9,265 research outputs found
Thermal response of jointed rock masses inferred from infrared thermographic surveying (Acuto test-site, Italy)
The Mediterranean region is affected by considerable daily and seasonal temperature variations due to intense solar radiation. In mid-seasons, thermal excursions can exceed tens of degrees thus influencing the long-term behaviour of jointed rock masses acting as a preparatory factor for rock slope instabilities. In order to evaluate the thermal response of a densely jointed rock-block, monitoring has been in operation since 2016 by direct and remote sensing techniques in an abandoned quarry in Acuto (central Italy). Monthly InfraRed Thermographic (IRT) surveys were carried out on its exposed faces and along sections of interest across monitored main joints. The results highlight the daily and seasonal cyclical behaviour, constraining amplitudes and rates of heating and cooling phases. The temperature time-series revealed the effect of sun radiation and exposure on thermal response of the rock-block, which mainly depends on the seasonal conditions. The influence of opened joints in the heat propagation is revealed by the differential heating experienced across it, which was verified under 1D and 2D analysis. IRT has proved to be a valid monitoring technique in supporting traditional approaches, for the definition of the surficial temperature distribution on rock masses or stone building materials
Profile extrema for visualizing and quantifying uncertainties on excursion regions. Application to coastal flooding
We consider the problem of describing excursion sets of a real-valued
function , i.e. the set of inputs where is above a fixed threshold. Such
regions are hard to visualize if the input space dimension, , is higher than
2. For a given projection matrix from the input space to a lower dimensional
(usually ) subspace, we introduce profile sup (inf) functions that
associate to each point in the projection's image the sup (inf) of the function
constrained over the pre-image of this point by the considered projection.
Plots of profile extrema functions convey a simple, although intrinsically
partial, visualization of the set. We consider expensive to evaluate functions
where only a very limited number of evaluations, , is available, e.g.
, and we surrogate with a posterior quantity of a Gaussian process
(GP) model. We first compute profile extrema functions for the posterior mean
given evaluations of . We quantify the uncertainty on such estimates by
studying the distribution of GP profile extrema with posterior
quasi-realizations obtained from an approximating process. We control such
approximation with a bound inherited from the Borell-TIS inequality. The
technique is applied to analytical functions () and to a -dimensional
coastal flooding test case for a site located on the Atlantic French coast.
Here is a numerical model returning the area of flooded surface in the
coastal region given some offshore conditions. Profile extrema functions
allowed us to better understand which offshore conditions impact large flooding
events
Spatio-temporal modelling of wave formation in an excitable chemical medium based on a revised FitzHugh-Nagumo model
The wavefront profile and the propagation velocity of waves in an experimentally observed Belousov-Zhabotinskii reaction are analyzed and a revised FitzHumgh-Nagumo(FHN)
model of these systems is identified. The ratio between the excitation period and the recovery period, for a solitary wave are studied, and included within the model. Averaged
travelling velocities at different spatial positions are shown to be consistent under the same experimental conditions. The relationship between the propagation velocity and the curvature of the wavefront are also studied to deduce the diffusion coefficient in the model, which is a function of the curvature of the wavefront and not a constant. The application of the identified model is demonstrated on real experimental data and validated using multi-step ahead predictions
Ghana airborne geophysics project in the Volta and Keta Basin : BGS final report
This report describes the work undertaken by BGS between November 2006 and March 2009 in
collaboration with Fugro Airborne Surveys Pty Ltd on an airborne geophysical survey and
ground reconnaissance mapping of the Volta River and Keta Basins, Ghana. The project was
supported by the EU as part of the Mining Sector Support Programme, Project Number 8ACP
GH 027/13. The initial contract duration was three years, but this was extended by five months
to account for acquisition of gravity data by another project.
Some parts of Ghana have been airborne surveyed as part of the Mining Sector Development and
Environmental Project, co-funded by the World Bank and the Nordic Development Fund, but no
work was carried out on the Volta River and Keta basins, which together form a major portion of
the Ghanaian territory.
The approximate areas covered by the surveys are estimated at 98,000 km² for the satellite
imagery and the airborne geophysics, except for the Time Domain Electromagnetic (TDEM)
survey which was limited to 60,000 km².
The main beneficiary of this project is the Geological Survey Department, GSD. The work
enhanced its geological infrastructure and its personnel received hands-on training on modern
geological mapping technology. Indirect beneficiaries were the mining and exploration
companies that can follow up the reconnaissance work with detailed exploration work.
The project was conducted in five phases, and this document reports on the BGS input to Phase
1, 4 and 5, with no inputs required in Phases 2 and 3:
• Phase1: geological outline through Radar and optical satellite imageries.
• Phase 2: airborne geophysical survey over the two basins for magnetics and
Gamma Ray spectrometry (Fugro survey).
• Phase 3: airborne electromagnetic and magnetic geophysical survey of specific
areas, following the completion and interpretation of phase 2, using fixed wing
time domain technology (Fugro survey).
• Phase 4: interpretation of the combined geology and geophysics.
• Phase 5: production of factual and interpretation maps.
The full list of BGS products is outlined in Table 1 below, while Jordan et al. (2006) describe the
products delivered on schedule in Phase 1
Roughness variability estimation of microscopic surfaces during engineering wear process-Application to total hip implant
International audienceThis paper proposes a new method to estimate the roughness changes from topographic features of microscopic surfaces during an engineering wear process. We demonstrate that the evolution of the significant upcrossings of surface topography is the most efficient way to estimate the roughness changes associated with the small-scale changes during the time of wear process. The motivation of this work comes from the fact that the surface roughness is, largely, interpolated with many important mechanical and physical phenomena, such as friction, and wear behaviour during the mechanical contact between joined and sliding surfaces. A special application is investigated on UHMWPE (Ultra High Molecular Weight Polythene) components involved in total hip implants. The aim is to understand the in-vitro wear mechanism of the UHMWPE surface by estimating its roughness evolution
Variation of the Diameter of the Sun as Measured by the Solar Disk Sextant (SDS)
The balloon-borne Solar Disk Sextant (SDS) experiment has measured the
angular size of the Sun on seven occasions spanning the years 1992 to 2011. The
solar half-diameter -- observed in a 100-nm wide passband centred at 615 nm --
is found to vary over that period by up to 200 mas, while the typical estimated
uncertainty of each measure is 20 mas. The diameter variation is not in phase
with the solar activity cycle; thus, the measured diameter variation cannot be
explained as an observational artefact of surface activity. Other possible
instrument-related explanations for the observed variation are considered but
found unlikely, leading us to conclude that the variation is real. The SDS is
described here in detail, as is the complete analysis procedure necessary to
calibrate the instrument and allow comparison of diameter measures across
decades.Comment: 41 pages; appendix and 2 figures added plus some changes in text
based on referee's comments; to appear in MNRA
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