Experimental demonstration of subwavelength focusing of electromagnetic waves by labyrinth-based two-dimensional metamaterials

We studied focusing in a two-dimensional metamaterial that was based on a labyrinth structure. We theoretically showed that the labyrinth-based metamaterial exhibits negative indices of refraction between 6 and 6.4 GHz. We experimentally studied the focusing effect by measuring electric field intensities on the output side of the metamaterial when the source was placed in front of the input side of the metamaterial. Our experimental results showed that it is in fact possible to focus the source field with half-widths as small as wavelength/4 by using the labyrinth-based metamaterial.     

Experimental analysis of true left-handed behaviour and transmission properties of composite metamaterials

We report the true left-handed transmission of a composite metamaterial (CMM) consisting of periodically stacked split-ring resonator (SRR) and wire elements. The negative permeability (μ < 0) gap is demonstrated explicitly by comparing SRR and closed-ring resonator structures. We confirm experimentally that the plasma cut-off frequency of the CMM is determined by the combined dielectric response of SRR and wire elements, and it is much lower than that of the wire-only medium. This is crucial to identify the left-handed transmission bands of the CMM. We further investigate the effect of intralayer and interlayer disorder on the transmission spectrum of CMM arising from misaligned fabrication and stacking of the SRR layers. We found that the intralayer disorder affects the μ < 0 gap of SRRs and the left-handed transmission band of CMM significantly, whereas the SRR transmission is rather immune to interlayer disorder.     

Effect of Catalytically Active Zinc Oxide−Carbon Nanotube Composite on Sensitive Assay of Desloratadine Metabolite

Desloratadine is one of the most effective second‐generation antihistamines and the electrochemical behavior of the active agent of desloratadine was investigated with a new nanosensor designed with the addition of zinc oxide and multiwalled carbon nanotube (ZnO : MWCNT) mixture on glassy carbon (GCE). By investigating and using cyclic, differential pulse and square wave voltammetry techniques with ZnO : MWCNT/GCE, it is planned to obtain information about quantification and mechanism of desloratadine. The efficiency of experimental parameters such as pH, scan rate, accumulation potential and time on the anodic response of desloratadine were studied. Differential pulse voltammetry was selected as assay method and under developed method and optimized conditions, the current showed linear dependence with concentration in the range between 2×10^?8 and 8×10^?6 M in pH 5.5 acetate buffer. The achieved limits of detection (LOD) and quantification (LOQ) are 0.769 nM and 2.56 nM respectively. Applicability of the methods was demonstrated by their implementation in pharmaceutical dosage forms of desloratadine and the accuracy, precision, selectivity, sensitivity, intra‐day and day‐to‐day reproducibility of the methods were clearly explored. Finally, this sensor was successfully applied on real sample as a selective, simple, reproducible, repeatable an electrochemical sensor.     

A Robust,Precious-Metal-Free Dye-Sensitized Photoanode for Water Oxidation: A Nanosecond-Long Excited-State Lifetime through a Prussian Blue Analogue

Herein, we establish a simple synthetic strategy affording a heterogeneous, precious metal-free, dye-sensitized photoelectrode for water oxidation, which incorporates a Prussian blue (PB) structure for the sensitization of TiO₂ and water oxidation catalysis. Our approach involves the use of a Fe(CN)₅ bridging group not only as a cyanide precursor for the formation of a PB-type structure but also as an electron shuttle between an organic chromophore and the catalytic center. The resulting hetero-functional PB-modified TiO₂ electrode demonstrates a low-cost and easy-to-construct photoanode, which exhibits favorable electron transfers with a remarkable excited state lifetime on the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Our approach paves the way for a new family of precious metal-free robust dye-sensitized photoelectrodes for water oxidation, in which a variety of common organic chromophores can be employed in conjunction with CoFe PB structures.     

Assessing the Influence of Electrode Polarity on the Treatment of Poultry Slaughterhouse Wastewater

