284 research outputs found
Influence of Disorder Strength on Phase Field Models of Interfacial Growth
We study the influence of disorder strength on the interface roughening
process in a phase-field model with locally conserved dynamics. We consider two
cases where the mobility coefficient multiplying the locally conserved current
is either constant throughout the system (the two-sided model) or becomes zero
in the phase into which the interface advances (one-sided model). In the limit
of weak disorder, both models are completely equivalent and can reproduce the
physical process of a fluid diffusively invading a porous media, where
super-rough scaling of the interface fluctuations occurs. On the other hand,
increasing disorder causes the scaling properties to change to intrinsic
anomalous scaling. In the limit of strong disorder this behavior prevails for
the one-sided model, whereas for the two-sided case, nucleation of domains in
front of the invading front are observed.Comment: Accepted for publication in PR
Instability and wavelength selection during step flow growth of metal surfaces vicinal to fcc(001)
We study the onset and development of ledge instabilities during growth of
vicinal metal surfaces using kinetic Monte Carlo simulations. We observe the
formation of periodic patterns at [110] close packed step edges on surfaces
vicinal to fcc(001) under realistic molecular beam epitaxy conditions. The
corresponding wavelength and its temperature dependence are studied by
monitoring the autocorrelation function for step edge position. Simulations
suggest that the ledge instability on fcc(1,1,m) vicinal surfaces is controlled
by the strong kink Ehrlich-Schwoebel barrier, with the wavelength determined by
dimer nucleation at the step edge. Our results are in agreement with recent
continuum theoretical predictions, and experiments on Cu(1,1,17) vicinal
surfaces.Comment: 4 pages, 4 figures, RevTe
Eighth-order phase-field-crystal model for two-dimensional crystallization
We present a derivation of the recently proposed eighth order phase field
crystal model [Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the
crystallization of a solid from an undercooled melt. The model is used to study
the planar growth of a two dimensional hexagonal crystal, and the results are
compared against similar results from dynamical density functional theory of
Marconi and Tarazona, as well as other phase field crystal models. We find that
among the phase field crystal models studied, the eighth order fitting scheme
gives results in good agreement with the density functional theory for both
static and dynamic properties, suggesting it is an accurate and computationally
efficient approximation to the density functional theory
Kinetic Roughening in Slow Combustion of Paper
Results of experiments on the dynamics and kinetic roughening of
one-dimensional slow-combustion fronts in three grades of paper are reported.
Extensive averaging of the data allows a detailed analysis of the spatial and
temporal development of the interface fluctuations. The asymptotic scaling
properties, on long length and time scales, are well described by the
Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To
obtain a more detailed picture of the strong-coupling fixed point,
characteristic of the KPZ universality class, universal amplitude ratios, and
the universal coupling constant are computed from the data and found to be in
good agreement with theory. Below the spatial and temporal scales at which a
cross-over takes place to the standard KPZ behavior, the fronts display higher
apparent exponents and apparent multiscaling. In this regime the interface
velocities are spatially and temporally correlated, and the distribution of the
magnitudes of the effective noise has a power-law tail. The relation of the
observed short-range behavior and the noise as determined from the local
velocity fluctuations is discussed.Comment: RevTeX v3.1, 13 pages, 12 Postscript figures (uses epsf.sty), 3
tables; submitted to Phys. Rev.
Interface Equations for Capillary Rise in Random Environment
We consider the influence of quenched noise upon interface dynamics in 2D and
3D capillary rise with rough walls by using phase-field approach, where the
local conservation of mass in the bulk is explicitly included. In the 2D case
the disorder is assumed to be in the effective mobility coefficient, while in
the 3D case we explicitly consider the influence of locally fluctuating
geometry along a solid wall using a generalized curvilinear coordinate
transformation. To obtain the equations of motion for meniscus and contact
lines, we develop a systematic projection formalism which allows inclusion of
disorder. Using this formalism, we derive linearized equations of motion for
the meniscus and contact line variables, which become local in the Fourier
space representation. These dispersion relations contain effective noise that
is linearly proportional to the velocity. The deterministic parts of our
dispersion relations agree with results obtained from other similar studies in
the proper limits. However, the forms of the noise terms derived here are
quantitatively different from the other studies
On-chip Maxwell's demon as an information-powered refrigerator
We present an experimental realization of an autonomous Maxwell's Demon,
which extracts microscopic information from a System and reduces its entropy by
applying feedback. It is based on two capacitively coupled single electron
devices, both integrated on the same electronic circuit. This setup allows a
detailed analysis of the thermodynamics of both the Demon and the System as
well as their mutual information exchange. The operation of the Demon is
directly observed as a temperature drop in the System. We also observe a
simultaneous temperature rise in the Demon arising from the thermodynamic cost
of generating the mutual information.Comment: 10 pages, 7 figure
Dynamics near the Surface Reconstruction of W(100)
Using Brownian molecular dynamics simulation, we study the surface dynamics
near the reconstruction transition of W(100) via a model Hamiltonian. Results
for the softening and broadening of the surface phonon spectrum near the
transition are compared with previous calculations and with He atom scattering
data. From the critical behavior of the central peak in the dynamical structure
factor, we also estimate the exponent of the power law anomaly for adatom
diffusion near the transition temperature.Comment: 8 pages, 8 figures, to appear in Phys. Rev.
Equilibrium Shape and Size of Supported Heteroepitaxial Nanoislands
We study the equilibrium shape, shape transitions and optimal size of
strained heteroepitaxial nanoislands with a two-dimensional atomistic model
using simply adjustable interatomic pair potentials. We map out the global
phase diagram as a function of substrate-adsorbate misfit and interaction. This
phase diagram reveals all the phases corresponding to different well-known
growth modes. In particular, for large enough misfits and attractive substrate
there is a Stranski-Krastanow regime, where nano-sized islands grow on top of
wetting films. We analyze the various terms contributing to the total island
energy in detail, and show how the competition between them leads to the
optimal shape and size of the islands. Finally, we also develop an analytic
interpolation formula for the various contributions to the total energy of
strained nanoislands.Comment: 9 pages, 7 figure
Determinants of OSS revenue model choices
The open source software movement is traditionally not affiliated to profit-oriented business behaviour. However, commercial activity has become increasingly common, and, business models have institutionalized in the field of open source software. The aim of this research paper is to explore the determinants of profitable revenue models for businesses based on open source software. Therefore, the study focuses on analysing different revenue options of open source software businesses as a part of more comprehensive open source software (OSS) business models. We explore other business model elements as the potential determinants of firm-level revenue model choices. This study draws on a qualitative research approach on the issue through two analytical business cases – MySQL and Red Hat – both of which illustrate the complexity and heterogeneity of solutions and options in the field of OSS. Thus, we analyse the business models of the selected case companies and identify the underlying endogenous elements, i.e. offerings, resources and relationships within them. Finally, we discuss the managerial implications derived from the cases to describe how these business model elements affect the development of successful revenue models in the field of open source software
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