3,134 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
Understanding Job Stress among Healthcare Staff
Introduction: Job life is an important part of a person’s daily life. There are many aspects of a job. A person may be satisfied with one or more aspects of his/her job but at the same time may be unhappy with other things related to the job. Objective: To evaluate the sources of job stress (stressful aspects of work) among the staff of a super specialty hospital & to suggest measures to decrease level of job stress. Methodology: Descriptive study employing 381 staff members of a super specialty hospital using a structured personal interview questionnaire consisting of 21 sources of stress. The hospital staff was asked to rate each item according to the extent to which it had contributed to their stress as experienced in their jobs in the past few months on a scale of 0 (not at all),1(a little), 2(quite a bit), 3 (a lot). A global rating of stress was also obtained. Result: The prime sources of stress were found to be underpayment (76%), excessive workload (70.3%), inadequate staff (48.6), & being involved in the emotional distress of patients (46.7%). Conclusion: The staffs of the hospital were in moderate stress due to the prime stressors so adequate measures should be taken to alleviate these stressors. This could be achieved through workload management, job redesign, & by offering occupational health education
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
Extreme Value Theory and the Solar Cycle
We investigate the statistical properties of the extreme events of the solar
cycle as measured by the sunspot number. The recent advances in the methodology
of the theory of extreme values is applied to the maximal extremes of the time
series of sunspots. We focus on the extreme events that exceed a carefully
chosen threshold and a generalized Pareto distribution is fitted to the tail of
the empirical cumulative distribution. A maximum likelihood method is used to
estimate the parameters of the generalized Pareto distribution and confidence
levels are also given to the parameters. Due to the lack of an automatic
procedure for selecting the threshold, we analyze the sensitivity of the fitted
generalized Pareto distribution to the exact value of the threshold. According
to the available data, that only spans the previous ~250 years, the cumulative
distribution of the time series is bounded, yielding an upper limit of 324 for
the sunspot number. We also estimate that the return value for each solar cycle
is ~188, while the return value for a century increases to ~228. Finally, the
results also indicate that the most probable return time for a large event like
the maximum at solar cycle 19 happens once every ~700 years and that the
probability of finding such a large event with a frequency smaller than ~50
years is very small. In spite of the essentially extrapolative character of
these results, their statistical significance is very large.Comment: 6 pages, 4 figures, accepted for publication in A&
An Investigation of How Wavelet Transform can Affect the Correlation Performance of Biomedical Signals : The Correlation of EEG and HRV Frequency Bands in the frontal lobe of the brain
© 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reservedRecently, the correlation between biomedical signals, such as electroencephalograms (EEG) and electrocardiograms (ECG) time series signals, has been analysed using the Pearson Correlation method. Although Wavelet Transformations (WT) have been performed on time series data including EEG and ECG signals, so far the correlation between WT signals has not been analysed. This research shows the correlation between the EEG and HRV, with and without WT signals. Our results suggest electrical activity in the frontal lobe of the brain is best correlated with the HRV.We assume this is because the frontal lobe is related to higher mental functions of the cerebral cortex and responsible for muscle movements of the body. Our results indicate a positive correlation between Delta, Alpha and Beta frequencies of EEG at both low frequency (LF) and high frequency (HF) of HRV. This finding is independent of both participants and brain hemisphere.Final Published versio
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