17 research outputs found
Direct imaging of a zero-field target skyrmion and its polarity switch in a chiral magnetic nanodisk
A target skyrmion is a flux-closed spin texture that has two-fold degeneracy
and is promising as a binary state in next generation universal memories.
Although its formation in nanopatterned chiral magnets has been predicted, its
observation has remained challenging. Here, we use off-axis electron holography
to record images of target skyrmions in a 160-nm-diameter nanodisk of the
chiral magnet FeGe. We compare experimental measurements with numerical
simulations, demonstrate switching between two stable degenerate target
skyrmion ground states that have opposite polarities and rotation senses and
discuss the observed switching mechanism.Comment: 18 pages, 4 figure
Diverse nitrogen enrichments enhance photosynthetic resistance of Sargassum horneri to ultraviolet radiation
In recent years, golden tides caused by floating Sargassum have induced severe ecological disasters globally. Eutrophication is a significant factor contributing to the massive spread of Sargassum golden tides. Furthermore, the thalli of Sargassum that float on the ocean surface are subjected to more ultraviolet radiation (UVR). The coupled impact of eutrophication and UVR on the photosynthetic physiology of golden tide species remains unclear. In this study, the thalli of Sargassum horneri, known to cause golden tide, were cultured and acclimated to three distinct nitrogen (N) conditions (natural seawater, NSW; NH4+-N enrichment; and NO3âN enrichment) for 6 days. Subsequently, the thalli were exposed to two different radiation treatments (photosynthetically active radiation (150 W m-2), PAR, 400â700 nm; PAR (150 W m-2) + UVR (28 W m-2), 280â700 nm) for 120 min, to investigate the photosynthetic effects of UVR and N on this alga. The findings demonstrated that exposure to UVR impeded the photosynthetic capacity of S. horneri, as evidenced by a decrease in the maximum photochemical quantum yield (Fv/Fm), photosynthetic efficiency (α) and chlorophyll content. Under diverse N-enrichment conditions, the alga tended to adopt various strategies to mitigate the adverse effects of UVR. NH4+-enrichment dissipated excess UVR energy through a greater increase in non-photochemical quenching (NPQ). While NO3âenrichment protected alga by enhancing N assimilation (higher nitrate reductase activity (NRA) and soluble protein content), and maintained a stable energy captured per unit reaction center for electron transfer (ET0/RC) and a higher net photosynthetic rate. Although different N enrichments could not completely offset the damage caused by UV radiation, they secured the photoprotective ability of S. horneri in several ways
Toward the development of smart capabilities for understanding seafloor stretching morphology and biogeographic patterns via DenseNet from high-resolution multibeam bathymetric surveys for underwater vehicles
The increasing use of underwater vehicles facilitates deep-sea exploration at a wide range of depths and spatial scales. In this paper, we make an initial attempt to develop online computing strategies to identify seafloor categories and predict biogeographic patterns with a deep learning-based architecture, DenseNet, integrated with joint morphological cues, with the expectation of potentially developing its embedded smart capacities. We utilized high-resolution multibeam bathymetric measurements derived from MBES and denoted a collection of joint morphological cues to help with semantic mapping and localization. We systematically strengthened dominant feature propagation and promoted feature reuse via DenseNet by applying the channel attention module and spatial pyramid pooling. From our experiment results, the seafloor classification accuracy reached up to 89.87%, 82.01%, and 73.52% on average in terms of PA, MPA, and MIoU metrics, achieving comparable performances with the state-of-the-art deep learning frameworks. We made a preliminary study on potential biogeographic distribution statistics, which allowed us to delicately distinguish the functionality of probable submarine benthic habitats. This study demonstrates the premise of using underwater vehicles through unbiased means or pre-programmed path planning to quantify and estimate seafloor categories and the exhibited fine-scale biogeographic patterns
Combined Influences of Light and Nitrogen Enrichment on the Physiological Performance of a Golden Tide Alga (Sargassum horneri)
Sargassum golden tides (GT) are common in numerous coastal areas all over the world, and it adversely affects local marine life. Eutrophication is critical for Sargassum GT development. However, its physiological and ecological mechanism remains unclear. To investigate the responses of drifting Sargassum horneri, the species causing GT in the western Pacific, to light and enriched nitrogen, we set three light conditions (Low-light (LL), 10 μmol photons m−2 s−1; Middle-light (ML), 60 μmol photons m−2 s−1; and High-light (HL), 300 μmol photons m−2 s−1) and three nitrogen conditions (Natural seawater, the final concentration of N was 31.8 μmol L−1, including 30.5 μmol L−1 of NO3− and 1.3 μmol L−1 of NH4+; Enrichment of NO3−, final concentration of N was 200 μmol L−1; and Enrichment of NH4+, the final concentration of N was 200 μmol L−1), and grew the thalli under varying conditions for 10 days before determining the growth and utilization of carbon and nitrogen. Based on the accumulated data, the elevated light level led to a higher growth rate of alga. In the LL culture, the higher capacity for carbon utilization, which was reflected by the higher maximum photosynthetic carbon fixation rate (Vmax), resulted in the elevated growth rates of thalli in the nitrogen-enriched media as compared with the natural seawater. Furthermore, a higher growth rate was found in the enrichment of NH4+ despite a low affinity for inorganic carbon indicated by a higher