17,251 research outputs found
Temperature dependence of surface reconstructions of Au on Pd(110)
Surface reconstructions of Au film on Pd(110) substrate are studied using a
local Einstein approximation to quasiharmonic theory with the Sutton-Chen
interatomic potential. Temperature dependent surface free energies for
different coverages and surface structures are calculated. Experimentally
observed transformations from to and
structures can be explained in the framework of this model. Also conditions for
Stranski-Krastanov growth mode are found to comply with experiments. The domain
of validity of the model neglecting mixing entropy is analyzed.Comment: 7 pages, REVTeX two-column format, 3 postscript figures available on
request from [email protected] To appear in Phys. Rev. Letter
Synthesizing Program Input Grammars
We present an algorithm for synthesizing a context-free grammar encoding the
language of valid program inputs from a set of input examples and blackbox
access to the program. Our algorithm addresses shortcomings of existing grammar
inference algorithms, which both severely overgeneralize and are prohibitively
slow. Our implementation, GLADE, leverages the grammar synthesized by our
algorithm to fuzz test programs with structured inputs. We show that GLADE
substantially increases the incremental coverage on valid inputs compared to
two baseline fuzzers
A tight binding model for water
We demonstrate for the first time a tight binding model for water
incorporating polarizable anions. A novel aspect is that we adopt a "ground up"
approach in that properties of the monomer and dimer only are fitted.
Subsequently we make predictions of the structure and properties of hexamer
clusters, ice-XI and liquid water. A particular feature, missing in current
tight binding and semiempirical hamiltonians, is that we reproduce the almost
two-fold increase in molecular dipole moment as clusters are built up towards
the limit of bulk liquid. We concentrate on properties of liquid water which
are very well rendered in comparison with experiment and published density
functional calculations. Finally we comment on the question of the contrasting
densities of water and ice which is central to an understanding of the
subtleties of the hydrogen bond
Dynamics of Spreading of Small Droplets of Chainlike Molecules on Surfaces
Dynamics of spreading of small droplets on surfaces has been studied by the
molecular dynamics method. Simulations have been performed for mixtures of
solvent and dimer, and solvent and tetramer droplets. For solvent particles and
dimers, layering occurs leading to stepped droplet shapes. For tetramers such
shapes occur for relatively deep and strong surface potentials only. For wider
and more shallow potentials, more rapid spreading and rounded droplet shapes
occur. These results are in accordance with experimental data on small non -
volatile polymer droplets. PACS numbers: 68.10Gw, 05.70.Ln, 61.20.Ja, 68.45GdComment: to appear in Europhys. Letters (1994), Latex, 12 page
Towards a Universal Theory of Artificial Intelligence based on Algorithmic Probability and Sequential Decision Theory
Decision theory formally solves the problem of rational agents in uncertain
worlds if the true environmental probability distribution is known.
Solomonoff's theory of universal induction formally solves the problem of
sequence prediction for unknown distribution. We unify both theories and give
strong arguments that the resulting universal AIXI model behaves optimal in any
computable environment. The major drawback of the AIXI model is that it is
uncomputable. To overcome this problem, we construct a modified algorithm
AIXI^tl, which is still superior to any other time t and space l bounded agent.
The computation time of AIXI^tl is of the order t x 2^l.Comment: 8 two-column pages, latex2e, 1 figure, submitted to ijca
The equation of state of solid nickel aluminide
The pressure-volume-temperature equation of state of the intermetallic
compound NiAl was calculated theoretically, and compared with experimental
measurements. Electron ground states were calculated for NiAl in the CsCl
structure, using density functional theory, and were used to predict the cold
compression curve and the density of phonon states. The Rose form of
compression curve was found to reproduce the ab initio calculations well in
compression but exhibited significant deviations in expansion. A
thermodynamically-complete equation of state was constructed for NiAl. Shock
waves were induced in crystals of NiAl by the impact of laser-launched Cu
flyers and by launching NiAl flyers into transparent windows of known
properties. The TRIDENT laser was used to accelerate the flyers to speeds
between 100 and 600m/s. Point and line-imaging laser Doppler velocimetry was
used to measure the acceleration of the flyer and the surface velocity history
of the target. The velocity histories were used to deduce the stress state, and
hence states on the principal Hugoniot and the flow stress. Flyers and targets
were recovered from most experiments. The effect of elasticity and plastic flow
in the sample and window was assessed. The ambient isotherm reproduced static
compression data very well, and the predicted Hugoniot was consistent with
shock compression data
Validating accelerometry-derived proxies of energy expenditure using the doubly-labelled water method in the smallest penguin species
Acknowledgements We are grateful to Dr Catherine Hambly and Peter Thompson for technical assistance with the isotope analysis for the doubly labelled water measurements. We thank Parks Victoria (in particular, the rangers at Gabo Island and Port Campbell Offices) and Kevin Lotte for logistical support. Funding This project was funded by the Holsworth Wildlife Research Endowment ā Equity Trustees Charitable Foundation and the Ecological Society of Australia and Deakin University internal funds.Peer reviewedPublisher PD
Inelastic quantum transport: the self-consistent Born approximation and correlated electron-ion dynamics
A dynamical method for inelastic transport simulations in nanostructures is
compared with a steady-state method based on non-equilibrium Green's functions.
A simplified form of the dynamical method produces, in the steady state in the
weak-coupling limit, effective self-energies analogous to those in the Born
Approximation due to electron-phonon coupling. The two methods are then
compared numerically on a resonant system consisting of a linear trimer weakly
embedded between metal electrodes. This system exhibits enhanced heating at
high biases and long phonon equilibration times. Despite the differences in
their formulation, the static and dynamical methods capture local
current-induced heating and inelastic corrections to the current with good
agreement over a wide range of conditions, except in the limit of very high
vibrational excitations, where differences begin to emerge.Comment: 12 pages, 7 figure
- ā¦