Room-temperature Configurations Research Articles

Natural vibration of unsymmetric cross-ply laminates

This study considers the linear vibration characteristics of square [ 0 n / 90 n ] T laminates relative to their room-temperature static equilibrium configurations. A Rayleigh–Ritz approach combined with Hamilton's principle is used to provide approximate solutions to this vibration problem. The vibration mode shapes are assumed to have the same spatial dependence as used in past investigations to study the room-temperature configurations of these laminates, and are thus assumed to be perturbations on the static equilibrium configurations. Hamilton's principle then results in the so-called zero- and first-order equations. The zero-order equations lead to the classic static equilibrium results of past investigations, presented here in nondimensional form with analytical solutions at the bifurcation point. The first-order equations, combined with zero-order results, lead to the vibration characteristics for each zero-order static configuration. Interest centers on the lowest natural frequency and the associated mode shape for laminates clamped at their midpoints, with special attention as to how these vibration characteristics depend on the laminate side-length-to-thickness ratio. With an imaginary-valued frequency, the static saddle configuration for side-length-to-thickness ratios larger than the critical value is correctly assessed as unstable. A finite element model is also used to study the vibration characteristics and to compare with the findings for the developed analysis. The qualitative comparisons between the developed analysis and the finite element model are generally good, and the quantitative comparisons are also satisfactory.

Synthesis and Characterization of Ru(II) Tris(1,10-phenanthroline)-Electron Acceptor Dyads Incorporating the 4-Benzoyl-N-methylpyridinium Cation or N-Benzyl-N‘-methyl Viologen. Improving the Dynamic Range, Sensitivity, and Response Time of Sol−Gel-Based Optical Oxygen Sensors

The title compounds were synthesized by Sonogashira coupling reactions of appropriate Ru(II) complexes with the electron acceptors. Characterization was conducted in solution and in frozen matrixes. Finally, the title compounds were evaluated as dopants of sol−gel materials. It was found that the intramolecular quenching efficiency of 4-benzoyl-N-methylpyridinium cation in solution depends on the solvent: photoluminescence is quenched completely in CH3CN, but not in methanol or ethanol. On the other hand, intramolecular emission quenching by 4-benzyl-N-methyl viologen is complete in all solvents. The difference between the two quenchers is traced electrochemically to the solvation of the 4-benzoyl-N-methylpyridiniums by alcohol. In frozen matrixes or adsorbed on the surfaces of silica aerogel, both Ru(II) complex/electron acceptor dyads of this study are photoluminescent, and the absence of quenching has been traced to the environmental rigidity. When doped aerogels are cooled at 77 K, the emission intensity increases by ∼4×, and the spectra shift to the blue, analogous to what is observed with Ru(II) complexes in solutions undergoing fluid-to-rigid transition. However, in contrast to frozen solutions, the luminescent moieties in the bulk of aerogels kept at low temperatures are still accessible to gas-phase quenchers diffusing through the mesopores, leading to more sensitive platforms for sensors than other room-temperature configurations. Thus, the photoluminescence of our Ru(II) complex dyads adsorbed on aerogel is quenchable by O2 both at room temperature and at 77 K. Furthermore, it was also found that O2 modulates the photoluminescence of aerogels doped with 4-benzoyl-N-methylpyridinium -based dyads over a wider dynamic range compared with aerogels doped with either our viologen-based dyads or with Ru(II) tris(1,10-phenanthroline) itself.

In situ observation of domains in 0.9Pb(Zn1/3 Nb2/3)O3 − 0.1PbTiO3 single crystals

Domains in 0.9Pb(Zn 1/3 Nb2/3)O3 − 0.1 PbTiO3 or “PZN-PT single crystals under the application of electric field were investigated with an optical microscope. The dynamic response of the domains was studied under an electric field on PZNPT crystals is reported. In this study, electric field applied along [001]. The domain formation with the changing temperature showed the successive phase transitions from cubic to tetragonal and then to rhombohedral with decreasing temperature. The room temperature configuration showed the co-existence of both rhombohedral and tetragonal domains. Under the given experimental conditions we found that a single domain state could be induced only in the tetragonal state. Even though the temperature was lowered to −100°C, complete transformation to the rhombohedral state was not observed.

A Study on the Room-Temperature Curvature Shapes of Unsymmetric Laminates Including Slippage Effects

The room-temperature shapes of cured unsymmetric composite laminates have out-of-plane warping after autoclave processing. In addition, they exhibit two stable room-temperature configurations due to snap-through phenomena when the side length of laminates exceed a critical value. The cured shape of unsymmetric laminates are influenced by many factors. Experiments show that the effect of tool-plate cannot be ignored and has significant influence on the cured shape. This study examines slippage effects resulting from the interaction between the laminates and the tool-plate which are ignored in the previous researches. By introducing a dimensionless slippage coefficient and correlating the corresponding value with experimental results, the influence of processing parameters is investigated. Modeling is extended to predict curvatures of general lamination layup configurations.

Synthesis and Characterization of Ni 3S 2 Single Crystals

The synthesis and growth of single crystals of Ni 3S 2 are described. Structural information is provided on the room-temperature configuration of this compound. Measurements of electrical resistivity, magnetic susceptibility, and heat capacity below room temperature have been carried out and are briefly discussed. The material may be classified as a good metallic conductor.

Structure, energetics, and low-temperature behaviour of the Au(110) reconstructed surface

The structure and energetics of Au(110) is studied by means of a well-tested many-body force model. Molecular dynamics is used to search the lowest energy configuration at T =0, as well as the mean room temperature configuration. We find that a contracted and distorted (1×2) missing row geometry has the lowest surface energy, in agreement with experiment. However also the (1×3), (1×4), etc., missing row models are very close in energy. The low temperature properties of the surface are studied with molecular dynamics, including the Ising-like disappearance of a sliding distortion below room temperature.

Calculations of the Room-Temperature Shapes of Unsymmetric Laminatestwo

The cured shape of unsymmetric laminates do not always conform to the predictions of classical lamination theory. Classical lamination theory predicts the room-temperature shapes of all unsymmetric laminates to be a saddle. Experimental observations, however, indicate some unsymmetric laminates have cylindrical room-temperature shapes. In addition, some unsymmetric laminates exhibit two stable room-temperature configurations, both cylindircal. This paper presents a theory which explains these characteristics. The theory is based on an extension of classical lamination theory which accounts for geometric nonlinearities. A Rayleigh-Ritz approach to minimizing the total potential energy is used to obtain quantitative information regarding the room-temperature shapes of square T300/5208 [02/902] T and [04/904] T graphite-epoxy laminates. It is shown that, depending on the thickness of the laminate and the length of the side of the square, the saddle shape configuration is actually unstable. For values of length and thickness that render the saddle shape unstable, it is shown that two stable cylindrical shapes exist. The predictions of the theory are compared with existing experimental data.