value of the half-saturation constant (K0.5). In the ML treatment, an insignificant difference in growth rate was found in three nitrogen cultures, except for a slight increase in the enrichment of NH4+ than the enrichment of NO3−. In the HL treatment, compared with natural seawater culture, enrichment of NO3− or NH4+ accelerated the growth of alga, with no significant difference between the two nitrogen sources. Such enhancement in growth was related to the more photosynthetic carbon fixation, indicated by the higher value of Vmax and soluble carbohydrates content of alga cultured with NO3− and NH4+ enrichments. Additionally, the uptake and assimilation products of nitrogen, such as pigments and soluble proteins, remained unaffected by nitrogen source enrichment of NO3− or NH4+ at all three light levels. In conclusion, enrichment of NO3− and NH4+ exhibited different influences on the growth of S. horneri at different light levels, which was mainly associated with the capacity and efficiency of photosynthetic carbon utilization. At the HL level, both the enrichment of NO3− and NH4+ dramatically accelerate the growth of alga by stimulating the photosynthetic carbon fixation. Accordingly, we speculated that drifting S. horneri, exposed to HL level on the surface of the sea, were likely to develop rapidly to form GT in eutrophic oceanic areas with upwelled and river plume NO3− or NH4+ nutrients
Combined Influences of Light and Nitrogen Enrichment on the Physiological Performance of a Golden Tide Alga (<i>Sargassum horneri</i>)
Sargassum golden tides (GT) are common in numerous coastal areas all over the world, and it adversely affects local marine life. Eutrophication is critical for Sargassum GT development. However, its physiological and ecological mechanism remains unclear. To investigate the responses of drifting Sargassum horneri, the species causing GT in the western Pacific, to light and enriched nitrogen, we set three light conditions (Low-light (LL), 10 ÎŒmol photons mâ2 sâ1; Middle-light (ML), 60 ÎŒmol photons mâ2 sâ1; and High-light (HL), 300 ÎŒmol photons mâ2 sâ1) and three nitrogen conditions (Natural seawater, the final concentration of N was 31.8 ÎŒmol Lâ1, including 30.5 ÎŒmol Lâ1 of NO3â and 1.3 ÎŒmol Lâ1 of NH4+; Enrichment of NO3â, final concentration of N was 200 ÎŒmol Lâ1; and Enrichment of NH4+, the final concentration of N was 200 ÎŒmol Lâ1), and grew the thalli under varying conditions for 10 days before determining the growth and utilization of carbon and nitrogen. Based on the accumulated data, the elevated light level led to a higher growth rate of alga. In the LL culture, the higher capacity for carbon utilization, which was reflected by the higher maximum photosynthetic carbon fixation rate (Vmax), resulted in the elevated growth rates of thalli in the nitrogen-enriched media as compared with the natural seawater. Furthermore, a higher growth rate was found in the enrichment of NH4+ despite a low affinity for inorganic carbon indicated by a higher value of the half-saturation constant (K0.5). In the ML treatment, an insignificant difference in growth rate was found in three nitrogen cultures, except for a slight increase in the enrichment of NH4+ than the enrichment of NO3â. In the HL treatment, compared with natural seawater culture, enrichment of NO3â or NH4+ accelerated the growth of alga, with no significant difference between the two nitrogen sources. Such enhancement in growth was related to the more photosynthetic carbon fixation, indicated by the higher value of Vmax and soluble carbohydrates content of alga cultured with NO3â and NH4+ enrichments. Additionally, the uptake and assimilation products of nitrogen, such as pigments and soluble proteins, remained unaffected by nitrogen source enrichment of NO3â or NH4+ at all three light levels. In conclusion, enrichment of NO3â and NH4+ exhibited different influences on the growth of S. horneri at different light levels, which was mainly associated with the capacity and efficiency of photosynthetic carbon utilization. At the HL level, both the enrichment of NO3â and NH4+ dramatically accelerate the growth of alga by stimulating the photosynthetic carbon fixation. Accordingly, we speculated that drifting S. horneri, exposed to HL level on the surface of the sea, were likely to develop rapidly to form GT in eutrophic oceanic areas with upwelled and river plume NO3â or NH4+ nutrients
âCarbon Assimilationâ Inspired Design and Divergent Synthesis of Drimane Meroterpenoid Mimics as Novel Fungicidal Leads
With
structural diversity and versatile biological properties,
drimane meroterpenoids have drawn remarkable attention in drug development.
The stagnant progress made in the structure optimization and SAR study
of this kind of natural product for agrochemicals was mainly a result
of inefficient construction. Compared with the reported challenging
coupling reaction (â1 + 1â tactic), âcarbon assimilationâ
was conceived and used for the rapid construction of drimanyl meroterpenoid
mimics, in which the newly formed covalent bond was directly from
the old one of the drimanyl subunit (â2 + 0â tactic),
which features atom economy, step economy, and facile preparation.
The accompanying introduction of versatile heterocycles and application
of easily available feedstocks are beneficial for novel green agrochemical
discovery, in view of economic efficiency and improvement of physicochemical
properities. Heterocyclic mimics <b>3a</b> and <b>3c</b> are presented as potent fungicidal leads with novel skeletons against <i>Botrytis cinerea</i>, >25-fold and >40-fold more promising
than
the commercial fungicide carbendazim, respectively. Our design was
also rationalized by the 6-step synthesis and antifungal assay of
the original model of natural meroterpenoids. This tactic can also
be fostered or transferred directly to the design of novel natural
product mimics for medicinal chemistry or other related biological
exploration