377 research outputs found
Site-Specific Colloidal Crystal Nucleation by Template-enhanced Particle Transport
The monomer surface mobility is the single most important parameter that
decides the nucleation density and morphology of islands during thin film
growth. During template-assisted surface growth in particular, low surface
mobilities can prevent monomers from reaching target sites and this results in
a partial to complete loss of nucleation control. While in atomic systems a
broad range of surface mobilities can be readily accessed, for colloids, owing
to their large size, this window is substantially narrow and therefore imposes
severe restrictions in extending template-assisted growth techniques to steer
their self-assembly. Here, we circumvented this fundamental limitation by
designing templates with spatially varying feature sizes, in this case moire
patterns, which in the presence of short-range depletion attraction presented
surface energy gradients for the diffusing colloids. The templates serve a dual
purpose, first, directing the particles to target sites by enhancing their
surface mean free paths and second, dictating the size and symmetry of the
growing crystallites. Using optical microscopy, we directly followed the
nucleation and growth kinetics of colloidal islands on these surfaces at the
single-particle level. We demonstrate nucleation control, with high fidelity,
in a regime that has remained unaccessed in theoretical, numerical and
experimental studies on atoms and molecules as well. Our findings pave the way
for fabricating non-trivial surface architectures composed of complex colloids
and nanoparticles.Comment: 12 pages, 3 figure
Dynamical facilitation governs glassy dynamics in suspensions of colloidal ellipsoids
One of the greatest challenges in contemporary condensed matter physics is to
ascertain whether the formation of glasses from liquids is fundamentally
thermodynamic or dynamic in origin. While the thermodynamic paradigm has
dominated theoretical research for decades, the purely kinetic perspective of
the dynamical facilitation (DF) theory has attained prominence in recent times.
In particular, recent experiments and simulations have highlighted the
importance of facilitation using simple model systems composed of spherical
particles. However, an overwhelming majority of liquids possess anisotropy in
particle shape and interactions and it is therefore imperative to examine
facilitation in complex glass-formers. Here, we apply the DF theory to systems
with orientational degrees of freedom as well as anisotropic attractive
interactions. By analyzing data from experiments on colloidal ellipsoids, we
show that facilitation plays a pivotal role in translational as well as
orientational relaxation. Further, we demonstrate that the introduction of
attractive interactions leads to spatial decoupling of translational and
rotational facilitation, which subsequently results in the decoupling of
dynamical heterogeneities. Most strikingly, the DF theory can predict the
existence of reentrant glass transitions based on the statistics of localized
dynamical events, called excitations, whose duration is substantially smaller
than the structural relaxation time. Our findings pave the way for
systematically testing the DF approach in complex glass-formers and also
establish the significance of facilitation in governing structural relaxation
in supercooled liquids.Comment: 22 pages, 3 main figues, 3 supplementary figures. Submitted to
Proceedings of the National Academy of Sciences, USA, on the 15th of July,
201
Magnetic Characteristics of High Entropy Alloys
High entropy alloy (HEA) is a multi-principal alloy having at least five principal elements in the concentration range of 5–35 at.%. HEAs having excellent mechanical properties and further these properties can be altered by the addition of different alloying element. For example with the addition of Al in base alloy make them a ductile and the addition of Co, Ti, etc. transforms base alloy to brittle material. This characteristic of HEAs makes them a promising technologically important material. A soft magnetic material should have good mechanical property, structural stability at high temperature and low coercivity with high magnetization. Recently, reported FeCoNiMn0.25Al0.25 and CoCrFeNiM (M = Cu, Mn) HEAs got attention as a better soft magnetic material because these HEAs having good soft magnetic characteristics along with good mechanical and excellent structural stability at high-temperature. Recent reports described that the mechanical as well as magnetic characteristics of these alloys can be tuned by the variation and/or the addition of alloying element in the base alloys. The magnetic characteristics of these alloys basically depend on the alloying element and compositional variation of the magnetic element present in particular HEAs. We have summarized the key results of magnetic characteristics of some recently investigated promising high entropy alloys
Master equation of discrete time graphon mean field games and teams
In this paper, we present a sequential decomposition algorithm equivalent of
Master equation to compute GMFE of GMFG and graphon optimal Markovian policies
(GOMPs) of graphon mean field teams (GMFTs). We consider a large population of
players sequentially making strategic decisions where the actions of each
player affect their neighbors which is captured in a graph, generated by a
known graphon. Each player observes a private state and also a common
information as a graphon mean-field population state which represents the
empirical networked distribution of other players' types. We consider
non-stationary population state dynamics and present a novel backward recursive
algorithm to compute both GMFE and GOMP that depend on both, a player's private
type, and the current (dynamic) population state determined through the
graphon. Each step in computing GMFE consists of solving a fixed-point
equation, while computing GOMP involves solving for an optimization problem. We
provide conditions on model parameters for which there exists such a GMFE.
Using this algorithm, we obtain the GMFE and GOMP for a specific security setup
in cyber physical systems for different graphons that capture the interactions
between the nodes in the system.Comment: 26 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1905.0415
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