Dilation and Spalling in Axially Compressed Beams Subjected to Bending

Laboratory testing of rectangular beams using a synthetic rock was used to investigate the onset of dilation and spalling. The beams are axially compressed and subjected to 4-point bending to provide non-uniform compressive stresses. The maximum tangential stress occurs at the top of the beam and rapidly decreases with distance from the top of the beam. This stress distribution was used to simulate the maximum tangential stress distribution found around circular excavations. The results showed using this beam test configuration that the onset of dilation based on beam displacement and visually observed spalling began at approximately the same stress level. Discrete element numerical analyses (particle flow code) were used to evaluate the stress path at various locations in the beams. The analyses revealed that spalling and dilation in the beams occurred well below the peak strength failure envelope determined from conventional laboratory tests. The findings suggest that the onset of dilation in laboratory tests appears to be a good indicator for assessing the stress magnitudes required to initiate spalling.     

Apatite fission track and (U-Th)/He thermochronology of the Rochovce granite (Slovakia) – implications for the thermal evolution of the Western Carpathian-Pannonian region

The thermal evolution of the only known Alpine (Cretaceous) granite in the Western Carpathians (Rochovce granite) is studied by low-temperature thermochronological methods. Our apatite fission track and apatite (U-Th)/He ages range from 17.5 ± 1.1 to 12.9 ± 0.9 Ma, and 12.9 ± 1.8 to 11.3 ± 0.8 Ma, respectively. The data thus show that the Rochovce granite records a thermal event in the Middle to early Late Miocene, which was likely related to mantle upwelling, volcanic activity, and increased heat flow. During the thermal maximum between ~17 and 8 Ma, the granite was heated to temperatures ? 60 °C. Increase of cooling rates at ~12 Ma recorded by the apatic fission track and (U-Th)/He data is primarily related to the cessation of the heating event and relaxation of the isotherms associated with the termination of the Neogene volcanic activity. This contradicts the accepted concept, which stipulates that the internal parts of the Western Carpathians were not thermally affected during the Cenozoic period. The Miocene thermal event was not restricted to the investigated part of the Western Carpathians, but had regional character and affected several basement areas in the Western Carpathians, the Pannonian basin and the margin of the Eastern Alps.     

Orthogneisses of the Spessart crystalline complex,Northwest Bavaria: Indicators of the geotectonic environment?

The orthogneisses of the Spessart crystalline complex are derived from a granitic to granodioritic magma of S-type character which must have formed by anatexis of continental crust. It intruded into a relatively shallow crustal level, 410–420 Ma ago, at the Silurian. Trace element characteristics are consistent with a post-collision geotectonic environment testifying to extensional tectonics at the end of the Caledonian era.

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Zusammenfassung Die Orthogneise des Spessartkristallins lassen sich von einem granitischen bis granodioritischen Magma von S-Typ-Charakter ableiten, das durch Anatexis kontinentaler Kruste entstanden sein mu\ und in ein relativ oberflächennahes Krustenniveau intrudierte. Die Platznahme erfolgte vor 410–420 Ma, d. h. im Silur. Die Spurenelement-Muster der Orthogneise entsprechen denen von Post-Kollisions-Granitoiden, was als Hinweis auf eine Phase der Dehnungstektonik am Ende der kaledonischen ära bewertet werden kann.

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Résumé Les orthogneiss du Spessart sont dérivés d'un magma granitique à granodioritique de type S qui doit s'Être formé par anatexie de la croûte continentale. Ce magma a été intrudé dans un niveau peu profond de la croûte il y a 410–420 Ma c'est-à-dire au Silurien. La distribution des éléments en traces est en accord avec celle des granitoÏdes formés dans un contexte géodynamique de post-collision. Cette observation est en faveur d'une phase d'extension tectonique à la fin du cycle calédonien.

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Changes in the northern Gulf of St. Lawrence ecosystem estimated by inverse modelling: Evidence of a fishery-induced regime shift?

