1,332 research outputs found
Growth-induced mass flows in fungal networks
Cord-forming fungi form extensive networks that continuously adapt to
maintain an efficient transport system. As osmotically driven water uptake is
often distal from the tips, and aqueous fluids are incompressible, we propose
that growth induces mass flows across the mycelium, whether or not there are
intrahyphal concentration gradients. We imaged the temporal evolution of
networks formed by Phanerochaete velutina, and at each stage calculated the
unique set of currents that account for the observed changes in cord volume,
while minimising the work required to overcome viscous drag. Predicted speeds
were in reasonable agreement with experimental data, and the pressure gradients
needed to produce these flows are small. Furthermore, cords that were predicted
to carry fast-moving or large currents were significantly more likely to
increase in size than cords with slow-moving or small currents. The
incompressibility of the fluids within fungi means there is a rapid global
response to local fluid movements. Hence velocity of fluid flow is a local
signal that conveys quasi-global information about the role of a cord within
the mycelium. We suggest that fluid incompressibility and the coupling of
growth and mass flow are critical physical features that enable the development
of efficient, adaptive, biological transport networks.Comment: To be published in PRSB. 20 pages, plus 8 pages of supplementary
information, and 3 page bibliograph
Conceptualising and Teaching Biomedical Uncertainty to Medical Students: an Exploratory Qualitative Study
Introduction
Certainty/uncertainty in medicine is a topic of popular debate. This study aims to understand how biomedical uncertainty is conceptualised by academic medical educators and how it is taught in a medical school in the UK.
Methods
This is an exploratory qualitative study grounded in ethnographic principles. This study is based on 10 observations of teaching sessions and seven semi-structured qualitative interviews with medical educators from various biomedical disciplines in a UK medical school. The data set was analysed via a thematic analysis.
Results
Four main themes were identified after analysis: (1) ubiquity of biomedical uncertainty, (2) constraints to teaching biomedical uncertainty, (3) the āmedic filterā and (4) fluid distinction: core versus additional knowledge. While medical educators had differing understandings of how biomedical uncertainty is articulated in their disciplines, its presence was ubiquitous. This ubiquity did not translate into teaching due to time constraints and assessment strategies. The āmedic filterā emerged as a strategy that educators employed to decide what to include in their teaching. They made distinctions between core and additional knowledge which were defined in varied ways across disciplines. Additional knowledge often encapsulated biomedical uncertainty.
Discussion
Even though the perspective that knowledge is socially constructed is not novel in medical education, it is neither universally valued nor universally applied. Moving beyond situativity theories and into broader debates in social sciences provides new opportunities to discuss the nature of scientific knowledge in medical education. We invite a move away from situated learning to situated knowledge
Fluid and Diffusion Limits for Bike Sharing Systems
Bike sharing systems have rapidly developed around the world, and they are
served as a promising strategy to improve urban traffic congestion and to
decrease polluting gas emissions. So far performance analysis of bike sharing
systems always exists many difficulties and challenges under some more general
factors. In this paper, a more general large-scale bike sharing system is
discussed by means of heavy traffic approximation of multiclass closed queueing
networks with non-exponential factors. Based on this, the fluid scaled
equations and the diffusion scaled equations are established by means of the
numbers of bikes both at the stations and on the roads, respectively.
Furthermore, the scaling processes for the numbers of bikes both at the
stations and on the roads are proved to converge in distribution to a
semimartingale reflecting Brownian motion (SRBM) in a -dimensional box,
and also the fluid and diffusion limit theorems are obtained. Furthermore,
performance analysis of the bike sharing system is provided. Thus the results
and methodology of this paper provide new highlight in the study of more
general large-scale bike sharing systems.Comment: 34 pages, 1 figure
A high resolution, three-dimensional view of the D-28 calving event from Amery Ice Shelf with ICESat-2 and satellite imagery
Author Posting. Ā© American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(3), (2021): e2020GL091200, doi:10.1029/2020GL091200.Tabular calving events occur from Antarctica's large ice shelves only every few decades, and are preceded by rift propagation. We used high-resolution imagery and ICESat-2 data to determine the propagation rates for the three active rifts on Amery Ice Shelf (AIS; T1, T2, and E3) and observe the calving of D-28 on September 25, 2019 along T1. AIS front advance accelerated downstream of T1 in the years before calving, possibly increasing stress at the rift tip. T1 experienced significant acceleration for 12 days before calving, coinciding with a jump in propagation of E3. ICESat-2's high resolution and repeat acquisitions every 91 days allowed for analysis of the ice front before and after calving, and rift detection where it was not visible in imagery as a ā¼1 m surface depression, suggesting that it propagates as a basal fracture. Our results show that ICESat-2 can provide process-scale information about iceberg calving.We received funding from the following sources: NASA NNX15AC80G and NSF grant 1443677 (Fricker and Becker) and NASA 80NSSC20K0960 (Walker). We are grateful to Mike Cloutier, Polar Geospatial Center for assistance with WorldView imagery. Geospatial support was provided by Polar Geospatial Center under NSF-OPP awards 1043681 and 1559691.2021-07-1
The Mobility Enterprise - Improving Auto Productivity
The Mobility Enterprise is a particular version of a shared vehicle fleet, aimed at solving the problem of low automobile productivity. The automobile consumes a large portion of Americaās transportation energy supply. It also operates much of the time with unused capacity: vacant seats and empty cargo space. Since programs to fill those vacant seats āride sharing and high occupancy vehicle incentives āhave fallen so far short of their objectives, a new approach is warranted. The enterpriseās central concept is matching vehicle attributes to travel needs. Generally, a household purchases vehicles for those few trips that require a large capacity, rather than for the majority of trips (usually to work) that have minimal vehicular needs. If a household could tailor its āimmediate accessā fleet to these frequent trips and still retain reasonable access to larger-capacity special purpose vehicles (SPVās), considerable economies could be achieved. The household is relieved of owning seldom-used excess capacity, and automobile productivity and efficiency are greatly improved. Having easy access to a shared fleet of SPVās also affords a household an increase in the quality and economy of its travel experiences. This paper describes a research project recently begun at Purdue that involves a comprehensive investigation of the Mobility Enterprise concept. Questions of institutional barriers, consumer response, and organization and management are discussed here as keys to the fate of the enterprise in the transportation climate of the foreseeable future
