1,354,401 research outputs found
The Color and Stability of Maya Blue: TDDFT Calculations
No full textCar-Parrinello structural optimizations of realistic models of the Maya Blue (MB) hybrid material are combined with TDDFT calculations of the electronic excitation spectra to identify the nature of the fundamental guest-host interactions leading to the unusual stability of this pigment. The comparison with the features of the experimental visible spectrum reveals that the main mode of interaction between the host solid (the palygorskite clay) and the guest molecule (the organic indigo dye) involves the coordination of the carbonyl group of the dye by Al3+ ions exposed at the edge of the palygorskite tunnels. Analogous Mg2+-dye interactions which do not strongly affect the MB visible spectrum can also be present. Thermal treatment used in the preparation of the pigment appears therefore essential to release some of the structural water molecules tightly bound to the Al3+ ions in the internal clay surface, thus leaving them available to coordinate the organic molecule. Moderate heating also favors the oxidation of indigo to dehydroindigo (DHI): the spectral features of the latter complex with Al3+ are in remarkable agreement with the experimental spectrum, thus confirming the substantial role of DHI in the properties of Maya Blue
Scent of a Killer: Microbial Volatilome and Its Role in the Biological Control of Plant Pathogens
No full textThe use of synthetic fungicides represents the most common strategy to control plant pathogens. Excessive and/or long-term distribution of chemicals is responsible for increased levels of environmental pollution, as well as adverse health consequence to humans and animals. These issues are deeply influencing public perception, as reflected by the increasing demand for safer and eco-friendly agricultural commodities and their by-products. A steadily increasing number of research efforts is now devoted to explore the use of safer and innovative approaches to control plant pathogens. The use of microorganisms as biological control agents (BCAs) represents one of the most durable and promising strategies. Among the panoply of microbial mechanisms exerted by BCAs, the production of volatile organic compounds (VOCs) represents an intriguing issue, mostly exploitable in circumstances where a direct contact between the pathogen and its antagonist is not practicable. VOCs are potentially produced by all living microorganisms, and may be active in the biocontrol of phytopathogenic oomycetes, fungi, and bacteria by means of antimicrobial activity and/or other cross-talk interactions. Their biological effects, the reduced residuals in the environment and on agricultural commodities, and the ease of application in different agricultural systems make the use of VOCs a promising and sustainable approach to replace synthetic fungicides in the control of plant pathogens. In this review, we focus on VOCs produced by bacteria and fungi and on their role in the cross-talk existing between the plant pathogens and their host. Biologic systemic effect of the microbial volatile blends on both pathogen and host plant cells is also briefly reviewed
Diffusion and vibrational relaxation of a diatomic molecule in the pore network of a pure silica zeolite: a Molecular Dynamics study
No full textIn-plane behaviour of FRCM-strengthened masonry panels
No full textThe evolution of seismic design regulations together with the degradation of the monumental heritage made necessary to increase the structural safety of a large variety of masonry buildings. A recent strengthening technique consists in the application of a fiber grid/unidirectional sheet with lime or cementitious mortar (FRCM), thanks to several advantages of this retrofitting system in comparison to traditional epoxy-based materials (FRPs), such as better compatibility with the masonry substrate, resistance to high temperatures and reversibility. In this paper, the results of in-plane tests performed on panels strengthened with different types of FRCM systems (that differ in layout, matrix, grid materials and spacing) are presented, after a complete mechanical characterization of FRCM materials, carried out through direct tensile tests and single-lap shear tests. In diagonal compression tests (DCT), failure modes and global behavior of the panels were also analyzed using Digital Image Correlation (DIC) technique, for a better understanding of their in-plane behaviour
Environmental durability of FRCM strengthening systems and comparison with dry fabrics
No full textFiber Reinforced Cementitious Matrix (FRCM) composites have been recently introduced for repairing and strengthening masonry structures. Even if they proved to be an effective solution for structural applications, their durability is still an open issue, which is fundamental to guarantee the long-term effectiveness of the strengthening intervention. In fact, FRCMs may be subjected to a combination of different environmental conditions that may affect their performances: humidity, rainfall, freeze/thaw cycles, exposure to saline and alkaline environments are some of the conditions that may promote deterioration over time. In order to investigate FRCMs durability, an extensive experimental campaign has been carried out on different FRCM systems (basalt, glass and steel fibers) through tensile tests on conditioned and unconditioned samples. Tests have been performed both on FRCM coupons and on dry fabrics, with the aim of analyzing the effect of the matrix in terms of mechanical behavior and external protection of the fabric under aggressive environments. The creation of an experimental database on the effects of environmental conditions is a first step to analyze long-term properties of these composite materials and to suggest appropriate strength reduction factors to be taken into account for the design of durable retrofitting interventions
Diffusion of small flexible molecules in silicalite: computer simulations and test of statistical models
No full textApplication of correlated and uncorrelated models to the diffusion of linear molecules in silicalite
No full textA Classical molecular dynamics study of recombination reactions in a microporous solid
No full textClassical molecular dynamics calculations have been applied to the study of the recombination reaction of photodissociated radical species. Within a simplified reaction scheme it has been possible to get qualitative information about the influence of the environment. A comparison has been made between reactions in a liquid solvent and in a complex structured environment, such as a microporous silicate. Marked differences in the recombination yield and in the energy relaxation mechanism have been observed
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