17 research outputs found
Multistability and chaos in SEIRS epidemic model with a periodic time-dependent transmission rate
In this work, we study the dynamics of a SEIRS epidemic model with a periodic
time-dependent transmission rate. Emphasizing the influence of the seasonality
frequency on the system dynamics, we analyze the largest Lyapunov exponent
along parameter planes finding large chaotic regions. Furthermore, in some
ranges there are shrimp-like periodic strutures. We highlight the system
multistability, identifying the coexistence of periodic orbits for the same
parameter values, with the infections maximum distinguishing by up one order of
magnitude, depending only on the initial conditions. In this case, the basins
of attraction has self-similarity. Parametric configurations, for which both
periodic and non-periodic orbits occur, cover of the evaluated range.
We also identified the coexistence of periodic and chaotic attractors with
different maxima of infectious cases, where the periodic scenario peak reaching
approximately higher than the chaotic one
Structural connectivity modifications in the brain of selected patients with tumour after its removal by surgery (a case study)
Acknowledgments This study was possible by partial financial support from the following agencies: FundažcËao AraucÂŽaria, Brazilian National Council for Scientific and Technological Development (CNPq), and Coordination for the Improvement of Higher Education Personnel (CAPES). SËao Paulo Research Foundation (FAPESP 2018/03211-6, 2022/13761-9). We thank 105 Group Science (www.105groupscience.com).Peer reviewe
Unpredictability in seasonal infectious diseases spread
In this work, we study the unpredictability of seasonal infectious diseases
considering a SEIRS model with seasonal forcing. To investigate the dynamical
behaviour, we compute bifurcation diagrams type hysteresis and their respective
Lyapunov exponents. Our results from bifurcations and the largest Lyapunov
exponent show bistable dynamics for all the parameters of the model. Choosing
the inverse of latent period as control parameter, over 70% of the interval
comprises the coexistence of periodic and chaotic attractors, bistable
dynamics. Despite the competition between these attractors, the chaotic ones
are preferred. The bistability occurs in two wide regions. One of these regions
is limited by periodic attractors, while periodic and chaotic attractors bound
the other. As the boundary of the second bistable region is composed of
periodic and chaotic attractors, it is possible to interpret these critical
points as tipping points. In other words, depending on the latent period, a
periodic attractor (predictability) can evolve to a chaotic attractor
(unpredictability). Therefore, we show that unpredictability is associated with
bistable dynamics preferably chaotic, and, furthermore, there is a tipping
point associated with unpredictable dynamics
Fractional dynamics and recurrence analysis in cancer model
In this work, we analyze the effects of fractional derivatives in the chaotic
dynamics of a cancer model. We begin by studying the dynamics of a standard
model, {\it i.e.}, with integer derivatives. We study the dynamical behavior by
means of the bifurcation diagram, Lyapunov exponents, and recurrence
quantification analysis (RQA), such as the recurrence rate (RR), the
determinism (DET), and the recurrence time entropy (RTE). We find a high
correlation coefficient between the Lyapunov exponents and RTE. Our simulations
suggest that the tumor growth parameter () is associated with a chaotic
regime. Our results suggest a high correlation between the largest Lyapunov
exponents and RTE. After understanding the dynamics of the model in the
standard formulation, we extend our results by considering fractional
operators. We fix the parameters in the chaotic regime and investigate the
effects of the fractional order. We demonstrate how fractional dynamics can be
properly characterized using RQA measures, which offer the advantage of not
requiring knowledge of the fractional Jacobian matrix. We find that the chaotic
motion is suppressed as decreases, and the system becomes periodic for
. We observe limit cycles for and fixed points for . The fixed point is
determined analytically for the considered parameters. Finally, we discover
that these dynamics are separated by an exponential relationship between
and . Also, the transition depends on a supper transient which
obeys the same relationship
Effects of drug resistance in the tumour-immune system with chemotherapy treatment
Acknowledgement This study was possible by partial financial support from the following Brazilian government agencies: Fundaao Araucaria, National Council for Scientific and Technological Development, Coordination for the Improvement of Higher Education Personnel, and Sao Paulo Research Foundation (2015/07311-7, 2017/18977- 1, 2018/03211-6, 2020/04624-2)Peer reviewedPostprin
Applications of Computer Technology in Complex Craniofacial Reconstruction
Background:. To demonstrate our use of advanced 3-dimensional (3D) computer technology in the analysis, virtual surgical planning (VSP), 3D modeling (3DM), and treatment of complex congenital and acquired craniofacial deformities.
