4,963 research outputs found
Noncommutative QED and Anomalous Dipole Moments
We study QED on noncommutative spaces, NCQED. In particular we present the
detailed calculation for the noncommutative electron-photon vertex and show
that the Ward identity is satisfied. We discuss that in the noncommutative case
moving electron will show {\it electric} dipole effects. In addition, we work
out the electric and magnetic dipole moments up to one loop level. For the
magnetic moment we show that noncommutative electron has an intrinsic (spin
independent) magnetic moment.Comment: 27 pages, several .ps and .eps figures, v3:typos in some formula
corrected, version appeared in JHE
Achievable Information Rates for Coded Modulation with Hard Decision Decoding for Coherent Fiber-Optic Systems
We analyze the achievable information rates (AIRs) for coded modulation
schemes with QAM constellations with both bit-wise and symbol-wise decoders,
corresponding to the case where a binary code is used in combination with a
higher-order modulation using the bit-interleaved coded modulation (BICM)
paradigm and to the case where a nonbinary code over a field matched to the
constellation size is used, respectively. In particular, we consider hard
decision decoding, which is the preferable option for fiber-optic communication
systems where decoding complexity is a concern. Recently, Liga \emph{et al.}
analyzed the AIRs for bit-wise and symbol-wise decoders considering what the
authors called \emph{hard decision decoder} which, however, exploits \emph{soft
information} of the transition probabilities of discrete-input discrete-output
channel resulting from the hard detection. As such, the complexity of the
decoder is essentially the same as the complexity of a soft decision decoder.
In this paper, we analyze instead the AIRs for the standard hard decision
decoder, commonly used in practice, where the decoding is based on the Hamming
distance metric. We show that if standard hard decision decoding is used,
bit-wise decoders yield significantly higher AIRs than symbol-wise decoders. As
a result, contrary to the conclusion by Liga \emph{et al.}, binary decoders
together with the BICM paradigm are preferable for spectrally-efficient
fiber-optic systems. We also design binary and nonbinary staircase codes and
show that, in agreement with the AIRs, binary codes yield better performance.Comment: Published in IEEE/OSA Journal of Lightwave Technology, 201
Iterative Bounded Distance Decoding of Product Codes with Scaled Reliability
We propose a modified iterative bounded distance decoding of product codes.
The proposed algorithm is based on exchanging hard messages iteratively and
exploiting channel reliabilities to make hard decisions at each iteration.
Performance improvements up to 0.26 dB are achieved
Binary Message Passing Decoding of Product-like Codes
We propose a novel binary message passing decoding algorithm for product-like
codes based on bounded distance decoding (BDD) of the component codes. The
algorithm, dubbed iterative BDD with scaled reliability (iBDD-SR), exploits the
channel reliabilities and is therefore soft in nature. However, the messages
exchanged by the component decoders are binary (hard) messages, which
significantly reduces the decoder data flow. The exchanged binary messages are
obtained by combining the channel reliability with the BDD decoder output
reliabilities, properly conveyed by a scaling factor applied to the BDD
decisions. We perform a density evolution analysis for generalized low-density
parity-check (GLDPC) code ensembles and spatially coupled GLDPC code ensembles,
from which the scaling factors of the iBDD-SR for product and staircase codes,
respectively, can be obtained. For the white additive Gaussian noise channel,
we show performance gains up to dB and dB for product and
staircase codes compared to conventional iterative BDD (iBDD) with the same
decoder data flow. Furthermore, we show that iBDD-SR approaches the performance
of ideal iBDD that prevents miscorrections.Comment: Accepted for publication in the IEEE Transactions on Communication
Binary Message Passing Decoding of Product Codes Based on Generalized Minimum Distance Decoding
We propose a binary message passing decoding algorithm for product codes
based on generalized minimum distance decoding (GMDD) of the component codes,
where the last stage of the GMDD makes a decision based on the Hamming distance
metric. The proposed algorithm closes half of the gap between conventional
iterative bounded distance decoding (iBDD) and turbo product decoding based on
the Chase--Pyndiah algorithm, at the expense of some increase in complexity.
Furthermore, the proposed algorithm entails only a limited increase in data
flow compared to iBDD.Comment: Invited paper to the 53rd Annual Conference on Information Sciences
and Systems (CISS), Baltimore, MD, March 2019. arXiv admin note: text overlap
with arXiv:1806.1090
Probabilistically-Shaped Coded Modulation with Hard Decision Decoding for Coherent Optical Systems
We consider probabilistic shaping to maximize the achievable information rate
of coded modulation (CM) with hard decision decoding. The proposed scheme using
binary staircase codes outperforms its uniform CM counterpart by more than 1.3
dB for 64-QAM and 5 bits/symbol
Associations between hypothalamic-pituitary-adrenal axis system gene variants and cortisol reactivity in preschoolers: Main effects and gene-environment interactions
Exposure to stressful events during early development has consistently been shown to produce long lasting effects on the hypothalamic-pituitary-adrenal (HPA) axis, which may increase vulnerability to mood and anxiety disorders. Recently reported genetic association studies indicate that these disorders may be influenced, in part, by gene-environment interactions (GxE) involving polymorphisms within the corticotrophin-releasing hormone and monoaminergic system genes. However, little is known about how genetic variants and life stress work to shape children’s neuroendocrine reactivity and emerging symptoms. Therefore, the aim of this thesis is to examine main effects of candidate genes and GxE on the neuroendocrine stress response and internalizing symptoms in a community sample of 409 preschoolers.
In Chapter 2 analyses show associations between variants of the CRHR1 and CRHBP genes and children’s cortisol responses to a standardized laboratory stress task. I also found evidence for GxE, where variants of the CRH system genes moderated the impact of childhood stress on early-emerging symptoms of depression and anxiety.
A functional polymorphism of the catechol-O-methyltransferase (COMT) gene, the val158met, has been implicated in the etiology of stress-related mood disorders. Therefore, in Chapter 3, I examined links between the val158met polymorphism, cortisol reactivity to stress, and internalizing symptoms. I found evidence for association between the val158met genotype and cortisol reactivity to stress. Additionally, the val158met genotype moderated the link between childhood stress and emerging symptoms of anxiety.
Due to the proposed role of dopamine and serotonin gene polymorphisms in research on GxE in internalizing disorders, in Chapters 4 and 5, I examined whether associations between dopaminergic and serotonin candidate gene polymorphisms and childhood cortisol reactivity and internalizing symptoms were moderated by childhood life stress. Analyses showed evidence for GxE predicting children’s symptoms. Specifically, polymorphisms of DRD2 and DAT1 genes moderated the effect of childhood stress on emerging symptoms of anxiety. With regard to serotonin pathway polymorphisms, I found associations between the serotonin transporter promoter polymorphism (5-HTTLPR) and children’s anxious symptoms. Additionally, consistent with previously reported findings, the interaction between MAOA 30bp VNTR and childhood stress predicted child anxiety symptoms. Limitations of this work include a relatively small sample size for genetic analyses, as well as the examination of a limited number of markers at each gene. Additionally, I did not correct for multiple statistical tests in some analyses due to the hypothesis-driven nature of the work.
Taken together, the analyses show the complex underpinnings of individual differences in stress regulation, and highlight specific genetic vulnerabilities that influence early psychophysiological reactivity, that may in turn contribute to the development of stress-related disorders later in development
Meantime (Original writing).
Abstract Not Available. Source: Masters Abstracts International, Volume: 37-01, page: 0069. Adviser: Alistair MacLeod. Thesis (M.A.)--University of Windsor (Canada), 1997
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