3,177 research outputs found
Crystal growth and quantum oscillations in the topological chiral semimetal CoSi
We survey the electrical transport properties of the single-crystalline,
topological chiral semimetal CoSi which was grown via different methods.
High-quality CoSi single crystals were found in the growth from tellurium
solution. The sample's high carrier mobility enables us to observe, for the
first time, quantum oscillations (QOs) in its thermoelectrical signals. Our
analysis of QOs reveals two spherical Fermi surfaces around the R point in the
Brillouin zone corner. The extracted Berry phases of these electron orbits are
consistent with the -2 chiral charge as reported in DFT calculations. Detailed
analysis on the QOs reveals that the spin-orbit coupling induced band-splitting
is less than 2 meV near the Fermi level, one order of magnitude smaller than
our DFT calculation result. We also report the phonon-drag induced large Nernst
effect in CoSi at intermediate temperatures
(Z)-Isobutyl 2-benzamido-3-(4-chlorophenyl)acrylate
The title compound, C20H20ClNO3, is a α-amino acid derivative which displays a Z configuration about the C=C double bond. The dihedral angle betwen the aromatic rings is 87.75 (12)°. The molecular conformation is stabilized by an intramolecular C—H⋯N hydrogen bond. In the crystal structure, centrosymmetrically related molecules interact through intermolecular C—H⋯O hydrogen-bond interactions, forming dimers. The dimers are further linked into chains parallel to the a axis by N—H⋯O hydrogen bonds. The methyl groups of the isopropyl group are disordered over two positions with occupancy factors of 0.5
Recent advances in the extraction, purification, structural-property correlations, and antiobesity mechanism of traditional Chinese medicine-derived polysaccharides: a review
Traditional Chinese medicine (TCM) has displayed preventive and therapeutic effects on many complex diseases. As natural biological macromolecules, TCM-derived antiobesogenic polysaccharides (TCMPOs) exhibit notable weight-loss effects and are seen to be a viable tactic in the fight against obesity. Current studies demonstrate that the antiobesity activity of TCMPOs is closely related to their structural characteristics, which could be affected by the extraction and purification methods. Therefore, the extraction, purification and structural-property correlations of TCMPOs were discussed. Investigation of the antiobesity mechanism of TCMPOs is also essential for their improved application. Herein, the possible antiobesity mechanisms of TCMPOs are systematically summarized: (1) modulation of appetite and satiety effects, (2) suppression of fat absorption and synthesis, (3) alteration of the gut microbiota and their metabolites, and (4) protection of intestinal barriers. This collated information could provide some insights and offer a new therapeutic approach for the management and prevention of obesity
Multilayered Molybdate Microflowers Fabricated by One-Pot Reaction for Efficient Water Splitting
The development of high-performance, low-cost and rapid-production bifunctional electrocatalysts towards overall water splitting still poses huge challenges. Herein, the authors utilize a facile hydrothermal method to synthesize a novel structure of Co-doped ammonium lanthanum molybdate on Ni foams (Co-ALMO@NF) as self-supported electrocatalysts. Owing to large active surfaces, lattice defect and conductive channel for rapid charge transport, Co-ALMO@NF exhibits good electrocatalytic performances which requires only 349/341 mV to achieve a high current density of 600 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Besides, a low cell voltage of 1.52 V is required to reach the current density of 10 mA cm-2 in alkaline medium along with an excellent long-term stability for two-electrode configurations. Density functional theory calculations are performed to reveal the reaction mechanism on Co-ALMO@NF, which shows that the Mo site is the most favorable ones for HER, while the introduction of Co is beneficial to reduce the adsorption intensity on the surface of Co-ALMO@NF, thus accelerating OER process. This work highlighted the importance of the structural design for self-supporting electrocatalysts
Dynamic Coarse-to-Fine Learning for Oriented Tiny Object Detection
Detecting arbitrarily oriented tiny objects poses intense challenges to
existing detectors, especially for label assignment. Despite the exploration of
adaptive label assignment in recent oriented object detectors, the extreme
geometry shape and limited feature of oriented tiny objects still induce severe
mismatch and imbalance issues. Specifically, the position prior, positive
sample feature, and instance are mismatched, and the learning of extreme-shaped
objects is biased and unbalanced due to little proper feature supervision. To
tackle these issues, we propose a dynamic prior along with the coarse-to-fine
assigner, dubbed DCFL. For one thing, we model the prior, label assignment, and
object representation all in a dynamic manner to alleviate the mismatch issue.
