Micro-scale Environments in Biofilms

To simulate polymer flows in microscale environments we have developed a numerical method that couples stochastic particle dynamics with an efficient incompressible Navier–Stokes solver. Here, we examine properties of the particle solver alone. We derive a Duhamel-form stochastic particle method for freely jointed polymers and demonstrate that it achieves 2-order weak convergence and 3/2-order strong convergence with holonomic constraints. For time steps approaching the relaxation time, our method displays greatly enhanced stability relative to comparable solvers based on linearised dynamics. Under these same conditions, our method has solution errors that are approximately six orders of magnitude smaller than that for the linearised algorithm.

Chemical hydrogeology in natural and contaminated environments

The microscale environment (e.g., current velocity) along the migratory route of aquatic organisms may directly affect their performance (e.g., migration speed or survival). We used minnow traps to evaluate how stocked Chum Salmon Oncorhynchus keta fry use stream velocity to optimize seaward migration. We found that fry were primarily captured at night and the number of fry collected was higher in traps with faster velocity water at the entrance to the trap. We interpreted this to mean that the fry were optimizing their migration efficiency by using faster velocity areas, which promote more rapid downstream migration.

Advances in sensitive optical measurement schemes have led to the detection and the physical and chemical characterization of single biological cells and individual molecules. These technological achievements are much more than the ultimate milestone in low‐level monitoring. Potential applications include DNA sequencing at high speeds, probing microscale environments, monitoring environmental pollution, studying the variability of molecular conformations, detecting disease infection at an early stage, and devising molecular‐scale imaging probes.

Marine microbial ecology is usually investigated over large spatial and temporal scales, under the assumption that planktonic organisms and solutes are homogeneously mixed. However, it is becoming increasingly apparent that the seascape experienced by marine microorganisms is in fact rather heterogeneous and punctuated by chemical hotspots derived from planktonic organisms as well as sinking and suspended organic particles. Motile bacteria and archaea can exploit these hotspots to enhance their growth. Within these chemically rich microscale environments shaped by diffusion and flow, individual cells can also interact with other microorganisms, inducing ripple effects that have consequences across the entire marine food web. Here we describe the physical and biological processes that structure the ocean at the scale of marine microbes, the adaptations enabling them to navigate this patchy seascape, and the way these microscale behaviors can scale-up to influence large-scale biogeochemical processes.KeywordsChemotaxisMicroscale diffusionMotilityParticlesSymbiosisTurbulence

Tsunami evacuation planning is a critical and urgent social issue that requires consideration of traffic impediments and road blockages caused by earthquakes and flooding. Traditional pedestrian evacuation models have focused primarily on micro-scale environments spanning a few dozen meters within buildings, limiting their applicability to tsunami scenarios involving travel over hundreds of meters. This study aims to (1) extend a cell FD-based dynamic traffic distribution model into a zonal MFD-based model and (2) apply it to pedestrian traffic to construct an optimization model that outputs efficient evacuation directions. Focusing on real local cities in Japan, we compare optimal solutions for different pedestrian evacuation direction scenarios. The results confirm that if pedestrians can preemptively understand multiple safe evacuation routes, rather than relying solely on the nearest facilities, efficient directional guidance that reduces congestion can be achieved.

Semantic volume texture for virtual city building model visualisation

We report the fabrication and characterization of individual nanotube-based, long and straight needle nanoprobes for electrochemistry and the study of their applicability and behavior in microenvironments. The needle nanoprobe, with a nanoscale ring-shaped Au electrode at the tip of the needle serving as the active electrode, was characterized by electrochemical current measurement and cyclic voltammetry and analyzed with electrochemical models. Such a needle nanoprobe, in combination with another metal-coated nanowire as a reference electrode, was further used, for the first time, for local electrochemical sensing inside microdroplets having volumes down to a few picoliters. We explain the acquired voltammetric behaviors of redox-active molecules in confined microscale environments and reveal a unique electrochemical mechanism which allows the regeneration of the redox-active molecules and the establishment of a stable reference potential in the microenvironments.

Magnetic microrobots have been developed for navigating microscale environments by means of remote magnetic fields. However, limited propulsion speeds at small scales remain an issue in the maneuverability of these devices as magnetic force and torque are proportional to their magnetic volume. Here, a microrobotic superstructure is proposed, which, as analogous to a supramolecular system, consists of two or more microrobotic units that are interconnected and organized through a physical (transient) component (a polymeric frame or a thread). The superstructures consist of microfabricated magnetic helical micromachines interlocked by a magnetic gelatin nanocomposite containing iron oxide nanoparticles (IONPs). While the microhelices enable the motion of the superstructure, the IONPs serve as heating transducers for dissolving the gelatin chassis via magnetic hyperthermia. In a practical demonstration, the superstructure's motion with a gradient magnetic field in a large channel, the disassembly of the superstructure and release of the helical micromachines by a high-frequency alternating magnetic field, and the corkscrew locomotion of the released helices through a small channel via a rotating magnetic field, is showcased. This adaptable microrobotic superstructure reacts to different magnetic inputs, which can be used to perform complex delivery procedures within intricate regions of the human body.