First-principles prediction of redox potentials in transition-metal compounds with LDA+U

First-principles calculations within the Local Density Approximation (LDA) or Generalized Gradient Approximation (GGA), though very successful, are known to underestimate redox potentials, such as those at which lithium intercalates in transition metal compounds. We argue that this inaccuracy is related to the lack of cancellation of electron self-interaction errors in LDA/GGA and can be improved by using the DFT+$U$ method with a self-consistent evaluation of the $U$ parameter. We show that, using this approach, the experimental lithium intercalation voltages of a number of transition metal compounds, including the olivine Li$_{x}$MPO$_{4}$ (M=Mn, Fe Co, Ni), layered Li$_{x}$MO$_{2}$ ($x=$Co, Ni) and spinel-like Li$_{x}$M$_{2}$O$_{4}$ (M=Mn, Co), can be reproduced accurately.Comment: 19 pages, 6 figures, Phys. Rev. B 70, 235121 (2004

The influence of stacking fault energies and solute segregation on high temperature creep strength in L12-containing Co-based Superalloys

Co-based superalloys strengthened by the γ’-(L12) phase exhibit comparable and, in some cases, superior high temperature creep resistance to 1st-generation Ni-based superalloys. Despite the comparable creep resistance between Co- and Ni-based superalloys, the high temperature creep deformation modes are markedly different: the γ’ phase in Ni-based superalloys is typically sheared via coupled a/2\u3c110\u3e matrix dislocations, whereas the γ’ phase in Co-based superalloys is sheared via Shockley superpartial a/3\u3c112\u3e dislocations, which leave superlattice intrinsic stacking faults (SISF) behind in their wake. Previous investigations have shown that the creep strength of Co-based alloys increases with increasing SISF energy. In this contribution, the SISF energies for Co3(Al,W,X) and Co3(Al,Mo,X) compounds (X = Cr, Ta, Ti, Nb, and V) are calculated using density functional theory and special quasi-random structures (SQS) in order to assess the potency for quaternary alloying additions to increase the SISF energy, and thus the high temperature creep strength. In all alloy systems except Co-Al-W-Ti, quaternary compositions exhibited higher SISF energies compared to binary or ternary compositions. This implies that higher-order alloying additions that partition to the γ’ phase will always aid to increase the SISF energy and the high temperature creep strength as well. Recent work incorporating vibrational entropy in order to determine temperature-dependent SISF energies will be presented. Additionally, recent observations via high resolution microscopy and atom probe tomography of solute segregation at the SISFs will be presented. The relationship between solute segregation, SISF energy, and high temperature creep strength will be exemplified. Please click Additional Files below to see the full abstract

Differential Expression of Proinflammatory Cytokines and Their Inhibitors during the Course of Meningococcal Infections

Circulating concentrations of tumor necrosis factor-α (TNF), interleukin (IL)-1β, IL-6, IL-1 receptor antagonist (IL-1ra), and soluble TNF receptors p55 (sTNFr-55) and p75 (sTNFr-75) and ex vivo production ofTNF, IL-1, IL-6, and IL-1ra using a whole blood culture system were measured during the acute and convalescent stages of meningococcal infection. Circulating TNF and IL-1 were below detection level, whereas IL-6 and IL-1ra, sTNFr-55, and sTNFr-75 were increased at admission. The ex vivo production of proinflammatory cytokines TNF, IL-1, and IL-6 was suppressed at admission and restored gradually during recovery. On the contrary, the production of the antiinflammatory IL-1ra was increased at admission. The elevated concentrations of both IL-1ra and sTNFr early in the course of infection suggest a regulatory role for these antiinflammatory compounds. The observed down-regulation of the ex vivo production of TNF, IL-1, and IL-6 and up-regulation of the production of IL-1 ra in the acute stage may indicate a protective regulation mechanis

An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277

All massive galaxies likely have supermassive black holes at their centers, and the masses of the black holes are known to correlate with properties of the host galaxy bulge component. Several explanations have been proposed for the existence of these locally-established empirical relationships; they include the non-causal, statistical process of galaxy-galaxy merging, direct feedback between the black hole and its host galaxy, or galaxy-galaxy merging and the subsequent violent relaxation and dissipation. The empirical scaling relations are thus important for distinguishing between various theoretical models of galaxy evolution, and they further form the basis for all black hole mass measurements at large distances. In particular, observations have shown that the mass of the black hole is typically 0.1% of the stellar bulge mass of the galaxy. The small galaxy NGC4486B currently has the largest published fraction of its mass in a black hole at 11%. Here we report observations of the stellar kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x 10^11 Msun. From the data, we determine that the mass of the central black hole is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have properties similar to NGC 1277 and therefore may also contain over-sized black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated galaxies fail to follow the normal black hole mass scaling relations.Comment: 7 pages. 6 figures. Nature. Animation at http://www.mpia.de/~bosch/blackholes.htm

Polychlorinated Biphenyls: The Occurrence of the Main Congeners in Follicular and Sperm Fluids

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