Mejoras a un algoritmo de programación dinámica para el problema del viajante de comercio con un drone

En la última década surgieron distintos problemas de ruteo en los que una flota de camiones y drones se agrupan para realizar envíos al consumidor en problemas de logística de última milla. La idea es aprovechar las ventajas de ambos tipos de vehículos: los camiones transportan una gran cantidad de mercadería aunque se mueven lentamente por la red de tráfico; los drones se desplazan velozmente por moverse fuera de la red de tráfico, aunque tienen menor capacidad y autonomía. En este contexto, los problemas más simples consisten en la generación de una única ruta en la que un camión y un drone se unen para atender a un conjunto de clientes. En el problema de viajante de comercio con un drone (TSP-D) el camión parte de un depósito llevando un drone en su interior. Cada vez que el camión visita un cliente v, puede optar por lanzar el drone con un único paquete para visitar un cliente w que no va a ser visitado por el camión. Luego, el camión y el drone continúan sus rutas por separado. Una vez que el drone atiende a w, el mismo viaja a la ubicación de otro cliente z / r donde se encuentra con el camión nuevamente para continuar con la ruta en forma conjunta. El objetivo es minimizar el tiempo que demoran el camión y el drone en atender a todos los clientes y volver al depósito, sin tener en cuenta los tiempos de servicio, carga del drone o sincronización entre ambos vehículos. Recientemente Roberti y Ruthmair (Exact methods for the traveling salesman problem with drone. Transp. Sci., 55(2): 315-335, 2021) propusieron un algoritmo de programación dinámica, basado en un esquema de labeling, para resolver TSP-D. Embebiendo una versión relajada del mismo dentro de un algoritmo de tipo branch- cut-and-price pudieron resolver todas las instancias (de prueba) con 19 clientes, la mayoría con 29 clientes y algunas con 39 clientes. En esta charla mostramos nuevas reglas de dominación para mejorar la eficiencia del algoritmo de labeling. Asimismo, estudiamos distintas opciones para la relajación del algoritmo que permiten mejorar las cotas inferiores al resolver cada nodo del árbol de branching. El nuevo algoritmo resuelve varias de las instancias (de prueba) previamente no resueltas en la misma cantidad de tiempo.Sociedad Argentina de Informática e Investigación Operativ

Assortment optimisation under a general discrete choice model: A tight analysis of revenue-ordered assortments

The assortment problem in revenue management is the problem of deciding which subset of products to offer to consumers in order to maximise revenue. A simple and natural strategy is to select the best assortment out of all those that are constructed by fixing a threshold revenue $\pi$ and then choosing all products with revenue at least $\pi$. This is known as the revenue-ordered assortments strategy. In this paper we study the approximation guarantees provided by revenue-ordered assortments when customers are rational in the following sense: the probability of selecting a specific product from the set being offered cannot increase if the set is enlarged. This rationality assumption, known as regularity, is satisfied by almost all discrete choice models considered in the revenue management and choice theory literature, and in particular by random utility models. The bounds we obtain are tight and improve on recent results in that direction, such as for the Mixed Multinomial Logit model by Rusmevichientong et al. (2014). An appealing feature of our analysis is its simplicity, as it relies only on the regularity condition. We also draw a connection between assortment optimisation and two pricing problems called unit demand envy-free pricing and Stackelberg minimum spanning tree: These problems can be restated as assortment problems under discrete choice models satisfying the regularity condition, and moreover revenue-ordered assortments correspond then to the well-studied uniform pricing heuristic. When specialised to that setting, the general bounds we establish for revenue-ordered assortments match and unify the best known results on uniform pricing.Comment: Minor changes following referees' comment

The Assortment Packing Problem: Multiperiod Assortment Planning for Short-Lived Products

Motivated by retailers ’ frequent introduction of new items to refresh product lines and maintain their market shares, we present the assortment packing problem in which a firm must decide, in advance, the release date of each product in a given collection over a selling season. Our formulation models the trade-offs among profit margins, preference weights, and limited life cycles. A key aspect of the problem is that each product is short-lived in the sense that, once introduced, its attractiveness lasts only a few periods and vanishes over time. The objective is to determine when to introduce each product to maximize the total profit over the selling season. Even for two periods, the corresponding optimization problem is shown to be NP-complete. As a result, we study a continuous relaxation of the problem that approximates the problem well, when the number of products is large. When margins are identical and product preferences decay exponentially, its solution can be characterized: it is optimal to introduce products with slower decays earlier. The structural properties of the relaxation also help us to develop several heuristics, for which we establish performance guarantees. We test our heuristics with data on sales and release dates of woman handbags from an accessories retailer. The numerical experiments show that the heuristics perform very well and can yield significant improvements in profitability. 1

Valoración radiobiológica de tratamientos radiantes mediante el programa Albireo Target .

