122 research outputs found
Modelling debris flows down general channels
This paper is an extension of the single-phase cohesionless dry granular avalanche model over curved and twisted channels proposed by Pudasaini and Hutter (2003). It is a generalisation of the Savage and Hutter (1989, 1991) equations based on simple channel topography to a two-phase fluid-solid mixture of debris material. Important terms emerging from the correct treatment of the kinematic and dynamic boundary condition, and the variable basal topography are systematically taken into account. For vanishing fluid contribution and torsion-free channel topography our new model equations exactly degenerate to the previous Savage-Hutter model equations while such a degeneration was not possible by the Iverson and Denlinger (2001) model, which, in fact, also aimed to extend the Savage and Hutter model. The model equations of this paper have been rigorously derived; they include the effects of the curvature and torsion of the topography, generally for arbitrarily curved and twisted channels of variable channel width. The equations are put into a standard conservative form of partial differential equations. From these one can easily infer the importance and influence of the pore-fluid-pressure distribution in debris flow dynamics. The solid-phase is modelled by applying a Coulomb dry friction law whereas the fluid phase is assumed to be an incompressible Newtonian fluid. Input parameters of the equations are the internal and bed friction angles of the solid particles, the viscosity and volume fraction of the fluid, the total mixture density and the pore pressure distribution of the fluid at the bed. Given the bed topography and initial geometry and the initial velocity profile of the debris mixture, the model equations are able to describe the dynamics of the depth profile and bed parallel depth-averaged velocity distribution from the initial position to the final deposit. A shock capturing, total variation diminishing numerical scheme is implemented to solve the highly non-linear equations. Simulation results present the combined effects of curvature, torsion and pore pressure on the dynamics of the flow over a general basal topography. These simulation results reveal new physical insight of debris flows over such non-trivial topography. Model equations are applied to laboratory avalanche and debris-flow-flume tests. Very good agreement between the theory and experiments is established
An Open Data and Citizen Science Approach to Building Resilience to Natural Hazards in a Data-Scarce Remote Mountainous Part of Nepal
The citizen science approach has gained momentum in recent years. It can enable both experts and citizen scientists to co-create new knowledge. Better understanding of local environmental, social, and geographical contexts can help in designing appropriate plans for sustainable development. However, a lack of geospatial data, especially in the context of developing countries, often precludes context-specific development planning. This study therefore tests an innovative approach of volunteer citizen science and an open mapping platform to build resilience to natural hazards in the remote mountainous parts of western Nepal. In this study, citizen scientists and mapping experts jointly mapped two districts of Nepal (Bajhang and Bajura) using the OpenStreetMap (OSM) platform. Remote mapping based on satellite imagery, capacity building, and mobilization of citizen scientists was performed to collect the data. These data were then uploaded to OSM and later retrieved in ArcGIS to produce a usable map that could be exploited as a reference resource for evidence-based decision-making. The collected data are freely accessible to community members as well as government and humanitarian actors, and can be used for development planning and risk reduction. By piloting in two communities of western Nepal, we found that using open data platforms for collecting and analyzing location-based data has a mutual benefit for researchers and communities. Such data could be vital in understanding the local landscape, environmental risk, and distribution of resources. Furthermore, they enable both researchers and local people to transfer technical knowledge, collect location-specific data, and use them for better decision-making
Development of a prototype superconducting radio-frequency cavity for conduction-cooled accelerators
The higher efficiency of superconducting radio-frequency (SRF) cavities
compared to normal-conducting ones enables the development of high-energy
continuous-wave linear accelerators (linacs). Recent progress in the
development of high-quality NbSn film coatings along with the availability
of cryocoolers with high cooling capacity at 4 K makes it feasible to operate
SRF cavities cooled by thermal conduction at relevant accelerating gradients
for use in accelerators. A possible use of conduction-cooled SRF linacs is for
environmental applications, requiring electron beams with energy of
MeV and 1 MW of power. We have designed a 915 MHz SRF linac for such an
application and developed a prototype single-cell cavity to prove the proposed
design by operating it with cryocoolers at the accelerating gradient required
for 1 MeV energy gain. The cavity has a m thick NbSn film on
the inner surface, deposited on a mm thick bulk Nb substrate and a bulk
mm thick Cu outer shell with three Cu attachment tabs. The cavity was
tested up to a peak surface magnetic field of 53 mT in liquid He at 4.3 K. A
horizontal test cryostat was designed and built to test the cavity cooled with
three Gifford-McMahon cryocoolers. The rf tests of the conduction-cooled
cavity, performed at General Atomics, achieved a peak surface magnetic field of
50 mT and stable operation was possible with up to 18.5 W of rf heat load. The
peak frequency shift due to microphonics was 23 Hz. These results represent the
highest peak surface magnetic field achieved in a conduction-cooled SRF cavity
to date and meet the requirements for a 1 MeV energy gain
Key directions for research and development of superconducting radio frequency cavities
Radio frequency superconductivity is a cornerstone technology for many future
HEP particle accelerators and experiments from colliders to proton drivers for
neutrino facilities to searches for dark matter. While the performance of
superconducting RF (SRF) cavities has improved significantly over the last
decades, and the SRF technology has enabled new applications, the proposed HEP
facilities and experiments pose new challenges. To address these challenges,
the field continues to generate new ideas and there seems to be a vast room for
improvements. In this paper we discuss the key research directions that are
aligned with and address the future HEP needs.Comment: contribution to Snowmass 202
Training during the COVID-19 lockdown : knowledge, beliefs, and practices of 12,526 athletes from 142 countries and six continents
OBJECTIVE Our objective was to explore the training-related knowledge, beliefs, and practices of athletes and the influence of
lockdowns in response to the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2).
