Showing papers by "University of Cologne published in 1989"

Correlated fermions on a lattice in high dimensions

Abstract: The limit of infinite dimension of the Hubbard model was recently introduced by Metzner and Vollhardt as a new type of model with interesting implications. In the present paper the same limit is applied to a family of lattice fermion models with generalized kinetic and potential energies. A simple method is introduced for investigating the important issue of handling momentum conservation at the interaction vertices. It is shown that the irrelevance of momentum conservation found by Metzner and Vollhardt applies more generally than their Gaussian density of states. Interactions between particles on different sites are shown to simplify to their Hartree substitute. This leaves on-site interactions as the only dynamical interactions in the limit of infinite dimension.

A Survey of Priority Rule-Based Scheduling

Abstract: In this paper, we survey the literature on heuristic priority rule-based job shop scheduling. Priority rules have been intensively investigated over the last 30 years by means of simulation experiments. They are also used in Shop Floor Control software systems. We present a classification, a characterization, and an evaluation of elementary priority rules. Some priority rule-related model extensions are discussed.

Fracture of disordered, elastic lattices in two dimensions.

Abstract: We study via simulation how a lattice breaks if each bond is an elastic beam having longitudinal and flexural breaking thresholds randomly selected according to various probability distributions. We observe scaling of force, displacement, and number of broken beams in the controlled regime. The distribution of local forces just before breaking is characterized by a multifractal spectrum f(\ensuremath{\alpha}).

PCR-based cDNA library construction: general cDNA libraries at the level of a few cells

Abstract: A procedure for the construction of general cDNA libraries is described which is based on the amplification of total cDNA in vitro. The first cDNA strand is synthesized from total RNA using an oligo(dT)-containing primer. After oligo(dG) tailing the total cDNA is amplified by PCR using two primers complementary to oligo(dA) and oligo(dG) ends of the cDNA. For insertion of the cDNA into a vector a controlled trimming of the 3' ends of the cDNA by Klenow enzyme was used. Starting from 10 J558L micron3 myeloma cells, total cDNA was synthesized and amplified approximately 10(5) fold. A library containing 10(6) clones was established from 1/6 of the amplified cDNA. Screening of the library with probes for three genes expressed in these cells revealed a number of corresponding clones in each case. The longest obtained clones contained inserts of 1.5 kb length. No sequences originating from carriers or from rRNA was found in 14 randomly picked clones.

A benchmark comparison for mantle convection codes

Abstract: Summary We have carried out a comparison study for a set of benchmark problems which are relevant for convection in the Earth's mantle The cases comprise steady isoviscous convection, variable viscosity convection and time-dependent convection with internal heating We compare Nusselt numbers, velocity, temperature, heat-flow, topography and geoid data Among the applied codes are finite-difference, finite-element and spectral methods In a synthesis we give best estimates of the ‘true’ solutions and ranges of uncertainty We recommend these data for the validation of convection codes in the future

Stable expression and somatic hypermutation of antibody V regions in B-cell developmental pathways

Abstract: Etude des differentes voie de differenciation des cellules B grâce a l'etude du rearrangement des genes des regions variables

Gyrification in the cerebral cortex of primates.

Abstract: The degree of cortical folding in primates has been analyzed using a gyrification index (GI). Correlation analyses of the GI with body weight, brain weight and neopallial volume show that the human data fit the general trend of the nonhuman anthropoids. Bigger primate brains exhibit a higher degree of fissurization, but a taxonomic difference that is independent of brain weight between prosimians and anthropoids has also been observed. In these regressions, anthropoids differed from prosimians by having a larger increase in gyrification for every unit increase in body or brain weight or neopallial volume. A stepwise regression also shows a prosimian-anthropoid difference. The best predictor for convolutedness in anthropoids is neocortical volume, while in prosimians it is brain weight. The GI in catarrhines is correlated with total sulcal length but not number of sulci. This result suggests paleontological studies of total sulcal length can give direct information on the evolution of cortical folding in primates.

Closely related transcripts encoded by the neurogenic gene complex enhancer of split of Drosophila melanogaster.

