Trail-using ant behavior based energy-efficient routing protocol in wireless sensor networks.

Swarm Intelligence (SI) observes the collective behavior of social insects and other animal societies. Ant Colony Optimization (ACO) algorithm is one of the popular algorithms in SI. In the last decade, several routing protocols based on ACO algorithm have been developed for Wireless Sensor Networks (WSNs). Such routing protocols are very flexible in distributed system but generate a lot of additional traffic and thus increase communication overhead. This paper proposes a new routing protocol reducing the overhead to provide energy efficiency. The proposed protocol adopts not only the foraging behavior of ant colony but also the trail-using behavior which has never been adopted in routing. By employing the behaviors, the protocol establishes and manages the routing trails energy efficiently in the whole network. Simulation results show that the proposed protocol has low communication overhead and reduces up to 55% energy consumption compared to the existing ACO algorithm.N/

Terahertz Pulse Generation from GaAs Metasurfaces

Ultrafast optical excitation of select materials gives rise to the generation of broadband terahertz (THz) pulses. This effect has enabled the field of THz time-domain spectroscopy and led to the discovery of many physical mechanisms behind THz generation. However, only a few materials possess the required properties to generate THz radiation efficiently. Optical metasurfaces can relax stringent material requirements by shifting the focus onto the engineering of local electromagnetic fields to boost THz generation. Here we demonstrate the generation of THz pulses in a 160 nm thick nanostructured GaAs metasurface. Despite the drastically reduced volume, the metasurface emits THz radiation with efficiency comparable to that of a thick GaAs crystal. We reveal that along with classical second-order volume nonlinearity, an additional mechanism contributes strongly to THz generation in the metasurface, which we attribute to surface nonlinearity. Our results lay the foundation for engineering of semiconductor metasurfaces for efficient and versatile THz radiation emitters

Wireless-Powered Chemical Sensor by 2.4 GHz Wi-Fi Energy-Harvesting Metamaterial

Metamaterial Sensors show significant potential for applications ranging from hazardous chemical detection to biochemical analysis with high-quality sensing properties. However, they require additional measurement systems to analyze the resonance spectrum in real time, making it difficult to use them as a compact and portable sensor system. Herein, we present a novel wireless-powered chemical sensing system by using energy-harvesting metamaterials at microwave frequencies. In contrast to previous studies, the proposed metamaterial sensor utilizes its harvested energy as an intuitive sensing indicator without complicated measurement systems. As the spectral energy-harvesting rate of the proposed metamaterial sensor can be varied by changing the chemical components and their mixtures, we can directly distinguish the chemical species by analyzing the resulting output power levels. Moreover, by using a 2.4 GHz Wi-Fi source, we experimentally realize a prototype chemical sensor system that wirelessly harvests the energy varying from 0 mW up to 7 mW depending on the chemical concentration of the water-based binary mixtures

Copper foam-derived electrodes as efficient electrocatalysts for conventional and hybrid water electrolysis

Electrochemical water splitting has been demonstrated as a promising technology for the renewable generation of green hydrogen from water. Despite the extensive progress in materials science, one particular challenge for further development towards industrial application lies in the rational design and exploitation of efficient and cost-effective materials, especially oxygen evolution reaction (OER) electrocatalysts at the anode. In addition, attempts to replace the OER with other more oxidizable anode reactions are being evaluated as a groundbreaking strategy for generating hydrogen at lower potentials and reducing overall energy costs while producing valuable chemicals simultaneously. Compared with Fe/Co/Ni-based compounds, Cu-based materials have not received extensive research attention for electrode designs despite their high conductivity and abundant earth reserves. In this review, combining with the advantages of a three-dimensional network structure of metal foams, we summarize recent progress on Cu foam (CF)-derived materials as efficient electrocatalysts towards pure water electrolysis and hybrid water electrolysis. The advantages of CF and design strategies to enhance the electrocatalytic activity and operational durability are presented first. Catalyst design and fabrication strategies are then highlighted and the structure-activity relationship is also discussed. Finally, we propose challenges and perspectives on self-supported electrodes beyond CF-derived materials

Active spectral filtering through turbid media

We demonstrate controlled wavelength-dependent light focusing through turbid media using wavefront shaping. Due to the dispersion caused by multiple light scattering, light propagation through turbid media can be independently controlled between different wavelengths. Foci with various wavelengths can be generated by applying different optimized wavefronts to a highly scattering layer. Given the linearity of the transmission matrix, multiple foci with different wavelengths can also be simultaneously constructed. (C) 2012 Optical Society of Americclos

Dynamic active wave plate using random nanoparticles

Current non-invasive imaging and manipulation of biological systems heavily rely on using light as the probing tool. However, light propagation through highly turbid media such as biological tissue undergo multiple light scattering which results in significant scrambling of light paths and polarization information. Here we demonstrate the full control of polarization dependent light paths through a highly scattering medium by only shaping the incoming wavefront. The resulting polarized state is independent of the incident beam's polarization and has no spatial restrictions. We also show that a turbid medium can be used as a dynamic wave plate by controlling the phase of combined orthogonal polarization states. This approach may find direct applications in efficient energy transfer for photothermal therapy and the transfer of angular momentum in optical manipulation of biological systems. (C) 2012 Optical Society of Americclos