Modelado numérico para estudiar interfases fluido-sólidas ante excitaciones dinámicas

ResumenEste trabajo trata sobre la propagación de ondas en interfases fluido-sólidas debidas a excitaciones dinámicas, que son conocidas como ondas de Scholte. Se ha estudiado una amplia gama de materiales sólidos elásticos empleados en la ingeniería. La interfase une un medio acústico (fluido) y otro sólido. Se ha demostrado que por medio de un análisis de ondas difractadas en un fluido es posible deducir las características mecánicas del medio sólido, específicamente sus velocidades de propagación. Para este propósito, el campo difractado de onda de presión y desplazamientos, debido a una onda inicial de presión en el fluido, se expresa mediante las representaciones integrales de frontera, las cuales satisfacen la ecuación de movimiento. La presión inicial en el fluido es representada mediante una función de Hankel de segunda especie y orden cero. La solución a este problema de propagación de ondas se obtiene por medio del método indirecto de elementos frontera, que es equivalente al bien conocido teorema de representación de Somigliana. La validación de los resultados se realiza por medio del método del número de onda discreto. En primer lugar, se muestran espectros de presiones que ilustran el comportamiento del fluido para cada material sólido considerado, y después se aplica la transformada rápida de Fourier para mostrar los resultados en el dominio del tiempo, donde se ejemplifica la aparición de las ondas de Scholte y la cantidad de energía que transportan.AbstractThis work shows the wave propagation in fluid-solid interfaces due to dynamic excitations, such interface waves are known as Scholte's waves. We studied a wide range of elastic solid materials used in engineering. The interface connects an acoustic medium (fluid) and another solid. It has been shown that by means of an analysis of diffracted waves in a fluid, it is possible to deduce the mechanical characteristics of the solid medium, specifically, its propagation velocities. For this purpose, the diffracted field of pressures and displacements, due to an initial pressure in the fluid, are expressed using boundary integral representations, which satisfy the equation of motion. The initial pressure in the fluid is represented by a Hankel's function of second kind and zero order. The solution to this problem of wave propagation is obtained by means of the Indirect Boundary Element Method, which is equivalent to the well-known Somigliana's representation theorem. The validation of the results was performed by means of the Discrete Wave Number Method. Firstly, spectra of pressures to illustrate the behavior of the fluid for each solid material considered are included, then, the Fast Fourier Transform algorithm to display the results in the time domain is applied, where the emergence of Scholte's waves and the amount of energy that they carry are highlighted

Propagation of Rayleighs waves in cracked media

Este trabajo está enfocado a la obtención de resultados numéricos que permitan la detección y caracterización de grietas sub-superficiales en sólidos mediante la incidencia de ondas elásticas de Rayleigh. Los resultados se obtienen a partir de ecuaciones integrales de frontera, que pertenecen al campo de la elastodinámica. Una vez que se aplican las condiciones de frontera se obtiene un sistema de ecuaciones integrales del tipo Fredholm de segunda especie y orden cero, el cual es resuelto mediante eliminación gaussiana. El método que se emplea para la discretización de dichas ecuaciones es conocido como «método indirecto de elementos frontera», el cual puede ser visto como una derivación del teorema clásico de Somigliana. A partir de los análisis realizados en el dominio de la frecuencia emergen picos de resonancia que permiten inferir la presencia de grietas mediante los cocientes espectrales. Se analizaron varios modelos de medios agrietados donde se pretende evidenciar la gran utilidad que presenta el uso de los cocientes espectrales para identificar grietas. Se estudiaron los efectos de la orientación y la localización de las grietas. Los resultados obtenidos presentan buena concordancia con los publicados previamente.This work is focused on the finding of numerical results for detection and characterization of sub-surface cracks in solids under the incidence of Rayleighs elastic waves. The results are obtained from boundary integral equations, which belong to the field of dynamics of elasticity. Once applied the boundary conditions, a system of Fredholms integral equations of second kind and zero order is obtained, which is solved using Gaussian elimination. The method that is used for the solution of such integral equations is known as the Indirect Boundary Element Method, which can be seen as a derivation of the Somiglianas classic theorem. On the basis of the analysis made in the frequency domain, resonance peaks emerge and allow us to infer the presence of cracks through the spectral ratios. Several models of cracked media were analyzed, where analyses reveal the great utility that displays the use of spectral ratios to identify cracks. We studied the effects of orientation and location of cracks. The results show good agreement with the previously published.Peer Reviewe

Árboles del Santuario Histórico de Machu Picchu: Monitoreo de diversidad y carbono a largo plazo

