2,875 research outputs found
Full-field pulsed magneto-photoelasticity â Experimental Implementation
This paper contains a description of the experimental procedure employed when using a pulsed-magneto-polariscope (PMP) and some initial full-field through-thickness measurements of the stress distribution present in samples containing 3D stresses. The instrument uses the theory of magneto-photoelasticity (MPE), which is an experimental stress analysis technique that involves the application of a magnetic field to a birefringent model within a polariscope. MPE was developed for through-thickness stress measurement where the integrated through-thickness birefringent measurement disguises the actual stress distribution. MPE is mainly used in toughened glass where the through-thickness distribution can reduce its overall strength and so its determination is important.
To date MPE has been a single-point 2D through-thickness measurement and the analysis time is prohibitive for the investigation of an area which may contain high localised stresses. The pulsed-magneto-polariscope (PMP) has been designed to enable the application of full-field 3D MPE [ ]. Using a proof-of concept PMP several experimental measurements were made, these were promising and demonstrate the potential of the new instrument. Further development of this technique presents several exciting possibilities including a tool for the measurement of the distribution of principal stress difference seen in a general 3D model
Structure preserving specification languages for knowledge-based systems
Much of the work on validation and verification of knowledge based systems (KBSs) has been done in terms of implementation languages (mostly rule-based languages). Recent papers have argued that it is advantageous to do validation and verification in terms of a more abstract and formal specification of the system. However, constructing such formal specifications is a difficult task. This paper proposes the use of formal specification languages for KBS-development that are closely based on the structure of informal knowledge-models. The use of such formal languages has as advantages that (i) we can give strong support for the construction of a formal specification, namely on the basis of the informal description of the system; and (ii) we can use the structural correspondence to verify that the formal specification does indeed capture the informally stated requirements
Rupture and afterslip controlled by spontaneous local fluid flow in crustal rock
Shear rupture and fault slip in crystalline rocks like granite produce large
dilation, which impacts the spatiotemporal evolution of fluid pressure in the
crust during the seismic cycle. To explore how fluid pressure variations are
coupled to rock deformation and fault slip, we conducted laboratory rock
failure experiments under upper crustal conditions while monitoring acoustic
emission locations and in situ fluid pressure. Our results show the existence
of two separate faulting stages: an initial shear rupture propagation phase,
associated with large dilatancy and stabilised by local fluid pressure drops,
followed by a sliding phase on the newly formed fault, promoted by local fluid
pressure recharge from the fault walls. This latter stage had not been
previously recognised and can be understood as fluid-induced afterslip,
co-located with the main rupture patch. Upscaling our laboratory results to the
natural scale, we expect that spontaneous fault zone recharge could be
responsible for early afterslip in locally dilating regions of major crustal
faults, independently from large-scale fluid flow patterns
Temporal and spectral variation of desert dust and biomass burning aerosol scenes from 1995?2000 using GOME
International audienceGlobal Ozone Monitoring Experiment (GOME) Absorbing Aerosol Index (AAI) and AAI-related residue data were used to investigate areas with UV-absorbing aerosols. Time series of regionally averaged residues show the seasonal variation and trends of aerosols and clouds in climatologically important parts of the globe. GOME spectra were used to study scenes containing specific types of aerosols. AAI data are specifically sensitive to biomass burning aerosols (BBA) and desert dust aerosols (DDA). Areas where these aerosols are regularly found were analysed to find spectral fingerprints in the ultraviolet (UV), visible and near-infrared (near-IR), to establish an aerosol type classification of BBA and DDA. Spectral residues are different for BBA and DDA, but over deserts the surface albedo is dominant beyond the UV and spectral residues cannot be used over land. Over oceans, about half of the BBA scenes show a very high reflectance that is never observed for DDA scenes. However, in the case of low reflectance scenes BBA and DDA cannot be distinguished. This is in part due to the microphysical and optical properties of biomass burning aerosols, which are highly variable in time, making it difficult to specify them spectrally as one type. Because of their high hygroscopicity BBA are often found in the presence of clouds, which disturb the spectrum of the scenes. Desert dust aerosols are much less hygroscopic and behave spectrally more uniformly
Variation of hydraulic properties due to dynamic fracture damage: Implications for fault zones
High strain rate loading causes pervasive dynamic microfracturing in crystalline materials,
with dynamic pulverization being the extreme end-member. Hydraulic properties (permeability,
porosity, and storage capacity) are primarily controlled by fracture damage and will therefore change
significantly by intense dynamic fracturingâby how much is currently unknown. Dynamic fracture
damage observed in the damage zones of seismic faults is thought to originate from dynamic stresses near
the earthquake rupture tip. This implies that during an earthquake, hydraulic properties in the damage
zone change early. The immediate effect this has on fluid-driven coseismic slip processes following the
rupture, and on postseismic and interseismic fault zone processes, is not yet clear. Here, we present
hydraulic properties measured on the full range of dynamic fracture damage up to dynamic pulverization.
