Erratum to: Carl Christian Tscherning: a scientific adventure in Geodesy

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Two different methodologies for geoid determination from ground and airborne gravity data

In this study, two methodologies are investigated for geoid determination from ground and airborne gravity data. These two methodologies depend on the downward continuation method used. The first is the inverse Poisson integral; the second is the normal free-air gradient. Each of the two methods requires different treatment of the terrain effects and in turn different approaches to determine the geoid. The two geoid solutions, from ground data, are compared with existing GPS/levelling benchmarks and it is found that the second method gives a better fit due to the bias introduced from the inverse Poisson integral. The same process was applied to the airborne data, but with additional processing, that is the filtering of the terrain effects to preserve the consistency of the data due to the filtering of the airborne data. A study on the effect of filtering was also carried out in this paper and it concluded that filtering the terrain effects has no impact on the geoid. In addition, the airborne data, filtered to three different cut-off frequencies, were used to compute the geoid to investigate the possibility of using the denser data, of lower accuracy, to determine a high-resolution geoid. Even though the data filtered to small cut-off frequency have poorer agreement with the ground data, the geoids computed from the different filtered data is the nearly the sam

Different topographic reduction methods in practical gravimetric geoid determination

Three different topographic reduction methods in geoid determination were investigated. The first method is the classical Helmert second method of condensation yielding the geoid, the second is the Residual Terrain Model (RTM) method yielding the quasigeoid and the third is the Rudzki inversion method. The different types of indirect effects (indirect effect on gravity and indirect effect on geoid) in Helmert's method were also investigated. All three methods use the remove-restore technique and the EGM96 geopotential model as the reference gravity field. A mountainous area, ranging from 32°S to 42°S in latitude and 72°W to 68°W in longitude, was chosen as test area. The area was selected due to its high topography, with a maximum height of 6795 meters and a mean height of 1188 meters, and due to the existence of GPS/leveling points in three different networks. The topography in the test area is-represented by a digital terrain model (DTM) with a grid spacing of 1 km x 1 km. Another test was carried out in a flat area with denser data coverage. The external accuracy of the three gravimetric geoids was evaluated by comparing them to undulations derived from GPS/leveling.En el siguiente trabajo se investigan tres métodos diferentes de reducciones gravimétricas para la determinación práctica del geoide gravimétrico: el clásico segundo método de condensación de Helmert, el modelo residual de terreno y el método de inversión de Rudzki. Los tres métodos utilizan la técnica remover-restaurar y el modelo de geopotencial EGM96. Fueron seleccionadas dos áreas, una en una zona montañosa de alta topografía con una altura máxima de 6795 metros y una altura promedio de 1188 metros y otra en una zona plana con cobertura más densa. La topografía está representada por un modelo digital de terreno con un espaciamiento de grillado de un kilómetro por un kilómetro. La evaluación externa del geoide gravimétrico se realiza comparándolo con ondulaciones obtenidas a partir de puntos GPS sobre nivelación.Asociación Argentina de Geofísicos y Geodesta

Malignant paraganglioma of the mesentery: a case report and review of literature

Paragangliomas represent only 10% of chromaffin tissue tumors and those arising from the mesentery seem to be a rare occurrence. We report a case of a 55 year old man in whom an abdominal mass was discovered fortuitously by ultrasonography during a routine health exam. He presented occasional heart palpitations and diaphoresis as well as a well-demarcated mass upon abdominal physical examination. CT scan revealed a solid polylobulated mass in the right lower quadrant. Exploration laparotomy revealed a voluminous multi-nodular tumoral mass, which contained hemorrhagic spots. Histopathological studies confirmed the presence of a paraganglioma. The excision of the mass as well as the surrounding intestine and mesentery also revealed two lymphatic metastases, the first among 14 documented cases to be described concerning mesenteric paragangliomas. One year follow up and CT scan revealed neither recurrence nor the presence of distant metastases