Understanding how the richness, diversity, and carbon monitoring vary and are distributed through altitudinal gradients in Andean montane forests is essential to understand how these forests are adapting to global warming effects. Botanical explorations and general collections were carried out within the limits of the Historic Sanctuary of Machu Picchu in an altitude gradient of 1600 to 4200 m.a.s.l. Two permanent plots of 1.0 ha were established in the sectors of Intipunku (SHM – 01) at an altitude of 2,653 m.a.s.l and Kantupata (SHM-02) at an altitude of 3,200 m.a.s.l., with the standardized methodology of RAINFOR in 2013 and remedied in 2016. We updated the number of tree species for the Historic Sanctuary of Machu Picchu, 364 species are reported so far, this catalog includes all wild and cultivated species but also tree ferns and palm trees. In recent years, four new tree species have been described whose TYPE collections come from SHM forests: Ocotea alveatavan der Werff, Ocotea mollivillosavan der Werff (Lauraceae), Bunchosia cuscanaW.R. Anderson (Malpighiaceae), Ficus machupicchuensisC.C. Berg (Moraceae). In the two permanent plots, a total of 69 species were recorded in 1286 individuals. Individually in the SHM – 01 plot, 26 families, 36 genera and 45 species were recorded in 682 individuals; and in the SHM – 02 plot: 22 families, 28 genera and 31 species in 604 individuals. Stored aerial biomass was higher in the Intipunku sector (146 Mg ha-1) compared to Kantupata sector (101 Mg ha-1). Our research shows that the Andean forests of Machu Picchu provide important ecosystem services, and there is still much to do in terms of scientic research. The continued discovery of new tree species in the locality demonstrates the need for conservation to protect forests that support some of the highest levels of endemism in the world

The only African wild tobacco, Nicotiana africana: Alkaloid content and the effect of herbivory

Herbivory in some Nicotiana species is known to induce alkaloid production. This study examined herbivore-induced defenses in the nornicotine-rich African tobacco N. africana, the only Nicotiana species indigenous to Africa. We tested the predictions that: 1) N. africana will have high constitutive levels of leaf, flower and nectar alkaloids; 2) leaf herbivory by the African bollworm Helicoverpa armigera will induce increased alkaloid levels in leaves, flowers and nectar; and 3) increased alkaloid concentrations in herbivore-damaged plants will negatively affect larval growth. We grew N. africana in large pots in a greenhouse and exposed flowering plants to densities of one, three and six fourth-instar larvae of H. armigera, for four days. Leaves, flowers and nectar were analyzed for nicotine, nornicotine and anabasine. The principal leaf alkaloid was nornicotine (mean: 28 µg/g dry mass) followed by anabasine (4.9 µg/g) and nicotine (0.6 µg/g). Nornicotine was found in low quantities in the flowers, but no nicotine or anabasine were recorded. The nectar contained none of the alkaloids measured. Larval growth was reduced when leaves of flowering plants were exposed to six larvae. As predicted by the optimal defense theory, herbivory had a localized effect and caused an increase in nornicotine concentrations in both undamaged top leaves of herbivore damaged plants and herbivore damaged leaves exposed to one and three larvae. The nicotine concentration increased in damaged compared to undamaged middle leaves. The nornicotine concentration was lower in damaged leaves of plants exposed to six compared to three larvae, suggesting that N. africana rather invests in new growth as opposed to protecting older leaves under severe attack. The results indicate that the nornicotine-rich N. africana will be unattractive to herbivores and more so when damaged, but that potential pollinators will be unaffected because the nectar remains alkaloid-free even after herbivory

Magnitude and Timing of Leaf Damage Affect Seed Production in a Natural Population of Arabidopsis thaliana (Brassicaceae)

Background: The effect of herbivory on plant fitness varies widely. Understanding the causes of this variation is of considerable interest because of its implications for plant population dynamics and trait evolution. We experimentally defoliated the annual herb Arabidopsis thaliana in a natural population in Sweden to test the hypotheses that (a) plant fitness decreases with increasing damage, (b) tolerance to defoliation is lower before flowering than during flowering, and (c) defoliation before flowering reduces number of seeds more strongly than defoliation during flowering, but the opposite is true for effects on seed size. Methodology/Principal Findings: In a first experiment, between 0 and 75% of the leaf area was removed in May from plants that flowered or were about to start flowering. In a second experiment, 0, 25%, or 50% of the leaf area was removed from plants on one of two occasions, in mid April when plants were either in the vegetative rosette or bolting stage, or in mid May when plants were flowering. In the first experiment, seed production was negatively related to leaf area removed, and at the highest damage level, also mean seed size was reduced. In the second experiment, removal of 50% of the leaf area reduced seed production by 60% among plants defoliated early in the season at the vegetative rosettes, and by 22% among plants defoliated early in the season at the bolting stage, but did not reduce seed output of plants defoliated one month later. No seasonal shift in the effect of defoliation on seed size was detected. Conclusions/Significance: The results show that leaf damage may reduce the fitness of A. thaliana, and suggest that in this population leaf herbivores feeding on plants before flowering should exert stronger selection on defence traits than those feeding on plants during flowering, given similar damage levels

