Estimation of modal parameters ofcivil structures from frequency response function

Este trabajo se centra en estimar los parámetros modales del sistema dinámico que constituye la pasarela peatonal del Museo de la Ciencia de la ciudad de Valladolid (Spain). El trabajo consiste no sólo en calcular frecuencias propias o naturales y factores de amortiguamiento asociados a cada uno de los modos estimados, como proporcionan muchos programas comerciales a partir de los registros de aceleraciones de ensayos OMA (Operational Modal Analysis) y/o EMA (Experimental Modal Analysis), sino que el objetivo de este articulo es calcular las masas generalizadas correspondientes a cada uno de los modos estimados de la estructura. Para ello, en primer lugar se obtiene una representación del sistema dinámico en el espacio de estados mediante la técnica SSI (Stochastic Subspace Identification), y en segundo lugar se escalan los modos de vibración a partir de la estimación de los residuos de la descomposición en fracciones parciales de la función de respuesta en frecuencia (FRF) de las mediciones. Con este método se consiguen obtener buenas precisiones en los resultados, siempre que se consigan excitar los modos de vibración de los que queramos estimar los parámetros, lo que nos permite simular la respuesta dinámica de la estructura sin tener que recurrir a otros procedimientos como la actualización de un modelo de elementos finitos de la estructura en estudio.This paper focuses on estimating the modal parameters of the dynamic system that constitutes the pedestrian footbridge of the Science Museum of the city of Valladolid (Spain). The work consists not only of calculating natural frequencies and damping factors associated to each of the estimated modes, as many commercial software provide from acceleration measurements of tests OMA (Operational Modal Analysis) and/or EMA (Experimental modal Analysis), but the aim of this paper is to calculate the generalized masses corresponding to each of the estimated modes of the structure. For this purpose, firstly a representation of the dynamic system is obtained in the state space by SSI technique (Stochastic Subspace Identification), and secondly, vibration modes are scaled from the estimation of the residues of the decomposition in partial fractions of the frequency response function (FRF) measurements. This method gets accurate estimations in the results whose vibration modes are excited, allowing the simulation of the dynamic response of the structure without the need for updating a finite element model of the structure under study.Peer Reviewe

Estimation of modal masses for an in-service structure by transformation in the state space

Este trabajo se centra en presentar una metodología práctica para estimar los parámetros modales de estructuras en uso y se aplica a la pasarela peatonal del Museo de Ciencia de la ciudad de Valladolid, España. El trabajo consiste no sólo en calcular frecuencias propias y factores de amortiguamiento asociados a cada uno de los modos estimados, como proporcionan muchos programas comerciales a partir de los registros de aceleraciones de ensayos OMA (Operational Modal Analysis ) y/o EMA (Experimental Modal Analysis ), sino también calcular las masas generalizadas correspondientes a cada uno de los modos estimados de la estructura. Para ello, en primer lugar se obtiene una representación del sistema dinámico en el espacio de estados mediante la técnica SSI (Stochastic Subspace Identification ) y en segundo lugar, mediante la adecuada matriz de transformación se llega a la representación que permite identificar los parámetros físicos del sistema (matrices de masa, amortiguamiento y rigidez), lo que permite obtener masas modales y/o modos normalizados respecto de la matriz de masa, principal novedad de la metodología propuesta.This paper focuses on estimating the modal parameters of in-service infrastructures, applied to the pedestrian footbridge of the Science Museum of the city of Valladolid (Spain). The work consists not only on determining natural frequencies and damping factors associated to each of the estimated modes, as many commercial software provide from acceleration measurements through OMA (Operational Modal Analysis ) and/or EMA (Experimental modal Analysis ), but also to calculate the generalized masses corresponding to each of the estimated modes of the structure. For this purpose, firstly a dynamic representation of the system is obtained in the state space by SSI technique (Stochastic Subspace Identification ) and secondly, by the appropriate transformation matrix, it leads to the representation that identifies the physical parameters of the system (matrices of mass, damping and stiffness), which allows to obtain modal masses and/or normalized mode shapes with respect to the mass matrix, which is the main contribution of the practical methodology presented in this paper.Peer Reviewe

Antidepressants increase human hippocampal neurogenesis by activating the glucocorticoid receptor

