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Abstract Trusses with geometric and loading symmetries have been used in many structures to reduce the complexity of the design. Slight asymmetries in geometry and in loading could lead to bifurcation in the structural response. Failure of such structures still occur occasionally causing major damage to the property and to the human lives. A fully nonlinear structural analysis is expected to detect such symmetry breaking bifurcations. In this paper, we conducted the bifurcation analysis of a two-bar truss and a shallow arch structure with seven bars. Two program packages Gesa and Ansys based on finite elements method have been used to detect the symmetry breaking bifurcation points. However, unlike typical bifurcation analysis packages they cannot detect the bifurcation point without inserting a small perturbation in the initial geometry or the loading of the structure. Such a bifurcation can be easily missed in finite element-based analysis. The theoretical analysis reveals that the bifurcation leads to a much lower critical load in the presence of small asymmetry compared to the symmetric case. The results are verified by using Gesa program in Matlab for fully nonlinear analysis and with results by using Ansys commercial program. The two structural examples serve to illustrate the limitations of widely used finite element analysis packages for nonlinear bifurcation analysis. Highlights • Applied commercial finite element method packages for bifurcation analysis. • Demonstrated capabilities and limitations of commercial packages. • Obtained analytical results on symmetry breaking bifurcations of two structures. • Demonstrated the agreement among theoretical and numerical results. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, by Kirchhoff transformation of the temperature variable, the temperature dependence of thermal conductivity is eliminated, thereby simplifying the 3-dimensional heat conduction equation. Through Hadamard Factorization Theorem, transfer function relating the front and back surface temperature as infinite product of polynomial is established. The inverse Laplace transform of the polynomial provide the relationship for every mode in the time domain. The front surface temperature is revealed through iterative time domain operations from the data on the back surface. Seven points for smoothing and third order polynomial in derivative calculation were used in Savitzky–Golay (S–G) method. The comparison between direct solution, Conjugate Gradient Method (CGM) and DCT/Laplace transform solutions are given. Root Mean Square (RMS) of the errors at different time steps for DCT/Laplace solution and CGM method are also presented. [Copyright &y& Elsevier]

Abstract: We present a new method of solving the three-dimensional inverse heat conduction (3D IHC) problem with the special geometry of a thin sheet. The 3D heat equation is first simplified to a 1D equation through modal expansions. Through a Laplace transform, algebraic relationships are obtained that express the front surface temperature and heat flux in terms of those same thermal quantities on the back surface. We expand the transfer functions as infinite products of simple polynomials using the Hadamard Factorization Theorem. The straightforward inverse Laplace transforms of these simple polynomials lead to relationships for each mode in the time domain. The time domain operations are implemented through iterative procedures to calculate the front surface quantities from the data on the back surface. The iterative procedures require numerical differentiation of noisy sensor data, which is accomplished by the Savitzky–Golay method. To handle the case when part of the back surface is not accessible to sensors, we used the least squares fit to obtain the modal temperature from the sensor data. The results from the proposed method are compared with an analytical solution and with the numerical solution of a 3D heat conduction problem with a constant net heat flux distribution on the front surface. [Copyright &y& Elsevier]

Abstract: Laplace transform is used to solve the problem of heat conduction over a finite slab. The temperature and heat flux on the two surfaces of a slab are related by the transfer functions. These relationships can be used to calculate the front surface heat input (temperature and heat flux) from the back surface measurements (temperature and/or heat flux) when the front surface measurements are not feasible to obtain. This paper demonstrates that the front surface inputs can be obtained from the sensor data without resorting to inverse Laplace transform. Through Hadamard Factorization Theorem, the transfer functions are represented as infinite products of simple polynomials. Consequently, the relationships between the front and back surfaces are translated to the time-domain without inverse Laplace transforms. These time-domain relationships are used to obtain approximate solutions through iterative procedures. We select a numerical method that can smooth the data to filter out noise and at the same time obtain the time derivatives of the data. The smoothed data and time derivatives are then used to calculate the front surface inputs. [ABSTRACT FROM AUTHOR]

