Charge correlations in the weakly doped t-J model calculated by projection technique

We study frequency- and wave-vector dependent charge correlations in weakly doped antiferromagnets using Mori-Zwanzig projection technique. The system is described by the two-dimensional t-J model. The ground state is expressed within a cumulant formalism which has been successfully applied to study magnetic properties of the weakly doped system. Within this approach the ground state contains independent spin-bag quasiparticles (magnetic polarons). We present results for the charge-density response function and for the optical conductivity at zero temperature for different values of t/J. They agree well with numerical results calculated by exact diagonalization techniques. The density response function for intermediate and large momenta shows a broad continuum on energy scales of order of several t whereas the optical conductivity for \omega > 0 is dominated by low energy excitations (at 1.5 - 2 J). We show that these weak-doping properties can be well understood by transitions between excited states of spin-bag quasiparticles.Comment: 10 pages, 5 figs., to appear in Europ. Phys. J.

Magnetic properties and spin waves of bilayer magnets in a uniform field

The two-layer square lattice quantum antiferromagnet with spins 1/2 shows a zero-field magnetic order-disorder transition at a critical ratio of the inter-plane to intra-plane couplings. Adding a uniform magnetic field tunes the system to canted antiferromagnetism and eventually to a fully polarized state; similar behavior occurs for ferromagnetic intra-plane coupling. Based on a bond operator spin representation, we propose an approximate ground state wavefunction which covers all phases by means of a unitary transformation. The excitations can be efficiently described as independent bosons; in the antiferromagnetic phase these reduce to the well-known spin waves, whereas they describe gapped spin-1 excitations in the singlet phase. We compute the spectra of these excitations as well as the magnetizations throughout the whole phase diagram.Comment: 12 pages, 9 figs; added references; final version as publishe

Development of a bioactive epicardial composite patch for support of myocardial regeneration

After progression to heart failure, the only treatment option to date is a heart transplant, but this is limited due to a lack of donor organs. One response to a myocardial infarction is the activation of epicardial cells, ultimately differentiating towards the cardiac lineage in the myocardium. One promising therapy, injection of progenitor cells in the infarcted area, has been met with contradictory success in the clinic. In contrast, epicardial patches, of polymeric or biological background, allow controlled local treatment to induce cardiac regeneration in preclinical attempts. The aim of this project was to develop an epicardial composite patch to support the cardiac regeneration process. It consists of human cardiac extracellular matrix (hcECM), providing specific bioactivity and a polymeric or amniotic scaffold, with basic biocompatibility providing the required mechanical stability. The hcECM was processed to a hydrogel (hgECM) and the scaffolds were coated with hgECM. Morphology and mechanical properties were measured determined. A hgECM coating caused a stabile nano-scaffold on the scaffolds and mechanical properties were unchanged. Then, transdifferentiated induced cardiomyocytes progenitors (iCMP) were cultured on the scaffolds to achieve a cellular bio enhancement. After hgECM coating, biocompatibility was assessed by adhesion capacity, LDH-release, BrdU-incorporation and LIVE/DEAD staining. We found a clearly improved adhesion of several cardiac cells and iCMPs. Also, hgECM reduced cell necrosis and improved cell proliferation determined by LDH-release and BrdU-incorporation. Moreover, more alive cells were detected on hgECM coated scaffolds. ELISA technology revealed a reduction of proinflammatory cytokine secretion by LPS-activated monocytes on both hgECM coated scaffolds and by naïve monocytes on polymeric scaffold. No activation and impact by hgECM coating was observed regarding T cell proliferation and macrophage polarization determined by ELISA technology and flow cytometry. Additionally, an in vitro assay was established based on the first response of the immune system: Polymorph Nuclear Cells. The amnion membrane as the “proof-of-principle” implant showed no immune response in this test and translation to any material is possible. Here, we developed a new composite epicardial scaffold with hECM that has the potential to be used in large animal experiments and ultimately clinical studies. As a cell-free material, the production process can readily be scaled-up under GMP conditions. Further in vivo testing will reveal whether the composite patch is able to significantly modify post-infarct remodeling processes. In any event, it may serve as a universal platform for epicardial delivery of a broad spectrum of cells and therapeutic agents.Nach Fortschreiten der Herzinsuffizienz ist eine Herztransplantation bisher die einzige Behandlungsoption, die jedoch aufgrund fehlender Spenderorgane begrenzt ist. Eine Antwort auf einen Herzinfarkt ist die Aktivierung von Epikardzellen, die sich letztendlich zur Herzlinie im Myokard hin differenzieren können. Injizierung von Vorläuferzellen in den Infarktbereich zeigten in der Klinik widersprüchlichen Erfolg. Im Gegensatz dazu ermöglichen Epikard-Patches mit polymerem oder biologischem Hintergrund eine kontrollierte lokale Behandlung, um die Regeneration des Herzens zu stärken. Dieses Projekt hatte die Entwicklung eines epikardialen Komposite-Patches zur Unterstützung des kardialen Regenerationsprozesses zum Ziel. Es besteht aus humaner extrazellulärer Herzmatrix (hECM), die eine spezifische Bioaktivität und eine optimale Zellumgebung bietet, und einem polymeren oder amniotischen Gerüst mit basaler Biokompatibilität, die die erforderliche mechanische Stabilität liefert. Die hECM wurde zu einem Hydrogel (hgECM) verarbeitet, und Gerüste wurden mit hgECM beschichtet. Die grundlegende Morphologie und die mechanischen Eigenschaften wurden durch einachsige Ziehversuche und Elektronenmikroskopie gemessen. Die Biokompatibilität wurde durch Adhäsionskapazität, LDH-Freisetzung, BrdU-Einbau und LIVE/DEAD-Färbung bewertet und die Immunogenität wurde durch Zytokinsekretion, Makrophagenpolarisation und T-Zellproliferation bestimmt. Darüber hinaus wurden transdifferenzierte induzierte Kardiomyozyten-Vorläufer (iCMP) auf Gerüsten zur zellulären Bioverbesserung kolonialisiert. Eine hgECM-Beschichtung bewirkte eine stabile Nanobeschichtung auf den Gerüsten und die mechanischen Eigenschaften wurden nicht beeinflusst. Nach der hgECM-Beschichtung verbesserte sich die Adhäsion bei mehreren Herzzellen und iCMP deutlich. Darüber hinaus induzierte hgECM eine verringerte Zellnekrose und verbesserte Zellproliferation, bestimmt durch LDH-Freisetzung und BrdU-Einbau. Durch LIVE/DEAD-Färbung wurden auf hgECMbeschichteten Gerüsten mehr Zellen als lebendig indentifiziert. Eine hgECM-Beschichtung verursachte eine Verringerung der proinflammatorischen Zytokinsekretion bei LPS-aktivierten Monozyten auf beiden Gerüsten und auch von naiven Monozyten auf polymeren Gerüsten. In Bezug auf die Proliferation von T-Zellen und die Polarisation von Makrophagen wurde keine Aktivierung und keine Beeinflussung durch hgECM-Beschichtung beobachtet. Zusätzlich wurde ein in vitro Test basierend auf der ersten Reaktion des Immunsystems etabliert: Polymorph Nuclear Cells. Die Amnionmembran als „Proof-of-Principle“ -Implantat zeigte in diesem Test keine Immunreaktion, und eine Translation auf jedes Material ist möglich. Wir haben hier ein neues zusammengesetztes Epikard-Gerüst mit humaner Herz-ECM entwickelt, das das Potenzial hat, in Großtierstudien und schließlich in klinischen Studien eingesetzt zu werden. Als zellfreies Material kann der Produktionsprozess unter GMPBedingungen problemlos skaliert werden. Weitere in vivo Tests zeigen, ob das Komposit-Pflaster Post-Infarkt-Remodellierungsprozesse signifikant modifizieren kann. In jedem Fall kann es als universelle Plattform für die epikardiale Abgabe eines breiten Spektrums von Zellen und Therapeutika dienen