Mass-balance models have been constructed using inverse methodology for the northern Gulf of St. Lawrence for the mid-1980s, the mid-1990s, and the early 2000s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for each time period. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by demersal (cod, redfish) and small-bodied forage (e.g., capelin, mackerel, herring, shrimp) species to one now dominated by small-bodied forage species. Overfishing removed a functional group in the late 1980s, large piscivorous fish (primarily cod and redfish), which has not recovered 14 years after the cessation of heavy fishing. This has left only marine mammals as top predators during the mid-1990s, and marine mammals and small Greenland halibut during the early 2000s. Predation by marine mammals on fish increased from the mid-1980s to the early 2000s while predation by large fish on fish decreased. Capelin and shrimp, the main prey in each period, showed an increase in biomass over the three periods. A switch in the main predators of capelin from cod to marine mammals occurred, while Greenland halibut progressively replaced cod as shrimp predators. Overfishing influenced community structure directly through preferential removal of larger-bodied fishes and indirectly through predation release because larger-bodied fishes exerted top-down control upon other community species or competed with other species for the same prey. Our modelling estimates showed that a change in predation structure or flows at the top of the trophic system led to changes in predation at all lower trophic levels in the northern Gulf of St. Lawrence. These changes represent a case of fishery-induced regime shift.     

Nocturnal CO2 exchange over a tall forest canopy associated with intermittent low-level jet activity

Summary Nocturnal eddy-covariance carbon dioxide fluxes have uncertainties arising from non-stationary atmospheric processes. Low-level jets (LLJ) are one of the prominent nocturnal boundary-layer phenomena observed over non-mountainous terrain, and are capable of generating shear and turbulence close to the ground. The influence of intermittent LLJ activity on nocturnal carbon dioxide exchange measurements is investigated using wind profile observations and eddy-covariance flux measurements over a tall forest canopy. Results suggest that the buildup and venting of CO₂ are closely associated with LLJ activity during the night. Of significance in quantifying nocturnal fluxes, this paper demonstrates how low-level jet activity introduces sporadic coupling between the canopy and the atmosphere.     

Influence of disturbance and nutrient enrichment on early successional fouling communities in an oligotrophic marine system

Disturbance and productivity are often cited as the main factors determining temporal and spatial patterns in species distribution and the diversity of communities. A field experiment was conducted to test the role of these factors in the structuring of early successional fouling communities in a nutrient limited system at the south coast of Madeira Island. Macro‐benthic sessile communities, established on artificial settlement substrata, were manipulated and surveyed over a 9‐week period. We applied mechanical disturbances of four different frequencies crossed with three levels of inorganic nutrient enrichment. Fertilization enhanced community diversity by favouring the establishment and growth of macroalgae. Disturbance reduced diversity by eliminating species – but only at the highest nutrient level. This is explained by a multiple‐stressor model; species most sensitive to nutrient deficiency (only present in the highest enrichment treatment) were simultaneously the most sensitive to disturbance.     

Vergleich einiger Methoden zur Untersuchung von geochemischen Vorgängen bei der Verwitterung

Summary Chemical analyses are used by many authors to describe processes of soil development or laterite formation. In this paper some methods of balance calculations are compared by using samples of a laterite profile on granite from India as testing material. It should be proved which of these calculations of transported matter between the different layers are fitting to the mineral analyses of the laterite profile.Only the results of the method proposed byMashall by using an index-mineral as a base for comparison is confirmed by the mineral analyses.The method ofStreng differs from the above described calculation by using a chemical element as an index. FollowingStreng it is supposed that this element remains unchanged during the weathering processes. But certain chemical elements can be constituents of several minerals of a parent rock. During laterite formation all or almost all minerals of the original rock will be altered and the elements will be transported by weathering solutions. Therefore chemical elements do not serve as an index for balance calculations within a laterite complex.UsingGrossers method one cannot decide wether the abundance of a certain element is caused by accumulation of this element or by lost of other constituents and vice-versa.The use of the method developed byMillot u.Bonifas is not advisable except the structure of the original rock is preserved unaltered during laterite formation. This is not indicated in our case.     

Induction of abnormal polychaete larvae by heavy metals

A little known observation that exposure to sublethal concentrations of detergent cause fatal abnormalities in the second generation of a polychaete has been followed up and similar abnormalities have been observed in the first or second generation of larvae exposed to sublethal concentrations of copper and zinc. Few toxicity tests extend beyond the responses of the exposed individuals. The discovery of a delayed reaction to sublethal concentrations of common contaminants of the sea has unknown but potentially important ecological implications.