2,016 research outputs found
Climate Change and National Laws across Commonwealth Countries
This paper furthers the Commonwealth agenda on climate action by exploring the kinds of ‘practical and swift action’ that might be taken through national legal frameworks to implement the Paris Agreement. The paper reviews national laws of Commonwealth member countries as they currently apply to and intersect with climate change. The paper investigates legal measures that relate directly to implement climate change policy, including climate change legislation and regulatory instruments such as emissions trading schemes and energy efficiency measures. It also considers indirect legal measures that can provide ‘co-benefits’ in relation to climate change policy, such as waste legislation and air quality measures. The paper presents examples of these different kinds of climate intersections in different Commonwealth legal systems, highlighting examples of what has worked well and what has not worked well to date, within different legal, economic and political cultures, and in different geographies and climates
Astrometric Monitoring of the HR 8799 Planets: Orbit Constraints from Self-Consistent Measurements
We present new astrometric measurements from our ongoing monitoring campaign
of the HR 8799 directly imaged planetary system. These new data points were
obtained with NIRC2 on the W.M. Keck II 10 meter telescope between 2009 and
2014. In addition, we present updated astrometry from previously published
observations in 2007 and 2008. All data were reduced using the SOSIE algorithm,
which accounts for systematic biases present in previously published
observations. This allows us to construct a self-consistent data set derived
entirely from NIRC2 data alone. From this dataset, we detect acceleration for
two of the planets (HR 8799b and e) at 3. We also assess possible
orbital parameters for each of the four planets independently. We find no
statistically significant difference in the allowed inclinations of the
planets. Fitting the astrometry while forcing coplanarity also returns
consistent to within 1 of the best fit values, suggesting that if
inclination offsets of 20 are present, they are not detectable
with current data. Our orbital fits also favor low eccentricities, consistent
with predictions from dynamical modeling. We also find period distributions
consistent to within 1 with a 1:2:4:8 resonance between all planets.
This analysis demonstrates the importance of minimizing astrometric systematics
when fitting for solutions to highly undersampled orbits.Comment: 18 pages, 11 figures. Accepted for publication in A
WFIRST Coronagraph Technology Requirements: Status Update and Systems Engineering Approach
The coronagraphic instrument (CGI) on the Wide-Field Infrared Survey
Telescope (WFIRST) will demonstrate technologies and methods for high-contrast
direct imaging and spectroscopy of exoplanet systems in reflected light,
including polarimetry of circumstellar disks. The WFIRST management and CGI
engineering and science investigation teams have developed requirements for the
instrument, motivated by the objectives and technology development needs of
potential future flagship exoplanet characterization missions such as the NASA
Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR
Surveyor (LUVOIR). The requirements have been refined to support
recommendations from the WFIRST Independent External Technical/Management/Cost
Review (WIETR) that the WFIRST CGI be classified as a technology demonstration
instrument instead of a science instrument. This paper provides a description
of how the CGI requirements flow from the top of the overall WFIRST mission
structure through the Level 2 requirements, where the focus here is on
capturing the detailed context and rationales for the CGI Level 2 requirements.
The WFIRST requirements flow starts with the top Program Level Requirements
Appendix (PLRA), which contains both high-level mission objectives as well as
the CGI-specific baseline technical and data requirements (BTR and BDR,
respectively)... We also present the process and collaborative tools used in
the L2 requirements development and management, including the collection and
organization of science inputs, an open-source approach to managing the
requirements database, and automating documentation. The tools created for the
CGI L2 requirements have the potential to improve the design and planning of
other projects, streamlining requirement management and maintenance. [Abstract
Abbreviated]Comment: 16 pages, 4 figure
The Development of a Caribbean Regional Network of Fisherfolk Organisations and its role in influencing fisheries policy
Magnon softening in a ferromagnetic monolayer: a first-principles spin dynamics study
We study the Fe/W(110) monolayer system through a combination of first
principles calculations and atomistic spin dynamics simulations. We focus on
the dispersion of the spin waves parallel to the [001] direction. Our results
compare favorably with the experimental data of Prokop et al. [Phys. Rev. Lett.
