The possible effect of stratospheric quasi-biennial oscillation on the critical frequency of the ionospheric F2-layer

In this work, active control method is proposed for controlling and synchronising seven-dimensional (7D) hyperchaotic systems. The seven-dimensional hyperchaotic system is considered for the implementation. Seven-dimensional hyperchaotic system is also investigated via time series, phase portraits and bifurcation diagrams. For understanding the impact of active controllers on global asymptotic stability of synchronisation and control errors, the Lyapunov function is used. Numerical analysis is done to reveal the effectiveness of applied active control method and the results are discussed.     

Symbolic research of the periodic solutions of the nonintegrable Hamiltonian system of Ollongren

The main aim of this work is to look for the periodic solutions of the nonintegrable Hamiltonian system of Ollongren in the neighborhood of the origin. We apply a functional algorithm derived from the method of Lindstedt-Poincaré. We first show that the system admits six main periodic families and then, by means of the computer algebra system “Mathematica”, compute the series corresponding to these families up to O(ε¹⁴A²⁹) as well as to their periods up to O(ε¹⁵A³⁰), where A is the zeroth-order amplitude and έ is a perturbative parameter. Reducing the system to one degree of freedom we also prove that the period of the two “oblique” periodic families is rigorously equal to a Gauss hypergeometric series. Moreover, we study numerically the convergence of the L-P series and test the validity of these series using a numerical integration technique. Finally, we compare our results with those of a geometrical method and a Lie series method. This revised version was published online in June 2006 with corrections to the Cover Date.     

Incomplete-Fusion-Fragmentation Model and Nuclear Liquid-Gas Phase Transition

Incomplete-Fusion-Fragmentation Model is used to analyze the multifragmentation of the projectile remnant in 600MeV/u Au+Au reaction.The theoretical resultsof the mass number,the excitation energy and the thermodynamical temperature of the projectile remnant agree well with experimental data.The backbending structure in the curve of temperature as a function of the excitation energy per nucleon,i.e. the evidence of liquid-gas phase transition,is reproduced and reasonably related to the decay modes phase transformation from dominance of the multifragmentation mode to the vaporization mode.     

String Tension and Production of Strange Particles

The increase of effective string tension as a result of the hard gluon kinks on a string is investigated using a parametrization form. In this form the effective string tension increasing with energies in hadron-hadron collisions is due to the mini-jet (gluon) production in the collisions. The data for the energy dependence of the strange quark suppression factor in hadron-hadron collisions are very well reproduced with this mechanism. Meanwhile, the experimental phenomena of approximate energy independence of the strange quark suppression factor in e⁺e^－ -annihilations are discussed.     

Influence of density of states on optical properties of GaSe thin film

A systematic investigation on the effect of substrate temperature on the structure, optical absorption and density of states of vacuum evaporated gallium monoselenide (GaSe) thin films is reported. The X‐ray diffraction analysis shows an occurrence of amorphous to polycrystalline transformation in the films deposited at higher‐temperature substrates (573K). The compositional analysis is made with Auger Electron Spectroscopy (AES). The thickness of the film (175nm) is measured by a multiple beam interferometery. Optical characteristics of the GaSe sample have been analyzed using spectrophotometer in the photon energy range of 1.0 ‐ 4 eV. The absorption mechanism has been recognized and the allowed indirect as well as forbidden direct transitions have been found. As‐deposited films show two indirect and allowed transitions due to spin‐orbit splitting of the valence band, as reported here for the first time. Low field conduction have enabled us to determine the density of states in amorphous and poly‐GaSe films. The amorphous and polycrystalline GaSe thin films have localized states density values of N (E_F) = 1.686 × 10¹⁷ cm^‐3 eV^‐1 and 1.257 × 10¹⁵ cm^‐3 eV^‐1 respectively. The experimental results are interpreted in terms of variations in the density of localized states due to progressive decrease of the unsaturated bonds during deposition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Conduction Studies on Bismuth Selenide Thin Films

Thin films of Bi₂Se₃ have been prepared by vacuum deposition technique onto well cleaned glass and freshly cleaved KBr substrates. The film thicknesses are measured by Tolansky technique. The capacitance and dielectric constant have been measured from 303 K to 383 K in the frequency range of 10 kHz to 10 MHz. The a.c. conductivity s is calculated at different frequencies for various temperatures. The relation s μ wn fits well and the value of n is found to be greater than 1.5 and above at high frequencies suggests that the conduction mechanism in Bi₂Se₃ thin film is hopping. The d.c. conduction studies revealed the non-ohmic type of conduction( Log I versus Log V plot). From the Log I versus F1/2 plot, the field lowering coefficient b is evaluated.     

