Stepping beyond perfectly mixed conditions in soil hydrological modelling using a Lagrangian approach

A recent experiment of Bowers et al. (2020) revealed that diffusive mixing of water isotopes (δ2H, δ18O) over a fully saturated soil sample of a few centimetres in length required several days to equilibrate completely. In this study, we present an approach to simulate such time-delayed diffusive mixing processes on the pore scale beyond instantaneously and perfectly mixed conditions. The diffusive pore mixing (DIPMI) approach is based on a Lagrangian perspective on water particles moving by diffusion over the pore space of a soil volume and carrying concentrations of solutes or isotopes. The idea of DIPMI is to account for the self-diffusion of water particles across a characteristic length scale of the pore space using pore-size-dependent diffusion coefficients. The model parameters can be derived from the soil-specific water retention curve and no further calibration is needed. We test our DIPMI approach by simulating diffusive mixing of water isotopes over the pore space of a saturated soil volume using the experimental data of Bowers et al. (2020). Simulation results show the feasibility of the DIPMI approach to reproduce measured mixing times and concentrations of isotopes at different tensions over the pore space. This result corroborates the finding that diffusive mixing in soils depends on the pore size distribution and the specific soil water retention properties. Additionally, we perform a virtual experiment with the DIPMI approach by simulating mixing and leaching processes of a solute in a vertical, saturated soil column and comparing results against simulations with the common perfect-mixing assumption. Results of this virtual experiment reveal that the frequently observed steep rise and long tailing of breakthrough curves, which are typically associated with non-uniform transport in heterogeneous soils, may also occur in homogeneous media as a result of imperfect subscale mixing in a macroscopically homogeneous soil matrix.

Determination of functional structure of soft-bottom marine macrobenthic communities of the Samsun Shelf Area using biological traits analysis

Biological Traits Analysis (BTA) was used to investigate the functional structure of marine macrobenthic communities along the Samsun Shelf Area (SSA). Benthic samples were collected seasonally from five different locations and at four different depths using a Van Veen grab sampler. Macrofaunal communities distributed in the SSA were assessed using 10 biological traits to identify characteristic traits for each depth and location. It was found that variability of benthic ecosystem functions in the SSA was driven by biological traits such as maximum size, living habit, sediment position, feeding mode and type of reproductive behavior. Bivalves, polychaetes and crustaceans of small to medium size, biodepositing, burying themselves in the sediment (burrowers) and feeding in suspension were relatively more abundant at depths of 0–60 m. However, the biomass of Amphiura, Abra, Papillicardium and some polychaetes characterized by medium to large sizes, diffusive mixing, free living and feeding on deposit and subsurface deposit showed higher values at depths below 60 m. In general, it is concluded that the functional structure of the benthic infauna in the SSA has adapted to physical disturbance, and communities distributed in this area consist mainly of taxa resistant to mechanical pressure.

Flow Configurations of Membraneless Microfluidic Fuel Cells: A Review

Membraneless microfluidic fuel cells (MMFCs) are being studied extensively as an alternative to batteries and conventional membrane fuel cells because of their simple functioning and lower manufacturing cost. MMFCs use the laminar flow of reactant species (fuel and oxidant) to eliminate the electrolyte membrane, which has conventionally been used to isolate anodic and cathodic half-cell reactions. This review article summarizes the MMFCs with six major categories of flow configurations that have been reported from 2002 to 2020. The discussion highlights the critical factors that affect and limit the performance of MMFCs. Since MMFCs are diffusion-limited, most of this review focuses on how different flow configurations act to reduce or modify diffusive mixing and depletion zones to enhance the power density output. Research opportunities are also pointed out, and the challenges in MMFCs are suggested to improve cell performance and make them practical in the near future.

MODULAR PLANT FOR THE PRODUCTION OF MEDICINAL MIXED FEEDSAND PREMIXES IN FARMS

The article presents the results of research on the optimization of machine technology and rational design of modular units for fractional grinding of grain components of the farms own production and a ball mixer that provides high uniformity of compound feeds and a mixture of premixes from medicinal preparations, vitamin and mineral additives with filler. The specified fractional composition of the grinding (crushing ratio) is the original design of hammer mill with a vertical cylindrical interchangeable perforated sieve with perforations 4; 5; 6 mm (instead of 2 or 3 mm as used crushers) through which the particle grinding as their education freely transported by the air stream from the crusher through the cyclone to woven sieve mill, where the grinding is divided into checkpoint – specified fraction and not the checkpoint – the gathering – a large part of which is 10…15 % and pitched the Board shall be sent to the crusher for re-crushing. This results in the grinding of a given fraction, a multiple reduction in the presence of flour dust, and the elimination of energy costs for its formation. Experience has proven (23) that the fractional grinding unit provides a grinding modulus of 1,8 versus 2,4 on the crushers used, reducing the specific energy costs by 1,8…2,7 times, and operating costs are lower by 29 %. The modularity of the units with a capacity of 2,0, 4,0 and 6,0 t/h is based on the constructive interchangeability. It is taken as the basic unit with a capacity of 4,0 t/h, and in the rest, only the power of the electric motor for driving the crusher and small design changes of the crushing chamber are replaced. The set of modular installations does not have a large and metal-intensive mixer. A ball chopper-mixer is proposed, which provides a high degree of homogeneity of the mixture (95…98 %) due to simultaneous selective and diffusive mixing methods. The forms for calculating the plant's performance are presented, taking into account the daily demand and the time lost for troubleshooting, configuration and maintenance

Double-diffusive mixing makes a small contribution to the global ocean circulation

Double-diffusive processes enhance diapycnal mixing of heat and salt in the open ocean. However, observationally based evidence of the effects of double-diffusive mixing on the global ocean circulation is lacking. Here we analyze the occurrence of double-diffusive thermohaline staircases in a dataset containing over 480,000 temperature and salinity profiles from Argo floats and Ice-Tethered Profilers. We show that about 14% of all profiles contains thermohaline staircases that appear clustered in specific regions, with one hitherto unknown cluster overlying the westward flowing waters of the Tasman Leakage. We estimate the combined contribution of double-diffusive fluxes in all thermohaline staircases to the global ocean’s mechanical energy budget as 7.5 GW [0.1 GW; 32.8 GW]. This is small compared to the estimated energy required to maintain the observed ocean stratification of roughly 2 TW. Nevertheless, we suggest that the regional effects, for example near Australia, could be pronounced.

Global dataset of thermohaline staircases obtained from Argo floats and Ice-Tethered Profilers

Thermohaline staircases are associated with double-diffusive mixing. They are characterized by stepped structures consisting of mixed layers of typically tens of metres thick that are separated by much thinner interfaces. Through these interfaces enhanced diapycnal salt and heat transport take place. In this study, we present a global dataset of thermohaline staircases derived from observations of Argo profiling floats and Ice-Tethered Profilers using a novel detection algorithm. To establish the presence of thermohaline staircases, the algorithm detects subsurface mixed layers and analyses the interfaces in between. Of each detected staircase, the conservative temperature, absolute salinity, depth, and height, as well as some other properties of the mixed layers and interfaces, are computed. The algorithm is applied to 487 493 quality-controlled temperature and salinity profiles to obtain a global dataset. The performance of the algorithm is verified through an analysis of independent regional observations. The algorithm and global dataset are available at https://doi.org/10.5281/zenodo.4286170.