Tribochemistry of graphene on iron and its possible role in lubrication of steel

Recent tribological experiments revealed that graphene is able to lubricate macroscale steel-on-steel sliding contacts very effectively both in dry and humid conditions. This effect has been attributed to a mechanical action of graphene related to its load-carrying capacity. Here we provide further insight into the functionality of graphene as lubricant by analysing its tribochemical action. By means of first principles calculations we show that graphene binds strongly to native iron surfaces highly reducing their surface energy. Thanks to a passivating effect, the metal surfaces coated by graphene become almost inert and present very low adhesion and shear strength when mated in a sliding contact. We generalize the result by establishing a connection between the tribological and the electronic properties of interfaces, which is relevant to understand the fundamental nature of frictional forces.Comment: 19 pages, 6 figure

Zinc dialkyldithiophosphates adsorption and dissociation on ferrous substrates: an ab initio study

Zinc dialkyldithiophosphates (ZDDPs) have been commonly used as anti-wear additives in the automotive industry for the past 80 years. The morphology, composition and structure of the ZDDPs phosphate-based tribofilm, which is essential for its lubricant functioning, have been widely studied experimentally. However, despite their widespread use, a general agreement on their primary functioning mechanism is still lacking. The morphology and composition of the ZDDPs phosphate-based tribofilm have been widely studied experimentally, but the formation process and the relevant driving forces are still largely debated. In particular, it is unclear whether the stress-induced molecular dissociation occurs in the bulk oil or on the substrate. In this work, we employ ab initio density-functional theory simulations to compare ZDDP fragmentation in vacuum and over a reactive substrate, considering the effects of surface oxidation on the dissociation path. Our results show that the molecular dissociation is highly endothermic in the absence of a supporting substrate, while in the presence of an iron substrate it becomes highly energetically favoured. Moreover, the presence of the substrate changes the reaction path. At the same time, surface oxidation reduces the molecule-substrate interaction. These findings provide valuable insights into the early stages of the formation of phosphate-based tribofilms

Xsorb: a software for identifying the most stable adsorption configuration and energy of a molecule on a crystal surface

Molecular adsorption is the first important step of many surface-mediated chemical processes, from catalysis to tribology. This phenomenon is controlled by physical/chemical interactions, which can be accurately described by first principles calculations. In recent years, several computational tools have been developed to study molecular adsorption based on high throughput/automatized approaches. However, these tools can sometimes be over-sophisticated for non-expert users. In this work, we present Xsorb, a Python-based code that automatically generates adsorption configurations, guides the user in the identification the most relevant ones, which are then fully optimized. The code relies on well-established Python libraries, and on an open source package for density functional theory calculations. We show the program capabilities through an example consisting of a hydrocarbon molecule, 1-hexene, adsorbed over the (110) surface of iron. The presented computational tool will help users, even non-expert, to easily identify the most stable adsorption configuration of complex molecules on substrates and obtain accurate adsorption geometries and energies

Análisis de la utilización de las principales herramientas de marketing digital aplicables a un sitio web regional y el efecto en su estructura y rendimiento: el caso de www.futbolya.com

El sitio www.futbolya.com desde su creación ha utilizado la mayoría de las herramientas que el marketing digital ofrece con el fin de promocionarse. Las estrategias de promoción tradicionales, como por ejemplo la impresión de volantes o presencia en prensa escrita, no ha sido la utilizada por esta página web, no sólo debido a sus costos, sino también por su poca efectividad en el momento de medir los resultados

Modeling phosphorene and MoS2 interacting with iron: lubricating effects compared to graphene

Phosphorene, a single layer of black phosphorus, is attracting interest for several applications, among which tribology. Here, we investigate its possible use as a solid lubricant for iron-based materials by comparing its friction-reduction properties with MoS2 and graphene. Through first-principle calculations, we predict that phosphorene adheres more strongly to the native iron surface than the other considered 2D materials. The higher adhesion suggests that a stable and durable coverage of reactive surface regions can be obtained with phosphorene. Furthermore, our simulation uncovers the peculiar behavior of phosphorene to exfoliate into two atomic-thin layers upon interface intercalation. This capability makes phosphorene reduce the nano-asperity adhesion very efficiently thanks to the simultaneous passivation of the surface and countersurface. These results suggest that better performances could be obtained by phosphorene than other solid lubricants at low concentrations

