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A Method to Supress Interferences in Wigner-Ville Distribution
Pikula, Stanislav ; Pazdera, Luboš (referee) ; Hájek, Karel (referee) ; Beneš, Petr (advisor)
The doctoral thesis focuses on signal representation in the time-frequency domain with constant resolution. In theoretical introduction the possibilities of displaying a signal in time and frequency are summarized. Attention is concentrated on comparison of short-time Fourier Transform (STFT) and Wigner-Ville Distribution (WVD). The latter achieves a significantly better resolution, especially for a linearly modulated signal. The disadvantage of WVD, which is the presence of interferences resulting from the calculation of the instantaneous autocorrelation function, is described in detail. These interferences are due to the presence of multiple components in the signal or its non-linear modulation. Subsequently, several methods are discussed, which can suppress these interferences, but at the cost of resolution loss. One of the interference suppression methods is smoothed pseudo Wigner-Ville distribution. It is further used in this thesis for the analysis of interference suppression when various filtrations in the time-frequency plane are applied. Several signals with multiple components or various non-linear modulations are used. Based on the analysis, a method using a set of variously smoothed pseudo Wigner-Ville distributions is designed to estimate the time-frequency representation with high resolution and minimal interferences. To compare the results to other methods, the quantitative metrics used in the literature are compared. To select the appropriate one a new metric is suggested. It is applicable to simulated signals and uses mean square error. Based on the comparison, the Stankovi\'{c} measure is selected as the most appropriate for comparing results. The selected metric is used to determine the appropriate minimal number of differently smoothed pseudo Wigner-Ville distributions. Using the selected metric, the proposed method is compared with other methods. These are STFT with optimized window length, S-method with optimized parameter and optimization method using radial Gaussian kernel (RGK). These methods are compared based on the set of signals previously used for interference suppression analysis. In addition, noises are added to the signals. Finally, the methods are also compared based on the real bat echo signal. In conclusion, the proposed method outperforms the compared methods in suppressing interference and resolution.
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Charge Transport and Storage in a Supercapacitor Structure
Kuparowitz, Tomáš ; Zedníček, Tomáš (referee) ; Hájek, Karel (referee) ; Sedlák, Petr (advisor)
Práce se zabývá studiem superkondenzátorů (SC). Výstupem je detailní studie principů přenosu náboje ve struktuře SC, ukládání energie a nový náhradní model SC, který je založen na fyzikálních zákonitostech a principech SC. Dále byl vytvořen matematický model SC, který popisuje chování náboje v jeho aktivní vrstvě. SC byly testovány metodami umělého stárnutí. Závislosti poklesu parametrů SC vlivem různých metodik stárnutí jsou v práci shrnuty.
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Eddy Current Probe Design and its Application on Aircraft Composite Structures
Boháčová, Marie ; Hájek, Karel (referee) ; Kopec, Bernard (referee) ; Mazal, Pavel (advisor)
This thesis deals with design of an eddy current transducer which enables non-destructive inspection of composite aircraft structures primarily carbon fiber reinforced plastic (CFRP) in areas of manufacture and maintenance. The design of the transducer is based on analytical-experimental approach and its electrical and mechanical parameters were optimized to ensure a good signal to noise ratio at the six composite samples. These samples contain artificial discontinuities in the form of various types of defects. These defects are simulating the various types of damage created in the aircraft structure, especially delamination or thickness changes of composite materials. The experimental measurements, data collection and non-destructive evaluation were performed during the period. The result of this work is functional eddy current probe, which is reliably able to detect some damage of the carbon composite structures to the depth of 3,9 mm.
