1,134 research outputs found
Space-Time Coded Spatial Modulated Physical Layer Network Coding for Two-Way Relaying
Using the spatial modulation approach, where only one transmit antenna is
active at a time, we propose two transmission schemes for two-way relay channel
using physical layer network coding with space time coding using Coordinate
Interleaved Orthogonal Designs (CIOD's). It is shown that using two
uncorrelated transmit antennas at the nodes, but using only one RF transmit
chain and space-time coding across these antennas can give a better performance
without using any extra resources and without increasing the hardware
implementation cost and complexity. In the first transmission scheme, two
antennas are used only at the relay, Adaptive Network Coding (ANC) is employed
at the relay and the relay transmits a CIOD Space Time Block Code (STBC). This
gives a better performance compared to an existing ANC scheme for two-way relay
channel which uses one antenna each at all the three nodes. It is shown that
for this scheme at high SNR the average end-to-end symbol error probability
(SEP) is upper bounded by twice the SEP of a point-to-point fading channel. In
the second transmission scheme, two transmit antennas are used at all the three
nodes, CIOD STBC's are transmitted in multiple access and broadcast phases.
This scheme provides a diversity order of two for the average end-to-end SEP
with an increased decoding complexity of for an arbitrary
signal set and for square QAM signal set.Comment: 9 pages, 7 figure
A probabilistic approach to reduce the route establishment overhead in AODV algorithm for manet
Mobile Ad-hoc Networks (MANETS) is a collection of wireless nodes without any
infrastructure support. The nodes in MANET can act as either router or source
and the control of the network is distributed among nodes. The nodes in MANETS
are highly mobile and it maintains dynamic interconnection between those mobile
nodes. MANTEs have been considered as isolated stand-alone network. This can
turn the dream of networking "at any time and at any where" into reality. The
main purpose of this paper is to study the issues in route discovery process in
AODV protocol for MANET. Flooding of route request message imposes major
concern in route establishment. This paper suggests a new approach to reduce
the routing overhead during the route discovery phase. By considering the
previous behaviour of the network, the new protocol reduces the unwanted
searches during route establishment processComment: International Journal of Distributed and Parallel Systems (IJDPS)
Vol.3, No.2, March 201
Initial wave packets and the various power-law decreases of scattered wave packets at long times
The long time behavior of scattered wave packets from a
finite-range potential is investigated, by assuming to be
initially located outside the potential. It is then shown that can
asymptotically decrease in the various power laws at long time, according to
its initial characteristics at small momentum. As an application, we consider
the square-barrier potential system and demonstrate that exhibits
the asymptotic behavior , while another behavior like can
also appear for another .Comment: 5 pages, 1 figur
Prevalence of fatty liver disease in children with obesity- a diagnostic study based on its ultrasound appearance
Background: Non-alcoholic fatty liver disease is an asymptomatic involvement of the liver, can progress to chronic liver disease and must be identified at an early stage for good prognosis. The implementation of the appropriate therapeutic interventions is determinant of the attempts to treat it. For that purpose, early diagnosis and staging of the disease is essential. It seems that diagnostic imaging should be a first-line tool for the staging and monitoring pediatric NAFLD/NASH for appropriate interventions to be implanted in a timely way. This study evaluated the prevalence of fatty liver in relation with body mass index (BMI) by means of ultrasound in children of age group 6-15 years.Methods: In this cross-sectional study, 83 children aged 6 to 15 years, were selected randomly. The participants were examined by a pediatrician. Liver ultrasound was performed for all children and grade of fatty liver was determined.Results: There was a significant correlation between grade of fatty liver with BMI, our study showed a strong association between BMI and prevalence of fatty liver on ultrasound.Conclusions: According to the study hypothesis, based on BMI, the degree of NAFLD in children were predictable. Ultrasound of liver in grading of fatty liver is one of the assessments methods of fatty liver but it is not a diagnostic method; it is useful for prevention to reduce BMI
Free initial wave packets and the long-time behavior of the survival and nonescape probabilities
The behavior of both the survival S(t) and nonescape P(t) probabilities at
long times for the one-dimensional free particle system is shown to be closely
connected to that of the initial wave packet at small momentum. We prove that
both S(t) and P(t) asymptotically exhibit the same power-law decrease at long
times, when the initial wave packet in momentum representation behaves as O(1)
or O(k) at small momentum. On the other hand, if the integer m becomes greater
than 1, S(t) and P(t) decrease in different power-laws at long times.Comment: 4 pages, 3 figures, Title and organization changed, however the
results not changed, To appear in Phys. Rev.
Measurements of plasma temperature and electron density in laser-induced copper plasma by time-resolved spectroscopy of neutral atom and ion emissions
Plasma produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a copper solid sample in air at atmospheric pressure is studied spectroscopically. The temperature and electron density characterizing the plasma are measured by time-resolved spectroscopy of neutral atom and ion line emissions in the time window of 300-2000 ns. An echelle spectrograph coupled with a gated intensified charge coupled detector is used to record the plasma emissions. The temperature is obtained using the Boltzmann plot method and the electron density is determined using the Saha-Boltzmann equation method. Both parameters are studied as a function of delay time with respect to the onset of the laser pulse. The results are discussed. The time window where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the laser-induced breakdown spectroscopy (LIBS) analysis of samples, is deduced from the temporal evolution of the intensity ratio of two Cu I lines. It is found to be 700-1000 ns
Standard and derived Planck quantities: selected analysis and derivations
We provide an overview of the fundamental units of physical quantities
determined naturally by the values of fundamental constants of nature. We
discuss a comparison between the 'Planck units', now widely used in theoretical
physics and the pre-quantum 'Stoney units' in which, instead of the Planck
constant, the charge of the electron is used with very similar quantitative
results. We discuss some of the physical motivation for these special units,
attributed much after they were introduced, and also put forth a summary of the
arguments supporting various cases for making specific physical interpretations
of the meanings of some of these units. The new aspects we discuss are a
possible physical basis for the Stoney units, their link to the Planck units,
and also the importance of Planck units for thermodynamical quantities in the
context of quantum gravity.Comment: 22 pages, 1 tabl
The various power decays of the survival probability at long times for free quantum particle
The long time behaviour of the survival probability of initial state and its
dependence on the initial states are considered, for the one dimensional free
quantum particle. We derive the asymptotic expansion of the time evolution
operator at long times, in terms of the integral operators. This enables us to
obtain the asymptotic formula for the survival probability of the initial state
, which is assumed to decrease sufficiently rapidly at large .
We then show that the behaviour of the survival probability at long times is
determined by that of the initial state at zero momentum . Indeed,
it is proved that the survival probability can exhibit the various power-decays
like for an arbitrary non-negative integers as ,
corresponding to the initial states with the condition as .Comment: 15 pages, to appear in J. Phys.
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