High quality TbMnO3 films deposited on YAlO3

High quality thin films of TbMnO₃ were grown by pulsed laser deposition on orthorhombicYAlO₃ (1 0 0). The interface and surface roughness of a 55 nm thick film were probed by X-ray reflectometry and atomic force microscopy, yielding a roughness of 1 nm. X-ray diffraction revealed untwinned films and a small mosaic spread of 0.04° and 0.2° for out-of-plane and in-plane reflections, respectively. This high degree of epitaxy was also confirmed by Rutherford backscattering spectrometry. Using polarized neutron diffraction we could identify a magnetic structure with the propagation vector (0 0.27 0), identical to the bulk magnetic structure of TbMnO₃.     

An Improved On-line Contingency Screening for Power System Transient Stability Assessment

This paper presents a contingency screening method and a framework for its on-line implementation. The proposed method carries out contingency screening and on-line stability assessment with respect to first-swing transient stability. For that purpose, it utilizes the single machine equivalent method and aims at improving the prior developed contingency screening approaches. In order to determine vulnerability of the system with respect to a particular contingency, only one time-domain simulation needs to be performed. An early stop criteria is proposed so that in a majority of the cases the simulation can be terminated after a few hundred milliseconds of simulated system response. The method’s outcome is an assessment of the system’s stability and a classification of each considered contingency. The contingencies are categorized by exploiting parameters of an equivalent one machine infinite bus system. A novel island detection approach, appropriate for an on-line application since it utilizes efficient algorithms from graph theory and enables stability assessment of individual islands, is also introduced. The New England and New York system as well as the large-scale model of the Continental-European interconnected system are used to test the proposed method with respect to assessment accuracy and computation time.     

A web application for follow-up of results from a mobile device test battery for Parkinson's disease patients

Contrast-enhanced ultrasound (CEU) is an ultrasound imaging technique used to assess tissue perfusion. Analysis of microvascular recruitment necessitates the definition of a region of interest (ROI) containing exclusively the tissues to be studied. Conventional ROI selection requires examining the images and drawing the ROI by hand, making the analysis of CEU images non-reproducible and analyst-dependent. We have designed a systematic ROI selection method that is both reproducible and analyst-independent. Microvascular blood volume (MBV) assessed in 21 sequences of images was used to correlate the systematic ROI selection method with the conventional method performed by two independent analysts (correlation of 0.88 and 0.87 respectively) and the MBV sample distribution from the systematic method was not significantly different from those obtained from the conventional one. Using the systematic method, we found no significant insulin-induced capillary recruitment in subjects with type 1 diabetes mellitus, which might be related to the observed low glucose uptake during the hyperinsulinemic euglycemic clamp compared to healthy patients.     

Feasible adjoint sensitivity technique for EM design optimization

An adjoint-variable approach to frequency-domain design sensitivity analysis is proposed for the optimization of high-frequency structures with full-wave electromagnetic solvers. We investigate sensitivity estimations based on a feasible perturbation technique which is versatile and requires only minor modifications of existing analysis algorithms. It extends the feasible adjoint-sensitivity technique previously applied in nonlinear microwave circuits to full-wave electromagnetic analysis. The solution to the adjoint problem is obtained with very little overhead once the original problem is solved. The gradient of the objective function is consequently computed through a single analysis regardless of the number of the design parameters. The concept is illustrated through the sensitivity analysis and the design of a Yagi-Uda array and a rectangular patch antenna using suitable method of moments simulators.     

Establishing an efficient regulatory mechanism—Prerequisite for successful energy activities regulation

An analytic approach to determine appropriate regulatory strategies for the energy sector is proposed in this paper. A basic model of the regulatory system in the energy sector is defined, and the regulatory mechanism functions in this context are outlined. The basic problem of unknown factors (i.e., system entropy) is highlighted. An original algorithm developed to analyze regulatory background context and regulatory mechanism functions is discussed. A useful method for defining existing level of energy activities regulation is also presented using the Croatian regulatory framework as an example.     

A general-purpose symbolically assisted numeric computation environment as a support in power engineering education

This paper describes and illustrates a Windows-based, general-purpose, symbolically assisted numeric computation environment within power engineering education applications. The examples considered include fundamental problems derived from three areas: power system analysis and optimization, electric machinery, and feedback control systems.     

Estimation of rotor angles of synchronous machines using artificial neural networks and local PMU-based quantities

This paper investigates a possibility for estimating rotor angles in the time frame of transient (angle) stability of electric power systems, for use in real-time. The proposed dynamic state estimation technique is based on the use of voltage and current phasors obtained from a phasor measurement unit supposed to be installed on the extra-high voltage side of the substation of a power plant, together with a multilayer perceptron trained off-line from simulations. We demonstrate that an intuitive approach to directly map phasor measurement inputs to the neural network to generator rotor angle does not offer satisfactory results. We found out that a good way to approach the angle estimation problem is to use two neural networks in order to estimate the sin(δ) and cos(δ) of the angle and recover the latter from these values by simple post-processing.Simulation results on a part of the Mexican interconnected system show that the approach could yield satisfactory accuracy for real-time monitoring and control of transient instability.     

Clustering multidimensional sequences in spatial and temporal databases

Many environmental, scientific, technical or medical database applications require effective and efficient mining of time series, sequences or trajectories of measurements taken at different time points and positions forming large temporal or spatial databases. Particularly the analysis of concurrent and multidimensional sequences poses new challenges in finding clusters of arbitrary length and varying number of attributes. We present a novel algorithm capable of finding parallel clusters in different subspaces and demonstrate our results for temporal and spatial applications. Our analysis of structural quality parameters in rivers is successfully used by hydrologists to develop measures for river quality improvements.