Celoškolská pracoviště / All-University Departments
http://hdl.handle.net/10084/14171
2018-01-09T19:27:52ZOn unbounded solutions of singular IVPs with phi-Laplacian
http://hdl.handle.net/10084/122512
On unbounded solutions of singular IVPs with phi-Laplacian
Rohleder, Martin; Burkotová, Jana; López-Somoza, Lucía; Stryja, Jakub
The paper deals with a singular nonlinear initial value problem with a phi-Laplacian
(p(t)phi(u'(t)))' + p(t)f(phi(u(t))) = 0, t > 0, u (0) = u(0)is an element of[L-0, L], u' (0) = 0.
Here, f is a continuous function with three roots phi(L-0) < 0 < phi(L), phi : R -> R is an increasing homeomorphism and function p is positive and increasing on (0, infinity). The problem is singular in the sense that p (0) = 0 and 1/p may not be integrable in a neighbourhood of the origin. The goal of this paper is to prove the existence of unbounded solutions. The investigation is held in two different ways according to the Lipschitz continuity of functions phi(-1) and f. The case when those functions are not Lipschitz continuous is more involved that the opposite case and it is managed by means of the lower and upper functions method. In both cases, existence criteria for unbounded solutions are derived.
2017-01-01T00:00:00ZExperimental demonstration of magnetoplasmon polariton at InSb(InAs)/dielectric interface for terahertz sensor application
http://hdl.handle.net/10084/121133
Experimental demonstration of magnetoplasmon polariton at InSb(InAs)/dielectric interface for terahertz sensor application
Chochol, Jan; Postava, Kamil; Čada, Michael; Pištora, Jaromír
We experimentally demonstrate surface plasmon resonance (SPR) in the terahertz range in InSb and InAs. The surface plasmon is excited on the interface between a thin polymer film and the semiconductor using a silicon prism in Otto configuration. The low effective mass of InSb and InAs permits tuning of the SPR by an external magnetic field in the transversal configuration. The data show a good agreement with a model. Strong excitation of the surface plasmon is present in both materials, with a shifting of resonance position by more than 100 GHz for the field of 0.25 T, to both higher and lower energies with opposite orientation of the magnetic field. Applicability of the terahertz SPR sensor is discussed, along with modeled design for the Kretschmann configuration.
2017-01-01T00:00:00ZSynthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4
http://hdl.handle.net/10084/120947
Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4
Praus, Petr; Svoboda, Ladislav; Dvorský, Richard; Reli, Martin; Kormunda, Martin; Mančík, Pavel
The nanocomposites of WO3 nanoparticles and exfoliated graphitized C3N4 (g-C3N4) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.
The WO3 nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C3N4 particles were prepared by calcination of melamine forming bulk g-C3N4, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m(2) g(-1). The nanocomposites were prepared by mixing of WO3 nanoparticles and g-C3N4 structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 degrees C. The real content of WO3 was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C3N4 particles were covered by the WO3 nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO3 nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.
The formation of heterojunction between both components was investigated by UV Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO3, which was explained by shielding of the g-C3N4 surface by bigger WO3 agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.
2017-01-01T00:00:00ZPrecision comparison of analytical and statistical-regression models for AWJ cutting
http://hdl.handle.net/10084/120438
Precision comparison of analytical and statistical-regression models for AWJ cutting
Hlaváč, Libor; Krajcarz, Daniel; Hlaváčová, Irena; Spadło, Sławomir
The article is focused at the comparison of results calculated using analytical model for determination of abrasive water jet cutting and equations prepared via application of the statistical-regression approach. The statistical-regression model (SRM) is based on measurement of a set of column holes cut in a plan parallel brass plate according to Box-Behnken design. The material and respective range of factors were selected so that they cover the largest possible scale of varying kerf shapes; brass 2.0402 (CuZn4OPb2), water pressure from 280 to 380 MPa, abrasive mass flow rate from 150 to 450 g/min and variable traverse speed from 25 to 75 mm/min. The main results arising from the experiments were the ideal diameters of the holes' sections in several selected depths of material and the cylindricity, i.e. the difference of the real shape of the "column" hole from the ideal one represented by a column with ideal diameter. The statistical-regression equations for calculation of the selected parameters were set-up. The comparison of the analytical model and the one created via statistical-regression was performed for bottom diameters of the produced holes. The reliability of the statistical-regression model is high within the tested scope of factors. However, its precision can be significantly reduced beyond the selected range of factors or by changes that cannot be involved in the regression (change of material wear character, etc.). Statistical processing of the measured data yields interesting relations between certain factors (abrasive mass flow rate, pressure) and respective results (diameters of holes, cylindricity). Therefore, the respective statistical-regression equations are also presented graphically. The comparison proved that the analytical model also has a very high accuracy and, moreover, its application is not limited by the selected ranges of factors.
V článku uvedeno Libor M. Hlaváč a Irena M. Hlaváčová.
2017-01-01T00:00:00Z