rodrigo miranda - Academia.edu (original) (raw)
Papers by rodrigo miranda
Monthly Notices of the Royal Astronomical Society, 2015
We study the development of coherent structures in local simulations of the magnetorotational ins... more We study the development of coherent structures in local simulations of the magnetorotational instability in accretion discs in regimes of on-off intermittency. In a previous paper, we have shown that the laminar and bursty states due to the on-off spatiotemporal intermittency in a onedimensional model of non-linear waves correspond, respectively, to non-attracting coherent structures with higher and lower degrees of amplitude-phase synchronization. In this paper, we extend these results to a three-dimensional model of magnetized Keplerian shear flows. Keeping the kinetic Reynolds number and the magnetic Prandtl number fixed, we investigate two different intermittent regimes by varying the plasma beta parameter. The first regime is characterized by turbulent patterns interrupted by the recurrent emergence of a large-scale coherent structure known as two-channel flow, where the state of the system can be described by a single Fourier mode. The second regime is dominated by the turbulence with sporadic emergence of coherent structures with shapes that are reminiscent of a perturbed channel flow. By computing the Fourier power and phase spectral entropies in three dimensions, we show that the large-scale coherent structures are characterized by a high degree of amplitude-phase synchronization.
Proceedings of the International Astronomical Union, 2009
We apply single- and multi-spacecraft techniques to search for currents sheets in the solar wind ... more We apply single- and multi-spacecraft techniques to search for currents sheets in the solar wind during the ICME event of 21 January 2005, using the Cluster magnetic field data. Two large-scale currents sheets are detected at the leading boundary of the ICME ejecta using the single-spacecraft technique, which exhibit physical characteristics typical of magnetic reconnection exhausts in the solar wind.
Physics of Fluids, 2009
Transition to intermittent spatiotemporal chaos is studied in the regularized long-wave equation,... more Transition to intermittent spatiotemporal chaos is studied in the regularized long-wave equation, a nonlinear model of shallow water waves. A mechanism for the onset of on-off spatiotemporal intermittency is explored. In this mechanism, the coupling of two chaotic saddles triggers random switching between phases of laminar and bursty behaviors. The average time between bursts as a function of the control parameter follows a power law typical of crisis transitions in chaotic systems. The degree of spatiotemporal disorder in the observed fluid patterns is quantified by means of the time-averaged spectral entropy for both chaotic attractors and chaotic saddles. The implications of these results to other fluid systems are discussed.
Physical Review Letters, 2010
Amplitude and phase synchronization due to multiscale interactions in chaotic saddles at the onse... more Amplitude and phase synchronization due to multiscale interactions in chaotic saddles at the onset of permanent spatiotemporal chaos is analyzed using the Fourier-Lyapunov representation. By computing the power-phase spectral entropy and the time-averaged power-phase spectra, we show that the laminar (bursty) states in the on-off spatiotemporal intermittency correspond, respectively, to the nonattracting coherent structures with higher (lower) degrees of amplitude-phase synchronization across spatial scales.
Physical Review E, 2007
In a recent study ͓Rempel and Chian, Phys. Rev. Lett. 98, 014101 ͑2007͔͒, it has been shown that ... more In a recent study ͓Rempel and Chian, Phys. Rev. Lett. 98, 014101 ͑2007͔͒, it has been shown that nonattracting chaotic sets ͑chaotic saddles͒ are responsible for intermittency in the regularized long-wave equation that undergoes a transition to spatiotemporal chaos ͑STC͒ via quasiperiodicity and temporal chaos. In the present paper, it is demonstrated that a similar mechanism is present in the damped Kuramoto-Sivashinsky equation. Prior to the onset of STC, a spatiotemporally chaotic saddle coexists with a spatially regular attractor. After the transition to STC, the chaotic saddle merges with the attractor, generating intermittent bursts of STC that dominate the post-transition dynamics.