Methods:. We present a series of craniofacial defects treated at a tertiary craniofacial referral center utilizing state-of-the-art 3D computer technology. All patients treated at our center using computer-assisted VSP, prefabricated custom-designed 3DMs, and/or 3D printed custom implants (3DPCI) in the reconstruction of craniofacial defects were included in this analysis.
Results:. We describe the use of 3D computer technology to precisely analyze, plan, and reconstruct 31 craniofacial deformities/syndromes caused by: Pierre-Robin (7), Treacher Collins (5), Apertâs (2), Pfeiffer (2), Crouzon (1) Syndromes, craniosynostosis (6), hemifacial microsomia (2), micrognathia (2), multiple facial clefts (1), and trauma (3). In select cases where the available bone was insufficient for skeletal reconstruction, 3DPCIs were fabricated using 3D printing. We used VSP in 30, 3DMs in all 31, distraction osteogenesis in 16, and 3DPCIs in 13 cases. Utilizing these technologies, the above complex craniofacial defects were corrected without significant complications and with excellent aesthetic results.
Conclusion:. Modern 3D technology allows the surgeon to better analyze complex craniofacial deformities, precisely plan surgical correction with computer simulation of results, customize osteotomies, plan distractions, and print 3DPCI, as needed. The use of advanced 3D computer technology can be applied safely and potentially improve aesthetic and functional outcomes after complex craniofacial reconstruction. These techniques warrant further study and may be reproducible in various centers of care
Anomalous Relaxation and Three-Level System: A Fractional Schrödinger Equation Approach
We investigate a three-level system in the context of the fractional Schrödinger equation by considering fractional differential operators in time and space, which promote anomalous relaxations and spreading of the wave packet. We first consider the three-level system omitting the kinetic term, i.e., taking into account only the transition among the levels, to analyze the effect of the fractional time derivative. Afterward, we incorporate a kinetic term and the fractional derivative in space to analyze simultaneous wave packet transition and spreading among the levels. For these cases, we obtain analytical and numerical solutions. Our results show a wide variety of behaviors connected to the fractional operators, such as the non-conservation of probability and the anomalous spread of the wave packet
Dynamics of a perturbed random neuronal network with burst-timing-dependent plasticity
Neuroplasticity, also known as brain plasticity or neuronal plasticity, allows the brain to improve its connections or rewire itself. The synaptic modifications can help the brain to enhance fitness, to promote existing cognitive capabilities, and to recover from some brain injuries. Furthermore, brain plasticity has impacts on neuronal synchronisation. In this work, we build a neuronal network composed of coupled Rulkov neurons with excitatory connections randomly distributed. We consider burst-timing-dependent plasticity to investigate the effects of external perturbations, such as periodic and random pulses, on the neuronal synchronous behaviour. The plasticity changes the synaptic weights between the presynaptic and postsynaptic neurons, and as a consequence the burst synchronisation. We verify that the external periodic and random pulsed perturbations can induce synchronisation and desynchronisation states. One of our main results is to demonstrate that bursting synchronisation and desynchronisation in a network with burst-timing-dependent plasticity can emerge according to alterations of the initial synaptic weights. Furthermore, we show that external periodic and random pulsed currents can be an effective method to suppress neuronal activities related to pathological synchronous behaviour
Fractional Diffusion Equation under Singular and Non-Singular Kernel and Its Stability
The fractional reactionâdiffusion equation has been used in many real-world applications in fields such as physics, biology, and chemistry. Motivated by the huge application of fractional reactionâdiffusion, we propose a numerical scheme to solve the fractional reactionâdiffusion equation under different kernels. Our method can be particularly employed for singular and non-singular kernels, such as the RiemannâLiouville, Caputo, FabrizioâCaputo, and AtanganaâBaleanu operators. Moreover, we obtained general inequalities that guarantee that the stability condition depends explicitly on the kernel. As an implementation of the method, we numerically solved the diffusion equation under the power-law and exponential kernels. For the power-law kernel, we solved by considering fractional time, space, and both operators. In another example, we considered the exponential kernel acting on the time derivative and compared the numerical results with the analytical ones. Our results showed that the numerical procedure developed in this work can be employed to solve fractional differential equations considering different kernels