430 research outputs found
ECA: High Dimensional Elliptical Component Analysis in non-Gaussian Distributions
We present a robust alternative to principal component analysis (PCA) ---
called elliptical component analysis (ECA) --- for analyzing high dimensional,
elliptically distributed data. ECA estimates the eigenspace of the covariance
matrix of the elliptical data. To cope with heavy-tailed elliptical
distributions, a multivariate rank statistic is exploited. At the model-level,
we consider two settings: either that the leading eigenvectors of the
covariance matrix are non-sparse or that they are sparse. Methodologically, we
propose ECA procedures for both non-sparse and sparse settings. Theoretically,
we provide both non-asymptotic and asymptotic analyses quantifying the
theoretical performances of ECA. In the non-sparse setting, we show that ECA's
performance is highly related to the effective rank of the covariance matrix.
In the sparse setting, the results are twofold: (i) We show that the sparse ECA
estimator based on a combinatoric program attains the optimal rate of
convergence; (ii) Based on some recent developments in estimating sparse
leading eigenvectors, we show that a computationally efficient sparse ECA
estimator attains the optimal rate of convergence under a suboptimal scaling.Comment: to appear in JASA (T&M
Financial model calibration using consistency hints
We introduce a technique for forcing the calibration of a financial model to produce valid parameters. The technique is based on learning from hints. It converts simple curve fitting into genuine calibration, where broad conclusions can be inferred from parameter values. The technique augments the error function of curve fitting with consistency hint error functions based on the Kullback-Leibler distance. We introduce an efficient EM-type optimization algorithm tailored to this technique. We also introduce other consistency hints, and balance their weights using canonical errors. We calibrate the correlated multifactor Vasicek model of interest rates, and apply it successfully to Japanese Yen swaps market and US dollar yield market
Lake Volume Data Analyses: A Deep Look into the Shrinking and Expansion Patterns of Lakes Azuei and Enriquillo, Hispaniola
This paper presents the development of an evenly spaced volume time series for Lakes Azuei and Enriquillo both located on the Caribbean island of Hispaniola. The time series is derived from an unevenly spaced Landsat imagery data set which is then exposed to several imputation methods to construct the gap filled uniformlyâspaced time series so it can be subjected to statistical analyses methods. The volume time series features both gradual and sudden changes the latter of which is attributed to North Atlantic cyclone activity. Relevant cyclone activity is defined as an event passing within 80 km and having regional monthly rainfall averages higher than a threshold value of 87 mm causing discontinuities in the lake responses. Discontinuities are accounted for in the imputation algorithm by dividing the time series into two subâsections: Before/after the event. Using leaveâpâout crossâvalidation and computing the NRMSE index the Stineman interpolation proves to be the best algorithm among 15 different imputation alternatives that were tested. The final time series features 16âday intervals which is subsequently resampled into one with monthly time steps. Data analyses of the monthly volume change time series show Lake Enriquilloâs seasonal periodicity in its behavior and also its sensitivity due to the occurrence of storm events. Response times feature a growth pattern lasting for one to two years after an extreme event, followed by a shrinking pattern lasting 5â7 years returning the lake to its original state. While both lakes show a remarkable long term increase in size starting in 2005, Lake Azuei is different in that it is much less sensitive to storm events and instead shows a stronger response to just changing seasonal rainfall patterns
A Search for the Flavor-Changing Neutral Current Decay B0_s -> mu^+mu^- in pp(bar) Collisions at \sqrt{s} = 1.96 TeV with the D0 Detector
We present the results of a search for the flavor-changing neutral current
decay B0_s -> mu+ mu- using a data set with integrated luminosity of 240
pb^{-1} of pp(bar) collisions at sqrt{s}=1.96 TeV collected with the D0
detector in Run II of the Fermilab Tevatron collider. We find the upper limit
on the branching fraction to be Br(B0_s -> mu+ mu-) \leq 5.0 x 10^{-7} at the
95% C.L. assuming no contributions from the decay B0_d -> mu+ mu- in the signal
region. This limit is the most stringent upper bound on the branching fraction
B0_s -> mu+ mu- to date.Comment: 7 pages, 3 figures, LaTeX, to be submitted to Physical Review
Letters, minor changes to text, reference adde
Sensitivity of Helioseismic Measurements of Normal-mode Coupling to Flows and Sound-speed Perturbations
In this article, we derive and compute the sensitivity of measurements of
coupling between normal modes of oscillation in the Sun to underlying flows.
The theory is based on first-Born perturbation theory, and the analysis is
carried out using the formalism described by \citet{lavely92}. Albeit tedious,
we detail the derivation and compute the sensitivity of specific pairs of
coupled normal modes to anomalies in the interior. Indeed, these kernels are
critical for the accurate inference of convective flow amplitudes and
large-scale circulations in the solar interior. We resolve some inconsistencies
in the derivation of \citet{lavely92} and reformulate the fluid-continuity
condition. We also derive and compute sound-speed kernels, paving the way for
inverting for thermal anomalies alongside flows.Comment: 24 pages, 8 Figures; MNRA
Introduction to flavour physics
We give a brief introduction to flavour physics. The first part covers the
flavour structure of the Standard Model, how the Kobayashi-Maskawa mechanism is
tested and provides examples of searches for new physics using flavour
observables, such as meson mixing and rare decays. In the second part we give a
brief overview of the recent flavour anomalies and how the Higgs can act as a
new flavour probe.Comment: 32 pages, 22 figures, the write-up is a combination of lectures given
at ESHEP 2018, SSI 2018 and the US Belle II summer schools, Fig. 1 corrected,
several typographical errors fixe
Segmentation and Optimal Region Selection of Physiological Signals using Deep Neural Networks and Combinatorial Optimization
Physiological signals, such as the electrocardiogram and the phonocardiogram
are very often corrupted by noisy sources. Usually, artificial intelligent
algorithms analyze the signal regardless of its quality. On the other hand,
physicians use a completely orthogonal strategy. They do not assess the entire
recording, instead they search for a segment where the fundamental and abnormal
waves are easily detected, and only then a prognostic is attempted.
Inspired by this fact, a new algorithm that automatically selects an optimal
segment for a post-processing stage, according to a criteria defined by the
user is proposed. In the process, a Neural Network is used to compute the
output state probability distribution for each sample. Using the aforementioned
quantities, a graph is designed, whereas state transition constraints are
physically imposed into the graph and a set of constraints are used to retrieve
a subset of the recording that maximizes the likelihood function, proposed by
the user.
The developed framework is tested and validated in two applications. In both
cases, the system performance is boosted significantly, e.g in heart sound
segmentation, sensitivity increases 2.4% when compared to the standard
approaches in the literature
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