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Determination of absolute quantum yield of luminescence
Smísitel, Petr ; Valenta, Jan (advisor) ; Herynková, Kateřina (referee)
In this bachelor thesis we will study the determination of absolute quantum yields (efficiency) of photoluminiscence, which is equal to the ratio of number of emitted photons and number of absorbed photons. The common approach is to compare the absorption and luminescence spectrum. The main experimental problem is to eliminate the influence of angular dependence of reflection, emission and scattering. Therefore it is convenient to use the integrating sphere which eliminate most of the problems of relative measurements of quantum yield. In detail we will describe the method to determine the quantum yields of luminescence using the integrating sphere including the description of the experimental equipment and the procedure of processing data and estimation of uncertainty. Finally, we apply the procedure to solid and liquid samples containing silicon nanocrystals. We will measure the dependence of quantum yields on the applied excitation wavelength. 1
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Nanoscopy, spectroscopy and modication of individual nanoobjects in liquid environment
Smísitel, Petr ; Valenta, Jan (advisor) ; Galář, Pavel (referee)
In this diploma thesis we will study the luminescence properties of nanocrystals. We will summarize the basic division according to size and standard method of theoretical description of semiconductor and metal nanocrystals. We will describe the luminescence properties of nanocrystals and the influence of the surrounding environment. In the se- cond part of the thesis we will follow up the construction of an apparatus for imaging luminescence spectroscopy intended for the measurement of individual nanoobjects in a liquid environment. Finally, we will study luminescence properties of organixally passi- vated metal clusters in a liquid environment with changes in temperature and excitation intensity. We compare the luminescence of gold nanocrystals with and without long po- lyethylene glycol chains bound on the surface. 1
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Construction of velocity sections in seismic prospection
Mokrá, Zuzana ; Vilhelm, Jan (advisor) ; Valenta, Jan (referee)
Aim of this thesis was to compare four different methods of construction of velocity sections in seismic prospection: t0 method, general inversion method, method based on presumption of linear velocity gradient medium and tomography. Each method assumes medium with different characteristics, calculations solve both direct and inverse problems, various types of seismic waves are utilised in calculations. It was determined, under which conditions any of afore mentioned methods can be used in common 2D seismic survey. Further on the thesis examines alternative source of seismic energy - set for dynamic penetration testing, which is commonly used in engineering geology. This source is compared to standard seismic hammer source. The thesis evaluated possibility of use this alternative source in seismic survey.
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Optical responses of biomolecules on regular metal plasmonic nanostructures
Šubr, Martin ; Procházka, Marek (advisor) ; Michl, Martin (referee) ; Valenta, Jan (referee)
Title: Optical Responses of Biomolecules on Regular Metal Plasmonic Nanostructures Author: Martin Šubr Department: Institute of Physics of Charles University Supervisor of the doctoral thesis: prof. RNDr. Marek Procházka, Dr., Institute of Physics of Charles University Abstract: Adsorption of molecules on metal plasmonic nanostructures leads to significant enhancement of many optical processes, such as Raman scattering (surface-enhanced Raman scattering - SERS) or fluorescence (surface-enhanced fluorescence - SEF). Two groups of substrates were tested within this thesis: (i) Silver nanorods prepared by oblique angle vapor deposition, and (ii) silver and gold nanoislands growing on magnetron-sputtered polytetrafluoroethylene film. Step-by- step optimization process was performed on the nanoislands in order to obtain optimum SERS sensitivity and reproducibility. Detailed SERS intensity profiles were obtained using gradient nanostructures with the localized surface plasmon resonance (LSPR) condition varying across the sample and three different excitation wavelengths. It was also found that spectral position and height of the LSPR band can be controlled simultaneously using mixed gold/silver nanoislands. Detailed investigation of polarization- and angular- dependences of anisotropic silver nanorods was...
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Sociological aspects of translation norms in legal environments
Valenta, Jan ; Králová, Jana (advisor) ; Ježková, Slavomíra (referee)
This thesis paper attempts to discover the processes used to set up and negotiate translation norms in legal environments. It is based on the existing theoretical knowledge of legal translation and on the theoretical works on translation norms, especially the works by Gideon Toury, Theo Hermans, Andrew Chesterman and other authors. The aim of this thesis paper is to confront these theories with the every-day experiences of translating in legal environments. The research method used for this purpose is qualitative sociological research - a combination of the analytical procedures of grounded theory first drafted by Strauss and Glaser and data collection procedures based on "problem-centered interviews" and on the investigation of documents. The total of 10 respondents - translators who work or have worked in law firms - have participated in the survey. Legal translation is very specific in terms of the processes whereby translation norms are set up and negotiated. The key issue is the issue of liability. Translators employed in law firms are not liable for the final wording of the translation - it is the lawyer who is held liable for the translation that forms a part of his or her legal service or advice. This influences the mutual relations between the translator and the lawyer who plays the role of the...
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New approaches in higt-resolution shallow seismic prospection
Valenta, Jan ; Dohnal, Jiří (advisor) ; Rudajev, Vladimír (referee) ; Bárta, Jaroslav (referee)
This work deals with the application of seismic methods in high-resolution near-surface prospection. Two topics are covered in this text. The first one describes processing and application of 3D shallow seismic refraction, while the second one deals with possible methods of identification and filtration of S-waves. The processing of the 3D seismic refraction data is currently carried out mainly by means of the seismic tomography. Because the tomography method usually works with the gradient model of the subsurface, an approach to the layer-based model was sought. The solution was found in a modification of the time-term method. The time- term method was modified to handle also the lateral variations of velocity in highly heterogeneous media. REFRACT3D computer program for data processing using the time-term method was developed. The modified time-term method was successfully tested during the archaeological prospection of the Děvin Castle and during the pro- spection of the shallow subsurface of the Ostaš seismic station. The results from the time-term method were compared with the results obtained by the first arrival travel time tomography. In the case of the Děvin Castle the time-term results surpass the tomography one, while at the locality of Ostaš the tomography results are better. The imaging...
