The global geometrical property of jet events in high-energy nuclear collisions

We present the first theoretical study of medium modifications of the global geometrical pattern, i.e., transverse sphericity ($S_{\perp}$) distribution of jet events with parton energy loss in relativistic heavy-ion collisions. In our investigation, POWHEG+PYTHIA is employed to make an accurate description of transverse sphericity in the p+p baseline, which combines the next-to-leading order (NLO) pQCD calculations with the matched parton shower (PS). The Linear Boltzmann Transport (LBT) model of the parton energy loss is implemented to simulate the in-medium evolution of jets. We calculate the event normalized transverse sphericity distribution in central Pb+Pb collisions at the LHC, and give its medium modifications. An enhancement of transverse sphericity distribution at small $S_{\perp}$ region but a suppression at large $S_{\perp}$ region are observed in A+A collisions as compared to their p+p references, which indicates that in overall the geometry of jet events in Pb+Pb becomes more pencil-like. We demonstrate that for events with 2 jets in the final-state of heavy-ion collisions, the jet quenching makes the geometry more sphere-like with medium-induced gluon radiation. However, for events with $\ge 3$~jets, parton energy loss in the QCD medium leads to the events more pencil-like due to jet number reduction, where less energetic jets may lose their energies and then fall off the jet selection kinematic cut. These two effects offset each other and in the end result in more jetty events in heavy-ion collisions relative to that in p+p.Comment: 9 pages, 9 figure

Josephson junction on one edge of a two dimensional topological insulator affected by magnetic impurity

Current-phase relation in a Josephson junction formed by putting two s-wave superconductors on the same edge of a two dimensional topological insulator is investigated. We consider the case that the junction length is finite and magnetic impurity exists. The similarity and difference with conventional Josephson junction is discussed. The current is calculated in the semiconductor picture. Both the $2\pi$- and $4\pi$-period current-phase relations ($I_{2\pi}(\phi), I_{4\pi}(\phi)$) are studied. There is a sharp jump at $\phi=\pi$ and $\phi=2\pi$ for $I_{2\pi}$ and $I_{4\pi}$ respectively in the clean junction. For $I_{2\pi}$, the sharp jump is robust against impurity strength and distribution. However for $I_{4\pi}$, the impurity makes the jump at $\phi=2\pi$ smooth. The critical (maximum) current of $I_{2\pi}$ is given and we find it will be increased by asymmetrical distribution of impurity.Comment: 7 pages, 5 figure

Cγ- and Cα-Subunits Provide the Specificity for cAMP/PKA Function

The Cα and Cγ of the cAMP-dependent protein kinase (PKA) are two highly homologous (83% amino acid identity), yet functionally distinct isozymes in vitro for substrate and pseudosubstrate specificity, and in intact cells for cell phenotypes (Beebe, 1992). To determine the molecular mechanisms underlying the distinct functions in cell phenotypes, in vitro experiments were designed to make a detailed comparison of Cγ and Cα for substrate and pseudosubstrate specificity. To this end, Cγ and Cα were expressed m mammalian cells, bacteria and Sf9 insect cells using baculovirus. Abundant expression of active enzyme was cell system specific. Cγ and Cα expressed in Sf9 cells and bacteria, respectively, were purified to homogeneity. Kinetic analysis showed that Cγ and Cα shared primary substrate phosphorylation specificity. Cγ exhibited similar or lower Km values, but lower Vmax values in substrate phosphorylation than Cα. Different isoforms of PKI and R-subunit expressed in bacteria were purified to homogeneity. The kinetic comparison on these pseudosubstrate-inhibition of phosphotransferase activity showed Cγ was insensitive to PKI-inhibition and required the C-terminal residues in the pseudosubstrate site for RIα-inhibition. In vitro data suggested that Cγ had unique substrate and pseudosubstrate specificity. Intact cell experiments were designed to determine the distinct role of Cγ and Cα in the regulation of cAMP-responsive gene expression. To this end, Cγ and Cα were compared in the regulation of CRE (cAMP responsive elements)-reporter gene activity, and in the events which were associated with CRE-reporter gene expression using HEK293 cells and Y1/Kin8 clones permanently transfected with Cγ - and Cα-subunits. In response to cAMP stimulation, both Cγ and Cα migrated to the nucleus, phosphorylated CREB (cAMP responsive element binding protein) and increased the levels of immunoreactive CREB. Phosphorylated CREB in the nuclear extracts of Cγ and Cα clones bound to a CRE element in super gel mobility shift assay. Surprisingly, Cα, but not Cγ induced CRE-reporter gene activity and only Cα clone restored steroidogenesis to cAMP resistant Kin8 mutant. However, Cγ could both positively and negatively modulate Cα-mediated regulation of reporter gene activity. Results from Gal4-luc/Gal4-CREB reporter gene study showed that CRE and CREB dimerization were not necessary for Cγ to modulate the Cα-mediated regulation of CRE-reporter gene activity, suggesting that Cγ and Cα played different roles in the regulation of cAMP-responsive gene activity by an intra-CREB-molecular mechanism. The presence of two kinetically and functionally distinct C-subunit isoforms provides the potential to fine-tune and/or to diversify cAMP signal transduction downstream of PKA activation, which is mediated by R-subunits and PKI, and/or activation of C-isoforms with different specificity

Fragmentation functions of polarized heavy quarkonium

Study of the polarized heavy quarkonium production in recently proposed QCD factorization formalism requires knowledge of a large number of input fragmentation functions (FFs) from a single parton or a heavy quark-antiquark pair to a polarized heavy quarkonium. In this paper, we calculate these FFs at the input scale in terms of nonrelativistic QCD (NRQCD) factorization. We derive all relevant polarized NRQCD long-distance matrix elements based symmetries and propose a self-consistent scheme to define them in arbitrary $d$ dimensions. We then calculate polarized input FFs contributed from all $S$-wave and $P$-wave NRQCD intermediate states. With our calculation of the polarized input FFs, and the partonic hard part available in literatures, the QCD factorization formalism is ready to be applied to polarized heavy quarkonium production.Comment: 30 pages, 1 figur

N-(4-Bromo-2-methyl­phen­yl)pivalamide

The conformation of the N—H bond in the title compound, C12H16BrNO, is syn to the ortho-methyl substituent. There are two unique molecules in the asymmetric unit. In the crystal structure, inter­molecular N—H⋯O hydrogen bonds link the mol­ecules, forming infinite chains down [010]