The present work concerns a Human-Computer Interaction (HCI) experiment in an Immersive Virtual Reality (IVR) environment. The user is located at the focal point of a four metre hemispherical dome projection screen. By combining a 5DT data glove with an iPhone 3G, the user can directly interact with a computer program/client. The visualisation is implemented with the Unity 3D 2.5 multiplatform game development tool. The client communicates with a .NET socket server allowing continuous data streaming from connected sensors, i.e., finger flexures, hand gestures (from the data glove) and orientation data (from the iPhone's accelerometer sensors). The main goal of the experiment is to evaluate interactive techniques for users who are training in an IVR environment. An IVR application is demonstrated to highlight the value of the proposed method in an intuitive e-learning experience associated with the teleoperation of underground coal mining equipment.

The scaling to characterize unsteady boundary layer development for thermo-magnetic convection of paramagnetic fluids with the Prandtl number greater than one is developed. Under the consideration is a square cavity with initially quiescent isothermal fluid placed in microgravity condition (g = 0) and subject to a uniform, vertical gradient magnetic field. A distinct magnetic thermal-boundary layer is produced by sudden imposing of a higher temperature on the vertical sidewall and as an effect of magnetic body force generated on paramagnetic fluid. The transient flow behavior of the resulting boundary layer is shown to be described by three stages: the start-up stage, the transitional stage and the steady state. The scaling is verified by numerical simulations with the magnetic momentum parameter m variation and the parameter γRa variation.

The objective of the current paper is to present recent results on e-learning, including a virtual laboratory, designed for education of power electronics. The e-learning curriculum is suitable for both academic and industrial education in the frame of vocational training. It contains multimedia-rich presentation screens to teach the principles of the respective phenomena; furthermore, the interactive parts strongly support the deepening of the fresh knowledge. The interactive calculation tools facilitate the fast and simple model-development in web browsers for several often-used power electronic circuits (eg. static and dynamic models of DC-DC converters). Providing access to real circuits via online laboratory experiments is the next step for the trainees, allowing the change of several circuit parameters and the continuous monitoring of the system, even from long distances. It can have an important role in distance education too.

The current paper is dedicated to present browser-based multimedia-rich software tools and e-learning curriculum to support the design and modeling process of power electronics circuits and to explain sometimes rather sophisticated phenomena. Two projects will be discussed. The so-called Inetele project is financed by the Leonardo da Vinci program of the European Union(EU). It is a collaborative project between numerous EU universities and institutes to develop state-of-the art curriculum in electrical engineering. Another cooperative project with participation of Japanese, European and Australian institutes focuses especially on developing e-learning curriculum, interactive design and modeling tools, furthermore on development of a virtual laboratory. Snapshots from these two projects will be presented.

Chaos-based cryptography emerged in the early 1990s as an innovative application of nonlinear dynamics in the chaotic regime. Even if in theory chaotic dynamics was thought to evolve into a new revolution in cryptography, in real-life an efficient and reliable chaos-based cryptosystem didn't emerge. The main but not the only reason is the dynamic degradation of digital chaotic systems, a subject that became very popular in the last few years. This paper presents a new theoretical background related to this issue that proves the inefficiency of chaos-based encryption algorithms. Even more, in one of the two relevant case studies presented, another myth is demolished: the analog encryption base on synchronized chaos.

Even if their resources in terms of energy, memory, computational power and bandwidth are strictly limited, sensor networks have proved their huge viability in the real world, being just a matter of time until this kind of networks will be standardized and used broadly in the field. One of the important problems that are related to the use of wireless sensor networks in harsh environments is the gap in their security. This paper provides a solution to discover malicious nodes in wireless sensor networks using an on-line neural network predictor based on past and present values obtained from neighboring nodes. This solution can be also a way to discover the malfunctioning nodes that were not a subject of an attack. Being localized on the base station level, our algorithm is suitable even for large-scale sensor networks.

Even if their resources in tenus of energy, memory, computational power and bandwidth are strictly limited, sensor networks have proved their huge viability in the real world, being just a matter of time until this kind of networks will be standardized and used broadly in the field. One of the important problems that are related to the use of wireless sensor networks in harsh environments is the gap in their security. This paper provides a solution to discover malicious nodes in wireless sensor networks using an on-line neural network predictor based on past and present values obtained from neighboring nodes. This solution can be also a way to discover the malfunctioning nodes that were not a subject of an attack. Being localized on the base station level, our algorithm is suitable even for large-scale sensor networks.

In this paper we propose a strategy based on past/present values provided by each sensor of a network for detecting their malicious activity. Basically, we will compare at each moment the sensor's output with its estimated value computed by an autoregressive predictor. In case the difference between the two values is higher then a chosen threshold, the sensor node becomes suspicious and a decision block is activated.

