Thermoluminescence study of persistent luminescence materials: Eu2+- and R3+-doped calcium aluminates, CaAl2O4:Eu2+,R3+

Thermoluminescence properties of the Eu2+-, R3+-doped calcium aluminate materials, CaAl2O4:Eu2+,R3+, were studied above room temperature. The trap depths were estimated with the aid of the preheating and initial rise methods. The seemingly simple glow curve of CaAl2O4:Eu2+ peaking at ca. 80 degrees C was found to correspond to several traps. The Nd3+ and Tm3+ ions, which enhance most the intensity of the high-temperature TL peaks, form the most suitable traps for intense and long-lasting persistent luminescence, too. The location of the 4f and 5d ground levels of the R3+ and R2+ ions were deduced in relation to the band structure of CaAl2O4. No clear correlation was found between the trap depths and the R3+ or R2+ level locations. The traps may thus involve more complex mechanisms than the simple charge transfer to (or from) the R3+ ions. A new persistent luminescence mechanism presented is based on the photoionization of the electrons from Eu2+ to the conduction band followed by the electron trapping to an oxygen vacancy, which is aggregated with a calcium vacancy and a R3+ ion. The migration of the electron from one trap to another and also to the aggregated R3+ ion forming R2+ (or R3+-e-) is then occurring. The reverse process of a release of the electron from traps to Eu2+ will produce the persistent luminescence. The ability of the R3+ ions to trap electrons is probably based on the different reduction potentials and size of the R3+ ions. Hole trapping to a calcium vacancy and/or the R3+ ion may also occur. The mechanism presented can also explain why Na+, Sm3+, and Yb3+ suppress the persistent luminescence.     

Stark effect and generalized Bloch-Siegert shift in a strongly driven two-level system

A superconducting qubit was driven in an ultrastrong fashion by an oscillatory microwave field, which was created by coupling via the nonlinear Josephson energy. The observed Stark shifts of the "atomic" levels are so pronounced that corrections even beyond the lowest-order Bloch-Siegert shift are needed to properly explain the measurements. The quasienergies of the dressed two-level system were probed by resonant absorption via a cavity, and the results are in agreement with a calculation based on the Floquet approach.     

Measurement of a linkage among environmental,operational, and financial performance in Japanese manufacturing firms: A use of Data Envelopment Analysis with strong complementary slackness condition

This study investigates a linkage among environmental, operational and financial performance in Japanese manufacturing industry. All manufacturing firms examined in this study are listed in Tokyo stock exchange market. We use DEA (Data Envelopment Analysis) as an evaluation methodology. This study finds that large firms have managerial capabilities to improve their operational and environmental performance. The improvement leads to the enhancement of their financial performance. However, we cannot find such a business linkage in small and medium-sized firms. They improve their operational performance and then direct themselves toward the improvement of their environmental performance. Their environmental performance is, not the first priority, the second priority for the small and medium-sized firms even though Japanese government is currently making a policy pressure on all manufacturing firms to pay attention to various environmental issues related to the global warming and climate change. The environmental protection policy is effective on only large Japanese manufacturing firms that have technological and financial capabilities for environmental protection.     

DTI segmentation by statistical surface evolution

We address the problem of the segmentation of cerebral white matter structures from diffusion tensor images (DTI). A DTI produces, from a set of diffusion-weighted MR images, tensor-valued images where each voxel is assigned with a 3 x 3 symmetric, positive-definite matrix. This second order tensor is simply the covariance matrix of a local Gaussian process, with zero-mean, modeling the average motion of water molecules. As we will show in this paper, the definition of a dissimilarity measure and statistics between such quantities is a nontrivial task which must be tackled carefully. We claim and demonstrate that, by using the theoretically well-founded differential geometrical properties of the manifold of multivariate normal distributions, it is possible to improve the quality of the segmentation results obtained with other dissimilarity measures such as the Euclidean distance or the Kullback-Leibler divergence. The main goal of this paper is to prove that the choice of the probability metric, i.e., the dissimilarity measure, has a deep impact on the tensor statistics and, hence, on the achieved results. We introduce a variational formulation, in the level-set framework, to estimate the optimal segmentation of a DTI according to the following hypothesis: Diffusion tensors exhibit a Gaussian distribution in the different partitions. We must also respect the geometric constraints imposed by the interfaces existing among the cerebral structures and detected by the gradient of the DTI. We show how to express all the statistical quantities for the different probability metrics. We validate and compare the results obtained on various synthetic data-sets, a biological rat spinal cord phantom and human brain DTIs.     

