7,538 research outputs found
Distributed Linear Convolutional Space-Time Coding for Two-Relay Full-Duplex Asynchronous Cooperative Networks
In this paper, a two-relay full-duplex asynchronous cooperative network with
the amplify-and-forward (AF) protocol is considered. We propose two distributed
space-time coding schemes for the cases with and without cross-talks,
respectively. In the first case, each relay can receive the signal sent by the
other through the cross-talk link. We first study the feasibility of cross-talk
cancellation in this network and show that the cross-talk interference cannot
be removed well. For this reason, we design space-time codes by utilizing the
cross-talk signals instead of removing them. In the other case, the self-coding
is realized individually through the loop channel at each relay node and the
signals from the two relay nodes form a space-time code. The achievable
cooperative diversity of both cases is investigated and the conditions to
achieve full cooperative diversity are presented. Simulation results verify the
theoretical analysis.Comment: 11 pages, 7 figures, accepted by IEEE transactions on wireless
communication
Thermodynamics of modified black holes from gravity's rainbow
We study the thermodynamics of modified black holes proposed in the context
of gravity's rainbow. A notion of intrinsic temperature and entropy for these
black holes is introduced. In particular for a specific class of modified
Schwarzschild solutions, their temperature and entropy are obtained and
compared with those previously obtained from modified dispersion relations in
deformed special relativity. It turns out that the results of these two
different strategies coincide, and this may be viewed as a support for the
proposal of deformed equivalence principle.Comment: 3 pages, Revte
Multiscale examination of strain effects in Nd-Fe-B permanent magnets
We have performed a combined first-principles and micromagnetic study on the
strain effects in Nd-Fe-B magnets. First-principles calculations on Nd2Fe14B
reveal that the magnetocrystalline anisotropy (K) is insensitive to the
deformation along c axis and the ab in-plane shrinkage is responsible for the K
reduction. The predicted K is more sensitive to the lattice deformation than
what the previous phenomenological model suggests. The biaxial and triaxial
stress states have a greater impact on K. Negative K occurs in a much wider
strain range in the ab biaxial stress state. Micromagnetic simulations of
Nd-Fe-B magnets using first-principles results show that a 3-4% local strain in
a 2-nm-wide region near the interface around the grain boundaries and triple
junctions leads to a negative local K and thus decreases the coercivity by
~60%. The local ab biaxial stress state is more likely to induce a large loss
of coercivity. In addition to the local stress states and strain levels
themselves, the shape of the interfaces and the intergranular phases also makes
a difference in determining the coercivity. Smoothing the edge and reducing the
sharp angle of the triple regions in Nd-Fe-B magnets would be favorable for a
coercivity enhancement.Comment: 9 figure
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