Optimal Fair Scheduling in S-TDMA Sensor Networks for Monitoring River Plumes

Underwater wireless sensor networks (UWSNs) are a promising technology to provide oceanographers with environmental data in real time. Suitable network topologies to monitor estuaries are formed by strings coming together to a sink node.This network may be understood as an oriented graph. A number of MAC techniques can be used in UWSNs, but Spatial-TDMA is preferred for fixed networks. In this paper, a scheduling procedure to obtain the optimal fair frame is presented, under ideal conditions of synchronization and transmission errors. The main objective is to find the theoretical maximum throughput by overlapping the transmissions of the nodes while keeping a balanced received data rate from each sensor, regardless of its location in the network. The procedure searches for all cliques of the compatibility matrix of the network graph and solves a Multiple-Vector Bin Packing (MVBP) problem. This work addresses the optimization problem and provides analytical and numerical results for both the minimum frame length and the maximum achievable throughput

Altruism through experience - framework and experiment

The aim of this study is to investigate whether past experience affects ones altruism. Does having been poor makes a person more altruistic when rich, does her concept of fairness change as it gets richer? An adaption of the classic Public Goods Game with heterogeneous endowments was used for the purpose

Operación multihop eficiente en redes acústicas submarinas de sensores con planificación TDMA

Dos de los problemas a los que se enfrentan las comunicaciones inalámbricas submarinas, y que limitan sobremanera la velocidad de transmisión de los datos, son (i) la atenuación en el medio acuático, que es selectiva en frecuencia, y (ii) el alto retardo de propagación. El primer factor, obliga a usar frecuencias bajas (acústicas), con una consiguiente degradación en la velocidad de transmisión de datos, que limita las aplicaciones posibles. El segundo problema, hace que las técnicas empleadas para el acceso y transmisión de los nodos (capa de enlace OSI o MAC), deban ser lo más eficientes posible para no demorar en demasía la entrega de datos. En concreto, en esta comunicación abordamos el problema de una red de nodos con sensores que pretende ser diseñada para minimizar el impacto de los dos problemas anteriormente citados. Para ello, se establece una técnica TDMA en el acceso al medio y se estudia el efecto que tiene una disciplina de servicio para la capa MAC para transmitir paquetes, basada en una cola FIFO con prioridad, bajo una planificación eficiente de transmisiones en la red. Se plantean distintos escenarios de tráfico generado uniforme o no uniforme por los nodos sensores, además de introducir una métrica (índice de Gini) para la uniformidad de paquetes entregados al Gateway por cada nodo, que es un criterio para que la red sea justa (fairness). Como resultados, se aportan medidas de throughput, retardo extremo a extremo de los paquetes, así como tamaño medio y máximo de las colas de cada nodo.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Imaging study of NGC 3372, the Carina nebula : I. UBVRIJHK photometry of Tr 14, Tr 15, Tr 16 and Car I

We present the results of a large-scale imaging photometric study of the stellar population in the northern part of NGC 3372 in the UBVRIJHK bands with a wavelength coverage from 0.33 to 2.5 μm. The observations were made at Las Campanas Observatory. The optical CCD mosaics cover an area approximately of 32 × 22 arcmin2 centred between the Tr 14 and Tr 16 clusters. The survey was extended to cover 12 × 12 arcmin2 at the location of Tr 15. Near-infrared NICMOS3 mosaics covering the areas occupied by these clusters were obtained in the JHK photometric bands. By means of star counts in V, the centres and sizes of each cluster were redetermined yielding: Tr 14 (r = 264 arcsec), Tr 15 (r = 320 arcsec) and Tr 16 (r = 320 arcsec). It was confirmed that Cr 232 is not a true cluster. Multicolour optical photometry was obtained for 4152 stars. Two colour and colour-magnitude diagrams are presented and analysed for each individual cluster and compared to those of the field. We confirm the widespread variations in the dust density and also in the dust size distribution leading to widely different values of AV and reddening laws towards Tr 14 and Tr 16. No spatial patterns were found for these variations. Spectroscopic parallaxes were computed and the results are consistent with all three clusters being at a similar distance from the Sun (〈d〉 = 2.7 kpc) but the data have shown very large scatter in both AV and d. Analyses of the extinction-corrected colour-magnitude diagrams suggest ages between 3 and 60 million years for the stars in Tr 15 and between less than 1 and 6 million years for Tr 14 and Tr 16. A small number of infrared-excess stars were found in Tr 16 and Tr 14 but not in Tr 15. The distribution of stars in Tr 14 seen in the near-infrared suggests that this cluster is partially embedded in a molecular cloud. This molecular cloud extends towards the west reaching its highest density, marked by a CO peak emission, some three arcmin to the south-west of the nucleus of Tr 14. The rich ultraviolet field created by the Tr 14 stars ionizes most of the visible H II region in its vicinity and most of the radio H II region Car I. Evidence is found of ionization fronts leading into the molecular cloud, which appears to be 'wrapping' the Tr 14 cluster. Deep JHK images of the Car I region reveal the presence of an embedded stellar population illuminating a large infrared reflection nebula. It includes at least one O9-B0 star associated with an ultracompact H II region. Nebulous 2.2 μm emission from three of the mid-infrared sources in the Tr 14 region is also found.Facultad de Ciencias Astronómicas y Geofísica

