During gastrulation, endodermal cells actively migrate to the interior of the embryo, but the signals that initiate and coordinate this migration are poorly understood. By transplanting ectopically ...induced endodermal cells far from the normal location of endoderm specification, we identified the inputs that drive internalization without the confounding influences of fate specification and global morphogenic movements. We find that Nodal signaling triggers an autocrine circuit for initiating endodermal internalization. Activation of the Nodal receptor directs endodermal specification through
and also induces expression of more Nodal ligands. These ligands act in an autocrine fashion to initiate endodermal cell sorting. Our work defines an 'AND' gate consisting of
-dependent endodermal specification and Nodal ligand reception controlling endodermal cell sorting to the inner layer of the embryo at the onset of gastrulation.
A novel control strategy that is based on iterative calculation of structural parameters is proposed for grid-connected inverter in this paper. The proposed strategy has a good dynamic performance, ...which makes it particularly suitable for the application of PV grid-connected generation. First, a second-order discretization mathematical model of grid-connected inverter control is established in the dq frame. The corresponding relation between the control signal and the output current is deduced in formulas. Then, the values of structural parameters in the formulas can be obtained through iterative calculation, which can further reduce the amount of calculation. After several iteration cycles, the structural parameters are approximately equal to their actual values and the inverter can be controlled as an open-loop system with its dynamic performance optimized. At last, simulation and experiments are performed. The results show that the static performance of the proposed strategy is as good as that of the classical ones, but its dynamic performance is improved significantly.
Field electron emission vacuum photodiode is promising for converting free-space electromagnetic radiation into electronic signal within an ultrafast timescale due to the ballistic electron transport ...in its vacuum channel. However, the low photoelectric conversion efficiency still hinders the popularity of vacuum photodiode. Here, we report an on-chip integrated vacuum nano-photodiode constructed from a Si-tip anode and a single-crystal CsPbBr3 cathode with a nano-separation of ~30 nm. Benefiting from the nanoscale vacuum channel and the high surface work function of the CsPbBr3 (4.55 eV), the vacuum nano-photodiode exhibits a low driving voltage of 15 V with an ultra-low dark current (50 pA). The vacuum nano-photodiode demonstrates a high photo responsivity (1.75 AW−1@15 V) under the illumination of a 532-nm laser light. The estimated external quantum efficiency is up to 400%. The electrostatic field simulation indicates that the CsPbBr3 cathode can be totally depleted at an optimal thickness. The large built-in electric field in the depletion region facilitates the dissociation of photoexcited electron–hole pairs, leading to an enhanced photoelectric conversion efficiency. Moreover, the voltage drop in the vacuum channel increases due to the photoconductive effect, which is beneficial to the narrowing of the vacuum barrier for more efficient electron tunneling. This device shows great promise for the development of highly sensitive perovskite-based vacuum opto-electronics.
N-H sites are crucial to proton transportation for phosphoric acid (PA)-doped polybenzimidazole (PBI). However, these sites in crosslinked PBI are easily reacted by crosslinker, leading to a ...decreasing proton conductivity. Herein, a novel crosslinker is synthesized and a series of crosslinked PBIs containing branched structure without sacrifice of effective N-H sites are prepared using the special crosslinker. The branching structure can effectively elevate free volume and PA absorption of these membranes, while N-H sites in the PBIs still remain for efficient proton transport. The prepared membranes exhibit improved proton conductivity (0.073 S cm−1, 160 °C, anhydrous), mechanical performance and superior oxidative stability. In the case of actual usage in a single cell, a peak power density of 690 mW cm−2 is measured, single-cell performance under laboratory conditions at 160 °C with a constant current load (200 mA cm−2) is maintained for 200 h without membrane degradation, and H2 permeability remains almost unaffected during this test. The results indicate that the crosslinked PBIs containing branching structure with no sacrifice of effective N-H sites can potentially be used as high temperature proton exchange membrane.
