The emergence of a "digital underclass" in Great Britain and Sweden: changing reasons for digital exclusion

Research into reasons for Internet non-use has been mostly based on one-off cohort studies and focused on single-country contexts. This article shows that motivations for being offline changed between 2005 and 2013 among non- and ex-users in two high-diffusion European countries. Analyses of Swedish and British data demonstrate that non-user populations have become more concentrated in vulnerable groups. While traditional digital divide reasons related to a lack of access and skills remain important, motivational reasons increased in importance over time. The ways in which these reasons gain importance for non- and ex-user groups vary, as do explanations for digital exclusion in the different countries. Effective interventions aimed at tackling digital exclusion need to take into consideration national contexts, changing non-user characteristics, and individual experience with the Internet. What worked a decade ago in a particular country might not work currently in a different or even the same country.</jats:p

Nuclear stopping and flow in heavy ion collisions and the in-medium NN cross section

We present transport calculations for heavy ion reactions in which the mean field and the in-medium nucleon-nucleon cross section are consistently based on the same effective interaction, i.e. the in-medium T-matrix from microscopic Dirac-Brueckner calculations. Doing so, the stopping in central reactions in terms of the recently proposed $var_{\rm tl}$ observable and the correlation to the behavior of the directed flow is investigated. The relation to the nuclear shear viscosity is discussed.Comment: 9 pages, 4 figure

Competition of fusion and quasi-fission in the reactions leading to production of the superheavy elements

The mechanism of fusion hindrance, an effect observed in the reactions of cold, warm and hot fusion leading to production of the superheavy elements, is investigated. A systematics of transfermium production cross sections is used to determine fusion probabilities. Mechanism of fusion hindrance is described as a competition of fusion and quasi-fission. Available evaporation residue cross sections in the superheavy region are reproduced satisfactorily. Analysis of the measured capture cross sections is performed and a sudden disappearance of the capture cross sections is observed at low fusion probabilities. A dependence of the fusion hindrance on the asymmetry of the projectile-target system is investigated using the available data. The most promising pathways for further experiments are suggested.Comment: 8 pages, 7 figures, talk presented at 7th International School-Seminar on Heavy-Ion Physics, May 27 - June 1, 2002, Dubna, Russi

Can shadowing mimic the QCD phase transition?

The directed flow of protons is studied in the quark-gluon string model as a function of the impact parameter for S+S and Pb+Pb reactions at 160 AGeV/c. A significant reduction of the directed flow in midrapidity range, which can lead to the development of the antiflow, is found due to the absorption of early emitted particles by massive spectators (shadowing effect). This effect can mimic the formation of the quark-gluon plasma (QGP). However, in the absorption scenario the antiflow is stronger for the system of light colliding nuclei than for the heavy ones, while in the case of the plasma creation the effect should be opposite.Comment: REVTEX, 11 pages, 5 figures embedded, accepted for publication in Physics Letters

Modelling of compound nucleus formation in fusion of heavy nuclei

A new model that includes the time-dependent dynamics of the single-particle (s.p.) motion in conjunction with the macroscopic evolution of the system is proposed for describing the compound nucleus (CN) formation in fusion of heavy nuclei. The diabaticity initially keeps the entrance system around its contact configuration, but the gradual transition from the diabatic to the adiabatic potential energy surface (PES) leads to fusion or quasifission. Direct measurements of the probability for CN formation are crucial to discriminate between the current models.Comment: 4 pages,2 figures,1 table, Submitted to PR

Asymmetric Colliding Nuclear Matter Approach in Heavy Ion Collisions

The early stage of a heavy ion collision is governed by local non-equilibrium momentum distributions which have been approximated by colliding nuclear matter configurations, i.e. by two Lorentz elongated Fermi ellipsoids. This approach has been extended from the previous assumption of symmetric systems to asymmetric 2-Fermi sphere configurations, i.e. to different densities. This provides a smoother transition from the limiting situation of two interpenetrating currents to an equilibrated system. The model is applied to the dynamical situations of heavy ion collisions at intermediate energies within the framework of relativistic transport (RBUU) calculations. We find that the extended colliding nuclear matter approach is more appropriate to describe collective reaction dynamics in terms of flow observables, in particular, for the elliptic flow at low energies.Comment: 21 pages, 8 figures, accepted for publication in Nuclear Physics