Revista médica de Chile, 2007
Oxidative stress and inflammation in heart failure: Mechanisms of damage and therapeutic alternat... more Oxidative stress and inflammation in heart failure: Mechanisms of damage and therapeutic alternatives Despite advances in treatment, chronic heart failure still is associated with a poor prognosis and remains a leading cause of cardiovascular death. Cumulating evidence suggests that imbalances in redox state lead to a higher generation of reactive oxygen species. This phenomenon, along with pro-inflammatory cytokine activation and extra cellular matrix alterations with reactive fibrosis, play an important role in the pathogenesis and progression of heart failure, through the development of endothelial and myocardial dysfunction. The understanding of the underlying phenomena and the metabolic pathways involved will allow further development of therapies aiming to change the natural history of heart failure (
FLORESTA, 2022
Different sampling methods can be used in forest surveys. It is important to know the precision a... more Different sampling methods can be used in forest surveys. It is important to know the precision and accuracy of these sampling methods, and which one is the most appropriate in specific conditions of the forest population. The aim of this study was to compare estimates of a forest inventory performed by different sampling methods with forest census results. The sampling methods evaluated were the fixed-area method and the variable-area methods of Bitterlich, Prodan, and Strand. The data were obtained in a 15-year-old thinned stand of Pinus taeda L., located in the municipality of Teixeira Soares, southern Brazil, with a total area of 12.80 ha. Initially, the forest census was carried out, and subsequently, the sample units for each sampling method were distributed in the stand, with a common starting point. The variables used to compare the sample results with the census means were quadratic diameter, number of trees, basal area, and volume, per hectare. Precision and accuracy were ...
Metals, 2021
The mining industry sector is notable for the severe service loads and varied environmental condi... more The mining industry sector is notable for the severe service loads and varied environmental conditions that it imposes on its equipment and mechanical systems. It has become essential to identify the causes of failures and use the information to avoid similar failures and improve projects. In this paper, a study on shaft failure in a speed reduction box was carried out. A section of a fractured shaft made of hardened austempered steel was analyzed to determine the cause of the break. Fractography was performed to characterize the failure mode on the fracture surface. The microstructural analysis and hardness profile revealed that the shaft was inadequately heat treated, resulting in low resistance microstructures and the development of a thin layer of bainite at the shaft edge. Large amounts of inclusions were found in the fracture region, and the tensile tests revealed that the material had an elongation below the specification. The analyses showed that the combination of factors o...
Advances in Dermatology and Allergology, 2020
Scientific reports, Jan 12, 2018
Equatorial plasma depletions have significant impact on radio wave propagation in the upper atmos... more Equatorial plasma depletions have significant impact on radio wave propagation in the upper atmosphere, causing rapid fluctuations in the power of radio signals used in telecommunication and GPS navigation, thus playing a crucial role in space weather impacts. Complex structuring and self-organization of equatorial plasma depletions involving bifurcation, connection, disconnection and reconnection are the signatures of nonlinear evolution of interchange instability and secondary instabilities, responsible for the generation of coherent structures and turbulence in the ionosphere. The aims of this paper are three-fold: (1) to report the first optical imaging of reconnection of equatorial plasma depletions in the South Atlantic Magnetic Anomaly, (2) to investigate the optical imaging of equatorial ionospheric intermittent turbulence, and (3) to compare nonlinear characteristics of optical imaging of equatorial plasma depletions for two different altitudes at same times. We show that t...
PloS one, 2018
The ability to discriminate between normal and impaired dynamic cerebral autoregulation (CA), bas... more The ability to discriminate between normal and impaired dynamic cerebral autoregulation (CA), based on measurements of spontaneous fluctuations in arterial blood pressure (BP) and cerebral blood flow (CBF), has considerable clinical relevance. We studied 45 normal subjects at rest and under hypercapnia induced by breathing a mixture of carbon dioxide and air. Non-linear models with BP as input and CBF velocity (CBFV) as output, were implemented with support vector machines (SVM) using separate recordings for learning and validation. Dynamic SVM implementations used either moving average or autoregressive structures. The efficiency of dynamic CA was estimated from the model's derived CBFV response to a step change in BP as an autoregulation index for both linear and non-linear models. Non-linear models with recurrences (autoregressive) showed the best results, with CA indexes of 5.9 ± 1.5 in normocapnia, and 2.5 ± 1.2 for hypercapnia with an area under the receiver-operator curve...