Antidepressants increase adult hippocampal neurogenesis in animal models, but the underlying molecular mechanisms are unknown. In this study, we used human hippocampal progenitor cells to investigate the molecular pathways involved in the antidepressant-induced modulation of neurogenesis. Because our previous studies have shown that antidepressants regulate glucocorticoid receptor (GR) function, we specifically tested whether the GR may be involved in the effects of these drugs on neurogenesis. We found that treatment (for 3–10 days) with the antidepressant, sertraline, increased neuronal differentiation via a GR-dependent mechanism. Specifically, sertraline increased both immature, doublecortin (Dcx)-positive neuroblasts (+16%) and mature, microtubulin-associated protein-2 (MAP2)-positive neurons (+26%). This effect was abolished by the GR-antagonist, RU486. Interestingly, progenitor cell proliferation, as investigated by 5′-bromodeoxyuridine (BrdU) incorporation, was only increased when cells were co-treated with sertraline and the GR-agonist, dexamethasone, (+14%) an effect which was also abolished by RU486. Furthermore, the phosphodiesterase type 4 (PDE4)-inhibitor, rolipram, enhanced the effects of sertraline, whereas the protein kinase A (PKA)-inhibitor, H89, suppressed the effects of sertraline. Indeed, sertraline increased GR transactivation, modified GR phosphorylation and increased expression of the GR-regulated cyclin-dependent kinase-2 (CDK2) inhibitors, p27Kip1 and p57Kip2. In conclusion, our data suggest that the antidepressant, sertraline, increases human hippocampal neurogenesis via a GR-dependent mechanism that requires PKA signaling, GR phosphorylation and activation of a specific set of genes. Our data point toward an important role for the GR in the antidepressant-induced modulation of neurogenesis in humans

Session 17 Ecophysiology

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Estimation of modal parameters ofcivil structures from frequency response function

This paper focuses on estimating the modal parameters of the dynamic system that constitutes the pedestrian footbridge of the Science Museum of the city of Valladolid (Spain). The work consists not only of calculating natural frequencies and damping factors associated to each of the estimated modes, as many commercial software provide from acceleration measurements of tests OMA (Operational Modal Analysis) and/or EMA (Experimental modal Analysis), but the aim of this paper is to calculate the generalized masses corresponding to each of the estimated modes of the structure. For this purpose, firstly a representation of the dynamic system is obtained in the state space by SSI technique (Stochastic Subspace Identification), and secondly, vibration modes are scaled from the estimation of the residues of the decomposition in partial fractions of the frequency response function (FRF) measurements. This method gets accurate estimations in the results whose vibration modes are excited, allowing the simulation of the dynamic response of the structure without the need for updating a finite element model of the structure under study

Modal and dynamic analysis of a footbridge in service

Obras de ingeniería civil como las pasarelas peatonales son estructuras cada vez más esbeltas, ambiciosas y complejas en las que los efectos dinámicos producidos por las solicitaciones a las que están sometidas (peatones) pueden inducir problemas de servicio y/o amplificaciones importantes o repetitivas de los esfuerzos y deformaciones. Ésto junto con las actuales demandas sociales relativas a la percepción y confort suscitan la necesidad de integrar el análisis y diseño asistido por ordenador en la evaluación de las vibraciones generadas por las cargas a las que están sometidas. El empleo de los programas comerciales de elementos finitos no ha proliferado tanto como en otros campos de la ingeniería por la existencia de metodologías simplificativas en numerosas guías y normativas nacionales e internacionales y por la dificultad de hacer modelos realistas en el caso de estructuras complejas. Sin embargo, el conocimiento generado por el análisis de este tipo de modelos numéricos resultaría especialmente útil en las fases más tempranas del diseño de estructuras similares, tanto inicial como de las modificaciones necesarias para solucionar problemas dinámicos existentes, ya que es en estas etapas cuando se podría aplicar la mejor solución desde un punto de vista técnico y económico. En el presente artículo se describe el proceso de generación y ajuste del modelo mecánico de una pasarela actualmente en servicio y la simulación de la solicitación de dos tipos de carga: una excitación generada por un shaker y una carga peatonal, contrastando los resultados generados mediante el modelo numérico con los obtenidos experimentalmente.Civil engineering constructions like pedestrian footbridges are structures increasingly slender, ambitious and complex in which the dynamic effects caused by the loads to which they are subjected (pedestrians) may induce service problems and / or significant or repetitive amplifications of the efforts and deformations. This fact together with the current social demands related to the perception and comfort raise the need to integrate the analysis and computer-aided design in the evaluation of the vibrations generated by the loads this type of structures supports. In the specific case of finite element commercial programs, their use has not proliferated as much as in other engineering fields due to the existence of simplified methodologies in numerous national and international guidelines and regulations and the difficulty of making realistic models in the case of complex structures. However, the knowledge generated by the analysis of this type of numerical models would be especially useful in the earlier phases of the design of similar structures, so much initial as of the necessary modifications to solve existing dynamic problems, since it is in these stages when the best solution could be applied from both a technical and an economic point of view. This article describes the process of generation and updating of the mechanical finite element model (FEM) of a footbridge in service and the simulation of two types of load: an excitation generated by a shaker and a pedestrian load, contrasting the results generated by the numerical model with those obtained experimentally.Peer Reviewe