Abstract: Effects of CdCl2 post-growth treatments and annealing under different conditions on the surface and interface properties of CdS/SnO2/glass heterostructure were studied. CdS thin films were grown on SnO2-coated glass substrates for CdS/CdTe heterojunction solar cells by the solution growth technique. It was found that CdCl2 post-growth treatments and annealing enhanced the CdS-related XRD peaks, narrowed the CdS characteristic Raman bands, removed or depressed the disorder related Raman features, and improved the CdS film crystalline quality significantly, which are advantageous to the application in solar cells as a window layer material. [Copyright &y& Elsevier]

Abstract: Laplace transform is used to solve the problem of heat conduction over a finite slab. The transfer functions relating the temperature and heat flux on the front and back surfaces of the finite slab are developed. Although there are many competing methods for constructing the inverse Laplace transform, we use polynomial approximation of the transfer function. Therefore, transient solutions for given boundary conditions are easily obtained using SIMULINK. This process is much simpler than other numerical solution methods for the heat equation. Most importantly, our method of solution allows us to obtain, in real-time, the front surface temperature and heat flux based on the thermodynamic measurements on the back surface. We also demonstrate the feasibility of reconstructing the front surface temperature when sensor noise is incorporated to the back surface measurements. [Copyright &y& Elsevier]

Abstract: The effect of temperature and excitation power on the characteristics of InGaN/GaN single quantum well (SQW) and multiple quantum well (MQW) light-emitting diodes (LED) has been investigated in-depth over a broad range of temperatures from 9 to 300K. It was found that the device with a stair-shaped SQW structure exhibited stronger localization effect, as well as had higher internal quantum efficiency than that of the conventional MQW and SQW LEDs. This is interpreted as due to the stair-shaped SQW configuration, which offered a large contribution to the exciton capturing. The adoption of an appropriate heterostructure in active region allows the achievement of improved LED performance. With increasing the excitation power intensity, QW photoluminescence (PL) line broadening and emission peak blue shifts were observed, which are assumed to be caused by the disordering formed in the In-rich heterostructures of QW ensembles. We expect that distinct degree of carrier localization occurs in these samples. [Copyright &y& Elsevier]

Highly textured lead lanthanum titanate (Pb1-xLax)TiO3 (PLT) thin films have been grown on fused quartz substrates by metalorganic chemical deposition (MOCVD). A series of PLT with different x between 0 and 0.32 were prepared and studied by Raman scattering. Raman spectra, measured at 300 K and 80 K, showed the features from the PLT film and quartz substrate. By using a “difference Raman” technique, more PLT modes are shown. The variations of the PLT Raman modes with the La composition and the measurement temperature are studied, and related physical phenomena and problems are discussed. [Copyright &y& Elsevier]

New phonon-assisted defect features are observed using photoluminescence (PL) and Raman scattering spectroscopy on 3C-SiC/Si(1 0 0) films grown by chemical vapor deposition (CVD) technique. The ultraviolet excitation room-temperature (RT) PL-Raman spectra show a luminescence band near 2.3 eV due to RT recombination over the 3C-SiC indirect band gap. In addition to the strong Raman lines characteristic of Si substrate and 3C-SiC we also observed weaker impurity modes near 620, 743 and 833 cm-1. These frequencies are compared with the results of Green''s function simulations of impurity modes with plausible defect structures to best support the observed Raman features as well as modes of some prototypical defect center. [Copyright &y& Elsevier]

Zn-doped InGaN thin films were deposited on GaN/sapphire by metalorganic chemical vapor deposition, and studied by a combination of high-resolution X-ray diffraction (HR-XRD), micro-photoluminescence (PL) and secondary ion mass spectrometry (SIMS). Indium phase separation is studied comparatively. HR-XRD exhibits a GaN band and a single band from InGaN for samples without phase separation, but two InGaN bands corresponding to different x(In) for samples with phase separation. PL excitation power dependence measurements reveal 2 sets of InGaN PL emissions for samples with phase separation, but only 1 set for samples without phase separation. SIMS data showed that phase separated InGaN:Zn films possess a high Zn concentration near the InGaN–GaN interface and non-uniform distributions of In and Zn contents, which are in contrast with data from InGaN:Zn films with no In-phase separation. [Copyright &y& Elsevier]