102, 177206], and correctly capture a drastic softening of the magnon spectrum,
with respect to bulk bcc Fe. The suggested shortcoming of the itinerant
electron model, in particular that given by density functional theory, is
refuted. We also demonstrate that finite temperature effects are significant,
and that atomistic spin dynamics simulations represent a powerful tool with
which to include these.Comment: v1: 11 pages, 3 figures. v2: double column, 5 pages, 3 figures, typos
corrected, references adde
The VAST Survey - III. The multiplicity of A-type stars within 75 pc
With a combination of adaptive optics imaging and a multi-epoch common proper
motion search, we have conducted a large volume-limited (D 75 pc)
multiplicity survey of A-type stars, sensitive to companions beyond 30 au. The
sample for the Volume-limited A-STar (VAST) survey consists of 435 A-type
stars: 363 stars were observed with adaptive optics, 228 stars were searched
for wide common proper motion companions and 156 stars were measured with both
techniques. The projected separation coverage of the VAST survey extends from
30 to 45,000 au. A total of 137 stellar companions were resolved, including 64
new detections from the VAST survey, and the companion star fraction, projected
separation distribution and mass ratio distribution were measured. The
separation distribution forms a log-normal distribution similar to the
solar-type binary distribution, but with a peak shifted to a significantly
wider value of 387 (+132,-98) au. Integrating the fit to the distribution over
the 30 to 10,000 au observed range, the companion star fraction for A-type
stars is estimated as 33.8%+-2.6%. The mass ratio distribution of closer (<125
au) binaries is distinct from that of wider systems, with a flat distribution
for close systems and a distribution that tends towards smaller mass ratios for
wider binaries. Combining this result with previous spectroscopic surveys of
A-type stars gives an estimate of the total companion star fraction of
68.9%+-7.0%. The most complete assessment of higher order multiples was
estimated from the 156-star subset of the VAST sample with both adaptive optics
and common proper motion measurements, combined with a literature search for
companions, yielding a lower limit on the frequency of single, binary, triple,
quadruple and quintuple A-type star systems of 56.4 (-4.0,+3.8), 32.1
(-3.5,+3.9), 9.0 (-1.8,+2.8), 1.9 (-0.6,+1.8) and 0.6 (-0.2,+1.4) per cent,
respectively.Comment: 46 pages, 24 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Society, 7th October 201
The Structure of High Strehl Ratio Point-Spread Functions
We describe the symmetries present in the point-spread function (PSF) of an
optical system either located in space or corrected by an adaptive o to Strehl
ratios of about 70% and higher. We present a formalism for expanding the PSF to
arbitrary order in terms of powers of the Fourier transform of the residual
phase error, over an arbitrarily shaped and apodized entrance aperture. For
traditional unapodized apertures at high Strehl ratios, bright speckles pinned
to the bright Airy rings are part of an antisymmetric perturbation of the
perfect PSF, arising from the term that is first order in the residual phase
error. There are two symmetric second degree terms. One is negative at the
center, and, like the first order term, is modulated by the perfect image's
field strength -- it reduces to the Marechal approximation at the center of the
PSF. The other is non-negative everywhere, zero at the image center, and can be
responsible for an extended halo -- which limits the dynamic range of faint
companion detection in the darkest portions of the image. In regimes where one
or the other term dominates the speckles in an image, the symmetry of the
dominant term can be exploited to reduce the effect of those speckles,
potentially by an order of magnitude or more. We demonstrate the effects of
both secondary obscuration and pupil apodization on the structure of residual
speckles, and discuss how these symmetries can be exploited by appropriate
telescope and instrument design, observing strategies, and filter bandwidths to
improve the dynamic range of high dynamic range AO and space-based
observations. Finally, we show that our analysis is relevant to high dynamic
range coronagraphy.Comment: Accepted for publication in ApJ; 20 pages, 4 figure
Opioids depress cortical centers responsible for the volitional control of respiration
Respiratory depression limits provision of safe opioid analgesia and is the main cause of death in drug addicts. Although opioids are known to inhibit brainstem respiratory activity, their effects on cortical areas that mediate respiration are less well understood. Here, functional magnetic resonance imaging was used to examine how brainstem and cortical activity related to a short breath hold is modulated by the opioid remifentanil. We hypothesized that remifentanil would differentially depress brain areas that mediate sensory-affective components of respiration over those that mediate volitional motor control. Quantitative measures of cerebral blood flow were used to control for hypercapnia-induced changes in blood oxygen level-dependent (BOLD) signal. Awareness of respiration, reflected by an urge-to-breathe score, was profoundly reduced with remifentanil. Urge to breathe was associated with activity in the bilateral insula, frontal operculum, and secondary somatosensory cortex. Localized remifentanil-induced decreases in breath hold-related activity were observed in the left anterior insula and operculum. We also observed remifentanil-induced decreases in the BOLD response to breath holding in the left dorsolateral prefrontal cortex, anterior cingulate, the cerebellum, and periaqueductal gray, brain areas that mediate task performance. Activity in areas mediating motor control (putamen, motor cortex) and sensory-motor integration (supramarginal gyrus) were unaffected by remifentanil. Breath hold-related activity was observed in the medulla. These findings highlight the importance of higher cortical centers in providing contextual awareness of respiration that leads to appropriate modulation of respiratory control. Opioids have profound effects on the cortical centers that control breathing, which potentiates their actions in the brainstem
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