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  • 1
    Publikationsdatum: 1989-08-01
    Print ISSN: 0556-2791
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Publiziert von American Physical Society
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 1522-9602
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Mathematik
    Notizen: Abstract Based on experimental work on the ontogeny of the electroretinogram circadian rhythm in crayfish, we present a mathematical model simulating changes in both frequency and amplitude of the electroretinogram oscillation during several developmental stages until shortly before the adult age. Simultaneously, we propose a hypothetical oscillation in the hormonal release whose frequency is imposed on the electroretinogram oscillation. The model consists of two coupled nonlinear oscillators in which a dynamical response is obtained mainly through an Andronov-Hopf bifurcation. Through the construction of the model, a biological hypothesis about the essential elements underlying the ERG circadian rhythm and their interrelations is formulated and discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of mathematical biology 55 (1993), S. 561-583 
    ISSN: 1522-9602
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Mathematik
    Notizen: Abstract A general model of zymogen activation is proposed and explicit kinetic equations for the time courses of the various species and products involved are given. These equations are valid for the whole course of the reaction and therefore for both the transient phase and the steady state. This model is sufficiently general to include mechanisms possessing one or more steps of zymogen activation besides possible steps of inhibition (reversible or irreversible) or inactivation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 1572-8854
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract The theophyllinium tetrabromopalladate(II), [Thph]2PdBr4, has been synthesized and its molecular structure has been determined by single crystal X-ray diffraction. The salt crystallizes in the monoclinic space group C2 with two formula units in a cell of dimensionsa=11.074(1),b=8.545(2),c=11.804(2) Å;β=95.22(1)°,V=1112.3(4) Å3,D c=2.353 mg m−3,D exp=2.352 mg m−3,M w=788.4, μ(MoKα)=84.5 cm−1,F(000)=752. The structure has been refined by full-matrix least-squares techniques to a final value of theR factor of 0.058 based on 907 independent intensities. The compound consists of theophyllinium cations protonated at N(9). The [PdBr4]2− anion is planar, with distances Pd-Br(1)=2.441(12) and Pd-Br(2)=2.412(6) Å, and Br(1)-Pd-Br(2) and Br(1)-Pd-Br(3) angles of 90.34(14)° and 89.66(14)°, respectively. The1H-NMR spectrum of [Thph]2PdBr4 in DMSO-d6 (300 MHz) is consistent with the observed solid-state structure, and its thermal behavior shows two steps: (i) a dehalogenation process about 327°C and (ii) a rapid pyrolitic decomposition in the 340–575°C temperature range giving PdO as final product.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 309-311 
    ISSN: 1432-0649
    Schlagwort(e): 42.60.By ; 32.30.Rj
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We report lasing for the first time in nickel on the neon-like J=0→1, 3p→3s transition at 231 Å as well as several weaker transitions including the J=2»1 lines at 298 Å and 304 Å. Amplification is seen only when the prepulse technique of using a low intensity prepulse before the main optical drive pulse is used to illuminate the nickel target. The prepulse technique is also shown to produce lasing in copper and dramatically improve the output of the germanium laser.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Earth, moon and planets 46 (1989), S. 207-219 
    ISSN: 1573-0794
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Beschreibung / Inhaltsverzeichnis: Resumen Se presentan los resultados obtenidos de las observaciones espectroscópicas de las principales zonas y cinturones de Júpiter realizadas durante la oposición de 1987 como una contribución al International Jupiter Watch Program. Las observaciones fueron llevadas a cabo haciendo uso del foco coudé del telescopio de 1.52 m del observatorio hispanoalemán de Calar Alto (España), habiéndose obtenido algo más de cien espectros, de resolución media, en la región espectral de 6000–6600 ». Se exponen los resultados de las anchuras equivalentes de las bandas de absorción del metano en 6190 » y del amoniaco en 6450 », estudiándose, al mismo tiempo, la distribución tanto longitudinal como latitudinal de las mismas. Mientras que los resultados para la banda del metano presentan un comportamiento simétrico en todas las regiones analizadas, las anchuras equivalentes para la banda NH3-6450 » presentan un comportamiento asimétrico en algunas regiones del planeta, con una mayor absorción hacia el limbo del oeste que hacia el del este. Los resultados son interpretados en base a un modelo de ‘scattering’ no homogéneo, variando, simultáneamente, el espesor óptico y la altitud de la nube de amoniaco. Los espectros tomados en la dirección norte-sur, aunque presentan una dependencia latitudinal pequeña en la absorción de las bandas mencionadas, sugieren una relación entre la absorción y las variaciones de reflectividad en el continuo.