Modal and dynamic analysis of a footbridge in service

Civil engineering constructions like pedestrian footbridges are structures increasingly slender, ambitious and complex in which the dynamic effects caused by the loads to which they are subjected (pedestrians) may induce service problems and / or significant or repetitive amplifications of the efforts and deformations. This fact together with the current social demands related to the perception and comfort raise the need to integrate the analysis and computer-aided design in the evaluation of the vibrations generated by the loads this type of structures supports. In the specific case of finite element commercial programs, their use has not proliferated as much as in other engineering fields due to the existence of simplified methodologies in numerous national and international guidelines and regulations and the difficulty of making realistic models in the case of complex structures. However, the knowledge generated by the analysis of this type of numerical models would be especially useful in the earlier phases of the design of similar structures, so much initial as of the necessary modifications to solve existing dynamic problems, since it is in these stages when the best solution could be applied from both a technical and an economic point of view. This article describes the process of generation and updating of the mechanical finite element model (FEM) of a footbridge in service and the simulation of two types of load: an excitation generated by a shaker and a pedestrian load, contrasting the results generated by the numerical model with those obtained experimentally

Estimation of modal masses for an in-service structure by transformation in the state space

This paper focuses on estimating the modal parameters of in-service infrastructures, applied to the pedestrian footbridge of the Science Museum of the city of Valladolid (Spain). The work consists not only on determining natural frequencies and damping factors associated to each of the estimated modes, as many commercial software provide from acceleration measurements through OMA (Operational Modal Analysis ) and/or EMA (Experimental modal Analysis ), but also to calculate the generalized masses corresponding to each of the estimated modes of the structure. For this purpose, firstly a dynamic representation of the system is obtained in the state space by SSI technique (Stochastic Subspace Identification ) and secondly, by the appropriate transformation matrix, it leads to the representation that identifies the physical parameters of the system (matrices of mass, damping and stiffness), which allows to obtain modal masses and/or normalized mode shapes with respect to the mass matrix, which is the main contribution of the practical methodology presented in this paper

Pituitary adenylate cyclase-activating polypeptide (PACAP) decreases ischemic neuronal cell death in association with IL-6

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been reported to decrease ischemic neuronal damage and increase IL-6 secretion in rats. However, the mechanisms underlying neuroprotection are still to be fully elucidated. The present study was designed to investigate the role played by PACAP and IL-6 in mediating neuroprotection after ischemia in a null mouse. Infarct volume, neurological deficits, and cytochrome c in cytoplasm were higher in PACAP(+/−) and PACAP(−/−) mice than in PACAP(+/+) animals after focal ischemia, although the severity of response was ameliorated by the injection of PACAP38. A decrease in mitochondrial bcl-2 was also accentuated in PACAP(+/−) and PACAP(−/−) mice, but the decrease could be prevented by PACAP38 injection. PACAP receptor 1 (PAC1R) immunoreactivity was colocalized with IL-6 immunoreactivity in neurons, although the intensity of IL-6 immunoreactivity in PACAP(+/−) mice was less than that in PACAP(+/+) animals. IL-6 levels increased in response to PACAP38 injection, an effect that was canceled by cotreatment with the PAC1R antagonist. However, unlike in wild-type controls, PACAP38 treatment did not reduce the infarction in IL-6 null mice. To clarify the signaling pathway associated with the activity of PACAP and IL-6, phosphorylated STAT (signal transducer and activator of transcription) 3, ERK (extracellular signal-regulated kinase), and AKT levels were examined in PACAP(+/−) and IL-6 null mice after ischemia. Lower levels of pSTAT3 and pERK were observed in the PACAP(+/−) mice, whereas a reduction in pSTAT3 was recorded in the IL-6 null mice. These results suggest that PACAP prevents neuronal cell death after ischemia via a signaling mechanism involving IL-6