Papers by Minvydas Ragulskis
SAE Technical Paper Series, 1999
Vibroengineering PROCEDIA
Convolutional neural networks have been created as deep learning-based approaches to automaticall... more Convolutional neural networks have been created as deep learning-based approaches to automatically analyze photographs of concrete surfaces for crack diagnosis applications. Although deep learning-based systems assert to have extremely high accuracy, they frequently overlook how difficult it is to acquire images. Complex lighting situations, shadows, the irrationality of crack forms and widths, imperfections, and concrete spall frequently have an influence on real-world photos. The focus of the published research and accessible shadow databases is on photographs shot in controlled laboratory settings. In this research, we investigate the challenging underwater optical effects settings and the complexity of image classification for concrete crack detection. This research elaborates on difficulties encountered when using deep learning-based techniques to identify concrete cracks when optical effects are present. To improve the precision of automatically detecting concrete cracks on un...
Applied Sciences
In this present paper, the dynamic stiffness method (DSM) was formulated to investigate the out-o... more In this present paper, the dynamic stiffness method (DSM) was formulated to investigate the out-of-plane natural vibration of a thin orthotropic plate using the classical plate theory (CPT). Hamilton’s principle was implemented to derive the governing differential equation of motion for free vibration of the orthotropic plate for Levy-type boundary conditions. The Wittrick–Williams (W–W) algorithm was used as a solution technique to compute the natural frequencies of a thin orthotropic plate for different boundary conditions, aspect ratios, thickness ratios, and modulus ratios. The obtained results are compared with the results by the finite element method using commercial software (ANSYS and those available) in the published literature. The presented results by the dynamic stiffness method can be used as a benchmark solution to compare the natural frequencies of orthotropic plates.
Asian Review of Environmental and Earth Sciences, 2022
The impact of the local Earth magnetic field (LEMF) on cardiovascular events has been studied rec... more The impact of the local Earth magnetic field (LEMF) on cardiovascular events has been studied recently. Data gathered during past years encouraged us to conduct this epidemiological analysis evaluating the association between changes in LEMF and hospital admissions due to AMI in Lithuania between August 2014 and September 2019. This study is unique due to its coverage of all Lithuanian patients. The frequency of morbidity of AMI was compared with the intensity of the LEMF and correlation coefficient was evaluated. The LEMF was measured by the Global Coherence Monitoring Network magnetometer located in Lithuania. LEMF was measured by pikotesla square (pT²). The LEMF was analized in five frequency ranges [Hz], generally called between Schumann resonance, which overlap with the human brain activity waves on electroencefalogram (EEG) frequency ranges (here, they are named as SDelta (0-3.5Hz), STheta (3.5-7Hz), SAlpha (7-15Hz), SBeta (15-32Hz) and SGamma (32-65Hz) to distinguish from the...
Diagnostics, 2021
The analysis of human physiological systems from the point of view of complex systems theory rema... more The analysis of human physiological systems from the point of view of complex systems theory remains a very ambitious task. The complexity of the problem often encourages the use of innovative mathematical methods analyzing the processes that take place in space and time. The main goal of this paper is to visualize the cardiovascular system during auricular vagus nerve stimulation (aVNS) using the matrix differences to evaluate the dynamic signal interfaces by cointegrating the initial signal data into the matrices during each case. Algebraic relationships between RR/JT and JT/QRS cardiac intervals are used not only to track the cardiovascular changes during aVNS but also to characterize individual features of the person during the transit through the therapy. This paper presents the computational techniques that can visualize the complex dynamical processes taking place in the cardiovascular system using the electrical aVNS therapy. Four healthy volunteers participated in two verum...
Applied Sciences, 2021
Changes in geomagnetic conditions have been shown to affect the rhythms produced by the brain and... more Changes in geomagnetic conditions have been shown to affect the rhythms produced by the brain and heart and that human autonomic nervous system activity reflected in heart rate variability (HRV) over longer time periods can synchronize to changes in the amplitude of resonant frequencies produced by geomagnetic field-line and Schumann resonances. During a 15-day period, 104 participants located in California, Lithuania, Saudi Arabia, New Zealand, and England underwent continuous ambulatory HRV monitoring. The local time varying magnetic field (LMF) intensity was obtained using a time synchronized and calibrated network of magnetometers located at five monitoring sites in the same geographical locations as the participant groups. This paper focuses on the results of an experiment conducted within the larger study where all of the participants simultaneously did a heart-focused meditation called a Heart Lock-In (HLI) for a 15-min period. The participant’s level of HRV coherence and HRV...