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Diagnostics and therapy of spiritual emergency - orienting study
Janečková, Barbora ; Bahbouh, Radvan (advisor) ; Břicháček, Václav (referee) ; Hájek, Karel (referee)
The doctoral dissertation contains of a definition of spiritual emergency, differential diagnosis, description of kinds of spiritual emergency. It looks on the therapeutical possibilities in working with these states. Part of the dissertation is analysis of semistructured interviews with clients and therapists who work with these kinds of problems. In the analysis of the interviews with therapists I center on their experience with the dynamics of spiritual emergence, its manifestation and possible existence of similar traits of clients with this diagnosis. Important parts of the interviews are the most effective ways of working with these clients. I was also interested in their own perception on how spiritual emergence occurs and on the possible change in the quality of life of the client after this episode. In the analysis of the interviews with the clients I question when spiritual emergence occurred, how it started, how long did it last and what were the reactions from outside. Important part is centered on the interventions which the client experienced and their efficiency. Case studies demonstrate typical traits described at spiritual emergency, as quite dramatic beginning, complete recovery and also an important change in value system.
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Diagnostics and therapy of spiritual emergency - orienting study
Janečková, Barbora ; Bahbouh, Radvan (advisor) ; Břicháček, Václav (referee) ; Hájek, Karel (referee)
The doctoral dissertation contains of a definition of spiritual emergency, differential diagnosis, description of kinds of spiritual emergency. It looks on the therapeutical possibilities in working with these states. Part of the dissertation is analysis of semistructured interviews with clients and therapists who work with these kinds of problems. In the analysis of the interviews with therapists I center on their experience with the dynamics of spiritual emergence, its manifestation and possible existence of similar traits of clients with this diagnosis. Important parts of the interviews are the most effective ways of working with these clients. I was also interested in their own perception on how spiritual emergence occurs and on the possible change in the quality of life of the client after this episode. In the analysis of the interviews with the clients I question when spiritual emergence occurred, how it started, how long did it last and what were the reactions from outside. Important part is centered on the interventions which the client experienced and their efficiency. Case studies demonstrate typical traits described at spiritual emergency, as quite dramatic beginning, complete recovery and also an important change in value system.
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Electrical installation of family house - implementing documentation
Hájek, Karel ; Morávek, Jan (referee) ; Mastný, Petr (advisor)
Main goals of this bechelor´s thesis are devided into three parts. First part introduces reader with power and data instalations issues including legislation necessary for project creation in electrickal engineering, object connection to distribution network, basic electric wiring including circuit breakers and electric wiring design in residential buildings, which mainly speaks about ways of installation of electric wiring and elektrical zones. In addition internal and external lighting protection and basic information about switchgear. Second part defines of project documentation creation, both design and text part. The last part is the practical part that looks into complete electrical installation of family house project, which contains marking both low-power and high-power circuits into plan view, house switchgear and electro meter scheme, LPS design and technical report with economical evaluation.
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Memristor with PWL-type characteristic
Holas, Jiří ; Hájek, Karel (referee) ; Biolek, Dalibor (advisor)
Bachelor’s thesis deals with an analog emulation of memristor memory with PWL-type characteristic which is designed for modern digital memories. The first part of the document summarizes the basic memristor characteristics and rules of their proper modeling. The next parts present the circuit implementation and computer simulation. The printed circuit board design and prototype measurement are included.
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Memcapacitor Emulator
Weiss, Lukáš ; Hájek, Karel (referee) ; Biolek, Dalibor (advisor)
This bacherol's thesis deals with designing a memcapacitor with piecewise linear (PWL) characteristic. The memcapacitor is a part of mem-systems predicted by Leon Chua in 70's and 80's of the last century. A big attention was given to mem-devices and mem-systems in the field of electrical engineering after the memristor's discovery in HP laboratories in 2008. In the first step, the summary of basic information about mem-systems is reported. The second part contains some design solutions of the analogue memcapacitor emulator. The third part implements selected circuit into the PSPICE simulation. Concrete models of modern active integrated circuits are used. The last part contains a circuit solution of the designed model on the PCB.
