ABSTRACT Given the importance of knowing the mechanical response of the soil as one of the variables to be taken into account in the design of implements and machines capable of preserving the physical qualities of the soil, several constitutive models have been developed that represent the soil as a non-linear material elastic or elastoplastic. The objective of this paper was to analyze the current state of the constitutive models used in the modeling of agricultural soils in order to define which of them is the most adequate to simulate the mechanical response of agricultural soils with clay texture (Oxisol, Inceptisol and Vertisol). Constitutive models that are used in the simulation of the mechanical response of agricultural soils by means of the finite element method are analyzed critically, taking into account the properties and parameters of input, determination of these and their implementation in the softwares for simulation using the finite element method. Finally, it is concluded that the Drucker Prager Extended model as the most adequate to simulate the mechanical response of an Oxisol, prioritizing in this decision its simplicity, convenience when determining its parameters, accuracy in estimating the stress-strain relationship of the soil , and inclusion in most commercial software.

RESUMEN Dada la importancia que tiene conocer la respuesta mecánica del suelo como una de las variables a tener en cuenta en el diseño de los aperos y maquinas capaces de conservar las cualidades físicas del suelo se han desarrollado varios modelos constitutivos que representan al suelo un material no lineal elástico o elastoplástico. El presente trabajo tuvo como objetivo analizar el estado actual de los modelos constitutivos empleados en la modelación de suelos agrícolas. Permitiendo definir cuál de ellos es el más adecuado para simular la respuesta mecánica de suelos agrícolas con textura arcillosa (Oxisol, Inceptisol y Vertisol). En el mismo se analizan críticamente los modelos constitutivos que se emplean en la simulación de la respuesta mecánica de los suelos agrícolas mediante el método de elementos finitos, teniendo en cuenta las propiedades y parámetros de entrada, determinación de estos y su implementación en los softwares para la simulación mediante el método de elementos finitos. Finalmente, se concluye que el modelo Drucker Prager Extendido como el más adecuado para simular la repuesta mecánica de un Oxisol, primando en esta decisión su sencillez, conveniencia a la hora de determinar sus parámetros, exactitud en la estimación de la relación esfuerzo-deformación del suelo, y la inclusión en la mayoría de los software comerciales.

Pleural effusion is a common condition in critically ill patients (both clinical and surgical). Its diagnosis and classification are important for followup of patients with cardiorespiratory difficulty. Lung ultrasound is used for this purpose, but no reports have been published on its use in Cuba with critically ill patients in intensive care units. We performed lung ultrasound on 144 such patients with cardiorespiratory illnesses, average age 54 years, predominantly men (66%; 95/144), with average APACHE II score 13.6, and 22.1% mortality risk. Patients were divided into two groups: clinical (bronchopneumonia and cardiac insufficiency) and surgical (postoperative liver and kidney transplant or vascular and cardiovascular surgery) to diagnose and classify pleural effusion according to locus (right, left and bilateral) and structural pattern (I, II A, II B, III and IV). Pleural effusions were diagnosed in 81.2% (117/144) of patients (clinical 44.4%, 52/117; surgical 55.6%, 65/117). Bilateral location was the most common (68.4%, 80/117), followed by right (23.9%, 28/117) and then left (7.7%, 9/117). Structural pattern I (anechoic appearance) was observed in 61.5% of cases (72/117); 21.4% (25/117) were II A, 12.8% (15/117) II B, 3.4% (4/117) III, and 0.9% (1/117) were IV. We found no association between pleural effusion localization and ultrasound structural pattern in clinical patients (Fisher exact test 4.2 p = 0.9). In surgical patients, however, complex ultrasound patterns (II A, II B and III) were significantly more common in bilateral forms (Fisher exact test 14.1; p = 0.009). Further studies of this type in Cuba will help provide useful data for prompt treatment and followup of these patients.

This research work was carried out with the aim of adjusting the constitutive parameters of the Extended Drucker-Prager (EDP) model which defines the phase of plastic deformation of soil in the simulation of the mechanical response of clayey soil (Vertisol). The stress-strain curve is divided into two parts and two equations describing its path were obtained. Initial data were consistent with the experimentally determined data. Starting from these results, the approximate values of both the internal friction angle of the fault plane of the Extended Drucker-Prager model, as well as the angle of dilatancy were searched out. Finally the optimum values of these angles were estimated, reducing errors in the predictions of the EDP model below 4.35% and turning this model adequate for simulating the mechanical response of the soil object of investigation

