42,670 research outputs found
Theoretical spin-wave dispersions in the antiferromagnetic phase AF1 of MnWO based on the polar atomistic model in P2
The spin wave dispersions of the low temperature antiferromagnetic phase
(AF1) MnWO have been numerically calculated based on the recently reported
non-collinear spin configuration with two different canting angles. A
Heisenberg model with competing magnetic exchange couplings and single-ion
anisotropy terms could properly describe the spin wave excitations, including
the newly observed low-lying energy excitation mode =0.45 meV
appearing at the magnetic zone centre. The spin wave dispersion and intensities
are highly sensitive to two differently aligned spin-canting sublattices in the
AF1 model. Thus this study reinsures the otherwise hardly provable hidden polar
character in MnWO.Comment: 7 pages, 5 figure
Pomeron loops in zero transverse dimensions
We analyze a toy model which has a structure similar to that of the recently
found QCD evolution equations, but without transverse dimensions. We develop
two different but equivalent methods in order to compute the leading-order and
next-to-leading order Pomeron loop diagrams. In addition to the leading-order
result which has been derived from Mueller's toy model~\cite% {Mueller:1994gb},
we can also calculate the next-to-leading order contribution which provides the
correction. We interpret this result and discuss its
possible implications for the four-dimensional QCD evolution.Comment: 11 pages, 4 figure
Joint Iterative Optimization Based Low-Complexity Adaptive Hybrid Beamforming for Massive MU-MIMO Systems
IEEE This paper proposes a joint iterative optimization based hybrid beamforming technique for massive MU-MIMO systems. The proposed technique jointly and iteratively optimizes the transmitter precoders and combiners, aiming to approach the global optimum solution for the system sum-rate maximization problem. The proposed technique develops an adaptive algorithm exploiting the stochastic gradients (SG) of the local beamformers and provides low-complexity closed-form solutions. Furthermore, an efficient adaptive scheme is developed based on the proposed adaptive algorithm and the closed-form solutions. The proposed algorithm requires the signal-to-interference-plus-noise ratio (SINR) feedback from each user and a limited size transition vector to be exchanged between the transmitter and receivers at each step to update beamformers locally. Analytic result shows that the proposed adaptive algorithm achieves low-complexity when the array size is large and is able to converge within a small number of iterations. Simulation result shows that the proposed technique is able to achieve superior performance comparing to the existing state-of-art techniques. In addition, the knowledge of instantaneous channel state information (CSI) is not required as the channels are also adaptively estimated with each coherence time which is a practical assumption since the CSI is usually unavailable or have time-varying nature in real-time applications
Tunable magnetization damping in transition metal ternary alloys
We show that magnetization damping in Permalloy, Ni80Fe20 (``Py''), can be
enhanced sufficiently to reduce post-switching magnetization precession to an
acceptable level by alloying with the transition metal osmium (Os). The damping
increases monotonically upon raising the Os-concentration in Py, at least up to
9% of Os. Other effects of alloying with Os are suppression of magnetization
and enhancement of in-plane anisotropy. Magnetization damping also increases
significantly upon alloying with the five other transition metals included in
this study (4d-elements: Nb, Ru, Rh; 5d-elements: Ta, Pt) but never as strongly
as with Os.Comment: 4 pages, submitted to Appl. Phys. Let
Tunable nonlinearity in atomic response to a bichromatic field
Atomic response to a probe beam can be tailored, by creating coherences
between atomic levels with help of another beam. Changing parameters of the
control beam will change the nature of coherences and hence the nature of
atomic response as well. Such change can depend upon intensity of both probe
and control beams, in a nonlinear fashion. We present a situation where this
nonlinearity in dependence can be precisely controlled, as to obtain different
variations as desired. We also present a detailed analysis of how this
nonlinear dependency arises and show that this is an interesting effect of
several Coherent Population Trap(CPT) states that exist and a competition among
them to trap atomic population in them.Comment: 16 pages and 6 figure
- …