Centrality dependence of the expansion dynamics in Pb-Pb collisions at 158 A GeV/c

Two-particle correlation functions of negatively charged hadrons from Pb-Pb collisions at 158 GeV/c per nucleon have been measured by the WA97 experiment at the CERN SPS. A Coulomb correction procedure that assumes an expanding source has been implemented. Within the framework of an expanding thermalized source model the size and dynamical state of the collision fireball at freeze-out have been reconstructed as a function of the centrality of the collision. Less central collisions exhibit a different dynamics than central ones: both transverse and longitudinal expansion velocities are slower, the expansion duration is shorter and the system freezes out showing smaller dimensions and higher temperature.Comment: 22 pages, 11 figures, Te

A relational, indirect, meso-level approach to CSCL design in the next decade

This paper reviews some foundational issues that we believe will affect the progress of CSCL over the next ten years. In particular, we examine the terms technology, affordance, and infrastructure and we propose a relational approach to their use in CSCL. Following a consideration of networks, space, and trust as conditions of productive learning, we propose an indirect approach to design in CSCL. The work supporting this theoretical paper is based on the outcomes of two European networks: E-QUEL, a network investigating e-quality in e-learning; and Kaleidoscope, a European Union Framework 6 Network of Excellence. In arguing for a relational understanding of affordance, infrastructure, and technology we also argue for a focus on what we describe as meso-level activity. Overall this paper does not aim to be comprehensive or summative in its review of the state of the art in CSCL, but rather to provide a view of the issues currently facing CSCL from a European perspective

Modelling CO formation in the turbulent interstellar medium

We present results from high-resolution three-dimensional simulations of turbulent interstellar gas that self-consistently follow its coupled thermal, chemical and dynamical evolution, with a particular focus on the formation and destruction of H2 and CO. We quantify the formation timescales for H2 and CO in physical conditions corresponding to those found in nearby giant molecular clouds, and show that both species form rapidly, with chemical timescales that are comparable to the dynamical timescale of the gas. We also investigate the spatial distributions of H2 and CO, and how they relate to the underlying gas distribution. We show that H2 is a good tracer of the gas distribution, but that the relationship between CO abundance and gas density is more complex. The CO abundance is not well-correlated with either the gas number density n or the visual extinction A_V: both have a large influence on the CO abundance, but the inhomogeneous nature of the density field produced by the turbulence means that n and A_V are only poorly correlated. There is a large scatter in A_V, and hence CO abundance, for gas with any particular density, and similarly a large scatter in density and CO abundance for gas with any particular visual extinction. This will have important consequences for the interpretation of the CO emission observed from real molecular clouds. Finally, we also examine the temperature structure of the simulated gas. We show that the molecular gas is not isothermal. Most of it has a temperature in the range of 10--20 K, but there is also a significant fraction of warmer gas, located in low-extinction regions where photoelectric heating remains effective.Comment: 37 pages, 15 figures; minor revisions, matches version accepted by MNRA

Inhomogeneous Superconductivity in Condensed Matter and QCD

Inhomogeneous superconductivity arises when the species participating in the pairing phenomenon have different Fermi surfaces with a large enough separation. In these conditions it could be more favorable for each of the pairing fermions to stay close to its Fermi surface and, differently from the usual BCS state, for the Cooper pair to have a non zero total momentum. For this reason in this state the gap varies in space, the ground state is inhomogeneous and a crystalline structure might be formed. This situation was considered for the first time by Fulde, Ferrell, Larkin and Ovchinnikov, and the corresponding state is called LOFF. The spontaneous breaking of the space symmetries in the vacuum state is a characteristic feature of this phase and is associated to the presence of long wave-length excitations of zero mass. The situation described here is of interest both in solid state and in elementary particle physics, in particular in Quantum Chromo-Dynamics at high density and small temperature. In this review we present the theoretical approach to the LOFF state and its phenomenological applications using the language of the effective field theories.Comment: RevTex, 83 pages, 26 figures. Submitted to Review of Modern Physic

