RESUMO

We investigate chaotic impurity transport in toroidal fusion plasmas (tokamaks) from the point of view of passive advection of charged particles due to E×B drift motion. We use realistic tokamak profiles for electric and magnetic fields as well as toroidal rotation effects, and consider also the effects of electrostatic fluctuations due to drift instabilities on particle motion. A time-dependent one degree-of-freedom Hamiltonian system is obtained and numerically investigated through a symplectic map in a Poincaré surface of section. We show that the chaotic transport in the outer plasma region is influenced by fractal structures that are described in topological and metric point of views. Moreover, the existence of a hierarchical structure of islands-around-islands, where the particles experience the stickiness effect, is demonstrated using a recurrence-based approach.

RESUMO

Recent evidence shows that heteroclinic bifurcations in magnetic islands may be caused by the amplitude variation of resonant magnetic perturbations in tokamaks. To investigate the onset of these bifurcations, we consider a large aspect ratio tokamak with an ergodic limiter composed of two pairs of rings that create external primary perturbations with two sets of wave numbers. An individual pair produces hyperbolic and elliptic periodic points, and its associated islands, that are consistent with the Poincaré-Birkhoff fixed-point theorem. However, for two pairs producing external perturbations resonant on the same rational surface, we show that different configurations of isochronous island chains may appear on phase space according to the amplitude of the electric currents in each pair of the ergodic limiter. When one of the electric currents increases, isochronous bifurcations take place and new islands are created with the same winding number as the preceding islands. We present examples of bifurcation sequences displaying (a) direct transitions from the island chain configuration generated by one of the pairs to the configuration produced by the other pair, and (b) transitions with intermediate configurations produced by the limiter pairs coupling. Furthermore, we identify shearless bifurcations inside some isochronous islands, originating nonmonotonic local winding number profiles with associated shearless invariant curves.

RESUMO

The E×B drift motion of particles in tokamaks provides valuable information on the turbulence-driven anomalous transport. One of the characteristic features of the drift motion dynamics is the presence of chaotic orbits for which the guiding center can experience large-scale drifts. If one or more exits are placed so that they intercept chaotic orbits, the corresponding escape basins structure is complicated and, indeed, exhibits fractal structures. We investigate those structures through a number of numerical diagnostics, tailored to quantify the final-state uncertainty related to the fractal escape basins. We estimate the escape basin boundary dimension through the uncertainty exponent method and quantify final-state uncertainty by the basin entropy and the basin boundary entropy. Finally, we recall the Wada property for the case of three or more escape basins. This property is verified both qualitatively and quantitatively using a grid approach.

RESUMO

INTRODUCTION: This study aimed to compare the characteristics and outcomes of critically ill patients with COVID-19-associated acute kidney injury (AKI) who were treated with kidney replacement therapy (KRT) in the first and second waves of the pandemic in the megalopolis of Sao Paulo, Brazil. METHODS: A multicenter retrospective study was conducted in 10 intensive care units (ICUs). Patients aged ≥18 years, and treated with KRT due to COVID-19-associated AKI were included. We compared demographic, laboratory and clinical data, KRT parameters and patient outcomes in the first and second COVID-19 waves. RESULTS: We assessed 656 patients (327 in the first wave and 329 in the second one). Second-wave patients were admitted later (7.1±5.0 vs. 5.6±3.9 days after the onset of symptoms, p<0.001), were younger (61.4±13.7 vs. 63.8±13.6 years, p = 0.023), had a lower frequency of diabetes (37.1% vs. 47.1%, p = 0.009) and obesity (29.5% vs. 40.0%, p = 0.007), had a greater need for vasopressors (93.3% vs. 84.6%, p<0.001) and mechanical ventilation (95.7% vs. 87.8%, p<0.001), and had higher lethality (84.8% vs. 72.7%, p<0.001) than first-wave patients. KRT quality markers were independently associated with a reduction in the OR for death in both pandemic waves. CONCLUSIONS: In the Sao Paulo megalopolis, the lethality of critically ill patients with COVID-19-associated AKI treated with KRT was higher in the second wave of the pandemic, despite these patients being younger and having fewer comorbidities. Potential factors related to this poor outcome were difficulties in health care access, lack of intra-hospital resources, delay vaccination and virus variants.