The main objective of the paper is to present new browser-based, interactive software tools for modeling of various power electronics circuits. The static and dynamic operation, including the continuous and discrete time linearization of widely applied DC-DC converter cells are discussed in the first part of the paper. The second part focuses on the basics of the pulse-width-modulation and its application in one-phase sinusoidal inverters. The interactive tools provide numerous excellent opportunities for industrial and academic education. Another application field of numerous embedded interactive software components is their utilization as fast, real-time model-building tools

This paper studies a system of parallel-connected dc/dc buck converters under current-mode control. The effects of variations of the reference current are studied. It has been observed that the system exhibits low-frequency bifurcation behaviour while period-doubling at switching frequency is suppressed. Extensive simulations are used to capture the behaviour. Time-domain waveforms, stroboscopic maps and trajectories are shown. The paper reveals the drastic alteration of bifurcation behaviour of dc/dc converters due to subtle coupling.

Exploiting the recent achievements of the information and communication technologies, a new e-learning initiation entitled Yoto project was launched in 2004. On longer run its most important objective is to build up and maintain an electrical engineering knowledge base, on shorter run it helps giving more and more publicity to some relevant fields, especially power electronics, drives and motion control. The multimedia rich content can be utilized in the high level academic education, in the industrial vocational trainings and also in supporting the circuit and system design specialists by fast interactive tools. This paper presents a new e-module attached to the Yoto project about the dynamic operation and modeling of dc-dc converters.

Power-factor-correction (PFC) power supplies are required to provide high input power factor and tight output voltage regulation. The usual configuration takes a two-stage cascade structure, consisting of a PFC preregulator and a dc/dc converter. Previous studies of the dynamical behaviour mainly focused on the boost PFC preregulator, assuming that it is being terminated by a resistive load. However, in practice, as the PFC preregulator is terminated by a dc/dc converter whose characteristics differ from resistive load's, the assumption of resistive load termination gives rather inaccurate information about the stability of the system. In this paper we study the complete two-stage PFC power supply and show that the interaction between the PFC stage and the dc/dc converter stage plays an important role in determining the stability of the system.

Variable-structure piecewise-linear nonlinear dynamic feedback systems emerge frequently in power electronics. This paper is concerned with the stability analysis of these systems. Although it applies the usual well-known and widely used approach, namely, the eigenvalues of the Jacobian matrix of the Poincare/spl acute/ map function belonging to a fixed point of the system to ascertain the stability, this paper offers two contributions for simplification as well that utilize the periodicity of the structure or configuration sequence and apply an alternative simpler and faster method for the determination of the Jacobian matrix. The new method works with differences of state variables rather than derivatives of the Poincare/spl acute/ map function (PMF) and offers geometric interpretations for each step. The determination of the derivates of PMF is not needed. A key element is the introduction of the so-called auxiliary state vector for preserving the switching instant belonging to the periodic steady-state unchanged even after the small deviations of the system orbit around the fixed point. In addition, the application of the method is illustrated on a resonant dc-dc buck converter.

This paper studies a single buck converter and a system of parallel-connected dc/dc buck converters under current-mode control. The effects of variations of the reference current are studied. It has been observed that the system exhibits low-frequency bifurcation behaviour while period-doubling at switching frequency is suppressed. Extensive simulations are used to capture the behaviour. Time domain waveforms, stroboscopic maps, and trajectories are shown. The paper reveals the drastic alteration of bifurcation behaviour of dc/dc converters due to subtle coupling.

This paper studies the bifurcation behaviour of a system of coupled buck converters under current-mode control. The effects due to the variation of the reference current are studied. It has been observed that the system exhibits low-frequency bifurcation behaviour while period-doubling at switching frequency is suppressed. Extensive simulations are used to capture the findings. Time-domain waveforms, stroboscopic maps and trajectories are shown. The results show the drastic alteration of bifurcation behavior of dc/dc converter systems due to subtle coupling. Index Terms‐ Bifurcation, parallel-connected dc/dc converters, instability.

Previous studies have already introduced a variable active-passive reactance (VAPAR) to be used as virtual inductance in power circuits. Its most remarkable feature of generating a negative virtual inductance can be used to cancel an undesired existing inductance. It has found applications in the rapid power flow control of power systems, for flexible AC transmission systems, where the power flow is essentially restricted by a line inductance. Therefore, the operation of VAPAR has been investigated within the frame of an RL configuration. The present paper aims to contribute to the control design of VAPAR, which has to avoid the occurrence of any bifurcation within the intended range of the parameters. A stability analysis is carried out by modelling the periodic steady-state operation of the variable-structure piecewise-linear system by a stroboscopic map. Determining the eigenvalues of the Jacobian matrix of the stroboscopic map, evaluated at its fixed point, reveals bifurcation behaviour as a result of varying the control parameters, as well as the effect on the overall system dynamics. The approach allows convenient and accurate identification of the control domain in the parameter space of the virtual negative inductance and the control parameters, which guarantee stable operation and good transient performances.