Abstract: Genetic evidence suggests that E(spl), one of the neurogenic loci of Drosophila, is a gene complex comprising an as yet incompletely established number of transcription units. In order to correlate the various transcription units with E(spl) functions, wild-type flies were transformed with genomic DNA encoding the transcription unit m8 from the mutant E(spl)D, which was known to be altered in embryos carrying this mutant allele. Transformants show the same dominant enhancement of the spl phenotype as E(spl)D itself. Since m8 has a virtually identical pattern of expression as m4, m5 and m7, we have determined the sequence of these four transcripts. The deduced protein products of m5, m7 and m8 exhibit extensive sequence homology with each other. All three encode a sequence similar to one of the conserved domains of representatives of the vertebrate myc gene family which is also present in the deduced protein sequences of the Drosophila achaete-scute gene complex. Sequence analysis of the m8 transcription unit in the E(spl)D mutation revealed several DNA lesions. One of the lesions is a deletion in the region upstream of the transcription start site. Another lesion is a deletion in the coding region that leads to a shorter protein which, in addition, differs in its carboxy-terminal end from the wild-type protein by the presence of nine amino acids.

Magnetic Fields at Neptune

Abstract: The Voyager 2 magnetic field experiment discovered a complex and powerful magnetic field in Neptune, as well as an associated magnetosphere and magnetic tail. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar. The auroral zones are probably located far from the rotation poles, and may possess complex geometry. The Neptune rings and all its known moons are imbedded deep within the magnetosphere (except for Nereid, which is outside when it lies sunward of the planet); the radiation belts have a complex structure due to the absorption of energetic particles by the moons and rings of Neptune, as well as losses associated with the significant changes in the diurnally varying magnetosphere configuration.

Toward a Formal Language for Unsharp Properties

Abstract: Some algebraic structures of the set of all effects are investigated and summarized in the notion of a(weak) orthoalgebra. It is shown that these structures can be embedded in a natural way in lattices, via the so-calledMacNeille completion. These structures serve as a model ofparaconsistent quantum logic, orthologic, andorthomodular quantum logic.

The Hubbard model at high dimensions: some exact results and weak coupling theory

Abstract: Recently it was shown that the theory of systems of correlated fermions on a lattice is greatly simplified in the limit of high dimensions as compared to lattice systems of dimensions 2 or 3 or to isotropic systems. We discuss here the implications of the limit of high dimensions on the single particle propagator of the Hubbard model. It is shown that all the typical Fermi liquid features are retained at high dimensions. Some exact results are obtained for infinite dimension: the shape of the Fermi surface as well as the density of states at the Fermi surface are not renormalized at all by the Coulomb interaction as long as the symmetry of the system is not broken. The self-consistent weak coupling theory is cast into a form which is solved numerically with very little effort.

The Development of Statement Reality Analysis

Abstract: The development of the Statement Reality Analysis (SRA) technique is described. The technique is employed to assess the credibility of witness evidence in criminal cases. An expert psychologist is appointed by the court in cases in which a child’s evidence is central in criminal proceedings. The expert interviews the child, other principals in the event, reviews the forensic evidence, attends the trial and then renders an opinion to the court of the credibility of the child’s evidence. Procedures like SRA are employed in both parts of Germany and in Sweden.

Neuroblastoma consensus deletion maps to 1p36.1-2.

Abstract: At least 70% of human neuroblastomas display cytogenetically visible aberrations in the short arm of chromosome 1. We have used a panel of probes detecting polymorphic DNA loci, most of which were derived from a library of microdissected distal 1p chromosome fragments, to compare the hybridization pattern of DNA on nine different tumors and the corresponding normal tissue. In eight of the neuroblastomas allelic loss was observed with at least two probes. The deletions were of different size. Since a consensus deletion in all eight tumors included the segment 1p36.1-2, we conclude that genetic information related to neuroblastoma tumorigenesis is located within this approximately 10 megabase segment. Previous studies have revealed the amplification of MYCN in neuroblastomas. Our study did not provide evidence for a correlation between MYCN amplification and the 1p deletion, suggesting that the two genetic alterations result from molecular mechanisms that are not directly related to each other.

