270 research outputs found
Enhancenig OLSR routing protocol using K-means clustering in MANETs
The design of robust routing protocol schemes for MANETs is quite complex, due to the characteristics and structural constraints of this network. A numerous variety of protocol schemes have been proposed in literature. Most of them are based on traditional method of routing, which doesn’t guarantee basic levels of Qos, when the network becomes larger, denser and dynamic. To solve this problem we use one of the most popular methods named clustering. In this work we try to improve the Qos in MANETs. We propose an algorithm of clustering based in the new mobility metric and K-Means method to distribute the nodes into several clusters; it is implemented to standard OLSR protocol giving birth a new protocol named OLSR Kmeans-SDE. The simulations showed that the results obtained by OLSR Kmeans-SDE exceed those obtained by standard OLSR Kmeans and OLSR Kmed+ in terms of, traffic Control, delay and packet delivery ratio
Novel Clustering Method Based on K-Medoids and Mobility Metric
The structure and constraint of MANETS influence negatively the performance of QoS, moreover the main routing protocols proposed generally operate in flat routing. Hence, this structure gives the bad results of QoS when the network becomes larger and denser. To solve this problem we use one of the most popular methods named clustering. The present paper comes within the frameworks of research to improve the QoS in MANETs. In this paper we propose a new algorithm of clustering based on the new mobility metric and K-Medoid to distribute the nodes into several clusters. Intuitively our algorithm can give good results in terms of stability of the cluster, and can also extend life time of cluster head
Experiments on joint source-channel fractal image coding with unequal error protection
We propose a joint source-channel coding system for fractal image compression. We allocate the available total bit rate between the source code and a range of error-correcting codes using a Lagrange multiplier optimization technique. The principle of the proposed unequal error protection strategy is to partition the information bits into sensitivity classes and to assign one code from a range of error-correcting codes to each sensitivity class in a nearly optimal way. Experimental results show that joint source-channel coding with fractal image compression is feasible, leads to ef"cient protection strategies, and outperforms previous works in this "eld that only covered channel coding with a "xed source rate
Patterns in the Fermion Mixing Matrix, a bottom-up approach
We first obtain the most general and compact parametrization of the unitary
transformation diagonalizing any 3 by 3 hermitian matrix H, as a function of
its elements and eigenvalues. We then study a special class of fermion mass
matrices, defined by the requirement that all of the diagonalizing unitary
matrices (in the up, down, charged lepton and neutrino sectors) contain at
least one mixing angle much smaller than the other two. Our new parametrization
allows us to quickly extract information on the patterns and predictions
emerging from this scheme. In particular we find that the phase difference
between two elements of the two mass matrices (of the sector in question)
controls the generic size of one of the observable fermion mixing angles: i.e.
just fixing that particular phase difference will "predict" the generic value
of one of the mixing angles, irrespective of the value of anything else.Comment: 29 pages, 3 figures, references added, to appear in PR
Development of Photonic Crystal Fiber Based Gas/ Chemical Sensors
The development of highly-sensitive and miniaturized sensors that capable of
real-time analytes detection is highly desirable. Nowadays, toxic or colorless
gas detection, air pollution monitoring, harmful chemical, pressure, strain,
humidity, and temperature sensors based on photonic crystal fiber (PCF) are
increasing rapidly due to its compact structure, fast response and efficient
light controlling capabilities. The propagating light through the PCF can be
controlled by varying the structural parameters and core-cladding materials, as
a result, evanescent field can be enhanced significantly which is the main
component of the PCF based gas/chemical sensors. The aim of this chapter is to
(1) describe the principle operation of PCF based gas/ chemical sensors, (2)
discuss the important PCF properties for optical sensors, (3) extensively
discuss the different types of microstructured optical fiber based gas/
chemical sensors, (4) study the effects of different core-cladding shapes, and
fiber background materials on sensing performance, and (5) highlight the main
challenges of PCF based gas/ chemical sensors and possible solutions
SUSY, the Third Generation and the LHC
We develop a bottom-up approach to studying SUSY with light stops and
sbottoms, but with other squarks and sleptons heavy and beyond reach of the
LHC. We discuss the range of squark, gaugino and Higgsino masses for which the
electroweak scale is radiatively stable over the "little hierarchy" below ~ 10
TeV. We review and expand on indirect constraints on this scenario, in
particular from flavor and CP tests. We emphasize that in this context,
R-parity violation is very well motivated. The phenomenological differences
between Majorana and Dirac gauginos are also discussed. Finally, we focus on
the light subsystem of stops, sbottom and neutralino with R-parity, in order to
probe the current collider bounds. We find that 1/fb LHC bounds are mild and
large parts of the motivated parameter space remain open, while the 10/fb data
can be much more decisive.Comment: 42 pages, 8 figures, 1 table. V2: minor corrections, references adde