For another, we leverage the coarse prior matching and finer posterior
constraint to dynamically assign labels, providing appropriate and relatively
balanced supervision for diverse instances. Extensive experiments on six
datasets show substantial improvements to the baseline. Notably, we obtain the
state-of-the-art performance for one-stage detectors on the DOTA-v1.5,
DOTA-v2.0, and DIOR-R datasets under single-scale training and testing. Codes
are available at https://github.com/Chasel-Tsui/mmrotate-dcfl.Comment: Accepted by CVPR202
The Study of Owl's Silent Flight and Noise Reduction on Fan Vane with Bionic Structure
In light of the bionics engineering point of view, we use the biological non-smooth surface in the surface design of the fan blade in order to reduce the fan noise and improve air flow and efficiency .We design several kinds of Sawtooth-shaped distribution, and apply the non-smooth form on the fan model. We analyzed the acoustic performance of various non-smooth fan blades that was reflected when the fan was rotating. Through the wind tunnel test, we obtained the spectrum map, wind comparison chart, efficiency curve and other important parameters that came from the comparison between smooth and non-smooth models and the noise of the fan. This paper will reveal that the non-smooth shape practically is good for preventing formation of off-body vortex, which is caused by turbulent boundary layer on the vane surface, and it will have reference significance for exploring the mechanism of noise reduction on fan vane. Key words: Owl; Bionic; Noise Reduction; Optimization Tes
Low compressible noble metal carbides with rock-salt structure: ab initio total energy calculations of the elastic stability
We have systematically studied the mechanical stability of all noble metal
carbides with the rock-salt structure by calculating their elastic constants
within the density function theory scheme. It was found that only four carbides
(RuC, PdC, AgC and PtC) are mechanically stable. In particular, we have shown
that RuC, PdC, and PtC have very high bulk modulus, which has been remarkably
observed by the most recent experiment for the case of PtC. From the calculated
density of states, we can conclude that these compounds are metallic, like the
conventional group IV and group V transition metal carbides.Comment: Appl. Phys. Lett. 89, 071913 (2006
The active oxygen species promoted catalytic oxidation of 5-hydroxymethyl-2-furfural on facet-specific Pt nanocrystals
This work was supported by Natural Science Foundation of Tianjin (Grant No. 17JCYBJC22600) and the Fundamental Research Funds for the Central Universities.The aerobic oxidation of alcohols and aldehydes over noble metal catalysts is a critical reaction for the catalytic conversion of carbohydrates into value-added chemicals from biomass. However, to fully understand the reaction mechanism, in particular the role of O2 and the generated active oxygen species in these reactions is still a challenging target. In the present work, the sub-10 nm Pt nanocrystals with cubic (Pt-NCs), octahedral (Pt-NOs) and spherical (Pt-NSs) morphologies were synthesized and used as catalysts in aerobic oxidation of HMF. Through experimental and computational investigations, the facet-dependent O2 conversion pathway and catalytic oxidation performance were discussed. The molecular O2 tends to be dissoci-ated to generate •OH on Pt(100) surface, but prefers to be reduced to •O2- on Pt(111) surface. Moreover, Pt-NCs enclosed by the {100} facets exhibited significantly enhanced catalytic activity than Pt-NOs enclosed by the {111} facets and Pt-NSs, in particular for alcohol oxidation step. Based on the experimental data and density functional theory (DFT) calculations, an active oxygen species promoted dehydrogenation mechanism for aerobic oxidation of HMF was proposed. The dehydrogena-tion of alcohol group is more favourable on the Pt(100) surface with an assistance of •OH, which are the dominant active oxygen species on the Pt(100) surface. We anticipate that this work would provide a new insight into the role of active oxy-gen species in aerobic oxidation of alcohols and aldehydes over noble metal catalysts.PostprintPeer reviewe
Effect and mechanism of exogenous selenium on selenium content and quality of fresh tea leaves
To study the effect and mechanism of selenium sources on the selenium content and quality of fresh tea leaves, tea seedlings (Camellia sinensis (L.) O. Kuntze) were the research object. A solution of 100 mg/L sodium selenate (Na2SeO4), sodium selenite (Na2SeO3), and selenium yeast (selenium yeast) were applied on the leaves surface of 5-week-old tea plants, and the selenium levels in the leaves, roots, and stems were determined at 20 weeks of age. The effects of different selenium sources on the mineral nutrient content, antioxidant enzyme activity, and quality parameters content in leaves were analyzed. The mechanism was analyzed by detecting the expression levels of related genes. The results showed that the three selenium sources can increase the growth of tea seedlings and the selenium content in leaves and stems, and the selenium yeast treatment had the most significant effect. Selenium spraying promoted the absorption of mineral nutrients such as nitrogen, phosphorus, and potassium, but had no significant impact on the absorption of calcium and magnesium. Spraying the three selenium sources dramatically increased the activities of APX, POD, and SOD antioxidant enzymes, among which the selenium yeast treatment had the most significant effect. However, there was no significant impact on the MDA level in this study. Selenium sources markedly increased leaves total amino acid levels, accompanied by up-regulation the genes of amino acid synthetic enzymes (CsGS, CsGOGAT, and CsGDH). Leaves glucose, tea polyphenol, total soluble protein, catechin, flavonoid contents, and sucrose were higher in selenium sources treatments than in control treatment seedlings. Moreover, selenium sources up-regulated expression of CsHMGR, CsAPX, and CsTCS1 genes. selenium yeast had the best comprehensive effect of the three selenium sources. These results confirmed that selenium sources play a positive role on the selenium content and quality of tea by increasing the antioxidant capacity of leaves, the absorption rate of mineral nutrients, and regulating expression of related genes in Camellia sinensis
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