Showing papers by "Bielefeld University published in 1988"

The lexical approach to personality: A historical review of trait taxonomic research

Abstract: We review research aimed at the development of a compelling taxonomy of personality‐descriptive terms. We identify five issues central to the construction of personality taxonomies and discuss the ...

Color screening and deconfinement for bound states of heavy quarks

Abstract: We study the binding and deconfinement of heavy quarks in a thermal environment, using a non-relativistic confinement potential model with color screening. As a result, we obtain the dependence of the dissociation energies, the binding radii and the masses of heavy quark resonances (charmonium and bottonium states) on the color screening lengthrD of the medium, and we determine for the different resonances those values ofrD below which no more binding is possible. Finally, we consider the implication of our results on resonance suppression as signal for deconfinement.

Quasi-Landau Spectrum of the Chaotic Diamagnetic Hydrogen Atom

Abstract: The highly excited hydrogen atom in static magnetic fields has been in recent years a subject of intense experimental [1–4] and theoretical [4–9] studies which have led to substantial progress in the understanding of this previously unsolved elementary problem. Described by the Hamiltonian (in atomic units) $$H=\frac{1}{2}{{P}^{2}}+\frac{1}{2}\gamma {{L}_{z}}+\frac{1}{8}{{\gamma }^{2}}{{\rho }^{2}}-\frac{1}{\gamma }$$ (1) (cylindrical coordinates, r = (ρ2 + z2)½ field parameter γ = B/Bo with Bo = 2.35 × 105 Tesla) the magnetized atom is of particular interest in the quasiLandau regime of strong mixing of the Coulomb and diamagnetic interactions, i.e. where the two forces are of comparable strength. In this regime the motion of the Rydberg electron becomes classically chaotic [10]. It is this aspect which has recently attracted much attention, as the magnetized atom constitutes an ideal model case for detailed experimental studies of the quantum mechanics of a most simple atomic system in classical chaos.

Identification and mapping of nitrogen fixation genes of Rhodobacter capsulatus: duplication of a nifA-nifB region.

Abstract: Rhodobacter capsulatus mutants unable to fix nitrogen were isolated by random transposon Tn5 mutagenesis. The Tn5 insertion sites of 30 Nif- mutants were mapped within three unlinked chromosomal regions designated A, B, and C. The majority of Tn5 insertions (21 mutants) map within nif region A, characterized by two ClaI fragments of 2.5 and 25 kilobases (kb). The 17-kb ClaI fragment of nif region B contains six nif::Tn5 insertions, and the three remaining mutations are located on a 32-kb ClaI fragment of nif region C. Hybridization experiments using all 17 Klebsiella pneumoniae nif genes individually as probes revealed homology to nifE, nifS, nifA, and nifB in nif region A. The nifHDK genes were localized in nif region B. About 2 kb away from this operon, a second copy of the DNA fragments homologous to nifA and nifB, originally found in nif region A, was identified.

Genetic characterization and sequence analysis of the duplicated nifA/nifB gene region of Rhodobacter capsulatus.

Abstract: A DNA region showing homology to Klebsiella pneumoniae nifA and nifB is duplicated in Rhodobacter capsulatus. The two copies of this region are called nifA/nifB copy I and nifA/nifB copy II. Deletion mutagenesis demonstrated that either of the two copies is sufficient for growth in nitrogen-free medium. In contrast, a double deletion mutant turned out to be deficient in nitrogen fixation. The complete nucleotide sequence of a 4838 bp fragment containing nifA/nifB copy I was determined. Two open reading frames coding for a 59,653 (NifA) and a 49,453 (NifB) dalton protein could be detected. Comparison of the amino acid sequences revealed that the R. capsulatus nifA and nifB gene products are more closely related to the NifA and NifB proteins of Rhizobium meliloti and Rhizobium leguminosarum than to those of K. pneumoniae. A rho-independent termination signal and a typical nif promoter region containing a putative NifA binding site and a consensus nif promoter are located within the region between the R. capsulatus nifA and nifB genes. The nifB sequence is followed by an open reading frame (ORF1) coding for a 27721 dalton protein in nifA/nifB copy I. DNA sequence analysis of nifA/nifB copy II showed that both copies differ in the DNA region downstream of nifB and in the noncoding sequence in front of nifA. All other regions compared, i.e. the 5' part of nifA, the intergenic region and the 3' part of nifB, are identical in both copies.

