Topological Transitions in Metamaterials Krishnamoorthy, Harish N. S.; Jacob, Zubin; Narimanov, Evgenii ...
Science (American Association for the Advancement of Science),
04/2012, Letnik:
336, Številka:
6078
Journal Article
Recenzirano
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Light-matter interactions can be controlled by manipulating the photonic environment. We uncovered an optical topological transition in strongly anisotropic metamaterials that results in a dramatic ...increase in the photon density of states—an effect that can be used to engineer this interaction. We describe a transition in the topology of the iso-frequency surface from a closed ellipsoid to an open hyperboloid by use of artificially nanostructured metamaterials. We show that this topological transition manifests itself in increased rates of spontaneous emission of emitters positioned near the metamaterial. Altering the topology of the iso-frequency surface by using metamaterials provides a fundamentally new route to manipulating light-matter interactions.
Queens Dube, Oeindrila; Harish, S. P.
The Journal of political economy,
07/2020, Letnik:
128, Številka:
7
Journal Article
Recenzirano
Do states experience more peace under female leadership? We examine this question in the context of Europe over the fifteenth to twentieth centuries. We use gender of the firstborn and presence of a ...sister among previous monarchs as instruments for queenly rule. We find that polities led by queens engaged in war more than polities led by kings. While single queens were more likely to be attacked than single kings, married queens were more likely to attack than married kings. These results suggest asymmetries in the division of labor: married queens were more inclined to enlist their spouses in helping them rule, which enabled them ultimately to pursue more aggressive war policies.
Exploring highly efficient visible-light-driven photocatalyst for the elimination organic pollutants is a great concern for constructing sustainable green energy systems. In the current work, a novel ...hybrid ternary WO3@g-C3N4@MWCNT nanocomposites have been fabricated for visible-light-driven photocatalyst by self-assembly method. The as-prepared photocatalyst was examined by XRD, Raman, FESEM, HRTEM, XPS EDS, EIS, UV–visible DRS, and PL analysis. The experimental results revealed that the photocatalytic activity of WO3@g-C3N4@MWCNT nanocomposites on the degradation of Tetracycline (TC) is 79.54% at 120 min, which is higher than the binary WO3@g-C3N4 composite and pristine WO3. The improved degradation performance towards TC is recognized for its higher surface area, intense light absorption towards the visible region, and enhanced charge separation efficiency. Consequently, the fabricated catalyst endows a promising application for antibiotic degradation.
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•We fabricated WO3/g-C3N4/MWCNT hybrid nanostructure by simple low temperature hydrothermal process.•Photocatalytic degradation of TC were observed under visible light.•WO3/g-C3N4/MWCNT sample showed excellent degradation of tetracycline.•WO3/g-C3N4/MWCNT hybrid structure has been probed as a potential applicant for visible light driven photocatalyst.
Numerous inorganic and organic counter electrodes (CEs) have been fabricated for dye-sensitized solar cells (DSSCs) instead of platinum (Pt) CE. However, MoS2 and carbon nanocomposite have played an ...important role in CEs due to their superior electrochemical properties and high chemical stability. N-doped graphene quantum dot (N-GQD) @ MoS2 @ reduced graphene oxide (rGO) nanocomposite was synthesized by the two-step hydrothermal method. The morphology of as-synthesized nanocomposites was studied using field emission scanning electron microscope (FE-SEM) and scanning transmission electron microscopy (STEM). It confirms the formation of sphere-like MoS2 composed of nanosheets on the surface of rGO sheets. The N-GQD@MoS2@rGO composites confirmed the presence of MoS2, rGO, and N-GQD by X-ray diffraction (XRD) and Raman spectra. The chemical composition and purity of N-GQD@MoS2@rGO was examined by the X-ray photoelectron spectroscopy analysis technique. The electrochemical property of the as-fabricated CEs was studied by cyclic voltammetry (CV) analysis by using the iodine-based electrolyte. The N-GQD@MoS2@rGO shows the superior catalytic property due to more electrochemical active site and electrical conductivity property of rGO and MoS2. The DSSCs device assembled with as-fabricated CEs and their photovoltaic power conversion efficiency (η) of MoS2 was 2.01%, MoS2@rGO was 3.92%, N-GQD@MoS2 was 3.53%, N-GQD@MoS2@rGO was 4.65%, and Pt was 5.17%.
