25 research outputs found
Key courses of academic curriculum uncovered by data mining of students' grades
Learning is a complex cognitive process that depends not only on an
individual capability of knowledge absorption but it can be also influenced by
various group interactions and by the structure of an academic curriculum. We
have applied methods of statistical analyses and data mining (Principal
Component Analysis and Maximal Spanning Tree) for anonymized students' scores
at Faculty of Physics, Warsaw University of Technology. A slight negative
linear correlation exists between mean and variance of course grades, i.e.
courses with higher mean scores tend to possess a lower scores variance.
There are courses playing a central role, e.g. their scores are highly
correlated to other scores and they are in the centre of corresponding Maximal
Spanning Trees. Other courses contribute significantly to students' score
variance as well to the first principal component and they are responsible for
differentiation of students' scores. Correlations of the first principal
component to courses' mean scores and scores variance suggest that this
component can be used for assigning ECTS points to a given course. The analyse
is independent from declared curricula of considered courses. The proposed
methodology is universal and can be applied for analysis of student's scores
and academic curriculum at any faculty
The role of emotional variables in the classification and prediction of collective social dynamics
We demonstrate the power of data mining techniques for the analysis of
collective social dynamics within British Tweets during the Olympic Games 2012.
The classification accuracy of online activities related to the successes of
British athletes significantly improved when emotional components of tweets
were taken into account, but employing emotional variables for activity
prediction decreased the classifiers' quality. The approach could be easily
adopted for any prediction or classification study with a set of
problem-specific variables.Comment: 16 pages, 9 figures, 2 tables and 1 appendi
Temporal Taylor's scaling of facial electromyography and electrodermal activity in the course of emotional stimulation
High frequency psychophysiological data create a challenge for quantitative
modeling based on Big Data tools since they reflect the complexity of processes
taking place in human body and its responses to external events. Here we
present studies of fluctuations in facial electromyography (fEMG) and
electrodermal activity (EDA) massive time series and changes of such signals in
the course of emotional stimulation. Zygomaticus major (ZYG, "smiling" muscle)
activity, corrugator supercilii (COR, "frowning"bmuscle) activity, and phasic
skin conductance (PHSC, sweating) levels of 65 participants were recorded
during experiments that involved exposure to emotional stimuli (i.e., IAPS
images, reading and writing messages on an artificial online discussion board).
Temporal Taylor's fluctuations scaling were found when signals for various
participants and during various types of emotional events were compared. Values
of scaling exponents were close to 1, suggesting an external origin of system
dynamics and/or strong interactions between system's basic elements (e.g.,
muscle fibres). Our statistical analysis shows that the scaling exponents
enable identification of high valence and arousal levels in ZYG and COR
signals
Flux calculations in an inhomogeneous Universe: weighting a flux-limited galaxy sample
Many astrophysical problems arising within the context of ultra-high energy
cosmic rays, very-high energy gamma rays or neutrinos, require calculation of
the flux produced by sources tracing the distribution of galaxies in the
Universe. We discuss a simple weighting scheme, an application of the method
introduced by Lynden-Bell in 1971, that allows the calculation of the flux sky
map directly from a flux-limited galaxy catalog without cutting a
volume-limited subsample. Using this scheme, the galaxy distribution can be
modeled up to large scales while representing the distribution in the nearby
Universe with maximum accuracy. We consider fluctuations in the flux map
arising from the finiteness of the galaxy sample. We show how these
fluctuations are reduced by the weighting scheme and discuss how the remaining
fluctuations limit the applicability of the method.Comment: 8 pages, 10 figures, accepted for publication in MNRA
Long-term IR Photometry of Seyferts
Long-term (up to 10000d) monitoring has been undertaken for 41 Seyferts in
the near-IR (JHKL). All but 2 showed variability, with K ampl in the range <0.1
to > 1.1 mags. The timescale for detectable change is from about one week to a
few years. A simple cross-correlation study shows evidence for delays of up to
several hundred days between the variations seen at the shortest wavelengths
and the longest in many galaxies. In particular, the data for F9 now extend to
twice the interval covered earlier and the delay between its UV and IR outputs
persists. An analysis of the fluxes shows that, for any given galaxy, the
colours of the variable component are usually independent of the level of
activity. The state of activity can be parameterized. Taken over the whole
sample, the colours of the variable components fall within moderately narrowly
defined ranges. In particular, the H-K colour is appropriate to a black body of
temperature 1600K. The H-K excess for a heavily reddened nucleus can be
determined and used to find E_{B-V}, which can be compared to the values found
from the visible region broad line fluxes. Using flux-flux diagrams, the flux
within the aperture from the underlying galaxy can often be determined without
the need for model surface brightness profiles. In many galaxies it is apparent
that here must be an additional constant contribution from warm dust.Comment: Better quality available from ftp://ftp.saao.ac.za/pub/isg/seyf.pd
A calibrated measure to compare fluctuations of different entities across timescales
© 2020 The Authors. Published by Springer. This is an open access article available under a Creative Commons licence.