An experimental test of host’s life history traits modulation in response to cuckoo parasitism risk

Hosts can counteract parasites through defences based on resistance and/or tolerance. The mechanistic basis of tolerance, which involve defensive mechanisms minimizing parasite damage after a successful parasitic attack, remains poorly explored in the study of cuckoo-host interactions. Here, we experimentally explore the possibility that the risk of great spotted cuckoo Clamator glandarius parasitism may induce tolerance defences in magpie Pica pica hosts through plasticity in life-history traits. We predict that magpies exposed to auditory cues indicating high parasitism risk will more likely exhibit resistance and/or modify their life-history traits to minimize parasitism costs (i.e. tolerance) compared to magpies under low parasitism risk. We found that manipulating the perceived parasitism risk did not affect host resistance (i.e. rejection of parasitic eggs) nor host life-history traits. Unexpectedly, host's egg volume increased over the season in nests exposed to auditory cues of control non-harmful hoopoes Upupa epops. Our results do not provide support for inducible defences (either based on resistance or tolerance) in response to risk of parasitism in magpie hosts. Even so, we encourage studying plastic expression of breeding strategies in response to risk of cuckoo parasitism to achieve a better understanding of the mechanistic basis of tolerance defences.This work was supported by the Spanish Ministry of Education and Science/FEDER (Projects CGL2011-27561/BOS and CGL2014-56769-P to D. P. and J.M.A.). D.P. was supported by the Government of Extremadura while writing (contract number TA13002). M.E.G. was supported by the Spanish Ministry of Economy and Competitiveness (grant number BES-2012-051898).

Global urban environmental change drives adaptation in white clover.

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Association Between Preexisting Versus Newly Identified Atrial Fibrillation and Outcomes of Patients With Acute Pulmonary Embolism

Background Atrial fibrillation (AF) may exist before or occur early in the course of pulmonary embolism (PE). We determined the PE outcomes based on the presence and timing of AF. Methods and Results Using the data from a multicenter PE registry, we identified 3 groups: (1) those with preexisting AF, (2) patients with new AF within 2 days from acute PE (incident AF), and (3) patients without AF. We assessed the 90-day and 1-year risk of mortality and stroke in patients with AF, compared with those without AF (reference group). Among 16 497 patients with PE, 792 had preexisting AF. These patients had increased odds of 90-day all-cause (odds ratio [OR], 2.81; 95% CI, 2.33-3.38) and PE-related mortality (OR, 2.38; 95% CI, 1.37-4.14) and increased 1-year hazard for ischemic stroke (hazard ratio, 5.48; 95% CI, 3.10-9.69) compared with those without AF. After multivariable adjustment, preexisting AF was associated with significantly increased odds of all-cause mortality (OR, 1.91; 95% CI, 1.57-2.32) but not PE-related mortality (OR, 1.50; 95% CI, 0.85-2.66). Among 16 497 patients with PE, 445 developed new incident AF within 2 days of acute PE. Incident AF was associated with increased odds of 90-day all-cause (OR, 2.28; 95% CI, 1.75-2.97) and PE-related (OR, 3.64; 95% CI, 2.01-6.59) mortality but not stroke. Findings were similar in multivariable analyses. Conclusions In patients with acute symptomatic PE, both preexisting AF and incident AF predict adverse clinical outcomes. The type of adverse outcomes may differ depending on the timing of AF onset.info:eu-repo/semantics/publishedVersio

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Data from: Evolutionary changes in plant tolerance against herbivory through a resurrection experiment

Both theoretical and empirical works have highlighted the difference in the evolutionary implications of host resistance and tolerance against their enemies. However, it has been difficult to show evolutionary changes in host defences in natural populations; thus, evaluating theoretical predictions of simultaneous evolution of defences remains a challenge. We studied the evolutionary changes in traits related to resistance and tolerance against herbivory in a natural plant population using seeds from two collections made in a period of 20 years. In a common garden experiment, we compared defensive traits of ancestral (1987) and descendant (2007) subpopulations of the annual plant Datura stramonium that shows genetic variation for tolerance and to which the specialist herbivore Lema daturaphila is locally adapted. We also examined the effects of different plant genotypes on the herbivore for testing the plant genetic variation in resistance. Based on the response to the contemporary herbivore populations, results revealed a nonsignificant response in plant resistance traits (herbivore consumption, foliar trichomes and tropane alkaloids), but a significant one in tolerance. The survival of herbivores in laboratory experiments depended on the plant genotype, which suggests genetic variation in plant resistance. Although we cannot identify the selective agent for the change nor exclude genetic drift, the results are consistent with the expectation that when resistance fails to control herbivory, tolerance should play a more important role in the evolution of the interaction