The application of three-dimensional (3D) plasmonic nanostructures as metamaterials (MMs), nano-antennas, and other devices faces challenges in producing metallic nanostructures with easily definable orientations, sophisticated shapes, and smooth surfaces that are operational in the optical regime and beyond. Here, we demonstrate that complex 3D nanostructures can be readily achieved with focused-ion-beam irradiation-induced folding and examine the optical characteristics of plasmonic ''nanograter'' structures that are composed of free-standing Au films. These 3D nanostructures exhibit interesting 3D hybridization in current flows and exhibit unusual and well-scalable Fano resonances at wavelengths ranging from 1.6 to 6.4 mm. Upon the introduction of liquids of various refractive indices to the structures, a strong dependence of the Fano resonance is observed, with spectral sensitivities of 1400 nm and 2040 nm per refractive index unit under figures of merit of 35.0 and 12.5, respectively, for low-order and high-order resonance in the near-infrared region. This work indicates the exciting, increasing relevance of similarly constructed 3D free-standing nanostructures in the research and development of photonics and MMs.

Abstract. The Inner Mongolia grassland, one of the most important grazing regions in China, has long been threatened by land degradation and desertification, mainly due to overgrazing. To understand vegetation responses over the last decade, this study evaluated trends in vegetation cover and phenology dynamics in the Inner Mongolia grassland by applying a normalized difference vegetation index (NDVI) time series obtained by the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) during 2002-2014. The results showed that the cumulative annual NDVI increased to over 77.10 % in the permanent grassland region (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014). The mean value of the total change showed that the start of season (SOS) date and the peak vegetation productivity date of the season (POS) had advanced by 5.79 and 2.43 days, respectively. The end of season (EOS) was delayed by 5.07 days. These changes lengthened the season by 10.86 days. Our results also confirmed that grassland changes are closely related to spring precipitation and increasing temperature at the early growing period because of global warming. Overall, productivity in the Inner Mongolia Autonomous Region tends to increase, but in some grassland areas with grazing, land degradation is ongoing.

We propose an ultra-thin planar metasurface with phase discontinuities for highly efficient beam steering. The effect benefits from the broadband transparency and flexible phase modulation of stacked metal/dielectric multi-layers that is perforated with coaxial annular apertures. Proof-of-principle experiments verify that an efficiency of 65% and a deflection angle of 18° at 10 GHz are achieved for the transmitted beam, which are also in good agreement with the finite-difference-method-in-time-domain (FDTD) simulations. The scheme shall be general for the design of beam-steering transmitters in all frequencies.

Metasurfaces have shown great potential to reshape the wavefront of electromagnetic (EM) waves, but transmissive meta-devices face challenges of low-efficiency and/or fabrication complexities. Here, an alternative approach to realize high-efficiency transmission-mode meta-devices to control EM wavefronts, based on hyperbolic metamaterial (HMM) waveguides supporting tailored spoof surface plasmons (SSPs) on their side walls, is proposed. By manipulating the dispersions of SSPs through adjusting the HMM geometrical parameters, the phases of EM waves passing through such waveguides, which enables the design of meta-devices with desired transmission-phase profiles for particular wave-manipulation applications, can be controlled. Microwave experiments are implemented to demonstrate two wave-control effects based on the mechanism, that is, beam-deflection and focusing, and a maximum conversion efficiency of 42.9% is achieved for the anomalous refracted beam. By scaling down the HMM meta-devices, the proposal herein is applicable to optical frequencies and in principle promises significantly raised conversion efficiencies. The scheme herein can offer a higher effective refractive index and more tunable dispersion without using high-index dielectric materials, and thus can serve as an effective and robust approach to make high-efficiency transmissive meta-devices with diversified functionalities.approach to the extreme control of EM waves, leading to a variety of intriguing phenomena and applications that are unattainable with natural materials such as negative refraction, [4] super-resolution imaging, [5] and invisibility cloaking. [6] As the 2D equivalent of metamaterials, metasurfaces have shown great promises to control EM waves by locally modulating the phase, amplitude and/or polarization of the scattered field. [7][8][9][10][11][12][13] Distinct from traditional photonic devices (e.g., lenses) that rely on propagation phases accumulated inside the device to shape the wavefront, metasurfaces utilize the interfacial phase discontinuities introduced by subwavelength-sized planar resonators to locally control the amplitude and phase of scattered waves and thus to reshape the wavefront of EM waves. Many fascinating wave-manipulation effects were discovered based on metasurfaces, such as light bending, [7,11,13] unidirectional surface plasmon coupling, [8,14] invisibility cloaks, [6,15] flat lenses, [9,16] holography, [17,18] and generation of vortex beam. [7,19] Transmissive metasurfaces are particularly useful in practice, but the working efficiencies of single-layer plasmonic metasurfaces are typically low. For example, a single-layer Pancharatnam-Berry (PB) metasurface, working for circularly polarized (CP) light, cannot exhibit an efficiency higher than 25%, due to

Abstract:Concentrations of chlorophyll-a (Chl-a) and total suspended solids (TSS) are significant parameters used to assess water quality. The objective of this study is to establish a quantitative model for estimating the Chl-a and the TSS concentrations in irrigation ponds in Higashihiroshima, Japan, using field hyperspectral measurements and statistical analysis. Field experiments were conducted in six ponds and spectral readings for Chl-a and TSS were obtained from six field observations in 2014. For statistical approaches, we used two spectral indices, the ratio spectral index (RSI) and the normalized difference spectral index (NDSI), and a partial least squares (PLS) regression. The predictive abilities were compared using the coefficient of determination (R 2 ), the root mean squared error of cross validation (RMSECV) and the residual predictive deviation (RPD). Overall, iterative stepwise elimination based on PLS (ISE-PLS), using the first derivative reflectance (FDR), showed the best predictive accuracy, for both Chl-a (R 2 = 0.98, RMSECV = 6.15, RPD = 7.44) and TSS (R 2 = 0.97, RMSECV = 1.91, RPD = 6.64). The important wavebands for estimating Chl-a (16.97% of all wavebands) and TSS (8.38% of all wavebands) were selected by ISE-PLS from all 501 wavebands over the 400-900 nm range. These findings suggest that ISE-PLS based on field hyperspectral measurements can be used to estimate water Chl-a and TSS concentrations in irrigation ponds.

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Many infrastructure-free indoor positioning systems rely on fine-grained location-dependent fingerprints to train models for localization. The site survey process to collect fingerprints is laborious and is considered one of the major obstacles to deploying such systems. In this paper, we propose TuRF, a fast path-based fingerprint collection mechanism for site survey. We demonstrate the feasibility to collect fingerprints for indoor localization during walking along predefined paths. A step counter is utilized to accommodate the variations in walking speed. Approximate location labels inferred from the steps are then used to train a Gaussian Process regression model. Extensive experiments show that TuRF can significantly reduce the required time for site survey, without compromising the localization performance.