5,193 research outputs found
Strong Electron-Phonon Interaction and Colossal Magnetoresistance in EuTiO
At low temperatures, EuTiO system has very large resistivities and
exhibits colossal magnetoresistance. Based on a first principle calculation and
the dynamical mean-field theory for small polaron we have calculated the
transport properties of EuTiO. It is found that due to electron-phonon
interaction the conduction band may form a tiny subband which is close to the
Fermi level. The tiny subband is responsible for the large resistivity.
Besides, EuTiO is a weak antiferromagnetic material and its magnetization
would slightly shift the subband via exchange interaction between conduction
electrons and magnetic atoms. Since the subband is close to the Fermi level, a
slight shift of its position gives colossal magnetoresistance.Comment: 6 pages, 5 figure
Contouring Accuracy Improvement Using an Adaptive Feedrate Planning Method for CNC Machine Tools
AbstractThe reduction of contour error plays an important role in achieving high accuracy machining. To reduce contour error, most of previous studies have focused on developing advanced control strategies. As an alternative strategy, contouring accuracy improvement using an adaptive feedrate planning method is proposed in this paper. First, a typical PID controller is adopted to build the contour error model, from which the feedrate can be scheduled in the contour error violated zones. Then, the relations between each constraint and the cutter tip feedrate are derived. After that, a linear programming model is applied to obtain the optimal feedrate profile on the sampling positions of the given tool path. Finally, illustrated examples are given to validate the feasibility and applicability of the proposed feedrate planning method. The comparison results show that the proposed method has a significant effect on improving contouring accuracy
Robust Guidance Algorithm against Hypersonic Targets
This chapter presents a robust guidance algorithm for intercepting hypersonic targets. Since the differential of the line-of-sight rate is more sensitive to the target maneuver, a nonlinear proportional and differential guidance law (NPDG) is given by employing the differential of the line-of-sight rate produced by a nonlinear tracking differentiator. Based on the NPDG, a fractional calculus guidance law (FCG) is presented by utilizing the differential definition of fractional order. On the basis of interceptor-target relative motions, the stability criteria of the guidance system of the FCG are deduced. In different target maneuver and noisy cases, simulation results verify that the proposed guidance laws have small miss distances and the FCG has a stronger robustness
Singular equivalences induced by bimodules and quadratic monomial algebras
We investigate the problem when the tensor functor by a bimodule yields a
singular equivalence. It turns out that this problem is equivalent to the one
when the Hom functor given by the same bimodule induces a triangle equivalence
between the homotopy categories of acyclic complexes of injective modules. We
give conditions on when a bimodule appears in a pair of bimodules, that defines
a singular equivalence with level. We construct an explicit bimodule, which
yields a singular equivalence between a quadratic monomial algebra and its
associated algebra with radical square zero. Under certain conditions which
include the Gorenstein cases, the bimodule does appear in a pair of bimodules
defining a singular equivalence with level.Comment: 20 pages, all comments are welcome
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