Seed bank dynamics in a Great Basin salt playa

Salt playa are common in the Great Basin area with halophytes as the dominant flora. The relationship between the seed bank flora and existing vegetation was studied. The seed bank flora showed a high degree of similarity with that of perennial and annual halophytic vegetation. Both above and below ground components of the community are dominated by halophyte species like Allenrolfea occidentalis, Holosteum umbellatum, Salicornia rubra and Salicornia utahensis. Seasonal variation in the seed bank was also studied for the 1995–1996 and 1996–1997 growing seasons. The seeds of A. occidentalis persist in the soil of the upper zone in large densities. Salicornia utahensis was much higher in the upper zone throughout the study period. Most species demonstrated the persistent nature of the seed banks with their numbers increasing after seed dispersal and decreasing in subsequent months. The variation illustrates the transient nature of the seed bank. We concluded that A. occidentalis is more dependent on a large seed bank for maintaining its population than the two annual halophytes. The significance of the seed bank and their variation due to environmental conditions for perennial and annual species of the Great Basin salt playa community is discussed.     

Search for finite dimensional attractors in atmospheric turbulence

The question is investigated whether the dynamics of turbulent wind fields in the atmospheric boundary layer can be satisfactorily described by a low-dimensional deterministic system. Special emphasis is laid on the detection of a possibly existing, underlying strange attractor. Fast response wind measurements of an ultrasonic anemometer with a sampling rate of 21 Hz were carried out over periods of several days in the near surface boundary layer. The correlation dimension of the resulting time series, several million data points long, is estimated by means of the Grassberger-Procaccia algorithm. No sign of a low dimensional attractor can be detected. By comparison with different types of random noise, the existence of an attractor with dimension lower than six can be excluded in the present data sets.     

Incorporation of strontium into reef coral skeletal carbonate

Two thousand and twenty well-characterized coral specimens from 17 localities have been analyzed for Sr. Seventy-three genera and subgenera, mostly hermatypic scleractinians, are represented. For some genera, specimens living in surface reef environments are compared with those from 18.3 m depths on the same reefs. Growth rates for some species have also been measured at these depths at one of the sampling sites. Skeletal strontium for a given genus decreases with increasing water temperature, a relationship which previously eluded detection. Aragonite deposited by corals living on the reef at a depth of 18.3 m contains more strontium than the skeletal aragonite of the same coral genera from shallow-water, surface environments. Quantitative treatment of the data for Acropora, one of the most abundant and widely distributed of the reef-building corals, suggests that the observed strontium variations may reflect variations in the rate of skeletal calcification, rather than direct dependence upon temperature or water depth. There is evidence for ‘species effects’, apparently unrelated to growth rate differences, in that certain coral genera are consistently enriched or depleted in skeletal strontium content relative to other genera living in the same reef environments under identical ambient conditions. Temperature, salinity, water depth, seawater composition, and/or other such parameters may in part determine the levels of trace element concentration in carbonates deposited by corals and other marine invertebrates, but it would appear that these variables more directly affect physiological processes which in turn control skeletal chemistry.     

Lead(II) complexation by fulvic acid: how it differs from fulvic acid complexation of copper(II) and cadmium(II)

Pb²⁺, like Cu²⁺, forms strong complexes with fulvic acids (Cd²⁺-fulvate complexes are much weaker), but Pb-fulvate precipitates at a much lower mole ratio of metal ion to fulvic acid than either Cu-fulvate or Cd-fulvate does. Physical association of Pb²⁺ with Pb-fulvate solids as well as complexation by sites still available in the precipitates probably causes the increased removal of free Pb²⁺ from solution after precipitation begins.     

Response of a nuclear power plant on aseismic bearings to horizontally propagating waves

The nuclear island of Koeberg with a large basemat, a non-linear base isolation effective in the horizontal direction only, founded on rock, is analysed for inclined body waves and for a combination of surface and body waves associated with prescribed horizontal and vertical components of the control motion. When compared to vertical incidence, an additional rocking component arises, generated by the horizontally propagating vertical component. As the aseismic bearings do not isolate against this rocking component, the corresponding horizontal response bears comparison with that of a conventional structure. The ratio of the response for horizontally propagating waves and that for vertically incident waves is thus considerably larger for the base-isolated structure than for a conventional one. However, the actual design incorporating other loading cases is affected much less.     

Coral growth rate: Variation with depth

Light and temperature are two of the most important physical factors affecting rates of growth of reef corals. The effect of light has been determined by X-radiographic measurement of long-term growth rates for 89 colonies of the coralMontastrea annularis collected over a 27.5-m depth range from St. Croix, U.S. Virgin Islands. These measurements, in conjunction with measurements of skeletal density, have established thatM. annularis calcifies most rapidly at intermediate depths, and they have confirmed the identification of two distinct populations within this important frame-building species.     

Die Laufzeitfunktion in der Reflexionsseismik des quasi Einachsig inhomogenen Körpers

Zusammenfassung Es wird die Laufzeitfunktion (Reflexionsseismik) für einen quasi einachsig inhomogenen Körper berechnet und zwei einfache Beispiele und ihre Anwendungen behandelt.

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Summary The travel-time function (reflection seismic) for a quasi uniaxial inhomogeneous medium is calculated and two simple examples are given.

     

Das ebenen-Schichtenproblem der Reflexionsseismik mit konstanten Frontgeschwindigkeiten,beliebigen Neigungen und beliebiger Lage der Quelle

Zusammenfassung Es wird das ebenen-Schichtenproblem der Reflexionsseismik mit konstanten Frontgeschwindigkeiten, beliebigen Neigungen und beliebiger Lage der Quelle allgemein behandelt und durch Verallgemeinerung der tt Methode ein einfaches Aufschlussverfahren für geneigte Schichten entwickelt.

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Summary The two-dimensional problem of the reflection seismic with arbitrary inclined surfaces of discontinuity, const. wave-velocities and an arbitrary position of the source is generally treated. Finally a tt method for inclined layers is outlined.