Showing papers by "University of Bonn published in 1988"

Parameter Estimation and Hypothesis Testing in Linear Models

Abstract: This textbook on theoretical geodesy deals with the estimation of unknown parameters, the testing of hypothesis and the estimation of intervals in linear models. The reader will find presentations of the Gauss-Markoff model, the analysis of variance, the multivariate model, the model with unknown variance and covariance components and the regression model, as well as the mixed model for estimation random parameters. To make the book self-contained most of the necessary theorems of vector and matrix-algebra and the probability distributions for the test statistics are derived. Students of geodesy, as well as of mathematics and engineering, will find the geodetical application of mathematical and statistical models extremely useful.

Models of dispersal in biological systems

Abstract: In order to provide a general framework within which the dispersal of cells or organisms can be studied, we introduce two stochastic processes that model the major modes of dispersal that are observed in nature. In the first type of movement, which we call the position jump or kangaroo process, the process comprises a sequence of alternating pauses and jumps. The duration of a pause is governed by a waiting time distribution, and the direction and distance traveled during a jump is fixed by the kernel of an integral operator that governs the spatial redistribution. Under certain assumptions concerning the existence of limits as the mean step size goes to zero and the frequency of stepping goes to infinity the process is governed by a diffusion equation, but other partial differential equations may result under different assumptions. The second major type of movement leads to what we call a velocity jump process. In this case the motion consists of a sequence of "runs" separated by reorientations, during which a new velocity is chosen. We show that under certain assumptions this process leads to a damped wave equation called the telegrapher's equation. We derive explicit expressions for the mean squared displacement and other experimentally observable quantities. Several generalizations, including the incorporation of a resting time between movements, are also studied. The available data on the motion of cells and other organisms is reviewed, and it is shown how the analysis of such data within the framework provided here can be carried out.

Reaction kinetics of the adsorption and desorption of nickel, zinc and cadmium by goethite. I. Adsorption and diffusion of metals

Abstract: SUMMARY The reactions of Ni, Zn and Cd with goethite were studied over a range of initial metal concentrations (10−6 to 10−4M), pH values (4 to 8), reaction times (2h to 42d) and temperatures (5 to 35°C). The adsorption of metals increased with pH, reaction time and temperature. Adsorption of Ni increased relative to Zn and Cd with increasing time and temperature. The initially rapid adsorption of metals within a few hours was followed by a much slower reaction linearly related to time1/2, interpreted as diffusion–controlled penetration of goethite. The pH–dependent relative diffusion rates (Ni > Zn > Cd) were influenced by both affinity for goethite surfaces and by ionic radius. Diffusion coefficients of the three metals ranged from about 10−19to 10−20cm2s−1. The corresponding activation energies of diffusion were also calculated (Ni 35, Cd 55, Zn 90 kJ mol−1). Our view about the reactions of heavy metals with goethite involves (i) adsorption of metals on external surfaces, (ii) solid–state diffusion of metals from external to internal binding sites, and (iii) metal binding and fixation at positions inside the goethite particles. The general parameters of these processes are related to the hydrolytic properties (pK values) and the ionic radii of the metals. The results show that goethite may be an efficient sink for trace metals.

How Far are Automatically Chosen Regression Smoothing Parameters from their Optimum

Abstract: We address the problem of smoothing parameter selection for nonparametric curve estimators in the specific context of kernel regression estimation. Call the “optimal bandwidth” the minimizer of the average squared error. We consider several automatically selected bandwidths that approximate the optimum. How far are the automatically selected bandwidths from the optimum? The answer is studied theoretically and through simulations. The theoretical results include a central limit theorem that quantifies the convergence rate and gives the differences asymptotic distribution. The convergence rate turns out to be excruciatingly slow. This is not too disappointing, because this rate is of the same order as the convergence rate of the difference between the minimizers of the average squared error and the mean average squared error. In some simulations by John Rice, the selectors considered here performed quite differently from each other. We anticipated that these differences would be reflected in differ...

Scheduling project networks with resource constraints and time windows

Abstract: Project networks with time windows are generalizations of the well-known CPM and MPM networks that allow for the introduction of arbitrary minimal and maximal time lags between the starting and completion times of any pair of activities. We consider the problem to schedule such networks subject to arbitrary (even time dependent) resource constraints in order to minimize an arbitrary regular performance measure (i.e. a non-decreasing function of the vector of completion times). This problem arises in many standard industrial construction or production processes and is therefore particularly suited as a background model in general purpose decision support systems. The treatment is done by a structural approach that involves a generalization of both the disjunctive graph method in job shop scheduling [1] and the order theoretic methods for precedence constrained scheduling [18,23,24]. Besides theoretical insights into the problem structure, this approach also leads to rather powerful branch-and-bound algorithms. Computational experience with this algorithm is reported.

