1,277 research outputs found
Submonolayer Epitaxy Without A Critical Nucleus
The nucleation and growth of two--dimensional islands is studied with Monte
Carlo simulations of a pair--bond solid--on--solid model of epitaxial growth.
The conventional description of this problem in terms of a well--defined
critical island size fails because no islands are absolutely stable against
single atom detachment by thermal bond breaking. When two--bond scission is
negligible, we find that the ratio of the dimer dissociation rate to the rate
of adatom capture by dimers uniquely indexes both the island size distribution
scaling function and the dependence of the island density on the flux and the
substrate temperature. Effective pair-bond model parameters are found that
yield excellent quantitative agreement with scaling functions measured for
Fe/Fe(001).Comment: 8 pages, Postscript files (the paper and Figs. 1-3), uuencoded,
compressed and tarred. Surface Science Letters, in press
Fractal formation and ordering in random sequential adsorption
We reveal the fractal nature of patterns arising in random sequential
adsorption of particles with continuum power-law size distribution, , . We find that the patterns become more and
more ordered as increases, and that the Apollonian packing is obtained
at limit. We introduce the entropy production rate as a
quantitative criteria of regularity and observe a transition from an irregular
regime of the pattern formation to a regular one. We develop a scaling theory
that relates kinetic and structural properties of the system.Comment: 4 pages, RevTex, 4 postscript figures. To appear in Phys.Rev.Let
A Reverse Dynamical Investigation of the Catastrophic Wood-Snow Avalanche of 18 January 2017 at Rigopiano, Gran Sasso National Park, Italy
On 18 January 2017 a catastrophic avalanche destroyed the Rigopiano Gran Sasso Resort & Wellness (Rigopiano Hotel) in the Gran Sasso National Park in Italy, with 40 people trapped and a death toll of 29. This article describes the location of the disaster and the general meteorological scenario, with field investigations to provide insight on the avalanche dynamics and its interaction with the hotel buildings. The data gathered in situ suggest that the avalanche was a fluidized dry snow avalanche, which entrained a sligthtly warmer snow cover along the path and reached extremely long runout distances with braking effect from mountain forests. The avalanche that reached the Rigopiano area was a “wood-snow” avalanche—a mixture of snow and uprooted and crushed trees, rocks, and other debris. There were no direct eyewitnesses at the event, and a quick post-event survey used a numerical model to analyze the dynamics of the event to estimate the pressure, velocity, and direction of the natural flow and the causes for the destruction of the hotel. Considering the magnitude and the damage caused by the event, the avalanche was at a high to very high intensity scale
Adsorption of Line Segments on a Square Lattice
We study the deposition of line segments on a two-dimensional square lattice.
The estimates for the coverage at jamming obtained by Monte-Carlo simulations
and by -order time-series expansion are successfully compared. The
non-trivial limit of adsorption of infinitely long segments is studied, and the
lattice coverage is consistently obtained using these two approaches.Comment: 19 pages in Latex+5 postscript files sent upon request ; PTB93_
Kinetic Roughening in Deposition with Suppressed Screening
Models of irreversible surface deposition of k-mers on a linear lattice, with
screening suppressed by disallowing overhangs blocking large gaps, are studied
by extensive Monte Carlo simulations of the temporal and size dependence of the
growing interface width. Despite earlier finding that for such models the
deposit density tends to increase away from the substrate, our numerical
results place them clearly within the standard KPZ universality class.Comment: nine pages, plain TeX (4 figures not included
Scaling of Heteroepitaxial Island Sizes
Monte Carlo simulations of an atomistic solid-on-solid model are used to
study the effect of lattice misfit on the distribution of two-dimensional
islands sizes as a function of coverage in the submonolayer
aggregation regime of epitaxial growth. Misfit promotes the detachment of atoms
from the perimeter of large pseudomorphic islands and thus favors their
dissolution into smaller islands that relieve strain more efficiently. The
number density of islands composed of atoms exhibits scaling in the form
\mbox{)} where is the average island size. Unlike the
case of homoepitaxy, a rate equation theory based on this observation leads to
qualitatively different behavior than observed in the simulations.Comment: 10 pages, LaTeX 2.09, IC-DDV-94-00
Exact Solution of a Drop-push Model for Percolation
Motivated by a computer science algorithm known as `linear probing with
hashing' we study a new type of percolation model whose basic features include
a sequential `dropping' of particles on a substrate followed by their transport
via a `pushing' mechanism. Our exact solution in one dimension shows that,
unlike the ordinary random percolation model, the drop-push model has
nontrivial spatial correlations generated by the dynamics itself. The critical
exponents in the drop-push model are also different from that of the ordinary
percolation. The relevance of our results to computer science is pointed out.Comment: 4 pages revtex, 2 eps figure
A Compact Gas Cerenkov Detector with Novel Optics
We discuss the design and performance of a threshold Cerenkov counter for
identification of charged hadrons. The radiator is pressurized gas, which is
contained in thin-walled cylindrical modules. A mirror system of novel design
transports Cerenkov photons to photomultiplier tubes. This system is compact,
contains relatively little material, and has a large fraction of active volume.
A prototype of a module designed for the proposed CLEO III detector has been
studied using cosmic rays. Results from these studies show good agreement with
a detailed Monte Carlo simulation of the module and indicate that it should
achieve separation of pions and kaons at the 2.5-3.0sigma level in the momentum
range 0.8-2.8 GeV/c. We predict performance for specific physics analyses using
a GEANT-based simulation package.Comment: Submitted to NIM. 23 pages, 11 postscript figures. Postscript file is
also available at http://w4.lns.cornell.edu/public/CLNS/199
Step Position Distributions and the Pairwise Einstein Model for Steps on Crystal Surfaces
The Pairwise Einstein Model (PEM) of steps not only justifies the use of the
Generalized Wigner Distribution (GWD) for Terrace Width Distributions (TWDs),
it also predicts a specific form for the Step Position Distribution (SPD),
i.e., the probability density function for the fluctuations of a step about its
average position. The predicted form of the SPD is well approximated by a
Gaussian with a finite variance. However, the variance of the SPD measured from
either real surfaces or Monte Carlo simulations depends on , the
length of step over which it is calculated, with the measured variance
diverging in the limit . As a result, a length scale
can be defined as the value of at which the measured and
theoretical SPDs agree. Monte Carlo simulations of the terrace-step-kink model
indicate that , where is the correlation
length in the direction parallel to the steps, independent of the strength of
the step-step repulsion. can also be understood as the length over
which a {\em single} terrace must be sampled for the TWD to bear a "reasonable"
resemblence to the GWD.Comment: 4 pages, 3 figure
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