The age and growth of young-of-the-year spot,Leiostomus xanthurus Lacépède,in South Carolina     

Daniel W. Beckman  John Mark Dean 《Estuaries and Coasts》1984,7(4):487-496

Young-of-the-year spot,Leiostomus xanthurus, were sampled in Town Creek of North Inlet Estuary, South Carolina, with towed plankton nets, seines, and stationary block nets from February 14 to May 2, 1981. Age estimates obtained by analysis of daily growth increments in the sagittal otoliths showed that these fish hatched between late November 1980 and mid-February 1981. The youngest spot was estimated to be 60 days old, indicating a prolonged migration period from offshore spawning grounds. Age-length regressions permitted calculations of growth and estimates of age from standard length measurements. An increase in growth rate was observed with an increase in size of fish; however, growth of fish of equal sizes was lower in April and early May than in February and March. Age estimates suggested that the hatching period for young-of-the-year spot was concentrated between late November and mid-January. Recruitment of three separate cohorts into Town Creek occurred at approximately monthly intervals, and immigration of each cohort into the estuary took place approximately 2 months after its estimated date-of-hatch.  相似文献   

Close interval sampling of interstitial silicate and porosity in marine sediments     

Daniel Andrews  Barry T. Hargrave 《Geochimica et cosmochimica acta》1984,48(4):711-722

A method was developed to measure porosity and dissolved interstitial silicate at millimeter intervals or less in a sediment core. In cores from Emerald Basin (Scotian Shelf), interstitial concentrations near the sediment surface did not drop rapidly to bottom-water concentrations as measured in bottle casts (28 μM) but remained as high as 166 μM in the upper 0.5 mm of sediment High rates of benthic silicate release were measured which could not be accounted for by interstitial concentration gradients or by ventilation of macro-invertebrate burrows. The silicate discontinuity observed between the sediments and water column suggests that a diffusive sublayer exists in a zone of viscous flow above the sediment surface. This is possible only if a surface reaction is primarily responsible for silicate release. By assuming a linear concentration gradient across this diffusive sublayer, the silicate release rates were used to estimate the thickness of the sublayer to be about 2 mm.  相似文献   

Compositional trends and cooling rates of group IVB iron meteorites     

Kaare L. Rasmussen  Daniel J. Malvin  Vagn F. Buchwald  John T. Wasson 《Geochimica et cosmochimica acta》1984,48(4):805-813

Based on new neutron activation data for group IVB we find that log-element — log-Ni trends are best understood in terms of core formation and fractional crystallization. The limited compositional range found in group IVB seems to reflect the fact that, because of the low concentrations of S, P and C and the high concentration of Ni, $\text{k}{}_{\mathrm{\chi }}$ values are nearer unity than are those in other magmatic groups. Mean volatile abundances in group IVB are much lower than those found in any group of chondritic meteorites, suggesting that these low abundances were not entirely the result of nebular processes, but that planetary outgassing was also involved.We calculated cooling rates on the basis of a computer simulation of the growth of kamacite crystals; these calculations are particularly straightforward for the high-Ni irons since no local bulk Ni enrichment is involved. We estimate a mean IVB cooling rate of 170–230 K/Ma, the lower values based on 20 K undercooling, the higher on no undercooling. There is no dependence of cooling rate on chemical composition. The mean cooling rate of the low-volatile groups IVB and IVA are both much higher than those typical of iron-meteorite groups. This indicates small parent bodies, and reinforces the above suggestion that the low volatile contents resulted from planetary outgassing.There is a small compositional hiatus in group IVB, but since the sets on both sides of the hiatus form continuous trends on log-element — log-Ni diagrams and have the same cooling rates, it appears that both sets originated in a single oxidized, refractory-rich parent body. This sampling hiatus corresponds to 26% of the original core, a value shown to be typical for a random sequence sampled 11 times.  相似文献   

