8,137 research outputs found

    Multi-site H-bridge breathers in a DNA--shaped double strand

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    We investigate the formation process of nonlinear vibrational modes representing broad H-bridge multi--site breathers in a DNA--shaped double strand. Within a network model of the double helix we take individual motions of the bases within the base pair plane into account. The resulting H-bridge deformations may be asymmetric with respect to the helix axis. Furthermore the covalent bonds may be deformed distinctly in the two backbone strands. Unlike other authors that add different extra terms we limit the interaction to the hydrogen bonds within each base pair and the covalent bonds along each strand. In this way we intend to make apparent the effect of the characteristic helicoidal structure of DNA. We study the energy exchange processes related with the relaxation dynamics from a non-equilibrium conformation. It is demonstrated that the twist-opening relaxation dynamics of a radially distorted double helix attains an equilibrium regime characterized by a multi-site H-bridge breather.Comment: 27 pages and 10 figure

    Why using a general model in Solvency II is not a good idea : an explanation from a Bayesian point of view

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    The passing of Directive 2009/138/CE (Solvency II) has opened a new era in the European insurance market. According to this new regulatory environment, the volume of own resources will be determined depending on the risks that any insurer would be holding. So, nowadays, the model to estimate the amount of economic capital is one of the most important elements. The Directive establishes that the European entities can use a general model to perform these tasks. However, this situation is far from being optimal because the calibration of the general model has been made using figures that reflects and average behaviour. This paper shows that not all the companies operating in a specific market has the same risk profile. For this reason, it is unsatisfactory to use a general model for all of them. We use the PAM clustering method and afterwards some Bayesian tools to check the results previously obtained. Analysed data (public information belonging to Spanish insurance companies about balance sheets and income statements from 1998 to 2007) comes from the DGSFP (Spanish insurance regulator).Solvency II, PAM, Longitudinal multinomial model

    Can we simulate the biomechanical effects of exoskeletons prior to workstation implementation? Application of the Forces ergonomic method

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    Increasingly, exoskeletons are becoming a valuable tool for prevention technicians to promote occupational health and reduce the risk of musculoskeletal disorders in industry. However, the effective implementation of industrial exoskeletons is a complex challenge. Deciding whether these devices are the optimal solution to the detected ergonomic risks at a specific workstation is not straightforward. This study presents the modelling of three commercial passive exoskeletons, one for lumbar and two for shoulder risk reduction, to be considered in the musculoskeletal risk assessment of industrial workstations. The presented modelling considers the forces and moments applied by exoskeletons to the body using the Forces ergonomic method, providing the musculoskeletal risk for each joint based on inertial motion capture data registered at each workstation. This approach is exemplified on simulated and actual production workstations. The results reveal that the modelling application allows an objective understanding of the biomechanical effects of exoskeletons. Modelling establishes a predictive tool to assess and make decisions regarding the suitability of the exoskeleton prior to implementation at a workstation

    Multiple hypothesis testing and clustering with mixtures of non-central t-distributions applied in microarray data analysis

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    Multiple testing analysis, based on clustering methodologies, is usually applied in Microarray Data Analysis for comparisons between pair of groups. In this paper, we generalize this methodology to deal with multiple comparisons among more than two groups obtained from microarray expressions of genes. Assuming normal data, we define a statistic which depends on sample means and sample variances, distributed as a non-central t-distribution. As we consider multiple comparisons among groups, a mixture of non-central t-distributions is derived. The estimation of the components of mixtures is obtained via a Bayesian approach, and the model is applied in a multiple comparison problem from a microarray experiment obtained from gorilla, bonobo and human cultured fibroblasts.Clustering, MCMC computation, Microarray analysis, Mixture distributions, Multiple hypothesis testing, Non-central t-distribution

    Effect of the Introduction of Impurities on the Stability Properties of Multibreathers at Low Coupling

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    sing a theorem dubbed the {\em Multibreather Stabiliy Theorem} [Physica D 180 (2003) 235-255] we have obtained the stability properties of multibreathers in systems of coupled oscillators with on-site potentials, with an inhomogeneity. Analytical results are obtained for 2-site, 3-site breathers, multibreathers, phonobreathers and dark breathers. The inhomogeneity is considered both at the on-site potential and at the coupling terms. All the results have been checked numerically with excellent agreement. The main conclusion is that the introduction of a impurity does not alter the stability properties.Comment: 20 pages, 9 figure

