Microstructure evolution in Pr-Co-C-Ti nanophase magnets

The microstructures of nanophase Pr-Co-C-(Ti) materials, which have improved magnetic properties, were investigated by means of transmission electron microscopy (TEM) to reveal their phase assemblage and grain-boundary structure. The phase assemblage was carefully controlled by the introduction of TiC nanoparticles and annealing. The optimal nanostructure contained uniformly distributed PrCo₅ and PrCo₂ nanophases without any magnetically soft phases, resulting in high coercivity and the characteristics of a single, hard magnetic phase. TEM analysis confirmed the presence of an amorphous grain-boundary phase surrounding the grains in alloys without TiC. In contrast, alloys with added TiC showed no amorphous phase and also showed higher coercivity compared to Co-Pr-C. Therefore, the variation of the grain boundary phases may be effective in changing the degree of exchange coupling. Controlling the formation of a uniform nanoscale microstructure, leading to improved magnetic properties, is discussed. Received: 5 September 2002 / Accepted: 10 September 2002 / Published online: 22 January 2003 RID="*" ID="*"Corresponding author. Fax: +1-630/252-7777, E-mail: ytang@anl.gov     

Phase transition in the superconducting state in Gd-rich pseudoternary compounds (La1-xGdx)1.0Mo6Se8

A pronounced lambda-type specific heat anomaly in the superconducting state is reported for Gd-rich pseudoternary compounds (La_1-xGd_x)_1.0Mo₆Se₈. The anomaly is very similar to that previously reported for the compound Gd_1.2Mo₆Se₈. Both the temperature of the lambda anomaly (≈ 3.5 K) and the Curie-Weiss temperature were found to be nearly independent of x. In addition, evidence for the occurence of magnetic ordering at 0.8 K in Gd_1.2Mo₆Se₈ is presented. These observations support our earlier conjecture that the lambda anomaly at 3.5 K does not arise from magnetic ordering of the Gd³⁺ ions. The anomaly appears instead to be due to a different type of phase transition which is associated with the presence of the localized 4f electrons of the Gd³⁺ ions, but the exact nature of the transition remains to be established.     

Comparison between the magnetic specific heat of NdBa2Cu3O x and DyBa2Cu3O x

Low temperature heat-capacity measurements have been performed to study the magnetic ordering in NdBa₂Cu₃O _x and DyBa₂Cu₃O _x . In order to investigate the type of ordering, magnetic fields up to 6 T and hydrostatic pressures up to 4.5 kbar were applied. While for NdBa₂Cu₃O _x and DyBa₂Cu₃O _x both the fully oxidized and the fully oxygen reduced samples display long rang antiferromagnetic ordering, only magnetic short range interaction could be found for samples in an intermediate range of oxygen concentration. For NdBa₂Cu₃O _x , where superexchange is believed to be the dominant magnetic interaction,T _N is three times higher in the sample withx=6.26 compared to the one withx=6.98. In contrast,T _N of DyBa₂Cu₃O _x is almost oxygen independent as expected for this mainly dipolar interacting system.     

Stabilization of Aliphatic Phosphines by Auxiliary Phosphine Sulfides Offers Zeptomolar Affinity and Unprecedented Selectivity for Probing Biological CuI

Full elucidation of the functions and homeostatic pathways of biological copper requires tools that can selectively recognize and manipulate this trace nutrient within living cells and tissues, where it exists primarily as Cu^I. Buffered at attomolar concentrations, intracellular Cu^I is, however, not readily accessible to commonly employed amine and thioether‐based chelators. Herein, we reveal a chelator design strategy in which phosphine sulfides aid in Cu^I coordination while simultaneously stabilizing aliphatic phosphine donors, producing a charge‐neutral ligand with low‐zeptomolar dissociation constant and 10¹⁷‐fold selectivity for Cu^I over Zn^II, Fe^II, and Mn^II. As illustrated by reversing ATP7A trafficking in cells and blocking long‐term potentiation of neurons in mouse hippocampal brain tissue, the ligand is capable of intercepting copper‐dependent processes. The phosphine sulfide‐stabilized phosphine (PSP) design approach, which confers resistance towards protonation, dioxygen, and disulfides, could be readily expanded towards ligands and probes with tailored properties for exploring Cu^I in a broad range of biological systems.     

