A materials failure relation of accelerating creep as empirical description of damage accumulation

A general materials failure relation, , describes accelerating creep of materials with rate coefficients andA, by relating rates of deformation, , to changes in deformation rate, (Voight, 1988). Time of failure can be extrapolated from inverse rate versus time data, and andA may be derived to permit one to calculate the failure time. The method is of value for quantitative hazard assessments.Mechanisms leading to damage accumulation during accelerating creep include creep fracture by stress corrosion and power law lattice deformation. These mechanisms are examined here as phenomenologically related to the materials failure relation. Apparently, both mechanisms favour , where is the parameter of the materials failure relation controlling the sensitivity to accelerating activity. For pure shear governed by power law creep of powerp, under constant load, =2.0 andA=p. Stress corrosion is widely described by Charles' equation, relating crack velocity to stress intensity during subcritical crack growth by the stress corrosion indexn. The relationship betweenn and is given by =(2n–2)/n.     

Über einige Probleme der penninischen Zone der Westalpen

Ohne Zusammenfassung     

Change of black shale organic material surface area during oxidative weathering: Implications for rock-water surface evolution

Black shale oxidative weathering plays a significant role in a variety of processes including acid mine drainage and atmospheric CO₂ control. The modeling of weathering is highly dependent on reactive surface area. In this study it is shown that black shale oxidative weathering is regulated mainly by the external, geometrical surface area of rock polyhedrons and the organic matter’s (OM) internal surface area. The internal rock surface area decreases dramatically during OM dissolution from ∼15 m²/g to ∼5 m²/g. A linear relationship was found between the decrease of internal rock surface area and quantity of OM dissolved. Optical roughness analyses of black and bleached shale surface area reveal the formation of macropores due to the dissolution of mesoporous and probably microporous OM. However, due to deconsolidation, the geometrical external rock polyhedron surface area increases during weathering. Black shale polyhedrons show a doubling of their external surface area as OM decreases. This provokes an increase of the shale volume which is easily accessible by fluids. The increase of the external rock surface area seems to be self-accelerating during weathering. The upscaling of external and internal rock surface area evolution during weathering presented in this study demonstrates the possible application of these results to the improved understanding of a chemical transport in a variety of natural systems.     

Carbonate-rich melt infiltration in peridotite xenoliths from the Eurasian–North American modern plate boundary (Chersky Range,Yakutia)

A suite of mainly spinel peridotite and subordinate pyroxenite xenoliths and megacrysts were studied in detail, enabling us to characterize upper mantle conditions and processes beneath the modern North American–Eurasian continental plate boundary. The samples were collected from 37-Ma-old basanites cropping out in the Main Collision Belt of the Chersky Range, Yakutia Republic (Russian Far East). The spinel lherzolites reflect a mantle sequence, equilibrated at temperatures of 890–1,025 °C at pressures of 1.1–2 GPa, with melt extraction estimated to be around 2–6 %. The spinel harzburgites are characterized by lower P–T equilibration conditions and estimated melt extraction up to 12 %. Minor cryptic metasomatic processes are recorded in the clinopyroxene trace elements, revealing that percolating hydrous fluid-rich melts and basaltic melts affected the peridotites. One of the lherzolites preserves a unique melt droplet with primary dolomite in perfect phase contact with Na-rich aluminosilicate glass and sodalite. On the basis of the well-constrained P–T frame of the xenolith suite, as well as the rigorously documented melt extraction and metasomatic history of this upper mantle section, we discuss how a carbonated silicate melt infiltrated the lherzolite at depth and differentiated into an immiscible carbonate and silicate liquid shortly before the xenolith was transported to the surface by the host basalt. Decreasing temperatures triggered crystallization of primary dolomite from the carbonate melt fraction and sodalite as well as quenched glass from the Na-rich aluminosilicate melt fraction. Rapid entrainment and transport to the Earth’s surface prevented decarbonatization processes as well as reaction phenomena with the host lherzolite, preserving this exceptional snapshot of upper mantle carbonatization and liquid immiscibility.     

