6,339 research outputs found
From circular paths to elliptic orbits: A geometric approach to Kepler's motion
The hodograph, i.e. the path traced by a body in velocity space, was
introduced by Hamilton in 1846 as an alternative for studying certain dynamical
problems. The hodograph of the Kepler problem was then investigated and shown
to be a circle, it was next used to investigate some other properties of the
motion. We here propose a new method for tracing the hodograph and the
corresponding configuration space orbit in Kepler's problem starting from the
initial conditions given and trying to use no more than the methods of
synthetic geometry in a sort of Newtonian approach. All of our geometric
constructions require straight edge and compass only.Comment: 9 pages, 4 figure
Predicción de la frescura del aceite de oliva virgen extra durante el almacenamiento mediante espectroscopía de fluorescencia
Virgin olive oil quality relates to flavor and unique health benefits. Some of these properties are
at the most desirable level when the oil is just extracted, since it is not a product that improves with age. On the
contrary, the concentrations of many compounds change during its shelf-life. These changes reveal the aging of
the oil but do not necessarily mean decay in sensory properties, so in some cases an aged oil from healthy olives
may be better qualified than a fresh one from olives affected by fermentation. The aim of this work is to analyze
different methodologies proposed for assessing the quality of virgin olive oil with implications in freshness and
aging of the oil, and to highlight the possibilities of rapid spectrofluorimetric techniques for assessing oil freshness by checking the evolution of pigments during storage. The observed change in the selected spectral features
and mathematical modelling over time was compared with the accepted model for predicting the amount of
pyropheophytin a, which is based on isokinetic studies. The best regression was obtained for 655 nm (adjustedR2
= 0.91) wavelength, which matches the distinctive band of pigments. The two mathematical models described
in this study highlight the usefulness of pigments in the prediction of the shelf-life of extra virgin olive oil.La calidad del aceite de oliva virgen está relacionada con su flavor y sus beneficios
únicos para la salud. Algunas de estas propiedades se encuentran en el nivel más deseable cuando el aceite está
recién extraído, ya que no es un producto que mejore con el tiempo. Por el contrario, las concentraciones de
muchos compuestos cambian a lo largo de la vida útil. Estos cambios revelan el envejecimiento del aceite, pero
no implican necesariamente la alteración de las propiedades sensoriales, por lo que en algunos casos un aceite
envejecido procedente de aceitunas sanas puede presentar mejor calidad que uno fresco procedente de aceitunas
afectadas por procesos de fermentación. El objetivo de este trabajo es estudiar diferentes metodologías propuestas para evaluar la calidad del aceite de oliva virgen con implicaciones en la frescura y el envejecimiento del
aceite, destacando las posibilidades de las rápidas técnicas espectrofluorométricas para evaluar la frescura del
aceite verificando la evolución de los pigmentos durante el almacenamiento. El cambio observado en las características espectrales seleccionadas y su modelado matemático a lo largo del tiempo se comparó con el modelo
aceptado para predecir la cantidad de pirofeofitina a, que se basa en estudios isocinéticos. Los dos modelos
matemáticos descritos en este estudio pusieron de manifiesto la utilidad de los pigmentos en la predicción de la
vida útil del aceite de oliva virgen extra. La mejor regresión se obtuvo para 655 nm (R2
-ajustado = 0,91), longitud de onda que coincide con la banda distintiva de pigmentos.Secretaría de Estado de Investigación, Desarrollo e Innovación de España-AGL2015-69320-
Predicción de la frescura del aceite de oliva virgen extra durante el almacenamiento mediante espectroscopía de fluorescencia
Virgin olive oil quality relates to flavor and unique health benefits. Some of these properties are
at the most desirable level when the oil is just extracted, since it is not a product that improves with age. On the
contrary, the concentrations of many compounds change during its shelf-life. These changes reveal the aging of
the oil but do not necessarily mean decay in sensory properties, so in some cases an aged oil from healthy olives
may be better qualified than a fresh one from olives affected by fermentation. The aim of this work is to analyze
