22 research outputs found
Nuclear EMC Effect in a Statistical Model
A simple statistical model in terms of light-front kinematic variables is
used to explain the nuclear EMC effect in the range , which
was constructed by us previously to calculate the parton distribution functions
(PDFs) of the nucleon. Here, we treat the temperature as a parameter of the
atomic number , and get reasonable results in agreement with the
experimental data. Our results show that the larger , the lower thus the
bigger volume , and these features are consistent with other models.
Moreover, we give the predictions of the quark distribution ratios,
\emph{i.e.}, , , and , and also the gluon ratio for iron as an example. The
predictions are different from those by other models, thus experiments aiming
at measuring the parton ratios of antiquarks, strange quarks, and gluons can
provide a discrimination of different models.Comment: 26 latex pages, 3 figure
Properties of charmed and bottom hadrons in nuclear matter: A plausible study
Changes in properties of heavy hadrons with a charm or a bottom quark are
studied in nuclear matter. Effective masses (scalar potentials) for the hadrons
are calculated using quark-meson coupling model. Our results also suggest that
the heavy baryons containing a charm or a bottom quark will form charmed or
bottom hypernuclei, which was first predicted in mid 70's. In addition a
possibility of -nuclear bound (atomic) states is briefly discussed.Comment: Latex, 11 pages, 3 figures, text was expanded substantially, version
to appear in Phys. Lett.
Transverse Polarisation of Quarks in Hadrons
We review the present state of knowledge regarding the transverse
polarisation (or transversity) distributions of quarks. After some generalities
on transverse polarisation, we formally define the transversity distributions
within the framework of a classification of all leading-twist distribution
functions. We describe the QCD evolution of transversity at leading and
next-to-leading order. A comprehensive treatment of non-perturbative
calculations of transversity distributions (within the framework of quark
models, lattice QCD and QCD sum rules) is presented. The phenomenology of
transversity (in particular, in Drell-Yan processes and semi-inclusive
leptoproduction) is discussed in some detail. Finally, the prospects for future
measurements are outlined.Comment: small changes, references added, as finally published in Physics
Report
Light flavor asymmetry of nucleon sea
The light flavor antiquark distributions of the nucleon sea are calculated in
the effective chiral quark model and compared with experimental results. The
contributions of the flavor-symmetric sea-quark distributions and the nuclear
EMC effect are taken into account to obtain the ratio of Drell-Yan cross
sections , which can match well
with the results measured in the FermiLab E866/NuSea experiment. The calculated
results also match the measured from different
experiments, but unmatch the behavior of derived
indirectly from the measurable quantity
by the FermiLab E866/NuSea
Collaboration at large . We suggest to measure again
at large from precision experiments with careful experimental data
treatment. We also propose an alternative procedure for experimental data
treatment.Comment: 10 pages, 8 figures, final version to appear in EPJ
Thermal Dileptons at LHC
We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb
collisions at LHC. Hadronic emission in the low-mass region is calculated using
in-medium spectral functions of light vector mesons within hadronic many-body
theory. In the intermediate-mass region thermal radiation from the Quark-Gluon
Plasma, evaluated perturbatively with hard-thermal loop corrections, takes
over. An important source over the entire mass range are decays of correlated
open-charm hadrons, rendering the nuclear modification of charm and bottom
spectra a critical ingredient.Comment: 2 pages, 2 figures, contributed to Workshop on Heavy Ion Collisions
at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun
2007 v2: acknowledgment include
The quark-meson coupling model for Lambda, Sigma and Xi hypernuclei
The quark-meson coupling (QMC) model, which has been successfully used to
describe the properties of both infinite nuclear matter and finite nuclei, is
applied to a systematic study of and hypernuclei.
Assumptions made in the present study are, (i) the (self-consistent) exchanged
scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6)
valence quark model for the bound nucleons and hyperon. The model automatically
leads to a very weak spin-orbit interaction for the in a
hypernucleus. Effects of the Pauli blocking at the quark level, particularly in
the open, coupled, channel (strong conversion), is also
taken into account in a phenomenological way.Comment: 27 pages, 14 postscript figures, uses epsfig.sty. Version to appear
in Nucl. Phys.
Rational Diversification of a Promoter Providing Fine-Tuned Expression and Orthogonal Regulation for Synthetic Biology
Yeast is an ideal organism for the development and application of synthetic biology, yet there remain relatively few well-characterised biological parts suitable for precise engineering of this chassis. In order to address this current need, we present here a strategy that takes a single biological part, a promoter, and re-engineers it to produce a fine-graded output range promoter library and new regulated promoters desirable for orthogonal synthetic biology applications. A highly constitutive Saccharomyces cerevisiae promoter, PFY1p, was identified by bioinformatic approaches, characterised in vivo and diversified at its core sequence to create a 36-member promoter library. TetR regulation was introduced into PFY1p to create a synthetic inducible promoter (iPFY1p) that functions in an inverter device. Orthogonal and scalable regulation of synthetic promoters was then demonstrated for the first time using customisable Transcription Activator-Like Effectors (TALEs) modified and designed to act as orthogonal repressors for specific PFY1-based promoters. The ability to diversify a promoter at its core sequences and then independently target Transcription Activator-Like Orthogonal Repressors (TALORs) to virtually any of these sequences shows great promise toward the design and construction of future synthetic gene networks that encode complex “multi-wire” logic functions