Oscillator Dispersion Research Articles

Enhanced band structure, optoelectronic and magnetic properties of spray pyrolysis Ni-doped SnO2 nanostructured films

Pure and Nickel-doped Tin Oxide at 0, 1, 2, 4, 5, 6, and 7 wt % of Ni nanocrystalline thin films were synthesized by home-made Spray Pyrolysis technique on glass substrate. The microstructural, morphological, optical and magnetic properties of the films have been investigated. The XRD patterns of the films exhibit a tetragonal type structure with no signature of extra phases. The solubility limit of the incorporation of Ni into the SnO2 semiconducting matrix has been observed at x > 0.05. The nanocrystalline feature of the films is confirmed from AFM and SEM investigations. It was found that the optical energy gap Eg diminishes with the increasing of Ni content up to x ≤ 0.05 and then increases due to the solubility limit of Ni, suggesting the enhancement in the band structure. The decrease of the optical band gap could be attributed to the sp-d exchange interaction while the increase of Eg is explained according to the Burstein–Moss effect. The dispersion and single oscillator parameters of the films were estimated by analyzing the dispersion data based on Wemple–DiDomenico single-effective-oscillator model. The room temperature ferromagnetic behaviour of the films has been observed and discussed according to the bound magnetic polarons model.

Characteristic mixed volume element for compressible two-phase displacement in porous media

Numerical simulation of a two-phase compressible displacement problem is considered in this paper, modelled by a nonlinear system of PDEs. Considering the characters of mathematical model, we present an efficient combination algorithm of the method of characteristics (MOC) and mixed finite volume element (MFVE). The MFVE is used for computing the pressure, Darcy velocity and the saturation. Furthermore, the saturation equation is convection-dominated. MOC eliminates numerical dispersion and nonphysical oscillation, and computes the values at the sharp fronts well. An MFVE-MOC is formed for the saturation. An optimal error estimates in l2 norm is concluded. Finally, numerical examples are given to show the effectiveness and practicability. The composite scheme possibly solves this actual problem well.

Numerical simulations of strong-field processes in momentum space**Project supported by the National Key Research and Development Program of China (Grant No. 2019YFA0307702), the National Natural Science Foundation of China (Grants Nos. 91850121 and 11674363), the Science Fund of Educational Department of Henan Province of China (Grant No. 2011C140001), and the Ninth Group of Key Disciplines in Henan Province, China (Grant

The time-dependent Schrödinger equation (TDSE) is usually treated in the real space in the textbook. However, it makes the numerical simulations of strong-field processes difficult due to the wide dispersion and fast oscillation of the electron wave packets under the interaction of intense laser fields. Here we demonstrate that the TDSE can be efficiently solved in the momentum space. The high-order harmonic generation and above-threshold ionization spectra obtained by numerical solutions of TDSE in momentum space agree well with previous studies in real space, but significantly reducing the computation cost.

Mixed finite volume element-upwind mixed volume element of compressible two-phase displacement and its numerical analysis

A fundamental topic in numerical simulation of two-phase displacement is discussed in this paper. The mathematical model for the compressible problem is defined mainly by two nonlinear partial differential equations: a parabolic equation for the pressure and a convection–diffusion equation for the saturation. The Darcy velocity is determined by the pressure, and affects the whole physical process. The system is solved by a composite numerical scheme. The conservative mixed volume element is used for the first equation. The computational accuracy is improved for the Darcy velocity. The second equation is solved by a conservative upwind mixed volume element, where the mixed volume element and upwind approximation treat the diffusion and convection, respectively. The upwind method preserves the high computational accuracy, and numerical dispersion and nonphysical oscillation are eliminated. The saturation and its adjoint vector function are obtained simultaneously. An important feature in numerical scheme, the conservation of mass, is proved. By the traditional theoretical work of numerical analysis such as a priori estimates of differential equations, the optimal order error estimate is obtained. Finally, numerical tests show the effectiveness and practicability, then the present method possibly solves the challenging problems as a powerful tool.

Generation of high-intensity optical breathers via soliton collision in fibres with variable dispersion

An approach for the generation of high-intensity pulses via inelastic collision of solitons in dispersion variable fiber is proposed. The rogue-like pulse arises due to stimulated soliton collisions and non-adiabatic variation of the fiber dispersion. The analysis of the eigenvalues of Zakharov–Shabat spectral problem is given. We showed that the eigenvalues are affected by the fast change of the dispersion at the moment of soliton collision. High-intensity pulse generation under simultaneous effect of dispersion oscillation and stimulated Raman scatering is demonstarted. We proposed to use segmented fiber to generate the high-intensity pulse from inelastic soliton collision.