La radioterapia es una técnica de tratamiento usada en oncología basada en el efecto de las radiaciones ionizantes sobre las células. Sus objetivos son lograr la regresión tumoral protegiendo tanto como sea posible los tejidos sanos adyacentes. Se planifica el tratamiento siguiendo estos objetivos expresados en la prescripción médica. El médico debe elegir, frecuentemente entre varias, la planificación más adecuada para el paciente. Las herramientas de análisis que los planificadores le ofrecen al médico no siempre son suficientes. El programa informático Albireo Target incorpora modelos radiobiológicos que cuantifican aspectos relevantes en la clínica diaria. Este trabajo evalúa el desempeño del programa analizando datos exportados de tratamientos radiantes planificados. Se analizaron 7 casos comparando planificaciones con igual fraccionamiento y 1 con variación del mismo. Se realizó un estudio de compensación por interrupciones en el curso del tratamiento. La incorporación de Albireo Target mejora la evaluación de tratamientos radiantes agregando nuevos elementos. Sin embargo, se reconocen limitaciones debido al índice UTCP que no contempla el grado de apartamiento de la dosis recibida por los OARs respecto su dosis de tolerancia, en los casos en los que ésta no es superada

Memoirs: The Embryonic Development of Trichogramma evanescens, Westw., Monembryonic Egg Parasite of Donacia Simplex, Fab

Volume: 62Start Page: 149End Page: 18

Memoirs: The Cytoplasmic Inclusions of the Germ-Cells. Part V. The Gametogenesis and early Development of Limn\ue6a Stagnalis (L.), with Special Reference to the Golgi Apparatus and the Mitochondria

Volume: 63Start Page: 445End Page: 49

Memoirs: Some Notes on the Gametogenesis of Ornithorhynchus Paradoxus

Volume: 66Start Page: 475End Page: 49

Memoirs: The Cytoplasmic Inclusions of the Germ-Cells: Part X. The Gametogenesis of Saccocirrus

Volume: 66Start Page: 1End Page: 4

A branch-cut-and-price algorithm for the time-dependent electric vehicle routing problem with time windows

The adoption of electric vehicles (EVs) within last-mile deliveries is considered one of the key transformations towards more sustainable logistics. The inclusion of EVs introduces new operational constraints to the models such as a restricted driving range and the possibility to perform recharges en route. The discharge of the typical batteries is complex and depends on several variables, including the vehicle travel speed, but most of the approaches assume that the energy consumption depends only on the distance traveled. This becomes relevant in different logistics contexts, such as last-mile distrubtion in large cities and mid-haul logistics in retail, where traffic congestion affects severely the travel speeds. In this paper, we introduce a general version of the Time-Dependent Electric Vehicle Routing Problem with Time Windows (TDEVRPTW), which incorporates the time-dependent nature of the transportation network both in terms of travel times and the energy consumption. We propose a unifying framework to integrate other critical variable times arising during the operations previously studied in the literature, such as the time-dependent waiting times and non-linear charging times. We propose a state of the art branch-cut-and-price (BCP) algorithm. Based on extensive computational experiments, we show that the approach is very effective solving instances with up to 100 customers with different time dependent configurations. From a managerial standpoint, our experiments indicate that neglecting the travel speeds can affect the quality of the solutions obtained, where up to 40 percent of the infeasibilities induced by neglecting the time dependency can be caused by exceeding the battery capacity.Por motivos relacionados con los derechos de autor este documento solo puede ser consultado en la Biblioteca Di Tella. Para reservar una cita podés ponerte en contacto con [email protected].//Publicado en European Journal of Operational Research 312 (2024) 978-99

Guiding the formation of single-handed enantiomeric porphyrin domains using kinked and chiral stepped surfaces

The self-assembly of nickel tetraphenyl porphyrin (NiTPP) on achiral Au(111), which includes randomly located kinked steps, and chiral Au(1036 1070 1035) and (1036 1035 1070) surfaces has been studied using UHV scanning tunneling microscopy. The clean surfaces of the achiral and chiral gold crystals were characterized with STM. Subsequently, NiTPP molecules were deposited on each surface. On achiral Au(111), the porphyrins assemble into racemic mixtures of enantiomerically resolved domains. It is concluded that, on large flat terraces, intermolecular interactions are the dominant factor in the chiral assembly. Moreover, it is found that the chirality of the molecular array can be guided using the handedness of locally kinked step edges. Preliminary work has begun on the chiral crystal surfaces. Initial findings suggest that the chirality of the kinked step edges induces formation of a single-handed domain of molecules across a terrace