The putative transposase of transposable element Ac from Zea mays L. interacts with subterminal sequences of Ac

Abstract: The Ac-specific ORFa protein, overexpressed in a baculovirus system, specifically binds to several subterminal fragments of Ac. The 11 bp long inverted repeats of the transposable element are not bound by the ORFa protein. Major ORFa protein-binding sites were delineated on 60 and 70 bp long sequence segments that lie 100 bp inside of the 5' Ac terminus and 40 bp inside of the 3' terminus respectively. Within all strongly bound fragments, and particularly in these 60 or 70 bp long segments, the hexamer motif AAACGG is repeated several times in direct or inverted orientation. The ORFa protein binds to synthetic concatemers of this motif, whereas the mutant motif AAAGGG is not complexed. Methylation of the cytosine residues in the AAACGG motif and/or its complementary strand has pronounced effects: whereas one of the two hemimethylated sequences has a higher affinity to the ORFa protein than both unmethylated and holomethylated DNAs, the other hemimethylated DNA is virtually not complexed at all. The native ORFa protein binding sites are more complex than the AAACGG sequence: certain Ac and Ds1 fragments devoid of AAACGG motifs (but containing several similar sequences) are weakly bound by the ORFa protein.

Adrenal masses: evaluation with fast gradient-echo MR imaging and Gd-DTPA-enhanced dynamic studies.

Abstract: Fast gradient-echo magnetic resonance (MR) imaging of 38 adrenal masses with proved diagnosis was performed during suspended respiration with various repetition times (TRs), echo times (TEs), and flip angles. Dynamic perfusion studies after gadolinium diethylenetriamine-pentaacetic acid (DTPA) administration were performed by repeated imaging at short time intervals. With more T2 weighting (TR = 60 msec, TE = 30 msec, and flip angle = 15 degrees), malignant tumors and pheochromocytomas had a significantly higher relative signal intensity than adenomas; overlap of signal intensity led to equivocal findings in nine cases. After administration of Gd-DTPA, adenomas showed only mild enhancement and quick washout; malignant tumors and pheochromocytomas showed strong enhancement and slower washout. Five of the nine cases that were equivocal in precontrast images could thus be correctly classified. In addition to this improved classification of adrenal masses, fast, dynamic contrast material-enhanced MR imaging resulted in a reduction in total examination time.

Flow cytometric analysis of cell proliferation dynamics in the B cell compartment of the mouse.

Abstract: Using a method which allows simultaneous flow cytometric detection of cell surface markers and 5-bromo-2'-deoxyuridine (BrdU) incorporation, the distribution and proliferative behavior of B lineage subpopulations was studied in intact adult mice. In the bone marrow we could define two subsets of B cells on the basis of differential expression of the pan-B cell marker B220 and of membrane-associated mu and delta immunoglobulin heavy chains. B220dull mu+ delta- B cells were found to emerge from rapidly dividing cells and probably represent B cells recently generated from B220dull mu- pre-B cells. In contrast, only few, if any, of the B220bright mu+ delta+ B cells were labeled with BrdU after a period of 8 days, suggesting that these cells represent long-lived B cells residing in the bone marrow. Analysis of BrdU-incorporation into splenic B cells showed that only 20% of these cells had gone through cell division during the preceding 8 days. Almost none of the B cells in the peritoneum, a large fraction of which belongs to the Ly1 B subset, were labeled with BrdU over a period of 7 days in 8-month-old animals.

Rapid induction of transcription of unrearranged S gamma 1 switch regions in activated murine B cells by interleukin 4.

Abstract: The distribution of immunoglobulin isotypes in activated B lymphocytes can be modulated by interleukin 4 (IL4), which enhances IgG1 and suppresses IgG3. We show here that IL4 induces transcription of the region 5' adjacent to the s gamma 1 switch region within hours after onset of activation of B cells by bacterial lipopolysaccharide (LPS). Transcripts of 1.7 and 3.2 kb size containing sequences of the region 5' of s gamma 1 are detected. This transcription precedes class switch recombination between s mu and s gamma 1 and reflects the rapid opening of the s gamma 1 region as induced by IL4. This suggests that IL4 directs class switching to IgG1 by opening the s gamma 1 switch region, thus making it accessible for switch recombination.

Isolation and molecular analysis of the maize P locus.

