1,259 research outputs found
Measurement of the WW Cross Section in 7 TeV pp Collisions with the ATLAS Detector
We report a measurement of the WW production cross section in pp collisions
at 7 TeV. The WW leptonic decay channels are analyzed using data corresponding
to 1.02 /fb of integrated luminosity collected by the ATLAS detector during
2011 at the CERN Large Hadron Collider. With 414 observed WW candidate events
and an estimated background of 17028 events, the measured WW production
cross section is pb, in agreement with the Standard Model NLO prediction of
463 pb.Comment: 9 pages, proceedings of the DPF-2011 Conference, Providence, RI,
August 8-13, 201
Pulling hairpinned polynucleotide chains: Does base-pair stacking interaction matter?
Force-induced structural transitions both in relatively random and in
designed single-stranded DNA (ssDNA) chains are studied theoretically. At high
salt conditions, ssDNA forms compacted hairpin patterns stabilized by
base-pairing and base-pair stacking interactions, and a threshold external
force is needed to pull the hairpinned structure into a random coiled one. The
base-pair stacking interaction in the ssDNA chain makes this hairpin-coil
conversion a discontinuous (first-order) phase transition process characterized
by a force plateau in the force-extension curve, while lowering this potential
below some critical level turns this transition into continuous (second-order)
type, no matter how strong the base-pairing interaction is. The phase diagram
(including hairpin-I, -II, and random coil) is discussed as a function of
stacking potential and external force. These results are in quantitative
agreement with recent experimental observations of different ssDNA sequences,
and they reveal the necessity to consider the base-pair stacking interactions
in order to understand the structural formation of RNA, a polymer designed by
nature itself. The theoretical method used may be extended to study the
long-range interaction along double-stranded DNA caused by the topological
constraint of fixed linking number.Comment: 8 pages using Revte
Collapse Transition of Two-Dimensional Flexible and Semiflexible Polymers
The nature of the globule-coil transition of surface-confined polymers has
been an issue of debate. Here this 2D collapse transition is studied through a
partially directed lattice model. In the general case of polymers with positive
bending stiffness (), the collapse transition is {\em first-order};
it becomes {\em second-order} only in the limiting case of zero bending
stiffness (). These analytical results are confirmed by Monte
Carlo simulations. We also suggest some possible future experiments.Comment: 4 pages, 3 figure
Test of conformal gravity with astrophysical observations
Since it can describe the rotation curves of galaxies without dark matter and
can give rise to accelerated expansion, conformal gravity attracts much
attention recently. As a theory of modified gravity, it is important to test
conformal gravity with astrophysical observations. Here we constrain conformal
gravity with SNIa and Hubble parameter data and investigate whether it suffers
from an age problem with the age of APM~08279+5255. We find conformal gravity
can accommodate the age of APM~08279+5255 at 3 deviation, unlike most
of dark energy models which suffer from an age problem.Comment: 6 pages, 2 figure
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