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Topic review
Updated time: 25 Aug 2021
Submitted by: Agostinho Lemos
Definition: The suitability of the 18F radioisotope in positron emission tomography (PET) demanded novel approaches for 18F-fluorination and 18F-fluoroalkylation. The difluoromethyl (CF2H) group has gained increasing attention in medicinal chemistry due to its lipophilic hydrogen-bond donor properties. In non-radioactive chemistry, difluoromethyl heteroaryl-sulfones has been extensively used in difluoromethylation of substrates bearing C=C, C≡C, and C≡N bonds by visible light photoredox catalysis. Herein, we highlight our recent work on the synthesis of [18F]difluoromethyl heteroaryl-sulfones with improved molar activities and their application in photoinduced C-H 18F-difluoromethylation of N-containing heteroarenes via a radical-mediated pathway.
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Topic review
Updated time: 13 Oct 2021
Submitted by: Anuja Bokare
Definition: For anatase TiO2, the {001} crystal facets are the most reactive because they exhibit unique surface characteristics such as visible light responsiveness, dissociative adsorption, efficient charge separation capabilities and photocatalytic selectivity. In this review, a concise survey of the literature in the field of {001} dominated anatase TiO2 crystals and their composites is presented. Even though the design and morphologically controlled synthesis of TiO2-001 is considered to be a hot spot in scientific research, it still has some drawbacks like its wide band gap and high recombination rate. These drawbacks can easily be overcome by coupling them with other materials to form TiO2-001-based composites. This review focusses on the synthesis, properties and applications of TiO2-001-based composites.
Topic review
Updated time: 25 Aug 2021
Submitted by: Mohammad Nur E Alam
Definition: The development of magnetic photonic crystals (MPC) has been a rapidly evolving research area since the late 1990s. Magneto-optic (MO) materials and the techniques for their characterization have also continually undergone functional and property-related improvements. MPC Optimization is a feature-rich Windows software application designed to enable researchers to analyse the optical and magneto-optical spectral properties of multilayers containing gyrotropic constituents. A set of computational approaches, and a custom software package have been described, designed to enable the design and optimization of 1D magnetic photonic crystals in terms of the achievable combinations of Faraday rotation, transmission, and reflection spectra.
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Topic review
Updated time: 09 Sep 2021
Submitted by: Marcelo I. Guzman
Definition: Atmospheric organic aerosols play a major role in climate, demanding a better understanding of their formation mechanisms by contributing multiphase chemical reactions with the participation of water. The sunlight driven aqueous photochemistry of small 2-oxocarboxylic acids is a potential major source of organic aerosol, which prompted the investigations into the mechanisms of glyoxylic acid and pyruvic acid photochemistry reviewed here. While 2-oxocarboxylic acids can be contained or directly created in the particles, the majorities of these abundant and available molecules are in the gas phase and must first undergo the surface uptake process to react in, and on the surface, of aqueous particles. Thus, the work also reviews the acid-base reaction that occurs when gaseous pyruvic acid meets the interface of aqueous microdroplets, which is contrasted with the same process for acetic acid.
Entry Collection : Environmental Sciences
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Topic review
Updated time: 25 Aug 2021
Submitted by: Bo Fu
Definition: Ultrafast lasers are the key component of ultrafast photonics, which have come into practice in various fields, such as micromachining, communication, medical procedures, gas detection, and remote sensing. With the advantages of stability, compactness, and easy implementation, mode-locking and Q-switching are two notable techniques to achieve ultrafast pulsed lasers, where SAs perform crucial roles in many types of ultrafast lasers, such as fiber, solid-state, and waveguide lasers.
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Topic review
Updated time: 06 May 2021
Submitted by: Paul Chinonso Uzoma
Definition: Materials can be rightly characterized as 2D material or nanosheet if only one of its dimensions is in nano-size, they usually resemble a large sheet with one or few atomic thickness layers (more like a sheet of paper). This explains the fundamental characteristic of 2D materials and their unique properties that made them very attractive in tribological applications. Also, the method of preparation of the materials are highlighted.
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Topic review
Updated time: 28 Sep 2021
Submitted by: Mustapha Jouiad
Definition: Two-dimensional (2D) materials are generally defined as crystalline substances with a few atoms thickness.Two-dimensional transition metal dichalcogenide (2D-TMDs) semiconducting (SC) materials have exhibited unique optical and electrical properties. The layered configuration of the 2D-TMDs materials is at the origin of their strong interaction with light and the relatively high mobility of their charge carriers, which in turn prompted their use in many optoelectronic applications, such as ultra-thin field-effect transistors, photo-detectors, light emitting diode, and solar-cells. Generally, 2D-TMDs form a family of graphite-like layered thin semiconducting structures with the chemical formula of MX2, where M refers to a transition metal atom (Mo, W, etc.) and X is a chalcogen atom (Se, S, etc.). The layered nature of this class of 2D materials induces a strong anisotropy in their electrical, chemical, mechanical, and thermal properties. In particular, molybdenum disulfide (MoS2) is the most studied layered 2D-TMD.
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Topic review
Updated time: 25 Aug 2021
Submitted by: Niels Grigat
Definition: 3D braiding technologies enable the production of structures with complex geometry, which are often used for lightweight solutions, for example in automotive engineering. In addition, medical technology offers wide-ranging applications for 3D braiding technology. 3D braided structures are defined as those with yarns that intersect in all three spatial directions. 3D braiding processes allow the fiber orientation to be easily influenced, thus ensuring high strength and stiffness with reduced mass.
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Topic review
Updated time: 25 Aug 2021
Submitted by: Zengyong Chu
Definition: Air pollution is becoming an increasingly important global issue. Toxic gases such as ammonia, nitrogen dioxide, and volatile organic compounds (VOCs) like phenol are very common air pollutants. To date, various sensing methods have been proposed to detect these toxic gases. Researchers are trying their best to build sensors with the lowest detection limit, the highest sensitivity, and the best selectivity. As a 2D material, graphene is very sensitive to many gases and so can be used for gas sensors. Recent studies have shown that graphene with a 3D structure can increase the gas sensitivity of the sensors. The limit of detection (LOD) of the sensors can be upgraded from ppm level to several ppb level.
Entry Collection : Environmental Sciences
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Topic review
Updated time: 17 Apr 2021
Submitted by: Houwen Matthew Pan
Definition: Osteoarthritis of the knee with meniscal pathologies is a severe meniscal pathology suffered by the aging population worldwide. However, conventional meniscal substitutes are not 3D-printable and lack the customizability of 3D printed implants and are not mechanically robust enough for human implantation. Similarly, 3D printed hydrogel scaffolds suffer from drawbacks of being mechanically weak and as a result patients are unable to execute immediate post-surgical weight-bearing ambulation and rehabilitation. To solve this problem, we have developed a 3D silicone meniscus implant which is (1) cytocompatible, (2) resistant to cyclic loading and mechanically similar to native meniscus, and (3) directly 3D printable. The main focus of this study is to determine whether the purity, composition, structure, dimensions and mechanical properties of silicone implants are affected by the use of a custom-made in-house 3D-printer. We have used the phosphate buffer saline (PBS) absorption test, Fourier transform infrared (FTIR) spectroscopy, surface profilometry, thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) to effectively assess and compare material properties between molded and 3D printed silicone samples.
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