68,474 research outputs found
The trimer-based spin liquid candidate Ba4NbIr3O12
Ba4NbIr3O12, a previously unreported material with a triangular planar
geometry of Ir3O12 trimers, is described. Magnetic susceptibility measurements
show no magnetic ordering down to 1.8 K despite the Curie-Weiss temperature of
-13 K. The material has a very low effective magnetic moment of 0.80
{\mu}B/f.u. To look at the lower temperature behavior, the specific heat (Cp)
was measured down to 0.35 K; it shows no indication of magnetic ordering and
fitting a power law to Cp vs. T below 2 K yields the power {\alpha} = 3/4.
Comparison to the previously unreported trimer compound made with the 4d
element Rh in place of the 5d element Ir, Ba4NbRh3O12, is presented. The
analysis suggests that Ba4NbIr3O12 is a candidate spin liquid material.Comment: 19 pages, 7 main figures, 2 SI figure
Differential Amplify-and-Forward Relaying in Time-Varying Rayleigh Fading Channels
This paper considers the performance of differential amplify-and-forward
(D-AF) relaying over time-varying Rayleigh fading channels. Using the
auto-regressive time-series model to characterize the time-varying nature of
the wireless channels, new weights for the maximum ratio combining (MRC) of the
received signals at the destination are proposed. Expression for the pair-wise
error probability (PEP) is provided and used to obtain an approximation of the
total average bit error probability (BEP). The obtained BEP approximation
clearly shows how the system performance depends on the auto-correlation of the
direct and the cascaded channels and an irreducible error floor exists at high
signal-to-noise ratio (SNR). Simulation results also demonstrate that, for
fast-fading channels, the new MRC weights lead to a better performance when
compared to the classical combining scheme. Our analysis is verified with
simulation results in different fading scenarios
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