Showing papers by "University of Konstanz published in 2001"

A faster algorithm for betweenness centrality

Abstract: Motivated by the fast‐growing need to compute centrality indices on large, yet very sparse, networks, new algorithms for betweenness are introduced in this paper. They require O(n + m) space and run in O(nm) and O(nm + n2 log n) time on unweighted and weighted networks, respectively, where m is the number of links. Experimental evidence is provided that this substantially increases the range of networks for which centrality analysis is feasible. The betweenness centrality index is essential in the analysis of social networks, but costly to compute. Currently, the fastest known algorithms require ?(n 3) time and ?(n 2) space, where n is the number of actors in the network.

A Theory of Reciprocity

Abstract: This paper presents a formal theory of reciprocity. Reciprocity means that people reward kind actions and punish unkind ones. The theory takes into account that people evaluate the kindness of an action not only by its consequences but also by the intention underlying this action. The theory explains the relevant stylized facts of a wide range of experimental games. Among them are the ultimatum game, the gift-exchange game, a reduced best-shot game, the dictator game, the prisoner's dilemma, and public goods games. Furthermore, the theory explains why the same consequences trigger different reciprocal responses in different environments Finally the theory explains why in bilaterial interactions outcomes tend to be "fair" whereas in competitive markets even extremely unfair distributions may arise.

DNA Fragments in the Blood Plasma of Cancer Patients: Quantitations and Evidence for Their Origin from Apoptotic and Necrotic Cells

Abstract: Increased levels of DNA fragments have frequently been found in the blood plasma of cancer patients. Published data suggest that only a fraction of the DNA in blood plasma is derived from cancer cells. However, it is not known how much of the circulating DNA is from cancer or from noncancer cells. By quantitative methylation-specific PCR of the promoter region of the CDKN2A tumor suppressor gene, we were able to quantify the fraction of plasma DNA derived from tumor cells. In the plasma samples of 30 unselected cancer patients, we detected quantities of tumor DNA from only 3% to as much as 93% of total circulating DNA. We investigated possible origins of nontumor DNA in the plasma and demonstrate here a contribution of T-cell DNA in a few cases only. To investigate the possibility that plasma DNA originates from apoptotic or necrotic cells, we performed studies with apoptotic (staurosporine) and necrotic (staurosporine plus oligomycin) cells in vitro and with mice after induction of apoptotic (anti-CD95) or necrotic (acetaminophen) liver injury. Increasing amounts of DNA were found to be released in the supernatants of cells and in the blood plasma samples of treated animals. A clear discrimination of apoptotic and necrotic plasma DNA was possible by gel electrophoresis. The same characteristic patterns of DNA fragments could be identified in plasma derived from different cancer patients. The data are consistent with the possibility that apoptotic and necrotic cells are a major source for plasma DNA in cancer patients.

The automated will: Nonconscious activation and pursuit of behavioral goals.

Abstract: It is proposed that goals can be activated outside of awareness and then operate nonconsciously to guide self-regulation effectively (J. A. Bargh, 1990). Five experiments are reported in which the goal either to perform well or to cooperate was activated, without the awareness of participants, through a priming manipulation. In Experiment 1 priming of the goal to perform well caused participants to perform comparatively better on an intellectual task. In Experiment 2 priming of the goal to cooperate caused participants to replenish a commonly held resource more readily. Experiment 3 used a dissociation paradigm to rule out perceptual-construal alternative explanations. Experiments 4 and 5 demonstrated that action guided by nonconsciously activated goals manifests two classic content-free features of the pursuit of consciously held goals. Nonconsciously activated goals effectively guide action, enabling adaptation to ongoing situational demands.

