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  • Polymer and Materials Science  (7)
  • 75.50.Ee  (2)
  • Cardioplegia  (2)
  • Mitochondrial swelling  (2)
  • Nitrogen  (2)
  • 1
    Electronic Resource
    Electronic Resource
    The ultrastructural effects of global ischaemia on Purkinje fibres compared with working myocardium: A qualitative and morphometric investigation on the canine heart (1991)
    Springer
    Virchows Archiv 418 (1991), S. 17-25 
    Details
    ISSN: 1432-2307
    Keywords: Purkinje fibres ; Ischaemia tolerance ; Qualitative and quantitative ultrastructure ; Cardioplegia ; Arrhythmias
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary During open heart surgery, reperfusion-induced arrhythmias arising after short periods of ischaemia may originate from subendocardial Purkinje fibres. We investigated the ultrastructure of these fibres during 30 min of global ischaemia at 25° C. The effects both with myocardial protection (HTK cardioplegia) and without it (pure ischaemia) were compared qualitatively and morphometrically. After 30 min pure ischaemia overcontraction of sarcomeres, hypercontraction and contraction bands, together with considerable changes in organelles, predominate over cellular oedema. In Purkinje fibres, both cellular and mitochondrial swelling were significantly increased within this 30-min time period from the onset of pure ischaemia. In contrast, following HTK cardioplegia and 30 min ischaemia, cellular and mitochondrial swelling remain moderate and over-contractions are almost entirely lacking. This means that despite remarkable differences between pure ischaemia and HTK cardioplegia in the degree of protection attained it is clear that, compared with the working myocardium, subendocardial Purkinje fibres do not display a higher resistance to early global ischaemia. Further investigations of this sensitivity of Purkinje fibres to global ischaemia and certain drugs may bring about new insights into myocardial protection and pharmacotherapy of arrhythmias.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01600240
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  • 2
    Electronic Resource
    Electronic Resource
    The surface to volume ratio of mitochondria, a suitable parameter for evaluating mitochondrial swelling (1990)
    Springer
    Virchows Archiv 416 (1990), S. 305-315 
    Details
    ISSN: 1432-2307
    Keywords: Myocardial ultrastructure ; Mitochondrial swelling ; Stereology ; Correlations of structural parameters ; Cardiac arrest and global ischaemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Cellular changes occuring in the left ventricular myocardium during ischaemia after different methods of cardiac arrest have been evaluated by morphological and morphometric parameters: volume densities of mitochondria (VVMi), sarcoplasm (VVSp), myofibrils (VVMf), surface densities of mitochondria (SVMi). The surface to volume ratio of mitochondria (SVratioMi) has been used as an independent parameter of mitochondrial swelling. Since ischaemic swelling of myocardial cells increases the volume of the reference space and ischaemic swelling of mitochondria decreases the free sarcoplasm, VVMi and VVSp cannot be considered as reliable indicators of the degree of oedema. SVMi/VVMf remains nearly constant after different forms of cardiac arrest, demonstrating the integrity of mitochondrial outer membranes. The inverse linear ratio between SVratioMi and the mean mitochondrial volume indicates that the increase in mitochondrial volume is achieved by surface smoothing. Loss of matrix structure and fragmentation of cristae occur at an SVratioMi of about 5.8, cristolysis at 5.5 to 5.6 and amorphous matrix densities at an SVratioMi of less than 5.5 μm2/μm3. The SVratioMi is a suitable parameter for evaluating mitochondrial swelling both at the onset and during global myocardial ischaemia, independent of the method of cardiac arrest used. It serves as an indicator of the state of structural preservation of mitochondria during ischaemia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01605291
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of ischaemia and preservation on the ultrastructure of the bronchiolar epithelium (1996)
    Springer
    Virchows Archiv 429 (1996), S. 109-118 
    Details
    ISSN: 1432-2307
    Keywords: Lung-transplantation pathology ; Bronchi-epithelium ; Ischaemia ; Mitochondrial swelling ; Scanning electron microscopy ; Transmission electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In ten cases of clinical human single-lung transplantation, the nontransplanted Euro-Collins-preserved contralateral lungs were examined using electron microscopy to determine the effects of ischaemia on the bronchiolar epithelium. Existing structural damage at the time of transplantation was characterized using this approach, and nine nonpreserved canine single lungs were also investigated to identify the impact of ischaemia. The study revealed a significant correlation between the duration of ischaemia and the mitochondrial surface-to-volume ratio, which can serve as a morphometric criterion for mitochondrial damage, in canine lungs. However, this correlation was not found in the human donor lungs. Further examination of human donor lungs showed slight to moderate damage to the endoplasmic reticulum and nuclear chromatin. In addition, various degrees of damage to mitochondrial structure, ranging from inconspicuous to severe, were found. The mitochondrial surface-to-volume ratio can be considered to be a suitable criterion for the quantification of ischaemic damage of the bronchiolar epithelium under experimental conditions. Ultrastructural analysis of human donor lungs revealed intact bronchiolar epithelial cell structures at the time of transplantation, reflecting adequate organ preservation with Euro-Collins solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192433
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum fluctuations in structurally disordered antiferrromagnets (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 359-361 
    Details
    ISSN: 1573-7357