Electrocardiographic and Electrophysiologic Characteristics of Ventricular Extrasystoles Arising from the Aortomitral Continuity

Left ventricular outflow tract arrhythmias originating from the aortomitral continuity, the left coronary cusp, the superior basal septum, and the epicardial left ventricular summit display common electrocardiographic and electrophysiological features, probably due to the close proximity of those locations. Catheter ablation of these arrhythmias can be challenging. The case of a 68-year-old male with frequent premature ventricular extrasystoles arising from the aortomitral continuity of the basal left ventricle is described. The electrocardiographic and electrophysiologic characteristics of this arrhythmia are discussed

Current Ablation Strategies for Persistent and Long-Standing Persistent Atrial Fibrillation

Atrial fibrillation (AF) is associated with an increased risk of cardiac and overall mortality. Restoration and maintenance of sinus rhythm is of paramount importance if it can be accomplished without the use of antiarrhythmic drugs. Catheter ablation has evolved into a well-established treatment option for patients with symptomatic, drug-refractory AF. Ablation strategies which target the pulmonary veins are the cornerstone of AF ablation procedures, irrespective of the AF type. Ablation strategies in the setting of persistent and long-standing persistent AF are more complex. Many centers follow a stepwise ablation approach including pulmonary vein antral isolation as the initial step, electrogram-based ablation at sites exhibiting complex fractionated atrial electrograms, and linear lesions. Up to now, no single strategy is uniformly effective in patients with persistent and long-standing persistent AF. The present study reviewed the efficacy of the current ablation strategies for persistent and long-standing persistent AF

Catheter Ablation of Incessant Ventricular Tachycardia in a Patient With Coronary Artery Disease

A 67-year-old male with known coronary artery disease was referred to our hospital for catheter ablation of incessant ventricular tachycardia (VT). Transthoracic echocardiography revealed severe wall motion abnormalities of the left ventricle along with an apical aneurysm. Left ventricular voltage mapping showed a region with low voltage (<1.5 mV) at the left ventricular apex. Propagation mapping revealed a macro-reentry circuit around the apical aneurysm. Mid-diastolic potentials were recorded during the VT (Fig. 1, left panel, arrows), while entrainment mapping was excellent. The first radiofrequency energy application terminated the tachycardia. A circumferential lesion around the aneurysm was finally performed (Fig. 1, right panel, red dots). Ventricular tachycardia became non-inducible, and the patient is free from arrhythmic events during the last six months... (excerpt