Multiscale modeling of submonolayer growth for Fe/Mo (110)

We use a multiscale approach to study a lattice-gas model of submonolayer growth of Fe/Mo (110) by Molecular Beam Epitaxy. To begin with, we construct a two-dimensional lattice-gas model of the Fe/Mo (110) system based on our first-principles calculations of the monomer diffusion barrier and adatom-adatom interactions. The model is investigated by equilibrium Monte Carlo (MC) simulations to compute the diffusion coefficients of Fe islands of different sizes. These diffusion coefficients are used as input to the coarse-grained kinetic rate equation (KRE) approach. We also evaluate effects of the range of Fe-Fe interaction, restriction of interaction to third nearest neighbors allowed to develop feasible atomistic kinetic Monte Carlo (KMC) model. We calculate time evolution of the island size distributions by both KMC and KRE methods and find good agreement between the two methods.     

Influence of Gd and Fe on crystallization of Al87Y5Ni8 amorphous alloy

Crystallization of amorphous Al-based alloys (Al-Y-Gd-Ni-Fe) was investigated by applying differential scanning calorimetry (DSC), X-ray diffraction (XRD) and high resolution electron microscopy (HREM). It was shown that the crystallization in the examined alloys proceeds in three stages (DSC maxima). The two first stages are attributed to formation of solid solution of fcc Al(RE) nanograins in amorphous matrix. In the third stage the precipitation of ternary compound Al₁₉Ni₅RE₃ of the orthorhombic Al₁₉Ni₅Gd₃-type structure was observed. A partial substitution of Ni by Fe causes a change of stoichiometry and crystal structure of the ternary compounds: Al₈TM₄RE (TM = Fe, Ni; RE = Y, Gd) of the tetragonal ThMn₁₂ (Al₈Mn₄Ce)-type structure. A partial replacing of Y atoms by Gd in the Al₈₇Y₅Ni₈ based alloy shifts the Al(RE) nanocrystallization to lower temperatures. In contrast to this a partial replacing of Ni by Fe shifts the nanocrystallization to higher temperatures.     

Planarized Phenyldithienylboranes: Effects of the Bridging Moieties and π-Extension on the Photophysical Properties and Lewis Acidity

Two kinds of planarized phenyldithienylboranes, which contain (CH₃)₂C- or CH₂-bridging moieties, were synthesized. The difference of the bridging moieties affects their packing structures and photophysical properties. In particular, the (CH₃)₂C-bridged derivative exhibits a large Stokes shift, unusual for such planarized compounds, that results from a large structural relaxation in the excited state. A series of π-extended derivatives was synthesized, among which a p-(diphenylamino)phenyl-substituted derivative shows large solvatochromism in the fluorescence spectra, while maintaining high quantum yields even in polar solvents. The Lewis acidity of the phenyldithienylborane derivatives was also assessed by titration with pyridine. The Lewis acidity of the boron center is affected not only by the difference in the steric bulk of the bridging moieties, but also by the electronic effect of the substituents introduced at remote positions relative to the boron atom. These results demonstrate the characteristic features of planarized phenyldithienylboranes as building blocks for boron-based π-electron materials.     

Um den Nachweis von Substanzen mittels der Boraxperle

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