18,822 research outputs found
Radiative Transfer in a Discrete Random Medium Adjacent to a Half-Space with a Rough Interface
For a macroscopically plane-parallel discrete random medium, the boundary conditions for the specific coherency dyadic at a rough interface are derived. The derivation is based on a modification of the Twersky approximation for a scattering system consisting of a group of particles and the rough surface, and reduces to the solution of the scattering problem for a rough surface illuminated by a plane electromagnetic wave propagating in a discrete random medium with non-scattering boundaries. In a matrix-form setting, the boundary conditions for the specific coherency dyadic imply the boundary conditions for specific intensity column vectors which in turn, yield the expressions for the reflection and transmission matrices. The derived expressions are shown to be identical to those obtained by applying a phenomenological approach based on a facet model to the solution of the scattering problem for a rough surface illuminated by a plane electromagnetic wave
Characterization and mapping of surface physical properties of Mars from CRISM multi-angular data: application to Gusev Crater and Meridiani Planum
The analysis of the surface texture from the particle (grain size, shape and
internal structure) to its organization (surface roughness) provides
information on the geological processes. CRISM multi-angular observations
(varied emission angles) allow to characterize the surface scattering behavior
which depends on the composition but also the material physical properties
(e.g., grain size, shape, internal structure, the surface roughness). After an
atmospheric correction by the Multi-angle Approach for Retrieval of the Surface
Reflectance from CRISM Observations, the surface reflectances at different
geometries are analyzed by inverting the Hapke photometric model depending on
the single scattering albedo, the 2-term phase function, the macroscopic
roughness and the 2-term opposition effects. Surface photometric maps are
created to observe the spatial variations of surface scattering properties as a
function of geological units at the CRISM spatial resolution (200m/pixel). An
application at the Mars Exploration Rover (MER) landing sites located at Gusev
Crater and Meridiani Planum where orbital and in situ observations are
available, is presented. Complementary orbital observations (e.g. CRISM
spectra, THermal EMission Imaging System, High Resolution Imaging Science
Experiment images) are used for interpreting the estimated Hapke photometric
parameters in terms of physical properties. The in situ observations are used
as ground truth to validate the interpretations. Varied scattering properties
are observed inside a CRISM observation (5x10km) suggesting that the surfaces
are controlled by local geological processes (e.g. volcanic resurfacing,
aeolian and impact processes) rather than regional or global. Consistent
results with the in situ observations are observed thus validating the approach
and the use of photometry for the characterization of Martian surface physical
properties
Surface effects on the orbital order in the single layered manganite La0.5Sr1.5MnO4
We report the first observation of `orbital truncation rods' -- the
scattering arising from the termination of bulk orbital order at the surface of
a crystal. The x-ray measurements, performed on a cleaved, single-layered
perovskite, La0.5Sr1.5MnO4, reveal that while the crystallographic surface is
atomically smooth, the orbital `surface' is much rougher, with an r.m.s.
deviation from the average `surface' of ~0.7nm. The temperature dependence of
this scattering shows evidence of a surface-induced second order transition.Comment: 13 pages, 4 figure
The application of ultrasonic NDT techniques in tribology
The use of ultrasonic reflection is emerging as a technique for studying tribological contacts. Ultrasonic waves can be transmitted non-destructively through machine components and their behaviour at an interface describes the characteristics of that contact. This paper is a review of the current state of understanding of the mechanisms of ultrasonic reflection at interfaces, and how this has been used to investigate the processes of dry rough surface contact and lubricated contact. The review extends to cover how ultrasound has been used to study the tribological function of certain engineering machine elements
Near-field heat transfer between a nanoparticle and a rough surface
In this work we focus on the surface roughness correction to the near-field
radiative heat transfer between a nanoparticle and a material with a rough
surface utilizing a direct perturbation theory up to second order in the
surface profile. We discuss the different distance regimes for the local
density of states above the rough material and the heat flux analytically and
numerically. We show that the heat transfer rate is larger than that
corresponding to a flat surface at short distances. At larger distances it can
become smaller due to surface polariton scattering by the rough surface. For
distances much smaller than the correlation length of the surface profile, we
show that the results converge to a proximity approximation, whereas in the
opposite limit the rough surface can be replaced by an equivalent surface
layer
Grazing Incidence Small Angle X-Ray Scattering (GISAXS) on Small Targets Using Large Beams
GISAXS is often used as a versatile tool for the contactless and
destruction-free investigation of nanostructured surfaces. However, due to the
shallow incidence angles, the footprint of the X-ray beam is significantly
elongated, limiting GISAXS to samples with typical target lengths of several
millimetres. For many potential applications, the production of large target
areas is impractical, and the targets are surrounded by structured areas.
Because the beam footprint is larger than the targets, the surrounding
structures contribute parasitic scattering, burying the target signal. In this
paper, GISAXS measurements of isolated as well as surrounded grating targets in
Si substrates with line lengths from down to
are presented. For the isolated grating targets, the changes in the scattering
patterns due to the reduced target length are explained. For the surrounded
grating targets, the scattering signal of a target grating structure is separated from the
scattering signal of nanostructured
surroundings by producing the target with a different orientation with respect
to the predominant direction of the surrounding structures. The described
technique allows to apply GISAXS, e.g. for characterization of metrology fields
in the semiconductor industry, where up to now it has been considered
impossible to use this method due to the large beam footprint
Propagation and filtering of elastic and electromagnetic waves in piezoelectric composite structures
In this article we discuss the modelling of elastic and electromagnetic wave
propagation through one- and two-dimensional structured piezoelectric solids.
Dispersion and the effect of piezoelectricity on the group velocity and
positions of stop bands are studied in detail. We will also analyze the
reflection and transmission associated with the problem of scattering of an
elastic wave by a heterogeneous piezoelectric stack. Special attention is given
to the occurrence of transmission resonances in finite stacks and their
dependence on a piezoelectric effect. A 2D doubly-periodic piezoelectric
checkerboard structure is subsequently introduced, for which the dispersion
surfaces for Bloch waves have been constructed and analysed, with the emphasis
on the dynamic anisotropy and special features of standing waves within the
piezoelectric structure.Comment: 24 pages, 18 figures, 3 tables. Preprint version of a research
article, accepted for publication in "Mathematical Methods in the Applied
Science (2016)
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