Mobile RF Scenario Design for Massive-Scale Wireless Channel Emulators

Large-scale wireless emulation is gaining momentum nowadays, thanks to its potential in the development and deployment of advanced use cases for next-generation wireless networks. Several novel use cases are indeed emerging, including massive MIMO, millimeter wave beamforming and AI-based Vehicle-to-Everything (V2X) optimized communication. The development and testing of a wireless application, especially at a large scale and when dealing with mobile nodes, faces several challenges that cannot be solved by simulation frameworks alone. Thus, massive-scale channel emulators are emerging, enabling the emulation of realistic scenarios which leverage real hardware and radio signals. However, this is a complex task due to the lack of realistic scenarios based on real datasets. We thus propose a novel framework for the design and generation of channel emulation scenarios starting from real mobility traces, either generated by means of dedicated tools, or collected on the field. Our framework provides a practical way of generating mobility scenarios with vehicles, pedestrians, drones and other mobile entities. We detail all the steps foreseen by our framework, from the provision of the traces and radio parameters, to the generation of a matrix describing the delay and IQ samples for each time instant and node in the scenario. We also showcase the potentiality of our proposal by designing and creating a vehicular 5G scenario with 13 vehicles, starting from a recently-disclosed open dataset. This scenario is then validated on the Colosseum channel emulator, proving how our framework can provide an effective tool for large-scale wireless networking evaluation

Cover crops for managing weeds, soil chemical fertility and nutritional status of organically grown orange orchard in Sicily

Cover crops can offer significant advantages in the agronomic management of citrus orchards in Mediterranean environments. Therefore, a three-year research was conducted in eastern Sicily aimed at studying the effects of four cover crop sequences (Sinapis arvensis-Trigonella foenum-graecum-T. foenum-graecum; Medicago scutellata-Avena sativa-Lolium perenne; Vicia faba minor-A. sativa-A. sativa; A. sativa-V. faba. minor-L. perenne) on weeds, major soil chemical properties and nutritional status of an organically grown orange orchard. The results highlighted that, among the studied cover crop sequences, Vicia faba-Avena-Avena was the most beneficial for weeds control within the orchard (92%, of cover crop cover, and 586 and 89 g DW m–2 of cover crop aboveground biomass and weeds aboveground biomass, respectively). Overall, the chemical fertility of the soil was positively influenced. In particular, it was observed an increase of the content of total nitrogen and available phosphorus in the soil by both Sinapis-Trigonella-Trigonella (0.75 g kg–1 and 59.0 mg kg–1, respectively) and Vicia faba-Avena-Avena (0.70 g kg–1 and 56.0 mg kg–1, respectively) cover crop sequences. Medicago-Avena-Lolium sequence seemed to be the most useful to ensure a better nutritional status of the orange orchard

Saccharomyces hybrids as a tool for improving the quality of Moscato di Siracusa DOC wine

The study aimed to evaluate four Saccharomyces cerevisiae strains, one intraspecific S. cerevisiae hybrid, and five interspecific S. cerevisiae×S. uvarum hybrids with respect to the quality of Moscato di Siracusa DOC wine by comparing them with a commercial Saccharomyces cerevisiae strain. Most of the interspecific hybrids maintained volatile acidity (VA) at very low levels, produced high concentrations of glycerol, malic and succinic acid, and yielded the highest concentration of positive sensory attributes. On the basis of the results of these experimental fermentation trials, a real opportunity to produce special wines employing S. cerevisiae×S. uvarum hybrids is proposed.The study aimed to evaluate four Saccharomyces cerevisiae strains, one intraspecific S. cerevisiae hybrid, and five interspecific S. Cerevisiae×S. uvarum hybrids with respect to the quality of Moscato di Siracusa DOC wine by comparing them with a commercial Saccharomyces cerevisiae strain.Most of the interspecific hybrids maintained volatile acidity (VA) at very low levels, producedhigh concentrations of glycerol, malic and succinic acid, and yielded the highest concentrationof positive sensory attributes.On the basis of the results of these experimental fermentation trials, a real opportunity to producespecial wines employing S. cerevisiae×S. uvarum hybrids is proposed

Sangiovese cv Pomace seeds extract-fortified Kefir exerts anti-inflammatory activity in an in vitro model of intestinal epithelium using Caco-2 cells

Inflammatory bowel disease and food allergies are a growing topic in the field of nutrition science. Polyphenols, which are the most important secondary metabolites of plants, demonstrated to modulate the expression and/or production of numerous proteins, but also to regulate the intestinal ecosystem. In this context, our aim was the investigation of protective effects against the gastrointestinal mucosa of fortified milk kefir obtained by adding seeds extract from Sangiovese cv. Pomace. Methods: An ultrasound-assisted method was used to obtain the extracts. All the extracts were assayed for the antioxidant activity. The best extract was used as an additive of fermented milk kefir to obtain a fortified final product. Kefir samples were analyzed by NMR spectroscopy. The efficiency of the barrier functions was evaluated by measuring trans-epithelial electric resistance (TEER) using a voltmeter. Results: the enriched kefir (Ksgn) possesses higher antioxidant performances compared to the unfortified sample (Kwht). Kwht and Ksgn did not alter Caco-2 TEER in basal condition