Laser performance and photostability of Rhodamin B in solid host matrices

Laser dye Rhodamine B was incorporated at different concentrations in GMA polymer, sol–gel glass and organic–inorganic hybrid material synthesized using the sol–gel process. The amplified spontaneous emission (ASE) was studied using Nd-YAG laser of 532 nm. The effect of laser excitation in transfer pumping configuration and the influence of dye concentration on the ASE were studied. Also, the gain and the energy conversion efficiencies were investigated. Relatively high efficiencies (to ～48%) were obtained with good photostabilities where a decrease to ～30% of the initial amplified spontaneous emission output energy were observed after pumping by 35000 shots at relatively high repetition rate (10 Hz) and energy (15 mJ). The composition and the properties of the matrix were found that optimize the laser performance and photostability of an investigated dye.     

Chelation and Analytical Application of Thiosemicarbazides Toward Platinum(IV) Ions

N(1)H derivatives of ethyl- and phenyl-thiosemicarbazides have been prepared and identified so as to produce new complexes with H₂PtCl₆. The obtained complexes have been investigated by thermal, magnetic and spectral studies. They were found to be diamagnetic and to have an octahedral structure. The IR data reveal different modes of coordination for the investigated ligands. The thermal decomposition of some complexes ended with PtS₂ as a final product. The formation of a green associate with 1-phenyl-4-ethylthiosemicarbazide (HPETS) was found suitable for the preconcentration and determination of Pt(IV). A simple and effective separation–determination procedure was achieved through the use of the flotation technique. The deprotonation constants of the ligands and the stability constants of the complexes formed in solution were evaluated by electrochemical methods, Methylthiosemicarbazide (HMTS) complexes were found to be the most stable in solution.     

Microscopic observation of oxygen reaction pathway on high temperature electrode materials

Attempts have been made to develop experimental techniques for obtaining microscopic information on high temperature electrodes under current flow. Several techniques are proposed to investigate the geometrical distribution of the series and parallel processes inside the electrode layer. Based on the local equilibrium concept, the contribution of the series processes were studied by probing the local oxygen potential. A microprobe oxygen sensor was developed to measure the oxygen potential profile on a model electrode of (La,Sr)MnO₃ on YSZ. Use of alternative methods that detect the valence state of the cations in the electrode material were also proposed. As an ex-situ technique, active sites for gas–solid oxygen exchange reaction were investigated by using isotope exchange and SIMS (secondary ion mass spectrometry) analysis. The three-dimensional distribution of the isotope ratio was obtained by SIMS with imaging capability. A non-uniform distribution of the reaction rate on the electrode surface was visualized for the electrode material with and without current flow. By the imaging technique, an extraordinary fast oxygen exchange site was found on (La,Sr)₂CoO₄/(La,Sr)CoO₃ boundaries.     

Symmetric patterns in the Dirichlet problem for a two-cell cubic autocatalytor reaction model

By using an approach developed by one of the authors, approximate solutions of the soft periodic boundary conditions for a two-cell reaction diffusion model have been obtained. The system is considered with reactant A and autocatalyst B. The reaction is taken cubic in the autocatalyst in the two-cell with linear exchange through A. The formal exact solution is obtained which is symmetric with respect to the mid-point of the container. Approximate solutions are found through the Picard iterative sequence of solutions constructed after the exact one. It is found that the solution obtained is not unique. When the initial conditions are periodic, the most dominant modes initiate to traveling waves in systems with moderate size. Symmetric configurations forming a parabolic one for large time are observed. In systems of large size, spatially symmetric chaos are produced which are stationary in time. Furthermore, it is found the symmetric pattern formation hold irrespective of the condition of linear instability against small spatial disturbance.     

