29,301 research outputs found

    Domain wall propagation due to the synchronization with circularly polarized microwaves

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    Finding a new control parameter for magnetic domain wall (DW) motion in magnetic nanostructures is important in general and in particular for the spintronics applications. Here, we show that a circularly polarized magnetic field (CPMF) at GHz frequency (microwave) can efficiently drive a DW to propagate along a magnetic nanowire. Two motion modes are identified: rigid-DW propagation at low frequency and oscillatory propagation at high frequency. Moreover, DW motion under a CPMF is equivalent to the DW motion under a uniform spin current in the current perpendicular to the plane magnetic configuration proposed recently by Khvalkovskiy et al. [Phys. Rev. Lett. 102, 067206 (2009)], and the CPMF frequency plays the role of the current

    Dynamic localization versus photon-assisted transport in semiconductor superlattices driven by dc-ac fields

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    Via the numerical analysis on the intraband dynamics of optically excited semiconductor superlattices, we find that time-integrated squared THz emission signals can be used for probing both dynamic localization and multi-photon resonance in the coherent regime. Competition effect between dynamic localization and photon-assisted transport has also been discussed.Comment: 7 pages, 3 figures, Revtex, Postcsript figure

    Static Solution in Source-Free SU(2) Yang-Mills Theory

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    We show that a non-trivial topological effect breaks the conformal invariance of pure Yang-Mills theory. Thus it is possible that classic particle-like solutions exists in pure non-Abelian Yang-Mills theory. We find a static, non-singular solution in source-free SU(2) Yang-Mills theory in four-dimensional Minkowski space. This solution is a stable soliton characterized by non-trivial topology and imaginary A0aA_0^a, i.e., A0aA0a<0A_0^aA_0^a<0. It yields hermitian Hamilton, and finite, positive energy.Comment: revtex, 4 pages, 1 figur

    Old and New Morry Spaces via Heat Kernel Bounds

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    Given p[1,)p\in [1,\infty) and λ(0,n)\lambda\in (0,n), we study Morrey space Lp,λ(Rn){\rm L}^{p,\lambda}({\mathbb R}^n) of all locally integrable complex-valued functions ff on Rn{\mathbb R}^n such that for every open Euclidean ball BRnB\subset{\mathbb R}^n with radius rBr_B there are numbers C=C(f)C=C(f) (depending on ff) and c=c(f,B)c=c(f,B) (relying upon ff and BB) satisfying rBλBf(x)cpdxC r_B^{-\lambda}\int_{B}|f(x)-c|^pdx\le C and derive old and new, two essentially different cases arising from either choosing c=fB=B1Bf(y)dyc=f_B=|B|^{-1}\int_{B}f(y)dy or replacing cc by PtB(x)=tBptB(x,y)f(y)dyP_{t_B}(x)=\int_{t_B}p_{t_B}(x,y)f(y)dy -- where tBt_B is scaled to rBr_B and pt(,)p_t(\cdot,\cdot) is the kernel of the infinitesimal generator LL of an analytic semigroup {etL}t0\{e^{-tL}\}_{t\ge0} on L2(Rn){\rm L}^2({\mathbb R}^n). Consequently, we are led to simultaneously characterize the old and new Morrey spaces, but also to show that for a suitable operator LL, the new Morrey space is equivalent to the old one

    Giant magnetoimpedance in crystalline Mumetal

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    We studied giant magnetoimpedance (GMI) effect in commercial crystalline Mumetal, with the emphasis to sample thickness dependence and annealing effects. By using appropriate heat treatment one can achieve GMI ratios as high as 310%, and field sensitivity of about 20%/Oe, which is comparable to the best GMI characteristics obtained for amorphous and nanocrystalline soft magnetic materials.Comment: 8 pages, 3 figure

    Reply to "Comment on 'Detecting Non-Abelian Geometric Phases with Three-Level \Lambda\ Atoms' "

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    In this reply, we address the comment by Ericsson and Sjoqvist on our paper [Phys. Rev. A {\bf 84}, 034103 (2011)]. We point out that the zero gauge field is not the evidence of trivial geometric phase for a non-Abelian SU(2) gauge field. Furthermore, the recalculation shows that the non-Abelian geometric phase we proposed in the three-level Λ\Lambda system is indeed experimentally detectable.Comment: 3 pages,1 figur

    Low-Complexity Linear Precoding for Secure Spatial Modulation

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    In this work, we investigate linear precoding for secure spatial modulation. With secure spatial modulation, the achievable secrecy rate does not have an easy-to-compute mathematical expression, and hence, has to be evaluated numerically, which leads to high complexity in the optimal precoder design. To address this issue, an accurate and analytical approximation of the secrecy rate is derived in this work. Using this approximation as the objective function, two low-complexity linear precoding methods based on gradient descend (GD) and successive convex approximation (SCA) are proposed. The GD-based method has much lower complexity but usually converges to a local optimum. On the other hand, the SCA-based method uses semi-definite relaxation to deal with the non-convexity in the precoder optimization problem and achieves near-optimal solution. Compared with the existing GD-based precoder design in the literature that directly uses the exact and numerically evaluated secrecy capacity as the objective function, the two proposed designs have significantly lower complexity. Our SCA-based design even achieves a higher secrecy rate than the existing GD-based design.Comment: 11pages, 8figure

    Enumerative Gadget Phenomena for (4,1)(4,1)-Adinkras

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    Adinkras are combinatorial objects developed to study supersymmetry representations. Gates et al. introduced the "gadget" as a function of pairs of adinkras, obtaining some mysterious results for (n=4,k=1)(n=4, k=1) adinkras with computer-aided computation. Specifically, very few values of the gadget actually appear, suggesting a great deal of symmetry in these objects. In this paper, we compute gadgets symbolically and explain some of these observed phenomena with group theory and combinatorics. Guided by this work, we give some suggestions for generalizations of the gadget to other values of the nn and kk parameters

    Motors and Impossible Firing Patterns in the Parallel Chip-Firing Game

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    The parallel chip-firing game is an automaton on graphs in which vertices "fire" chips to their neighbors when they have enough chips to do so. The game is always periodic, and we concern ourselves with the firing sequences of vertices. We introduce the concepts of motorized parallel chip-firing games and motor vertices, study the effects of motors connected to a tree and show that motorized games can be transformed into ordinary games if the motors' firing sequences occur in some ordinary game. We then characterize exactly which periodic firing patterns can occur in an ordinary game and state some implications of the finding.Comment: 19 pages; added higher-level explanation of main theorem's proof, typo correction

    Dynamics of small trapped one-dimensional Fermi gas under oscillating magnetic fields

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    Deterministic preparation of an ultracold harmonically trapped one-dimensional Fermi gas consisting of a few fermions has been realized by the Heidelberg group. Using Floquet formalism, we study the time dynamics of two- and three-fermion systems in a harmonic trap under an oscillating magnetic field. The oscillating magnetic field produces a time-dependent interaction strength through a Feshbach resonance. We explore the dependence of these dynamics on the frequency of the oscillating magnetic field for non-interacting, weakly interacting, and strongly interacting systems. We identify the regimes where the system can be described by an effective two-state model and an effective three-state model. We find an unbounded coupling to all excited states at the infinitely strong interaction limit and several simple relations that characterize the dynamics. Based on our findings, we propose a technique for driving transition from the ground state to the excited states using an oscillating magnetic field.Comment: 11 pages, 7 figure
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