Showing papers by "Bielefeld University published in 1982"

Centrifugal innervation of the retina by luteinizing hormone releasing hormone (LHRH)-immunoreactive telencephalic neurons in teleostean fishes.

Abstract: In cichlid, poecilid and centrarchid fishes luteinizing hormone releasing hormone (LHRH)-immunoreactive neurons are found in a cell group (nucleus olfactoretinalis) located at the transition between the ventral telencephalon and olfactory bulb. Processes of these neurons project to the contralateral retina, traveling along the border between the internal plexiform and internal nuclear layer, and probably terminating on amacrine or bipolar cells. Horseradish peroxidase (HRP) injected into the eye or optic nerve is transported retrogradely in the optic nerve to the contralateral nucleus olfactoretinalis where neuronal perikarya are labeled. Labeled processes leave this nucleus in a rostral direction and terminate in the olfactory bulb. The nucleus olfactoretinalis is present only in fishes, such as cichlids, poecilids and centrarchids, in which the olfactory bulbs border directly the telencephalic hemispheres. In cyprinid, silurid and notopterid fishes, in which the olfactory bulbs lie beneath the olfactory epithelium and are connected to the telencephalon via olfactory stalks, the nucleus olfactoretinalis or a comparable arrangement of LHRH-immunoreactive neurons is lacking. After retrograde transport of HRP in the optic nerve of these fishes no labeling of neurons in the telencephalon occurred. It is proposed that the nucleus olfactoretinalis anatomically and functionally interconnects and integrates parts of the olfactory and optic systems.

Narrowband tunable VUV radiation generated by nonresonant sum- and difference-frequency mixing in xenon and krypton.

Abstract: Nonresonant sum- and difference-frequency mixing of the fundamental omega(L) and the second harmonic omega(UV) radiation of a powerful narrowband pulsed dye laser system excited by an Nd:YAG laser (lambda(L) = 5500-6500 A) generates intense VUV radiation in krypton and xenon with the frequency omega(VUV) = 2omega(UV) micro omega(L) The sum-frequency is tunable in spectral regions of negative dispersion between 1100 and 1300 A The maximum VUV pulse power exceeds 20 W (5 x 10(10) photons/pulse) VUV light pulses with up to 60 W (23 x 10(11) photons/pulse) are provided by the difference-frequency at wavelengths between 1850 and 2070 A In addition the conversion process omega(VUV) = 2omega(UV) - omega(IR) (omega(IR) is the frequency of the Nd:YAG laser) generates radiation in the wavelength range of 1595-1866 A With present laser systems the tuning range of the difference-frequency could be extended to wavelengths as short as 1226 A The sum- and difference-frequency conversion will thus provide intense coherent VUV light continuously tunable between 1100 and 2100 A

Laser Doppler spectroscopy of atomic hydrogen in the photodissociation of HI

Abstract: Laser induced fluorescence Doppler spectroscopy has been applied for the first time to atomic hydrogen using tunable VUV light at the Lyman-α line. The dissociation of HI at 266 nm into H+I(P 1/2) and H+I(P 3/2) has been investigated. The recoil energy, angular distribution and branching ratio of the H atom have been measured, serving to test and study the feasibility and applicability of the technique.

Linear lexicographic optimization

Abstract: The relevance of lexicographic optimization may be located in the field of multiple criteria decision making as well as in mathematical programming. In this paper we shall introduce the lexicographic simplex method and the underlying existence and duality theory. Some applications of lexicographic optimization will also be outlined. Dieser Beitrag beschaftigt sich mit dem linearen lexikographischen Optimierungsproblem. Es werden Anwendungen dargestellt sowie ein Losungsverfahren und die ihm zugrunde liegende Existenz- und Dualitatstheorie vorgestellt.

