Searching for overturning convection in penumbral filaments: slit spectroscopy at 0.2 arcsec resolution

Recent numerical simulations of sunspots suggest that overturning convection is responsible for the existence of penumbral filaments and the Evershed flow, but there is little observational evidence of this process. Here we carry out a spectroscopic search for small-scale convective motions in the penumbra of a sunspot located 5 deg away from the disk center. The position of the spot is very favorable for the detection of overturning downflows at the edges of penumbral filaments. Our analysis is based on measurements of the Fe I 709.0 nm line taken with the Littrow spectrograph of the Swedish 1 m Solar Telescope under excellent seeing conditions. We compute line bisectors at different intensity levels and derive Doppler velocities from them. The velocities are calibrated using a nearby telluric line, with systematic errors smaller than 150 m/s. Deep in the photosphere, as sampled by the bisectors at the 80%-88% intensity levels, we always observe blueshifts or zero velocities. The maximum blueshifts reach 1.2 km/s and tend to be cospatial with bright penumbral filaments. In the line core we detect blueshifts for the most part, with small velocities not exceeding 300 m/s. Redshifts also occur, but at the level of 100-150 m/s, and only occasionally. The fact that they are visible in high layers casts doubts on their convective origin. Overall, we do not find indications of downflows that could be associated with overturning convection at our detection limit of 150 m/s. Either no downflows exist, or we have been unable to observe them because they occur beneath tau=1 or the spatial resolution/height resolution of the measurements is still insufficient.Comment: Accepted for publication in Ap

A dynamical model for the penumbral fine structure and the Evershed effect in sunspots

Relying on the assumption that the interchange convection of magnetic flux tubes is the physical cause for the existence of sunspot penumbrae, we propose a model in which the dynamical evolution of a thin magnetic flux tube reproduces the Evershed effect and the penumbral fine structure such as bright and dark filaments and penumbral grains. According to our model, penumbral grains are the manifestation of the footpoints of magnetic flux tubes, along which hot subphotospheric plasma flows upwards with a few km/s. Above the photosphere the hot plasma inside the tube is cooled by radiative losses as it flows horizontally outwards. As long as the flowing plasma is hotter than the surroundings, it constitutes a bright radial filament. The flow confined to a thin elevated channel reaches the temperature equilibrium with the surrounding atmosphere and becomes optically thin near the outer edge of the penumbra. Here, the tube has a height of approximately 100 km above the continuum and the flow velocity reaches up to 14 km/s. Such a flow channel can reproduce the observed signatures of the Evershed effect.Comment: 5 pages, 2 figures, accepted for publication in ApJ letter

Degradation investigation in a postbuckling composite stiffened fuselage panel

COCOMAT is a four-year project under the European Commission 6th Framework Programme that aims to exploit the large strength reserves of composite structures through a more accurate prediction of collapse. Accordingly, one of the COCOMAT work packages involves the design of test panels with a focus on investigating the progression of composite damage mechanisms. This paper presents the collaborative results of some of the partners for this task. Different design alternatives were investigated for fuselage-representative test panels. Non-linear structural analyses were performed using MSC.Nastran and ABAQUS/Standard. Numerical predictions were also made applying a stress-based adhesive degradation model, previously implemented into a material user subroutine for ABAQUS/Standard. Following this, a fracture mechanics analysis using MSC.Nastran was performed along all interfaces between the skin and stiffeners, to examine the stiffener disbonding behaviour of each design. On the basis of the structural and fracture mechanics analyses, a design was selected as being the most suitable for the experimental investigation within COCOMAT. Though the COCOMAT panels have yet to be manufactured and tested, experimental data on the structural performance and damage mechanisms were available from a separate project for a panel identical to the selected design. This data was compared to the structural, degradation and fracture mechanics predictions made using non-linear finite element solutions, and the application of the design within the COCOMAT project was discussed

The Evershed Effect with SOT/Hinode

The Solar Optical Telescope onboard Hinode revealed the fine-scale structure of the Evershed flow and its relation to the filamentary structures of the sunspot penumbra. The Evershed flow is confined in narrow channels with nearly horizontal magnetic fields, embedded in a deep layer of the penumbral atmosphere. It is a dynamic phenomenon with flow velocity close to the photospheric sound speed. Individual flow channels are associated with tiny upflows of hot gas (sources) at the inner end and downflows (sinks) at the outer end. SOT/Hinode also discovered ``twisting'' motions of penumbral filaments, which may be attributed to the convective nature of the Evershed flow. The Evershed effect may be understood as a natural consequence of thermal convection under a strong, inclined magnetic field. Current penumbral models are discussed in the lights of these new Hinode observations.Comment: To appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200

Disintegration of Magnetic Flux in Decaying Sunspots as Observed with the Hinode SOT