schematic diagram of DSSCs fabrication with N-GQD@MoS2@rGO CEs. Display omitted
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Phonon scattering by intrinsic defects and nanostructures has been the primary strategy for minimizing the thermal conductivity in thermoelectric materials. In this work, we present ...the effect of Isovalent substitution as a method to decouple the Seebeck coefficient and the thermal conductivity of antimony (Sb) substituted bismuth selenide (Bi2Se3). Transmission electron microscopy studies present the nanostructured Bi2-xSbxSe3 thermoelectric system represents the coexistence of hierarchical defect structure and dislocations. The observed giant reduction in thermal conductivity is due to the multi-scale phonon scattering caused by a combination of stacking faults, lattice dislocations and grain boundary scattering. This study reveals that a large number of dislocations about ∼1.09 × 1016 m−2 are particularly effective at lowering thermal conductivity. We achieved one of the ultra-low thermal conductivity values (∼0.26 W/m K) for the maximized dislocation concentration. Moreover, Isovalent substitution provides a new avenue for the reduction in thermal conductivity and significant enhancement in the Seebeck coefficient of thermoelectric materials.
•Titanium dioxide (TiO2) nanorods under different pH conditions were synthesized by a hydrothermal method.•XRD results confirm the tetragonal structure of anatase phase TiO2 nanopowders.•The ...degradation of 67% of MO was achieved by the irradiation of UV light for 150 min.
Surfactant free Titanium dioxide (TiO2) nanorods under different pH conditions were synthesized by a hydrothermal method. The structure, morphology and framework substitution of the as – prepared nanorods was characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV–Visible, Fourier Transform Infrared (FTIR) and X-ray Photon Spectroscopy (XPS). XRD analysis confirms the formation of anatase phase of TiO2 with tetragonal structure. FESEM micrograph confirms the formation of nanorods. The calculated band gap values of TiO2 nanorods was found to decrease with increasing pH from the optical absorption spectra. XPS spectra confirm the presence of Ti 2p and O 1s states. The photocatalytic activity of the nanorods against methyl orange (MO) was examined and their results have shown highest degradation (51%) of MO was achieved within 150 min.
•The decoration of CuO on the surface of ZnO were synthesized by hydrothermal growth.•The functional properties of the ZnO/CuO nanostructures were extensively studied.•The formation of ZnO/CuO ...hetero-junction improved the separation of photogenerated electrons and holes which results in enhanced activity.•The enhanced photocatalytic activity is 10 times higher than pure ZnO.
Degradation of organic pollutant using ZnO/CuO composites has become an attractive method for detoxification of water. The effect of copper acetate concentration and the functional properties of nanocomposites were investigated. The morphological analysis revealed that CuO nanoparticles dispersed uniformly on the surface of ZnO nanorods. X-ray photoelectron spectra analysis showed peak shift in the electronic states of Zn and Cu states. Elemental clearly confirms the presence of CuO were uniformly distributed on the surface of ZnO. The photocatalytic activity of ZnO/CuO composites was enhanced compared to pure ZnO under visible light irradiation. The optimal CuO content for the photocatalytic activity of the ZnO/CuO composites is 1%, which is almost ten times higher than that of pure ZnO. Owing to these synergic advantages, the degradation efficiency of ZnO/CuO composites reached 92.52% after 5min of irradiation. The synergistic photocatalytic mechanism was proposed based on the photodegradation results.
CuCo2O4 films with different morphologies of either mesoporous nanosheets, cubic, compact‐granular, or agglomerated embossing structures are fabricated via a hydrothermal growth technique using ...various solvents, and their bifunctional activities, electrochemical energy storage and oxygen evolution reaction (OER) for water splitting catalysis in strong alkaline KOH media, are investigated. It is observed that the solvents play an important role in setting the surface morphology and size of the crystallites by controlling nucleation and growth rate. An optimized mesoporous CuCo2O4 nanosheet electrode shows a high specific capacitance of 1658 F g−1 at 1 A g−1 with excellent restoring capability of ≈99% at 2 A g−1 and superior energy density of 132.64 Wh kg−1 at a power density of 0.72 kW kg−1. The CuCo2O4 electrode also exhibits excellent endurance performance with capacity retention of 90% and coulombic efficiency of ≈99% after 5000 charge/discharge cycles. The best OER activity is obtained from the CuCo2O4 nanosheet sample with the lowest overpotential of ≈290 mV at 20 mA cm−2 and a Tafel slope of 117 mV dec−1. The superior bifunctional electrochemical activity of the mesoporous CuCo2O4 nanosheet is a result of electrochemically favorable 2D morphology, which leads to the formation of a very large electrochemically active surface area.
The direct growth of shape‐controlled CuCo2O4 electrodes on a 3D architecture of Ni foam is achieved via a hydrothermal growth technique using various solvents, followed by air annealing treatment. The high bifunctional electrochemical activity of the mesoporous CuCo2O4 nanosheet is a result of the electrochemically favorable 2D morphology, which leads to the formation of a very large electrochemically active surface area.
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