Hierarchical stack filtering : a bitplane-based algorithm for massively parallel processors

With the development of novel parallel architectures for image processing, the implementation of well-known image operators needs to be reformulated to take advantage of the so-called massive parallelism. In this work, we propose a general algorithm that implements a large class of nonlinear filters, called stack filters, with a 2D-array processor. The proposed method consists of decomposing an image into bitplanes with the bitwise decomposition, and then process every bitplane hierarchically. The filtered image is reconstructed by simply stacking the filtered bitplanes according to their order of significance. Owing to its hierarchical structure, our algorithm allows us to trade-off between image quality and processing time, and to significantly reduce the computation time of low-entropy images. Also, experimental tests show that the processing time of our method is substantially lower than that of classical methods when using large structuring elements. All these features are of interest to a variety of real-time applications based on morphological operations such as video segmentation and video enhancement

A simple test of momentum in foreign exchange markets

This study proposes a new method for testing for the presence of momentum in nominal exchange rates, using a probabilistic approach. We illustrate our methodology estimating a binary response model using information on local currency / US dollar exchange rates of eight emerging economies. After controlling for important variables a§ecting the behavior of exchange rates in the short-run, we show evidence of exchange rate inertia; in other words, we Önd that exchange rate momentum is a common feature in this group of emerging economies, and thus foreign exchange traders participating in these markets are able to make excess returns by following technical analysis strategies. We Önd that the presence of momentum is asymmetric, being stronger in moments of currency depreciation than of appreciation. This behavior may be associated with central bank intervention.Momentum, foreign exchange markets, hazard duration analysis, emerging economies.

Water-pumping permanent magnet synchronous motor optimization based on customized torque-speed operating area and performance characteristics

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThis paper presents a novel methodology for optimizing Permanent Magnet Synchronous Motors for Water-Pumping applications. The algorithm is designed to start the optimization process from a predefined torque-speed area, its desired envelope, and the performance characteristics of the motor to be obtained after the optimization process, providing the information in an efficiency map, according to a predefined control strategy (MTPA, MTPV, etc.). This work also implements an image comparison technique based on the structural similarity index to evaluate the objective function.Peer ReviewedPostprint (author's final draft

Coherence in ongoing varieties. The effect of mesosocial and small-scale variables on the use of the intermediate (standard/vernacular) variety in southern Spain.

This paper addresses some questions regarding coherence within ongoing urban varieties, such as the one boosted by urban middle-class speakers from southern Spain since the fifties of the 20th century (Villena and Vida 2017, 2018). The main issues we focus on here are (1) whether covariation and coherence actually exist within a variety which has primarily emerged on the basis of correction and levelling of vernacular features, and (2) to what extent it is feasible to build a multivariate model able to depict interaction between the macrosocial, mesocial and small-scales variables underlying the speaker’s use of the new variety.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Stability analysis of a grid-connected VSC controlled by SPC

In the near future a large part of traditional generation based on conventional synchronous machines (SM) will be replaced by renewable generation based on voltage source converters (VSC). In this sense, power system operators have begun to demand VSC-based power plants be able to participate in the frequency and voltage regulation, and are also interested in services like inertia emulation and damping of power oscillation, functions that today are carried out by large synchronous generators. Therefore, several studies have suggested new ways to control voltage source converters, that try to emulate the behavior of synchronous generators and are known generically as Virtual Synchronous Machines. The synchronous power controller (SPC) is a flexible solution that emulates the classical swing equation of a synchronous machine and improves its response. The SPC inherits the advantages of conventional synchronous generators, while it fixes many of its drawbacks. In this work, a sensitivity analysis of a VSC connected to the grid and controlled by SPC is performed. In this sense, a non-linear mathematical model of the system is first developed. This non-linear model is then linearized, obtaining a linear model from which the eigenvalues and sensitivities of the system to some relevant parameters are calculated. Finally, time-domain simulations are performed to confirm the results of the sensitivity analysis.Postprint (author's final draft

