673 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
Dynamical electron transport through a nanoelectromechanical wire in a magnetic field
We investigate dynamical transport properties of interacting electrons moving
in a vibrating nanoelectromechanical wire in a magnetic field. We have built an
exactly solvable model in which electric current and mechanical oscillation are
treated fully quantum mechanically on an equal footing. Quantum mechanically
fluctuating Aharonov-Bohm phases obtained by the electrons cause nontrivial
contribution to mechanical vibration and electrical conduction of the wire. We
demonstrate our theory by calculating the admittance of the wire which are
influenced by the multiple interplay between the mechanical and the electrical
energy scales, magnetic field strength, and the electron-electron interaction
Fabry-Perot interference and spin filtering in carbon nanotubes
We study the two-terminal transport properties of a metallic single-walled
carbon nanotube with good contacts to electrodes, which have recently been
shown [W. Liang et al, Nature 441, 665-669 (2001)] to conduct ballistically
with weak backscattering occurring mainly at the two contacts. The measured
conductance, as a function of bias and gate voltages, shows an oscillating
pattern of quantum interference. We show how such patterns can be understood
and calculated, taking into account Luttinger liquid effects resulting from
strong Coulomb interactions in the nanotube. We treat back-scattering in the
contacts perturbatively and use the Keldysh formalism to treat non-equilibrium
effects due to the non-zero bias voltage. Going beyond current experiments, we
include the effects of possible ferromagnetic polarization of the leads to
describe spin transport in carbon nanotubes. We thereby describe both
incoherent spin injection and coherent resonant spin transport between the two
leads. Spin currents can be produced in both ways, but only the latter allow
this spin current to be controlled using an external gate. In all cases, the
spin currents, charge currents, and magnetization of the nanotube exhibit
components varying quasiperiodically with bias voltage, approximately as a
superposition of periodic interference oscillations of spin- and
charge-carrying ``quasiparticles'' in the nanotube, each with its own period.
The amplitude of the higher-period signal is largest in single-mode quantum
wires, and is somewhat suppressed in metallic nanotubes due to their sub-band
degeneracy.Comment: 12 pages, 6 figure
High-throughput avian molecular sexing by SYBR green-based real-time PCR combined with melting curve analysis
<p>Abstract</p> <p>Background</p> <p>Combination of <it>CHD </it>(chromo-helicase-DNA binding protein)-specific polymerase chain reaction (PCR) with electrophoresis (PCR/electrophoresis) is the most common avian molecular sexing technique but it is lab-intensive and gel-required. Gender determination often fails when the difference in length between the PCR products of <it>CHD-Z </it>and <it>CHD-W </it>genes is too short to be resolved.</p> <p>Results</p> <p>Here, we are the first to introduce a PCR-melting curve analysis (PCR/MCA) to identify the gender of birds by genomic DNA, which is gel-free, quick, and inexpensive. <it>Spilornis cheela hoya </it>(<it>S. c. hoya</it>) and <it>Pycnonotus sinensis </it>(<it>P. sinensis</it>) were used to illustrate this novel molecular sexing technique. The difference in the length of <it>CHD </it>genes in <it>S. c. hoya </it>and <it>P. sinensis </it>is 13-, and 52-bp, respectively. Using Griffiths' P2/P8 primers, molecular sexing failed both in PCR/electrophoresis of <it>S. c. hoya </it>and in PCR/MCA of <it>S. c. hoya </it>and <it>P. sinensis</it>. In contrast, we redesigned sex-specific primers to yield 185- and 112-bp PCR products for the <it>CHD-Z </it>and <it>CHD-W </it>genes of <it>S. c. hoya</it>, respectively, using PCR/MCA. Using this specific primer set, at least 13 samples of <it>S. c. hoya </it>were examined simultaneously and the Tm peaks of <it>CHD-Z </it>and <it>CHD-W </it>PCR products were distinguished.</p> <p>Conclusion</p> <p>In this study, we introduced a high-throughput avian molecular sexing technique and successfully applied it to two species. This new method holds a great potential for use in high throughput sexing of other avian species, as well.</p
Dark energy as a mirage
Motivated by the observed cosmic matter distribution, we present the
following conjecture: due to the formation of voids and opaque structures, the
average matter density on the path of the light from the well-observed objects
changes from Omega_M ~ 1 in the homogeneous early universe to Omega_M ~ 0 in
the clumpy late universe, so that the average expansion rate increases along
our line of sight from EdS expansion Ht ~ 2/3 at high redshifts to free
expansion Ht ~ 1 at low redshifts. To calculate the modified observable
distance-redshift relations, we introduce a generalized Dyer-Roeder method that
allows for two crucial physical properties of the universe: inhomogeneities in
the expansion rate and the growth of the nonlinear structures. By treating the
transition redshift to the void-dominated era as a free parameter, we find a
phenomenological fit to the observations from the CMB anisotropy, the position
of the baryon oscillation peak, the magnitude-redshift relations of type Ia
supernovae, the local Hubble flow and the nucleosynthesis, resulting in a
concordant model of the universe with 90% dark matter, 10% baryons, no dark
energy, 15 Gyr as the age of the universe and a natural value for the
transition redshift z_0=0.35. Unlike a large local void, the model respects the
cosmological principle, further offering an explanation for the late onset of
the perceived acceleration as a consequence of the forming nonlinear
structures. Additional tests, such as quantitative predictions for angular
deviations due to an anisotropic void distribution and a theoretical derivation
of the model, can vindicate or falsify the interpretation that light
propagation in voids is responsible for the perceived acceleration.Comment: 33 pages, 2 figs; v2: minor clarifications, results unchanged; v3:
matches the version published in General Relativity and Gravitatio
Transport of interacting electrons through a double barrier in quantum wires
We generalize the fermionic renormalization group method to describe
analytically transport through a double barrier structure in a one-dimensional
system. Focusing on the case of weakly interacting electrons, we investigate
thoroughly the dependence of the conductance on the strength and the shape of
the double barrier for arbitrary temperature T. Our approach allows us to
systematically analyze the contributions to renormalized scattering amplitudes
from different characteristic scales absent in the case of a single impurity,
without restricting the consideration to the model of a single resonant level.
