Are there stable long-range ordered Fe(1-x)Cr(x) compounds?

The heat of formation of Fe-Cr alloys undergoes an anomalous change of sign at small Cr concentrations. This observation raises the question whether there are intermetallic phases present in this composition range. Here we report the discovery of several long-range ordered structures that represent ground state phases at zero Kelvin. In particular we have identified a structure at 3.7% Cr with an embedding energy which is 49 meV/Cr atom below the solid solution. This implies there is an effective long-range attractive interaction between Cr atoms. We propose that the structures found in this study complete the low temperature-low Cr region of the phase diagram.Comment: 3 pages, 2 figure

Short-range order and precipitation in Fe-rich Fe-Cr alloys: Atomistic off-lattice Monte Carlo simulations

Short-range order (SRO) in Fe-rich Fe-Cr alloys is investigated by means of atomistic off-lattice Monte Carlo simulations in the semi-grand canonical ensemble using classical interatomic potentials. The SRO parameter defined by Cowley [Phys. Rev. B 77, 669 (1950)] is used to quantify the degree of ordering. In agreement with experiments a strong ordering tendency in the Cr distribution at low Cr concentrations (~< 5%) is observed, as manifested in negative values of the SRO parameters. For intermediate Cr concentrations (5% ~< c_Cr ~< 15%) the SRO parameter for the alpha-phase goes through a minimum, but at the solubility limit the alpha-phase still displays a rather strong SRO. In thermodynamic equilibrium for concentrations within the two-phase region the SRO parameter measured over the entire sample therefore comprises the contributions from both the alpha and alpha-prime phases. If both of these contributions are taken into account, it is possible to quantitatively reproduce the experimental results and interpret their physical implications. It is thereby shown that the inversion of the SRO observed experimentally is due to the formation of stable (supercritical) alpha-prime precipitates. It is not related to the loss of SRO in the alpha-phase or to the presence of unstable (subcritical) Cr precipitates in the alpha-phase.Comment: 9 pages, 8 figure

T-cell modulation for the treatment of chronic plaque psoriasis with efalizumab (Raptiva (TM)): Mechanisms of action

Psoriasis is a chronic, incurable, auto-immune disorder with cutaneous manifestations. New evidence on the central role of the immune system in the pathogenesis of psoriasis increasingly provides insight into pathogenic steps that can be modulated to provide disease control. Numerous biological therapies are in various stages of clinical development, with expectation of providing enhanced safety and efficacy over currently available psoriasis therapies. Efalizumab, a recombinant humanized monoclonal IgG1 antibody, is a novel targeted T-cell modulator that inhibits multiple steps in the immune cascade that result in the production and maintenance of psoriatic plaques, including initial T-cell activation and T-cell trafficking into sites of inflammation, including psoriatic skin, with subsequent reactivation in these sites. This article reviews the pharmacodynamic, pharmacokinetic and clinical effects observed during phase I, II and III efalizumab trials in patients with moderate to severe chronic plaque psoriasis. Copyright (C) 2004 S. Karger AG, Basel

CLASSIC MANY BODY POTENTIAL FOR CONCENTRATED ALLOYS, AND THE INVERSION OF ORDER IN FE-CR

Atomistic simulations of alloys at the classic--or empirical--level face the challenge to correctly model basic thermodynamic properties. In this work we propose a methodology to generalize many-body classic potentials to incorporate complex formation energy curves. Application to Fe-Cr allows us to correctly predict the order vs segregation tendency in this alloy, as observed experimentally and calculated with ab initio techniques, providing in this way a potential suitable for radiation damage studies

Towards durable multistakeholder-generated solutions: The pilot application of a problem-oriented policy learning protocol to legality verification and community rights in Peru

