Andres Peña - Academia.edu (original) (raw)

Papers by Andres Peña

Anthropogenic change is associated with population growth, land use change, and changing economie... more Anthropogenic change is associated with population growth, land use change, and changing economies. However, internal migration patterns and armed conflicts are also key drivers behind anthropogenic and demographic processes. To better understand this sort of change, we explore the spatial relationship between forced migration due to armed conflict and changing demographic factors in Colombia, a country which has a recent history of 7 million internal migrants. In addition, we use remote sensing, Google Earth Engine, as well as spatial statistical analyses of demographic data in order to measure anthropogenic change between 1984 and 2008; and we look into spatiotemporal relationships between both demographic and anthropogenic changes, which are caused by forced migration. We find, thus, that the latter is significantly and positively related to an increasing rural-urban kind of migration which originates in armed conflict, and results show that it is also negatively associated with ...

Brasil: ¿Hegemonía a pesar de todo?, 2017

A partir del 2014, Brasil entro en una fase de repliegue economico y social que muchos califican ... more A partir del 2014, Brasil entro en una fase de repliegue economico y social que muchos califican enfaticamente como una de las crisis mas graves que el gigante del Sur haya tenido en su historia reciente. Los mas alarmistas de los analistas ya predicen la desaparicion de Brasil del escenario internacional y el fin de su protagonismo en la region. Sin embargo, y como se demuestra en este analisis riguroso, los elementos materiales del poder brasileno solo se han consolidado desde principios del siglo XXI. De hecho, sin importar la retorica escogida por el gobierno de turno, desde la dictadura militar en los 80, se pueden evidenciar comportamientos reiterados que hablan por si solos. El estado brasileno sigue una estrategia de dominacion de su entorno politico y geografico utilizando los medios materiales a su disposicion. En funcion del momento historico, de la coyuntura economica y politica, los gobiernos han escogido tacticas directas/ofensivas o tacticas indirectas/defensivas, pero la prioridad siempre ha sido la salvaguardia del territorio y de las capacidades productivas y destructivas del pais.

PLOS ONE, 2020

Anthropogenic change has been associated with population growth, land use change, and changing ec... more Anthropogenic change has been associated with population growth, land use change, and changing economies. However, internal migration patterns and armed conflicts are also key drivers of anthropogenic and demographic processes. To better understand the processes associated with this change, we explore the spatial relationship between forced migration due to armed conflict and changing socioeconomic factors in Colombia, a country which has a recent history of 7 million internal migrants. In addition, we use remote sensing, Google Earth Engine, as well as spatial statistical analyses of demographic data in order to measure anthropogenic change between 1984 and 2013—a socio-politically important period in Colombia’s armed conflict. We also analyze spatiotemporal relationships between socioeconomic and anthropogenic changes, which are caused by forced migration. We found that forced migration is significantly and positively related to an increasing rural-urban type of migration which re...

Anthropogenic change is generally associated with population growth, land use change, and changin... more Anthropogenic change is generally associated with population growth, land use change, and changing economies. However, internal migration patterns and armed conflicts can also be key drivers behind these anthropogenic change and demographic change processes. To better understand this dynamic, we explore the spatial relationship between forced migration due to armed conflict and changing demographic factors in Colombia; a country with a recent history of 7 million internal migrants. First, we spatiotemporally analyzed the relationship between anthropogenic and demographic change due to forced migration from internal armed conflicts using remote sensing to measure anthropogenic change during 1984-2018 and we then used statistical and spatial analyses of demographic data. We found that anthropogenic change is significantly and positively related with increased rural-urban migration. Results show that interregional expulsion is also negatively associated with such anthropogenic change. ...

