Numerous studies have reported that gravity alteration displays a remarkable influence on the biological processes of cancer cells. Therefore, gravity-related experiments have become a promising method of improving knowledge in the field of cancer biology and may be useful to detect remarkable implications for future cancer treatment. Taking this concept further, we used a 3D clinostat (3D-C; 10 rpm of changing direction) to analyse the effect of short-term exposure to simulated microgravity (sμg) on cisplatin sensitivity of drug resistant human ovarian cancer cells SKOV-3. This allowed us to investigate whether altered gravity affects drug susceptibility of cancer cells. Our studies revealed that sμg exposure affects SKOV-3 cells morphology and drug efficiency. We observed the altered cell shape, the presence of membrane blebbing and lamellipodia as well as the lack of filopodia when the cells had been cultured on 3D-C for 2 h. Cytotoxicity, cell death and cell cycle assays showed an increased percentage of apoptotic cells and G0/G1 cell cycle arrest after exposure on the 3D-C with cisplatin in comparison to the static control, non clinorotated cells. Cell proliferation and migration were altered after the exposure to sμg as well. Our studies suggest that the altered gravity conditions affected cellular mechanisms involved in cisplatin resistance, resulting in higher sensitivity of cancer cells to the chemotherapeutic. The investigation and clarification of these results may be a crucial step toward improving our understanding of the relationship between cellular resistance to chemotherapy and the response to altered gravitational conditions.

The supercritical modes of water convection at room temperature in an elongated horizontal cavity, with a ratio of width to height from 1:1 to 5:1 are investigated. The Prandtl number is assumed to be seven. A constant heat flux is set at the upper free and lower solid boundaries, and the side solid walls are assumed to be thermally insulated. Calculations carried out by the finite-difference method for values of the Grashof number exceeding the critical one by up to fifty times have shown that in the considered range of Grashof numbers in moderately elongated cavities, with the aspect ratios of up to 4:1, a single-vortex stationary regime is realized in the supercritical region. In a cavity with the aspect ratio of 5:1 for a wide range of Grashof numbers, a multiplicity of stationary regimes is possible, from onevortex to three-vortex. Hysteresis transitions between them, taking place at a smooth and stepwise change in the Grashof number, have been discovered and investigated.

In order to reveal the effect of substrate microstructure on heat transfer of nanofluid droplet evaporation, the thermocapillary flow characteristics and heat transfer performance of nanofluid droplet on different substrates are investigated. The two-phase mixture model is used to simulate the nanofluid flow, and three kinds of micro-structured substrates (namely, sawtooth, rectangle, and parabola structures) are considered. The computational results show that micro-structured substrate can affect the temperature and flow field distributions inside the droplet, and the petal structure of isotherm and flow velocity of smooth substrate is larger than that with micro-structured substrates. The average heat flux at droplet surface increases with substrate temperature increasing, the average heat flux with rectangle substrate is larger than smooth substrate, while that of sawtooth and parabola substrate is smaller. With the increase of nanoparticle volume fraction the average heat flux at droplet surface almost increases linearly.

The inhibition of the cytotoxicity of NK cells by microgravity in space is of serious concern to the health of astronauts. However, there remains a lack of in-depth research into the mechanisms of action of this suppression. In the present study, the effects of simulated microgravity (SMG) on the morphology, survival rate and the ability of NK cells to kill were studied initially and then the mechanism of SMG in the inhibition of NK cytotoxicity was preliminarily investigated from the perspectives of stimulatory and inhibitory receptor expression. Further, the present study attempted to reveal the molecular mechanisms of SMG inhibition of the stimulatory receptor NKG2D from the perspective of DNA methylation and the expression of its adaptor protein DAP10. The results demonstrated that down-regulation of stimulatory receptor NKG2D expression and significantly up-regulated expression of inhibitory receptor CD158a may be important in explaining for the inhibition of NK cell cytotoxicity by SMG. The down-regulation of DAP10 expression, and not its DNA methylation, that is the possible cause of the down-regulation of NKG2D expression by SMG and the subsequent suppression of NK cell activity. However, inhibition of DAP10 expression by SMG was also not achieved by influencing methylation, and so additional analysis of the mechanism is required. The results of the present study lay the foundations for finally elucidating the molecular mechanisms by which microgravity leads to a decline in NK cell activity and contributes important evidence for interpreting the regulatory mechanisms of NK cell cytotoxicity.