PloS one, 2018
While diseases caused by nematodes remains a considerable drawback for the livestock, agriculture... more While diseases caused by nematodes remains a considerable drawback for the livestock, agriculture and public health, anthelmintics drug resistance has been observed over the past years and is a major concern for parasite control. Ivermectin, initially considered as a highly potent drug, currently presents a reduced anti-helminthic efficacy, which is influenced by expression of several ATP-binding cassette transporters (ABC), among them the P-glycoproteins (Pgps). Here we present some evidences of Pgps dominance during Ivermectin resistance/susceptibility using Pgps double silencing in C. elegans and the phylogenetic relationship of Pgps among nematodes, which strengthen the use of this model for study of drug resistance in nematodes. Firstly, we evaluated the quantitative gene expression of 12 out the 15 known Pgps from resistant and WT strains of C. elegans, we demonstrated the upregulation of Pgps 12 and 13 and downregulation of all remaining Pgps in ivermectin resistant strain. B...
European Journal of Cardio-Thoracic Surgery, 2017
et al. Stopping versus continuing acetylsalicylic acid before coronary artery bypass surgery: A s... more et al. Stopping versus continuing acetylsalicylic acid before coronary artery bypass surgery: A systematic review and meta-analysis of 14 randomized controlled trials with 4499 patients.
Indian Pacing and Electrophysiology Journal, 2012
In this "featured arrhythmia" article we present a set of unusual intracardiac electrode tracings... more In this "featured arrhythmia" article we present a set of unusual intracardiac electrode tracings that were recorded in a patient with typical clockwise flutter but a very dilated right atrium. The potential mechanism underlying this phenomenon is discussed with reference to the current literature.
Revista chilena de cardiología, 2015
Bajos niveles de colesterol HDL es un predictor de mortalidad y de fibrilación auricular postoper... more Bajos niveles de colesterol HDL es un predictor de mortalidad y de fibrilación auricular postoperatoria posterior... Vargas C., et al. Conclusion: Low C-HDL is an independent predictor of POAF and mortality after coronary artery revascularization surgery.
Circulation. Arrhythmia and electrophysiology, 2012
Cardiac resynchronization therapy is widely used for the treatment of heart failure. Recent data ... more Cardiac resynchronization therapy is widely used for the treatment of heart failure. Recent data suggest that electric separation during left ventricular pacing varies within the right ventricle (RV). We hypothesized that placement of the RV lead guided by maximal electric separation (MES) would improve response to cardiac resynchronization therapy compared with standard apical placement. A single-blind, randomized controlled trial was conducted. Patients eligible for cardiac resynchronization therapy-D were enrolled. Left ventricular lead placement was performed at the coronary sinus branch. The RV outflow tract, septum, and apex were mapped during left ventricular pacing and MES recorded. Patients were randomized to receive either apical placement or RV lead placement at the site mapping MES. Left ventricular ejection fraction, 6-minute walk distance, and New York Heart Association functional class were recorded at baseline and 3 months by blinded observers. Response was defined a...
Proceedings of the International Astronomical Union, 2009
We apply two nonlinear techniques, kurtosis and phase coherence index, to analyze magnetic field ... more We apply two nonlinear techniques, kurtosis and phase coherence index, to analyze magnetic field measurements from SOHO MDI solar images, ACE and Cluster data in the solar wind, and ground magnetometers in Brazil. We focus on two events: a non-ICME event in February 2002 and an ICME event in January 2005. Finite degree of non-Gaussianity and phase synchronization are observed in all datasets. The nonlinear response of the Earth's geomagnetic field to an ICME event in the solar wind is discussed.