Going Beyond Silver in Ethylene Epoxidation with First-Principles Catalyst Screening

Ethylene epoxidation is industrially and commercially one of the most important selective oxidations. Silver catalysts have been state-of-the-art for decades, their efficiency steadily improving with empirical discoveries of dopants and co-catalysts. Herein, we perform a computational screening of the metals in the periodic table, identify prospective superior catalysts and experimentally demonstrate that Ag/CuPb, Ag/CuCd and Ag/CuTl outperform the pure-Ag catalysts, while they still confer an easily scalable synthesis protocol. Furthermore, we show that to harness the potential of computationally-led discovery of catalysts fully, it is essential to include the relevant in situ conditions e.g., surface oxidation, parasitic side reactions and ethylene epoxide decomposition, as neglecting such effects leads to erroneous predictions. We combine ab initio calculations, scaling relations, and rigorous reactor microkinetic modelling, which goes beyond conventional simplified steady-state or rate-determining modelling on immutable catalyst surfaces. The modelling insights have enabled us to both synthesise novel catalysts and theoretically understand experimental findings, thus, bridging the gap between first-principles simulations and industrial applications. We show that the computational catalyst design can be easily extended to include larger reaction networks and other effects, such as surface oxidations. The feasibility was confirmed by experimental agreement.     

Optical and opto‐electronic properties of polycrystalline Cd0.96Zn0.04Te thin films

Cd_0.96Zn_0.04Te thin films are deposited onto thoroughly cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films are found to have good stoichiometry as analyzed by Rutherford Backscattering Spectrometry. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the films evaluated by AFM is 3.7 nm. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E) at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+ Δ₁ and E₂ critical points. The band gap energy of the films measured by optical transmittance measurement is 1.523 eV. The PL spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and deeper impurity levels. The PL line shapes give indications of the high quality of the layers.     

Influence of thermal annealing on the composition and structural parameters of DC magnetron sputtered titanium dioxide thin films

Titanium dioxide films have been deposited using DC magnetron sputtering technique. Films were deposited onto RCA cleaned p‐silicon substrates at the ambient temperature at an oxygen partial pressure of 7 × 10^–5 mbar and sputtering pressure of 1 × 10 ^–3 mbar. The deposited films were annealed in the temperature range 673–873 K. The structure and composition of the films were confirmed using X‐ray diffraction and Auger electron spectroscopy. The structure of the films deposited at the ambient was found to be amorphous and the films annealed at 673 K and above were crystalline with anatase structure. The lattice constants, grain size, microstrain and the dislocation density of the film are calculated and correlated with annealing temperature.     

Crystal Engineering of BiVO4 for Photochemical Sensing of H2S Gas at Ultra-low Concentration

We report a photochemical bismuth vanadate (BiVO₄) sensing material, which possesses a large proportion of (110) and (011) facets combined with the additional (111) facets, for the selective detection of ultra-low concentration hydrogen sulfide (H₂S) driven by visible light. Specifically, the obtained octadecahedron BiVO₄ (Octa-BiVO₄) performs a high response value (67) and short response time (47.4 s) to 100 ppm H₂S with good stability for nearly 100 days, as well as undisturbedness by moist air. With the combination of experimental and theoretical calculation results, the adsorption and carrier transfer behaviors of H₂S molecules on the Octa-BiVO₄ crystal surface are investigated. By adjusting the ratio of different crystal facets and controlling the facets with characteristic adsorption, we achieve improved anisotropic photoinduced carrier separation and high selectivity for a specific gas. Furthermore, this facial facet engineering can be extended to the synthesis of other sensing materials, offering huge opportunities for fundamental research and technological applications.