An algorithm to initialize the searchof solutions of polynomial systems

AbstractOne of the main problems dealing with iterative methods for solving polynomial systemsis the initialization of the iteration. This paper provides an algorithm to initialize the search of solutions of polynomial systems

Mitochondrial bioenergetics is affected by the herbicide paraquat

AbstractThe potential toxicity of the herbicide paraquat (1,1-dimethyl-4,4′-bipyridylium dichloride) was tested in bioenergetic functions of isolated rat liver mitochondria. Paraquat increases the rate of State 4 respiration, doubling at 10 mM, indicating uncoupling effects. Additionally, State 3 respiration is depressed by about 15%, at 10 mM paraquat, whereas uncoupled respiration in the presence of CCCP is depressed by about 30%. Furthermore, paraquat partially inhibits the ATPase activity through a direct effect on this enzyme complex. However, at high concentrations (5–10 mM), the ATPase activity is stimulated, probably as consequence of the described uncoupling effect. Depression of respiratory activity is mediated through partial inhibitions of mitochondrial complexes III and IV. Paraquat depresses Δψ as a function of herbicide concentration. In addition, the depolarization induced by ADP is decreased and repolarization is biphasic suggesting a double effect. Repolarization resumes at a level consistently higher than the initial level before ADP addition, for paraquat concentrations up to 10 mM. This particular effect is clear at 1 mM paraquat and tends to fade out with increasing concentrations of the herbicide

Argumentos ontológicos

En este artículo proponemos una revisión a fondo de los argumentos ontológicos clásicos: de Anselmo, Descartes, Spinoza y Leibniz. En la introducción se precisa la noción de argumento ontológico y señalamos la importante distinción que hacemos en lógica entre la validez de un argumento y su solidez, esta última tiene en cuenta no sólo la corrección formal del mismo sino también la verdad de las hipótesis. En las siguientes secciones se analizan por turno los argumentos de Anselmo, Descartes, Spinoza y Leibniz. En todos los casos hemos traducido los pasajes correspondientes del argumento original y formalizado sus hipótesis y conclusión. En algunos casos hemos reconstruido el argumento y destacado como hipótesis todos los enunciados que de hecho se usan en la demostración por parte de los autores en estudio. De esta forma a veces nos separamos de lo que tradicionalmente es considerado el argumento (por ejemplo, tal y como se presentan en Logic and Theism [Sobel]) y la mayor parte de los argumentos deviene en formalmente válidos. Somos conscientes de que de esa manera hemos explicitado las premisas ocultas que validan el argumento pero a la vez disminuyen la solidez del mismo por tratarse de hipótesis de difícil justificación y con carga filosófica en muchos casos, incluso de falacias de petición de principio. Frecuentemente se trata de hipótesis existenciales, que claramente permiten pasar de una definición, que simplemente establece una correspondencia entre propiedades, a una asunción de consistencia, estableciendo que no son vacíos ciertos conjuntos. Se mencionan los temas relevantes a este estudio: el de la consideración de la existencia como un predicado, el de las descripciones impropias, el compromiso o aporte existencial de los enunciados universales, las categorías modales y el eventual colapso modal. Habría que destacar el esfuerzo de formalización para la que hemos empleado varias lógicas: clásica de primer, de orden superior (con descriptores como operadores lógicos) y lógica modal. Finalizamos señalando que el tema de los argumentos ontológicos sigue fascinando a los lógicos y filósofos, recibió mucha atención en el siglo XX y también en el XXI.Palabras clave: argumento ontológico, lógica de primer orden, lógica de orden superior, lógica modal, aporte existencial, colapso modal, descripciones impropiasAbstract:In this paper we propose a deep revision of the classical ontological arguments of Anselm, Descartes, Leibniz and Spinoza. The introduction clarifies the concept of ontological argument and point out the important logic distinction between the validity of an argument and its soundness, where besides validity it is required that all premises are actually true. The following sections discuss in turn the arguments of Anselm, Descartes, Spinoza and Leibniz. In all cases we have translated the relevant passages of the original argument and formalized its hypothesis and conclusion. In some cases we reconstructed the whole argument and added as hypothesis all statements that served the authors to prove their thesis. By doing this we detached ourselves from what is traditionally considered the argument (for example, as seen in Logic and Theism [Sobel]) and most of the arguments become formally valid.We are aware of the fact that in this way we made explicit the hidden assumptions that made the argument valid while weakening its strength. The reason why is that the new hypothesis are hard to justify as in many cases they have philosophical import and they even committed the fallacy known as petitio principii. Very often the new hypothesis are existential statements, which clearly allow passing from a definition, which simply establishes a correspondence between properties, to an assumption of consistency, stating that certain sets are not empty. The paper includes the issues relevant to this study: the consideration of existence as a predicate, improper descriptions, existential import of universal statements, modal categories and the eventual modal collapse. We should highlight the effort of formalization for which we have used several logics: classical first order logic, higher order (with a description operator) and modal logic. We conclude by pointing out that the subject of ontological arguments still fascinate logicians and philosophers and received attention in the twentieth and the twenty first century.Keywords: ontological argument, first order logic, higher-order logic, modal logic, existential import, modal collapse, improper description.</p

Dense nanostructured zirconia compacts obtained by colloidal filtration of binary mixtures