Journal of the American College of Surgeons, 2014
Revista médica de Chile, 2007
Hypokalemia, hypovolemia and electrocardiographic changes due to furosemide abuse. Report of one ... more Hypokalemia, hypovolemia and electrocardiographic changes due to furosemide abuse. Report of one case Hypokalemia (serum K + <3.5 mEq/l) is a potentially serious adverse effect of diuretic ingestion. We report a 27 year-old woman admitted with muscle weakness, a serum potassium of 2.0 mEq/1, metabolic alkalosis and EKG abnormalities simulating cardiac ischemia, that reverted with potassium chloride administration. She admitted high dose furosemide self-medication for edema. Glomerular filtration rate, tubular sodium reabsortion, potassium secretion, the renin-aldosterone system, total body water distribution and capillary permeability, were studied sequentially until 90 days after her admission. There was hyperactivity of the renin-aldosterone axis, reduction in extracellular and intracellular volumes, normal capillary permeability and high sodium tubular reabsorption, probably explained by a "rebound" salt retention associated with her decreased
Monthly Notices of the Royal Astronomical Society, 2015
We study the development of coherent structures in local simulations of the magnetorotational ins... more We study the development of coherent structures in local simulations of the magnetorotational instability in accretion discs in regimes of on-off intermittency. In a previous paper, we have shown that the laminar and bursty states due to the on-off spatiotemporal intermittency in a onedimensional model of non-linear waves correspond, respectively, to non-attracting coherent structures with higher and lower degrees of amplitude-phase synchronization. In this paper, we extend these results to a three-dimensional model of magnetized Keplerian shear flows. Keeping the kinetic Reynolds number and the magnetic Prandtl number fixed, we investigate two different intermittent regimes by varying the plasma beta parameter. The first regime is characterized by turbulent patterns interrupted by the recurrent emergence of a large-scale coherent structure known as two-channel flow, where the state of the system can be described by a single Fourier mode. The second regime is dominated by the turbulence with sporadic emergence of coherent structures with shapes that are reminiscent of a perturbed channel flow. By computing the Fourier power and phase spectral entropies in three dimensions, we show that the large-scale coherent structures are characterized by a high degree of amplitude-phase synchronization.
Proceedings of the International Astronomical Union, 2009
We apply single- and multi-spacecraft techniques to search for currents sheets in the solar wind ... more We apply single- and multi-spacecraft techniques to search for currents sheets in the solar wind during the ICME event of 21 January 2005, using the Cluster magnetic field data. Two large-scale currents sheets are detected at the leading boundary of the ICME ejecta using the single-spacecraft technique, which exhibit physical characteristics typical of magnetic reconnection exhausts in the solar wind.
Physics of Fluids, 2009
Transition to intermittent spatiotemporal chaos is studied in the regularized long-wave equation,... more Transition to intermittent spatiotemporal chaos is studied in the regularized long-wave equation, a nonlinear model of shallow water waves. A mechanism for the onset of on-off spatiotemporal intermittency is explored. In this mechanism, the coupling of two chaotic saddles triggers random switching between phases of laminar and bursty behaviors. The average time between bursts as a function of the control parameter follows a power law typical of crisis transitions in chaotic systems. The degree of spatiotemporal disorder in the observed fluid patterns is quantified by means of the time-averaged spectral entropy for both chaotic attractors and chaotic saddles. The implications of these results to other fluid systems are discussed.
Physical Review Letters, 2010
Amplitude and phase synchronization due to multiscale interactions in chaotic saddles at the onse... more Amplitude and phase synchronization due to multiscale interactions in chaotic saddles at the onset of permanent spatiotemporal chaos is analyzed using the Fourier-Lyapunov representation. By computing the power-phase spectral entropy and the time-averaged power-phase spectra, we show that the laminar (bursty) states in the on-off spatiotemporal intermittency correspond, respectively, to the nonattracting coherent structures with higher (lower) degrees of amplitude-phase synchronization across spatial scales.
Physical Review E, 2007
In a recent study ͓Rempel and Chian, Phys. Rev. Lett. 98, 014101 ͑2007͔͒, it has been shown that ... more In a recent study ͓Rempel and Chian, Phys. Rev. Lett. 98, 014101 ͑2007͔͒, it has been shown that nonattracting chaotic sets ͑chaotic saddles͒ are responsible for intermittency in the regularized long-wave equation that undergoes a transition to spatiotemporal chaos ͑STC͒ via quasiperiodicity and temporal chaos. In the present paper, it is demonstrated that a similar mechanism is present in the damped Kuramoto-Sivashinsky equation. Prior to the onset of STC, a spatiotemporally chaotic saddle coexists with a spatially regular attractor. After the transition to STC, the chaotic saddle merges with the attractor, generating intermittent bursts of STC that dominate the post-transition dynamics.
