1,359 research outputs found
1-D Coordinate Based on Local Information for MAC and Routing Issues in WSNs
More and more critical Wireless Sensor Networks (WSNs) applications are
emerging. Those applications need reliability and respect of time constraints.
The underlying mechanisms such as MAC and routing must handle such
requirements. Our approach to the time constraint problem is to bound the
hop-count between a node and the sink and the time it takes to do a hop so the
end-to-end delay can be bounded and the communications are thus real-time. For
reliability purpose we propose to select forwarder nodes depending on how they
are connected in the direction of the sink. In order to be able to do so we
need a coordinate (or a metric) that gives information on hop-count, that
allows to strongly differentiate nodes and gives information on the
connectivity of each node keeping in mind the intrinsic constraints of WSWs
such as energy consumption, autonomy, etc. Due to the efficiency and
scalability of greedy routing in WSNs and the financial cost of GPS chips,
Virtual Coordinate Systems (VCSs) for WSNs have been proposed. A category of
VCSs is based on the hop-count from the sink, this scheme leads to many nodes
having the same coordinate. The main advantage of this system is that the hops
number of a packet from a source to the sink is known. Nevertheless, it does
not allow to differentiate the nodes with the same hop-count. In this report we
propose a novel hop-count-based VCS which aims at classifying the nodes having
the same hop-count depending on their connectivity and at differentiating nodes
in a 2-hop neighborhood. Those properties make the coordinates, which also can
be viewed as a local identifier, a very powerful metric which can be used in
WSNs mechanisms.Comment: (2011
Short Term Topological Changes of Coronal Holes Associated with Prominence Eruptions and Subsequent CMEs
We study the short--term topological changes of equatorial and polar coronal
hole (CH) boundaries, such as a variation of their area and disintegration,
associated to reconnection with nearby (within 15 distance) quiescent
prominence magnetic fields leading to eruptions and subsequent Coronal Mass
Ejections (CMEs). The examples presented here correspond to the recent solar
minimum years 2008 and 2009. We consider a temporal window of one day between
the CH topological changes and the start and end times of prominence eruptions
and onset of CMEs. To establish this association we took into account
observational conditions related to the instability of prominence/filaments,
the occurrence of a CME, as well as the subsequent evolution after the CME. We
found an association between short--term local topological changes in CH
boundaries and the formation/disappearance of bright points near them, as well
as, between short--term topological changes within the whole CH and eruptions
of nearby quiescent prominences followed by the appearance of one or more CMEs.Comment: 15 pages, 11 figures; Journal Advances Space Research (2012
RTXP : A Localized Real-Time Mac-Routing Protocol for Wireless Sensor Networks
Protocols developed during the last years for Wireless Sensor Networks (WSNs)
are mainly focused on energy efficiency and autonomous mechanisms (e.g.
self-organization, self-configuration, etc). Nevertheless, with new WSN
applications, appear new QoS requirements such as time constraints. Real-time
applications require the packets to be delivered before a known time bound
which depends on the application requirements. We particularly focus on
applications which consist in alarms sent to the sink node. We propose
Real-Time X-layer Protocol (RTXP), a real-time communication protocol. To the
best of our knowledge, RTXP is the first MAC and routing real-time
communication protocol that is not centralized, but instead relies only on
local information. The solution is cross-layer (X-layer) because it allows to
control the delays due to MAC and Routing layers interactions. RTXP uses a
suited hop-count-based Virtual Coordinate System which allows deterministic
medium access and forwarder selection. In this paper we describe the protocol
mechanisms. We give theoretical bound on the end-to-end delay and the capacity
of the protocol. Intensive simulation results confirm the theoretical
predictions and allow to compare with a real-time centralized solution. RTXP is
also simulated under harsh radio channel, in this case the radio link
introduces probabilistic behavior. Nevertheless, we show that RTXP it performs
better than a non-deterministic solution. It thus advocates for the usefulness
of designing real-time (deterministic) protocols even for highly unreliable
networks such as WSNs
Relationship between perceived leadership qualities of the coaches of the Major Indoor Lacrosse League teams and athletes\u27 perceived team climate
This study investigated the relationship between perceived leadership qualities of the coaches of the Major Indoor Lacrosse League (MILL) teams and athletes\u27 perceived team climate.
[This is an excerpt from the abstract. For the complete abstract, please see the document.
Simulating ice processes using the finite element, unstructured, adaptive model fluidity
The cryosphere impacts global climate in various ways. Snow and ice have a higher albedo than land or the open ocean and therefore affect the total reflectivity of the earth. Sea ice forms an insulating layer over the polar oceans controlling both heat and water vapour fluxes between the atmosphere and polar ocean. Ice sheets hold around 77% of Earth's freshwater reserves, and recent increases in ice loss from the Earth's ice sheets are cause for concern. This thesis develops numerical tools that can be used for the study of various ice processes such as ocean -- sea ice interaction, ice sheet and glacier dynamics.
A coupled ocean - sea ice model is developed, using the open source, unstructured, adaptive ocean model Fluidity and a finite element sea ice model developed at the Alfred Wegener Institute of Polar and Marine Research, FESIM. The tightly coupled model is verified and validated through a series of tests, demonstrating its dynamical capabilities. The sea ice dynamics are a model of Elastic-Viscous-Plastic rheology, as described in Hunke and Dukowicz. The thermodynamic parameterisation is similar to the 1D simplest model of Parkinson and Washington which is based on the zero-layer approach of Semtner.
Furthermore, a new computational framework for carrying out ice sheet simulations is presented. A thermo-mechanical, non-linear, full-Stokes model is used to carry out the exercises of the Ice Sheet Model Intercomparison Project for higher--order models (ISMIP--HOM). The results presented here show that Fluidity compares favourably with other ice sheet models. Further tests are performed to demonstrate the use of dynamic adaptive remeshing in lowering the computational cost of models compared to their structured, fixed-mesh counterparts, by focusing resolution only where and when required. Finally, initial simulations of the full Greenland ice sheet are performed demonstrating the potential utility of adaptive meshes for large-scale, full-Stokes modelling.Open Acces
Rectangular Photonic Crystal Nanobeam Cavities in Bulk Diamond
We demonstrate the fabrication of photonic crystal nanobeam cavities with
rectangular cross section into bulk diamond. In simulation, these cavities have
an unloaded quality factor (Q) of over 1 million. Measured cavity resonances
show fundamental modes with spectrometer-limited quality factors larger than
14,000 within 1nm of the NV center's zero phonon line at 637nm. We find high
cavity yield across the full diamond chip with deterministic resonance trends
across the fabricated parameter sweeps
Remote monitoring of patient vital signs for personalized healthcare
Remote vital monitoring has the potential to vastly improve outcomes in assisted living, patient care, rehabilitation, and athletic performance. The emergence of compact sensors coupled with ease of access to wirelessly connected mobile technologies has propelled remote monitoring to the forefront of healthcare. A challenge associated with this field is the filtering of large datasets: for systems to be useful to patients and practitioners data must be both easily accessible and actionable. In this session we will present the development of a suite of real-time wireless biphotonic sensors for connected health. From cuff-less and accurate blood pressure to heart rate and SpO2, we have developed a full stack remote patient monitoring system that can be used in numerous health and wellness scenarios. In particular we will address issues of reading, transmitting, storing, and analyzing data in the clou
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