8,011 research outputs found
Stabilized Nearest Neighbor Classifier and Its Statistical Properties
The stability of statistical analysis is an important indicator for
reproducibility, which is one main principle of scientific method. It entails
that similar statistical conclusions can be reached based on independent
samples from the same underlying population. In this paper, we introduce a
general measure of classification instability (CIS) to quantify the sampling
variability of the prediction made by a classification method. Interestingly,
the asymptotic CIS of any weighted nearest neighbor classifier turns out to be
proportional to the Euclidean norm of its weight vector. Based on this concise
form, we propose a stabilized nearest neighbor (SNN) classifier, which
distinguishes itself from other nearest neighbor classifiers, by taking the
stability into consideration. In theory, we prove that SNN attains the minimax
optimal convergence rate in risk, and a sharp convergence rate in CIS. The
latter rate result is established for general plug-in classifiers under a
low-noise condition. Extensive simulated and real examples demonstrate that SNN
achieves a considerable improvement in CIS over existing nearest neighbor
classifiers, with comparable classification accuracy. We implement the
algorithm in a publicly available R package snn.Comment: 48 Pages, 11 Figures. To Appear in JASA--T&
Electric Fields and Chiral Magnetic Effect in Cu + Au Collisions
The non-central Cu + Au collisions can create strong out-of-plane magnetic
fields and in-plane electric fields. By using the HIJING model, we study the
general properties of the electromagnetic fields in Cu + Au collisions at 200
GeV and their impacts on the charge-dependent two-particle correlator
(see main text for
definition) which was used for the detection of the chiral magnetic effect
(CME). Compared with Au + Au collisions, we find that the in-plane electric
fields in Cu + Au collisions can strongly suppress the two-particle correlator
or even reverse its sign if the lifetime of the electric fields is long.
Combining with the expectation that if is induced by
elliptic-flow driven effects we would not see such strong suppression or
reversion, our results suggest to use Cu + Au collisions to test CME and
understand the mechanisms that underlie .Comment: V1: 7 pages, 8 figures. V2: Add 2 new figures. Published versio
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