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

Extinction risk of Chinese angiosperms varies between woody and herbaceous species

Aim: Understanding how species' traits and environmental contexts relate to extinction risk is a critical priority for ecology and conservation biology. This study aims to identify and explore factors related to extinction risk between herbaceous and woody angiosperms to facilitate more effective conservation and management strategies and understand the interactions between environmental threats and species' traits. Location: China. Taxon: Angiosperms. Methods: We obtained a large dataset including five traits, six extrinsic variables, and 796,118 occurrence records for 14,888 Chinese angiosperms. We assessed the phylogenetic signal and used phylogenetic generalized least squares regressions to explore relationships between extinction risk, plant traits, and extrinsic variables in woody and herbaceous angiosperms. We also used phylogenetic path analysis to evaluate causal relationships among traits, climate variables, and extinction risk of different growth forms. Results: The phylogenetic signal of extinction risk differed among woody and herbaceous species. Angiosperm extinction risk was mainly affected by growth form, altitude, mean annual temperature, normalized difference vegetation index, and precipitation change from 1901 to 2020. Woody species' extinction risk was strongly affected by height and precipitation, whereas extinction risk for herbaceous species was mainly affected by mean annual temperature rather than plant traits. Main conclusions: Woody species were more likely to have higher extinction risks than herbaceous species under climate change and extinction threat levels varied with both plant traits and extrinsic variables. The relationships we uncovered may help identify and protect threatened plant species and the ecosystems that rely on them

Systematic biases in determining dust attenuation curves through galaxy SED fitting

While the slope of the dust attenuation curve ($\delta$) is found to correlate with effective dust attenuation ($A_V$) as obtained through spectral energy distribution (SED) fitting, it remains unknown how the fitting degeneracies shape this relation. We examine the degeneracy effects by fitting SEDs of a sample of local star-forming galaxies (SFGs) selected from the Galaxy And Mass Assembly survey, in conjunction with mock galaxy SEDs of known attenuation parameters. A well-designed declining starburst star formation history is adopted to generate model SED templates with intrinsic UV slope ($\beta_0$) spanning over a reasonably wide range. The best-fitting $\beta_0$ for our sample SFGs shows a wide coverage, dramatically differing from the limited range of $\beta_0<-2.2$ for a starburst of constant star formation. Our results show that strong degeneracies between $\beta_0$, $\delta$, and $A_V$ in the SED fitting induce systematic biases leading to a false $A_V$--$\delta$ correlation. Our simulation tests reveal that this relationship can be well reproduced even when a flat $A_V$--$\delta$ relation is taken to build the input model galaxy SEDs. The variations in best-fitting $\delta$ are dominated by the fitting errors. We show that assuming a starburst with constant star formation in SED fitting will result in a steeper attenuation curve, smaller degeneracy errors, and a stronger $A_V$--$\delta$ relation. Our findings confirm that the $A_V$--$\delta$ relation obtained through SED fitting is likely driven by the systematic biases induced by the fitting degeneracies between $\beta_0$, $\delta$, and $A_V$.Comment: 21 pages, 13 figures, accepted for publication in the MNRAS, Comments welcome

The chemical characteristics of seawater in the Prydz Bay, Antarctica

Based on some data obtained in the Sixth Chinese Antarctic Research Expedition during 1989/1990, the relationship between the distribution of nutrient and that of productivity in the Prydz Bay was discussed. The results show that outside the Emery Ice Shelf there exists an expanse of warm and salty waters, where within the euphotic layer the content of nutrient is relatively low, the saturation of dissolved oxygen is up to 120% and the content of chlorophyll a is more than 1.00 mg/m3, all this indicating that the Prydz Bay may be considered as a high productivity area in Antarctica. The vertical distribution of chemical elements showed a strong spring layer like the thermocline, but at 350m layer abnormal vertical nutrient distribution turned up, even though there was no distinct halocline. Finally the various factors causing this abnormally were discussed

Sequentially tunable buckling in 3D printing auxetic metamaterial undergoing twofold viscoelastic resonances

With the development of metamaterials, tunable auxetic structures have attracted extensive attention due to their unusual mechanical behaviors. In this study, we design and 3D print an auxetic shape-memory dual-moiety structure, and achieve a reversible and sequential buckling behavior by means of the local instability. Effects of hollowness radius, Young's modulus ratio and temperature on the buckling behavior of this auxetic dual-moiety structure have been studied by the finite element method analysis. The constitutive relationships between stress, strain, hollowness radius and Young's modulus have been presented and discussed. Finally, the buckling behaviors have been investigated by the mechanical tests, and the accuracy of numerical results has then been verified by using the experimentally obtained data. This study is expected to provide a design guideline for auxetic dual-moiety structure with sequentially tunable buckling behaviors by means of twofold viscoelastic resonances.This work was financially supported by the National Natural Science Foundation of China (NSFC) under Grant No. 11725208

3D printing auxetic draft-angle structures towards tunable buckling complexity

With the development of 3D printing technology, auxetic structures have attracted extensive attention due to their unusual mechanical properties. In this study, we design a 3D printed auxetic structure using 2D draft angles to achieve a tunable out-of-plane double hyperbolic buckling behavior by effectively continuously varying stiffness across thickness. The influences of radii and draft angles on the buckling behaviors of the 3D printed draft-angle auxetic structures are studied by finite element method. The constitutive relationships between stress, strain, radius, and draft angle have been formulated and discussed to identify the working principle behind the mechanical performance of draft-angle auxetic structures. Finally, the buckling behavior is modelled by a laminate structure, and the accuracy of these analytical results has then been verified by experiment. This study is expected to provide a design guideline for achieving tunable buckling behavior of auxetic structures via the novel stress mismatch of draft angles and thus continuously varying stiffness along the thickness direction. The current work constitutes an initial attempt to realize the tunability of the 3D out of plane deformation of 2D plane structures under in-plane compression.This work was financially supported by the National Natural Science Foundation of China (NSFC) under Grant No.11725208