152 research outputs found
Remote Sensing of Permafrost by Ground-Penetrating Radar at Two Airports in Arctic Canada
Over a cycle of seasons, ground-penetrating radar studies were carried out at Inuvik and Rankin Inlet, Northwest Territories. The two airports are part of the Forward Operating Location (FOL) program of the Department of National Defence and have been slated for significant upgrading of runways, taxiways and parking aprons. This provided a good opportunity to investigate the extent of permafrost and its seasonal variation at two locations distributed over a wide geographic area. The study method involved specific and repeated traverses with a Pulse EKKO III ground-penetrating radar unit. The survey was successful in locating massive ice bodies, imaging several existing problem areas beneath runways and mapping the seasonal depth of thaw in permafrost. The study results imply that future monitoring at FOL sites should be continued in light of suggested ground stability problems due to global warming.Key words: Canadian Arctic, ground-penetrating radar, permafrost, global warming, airport, Forward Operating LocationMot clés: Arctic canadien, géoradar, pergélisol, réchauffement atmosphéric, aéroport, Emplacemen Avancés d’opération
Determinants of job satisfaction for salaried and self-employed professionals in Finland
This paper contributes to our knowledge of the determinants of job satisfaction by analysing the effects of employment status (self-employed or salaried employee) and work characteristics (autonomy, variety, task identity, task significance and feedback) on job satisfaction in a sample of 2327 Finnish professionals. The results of the structural equation model analysis show that although the self-employed are significantly more satisfied with their jobs than their salaried counterparts also in Finland, employment status as such does not explain job satisfaction when the five work characteristics are added to the structural model. Further, the analysis finds that task significance, variety and autonomy have similar effects on the level of job satisfaction among both employees and self-employed individuals, while feedback has a weaker effect when the individual is self-employed and task identity does not affect job satisfaction in either group. Overall the study points to the need to develop jobs that are high in autonomy, variety and task significance for professionals in order to enhance job satisfaction
The magnitude and temporal changes of response in the placebo arm of surgical randomized controlled trials: a systematic review and meta-analysis
Background
Understanding changes in the placebo arm is essential for correct design and interpretation of randomized controlled trials (RCTs). It is assumed that placebo response, defined as the total improvement in the placebo arm of surgical trials, is large; however, its precise magnitude and properties remain to be characterized. To the best of our knowledge, the temporal changes in the placebo arm have not been investigated. The aim of this paper was to determine, in surgical RCTs, the magnitude of placebo response and how it is affected by duration of follow-up.
Methods
The databases of MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials and ClinicalTrials.gov were searched from their inception to 20 October 2015 for studies comparing the efficacy of a surgical intervention with placebo. Inclusion was not limited to any particular condition, intervention, outcome or patient population. The magnitude of placebo response was estimated using standardized mean differences (SMDs). Study estimates were pooled using random effects meta-analysis. Potential sources of heterogeneity were evaluated using stratification and meta-regression.
Results
Database searches returned 88 studies, but for 41 studies SMDs could not be calculated, leaving 47 trials (involving 1744 participants) eligible for inclusion. There were no temporal changes in placebo response within the analysed trials. Meta-regression analysis showed that duration of follow-up did not have a significant effect on the magnitude of the placebo response and that the strongest predictor of placebo response was subjectivity of the outcome. The pooled effect in the placebo arm of studies with subjective outcomes was large (0.64, 95% CI 0.5 to 0.8) and remained significantly different from zero regardless of the duration of follow-up, whereas for objective outcomes, the effect was small (0.11, 95% CI 0.04 to 0.26) or non-significant across all time points.
Conclusions
This is the first study to investigate the temporal changes of placebo response in surgical trials and the first to investigate the sources of heterogeneity of placebo response. Placebo response in surgical trials was large for subjective outcomes, persisting as a time-invariant effect throughout blinded follow-up. Therefore, placebo response cannot be minimized in these types of outcomes through their appraisal at alternative time points. The analyses suggest that objective outcomes may be preferable as trial end-points. Where subjective outcomes are of primary interest, a placebo arm is necessary to control for placebo response
Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed Processes
A chromosphere is a universal attribute of stars of spectral type later than
~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae
binaries) show extended and highly turbulent chromospheres, which develop into
slow massive winds. The associated continuous mass loss has a significant
impact on stellar evolution, and thence on the chemical evolution of galaxies.
