In this paper we study nutrient uptake by a very simple model of a swimming microorganism, a sphere moving its surface tangentially to itself with constant concentration on the surface. The effect of its swimming motions on the concentration field and uptake is investigated. We find the relationship between the Sherwood number (Sh), a measure of the mass transfer across the surface, and the Péclet number (Pe), which indicates the relative effect of convection versus diffusion. Then we compare the results with those for a rigid sphere moving at the same speed under the action of an external force.

We present results for the average mass transfer to a spherical squirmer, a model micro-organism whose surface oscillates tangentially to itself. The surface motion drives a low-Reynolds-number flow which enables the squirmer either to swim relative to the fluid at infinity, at an average speed proportional to a streaming parameter, $W$, or to stir the fluid around it while remaining, on average, at rest (if $W\,{=}\,0$), as represented by a hovering parameter, $b$. We assume that the amplitude of the time-periodic surface distortions is scaled by a dimensionless small parameter $\epsilon$, and consider only high Péclet numbers $P$ – a measure of convection versus diffusion – by setting $P^{-1acute;\,{=}\,\epsilon^2 \gamma$, where $\gamma$ is a parameter of $O(1)$. It is shown that the average mass concentration distribution satisfies a steady convection–diffusion equation with an effective velocity field that is different from the actual mean velocity field. The model is used to calculate the mass transfer across the surface of the squirmer, measured by the mean Sherwood number $Sh$. We find asymptotic solutions for small and large $\gamma$ and numerical results for the whole range of values. While the large-$\gamma$ expansions are reproduced well by the numerical results, there is a discrepancy between the two at small $\gamma$. We believe this is due to very small recirculation regions, attached to the surface of the squirmer, which make boundary layer theory applicable only when $1/\gamma$ is immense. For the parameters chosen in this study, results indicate that both hovering and streaming contribute to the mass transfer, although streaming has a greater effect. Also, energy dissipation considerations show that an optimum swimming mode exists, at least at small and large $\gamma$, for any given uptake rate. However, other factors have still to be taken into account, and the model realism improved, if we want to make predictions for real aquatic micro-organisms.

We present a review of wind energy development in Mexico, factors hampering this development, and proposals for solutions to address this hampering. This review is relevant in the context of climate change mitigation strategies and the achievement of the United Nations’ sustainable development goals. Wind energy can be harvested at competitive costs to solve society’s energy poverty and climate change problems. Firstly, we present the current wind energy installed capacity and wind power generation status globally and in Mexico and discuss why Mexico is lagging behind, particularly since 2020. Despite this lag, several state governors are still considering wind energy developments. The current economic context is then considered, with community wind energy as a solution forward for wind energy development, using a successful case study from the UK that has addressed energy poverty and provided an additional income source for an island community. Any community energy project using wind as its main energy resource relies on accurate wind energy assessment in its feasibility analysis. Thus, an evaluation of different wind energy atlases for Mexico was performed, which showed that models considering microscale processes could lead to a relative difference of more than 50% when compared to those that do not consider them. This led to the conclusion that microscale effects must be considered in wind energy characterization models. Furthermore, it is acknowledged that wind faces other challenges, such as the effect of future climate change scenarios, grid planning, and vulnerability and risk associated with tropical storms, which can be substantial in Mexico. Solutions are proposed in the form of possible wind power generation scenarios, planning and implementation of centralized and distributed transmission lines, and possible wind siting and technological choices to reduce the vulnerability and risk to tropical storms. Finally, we close with some future perspectives for researchers and decision-makers. The main conclusions are that sustainable growth can only be compatible with a transition to renewable sources of energy, energy community projects can address energy poverty and achieve sustainable development goals, wind energy feasibility studies need to include microscale effects, return of investment can be improved by siting the wind farms in regions of low vulnerability and risk to extreme events, and high-voltage transmission lines are crucial for sustainable development, even with the important role that distributed systems play. Finally, turbine growth and materials recycling, among other factors, must be considered when assessing the environmental impacts of wind farm decommissioning.