Journal of Complexity in Health Sciences, 2021
Daily energy expenditure includes resting metabolism (RMR), endogenous thermogenesis (or thermal ... more Daily energy expenditure includes resting metabolism (RMR), endogenous thermogenesis (or thermal effects of food), and energy expenditure associated with exercise. RMR depends on body weight, age, gender, genetic factors, medications used and health status. Every living organism is affected by external factors. Fluctuations in magnetic fields can affect almost every biological system more or less, depending on the characteristics of the particular biological system and magnetic fluctuations. Environmental energy phenomena affect psychophysical processes that can affect people in a variety of ways, depending on their sensitivity, health status, and ability to self-regulate. The aim of this study: to investigate the correlations between basal metabolic rate in humans with different age, gender, BMI and local Earth magnetic field activity. Information on gas metabolism during respiration was obtained by indirect calorimetry where the gas flow was continuously analysed. O2 consumption a...
Applied Sciences, 2021
Detection and assessment of cracks in civil engineering structures such as roads, bridges, dams a... more Detection and assessment of cracks in civil engineering structures such as roads, bridges, dams and pipelines are crucial tasks for maintaining the safety and cost-effectiveness of those concrete structures. With the recent advances in machine learning, the development of ANN- and CNN-based algorithms has become a popular approach for the automated detection and identification of concrete cracks. However, most of the proposed models are trained on images taken in ideal conditions and are only capable of achieving high accuracy when applied to the concrete images devoid of irregular illumination conditions, shadows, shading, blemishes, etc. An overview of challenges related to the automatic detection of concrete cracks in the presence of shadows is presented in this paper. In particular, difficulties associated with the application of deep learning-based methods for the classification of concrete images with shadows are demonstrated. Moreover, the limitations of the shadow removal te...
Nonlinear Dynamics, 2020
Bearing fault diagnosis based on the classification of patterns of permutation entropy is present... more Bearing fault diagnosis based on the classification of patterns of permutation entropy is presented in this paper. Patterns of permutation entropy are constructed by using non-uniform embedding of the vibration signal into a delay coordinate space with variable time lags. These patterns are interpreted, processed and classified by employing deep learning techniques based on convolutional neural networks. Computational experiments are used to compare the accuracy of classification with other methods and to demonstrate the efficacy of the presented early defect detection and classification method.
Applied Sciences, 2021
The main objective of this paper is to explore if the JT/ST algebraic relationship could be helpf... more The main objective of this paper is to explore if the JT/ST algebraic relationship could be helpful for the identification of ischemic changes in the human cardiovascular system. The suggested visualization technique highlights the specifics of complex dynamical processes in the self-organization of the heart system during the load and recovery processes. It is demonstrated that the nonlinear algebraic relationship between the duration of the JT interval and the ST amplitude can be beneficial for a deeper interpretation of dynamical processes in the human cardiovascular system. The JT/ST relationship is used for the identification of the ischemic changes and for the characterization of individual performance of the person during the load and recovery processes.
Vibroengineering PROCEDIA, 2018
To broaden the engineering application of inverse substructuring analysis, the mechanical assembl... more To broaden the engineering application of inverse substructuring analysis, the mechanical assembly via planar surface is experimentally studied. Specifically, the first and the second schemes of indirect inverse substructuring analysis are applied to identify the coupling dynamic stiffness of the assembly. The experimental model of the assembly is designed, and the surface is then discretized equivalently into point-to-point connections for testing the frequency response functions (FRFs) involved in the schemes. Experimental results show that, applying both of the schemes are feasible for the identification, and the identified stiffnesses approach to be stable as the number of discretized points increases.
Communications in Nonlinear Science and Numerical Simulation, 2021
A theoretical framework describing the dynamics of nonlinear iterative maps of matrices is derive... more A theoretical framework describing the dynamics of nonlinear iterative maps of matrices is derived in this paper. It is shown that an iterative map of matrices does exhibit the effect of exponential divergence if the following two conditions are satisfied simultaneously. The first condition is that at least one of the multiplicity indexes of the eigenvalues of the matrix of initial conditions must be greater than one. The second condition is that the Lyapunov exponent of the corresponding scalar iterative map is greater than zero. The concept of packing and divergence codes is introduced to characterize the rate of the divergence of nonlinear iterative maps of matrices. Theoretical derivations and computational simulations yield counterintuitive results that the divergence rate of the logistic map of matrices is the same as of the circle map of matrices-even though the higher-order derivatives of the circle mapping function do not vanish.
