Efecto de la Onda de Choque Generada en una Explosión sobre los Soportes de Recipientes Horizontales a Presión

El almacenamiento de importantes cantidades de productos o materiales peligrosos requiere de medidas de prevención y protección para evitar incidentes tales como incendios, explosiones y proyectiles. Sin embargo, a pesar de la gravedad que pueden alcanzar los sucesos que afectan la integridad de los recipientes a presión, la mayoría de los códigos y prácticas recomendadas no incluye el efecto de una deflagración entre sus especificaciones de diseño. Actualmente el estudio de las explosiones y sus consecuencias es cada vez más importante para evaluar riesgos y amenazas, y desarrollar formas de proteger a las personas y los bienes que puedan ser afectados. Las consecuencias de las ondas de presión sobre una estructura dependen tanto de las propiedades de la onda como de las características del objeto impactado (masa, frecuencia natural de vibración, resistencia dinámica, etc.). En este sentido se han realizado varias investigaciones sobre el modo de falla típico de diferentes clases de equipos industriales. Para el caso de los recipientes a presión horizontales e intercambiadores de calor, el principal modo de falla es el colapso de los soportes. Los recipientes a presión horizontales generalmente son soportados por silletas (“saddle”). Para el diseño de las mismas, las normas y las prácticas recomendadas permiten un ángulo de contacto entre la silleta y el recipiente a presión que varía entre 120⁰ y 180⁰. Con el objetivo de estudiar la influencia del ángulo de contacto de las silletas en los esfuerzos producidos por la onda de choque de una explosión se llevaron a cabo diferentes simulaciones utilizando el programa Autodesk Simulation Multiphysic. En este trabajo se utilizan perfiles de ondas de presión con un valor de sobrepresión positivo y una fase negativa y se estudia su impacto sobre recipientes a presión horizontales. A fin de identificar la influencia que tiene el ángulo de contacto de la silleta en los esfuerzos producidos por la onda de choque de una explosión, el ángulo se incrementó hasta 180⁰ y se observó el comportamiento obtenido. Como resultado del análisis se puede concluir que, a medida que se aumenta el ángulo de contacto disminuyen los esfuerzos máximos; este comportamiento se mantiene hasta un ángulo de contacto de 150⁰. A partir de este punto la tendencia se invierte y los esfuerzos aumentan pero en una menor proporción.Fil: Morales Velasco, Mauricio Xavier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Maiz, Santiago. Universidad Nacional del Sur. Departamento de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tonelli, Stella Maris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentin

Measuring the Systematic Risk of Sectors within the US Market Via Principal Components Analysis: Before and during the COVID-19 Pandemic

This research measures the systematic risk of 10 sectors in the American Stock Market, discerning the COVID-19 pandemic period. The novelty of this study is the use of the Principal Component Analysis (PCA) technique to measure the systematic risk of each sector, selecting five stocks per sector with the greatest market capitalization. The results show that the sectors that have the greatest increase in exposure to systematic risk during the pandemic are restaurants, clothing, and insurance, whereas the sectors that show the greatest decrease in terms of exposure to systematic risk are automakers and tobacco. Due to the results of this study, it seems advisable for practitioners to select stocks that belong to either the automakers or tobacco sector to get protection from health crises, such as COVID-19

Wide-field HST/ACS images of M81: The Population of Compact Star Clusters

We study the population of compact stellar clusters (CSCs) in M81, using the HST/ACS images in the filters F435W, F606W and F814W covering, for the first time, the entire optical extent of the galaxy. Our sample contains 435 clusters of FWHM less than 10 ACS pixels (9 pc). The sample shows the presence of two cluster populations, a blue group of 263 objects brighter than B=22 mag, and a red group of 172 objects, brighter than B=24 mag. Based on the analysis of colour magnitude diagrams and making use of simple stellar population models, we find the blue clusters are younger than 300 Myr with some clusters as young as few Myr, and the red clusters are as old as globular clusters. The luminosity function of the blue group follows a power-law distribution with an index of 2.0, typical value for young CSCs in other galaxies. The power-law shows unmistakable signs of truncation at I=18.0 mag (M_I=-9.8 mag), which would correspond to a mass-limit of 4x10^4 M_solar if the brightest clusters are younger than 10 Myr. The red clusters have photometric masses between 10^5 to 2x10^7 M_solar for the adopted age of 5 Gyr and their luminosity function resembles very much the globular cluster luminosity function in the Milky Way. The brightest GC in M81 has M_B^0=-10.3 mag, which is ~0.9 mag brighter than w-Cen, the most massive GC in the Milky Way.Comment: Accepted by MNRAS. The paper contains 10 figures and 3 tables. Table 3 will be published in full online onl

Comments on "Free vibration of super elliptical plates with constant and variable thickness by Ritz method"

Free vibration of super elliptical plates with constant and variable thickness by Ritz method has been reported. the shape of the plate in the x y plane can be defined by the super elliptical function. Calculating the area and perimeter of the region may give an idea about the convergence of the integration. the discussers also obtained the area sand perimeters using a finite element code, to be sure about the good precision of their values. The re-calculated values are in excellent agreement with Wang's results. The calculations have been performed for simply supported and clamped super elliptical plates with aspect ratio a/b=1, 1.2, 2, 3; with n=8 and n=10.Fil: Bambill, Diana Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Maiz, Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Rossi, Raul Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; Argentin