Detection of inter-turn faults in multi-phase ferrite-PM assisted synchronous reluctance machine

Inter-turn winding faults in five-phase ferrite-permanent magnet-assisted synchronous reluctance motors (fPMa-SynRMs) can lead to catastrophic consequences if not detected in a timely manner, since they can quickly progress into more severe short-circuit faults, such as coil-to-coil, phase-to-ground or phase-to-phase faults. This paper analyzes the feasibility of detecting such harmful faults in their early stage, with only one short-circuited turn, since there is a lack of works related to this topic in multi-phase fPMa-SynRMs. Two methods are tested for this purpose, the analysis of the spectral content of the zero-sequence voltage component (ZSVC) and the analysis of the stator current spectra, also known as motor current signature analysis (MCSA), which is a well-known fault diagnosis method. This paper compares the performance and sensitivity of both methods under different operating conditions. It is proven that inter-turn faults can be detected in the early stage, with the ZSVC providing more sensitivity than the MCSA method. It is also proven that the working conditions have little effect on the sensitivity of both methods. To conclude, this paper proposes two inter-turn fault indicators and the threshold values to detect such faults in the early stage, which are calculated from the spectral information of the ZSVC and the line currentsPeer ReviewedPostprint (published version

Microalgae recycling improves biomass recovery from wastewater treatment high rate algal ponds

Microalgal biomass harvesting by inducing spontaneous flocculation (bioflocculation) sets an attractive approach, since neither chemicals nor energy are needed. Indeed, bioflocculation may be promoted by recycling part of the harvested microalgal biomass to the photobioreactor in order to increase the predominance of rapidly settling microalgae species. The aim of the present study was to improve the recovery of microalgal biomass produced in wastewater treatment high rate algal ponds (HRAPs) by recycling part of the harvested microalgal biomass. The recirculation of 2% and 10% (dry weight) of the HRAPs microalgal biomass was tested over one year in an experimental HRAP treating real urban wastewater. Results indicated that biomass recycling had a positive effect on the harvesting efficiency, obtaining higher biomass recovery in the HRAP with recycling (R-HRAP) (92–94%) than in the control HRAP without recycling (C-HRAP) (75–89%). Microalgal biomass production was similar in both systems, ranging between 3.3 and 25.8 g TSS/m2d, depending on the weather conditions. Concerning the microalgae species, Chlorella sp. was dominant overall the experimental period in both HRAPs (abundance >60%). However, when the recycling rate was increased to 10%, Chlorella sp. dominance decreased from 97.6 to 88.1%; while increasing the abundance of rapidly settling species such as Stigeoclonium sp. (16.8%, only present in the HRAP with biomass recycling) and diatoms (from 0.7 to 7.3%). Concerning the secondary treatment of the HRAPs, high removals of COD (80%) and N-NH4+ (97%) were found in both HRAPs. Moreover, by increasing the biomass recovery in the R-HRAP the effluent total suspended solids (TSS) concentration was decreased to less than 35 mg/L, meeting effluent quality requirements for discharge. This study shows that microalgal biomass recycling (10% dry weight) increases biomass recovery up to 94% by selecting the most rapidly settling microalgae species without compromising the biomass production and improving the wastewater treatment in terms of TSS removal.Peer ReviewedPostprint (author's final draft

The cyclical behavior of bank capital buffers in an emerging economy: size do matters

Using a panel of Colombian banks and quarterly data between 1996:1 and 2010:3, we study the relationship between short-run adjustments in bank capital buffers and the business cycle. We follow a partial adjustment framework and control for several variables that have been identified as important determinants of bank capital buffers in previous studies, and find that bank capital buffers vary overthe business cycle. We are able to identify a negative co-movement of capital buffers and and the business cycle. However, we also find that capital buffers of small and large banks behave asymmetrically during the business cycle. While the former appear to be constant over time, once the appropriate set of control variables is used, the latter present a countercyclical behavior. Our results suggest the possible need of the implementation of regulatory policy measures in developing countries.Bank capital bu§ers; Credit risk; Regulation; Colombia