SUPERB: A tool for semi-automatic MIMD/SIMD parallelization☆

Abstract: This paper describes the design of an interactive system for the semi-automatic transformation of FORTRAN 77 programs into parallel programs for the SUPERNUM machine. The system is characterized by a powerful analysis component, a catalog of MIMD and SIMD parallelization transformations, and a flexible dialog facility. It contains specific knowledge about the parallelization of an important class of numerical algorithms.

Histamine H3 receptor-mediated inhibition of serotonin release in the rat brain cortex.

Abstract: Rat brain cortex slices preincubated with 3H-serotonin were superfused with physiological salt solution (containing citalopram, an inhibitor of serotonin uptake) and the effect of histamine on the electrically (3 Hz) evoked 3H overflow was studied. Histamine decreased the evoked overflow in a concentration-dependent manner. The inhibitory effect of histamine was antagonized by impromidine and burimamide, but was not affected by pheniramine, ranitidine, metitepine and phentolamine. Given alone, impromidine facilitated the evoked overflow, whereas burimamide, pheniramine and ranitidine had no effect. The results suggest that histamine inhibits serotonin release in the rat brain cortex via histamine H3 receptors, which may be located presynaptically.

Bootstrapping in Nonparametric Regression: Local Adaptive Smoothing and Confidence Bands

Abstract: The operation of the bootstrap in the context of nonparametric regression is considered. Bootstrap samples are taken from estimated residuals to study the distribution of a suitably recentered kernel estimator. The application of this principle to the problem of local adaptive choice of bandwidth and to the construction of confidence bands is investigated and compared with a direct method based on asymptotic means and variances. The technique of the bootstrap is to replace any occurrence of the unknown distribution in the definition of the statistical function of interest by the empirical distribution function of the observed errors. In a regression context these errors are not directly observed, although their role can be played by the residuals from the fitted model. In this article the fitted model is a kernel nonparametric regression estimator. Since nonparametric smoothing is involved, an additional difficulty is created by the bias incurred in smoothing. This bias, however, can be estimated...

Total intravenous anaesthesia with propofol and alfentanil by computer-assisted infusion.

Abstract: The combination of propofol and alfentanil was administered to 20 patients for total intravenous anaesthesia during general surgery. The infusion rates for both drugs were controlled by microprocessors in order to institute constant blood levels adapted to the patients' varying needs. The mean blood level of propofol required for adequate hypnosis during anaesthesia was 2.42 micrograms/ml (SD 0.43). Awakening occurred 7.9 minutes (SD 3.4) after the end of the infusion, at a propofol blood level of 1.59 micrograms/ml (SD 0.34). The plasma level of alfentanil was 285 ng/ml (SD 72) during major noxious stimulation and 148 ng/ml (SD 56) during minor stimulation. The computer-assisted infusions showed a measured/predicted ratio of 1.01 (SD 0.28) for alfentanil and 0.88 (SD 0.22) for propofol. This indicates that the administration device used in this study is reasonably reliable. The technique of total intravenous anaesthesia was characterised by a smooth induction without significant haemodynamic alterations, by good control during anaesthesia and by a very fast recovery without major side effects.

Embedded minimal surfaces derived from Scherk's Examples.

Abstract: In this article we construct embedded minimal surfaces which are, at least heuristically, derived from Scherk's first and second surface. Our examples are either parametrized by punctured spheres and then have one translational period or one screw motion period; or they are parametrized by rectangular tori and then have one or two translational periods. The helicoidal examples contain nonisometric ∈-deformations in the sense of Rosenberg [R].

Both GA2, GM2, and GD2 synthases and GM1b, GD1a, and GT1b synthases are single enzymes in Golgi vesicles from rat liver.

Abstract: Competition experiments using lactosylceramide, ganglioside GM3 and ganglioside GD3 as substrates, as well as mutual inhibitors for ganglioside N-acetylgalactosaminyltransferase, in Golgi vesicles derived from rat liver suggested that N-acetylgalactosamine transfer to these three respective compounds, leading to gangliosides GA2, GM2, and GD2, respectively, is catalyzed by one enzyme. Analogous studies with gangliosides GA1, GM1, and GD1b as glycolipid acceptors in sialyltransferase assays indicated GM1b, GD1a, and GT1b synthases to be identical. These results are incorporated into a model for ganglioside biosynthesis and its regulation.

