64 research outputs found
Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion
In an effort to understand skyrmion behavior on a coarse-grained level, skyrmions are often described as 2D quasiparticles evolving according to the Thiele equation. Interaction potentials are the key missing parameters for predictive modeling of experiments. Here, the Iterative Boltzmann Inversion technique commonly used in soft matter simulations is applied to construct potentials for skyrmion-skyrmion and skyrmion-magnetic material boundary interactions from a single experimental measurement without any prior assumptions of the potential form. It is found that the two interactions are purely repulsive and can be described by an exponential function for micrometer-sized skyrmions in a ferromagnetic thin film multilayer stack. This captures the physics on experimental length and time scales that are of interest for most skyrmion applications and typically inaccessible to atomistic or micromagnetic simulations
Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion
In an effort to understand skyrmion behavior on a coarse-grained level, skyrmions are often described as 2D quasiparticles evolving according to the Thiele equation. Interaction potentials are the key missing parameters for predictive modeling of experiments. Here, the Iterative Boltzmann Inversion technique commonly used in soft matter simulations is applied to construct potentials for skyrmion-skyrmion and skyrmion-magnetic material boundary interactions from a single experimental measurement without any prior assumptions of the potential form. It is found that the two interactions are purely repulsive and can be described by an exponential function for micrometer-sized skyrmions in a ferromagnetic thin film multilayer stack. This captures the physics on experimental length and time scales that are of interest for most skyrmion applications and typically inaccessible to atomistic or micromagnetic simulations
Homochiral antiferromagnetic merons, antimerons and bimerons realized in synthetic antiferromagnets
The ever-growing demand for device miniaturization and energy efficiency in
data storage and computing technology has prompted a shift towards
antiferromagnetic (AFM) topological spin textures as information carriers,
owing to their negligible stray fields, leading to possible high device density
and potentially ultrafast dynamics. We realize, in this work, such chiral
in-plane (IP) topological antiferromagnetic spin textures, namely merons,
antimerons, and bimerons in synthetic antiferromagnets by concurrently
engineering the effective perpendicular magnetic anisotropy, the interlayer
exchange coupling, and the magnetic compensation ratio. We demonstrate by
three-dimensional vector imaging of the N\'eel order parameter, the topology of
those spin textures and reveal globally a well-defined chirality, which is a
crucial requirement for controlled current-induced dynamics. Our analysis
reveals that the interplay between interlayer exchange and interlayer magnetic
dipolar interactions plays a key role in significantly reducing the critical
strength of the Dzyaloshinskii-Moriya interaction required to stabilize
topological spin textures, such as AFM merons, making synthetic
antiferromagnets a promising platform for next-generation spintronics
applications.Comment: 18pages, 5 figure
A six-dimensional gauge-Higgs unification model based on gauge symmetry
We construct a six-dimensional gauge-Higgs unification model with the
enlarged gauge group of on orbifold compactification. The
standard model particle contents and gauge symmetry are obtained by utilizing a
monopole background field and imposing appropriate parity conditions on the
orbifold. In particular, a realistic Higgs potential suitable for breaking the
electroweak gauge symmetry is obtained without introducing extra matter or
assuming an additional symmetry relation between the SU(2) isometry
transformation on the and the gauge symmetry. The Higgs boson is a KK
mode associated with the extra-dimensional components of gauge field. Its odd
KK-parity makes it a stable particle, and thus a potential dark matter
candidate in the model. We also compute the KK masses of all fields at tree
level.Comment: 25 pages, references adde
Destruxin E Decreases Beta-Amyloid Generation by Reducing Colocalization of Beta-Amyloid-Cleaving Enzyme 1 and Beta-Amyloid Protein Precursor
Alzheimer-disease-associated beta-amyloid (A beta) is produced by sequential endoproteolysis of beta-amyloid protein precursor (beta APP): the extracellular portion is shed by cleavage in the juxtamembrane region by beta-amyloid-cleaving enzyme (BACE)/beta-secretase, after which it is cleaved by presenilin (PS)/gamma-secretase near the middle of the transmembrane domain. Thus, inhibition of either of the secretases reduces A beta generation and is a fundamental strategy for the development of drugs to prevent Alzheimer disease. However, it is not clear how small compounds reduce A beta production without inhibition of the secretases. Such compounds are expected to avoid some of the side effects of secretase inhibitors. Here, we report that destruxin E (Dx-E), a natural cyclic hexadepsipeptide, reduces A beta generation without affecting BACE or PS/gamma-secretase activity. In agreement with this, Dx-E did not inhibit Notch signaling. We found that Dx-E decreases colocalization of BACE1 and beta APP, which reduces beta-cleavage of beta APP. Therefore, the data demonstrate that Dx-E represents a novel A beta-reducing process which could have fewer side effects than secretase inhibitors. Copyright (C) 2009 S. Karger AG, Base
The Constrained Maximal Expression Level Owing to Haploidy Shapes Gene Content on the Mammalian X Chromosome.
X chromosomes are unusual in many regards, not least of which is their nonrandom gene content. The causes of this bias are commonly discussed in the context of sexual antagonism and the avoidance of activity in the male germline. Here, we examine the notion that, at least in some taxa, functionally biased gene content may more profoundly be shaped by limits imposed on gene expression owing to haploid expression of the X chromosome. Notably, if the X, as in primates, is transcribed at rates comparable to the ancestral rate (per promoter) prior to the X chromosome formation, then the X is not a tolerable environment for genes with very high maximal net levels of expression, owing to transcriptional traffic jams. We test this hypothesis using The Encyclopedia of DNA Elements (ENCODE) and data from the Functional Annotation of the Mammalian Genome (FANTOM5) project. As predicted, the maximal expression of human X-linked genes is much lower than that of genes on autosomes: on average, maximal expression is three times lower on the X chromosome than on autosomes. Similarly, autosome-to-X retroposition events are associated with lower maximal expression of retrogenes on the X than seen for X-to-autosome retrogenes on autosomes. Also as expected, X-linked genes have a lesser degree of increase in gene expression than autosomal ones (compared to the human/Chimpanzee common ancestor) if highly expressed, but not if lowly expressed. The traffic jam model also explains the known lower breadth of expression for genes on the X (and the Z of birds), as genes with broad expression are, on average, those with high maximal expression. As then further predicted, highly expressed tissue-specific genes are also rare on the X and broadly expressed genes on the X tend to be lowly expressed, both indicating that the trend is shaped by the maximal expression level not the breadth of expression per se. Importantly, a limit to the maximal expression level explains biased tissue of expression profiles of X-linked genes. Tissues whose tissue-specific genes are very highly expressed (e.g., secretory tissues, tissues abundant in structural proteins) are also tissues in which gene expression is relatively rare on the X chromosome. These trends cannot be fully accounted for in terms of alternative models of biased expression. In conclusion, the notion that it is hard for genes on the Therian X to be highly expressed, owing to transcriptional traffic jams, provides a simple yet robustly supported rationale of many peculiar features of X's gene content, gene expression, and evolution
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