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  • 1
    Electronic Resource
    Electronic Resource
    Elektronenmikroskopische Untersuchungen über die Photoreceptoren und Receptorensynapsen bei reinen Stäbchen- und Zapfennetzhäuten (1968)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 174 (1968), S. 289-320 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The morphological basis of the duplicity of the retina have until now not been sufficiently elucidated; therefore it seemed of advantage to study the structures of the photoreceptors and their synapses in mammals whose receptor apparatus in the light microscope is uniform and of known visual function. The retinas of two primates, Tupaia glis and Galago crassicaudatus and two domestic mice, Sylvaemus sylvaticus and Sylvaemus flavicolus, were analyzed with the electron microscope. Contrary to light microscope findings, Tupaia glis possesses rods and cones. The cone cells show a number of structural peculiarities which had hitherto not been found in mammals. The rods are very rare. Galago crassicaudatus, Sylvaemus sylvaticus and Sylvaemus flavicolus have two types of rods with distinctive characteristics; cones were not to be found. The results are correlated with the problem of the centralization of the retina (Rohen) and compared with recent electron microscopic findings of other authors. At the same time they are compared with the results of electrophysiological investigations of the visual function and of behavioral studies. The neuronal junctions of the outer plexiform and inner nuclear layers seem to be of great importance for the function of the retina. An increase of the contacts of the synaptic bodies with each other could intensify the picture contrast (diurnal vision), while the greater number of bipolar cells in the retinas of nocturnal animals could be connected with the summation of weak light.
    Notes: Zusammenfassung Die morphologischen Grundlagen der Duplizitätstheorie der Netzhaut sind bisher noch nicht ausreichend geklärt. Es schien daher lohnend, die Strukturen von Photoreceptoren und deren Synapsen bei Säugetieren zu untersuchen, die lichtmikroskopisch einen einheitlichen Receptorenapparat besitzen und deren Sehfunktion bekannt ist. Es werden die Netzhäute zweier Halbaffen, Tupaia glis und Galago crassicaudatus und zweier einheimischer Mäusearten, Sylvaemus sylvaticus und Sylvaemus flavicolus elektronenmikroskopisch analysiert. Tupaia glis besitzt entgegen lichtmikroskopischen Befunden Stäbchen und Zapfen. Die Zapfenzellen zeigen eine Reihe von Struktureigentümlichkeiten, die bisher in Photoreceptoren von Säugetieren nicht gefunden wurden. Stäbchen sind sehr selten. Galago crassicaudatus, Sylvaemus sylvaticus und Sylvaemus flavicolus haben in der Netzhaut zwei Typen von Stäbchenzellen mit charakteristischen Unterscheidungsmerkmalen. Zapfen sind nicht nachzuweisen. Die Ergebnisse der Untersuchungen werden zum Problem der Zentralisation der Netzhaut in Beziehung gesetzt und mit neueren elektronen-mikroskopischen Befunden anderer Autoren verglichen. Gleichzeitig werden sie den Ergebnissen der elektrophysiologischen Untersuchungen über die Sehfunktion und Studien der Verhaltensweisen gegenübergestellt. Danach scheint den neuronalen Verknüpfungen der Zellen in der äußeren plexiformen und inneren Körnerschicht eine wesentliche Rolle bei der Netzhautfunktion zuzukommen. Eine Vermehrung der Kontakte synaptischer Körper untereinander dürfte dabei zu einer Steigerung des Bildkontrastes beitragen (Tagessehen), während die größere Zahl von Bipolarenzellen in der Retina von Dämmerungsund Nachttieren wohl mit der Summation schwacher Lichtreize in Zusammenhang steht.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00406626
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Fine structural observations of the pecten oculi capillaries of the chicken (1973)
    Springer
    Cell & tissue research 146 (1973), S. 473-489 
    Details
    ISSN: 1432-0878
    Keywords: Pecten oculi ; Chicken ; Capillaries ; Transmission and scanning electron microscopy ; Freeze-etching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Der Pecten oculi des Haushuhns wurde licht-, scanning- und transmissions-elektronenmikroskopisch sowie mit der Gefrierätz-Technik unter besonderer Berücksichtigung seiner Kapillarstruktur untersucht. Die Kapillaren bilden ausgedehnte anastomosierende Netze. Ihre Endothelzellen besitzen sowohl apikal (luminal) als auch basal längsorientierte Mikrofalten. Es wird angenommen, daß die Ausbildung der apikalen endothelialen Oberflächendifferenzierung haemodynamisch bedingt ist. Hierbei wird gleichzeitig ausreichend Platz für membrangebundene Fermente geschaffen, die für aktive energie-verbrauchende transzelluläre Transportprozesse benötigt werden. Die Gefrierätzbefunde lassen unterschiedlich strukturierte Membranoberflächen an den Mikrofalten erkennen, die im Zusammenhang mit Transportfunktionen der Kapillarendothelzellen des Pectenoculi diskutiert werden. Vermutlich spielt der Pecten eine wichtige Rolle für die Ernährung von Retina und Glaskörper.
