Boron nitride nanosheets were dispersed in polymers to give composite films with excellent thermal transport performances approaching the record values found in polymer/graphene nanocomposites. ...Similarly high performance at lower BN loadings was achieved by aligning the nanosheets in poly(vinyl alcohol) matrix by simple mechanical stretching (see picture).
Hexagonal boron nitride nanosheets (BNNs) are analogous to their two‐dimensional carbon counterparts in many materials properties, in particular, ultrahigh thermal conductivity, but also offer some ...unique attributes, including being electrically insulating, high thermal stability, chemical and oxidation resistance, low color, and high mechanical strength. Significant recent advances in the production of BNNs, understanding of their properties, and the development of polymeric nanocomposites with BNNs for thermally conductive yet electrically insulating materials and systems are highlighted herein. Major opportunities and challenges for further studies in this rapidly advancing field are also discussed.
Carbon copy? Significant recent advances in boron nitride nanosheets, including their production, properties, and dispersion into polymeric matrices for thermally conductive yet electrically insulating nanocomposite materials and systems, are highlighted.
Elaborated molecular architectures including complex carbocycles, heterocycles, and polycyclic molecular structures represent an important class of organic compounds because they are ubiquitous ...structural units in a broad variety of biologically and pharmacologically relevant natural products, medicinal molecules, and functional materials. A major challenge in modern synthetic methodology is the development of strategically efficient and selective construction of these compounds from readily available starting materials. Transition‐metal‐catalyzed transformations involving Heck reaction as the pivotal step have afforded a powerful approach for accessing sophisticated polycyclic skeletons from a set of easy‐to handle starting materials, thus highlighting its potential significance in streamlining the drug discovery process. Over the past few decades, significant effort has been devoted to accessing complex polycyclic derivatives in efficient and versatile routes, and a number of powerful and direct synthetic strategies have been reported. In this review, the latest advances in transition‐metal‐catalyzed transformations involving Heck reaction as the critical step are summarized, which could be divided into six categories: 1) Heck/Sonogashira tandem reaction; 2) Heck/Suzuki tandem reaction; 3) Heck/Heck tandem reaction; 4) Heck/Hiyama tandem reaction; 5) Heck/Cacchi tandem reaction; 6) Heck/C−H bond functionalization tandem reaction.
Elaborated molecular architectures, especially carbocyclic, heterocyclic, endocyclic, and polycyclic molecular structures, serve as an important class of organic complexes because they are frequently ...occurring core structural units in a variety of biologically and pharmacologically relevant natural products, drug molecules, agrochemicals, and functional materials. A main challenge of current synthetic approaches is the development of strategically efficient and selective formation of these compounds from easy‐to‐handle starting materials. The cascade cyclizations of 1,7‐enynes have afforded an indispensable method for accessing molecular complexity and diversity, thus highlighting their potential significance in both academic and industrial communities. In the last decades, tremendous efforts have been devoted to discovering convenient routes to access sophisticated annulation derivatives, and a wide range of powerful and straightforward synthetic strategies have been reported. In this review, the latest achievements in the cascade cyclization reactions of 1,7‐enynes are summarized, which could be separated into three categories: (1) Visible‐light‐induced reactions of 1,7‐enynes; (2) Metal‐free catalyzed reactions of 1,7‐enynes; (3) Transition‐metal‐catalyzed reactions of 1,7‐enynes.
Zn-air batteries (ZABs) represent promising candidates for the next generation energy conversion and storage systems based on their superior features to those of lithium-ion batteries, including high ...theoretical energy density, low cost, and high safety. However, their further development and application is severely lagged due to the lack of high efficient and durable bifunctional oxygen electrocatalysts. The widely applied carbon-based catalysts are thermodynamically instable during battery charging. Herein, TiC supported amorphous MnOx (a-MnOx/TiC) is reported for the first time as electrocatalyst for the corrosion resistant oxygen electrodes of ZABs. A-MnOx/TiC delivers a remarkable activity and stability toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with a high half-wave potential (0.8 V) for ORR and a low potential (1.56 V) at 10 mA cm−2 for OER, which far outperforms the state of the art ORR catalyst (Pt/C) and OER catalyst (IrO2), as well as the Pt/C-IrO2 and a-MnOx/C bifunctional catalysts. The excellent bifunctional activity of a-MnOx/TiC can be attributed to the efficient synergistic effect between the active amorphous MnOx catalyst and the highly conductive and stable TiC support. More impressively, a-MnOx/TiC demonstrates an outstanding electrochemical stability in strong alkaline electrolyte under OER condition in contrast to the readily oxidized carbon-based a-MnOx/C catalysts. ZAB with a-MnOx/TiC delivers a greater discharge performance with a peak power density of 217.1 mW cm−2 than that of Pt/C-based ZAB, and a surpassing discharge and charge cycling performance and stability to ZABs with Pt/C-IrO2 and a-MnOx/C. Furthermore, a-MnOx/TiC can be applied for solid-state ZABs which exhibit excellent mechanical flexibility and cycle stability under their flat and bent states. The a-MnOx/TiC bifunctional electrocatalyst with extraordinarily high activity and electrochemical stability provides a promising approach for exploring corrosion resistant electrocatalysts for Zn-air batteries with high efficiency and long-term cycling stability.
