2,224 research outputs found
The Role of Boolean Function in Fractal Formation and it s Application to CDMA Wireless Communication
In this paper, a new transformation is generated from a three variable
Boolean function 3, which is used to produce a self-similar fractal pattern of
dimension 1.58. This very fractal pattern is used to reconstruct the whole
structural position of resources in wireless CDMA network. This reconstruction
minimizes the number of resources in the network and so naturally network
consumption costs are getting reduced. Now -a -days resource controlling and
cost minimization are still a severe problem in wireless CDMA network. To
overcome this problem fractal pattern produced in our research provides a
complete solution of structural position of resources in this Wireless CDMA
Network.Comment: 8 pages, 14 figure
Role of disconnections in mobility of the austenite-ferrite inter-phase boundary in Fe
Austenite ({\gamma}-Fe, face centered cubic (FCC)) to ferrite ({\alpha}-Fe,
body centered cubic (BCC)) phase transformation in steel is of great
significance from the point of view of industrial applications. In this work,
using classical molecular dynamics simulations, we study the atomistic
mechanisms involved during the nucleation and growth of the ferrite phase
embedded in an austenite phase. We find that the disconnections present at the
inter-phase boundary can act as the nucleation centers for the ferrite phase.
Relatively small interface velocities (1.19 - 4.67 m/s) confirm a phase change
via massive transformation mechanism. Boundary mobilities obtained in a
temperature range of 1000 to 1400 K show an Arrhenius behavior, with activation
energies ranging from 30 - 40 kJ/mol.Comment: 8 pages, 7 figure
The impact of non-Gaussianity on the Epoch of Reionization parameter forecast using 21-cm power spectrum measurements
Measurements of the Epoch of Reionization (EoR) 21-cm signal hold the
potential to constrain models of reionization. In this paper we consider a
reionization model with three astrophysical parameters namely (1) the minimum
halo mass which can host ionizing sources, , (2) the number of
ionizing photons escaping into the IGM per baryon within the halo, and (3) the mean free path of the ionizing photons within the IGM,
. We predict the accuracy with which these parameters can be
measured from future observations of the 21-cm power spectrum (PS) using the
upcoming SKA-Low. Unlike several earlier works, we account for the
non-Gaussianity of the inherent EoR 21-cm signal. Considering cosmic variance
only and assuming that foregrounds are completely removed, we find that
non-Gaussianity increases the volume of the error ellipsoid of the
parameters by a factor of relative to the Gaussian predictions, the
orientation is also different. The ratio of the volume of error ellipsoids is
and for observation times of and hours
respectively, when all the modes within the foreground wedge are
excluded. With foreground wedge excluded and for hours, the 1D
marginalized errors are which are respectively , and larger than the
respective Gaussian predictions. The impact of non-Gaussianity increases for
longer observations, and it is particularly important for .Comment: 16 pages, 7 figures, 3 tables, Accepted for publication in MNRA
Predictions for measuring the cross power spectrum of the HI 21-cm signal and the Lyman- forest using OWFA
We have studied the possibility of measuring the cross-correlation of the
redshifted HI 21-cm signal and the Lyman- forest using an upcoming
radio-interferometric array OWFA and an spectroscopic observation like SDSS-IV.
Our results shows that it is possible to have a detection of the
cross-correlation signal with OWFA PII using an observing time of hrs
each in independent fields-of-view. However, not much can be done
beyond this using the cross-correlation signal for and . Apart from this, we have also envisaged a situation where
observations are carried out at and which lie closer to the
peak of the quasar distribution at and with a larger bandwidth of . We see that the SNR of the cross-correlation detection can
be significantly enhanced to for and . It is then possible to measure and individually with
an by combining the cross-correlation with the HI 21-cm
auto-correlation measurements. We further find that a measurement of the binned
cross-correlation power spectrum with is also possible in
several bins at .Comment: To be submitted in JCA
An analytical method to simulate the HI 21-cm visibility signal for intensity mapping experiments
Simulations play a vital role in testing and validating HI 21-cm power
spectrum estimation techniques. Conventional methods use techniques like N-body
simulations to simulate the sky signal which is then passed through a model of
the instrument. This makes it necessary to simulate the HI distribution in a
large cosmological volume, and incorporate both the light-cone effect and the
telescope's chromatic response. The computational requirements may be
particularly large if one wishes to simulate many realizations of the signal.
