740 research outputs found
Models for the Magnitude-Distribution of Brightest Cluster Galaxies
The brightest, or first-ranked, galaxies (BCGs) in rich clusters show a very
small dispersion in luminosity, making them excellent standard candles. This
small dispersion has raised questions about the nature of BCGs. Are they simply
the extremes of normal galaxies formed via a stochastic process, or do they
belong to a special class of atypical objects? Arguments have been proposed on
both sides of the debate. Bhavsar (1989) suggested that the distribution in
magnitudes can only be explained by a two-population model. Thus, a new
controversy has arisen. Do first-ranked galaxies consist of one or two
populations of objects? We examine an older and newer data set and present our
results. Two-population models do better than do one-population models. A
simple model where a random boost in the magnitude of a fraction of bright
normal galaxies forms a class of atypical galaxies best describes the observed
distribution of BCG magnitudes. Moreover, the parameters that describe the
model and the parameters of the boost have a strong physical basis.Comment: Abstract submitted to AAS. Paper (6 pages, 4 figs.) to be published
in the MNRAS; uses mn.st
A catalog of Nearby Poor Clusters of Galaxies
A catalog of 732 optically selected, nearby poor clusters of galaxies
covering the entire sky north of declination is presented. The
poor clusters, called WBL clusters, were identified as concentrations of 3 or
more galaxies with photographic magnitudes brighter than 15.7, possessing a
galaxy surface overdensity of . These criteria are consistent with
those used in the identification of the original Yerkes poor clusters, and this
new catalog substantially increases the sample size of such objects. These poor
clusters cover the entire range of galaxy associations up to and including
Abell clusters, systematically including poor and rich galaxy systems spanning
over three orders of magnitude in the cluster mass function. As a result, this
new catalog contains a greater diversity of richness and structures than other
group catalogs, such as the Hickson or Yerkes catalogs. The information on
individual galaxies includes redshifts and cross-references to other galaxy
catalogs. The entries for the clusters include redshift (where available) and
cross-references to other group and cluster catalogs.Comment: 27 pages, 7 figures, + one 20-page landscape table, accepted for
publication in A
Assessing Variability of EEG and ECG/HRV Time Series Signals Using a Variety of Non-Linear Methods
Time series signals, such as Electroencephalogram (EEG) and Electrocardiogram
(ECG) represent the complex dynamic behaviours of biological systems.
The analysis of these signals using variety of nonlinear methods is essential
for understanding variability within EEG and ECG, which potentially
could help unveiling hidden patterns related to underlying physiological mechanisms.
EEG is a time varying signal, and electrodes for recording EEG at different
positions on the scalp give different time varying signals. There might
be correlation between these signals. It is important to know the correlation
between EEG signals because it might tell whether or not brain activities from
different areas are related. EEG and ECG might be related to each other because
both of them are generated from one co-ordinately working body. Investigating
this relationship is of interest because it may reveal information about
the correlation between EEG and ECG signals.
This thesis is about assessing variability of time series data, EEG and ECG, using
variety of nonlinear measures. Although other research has looked into the
correlation between EEGs using a limited number of electrodes and a limited
number of combinations of electrode pairs, no research has investigated the
correlation between EEG signals and distance between electrodes. Furthermore,
no one has compared the correlation performance for participants with
and without medical conditions. In my research, I have filled up these gaps
by using a full range of electrodes and all possible combinations of electrode
pairs analysed in Time Domain (TD). Cross-Correlation method is calculated
on the processed EEG signals for different number unique electrode pairs from
each datasets. In order to obtain the distance in centimetres (cm) between
electrodes, a measuring tape was used. For most of our participants the head
circumference range was 54-58cm, for which a medium-sized I have discovered
that the correlation between EEG signals measured through electrodes
is linearly dependent on the physical distance (straight-line) distance between
them for datasets without medical condition, but not for datasets with medical
conditions.
Some research has investigated correlation between EEG and Heart Rate Variability
(HRV) within limited brain areas and demonstrated the existence of
correlation between EEG and HRV. But no research has indicated whether or
not the correlation changes with brain area. Although Wavelet Transformations
(WT) have been performed on time series data including EEG and HRV
signals to extract certain features respectively by other research, so far correlation
between WT signals of EEG and HRV has not been analysed. My research
covers these gaps by conducting a thorough investigation of all electrodes on
the human scalp in Frequency Domain (FD) as well as TD. For the reason of
different sample rates of EEG and HRV, two different approaches (named as
Method 1 and Method 2) are utilised to segment EEG signals and to calculate
Pearsonâs Correlation Coefficient for each of the EEG frequencies with each
of the HRV frequencies in FD. I have demonstrated that EEG at the front area
of the brain has a stronger correlation with HRV than that at the other area in
a frequency domain. These findings are independent of both participants and
brain hemispheres.
