Showing papers by "University of Bonn published in 1973"

Variation of hodge structure: The singularities of the period mapping

Abstract: Table of

Cell Motility: Mechanisms in Protoplasmic Streaming and Ameboid Movement

Abstract: Publisher Summary This chapter discusses recent results obtained on amebas and slime-mold plasmodia in the context of protoplasmic streaming and ameboid movement. Ameboid movement is a complex expression of a cell activity and results from multiple interactions of different mechanisms. Protoplasmic streaming, or cytoplasmic streaming, comprises various patterns of movement of the protoplasm, or cytoplasm, within a cell. Four different systems are involved in motive force generation: (1) the actomyosin system, (2) the tubulin–dynein system, (3) the flagellin system, and (4) the myoneme system of stalked ciliates. Advances in causal analysis indicate that the molecular mechanisms underlying protoplasmic streaming and ameboid movement, on the one hand, and muscular contraction, on the other, are basically the same. Therefore, these kinds of motions are collectively classified as “contractile movements.” This term is also applicable to various movements involved in cell cleavage, morphogenesis, and development, which probably involve an actomyosin system and are caused by the contraction of fibrillar structures.

Magnetic storm characteristics of the thermosphere

Abstract: Energy and diffusive mass transport associated with the thermospheric circulation are considered in a self-consistent, though mathematically relatively simple form to describe in a three-dimensional two-constituent model magnetic storm characteristics in composition (N2, O, and He), temperature and mass-density. It is shown that during disturbed conditions the latitudinal variations of composition and gas temperature T sub g reflect the local nature of the magnetic storm heat input assumed to be primarily confined to the auroral zones. Thereby T sub g and N2 increase, He decreases and O remains constant through the auroral zones at exospheric heights (due to the superposition of temperature and diffusion effects) in agreement with OGO-6 mass spectrometer measurements. In contrast, the magnetic storm response in the total mass density is characterized by a strong world-wide component and a relatively insignificant increase toward the poles with the density peak occurring between two (poles) and eight (equator) hours after the maximum energy input, in substantial agreement with satellite drag data.

Higher Dimensional Dedekind Sums

Abstract: In this paper we will study the number-theoretical properties of the expression v1 nkal rcka,, d(p; a I . . . . . an) = ( 1) n/2 ~ cot cot (1) k=l P P and of related finite trigonometric sums. In Eq. (I), p is a positive integer, a~ . . . . . a, are integers prime to p, and n is even (for n odd the sum is clearly equal to zero). There are two reasons for being interested in sums of this type. First of all, the case n = 2 is, up to a factor, the classical Dedekind sum:

High resolution field desorption mass spectrometry—I: Nucleosides and nucleotides

Abstract: The first complete high resolution (HR) field desorption (FD) mass spectra (MS) are presented and constitute a helpful tool in the structure elucidation of biologically significant compounds. This is especially relevant for the determination of the molecular weight of substances with very low volatilities which suffer from thermal decomposition when evaporated into the ion source. An additional advantage is the very small sample consumption (in the submicrogram range). Further improvements in the ion production method are the introduction of high temperature activated emitters and a specially designed micromanipulator for optimal adjustment of the field anodes. These enabled values of mass resolution between 15000 and 25000 (10% valley definition) to be achieved when vacuum evaporated Ag Br plates were used for photographic recording.

Ultrastructural observations on cell necrosis during formation of the neural tube in mouse embryos.

Abstract: Spontaneous cell death in the developing brain of 8.5–9 day old mouse embryos has been investigated with the electron microscope. Before closure of the neural tube, areas of cell death are found at the neuro-somatic junction. After closure of the neural tube degenerating cells are found in the dorsal midline of the prospective diencephalon. Ultrastructurally, cell degeneration is marked by chromatin condensation, increase in electron density of the structures in the cytoplasm and, in later stages, by a marked pycnosis of the dying cell. After fragmentation, the necrotic material as well as entire pycnotic cells are phagocytized and digested by cells of the neuroepithelium. An invasion of macrophages has not been observed. The significance of cell necrosis is discussed in relation to the normal formation of the neural tube and to the occurrence of certain induced malformations (exencephalies).

