Dynamics of Resonances in Strongly Interacting Systems

The effects of the propagation of particles which have a finite life-time and an according broad distribution in their mass spectrum are discussed in the context of a transport descriptions. In the first part some example cases of mesonic modes in nuclear matter at finite densities and temperatures are presented. These equilibrium calculations illustrate the dynamical range of spectral distributions to be adequately covered by non-equilibrium description of the dynamics of two nuclei colliding at high energies. The second part addresses the problem of transport descriptions which properly account for the damping width of the particles. A systematic and general gradient approximation is presented in the form of diagrammatic rules which permit to derive a self-consistent transport scheme from the Kadanoff--Baym equation. The scheme is conserving and thermodynamically consistent provided the self-energies are obtained within the Phi-derivable two-particle irreducible (2PI) method of Baym. The merits, the limitations and partial cures of the limitations of this transport scheme are discussed in detail.Comment: To appear in the proceedings of the International Conference "Progress in Nonequilibrium Green's Functions III", Kiel, 22.-26. August 200

The spectral function of the omega meson in nuclear matter from a coupled-channel resonance model

We calculate the spectral function of the omega meson in nuclear matter at zero temperature by means of the low-density theorem. The omega N forward scattering amplitude is calculated within a unitary coupled-channel effective Lagrangian model that has been applied successfully to the combined analysis of pion- and photon-induced reactions. While the peak of the omega spectral distribution is shifted only slightly, we find a considerable broadening of the omega meson due to resonance-hole excitations. For omega mesons at rest with respect to the surrounding nuclear medium, we find an additional width of about 60 MeV at saturation density.Comment: 26 pages, 10 figures, added short discussio

Strongly Correlated Quantum Fluids: Ultracold Quantum Gases, Quantum Chromodynamic Plasmas, and Holographic Duality

Strongly correlated quantum fluids are phases of matter that are intrinsically quantum mechanical, and that do not have a simple description in terms of weakly interacting quasi-particles. Two systems that have recently attracted a great deal of interest are the quark-gluon plasma, a plasma of strongly interacting quarks and gluons produced in relativistic heavy ion collisions, and ultracold atomic Fermi gases, very dilute clouds of atomic gases confined in optical or magnetic traps. These systems differ by more than 20 orders of magnitude in temperature, but they were shown to exhibit very similar hydrodynamic flow. In particular, both fluids exhibit a robustly low shear viscosity to entropy density ratio which is characteristic of quantum fluids described by holographic duality, a mapping from strongly correlated quantum field theories to weakly curved higher dimensional classical gravity. This review explores the connection between these fields, and it also serves as an introduction to the Focus Issue of New Journal of Physics on Strongly Correlated Quantum Fluids: from Ultracold Quantum Gases to QCD Plasmas. The presentation is made accessible to the general physics reader and includes discussions of the latest research developments in all three areas.Comment: 138 pages, 25 figures, review associated with New Journal of Physics special issue "Focus on Strongly Correlated Quantum Fluids: from Ultracold Quantum Gases to QCD Plasmas" (http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Strongly%20Correlated%20Quantum%20Fluids%20-%20from%20Ultracold%20Quantum%20Gases%20to%20QCD%20Plasmas

Altered Metabolism and Persistent Starvation Behaviors Caused by Reduced AMPK Function in Drosophila

Organisms must utilize multiple mechanisms to maintain energetic homeostasis in the face of limited nutrient availability. One mechanism involves activation of the heterotrimeric AMP-activated protein kinase (AMPK), a cell-autonomous sensor to energetic changes regulated by ATP to AMP ratios. We examined the phenotypic consequences of reduced AMPK function, both through RNAi knockdown of the gamma subunit (AMPKγ) and through expression of a dominant negative alpha (AMPKα) variant in Drosophila melanogaster. Reduced AMPK signaling leads to hypersensitivity to starvation conditions as measured by lifespan and locomotor activity. Locomotor levels in flies with reduced AMPK function were lower during unstressed conditions, but starvation-induced hyperactivity, an adaptive response to encourage foraging, was significantly higher than in wild type. Unexpectedly, total dietary intake was greater in animals with reduced AMPK function yet total triglyceride levels were lower. AMPK mutant animals displayed starvation-like lipid accumulation patterns in metabolically key liver-like cells, oenocytes, even under fed conditions, consistent with a persistent starved state. Measurements of O2 consumption reveal that metabolic rates are greater in animals with reduced AMPK function. Lastly, rapamycin treatment tempers the starvation sensitivity and lethality associated with reduced AMPK function. Collectively, these results are consistent with models that AMPK shifts energy usage away from expenditures into a conservation mode during nutrient-limited conditions at a cellular level. The highly conserved AMPK subunits throughout the Metazoa, suggest such findings may provide significant insight for pharmaceutical strategies to manipulate AMPK function in humans

The Comprehensive Native Interactome of a Fully Functional Tagged Prion Protein

The enumeration of the interaction partners of the cellular prion protein, PrPC, may help clarifying its elusive molecular function. Here we added a carboxy proximal myc epitope tag to PrPC. When expressed in transgenic mice, PrPmyc carried a GPI anchor, was targeted to lipid rafts, and was glycosylated similarly to PrPC. PrPmyc antagonized the toxicity of truncated PrP, restored prion infectibility of PrPC-deficient mice, and was physically incorporated into PrPSc aggregates, indicating that it possessed all functional characteristics of genuine PrPC. We then immunopurified myc epitope-containing protein complexes from PrPmyc transgenic mouse brains. Gentle differential elution with epitope-mimetic decapeptides, or a scrambled version thereof, yielded 96 specifically released proteins. Quantitative mass spectrometry with isotope-coded tags identified seven proteins which co-eluted equimolarly with PrPC and may represent component of a multiprotein complex. Selected PrPC interactors were validated using independent methods. Several of these proteins appear to exert functions in axomyelinic maintenance

