4,203 research outputs found
The Near-Infrared Broad Emission Line Region of Active Galactic Nuclei -- I. The Observations
We present high quality (high signal-to-noise ratio and moderate spectral
resolution) near-infrared (near-IR) spectroscopic observations of 23 well-known
broad-emission line active galactic nuclei (AGN). Additionally, we obtained
simultaneous (within two months) optical spectroscopy of similar quality. The
near-IR broad emission line spectrum of AGN is dominated by permitted
transitions of hydrogen, helium, oxygen, and calcium, and by the rich spectrum
of singly-ionized iron. In this paper we present the spectra, line
identifications and measurements, and address briefly some of the important
issues regarding the physics of AGN broad emission line regions. In particular,
we investigate the excitation mechanism of neutral oxygen and confront for the
first time theoretical predictions of the near-IR iron emission spectrum with
observations.Comment: 45 pages, 17 figures, accepted by ApJ
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Woven natural fibre reinforced composite materials for medical imaging
Repeatable patient positioning is key to minimising the burden on planning radiotherapy treatment. There are very few materials commercially available which are suitable for use in all common imaging and treatment modalities such as magnetic resonance imaging (MRI), X-Ray computed tomography (CT) and radiotherapy. In this article, we present several such materials based on woven natural fibres embedded in a range of different resin materials which are suitable for such applications. By investigating a range of resins and natural fibre materials in combination and evaluating their performance in terms of MRI and X-Ray imaging, we show that a woven cotton material impregnated with a two-part epoxy resin provides a 15% improvement in passage of X-Rays and has no impact on the MRI signal (unlike the 40% MRI signal attenuation from carbon fibre), whilst also retaining a flexural modulus up to 71% of that of carbon fibre. These results demonstrate that natural fibre composites produced using such materials provide desirable properties for use in patient support and positioning devices for multi-modal imaging, without the need to significantly compromise on the strength of the material
Characteristics of Clinical Shoulder Research Over the Last Decade: A Review of Shoulder Articles in \u3cem\u3eThe Journal of Bone & Joint Surgery\u3c/em\u3e from 2004 to 2014
Background: The purpose of this study was to determine characteristics and trends in published shoulder research over the last decade in a leading orthopaedic journal.
Methods: We examined all clinical shoulder articles published in The Journal of Bone & Joint Surgery from 2004 to 2014. The number of citations, authorship, academic degrees of the authors, country and institution of origin, topic, level of evidence, positive or nonpositive outcome, and inclusion of validated patient-reported outcome measures were assessed for each article.
Results: Shoulder articles that included an author with an advanced research degree (MD [Doctor of Medicine] with a PhD [Doctor of Philosophy] or other advanced degree) increased during the study period (p = 0.047). Level-I, II, and III studies were more likely to have an author with an advanced research degree, and Level-IV studies were more likely to have MDs only (p = 0.03). Overall, there was great variability of outcome measures, with at least thirty-nine different validated or nonvalidated outcome measures reported.
Conclusions: Over the last decade, there was an improvement in the level of evidence of shoulder articles published in The Journal of Bone & Joint Surgery that corresponds with recent emphasis on evidence-based medicine. A consensus is needed in shoulder research for more consistent application of validated patient-reported outcome measurement tools
Current Topics in Children's Learning and Cognition
Learning in Cognitive Niches / Gerhardt, Ana FlaÌvia Lopes Magela -- Using the Dynamics of a Person-Context System to Describe Childrenâs Understanding of Air Pressure / Steen, Steffie Van der; Steenbeek, Henderien; Geert, Paul Van -- Preschoolers Learning Science: Myth or Reality? / Kloos, Heidi; Baker, Heather; Luken, Eleanor; Brown, Rhonda; Pfeiffer, David; Carr, Victoria -- The Emergence of Scientific Reasoning / Morris, Bradley J.; Croker, Steve; Masnick, Amy M.; Zimmerman, Corinne -- Cognition and the Child Witness : Understanding the Impact of Cognitive Development in Forensic Contexts / Segovia, Daisy A.; Crossman, Angela M. -- Beyond the Black-and-White of Autism : How Cognitive Performance Varies with Context / Amaral, Joseph L.; Collins, Susan; Bohache, Kevin T.; Kloos, Heidi -- Psychological Fitness in Young Adult Video Game Players / Pokorski, Mieczyslaw; Borecki, Lukasz; Jernajczyk, Urszula -- The Impact of Moving Away from Home on Undergraduate Metacognitive Development / Downing, KevinAs a whole, the essays in this book address theoretical and empirical issues related to children's learning and cognition. The first essay, titled Learning in Cognitive Niches, treats the process of sense making on a theoretical level, discussing the complexity of factors that give rise to children's learning. It is followed by an essay, titled Using the Dynamics of a Person-Context System to Describe Children's Understanding of Air Pressure, that applies ideas from complexity science and dynamics-systems theory to children's learning about science. The next four essays summarize and synthesize already published findings, in an effort to go beyond individual viewpoints and present a more nuanced picture of children's sense making. In particular, two of these summaries, Preschoolers Learning Science: Myth or Reality? and The Emergence of Scientific Reasoning, focus on children's ability to make sense of their physical environment. The essay Cognition and the Child Witness: Understanding the Impact of Cognitive Development in Forensic Contexts seeks to shed light on children's sense making relevant to forensic issues. And the essay Beyond the Black-and-White of Autism: How Cognitive Performance Varies with Context ventures in the area of autism, a disorder that demonstrates atypical processes of combining pieces of information. The final two essays provide original data to add to the discussion of what factors affect cognitive functioning. In particular, the essay Cognitive Fitness in Young Adult Video Game Players seeks to re-assess the often-assumed relation between video gaming and various aspects of thinking, memory, intelligence, and visual-spatial abilities. And the essay Impact of Moving Away from Home on Undergraduate Metacognitive Development explicitly connects life circumstances to the ability to monitor and control one's thinking. Together, the collection of essays are a further step towards understanding the process of sense making as children and young adults interact with their environment
