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  • 1
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    Evidence of Bedform Superimposition and Flow Unsteadiness In Unit-Bar Deposits, South Saskatchewan River, Canada (2011)
    Society for Sedimentary Geology (SEPM)
    Details
    Publication Date: 2011-11-01
    Description: Unit-bar deposits are ubiquitous components of river-channel deposits and strongly influence their hydrological properties, yet they are not easy to interpret. This paper concerns details of the internal structures of six unit bars from the South Saskatchewan River, Canada, that were investigated using trenches, epoxy resin peels, and 900 MHz ground-penetrating radar (GPR) profiles. The composition of unit bars depends on flow unsteadiness and superimposed bedforms. Flow unsteadiness causes changes in the mean grain size of the sediment in transport, but is expressed primarily as a change in the type and direction of migration of smaller ripple- and dune-scale bedforms superimposed on unit bars. Superimposed bedforms with heights that exceed 25% of the host bedform height reduce their host's slope and generate inclined sets. Host bedforms with smaller superimposed bedforms form angle-of-repose cross strata with a visible pre-sorting pattern. The relationship between the formative host- and superimposed bedforms and such pre-sorted cross strata can be used to interpret numerous aspects of the three-dimensional geometries of the bedforms. Such detailed interpretations rely on: (i) regularly spaced fine-grained drapes deposited during the passage of troughs of superimposed bedforms, (ii) grain-size sorting patterns generated by sorting within the superimposed bedforms before deposition, (iii) grain-size sorting during deposition by grainfall and intermittent grainflows down the bar lee-slope, and (iv) the presence and nature of low-angle reactivation surfaces.The detailed interpretations revealed that the deposits of dam-related floods were significantly smaller than the deposits of individual unit bars in this study. The unsteady flow and sediment transport conditions are reflected by changes in the structural composition of the unit bars. Reactivation surfaces associated with flow unsteadiness, as opposed to those formed by large superimposed bedforms, were characterized by changes in mean grain size, the buildup of sediment at the base of the bar lee slope, and changes in structures formed by superimposed bedforms. Reactivation surfaces generated by large superimposed bedforms indicate that bedform preservation is likely increased in areas of flow deceleration. The trough deposits of exposed unit bars contained bubble sand, planar laminae due to upper-stage plane beds, and low-angle inclined laminae due to antidunes. These structures indicate that unit-bar troughs can act as ephemeral channels. The composition of the investigated unit bars thus emphasizes the interplay between flow unsteadiness and bed morphology in the formation of sedimentary structures in river channels.Sediment surfaces generate visible GPR reflections where the thickness and contrast in electrical properties of the sediment layers are sufficiently large. Most cross-stratified sets were represented only by reflections from the base of the set, and not by high-angle inclined reflections from the cross strata. The local absence of reflections from cross strata is attributed to the lack of contrast in electrical properties of the well-sorted cross strata and their limited thickness relative to the radar wavelength. In contrast to cross strata, reactivation surfaces formed by large superimposed bedforms and flow unsteadiness were commonly associated with distinct inclined reflections.
    Print ISSN: 1527-1404
    Topics: Geosciences
    Published by Society for Sedimentary Geology (SEPM)
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  • 2
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    The relationship between charge movements associated with ICa and INa-Ca in cardiac myocytes (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-04-20
    Description: Ventricular myocytes exhibit a nifedipine-sensitive inward calcium current (ICa) and contracture when they are voltage clamped from -40 to 0 millivolt in the presence of caffeine and in the absence of extracellular sodium. However, upon repolarization they fail to relax because neither the sarcoplasmic reticulum nor the sodium-calcium exchange can reduce intracellular calcium. Sudden application of extracellular sodium during the contracture (but after repolarization) causes immediate relaxation and activates a transient inward sodium-calcium exchange current (INa-Ca), whose peak slightly precedes mechanical relaxation. The total charge carried by the nifedipine-sensitive ICa is twice the total charge carried by the transient inward INa-Ca. Assuming an exchange stoichiometry of three sodium to one calcium, these results indicate that all the calcium entering the cell during the initial depolarization is extruded by the sodium-calcium exchange.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bridge, J H -- Smolley, J R -- Spitzer, K W -- HL34288/HL/NHLBI NIH HHS/ -- HL42357/HL/NHLBI NIH HHS/ -- HL42873/HL/NHLBI NIH HHS/ -- New York, N.Y. -- Science. 1990 Apr 20;248(4953):376-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City 84112.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2158147" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Caffeine/pharmacology ; Calcium/metabolism ; Calcium Channels/*physiology ; Carrier Proteins/*physiology ; Electric Conductivity ; Guinea Pigs ; Heart/*physiology ; Membrane Potentials ; Myocardial Contraction/drug effects ; Myocardium/metabolism ; Nifedipine/pharmacology ; Sarcoplasmic Reticulum/metabolism ; Sodium/metabolism/pharmacology ; Sodium-Calcium Exchanger
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Uphill sodium transport driven by an inward calcium gradient in heart muscle (1983)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1983-01-14
    Description: Heart cells were loaded with sodium by treatment with toxic doses of acetyl strophanthidin. After this treatment, an increase in extracellular calcium resulted in a transient net outward sodium flux against its electrochemical gradient and in net cellular uptake of calcium. It is concluded that the free energy for the net outward sodium movement was derived from the increased calcium gradient and that these ion movements took place through the sodium-calcium exchange. While in the normal physiological state the sodium-calcium exchange produces calcium extrusion from the cell, these experiments demonstrate its reversibility.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3521047/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3521047/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bridge, J H -- Bassingthwaighte, J B -- P41 RR001243/RR/NCRR NIH HHS/ -- P41 RR001243-190021/RR/NCRR NIH HHS/ -- New York, N.Y. -- Science. 1983 Jan 14;219(4581):178-80.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/6849128" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biological Transport, Active ; Calcium/*metabolism ; Cytoplasm/metabolism ; Membrane Potentials ; Myocardium/*metabolism ; Potassium/metabolism ; Rabbits ; Sarcolemma/metabolism ; Sodium/*metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Relaxation of isolated ventricular cardiomyocytes by a voltage-dependent process (1988)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1988-08-12
    Description: Cell contraction and relaxation were measured in single voltage-clamped guinea pig cardiomyocytes to investigate the contribution of sarcolemmal Na+-Ca2+ exchange to mechanical relaxation. Cells clamped from -80 to 0 millivolts displayed initial phasic and subsequent tonic contractions; caffeine reduced or abolished the phasic and enlarged the tonic contraction. The rate of relaxation from tonic contractions was steeply voltage-dependent and was significantly slowed in the absence of a sarcolemmal Na+ gradient. Tonic contractions elicited in the absence of a Na+ gradient promptly relaxed when external Na+ was applied, reflecting activation of Na+-Ca2+ exchange. It appears that a voltage-dependent Na+-Ca2+ exchange can rapidly mechanically relax mammalian heart muscle.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bridge, J H -- Spitzer, K W -- Ershler, P R -- HL31140/HL/NHLBI NIH HHS/ -- HL34288/HL/NHLBI NIH HHS/ -- New York, N.Y. -- Science. 1988 Aug 12;241(4867):823-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, UT.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/3406740" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Caffeine/pharmacology ; Electric Stimulation ; Guinea Pigs ; Heart/*physiology ; In Vitro Techniques ; Membrane Potentials/drug effects ; *Myocardial Contraction/drug effects ; Perfusion ; Sarcolemma/drug effects/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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