AMP-activated protein kinase - not just an energy sensor

Orthologues of AMP-activated protein kinase (AMPK) occur in essentially all eukaryotes as heterotrimeric complexes comprising catalytic α subunits and regulatory β and γ subunits. The canonical role of AMPK is as an energy sensor, monitoring levels of the nucleotides AMP, ADP, and ATP that bind competitively to the γ subunit. Once activated, AMPK acts to restore energy homeostasis by switching on alternate ATP-generating catabolic pathways while switching off ATP-consuming anabolic pathways. However, its ancestral role in unicellular eukaryotes may have been in sensing of glucose rather than energy. In this article, we discuss a few interesting recent developments in the AMPK field. Firstly, we review recent findings on the canonical pathway by which AMPK is regulated by adenine nucleotides. Secondly, AMPK is now known to be activated in mammalian cells by glucose starvation by a mechanism that occurs in the absence of changes in adenine nucleotides, involving the formation of complexes with Axin and LKB1 on the surface of the lysosome. Thirdly, in addition to containing the nucleotide-binding sites on the γ subunits, AMPK heterotrimers contain a site for binding of allosteric activators termed the allosteric drug and metabolite (ADaM) site. A large number of synthetic activators, some of which show promise as hypoglycaemic agents in pre-clinical studies, have now been shown to bind there. Fourthly, some kinase inhibitors paradoxically activate AMPK, including one (SU6656) that binds in the catalytic site. Finally, although downstream targets originally identified for AMPK were mainly concerned with metabolism, recently identified targets have roles in such diverse areas as mitochondrial fission, integrity of epithelial cell layers, and angiogenesis

First observation of in-medium modifications of the omega meson

The photoproduction of omega mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium modifications of the omega meson via the reaction A(gamma, omega)X. Results obtained for Nb are compared to a reference measurement on a liquid hydrogen target. While for recoiling, long-lived mesons (pi, eta and etaprime), which decay outside of the nucleus, a difference in the lineshape for the two data samples is not observed, we find a significant enhancement towards lower masses for omega mesons with low momenta produced on the Nb target.Comment: Latex, 4 pages, 4 figures, accepted by Phys. Rev. Lett; references re-arranged, now references in chronological order in first paragrap

Expression of Mutant or Cytosolic PrP in Transgenic Mice and Cells Is Not Associated with Endoplasmic Reticulum Stress or Proteasome Dysfunction

The cellular pathways activated by mutant prion protein (PrP) in genetic prion diseases, ultimately leading to neuronal dysfunction and degeneration, are not known. Several mutant PrPs misfold in the early secretory pathway and reside longer in the endoplasmic reticulum (ER) possibly stimulating ER stress-related pathogenic mechanisms. To investigate whether mutant PrP induced maladaptive responses, we checked key elements of the unfolded protein response (UPR) in transgenic mice, primary neurons and transfected cells expressing two different mutant PrPs. Because ER stress favors the formation of untranslocated PrP that might aggregate in the cytosol and impair proteasome function, we also measured the activity of the ubiquitin proteasome system (UPS). Molecular, biochemical and immunohistochemical analyses found no increase in the expression of UPR-regulated genes, such as Grp78/Bip, CHOP/GADD153, or ER stress-dependent splicing of the mRNA encoding the X-box-binding protein 1. No alterations in UPS activity were detected in mutant mouse brains and primary neurons using the UbG76V-GFP reporter and a new fluorogenic peptide for monitoring proteasomal proteolytic activity in vivo. Finally, there was no loss of proteasome function in neurons in which endogenous PrP was forced to accumulate in the cytosol by inhibiting cotranslational translocation. These results indicate that neither ER stress, nor perturbation of proteasome activity plays a major pathogenic role in prion diseases

Confidence in uncertainty: Error cost and commitment in early speech hypotheses

© 2018 Loth et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Interactions with artificial agents often lack immediacy because agents respond slower than their users expect. Automatic speech recognisers introduce this delay by analysing a user’s utterance only after it has been completed. Early, uncertain hypotheses of incremental speech recognisers can enable artificial agents to respond more timely. However, these hypotheses may change significantly with each update. Therefore, an already initiated action may turn into an error and invoke error cost. We investigated whether humans would use uncertain hypotheses for planning ahead and/or initiating their response. We designed a Ghost-in-the-Machine study in a bar scenario. A human participant controlled a bartending robot and perceived the scene only through its recognisers. The results showed that participants used uncertain hypotheses for selecting the best matching action. This is comparable to computing the utility of dialogue moves. Participants evaluated the available evidence and the error cost of their actions prior to initiating them. If the error cost was low, the participants initiated their response with only suggestive evidence. Otherwise, they waited for additional, more confident hypotheses if they still had time to do so. If there was time pressure but only little evidence, participants grounded their understanding with echo questions. These findings contribute to a psychologically plausible policy for human-robot interaction that enables artificial agents to respond more timely and socially appropriately under uncertainty