8,228 research outputs found
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 () 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 region but a suppression at large
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 ~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 - and -period current-phase relations
() are studied. There is a sharp jump at
and for and respectively in the
clean junction. For , the sharp jump is robust against impurity
strength and distribution. However for , the impurity makes the jump
at smooth. The critical (maximum) current of 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
dimensions. We then calculate polarized input FFs contributed from all -wave
and -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-methylÂphenÂyl)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, interÂmolecular N—H⋯O hydrogen bonds link the molÂecules, forming infinite chains down [010]
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