Cathepsin B Acts as a Dominant Execution Protease in Tumor Cell Apoptosis Induced by Tumor Necrosis Factor

Abstract: Death receptors can trigger cell demise dependent or independent of caspases In WEHI-S fibrosarcoma cells, tumor necrosis factor (TNF) induced an increase in cytosolic cathepsin B activity followed by death with apoptotic features Surprisingly, this process was enhanced by low, but effectively inhibiting, concentrations of pan-caspase inhibitors Contrary to caspase inhibitors, a panel of pharmacological cathepsin B inhibitors, the endogenous cathepsin inhibitor cystatin A as well as antisense-mediated depletion of cathepsin B rescued WEHI-S cells from apoptosis triggered by TNF or TNF-related apoptosis-inducing ligand Thus, cathepsin B can take over the role of the dominant execution protease in death receptor-induced apoptosis The conservation of this alternative execution pathway was further examined in other tumor cell lines Here, cathepsin B acted as an essential downstream mediator of TNF-triggered and caspase-initiated apoptosis cascade, whereas apoptosis of primary cells was only minimally dependent on cathepsin B These data imply that cathepsin B, which is commonly overexpressed in human primary tumors, may have two opposing roles in malignancy, reducing it by its proapoptotic features and enhancing it by its known facilitation of invasion

Transactional Information Systems: Theory, Algorithms, and the Practice of Concurrency Control and Recovery

Abstract: Transactional Information Systems is the long-awaited, comprehensive work from leading scientists in the transaction processing field. Weikum and Vossen begin with a broad look at the role of transactional technology in today's economic and scientific endeavors, then delve into critical issues faced by all practitioners, presenting today's most effective techniques for controlling concurrent access by multiple clients, recovering from system failures, and coordinating distributed transactions. The authors emphasize formal models that are easily applied across fields, that promise to remain valid as current technologies evolve, and that lend themselves to generalization and extension in the development of new classes of network-centric, functionally rich applications. This book's purpose and achievement is the presentation of the foundations of transactional systems as well as the practical aspects of the field what will help you meet today's challenges. * Provides the most advanced coverage of the topic available anywhere--along with the database background required for you to make full use of this material. * Explores transaction processing both generically as a broadly applicable set of information technology practices and specifically as a group of techniques for meeting the goals of your enterprise. * Contains information essential to developers of Web-based e-Commerce functionality--and a wide range of more "traditional" applications. * Details the algorithms underlying core transaction processing functionality. Table of Contents PART ONE - BACKGROUND AND MOTIVATION Chapter 1 What Is It All About? Chapter 2 Computational Models PART TWO - CONCURRENCY CONTROL Chapter 3 Concurrency Control: Notions of Correctness for the Page Model Chapter 4 Concurrency Control Algorithms Chapter 5 Multiversion Concurrency Control Chapter 6 Concurrency Control on Objects: Notions of Correctness Chapter 7 Concurrency Control Algorithms on Objects Chapter 8 Concurrency Control on Relational Databases Chapter 9 Concurrency Control on Search Structures Chapter 10 Implementation and Pragmatic Issues PART THREE - RECOVERY Chapter 11 Transaction Recovery Chapter 12 Crash Recovery: Notion of Correctness Chapter 13 Page Model Crash Recovery Algorithms Chapter 14 Object Model Crash Recovery Chapter 15 Special Issues of Recovery Chapter 16 Media Recovery Chapter 17 Application Recovery PART FOUR - COORDINATION OF DISTRIBUTED TRANSACTIONS Chapter 18 Distributed Concurrency Control Chapter 19 Distributed Transaction Recovery PART FIVE - APPLICATIONS AND FUTURE PERSPECTIVES Chapter 20 What Is Next?

Fleeting images: a new look at early emotion discrimination.

Abstract: The visual brain quickly sorted stimuli for emotional impact despite high-speed presentation ~ 3o r 5p er s !in a sustained, serial torrent of 700 complex pictures. Event-related potentials, recorded with a dense electrode array, showed selective discrimination of emotionally arousing stimuli from less affective content. Primary sources of this activation were over the occipital cortices, extending to right parietal cortex, suggesting a processing focus in the posterior visual system. Emotion discrimination was independent of formal pictorial properties ~color, brightness, spatial frequency, and complexity!. The data support the hypothesis of a very short-term conceptual memory store ~M. C. Potter, 1999!—shown here to include a fleeting but reliable assessment of affective meaning.

