Coordination of Mobile Mules via Facility Location Strategies

In this paper, we study the problem of wireless sensor network (WSN) maintenance using mobile entities called mules. The mules are deployed in the area of the WSN in such a way that would minimize the time it takes them to reach a failed sensor and fix it. The mules must constantly optimize their collective deployment to account for occupied mules. The objective is to define the optimal deployment and task allocation strategy for the mules, so that the sensors' downtime and the mules' traveling distance are minimized. Our solutions are inspired by research in the field of computational geometry and the design of our algorithms is based on state of the art approximation algorithms for the classical problem of facility location. Our empirical results demonstrate how cooperation enhances the team's performance, and indicate that a combination of k-Median based deployment with closest-available task allocation provides the best results in terms of minimizing the sensors' downtime but is inefficient in terms of the mules' travel distance. A k-Centroid based deployment produces good results in both criteria.Comment: 12 pages, 6 figures, conferenc

Context-Aware Scenarios : Course on Context-Aware Computing 2003

According to a recent definition by Dey and Abowd context is any information that can be used to characterize the situation of an entity. An entity is a person, place or object that is considered relevant to the interaction between a user and an application, including the user and the application themselves. A system is context-aware if it uses context to provide relevant information and/or services to the user, where relevancy depends on the user's task. The following report contains ten scenarios about how context-aware applications could affect ordinary persons in fifteen years. The scenarios have been written by students participating in a course on context-aware computing in the autumn of 2003.Peer reviewe

A Hitchhiker’s Guide to Invasion Biology: Describing the Ecological Mechanisms Underlying the Range Expansions of Two Ixodid Tick Species

Increasing incidence of many tick-borne diseases have been linked to recent expansions of tick species distributions. Many tick species are expanding their ranges because of anthropogenic changes in the landscape, shifting climatic variables, and increasing populations of suitable host species and tick habitat. Few empirical studies have been performed, however, investigating the ecological mechanisms underlying these range expansions. Ticks are parasitic organisms that disperse across landscape by hitchhiking on hosts, but must then survive in the environment for long periods of time between bloodmeals. Two species of ixodid tick, Ixodes affinis and Amblyomma maculatum, are simultaneously expanding their ranges throughout the Mid-Atlantic region of the United States, and provide a case study from which to examine the relative importance of host choice and apparent habitat preference in the resulting patterns of range expansion. The first objective of this research was to use field studies to describe the life history of each of these species in Virginia, and determine important host and habitat characteristics for the survival and expansion of these species in the Mid-Atlantic. Tick surveillance data were collected over five years in a variety of habitats throughout southeastern Virginia. These data were used to answer basic natural history questions about these ticks in novel habitats, including determining tick abundance and phenology, as well as habitat and host preferences. Although both tick species parasitized many of the same host species, differences in the habitat conditions necessary for tick population establishment resulted in different patterns of invasion. Understanding how and where these ticks establish is useful in understanding the public health risks associated with areas being invaded. The second objective of this research was to determine the ancestry of the northern populations of these ticks, using genetic connectivity among populations to determine the mostly likely pathways for dispersal from ancestral populations to the Mid-Atlantic. Despite overlapping host preferences throughout ontogeny, each species exhibited very different genetic and geographic patterns of population establishment and connectivity. Genetic evidence suggests that these species may rely on different key life stages to disperse successfully into novel environments, and that host vagility, habitat stability and habitat connectivity all play critical roles in the establishment of new tick populations. The third objective of this research was to use metrics derived from field and genetic studies to parameterize agent-based models, simulating tick range expansions under different habitat and host conditions. Incorporating parameter values specific to I. affinis and A. maculatum life history, host ranges, habitat preferences, and genetic diversity allowed for hypothesis testing on whether habitats or hosts have greater influences on the invasions of these species in the Mid-Atlantic. This research describes the first comparative case study of two tick species with unique host and habitat preferences dispersing simultaneously across a landscape, and increases our understanding of the relative importance of hosts and habitat in hitchhiker invasions