Dynamic damage was induced in quartz-monzonite samples by performing uniaxial high strain rate
(> 100 sâ1) experiments in compression using a split-Hopkinson pressure bar. Hydraulic properties were
measured on samples subjected to single and successive loadings, the latter to simulate cumulative damage
from repeated rupture events. We show that permeability increases by 6 orders of magnitude and porosity
by 15% with dissipated energy up to dynamic pulverization, for both single and successive loadings. We
present damage zone permeability profiles induced by earthquake rupture and how it evolves with
repeated ruptures. We propose that the enhanced hydraulic properties measured for pulverized rock
decrease the efficiency of thermal pressurization, when emplaced adjacent to the principal slip zone
A call for viewshed ecology : Advancing our understanding of the ecology of information through viewshed analysis
JA was supported by funding from the European Unionâs Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 661211, and JMJT by NERC grant NE/J008001/1.Peer reviewedPostprin
The effect of sensor resolution on the number of cloud-free observations from space
International audienceAir quality and surface emission inversions are likely to be focal points for future satellite missions on atmospheric composition. Most important for these applications is sensitivity to the atmospheric composition in the lowest few kilometers of the troposphere. Reduced sensitivity by clouds needs to be minimized. In this study we have quantified the increase in number of useful footprints, i.e. footprints which are sufficient cloud-free, as a function of sensor resolution (footprint area). High resolution (1 kmĂ1 km) MODIS TERRA cloud mask observations are aggregated to lower resolutions. Statistics for different thresholds on cloudiness are applied. For each month in 2004 two days of MODIS data are analyzed. Globally the fraction of cloud-free observations drops from 16% at 100 km2 resolution to only 3% at 10 000 km2 if not a single MODIS observation within a footprint is allowed to be cloudy. If up to 5% or 20% of a footprint is allowed to be cloudy, the fraction of cloud-free observations is 9% or 17%, respectively, at 10 000 km2 resolution. The probability of finding cloud-free observations for different sensor resolutions is also quantified as a function of geolocation and season, showing examples over Europe and northern South America
Potential of the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor for the monitoring of terrestrial chlorophyll fluorescence
Global monitoring of sun-induced chlorophyll fluorescence (SIF) is improving our knowledge about the photosynthetic functioning of terrestrial ecosystems. The feasibility of SIF retrievals from spaceborne atmospheric spectrometers has been demonstrated by a number of studies in the last years. In this work, we investigate the potential of the upcoming TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite mission for SIF retrieval. TROPOMI will sample the 675â775 nm spectral window with a spectral resolution of 0.5 nm and a pixel size of 7 km Ă 7 km. We use an extensive set of simulated TROPOMI data in order to assess the uncertainty of single SIF retrievals and subsequent spatio-temporal composites. Our results illustrate the enormous improvement in SIF monitoring achievable with TROPOMI with respect to comparable spectrometers currently in-flight, such as the Global Ozone Monitoring Experiment-2 (GOME-2) instrument. We find that TROPOMI can reduce global uncertainties in SIF mapping by more than a factor of 2 with respect to GOME-2, which comes together with an approximately 5-fold improvement in spatial sampling. Finally, we discuss the potential of TROPOMI to map other important vegetation parameters at a global scale with moderate spatial resolution and short revisit time. Those include leaf photosynthetic pigments and proxies for canopy structure, which will complement SIF retrievals for a self-contained description of vegetation condition and functioning
A stochastic movement simulator improves estimates of landscape connectivity
Acknowledgments This publication issued from the project TenLamas funded by the French MinistĂšre de l'Energie, de l'Ecologie, du DĂ©veloppement Durable et de la Mer through the EU FP6 BiodivERsA Eranet; by the Agence Nationale de la Recherche (ANR) through the open call INDHET and 6th extinction MOBIGEN to V. M. Stevens, M. Baguette, and A. Coulon, and young researcher GEMS (ANR-13-JSV7-0010-01) to V. M. Stevens and M. Baguette; and by a VLIR-VLADOC scholarship awarded to J. Aben. L. Lens, J. Aben, D. Strubbe, and E. Matthysen are grateful to the Research Foundation Flanders (FWO) for financial support of fieldwork and genetic analysis (grant G.0308.13). V. M. Stevens and M. Baguette are members of the âLaboratoire d'Excellenceâ (LABEX) entitled TULIP (ANR-10-LABX-41). J. M. J. Travis and S. C. F. Palmer also acknowledge the support of NERC. A. Coulon and J. Aben contributed equally to the work.Peer reviewedPublisher PD
Water vapour total columns from SCIAMACHY spectra in the 2.36 ÎŒm window
The potential of the shortwave infrared channel of the atmospheric spectrometer SCIAMACHY on Envisat to provide accurate measurements of total atmospheric water vapour columns is explored. It is shown that good quality results can be obtained for cloud free scenes above the continents using the Iterative Maximum Likelihood Method. In addition to the standard cloud filter employed in this method, further cloud screening is obtained by comparing simultaneously retrieved methane columns with values expected from models. A novel method is used to correct for the scattering effects introduced in the spectra by the ice layer on the detector window.
The retrieved water vapour total vertical columns for the period 2003â2007 are compared with spatially and temporally collocated values from the European Centre for Mid-Range Weather Forecast (ECMWF) data. The observed differences for individual measurements have standard deviations not higher than 0.3 g/cm^2 and an absolute mean value smaller than 0.01 g/cm^2 with some regional excursions.
The use of recently published spectroscopic data for water vapour led to a significant improvement in the agreement of the retrieved water vapour total columns and the values derived from ECMWF data. This analysis thus supports the superior quality of the new spectroscopic information using atmospheric data
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