Surface tension gradients may induce the motions of a floating solid fragment. This mechanism has been employed to drive miniaturized objects on a water surface, which could potentially serve as rotators, mixers, locomotives, and so on. To properly apply these objects, it is important to understand their motions. The previous consideration mainly focused on the horizontal motions of these small objects. In this work, we considered translational and rotational motions of a mm-scaled SU-8 boat in the vertical plane, which were so-called squat and trim phenomena, respectively, in the case of a macroboat. Through two types of tests, we demonstrated that dramatic squat and trim phenomena observed in the motions of the SU-8 boat were mainly induced by the surface tension difference between water and isopropyl alcohol (boat propellant), instead of horizontal movements of the miniaturized boat. This difference created a hollow spot behind the stern and made the boat sink and tilt along the sidewall of the hollow spot. In addition, we found that the motion of a SU-8 boat in a channel included two stages. In the first stage, it was propelled due to the difference between foreand-aft surface tensions. In addition to moving forward, it also had dramatic squat and trim movements. However, in the second stage, in which no more isopropyl alcohol exited the boat, it was driven by a water wave generated in the first stage and did not show any visible squat and trim phenomena. The results of this work provided a better understanding of motions of the SU-8 boats. These results might also apply to surface tension-driven motions of other miniaturized objects.

In recent years, high energy consumption has gradually become a prominent problem in a data center. With the advent of cloud computing, computing and storage resources are bringing greater challenges to energy consumption. Virtual machine (VM) initial placement plays an important role in affecting the size of energy consumption. In this paper, we use binary particle swarm optimization (BPSO) algorithm to design a VM placement strategy for low energy consumption measured by proposed energy efficiency fitness, and this strategy needs multiple iterations and updates for VM placement. Finally, the strategy proposed in this paper is compared with other four strategies through simulation experiments. The results show that our strategy for VM placement has better performance in reducing energy consumption than the other four strategies, and it can use less active hosts than others.

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The copper foil is taped to the side wall of a petri dish. Then warm LB agar liquid (10 g agar powder in 1 L medium, autoclaved) is poured into the dish and let consolidate to form agar plate. 50 µL of 1 × 10 6 CFU mL −1 S. aureus is added at the center of the agar plate and spread into a rectangular area with a cell spreader. The dish is moved under the plasma plume in a letter-writing route. Then the plates are incubated at 37 °C for 18 h after plasma treatment.