Both a sequential resonant tunneling for high T and a resonant transmission for
T smaller than the resonance width are studied within the unified treatment of
transport through strong barriers. For weak barriers, we show that two
different regimes are possible. Moderately weak impurities may get strong due
to a renormalization by interacting electrons, so that transport is described
in terms of theory for initially strong barriers. The renormalization of very
weak impurities does not yield any peak in the transmission probability;
however, remarkably, the interaction gives rise to a sharp peak in the
conductance, provided asymmetry is not too high.Comment: 18 pages, 8 figures; figures added, references updated, extended
discussio
Confirmation of a pi_1^0 Exotic Meson in the \eta \pi^0 System
The exclusive reaction , at 18 GeV has been studied with a partial wave analysis on a sample
of 23~492 events from BNL experiment E852. A mass-dependent fit
is consistent with a resonant hypothesis for the wave, thus providing
evidence for a neutral exotic meson with , a mass of MeV, and a width of MeV. New
interpretations of the meson exotics in neutral system observed in
E852 and Crystal Barrel experiments are discussed.Comment: p3, rewording the paragraph (at the bottom) about the phase
variations. p4, rewording paragrath "The second method ..." . p4, at the
bottom of paragrath "The third method ..." added consistent with the results
of methods 1 and 2
Tomonaga-Luttinger parameters for quantum wires
The low-energy properties of a homogeneous one-dimensional electron system
are completely specified by two Tomonaga-Luttinger parameters and
. In this paper we discuss microscopic estimates of the values of
these parameters in semiconductor quantum wires that exploit their relationship
to thermodynamic properties. Motivated by the recognized similarity between
correlations in the ground state of a one-dimensional electron liquid and
correlations in a Wigner crystal, we evaluate these thermodynamic quantities in
a self-consistent Hartree-Fock approximation. According to our calculations,
the Hartree-Fock approximation ground state is a Wigner crystal at all electron
densities and has antiferromagnetic order that gradually evolves from
spin-density-wave to localized in character as the density is lowered. Our
results for are in good agreement with weak-coupling perturbative
estimates at high densities, but deviate strongly at low
densities, especially when the electron-electron interaction is screened at
long distances. vanishes at small carrier density
whereas we conjecture that when , implying that
should pass through a minimum at an intermediate density.
Observation of such a non-monotonic dependence on particle density would allow
to measure the range of the microscopic interaction. In the spin sector we find
that the spin velocity decreases with increasing interaction strength or
decreasing . Strong correlation effects make it difficult to obtain fully
consistent estimates of from Hartree-Fock calculations. We
conjecture that v_{\sigma}/\vf\propto n/V_0 in the limit where
is the interaction strength.Comment: RevTeX, 23 pages, 8 figures include
The nuclear energy density functional formalism
The present document focuses on the theoretical foundations of the nuclear
energy density functional (EDF) method. As such, it does not aim at reviewing
the status of the field, at covering all possible ramifications of the approach
or at presenting recent achievements and applications. The objective is to
provide a modern account of the nuclear EDF formalism that is at variance with
traditional presentations that rely, at one point or another, on a {\it
Hamiltonian-based} picture. The latter is not general enough to encompass what
the nuclear EDF method represents as of today. Specifically, the traditional
Hamiltonian-based picture does not allow one to grasp the difficulties
associated with the fact that currently available parametrizations of the
energy kernel at play in the method do not derive from a genuine
Hamilton operator, would the latter be effective. The method is formulated from
the outset through the most general multi-reference, i.e. beyond mean-field,
implementation such that the single-reference, i.e. "mean-field", derives as a
particular case. As such, a key point of the presentation provided here is to
demonstrate that the multi-reference EDF method can indeed be formulated in a
{\it mathematically} meaningful fashion even if does {\it not} derive
from a genuine Hamilton operator. In particular, the restoration of symmetries
can be entirely formulated without making {\it any} reference to a projected
state, i.e. within a genuine EDF framework. However, and as is illustrated in
the present document, a mathematically meaningful formulation does not
guarantee that the formalism is sound from a {\it physical} standpoint. The
price at which the latter can be enforced as well in the future is eventually
alluded to.Comment: 64 pages, 8 figures, submitted to Euroschool Lecture Notes in Physics
Vol.IV, Christoph Scheidenberger and Marek Pfutzner editor
CLT in Functional Linear Regression Models
International audienceWe propose in this work to derive a CLT in the functional linear regression model to get confidence sets for prediction based on functional linear regression. The main difficulty is due to the fact that estimation of the functional parameter leads to a kind of ill-posed inverse problem. We consider estimators that belong to a large class of regularizing methods and we first show that, contrary to the multivariate case, it is not possible to state a CLT in the topology of the considered functional space. However, we show that we can get a CLT for the weak topology under mild hypotheses and in particular without assuming any strong assumptions on the decay of the eigenvalues of the covariance operator. Rates of convergence depend on the smoothness of the functional coefficient and on the point in which the prediction is made
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