82 research outputs found
Dynamic Bridge Response for a Bridge-friendly Truck
A truck with controlled semi-active suspensions traversing a bridge is examined for benefits to the bridge structure. The original concept of a road-friendly truck was extended to a bridge-friendly vehicle, using the same optimization tools. A half-car model with two independently driven axles is coupled with simply supported bridges (beam, slab model) with the span range from 5 m to 50 m. Surface profile of the bridge deck is either stochastic or in the shape of a bump or a pot in the mid-span. Numerical integration in the MATLAB/SIMULINK environment solves coupled dynamic equations of motion with optimized truck suspensions. The rear axle generates the prevailing load and to a great extent determines the bridge response. A significant decrease in contact road-tire forces is observed and the mid-span bridge deflections are on average smaller, when compared to commercial passive suspensions.
Interstitial Mn in (Ga,Mn)As: Binding energy and exchange coupling
We present ab initio calculations of total energies of Mn atoms in various
interstitial positions. The calculations are performed by the full-potential
linearized plane-wave method. The minimum energy is found for tetrahedral
T(As4) position, but the energy of the T(Ga4) site differs by only a few meV.
The T(Ga4) position becomes preferable in the p-type materials. In samples with
one substitutional and one interstitial Mn the Mn atoms tend to form close pair
with antiparallel magnetic moments. We also use the spin-splitting of the
valence band to estimate the exchange coupling Jpd for various positions of Mn.
It is the same for the substitutional and T(As4) position and it is only
slightly reduced for the T(Ga4) position. The hybridization of Mn d-states with
six next-nearest neighbors of the interstitial Mn explains the insensitivity of
Jpd to the position of Mn.Comment: 6 pages, 3 figures, 3 tables, submitted to the Physical Review
Diffusion rates of Cu adatoms on Cu(111) in the presence of an adisland nucleated at FCC or HCP sites
The surface diffusion of Cu adatoms in the presence of an adisland at FCC or
HCP sites on Cu(111) is studied using the EAM potential derived by Mishin {\it
et al.} [Phys. Rev. B {\bf 63} 224106 (2001)]. The diffusion rates along
straight (with close-packed edges) steps with (100) and (111)-type microfacets
(resp. step A and step B) are first investigated using the transition state
theory in the harmonic approximation. It is found that the classical limit
beyond which the diffusion rates follow an Arrhenius law is reached above the
Debye temperature. The Vineyard attempt frequencies and the (static) energy
barriers are reported. Then a comparison is made with the results of more
realistic classical molecular dynamic simulations which also exhibit an
Arrhenius-like behavior. It is concluded that the corresponding energy barriers
are completely consistent with the static ones within the statistical errors
and that the diffusion barrier along step B is significantly larger than along
step A. In contrast the prefactors are very different from the Vineyard
frequencies. They increase with the static energy barrier in agreement with the
Meyer-Neldel compensation rule and this increase is well approximated by the
law proposed by Boisvert {\it et al.} [Phys. Rev. Lett. {\bf 75} 469 (1995)].
As a consequence, the remaining part of this work is devoted to the
determination of static energy barriers for a large number of diffusion events
that can occur in the presence of an adisland. In particular, it is found that
the corner crossing diffusion process for triangular adislands is markedly
different for the two types of borders (A or B). From this set of results the
diffusion rates of the most important atomic displacements can be predicted and
used as input in Kinetic Monte-Carlo simulations
Microscopic analysis of the valence band and impurity band theories of (Ga,Mn)As
We analyze microscopically the valence and impurity band models of
ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with
conventional parameterization and the full potential LDA+U calculations give a
very similar picture of states near the Fermi energy which reside in an
exchange-split sp-d hybridized valence band with dominant orbital character of
the host semiconductor; this microscopic spectral character is consistent with
the physical premise of the k.p kinetic-exchange model. On the other hand, the
various models with a band structure comprising an impurity band detached from
the valence band assume mutually incompatible microscopic spectral character.
By adapting the tight-binding Anderson calculations individually to each of the
impurity band pictures in the single Mn impurity limit and then by exploring
the entire doping range we find that a detached impurity band does not persist
in any of these models in ferromagnetic (Ga,Mn)As.Comment: 29 pages, 25 figure
Ab initio study of canted magnetism of finite atomic chains at surfaces
By using ab initio methods on different levels we study the magnetic ground
state of (finite) atomic wires deposited on metallic surfaces. A
phenomenological model based on symmetry arguments suggests that the
magnetization of a ferromagnetic wire is aligned either normal to the wire and,
generally, tilted with respect to the surface normal or parallel to the wire.
From a first principles point of view, this simple model can be best related
to the so--called magnetic force theorem calculations being often used to
explore magnetic anisotropy energies of bulk and surface systems. The second
theoretical approach we use to search for the canted magnetic ground state is
first principles adiabatic spin dynamics extended to the case of fully
relativistic electron scattering. First, for the case of two adjacent Fe atoms
an a Cu(111) surface we demonstrate that the reduction of the surface symmetry
can indeed lead to canted magnetism. The anisotropy constants and consequently
the ground state magnetization direction are very sensitive to the position of
the dimer with respect to the surface. We also performed calculations for a
seven--atom Co chain placed along a step edge of a Pt(111) surface. As far as
the ground state spin orientation is concerned we obtain excellent agreement
with experiment. Moreover, the magnetic ground state turns out to be slightly
noncollinear.Comment: 8 pages, 5 figures; presented on the International Conference on
Nanospintronics Design and Realizations, Kyoto, Japan, May 2004; to appear in
J. Phys.: Cond. Matte
How to achieve a healthier and more sustainable europe by 2040 according to the public? Results of a five-country questionnaire survey
The aim of this paper is to understand public preferences for several future scenarios of achieving a healthier, more equitable and sustainable Europe, which differ in the way the society is organized (individualistically vs. collectively) and in the driving sector (public vs. private). To achieve this aim, we conducted a questionnaire survey using representative samples for five European countries in 2018. About three thousand respondents chose among the four scenarios presented within four different contexts (green spaces, active mobility, energy-efficient housing, food consumption) or none of them. A majority of people in the five European countries were ready to accept one of the scenarios. We found significant differences in preferences according to socioeconomic backgrounds and values of respondents. People above 35 years old, those who were less educated, and those in the lowest household income tertile were less supportive of all scenarios. The heterogeneity in preferences associated with differences in socioeconomic backgrounds was larger for the scenario in which society is organized individualistically and driven by the private sector. Smaller distinctions were found in case of the scenario in which society is organized collectively and is driven by the public sector. Departing from social psychological theories, we examine the role of altruistic, biospheric, egoistic, hedonic, and security values. People with stronger biospheric values were more likely to accept scenarios, particularly those which are driven by the public sector and where there is more collective organisation. Those with a more egoistic value orientation were more likely to have higher preferences for scenarios where the private sector had a dominant role. The policy implications, in terms of the selection and framing of policy measures to enhance public support, are discussed.info:eu-repo/semantics/publishedVersio
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