Conservation and co-option in developmental programmes: the importance of homology relationships

One of the surprising insights gained from research in evolutionary developmental biology (evo-devo) is that increasing diversity in body plans and morphology in organisms across animal phyla are not reflected in similarly dramatic changes at the level of gene composition of their genomes. For instance, simplicity at the tissue level of organization often contrasts with a high degree of genetic complexity. Also intriguing is the observation that the coding regions of several genes of invertebrates show high sequence similarity to those in humans. This lack of change (conservation) indicates that evolutionary novelties may arise more frequently through combinatorial processes, such as changes in gene regulation and the recruitment of novel genes into existing regulatory gene networks (co-option), and less often through adaptive evolutionary processes in the coding portions of a gene. As a consequence, it is of great interest to examine whether the widespread conservation of the genetic machinery implies the same developmental function in a last common ancestor, or whether homologous genes acquired new developmental roles in structures of independent phylogenetic origin. To distinguish between these two possibilities one must refer to current concepts of phylogeny reconstruction and carefully investigate homology relationships. Particularly problematic in terms of homology decisions is the use of gene expression patterns of a given structure. In the future, research on more organisms other than the typical model systems will be required since these can provide insights that are not easily obtained from comparisons among only a few distantly related model species

Auswirkung intracerebroventrikulärer Baclofenapplikation auf Glutamat-, Aspartat- und Glycinfreisetzung und das Dopaminerge System im Ncl. paraventricularis hypothalami der Ratte

Eine Studie über den Einfluß intracerebroventrikulärer Baclofenapplikation auf Glutamat-, Aspartat- und Glycinfreisetzung und das Dopaminerge System im Ncl. paraventricularis hypothalami der Ratte. Tierxperimentelle Arbeit am Zentrum für Neurochirurgie

Decoding implicit hate speech: The example of antisemitism

This article deals with the problem and the different levels of implicity in the context of antisemitic hate speech. By means of authentic examples stemming from social media debates, we show how alluded antisemitic concepts can be inferred on the basis of conservative interpretation. We point out the role of different sources of knowledge in reconstructing the ideas implied in a statement as well as potential sources of error in the interpretation process. The article thus focuses on the methods and findings of the interdisciplinary research project "Decoding Antisemitism" conducted at the Center for Research on Antisemitism (ZfA) at TU Berlin. By doing so, it explains the procedure of qualitative content analysis as a fruitful approach to understand the actual repertoire of antisemitic hate speech online

Accelerating Parametric Probabilistic Verification

We present a novel method for computing reachability probabilities of parametric discrete-time Markov chains whose transition probabilities are fractions of polynomials over a set of parameters. Our algorithm is based on two key ingredients: a graph decomposition into strongly connected subgraphs combined with a novel factorization strategy for polynomials. Experimental evaluations show that these approaches can lead to a speed-up of up to several orders of magnitude in comparison to existing approache