Counter-current chromatography for the separation of terpenoids: A comprehensive review with respect to the solvent systems employed
Copyright @ 2014 The Authors.This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.Natural products extracts are commonly highly complex mixtures of active compounds and consequently their purification becomes a particularly challenging task. The development of a purification protocol to extract a single active component from the many hundreds that are often present in the mixture is something that can take months or even years to achieve, thus it is important for the natural product chemist to have, at their disposal, a broad range of diverse purification techniques. Counter-current chromatography (CCC) is one such separation technique utilising two immiscible phases, one as the stationary phase (retained in a spinning coil by centrifugal forces) and the second as the mobile phase. The method benefits from a number of advantages when compared with the more traditional liquid-solid separation methods, such as no irreversible adsorption, total recovery of the injected sample, minimal tailing of peaks, low risk of sample denaturation, the ability to accept particulates, and a low solvent consumption. The selection of an appropriate two-phase solvent system is critical to the running of CCC since this is both the mobile and the stationary phase of the system. However, this is also by far the most time consuming aspect of the technique and the one that most inhibits its general take-up. In recent years, numerous natural product purifications have been published using CCC from almost every country across the globe. Many of these papers are devoted to terpenoids-one of the most diverse groups. Naturally occurring terpenoids provide opportunities to discover new drugs but many of them are available at very low levels in nature and a huge number of them still remain unexplored. The collective knowledge on performing successful CCC separations of terpenoids has been gathered and reviewed by the authors, in order to create a comprehensive document that will be of great assistance in performing future purifications. © 2014 The Author(s)
Neutrino Mass, Sneutrino Dark Matter and Signals of Lepton Flavor Violation in the MRSSM
We study the phenomenology of mixed-sneutrino dark matter in the Minimal
R-Symmetric Supersymmetric Standard Model (MRSSM). Mixed sneutrinos fit
naturally within the MRSSM, as the smallness (or absence) of neutrino Yukawa
couplings singles out sneutrino A-terms as the only ones not automatically
forbidden by R-symmetry. We perform a study of randomly generated sneutrino
mass matrices and find that (i) the measured value of is well
within the range of typical values obtained for the relic abundance of the
lightest sneutrino, (ii) with small lepton-number-violating mass terms
for the right-handed sneutrinos, random
matrices satisfying the constraint have a decent probability of
satisfying direct detection constraints, and much of the remaining parameter
space will be probed by upcoming experiments, (iii) the terms radiatively generate appropriately small Majorana neutrino
masses, with neutrino oscillation data favoring a mostly sterile lightest
sneutrino with a dominantly mu/tau-flavored active component, and (iv) a
sneutrino LSP with a significant mu component can lead to striking signals of
e-mu flavor violation in dilepton invariant-mass distributions at the LHC.Comment: Revised collider analysis in Sec. 5 after fixing error in particle
spectrum, References adde
A Supersymmetric Explanation of the Excess of Higgs-Like Events at LEP
Searches for the Standard Model Higgs boson by the four LEP experiments found
excess events in two mass ranges: a 2.3 sigma excess around 98 GeV, and an 1.7
sigma excess around 115 GeV. The latter has been discussed widely in the
literature, but the former has attracted little attention so far. In this paper
I explore the possibility of explaining the excess near 98 GeV through
production of the lighter CP--even Higgs boson in the Minimal Supersymmetric
Standard Model (MSSM). It is shown that this allows to simultaneously explain
the excess near 115 GeV through the production of the heavier CP--even MSSM
Higgs boson. The resulting light Higgs sector offers opportunities for charged
Higgs boson searches at the Tevatron and LHC. Neutral Higgs boson searches at
the LHC in the di--muon channel are also promising. However, conclusive tests
of this scenario may have to wait for the construction of a linear e+ e-
collider.Comment: LaTeX, 14 pages, 7 .eps-files (included). Added references and a
couple of footnotes; results unchanged. Version to appear in PR
Higgs-mediated leptonic decays of B_s and B_d mesons as probes of supersymmetry
If tan(beta) is large, down-type quark mass matrices and Yukawa couplings
cannot be simultaneously diagonalized, and flavour violating couplings of the
neutral Higgs bosons are induced at the 1-loop level. These couplings lead to
Higgs-mediated contributions to the decays B_s -> mu+ mu- and B_d -> tau+ tau-,
at a level that might be of interest for the current Tevatron run, or possibly,
at B-factories. We evaluate the branching ratios for these decays within the
framework of minimal gravity-, gauge- and anomaly-mediated SUSY breaking
models, and also in SU(5) supergravity models with non-universal gaugino mass
parameters at the GUT scale. We find that the contribution from gluino loops,
which seems to have been left out in recent phenomenological analyses, is
significant. We explore how the branching fraction varies in these models,
emphasizing parameter regions consistent with other observations.Comment: Revised to accommodate minor changes in original text and update
reference
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