Impulsive phase flare energy transport by large-scale Alfven waves and the electron acceleration problem

The impulsive phase of a solar flare marks the epoch of rapid conversion of energy stored in the pre-flare coronal magnetic field. Hard X-ray observations imply that a substantial fraction of flare energy released during the impulsive phase is converted to the kinetic energy of mildly relativistic electrons (10-100 keV). The liberation of the magnetic free energy can occur as the coronal magnetic field reconfigures and relaxes following reconnection. We investigate a scenario in which products of the reconfiguration - large-scale Alfven wave pulses - transport the energy and magnetic-field changes rapidly through the corona to the lower atmosphere. This offers two possibilities for electron acceleration. Firstly, in a coronal plasma with beta < m_e/m_p, the waves propagate as inertial Alfven waves. In the presence of strong spatial gradients, these generate field-aligned electric fields that can accelerate electrons to energies on the order of 10 keV and above, including by repeated interactions between electrons and wavefronts. Secondly, when they reflect and mode-convert in the chromosphere, a cascade to high wavenumbers may develop. This will also accelerate electrons by turbulence, in a medium with a locally high electron number density. This concept, which bridges MHD-based and particle-based views of a flare, provides an interpretation of the recently-observed rapid variations of the line-of-sight component of the photospheric magnetic field across the flare impulsive phase, and offers solutions to some perplexing flare problems, such as the flare "number problem" of finding and resupplying sufficient electrons to explain the impulsive-phase hard X-ray emission.Comment: 31 pages, 6 figure

​Residential mobility:Towards progress in mobility health research

Research into health disparities has long recognized the importance of residential mobility as a crucial factor in determining health outcomes. However, a lack of connectivity between the health and mobility literatures has led to a stagnation of theory and application on the health side, which lacks the detail and temporal perspectives now seen as critical to understanding residential mobility decisions. Through a critical re-think of mobility processes with respect to health outcomes and an exploitation of longitudinal analytical techniques, we argue that health geographers have the potential to better understand and identify the relationship that residential mobility has with health.“The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 615159 (ERC Consolidator Grant DEPRIVEDHOODS, Socio-spatial inequality, deprived neighbourhoods, and neighbourhood effects)”OLD Urban Renewal and Housin

The decline and rise of neighbourhoods: the importance of neighbourhood governance

There is a substantial literature on the explanation of neighbourhood change. Most of this literature concentrates on identifying factors and developments behind processes of decline. This paper reviews the literature, focusing on the identification of patterns of neighbourhood change, and argues that the concept of neighbourhood governance is a missing link in attempts to explain these patterns. Including neighbourhood governance in the explanations of neighbourhood change and decline will produce better explanatory models and, finally, a better view about what is actually steering neighbourhood change

New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation

(abridged) The heating mechanism at high densities during M dwarf flares is poorly understood. Spectra of M dwarf flares in the optical and near-ultraviolet wavelength regimes have revealed three continuum components during the impulsive phase: 1) an energetically dominant blackbody component with a color temperature of T $\sim$ 10,000 K in the blue-optical, 2) a smaller amount of Balmer continuum emission in the near-ultraviolet at lambda $<$ 3646 Angstroms and 3) an apparent pseudo-continuum of blended high-order Balmer lines. These properties are not reproduced by models that employ a typical "solar-type" flare heating level in nonthermal electrons, and therefore our understanding of these spectra is limited to a phenomenological interpretation. We present a new 1D radiative-hydrodynamic model of an M dwarf flare from precipitating nonthermal electrons with a large energy flux of $10^{13}$ erg cm$^{-2}$ s$^{-1}$. The simulation produces bright continuum emission from a dense, hot chromospheric condensation. For the first time, the observed color temperature and Balmer jump ratio are produced self-consistently in a radiative-hydrodynamic flare model. We find that a T $\sim$ 10,000 K blackbody-like continuum component and a small Balmer jump ratio result from optically thick Balmer and Paschen recombination radiation, and thus the properties of the flux spectrum are caused by blue light escaping over a larger physical depth range compared to red and near-ultraviolet light. To model the near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer lines, we include the extra Balmer continuum opacity from Landau-Zener transitions that result from merged, high order energy levels of hydrogen in a dense, partially ionized atmosphere. This reveals a new diagnostic of ambient charge density in the densest regions of the atmosphere that are heated during dMe and solar flares.Comment: 50 pages, 2 tables, 13 figures. Accepted for publication in the Solar Physics Topical Issue, "Solar and Stellar Flares". Version 2 (June 22, 2015): updated to include comments by Guest Editor. The final publication is available at Springer via http://dx.doi.org/10.1007/s11207-015-0708-

Treatment of Full-Thickness Acetabular Chondral Flaps during Hip Arthroscopy: Bone Marrow Aspirate Concentrate versus Microfracture