Electrochemical methods have been increasingly gaining popularity in the field of wastewater treatment. However, the performance of these methods can be highly affected by the polarity direction as determined by the electrodes arrangement (anode to cathode or cathode to anode); as well as the characteristics of the wastewater to be treated as determined by the type of wastewater. The presented research work investigated the relationship between polarity direction and the removal of pollutants from poultry slaughterhouse wastewater using titanium and aluminium electrode materials. In the first case, the wastewater was exposed to the Ti (anode)-Al (cathode) combination, whereas in the second case the wastewater was subjected to the Al (anode)-Ti (cathode) arrangement. The two cases were designed to see if the polarity direction of the chosen electrode materials affected the removal of pollutants. The removal efficiencies were computed as a ratio of the remaining concentration in the treated effluent to the concentration before treatment. It was observed that the production processes generate highly fluctuating wastewater in terms of pollution loading; for instance, 422 to 5340 Pt-Co (minimum to maximum) were recorded from color, 126 to 2264 mg/L were recorded from total dissolved solids, and 358 to 5998 mg/L from chemical oxygen demand. Also, the research results after 40 min of retention time showed that both electrode arrangements achieved relatively high removal efficiencies; Whereby, the aluminium to titanium polarity achieved up to 100% removal efficiency from turbidity while the titanium to aluminium polarity achieved a maximum of 99.95% removal efficiency from turbidty. Also, a similar phenomenon was observed from total dissolved solids; whereby, on average 0 mg/L was achieved when the wastewater was purified using the aluminium to titanium arrangement, while on average 2 mg/L was achieved from the titanium to aluminium arrangement. A little higher removal efficiency discrepancy was observed from ammonia; whereby, the aluminium to titanium arrangement outperformed the titanium to aluminium arrangement with average removal efficiencies of 82.27% and 64.11%, respectively.     

On the well-posedness of periodic problems for the system of hyperbolic equations with finite time delay

A periodic problem for the system of hyperbolic equations with finite time delay is investigated. The investigated problem is reduced to an equivalent problem, consisting the family of periodic problems for a system of ordinary differential equations with finite delay and integral equations using the method of a new functions introduction. Relationship of periodic problem for the system of hyperbolic equations with finite time delay and the family of periodic problems for the system of ordinary differential equations with finite delay is established. Algorithms for finding approximate solutions of the equivalent problem are constructed, and their convergence is proved. Criteria of well-posedness of periodic problem for the system of hyperbolic equations with finite time delay are obtained.     

InGaN green light emitting diodes with deposited nanoparticles

We grew an InGaN/GaN-based light-emitting diode (LED) wafer by metal–organic chemical vapor deposition (MOCVD), fabricated devices by optical lithography, and successfully deposited ellipsoidal Ag nano-particles by way of e-beam lithography on top. The diodes exhibited good device performance, in which we expected an enhancement of the radiated intensity by the simulations and emission measurements. The obtained results showed the feasibility of plasmon-assisted LED emission enhancement.     

Propagation of light through localized coupled-cavity modes in one-dimensional photonic band-gap structures

We report on the observation of a new type of propagation mechanism through evanescent coupled optical cavity modes in one-dimensional photonic crystals. The crystal is fabricated from alternating silicon-oxide/silicon-nitride pairs with silicon-oxide cavity layers. We achieved nearly full transmission throughout the guiding band of the periodic coupled cavities within the photonic band gap. The tight-binding (TB) parameter κ is determined from experimental results, and the dispersion relation, group velocity and photon lifetime corresponding to the coupled-cavity structures are analyzed within the TB approximation. The measurements are in good agreement with transfer-matrix-method simulations and predictions of the TB photon picture. Received: 21 August 2000 / Revised version: 22 August 2000 / Published online: 9 November 2000     

Electrochemical Determination and in silico Studies of Fludarabine on NH2 Functionalized Multiwalled Carbon Nanotube Modified Glassy Carbon Electrode

A sensitive voltammetric technique has been developed for the determination of Fludarabine using amine‐functionalized multi walled carbon nanotubes modified glassy carbon electrode (NH₂‐MWCNTs/GCE). Molecular dynamics simulations, an in silico technique, were employed to examine the properties including chemical differences of Fludarabine‐ functionalized MWCNT complexes. The redox behavior of Fludarabine was examined by cyclic, differential pulse and square wave voltammetry in a wide pH range. Cyclic voltammetric investigations emphasized that Fludarabine is irreversibly oxidized at the NH₂‐MWCNTs/GCE. The electrochemical behavior of Fludarabine was also studied by cyclic voltammetry to evaluate both the kinetic (k_s and E_a) and thermodynamic (ΔH, ΔG and ΔS) parameters on NH₂‐MWCNTs/GCE at several temperatures. The mixed diffusion‐adsorption controlled electrochemical oxidation of Fludarabine revealed by studies at different scan rates. The experimental parameters, such as pulse amplitude, frequency, deposition potential optimized for square‐wave voltammetry. Under optimum conditions in phosphate buffer (pH 2.0), a linear calibration curve was obtained in the range of 2×10^?7 M–4×10^?6 M solution using adsorptive stripping square wave voltammetry. The limit of detection and limit of quantification were calculated 2.9×10^?8 M and 9.68×10^?8 M, respectively. The developed method was applied to the simple and rapid determination of Fludarabine from pharmaceutical formulations.