Surface effects often play a significant role in the physical properties of micro- and nanosized materials and structures. In this letter, the authors presented a theoretical model directed towards investigation of the effects of both surface elasticity and residual surface tension on the natural frequency of microbeams. A thin surface layer was introduced on the upper and lower surfaces to rationalize the near-surface material properties that are different from the bulk material. An explicit solution is derived for the natural frequency of microbeams with surface effects. This study might be helpful for the design of microbeam-based sensors and some related measurement techniques.

Based on the conventional Euler buckling model, uniaxial compression tests have been utilized recently to measure the mechanical properties of nanowires. However, owing to the increasing ratio of surface area to bulk at nanoscale, the influence of surface energy becomes prominent and should be taken into consideration. In this letter, an analytical relation is given for the critical force of axial buckling of a nanowire by accounting for both the effects of surface elasticity and residual surface tension. This study might be helpful to characterize the mechanical properties of nanowires or design nanobeam-based devices in a wide range of applications.

Surface microstructures of solids play a significant role in producing superhydrophobic surfaces. In the present paper, the Cassie-Baxter and Wenzel models on a rough substrate are examined from the viewpoints of geometry and energy. The result shows that if the air beneath a droplet on a sinusoidal substrate is open to the atmosphere, the superhydrophobic state can exist only when the substrate is hydrophobic, and that the geometric parameters of the microstructure have a great influence on the wetting behavior. Two mechanisms that may lead to a superhydrophobic property from a hydrophilic substrate are addressed. Firstly, for closed or airproof microstructures (e.g. honeycomb structures), a negative Laplace pressure difference caused by the trapped air under the drop can keep the balance of the liquid/vapor interface. Secondly, some special topologies of surface structures satisfying a certain geometric condition may also lead to the formation of a Cassie-Baxter state even if the microstructures are open to the air. Therefore, some surface morphologies may be designed to obtain superhydrophobic properties on hydrophilic surfaces. The present study is also helpful to understand some superhydrophobic phenomena observed in experiments and in nature.

Plasma membrane NADPH oxidases (Noxs) are key producers of reactive oxygen species under both normal and stress conditions in plants. We demonstrate that at least eleven genes in the genome of rice (Oryza sativa L.) were predicted to encode Nox proteins, including nine genes (OsNox1–9) that encode typical Noxs and two that encode ancient Nox forms (ferric reduction oxidase 1 and 7, OsFRO1 and OsFRO7). Phylogenetic analysis divided the Noxs from nine plant species into six subfamilies, with rice Nox genes distributed among subfamilies I to V. Gene expression analysis using semi-quantitative RT-PCR and real-time qRT-PCR indicated that the expression of rice Nox genes depends on organs and environmental conditions. Exogenous calcium strongly stimulated the expression of OsNox3, OsNox5, OsNox7, and OsNox8, but depressed the expression of OsFRO1. Drought stress substantially upregulated the expression of OsNox1–3, OsNox5, OsNox9, and OsFRO1, but downregulated OsNox6. High temperature upregulated OsNox5–9, but significantly downregulated OsNox1–3 and OsFRO1. NaCl treatment increased the expression of OsNox2, OsNox8, OsFRO1, and OsFRO7, but decreased that of OsNox1, OsNox3, OsNox5, and OsNox6. These results suggest that the expression profiles of rice Nox genes have unique stress-response characteristics, reflecting their related but distinct functions in response to different environmental stresses.

Owing to the superhydrophobicity of their legs, such creatures as water striders and fisher spiders can stand effortlessly, walk and jump quickly on water. Directed toward understanding their superior repellency ability, we consider hydrophobic thin rods of several representative cross sections pressing a water surface. First, the shape function of the meniscus surrounding a circular rod is solved analytically, and thereby the maximal buoyant force is derived as a function of the Young's contact angle and the rod radius. Then we discuss the critical conditions for a rod to sink into water, including the maximal volume condition and the meniscus-contact condition. Furthermore, we study the sinking conditions and the maximal buoyant forces of hydrophobic long rods with elliptical, triangular, or hexagonal cross-section shapes. The theoretical solutions are quantitatively consistent with existing experimental and numerical results. Finally, the optimized structures of water strider legs are analyzed to elucidate why they can achieve a very big buoyant force on water.