Biology of the Predaceous Earwig Labidura riparia (Dermaptera: Labiduridae),

Abstract: The striped earwig, Labidura riparia (Pallas), was successfully reared for the first time on an oligidic medium in the laboratory and we studied the earwig's biology. Eggs hatched in 8 days at 26.7±1.1°C, and development time through the nymphal stages for females and small male morphotypes was 33.27 and 33.06 days, respectively. Head-capsule sizes and weights of smaller adult males and females were not significantly different. Females and smaller males passed through 5 stadia. The larger male morphotype had 6 nymphal stages. Females with permanent mates produced an average of 10 egg batches totaling 440 eggs during their adult life (114.8 days). Fertility and fecundity were reduced when females were paired with males for only 24 hours and then separated. Predatory activity and functional response studies were carried out using larvae of the wireworm, Melanotus communis (Gyllenhal). Locomotor and mating activity were nocturnal. Investigations of subsocial behavior using 32P indicated possible exchange of materials from the female parent to its offspring.

Non-Thermal Solar Wind Heating by Supra-Thermal Ions

Abstract: The effect of a new energy source due to energies transferred from supra-thermal secondary ions on the temperature profile of the solar wind has been considered. For this purpose a solution of a tri-fluid model of the solar wind including solar electrons, protons, and α-particles, and starting with the boundary conditions of Hartle and Barnes at 0.5 AU is given. On the base of the assumption that suprathermal He+-ions which have four times the temperature of suprathermal protons are predominantly coupled to solar α-particles by Alfven waves, it is shown that the temperature T α of solar α-particles should be appreciably higher than those T p of solar protons beyond the orbit of the Earth. For 1 AU a temperature excess T α over T p according to that which has been found in some solar wind ion spectrograms can only be explained for a small part of the orbit of the earth which is inside the cone of enhanced helium densities. Around 1 AU the temperatures T α and T p are found to decrease much slighter with solar distance than given in the two-fluid model of Hartle and Barnes. Beyond 1.7 and 2.2 AU the temperatures T α and T p even start increasing with solar distance and come up to about 105 at about 10 AU. These predictions should lend some support to future temperature measurements with deep-space probes reaching Solar distances of some AU.

Morphologische untersuchungen der tibialen tympanalorgane von neun einheimischen laubheuschrecken-arten (Orthoptera, Tettigonioidea)

Abstract: 1. Die tibialen Tympanalorgane von neun einheimischen Laubheuschrecken-Amen wurden genauer untersucht. 2. Besonderes Interesse galt dem Verlauf der Beintrachee and der beiden in die Vorderextremitat eintretenden Nerven (Abb. 4). 3. Die Tibien- and “Cristalangen” sowie die Anzahl der Scolopidien der Crista acustica and deren durchschnittliche Lange wurden im Vergleich dargestellt. 4. Bemerkenswert vor allem ist die Artspezifitat der “Cristalange” und der Anzahl der Scolopidien der Horleiste. 5. Dies last vermuten, das die Perzeption der artspezifischen Stridulation mit Hilfe der Tympanalorgane eng mit der unter 4. dargestellten Erkenntnis korreliert ist.

[Identification of merozoites of 4 cyst-forming Coccidia (Sarcocystis, Toxoplasma, Besnoitia, Frenkelia) by means of electron microscopy (author's transl].