Journal of the American Academy of Orthopaedic Surgeons, 2019

Background Data: A new pilon fracture classification system based on CT scan data was recently pu... more Background Data: A new pilon fracture classification system based on CT scan data was recently published, showing almost perfect interobserver and intraobserver agreement among the authors who developed it. However, an independent assessment has not been done. Objective: To do an independent agreement evaluation of the new pilon fracture classification system with physicians with different levels of expertise in the management of pilon fractures. Methods: Seventy-one cases of acute pilon fracture were retrospectively collected. Fractures were classified by six evaluators (three foot and ankle surgeons and three orthopaedic surgery residents) using CT scans according to the morphological grading of the new pilon fracture classification system developed by Leonetti et al. Cases were presented to the same evaluators in a random sequence after a 6-week interval to determine intraobserver agreement. The kappa coefficient (k) was used to determine agreement among evaluators. Results: The interobserver agreement was substantial regarding the main fracture type (I, II, III, or IV), with an overall k value of 0.69 (0.65 to 0.72). When including the II and III subtypes, the overall agreement was still substantial, with a k value of 0.61 (95% confidence interval: 0.58 to 0.64). The intraobserver agreement was substantial when considering the main fracture categories (I, II, III, or IV), with a k value of 0.78 (confidence interval: 0.72 to 0.84), and full agreement at the type level was observed in 76% (324/426) of evaluations. There was no notable difference between the foot and ankle surgeons and orthopaedic surgery residents in the interobserver and intraobserver agreement. Conclusion: The new classification system demonstrated substantial interobserver and intraobserver agreement between evaluators with different levels of expertise in the management of pilon fractures. Prospective studies should be done to evaluate its prognostic value and utility in clinical practice.

Revista Relaciones Internacionales, Estrategia y Seguridad, 2018

Basado en un análisis neo-realista y en contra posición a los planteamientos del soft power, este... more Basado en un análisis neo-realista y en contra posición a los planteamientos del soft power, este artículo estudia la política exterior brasileña respecto a posibles diseños hegemónicos regionales. La investigación examina avances cruciales en el poder militar del Estado sudamericano, pero también tiene en cuenta la capacidad demográfica y económica brasileña y su posibilidad de desarrollar armas nucleares, como elementos condicionantes para equilibrar el poder en el escenario global. El análisis se contextualiza en la estructura sistémica internacional, donde Estados Unidos, como la gran potencia, debe impedir que otros Estados adquieran poder.

AIP Conference Proceedings, 2009

The existence and uniqueness of the so-called critical state in soil mechanics is validated in ou... more The existence and uniqueness of the so-called critical state in soil mechanics is validated in our DEM simulations of irregular polygonal particles. For different particle shape characteristics, the critical state is found to be independent of the initial stress and density conditions. We retain low stress levels, since we do not take into account the crushing of particles. In biaxial test simulations isotropic particles evolve toward a limiting state in which the system reaches a critical void ratio and deforms with constant volume, deviatoric stress, fabric anisotropy, and mechanical coordination number. The last one has been found to be the first variable to attain a critical value making possible for the rest of micro-and-macro-mechanical variables the convergence to the critical state. In periodic shear cell tests, for large shear deformations samples with anisotropic particles reach at the macro-mechanical level the same critical value for both shear force and void ratio. At the micro-mechanical level the components of the stress tensor, the fabric tensor and the inertia tensor of the particles also reach the same stationary state. By varying the aspect ratio of the particles we stated the strong influence of particle shape anisotropy on the parameters that the granular packing attain at the critical state.

AIP Conference Proceedings, 2009

We study topological and dynamical properties in sheared granular media particularly when avalanc... more We study topological and dynamical properties in sheared granular media particularly when avalanches occur, i.e. at the abrupt increase of the total kinetic energy during the shear process. Our model considers irregular polygonal particles compressed between two moving plates. At the occurrence of an avalanche, we monitor the time evolution of the underlying contact force network. When all contact forces are considered, topological and dynamical quantities vary as a reaction to the avalanche, while the decomposition of the contact force network into strong and weak contacts uncovers a topology that is strongly correlated with the occurrence of avalanches.

Spine, 2015

Objective. To perform an independent interobserver and intraobserver agreement evaluation of the ... more Objective. To perform an independent interobserver and intraobserver agreement evaluation of the new AOSpine Thoracolumbar Spine Injury Classifi cation System. Summary of Background Data. The new AOSpine Thoracolumbar Spine Injury Classifi cation System was recently published. It showed substantial reliability and reproducibility among the surgeons who developed it; however, an independent evaluation has not been performed. Methods. Anteroposterior and lateral radiographs, and computed tomographic scans of 70 patients with acute traumatic thoracolumbar injuries were selected and classifi ed using the morphological grading of the new AOSpine Thoracolumbar Spine Injury Classifi cation System by 6 evaluators (3 spine surgeons and 3 orthopedic surgery residents). After a 6-week interval, the 70 cases were presented in a random sequence to the same evaluators for repeat evaluation. The Kappa coeffi cient (κ) was used to determine the interobserver and intraobserver agreement. Results. The interobserver reliability was substantial when considering the fracture type (A, B, or C), with a κ = 0.62 (0.57-0.66). The interobserver agreement when considering the subtypes was moderate; κ = 0.55 (0.52-0.57). The intraobserver reproducibility was also substantial, with 85.95% full intraobserver reproducibility considering the fracture type, with κ = 0.77 (0.72-0.83), and was also substantial when considering subtypes with From the