As starting materials two commercial nanosized zirconias doped with 3 mol% of Y 2O 3 were used: a powder of about 100 nm (TZ3YE, Tosoh, Japan) and a colloidal suspension of about 15 nm (Mel Chemicals, UK). Colloidal stability in water was studied for both zirconias in terms of zeta potential as a function of deflocculant concentration and pH. Concentrated suspensions were prepared by dispersing the powder in the colloidal suspension to solids loadings ranging from 5 to 30 vol.% using a sonication probe to achieve dispersion. The rheological behavior was optimized in terms of solids content, deflocculant content and sonication time. Optimized suspensions with up to 25 vol.% solids showed a nearly Newtonian behavior and extremely low viscosities and maintain stable for long times (days) which is an important drawback of conventional nanoparticle suspensions. Samples obtained by slip casting in plaster moulds were used for dynamic sintering studies and dense, nanostructured specimens were obtained at temperatures of 1300-1400°C.This work has been supported by Spanish Ministry of Science and Innovation (Projects MAT2009-14144-C03-02 and MAT2009-14369-C02-01). R. Moreno thanks to Universidad Politecnica de Valencia for the concession of a grant in the frame of its Programme of Support to R + D (PAID-02-11, R-1752).Benavente Martínez, R.; Salvador Moya, MD.; Alcázar, M.; Moreno, R. (2012). Dense nanostructured zirconia compacts obtained by colloidal filtration of binary mixtures. Ceramics International. 38(3):2111-2117. https://doi.org/10.1016/j.ceramint.2011.10.051S2111211738

Double-zero degeneracy and heteroclinic cycles in a perturbation of the Lorenz system

In this paper we consider a 3D three-parameter unfolding close to the normal form of the triple-zero bifurcation exhibited by the Lorenz system. First we study analytically the double-zero degeneracy (a double-zero eigenvalue with geometric multiplicity two) and two Hopf bifurcations. We focus on the more complex case in which the double-zero degeneracy organizes several codimension-one singularities, namely transcritical, pitchfork, Hopf and heteroclinic bifurcations. The analysis of the normal form of a Hopf-transcritical bifurcation allows to obtain the expressions for the corresponding bifurcation curves. A degenerate double-zero bifurcation is also considered. The theoretical information obtained is very helpful to start a numerical study of the 3D system. Thus, the presence of degenerate heteroclinic and homoclinic orbits, T-point heteroclinic loops and chaotic attractors is detected. We find numerical evidence that, at least, four curves of codimension-two global bifurcations are related to the triple-zero degeneracy in the system analyzed.Ministerio de Economía y Competitividad MTM2017-87915-C2-1-PMinisterio de Ciencia, Innovación y Universidades - Fondos FEDER PGC2018-096265-B-I0Consejería de Economía, Innovación, Ciencia y Empleo - Junta de Andalucía FQM-276, TIC-0130, UHU-1260150 y P20_0116

Fine root dynamics for forests on contrasting soils in the Colombian Amazon

It has been hypothesized that as soil fertility increases, the amount of carbon allocated to below-ground production (fine roots) should decrease. To evaluate this hypothesis, we measured the standing crop fine root mass and the production of fine roots (<2 mm) by two methods: (1) ingrowth cores and, (2) sequential soil coring, during 2.2 years in two lowland forests growing on different soils types in the Colombian Amazon. Differences of soil resources were defined by the type and physical and chemical properties of soil: a forest on clay loam soil (Endostagnic Plinthosol) at the Amacayacu National Natural Park and, the other on white sand (Ortseinc Podzol) at the Zafire Biological Station, located in the Forest Reservation of the Calderón River. We found that the standing crop fine root mass and the production was significantly different between soil depths (0–10 and 10–20 cm) and also between forests. The loamy sand forest allocated more carbon to fine roots than the clay loam forest with the production in loamy sand forest twice (mean±standard error=2.98±0.36 and 3.33±0.69 Mg C ha−1 yr−1, method 1 and 2, respectively) as much as for the more fertile loamy soil forest (1.51±0.14, method 1, and from 1.03±0.31 to 1.36±0.23 Mg C ha−1 yr−1, method 2). Similarly, the average of standing crop fine root mass was higher in the white-sands forest (10.94±0.33 Mg C ha−1) as compared to the forest on the more fertile soil (from 3.04±0.15 to 3.64±0.18 Mg C ha−1). The standing crop fine root mass also showed a temporal pattern related to rainfall, with the production of fine roots decreasing substantially in the dry period of the year 2005. These results suggest that soil resources may play an important role in patterns of carbon allocation to the production of fine roots in these forests as the proportion of carbon allocated to above- and below-ground organs is different between forest types. Thus, a trade-off between above- and below-ground growth seems to exist with our results also suggesting that there are no differences in total net primary productivity between these two forests, but with higher below-ground production and lower above-ground production for the forest on the nutrient poor soi

Molecular recognition with nanostructures fabricated by photopolymerization within metallic subwavelength apertures

The first demonstration of fabrication of submicron lateral resolution molecularly imprinted polymer (MIP) patterns by photoinduced local polymerization within metal subwavelength apertures is reported. The size of the photopolymerized MIP features is finely tuned by the dose of 532 nm radiation. Rhodamine 123 (R123) has been selected as a fluorescent model template to prove the recognition capability of the MIP nanostructures, which has been evaluated by fluorescence lifetime imaging microscopy (FLIM) with single photon timing measurements. The binding selectivity provided by the imprinting effect has been confirmed in the presence of compounds structurally related to R123. These results pave the way to the development of nanomaterial architectures with biomimetic artificial recognition properties for environmental, clinical and food testing