Iskanje po katalogu digitalne knjižnice

Opis: Many details of glucose-stimulated intracellular calcium changes in [beta] cells during activation, activity, and deactivation, as well as their concentration-dependence, remain to be analyzed. Classical physiological experiments indicated that in islets, functional differences between individual cells are largely attenuated, but recent findings suggest considerable intercellular heterogeneity, with some cells possibly coordinating the collective responses. To address the above with an emphasis on heterogeneity and describing the relations between classical physiological and functional network properties, we performed functional multicellular calcium imaging in mouse pancreas tissue slices over a wide range of glucose concentrations. During activation, delays to activation of cells and any-cell-to-first-responder delays are shortened, and the sizes of simultaneously responding clusters increased with increasing glucose concentrations. Exactly the opposite characterized deactivation. The frequency of fast calcium oscillations during activity increased with increasing glucose up to 12 mM glucose concentration, beyond which oscillation duration became longer, resulting in a homogenous increase in active time. In terms of functional connectivity, islets progressed from a very segregated network to a single large functional unit with increasing glucose concentration. A comparison between classical physiological and network parameters revealed that the first-responders during activation had longer active times during plateau and the most active cells during the plateau tended to deactivate later. Cells with the most functional connections tended to activate sooner, have longer active times, and deactivate later. Our findings provide a common ground for recent differing views on [beta] cell heterogeneity and an important baseline for future studies of stimulus-secretion and intercellular coupling. NEW & NOTEWORTHY: We assessed concentration-dependence in coupled [beta] cells, degree of functional heterogeneity, and uncovered possible specialized subpopulations during the different phases of the response to glucose at the level of many individual cells. To this aim, we combined acute mouse pancreas tissue slices with functional multicellular calcium imaging over a wide range from threshold (7 mM) and physiological (8 and 9 mM) to supraphysiological (12 and 16 mM) glucose concentrations, classical physiological, and advanced network analyses.
Ključne besede: beta cells, calcium imaging, glucose-dependence, network analysis
Objavljeno v DKUM: 15.10.2024; Ogledov: 0; Prenosov: 19
Celotno besedilo (4,37 MB)
Gradivo ima več datotek! Več...

Opis: Although mice are a very instrumental model in islet beta cell research, possible phenotypic differences between strains and substrains are largely neglected in the scientific community. In this study, we show important phenotypic differences in beta cell responses to glucose between C57BL/6J, C57BL/6N, and NMRI mice, i.e., the three most commonly used strains. High-resolution multicellular confocal imaging of beta cells in acute pancreas tissue slices was used to measure and quantitatively compare the calcium dynamics in response to a wide range of glucose concentrations. Strain- and substrain-specific features were found in all three phases of beta cell responses to glucose: a shift in the dose-response curve characterizing the delay to activation and deactivation in response to stimulus onset and termination, respectively, and distinct concentration-encoding principles during the plateau phase in terms of frequency, duration, and active time changes with increasing glucose concentrations. Our results underline the significance of carefully choosing and reporting the strain to enable comparison and increase reproducibility, emphasize the importance of analyzing a number of different beta cell physiological parameters characterizing the response to glucose, and provide a valuable standard for future studies on beta cell calcium dynamics in health and disease in tissue slices.
Ključne besede: beta cell, mouse models, calcium imaging, glucose-dependence, tissue slice
Objavljeno v DKUM: 15.07.2024; Ogledov: 148; Prenosov: 22
Celotno besedilo (4,45 MB)
Gradivo ima več datotek! Več...

Opis: Calorimetry is a commonly used method in plasma characterization, but the accuracy of the method is tied to the accuracy of the recombination coefficient, which in turn depends on a number of surface effects. Surface effects also govern the kinetics in advanced methods such as atomic layer oxidation of inorganic materials and functionalization of organic materials. The flux of the reactive oxygen atoms for the controlled oxidation of such materials depends on the recombination coefficient of materials placed into the reaction chamber, which in turn depends on the surface morphology, temperature, and pressure in the processing chamber. The recombination coefficient of a well-oxidized cobalt surface was studied systematically in a range of temperatures from 300 to 800 K and pressures from 40 to 200 Pa. The coefficient increased monotonously with decreasing pressure and increasing temperature. The lowest value was about 0.05, and the highest was about 0.30. These values were measured for cobalt foils previously oxidized with oxygen plasma at the temperature of 1300 K. The oxidation caused a rich morphology with an average roughness as deduced from atomic force images of 0.9 µm. The results were compared with literature data, and the discrepancy between results reported by different authors was explained by taking into account the peculiarities of their experimental conditions.
Ključne besede: heterogeneous surface recombination, recombination coefficient, cobalt, cobalt oxide, temperature dependence, pressure dependence, plasma, oxygen
Objavljeno v DKUM: 26.03.2024; Ogledov: 228; Prenosov: 18
Celotno besedilo (3,59 MB)
Gradivo ima več datotek! Več...

Opis: Decision-making about server selection is one of the multi-criteria decision-making (MCDM) processes where interactions among criteria should be considered. The paper introduces and develops some solutions for considering interactions among criteria in the MCDM problems. In the frame procedure for MCDM by using the group of methods, based on assigning weights, special attention is given to the synthesis of the local alternatives' values into the aggregate values where the mutual preferential independence between two criteria is not assumed. Firstly, we delineate how to complete the additive model into the multiplicative one with synergic and redundancy elements in the case that criteria are structured in one level and in two levels. Furthermore, we adapted the concept of the fuzzy Choquet integral to the multi-attribute value theory. Studying and comparing the results of the example case of the server selection obtained by both aggregation approaches, the paper highlights the advantages of the first one since it does not require from decision makers to determine the weights of all possible combinations of the criteria and it enables the further use of the most preferred MCDM methods.
Ključne besede: interaction, multi-criteria decision-making, preferential dependence, server
Objavljeno v DKUM: 03.08.2017; Ogledov: 1375; Prenosov: 112
Celotno besedilo (1,00 MB)
Gradivo ima več datotek! Več...

Opis: The detection of trace amounts of explosive like trinitrotoluene (TNT) is an important issue in the prevention of terrorist attacks. Surface enhanced Raman scattering (SERS) spectroscopy has become a powerful detection technique for identification of minute amounts of analytes. This thesis presents data of TNT in solution, deposited on a nanostructured gold surface, which is heated up to 60 °C. The observed changes in the microscopy images and in the SERS spectra are explained by evaporation, phase transition and decomposition of the TNT molecules. The impact of temperature dependence of SERS effect is studied on a chemisorbed 4-Nitrothiophenol monolayer. To minimize the evaporation of TNT molecules, a self-assembled monolayer of mercaptohexanol (MCH) was inserted between plasmonic surface and TNT.
Ključne besede: surface enhanced Raman spectroscopy, explosives, temperature dependence, microscopy, evaporation, phase transition, decomposition
Objavljeno v DKUM: 05.11.2015; Ogledov: 2132; Prenosov: 107
Celotno besedilo (2,25 MB)