The main idea of this work is to demonstrate an application of the generalized perturbation-based Stochastic Finite Element Method for a determination of the reliability indicators concerning elastic stability for a certain spectrum of the civil engineering structures. The reliability indicator is provided after the Eurocode according to the First Order Reliability Method, and computed using the higher order Taylor expansions with random coefficients. Computational implementation provided by the hybrid usage of the FEM system ROBOT and the computer algebra system MAPLE enables for reliability analysis of the critical forces in the most popular civil engineering structures like simple Euler beam, 2 and 3D single and multi-span steel frames, as well as polyethylene underground cylindrical shell. A contrast of the perturbation-based numerical approach with the Monte-Carlo simulation technique for the entire variability of the input random dispersion included into the Euler problem demonstrates the probabilistic efficiency of the perturbation method proposed.
The paper deals with the application of the feed-forward and cascade-forward neural networks to mechanical state variable estimation of the drive system with elastic coupling. The learning procedure of neural estimators is described and the influence of the input vector size and neural network structure to the accuracy of state variable estimation is investigated. The quality of state estimation by neural estimators of different types is tested and compared. The simple optimisation procedure is proposed. Optimised neural estimators of the torsional torque and the load machine speed are tested in the open-loop and closed-loop control structure of the drive system with elastic joint, with additional feedbacks from the shaft torque and the difference between the motor and the load speeds. It is shown that torsional vibrations of the two-mass system are damped effectively using the closed-loop control structure with additional feedbacks obtained from the developed neural estimators. The simulation results are confirmed by laboratory experiments.
In the paper, a research on effects of baking temperature on chromite sand base of moulding sands bonded with sodium silicate is
presented. Pure chromite sand and its chromite-based moulding sand prepared with use of sodium silicate were subjected to heating within
100 to 1200 °C. After cooling-down, changes of base grains under thermal action were determined. Chromite moulding sand was prepared
with use of 0.5 wt% of domestic made, unmodified sodium silicate (water-glass) grade 145. After baking at elevated temperatures, creation
of rough layer was observed on grain surfaces, of both pure chromite sand and that used as base of a moulding sand. Changes of sand
grains were evaluated by scanning microscopy and EDS analyses. It was found that changes on grain surfaces are of laminar nature. The
observed layer is composed of iron oxide (II) that is one of main structural components of chromite sand. In order to identify changes in
internal structure of chromite sand grains, polished sections were prepared of moulding sand hardened with microwaves and baked at
elevated temperatures. Microscopic observations revealed changes in grains structure in form of characteristically crystallised acicular
particles with limited magnesium content, intersecting at various angles. EDS analysis showed that these particles are composed mostly of
chromium oxide (III) and iron oxide (II). The temperature above that the a.m. changes are observed in both chromite-based moulding sand
and in pure chromite sand. The observed phenomena were linked with hardness values and mass of this sand.
In the paper, a research on effects of baking temperature on chromite sand base of moulding sands bonded with sodium silicate is
presented. Pure chromite sand and its chromite-based moulding sand prepared with use of sodium silicate were subjected to heating within
100 to 1200 °C. After cooling-down, changes of base grains under thermal action were determined. Chromite moulding sand was prepared
with use of 0.5 wt% of domestic made, unmodified sodium silicate (water-glass) grade 145. After baking at elevated temperatures, creation
of rough layer was observed on grain surfaces, of both pure chromite sand and that used as base of a moulding sand. Changes of sand
grains were evaluated by scanning microscopy and EDS analyses. It was found that changes on grain surfaces are of laminar nature. The
observed layer is composed of iron oxide (II) that is one of main structural components of chromite sand. In order to identify changes in
internal structure of chromite sand grains, polished sections were prepared of moulding sand hardened with microwaves and baked at
elevated temperatures. Microscopic observations revealed changes in grains structure in form of characteristically crystallised acicular
particles with limited magnesium content, intersecting at various angles. EDS analysis showed that these particles are composed mostly of
chromium oxide (III) and iron oxide (II). The temperature above that the a.m. changes are observed in both chromite-based moulding sand
and in pure chromite sand. The observed phenomena were linked with hardness values and mass of this sand.
The propagation of EEG activity during the Continuous Attention Test (CAT) was determined by means of Short-time Directed Transfer Function (SDTF). SDTF supplied the information on the direction, spectral content and time evolution of the propagating EEG activity. The differences in propagation for target and non-target conditions were found mainly in the frontal structures of the brain.
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