Abstract: The maize P locus is involved in the synthesis of a red flavonoid pigment in the pericarp, cob and other floral tissues. The tissue-specific pattern of expression of certain P alleles suggests that P may be a complex locus, with more than one functional unit. The P-VV allele, which specifies variegated pericarp and variegated cob, however, shows that insertion and excision of the transposable element Ac affects both pericarp and cob expression as though cob and pericarp pigmentation are controlled by a single gene. Using Ac as a transposon tag, we have isolated 34 kb of genomic DNA from the P-VV and P-RR allele. The cloned DNA contains two 5.8 kb cross-hybridizing regions, in direct orientation relative to each other, separated by 6.6 kb of intervening DNA. A sequence motif of 250 bp is repeated at three locations within the cloned region: once within each of the 5.8 kb repeats, and once outside the 5.8 kb repeats. DNA fragments flanking the Ac element detect five transcripts in RNA from wild type (P-RR) that are absent from mutant (P-VV) tissues. To localize the transcribed sequences, DNA probes spanning the 34 kb of cloned DNA were used in Northern analysis of RNA from mutant and wild-type kernels. The results suggest the presence of a single transcriptional unit located primarily within the DNA between the 5.8 kb repeats. The five RNAs transcribed from this region may be formed by alternative splicing. The size of the P gene derived from the length of the transcribed region seems much smaller than the gene size estimated from Ac-induced P-VV mutations.

Pre-existing neuronal pathways in the developing optic lobes of Drosophila.

Abstract: We have identified a set of larval neurones in the developing adult optic lobes of Drosophila by selectively labelling cells that have undergone only a few mitoses. A cluster of three cells is located in each of the optic lobes near the insertion site of the optic stalk. Their axons fasciculate with fibres of the larval optic nerve, the Bolwig's nerve, and then form part of the posterior optic tract. These cells are likely to be first order interneurones of the larval visual system. Unlike the Bolwig's nerve, they persist into the adult stage. The possibility of a pioneering function of the larval visual system during formation of the adult optic lobe neuropil is discussed.

The determination of the past and the future of a physical system in quantum mechanics

Abstract: The determination of the past and the future of a physical system are complementary aims of measurements An optimal determination of the past of a system can be achieved by an informationally complete set of physical quantities Such a set is always strongly noncommutative An optimal determination of the future of a physical system can be obtained by a Boolean complete set of quantities The two aims can be reconciled to a reasonable degree with using unsharp measurements

General static axisymmetric solution of Einstein's vacuum field equations in prolate spheroidal coordinates.

Abstract: A solution of Einstein's vacuum field equations is presented explicitly in Eqs. (22), (28), and (43). This completes our stationary metric presented previously and therefore gives the exact solution to the problem of describing the exterior field of rotating deformed bodies. The metric given here is equivalent to the general Weyl metric; however, we use prolate spheroidal coordinates for conve- nience. We investigate the Newtonian and the relativistic (Geroch-Hansen) multipole moments of the solution and conclude that it describes the exterior gravitational field of a static axisymmetric mass distribution.

Rupture of central-force lattices

Abstract: We study numerically the rupture of elastic lattices consisting of fragile elastic springs which can freely rotate around nodes. All bonds are given an identical force constant but the threshold force for which they break is randomly attributed to each bond according to a uniform probability distribution between 0 and 1. We analyse the overall force-displacement characteristics of the lattices and other physical parameters as function of lattice size. Various scaling relations are found. Finally, we found evidence for a multifractal distribution of forces at the ultimate stage of the rupture Nous etudions numeriquement la rupture de treillis reticules elastiques dont les liens sont elastiques-fragiles. Tous les liens ont une meme raideur, mais une force critique de rupture distribuee aleatoirement de facon uniforme entre 0 et 1. Nous analysons la caracteristique globale moyenne force-deplacement ainsi que d'autres parametres physiques en fonction de la taille du systeme. Nous presentons des relations d'echelle liant ces quantites. Finalement, nous montrons que la distribution des forces est multifractale au seuil ultime de rupture du reseau

Sequences near the termini are required for transposition of the maize transposon Ac in transgenic tobacco plants.

Abstract: Deletion derivatives of the maize transposable element Activator (Ac) were constructed in vitro and inserted into a kanamycin resistance gene. These constructions were then introduced into tobacco protoplasts derived from plants previously transformed with Ac. The ability of each deletion derivative to excise was measured by whether or not kanamycin-resistant tobacco calli were recovered. This allowed us to determine the length of DNA present at each terminus that is required to respond to the products expressed by the Ac element present in the genome. We show that around 200 base pairs (bp) are required at both ends for excision to occur at wild-type levels. When between 100 and 200 bp were retained at one of the ends, reduced frequencies of excision were detected. With less than 100 bp remaining at either end, no excision was detected. In addition, we show that although similar lengths of DNA are required at each terminus, the termini are not interchangeable. The significance of these data is discussed with respect to the protein(s) which interact(s) with the termini of Ac.