Showing papers by "Humboldt University of Berlin published in 1983"

Quasi-steady-state approximation in the mathematical modeling of biochemical reaction networks

Abstract: In the mathematical modeling of biochemical reaction networks the application of the quasi-steady-state approximation permits a reduction of the number of dynamic variables as well as of the number of parameters. It is shown that the quasi-steady-state approximation represents the zeroth approximate solution of the perturbation problem dX dt = RV(X)+ 1 μ S W (X) with μ ⪡ 1. The perturbation equation develops by subdivision of the flux rates of the model into the rates w i (X) = (1/μ) w i (X) of fast reactions and the rates vj(X) of slow reactions. The matrix C=(R⋮S) denotes the stochiometric matrix of the reaction network. The analysis of this perturbation problem provides conditions for the applicability of the quasi-steady-state approximation in a given network. The paper presents a practical guide for the construction of the approximate solution.

Composition and ecology of deep-water coral associations

Abstract: Between 1966 and 1978 SCUBA investigations were carried out in French Polynesia, the Red Sea, and the Caribbean, at depths down to 70 m. Although there are fewer coral species in the Caribbean, the abundance of Scleractinia in deep-water associations below 20 m almost equals that in the Indian and Pacific Oceans. The assemblages of corals living there are described and defined as deep-water coral associations. They are characterized by large, flattened growth forms. Only 6 to 7 % of the species occur exclusively below 20 m. More than 90 % of the corals recorded in deep waters also live in shallow regions. Depth-related illumination is not responsible for depth differentiations of coral associations, but very likely, a complex of mechanical factors, such as hydrodynamic conditions, substrate conditions, sedimentation etc. However, light intensity determines the general distribution of hermatypic Scleractinia in their bathymetric range as well as the platelike shape of coral colonies characteristic for deep water associations. Depending on mechanical factors,Leptoseris, Montipora, Porites andPachyseris dominate as characteristic genera in the Central Pacific Ocean,Podabacia, Leptoseris, Pachyseris andCoscinarea in the Red Sea,Agaricia andLeptoseris in the tropical western Atlantic Ocean.

Deficiency, transposition, and duplication of one 15q region may be alternatively associated with Prader-Willi (or a similar) syndrome. Analysis of seven cases after varying ascertainment

Abstract: Seven patients are described who have some or all of the symptoms of Prader-Willi syndrome. They were ascertained by varying criteria starting either from the clinical picture or from the identification of a chromosome abnormality involving the proximal portion of the long arm of chromosome 15. The chromosome abnormalities consisted of two balanced translocations (15;18 and 8;15), three unbalanced ones (15;18, 15;19, and 9;15), and one interstitial deletion of bands 15q11 and q12. The seventh case had an unidentified extra chromosome. These data and a review of the literature led to the conclusion that deficiency, transposition, and even duplication of the region(s) 15q11-q13 may all result in a syndrome which is identifiable with or similar to the Prader-Willi syndrome.

Growth Kinetics of Microcystis aeruginosa (KÜTZ) KÜTZ as a Basis for Modelling its Population Dynamics

Abstract: The dependence of the specific growth rate of Microcystis aeruginosa (KUTZ); KUTZ f. aeruginosa upon temperature and light intensity was determined under continuous illumination in batch cultures. The result can be well described by the function: where μmax = 3.44.d−1, Topt = 33.2°C, Tmin = 18.3°C and KI = 71.4 Wm−2. The validity of this function is limited to the range of 10–28 °C and light intensities from 5–25 Wm−2. The dependence of the specific growth rate on the nutrient concentration was investigated a t 25°C and 24 Wm−2 light intensity by means of chemostat cultures. The half saturation constants related to the maximum specific growth rate of 1.1 d−1 measured under these conditions were 0.44 μmol.I−1, 4.3 μmol.I−1 and 26.5 μmol.−1 for orthophosphate, nitrate, and ammonium, respectively.