The action potential of Dionaea muscipula Ellis.

Abstract: The intention of this investigation was to acquire more concise information about the nature of the action potential of Dionaea muscipula Ellis and the different types of cells generating and conducting it. It is shown by microelectrode measurements that, besides the sensory cells, all the major tissues of the trap lobes are excitable, firing action potentials with pronounced after-hyperpolarizations. The action potentials are strictly dependent on Ca2+. Their peak depolarizations are shifted 25–27 mV in a positive direction after a tenfold increase in external Ca2+ concentration. Perfusions with 1 mM ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) or 1 mM LaCl3 completely inhibit excitability. Magnesium ions only slightly affect the peak depolarizations but considerably prolong action potentials. Sodium azide and 2,4-dinitrophenol also abolish excitation, probably by reducing the intracellular ATP concentration. Furthermore, it is tested whether the sensory cells can be distinguished from the other cells of the trap by their electrical behaviour. The resting potentials of sensory cells (-161±7 mV) and mesophyll cells (-155±8 mV) are of the same magnitude. Changes in external ion concentrations affect resting and action potentials in both cell types in a similar way. Additional freeze-fracture studies of both cell types reveal similar numbers and distributions of intramembrane particles on the fracture faces of the plasma membrane, which is most likely the mechanosensor. These findings stress the view that the high mechanosensitivity of the sensory hair results from its anatomy and not from a specialized perception mechanism. It is proposed that trap closure is triggered by a rise in the cytoplasmic concentration of Ca2+ or a Ca2+-activated regulatory complex, which must exceed a threshold concentration. Since the Ca2+ influx during a single action potential does not suffice to reach this threshold, at least two stimulations of the trap are necessary to elicit movement.

Measurement of Inequality: An Attempt at Unification and Generalization

Abstract: This paper reviews and extends the theory of ethical inequality indices. It presents a novel axiom (strict separability of social welfare orderings in rank-ordered subspaces). This axiom allows to provide joint characterizations of the most important inequality measures (Atkinson family, Kolm-Pollak family and Generalized Ginis) and of some new more general classes of indices. The whole derivation is based on weak assumptions. In an ordinal framework only continuity of the underlying ordering is required and no cardinal properties are employed.

Mode of action of the staphylococcinlike peptide Pep 5: voltage-dependent depolarization of bacterial and artificial membranes.

Abstract: The cationic staphylococcinlike peptide Pep 5 is shown to depolarize bacterial and planar lipid membranes in a voltage-dependent manner. An artificial valinomycin-induced potassium diffusion potential across the cytoplasmic membrane of Staphylococcus cohnii 22 was sufficient to promote Pep 5 action. Thus, evidence is provided that a membrane potential of sufficient magnitude is the only prerequisite for Pep 5 activity. The voltage dependence was elucidated by macroscopic conductance measurements with black lipid membranes. A threshold potential of about -90 to -100 mV, which was deduced from experiments with bacterial cells, could be confirmed. Single pores were resolved which often occur as short-lived bursts and fluctuate among different conductance levels. Pore diameters were calculated ranging from 0.1 to 1 nm. Succinylation of the lysine residues of Pep 5 resulted in prolonged pore lifetimes and maintenance of distinct conductance levels. However, the succinylated peptide required a higher threshold potential, approximately -150 mV, than the native peptide, which is probably the reason for the reduced activity of the modified peptide against intact gram-positive bacteria.

Fucose-containing oligosaccharides from human milk from a donor of blood group 0 Le(a) nonsecretor.

Abstract: The neutral oligosaccharides from the milk of a single donor with blood group 0, Lewis(a+b-) nonsecretor were separated into 18 fractions essentially according to the number of carbohydrate constituents using gel permeation chromatography on Biogel P-4 and Fractogel TSK HW-40. Further separation was achieved by HPLC and by HPTLC after reduction and peracetylation. The fractions obtained were analysed by FAB mass spectrometry with and without derivatization and by one- and two-dimensional proton NMR. Besides the already described 3-fucosidolactose, fucopentaose II (2), fucopentaose III (6) and difucohexaose II (4) the following fucosylated oligosaccharides could be identified. Among the higher oligosaccharides a branched lacto-N-decaose (12) was obtained in pure form after removal of the fucose residues by mild acid treatment.

