274 research outputs found
An objective based classification of aggregation techniques for wireless sensor networks
Wireless Sensor Networks have gained immense popularity in recent years due to their ever increasing capabilities and wide range of critical applications. A huge body of research efforts has been dedicated to find ways to utilize limited resources of these sensor nodes in an efficient manner. One of the common ways to minimize energy consumption has been aggregation of input data. We note that every aggregation technique has an improvement objective to achieve with respect to the output it produces. Each technique is designed to achieve some target e.g. reduce data size, minimize transmission energy, enhance accuracy etc. This paper presents a comprehensive survey of aggregation techniques that can be used in distributed manner to improve lifetime and energy conservation of wireless sensor networks. Main contribution of this work is proposal of a novel classification of such techniques based on the type of improvement they offer when applied to WSNs. Due to the existence of a myriad of definitions of aggregation, we first review the meaning of term aggregation that can be applied to WSN. The concept is then associated with the proposed classes. Each class of techniques is divided into a number of subclasses and a brief literature review of related work in WSN for each of these is also presented
A Bayesian strategy to enhance the performance of indoor localization systems
This work describes the probabilistic modelling af a Bayesian-based mechanism to improve location estimates of an already deployed location system by fusing its outputs with low-cost binary sensors. This mechanism takes advantege of the localization captabilities of different technologies usually present in smart environments deployments. The performance of the proposed algorithm over a real sensor deployment is evaluated using simulated and real experimental data
Phonon thermal conductivity in doped : Relevant scattering mechanisms
Results of in-plane and out-of-plane thermal conductivity measurements on
() single crystals are
presented. The most characteristic features of the temperature dependence are a
pronounced phonon peak at low temperatures and a steplike anomaly at ,
i.e., at the transition to the low temperature tetragonal phase (LTT-phase),
which gradually decrease with increasing Sr-content. Comparison of these
findings with the thermal conductivity of and clearly reveals that in the most effective
mechanism for phonon scattering is impurity-scattering (dopants), as well as
scattering by soft phonons that are associated with the lattice instability in
the low temperature orthorhombic phase (LTO-phase). There is no evidence that
stripe correlations play a major role in suppressing the phonon peak in the
thermal conductivity of .Comment: 7 pages, 4 figure
Improved understanding of self-sustained, sub-micrometric multi-composition surface Constantan wires interacting with H2 at high temperatures: experimental evidence of Anomalous Heat Effects
This article is an extension of what presented by our team at 17th International Conference on Cold Fusion, ICCF-17, in Daejon, Korea, in 2012 [1]. It documents the improvements on Constantan-related experiments, started in 2011, in order to study the feasibility of new Nickel based alloys that are able to absorb proper amounts of Hydrogen (H2) and/or Deuterium (D2) and that have, in principle, some possibility to generate anomalous thermal effects at temperatures >100°C. The interest in Ni comes in part because there is the possibility to use also H2 instead of expensive D2. Moreover, cross-comparison of results using H2 instead of D2 can be made and could help the understanding of the phenomena involved (atomic, nuclear, super-chemical origin?) due to the use of such isotopes. Keywords: calorimeter, LENR, Nickel based alloys, sub-micrometric surface
Breakup reaction models for two- and three-cluster projectiles
Breakup reactions are one of the main tools for the study of exotic nuclei,
and in particular of their continuum. In order to get valuable information from
measurements, a precise reaction model coupled to a fair description of the
projectile is needed. We assume that the projectile initially possesses a
cluster structure, which is revealed by the dissociation process. This
structure is described by a few-body Hamiltonian involving effective forces
between the clusters. Within this assumption, we review various reaction
models. In semiclassical models, the projectile-target relative motion is
described by a classical trajectory and the reaction properties are deduced by
solving a time-dependent Schroedinger equation. We then describe the principle
and variants of the eikonal approximation: the dynamical eikonal approximation,
the standard eikonal approximation, and a corrected version avoiding Coulomb
divergence. Finally, we present the continuum-discretized coupled-channel
method (CDCC), in which the Schroedinger equation is solved with the projectile
continuum approximated by square-integrable states. These models are first
illustrated by applications to two-cluster projectiles for studies of nuclei
far from stability and of reactions useful in astrophysics. Recent extensions
to three-cluster projectiles, like two-neutron halo nuclei, are then presented
and discussed. We end this review with some views of the future in
breakup-reaction theory.Comment: Will constitute a chapter of "Clusters in Nuclei - Vol.2." to be
published as a volume of "Lecture Notes in Physics" (Springer
Limits on the gravity wave contribution to microwave anisotropies
We present limits on the fraction of large angle microwave anisotropies which
could come from tensor perturbations. We use the COBE results as well as
smaller scale CMB observations, measurements of galaxy correlations, abundances
of galaxy clusters, and Lyman alpha absorption cloud statistics. Our aim is to
provide conservative limits on the tensor-to-scalar ratio for standard
inflationary models. For power-law inflation, for example, we find T/S<0.52 at
95% confidence, with a similar constraint for phi^p potentials. However, for
models with tensor amplitude unrelated to the scalar spectral index it is still
currently possible to have T/S>1.Comment: 23 pages, 7 figures, accepted for publication in Phys. Rev. D.
