1,116 research outputs found
Telecommunications systems design techniques handbook
Handbook presents design and analysis of tracking, telemetry, and command functions utilized in these systems with particular emphasis on deep-space telecommunications. Antenna requirements are also discussed. Handbook provides number of tables outlining various performance criteria. Block diagrams and performance charts are also presented
Designing citizen science tools for learning: lessons learnt from the iterative development of nQuire
This paper reports on a 4-year research and development case study about the design of citizen science tools for inquiry learning. It details the process of iterative pedagogy-led design and evaluation of the nQuire toolkit, a set of web-based and mobile tools scaffolding the creation of online citizen science investigations. The design involved an expert review of inquiry learning and citizen science, combined with user experience studies involving more than 200 users. These have informed a concept that we have termed ‘citizen inquiry’, which engages members of the public alongside scientists in setting up, running, managing or contributing to citizen science projects with a main aim of learning about the scientific method through doing science by interaction with others. A design-based research (DBR) methodology was adopted for the iterative design and evaluation of citizen science tools. DBR was focused on the refinement of a central concept, ‘citizen inquiry’, by exploring how it can be instantiated in educational technologies and interventions. The empirical evaluation and iteration of technologies involved three design experiments with end users, user interviews, and insights from pedagogy and user experience experts. Evidence from the iterative development of nQuire led to the production of a set of interaction design principles that aim to guide the development of online, learning-centred, citizen science projects. Eight design guidelines are proposed: users as producers of knowledge, topics before tools, mobile affordances, scaffolds to the process of scientific inquiry, learning by doing as key message, being part of a community as key message, every visit brings a reward, and value users and their time
Discovery of a new Transient X-ray Pulsar in the Small Magellanic Cloud
Rossi X-Ray Timing Explorer observations of the Small Magellanic Cloud have
revealed a previously unknown transient X-ray pulsar with a pulse period of
95s. Provisionally designated XTE SMC95, the pulsar was detected in three
Proportional Counter Array observations during an outburst spanning 4 weeks in
March/April 1999. The pulse profile is double peaked reaching a pulse fraction
\~0.8. The source is proposed as a Be/neutron star system on the basis of its
pulsations, transient nature and characteristically hard X-ray spectrum. The
2-10 keV X-ray luminosity implied by our observations is > 2x10^37 erg/s which
is consistent with that of normal outbursts seen in Galactic systems. This
discovery adds to the emerging picture of the SMC as containing an extremely
dense population of transient high mass X-ray binaries.Comment: Accepted by A&A. 7 pages, 6 figure
Analysing the Suzaku Spectra of the Broad-Line Seyfert 1 Galaxy CBS 126
We analysed new simultaneous \emph{Suzaku} and \emph{Swift} data of the Broad
Line Seyfert 1 (BLS1) galaxy CBS 126. A clear Fe emission line and a strong
soft excess are present in the source spectra. We fit the spectra with a
relativistic reflection model and find the model tends to fit the data with a
high iron abundance possibly due to the large soft excess present. By checking
the difference and the RMS spectra, we find there is likely an absorption edge
at 0.89 keV, which might be caused by oxygen or neon. We also produced
an analysis of the time-resolved spectra in order to examine the existence of
the edge. Although high iron abundance is required more in the time-resolved
spectra, a model of solar iron abundance together with an absorption edge gives
a more physical explanation. Variation of the ionisation parameter is an
alternative, plausible explanation for the excess seen in the difference
spectra. It is difficult to know if there are warm absorbers in this source
from the current data. To further investigate the presence of possible warm
absorbers, higher signal-to-noise low-energy data are needed. The work
presented here tentatively suggests that the spectra of a BLS1 can be explained
by a relativistic reflection model similar to that often seen in their
narrow-line cousins.Comment: 10 pages, 12 figures, accepted for publication in MNRA
A Spectroscopic and Photometric Study of Short-Timescale Variability in NGC5548
Results of a ground-based optical monitoring campaign on NGC5548 in June 1998
are presented. The broad-band fluxes (U,B,V), and the spectrophotometric
optical continuum flux F_lambda(5100 A) monotonically decreased in flux while
the broad-band R and I fluxes and the integrated emission-line fluxes of Halpha
and Hbeta remained constant to within 5%. On June 22, a short continuum flare
was detected in the broad band fluxes. It had an amplitude of about ~18% and it
lasted only ~90 min. The broad band fluxes and the optical continuum
F_lambda(5100 A) appear to vary simultaneously with the EUV variations. No
reliable delay was detected for the broad optical emission lines in response to
the EUVE variations. Narrow Hbeta emission features predicted as a signature of
an accretion disk were not detected during this campaign. However, there is
marginal evidence for a faint feature at lambda = 4962 A with FWHM=~6 A
redshifted by Delta v = 1100 km/s with respect to Hbeta_narrow.Comment: 12 pages, 7 figures, accepted for publishing in A&
Reverberation Mapping and the Physics of Active Galactic Nuclei
Reverberation-mapping campaigns have revolutionized our understanding of AGN.