Assuntos

RESUMO

We consider a dissipative version of the standard nontwist map. Nontwist systems present a robust transport barrier, called the shearless curve, that becomes the shearless attractor when dissipation is introduced. This attractor can be regular or chaotic depending on the control parameters. Chaotic attractors can undergo sudden and qualitative changes as a parameter is varied. These changes are called crises, and at an interior crisis the attractor suddenly expands. Chaotic saddles are nonattracting chaotic sets that play a fundamental role in the dynamics of nonlinear systems; they are responsible for chaotic transients, fractal basin boundaries, and chaotic scattering, and they mediate interior crises. In this work we discuss the creation of chaotic saddles in a dissipative nontwist system and the interior crises they generate. We show how the presence of two saddles increases the transient times and we analyze the phenomenon of crisis induced intermittency.

RESUMO

The form of analysis of the cardiac signal most used today is the electrocardiogram (ECG). However, in addition to this form of data visualization, there is the vectorcardiogram (VCG), that allows a visualization of the signal in 3 dimensions. This study aims to compare the different ECG to VCG transformation matrices Kors and Inverse Dower (iDower), by analyzing some known parameters taken from VCG's mathematically synthesized from 12-lead ECG's of amyloidosis patients. The idea is also to compare that similarity for patients with different types of amyloidosis. The study was done through the analysis of electrocardiograms taken from a sample of 12 humans who have amyloidosis, either mutant or wild-type. The results indicated that there is not much similarity between the signals, although the similarity was higher for patients with mutant amyloidosis than for those with wild-type amyloidosis.

Assuntos

RESUMO

We analyze nonlinear aspects of the self-consistent wave-particle interaction using Hamiltonian dynamics in the single wave model, where the wave is modified due to the particle dynamics. This interaction plays an important role in the emergence of plasma instabilities and turbulence. The simplest case, where one particle (N=1) is coupled with one wave (M=1), is completely integrable, and the nonlinear effects reduce to the wave potential pulsating while the particle either remains trapped or circulates forever. On increasing the number of particles ( N=2, M=1), integrability is lost and chaos develops. Our analyses identify the two standard ways for chaos to appear and grow (the homoclinic tangle born from a separatrix, and the resonance overlap near an elliptic fixed point). Moreover, a strong form of chaos occurs when the energy is high enough for the wave amplitude to vanish occasionally.

RESUMO

INTRODUÇÃO: O eletrocardiograma (ECG) é uma ferramenta diagnóstica primordial em cardiologia. Através de técnicas de pós-processamento do ECG digital é possível extrair dados do clássico vetorcardiograma (VCG) e ampliar as possibilidades do método. OBJETIVO: Comparar os dados matriciais do ECG entre os pacientes portadores de hipertrofia ventricular patológica (Cardiomiopatia Hipertrófica e Amiloidose Cardíaca) e o grupo controle utilizando duas matrizes diferentes de transformação de ECG para VCG: a matriz inversa de Dower (iDower) e a matriz de Kors. MÉTODOS: Foram analisados VCGs sintetizados a partir das duas matrizes, iDower e Kors, e tais exames foram obtidos para o grupo hipertrófico, composto por 11 pacientes, e para o grupo controle, com cinco pacientes. O tempo de coleta do ECG foi de 10 minutos e, para cada paciente, foram analisados 10 VCGs, referentes a cada minuto da coleta. Foram analisados a amplitude cúbica (mV), por meio da análise da variação dos valores, e o ângulo do complexo QRS e da onda T, por meio da análise de dados circulares. RESULTADOS: Em relação aos ângulos, as médias dos ângulos de cada grupo tiveram maior proximidade no grupo controle e menor no grupo hipertrófico. A variação destes ângulos foi maior utilizando a matriz de Kors para o grupo controle (Figura.1); no entanto, no grupo hipertrófico a maior variação no observada na matriz iDower (Figura 2). Em relação à amplitude cúbica das ondas, a variação foi pequena para ambos os grupos, porém com proximidade maior na onda T, e não houve diferença notável em relação às matrizes. CONCLUSÃO: Analisando as variáveis angulares e de amplitude cúbica nas ondas QRS e T para o grupo controle e hipertrófico, não foi observada diferença significativa entre os grupos. Tal proximidade entre as variáveis também foi observada considerando as matrizes de transformação.