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Noise and Transport Analysis of the Niobium Oxide Layers
Sita, Zdeněk ; Hájek, Karel (referee) ; Koktavý, Bohumil (referee) ; Grmela, Lubomír (advisor)
Kondenzátor na bázi oxidu niobu je novým typem pasívní součástky, jehož vývoj byl motivován snahou vyřešit hlavní nedostatky tantalového kondenzátoru – omezený zdroj tantalové suroviny a nebezpečí hoření při průrazu. Chování kondenzátoru na bázi oxidu niobu lze stejně jako u tantalového kondenzátoru popsat prostřednictvím reverzní MIS struktury. Pro studium mechanismu transportu nosičů nábojů v dielektriku Nb2O5 a pro stanovení fyzikálních parametrů, které řídí zbytkový proud, bylo využito měření V-A charakteristik v normálním a reverzním módu při 77 a 300K, dále závislosti kapacity ochuzené vrstvy na napětí a frekvenci, teplotní a časové závislosti zbytkového proudu a spektrální hustoty šumu ve frekvenční a časové doméně při různých napětích. Experimentální data potvrdila platnost navrženého pásového diagramu MIS struktury a poskytla jeho klíčové parametry. Bylo ověřeno, že transport nosičů náboje v NbO kondenzátorech je určen ohmickou, Poole-Frenkelovou a tunelovou složkou v normálním módu, a Schottkyho emisí v reverzním módu. V rozsahu standardních aplikačních napětí dominují v normálním módu Poole-Frenkelova emise a v reverzním módu Schottkyho emise. Při vyšších napětích v normálním módu určuje průrazné napětí kondenzátoru tunelový mechanismus. V reverzním módu rozhoduje o odolnosti vůči tepelnému průrazu kondenzátoru výška bariéry mezi dielektrikem a anodou. Bylo zjištěno, že NbO a Tantalové kondenzátory mají stejný mechanismus vodivosti. Specifika NbO anody se projevují pouze v rozdílných hodnotách parametrů pásového diagramu, nikoliv v principech mechanismu transportu nosičů náboje. To vysvětluje základní rozdíl mezi oběma kondenzátory, který je v kvalitě dielektrické vrstvy na přechodu anody a dielektrika. Nižší potenciálové bariéry a vyšší počet defektů v dielektriku, který je způsoben dalším stabilním oxidem, má za následek vyšší zbytkový proud NbO kondenzátoru. Tento jev však nemá žádný vliv na spolehlivost součástky. Teoretické modely a vybrané testovací metody byly použity k volbě vhodných materiálů anody, ke stanovení vhodných dopantů a k optimalizaci technologie anodické oxidace. Byla nalezena korelace mezi parametry transportu nosičů náboje a spolehlivostí, a na základě experimentálních dat byly navrženy optimalizace výrobního procesu kondenzátorů. Lepší porozumění transportním mechanismům v NbO kondenzátorech umožnilo úplný popis nové součástky na bázi oxidu niobu. Byly zdůrazněny silné a slabé stránky této nové technologie a nalezeny nástroje pro optimalizaci procesů, které umožní vyšší spolehlivost a efektivitu NbO kondenzátorů.
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Correlation of AE Signal Changes to Rolling Contact Damage Propagation
Nohál, Libor ; Čermák, Jan (referee) ; Hájek, Karel (referee) ; Hutař, Pavel (referee) ; Mazal, Pavel (advisor)
This PhD thesis deals with the experimental study of more precise rolling contact fatigue damage detection using acoustic emission method. A series of experiments was carried out on two representatives bearing steels and the analysis of sensitivity for the presence of contact damage was performed on selected parameters of acoustic emission. The extent of damage was classified into four classes and signal parameters the most characterizing the development of damage were correlated with the extent of damage. It was also verified the influence of lubricants on acoustic emission signals. The results have an impact on the implementation of more precise rolling contact fatigue tests and evaluation of parameters of acoustic emission signal. On the basis of experiments was established methodology for more precise RCF testing method using acoustic emission on test-rig AXMAT II.
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