Laser induced fluorescence - particle tracking velocimetry (lif-ptv) measurements of water flow through snow

LIF-PTV-measurements of the micro-scale water flow through the pore space of a wet snow sample driven by either gravitational or capillary forces are presented. For the measurements, fluorescent micron-sized particles in the water are illuminated with a laser light sheet and tracked with a high-speed camera. The results show the existence of a potential preferential flow path and a loop flow in a pore space in case of a gravity driven flow. Generally, the water flow is found to be highly 3-dimensional. The average flow velocities in the pore spaces are 11.3 mm/s for the gravity driven flow and 9.6 mm/s for the upward flow driven by capillary forces. Flow acceleration and deceleration was stronger for the gravity driven flow with particle decelerations stronger than accelerations in both cases

Submuscular transposition with musculofascial lengthening for persistent or recurrent cubital tunnel syndrome in 34 patients

The two main surgical options for patients with persistent or recurrent cubital tunnel syndrome are subcutaneous and submuscular transposition. We retrospectively analysed the results of 34 patients with recalcitrant cubital tunnel syndrome who underwent submuscular transposition with musculofascial lengthening at our institutions. Of the 34 patients, 21 improved clinically after submuscular transposition with musculofascial lengthening, of which 16 were still satisfied at a mean follow-up of four years. In addition, all articles published between 1974 and January 2015 on subcutaneous and/or submuscular transposition of the ulnar nerve for recalcitrant cubital tunnel syndrome were reviewed. We found that previously published studies on this subject are too heterogeneous to compare. No recommendation can thus be made regarding the surgical technique for persistent or recurrent cubital tunnel syndrome. Our series shows that the musculofascial lengthening technique for submuscular transposition is a good option. More research is needed to compare the different surgical treatments. Level of evidence: IV

A wind-driven snow redistribution module for Alpine3D v3.3.0: adaptations designed for downscaling ice sheet surface mass balance

Ice sheet surface mass balance describes the net snow accumulation at the ice sheet surface. On the Antarctic ice sheet, winds redistribute snow, resulting in a surface mass balance that is variable in both space and time. Representing wind-driven snow redistribution processes in models is critical for local assessments of surface mass balance, repeat altimetry studies, and interpretation of ice core accumulation records. To this end, we have adapted Alpine3D, an existing distributed snow modeling framework, to downscale Antarctic surface mass balance to horizontal resolutions up to 1 km. In particular, we have introduced a new two-dimensional advection-based wind-driven snow redistribution module that is driven by an offline coupling between WindNinja, a wind downscaling model, and Alpine3D. We then show that large accumulation variability can be at least partially explained by terrain-induced wind speed variations which subsequently redistribute snow around rolling topography. By comparing Alpine3D to airborne-derived snow accumulation measurements within a testing domain over Pine Island Glacier in West Antarctica, we demonstrate that our Alpine3D downscaling approach improves surface mass balance estimates when compared to the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), a global atmospheric reanalysis which we use as atmospheric forcing. In particular, when compared to MERRA-2, Alpine3D reduces simulated surface mass balance root mean squared error by 23.4 mmw.e.yr-1 (13 %) and increases variance explained by 24 %. Despite these improvements, our results demonstrate that considerable uncertainty stems from the employed saltation model, confounding simulations of surface mass balance variability.</p

Integrating repair into product design education: Insights on repair, design and sustainability

Copyright © 2021 The Authors. With the pressure of growing environmental problems, the world is changing, and so is the paradigm of design. Accordingly, the calls for change in design education are increasing throughout the literature day by day. As the designers of the future, students must be prepared for alternative scenarios. This paper provides insights into students’ learning outcomes and competencies related to repair and sustainability in the context of an assignment that integrates repair into design education. This assignment has been part of the master’s degree design course at Linköping University for the last 3 years. During these 3 years, 52 repair projects, including a diverse range of products, were developed. Aiming to find out the insights of this process, focus group sessions were conducted. As a result of these focus group sessions, 12 insights were developed, such as the concepts of brokenness, designed repair, and repair-worthy objects. Findings show that practices of repair constitute complex sites of learning, technical skill and knowledge which could enable novice designers to become competent in circular design. This paper is of value for design educators and researchers, especially those concerned with the repair and circular economy, as it can facilitate future attempts to further integrate circular strategies into design education

Fracture et déclenchement des avalanches de plaque : conditions critiques pour la propagation de la fracture

International audienceThe failure of a weak snow layer buried below cohesive slab layers is a necessary, but insufficient, condition for the release of a dry-snow slab avalanche. The size of the crack in the weak layer must also exceed a critical length to propagate across a slope. In contrast to pioneering shear-based approaches, recent developments account for weak layer collapse and allow for better explaining typical observations of remote triggering from low-angle terrain. However, these new models predict a critical length for crack propagation that is almost independent of slope angle, a rather surprising and counterintuitive result. Based on discrete element simulations we propose a new analytical expression for the critical crack length. This new model reconciles past approaches by considering for the first time the complex interplay between slab elasticity and the mechanical behavior of the weak layer including its structural collapse. The crack begins to propagate when the stress induced by slab loading and deformation at the crack tip exceeds the limit given by the failure envelope of the weak layer. The model can reproduce crack propagation on low-angle terrain and the decrease in critical length with increasing slope angle as modeled in numerical experiments. The good agreement of our new model with extensive field data and the ease of implementation in the snow cover model SNOWPACK opens a promising prospect for improving avalanche forecasting

