Applying MILP-based algorithms to automated job-shop scheduling problems in aircraft-part manufacturing

This work presents efficient algorithms based on Mixed-Integer Linear Programming (MILP) for complex job-shop scheduling problems raised in Automated Manufacturing Systems. The aim of this work is to find alternative solution approaches of production and transportation operations in a multi-product multistage production process that can be used to solve industrial-scale problems with reasonable computational effort. The MILP model developed must take into account; dissimilar recipes, single unit per production stage, re-entrant flows, sequence- dependent free transferring times and load transfer movements in a single automated material-handling device. In addition, logical-based strategies are proposed to iteratively find and improve the solutions generated over time. These approaches were tested in different real-world problems appeared in the surfacetreatment process of metal components in aircraft manufacturing industry.Sociedad Argentina de Informática e Investigación Operativ

Applying MILP-based algorithms to automated job-shop scheduling problems in aircraft-part manufacturing

This work presents efficient algorithms based on Mixed-Integer Linear Programming (MILP) for complex job-shop scheduling problems raised in Automated Manufacturing Systems. The aim of this work is to find alternative solution approaches of production and transportation operations in a multi-product multistage production process that can be used to solve industrial-scale problems with reasonable computational effort. The MILP model developed must take into account; dissimilar recipes, single unit per production stage, re-entrant flows, sequence- dependent free transferring times and load transfer movements in a single automated material-handling device. In addition, logical-based strategies are proposed to iteratively find and improve the solutions generated over time. These approaches were tested in different real-world problems appeared in the surfacetreatment process of metal components in aircraft manufacturing industry.Sociedad Argentina de Informática e Investigación Operativ

Applying MILP-based algorithms to automated job-shop scheduling problems in aircraft-part manufacturing

This work presents efficient algorithms based on Mixed-Integer Linear Programming (MILP) for complex job-shop scheduling problems raised in Automated Manufacturing Systems. The aim of this work is to find alternative solution approaches of production and transportation operations in a multi-product multistage production process that can be used to solve industrial-scale problems with reasonable computational effort. The MILP model developed must take into account; dissimilar recipes, single unit per production stage, re-entrant flows, sequence- dependent free transferring times and load transfer movements in a single automated material-handling device. In addition, logical-based strategies are proposed to iteratively find and improve the solutions generated over time. These approaches were tested in different real-world problems appeared in the surfacetreatment process of metal components in aircraft manufacturing industry.Sociedad Argentina de Informática e Investigación Operativ

Influence of CaCl2.2H2O Content on the Productive Process of Composites from Cotton Gin Waste

AbstractPrevious studies have shown the feasibility of production of masonry blocks and panels from agglomeration of cotton gin waste and calcium binders. Cotton gin waste is a serious problem for ginning plants, because in Argentina approximately 300,000 t of lignocellulosic wastes are produced annually without any final disposal destination. The accumulation of these residues is associated with pests and fire hazards. Since these composites are produced with simple equipment and a minimum energy requirement, their cost depends mainly on the binder (Portland cement) used and the process efficiency, since with a high productivity model, labor and equipment depreciation costs are significantly reduced. This paper analyzes the influence of CaCl2.2H2O (added as an accelerator for cement paste strength) on the minimum molding time required for composites manufacturing. A central composite experimental design was developed in order to study the interrelated variables. The influence of CaCl2.2H2O content on physical-mechanical cement paste properties and their relationship with composites stability are also evaluated. The results of this work show that CaCl2.2H2O content has significant influence on the efficiency of composites manufacturing as it reduces the molding time required

Stellar evolution and modelling stars

In this chapter I give an overall description of the structure and evolution of stars of different masses, and review the main ingredients included in state-of-the-art calculations aiming at reproducing observational features. I give particular emphasis to processes where large uncertainties still exist as they have strong impact on stellar properties derived from large compilations of tracks and isochrones, and are therefore of fundamental importance in many fields of astrophysics.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Metástasis Vertebrales

La incidencia de las metástasis en columna vertebral está aumentando por el incremento de la población anciana, la mayor esperanza de vida y las mejores en el tratamiento de los pacientes con cáncer. Revi - samos el diagnóstico y tratamiento de estos pacientes.The incidence of spinal metastases is increasing with increasingly older populations, longer life expectancy and improvements in medical treatment of the patients with cancer. So, metastases to the spine repre - sent a challenging problem. We review diagnosis and treatment these patients

Changes in seasonal streamflow extremes experienced in rivers of Northwestern South America (Colombia)

A measure of the variability in seasonal extreme streamflow was estimated for the Colombian Caribbean coast, using monthly time series of freshwater discharge from ten watersheds. The aim was to detect modifications in the streamflow monthly distribution, seasonal trends, variance and extreme monthly values. A 20-year length time moving window, with 1-year successive shiftments, was applied to the monthly series to analyze the seasonal variability of streamflow. The seasonal-windowed data were statistically fitted through the Gamma distribution function. Scale and shape parameters were computed using the Maximum Likelihood Estimation (MLE) and the bootstrap method for 1000 resample. A trend analysis was performed for each windowed-serie, allowing to detect the window of maximum absolute values for trends. Significant temporal shifts in seasonal streamflow distribution and quantiles (QT), were obtained for different frequencies. Wet and dry extremes periods increased significantly in the last decades. Such increase did not occur simultaneously through the region. Some locations exhibited continuous increases only at minimum QT

