Architecture of the RNA polymerase II-Paf1C-TFIIS transcription elongation complex.

The conserved polymerase-associated factor 1 complex (Paf1C) plays multiple roles in chromatin transcription and genomic regulation. Paf1C comprises the five subunits Paf1, Leo1, Ctr9, Cdc73 and Rtf1, and binds to the RNA polymerase II (Pol II) transcription elongation complex (EC). Here we report the reconstitution of Paf1C from Saccharomyces cerevisiae, and a structural analysis of Paf1C bound to a Pol II EC containing the elongation factor TFIIS. Cryo-electron microscopy and crosslinking data reveal that Paf1C is highly mobile and extends over the outer Pol II surface from the Rpb2 to the Rpb3 subunit. The Paf1-Leo1 heterodimer and Cdc73 form opposite ends of Paf1C, whereas Ctr9 bridges between them. Consistent with the structural observations, the initiation factor TFIIF impairs Paf1C binding to Pol II, whereas the elongation factor TFIIS enhances it. We further show that Paf1C is globally required for normal mRNA transcription in yeast. These results provide a three-dimensional framework for further analysis of Paf1C function in transcription through chromatin

Charged pions from Ni on Ni collisions between 1 and 2 AGeV

Charged pions from Ni + Ni reactions at 1.05, 1.45 and 1.93 AGeV are measured with the FOPI detector. The mean $\pi^{\pm}$ multiplicities per mean number of participants increase with beam energy, in accordance with earlier studies of the Ar + KCl and La + La systems. The pion kinetic energy spectra have concave shape and are fitted by the superposition of two Boltzmann distributions with different temperatures. These apparent temperatures depend only weakly on bombarding energy. The pion angular distributions show a forward/backward enhancement at all energies, but not the $\Theta = 90^0$ enhancement which was observed in case of the Au + Au system. These features also determine the rapidity distributions which are therefore in disagreement with the hypothesis of one thermal source. The importance of the Coulomb interaction and of the pion rescattering by spectator matter in producing these phenomena is discussed.Comment: 22 pages, Latex using documentstyle[12pt,a4,epsfig], to appear in Z. Phys.

Influence of the in-medium pion dispersion relation in heavy ion collisions

We investigate the influence of medium corrections to the pion dispersion relation on the pion dynamics in intermediate energy heavy ion collisions. To do so a pion potential is extracted from the in-medium dispersion relation and used in QMD calculations and thus we take care of both, real and imaginary part of the pion optical potential. The potentials are determined from different sources, i.e. from the $\Delta$--hole model and from phenomenological approaches. Depending on the strength of the potential a reduction of the anti-correlation of pion and nucleon flow in non-central collisions is observed as well as an enhancement of the high energetic yield in transverse pion spectra. A comparison to experiments, in particular to $p_t$-spectra for the reaction Ca+Ca at 1 GeV/nucleon and the pion in-plane flow in Ne+Pb collisions at 800 MeV/nucleon, generally favours a weak potential.Comment: 25 pages, using REVTeX, 6 postscript figures; replaced by published versio

Dielectron Cross Section Measurements in Nucleus-Nucleus Reactions at 1.0 A GeV

We present measured dielectron production cross sections for Ca+Ca, C+C, He+Ca, and d+Ca reactions at 1.0 A GeV. Statistical uncertainties and systematic effects are smaller than in previous DLS nucleus-nucleus data. For pair mass < 0.35 GeV/c2 : 1) the Ca+Ca cross section is larger than the previous DLS measurement and current model results, 2) the mass spectra suggest large contributions from pi0 and eta Dalitz decays, and 3) dsigma/dM is proportional to ApAt. For M > 0.5 GeV/c2 the Ca+Ca to C+C cross section ratio is significantly larger than the ratio of ApAt values.Comment: Submitted to Physical Review Letters. Further analysis information will be posted on our web pages -- http://macdls.lbl.gov Figure 1 has been redrawn to make more legible. Text modified to support redrawn figur

