21,188 research outputs found
Optical Monitoring of PKS 1510-089: A Binary Black Hole System?
Three deep flux minima were observed with nearly the same time-scales and
intervals for the blazar PKS 1510-089 in the past few years. A binary black
hole system was proposed to be at the nucleus of this object, and a new minimum
was predicted to occur in 2002 March. We monitored this source with a 60/90 cm
Schmidt telescope from 2002 February to April. In combination with the data
obtained by Xie et al. (2004) in the same period, we presented for the 2002
minimum a nearly symmetric light curve, which would be required by an eclipsing
model of a binary black hole system. We also constrained the time-scale of the
minimum to be 35 min, which is more consistent with the time-scales ~42 min of
the three previous minima than the 89 min time-scale given by the same authors.
The wiggling miniarcsecond radio jet observed in this object is taken as a
further evidence for the binary black hole system. The `coupling' of the
periodicity in light curve and the helicity in radio jet is discussed in the
framework of a binary black hole system.Comment: 5 pages, 4 figures, accepted by MNRA
Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination
Two aspects of the contribution of grazing incidence fast atom diffraction
(GIFAD) to molecular beam epitaxy (MBE) are reviewed here: the ability of GIFAD
to provide \emph{in-situ} a precise description of the atomic-scale surface
topology, and its ability to follow larger-scale changes in surface roughness
during layer-by-layer growth. Recent experimental and theoretical results
obtained for the He atom beam incident along the highly corrugated direction of the (24) reconstructed GaAs(001) surface are
summarized and complemented by the measurements and calculations for the beam
incidence along the weakly corrugated [010] direction where a periodicity twice
smaller as expected is observed. The combination of the experiment, quantum
scattering matrix calculations, and semiclassical analysis allows in this case
to reveal structural characteristics of the surface. For the in situ
measurements of GIFAD during molecular beam epitaxy of GaAs on GaAs surface we
analyse the change in elastic and inelastic contributions in the scattered
beam, and the variation of the diffraction pattern in polar angle scattering.
This analysis outlines the robustness, the simplicity and the richness of the
GIFAD as a technique to monitor the layer-by-layer epitaxial growth
Visual Analysis of Spatio-Temporal Event Predictions: Investigating the Spread Dynamics of Invasive Species
Invasive species are a major cause of ecological damage and commercial
losses. A current problem spreading in North America and Europe is the vinegar
fly Drosophila suzukii. Unlike other Drosophila, it infests non-rotting and
healthy fruits and is therefore of concern to fruit growers, such as vintners.
Consequently, large amounts of data about infestations have been collected in
recent years. However, there is a lack of interactive methods to investigate
this data. We employ ensemble-based classification to predict areas susceptible
to infestation by D. suzukii and bring them into a spatio-temporal context
using maps and glyph-based visualizations. Following the information-seeking
mantra, we provide a visual analysis system Drosophigator for spatio-temporal
event prediction, enabling the investigation of the spread dynamics of invasive
species. We demonstrate the usefulness of this approach in two use cases
GiViP: A Visual Profiler for Distributed Graph Processing Systems
Analyzing large-scale graphs provides valuable insights in different
application scenarios. While many graph processing systems working on top of
distributed infrastructures have been proposed to deal with big graphs, the
tasks of profiling and debugging their massive computations remain time
consuming and error-prone. This paper presents GiViP, a visual profiler for
distributed graph processing systems based on a Pregel-like computation model.
