Preparation of highly efficient Al-doped ZnO photocatalyst by combustion synthesis

Novel Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5–6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 °C for 3 h. The obtained nanopowders were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) combined with EDX, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy and photoluminescence spectroscopy. The XRD patterns of AZO nanopowders were assigned to wurtzite structure of ZnO with the smallest crystallite size about 11 nm consistent with the results from TEM. The doping of Al in ZnO crystal structure successfully suppressed the growth of ZnO nanoparticles confirmed by XRD patterns. The absorption spectra analysis showed that the optical band gap energy (E_g) for the AZO nanopowders were in the range of 3.12–3.21 eV and decreased with increasing of Al dopant. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange under visible light (λ ≥ 420 nm) and sunlight irradiation. The results showed that the AZO photocatalyst doped with 4.0 mol% Al exhibited five times enhanced photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity could be attributed to extended visible light absorption, inhibition of the electron–hole pair's recombination and enhanced adsorptivity of MO dye molecule on the surface of AZO nanopowders.     

The energy transfer mechanism in Ce,Tb co-doped LaF3 nanoparticles

LaF₃ pure host, LaF₃:Ce, LaF₃:Tb as well as LaF₃:Ce,Tb phosphors were synthesized by the hydrothermal method. X-ray diffraction measurements were in good agreement with the standard data of LaF₃ from JCPDS card No. 32-0483 and indicated that the material was nanocrystalline with an average particle size of about 36 nm. Photoluminescence spectra of co-doped samples revealed that the Ce³⁺ emission was quenched while Tb³⁺ emission was enhanced, implying that energy was transferred from Ce³⁺ (the donor) to Tb³⁺ (the acceptor) in this system. The luminescence intensities and lifetimes of the donor for different concentrations of the acceptor were fitted to theoretical models in order to investigate the energy transfer mechanism. The quadrupole–quadrupole and exchange interaction mechanisms gave the best fit between the experimental data and the theoretical curves. The effective average Bohr radius from the fit to the exchange model is 0.095 nm. Since this is close to the ionic radii of the Ce³⁺ and Tb³⁺ ions, it suggests that the exchange interaction mechanism contributes to the energy transfer.     

Variable fluid properties and variable heat flux effects on the flow and heat transfer in a non-Newtonian Maxwell fluid over an unsteady stretching sheet with slip velocity

The effects of variable fluid properties and variable heat flux on the flow and heat transfer of a non-Newtonian Maxwell fluid over an unsteady stretching sheet in the presence of slip velocity have been studied. The governing differential equations are transformed into a set of coupled non-linear ordinary differential equations and then solved with a numerical technique using appropriate boundary conditions for various physical parameters. The numerical solution for the governing non-linear boundary value problem is based on applying the fourth-order Runge-Kutta method coupled with the shooting technique over the entire range of physical parameters. The effects of various parameters like the viscosity parameter, thermal conductivity parameter, unsteadiness parameter, slip velocity parameter, the Deborah number, and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. Comparison of numerical results is made with the earlier published results under limiting cases.     

High-Efficiency Laser-Power Transmission With All Optical Amplification for High-Transmission-Capacity Submarine Cables

We present new trends in the performance evaluation of submarine fiber cable system with different ultrahigh multiplexing and propagation techniques over a wide range of the affecting parameters. Our model takes into account the ultimate optical transmission of huge submarine cables with 14,400 channels under different depth conditions. We employ Raman and erbium-doped fiber amplifiers in our study. We investigate the double impact of both temperature and pressure through the defined depth penalty. We also study the soliton transmission technique using two multiplexing methods considered in the design of ultra-wide wavelength division multiplexing (UW-WDM) with 14,400 optical channels and ultra-wide space division multiplexing (UW-SDM) with 440 fiber links. Based on experimental data, both the deep ocean water temperature and pressure are obtained as functions of the water depth.     