General Mechanisms for Solute Transport Across the Tonoplast of Plant Vacuoles: a Patch‐Clamp Survey of Ion Channels and Proton Pumps

Abstract: The electrical properties of the tonoplast from a large variety of plant materials such as mesophyll cells, storage cells, tumor cells, suspension cultured cells, guard cells, coleoptile cells, and liverwort cells have been investigated using the patch-clamp technique. Whole-vacuole recordings were employed to study the dynamics of an ATP-dependent proton pump by directly measuring the electrogenic currents. The addition of Mg-ATP induced an inwardly directed current which depolarized the tonoplast (the vacuole becoming positive inside). Furthermore, voltage-dependent passive ion fluxes were analyzed using whole vacuoles and isolated membrane patches. Whole-vacuolar currents and single-channel currents were induced at hyperpolarizing potentials, whereas currents decreased at positive trans-tonoplast potentials. The electrical properties of the tonoplast of vacuoles from various plant tissues were similar and it was concluded that ion fluxes across the tonoplast follow the same general mechanisms.

Gabapentin augments whole blood serotonin in healthy young men.

Abstract: It has been previously demonstrated that gabapentin, a gamma-amino butyric acid analogue, inhibits monoaminergic neurotransmitter release from rabbit caudate nucleus slices and from rat cortex. In humans this drug has been shown to have anti-epileptogenic activity. Serotonin may act as an inhibitory neurotransmitter and its interaction with blood platelets is thought to reflect its central actions. We investigated sleep stages, whole blood serotonin levels, and serum melatonin in healthy men after the administration of gabapentin. With increasing serum gabapentin levels six healthy subjects showed an increase in sleep stages 3 and 4 and in whole blood serotonin (P less than 0.05) Serum melatonin levels were not influenced. On account of these results we speculate that gabapentin modulates the release of serotonin from blood platelets. The increase in peripheral serotonin points paradigmatically to an increase in the bioavailability of serotonin which may account for the increase in sleep stages 3 and 4.

Motor neuron syndrome and monoclonal IgM with antibody activity against gangliosides GM1 and GD1b.

Abstract: We demonstrated that an IgM M-protein from a patient with motor neuron syndrome had antibody activity against gangliosides GM1, GD1b, and asialo GM1. Studies with a sugar-binding lectin suggested that the epitope in the patient's M-IgM involved the Gal(beta 1-3) GalNAc moiety. Immunohistological techniques demonstrated staining of axons in the lumbar roots, granular cells, and white matter in the cerebellum by the patient's M-IgM. We propose that, in this case, an autoimmune mechanism of motor neuron syndrome associated with a monoclonal protein is most likely.

Development of resistance to nalidixic acid and the fluoroquinolones after the introduction of norfloxacin and ofloxacin.

Abstract: Since 1975, the group Resistenz of the Paul-Ehrlich-Gesellschaft fur Chemotherapie has monitored the development of resistance in isolates of members of the family Enterobacteriaceae, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis in the Federal Republic of Germany, West Berlin, Austria, and Switzerland. Despite a marked increase in the use of 4-quinolones, there was no increase in the percentages of nalidixic acid-resistant strains of Enterobacteriaceae between 1975 and 1986. However, different bacterial species showed considerable variation, and there were also considerable differences in the percentages of nalidixic acid-resistant strains of Enterobacteriaceae from different centers. The frequency of resistance to fluoroquinolones was unchanged from 1983 to 1986 and was less than 4% in all species except P. aeruginosa. In this species, there was an increase from about 3 to 10% from 1983 to 1986 for strains for which the MIC was fourfold above the mode MIC of ciprofloxacin, enoxacin, and ofloxacin.

The precursor of sulfatide activator protein is processed to three different proteins.

