Accelerated inexact composite gradient methods for nonconvex spectral optimization problems

Computational Optimization and Applications - This paper presents two inexact composite gradient methods, one inner accelerated and another doubly accelerated, for solving a class of nonconvex...     

A new construction of Radon curves and related topics

We present a new construction of Radon curves which only uses convexity methods. In other words, it does not rely on an auxiliary Euclidean background metric (as in the classical works of J. Radon, W. Blaschke, G. Birkhoff, and M. M. Day), and also it does not use typical methods from plane Minkowski Geometry (as proposed by H. Martini and K. J. Swanepoel). We also discuss some properties of normed planes whose unit circle is a Radon curve and give characterizations of Radon curves only in terms of Convex Geometry.     

Probing the local activity of CO2 reduction on gold gas diffusion electrodes: effect of the catalyst loading and CO2 pressure

Large scale CO₂ electrolysis can be achieved using gas diffusion electrodes (GDEs), and is an essential step towards broader implementation of carbon capture and utilization strategies. Different variables are known to affect the performance of GDEs. Especially regarding the catalyst loading, there are diverging trends reported in terms of activity and selectivity, e.g. for CO₂ reduction to CO. We have used shear–force based Au nanoelectrode positioning and scanning electrochemical microscopy (SECM) in the surface-generation tip collection mode to evaluate the activity of Au GDEs for CO₂ reduction as a function of catalyst loading and CO₂ back pressure. Using a Au nanoelectrode, we have locally measured the amount of CO produced along a catalyst loading gradient under operando conditions. We observed that an optimum local loading of catalyst is necessary to achieve high activities. However, this optimum is directly dependent on the CO₂ back pressure. Our work does not only present a tool to evaluate the activity of GDEs locally, it also allows drawing a more precise picture regarding the effect of catalyst loading and CO₂ back pressure on their performance.

Large scale CO₂ electrolysis can be achieved using gas diffusion electrodes (GDEs), and is an essential step towards broader implementation of carbon capture and utilization strategies.     

A Comprehensive Study of CO2 Absorption and Desorption by Choline-Chloride/Levulinic-Acid-Based Deep Eutectic Solvents

Amine absorption (or amine scrubbing) is currently the most established method for CO₂ capture; however, it has environmental shortcomings and is energy-intensive. Deep eutectic solvents (DESs) are an interesting alternative to conventional amines. Due to their biodegradability, lower toxicity and lower prices, DESs are considered to be “more benign” absorbents for CO₂ capture than ionic liquids. In this work, the CO₂ absorption capacity of choline-chloride/levulinic-acid-based (ChCl:LvAc) DESs was measured at different temperatures, pressures and stirring speeds using a vapour–liquid equilibrium rig. DES regeneration was performed using a heat treatment method. The DES compositions studied had ChCl:LvAc molar ratios of 1:2 and 1:3 and water contents of 0, 2.5 and 5 mol%. The experimental results showed that the CO₂ absorption capacity of the ChCl:LvAc DESs is strongly affected by the operating pressure and stirring speed, moderately affected by the temperature and minimally affected by the hydrogen bond acceptor (HBA):hydrogen bond donator (HBD) molar ratio as well as water content. Thermodynamic properties for CO₂ absorption were calculated from the experimental data. The regeneration of the DESs was performed at different temperatures, with the optimal regeneration temperature estimated to be 80 °C. The DESs exhibited good recyclability and moderate CO₂/N₂ selectivity.     

Structural and thermal investigations of starch polymers as matrices for retention of rhynchophorol aggregation pheromone

The present study aimed to prepare and characterize amylose inclusion complexes with rhynchophorol aggregation pheromone. The potato and cassava V-amylose–rhynchophorol complexes were successfully obtained, but the B-type polymorph was also formed. The potato (64.6%) and cassava (40.9%) amylose complexes have presented high crystalline indexes, confirmed by the XRD technique. No endothermic peaks associated with the melting of crystalline arrays were noticed between 30 and 100°C. The dynamic TG runs demonstrated that both the degree of order of crystalline arrays and molecular weights influence the thermal stabilities of the V-amyloses-rhynchophorol. The isothermal TG showed that the retention of rhynchophorol seems to be directly proportional to the molecular weights of starch polymers. The recovered rhynchophorol contents were in the order of 10^?7 grams per 50 milligrams of dried powders, which would be useful for insect attraction as demonstrated by the GC–MS technique. The starch polymers studied have presented suitable for retention of rhynchophorol guest molecules.

     

Chemical composition and antiproliferative activity of Croton campestris A.St.-Hil. essential oil

Herein, the antiproliferative potential of the essential oil obtained from fresh leaves of Croton campestris against human tumour cell lines was investigated for the first time. Furthermore, the essential oil obtained by hydrodistillation had the composition determined by gas chromatography–mass spectrometry (GC/MS). Ten major components were identified that comprised 91.59% of the total content, with 23.8% consisting of (Z)-caryophyllene and 16.08% consisting of γ-elemene as main components. The cytotoxic activity was observed mainly for breast (MCF-7) and colon (HT-29) human tumour cell lines, with GI₅₀ (50% growth inhibition) concentration of 8.61 and 9.94 μg/mL, respectively. The results of this study showed that the essential oil obtained from Croton campestris A.St.-Hil. represents a potential source for the search of new antitumour agents.     

Cytotoxic Plant Extracts towards Insect Cells: Bioactivity and Nanoencapsulation Studies for Application as Biopesticides

The potential of plant extracts as bioinsecticides has been described as a promising field of agricultural development. In this work, the extracts of Punica granatum (pomegranate), Phytolacca americana (American pokeweed), Glandora prostrata (shrubby gromwell), Ulex europaeus (gorce), Tagetes patula (French marigold), Camellia japonica red (camellia), Ruta graveolens (rue or herb-of-grace) were obtained, purified, and their activity against Spodoptera frugiperda (Sf9) insect cells was investigated. From the pool of over twenty extracts obtained, comprising different polarities and vegetable materials, less polar samples were shown to be more toxic towards the insect cell line Sf9. Among these, a dichloromethane extract of R. graveolens was capable of causing a loss of viability of over 50%, exceeding the effect of the commercial insecticide chlorpyrifos. This extract elicited chromatin condensation and the fragmentation in treated cells. Nanoencapsulation assays of the cytotoxic plant extracts in soybean liposomes and chitosan nanostructures were carried out. The nanosystems exhibited sizes lower or around 200 nm, low polydispersity, and generally high encapsulation efficiencies. Release assays showed that chitosan nanoemulsions provide a fast and total extract release, while liposome-based systems are suitable for a more delayed release. These results represent a proof-of-concept for the future development of bioinsecticide nanoformulations based on the cytotoxic plant extracts.