Abreu e... dintorni

Il volume raccoglie una serie di saggi di studiosi che sono in rapporto fra loro in forma non episodica. Essi trattano da diverse prospettive El Sistema Abreu, ognuno sulla base delle proprie esperienze e dei propri studi

The influence of different soil types in the pesticide residue analysis method performance

Pesticide residues in soils cause increasing environmental problems. The underlying biological activity of herbicides from one cropping season to another could affect the productivity of the new crops. Agricultural practices also influence the herbicide level and their accumulation in soil. They interact with soil particles through absorption or adsorption by ionic interactions and other forces ruled by physicochemical properties such as Kow, Henry´s law constant, and Koc, as concentration dependent phenomena but soil texture and composition  play a decisive role in their environmental behavior. To understand the general effect, the residues concentrations have to be precisely known.  Although traditional pesticides such as organophosphates, pyerthorids and carbamates can be straightforward analysed in soils through general multirresidue methods, the determination of multiherbicide residues is a difficult task because soil is a complex and variable analytical matrix as different analyte/matrix interactions present. Herbicides are seldom applied alone but there are few methods reported capable of analysing high number of compounds. We studied the influence of 4 characteristics soils from Uruguay in 4 different methods for the residue analysis of 18 herbicides. Loam soils are the most common soils in Uruguay followed by clay ones and combinations of the two, with variable amounts of organic matter. The key step in this type of analysis is the extraction step. Seeking for a method usefull to analyze most of the soils types in Uruguay, we faced a systematic study using four different extraction procedures ( Methanol, Mixtures MeOH-Ethyl Acetate and Methanol-basic water). Nevertheless, in a first approach, we were not able to find a single method with aceptable performance for every soil under study. According to the type of soil, the best extraction solvent varied. The amount of organic matter played a role but also the texture of the soils was determinant for the method success. Finally, a two step extraction method gave the best results. The soil is firstly extracted with MeOH followed by a water extraction. The extracts are combined and analyzeed using LC-MS/MS. Herbicides could be determined at 0,1-1µg/Kg level. The method was succesfully applied to the herbicide residue analysis of more than 80 soil samples during three cropping seasons, where many pesticides were detected (Clomazone, Quinclorac, Benzosulfuron, Propanyl, Atrazine,Ametryn, among others )

Transferring Axial Molecular Chirality Through a Sequence of On-Surface Reactions

Fine management of chiral processes on solid surfaces has progressed over the years, yet still faces the need for the controlled and selective production of advanced chiral materials. Here, we report on the use of enantiomerically enriched molecular building blocks to demonstrate the transmission of their intrinsic chirality along a sequence of on-surface reactions. Triggered by thermal annealing, the on-surface reac-tions induced in this experiment involve firstly the coupling of the chiral reactants into chiral polymers and subsequently their transformation into planar prochiral graphene nanoribbons. Our study reveals that the axial chirality of the reactant is not only transferred to the polymers, but also to the planar chirality of the graphene nanoribbon end products. Such chirality transfer consequently allows, starting from ad-equate enantioenriched reactants, for the controlled production of chiral and prochiral organic nanoarchi-tectures with pre-defined handedness

Validation of Modern JSON Schema: Formalization and Complexity

JSON Schema is the de-facto standard schema language for JSON data. The language went through many minor revisions, but the most recent versions of the language, starting from Draft 2019-09, added two novel features, dynamic references and annotation-dependent validation, that change the evaluation model. Modern JSON Schema is the name used to indicate all versions from Draft 2019-09, which are characterized by these new features, while Classical JSON Schema is used to indicate the previous versions. These new "modern"features make the schema language quite difficult to understand and have generated many discussions about the correct interpretation of their official specifications; for this reason, we undertook the task of their formalization. During this process, we also analyzed the complexity of data validation in Modern JSON Schema, with the idea of confirming the polynomial complexity of Classical JSON Schema validation, and we were surprised to discover a completely different truth: data validation, which is expected to be an extremely efficient process, acquires, with Modern JSON Schema features, a PSPACE complexity. In this paper, we give the first formal description of Modern JSON Schema, which we have discussed with the community of JSON Schema tool developers, and which we consider a central contribution of this work. We then prove that its data validation problem is PSPACE-complete. We prove that the origin of the problem lies in the Draft 2020-12 version of dynamic references, and not in annotation-dependent validation. We study the schema and data complexities, showing that the problem is PSPACE-complete with respect to the schema size even with a fixed instance but is in P when the schema is fixed and only the instance size is allowed to vary. Finally, we run experiments that show that there are families of schemas where the difference in asymptotic complexity between dynamic and static references is extremely visible, even with small schemas

Steering alkyne homocoupling with on-surface synthesized catalysts

We report a multi-step on-surface synthesis strategy. The first step consists in the surface-supported synthesis of metal-organic complexes, which are subsequently used as catalysts to steer on-surface alkyne coupling reactions. In addition, we analyze and compare the electronic properties of the different coupling motifs obtained

On-surface synthesis of heptacene on Ag(001) from brominated and non-brominated tetrahydroheptacene precursors

Achieving the Ag(001)-supported synthesis of heptacene from two related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy.Fil: Colazzo, Luciano. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Mohammed, Mohammed S. G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Dorel, Ruth. Barcelona Institute of Science and Technology; EspañaFil: Nita, Pawel. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: García Fernández, Carlos. Donostia International Physics Center; EspañaFil: Abufager, Paula Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lorente Palacios, Nicolas. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Echavarren, Antonio M.. Barcelona Institute of Science and Technology; España. Universitat Rovira I Virgili; EspañaFil: De Oteyza, Dimas G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; España. Ikerbasque; Españ

Width-Dependent Band Gap in Armchair Graphene Nanoribbons Reveals Fermi Level Pinning on Au(111)

We report the energy level alignment evolution of valence and conduction bands of armchair-oriented graphene nanoribbons (aGNR) as their band gap shrinks with increasing width. We use 4,4\u2033-dibromo-para-terphenyl as the molecular precursor on Au(111) to form extended poly-para-phenylene nanowires, which can subsequently be fused sideways to form atomically precise aGNRs of varying widths. We measure the frontier bands by means of scanning tunneling spectroscopy, corroborating that the nanoribbon's band gap is inversely proportional to their width. Interestingly, valence bands are found to show Fermi level pinning as the band gap decreases below a threshold value around 1.7 eV. Such behavior is of critical importance to understand the properties of potential contacts in GNR-based devices. Our measurements further reveal a particularly interesting system for studying Fermi level pinning by modifying an adsorbate's band gap while maintaining an almost unchanged interface chemistry defined by substrate and adsorbate