Energy dissipation in skimming flow at stepped spillways with 1V:1H slope

[EN] The energy dissipation along the chute is the stepped spillway’s main function. With those structures the reduction of residual energy at the dam’s toe is sought, allowing lower cost with the construction of dissipation structures downstream the spillway. The study characterizes energy dissipation on sliding flow in skimming flow on stepped spillways with slope of 45° (1V:1H), through experimental analysis in 4 physical models, one with flat chute and three stepped chutes with steps of 30mm, 60mm and 90mm. Aspects related to flow’s energy dissipation were evaluated, especially those related to mean levels of water on aerated and non-aerated flow regions, allowing the establishment of representative dimensionless parameters of dissipated energy along the stepped chute.[PT] A dissipação de energia ao longo da calha é a principal função dos vertedouros em degraus. Com essas estruturas se busca a redução da energia residual no pé da barragem, proporcionando menores custos com a construção de estruturas de dissipação a jusante do vertedouro. Este estudo caracteriza a dissipação da energia do escoamento deslizante sobre turbilhões em vertedouros em degraus com declividade de 45° (1V:1H) através da análise experimental em quatro modelos físicos, sendo um com calha lisa e três com calhas em degraus de alturas constantes iguais a 30mm, 60mm e 90mm. Foram avaliados os aspectos relacionados a dissipação de energia do escoamento, especialmente aqueles relacionados aos níveis médios da água nas regiões aeradas e não aeradas do fluxo, permitindo o estabelecimento de parâmetros adimensionais representativos da energia dissipada ao longo da calha em degrausÀ Eletrobrás-Furnas a partir do projeto de Pesquisa e Desenvolvimento “Características dos Escoamentos sobre Vertedouros em Degraus”, inserido no programa de P&D ANEEL. Aos engenheiros Jaime Federici Gomes e Rafael André Wiest pela colaboração na equipe do projeto.Dai Prá, M.; Priebe, P.; Sanagiotto, D.; Marques, M. (2016). Dissipação de energia do escoamento deslizante sobre turbilhões em vertedouros em degraus de declividade 1V:1H. Ingeniería del Agua. 20(1):1-12. doi:10.4995/ia.2016.3714.SWORD112201Chamani, M. R., Rajaratnam, N. (1999). Characteristics of Skimming Flow over Stepped Spillways. Journal of Hydraulic Engineering, 125(4), 361-368. http://dx.doi.org/10.1061/(ASCE)0733-9429(1999)125:4(361)Chanson, H. (1993). Stepped Spillway Flow and Air Entrainment. Canadian Journal of Civil Engineering, 20(3), 422-435. http://dx.doi.org/10.1139/l93-057Chanson, H. (1995). History of Stepped Channels and Spillways: a Rediscovery of the "Wheel". Canadian Journal of Civil Engineering, 22(2), 247-259. http://dx.doi.org/10.1139/l95-034Dai Prá, M. (2004). Características do Escoamento sobre Vertedouro em Degraus de Declividade 1V:1H. 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Avaliação da Energia Residual a Jusante de Vertedouros em Degraus com Fluxo em Regime Skimming Flow. Dissertação de Mestrado, Universidade Federal do Paraná. Curitiba: UFPR, 141 p.Rajaratnam, N. (1990). Skimming Flow in Stepped Spillways. Journal of Hydraulic Engineering, 116(4), 587-591. http://dx.doi.org/10.1061/(ASCE)0733-9429(1990)116:4(587)Rice, C.E., Kadavy, K.C. (1996). Model Study of a Roller Compacted Concrete Stepped Spillway. Journal of Hydraulic Engineering, 122(6), 292-297. http://dx.doi.org/10.1061/(ASCE)0733-9429(1996)122:6(292)Sanagiotto, D.G. (2003). Características do Escoamento sobre Vertedouros em Degraus de Declividade 1V:0,75H. Dissertação de Mestrado, Universidade Federal do Rio Grande do Sul. Porto Alegre: UFRGS, 118 p.Sorensen, R.M. (1985). Stepped Spillway Hydraulic Model Investigation. Journal of Hydraulic Engineering, 111(12), 1461-1472.Stephenson, D. (1991). Energy Dissipation down Stepped Spillways. 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Age-related shift in LTD is dependent on neuronal adenosine A(2A) receptors interplay with mGluR5 and NMDA receptors

Synaptic dysfunction plays a central role in Alzheimer's disease (AD), since it drives the cognitive decline. An association between a polymorphism of the adenosine A2A receptor (A2AR) encoding gene-ADORA2A, and hippocampal volume in AD patients was recently described. In this study, we explore the synaptic function of A2AR in age-related conditions. We report, for the first time, a significant overexpression of A2AR in hippocampal neurons of aged humans, which is aggravated in AD patients. A similar profile of A2AR overexpression in rats was sufficient to drive age-like memory impairments in young animals and to uncover a hippocampal LTD-to-LTP shift. This was accompanied by increased NMDA receptor gating, dependent on mGluR5 and linked to enhanced Ca(2+) influx. We confirmed the same plasticity shift in memory-impaired aged rats and APP/PS1 mice modeling AD, which was rescued upon A2AR blockade. This A2AR/mGluR5/NMDAR interaction might prove a suitable alternative for regulating aberrant mGluR5/NMDAR signaling in AD without disrupting their constitutive activity

Adsorption dynamics of hydrophobically modified polymers at an air-water interface

The adsorption dynamics of a series of hydrophobically modified polymers, PAAαCn, at the air-water interface is studied by measuring the dynamic surface tension. The PAAαCn are composed of a poly(acrylic acid) backbone grafted with a percentage α of C8 or C12 alkyl moieties, at pH conditions where the PAA backbone is not charged. The observed adsorption dynamics is very slow and follows a logarithmic behavior at long times indicating the building of an energy barrier which grows over time. After comparison of our experimental results to models from the literature, a new model which accounts for both the deformation of the incoming polymer coils as well as the deformation of the adsorbed pseudo-brush is described. This model enables to fit very well the experimental data. The two fitting parameters give expected values for the monomer size and for the area per adsorbed polymer chain.This article is uploaded in "arXiv.org" https://arxiv.org/abs/1706.0710