This paper reports and reflects on the pilot application of an 11-step policy learning protocol that was developed by Cashore and Lupberger (2015) based on several years of Cashore’s multi-author collaborations. The protocol was applied for the first time in Peru in 2015 and 2016 by the IUFRO Working Party on Forest Policy Learning Architectures (hereinafter referred to as the project team). The protocol integrates insights from policy learning scholarship (Hall 1993, Sabatier 1999) with Bernstein and Cashore’s (2000, 2012) four pathways of influence framework. The pilot implementation in Peru focused on how global timber legality verification interventions might be harnessed to promote local land rights. Legality verification focuses attention on the checking and auditing of forest management units in order to verify that timber is harvested and traded in compliance with the law. We specifically asked: How can community legal ownership of, and access to, forestland and forest resources be enhanced? The protocol was designed as a dynamic tool, the implementation of which fosters iterative rather than linear processes. It directly integrated two objectives: 1) identifying the causal processes through which global governance initiatives might be harnessed to produce durable results ‘on the ground’; 2) generating insights and strategies in collaboration with relevant stakeholders. This paper reviews and critically evaluates our work in designing and piloting the protocol. We assess what seemed to work well and suggest modifications, including an original diagnostic framework for nurturing durable change. We also assess the implications of the pilot application of the protocol for policy implementation that works to enhance the influence of existing international policy instruments, rather than contributing to fragmentation and incoherence by creating new ones

Nonadiabatic forces in ion-solid interactions: the initial stages of radiation damage

The Born-Oppenheimer approximation is the keystone for molecular dynamics simulations of radiation damage processes; however, actual materials response involves nonadiabatic energy exchange between nuclei and electrons. In this work, time dependent density functional theory is used to calculate the electronic excitations produced by energetic protons in Al. We study the influence of these electronic excitations on the interatomic forces and find that they differ substantially from the adiabatic case, revealing a nontrivial connection between electronic and nuclear stopping that is absent in the adiabatic case. These results unveil new effects in the early stages of radiation damage cascades

Kinetic Theory of Collisionless Self-Gravitating Gases: II. Relativistic Corrections in Galactic Dynamics

In this paper we study the kinetic theory of many-particle astrophysical systems imposing axial symmetry and extending our previous analysis in Phys. Rev. D 83, 123007 (2011). Starting from a Newtonian model describing a collisionless self-gravitating gas, we develop a framework to include systematically the first general relativistic corrections to the matter distribution and gravitational potentials for general stationary systems. Then, we use our method to obtain particular solutions for the case of the Morgan & Morgan disks. The models obtained are fully analytical and correspond to the post-Newtonian generalizations of classical ones. We explore some properties of the models in order to estimate the importance of post-Newtonian corrections and we find that, contrary to the expectations, the main modifications appear far from the galaxy cores. As a by-product of this investigation we derive the corrected version of the tensor virial theorem. For stationary systems we recover the same result as in the Newtonian theory. However, for time dependent backgrounds we find that there is an extra piece that contributes to the variation of the inertia tensor.Comment: 30 pages, 8 figures. v2: Minor corrections and references added. Conclusions unchanged. v3: Version published in PR

Systematic effects from black hole-neutron star waveform model uncertainties on the neutron star equation of state

We identify various contributors of systematic effects in the measurement of the neutron star (NS) tidal deformability and quantify their magnitude for several types of neutron star - black hole (NSBH) binaries. Gravitational waves from NSBH mergers contain information about the components' masses and spins as well as the NS equation of state. Extracting this information requires comparison of the signal in noisy detector data with theoretical templates derived from some combination of post-Newtonian (PN) approximants, effective one-body (EOB) models and %analytic fits to numerical relativity (NR) simulations. The accuracy of these templates is limited by errors in the NR simulations, by the approximate nature of the PN/EOB waveforms, and by the hybridization procedure used to combine them. In this paper, we estimate the impact of these errors by constructing and comparing a set of PN-NR hybrid waveforms, for the first time with NR waveforms from two different codes, namely, SpEC and SACRA, for such systems. We then attempt to recover the parameters of the binary using two non-precessing template approximants. We find that systematic errors are too large for tidal effects to be accurately characterized for any realistic NS equation of state model. We conclude that NSBH waveform models must be significantly improved if they are to be useful for the extraction of NS equation of state information or even for distinguishing NSBH systems from binary black holes