Two classes of Rhizobium meliloti infection mutants differ in exopolysaccharide production and in coinoculation properties with nodulation mutants

Abstract: Symbiotic mutants of Rhizobium meliloti were isolated following Tn5 mutagenesis. Besides four nodulation mutants (Nod-) unable to induce nodule formation on alfalfa, five infection mutants (Inf-), which induce the formation of root nodules without detectable infection threads or bacteroids, were obtained. The Inf- mutants were subdivided into two classes. One class contains mutants which fail to synthesize acidic exopolysaccharide (EPS-). The other class is comprised of mutants which produce excess amounts of acidic exopolysaccharide (EPS*). 13C nuclear magnetic resonance spectroscopy of the exopolysaccharide isolated from one of the latter type of Inf- mutant, 101.45, revealed that the side chain of the repeating octosaccharide unit lacks the terminal pyruvate residue. Complementing cosmids were isolated for all Inf- mutants. In the case of the Inf- EPS- mutants the complementing cosmids contain DNA segments which overlap and are part of megaplasmid 2. For two mutants the mutations were found to map on a 7.8 kb EcoRI fragment. In the case of the Inf- EPS* mutants the complementing cosmids carry chromosomal DNA. The mutations of two Inf- EPS* mutants were localized on a 6.4 kb EcoRI fragment. Coinoculation of alfalfa plants with Nod- and Inf- EPS- mutants resulted in effective symbiosis. The nodules appeared wild type and fixed nitrogen. In constrast, coinoculations with Nod- mutants and the Inf- EPS* mutant 101.45 did not result in the formation of effective nodules.

The microtubular cytoskeleton and chromosomes of unfertilized human oocytes aged in vitro.

Abstract: To detect structural alterations in human oocytes that may give rise to predisposition to aneuploidy, unfertilized human oocytes from an IVF programme were processed for indirect anti-tubulin immunofluorescence. The spindle of oocytes aged for 2 days is rather small, and bi- or multipolar. Chromosomes are no longer aligned at the spindle equator but are scattered all over the degenerating spindle. This implies that human oocytes aged for 2 days may no longer be able to develop into a chromosomally balanced, normal embryo. In oocytes aged for 3–4 days the chromosomes become more decondensed and form a restitution nucleus. Microtubules radiate out from the latter towards the cell periphery and form a network of fibres in the cytoplasm. A similar alignment of tubules is found in unfertilized, activated oocytes. Oocytes with an aberrant cytoskeleton and chromosomal array were predominantly obtained from aged females. They include two binucleated oocytes with two sets of chromosomes and two oocytes with displaced chromosomes one of which had a tripolar spindle.

The stromacentre inAvena plastids: an aggregation ofβ-glucosidase responsible for the activation of oat-leaf saponins.

Abstract: The stromacentre, a particular structure in the plastids of mostAvena species, was isolated from etioplasts ofAvena sativa and then characterized to determine its biological function. When comparing differentAvena species with or without stromacentre, it was shown that the stromacentre, a 63-kDa protein, and saponins (characteristic compounds ofAvena sativa) either occur together or not at all. This linkage was confirmed by demonstrating a transformation of saponins by the isolated stromacentre protein: avenacosides were hydrolyzed to 26-desgluco-avenacosides. Therefore, the stromacentre protein had to be regarded as aβ-glucosidase. Enzyme assays usingp-nitrophenyl-β-d-glucopyranoside as substrate showed that thisβ-glucosidase has a pH optimum at pH 6.0. The calculatedK m value for this substrate was 2.2·10-3 M. Antibodies against the stromacentre protein inhibitedβ-glucosidase activity. The determination of the molecular weight of theβ-glucosidase by sodium dodecyl sulfate-gel electrophoresis showed that it consists of subunits of 63 kDa. After gel electrophoresis under non-denaturing conditions, enzymatically active molecules were shown to consist of at least two of these subunits. Molecules aggregated up to about 106 Da also had enzyme activity. Enzyme assays using avenacosides as substrate showed a pH optimum at pH 6.0. The calculatedK m value for this substrate was 1.2·10-5 M. The high affinity to the avenacosides and the high specificity for the C-26 bound glucose indicate that avenacosides are the natural substrates for thisβ-glucosidase. Assuming that the avenacosides in oat leaves play a role as preformed chemical inhibitory substances against phytopathogenic microorganisms, a model is presented showing the stromacentre with a central role in activating the fungitoxicity of avenacosides.

