•Mathematical description of the heart functioning through coupled nonlinear oscillators.•Normal and pathological ECGs are reproduced in close agreement with experimental observations.•Lyapunov ...exponents, Poincaré maps and bifurcations are employed to characterize different heart behaviors.•Bifurcations from normal to pathological behaviors can be applied to avoid undesirable critical pathologies.
Biological rhythms are fundamental for the understanding of the physiological functioning of organisms, being useful in disease prevention and treatments. This work deals with the analysis of cardiac rhythms evaluating the electrical activity of the heart based on ECG observations. A mathematical model composed by three nonlinear oscillators coupled by time-delayed connections is employed for heartbeat description. Numerical simulations reproduce synthetic ECGs with a broad variety of responses, including normal and pathological rhythms. Atrial flutter, atrial fibrillation, ventricular flutter and two different kinds of ventricular fibrillation are investigated showing the model capability to capture the general functioning of the heart dynamics. Nonlinear tools are employed in order to help the physiology understanding, being potential interesting to help the characterization of the different behaviors. In this regard, Poincaré maps and bifurcation analysis are of concern. Poincaré maps can highlight dynamical characteristics of each rhythm while bifurcation analysis can be useful to investigate the routes from normal functioning to pathologies, which can be useful to establish an early identification of critical situations. In general, results show that dynamical perspective can be useful for physiology comprehension that can also help to pathology characterization.
Purpose
To present the state-of-art of radiomics in the context of pancreatic neuroendocrine tumors (PanNETs), with a focus on the methodological and technical approaches used, to support the search ...of guidelines for optimal applications. Furthermore, an up-to-date overview of the current clinical applications of radiomics in the field of PanNETs is provided.
Methods
Original articles were searched on PubMed and Science Direct with specific keywords. Evaluations of the selected studies have been focused mainly on (i) the general radiomic workflow and the assessment of radiomic features robustness/reproducibility, as well as on the major clinical applications and investigations accomplished so far with radiomics in the field of PanNETs: (ii) grade prediction, (iii) differential diagnosis from other neoplasms, (iv) assessment of tumor behavior and aggressiveness, and (v) treatment response prediction.
Results
Thirty-one articles involving PanNETs radiomic-related objectives were selected. In regard to the grade differentiation task, yielded AUCs are currently in the range of 0.7–0.9. For differential diagnosis, the majority of studies are still focused on the preliminary identification of discriminative radiomic features. Limited information is known on the prediction of tumors aggressiveness and of treatment response.
Conclusions
Radiomics is recently expanding in the setting of PanNETs. From the analysis of the published data, it is emerging how, prior to clinical application, further validations are necessary and methodological implementations require optimization. Nevertheless, this new discipline might have the potential in assisting the current urgent need of improving the management strategies in PanNETs patients.
Heartbeat rhythms are related to a complex dynamical system based on electrical activity of the cardiac cells usually measured by the electrocardiogram (ECG). This paper presents a mathematical model ...to describe the electrical activity of the heart that consists of three nonlinear oscillators coupled by delayed Duffing-type connections. Coupling alterations and external stimuli are responsible for different cardiac rhythms. The proposed model is employed to build synthetic ECGs representing a variety of responses including normal and pathological rhythms: ventricular flutter, torsade de pointes, atrial flutter, atrial fibrillation, ventricular fibrillation, polymorphic ventricular tachycardia and supraventricular extrasystole. Moreover, the sinoatrial rhythm variations are described by time-dependent frequency, representing transient disturbances. This kind of situation can represent transitions between different pathological behaviors or between normal and pathological physiologies. In this regard, a nonlinear dynamics perspective is employed to describe cardiac rhythms, being able to represent either normal or pathological behaviors.
The Daisyworld model illustrates the concept of biological homeostasis in the global environment by establishing a connection between the biota and environment, resulting in a single intertwined ...system known as Gaia. In essence, the Daisyworld model represents life by daisy populations whereas temperature represents the environment, establishing a population dynamics model to represent life–environment ecological interactions. The recent occurrence of extreme weather events due to climate change and the critical crises brought on by the COVID-19 pandemic are strengthening the arguments for the revenge of Gaia, a term used to describe the protective response of the global biota-environment system. This paper presents a novel Daisyworld parable to describe ecological life–environment interactions including the revenge of Gaia and the greenhouse effect. The revenge of Gaia refers to a change in the interplay between life and environment, characterized by the Gaia state that establishes the life-environment state of balance and harmony. This results in reaction effects that impact the planet’s fertile regions. On the other hand, the greenhouse effect is incorporated through the description of the interactions of greenhouse gases with the planet, altering its albedo. Numerical simulations are performed using a nonlinear dynamics perspective, showing different ecological scenarios. An investigation of the system reversibility is carried out together with critical life–environment interactions. This parable provides a qualitative description that can be useful to evaluate ecological scenarios.
