A method for the visualization of high phase gradients in a microscopic image

Holografická mikroskopie je nekonvenční mikroskopická technika, vhodná zvláště pro vzorky s malou optickou hustotou, která umožňuje zviditelnit index lomu pozorovaných objektů. Na Ústavu fyzikálního inženýrství Fakulty strojního inženýrství VUT v Brně byl sestrojen unikátní transmisní digitální holografický mikroskop (TDHM). Pořízené snímky (hologramy) jsou zpracovány metodou založenou na Fourierově ransformaci, čímž je zrekonstruována intenzita a fáze světelné vlny procházející pozorovaným objektem. Fáze popisuje index lomu a tloušťku pozorovaného objektu. V místech, kde se mění index lomu nebo tloušťka, dochází i ke změně fáze. Úkolem této bakalářské práce bylo najít metodu pro zviditelnění míst s vysokým gradientem fáze. Podařilo se vytvořit metodu, která nevyžaduje navazování fáze, a proto je vhodná pro libovolné obrazy pořízené TDHM. Tato metoda byla implementována do počítačového programu Gradient3D, který kromě výpočtu gradientu ve dvou a třech rozměrech umožňuje i vytváření barevných obrazů, jejichž složkami jsou kombinace intenzity, fáze a gradientu. Program též umožňuje odstranění falešných gradientů v místech s nízkou intenzitou, kde je hodnota fáze nespolehlivá. Program byl testován na několika souborech hologramů pořízených TDHM při pozorování biologických vzorků.Holographic microscopy is an unconventional microscopy technique suitable especially for transparent samples. It enables to visualize the refractive index of observed objects. A unique transmitted-light digital holographic microscope (TDHM) has been constructed at Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology. Holograms captured by the microscope are processed by means of a technique based on the Fourier transform in order to reconstruct the intensity and phase of the light waves passing through the observed object. The phase describes the object refractive index and thickness. In places where the object refractive index or thickness changes, also the phase does. The task of this bachelor thesis was to find a method for visualizing places with high phase gradient. A gradient computation method which was created does not require phase unwrapping and is therefore suitable generally for any images. The method was implemented in a computer software called Gradient3D, which enables not only to compute the phase gradient in two and three dimensions, but also to create color images composed from combinations of intensity, phase and gradient. It also contains methods for handling places with low reconstructed intensity where the phase value is unreliable and usually causes false phase gradients. The program has been tested on several image sets from the TDHM capturing biological specimens.

Study of Hydrophobic Domains in Humic Acids

Fyzikálně-chemická povaha hydrofobních domén huminových kyselin byla studována z několika hledisek. K objasnění významu fluorescenčních spekter byly vzorky podrobeny sekvenční frakcionaci, která pomohla k částečnému objasnění vlivu vodorozpustných složek, volných a vázaných lipidů na optické vlastnosti huminových kyselin. Výsledky naznačily, že fluorescenční píky tradičně přiřazované superpozici jednotlivých struktur jsou spíše důsledkem agregačních vlastností huminových molekul tvořících vlivem hydrofobního efektu zdánlivě vysoce aromatické struktury. Dále pak bylo zjištěno, že na optických vlastnostech huminových kyselin mají podíl i molekuly, které nemají primárně fluoroforní nebo chromoforní vlastnosti. Tento pohled je v souladu s teorií supramolekulárního uspořádání huminových kyselin. Dále byly studovány agregace, konformační chování a termodynamická stabilita huminových kyselin pomocí metody vysoce rozlišovací ultrazvukové spektroskopie. Bylo prokázáno, že huminové kyseliny mají schopnost agregovat už od velmi nízkých koncentrací (The nature of hydrophobic domains in humic acids was studied from different points of view. To shed light on the meaning of fluorescent spectra, the measured samples underwent the sequential extraction which partially revealed the role of water-soluble components, free and bond lipids in optical properties of humic acids. The results indicated that the fluorescence peaks traditionally attributed to the superposition of individual chemical structures are rather a result of aggregation properties of humic molecules and hydrophobic effect driving aromatic molecules together forming aggregates apparently large molecular weight. Further, it seems that there is a significant influence of non-fluorophores and non-chromophores on the optical properties of humic acids. Results are consistent with the theory on supramolecular structure of humic acids. Next, the aggregation, conformational behaviour and thermodynamic stability of humic acids were studied by high resolution ultrasonic spectroscopy. It was demonstrated that humic molecules are able to interact and form aggregates at very low concentration (