Evidence-Based Imaging in Pediatrics, 2009

Page 324. 22 Imaging of Legg–Calvé–Perthes DiseaseinChildren Neil Vachhani, Andres H. Peña, and D... more Page 324. 22 Imaging of Legg–Calvé–Perthes DiseaseinChildren Neil Vachhani, Andres H. Peña, and Diego Jaramillo Issues I. What is the role of imaging in the diagnosis of Legg–Calvé–Perthes (LCP) disease? II. Can plain ...

Pediatric Radiology, 2011

Proximal focal femoral deficiency (PFFD) is a rare congenital anomaly characterized by abnormal d... more Proximal focal femoral deficiency (PFFD) is a rare congenital anomaly characterized by abnormal development of the proximal femur. The most common radiographic classification (Aitken) does not evaluate the cartilaginous and soft-tissue abnormalities. To demonstrate MR findings of PFFD focusing on features not seen with radiographs. Nine MR examinations of the hip and femurs of seven children with PFFD were retrospectively reviewed. Imaging was quantitatively and qualitatively assessed comparing the affected limb to the contralateral limb and age-matched controls. The children were classified via the Aitken classification. All children had at least mild acetabular dysplasia, and one type D patient had no acetabulum. MR demonstrated that 4/6 children had labral hypertrophy with a decreased distance from the greater trochanter to the acetabular rim, suggesting impingement (P<0.05). The proximal femoral physis was abnormal in all cases. The connection between the femoral head and shaft if present was fibrous or fibrocartilaginous. MRI can help in evaluation of PFFD by defining the anatomy. MR demonstrates features of the acetabulum and cartilaginous femoral epiphysis and depicts ligamentous abnormalities of the knee.

Gastroenterology, 2017

Background Caustic ingestion is a potentially severe condition and early identification of poor o... more Background Caustic ingestion is a potentially severe condition and early identification of poor outcome is essential to improve management; however, prediction based on endoscopy alone can overestimate severity. This study aimed to develop and validate a prognostic score.

Anthropogenic change is associated with population growth, land use change, and changing economie... more Anthropogenic change is associated with population growth, land use change, and changing economies. However, internal migration patterns and armed conflicts are also key drivers behind anthropogenic and demographic processes. To better understand this sort of change, we explore the spatial relationship between forced migration due to armed conflict and changing demographic factors in Colombia, a country which has a recent history of 7 million internal migrants. In addition, we use remote sensing, Google Earth Engine, as well as spatial statistical analyses of demographic data in order to measure anthropogenic change between 1984 and 2008; and we look into spatiotemporal relationships between both demographic and anthropogenic changes, which are caused by forced migration. We find, thus, that the latter is significantly and positively related to an increasing rural-urban kind of migration which originates in armed conflict, and results show that it is also negatively associated with ...

Brasil: ¿Hegemonía a pesar de todo?, 2017

A partir del 2014, Brasil entro en una fase de repliegue economico y social que muchos califican ... more A partir del 2014, Brasil entro en una fase de repliegue economico y social que muchos califican enfaticamente como una de las crisis mas graves que el gigante del Sur haya tenido en su historia reciente. Los mas alarmistas de los analistas ya predicen la desaparicion de Brasil del escenario internacional y el fin de su protagonismo en la region. Sin embargo, y como se demuestra en este analisis riguroso, los elementos materiales del poder brasileno solo se han consolidado desde principios del siglo XXI. De hecho, sin importar la retorica escogida por el gobierno de turno, desde la dictadura militar en los 80, se pueden evidenciar comportamientos reiterados que hablan por si solos. El estado brasileno sigue una estrategia de dominacion de su entorno politico y geografico utilizando los medios materiales a su disposicion. En funcion del momento historico, de la coyuntura economica y politica, los gobiernos han escogido tacticas directas/ofensivas o tacticas indirectas/defensivas, pero la prioridad siempre ha sido la salvaguardia del territorio y de las capacidades productivas y destructivas del pais.

