96,092 research outputs found
Near-Surface Interface Detection for Coal Mining Applications Using Bispectral Features and GPR
The use of ground penetrating radar (GPR) for detecting the presence of near-surface interfaces is a scenario of special interest to the underground coal mining industry. The problem is difficult to solve in practice because the radar echo from the near-surface interface is often dominated by unwanted components such as antenna crosstalk and ringing, ground-bounce effects, clutter, and severe attenuation. These nuisance components are also highly sensitive to subtle variations in ground conditions, rendering the application of standard signal pre-processing techniques such as background subtraction largely ineffective in the unsupervised case. As a solution to this detection problem, we develop a novel pattern recognition-based algorithm which utilizes a neural network to classify features derived from the bispectrum of 1D early time radar data. The binary classifier is used to decide between two key cases, namely whether an interface is within, for example, 5 cm of the surface or not. This go/no-go detection capability is highly valuable for underground coal mining operations, such as longwall mining, where the need to leave a remnant coal section is essential for geological stability. The classifier was trained and tested using real GPR data with ground truth measurements. The real data was acquired from a testbed with coal-clay, coal-shale and shale-clay interfaces, which represents a test mine site. We show that, unlike traditional second order correlation based methods such as matched filtering which can fail even in known conditions, the new method reliably allows the detection of interfaces using GPR to be applied in the near-surface region. In this work, we are not addressing the problem of depth estimation, rather confining ourselves to detecting an interface within a particular depth range
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Technical Review of Residential Programmable Communicating Thermostat Implementation for Title 24-2008
Three basic issues concerning interface dynamics in nonequilibrium pattern formation
These are lecture notes of a course given at the 9th International Summer
School on Fundamental Problems in Statistical Mechanics, held in Altenberg,
Germany, in August 1997. In these notes, we discuss at an elementary level
three themes concerning interface dynamics that play a role in pattern forming
systems: (i) We briefly review three examples of systems in which the normal
growth velocity is proportional to the gradient of a bulk field which itself
obeys a Laplace or diffusion type of equation (solidification, viscous fingers
and streamers), and then discuss why the Mullins-Sekerka instability is common
to all such gradient systems. (ii) Secondly, we discuss how underlying an
effective interface description of systems with smooth fronts or transition
zones, is the assumption that the relaxation time of the appropriate order
parameter field(s) in the front region is much smaller than the time scale of
the evolution of interfacial patterns. Using standard arguments we illustrate
that this is generally so for fronts that separate two (meta)stable phases: in
such cases, the relaxation is typically exponential, and the relaxation time in
the usual models goes to zero in the limit in which the front width vanishes.
(iii) We finally summarize recent results that show that so-called ``pulled''
or ``linear marginal stability'' fronts which propagate into unstable states
have a very slow universal power law relaxation. This slow relaxation makes the
usual ``moving boundary'' or ``effective interface'' approximation for problems
with thin fronts, like streamers, impossible.Comment: 48 pages, TeX with elsart style file (included), 9 figure
Polarization Modeling and Predictions for DKIST Part 2: Application of the Berreman Calculus to Spectral Polarization Fringes of Beamsplitters and Crystal Retarders
We outline polarization fringe predictions derived from a new application of
the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder
optics. The DKIST retarder baseline design used 6 crystals, single-layer
anti-reflection coatings, thick cover windows and oil between all optical
interfaces. This new tool estimates polarization fringes and optic Mueller
matrices as functions of all optical design choices. The amplitude and period
of polarized fringes under design changes, manufacturing errors, tolerances and
several physical factors can now be estimated. This tool compares well with
observations of fringes for data collected with the SPINOR spectropolarimeter
at the Dunn Solar Telescope using bi-crystalline achromatic retarders as well
as laboratory tests. With this new tool, we show impacts of design decisions on
polarization fringes as impacted by anti-reflection coatings, oil refractive
indices, cover window presence and part thicknesses. This tool helped DKIST
decide to remove retarder cover windows and also recommends reconsideration of
coating strategies for DKIST. We anticipate this tool to be essential in
designing future retarders for mitigation of polarization and intensity fringe
errors in other high spectral resolution astronomical systems.Comment: Accepted for publication in JATI
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