Quantum State Reconstruction of the Single-Photon Fock State

Abstract: We have reconstructed the quantum state of optical pulses containing single photons using the method of phase-randomized pulsed optical homodyne tomography. The single-photon Fock state 1> was prepared using conditional measurements on photon pairs born in the process of parametric down-conversion. A probability distribution of the phase-averaged electric field amplitudes with a strongly non-Gaussian shape is obtained with the total detection efficiency of (55+/-1)%. The angle-averaged Wigner function reconstructed from this distribution shows a strong dip reaching classically impossible negative values around the origin of the phase space.

Self-regulation of goal-setting: Turning free fantasies about the future into binding goals.

Abstract: Fantasy realization theory states that when people contrast their fantasies about a desired future with reflections on present reality, a necessity to act is induced that leads to the activation and use of relevant expectations. Strong goal commitment arises in light of favorable expectations, and weak goal commitment arises in light of unfavorable expectations. To the contrary, when people only fantasize about a desired future or only reflect on present reality, expectancy-independent moderate goal commitment emerges. Four experiments pertaining to various life domains supported these hypotheses. Strength of goal commitment was assessed in cognitive (e.g., making plans), affective (e.g., felt attachment), and behavioral terms (e.g., effort expenditure, quality of performance). Implications for theories on goal setting and goal striving are discussed.

Comparative genomics provides evidence for an ancient genome duplication event in fish.

Abstract: There are approximately 25 000 species in the division Teleostei and most are believed to have arisen during a relatively short period of time ca. 200 Myr ago. The discovery of 'extra' Hox gene clusters in zebrafish (Danio rerio), medaka (Oryzias latipes), and pufferfish (Fugu rubripes), has led to the hypothesis that genome duplication provided the genetic raw material necessary for the teleost radiation. We identified 27 groups of orthologous genes which included one gene from man, mouse and chicken, one or two genes from tetraploid Xenopus and two genes from zebrafish. A genome duplication in the ancestor of teleost fishes is the most parsimonious explanation for the observations that for 15 of these genes, the two zebrafish orthologues are sister sequences in phylogenies that otherwise match the expected organismal tree, the zebrafish gene pairs appear to have been formed at approximately the same time, and are unlinked. Phylogenies of nine genes differ a little from the tree predicted by the fish-specific genome duplication hypothesis: one tree shows a sister sequence relationship for the zebrafish genes but differs slightly from the expected organismal tree and in eight trees, one zebrafish gene is the sister sequence to a clade which includes the second zebrafish gene and orthologues from Xenopus, chicken, mouse and man. For these nine gene trees, deviations from the predictions of the fish-specific genome duplication hypothesis are poorly supported. The two zebrafish orthologues for each of the three remaining genes are tightly linked and are, therefore, unlikely to have been formed during a genome duplication event. We estimated that the unlinked duplicated zebrafish genes are between 300 and 450 Myr. Thus, genome duplication could have provided the genetic raw material for teleost radiation. Alternatively, the loss of different duplicates in different populations (i.e. 'divergent resolution') may have promoted speciation in ancient teleost populations.

Transitions of muscle fiber phenotypic profiles.

Abstract: Skeletal muscle is a complex, versatile tissue composed of a large variety of functionally diverse fiber types. The overall properties of a muscle largely result from a combination of the individual properties of its different fiber types and their proportions. Skeletal muscle fiber types, which can be delineated according to various parameters, for example, myofibrillar protein isoforms, metabolic enzyme profiles, and structural and contractile properties, are not fixed units but are capable of responding to altered functional demands and a variety of signals by changing their phenotypic profiles. This brief review summarizes our current understanding of the delineation of fiber types, modulations of their phenotypic profiles as induced under various conditions, and potential mechanisms involved in these transitions.

Structure-function relationship of cytokine induction by lipoteichoic acid from Staphylococcus aureus.

