1,189 research outputs found
Array Configuration Effect on the Spatial Correlation of MU-MIMO Channels in NLoS Environments
In this paper, three different base-station antenna (BSA) configurations are compared in terms of inter-user spatial correlation in a two dimensional (2D) non-line-of-sight (NLoS) environment. The three configurations are: (i) a regular uniform linear array (ULA); (ii) a periodic sparse array; and (iii) an aperiodic sparse array. Electromagnetic modeling of the NLoS channel is proposed where scatterers are considered as resonant dipoles confined in clusters of scatterers (CoSs). While the probability of facing highly correlated user-equipments (UEs) in a multi-user multiple-input multiple-output (MU-MIMO) system is decreasing as the richness of mutipath increases, the sparsity (increased inter-element spacing) is seen to be capable of reducing this probability as well. This is due to the larger spatial variations experienced by the sparse array. Moreover, the results show that further improvement can be achieved by deploying an aperiodic distribution of antenna elements into the sparse antenna aperture
On the sign of the linear magnetoelectric coefficient in CrO
We establish the sign of the linear magnetoelectric (ME) coefficient,
, in chromia, CrO. CrO is the prototypical linear ME
material, in which an electric (magnetic) field induces a linearly proportional
magnetization (polarization), and a single magnetic domain can be selected by
annealing in combined magnetic (H) and electric (E) fields. Opposite
antiferromagnetic domains have opposite ME responses, and which
antiferromagnetic domain corresponds to which sign of response has previously
been unclear. We use density functional theory (DFT) to calculate the magnetic
response of a single antiferromagnetic domain of CrO to an applied
in-plane electric field at 0 K. We find that the domain with nearest neighbor
magnetic moments oriented away from (towards) each other has a negative
(positive) in-plane ME coefficient, , at 0 K. We show that this
sign is consistent with all other DFT calculations in the literature that
specified the domain orientation, independent of the choice of DFT code or
functional, the method used to apply the field, and whether the direct
(magnetic field) or inverse (electric field) ME response was calculated. Next,
we reanalyze our previously published spherical neutron polarimetry data to
determine the antiferromagnetic domain produced by annealing in combined E and
H fields oriented along the crystallographic symmetry axis at room temperature.
We find that the antiferromagnetic domain with nearest-neighbor magnetic
moments oriented away from (towards) each other is produced by annealing in
(anti-)parallel E and H fields, corresponding to a positive (negative) axial ME
coefficient, , at room temperature. Since
at 0 K and at room temperature are known to be of opposite
sign, our computational and experimental results are consistent.Comment: 11 pages, 5 figure
Wheel Abrasion Experiment Metals Selection for Mars Pathfinder Mission
A series of metals was examined for suitability for the Wheel Abrasion Experiment, one of ten microrover experiments of the Mars Pathfinder Mission. The seven candidate metals were: Ag, Al, Au, Cu, Ni, Pt, and W. Thin films of candidate metals from 0.1 to 1.0 micrometer thick were deposited on black anodized aluminum coupons by e-beam and resistive evaporation and chemical vapor deposition. Optical, corrosion, abrasion, and adhesion criteria were used to select Al, Ni, and Pt. A description is given of the deposition and testing of thin films, followed by a presentation of experimental data and a brief discussion of follow-on testing and flight qualification
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