Equilibrium Point Selection in a Class of Market Entry Games

Abstract: It is the purpose of this paper to investigate a class of games, where each player has to decide whether to enter a market or not A player’s payoff is the difference of two components, market profits and entry costs The game is symmetric with respect to market profits, but entry costs are different for each player Since only the entry decisions are modelled explicitly each player has two pure strategies

Determination of All Minimal Cut-Sets between a Vertex Pair in an Undirected Graph

Abstract: An efficient enumeration algorithm generates all minimal cut-sets separating a special vertex pair in an undirected graph. The algorithm is based on a blocking mechanism that guarantees that every minimal cut-set between the two specified vertices is generated exactly once. The algorithm is intended for computer implementation, and computational times are provided.

Mitochondrial and nuclear myxothiazol resistance in Saccharomyces cerevisiae.

Abstract: Mitochondrial and nuclear mutants resistant to myxothiazol were isolated and characterized. The mitochondrial mutants could be assigned to two loci, myx1 and myx2, by allelism tests. The two loci map in the box region, the split gene coding for apocytochrome b. Locus myx1 maps in the first exon (box4/5) whereas myx2 maps in the last exon (box6). The nuclear mutants could be divided into three groups: two groups of recessive mutations and one of dominant mutations. Respiration of isolated mitochondria from mitochondrial mutants is resistant to myxothiazol. These studies support the conclusion that myxothiazol is an inhibitor of the respiratory chain of yeast mitochondria. The site of action of myxothiazol is mitochondrial cytochrome b.

Proton-induced alignment of theL 3-subshell in heavy atoms

Abstract: The proton-induced alignment of theL-shell in heavy atoms (54≦Z≦92) has been studied by measuring the anisotropy of the emitted x radiation. The proton energies ranged from 150 keV to 10 MeV. The alignment in different target atoms was found to approximately follow a universal curve. Calculations in Born approximation as well as in the semiclassical approach give a good description of the observed alignment at high projectile velocities. In the low energy regime the deflection of the projectile in the Coulomb field of the target nucleus has to be taken into account to obtain agreement between theory and experiment.

Feynman path integrals and the trace formula for the Schrödinger operators

Abstract: We study Schrodinger operators of the form\(H = - \frac{{h^2 }}{2}\Delta + \frac{1}{2}x \cdot A^2 x + V(x)\) on ℝd, whereA2 is a strictly positive symmetricd×d matrix andV(x) is a continuous real function which is the Fourier transform of a bounded measure. If λn are the eigenvalues ofH we show that the theta function\(\theta (t) = \sum\limits_n {\exp \left( { - \frac{i}{h}t\lambda _n } \right)}\) is explicitly expressible in terms of infinite dimensional oscillatory integrals (Feynman path integrals) over the Hilbert space of closed trajectories. We use these explicit expressions to give the asymptotic behaviour of θ(t) for smallh in terms of classical periodic orbits, thus obtaining a trace formula for the Schrodinger operators. This then yields an asymptotic expansion of the spectrum ofH in terms of the periodic orbits of the corresponding classical mechanical system. These results extend to the physical case the recent work on Poisson and trace formulae for compact manifolds.

Efferent neurons of the lateral-line system and the VIII cranial nerve in the brainstem of anurans. A comparative study using retrograde tracer methods.

Abstract: The octavo-lateral efferent system of several anuran species was studied by means of retrograde transport of horseradish peroxidase. This system is organized similarly in all larval anurans and in all adult aglossids. All have two groups of efferent neurons in the nucleus reticularis medialis between the VIIIth and the IXth motor nucleus. The caudal group consists of efferent neurons that supply the posterior lateral-line nerve (NLLp) and a considerably smaller group of neurons supplying both the NLLp and the anterior lateral-line nerve (NLLa). The rostral group is composed of efferent neurons supplying the NLLa, neurons projecting to the inner ear and neurons supplying both the inner ear and the NLLa. Efferent neurons of the VIIIth cranial nerve exhibit a rostrocaudal cytoarchitectonic differentiation. Caudal perikarya, which are rounder in shape than those of the rostral part, have a dendritic projection to the superior olive. It is suggested that this differentiation reflects a functional differentiation of acoustic and vestibular efferent neurons.