Estimation via compressed information

Abstract: Some results from classical estimation theory are extended to the case in which data must be communicated from several places where observations are made to the place where the estimate is generated. Particular emphasis is placed on determining how the variance of an unbiased estimator depends on the communication rates. Explicit result are given for Gaussian sources. >

The CBA mouse as a model for age-related aneuploidy in man: studies of oocyte maturation, spindle formation and chromosome alignment during meiosis.

Abstract: To elucidate the possible mechanism of disturbances in chromosome segregation leading to the increase in aneuploidy in oocytes of aged females we examined the meiotic spindles of CBA/Ca mice. Employing immunofluorescence with an anti-tubulin antibody, and human scleroderma serum, as well as 4′-6-diamidino-2-phenylindole (DAPI) staining of chromosomes the microtubular cytoskeleton could be visualized, and the behaviour of chromosomes and centromeres of oocytes spontaneously maturing in vitro could be studied. The morphology of spindles during the first meiotic division was not conspiciously different in oocytes from young and aged mice as far as the cytoskeletal elements were concerned. Neither multipolar spindles nor pronounced cytoplasmic asters appeared in oocytes of mice approaching the end of their reproductive life (9 months and older). Oocytes of aged females also did not exhibit any sign of premature separation of parental chromosomes at prophase, obvious malorientations of bivalents, or significant lagging of chromosomes during ana and telophase. Metaphase I with all bivalents aligned at the spindle equator appeared to be a relatively brief stage in oocyte development compared with pro-and prometaphase. Therefore, already slight disturbances occuring in the timing of the developmental programme which leads to a premature anaphase transition may be responsible for the high incidence of chromosomally unbalanced gametes in aged females, rather than non-separation and lagging of chromosomes during late ana-and telophase. In a second set of experiments we compared the metaphase II spindles of spontaneously ovulated oocytes obtained from animals at different ages. Previous studies have shown that spindle length and chromosome alignment may be altered in cells predisposed to aneuploidy. To distinguish between the significance of the chronological age of the female and the physiological age of the ovaries (as indicated by the total number of oocytes remaining) we examined the spindle apparatus in young (3–4 months old) and aged (9 months and older) mice as well as CBA females which had been unilaterally ovariectomized (uni-ovx) early in adult life and were approaching the end of their reproductive life at 6–7 months of age. Measurements of the pole-to-pole distance implied that spindle length may be related to maternal age. In oocytes of aged (9 month), uni-ovx (6 month) as well as 6-month-old sham-operated controls the metaphase II spindle was significantly shorter than in oocytes of young mice. By contrast, chromosome disorder and displacement was most pronounced in the aged and uni-ovx mice whilst most oocytes from young mice and moderately aged shamtreated controls exhibited a more regular alignment of chromosomes. These results, which are consistent with recent findings in CBA mice of an increased rate of aneuploidy in females approaching the end of their reproductive life, are discussed with respect to the hypothesis that the aetiology of aneuploidy rests on the critical timing of different events in oocyte development.

Excretion of ions (Cd2+, Li+, Na+ and Cl−) by Tamarix aphylla

Abstract: Excretion of minerals by the NaCl-resistant and comparatively cadmium-resistant tree Tamarix aphylla (L.) Karst, was investigated. Cd2+ was excreted by plants exposed for 1–10 days to 9 or 45 μM Cd2+ solutions. Excretion of this toxic ion increased considerably with time but was less than 5% of the quantities that had been accumulated in the shoots. Excretion of Na+ and Cl− was positively correlated with NaCl concentration (1.5, 10, 50 mM) of the medium. The Na+/Cl− ratios of the excrete were positively correlated with the concentration of the treatment solution. Ca2+ excretion decreased with increasing NaCl concentrations of the solution. Excretion of K+ and Mg2+ was only little affected by NaCl. Excretion of Li+ occurred whenever this element was supplied in the uptake solution; daily excretion rates of Li+ increased with time. The ecological significance of excretion is discussed in relation to the low selectivity of the mechanism in T. aphylla.

