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  • 1
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The coherent two-dimensional motion of a hole generated in a high-T c superconductor at half-filling is discussed. The system is described by thet-J model which reduces to the Heisenberg antiferromagnet (HAF) at half-filling. Special attention is payed to the influence of spin fluctuations in the ground state on the hole motion. Spin fluctuations can be considered as deviations of the true ground state of the Heisenberg antiferromagnet from the Néel state. The calculations are based on the introduction of a new trial wave function. It generalizes a wave function which was originally proposed by Shraiman and Siggia for the hole motion in the Néel state. As a result, we find that the excitation energy for the hole has a bandwidth which is reduced by a factor 0.7 as compared to the case without spin fluctuations. Moreover, the dispersion relation contains cubic harmonics which are due to effective hopping processes to more distant than second-or third-nearest neighbors. For larger values of the ratiot/J the band is substantially deformed. We compare our theory with results obtained from the exact diagonalization of finite clusters and find good agreement.
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  • 2
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A theory of ultrasonic attenuation in metallic systems containing crystalline-field split Rare Earth ions is presented. It is shown that two types of absorption mechanisms can occur. The first one is of the well known Pippard type and describes the energy dissipation of the ultrasonic waves directly into the conduction electron system. However in addition to that mechanism there is another one which is of importance and which describes the energy dissipation into the Rare-Earth ion system. In order to distinguish between both mechanisms the change of the attenuation in an applied magnetic field is investigated. For the purpose of demonstration the theory is applied to aΓ 7–Γ 8 crystal field level scheme as it applies for Ce3+ or Sm3+ in cubic symmetry. An estimation of the relative strength of both absorption mechanisms is given.
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  • 3
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A recently developed method based on projection techniques is applied to the computation of electron correlations in excited states of semiconductors. In particular it is shown that the method is able to reproduce the results previously obtained by applying the variational Local Ansatz. The advantages of the present approach are its conceptual simplicity and that it can be applied not only to weakly but also to strongly correlated electronic systems.
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  • 4
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A theory is developed for the line width of crystal-field excitations in metallic rare-earth systems were the damping is due to conduction electron-hole excitations. First the single ion or dilute alloy case is studied. As an example the theory is applied to Ce in LaAl2 and compared with recent experiments. Then the case of a regular lattice of rare-earth ions is considered. The theory is applied to theΓ 1 –Γ 4 system. Special attention is paid to the behaviour of the central peak near an induced-moment phase transition. It is shown that the dynamics of the conduction electrons leads to observable effects in the centralpeak intensity and can not be neglected as it is usually done. The theoretical predictions are in agreement with recent experimental findings on Pr3Tl.
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  • 5
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A derivation within the projection operator technique is given for the density and current response functions of a system of independent particles moving in a random potential. The essential point is the derivation of kinetic equations for the current relaxation kernel instead of for the density propagator as in a previous treatment on the basis of the projection operator formalism. In these equations the divergent contributions from the 2k F -scattering mechanism can be systematically separated from those of diffusional scattering. Especially, both the self-consistent current relaxation theory, developed by Götze and the self-consistent treatment of Vollhardt and Wölfle are rederived from simple approximations of the kinetic equations. The outlined method represents a systematic approach to the Anderson localization. It may be applicable also to more realistic models for the Anderson localization as well as extended to the evaluation of general transport coefficients on a level far beyond the usual perturbation theories.
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  • 6
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A recently developed new form of projection technique is applied to the computation of the ground-state energyE 0 of the antiferromagnetic Heisenberg Hamiltonian on a square lattice, demonstrating its usufulness. The calculations are done analytically and do neither require the use of time-dependent operators nor Wick's theorem. A value ofE 0=−2NJ0.3337 is found whereN is the number of sites in good agreement with series expansions.
