|
|
Optical levitation of dielectric objects in an external electric field
Zemánková, Tereza ; Flajšmanová,, Jana (referee) ; Svak, Vojtěch (advisor)
The bachelor's thesis deals with the optical levitation of a dielectric microparticle in vacuum and its displacement by an external electric field. The theoretical part mathematically describes the laser beam, in which particles are stably trapped. Subsequently, the principles of optical trapping, particle confinement and the most common experimental geometries of optical traps, e.g. counter-propagating beams, optical levitation and optical tweezers, are introduced. Because the trapped particle behaves very similarly to a harmonic oscillator excited by white noise, at the end of the theoretical part there are presented the equations of motion of the particle and their solutions for various cases, including Langevin equation of motion. The experimental part describes two experimental setups, in the assembly of which I participated. In the last part results of two main experiments are presented - displacement of the trapped particle by an external electric field, including determination of its charge, driving the particle by controlled white noise and determination of the effective temperature of stochastic motion of the particle.
|
|
|
Cooling of thermal motion of optically levitated nanoobjects
Zemánková, Tereza ; Flajšmanová, Jana (referee) ; Jonáš, Alexandr (advisor)
Diplomová práce se zabývá optickou levitací dielektrických nanočástic a chlazením jejich tepelného pohybu. Zafokusováním dvou protiběžných laserových svazků lze částici stabilně zachytit mezi ohnisky obou svazků. Následnou aplikací vnějšího elektrického pole na opticky zachycenou nabitou částici a správným nastavením zpětnovazebné smyčky je možné částici odebírat energii, zmenšovat její varianci polohy, a tedy chladit tepelný pohyb částice. Práce je rozdělena do tří hlavních kapitol. V první je rozebrán teoretický úvod do optického chytání, popsána dynamika zachycené částice a propojení s experimentální částí. Je zde popsáno schéma experimentální sestavy, příprava částic pro experimenty, detekce polohy částice, návod, jak správně optickou sestavu naladit, a kalibrace dat na jednotky SI. Ve druhé části jsou uvedeny různé způsoby chlazení tepelného pohybu opticky levitující částice. Experimenty provedené s jednou zachycenou částicí jsou porovnány s teoretickým modelem. V laserovém svazku s kruhovým profilem byla částice chlazena v jedné ose a eliptický profil svazku umožnil chladit tepelný pohyb částice ve dvou osách. Ve třetí části je rozebráno zachycení a interakce dvou levitujících částic, vznik normálních módů a jejich následné chlazení. Experimentálně získaná data jsou porovnána s teoretickými modely.
|
|
|
Optical levitation of dielectric objects in an external electric field
Zemánková, Tereza ; Flajšmanová,, Jana (referee) ; Svak, Vojtěch (advisor)
The bachelor's thesis deals with the optical levitation of a dielectric microparticle in vacuum and its displacement by an external electric field. The theoretical part mathematically describes the laser beam, in which particles are stably trapped. Subsequently, the principles of optical trapping, particle confinement and the most common experimental geometries of optical traps, e.g. counter-propagating beams, optical levitation and optical tweezers, are introduced. Because the trapped particle behaves very similarly to a harmonic oscillator excited by white noise, at the end of the theoretical part there are presented the equations of motion of the particle and their solutions for various cases, including Langevin equation of motion. The experimental part describes two experimental setups, in the assembly of which I participated. In the last part results of two main experiments are presented - displacement of the trapped particle by an external electric field, including determination of its charge, driving the particle by controlled white noise and determination of the effective temperature of stochastic motion of the particle.
|
|
|
The Influence of Online Social Networks on the Perception of Public and Privat Categories: Sharing Information Within a profile on Facebook
Zemánková, Tereza ; Řehořová, Irena (advisor) ; Marcelli, Miroslav (referee)
The main theme of the thesis are social networks which has become more and more significant communication means these days. It mainly focus on the "public" and "private" categories that appear at social networks - especially on Facebook. Theory brings different views of traditional authors Hannah Arendt and Jürgen Habermas based on antagonistic nature of this dichotomy - public and private. These approaches are complemented by a modern concept of an american anthropologist Susan Gal, which serves as an alternative. The second part deals with the qualitative research and its results that show how Facebook users percieve and build private and public areas on this social network. Where is the border between them and if there is a possibility in this dynamic environment to find similarities or differences from the traditional conception. Key words Social Network Sites, Facebook, New media, Private, Public.
|
|
| |
guest ::
RSS feed.