Ciclo reproductivo en dos bancos de Modiolus capax (Bivalvia: Mytilidae) a diferente profundidad en la Ensenada de La Paz, Golfo de California, México

Background. The mussel Modiolus capax is a commercially important resource in the northwest of Mexico; however few studies evaluate its reproduction. Goals.  The reproductive activity and the gonadosomatic index of were used to describe the seasonal variations in the reproductive cycle of the M. capax and the relationship with the environmental changes. Methods. Approximately 24 specimens were collected per month in two localities at La Paz inlet, Baja California Sur, Mexico, between October 2008 and December 2010. Relationships between gonad developmental states and size were estimated; also, its relationships with temperature and chlorophyll-a. Results. The results indicated a synchronous spawning between males and females in March in one locality and in January in the other. In both localities, ripe and post-spawning females showed follicular atresia, in up to 82% of all females in one locality. The smallest organisms were found in the early gametogenesis stage; the largest, in the spawning stage. The gonadosomatic index differed between localities, and was positively correlated with the increase in chlorophyll-a. A significant relationship was observed between temperature and the frequencies of the gametogenesis and ripening stages. Conclusions. The study of the reproduction of M. capax revealed that environmental changes affect on the activity and reproductive status and favored the development of follicular atresia.  Antecedentes: El mejillón Modiolus capax es una especie de importancia comercial en el noroeste de México; sin embargo existen pocos trabajos que evalúan su reproducción. Objetivos: Comparar el ciclo reproductivo de M. capax en dos bancos ubicados a diferentes profundidades en la Ensenada de La Paz, B.C.S., México, y sus relaciones con las variables ambientales. La talla de primera madurez (L50) se estimó utilizando un modelo logístico para obtener el valor de longitud en el que el 50% de la población se encuen­tran maduros. Métodos: Se recolectaron aproximadamente 25 (± 4.5) especímenes, entre octubre de 2008 y diciembre de 2010, en un banco poco profundo de la zona intermareal (Banco A) y 23 (± 4) en un banco superficial profundo (Banco B). El tamaño en la primera madurez sexual (L50) se estimó utilizando un modelo logístico para obtener el tamaño en un 50% de madurez. Las evaluaciones mensuales de la información bio­lógica individual se complementaron con el análisis histológico de las gónadas, en diferentes momentos del ciclo reproductivo. Se estimó la relación entre los estadios de desarrollo gonadal y el índice gonadosomático, también su relación con la temperatura y la clorofila. Resultados: Los resultados indican que ocurrió un pico de desove en marzo (Banco A) y en enero en el otro (Banco B). En ambas localidades, las hembras maduras y en post-desove presentaron atresia folicular, hasta el 82% en el banco B. La L50 fue de 74.12 mm para el banco A y 71.74 mm para el B. El índice gonadosomático difirió entre bancos y se correlacionó positivamente con el aumento de clorofila-a (Banco A). Se observó una relación negativa significativa entre la temperatura y el estadio de madurez (Banco A). Conclusiones: El estudio de la reproducción de M. capax reveló que los bancos analizados presentan una periodicidad reproductiva diferente y que los cambios ambientales afectan la actividad reproductiva, favorecieron el desarrollo de atresia folicular

Experimental determination of the optimum working conditions of a transcritical CO2 refrigeration plant with integrated mechanical subcooling

Subcooling methods for transcritical CO2 plants are being studied in order to improve their behavior. Among them, the Integrated Mechanical Subcooling system is one of the most promising owing that performs with high efficiency and it is a total-CO2 system. This work presents the experimental determination of the optimum working conditions of a transcritical CO2 plant working with an integrated mechanical subcooling system. The plant was tested at different pressure and subcooling conditions in order to optimize the COP of the plant and determine the optimal conditions for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and evaporation levels between −15.6 °C and −4.1 °C. Optimum operating conditions were determined and two correlations are proposed to determine the optimal pressure and subcooling as function the gas-cooler outlet temperature and the evaporation level