Optical absorption and dispersion properties of 2-aminoanthracene-9,10- dione thin films for photodetector applications

Recent evidence suggests that the need for employing a new characteristic with low-cost preparation tools and high performance for applications. These properties have been achieved by using a high stable 2-aminoanthracene-9,10- dione thin films (AAD), prepared by thermal evaporation technique under a vacuum of 10−5 Torr. The surface of the films was checked by SEM for studying the RMS-roughness characteristics and grain – boundary influence. Added to this study, the crystalline performance was also considered as the main requirement for identifying the main crystal parameters. Most important results were focused on TGA results for confirming the thermal stability through the chosen measurements. The investigation of the spectral dependence of the absorption of the AAD films specifies the occurrence of high probability for indirect transition as compared to the direct allowed with energy gaps of 1.55 and 2.28 eV. The dispersion energy and oscillator energy, as well as most parameters, were computed using the well-known Wimple–DiDomenico formula under consideration of the single oscillator model. The spectral dependence of the linear and nonlinear controlling parameters were studied for subscription the prospect applications in photodetectors.

Optimized composite finite difference schemes for atmospheric flow modeling

AbstractIn this paper, we use some finite difference methods in order to solve an atmospheric flow problem described by an advection–diffusion equation. This flow problem was solved by Clancy using forward‐time central space (FTCS) scheme and is challenging to simulate due to large errors in phase and amplitude which are generated especially over long propagation times. Clancy also derived stability limits for FTCS scheme. We use Von Neumann stability analysis and the approach of Hindmarsch et al. which is an improved technique over that of Clancy in order to obtain the region of stability of some methods such as FTCS, Lax–Wendroff (LW), Crank–Nicolson. We also construct a nonstandard finite difference (NSFD) scheme. Properties like stability and consistency are studied. To improve the results due to significant numerical dispersion or numerical dissipation, we derive a new composite scheme consisting of three applications of LW followed by one application of NSFD. The latter acts like a filter to remove the dispersive oscillations from LW. We further improve the composite scheme by computing the optimal temporal step size at a given spatial step size using two techniques namely; by minimizing the square of dispersion error and by minimizing the sum of squares of dispersion and dissipation errors.

The method of mixed volume element-characteristic mixed volume element and its numerical analysis for groundwater pollution in binary medium

Groundwater pollution is an important topic of environmental sciences. Since the geologic structure is usually of crack-hole binary medium, its mathematical model is formulated by a nonlinear initial-boundary value problem of partial differential equations. The pressure is defined by an elliptic flow equation. The concentration of pollution is defined by a convection-diffusion equation. The surface adsorption concentration is defined by a first-order ordinary differential equation. The transport pressure appears within the concentration, and Darcy velocity controls the concentration. The flow equation is solved by the conservative mixed volume element and the computational accuracy of Darcy velocity is improved by one order. The mixed volume element with the characteristics is applied to approximate the concentration, i.e., the diffusion and convection are discretized by the method of mixed volume element and the characteristics, respectively. Sharp fronts are resolved stably by the characteristic discretizations without numerical dispersion or nonphysical oscillation. Large and accurate timesteps are used while the scheme has much smaller time truncation errors than those of standard methods on coarse grids. The mixed volume element is applied to approximate the diffusion. The concentration and its adjoint vector function are computed simultaneously, and the locally conservative law of mass is ensured. Using the theory and technique of a priori estimates of differential equations, we derive an optimal second order error in l2 norm. Numerical examples are given to show the effectiveness and practicability and the method is testified as a powerful tool in solving some actual applications.

