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2. Pacemaker-driven stochastic resonance on diffusive and complex networks of bistable oscillatorsMatjaž Perc, Marko Gosak, 2008, izvirni znanstveni članek Opis: We study the phenomenon of stochastic resonance on diffusive, small-world and scale-free networks consisting of bistable overdamped oscillators. Important thereby is the fact that the external subthreshold periodic forcing is introduced only to a single oscillator of the network. Hence, the forcing acts as a pacemaker trying to impose its rhythm on the whole network through the unit to which it is introduced. Without the addition of additive spatiotemporal noise, however, the whole network, including the unit that is directly exposed to the pacemaker, remains trapped forever in one of the two stable steady states of the local dynamics. We show that the correlation between the frequency of subthreshold pacemaker activity and the response of the network is resonantly dependent on the intensity of additive noise. The reported pacemaker-driven stochastic resonance depends most significantly on the coupling strength and the underlying network structure. Namely, the outreach of the pacemaker obeys the classic diffusion law in the case of nearest-neighbor interactions, thus being proportional to the square root of the coupling strength, whereas it becomes superdiffusive by an appropriate small-world or scale-free topology of the interaction network. In particular, the scale-free topology is identified as being optimal for the dissemination of localized rhythmic activity across the whole network. Also, we show that the ratio between the clustering coefficient and the characteristic path length is the crucial quantity defining the ability of a small-world network to facilitate the outreach of the pacemaker-emitted subthreshold rhythm. We additionally confirm these findings by using the FitzHugh-Nagumo excitable system as an alternative to the bistable overdamped oscillator. Ključne besede: noise, bistable dynamics, stochastic simulations, complex networks Objavljeno v DKUM: 03.07.2017; Ogledov: 1319; Prenosov: 429 Celotno besedilo (2,18 MB) Gradivo ima več datotek! Več... |
3. Synchronous bursts on scale-free neuronal networks with attractive and repulsive couplingQingyun Wang, Guanrong Chen, Matjaž Perc, 2011, izvirni znanstveni članek Opis: This paper investigates the dependence of synchronization transitions of bursting oscillations on the information transmission delay over scale-free neuronal networks with attractive and repulsive coupling. It is shown that for both types of coupling, the delay always plays a subtle role in either promoting or impairing synchronization. In particular, depending on the inherent oscillation period of individual neurons, regions of irregular and regular propagating excitatory fronts appear intermittently as the delay increases. These delay-induced synchronization transitions are manifested as well-expressed minima in the measure for spatiotemporal synchrony. For attractive coupling, the minima appear at every integer multiple of the average oscillation period, while for the repulsive coupling, they appear at every odd multiple of the half of the average oscillation period. The obtained results are robust to the variations of the dynamics of individual neurons, the system size, and the neuronal firing type. Hence, they can be used to characterize attractively or repulsively coupled scale-free neuronal networks with delays. Ključne besede: synchronization, neuronal networks, noise, stochastic processes, scale-free networks, information transmission delay Objavljeno v DKUM: 19.06.2017; Ogledov: 1064; Prenosov: 373 Celotno besedilo (933,65 KB) Gradivo ima več datotek! Več... |
4. ERROR PROBABILITY MODEL FOR IEEE 802.15.4 WIRELESS TRANSMISSION WITH CO-CHANNEL INTERFERENCE AND BACKGROUND NOISEUroš Pešović, 2016, doktorska disertacija Opis: Data transmission sent through wireless channel is usually affected by background noise, multipath fading and interference which cause data errors. Influence of such disturbances is the most commonly expressed in a form of error probability statistics. Effects of these disturbances on IEEE 802.15.4 wireless transmissions are previously studied, except influence of co-channel interference (CCI) which originates from collision between IEEE 802.15.4 devices which perform simultaneous radio transmission. Our thesis puts forward the assumption that it is possible to derive more accurate analytical error probability model for higher data level error probability parameters without the idealization of PN spreading sequences. Additionally, thesis is that is possible to derive an accurate analytical error probability model in the case of CCI influenced by background noise by consideration of constellation diagram. IEEE 802.15.4 standard uses CSMA/CA (Carrier Sense Multiple Access with Collision Detection) channel access mechanism to prevent collisions between devices, but this mechanism doesn't provide protection from hidden node problem which is primary source of co-channel interference. Using Monte Carlo simulations we determined frequency of hidden node collisions, which shown that co-channel interference frequently occur in parts of the network with high traffic load. Some prior works in this field tend to idealize these non-ideal spreading sequences in order to simplify calculations for error probability parameters. Our doctor thesis presents analytical model of data level error probability parameters (symbol, bit and packet) for IEEE 802.15.4, which uses original non-ideal spreading sequences without their idealization. Proposed error probability model consists of mutually dependent chip, symbol, bit and packet error probability models. Derived error probability models are linked together, so each of error probability parameters can be determined using error probability parameter from the previous stage. Error probability model for IEEE 802.15.4 wireless communication could be used in network simulation tools in order to accurately simulate energy efficient medium access protocols in realistic scenarios. Presented theoretical results are tested by independent numerical simulation of IEEE 802.15.4 transmission according to Monte Carlo method. Simulation results shows that derived models