The field lines of Poynting vector around a small particle are investigated on the basis of classical Mie theory. A particle can effectively absorb incident energy near the optical resonance, where its optical absorption cross-section becomes much greater than its geometrical cross-section. It is shown that absorbed energy flows into the particle through some limited portion of its surface ("input window") instead of the whole surface as it follows from the dipole approximation. This "input window" expands with the increasing value of the imaginary part Љ of the dielectric function of the particle. For a small Љ the absorbed energy is released by the plasmon radiation. Interference of this radiation with the incident wave creates complex patterns of energy flux in the near-field region. These patterns cannot be understood within the frame of a dipole approximation and the terms of higher orders with respect to size parameter q =2a / (a is the radius of the particle and is radiation wavelength) should be taken into account.

We demonstrate micromachined reconfigurable metamaterials working at multiple frequencies simultaneously in the terahertz range. The proposed metamaterial structures can be structurally reconfigured by employing flexible microelectromechanical system-based cantilevers in the resonators, which are designed to deform out of plane under an external stimulus. The proposed metamaterial structures provide not only multiband resonance frequency operation but also polarization-dependent tunability. Three kinds of metamaterials are investigated as electric split-ring resonator (eSRR) arrays with different positions of the split. By moving the position of the split away from the resonator's center, the eSRR exhibits anisotropy, with the dipole resonance splitting into two resonances. The dipole-dipole coupling strength can be continuously adjusted, which enables the electromagnetic response to be tailored by adjusting the direct current (DC) voltage between the released cantilevers and the silicon substrate. The observed tunability of the eSRRs is found to be dependent on the polarization of the incident terahertz wave. This polarization-dependent tunability is demonstrated by both experimental measurements and electromagnetic simulations. Keywords: MEMS; reconfigurable metamaterials; split-ring resonator; terahertz; tunability INTRODUCTION Electromagnetic waves in the terahertz (THz) frequency range have received tremendous attention due to their various advantages. Much research has been carried out to characterize the interactions of these waves with matter, for which potential applications include medical imaging, security screening and non-destructive evaluation. However, there are still several restrictions that limit the full exploitation of fruitful applications covering the THz region due to the lack of an appropriate response at these frequencies for many naturally existing materials. [1][2][3][4] As artificially structured electromagnetic materials, metamaterials have been extensively investigated for the possibility of creating novel electromagnetic properties that are not available in natural materials, such as a negative refractive index, superlensing and cloaking.1-4 The electric permittivity and magnetic permeability of metamaterials can be designed for desired specifications and can be scaled to operate over nearly the entire electromagnetic spectrum. These artificial materials could find potential applications in the development of novel THz devices, which is traditionally difficult to achieve due to the absence of suitable functional sources and detectors. [5][6][7][8][9] Due to the limitations of fabrication and characterization technology, 10-12 investigations of metamaterial-based devices were initially implemented in the microwave frequency range. Metamaterials that operate in the THz range have attracted intense interest along with the advancement of fabrication technologies. 7,[13][14][15] Inspired by the realization of tunability, the research on metamaterials has been extended from the structura...

Reserve lipids of microalgae are promising for biodiesel production. However, optimization of cultivation conditions for both biomass yield and lipid production of microalgae is a contradictory problem because required conditions for both targets are different. In this study, a twostage cultivation strategy is proposed to enhance lipid production of the microalga Nannochloropsis oculata. Biomass growth and lipid production were carried out in two separate and non-interacting stages. In first-stage cultivation, microalgae were cultivated in optimal conditions for cell growth. Then, microalgae were harvested and transferred into a growth-limited environment, thus enhancing lipid production of microalgae. Here, optimization of the lipid production stage (second stage) with respect to different levels of inoculum concentration, salinity of culture broth, and intensity of irradiance was performed. The results show that irradiance exhibits a significant influence on lipid production. The highest lipid productivity of 0.324 g L −1 day −1 was obtained with an inoculum concentration of 2.3 g L −1 , a salinity of 35 g L −1 , and an irradiance of 500 μmol photons m −2 s −1 . The final yield of lipid obtained from the two-stage process was 2.82-times higher than that from traditional single-stage batch cultivation systems.

SnO 2 hollow nanospheres were synthesized from glucose and SnCl 2 solution under hydrothermal environment and calcinations. The carbon layer was then deposited as a buffer layer via hydrothermally treated glucose solution. The thickness of the SnO 2 shell in the hollow structures could be adjusted by changing the concentration of the SnCl 2 coating solution. The crystalline structure and morphological observation of the as-synthesized hollow structures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thickness of SnO 2 under 0.1 and 1 M SnCl 2 coating solution was 15 and 60 nm, respectively. It was demonstrated that the electrochemical performance was significantly improved by the hollow structure and strongly affected by the shell thickness of SnO 2 . The hollow structure with 15 nm in SnO 2 thickness exhibited an outstanding reversible capacity of 500 mA hg -1 at 5 C. The extraordinary performance should be associated with the ultrathin SnO 2 shell and the carbon layer, which could accommodate the volume changes and prevent the agglomeration of Sn particles during cycling.