    Keywords: 75.10.Jm ; 75.50.Ee ; 71.55.Jv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present exact diagonalisation data for the ground state of finite two-dimensional spin 1/2 Heisenberg antiferromagnets with structural disorder. The combination of antiferromagnetic coupling and structural disorder creates frustation and a local singlet formation which may strongly influence the magnetic ordering. In detail we study the magnetic radial distribution function, the magnetic order parameter M2 as well as a parameter measuring the spin misfit and present these quantities in dependence on the strength of the structural disorder. We estimate the critical disorder where the antiferromagnetic long-range order breaks down.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752309
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils (1996)
    Springer
    Nutrient cycling in agroecosystems 47 (1996), S. 81-91 
    Details
    ISSN: 1573-0867
    Keywords: China ; Loess Plateau ; maize ; 15N ; Nitrogen ; urea ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Field trials were carried out to study the fate of15N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha−1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha−1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha−1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha−1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01985721
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of the ground-state wave function of theJ 1-J 2 quantum Heisenberg antiferromagnet (1993)
    Springer
    The European physical journal 93 (1993), S. 21-31 
    Details
    ISSN: 1434-6036
    Keywords: 75.10.Jm ; 75.40.Cx ; 75.50.Ee
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigate the ground-state wave function $$|\psi \rangle = \sum\limits_n {\alpha _n } |n\rangle $$ of the spin-1/2J 1-J 2 model on finite square lattices ofN=16(4×4) andN=24(4×6) sites. We find that the Marshall-Peierls phase rule for coefficientsα n , which was derived for unfrustrated bipartite lattices (J 2=0), holds exactly for comparably large frustration up toJ 2/J 1=0.28 (N=16) and up toJ 2/J 1=0.20 (N=24). But even for strong frustration up toJ 2/J 1≈0.45 the Marshall-Peierls rule describes the phase relationships in the ground state excellently. In the region of dominatingJ 2 a phase rule can be formulated as a product of the rules for two independent antiferromagnets. We find that the violation of the Marshall-Peierls sign rule does not dramatically affect the order parameters up toJ 2/J 1≈0.6. To calculate the magnitude of the coefficientsα n by a variational procedure we search for a represantative relationship between theα n and (a few) parametersP 1,n ...P k, n classifying the Ising basis states |n〉. By comparison with the exact ground state we analyze classification schemes based on pair correlations (Jastrow type wave functions) as well as schemes taking into account cluster parameters. While for small frustrationJ 2/J 1〈0.2 a short-range Jastrow description (nearest-neighbour and next nearestneighbour pairing) seems to be sufficient for the adequate description of the ground state one definitly needs longrange pairing and/or cluster parameters to construct a reasonable trial wave function for strong frustration. As an example for a special Jastrow type wave function we discuss an ansatz coming from the spin-wave theory. Finally, we consider the influence of the anisotropic exchangeJ zz ≠J xx ,J yy on the quality of the short-range Jastrow wave function and find and excellent agreement with the exact ground state already for Ising exchange anisotropiesJ xx =J yy ≈0.5J zz .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01308803
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of nitrogen regime in loess soils in the winter half-year: comparison between field measurements and simulations (1985)
    Springer
    Plant and soil 83 (1985), S. 419-432 
    Details
    ISSN: 1573-5036
    Keywords: Loess soil ; Nitrogen ; Simulation model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Periodic N-min measurements were used to validate a simple model describing N regime of cropped Loess soils over the winter half-year. The model comprises of submodels for N mineralization, nitrate transport and N uptake by plants. The description of mineralization is based on kinetic studies in the lab by means of incubation experiments. The transport model is as described earlier4 avoiding an explicite modeling of water movement through soils. Plant uptake for this period was modelled only roughly. The agreement between measurement and simulation is for about 90% of all cases within the confidence interval of the measured values. Possible reasons for the observed deviations are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02184454
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  • 8
    Electronic Resource
    Electronic Resource
    Beobachtungen zur Ausbreitung von Spannungskorrosionsrissen in einer reinen AlZnMg3-LegierungAuszug aus der Diplomarbeit J. Richter, Erlangen 1974 (1977)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 28 (1977), S. 602-606 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Observations concerning stress corrosion crack propagation in a pure AlZnMg3 alloyThe propagation of stress corrosion cracks has been studied (by micro fotography) using potentionstatically polarized specimens notched on one side and held underconstant load in air saturated NaCl solution. According to the results obtained crack propagation is discontinuous; the stop points visible in the crack length-time-curve may be characterized as collisions between crack tips and grain boundary triple points. At - 1100 mV the crack propagation velocity is higher than at -mV provided the particular potential has been given from the very beginning. If, however, the potentials is varies from-1100 to -1300 MV during the measurement the change in crack propagation velocity is negligable (the same applies to potential changes at the time of small crack length). The discontinuity in crack propagation may be explained by assuming hydrogen embrittlement or selective corrosin to occur at the crack tip.
