The effects of Bi/Ta and Sr/Ta mole ratios on ferroelectric properties of Sr x Bi y Ta2O z [ SBIT(x/y/2.0); 0.7≤x≤1.0, 2.0≤y≤2.6] thin-film capacitors were investigated. The SBIT films were grown by the sol-gel method using a spin-on coating on Pt/Ta/SiO2/Si and Pt/Ti/SiO2/Si substrates. The films were annealed at 800° C for one hour in oxygen atmosphere. Remanent polarization (Pr) depended strongly on the Sr/Ta mole ratio, and increased with decrease of the Sr/Ta mole ratio. On the other hand, Pr was almost independent of the Bi/Ta mole ratio. Scanning electron microscopy (SEM) images show that crystal grains grew with decrease of the Sr/Ta mole ratio. Electron probe micro analyzer (EPMA) analysis revealed that Bi content in SBIT films increased with decrease in Sr composition from stoichiometry.

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Human centromeres remain poorly characterized regions of the human genome despite their importance for the maintenance of chromosomes. In part this is due to the difficulty of cloning of highly repetitive DNA fragments and distinguishing chromosome-specific clones in a genomic library. In this work we report the highly selective isolation of human centromeric DNA using transformation-associated recombination (TAR) cloning. A TAR vector with alphoid DNA monomers as targeting sequences was used to isolate large centromeric regions of human chromosomes 2, 5, 8, 11, 15, 19, 21 and 22 from human cells as well as monochromosomal hybrid cells. The alphoid DNA array was also isolated from the 12 Mb human mini-chromosome DeltaYq74 that contained the minimum amount of alphoid DNA required for proper chromosome segregation. Preliminary results of the structural analyses of different centromeres are reported in this paper. The ability of the cloned human centromeric regions to support human artificial chromosome (HAC) formation was assessed by transfection into human HT1080 cells. Centromeric clones from DeltaYq74 did not support the formation of HACs, indicating that the requirements for the existence of a functional centromere on an endogenous chromosome and those for forming a de novo centromere may be distinct. A construct with an alphoid DNA array from chromosome 22 with no detectable CENP-B motifs formed mitotically stable HACs in the absence of drug selection without detectable acquisition of host DNAs. In summary, our results demonstrated that TAR cloning is a useful tool for investigating human centromere organization and the structural requirements for formation of HAC vectors that might have a potential for therapeutic applications.

A series of directional solidification experiments have been conducted to elucidate the formation mechanism of eta and Cr-rich phases in the Ni-base superalloy IN792 + Hf. Both eta and Cr-rich phases were found to be the final solidification products developed from the remaining liquid after c/c¢ eutectic reaction. The (Ti + Ta + Hf)/Al ratio in the residual liquid played a significant role in the nucleation of eta phase. During the solidification of c/c¢ eutectic, the continual increase of (Ti + Ta + Hf)/Al ratio in the residual liquid eventually led to the completion of c/c¢ eutectic reaction and caused the nucleation of eta phase. The results of electron probe microanalysis and transmission electron microscopy revealed that the Cr-rich phase was Cr, Mo, and W containing M 5 B 3 and M 3 B 2 type borides. The formation of these boride phases was found to be strongly influenced by the formation of c/c¢ eutectic. Because of the limited solubility of Cr, Mo, and W in c¢ phase, these elements were enriched in the residual liquid during the solidification of c/c¢ eutectic. In addition, boron would preferentially segregate into liquid due to its very limited solubility in both c and c¢ phases so that the possibility of boride formation in the residual liquid ahead of the c/c¢ eutectic was increased. A modified Scheil model was adopted to explain the influence of solidification rate on the formation of eta phase and borides, and the results were discussed.

We propose a method to calculate percolation thresholds pE and their error bars Apc of two-dimensional (2D) lattices. The characteristic feature of our method is an efficient extraction of information from the results of Monte Carlo (MC) simulations. We apply this method to some ZD systems such as a square, KagomC and dice lattice, Penrose tiling and a Penrose dual lattice. Our method enables us to estimate thresholds very accurately even when we use the MC data obtained from fairly small sizes. For instance, we achieve three significant figures for pc from the MC data obtained from lattices with sizes less than 300 x 300 and the increment 0.002 of p.