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951.
Silvia Gentiluomo Dr. Sanjay B. Thorat Dr. Antonio Esau Del Río Castillo Dr. Peter S. Toth Dr. Jaya Kumar Panda Dr. Vittorio Pellegrini Dr. Francesco Bonaccorso 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(29):6715-6725
One of the applications of graphene in which its scalable production is of utmost importance is the development of polymer composites. Among the techniques used to produce graphene flakes, the liquid-phase exfoliation (LPE) of graphite stands out due to its versatility and scalability. However, solvents suitable for the LPE process are generally toxic and have a high boiling point, making the processing challenging. The use of low boiling point solvents could be convenient for the processing, due to the easiness of their removal. In this study, the use of poly(methyl methacrylate) (PMMA) as a stabilizing agent is proposed for the production of graphene flakes in a low boiling point solvent, that is, acetone. The graphene dispersions produced in the mixture acetone-PMMA have higher concentration, +175 %, and contain a higher percentage of few-layer graphene flakes (<5 layers), that is, +60 %, compared to the dispersions prepared in acetone. The as-produced graphene dispersions are used to develop graphene/acrylonitrile-butadiene-styrene composites. The mechanical properties of the pristine polymer are improved, that is, +22 % in the Young's modulus, by adding 0.01 wt. % of graphene flakes. Moreover, a decrease of ≈20 % in the oxygen permeability is obtained by using 0.1 wt. % of graphene flakes filler, compared to the unloaded matrix. 相似文献
952.
Bettina S. J. Heller Matthias Lexow Francesco Greco Dr. Sunghwan Shin Dr. Gabriel Partl Dr. Florian Maier Prof. Dr. Hans-Peter Steinrück 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(5):1117-1126
Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), we investigate the topmost nanometers of various binary ionic liquid (IL) mixtures at different temperatures in the liquid state. The mixtures consist of ILs with the same [PF6]− anion but two different cations, namely 3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate, [PFBMIm][PF6], and 1-butyl-3-methylimidazolium hexafluorophosphate, [C4C1Im][PF6], with 10, 25, 50 and 75 mol % content of [PFBMIm][PF6]. We observe a preferential enrichment of the fluorinated chain in the topmost layer, relative to the bulk composition, which is most pronounced for the lowest content of [PFBMIm][PF6]. Upon cooling the mixtures stepwise from 95 °C until surface charging effects in XPS indicate solidification, we observe a pronounced increase in surface enrichment of the fluorinated chain with decreasing temperature in the liquid state. In contrast to the mixtures with lower [PFBMIm][PF6] contents, cooling the 75 mol % mixture additionally shows an abrupt decrease of the fluorinated chain signal before complete solidification occurs, which is assigned to partial precipitation effects. 相似文献
953.
De Falco Maria de Giovanni Francesco Musella Carmela 《Monatshefte für Mathematik》2020,191(2):249-256
Monatshefte für Mathematik - If G is an uncountable group of regular cardinality $$\aleph $$, we shall denote by $${\mathfrak {L}L}_\aleph (G)$$ the set of all subgroups of G of cardinality... 相似文献
954.
Dr. Francesco Zaccaria Dr. Stephanie C. C. van der Lubbe Celine Nieuwland Dr. Trevor A. Hamlin Prof. Dr. Célia Fonseca Guerra 《Chemphyschem》2021,22(22):2286-2296
The formation of guanine quadruplexes (GQ) in DNA is crucial in telomere homeostasis and regulation of gene expression. Pollution metals can interfere with these DNA superstructures upon coordination. In this work, we study the affinity of the internal GQ channel site towards alkaline earth metal (Mg2+, Ca2+, Sr2+, and Ba2+), and (post-)transition metal (Zn2+, Cd2+, Hg2+, and Pb2+) cations using density functional theory computations. We find that divalent cations generally bind to the GQ cavity with a higher affinity than conventional monovalent cations (e. g. K+). Importantly, we establish the nature of the cation-GQ interaction and highlight the relationship between ionic and nuclear charge, and the electrostatic and covalent interactions. The covalent interaction strength plays an important role in the cation affinity and can be traced back to the relative stabilization of cations’ unoccupied atomic orbitals. Overall, our findings contribute to a deeper understanding of how pollution metals could induce genomic instability. 相似文献
955.
