| 1. |
- Zhang, Juqing, et al.
(författare)
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Super-enhancers conserved within placental mammals maintain stem cell pluripotency
- 2022
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 119:40
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Tidskriftsartikel (refereegranskat)abstract
- Despite pluripotent stem cells sharing key transcription factors, their maintenance involves distinct genetic inputs. Emerging evidence suggests that super-enhancers (SEs) can function as master regulatory hubs to control cell identity and pluripotency in humans and mice. However, whether pluripotency-associated SEs share an evolutionary origin in mammals remains elusive. Here, we performed comprehensive comparative epigenomic and transcription factor binding analyses among pigs, humans, and mice to identify pluripotency-associated SEs. Like typical enhancers, SEs displayed rapid evolu-tion in mammals. We showed that BRD4 is an essential and conserved activator for mammalian pluripotency-associated SEs. Comparative motif enrichment analysis revealed 30 shared transcription factor binding motifs among the three species. The majority of transcriptional factors that bind to identified motifs are known regulators associated with pluripotency. Further, we discovered three pluripotency-associated SEs (SE-SOX2, SE-PIM1, and SE-FGFR1) that displayed remarkable conservation in pla-cental mammals and were sufficient to drive reporter gene expression in a pluripotency-dependent manner. Disruption of these conserved SEs through the CRISPR-Cas9 approach severely impaired stem cell pluripotency. Our study provides insights into the understanding of conserved regulatory mechanisms underlying the maintenance of plu-ripotency as well as species-specific modulation of the pluripotency-associated regula-tory networks in mammals.
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| 2. |
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| 3. |
- Li, Zhaoyu, et al.
(författare)
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Ctenodactylid rodents (Rodentia, Ctenodactylidae) from the early Oligocene Nanpoping fauna of Lanzhou Basin, Northwest China
- 2023
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Ingår i: Palaeontographica. Abteilung A, Palaozoologie, Stratigraphie. - : Schweizerbart. - 0375-0442. ; 326:1-6, s. 151-182
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Tidskriftsartikel (refereegranskat)abstract
- Ctenodactylid rodents prospered during the Paleogene in East and Central Asia, and due to their high diversification, they are important for biostratigraphic correlations. Here, we present new and diverse material from the late early Oligocene Nanpoping mammal fauna of the Lower Member of the Xianshuihe Formation from the Lanzhou Basin, Central China. Nine species -Tataromys plicidens, Tataromys sigmodon, Tataromys minor, Yindirtemys ulantatalensis, Yindirtemys shevyrevae, Alashania tengkoliensis, Karakoromys decessus, ?Euryodontomys ampliatus and Helanshania deserta -were recognized and described here in detail, the latter five species for the first time from early Oligocene Nanpoping fauna of the Lanzhou Basin. For the Lanzhou Basin, ctenodactylids show the maximum richness in the early Oligocene and have a comparatively high diversity compared with other contemporaneous faunas until the abrupt decline at the late Oligocene, with only Yindirtemys left. Ctenodactylid diversification in the early Oligocene may be related to the semi-arid climate with episodes of higher precipitation, and the following niche partitioning.
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| 4. |
- Li, Zhaoyu, 1990-, et al.
(författare)
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New Material of Schizotheriine Chalicothere (Perissodactyla, Chalicotheriidae) from the Xianshuihe Formation (Early Miocene) of Lanzhou Basin, Northwest China
- 2022
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Ingår i: Journal of mammalian evolution. - Berlin : Springer. - 1064-7554 .- 1573-7055. ; 29:4, s. 877-889
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Tidskriftsartikel (refereegranskat)abstract
- A new schizotheriine mandible from the early Miocene Xianshuihe Formation in Lanzhou Basin, Northwest China is described here. Compared with other contemporaneous taxa, the lower jaw is most similar to Borissiakia betpakdalensis from Kazakhstan based on mandibular morphology and dental features, except for a much smaller body size which is hardly explained by intraspecific variation and suggests it represents a smaller body-sized species of Borissiakia. The type specimen of Phyllotillon huangheensis, from the same strata of the Lanzhou Basin, shares characters with the new specimen in the lower cheek teeth and the tapered morphology of the anterior horizontal ramus. Differences between both are reflected in the height of the ramus, especially the level of the symphysis, which may be an expression of sexual dimorphism. Therefore, schizotheriine mandibles from the early Miocene of Lanzhou Basin are regarded as the same taxon, and both are recognized as Borissiakia huangheensis. The occurrence of a chalicothere and other large perissodactyls may suggest that a certain amount of open woodland was distributed across the basin and that the paleoclimate might have been more humid during the early Miocene.
