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121.
Andrés Alessandro León Baldelli Blaise Bourdin Jean-Jacques Marigo Corrado Maurini 《Continuum Mechanics and Thermodynamics》2013,25(2-4):243-268
We study multi-fissuration and debonding phenomena of a thin film bonded to a stiff substrate using the variational approach to fracture mechanics. We consider a reduced one-dimensional membrane model where the loading is introduced through uniform inelastic (e.g., thermal) strains in the film or imposed displacements of the substrate. Fracture phenomena are accounted for by adopting a Griffith model for debonding and transverse fracture. On the basis of energy minimization arguments, we recover the key qualitative properties of the experimental evidences, like the periodicity of transverse cracks and the peripheral debonding of each regular segment. Phase diagrams relate the maximum number of transverse cracks that may be created before debonding takes place, as a function of the material properties and the sample’s geometry. The theoretical results are illustrated with numerical simulations obtained through a finite element discretization and a regularized variational formulation of the Ambrosio–Tortorelli type, which is suited to further extensions in two-dimensional settings. 相似文献
122.
Norberto Manfredi Alberto Bianchi Valerio Causin Riccardo Ruffo Roberto Simonutti Alessandro Abbotto 《Journal of polymer science. Part A, Polymer chemistry》2014,52(5):719-727
The first use of PSn‐b‐PEOm‐b‐PSn block copolymers (PS = polystyrene, PEO = poly(ethylene oxide)) as solid hosts for iodine/iodide electrolytes in dye‐sensitized solar cells (DSSCs) is described. Using the benchmark photosensitizer N719, DSSC based on the quasi solid‐state electrolytes afforded efficiencies up to 6.7%, to be compared with an efficiency of 7.3% obtained in similar conditions with a conventional iodine/iodide liquid electrolyte. By varying the PS:PEO relative volume ratio in the block copolymers different properties and morphologies were obtained. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 719–727 相似文献
123.
Pierre Thesmar Seemon Coomar Dr. Alessandro Prescimone Prof. Dr. Daniel Häussinger Prof. Dr. Dennis Gillingham Prof. Dr. Olivier Baudoin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(66):15298-15312
This article provides a detailed report of our efforts to synthesize the dithiodiketopiperazine (DTP) natural products (−)-epicoccin G and (−)-rostratin A using a double C(sp3)−H activation strategy. The strategy's viability was first established on a model system lacking the C8/C8’ alcohols. Then, an efficient stereoselective route including an organocatalytic epoxidation was secured to access a key bis-triflate substrate. This bis-triflate served as the functional handles for the key transformation of the synthesis: a double C(sp3)−H activation. The successful double activation opened access to a common intermediate for both natural products in high overall yield and on a multigram scale. After several unsuccessful attempts, this intermediate was efficiently converted to (−)-epicoccin G and to the more challenging (−)-rostratin A via suitable oxidation/reduction and protecting group sequences, and via a final sulfuration that occurred in good yield and high diastereoselectivity. These efforts culminated in the synthesis of (−)-epicoccin G and (−)-rostratin A in high overall yields (19.6 % over 14 steps and 12.7 % over 17 steps, respectively), with the latter being obtained on a 500 mg scale. Toxicity assessments of these natural products and several analogues (including the newly synthesized epicoccin K) in the leukemia cell line K562 confirmed the importance of the disulfide bridge for activity and identified dianhydrorostratin A as a 20x more potent analogue. 相似文献
124.
Liam P. D. Ratcliffe Matthew J. Derry Alessandro Ianiro Remco Tuinier Steven P. Armes 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):19140-19146
It is well‐known that the self‐assembly of AB diblock copolymers in solution can produce various morphologies depending on the relative volume fraction of each block. Recently, polymerization‐induced self‐assembly (PISA) has become widely recognized as a powerful platform technology for the rational design and efficient synthesis of a wide range of block copolymer nano‐objects. In this study, PISA is used to prepare a new thermoresponsive poly(N‐(2‐hydroxypropyl) methacrylamide)‐poly(2‐hydroxypropyl methacrylate) [PHPMAC‐PHPMA] diblock copolymer. Remarkably, TEM, rheology and SAXS studies indicate that a single copolymer composition can form well‐defined spheres (4 °C), worms (22 °C) or vesicles (50 °C) in aqueous solution. Given that the two monomer repeat units have almost identical chemical structures, this system is particularly well‐suited to theoretical analysis. Self‐consistent mean field theory suggests this rich self‐assembly behavior is the result of the greater degree of hydration of the PHPMA block at lower temperature, which is in agreement with variable temperature 1H NMR studies. 相似文献
125.
We establish an optimal regularity result for parametrized two-dimensional stationary varifolds. Namely, we show that the parametrization map is a smooth minimal branched immersion and that the multiplicity function is constant. We provide some applications of this regularity result, especially in the calculus of variations for the area functional. © 2020 Wiley Periodicals LLC 相似文献
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128.
Giacomo Luigi Petretto Carlo Ignazio G. Tuberoso Gina Vlahopoulou Alessandro Atzei Alberto Mannu Saadia Zrira 《Natural product research》2016,30(3):286-292
Seven commercial Moroccan honeys were considered for chemical characterisation. Volatile fraction, total polyphenols content, antioxidant and antiradical activities were evaluated by employing different analytical methodologies. Several physical parameters such as refractive index, pH, water content, solids content and colour were measured. Volatile fraction revealed an abundant presence of cis- and trans-linalool oxide in the seven studied samples. The presence of high levels of compounds related to the Maillard reaction, like furfural and hydroxymethylfurfural, could be the result of thermal treatments used to liquefy commercial honeys or of long storage times. The CIE L*a*b*Cab*hab° chromatic coordinates confirmed the advanced stage of the Maillard reaction, showing L* values lower than the common values found for honey of similar typologies. 相似文献
129.
Dr. Marzia Dell'Aera Dr. Filippo Maria Perna Dr. Paola Vitale Dr. Angela Altomare Prof. Alessandro Palmieri Dr. Lewis C. H. Maddock Leonie J. Bole Dr. Alan R. Kennedy Prof. Eva Hevia Prof. Vito Capriati 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(40):8742-8748
We report the first transition metal catalyst- and ligand-free conjugate addition of lithium tetraorganozincates (R4ZnLi2) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R4ZnLi2 provide access to valuable nitroalkanes in up to 98 % yield under mild conditions (0 °C) and short reaction time (30 min). This is particularly remarkable when employing β-nitroacrylates and β-nitroenones, where despite the presence of other electrophilic groups, selective 1,4 addition to the C=C is preferred. Structural and spectroscopic studies confirmed the formation of tetraorganozincate species in solution, the nature of which has been a long debated issue, and allowed to unveil the key role played by donor additives on the aggregation and structure of these reagents. Thus, while chelating N,N,N’,N’-tetramethylethylenediamine (TMEDA) and (R,R)-N,N,N’,N’-tetramethyl-1,2-diaminocyclohexane (TMCDA) favour the formation of contacted-ion pair zincates, macrocyclic Lewis donor 12-crown-4 triggers an immediate disproportionation process of Et4ZnLi2 into equimolar amounts of solvent-separated Et3ZnLi and EtLi. 相似文献
130.