4,531 research outputs found
Contributions to the mixed-alkali effect in molecular dynamics simulations of alkali silicate glasses
The mixed-alkali effect on the cation dynamics in silicate glasses is
analyzed via molecular dynamics simulations. Observations suggest a description
of the dynamics in terms of stable sites mostly specific to one ionic species.
As main contributions to the mixed--alkali slowdown longer residence times and
an increased probability of correlated backjumps are identified. The slowdown
is related to the limited accessibility of foreign sites. The mismatch
experienced in a foreign site is stronger and more retarding for the larger
ions, the smaller ions can be temporarily accommodated. Also correlations
between unlike as well as like cations are demonstrated that support
cooperative behavior.Comment: 10 pages, 12 figures, 1 table, revtex4, submitted to Phys. Rev.
Strategic Foresight in multinational enterprises – a case study on the Deutsche Telekom Laboratories
Strategic Foresight activities enable companies to use weak signals to identify opportunities and threats. Research on Strategic Foresight proposes different methods, discusses their implementation and gives recommendations on how to link Strategic Foresight with other functions in an organization. Based on a literature review, we define a generic framework for the management of Strategic Foresight activities on the strategic, tactical and operational level and identify and discuss actors, methods and systems of Strategic Foresight. Building on an in-depth case study of the Deutsche Telekom Laboratories we shed light on the implementation of Strategic Foresight activities. In the discussion we focus on the interaction of methods from Consumer Foresight and Technology Intelligence. Taking an example project, we explore how Strategic Foresight is used on the operational level of innovation management. We conclude that Strategic Foresight can successfully contribute to coping with uncertainty and complexity and can feed the front-end of innovation from the market (customer needs) and technology (realization opportunities) perspective.strategic foresight; consumer foresight; technology foresight; technology intelligence; market foresight; trend analysis; future studies; future analysis; telecommunication industry
Deep-Elastic pp Scattering at LHC from Low-x Gluons
Deep-elastic pp scattering at c.m. energy 14 TeV at LHC in the momentum
transfer range 4 GeV*2 < |t| < 10 GeV*2 is planned to be measured by the TOTEM
group. We study this process in a model where the deep-elastic scattering is
due to a single hard collision of a valence quark from one proton with a
valence quark from the other proton. The hard collision originates from the
low-x gluon cloud around one valence quark interacting with that of the other.
The low-x gluon cloud can be identified as color glass condensate and has size
~0.3 F. Our prediction is that pp differential cross section in the large |t|
region decreases smoothly as momentum transfer increases. This is in contrast
to the prediction of pp differential cross section with visible oscillations
and smaller cross sections by a large number of other models.Comment: 10 pages, including 4 figure
Compressing nearly hard sphere fluids increases glass fragility
We use molecular dynamics to investigate the glass transition occurring at
large volume fraction, phi, and low temperature, T, in assemblies of soft
repulsive particles. We find that equilibrium dynamics in the (phi, T) plane
obey a form of dynamic scaling in the proximity of a critical point at T=0 and
phi=phi_0, which should correspond to the ideal glass transition of hard
spheres. This glass point, `point G', is distinct from athermal jamming
thresholds. A remarkable consequence of scaling behaviour is that the dynamics
at fixed phi passes smoothly from that of a strong glass to that of a very
fragile glass as phi increases beyond phi_0. Correlations between fragility and
various physical properties are explored.Comment: 5 pages, 3 figures; Version accepted at Europhys. Let
Cation Transport in Polymer Electrolytes: A Microscopic Approach
A microscopic theory for cation diffusion in polymer electrolytes is
presented. Based on a thorough analysis of molecular dynamics simulations on
PEO with LiBF the mechanisms of cation dynamics are characterised. Cation
jumps between polymer chains can be identified as renewal processes. This
allows us to obtain an explicit expression for the lithium ion diffusion
constant D_{Li} by invoking polymer specific properties such as the Rouse
dynamics. This extends previous phenomenological and numerical approaches. In
particular, the chain length dependence of D_{Li} can be predicted and compared
with experimental data. This dependence can be fully understood without
referring to entanglement effects.Comment: 4 pages, 4 figures, Physical Review Letters in pres
Origin of non-exponential relaxation in a crystalline ionic conductor: a multi-dimensional 109Ag NMR study
The origin of the non-exponential relaxation of silver ions in the
crystalline ion conductor Ag7P3S11 is analyzed by comparing appropriate
two-time and three-time 109Ag NMR correlation functions. The non-exponentiality
is due to a rate distribution, i.e., dynamic heterogeneities, rather than to an
intrinsic non-exponentiality. Thus, the data give no evidence for the relevance
of correlated back-and-forth jumps on the timescale of the silver relaxation.Comment: 4 pages, 3 figure
Modelling the atomic arrangement of amorphous 2D silica: a network analysis
The recent experimental discovery of a semi two-dimensional silica glass has offered a realistic description of the random network theory of a silica glass structure, initially discussed by Zachariasen. To study the structure formation of silica in two dimensions, we introduce a two-body force field, based on a soft core Yukawa potential. The different configurations, sampled via Molecular dynamics simulations, can be directly compared with the experimental structures, which have been provided in the literature. The parameters of the force field are obtained from comparison of the nearest-neighbor distances between experiment and simulation. Further key properties such as angle distributions, distribution of ring sizes and triplets of rings are analyzed and compared with the experiment. Of particular interest is the spatial correlation of ring sizes. In general, we observe a very good agreement between experiment and simulation. Additional insight from the simulations is provided about the temporal and spatial stability of the rings in dependence of their size
Backward correlations and dynamic heterogeneities: a computer study of ion dynamics
We analyse the correlated back and forth dynamics and dynamic
heterogeneities, i.e. the presence of fast and slow ions, for a lithium
metasilicate system via computer simulations. For this purpose we define, in
analogy to previous work in the field of glass transition, appropriate
three-time correlation functions. They contain information about the dynamics
during two successive time intervals. First we apply them to simple model
systems in order to clarify their information content. Afterwards we use this
formalism to analyse the lithium trajectories. A strong back-dragging effect is
observed, which also fulfills the time-temperature superposition principle.
Furthermore, it turns out that the back-dragging effect is long-ranged and
exceeds the nearest neighbor position. In contrast, the strength of the dynamic
heterogeneities does not fulfill the time-temperature superposition principle.
The lower the temperature, the stronger the mobility difference between fast
and slow ions. The results are then compared with the simple model systems
considered here as well as with some lattice models of ion dynamics.Comment: 12 pages, 10 figure
Characterization of local dynamics and mobilities in polymer melts - a simulation study
The local dynamical features of a PEO melt studied by MD simulations are
compared to two model chain systems, namely the well-known Rouse model as well
as the semiflexible chain model (SFCM) that additionally incorporates chain
stiffness. Apart from the analysis of rather general quantities such as the
mean square displacement (MSD), we present a new statistical method to extract
the local bead mobility from the simulation data on the basis of the Langevin
equation, thus providing a complementary approach to the classical Rouse-mode
analysis. This allows us to check the validity of the Langevin equation and, as
a consequence, the Rouse model. Moreover, the new method has a broad range of
applications for the analysis of the dynamics of more complex polymeric systems
like comb-branched polymers or polymer blends.Comment: 6 pages, 5 figure
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