El presente trabajo se realizó con el objetivo de ajustar los parámetros constitutivos del modelo de Drucker-Prager Extendido (DPE) que definen la fase de deformación plástica del suelo en la simulación de la respuesta mecánica de un suelo de textura arcillosa (Vertisol). La curva esfuerzo-deformación se dividió en dos partes y se buscaron dos ecuaciones que describen su trayectoria. Los datos iniciales se correspondieron con los datos determinados experimentalmente. A partir de estos se buscarán los valores aproximados tanto del ángulo de fricción interna del plano de falla del modelo de Drucker-Prager Extendido, así como, el ángulo de dilatancia. Finalmente se estimaron los valores óptimos de estos ángulos, disminuyendo los errores en las predicciones del modelo DPE por debajo del 4,35% haciéndolo adecuado para la simulación de la respuesta mecánica del suelo investigado

The present work takes place with the aim of evaluating the constituent model Drucker Prager Extended for the simulation of the mechanical answer of a Vertisol of the central region of Cuba through method of finite elements. For the simulation of the mechanical answer of the soil in study the software ABAQUS/CAE 6.8.1 was used as a computer tool. The simulation included: the description of the problem to simulate, definition of the virtual model, definition of the properties and parameters required by the constituent model, the establishment of the conditions of border, the creation of meshes of the finite element, the simulation of the mechanical answer of the soil determination of the prognosis mistake and if statistically significant difference between the accumulated distributions of the observed and predicted magnitudes exists. The results demonstrate that the exactitude of the model Drucker Prager Extended in the prediction of the mechanical answer of the soil study object, depends on their state of humidity and density bulk, as well as of the configuration of the model. The smaller mistake in the predictions (4,14 to 31,04%) were obtained, for a rank of values of humidity of 30 to 40% and density bulk of 1,05 to 1,10 g cm-3 respectively.

El presente trabajo se efectúa con el objetivo de evaluar el modelo constitutivo Drucker Prager Extendido para la simulación de la respuesta mecánica de un Vertisol de la región central de Cuba a través del método de elementos finitos. Para la simulación de la respuesta mecánica del suelo en estudio se emplea el software ABAQUS/CAE 6.8.1 como herramienta computacional. La simulación comprendió: la descripción del problema a simular, definición del modelo virtual, definición de las propiedades y parámetros requeridos por el modelo constitutivo, el establecimiento de las condiciones de frontera, la creación de la malla del elemento finito, la simulación de la respuesta mecánica del suelo, determinación del error de pronóstico y si existe diferencia estadísticamente significativa entre las distribuciones acumuladas de las magnitudes observadas y predichas. Los resultados evidencian que la exactitud del modelo Drucker Prager Extendido en la predicción de la respuesta mecánica del suelo objeto de estudio, depende de su estado de humedad y densidad, así como de la configuración del modelo. Los menores errores en las predicciones (4,14 a 31,04%) se obtuvieron, para un rango de valores de humedad de 30 a 40% y densidad de 1,05 a 1,10 g cm-3 respectivamente.

Introduction: lower respiratory infections rank first among related infections in health care intensive care units. Objectives: to describe the incidence and consequences of stay and mortality of ventilator-associated tracheobronchitis (TAVM) in ICU. Methods: a multicenter, descriptive, prospective and cross-sectional study was conducted in 6 adult ICU. 454 patients were studied. The study variables were collected in two databases. Results: TAVM incidence rate: 1.76 %, relative to the total number of patients with risk factor: 6.06 %. Incidence density: 7.61 % by 1000 d with risk factor. Average stay, TAVM: 13.13 d, patients without IRCS: 5.49 d (p = 0.006). Mortality, TAVM: 25 %, VAP: 55.2 %, patients without IRCS: 14.9 % (p = 0.000). Conclusions: TAVM is not uncommon in ICU. Its diagnosis involves increased stay and its mortality in ventilated patients. The implementation of surveillance and prevention measures is requiered.

Introducción: las infecciones respiratorias bajas ocupan el primer lugar entre las infecciones relacionadas con el cuidado sanitario en unidades de cuidados intensivos. Objetivos: describir la incidencia y las consecuencias, sobre estadía y mortalidad, de la traqueobronquitis asociada a ventilación mecánica (TAVM) en UCI. Métodos: estudio multricéntrico, descriptivo, prospectivo y transversal, en 6 UCI de adultos. Se estudiaron 454 pacientes. Las variables de estudio fueron recogidas en 2 bases de datos. Resultados: tasa de incidencia de TAVM: 1,76 %. Con respecto al número total de pacientes con factor de riesgo: 6,06 %. Densidad de incidencia: 7,61 ‰ por 1 000 d con factor de riesgo. Estadía media, TAVM: 13,13 d, pacientes sin IRCS: 5,49 d (p=0,006). Mortalidad, TAVM: 25 %, NAVM: 55,2 %, pacientes sin IRCS: 14,9 % (p=0,000). Conclusiones: la TAVM no es infrecuente en UCI. Su diagnóstico implica aumento de estadía y mortalidad en pacientes ventilados. Se justifica la implementación de medidas de vigilancia y prevención.

