Global Optimization strategies for two-mode clustering

Two-mode clustering is a relatively new form of clustering that clusters both rows and columns of a data matrix. To do so, a criterion similar to k-means is optimized. However, it is still unclear which optimization method should be used to perform two-mode clustering, as various methods may lead to non-global optima. This paper reviews and compares several optimization methods for two-mode clustering. Several known algorithms are discussed and a new, fuzzy algorithm is introduced. The meta-heuristics Multistart, Simulated Annealing, and Tabu Search are used in combination with these algorithms. The new, fuzzy algorithm is based on the fuzzy c-means algorithm of Bezdek (1981) and the Fuzzy Steps approach to avoid local minima of Heiser and Groenen (1997) and Groenen and Jajuga (2001). The performance of all methods is compared in a large simulation study. It is found that using a Multistart meta-heuristic in combination with a two-mode k-means algorithm or the fuzzy algorithm often gives the best results. Finally, an empirical data set is used to give a practical example of two-mode clustering.algorithms;fuzzy clustering;multistart;simulated annealing;simulation;tabu search;two-mode clustering

Environmental changes during secondary succession in a tropical dry forest in Mexico

Vegetation and environment change mutually during secondary succession, yet the idiosyncrasies of the vegetation effect on the understorey environment are poorly understood. To test whether the successional understorey environment changes predictably and is shaped by the structure and seasonality of tropical dry forests, we estimated basal area and vegetation cover, and measured understorey temperature, light and moisture conditions, in 17 plots forming a 60-y chronosequence and a mature forest. Light and air and soil temperature decreased with time (75-15% of open-sky radiation, 31.7-29.3 °C, and +2.5 °C to -0.5 °C relative to ambient, respectively), whereas relative humidity increased (67-74%). Soil water availability increased with early-successional development (-45 to -1 kPa) but decreased afterwards (to -18 kPa). The first axis of a PCA of the rainy-season environment explained 60% of the variation and was strongly related to air temperature and relative humidity. During tropical dry-forest succession, such factors may be more important than light, the reduction in which is not extreme compared with taller and more vertically stratified wet forests. Seasonality significantly affected the successional environmental gradients, which were marked mainly during the wet season. Environmental heterogeneity was higher in the wet than in the dry season, and larger for resources (light and water) than for conditions (temperature and humidity). The wet-season increase in environmental heterogeneity potentially creates differential growing scenarios; the environmental harshness of the dry season would mostly challenge seedling survival

Coronavirus in Colombia: Stigma and quarantine

This study describes a brief history of the spread of coronavirus, listing the disease’s main characteristics. The decisions made by the Colombian government are presented, as there have been progressively more cases of infection, death and recovery, in addition to the stigmatisation that the medical personnel who are treating COVID-19 patients have experienced from some people in Colombia. Issues related to intra-family and domestic partner violence occurring in Colombia because of the quarantine processes are also addressed. Early stress studies in general population and medical professionals. The lines of work being implemented by the Colombian Association of Psychology (COLPSIC, for its Spanish acronym) for psychological help towards the affected population are described. Finally, psychological intervention initiatives that are important to implement for mental well-being are discussed

Modeling of PV Systems Based on Inflection Points Technique Considering Reverse Mode

Este artículo propone una metodología para el modelado de sistemas fotovoltaicos, considerando su comportamiento tanto en el modo de operación directo como en modo inverso bajo condiciones no uniformes de irradiación. La metodología propuesta se basa en la técnica de puntos de inflexión con una aproximación lineal del modelo del diodo de bypass y un modelo simplificado del módulo fotovoltaico. El modelo matemático planteado permite evaluar el rendimiento energético de un sistema fotovoltaico, con tiempos cortos de simulación para arreglos de gran tamaño. Adicionalmente, esta metodología permite estimar el estado de los módulos afectados por el sombreo parcial ya que es posible conocer la potencia disipada debido a la operación en el segundo cuadrante.This paper proposes a methodology for photovoltaic (PV) systems modeling, considering their behavior in both direct and reverse operating mode and considering mismatching conditions. The proposed methodology is based on the inflection points technique with a linear approximation to model the bypass diode and a simplified PV model. The proposed mathematical model allows to evaluate the energetic performance of a PV system, exhibiting short simulation times in large PV systems. In addition, this methodology allows to estimate the condition of the modules affected by the partial shading since it is possible to know the power dissipated due to its operation at the second quadrant

