Showing papers by "Bielefeld University published in 2002"

Time-resolved atomic inner-shell spectroscopy

Abstract: The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the time domain with attosecond resolution. We have measured a lifetime of 7.9(-0.9)(+1.0) fs of M-shell vacancies of krypton in such a pump-probe experiment.

Attitudes and Attitude Change

Abstract: Attitudes and attitude change remain core topics of contemporary social psychology. This selective review emphasizes work published from 2005 to 2009. It addresses constructionist and stable-entity conceptualizations of attitude, the distinction between implicit and explicit measures of attitude, and implications of the foregoing for attitude change. Associative and propositional processes in attitude change are considered at a general level and in relation to evaluative conditioning. The role of bodily states and physical perceptions in attitude change is reviewed. This is followed by an integrative perspective on processing models of persuasion and the consideration of meta-cognitions in persuasion. Finally, effects of attitudes on information processing, social memory, and behavior are highlighted. Core themes cutting across the areas reviewed are attempts at integrative theorizing bringing together formerly disparate phenomena and viewpoints.

Secure network coding

Abstract: Recent work on network coding renders a new view on multicasting in a network In the paradigm of network coding, the nodes in a network are allowed to encode the information received from the input links The usual function of switching at a node is a special case of network coding The advantage of network coding is that the full capacity of the network can be utilized In this paper, we propose a new model which incorporates network coding and information security Specifically, a collection of subsets of links is given, and a wiretapper is allowed to access any one (but not more than one) of these subsets without being able to obtain any information about the message transmitted Our model includes secret sharing as a special case We present a construction of secure linear network codes provided a certain graph-theoretic sufficient condition is satisfied

Strong converse for identification via quantum channels

Abstract: We present a simple proof of the strong converse for identification via discrete memoryless quantum channels, based on a novel covering lemma. The new method is a generalization to quantum communication channels of Ahlswede's (1979, 1992) approach to classical channels. It involves a development of explicit large deviation estimates to the case of random variables taking values in self-adjoint operators on a Hilbert space. This theory is presented separately in an appendix, and we illustrate it by showing its application to quantum generalizations of classical hypergraph covering problems.

QCD thermal phase transition in the presence of a small chemical potential

Abstract: We propose a new method to investigate the thermal properties of QCD with a small quark chemical potential mu. Derivatives of quark and gluonic observables with respect to mu are computed at mu=0 for two flavors of p4 improved staggered fermions with ma=0.1,0.2 on a 16(3)x4 lattice, and used to calculate the leading order Taylor expansion in mu of the location of the pseudocritical point about mu=0. This expansion should be well behaved for the small values of mu(q)/T(c)similar to0.1 relevant for BNL RHIC phenomenology, and predicts a critical curve T-c(mu) in reasonable agreement with estimates obtained using exact reweighting. In addition, we contrast the case of isoscalar and isovector chemical potentials, quantify the effect of munot equal0 on the equation of state, and comment on the complex phase of the fermion determinant in QCD with munot equal0.

Steering Attosecond Electron Wave Packets with Light

Abstract: Photoelectrons excited by extreme ultraviolet or x-ray photons in the presence of a strong laser field generally suffer a spread of their energies due to the absorption and emission of laser photons. We demonstrate that if the emitted electron wave packet is temporally confined to a small fraction of the oscillation period of the interacting light wave, its energy spectrum can be up- or downshifted by many times the laser photon energy without substantial broadening. The light wave can accelerate or decelerate the electron's drift velocity, i.e., steer the electron wave packet like a classical particle. This capability strictly relies on a sub-femtosecond duration of the ionizing x-ray pulse and on its timing to the phase of the light wave with a similar accuracy, offering a simple and potentially single-shot diagnostic tool for attosecond pump-probe spectroscopy.

Efficient electrotransformation of corynebacterium diphtheriae with a mini-replicon derived from the Corynebacterium glutamicum plasmid pGA1.

