906 research outputs found
Investigation of the Dzyaloshinskii-Moriya interaction and room temperature skyrmions in W/CoFeB/MgO thin films and microwires
Recent studies have shown that material structures, which lack structural
inversion symmetry and have high spin-orbit coupling can exhibit chiral
magnetic textures and skyrmions which could be a key component for next
generation storage devices. The Dzyaloshinskii-Moriya Interaction (DMI) that
stabilizes skyrmions is an anti-symmetric exchange interaction favoring
non-collinear orientation of neighboring spins. It has been shown that material
systems with high DMI can lead to very efficient domain wall and skyrmion
motion by spin-orbit torques. To engineer such devices, it is important to
quantify the DMI for a given material system. Here we extract the DMI at the
Heavy Metal (HM) /Ferromagnet (FM) interface using two complementary
measurement schemes namely asymmetric domain wall motion and the magnetic
stripe annihilation. By using the two different measurement schemes, we find
for W(5 nm)/Co20Fe60B20(0.6 nm)/MgO(2 nm) the DMI to be 0.68 +/- 0.05 mJ/m2 and
0.73 +/- 0.5 mJ/m2, respectively. Furthermore, we show that this DMI stabilizes
skyrmions at room temperature and that there is a strong dependence of the DMI
on the relative composition of the CoFeB alloy. Finally we optimize the layers
and the interfaces using different growth conditions and demonstrate that a
higher deposition rate leads to a more uniform film with reduced pinning and
skyrmions that can be manipulated by Spin-Orbit Torques
Chiral Supersymmetric Gepner Model Orientifolds
We explicitly construct A-type orientifolds of supersymmetric Gepner models.
In order to reduce the tadpole cancellation conditions to a treatable number we
explicitly work out the generic form of the one-loop Klein bottle, annulus and
Moebius strip amplitudes for simple current extensions of Gepner models.
Equipped with these formulas, we discuss two examples in detail to provide
evidence that in this setting certain features of the MSSM like unitary gauge
groups with large enough rank, chirality and family replication can be
achieved.Comment: 37 pages, TeX (harvmac), minor changes, typos corrected, to appear in
JHE
How much of Me do I see in You: Neural correlates of self-other distinction in the affective domain
When inferring mental states of others, individuals’ judgments are influenced by their own state of mind, which has been referred to as egocentric bias. Especially in situations where one holds a different mental state than another person to be interpreted, self-other differentiation is key for an accurate interpretation on the other person’s mind. It has been suggested that the right supramarginal gyrus (rSMG) is involved in self-other differentiation and overcoming egocentric bias in the affective domain. In a double-blind, randomized study 47 healthy adults received active or sham anodal tDCS (1mA, 20min) or a sham stimulation to the rSMG prior to performing a newly developed emotional egocentricity paradigm (SOFE, Self-Other Facial Emotion Judgment Task). In SOFE, subjects are presented with emotionally ambiguous situations (happy or fearful) in which they have to continuously rate 1) their own emotion and 2) the emotion of another person whose facial expression is either congruent or incongruent to the subject’s emotion. Analyses confirmed the presence of an emotional egocentric bias in incongruent trials. We furthermore found that active tDCS applied to the rSMG increased subjects’ ability to overcome egocentric judgments. This effect was valence dependent with significant effects when inferring affective states of happy faces right after imagining oneself in a fear-evoking situation (p<0.05). Our findings extend previous research showing a causal role of the rSMG for emotional self-other distinction to the inferring of emotional states from pictorial stimuli. They additionally point towards valence-specific patterns of rSMG functionality. In a next step the SOFE task will be applied in autism spectrum disorder to characterize egocentric bias suppression and SMG network integrity in an effort to elucidate social cognitive dysfunction in affected individuals
Influence of random point defects introduced by proton irradiation on critical current density and vortex dynamics of Ba(Fe0.925Co0.075)2As2 single crystals
