4,164 research outputs found
Transmission Power Measurements for Wireless Sensor Nodes and their Relationship to the Battery Level
In this work we focus on the new generation EYESIFXv2 [1] wireless sensor nodes by carrying out experimental measurements on power related quantities. In particular, our aim is to characterize the relationship between the level of the battery and the transmission power radiated by the node. The present results point out the non linear and non trivial effects due to the output potentiometer which can be used to tune the transmission power. It shall be observed that a thorough study of how battery and/or potentiometer settings translate to actual transmitted power levels is crucial to e.g. design correct power control algorithms, which can effectively operate under any operational condition of the wireless sensor device
The Role of Change Agent and Event Context in Sport-for-Development Projects
This study aims to contribute to the debate around the role of change agents and event contexts by providing a case study of the Spetses Mini Marathon event conducted in Spetses, an island located 54 nautical miles south of Athens, Greece. The idea of the event was conceived in 2010 by a private public relations and communication entity in Greece with the vision to stage an annual, mass participation sport event in collaboration with the local Municipality. Against the background of an economic crisis and an increasingly unstable political situation in the country that resulted in tensions in and between communities, the purpose of this study was to: (a) identify perceptions of various stakeholders towards the role of external private for-profit entities (i.e., change agents) in S4D event projects, (b) examine organizational matters that result in social impacts/outcomes for the host community through S4D projects, and (c) discuss the (potentially important role of the) event context and origin as the foundation for initiation and sustainability of S4D projects
Digital Phenotyping and Dynamic Monitoring of Adolescents Treated for Cancer to Guide Intervention: Embracing a New Era
Maximal Sharing in the Lambda Calculus with letrec
Increasing sharing in programs is desirable to compactify the code, and to
avoid duplication of reduction work at run-time, thereby speeding up execution.
We show how a maximal degree of sharing can be obtained for programs expressed
as terms in the lambda calculus with letrec. We introduce a notion of `maximal
compactness' for lambda-letrec-terms among all terms with the same infinite
unfolding. Instead of defined purely syntactically, this notion is based on a
graph semantics. lambda-letrec-terms are interpreted as first-order term graphs
so that unfolding equivalence between terms is preserved and reflected through
bisimilarity of the term graph interpretations. Compactness of the term graphs
can then be compared via functional bisimulation.
We describe practical and efficient methods for the following two problems:
transforming a lambda-letrec-term into a maximally compact form; and deciding
whether two lambda-letrec-terms are unfolding-equivalent. The transformation of
a lambda-letrec-term into maximally compact form proceeds in three
steps:
(i) translate L into its term graph ; (ii) compute the maximally
shared form of as its bisimulation collapse ; (iii) read back a
lambda-letrec-term from the term graph with the property . This guarantees that and have the same unfolding, and that
exhibits maximal sharing.
The procedure for deciding whether two given lambda-letrec-terms and
are unfolding-equivalent computes their term graph interpretations and , and checks whether these term graphs are bisimilar.
For illustration, we also provide a readily usable implementation.Comment: 18 pages, plus 19 pages appendi
Thermoelastic Damping in Micro- and Nano-Mechanical Systems
The importance of thermoelastic damping as a fundamental dissipation
mechanism for small-scale mechanical resonators is evaluated in light of recent
efforts to design high-Q micrometer- and nanometer-scale electro-mechanical
systems (MEMS and NEMS). The equations of linear thermoelasticity are used to
give a simple derivation for thermoelastic damping of small flexural vibrations
in thin beams. It is shown that Zener's well-known approximation by a
Lorentzian with a single thermal relaxation time slightly deviates from the
exact expression.Comment: 10 pages. Submitted to Phys. Rev.
