715 research outputs found
Dissociation of O2 at Al(111): The Role of Spin Selection Rules
A most basic and puzzling enigma in surface science is the description of the
dissociative adsorption of O2 at the (111) surface of Al. Already for the
sticking curve alone, the disagreement between experiment and results of
state-of-the-art first-principles calculations can hardly be more dramatic. In
this paper we show that this is caused by hitherto unaccounted spin selection
rules, which give rise to a highly non-adiabatic behavior in the O2/Al(111)
interaction. We also discuss problems caused by the insufficient accuracy of
present-day exchange-correlation functionals.Comment: 4 pages including 3 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
A Fourth-Generation High-Dimensional Neural Network Potential with Accurate Electrostatics Including Non-local Charge Transfer
Machine learning potentials have become an important tool for atomistic
simulations in many fields, from chemistry via molecular biology to materials
science. Most of the established methods, however, rely on local properties and
are thus unable to take global changes in the electronic structure into
account, which result from long-range charge transfer or different charge
states. In this work we overcome this limitation by introducing a
fourth-generation high-dimensional neural network potential that combines a
charge equilibration scheme employing environment-dependent atomic
electronegativities with accurate atomic energies. The method, which is able to
correctly describe global charge distributions in arbitrary systems, yields
much improved energies and substantially extends the applicability of modern
machine learning potentials. This is demonstrated for a series of systems
representing typical scenarios in chemistry and materials science that are
incorrectly described by current methods, while the fourth-generation neural
network potential is in excellent agreement with electronic structure
calculations.Comment: 13 pages, 11 figure
The ASDEX Upgrade UTDC and DIO cards - A family of PCI/cPCI devices for real-time DAQ under Solaris
A Universal Time to Digital Converter (UTDC) and a Digital I/O (DIO) card have been built to purpose for the new ASDEX Upgrade control system, the Thomson Scattering diagnostic, a renovation of the Magnetic Measurement, and a couple of other diagnostics requiring renewed timing or real-time features. The salient features of these cards will be presented, and we will show how synergy in hardware and software development could be achieved. Examples of real-life applications in diagnostics will be given. Measurements of the real-time behaviour of those diagnostics show a low jitter of the Solaris operating system and highly reliable function under moderate real-time conditions. Future extension of the usability of this family of cards will be described as an outlook. Topic: Diagnostic Control and Data Acquisitio
Ab initio thermodynamics of liquid and solid water
Thermodynamic properties of liquid water as well as hexagonal (Ih) and cubic
(Ic) ice are predicted based on density functional theory at the
hybrid-functional level, rigorously taking into account quantum nuclear motion,
anharmonic fluctuations and proton disorder. This is made possible by combining
advanced free energy methods and state-of-the-art machine learning techniques.
The ab initio description leads to structural properties in excellent agreement
with experiments, and reliable estimates of the melting points of light and
heavy water. We observe that nuclear quantum effects contribute a crucial 0.2
meV/HO to the stability of ice Ih, making it more stable than ice Ic. Our
computational approach is general and transferable, providing a comprehensive
framework for quantitative predictions of ab initio thermodynamic properties
using machine learning potentials as an intermediate step
Non-Adiabatic Potential-Energy Surfaces by Constrained Density-Functional Theory
Non-adiabatic effects play an important role in many chemical processes. In
order to study the underlying non-adiabatic potential-energy surfaces (PESs),
we present a locally-constrained density-functional theory approach, which
enables us to confine electrons to sub-spaces of the Hilbert space, e.g. to
selected atoms or groups of atoms. This allows to calculate non-adiabatic PESs
for defined charge and spin states of the chosen subsystems. The capability of
the method is demonstrated by calculating non-adiabatic PESs for the scattering
of a sodium and a chlorine atom, for the interaction of a chlorine molecule
with a small metal cluster, and for the dissociation of an oxygen molecule at
the Al(111) surface.Comment: 11 pages including 7 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Rituximab therapy for pure red cell aplasia due to anti-epoetin antibodies in a woman treated with epoetin-alfa: a case report
<p>Abstract</p> <p>Introduction</p> <p>Pure red cell aplasia due to anti-epoetin antibodies is a known complication of epoetin therapy for anemia due to chronic kidney disease. This disease has not previously been well described in the setting of therapy for chronic hepatitis C virus infection. While treatment for pure red cell aplasia due to anti-epoetin antibodies is usually with immunosuppressive therapy such as calcineurin inhibition, the safety of this treatment in chronic hepatitis C virus infection is unknown. To date, little has been published on the efficacy of rituximab on pure red cell aplasia due to anti-epoetin antibodies.</p> <p>Case presentation</p> <p>This report describes a 65-year-old Asian-American woman who developed pure red cell aplasia from high titer neutralizing anti-epoetin antibodies after epoetin-alfa therapy during ribavirin and peg-interferon treatment for chronic hepatitis C virus infection. We describe the outcome of her treatment with rituximab. The reticulocyte count increased, and anti-epoetin antibody titer decreased with a loss of neutralizing activity <it>in vitro</it>, leading to a reduction in blood transfusions, and eventual resolution of anemia, without reactivation of hepatitis C virus.</p> <p>Conclusion</p> <p>The diagnosis of pure red cell aplasia from anti-epoetin antibodies should be considered in patients undergoing therapy for chronic hepatitis C virus infection who develop severe anemia after administration of erythropoietin or darbepoetin. Though it is currently an off-label indication, rituximab is a therapeutic option for patients with pure red cell aplasia due to anti-epoetin antibodies.</p
Non-adiabatic Effects in the Dissociation of Oxygen Molecules at the Al(111) Surface
The measured low initial sticking probability of oxygen molecules at the
Al(111) surface that had puzzled the field for many years was recently
explained in a non-adiabatic picture invoking spin-selection rules [J. Behler
et al., Phys. Rev. Lett. 94, 036104 (2005)]. These selection rules tend to
conserve the initial spin-triplet character of the free O2 molecule during the
molecule's approach to the surface. A new locally-constrained
density-functional theory approach gave access to the corresponding
potential-energy surface (PES) seen by such an impinging spin-triplet molecule
and indicated barriers to dissociation which reduce the sticking probability.
Here, we further substantiate this non-adiabatic picture by providing a
detailed account of the employed approach. Building on the previous work, we
focus in particular on inaccuracies in present-day exchange-correlation
functionals. Our analysis shows that small quantitative differences in the
spin-triplet constrained PES obtained with different gradient-corrected
functionals have a noticeable effect on the lowest kinetic energy part of the
resulting sticking curve.Comment: 17 pages including 11 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
A Study of the Correlation between Endoscopic and Histological Diagnoses in Gastroduodenitis
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72433/1/j.1572-0241.1987.tb01777.x.pd
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