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Maritime transportation is crucial to national economic development as it offers a low-cost, safe, and efficient alternative for movement of freight compared to its land or air counterparts. River and channel dredging protocols are often adopted in many ports and harbors of the world to meet the increasing demand for freight and ensure safe passage of larger vessels. However, such protocols may have unintended adverse consequences on flood risks and functioning of coastal ecosystems and thereby compromising the valuable services they provide to society and the environment. This study analyzes the compound effects of dredging protocols under a range of terrestrial and coastal flood drivers, including the effects of sea level rise (SLR) on compound flood risk, vessel navigability, and coastal wetland inundation dynamics in Mobile Bay (MB), Alabama. We develop a set of hydrodynamic simulation scenarios for a range of river flow and coastal water level regimes, SLR projections, and dredging protocols designed by the U.S. Army Corps of Engineers. We show that channel dredging helps increase bottom (‘underkeel’) clearances by a factor of 3.33 under current mean sea level and from 4.20 to 4.60 under SLR projections. We find that both low and high water surface elevations (WSEs) could be detrimental, with low WSE (< -1.22 m) hindering safe navigation whereas high WSE (> 0.87 m) triggering minor to major flooding in the surrounding urban and wetland areas. Likewise, we identify complex inundation patterns emerging from nonlinear interactions of SLR, flood drivers, and dredging protocols, and additionally estimate probability density functions (PDFs) of wetland inundation. We show that changes in mean sea level due to SLR diminish any effects of channel dredging on wetland inundation dynamics and shift the PDFs beyond pre-established thresholds for moderate and major flooding. In light of our results, we recommend the need for integrated analyses that account for compound effects on vessel navigation and wetland inundation, and provide insights into environmental-friendly solutions for increasing cargo transportation.

We report performance of 15 heuristics and 4 metaheuristics to solve a frequency assignment problem where the value of an assigned frequency depends on the weights of the corresponding site where the frequency is assigned. Different algorithms where tested on two sets of problems, the first one corresponds to the well-known Philadelphia problems and the second one to situations similar to the assignment of FM frequencies in Mexico. Experimental results showed that the heuristics that take into account the site weights performed the best and, among the four metaheuristics tested, the algorithm based on simulated annealing performed the best. En este artículo se reporta el desempeño de 15 métodos heurísticos para encontrar soluciones iniciales y 4 meta-heurísticas para resolver un problema de asignación de frecuencias en el que el valor de las frecuencias asignadas depende de pesos correspondientes a los sitios donde se asigna la frecuencia. Los diferentes algoritmos fueron probados en un conjunto de problemas que se generaron utilizando un generador que representa situaciones similares a la asignación de frecuencias FM en México. Los resultados experimentales mostraron que las heurísticas que consideran los pesos de los sitios tienen un mejor desempeño y, de entre las 4 meta-heurísticas probadas, el mejor desempeño lo obtuvo el algoritmo basado en templado simulado.

The Instituto para el Depósito de Valores (INDEVAL) is the Central Securities Depository of Mexico. It is the only Mexican institution authorized to perform, in an integrated manner, the activities of safe-keeping, custody, management, clearing, settlement and transfer of securities. In this article, we report the modeling, simulation and analysis of a new Securities Settlement System (SSS) implemented by INDEVAL, as part of a project for the implementation of a safer and more efficient operating system. The main objective of this research was to use reduced amounts of cash and securities, within reasonable periods of time, for the settlement of securities of the Mexican market. A linear programming model for the netting and clearing of operations was used. The performance of the new SSS was evaluated by performing experiments using a deterministic simulation model under different operation parameters, such as the number and monetary value of transactions, the time between clearing cycles and also under a new set of rules for pre-settlement operations. The results presented may be used by other Central Securities Depositories to make decisions related to the efficient and safer use of their resources. The implementation of the model took more than three years. Now many transactions that would remain pending if processed individually are settled together, thus reducing liquidity requirements dramatically —by 52% in cash and 26% in securities.

En este artículo se presentan resultados experimentales sobre la comparación de cinco metodologías para estimar los parámetros de la distribución lognormal con traslado. Los métodos considerados son el método de momentos, el método de máxima verosimilitud local, un método propuesto por Nagatsuka y Balakrishnan, una modificación de este último, y un nuevo método propuesto en este artículo. El método de máxima verosimilitud local proporcionó estimadores que tienen buenas propiedades cuando el tamaño de la muestra no es muy pequeño y el método no falla. Por otro lado, el método de Nagatsuka y Balakrishnan modificado tuvo el mejor desempeño desde el punto de vista de los errores cuadráticos promedio de los estimadores. El nuevo método propuesto en este trabajo mostró el mejor desempeño desde el punto de vista de una medida de bondad de ajuste. This article presents the results of the comparison done using five methodologies for the fitting of parameters of a shifted lognormal distribution. The methods considered in this research are: the method of moments, the method of local maximum likelihood, a method proposed by Nagatsuka and Balakrishnan, a modification of this latter method, and a new method proposed in this article. The method of local maximum likelihood provided estimators with good properties when the sample size is not too small and the method did not fail. On the other hand, the modified method of Nagatsuka and Balakrishnan exhibited the best performance from the point of view of the mean squared error. The new method proposed in this work exhibited the best performance from the point of view of a measure of goodness of fit.

En este artículo se presenta una revisión de las principales técáicas que se han propuesto para el análisis de los componentes aleatorios de una simulación estocástica. Se discuten dos temas principales: el modelado clásico utilizando familias univariadas de distribuciones y el modelado avanzado de la entrada. En el primer tema se introduce el uso de una librería, llamada Analizador Simple (Simple Analyzer), que puede ser descargada libremente desde la red, mientras que en el segundo tema se discuten las técáicas para el modelado de la entrada que actualmente no están incluidas en el software disponible para el análisis de la entrada de experimentos por simulación. Se analiza también el ajuste de datos de entradas multimodales, correlacionadas y dependientes del tiempo, y se incorpora la incertidumbre paramétrica en el modelo de entrada. In this article, a review of the main techniques proposed for the analysis of random components in stochastic simulations is presented. Two main topics are discussed: classical modeling using univariate distributions and advanced modeling techniques. The use of a library is introduced in the first topic; this library is named Simple Analyzer and can be downloaded for free from the web. In the second topic, techniques for input analysis that are currently not included in available commercial software of simulation experiments are discussed. Also the fitting of data of multimodal, correlated and time-dependent input components, and the incorporation of parameter uncertainty in the input model are analyzed.

En este artículo se presenta una comparación empírica entre los métodos de repeticiones independientes, grupos consecutivos y grupos espaciados para estimar la esperanza, la varianza y el 90%-cuantil del tiempo en la fila de espera (en estado estable) de una cola M/M/1. La comparación está basada en el cubrimiento empírico, el sesgo y el error relativo de los intervalos del 90% de confianza, a través de 1000 repeticiones independientes de las estimaciones. Los resultados experimentales muestran que los tres métodos proporcionan cubrimientos similares (y asintóticamente válidos) para estimar la esperanza, la varianza y el cuantil, mientras que el método de grupos consecutivos proporciona sesgos y errores relativos más pequeños que los otros dos métodos. Además se presenta el ejemplo de una cadena de Markov con espacio de estados continuo, en el que se obtienen intervalos de confianza válidos, siendo que esta cadena no es geométricamente ergódica.