Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

Karst Detection Beneath the Pyramid of El Castillo, Chichen Itza, Mexico, by Non-Invasive ERT-3D Methods

Currently, archaeologists perform excavations determined by previous geophysical studies to accurately establish the prospective targets and minimize site disturbance. Among others, one of the methods most widely employed is the Electrical Resistivity Tomography (ERT-2D, -3D). However, investigation of the subsoil of archaeological buildings is not possible to carry out with traditional geophysical methods, because the structure itself prevents it. Therefore, it is necessary to design non-invasive special arrays capable of characterizing the subsoil of such buildings, while preserving their historical context. Here we show how this procedure combined with sequences of resistivity observations at depth allowed us to detect a low resistivity body beneath the pyramid of El Castillo in Chichen Itza (Mexico). This feature may be associated with a cavity (karst) partially filled with sweet water. On the other hand, a natural cavity was discovered under El Osario pyramid (south of El Castillo), at the end of the 19th century. Therefore, this pyramid was also studied to validate the effectiveness of this methodology, obtaining outstanding results. This method provides an interesting procedure to investigate the subsoil of archaeological structures for unveiling evidences that allow specialists to understand the religious meaning of these temples

Karst Detection Beneath the Pyramid of El Castillo, Chichen Itza, Mexico, by Non-Invasive ERT-3D Methods

Currently, archaeologists perform excavations determined by previous geophysical studies to accurately establish the prospective targets and minimize site disturbance. Among others, one of the methods most widely employed is the Electrical Resistivity Tomography (ERT-2D, -3D). However, investigation of the subsoil of archaeological buildings is not possible to carry out with traditional geophysical methods, because the structure itself prevents it. Therefore, it is necessary to design non-invasive special arrays capable of characterizing the subsoil of such buildings, while preserving their historical context. Here we show how this procedure combined with sequences of resistivity observations at depth allowed us to detect a low resistivity body beneath the pyramid of El Castillo in Chichen Itza (Mexico). This feature may be associated with a cavity (karst) partially filled with sweet water. On the other hand, a natural cavity was discovered under El Osario pyramid (south of El Castillo), at the end of the 19th century. Therefore, this pyramid was also studied to validate the effectiveness of this methodology, obtaining outstanding results. This method provides an interesting procedure to investigate the subsoil of archaeological structures for unveiling evidences that allow specialists to understand the religious meaning of these temples

Two algorithms to compute the electric resistivity response using Green's functions for 3D structures

Se introduce una solución integral para el problema directo de la respuesta geoeléctrica DC para cuerpos tri-dimensionales en un semi-espacio, mediante las funciones de Green. El primer algoritmo que se presenta se basa en el método integral de volumen (MIV); aquí, únicamente la corriente eléctrica primaria se utiliza para calcular el potencial eléctrico. El segundo caso emplea el método integral de superficie (MIS), en donde se asume que la carga inducida es debida al campo eléctrico primario. Ambos algoritmos son una combinación de integrales de volumen y de condiciones de frontera. Este artículo muestra la aplicabilidad de estos algoritmos para generar imágenes de perfiles de resistividad que reproducen algunos arreglos de electrodos para ejemplos sintéticos tradicionales, y posteriormente estas imágenes se comparan con resultados ya publicados en la literatura. Finalmente, la comparación entre estos resultados muestra que el concepto de carga inducida utilizada en MIS produce una mejor aproximación, que el esquema MIV en el cálculo del potencial eléctrico. doi: https://doi.org/10.1016/j.gi.2015.04.00

Structural pattern of subsidence in an urban area of the southeastern Mexico Basin inferred from electrical resistivity tomography

La mayor parte de la zona urbana de la Cuenca de México está construida sobre los sedimentos de los antiguos lagos de Chalco, Xochimilco, México, Texcoco, Xaltocan y Zumpango, lo cual ofrece poca resistencia a las obras civiles que se asientan sobre ella. Adicionalmente, los requerimientos para el abastecimiento de agua potable para la población han generado la sobreexplotación de los acuíferos, exacerbando el fenómeno de subsidencia y el colapso de edificios, unidades habitacionales y caminos. Con la finalidad de entender el patrón de fracturamiento, así como su ubicación, se implementó un estudio geofísico con la técnica de tomografía de resistividad eléctrica en una zona poblada ubicada al sureste de la Cuenca de México. Cinco secciones bidimensionales fueron calculadas a partir de los datos de resistividad adquiridos. En todas ellas fue posible identificar un horizonte resistivo discontinuo probablemente compuesto por algún material ígneo extrusivo. Las discontinuidades de este horizonte pueden ser relacionadas con grietas o fracturas identificadas con antelación sobre la superficie y que afectan obras civiles. Además, un modelo tridimensional de resistividad fue calculado. La imagen 3D coincide con los resultados obtenidos de los modelos 2D, mostrando una capa resistiva con discontinuidades laterales. El patrón estructural de las fracturas inferido presenta una dirección preferencial NW–SE, el cual también genera el proceso de subsidencia en la zona, producido por la sobreexplotación del acuífero. doi: https://doi.org/10.22201/igeof.00167169p.2011.50.4.15

TOMOGRAFÍA DE RESISTIVIDAD ELÉCTRICA 3D EN LA CATEDRAL DE MORELIA, MÉXICO (3D Electrical Resistivity Tomography in Morelia Cathedral, Mexico)

La tradición oral en la ciudad de Morelia, México, así como evidencias parciales en algunos edificios, han llevado a la creencia de la existencia de túneles subterráneos en el centro de esta ciudad, los cuales pertenecerían a la época colonial de nuestro país. Dicho centro fue declarado patrimonio cultural de la humanidad en 1991 por la UNESCO, por lo que es poco factible la excavación o perforación directa destructiva con la intención de explorar. En este contexto, la implementación de técnicas no invasivas es perfecta para localizar zonas de interés, de tal forma que los métodos de exploración geofísica son adecuados, al no ser destructivos y proporcionar una imagen del subsuelo para corroborar la existencia indirecta de estructuras en profundidad. Se presentan los estudios con tomografía de resistividad eléctrica tridimensional (TRE-3D) llevados a cabo en 2014, 2016 y 2017 en la Catedral de Morelia y su frente norte, en donde se pueden ubicar estructuras organizadas no acordes con el entorno geológico del sitio, los cuales pueden suministrar indicios de la existencia de diversas estructuras de origen antrópico. La TRE-3D aplicada para este estudio es una combinación entre metodologías convencionales y no convencionales; ofrece una imagen de la distribución de estructuras en profundidad que muestran características concordantes con tradiciones orales y hechos históricos documentados referentes al desarrollo de la Catedral de Morelia a través del tiempo. ENGLISH: Oral traditions, as well as partial evidence in some buildings, have led to a belief in the existence of underground tunnels dating to the colonial period in downtown Morelia, Mexico. The city of Morelia was declared a UNESCO World Heritage Site in 1991, making excavation impossible. Nondestructive geophysical exploration methods, however, can provide an image of the subsoil to test for existence of tunnels or other subterranean structures. This paper reports results from survey using three-dimensional electrical resistivity tomography (TRE-3D) carried out in 2014, 2016 and 2017, in Morelia Cathedral and along its northern front. The survey identified the location of deep structures which cannot be explained by geological context, suggesting the existence of a variety of subterranean structures of anthropogenic origin. The TRE-3D used in this study combines conventional and unconventional methodologies to offer insights into the distribution of subterranean structures at Morelia Cathedral, in accordance with both oral traditions and documented history

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AimThe SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery.MethodsThis was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin.ResultsOverall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P ConclusionOne in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease