Through a series of molecular dynamics simulations based on the flexible three-centered water model, this study analyzes the structural changes induced in liquid water by the application of a magnetic field with a strength ranging from 1 to 10 T. It is found that the number of hydrogen bonds increases slightly as the strength of the magnetic field is increased. This implies that the size of a water cluster can be controlled by the application of an external magnetic field. The structure of the water is analyzed by calculating the radial distribution function of the water molecules. The results reveal that the structure of the water is more stable and the ability of the water molecules to form hydrogen bonds is enhanced when a magnetic field is applied. In addition, the behavior of the water molecules changes under the influence of a magnetic field; for example, the self-diffusion coefficient of the water molecules decreases.

A three-dimensional model of molecular dynamics (MD) is proposed to study the effects of tool geometry and processing resistance on the atomic-scale cutting mechanism. The model includes the utilization of the Morse potential function to simulate the interatomic force between the workpiece and a tool. The results show that the cutting resistance increases with the angle of the pin tool and the depth of cut, and the cutting force is essentially constant over the range of velocities simulated. In addition, the obtained cutting resistance of present MD simulation exhibits an evident relationship to the ratio of the vertical and the horizontal contact area between the tool and the workpiece within the range of a pin angle of 90-150 • . Finally, work hardening and stick-slip phenomena during the process are also observed.

This study presents a new suction-type, pneumatically driven microfluidic device for liquid delivery and mixing. The three major components, including two symmetrical, normally closed micro-valves and a sample transport/mixing unit, are integrated in this device. Liquid samples can be transported by the suction-type sample transport/mixing unit, which comprised a circular air chamber and a fluidic reservoir. Experimental results show that volume flow rates ranging from 50 to 300 ll/min can be precisely controlled during the sample transportation processes. Moreover, the transport/mixing unit can also be used as a micro-mixer to generate efficient mixing between two reaction chambers by regulating the time-phased deformation of the polydimethylsiloxane (PDMS) membranes. A mixing efficiency as high as 98.4% can be achieved within 5 s utilizing this prototype pneumatic microfluidic device. Consequently, the development of this new suction-type, pneumatic microfluidic device can be a promising tool for further biological applications and for chemical analysis when integrated into a micro-total analysis system (l-TAS) device.

Molecular dynamics simulations are performed to investigate the structural and dynamic properties of water molecules close to clean gold nanoclusters and four different Monolayer Protected Clusters (MPCs) comprising gold nanoclusters and alkanethiol surfactants with methyl, carboxyl, amine and hydroxyl tail group. The effects of these tail groups on the local structure of water are quantified by the analysis of the reduced density profiles, the average number of hydrogen bonds, and the water orientation distribution. Moreover, the dynamic properties of the water molecules are evaluated by means of diffusion coefficients and residence time. The simulation results indicate that water molecules close to clean gold nanoclusters and nonpolar methyl MPCs form a two-shelled structure in which the molecules in the first shell prefer lying on the surface of the nanocluster or methyl MPCs. The existence of interfacial hydrogen bonds between the water molecules and the tail group of MPCs results in a weakening of the water−water hydrogen bond network. Moreover, the presence of the two water shells constrains the motion of the water molecules close to the clean nanocluster and nonpolar MPC. As a result, the residence time of the water molecules adjacent to the clean nanocluster and nonpolar MPC are significantly longer than those of the molecules close to the three polar MPCs.

New models that describe gas flow behaviour in microtubes are presented. To avoid time-consuming calculations in solving the integral equation which is obtained from the microscopic point of view, the high-order slip-flow boundary condition is utilized to correct the gas flow in such a micron or submicron spacing. The proposed model can be applied to arbitrary Knudsen number conditions under the assumption that the bulk flow velocity is negligible compared with the sonic velocity of the gas. The analytical solution of the pressure distribution for the first-order slip-flow model is obtained. The results show that the first-order slip-flow model is in good agreement with this model. The nonlinear pressure distribution is due to gas compressibility. The dominant mechanism influencing the nonlinear pressure distribution comes from the rarefaction of gas and the inlet pressure. The rarefaction effect increases the pressure drop at the inlet region of the channel and decreases the pressure drop at the exit region of the channel. The decrease of inverse Knudsen number changes the pressure distribution from concave to almost linear and increases the mass flow.

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The machining characteristics of nano-lithography are studied using atomic force microscopy (AFM). Scribing (scratching) experiments containing reciprocal single line furrows and multiple furrows are conducted to investigate the influence of the working parameters on the machined surface's properties, and upon the machining efficiency. The influence of the working parameters, including the applied load on the cantilever, scribing cycles, scribing speed and scribing feed, on the surface roughness, surface depth and material removal rate can then be accessed. Results indicate that the applied load is more significant than the scribing cycles on the groove depth. However, rougher surfaces are produced at larger loads. In multiple furrows produced with larger applied loads in order to obtain deeper furrows, surface roughness is improved by adjusting the scribing feed to a small value.

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