Methodological Diversity in Citizen Science Mosquito Surveillance: A Scoping Review
Global concern regarding mosquito-borne disease emergence and re-emergence has driven the development of citizen science mosquito surveillance initiatives. Although these initiatives have shown great potential to assist local health authorities, ensuring outcomes are translatable to improved public health policy and practice remains challenging. Here we present a summary of citizen science mosquito surveillance programs worldwide, their focus, strategies, and outcomes, with a view to how best to apply this approach in their local areas. A scoping review of studies and reports was conducted through systematic search on electronic databases (Scopus, PubMed, Web of Science, and Google Scholar), grey literature, and other documents listed in the references of selected articles. A total of 33 citizen science studies included in this review described 29 citizen science mosquito surveillance projects operating in 16 countries, besides three programs with wide geographic coverage. The selected programs focused on different strategies and methods according to their local and national contextual needs. The majority of the programs reported being free or low in cost, and amenable to participants. Also, citizen scientists valued the opportunity to actively contribute to a scientific activity in which they saw value. Local and national programs have been successful in involving the broader public and yielding data on mosquito populations. However, to ensure the best public health outcomes, sustainability, and scalability, there is a need to continue engaging with stakeholders, including community members, researchers, public health agents, industry, and policymakers, and to bridge existing collaborations across different sectors
Advection, diffusion and delivery over a network
Many biological, geophysical and technological systems involve the transport
of resource over a network. In this paper we present an algorithm for
calculating the exact concentration of resource at any point in space or time,
given that the resource in the network is lost or delivered out of the network
at a given rate, while being subject to advection and diffusion. We consider
the implications of advection, diffusion and delivery for simple models of
glucose delivery through a vascular network, and conclude that in certain
circumstances, increasing the volume of blood and the number of glucose
transporters can actually decrease the total rate of glucose delivery. We also
consider the case of empirically determined fungal networks, and analyze the
distribution of resource that emerges as such networks grow over time. Fungal
growth involves the expansion of fluid filled vessels, which necessarily
involves the movement of fluid. In three empirically determined fungal networks
we found that the minimum currents consistent with the observed growth would
effectively transport resource throughout the network over the time-scale of
growth. This suggests that in foraging fungi, the active transport mechanisms
observed in the growing tips may not be required for long range transport.Comment: 54 pages including appendix, 10 figure
Large closed queueing networks in semi-Markov environment and its application
The paper studies closed queueing networks containing a server station and
client stations. The server station is an infinite server queueing system,
and client stations are single-server queueing systems with autonomous service,
i.e. every client station serves customers (units) only at random instants
generated by a strictly stationary and ergodic sequence of random variables.
The total number of units in the network is . The expected times between
departures in client stations are . After a service completion
in the server station, a unit is transmitted to the th client station with
probability , and being processed in the th client
station, the unit returns to the server station. The network is assumed to be
in a semi-Markov environment. A semi-Markov environment is defined by a finite
or countable infinite Markov chain and by sequences of independent and
identically distributed random variables. Then the routing probabilities
and transmission rates (which are expressed via
parameters of the network) depend on a Markov state of the environment. The
paper studies the queue-length processes in client stations of this network and
is aimed to the analysis of performance measures associated with this network.
The questions risen in this paper have immediate relation to quality control of
complex telecommunication networks, and the obtained results are expected to
lead to the solutions to many practical problems of this area of research.Comment: 35 pages, 1 figure, 12pt, accepted: Acta Appl. Mat
Traitābased approaches reveal fungal adaptations to nutrientālimiting conditions
The dependency of microbial activity on nutrient availability in soil is only partly understood, but highly relevant for nutrient cycling dynamics. In order to achieve more insight on microbial adaptations to nutrient limiting conditions, precise physiological knowledge is needed. Therefore, we developed an experimental system assessing traits of 16 saprobic fungal isolates in nitrogen (N) limited conditions. We tested the hypotheses that (1) fungal traits are negatively affected by N deficiency to a similar extent and (2) fungal isolates respond in a phylogenetically conserved fashion. Indeed, mycelial density, spore production and fungal activity (respiration and enzymatic activity) responded similarly to limiting conditions by an overall linear decrease. By contrast, mycelial extension and hyphal elongation peaked at lowest N supply (C:N 200), causing maximal biomass production at intermediate N contents. Optimal N supply rates differed among isolates, but only the extent of growth reduction was phylogenetically conserved. In conclusion, growth responses appeared as a switch from explorative growth in low nutrient conditions to exploitative growth in nutrientārich patches, as also supported by responses to phosphorus and carbon limitations. This detailed traitābased pattern will not only improve fungal growth models, but also may facilitate interpretations of microbial responses observed in field studies
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