1,720,952 research outputs found
Thermal desorption studies of volatiles released during heating of food oils
No full textLipid degradation occurs extensively during deep fat frying, and controlling it is a great challenge, at least in part because the reaction mechanisms responsible remain controversial. With current trends towards increasing unsaturated fats in frying oils, a more complete understanding of these pathways becomes critical. To gain more detailed information about reactions involved in thermal decomposition kinetics and products of frying oils, corn oil/ high oleic sunflower oil blends (fresh, stripped, and steady-state) were heated at 180°C for three hours in an OxipresTM oxygen bomb under 2 bars air pressure. Upon release of pressure, the headspace was vented through a Tenax-Carboxen thermal desorption trap to trap volatiles which were then identified and quantitated by gas chromatography-mass spectrometry. Volatile levels and distributions were integrated with oxygen consumption and non-volatile product data from another study to assess relative contributions of thermal scission and autoxidation reaction mechanisms in overall degradation. Effects of catalytic factors on oil degradation were evaluated by adding metals, phospholipids, fatty acids, and water to the oil blends during heating. Fresh, stripped, and steady-state oils all generated comparable volatile products, but with differing concentrations and distributions. The main peaks coeluting isopentane/ pentane octane/ hexanal > pentanal/heptanes. Peak analyses revealed homologous series of alkanes, aldehydes, alkenes, ketones, cycloalkanes, and furans were also present. Levels of products generally decreased with chain length. No 2,4-decadienal was detected. This product pattern and the kinetics of evolution of different products provides strong support for thermal scission as the dominant degradation mechanism that occurs first to generate scission radicals that yield alkanes directly or oxidize to hydroperoxides, aldehydes, and carboxylic acids. Secondary reactions then initiate autoxidation chains. Factors known to have strong effects on lipid oxidation at room temperature appear to influence product distribution rather than degradation kinetics in heated oils. Integration of volatiles and non-volatiles data with oxygen consumption suggests there are pathways active in thermal degradation that are not being accounted for in current analyses, and these need to be elucidated to fully understand how various factors influence oil degradation as well as to learn how to improve frying oil stabilization.M.S.Includes bibliographical referencesby Ilona Repko Reade
Příprava magnetických a optických nanočástic
Full text linkTitle: Preparation of magnetic and optical nanoparticles Author: Anton Repko Department: Department of Inorganic Chemistry, Faculty of Science, Charles University of Prague Supervisor: RNDr. Daniel Nižňanský, Ph.D. Supervisor's e-mail address: [email protected] Abstract: In the present work we study methods of preparation of magnetic and optical nanoparticles by hydrothermal method. Specifically, we prepared particles of cobalt ferrite (CoFe2O4) and sodium yttrium fluoride (NaYF4) doped by Yb3+ a Er3+ from corresponding nitrates in the system of water - ethanol - oleic acid, and in modified systems. By this method, it is possible to prepare particles of narrow size distribution (monodisperse particles). Pre- pared particles of ferrite show superparamagnetism and particles of NaYF4 up-conversion, i.e. conversion of infrared (980 nm) to visible light. Keywords: nanocrystals, superparamagnetism, up-conversion, CoFe2O4, NaYF4, hydrothermal synthesisNázev práce: Příprava magnetických a optických nanočástic Autor: Anton Repko Katedra: Katedra anorganické chemie, PřF UK Praha Vedoucí diplomové práce: RNDr. Daniel Nižňanský, Ph.D. e-mail vedoucího: [email protected] Abstrakt: V předložené práci studujeme možnosti přípravy magnetických a optických nanočástic hydrotermální metodou. Konkrétně se jedná o přípravu částic feritu kobaltnatého (CoFe2O4) a fluoridu sodno-yttritého (NaYF4) dopovaného Yb3+ a Er3+ z příslušných dusičnanů v prostředí voda - ethanol - kyselina olejová a modifikace této metody. Touto metodou je možno připravit částice s úzkou distribucí velikostí (monodisperzní částice). Připravené čás- tice feritu vykazují superparamagnetismus a částice NaYF4 tzv. up-conversion, přeměnu infračerveného záření (980 nm) na viditelné světlo. Klíčová slova: nanokrystaly, superparamagnetismus, up-conversion, CoFe2O4, NaYF4, hydrotermální přípravaDepartment of Inorganic ChemistryKatedra anorganické chemieFaculty of SciencePřírodovědecká fakult
Příprava magnetických a optických nanočástic
Full text linkTitle: Preparation of magnetic and optical nanoparticles Author: Anton Repko Department: Department of Inorganic Chemistry, Faculty of Science, Charles University of Prague Supervisor: RNDr. Daniel Nižňanský, Ph.D. Supervisor's e-mail address: [email protected] Abstract: In the present work we study methods of preparation of magnetic and optical nanoparticles by hydrothermal method. Specifically, we prepared particles of cobalt ferrite (CoFe2O4) and sodium yttrium fluoride (NaYF4) doped by Yb3+ a Er3+ from corresponding nitrates in the system of water - ethanol - oleic acid, and in modified systems. By this method, it is possible to prepare particles of narrow size distribution (monodisperse particles). Pre- pared particles of ferrite show superparamagnetism and particles of NaYF4 up-conversion, i.e. conversion of infrared (980 nm) to visible light. Keywords: nanocrystals, superparamagnetism, up-conversion, CoFe2O4, NaYF4, hydrothermal synthesi
Preparation of magnetic and optical nanoparticles
No full textTitle: Preparation of magnetic and optical nanoparticles Author: Anton Repko Department: Department of Inorganic Chemistry, Faculty of Science, Charles University of Prague Supervisor: RNDr. Daniel Nižňanský, Ph.D. Supervisor's e-mail address: [email protected] Abstract: In the present work we study methods of preparation of magnetic and optical nanoparticles by hydrothermal method. Specifically, we prepared particles of cobalt ferrite (CoFe2O4) and sodium yttrium fluoride (NaYF4) doped by Yb3+ a Er3+ from corresponding nitrates in the system of water - ethanol - oleic acid, and in modified systems. By this method, it is possible to prepare particles of narrow size distribution (monodisperse particles). Pre- pared particles of ferrite show superparamagnetism and particles of NaYF4 up-conversion, i.e. conversion of infrared (980 nm) to visible light. Keywords: nanocrystals, superparamagnetism, up-conversion, CoFe2O4, NaYF4, hydrothermal synthesi