Shape memory alloys (SMA) are materials that have the ability to return to a former shape when subjected to an appropriate thermomechanical procedure. Pseudoelastic and shape memory effects are some ...of the behaviors presented by these alloys. The unique properties concerning these alloys have encouraged many investigators to look for applications of SMA in different fields of human knowledge. The purpose of this review article is to present a brief discussion of the thermomechanical behavior of SMA and to describe their most promising applications in the biomedical area. These include cardiovascular and orthopedic uses, and surgical instruments.
Synchronization phenomenon appears in several natural systems being associated with physical, chemical and biological processes. In brief, synchronization may be understood as a harmonization of two ...or more system behaviors following some patterns. This paper deals with synchronization analysis of a mechanical pendulum-chart system composed by a hierarchical network of three pendula coupled to each other through their own chart that receives continuous supply of energy via a base excitation. Dynamical patterns are classified and investigated in order to understand the conditions to each one of them. Asynchronous behaviors are analyzed including the chimera state defined as a symmetry break of the behavior of identical oscillator network. Numerical simulations indicate that patterns do not have a direct relation with periodicity. An energetic approach is proposed in order to define a measure of synchronized states, providing new insights about the origin of chimera state and its relationship with natural frequencies.
Smart material systems and structures have remarkable properties responsible for their application in different fields of human knowledge. Shape memory alloys, piezoelectric ceramics, ...magnetorheological fluids, and magnetostritive materials constitute the most important materials that belong to the smart materials category. Shape memory alloys (SMAs) are metallic alloys usually employed when large forces and displacements are required. Applications in aerospace structures, rotordynamics and several bioengineering devices are investigated nowadays. In terms of applied dynamics, SMAs are being used in order to exploit adaptive dissipation associated with hysteresis loop and the mechanical property changes due to phase transformations. This paper presents a general overview of nonlinear dynamics and chaos of smart material systems built with SMAs. Oscillators, vibration absorbers, impact systems and structural systems are of concern. Results show several possibilities where SMAs can be employed for dynamical applications.
•Development of constitutive models for shape memory alloys.•Nonlinear dynamics of smart systems and structures with shape memory alloy elements, discussing complex behaviors as chaos.•Vibration reduction of SMA systems including adaptive–passive vibration absorbers and impact systems.•Numerical simulations and experimental investigation of smart material systems.
Oil drilling operations is usually associated with drill-string severe vibration conditions that lead to an onerous and inefficient process. In order to avoid or minimize the impact of vibrations on ...operation conditions it is essential a deep dynamical investigation that allows a proper understanding of system dynamics. Drill-string dynamics may be analyzed by considering different vibration modes: axial, torsional and lateral. The coupled analysis of these modes gives a proper comprehension of the system dynamics, elucidating several critical vibration responses. In general, lumped models present a proper description of the system dynamics. This paper deals with a coupled drill-string vibration considering a four-degree of freedom nonsmooth model that presents axial-torsional-lateral coupling. Bit-rock and wellbore interactions, eccentricity and hydrodynamic forces due to fluid resistance to lateral bending are the main system coupling aspects. A parametric study is carried out treating bit-bounce, stick-slip, whirl, and the combined effects. Numerical results present qualitative agreement with experimental field observations. Critical operational conditions are discussed especially those related to interaction among bit-bounce, stick-slip and whirl conditions.
Energy harvesting from ambient vibration through piezoelectric devices has received a lot of attention in recent years from both academia and industry. One of the main challenges is to develop ...devices capable of adapting to diverse sources of environmental excitation, being able to efficiently operate over a broadband frequency spectrum. This work proposes a novel multimodal design of a piezoelectric energy harvesting system to harness energy from a wideband ambient vibration source. Circular-shaped and pizza-shaped designs are employed as candidates for the device, comparing their performance with classical beam-shaped devices. Finite element analysis is employed to model system dynamics using ANSYS Workbench. An optimization procedure is applied to the system aiming to seek a configuration that can extract energy from a broader frequency spectrum and maximize its output power. A comparative analysis with conventional energy harvesting systems is performed. Numerical simulations are carried out to investigate the harvester performances under harmonic and random excitations. Results show that the proposed multimodal harvester has potential to harness energy from broadband ambient vibration sources presenting performance advantages in comparison to conventional single-mode energy harvesters.
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