Energy Prediction in Urban Photovoltaic Systems

Este artículo propone un nuevo método para estimar la potencia y energía producida por sistemas fotovoltaicos urbanos, los cuales son comúnmente cubiertos por sombras que afectan su desempeño. La solución se basa en un algoritmo para procesar, rápidamente, un modelo preciso que considera el efecto de las sombras. Esta solución provee un mejor desempeño en comparación con aproximaciones clásicas, ya que reduce significativamente el tiempo de cálculo sin introducir errores sensibles, permitiendo la simulación de largos periodos de operación, e.g. meses y años. Por lo tanto, esta solución es apropiada para realizar estimaciones de energía orientadas a análisis económicos, e.g. cálculo del tiempo de retorno de la inversión, así como para soportar el diseño de instalaciones fotovoltaicas, permitiendo el cálculo preciso del número de módulos requeridos para suplir el perfil de carga.This paper proposes a new method to accurately estimate the power and energy production in urban photovoltaic (PV) systems, which are commonly covered by shades affecting its performance. The solution is based on an efficient algorithm designed to compute, in short time, an accurate model accounting for the shades impact. In such a way, the proposed approach improves classical solutions by significantly reducing the processing time to simulate long periods, e.g. months and years, but without introducing sensible errors. Therefore, this approach is suitable to estimate the production of PV systems for economical analyses such as the return-of-invested time calculation, but also to accurately design PV installations by selecting the right number of photovoltaic modules to supply the required load power.  

Equivalent circuits for simulating irregular PV arrays under partial shading conditions

El modelado y simulación de sistemas fotovoltaicos (PV) son áreas de investigación abiertas ya que las curvas I-V y P-V son comúnmente requeridas para analizar el desempeño de instalaciones PV. Para obtener dichas curvas se pueden utilizar paquetes de cómputo, sin embargo, el tipo de conexión y el tamaño del arreglo PV pueden ocasionar largos tiempos de simulación. Para superar dicha dificultad se han propuesto técnicas basadas en los puntos de inflexión para modelar el arreglo PV con el objetivo de reconstruir exactamente las curvas eléctricas requeridas. Sin embargo, tal análisis ha sido aplicado solo a la configuración serie-paralelo (SP), la cual es solo una de las alternativas para conectar arreglos PV entre otras opciones de conexión regular o irregular. Por esto, se requiere una aproximación más general. Este artículo presenta una proximación para obtener las curvas características de cualquier arreglo PV, regular o irregular, extendiendo el análisis de los puntos de inflexión. Entonces, de las curvas eléctricas del arreglo PV es simplificado utilizando circuitos equivalentes en intervalos definidos por los puntos de inflexión. Tal procedimiento está basado en definir cuáles módulos se activan debido al comportamiento de los diodos de bypass. Finalmente, la aproximación propuesta permite analizar cualquier arreglo PV sin requerir de simulaciones largas. La solución fue validada por medio de resultados de simulación obtenidos en Matlab®.Modeling and simulation of photovoltaic (PV) systems are open research areas since I-V and P-V curves are commonly required to analyze the performance of PV installations. To obtain such curves commercial software packages can be used, however the connection type and size of the PV array may cause large simulation times. To overcome such an issue several techniques based on analyzing the inflection points have been proposed to model the PV array with the aim of reconstruct accurately the required electrical curves. However, such analysis has been applied only for series-parallel (SP) configuration, which is just one alternative to connect PV arrays among several other regular or irregular options. Therefore, a more general approach is needed. This paper presents an approach to obtain the characteristics curves for any PV array, regular or irregular, by extending the inflection points analysis. Then, the calculation of the PV array electrical curves is simplified by using equivalent circuits within the intervals defined by the inflection points. Such a procedure is based on defining which modules become active due to the behavior of the bypass diodes. Finally, the proposed approach enables to analyze any PV array without requiring long electrical simulations. The solution was validated by means of simulation results obtained in Matlab®

Global Optimization strategies for two-mode clustering

Two-mode clustering is a relatively new form of clustering that clusters both rows and columns of a data matrix. To do so, a criterion similar to k-means is optimized. However, it is still unclear which optimization method should be used to perform two-mode clustering, as va

Koinonia

Guiding Principles: Toward Development of An Ethic of National and Community Service with an Emphasis Upon Higher Education, Cliff Briggs President\u27s Corner Focus on the ACSD 1993 National Conference: Mirrors of the Past, Directions for the Future When Goals Hinder Vision CoCCA: Planning Activities for Adult Students; Hot Program and Promotional Tips Males\u27 Attributions and Expectancies about Potential Mates as a Function of Sex Roles Part IIhttps://pillars.taylor.edu/acsd_koinonia/1048/thumbnail.jp

Traffic characterization in a communications channel for monitoring and control in real-time systems

The response time for remote monitoring and control in real-time systems is a sensitive issue in device interconnection elements. Therefore, it is necessary to analyze the traffic of the communication system in pre-established time windows. In this paper, a methodology based on computational intelligence is proposed for identifying the availability of a data channel and the variables or characteristics that affect the performance and data transfer, which is made up of four stages: a) integration of a communication system with an acquisition module and a final control structure; b) communication channel characterization by means of traffic variables; and c) relevance analysis from the characterization space using SFFS (sequential forward oating selection); d) Channel congestion classification as Low or High using a classifier based on Naive Bayes algorithm. The experimental setup emulates a real process using an on/off remote control of a DC motor on an Ethernet network. The communication time between the client and server was integrated with the operation and control times, to study the whole response time. This proposed approach allows support decisions about channel availability, to establish predictions about the length of the time window when the availability conditions are unknown