Sensitization and Intra-molecular Energy Transfer of Eu^(3+) by Tb^(3+) in Eu-Tb Binuclear Complexes/PMMA

A series of Eu0.5Tb0.5（TTA）3Phen/PMMA （TTA=thenoyltrifluoroacetone,Phen=phenanthroline） and Eu0.5Tb0.5（TTA）3Dipy/PMMA （Dipy=2,2’-dipyridyl） were prepared by in-situ polymerization.The structures of the composites were characterized by IR spectra and electron spectrum.Photoluminescence properties were investigated by UV-Vis spectra and fluorescence spectra.Meanwhile,the energy transfer models were set up.The results indicated that polymer parts were attached with the rare-earth molecular parts in the composite luminescent materials.Eu0.5Tb0.5（TTA）3Phen/PMMA and Eu0.5Tb0.5（TTA）3Dipy/PMMA emitted mostly characteristic fluorescence of europium ion and intense red fluorescence with peak wavelength at 611.8 nm and bandwidth of 10.4 nm under UV excitation at 365 nm.Fluorescence intensity of Eu0.5Tb0.5（TTA）3Phen/PMMA was found to be influenced with the content of MMA.The fluorescence emission of europium ions was greatly sensitized by terbium ions and the enhancement of red emission was most likely due to the energy transfer enhancement from Tb3＋ to Eu3＋.

Theoretical Calculation about the High Energy Density Molecules of Nitrate Ester Substitution Derivatives of Prismane

The nitrate ester substitution derivatives of prismane were studied at the B3LYP/6-311G＊＊ level. The sublimation enthalpies and heats of formation in gas phase and solid state were calculated. The detonation performances were also predicted by using the famous Kamlet-Jacbos equation. Our calculated results show that introducing nitrate ester group into prismane is helpful to enhance its detonation properties. Stabilities were evaluated through the bond dissociation energies, bond order, characteristic heights（H50） and band gap calculations. The trigger bonds in the pyrolysis process of prismane derivatives were confirmed as O–ON2 bond. The BDEs of all compounds were large, so these prismane derivatives have excellent stability consistent with the results of H50 and band gap.

Sustainability of Wind Energy under Changing Wind Regimes—A Case Study

A method was introduced to assess the sustainability of energy production over the lifetime (~20 y) of wind turbines. Community Earth System Model simulations were downscaled for the tourist seasons (mid-May to mid-September) of 2006 to 2012 (CESM-P1) and 2026 to 2032 (CESM-P2) to obtain a reference and projected wind-speed climatology, respectively. The wind speeds served to calculate the potential power output and capacity factors of seven turbine types. CESM-P1 wind-speed climatology, power output, and capacity factors were compared to those derived from wind speeds obtained by numerical weather forecasts for reference to known standard to wind-farm managers. Juneau, Alaska served as a virtual testbed as this region is known to experience changes in wind speeds in response to the Pacific Decadal Oscillation. CESM-P2 suggested about 2% decrease for wind speeds between the speeds at cut-in and rated power, and about 8% - 10% decrease in potential wind-power output. This means that in regions of decadal climate variations, the sustainability of wind-energy production should be part of the decision-making process. The study demonstrated that using mean values of wind-speeds can provide qualitative knowledge about decreases/increases in potential energy production, but not about the magnitude. Using the total individual wind-speed data of all seasons provided the same amount of total power output than summing up the power outputs of individual seasons. The main advantage of calculating individual seasonal wind-power outputs, however, is that it theoretically permits assessment of interannual variability in power output and capacity factors. Comparison to a known standard may help stakeholders in understanding of uncertainty and interpretation of projected changes.

