822 research outputs found
Distinguishing step relaxation mechanisms via pair correlation functions
Theoretical predictions of coupled step motion are tested by direct STM
measurement of the fluctuations of near-neighbor pairs of steps on
Si(111)-root3 x root3 R30 - Al at 970K. The average magnitude of the
pair-correlation function is within one standard deviation of zero, consistent
with uncorrelated near-neighbor step fluctuations. The time dependence of the
pair-correlation function shows no statistically significant agreement with the
predicted t^1/2 growth of pair correlations via rate-limiting atomic diffusion
between adjacent steps. The physical considerations governing uncorrelated step
fluctuations occurring via random attachment/detachment events at the step edge
are discussed.Comment: 17 pages, 4 figure
Nanoscale periodicity in stripe-forming systems at high temperature: Au/W(110)
We observe using low-energy electron microscopy the self-assembly of
monolayer-thick stripes of Au on W(110) near the transition temperature between
stripes and the non-patterned (homogeneous) phase. We demonstrate that the
amplitude of this Au stripe phase decreases with increasing temperature and
vanishes at the order-disorder transition (ODT). The wavelength varies much
more slowly with temperature and coverage than theories of stress-domain
patterns with sharp phase boundaries would predict, and maintains a finite
value of about 100 nm at the ODT. We argue that such nanometer-scale stripes
should often appear near the ODT.Comment: 5 page
Decay properties of new D-mesons
We consider radiative and pionic decays of the new D_s-mesons in the
framework of a phenomenologically motivated approach. Present data on ratios of
the two kinds of decays can be described without explicit using a 4-quark
component. Most probably, the isospin violation in decays of different
D_s-mesons is not universal, and the binding potential should be different from
Coulombic. New precise measurements may provide further clarification for the
nature of the D_s excited states.Comment: 12 pages, Late
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
CP Violation and Lifetime Differences of Neutral B Mesons from Correlated B^0-B^0bar Pairs
We present a technique to determine the CP violating phases, as well as, the
lifetime differences of the mass eigenstates for both and , by
considering correlated pairs produced at the resonances.
We do not require a detailed time dependent study, but only partial time
integrated rates, with the tag time, either preceding or following the decay of
the other meson to a final state f. f may be a CP eigenstate or a non-CP
eigenstate.Comment: 11 Pages Revte
Survival in equilibrium step fluctuations
We report the results of analytic and numerical investigations of the time
scale of survival or non-zero-crossing probability in equilibrium step
fluctuations described by Langevin equations appropriate for
attachment/detachment and edge-diffusion limited kinetics. An exact relation
between long-time behaviors of the survival probability and the autocorrelation
function is established and numerically verified. is shown to exhibit
simple scaling behavior as a function of system size and sampling time. Our
theoretical results are in agreement with those obtained from an analysis of
experimental dynamical STM data on step fluctuations on Al/Si(111) and Ag(111)
surfaces.Comment: RevTeX, 4 pages, 3 figure
Simulation study of random sequential adsorption of mixtures on a triangular lattice
Random sequential adsorption of binary mixtures of extended objects on a
two-dimensional triangular lattice is studied numerically by means of Monte
Carlo simulations. The depositing objects are formed by self-avoiding random
walks on the lattice. We concentrate here on the influence of the symmetry
properties of the shapes on the kinetics of the deposition processes in
two-component mixtures. Approach to the jamming limit in the case of mixtures
is found to be exponential, of the form: and the values of the parameter
are determined by the order of symmetry of the less symmetric object
in the mixture. Depending on the local geometry of the objects making the
mixture, jamming coverage of a mixture can be either greater than both
single-component jamming coverages or it can be in between these values.
Results of the simulations for various fractional concentrations of the objects
in the mixture are also presented.Comment: 11 figures, 2 table
Effects of Possible Transitions in Neutral Meson Decays}
We explore the possibility that the existing data on like-sign dileptons at
the resonance consist of events arising from mixing and also from transitions. The
consequences of these nonstandard transitions for certain time-asymmetries
which are likely to be measured at the factories are studied.Comment: {\LARGE \bf 10 pages, no figures, process using latex, TIFR/TH/93-5
Analysis of hadronic invariant mass spectrum in inclusive charmless semileptonic B decays
We make an analysis of the hadronic invariant mass spectrum in inclusive
charmless semileptonic B meson decays in a QCD-based approach. The decay width
is studied as a function of the invariant mass cut. We examine their
sensitivities to the parameters of the theory. The theoretical uncertainties in
the determination of from the hadronic invariant mass spectrum are
investigated. A strategy for improving the theoretical accuracy in the value of
is described.Comment: 13 pages, 5 Postscript figure
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
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