An upwind approximation combined with mixed volume element for a positive semi-definite contamination treatment from nuclear waste

A positive semi-definite problem of three-dimensional contamination treatment from nuclear waste in porous media is discussed in this paper. The mathematical model is defined by a nonlinear initial-boundary system consisting of partial differential equations. An elliptic equation, two convection–diffusion equations and a heat conductor equation are given to determine the pressure, the concentrations of brine and radionuclide, and the temperature, respectively. The parabolic equations include Darcy velocity dependent on the pressure, and the pressure affects the whole physical process. A conservative mixed volume element is used. One-order computational accuracy is improved for Darcy velocity. The main physical unknowns are solved by an upwind-mixed volume element, where the diffusions and convection terms are treated by a mixed volume element and an upwind approximation, respectively. This composite method could eliminate numerical dispersion and nonphysical oscillations, thus this problem may be solved well. The mixed volume element can obtain the concentrations, temperature and their adjoint vectors simultaneously, and has the conservation of mass or energy, an important law in numerical simulation. Applying the theory and special treatment of a priori estimates, we obtain optimal order estimates in $$L^2$$ -norm. Numerical experiments show the efficiency and applicability for solving such complicated problems.

The influence of Ar pressure on the structure and optical properties of non-hydrogenated a-Si thin films grown by rf magnetron sputtering onto room-temperature glass substrates

Seven 1.1–1.4-μm-thick hydrogen-free amorphous‑silicon (a-Si) thin films were deposited at high rates (larger than 10 Å/s), by rf magnetron sputtering (RFMS) onto room-temperature glass substrates. The influence of argon-gas pressure on the structural and optical properties of these amorphous films has been systematically studied. We have used the Wemple-DiDomenico (WD) single-effective-oscillator model, n2(ℏω) − 1 = EdE0/(E02 − (ℏω)2), in order to determine the WD parameters oscillator strength or dispersion energy, Ed, and oscillator energy, E0. The amorphous-to-crystalline mass-density ratio, ρa/ρx, in the empirical expression for Ed, proposed by Wemple, is the key factor in understanding the refractive-index behaviour of the RFMS-a-Si thin films. The value of the static refractive index, n(0), which is related to both the atomic structure and mass density, remains approximately constant up to a threshold Ar-gas pressure of nearly 1 Pa, and then it starts dropping rather abruptly. The decrease found in the Urbach energy, EU, as well as the increase observed in the Tauc gap and slope, Eg and B respectively, for Ar-gas pressures higher than the voided-structure threshold sputtering pressure, clearly suggests that the amount of intermediate-range order present within the RFMS-a-Si layers under study, is increasing in direct response to the increase in the Ar-gas pressure, during the deposition process. This is independently corroborated by the decreasing values of the Raman-intensity ratio, ITA/ITO, as the sputtering pressure increases, in the case of high Ar pressure a-Si films.

Frequency comb generation through the locking of domain walls in doubly resonant dispersive optical parametric oscillators.

In this Letter we theoretically investigate the formation of localized temporal dissipative structures, and their corresponding frequency combs in doubly resonant dispersive optical parametric oscillators. We derive a nonlocal mean field model, and show that domain wall locking allows for the formation of stable coherent optical frequency combs.

Effect of Oxygen Flow Rate on Structural, Electrical and Optical Properties of Zinc Aluminum Oxide Thin Films Deposited by DC Magnetron Sputtering

Zinc Aluminum Oxide thin films were deposited on glass substrates by reactive DC magnetron sputtering method by varying oxygen flow rates from 1 to 4 sccm. Glancing angle X-ray diffraction patterns ofzinc aluminum oxide thin films exhibits (0 0 2) peak with c-plane preferentially oriented parallel to the substrate. The surface morphology and elemental analysis of the films was observed by field emission scanning electron microscopy attached with energy dispersive X-ray analysis spectroscopy. An average optical transmittance of 83–90% is obtained for the films deposited at various oxygen flow rates. The optical band gap of the films increases from 3.41 to 3.53 eV with the increase of oxygen flow rate due to Burstein–Moss effect. The optical dispersion parameters such as dispersion energy (Ed), oscillator energy (Eo) and static refractive index (no) were determined using the Wemple-DiDomenico (W-D) single oscillator model. The nonlinear optical parameters such as optical susceptibility (χ(1)), third order nonlinear optical susceptibility (χ(3)) and nonlinear refractive index (n2) were also determined.