Abstract: Efficient transformation of the human pathogen Corynebacterium diphtheriae was achieved with novel cloning vectors consisting of a mini-replicon from the cryptic C. glutamicum plasmid pGA1 as well as of the aph(3')-IIa or tetA(Z ) antibiotic resistance genes. Plasmid-containing transformants of C. diphtheriae were recovered at frequencies ranging from 1.3 x 10(5) to 4.8 x 10(6) colony forming units (cfu)/microg of plasmid DNA. Vector DNA was directly transferred from Escherichia coli into C. diphtheriae with frequencies up to 5.6 x 10(5) cfu/microg of plasmid DNA. On the basis of the pGA1 mini-replicon, an expression vector system was established for C. diphtheriae by means of the P(tac) promoter and the green fluorescent reporter protein. In addition, other commonly used vector systems from C. glutamicum, including the pBL1 and pHM1519 replicons, and the sacB conditionally lethal selection marker from Bacillus subtilis, were shown to be functional in C. diphtheriae. Thus, the ability to apply the standard methods of C. glutamicum recombinant DNA technology will greatly facilitate the functional analysis of the recently completed C. diphtheriae genome sequence.

Network coding and error correction

Abstract: We introduce network error-correcting codes for error correction when a source message is transmitted to a set of receiving nodes on a network. The usual approach in existing networks, namely link-by-link error correction, is a special case of network error correction. The network generalizations of the Hamming bound and the Gilbert-Varshamov bound are derived.

Characteristic patterns of chronic and dynamic photoinhibition of different functional groups in a Mediterranean ecosystem

Abstract: To analyse characteristic patterns of dynamic and chronic photoinhibition within a plant community, a new technique is proposed, which is based on the long- and short-term recovery time of maximum photochemical efficiency of PSII (F v/F m) after environmental stress. Chronic photoinhibition was determined as a sustainable decrease in predawn F v/F m, occurring during periods of prolonged stress, whereas dynamic photoinhibition was assessed from the fully reversible diurnal decline in F v/F m. Applied to a Mediterranean macchia ecosystem, this definition allowed the characterization of typical annual patterns of chronic and dynamic photoinhibition. Both types of photoinhibition were highest during summer drought. However, differences emerged among the ten dominant macchia species regarding their susceptibility to chronic photoinhibition during different seasons. Chronic and dynamic photoinhibition were dependent on leaf orientation. Semi-deciduous species avoided enhanced chronic photoinhibition through a reduction of excessive light interception by vertical foliage orientation during summer, whereas evergreen sclerophylls did not exhibit pronounced structural photoprotective mechanisms. Chronic and total photoinhibition were significantly correlated with predawn and midday water potentials, respectively, and a grouping of the macchia species into three functional groups is proposed according to this relationship.

A possible stress physiological role of abscisic acid conjugates in root‐to‐shoot signalling

Abstract: Abscisic acid (ABA) conjugates, predominantly their glucose esters, have recently been shown to occur in the xylem sap of different plants. Under stress conditions, their concentration can rise substantially to levels that are higher than the concentration of free ABA. External ABA conjugates cannot penetrate apoplastic barriers in the root. They have to be hydrolysed by apoplastic enzymes in the root cortex. Liberated free ABA can then be redistributed to the root symplast and dragged directly across the endodermis to the stele. Endogenous ABA conjugates are formed in the cytosol of root cells, transported symplastically to the xylem parenchyma cells and released to the xylem vessels. The mechanism of release is unknown; it may include the action of ABC-transporters. Because of its extremely hydrophilic properties, ABA-GE is translocated in the xylem of the stem without any loss to the surrounding parenchyma. After arrival in the leaf apoplast, transporters for ABA-GE in the plasmalemma have to be postulated to redistribute the conjugates to the mesophyll cells. Additionally, apoplastic esterases can cleave the conjugate and release free ABA to the target cells and tissues. The activity of these esterases is increased when barley plants are subjected to salt stress.

The "Double Face" of Lifelong Learning: Two Analytical Perspectives on a "Silent Revolution.".

Abstract: This article focuses on the tensions between two perspectives on lifelong learning. Perspective I examines the social framework for lifelong learning. In perspective II we put forward our own theoretical view on ‘education in the life span’, namely the concept of biographical learning, and outline the idea of the ‘biographicity’ of social learning processes. This discussion is set within the context of the globalising imperatives and international discourses of lifelong learning. In the conclusion, we suggest the main perspectives and desiderata for research

Manipulation of the oocyte: possible damage to the spindle apparatus.