High-pT pi^zero Production with Respect to the Reaction Plane in Au + Au Collisions at sqrt(s_NN) = 200 GeV

Measurements of the azimuthal anisotropy of high-\pT neutral pion neutral pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV by the PHENIX experiment are presented. The data included in this paper were collected during the 2004 RHIC running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of pi^0s detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v_2) of the angular distributions are presented as a function of pi^0 transverse momentum p_T for different bins in collision centrality. Measured reaction plane dependent pi^0 yields are used to determine the azimuthal dependence of the pi^0 suppression as a function of p_T, R_AA (Delta phi,p_T). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the pi^0 suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region, and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.Comment: 344 authors, 35 pages text, RevTeX-4, 24 figures, 8 tables. Submitted to Physical Review

Circular RNAs Are the Predominant Transcript Isoform from Hundreds of Human Genes in Diverse Cell Types

Most human pre-mRNAs are spliced into linear molecules that retain the exon order defined by the genomic sequence. By deep sequencing of RNA from a variety of normal and malignant human cells, we found RNA transcripts from many human genes in which the exons were arranged in a non-canonical order. Statistical estimates and biochemical assays provided strong evidence that a substantial fraction of the spliced transcripts from hundreds of genes are circular RNAs. Our results suggest that a non-canonical mode of RNA splicing, resulting in a circular RNA isoform, is a general feature of the gene expression program in human cells

Transverse-energy distributions at midrapidity in pp++pp, dd++Au, and Au++Au collisions at sNN=62.4\sqrt{s_{_{NN}}}=62.4--200~GeV and implications for particle-production models

Measurements of the midrapidity transverse energy distribution, d\Et/d\eta, are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and additionally for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 130 GeV. The d\Et/d\eta distributions are first compared with the number of nucleon participants $N_{\rm part}$, number of binary collisions $N_{\rm coll}$, and number of constituent-quark participants $N_{qp}$ calculated from a Glauber model based on the nuclear geometry. For Au$+$Au, \mean{d\Et/d\eta}/N_{\rm part} increases with $N_{\rm part}$, while \mean{d\Et/d\eta}/N_{qp} is approximately constant for all three energies. This indicates that the two component ansatz, $dE_{T}/d\eta \propto (1-x) N_{\rm part}/2 + x N_{\rm coll}$, which has been used to represent $E_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in $E_T$ distributions. The $dE_{T}/d\eta$ distributions of Au$+$Au and $d$$+$Au are then calculated from the measured $p$$+$$p$ $E_T$ distribution using two models that both reproduce the Au$+$Au data. However, while the number-of-constituent-quark-participant model agrees well with the $d$$+$Au data, the additive-quark model does not.Comment: 391 authors, 24 pages, 19 figures, and 15 Tables. Submitted to Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are publicly available at http://www.phenix.bnl.gov/papers.htm

Quantitative Constraints on the Transport Properties of Hot Partonic Matter from Semi-Inclusive Single High Transverse Momentum Pion Suppression in Au+Au collisions at sqrt(s_NN) = 200 GeV

The PHENIX experiment has measured the suppression of semi-inclusive single high transverse momentum pi^0's in Au+Au collisions at sqrt(s_NN) = 200 GeV. The present understanding of this suppression is in terms of energy-loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dN^g/dy, the medium transport coefficient , or the initial energy-loss parameter epsilon_0. We find that high transverse momentum pi^0 suppression in Au+Au collisions has sufficient precision to constrain these model dependent parameters at the +/1 20%-25% (one standard deviation) level. These constraints include only the experimental uncertainties, and further studies are needed to compute the corresponding theoretical uncertainties.Comment: 422 authors, 13 pages text, RevTeX-4, 9 figures, 2 tables. This version is updated with changes made during the review process and is now the same as what was published in Physical Review C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are publicly available at http://www.phenix.bnl.gov/papers.htm