Niche complementarity and facilitation drive positive diversity effects on biomass production in experimental benthic diatom biofilms

Up to now, relatively few diversity-production experiments have been performed using microorganisms. Benthic diatom communities from estuarine intertidal mudflats are especially interesting for this purpose as they are relatively species poor and are thus more easy to simulate in laboratory conditions. We studied the effect of diversity on biomass production during microcosm experiments with diatoms assembled in combinations of up to eight species. Our results demonstrate a highly positive effect of biodiversity on production, with transgressive overyielding occurring in more than half of the combinations. These strong positive diversity effects could largely be attributed to positive complementarity effects (covering both niche complementarity and facilitation), although negative selection effects effects at higher diversities. We found a significant positive relation between functional diversity and the net biodiversity effects, indicating niche complementarity. In addition, we provide one of the first mechanistic evidences for facilitation by which biodiversity can enhance ecosystem functioning. This was demonstrated by the improved growth of Cylindrotheca closterium after addition of spent medium obtained from other diatom species. The stimulated growth of C. closterium was explained by a shift to mixotrophic growth with a down-regulation of the photosynthetic apparatus

Viewership footprint for a low-resource, student-centred collaborative video platform to teach orthopaedics in southern Africa

Background. Institutions are increasingly using technology to augment the class learning experience of medical students. Especially in Africa, local content is key to allow insights and knowledge to emerge and build transformative capacity for students and patients. There is currently no peer-reviewed video content produced by students with the aim of providing education on orthopaedic topics for medical students and patients in this region.Objectives. To evaluate the demographic and geographical viewership as well as video-specific statistics of orthopaedic teaching videos for medical students on a YouTube channel, with the expressed aim of informing future content production.Methods. Videos were produced by South African (SA) medical students as a problem-based collaborative project. Student-owned smartphones and various types of free video editing software were used to produce these videos, which were then assessed by a group of orthopaedic specialists and uploaded onto a YouTube channel (UCTeach). The analytical reports of this channel generated by Google and YouTube were analysed regarding watch time per day (minutes), average view duration (minutes), most watched videos, top geographies, age and gender.Results. A total of 83 videos were uploaded to the UCTeach Ortho channel during a 2-year period, with a total watch time of 857 062 minutes and 337 983 views. The majority of viewers were between the ages of 18 and 34 years (85%). India had the most views (n=69 089), followed by the USA (n=66 257) and SA (n=21 882). Most of the videos were watched on mobile phones (n=183 299) and computers (n=128 228). The most watched video, produced in April 2016, was on physiological and pathological gait, with 51 314 views.Conclusions. Our study provides proof of concept for a new educational material creation and dissemination strategy. A low-cost local collaborative orthopaedic video project by medical students for medical students can lead to high view counts and watch time on YouTube. It is accessible to audiences in low-, middle- and high-income countries. The students’ educational videos also reached a global audience consistently over a 3-year period

Role for dithiolopyrrolones in disrupting bacterial metal homeostasis

Antibiotic resistance is a rising health threat worldwide, against which novel strategies are urgently needed. We have taken a systems approach to examine a potent and underexplored class of broad-spectrum antibiotics, the dithiolopyrrolones (DTPs). Our results indicate that DTPs disrupt cellular processes by high-affinity chelation of essential metal ions and inhibition of a subset of metalloenzymes. This mode of action is unique amongst antibiotics and may be further explored for treatment of multidrug-resistant infections. Our study also highlights chemical genomics as a powerful approach for the identification of antimicrobial mechanisms of action

Model simulations of the modulating effect of the snow cover in a rain-on-snow event

In October 2011, the Swiss Alps underwent a marked rain-on-snow (ROS) event when a large snowfall on 8 and 9 October was followed by intense rain on 10 October. This resulted in severe flooding in some parts of Switzerland. Model simulations were carried out for 14 meteorological stations in two affected regions of the Swiss Alps using the detailed physics-based snowpack model SNOWPACK. We also conducted an ensemble sensitivity study, in which repeated simulations for a specific station were done with meteorological forcing and rainfall from other stations. This allowed the quantification of the contribution of rainfall, snow melt and liquid water storage on generating snowpack runoff. In the simulations, the snowpack produced runoff about 4-6 h after rainfall started, and total snowpack runoff became higher than total rainfall after about 11-13 h. These values appeared to be strongly dependent on snow depth, rainfall and melt rates. Deeper snow covers had more storage potential and could absorb all rain and meltwater in the first hours, whereas the snowpack runoff from shallow snow covers reacts much more quickly. However, the simulated snowpack runoff rates exceeded the rainfall intensities in both snow depth classes. In addition to snow melt, the water released due to the reduction of liquid water storage contributed to excess snowpack runoff. This effect appears to be stronger for deeper snow covers and likely results from structural changes to the snowpack due to settling and wet snow metamorphism. These results are specifically valid for the point scale simulations performed in this study and for ROS events on relatively fresh snow