Positron Trapping Effects in Water-filled Nanopores of Spinel Ceramics

The water-sensitive positron trapping modes in nanoporous MgAl2O4 ceramics with a spinel structure are studied. It is shown that water-sorption processes in these ceramics leads to increase in positron trapping rates of extended defects located near intergranual boundaries. The fixation of direct positron lifetime components allows refining the most significant changes in positron trapping rate. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3503

Study of nanoporous in humidity-sensitive MgAl₂O₄ ceramics with positron annihilation lifetime spectroscopy

It has been shown that positron annihilation lifetime spectroscopy is a quite promising tool for nanostructural characterization of humidity-sensitive spinel-type MgAl₂O₄ceramics. The results have been achieved using the four-component fitting procedure with arbitrary lifetimes that is applied to mathematically treat the measured spectra. It has been shown that the Tao-Eldrup model is adequate to calculate the nanopore size in MgAl₂O₄ ceramics if using the lifetime values of the third and fourth components

Detecting Outliers and Influential Data Points in Receiver Operating Characteristic (ROC) Analysis

Receiver operating characteristic (ROC) studies and analyses are often used to evaluate medical tests and are very useful in the field of radiology to evaluate a single diagnostic imaging system, to compare the accuracy of two or more diagnostic imaging systems, or to assess observer performance.  There have been many refinements in the development of different ROC type study designs and the corresponding statistical analysis. These methods have become increasingly important and ROC methods are the principal approach for evaluating imaging technologies and/or observer performances. The systems that are often evaluated using ROC methodology include digital and radiographic images of the chest and breast. An improved method of evaluating diagnostic imaging systems contributes to the development of better diagnostic methods; hence, improving imaging systems for diagnoses of breast and lung cancer would have major public health significance. In our work with observer performance studies, in which receiver operating characteristic (ROC) analysis is used, we have noted that some contributions of readers and cases can substantially alter the conclusions of the analysis.  To the best of our knowledge, to date there is no statistical test cited in the statistical literature that addresses the detection and influence of outliers on the estimate of the area under the ROC curve.  Evaluating outliers may be especially important for the ROC model since subtle (difficult) cases have the potential for being missed by a reader (e.g. a difficult positive case is rated as an unquestionably negative case), and can have a considerable influence on the estimated area under the ROC curve, especially if the study has a small set of cases.  Therefore, we believe it is important to develop a method for detecting and measuring the influence of outliers for ROC models.  The development of this method will involve deriving a test statistic for outliers based on the jackknife influence values and conducting a preliminary validation of the test.</p

Positron Trapping Processes in Temperature-Sensitive Thick- film Structures

Positron trapping processes in so-called “free” thick-film structures based on spinel-type Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics are studied. The observed positron trapping can be fully defined within the two-state positron trapping model. The defect-related component in the fit of the experimentally measured positron lifetime spectra for thick films and bulk ceramics testifies to similarity of positron trapping processes in spinel-based materials. It is shown that in some cases the size of free-volume entities in thick films can rise due to redistribute space of their inner structure at addition glasses and other compounds. But positrons are trapped more strongly in bulk ceramics due to more ramified their grain/pores structure

Structural investigation of crystallized Ge-Ga-Se chalcogenide glasses

H. Klym thanks to the Ministry of Education and Science of Ukraine for support and Dr. P. Demchenko for the assistance in XRD experiments.Crystallization transformation in the 80GeSe2-20Ga2Se3 chalcogenide glasses caused by annealing at 380 °C during different duration (25, 50, 80 and 100 hours) are studied using X-ray diffraction and atomic force microscopy methods. It is established that GeGa4Se phase of low- and high-temperature modification, Ga2Se3 phase (α- and γ-modification) and GeSe2 phases are crystallized during this process. It is shown that annealing duration over 50 h does not lead to further internal structural crystallization, while annealing for 80 h result in processes of surface crystallization.Ministry of Education and Science of Ukraine; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Positronium Characterization of Nanopores in Technologically Modified MgO-Al2O3 Ceramics

It is established that positron annihilation lifetime spectroscopy can be successful used as porosimetry method to study of nanopores size and transformation of free volume in humidity-sensitive MgO-Al2O3 ceramics in adsorption-desorption cycles using lifetimes of ortho-positronium-related components. It is shown that the fourth component gives information about water-free volume or nanopores size, while the third component reflects positronium trapping both in nanopores and in water “bubbles”

Positronium Characterization of Nanopores in Technologically Modified MgO-Al2O3 Ceramics

It is established that positron annihilation lifetime spectroscopy can be successful used as porosimetry method to study of nanopores size and transformation of free volume in humidity-sensitive MgO-Al2O3 ceramics in adsorption-desorption cycles using lifetimes of ortho-positronium-related components. It is shown that the fourth component gives information about water-free volume or nanopores size, while the third component reflects positronium trapping both in nanopores and in water “bubbles”

Nanoporous characterization of modified humidity-sensitive MgO-Al2O3 ceramics by positron annihilation lifetime spectroscopy method

The work was supported by the Ukrainian Ministry of Education and Science. H. Klym thanks Prof. O. Shpotyuk for the fruitful discussion.Investigation of nanopores in the humidity-sensitive MgO-Al2O3 ceramics modified at 1100°C for 2 hours was performed using positron annihilation lifetime spectroscopy method. Lifetimes of the third and fourth components of positron annihilation lifetime spectra obtained by four-component fitting procedure were used for calculation of nanopores radii. Transformation in free volumes was studied in ceramics after drying and exposure to water vapor. It is established that the lifetime of the third component decreases and the intensity of this component increases in ceramics exposed to water vapor reflecting ortho-positronium decay in nanopores simultaneously with annihilation in water bubbles. The characteristics of the fourth component (lifetime and intensity) decrease in ceramics exposed to water vapor reflecting ortho-positronium trapping in free-water volume of nanopores. Final drying of the MgO-Al2O3 ceramics results in returning of ortho-positronium lifetimes and intensities to the initial values confirming good desorption of water from nanopores of ceramics.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Cathodoluminescence characterization of polystyrene-BaZrO₃ hybrid composites

The radiation properties and the electronic structure of hybrid composites based on suspension polystyrene (PS) and nanocrystals of BaZrO₃ (BZO) ( d < 50 nm) have been studied using luminescent spectroscopy and x-ray analysis. A strong cathodoluminescence (CL) in BZO-nanocrystals is observed in temperature range 80–293 K. It is modified in BZO-PS composites: both the low- and a high-energy bands (near 4 eV) appear, together with a significant reduction in the CL intensity. A decrease of the lattice parameter a for BZO phase in the composite and the modification of CL spectra indicate for changes in the nanocrystalline structure induced by the polymer