6,013 research outputs found
Island Distance in One-Dimensional Epitaxial Growth
The typical island distance in submonlayer epitaxial growth depends on
the growth conditions via an exponent . This exponent is known to
depend on the substrate dimensionality, the dimension of the islands, and the
size of the critical nucleus for island formation. In this paper we study
the dependence of on in one--dimensional epitaxial growth. We
derive that for and confirm this result
by computer simulations.Comment: 5 pages, 3 figures, uses revtex, psfig, 'Note added in proof'
appende
PUBLIC CHOICE IN INTERNATIONAL POLLUTION
Environmental Economics and Policy,
Orientation Dependence of Step Stiffness: Failure of SOS and Ising Models to Describe Experimental Data
We have investigated the step stiffness on Cu(001) surfaces as a function of
step orientation by two independent methods at several temperatures near 300 K.
Both sets of data agree well and show a substantial dependence of the stiffness
on the angle of orientation. With the exception of steps oriented along
, the experimental stiffness is significantly larger than the stiffness
calculated within the solid-on-solid (SOS) model and the Ising-model, even if
next nearest-neighbor interactions are taken into account. Our results have
considerable consequences for the understanding and for the theoretical
modeling of equilibrium and growth phenomena, such as step meandering
instabilities.Comment: 5 pages, 2 figure
Utility Functions of Equivalent Form and the Effect of Parameter Changes on Optimum Decision Making
We derive a class of utility functions that are equivalent with respect to a well-defined functional form. We study the case of constant relative risk aversion (of some order) to investigate on different equivalence relations in order to determine the, possibly infinite, number of equivalence classes when utility functions satisfy a specific form. Then we apply our results to standard applications in economics and finance, for example, to the effect of price volatility on optimum hedging. --equivalence class,risk aversion,sensitivity analysis
Dielectric tuning and coupling of whispering gallery modes using an anisotropic prism
Optical whispering gallery mode (WGM) resonators are a powerful and versatile
tool used in many branches of science. Fine tuning of the central frequency and
line width of individual resonances is however desirable in a number of
applications including frequency conversion, optical communications and
efficient light-matter coupling. To this end we present a detailed theoretical
analysis of dielectric tuning of WGMs supported in axisymmetric resonators.
Using the Bethe-Schwinger equation and adopting an angular spectrum field
representation we study the resonance shift and mode broadening of high
WGMs when a planar dielectric substrate is brought close to the resonator.
Particular focus is given to use of a uniaxial substrate with an arbitrarily
aligned optic axis. Competing red and blue resonance shifts ( MHz),
deriving from generation of a near field material polarisation and back action
from the radiation continuum respectively, are found. Anomalous resonance
shifts can hence be observed depending on the substrate material, whereas mode
broadening on the order of MHz can also be simply realised.
Furthermore, polarisation selective coupling with extinction ratios of
can be achieved when the resonator and substrate are of the same composition
and their optic axes are chosen correctly. Double refraction and properties of
out-coupled beams are also discussed
A SYSTEMS MODEL OF THE INDIRECT ENERGY EXPENDED IN FARM MACHINERY PRODUCTION AND USE
Resource /Energy Economics and Policy,
Resonant Electro-Optic Frequency Comb
High speed optical telecommunication is enabled by wavelength division
multiplexing, whereby hundreds of individually stabilized lasers encode the
information within a single mode optical fiber. In the seek for larger
bandwidth the optical power sent into the fiber is limited by optical
non-linearities within the fiber and energy consumption of the light sources
starts to become a significant cost factor. Optical frequency combs have been
suggested to remedy this problem by generating multiple laser lines within a
monolithic device, their current stability and coherence lets them operate only
in small parameter ranges. Here we show that a broadband frequency comb
realized through the electro-optic effect within a high quality whispering
gallery mode resonator can operate at low microwave and optical powers.
Contrary to the usual third order Kerr non-linear optical frequency combs we
rely on the second order non-linear effect which is much more efficient. Our
result uses a fixed microwave signal which is mixed with an optical pump signal
to generate a coherent frequency comb with a precisely determined carrier
separation. The resonant enhancement enables us to operate with microwave
powers three order magnitude smaller than in commercially available devices. We
can expect the implementation into the next generation long distance
telecommunication which relies on coherent emission and detection schemes to
allow for operation with higher optical powers and at reduced cost
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