different methodologies proposed for assessing the quality of virgin olive oil with implications in freshness and
aging of the oil, and to highlight the possibilities of rapid spectrofluorimetric techniques for assessing oil freshness by checking the evolution of pigments during storage. The observed change in the selected spectral features
and mathematical modelling over time was compared with the accepted model for predicting the amount of
pyropheophytin a, which is based on isokinetic studies. The best regression was obtained for 655 nm (adjustedR2
= 0.91) wavelength, which matches the distinctive band of pigments. The two mathematical models described
in this study highlight the usefulness of pigments in the prediction of the shelf-life of extra virgin olive oil.La calidad del aceite de oliva virgen está relacionada con su flavor y sus beneficios
únicos para la salud. Algunas de estas propiedades se encuentran en el nivel más deseable cuando el aceite está
recién extraído, ya que no es un producto que mejore con el tiempo. Por el contrario, las concentraciones de
muchos compuestos cambian a lo largo de la vida útil. Estos cambios revelan el envejecimiento del aceite, pero
no implican necesariamente la alteración de las propiedades sensoriales, por lo que en algunos casos un aceite
envejecido procedente de aceitunas sanas puede presentar mejor calidad que uno fresco procedente de aceitunas
afectadas por procesos de fermentación. El objetivo de este trabajo es estudiar diferentes metodologías propuestas para evaluar la calidad del aceite de oliva virgen con implicaciones en la frescura y el envejecimiento del
aceite, destacando las posibilidades de las rápidas técnicas espectrofluorométricas para evaluar la frescura del
aceite verificando la evolución de los pigmentos durante el almacenamiento. El cambio observado en las características espectrales seleccionadas y su modelado matemático a lo largo del tiempo se comparó con el modelo
aceptado para predecir la cantidad de pirofeofitina a, que se basa en estudios isocinéticos. Los dos modelos
matemáticos descritos en este estudio pusieron de manifiesto la utilidad de los pigmentos en la predicción de la
vida útil del aceite de oliva virgen extra. La mejor regresión se obtuvo para 655 nm (R2
-ajustado = 0,91), longitud de onda que coincide con la banda distintiva de pigmentos.Secretaría de Estado de Investigación, Desarrollo e Innovación de España-AGL2015-69320-
Geminivirus C2 protein represses genes involved in sulphur assimilation and this effect can be counteracted by jasmonate treatment
Geminiviruses are plant viruses that infect a broad range of crops and cause extensive losses worldwide, having an important economic impact. C2, a multifunctional pathogenicity factor encoded by geminiviruses, has been recently shown to suppress the responses to jasmonates in the host plant, which might at least partially explain its well-established role in pathogenicity. Sulphur is one of the essential macro-elements for plant life, and is considered to have a role in plant defence, in a phenomenon named sulphur-induced resistance (SIR) or sulphur-enhanced defence (SED). In this work, we show that geminivirus C2 protein represses the expression of genes involved in the sulphur assimilation pathway in Arabidopsis, but, interestingly, this effect can be neutralized by exogenous jasmonate treatment. These preliminary results may raise the idea that geminiviruses might be affecting sulphur metabolism, and maybe counteracting SIR/SED, through the manipulation of the jasmonate signalling pathway, which would define a novel strategy in plant-virus interactions and may unveil SIR/SED as an important player in the plant defence against viruses.Ministerio de Ciencia y Innovación/FEDER AGL2007-66062-C02-02/AGR AGL2010-22287-CO2European Regional Development Fund (ERDF) BIO2010-15201Junta de Andalucía BIO27
Review of Cephalanthus (Rubiaceae), with the segregation of the new African genus Sylvainia