The Influence of NaBr/NaCl Ratio on the Br--Catalysed Production of Halogenated Radicals

The activation of Br^- and Cl^- to atomic Br and Cl in sea-spray aerosol was investigated in smog-chamber experiments. In the presence of O₃, hydrocarbons and NaCl aerosol alone no activation was observed. By adding Br^- to the aerosol, the chain reaction: Br + O₃ BrO, BrO + HO₂ HOBr, HOBr HOBr(aq), HOBr(aq) + H⁺ + Br^- Br₂ (6), HOBr(aq) + H⁺ + Cl^- BrCl (7) was verified. The step from reaction (6) to (7) is accompanied by a decrease of the Br^-/Cl^- ratio from 1/600 to less than 1/2000. In the absence of sulphate, the chain is initiated by the reaction of OH(aq) with Br^-. The pH value decreases to less than 2 during the first minutes of the experiment and later on to almost 1 (in the absence of NO_x or SO₂). This is caused by the formation of oxalic acid from alkanes and toluene. In stopped flow experiments, the reduction of Br₂ by oxalic acid was observed to occur through a two-step mechanism: HC₂O₄ ^- + Br₂ Br^- + BrC₂O₄H (k₂₂, k_-22), BrC₂O₄H Br^- + H⁺ + 2 CO₂ (23) with the following rate constants and ratios of rate constants, k ± 2: k₂₂k_-23 / k_-22 = (2.9 ± 0.3) · 10^-4 s^-1, k_-22 / k_-23 = 7000 ± ₃₀₀₀ ¹³⁰⁰⁰ M^-1, k₂₂ = 2 ±_-1 ⁴ M^-1 s^-1, and k_-23 > 0.1 s^-1, k_-22 > 600 M^-1 s^-1. Oxalic acid may be responsible for the inhibition of the chain reaction observed at the end of the experiments.     

Geologische Beobachtungen in den italienischen Teilen des Albigna-Disgraziamassivs

Ohne Zusammenfassung     

Interaction of Aquifer and River‐Canal Network near Well Field

The article presents semi‐analytical mathematical models to asses (1) enhancements of seepage from a canal and (2) induced flow from a partially penetrating river in an unconfined aquifer consequent to groundwater withdrawal in a well field in the vicinity of the river and canal. The nonlinear exponential relation between seepage from a canal reach and hydraulic head in the aquifer beneath the canal reach is used for quantifying seepage from the canal reach. Hantush's (1967) basic solution for water table rise due to recharge from a rectangular spreading basin in absence of pumping well is used for generating unit pulse response function coefficients for water table rise in the aquifer. Duhamel's convolution theory and method of superposition are applied to obtain water table position due to pumping and recharge from different canal reaches. Hunt's (1999) basic solution for river depletion due to constant pumping from a well in the vicinity of a partially penetrating river is used to generate unit pulse response function coefficients. Applying convolution technique and superposition, treating the recharge from canal reaches as recharge through conceptual injection wells, river depletion consequent to variable pumping and recharge is quantified. The integrated model is applied to a case study in Haridwar (India). The well field consists of 22 pumping wells located in the vicinity of a perennial river and a canal network. The river bank filtrate portion consequent to pumping is quantified.     

Relational Hubs for Collaborative Landscape Stewardship

Abstract

Landscape stewardship is considered an important place-based approach to addressing sustainability challenges. Working at landscape-level requires collaboration between diverse landscape stakeholders. In this study, we partnered with local stewardship practitioners across six cases in South Africa to investigate how they facilitate collaboration towards social-ecological sustainability outcomes. We found that practitioners facilitate collaboration among stakeholders by operating as relational hubs in the landscape. Through these hubs, they build new inter-personal relationships among stakeholders, creating social networks which enable stewardship practice. The hubs deepen human-nature relationships by creating enabling conditions for stewards to put stewardship ethics into action. Drawing on insights from these cases, we call for a relational approach to landscape stewardship which focuses on human-to-human and human-to-nature relationships. Moreover, we argue that landscape stewardship initiatives need to re-focus stewardship on stewards, recognizing them as key agents of change in addressing the conflict between agriculture and conservation inherent in many landscapes.     

Zur Frage der Absatzbedingungen der Radiolarite

Ohne Zusammenfassung