Point-particle method to compute diffusion-limited cellular uptake

We present an efficient point-particle approach to simulate reaction-diffusion processes of spherical absorbing particles in the diffusion-limited regime, as simple models of cellular uptake. The exact solution for a single absorber is used to calibrate the method, linking the numerical parameters to the physical particle radius and uptake rate. We study configurations of multiple absorbers of increasing complexity to examine the performance of the method, by comparing our simulations with available exact analytical or numerical results. We demonstrate the potentiality of the method in resolving the complex diffusive interactions, here quantified by the Sherwood number, measuring the uptake rate in terms of that of isolated absorbers. We implement the method in a pseudo-spectral solver that can be generalized to include fluid motion and fluid-particle interactions. As a test case of the presence of a flow, we consider the uptake rate by a particle in a linear shear flow. Overall, our method represents a powerful and flexible computational tool that can be employed to investigate many complex situations in biology, chemistry and related sciences.Comment: 13 pages, 13 figure

Turbulent fluid acceleration generates clusters of gyrotactic microorganisms

The motility of microorganisms is often biased by gradients in physical and chemical properties of their environment, with myriad implications on their ecology. Here we show that fluid acceleration reorients gyrotactic plankton, triggering small-scale clustering. We experimentally demonstrate this phenomenon by studying the distribution of the phytoplankton Chlamydomonas augustae within a rotating tank and find it to be in good agreement with a new, generalized model of gyrotaxis. When this model is implemented in a direct numerical simulation of turbulent flow, we find that fluid acceleration generates multi-fractal plankton clustering, with faster and more stable cells producing stronger clustering. By producing accumulations in high-vorticity regions, this process is fundamen- tally different from clustering by gravitational acceleration, expanding the range of mechanisms by which turbulent flows can impact the spatial distribution of active suspensions.Comment: 5 pages, 4 figure

Attenuating surface gravity waves with mechanical metamaterials

4noMetamaterials and photonic/phononic crystals have been successfully developed in recent years to achieve advanced wave manipulation and control, both in electromagnetism and mechanics. However, the underlying concepts are yet to be fully applied to the field of fluid dynamics and water waves. Here, we present an example of the interaction of surface gravity waves with a mechanical metamaterial, i.e., periodic underwater oscillating resonators. In particular, we study a device composed of an array of periodic submerged harmonic oscillators whose objective is to absorb wave energy and dissipate it inside the fluid in the form of heat. The study is performed using a state-of-the-art direct numerical simulation of the Navier-Stokes equation in its two-dimensional form with free boundary and moving bodies. We use a volume of fluid interface technique for tracking the surface and an immersed boundary method for the fluid-structure interaction. We first study the interaction of a monochromatic wave with a single oscillator and then add up to four resonators coupled only fluid-mechanically. We study the efficiency of the device in terms of the total energy dissipation and find that by adding resonators, the dissipation increases in a nontrivial way. As expected, a large energy attenuation is achieved when the wave and resonators are characterized by similar frequencies. As the number of resonators is increased, the range of attenuated frequencies also increases. The concept and results presented herein are of relevance for coastal protection applications.openpartially_openembargoed_20220426De Vita F.; De Lillo F.; Bosia F.; Onorato M.De Vita, F.; De Lillo, F.; Bosia, F.; Onorato, M

Measuring surface gravity waves using a Kinect sensor

We present a technique for measuring the two-dimensional surface water wave elevation both in space and time based on the low-cost Microsoft Kinect sensor. We discuss the capabilities of the system and a method for its calibration. We illustrate the application of the Kinect to an experiment in a small wave tank. A detailed comparison with standard capacitive wave gauges is also performed. Spectral analysis of a random-forced wave field is used to obtain the dispersion relation of water waves, demonstrating the potentialities of the setup for the investigation of the statistical properties of surface waves

Alignment of Nonspherical Active Particles in Chaotic Flows

We study the orientation statistics of spheroidal, axisymmetric microswimmers, with shapes ranging from disks to rods, swimming in chaotic, moderately turbulent flows. Numerical simulations show that rod-like active particles preferentially align with the flow velocity. To explain the underlying mechanism we solve a statistical model via perturbation theory. We show that such alignment is caused by correlations of fluid velocity and its gradients along particle paths combined with fore-aft symmetry breaking due to both swimming and particle nonsphericity. Remarkably, the discovered alignment is found to be a robust kinematical effect, independent of the underlying flow evolution. We discuss its possible relevance for aquatic ecology.Comment: 5 pages, 3 figures, Supplements in Ancillary directory, accepted in Physical Review Letter

Preliminary bioassays on the susceptibility of stone fruits rootstocks to Capnodis tenebrionis (L.).

Capnodis tenebrionis (L.) (Coleoptera: Buprestidae), the so called Mediterranean flat-headed root-borer, is an economically important phytophagous pest species mainly on stone fruit trees (apricot, plum, cherry, peach and nectarine). Chemicals and Entomopathogenic nematodes are used for the control of adults and neonate larvae, respectively. Further control means are under investigations in order to have more options within Integrated Pest Control strategies. This study is aimed at investigating the susceptibility of rootstocks to the larvae of C. tenebrionis. Two bioassays were carried out during 2016 and 2017. A first bioassay was based on the evaluation of a potential antixenosis action expressed by neonate larvae infesting twigs of rootstocks (Marianna 26, Barrier, Adesoto, Mylaboran 29C, GF677, Garnem, Cab 6P, Max Ma60 and Colt). This bioassay allowed to process a high number of different rootstocks in a short time. It has a preliminary value. The second bioassay assessed the antibiosis influence of the rootstocks through the breeding of larvae (since the neonate ones) on artificial diets containing bark flour of Adesoto, Cab 6P, Colt, Garnem, GF677, Max Ma60, Montclar and 29C rootstock. The first bioassay showed that Colt, Mylaboran 29C and GF677 were the most susceptible rootstocks to larval infestation of C. tenebrionis and Max Ma60 was less favorable to the pest. Concerning the effects of the diet, larvae reared on a diet containing Montclar, Cab 6P and GF 677 bark flour had a mean daily increase of their weight higher that those reared on cortex tissues of other genotypes whereas Garnem and Colt had a lower increase