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•TiC supported amorphous MnOx (a-MnOx/TiC) exhibits high activity for ORR and OER.•A-MnOx/TiC is more stable than carbon-based oxygen electrocatalysts during OER.•A-MnOx/TiC surpasses Pt/C and IrO2 benchmark in bifunctional activity and stability.•Zn-air batteries using a-MnOx/TiC achieve high power density and cycling stability.
Aeolian desertification, one of the most serious environmental issues, has hampered socioeconomic development on the Qinghai-Tibet Plateau (QTP). However, research on aeolian desertification in this ...region has been limited. To develop a set of science-based preventive measures to mitigate desertification in this region, it is first necessary to clarify the status, evolution, and driving factors of aeolian desertification. In this study, based on extensive field investigations and a current classification system for aeolian desertification, we established a new system for interpreting aeolian desertified land (ADL) on the plateau using Landsat images from 1977, 1990, 2000, 2010, and 2015 and obtained the distribution of ADL through visual interpretation of the images. The results showed that ADL covered 392,914km2 (15.1% of the study area) in 2015, including gravel ADL, sandy ADL, and aeolian monadnocks. Controlled by climate, landforms, the type of Quaternary deposit, and human activities, ADL is scattered throughout the plateau but is concentrated mostly in the western and northern parts. Aeolian desertification on the plateau expanded from 1977 to 2000 and then began to reverse. The evolution during the study period is the result of the combined effects of natural and human factors. Irrational human activities were the dominant factor responsible for the expansion of ADL prior to 2000, whereas the subsequent reversal was mainly caused by climate change combined with large ecological restoration projects.
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•Desertification from 1977 to 2015 in QTP was monitored using Landsat images.•The spatial-temporal distribution of ADL in different stages was identified.•The spatial distribution of ADL was controlled by natural and human factors.•Human activities were responsible for the expansion of ADL before 2000.•Ecological protection projects and climate change contributed to the reversal of ADL.
The physiological role of microRNAs (miRNAs) in osteoblast differentiation remains elusive. Exosomal miRNAs isolated from human bone marrow-derived mesenchymal stem cells (BMSCs) culture were ...profiled using miRNA arrays containing probes for 894 human matured miRNAs. Seventy-nine miRNAs (∼8.84%) could be detected in exosomes isolated from BMSC culture supernatants when normalized to endogenous control genes RNU44. Among them, nine exosomal miRNAs were up regulated and 4 miRNAs were under regulated significantly (Relative fold>2, p<0.05) when compared with the values at 0 day with maximum changes at 1 to 7 days. Five miRNAs (miR-199b, miR-218, miR-148a, miR-135b, and miR-221) were further validated and differentially expressed in the individual exosomal samples from hBMSCs cultured at different time points. Bioinformatic analysis by DIANA-mirPath demonstrated that RNA degradation, mRNA surveillance pathway, Wnt signaling pathway, RNA transport were the most prominent pathways enriched in quantiles with differential exosomal miRNA patterns related to osteogenic differentiation. These data demonstrated exosomal miRNA is a regulator of osteoblast differentiation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In vitro culture of follicles is a promising technology to generate large quantities of mature oocytes and it could offer a novel option of assisted reproductive technologies. Here we described a ...2‐dimensional follicular serum‐free culture system with 3‐dimensional effect that can make secondary follicles develop into antral follicles (78.52%), generating developmentally mature oocytes in vitro (66.45%). The oocytes in this serum‐free system completed the first meiosis; spindle assembly and chromosome congression in most oocytes matured from follicular culture were normal. However, these oocytes showed significantly lower activation and embryonic development rates, and their ability to produce Ca2+oscillations was also lower in response to parthenogenetic activation, after which a 2‐cell embryonic developmental block occurred. Oocytes matured from follicular culture displayed increased abnormal mitochondrial distribution and increased reactive oxygen species levels when compared to in vivo matured oocytes. These data are important for understanding the reasons for reduced developmental potential of oocytes matured from follicular culture, and for further improving the cultivation system.
Here we described a 2‐dimensional follicular serum‐free culture system with 3‐dimensional effect that can make secondary follicles develop into antral follicles (78.52%), generating developmentally mature oocytes in vitro (66.45%). The oocytes in this serum‐free system completed the first meiosis; spindle assembly and chromosome congression in most oocytes matured from follicular culture were normal.
Because of the discovery of the hidden-charm pentaquark Pc states by the LHCb Collaboration, the interests in the candidates of hidden-bottom pentaquark Pb states are increasing. They are anticipated ...to exist as the analogs of the Pc states in the bottom sector and predicted by many models. We give an exploration of searching for a typical Pb in the γ p → Υ p reaction, which shows a promising potential to observe it at an electron-ion collider. The possibility of searching for Pb in open-bottom channels is also briefly discussed. Meanwhile, the t -channel nonresonant contribution, which in fact covers several interesting topics at low energies, is systematically investigated.
A novel copper‐catalyzed cascade radical sulfonylation of N‐propargyl‐substituted indoles with concomitant 1,2‐aryl migration was described. The protocol, which has good functional‐group tolerance, ...provides practical, versatile and atom‐economical method of accessing a new class of fascinating 2‐sulfonated pyrrolo1,2‐αindole derivatives in moderate to good yields through the formation of the new C−S, C−C and C=O bonds in a one‐step.
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