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排序方式: 共有373条查询结果,搜索用时 31 毫秒
291.
Hiroaki Yoshida Zhenhua Pan Ryota Shoji Vikas Nandal Hiroyuki Matsuzaki Kazuhiko Seki Lihua Lin Masanori Kaneko Tsuyoshi Fukui Koichi Yamashita Tsuyoshi Takata Takashi Hisatomi Kazunari Domen 《Angewandte Chemie (International ed. in English)》2023,62(46):e202312938
Photocatalytic water splitting is a simple means of converting solar energy into storable hydrogen energy. Narrow-band gap oxysulfide photocatalysts have attracted much attention in this regard owing to the significant visible-light absorption and relatively high stability of these compounds. However, existing materials suffer from low efficiencies due to difficulties in synthesizing these oxysulfides with suitable degrees of crystallinity and particle sizes, and in constructing effective reaction sites. The present work demonstrates the production of a Gd2Ti2O5S2 (λ<650 nm) photocatalyst capable of efficiently driving photocatalytic reactions. Single-crystalline, plate-like Gd2Ti2O5S2 particles with atomically ordered surfaces were synthesized by flux and chemical etching methods. Ultrafine Pt-IrO2 cocatalyst particles that promoted hydrogen (H2) and oxygen (O2) evolution reactions were subsequently loaded on the Gd2Ti2O5S2 while ensuring an intimate contact by employing a microwave-heating technique. The optimized Gd2Ti2O5S2 was found to evolve H2 from an aqueous methanol solution with a remarkable apparent quantum efficiency of 30 % at 420 nm. This material was also stable during O2 evolution in the presence of a sacrificial reagent. The results presented herein demonstrates a highly efficient narrow-band gap oxysulfide photocatalyst with potential applications in practical solar hydrogen production. 相似文献
292.
293.
Thermally actuated shape-memory polymers: Experiments, theory, and numerical simulations 总被引:2,自引:0,他引:2
Vikas Srivastava 《Journal of the mechanics and physics of solids》2010,58(8):1100-1124
With the aim of developing a thermo-mechanically coupled large-deformation constitutive theory and a numerical-simulation capability for modeling the response of thermally actuated shape-memory polymers, we have (i) conducted large strain compression experiments on a representative shape-memory polymer to strains of approximately unity at strain rates of 10−3 and 10−1 s−1, and at temperatures ranging from room temperature to approximately 30 °C above the glass transition temperature of the polymer; (ii) formulated a thermo-mechanically coupled large-deformation constitutive theory; (iii) calibrated the material parameters appearing in the theory using the stress-strain data from the compression experiments; (iv) numerically implemented the theory by writing a user-material subroutine for a widely used finite element program; and (v) conducted representative experiments to validate the predictive capability of our theory and its numerical implementation in complex three-dimensional geometries. By comparing the numerically predicted response in these validation simulations against measurements from corresponding experiments, we show that our theory is capable of reasonably accurately reproducing the experimental results. As a demonstration of the robustness of the three-dimensional numerical capability, we also show results from a simulation of the shape-recovery response of a stent made from the polymer when it is inserted in an artery modeled as a compliant elastomeric tube. 相似文献
294.
Hard biomaterials such as bone, dentin, and nacre have primarily an organic phase (e.g. tropocollagen (TC)) and a mineral phase (e.g. hydroxyapatite (HAP) or aragonite) arranged in a staggered arrangement at the nanoscopic length scale. Interfacial interactions between the organic phase and the mineral phase as well as the structural effects arising due to the staggered arrangement significantly affect the strength of such biomaterials. The effect of such factors is intricately intertwined with the chemical environment of such materials. In the present investigation, an idealized TC–HAP composite system under tensile loading is analyzed using explicit three-dimensional (3-D) molecular dynamics (MD) simulations to develop an understanding of these factors. The material system is analyzed in three different environments: (1) in the absence of water molecules (non-hydrated), (2) in the presence of water molecules (hydrated), and (3) in the presence of water molecules with calcium ions (ionized water). The analyses focus on understanding the correlations among factors such as the structural arrangement, the peak stress during deformation, Young's modulus, the peak interfacial strength, and the length scale of the localization of peak stress during deformation. Analyses show that maximizing the contact area between the TC and HAP phases results in higher interfacial strength as well as higher fracture strength. Due to the staggered arrangement, the orientation of HAP crystals has insignificant effect on the biomaterial strength. Analyses based on strength scaling as a function of structural hierarchy level reveal that while peak strength follows a multiscaling relation, the fracture strength does not. The peak strain for failure was found to be independent of the changes in levels of structural hierarchy. Overall, the analyses, being limited in size due to the computational time constraint, point out important correlations between the mechanical strength and chemically influenced structural hierarchy of biomaterials. 相似文献
295.