Photoelectron spectroscopy of jet-cooled aluminium cluster anions

Abstract: Aluminium cluster anions (A12) are produced by laser vaporization without additional ionization and cooled by supersonic expansion. Photoelectrons from mass-identified anion bunches (n=2...25) are detached by laser light (hv = 3.68 eV) and undergo energy analysis in a magnetic bottle-type time-of-flight spectrometer. The measurements provide information about the electronic excitation energies from ionic ground states to neutral states of the clusters. In contrast to bulk aluminium these cluster photoelectron spectra partially have well-resolved bands which originate from low-lying excited bands. For small clusters, especially the aluminium dimer and trimer, quantum-chemical calculations will be compared to the measurements. The electron affinity size dependence of larger clusters shows conclusive evidence for "shell" effects.

The visual field and visually guided behavior in the zebra finch (Taeniopygia guttata)

Abstract: Measurements were made of the physical properties of the visual system of the zebra finch, a bird with laterally placed eyes. The use of the visual system in pecking and courtship behavior was examined. It was demonstrated that the optical axis and the fovea of the eye point in a direction about 62° from the sagittal axis of the head. The visual field of each eye covers about 170° in the horizontal plane. In the frontal region there is an overlap of about 30°–40° where the birds can see binocularly; caudally there is a ‘gap’ in the visual field of 60°. The point of best binocular viewing is in the sagittal plane at 16.5° below the beak.

Defect correction method for the solution of algebraic Riccati equations

Abstract: The solution of discrete and continuous algebraic Riccati equations is considered. It is shown that if an approximate solution is obtained, then the defect for this solution again solves an algebraic Riccati equation of the same form, and that the system properties of detectability and stabilizability are inherited by this defect equation. On the basis of these results, a general defect-correction method is proposed and numerical examples are given for the use of this method in combination with A. Bunse-Gerstner and V. Mehrmann's (1986) SR method. >

Melanin production encoded by a cryptic plasmid in a Rhizobium leguminosarum strain

Abstract: Rhizobium leguminosarum strain VF39, isolated from nodules of field-grown faba beans in the Federal Republic of Germany, was shown to contain six plasmids ranging in molecular weight from 90 to 400 Md. Hybridisation to nif gene probes, plasmid curing, and mobilisation to other strains of Rhizobium and to Agrobacterium showed that the third largest plasmid, pRleVF39d (220 Md), carried genes for nodulation and nitrogen fixation. This plasmid was incompatible with pRL10JI, the Sym plasmid of R. leguminosarum strain JB300. Of the other plasmids, the two smallest (pRleVF39a and pRleVF39b, 90 and 160 Md respectively) were shown to be self-transmissible at a low frequency. Although melanin production is as yet unreported in strains of R. leguminosarum biovar viceae, strain VF39 produced a dark pigment, which, since it was not produced on minimal media and its production was greatly enhanced by the presence of tyrosine in the media, is probably melanin-like. Derivatives of VF39 cured of pRleVF39a no longer produced this pigment, but regained the ability to produce it when this plasmid was transferred into them. Strains of Agrobacterium tumefaciens, R. meliloti, and some strains of R. leguminosarum carrying pRleVF39a did not produce this pigment, indicating perhaps that some genes elsewhere on the VF39 genome are also involved in pigment production. Plasmid pRleVF39a appeared to be incompatible with the cryptic Rhizobium plasmids pRle336b and pRL8JI (both ca. 100 Md), but was compatible with the R. leguminosarum biovar phaseoli Sym plasmids pRP1JI, pRP2JI and pRph51a, all of which also code for melanin production. The absence of pRleVF39a in cured derivatives of VF39 had no effect on the symbiotic performance or competitive ability of this strain.