    Notes: Summary The pecten oculi of the domestic chicken was examined with light, scanning and transmission electron microscopy and with freeze-etching techniques. Particular attention has been given to the capillary structure. The capillaries form an extensive anastomotic network. Their endothelial cells have apical (luminal), as well as basal, longitudinally oriented microfolds. It is assumed that the formation of apical differentiations of the endothelial surface is due to haemodynamic influences. Thus, sufficient surface area for membrane bound enzymes is achieved. These enzymes are necessary for active transcellular transport processes that require energy. In freeze-etched material, two different structures of the membrane surface of microfolds can be recognized. These results are discussed in relation to transport functions through capillary endothelial cells of the pecten. It is assumed that the pecten plays an important role in the nourishment of the retina and vitreous body.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02347177
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  • 3
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    Assimilation of altimetric data and mean sea surface height into an eddy-permitting model of the North Atlantic (2001)
    In:  EPIC3Progress in Oceanography, 48(2), pp. 313-335, ISSN: 0079-6611
    Details
    Publication Date: 2019-07-17
    Description: This paper shows that the mean flow of an eddy-permitting model can be altered by assimilationof surface height variability, providing that information about the mean sea surface is included,using an adaption of a statistical-dynamical method devised by Oschlies and Willebrand. Weshow that for a restricted depth range (about 1000 m), dynamical knowledge can make up for thenull space present in surface data whose temporal extent may be too short to distinguish betweenvertical modes. The lack of an accurate geoid has meant that most assimilation methods, whilerepresenting variability well, have been unable to modify the mean flow to any extent. However,we show that by including several approximate forms for the mean sea surface, the mean interiorflow in the upper kilometer can be rapidly adjusted towards reality by the assimilation, with thelocation of major current systems moved by hundreds of kilometers.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 4
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    Seasonal cycle of meridional heat transport in the subtropical North Atlantic: a model intercomparison in relation to observations near 25 (2001)
    In:  EPIC3Progress in Oceanography, 48(2), pp. 231-253, ISSN: 0079-6611
    Details
    Publication Date: 2019-07-17
    Description: Three different, eddy-permitting numerical models are used to examine the seasonal variation ofmeridional mass and heat flux in the North Atlantic, with a focus on the transport mechanisms inthe subtropics relating to observational studies near 25°N. The models, developed in theDYNAMO project, cover the same horizontal domain, with a locally isotropic grid of 1/3° resolutionin longitude, and are subject to the same monthly-mean atmospheric forcing based on athree-year ECMWF climatology. The models differ in the vertical-coordinate scheme(geopotential, isopycnic, and sigma), implying differences in lateral and diapycnic mixingconcepts, and implementation of bottom topography. As shown in the companion paper ofWillebrand et al. (2001), the model solutions exhibit significant discrepancies in the annual-meanpatterns of meridional mass and heat transport, as well as in the structure of the western boundarycurrent system.Despite these differences in the mean properties, the seasonal anomalies of the meridional fluxesare in remarkable agreement, demonstrating a robust model behavior that is primarily dependenton the external forcing, and independent of choices of numerics and parameterization. The annualrange is smaller than in previous model studies in which wind stress climatologies based on marineobservations were used, both in the equatorial Atlantic (1.4 PW) and in the subtropics (0.4-0.5PW). This is a consequence of a weaker seasonal variation in the zonal wind stresses based onthe ECMWF analysis than those derived from climatologies of marine observations.The similarities in the amplitude and patterns of the meridional transport anomalies betwen thedifferent model realizations provide support for previous model conclusions concerning themechanism of seasonal and intraseasonal heat flux variations: they can be rationalized in terms of atime-varying Ekman transport and their predominantly barotropic compensation at depth. Analysisfor 25°N indicates that the net meridional flow variation at depth is concentrated near the westernboundary, but cannot be inferred from transport measurements in the western boundary currentsystem, because of significant and complex recirculations over the western half of the basin. Themodel results instead suggest that the main requirement for estimating the annual cycle of heatflux through a transoceanic section, and the major source of error in model simulations, is anaccurate knowledge of the wind stress variation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    The role of variable wind forcing in generating eddy energy in the North Atlantic (2001)
    In:  EPIC3Progress in Oceanography, 48(2), pp. 289-311, ISSN: 0079-6611
    Details
    Publication Date: 2019-07-17
