991 research outputs found
Spontaneous Breaking of Flavor Symmetry and Naturalness of Nearly Degenerate Neutrino Masses and Bi-maximal Mixing
The gauge model with flavor symmetry and three Higgs triplets is
studied. We show how the intriguing nearly degenerate neutrino mass and
bi-maximal mixing scenario comes out naturally after spontaneous breaking of
the symmetry. The hierarchy between the neutrino mass-squared differences,
which is needed for reconciling both solar and atmospheric neutrino data, is
naturally resulted from an approximate permutation symmetry. The model can also
lead to interesting phenomena on lepton-flavor violations via the
gauge interactions.Comment: 13 pages, latex, no figures, the version appearing in SCIENCE IN
CHINA (Series A), Vol.35 No.9 (2000
Reduced order models for control of fluids using the Eigensystem Realization Algorithm
In feedback flow control, one of the challenges is to develop mathematical
models that describe the fluid physics relevant to the task at hand, while
neglecting irrelevant details of the flow in order to remain computationally
tractable. A number of techniques are presently used to develop such
reduced-order models, such as proper orthogonal decomposition (POD), and
approximate snapshot-based balanced truncation, also known as balanced POD.
Each method has its strengths and weaknesses: for instance, POD models can
behave unpredictably and perform poorly, but they can be computed directly from
experimental data; approximate balanced truncation often produces vastly
superior models to POD, but requires data from adjoint simulations, and thus
cannot be applied to experimental data.
In this paper, we show that using the Eigensystem Realization Algorithm (ERA)
\citep{JuPa-85}, one can theoretically obtain exactly the same reduced order
models as by balanced POD. Moreover, the models can be obtained directly from
experimental data, without the use of adjoint information. The algorithm can
also substantially improve computational efficiency when forming reduced-order
models from simulation data. If adjoint information is available, then balanced
POD has some advantages over ERA: for instance, it produces modes that are
useful for multiple purposes, and the method has been generalized to unstable
systems. We also present a modified ERA procedure that produces modes without
adjoint information, but for this procedure, the resulting models are not
balanced, and do not perform as well in examples. We present a detailed
comparison of the methods, and illustrate them on an example of the flow past
an inclined flat plate at a low Reynolds number.Comment: 22 pages, 7 figure
Gravitino constraints on models of neutrino masses and leptogenesis
In the supersymmetric extensions of the standard model, neutrino masses and
leptogenesis requires existence of new particles. We point out that if these
particles with lepton number violating interactions have standard model gauge
interactions, then they may not be created after reheating because of the
gravitino problem. This will rule out all existing models of neutrino masses
and leptogenesis, except the one with right-handed singlet neutrinos.Comment: 12 pages latex file with one postscript figur
Energy Independent Solution to the Solar Neutrino Anomaly including the SNO data
The global data on solar neutrino rates and spectrum, including the SNO
charged current rate, can be explained by LMA, LOW or the energy independent
solution -- corresponding to near-maximal mixing. All the three favour a mild
upward renormalisation of the Cl rate. A mild downward shift of the
neutrino flux is favoured by the energy independent and to a lesser extent the
LOW solution, but not by LMA. Comparison with the ratio of SK elastic and SNO
charged current scattering rates favours the LMA over the other two solutions,
but by no more than .Comment: 18 pages, latex, 3 figure
Gene expression profiling of dedifferentiated human articular chondrocytes in monolayer culture
Objective\ud
When primary chondrocytes are cultured in monolayer, they undergo dedifferentiation during which they lose their phenotype and their capacity to form cartilage. Dedifferentiation is an obstacle for cell therapy for cartilage degeneration. In this study, we aimed to systemically evaluate the changes in gene expression during dedifferentiation of human articular chondrocytes to identify underlying mechanisms.\ud
\ud
Methods\ud
RNA was isolated from monolayer-cultured primary human articular chondrocytes at serial passages. Gene expression was analyzed by microarray. Based on the microarray analysis, relevant genes and pathways were identified. Their functions in chondrocyte dedifferentiation were further investigated.\ud
\ud