Sample Entropy (SE) is used to predict complexity of time series data. Recent
research has proposed new calculation methods for SE, aiming to improve the
accuracy. To my knowledge, no one has attempted to reduce the computational
time of SE calculation. I have developed a new calculation method for time
series complexity which could improve computational time significantly in the
context of calculating a correlation between EEG and HRV. The results have
a parsimonious outcome of SE calculation by exploiting a new method of SE
implementation. In addition, it is found that the electrical activity in the frontal
lobe of the brain appears to be correlated with the HRV in a time domain.
Time series analysis method has been utilised to study complex systems that
appear ubiquitous in nature, but limited to certain dynamic systems (e.g. analysing
variables affecting stock values). In this thesis, I have also investigated the nature
of the dynamic system of HRV. I have disclosed that Embedding Dimension
could unveil two variables that determined HRV
A Sense of Belonging
National Collegiate Honors Council President delivers his address at the NCHCâs 2021 conference, describing that, despite the privileges he has chosen and enjoyed, expressions of otherness have led to feelings of estrangement. Considering the question of how to face this challenge in honors, the author emphasizes the imperative of creating a sense of belonging for every student
The Superiority of the Minimal Spanning Tree in Percolation Analyses of Cosmological Datasets
In this work we demonstrate the ability of the Minimal Spanning Tree to
duplicate the information contained within a percolation analysis for a point
dataset. We show how to construct the percolation properties from the Minimal
Spanning Tree, finding roughly an order of magnitude improvement in the
computer time required. We apply these statistics to Particle-Mesh simulations
of large-scale structure formation. We consider purely scale-free Gaussian
initial conditions (, with ) in a
critical density universe. We find in general the mass of the percolating
cluster is a much better quantity by which to judge the onset of percolation
than the length of the percolating cluster.Comment: 7 pages, 4 figures included, uses mn.sty & epsf.sty. Accepted by
MNRA
Development of dithizone based fibre optic evanescent wave sensor for heavy metal ion detection in aqueous environments.
Detection of highly toxic heavy metal ions requires rapid, simple, sensitive and selective detection methods in the environment. Optical fibre based sensing facilitates the remote, continuous and in-situ detection approaches in the environment. Herein, we report the development of a dithizone based fibre optic sensor with a simple procedure to detect heavy metal ions in the aqueous environment using an evanescent wave sensing approach. The chromogenic ligand dithizone and its spectral specificity with metal ions has been elaborated in this work. Paper presented at Sensors and their Applications XVII, held 16-18 September 2013 at Rixos Libertas, Dubrovnik, Croatia
Sugar-hydrolysing enzymes in gustatory mutants of Drosophila
The distribution of the isozymes of α-glucosidase in different parts of Drosophila melanogaster was examined. Two of the eight glucosidase bands are associated with tarsi. The gustatory mutations in the genes gustB and gustC greatly reduce tarsal glucosidase activity, but the enzyme deficiency is not correlated with inability to taste sugars
Status of quarkonia - like negative and positive parity states in a relativistic confinement scheme
Properties of quarkonia - like states in the charm and bottom sector have
been studied in the frame work of relativistic Dirac formalism with a linear
confinement potential. We have computed the mass spectroscopy and decay
properties (vector decay constant and leptonic decay width) of several
quarkonia - like states. Present study is also intended to identify some of the
unexplained states as mixed P-wave and mixed S-D wave states of Charmonia and
Bottomonia. The results indicate that the X(4140) state can be an admixture of
two P states of charmonium. And the charmonium like states X(4630) and X(4660)
are the admixed state of S - D waves. Similarly, the state recently
reported by Belle II can be a mixed P - states of bottomonium. In the
relativistic framework we have computed vector decay constant and the leptonic
decay width for S wave charmonium and bottomonium. The leptonic decay width for
the mixed states are also predicted. Further, both the masses
and the leptonic decay width are considered for the identification of the
quarkonia-like states.Comment: 14 pages, 2 figure
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