98 research outputs found
Synthesis dependent characteristics of Sr1-xMnxTiO3 (x=0.03, 0.05, 0.07 and 0.09)
Sr1-xMnxTiO3 (where x = 0.03, 0.05, 0.07 and 0.09) was synthesized via
different routes that include solid-state, oxalate precipitation and freeze
drying. In oxalate precipitation technique, compositions corresponding to 3 and
5 mol % doping of Mn were monophasic whereas the higher compositions revealed
the presence of the secondary phases such as MnO, Mn3O4 etc., as confirmed by
high resolution X-ray diffraction (XRD) studies. The decomposition behavior of
the precursors prepared using oxalate precipitation method corresponding to the
above mentioned compositions was studied. Nanopowders of compositions
pertaining to 5 to 9 mol % of Mn doping were obtained using freeze-drying
technique. The average crystallite size of these nanopowders was found to be in
the 35 to 65 nm range. The microstructural studies carried out on the sintered
ceramics, fabricated using powders synthesized by different routes established
the fine grained nature (< 1 microm) of the one obtained by freeze drying
method. Raman scattering studies were carried out in order to complement the
observations made from XRD regarding the phase purity. The dielectric
properties of the ceramics obtained by different synthesis routes were studied
in the 80 - 300 K temperature range at 100 kHz and the effect of grain size has
been discussed.Comment: 38 pages, 4 tables, 13 figure
Nature, strength, and consequences of indirect adsorbate interactions on metals
Atoms and molecules adsorbed on metals affect each other indirectly even over considerable distances. Via systematic density-functional calculations, we establish the nature and strength of such interactions, and explain for what adsorbate systems they critically affect important materials properties. This is verified in kinetic Monte Carlo simulations of epitaxial growth, which help rationalize a number of recent experimental reports on anomalously low diffusion prefactors
Implication of the overlap representation for modelling generalized parton distributions
Based on a field theoretically inspired model of light-cone wave functions,
we derive valence-like generalized parton distributions and their double
distributions from the wave function overlap in the parton number conserved
s-channel. The parton number changing contributions in the t-channel are
restored from duality. In our construction constraints of positivity and
polynomiality are simultaneously satisfied and it also implies a model
dependent relation between generalized parton distributions and transverse
momentum dependent parton distribution functions. The model predicts that the
t-behavior of resulting hadronic amplitudes depends on the Bjorken variable
x_Bj. We also propose an improved ansatz for double distributions that embeds
this property.Comment: 15 pages, 8 eps figure
Island diffusion on metal fcc(100) surfaces
We present Monte Carlo simulations for the size and temperature dependence of
the diffusion coefficient of adatom islands on the Cu(100) surface. We show
that the scaling exponent for the size dependence is not a constant but a
decreasing function of the island size and approaches unity for very large
islands. This is due to a crossover from periphery dominated mass transport to
a regime where vacancies diffuse inside the island. The effective scaling
exponents are in good agreement with theory and experiments.Comment: 13 pages, 2 figures, to be published in Phys. Rev. Let
Changing shapes in the nanoworld
What are the mechanisms leading to the shape relaxation of three dimensional
crystallites ? Kinetic Monte Carlo simulations of fcc clusters show that the
usual theories of equilibration, via atomic surface diffusion driven by
curvature, are verified only at high temperatures. Below the roughening
temperature, the relaxation is much slower, kinetics being governed by the
nucleation of a critical germ on a facet. We show that the energy barrier for
this step linearly increases with the size of the crystallite, leading to an
exponential dependence of the relaxation time.Comment: 4 pages, 5 figures. Accepted by Phys Rev Let
Patterned nanostructure in AgCo/Pt/MgO(001) thin film
The formation of patterned nanostructure in AgCo/Pt/MgO(001) thin film is
simulated by a technique of combining molecular dynamics and phase-field
theory. The dislocation (strain) network existing in Pt/MgO is used as a
template whose pattern is transferred to AgCo phase in spinodal decomposition,
resulting in regular arrays of Co islands that are attracted by the
dislocations. The influence of various factors, such as component concentration
and film thickness, is studied. It is found that the spinodal decomposition of
AgCo in this system is mainly characterized by a competition between a
surface-directed layer structure and the strain-induced patterned structure,
where the patterned Ag-Co structure only dominates in a small range near the
interface (less than 10 atomic layers). However, if the interlayer diffusion
can be minimized by controlling film growth conditions, it is shown that the
patterned structure can be formed throughout the entire film.Comment: 8 pages, 12 figure
Improved adsorption energetics within density-functional theory using revised Perdew-Burke-Ernzerhof functionals
Careers in context: An international study of career goals as mesostructure between societies' career-related human potential and proactive career behaviour
Careers exist in a societal context that offers both constraints and opportunities for career actors. Whereas most studies focus on proximal individual and/or organisational-level variables, we provide insights into how career goals and behaviours are understood and embedded in the more distal societal context. More specifically, we operationalise societal context using the career-related human potential composite and aim to understand if and why career goals and behaviours vary between countries. Drawing on a model of career structuration and using multilevel mediation modelling, we draw on a survey of 17,986 employees from 27 countries, covering nine of GLOBE's 10 cultural clusters, and national statistical data to examine the relationship between societal context (macrostructure building the career-opportunity structure) and actors' career goals (career mesostructure) and career behaviour (actions). We show that societal context in terms of societies' career-related human potential composite is negatively associated with the importance given to financial achievements as a specific career mesostructure in a society that is positively related to individuals' proactive career behaviour. Our career mesostructure fully mediates the relationship between societal context and individuals' proactive career behaviour. In this way, we expand career theory's scope beyond occupation- and organisation-related factors
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