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Many of the compounds in drugs cannot be effectively delivered using current drug delivery techniques (e.g., pills and injections). Transdermal delivery is an attractive alternative, but it is limited by the extremely low permeability of the skin. As the primary barrier to transport is located in the upper tissue, MicroElectro-Mechanical-System (MEMS) technology provides novel means, such as microneedle array and PZT pump, in order to increase permeability of human skin with efficiency, safety and painless delivery, and to decrease the size of the pump. Microneedle array has many advantages, including minimal trauma at penetration site because of the small size of the needle, free from condition limitations, painless drug delivery, and precise control of penetration depth. These will promote the development of biomedical sciences and technology and make medical devices more humanized. So far, most of the insulin pumps being used are mechanical pumps. We present the first development of this novel technology, which can assemble the PZT pump and the microneedle array together for diabetes mellitus. The microneedle array based on a flexible substrate can be mounted on non-planar surface or even on flexible objects such as a human fingers and arms. The PZT pump can pump the much more precision drug accurately than mechanical pump and the overall size is much smaller than those mechanical pumps. The hollow wall straight microneedle array is fabricated on a flexible silicon substrate by inductively coupled plasma (ICP) and anisotropic wet etching techniques. The fabricated hollow microneedles are 200 lm in length and 30 lm in diameter. The microneedle array, which is built with onboard fluid pumps, has potential applications in the chemical and biomedical fields for localized chemical analysis, programmable drug-delivery systems, and very small, precise fluids sampling. The microneedle array has been installed in an insulin pump for demonstration and a leak free packaging is introduced.

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The solar wind is a magnetized and turbulent plasma. Its turbulence is often dominated by Alfvénic fluctuations and often deemed as nearly incompressible far away from the Sun, as shown by in situ measurements near 1 au. However, for solar wind closer to the Sun, the plasma β decreases (often lower than unity) while the turbulent Mach number M t increases (can approach unity, e.g., transonic fluctuations). These conditions could produce significantly more compressible effects, characterized by enhanced density fluctuations, as seen by several space missions. In this paper, a series of 3D MHD simulations of turbulence are carried out to understand the properties of compressible turbulence, particularly the generation of density fluctuations. We find that, over a broad range of parameter space in plasma β, cross helicity, and polytropic index, the turbulent density fluctuations scale linearly as a function of M t , with the scaling coefficients showing weak dependence on parameters. Furthermore, through detailed spatiotemporal analysis, we show that the density fluctuations are dominated by low-frequency nonlinear structures, rather than compressible MHD eigenwaves. These results could be important for understanding how compressible turbulence contributes to solar wind heating near the Sun.

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Thermocompression bonding of carbon nanotubes (CNTs) to metallic substrates is studied using molecular dynamics. The interaction of the CNT and the metal cluster at high temperature is investigated first. For the diffusion bonding process, the effects of temperature and external pressure are examined. In addition, we apply the tensile loading to examine the mechanical properties and the failure modes during the debonding process. The results show that formation of coalescence structure between the CNT and the metal cluster provides a nanoscale metal surface to facilitate diffusion bonding. Both high temperature and high pressure will enhance the bonding. In addition, the debonding position of the samples under the tensile loading depends on the competition of CNT-metal and metal-metal interface strength. For samples bonded under high temperature and high pressure, the debonding first occurs at the CNT-metal interface. While for samples bonded under low temperature and low pressure, the interdiffusion is not sufficient and therefore the debonding occurs at metal-metal interface. These behaviors indicate that, to obtain larger bonding strength, it is necessary to select the metal with excellent adhesion property to the CNT surface as the medium layer and guarantee full interface contact between the metal cluster and the metallic substrate during the diffusion bonding.