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| 5. |
- Meng, Lu, et al.
(författare)
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Study on the safety performance of an offshore stationary lead-cooled fast reactor design loaded with nitride fuel
- 2024
-
Ingår i: Annals of Nuclear Energy. - 0306-4549 .- 1873-2100. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- As a new generation of reactor type, lead-cooled fast reactors, have better safety behaviors, higher reliability, and better economic performance, aiming at island power supply through nuclear energy, seawater desalination, optimization of nuclear submarines, etc. Its evolution of nuclear waste and the advantages of nuclear non-proliferation provide a good prospect for development. This paper studied the safety performances of an offshore stationary lead-cooled reactor (OSLR) proposed in the National Key Research and Development Program of China. The transient analysis code SAS4A/SASSYS-1 was used to perform simulations of unprotected over-power accidents (UTOP) and unprotected loss of heat sink (ULOHS) accidents. The results indicated that offshore stationary lead-cooled reactors can withstand a maximum positive reactivity insertion of 0.5$ within 1 s during UTOP accidents without exceeding the working limits of the core. In ULOHS accidents, the inherent safety characteristics of OSLR allowed it to withstand 75 % heat removal capability of IHX. The simulation results were used to analyze the response of this stationary offshore reactor to transient accident conditions and the limits of its ability to withstand accidents in order to provide reference data for subsequent design and ideas for possible development of natural cycle lead-cooled reactors in the future.
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| 6. |
- Li, Yunxiang, et al.
(författare)
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De-agglomeration of IZM-2 zeolite crystals by post-synthetic treatment
- 2016
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 225, s. 185-191
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Tidskriftsartikel (refereegranskat)abstract
- Highly intergrown nanocrystals are commonly observed in zeolite samples, and the densely packed agglomerates may result in small secondary porosity, which restricts the advantage of hierarchical structures. In this work we take IZM-2 zeolite as an example to demonstrate a post-treatment method with diluted hydrofluoric acid solution, which de-agglomerates intergrown zeolite nanocrystals and improves the secondary porosity. The treated samples preserve high crystallinity, similar framework composition and distinctively higher external surface area compared to the agglomerated ones. The results show that this treatment is an effective method for de-agglomeration of intergrown nanocrystals without affecting the original framework.
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| 7. |
- Li, Yunxiang, 1986, et al.
(författare)
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Micellization of true amphoteric surfactants
- 2013
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 411, s. 47-52
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Tidskriftsartikel (refereegranskat)abstract
- The physical chemical behavior of a series of N-alkyl amino acid-based surfactants has been investigated. The series comprises four different types of amino acids as polar headgroups: glycine, aminomalonic acid, aspartic acid and glutamic acid, and for each type three homologues were synthesized: the octyl, decyl and dodecyl derivative. Aminomalonic acid, aspartic acid and glutamic acid are dicarboxylic amino acids with one, two and three methylene groups as spacer between the carboxylic groups, respectively. Compared with the more common N-acyl surfactants based on the same amino acids, many of the N-alkyl derivatives exhibited relatively high Krafft temperatures. The N-alkyl derivatives also had considerably lower critical micelle concentrations (CMCs) and they gave low values of surface tension at the CMC. The length of the spacer between the two carboxylic groups did not much influence the micellization. Some of the surfactants, in particular the lower homologues of N-alkylglycinate surfactants, gave unusually low surface tension values. The low values are most likely due to formation of a mixed monolayer at the surface, comprising of alternating anionic N-alkylglycinate and cationic N-protonated-N-alkylglycine. In a plot of conductivity vs. surfactant concentration there was no kink on the curve around the CMC, as determined by tensiometry. The absence of such a kink is in accordance with the view that self-assembly of the N-alkyl amino acid-based surfactants involves formation of mixed micelles consisting of alternating N-alkyl amino acid anion and N-protonated-N-alkyl amino acid also in the bulk solution. The protonation of the N-alkyl amino acid anion, which generates hydroxyl ions, is driven by the energetically favorable formation of mixed micelles consisting of anionic and cationic amphiphiles.
