Showing papers by "Bielefeld University published in 2000"

Network information flow

Abstract: We introduce a new class of problems called network information flow which is inspired by computer network applications. Consider a point-to-point communication network on which a number of information sources are to be multicast to certain sets of destinations. We assume that the information sources are mutually independent. The problem is to characterize the admissible coding rate region. This model subsumes all previously studied models along the same line. We study the problem with one information source, and we have obtained a simple characterization of the admissible coding rate region. Our result can be regarded as the max-flow min-cut theorem for network information flow. Contrary to one's intuition, our work reveals that it is in general not optimal to regard the information to be multicast as a "fluid" which can simply be routed or replicated. Rather, by employing coding at the nodes, which we refer to as network coding, bandwidth can in general be saved. This finding may have significant impact on future design of switching systems.

Nature over nurture: temperament, personality, and life span development.

Abstract: Temperaments are often regarded as biologically based psychological tendencies with intrinsic paths of development. It is argued that this definition applies to the personality traits of the five-factor model. Evidence for the endogenous nature of traits is summarized from studies of behavior genetics, parent-child relations, personality structure, animal personality, and the longitudinal stability of individual differences. New evidence for intrinsic maturation is offered from analyses of NEO Five-Factor Inventory scores for men and women age 14 and over in German, British, Spanish, Czech, and Turkish samples (N = 5,085). These data support strong conceptual links to child temperament despite modest empirical associations. The intrinsic maturation of personality is complemented by the culturally conditioned development of characteristic adaptations that express personality; interventions in human development are best addressed to these.

Algebras and Modules in Monoidal Model Categories

Abstract: In recent years the theory of structured ring spectra (formerly known as A$_{\infty}$- and E$_{\infty}$-ring spectra) has been simplified by the discovery of categories of spectra with strictly associative and commutative smash products. Now a ring spectrum can simply be defined as a monoid with respect to the smash product in one of these new categories of spectra. In this paper we provide a general method for constructing model category structures for categories of ring, algebra, and module spectra. This provides the necessary input for obtaining model categories of symmetric ring spectra, functors with smash product, $\Gamma$-rings, and diagram ring spectra. Algebraic examples to which our methods apply include the stable module category over the group algebra of a finite group and unbounded chain complexes over a differential graded algebra. 1991 Mathematics Subject Classification: primary 55U35; secondary 18D10.

Subcellular localization and speciation of nickel in hyperaccumulator and non-accumulator Thlaspi species

Abstract: The ability of Thlaspi goesingense Halacsy to hyperaccumulate Ni appears to be governed by its extraordinary degree of Ni tolerance. However, the physiological basis of this tolerance mechanism is unknown. We have investigated the role of vacuolar compartmentalization and chelation in this Ni tolerance. A direct comparison of Ni contents of vacuoles from leaves of T. goesingense and from the non-tolerant non-accumulator Thlaspi arvense L. showed that the hyperaccumulator accumulates approximately 2-fold more Ni in the vacuole than the non-accumulator under Ni exposure conditions that were non-toxic to both species. Using x-ray absorption spectroscopy we have been able to determine the likely identity of the compounds involved in chelating Ni within the leaf tissues of the hyperaccumulator and non-accumulator. This revealed that the majority of leaf Ni in the hyperaccumulator was associated with the cell wall, with the remaining Ni being associated with citrate and His, which we interpret as being localized primarily in the vacuolar and cytoplasm, respectively. This distribution of Ni was remarkably similar to that obtained by cell fractionation, supporting the hypothesis that in the hyperaccumulator, intracellular Ni is predominantly localized in the vacuole as a Ni-organic acid complex.

Suppressed molecular ionization for a class of diatomics in intense femtosecond laser fields

Abstract: It is shown that the puzzling experimental observation of suppressed molecular ionization, in intense laser fields, of ${\mathrm{O}}_{2}$, and its absence in ${\mathrm{N}}_{2}$, is a symmetry induced dynamical effect. More generally, it is predicted that the ionization signal of the class of homonuclear diatomic molecules having valence orbitals with an antibonding symmetry (e.g., ${\ensuremath{\sigma}}_{u}$, ${\ensuremath{\pi}}_{g}$) would be suppressed, but not those with a bonding symmetry (e.g., ${\ensuremath{\sigma}}_{g}$, ${\ensuremath{\pi}}_{u}$). The suppression effect can be visualized as due to an effective destructive interference between the two subwaves of the ionizing electron emerging from the two atomic centers.

Surfactant-encapsulated clusters (SECs): (DODA)20(NH4)[H3Mo57V6(NO)6O183(H2O)18], a case study.

