16,867 research outputs found
On the Spatial Distribution of Hard X-Rays from Solar Flare Loops
The aim of this paper is to investigate the spatial structure of the
impulsive phase hard X-ray emission from solar flares. This work is motivated
by the YOHKOH and the forthcoming HESSI observations. Summarizing past results,
it is shown that the transport effects can account for the observations by
inhomogeneous loops where there is a strong field convergence and/or density
enhancement at the top of the flaring loop. Scattering by plasma turbulence at
the acceleration site or pancake type pitch angle distribution of the
accelerated electrons can also give rise to enhanced emission at the loop tops.
These could be a natural consequence of acceleration by plasma waves. This
paper considers a general case of stochastic scattering and acceleration that
leads to an isotropic pitch angle distribution and an enhanced emission from
the loop tops or the acceleration site.
Following the formalism developed in earlier papers the strength and the
spectrum of the radiation expected from the acceleration site and the foot
points are evaluated and their dependence on the parameters describing the
acceleration process and the flare plasma are determined. The theoretical ratio
of these two intensities and relative values of their spectral indices are
compared with the YOHKOH observations, demonstrating that the above mentioned
parameters can be constrained with such observations. It is shown that future
high spatial and spectral resolution observations, for example those expected
from HESSI, can begin to distinguish between different models and constrain
their parameters.Comment: 37 pages with 20 figures. Accepted for publication in ApJ
http://www.astronomy.stanford.ed
Shock Diffraction by Convex Cornered Wedges for the Nonlinear Wave System
We are concerned with rigorous mathematical analysis of shock diffraction by
two-dimensional convex cornered wedges in compressible fluid flow governed by
the nonlinear wave system. This shock diffraction problem can be formulated as
a boundary value problem for second-order nonlinear partial differential
equations of mixed elliptic-hyperbolic type in an unbounded domain. It can be
further reformulated as a free boundary problem for nonlinear degenerate
elliptic equations of second order. We establish a first global theory of
existence and regularity for this shock diffraction problem. In particular, we
establish that the optimal regularity for the solution is across the
degenerate sonic boundary. To achieve this, we develop several mathematical
ideas and techniques, which are also useful for other related problems
involving similar analytical difficulties.Comment: 50 pages;7 figure
A dispersive wave pattern on Jupiter's fastest retrograde jet at S
A compact wave pattern has been identified on Jupiter's fastest retrograding
jet at 20S (the SEBs) on the southern edge of the South Equatorial Belt. The
wave has been identified in both reflected sunlight from amateur observations
between 2010 and 2015, thermal infrared imaging from the Very Large Telescope
and near infrared imaging from the Infrared Telescope Facility. The wave
pattern is present when the SEB is relatively quiescent and lacking large-scale
disturbances, and is particularly notable when the belt has undergone a fade
(whitening). It is generally not present when the SEB exhibits its usual
large-scale convective activity ('rifts'). Tracking of the wave pattern and
associated white ovals on its southern edge over several epochs have permitted
a measure of the dispersion relationship, showing a strong correlation between
the phase speed (-43.2 to -21.2 m/s) and the longitudinal wavelength, which
varied from 4.4-10.0 deg. longitude over the course of the observations.
Infrared imaging sensing low pressures in the upper troposphere suggest that
the wave is confined to near the cloud tops. The wave is moving westward at a
phase speed slower (i.e., less negative) than the peak retrograde wind speed
(-62 m/s), and is therefore moving east with respect to the SEBs jet peak.
Unlike the retrograde NEBn jet near 17N, which is a location of strong vertical
wind shear that sometimes hosts Rossby wave activity, the SEBs jet remains
retrograde throughout the upper troposphere, suggesting the SEBs pattern cannot
be interpreted as a classical Rossby wave. Cassini-derived windspeeds and
temperatures reveal that the vorticity gradient is dominated by the baroclinic
term and becomes negative (changes sign) in a region near the cloud-top level
(400-700 mbar) associated with the SEBs, suggesting a baroclinic origin for
this meandering wave pattern. [Abr]Comment: 19 pages, 11 figures, article accepted for publication in Icaru
Marine governance in the English Channel (La Manche): Linking science and management.