Yet despite the fundamental importance of those winds in astrophysics, the
question of their origin(s) remains unsolved. What sources heat a chromosphere?
What is the role of the chromosphere in the formation of stellar winds? This
chapter provides a review of the observational requirements and theoretical
approaches for modeling chromospheric heating and the acceleration of winds in
single cool, evolved stars and in eclipsing binary stars, including physical
models that have recently been proposed. It describes the successes that have
been achieved so far by invoking acoustic and MHD waves to provide a physical
description of plasma heating and wind acceleration, and discusses the
challenges that still remain.Comment: 46 pages, 9 figures, 1 table; modified and unedited manuscript;
accepted version to appear in: Giants of Eclipse, eds. E. Griffin and T. Ake
(Berlin: Springer
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Arthroscopic subacromial decompression for subacromial shoulder pain (CSAW):a multicentre, pragmatic, parallel group, placebo-controlled, three-group, randomised surgical trial
Background: Arthroscopic sub-acromial decompression (decompressing the sub-acromial space by removing bone spurs and soft tissue arthroscopically) is a common surgery for subacromial shoulder pain, but its effectiveness is uncertain. We did a study to assess its effectiveness and to investigate the mechanism for surgical decompression.
Methods: We did a multicentre, randomised, pragmatic, parallel group, placebo-controlled, three-group trial at 32 hospitals in the UK with 51 surgeons. Participants were patients who had subacromial pain for at least 3 months with intact rotator cuff tendons, were eligible for arthroscopic surgery, and had previously completed a non-operative management programme that included exercise therapy and at least one steroid injection. Exclusion criteria included a full-thickness torn rotator cuff. We randomly assigned participants (1:1:1) to arthroscopic subacromial decompression, investigational arthroscopy only, or no treatment (attendance of one reassessment appointment with a specialist shoulder clinician 3 months after study entry, but no intervention). Arthroscopy only was a placebo as the essential surgical element (bone and soft tissue removal) was omitted. We did the randomisation with a computer-generated minimisation system. In the surgical intervention groups, patients were not told which type of surgery they were receiving (to ensure masking). Patients were followed up at 6 months and 1 year after randomisation; surgeons coordinated their waiting lists to schedule surgeries as close as possible to randomisation. The primary outcome was the Oxford Shoulder Score (0 [worst] to 48 [best]) at 6 months, analysed by intention to treat. The sample size calculation was based upon a target difference of 4·5 points (SD 9·0). This trial has been registered at ClinicalTrials.gov, number NCT01623011.
Findings: Between Sept 14, 2012, and June 16, 2015, we randomly assigned 313 patients to treatment groups (106 to decompression surgery, 103 to arthroscopy only, and 104 to no treatment). 24 [23%], 43 [42%], and 12 [12%] of the decompression, arthroscopy only, and no treatment groups, respectively, did not receive their assigned treatment by 6 months. At 6 months, data for the Oxford Shoulder Score were available for 90 patients assigned to decompression, 94 to arthroscopy, and 90 to no treatment. Mean Oxford Shoulder Score did not differ between the two surgical groups at 6 months (decompression mean 32·7 points [SD 11·6] vs arthroscopy mean 34·2 points [9·2]; mean difference −1·3 points (95% CI −3·9 to 1·3, p=0·3141). Both surgical groups showed a small benefit over no treatment (mean 29·4 points [SD 11·9], mean difference vs decompression 2·8 points [95% CI 0·5–5·2], p=0·0186; mean difference vs arthroscopy 4·2 [1·8–6·6], p=0·0014) but these differences were not clinically important. There were six study-related complications that were all frozen shoulders (in two patients in each group).
Interpretation: Surgical groups had better outcomes for shoulder pain and function compared with no treatment but this difference was not clinically important. Additionally, surgical decompression appeared to offer no extra benefit over arthroscopy only. The difference between the surgical groups and no treatment might be the result of, for instance, a placebo effect or postoperative physiotherapy. The findings question the value of this operation for these indications, and this should be communicated to patients during the shared treatment decision-making process.
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Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Gestão ambiental e estratégia empresarial em pequenas e médias empresas: um estudo comparativo de casos
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