6,093 research outputs found
Ballistic conductance of magnetic Co and Ni nanowires with ultrasoft pseudo-potentials
The scattering-based approach for calculating the ballistic conductance of
open quantum systems is generalized to deal with magnetic transition metals as
described by ultrasoft pseudo-potentials. As an application we present
quantum-mechanical conductance calculations for monatomic Co and Ni nanowires
with a magnetization reversal. We find that in both Co and Ni nanowires, at the
Fermi energy, the conductance of electrons is blocked by a magnetization
reversal, while the states (one per spin) are perfectly transmitted.
electrons have a non-vanishing transmission in a small energy window below the
Fermi level. Here, transmission is larger in Ni than in Co.Comment: 9 pages, 6 figures, to appear in PR
Phonons Softening in Tip-Stretched Monatomic Nanowires
It has been shown in recent experiments that electronic transport through a
gold monatomic nanowire is dissipative above a threshold voltage due to
excitation of phonons via the electron-phonon interaction. We address that data
by computing, via density functional theory, the zone boundary longitudinal
phonon frequency of a perfect monatomic nanowire during its mechanical
elongation. The theoretical frequency that we find for an ideally strained
nanowire is not compatible with experiment if a uniformly distributed stretch
is assumed. With the help of a semi-empirical Au-Au potential, we model the
realistic nanowire stretching as exerted by two tips. In this model we see that
strain tends to concentrate in the junctions, so that the mean strain of the
nanowire is roughly one half of the ideal value. With this reduced strain, the
calculated phonon softening is in much better agreement with experiment.Comment: 9 pages,3 figures, Surface Science, in pres
Will the Home Team Win? On the Road to 1.5 Billion Tweets and Six Thousand Baseball Games Providing Insight!!!
Researchers operate with limited budgets and inadequate resources. This prohibits big data research and suppresses innovation needed to direct inquiry and construct robust research-based information systems. Such issues are not insuperable, e.g., this project is initialized with limited resources and attempts to build theory, describe architecture, and set the vision for future work. This first “On the Road to …” paper tenders a methodology that examines the use of social media variables as a proxy for human emotion and epistemic activity. A social media corpus is processed and a regression model considers MLB team wins as the dependent variable and a social media tweet corpus, operationalized via NLP, as the independent variable. Results are presented. Future work describes a predictive GIS artifact that will input, process, and visualize a spatial and time-based, NLP processed, social media corpus and is integration with geospatial indexing
Separatrix Reconnections in Chaotic Regimes
In this paper we extend the concept of separatrix reconnection into chaotic
regimes. We show that even under chaotic conditions one can still understand
abrupt jumps of diffusive-like processes in the relevant phase-space in terms
of relatively smooth realignments of stable and unstable manifolds of unstable
fixed points.Comment: 4 pages, 5 figures, submitted do Phys. Rev. E (1998
On-surface and Subsurface Adsorption of Oxygen on Stepped Ag(210) and Ag(410) Surfaces
The adsorption of atomic oxygen and its inclusion into subsurface sites on
Ag(210) and Ag(410) surfaces have been investigated using density functional
theory. We find that--in the absence of adatoms on the first metal
layer--subsurface adsorption results in strong lattice distortion which makes
it energetically unfavoured. However subsurface sites are significantly
stabilised when a sufficient amount of O adatoms is present on the surface. At
high enough O coverage on the Ag(210) surface the mixed on-surface + subsurface
O adsorption is energetically favoured with respect to the on-surface only
adsorption. Instead, on the Ag(410) surface, at the coverage we have considered
(3/8 ML), the existence of stable terrace sites makes the subsurface O
incorporation less favourable. These findings are compatible with the results
of recent HREEL experiments which have actually motivated this work.Comment: 8 pages, 4 figures and 1 tabl
Mechanical Mixing in Nonlinear Nanomechanical Resonators
Nanomechanical resonators, machined out of Silicon-on-Insulator wafers, are
operated in the nonlinear regime to investigate higher-order mechanical mixing
at radio frequencies, relevant to signal processing and nonlinear dynamics on
nanometer scales. Driven by two neighboring frequencies the resonators generate
rich power spectra exhibiting a multitude of satellite peaks. This nonlinear
response is studied and compared to -order perturbation theory and
nonperturbative numerical calculations.Comment: 5 pages, 7 figure
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