METHODS Athletes (n = 12,526, comprising 13% world class, 21% international, 36% national, 24% state, and 6% recreational)
completed an online survey that was available from 17 May to 5 July 2020 and explored their training behaviors (training
knowledge, beliefs/attitudes, and practices), including specific questions on their training intensity, frequency, and session
duration before and during lockdown (MarchâJune 2020).
RESULTS Overall, 85% of athletes wanted to âmaintain training,â and 79% disagreed with the statement that it is âokay to not
train during lockdown,â with a greater prevalence for both in higher-level athletes. In total, 60% of athletes considered âcoaching
by correspondence (remote coaching)â to be sufficient (highest amongst world-class athletes). During lockdown, < 40%
were able to maintain sport-specific training (e.g., long endurance [39%], interval training [35%], weightlifting [33%], most (83%) training for âgeneral fitness and health maintenanceâ during lockdown. Athletes trained alone (80%) and focused
on bodyweight (65%) and cardiovascular (59%) exercise/training during lockdown. Compared with before lockdown, most
athletes reported reduced training frequency (from between five and seven sessions per week to four or fewer), shorter training
sessions (from â„ 60 to < 60 min), and lower sport-specific intensity (~ 38% reduction), irrespective of athlete classification.
CONCLUSIONS COVID-19-related lockdowns saw marked reductions in athletic training specificity, intensity, frequency, and
duration, with notable within-sample differences (by athlete classification). Higher classification athletes had the strongest
desire to âmaintainâ training and the greatest opposition to ânot trainingâ during lockdowns. These higher classification
athletes retained training specificity to a greater degree than others, probably because of preferential access to limited training
resources. More higher classification athletes considered âcoaching by correspondenceâ as sufficient than did lower
classification athletes. These lockdown-mediated changes in training were not conducive to maintenance or progression of
athletesâ physical capacities and were also likely detrimental to athletesâ mental health. These data can be used by policy
makers, athletes, and their multidisciplinary teams to modulate their practice, with a degree of individualization, in the
current and continued pandemic-related scenario. Furthermore, the data may drive training-related educational resources
for athletes and their multidisciplinary teams. Such upskilling would provide athletes with evidence to inform their training
modifications in response to germane situations (e.g., COVID related, injury, and illness).A specific funding was provided by the National Sports Institute
of Malaysia for this study.The National Sports Institute of Malaysia.https://www.springer.com/journal/40279am2023Sports Medicin
COVID-19 lockdown : a global study investigating athletesâ sport classification and sex on training practices
PURPOSE : To investigate differences in athletesâ knowledge, beliefs, and training practices during COVID-19 lockdowns with reference to sport classification and sex. This work extends an initial descriptive evaluation focusing on athlete classification. METHODS : Athletes (12,526; 66% male; 142 countries) completed an online survey (MayâJuly 2020) assessing knowledge, beliefs, and practices toward training. Sports were classified as team sports (45%), endurance (20%), power/technical (10%), combat (9%), aquatic (6%), recreational (4%), racquet (3%), precision (2%), parasports (1%), and others (1%). Further analysis by sex was performed. RESULTS : During lockdown, athletes practiced body-weight-based exercises routinely (67% females and 64% males), ranging from 50% (precision) to 78% (parasports). More sport-specific technical skills were performed in combat, parasports, and precision (âŒ50%) than other sports (âŒ35%). Most athletes (range: 50% [parasports] to 75% [endurance]) performed cardiorespiratory training (trivial sex differences). Compared to prelockdown, perceived training intensity was reduced by 29% to 41%, depending on sport (largest decline: âŒ38% in team sports, unaffected by sex). Some athletes (range: 7%â49%) maintained their training intensity for strength, endurance, speed, plyometric, change-of-direction, and technical training. Athletes who previously trainedââ„5 sessions per week reduced their volume (range: 18%â28%) during lockdown. The proportion of athletes (81%) trainingââ„60 min/session reduced by 31% to 43% during lockdown. Males and females had comparable moderate levels of training knowledge (56% vs 58%) and beliefs/attitudes (54% vs 56%). CONCLUSIONS : Changes in athletesâ training practices were sport-specific, with few or no sex differences. Team-based sports were generally more susceptible to changes than individual sports. Policy makers should provide athletes with specific training arrangements and educational resources to facilitate remote and/or home-based training during lockdown-type events.https://journals.humankinetics.com/view/journals/ijspp/ijspp-overview.xmlhj2023Sports Medicin
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