Comments on "faber series method for two-dimensional problems of an arbitrarily shaped inclusion in piezoelectric materials" by C.-F. Gao and N. Noda (Acta Mech. 171, 1-13, August 2004)

The writers wish to congratulate the authors for their rigorous treatment of an important anddifficult problem. As stated by Gao and Noda, the inclusion problem is of fundamentalimportance in engineering sciences and has received considerable attention from both theore-ticians and experimentalists.Fil: Laura, Patricio Adolfo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur; ArgentinaFil: Rossit, Carlos Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur; ArgentinaFil: Maiz, Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur; Argentin

Transverse vibrations of a clamped elliptical plate carrying a concentrated mass at an arbitrary position

Free vibrations of clamped, thin elliptical plates carrying a concentrated mass at an arbitrary position are studied in order to analyze the mass effect on the natural frequencies and mode shapes of the plate. A variational approach, the well-known Ritz method, is used, where the displacement amplitude is approximated by polynomial expressions in the Cartesian coordinates. The present proposal exhibits excellent agreement with particular cases of the problem available in the literature and also with an independent solution obtained by means of the finite element method. Some new results are presented for the natural frequencies and modes of clamped elliptical plates with a concentrated mass.Fil: Maiz, Santiago. Universidad Nacional del Sur. Departamento de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rossit, Carlos Adolfo. Universidad Nacional del Sur. Departamento de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bambill, Diana Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Susca, Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Vibrations of L-Shaped Beam Structures With a Crack: Analytical Approach and Experimental Validation

A crack on a structural member introduces a local flexibility which is function of the crack depth. This new flexibility condition changes the dynamic behavior of the structure. The knowledge of the influence of the crack on the characteristic dynamic parameters makes it possible to determine both the crack position and its magnitude. A large number of research papers have been written on the subject, most of them on straight beams of a single segment. However, despite the importance of L-shaped beams in a variety of technological applications, very limited information is available for the case of such structures. In this article, a cracked L-beam structure is studied by an analytical approach which is validated by experimental measurements. The Euler–Bernoulli beam theory is assumed to describe the transversal displacements and the crack is modeled by means of an elastically restrained hinge. A special device was designed to measure experimentally the natural frequencies of steel L-beams structures. The natural frequencies of in plane vibrations of L-beam structures are obtained considering a crack at different positions as well as of different depths. Values obtained with the analytical solution are satisfactorily compared with experimentally measured frequencies and the values reported in previous studies on the subject published by other authors.Fil: Rossit, Carlos Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Bambill, Diana Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Ratazzi, Alejandro Ruben. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Maiz, Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; Argentin

Transverse vibration of Bernoulli-Euler beams carrying point masses and taking into account their rotatory inertia: exact solution

The situation of structural elements supporting motors or engines attached to them is usual in technological applications. The operation of the machine may introduce severe dynamic stresses on the beam. It is important, then, to know the natural frequencies of the coupled beam-mass system, in order to obtain a proper design of the structural elements. An exact solution for the title problem is obtained in closed-form fashion, considering general boundary conditions by means of translational and rotatory springs at both ends. The model allows to analyze the influence of the masses and their rotatory inertia on the dynamic behavior of beams with all the classic boundary conditions, and also, as particular cases, to determine the frequencies of continuous beams.Fil: Maiz, Santiago. Universidad Nacional del Sur. Departamento de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; ArgentinaFil: Bambill, Diana Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Rossit, Carlos Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Laura, Patricio Adolfo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería; Argentin

Insulin-secretion abnormalities and clinical deterioration related to impaired glucose tolerance in cystic fibrosis.

[eng] Objective: To evaluate insulin-secretion kinetics and insulin sensitivity in cystic fibrosis (CF) patients with normal glucose tolerance (CF-NGT), impaired glucose tolerance (CF-IGT) or CF-related diabetes (CFRD), and the potential effects of moderate hyperglycemia on clinical and nutritional status. Design and methods: Cross-sectional study including 50 outpatients with CF. Patients underwent both oral (OGGT) and intravenous (IVGTT) glucose tolerance tests in order to assess insulin secretion and peripheral insulin sensitivity. Homeostasis assessment model and OGGT were used to investigate insulin sensitivity. Forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC) were measured to evaluate pulmonary function. Body mass index (BMI) was determined to assess nutritional status. Results: Insulin secretion was significantly decreased (and delayed at OGTT) in the CFRD group (n = 9) versus the CF-IGT group (n = 10) and the CF-IGT versus the CF-NGT group (n = 31). Insulin sensitivity was significantly different in the CF-IGT and CFRD groups versus the CF-NGT group. FEV1, FVC and BMI presented a significant linear correlation with plasma glucose value at 120 min at OGTT and were significantly lower in both CF-IGT and CFRD versus the CF-NGT group, whereas no differences were found between the CF-IGT and CFRD groups. Conclusions: CF patients with IGT present diminished insulin secretion and increased peripheral insulin resistance, correlating with a worse clinical status, undernutrition and impaired pulmonary function. These findings open the question of whether early treatment of mild alterations of glucose metabolism with insulin secretagogues or short-action insulin may lead to improvement of clinical status in CF patients