21 research outputs found

    A coupled hydrological and hydrodynamic model for flood simulation

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    This paper presents a new flood modelling tool developed by coupling a full 2D hydrodynamic model with hydrological models. The coupled model overcomes the main limitations of the individual modelling approaches, i.e. high computational costs associated with the hydrodynamic models and less detailed representation of the underlying physical processes related to the hydrological models. When conducting a simulation using the coupled model, the computational domain (e.g. a catchment) is first divided into hydraulic and hydrological zones. In the hydrological zones that have high ground elevations and relatively homogeneous land cover or topographic features, a conceptual lumped model is applied to obtain runoff/net rainfall, which is then routed by a group of pre-acquired ‘unit hydrographs’ to the zone borders. These translated hydrographs will then be used to drive the full 2D hydrodynamic model to predict flood dynamics at high resolution in the hydraulic zones that are featured with complex topographic settings, including roads, buildings, etc. The new coupled flood model is applied to reproduce a major flood event that occurred in Morpeth, northeast England in September 2008. While producing similar results, the new coupled model is shown to be computationally much more efficient than the full hydrodynamic model

    Freeze–Thaw-Induced Gelation of Hyaluronan: Physical Cryostructuration Correlated with Intermolecular Associations and Molecular Conformation

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    Physically cross-linked hydrogels from hyaluronan (hyaluronic acid, HA) were prepared by a freeze–thaw technique at low pH. The effect of the freezing–thawing of HA solutions on the formation of physical cryogels is typical for the processes of noncovalent cryostructuration that takes the advantages of mild fabrication conditions and the absence of organic solvents and toxically cross-linking agents. The effects of processing steps (freezing time and number of freeze–thaw cycles), HA molecular weight (<i>M</i><sub>w</sub>), and the addition of typical polycarboxylic and polyhydric small molecules such as dicarboxylic acids and polyols on the formation of HA cryotropic hydrogels were investigated. Results verified that long freezing time and repeated freeze–thaw cycles benefited the alignment of polymer chains in the unfrozen liquid microphase, thereby promoting the formation of intermolecular aggregations and dense fibrillar network structures. High <i>M</i><sub>w</sub> of HA endowed the cryogel with strong mechanical strength. The influences of various small molecules on the cryogelation of HA revealed the different intermolecular association patterns in the gel network. Both succinic and glutaric acids participated in HA cryogelation, whereas oxalic, malic, and tartaric acids as well as some polyols (glycol, butanediol, and glycerol) inhibited the cryostructuration of HA. Hydrogen bonding and intermolecular interactions in acidic cryogels and in neutral cryogels obtained by <i>in situ</i> neutralizing the acidic cryogel were discussed at the molecular level in correlation with intermolecular associations and molecular conformation. A gelation mechanism for HA cryogel was proposed. In addition, experimental findings showed that the neutral HA cryogels possessed enhanced thermostability, resistance to acid decomposition, and enzyme degradation which are essentially important properties for biomaterials

    Arylations of Substituted Enamides by Aryl Iodides: Regio- and Stereoselective Synthesis of (<i>Z</i>)‑β-Amido-β-Arylacrylates

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    Arylations of substituted enamides by aryl iodides were achieved for the first time via an unusual PdCl<sub>2</sub>(COD)/Ag<sub>3</sub>PO<sub>4</sub> catalytic system. A broad range of (<i>Z</i>)-β-amido-β-arylacrylates were prepared regio- and stereoselectively in a highly efficient manner

    Seeding Bundlelike MFI Zeolite Mesocrystals: A Dynamic, Nonclassical Crystallization via Epitaxially Anisotropic Growth

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    Direct synthesis by assembly of precursor nanoparticles is a promising strategy for preparing distinct mesoscopic-structured crystals, especially when high controllability is realized. However, uncertain properties of amorphous precursors and inner complicacy of crystallization mechanisms hamper controllable synthesis of zeolite mesocrystals. Here, we develop a salt-aided seed-induced organic-free method to facilely synthesize anisotropic MFI-type nanorod-bundle zeolite mesocrystals. An epitaxial, anisotropic assembly and crystallization of precursor particles on seed crystals is successfully achieved via a distinctively dynamic, nonclassical process, from relatively disordered to ordered attachment (OA), triggering an enhanced one-dimensional (1D) growth, thus constructing a unique core–shell–shell structure. This work sheds new light on the insights of both zeolite mesocrystal properties and a nonclassical crystallization mechanism. With an understanding of the mechanism, this nonclassical process can be exploited to systematically tune mesocrystal properties and create zeolite materials with novel or enhanced physical and chemical performance

    Synthesis of the Putative Structure of (±)-Amarbellisine

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    The title compound was synthesized mainly by palladium catalytic coupling, cyclopropyl ring-opening rearrangement, epoxidation, Swern oxidation, demethanol reactions, and selective reduction. This synthesis was achieved in 16 steps with 9.7% overall yield. Unfortunately, the published spectroscopic data do not match with those of our synthetic compound

    High-Responsivity, High-Detectivity, Ultrafast Topological Insulator Bi<sub>2</sub>Se<sub>3</sub>/Silicon Heterostructure Broadband Photodetectors