Effect of Fluctuation on Plane Front Propagation in Bistable Nonequilibrium Systems

Abstract: A theory of front propagation in bistable stochastic media is developed. The effect of fluctuations is twofold: 1) they lead to random variations of the front shape. 2) they result in random motion of the front positions. Its general expression for the dispersion of the position for arbitrary stochastic noises wit,h spatial correlation length I, and correlation time t, is given. For rate functions with cubic non1,inearities the dispersion formula is further analysed. Fluktuationseffekte bei der Ausbreitung einer ebenen Front in bistsbilen Nichtgleichgewichtssystemen Inhaltsubersicht . Eine Theorie der Frontausbreitung in bistabilen stochastischen Medien wird entwickelt. Der EinfluB der Fluktuationen fiihrt zu einer zufiilligen Veriinderung der Form der Front, wie auch zu einer Zufallsbewegung der Frontposition. Ein allgemeiner Ausdruck fur die Dis- persion der Frontposition fur beliebige stochastische Quellen mit einer riiumlichen Korrelationsliinge I, und einer Korrelationszeit tc wird gegeben. Fur Ratenfunktionen mit kubischer Nichtlinearitat wird die Dispersionsformel weiter analysiert.

Isoelectrofocusing in the study of the Bf system: existence of two common subtypes of the BfF allele.

Abstract: The inherited polymorphism of the properdin factor B (Bf system) was studied by isoelectrofocusing in polyacrylamide gel (PAGIF, pH range 5.0-8.0), followed by immunofixation. Using the described technique, two different subtypes of F bands are visible (designated as F' and F"). Studies of 13 families and 48 mother-child pairs are not in contradiction to the assumption of a codominant inheritance by two alleles (BfF' and BfF") at a single locus.

Inverse dielectric function for a semi‐infinite solid

Abstract: An old problem is addressed being the description of the dielectric response of electrons near the surface of an infinite half space to perturbing potentials and external charges. Taking into account spatial dispersion, expressions are derived for the screened potential and the inverse dielectric function within the approximation of specular electron reflection. The expressions generalize former results in a way that spatial symmetries of the problem are properly reflected. The boundary conditions are shown to follow from the definition of the screened potential. The inverse dielectric function obtained in the treatment fulfils the orthogonality relation to the dielectric function and the f-sum rule. Der dielektrische Response von Elektronen an der Oberflache eines unendlichen Halbraumes auf ausere Felder und Ladungen wird unter Berucksichtigung raumlicher Dispersion beschrieben. In der Naherung der spiegelartigen Elektronenreflexion werden Ausdrucke fur das abgeschirmte Potential und die inverse dielektrische Funktion abgeleitet, die bereits bekannte Resultate in der Hinsicht verallgemeinern, das sie die raumlichen Symmetrien des Problems richtig widerspiegeln. Es wird gezeigt, das die verwendeten Grenzbedingungen aus der Definition des abgeschirmten Potentials folgen. Die berechnete inverse dielektrische Funktion erfullt die Orthogonalitatsrelation und den f-Summensatz.

A globally convergent algorithm based on imbedding and parametric optimization

Abstract: The continuation method, well-established for the solution of nonlinear equations is extended to restricted optimization problems. Only the locally active restrictions are considered along the homotopy path. It is assumed that there are only finitely many critical points, i. e. that there are only finitely many changes of the index set of active restrictions. The globally convergent algorithm which we present proceeds in three stages: For the class of convex problems, the hypotheses for the convergence of the algorithm may be secured. The algorithm is applied to several examples.

