In this paper, Cu-doped carbon quantum dots (Cu-CQDs) were prepared by carrying out thermolysis of Na2[Cu(EDTA)] and hydroxylamine hydrochloride at 300 ºC for 2 h. The as-prepared Cu-CQDs were characterized by UV-Vis, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The Cu-CQDs exhibited good fluorescence property, high stability, excitation-dependent emission behavior and a quantum yield of 9.8%. More significantly, the synthesized Cu-CQDs were developed for sensing rutin (RT) based on the fluorescence quenching of the prepared Cu-CQDs. A good linear relationship between the fluorescence quenching of Cu-CQDs and different concentrations of RT was obtained in the range of 0.1-15 µg mL-1 with a correlation coefficient of 0.9959. The detection limit was as low as 0.05 µg mL-1 (signal-to-noise ratio, S/N = 3). The possible mechanism of fluorescence quenching was explored, which was proved to be inner filter effect. Importantly, the proposed method was successfully applied in the detection of RT tablet samples and with satisfactory results, showing the practical applications.

RESUMO: O composto de ácido 5-aminolevulínico (ALA) é um precursor chave na biossíntese de porfirinas, tais como clorofilae porfirinas, e verificou-se induzir elevações temporárias na taxa de fotossíntese e APX. Além disso, ele tem vários efeitos fisiológicos sobre os vegetais. Após o tratamento, Ala (50mg L-1, 100mg L-1 e 150mg L-1) ou água (controlo) foi aplicado a frutos maduros branco "Sweet Charlie" de morango. As atividades índice de decadência, taxa de respiração, superóxido dismutase e ascorbato peroxidase, conteúdo de sólidos solúveis, acidez titulável, teor de antocianinas, taxa de produção de O2-, e conteúdo malondialdehyde foi avaliada nos frutos ALA-tratados e morango controle durante a armazenagem a 4°C. Os resultados mostraram que a aplicação exógena de ALA retarda a senescência e melhorou o valor nutricional das frutas de morango durante o armazenamento.

ABSTRACT: The compound 5-aminolevulinic acid (ALA) is a key precursor in the biosynthesis of porphyrins, such as chlorophyll, heme and phytochromobilin, and has multiple physiological effects on plants. Varying concentrations of ALA (50mg L-1, 100mg L-1, and 150mg L-1) and water (control) were applied to white stage 'Sweet Charlie' strawberry fruit. All ALA treatments delayed senescence and improved the qualities of strawberries fruit during storage. Among the treatments, 150mg L-1 ALA was the most effective dosage concentration. Exogenously applied ALA significantly reduced the decay index, respiration rate, O2 - production rate (O2 -), H2O2 and malondialdehyde (MDA) content, increased superoxide dismutase (SOD), ascorbate peroxidase activities (APX), total soluble solids (TSS) content, titratable acidity (TA) and anthocyanin content during the initial stage of storage. These results supported the pre harvest application of ALA as a beneficial strategy for the prevention of postharvest decay of strawberry fruit.

Abstract The dynamic response and energy absorption capabilities of clamped shallow sandwich arches with aluminum foam core were numerically investigated by impacting the arches at mid-span with metallic foam projectiles. The typical deformation modes, deflection response, and core compression of sandwich arches obtained from the tests were used to validate the computation model. The resistance to impact loading was quantified by the permanent transverse deflection at mid-span of the arches as a function of projectile momentum. The sandwich arches have a higher shock resistance than the monolithic arches of equal mass, and shock resistance could be significantly enhanced by optimizing geometrical configurations. Meanwhile, decreasing the face-sheet thickness and curvature radius could enhance the energy absorption capability of the sandwich arches. Finite element calculations indicated that the ratio of loading time to structural response time ranged from 0.1 to 0.4. The projectile momentum, which was solely used to quantify the structural response of sandwich arches, was insufficient. These findings could provide guidance in conducting further theoretical studies and producing the optimal design of metallic sandwich structures subjected to impact loading.

Abstract Finite element analysis was used to investigate the impact behavior of the foam-cored sandwich shells under the ballistic impact. The ballistic limit, failure mode of the face-sheet and energy absorption of the uniform/graded core were discussed in this paper. Based on the impact phase diagrams, the effects of several factors (i.e. projectile shape and diameter, face-sheet curvature and thickness) on the normal/oblique impact behavior were analyzed in detail. Results indicate that blunter and larger projectiles, higher impact velocity and thicker face-sheets can significantly raise the impact-resistance performance of the targets. In addition, the behavior of ballistic impact becomes more complex as the result of the increasing oblique angle.