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 ‘medic filter’ 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 ‘medic filter’ 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 $N^{2}$-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. © 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 ∼1 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 America’s 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 —ride sharing and high occupancy vehicle incentives —have fallen so far short of their objectives, a new approach is warranted. The enterprise’s 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 “immediate access” fleet to these frequent trips and still retain reasonable access to larger-capacity special purpose vehicles (SPV’s), 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 SPV’s 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 $k$ 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 $N$. The expected times between departures in client stations are $(N\mu_j)^{-1}$. After a service completion in the server station, a unit is transmitted to the $j$th client station with probability $p_{j}$ $(j=1,2,...,k)$, and being processed in the $j$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 $p_{j}$ $(j=1,2,...,k)$ 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

Trait‐based approaches reveal fungal adaptations to nutrient‐limiting 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 nutrient‐rich patches, as also supported by responses to phosphorus and carbon limitations. This detailed trait‐based pattern will not only improve fungal growth models, but also may facilitate interpretations of microbial responses observed in field studies