4,104 research outputs found
Overview and Status of the CMS Silicon Strip Tracker
The CMS experiment at the LHC features the largest Silicon Strip Detector
ever built. The impact of the operating conditions and physics requirements on
the design choices of the CMS Silicon Tracker is reviewed. The readiness of the
Silicon Strip Tracker for the tentatively scheduled CMS commissioning in Summer
2008 is briefly described.Comment: 3 pages, 2 figures, conference proceedings for the 2007 Europhysics
Conference on High Energy Physics, Manchester, England, 19-25 July 200
Secure Cascade Channel Synthesis
We consider the problem of generating correlated random variables in a
distributed fashion, where communication is constrained to a cascade network.
The first node in the cascade observes an i.i.d. sequence locally before
initiating communication along the cascade. All nodes share bits of common
randomness that are independent of . We consider secure synthesis - random
variables produced by the system appear to be appropriately correlated and
i.i.d. even to an eavesdropper who is cognizant of the communication
transmissions. We characterize the optimal tradeoff between the amount of
common randomness used and the required rates of communication. We find that
not only does common randomness help, its usage exceeds the communication rate
requirements. The most efficient scheme is based on a superposition codebook,
with the first node selecting messages for all downstream nodes. We also
provide a fleeting view of related problems, demonstrating how the optimal rate
region may shrink or expand.Comment: Submitted to IEEE Transactions on Information Theor
Ferrodistorsive orbital ordering in the layered nickelate NaNiO_2: A density-functional study
The electronic structure and magnetism in the sodium nickelate NaNiO_2 in the
low-temperature phase is studied from density-functional calculations using the
linear muffin-tin orbitals method. An antiferromagnetic solution with a
magnetic moment of 0.7 m_B per Ni ion is found. A ferrodistorsive orbital
ordering is shown to occur due to the Jahn-Teller distortion around the Ni^{3+}
ion in agreement with the orbital ordering inferred from neutron diffraction.
While the intralayer exchange is ferromagnetic, the interlayer exchange is
weakly antiferromagnetic, mediated by a long Ni-O-Na-O-Ni superexchange path.Comment: 4 pages, 5 figures Submitted to MMM2004 conference Proceeding
On the Ruderman-Kittel-Kasuya-Yosida interaction in graphene
The two dimensionality plus the linear band structure of graphene leads to
new behavior of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, which is
the interaction between two magnetic moments mediated by the electrons of the
host crystal. We study this interaction from linear response theory. There are
two equivalent methods both of which may be used for the calculation of the
susceptibility, one involving the integral over a product of two Green's
functions and the second that involves the excitations between occupied and
unoccupied states, which was followed in the original work of Ruderman and
Kittel. Unlike the behavior of an
ordinary two-dimensional (2D) metal, in graphene falls off as ,
shows the -type of behavior, which contains
an interference term between the two Dirac cones, and it oscillates for certain
directions and not for others. Quite interestingly, irrespective of any
oscillations, the RKKY interaction in graphene is always ferromagnetic for
moments located on the same sublattice and antiferromagnetic for moments on the
opposite sublattices, a result that follows from particle-hole symmetry.Comment: 12 pages, 5 figures, submitted to AIP Conference Proceeding
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