Stacking-symmetry governed second harmonic generation in graphene trilayers

Crystal symmetry plays a central role in governing a wide range of fundamental physical phenomena. One example is the nonlinear optical second harmonic generation (SHG), which requires inversion symmetry breaking. Here we report a unique stacking-induced SHG in trilayer graphene, whose individual monolayer sheet is centrosymmetric. Depending on layer stacking sequence, we observe a strong optical SHG in Bernal (ABA) stacked non-centrosymmetric trilayer, while it vanishes in rhombohedral (ABC) stacked one which preserves inversion symmetry. This highly contrasting SHG due to the distinct stacking symmetry enables us to map out the ABA and ABC crystal domains in otherwise homogeneous graphene trilayer. The extracted second order nonlinear susceptibility of the ABA trilayer is surprisingly large, comparable to the best known 2D semiconductors enhanced by excitonic resonance. Our results reveal a novel stacking order induced nonlinear optical effect, as well as unleash the opportunity for studying intriguing physical phenomena predicted for stacking-dependent ABA and ABC graphene trilayers.Comment: To appear in Science Advance

Effect of Spirulina Powder on Rheological Properties and Gluten Structure of Dough

The effect of Spirulina powder on the rheological properties, microstructure and gluten properties of wheat flour dough was investigated. The results showed that in terms of mixograph characteristics, the addition of Spirulina powder generally increased the water absorption rate, development time and peak curve area of dough, and increased the energy required to form dough. Adding a small amount of Spirulina powder enhanced the strength and reduced the viscosity of dough, but the kneading resistance became weaker at higher concentrations of added Spirulina powder. After adding Spirulina powder, the breaking force of dough gradually increased and the breaking distance decreased. Meanwhile, the free sulfhydryl content increased and the disulfide bond content decreased. When the amount of added Spirulina powder was more than 6%, the wet gluten content decreased significantly, and the micrograph showed that the gluten network was seriously damaged. Polyacrylamide gel electrophoresis (PAGE) showed that the proportion of high-molecular-mass glutenin decreased and the proportion of low-molecular-weight glutenin increased after adding Spirulina powder. The results of Fourier transform infrared (FT-IR) spectroscopy showed that the addition of Spirulina powder reduced the content of ordered structure and increased the content of disordered structure in gluten proteins. Therefore, it is speculated that when a small amount of Spirulina powder is added to dough, dietary fiber in Spirulina fills the gluten network in dough after absorbing water, strengthening the adhesive state of the gluten protein network and improving dough strength. However, when the amount of added Spirulina powder is higher than 6%, the cross-linking of gluten proteins is hindered, thereby weakening gluten, reducing the ordered structure content of gluten proteins, and ultimately deteriorating the rheological properties of dough

The mitochondrial gene orfH79 plays a critical role in impairing both male gametophyte development and root growth in CMS-Honglian rice

<p>Abstract</p> <p>Background</p> <p>Cytoplasmic male sterility (CMS) has often been associated with abnormal mitochondrial open reading frames. The mitochondrial gene <it>orfH79 </it>is a candidate gene for causing the CMS trait in CMS-Honglian (CMS-HL) rice. However, whether the <it>orfH79 </it>expression can actually induce CMS in rice remains unclear.</p> <p>Results</p> <p>Western blot analysis revealed that the ORFH79 protein is mainly present in mitochondria of CMS-HL rice and is absent in the fertile line. To investigate the function of ORFH79 protein in mitochondria, this gene was fused to a mitochondrial transit peptide sequence and used to transform wild type rice, where its expression induced the gametophytic male sterile phenotype. In addition, excessive accumulation of reactive oxygen species (ROS) in the microspore, a reduced ATP/ADP ratio, decreased mitochondrial membrane potential and a lower respiration rate in the transgenic plants were found to be similar to those in CMS-HL rice. Moreover, retarded growth of primary and lateral roots accompanied by abnormal accumulation of ROS in the root tip was observed in both transgenic rice and CMS-HL rice (YTA).</p> <p>Conclusion</p> <p>These results suggest that the expression of <it>orfH79 </it>in mitochondria impairs mitochondrial function, which affects the development of both male gametophytes and the roots of CMS-HL rice.</p

Local nearly non-strained perovskite lattice approaching a broad environmental stability window of efficient solar cells

Twist and fracture of surface lattice tend to occur under harsh condition due to the soft lattice natures of hybrid perovskite materials. Accordingly, surface defects and lattice distortion are produced, which allow the performance loss and notorious degradation in perovskite solar cells (PSCs). In our work, judiciously selected conjugated ligand was employed as the film intermediary, from which rigid and delocalization 4-phenylpyridine (4-pPy) exhibited the most significant improvement on both optoelectrical performance and stability of PSCs. By regulating the film crystallization kinetics, high-quality perovskite films can be obtained with preferable crystal orientation. Moreover, benefiting from the defects passivation and unidirectional bonding effect, coordinated 4-pPy “scaffold” on the lattice surface could mitigate vacancy formation and lattice twist/fracture under severe conditions. The resulted p-i-n planar device shows a considerable PCE of 21.12% (certified 20.2%) with negligible hysteresis, as well as an excellent storage (90% of original PCE after 1000 h at 60% RH), operating (90% of original PCE after 600 h at maximum power point) and thermal stress (89% of original PCE after 500 h at 85 °C) stability. It is hoped that our findings could open a new way to accelerate continued progress on PSCs regimes for efficieny maximization and stability prolongation