Hadron Production in Heavy Ion Collisions

We review hadron production in heavy ion collisions with emphasis on pion and kaon production at energies below 2 AGeV and on partonic collectivity at RHIC energies.Comment: 31 pages, 26 figures, accepted for publication in Landolt-Boernstein Volume 1-23

Relativistic quantum transport theory of hadronic matter: the coupled nucleon, delta and pion system

We derive the relativistic quantum transport equation for the pion distribution function based on an effective Lagrangian of the QHD-II model. The closed time-path Green's function technique, the semi-classical, quasi-particle and Born approximation are employed in the derivation. Both the mean field and collision term are derived from the same Lagrangian and presented analytically. The dynamical equation for the pions is consistent with that for the nucleons and deltas which we developed before. Thus, we obtain a relativistic transport model which describes the hadronic matter with $N$, $\Delta$ and $\pi$ degrees of freedom simultaneously. Within this approach, we investigate the medium effects on the pion dispersion relation as well as the pion absorption and pion production channels in cold nuclear matter. In contrast to the results of the non-relativistic model, the pion dispersion relation becomes harder at low momenta and softer at high momenta as compared to the free one, which is mainly caused by the relativistic kinetics. The theoretically predicted free $\pi N \to \Delta$ cross section is in agreement with the experimental data. Medium effects on the $\pi N \to \Delta$ cross section and momentum-dependent $\Delta$-decay width are shown to be substantial.Comment: 66 pages, Latex, 12 PostScript figures included; replaced by the revised version, to appear in Phys. Rev.

Radiation Damping in FRW Space-times with Different Topologies

We study the role played by the compactness and the degree of connectedness in the time evolution of the energy of a radiating system in the Friedmann-Robertson-Walker (FRW) space-times whose $t=const$ spacelike sections are the Euclidean 3-manifold ${\cal R}^3$ and six topologically non-equivalent flat orientable compact multiply connected Riemannian 3-manifolds. An exponential damping of the energy $E(t)$ is present in the ${\cal R}^3$ case, whereas for the six compact flat 3-spaces it is found basically the same pattern for the evolution of the energy, namely relative minima and maxima occurring at different times (depending on the degree of connectedness) followed by a growth of $E(t)$. Likely reasons for this divergent behavior of $E(t)$ in these compact flat 3-manifolds are discussed and further developments are indicated. A misinterpretation of Wolf's results regarding one of the six orientable compact flat 3-manifolds is also indicated and rectified.Comment: 13 pages, RevTeX, 5 figures, To appear in Phys. Rev. D 15, vol. 57 (1998

Spatio-Temporal Characteristics of Global Warming in the Tibetan Plateau during the Last 50 Years Based on a Generalised Temperature Zone - Elevation Model

Temperature is one of the primary factors influencing the climate and ecosystem, and examining its change and fluctuation could elucidate the formation of novel climate patterns and trends. In this study, we constructed a generalised temperature zone elevation model (GTEM) to assess the trends of climate change and temporal-spatial differences in the Tibetan Plateau (TP) using the annual and monthly mean temperatures from 1961-2010 at 144 meteorological stations in and near the TP. The results showed the following: (1) The TP has undergone robust warming over the study period, and the warming rate was 0.318°C/decade. The warming has accelerated during recent decades, especially in the last 20 years, and the warming has been most significant in the winter months, followed by the spring, autumn and summer seasons. (2) Spatially, the zones that became significantly smaller were the temperature zones of -6°C and -4°C, and these have decreased 499.44 and 454.26 thousand sq km from 1961 to 2010 at average rates of 25.1% and 11.7%, respectively, over every 5-year interval. These quickly shrinking zones were located in the northwestern and central TP. (3) The elevation dependency of climate warming existed in the TP during 1961-2010, but this tendency has gradually been weakening due to more rapid warming at lower elevations than in the middle and upper elevations of the TP during 1991-2010. The higher regions and some low altitude valleys of the TP were the most significantly warming regions under the same categorizing criteria. Experimental evidence shows that the GTEM is an effective method to analyse climate changes in high altitude mountainous regions