Calculations extended to blue spectral index, Fig. 6 added, discussion of
results expande
Interstellar MHD Turbulence and Star Formation
This chapter reviews the nature of turbulence in the Galactic interstellar
medium (ISM) and its connections to the star formation (SF) process. The ISM is
turbulent, magnetized, self-gravitating, and is subject to heating and cooling
processes that control its thermodynamic behavior. The turbulence in the warm
and hot ionized components of the ISM appears to be trans- or subsonic, and
thus to behave nearly incompressibly. However, the neutral warm and cold
components are highly compressible, as a consequence of both thermal
instability in the atomic gas and of moderately-to-strongly supersonic motions
in the roughly isothermal cold atomic and molecular components. Within this
context, we discuss: i) the production and statistical distribution of
turbulent density fluctuations in both isothermal and polytropic media; ii) the
nature of the clumps produced by thermal instability, noting that, contrary to
classical ideas, they in general accrete mass from their environment; iii) the
density-magnetic field correlation (or lack thereof) in turbulent density
fluctuations, as a consequence of the superposition of the different wave modes
in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio
(MFR) in density fluctuations as they are built up by dynamic compressions; v)
the formation of cold, dense clouds aided by thermal instability; vi) the
expectation that star-forming molecular clouds are likely to be undergoing
global gravitational contraction, rather than being near equilibrium, and vii)
the regulation of the star formation rate (SFR) in such gravitationally
contracting clouds by stellar feedback which, rather than keeping the clouds
from collapsing, evaporates and diperses them while they collapse.Comment: 43 pages. Invited chapter for the book "Magnetic Fields in Diffuse
Media", edited by Elisabete de Gouveia dal Pino and Alex Lazarian. Revised as
per referee's recommendation
Photoproduction of mesons off nuclei
Recent results for the photoproduction of mesons off nuclei are reviewed.
These experiments have been performed for two major lines of research related
to the properties of the strong interaction. The investigation of nucleon
resonances requires light nuclei as targets for the extraction of the isospin
composition of the electromagnetic excitations. This is done with quasi-free
meson photoproduction off the bound neutron and supplemented with the
measurement of coherent photoproduction reactions, serving as spin and/or
isospin filters. Furthermore, photoproduction from light and heavy nuclei is a
very efficient tool for the study of the interactions of mesons with nuclear
matter and the in-medium properties of hadrons. Experiments are currently
rapidly developing due to the combination of high quality tagged (and
polarized) photon beams with state-of-the-art 4pi detectors and polarized
targets
Comparative analysis of decision tree algorithms on quality of water contaminated with soil
The integrated Sachs-Wolfe Effect -- Large Scale Structure Correlation
We discuss the correlation between late-time integrated Sachs-Wolfe (ISW)
effect in the cosmic microwave background (CMB) temperature anisotropies and
the large scale structure of the local universe. This correlation has been
proposed and studied in the literature as a probe of the dark energy and its
physical properties. We consider a variety of large scale structure tracers
suitable for a detection of the ISW effect via a cross-correlation. In addition
to luminous sources, we suggest the use of tracers such as dark matter halos or
galaxy clusters. A suitable catalog of mass selected halos for this purpose can
be constructed with upcoming wide-field lensing and Sunyaev-Zel'dovich (SZ)
effect surveys. With multifrequency data, the presence of the ISW-large scale
structure correlation can also be investigated through a cross-correlation of
the frequency cleaned SZ and CMB maps. While convergence maps constructed from
lensing surveys of the large scale structure via galaxy ellipticities are less
correlated with the ISW effect, lensing potentials that deflect CMB photons are
strongly correlated and allow, probably, the best mechanism to study the
ISW-large scale structure correlation with CMB data alone.Comment: 10 Pages, PRD submitte
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