DSpace Community: Elektronikos fakultetas / Faculty of ElectronicsElektronikos fakultetas / Faculty of Electronicshttp://dspace.vgtu.lt:80/handle/1/52019-05-19T15:00:26Z2019-05-19T15:00:26ZInfluence of the piezoelectric ringing on the temperature of the beta barium borate crystalSinkevičius, GiedriusBaškys, AlgirdasPaulauskas, Nerijushttp://dspace.vgtu.lt:80/handle/1/37662018-12-13T13:23:18Z2017-12-31T22:00:00ZTitle: Influence of the piezoelectric ringing on the temperature of the beta barium borate crystal
Authors: Sinkevičius, Giedrius; Baškys, Algirdas; Paulauskas, Nerijus
Abstract: The influence of the piezoelectric ringing on the temperature of the beta barium borate Pockels cell crystal has been investigated. The experimental setup for the investigations was developed. The measurements of the Pockels cell crystal contrast ratio and temperature dependences on the applied high voltage pulse frequency for 10 different 3 mm_3 mm_25 mm beta barium borate Pockels cell crystals were performed. The transients of the beta barium borate Pockels cell temperature were measured at various high voltage pulse frequencies. Two parameters were recorded: the contrast ratio and the crystal temperature. The frequencies, at which the temperature increase caused by the piezoelectric ringing occurs, were determined. It has been shown that the contrast ratio of the beta barium borate Pockels cell crystal does not depend on the temperature. Additionally, the investigation of the deuterated potassium dihydrogen phosphate Pockels cell crystal ringing phenomenon was performed. It has been shown that from the point of view of the contrast ratio temperature stability Pockels cells based on the beta barium borate crystals are more preferable.2017-12-31T22:00:00ZApplication of local outlier factor algorithm to detect anomalies in computer networkAuškalnis, JuozasPaulauskas, NerijusBaškys, Algirdashttp://dspace.vgtu.lt:80/handle/1/37262018-09-11T11:32:35Z2017-12-31T22:00:00ZTitle: Application of local outlier factor algorithm to detect anomalies in computer network
Authors: Auškalnis, Juozas; Paulauskas, Nerijus; Baškys, Algirdas
Abstract: Gap between the new attack appearance and signature creation for this attack may be critical. During this time, many computer systems may be affected and valuable resources may be lost. Even after signature creation, many computer systems still stay vulnerable because of bad security practice, i.e. patches and updates are not installed as needed. Therefore, anomaly intrusion detection system (IDS) that is capable to detect new unknown attacks is valuable security tool. This paper analyses the use of Local Outlier Factor (LOF) to detect anomalies in the computer network. The application of the LOF algorithm for the detection of anomalies when only normal network data are used for the model training has been demonstrated. Experimental results of different threshold values influence on the anomaly detection accuracy using NSLKDD dataset is presented.2017-12-31T22:00:00ZDelay systems synthesis using multi-layer perceptron networkPlonis, DariusKatkevičius, AndriusUrbanavičius, VytautasMiniotas, DariusSerackis, ArtūrasGurskas, Antanashttp://dspace.vgtu.lt:80/handle/1/37222018-09-11T07:37:01Z2017-12-31T22:00:00ZTitle: Delay systems synthesis using multi-layer perceptron network
Authors: Plonis, Darius; Katkevičius, Andrius; Urbanavičius, Vytautas; Miniotas, Darius; Serackis, Artūras; Gurskas, Antanas
Abstract: The aim of this paper is to accelerate development and investigation of the delay systems. The computational time for investigation of particular design of delay system may take from several minutes up to several days. To achieve the required constructional parameters of the system, the iterative calculations usually should be repeated many times. In this paper, an artificial neural network is proposed to be used as the universal approximator for solving mathematical problems of delay system investigation instead of usual analytical and numerical techniques. The application of a multi-layer perceptron is proposed for approximation of solution space with discrete estimates, which were initially received by application of numerical techniques. Different structures of the multi-layer perceptron were tested for approximation. The difference between delay systems synthesis, which was estimated using numerical techniques and trained multi-layer perceptron did not exceed 5% for any of the six design parameter values. The execution time for estimating single delay system was reduced from 240 s to 20 ms. Such fast estimation of design parameters enables performing delay system analysis and design in real time, preserving time for structure visualization in 3D or virtual reality environment.2017-12-31T22:00:00ZOn-line approach for fast convolution over sensor networksNavakauskas, DaliusPupeikis, Rimantashttp://dspace.vgtu.lt:80/handle/1/36672018-07-16T09:09:27Z2017-12-31T22:00:00ZTitle: On-line approach for fast convolution over sensor networks
Authors: Navakauskas, Dalius; Pupeikis, Rimantas
Abstract: It is assumed that at some time moment, in wireless sensor networks the new set of current samples of input and system impulse response enter a digital memory replacing the previous samples. It is urgent for each new sample or for a small part of new samples to update a convolution as well. Therefore, a recursive fast convolution algorithm is proposed here to solve a linear filtering problem for a nonstationary system. The calculation operations are reduced because most columns of Fourier code matrices and respective rows of the right-hand side vectors were deleted for equal previous and current samples. An example with the ordinary and modified 8-point Fourier code matrices is presented for a nonstationary linear system. The amounts of operations, necessary for recursive and fast Fourier transform algorithms, are calculated. Results are discussed, and the conclusion is given.2017-12-31T22:00:00Z