29,301 research outputs found

### Domain wall propagation due to the synchronization with circularly polarized microwaves

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

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

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 $A_0^a$, i.e.,
$A_0^aA_0^a<0$. It yields hermitian Hamilton, and finite, positive energy.Comment: revtex, 4 pages, 1 figur

### Old and New Morry Spaces via Heat Kernel Bounds

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

### Giant magnetoimpedance in crystalline Mumetal

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' "

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 $\Lambda$ system is indeed experimentally
detectable.Comment: 3 pages,1 figur

### Low-Complexity Linear Precoding for Secure Spatial Modulation

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 $(4,1)$-Adinkras

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 $(n=4, k=1)$ 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 $n$
and $k$ parameters

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

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

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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