Abstract: Lipoteichoic acids (LTAs) have been proposed as putative Gram-positive immunostimulatory counterparts to Gram-negative lipopolysaccharides. However, LTA from Staphylococcus aureus, the clinically most frequent Gram-positive pathogen, was inactive after purification. Here, a novel isolation procedure to prepare pure (>99%) biologically active LTA, allowing the first structural analysis by nuclear magnetic resonance and mass spectrometry, is described. A comparison with LTA purified by standard techniques revealed that alanine substituents are lost during standard purification, resulting in attenuated cytokine induction activity. In line with this finding, hydrolysis of alanine substituents of active LTA decimated cytokine induction. LTA represents a major immunostimulatory component of S. aureus.

Entropy dissipation methods for degenerate parabolic problems and generalized Sobolev inequalities

Abstract: We analyse the large-time asymptotics of quasilinear (possibly) degenerate parabolic systems in three cases: 1) scalar problems with confinement by a uniformly convex potential, 2) unconfined scalar equations and 3) unconfined systems. In particular we are interested in the rate of decay to equilibrium or self-similar solutions. The main analytical tool is based on the analysis of the entropy dissipation. In the scalar case this is done by proving decay of the entropy dissipation rate and bootstrapping back to show convergence of the relative entropy to zero. As by-product, this approach gives generalized Sobolev-inequalities, which interpolate between the Gross logarithmic Sobolev inequality and the classical Sobolev inequality. The time decay of the solutions of the degenerate systems is analyzed by means of a generalisation of the Nash inequality. Porous media, fast diffusion, p-Laplace and energy transport systems are included in the considered class of problems. A generalized Csiszar–Kullback inequality allows for an estimation of the decay to equilibrium in terms of the relative entropy.

Segregation of nitrogen fixation and oxygenic photosynthesis in the marine cyanobacterium Trichodesmium.

Abstract: In the modern ocean, a significant amount of nitrogen fixation is attributed to filamentous, nonheterocystous cyanobacteria of the genus Trichodesmium. In these organisms, nitrogen fixation is confined to the photoperiod and occurs simultaneously with oxygenic photosynthesis. Nitrogenase, the enzyme responsible for biological N2 fixation, is irreversibly inhibited by oxygen in vitro. How nitrogenase is protected from damage by photosynthetically produced O2 was once an enigma. Using fast repetition rate fluorometry and fluorescence kinetic microscopy, we show that there is both temporal and spatial segregation of N2 fixation and photosynthesis within the photoperiod. Linear photosynthetic electron transport protects nitrogenase by reducing photosynthetically evolved O2 in photosystem I (PSI). We postulate that in the early evolutionary phase of oxygenic photosynthesis, nitrogenase served as an electron acceptor for anaerobic heterotrophic metabolism and that PSI was favored by selection because it provided a micro-anaerobic environment for N2 fixation in cyanobacteria.

Do civil and political repression really boost foreign direct investments

Abstract: Multinational enterprises are often accused to have a preference for investing in countries in which the working populations' civil and political rights are largely disregarded. This paper presents an empirical investigation of the popular "political repression boosts FDI" hypothesis and arrives at the conclusion that the hypothesis is not supported. On the contrary, multinational enterprises rather appear to be attracted by countries in which civil and political freedom is respected. Our finding thus supports the notion that there is a positive relationship between democracy and economic growth.

Cellular compartmentation of nickel in the hyperaccumulators Alyssum lesbiacum, Alyssum bertolonii and Thlaspi goesingense