SPECTROSCOPIC ELLIPSOMETRY STUDIES ON ZINC OXIDE THIN FILMS DEPOSITED BY SOL–GEL METHOD WITH VARIOUS PRECURSOR CONCENTRATIONS

Zinc Oxide thin films were deposited on glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, 2-methoxyethanol and monoethanolamine were used as precursor, solvent and stabilizer, respectively. Zinc acetate dihydrate was used with different molar concentrations of 0.15, 0.25 and 0.5 M. Optical properties of ZnO thin films such as dielectric constants, absorption coefficient, Urbach energy and optical band gap energy were calculated by spectroscopic ellipsometry (SE) method. The effect of zinc acetate concentration on optical properties of ZnO thin films is investigated. ZnO thin film with Zn concentration of 0.25 M had the highest optical band gap. Wemple DiDomenico oscillator model was used for calculation of the energy of effective dispersion oscillator, the dispersion energy, the high frequency dielectric constant, the long wavelength refractive index and the free carrier concentration.

Low temperature processing of BaTiO3-PMMA-PVP hybrid films as transparent dielectric gate

Transparent thin films based on nanocomposites of BaTiO3, (PMMA) and poly (4-vinylphenol) (PVP) are synthesized and deposited on fluorine doped tin oxide (FTO) coated glass substrate by spin coating technique. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) are applied to investigate the chemical bonds and structural properties of the samples. The optical transmittance and reflectance of nanocomposite films are investigated in the 200–900 nm wavelength range. The calculation of optical band gaps of thin films showed that the thin film has directly allowed transition with the values from 3.3 eV to 3.4 eV. Dispersion parameters are calculated based on the single oscillator model. The important parameters such as dispersion energy, oscillator energy and lattice dielectric constant are extracted for thin film. The electrical properties such as capacitance and electrical behavior are investigated for sample. The obtained results of nanocomposite thin films can be useful for using in transparent organic thin film transistor.

High-Power and Large-Energy Dissipative Soliton Resonance in a Compact Tm-Doped All-Fiber Laser

We report the direct generation of high-power and large-energy dissipative soliton resonance square pulses at 1940.8 nm from a compact mode-locked Tm-doped all-fiber laser. A fiber loop mirror of 10/90 splitting ratio and a fiber Bragg grating with high reflectivity of >99% constitute the cavity mirrors together. The fiber loop mirror not only acts as a broadband reflective mirror and output port but also initiates the mode-locked fiber laser. The strictly all-fiber structure and proper selection of fiber types allow the laser to work in a high pump power state. By increasing the pump power, pulse duration extends from 5.9 to 14.5 ns, while the pulse peak power and 3-dB spectrum bandwidth almost keep constant. At the maximum pump power of 13 W, we acquire maximum output average power of 1.98 W and single pulse energy of 684 nJ. To the best of our knowledge, this is the highest average output power and single pulse energy in an all-fiber Tm-doped mode-locked oscillator. At the same time, the output power is also a record value in all-fiber net anomalous dispersion oscillators.

A mixed volume element with upwind multistep mixed volume element and convergence analysis for numerical simulation of nuclear waste contaminant disposal

In this paper the authors discuss a numerical simulation problem of three-dimensional contamination treatment from nuclear waste. The mathematical model is defined by a nonlinear system of an initial–boundary problem of four partial differential equations: an elliptic equation for the fluid pressure, three convection–diffusion equations for the brine, radionuclides and heat. The pressure appears within the concentration equations and heat conduction equation, and the Darcy velocity controls the concentrations and the temperature. The pressure is solved by the conservative mixed volume element method, and the order of accuracy is improved by the Darcy velocity. The concentrations and temperature are treated by a combination of a multistep method, the upwind approximation and a mixed volume element. The partial derivatives to time variable are approximated by a multistep method. A mixed volume element and an upwind scheme are used to discretize the diffusion and the convection, respectively. The composite method can solve the convection-dominated diffusion problems well because it eliminates numerical dispersion and nonphysical oscillation and has high order computational accuracy. The mixed volume element has the local conservation of mass and energy, and it can obtain the concentrations and temperature and their adjoint vector functions simultaneously. The conservation nature plays an important role in numerical simulation of underground fluid. By the technique of a priori estimates of differential equations, we derive an optimal second order result in L 2 norm. Numerical examples are given to show the effectiveness and practicability of our approach and the composite method is testified as a powerful tool for solving the challenging benchmark problem.

