We have demonstrated the synthesis of γ-Fe2O3 nano-particles through a facile and novel calcination process in the air. There is no pH regulation, gas atmosphere, additive, centrifugation or other complicated procedures during the preparing process. A detailed formation process of the nano-particles is proposed, and DMF as a polar solvent may slower the reaction process of calcination. The structures, morphologies, and magnetic properties of γ-Fe2O3 nano-particles were investigated systematically, and the pure γ-Fe2O3 nano-particles obtained at 200 °C display uniform morphology good magnetic property. The saturation magnetization of obtained pure γ-Fe2O3 is about 74 emu/g, which is comparable with bulk material (76 emu/g) and larger than other results. In addition, the photocatalytic activity for degradation of methylene blue is also studied, which shows proper photocatalytic activity.

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Through flow field simplification, a set of differential equations governing the fluid flow and fluid–membrane coupling are obtained for a valveless micropump. The dimensional analysis on the equations reveals that the ratio of the inertial force of the fluid to the viscous loss is dependent on the size ratios among internal elements of the pump. For a micropump working at high frequencies, these two forces possess the same order of magnitude, and this phenomenon is independent of the excitation frequency and fluid type. For the liquid medium, the inertial force of the fluid is around O(102)–O(103) times as that of the plate membrane, and is also larger than the elastically deformed force of the plate when the excitation frequency is close to the plate fundamental frequency. For the case where there is no pressure difference between the inlet and the outlet, an approximate analytical solution is derived for the micropump under the action of an external sinusoidal excitation force. It shows that a phase shift lagging the excitation force exists in the vibration response. For certain combinations of micropump size and fluid–solid density ratios, the phase shift can come to 90° at a specific excitation frequency ω* due to the action of fluid inertia. Away from ω*, the phase shift becomes smaller. The amplitude response of coupling vibration changes nonlinearly with the excitation frequency and reaches maximum at another frequency ω** ≠ ω*. Due to the nonlinearity of viscous loss, resonance does not seem to occur at any frequency. To obtain a larger average flux, the two loss coefficients of the nozzle should be minimized while their difference should be maximized. Under the action of the fluid inertia, there exists an optimal working frequency (equal to ω*) at which the average flux is maximum. This optimal frequency is dependent on the size of the micropump, the material properties of the plate, the fluid properties and has no relation with the excitation force. For the case where a pressure difference between the inlet and the outlet exists, a constraint condition between the excitation force and the pressure difference is obtained.

A qualitative analysis is first carried out to determine the slip coefficient as a function of two dimensionless parameters. An intensive computation using the direct simulation Monte Carlo method is then carried out to simulate the Couette flows between two walls for different gas, number density, wall (plate) velocity (U w ), wall temperature (T w ) and distance between the two walls. Numerical results show that the slip coefficient is proportional to the mean free path λ gw of molecules colliding with the wall, which is affected by the number density, the wall temperature and gas mass. The slip coefficient is finally found to be 1.125 λ gw . This slip coefficient is verified for five gases, and validated under the conditions of U w 300 m s −1 and T w 500 K. This slip coefficient is very useful for slip flow analysis in micro-electro-mechanical systems using N-S equations.

Width-controlled M-type hexagonal SrFe12O19 nanoribbons were synthesized for the first time via polyvinylpyrrolidone (PVP) sol assisted electrospinning followed by heat treatment in air, and their chemical composition, microstructure and magnetic performance were investigated. Results demonstrated that as-obtained SrFe12O19 nanoribbons were well-crystallized with high purity. Each nanoribbon was self-assembled by abundant single-domain SrFe12O19 nanoparticles and was consecutive on structure and uniform on width. PVP in the spinning solution played a significant influence on the microstructure features of SrFe12O19 nanoribbons. With PVP concentration increasing, the ribbon-width was increased but the particle-size was reduced, which distributed on a same ribbon were more intensive, and then the ribbon-surface became flat. The room temperature magnetic performance investigation revealed that considerable large saturation magnetization (Ms) and coercivity (Hc) were obtained for all SrFe12O19 nanoribbons, and they increased with the ribbon-width broadening. The highest Ms of 67.9 emu·g−1 and Hc of 7.31 kOe were concurrently acquired for SrFe12O19 nanoribbons with the maximum ribbon-width. Finally, the Stoner-Wohlfarth curling model was suggested to dominate the magnetization reverse of SrFe12O19 nanoribbons. It is deeply expected that this work is capable of opening up a new insights into the architectural design of 1D magnetic materials and their further utilization.

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An analytical solution of the velocity field in a microbearing of finite length is derived based on a slip-flow model. Flow characteristics, such as velocity and friction torque for different slip coefficients are investigated in detail. The results show that the flow and load characteristics inside the microbearing depend on not only the magnitude of the slip coefficient but also the boundary conditions at both ends of the microbearing. It is found that when the slip coefficient decreases from 0.4 to 0.01, the friction torque exerted on the rotating shaft increases, and the effect of bearing ends becomes larger and larger. At = 0.01, the torque near the ends of the bearing rises to four times that in the middle of the rotating shaft. As the slip coefficient continues to decrease from 0.01, the friction torque in the middle of the shaft remains unchanged, while the distribution characteristic of the torque near the shaft ends approaches that in a macrobearing.

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