198 research outputs found
Skyrmion Lattice in Two-Dimensional Chiral Magnet
We develop a theory of the magnetic field-induced formation of Skyrmion
crystal state in chiral magnets in two spatial dimensions, motivated by the
recent discovery of the Skyrmionic phase of magnetization in thin film of
FeCoSi and in the A-phase of MnSi. Ginzburg-Landau functional
of the chiral magnet re-written in the CP representation is shown to be a
convenient framework for the analysis of the Skyrmion states. Phase diagram of
the model at zero temperature gives a sequence of ground states, helical spin
Skyrme crystal ferromagnet, as the external field
increases, in good accord with the thin-film experiment. In close analogy
with Abrikosov's derivation of the vortex lattice solution in type-II
superconductor, the CP mean-field equation is solved and shown to reproduce
the Skyrmion crystal state.Comment: 10 pages, 7 figure
Security feature measurement for frequent dynamic execution paths in software system
© 2018 Qian Wang et al. The scale and complexity of software systems are constantly increasing, imposing new challenges for software fault location and daily maintenance. In this paper, the Security Feature measurement algorithm of Frequent dynamic execution Paths in Software, SFFPS, is proposed to provide a basis for improving the security and reliability of software. First, the dynamic execution of a complex software system is mapped onto a complex network model and sequence model. This, combined with the invocation and dependency relationships between function nodes, fault cumulative effect, and spread effect, can be analyzed. The function node security features of the software complex network are defined and measured according to the degree distribution and global step attenuation factor. Finally, frequent software execution paths are mined and weighted, and security metrics of the frequent paths are obtained and sorted. The experimental results show that SFFPS has good time performance and scalability, and the security features of the important paths in the software can be effectively measured. This study provides a guide for the research of defect propagation, software reliability, and software integration testing
Edge-Mediated Skyrmion Chain and Its Collective Dynamics in a Confined Geometry
The emergence of a topologically nontrivial vortex-like magnetic structure,
the magnetic skyrmion, has launched new concepts for memory devices. There,
extensive studies have theoretically demonstrated the ability to encode
information bits by using a chain of skyrmions in one-dimensional nanostripes.
Here, we report the first experimental observation of the skyrmion chain in
FeGe nanostripes by using high resolution Lorentz transmission electron
microscopy. Under an applied field normal to the nanostripes plane, we observe
that the helical ground states with distorted edge spins would evolves into
individual skyrmions, which assemble in the form of chain at low field and move
collectively into the center of nanostripes at elevated field. Such skyrmion
chain survives even as the width of nanostripe is much larger than the single
skyrmion size. These discovery demonstrates new way of skyrmion formation
through the edge effect, and might, in the long term, shed light on the
applications.Comment: 7 pages, 3 figure
Electrical Probing of Field-Driven Cascading Quantized Transitions of Skyrmion Cluster States in MnSi Nanowires
Magnetic skyrmions are topologically stable whirlpool-like spin textures that
offer great promise as information carriers for future ultra-dense memory and
logic devices1-4. To enable such applications, particular attention has been
focused on the skyrmions properties in highly confined geometry such as one
dimensional nanowires5-8. Hitherto it is still experimentally unclear what
happens when the width of the nanowire is comparable to that of a single
skyrmion. Here we report the experimental demonstration of such scheme, where
magnetic field-driven skyrmion cluster (SC) states with small numbers of
skyrmions were demonstrated to exist on the cross-sections of ultra-narrow
single-crystal MnSi nanowires (NWs) with diameters, comparable to the skyrmion
lattice constant (18 nm). In contrast to the skyrmion lattice in bulk MnSi
samples, the skyrmion clusters lead to anomalous magnetoresistance (MR)
behavior measured under magnetic field parallel to the NW long axis, where
quantized jumps in MR are observed and directly associated with the change of
the skyrmion number in the cluster, which is supported by Monte Carlo
simulations. These jumps show the key difference between the clustering and
crystalline states of skyrmions, and lay a solid foundation to realize
skyrmion-based memory devices that the number of skyrmions can be counted via
conventional electrical measurements
Disagreement and fragmentation in growing groups
The arise of disagreement is an emergent phenomenon that can be observed
within a growing social group and, beyond a certain threshold, can lead to
group fragmentation. To better understand how disagreement emerges, we
introduce an analytically tractable model of group formation where individuals
have multidimensional binary opinions and the group grows through a noisy
homophily principle, i.e., like-minded individuals attract each other with
exceptions occurring with some small probability. Assuming that the level of
disagreement is correlated with the number of different opinions coexisting
within the group, we find analytically and numerically that in growing groups
disagreement emerges spontaneously regardless of how small the noise in the
system is. Moreover, for groups of infinite size, fragmentation is inevitable.
We also show that the model outcomes are robust under different group growth
mechanisms.Comment: 17 pages, 3 figure
Predicting the early risk of ophthalmopathy in Graves\u27 disease patients using TCR repertoire.
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Single-shot 3D coherent diffractive imaging of core-shell nanoparticles with elemental specificity.
We report 3D coherent diffractive imaging (CDI) of Au/Pd core-shell nanoparticles with 6.1 nm spatial resolution with elemental specificity. We measured single-shot diffraction patterns of the nanoparticles using intense x-ray free electron laser pulses. By exploiting the curvature of the Ewald sphere and the symmetry of the nanoparticle, we reconstructed the 3D electron density of 34 core-shell structures from these diffraction patterns. To extract 3D structural information beyond the diffraction signal, we implemented a super-resolution technique by taking advantage of CDI's quantitative reconstruction capabilities. We used high-resolution model fitting to determine the Au core size and the Pd shell thickness to be 65.0 ± 1.0 nm and 4.0 ± 0.5 nm, respectively. We also identified the 3D elemental distribution inside the nanoparticles with an accuracy of 3%. To further examine the model fitting procedure, we simulated noisy diffraction patterns from a Au/Pd core-shell model and a solid Au model and confirmed the validity of the method. We anticipate this super-resolution CDI method can be generally used for quantitative 3D imaging of symmetrical nanostructures with elemental specificity
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