Das Konzept von der eigenen Begabung

Abstract: Selbstkonzept: Menschen haben im allgemeinen sehr viele Vorstellungen uber ihre eigene Person. So kann man Vorstellungen uber die eigene Sport-lichkeit haben und sich fur einen guten oder schlechten Sportler halten oder Vorstellungen uber die eigene Attraktivitat und sich fur mehr oder weniger attraktiv halten. Weiter hat man unter Umstanden Vorstellungen uber eigene politische Auffassungen und halt sich fur fortschrittlich oder konservativ. Viele Vorstellungen uber die eigene Person kreisen um das eigene Konnen bzw. die eigenen Fahigkeiten. So kann man sich als mehr oder weniger begabt in akademischen, in anschlusthematischen oder aber auch in handwerklichen Bereichen einschatzen.

Dilepton production at finite temperature: Perturbative treatment at order alpha s.

Abstract: In the framework of finite-temperature perturbative QCD we examine the first-order corrections to the rate of lepton pairs produced in a thermalized quark-gluon plasma. The dilepton rate is calculated using the real-time formalism in two different ways by (i) applying the Feynman amplitude approach and by (ii) analyzing the relationship to the discontinuity of the two-loop photon self-energy at finite temperature. We mainly study the infrared and mass singular behavior and we show that up to order ${\ensuremath{\alpha}}_{s}$ the rate is free of these divergences in the limit of vanishing gluon and quark masses.

Laser spectroscopy of desorbing molecules

Abstract: In this article the application of tunable dye lasers to desorption phenomena is illuminated. These lasers provide radiation continuously tunable from 105 nm in the vacuum ultraviolet to about 10 μm in the mid-IR. By employing either laser induced fluorescence (LIF) or resonance enhanced multiphoton ionization (REMPI) spectroscopy almost all diatomic and many polyatomic molecules can be probed with the sensitivity required to detect desorbing molecules under UHV conditions. The spectral resolution of the lasers is sufficiently high that rotational state selectivity is achieved. Recent developments permit in addition the velocity distributions of molecules to be determined with internal quantum state resolution. Therefore very detailed information about the molecular dynamics has been obtained. In most experiments so far reactive recombinations off surfaces have been investigated. In this paper special emphasis will be given to the recombination of hydrogen on copper and palladium surfaces. For these systems very detailed data about the internal state populations at various surface temperatures have been obtained. The rotational cooling previously observed in molecular beam scattering has also been established for desorption. Strong vibrational excitation has been observed, which in the case of desorption from copper may be associated with the recombination dynamics, whereas for desorption of D2 from Pd(100) a molecular precursor state might be responsible. By measuring the velocity distribution in each quantum state, the complete energetics of the desorbing molecules has been determined. Some first experiments on laser induced desorption with state selective detection of the desorbing molecules will also be discussed. Finally, making use of the polarization analysis of the signal, alignment effects in the desorption can be observed, permitting observation of molecular dynamics with a “magnifying glass”.

Topographic relations between ocular dominance and orientation columns in the cat striate cortex.

Abstract: In the visual cortex of four adult cats ocular dominance and orientation columns were visualized with (3H)proline and (14C)deoxyglucose autoradiography. The two columnar systems were reconstructed from serial horizontal sections or from flat-mount preparations and graphically superimposed. They share a number of characteristic features: In both systems the columns have a tendency to form regularly spaced parallel bands whose main trajectory is perpendicular to the border between areas 17 and 18. These bands frequently bifurcate or terminate in blind endings. The resulting irregularities are much more pronounced in the ocular dominance than in the orientation system. The periodicity of the columnar patterns was assessed along trajectories perpendicular to the main orientation of the bands and differed in the two columnar systems. The spacing of the ocular dominance stripes was significantly narrower than the spacing of orientation bands. The mean periodicity of a particular columnar system was virtually identical in the two hemispheres of the same animal but it differed substantially in different animals. However, the spacing of orientation columns covaried with that of the ocular dominance columns, the ratios of the mean spacings of the two columnar systems being similar in the four cats. The superposition of the two columnar systems revealed no obvious topographic relation between any of the organizational details such as the location of bifurcations, blind endings and intersections. We suggest the following conclusions: 1. The developmental processes generating the two columnar systems seem to obey the same algorithms but they act independently of each other. 2. The space constants of the two systems are rigorously specified and appear to depend on a common variable. 3. The main orientation of the bands in both columnar systems is related to a) the representation of the vertical meridian, b) the anisotropy of the cortical magnification factor, and c) the tangential spread of intracortical connections.