An approach driven by mobile agents for data management in vehicular networks

In the last years, and thanks to improvements on computing and communications technologies, wireless networks formed by vehicles (called vehicular networks) have emerged as a key topic of interest. In these networks, the vehicles can exchange data by using short-range radio signals in order to get useful information related to traffic conditions, road safety, and other aspects. The availability of different types of sensors can be exploited by the vehicles to measure many parameters from their surroundings. These data can then be shared with other drivers who, on the other side, could also explicitly submit queries to retrieve information available in the network. This can be a challenging task, since the data is scattered among the vehicles belonging to the network and the communication links among them have usually a short life due to their constant movement. In this paper, we use mobile agent technology to help to accomplish these tasks, since mobile agents have a number of features that are very well suited for mobile environments, such as autonomy, mobility, and intelligence. Specifically, we analyze the benefits that mobile agents can bring to vehicular networks and the potential difficulties for their adoption. Moreover, we describe a query processing approach based on the use of mobile agents. We focus on range queries that retrieve interesting information from the vehicles located within a geographic area, and perform an extensive experimental evaluation that shows the feasibility and the interest of the proposal

Accessing Space: A Catalogue of Process, Equipment and Resources for Commercial Users, 1990

A catalogue is presented which is intended for commercial developers who are considering, or who have in progress, a project involving the microgravity environment of space or remote sensing of the Earth. An orientation is given to commercial space activities along with a current inventory of equipment, apparatus, carriers, vehicles, resources, and services available from NASA, other government agencies and U.S. industry. The information describes the array of resources that commercial users should consider when planning ground or space based developments. Many items listed have flown in space or been tested in labs and aboard aircraft and can be reused, revitalized, or adapted to suit specific requirements. New commercial ventures are encouraged to exploit existing inventory and expertise to the greatest extent possible

Distributed Data Management in Vehicular Networks Using Mobile Agents

En los últimos años, las tecnologías de la información y las comunicaciones se han incorporado al mundo de la automoción gracias a sus avances, y han permitido la creación de dispositivos cada vez más pequeños y potentes. De esta forma, los vehículos pueden ahora incorporar por un precio asequible equipos informáticos y de comunicaciones.En este escenario, los vehículos que circulan por una determinada zona (como una ciudad o una autopista) pueden comunicarse entre ellos usando dispositivos inalámbricos que les permiten intercambiar información con otros vehículos cercanos, formando así una red vehicular ad hoc, o VANET (Vehicular Ad hoc Network). En este tipo de redes, las comunicaciones se establecen con conexiones punto a punto por medio de dispositivos tipo Wi-Fi, que permiten la comunicación con otros del mismo tipo dentro de su alcance, sin que sea necesaria la existencia previa de una infraestructura de comunicaciones como ocurre con las tecnologías de telefonía móvil (como 3G/4G), que además requieren de una suscripción y el pago de una tarifa para poder usarlas.Cada vehículo puede enviar información y recibirla de diversos orígenes, como el propio vehículo (por medio de los sensores que lleva incorporados), otros vehículos que se encuentran cerca, así como de la infraestructura de tráfico presente en las carreteras (como semáforos, señales, paneles electrónicos de información, cámaras de vigilancia, etc.). Todos estas fuentes pueden transmitir datos de diversa índole, como información de interés para los conductores (por ejemplo, atascos de tráfico o accidentes en la vía), o de cualquier otro tipo, mientras sea posible digitalizarla y enviarla a través de una red.Todos esos datos pueden ser almacenados localmente en los ordenadores que llevan los vehículos a medida que son recibidos, y sería muy interesante poder sacarles partido por medio de alguna aplicación que los explotara. Por ejemplo, podrían utilizarse los vehículos como plataformas móviles de sensores que obtengan datos de los lugares por los que viajan. Otro ejemplo de aplicación sería la de ayudar a encontrar plazas de aparcamiento libres en una zona de una ciudad, usando la información que suministrarían los vehículos que dejan una plaza libre.Con este fin, en esta tesis se ha desarrollado una propuesta de la gestión de datos basada en el uso de agentes móviles para poder hacer uso de la información presente en una VANET de forma eficiente y flexible. Esta no es una tarea trivial, ya que los datos se encuentran dispersos entre los vehículos que forman la red, y dichos vehículos están constantemente moviéndose y cambiando de posición. Esto hace que las conexiones de red establecidas entre ellos sean inestables y de corta duración, ya que están constantemente creándose y destruyéndose a medida que los vehículos entran y salen del alcance de sus comunicaciones debido a sus movimientos.En un escenario tan complicado, la aproximación que proponemos permite que los datos sean localizados, y que se puedan hacer consultas sobre ellos y transmitirlos de un sitio cualquiera de la VANET a otro, usando estrategias multi-salto que se adaptan a las siempre cambiantes posiciones de los vehículos. Esto es posible gracias a la utilización de agentes móviles para el procesamiento de datos, ya que cuentan con una serie de propiedades (como su movilidad, autonomía, adaptabilidad, o inteligencia), que hace que sean una elección muy apropiada para este tipo de entorno móvil y con un elevado grado de incertidumbre.La solución propuesta ha sido extensamente evaluada y probada por medio de simulaciones, que demuestran su buen rendimiento y fiabilidad en redes vehiculares con diferentes condiciones y en diversos escenarios.<br /