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Advanced spectroscopic characterization of quantum dot ensembles
Greben, Michael ; Valenta, Jan (advisor) ; Linnros, Jan (referee) ; Vácha, Martin (referee)
Title: Advanced spectroscopic characterization of quantum dot ensembles Author: Michael Greben Department: Department of Chemical Physics and Optics Supervisor of the doctoral thesis: Prof. Jan Valenta, Ph.D. Abstract: Semiconductor quantum dots (QDs) are small crystallites whose sizes (of the order of nm) cause spatial confinement of carriers in all 3 dimensions. As result, QDs often reveal very different physical properties in comparison with their bulk counterparts. From the optical point of view, the broadening of bandgap with QD-size shrinking is particularly interesting. It is a purely quantum mechanical effect that results from quantum confinement (QC), i.e. dimensional limitations of excitons. A strong spatial confinement leads to a relaxation of momentum (Heisenberg uncertainty principle), consequently, larger overlap of the wave-functions of carriers results in significant increase of probability of radiative recombination. Therefore ensembles of QDs are promising candidates for new generations of photonic and photovoltaic devices. This PhD thesis is primary focused on detailed spectroscopic characterization of ensembles of direct (PbS) and indirect (Si) semiconductor QDs in both colloidal (toluene) and matrix-embedded (oxide or oxinitrides multilayers) forms. The oleic- acid capped PbS QDs were...
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4D Characteristics of Electric Resistivities and Elastic Parameters of Crystalline Rock Massif
Jirků, Jaroslav ; Vilhelm, Jan (advisor) ; Hartvich, Filip (referee) ; Valenta, Jan (referee)
6 Abstract (ENG) The thesis deals with the use of geophysical methods for non-invasive monitoring of geological processes occurring in crystalline massifs. Such a methodology can be used, for example, in monitoring the processes in future and existing deep geological repositories. The main geophysical methods monitoring changes in the rock mass are multielectrode electrical resistivity tomography (ERT) and high-frequency seismics. Monitored parameters that change over time are the apparent electrical resistivity and parameters of excited elastic waves. Based on long-term measurements at the field bases, changes in the rock mass are described. Interpretations of such changes are made using our own laboratory measurements quantifying the effect of groundwater saturation of samples and the effect of sample disruption (mechanical / thermal) on their electrical resistivity. With respect to modelling and interpretation of the apparent resistivity cross-sections the sensitivity function calculation was proposed and carried out in the geometry of used field layout. It was proven that seismic transmission may be carried out in an underground work reliably for long time. Seismic measurement shows that in the environment of underground works excavated decades ago, we practically do not observe any changes in the...
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Separation of induced and remanent sources of magnetic anomalies on the Moon
Vávra, Ondřej ; Kletetschka, Günther (advisor) ; Valenta, Jan (referee)
During every full Moon our natural satellite passes through the Earth's magnetotail. For about 6 days the moon is exposed to a much stronger magnetic field, which induces magnetization in the paramagnetic and ferromagnetic minerals.. I'm trying to find a trace of these minerals in orbital magnetometric data and suggest a new way of analysing the magnetometer data suited for finding iron deposits. In the theoretical part of this work, I presented basic concepts of magnetism, described the magnetosphere, focusing on the dynamic nature of the magnetotail, which is directly influenced by the interaction of the magnetosphere with the fast moving particles of the solar wind. In the computational part, I plotted maps of the magnetometric data from the satellite Kaguya (SELENE) for times in which the Moon is in the Earth's magnetotail and reference maps from times in which the Moon is in the interplanetary magnetic field. I subtracted the data thus making a plot of the induced anomalies. I managed to confirm the occurrence of one of the anomalies in two separate magnetotail events. The induced anomaly located on the northern rim of the South Pole - Aitken Basin likely shows a signature of significant iron deposits.
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Advanced spectroscopic characterization of quantum dot ensembles
Greben, Michael ; Valenta, Jan (advisor)
Title: Advanced spectroscopic characterization of quantum dot ensembles Author: Michael Greben Department: Department of Chemical Physics and Optics Supervisor of the doctoral thesis: Prof. Jan Valenta, Ph.D. Abstract: Semiconductor quantum dots (QDs) are small crystallites whose sizes (of the order of nm) cause spatial confinement of carriers in all 3 dimensions. As result, QDs often reveal very different physical properties in comparison with their bulk counterparts. From the optical point of view, the broadening of bandgap with QD-size shrinking is particularly interesting. It is a purely quantum mechanical effect that results from quantum confinement (QC), i.e. dimensional limitations of excitons. A strong spatial confinement leads to a relaxation of momentum (Heisenberg uncertainty principle), consequently, larger overlap of the wave-functions of carriers results in significant increase of probability of radiative recombination. Therefore ensembles of QDs are promising candidates for new generations of photonic and photovoltaic devices. This PhD thesis is primary focused on detailed spectroscopic characterization of ensembles of direct (PbS) and indirect (Si) semiconductor QDs in both colloidal (toluene) and matrix-embedded (oxide or oxinitrides multilayers) forms. The oleic- acid capped PbS QDs were...
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