The English Channel is one of the world's busiest sea areas with intense shipping and port activity juxtaposed with recreation, communications and important conservation areas. Opportunities for marine renewable energy vie with existing activities for space. The current governance of the English Channel is reviewed and found to lack integration between countries, sectors, legislation and scientific research. Recent developments within the EU's marine management frameworks are significantly altering our approach to marine governance and this paper explores the implications of these new approaches to management of the English Channel. Existing mechanisms for cross-Channel science and potential benefits of an English Channel scale perspective are considered. In conclusion, current management practices are considered against the 12 Malawi Principles of the ecosystem approach resulting in proposals for enhancing governance of the region through science at the scale of the English Channel
Seasonal Variability of Saturn's Tropospheric Temperatures, Winds and Para-H from Cassini Far-IR Spectroscopy
Far-IR 16-1000 m spectra of Saturn's hydrogen-helium continuum measured
by Cassini's Composite Infrared Spectrometer (CIRS) are inverted to construct a
near-continuous record of upper tropospheric (70-700 mbar) temperatures and
para-H fraction as a function of latitude, pressure and time for a third of
a Saturnian year (2004-2014, from northern winter to northern spring). The
thermal field reveals evidence of reversing summertime asymmetries superimposed
onto the belt/zone structure. The temperature structure that is almost
symmetric about the equator by 2014, with seasonal lag times that increase with
depth and are qualitatively consistent with radiative climate models. Localised
heating of the tropospheric hazes (100-250 mbar) create a distinct perturbation
to the temperature profile that shifts in magnitude and location, declining in
the autumn hemisphere and growing in the spring. Changes in the para-H
() distribution are subtle, with a 0.02-0.03 rise over the spring
hemisphere (200-500 mbar) perturbed by (i) low- air advected by both the
springtime storm of 2010 and equatorial upwelling; and (ii) subsidence of
high- air at northern high latitudes, responsible for a developing
north-south asymmetry in . Conversely, the shifting asymmetry in the
para-H disequilibrium primarily reflects the changing temperature structure
(and the equilibrium distribution of ), rather than actual changes in
induced by chemical conversion or transport. CIRS results interpolated to
the same point in the seasonal cycle as re-analysed Voyager-1 observations show
qualitative consistency, with the exception of the tropical tropopause near the
equatorial zones and belts, where downward propagation of a cool temperature
anomaly associated with Saturn's stratospheric oscillation could potentially
perturb tropopause temperatures, para-H and winds. [ABRIDGED]Comment: Preprint accepted for publication in Icarus, 29 pages, 18 figure
Systemic inflammation predicts all-cause mortality: a Glasgow Inflammation Outcome Study
Introduction:
Markers of the systemic inflammatory response, including C-reactive protein and albumin (combined to form the modified Glasgow Prognostic Score), as well as neutrophil, lymphocyte and platelet counts have been shown to be prognostic of survival in patients with cancer. The aim of the present study was to examine the prognostic relationship between these markers of the systemic inflammatory response and all-cause, cancer, cardiovascular and cerebrovascular mortality in a large incidentally sampled cohort.<p></p>
Methods:
Patients (n = 160 481) who had an incidental blood sample taken between 2000 and 2008 were studied for the prognostic value of C-reactive protein (>10mg/l, albumin (>35mg/l), neutrophil (>7.5Ă109/l) lymphocyte and platelet counts. Also, patients (n = 52 091) sampled following the introduction of high sensitivity C-reactive protein (>3mg/l) measurements were studied. A combination of these markers, to make cumulative inflammation-based scores, were investigated.<p></p>
Results:
In all patients (n = 160 481) C-reactive protein (>10mg/l) (HR 2.71, p<0.001), albumin (>35mg/l) (HR 3.68, p<0.001) and neutrophil counts (HR 2.18, p<0.001) were independently predictive of all-cause mortality. These associations were also observed in cancer, cardiovascular and cerebrovascular mortality before and after the introduction of high sensitivity C-reactive protein measurements (>3mg/l) (n = 52 091). A combination of high sensitivity C-reactive protein (>3mg/l), albumin and neutrophil count predicted all-cause (HR 7.37, p<0.001, AUC 0.723), cancer (HR 9.32, p<0.001, AUC 0.731), cardiovascular (HR 4.03, p<0.001, AUC 0.650) and cerebrovascular (HR 3.10, p<0.001, AUC 0.623) mortality.
