Resumo O avanço no desenvolvimento de peças automotivas exige novos materiais de baixo custo com propriedades mecânicas superiores e com maior resistência ao desgaste em comparação com os materiais existentes. Por exemplo, compósitos com matriz de alumínio (AMC) mostram melhores propriedades mecânicas como resistência à abrasão e ao desgaste, alta resistência e estabilidade química e dimensional. A indústria automotiva tem centrado em AMC para uma variedade de aplicações em peças automotivas, a fim de melhorar a economia de combustível, minimizar as emissões dos veículos, melhorar as opções de design e aumentar o desempenho. A Resistência ao desgaste é um fator importante a determinar para a vida útil dos componentes automotivos, em geral naqueles componentes submetidos a sistemas mecânicos como freios e suspensões. O processo de soldagem por fricção e mistura mecânica (FSW - Friction Stir Welding) surge como um processo capaz de unir AMC, principalmente com a capacidade de soldar sem comprometer seu reforço cerâmico. O objetivo deste estudo é focado na análise de características de desgaste da junta soldada por FSW de matriz de alumínio reforçados com 20 por cento em peso de compósito de carboneto de silício (A359 / SiC / 20p). O procedimento experimental consistiu em cortar amostras em pequenas placas e realizar três soldas nestas placas utilizando uma máquina FSW com uma ferramenta com ombro de 20 mm de diâmetro e pino de 8 mm de diâmetro. As características de desgaste das três juntas soldadas e metal base foram analisados aplicando carga constante de 5 N e uma velocidade de rotação de 100 rpm utilizando um aparelho de teste Pin-on-disk, usando uma esfera de aço de com safira com 6 mm de diâmetro. Os resultados experimentais indicam que as três juntas soldadas apresentaram baixo coeficiente de fricção comparado com o metal base. Os resultados determinaram que os parâmetros do processo FSW afetam a resistência ao desgaste das juntas soldadas, devido a diferentes modificações microestruturais durante a soldagem, que provoca uma baixa resistência ao desgaste na zona soldada.

Abstract Advancement in automotive part development demands new cost-effective materials with higher mechanical properties and improved wear resistance as compared to existing materials. For instance, Aluminum Matrix Composites (AMC) shows improved mechanical properties as wear and abrasion resistance, high strength, chemical and dimensional stability. Automotive industry has focused in AMC for a variety of applications in automotive parts in order to improve the fuel economy, minimize vehicle emissions, improve design options, and increase the performance. Wear resistance is one of the most important factors in useful life of the automotive components, overall in those components submitted to mechanical systems like automotive brakes and suspensions. Friction Stir Welding (FSW) rises as the most capable process to joining AMC, principally for the capacity to weld without compromising their ceramic reinforcement. The aim of this study is focused on the analysis of wear characteristics of the friction-stir welded joint of aluminum matrix reinforced with 20 percent in weight silicon carbide composite (A359/SiC/20p). The experimental procedure consisted in cut samples into small plates and perform three welds on these with a FSW machine using a tool with 20 mm shoulder diameter and 8 mm pin diameter. The wear features of the three welded joints and parent metal were analyzed at constant load applying 5 N and a rotational speed of 100 rpm employing a Pin-on - Disk wear testing apparatus, using a sapphire steel ball with 6 mm diameter. The experimental results indicate that the three welded joints had low friction coefficient compared with the parent metal. The results determine that the FSW process parameters affect the wear resistance of the welded joints owing to different microstructural modifications during welding that causes a low wear resistance on the welded zone.

The need to strictly control glucose levels, even in non-diabetic patients, has recently emerged following the publication of the results that indicate the possibility of reducing the morbidity and mortality in critically ill patients. Since hyperglycemia is one of the most frequent metabolic impairments in these patients, insulin therapy is a necessity in most of the cases. In order to prevent hyperglycemia and its associated complications, nutritional support must be adjusted to the patient's requirements, avoiding hyponutrition. Whenever possible, nutrients supply should be done through the digestive route. Parenteral nutrition is more often accompanied by hyperglycemia and requires an increase in insulin dosage to control it. There are two types of enteral diets designed to help controlling hyperglycemic conditions: carbohydrates rich diets, and fat rich diets. In general terms, carbohydrates rich diets may be recommended in type 1 diabetic patients who are in a stable condition, and fat rich diets in type 2 diabetes and in stress hyperglycemia. In both cases, the use of low glycemic index carbohydrates is recommended. Protein in-take should be adjusted to the patients' metabolic stress level. In diabetic patients with acute disease, an increase in antioxidants intake is recommended.