GiViP captures the huge amount of messages exchanged throughout a computation
and provides an interactive user interface for the visual analysis of the
collected data. We show how to take advantage of GiViP to detect anomalies
related to the computation and to the infrastructure, such as slow computing
units and anomalous message patterns.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
Photometry of Proxima Centauri and Barnard's Star Using HST Fine Guidance Sensor 3: A Search for Periodic Variations
We have observed Proxima Centauri and Barnard's Star with Hubble Space
Telescope Fine Guidance Sensor 3. Proxima Centauri exhibits small-amplitude,
periodic photometric variations. Once several sources of systematic photometric
error are corrected, we obtain 2 milli-magnitude internal photometric
precision. We identify two distinct behavior modes over the past four years:
higher amplitude, longer period; smaller amplitude, shorter period. Within the
errors one period (P ~ 83d) is twice the other. Barnard's Star shows very weak
evidence for periodicity on a timescale of approximately 130 days. If we
interpret these periodic phenomena as rotational modulation of star spots, we
identify three discrete spots on Proxima Cen and possibly one spot on Barnard's
Star. We find that the disturbances change significantly on time scales as
short as one rotation period.Comment: 39 pages, 17 figure
Health Figures: An Open Source JavaScript Library for Health Data Visualization
The way we look at data has a great impact on how we can understand it,
particularly when the data is related to health and wellness. Due to the
increased use of self-tracking devices and the ongoing shift towards preventive
medicine, better understanding of our health data is an important part of
improving the general welfare of the citizens. Electronic Health Records,
self-tracking devices and mobile applications provide a rich variety of data
but it often becomes difficult to understand. We implemented the hFigures
library inspired on the hGraph visualization with additional improvements. The
purpose of the library is to provide a visual representation of the evolution
of health measurements in a complete and useful manner. We researched the
usefulness and usability of the library by building an application for health
data visualization in a health coaching program. We performed a user evaluation
with Heuristic Evaluation, Controlled User Testing and Usability
Questionnaires. In the Heuristics Evaluation the average response was 6.3 out
of 7 points and the Cognitive Walkthrough done by usability experts indicated
no design or mismatch errors. In the CSUQ usability test the system obtained an
average score of 6.13 out of 7, and in the ASQ usability test the overall
satisfaction score was 6.64 out of 7. We developed hFigures, an open source
library for visualizing a complete, accurate and normalized graphical
representation of health data. The idea is based on the concept of the hGraph
but it provides additional key features, including a comparison of multiple
health measurements over time. We conducted a usability evaluation of the
library as a key component of an application for health and wellness
monitoring. The results indicate that the data visualization library was
helpful in assisting users in understanding health data and its evolution over
time.Comment: BMC Medical Informatics and Decision Making 16.1 (2016
Variable stars in the field of the old open cluster Melotte 66
We report the results of photometric monitoring of the Melotte 66 field in
BVI filters. Ten variables were identified with nine being new discoveries. The
sample includes eight eclipsing binaries of which four are W UMa type stars,
one star is a candidate blue straggler. All four contact binaries are likely
members of the cluster based on their estimated distances. Ten blue stars with
U-B<-0.3 were detected inside a 14.8 x 22.8 arcmin^2 field centred on the
cluster. Time series photometry for 7 of them showed no evidence for any
variability. The brightest object in the sample of blue stars is a promising
candidate for a hot subdwarf belonging to the cluster. We show that the
anomalously wide main sequence of the cluster, reported in some earlier
studies, results from a combination of two effects: variable reddening occuring
across the cluster field and the presence of a rich population of binary stars
in the cluster itself. The density profile of the cluster field is derived and
the total number of member stars with 16<V<21 or 2.8<M_{V}<7.8 is estimated
conservatively at about 1100.Comment: 8 pages, 12 figures, accepted to MNRAS - 29 June 200
The Burrell-Optical-Kepler-Survey (BOKS). I. Survey Description and Initial Results
We present the initial results of a 40 night contiguous ground-based campaign of time series photometric observations of a 1.39 deg^2 field located within the NASA Kepler Mission field of view. The goal of this pre-launch survey was to search for transiting extrasolar planets and to provide independent variability information of stellar sources. We have gathered a data set containing light curves of 54,687 stars from which we have created a statistical sub-sample of 13,786 stars between 14 < r < 18.5 and have statistically examined each light curve to test for variability. We present a summary of our preliminary photometric findings including the overall level and content of stellar variability in this portion of the Kepler field and give some examples of unusual variable stars found within. We present a preliminary catalog of 2,457 candidate variable stars, of which 776 show signs of periodicity. We also present three potential exoplanet candidates, all of which should be observable by the Kepler mission
The XMM-Newton survey of the Small Magellanic Cloud: XMMUJ005011.2-730026 = SXP214, a Be/X-ray binary pulsar
In the course of the XMM-Newton survey of the Small Magellanic Cloud (SMC), a
region to the east of the emission nebula N19 was observed in November 2009. To
search for new candidates for high mass X-ray binaries the EPIC PN and MOS data
of the detected point sources were investigated and their spectral and temporal
characteristics identified. A new transient (XMMUJ005011.2-730026= SXP214) with
a pulse period of 214.05 s was discovered; the source had a hard X-ray spectrum
with power-law index of ~0.65. The accurate X-ray source location permits the
identification of the X-ray source with a ~15th magnitude Be star, thereby
confirming this system as a new Be/X-ray binary.Comment: 8 pages 11 figures. Accepted for publication in MNRA
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