4,376 research outputs found
Sensor Networks for Maritime Deployment: Modeling and Simulation
Simulation is widely used in Wireless Sensor Networks to assess the feasibility and performance of design decisions before the deployment, assisting the development of optimal solutions or trade-offs. In this paper, we address the particular case of a sensor network deployed at sea, where hundreds or thousands of sensing nodes drift with the stream and organise into a network capable of transmitting results to a remote station. A new simulator was built to address the particularities of the wireless models required to correctly understand the application scenario. The models provide realistic channel simulation, along with additive interference from other sources, where all transmissions are considered independently. The receiver decides which transmission was first and what is the level of noise from the environment and contending nodes. Network algorithms were implemented and compared using different network sizes and parameters. Results show that algorithms are sensitive to deployment conditions and respond differently to each set of environmental parameters
Nematoxic effect of essential oils and their fractions against the pinewood nematode, Bursaphelenchus xylophilus
The pinewood nematode (PWN) Bursaphelenchus xylophilus is a highly pathogenic
plant parasite that greatly affects pine forests. In Portugal, the most affected species is
Pinus pinaster Aiton. Despite great efforts, since its fist detection in 1999, the PWN has
spread through the country, including Madeira Island, having been recently detected in
Spain [1,2]. Containing this pest is of the utmost importance for European pine forest
safeguard.
Since most synthetic chemicals used to control phytoparasites are toxic to humans and
animals, and can accumulate in the soil and in food plants [3], in the present work, the
nematoxic potential of over 80 essential oils (EOs), isolated from the Portuguese flora,
were assessed against the PWN. EOs were isolated by hydrodistillation and analysed by
GC and GC-MS [3]. EOs hydrocarbon and oxygen-containing fractions were obtained as
in [4]. Direct-contact assays, adapted from [3], were performed by adding EOs/methanol
stock-solutions to 50-100 mixed-stage PWN suspensions. After 24h in darkness, dead
and live nematodes were counted under an inverted microscope. Assays were repeated
at least 10 times in two series.
Mortalities ≥96% were obtained with 2μL/mL of the EOs isolated from Cymbopogon
citratus, Eucalyptus citriodora, Mentha arvensis, Origanum virens, Origanum vulgare,
Ruta graveolens, Satureja montana, Syzygium aromaticum, Thymbra capitata, Thymus
caespititius (carvacrol and/or thymol-rich), Thymus vulgaris and Thymus zygis. These
EOs were further tested at 1, 0.5 and 0.25ÎĽL/mL. Minimum lethal concentrations (LC100)
<0.4ÎĽL/mL, were obtained for the 2-undecanone-rich R. graveolens EO and the carvacrol
and Îł-terpinene-rich S. montana and T. capitata EOs. Assays with EO fractions revealed
that the monoterpene-rich nematoxic EOs control PWN through their combined
hydrocarbon and oxygen-containing fractions through additive and/or synergic relations.
As complex mixtures of active components, EOs may prove to be effective nematoxic
age nts
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The retardation of growth in A. aegypti (L.) larvae exposed to the vital dyes methylene blue and neutral red.
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Some effects of overcrowding on the respiration of larval Aedes aegypti (L.).
Scalable wireless sensor networks for dynamic communication environments: simulation and modelling
This thesis explores the deployment of Wireless Sensor Networks (WSNs) on localised maritime events. In particular, it will focus on the deployment of a WSN at sea and estimating what challenges derive from the environment and how they affect communication. This research addresses these challenges through simulation and modelling of communication and environment, evaluating the implications of hardware selection and custom algorithm development. The first part of this thesis consists of the analysis of aspects related to the Medium Access Control layer of the network stack in large-scale networks. These details are commonly hidden from upper layers, thus resulting in misconceptions of real deployment characteristics. Results show that simple solutions have greater advantages when the number of nodes within a cluster increases. The second part considers routing techniques, with focus on energy management and packet delivery. It is shown that, under certain conditions, relaying data can increase energy savings, while at the same time allows a more even distribution of its usage between nodes. The third part describes the development of a custom-made network simulator. It starts by considering realistic radio, channel and interference models to allow a trustworthy simulation of the deployment environment. The MAC and Routing techniques developed thus far are adapted to the simulator in a cross-layer manner. The fourth part consists of adapting the WSN behaviour to the variable weather and topology found in the chosen application scenario. By analysing the algorithms presented in this work, it is possible to find and use the best alternative under any set of environmental conditions. This mechanism, the environment-aware engine, uses both network and sensing data to optimise performance through a set of rules that involve message delivery and distance between origin and cluster hea
Control of the pinewood nematode Bursaphelenchus xylophilus by essential oils and extracts obtained from plants: a review.
The pinewood nematode (PWN), Bursaphelenchus xylophilus, is a serious threat to
forest ecosystems at a global scale. The nematode has become a major quarantine
problem due to its capability to completely destroy Pinus spp. trees, with great damage to
the wood industry. Controlling the nematode inside a living tree is quite difficult, the
techniques used being often ineffective and quite expensive. In the coming years, most
chemicals used to control nematodes will be banned and replaced by safer and
environmentally friendly products. As so, chemicals naturally produced by plants will play
an important role in controlling diseases such as pine wilt. Plants, particularly aromatic
ones, are commonly used due to the chemical properties of their secondary metabolites.
Among these, essential oils and/or extracts are highly employed and are being tested as
possible control of some organisms, like nematodes. Recent publications have evaluated
essential oils derived from different plant species as natural nematicides [1; 2], antibacterial
[3], anti-fungal [4] as well as insecticidal [5]. Concerning control of the PWN, a
significant amount of information on plants tested, results obtained and employed
techniques, is available. Our revision has extensively gathered this information, making it
easier to search, read and use. It may become useful information for future studies on the
subject, since it will be possible to check the plants already tested. Although numbers
aren´t definitive, so far, tested plants are distributed amongst 148 families. The extracts or
essential oils of plants belonging to the Asteraceae, Lamiaceae and Euphorbiaceae
families show promising results on controlling the pinewood nematode
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