Effect of γ-dose rate on crystallinity and morphological changes of γ-sterilized biomedical polypropylene

The present work is aimed to study the changes in crystallinity and morphology of biomedical polyolefins after γ-sterilization. The isotactic polypropylene (iPP) films were sterilized by γ-radiation and the changes were characterized by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) techniques. The effect of dose rate on crystallinity changes also was focused. It was found that crystallinity and morphology significantly changed with γ-irradiation. There was an increase in crystallinity up to 10 kGy accompanied with decrease in viscosity and mechanical properties. The changes in crystallinity mainly depend on γ-irradiation dose and dose rate. The rise in crystallinity was attributed to chain scission and forming new perfect lamellae. However, the reduction was accompanied by occurrence of γ- and β-phases and crosslinking. Possible explanations for transitions in phases are also discussed based on our results.     

Photo-physical properties and quantum yield of some laser dyes in new polymer host

The field of laser dyes-active solid polymer materials is a promising field and quite competitive with liquid dye lasers. This paper investigates some photo-physical parameters of pyromethene (PM-567, PM-597) and Rhodamine B dyes incorporated into glycidyl methacrylate (GMA) promising polymeric host matrix. These parameters are: absorption and emission cross-sections, fluorescence lifetime and quantum yield, in addition to FT-Raman spectra as an indication for binding the dye molecules with the backbones of GMA polymeric chain.     

Solution for fractional Zakharov–Kuznetsov equations by using two reliable techniques

In this paper, the approximated analytical solutions for nonlinear dispersive fractional Zakharov-Kuznetsov (FZK(a, b, c)) equations are obtained with the help of two novel techniques, called fractional natural decomposition method (FNDM) and q-homotopy analysis transform method (q-HATM). In order to validate and illustrate the efficiency of the proposed techniques, we consider two special cases FZK(2, 2, 2) and FZK(3, 3, 3) in FZK(a, b, c). The numerical simulations have been conducted in order to verify the proposed techniques are reliable and accurate. The outcomes are revealed through the plots and tables. The comparison between the obtained solutions with the exact solutions exhibits that, both the featured schemes are efficient and effective in solving nonlinear complex problems.     

The Riccati Equation Method Combined with the Generalized Extended $(G'/G)$-Expansion Method for Solving the Nonlinear KPP Equation

An analytic study of the nonlinear Kolmogorov-Petrovskii-Piskunov (KPP) equation is presented in this paper. The Riccati equation method combined with the generalized extended $(G''/G)$-expansion method is an interesting approach to find more general exact solutions of the nonlinear evolution equations in mathematical physics. We obtain the traveling wave solutions involving parameters, which are expressed by the hyperbolic and trigonometric function solutions. When the parameters are taken as special values, the solitary and periodic wave solutions are given. Comparison of our new results in this paper with the well-known results are given.     

Quantum tetrahedra and simplicial spin networks

A new link between tetrahedra and the group SU(2) is pointed out: by associating to each face of a tetrahedron an irreducible unitary SU(2) representation and by imposing that the faces close, the concept of the quantum tetrahedron is seen to emerge. The Hilbert space of the quantum tetrahedron is introduced and it is shown that, due to an uncertainty relation, the “geometry of the tetrahedron” exists only in the sense of “mean geometry”.A kinematical model of quantum gauge theory is also proposed, which shares the advantages of the loop representation approach in handling in a simple way gauge- and diff-invariances at a quantum level, but is completely combinatorial. The concept of quantum tetrahedron finds a natural application in this model, giving a possible interpretation of SU(2) spin networks in terms of geometrical objects.     

Structural control of Fano resonances in semiconductor heterostructures

Structural control of quantum interference in the optical intrasubband absorption spectrum of GaAs/AlGaAs multi-quantum wells is investigated theoretically. Our study shows that pronounced Fano resonances are in general difficult to obtain in quantum well heterostructures, with a presence of distinct Fano resonance features being the exception rather than the rule. Guided by an analogy to Young’s double-slit experiment, we design increasingly improved structures to display Fano resonances. Best results are achieved in structures where there is strong overlap between the ground-state wavefunction and scattering states associated with the uncoupled continuum. Alternatively one may use ionization via two or more resonances. In this case, resonances should not be separated by more than 25 meV to give significant effects. Moreover, we show that resonance features may also be induced without potential barriers to a continuum merely via orthogonality between bound and excited states.