Summary By analogy with the calculation from data of angular momentum flow across latitude surfaces in the earth's atmosphere, the corresponding calculation is proposed for the case of our galaxy and possibly other spiral nebulae. A cylindrical wall of constant radius is used to replace the latitude wall, and the subject is developed through consideration of an ideal model. Gravitational torques enter the problem in addition to advective effects and possible other torques in actual systems. The relation of gravitational torques to the structure of ordinary spirals is discussed, and certain more special effects for the case of barred spirals are introduced and discussed. The connection of the subject with the classical theory of tidal evolution is pointed out.
Zusammenfassung Analog mit der Berechnung von Daten des Flusses des Momentes der Bewegungsgrösse über Breiten-Oberflächen in der Erd-Atmosphäre wird eine korrespondierende Berechnung für den Fall unseres Sternsystems und eventuell anderer spiraler Himmelskörper vorgeschlagen. Eine zylindrische Wand mit konstantem Radius wird benutzt, um die Breitenwand zu ersetzen, und dieses Problem wird entwickelt durch die Betrachtung eines idealen Modelles. Drehmomente der Schwerkraft kommen bei diesen Problem hinzu, zusätzlich der Wirkungen von Advektion und in aller Wahrscheinlichkeit anderer Drehmomente in den vorhandenen Systemen. Die Beziehung der Drehmomente der Schwerkraft in Bezug auf gewöhnliche Spiralen ist besprochen, und gewisse mehr spezialisierte Wirkungen für den Fall von Stangen-Spiralen werden eingeführt und besprochen. Der Zusammenhang dieses Problems mit der klassischen Theorie von Drehmomenten der Gezeiten ist nachgewiesen.
Sommario In analogia ai calcoli che, partendo da dati sperimentali, vengono fatti sul trasferimento del momento angolare fra zone dell'atmosfera a diverse latitudini, vengono qui proposti corrispondenti calcoli per la nostra galassia e possibilmente per altre nebulose a spirale. Viene usata una superficie cilindrica a raggio costante in sostituzione della superficie conica a latitudine costante; l'argomento è sviluppato secondo un modello ideale. La coppia gravitazionale viene presa in considerazione insieme agli effetti convettivi e ad altre possibili coppie. Viene discussa la relazione fra la coppia gravitazionale e la struttura di una spirale ordinaria; sono quindi introdotti e discussi certi effetti nel caso di spirali a sbarra. Infine viene messo in luce la relazione del presente argomento con la teoria classica della coppia dovuta alle marce.
The molluscan macrofauna living in shallow muddy bottoms with the green algae Caulerpa prolifera was studied monthly between February 1994 and January 1996 in the inner Bay of Cádiz (SW Spain). The molluscan assemblage followed a similar pattern over the 2 years, displaying seasonal trends in species richness, abundance and structure. During the autumn and winter months, a decrease in abundance, species richness and diversity and an increase in evenness occurred. During the spring and summer months, the molluscan assemblage was characterised by an increase in species richness, abundance and diversity. These seasonal trends were supported statistically by the presence of significantly different groupings of seasonal samples in multivariate analyses.Despite human impacts in the bay (e.g. aquaculture activities, sewage), the presence of repetitive seasonal trends, based on the qualitative and quantitative data, indicates the stability of the molluscan assemblage over 2 years. Benthic characteristics from the inner Bay of Cádiz, such as shallow soft bottoms with the presence of macrophytes and current dynamics, seem to be key factors influencing the composition and seasonality of this molluscan assemblage. 相似文献
Despite the increasing understanding of bentonite behaviour, there is still missing evidence on how different hydro-mechanical loadings, including sequences of hydration and compression, affect the fabric and the volume change behaviour of the material. It is generally assumed that the interplay between the behaviour of clay assemblages and the overall fabric of the material is the reason of having final states that are dependent on the stress path followed. Here the results of an experimental campaign aiming to study these factors are reported and discussed. Free swelling and swelling pressure tests were performed, both followed by compression to a relatively high stress. The experimental program involved various samples that were dismantled at intermediate states in order to perform microstructural observations by means of mercury intrusion porosimetry and electronic scanning microscopy. It was observed that while the void ratio at a given stress level depends on the stress path, subsequent compression led to a unique virgin compression line. The data obtained at the microscale gave further insight for an interpretation of the volume change behaviour observed at the macroscale, showing that at high stress the material tends to recover the same fabric regardless of the path to saturation.