A simple photometer for precise determination of dissolved oxygen concentration by the Winkler method with recommendations for improving respiration rate measurements in aquatic organisms     

Sandra L. Vargo  R. Ken Forcé 《Estuaries and Coasts》1981,4(1):70-74

A simple inexpensive photometer designed for Winkler titration end-point detection is described. The precision of replicate dissolved oxygen measurements using this instrument was 0.06–0.22%. This high precision is needed to measure the small changes in dissolved oxygen concentration for determining the respiration rate of small aquatic organisms. Other recommendations for improving precision are also presented.  相似文献   

The stable isotopic composition of coral skeletons: control by environmental variables   总被引：1，自引：0，他引：1  

Sandra M. Weil  Robert W. Buddemeier  Stephen V. Smith  Peter M. Kroopnick 《Geochimica et cosmochimica acta》1981,45(7):1147-1153

The reef corals Pocillopora damicornis and Montipora verrucosa were cultured under various controlled temperature and light conditions. The corals were analyzed for growth rate, tissue pigment content and skeletal ¹³C and ¹⁸O. Coral skeletal δ¹³C values varied with light dose and correlated with changes in zooxanthellar pigment. The δ¹³C values of skeletal aragonite seem to be modified by oxidation of photosynthetically produced organic matter.Functionally significant relationships between coral skeletal δ¹⁸O values and temperature have been determined. The temperature coefficients of the δ¹⁸O values [?4.4°C (%.)^?1] are similar to the first order coefficient in the equilibrium paleotemperature equation, but the δ¹⁸O values have taxonomically consistent offsets from equilibrium. The offsets may be attributed to the coral metabolism with slight but statistically significant differences between the two genera. Environmental and metabolic variables other than temperature have little or no effect on skeletal δ¹⁸O.  相似文献   

Diffusion of ions in sea water and in deep-sea sediments   总被引：3，自引：0，他引：3  

Sandra Gregory 《Geochimica et cosmochimica acta》1974,38(5):703-714

The tracer-diffusion coefficient of ions in water, D_j⁰, and in sea water, $\text{D}{}_{\mathrm{j}}{}^1$, differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective $\text{D}{}_{\mathrm{j}}{}^1$ or D_j⁰ values. The tracer diffusion coefficients of ions in deep-sea sediments, D_j,sed., can be related to $\text{D}{}_{\mathrm{j}}{}^1$ by $\text{D}{}_{\mathrm{j,sed.}}\text{= D}{}_{\mathrm{j}}{}^1\text{·}\text{α}\text{θ}{}^2$, where θ is the tortuosity of the bulk sediment and a a constant close to one.  相似文献   

Bimodal early proterozoic volcanism in the Grythytte field and associated volcano-plutonic complexes,Bergslagen, Central Sweden     

Willem van der Velden  James Baker  Sandra de Maesschalck  Thea van Meerten 《International Journal of Earth Sciences》1982,71(1):171-181

The Grythytte field sequence forms a NNW belt of acid-basic metavolcanic and metasedimentary rocks. The geology shows characteristics of a dynamic process of trough-forming and infilling which to a large extent post-dates the Hjulsjö volcanoplutonic complex situated to the east. In the latter complex acid metapyroclastics strike around a centre of granite and granophyre, which cut and are cut by basic sills and dykes. Field and petrochemical evidence points to a distinct bimodal magmatism that ist manifested during one short phase of a rifting period.

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Zusammenfassung Die Grythytte Schichtenfolge bildet einen NNW verlaufenden Gürtel aus sauren und basischen Metavulkaniten und Metasedimenten. Die geologischen Befunde weisen auf einen dynamischen Entstehungsprozeß von Grabenbildung und Füllung hin. Im weiter östlich gelegenen vulkanisch-plutonischen Hjulsjö-Komplex streichen älteren metamorphen pyroklastischen Gesteine rund ein Granit-Granophyr Zentrum. Dieser Komplex durchschneidet und wird durchschnitten von basischen Sills und Gängen. Feldgeologische und geochemische Untersuchungen weisen deutlich auf einen bimodalen Magmatismus hin, der während einer kurzen Phase der Grabenbildung stattfand.