Conclusion
The results of the present study showed that an inflammation-based prognostic score, combining high sensitivity C-reactive protein, albumin and neutrophil count is prognostic of all-cause mortality
How should we measure psychological resilience in sport performers?
Psychological resilience is important in sport because athletes must constantly withstand a wide range of pressures to attain and sustain high performance. To advance psychologistsĂąâŹâą understanding of this area, there exists an urgent need to develop a sport-specific measure of resilience. The purpose of this paper is to review psychometric issues in resilience research and to discuss the implications for sport psychology. Drawing on the wider general psychology literature to inform the discussion, the narrative is divided into three main sections relating to resilience and its assessment: adversity, positive adaptation, and protective factors. The first section reviews the different ways that adversity has been measured and considers the potential problems of using items with varying degrees of controllability and risk. The second section discusses the different approaches to assessing positive adaptation and examines the issue of circularity pervasive in resilience research. The final section explores the various issues related to the assessment of protective factors drawing directly from current measures of resilience in other psychology sub-disciplines. The commentary concludes with key recommendations for sport psychology researchers seeking to develop a measure of psychological resilience in athletes
The Origin of Nitrogen on Jupiter and Saturn from the N/N Ratio
The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA's
Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia
absorption features on both Jupiter and Saturn in February 2013. Ammonia is the
principle reservoir of nitrogen on the giant planets, and the ratio of
isotopologues (N/N) can reveal insights into the molecular
carrier (e.g., as N or NH) of nitrogen to the forming protoplanets, and
hence the source reservoirs from which these worlds accreted. We targeted two
spectral intervals (900 and 960 cm) that were relatively clear of
terrestrial atmospheric contamination and contained close features of
NH and NH, allowing us to derive the ratio from a single
spectrum without ambiguity due to radiometric calibration (the primary source
of uncertainty in this study). We present the first ground-based determination
of Jupiter's N/N ratio (in the range from to
), which is consistent with both previous space-based studies
and with the primordial value of the protosolar nebula. On Saturn, we present
the first upper limit on the N/N ratio of no larger than
for the 900-cm channel and a less stringent
requirement that the ratio be no larger than for the
960-cm channel ( confidence). Specifically, the data rule out
strong N-enrichments such as those observed in Titan's atmosphere and in
cometary nitrogen compounds. To the extent possible with ground-based
radiometric uncertainties, the saturnian and jovian N/N ratios
appear indistinguishable, implying that N-enriched ammonia ices could
not have been a substantial contributor to the bulk nitrogen inventory of
either planet, favouring the accretion of primordial N from the gas phase
or as low-temperature ices.Comment: 33 pages, 19 figures, manuscript accepted for publication in Icaru
The optical transmission spectrum of the hot Jupiter HAT-P-32b: clouds explain the absence of broad spectral features?
We report Gemini-North GMOS observations of the inflated hot Jupiter
HAT-P-32b during two primary transits. We simultaneously observed two
comparison stars and used differential spectro-photometry to produce
multi-wavelength light curves. 'White' light curves and 29 'spectral' light
curves were extracted for each transit and analysed to refine the system
parameters and produce transmission spectra from 520-930nm in ~14nm bins. The
light curves contain time-varying white noise as well as time-correlated noise,
and we used a Gaussian process model to fit this complex noise model. Common
mode corrections derived from the white light curve fits were applied to the
spectral light curves which significantly improved our precision, reaching
typical uncertainties in the transit depth of ~2x10^-4, corresponding to about
half a pressure scale height. The low resolution transmission spectra are
consistent with a featureless model, and we can confidently rule out broad
features larger than about one scale height. The absence of Na/K wings or
prominent TiO/VO features is most easily explained by grey absorption from
clouds in the upper atmosphere, masking the spectral features. However, we
cannot confidently rule out clear atmosphere models with low abundances (~10^-3
solar) of TiO, VO or even metal hydrides masking the Na and K wings. A smaller
scale height or ionisation could also contribute to muted spectral features,
but alone are unable to to account for the absence of features reported here.Comment: 17 pages, 11 figures, 2 tables, accepted for publication in MNRA
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