Abstract: Oocytes are structured, polarized cells. For high developmental potential, it is essential that the distribution of organelles and molecules, and the function of meiotic spindles remain intact during handling of oocytes in assisted reproduction. Spindles are dynamic cell organelles. Spindle formation depends on activity of motor proteins, energy supply and temperature. Disturbances in spindle function may predispose oocytes to aneuploidy or maturation arrest. Thus, perturbation of the cytoskeletal integrity of oocytes may critically influence the fate of the embryo. Recently, enhanced polarizing microscopy has been developed for non-invasive analysis of spindle morphology in living mammalian oocytes. Chemically induced dynamic alterations have been characterized in the spindle in individual mouse oocytes and it has been shown that spindle aberrations are predictive of risks for non-disjunction. Spindle imaging identified adverse, irreversible effects of handling in living human oocytes (for instance, the extreme susceptibility of human oocytes to cooling). Also, oocyte immaturity may be detected. Selection of metaphase II oocytes and an injection site for intracytoplasmic sperm injection (ICSI) that avoids spindle damage may increase the yield of euploid embryos. The detection of genetic, environmentally induced, or treatment-related defects in oocyte maturation by non-invasive spindle imaging can improve quality control and assist in the selection of morphologically normal oocytes for assisted reproduction.

Phosphorus Heterocycles: From Laboratory Curiosities to Ligands in Highly Efficient Catalysts

Abstract: Phosphabenzenes and phosphaferrocenes were among the first compounds with P-C multiple bonds. For nearly 30 years the chemistry of these molecules was essentially a domain left to basic researchers. Recently, however, it was reported that transition metal complexes with phosphabenzene and phosphaferrocene ligands exhibit remarkable potential as catalysts. Catalysts based on rhodium (i) and various phosphabenzenes appear to be superior to classical systems in the hydroformylation of terminal and internal alkenes. In addition planar-chiral phosphaferrocene species display an excellent performance as directing ligands in a series of enantioselective asymmetric syntheses.

The Expression of HAK-Type K+ Transporters Is Regulated in Response to Salinity Stress in Common Ice Plant

Abstract: Four transcripts homologous to K(+) transporters of the HAK/KT/KUP family have been characterized from the common ice plant (Mesembryanthemum crystallinum). We report tissue-specific expression of McHAK1 and McHAK4 transcripts abundant in roots, leaves, and stems. McHAK2 was predominantly present in stems and McHAK3 in root tissues. By in situ hybridizations, the McHAKs showed signals in the leaf vascular bundles, mesophyll, and epidermal cells as well as in epidermal bladder cells. In mature roots, transcripts were mainly localized to the vasculature, and in differentiated root tips, the strongest signals were obtained from the epidermis. Expression of McHAK1, McHAK2, and McHAK4 complemented a yeast mutant defective in low- and high-affinity K(+) uptake. Growth of the yeast mutant was restored at low-millimolar K(+) concentrations and was inhibited by Rb(+) and Cs(+) but was not affected by Na(+). Transcript levels of McHAK1 and McHAK4 increased by K(+) starvation and by salt stress of 400 mM NaCl in leaves and roots. Expression of McHAK2 and McHAK3 was stimulated in leaves and was transiently induced in roots in response to high salinity with prestress transcript levels restored in salt-adapted plants. We discuss possible roles for such transporters in ion homeostasis at high salinity.