Development of Elite BPH-Resistant Wide-Spectrum Restorer Lines for Three and Two Line Hybrid Rice

Hybrid rice has contributed significantly to the world food security. Breeding of elite high-yield, strong-resistant broad-spectrum restorer line is an important strategy for hybrid rice in commercial breeding programs. Here, we developed three elite brown planthopper (BPH)-resistant wide-spectrum restorer lines by pyramiding big-panicle gene Gn8.1, BPH-resistant genes Bph6 and Bph9, fertility restorer genes Rf3, Rf4, Rf5, and Rf6 through molecular marker assisted selection. Resistance analysis revealed that the newly developed restorer lines showed stronger BPH-resistance than any of the single-gene donor parent Luoyang-6 and Luoyang-9. Moreover, the three new restorer lines had broad spectrum recovery capabilities for Honglian CMS, Wild abortive CMS and two-line GMS sterile lines, and higher grain yields than that of the recurrent parent 9,311 under nature field conditions. Importantly, the hybrid crosses also showed good performance for grain yield and BPH-resistance. Thus, the development of elite BPH-resistant wide-spectrum restorer lines has a promising future for breeding of broad spectrum BPH-resistant high-yield varieties

Dual‐Defect Manipulation Enables Efficient and Spectrally Stable Blue Perovskite Light‐Emitting Diodes

Performance of blue solution‐processed perovskite light‐emitting diodes (LEDs) is limited by availability of blue perovskite materials. Herein, 4‐(trifluoromethyl)benzoyl ammonium bromide (4‐TMBABr) is used with abundant N H and C O groups to passivate the defects and produce highly stable PEAxPA2‐x(CsPbBr3)n‐1PbBr4 perovskites for blue LED applications. The N H group in the 4‐TMBABr suppresses the Br‐ion mismatch through hydrogen bonds (N‐H···Br) and C O group coordinates the unsaturated lead dangling bonds (C O:Pb). The effective defect passivation by 4‐TMBABr reduces the nonradiative recombination in the perovskite films, hence enhancing its optical performance. In the LED structure, the sodium bis(trifluoromethanesulfonyl)imide (SBTI) modified NiOx films are used to improve the hole transport and to inhibit the fluorescence quenching of the perovskite layer. The dual‐defect manipulation strategy is advantageous for producing efficient and spectrally stable blue perovskite LEDs, and the authors demonstrate an LED with maximum luminance of 1094 cd m−2 and external quantum efficiency of 10.3%. This work can inform and underpin future development of blue perovskite LEDs with highly efficient and stabile performance

A Catalyst‐Like System Enables Efficient Perovskite Solar Cells

High-quality perovskite films are essential for achieving high performance of optoelectronic devices; However, solution-processed perovskite films are known to suffer from compositional and structural inhomogeneity due to lack of systematic control over the kinetics during the formation. Here, the microscopic homogeneity of perovskite films is successfully enhanced by modulating the conversion reaction kinetics using a catalyst-like system generated by a foaming agent. The chemical and structural evolution during this catalytic conversion is revealed by a multimodal synchrotron toolkit with spatial resolutions spanning many length scales. Combining these insights with computational investigations, a cyclic conversion pathway model is developed that yields exceptional perovskite homogeneity due to enhanced conversion, having a power conversion efficiency of 24.51% for photovoltaic devices. This work establishes a systematic link between processing of precursor and homogeneity of the perovskite films

نقش بمبزين در سيری پيش از جذب

پس از صرف غذا و پيش از آنکه مواد غذايی هضم و جذب شوند، دريافت غذا بسرعت وقفه می يابد و انسان احساس سيری می کند. اين موضوع نشان می دهد که اطلاعات مربوط به اعصاب حسی يا مواد هورمونی مترشحه از بخش های فوقانی لوله گوارش موجب سيری پيش از جذب می شود. بعضي نوروترانسميترها و مواد هورمونی به عنوان عوامل فرضی سيری شناخته شده اند که يکی از آنها بمبزين است. بمبزين اعمال يک نوروترانسميتر را در تشکيلات عصبی لوله گوارش پستانداران Bombesin تقليد می کند. بمبزين به کار رفته در بطن های جانبی مغز با فعال کردن سوبستراهای عصبی پاراونتريکولار موجب وقفه دريافت غذا و هيپوانسولينمی می گردد. با تزريق داخل صفاتی بمبزين نه تنها ميزان دريافت غذا کاهش (Gastrin Releasing) GBP می يابد بلکه فاصله بين غذا نيز افزايش می يابد. بعلاوه بمبزين و سبب آزاد شدن هورمونهايی در روده می شوند که اين مواد خود بعنوان عوامل بروز سيری Peptide عمل می کنن