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Keywords: LIBS, laser-induced plasma, plasma parameters, copper plasma
Published in RUNG: 25.04.2023; Views: 1118; Downloads: 14
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Abstract: The allotropes of carbon nanomaterials such as carbon nanotubes (CNTs) and nanoparticles (CNPs) have emerged as a thrust area of research during the last decade because of their unique properties.CNTs are widely used in microelectronic, sensor, bio-imaging, supercapacitors, fuel cell, and etc. applications. In the present work, we report the thermal induced order fluctuations in the CNPs with CNTs synthesized from camphor. The samples annealed to different temperatures are characterized by various spectroscopic techniques such as UV–Visible, Raman, Fourier Transform Infrared, and X-ray Photoelectron Spectroscopy. Samples’ structure and morphology are analyzed by scanning and transmission electron microscopes, and X-ray diffraction. The thermogravimetric analysis indicates not only the mass variation upon annealing but the thermal stability also. The spectroscopic and thermal analyses reveal the thermal induced oscillations in the carbon system which can be assigned to the dynamics in CNTs through desorption of hydrogen/ thinning or shortening of multi-walled CNTs/sp2 - sp3 conversions and the removal of amorphous carbon (AC). Since the amount of CNTs in the sample decides the electrical behavior, the sample can be tuned to a desired electrical conductivity by annealing and thus making it a tunable material for electronic applications.
Keywords: Carbon nanotubes, Camphor, Thermal induced oscillations
Published in RUNG: 05.07.2022; Views: 976; Downloads: 0
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Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays (UHECR), UHECR arrival directions, Galactic magnetic field (GMF), UHECR deflection patterns in GMF, search for magnetically-induced signatures in UHECR arrival directions
Published in RUNG: 21.12.2020; Views: 2210; Downloads: 69
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Abstract: This work is primarily focused on application of standard first-principle computational approaches to model oxygen excess related point defects in amorphous silica. Atomic models with their respective electronic and optical properties are explored together with some conversion mechanisms between defect models. The first chapter overviews extensive literature about the already known properties of oxygen related defects. Second chapter briefly introduces main methods that have been used in this research, in particular Density Functional Theory (DFT) as energy and force engine with short description of minimal energy path (MEP) algorithm used for modeling chemical/migration reactions, GW approximation for charged electronic excitations (band structure) and Bethe-Salpeter Equation (BSE) for neutral excitations (optical absorption and excitonic structure including electron hole interaction). The third chapter is devoted to the presentation of results. Thanks to the calculation of optical properties of peroxy bridge (POL), a correlation has been found between structural disorder, specifically dihedral angle dispersion, and low coupling with light, which has been identified as main reason why no clear absorption bands have been assigned to the POL. Structure and stability of some other defects, like interstitial ozone molecule (ozonyl) and dioxasilirane (silicon analogy of dioxirane), have been studied. These defects are usually not considered as most important species, however their calculated formation energies are lower compared to some known defects, which indicates they might be present in silica. From a detailed study on possible reaction mechanisms, it has been found that ozonyl might be one of the most important intermediate steps for oxygen exchange reactions. Results also show that dioxasilirane can be spontaneously created during the interaction of oxygen with lone pair defects. By exploring different reactions between oxygen and pre-existing oxygen deficiency centers (ODCs), calculations predict two kinds of passivation behaviors: single-barrier reversible mechanisms with the formation of dioxasilirane-like groups, for which the network keeps the memory of the precursory lone pair defects, and single or multiple-barrier mechanisms, for which the network loses its memory, either because of the high reverse barrier or because of a reconstruction. Final part of this research has been devoted to experimental characterization of the response and tolerance of optical fibers loaded with oxygen under irradiation. These include experiments on commercial fiber along with canonical samples (Optical fibers developed with the intention of studying correlations between different fabrication parameters, dopant/impurity concentration and doping concentrations). Studied fibers also include rare-earth doped fibers.
Keywords: Silica, DFT, GW-approximation, Bethe-Salpeter equation, NEB, defect, oxygen, oxygen excess centers, oxygen deficiency centers, optical absorption, optical fibers, radiation induced attenuation.
Published in RUNG: 07.05.2019; Views: 4371; Downloads: 199
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Abstract: Complexity-based analyses may quantify abnormalities in heart rate variability (HRV). The aim of this study was to investigate the clinical and prognostic significances of dynamic HRV changes in patients with stress-induced cardiomyopathy Takotsubo syndrome (TS) by means of linear and nonlinear analysis. Patients with TS were included in study after complete noninvasive and invasive cardiovascular diagnostic evaluation and compared to an age and gender matched control group of healthy subjects. Series of R–R interval and of ST–T interval values were obtained from 24-h ECG recordings after digital sampling. HRV analysis was performed by ‘range rescaled analysis’ to determine the Hurst exponent, by detrended fluctuation analysis to quantify fractal longrange correlation properties, and by approximate entropy to assess time-series predictability. Short- and long-term fractal-scaling exponents were significantly higher in patients with TS in acute phases, opposite to lower approximate entropy and Hurst exponent, but all variables normalized in a few weeks. Dynamic HRV analysis allows assessing changes in complexity features of HRV in TS patients during the acute stage, and to monitor recovery after treatment, thus complementing traditional ECG and clinically analysis.
Keywords: Heart rate variability, Nonlinear dynamics, Chaos theory, Stress-induced cardiomyopathy, Takotsubo syndrome
Published in RUNG: 13.07.2017; Views: 5058; Downloads: 0
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