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| 8. |
- Li, Yunxiang, et al.
(författare)
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Microporous pure-silica IZM-2
- 2017
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 237, s. 222-227
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Tidskriftsartikel (refereegranskat)abstract
- Pure-silica IZM-2 was synthesized for the first time, and the concentration of sodium hydroxide used during synthesis affected the phase purity and size of crystals. Most of the micropores in calcined pure silica IZM-2 that was synthesized in the presence of high concentrations of sodium hydroxide were inaccessible to N-2 adsorption; however, the micropores could be rendered accessible by applying either of two different post-synthetic treatments. Pure-silica IZM-2 could also be synthesized without sodium ions using the hydroxide version of the template. In this case, the micropores were accessible to N-2 directly after calcination. The size of pure-silica IZM-2 crystals obtained increased with the concentration of sodium hydroxide, with the highest concentrations giving spherical and micrometer-sized aggregates of pure-silica IZM-2 that consisted of intergrown particles (60-500 nm). The nature of the defects in pure-silica IZM-2 was studied with a combination of H-1, and Si-29 solid-state NMR spectroscopy. As expected, direct-polarization Si-29 NMR spectroscopy showed that the number of non-condensed silica groups decreased upon calcination. Calcined samples also showed broader Si-29 NMR bands for the fully condensed silica moieties, which indicated a broader distribution of bond angles and/or bond lengths. The siloxy and silanol groups in calcined pure-silica IZM-2 were accessible to protonation as determined by H-1 NMR spectroscopy. We could not determine the structure of pure-silica IZM-2 in its aggregated form; however, further studies of the synthetic conditions could yield larger, non-aggregated crystals that would facilitate structural determination.
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| 9. |
- Li, Yunxiang, 1986-
(författare)
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Modification of zeolites and synthesis of SAPO-templated carbon
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zeolites are crystalline aluminosilicates with diverse structures and uniform porosities. They are widely used as catalysts, adsorbents and ion-exchangers in industry. Direct or post modifications optimize the performance of zeolites for different applications. In this thesis, IZM-2 and TON-type zeolites were synthesized, modified and studied. In addition, FAU-type zeolite and silicoaluminophosphate (SAPO) molecular sieves were applied as templates for the preparation of microporous carbons.In the first part of this thesis, the IZM-2 zeolite with an unknown structure was synthesized. We focused on the increasing the secondary porosity and the varied framework compositions upon post modifications.The structure determination of this IZM-2 zeolite was hindered by the small size of crystals. In the second part of this thesis, the synthesis composition was directly modified in order to increase the crystal sizes. IZM-2 crystals were enlarged by excluding the aluminium atoms from the framework. The micropores of the obtained pure-silica polymorphs were activated by ion-exchanging alkali-metal ions with protons.Typically, TON-type zeolites that are synthesized at hydrothermal conditions under stirring have needle-shaped crystals. In the third part of this thesis, snowflake-shaped aggregates were produced by using static hydrothermal conditions for the synthesis of TON-type zeolites. The effects of synthesis parameters on the growth and morphology of crystals were discussed in detail.In the last part of this thesis, microporous carbons with a structural regularity were prepared by chemical vapour deposition (CVD) of propylene using a silicoaluminophosphate (SAPO-37) template. Compared to the conventional zeolite templates, the SAPO template could be removed under mild conditions, without using hydrofluoric acid, and the generated carbons had a large specific surface area and a high fraction of ultrasmall micropores.