Francesco Biccari Travis Hamilton Andrea Ristori Stefano Sanguinetti Sergio Bietti Massimo Gurioli Hooman Mohseni 《Particle & Particle Systems Characterization》2020,37(1):1900431
In recent years, dielectric microspheres have been used in conjunction with optical microscopes to beat the diffraction limit and to obtain superresolution imaging. The use of microspheres on quantum dots (QDs) is investigated, for the first time, to enhance the light coupling efficiency. The enhancement of the QD luminescence collection in terms of extraction and directionality is demonstrated, as well as the enhancement of spatial resolution. In particular, it is found that a dielectric microsphere, placed on top of an epitaxial QD, increases the collected radiant energy by about a factor of 42, when a low numerical aperture objective is used. Moreover, if two or more QDs are present below the microsphere, the modification of the far field emission pattern allows selective collection of the luminescence from a single QD by simply changing the collection angle. Dielectric microspheres present a simple and efficient tool to improve the QD spectroscopy, and potentially QD-based devices. 相似文献
956.
Evgeny Pozhidaev Sofia Torgova Vadim Barbashov Vladimir Kesaev Francesco Laviano 《Liquid crystals》2019,46(6):941-951
We propose an approach for development of ferroelectric liquid crystals (FLC) with low birefringence Δn. Two basic principles have been used to get lowering of Δn: selection of molecules with short chains of conjugation as components for achiral matrix and averaging of local refractive indices by FLC helical structure. FLC mixtures with low birefringence (0.07 < Δn < 0.10 at wavelength 589.3 nm of sodium line) were elaborated and investigated. They consist of an achiral matrix including both nematic and smectic liquid crystal components and of phenylpyrimidine derivatives as chiral dopants. The materials developed can be used for all basic electro-optical FLC modes such as surface stabilised FLC (SSFLC), deformed helix ferroelectrics (DHF) and electrically suppressed helix (ESH). The mixtures developed allow to reduce the FLC cells chromatic retardance variation due to the weaker birefringence dispersion as compared with the known FLC materials to date. 相似文献
957.
Meccanica - The internal resonance of a two degree-of-freedom mechanical system with all typical (quadratic and cubic) geometric nonlinearities is studied, limiting to the case of free dynamics.... 相似文献
958.
In this note, with a purely geometric approach, the covering radius of the group is determined. Also, a new proof establishing the covering radii of and is provided. 相似文献
959.
Francesco Noto Giuseppe Costa Luigi Celona Francesco Chines Santo Gammino Ornella Leonardi 《辐射效应与固体损伤》2019,174(11-12):1076-1088
ABSTRACTThe ion sources for accelerators devoted to medical applications must provide intense ion beams, with high reproducibility, stability and brightness. AISHa (Advanced Ion Source for Hadron therapy) is a compact ECRIS whose hybrid magnetic system consists of a permanent Halbach-type hexapole magnet and a set of independently energized superconducting coils. These coils will be enclosed in a compact cryostat with two cryocoolers for LHe-free operation. The AISHa ion source has been designed by taking into account the typical requirements of hospital-based facilities, where the minimization of the mean time between failures (MTBF) is a key point together with the maintenance operations which should be fast and easy. It is a multipurpose device, operating at 18?GHz, in order to achieve higher plasma densities able to provide enough versatility for future needs of the hadron therapy, including the ability to run at larger microwave power to produce different species and highly charged ion beams. In this paper, the innovative solutions, used for the plasma containment chamber and for the permanent magnet hexapole holder, are presented to solve the insulation and structural issues. The choice of the different materials used is hereinafter discussed together with all the involved processes (spinning, curing and machining). The glass fibers and carbon fibers are used to reinforce polymer matrices and give rise to structural composites and composites by molding. The paper shows also some results of ion source commissioning along with next developments. Innovative active coupling techniques are planned to be tested to optimize the first pass wave absorption, which plays an important role in the coupling optimization of the new-generation ECRIS. 相似文献
960.
Michele D'Ambrosio Antonio Guerriero Ccile Debitus Olivier Ribes Bertrand Richer De Forges Francesco Pietra 《Helvetica chimica acta》1989,72(7):1451-1454
It is shown that the demosponge Corallistes sp. (Tetractinomorpha, Lithistida, Corallistidae) collected in the Coral Sea, contains corallistin A ( 1 ), the second example, of a free porphyrin from a living organism. The compound proved to be active against the Kb cell line. In contrast with the geoporphyrins which do not bear any O-atom corallistin A ( 1 ) carries two carboxylic groups. 相似文献