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  • 1995-1999  (5)
  • Chromium  (2)
  • RNA secondary structures  (2)
  • Brain infarcts  (1)
  • 1
    ISSN: 1432-1920
    Keywords: Key words Magnetic resonance imaging ; Perfusion studies ; Dynamic contrast-enhanced imaging ; Cerebral blood volume ; Brain infarcts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract MRI perfusion studies have focussed mainly on acute ischaemia and characterisation in ischaemia. Our purpose was to analyse regional brain haemodynamic information in acute, subacute, and chronic ischaemia. We performed 16 examinations of 11 patients on a 1.5 T MR images. Conventional and dynamic contrast-enhanced imaging were employed in all examinations. For the dynamic susceptibility sequences, a bolus (0.2 mmol/kg) of gadopentetate dimeglumine was injected. Reconstructed regional relative cerebral blood volume (rCBV) maps, bolus maps, and conventional images were analysed by consensus reading. In all examinations decreases in rCBV were observed in the lesions. The distribution of regional rCBV in lesions was heterogeneous. The rCBV of the periphery of the lesions was higher than that at their center. There was a correlation between the time since onset and abnormalities on the rCBV map and T2-weighted images (T2WI). In the early stage of acute stroke, the abnormalities tended to be larger on the rCBV than on T2WI. Many patterns of bolus passage were observed in ischaemic regions. rCBV maps provide additional haemodynamic information in patients with brain infarcts.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-4475
    Keywords: Neutral networks ; Percolation of sequence space ; RNA folding ; RNA secondary structures ; Shape space covering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Beziehungen zwischen RNA-Sequenzen und ihren Sekundärstrukturen werden durch vollständiges Falten allerGC- undAU-Sequenzen mit Kettenlängen bis zun=30 untersucht. Die aus der Informatik bekannte Technik derTries wird zur ökonomischen Datenspeicherung und für rasches Retrieval der gespeicherten Information angewendet. Die berechneten Strukturdaten werden durch vollständiges Abzählen ausgewertet. Sie dienen unter anderem als eine exakte Referenz zum Testen analytischer Resultate aus mathematischen Modellen sowie zur Überprüfung der Ergebnisse statistischer Probennahmen. Verschiedene neuartige Konzepte zur Behandlung der Zusammenhänge zwischen RNA-Sequenzen und Sekundärstrukturen wurden anhand der gewonnenen Daten eingehend untersucht. Unter ihnen befinden sich die Struktur derneutralen Netzwerke (die Gesamtheit der RNA-Sequenzen, die eine bestimmte Struktur ausbilden), diePerkolation des Sequenzraumes durch neutrale Netzwerke sowie das Prinzip derErfassung des Strukturraumes durch einen kleinen Ausschnitt des Sequenzraumes. Die durch vollständiges Abzählen erhaltenen Daten werden mit den analytischen Ergebnissen eines auf der Theorie der Zufallsgraphen aufbauenden Modells verglichen. Dieses Modell gibt die generischen Eigenschaften von Sequenz-Struktur-Relationen wieder, welche lediglich aus der Existenz einer Paarungslogik resultieren. Differenzen zwischen den numerischen und den analytischen Resultaten können als Konsequenzen der spezifischen biophysikalischen Eigenschaften von RNA-Molekülen interpretiert werden.
    Notes: Summary The relations between RNA sequences and secondary structures are investigated by exhaustive folding of allGC andAU sequences with chain lengths up to 30. The technique oftries is used for economic data storage and fast retrieval of information. The computed structural data are evaluated through exhaustive enumeration and used as an exact reference for testing analytical results derived from mathematical models and sampling based on statistical methods. Several new concepts of RNA sequence to secondary structure mappings are investigated, among them the structure ofneutral networks (being sets of RNA sequences folding into the same structure),percolation of sequence space by neutral networks, and the principle ofshape space covering. The data of exhaustive enumeration are compared to the analytical results of arandom graph model that reveals the generic properties of sequence to structure mappings based on some base pairing logic. The differences between the numerical and the analytical results are interpreted in terms of specific biophysical properties of RNA molecules.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 91 (1995), S. 157-167 
    ISSN: 1432-2234
    Keywords: Density functional theory ; Metal-ligand bond energies ; Chromium ; Arene complexes ; Chalcocarbonyls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Quantum chemical calculations based on density functional theory have been performed on Cr(CO)6, (η6-C6H6)Cr(CO)3 and (η6-C6H6)Cr(CO)2(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal-ligand binding energies. In particular, a comparison of metal-arene bond energies calculated for the (η6-C6H6)Cr(CO)3 and (η6-C6H6)Cr(CO)2(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger π-backbonding charge transfer to the CS ligand as compared with CO.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-4475
    Keywords: Neutral networks ; Random graphs ; RNA secondary structures ; Zipf's law
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die globalen Benziehungen zwischen RNA-Sequenzen und Sekundärstrukturen werden als Abbildungen aus einem Raum aller Sequenzen in einen Raum aller Strukturen aufgefaßt. Diese Abbildungen werden durch Falten aller binären Sequenzen desGC-undAU-Alphabets mit Kettenlängen bis zun=30 untersucht. Die berechneten Strukturdaten werden durch vollständiges Abzählen ausgewertet und als eine exakte Referenz zum Überprüfen analytischer Resultate aus mathematischen Modellen sowie zum Testen statistisch erhobener Proben verwendet. Einige neuartige Konzepte zur Beschreibung der Beziehungen zwischen Sequenzen und Strukturen werden eingehend untersucht, unter ihnen der Begriff derneutralen Netzwerke. Ein neutrales Netzwerk besteht aus allen Sequenzen, die eine bestimmte Struktur ausbilden. Vollständiges Abzählen ermöglicht beispielsweise die Bestimmung aller Strukturen minimaler freier Energie in Abhängigkeit von der Kettenlänge ebenso wie die Bestimmung der Häufigkeitsverteilungen der Strukturen bei konstanten Kettenlängen. Die letzteren folgen einer verallgemeinerten FormZipfschen Gesetzes.
    Notes: Summary Global relations between RNA sequences and secondary structures are understood as mappings from sequence space into shape space. These mappings are investigated by exhaustive folding of allGC andAU sequences with chain lengths up to 30. The computed structural data are evaluated through exhaustive enumeration and used as an exact reference for testing analytical results derived from mathematical models and sampling based on statistical methods. Several new concepts of RNA sequence to secondary structure mappings are investigated, among them that ofneutral networks (being sets of sequences folding into the same structure). Exhaustive enumeration allows to test several previously suggested relations: the number of (minimum free energy) secondary structures as a function of the chain length as well as the frequency distribution of structures at constant chain length (commonly resulting in generalized forms ofZipf's law).
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Theoretica chimica acta 91 (1995), S. 157-167 
    ISSN: 0040-5744
    Keywords: Key words: Density functional theory ; Metal-ligand bond energies ; Chromium ; Arene complexes ; Chalcocarbonyls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  Quantum chemical calculations based on density functional theory have been performed on Cr(CO)6, (η6-C6H6)Cr(CO)3 and (η6-C6H6)Cr(CO)2(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal–ligand binding energies. In particular, a comparison of metal–arene bond energies calculated for the (η6-C6H6)Cr(CO)3 and (η6-C6H6)Cr(CO)2(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger π-backbonding charge transfer to the CS ligand as compared with CO.
    Type of Medium: Electronic Resource
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