Vibrational and translational enhancement of endothermic reactions: K + HCl(υ = 0,1) and K + HF(υ = 0,1)

Abstract: The relative integral cross section for the two endothermic reactions K + HCl(υ = 0 and 1) → KCl + H and K + HF(υ = 0 and 1) → KF + H has been measured as a function of the collision energy E using the crossed molecular beam technique. The vibrationally excited state (υ = 1) has been populated thermally by heating the beam source to temperatures around 2000 K. The variation of the collision energy from thermal up to around 2.1 eV was achieved by seeding the K-beam with various carrier gases. The molecular reaction product was detected by surface ionization in connection with a time-of-flight method. The total energy threshold of the reactions has been found to be equal to or only slightly above the corresponding endothermicities. This suggests a vanishing or very low barrier crest on the potential energy hypersurfaces which is contradictory to recent theoretical results. The inclusion of tunneling in case of K + HF leads to a negligible rise of the barrier heights. The efficacy of translational and vibrational energy in promoting the reactive process has been directly compared over a wide range of collision energies. For K + HCl the vibrational enhancement of the reactivity descends with increasing E from approximately a factor of 10 at E = 0.08 eV to around unity for E ⩾ 0.5 eV. The good agreement of this experimental result with phase space calculations suggests that the marked enhancements are predominantly caused by the long-range attraction between reagents in connection with an “early” barrier on the potential energy surface. In case of K + HF vibrational energy is by a factor of up to 380 more favourable in promoting the reaction than the same amount of translational energy. Again, with rising collision energy its efficacy decreases but promotes the reaction still by a factor of 70 at E = 1.7 eV. Since phase space theory fails here the reaction is certainly non-statistical and we conclude that the observed large efficacy of vibrational energy is due to a “late” barrier. The proposed barrier positions for the two systems are in accordance with theoretical results.

Spatial distribution of recoiling atoms with a specific momentum generated in a collision cascade

Abstract: The spatial distribution of the momentum spectrum of recoiling atoms in an elastic collision cascade, produced by an energetic ion injected into a random solid, is investigated. Recoils are counted when accelerated from rest, or decelerated from above an energy boundary E/sub 1/ into an energy interval (E/sub 0/, E/sub 0/+dE/sub 0/) in a single collision. Pronounced cascade anisotropies are observed, the magnitude and direction depending on the recoil energy and the depth.

13C labelling study of the interconversion of ethylbenzene, 7‐methylcycloheptatriene and p‐xylene ions

Abstract: The isomerization of the molecular ions of ethylbenzene, 7-methylcycloheptatriene and p-xylene by skeletal rearrangement prior to the formation of [C7H7]+ ions has been investigated by using 13C labelled compounds. The results obtained for ions generated by 70 eV and 12 eV electron impact, and fragmenting in the ion source, the 1st field free region and the 2nd field free region, respectively, are compared with those obtained from D labelled derivatives. It is shown that at long reaction times metastable p-xylene ions lose a methyl radical after scrambling of all C atoms and H atoms, while the unstable molecular ions in the ion source react by specific loss of one of the methyl substituents. Both unstable and metastable ethylbenzene ions fragment by two competing mechanisms, one corresponding to specific loss of the terminal methyl group, and the other involving scrambling of all C and H atoms. These results are discussed by use of a dynamic model developed for the mutual interconversion and fragmentation of the molecular ions of ethylbenzene, methylcyclo-heptatriene and p-xylene. The experimental results can be explained by an equilibrium between metastable methylcycloheptatriene ions and p-xylene ions with sufficient energy for skeletal rearrangement, while about 40% of the metastable ethylbenzene ions fragment after rearrangement to methylcycloheptatriene ions and about 60% of the ethylbenzene ions rearrange further to xylene ions before fragmentation. Metastable methylcycloheptatriene ions, mainly lose a methyl group without a skeletal rearrangement, however, because the rearranged ions are kinetically trapped as ‘stable’ xylene ions or ethylbenzene ions.

A Jost-Schroer theorem for string fields

Abstract: It is shown that the truncated Wightman functions of three or more string-localized fields vanish if they are solutions of a Klein-Gordon equation in each variable. As an application it is shown that a string field is a free field if its two-point functions are those of a free field. Another application to perturbation theory is pointed out.