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Improved methodologies for continuous-flow analysis of stable water isotopes in ice cores
Water isotopes in ice cores are used as a climate proxy
for local temperature and regional atmospheric circulation as well as
evaporative conditions in moisture source regions. Traditional measurements
of water isotopes have been achieved using magnetic sector isotope ratio
mass spectrometry (IRMS). However, a number of recent studies have shown
that laser absorption spectrometry (LAS) performs as well or better than
IRMS. The new LAS technology has been combined with continuous-flow analysis
(CFA) to improve data density and sample throughput in numerous prior ice
coring projects. Here, we present a comparable semi-automated LAS-CFA system
for measuring high-resolution water isotopes of ice cores. We outline new
methods for partitioning both system precision and mixing length into liquid
and vapor components â useful measures for defining and improving the
overall performance of the system. Critically, these methods take into
account the uncertainty of depth registration that is not present in IRMS
nor fully accounted for in other CFA studies. These analyses are achieved
using samples from a South Pole firn core, a Greenland ice core, and the
West Antarctic Ice Sheet (WAIS) Divide ice core. The measurement system
utilizes a 16-position carousel contained in a freezer to consecutively
deliver ââŒââŻ1âŻmâŻâĂââŻ1.3âŻcm<sup>2</sup> ice sticks to a
temperature-controlled melt head, where the ice is converted to a continuous liquid
stream and eventually vaporized using a concentric nebulizer for isotopic
analysis. An integrated delivery system for water isotope standards is used
for calibration to the Vienna Standard Mean Ocean Water (VSMOW) scale, and depth registration is achieved using
a precise overhead laser distance device with an uncertainty of ±0.2
âŻmm. As an added check on the system, we perform inter-lab LAS comparisons
using WAIS Divide ice samples, a corroboratory step not taken in prior CFA
studies. The overall results are important for substantiating data obtained
from LAS-CFA systems, including optimizing liquid and vapor mixing lengths,
determining melt rates for ice cores with different accumulation and
thinning histories, and removing system-wide mixing effects that are
convolved with the natural diffusional signal that results primarily from
water molecule diffusion in the firn column
Optimization of cw sodium laser guide star efficiency
Context: Sodium laser guide stars (LGS) are about to enter a new range of
laser powers. Previous theoretical and numerical methods are inadequate for
accurate computations of the return flux and hence for the design of the
next-generation LGS systems.
Aims: We numerically optimize the cw (continuous wave) laser format, in
particular the light polarization and spectrum.
Methods: Using Bloch equations, we simulate the mesospheric sodium atoms,
including Doppler broadening, saturation, collisional relaxation, Larmor
precession, and recoil, taking into account all 24 sodium hyperfine states and
on the order of 100 velocity groups.
Results: LGS return flux is limited by "three evils": Larmor precession due
to the geomagnetic field, atomic recoil due to radiation pressure, and
transition saturation. We study their impacts and show that the return flux can
be boosted by repumping (simultaneous excitation of the sodium D2a and D2b
lines with 10-20% of the laser power in the latter).
Conclusions: We strongly recommend the use of circularly polarized lasers and
repumping. As a rule of thumb, the bandwidth of laser radiation in MHz (at each
line) should approximately equal the launched laser power in Watts divided by
six, assuming a diffraction-limited spot size.Comment: 15 pages, 12 figures, to be published in Astronomy & Astrophysics,
AA/2009/1310
Search for the Neutron Decay n X+ where X is a dark matter particle
In a recent paper submitted to Physical Review Letters, Fornal and Grinstein
have suggested that the discrepancy between two different methods of neutron
lifetime measurements, the beam and bottle methods can be explained by a
previously unobserved dark matter decay mode, n X+ where X
is a dark matter particle. We have performed a search for this decay mode over
the allowed range of energies of the monoenergetic gamma ray for X to be a dark
matter particle. We exclude the possibility of a sufficiently strong branch to
explain the lifetime discrepancy with greater than 4 sigma confidence.Comment: 6 pages 3 figure
To Binge or not To Binge: viewersâ moods and behaviors during the consumption of subscribed video streaming
The popularity of internet-distributed TV entertainment services, such
as Netflix, has transformed TV consumption behavior. Currently, the level of
control viewers have over their TV experiences, along with the release of com plete seasons at once, are some of the factors that stimulate the so-called binge watching phenomenon (the consumption of several episodes of a program in a
single sitting). Most of binge-watching studies have focused on viewersâ habits
and health effects. This paper presents a study that relates to viewersâ behaviors
and moods. It was carried out with 13 young participants at their home, watching
online content, collecting physiological, inertial, and self-reported data. We iden tify and compare binge-watching with non-binge-watching behaviors. Our results
suggest that while viewers recur to online serial entertainment in pursuit of lei sure related needs, such as relaxation, relief from boredom and escapism, the act
of binge-watching tends to make them feel rather unsatisfied with no change in
Arousal. Nevertheless, in binge-watching the Positive Affect increases while the
Negative decreases. Moreover, watching a single episode only, tends to result in
increased arousal and but not necessarily in increased satisfaction. This prelimi nary finding can be the starting point of fruitful future investigations on unpack ing further motives and nuances from this outcome.info:eu-repo/semantics/publishedVersio
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