Expression in in-vivo and in-vitro growing and maturing oocytes: Focus on regulation of expression at the translational level

Abstract: Studies of expression in in-vivo and in-vitro maturing oocytes have the potential to elucidate signalling pathways involved in the intricate crosstalk between the oocyte and its somatic compartment during differentiation and morphogenetic processes, and the origin of disturbances in oocyte maturation possibly involved in reduced fertility. This review summarizes data on expression studies with focus on regulation of expression at the translational level in the maturing oocyte. The regulation of gene expression at the translational level as analysed in in-vitro maturing oocytes is complex and highly conserved between different species. It is characterized by differential degradation, and by storage and recruitment of distinct maternal mRNAs involving conserved consensus sequences in the 5' or 3' untranslated regions (UTRs) of mRNAs. Proteins interacting with such sequences affect the temporal 3' polyadenylation, and bring the 5' and 3' UTRs of mRNAs into close proximity for efficient initiation of translation. Post-translational modifications of mRNA-associated proteins contribute to maturation- and developmentally controlled and to cell cycle-dependent expression. New methodologies for analysis of ovary-specific gene expression and function of genes in oogenesis are also reviewed, e.g. RT-PCR, SAGE-PCR, real-time rapid cycle fluorescence monitored RT-PCR, differential display techniques, and microinjection of anti-sense RNA, double-stranded RNAs or mRNAs expressing green fluorescent protein-tagged proteins into maturing oocytes.

Infinitely many star products to play with

Abstract: While there has been growing interest for noncommutative spaces in recent times, most examples have been based on the simplest noncommutative algebra: [x i ,x j ] = iθ ij Here we present new classes of (non-formal) deformed products associated to linear Lie algebras of the kind [x i ,x j ] = ic ij k x k For all possible three-dimensional cases, we define a new star product and discuss its properties To complete the analysis of these novel noncommutative spaces, we introduce noncompact spectral triples, and the concept of star triple, a specialization of the spectral triple to deformations of the algebra of functions on a noncompact manifold We examine the generalization to the noncompact case of Connes' conditions for noncommutative spin geometries, and, in the framework of the new star products, we exhibit some candidates for a Dirac operator On the technical level, properties of the Moyal multiplier algebra M(θ 2n ) are elucidated

Chapter 4 – Numerical Continuation, and Computation of Normal Forms

Abstract: This chapter describes numerical continuation methods for analyzing the solution behavior of the dynamical system. Time-integration of a dynamical system gives much insight into its solution behavior. However, once a solution type has been computed—for example, a stationary solution (equilibrium) or a periodic solution (cycle)—then continuation methods become very effective in determining the dependence of this solution on the parameter α. Once a co-dimension-1 bifurcation has been located, it can be followed in two parameters—that is, with α e ℝ 2 . However, in many cases, detection of higher co-dimension bifurcations requires computation of certain normal forms for equations restricted to center manifolds at the critical parameter values. Pseudo-arclength continuation method allows the continuation of any regular solution, including folds. Geometrically, it is the most natural continuation method. The periodic solution continuation method is very suitable for numerical computations, and it is not difficult to establish the Poincare continuation with the help of it.

“Molecular Symmetry Breakers” Generating Metal-Oxide-Based Nanoobject Fragments as Synthons for Complex Structures: [{Mo128Eu4O388H10(H2O)81}2]20−, a Giant-Cluster Dimer†