Continuous observations of sunspot penumbrae with the Solar Optical Telescope aboard \textit{Hinode} clearly show that the outer boundary of the penumbra fluctuates around its averaged position. The penumbral outer boundary moves inward when granules appear in the outer penumbra. We discover that such granules appear one after another while moving magnetic features (MMFs) are separating from the penumbral ``spines'' (penumbral features that have stronger and more vertical fields than those of their surroundings). These granules that appear in the outer penumbra often merge with bright features inside the penumbra that move with the spines as they elongate toward the moat region. This suggests that convective motions around the penumbral outer boundary are related to the disintegration of magnetic flux in the sunspot. We also find that dark penumbral filaments frequently elongate into the moat region in the vicinity of MMFs that detach from penumbral spines. Such elongating dark penumbral filaments correspond to nearly horizontal fields extending from the penumbra. Pairs of MMFs with positive and negative polarities are sometimes observed along the elongating dark penumbral filaments. This strongly supports the notion that such elongating dark penumbral filaments have magnetic fields with a ``sea serpent''-like structure. Evershed flows, which are associated with the penumbral horizontal fields, may be related to the detachment of the MMFs from the penumbral spines, as well as to the formation of the MMFs along the dark penumbral filaments that elongate into the moat region.Comment: Accepted for publication in Ap

Agreement between definitions of pharmaceutical opioid use disorders and dependence in people taking opioids for chronic non-cancer pain (POINT): a cohort study

Background Classification of patients with pharmaceutical opioid use disorder and dependence varies depending on which definition is used. We compared how WHO\u27s ICD-10 and proposed ICD-11 and the American Psychiatric Association\u27s DSM-IV and DSM-5 classified individuals in a community-based sample of Australians with chronic non-cancer pain for which opioids have been prescribed. Methods We studied participants in the Pain and Opioid IN Treatment (POINT) cohort, a 2 year prospective cohort study of 1514 people prescribed pharmaceutical opioids for their chronic pain who were recruited in 2012–13 from community-based pharmacies across Australia. After giving patients the Composite International Diagnostic Interview about their opioid use, we assessed which patients would be categorised as having disorders of pharmaceutical opioid use by ICD-10, the draft ICD-11, DSM-IV, and DSM-5. We examined agreement between classification systems, and tested the unidimensionality of the syndrome with confirmatory factor analysis. Findings We included 1422 participants (median time of pain disorder 10 years [IQR 5–20]; median length of strong opioid prescription 4 years [IQR 1·5–10·0]; mean age 58 years). Similar proportions of individuals met lifetime criteria for dependence with DSM-IV (127; 8·9%), ICD-10 (121; 8·5%), and ICD-11 (141; 9·9%). Criteria in DSM-5 classified 127 (8·9%) participants with moderate or severe use disorder. There was excellent agreement between ICD-10, ICD-11 and DSM-IV dependence (κ\u3e0·90). However, there was only fair to moderate agreement between ICD-10 and DSM-IV dependence diagnoses, and DSM-5 use disorder (mild, moderate, or severe). There was only good agreement between moderate to severe use disorder in DSM-5 and the other definitions. Criteria for all definitions loaded well on a single factor; the best model fit was for the definition for dependence in the draft ICD-11, the worst was in DSM-5. Interpretation Classification of problematic pharmaceutical opioid use varies across editions of ICD and DSM. The much lower levels of agreement between DSM-5 and other definitions than between other definitions might be attributed to DSM-5 containing an increased number of criteria and treating dependence and problematic use as a continuum. The more parsimonious ICD-11 dependence definition showed excellent model fit and excellent agreement with previous classificatory systems

Diversion of prescribed opioids by people living with chronic pain: Results from an Australian community sample

Introduction and Aims There has been an increase in prescription of opioids for chronic non‐cancer pain, and concern exists over possible diversion of prescription opioids to the illicit marketplace. Recent media coverage suggests that elderly patients sell their prescribed opioids for additional income. This study investigated the extent to which an Australian community sample of chronic pain patients prescribed opioids reported supplying their prescribed opioids to others. Design and Methods Participants living with chronic non‐cancer pain and prescribed opioids for their pain (n = 952) were recruited across Australia via advertisements at pharmacies. A telephone interview included questions about their pain condition and opioid medication. Results Participants had been living with pain for a mean of 14.2 years; most common conditions included chronic back/neck problems and arthritis/rheumatism. Around half (43%) were currently prescribed one opioid, and 55% had been prescribed 2-5 opioids; the most common was oxycodone. Forty‐two participants (4%) reported ever supplying prescribed opioids to another person; one participant reported receiving payment. Participants who supplied opioids to others were younger (odds ratio 0.97, 95% confidence interval 0.95-0.99) and engaged in a greater number of aberrant behaviours relating to their opioid medication (odds ratio 1.77, 95% confidence interval 1.45-2.17), including tampering with doses, taking opioids by alternative routes, seeing doctors to obtain extra opioids and refilling prescriptions early. Discussion and Conclusion Few people with chronic non‐cancer pain divert their opioids to others. Media reports of elderly patients selling their opioids to supplement their income may be reflective of exceptional cases. Future studies may investigate the extent to which other patient groups divert prescription opioids to the illicit marketplace