    Notizen: Abstract Spectroscopic observations in the spectral region λλ 6000–6600 » of major belts and zones of Jupiter have been carried out at Calar Alto Observatory (Spain) during the 1987 opposition, in support to the International Jupiter Watch Program. More than a hundred long-slit, medium resolution spectra have been taken at the coudé focus of the 1.52 m telescope. The longitudinal and latitudinal distribution of the equivalent widths of the methane and ammonia absorption bands at 6190 » and 6450 » have been investigated. Unlike the CH4-6190 » band, the longitudinal distribution in the NH3-6450 » band shows asymmetries in some of the Jovian regions analyzed, being the absorption greater at West than at East limbs. These results are interpreted in terms of inhomogeneous scattering models by the simultaneous variation of the NH3 cloud optical thickness and its altitude level. The north-south scans show little latitudinal dependence on absorption in both methane and ammonia bands, although some relationship could be established between the absorption and relative continuum reflectivity variation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Solar physics 144 (1993), S. 399-402 
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The distribution of significant solar activity for the northern and southern solar hemispheres from 1964 through 1979 is studied. Two 90-degree wide active longitudes, separated 180 degrees and rotating with a velocity 1% faster than the solar surface, are proposed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 651-658 
    ISSN: 1432-0827
    Schlagwort(e): Salivary proteins ; Hydroxyapatite ; Adsorption ; Precipitation-inhibitor ; Phosphoserine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Inhibition of seeded apatitic crystal growth by human salivary acidic proline-rich phosphoproteins (PRP) has been related to their adsorption onto the apatite seeds. The amino-terminal 30-residue segment of the PRP makes an important contribution to this adsorption. This peptide (PRP1(T1)) and its dephosphorylated analogue from PRP3 (PRP3(T1)DP) were prepared. They have identical sequences, except the phosphates at residues 8 and 22 in PRP1(T1) are absent from PRP3(T1)DP. Adsorption of these peptides onto hydroxyapatite and their effect on crystal growth from a defined supersaturated solution was studied. Adsorption behavior was adequately described by the Langmuir adsorption isotherm. The adsorption affinity constant of PRP1(T1) (K=20,200 ml/µmol) was more than 10 times the corresponding value for PRP3(T1)DP (1,800 ml/µmol), and similar to that of the parent protein, PRP1 (26,200 ml/µmol). Inhibition of crystal growth by the peptides was interpreted in terms of the fractional coverage of the maximum number of adsorption sites (as derived from the adsorption isotherms), suggesting that the molecules block, by adsorption, specific growth sites on these surfaces. Comparison of precipitation kinetics showed that PRP1(T1) is a more effective inhibitor than PRP3(T1)DP at the same initial concentration (10−6−10−7 M). However, on the basis of per mol adsorbed, PRP3(T1)DP displays a greater inhibitory activity; such a behavior is consistent with a more open molecular structure which blocks more growth sites per mol adsorbed than PRP1(T1). Because of its high affinity constant, preadsorbed PRP1(T1) remains in the condensed state in the supersaturated solution used, whereas the preadsorbed PRP3(T1)DP molecules desorb to some extent, resulting in a decrease in inhibitory activity. The results show that the amino-terminal segment of the PRP and the two phosphoserine residues present in this segment are particularly important in the function proposed for these proteins in the oral environment.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 48-59 
    ISSN: 1432-0827
    Schlagwort(e): Salivary proteins ; Adsorption ; Thermodynamics ; Kinetics ; Hydroxyapatite
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Equilibrium and kinetic experiments were conducted to investigate the factors determining the adsorption of salivary macromolecules onto hydroxyapatite. Using amino acids and other small adsorbates, it was determined that the carboxyl attached to the α carbon does not appear to adsorb onto HA and the affinities of side-chain carboxyls are much smaller than that of the phosphate group (phosphoserine). Hydroxyl (serine) displays an extremely high affinity, but its adsorption site on HA is different and the number of such sites is much smaller than found for the rest of the functional groups investigated. It is shown that the information obtained from small molecules cannot be readily applied to prediction of the adsorption behavior of salivary macromolecules and polypeptides. The kinetics of adsorption of the salivary phosphopeptide statherin, a polyaspartate, and the salivary prolinerich phosphoprotein PRP3 are consistent with the reversibility of the adsorption process; no conclusion was possible in the case of the protein PRP1. Apparent irreversibility cannot be explained on the basis of multipoint binding or the properties of the carboxyl versus phosphate group; it appears that secondary structure determines to a significant extent the adsorption properties of the macromolecules. Calculation of the thermodynamic molar quantities of adsorption of PRP1, PRP3, andl-ASP onto HA showed that the process is entropically driven. The functional relationship between partial molar entropy and adsorption coverage is similar for the two proteins, but quite different from that for aspartate. Explanations for these results are advanced on the bases of changes in structure configurations and displacement of water from the adsorbate and the adsorbent surface, the second factor being the dominant one in the adsorption of a small molecule such asl-ASP.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Biological cybernetics 37 (1980), S. 25-31 
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract The model is based on the concept that non-linear lateral interaction at the inner plexiform layer accounts for most of the specialization and marked non-linearities in cat's retinal ganglion cell responses. The inputs to the lateral interaction processes are a spatio-temporal signal and its retarded, as suggested by the behaviour of simple ganglion cells. Lateral interaction in the model consists of lateral linear inhibition followed by local half wave rectification. The resulting signals are weighted and summated by the ganglion cell thereafter. A transparent and general expression is obtained for the response of the cell model which, albeit its simplicity, leads to most of known types of non-linear responses, including the rarely encountered specialized cells in cat's, retina, except colour coding units. For negligible lateral interaction, the model reduces to spatio-temporal linear models under the two paths hypothesis. A discussion of the possible role of anatomical units in these retinal processes in presented, where a general interpretation for visual processing in cat's retina evolves from.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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