30 research outputs found
Cu/Ag EAM Potential Optimized for Heteroepitaxial Diffusion from ab initio Data
A binary embedded-atom method (EAM) potential is optimized for Cu on Ag(111)
by fitting to ab initio data. The fitting database consists of DFT calculations
of Cu monomers and dimers on Ag(111), specifically their relative energies,
adatom heights, and dimer separations. We start from the Mishin Cu-Ag EAM
potential and first modify the Cu-Ag pair potential to match the FCC/HCP site
energy difference then include Cu-Cu pair potential optimization for the entire
database. The optimized EAM potential reproduce DFT monomer and dimer relative
energies and geometries correctly. In trimer calculations, the potential
produces the DFT relative energy between FCC and HCP trimers, though a
different ground state is predicted. We use the optimized potential to
calculate diffusion barriers for Cu monomers, dimers, and trimers. The
predicted monomer barrier is the same as DFT, while experimental barriers for
monomers and dimers are both lower than predicted here. We attribute the
difference with experiment to the overestimation of surface adsorption energies
by DFT and a simple correction is presented. Our results show that the
optimized Cu-Ag EAM can be applied in the study of larger Cu islands on
Ag(111).Comment: 15 pages, 7 figure
Fisher Waves and Front Roughening in a Two-Species Invasion Model with Preemptive Competition
We study front propagation when an invading species competes with a resident;
we assume nearest-neighbor preemptive competition for resources in an
individual-based, two-dimensional lattice model. The asymptotic front velocity
exhibits power-law dependence on the difference between the two species' clonal
propagation rates (key ecological parameters). The mean-field approximation
behaves similarly, but the power law's exponent slightly differs from the
individual-based model's result. We also study roughening of the front, using
the framework of non-equilibrium interface growth. Our analysis indicates that
initially flat, linear invading fronts exhibit Kardar-Parisi-Zhang (KPZ)
roughening in one transverse dimension. Further, this finding implies, and is
also confirmed by simulations, that the temporal correction to the asymptotic
front velocity is of .Comment: 8 pages, 5 figures; Papers on related work can be found at
http://www.rpi.edu/~korniss/Researc
Orbital Nature of Carboionic Monoradicals Made from Diradicals
The electronic, optical, and solid state properties of a series of monoradicals, anions and cations obtained from starting neutral diradicals have been studied. Diradicals based on s-indacene and indenoacenes, with benzothiophenes fused and in different orientations, feature a varying degree of diradical character in the neutral state, which is here related with the properties of the radical redox forms. The analysis of their optical features in the polymethine monoradicals has been carried out in the framework of the molecular orbital and valence bond theories. Electronic UVVis-NIR absorption, X-ray solid-state diffraction and quantum
chemical calculations have been carried out. Studies of the different positive-/negative-charged species, both residing in the same skeletal Ï-conjugated backbone, are rare for organic molecules. The key factor for the dual stabilization is the presence of the starting diradical character that enables to indistinctively accommodate a pseudo-hole and a pseudoelectron defect with certainly small reorganization energies for ambipolar charge transport.The authors thank the Spanish Ministry of Science and Innovation (projects MINECO/FEDER PGC2018-098533-B-100
and PID2021-127127NB-I00) and the Junta de AndalucĂa, Spain (UMA18FEDERJA057 and Proyecto de Excelencia PROYEXCEL- 00328). We also thank the Research Central Services (SCAI) of the University of MĂĄlaga and the US National Science Foundation (CHE-1954389 to M.M.H., CHE-2003411 to M.A. P.). F.N and Y.D. acknowledge support from âValutazione della Ricerca di Ateneoâ (VRA)-University of Bologna. Y.D. acknowledges Ministero dellâUniversitĂ e della Ricerca (MUR) for her
Ph.D. fellowship.
Funding for open access charge: Universidad de MĂĄlaga / CBU
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
Characterisation and internalisation of recombinant humanised HMFG-1 antibodies against MUC1
The humanised HMFG-1 immunoglobulin has been extensively developed as a clinical immunotherapeutic agent for MUC1 expressing tumours. We have constructed a single-chain Fv (scFv) and Fab fragment from this antibody and shown that both these species retain their specificity for MUC1. The scFv was less stable and less soluble than the Fab. Detailed analyses of the binding kinetics of the whole IgG and Fab fragment show that the affinity for MUC1 synthetic peptides is low (approximately 100ân for the IgG and 10âÎŒ for the Fab), with particularly low but similar dissociation rate constants (0.031â0.095âsâ1). Binding to native antigen on the cell surface is over two orders of magnitude better. Confocal immunofluorescence microscopy shows that both the IgG and Fab are internalised rapidly (the IgG is internalised within 15âmin) and colocalise to early endosomes. This work provides an appreciation of the binding, internalising and trafficking kinetics, important for the development of future therapeutics based on this antibody
Atomistic study of edge and screw textless c plus a textgreater dislocations in magnesium
The gamma surfaces in the pyramidal I {1 -1 0 1} and II {1 1 -2 2} planes for hexagonal close packed Mg have been calculated using two embedded-atom-method potentials and by ab initio methods, and reasonable agreement is obtained for key stacking fault energies. Screw and edge textless c + a textgreater dislocation core structures and Peierls stresses at 0 K and finite temperature have been examined using the embedded-atom-method potentials. Screw textless c + a textgreater dislocations glide in the {1 -1 0 1} pyramidal plane I, and in the prism plane for larger stresses, but not in the {1 1 -2 2} plane as observed in experiments. However, the preference for pyramidal I glide correlates well with the gamma surfaces. New low energy edge textless c + a textgreater dislocation cores were found in addition to the sessile Type I and Type III cores observed in previous simulations while the Type II core was not observed. The lowest energy core is a glissile core that lies in the {1 1 -2 2} plane and has a 3 nm long {1 1 -2 1} twin embryo, rather than the sessile Type III core found in previous simulations. As the temperature increases from 0 to 300 K, the Peierls stresses in compression/tension drop from -80 MPa/+140 MPa and -140 MPa/+220 MPa for the most glissile screw and edge dislocations to -5/+2.5 MPa and -27/+5 MPa, and dislocation glide changes from kink motion to face-centered-cubic-like motion. At 300 K and under an applied stress, almost all the edge cores found at low temperature transform into a glissile core denoted IT, which glides at low stresses. Thus, at 300 K both screw and edge textless c + a textgreater dislocations were found to glide at stresses smaller than the similar to 40 MPa measured experimentally. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved