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  • 1
    Electronic Resource
    Electronic Resource
    Geochemistry and provenance of the Middle Ordovician Austin Glen Member (Normanskill Formation) and the Taconian Orogeny in New England (1998)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 45 (1998), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Austin Glen Member of the upper Middle Ordovician Normanskill Formation is a sandstone-shale flysch succession deposited in the foreland of the Taconian Orogen. Petrographic, major and trace element, and Nd–Pb isotopic data provide substantial constraints on its provenance. Lack of K-feldspar and paucity of plagioclase, in addition to the dominance of sedimentary rock fragments, indicate that the source was dominated by recycled, sedimentary components. Major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same. No evidence of an ophiolitic or volcanic component was observed. Interpretation of Nd isotopic characteristics are complicated by a partial resetting of the Nd isotope system at about the time of sedimentation but indicate that the provenance of the Austin Glen Member had a long-term history of light rare earth element (LREE) enrichment (average TDM = 1·8 Ga). Furthermore, Nd isotopic compositions are extremely homogeneous (ɛNd = –8·1 ± 0·6; 1 s.d.; n = 23) at 450 Ma, the approximate depositional age, indicating either a single source or very well-mixed sources. 207Pb/204Pb ratios are variable but within the range of Pb isotopic compositions typically described as Grenvillian. The range of 207Pb/204Pb is greater than expected for the range of 206Pb/204Pb and suggests an additional component of Pb, possibly introduced during diagenesis. The immediate source of the Austin Glen Member may have been the accretionary prism that developed as older sediments of the Laurentian margin were scraped off the basin floor, incorporated within the accretionary prism and shed into the basin. No evidence indicating the arrival of an undifferentiated island arc or continental fragment during the Taconian Orogeny has been found. The data acquired during this study can be explained almost exclusively by Grenville Province source components but with possible additional contributions from older Laurentian terranes and Late Proterozoic rift volcanics that are not readily quantified but likely to have been minor. Accordingly, we conclude that the Taconian Orogeny in New England involved either: (1) a continental arc that involved exclusively Laurentia; (2) collision of a continental block with identical geochemical characteristics as Laurentia; or (3) essentially no detritus from any exotic colliding block (island arc or continental fragment) reached the foreland basin at the time of Austin Glen deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.1998.00168.x
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  • 2
    Electronic Resource
    Electronic Resource
    Scale and timing of Rare Earth Element redistribution in the Taconian foreland of New England (2004)
    Oxford, UK : Blackwell Science Ltd
    Sedimentology 51 (2004), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Clastic sedimentary rocks, deposited on eastern North America in response to the Taconian Orogeny, commonly have Sm/Nd isotope relationships indicating substantial isotope disturbance near or subsequent to the time of sedimentation that may be associated with severe depletion in light rare earth elements (LREE). Affected units [Normanskill Formation (Austin Glen and Pawlet Members), Frankfort Formation and Perry Mountain Formation] are widely separated both geographically (western New York to western Maine) and stratigraphically (Middle Ordovician to Silurian). A model is proposed for the most likely explanation of the observed REE and Sm/Nd isotope relationships involving a two-stage process. In the first stage, REE are redistributed on a mineralogical scale (dissolution/precipitation on a sample scale) often with the involvement of REE-enriched trace phases such as apatite and monazite. This stage typically takes place during diagenesis but may also take place later during metamorphism and/or recent weathering, and results in isotope re-equilibration on a sample scale. The second stage occurs when one or more of these phases is redissolved and REE are transported on large advective scales. Where LREE-enriched phases are involved, this gives rise to LREE depletion in whole rocks. The timing of this second stage cannot be constrained from Sm/Nd isotope data and may take place at any time subsequent to the isotope re-equilibration. Such complex histories of REE redistribution may result in serious errors in estimating Nd model ages but not in estimating the Nd isotope composition at the age of sedimentation. Thus, Sm/Nd ratios even of unmetamorphosed sedimentary rocks have to be carefully evaluated before the calculation of depleted mantle model ages for the provenance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.2004.00656.x
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  • 3
    Electronic Resource
    Electronic Resource
    Planetary science Bedrock formation at Meridiani Planum (2006)
    [s.l.] : Nature Publishing Group
    Nature 443.2006, 7107, E1-, (2 S.) 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Arising from: T. M. McCollom & B. M. Hynek Nature 438, 1129–1131 (2005); McCollom & Hynek reply The Mars Exploration Rover Opportunity discovered sulphate-rich sedimentary rocks at Meridiani Planum on Mars, which are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05212
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  • 4
    Electronic Resource
    Electronic Resource
    A lower crustal origin for massif-type anorthosites (1984)
    [s.l.] : Nature Publishing Group
    Nature 311 (1984), S. 372-374 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Anorthosites may be classified broadly into two types: Archaean and massif. The Archaean anorthosites typically occur as components of layered igneous intrusions1 of moderate size and are clearly of mantle origin. Plagioclase compositions lie in the range An80_95. In contrast, the massif-type ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/311372a0
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of sedimentary sorting on neodymium isotopes in deep-sea turbidites (1989)
    [s.l.] : Nature Publishing Group
    Nature 337 (1989), S. 547-549 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The neodymium model age of a sediment or sedimentary rock is generally interpreted as the average age of extraction from the mantle of the various provenance components1. Complications involving uncertainties in mantle evolution models and possible changes in the Sm/Nd ratio during crustal ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/337547a0
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  • 6
    Electronic Resource
    Electronic Resource
    The Thermal stability of collagen in diabetic rats: correlation with severity of diabetes and non-enzymatic glycosylation (1983)
    Springer
    Diabetologia 24 (1983), S. 282-285 
    Details
    ISSN: 1432-0428
    Keywords: Diabetes ; rat collagen ; thermal stability ; glycosylated haemoglobin ; ageing ; non-enzymatic glycosylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The thermal stability of collagen fibres from rat tail tendon was studied in both normal and diabetic rats. Results were correlated with the age of the animals, glycosylated haemoglobin level and the degree of non-enzymatic glycosylation of the collagen. Age was found to be the most important single determinant of the thermal rupture time of collagen fibres (r=0.87, p 〈 0.005). Thermal rupture time was also increased in diabetes and showed good correlation with glycosylated haemoglobin (r=0.69, p 〈 0.005) and non-enzymatic glycosylation of collagen (r=0.51, p 〈 0.005). The correlation of glycosylated haemoglobin level and thermal rupture time was significant, independent of age and non-enzymatic glycosylation of collagen. Experiments in vitro showed that incubation of collagen fibres with glucose increased the thermal stability of collagen. These results demonstrated an independent effect of severity of diabetes on the physical properties of collagen. The role of non-enzymatic glycosylation in causing the changes in collagen properties in diabetes remains to be fully elucidated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00282714
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  • 7
    Electronic Resource
    Electronic Resource
    Non-enzymatic glycosylation of tissue protein in diabetes in the rat (1983)
    Springer
    Diabetologia 24 (1983), S. 377-381 
    Details
    ISSN: 1432-0428
    Keywords: Non-enzymatic glycosylation ; diabetes ; glycosylated haemoglobin ; complications ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Non-enzymatic glycosylation of tissue and haemolysate proteins has been studied in normal and diabetic rats by reduction with tritiated sodium borohydride (NaB3H4) alone or in combination with chromatography on m-aminophenyl-boronic acid coupled to Biogel P-6. With NaB3H4 reduction alone, there was a linear relationship between plasma glucose and tritium incorporation into haemolysate protein. However, increased non-enzymatic glycosylation of tissue protein could not be demonstrated with NaB3H4 reduction alone. Tritiated glycosylated amino acids could be selectively removed by maminophenylboronic acid immobilized on Biogel P-6, then eluted by acidification and the radioactivity in the acidic peak used to estimate non-enzymatic glycosylation. Using the combined techniques, an increase in non-enzymatic glycosylation was observed in heart, kidney and liver obtained from rats with diabetes of 18 weeks duration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00251828