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| 10. |
- Li, Yunxiang, et al.
(författare)
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Nanocrystalline TON-type zeolites synthesized under static conditions
- 2018
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 256, s. 84-90
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Tidskriftsartikel (refereegranskat)abstract
- Pure-phase zeolites of the TON-type were synthesized under static hydrothermal conditions, which previously have, typically, required stirring during synthesis. Heterocyclic structure directing agents (SDAs) were observed to play important roles in both the selection of the polymorphs as well as in affecting the morphology of the particles formed. When an imidazole-based SDA was used snowflake shaped particles formed, which indicated a dendritic growth pattern of the zeolite. These zeolite particles possessed intercrystalline mesopores. To the best of our knowledge, it is for the first time that snowflake-shaped particles have been observed for TON-type zeolites. Other synthesis parameters were optimized to obtain crystals with short c-axes. The c-axis shortened with an increased solid concentration used during synthesis. This shortening was attributed to both the degree of supersaturation, and a change of the crystal growth mechanism. Short c-axes could increase the concentration of pore mouths in TON-type zeolites. Altogether, synthesis of nanocrystalline zeolites of the TON type under static condition could, potentially, be advantageous to large-scale production.
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| 11. |
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| 12. |
- Li, Yunxiang, et al.
(författare)
-
SAPO-templated carbon
-
Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 13. |
- Li, Yunxiang, et al.
(författare)
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Silicoaluminophosphate (SAPO)-Templated Activated Carbons
- 2019
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:6, s. 9889-9895
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Tidskriftsartikel (refereegranskat)abstract
- Microporous activated carbon was prepared by depositing and pyrolyzing propylene within the microporous voids of SAPO-37 and subsequently removing the template by a treatment with HCl and NaOH. The carbon had a high surface area and large micropore and ultramicropore volumes. The yield, crystallinity, morphology, and adsorption properties compared well with those of a structurally related zeolite-Y-templated carbon. No HF was needed to remove the SAPO-37 template in contrast to the zeolite Y template, which could be of industrial importance.
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| 14. |
- Liu, Tong, et al.
(författare)
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Semitransparent polymer solar cell/triboelectric nanogenerator hybrid systems: Synergistic solar and raindrop energy conversion for window-integrated applications
- 2022
-
Ingår i: Nano Energy. - : ELSEVIER. - 2211-2855 .- 2211-3282. ; 103
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Tidskriftsartikel (refereegranskat)abstract
- Development of photovoltaic (PV)-derived hybrid power systems can overcome the weather-dependent elec-tricity production and increase the amount of dispatchable renewable energy generation. Herein, monolithic hybrid devices are developed via rational integration of high-performance semitransparent polymer solar cells (ST-PSCs) and liquid-solid triboelectric nanogenerators (TENGs). High-performance PSCs with efficiencies of 17.4% for rigid and 15.7% for flexible devices are achieved. Further electrode modifications and integration of transparent TENGs synergistically balance the above-bandgap photon harvesting and transparency in a broad wavelength range (380 -1000 nm), yet significantly reduce the transmittance in the near-infrared wavelength range (1000 -2500 nm) of hybrid devices. The hybrid devices simultaneously provide high visible light transparency, good color fidelity, efficient heat resistance and possibility to integrate on rigid and flexible substrates. The hybrid devices attain a high solar conversion efficiency of 10.1% under 1 sun, indicating efficient light-to-electricity conversion (a maximum electrical power output: 101 W m-2) on sunny days. The hybrid devices can also generate a maximum electrical power output of 2.62 W m- 2 through waterdrop energy con-version, implying complementary green electricity production on rainy days. The controlled ambient tempera-ture and specific transmittance windows provided by the hybrid devices sustain plant growth and highlight their great potential in agricultural applications. Gratifyingly, this work demonstrates the first example of ST-PSC/ TENG hybrid systems for scaling up renewable power generation in different weather conditions, considering architectural and agricultural applications.
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| 15. |
- Siddique, Suniya, et al.
