Browsing by Author "Milutinović-Smiljanić, Sanja (23971105900)"

Copula density is a function that quantifies the level of dependency between two, or more, related time series, and also visualizes their (non)linear dependency structures. This paper aims to analyze and compare different methods for copula density estimation: local (naïve) estimation, kernel estimation, K nearest neighbors, Markov state approach, histograms, and Voronoi decomposition. The methods are compared by mapping the copula density into a time series (dependency level time series) and applying Sample Entropy estimates over the range of parameters. Application examples include systolic blood pressure and pulse interval signals recorded from conscious laboratory rats, treated either with vasopressin selective V1a and V2 receptor antagonists (100 ng and 500 ng) or with saline (control group). The signals are analyzed using composite multiscale entropy. It is shown that each estimation method suffers from bias, but, for each case, a stable working region can be found. It was also shown that the analysis of the dependency level time series could reveal the information that could not be extracted from the classical beat-to-beat time series, and that the copula density, transformed to real signals domain, visualizes the regions where the dependency of cardiovascular signals is exhibited the most, reflecting their mutual relationship and providing the possibility for further research. © 2021

Copula density is a function that quantifies the level of dependency between two, or more, related time series, and also visualizes their (non)linear dependency structures. This paper aims to analyze and compare different methods for copula density estimation: local (naïve) estimation, kernel estimation, K nearest neighbors, Markov state approach, histograms, and Voronoi decomposition. The methods are compared by mapping the copula density into a time series (dependency level time series) and applying Sample Entropy estimates over the range of parameters. Application examples include systolic blood pressure and pulse interval signals recorded from conscious laboratory rats, treated either with vasopressin selective V1a and V2 receptor antagonists (100 ng and 500 ng) or with saline (control group). The signals are analyzed using composite multiscale entropy. It is shown that each estimation method suffers from bias, but, for each case, a stable working region can be found. It was also shown that the analysis of the dependency level time series could reveal the information that could not be extracted from the classical beat-to-beat time series, and that the copula density, transformed to real signals domain, visualizes the regions where the dependency of cardiovascular signals is exhibited the most, reflecting their mutual relationship and providing the possibility for further research. © 2021

Background/Aim. The materials used nowadays for bone replacement do not fully meet the requirements for complete regeneration, which is why new ones are being tested. Despite numerous attempts to improve bone tissue regeneration, no fulfilling material has been found yet. This study investigated the influence of poly-lactide-co-glycolide (PLGA) and polyethyleneimine (PEI) as coatings for hydroxyapatite (HAP) bone carriers on bone tissue regenerative potential in rabbits’ calvarial defect. Methods. Calvarial defects measuring 6 mm in diameter were made in 19 skeletally mature rabbits. Defects were filled with one of the following materials: PLGA coated HAP (HAP + PLGA), PEI coated HAP (HAP + PEI), and bovine HAP – Bio-Oss® (positive control). Unfilled defects represented negative control. Histological analysis was performed in order to determine the inflammatory response of the host tissue. The formation of the new bone was evaluated using histomorphometric analysis. All analyses have been conducted in samples obtained 3, 6, and 9 weeks after implantation. Results. Three weeks post-implantation, a trend toward increased healing in the HAP + PLGA group compared to other investigated materials was noticed, with no statistically significant difference between the study groups (p > 0.05). However, after 6 and 9 weeks, significant healing was observed in favor of the HAP coated with PLGA compared to other groups (p < 0.05). Within this group, greater bone healing was observed compared to the HAP + PEI and Bio-Oss® groups. Conclusion. PLGA demonstrated greater coating potential compared to PEI with respect to osteogenesis improvement in bone reconstructive surgery. © 2022 Inst. Sci. inf., Univ. Defence in Belgrade. All rights reserved.