10,687 research outputs found
Variance Estimation Using Refitted Cross-validation in Ultrahigh Dimensional Regression
Variance estimation is a fundamental problem in statistical modeling. In
ultrahigh dimensional linear regressions where the dimensionality is much
larger than sample size, traditional variance estimation techniques are not
applicable. Recent advances on variable selection in ultrahigh dimensional
linear regressions make this problem accessible. One of the major problems in
ultrahigh dimensional regression is the high spurious correlation between the
unobserved realized noise and some of the predictors. As a result, the realized
noises are actually predicted when extra irrelevant variables are selected,
leading to serious underestimate of the noise level. In this paper, we propose
a two-stage refitted procedure via a data splitting technique, called refitted
cross-validation (RCV), to attenuate the influence of irrelevant variables with
high spurious correlations. Our asymptotic results show that the resulting
procedure performs as well as the oracle estimator, which knows in advance the
mean regression function. The simulation studies lend further support to our
theoretical claims. The naive two-stage estimator which fits the selected
variables in the first stage and the plug-in one stage estimators using LASSO
and SCAD are also studied and compared. Their performances can be improved by
the proposed RCV method
Medical Image Segmentation Based on Multi-Modal Convolutional Neural Network: Study on Image Fusion Schemes
Image analysis using more than one modality (i.e. multi-modal) has been
increasingly applied in the field of biomedical imaging. One of the challenges
in performing the multimodal analysis is that there exist multiple schemes for
fusing the information from different modalities, where such schemes are
application-dependent and lack a unified framework to guide their designs. In
this work we firstly propose a conceptual architecture for the image fusion
schemes in supervised biomedical image analysis: fusing at the feature level,
fusing at the classifier level, and fusing at the decision-making level.
Further, motivated by the recent success in applying deep learning for natural
image analysis, we implement the three image fusion schemes above based on the
Convolutional Neural Network (CNN) with varied structures, and combined into a
single framework. The proposed image segmentation framework is capable of
analyzing the multi-modality images using different fusing schemes
simultaneously. The framework is applied to detect the presence of soft tissue
sarcoma from the combination of Magnetic Resonance Imaging (MRI), Computed
Tomography (CT) and Positron Emission Tomography (PET) images. It is found from
the results that while all the fusion schemes outperform the single-modality
schemes, fusing at the feature level can generally achieve the best performance
in terms of both accuracy and computational cost, but also suffers from the
decreased robustness in the presence of large errors in any image modalities.Comment: Zhe Guo and Xiang Li contribute equally to this wor
Flavor Violating Transitions of Charged Leptons from a Seesaw Mechanism of Dimension Seven
A mechanism has been suggested recently to generate the neutrino mass out of
a dimension-seven operator. This is expected to relieve the tension between the
occurrence of a tiny neutrino mass and the observability of other physics
effects beyond it. Such a mechanism would inevitably entail lepton flavor
violating effects. We study in this work the radiative and purely leptonic
transitions of the light charged leptons. In so doing we make a systematic
analysis of the flavor structure by providing a convenient parametrization of
the mass matrices in terms of independent physical parameters and diagonalizing
them explicitly. We illustrate our numerical results by sampling over two CP
phases and one Yukawa coupling which are the essential parameters in addition
to the heavy lepton mass. We find that with the stringent constraints coming
from the muon decays and the muon-electron conversion in nuclei taken into
account the decays of the tau lepton are severely suppressed in the majority of
parameter space. There exist, however, small regions in which some tau decays
can reach a level that is about 2 orders of magnitude below their current
bounds.Comment: v1: 25 pages, 8 figures; v2: proofread version for PRD. Included
muon-electron conversion in nuclei at the referee's suggestion and added
relevant refs accordingly; main conclusion not changed but bounds on tau
lepton decays becoming more stringent; linguistic and editing corrections
also mad
Highlights of Supersymmetric Hypercharge Triplets
The discovery of a standard model (SM)-like Higgs boson with a relatively
heavy mass and hints of di-photon excess has deep implication to
supersymmetric standard models (SSMs). We consider the SSM extended with
hypercharge triplets, and investigate two scenarios of it: (A) Triplets
significantly couple to the Higgs doublets, which can substantially raise
and simultaneously enhance the Higgs to di-photon rate via light chargino
loops; (B) Oppositely, these couplings are quite weak and thus can not be
raised. But the doubly-charged Higgs bosons, owing to the gauge group
structure, naturally interprets why there is an excess rather than a deficient
of Higgs to di-photon rate. Additionally, the pseudo Dirac triplet fermion is
an inelastic non-thermal dark matter candidate. Light doubly-charged particles,
especially the doubly-charged Higgs boson around 100 GeV in scenario B, are
predicted. We give a preliminary discussion on their search at the LHC.Comment: JHEP version. Typos fixed, comments, references and acknowledge adde
Localized Dimension Growth in Random Network Coding: A Convolutional Approach
We propose an efficient Adaptive Random Convolutional Network Coding (ARCNC)
algorithm to address the issue of field size in random network coding. ARCNC
operates as a convolutional code, with the coefficients of local encoding
kernels chosen randomly over a small finite field. The lengths of local
encoding kernels increase with time until the global encoding kernel matrices
at related sink nodes all have full rank. Instead of estimating the necessary
field size a priori, ARCNC operates in a small finite field. It adapts to
unknown network topologies without prior knowledge, by locally incrementing the
dimensionality of the convolutional code. Because convolutional codes of
different constraint lengths can coexist in different portions of the network,
reductions in decoding delay and memory overheads can be achieved with ARCNC.
We show through analysis that this method performs no worse than random linear
network codes in general networks, and can provide significant gains in terms
of average decoding delay in combination networks.Comment: 7 pages, 1 figure, submitted to IEEE ISIT 201
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