3 research outputs found
A combined model of aggregation, fragmentation, and exchange processes: insights from analytical calculations
We introduce a mean-field framework for the study of systems of interacting
particles sharing a conserved quantity. The work generalises and unites the
existing fields of asset-exchange models, often applied to socio-economic
systems, and aggregation-fragmentation models, typically used in modelling the
dynamics of clusters. An initial model includes only two-body collisions, which
is then extended to include many-body collisions and spontaneous fragmentation.
We derive self-consistency equations for the steady-state distribution, which
can be solved using a population dynamics algorithm, as well as a full solution
for the time evolution of the moments, corroborated with numerical simulations.
The generality of the model makes it applicable to many problems and allows for
the study of systems exhibiting more complex interactions that those typically
considered. The work is relevant to the modelling of barchan dune fields in
which interactions between the bedforms and spontaneous fragmentation due to
changes in the wind are thought to lead to size-selection. Our work could also
be applied in finding wealth distributions when agents can both combine assets
as well as split into multiple subsidiaries.Comment: 19 pages, 5 figures. To be published in Journal of Statistical
Mechanics: Theory and Experiment (JSTAT
Low-cost electronic sensors for environmental research: pitfalls and opportunities
Repeat observations underpin our understanding of environmental processes, but financial constraints often limit scientists’ ability to deploy dense networks of conventional commercial instrumentation. Rapid growth in the Internet-Of-Things (IoT) and the maker movement is paving the way for low-cost electronic sensors to transform global environmental monitoring. Accessible and inexpensive sensor construction is also fostering exciting opportunities for citizen science and participatory research. Drawing on 6 years of developmental work with Arduino-based open-source hardware and software, extensive laboratory and field testing, and incor- poration of such technology into active research programmes, we outline a series of successes, failures and lessons learned in designing and deploying environmental sensors. Six case studies are presented: a water table depth probe, air and water quality sensors, multi-parameter weather stations, a time-sequencing lake sediment trap, and a sonic anemometer for monitoring sand transport. Schematics, code and purchasing guidance to reproduce our sensors are described in the paper, with detailed build instructions hosted on our King’s College London Geography Environmental Sensors Github repository and the FreeStation project website. We show in each case study that manual design and construction can produce research-grade scientific instrumentation (mean bias error for calibrated sensors –0.04 to 23%) for a fraction of the conventional cost, provided rigorous, sensor-specific calibration and field testing is conducted. In sharing our collective experiences with build-it- yourself environmental monitoring, we intend for this paper to act as a catalyst for physical geographers and the wider environmental science community to begin incorporating low-cost sensor development into their research activities. The capacity to deploy denser sensor networks should ultimately lead to superior envi- ronmental monitoring at the local to global scales
Complementary classifications of aeolian dunes based on morphology, dynamics, and fluid mechanics
Dunes form where winds blow over a bed of mobile sediment grains – conditions that are common in our solar system. On Earth, dunes abound in arid continental interiors and along sandy coastlines. Dune fields have also been recognized on Venus, Mars, Saturn’s moon Titan, and Pluto. In response to the different boundary conditions and other environmental forcings, dunes adopt a rich diversity of shapes, sizes, and behaviors. Thus, people around the globe and over centuries have developed a rich vocabulary to describe dunes and their complexity. As a result, existing dune nomenclature often includes redundant terms with differing definitions across scientific communities. Previous studies have endeavoured to link dune shape to environmental forcing, usually by means of correlation. Although instructive, correlation-based classifications can be misleading if not based on an underlying mechanics and if dune morphogenetic classes are not uniquely defined. Here, we synthesize existing dune terminology and use the last two decades of research on dune morphodynamics to propose three complementary dune classification schemes based on: (1) descriptive dune gemorphology, (2) morphodynamic processes, and (3) fluid mechanics and physics of sediment transport. The first classification relates dune types to geomorphic setting, presence or absence of vegetation or obstacles, and dune shape (including planform shape, and cross-sectional symmetry or asymmetry). Dune classes can be further subdivided where the direction of sand transport is known independently. The second classification relates dune types and shapes to bed properties (sand-covered vs partially starved bed) and wind forcing (directional variability or the relative strengths and directions of wind modes) that together influence dune dynamics (growth, migration, elongation) and select the dominant processes by which dunes are shaped and oriented relative to the resultant transport direction. The third classification relates, for different planetary environments, the range of possible dune sizes, from minimum to maximum wavelength, to flow regime (rough or smooth) and response of sediment transport, which influence the coupling between sand bed topography, fluid flow, and sediment transport. These characteristic lengths are useful scales for comparative geomorphology. The three classification schemes provide complementary information. Together, they form a unified framework for geomorphologists, sedimentologists, geographers, physicists, and others to describe windblown sand dunes on Earth and beyond through their shape, dynamics, and size as a response to winds and boundary conditions