The genus Cephalanthus belongs to the tribe Naucleeae along with 26 other genera. Members o f Cephalanthus grow mainly in températe and subtropical wetlands in the Americas and Asia, but there is a single African species that is associated with forest maigins and rocky outcrops in humid températe grasslands. The genus comprises six species with a markedly disjunct distribution: three species are from the Americas: C. glabratus, C. occidentalis, and C. salicifolius-, two species are from tropical Asia: C. angustifolius and C. tetrandrus, and one species is from tropical Africa: C. natalensis. Recent molecular phylogenetic studies have supported the monophyly of the genus, however, most morphological synapomorphies are absent in the single African species, which is sister to the remaining species o f the genus. The aim o f this paper is to provide a brief taxonomic revisión o f the genus Cephalanthus, considering previously undervalued or unconsidered morphological aspects, and to describe a new monospecific genus based on comparative morphological analyses. Vegetative and reproductive material o f all Cephalanthus species was analysed following conventional taxonomic techniques. We transferred C. natalensis to a new genus, Sylvainia, taking into account the morphological similarities and diíferences between Cephalanthus and the new genus. Cephalanthus glabrifolius, a little-known species previously considered synonymous with C. tetrandrus, is resurrected as a valid species, bringing the number of Cephalanthus species back to six. The subtribe Cephalanthinae now has two genera, its type Cephalanthus with six species, and a new monospecific genus Sylvainia endemic to southeastem Africa. Based on the modified description of Cephalanthus, now absent from Alfica, the generic concept is substantially modified, being now represented by three American and three Asian species
Anisotropic Dirac cones in monatomic hexagonal lattices
In the last few years, the fascinating properties of graphene have been
thoroughly investigated. The existence of Dirac cones is the most important
characteristic of the electronic band-structure of graphene. In this
theoretical paper, hexagonal monolayers of silicon (h-Si) and germanium (h-Ge)
are examined using density functional theory, within the generalized gradient
approximation. Our numerical results indicate that both h-Si and h-Ge are
chemically stable. The lattice parameters, electronic dispersion relations and
densities of states for these systems are reported. The electronic dispersion
relations display Dirac cones with the symmetry of an equilateral triangle (the
group D) in the vicinity of the K points. Hence, the Fermi velocity depends
on the wave vector direction around points. Fermi velocities for holes and
electrons are significantly different. The maximum and minimum Fermi velocities
are also reported.Comment: 7 pages, 9 figures. Accepted for publication in The European Physical
Journal B (EPJB
Directed transport as a mechanism for protein folding in vivo
We propose a model for protein folding in vivo based on a Brownian-ratchet
mechanism in the multidimensional energy landscape space. The device is able to
produce directed transport taking advantage of the assumed intrinsic asymmetric
properties of the proteins and employing the consumption of energy provided by
an external source. Through such a directed transport phenomenon, the
polypeptide finds the native state starting from any initial state in the
energy landscape with great efficacy and robustness, even in the presence of
different type of obstacles. This model solves Levinthal's paradox without
requiring biased transition probabilities but at the expense of opening the
system to an external field.Comment: 16 pages, 7 figure
Changes in the Semantic Construction of Compassion after the Cognitively-Based Compassion Training (CBCT®) in Women Breast Cancer Survivors
The growing body of research on compassion has demonstrated its benefits for healthcare and wellbeing. However, there is no clear agreement about a definition for compassion, given the novelty of the research on this construct and its religious roots. The aim of this study is to analyze the mental semantic construction of compassion in Spanish-speaking women breast cancer survivors, and the effects of the Cognitively-Based Compassion Training (CBCT®) on the modification of this definition, compared to treatment-as-usual (TAU), at baseline, post-intervention, and six-month follow-up. Participants were 56 women breast cancer survivors from a randomized clinical trial. The Osgood''s Semantic Differential categories (evaluative, potency, and activity scales) were adapted to assess the semantic construction of compassion. At baseline, participants had an undefined idea about compassion. The CBCT influenced subjects'' semantic construction of what it means to be compassionate. Findings could lead to future investigations and compassion programs that adapt to a specific culture or population. © Universidad Complutense de Madrid and Colegio Oficial de Psicólogos de Madrid 2021
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