Ground-based facilities, such as clinostats and random positioning machines aiming at simulating microgravity conditions, are tools to prepare space experiments and identify gravity-related signaling pathways. A prerequisite is that the facilities are operated in an appropriate manner and potentially induced non-gravitational effects, such as shearing forces, have to be taken into account. Dinoflagellates, here P. noctiluca, as fast and sensitive reporter system for shear stress and hydrodynamic gradients, were exposed on a clinostat (constant rotation around one axis, 60 rpm) or in a random positioning machine, that means rotating around two axes, whose velocity and direction were chosen at random. Deformation of the cell membrane of P. noctiluca due to shear stress results in a detectable bioluminescence emission. Our results show that the amount of mechanical stress is higher on an random positioning machine than during constant clinorotation, as revealed by the differences in photon counts. We conclude that one axis clinorotation induced negligible non-gravitational effects in the form of shear forces in contrast to random operation modes tested. For the first time, we clearly visualized the device-dependent occurrence of shear forces by means of a bioassay, which have to be considered during the definition of an appropriate simulation approach and to avoid misinterpretation of results. Earth-based laboratories can now assess the accuracy of tools used to simulate living organism growth and behaviour in space with bioluminescent assays. Researchers often use rotating machines to minimize gravity effects during the design of extra-terrestrial experiments with plants, cells, and small animals. Jens Hauslage from the DLR German Aerospace Center and colleagues report that device-specific shear forces produced during mechanical movements may cause misinterpretations of initial test data. They developed a biosensor based on marine plankton, known as dinoflagellates, which have cell membranes that naturally emit light when touched by predators. Calibrating this bioluminescence against mechanical stress helped determine the top-like, 2D rotations of ‘‘clinostat’’ devices provided microgravity-like conditions. However, the unexpected 3D movements of Random Positioning Machines generated enough shear force to impact studies of cell signaling pathways or metabolic reactions.

Pyrocystis noctiluca represents an excellent bioassay for shear forces induced in ground-based microgravity simulators (clinostat and random positioning machine).

Review article: Microscale evaporative cooling technologies for high heat flux microelectronics devices: Background and recent advances

Evaporation-driven liquid flow through nanochannels

Molecular dynamics simulations and mathematical optimization method for surface structures regarding evaporation heat transfer enhancement at the nanoscale

Influences of Wire Diameters on Output Power in Electromagnetic Energy Harvester

Flow pattern transition of thermal–solutal capillary convection with the capillary ratio of −1 in a shallow annular pool

In order to understand the characteristics of pure solutocapillary flow in a shallow annular pool subjected to a constant radial solutal gradient, a series of three-dimensional numerical simulations were performed. The annular pool was filled with the toluene/n-hexane mixture fluid with the Schmidt number of 142.8. The inner and outer cylinders were respectively maintained at low and high solutal concentrations. Aspect ratio of the annular pool is fixed at e = 0.15 or 0.05. Results indicate that the solutocapillary flow is steady and axisymmetric at a small solutal capillary Reynolds number. The surface fluid flows radially from the inner cylinder toward the outer cylinder and a return flow exists near the bottom. With the increase of the solutal capillary Reynolds number, an axisymmetric oscillatory flow firstly appears and then becomes a three-dimensional oscillatory flow at e = 0.15. Whereas at e = 0.05 a direct transition from the steady and axisymmetric flow to the three-dimensional oscillatory flow is observed. Three types of the flow instabilities are the standing wave, hydrosolutal wave and source/sink type wave instabilities. Furthermore, the physical mechanism of the flow destabilization is analyzed.

Three-Dimensional Numerical Simulation of Pure Solutocapillary Flow in a Shallow Annular Pool for Mixture Fluid with High Schmidt Number

This paper presents a series of molecular dynamics simulations of the evaporating process of an argon droplet on heated substrates and the energy transport mechanism through the solid–liquid interface. Results indicate that the mass density through the liquid–vapor interface decreases sharply when the evaporation is in the steady state. Meanwhile, there is an adsorption layer in the form of clusters at the solid–liquid interface, which has a higher mass density than the droplet inside. Furthermore, the wetting property of the solid substrate is related to the system’s initial temperature and the solid–liquid potential energy parameter. The contact angle decreases with the increase of initial temperature and solid–liquid potential energy parameter. During the accelerated evaporation process, small part of energy transports into the liquid in the perpendicular direction to the solid–liquid interface and most of the energy transports along the parallel direction to the solid–liquid interface in the adsorptio...

Li Zhang

Papers

Flow pattern transition of thermal–solutal capillary convection with the capillary ratio of −1 in a shallow annular pool

Three-Dimensional Numerical Simulation of Pure Solutocapillary Flow in a Shallow Annular Pool for Mixture Fluid with High Schmidt Number

Molecular Dynamics Simulation of Heat Transport through Solid-Liquid Interface during Argon Droplet Evaporation on Heated Substrates.

Flow bifurcation routes to chaos of thermocapillary convection for low Prandtl number fluid in shallow annular pool with surface heat dissipation

Experimental study on Prandtl number dependence of thermocapillary-buoyancy convection in Czochralski configuration with different depths