•A series of polymeric crosslinking branched PBI membranes were prepared.•Crosslinked membranes could be obtained without sacrifice of the N-H sites.•Crosslinked branched PBI membranes exhibit good comprehensive performance.•The peak power density of the crosslinked branched membrane reached 690 mW cm−2.•No performance decline during a 200 h test period for long-term stability.
Although phosphoric acid-doped polybenzimidazoles (PA-doped PBIs) are widely accepted in high-temperature proton exchange membrane fuel cells, further improvement is desirable to obtain optimal fuel ...cell performance. Block copolymers applied as low-temperature proton exchange membranes have been recently shown to exhibit high proton conductivity and fuel cell properties. However, few block copolymers have been reported as high-temperature proton exchange membranes. In this work, a series of segmented block PA-doped PBIs are synthesized with various molar ratios and similar molecular weights. The block copolymer membranes show obvious nanophase-separated structures due to the combination of rigid and flexible segments in the copolymer. A high proton conductivity of the block membrane is obtained at lower phosphoric acid doping levels (0.1 S cm−1 at 180 °C). The fuel cell performance of the block membranes exhibits a maximum power density of 360 mW/cm2 at 160 °C, which is higher than that of pristine poly2,2′-(p-oxydiphenylene)-5,5′-benzimidazole (OPBI) membranes (268 mw/cm2). The results suggest that block PBI doped with phosphoric acid can potentially be applied as a high-temperature proton exchange membrane.
•A series of block copolymers with various molar ratios were prepared.•The combination of rigid and flexible segments resulted in nanophase separation.•The block membranes exhibited a high proton conductivity at a low ADL.•The power density of the block membrane reached 360 mW/cm2.
A portable, cheap and sensitive paper type electrochemical immunosensor was developed with conductive nanobiochar paper as the conductive layer and utilized for sensitive detection of microcystin-LR ...(MCLR) toxin in water. The paper immunosensor was constructed by coating of highly conductive and dispersible nanobiochar particle (nBC) and anti-MCLR antibody on the filter paper via dipping-drying method. The presence of MCLR could be specifically quantified amperometrically by the nBC-paper immunosensor with the response time of less than 5 min, and the lowest detection limit of 17 pM (0.017 μg/L) was achieved. Moreover, the proposed immunosensor exhibited high selectivity, reproducibility and storage stability, and was also used for environmental water detection with satisfactory recovery. The successful fabrication of low cost and ubiquitous biochar based paper type electrochemical immunosensing system would have significant value for the development of highly cost-effective electrochemical device.
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•Electrochemical immunosensor was constructed with conductive nanobiochar paper.•Such paper immunosensor was stable, simple and highly cost effective.•Ultrasensitive detection of MCLR with high selectivity was achieved.•It could be used for real environmental water detection with satisfactory recovery.
•A novel PMS based AOPs method was developed with SugBC900 as catalyst.•The SugBC900 is easy to prepare and highly cost effective.•High sp2 carbon content, surface area and electron transfer ability ...are key features.•1O2 and O2•− are dominant oxidative species instead of SO4•− and •OH.•It can effectively degrade BPA at broad pHs (1–11) and temperatures (10–45 °C).
Cost effective and environmental friendly biochar catalyst (SugBC900) with high catalytic activity toward peroxymonosulfate (PMS) was prepared by simple pyrolysis of sugarcane waste, and utilized for efficient degradation of organic pollutants. Taking advantages of high sp2 hybrid carbon content, large surface area and excellent electron transfer ability, the SugBC900 coupled with PMS presented far greater catalytic degradation ability toward bisphenol A (BPA) as model pollutant when compared to the SugBC700, SugBC800 and other carbonaceous catalysts. The oxidative species of 1O2 and O2•− were demonstrated to be dominant for catalytic degradation, and the role of SO4•− and •OH was minor. 20 mg/mL of BPA could be completely degraded with less than 60 min at pHs of 5.0–11.0, and at temperatures of 25–45 °C. And at the extremely acidic (pH of 1.0) or low temperature (10 °C) conditions, the degradation efficiencies could still reach more than 90%. The SugBC900 was also successfully utilized for the efficiently catalytic degradation of BPA and other organic pollutants in various real environmental water. Because of simple preparation by impregnating none of external elements, extremely low cost property, and robustness characteristic by having broad working conditions, the SugBC900 would have potential to be a good alternative to the conventional catalysts.