Annellation effects in the pyrene series and the classification of absorption spectra

The classification of absorption bands in the acene series (, p, β-bands) was first based on the annellation effect and later on the polarization of the bands with regard to the molecular axes (L_b,L_a,B_b,B_a-bands). Both give the same result since annelation axes and molecular axes coincide. This is not so in the pyrene series. Annellation axes and molecular axes are different and it is shown that the classification of bands can be based only on the annellation effects. Moreover, the electronic asymmetry of the pyrene system is demonstrated by a striking asymmetric annellation effect. A number of higher annellated pyrenes have been synthesized:

1·-benzonaphtho-(2″·3″ :6·7)-pyrene, dinaphto-(2'·3 :1·2)-(2″·3″:6·7)-pyrene, 1·14,4·5-dibenzo-pentacene, 5·,15·16-dibenzohexacene, 6·7,16·17-dibenzoheptacene, 1·16,4·5-dibenzohexacene and 7·8,17·18-dibenzo-octacene.     

Quantitative determination of singlet oxygen generated by excited state aromatic amino acids, proteins, and immunoglobulins

Singlet oxygen quantum yields generated by excited state aromatic amino acids (tryptophan, tyrosine, phenylalanine), N-acetylated amino acids (N-acetyl-tryptophan, N-acetyl-tyrosine, N-acetyl-phenylalanine), and from selected proteins and immunoglobulins have been quantified by time-resolved phosphorescence measurements. A small, but significant, quantum yield found for proteins and immunoglobulins demonstrates that molecular oxygen can diffuse through the polypeptide matrix and can be sensitized by residues buried within the folds of protein structure.     

Fine grained sampling of residue characteristics using molecular dynamics simulation

In a fine-grained computational analysis of protein structure, we investigated the relationships between a residue's backbone conformations and its side-chain packing as well as conformations. To produce continuous distributions in high resolution, we ran molecular dynamics simulations over a set of protein folds (dynameome). In effect, the dynameome dataset samples not only the states well represented in the PDB but also the known states that are not well represented in the structural database. In our analysis, we characterized the mutual influence among the backbone ?,ψ angles with the first side-chain torsion angles (χ₁) and the volumes occupied by the side-chains. The dependencies of these relationships on side-chain environment and amino acids are further explored. We found that residue volumes exhibit dependency on backbone 2° structure conformation: side-chains pack more densely in extended β-sheet than in α-helical structures. As expected, residue volumes on the protein surface were larger than those in the interior. The first side-chain torsion angles are found to be dependent on the backbone conformations in agreement with previous studies, but the dynameome dataset provides higher resolution of rotamer preferences based on the backbone conformation. All three gauche^?, gauche⁺, and trans rotamers show different patterns of ?,ψ dependency, and variations in χ₁ value are skewed from their canonical values to relieve the steric strains. By demonstrating the utility of dynameomic modeling on the native state ensemble, this study reveals details of the interplay among backbone conformations, residue volumes and side-chain conformations.     

High throughput ion implantation systems in western electric

Within Western Electric, a number of high throughput systems have been developed to meet the differing needs of high voltage and low voltage ion implantation applications. The PR-500 is a general purpose 500 kV machine which provides typical target currents of 0.5 ma of the common dopants and throughputs of 100 75-mm wafers/hour. The PR-200 is a 200 kV machine with typical target currents of 2.5 ma P, As, and Sb, and 1.0 ma B, and wafer throughputs of 150/hour. The PR-30 is a 30 kV single-species machine which can perform predeposition implants at rates of up to 450 wafers/hour. Typical PR-30 target currents are 5 ma P, As, and Sb. and 1.5 ma B. Each of these systems makes use of a common family of high current ion sources, and a rotating disk mechanical scanning system which permits a minimum implant time for 1 % uniformity of two seconds per wafer.