296.
Srimanta Guin Pravas Dolui Xinglong Zhang Satyadip Paul Vikas Kumar Singh Sukumar Pradhan Hediyala B. Chandrashekar S. S. Anjana Robert S. Paton Debabrata Maiti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5689-5694
Directed C?H functionalization has been realized as a complementary tool to the traditional approaches for a straightforward access of non‐proteinogenic amino acids; albeit such a process is restricted mostly up to the γ‐position. In the present work, we demonstrate the diverse (hetero)arylation of amino acids and analogous aliphatic amines selectively at the remote δ‐position by tuning the reactivity controlled by ligands. An organopalladium δ‐C(sp3)?H activated intermediate has been isolated and crystallographically characterized. Mechanistic investigations carried out experimentally in conjunction with computational studies shed light on the difference in the mechanistic picture depending on the substrate structure. 相似文献
297.
Sunil Chauhan Vikas Verma Devinder Kumar Ashwani Kumar 《Journal of heterocyclic chemistry》2019,56(9):2571-2579
In the present work, a series of 18 imidazole–triazole hybrids ( 4a–r ) has been synthesized in good yield from substituted naphthaldehydes and 1,2‐diketones in the presence of ammonium acetate. The synthesized imidazole–triazole hybrid compounds were characterized by spectral techniques and screened in vitro for their antimicrobial activity. Compound 4h was found to be most active against Staphylococcus epidermidis, and compound 4e exhibited promising activity against Escherichia coli. In the fungal species under test, compound 4q was most potent against Aspergillus niger, even better than the fluconazole. Further, compound 4e was docked in the binding site of DNA gyrase topoisomerase II of E. coli. 相似文献
298.
In this report, we compiled various strategies involving a ring-rearrangement metathesis as a key step to assemble diverse molecules. Popular name reactions such as Grignard reaction, Overman rearrangement, Fischer indolization, Beckmann rearrangement and Diels–Alder reaction were used in combination with ring-rearrangement metathesis to construct complex targets. Additionally, CH activation and RRM strategy has been used to assemble azacycles. In some instances, the ring-rearrangement metathesis was expected to occur; however, ring-opening metathesis products were realized. These methods were included in the miscellaneous section. We anticipate that the lessons learned here are useful in designing complex polycyclic and heterocyclic targets suitable for biological and material science applications. Beside our work, we have also included others work as a background information. 相似文献
299.
Goyal Vikas Singh Arashdeep Singh Jagpreet Singh Tarandip Al-Kheraif Abdulaziz A. Kaur Harpreet Kumar Sanjeev Rawat Mohit 《Journal of Cluster Science》2022,33(6):2831-2831
Journal of Cluster Science - The authors claimed that acknowledgement in published article is not same as provided in revised/accepted paper. 相似文献
300.
We report a simple, one-pot, and metal free benzannulation protocol to carbazoles starting with indoles, carbonyl compounds and an appropriate dienophiles. Mechanistically, this strategy generates an in situ diene by condensation between indole and carbonyl compound succeed and subsequent dehydration. Later, Diels–Alder reaction of this diene with a suitable dienophile followed by oxidation delivers the carbazole derivative. This methodology provide an easy access to carbazoles containing 1,4-naphthoquinone moiety. 相似文献