for error probability parameters were matched by two simulation scenarios in background noise, for multipath fading and co-channel interface, respectively Furthermore, the accuracy of derived mathematical models was tested in real-world experiment using IEEE 802.15.4 compliant wireless transceivers for creating co-channel interference. Packets were received by software defined radio platform, which enabled realization of coherent receiver in which all error probability statistics could be collected. The results of the experiment show consistency with proposed analytical error probability models, but some deviations are caused by poor preamble synchronization under low SNR (Signal to Noise Ratio) value. The thesis was proved with Monte Carlo simulations of the physical level of the IEEE 802.15.4 communication and experimental measurements on a real physical communication system. Ključne besede: IEEE 802.15.4 standard, error probability model, co-channel interference, Rician fading channel, additive white Gaussian noise, wireless transmission, wireless sensor networks, numerical simulations, software defined radio Objavljeno v DKUM: 14.10.2016; Ogledov: 2236; Prenosov: 135 Celotno besedilo (8,20 MB) |
5. Experimental analysis of the impact of particles on the cavitating flowBoštjan Gregorc, Andrej Predin, Drago Fabijan, Roman Klasinc, 2012, izvirni znanstveni članek Opis: The purpose of this paper is to present an analysis of the impact of solid particles on the development of cavitating flow conditions around a hydrofoil. Experimental studies have been conducted in a cavitation tunnel with three different mixtures of particles and water. We used a particle-like properties, such as are found in river water, and with increasing mass concentration. We performed measurements of torque and the relative noise in the hydrofoil. The point in the formation of vapour phase on the hydrofoil and the pronounced frequency effect were determined by measuring the relative noise. Based on the analysis the results show that the particles increase the intensity and extent of cavitation. Ključne besede: particles, cavitation, noise, measurements Objavljeno v DKUM: 10.07.2015; Ogledov: 5804; Prenosov: 89 Povezava na celotno besedilo |
6. Strains and stresses of workers caused by exposure to noiseAndrej Polajnar, Nataša Vujica-Herzog, Borut Buchmeister, Simona Jevšnik, 2012, izvirni znanstveni članek Opis: This paper examines basic aspects of determining strain due to noise on workers in an industrial environment. Technological development enables better working conditions which then demands changes in methods for measuring strain and stress loadings. A modified method is now presented since the existing method for determining strains caused by exposure to noise is proving insufficient. The objective of the modified method is to eliminate the shortcomings of the existing method by taking into account the complex effects of noise in specific working environments. The effects of exposure to noise will be assessed by using a new strain-assessment procedure which incorporates the effects of nature of noise, characteristics of noise, current standards on protection from noise, and the influence of noise on different jobs. This new noise-assessment approach uses new measurement techniques based on tonality and impulsive noise corrections. The modified method has been tested at various workplaces in the metal-working industry. A comparison of the results obtained by using both methods confirms the suitability of the modified method, thus providing a more complete approach to evaluating strain due to noise. Ključne besede: ergonomija, hrup na delovnem mestu, strain, stresses, ergonomic coefficient, noise, impulsive noise correction, tone correction Objavljeno v DKUM: 10.07.2015; Ogledov: 1030; Prenosov: 29 Povezava na celotno besedilo |
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8. Evolution under alliance-specific cyclical invasion rates : lecture, presented at the Satellite Workshop at ECCS 07, Dresden, 4th-5th October (Evolution of of noise), 2007Matjaž Perc, 2007, prispevek na konferenci brez natisa Ključne besede: hrup, intenziteta hrupa, dilema zapornika, kaos, nelinearni dinamični sistemi, noise, spatiotemporal noise, intensity, prisoner's dilemma, chaos, nonlinear dynamic systems Objavljeno v DKUM: 10.07.2015; Ogledov: 1492; Prenosov: 29 Povezava na celotno besedilo |
9. Cooperation out of noise : lecture, presented at the Satellite Workshop at ECCS 07, Dresden, 4th-5th OctoberMatjaž Perc, 2007, prispevek na konferenci brez natisa Ključne besede: hrup, intenziteta hrupa, dilema zapornika, kaos, nelinearni dinamični sistemi, noise, spatiotemporal noise, intensity, prisoner's dilemma, chaos, nonlinear dynamic systems Objavljeno v DKUM: 10.07.2015; Ogledov: 1473; Prenosov: 26 Povezava na celotno besedilo |
10. Acoustic noise emissions caused by transformer in a DC/DC converter for welding appliactaions [!]Gorazd Štumberger, Klemen Deželak, Drago Dolinar, Beno Klopčič, 2012, objavljeni znanstveni prispevek na konferenci (vabljeno predavanje) Opis: This paper deals with the acoustic noise emissions caused by the transformer operating as a part of DC/DC converter in an industrial resistance spot welding system. The discussed DC/DC converter is schematically shown in Fig. 1. The three-phase alternating voltages (u1, u2 and u3) are rectified and smoothed in order to obtain almost constant DC-bus voltage UDC. The H-bridge inverter is used to supply the transformerćs primary winding with voltage pulses uH. The two transformerćs secondary windings are connected to the two output rectifier diodes (D1 and D2) which provide the direct welding current iL flowing through the load represented by LL and RL. A new control scheme forresistance spot welding systems was proposed in [1,2]. During the testing of the proposed control scheme it became evident that the proposed control scheme not only improves utilization of the iron core and prevent it from becoming saturated, but also substantially reduces the acoustic noise emissions caused by the transformer. The reasons for reduction of acoustic noise emission are discussed in this paper. Ključne besede: DC/DC converter, acoustic noise emissions Objavljeno v DKUM: 10.07.2015; Ogledov: 2618; Prenosov: 48 Povezava na celotno besedilo |