Laccase was stably immobilized on a cost effective and nanosized magnetic biochar (L-MBC) by adsorption, precipitation and crosslinking, and it was used for high performance BPA removal. A large ...amount of enzyme could be immobilized on the magnetic biochar with high activity (2.251 U per mg MBC), and the L-MBC could be magnetically separated from the aqueous solution in 20 seconds. The successful immobilization of laccase was also confirmed
FTIR, SEM, and EDS analyses. The L-MBC presented better storage and stability performances, pH tolerance and thermal stability than the free laccase. It was found that BPA with an initial concentration of 25 mg L
could be thoroughly removed within 75 min, where BPA removal was attributed to enzymatic degradation and adsorption. In addition, the BPA removal efficiency by the L-MBC could be maintained above 85% even after seven cycles of repeated use. Due to high stability and efficient recyclability, the L-MBC-based biocatalyst has the potential to be a reliable method for treating BPA in environmental water sources.
Here we present a simple method to prepare a highly efficient three components nanocomposites via thermal degradation of layered double metal hydroxides (LDHs)@polyvinyl alcohol (PVA) composites. ...Co7Fe3/CoFe2O4@C obtained from this method is applied to activate peroxymonosulfate (PMS) to degrade polluted organics and showed excellent performance. The best removal RhB efficiency of Co7Fe3/CoFe2O4@C (Co/Fe = 1:1) is near 100% within 10 min and the lowest ions elution (∼0.05 mg/L) under pH = 7, which is also better than the performance of the precursor Co–Fe LDH. Through further cycling experiments and degradation of p-nitrophenol, the stability and catalytic performance of the catalyst were verified. Finally, free radical scavenging experiments prove ·OH and SO4·- radicals participating in the reaction, which are the key factors for degradation. Based on the above, the derivation of the mechanism of Co7Fe3/CoFe2O4@C (Co/Fe = 1:1) catalyzing PMS to degrade polluted organics was proposed, and we consider this catalyst has great application prospect.
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•Co7Fe3&CoFe2O4 synthesized from LDH@PVA by thermal decomposition method.•Co7Fe3&CoFe2O4@C has better performance than Co–Fe LDH and Co–Fe spinel for dye degradation.•Co7Fe3&CoFe2O4@C has achieved efficient degradation with low ionic dissolution.•RhB and p-nitrophenol were degraded efficiently by Co7Fe3&CoFe2O4@C in a neutral pH.
The genetic interrogation and reprogramming of cells requires methods for robust and precise targeting of genes for expression or repression. The CRISPR-associated catalytically inactive dCas9 ...protein offers a general platform for RNA-guided DNA targeting. Here, we show that fusion of dCas9 to effector domains with distinct regulatory functions enables stable and efficient transcriptional repression or activation in human and yeast cells, with the site of delivery determined solely by a coexpressed short guide (sg)RNA. Coupling of dCas9 to a transcriptional repressor domain can robustly silence expression of multiple endogenous genes. RNA-seq analysis indicates that CRISPR interference (CRISPRi)-mediated transcriptional repression is highly specific. Our results establish that the CRISPR system can be used as a modular and flexible DNA-binding platform for the recruitment of proteins to a target DNA sequence, revealing the potential of CRISPRi as a general tool for the precise regulation of gene expression in eukaryotic cells.
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•CRISPRi enables robust gene repression and activation in human cells•CRISPRi knockdown is specific with minimal off-target effects in human cells•CRISPRi can effectively repress endogenous genes in human and yeast•dCas9 enables modular and programmable RNA-guided genome regulation in eukaryotes
Catalytically inactive CRISPR can be targeted to specific loci in human and yeast cells to specifically repress and activate transcription. The study demonstrates the potential for adapting CRISPRi for multiple modes of transcriptional control, chromatin modification, and regulatory element mapping in a broad range of eukaryotes.
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