Analysis of soil following a police-led open area search and the recovery of a cold-case homicide grave
Diffuse Gamma-Ray Emission from Starburst Galaxies and M31
We present a search for high energy gamma-ray emission from 9 nearby
starburst galaxies and M31 with the EGRET instrument aboard CGRO. Though the
diffuse gamma-ray emission from starburst galaxies was suspected to be
detectable, we find no emission from NGC 253, M82 nor from the average of all 9
galaxies. The 2 sigma upper limit for the EGRET flux above 100 MeV for the
averaged survey observations is 1.8 x 10-8 ph cm-2 s-1. From a model of the
expected radio and gamma-ray emission, we find that the magnetic field in the
nuclei of these galaxies is > 25 micro Gauss, and the ratio of proton and
electron densities is < 400. The EGRET limits indicate that the rate of massive
star formation in the survey galaxies is only about an order of magnitude
higher than in the Milky Way. The upper limit to the gamma-ray flux above 100
MeV for M31 is 1.6 x 10-8 ph cm-2 s-1. At the distance of M31, the Milky Way
flux would be over twice this value, indicating higher gamma-ray emissivities
in our Galaxy. Therefore, since the supernova rate of the Milky Way is higher
than in M31, our null detection of M31 supports the theory of the supernova
origin of cosmic rays in galaxies.Comment: 17 pages, plus 1 Postscript figure, AAS Latex macros v4.0, accepted
for publication in ApJ Main Journa
Bose-Einstein statistics in thermalization and photoluminescence of quantum well excitons
Quasi-equilibrium relaxational thermodynamics is developed to understand
LA-phonon-assisted thermalization of Bose-Einstein distributed excitons in
quantum wells. We study the quantum-statistical effects in the relaxational
dynamics of the effective temperature of excitons . When is less
than the degeneracy temperature , well-developed Bose-Einstein statistics
of quantum well excitons leads to nonexponential and density-dependent
thermalization. At low bath temperatures the thermalization of
quantum-statistically degenerate excitons effectively slows down and . We also analyze the optical decay of Bose-Einstein
distributed excitons in perfect quantum wells and show how nonclassical
statistics influences the effective lifetime . In particular,
of a strongly degenerate gas of excitons is given by ,
where is the intrinsic radiative lifetime of quasi-two-dimensional
excitons. Kinetics of resonant photoluminescence of quantum well excitons
during their thermalization is studied within the thermodynamic approach and
taking into account Bose-Einstein statistics. We find density-dependent
photoluminescence dynamics of statistically degenerate excitons. Numerical
modeling of the thermalization and photoluminescence kinetics of
quasi-two-dimensional excitons are given for GaAs/AlGaAs quantum wells.Comment: 19 pages, 9 figures. Phys. Rev. B (accepted for publication
Measures for pathway analysis in brain white matter using diffusion tensor images
In this paper we discuss new measures for connectivity analysis of brain white matter, using MR diffusion tensor imaging. Our approach is based on Riemannian geometry, the viability of which has been demonstrated by various researchers in foregoing work. In the Riemannian framework bundles of axons are represented by geodesies on the manifold. Here we do not discuss methods to compute these geodesies, nor do we rely on the availability of geodesies. Instead we propose local measures which are directly computable from the local DTI data, and which enable us to preselect viable or exclude uninteresting seed points for the potentially time consuming extraction of geodesies. If geodesies are available, our measures can be readily applied to these as well. We consider two types of geodesic measures. One pertains to the connectivity saliency of a geodesic, the second to its stability with respect to local spatial perturbations. For the first type of measure we consider both differential as well as integral measures for characterizing a geodesic's saliency either locally or globally. (In the latter case one needs to be in possession of the geodesic curve, in the former case a single tangent vector suffices.) The second type of measure is intrinsically local, and turns out to be related to a well known tensor in Riemannian geometry.</p
Unification of trap-limited electron transport in semiconducting polymers
Electron transport in semiconducting polymers is usually inferior to hole transport, which is ascribed to charge trapping on isolated defect sites situated within the energy bandgap. However, a general understanding of the origin of these omnipresent charge traps, as well as their energetic position, distribution and concentration, is lacking. Here we investigate electron transport in a wide range of semiconducting polymers by current-voltage measurements of single-carrier devices. We observe for this materials class that electron transport is limited by traps that exhibit a Gaussian energy distribution in the bandgap. Remarkably, the electron-trap distribution is identical for all polymers considered: the number of traps amounts to 3 × 1023 traps per m3 centred at an energy of ∼3.6 eV below the vacuum level, with a typical distribution width of ∼0.1 eV. This indicates that the electron traps have a common origin that, we suggest, is most likely related to hydrated oxygen complexes. A consequence of this finding is that the trap-limited electron current can be predicted for any polymer. © 2012 Macmillan Publishers Limited. All rights reserved
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