145,720 research outputs found
Statistical methods applied to composition studies of ultrahigh energy cosmic rays
The mass composition of high energy cosmic rays above eV is a
crucial issue to solve some open questions in astrophysics such as the
acceleration and propagation mechanisms. Unfortunately, the standard procedures
to identify the primary particle of a cosmic ray shower have low efficiency
mainly due to large fluctuations and limited experimental observables. We
present a statistical method for composition studies based on several
measurable features of the longitudinal development of the CR shower such as
, , asymmetry, skewness and kurtosis. Principal component
analysis (PCA) was used to evaluate the relevance of each parameter in the
representation of the overall shower features and a linear discriminant
analysis (LDA) was used to combine the different parameters to maximize the
discrimination between different particle showers. The new parameter from LDA
provides a separation between primary gammas, proton and iron nuclei better
than the procedures based on only. The method proposed here was
successfully tested in the energy range from to eV even
when limitations of shower track length were included in order to simulate the
field of view of fluorescence telescopes
Application and evaluation of sediment fingerprinting techniques in the Manawatu River catchment, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Geography at Massey University, Palmerston North, New Zealand
Suspended sediment is an important component of the fluvial environment, contributing not only to the physical form, but also the chemical and ecological character of river channels and adjacent floodplains. Fluvial sediment flux reflects erosion of the contributing catchment, which when enhanced can lead to a reduction in agricultural productivity, effect morphological changes in the riparian environment and alter aquatic ecosystems by elevating turbidity levels and degrading water quality. It is therefore important to identify catchment-scale erosion processes and understand rates of sediment delivery, transport and deposition into the fluvial system to be able to mitigate such adverse effects. Sediment fingerprinting is a well-used tool for evaluating sediment sources, capable of directly quantifying sediment supply through differentiating sediment sources based on their inherent geochemical signatures and statistical modelling.
Confluence-based sediment fingerprinting has achieved broad scale geochemical discrimination within the 5870 km2 Manawatu catchment, which drains terrain comprising soft-rock Tertiary and Quaternary sandstones, mudstones, limestones and more indurated greywacke. Multiple sediment samples were taken upstream and downstream of major river confluences, sieved to 40 and > 35 respectively. The revised mixing model estimated Mudstone terrain to contribute 59.3 % and 61.8 %, with significant contributions estimated from Mountain Range (12.0 % and 11.4 %) and Hill Surface (11.5 % and 11.3 %) respectively, indicating that Tm, Ni, Cu, Ca, P, Mn and Cr have an influence on these sediment source estimations
A new composition-sensitive parameter for Ultra-High Energy Cosmic Rays
A new family of parameters intended for composition studies in cosmic ray
surface array detectors is proposed. The application of this technique to
different array layout designs has been analyzed. The parameters make exclusive
use of surface data combining the information from the total signal at each
triggered detector and the array geometry. They are sensitive to the combined
effects of the different muon and electromagnetic components on the lateral
distribution function of proton and iron initiated showers at any given primary
energy. Analytical and numerical studies have been performed in order to assess
the reliability, stability and optimization of these parameters. Experimental
uncertainties, the underestimation of the muon component in the shower
simulation codes, intrinsic fluctuations and reconstruction errors are
considered and discussed in a quantitative way. The potential discrimination
power of these parameters, under realistic experimental conditions, is compared
on a simplified, albeit quantitative way, with that expected from other surface
and fluorescence estimators.Comment: 27 pages, 17 figures. Submitted to a refereed journa
Extending Item Response Theory to Online Homework
Item Response Theory becomes an increasingly important tool when analyzing
``Big Data'' gathered from online educational venues. However, the mechanism
was originally developed in traditional exam settings, and several of its
assumptions are infringed upon when deployed in the online realm. For a large
enrollment physics course for scientists and engineers, the study compares
outcomes from IRT analyses of exam and homework data, and then proceeds to
investigate the effects of each confounding factor introduced in the online
realm. It is found that IRT yields the correct trends for learner ability and
meaningful item parameters, yet overall agreement with exam data is moderate.
It is also found that learner ability and item discrimination is over wide
ranges robust with respect to model assumptions and introduced noise, less so
than item difficulty
Learning Fair Naive Bayes Classifiers by Discovering and Eliminating Discrimination Patterns
As machine learning is increasingly used to make real-world decisions, recent
research efforts aim to define and ensure fairness in algorithmic decision
making. Existing methods often assume a fixed set of observable features to
define individuals, but lack a discussion of certain features not being
observed at test time. In this paper, we study fairness of naive Bayes
classifiers, which allow partial observations. In particular, we introduce the
notion of a discrimination pattern, which refers to an individual receiving
different classifications depending on whether some sensitive attributes were
observed. Then a model is considered fair if it has no such pattern. We propose
an algorithm to discover and mine for discrimination patterns in a naive Bayes
classifier, and show how to learn maximum likelihood parameters subject to
these fairness constraints. Our approach iteratively discovers and eliminates
discrimination patterns until a fair model is learned. An empirical evaluation
on three real-world datasets demonstrates that we can remove exponentially many
discrimination patterns by only adding a small fraction of them as constraints
Mass hierarchy discrimination with atmospheric neutrinos in large volume ice/water Cherenkov detectors
Large mass ice/water Cherenkov experiments, optimized to detect low energy
(1-20 GeV) atmospheric neutrinos, have the potential to discriminate between
normal and inverted neutrino mass hierarchies. The sensitivity depends on
several model and detector parameters, such as the neutrino flux profile and
normalization, the Earth density profile, the oscillation parameter
uncertainties, and the detector effective mass and resolution. A proper
evaluation of the mass hierarchy discrimination power requires a robust
statistical approach. In this work, the Toy Monte Carlo, based on an extended
unbinned likelihood ratio test statistic, was used. The effect of each model
and detector parameter, as well as the required detector exposure, was then
studied. While uncertainties on the Earth density and atmospheric neutrino flux
profiles were found to have a minor impact on the mass hierarchy
discrimination, the flux normalization, as well as some of the oscillation
parameter (\Delta m^2_{31}, \theta_{13}, \theta_{23}, and \delta_{CP})
uncertainties and correlations resulted critical. Finally, the minimum required
detector exposure, the optimization of the low energy threshold, and the
detector resolutions were also investigated.Comment: 23 pages, 16 figure
Multiscale autocorrelation function: a new approach to anisotropy studies
We present a novel catalog-independent method, based on a scale dependent
approach, to detect anisotropy signatures in the arrival direction distribution
of the ultra highest energy cosmic rays (UHECR). The method provides a good
discrimination power for both large and small data sets, even in presence of
strong contaminating isotropic background. We present some applications to
simulated data sets of events corresponding to plausible scenarios for charged
particles detected by world-wide surface detector-based observatories, in the
last decades.Comment: 18 pages, 9 figure
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