Antanas Cenys

Hyperchaos in coupled Colpitts oscillators

Abstract The paper suggests a simple solution of building a hyperchaotic oscillator. Two chaotic Colpitts oscillators, either identical or non-identical ones are coupled by means of two linear resistors Rk. The hyperchaotic output signal v(t) is a linear combination, specifically the mean of the individual chaotic signals, v(t)=(v1+v2)/2. The corresponding differential equations have been derived. The results of both, numerical simulations and hardware experiments are presented. The coupling coefficient k∝1/Rk should be small to avoid mutual synchronisation of the individual oscillators. The spectrum of the Lyapunov exponents (LE) have been calculated versus the coefficient k. For weakly coupled oscillators there are two positive LE indicating hyperchaotic behaviour of the overall system.

Very high and ultrahigh frequency hyperchaotic oscillators with delay line

Abstract The paper describes the results of numerical and experimental investigations of very high and ultrahigh frequency Mackey-Glass type hyperchaos oscillators with the ring structure. The oscillators consist of a non-linear unit, a linear amplifier and a transmission line in the feedback loop. Multiple positive Lyapunov exponents confirm hyperchaotic nature of the oscillations.

Synchronising hyperchaos in infinite-dimensional dynamical systems

Abstract Synchronisation of delay dynamical systems exhibiting hyperchaotic behaviour with multiple positive Lyapunov exponents is described. The linear synchronisation via the difference between the variables of the drive and the response systems and the synchronisation employing the drive variable in the non-linear unit of the response system are discussed and compared. A specific example, the Mackey–Glass system is considered in details. The experiment has been performed with an electronic analogue of the Mackey–Glass system.

DISTRIBUTION OF LAMINAR LENGTHS FOR NOISY ON-OFF INTERMITTENCY

Abstract A universal distribution of laminar lengths for the noisy on-off intermittency is obtained analytically. The distribution is well approximated by a power law with an exponent −3 2 for moderate laminar lengths and an exponential law describing fast falloff for large laminar lengths. The shoulder region, observed in previous numerical studies, is described by the same exponential law as the region of fast falloff.

Clustering visually similar web page elements for structured web data extraction

We propose a novel approach for extraction of structured web data called ClustVX. It clusters visually similar web page elements by exploiting their visual formatting and structural features. Clusters are then used to derive extraction rules. The experimental evaluation results of ClustVX system on three publicly available benchmark data sets outperform state-of-the-art structured data extraction systems.

Intermittency in low frequency current oscillations in semi-insulating GaAs

Abstract Spontaneous low frequency current oscillations were observed in semi-insulating crystalline GaAs. If the value of the applied voltage U was increased, a crisis induced intermittency was observed. The time intervals between successive transitions were measured. For values of the control parameter U larger than a critical value two interacting chaotic subattractors were observed. The average time intervals are scaling with the control parameter with a critical exponent very close to −1/2.

Electrical properties of an a-Si/Si(p)/Si(n) heterojunction device

The electrical I-U characteristics of the three-terminal device a-Si/Si(p)/Si(n) have been investigated. The device shows both transistor and switching behaviour depending on the magnitude of the base current. The influence of the base current on the holding and switching voltages has been studied. A model describing this behaviour of the device has been suggested. It is based on the existence of a narrow region adjacent to the a-Si/Si(p) junction, characterized by an extremely high recombination rate of the injected carriers.

Controls-based approach for evaluation of information security standards implementation costs

AbstractAccording to the PricewaterhouseCoopers analysis, the average cost of a single information security and data protections breaches has increased twice during 2015 (Pricewaterhouse Coopers 2015). Amount of organizations who reported serious breach has also risen (from 9% in 2015 to 17% in 2016) (PricewaterhouseCoopers 2016). To achieve their goals criminals are using different techniques starting from Social engineering (phishing, whaling) and finishing with malware execution (such as ransomware) on target machines. Recent attacks (attack on Central Bank of Bangladesh, fraud attack on Mattel CEO and attack on Thailand state-run Government bank ATM) show, that criminals are very well organized, equipped and spend a lot of money and time to prepare their attacks. To protect themselves organizations are required to ensure security in depth principles and implement complex Security solutions, which are able to ensure the needed level of information security in appropriate costs.However, information secu...

Evaluation of High-Speed Bipolar Transistors for Application to Chaotic Colpitts Oscillator

Characteristics of high-speed bipolar junction transistors are considered regarding their application to chaotic HF and UHF Colpitts oscillators. Chaotic domains are investigated in the parameter (current gain β versus threshold frequency f T ) plane. The highest achievable fundamental frequency f * of chaotic oscillations is found to be 10 times less than f T . The influence of the parasitic collector-base and emitter-base capacitances is analysed.

Current pulses and high-frequency oscillations in a-Si/Si(p)/Si(n) heterojunction device

A three-terminal a-Si/Si(p)/Si(n) heterojunction device was found to generate pulses of the collector current with a rise time of approximately 10-7 s and a fall time of approximately 4 ? 10-7 s. The voltage applied to the base (0.8-1.5 V) controlled the pulse repetition rate. When the voltage reaches ~1.0 V, the pulses start to overlap, and the output signal is a high-frequency oscillation (106-107 Hz) of the collector current. A simple mechanism explaining the pulse generation and the high-frequency oscillations has been proposed. It involves the extremely high recombination rate of the injected carriers in the thin a-Si layer of the a-Si/Si(p) interface.