Brno University of Technology

About: Brno University of Technology is a education organization based out in Brno, Czechia. It is known for research contribution in the topics: Computer science & Fracture mechanics. The organization has 6339 authors who have published 15226 publications receiving 194088 citations. The organization is also known as: Vysoké učení technické v Brně & BUT.

Thermodynamics of the Solar Corona and Evolution of the Solar Magnetic Field as Inferred from the Total Solar Eclipse Observations of 2010 July 11

Abstract: We report on multi-wavelength observations of the corona taken simultaneously in broadband white light, and in seven spectral lines, H-alpha 656.3 nm, Fe IX 435.9 nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm and Ni XV 670.2 nm. The observations were made during the total solar eclipse of 11 July 2010 from the atoll of Tatakoto in French Polynesia. Simultaneous imaging with narrow bandpass filters in each of these spectral lines and in their corresponding underlying continua maximized the observing time during less than ideal observing conditions and yielded outstanding quality data. The application of two complementary image processing techniques revealed the finest details of coronal structures at 1" resolution in white light, and 6.5" in each of the spectral lines. This comprehensive wavelength coverage confirmed earlier eclipse findings that the solar corona has a clear two-temperature structure: The open field lines, expanding outwards from the solar surface, are characterized by electron temperatures near 1 X 10(exp 6) K, while the hottest plasma around 2X 10(exp 6) K resides in loop-like structures forming the bulges of streamers. The first images of the corona in the forbidden lines of Fe IX and Ni XV, showed that there was very little coronal plasma at temperatures below 5 X 10(exp 5) K and above 2.5X 10(exp 6) K. The data also enabled temperature differentiations as low as 0:2 X 10(exp 6) K in different density structures. These observations showed how the passage of CMEs through the corona, prior to totality, produced large scale ripples and very sharp streaks, which could be identified with distinct temperatures for the first time. The ripples were most prominent in emission from spectral lines associated with temperatures around 10(exp 6) K. The most prominent streak was associated with a conical-shaped void in the emission from the coolest line of Fe IX and from the hottest line of Ni XV. A prominence, which erupted prior to totality, appeared in the shape of a hook in the cooler lines of Fe X and Fe XI, spanning 0.5 R(solar) in extent starting at a heliocentric distance of 1.3 R(solar), with a complex trail of hot and cool twisted structures connecting it to the solar surface. Simultaneous Fe X 17.4 nm observations from space by Proba2/SWAP provided an ideal opportunity for comparing emission from a coronal forbidden line, namely Fe X 637.4 nm, with a space-based EUV allowed line. Comparison of the Fe X 17.4 nm and 637.4 nm emission provided the first textbook example of the role of radiative excitation in extending the detectability of coronal emission to much larger heliocentric distances than its collisionally excited component. These eclipse observations demonstrate the unique capabilities of coronal forbidden lines for exploring the evolution of the coronal magnetic field in the heliocentric distance range of 1 - 3 R(solar), which is currently inaccessible to any space-borne or ground-based observatory.

Properties of Alkali Activated Aluminosilicate Material after Thermal Load

Abstract: The porosity, bulk density, compressive strength, bending strength, thermal conductivity, and specific heat capacity of a material based on alkali activated slag are determined at room temperature conditions for samples subjected to a thermal load up to 1200°C prior to the measurements and compared to reference material data. The results are discussed using material characterization experiments, namely, X-ray diffraction analysis and scanning electron microscopy. Experimental results show a remarkable high-temperature resistance of the studied material, which after pre-heating to 1200°C exhibits mechanical properties comparable to the reference material not exposed to any thermal load.

Lyapunov-function-based flux and speed observer for AC induction motor sensorless control and parameters estimation

Abstract: AC induction motors have become very popular for motion-control applications due to their simple and reliable construction. Control of drives based on ac induction motors is a quite complex task. Provided the vector-control algorithm is used, not only the rotor speed but also the position of the magnetic flux inside the motor during the control process should be known. In most applications, the flux sensors are omitted and the magnetic-flux phasor position has to be calculated. However, there are also applications in which even speed sensors should be omitted. In such a situation, the task of state reconstruction can be solved only from voltage and current measurements. In the current paper, a method based on deterministic evaluation of measurement using the state observer based on the Lyapunov function is presented. The method has been proven in testing on a real ac induction machine.

Effect of grain size on mechanical properties of 3y-tzp ceramics

Abstract: The dependence of mechanical properties of 3Y-TZP ceramics on their grain sizes in the range from 0.19 µm to 2.15 µm has been investigated. Vickers indentation tests were used to determine hardness and fracture toughness. The hardness decreased with increasing grain size. The fracture toughness was almost constant for ceramics with the grain size up to 0.40 µm and then grew with increasing grain size up to 7.8 MPam 0.5 for ceramics with grain size of 1.8 µm. Above this grain size a spontaneous transformation from tetragonal to monoclinic phase occurred. Ceramic samples with grain sizes of 0.30 µm and 0.78 µm yielded similar bending strength, 1020 and 1011 MPa, respectively. The microstructural coarsening required for achieving larger grain size resulted in a higher scatter of strength values, which was demonstrated by a lower Weibull modulus (13.0 vs. 7.54). The mechanical properties of nanocrystalline 3Y-zirconia ceramics coarsened to the grain size range from 0.085 to 0.70 µm were also investigated and compared. Differences in mechanical behaviour of investigated ceramics were observed and their possible causes discussed.