117 research outputs found
On Certain Large Random Hermitian Jacobi Matrices with Applications to Wireless Communications
In this paper we study the spectrum of certain large random Hermitian Jacobi
matrices. These matrices are known to describe certain communication setups. In
particular we are interested in an uplink cellular channel which models mobile
users experiencing a soft-handoff situation under joint multicell decoding.
Considering rather general fading statistics we provide a closed form
expression for the per-cell sum-rate of this channel in high-SNR, when an
intra-cell TDMA protocol is employed. Since the matrices of interest are
tridiagonal, their eigenvectors can be considered as sequences with second
order linear recurrence. Therefore, the problem is reduced to the study of the
exponential growth of products of two by two matrices. For the case where
users are simultaneously active in each cell, we obtain a series of lower and
upper bound on the high-SNR power offset of the per-cell sum-rate, which are
considerably tighter than previously known bounds
Lack of static lattice distortion in
We investigated the possibility of temperature dependent lattice distortions
in the pyrochlore compound TbTiO by measuring the internal
magnetic field distribution, using muon spin resonance, and comparing it to the
susceptibility. The measurements are done at temperatures as low as 70 mK and
external fields up to 6 kG. We find that the evolution of the width of the
field distribution can be explained by spin susceptibility only, thus ruling
out a temperature dependent hyperfine coupling. We conclude that lattice
deformations are absent in TbTiO.Comment: 8 pages, 5 figures, accepted for publication in J. Phys. Condens.
Matter. (Proceedings of Highly Frustrated Magnetism 2006); Corrections of
various typo
The symmetry of the spin Hamiltonian in herbertsmithite, a spin-1/2 kagom\'{e} lattice
We present magnetization measurements on oriented powder of
ZnCu(OH)Cl along and perpendicular to the orienting field. We
find a dramatic difference in the magnetization between the two directions. It
is biggest at low measurement fields or high temperatures. We show that the
difference at high temperatures must emerge from Ising-like exchange
anisotropy. This allows us to explain muon spin rotation data at in
terms of an exotic ferromagnetic ground state.Comment: 5 pages, 5 figure
Solitons in Nonlinear Media with an Infinite Range of Nonlocality: First Observation of Coherent Elliptic Solitons and of Vortex-Ring Solitons
We present an experimental study on wave propagation in highly nonlocal optically nonlinear media, for which far-away boundary conditions significantly affect the evolution of localized beams. As an example, we set the boundary conditions to be anisotropic and demonstrate the first experimental observation of coherent elliptic solitons. Furthermore, exploiting the natural ability of such nonlinearities to eliminate azimuthal instabilities, we perform the first observation of stable vortex-ring solitons. These features of highly nonlocal nonlinearities affected by far-away boundary conditions open new directions in nonlinear science by facilitating remote control over soliton propagation
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