The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1038/s41598-020-77660-4A common way to learn about a system’s properties is to analyze temporal fluctuations in associated variables. However, conclusions based on fluctuations from a single entity can be misleading when used without proper reference to other comparable entities or when examined only on one timescale. Here we introduce a method that uses predictions from a fluctuation scaling law as a benchmark for the observed standard deviations. Differences from the benchmark (residuals) are aggregated across multiple timescales using Principal Component Analysis to reduce data dimensionality. The first component score is a calibrated measure of fluctuations—the reactivityRA of a given entity. We apply our method to activity records from the media industry using data from the Event Registry news aggregator—over 32M articles on selected topics published by over 8000 news outlets. Our approach distinguishes between different news outlet reporting styles: high reactivity points to activity fluctuations larger than expected, reflecting a bursty reporting style, whereas low reactivity suggests a relatively stable reporting style. Combining our method with the political bias detector Media Bias/Fact Check we quantify the relative reporting styles for different topics of mainly US media sources grouped by political orientation. The results suggest that news outlets with a liberal bias tended to be the least reactive while conservative news outlets were the most reactive.The work was partially supported as RENOIR Project by the European Union Horizon 2020 research and innovation programme under the Marie Skłodowska–Curie Grant Agreement No. 691152 and by Ministry of Science and Higher Education (Poland), Grant Nos. 34/H2020/2016, 329025/PnH/2016 and by National Science Centre, Poland Grant No. 2015/19/B/ST6/02612. J.A.H. was partially supported by the Russian Scientific Foundation, Agreement #17-71-30029 with co-financing of Bank Saint Petersburg and by POB Research Centre Cybersecurity and Data Science of Warsaw University of Technology within the Excellence Initiative Program—Research University (IDUB).Published onlin
Constructing a bivariate distribution function with given marginals and correlation: application to the galaxy luminosity function
We show an analytic method to construct a bivariate distribution function
(DF) with given marginal distributions and correlation coefficient. We
introduce a convenient mathematical tool, called a copula, to connect two DFs
with any prescribed dependence structure. If the correlation of two variables
is weak (Pearson's correlation coefficient ), the
Farlie-Gumbel-Morgenstern (FGM) copula provides an intuitive and natural way
for constructing such a bivariate DF. When the linear correlation is stronger,
the FGM copula cannot work anymore. In this case, we propose to use a Gaussian
copula, which connects two given marginals and directly related to the linear
correlation coefficient between two variables. Using the copulas, we
constructed the BLFs and discuss its statistical properties. Especially, we
focused on the FUV--FIR BLF, since these two luminosities are related to the
star formation (SF) activity. Though both the FUV and FIR are related to the SF
activity, the univariate LFs have a very different functional form: former is
well described by the Schechter function whilst the latter has a much more
extended power-law like luminous end. We constructed the FUV-FIR BLFs by the
FGM and Gaussian copulas with different strength of correlation, and examined
their statistical properties. Then, we discuss some further possible
applications of the BLF: the problem of a multiband flux-limited sample
selection, the construction of the SF rate (SFR) function, and the construction
of the stellar mass of galaxies ()--specific SFR () relation. The
copulas turned out to be a very useful tool to investigate all these issues,
especially for including the complicated selection effects.Comment: 14 pages, 5 figures, accepted for publication in MNRAS
Structural properties of discs and bulges of early-type galaxies
We have used the EFAR sample of galaxies to study the light distributions of
early-type galaxies. We decompose the 2D light distribution of the galaxies in
a flattened spheroidal component with a Sersic radial light profile and an
inclined disc component with an exponential light profile. We show that the
brightest, bulge dominated elliptical galaxies have a fairly broad distribution
in the Sersic profile shape parameter n_B, with a median of about 3.7 and a
sigma of ~0.9. Other galaxies have smaller n_B values, meaning that spheroids
are in general less concentrated than the n_B=4 de Vaucouleurs-law profile.
The results of our light decompositions are robust, even though without
kinematic information we cannot prove that the spheroids and discs are really
pressure- and rotation-supported stellar systems. If we assume that the
detected spheroids and discs are indeed separate components, we can draw the
following conclusions: 1) the spheroid and disc scale sizes are correlated; 2)
bulge-to-total luminosity ratios, bulge effective radii, and bulge n_B values
are all positively correlated; 3) the bivariate space density distribution of
elliptical galaxies in the (luminosity, scale size)-plane is well described by
a Schechter luminosity function in and a log-normal scale-size distribution at
a given luminosity; 4) at the brightest luminosities, the scale size
distribution of elliptical galaxies is similar to those of bright spiral
galaxies; at fainter luminosities the elliptical scale size distribution peaks
at distinctly smaller sizes than the spiral galaxy distribution; and 5) bulge
components of early-type galaxies are typically a factor 1.5 to 2.5 smaller
than the disks of spiral galaxies, while disc components of early-type galaxies
are typically twice as large as the discs of spiral galaxies. [abridged]Comment: 16 pages, 18 figures. Accepted for publication in the MNRA
The Bivariate Brightness Function of Galaxies and a Demonstration of the Impact of Surface Brightness Selection Effects on Luminosity Function Estimations
In this paper we fit an analytic function to the Bivariate Brightness
Distribution (BBD) of galaxies. It is a combination of the classical Schechter
Function convolved with a Gaussian distribution in surface brightness: thus
incorporating the luminosity-surface brightness correlation as seen in many
recent datasets. We fit this function to a recent measurement of the BBD based
on 45,000 galaxies from the two-degree field Galaxy Redshift Survey (Cross et
al. 2001).
Using a BBF we explore the impact of the limiting detection isophote on
classical measures of the galaxy luminosity distribution. If Gaussian corrected
magnitudes are used these change to mags, and for mag
arcsec. Hence while the faint-end slope, , appears fairly robust
to surface brightness issues, both the and values are highly
dependent. The range over which these parameters were seen to vary is fully
consistent with the scatter in the published values, reproducing the range of
observed luminosity densities (Mpc
see Cross et al. 2001). We conclude that surface brightness selection effects
are primarily responsible for this variation. After due consideration of these
effects, we derive a value of Mpc.Comment: 10 pages, 7 figures, Accepted by MNRA