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This paper presents a new approach for solving accurate approximate analytical higher-order solutions for strong nonlinear Duffing oscillators with cubic-quintic nonlinear restoring force. The system is conservative and with odd n...
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This paper presents a new approach for solving accurate approximate analytical higher-order solutions for strong nonlinear Duffing oscillators with cubic-quintic nonlinear restoring force. The system is conservative and with odd non-linearity. The new approach couples Newton's method with harmonic balancing. Unlike the classical harmonic balance method, accurate analytical approximate solutions are possible because linearization of the governing differential equation by Newton's method is conducted prior to harmonic balancing. The approach yields simple linear algebraic equations instead of nonlinear algebraic equations without analytical solution. Using the approach, accurate higher-order approximate analytical expressions for period and periodic solution are established. These approximate solutions are valid for small as well as large amplitudes of oscillation. In addition, it is not restricted to the presence of a small parameter such as in the classical perturbation method. Illustrative examples are presented to verify accuracy and explicitness of the approximate solutions. The effect of strong quintic nonlinearity on accuracy as compared to cubic nonlinearity is also discussed.
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In order to improve tracking ability, an adaptive fusion algorithm based on adaptive neuro-fuzzy inference system (ANFIS) for radar/ infrared system is proposed, which combines the merits of fuzzy logic and neural network. Fuzzy a...
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In order to improve tracking ability, an adaptive fusion algorithm based on adaptive neuro-fuzzy inference system (ANFIS) for radar/ infrared system is proposed, which combines the merits of fuzzy logic and neural network. Fuzzy adaptive fusion algorithm is a powerful tool to make the actual value of the residual covariance consistent with its theoretical value. To overcome the defect of the dependence on the knowledge of the process and measurement noise statistics of Kalman filter, neural network is introduced, which has the ability to learn from examples and extract the statistical properties of the examples during the training sessions. The fusion system mainly consists of Kalman filters, ANFIS sensor confidence estimators (ASCEs) based on contextual information (CI) theory, knowledge base (KB) and track-to-track fusion algorithms. Experimental data are implemented to train ASCEs to obtain sensor confidence degree. Simulation results show that the algorithm can effectively adjust the system to adapt contextual changes and has strong fusion capability in resisting uncertain information.
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The relationship between band gap and biaxial stress in wurtzite ZnO thin films has been investigated by side-inclination x-ray diffraction technique and optical absorbance spectrum as well as ab initio calculation. The experiment...
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The relationship between band gap and biaxial stress in wurtzite ZnO thin films has been investigated by side-inclination x-ray diffraction technique and optical absorbance spectrum as well as ab initio calculation. The experimental result shows that differing from other semiconductor thin films with hexagonal structure, such as GaN, the band gap of ZnO thin films increases with the increase in biaxial tensile stress. For explaining the difference, ab initio calculation is performed to simulate the relationship between band gap and biaxial stress of wurtzite ZnO and GaN. The calculated result indicates that the band gap of ZnO increases under biaxial tensile stress but GaN is opposite, supporting our experimental result. The band offset calculation shows that the conduction-band minimum (CBM) and the valence-band maximum (VBM) of ZnO and GaN offset to low energy under biaxial tensile stress. The VBM offset of ZnO is larger than the CBM, responsible for the increase in band gap. The VBM offset of GaN is smaller than the CBM, responsible for the decrease in band gap. The difference between ZnO and GaN is attributed to the strong p-d coupling in valence band of ZnO, but strong p-p coupling in valence band of GaN.
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An inverse radiation analysis is presented for determining the three-dimensional temperature field in an inhomogeneous, absorbing, emitting and anisotropically scattering media of known radiative properties from the knowledge of t...
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An inverse radiation analysis is presented for determining the three-dimensional temperature field in an inhomogeneous, absorbing, emitting and anisotropically scattering media of known radiative properties from the knowledge of the exit radiative energy received by charge-coupled device (CCD) cameras at boundary surfaces. The forward Monte Carlo method was employed to describe the radiative energy propagation. The inverse problem was formulated as an ill-posed matrix equation and solved by least square QR decomposition (LSQR) method. The measured data were simulated by adding random errors to the exact solution of the direct problem. The effects of measurement errors, combinations of CCD cameras, concentration distributions of particles, and coefficient fluctuating errors on the accuracy of the inverse problem were investigated. The results show that the three-dimensional temperature field can be estimated accurately, even for the noisy data.
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The electromagnetic field (both E and B fields) is calculated for a solenoidal inductively coupled plasma (ICP) discharge. The model is based on two-dimensional cylindrical coordinates, and the finite difference method is used for...