    Notes: Die Ausbreitung von Spannungskorrosionsrissen wurde an potentiostatisch polarisierten, einseitig gekerbten Proben unter konstanter Belastung in luftgesättigter NaCl-Lösung mikrofotografisch verfolgt. Die Risse breiten sich danach diskontinuierlich aus; die in der Rißlänge-Zeit-Kurve erkennbaren. Haltepunkte können als Auftreffen von Rißspitzen auf Korngrenzen-Tripelpunkte identifiziert werden. Bei - 1100 mV breitet sich der Riß schneller aus als bei - 1300 mV, wenn das jeweilige Elektrodenpotential von Anfang an vorgegeben ist. Wird dagegen das Potential von - 1100 auf -1300 mV verändert, so ist die Rißgeschwindipkeit nur geringfügig verändert (gleiches gilt für Potentialveränderungen zum Zeitpunkt kleiner Rißausbreitung). Die diskontinuierliche Rißausbreitung kann da nach mit Hilfe der Annahme erklärt werden, daß an der Rißspitze Wasserstoffversprödung oder selektive Korrosion auftreten.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19770280903
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  • 9
    Electronic Resource
    Electronic Resource
    Interkristalline, Kornflächen- und Spannungsriß-Korrosion von ausgehärteten AlZnMg 1-LegierungenAuszug aus den Diplomarbeiten F. Stoll und W. Hornig, Erlangen 1977. (1978)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 29 (1978), S. 585-593 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Intercrystalline corrosion, grain-phase corrosion and stress-corrosion cracking of aged AlZnMg1 alloysPotentiostatic polarisation curves and stress corrosion crack propagation of a pure and a commercial AlZnMg1-alloy, both peakhardened either by warm or by double ageing, were investigated in airsaturated sodium halide and sulfate solutions at a temperature of 303 K. For this, propagation of crack tips was observed microphotographically under potentiostatic conditions and under constant stress using specimens precracked by fatique corrosion. The pure alloy contents (weight percent): Zn 4,4; Mg 1,26; Fe 0,05; Si 0,006; balance Al, the commercial alloy: Zn 5,05; Mg 1,2; Fe 0,23; Si 0,1; Mn 0,23; Cr 0,2; Cr 0,2; Ti 0,074; Zr 0,12; Cu 0,056; balance Al. In sodium halide solutions either grain boundary and grain attack or only grain attack occurs at a potential region more positive than the respective breakdown potential. At the more negative restpotential no attack can be observed. The influence of concentration of chloride ions on the velocity of discontinuous crack propagation in the pure alloy, which starts without any initiation stage, is different for both heat treatments. No crack propagation is observed in the commercial alloy and in any case in sulfate solutions. The obtained stress corrosion cracking results may be explained by hydrogen embrittlement of the area around the crack tip.