20 IS PLENTY: THE MOST INFAMOUS OF THE INVASIVE SPECIES

This informational resource was created to assist the general public in learning about the importance of invasive insects and provide help in identifying some of the most dangerous among them. This guide will also provide current information about prevention and control of these insects along with what high risk items travelers should be careful of returning with from abroad to control the spread of these pests. This resource also covers inter-state as well as intra-state pests of concern, illustrating the importance of adhering to quarantine guidelines while traveling through these regions. Whether or not this pest has become established, it is important for the public to be aware of their impact on controlling the spread of these extremely dangerous organisms. The effects these insects can have on the economy, human health and quality of life, can directly impact each and every one of us in some way. The pests listed contain their common name, scientific name, and sometimes an applicable abbreviation. These abbreviations are the ones often used by the United States Department of Agriculture (USDA), and are utilized in this resource for the sake of brevity and familiarity. This guide is written in an easy to understand and pleasant to read format, which is often difficult to find when trying to find out more about these pests in one centralized location. Each of us have the power to drastically minimize, if not eliminate, the risk of introducing one of these dangerous pests to other areas. One individual makes a difference, no matter how small the pest, because sometimes, it literally only takes one…and it’s done

Technology for large space systems: A bibliography with indexes (supplement 13)

This bibliography lists 399 reports, articles and other documents introduced into the NASA scientific and technical information system between January 1, 1985 and June 30, 1985. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems

The assessment of cadmium, chromium, copper, and nickel tolerance and bioaccumulation by shrub plant Tetraena qataranse

Heavy metals constitute some of the most significant environmental contaminants today. The abundance of naturally growing Tetraena qataranse around Ras Laffan oil and gas facilities in the state of Qatar reflects its toxitolerant character. This study examined the desert plant’s tolerance to Ba, Cd, Cr, Cu, Ni and Pb relative to soil concentration. Analysis by inductively coupled plasma – optical emission spectroscopy (ICP-OES) showed that the plant biomass accumulates higher Cd, Cr, Cu and Ni concentration than the soil, particularly in the root. The bioconcentration factor (BCF) of all metals in the root and shoot indicates the plant’s capacity to accumulate these metals. Cd had a translocation factor (TF) greater than one; however, it is less than one for all other metals, suggesting that the plant remediate Cd by phytoextraction, where it accumulates in the shoot and Cr, Cu and Ni through phytostabilization, concentrating the metals in the root. Metals phytostabilization restrict transport, shield animals from toxic species ingestion, and consequently prevent transmission across the food chain. Fourier Transform Infrared Spectroscopy (FTIR) analysis further corroborates ICP-OES quantitative data. Our results suggest that T. qataranse is tolerant of Cd, Cr, Cu, and Ni. Potentially, these metals can accumulate at higher concentration than shown here; hence, T. qataranse is a suitable candidate for toxic metals phytostabilization. © 2019, The Author(s).Qatar University's student grant QUST-CAS-SPR-2017-33 supports this study. The authors also wish to acknowledge the Environmental Studies Center (ESC) and Central Laboratory Unit at Qatar University for providing support to ICP-OES and FTIR analysis, respectively. We thank Dr. Chaevien S. Clandinen for the critical reading and language editing of revised manuscript. The publication of this article was funded by Qatar National Library.Scopu