Nodal curves with general moduli on K3 surfaces

We investigate the modular properties of nodal curves on a low genus K3 surface. We prove that a general genus g curve C is the normalization of a d-nodal curve X sitting on a primitively polarized K3 surface S of degree 2p-2, for p any integer between 3 and 11 and g = p - d between 2 and p. The proof is based on a local deformation-theoretic analysis of the map from the stack of pairs (S,X) to the moduli space of curves of genus g that associates to X the isomorphism class [C] of its normalization.Comment: 12 pages. Submitted preprin

Ulrich bundles on a general blow–up of the plane

We prove that on Xn, the plane blown–up at n general points, there are Ulrich line bundles with respect to a line bundle corresponding to curves of degree m passing simply through the n blown–up points, with m less than or equal to 2 times the square root of n 2, and such that the line bundle in question is very ample on Xn. We prove that the number of these Ulrich line bundles tends to infinity with n. We also prove the existence of slope–stable rank–r Ulrich vector bundles on Xn, for n > 2 and any r > 1 and we compute the dimensions of their moduli spaces. These computations imply that Xn is Ulrich wil

Valorisation of hemp inflorescence after seed harvest: Cultivation site and harvest time influence agronomic characteristics and essential oil yield and composition

Cannabis sativa L. is a multipurpose crop, whose industrial varieties, complying with the 0.2% Δ9-tetrahydrocannabinol (THC) threshold set by the EU legislation, can be cultivated without restrictions by farmers. Other than its traditional use as a source of bast fibres from the stems, the fixed oil extracted from its seeds represents a valuable nutritional product. Its inflorescence is also a further exploitable threshing residue originating from seed harvest, as they can be used for the extraction of the essential oil (EO), a high-value added product. This study aims at contributing to the re-evaluation of industrial hemp cultivation as an agro-environmentally sustainable crop for the diversification of Mediterranean cropping systems, by exploring the possibility of recovering the EO from the inflorescence after seed harvest. The influence of the cultivation site (lowland and upland of Pisa province, Tuscany, central Italy) and the harvest time (August and September) have been investigated on the ‘Fedora 17’ monoecious hemp cultivar: the main agronomic traits in term of stem, seed and inflorescence production, as well as essential oil yield and composition have been evaluated. The crops harvested in September exhibited higher total dry yield as well as higher inflorescence and stem yields, while neither the site nor the harvesting period influenced the seed production, which was significantly influenced by harvest time x cultivation site interaction. Both seed fixed oil and crude protein content were affected by the cultivation site only, but in the opposite sense: the highest seed oil content was reached in the upland area, while the plants grown in the plain area exhibited the largest seed protein content. All the extracted EOs were rich in sesquiterpenes (mostly β-caryophyllene and its oxidized derivatives, and α-humulene), but monoterpene hydrocarbons were significantly represented as well (mainly α- and β-pinene, and myrcene). The EOs extraction yields were slightly higher in the earlier harvest for both sites

Weeds for weed control: Asteraceae essential oils as natural herbicides.

The aim of this study was to test the botanical family of Asteraceae as a source of natural herbicides. Twenty Asteraceae species were collected during flowering time and evaluated in terms of the yield and quality of essential oils (germination inhibition and growth of weeds). Half the species showed a sufficient yield of essential oil (from about 0.1% to 1.43%) when testing these phytochemicals in vitro as germination inhibitors of two typical weeds, Amaranthus retroflexus and Setaria viridis. Despite the higher tolerance of S. viridis, the concentration of 100 lg L 1 of essential oils of the two Artemisia species and Xanthium strumarium could totally inhibit germination. In addition, at 10 lg L 1, the same essential oils showed full inhibition of A. retroflexus seeds. A comparison of their effectiveness at suboptimal doses led to a further selection of the most promising sources of essential oils. After their chemical characterisation, the essential oils were tested as post-emergence herbicides on seedlings of the above-cited weeds. After spraying the weeds at different concentrations (10, 100 and 1000 mg L 1) during two different phenological stages of weed seedlings (cotyledons and the third true leaf), the essential oils of Artemisia annua and X. strumarium showed the best performance. The essential oils of X. strumarium were then tested again on both weeds to monitor the dynamics of plant injury. A reduction in plant fresh weight (about 20%–30% after 10 days) and chlorophyll content (destroyed, after the same amount of time) was found, thus confirming the total and rapid effectiveness of these essential oils. In summary, A. annua and X. strumarium have elicited considerable agronomic interest and appear to be suitable as a source of essential oils to act as natural herbicides

Geographic variation in phytochemical constituents and allelopathic potential of Pinus halepensis barks

Aqueous extracts (10, 20, 30 and 40 g/L) of Pinus halepensis barks, collected from Bizerte (B), Tabarka (T), Seliana (S) and Oueslatia (O) to elucidate the influence of ecological sites on allelopathic potential. Aqueous barks extracts from (S) and (O) have revealed a higher rate of phenolic acids than those from (T) and (B), respectively 13.23, 13.8, 11.63 and 10.37 mg/mL. Alep pin barks were analyzed using HPLC/UV for the identification and quantification of the phenolic compounds, among which in particular the catechin acetate, the gallic acid, the rutine hydrate, luteolin 7 glucoside and the cinnamic acid. In fact, the aqueous extract of barks from (S) revealed a highest level, respectively 2.61, 1.74, 1.61, 1.36, and 1.21 mg/mL. The Pinus halepensis barks was analyzed by GC and GC-MS. As a result, 29 compounds were identified representing 89% made up basically by β-caryophyllene, α-humulene. As for allelopathic activity, aqueous extracts of barks significantly delayed germination, reduced its rate and affected the seedling growth mainly the (S) and (O) extracts. The root growth of the two targets has shown a high sensibility compared to the shoot lengths. Pot cultures were conducted by the incorporation of barks powder (50 and 100 g/kg) or the irrigation with their aqueous extracts at 20 and 40 g/L. Pinus halepensis barks and its extracts have shown a high herbicide potent, particularly the one collected from (S) and (O), may be favorably used for incorporating in agricultural systems for sustainable weed managemen