Background: The optimal treatment strategy for patients with full-thickness chondral flaps undergoing hip arthroscopy is controversial. Purpose: To compare functional outcomes of patients who underwent bone marrow aspirate concentrate (BMAC) application with those of patients who underwent microfracture. Study Design: Cohort study; Level of evidence, 3. Methods: This was a retrospective case series of prospectively collected data on patients who underwent arthroscopic acetabular labral repair by 1 surgeon between June 2014 and April 2020. The inclusion criteria for this study were age ≥18 years, preoperative radiographs of the pelvis, arthroscopic acetabular labral repair, exposed subchondral bone with overlying chondral flap seen at the time of hip arthroscopy, microfracture or BMAC to address this lesion, and completed patient-reported outcome measures (PROMs) (International Hip Outcome Tool-33 [iHOT-33], Hip Outcome Score-Activities of Daily Living [HOS-ADL], Hip Outcome Score-Sports Subscale [HOS-Sport], modified Harris Hip Score [mHHS], and visual analog scale [VAS] for pain) at enrollment and 12-month follow-up. Clinical outcomes were assessed using PROM scores. Results: A total of 81 hips with full-thickness chondral flaps were included in this study: 50 treated with BMAC and 31 treated with microfracture. There were no significant differences between groups in age, sex, body mass index, tear size, radiographic osteoarthritis, or radiographic femoroacetabular impingement. In the BMAC cohort, all PROM scores improved significantly from preoperatively to follow-up: 41.7 to 75.6 for iHOT-33, 67.6 to 91.0 for HOS-ADL, 41.5 to 72.3 for HOS-Sport, 59.4 to 87.2 for mHHS, and 6.2 to 2.2 for VAS pain (P \u3c .001 for all). In the microfracture cohort, the score improvements were 48.0 to 65.1 for iHOT-33 (P = .001), 80.5 to 83.3 for HOS-ADL (P = .275), 59.2 to 62.4 for HOS-Sport (P = .568), 70.4 to 78.3 for mHHS (P = .028), and 4.9 to 3.6 for VAS pain (P = .036). Regarding clinically meaningful outcomes, 77.6% of the BMAC group and 50.0% of the microfracture group met the minimal clinically important difference for iHOT-33 at the 12-month follow-up (P = .013). Conclusion: Patients with full-thickness chondral flaps at the time of hip arthroscopy experienced greater improvements in functional outcome scores at the 12-month follow-up when treated with BMAC as opposed to microfracture

Puncture Capsulotomy Technique for Hip Arthroscopy: Midterm Functional Outcomes

Background: The most common surgical approaches in hip arthroscopy are interportal and T-capsulotomy. However, these methods may introduce capsular instability. Puncture capsulotomy preserves capsuloligamentous integrity by avoiding iatrogenic transection of the iliofemoral capsular ligament. Purpose: To present minimum 2-year functional outcomes for patients who underwent arthroscopic treatment for acetabular labral tears and concomitant femoroacetabular impingement using the puncture capsulotomy technique. Study design: Case series; Level of evidence, 4. Methods: The authors conducted a retrospective review of prospectively collected data on patients who underwent arthroscopic acetabular labral tear treatment between December 2013 and May 2019. Included were patients aged ≥18 years who underwent hip arthroscopy by a single surgeon and completed a minimum of 2 years of patient-reported outcome measure (PROM) surveys. Intraoperatively, patients underwent hip arthroscopy via puncture capsulotomy to treat labral tears and any concomitant femoroacetabular impingement. Clinical outcome data consisted of PROMs. Results: A total of 163 hips were included; the mean patient follow-up was 30.4 months (range, 24-60 months; 95% CI, 28.5-32.3 months). Patients had a mean age of 37.9 years (range, 36.1-39.6 years), with a mean body mass index of 25.9 (range, 25.2-26.5). There were significant improvements in mean [95% CI] baseline to final follow-up scores for the 33-Item International Hip Outcome Tool (iHOT-33) (39.6 [36.8-42.4] vs 76.1 [72.7-79.6]), Hip Outcome Score-Activities of Daily Living (70.0 [67.0-73.0] vs 89.3 [87.3-91.3]), modified Harris Hip Score (60.1 [57.9-62.4] vs 84.9 [82.5-87.2]), and Hip Outcome Score-Sports Specific Subscale (41.8 [37.9-45.6] vs 75.7 [71.7-79.7]) (P \u3c .001 for all). Additionally, the mean [95% CI] visual analog scale pain scores were noted to significantly improve throughout the duration of the postoperative period (from 6.3 [5.9-6.7] to 2.2 [1.8-2.6]; P \u3c .001). There were no incidences of infection, avascular necrosis of the femoral head, dislocation/instability, or femoral neck fracture. At the 2-year follow-up, 81.0%, 62.0%, and 58.9% of hips achieved previously published clinically meaningful iHOT-33 thresholds for minimally clinically important difference, Patient Acceptable Symptom Score, and substantial clinical benefit, respectively. Conclusion: Puncture capsulotomy demonstrated significantly improved functional and clinically meaningful outcomes at a minimum 2-year follow-up, along with a minimal complication rate

Response of optical hydrogen lines to beam heating: I. Electron beams

We investigate the role of non-thermal electrons in the formation regions of Halpha, Hbeta, and Hgamma lines in order to unfold their influence on the formation of these lines. We concentrate on pulse-beam heating varying on a subsecond timescale. Furthermore, we theoretically explore possibility that a new diagnostic tool exists indicating the presence of non-thermal electrons in the flaring chromosphere based on observations of optical hydrogen lines. To model the evolution of the flaring atmosphere and the time-dependent hydrogen excitation and ionisation, we used a 1-D radiative hydrodynamic code combined with a test-particle code that simulates the propagation, scattering, and thermalisation of a power-law electron beam in order to obtain the flare heating and the non-thermal collisional rates due to the interaction of the beam with the hydrogen atoms. All calculated models have shown a time-correlated response of the modelled Balmer line intensities on a subsecond timescale, with a subsecond timelag behind the beam flux. Depending on the beam parameters, both line centres and wings can show pronounced intensity variations. The non-thermal collisional rates generally result in an increased emission from a secondary region formed in the chromosphere.Comment: 13 pages, 11 figures, accepted to Astronomy and Astrophysic