Imaging study of NGC 3372, the Carina nebula : I. UBVRIJHK photometry of Tr 14, Tr 15, Tr 16 and Car I

We present the results of a large-scale imaging photometric study of the stellar population in the northern part of NGC 3372 in the UBVRIJHK bands with a wavelength coverage from 0.33 to 2.5 μm. The observations were made at Las Campanas Observatory. The optical CCD mosaics cover an area approximately of 32 × 22 arcmin2 centred between the Tr 14 and Tr 16 clusters. The survey was extended to cover 12 × 12 arcmin2 at the location of Tr 15. Near-infrared NICMOS3 mosaics covering the areas occupied by these clusters were obtained in the JHK photometric bands. By means of star counts in V, the centres and sizes of each cluster were redetermined yielding: Tr 14 (r = 264 arcsec), Tr 15 (r = 320 arcsec) and Tr 16 (r = 320 arcsec). It was confirmed that Cr 232 is not a true cluster. Multicolour optical photometry was obtained for 4152 stars. Two colour and colour-magnitude diagrams are presented and analysed for each individual cluster and compared to those of the field. We confirm the widespread variations in the dust density and also in the dust size distribution leading to widely different values of AV and reddening laws towards Tr 14 and Tr 16. No spatial patterns were found for these variations. Spectroscopic parallaxes were computed and the results are consistent with all three clusters being at a similar distance from the Sun (〈d〉 = 2.7 kpc) but the data have shown very large scatter in both AV and d. Analyses of the extinction-corrected colour-magnitude diagrams suggest ages between 3 and 60 million years for the stars in Tr 15 and between less than 1 and 6 million years for Tr 14 and Tr 16. A small number of infrared-excess stars were found in Tr 16 and Tr 14 but not in Tr 15. The distribution of stars in Tr 14 seen in the near-infrared suggests that this cluster is partially embedded in a molecular cloud. This molecular cloud extends towards the west reaching its highest density, marked by a CO peak emission, some three arcmin to the south-west of the nucleus of Tr 14. The rich ultraviolet field created by the Tr 14 stars ionizes most of the visible H II region in its vicinity and most of the radio H II region Car I. Evidence is found of ionization fronts leading into the molecular cloud, which appears to be 'wrapping' the Tr 14 cluster. Deep JHK images of the Car I region reveal the presence of an embedded stellar population illuminating a large infrared reflection nebula. It includes at least one O9-B0 star associated with an ultracompact H II region. Nebulous 2.2 μm emission from three of the mid-infrared sources in the Tr 14 region is also found.Facultad de Ciencias Astronómicas y Geofísica

An energy-efficient integration of a digital modulator and a Class-D amplifier

Energy consumption is always a key feature in devices powered by electric accumulators. The power amplifier is the most energy-demanding module in mobile devices, portable appliances, static transceivers, and even nodes used in underwater acoustic networks. These devices incorporate a modulator, typically a pulse-width modulation (PWM) and a class-D power amplifier, for higher efficiency. We propose a technique to integrate the modulator of a transmitter and PW-modulator of a class-D amplifier to improve the overall efficiency of the system. This integrated set operates as an up-converter, phase modulator (PM), and binary phase-shift keying (BPSK) modulator under certain conditions. The theoretical concept is verified using Matlab and a model is designed and simulated in Simulink. For validation purposes, an electronic circuit is built and tested using Multisim. The results obtained by simulations and circuit implementation show that the proposed integrated system is an energy-efficient and cost-effective solution compared to conventional techniques