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  • 7
    ISSN: 1591-9528
    Keywords: Experimental cirrhosis of the liver ; Connective tissue ; Radioactive sulfate ; Cortisone ; Experimentelle Lebercirrhose ; Bindegewebe ; Radioaktives Sulfat-Cortison
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung 1. Bei der experimentellen Thioacetamidcirrhose der Ratte werden nach Gabe von radioaktivem Sulfat die sauren Mucopolysaccharide der Leber chromatographisch nach drei verschiedenen Verfahren aufgetrennt. Die Elutionsmuster ergeben sowohl bei gesunder als auch cirrhotischer Leber ähnliche Bilder, ein Einfluß einer Cortisongabe gleichzeitig mit der Sulfatgabe auf das Elutionsmuster ist nicht erkennbar. 2. An der Tetrachlorkohlenstoff- und der Thioacetamid-Cirrhose der Ratte werden die Wirkungen einer Langzeitbehandlung mit Cortison in einer Dosierung von 0,12 mg Prednisolonacetat, zweimal wöchentlich subcutan verabfolgt, morphologisch untersucht. Eine Cortisonbehandlung kann die Entstehung dieser experimentellen Lebercirrhosen nicht verhindern. Die Schädigungszeichen an den Leberparenchymzellen (kleintropflge Verfettung und Vacuolisierung, Kernalteration) nehmen sogar deutlich zu. Die Mortalität der behandelten Tiere ist gegenüber der der unbehandelten deutlich erhöht.
    Notes: Summary 1. In the experimental thioacetamide-cirrhosis after injection of radioactive sulfate the acid mucopolysaccharides of the liver are fractionated by three different methods. — There ist no significant influence of cortisone on the chromatographic elution pattern of the sulfated mucopolysaccharides in the normal as well as in the cirrhotic liver. 2. The influence of a long term treatment with cortisone is studied on the carbon tetrachloride cirrhosis and the thioacetamide cirrhosis. Cortisone cannot inhibit the development of a cirrhosis. The parenchymal cells show a higher degree of damage with an additional cortisone treatment. The mortality of the treated animals is higher.
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  • 8
    ISSN: 1591-9528
    Keywords: Cirrhosis ; Connective tissue ; Acid mucopolysaccharides ; Hexosamines ; Hydroxyproline ; Lebercirrhose ; Saure Mucopolysaccharide ; Hexosamine ; Hydroxyprolin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung 1. Die Konzentrationen von Glucosamin, Galaktosamin, Uronsäure, Hydroxyprolin wurden in 10 gesunden und 14 cirrhotischen menschlichen Lebern untersucht. Es handelt sich hierbei um Bausteine des Bindegewebes. Die sauren Mucopolysaccharide aus der Bindegewebsgrundsubstanz wurden abgetrennt und auf Cetylpyridiniumchlorid-Cellulose und Dowex 1×2 säulenchromatographisch getrennt. 2. Die Konzentration aller Bindegewebsbausteine nimmt erwartungsgemäß mit Entwicklung einer Cirrhose zu. Es kommt jedoch zu statistisch signifikanten Verschiebungen in den Konzentrationsverhältnissen. 3. Aus den Verschiebungen der Konzentrationsverhältnisse wird geschlossen, daß mit Entwicklung der Cirrhose: a) relativ mehr saure als neutrale Mucopolysaccharide in der Bindegewebsgrundsubstanz gebildet werden; b) daß vornehmlich galaktosaminhaltige saure Mucopolysaccharide gebildet werden; c) daß es sich bei den neugebildeten sauren Mucopolysacchariden wahrscheinlich um Dermatansulfat handelt. 4. Die Zusammensetzung des Bindegewebes bei der Cirrhose weist also gegenüber dem Bindegewebe einer gesunden Leber chemisch deutliche Unterschiede auf. Die Veränderungen in der Grundsubstanz haben u. U. Rückwirkungen auf die Ernährung der einzelnen Leberparenchymzellen im Sinne einer Verschlechterung der Ernährungsbedingungen.
    Notes: Summary 1. The concentrations of glucosamine, galactosamine, uronic acid, hydroxyproline were estimated in 10 normal and 14 cirrhotic human livers. These substances are constituents of the connective tissue. The acid mucopolysaccharides of the connective tissue ground substance were separated and fractionated on cetylpyridiniumchloride-cellulose and Dowex 1×2 by column chromatography. 2. With the development of a cirrhosis there rises the concentration of all connective tissue constituents. Besides this the relations of the concentrations are changed. 3. From the results is concluded that with the development of a cirrhosis: a) more acid than neutral mucopolysaccharides are synthetisized, b) among the acid mucopolysaccharides especially galactosamine-containing mucopolysaccharides are formed, c) that probably dermatane sulfate is the acid mucopolysaccharide which is mostly built in the connective tissue of a cirrhotic liver. 4. There are distinct differences in the composition of the connective tissue of a normal and cirrhotic human liver. The alterations of the ground substance may influence the nutrition of the parenchymal cells.