    Prolamin content and grain weight in RNAi silenced wheat lines under different conditions of temperature and nitrogen availability

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    Temperature and nitrogen (N) availability are two important environmental factors that may produce important changes in grain composition during grain filling of bread wheat. In this study, four wheat lines with the down-regulation of gliadins by means of RNA interference (RNAi) have been characterized to determine the effect of thermal stress and N availability on grain weight and quality; with focus on gliadin and glutenin protein fractions. Grain weight was reduced with heat stress (HS) in all RNAi lines, whereas gliadin content was increased in the wild-types. With respect to gliadin content, RNAi lines responded to HS and N availability differently from their respective wild-types, except for ω-gliadin content, indicating a very clear stability of silencing under different environmental conditions. In a context of increased temperature and HS events, and in environments with different N availability, the RNAi lines with down-regulated gliadins seem well suited for the production of wheat grain with low gliadin content.The Spanish Ministry of Economy and Competitiveness (Project AGL2016-80566-P) and the European Regional Development Fund (FEDER) supported this research

    Stationary and moving breathers in a simplified model of curved alpha--helix proteins

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    The existence, stability and movability of breathers in a model for alpha-helix proteins is studied. This model basically consists a chain of dipole moments parallel to it. The existence of localized linear modes brings about that the system has a characteristic frequency, which depends on the curvature of the chain. Hard breathers are stable, while soft ones experiment subharmonic instabilities that preserve, however the localization. Moving breathers can travel across the bending point for small curvature and are reflected when it is increased. No trapping of breathers takes place.Comment: 19 pages, 11 figure

    Frecuencia de agenesias, dientes supernumerarios y erupción ectópica en radiografías panorámicas en niños de 7 a 10 años, en tres centros odontológicos de Viña del Mar

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    Tesis (Cirujano Dentista)El desarrollo de la dentición es un aspecto crucial en la evaluación clínica del paciente odontológico infantil. Este desarrollo comienza con la odontogénesis, la cual corresponde a una serie de procesos embriológicos, que involucran mecanismos moleculares, histológicos y genéticos, que darán origen al germen dentario, y por lo tanto, a los dientes temporales y permanentes. Existen múltiples factores que pueden ocasionar alteraciones en las distintas etapas del desarrollo, las que afectarían eventualmente a los órganos dentarios en cuanto al número, forma o estructura, surgiendo así distintas anomalías. Las alteraciones relacionadas con el número de los dientes, como lo son las agenesias o hipodoncia y los supernumerarios o hiperdoncia, se producen en la etapa de iniciación del desarrollo de la dentición y se encuentran asociadas a la etiología de las maloclusiones dentarias. Por el contrario, si la odontogénesis se lleva a cabo con normalidad, comienza el proceso de erupción dentaria, el cual es el movimiento del diente desde su posición de desarrollo dentro del hueso alveolar, hasta que alcanza funcionalmente el plano oclusal. Si los dientes llegan a concretar su formación, existe la probabilidad de que la trayectoria de erupción de éstos no sea la adecuada y comiencen a producir reabsorción atípica de otros dientes, lo que se conoce como erupción ectópica. Para detectar a tiempo las tres alteraciones nombradas anteriormente y así evitar complicaciones que afecten la cronología o asimetría en la erupción dentaria, es fundamental solicitar a los pacientes de temprana edad, es decir, desde los 7 años, una radiografía panorámica de diagnóstico. Si bien estas alteraciones son poco frecuentes, es importante el nivel de impacto que provoca en la población, ya que sus consecuencias se traducen principalmente en maloclusiones que pueden causar apiñamientos, desviación de la línea media, retención de piezas dentarias e hipoplasia de maxilares en casos más severos (26). Esto no es un tema menor, puesto que en Chile, las maloclusiones son la tercera patología bucal más frecuente luego de caries y enfermedad periodontal (34). Con el fin de realizar vigilancia epidemiológica y detectar cambios en las tendencias de afección, es de vital importancia realizar este estudio y conocer la frecuencia de agenesia dentaria, dientes supernumerarios y erupción ectópica de primer molar permanente y de incisivo lateral permanente, ya que en Latinoamérica existe escasa evidencia con respecto al tema y en nuestro país solo existen cuatro publicaciones relacionadas con estas alteraciones
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