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showing 10 items of 15546 documents
Polarization and acoustic properties of barium-modified lead-free potassium–sodium niobate ceramics
2017
The publication costs of this article were covered by the Estonian Academy of Sciences and the University of Tartu.
Field effect in the viscosity of magnetic colloids studied by multi-particle collision dynamics
2019
Abstract Colloidal solutions of magnetic nanoparticles are usually employed when the fluidity and magnetic properties are required at the same time, either in technical or biomedical applications. However, when the magnetic size of the nanoparticles is large enough (>12–15 nm) the colloid may form an equilibrium structure with or without the external magnetic field, which can significantly influence its rheology. Using multi-particle collision dynamics we study the internal structure and viscosity of the magnetic colloids at varying magnitudes of the externally applied field. We show a generalized structural behavior across all studied regimes and an appreciable increase of flow resistance …
Coeval Cold Spray Additive Manufacturing Variances and Innovative Contributions
2017
Tremendous attention has been given to the cold spray process, even more today with the emergence of additive manufacturing, worldwide. Several inventions related to the cold spray technology have been patented for over a century and mostly since a couple of decades. But the cold spray technology knows a period of great innovations due to recent and current substantial explorations. Various technological solutions have been developed. The technical dimension, and particularly in terms of manufacturing method, has also always been a major genesis of progresses and novelties. This chapter is a technological survey of the cold spray additive manufacturing and reports variant methods and innova…
Stability of melt flow during magnetic sonication in a floating zone configuration
2018
Combined static and alternating magnetic fields are shown to create an oscillating pressure that can cause cavitation in molten metals. A time-averaged flow is also excited, consisting of two tori squeezed to thin boundary layers. Flow instability develops as a standing wave between these tori.
Preface for MMM 2016 focus issue
2017
International audience
Optical properties of InN nanocolumns: Electron accumulation at InN non‐polar surfaces and dependence on the growth conditions
2009
InN nanocolumns grown by plasma-assisted molecular beam epitaxy have been studied by photoluminescence (PL) and photoluminescence excitation (PLE). The PL peak energy was red-shifted with respect to the PLE onset and both energies were higher than the low temperature band-gap reported for InN. PL and PLE experiments for different excitation and detection energies indicated that the PL peaks were homogeneously broadened. This overall phenomenology has been attributed to the effects of an electron accumulation layer present atthe non-polar surfaces of the InN nanocolumns. Variations in the growth conditions modify the edge of the PLE spectra and the PL peak energies evidencing that the densit…
PD characteristics at Square Shaped Voltages Applying Two Different Detecting Techniques
2016
Nowadays power electronic converters are widely used and the fast switching voltage fronts results in an increased stress on the insulation material and may cause a reduction of the HV systems reliability. Nonsinusoidal voltage waveform have influence on the partial discharges (PD) characteristics in insulating systems due to the increased harmonic content which causes problems mainly in electrical PD measurement setups. In fact, impulse voltages cause strong switching disturbances, which make it much more difficult to distinguish PD signals from noise. This work investigates the influence of repetitive steep pulses on different types of test objects exposed to square wave voltages applying…
Partial discharges at different voltage waveshapes: Comparison between two different acquisition systems
2018
In modern HV apparatuses the wide use of electronic converters, increase the stress on the involved insulation systems and thus affect the reliability of the whole power grid. Additionally, such non-sinusoidal voltage shapes contain high gradient flanks that create problems in the detection of partial discharge (PD) activity. The aim of this paper is to discuss the methodology on how to suitably approach PD detection in insulation systems exposed to various voltage waveshapes in general by comparing two different measuring systems. The first one, equipped with a resonant PD decoupler, designed specifically for detection at typical power electronic waveshapes and the other one, based on an a…
High-frequency electrodeless lamps in argon–mercury mixtures
2005
In this paper, numerical and experimental investigations of high-frequency (HF) electrodeless lamps in argon–mercury mixtures are performed. The intensities of the mercury spectral lines having wavelengths λ = 404.66, 435.83, 546.07 nm (7 3S1–6 3P0,1,2) and the resonance line λ = 253.7 nm (6 3 P1–6 1S0) are measured at a wide range of mercury pressures, varying the HF generator current and argon filling pressure. A stationary self-consistent model of HF electrodeless discharge lamp is developed including kinetics of the excited mercury and argon atomic states. Based on the developed model, the radiation characteristics of the discharge plasma are calculated. Numerical simulation of the line…
Towards the Improvement of Citizen Communication Through Computational Intelligence
2016
When dealing with problems that arise from collective sharing of resources in metropolitan areas (i.e., energy, pollution, traffic, health) most of the interaction between citizens and local governance is usually carried out through the use of natural languages. Digital technologies allows smart cities residents to communicate with a broad range of experts (e.g. bureaucrats, legislators, urbanists, etc.) that routinely use technical terminology seldom accessible to the layperson, or linguistic styles that are not immediately understandable. Although information technology should encourage citizen participation in governance at many levels, the different levels of knowledge possessed by the …