Results\ud
In vitro expanded human chondrocytes showed progressive changes in gene expression. Strikingly, an overall decrease in total gene expression was detected, which was both gradual and cumulative. DNA methylation was in part responsible for the expression downregulation of a number of genes. Genes involved in many pathways such as the ERK and BMP pathways exhibited significant changes in expression. Inhibition of ERK pathway didnât show dramatic effects in counteracting dedifferentiation process. BMP-2 was able to decelerate the dedifferentiation and reinforce the maintenance of chondrocyte phenotype in monolayer culture.\ud
\ud
Conclusion\ud
Our study not only improves our knowledge of the intricate signaling network regulating maintenance of chondrocyte phenotype, but also contributes to improved chondrocyte expansion and chondrogenic performance for cell therapy
Genetics of diabetic microvascular disease
Publisher Copyright: © 2020 John Wiley & Sons, Inc.Diabetic microvascular complications, affecting the kidneys, retina, and the nervous system, are a heavy burden for both the diabetic individual and society. The complications seem to cluster in families suggesting a genetic component in their pathogenesis. However, the actual genetic factors have long remained unknown. During the past few years, major advances have been made with large-scale genetic studies that have identified common genetic risk factors, e.g. in the AFF3 and CNKSR3 gene loci affecting the risk of diabetic kidney disease (DKD) end-stage renal disease. There is increasing evidence that genetic factors affecting kidney disease in non-diabetic individuals also affect the risk in individuals with type 2 diabetes (T2D), while less evidence is found for individuals with type 1 diabetes (T1D). While genetic explorations for diabetic retinopathy remain limited in sample size, a recent genome-wide association study (GWAS) identified variants associated with retinopathy on the GRB2 gene. Nevertheless, the field is still lacking strong validated genetic markers. In the future, better phenotyping, larger studies, and exploration of the rare variation are essential to identify the genetic causes behind diabetic microvascular complications, and to understand the interplay between genes and environment.Peer reviewe
Role of lepton flavor violating (LFV) muon decay in Seesaw model and LSND
The aim of the work is to study LFV in a newly proposed Seesaw model of
neutrino mass and to see whether it could explain LSND excess. The motivation
of this Seesaw model was that there was no new physics beyond the TeV scale. By
studying \mu \to 3e in this model, it is shown that the upper bound on the
branching ratio requires Higgs mass m_{h} of a new scalar doublet with lepton
number L=-1 needed in the model has to be about 9 TeV. The predicted branching
ratio for \mu \to e\nu_{l}\bar{\nu}_{l} is too small to explain the LSND. PACS:
11.30.Hv, 14.60.PqComment: 05 pages, three figures, the version to appear in PR
A SUSY SU(5) Grand Unified Model of Tri-Bimaximal Mixing from A4
We discuss a grand unified model based on SUSY SU(5) in extra dimensions and
on the flavour group A4xU(1) which, besides reproducing tri-bimaximal mixing
for neutrinos with the accuracy required by the data, also leads to a natural
description of the observed pattern of quark masses and mixings.Comment: 19 page
Neutrino masses through see-saw mechanism in 3-3-1 models
Some years ago it was shown by Ma that in the context of the electroweak
standard model there are, at the tree level, only three ways to generate small
neutrino masses by the see-saw mechanism via one effective dimension-five
operator. Here we extend this approach to 3-3-1 chiral models showing that in
this case there are several dimension-five operators and we also consider their
tree level realization.Comment: RevTex, 7 pages and 4 .eps figures. Version published in Phys. Rev.
D. with a change in the titl
Bound state solutions of the Dirac-Rosen-Morse potential with spin and pseudospin symmetry
The energy spectra and the corresponding two- component spinor wavefunctions
of the Dirac equation for the Rosen-Morse potential with spin and pseudospin
symmetry are obtained. The wave ( state) solutions for this
problem are obtained by using the basic concept of the supersymmetric quantum
mechanics approach and function analysis (standard approach) in the
calculations. Under the spin symmetry and pseudospin symmetry, the energy
equation and the corresponding two-component spinor wavefunctions for this
potential and other special types of this potential are obtained. Extension of
this result to state is suggested.Comment: 18 page
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