Abstract: We present a comprehensive study of the partially reduced polyoxomolybdate [H3Mo57V6(NO)(6)O-183(H2O)(18)](21-) encapsulated in a shell of dimethyldioctadecylammonium (DODA) surfactant molecules. Treatment of an aqueous solution of (NH4)(21)[H3Mo57V6-(NO)(6)O-183(H2O)(18)]. 65H(2)O (1a) with a trichloromethane solution of the surfactant leads to instant transfer of the encapsulated complex anion into the organic phase. Results from vibrational spectroscopy, analytical ultracentrifugation, small-angle X-ray scattering, transmission electron microscopy, elemental analysis, and Langmuir compression isotherms are consistent with a single polyoxometalate core encapsulated within a shell of 20 DODA molecules. The molar mass of the supramolecular assembly is 20 249 g mol(-1) and the diameter is 3.5nm. A material with the empirical formula (DODA)(20)(NH4)[H-3-Mo57V6(NO)(6)O-183(H2O)(18)] (2) was isolated as a dark violet solid, which readily dissolves in organic solvents. Slow evaporation of solutions of 2 on solid substrates forces the hydrophobic particles to aggregate into a cubic lattice. Annealing these so-formed films at elevated temperature causes de-wetting with terrace formation similar to liquid crystals and block copolymers. Compound 2 forms a stable Langmuir monolayer at the air-water interface; Langmuir-Blodgett multilayers are readily prepared by repeated transfer of monolayers on solid substrates. The films were characterized by optical ellipsometry, Brewster angle microscopy, transmission electron microscopy, and X-ray reflectance.

Smashing subcategories and the telescope conjecture - an algebraic approach

Abstract: We prove a modified version of Ravenel's telescope conjecture. It is shown that every smashing subcategory of the stable homotopy category is generated by a set of maps between finite spectra. This result is based on a new characterization of smashing subcategories, which leads in addition to a classification of these subcategories in terms of the category of finite spectra. The approach presented here is purely algebraic; it is based on an analysis of pure-injective objects in a compactly generated triangulated category, and covers therefore also situations arising in algebraic geometry and representation theory.

Butterfly hysteresis loop and dissipative spin reversal in the S = 1/2, V15 molecular complex

Abstract: Time resolved magnetization measurements have been performed on a spin 1/2 molecular complex, so-called V15. Despite the absence of a barrier, magnetic hysteresis is observed over a time scale of several seconds. A detailed analysis in terms of a dissipative two-level model is given, in which fluctuations and splittings are of the same energy. Spin-phonon coupling leads to long relaxation times and to a particular "butterfly" hysteresis loop.

Colour deconfinement in nuclear collisions

Abstract: QCD predicts that strongly interacting matter will undergo a transition from a state of hadronic constituents to a plasma of unbound quarks and gluons. We first survey the conceptual features of this transition and its description in finite temperature lattice QCD, before we address its experimental investigation through high energy nucleus-nucleus collisions. After surveying the conditions achievable in such collisions, we discuss the possible probes to check if the produced medium in its early stages was indeed deconfined. We then elaborate the method that has emerged and the results which were obtained using the most extensively studied deconfinement probe, the suppression of charmonium production. In closing, we discuss possible corroborative information provided through the study of soft hadronic probes.

Colloidal crystals made of poly( N -isopropylacrylamide) microgel particles

Abstract: Poly (N-isopropylacrylamide) microgel particles are found to form colloidal crystals similar to those occurring in typical hard-sphere colloids like poly(methylmethacrylate) beads. Samples made of particles with different crosslinker concentrations are investigated and their deswelling ratio is determined using dynamic light scattering. Small-angle neutron scattering data are also presented and analysed in terms of a face-centred-cubic crystal structure. The characteristic length, a, of the elementary cell is found to be 535 +/- 16 and 495 +/- 15 nm for the two systems investigated. This leads to particle radii of 189 +/- 6 and 175 +/- 5 nm, respectively. These values compare well to the radii determined using several different methods.

Antisense Suppression of 2-Cysteine Peroxiredoxin in Arabidopsis Specifically Enhances the Activities and Expression of Enzymes Associated with Ascorbate Metabolism But Not Glutathione Metabolism

Abstract: The aim of this study was to characterize the effect of decreased 2-cysteine peroxiredoxin (2-CP) on the leaf anti-oxidative system in Arabidopsis. At three stages of leaf development, two lines of transgenic Arabidopsis mutants with decreased contents of chloroplast 2-CP were compared with wild type and a control line transformed with an empty vector. Glutathione contents and redox state were similar in all plants, and no changes in transcript levels for enzymes involved in glutathione metabolism were observed. Transcript levels for chloroplastic glutathione peroxidase were much lower than those for 2-CP, and both cytosolic and chloroplastic glutathione peroxidase were not increased in the mutants. In contrast, the foliar ascorbate pool was more oxidized in the mutants, although the difference decreased with plant age. The activities of thylakoid and stromal ascorbate peroxidase and particularly monodehydroascorbate reductase were increased as were transcripts for these enzymes. No change in dehydroascorbate reductase activity was observed, and effects on transcript abundance for glutathione reductase, catalase, and superoxide dismutase were slight or absent. The results demonstrate that 2-CP forms an integral part of the anti-oxidant network of chloroplasts and is functionally interconnected with other defense systems. Suppression of 2-CP leads to increased expression of other anti-oxidative genes possibly mediated by increased oxidation state of the leaf ascorbate pool.