PLOS ONE, 2020

Anthropogenic change has been associated with population growth, land use change, and changing ec... more Anthropogenic change has been associated with population growth, land use change, and changing economies. However, internal migration patterns and armed conflicts are also key drivers of anthropogenic and demographic processes. To better understand the processes associated with this change, we explore the spatial relationship between forced migration due to armed conflict and changing socioeconomic factors in Colombia, a country which has a recent history of 7 million internal migrants. In addition, we use remote sensing, Google Earth Engine, as well as spatial statistical analyses of demographic data in order to measure anthropogenic change between 1984 and 2013—a socio-politically important period in Colombia’s armed conflict. We also analyze spatiotemporal relationships between socioeconomic and anthropogenic changes, which are caused by forced migration. We found that forced migration is significantly and positively related to an increasing rural-urban type of migration which re...

Anthropogenic change is generally associated with population growth, land use change, and changin... more Anthropogenic change is generally associated with population growth, land use change, and changing economies. However, internal migration patterns and armed conflicts can also be key drivers behind these anthropogenic change and demographic change processes. To better understand this dynamic, we explore the spatial relationship between forced migration due to armed conflict and changing demographic factors in Colombia; a country with a recent history of 7 million internal migrants. First, we spatiotemporally analyzed the relationship between anthropogenic and demographic change due to forced migration from internal armed conflicts using remote sensing to measure anthropogenic change during 1984-2018 and we then used statistical and spatial analyses of demographic data. We found that anthropogenic change is significantly and positively related with increased rural-urban migration. Results show that interregional expulsion is also negatively associated with such anthropogenic change. ...

Journal of the American Academy of Orthopaedic Surgeons, 2019

Background Data: A new pilon fracture classification system based on CT scan data was recently pu... more Background Data: A new pilon fracture classification system based on CT scan data was recently published, showing almost perfect interobserver and intraobserver agreement among the authors who developed it. However, an independent assessment has not been done. Objective: To do an independent agreement evaluation of the new pilon fracture classification system with physicians with different levels of expertise in the management of pilon fractures. Methods: Seventy-one cases of acute pilon fracture were retrospectively collected. Fractures were classified by six evaluators (three foot and ankle surgeons and three orthopaedic surgery residents) using CT scans according to the morphological grading of the new pilon fracture classification system developed by Leonetti et al. Cases were presented to the same evaluators in a random sequence after a 6-week interval to determine intraobserver agreement. The kappa coefficient (k) was used to determine agreement among evaluators. Results: The interobserver agreement was substantial regarding the main fracture type (I, II, III, or IV), with an overall k value of 0.69 (0.65 to 0.72). When including the II and III subtypes, the overall agreement was still substantial, with a k value of 0.61 (95% confidence interval: 0.58 to 0.64). The intraobserver agreement was substantial when considering the main fracture categories (I, II, III, or IV), with a k value of 0.78 (confidence interval: 0.72 to 0.84), and full agreement at the type level was observed in 76% (324/426) of evaluations. There was no notable difference between the foot and ankle surgeons and orthopaedic surgery residents in the interobserver and intraobserver agreement. Conclusion: The new classification system demonstrated substantial interobserver and intraobserver agreement between evaluators with different levels of expertise in the management of pilon fractures. Prospective studies should be done to evaluate its prognostic value and utility in clinical practice.

Revista Relaciones Internacionales, Estrategia y Seguridad, 2018

Basado en un análisis neo-realista y en contra posición a los planteamientos del soft power, este... more Basado en un análisis neo-realista y en contra posición a los planteamientos del soft power, este artículo estudia la política exterior brasileña respecto a posibles diseños hegemónicos regionales. La investigación examina avances cruciales en el poder militar del Estado sudamericano, pero también tiene en cuenta la capacidad demográfica y económica brasileña y su posibilidad de desarrollar armas nucleares, como elementos condicionantes para equilibrar el poder en el escenario global. El análisis se contextualiza en la estructura sistémica internacional, donde Estados Unidos, como la gran potencia, debe impedir que otros Estados adquieran poder.

AIP Conference Proceedings, 2009

The existence and uniqueness of the so-called critical state in soil mechanics is validated in ou... more The existence and uniqueness of the so-called critical state in soil mechanics is validated in our DEM simulations of irregular polygonal particles. For different particle shape characteristics, the critical state is found to be independent of the initial stress and density conditions. We retain low stress levels, since we do not take into account the crushing of particles. In biaxial test simulations isotropic particles evolve toward a limiting state in which the system reaches a critical void ratio and deforms with constant volume, deviatoric stress, fabric anisotropy, and mechanical coordination number. The last one has been found to be the first variable to attain a critical value making possible for the rest of micro-and-macro-mechanical variables the convergence to the critical state. In periodic shear cell tests, for large shear deformations samples with anisotropic particles reach at the macro-mechanical level the same critical value for both shear force and void ratio. At the micro-mechanical level the components of the stress tensor, the fabric tensor and the inertia tensor of the particles also reach the same stationary state. By varying the aspect ratio of the particles we stated the strong influence of particle shape anisotropy on the parameters that the granular packing attain at the critical state.

