893 research outputs found
Effects of magnetohydrodynamics matter density fluctuations on the solar neutrino resonant spin-flavor precession
Taking into account the stringent limits from helioseismology observations on
possible matter density fluctuations described by magnetohydrodynamics theory,
we find the corresponding time variations of solar neutrino survival
probability due to the resonant spin-flavor precession phenomenon with
amplitude of order O(10%). We discuss the physics potential of high statistics
real time experiments, like as Superkamiokande, to observe the effects of such
magnetohydrodynamics fluctuations on their data. We conclude that these
observations could be thought as a test of the resonant spin-flavor precession
solution to the solar neutrino anomaly.Comment: 16 pages, 3 figure
Stationary Regime of Random Resistor Networks Under Biased Percolation
The state of a 2-D random resistor network, resulting from the simultaneous
evolutions of two competing biased percolations, is studied in a wide range of
bias values. Monte Carlo simulations show that when the external current is
below the threshold value for electrical breakdown, the network reaches a
steady state with a nonlinear current-voltage characteristic. The properties of
this nonlinear regime are investigated as a function of different model
parameters. A scaling relation is found between and , where
is the average resistance, the linear regime resistance and
the threshold value for the onset of nonlinearity. The scaling exponent is
found to be independent of the model parameters. A similar scaling behavior is
also found for the relative variance of resistance fluctuations. These results
compare well with resistance measurements in composite materials performed in
the Joule regime up to breakdown.Comment: 9 pages, revtex, proceedings of the Merida Satellite Conference
STATPHYS2
The index of symmetry of compact naturally reductive spaces
We introduce a geometric invariant that we call the index of symmetry, which measures how far is a Riemannian manifold from being a symmetric space. We compute, in a geometric way, the index of symmetry of compact naturally reductive spaces. In this case, the so-called leaf of symmetry turns out to be of the group type. We also study several examples where the leaf of symmetry is not of the group type. Interesting examples arise from the unit tangent bundle of the sphere of curvature 2, and two metrics in an Aloff-Wallach 7-manifold and the Wallach 24-manifold.submittedVersionFil: Olmos, Carlos Enrique. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Reggiani, Silvio Nicolás. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Tamuru, Hiroshi. Universidad de Hiroshima. Escuela de Ciencias. Departamento de Matemática; Japón.Matemática Pur
Radio Resource Management in NB-IoT Systems:Empowered by Interference Prediction and Flexible Duplexing
NB-IoT is a promising cellular technology for enabling low cost, low power, long-range connectivity to IoT devices. With the bandwidth requirement of 180 kHz, it provides the flexibility to deploy within the existing LTE band. However, this raises serious concerns about the performance of the technology due to severe interference from multi-tier 5G HetNets. Furthermore, as NB-IoT is based on HD-FDD, the symmetric allocation of spectrum band between the downlink and uplink results in underutilization of resources, particularly in the case of asymmetric traffic distribution. Therefore, an innovative RRM strategy needs to be devised to improve spectrum efficiency and device connectivity. This article presents the detailed design challenges that need to be addressed for the RRM of NB-IoT and proposes a novel framework to devise an efficient resource allocation scheme by exploiting cooperative interference prediction and flexible duplexing techniques
Anomalous crossover between thermal and shot noise in macroscopic diffusive conductors
We predict the existence of an anomalous crossover between thermal and shot
noise in macroscopic diffusive conductors. We first show that, besides thermal
noise, these systems may also exhibit shot noise due to fluctuations of the
total number of carriers in the system. Then we show that at increasing
currents the crossover between the two noise behaviors is anomalous, in the
sense that the low frequency current spectral density displays a region with a
superlinear dependence on the current up to a cubic law. The anomaly is due to
the non-trivial coupling in the presence of the long range Coulomb interaction
among the three time scales relevant to the phenomenon, namely, diffusion,
transit and dielectric relaxation time.Comment: 4 pages, 2 figure
Effect of long-range Coulomb interaction on shot-noise suppression in ballistic transport
We present a microscopic analysis of shot-noise suppression due to long-range
Coulomb interaction in semiconductor devices under ballistic transport
conditions. An ensemble Monte Carlo simulator self-consistently coupled with a
Poisson solver is used for the calculations. A wide range of injection-rate