Abstract: The synthesis and manipulation of a huge variety of nanoscaled species of similar chemical nature under one-pot reaction conditions requires access to a potential TMdynamic library∫ of appropriate building blocks.[1a] For instance, by exploiting a detailed knowledge of polyoxometalate chemistry, a variety of discrete clusters (see ref. [1b ± g]) and related extended structures[2] can be formed by the linking of welldefined metal ± oxygen building blocks. These types of compounds have been shown to exhibit unusual topological as well as electronic properties and, furthermore, are interesting for materials science.[3±5] A couple of years ago, we reported wheel-shaped mixed-valence molybdenum clusters of the type {Mo154}, {Mo176}, 6, 7] and {Mo248}; of these, the first two parent species–exhibiting nanometer-sized cavities and therefore presenting fascinating perspectives for a new type of host ± guest chemistry–can now be obtained in high yields in facile syntheses.[8] Herein, we describe for the first time a dimer of two giant clusters, that is, of structurally well-defined covalently linked nanoobjects with a rather high degree of complexity. The dimer contains two elliptical molybdenum oxide based units, linked together by two Eu-O-Mo bonds, each unit incorporates 128 MoVI/V and 4 EuIII centers and includes large fragments of the above-mentioned parent clusters. The interpretation would be that these dimers are formed by EuIII centers acting as symmetry breakers which prevent the corresponding highly symmetrical parent-ring closure.[1b, 6] Of general importance is that in systems showing growth, potential (abundant) agents, such as EuIII centers, can act as TMsymmetry breakers∫ which results in the generation of structural complexity. In any case, it is important to realize that large nanoobject fragments can, in principle, be used as synthons. The ability to connect or assemble clusters in a predefined manner may allow the design of nanoscopic devices using the TMbottom up∫ method (that is, generating large objects from small units). While the TMclassical∫ reduction of an acidified aqueous molybdate solution leads to the blue, wheel-shaped tetraand hexadecameric parent-cluster anions mentioned above,[6] the generation of smaller species requires the presence of electrophiles, such as PrIII ions which increase the curvature by replacing the larger electrophilic {Mo2} -type building units (see below). In the presence of smaller EuIII ions, even ring closure to the parent clusters does not take place, which allows the isolation of compound 1 containing a novel cluster collective. Compound 1 was characterized by single-crystal X-ray structure analysis[9] (including bond valence sum (BVS) calculation to aid in the determination of the (formal) number of MoV centers and protonation sites),[10] elemental analyses ((K), Eu, Mo; see details in ref. [12]), thermogravimetric analysis, redox titration (to aid in the determination of the (formal) number of MoV centers), IR, and EXAFS spectroscopy (Eu-LIII edge,[11] with the option to distinguish in principle between the different Eu centers in the lattice and cluster sites) as well as magnetic susceptibility measurements with a SQUID magnetometer.

Visual recognition of continuous hand postures

Abstract: This paper describes GREFIT (Gesture REcognition based on FInger Tips), a neural network-based system which recognizes continuous hand postures from gray-level video images (posture capturing). Our approach yields a full identification of all finger joint angles (making, however, some assumptions about joint couplings to simplify computations). This allows a full reconstruction of the three-dimensional (3-D) hand shape, using an articulated hand model with 16 segments and 20 joint angles. GREFIT uses a two-stage approach to solve this task. In the first stage, a hierarchical system of artificial neural networks (ANNs) combined with a priori knowledge locates the two-dimensional (2-D) positions of the finger tips in the image. In the second stage, the 2-D position information is transformed by an ANN into an estimate of the 3-D configuration of an articulated hand model, which is also used for visualization. This model is designed according to the dimensions and movement possibilities of a natural human hand. The virtual hand imitates the user's hand to an remarkable accuracy and can follow postures from gray scale images at a frame rate of 10 Hz.

Identification of Two prpDBC Gene Clusters in Corynebacterium glutamicum and Their Involvement in Propionate Degradation via the 2-Methylcitrate Cycle

Abstract: Genome sequencing revealed that the Corynebacterium glutamicum genome contained, besides gltA, two additional citrate synthase homologous genes (prpC) located in two different prpDBC gene clusters, which were designated prpD1B1C1 and prpD2B2C2. The coding regions of the two gene clusters as well as the predicted gene products showed sequence identities of about 70 to 80%. Significant sequence similarities were found also to the prpBCDE operons of Escherichia coli and Salmonella enterica, which are known to encode enzymes of the propionate-degrading 2-methylcitrate pathway. Homologous and heterologous overexpression of the C. glutamicum prpC1 and prpC2 genes revealed that their gene products were active as citrate synthases and 2-methylcitrate synthases. Growth tests showed that C. glutamicum used propionate as a single or partial carbon source, although the beginning of the exponential growth phase was strongly delayed by propionate for up to 7 days. Compared to growth on acetate, the specific 2-methylcitrate synthase activity increased about 50-fold when propionate was provided as the sole carbon source, suggesting that in C. glutamicum the oxidation of propionate to pyruvate occurred via the 2-methylcitrate pathway. Additionally, two-dimensional gel electrophoresis experiments combined with mass spectrometry showed strong induction of the expression of the C. glutamicum prpD2B2C2 genes by propionate as an additional carbon source. Mutational analyses revealed that only the prpD2B2C2 genes were essential for the growth of C. glutamicum on propionate as a sole carbon source, while the function of the prpD1B1C1 genes remains obscure.