Dynamics of a three level atom interacting with a detuned SU (1,1) quantum system

We study the stability of attractive atomic Bose-Einstein condensate and the macroscopic quantum many-body tunneling (MQT) in the anharmonic trap. We utilize correlated two-body basis function which keeps all possible two-body correlations. The anharmonic parameter (λ) is slowly tuned from harmonic to anharmonic. For each choice of λ the many-body equation is solved adiabatically. The use of the van der Waals interaction gives realistic picture which substantially differs from the mean-field results. For weak anharmonicity, we observe that the attractive condensate gains stability with larger number of bosons compared to that in the pure harmonic trap. The transition from resonances to bound states with weak anharmonicity also differs significantly from the earlier study of [N. Moiseyev, L.D. Carr, B.A. Malomed, Y.B. Band, J. Phys. B 37, L193 (2004)]. We also study the tunneling of the metastable condensate very close to the critical number N _cr of collapse and observe that near collapse the MQT is the dominant decay mechanism compared to the two-body and three-body loss rate. We also observe the power law behavior in MQT near the critical point. The results for pure harmonic trap are in agreement with mean-field results. However, we fail to retrieve the power law behavior in anharmonic trap although MQT is still the dominant decay mechanism.     

Preparation and thermoelectric power of SnBi4Se7

Polycrystalline samples of Bi₂Se₃ and a stoichiometric ternary compound in the quasi-binary system SnSe–Bi₂Se₃ have been prepared and characterized by X-ray powder diffraction analysis. At room temperature the carrier concentration values are n?=?1.1?×?10¹⁹?cm^?3 for Bi₂Se₃ and n?=?0.53?×?10¹⁹?cm^?3 for SnBi₄Se₇. The thermoelectric power has been measured over the temperature range 90–420?K. The thermoelectric power of Bi₂Se₃ is higher than that for SnBi₄Se₇, which shows that the Sn impurity has an acceptor character. Therefore, doping Bi₂Se₃ with tin atoms does not improve thermoelectric properties of this material, due to decrease the value of the power factor σS ². Transport properties of the studied polycrystalline samples are characterized by a mixed transport mechanism of free carriers. It is necessary to add more than one Sn atom to the Bi₂Se₃ compound in order to suppress the electron concentration by one electron. Such behaviour of the dopant is explained by the formation of various structural defects. Besides the dominant substitutional defect, Sn_Bi, tin atoms also form uncharged defects, corresponding to seven-layer lamellae of the composition Se–Bi–Se–Sn–Se–Bi–Se which corresponds to the structure of the SnBi₂Se₄.     

Structural study of NiXMg1–XFe2O4 ferrites

The ferrite system Ni _x Mg_1-x Fe₂O₄ with 0≤x≤1 was prepared using the usual ceramic technique. The prepared samples were studied by X-ray diffraction and IR spectroscopy. X-ray diffraction analysis proved that all the samples were single-phase with the cubic spinel structure. The lattice constant, radius of the tetrahedral ion, unshared octahedral edge, tetrahedral bond and tetrahedral edge decrease while the bulk and theoretical densities, radius of octahedral ion, octahedral bond and shared octahedral edge increase as nickel ion substitution increases. The positions and intensities of the four bands of IR absorption spectra characterizing ferrites are composition dependent.     

Study of the critical current density and the thermodynamic critical field in deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br organic superconductor

ABSTRACT

We have studied the reversible and irreversible part of the hysteresis loops as a function of slow cooling rate through the order–disorder transformation near 80?K for the deuterated (κ-D₈-Br) κ-(BEDT-TTF)₂Cu[N(CN)₂]Br organic superconductor. We estimated the critical current density J_C and the thermodynamic critical field H_C from the magnetic hysteresis loops. Temperature dependence of the critical current density derived from the irreversible part using Bean’s model. The thermodynamic critical field H_C has been obtained from the reversible part of the hysteresis loops.     

DC electrical resistivity for CoxNi5/3−xSb1/3Fe1O4 ferrites

The DC electrical resistivity (p) was studied for Co substituted SbNi ferrites as a function of temperature and composition. The experimental results showed that DC resistivity, Curie temperature and activation energies for electrical conduction increase as Co-ion substitution decreases. The DC electrical conductivity increases as temperature increases. The real part of dielectric constant (e') was found to be inversely proportional to the root mean square value of the electrical resistivity.     

1H and C-13 Nuclear Magnetic Resonance of Tiaprofenic Acid

¹H-NMR spectrum of tiaprofenic acid in CDCI3 was obtained and proton chemical shifts from tetramethylsilane were assigned to each proton and set of equivalent protons of the molecule. The hydroxy proton of the carboxylic acid group was confirmed by deuterium exchange. The natural abundance C-13 nuclear magnetic resonance spectrum of the compound in CDCI3 was recorded using Fourier transorm technique. The chemical shifts of carbon resonances have been assigned on the basis of the chemical shift additivity theory and the signal multiplicity observed in the single frequency off-resonance decoupled (SFORD) spectrum. Also comparison with carbon chemical shifts of model compounds were useful.