Abstract: The enzymic degradation of a number of sphingolipids in the lysosomes is stimulated by small acid glycoproteins named activator proteins. We purified and sequenced a new protein, called component C, which seems to be related to sulfatide activator and to a recently described activator of glucosylceramidase (A1 activator) (Kleinschmidt, T., Christomanou, H. & Braunitzer, G. (1987) Biol. Chem. Hoppe-Seyler 368, 1571-1578). It consists of 78 amino acids and carries one carbohydrate chain at aparagine 20. Component C shows 21.5% sequence homology to sulfatide activator and 34.2% homology to A1 activator. Structural similarities between these three proteins have also been detected. Recently the cDNA sequence of the sulfatide activator precursor has been published (Dewji, N.N., Wenger, D.A. & O'Brien, J.S. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 8652-8656). We could align the protein sequences of sulfatide activator, A1 activator and component C with that of this large precursor protein. After minor corrections of the DNA sequence we obtained total fit. Thus it seems that three different proteins are derived from the sulfatide activator precursor by proteolytic processing. Possible processing sites were found on the precursor at sites adjacent to the N-termini and C-termini of the mature proteins. The processing of sulfatide activator was studied by Fujibayashi and Wenger (Fujibayashi, S. & Wenger, D.A. (1986) Biochim. Biophys. Acta 875, 554-562). Their data support our assumption that processing occurs by simultaneous cleavage at all possible sites.

Velamen radicum micromorphology and classification of orchidaceae

Abstract: Roots of 344 species of 262 representative genera of Orchidaceae have been examined under systematic aspects by light and scanning electron microscopy; the paper is illustrated by 25 SEM-photos and schematic drawings. In particular the stratification and micromorphology of the rhizodermis (velamen radicum) exhibits a high diversity which can be applied taxonomically. Combinations of root characters are classified into 12 syndromes (“types”). A particularly remarkable cortex structure (tracheoidal cortex) is described and the term “pseudovelamen” introduced. Additional features relevant for taxonomic work are exodermis structure and occurence of “Stabkorper” (tilosomes). The distribution of these characters shows a high conformity with existing classifications of the family. However, in certain cases discussed in detail (e.g. Genyorchis) the characters are discordant with some taxonomic views.

Immunocytochemical localization of CCAP, a novel crustacean cardioactive peptide, in the nervous system of the shore crab, Carcinus maenas L.

Abstract: Polyclonal antibodies were raised in rabbits against synthetic crustacean cardioactive peptide (CCAP) conjugated to bovine thyroglobulin, and were used to map CCAP-immunoreactive structures in the central nervous system of Carcinus maenas. As expected, the neurohemal pericardial organs (PO) displayed abundant immunoreactivity in nerve fibers and terminals. In addition, immunoreactive neurons were demonstrated in other parts of the nervous system. At least some of them do not appear to terminate in neurohemal structures and may have a non-endocrine, as yet unknown function. Immunoreactive perikarya with a diameter of 25–30 μm occur in the brain. They project into the optic and antennary neuropil, and into the eyestalk. One cell was found in the medulla terminalis of the eyestalk and in the connective ganglion, respectively. From the latter, axonal branches could be traced into the brain and the thoracic ganglia (TG). In the TG, small-diameter perikarya give rise to extensive networks of varicose fibers. Some of the perikarya occur in a characteristic paired arrangement with larger CCAP-immunoreactive somata (diameter 40–50 μm). These pairs of one small and one large cell occur in all mouthpart and leg segments of the TG, except the abdominal ganglia (AG), where only large cells were found. The main projections of the large neurons comprise one or more fibers in each of the seven segmental nerves (SN), leading to neurosecretory terminals in the PO. The fibers in the SN are joined by branches of an ascending axonal tract from the large perikarya in the AG. The large-type perikarya are considered to be the principal source of CCAP in the PO. The optic ganglia in the eyestalk, except the medulla terminalis, the neurohemal sinus gland and the stomatogastric nervous system are devoid of CCAP-immunoreactivity.

New trigonal lattice hosts: stoicheiometric crystal inclusions of laterally trisubstituted benzenes—X-ray crystal structure of 1,3,5-tris-(4-carboxyphenyl)benzene·dimethylformamide

Abstract: New host molecules with a central 1,3,5-trisubstituted benzene ring and rigidly attached lateral arms composed of aryl or arylethynyl and extra functional groups are reported. They are shown to give more than thirty clathrates with a wide variety of organic solvents comprising alicyclic, aromatic, heterocyclic, dipolar aprotic, and protic molecules. Inclusion selectivities and stoicheiometries of the different clathrates are discussed. The crystal structure of (2a)·dimethylformamide (DMF)(1:3) inclusion compound has been determined from single-crystal X-ray diffraction. The crystals show R symmetry. There are six host and eighteen guest molecules in the hexagonal unit cell with a=b= 23.160(9) and c= 11.812(3)A. The final linear R is 0.082 for 1 518 unique reflections. The host molecules adopts a propeller conformation with perfect three-fold symmetry and acts as a donor in hydrogen bonds to three DMF molecules. In the crystal structure the host–guest units are arranged stack-wise.