Abstract: Nickel uptake and cellular compartmentation were investigated in three Ni hyperaccumulators: Alyssum bertolonii (Desv), Alyssum lesbiacum (Candargy) and Thlaspi goesingense (Hal acsy). The three species showed similar hyperaccumulation of Ni, but T. goesingense was less tolerant to Ni than the two Alyssum species. An addition of 500 mg Ni kg � 1 to a nutrient-rich growth medium significantly increased shoot biomass of all three species, suggesting that the Ni hyperaccumulators have a higher requirement for Ni than normal plants. Energy-dispersive X-ray microanalysis (EDXA) was performed on frozen- hydrated tissues of leaves (all species) and stems ( Alyssum only). In all species analysed, Ni was dis- tributed preferentially in the epidermal cells, most likely in the vacuoles, of the leaves and stems. In stems, there was a second peak of Ni in the bound- ary cells between the cortical parenchyma and the vascular cylinder. The non-glandular trichomes on the leaf surfaces of the two Alyssum species were highly enriched with Ca, but contained little Ni except in the base. In the leaves of T. goesingense, the large elongated epidermal cells contained more Ni than the cells of the stomatal complexes. The role of cel- lular compartmentation in Ni hyperaccumulation is discussed.

Lipopolysaccharide and ceramide docking to CD14 provokes ligand‐specific receptor clustering in rafts

Abstract: The glycosylphosphatidylinositol-anchored receptor CD14 plays a major role in the inflammatory response of monocytes to lipopolysaccharide. Here, we describe that ceramide, a constituent of atherogenic lipoproteins, binds to CD14 and induces clustering of CD14 to co-receptors in rafts. In resting cells, CD14 was associated with CD55, the Fcgamma-receptors CD32 and CD64 and the pentaspan CD47. Ceramide further recruited the complement receptor 3 (CD11b/CD18) and CD36 into proximity of CD14. Lipopolysaccharide, in addition, induced co-clustering with Toll-like receptor 4, Fcgamma-RIIIa (CD16a) and the tetraspanin CD81 while CD47 was dissociated. The different receptor complexes may be linked to ligand-specific cellular responses initiated by CD14.

The role of haustoria in sugar supply during infection of broad bean by the rust fungus Uromyces fabae.

Abstract: Biotrophic plant pathogenic fungi differentiate specialized infection structures within the living cells of their host plants. These haustoria have been linked to nutrient uptake ever since their discovery. We have for the first time to our knowledge shown that the flow of sugars from the host Vicia faba to the rust fungus Uromyces fabae seems to occur largely through the haustorial complex. One of the most abundantly expressed genes in rust haustoria, the expression of which is negligible in other fungal structures, codes for a hexose transporter. Functional expression of the gene termed HXT1 in Saccharomyces cerevisiae and Xenopus laevis oocytes assigned a substrate specificity for D-glucose and D-fructose and indicated a proton symport mechanism. Abs against HXT1p exclusively labeled haustoria in immunofluorescence microscopy and the haustorial plasma membrane in electron microscopy. These results suggest that the fungus concentrates this transporter in haustoria to take advantage of a specialized compartment of the haustorial complex. The extrahaustorial matrix, delimited by the plasma membranes of both host and parasite, constitutes a newly formed apoplastic compartment with qualities distinct from those of the bulk apoplast. This organization might facilitate the competition of the parasite with natural sink organs of the host.

Electrical magnetochiral anisotropy.

Abstract: Electrical conductors can be chiral, i.e., can exist in two forms where one is the other's mirror image. Thus far, no effect of chirality on magnetotransport has been observed. We argue that the electrical resistance of any chiral conductor should depend linearly both on the external magnetic field and the current through the conductor and on its handedness. We suggest two mechanisms to carry this effect and show experimentally on model systems that both are effective.

Cosmic antifriction and accelerated expansion

Abstract: We explain an accelerated expansion of the present Universe, suggested from observations of supernovae of type la at high redshift, by introducing an antifrictional force that is self-consistently exerted on the particles of the cosmic substratum. Cosmic antifriction. which is intimately related to "particle production," is shown to give rise to an effective negative pressure of the cosmic medium. While other explanations for an accelerated expansion (cosmological constant, quintessence) introduce a component of dark energy in addition to "standard" cold dark matter (CDM) we resort to a phenomenological one-component model of CDM with internal self-interactions. We demonstrate how the dynamics of the cold dark matter model with a cosmological constant may be recovered as a special case of cosmic antifriction. We discuss the connection with two-component models and obtain an attractor behavior for the ratio of the energy densities of both components which provides a possible phenomenological solution to the coincidence problem.

