Lot production size problem and simulation of urban transport

OBJECTIVES AND STUDY METHOD: There are two subjects in this thesis: “Lot production size for a parallel machine scheduling problem with auxiliary equipment” and “Bus holding for a simulated traffic network”. Although these two themes seem unrelated, the main idea is the optimization of complex systems. The “Lot production size for a parallel machine scheduling problem with auxiliary equipment” deals with a manufacturing setting where sets of pieces form finished products. The aim is to maximize the profit of the finished products. Each piece may be processed in more than one mold. Molds must be mounted on machines with their corresponding installation setup times. The key point of our methodology is to solve the single period lot-sizing decisions for the finished products together with the piece-mold and the mold-machine assignments, relaxing the constraint that a single mold may not be used in two machines at the same time. For the “Bus holding for a simulated traffic network” we deal with One of the most annoying problems in urban bus operations is bus bunching, which happens when two or more buses arrive at a stop nose to tail. Bus bunching reflects an unreliable service that affects transit operations by increasing passenger-waiting times. This work proposes a linear mathematical programming model that establishes bus holding times at certain stops along a transit corridor to avoid bus bunching. Our approach needs real-time input, so we simulate a transit corridor and apply our mathematical model to the data generated. Thus, the inherent variability of a transit system is considered by the simulation, while the optimization model takes into account the key variables and constraints of the bus operation. CONTRIBUTIONS AND CONCLUSIONS: For the “Lot production size for a parallel machine scheduling problem with auxiliary equipment” the relaxation we propose able to find solutions more efficiently, moreover our experimental results show that most of the solutions verify that molds are non-overlapping even if they are installed on several machines. We propose an exact integer linear programming, a Relax&Fix heuristic, and a multistart greedy algorithm to solve this problem. Experimental results on instances based on real-world data show the efficiency of our approaches. The mathematical model and the algorithm for the lot production size problem, showed in this research, can be used for production planners to help in the scheduling of the manufacturing. For the “Bus holding for a simulated traffic network” most of the literature considers quadratic models that minimize passenger-waiting times, but they are harder to solve and therefore difficult to operate by real-time systems. On the other hand, our methodology reduces passenger-waiting times efficiently given our linear programming model, with the characteristic of applying control intervals just every 5 minutes.

Growth, feed intake, survival, and histological response of white shrimp Litopenaeus vannamei fed diets containing grains naturally contaminated with aflatoxin = Crecimiento, consumo de alimento, supervivencia y respuesta histológica del camarón blanco Litopenaeus vannamei alimentado con dietas de granos contaminados naturalmente con aflatoxinas

Two feeding trials were carried out to evaluate the effect of diets containing corn or peanut grains naturally contaminated with aflatoxins on the growth, feed intake, survival, and histological response of the white shrimp Litopenaeus vannamei. In trial 1, four experimental diets were formulated to contain 0, 500, 1000, and 2000 g kg–1 of total aflatoxins (TA) and fed to L. vannamei juveniles for 28 days. In trial 2, six experimental diets were formulated to contain 0, 10, 20, 40, 60, and 120 g kg–1 TA and fed to L. vannamei juveniles for 64 days. Feed intake and weight gain were significantly affected by the presence of aflatoxins from naturally contaminated grains. Feed conversion rate increased significantly from a level of inclusion of 60 g kg–1. Survival was significantly reduced only for shrimp fed diets supplemented with 1000 and 2000 g kg–1 TA. Shrimp exposed to higher aflatoxin inclusion levels presented significantly lower lipid vacuole levels in R-cells (12–28%), lower B-cell activity, and lower mitotic E-cell activity. Tubular epithelial atrophy increased from the inclusion level of 20 g kg–1. Hepatopancreatocyte sloughing was significantly higher in shrimp fed diets supplemented with 1000 and 2000 g kg–1 TA. It is worth noting that shrimp fed 40 g kg–1 TA presented a high hepatopancreatocyte sloughing coefficient. Based on these results we conclude that the presence of aflatoxins, even at low levels, reduces feed intake and weight gain, and alters the cells of the hepatopancreas. RESUMEN. Se llevaron a cabo dos bioensayos para evaluar el efecto de granos de maíz y maní contaminados naturalmente con aflatoxinas sobre el crecimiento, consumo de alimento, supervivencia y daños histológicos de juveniles del camarón blanco Litopenaeus vannamei. Para el bioensayo 1, se formularon cuatro dietas con 0, 500, 1000 y 2000 g kg–1 de aflatoxinas totales (AT) y se proporcionaron a juveniles de L. vannamei durante 28 días. Para el bioensayo 2, se formularon seis dietas con 0, 10, 20, 40, 60 y 120 g kg–1 AT y se proporcionaron a juveniles de L. vannamei durante 64 días. El consumo de alimento fue significativamente afectado por la presencia de aflatoxinas. La tasa de conversión alimenticia incrementó significativamente a partir de un nivel de inclusión de 60 g kg–1. La supervivencia fue significativamente reducida solamente en los camarones que fueron alimentados con las dietas suplementadas con 1000 y 2000 g kg–1 AT. Los camarones expuestos a los niveles de inclusión altos presentaron un menor nivel de vacuolas lipídicas en las células R (12–28%), y una menor actividad de las células B y de la actividad mitótica de las células E. La atrofia de los túbulos del epitelio se incrementó a partir de un nivel de inclusión de 20 g kg–1. La descamación de las células del hepatopáncreas fue significativamente mayor en camarones alimentados con las dietas suplementadas con 1000 y 2000 g kg–1 AT, mientras que para las dosis bajas no se observaron diferencias significativas, aunque en camarones alimentados a partir de 40 g kg–1 AT se observa un coeficiente de descamación alto. Con base en los resultados, se concluye que la presencia de aflatoxinas, incluso a niveles bajos, reduce el consumo de alimento y el aumento de peso y altera las células del hepatopáncreas.