(författare)
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Realizing High Thermoelectric Performance in p-Type SnSe Crystals via Convergence of Multiple Electronic Valence Bands
- 2022
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:3, s. 4091-4099
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Tidskriftsartikel (refereegranskat)abstract
- SnSe crystals have gained considerable interest for their outstanding thermoelectric performance. Here, we achieve excellent thermoelectric properties in Sn0.99–xPbxZn0.01Se crystals via valence band convergence and point-defect engineering strategies. We demonstrate that Pb and Zn codoping converges the energy offset between multiple valence bands by significantly modifying the band structure, contributing to the enhancement of the Seebeck coefficient. The carrier concentration and electrical conductivity can be optimized, leading to an enhanced power factor. The dual-atom point-defect effect created by the substitution of Pb and Zn in the SnSe lattice introduces strong phonon scattering, significantly reducing the lattice thermal conductivity to as low as 0.284 W m–1 K–1. As a result, a maximum ZT value of 1.9 at 773 K is achieved in Sn0.93Pb0.06Zn0.01Se crystals along the bc-plane direction. This study highlights the crucial role of manipulating multiple electronic valence bands in further improving SnSe thermoelectrics.
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| 16. |
- Wang, Bo, et al.
(författare)
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Unprecedented differences in the diamond nucleation density between carbon- and silicon-faces of 4H-silicon carbides
- 2020
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Ingår i: Chinese Chemical Letters. - : ELSEVIER SCIENCE INC. - 1001-8417 .- 1878-5964. ; 31:7, s. 2013-2018
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Tidskriftsartikel (refereegranskat)abstract
- 4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction, heat sink and mechanical sealing. Nucleation plays a critical role in the deposition of the diamond film on 4H-silicon carbides. Nevertheless, as a typical polar material, the fundamental mechanism of diamond nucleation on different faces of 4H-silicon carbides has not been fully understood yet. In this contribution, nucleation of diamond was performed on the carbon- and silicon-faces of 4H-silicon carbides in a direct current chemical vapor deposition device. The nucleation density on the carbon-face is higher by 2-3 orders of magnitude compared to the silicon-face. Transmission electron microscopy verifies that there are high density diamond nuclei on the interface between the carbon-face and the diamond film, which is different from columnar diamond growth structure on the silicon-face. Transition state theory calculation reveals that the unprecedented distinction of the nucleation density between the carbon-face and the silicon-face is attributed to different desorption rates of the absorbed hydrocarbon radicals. In addition, kinetic model simulations demonstrate that it is more difficult to form CH2(s)-CH2(s) dimers on silicon-faces than carbon-faces, resulting in much lower nucleation densities on silicon-faces. (C) 2019 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
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| 17. |
- Xu, Chao, et al.
(författare)
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High-Performance Activated Carbons Synthesized from Nanocellulose for CO2 Capture and Extremely Selective Removal of Volatile Organic Compounds
- 2018
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Ingår i: Advanced Sustainable Systems. - : Wiley. - 2366-7486. ; 2:2
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Tidskriftsartikel (refereegranskat)abstract
- A series of sustainable activated carbons (ACs) with large surface areas and tunable pore sizes is synthesized from Cladophora cellulose and its chemically modified derivatives in a one-step physical carbonization/activation process. The molecular structure of the cellulose precursors and the carbonization/activation atmosphere (N-2 or CO2) significantly influence the pore structure of the ACs. When using oxidized cellulose and its further cross-linkages as the precursor, the ACs have a large volume of ultramicropores (pore diameter < 0.8 nm). Activation in CO2 results in ACs with surface areas up to 1241 m(2) g(-1). These ACs have a high CO2 uptake capacity (2.29 mmol g(-1) at 0.15 bar, 5.52 mmol g(-1) at 1 bar; 273 K) and a high CO2-over-N-2 selectivity (42 at 273 K). In addition, the capacity of the ACs to adsorb vapors of volatile organic compounds (VOCs) is remarkable, with values up to 0.97 mmol g(-1) at very low VOC concentrations (200 ppmv). The ACs have ultrahigh VOCs-over-N-2 selectivity up to 9.35 x 10(3) at 293 K for 0.02 vol%/99.8 vol% of benzene/N-2 mixture. It is anticipated that these ACs will be useful as sorbents for the postcombustion capture of CO2 and for indoor removal and direct air capture of various VOCs.
