A Terrestrial Multiple-Receiver Radio Link Experiment at 10.7 GHz - Comparisons of Results with Parabolic Equation Calculations

This work presents the results of a terrestrial multiple-receiver radio link experiment at 10.7 GHz. Results are shown in the form of the power levels recorded at several antennas attached to a receiving mast. Comparisons of the measurement data with theoretical predictions using a parabolic equation technique show that, due to the complex propagation environment of the troposphere in terms of the refractive index of air, closer agreement between measurements and simulations can be achieved during periods of standard refractive conditions

Every Large Point Set contains Many Collinear Points or an Empty Pentagon

We prove the following generalised empty pentagon theorem: for every integer $\ell \geq 2$, every sufficiently large set of points in the plane contains $\ell$ collinear points or an empty pentagon. As an application, we settle the next open case of the "big line or big clique" conjecture of K\'ara, P\'or, and Wood [\emph{Discrete Comput. Geom.} 34(3):497--506, 2005]

Atomic force microscopy analysis of nanoparticles in non-ideal conditions

Nanoparticles are often measured using atomic force microscopy or other scanning probe microscopy methods. For isolated nanoparticles on flat substrates, this is a relatively easy task. However, in real situations, we often need to analyze nanoparticles on rough substrates or nanoparticles that are not isolated. In this article, we present a simple model for realistic simulations of nanoparticle deposition and we employ this model for modeling nanoparticles on rough substrates. Different modeling conditions (coverage, relaxation after deposition) and convolution with different tip shapes are used to obtain a wide spectrum of virtual AFM nanoparticle images similar to those known from practice. Statistical parameters of nanoparticles are then analyzed using different data processing algorithms in order to show their systematic errors and to estimate uncertainties for atomic force microscopy analysis of nanoparticles under non-ideal conditions. It is shown that the elimination of user influence on the data processing algorithm is a key step for obtaining accurate results while analyzing nanoparticles measured in non-ideal conditions

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Matematicko-fyzikální fakulta Katedra aplikované matematiky Autoreferát doktorské práce Kombinatorická a v´ypočetní geometrie (Extremální otázky v geometrii) Jakub Čern´

Protective double-layer coatings prepared by plasma enhanced chemical vapor deposition on tool steel

Hydrogenated diamond-like carbon films were prepared on high-speed steel substrates using low pressure radio-frequency capacitively coupled discharge (13.56 MHz) using methane mixed either with hydrogen or argon. A dc self-bias was induced by the rf discharge and accelerated the ions towards the substrates during the whole deposition process. Prior to the carbon film deposition and to improve the adhesion, the substrates were subject to plasma nitriding and coated with a silicon oxide layer using the same reactor. The deposited films were optically characterized (UV-IR) and by using a combination of Rutherford backscattering spectroscopy and elastic recoil detection the atomic composition was determined. The carbon films high hardness (~ 18 GPa) was assessed from indentation tests. Adhesion tests revealed critical loads up to 13.6 N for the carbon films deposited on steel substrates using silicon oxide interlayer. Friction coefficient varied from 0.02 against diamond and 0.23 against steel counterpart. The results suggest that hard carbon films can be deposited on steel substrate using a silicon oxide intermediate layer deposited by the same plasma process with commercial potential

Building Entry Loss and Delay Spread Measurements on a Simulated HAP-to-Indoor Link at S-Band

<p/> <p>Results from a measurement campaign emulating the high altitude platform (HAP)-to-indoor communication channel at S-band are presented in this paper. A link was established between a transmitter carried by a helicopter, representing the HAP, and a receiver placed at several locations in different building types including an airport, an office building, a shopping mall, a residential house, and a skyscraper. A wideband, directive channel sounder was used to measure building entry loss and time delay spread. Results of the building entry loss are presented as a function of building type, elevation, and building entry angle. Results of delay spread for each building are also provided.</p