This paper analyzes the possibility of obtaining the selective transport of microparticles suspended in air in a microgravity environment through modulated channels without net displacement of air. Using numerical simulation and bifurcation analysis tools, we show the existence of intermittent particle drift under the Stokes assumption of the fluid flow. The particle transport can be selective and the direction of transport is controlled only by the kind of pumping used. The selective transport is interpreted as a deterministic ratchet effect due to spatial variations in the flow and the particle drag. This ratchet phenomenon could be applied to the selective transport of metal particles during the short duration of microgravity experiments.

Thermodiffusion of a binary electrolyte situated in the microgap between two ion-selective surfaces under external electric field is theoretically studied. It is assumed that temperature gradient occurs only by Joule heating of the electrolyte; and the concentration gradient may trigger an inner gravitational instability. There are three types of instability in such setup: electrokinetic, thermoelectrokinetic and internal gravitational instability. The direct numerical simulation of the problem shows that for the typical salts solutions such as NaCl or KCl the termodiffusion effect is negligible, while for some salts with bigger values of the reduced Soret coefficients of ions (for example, for tetra-n-butylammonium fluoride) the thermodiffusion may significantly affect the voltage-current characteristic. It is also obtained, that the negative thermodiffusion leads to the destabilization of the one-dimensional steady state regime and shifts the critical values of governing parameters for each aforementioned type of instability. The thermodiffusion mostly influences the classical electrokinetic instability and less — the internal gravitational instability. Under effect of both types of thermodiffusion (normal and negative), the thermoelectrokinetic instability manifests at smaller values of Rayleigh numbers.

Because the absence of sedimentation in zero-gravity makes the culture and the manipulation of cells or particles challenging, an attractive alternative is to use the Acoustic Radiation Force (ARF) as an artificial “acoustic gravity.” To evaluate the potential of this approach we studied the behavior of dense gold nanorods under ARF during a parabolic flight campaign. Using dense objects enhances the effect of gravity on the axial position of the so-called “levitation plane,” which is the equilibrium position at which ARF balances gravity in the laboratory. Further, using elongated objects, instead of spherical particles provides information about their spatial orientations in addition to their propulsion observed in standard gravity conditions. Our experiments clearly show a different collective organization and individual behavior of the rods in micro-gravity conditions. First, the axial location of the levitation plane is different in microgravity than in hypergravity: it matches the nodal pressure plane in microgravity while it is much lower than the nodal plane in hypergravity. Our experiments also show a sharp transition from horizontal to axial orientation of the rods axis. The propulsion of the rods also stops when transitioning to micro-gravity. A possible explanation for the sudden change of orientation and stopping of propulsion is the modification of the equilibrium between the axial and transverse components of the ARF. While these experiments show that some phenomena, like the propulsion of nanorods by ARF, may not be applicable in microgravity, they do confirm that acoustic manipulation of particles or cells in microgravity is possible, which paves for the development of many useful techniques for particles or cells manipulation, like cell cultures, during long-term space travel.

This paper refers to studying the effect of microgravity on the friction behavior of friction units and to further analyzing the influencing mechanism. The potential factors affecting the friction behavior of the moving joints of space mechanisms in microgravity environment were analyzed. A friction apparatus was designed and manufactured by reducing the complexity and costs. A microgravity test program was designed and performed using the Beijing Drop Tower platform with designing three positioning styles for the friction apparatus by changing the relationship between the normal load and gravity. For each positioning style of the friction apparatus, the friction behavior of friction unit in gravity and microgravity environment was compared. It was found that microgravity can not only change the value of friction, but also affect its dynamic characteristics. For different positioning styles of the friction apparatus, the influencing mechanism of microgravity on friction behavior was different. The normal load or the relative position between the connected bodies of the friction unit could be changed by microgravity, resulting in that the friction behavior was different from that in gravity environment.

The oscillation of liquid/gas free surface in a partially filled storage tank caused by an abrupt drop of gravity level is of critical importance for the fluid management in space. In the present study, the dynamic behavior of free surfaces in a model tank (tube) is numerically investigated using volume of fluid (VOF) method in the context of dynamic contact angle (DCA) model. It is concluded that the dynamic behavior of free surface could be captured pretty well using the selected DCA model, as shown by comparison with the results of Drop Tower Beijing experiment. The temporal evolution of free surface reproduces exactly the characteristics of damping oscillations. The detailed dynamic deflections of meniscus reveal crucial dependency between the oscillation frequency of free surface and the boundary condition in the contact line. The oscillation frequency increases when the range of the moving contact line transfers from the spherical-shaped part to the cylindrical part of the tank and maintains constant when the moving contact line remains always at the cylindrical part of the tank. Meanwhile, the oscillation amplitude decreases in line with the increase of oscillation frequency.