Vibroengineering PROCEDIA, 2018
A non-ideal connection of mechanical assembly with linear assembling interface is firstly conside... more A non-ideal connection of mechanical assembly with linear assembling interface is firstly considered in the coupling dynamic stiffness identification by applying the second scheme of indirect inverse substructuring analysis. The experimental model of the mechanical assembly is designed, and the interface is then discretized equivalently as ideal point-coupling for testing the frequency response functions (FRFs) involved in the scheme. As the results of the experimental study, applying the scheme is verified to be feasible for the stiffness identification of a mechanical assembly with linear connection, and the identified stiffness approaches to be stable with increase of the number of discretized points.
Nonlinear Dynamics, 2020
The convergence of the fractional difference logistic map is studied in this paper. A computation... more The convergence of the fractional difference logistic map is studied in this paper. A computational technique based on the visualisation of the algebraic complexity of transient processes is employed for that purpose. It is demonstrated that the dynamics of the fractional difference logistic map is similar to the behaviour of the extended invertible logistic map in the neighbourhood of unstable orbits. This counter-intuitive result provides a new insight into the transient processes of the fractional difference logistic map.
Complexity, 2018
A simple and effective algorithm for the identification of optimal time delays based on the geome... more A simple and effective algorithm for the identification of optimal time delays based on the geometrical properties of the embedded attractor is presented in this paper. A time series synchronization measure based on optimal time delays is derived. The approach is based on the comparison of optimal time delay sequences that are computed for segments of the considered time series. The proposed technique is validated using coupled chaotic Rössler systems.
Journal of Vibroengineering, 2016
The generalization of the classical Korteweg-de-Vries (KdV) solitary wave solution is presented i... more The generalization of the classical Korteweg-de-Vries (KdV) solitary wave solution is presented in this paper. The amplitude and the propagation speed of generalized KdV solitary waves vary in time. Generating partial differential equations and conditions of existence of the generalized KdV solitary waves are derived using the inverse balancing method. Computational experiments illustrate the variety of new solitary solutions and their generating equations.
Sensors, 2020
Vibration-based data-driven structural damage identification methods have gained large popularity... more Vibration-based data-driven structural damage identification methods have gained large popularity because of their independence of high-fidelity models of target systems. However, the effectiveness of existing methods is constrained by critical shortcomings. For example, the measured vibration responses may contain insufficient damage-sensitive features and suffer from high instability under the interference of random excitations. Moreover, the capability of conventional intelligent algorithms in damage feature extraction and noise influence suppression is limited. To address the above issues, a novel damage identification framework was established in this study by integrating massive datasets constructed by structural transmissibility functions (TFs) and a deep learning strategy based on one-dimensional convolutional neural networks (1D CNNs). The effectiveness and efficiency of the TF-1D CNN framework were verified using an American Society of Civil Engineers (ASCE) structural hea...
Lietuvos matematikos rinkinys, 2012
Computational techniques based on ranks of Hankel matrices is used to study the convergence to Ar... more Computational techniques based on ranks of Hankel matrices is used to study the convergence to Arnold tongues. It appears that the process of convergence to the phaselocked mode is far from being trivial. The stable, the unstable and the manifold of nonasymptotic convergence intertwine in the parameter plane of the circle map. Pseudoranks of Hankel matrices carry important physical information about transient processes taking place in discrete nonlinear iterative maps. These pictures in the parameter plane are also beautiful from the aesthetical point of view.
Lietuvos matematikos rinkinys, 2015
One of the kind in Europe magnetometer is situated in central Lithuania and registers local magne... more One of the kind in Europe magnetometer is situated in central Lithuania and registers local magnetic field intensity. The sensitivity of the device is of pT (pico teslas) order. Magnetic field intensity is a real world sequence and as a result does not have a rank. Nevertheless, H-rank based techniques enable to analyse the data as algebraic sequences. The work also pays a considerable amount of attention to the spectral distribution of the signal. A specialized software is being developed due to the amount of the data and computational time costs for problems investigated.
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Papers by Minvydas Ragulskis