In this work we analyze the influence of random point defects introduced by 3 MeV proton irradiation on the critical current density (Jc) and vortex dynamics of a Ba(Fe0.925Co0.075)2As2 single crystal. The results show that at low temperatures (T) the irradiation produces an enhancement of Jc of up to 2.6 times. However the Jc (T) retention at different magnetic fields (H) in the elastic regime, estimated by the n exponent in Jc vs (1-(T/Tc)2)n, is poorer after the irradiations, due to the thermal softening of the pinning by the random point defects. We found that the elastic to plastic crossover and melting lines are only affected by the reduction of the superconducting critical temperature (Tc); they are exactly the same after rescaling the phase diagram by T/Tc. The pinning mechanisms in the single crystals can be associated with a mixed pinning landscape that produces a modulation in S(H,T) as a consequence of a fishtail or second peak in the magnetization.Fil: Haberkorn, Nestor Fabian. Los Alamos National Laboratory; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Maiorov, B.. Los Alamos National Laboratory; Estados UnidosFil: Usov, I. O.. Los Alamos National Laboratory; Estados UnidosFil: Weigand, M.. Los Alamos National Laboratory; Estados UnidosFil: Hirata, W.. Osaka University; JapónFil: Miyasaka, S.. Osaka University; JapónFil: Tajima, S.. Osaka University; JapónFil: Chikumoto, N.. International Superconductivity Technology Center. Superconductivity Research Laboratory; JapónFil: Tanabe, K.. International Superconductivity Technology Center. Superconductivity Research Laboratory; JapónFil: Civale, Leonardo. Los Alamos National Laboratory; Estados Unido
Stellar ArAr reactions and their effect on light neutron-rich nuclide synthesis
The ArAr ( = 35 d) and
ArAr (269 y) reactions were studied for the first time
with a quasi-Maxwellian ( keV) neutron flux for Maxwellian Average
Cross Section (MACS) measurements at stellar energies. Gas samples were
irradiated at the high-intensity Soreq applied research accelerator
facility-liquid-lithium target neutron source and the Ar/Ar and
Ar/Ar ratios in the activated samples were determined by
accelerator mass spectrometry at the ATLAS facility (Argonne National
Laboratory). The Ar activity was also measured by low-level counting at
the University of Bern. Experimental MACS of Ar and Ar, corrected
to the standard 30 keV thermal energy, are 1.9(3) mb and 1.3(2) mb,
respectively, differing from the theoretical and evaluated values published to
date by up to an order of magnitude. The neutron capture cross sections of
Ar are relevant to the stellar nucleosynthesis of light neutron-rich
nuclides; the two experimental values are shown to affect the calculated mass
fraction of nuclides in the region A=36-48 during the weak -process. The new
production cross sections have implications also for the use of Ar and
Ar as environmental tracers in the atmosphere and hydrosphere.Comment: 18 pages + Supp. Mat. (13 pages) Accepted for publication in Phys.
Rev. Let
RAD sequencing resolves fine-scale population structure in a benthic invertebrate: implications for understanding phenotypic plasticity.
The field of molecular ecology is transitioning from the use of small panels of classical genetic markers such as microsatellites to much larger panels of single nucleotide polymorphisms (SNPs) generated by approaches like RAD sequencing. However, few empirical studies have directly compared the ability of these methods to resolve population structure. This could have implications for understanding phenotypic plasticity, as many previous studies of natural populations may have lacked the power to detect genetic differences, especially over micro-geographic scales. We therefore compared the ability of microsatellites and RAD sequencing to resolve fine-scale population structure in a commercially important benthic invertebrate by genotyping great scallops (Pecten maximus) from nine populations around Northern Ireland at 13 microsatellites and 10 539 SNPs. The shells were then subjected to morphometric and colour analysis in order to compare patterns of phenotypic and genetic variation. We found that RAD sequencing was superior at resolving population structure, yielding higher Fst values and support for two distinct genetic clusters, whereas only one cluster could be detected in a Bayesian analysis of the microsatellite dataset. Furthermore, appreciable phenotypic variation was observed in size-independent shell shape and coloration, including among localities that could not be distinguished from one another genetically, providing support for the notion that these traits are phenotypically plastic. Taken together, our results suggest that RAD sequencing is a powerful approach for studying population structure and phenotypic plasticity in natural populations
Non-Abelian Brane Worlds: The Heterotic String Story
We discuss chiral supersymmetric compactifications of the SO(32) heterotic
string on Calabi-Yau manifolds equipped with direct sums of stable bundles with
structure group U(n). In addition we allow for non-perturbative heterotic
five-branes. These models are S-dual to Type I compactifications with D9- and
D5-branes, which by themselves are mirror symmetric to general intersecting
D6-brane models. For the construction of concrete examples we consider
elliptically fibered Calabi-Yau manifolds with SU(n) bundles given by the
spectral cover construction. The U(n) bundles are obtained via twisting by line
bundles. We present a four-generation Pati-Salam and a three-generation
Standard-like model.Comment: 29 pages, 7 tables, LATEX; v2: refs adde
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