69 research outputs found
High-performance descriptor for magnetic materials:Accurate discrimination of magnetic symmetries
The magnetic structure is crucial in determining the physical properties
inherent in magnetic compounds. We present an adequate descriptor for magnetic
structure with proper magnetic symmetry and high discrimination performance,
which does not depend on artificial choices for coordinate origin, axis, and
magnetic unit cell in crystal. We extend the formalism called ``smooth overlap
of atomic positions'' (SOAP) providing a numerical representation of atomic
configurations to that of magnetic moment configurations. We introduce the
descriptor in terms of the vector spherical harmonics to describe a magnetic
moment configuration and partial spectra from the expansion coefficients. We
discuss that the lowest order partial spectrum is insufficient to discriminate
the magnetic structures with different magnetic anisotropy, and a higher order
partial spectrum is required in general to characterize detailed magnetic
structures on the same atomic configuration. We then introduce the fourth-order
partial spectrum and evaluate the discrimination performance for different
magnetic structures, mainly focusing on the difference in magnetic symmetry.
The modified partial spectra that are defined not to reflect the difference of
magnetic anisotropy are also useful in evaluating magnetic structures obtained
from first-principles calculations without spin-orbit coupling. We apply the
present method to the symmetry-classified magnetic structures for the crystals
of MnIr and MnSn, which are known to exhibit anomalous transport under
the antiferromagnetic order, and examine the discrimination performance of the
descriptor for different magnetic structures on the same crystal.Comment: 13 pages including supplementary information, 8 figure
Compact and scalable polarimetric self-coherent receiver using dielectric metasurface
The polarimetric self-coherent system using a direct-detection-based
Stokes-vector receiver (SVR) is a promising technology to meet both the cost
and capacity requirements of the short-reach optical interconnects. However,
conventional SVRs require a number of optical components to detect the state of
polarization at high speed, resulting in substantially more complicated
receiver configurations compared with the current
intensity-modulation-direct-detection (IMDD) counterparts. Here, we demonstrate
a simple and compact polarimetric self-coherent receiver based on a thin
dielectric metasurface and a photodetector array (PDA). With a single
1.05-m-thick metasurface device fabricated on a compact silicon-on-quartz
chip, we implement functionalities of all the necessary passive components: a
13 splitter, three polarization beam splitters with different
polarization bases, and six focusing lenses. Combined with a high-speed PDA, we
demonstrate self-coherent transmission of 20-GBd 16-ary quadrature amplitude
modulation (16QAM) and 50-GBd quadrature phase-shift keying (QPSK) signals over
a 25-km single-mode fiber. Owing to the surface-normal configuration, it can
easily be scaled to receive spatially multiplexed channels from a multicore
fiber or a fiber bundle, enabling compact and low-cost receiver modules for the
future highly parallelized self-coherent systems.Comment: 10 pages, 6 figures (main manuscript) + 2 pages, 2 figures
(supplementary info
Mechanosensory trichome cells evoke a mechanical stimuli–induced immune response in Arabidopsis thaliana
Perception of pathogen-derived ligands by corresponding host receptors is a pivotal strategy in eukaryotic innate immunity. In plants, this is complemented by circadian anticipation of infection timing, promoting basal resistance even in the absence of pathogen threat. Here, we report that trichomes, hair-like structures on the epidermis, directly sense external mechanical forces, including raindrops, to anticipate pathogen infections in Arabidopsis thaliana. Exposure of leaf surfaces to mechanical stimuli initiates the concentric propagation of intercellular calcium waves away from trichomes to induce defence-related genes. Propagating calcium waves enable effective immunity against pathogenic microbes through the CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3) and mitogen-activated protein kinases. We propose an early layer of plant immunity in which trichomes function as mechanosensory cells that detect potential risks
Discovery of the Fastest Early Optical Emission from Overluminous SN Ia 2020hvf: A Thermonuclear Explosion within a Dense Circumstellar Environment
Ia型超新星の爆発直後の閃光を捉えることに成功 --特異な爆発に至る恒星進化の謎に迫る--. 京都大学プレスリリース. 2021-12-10.In this Letter we report a discovery of a prominent flash of a peculiar overluminous Type Ia supernova, SN 2020hvf, in about 5 hr of the supernova explosion by the first wide-field mosaic CMOS sensor imager, the Tomo-e Gozen Camera. The fast evolution of the early flash was captured by intensive intranight observations via the Tomo-e Gozen high-cadence survey. Numerical simulations show that such a prominent and fast early emission is most likely generated from an interaction between 0.01 M⊙ circumstellar material (CSM) extending to a distance of ∼10¹³ cm and supernova ejecta soon after the explosion, indicating a confined dense CSM formation at the final evolution stage of the progenitor of SN 2020hvf. Based on the CSM–ejecta interaction-induced early flash, the overluminous light curve, and the high ejecta velocity of SN 2020hvf, we suggest that the SN 2020hvf may originate from a thermonuclear explosion of a super-Chandrasekhar-mass white dwarf (“super-MCh WD”). Systematical investigations on explosion mechanisms and hydrodynamic simulations of the super-MCh WD explosion are required to further test the suggested scenario and understand the progenitor of this peculiar supernova
Photoinduced Bisphosphination of Alkynes with Phosphorus Interelement Compounds and Its Application to Double-Bond Isomerization
The addition of interelement compounds with heteroatom-heteroatom single bonds to carbon-carbon unsaturated bonds under light irradiation is believed to be an atomically efficient method to procure materials with carbon-heteroatom bonds. In this study, we achieved the photoinduced bisphosphination of alkynes using the phosphorus interelement compound, tetraphenyldiphosphine monosulfide (1), to stereoselectively obtain the corresponding (E)-vic-1,2-bisphosphinoalkenes, which are important transition-metal ligands. The bisphosphination reaction was performed by mixing 1 and various alkynes and then exposing the mixture to light irradiation. Optimization of the conditions for the bisphosphination reaction resulted in a wide substrate range and excellent trans-selectivity. Moreover, the completely regioselective introduction of pentavalent and trivalent phosphorus groups to the terminal and internal positions of the alkynes, respectively, was achieved. We also found that the novel double-bond isomerization reaction of the synthesized bisphosphinated products occurred with a catalytic amount of a base under mild conditions. Our method for the photoinduced bisphosphination of carbon-carbon unsaturated compounds may have strong implications for both organic synthesis and organometallic and catalyst chemistry
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