Propiedades físicas y cristalinas del Cd1-x Znx Te (0 <= x <= 1)

El Cd1-xZnxTe (0 <= x <= 1) y el ZnTe son semiconductores de la familia II-VI, que se usan en forma monocristalina porque así poseen mejores propiedades estructurales y eléctricas. El CZT y el ZnTe deben poseer alta calidad cristalina y eléctrica para ser usados, el primero en detectores de rayos X y ?, y como sustratos ordenadores de películas epitaxiales aptas para la detección de la radiación IR y el segundo para la fabricación de diodos láser y emisores de luz de alta intensidad, ambos casos en el verde. En este trabajo el CZT se sintetizó por el método de Bridgman, bajo un gradiente de temperatura de 10ºC/cm a velocidades de 1, 66 mm/h y 3, 22 mm/h para diferentes concentraciones de Zn. Por otro lado, el ZnTe se sintetizó por transporte físico en fase vapor bajo un gradiente de temperatura de 6ºC/cm a una velocidad de 6mm/día. Por medio de revelado químico y microscopía electrónica de transmisión convencional TEM y de alta resolución (HRTEM) se estudió la calidad cristalina de ambos materiales. Se observó que los lingotes de CZT tenían una densidad de dislocaciones promedio similar en todos los lingotes crecidos en ambas velocidades y para todas las concentraciones mientras que el ZnTe mostró una menor densidad de dislocaciones. Las micrografías de TEM mostraron en todos estos materiales un orden estructural importante. Estas características indicaron que la calidad cristalina del CZT y del ZnTe era adecuada para fabricar dispositivos optoelectrónicos. También se midió la Conductividad Eléctrica, Difusividad Térmica, Calor Específico y Coeficiente Seebeck en función de la temperatura en estos materiales. Se analizó la influencia de las propiedades estructurales en sus propiedades físicas con el objeto de determinar la relación con los defectos cristalinos observados. Cd1-xZnxTe (0 = x = 1) and ZnTe are II-VI semiconductors, which are used in single crystalline structure to improve their crystalline and electrical properties. The CZT and ZnTe must possess high crystalline and electrical quality to be used, the first in x or ¿-ray detectors, and as substrates for suitable epitaxial films for detecting IR radiation and the second for the manufacture of laser diodes and high intensity light emitters, both cases in the green wavelengths. In this work CZT was synthesized by the Bridgman method employing a temperature gradient of 10ºC/cm at speeds of 1.66 mm/h and 3.22 mm/h for different Zn concentrations. Meanwhile ZnTe was synthesized by physical vapor transport employing a temperature gradient of 6ºC/cm at a speed of 6 mm/day. Chemical etching and low and high transmission electron microscopy (LRTEM and HRTEM) were employed to determine the crystalline quality of all materials. It was observed that CZT ingots had an average dislocations density similar in all ingots grown in both speeds and all concentrations while the ZnTe showed a lower dislocation density. HRTEM micrographs showed in all semiconductors an important structural order. These characteristics showed that the crystalline quality of CZT and ZnTe was suitable for manufacturing optoelectronic devices. Furthermore, Electrical Conductivity, Thermal Diffusivity, Specific Heat and Seebeck Coefficient were measured as temperature function in all these materials. The influence of structural properties in physical properties was analyzed in order to determine the relationship with the observed crystal defects

Categorizing Different Approaches to the Cosmological Constant Problem

We have found that proposals addressing the old cosmological constant problem come in various categories. The aim of this paper is to identify as many different, credible mechanisms as possible and to provide them with a code for future reference. We find that they all can be classified into five different schemes of which we indicate the advantages and drawbacks. Besides, we add a new approach based on a symmetry principle mapping real to imaginary spacetime.Comment: updated version, accepted for publicatio

Asteroseismic diagrams from a survey of solar-like oscillations with Kepler

Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the number of main-sequence and subgiant stars with detected solar-like oscillations. We present an ensemble asteroseismic analysis of 76 solar-type stars. Using frequencies determined from the Kepler time-series photometry, we have measured three asteroseismic parameters that characterize the oscillations: the large frequency separation (\Delta \nu), the small frequency separation between modes of l=0 and l=2 (\delta \nu_02), and the dimensionless offset (\epsilon). These measurements allow us to construct asteroseismic diagrams, namely the so-called C-D diagram of \delta \nu_02 versus \Delta \nu, and the recently re-introduced {\epsilon} diagram. We compare the Kepler results with previously observed solar-type stars and with theoretical models. The positions of stars in these diagrams places constraints on their masses and ages. Additionally, we confirm the observational relationship between {\epsilon} and T_eff that allows for the unambiguous determination of radial order and should help resolve the problem of mode identification in F stars.Comment: 6 pages, 5 figures, accepted for publication in The Astrophysical Journal Letter