52,546 research outputs found
LDPC Code Design for the BPSK-constrained Gaussian Wiretap Channel
A coding scheme based on irregular low-density parity-check (LDPC) codes is
proposed to send secret messages from a source over the Gaussian wiretap
channel to a destination in the presence of a wiretapper, with the restriction
that the source can send only binary phase-shift keyed (BPSK) symbols. The
secrecy performance of the proposed coding scheme is measured by the secret
message rate through the wiretap channel as well as the equivocation rate about
the message at the wiretapper. A code search procedure is suggested to obtain
irregular LDPC codes that achieve good secrecy performance in such context.Comment: submitted to IEEE GLOBECOM 2011 - Communication Theory Symposiu
Elliptic Flow from a Transversally Thermalized Fireball
The agreement of elliptic flow data at RHIC at central rapidity with the
hydrodynamic model has led to the conclusion of very rapid thermalization. This
conclusion is based on the intuitive argument that hydrodynamics, which assumes
instantaneous local thermalization, produces the largest possible elliptic flow
values and that the data seem to saturate this limit. We here investigate the
question whether incompletely thermalized viscous systems may actually produce
more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast
primordial longitudinal expansion of the reaction zone, we investigate a toy
model which exhibits thermalization only in the transverse directions but
undergoes collisionless free-streaming expansion in the longitudinal direction.
For collisions at RHIC energies, elliptic flow results from the model are
compared with those from hydrodynamics. With the final particle yield and
\kt-distribution fixed, the transversally thermalized model is shown not to
be able to produce the measured amount of elliptic flow. This investigation
provides further support for very rapid local kinetic equilibration at RHIC. It
also yields interesting novel results for the elliptic flow of massless
particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure
Experimental Investigation of Cold-formed Steel Beam-column Sub-frames: Pilot Study
This paper presents the findings of an experimental investigation on the structural performance of bolted moment connections in cold-formed steel beam-column sub-frames. A total of eight tests with three different connection configurations in both internal and external columns were carried out. Double lipped C-sections back-to-back with hot rolled steel gusset plates of 10 mm and of 16 mm in two different shapes were tested; four bolts per member were used in the connections. Among the tests, three different modes of failure were identified and the measured moment resistances at the connections were found to vary from 36% to 97% of the measured moment capacities of the cold-formed steel sections, demonstrating that bolted moment connections between cold-formed steel members are structurally feasible and economical. Furthermore, structural members with double lipped C sections back-to-back are shown to be practical in constructing short to medium span portal frames with bolted moment connections through rational design
Fully nonlinear excitations of non-Abelian plasma
We investigate fully nonlinear, non-Abelian excitations of quark-antiquark
plasma, using relativistic fluid theory in cold plasma approximation. There are
mainly three important nonlinearities, coming from various sources such as
non-Abelian interactions of Yang-Mills (YM) fields, Wong's color dynamics and
plasma nonlinearity, in our model. By neglecting nonlinearities due to plasma
and color dynamics we get back the earlier results of Blaizot {\it et. al.},
Phys. Rev. Lett. 72, 3317 (1994). Similarly, by neglecting YM fields
nonlinearity and plasma nonlinearity, it reduces to the model of Gupta {\it et.
al.}, Phys. Lett. B498, 223 (2005). Thus we have the most general non-Abelian
mode of quark-gluon plasma (QGP). Further, our model resembles the problem of
propagation of laser beam through relativistic plasma, Physica 9D, 96 (1983).
in the absence of all non-Abelian interactions.Comment: 8 pages, 2 figures, articl
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