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The electromagnetic field (both E and B fields) is calculated for a solenoidal inductively coupled plasma (ICP) discharge. The model is based on two-dimensional cylindrical coordinates, and the finite difference method is used for solving Maxwell equations in both the radial and axial directions. Through one-turn coil measurements, assuming that the electrical conductivity has a constant value in each cross section of the discharge tube, the calculated E and B fields rise sharply near the tube wall. The nonuniform radial distributions imply that the skin effect plays a significant role in the energy balance of the stable ICP. Damped distributions in the axial direction show that the magnetic flux gradually dissipates into the surrounding space. A finite difference calculation allows prediction of the electrical conductivity and plasma permeability, and the induction coil voltage and plasma current can be calculated, which are verified for correctness.
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Recently, high-transition-temperature (high-T_c) superconductivity was discovered in the iron pnictide RFeAsO_(1-x)F_x (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase...
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Recently, high-transition-temperature (high-T_c) superconductivity was discovered in the iron pnictide RFeAsO_(1-x)F_x (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO_(1-x)F_x as the system is tuned from a semimetal to a high-T_c superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x = 0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x > 0.06, resulting in an electronic phase diagram remarkably similar to that of the high-T_c copper oxides. Comparison of the structural evolution of CeFeAsO_(1-x)F_x with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-T_c superconductivity in these Fe pnictides.
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Thermal transport mechanism in a ferroelectricity-magnetism-coexisting system, hexagonal YMnO_3 is investigated. In addition to the acoustic phonon contribution, heat transport induced by optical phonon is taken into account to ex...
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Thermal transport mechanism in a ferroelectricity-magnetism-coexisting system, hexagonal YMnO_3 is investigated. In addition to the acoustic phonon contribution, heat transport induced by optical phonon is taken into account to explain the excess thermal conductivity above T_N. Magnetoelectric coupling effect on both acoustic and optical phonons is embodied by change in Debye and Einstein temperatures, respectively. Magnon-phonon resonant interaction is considered as one of the scattering mechanisms that correct relaxation time of acoustic phonon thermal conductivity. Our theoretical fitting is in good agreement with the experimental data.
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Resonance properties or a rectangular resonant cavity filled with an anisotropic metamaterial bilayer are investigated. Different from the isotropic case and the one-dimensional resonator, the resonance properties in such a cavity...
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Resonance properties or a rectangular resonant cavity filled with an anisotropic metamaterial bilayer are investigated. Different from the isotropic case and the one-dimensional resonator, the resonance properties in such a cavity are closely related to the dispersion relation of the anisotropic medium. Three cases including six subcases of different combinations of metamaterials are discussed and it is found that subwavelength resonance modes may occur in all subcases. Particularly, the relation between resonance modes and the transverse cavity width is investigated, and calculated results show that there are infinite subwavelength resonance modes as the transverse cavity width approaches zero. Requirements of the material and geometry parameters to construct a subwavelength resonant cavity are revealed by theoretical analysis, which demonstrates that this kind of subwavelength resonator brings more design flexibility and tolerance.
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A noncollinear-ferromagnetic spin-glass-like state was observed in Tb_(55)Co_(20)Al_(25) bulk metallic glass due to the strong random magnetic anisotropy. Associated with this behavior, we observed a comparatively large magnetic e...
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A noncollinear-ferromagnetic spin-glass-like state was observed in Tb_(55)Co_(20)Al_(25) bulk metallic glass due to the strong random magnetic anisotropy. Associated with this behavior, we observed a comparatively large magnetic entropy change (△S_m is 9.75 J K~(-1) kg~(-1)) in a field change of 7T and a correspondingly high value of the magnetic refrigeration capacity (RC is 540 J kg~(-1)) with almost no hysteresis loss in the vicinity of the so-called Curie temperature. This opens the possibility of using this material for magnetic cooling purposes.
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A series of Co_x(Alq_3)_(1-x) granular films were prepared using the co-evaporating technique. HRTEM images show typical characteristics of granular films with the average size of 2-5 nm. It shows a gradual change from superparama...
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A series of Co_x(Alq_3)_(1-x) granular films were prepared using the co-evaporating technique. HRTEM images show typical characteristics of granular films with the average size of 2-5 nm. It shows a gradual change from superparamagnetism to ferromagnetism with the rise of x. Negative magnetoresistance (MR) was observed, reaching -5.31% in x = 0.44 sample at 30K under the field of 10kOe. The concentration dependence of MR and resistivity is also investigated. The inter-particle tunneling is believed to account for the negative MR effect.
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