    Notes: An einer warm- und stufenausgelagerten vollausgehärteten, reinen und technischen AlZnMg l-Legierung wurden potentiostatische Stromspannungskurven und die SpK-Rißausbreitung in ruhenden, luftgesättigten Natriumhalogenid- und Natriumsulfatlösungen bei 303 K gemessen. Dabei wurde die Rißfront an einseitig mit einem interkristallinem Schwingungskorrosionsanriß versehenen Zugflachproben unter konstanter Last und potentiostatisch vorgegebenem Ruhepotential mikrofotographisch verfolgt. Die reine Legierung enthielt (in Gew.%) Zn 4,4; Mg 1,26; Fe 0,005; Si 0,006; die technische Legierung Zn 5,05; Mg 1,2; Fe 0,23; Si 0,1; Mn 0,23; Cr 0,2; Ti 0,074; Zr 0,12; Cu 0,056. In Natriumhalogenidlösungen tritt oberhalb dem gegenüber dem außenstromlosen Ruhepotential positiveren Durchbruchpotential Korngrenzen und/oder Kornflächenangriff auf. Bei der reinen Legierung ist der Einfluß der Chlorionenkonzentration auf die Geschwindigkeit der ohne Inkubationszeit einsetzenden, diskontinuierlichen SpK-Rißausbreitung für den warm- und stufenausgelagerten Zustand verschieden. In den entsprechenden technischen Legierungen und in Sulfatlösungen ist keine Rißausbreitung zu beobachten. Die Versuchsergebnisse lassen sich mit einer SpK-Rißausbreitung durch Versprödung der Rißspitze mittels Wasserstoff erklären.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19780290906
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  • 10
    Electronic Resource
    Electronic Resource
    Untersuchungen über die interkristalline Korrosion und Spannungsrißkorrosion einer reinen AlZnMg 2-Legierung in NaCl-Lösung (1984)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 35 (1984), S. 23-27 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Investigations Concerning the Intercrystalline Corrosion and Stress Corrosion Cracking of a Pure AIZnMg 2-Alloy in NaCl-SolutionIn a pure AIZnMg 2-alloy diversified fully step aged or overaged in one step intergranular corrosion (IG) and stress corrosion cracking (SCC) in airsaturated 1 N NaCl-solution or in deaerated 0,1 N NaCl-solution at 303 K were investigated under potentiostatic control. The pure AlZnMg 2-alloy had the following composition (weight percent): Zn: 4.60; Mg: 2.00; Fe: 0.005; Si: 0.006; balance Al.In the two step aged AlZnMg 2-alloys the IG-sensitivity is lowered by an increase of the first step aging time, while SCC-susceptibility and the yield point are raised. As possible mechanism of SCC hydrogen embrittlement is suspectet. At potentials noble to IG-breakdownpotential an interaction of intergranular corrosion and SCC brings about crack velocities, which are to be regarded as a sum of the velocity of intergranular corrosion, which is virtually independent of tensile stress, and the velocity of crack propagation due to SCC.In the overaged AlZnMg 2-alloy IG-attack was observed although in this state of aging no precipitate free zone anodic to the matrix can be assumed. A model to explain this variation of intergranular corrosion, that proofs to be dependent of tensile stress, is represented.
    Notes: Das Verhalten gegenüber interkristalliner Korrosion (IK) und Spannungsrißkorrosion (SpRK) wurde an einer reinen AlZnMg 2-Legierung im vollausgehärteten, unterschiedlich stufenausgelagerten sowie in einem überalterten, warmausgelagerten Zustand unter potentiostatischen Bedingungen in luftgesättigter 1 N NaCl-Lösung bzw in stickstoffgespülter 0,1 N NaCl-Lösung bei 303 K untersucht. Die reine AlZnMg2-Legierung enthielt (Gew-%): Zn: 4,60; Mg: 2,00; Fe: 0,005; Si: 0,006; Rest Al.Bei den stufenausgelagerten Legierungen nehmen mit längerer Zwischenauslagerungsdauer die IK-Empfindlichkeit ab und die SpRK-Empfindlichkeit und die Streckgrenze zu. Als möglicher SpRK-Mechanismus wird die Wasserstoffversprödung vermutet. Bei Versuchen oberhalb des IK-Durchbruchspotentials ergibt ein Zusammenwirken von interkristalliner und Spannungsrißkorrosion Rißgeschwindigkeiten, die als Summe der praktisch zugspannungsunabhängigen Geschwindigkeit der interkristallinen Korrosion und der Geschwindigkeit der Rißausbreitung durch SpRK anzusehen sind.In der überalterten Legierung wurde interkristalline Korrosion gefunden, obwohl in diesem Auslagerungszustand kein gegenüber der Matrix anodischer ausscheidungsfreier Saum (AFS) anzunehmen ist. Es wird ein Modell zur Erklärung dieser sich als zugspannungsabhängig erweisenden Spielart der interkristallinen Korrosion vorgestellt.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19840350105
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