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  • 1
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    Silica burial enhanced by iron limitation in oceanic upwelling margins (2014)
    In:  EPIC3Nature Geoscience, 7(7), pp. 541-546, ISSN: 1752-0894
    Details
    Publication Date: 2016-11-17
    Description: In large swaths of the ocean, primary production by diatoms may be limited by the availability of silica, which in turn limits the biological uptake of carbon dioxide. The burial of biogenic silica in the form of opal is the main sink of marine silicon. Opal burial occurs in equal parts in iron-limited open-ocean provinces and upwelling margins, especially the eastern Pacific upwelling zone. However, it is unclear why opal burial is so efficient in this margin. Here we measure fluxes of biogenic material, concentrations of diatom-bound iron and silicon isotope ratios using sediment traps and a sediment core from the Gulf of California upwelling margin. In the sediment trap material, we find that periods of intense upwelling are associated with transient iron limitation that results in a high export of silica relative to organic carbon. A similar correlation between enhanced silica burial and iron limitation is evident in the sediment core, which spans the past 26,000 years. A global compilation also indicates that hotspots of silicon burial in the ocean are all characterized by high silica to organic carbon export ratios, a diagnostic trait for diatoms growing under iron stress. We therefore propose that prevailing conditions of silica limitation in the ocean are largely caused by iron deficiency imposing an indirect constraint on oceanic carbon uptake.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Photodissociation Dynamics of Trimethylgallium on GaAs (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 11515-11522 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100029a033
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  • 3
    Electronic Resource
    Electronic Resource
    Further Characterisation of the 91500 Zircon Crystal (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Geostandards and geoanalytical research 28 (2004), S. 0 
    Details
    ISSN: 1751-908X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA-ICP-MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1751-908X.2004.tb01041.x
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  • 4
    Electronic Resource
    Electronic Resource
    Atmospheric transport of pollutants from North America to the North Atlantic Ocean (1984)
    [s.l.] : Nature Publishing Group
    Nature 308 (1984), S. 722-724 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Documenting source-transport-receptor relationships to pollution studies is an elusive, complex problem which contributes to most of the controversy over the origin of acid deposition in non-urban areas. While the combination of ground-based chemical measurements, meteorological trajectory analyses ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/308722a0
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  • 5
    Electronic Resource
    Electronic Resource
    Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites (1984)
    [s.l.] : Nature Publishing Group
    Nature 308 (1984), S. 169-172 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] No 26Mg excesses were observed in an earlier study of plagioclase from more evolved meteorites including aubrites, eucrites, type 6 ordinary chondrites and irons15. 26Mg excesses (if originally present) are, however, more likely to be preserved in type 3 ordinary chondrites which have undergone ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/308169a0
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  • 6
    Electronic Resource
    Electronic Resource
    Crystallization of NAD+-dependent phenylalanine dehydrogenase from Nocardia sp239 (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 269-272 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The NAD+-dependent phenylalanine dehydrogenase from Nocardia sp239 has been crystallized by the hanging-drop method of vapour diffusion using ammonium sulfate as the precipitant. Two crystal forms were obtained in the presence and absence of the enzyme substrates phenylpyruvic acid or phenylalanine and its coenzyme NADH. Crystals of the native protein belong to the hexagonal system, with the space group being one of the enantiomorphic pair P6122 or P6522. The cell dimensions are a = b = 111.0, c = 174.5 Å, α = β = 90 and γ = 120°. Crystals grown from the protein co-crystallized with its substrates all belong to the trigonal system, space group P3121 or P3221, with unit-cell dimensions of a = b = 88.1 , c = 112.6 Å, α = β = 90 and γ = 120°. Preliminary protein-sequencing experiments have established that this enzyme is related to the octameric PheDH's which are members of the wider superfamily of amino-acid dehydrogenases. However, gel-filtration studies suggest that this enzyme is active as a monomer. The full determination of the three-dimensional structure of this phenylalanine dehydrogenase will add to the understanding of the molecular basis of the differential substrate specificity within this enzyme superfamily. In turn this will contribute to the rational design of an amino-acid dehydrogenase which could be used for the diagnosis of phenylketonuria and for the chiral synthesis of high-value pharmaceuticals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444997009980
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  • 7
    Electronic Resource
    Electronic Resource
    COMPARATIVE ASPECTS OF THE HEPATOBILIARY TRANSPORT OF IgA (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 409 (1983), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1983.tb26886.x
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  • 8
    Electronic Resource
    Electronic Resource
    Lithium in staurolite and its petrologic significance (1986)