    Description: Seasonal changes in eddy energy are used to investigate the role of high-frequency wind forcingin generating eddy kinetic energy in the oceans. To this end, we analyze two experiments of aneddy-permitting model of the North Atlantic driven by daily and monthly mean wind stress fields,and compare results with corresponding changes in the variance of the wind fields, and relatedresults from previous studies using altimeter and current meter data.With daily wind-stress forcing the model is found to be in general agreement with altimetricobservations and reveal a complex pattern of temporal changes in variability over the NorthAtlantic. Observations and the model indicate enhanced levels of eddy energy during wintermonths over several areas of the northern and, particularly northeastern North Atlantic. Since thewind-generated variability is primarily barotropic, its signal can be detected mostly in thelow-energy regions of the northern and north-eastern North Atlantic, which are remote frombaroclinically unstable currents. There the winter-to-summer difference in simulated eddy kineticenergy caused by the variable wind forcing is 〈0.5cm2 s2 between 30° and 55°N, and is 1-3cm2 s2north of 55°N. Seasonal changes in kinetic energy are insignificant along the path of the NorthAtlantic current and south of about 30°N.The weak depth dependence of the seasonal changes in eddy energy implies that the relativeimportance of wind-generated eddy energy is maximum at depth where the general (baroclinic)variability level is low. Accordingly, a significant correlation is found between the seasonal cycle inthe variance of wind stress and the seasonal cycle in eddy energy over a substantially wider areathan near the surface, notably across the entire eastern North Atlantic between the North AtlanticCurrent and the North Equatorial Current.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Space-Borne Measurements of the Time-Dependent Geostrophic Ocean Flow Field (1999)
    In:  EPIC3Journal of Atmospheric and Oceanic Technology, 16(9), pp. 1198-1207, ISSN: 0739-0572
    Details
    Publication Date: 2019-07-17
    Description: A method is presented that can provide high-resolution (in space and time) satellite measurements of theabsolute and time-varying surface geostrophic flow field. Based on the analysis of a high-resolution circulationmodel of the North Atlantic, it is demonstrated that a tandem satellite mission as anticipated from the French-U.S.Jason and Ocean Topography Experiment (TOPEX)/Poseidon missions flown along parallel tracks would besuitable to measure the velocity of the geostrophic surface flow field and its higher statistical moments, such askinetic energy and Reynolds stresses, with a space and time resolution similar to that obtained currently for seasurface height data from the TOPEX/Poseidon mission. The anticipated remote geostrophic velocity observationswould allow unprecedented studies of the ocean general circulation, including its mean and eddy energies,eddy-eddy, and eddy-mean flow interactions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Circulation characteristics in three eddy-permitting models of the North Atlantic (2001)
    In:  EPIC3Progress in Oceanography, 48(2), pp. 123-161, ISSN: 0079-6611
    Details
    Publication Date: 2019-07-17
    Description: A systematic intercomparison of three realistic eddy-permitting models of the North Atlanticcirculation has been performed. The models use different concepts for the discretization of thevertical coordinate, namely geopotential levels, isopycnal layers, terrain-following (sigma)coordinates, respectively. Although these models were integrated under nearly identicalconditions, the resulting large-scale model circulations show substantial differences. The resultsdemonstrate that the large-scale thermohaline circulation is very sensitive to the modelrepresentation of certain localised processes, in particular to the amount and water massproperties of the overflow across the Greenland-Scotland region, to the amount of mixing withina few hundred kilometers south of the sills, and to several other processes at small or sub-gridscales. The different behaviour of the three models can to a large extent be explained as aconsequence of the different model representation of these processes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Modelling phytoplankton dynamics in the frontal systems of the Southern Ocean (1998)
    In:  EPIC3Bericht über den 6 JGOFS-Workshop am 4 /5 12 1997 in Bremen (M Pätzold, M, G Wefer, G , Hrsg ) Ber FB Geowissenschaften, Universität Bremen, 109, 26 p.
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 9
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    DYNAMO - Dynamics of North Atlantic Models Simulation and assimilation with high resolution models (1997)
    In:  EPIC3Berichte aus dem Institut für Meereskunde Kiel, 294, 333 p., ISSN: 0341-8561
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 10
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    The role of variable wind forcing in generating eddy energy in the North Atlantic (2001)
    Elsevier
    In:  Progress in Oceanography, 48 (2-3). pp. 289-312.
    Details
    Publication Date: 2016-10-07
    Description: Seasonal changes in eddy energy are used to investigate the role of high-frequency wind forcing in generating eddy kinetic energy in the oceans. To this end, we analyze two experiments of an eddy-permitting model of the North Atlantic driven by daily and monthly mean wind stress fields, and compare results with corresponding changes in the variance of the wind fields, and related results from previous studies using altimeter and current meter data. With daily wind-stress forcing the model is found to be in general agreement with altimetric observations and reveal a complex pattern of temporal changes in variability over the North Atlantic. Observations and the model indicate enhanced levels of eddy energy during winter months over several areas of the northern and, particularly northeastern North Atlantic. Since the wind-generated variability is primarily barotropic, its signal can be detected mostly in the low-energy regions of the northern and north-eastern North Atlantic, which are remote from baroclinically unstable currents. There the winter-to-summer difference in simulated eddy kinetic energy caused by the variable wind forcing is 〈0.5 cm2 s2 between 30° and 55°N, and is 1–3 cm2 s2 north of 55°N. Seasonal changes in kinetic energy are insignificant along the path of the North Atlantic current and south of about 30°N. The weak depth dependence of the seasonal changes in eddy energy implies that the relative importance of wind-generated eddy energy is maximum at depth where the general (baroclinic) variability level is low. Accordingly, a significant correlation is found between the seasonal cycle in the variance of wind stress and the seasonal cycle in eddy energy over a substantially wider area than near the surface, notably across the entire eastern North Atlantic between the North Atlantic Current and the North Equatorial Current.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0079-6611(01)00008-8
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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