Cheating the Textbook System

The price of my German textbook is equal to three months of rent with utilities back home. My books for Introduction to Cultural Anthropology equal the cost of feeding my family for a whole month. But these aren’t news. American Enterprise Institute reports that the college textbook prices “are 812 percent higher than they were a little more than three decades ago.” Some students came to Gettysburg aware of costs, so they moved into first year dorms armed with Amazon Prime memberships and accounts on sites for renting textbooks. Some looked for classes that offer cheaper (or no) textbooks in advance. Because that seems to be our only solution: to learn to shrug shoulders at the injustice and adapt because we learned that it’s normal to pay for education we’re already paying so much for. Having textbooks is considered a required part of enrolling in classes, and the sacrifice that students have to make to afford them is taken for granted. [excerpt

Build Your Resume and Leave an Impact: Publish in The Cupola

The Cupola actively serves as a resistance to the academic publishing system that makes knowledge exclusive to the wealthy and privileged who have the ability to access it. Instead of keeping scholarship “behind the paywall” with high subscription costs, The Cupola and the other open repositories keep the knowledge freely accessible to everyone at any time, anywhere in the world. The Cupola has only existed since April 2012, but we have already reached 1 million downloads (...) To find out more about how The Cupola is perceived on the campus and how to make more students interested in student nominations, I talked to professors, current students and alumni from Gettysburg College. We discussed the issues of representation in writing and publishing and the role of The Cupola in comparison. Thus, this article is a collection of various accounts on the importance of student scholarship and a collection of advice on how to use The Cupola to your benefit. [excerpt

PELUANG DAN TANTANGAN LAOS DALAM PROYEK KERETA CEPAT TIONGKOK-LAOS 2015-2023

This article discusses cooperation between Laos and China, namely the China-Laos high-speed train which began construction in 2016. This research uses dependency theory, where a country that continuously needs another country is indirectly dependent on that country. Many factors influence this, including superior technology, a stronger economy and others, such as Laos which needs China to carry out the China-Laos high-speed train project. This research is descriptive qualitative in nature which describes, illustrates and explains events or phenomena and facts by sorting, collecting and generalizing facts. In this research, the author presents and provides a detailed description of the opportunities and challenges faced by Laos in the 2015-2023 China-Laos high-speed train project. The China- Laos high-speed rail project provides benefits for both countries such as increased connectivity between regions. However, behind the benefits, there are also quite a few challenges faced by Laos in this project, starting from capital challenges, natural sustainability, increasing debt burdens and the emergence of Laos' dependence on China

The Empirical Determinants of the Adoption of a Political Risk Assessment Function in International Firms

This paper seeks to conceptualise a new approach to the identification of the factors influencing the adoption of a political risk assessment (PRA) function. The research population will comprise a convenience sample of Czech and Slovak international firms. The information whether or not a firm has set up a PRA function will be obtained via a questionnaire survey. By making use of firm value maximization and risk aversion and considering the rationale for risk management activities: (i) reducing the expected costs of financial distress; (ii) reducing the risk premiums payable to various partners; (iii) increasing investment possibilities; and (iv) reducing expected tax payments, we develop a number of determinants to be employed in PRA studies; and we propose a model for predicting the PRA adoption decision

Ground states of the generalized Falicov-Kimball model in one and two dimensions

A combination of small-cluster exact-diagonalization calculations and a well-controlled approximative method is used to study the ground-state phase diagram of the spin-one-half Falicov-Kimball model extended by the spin-dependent on-site interaction between localized ($f$) and itinerant ($d$) electrons. Both the magnetic and charge ordering are analysed as functions of the spin-dependent on-site interaction ($J$) and the total number of itinerant ($N_d$) and localized ($N_f$) electrons at selected $U$ (the spin-independent interaction between the $f$ and $d$ electrons). It is shown that the spin-dependent interaction (for $N_f=L$, where $L$ is the number of lattice sites) stabilizes the ferromagnetic (F) and ferrimagnetic (FI) state, while the stability region of the antiferromagnetic (AF) phase is gradually reduced. The precisely opposite effect on the stability of F, FI and AF phases has a reduction of $N_f$. Moreover, the strong coupling between the $f$ and $d$-electron subsystems is found for both $N_f=L$ as well as $N_f < L$.Comment: LaTex, 20 pages, 7 figure