113,174 research outputs found
A solvable model for excitonic complexes in one dimension
It is known experimentally that stable few-body clusters containing
negatively-charged electrons (e) and positively-charged holes (h) can exist in
low-dimensional semiconductor nanostructures. In addition to the familiar
exciton (e+h), three-body 'charged excitons' (2e+h and 2h+e) have also been
observed. Much less is known about the properties of such charged excitons
since three-body problems are generally very difficult to solve, even
numerically. Here we introduce a simple model, which can be considered as an
extended Calogero model, to calculate analytically the energy spectra for both
a charged exciton and a neutral exciton in a one-dimensional nanostructure,
such as a finite-length quantum wire. Apart from its physical motivation, the
model is of mathematical interest in that it can be related to the Heun (or
Heine) equation and, as shown explicitly, highly accurate, closed form
solutions can be obtained.Comment: 14 pages, 3 figures, To appear in J. Math. Phy
Auslander Systems
The authors generalize the dynamical system constructed by J. Auslander in 1959, resulting in perhaps the simplest family of examples of minimal but not strictly ergodic systems. A characterization of unique ergodicity and mean-L-stability is given. The new systems are also shown to have zero topological entropy and fail to be weakly rigid. Some results on the set of idempotents in the enveloping semigroup are also achieved
Free-energy landscape of nucleation with an intermediate metastable phase studied using capillarity approximation
Capillarity approximation is used to study the free-energy landscape of
nucleation when an intermediate metastable phase exists. The critical nucleus
that corresponds to the saddle point of the free-energy landscape as well as
the whole free-energy landscape can be studied using this capillarity
approximation, and various scenarios of nucleation and growth can be
elucidated. In this study we consider a model in which a stable solid phase
nucleates within a metastable vapor phase when an intermediate metastable
liquid phase exists. We predict that a composite critical nucleus that consists
of a solid core and a liquid wetting layer as well as pure liquid and pure
solid critical nuclei can exist depending not only on the supersaturation of
the liquid phase relative to that of the vapor phase but also on the wetting
behavior of the liquid surrounding the solid. The existence of liquid critical
nucleus indicates that the phase transformation from metastable vapor to stable
solid occurs via the intermediate metastable liquid phase, which is quite
similar to the scenario of nucleation observed in proteins and colloidal
systems. By studying the minimum-free-energy path on the free-energy landscape,
we can study the evolution of the composition of solid and liquid within nuclei
not limited to the critical nucleus.Comment: 9 pages, 8 figures, Journal of chemical physics to be publishe
Numerical model of solid phase transformations governed by nucleation and growth. Microstructure development during isothermal crystallization
A simple numerical model which calculates the kinetics of crystallization
involving randomly distributed nucleation and isotropic growth is presented.
The model can be applied to different thermal histories and no restrictions are
imposed on the time and the temperature dependencies of the nucleation and
growth rates. We also develop an algorithm which evaluates the corresponding
emerging grain size distribution. The algorithm is easy to implement and
particularly flexible making it possible to simulate several experimental
conditions. Its simplicity and minimal computer requirements allow high
accuracy for two- and three-dimensional growth simulations. The algorithm is
applied to explore the grain morphology development during isothermal
treatments for several nucleation regimes. In particular, thermal nucleation,
pre-existing nuclei and the combination of both nucleation mechanisms are
analyzed. For the first two cases, the universal grain size distribution is
obtained. The high accuracy of the model is stated from its comparison to
analytical predictions. Finally, the validity of the
Kolmogorov-Johnson-Mehl-Avrami model is verified for all the cases studied
Beyond the constraints underlying Kolmogorov-Johnson-Mehl-Avrami theory related to the growth laws
The theory of Kolmogorov-Johnson-Mehl-Avrami (KJMA) for phase transition
kinetics is subjected to severe limitations concerning the functional form of
the growth law. This paper is devoted to side step this drawback through the
use of correlation function approach. Moreover, we put forward an
easy-to-handle formula, written in terms of the experimentally accessible
actual extended volume fraction, which is found to match several types of
growths. Computer simulations have been done for corroborating the theoretical
approach.Comment: 18 pages ;11 figure
Structure of human transthyretin complexed with bromophenols: a new mode of binding
The binding of two organohalogen substances, pentabromophenol (PBP) and 2,4,6-tribromophenol (TBP), to human transthyretin (TTR), a thyroid hormone transport protein, has been studied by in vitro competitive binding assays and by X-ray crystallography. Both compounds bind to TTR with high affinity, in competition with the natural ligand thyroxine (
Multi-Agent Complex Systems and Many-Body Physics
Multi-agent complex systems comprising populations of decision-making
particles, have many potential applications across the biological,
informational and social sciences. We show that the time-averaged dynamics in
such systems bear a striking resemblance to conventional many-body physics. For
the specific example of the Minority Game, this analogy enables us to obtain
analytic expressions which are in excellent agreement with numerical
simulations.Comment: Accepted for publication in Europhysics Letter
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