Revista médica de Chile, 2007
Oxidative stress and inflammation in heart failure: Mechanisms of damage and therapeutic alternat... more Oxidative stress and inflammation in heart failure: Mechanisms of damage and therapeutic alternatives Despite advances in treatment, chronic heart failure still is associated with a poor prognosis and remains a leading cause of cardiovascular death. Cumulating evidence suggests that imbalances in redox state lead to a higher generation of reactive oxygen species. This phenomenon, along with pro-inflammatory cytokine activation and extra cellular matrix alterations with reactive fibrosis, play an important role in the pathogenesis and progression of heart failure, through the development of endothelial and myocardial dysfunction. The understanding of the underlying phenomena and the metabolic pathways involved will allow further development of therapies aiming to change the natural history of heart failure (
FLORESTA, 2022
Different sampling methods can be used in forest surveys. It is important to know the precision a... more Different sampling methods can be used in forest surveys. It is important to know the precision and accuracy of these sampling methods, and which one is the most appropriate in specific conditions of the forest population. The aim of this study was to compare estimates of a forest inventory performed by different sampling methods with forest census results. The sampling methods evaluated were the fixed-area method and the variable-area methods of Bitterlich, Prodan, and Strand. The data were obtained in a 15-year-old thinned stand of Pinus taeda L., located in the municipality of Teixeira Soares, southern Brazil, with a total area of 12.80 ha. Initially, the forest census was carried out, and subsequently, the sample units for each sampling method were distributed in the stand, with a common starting point. The variables used to compare the sample results with the census means were quadratic diameter, number of trees, basal area, and volume, per hectare. Precision and accuracy were ...
Metals, 2021
The mining industry sector is notable for the severe service loads and varied environmental condi... more The mining industry sector is notable for the severe service loads and varied environmental conditions that it imposes on its equipment and mechanical systems. It has become essential to identify the causes of failures and use the information to avoid similar failures and improve projects. In this paper, a study on shaft failure in a speed reduction box was carried out. A section of a fractured shaft made of hardened austempered steel was analyzed to determine the cause of the break. Fractography was performed to characterize the failure mode on the fracture surface. The microstructural analysis and hardness profile revealed that the shaft was inadequately heat treated, resulting in low resistance microstructures and the development of a thin layer of bainite at the shaft edge. Large amounts of inclusions were found in the fracture region, and the tensile tests revealed that the material had an elongation below the specification. The analyses showed that the combination of factors o...
Advances in Dermatology and Allergology, 2020
Scientific reports, Jan 12, 2018
Equatorial plasma depletions have significant impact on radio wave propagation in the upper atmos... more Equatorial plasma depletions have significant impact on radio wave propagation in the upper atmosphere, causing rapid fluctuations in the power of radio signals used in telecommunication and GPS navigation, thus playing a crucial role in space weather impacts. Complex structuring and self-organization of equatorial plasma depletions involving bifurcation, connection, disconnection and reconnection are the signatures of nonlinear evolution of interchange instability and secondary instabilities, responsible for the generation of coherent structures and turbulence in the ionosphere. The aims of this paper are three-fold: (1) to report the first optical imaging of reconnection of equatorial plasma depletions in the South Atlantic Magnetic Anomaly, (2) to investigate the optical imaging of equatorial ionospheric intermittent turbulence, and (3) to compare nonlinear characteristics of optical imaging of equatorial plasma depletions for two different altitudes at same times. We show that t...
PloS one, 2018
The ability to discriminate between normal and impaired dynamic cerebral autoregulation (CA), bas... more The ability to discriminate between normal and impaired dynamic cerebral autoregulation (CA), based on measurements of spontaneous fluctuations in arterial blood pressure (BP) and cerebral blood flow (CBF), has considerable clinical relevance. We studied 45 normal subjects at rest and under hypercapnia induced by breathing a mixture of carbon dioxide and air. Non-linear models with BP as input and CBF velocity (CBFV) as output, were implemented with support vector machines (SVM) using separate recordings for learning and validation. Dynamic SVM implementations used either moving average or autoregressive structures. The efficiency of dynamic CA was estimated from the model's derived CBFV response to a step change in BP as an autoregulation index for both linear and non-linear models. Non-linear models with recurrences (autoregressive) showed the best results, with CA indexes of 5.9 ± 1.5 in normocapnia, and 2.5 ± 1.2 for hypercapnia with an area under the receiver-operator curve...
