1,059 research outputs found
Opportunistic Spectrum Sharing using Dumb Basis Patterns: The Line-of-Sight Interference Scenario
We investigate a spectrum-sharing system with non-severely faded mutual
interference links, where both the secondary-to-primary and
primary-to-secondary channels have a Line-of-Sight (LoS) component. Based on a
Rician model for the LoS channels, we show, analytically and numerically, that
LoS interference hinders the achievable secondary user capacity. This is caused
by the poor dynamic range of the interference channels fluctuations when a
dominant LoS component exists. In order to improve the capacity of such system,
we propose the usage of an Electronically Steerable Parasitic Array Radiator
(ESPAR) antenna at the secondary terminals. An ESPAR antenna requires a single
RF chain and has a reconfigurable radiation pattern that is controlled by
assigning arbitrary weights to M orthonormal basis radiation patterns. By
viewing these orthonormal patterns as multiple virtual dumb antennas, we
randomly vary their weights over time creating artificial channel fluctuations
that can perfectly eliminate the undesired impact of LoS interference. Because
the proposed scheme uses a single RF chain, it is well suited for compact and
low cost mobile terminals
Mathematical modeling of the gas and powder flow in the (HVOF) systems to optimize their coatings quality
Thermally sprayed coatings have been extensively used to enhance materials properties and provide surface protection against their working environments in a number of industrial applications. Thermal barrier coatings (TBC) are used to reduce the thermal conductivity of aerospace turbine blades and improve the turbine overall thermal efficiency. TBC allows higher gas operating temperatures and lower blade material temperatures due to the thermal insulation provided by these ceramic coatings. In the automotive industry, coatings are currently applied to a number of moving parts that are subjected to friction and wear inside the engine such as pistons, cylinder liners, valves and crankshafts to enhance their wear resistance and prolong their useful operation and lifetime
Matter-Antimatter Asymmetry in the Large Hadron Collider
The matter-antimatter asymmetry is one of the greatest challenges in the
modern physics. The universe including this paper and even the reader
him(her)self seems to be built up of ordinary matter only. Theoretically, the
well-known Sakharov's conditions remain the solid framework explaining the
circumstances that matter became dominant against the antimatter while the
universe cools down and/or expands. On the other hand, the standard model for
elementary particles apparently prevents at least two conditions out of them.
In this work, we introduce a systematic study of the antiparticle-to-particle
ratios measured in various and collisions over the last three
decades. It is obvious that the available experimental facilities turn to be
able to perform nuclear collisions, in which the matter-antimatter asymmetry
raises from at AGS to at LHC. Assuming that the final
state of hadronization in the nuclear collisions takes place along the
freezeout line, which is defined by a constant entropy density, various
antiparticle-to-particle ratios are studied in framework of the hadron
resonance gas (HRG) model. Implementing modified phase space and distribution
function in the grand-canonical ensemble and taking into account the
experimental acceptance, the ratios of antiparticle-to-particle over the whole
range of center-of-mass-energies are very well reproduced by the HRG model.
Furthermore, the antiproton-to-proton ratios measured by ALICE in
collisions is also very well described by the HRG model. It is likely to
conclude that the LHC heavy-ion program will produce the same particle ratios
as the program implying the dynamics and evolution of the system would not
depend on the initial conditions. The ratios of bosons and baryons get very
close to unity indicating that the matter-antimatter asymmetry nearly vanishes
at LHC.Comment: 9 pages, 5 eps-figures, revtex4-styl
Multislice computed tomography evaluation of primary abdominal fat necrosis : a rare cause of acute abdominal pain
Purpose: Abdominal fat necrosis is a rare cause of abdominal acute pain, classified into primary or secondary according to the cause. Primary fat necrosis includes epiploic appendagitis or idiopathic infarction of the greater omentum. This retrospective study focuses on multislice computed tomography (MSCT) findings and diagnosis of primary abdominal fat necrosis as a cause of acute abdomen. Material and methods: This was a retrospective study with 20 patients included, presented to emergency room with acute abdominal pain diagnosed as primary fat necrosis. Retrospective evaluation was made of the patients' clinical data, presentation, CT studies done at the acute stage, and their primary and final diagnosis. Results: Twenty patients (eight male and 12 female, mean age 45 years, age range 20-70 years) diagnosed with abdominal fat necrosis (primary omental infarct) on CT imaging between October 2014 and June 2018 were evaluated. Clinically, five patients were suspected to be cholecystitis¸ eight patients as appendicitis, and four patients as diverticulitis. In addition, three patients had renal colic and were suspected to have ureteric stones; they showed suspected areas of abnormal fat density in non-contrast CT of the urinary tract. Idiopathic omental infarctions were detected in 13 patients on CT; all were on the right side. Laparoscopic excision was done for all. The other seven patients had epiploic appendagitis, seen on the left side, treated with conservative management. Conclusions: Primary fat necrosis, although rare, can be presented as acute abdomen. MSCT is the main diagnostic tool for diagnosis of omental infraction and differentiation between other causes of acute abdomen
Effects of quantum gravity on the inflationary parameters and thermodynamics of the early universe
The effects of generalized uncertainty principle (GUP) on the inflationary
dynamics and the thermodynamics of the early universe are studied. Using the
GUP approach, the tensorial and scalar density fluctuations in the inflation
era are evaluated and compared with the standard case. We find a good agreement
with the Wilkinson Microwave Anisotropy Probe data. Assuming that a quantum gas
of scalar particles is confined within a thin layer near the apparent horizon
of the Friedmann-Lemaitre-Robertson-Walker universe which satisfies the
boundary condition, the number and entropy densities and the free energy
arising form the quantum states are calculated using the GUP approach. A
qualitative estimation for effects of the quantum gravity on all these
thermodynamic quantities is introduced.Comment: 15 graghes, 7 figures with 17 eps graph
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