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| 18. |
- Xu, Chao, et al.
(författare)
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Porous Polymers and Porous Carbons for CO2 Capture and VOC Removal
- 2017
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Konferensbidrag (refereegranskat)abstract
- Porous materials have potential applications in gas capture and storage and heterogeneous catalysis.1 We have developed a series of porous polymers (PPs) and porous carbons (PCs) with high surface areas and tunable pore sizes. They were studied as potential sorbents for CO2 separation and volatile organic compounds (VOCs) removal.2 The PPs were synthesized by Schiff base polycondensations. The sustainable PCs were synthesized from natural abundant celluloses by a physical carbonization/ activation process. All the PPs and PCs had ultramicropores and displayed relatively high CO2 uptakes (0.93-2.29 mmol/g at 0.15 bar, 2.20-5.52 mmol/g at 1 bar; 273 K) and CO2-over-N2 selectivities (31-90 for CO2/N2 mixtures with 15 vol%/85 vol% at 273 K). In addition, the ACs displayed remarkable adsorption capacity for vapors of VOCs with values up to 0.97 mmol/g at very low VOC concentrations (200 ppmv) and with ultrahigh VOC-over-N2 selectivity (9.35 × 103 at 293 K for 0.02 vol%/99.8 vol% of benzene/N2 mixture). The diverse synthesis routes and rich functionalities of PPs allowed further post-modification to improve their performance in CO2 capture. The PPs modified by alkyl amines induced chemisorption of CO2, which was confirmed by the study of in situ infrared (IR) and solid-state 13C NMR spectroscopy. As a result, the amine-modified PPs had a large CO2 capacity and very high CO2-over-N2 selectivity at the CO2 concentrations relevant for post-combustion capture of CO2.
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| 19. |
- Zhang, Zhiqiang, et al.
(författare)
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Numerical Simulation of a Round Determinate Panel Test of Combined Concrete Panel and Welded Wire Mesh
- 2018
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Ingår i: Paper presented at the ISRM International Symposium - 10th Asian Rock Mechanics Symposium, Singapore, October 2018. - : International Society for Rock Mechanics and Rock Engineering / Society for Rock Mechanics and Engineering Geology.
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Konferensbidrag (refereegranskat)abstract
- The sprayed concrete layer, together with external welded wire mesh, has been widely used as an important surface support in underground excavation in civil and mining engineering. Recently, the load carrying capability of combined concrete layer and welded wire mesh was evaluated by a round determinate panel (RDP) test. However, performance assessment by using RDP specimens is hindered by the testing boundary condition and the failure pattern and mechanism of combined concrete layer and welded wire mesh remains unclear. In this paper, the numerical model of the RDP test was set up by means of a FEM code, ABAQUS, and a series of numerical tests were carried out to investigate the failure mechanism and the influence of boundary condition on the performance of the RDP tests. To ensure the constitutive model of concrete embedded in ABAQUS and the material parameters were correctly used, the numerical models were first calibrated by the laboratory results with different concrete panel thickness without using welded wire mesh. After that, the performance of the combined concrete layer and welded wire mesh was examined by using the calibrated concrete model and mesh model and the failure mechanism of the combined specimens was obtained. The results show that the failure pattern matches the laboratory observation rather well and the peak load carrying capacity of the combined concrete layer and welded wire mesh panel is a little higher than that of the concrete only panel but the residual load carrying capacity has been improved. The boundary condition has large effect on the load-displacement curve, which is discussed in detail in the paper. The objective was to develop a numerical methodology which could be used to evaluate the load carrying capacity of combined concrete layer and welded wire mesh and thereby improve the assessment of the performance of shotcrete and welded wire mesh on site.
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