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    As an exotic state of quantum matter, topological insulators have promising applications in new-generation electronic and optoelectronic devices. The realization of these applications relies critically on the preparation and properties understanding of high-quality topological insulators, which however are mainly fabricated by high-cost methods like molecular beam epitaxy. We here report the successful preparation of high-quality topological insulator Bi<sub>2</sub>Se<sub>3</sub>/Si heterostructure having an atomically abrupt interface by van der Waals epitaxy growth of Bi<sub>2</sub>Se<sub>3</sub> films on Si wafer. A simple, low-cost physical vapor deposition (PVD) method was employed to achieve the growth of the Bi<sub>2</sub>Se<sub>3</sub> films. The Bi<sub>2</sub>Se<sub>3</sub>/Si heterostructure exhibited excellent diode characteristics with a pronounced photoresponse under light illumination. The built-in potential at the Bi<sub>2</sub>Se<sub>3</sub>/Si interface greatly facilitated the separation and transport of photogenerated carriers, enabling the photodetector to have a high light responsivity of 24.28 A W<sup>–1</sup>, a high detectivity of 4.39 × 10<sup>12</sup> Jones (Jones = cm Hz<sup>1/2</sup> W<sup>–1</sup>), and a fast response speed of aproximately microseconds. These device parameters represent the highest values for topological insulator-based photodetectors. Additionally, the photodetector possessed broadband detection ranging from ultraviolet to optical telecommunication wavelengths. Given the simple device architecture and compatibility with silicon technology, the topological insulator Bi<sub>2</sub>Se<sub>3</sub>/Si heterostructure holds great promise for high-performance electronic and optoelectronic applications

    Total Synthesis of (+)-Chimonanthine, (+)-Folicanthine, and (−)-Calycanthine

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    Facile, straightforward, and asymmetric total syntheses of (+)-chimonanthine (<b>1</b>), (+)-folicanthine (<b>2</b>), and (−)-calycanthine (<b>3</b>) were accomplished in four to five steps from commercially available tryptamine. The synthesis features copper-mediated asymmetric cyclodimerization of chiral tryptamine derivative, which established a new entry into constructing the sterically hindered vicinal quaternary stereogenic carbon centers of dimeric hexahydropyrroloindole alkaloids in one procedure. An unprecedented base-induced isomerization from the chimonanthine skeleton to the calycanthine skeleton was observed and facilitated the synthesis of (−)-calycanthine (<b>3</b>)

    Copper-Catalyzed Arylation of <i>o</i>-Bromoanilides: Highly Flexible Synthesis of Hexahydropyrroloindole Alkaloids

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    In the presence of catalytic amount of copper iodide, a remote amide-assisted intramolecular arylation followed by alkylation leads to a general and flexible synthetic method toward the synthesis of medicinally interesting hexahydropyrroloindole alkaloids

    Fabrication of Robust Hydrogel Coatings on Polydimethylsiloxane Substrates Using Micropillar Anchor Structures with Chemical Surface Modification

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    A durable hydrophilic and protein-resistant surface of polydimethylsiloxane (PDMS) based devices is desirable in many biomedical applications such as implantable and microfluidic devices. This paper describes a stable antifouling hydrogel coating on PDMS surfaces. The coating method combines chemical modification and surface microstructure fabrication of PDMS substrates. Three-(trimethoxysilyl)­propyl methacrylates containing CC groups were used to modify PDMS surfaces with micropillar array structures fabricated by a replica molding method. The micropillar structures increase the surface area of PDMS surfaces, which facilitates secure bonding with a hydrogel coating compared to flat PMDS surfaces. The adhesion properties of the hydrogel coating on PDMS substrates were characterized using bending, stretching and water immersion tests. Long-term hydrophilic stability (maintaining a contact angle of 55° for a month) and a low protein adsorption property (35 ng/cm<sup>2</sup> of adsorbed BSA-FITC) of the hydrogel coated PDMS were demonstrated. This coating method is suitable for PDMS modification with most crosslinkable polymers containing CC groups, which can be useful for improving the anti-biofouling performance of PDMS-based biomedical microdevices

    Engineering Fractal MTW Zeolite Mesocrystal: Particle-Based Dendritic Growth via Twinning-Plane Induced Crystallization

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    Constructing superstructured crystalline materials by crystal engineering is an attractive objective for miscellaneous fields of researchers spanning biomimetics to catalytic materials. Zeolite is a kind of important crystalline catalyst, and superstructured zeolite has great potential for widespread applications. However, the ambiguous crystallization mechanisms hamper the effective and scientific fabrication of superstructured zeolite with exceptional properties. Herein, a fractal superstructured MTW zeolite with mesocrystal side branches is prepared via a nanoparticle-based nonclassical pathway with twinning-plane induced crystallization, which is distinct from the formation of general mesocrystal via crystal–crystal oriented attachment. Deformed atomic connection at a specific crystallographic plane contributes to the production of side branches. Moreover, this intriguing morphology could be regulated merely via adjusting the crystallization kinetics based on the unequivocal nonclassical crystallization mechanism. It will open a new avenue for design and synthesis of targeted crystals with superstructure and extraordinary properties