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Résumé La séquence de Grythytte forme une ceinture de roches métavolcaniques et métasédimentaires de direction NNO. La géologie fait apparaître les caractéristiques d'un processus dynamique de formation de fosse et de remplissage, qui s'est produit, pour la plus grande partie, après la formation du complexe volcano-plutonique de Hjulsjö situé à l'Est. Dans ce dernier complexe des produits pyroclastiques acides sont disposés autour d'un centre granitoïde et granophyrique, qui à son tour recoupe et est recoupé par des sills et des dykes basiques. Les observations de terrain et les faits pétrochimiques indiquent un procèssus magmatique distinctement bimodal qui s'est manifesté pendant une phase courte dans une période de «rifting».

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Grythytte , NNW . . Hjulsj -- . . , , .

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Statistical analysis of the largest possible earthquake magnitudes on the Ecuadorian coast for selected return periods     

Sandra García-Bustos  Jimmy Landín  Ricardo Moreno  A.S.E. Chong  Maurizio Mulas  Mónica Mite 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2020,14(1):56-68

ABSTRACT

In this work, we have studied the largest earthquake magnitudes on the Ecuadorian coast by using the principles of Extreme Value Analysis based on its two approaches: Block Maxima and Peaks-over-Threshold. First, before modelling the recorded earthquakes, the K-means clustering technique was applied to determine a classification according to the level of magnitude of the earthquakes. Then, models based on the Extreme Value theory of earthquake magnitudes were developed for each of the four clusters that were found, and finally, the best-fitted models were those known as Fréchet and Gumbel ones. The zone with the greatest earthquake magnitudes on the Ecuadorian coast is located between the north of the province of Manabí and the south of the province of Esmeraldas, with a return period of 50 years for an earthquake with magnitude greater than 7.7 M_W.  相似文献   

The carbon isotopic distribution of Murchison amino acids     

Sandra Pizzarello  Yongsong Huang 《Geochimica et cosmochimica acta》2004,68(23):4963-4969

The δ¹³C values of thirty-four individual amino acids and two pyridine carboxylic acids have been obtained fromthe Murchison meteorite. They were found to range from +4.9 to +52.8‰, with statistically significant differences observed both within and between amino acid subgroups. The ¹³C content of α-amino acids declines with increasing chain length, a trend similar to the ones previously observed for carboxylic acids and alkanes. Also 2-methyl-2-amino acids were found to be heavier in ¹³C than the corresponding 2-H homologues. The3-, 4-, and 5-amino acids do not show a comparable declining trend in δ¹³C values and neither do the amino dicarboxylic acids. This variability in δ ¹³C values can be interpreted as to indicate that the synthetic histories of soluble organics in meteorites may have been diverse even within groups of compounds with very similar functional group composition.  相似文献   

Coarse sediment transport in mountain streams in Colorado and Wyoming,USA     

Sandra E. Ryan  Laurie S. Porth  C. A. Troendle 《地球表面变化过程与地形》2005,30(3):269-288

Since the early 1990s, US Forest Service researchers have made thousands of bedload measurements in steep, coarse‐grained channels in Colorado and Wyoming, USA. In this paper we use data from 19 of those sites to characterize patterns and rates of coarse sediment transport for a range of channel types and sizes, including step–pool, plane‐bed, pool–riffle, and near‐braided channels. This effort builds upon previous work where we applied a piecewise regression model to (1) relate flow to rates of bedload transport and (2) define phases of transport in coarse‐grained channels. Earlier, the model was tested using bedload data from eight sites on the Fraser Experimental Forest near Fraser, Colorado. The analysis showed good application to those data and to data from four supplementary channels to which the procedure was applied. The earlier results were, however, derived from data collected at sites that, for the most part, have quite similar geology and runoff regimes. In this paper we evaluate further the application of piecewise regression to data from channels with a wider range of geomorphic conditions. The results corroborate with those from the earlier work in that there is a relatively narrow range of discharges at which a substantial change in the nature of bedload transport occurs. The transition from primarily low rates of sand transport (phase I) to higher rates of sand and coarse gravel transport (phase II) occurs, on average, at about 80 per cent of the bankfull (1·5‐year return interval) discharge. A comparison of grain sizes moved during the two phases showed that coarse gravel is rarely trapped in the samplers during phase I transport. Moreover, the movement and capture of the D₁₆ to D₂₅ grain size of the bed surface seems to correspond with the onset of phase II transport, particularly in systems with largely static channel surfaces. However, while there were many similarities in observed patterns of bedload transport at the 19 studied sites, each had its own ‘bedload signal’ in that the rate and size of materials transported largely reflected the nature of flow and sediment particular to that system. Published in 2005 by John Wiley & Sons, Ltd.  相似文献   

