17 research outputs found
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Error control techniques for the Z-channel
The asymmetric nature of bit errors in several practical applications provides grounds for efficient error control techniques. The Z-channel model and special classes of codes like asymmetric error detection codes and t-asymmetric error correcting/d-asymmetric error detecting codes can be successfully used in ARQ protocols for feedback error control enhancement. This thesis presents some efficient feedback error control techniques, suitable for the Z-channel. Precisely, some forms of hybrid ARQ protocols specific to the Z-channel characteristics are introduced. First a diversity combining scheme is presented and analyzed. The undetected error probability and the expected number of retransmissions are calculated for this protocol. Then the Bose-Lin codes are analyzed and feedback error control specific parameters are derived for them. Finally, a type I hybrid ARQ one-code scheme is proposed and analyzed. The proposed techniques improve the throughput efficiency of feedback error control protocols and decrease their accepted packet error rate. The coding analysis is also of theoretical value, in the sense that it solves some open problems in this area
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Convergence study for adaptive allpass filtering
Adaptive filtering may be applied in areas where an optimal filtering algorithm
may not be known a-priori and where the filtering operation may be non-stationary. This
field, or more generally, the field of adaptive systems, is one which may be regarded as
mature, having been the subject of considerable research effort in the areas of control and
signal processing for almost four decades.
DFE (decision feedback equalization) in various forms has been proposed for detection
on magnetic recording channel. An allpass filter is an alternative to the FIR (finite
impulse response) forward equalizer which is normally implemented with DFE. This is
because the allpass filter is a lower power and complexity alternative, though its behavior
and performance are not very well understood yet.
Here, an allpass structure implemented as first and second order IIR (infinite
impulse response) filters is examined. Convergence for the LMS (least mean square) adaptation
algorithm is studied and, moreover, some convergence conditions and bounds are
developed, similarly to the well known FIR case. This thesis provides an useful analytical
study of convergence of IIR adaptive filtering. This is accomplished by a systematic approximation
of the covariance terms of the adaptive coefficients. The range of the step-size
parameter of the LMS algorithm is developed under some simplifying assumptions. All
the results obtained are verified by simulation (Matlab and C routines are used)
Recombination between Polioviruses and Co-Circulating Coxsackie A Viruses: Role in the Emergence of Pathogenic Vaccine-Derived Polioviruses
Ten outbreaks of poliomyelitis caused by pathogenic circulating vaccine-derived polioviruses (cVDPVs) have recently been reported in different regions of the world. Two of these outbreaks occurred in Madagascar. Most cVDPVs were recombinants of mutated poliovaccine strains and other unidentified enteroviruses of species C. We previously reported that a type 2 cVDPV isolated during an outbreak in Madagascar was co-circulating with coxsackieviruses A17 (CA17) and that sequences in the 3′ half of the cVDPV and CA17 genomes were related. The goal of this study was to investigate whether these CA17 isolates can act as recombination partners of poliovirus and subsequently to evaluate the major effects of recombination events on the phenotype of the recombinants. We first cloned the infectious cDNA of a Madagascar CA17 isolate. We then generated recombinant constructs combining the genetic material of this CA17 isolate with that of the type 2 vaccine strain and that of the type 2 cVDPV. Our results showed that poliovirus/CA17 recombinants are viable. The recombinant in which the 3′ half of the vaccine strain genome had been replaced by that of the CA17 genome yielded larger plaques and was less temperature sensitive than its parental strains. The virus in which the 3′ portion of the cVDPV genome was replaced by the 3′ half of the CA17 genome was almost as neurovirulent as the cVDPV in transgenic mice expressing the poliovirus cellular receptor gene. The co-circulation in children and genetic recombination of viruses, differing in their pathogenicity for humans and in certain other biological properties such as receptor usage, can lead to the generation of pathogenic recombinants, thus constituting an interesting model of viral evolution and emergence
Modelling human choices: MADeM and decision‑making
Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)