1,560 research outputs found
Measuring the Hausdorff Dimension of Quantum Mechanical Paths
We measure the propagator length in imaginary time quantum mechanics by Monte
Carlo simulation on a lattice and extract the Hausdorff dimension . We
find that all local potentials fall into the same universality class giving
like the free motion. A velocity dependent action () in the path integral (e.g. electrons moving in
solids, or Brueckner's theory of nuclear matter) yields if and if . We discuss the
relevance of fractal pathes in solid state physics and in , in particular
for the Wilson loop in .Comment: uuencoded and compressed shell archive file. 8 pages with 7 figure
Evolution of unoccupied resonance during the synthesis of a silver dimer on Ag(111)
Silver dimers were fabricated on Ag(111) by single-atom manipulation using
the tip of a cryogenic scanning tunnelling microscope. An unoccupied electronic
resonance was observed to shift toward the Fermi level with decreasing
atom-atom distance as monitored by spatially resolved scanning tunnelling
spectroscopy. Density functional calculations were used to analyse the
experimental observations and revealed that the coupling between the adsorbed
atoms is predominantly direct rather than indirect via the Ag(111) substrate.Comment: 9 pages, 3 figure
Defect distribution in a-plane GaN on Al2O3
The authors studied the structural and point defect distributions of hydride vapor phase epitaxial GaN film grown in the [11−20] a direction on (1−102) r-plane sapphire with metal-organic vapor phase deposited a-GaN template using transmission electron microscopy, secondary ion mass spectrometry, and positron annihilation spectroscopy. Grown-in extended and point defects show constant behavior as a function of thickness, contrary to the strong nonuniform defect distribution observed in GaN grown along the [0001] direction. The observed differences are explained by orientation-dependent and kinetics related defect incorporation.Peer reviewe
Interfacial separation between elastic solids with randomly rough surfaces: comparison of experiment with theory
We study the average separation between an elastic solid and a hard solid
with a nominal flat but randomly rough surface, as a function of the squeezing
pressure. We present experimental results for a silicon rubber (PDMS) block
with a flat surface squeezed against an asphalt road surface. The theory shows
that an effective repulse pressure act between the surfaces of the form p
proportional to exp(-u/u0), where u is the average separation between the
surfaces and u0 a constant of order the root-mean-square roughness, in good
agreement with the experimental results.Comment: 6 pages, 10 figure
Tuning the properties of complex transparent conducting oxides: role of crystal symmetry, chemical composition and carrier generation
The electronic properties of single- and multi-cation transparent conducting
oxides (TCOs) are investigated using first-principles density functional
approach. A detailed comparison of the electronic band structure of
stoichiometric and oxygen deficient InO, - and
-GaO, rock salt and wurtzite ZnO, and layered InGaZnO
reveals the role of the following factors which govern the transport and
optical properties of these TCO materials: (i) the crystal symmetry of the
oxides, including both the oxygen coordination and the long-range structural
anisotropy; (ii) the electronic configuration of the cation(s), specifically,
the type of orbital(s) -- , or -- which form the conduction band;
and (iii) the strength of the hybridization between the cation's states and the
p-states of the neighboring oxygen atoms. The results not only explain the
experimentally observed trends in the electrical conductivity in the
single-cation TCO, but also demonstrate that multicomponent oxides may offer a
way to overcome the electron localization bottleneck which limits the charge
transport in wide-bandgap main-group metal oxides. Further, the advantages of
aliovalent substitutional doping -- an alternative route to generate carriers
in a TCO host -- are outlined based on the electronic band structure
calculations of Sn, Ga, Ti and Zr-doped InGaZnO. We show that the
transition metal dopants offer a possibility to improve conductivity without
compromising the optical transmittance
Assortativity Decreases the Robustness of Interdependent Networks
It was recently recognized that interdependencies among different networks
can play a crucial role in triggering cascading failures and hence system-wide
disasters. A recent model shows how pairs of interdependent networks can
exhibit an abrupt percolation transition as failures accumulate. We report on
the effects of topology on failure propagation for a model system consisting of
two interdependent networks. We find that the internal node correlations in
each of the two interdependent networks significantly changes the critical
density of failures that triggers the total disruption of the two-network
system. Specifically, we find that the assortativity (i.e. the likelihood of
nodes with similar degree to be connected) within a single network decreases
the robustness of the entire system. The results of this study on the influence
of assortativity may provide insights into ways of improving the robustness of
network architecture, and thus enhances the level of protection of critical
infrastructures
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