Uni- and bivariate statistical analysis of long-term wave climates
No full textFor the probability-based design and assesment of marine structures interacting with sea waves, a reliable knowledge of the long-term wave climate is required. Wave climate data are commonly presented in the form of histograms of spectral wave parameters. The severity of a sea state is usually expressed in terms of significant wave height H, and corresponding wave period T. From the earlier stages of the development of a statistical approach to wave climate, the advantage of an analytical representation of empirical distributions of data through parametric models was recognized. The compactness of analytical description, the standardization of the representation, and the filling of information gaps, led researchers to use specific marginal and bivariate parameter models, suitable for the description of wave height and wave period statistics. A large amount of case studies is present in the literature with regard to the marginal distribution functions of H, and T and with regard to the bivariate distribution functions of Hs and T.Besides the above bivariate models that are based on the marginal distribution functions also exist. The aim of the present study is to find a particular bivariate distribution function for Hs and T, which provides a close fit to long-term (extreme) wave data presenting a deep water wave field. Several types of joint distribution function for H, and T are compared with reference to measured data. The comparison is based on the utility of the distribution functions for predictions of extreme sea states. The report is thus concerned with the estimation of extreme significant wave heights and wave periods (zero-up-crossing periods or spectral peak periods). The present study of bivariate functions is similar to the above mentioned case studies of marginal distributions. It provides a detailed analysis of the influence of the data selection procedure, the parameter estimation method and the chosen distribution function on the estimation of bivariate return values. In total flve bivariate probability models are tested for the joint statistics of Hs and T. These are: 1. the bivariate Log-normal distribution 2. the bivariate Log-normal distribution with correction for skewness (the Fang and Hogben distribution) 3. the bivariate distribution constructed from a marginal distribution for Hs and a conditional distribution for T 4. the bivariate distribution based on a marginal distribution for Hs and a marginal distribution for the (deepwater) wave steepness 5. the bivariate distribution with given marginals developed by Morton and Bowers (1997) The fourth model is proposed by Vrijling (1996). It is based on the assumption that the significant wave height (Hs) and the wave steepness (s) are independent. With in the calculations, first the bivariate distribution of Hs and s is computed by simply taking the product of the marginals of Hs and s. Then the bivariate distribution of Hs and T is determined by transforming the joint model of H, and s. The fifth model is a distribution of the Frechet class. Morton and Bowers (1997) have published an article in which a detailed description is given about the application of the model to extreme wave height and windspeed observations. They obtained good results. No further tests of the model are known to the author. Therefore, the model is included in the present study.Hydraulic EngineeringCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Сreativity of a future teacher personality as a scientific category: historical and theoretical analysis
No full textOdarchenko V. Сreativity of a future teacher personality as a scientific category: historical and theoretical analysis / V. Odarchenko, I. Repko, I. Stepanets // Modernization of the pedagogical system of tertiary education in higher education institutions: collective monograph/ edited by G. F. Ponomarova, A. A. Kharkivska, L. O. Petrychenko and other ; Municipal Establishment «Kharkiv Humanitarian Pedagogical Academy» of Kharkiv Regional Council. – Kharkiv : Publishing house Education and Science s.r.o., 2021.– Р. 51–76.The scientific article is devoted to the historical and theoretical study of the phenomenon of creativity of the individual, in particular the student in the context of future pedagogical activity, based on such concepts as "personality", "creativity", "creative potential", "creative abilities", "pedagogical creativity". Approaches and author's understanding of basic concepts are clarified.
Analysis of the results of scientific research and the content of publications made by philosophers, psychologists, educators in their historical retrospect testified the existence of various theories and concepts of personality as a creative individual in ancient and Christian philosophy, in the Enlightenment, in Western philosophy XIX - early XX century, in the twentieth century and so far.
The most important result of the scientific research is the establishment of the social conditioning of creativity, in particular the determination of its formation and development by socio and cultural values, professional needs, social activity.
Categories of creativity are presented in philosophical, psychological and pedagogical senses, an attempt to compare them is made. The generalizing characteristics of the creative personality concerning its individuality, creative potential, readiness for creative activity are listed in the article.
The authorial vision of logic and interrelation of structural components of formation and development of creative personality which is to provide the unity of conditions and means for realization of creative potential of the personality of a future teacher in educational process (training, practice, extracurricular work) is presented.
The main results of the study include the establishment of approaches to the problem of creative abilities of the individual, the strategy of creative activity and components of the creative potential of the individual as its systemic characteristics.
Generalization of scientific concepts creates a sense of specificity of approaches to defining key categories of creativity and allows to determine their essential characteristics, which creates conditions for a more conscious and effective construction of the educational process, in particular in pedagogical institutions of higher education
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
