Functional interactions between polypyrimidine tract binding protein and PRI peptide ligand containing proteins.

Polypyrimidine tract binding protein (PTBP1) is a heterogeneous nuclear ribonucleoprotein (hnRNP) that plays roles in most stages of the life-cycle of pre-mRNA and mRNAs in the nucleus and cytoplasm. PTBP1 has four RNA binding domains of the RNA recognition motif (RRM) family, each of which can bind to pyrimidine motifs. In addition, RRM2 can interact via its dorsal surface with proteins containing short peptide ligands known as PTB RRM2 interacting (PRI) motifs, originally found in the protein Raver1. Here we review our recent progress in understanding the interactions of PTB with RNA and with various proteins containing PRI ligands.This work was supported by the Biotechnology and Biological Sciences Research Council [grant number BB/H004203/1 (to C.W.J.S.)]; the Wellcome Trust [grant number 092900 (to C.W.J.S.)]; the Boehringer Ingelheim Fond (to J.A.); the Medical Research Council [grant number MR/M026302/1 (to D.B.A. and D.E.V.P.)]; the Fundação de Amparo à Pesquisa do Estado de Minas Gerais [grant number MR/M026302/1 (to D.B.A. and D.E.V.P.)]; and the National Health and Medical Research Council CJ Martin Fellowship [grant number APP1072476 (to D.B.A.)]

Asymptotic Behavior of the Correlator for Polyakov Loops

The asymptotic behavior of the correlator for Polyakov loop operators separated by a large distance $R$ is determined for high temperature QCD. It is dominated by nonperturbative effects related to the exchange of magnetostatic gluons. To analyze the asymptotic behavior, the problem is formulated in terms of the effective field theory of QCD in 3 space dimensions. The Polyakov loop operator is expanded in terms of local gauge-invariant operators constructed out of the magnetostatic gauge field, with coefficients that can be calculated using resummed perturbation theory. The asymptotic behavior of the correlator is $\exp(-MR)/R$, where $M$ is the mass of the lowest-lying glueball in $(2+1)$-dimensional QCD. This result implies that existing lattice calculations of the Polyakov loop correlator at the highest temperatures available do not probe the true asymptotic region in $R$.Comment: 10 pages, NUHEP-TH-94-2

Quarkonium Suppression

I discuss quarkonium suppression in equilibriated strongly interacting matter. After a brief review of basic features of quarkonium production I discuss the application of recent lattice data on the heavy quark potential to the problem of quarkonium dissociation as well as the problem of direct lattice determination of quarkonium properties in finite temperature lattice QCD.Comment: Invited plenary talk presented on 4th International Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP-2001), November 26-30, 2001, Jaipur; 12 pp, LaTeX, uses pramana.st

Linking the chiral and deconfinement phase transitions

We show that the electric glueball becomes critical at the end-point of the deconfinement phase transition in finite temperature QCD. Based on this observation and existing lattice data, we argue that the chiral phase transition at a zero quark mass and the deconfinement phase transition at an infinite quark mass are continuously connected by the glueball-sigma mixing.Comment: 4 pages, terminology corrected. To appear in Phys. Rev.

RIXS observation of bond-directional nearest-neighbor excitations in the Kitaev material Na2_2IrO3_3

Spin-orbit coupling locks spin direction and spatial orientation and generates, in semi-classical magnets, a local spin easy-axis and associated ordering. Quantum spin-1/2's defy this fate: rather than spins becoming locally anisotropic, the spin-spin interactions do. Consequently interactions become dependent on the spatial orientation of bonds between spins, prime theoretical examples of which are Kitaev magnets. Bond-directional interactions imply the existence of bond-directional magnetic modes, predicted spin excitations that render crystallographically equivalent bonds magnetically inequivalent, which yet have remained elusive experimentally. Here we show that resonant inelastic x-ray scattering allows us to explicitly probe the bond-directional character of magnetic excitations. To do so, we use a scattering plane spanned by one bond and the corresponding spin component and scan a range of momentum transfer that encompasses multiple Brillouin zones. Applying this approach to Na$_2$IrO$_3$ we establish the different bond-directional characters of magnetic excitations at 10 meV and 45 meV. Combined with the observation of spin-spin correlations that are confined to a single bond, this experimentally validates the Kitaev character of exchange interactions long proposed for this material.Comment: 6 pages, 5 figures, plus 4 pages Supplementary Information (incl. 5 figures

Relation between the Polyakov loop and the chiral order parameter at strong coupling

We discuss the relation between the Polyakov loop and the chiral order parameter at finite temperature by using the Gocksch-Ogilvie model with fundamental or adjoint quarks. The model is based on the double expansion of strong coupling and large dimensionality on the lattice. In an analytic way with the mean field approximation employed, we show that the confined phase must be accompanied by the spontaneous breaking of the chiral symmetry for both fundamental and adjoint quarks. Then we proceed to numerical analysis to look into the coupled dynamics of the Polyakov loop and the chiral order parameter. In the case of fundamental quarks, the pseudo-critical temperature inferred from the Polyakov loop behavior turns out to coincide with the pseudo-critical temperature of the chiral phase transition. We discuss the physical implication of the coincidence of the pseudo-critical temperatures in two extreme cases; one is the deconfinement dominance and the other is the chiral dominance. As for adjoint quarks, the deconfinement transition of first order persists and the chiral phase transition occurs distinctly at higher temperature than the deconfinement transition does. The present model study gives us a plausible picture to understand the results from the lattice QCD and aQCD simulations.Comment: 19 pages, 9 figures, to appear in Phys.Rev.D. Appendix A is modified; references are adde

Quasimolecular electronic structure of the spin-liquid candidate Ba3InIr2O9

The mixed-valent iridate Ba3InIr2O9 has been discussed as a promising candidate for quantum spin-liquid behavior. The compound exhibits Ir4.5+ ions in face-sharing IrO6 octahedra forming Ir2O9 dimers with three t2g holes per dimer. Our results establish Ba3InIr2O9 as a cluster Mott insulator. Strong intradimer hopping delocalizes the three t2g holes in quasimolecular dimer states while interdimer charge fluctuations are suppressed by Coulomb repulsion. The magnetism of Ba3InIr2O9 emerges from spin-orbit entangled quasimolecular moments with yet unexplored interactions, opening up a new route to unconventional magnetic properties of 5d compounds. Using single-crystal x-ray diffraction we find the monoclinic space group C2/c already at room temperature. Dielectric spectroscopy shows insulating behavior. Resonant inelastic x-ray scattering reveals a rich excitation spectrum below 1.5 eV with a sinusoidal dynamical structure factor that unambiguously demonstrates the quasimolecular character of the electronic states. Below 0.3 eV, we observe a series of excitations. According to exact diagonalization calculations, such low-energy excitations reflect the proximity of Ba3InIr2O9 to a hopping-induced phase transition based on the condensation of a quasimolecular spin-orbit exciton. The dimer ground state roughly hosts two holes in a bonding j=12 orbital and the third hole in a bonding j=32 orbital

Towards a Phenomenology of Grief : insights from Merleau-Ponty

This paper shows how phenomenological research can enhance our understanding of what it is to experience grief. I focus specifically on themes in the work of Maurice Merleau-Ponty, in order to develop an account that emphasizes two importantly different ways of experiencing indeterminacy. This casts light on features of grief that are disorienting and difficult to describe, while also making explicit an aspect of experience upon which the possibility of phenomenological inquiry itself depends