La necesidad de controlar de manera estricta los niveles de glucemia, incluso en pacientes no diabéticos, ha surgido recientemente tras la publicación de los resultados que indican que con ello puede conseguirse un descenso en la morbi-mortalidad de los pacientes críticos. Dado que la hiperglucemia es una de las alteraciones metabólicas predominantes en estos pacientes, el tratamiento con insulina es una necesidad en la mayoría de los casos. Con el fin de prevenir la hiperglucemia y sus complicaciones asociadas, el aporte energético debe ajustarse a los requerimientos de los pacientes, evitando la hipernutrición. Siempre que sea posible, deberá intentarse al aporte de nutrientes por vía digestiva. La nutrición parenteral se acompaña con mayor frecuencia de hiperglucemia y requiere un aumento en las dosis de insulina necesarias para su control. Existen dos tipos de dietas enterales diseñadas para ayudar a corregir las situaciones hiperglucémicas: dietas ricas en carbohidratos y dietas ricas en grasa. En líneas generales, pueden recomendarse las dietas ricas en hidratos de carbono en los pacientes diabéticos tipo 1 que se encuentren en situación estable y las dietas ricas en grasas en la diabetes tipo 2 y en la hiperglucemia de estrés. Se recomienda, en ambos casos, el empleo de hidratos de carbono con bajo índice glucémico. El aporte proteico debe ajustarse al nivel de estrés metabólico de los pacientes. Se recomienda un aumento en el aporte de antioxidantes en los pacientes diabéticos con enfermedad aguda.

Patients submitted to hematopoietic stem cells transplantation (HSCT) have an increased risk for having hyponutrition, both in the phase prior to transplantation and after this one. The indication of specialized nutritional support is common in allogenic HSCT, whereas patients submitted to auto-HSCT need it in the presence of complications that compromise an adequate nutrients intake. Enteral nutrition through a nasogastric tube has difficulties in these patients; the presence of mucositis delays the indication for enteral nutrition, which usually is poorly tolerated. Thus, frequently parenteral nutrition needs to be used as the route for nutritional support. The use of specific substrates, such as glutamine, is a controversial issue.

Los enfermos sometidos a trasplante de células precursoras hematopoyéticas (TCPH) tienen un riesgo elevado de presentar desnutrición, tanto en la fase previa al trasplante como una vez realizado éste. La indicación de soporte nutricional especializado es habitual en los TCPH alogénicos, en tanto que los enfermos sometidos a TCPH autotrasplante lo requieren ante la presencia de complicaciones que comprometan la ingesta adecuada de nutrientes. La nutrición enteral por vía nasogástrica presenta problemas en estos enfermos; la presencia de mucositis retrasa la indicación de nutrición enteral y ésta es frecuentemente mal tolerada. Por ello, la nutrición parenteral necesita ser utilizada como vía para el soporte nutricional en muchas ocasiones. El empleo de substratos específicos, como la glutamina, es motivo de controversia.

Due to the characteristics of critically ill patients, elaborating recommendations on nutritional support for these patients is difficult. Usually the time of onset of nutritional support or its features are not well established, so that its application is based on experts' opinion. In the present document, recommendations formulated by the Metabolism and Nutrition Working Group of the Spanish Society of Intensive and Critical Medicine and Coronary Units (SEMICYUC) are presented. Recommendations are based on the literature analysis and further discussion by the working group members in order to define, consensually, the more relevant issues of metabolic and nutritional support of patients in a critical condition. Several clinical situations have been considered which are developed in the following articles of this publication. The present recommendations aim at providing a guideline for the less experienced clinicians when considering the metabolic and nutritional issues of critically ill patients.

Debido a las características de los pacientes críticos, la elaboración de recomendaciones sobre el soporte nutricional en estos pacientes es difícil. En muchas ocasiones no está claramente establecido el momento de inicio del soporte nutricional ni las características del mismo, por lo que su aplicación está basada en opiniones de expertos. En el presente documento se presentan las recomendaciones elaboradas por el Grupo de Trabajo de Metabolismo y Nutrición de la sociedad Española de Medicina Intensiva, Crítica y Unidades Coronarias (SEMICYUC). Las recomendaciones están basadas en el análisis de la literatura y en la posterior discusión entre los miembros del grupo de trabajo para definir, mediante consenso, los aspectos más relevantes del soporte metabólico y nutricional de los pacientes en situación crítica. Se han considerado diferentes situaciones clínicas, que se desarrollan en los artículos siguientes de esta publicación. Las presentes recomendaciones pretenden servir de guía para los clínicos con menor experiencia en la consideración de los aspectos metabólicos y nutricionales de los pacientes críticos.