Geoide gravimétrico en Argentina : Presente y futuro

En el siguiente trabajo se presenta el estado actual del geoide gravimétrico de la República Argentina. En el mismo se discuten la metodología y los datos utilizados para su cálculo y se plantean los trabajos futuros que se realizarán con el fin de mejorar su precisión y exactitud. ARG05_EGM96 es un geoide gravimétrico puro calculado durante 2005. Las ondulaciones del geoide ARG05_EGM96 se refieren al elipsoide geocéntrico GRS80 y fueron calculadas en una grilla de 5' x 5' cubriendo toda la Argentina (tierra y mar). El cálculo se realizó utilizando la técnica clásica remover-restaurar. La componente del geoide residual así como los efectos de terreno se calcula ron utilizando la transformada rápida de Fourier. Para el tratamiento de la topografía se empleó el segundo método de compensación de Helmert. ARG05 EGM96 fue determinado en cuatro componentes. La primera componente fue calculada a partir del modelo de geopotencial EGM96, la segunda componte representa la contribución de los datos de gravedad reducidos por el modelo de geopotencial, la tercera es la derivada de las correcciones topográficas y la cuarta componente representa el efecto indirecto primario sobre el geoide. De comparaciones externas realizadas entre ARG05_EGM96 y el geoide derivado de GPS y nivelación, se estima que la exactitud absoluta de ARG05 es de 32 cm en términos de desviación standard. La exactitud relativa, para toda la Argentina, es de 1.4 a 0.2 ppm para líneas bases entre 15 km y 115 km. En el presente trabajo se presentan, otras tres soluciones, denominadas: ARGÓ5EIGEN-CG01C (Tocho et al., 2005), ARG06EIGEN-CG03CyARG06_EIGEN-GL04C calculadas utilizando otros modelos de gravedad globales recientemente distribuidos. Finalmente se enumeran trabajos futuros, por ejemplo, la evaluación de modelos digitales de terreno y sus implicancias en la determinación práctica de geoides gravimétricos.The status of the gravimetric geoid for Argentina is presented in this paper. The methodology applied for its computation as well as the data used is discussed. A high-accuracy and high-precision gravimetric geoid model (ARG05 EGM96) for Argentina has been computed during 2005. ARG05 EGM96 is a purely gravimetric geoid model. The geoid undulations refer to the geocentric ellipsoid GRS80 and they were computed on a 5' x 5' grid covering all of Argentina (both land and ocean regions) ARG05_EGM96 was computed using the classical remove-compute-restore technique. The Fast Fourier Transform technique was employed in the computation of the residual geoid and terrain effects. The treatment of the topography inARG05_EGM96 was based on Helmert’s second method of condensation. ARG05 EGM96 is developed in four components. The first component is determined from the EGM96 global geopotential model, the second component represents the contribution of the local gravity data reduced by the global field, the third component was determined from the contribution of the terrain corrections to the geoid, and the four component is the primary indirect effect on the geoid. From comparisons between Global Positioning System (GPS) and Argentinean Height Datum (GPS/levelling-derived) geoid undulations withARG05_EGM96, it is estimated that the absolute accuracy of the new geoid, after fit, is around 32 cm in terms of standard deviation. The relative agreement for the whole Argentina is 1.4 to 0.2 ppm for baselines between 15 km and 115 km. Three new solutions,ARG06EIGEN-CG01C,ARG06_EIGEN-CG03CyARG06_EIGEN-GL04C, calculated with new global gravity models are presented in this paper. Finally, futures works are mention, especially those concerning with digital terrain models and their implications in practical geoid determination.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

Different topographic reduction methods in practical gravimetric geoid determination

Three different topographic reduction methods in geoid determination were investigated. The first method is the classical Helmert second method of condensation yielding the geoid, the second is the Residual Terrain Model (RTM) method yielding the quasigeoid and the third is the Rudzki inversion method. The different types of indirect effects (indirect effect on gravity and indirect effect on geoid) in Helmert's method were also investigated. All three methods use the remove-restore technique and the EGM96 geopotential model as the reference gravity field. A mountainous area, ranging from 32°S to 42°S in latitude and 72°W to 68°W in longitude, was chosen as test area. The area was selected due to its high topography, with a maximum height of 6795 meters and a mean height of 1188 meters, and due to the existence of GPS/leveling points in three different networks. The topography in the test area is-represented by a digital terrain model (DTM) with a grid spacing of 1 km x 1 km. Another test was carried out in a flat area with denser data coverage. The external accuracy of the three gravimetric geoids was evaluated by comparing them to undulations derived from GPS/leveling.En el siguiente trabajo se investigan tres métodos diferentes de reducciones gravimétricas para la determinación práctica del geoide gravimétrico: el clásico segundo método de condensación de Helmert, el modelo residual de terreno y el método de inversión de Rudzki. Los tres métodos utilizan la técnica remover-restaurar y el modelo de geopotencial EGM96. Fueron seleccionadas dos áreas, una en una zona montañosa de alta topografía con una altura máxima de 6795 metros y una altura promedio de 1188 metros y otra en una zona plana con cobertura más densa. La topografía está representada por un modelo digital de terreno con un espaciamiento de grillado de un kilómetro por un kilómetro. La evaluación externa del geoide gravimétrico se realiza comparándolo con ondulaciones obtenidas a partir de puntos GPS sobre nivelación.Asociación Argentina de Geofísicos y Geodesta