Representaciones moleculares: reflexiones sobre su enseñanza

Basados en el lugar de privilegio que tienen las representaciones moleculares en la Química, las dificultades que manifiestan los estudiantes en su comprensión, nos propusimos reflexionar sobre cuestiones derivadas de la problemática inherente a su representación e interpretación, de los aspectos epistemológicos que subyacen a las mismas y de su rol como parte del lenguaje que emplea la Química, así como también sobre estrategias que puedan favorecer su comprensión. Hemos fundamentado el presente trabajo, que tiene la expectativa de obtener conclusiones que permitan propiciar mejoras en la enseñanza y en el aprendizaje, en aportes provenientes del campo de la Filosofía de la Ciencia, la Semiótica, la Psicología Cognitiva y la Didáctica de las Ciencias.Facultad de Humanidades y Ciencias de la Educació

Química y medio ambiente: "¿y si nos ponemos las pilas?" : Una propuesta de taller para llevar al aula

En este trabajo se presenta una propuesta didáctica implementada, en el marco de la Semana de la Ciencia y la Tecnología, a través de la modalidad de taller para alumnos de escuelas secundarias referido a pilas y baterías y su impacto en el medio ambiente. Dicha propuesta tiene base en el enfoque Ciencia, Tecnología, Sociedad y Ambiente (CTSA), la cual tiende a favorecer la integración de las dimensiones cognitivas y actitudinales de los estudiantes así como también propender un trabajo interdisciplinario. El creciente consumo de pilas y baterías induce a reflexionar sobre su destino cuando quedan en desuso y el impacto ambiental que su acumulación origina. En este sentido, puede resultar de interés la implementación de esta propuesta de trabajo referida a aspectos generales y efectos en el medio ambiente de pilas y baterías así como también el análisis de las posibles vías de deposición. La escasez de información clara sobre el destino que se le debe dar a las pilas y el desconocimiento generalizado respecto al manejo de residuos peligrosos nos lleva a pensar en la necesidad de promover este tipo de reflexiones en el aula.Facultad de Humanidades y Ciencias de la Educació

Phytochemical data parallel morpho-colorimetric variation in Polygala flavescens DC

Phytochemical data, integrated with other sources of information, represent a valuable tool helping to solve different kinds of taxonomic problems in plant systematics. In the present study, a comparative investigation, in order to clarify the systematic relationships of the three subspecies currently recognized within the Italian endemic Polygala flavescens, was carried out. Preliminarily, a morphometric and colorimetric analysis, in order to test the degree of morphological distinctiveness among the taxa, was performed. Then, a phytochemical analysis based both on volatile and non-volatile compounds was obtained. Concerning the morpho-colorimetric analysis, our results confirm most of the characters as useful to discriminate the three subspecies. In addition, some volatile and non-volatile compounds are good taxonomic markers. Morpho-colorimetric variation is clearly paralleled by phytochemical results, confirming the value of this kind of data to infer relationships in plant systematics. Based on these results, we support a taxonomic treatment at subspecific level for the involved taxa. Finally, based on the most significant morphological characters, a revision of herbarium specimens allowed to redefine the distribution pattern of the three subspecies. Accordingly, the range of P. flavescens subsp. maremmana is limited to Mt. Argentario (southern Tuscany) only. A key is also reported for the identification of the three subspecies

Empezamos una nueva unidad... ¿Estequio... qué?

Estequiometría representa uno de los temas que mayor dificultad involucra para su aprendizaje por parte de los alumnos. Numerosos estudios avalan esta afirmación. En el presente trabajo nos proponemos realizar una reflexión sobre los aspectos que inciden en esta situación. En la resolución de los problemas estequiométricos confluyen una serie de cuestiones: el manejo simultáneo de diferentes niveles representacionales, las dificultades con la cuali y la cuantificación, los conceptos involucrados en la resolución y las teorías implícitas que modelan lo que los alumnos aprenden.Departamento de Ciencias Exactas y Naturale

Essential Oil of Phyllanthus reticulatus Poiret from Nigeria

The chemical composition of the essential oil obtained by hydrodistillation from the leaves of Phyllanthus reticulatus Poiret (Euphorbiaceae) growing in Nigeria has been studied. The constituents of the oil were analyzed by means of gas chromatography (GC-FID) and gas chromatography coupled with mass spectrometry (GC-MS). Monoterpenes (64.9%) were the dominant class of compounds, followed by sesquiterpenes (23.0%). The major constituents were α-pinene (6.0%), sabinene (7.6%), β-pinene (18.1%), linalool (6.9%) and camphor (7.7%), among the monoterpenes, and β-caryophyllene (11.9%) and germacrene D (8.6%) among the sesquiterpenes. This is the first report on the volatile constituents of Phyllanthus reticulatu