895 research outputs found
Pressure dependence of diffusion in simple glasses and supercooled liquids
Using molecular dynamics simulation, we have calculated the pressure
dependence of the diffusion constant in a binary Lennard-Jones Glass. We
observe four temperature regimes. The apparent activation volume drops from
high values in the hot liquid to a plateau value. Near the critical temperature
of the mode coupling theory it rises steeply, but in the glassy state we find
again small values, similar to the ones in the liquid. The peak of the
activation volume at the critical temperature is in agreement with the
prediction of mode coupling theory
Colossal Positive Magnetoresistance in a Doped Nearly Magnetic Semiconductor
We report on a positive colossal magnetoresistance (MR) induced by
metallization of FeSb, a nearly magnetic or "Kondo" semiconductor with 3d
ions. We discuss contribution of orbital MR and quantum interference to
enhanced magnetic field response of electrical resistivity.Comment: 5 pages, 5 figure
Theory of Adsorption and Surfactant Effect of Sb on Ag (111)
We present first-principles studies of the adsorption of Sb and Ag on clean
and Sb-covered Ag (111). For Sb, the {\it substitutional} adsorption site is
found to be greatly favored with respect to on-surface fcc sites and to
subsurface sites, so that a segregating surface alloy layer is formed. Adsorbed
silver adatoms are more strongly bound on clean Ag(111) than on Sb-covered Ag.
We propose that the experimentally reported surfactant effect of Sb is due to
Sb adsorbates reducing the Ag adatom mobility. This gives rise to a high
density of Ag islands which coalesce into regular layers.Comment: RevTeX 3.0, 11 pages, 0 figures] 13 July 199
Developmental origin of chronic diseases: toxicological implication
Human epidemiological and experimental animal studies show that suboptimal environments in fetal and neonatal life exerts a profound influence on physiological function and risk of disease in adult life. The molecular, cellular, metabolic, endocrine and physiological adaptations to intrauterine nutritional conditions result in permanent alterations of cellular proliferation and differentiation of tissues and organ systems, which in turn can manifest by pathological consequences or increased vulnerability to chronic diseases in adulthood. Intrauterine growth restriction (IUGR) due to intrauterine development derangements is considered the important factor in development of such diseases as essential hypertension, diabetes mellitus, ischemic diseases of the heart, osteoporosis, respiratory, neuropsychiatric and immune system diseases
Epitaxial growth in dislocation-free strained alloy films: Morphological and compositional instabilities
The mechanisms of stability or instability in the strained alloy film growth
are of intense current interest to both theorists and experimentalists. We
consider dislocation-free, coherent, growing alloy films which could exhibit a
morphological instability without nucleation. We investigate such strained
films by developing a nonequilibrium, continuum model and by performing a
linear stability analysis. The couplings of film-substrate misfit strain,
compositional stress, deposition rate, and growth temperature determine the
stability of film morphology as well as the surface spinodal decomposition. We
consider some realistic factors of epitaxial growth, in particular the
composition dependence of elastic moduli and the coupling between top surface
and underlying bulk of the film. The interplay of these factors leads to new
stability results. In addition to the stability diagrams both above and below
the coherent spinodal temperature, we also calculate the kinetic critical
thickness for the onset of instability as well as its scaling behavior with
respect to misfit strain and deposition rate. We apply our results to some real
growth systems and discuss the implications related to some recent experimental
observations.Comment: 26 pages, 13 eps figure
Multiple glass transitions in star polymer mixtures: Insights from theory and simulations
The glass transition in binary mixtures of star polymers is studied by mode
coupling theory and extensive molecular dynamics computer simulations. In
particular, we have explored vitrification in the parameter space of size
asymmetry and concentration of the small star polymers at
fixed concentration of the large ones. Depending on the choice of parameters,
three different glassy states are identified: a single glass of big polymers at
low and low , a double glass at high and low
, and a novel double glass at high and high which is
characterized by a strong localization of the small particles. At low
and high there is a competition between vitrification and phase
separation. Centered in the -plane, a liquid lake shows up
revealing reentrant glass formation. We compare the behavior of the dynamical
density correlators with the predictions of the theory and find remarkable
agreement between the two.Comment: 15 figures, to be published in Macromolecule
Equilibrium shapes and energies of coherent strained InP islands
The equilibrium shapes and energies of coherent strained InP islands grown on
GaP have been investigated with a hybrid approach that has been previously
applied to InAs islands on GaAs. This combines calculations of the surface
energies by density functional theory and the bulk deformation energies by
continuum elasticity theory. The calculated equilibrium shapes for different
chemical environments exhibit the {101}, {111}, {\=1\=1\=1} facets and a (001)
top surface. They compare quite well with recent atomic-force microscopy data.
Thus in the InP/GaInP-system a considerable equilibration of the individual
islands with respect to their shapes can be achieved. We discuss the
implications of our results for the Ostwald ripening of the coherent InP
islands. In addition we compare strain fields in uncapped and capped islands.Comment: 10 pages including 6 figures. Submitted to Phys. Rev. B. Related
publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm
Optical Properties of MFe_4P_12 filled skutterudites
Infrared reflectance spectroscopy measurements were made on four members of
the MFe_4P_12 family of filled skutterudites, with M=La, Th, Ce and U. In
progressing from M=La to U the system undergoes a metal-insulator transition.
It is shown that, although the filling atom induces such dramatic changes in
the transport properties of the system, it has only a small effect on lattice
dynamics. We discuss this property of the compounds in the context of their
possible thermoelectric applications.Comment: Manuscript in ReVTeX format, 7 figures in PostScirpt forma
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