One‐year monitoring of the Z24‐Bridge: environmental effects versus damage events

When using the analysis of vibration measurements as a tool for health monitoring of bridges, the problem arises of separating abnormal changes from normal changes in the dynamic behaviour. Normal changes are caused by varying environmental conditions such as humidity, wind and most important, temperature. The temperature may have an impact on the boundary conditions and the material properties. Abnormal changes on the other hand are caused by a loss of stiffness somewhere along the bridge. It is clear that the normal changes should not raise an alarm in the monitoring system (i.e. a false positive), whereas the abnormal changes may be critical for the structure's safety. In the frame of the European SIMCES‐project, the Z24‐Bridge in Switzerland was monitored during almost one year before it was artificially damaged. Black‐box models are determined from the healthy‐bridge data. These models describe the variations of eigenfrequencies as a function of temperature. New data are compared with the models. If an eigenfrequency exceeds certain confidence intervals of the model, there is probably another cause than the temperature that drives the eigenfrequency variations, for instance damage. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of channel deepening on tidal flow and sediment transport—part II: muddy channels

Natural tidal channels often need deepening for navigation purposes (larger vessels). The depth increase may lead to tidal amplification, salt intrusion over longer distances, and increasing sand and mud import. Increasing fine sediment import, in turn, may start a process in which the sediment concentration progressively increases until the river becomes hyper-turbid, which may lead to increased dredging volumes and to decreased ecological values. These effects can be modeled and studied using detailed 3D models. Reliable simplified models for a first quick engineering evaluation are however lacking. In this paper, we apply both simplified and detailed 3D models to analyze the effects of channel deepening in prismatic and weakly converging tidal channels with saturated mud flow. The objective is to gain quantitative understanding of the effects of channel deepening on mud transport. We developed a simplified tidal mud model describing most relevant processes and effects in saturated mud flows with only minor horizontal transport gradients (quasi uniform conditions). The simplified model is not valid for non-saturated mud flow conditions. This model can either be used in standalone mode or in post-processing mode with computed near-bed velocities from a 3D hydrodynamic model as an input. The standalone model has been compared to various field data sets. Mud transport processes in the mouth region of muddy tidal channels can be realistically represented by the simplified model, if sufficient salinity and sediment data are available for calibration. The simulation of tidal mud transport and the behavior of an estuarine turbidity maximum (ETM) in saturated and non-saturated mud flow conditions cannot be represented by the simplified model and requires the application of a detailed 3D model.     

Modelling the Effect of Tree Foliage on Sprayer Airflow in Orchards

The effect of tree foliage on sprayer airflow through pear trees in a fruit orchard was studied and modelled in detail. A new three-dimensional (3-D) computational fluid dynamics model that integrates the 3-D canopy architecture with a local closure model to simulate the effect of the stem and branches and leaves of trees separately on airflow was developed. The model was validated with field observations made in an experimental orchard (pcfruit, Sint-Truiden, Belgium) in spring and summer 2008 and was used to investigate the airflow from three air-assisted orchard sprayers (Condor V, Duoprop and AirJet quatt). Velocity magnitudes were measured before and behind leafless and fully-leafed pear canopies across the row while the operating sprayers are passing along the row, and were compared with the simulations. The simulation results predicted the measured values well with all the local relative errors within 20%. The effect of foliar density on airflow from the three air assisted sprayers was manifested by changing the magnitude and direction of the sprayers’ air velocity behind the canopy, especially at the denser regions of the canopy and by changing the pattern of velocity decay horizontally along the jet. The developed methodology will also allow a thorough investigation of atmospheric airflow in canopy structures.     

Initial public reactions to carbon capture and storage (CCS): differentiating general and local views

Carbon capture and storage (CCS) is considered a potential climate change mitigation option, but public opposition may hamper its implementation. A quasi-experimental approach is used to examine whether ‘not in my back yard’ (NIMBY) sentiments can be anticipated at the initial stage when CO₂ storage locations have been selected and communicated to the public. Furthermore, the psychological structure of initial reactions to CO₂ storage plans is studied to ascertain the differences between people living in the direct vicinity of a proposed CO₂ storage location (i.e. onsite residents) and people who do not (i.e. offsite residents). The results indicate that initial reactions to local CCS plans are not necessarily dominated by NIMBY sentiments. For onsite residents as well as offsite residents, trust in government affects their judgements of the risks and benefits associated with CCS, which in turn affects their inclination to protest against CCS plans. Onsite residents’ inclination to protest is affected by their perceptions of local safety risks, but this is less of a concern for offsite residents. The inclination to protest against CCS is unrelated to concern about climate change.     

Effects of crystalline massif tectonics on groundwater origin and catchment size of a large spring area in Zieleniec, Sudety Mountains, southwestern Poland

The recharge mechanism of a very large spring area in the town of Zieleniec in the Orlickie Mountains (part of the Sudety mountain chain) in southwestern Poland, was investigated and characterized. The spring area is located on a steep mountain slope at a high elevation, next to the continental water divide. It is estimated that at least 90% of the spring discharge comes from outside its topographic drainage basin. The study area has been strongly affected by tectonic episodes of different ages. Thus, there is a high density of fractures in the crystalline massif, which determines the water content of the area and the occurrence of large springs. The low variability in discharge of the Zieleniec spring area indicates the presence of a strong and stable component source of recharge. It has also been shown that gravitational drainage of solid-rock blocks and small fissures is also an important recharge component. The stable recharge component is associated with deep-water circulation from the B?lá River drainage basin in the Czech Republic, flowing beneath the continental divide. Water flows in conformity with a high hydraulic head gradient through deep, open, NW?CSE-oriented fissures.     

