211 research outputs found
The Geometry of Nonlinear Embeddings in Kernel Discriminant Analysis
Fisher's linear discriminant analysis is a classical method for
classification, yet it is limited to capturing linear features only. Kernel
discriminant analysis as an extension is known to successfully alleviate the
limitation through a nonlinear feature mapping. We study the geometry of
nonlinear embeddings in discriminant analysis with polynomial kernels and
Gaussian kernel by identifying the population-level discriminant function that
depends on the data distribution and the kernel. In order to obtain the
discriminant function, we solve a generalized eigenvalue problem with
between-class and within-class covariance operators. The polynomial
discriminants are shown to capture the class difference through the population
moments explicitly. For approximation of the Gaussian discriminant, we use a
particular representation of the Gaussian kernel by utilizing the exponential
generating function for Hermite polynomials. We also show that the Gaussian
discriminant can be approximated using randomized projections of the data. Our
results illuminate how the data distribution and the kernel interact in
determination of the nonlinear embedding for discrimination, and provide a
guideline for choice of the kernel and its parameters
Efficient quantile regression for heteroscedastic models
Quantile regression (QR) provides estimates of a range of conditional quantiles. This stands in contrast to traditional regression techniques, which focus on a single conditional mean function. Lee et al. [Regularization of case-specific parameters for robustness and efficiency. Statist Sci. 2012;27(3):350–372] proposed efficient QR by rounding the sharp corner of the loss. The main modification generally involves an asymmetric ℓ₂ adjustment of the loss function around zero. We extend the idea of ℓ₂ adjusted QR to linear heterogeneous models. The ℓ₂ adjustment is constructed to diminish as sample size grows. Conditions to retain consistency properties are also provided
Bayesian Restricted Likelihood Methods: Conditioning on Insufficient Statistics in Bayesian Regression
Bayesian methods have proven themselves to be successful across a wide range
of scientific problems and have many well-documented advantages over competing
methods. However, these methods run into difficulties for two major and
prevalent classes of problems: handling data sets with outliers and dealing
with model misspecification. We outline the drawbacks of previous solutions to
both of these problems and propose a new method as an alternative. When working
with the new method, the data is summarized through a set of insufficient
statistics, targeting inferential quantities of interest, and the prior
distribution is updated with the summary statistics rather than the complete
data. By careful choice of conditioning statistics, we retain the main benefits
of Bayesian methods while reducing the sensitivity of the analysis to features
of the data not captured by the conditioning statistics. For reducing
sensitivity to outliers, classical robust estimators (e.g., M-estimators) are
natural choices for conditioning statistics. A major contribution of this work
is the development of a data augmented Markov chain Monte Carlo (MCMC)
algorithm for the linear model and a large class of summary statistics. We
demonstrate the method on simulated and real data sets containing outliers and
subject to model misspecification. Success is manifested in better predictive
performance for data points of interest as compared to competing methods
Optical Torque from Enhanced Scattering by Multipolar Plasmonic Resonance
We present a theoretical study of the optical angular momentum transfer from
a circularly polarized plane wave to thin metal nanoparticles of different
rotational symmetries. While absorption has been regarded as the predominant
mechanism of torque generation on the nanoscale, we demonstrate numerically how
the contribution from scattering can be enhanced by using multipolar plasmon
resonance. The multipolar modes in non-circular particles can convert the
angular momentum carried by the scattered field, thereby producing
scattering-dominant optical torque, while a circularly symmetric particle
cannot. Our results show that the optical torque induced by resonant scattering
can contribute to 80% of the total optical torque in gold particles. This
scattering-dominant torque generation is extremely mode-specific, and deserves
to be distinguished from the absorption-dominant mechanism. Our findings might
have applications in optical manipulation on the nanoscale as well as new
designs in plasmonics and metamaterials.Comment: main article 20 pages, 4 figures; supplementary material 6 pages, 2
figure
Predictive Model Degrees of Freedom in Linear Regression
Overparametrized interpolating models have drawn increasing attention from
machine learning. Some recent studies suggest that regularized interpolating
models can generalize well. This phenomenon seemingly contradicts the
conventional wisdom that interpolation tends to overfit the data and performs
poorly on test data. Further, it appears to defy the bias-variance trade-off.
As one of the shortcomings of the existing theory, the classical notion of
model degrees of freedom fails to explain the intrinsic difference among the
interpolating models since it focuses on estimation of in-sample prediction
error. This motivates an alternative measure of model complexity which can
differentiate those interpolating models and take different test points into
account. In particular, we propose a measure with a proper adjustment based on
the squared covariance between the predictions and observations. Our analysis
with least squares method reveals some interesting properties of the measure,
which can reconcile the "double descent" phenomenon with the classical theory.
This opens doors to an extended definition of model degrees of freedom in
modern predictive settings.Comment: 47 pages, 18 figure
A Dominant Complement Fixation Pathway for Pneumococcal Polysaccharides Initiated by SIGN-R1 Interacting with C1q
The intricate system of serum complement proteins provides resistance to infection. A pivotal step in the complement pathway is the assembly of a C3 convertase, which digests the C3 complement component to form microbial binding C3 fragments recognized by leukocytes. The spleen and C3 provide resistance against blood-borne S. pneumoniae infection. To better understand the mechanisms involved, we studied SIGN-R1, a lectin that captures microbial polysaccharides in spleen. Surprisingly, conditional SIGN-R1 knockout mice developed deficits in C3 catabolism when given S. pneumoniae or its capsular polysaccharide intravenously. There were marked reductions in proteolysis of serum C3, deposition of C3 on organisms within SIGN-R1+ spleen macrophages, and formation of C3 ligands. We found that SIGN-R1 directly bound the complement C1 subcomponent, C1q, and assembled a C3 convertase, but without the traditional requirement for either antibody or factor B. The transmembrane lectin SIGN-R1 therefore contributes to innate resistance by an unusual C3 activation pathway
Perspectives of Apparel Sustainability Among Design Students from Different Cultural Backgrounds
Designers need to understand the breadth of strategies for developing more sustainable solutions (Shedroff, 2009). Design students’ concepts of sustainability are different depending on their cultural contexts and approaches to sustainability issues that universities have taken that vary across cultures. In this research, we examine how American and Korean design students perceive the importance of sustainability regarding their apparel as a user and professional and how they strategize sustainable practices. This cross-cultural comparison of American and Korean students perceptions of sustainability can provide valuable insight regarding how cultural factors shape and influence a group’s sustainable behavior and can help the instructor who wants to educate students as broadly as possible
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