121,571 research outputs found
Geochemical characterization of supraglacial debris via in situ and optical remote sensing methods: a case study in Khumbu Himalaya, Nepal
Surface glacier debris samples and field spectra were collected from the ablation zones of Nepal Himalaya Ngozumpa and Khumbu glaciers in November and December 2009. Geochemical and mineral compositions of supraglacial debris were determined by X-ray diffraction and X-ray fluorescence spectroscopy. This composition data was used as ground truth in evaluating field spectra and satellite supraglacial debris composition and mapping methods. Satellite remote sensing methods for characterizing glacial surface debris include visible to thermal infrared hyper- and multispectral reflectance and emission signature identification, semi-quantitative mineral abundance indicies and spectral image composites. Satellite derived supraglacial debris mineral maps displayed the predominance of layered silicates, hydroxyl-bearing and calcite minerals on Khumbu Himalayan glaciers. Supraglacial mineral maps compared with satellite thermal data revealed correlations between glacier surface composition and glacier surface temperature. Glacier velocity displacement fields and shortwave, thermal infrared false color composites indicated the magnitude of mass flux at glacier confluences. The supraglacial debris mapping methods presented in this study can be used on a broader scale to improve, supplement and potentially reduce errors associated with glacier debris radiative property, composition, areal extent and mass flux quantifications
Rock Joint Surfaces Measurement and Analysis of Aperture Distribution under Different Normal and Shear Loading Using GIS
Geometry of the rock joint is a governing factor for joint mechanical and
hydraulic behavior. A new method of evaluating aperture distribution based on
measurement of joint surfaces and three dimensional characteristics of each
surface is developed. Artificial joint of granite surfaces are
measured,processed, analyzed and three dimensional approaches are carried out
for surface characterization. Parameters such as asperity's heights, slope
angles, and aspects distribution at micro scale,local concentration of elements
and their spatial localization at local scale are determined by Geographic
Information System (GIS). Changes of aperture distribution at different normal
stresses and various shear displacements are visualized and interpreted.
Increasing normal load causes negative changes in aperture frequency
distribution which indicates high joint matching. However, increasing shear
displacement causes a rapid increase in the aperture and positive changes in
the aperture frequency distribution which could be due to unmatching, surface
anisotropy and spatial localization of contact points with proceeding shear
Bayesian Identification of Elastic Constants in Multi-Directional Laminate from Moir\'e Interferometry Displacement Fields
The ply elastic constants needed for classical lamination theory analysis of
multi-directional laminates may differ from those obtained from unidirectional
laminates because of three dimensional effects. In addition, the unidirectional
laminates may not be available for testing. In such cases, full-field
displacement measurements offer the potential of identifying several material
properties simultaneously. For that, it is desirable to create complex
displacement fields that are strongly influenced by all the elastic constants.
In this work, we explore the potential of using a laminated plate with an
open-hole under traction loading to achieve that and identify all four ply
elastic constants (E 1, E 2, 12, G 12) at once. However, the accuracy of the
identified properties may not be as good as properties measured from individual
tests due to the complexity of the experiment, the relative insensitivity of
the measured quantities to some of the properties and the various possible
sources of uncertainty. It is thus important to quantify the uncertainty (or
confidence) with which these properties are identified. Here, Bayesian
identification is used for this purpose, because it can readily model all the
uncertainties in the analysis and measurements, and because it provides the
full coupled probability distribution of the identified material properties. In
addition, it offers the potential to combine properties identified based on
substantially different experiments. The full-field measurement is obtained by
moir\'e interferometry. For computational efficiency the Bayesian approach was
applied to a proper orthogonal decomposition (POD) of the displacement fields.
The analysis showed that the four orthotropic elastic constants are determined
with quite different confidence levels as well as with significant correlation.
Comparison with manufacturing specifications showed substantial difference in
one constant, and this conclusion agreed with earlier measurement of that
constant by a traditional four-point bending test. It is possible that the POD
approach did not take full advantage of the copious data provided by the full
field measurements, and for that reason that data is provided for others to use
(as on line material attached to the article)
Deconvolving the information from an imperfect spherical gravitational wave antenna
We have studied the effects of imperfections in spherical gravitational wave
antenna on our ability to properly interpret the data it will produce. The
results of a numerical simulation are reported that quantitatively describe the
systematic errors resulting from imperfections in various components of the
antenna. In addition, the results of measurements on a room-temperature
prototype are presented that verify it is possible to accurately deconvolve the
data in practice.Comment: 5 pages, 2 figures, to be published in Europhysics Letter
Computation of a combined spherical-elastic and viscous-half-space earth model for ice sheet simulation
This report starts by describing the continuum model used by Lingle & Clark
(1985) to approximate the deformation of the earth under changing ice sheet and
ocean loads. That source considers a single ice stream, but we apply their
underlying model to continent-scale ice sheet simulation. Their model combines
Farrell's (1972) elastic spherical earth with a viscous half-space overlain by
an elastic plate lithosphere. The latter half-space model is derivable from
calculations by Cathles (1975). For the elastic spherical earth we use
Farrell's tabulated Green's function, as do Lingle & Clark. For the half-space
model, however, we propose and implement a significantly faster numerical
strategy, a spectral collocation method (Trefethen 2000) based directly on the
Fast Fourier Transform. To verify this method we compare to an integral formula
for a disc load. To compare earth models we build an accumulation history from
a growing similarity solution from (Bueler, et al.~2005) and and simulate the
coupled (ice flow)-(earth deformation) system. In the case of simple isostasy
the exact solution to this system is known. We demonstrate that the magnitudes
of numerical errors made in approximating the ice-earth system are
significantly smaller than pairwise differences between several earth models,
namely, simple isostasy, the current standard model used in ice sheet
simulation (Greve 2001, Hagdorn 2003, Zweck & Huybrechts 2005), and the Lingle
& Clark model. Therefore further efforts to validate different earth models
used in ice sheet simulations are, not surprisingly, worthwhile.Comment: 36 pages, 16 figures, 3 Matlab program
Discontinuities without discontinuity: The Weakly-enforced Slip Method
Tectonic faults are commonly modelled as Volterra or Somigliana dislocations
in an elastic medium. Various solution methods exist for this problem. However,
the methods used in practice are often limiting, motivated by reasons of
computational efficiency rather than geophysical accuracy. A typical
geophysical application involves inverse problems for which many different
fault configurations need to be examined, each adding to the computational
load. In practice, this precludes conventional finite-element methods, which
suffer a large computational overhead on account of geometric changes. This
paper presents a new non-conforming finite-element method based on weak
imposition of the displacement discontinuity. The weak imposition of the
discontinuity enables the application of approximation spaces that are
independent of the dislocation geometry, thus enabling optimal reuse of
computational components. Such reuse of computational components renders
finite-element modeling a viable option for inverse problems in geophysical
applications. A detailed analysis of the approximation properties of the new
formulation is provided. The analysis is supported by numerical experiments in
2D and 3D.Comment: Submitted for publication in CMAM
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