Tidal Stress Patterns on Europa's Crust

The ice crust of Europa probably floats over a deep liquid-water ocean, and has been continually resurfaced by tectonic and thermal processes driven by tides. Tidal working causes rotational torque, surface stress, internal heating, and orbital evolution. The stress patterns expected on such a crust due to reorientation of the tidal bulge by non-synchronous rotation and due to orbital eccentricity, which introduces periodic ('diurnal') variations in the tide, are shown as global maps. By taking into account the finite rate of crack propagation, global maps are generated of cycloidal features and other distinctive patterns, including the crack shapes characteristic of the wedges region and its antipode on the sub-Jovian hemisphere. Theoretical maps of tidal stress and cracking can be compared with observed tectonics, with the possibility of reconstructing the rotational history of the satellite.     

How realistic are water-balance closure assumptions? A demonstration from the southern sierra critical zone observatory and kings river experimental watersheds

The water balance is an essential tool for hydrologic studies and quantifying water-balance components is the focus of many research catchments. A fundamental question remains regarding the appropriateness of water-balance closure assumptions when not all components are available. In this study, we leverage in-situ measurements of water fluxes and storage from the Southern Sierra Critical Zone Observatory (SSCZO) and the Kings River Experimental Watersheds (KREW) to investigate annual water-balance closure errors across large (1016–5389 km²) river basins and small (0.5–5 km²) headwater-catchment scales in the southern Sierra Nevada. The results showed that while long-term water balance in river basins can be closed within 10% of precipitation, in the smaller headwater catchments as much as a quarter of precipitation remained unaccounted for. A detailed diagnosis of this water-balance closure error using distributed soil moisture measurements in the top 1 m suggests an unaccounted deeper storage and a net groundwater export from the headwater catchments. This imbalance was also found to be very sensitive to the timescales over which water-balance closures were attempted. While some of the closure errors in the simple water balance can be attributed to measurement uncertainties, we argue for a broader consideration of groundwater exchange when evaluating hydrological processes at headwater scales, as the assumption of negligible net groundwater exchange may lead to an overestimation of fluxes derived from the water balance method.     

Plant–water relationships and growth strategies of Jatropha curcas L. seedlings under different levels of drought stress

Although Jatropha curcas, an important tropical biofuel crop, is reputed for its drought resistance, its ability to perform under dry conditions has hardly been investigated. In a greenhouse experiment we investigated the plant–water relationships of Jatropha seedlings from different accessions under different levels of drought stress. There was little difference in plant–water relations between accessions. Drought significantly reduced leaf area, biomass and relative growth rate, but had no effect on specific leaf area, daily range in leaf water potential, leaf water content, transpiration efficiency or aboveground biomass water productivity, corrected for atmospheric conditions. Stem wood density was equally low (0.26 g cm^?3) for all treatments. Stem water content was lowest for dry treatment seedlings. Based on these results, Jatropha could be characterized as a stem-succulent tree. In contrast to other stem-succulent deciduous trees, leaves were not shed immediately after the seedlings were confronted with drought. Instead, at the onset of drought, leaves with a higher adaxial stomatal density were formed, after which leaves were only gradually shed. The role of the succulent stem in the water economy of Jatropha was confined to balancing the small water losses of the leaves during drought.     

In situ identification of a CAI candidate in 81P/Wild 2 cometary dust by confocal high resolution synchrotron X-ray fluorescence

We detected additional CAI-like material in STARDUST mission samples of comet 81P/Wild 2. Two highly refractory cometary dust fragments were identified in the impact track 110 [C2012, 0, 110, 0, 0] by applying high resolution synchrotron induced confocal and conventional XRF analysis (HR SR-XRF). The use of a polycapillary lens in front of the detector for confocal spectroscopy dramatically improves the fidelity of particle measurements by removing contribution from the surrounding aerogel. The high spatial resolution (300 × 300 nm²; 300 × 1000 nm²) obtained allowed the detailed non-destructive in situ (trapped in aerogel) study of impacted grains at the sub-μm level.For the two largest particles of the track, the terminal particle and a second particle along the impact track, Ca concentration is up to 30 times higher than CI and Ti is enriched by a factor of 2 compared to CI. High resolution (HR) SR-XRF mapping also reveals that the highest concentrations of Ca, Ti, Fe (and Ni) measured within each grain belongs to different areas of the respective maps which indicate that the particles are composed of several chemically diverse mineral phases. This is in agreement with the finding of a complex phase assemblage of highly refractory minerals in the first ever detected Stardust mission CAI grain “Inti” of Track 25.Principle component analysis (PCA) is a powerful tool for extracting the dominant mineral components and was applied to the two grains indicating that regions in the terminal particle and the second particle are consistent with anorthite or grossite and gehlenite, monticellite or Dmitryivanovite (CaAl₂O₄), respectively.Our new findings demonstrate that the HR SR-XRF with confocal geometry and PCA analysis is capable of identifying CAI-like fragments without the need to extract particles from the aerogel matrix which is a time-consuming, complex and destructive process.Furthermore, the detection of new CAI-like fragments in the coma dust of comet 81P/Wild 2 strengthens the observation that strong mixing effects and, therefore, mass transport before or during comet formation must have occurred at least up to the region where Kuiper Belt comets formed (30 AU).