PloS one, 2018
While diseases caused by nematodes remains a considerable drawback for the livestock, agriculture... more While diseases caused by nematodes remains a considerable drawback for the livestock, agriculture and public health, anthelmintics drug resistance has been observed over the past years and is a major concern for parasite control. Ivermectin, initially considered as a highly potent drug, currently presents a reduced anti-helminthic efficacy, which is influenced by expression of several ATP-binding cassette transporters (ABC), among them the P-glycoproteins (Pgps). Here we present some evidences of Pgps dominance during Ivermectin resistance/susceptibility using Pgps double silencing in C. elegans and the phylogenetic relationship of Pgps among nematodes, which strengthen the use of this model for study of drug resistance in nematodes. Firstly, we evaluated the quantitative gene expression of 12 out the 15 known Pgps from resistant and WT strains of C. elegans, we demonstrated the upregulation of Pgps 12 and 13 and downregulation of all remaining Pgps in ivermectin resistant strain. B...
European Journal of Cardio-Thoracic Surgery, 2017
et al. Stopping versus continuing acetylsalicylic acid before coronary artery bypass surgery: A s... more et al. Stopping versus continuing acetylsalicylic acid before coronary artery bypass surgery: A systematic review and meta-analysis of 14 randomized controlled trials with 4499 patients.
Indian Pacing and Electrophysiology Journal, 2012
In this "featured arrhythmia" article we present a set of unusual intracardiac electrode tracings... more In this "featured arrhythmia" article we present a set of unusual intracardiac electrode tracings that were recorded in a patient with typical clockwise flutter but a very dilated right atrium. The potential mechanism underlying this phenomenon is discussed with reference to the current literature.
Revista chilena de cardiología, 2015
Bajos niveles de colesterol HDL es un predictor de mortalidad y de fibrilación auricular postoper... more Bajos niveles de colesterol HDL es un predictor de mortalidad y de fibrilación auricular postoperatoria posterior... Vargas C., et al. Conclusion: Low C-HDL is an independent predictor of POAF and mortality after coronary artery revascularization surgery.
Circulation. Arrhythmia and electrophysiology, 2012
Cardiac resynchronization therapy is widely used for the treatment of heart failure. Recent data ... more Cardiac resynchronization therapy is widely used for the treatment of heart failure. Recent data suggest that electric separation during left ventricular pacing varies within the right ventricle (RV). We hypothesized that placement of the RV lead guided by maximal electric separation (MES) would improve response to cardiac resynchronization therapy compared with standard apical placement. A single-blind, randomized controlled trial was conducted. Patients eligible for cardiac resynchronization therapy-D were enrolled. Left ventricular lead placement was performed at the coronary sinus branch. The RV outflow tract, septum, and apex were mapped during left ventricular pacing and MES recorded. Patients were randomized to receive either apical placement or RV lead placement at the site mapping MES. Left ventricular ejection fraction, 6-minute walk distance, and New York Heart Association functional class were recorded at baseline and 3 months by blinded observers. Response was defined a...
Proceedings of the International Astronomical Union, 2009
We apply two nonlinear techniques, kurtosis and phase coherence index, to analyze magnetic field ... more We apply two nonlinear techniques, kurtosis and phase coherence index, to analyze magnetic field measurements from SOHO MDI solar images, ACE and Cluster data in the solar wind, and ground magnetometers in Brazil. We focus on two events: a non-ICME event in February 2002 and an ICME event in January 2005. Finite degree of non-Gaussianity and phase synchronization are observed in all datasets. The nonlinear response of the Earth's geomagnetic field to an ICME event in the solar wind is discussed.
Journal of the American College of Surgeons, 2014
Revista médica de Chile, 2007
Hypokalemia, hypovolemia and electrocardiographic changes due to furosemide abuse. Report of one ... more Hypokalemia, hypovolemia and electrocardiographic changes due to furosemide abuse. Report of one case Hypokalemia (serum K + <3.5 mEq/l) is a potentially serious adverse effect of diuretic ingestion. We report a 27 year-old woman admitted with muscle weakness, a serum potassium of 2.0 mEq/1, metabolic alkalosis and EKG abnormalities simulating cardiac ischemia, that reverted with potassium chloride administration. She admitted high dose furosemide self-medication for edema. Glomerular filtration rate, tubular sodium reabsortion, potassium secretion, the renin-aldosterone system, total body water distribution and capillary permeability, were studied sequentially until 90 days after her admission. There was hyperactivity of the renin-aldosterone axis, reduction in extracellular and intracellular volumes, normal capillary permeability and high sodium tubular reabsorption, probably explained by a "rebound" salt retention associated with her decreased