Geographical tourism research in the Federal Republic of Germany     

Chr. Becker  J. Maier  K. Ruppert  P. Weber  K. Wolf 《GeoJournal》1984,9(1):37-40

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Sm−Nd dating of multiple garnet growth events in an arc-continent collision zone,northwestern U.S. Cordillera     

Stephen R. Getty  Jane Selverstone  Brian P. Wernicke  Stein B. Jacobsen  Elaine Aliberti  Daniel R. Lux 《Contributions to Mineralogy and Petrology》1993,115(1):45-57

Integrated petrologic and Sm–Nd isotopic studies in garnet amphibolites along the Salmon River suture zone, western Idaho, delineate two periods of amphibolite grade metamorphism separated by at least 16 million years. In one amphibolite,P–T studies indicate a single stage of metamorphism with final equilibration at 600°C and 8–9 kbar. The Sm–Nd isotopic compositions of plagioclase, apatite, hornblende, and garnet define a precise, 8-point isochron of 128±3 Ma (MSWD=1.2) interpreted as mineral growth at the metamorphic peak. A⁴⁰Ar/³⁹Ar age for this hornblende indicates cooling through 525°C at 119±2 Ma. In a nearby amphibolite, garnets with a two-stage growth history consist of inclusion-rich cores surrounded by discontinuous, inclusion-free overgrowths. Temporal constraints for core and overgrowth development were derived from Sm–Nd garnet — whole rock pairs in which the garnet fractions consist of varying proportions of inclusion-free to inclusion-bearing fragments. Three garnet fractions with apparent ages of 144, 141, and 136 Ma are thought to represent mixtures between late Jurassic (pre-144 Ma) inherited radiogenic components preserved within garnet cores and early Cretaceous (128 Ma) garnet overgrowths. These observations confirm the resilience of garnet to diffusive exchange of trace elements during polymetamorphism at amphibolite facies conditions. Our geochronologic results show that metamorphism of arc-derived rocks in western Idaho was episodic and significantly older than in arc rocks along the eastern margin of the Wrangellian Superterrane in British Columbia and Alaska. The pre-144 Ma event may be an expression of the late Jurassic amalgamation of marginal oceanic arc-related terranes (e.g., Olds Ferry, Baker, Wallowa) during the initial phases of their collision with North American rocks. Peak metamorphism at 128 Ma reflects tectonic burial along the leading edge of the Wallowa arc terrane during its final penetration and suturing to cratonic North America.  相似文献   

Infrared imaging and spectroscopy with arrays at the University of Montreal     

Neil Rowlands  Daniel Nadeau  René Doyon 《Experimental Astronomy》1994,3(1-4):143-144

The Montreal Infrared Camera (MONICA) consists of a LN₂ cryostat enclosing a NICMOS3 array, re-imaging optics and a filter wheel mechanism containing broad-band and circular variable filters. A polarimetry mode with a warm half wave plate and a cold polarizer/filter combination is also supported. At the CFHT 0.5 (FWHM) images are routinely obtained with limiting magnitudes of 22.8 at J and 21.7 at K (S/N=3 in 1hr).The Spectrometre Infrarouge de Montréal (SIMON) is a versatile grating spectrometer with spectral resolutions ranging from 300 to 5000. Presently under construction, this spectrometer will initially contain a 512×512 HgCdTe array. Use of reflective optics will allow a future upgrade to a similar format InSb array, extending the wavelength coverage to 5m. SIMON will also have an imaging mode to facilitate the centering of objects within interchangeable slits.  相似文献   

4.8 – 20 μm Imaging of orion BN/KL: II. A new look at luminosity sources and the role of IRc2     

Daniel Y. Gezari  Dana E. Backman 《Experimental Astronomy》1994,3(1-4):45-52

We have reconsidered the energetics of the BN/KL infrared complex, using array images at nine wavelengths between 4.8 and 20 m, and find a much lower luminosity for IRc2 than the generally accepted value. The new observations resolve larcsec structure throughout the region, including several new compact sources within a few arcsec of IRc2 and significant details imaged in the 9.7 m silicate feature. Together with other recent work, the results suggest that luminous stars associated with three compact HII regions found within BN/KL, rather than IRc2, may be the more significant luminosity sources for the complex.  相似文献   