Investigating the microenvironments of inhomogeneous soft materials with multiple particle tracking

Abstract: We develop a multiple particle tracking technique for making precise, localized measurements of the mechanical microenvironments of inhomogeneous materials. Using video microscopy, we simultaneously measure the Brownian dynamics of roughly one hundred fluorescent tracer particles embedded in a complex medium and interpret their motions in terms of local viscoelastic response. To help overcome the inherent statistical limitations due to the finite imaging volume and limited imaging times, we develop statistical techniques and analyze the distribution of particle displacements in order to make meaningful comparisons of individual particles and thus characterize the diversity and properties of the microenvironments. The ability to perform many local measurements simultaneously allows more precise measurements even in systems that evolve in time. We show several examples of inhomogeneous materials to demonstrate the flexibility of the technique and learn new details of the mechanics of the microenvironments that small particles explore. This technique extends other microrheological methods to allow simultaneous measurements of large numbers of probe particles, enabling heterogeneous samples to be studied more effectively.

Induction of Cross-Tolerance by Lipopolysaccharide and Highly Purified Lipoteichoic Acid Via Different Toll-Like Receptors Independent of Paracrine Mediators

Abstract: Exposure of macrophages to LPS induces a state of hyporesponsiveness to subsequent stimulation with LPS termed LPS desensitization or tolerance. To date, it is not known whether similar mechanisms of macrophage refractoriness are induced on contact with components of Gram-positive bacteria. In the present study, we demonstrate that pretreatment with highly purified lipoteichoic acid (LTA) results in suppression of cytokine release on restimulation with LTA in vitro and in vivo in both C3H/HeN and C3H/HeJ mice, but not in macrophages from Toll-like receptor (TLR)-2-deficient mice. Furthermore, desensitization in response to LPS or LTA exposure also inhibits responses to the other stimulus (“cross-tolerance”), suggesting that signaling pathways shared by TLR2 and TLR4 are impaired during tolerance. Finally, we show that LPS- or LTA-induced cross-tolerance is not transferred to hyporesponsive cells cocultured with LPS/LTA-responsive macrophages, showing that soluble mediators do not suffice for tolerance induction in neighboring cells.

Electrohydrodynamic instabilities in polymer films

Abstract: We have studied the influence of electric fields on highly viscous polymer films An electrohydrodynamic (EHD) instability causes a wave pattern with a characteristic wavelength λ, leading to an array of polymer columns which span the gap of a capacitor device When represented as a master curve, the data is quantitatively described by an EHD model, without any adjustable parameters Our results suggest that EHD experiments using polymer films are well suited to study non-equilibrium pattern formation in quasi-two-dimensional systems

Do lending relationships matter?: Evidence from bank survey data in Germany

Abstract: Strong lending relationships between banks and small and medium-sized enterprises (SMEs) play a key role in the bank-based financial system of Germany. So far, they have been mainly described by the notion of a housebank and transactional features of long-term bank–customer relationships. In contrast, the present paper also considers interactional variables, which try to measure social relations between loan officer and firm manager. Using bank survey data, the relationship and interaction variables prove to affect loan prices, collateral requirements and credit availability.

Climatic warming causes regime shifts in lake food webs

Abstract: Spring clear water phases caused by grazing of zooplankton on algae are among the most spectacular and well-studied events in lake plankton dynamics. Such clear water phases are also important as windows of opportunity for recovery of aquatic vegetation and biodiversity in shallow waters. Here we use long time series from 71 shallow lakes to demonstrate that the probability of clear water phase increases with the temperature of lake water. We demonstrate that lake temperature has risen significantly over the past decades and is highly correlated with oscillations in the North Atlantic climate system. We also show a distinct climate-related shift in the timing of clear water phases in the shallow lakes as well as in an independent set of central European lakes. Simulations with a seasonally forced plankton model confirm that temperature rise is a plausible explanation for the observed changes.