    Springer
    Contributions to mineralogy and petrology 94 (1986), S. 496-506 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Natural metapelitic staurolites contain appreciable amounts of lithium. Lithium contents were determined by ion microprobe with concentrations of representative samples independently analyzed by atomic absorption spectrophotometry for calibration. Seventy-one percent of the analyzed staurolites contain 〉0.1 wt.% Li2O, although the distribution is skewed to values less than 0.3 wt.%. High Li contents observed in staurolite are attributed to one or more of several factors: initiation of staurolite breakdown, lack of additional host phases for lithium (e.g. biotite), pre-metamorphic Li-rich bulk rock composition, and/or interaction of the rock with Li-rich fluids. Li content is generally not correlated with the modal amount of staurolite in the rock, rather Li values tend to reflect variable host rock Li. Lithium most likely resides in the R2+ tetrahedral site. Its incorporation into the structure is probably related to a coupled substitution with Al: ivLi viA1/3 ivR −1 2+ vi□−1/3 When staurolite analyses yield low R2+ and high Al values, the possibility of high Li should be considered after accounting for variable H. Lithium partitions into common pelitic metamorphic minerals in the order staurolite〉cordierite〉biotite〉muscovite〉 garnet, tourmaline, and chloritoid. Partitioning is non-ideal in staurolite and a function of Fe content. Li in staurolite expands its stability field to a higher T relative to garnet and sillimanite, and to a lower T relative to chloritoid and Al-silicate. Analysis of staurolites for Li may provide further insight into this enigmatic mineral.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376341
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  • 9
    Electronic Resource
    Electronic Resource
    Type II collagen and TGF-βs in developing and aging porcine mandibular condylar cartilage: immunohistochemical studies (1997)
    Springer
    Cell & tissue research 289 (1997), S. 119-124 
    Details
    ISSN: 1432-0878
    Keywords: Key words: TGF-β ; Condylar cartilage ; Postnatal development ; Immunohistochemistry ; Pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Transforming growth factor-betas (TGF-βs) have been associated with the development and maintenance of articular cartilage. However, no studies have addressed their role in the postnatal development of mandibular condylar cartilage. This investigation represents the first immunohistochemical characterization of TGF-β isoforms and type II collagen in porcine mandibular condylar cartilage from various age groups. Furthermore, it is the first description of possible age-related changes in the expression of these proteins during postnatal development of this tissue. Condylar cartilage was dissected from freshly harvested temporomandibular joints of newborn, 6-, 12-, 24-, and 36-month-old farm swine. TGF-β1, TGF-β2, TGF-β3, and type II collagen were localized via standard immunohistochemical procedures. An immunoblot technique was employed to compare the relative amount of each protein present in the various age groups. Immunoreactivity was detected in mandibular condylar cartilage for all three isoforms of TGF-β and for Type II collagen. All age groups demonstrated some evidence of immunostaining, primarily in the cytoplasm of cells from most zones of the cartilage. Immunoblot results indicated that TGF-β isoforms had individualized patterns of expression. When newborn protein levels were taken as the baseline, TGF-β1 demonstrated a significant increase at ages 24 and 36 months. TGF-β2 significantly increased at 6, 12, 24, and 36 months (peak levels at 24 months; similar levels at 6, 12, and 36 months), whereas TGF-β3 remained stable at all ages. Type II collagen demonstrated increases that paralleled the increased levels of TGF-β1 and TGF-β2 at 24 and 36 months.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050857
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  • 10
    Electronic Resource
    Electronic Resource
    Electron microscopic examination of hepatic subcellular fractions for phosphatases (1973)
    Springer
    Journal of molecular histology 5 (1973), S. 199-223 
    Details
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Synopsis Lead capture techniques have been investigated for demonstrating phosphatase activity, with the aid of the electron microscope, in subcellular fractions isolated from rat liver. Controls with no exposure to the enzyme substrate showed little ‘staining’ (lead phosphate deposits). Results with preparations where the enzyme incubation period had been prolonged, and the lead phosphate deposits were heavy (‘over staining’), were also reassuring: the staining did not tend to become generalized. Particularly satisfactory results were obtained when the tissue fractions were used in the form of unfixed suspensions for ‘incubation’ with the substrate, this being performed with the minimum temperature and time needed to obtain representative staining of the elements present. Thus, for 5′-nucleotidase in plasma-membrane fragments there is good staining after only 10 min at 2°C. The favoured concentration of lead ions is 2mm. When the reaction period has elapsed, glutaraldehyde is added, and the tissue material repelleted; only then should osmium tetroxide be added. Glucose-6-phosphatase staining, particularly in rough microsomes, showed a time-lag which could be abolished by prior sonication or treatment with deoxycholate. In general, the cytochemical findings tallied well with the biochemical characterization of the various fractions examined, including zonalrotor fractions containing smooth vesicles the origin of which could not be established merely by morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01004989
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