Cones to model foundation vibrations: incompressible soil and axi-symmetric embedment of arbitrary shape     

John P. Wolf  Andrew J. Deeks   《Soil Dynamics and Earthquake Engineering》2004,24(12):963-978

The recently streamlined strength-of-materials approach using cones to calculate vibrations of foundations embedded in layered half-spaces and full-spaces is applied to incompressible and nearly-incompressible soil and to axi-symmetric embedments of arbitrary shape. For incompressible soil the axial-wave velocity in the cones is limited to twice the shear-wave velocity and a trapped mass for the vertical motion and a trapped mass moment of inertia for the rocking motion moving as a rigid body with the under-most disk of an embedded foundation are introduced. In the case of a fully embedded foundation, a mass and a mass moment of inertia are also assigned to the upper-most disk. For an axi-symmetric embedment of arbitrary shape, the disks have varying radii. No modifications to the formulation are, however, required. For these two extensions the strength-of-materials approach using cones leads to the same sufficient engineering accuracy as is achieved in other more conventional cases. This is demonstrated in a vast study. Thus the same other advantages also apply: physical insight with conceptual clarity, simplicity and sufficient generality.  相似文献   

Assessing streams in Germany with benthic invertebrates: development of a practical standardised protocol for macroinvertebrate sampling and sorting   总被引：4，自引：0，他引：4  

Peter Haase  Susanne Lohse  Steffen Pauls  Karin Schindehütte  Andrea Sundermann  Peter Rolauffs  Daniel Hering 《Limnologica》2004,34(4):349-365

In the past, no single standardised method for sampling and sorting benthic macroinvertebrates has been implemented in Germany. Therefore, we tested the suitability of two common sorting protocols, RIVPACS and AQEM/STAR, by taking samples with each protocol at 44 sampling sites. Our results reveal that different methods deliver slightly different assessment results. Moreover these two methods differ in costs. Although the AQEM/STAR protocol takes longer than the RIVPACS protocol, we favoured the AQEM/STAR protocol because of its higher level of standardisation. In order to limit costs to an acceptable level, a modification of the AQEM/STAR protocol (MAS method) is developed. This method is highly standardised, gives stable assessment results and is relatively inexpensive (€ 224.00 for processing of an average sample). A detailed protocol of the newly developed method is given.  相似文献   

Assessing streams in Germany with benthic invertebrates: Development of a multimetric invertebrate based assessment system   总被引：3，自引：0，他引：3  

Jürgen Bhmer  Claudia Rawer-Jost  Armin Zenker  Carolin Meier  Christian K. Feld  Regina Biss  Daniel Hering 《Limnologica》2004,34(4):416-432

The main aim of the study was to develop a multimetric assessment system for macroinvertebrate communities of small and mid-sized streams in Germany in accordance with the Water Framework Directive of the European Union. The system should be applicable by water authorities, capable of distinguishing between different impacts, and specifically adapted to all types of small and mid-sized rivers in Germany. An assessment system has been developed consisting of two modules based on the established indices for saprobic degradation and acidity, and a third module covering general degradation. For the third module a new multimetric index (MMI) was developed and tested using preclassifications for stream hydromorphological degradation, land use and general impairment as impact measures. More information on sampling method, season and the type of dominating human impairment allowed to further analyse the index' capabilities and sensitivity. It performed well in all seasons and detected all types of impairment except acidity. The usefulness of the impact measures used in this study is discussed with regard to the development of a multimetric index. The comparison of the new index with other indices showed that it is especially sensitive in detecting macroinvertebrate community responses to hydromorphological degradation and pollution such as the German AQEM index, while IBI 12 and Renkonen's similarity more reflect general community shifts caused by any type of disturbance. The new assessment system will be proposed for future use by state agencies for nationwide monitoring in the context of the Water Framework Directive implementation.  相似文献