Assuntos

RESUMO

We study the advection of blood particles in the carotid bifurcation, a site that is prone to plaque development. Previously, it has been shown that chaotic advection can take place in blood flows with diseases. Here, we show that even in a healthy scenario, chaotic advection can take place. To understand how the particle dynamics is affected by the emergence and growth of a plaque, we study the carotid bifurcation in three cases: a healthy bifurcation, a bifurcation with a mild stenosis, and the another with a severe stenosis. The result is non-intuitive: there is less chaos for the mild stenosis case even when compared to the healthy, non-stenosed, bifurcation. This happens because the partial obstruction of the mild stenosis generates a symmetry in the flow that does not exist for the healthy condition. For the severe stenosis, there is more irregular motion and more particle trapping as expected.

Assuntos

RESUMO

The use of hypotonic electrolytic solutions in enteral fluid therapy is still understudied in calves. The objective of the present study was to evaluate the effects of maintenance enteral electrolytic solutions with different concentrations of sodium acetate and different osmolarities in calves. For this, 18 Holstein calves, six male and 12 female, 20 days old and weighing around 52kg, were used. The animals were randomly divided into three groups and each group received one of the treatments. The three electrolytic solutions contained the same components in different concentrations, resulting in a hyposmotic, an isosmotic and a hyperosmotic solution. Each animal was maintained in enteral fluid therapy for 12 hours with infusion rate of 15mL kg-1 h-1. Abdominal circumference, body weight, feces consistency, glucose and plasma lactate, pH, pCO2, HCO- 3 and BE were measured at the following times: T0h, T6h, T12h and T24h. The hyposmotic solution did not generate the onset of diarrhea, while the isosmotic and the hyperosmotic did. Regardless of the dose used, acetate did not cause metabolic alkalosis in the evaluated animals. The results suggest that the use of hyposmotic solution in diarrheic calves, dehydrated and without metabolic acidosis, may be clinically important.(AU)

O uso de soluções eletrolíticas hipotônicas na hidratação enteral ainda é pouco estudado em bezerros. O objetivo do presente estudo foi avaliar os efeitos de soluções eletrolíticas enterais de manutenção com diferentes concentrações de acetato de sódio e diferentes osmolaridades em bezerros. Para isso, foram utilizados 18 bezerros, seis machos e 12 fêmeas, holandeses, com 20 dias de nascidos e pesando por volta dos 52kg. Os animais foram divididos aleatoriamente em três grupos e cada grupo recebeu um dos tratamentos. As três soluções eletrolíticas continham os mesmos componentes, mas em diferentes concentrações, resultando em uma solução hiposmótica, uma isosmótica e uma hiperosmótica. Cada animal foi mantido em hidratação enteral durante 12 horas com taxa de infusão de 15mL kg-1h-1. Foram aferidos perímetro abdominal, peso corporal, consistência das fezes, glicose e lactato plasmático, pH, pCO2, HCO- 3 e excesso de base nos seguintes tempos: T0h, T6h, T12h e T24h. A solução hiposmótica não gerou aparecimento de diarreia, enquanto a isosmótica e a hiperosmótica geraram. Independentemente da dose utilizada, o acetato não causou alcalose metabólica nos animais avaliados. Os resultados sugerem que o uso da solução hiposmótica em bezerros diarreicos, desidratados e sem acidose metabólica, pode ser clinicamente importante.(AU)

Assuntos