of the predecessors' signatures. However, in parallel multisignature scheme the verification of individual signatures is performed by a designated clerk. We show that our schemes are secure against existential forgery under adaptive chosen message attack in the random oracle model.
Journal:Informatica
Volume 17, Issue 2 (2006), pp. 157–176
Abstract
Determination of stress strain state components of butt welded joint with a mild interlayer at elasto-plastic tension is presented in this paper. Function of normal transverse stresses distribution on the thickness of mild interlayer and equations for determination of the stress intensity maximum value in hard metal at elasto-plastic deforming are proposed. The longitudinal stresses of mild and hard metals at elasto-plastic loading are determined from their integral equilibrium condition to mean value of external load by estimating equality of hard and mild metal longitudinal strains on their contact plane. Algorithm of stress strain state components calculation in separate zones of this model is presented. The strength of butt welded joint with a mild interlayer and longitudinal strain distribution at static and cyclic elasto-plastic loading on its surface calculated analytically is verified by the results of experimental investigations.
Journal:Informatica
Volume 17, Issue 1 (2006), pp. 137–150
Abstract
Generally, the task in a distributed system must achieve an agreement. It requires a set of processors to agree on a common value even if some components are corrupted. There are significant studies on this agreement problem in a regularized network environment, such as the Fully Connected, BroadCast and MultiCast Networks. Recently, many large complex networks have emerged and displayed a scale-free feature, which influences the system to reach a common value differently. Unfortunately, existing agreement protocols and results cannot cope with the new network environment and the agreement problem thus needs to be revisited. In this paper, we propose a new agreement protocol to adapt to the scale-free network environment and derive its bound of allowable faulty TMs with two rounds of message exchange. We have proved the correctness of this protocol and analyzed its complexity. It is observed that the scale-free network with the proposed agreement protocol can tolerate more faulty TMs than the networks based on previous studies.
Journal:Informatica
Volume 17, Issue 1 (2006), pp. 125–136
Abstract
New ways to estimate ranges of values of functions from standard and inner interval arithmetic have been proposed. Using the proposed ways ranges of values of mathematical test functions for global optimization and of objective functions for practical global optimization problems have been estimated and compared. Results of the experiments show that it is promising to use proposed balanced interval arithmetic in interval global optimization.
Journal:Informatica
Volume 17, Issue 1 (2006), pp. 111–124
Abstract
This paper investigates a variety of statistical cache-based language models built upon three corpora: English, Lithuanian, and Lithuanian base forms. The impact of the cache size, type of the decay function, including custom corpus derived functions, and interpolation technique (static vs. dynamic) on the perplexity of a language model is studied. The best results are achieved by models consisting of 3 components: standard 3-gram, decaying cache 1-gram and decaying cache 2-gram that are joined together by means of linear interpolation using the technique of dynamic weight update. Such a model led up to 36% and 43% perplexity improvement with respect to the 3-gram baseline for Lithuanian words and Lithuanian word base forms respectively. The best language model of English led up to a 16% perplexity improvement. This suggests that cache-based modeling is of greater utility for the free word order highly inflected languages.
Journal:Informatica
Volume 17, Issue 1 (2006), pp. 95–110
Abstract
An algorithm for scheduling the trajectory of a point object, which moves on a plane surface comprising a set of moving obstacles, is introduced. Different quantitative criteria may be met by the schedule, e.g., the course connecting two individual locations being the shortest in length, the least expensive, the fastest as regard to its duration, etc. A prototype system that implements the algorithm is presented. Several example scenarios are also discussed.
Journal:Informatica
Volume 17, Issue 1 (2006), pp. 85–94
Abstract
In this paper we consider two logics: temporal logic of common knowledge and temporal logic of common belief. These logics involve the discrete time linear temporal logic operators “next” and “until”. In addition the first logic contains an indexed set of unary modal operators “agent i knows”, the second one contains an indexed set of unary modal operators “agent i believes”. Also the first logic contains the modality of common knowledge and the second one contains the modality of common belief. For these logics we present sequent calculi with an analytic cut rule. The soundness and completeness for these calculi are proved.
Journal:Informatica
Volume 17, Issue 1 (2006), pp. 69–84
Abstract
The aim of this paper is to demonstrate that the techniques of Computer Aided Geometric Design such as spatial rational curves and surfaces could be applied to Kinematics, Computer Animation and Robotics. For this purpose we represent a method which utilizes a special class of rational curves called Rational Frenet–Serret (RF) curves for robot trajectory planning. RF curves distinguished by the property that the motion of their Frenet–Serret frame is rational. We describe an algorithm for interpolation of positions by a rational Frenet–Serret motion. Further more we present an algorithm for tracking the constructed RF motion to achieve the desired velocity distribution profile of robot arm.