Abstract: Die Cystenstadien vonSarcocystis tenella, Frenkelia spec.,Besnoitia jellisoni undToxoplasma gondii wurden elektronenoptisch untersucht und schematisch in Relation zu ihrer Grose dargestellt. Mikromorphologische Unterschiede erlauben eine eindeutige Identifikation dieser Coccidien. In allen Cysten sind Merozoiten enthalten, stets von bananenformiger Gestalt. Daruber hinaus weisen die Cysten vonS. tenella undFrenkelia spec. noch ovoide Metrocyten mit tiefen Einfaltungen auf. Sie liegen an der Peripherie der Cyste, dicht unterhalb der begrenzenden Primarhulle. Die Metrocyten beider Arten zeigen typische Merozoitenorganelle und sind auserdem noch durch einen walzenformigen bzw. kugeligen Bereich osmiophiler Grana im Nukleus ausgezeichnet. BeiFrenkelia spec. wird noch ein dritter Zelltypus ausgebildet, der als „intermediare Zelle” bezeichnet wird und bipolar aufgebaut ist. Als wichtige Kriterien der untersuchten Arten wurden folgende Merkmale herangezogen:S. tenella besitzt Metrocyten und Merozoiten, die nahezu doppelt so gros sind wie die der ubrigen Arten. Die Mikronemen treten in ausergewohnlich groser Anzahl auf (ca. 400), desgleichen die Rhoptrien (ca. 11).Frenkelia spec. bildet bipolare intermediare Zellen aus. Die Merozoiten zeigen einen besonderen hinteren Conus. Die Anzahl der Mikronemen ist auf etwa 50–70 beschrankt; etwa 5–8 Rhoptrien sind vorhanden.B. jellisoni-Merozoiten sind durch 20–30 sog. enigmatische Korper charakterisiert; etwa 80–100 Mikronemen und ca. 3–5 Rhoptrien sind vorhanden.T. gondii weist die kleinsten Merozoiten aller untersuchten Arten auf. Die Anzahl der Mikronemen ubersteigt 50 kaum. Alle hier untersuchten Stadien vermehren sich durch Endodyogenie. Mit Ausnahme der Metrocyten und intermediaren Zellen vonFrenkelia spec. konnten bei allen Formen 22 subpellikulare Mikrotubuli nachgewiesen werden. Die feinstrukturellen Ergebnisse wurden abschliesend auf ihren Wert als systematische Kriterien gepruft.

Solution of a Markovian decision problem by successive overrelaxation

Abstract: It is shown that successive overrelaxation can be applied in solving a discounted Markovian decision problem. An overrelaxation factor yielding minimum contraction factor is determined. The minimum contraction factor turns out to be at most equal to the discount factor.

[Ultrastructural observations on the functional morphology of the tubero-hypophyseal system of the rat].

Abstract: 1. Die Gefasfortsatze von ependymalen und subependymalen Zellen bilden in der subependymalen Zone und in der Zona interna des Ratteninfundibulum mit Nervenfasern kompakte neuro-gliose Faserbundel, die sich in der Zona externa aufzweigen. 2. In allen Zonen des Infundibulum kommen zwischen den Nervenfasern und den Gefasfortsatzen zahlreiche neuro-gliose Synapsen vor. In den Gefasfortsatzen fallt die hohe Zahl an Mikrotubuli sowie die zahlreichen, vielgestaltigen Einschlusse auf. 3. In der subependymalen Zone sind die Interzellularspalten an bestimmten Stellen auserordentlich weit. Sie haben eine kanalartige Beschaffenheit und enthalten feine Bundel von Nervenfasern. 4. Von den lateralen Anteilen des Infundibulum her erreichen Dendriten von Ganglienzellen des Nucleus infundibularis die Mitte des Infundibulum. In dieser Region sind axodendritische Synapsen anzutreffen. 5. Morphometrische Analysen der Nervenfaserendigungen der Zona externa von Normaltieren zeigen, das die prozentuale Verteilung der nach Granulagrose differenzierten Nervenfaserklassen fur Mitte und Seite der Zona externa etwa gleich ist. Zwischen der Grose der Elementargranula und der Anschnittflache der zugehorigen Nervenfasern besteht eine direkte Beziehung. 6. Die Nervenfaserendigungen erreichen die Basalmembran des perikapillaren Raumes fast ausschlieslich im Bereich von gefaswarts gerichteten Vorwolbungen der Zona externa. Das Ausmas, in dem Nervenfasern im Vergleich zu den Gefasfortsatzen von Ependymund Gliazellen den perivaskularen Raum erreichen, ist medial weitaus groser als lateral. 7. Bei bilateral adrenalektomierten Ratten nimmt in bestimmten, vorwiegend lateral gelegenen Nervenfasern die Zahl und Grose der Elementargranula in Abhangigkeit von der Uberlebensdauer zu. Dies durfte auf eine verstarkte Synthese und Speicherung von Corticotropin-Releasing Factor in diesen Nervenfasern zuruckzufuhren sein. Gegenuber dem Normalbefund ist die neurohamale Kontaktflache erheblich vergrosert. Der perivaskulare Raum enthalt zerfallene Nervenfaserteile, die durch Bindegewebszellen phagocytiert werden. Diese Veranderungen durften durch eine unter Versuchsbedingungen verstarkte Wachstumstendenz der Nervenfasern in Richtung auf die Blutgefase und durch eine Abschnurung der Nerven-faserendigungen ausgelost werden.