Excited states of bound excitons in wurtzite-type semiconductors

Abstract: Excitons bound to neutral impurities are studied with respect to excited states by means of excitation spectroscopy in CdS single crystals at 1.8 K. The symmetry of the four excited states of the exciton bound to neutral donor (placed energetically below the free exciton) can be deduced from the observed dependence of their optical transitions on the direction of the wave vector and the polarization. Theoretical considerations taking into account the complex valence band structure of wurtzite-type semiconductors lead to an explanation of these states in terms of excited (p- and d-like) hole states of the bound exciton. With respect to the exciton bound to neutral acceptor only the well-known I1B-states are found experimentally arising from the incorporation of a hole from the lower B-subvalence band in the complex. Mit Hilfe der Anregungsspektroskopie werden angeregte Zustande von gebundenen Exzitonen in CdS-Kristallen bei 1,8 K untersucht. Die Symmetrie der vier energetisch unterhalb des freien Exzitons gelegenen angeregten Zustande des am neutralen Donator gebundenen Exzitons kann aus der nachgewiesenen Abhangigkeit ihrer optischen Ubergange von der Richtung des Wellenvektors und der Polarisation abgeleitet werden. Umfangreiche theoretische Betrachtungen unter Berucksichtigung der komplexen Valenzbandstruktur von Wurtzit-Halbleitern fuhren zu einer Interpretation dieser Zustande als angeregte (p- und d-artige) Lochzustande des gebundenen Exzitons. Fur das am neutralen Akzeptor gebundene Exziton konnen nur die bekannten I1B-Zustande nachgewiesen werden, die sich aus der Beteiligung eines Loches aus dem tieferen B-Subvalenzband ergeben.

The Significance of Matrix Zones for Brain Regeneration and Brain Transplantation with Special Consideration of Lower Vertebrates

Abstract: Nearly 200 years aGo, Fontana (1787) Demonstrated successful regeneration in a severed peripheral nerve. In the same year, Arnemann (1787) showed that there was no regeneration in the central nervous system. These characteristic differences in regeneration in the two systems have been accepted by many scientists during the past two centuries. However, various studies during this period have suggested that regeneration in the central nervous system, although limited in degree, is possible. The issue of regeneration in the central nervous system has acquired a special significance, particularlys in light of recent research on transplantation of nervous tissues. Although this volume is addressed to the transplantation of nervous tissues, it is believed that transplantation and regeneration are intimately related. Regeneration may be considered as an important requirement for achieving successful transplantation. With this background, I would like to show some important interrelations between regeneration and transplantation, particularly in the lower vertebrates.

TEM precipitation studies in Te‐rich as‐grown PbTe single crystals

Abstract: In Te-rich as-grown PbTe single crystals small homogeneously distributed inhomogeneities are detected by TEM. They are identified as tellurium precipitates. The largest of them permit the determination of their orientation: (00.1) Te s| (111) PbTe, [11.0] Te | [110] PbTe. An estimation of the number of Te atoms absorbed by the precipitates results in values which are comparable with the maximum deviation from stoichiometry. The results allow a detailed comparison with literature data on precipitates in AIVBVI semiconductors. They support the idea of a diffusion-determined precipitation due to the retrograde course of the solidus line. In Te-reichen „as-grown”-PbTe-Einkristallen werden mittels TEM kleine, homogen verteilte Inhomogenitaten nachgewiesen, die als Tellurausscheidungen identifiziert werden konnen. Die grosten der Ausscheidungen erlauben die Bestimmung der Orientierungsbeziehung (00.1) Te | (111) PbTe, [11.0] Te | [110] PbTe. Eine Abschatzung ergibt, das die Anzahl der von den Ausscheidungen aufgenommenen Telluratome vergleichbar mit der maximal erlaubten Abweichung von der Stochiometrie ist. Die Ergebnisse ermoglichen einen ausfuhrlichen Vergleich mit der Literatur uber Ausscheidungen in AIVBVI -Halbleitern. Sie unterstutzen die Vorstellung einer diffusionsbestimmten Ausscheidung infolge des retrograden Verlaufs der Soliduslinie.

1H‐NMR‐, 13C‐NMR‐ und IR‐Untersuchungen zur Tautomerie von 15N‐markiertem 3‐Methyl‐1‐phenyl‐Δ2‐pyrazolin‐5‐on

