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Bubble dynamics in drinks
Broučková, Zuzana ; Trávníček, Zdeněk ; Šafařík, P.
This study introduces two physical effects known from beverages: the effect of sinking bubbles and the hot chocolate sound effect. The paper presents two simple „kitchen” experiments. The first and second effects are indicated by means of a flow visualization and microphone measurement, respectively. To quantify the second (acoustic) effect, sound records are analyzed using time-frequency signal processing, and the obtained power spectra and spectrograms are discussed.
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Oscillations of Bubbles Attached to a Capillary: Case of Pure Liquid
Vejražka, Jiří ; Vobecká, Lucie ; Tihon, Jaroslav
In this contribution, we therefore present results of a linear inviscid theory for shape oscillations of a spherical bubble, which is in contact with a solid support. The theory allows determining eigenmode, but also response of the bubble shape to a motion of its support or to volume variations. Present theory covers also the cases previously analyzed by Strani and Sabettaand Bostwick and Steen, and it can be applied to both bubbles and drops. The theory has been compared to experiments. Good agreement is found for the case of small bubbles, which have spherical static shape. Experimental results for larger bubbles and drops deviate from the theory, if a neck is formed. It is shown that this deviation correlates well with a ratio of bubble volume to the maximum volume, when a detachment occurs.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22012112614031 - PDF
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Microbubble Generation by Fluidics. Part II: Bubble Formation Mechanism
Tesař, Václav
Author develops a facility for generation of sub-millimetre sized air bubbles in water. A promising and economically viable method, based on author's earlier experience, is fragmentation of bubbles by oscillation while they are still at the aerator exit locations. Understanding the mechanism by which the oscillation affects bubble formation is a pre-requisite to new aerator design. Results obtained so far reveal a strange bubble size independence on the applied acoustic power, frequency of oscillation and the character of aeratoir body.
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Dynamics of Shape Oscillations of a Bubble Attached to a Capillary Tip
Vobecká, Lucie ; Vejražka, Jiří ; Orvalho, Sandra ; Zedníková, Mária ; Tihon, Jaroslav
The shape oscillations of a bubble, which is attached to a tip of a capillary tube, are studied experimentally. It is observed that the attachment leads to an appearance of an additional low-frequency mode (denoted as mode 1), when compared to standard theories of oscillations of free bubbles or drops. It is observed that the frequency of mode 1 scales with the bubble size as f ~ D^(-2). The oscillation dynamics of a bubble is strongly influenced if some surface active agent is present in the liquid. Due to interfacial elasticity, the surfactants presence in low concentration increases the oscillation frequency. The decay of oscillations is also faster, probably due to an increase of energy dissipation by Marangoni stresses.
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Oscillation of a Bubble in Surfactant Solution
Vobecká, Lucie ; Vejražka, Jiří ; Zedníková, Mária ; Orvalho, Sandra ; Tihon, Jaroslav
The decay of shape oscillations of a bubble in solutions of a soluble non-ionic surfactant are studied by means of high-speed imaging. The oscillations are induced by a sudden motion of a capillary, to which the bubble is attached. The bubble then either detaches or remains attached at the capillary. In both cases, the observed bubble shape is decomposed into eigenmodes (Legendre polynomials). The frequency f and the decay time τ of the lowest oscillation mode are evaluated. Their dependences on the surfactant concentration c, on the bubble size and on the bubble age are studied.
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Asset price bubbles of American markets - causes of their formation, impacts on the economy of the USA and world
Klimo, Ján ; Neumann, Pavel (advisor) ; Jelínek, Tomáš (referee)
The goal of this bachelor thesis is to identify the causes of the formation of asset price bubbles based on the observation of historic cases of price bubbles observed on the American markets, to show their impact on the economy and to project potential scenarios of the current financial crisis. The first chapter introduces basic psychological concepts of the formation of asset price bubbles and explains their macroeconomic implications. The second chapter focuses on specific American asset price bubbles. It applies the theoretical concepts from the first chapter, for each asset price bubble concrete causes and impacts on the economy are described. This section is concluded with a list of their common characteristics. The final chapter analyzes the current financial crisis. It explains its background, causes of the housing bubble and factors leading to its bust. The comparison of stock market crashes and housing market crashes serves as a basis for the projection of possible scenarios of the current financial crisis based on an empirical study of past banking crises. The author thereby presents potential development in five important economic areas: stock markets, housing market, real GDP per capita, unemployment and public debt.
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The circumstances of speculative bubbles presence in financial markets
Ševčík, Michal ; Veselá, Jitka (advisor)
This bachelor thesis is focused on financial crises arisen throughout economic history. It explains the term of financial crisis, speculative bubble, and it presents chosen models of financial crises, which can be identified within concrete historical cases analyzed in the first two chapters. Theoretical approaches to the circumstances of speculative bubbles presence are part of the final section of this work, where the main roles play the rationality and irrationality of an individual, crowd, and market and psychological factors as well. At the end, a possible usefulness is mentioned contrary to the events of the first two chapters.
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