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  • 9
    ISSN: 1617-4623
    Keywords: Transgenic mice ; Plasmid rescue ; HSV thymidine kinase gene ; Extrachromosomal DNA ; Transmission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This communication demonstrates the usefulness of the plamid rescue procedure for recovery of plasmids from transgenic mice. We have microinjected the plasmid pSK1 harbouring the Herpes simplex virus thymidine kinase gene into fertilized mouse oocytes and succeeded in recovering plasmids from newborns by transformation of E. coli either with HindIII cut cellular DNA or with uncut DNA. The majority of the rescued plasmids were indistinguishable from pSK1 by restriction analysis. The rescued plasmids proved to be functionally active in a transient expression assay in mouse Ltk- cells. The pSK1 DNA sequences were inherited by up to 90% of the second generation progeny mice, which is not in agreement with a Mendelian transmission of heterozygous markers integrated into a single site of the chromosome. These data support the assumption that germ line transmission of non-integrated episomal plasmids can occur.
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  • 10
    ISSN: 1591-9528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung 1. Mit35S-Sulfat und14C-Prolin wurden an 102 normalen und an 124 Ratten mit einer durch chronische Thioacetamidvergiftung erzeugten experimentellen Lebercirrhose die Synthese und der Umsatz von Bindegewebsgrundsubstanz und Kollagen in der Leber ermittelt. 2. Bei experimenteller Lebercirrhose ist die Synthese von Chondroitinsulfat und dessen spezifische Aktivität deutlich erhöht. Die Synthese von Kollagen ist ebenfalls gesteigert, seine spezifische Aktivität, bezogen auf den Hydroxyprolingehalt jedoch erniedrigt. Dies ergibt sich möglicherweise aus einer unterschiedlichen Beeinflussung der drei Kollagenfraktionen (neutralsalzlösliche, säurelösliche und unlösliche). 3. Eine kurzfristige Prednisolonbehandlung hat keinen Einfluß auf den Hexosamin-, Galaktosamin- und Hydroxyprolingehalt der Leber. Sie hemmt jedoch die pathologisch gesteigerte Chondroitinsulfat- und die Kollagensynthese, hemmt aber gleichzeitig den Abbau von Chondroitinsulfat. Die Bildungsgeschwindigkeit von Bindegewebe in der Leber wird zwar durch Cortison gehemmt, eine Cortisonbehandlung kann jedoch nicht die Entwicklung einer Cirrhose bei chronischer Intoxikation verhindern. Dies erklärt sich dadurch, daß nicht nur die Synthese, sondern gleichzeitig auch der Abbau von Bindegewebsgrundsubstanz gehemmt wird. 4. Bei chronischer Intoxikation mit Thioacetamid, die zu einer deutlichen Bindegewebsproliferation in der Leber führt, ist eine Aktivierung des Grundsubstanzwechsels in Knorpel und Schwanzsehne im Sinne einer unspezifischen Mesenchymreaktion nicht sicher erkennbar. Die Kollagensynthese in den genannten Organen wird, möglicherweise als Ausdruck einer allgemeinen Vergiftung, sogar gehemmt.
    Notes: Summary 1. With35S-sulfate and14C-proline the synthesis and turn over of the connective tissue ground substance and collagen of the liver was measured in 102 normal and 124 rats with an experimental cirrhosis of the liver. 2. In experimental cirrhosis of the liver the synthesis of chondroitin sulfuric acid and its specific activity are elevated. The synthesis of collagen is augmentated too, but nevertheless its specific activity (as to the hydroxyproline content) is lowered. This may be due to different rates of the synthesis and turnover of the three collagen fractions (salt soluble, acid soluble and insoluble). 3. A prednisolone treatment of two weeks has no measurable influence on the hexosamine, galaetosamine and hydroxyproline level of the liver. The pathologically accelerated synthesis of chondroitin sulfuric acid and collagen are diminished, but also the turnover rate of chondroitin sulfate. The development of a cirrhosis cannot be inhibited by a prednisolone treatment. 4. In chronic intoxication with thioacetamide, which induces a marked proliferation of the connective tissue in the liver there is no unspecific activation of the metabolism of the connective tissue ground substance in cartilageous and tendineous tissue detectable. The synthesis of collagen in these tissues is inhibited. This may be due to the general intoxication.
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