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21.
In this study, the mechanical buckling of functionally graded material cylindrical shell that is embedded in an outer elastic medium and subjected to combined axial and radial compressive loads is investigated. The material properties are assumed to vary smoothly through the shell thickness according to a power law distribution of the volume fraction of constituent materials. Theoretical formulations are presented based on a higher-order shear deformation shell theory (HSDT) considering the transverse shear strains. Using the nonlinear strain–displacement relations of FGMs cylindrical shells, the governing equations are derived. The elastic foundation is modelled by two parameters Pasternak model, which is obtained by adding a shear layer to the Winkler model. The boundary condition is considered to be simply-supported. The novelty of the present work is to achieve the closed-form solutions for the critical mechanical buckling loads of the FGM cylindrical shells surrounded by elastic medium. The effects of shell geometry, the volume fraction exponent, and the foundation parameters on the critical buckling load are investigated. The numerical results reveal that the elastic foundation has significant effect on the critical buckling load. 相似文献
22.
A thermal buckling analysis is presented for functionally graded rectangular plates that are integrated with surface-bonded piezoelectric actuators and are subjected to the combined action of thermal load and constant applied actuator voltage. The temperature-dependent material properties of the functionally graded plate are assumed to vary as a power form of the thickness coordinate. Derivation of the equations is based on the third-order shear deformation plate theory. Results for the critical buckling temperatures are obtained in closed-form solution, which are convenient to be used in engineering design applications. The effects of the applied actuator voltage, plate geometry, and volume fraction exponent of the functionally graded material on the buckling temperature are investigated. 相似文献
23.
A new setup for spatially resolved laser-induced breakdown spectroscopy (SR-LIBS) is used for the first time to analyze methane-air diffusion flames. Using this configuration, background continuum emission is reduced, signal-to-background noise ratio is increased up to eight times, and spatial resolution is enhanced. The local equivalence ratio is also quantitatively estimated and the width of the secondary combustion region at a specified height above the burner is determined for two different methane flow rates. Furthermore, the threshold energy for spark formation is measured for regions inside and outside the flame. The results show that threshold energy is larger at the secondary combustion region, near the border of the flame, than inside the flame. 相似文献
24.
BACKGROUND and OBJECTIVE: The purpose of this study was to compare morphologic changes following C02 laser or manual curette treatment of calculus-ladened tooth root surfaces. STUDY DESIGN/MATERIALS and METHODS: Laser treatment consisted of repeated single passes with a 6 Watt focused beam at 20 pulses per second, a pulse length of 0.01 second, and a manufacturer's laser efficiency rating of 86% (i.e., the amount of total power delivered through the aperture). The rate of beam passage over the target surface was controlled at 4 mm/second using an 0.8 mm diameter tip. The calculated energy density was 240 J/cm2 for each pass of the beam. Scaled and root planed surfaces were treated with a standardized force of 600 grams using new curettes. Specimens were evaluated by scanning electron microscopy. RESULTS: Laser-induced surface changes included charring, meltdown and resolidification of calculus mineral, and ablation of microbial plaque. Laser-treated specimens also exhibited residual calculus and microbial plaque deposits in areas directly adjacent to the beam path. Scaled and root planed surfaces featured smooth and/or scale like smear layers and islands of residual calculus and microbial plaque. CONCLUSIONS: The rough surface topography resulting from laser treatment and residual calculus and microbial plaque deposits indicates that C02 laser treatment of exposed root surfaces is, at best, an adjunct to traditional methods of therapy. 相似文献
25.
Analysis and measurement of a broadband spiral antenna 总被引:1,自引:0,他引:1
A broadband spiral antenna (2 to 18 GHz) is modeled using the FDTD method. The inner turn of the antenna is an Archimedean spiral, while the outer turn is an Archimedean spiral with a zigzag shape. The current-density distribution along the spiral arms is first presented in the time domain, interestingly manifesting the impulse current propagation from the feed point to the outer end of the spiral arms. The performance of the broadband spiral antenna is also measured in an anechoic chamber. The simulated and measured results showed the sensitivity of the axial ratio and radiation pattern to the current distribution. The simulated linear gain, radiation patterns, and axial ratios agree well with the measured data over all of the frequency range from 2 to 18 GHz. 相似文献
26.
M. N. Afsar Kenneth J. Button S. H. Groves 《Journal of Infrared, Millimeter and Terahertz Waves》1983,4(1):127-134
The hydrogen like 1s → 2p (m=?1,0,+1) transitions of two donors have been observed in high intensity magnetic fields up to 8.5T. The m=?1 transitions ocurred between 2 cm?1 and 25 cm?1. The signature curves for donors in ternary semiconductor In0.53Ga0.47As have now been established. 相似文献
27.
Ultimate method for unambiguous identification of all donors in epitaxial GaAs and related compounds
M. N. Afsar Kenneth J. Button A. Y. Cho H. Morkoc 《Journal of Infrared, Millimeter and Terahertz Waves》1981,2(6):1113-1121
When epitaxial GaAs is grown by the method of molecular beam epitaxy (mbe) it would be p-type unless it is intentionally doped lightly during growth by using a particular substitutional donor atom. We have chosen the tin donor in this case to render the specimen n-type. Then the conventional far infrared photoconductivity technique is used to observe the 1s to 2p transition of the electron of the tin donor. The identity of the donor, the energy of the quantum transition as a function of applied magnetic field intensity, and the line shape characteristics of that particular donor then become unquestionable. 相似文献
28.
M. N. Afsar Kenneth J. Button Gary L. McCoy 《Journal of Infrared, Millimeter and Terahertz Waves》1980,1(1):145-158
The chemical identity of unintentional contaminants in ultra-high purity eipitaxial GaAs and related semiconductor crystals can be distinguished by submillimeter wave magneto-spectroscopy at low temperature. An improved method of identifying hydrogen-like donors such as sulfur, silicon, selenium and germanium has been developed for the purpose of correcting some mistaken identifications that have been published during the past ten years. The new method requires the development of an experimental “signature curve” for each contaminant by measuring the energy of its 1s to 2p (m=?1) transition at several values of magnetic field intensity. The energy of this transition at a given magnetic field intensity is different depending upon the nucleus to which the electron is bound in the 1s state. The validity of the improved method was tested by means of transmutation doping. 相似文献
29.
M. N. Afsar Kenneth J. Button 《Journal of Infrared, Millimeter and Terahertz Waves》1982,3(3):319-329
These two promising millimeter wave materials were found to exhibit one order of magnitude higher absorption coefficient than the common low-loss ceramics such as alumina, fused silica and beryllia. A modular, polarizing, dispersive Fourier transform spectrometer capable of operating over the range 5 mm to 0.004 mm was used to provide a continuous spectrum of the refractive index and absorption coefficient to an accuracy of five decimal places and less than 1 percent, respectively. 相似文献
30.
There exist only a few papers in the literature which target the problem of “proposing a secure designated server identity-based encryption with keyword search scheme.” In this paper, we prove that they all suffer from security issues, and therefore, this challenging problem still remains open. 相似文献