In this paper we present an analytical method to simulate the HI visibility
signal. This is particularly efficient if one wishes to simulate a large number
of realizations of the signal. Our method is based on theoretical predictions
of the visibility correlation which incorporate both the light-cone effect and
the telescope's chromatic response. We have demonstrated this method by
applying it to simulate the HI visibility signal for the upcoming Ooty Wide
Field Array Phase I.Comment: 11 pages, 6 figures, MNRAS, stx234
Fisher Matrix Based Predictions for Measuring the z = 3.35 Binned 21-cm Power Spectrum using the Ooty Wide Field Array (OWFA)
We use the Fisher matrix formalism to predict the prospects of measuring the
redshifted 21-cm power spectrum in different -bins using observations with
the upcoming Ooty Wide Field Array (OWFA) which will operate at . This corresponds to neutral hydrogen (HI) at , and a measurement
of the 21-cm power spectrum provides an unique method to probe the large-scale
structures at this redshift. Our analysis indicates that a detection
of the binned power spectrum is possible in the range with hours of observation. We find that the
Signal-to-Noise ratio () peaks in the range where a detection is possible with hours of
observations. Our analysis also indicates that it is not very advantageous to
observe much beyond hours in a single field of view as the
increases rather slowly beyond this in many of the small -bins. The entire
analysis reported here assumes that the foregrounds have been completely
removed.Comment: To appear in the Special Section of the JAA on the Ooty Wide Field
Arra
Four allotropes of semiconducting layered Arsenic which switch into a topological insulator via an electric field: A computational study
We propose four different thermodynamically stable structural phases of
arsenic monolayers based on ab-initio density functional theory calculations
all of which undergo a topological phase transition on application of a
perpendicular electric field. All the four arsenic monolayer allotropes have a
wide band gap, varying from 1.21 eV to 3.0 eV (based on GW calculations), and
in general they undergo a metal-insulator quantum phase transition on
application of uniaxial in-layer strain. Additionally an increasing transverse
electric field induces band-inversion at the {\Gamma} point in all four
monolayer allotropes, leading to a nontrivial topological phase (insulating for
three and metallic for one allotrope), characterized by the switching of the Z2
index, from 0 (before band inversion) to 1 (after band inversion). The
topological phase tuned by the transverse electric field, should support
spin-separated gapless edge states which should manifest in quantum spin Hall
effect.Comment: 8 pages, 5 figures; Revised version with phonon dispersion; To appear
in PR
Thickness and electric field dependent polarizability and dielectric constant in phosphorene
Based on extensive first principle calculations, we explore the thickness
dependent effective di- electric constant and slab polarizability of few layer
black phosphorene. We find that the dielectric constant in ultra-thin
phosphorene is thickness dependent and it can be further tuned by applying an
out of plane electric field. The decreasing dielectric constant with reducing
number of layers of phosphorene, is a direct consequence of the lower
permittivity of the surface layers and the in- creasing surface to volume
ratio. We also show that the slab polarizability depends linearly on the number
of layers, implying a nearly constant polarizability per phosphorus atom. Our
calculation of the thickness and electric field dependent dielectric properties
will be useful for designing and interpreting transport experiments in gated
phosphorene devices, wherever electrostatic effects such as capacitance, charge
screening etc. are important.Comment: 8 pages, 6 figure
Effective Doping of Monolayer Phosphorene by Surface Adsorption of Atoms for Electronic and Spintronic Applications
We study the effect of surface adsorption of 27 different adatoms on the
electronic and magnetic properties of monolayer black phosphorus using density
functional theory. Choosing a few representative elements from each group,
ranging from alkali metals (group I) to halogens (group VII), we calculate the
band structure, density of states, magnetic moment and effective mass for the
energetically most stable location of the adatom on monolayer phosphorene. We
predict that group I metals (Li, Na, K), and group III adatoms (Al, Ga, In) are
effective in enhancing the n-type mobile carrier density, with group III
adatoms resulting in lower effective mass of the electrons, and thus higher
mobilities. Furthermore we find that the adatoms of transition metals Ti and
Fe, produce a finite magnetic moment (1.87 and 2.31 ) in monolayer
phosphorene, with different band gap and electronic effective masses (and thus
mobilities), which approximately differ by a factor of 10 for spin up and spin
down electrons opening up the possibility for exploring spintronic
applications.Comment: 7 pages, 4 figures and 1 table; revised versio
Interlayer decoupling in twisted bilayers of -phosphorus and arsenic: a computational study
We investigate magnetism and band structure engineering in Moir\'e
superlattice of blue phosphorus (-P) and grey arsenene (-As)
bilayers, using \textit{ab initio} calculations. The electronic states near the
valence and conduction band edges have significant character in both the
bilayers. Thus, twisting the layers significantly reduce the interlayer orbital
overlap, leading to a decrease in the binding energy (up to ) and an
increase in interlayer distance (up to ), compared to the most stable
AA-stacking. This interlayer decoupling also results in a notable increase (up
to 25-50\%) of the bandgap of twisted bilayers, with the valance band
edge becoming relatively flat with van-Hove singularities in the density of
states. Thus, hole doping induces a Stoner instability, leading to
ferromagnetic ground state, which is more robust in Moir\'e superlattices, than
that of AA-stacked -P and -As
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