Abstract: 1H-N. M. R., 13CN. M. R., and I. R.-Investigations Concerning Tautomerism of 15N-Labeled 3-Methyl-1-phenyl-Δ2-pyrazolin-5-one The behaviour of the 15N-mono and dilabeled compound in dependence on temperature and solvent polarity is described. Chemical shifts, nJ(15N1H), and nJ(15N13C) coupling constants (n = 1 – 3) have been determined. In the cases of 2, 2, 2-trifluoroethanole and hexafluoroisopropanole the Δ4-pyrazolin-3-one is stabilized and detected by 3J(15N2H4) = 3 Hz, 1J(13C315N2) = 11, 0 Hz and δ(13C5). In HMPT the 5-hydroxypyrazole form predominates and is characterized by 3J(15N1H4) = 5, 1 Hz and δ (13C5). Coupling constants 3J(15N2H4) and J(13C315N2) could not be observed in this solvent. In accordance with 1H- and 13C-n. m. r.-parameters i. r. measurements in dependence on temperature lead to the conclusion that in DMSO and THF for instance all three tautomers are present and variation of temperature does not change the equilibrium between the tautomers. A good relationship between the content of the CH2, OH and NH forms and the Donor Numbers (DN) and Acceptor Numbers (AN) by Gutmann has been found.

Eine einfache Synthese von β‐Chlorzimtsäurenitrilen nach einer modifizierten Vilsmeier‐Haack‐Arnold‐Reaktion

Abstract: A Simple Synthesis of β-Chlorocinnamonitriles by a Modified Vilsmeier-Haack-Arnold-Reaction A simple one-pot synthesis of β-chloro-cinnamonitriles 2 can be achieved by treating acetyl arenes 1 first with formamide chlorides and subsequently with hydroxyl amine hydrochloride. The formamide chlorides used are conveniently prepared from an excess of dimethyl formamide and phosphoryl chloride. However it is also possible to employ other N,N-disubstituted formamides or acid chlorides, respectively. For comparison purposes β-chloro-cinnamonitriles 2 have also been synthesized in a two-step process. Thus 3-aryl-3-chloro-(2)-iminium salts 4 are reacted with hydroxyl amine hydrochloride giving rise to 3-chloro-cinnamic aldoximes 5. The latter compounds are dehydrated to the corresponding nitriles 2 by refluxing in acetic anhydride following a known procedure.

Figurative features and the construction of visual images.

Abstract: Within the framework of a featural approach to conceptual representations, “figurative features” were defined as cognitive entities reflecting the sensory properties of objects in the human mind. In conceptual hierarchies such as taxonomies, “primary concepts” were defined as the most abstract concepts which could still be characterized by their richness in figurative features. The present experiment demonstrated that when subjects were required to form visual images in response to nouns, imagery latencies were shorter to nouns designating primary concepts than to nouns designating either more abstract or more specific concepts. Furthermore, when subjects were subsequently presented with a pictured object and were asked to categorize it as illustrating or not the previously designated concept, it took less time to decide that the object corresponded to a primary concept than to either more abstract or more specific concepts. Subjects classified as high imagers had shorter imagery latencies than low imagers to all kinds of nouns, but decision times in the picture-categorization task did not significantly differ in both groups. These data are discussed in reference to current models of mental imagery.

Morphology and biology of cerebellar neuroblastomas.

Abstract: A nodular neuroblastoma was partially removed from the cerebellar vermis of a 15-month-old boy. Postoperative irradiation and chemotherapy were performed. More than 5 years later, re-operation revealed a mature ganglioglioma. Problems relating to the maturation of ganglionic tumors are discussed. The present case emphasizes that it is not justified to regard all neuroblastomas of the central nervous system as highly malignant neoplasms (grade IV).

Determination of electron depth‐dose function for kilovolt electrons on GaAsP

Abstract: A new technique to determine the depth-dose function is described using the measurement of the electron beam induced barrier current on bevelled homo p-n junction structures. A universal depth-dose function on GaAsP is found in the form in the investigated energy range from 10 to 45 keV. The distance of the maximum under the surface can be obtained by the relation a = A0EPr1.65 with A0 = 2.95 × 10−3 (EPr in keV, a in μm). Die Tiefendosisfunktion wird mit Hilfe der Messung des elektronenstrahlinduzierten Barrierenstromes an Schragschliffen von Homoubergangen bestimmt. Die universelle Tiefendosisfunktion wird im Energiebereich von 10 bis 45 keV fur GaAsP als Quasi-Gausfunktion gefunden: . Der Abstand des Maximums der Verteilung unter der Oberflache kann durch die Beziehung a = A0EPr1,65 mit A0 = 2,95 × 10−3 (EPr in keV, a in μm) beschrieben werden.