Temperature and thermodynamic instabilities in heavy ion collisions

We investigate thermodynamic properties and instability conditions in intermediate energy heavy ion reactions. We define locally thermodynamic variables, i.e. density, pressure and temperature, directly from the phase space distribution of a relativistic transport calculation. In particular, temperatures are determined by a fit to two covariant hot Fermi distributions thus taking into account possible anisotropic momentum configurations. We define instability independent from the nuclear matter spinodal by the criterion that the effective compressibility becomes negative. The method is applied to a semi-central Au on Au reaction at 600 MeV/nucleon. We investigate in particular the center of the participant and the spectator matter. In the latter we find a clear indication of instability with conditions of density and temperature that are consistent with experimental determinations.Comment: 20 pages latex, 5 PS-figures, revised version (minor changes) accepted for publication in Nucl. Phys.

Heavy ion collisions with non-equilibrium Dirac-Brueckner mean fields

The influence of realistic interactions on the reaction dynamics in intermediate energy heavy ion collisions is investigated. The mean field in relativistic transport calculations is derived from microscopic Dirac-Brueckner (DB) self-energies, taking non-equilibrium effects, in particular the anisotropy of the local phase space configurations, into account. Thus this approach goes beyond the local density approximation. A detailed analysis of various in-plane and out-of-plane flow observables is presented for Au on Au reactions at incident energies ranging from 250 to 800 A.MeV and the results are compared to recent measurements of the FOPI collaboration. An overall good agreement with in-plane flow data and a reasonable description of the out-of-plane emission is achieved. For these results the intrinsic momentum dependence of the non-equilibrium mean fields is important. On the other hand, the local density approximation with the same underlying DB forces as well as a standard non-linear version of the $\sigma\omega$ model are less successful in describing the present data. This gives evidence of the applicability of self energies derived from the DB approach to nuclear matter also far from saturation and equilibrium.Comment: 63 pages Latex, using Elsevier style, 20 ps-figures, to appear in Nucl. Phys.

The cytosolic glutamine synthetase GLN1;2 plays a role in the control of plant growth and ammonium homeostasis in Arabidopsis rosettes when nitrate supply is not limiting

Glutamine synthetase (EC 6.3.1.2) is a key enzyme of ammonium assimilation and recycling in plants where it catalyses the synthesis of glutamine from ammonium and glutamate. In Arabidopsis, five GLN1 genes encode GS1 isoforms. GLN1;2 is the most highly expressed in leaves and is over-expressed in roots by ammonium supply and in rosettes by ample nitrate supply compared with limiting nitrate supply. It is shown here that the GLN1;2 promoter is mainly active in the minor veins of leaves and flowers and, to a lower extent, in the parenchyma of mature leaves. Cytoimmunochemistry reveals that the GLN1;2 protein is present in the companion cells. The role of GLN1;2 was determined by examining the physiology of gln1;2 knockout mutants. Mutants displayed lower glutamine synthetase activity, higher ammonium concentration, and reduced rosette biomass compared with the wild type (WT) under ample nitrate supply only. No difference between mutant and WT can be detected under limiting nitrate conditions. Despite total amino acid concentration was increased in the old leaves of mutants at high nitrate, no significant difference in nitrogen remobilization can be detected using 15N tracing. Growing plants in vitro with ammonium or nitrate as the sole nitrogen source allowed us to confirm that GLN1;2 is induced by ammonium in roots and to observe that gln1;2 mutants displayed, under such conditions, longer root hair and smaller rosette phenotypes in ammonium. Altogether the results suggest that GLN1;2 is essential for nitrogen assimilation under ample nitrate supply and for ammonium detoxification

Differential flow in heavy-ion collisions at balance energies

A strong differential transverse collective flow is predicted for the first time to occur in heavy-ion collisions at balance energies. We also give a novel explanation for the disappearance of the total transverse collective flow at the balance energies. It is further shown that the differential flow especially at high transverse momenta is a useful microscope capable of resolving the balance energy's dual sensitivity to both the nuclear equation of state and in-medium nucleon-nucleon cross sections in the reaction dynamics.Comment: Phys. Rev. Lett. (1999) in pres