AIP Conference Proceedings, 2009

We study topological and dynamical properties in sheared granular media particularly when avalanc... more We study topological and dynamical properties in sheared granular media particularly when avalanches occur, i.e. at the abrupt increase of the total kinetic energy during the shear process. Our model considers irregular polygonal particles compressed between two moving plates. At the occurrence of an avalanche, we monitor the time evolution of the underlying contact force network. When all contact forces are considered, topological and dynamical quantities vary as a reaction to the avalanche, while the decomposition of the contact force network into strong and weak contacts uncovers a topology that is strongly correlated with the occurrence of avalanches.

Spine, 2015

Objective. To perform an independent interobserver and intraobserver agreement evaluation of the ... more Objective. To perform an independent interobserver and intraobserver agreement evaluation of the new AOSpine Thoracolumbar Spine Injury Classifi cation System. Summary of Background Data. The new AOSpine Thoracolumbar Spine Injury Classifi cation System was recently published. It showed substantial reliability and reproducibility among the surgeons who developed it; however, an independent evaluation has not been performed. Methods. Anteroposterior and lateral radiographs, and computed tomographic scans of 70 patients with acute traumatic thoracolumbar injuries were selected and classifi ed using the morphological grading of the new AOSpine Thoracolumbar Spine Injury Classifi cation System by 6 evaluators (3 spine surgeons and 3 orthopedic surgery residents). After a 6-week interval, the 70 cases were presented in a random sequence to the same evaluators for repeat evaluation. The Kappa coeffi cient (κ) was used to determine the interobserver and intraobserver agreement. Results. The interobserver reliability was substantial when considering the fracture type (A, B, or C), with a κ = 0.62 (0.57-0.66). The interobserver agreement when considering the subtypes was moderate; κ = 0.55 (0.52-0.57). The intraobserver reproducibility was also substantial, with 85.95% full intraobserver reproducibility considering the fracture type, with κ = 0.77 (0.72-0.83), and was also substantial when considering subtypes with From the

Evidence-Based Imaging in Pediatrics, 2009

Page 324. 22 Imaging of Legg–Calvé–Perthes DiseaseinChildren Neil Vachhani, Andres H. Peña, and D... more Page 324. 22 Imaging of Legg–Calvé–Perthes DiseaseinChildren Neil Vachhani, Andres H. Peña, and Diego Jaramillo Issues I. What is the role of imaging in the diagnosis of Legg–Calvé–Perthes (LCP) disease? II. Can plain ...

Pediatric Radiology, 2011

Proximal focal femoral deficiency (PFFD) is a rare congenital anomaly characterized by abnormal d... more Proximal focal femoral deficiency (PFFD) is a rare congenital anomaly characterized by abnormal development of the proximal femur. The most common radiographic classification (Aitken) does not evaluate the cartilaginous and soft-tissue abnormalities. To demonstrate MR findings of PFFD focusing on features not seen with radiographs. Nine MR examinations of the hip and femurs of seven children with PFFD were retrospectively reviewed. Imaging was quantitatively and qualitatively assessed comparing the affected limb to the contralateral limb and age-matched controls. The children were classified via the Aitken classification. All children had at least mild acetabular dysplasia, and one type D patient had no acetabulum. MR demonstrated that 4/6 children had labral hypertrophy with a decreased distance from the greater trochanter to the acetabular rim, suggesting impingement (P<0.05). The proximal femoral physis was abnormal in all cases. The connection between the femoral head and shaft if present was fibrous or fibrocartilaginous. MRI can help in evaluation of PFFD by defining the anatomy. MR demonstrates features of the acetabulum and cartilaginous femoral epiphysis and depicts ligamentous abnormalities of the knee.

Gastroenterology, 2017

Background Caustic ingestion is a potentially severe condition and early identification of poor o... more Background Caustic ingestion is a potentially severe condition and early identification of poor outcome is essential to improve management; however, prediction based on endoscopy alone can overestimate severity. This study aimed to develop and validate a prognostic score.