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  • 8
    Electronic Resource
    Electronic Resource
    High glucose concentration inhibits the expression of membrane type metalloproteinase by mesangial cells: possible role in mesangium accumulation (2000)
    Springer
    Diabetologia 43 (2000), S. 642-648 
    Details
    ISSN: 1432-0428
    Keywords: Keywords Matrix metalloproteinase ; nephropathy ; extracellular matrix ; degradation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Aims/hypothesis. High glucose concentration decreases the degradation of mesangium matrix, an action substantially mediated by a reduction in the activities of the matrix metalloproteinases (MMPs). Metalloproteinase-2 is unique in that it is activated on the cell surface by one of the membrane type metalloproteinases (MT1-MMP), a process involving complex interactions with tissue inhibitor of metalloproteinase-2. The aim of this study was investigate the effects of glucose concentration on mesangial cell gene expression of MT1-MMP and its ability to modulate the activation of metalloproteinase-2. Methods. Gene expression was determined using competitive RT-PCR, protein expression of MMP-2 was measured by western blot and its activation by zymography. Concanavalin A, known to increase MT1-MMP expression was added in some experiments. Results. High glucose concentration decreased MT1-MMP gene expression (11.52 ± 1.63 and 4.84 ± 0.72 amol/μg RNA, 5 vs 25 mmol/l glucose, respectively) and decreased activation of MMP-2 by 30 % despite a twofold increase in gene expression of MMP-2. Concanavalin A increased expression of MT1-MMP and activation of MMP-2. Irrespective of whether MMP-2 was from endogenous or exogenous source there was an excellent correlation between the MT1-MMP expression and degree of MMP-2 activation, whereas the gene expression of TIMP-2 was not significantly altered by high glucose concentration or concanavalin A. Conclusions/interpretation. Our results indicate that in a high glucose milieu, suppression of MT1-MMP expression could explain the low MMP-2 activity in the presence of high MMP-2 expression. This process could contribute to the mesangium matrix accumulation in diabetic nephropathy. [Diabetologia (2000) 43: 642–648]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250051353
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  • 9
    Electronic Resource
    Electronic Resource
    Functional and structural abnormalities in the nerves of Type I diabetic baboons: aminoguanidine treatment does not improve nerve function (2000)
    Springer
    Diabetologia 43 (2000), S. 110-116 
    Details
    ISSN: 1432-0428
    Keywords: Keywords Diabetic complications, neuropathy, autonomic, nerve conduction velocity, aminoguanidine, monkey, morphometry, myelin, advanced glycation end products.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Aims/hypothesis. To improve understanding of the pathophysiology of diabetic neuropathy and to establish a primate model for experimental studies, we examined nerve changes in baboons with Type I (insulin-dependent) diabetes mellitus. We also examined the effect of aminoguanidine (an inhibitor of the formation of advanced glycation end products) on nerve function.¶Methods. Male baboons (Papio hamadryas) were assigned to four groups; control, diabetic, control and diabetic treated with aminoguanidine. Diabetes was induced with streptozotocin (60 mg/kg, intravenous). Insulin and aminoguanidine (10 mg/kg) were injected subcutaneously daily. Motor and sensory nerve conduction velocity was measured using standard techniques. Autonomic function was examined by measuring heart rate response to positional change. Sural nerve morphometry was analysed in the diabetic group (mean duration 5.5 years) along with their age-matched controls.¶Results. The diabetic groups were smaller in size with a mean HbA1 c of 8.9 ± 1.2 %. The nerve conduction velocity and heart rate response was reduced in the diabetic groups. Morphometric analysis of the diabetic sural nerve showed smaller axon diameter (2.99 ± 0.06 μm vs 3.29 ± 0.06 μm; p 〈 0.01) accompanied by thinner myelin (1.02 ± 0.02 μm vs 1.15 ± 0.02 μm, p 〈 0.01) with no change in the axon density. Treatment with aminoguanidine for 3 years had no effect on glycaemic control and did not restore conduction velocity or autonomic dysfunction in the diabetic animals, contrary to the studies in rats.¶Conclusions/interpretation. These results show that the primate is a good model to study diabetic neuropathy and suggest that the accumulation of advanced glycation end products are not an early mechanism of nerve damage in this disorder. [Diabetologia (2000) 43: 110–116]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250050014
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