Optical Study of Ge1Sb2Te4 and GeSbTe thin films

Extensive optical study has been carried out on as-deposited and annealed thin films of Ge1Sb2Te4 and GeSbTe chalcogenides prepared through vacuum thermal evaporation on glass substrates. These films are found to be amorphous in nature for as-dep samples. The modifications that manifest in these films upon annealing are thoroughly investigated in view of the optical parameters. UV–vis spectroscopy has been utilized as the major tool for computation of optical constants, optical bandgap energy, urbach energy, skin depth, optical conductivity etc. Theoretical models for optical analysis like Wemple Di-Domenico model and Single Sellmier model have been applied to evaluate the dispersion energy parameters and oscillator parameters. Comparative analysis has been carried out which highlights the phase change characteristics of Ge1Sb2Te4 and non-phase change behavior of GeSbTe.

Effect of oxygen flow rate on structural, electrical and optical properties of zinc aluminum oxide thin films deposited by DC magnetron sputtering -=SUP=-*-=/SUP=-

AbstractZinc Aluminum Oxide thin films were deposited on glass substrates by reactive DC magnetron sputtering method by varying oxygen flow rates from 1 to 4 sccm. Glancing angle X-ray diffraction patterns ofzinc aluminum oxide thin films exhibits (0 0 2) peak with c-plane preferentially oriented parallel to the substrate. The surface morphology and elemental analysis of the films was observed by field emission scanning electron microscopy attached with energy dispersive X-ray analysis spectroscopy. An average optical transmittance of 83–90% is obtained for the films deposited at various oxygen flow rates. The optical band gap of the films increases from 3.41 to 3.53 eV with the increase of oxygen flow rate due to Burstein–Moss effect. The optical dispersion parameters such as dispersion energy ( E _ d ), oscillator energy ( E _ o ) and static refractive index ( n _ o ) were determined using the Wemple-DiDomenico (W-D) single oscillator model. The nonlinear optical parameters such as optical susceptibility (χ^(1)), third order nonlinear optical susceptibility (χ^(3)) and nonlinear refractive index ( n _2) were also determined.

Experimental and Numerical Analyses of the Rational Loading Waveform in SHPB Test for Rock Materials

Aiming at the determination of the rational loading waveform for rock materials, the comparative impact tests under the loadings of rectangular and half-sine stress waves were performed on red sandstone using an Ø50 mm SHPB apparatus. Experimental results with the rectangular stress wave affirm that the waveform dispersion and stress-strain curve oscillation frequently exist during the test of rock materials, which signifies that the accuracy of test results derived from the rectangular stress wave loading cannot be guaranteed. Under the loading of the half-sine stress wave, the phenomenon of wave dispersion during the tests has been eliminated radically, and there is no oscillation in the stress-strain curves. To further demonstrate the rationality of the half-sine wave loading in the SHPB test, by utilizing the three-dimensional numerical simulation approach, the propagations of rectangular, triangular, and half-sine stress waves travelling in the axial and radial directions of the SHPB with four elastic bar diameter sizes are analyzed and compared. The results show that the waveform dispersion of the rectangular and triangular stress waves always exists and will be more and more serious with increasing diameter size and propagation distance. For the half-sine stress wave, the waveform dispersion effect is very weak and not affected by the bar diameter size and propagation distance. The half-sine stress wave is the rational loading waveform for rock SHPB tests with different bar diameters.

A Modified Characteristics-mixed Finite Element for Semiconductor Device of Heat Conduction and Numerical Analysis

Numerical simulation of a three-dimensional semiconductor device of heat conduction is a fundamental problem in modern information science. The mathematical model is formulated by a nonlinear system of initial-boundary problem, which is interpreted by four partial differential equations: an elliptic equation for electrostatic potential, two convection-diffusion equations for electron concentration and hole concentration, a heat conduction equation for temperature. The electrostatic potential appears within the latter three equations, and the electric field strength controls the concentrations and the temperature. The electric field potential is solved by a mixed finite element method, and the electric field strength is obtained simultaneously. The first order of the accuracy is improved for the latter. The concentrations and temperature are computed by the characteristics-finite element method, where the characteristic approximation is adopted for the hyperbolic term and finite element method is use to treat the diffusion. The composite computational scheme can solve the convection-dominated diffusion equations well because it can cancel numerical dispersion and nonphysical oscillation. The temperature is computed by finite element method, and an interesting simulation tool is proposed for solving semiconductor device problem numerically. By using the technique of a priori estimates of differential equations, an optimal order error estimates is obtained. A theoretical work is shown for numerical simulation of information science, and the actual problem is solved well.