THE LAYOUT OPTIMIZATION OF STIFFENERS FOR PLATE-SHELL STRUCTURES

The plate-shell structures with stiffeners are widely used in a broad range of engineering structures. This study presents the layout optimization of stiffeners. The minimum weight of stiffeners is taken as the objective function with the global stiffness constraint. In the layout optimization, the stiffeners should be placed at the locations with high strain energy/or stress. Conversely, elements of stiffeners with a small strain energy/or stress are considered to be used inefficiently and can be removed. Thus, to identify the element efficiency so that most inefficiently used elements of stiffeners can be removed, the element sensitivity of the strain energy of stiffeners is introduced, and a search criterion for locations of stiffeners is presented. The layout optimization approach is given for determining which elements of the stiffeners need to be kept or removed. In each iterative design, a high efficiency reanalysis approach is used to reduce the computational effort. The present approach is implemented for the layout optimization of stiffeners for a bunker loaded by the hydrostatic pressure. The numerical results show that the present approach is effective for dealing with layout optimization of stiffeners for plate-shell structures.

Dielectric Properties of Bi_4Ti_3O_(12) Ceramics by Impedance Spectroscopic Method

Various lead-free ceramics have been investigated in search for new high-temperature dielectrics. In particular, Bi_4Ti_3O_（12） is a type of ferroelectric ceramics, which is supposed to replace leadcontaining ceramics for its outstanding dielectric properties in the near future. Ferroelectric ceramics of Bi_4Ti_3O_（12） made by conventional mixed oxide route have been studied by impedance spectroscopy in a wide range of temperature. X-ray diffraction patterns show that Bi_4Ti_3O_（12） ceramics are a single-phase of ferroelectric Bi-layered perovskite structure whether it is calcined at 800 ℃ or after sintering production. This study focused on the effect of the grain size on the electric properties of BIT ceramics. The BIT ceramics with different grain sizes were prepared at different sintering temperatures. Grain becomes coarser with the sintering temperature increasing by 50 ℃, relative permittivity and dielectric loss also change a lot. When sintered at 1 100 ℃, r values peak can reach 205.40 at a frequency of 100 k Hz, the minimum dielectric losses of four different frequencies make no difference, all close to 0.027. The values of Ea range from 0.52 to 0.68 e V. The dielectric properties of the sample sintered at 1 100 ℃ are relatively better than those of the other samples by analyzing the relationship of the grain, the internal stresses, the homogeneity and the dielectric properties. SEM can better explain the results of the dielectric spectrum at different sintering temperatures. The results show that Bi_4Ti_3O_（12） ceramics are a kind of dielectrics. Thus, Bi_4Ti_3O_（12） can be used in high-temperature capacitors and microwave ceramics.

Cell Wall Buckling Mediated Energy Absorption in Lotus-type Porous Copper

The energy absorption characteristics of the lotus-type porous coppers at the strain rate of 10-3 s-1 to N2400 s 1 were systematically investigated. Depending on the relative density and loading rate, the energy absorption capability of the tested samples varied from -20 to -85 MJ m-1, while the energy absorption efficiency fluctuated around N0.6. An energy absorption efficiency curve based approach was proposed for unambiguous identification of the plateau regime, which gave an extension of -0.50 strain range for the presently investigated porous coppers. With detailed observations of cell wall morphologies at various deformation stages, it was suggested that buckling of cell wails was the dominant mechanism mediat- ing the energy absorption in lotus-type porous coppers.

Node shift method for stiffness-based optimization of single-layer reticulated shells

This paper presents a node shift method to find the optimal distribution of nodes in single-layer reticulated shells. The optimization process searches for the minimum strain energy configuration and this leads to reduced sensitivity in initial imper- fections. Strain energy sensitivity numbers are derived for free shift and restricted shift where nodes can move freely in the 3D space or have to move within a predefmed surface respectively. Numerical examples demonstrate the efficiency of the proposed approach. It was found that optimized structures achieve higher ultimate load and are less sensitive to imperfections than the initial structure. The configuration of the final structure is closely related to factors like the initial structural configuration, spatial conditions, etc. Based on different initial conditions, architects can be provided with diverse reasonable structures. Furthermore, by amending the defined shapes and nodal distributions, it is possible to improve the mechanical behavior of the structures.