The deuterium enrichment of individual amino acids in carbonaceous meteorites: A case for the presolar distribution of biomolecule precursors     

Sandra Pizzarello  Yongsong Huang 《Geochimica et cosmochimica acta》2005,69(3):599-605

The δD values of over 40 amino acids and two pyridine carboxylic acids of the Murchison and Murray meteorites have been obtained by compound-specific isotopic analyses. For compounds with no known terrestrial distribution, these values range from approximately +330‰ (for cyclic leucine) to +3600‰ (for 2-amino-2,3-dimethylbutyric acid). The latter value is the highest ever recorded for a soluble organic compound in meteorites and nears deuterium to hydrogen ratios observed remotely in interstellar molecules. Deuterium content varies significantly between molecular species and is markedly higher for amino acids having a branched alkyl chain. The δD value of Murray l-isovaline, with an enantiomeric excess of ∼ 6% in the meteorite, was within experimental error of that determined for the combined dl-isovaline enantiomers. Overall, the hydrogen isotope composition of meteoritic amino acids is relatively simple and their δD values appear to vary more with the structure of their carbon chains than with the number and relative distribution of their functionalities or ¹³C content. The magnitude and extent of deuterium enrichment shared by many and varied amino acids in meteorites indicate that cosmic regimes such as those found in the interstellar medium were capable of producing, if not all the amino acids directly, at least a suite of their direct precursors that was abundant, varied, and considerably saturated.  相似文献   

Erratum to Sandra Pizzarello and Yongsong Huang (2005) “The deuterium enrichment of individual amino acids in carbonaceous meteorites: A case for the presolar distribution of biomolecule precursors”, Geochimica et Cosmochimica Acta 69, 599-605     

Sandra Pizzarello 《Geochimica et cosmochimica acta》2005,69(21):5163

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Collapse of primordial clouds — II. The role of dark matter     

Sandra R. Oliveira  Oswaldo D. Miranda  & José C. N. de Araujo  Reuven Opher 《Monthly notices of the Royal Astronomical Society》1998,301(1):115-130

In this article we extend the study performed in our previous article of the collapse of primordial objects. We here analyse the behaviour of the physical parameters for clouds ranging from 10⁷ to 10¹⁵ M_⊙. We study the dynamical evolution of these clouds in two ways: as purely baryonic clouds and as clouds with non-baryonic dark matter included. We start the calculations at the beginning of the recombination era, following the evolution of the structure until the collapse (which we defined as the time when the density contrast of the baryonic matter is greater than 10⁴). We analyse the behaviour of several physical parameters of the clouds (e.g. the density contrast and the velocities of the baryonic matter and the dark matter) as a function of time and radial position in the cloud. In this study all physical processes that are relevant to the dynamical evolution of the primordial clouds, such as for example photon drag (due to the cosmic background radiation) and hydrogen molecular production, besides the expansion of the Universe, are included in the calculations. In particular we find that the clouds with dark matter collapse at higher redshift when we compare the results with the purely baryonic models. As a general result we find that the distribution of the non-baryonic dark matter is more concentrated than the baryonic one. It is important to stress that we do not take into account the putative virialization of the non-baryonic dark matter; we just follow the time and spatial evolution of the cloud, solving its hydrodynamical equations. We also studied the role of cooling–heating processes in the purely baryonic clouds.  相似文献