INTRODUCTION: Continuous venovenous hemodiafiltration, generally used in patients with acute renal failure, enables elimination of humoral mediators of systemic inflammatory response and sepsis from blood. This effect should improve treatment results in patients with multiple organ dysfunction, but evidence of improved survival is insufficient. OBJECTIVES: Describe the effect of continuous venovenous hemodiaflitration on patients with multiple organ dysfunction syndrome in terms of systemic and brain hemodynamics, oxygenation, metabolism and status on ICU separation. METHODS: An observational case series was done of 18 patients (11 men and 7 women) aged 24-78 years with multiple organ dysfunction syndrome treated with continuous venovenous hemodiafiltration in the Medical-Surgical Research Center's ICU in Havana. General, systemic and brain hemodynamic, oxygenation and metabolic variables were assessed immediately before and 12 hours after starting the procedure; vital status on separation from intensive care was recorded. For analysis, patients were grouped by whether cause of multiple organ dysfunction syndrome was septic or nonseptic. Variable means before and after treatment were compared using the Wilcoxon matched pairs test. Standardized mortality ratios were calculated for both groups, with survival efficacy defined by a ratio of <0.9. RESULTS: After 12 hours continuous venovenous hemodiafitration, the septic group showed clinical improvement, with statistically significant improvement in all variables except mean arterial pressure and brain hemodynamics. Survival to discharge from ICU was 64%, with a standardized mortality ratio of 0.66. In the nonseptic group, survival was 0% and ratio was 2.13; temperature was the only variable found to improve significantly. CONCLUSIONS: Continuous venovenous hemodiafltration improved clinical parameters and survival in patients with multiple organ dysfunction of septic origin. Further studies are needed with larger numbers of patients to corroborate these results.

This paper investigates the macrostructural properties, required for computer simulation of the soil-tillage tool interaction through the finite element method of vertisols from the northern coast of Villa Clara. The triaxial compression test has been used to determine the properties and macro parameters of the soils under study. The final results allow to know the values and trends of cohesion, internal friction angle, and Young's modulus for a range of soil moisture and density between 18-50% and 0.9 to 1,2 g/cm3, the results show the values of these three properties decrease when humidity increased, while the opposite occurred occurring when density increasing. The values and trends found match with those obtained by other authors in soils of similar nature.

En el presente trabajo se investigan las propiedades macroestructurales de un Vertisuelo de la costa norte villaclareña, requeridas para la simulación computacional de la interacción suelo-apero de labranza mediante el método de elementos finitos. Se recurre al ensayo de compresión triaxial, rápido, sin consolidar, no drenado, para determinar las propiedades objeto de estudio. Los resultados finales permiten conocer los valores y tendencias de la cohesión, ángulo de fricción interna, y módulo de Young para un rango de humedad y densidad del suelo que oscila entre 18 a 50% y 0,9 a 1,2 g/cm3, respectivamente. Tanto las tendencias como los valores encontrados están altamente condicionados por el contenido de humedad y densidad del suelo, concordando con los resultados obtenidos por otros autores en suelos de naturaleza semejante.

The method of finite elements (FEM) it has been broadly used in the simulation of the soil mechanical response. The central nucleus of the mathematical support that sustains this method is the constitutive models, inside these, that of Ducan and Chan it is one of those most used ones, for what the present work has as objective to determine the accuracy in the prediction of the relationship stress-strain of three cuban clay (Oxisol; Inceptisol; Vertisol). To execute this objective the mechanical properties of the soil are determined and the constitutive equations are implemented in the software Mathcad 14. The results show that the model possesses a great capacity to predict with accuracy the relationship stress-strain of the studied soils, when they exhibit a plastic failure, however when the soils fails in a fragile way, the model shows inability to predict the changes of tensions originated product of the deformation for softening or hardening.

El método de elementos finitos (MEF) ha sido ampliamente utilizado en la simulación de la respuesta mecánica del suelo. El núcleo central del soporte matemático que sustenta este método lo representan los modelos constitutivos, dentro de estos, el de Ducan y Chan es uno de los más utilizados, por lo que el presente trabajo tiene como objetivo determinar la exactitud en la predicción de la relación esfuerzo-deformación de tres suelos arcillosos cubanos (Oxisol; Inceptisol; Vertisol). Para cumplimentar dicho objetivo se determinan las propiedades mecánicas de los suelos y se implementan las ecuaciones constitutivas en el software Mathcad 14. Los resultados muestran que el modelo posee una gran capacidad para predecir con exactitud la relación esfuerzo-deformación de los suelos estudiados, cuando exhiben una falla plástica, sin embargo cuando el suelo falla de forma frágil, el modelo muestra incapacidad para predecir los cambios de tensiones originadas producto de la deformación por ablandamiento o endurecimiento.