They have allowed the direct determination of the broad-line region size,
enabled mapping of the gas distribution around the central black hole, and are
starting to resolve the continuum source structure. This review describes the
recent and successful campaigns of the International AGN Watch consortium,
outlines the theoretical background of reverberation mapping and the
calculation of transfer functions, and addresses the fundamental difficulties
of such experiments. It shows that such large-scale experiments have resulted
in a ``new BLR'' which is considerably different from the one we knew just ten
years ago. We discuss in some detail the more important new results, including
the luminosity-size-mass relationship for AGN, and suggest ways to proceed in
the near future.Comment: Review article to appear in Astronomical Time Series, Proceedings of
the Wise Observatory 25th Ann. Symposium. 24 pages including 7 figure
Interim Guidance for Basic and Advanced Life Support in Adults, Children, and Neonates With Suspected or Confirmed COVID-19: From the Emergency Cardiovascular Care Committee and Get With the Guidelines®-Resuscitation Adult and Pediatric Task Forces of the American Heart Association in Collaboration with the American Academy of Pediatrics, American Association for Respiratory Care, American College of Emergency Physicians, The Society of Critical Care Anesthesiologists, and American Society of Anesthesiologists: Supporting Organizations: American Association of Critical Care Nurses and National EMS Physicians.
Simultaneous X-ray and Ultraviolet spectroscopy of the Seyfert galaxy NGC 5548. III. X-ray time variability
The Seyfert 1 galaxy NGC 5548 was observed for a week by Chandra using both
the HETGS and LETGS spectrometers. In this paper we study the time variability
of the continuum radiation. During our observation, the source showed a gradual
increase in flux over four days, followed by a rapid decrease and flattening of
the light curve afterwards. Superimposed upon these relatively slow variations
several short duration bursts or quasi-periodic oscillations occured with a
typical duration of several hours and separation between 0.6-0.9 days. The
bursts show a delay of the hard X-rays with respect to the soft X-rays of a few
hours. We interprete these bursts as due to a rotating, fluctuating hot spot at
approximately 10 gravitational radii; the time delay of the hard X-rays from
the bursts agree with the canonical picture of Inverse Compton scattering of
the soft accretion disk photons on a hot medium that is relatively close to the
central black hole.Comment: 6 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
B and I-band optical micro-variability observations of the BL Lac objects S5 2007+777 and 3C371
We have observed S5 2007+777 and 3C371 in the B and I bands for 13 and 8
nights, respectively, during various observing runs in 2001, 2002 and 2004. The
observations resulted in almost evenly sampled light curves, 6-9 hours long. We
do not detect any flares within the observed light curves, but we do observe
small amplitude, significant variations, in both bands, on time scales of hours
and days. The average variability amplitude on time scales of minutes/hours is
2.5% and 1-1.5% in the case of S5 2007+777 and 3C371, respectively. The average
amplitudes increase to 5-12% and 4-6%, respectively, on time scales of days. We
find that the B and I band variations are highly correlated, on both short and
long time scales. During the 2004 observations, which resulted in the longest
light curves, we observe two well defined flux-decay and rising trends in the
light curves of both objects. When the flux decays, we observe significant
delays, with the B band flux decaying faster than the flux in the I band. As a
result, we also observe significant, flux related spectral variations as well.
The flux-spectral relation is rather complicated, with loop-like structures
forming during the flux evolution. The presence of spectral variations imply
that the observed variability is not caused by geometric effects. On the other
hand, our results are fully consistent with the hypothesis that the observed
variations are caused by perturbations which affect different regions in the
jet of the sources.Comment: Accepted for publication in Astronomy and Astrophysic
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