Heavy quark potentials in quenched QCD at high temperature

Abstract: Heavy quark potentials are investigated at high temperatures. The temperature range covered by the analysis extends from $T$ values just below the deconfinement temperature up to about ${4T}_{c}$ in the deconfined phase. We simulated the pure gauge sector of QCD on lattices with temporal extents of 4, 6, and 8, with spatial volumes of ${32}^{3}.$ On the smallest lattice a tree level improved action was employed, while in the other two cases the standard Wilson action was used. Below ${T}_{c}$ we find a temperature-dependent logarithmic term contributing to the confinement potential, and observe a string tension which decreases with rising temperature but retains a finite value at the deconfinement transition. Above ${T}_{c}$ the potential is Debye screened; however, simple perturbative predictions do not apply.

Interpretation of momentum distribution of recoil ions from laser induced nonsequential double ionization

Abstract: We show that the recently reported momentum distribution of recoil ions from laser induced nonsequential double ionization can be interpreted as a combined effect of interelectron correlation and final state field interaction ("Volkov dressing") of the two outgoing electrons. We also find a cutoff formula for the recoil momentum that gives the maximum momenta observed in the experiments.

Phenotypic and molecular characterization of conjugative antibiotic resistance plasmids isolated from bacterial communities of activated sludge

Abstract: In order to isolate antibiotic resistance plasmids from bacterial communities found in activated sludge, derivatives of the 3-chlorobenzoate-degrading strain Pseudomonas sp. B13, tagged with the green fluorescent protein as an identification marker, were used as recipients in filter crosses. Transconjugants were selected on agar plates containing 3-chlorobenzoate as the sole carbon source and the antibiotic tetracycline, streptomycin or spectinomycin, and were recovered at frequencies in the range of 10−5 to 10−8 per recipient. A total of 12 distinct plasmids, designated pB1–pB12, was identified. Their sizes ranged between 41 to 69 kb and they conferred various patterns of antibiotic resistance on their hosts. Two of the plasmids, pB10 and pB11, also mediated resistance to inorganic mercury. Seven of the 12 plasmids were identified as broad-host-range plasmids, displaying extremely high transfer frequencies in filter crosses, ranging from 10−1 to 10−2 per recipient cell. Ten of the 12 plasmids belonged to the IncP incompatibility group, based on replicon typing using IncP group-specific PCR primers. DNA sequencing of PCR amplification products further revealed that eight of the 12 plasmids belonged to the IncPβ subgroup, whereas two plasmids were identified as IncPα plasmids. Analysis of the IncP-specific PCR products revealed considerable differences among the IncPβ plasmids at the DNA sequence level. In order to characterize the gene “load” of the IncP plasmids, restriction fragments were cloned and their DNA sequences established. A remarkable diversity of putative proteins encoded by these fragments was identified. Besides transposases and proteins involved in antibiotic resistance, two putative DNA invertases belonging to the Din family, a methyltransferase of a type I restriction/modification system, a superoxide dismutase, parts of a putative efflux system belonging to the RND family, and proteins of unknown function were identified.

Phosphaalkenes with Inverse Electron Density

Abstract: This review gives an account of the syntheses, structures, and properties of phosphaalkenes (RP)-P-1=(CRR3)-R-2 with an inverse electron distribution at the P-C double bond (Pdelta-Cdelta+). The chemical reactivity of compounds of this type is novel and quite surprising compared to the chemistry of "classically polarized" phosphaalkenes (Pdelta+Cdelta-).

Letter: The Use of 2-[(2E)-3-(4-Tert-Butylphenyl)-2-Methylprop-2-Enylidene]Malononitrile as a Matrix for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry:

Abstract: 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB, dicyano.tert-butyl …) has proven to be an excellent nonprotic matrix for very labile compounds, especially for substituted fullerenes. This is mainly due to its extremely low onset of ion production. This matrix works mainly as an electron transfer agent, i.e. the ions produced are radical anions or cations, respectively. It works equally well to transfer evaporation energy to charged oligomers and with proton labile compounds (not shown here).