densities leading to different degrees of suppression is investigated. A sharp
tendency of noise suppression at increasing injection densities is found to
scale with a dimensionless Debye length related to the importance of
space-charge effects in the structure.Comment: RevTex, 4 pages, 4 figures, minor correction
The effect of chirality on a plasma media
The theoretical properties of a composite chiral-plasma medium are developed. By using the reaction theorem, for a magnetized chiroplasma, we obtain the proof of nonreciprocity based upon the constitutive relationships between electromagnetic vectors (E) over right arrow, (B) over right arrow, (H) over right arrow, (D) over right arrow. Using the Maxwell's equations and the proposed constitutive relations for a chiral-plasma medium, we derive the vectors (E) over right arrow and (H) over right arrow equations and from these equations, dispersion relations and (E) over right arrow-field polarization are obtained. For circularly polarized waves, a new mode conversion is founded due to the chiral effect. For the lower branch of the extraordinary wave mode there is no more bands of forbidden frequencies and the reflection point vanishes when the chiral parameter increases.426989100
Regionalisation for lake level simulation – the case of Lake Tana in the Upper Blue Nile, Ethiopia
In this study lake levels of Lake Tana are simulated at daily time step by solving the water balance for all inflow and outflow processes. Since nearly 62% of the Lake Tana basin area is ungauged a regionalisation procedure is applied to estimate lake inflows from ungauged catchments. The procedure combines automated multi-objective calibration of a simple conceptual model and multiple regression analyses to establish relations between model parameters and catchment characteristics. <br><br> A relatively small number of studies are presented on Lake Tana's water balance. In most studies the water balance is solved at monthly time step and the water balance is simply closed by runoff contributions from ungauged catchments. Studies partly relied on simple <i>ad-hoc</i> procedures of area comparison to estimate runoff from ungauged catchments. In this study a regional model is developed that relies on principles of similarity of catchments characteristics. For runoff modelling the HBV-96 model is selected while multi-objective model calibration is by a Monte Carlo procedure. We aim to assess the closure term of Lake Tana's water balance, to assess model parameter uncertainty and to evaluate effectiveness of a multi-objective model calibration approach to make hydrological modeling results more plausible. <br><br> For the gauged catchments, model performance is assessed by the Nash-Sutcliffe coefficient and Relative Volumetric Error and resulted in satisfactory to good performance for six, large catchments. The regional model is validated and indicated satisfactory to good performance in most cases. Results show that runoff from ungauged catchments is as large as 527 mm per year for the simulation period and amounts to approximately 30% of Lake Tana stream inflow. Results of daily lake level simulation over the simulation period 1994–2003 show a water balance closure term of 85 mm per year that accounts to 2.7% of the total lake inflow. Lake level simulations are assessed by Nash Sutcliffe (0.91) and Relative Volume Error (2.71%) performance measures
Discovery of a Companion Candidate in the HD169142 Transition Disk and the Possibility of Multiple Planet Formation
We present L' and J-band high-contrast observations of HD169142, obtained
with the VLT/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager,
respectively. A source located at 0".156+/-0".032 north of the host star
(PA=7.4+/-11.3 degrees) appears in the final reduced L' image. At the distance
of the star (~145 pc), this angular separation corresponds to a physical
separation of 22.7+/-4.7 AU, locating the source within the recently resolved
inner cavity of the transition disk. The source has a brightness of
L'=12.2+/-0.5 mag, whereas it is not detected in the J band (J>13.8 mag). If
its L' brightness arose solely from the photosphere of a companion and given
the J-L' color constraints, it would correspond to a 28-32 MJupiter object at
the age of the star, according to the COND models. Ongoing accretion activity
of the star suggests, however, that gas is left in the inner disk cavity from
which the companion could also be accreting. In this case the object could be
lower in mass and its luminosity enhanced by the accretion process and by a
circumplanetary disk. A lower mass object is more consistent with the observed
cavity width. Finally, the observations enable us to place an upper limit on
the L'-band flux of a second companion candidate orbiting in the disk annular
gap at ~50 AU, as suggested by millimeter observations. If the second companion
is also confirmed, HD169142 might be forming a planetary system, with at least
two companions opening gaps and possibly interacting with each other.Comment: Accepted to ApJL, see also Biller et al. 201
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