Página 1 dos resultados de 126 itens digitais encontrados em 0.019 segundos

Dynamical analysis of turbulence in fusion plasmas and nonlinear waves

Viana, Ricardo Luiz; Lopes, Sergio Roberto; Caldas, Ibere Luiz; Szezech Junior, Jose Danilo; Guimarães Filho, Zwinglio de Oliveira; Lima, Gustavo Zampier dos Santos; Galuzio, Paulo Paneque; Batista, Antonio Marcos; Kuznetsov, Yurii; Nascimento, Ivan Cunh
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.69%
Turbulence is one of the key problems of classical physics, and it has been the object of intense research in the last decades in a large spectrum of problems involving fluids, plasmas, and waves. In order to review some advances in theoretical and experimental investigations on turbulence a mini-symposium on this subject was organized in the Dynamics Days South America 2010 Conference. The main goal of this mini-symposium was to present recent developments in both fundamental aspects and dynamical analysis of turbulence in nonlinear waves and fusion plasmas. In this paper we present a summary of the works presented at this mini-symposium. Among the questions to be addressed were the onset and control of turbulence and spatio-temporal chaos. (C) 2011 Elsevier B. V. All rights reserved.; FAPESP; FAPESP; CNPq; CNPq; CAPES; CAPES; Fundacao Araucarias; Fundacao Araucarias; RNF-CNEN (Brazilian Fusion Network); RNFCNEN (Brazilian Fusion Network)

Oxidative stress in sickle cell disease: An overview of erythrocyte redox metabolism and current antioxidant therapeutic strategies

Silva, Danilo Grunig Humberto; Belini Junior, Edis; De Almeida, Eduardo Alves; Bonini-Domingos, Claudia Regina
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1101-1109
ENG
Relevância na Pesquisa
35.69%
Erythrocytes have an environment of continuous pro-oxidant generation due to the presence of hemoglobin (Hb), which represents an additional and quantitatively significant source of superoxide (O2 •-) generation in biological systems. To counteract oxidative stress, erythrocytes have a self-sustaining antioxidant defense system. Thus, red blood cells uniquely function to protect Hb via a selective barrier allowing gaseous and other ligand transport as well as providing antioxidant protection not only to themselves but also to other tissues and organs in the body. Sickle hemoglobin molecules suffer repeated polymerization/depolymerization generating greater amounts of reactive oxygen species, which can lead to a cyclic cascade characterized by blood cell adhesion, hemolysis, vaso-occlusion, and ischemia-reperfusion injury. In other words, sickle cell disease is intimately linked to a pathophysiologic condition of multiple sources of pro-oxidant processes with consequent chronic and systemic oxidative stress. For this reason, newer therapeutic agents that can target oxidative stress may constitute a valuable means for preventing or delaying the development of organ complications. © © 2013 Elsevier Inc. All rights reserved.

Unmasking of an unusual myelin basic protein epitope during the process of myelin degeneration in humans: a potential mechanism for the generation of autoantigens.

Matsuo, A.; Lee, G. C.; Terai, K.; Takami, K.; Hickey, W. F.; McGeer, E. G.; McGeer, P. L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1997 EN
Relevância na Pesquisa
35.69%
A rabbit antiserum (anti-EP), induced against a synthetic peptide corresponding to residues 68 to 86 of guinea pig myelin basic protein, powerfully immunostained abnormal-appearing oligodendrocytic processes and cell bodies in demyelinating areas associated with multiple sclerosis plaques. However, it failed to recognize any structures in normal human, rat, or guinea pig brain. The antiserum recognized the synthetic peptide QDENPVV, which corresponds to human myelin basic protein residues 82 to 88. Immunoabsorption with this peptide eliminated immunohistochemical staining. By contrast, several commercial antibodies recognizing nearby sequences of human myelin basic protein intensely stained all myelinated structures in both normal and multiple sclerosis tissue. The unusual epitope recognized by anti-EP appears to be accessible only in areas of myelin degeneration. If insults occur that repeatedly expose a region of MBP normally sheltered from immunosurveillance, a self-sustaining immune reaction might result.

Biomechanical simulations of the spine deformation process in adolescent idiopathic scoliosis from different pathogenesis hypotheses

Villemure, I.; Aubin, C. E.; Dansereau, J.; Labelle, H.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36%
It is generally recognized that progressive adolescent idiopathic scoliosis (AIS) evolves within a self-sustaining biomechanical process involving asymmetrical growth modulation of vertebrae due to altered spinal load distribution. A biomechanical finite element model of normal thoracic and lumbar spine integrating vertebral growth was used to simulate the progression of spinal deformities over 24 months. Five pathogenesis hypotheses of AIS were represented, using an initial geometrical eccentricity (gravity line imbalance of 3 mm or 2° rotation) at the thoracic apex to trigger the self-sustaining deformation process. For each simulation, regional (thoracic Cobb angle, kyphosis) and local scoliotic descriptors (axial rotation and wedging of the thoracic apical vertebra) were evaluated at each growth cycle. The simulated AIS pathogeneses resulted in the development of different scoliotic deformities. Imbalance of 3 mm in the frontal plane, combined or not with the sagittal plane, resulted in the closest representation of typical scoliotic deformities, with the thoracic Cobb angle progressing up to 39° (26° when a sagittal offset was added). The apical vertebral rotation increased by 7° towards the convexity of the curve, while the apical wedging increased to 8.5° (7.3° with the sagittal eccentricity) and this deformity evolved towards the vertebral frontal plane. A sole eccentricity in the sagittal plane generated a non-significant frontal plane deformity. Simulations involving an initial rotational shift (2°) in the transverse plane globally produced relatively small and non-typical scoliotic deformations. Overall...

qDIET: toward an automated, self-sustaining knowledge base to facilitate linking point-of-sale grocery items to nutritional content

Chidambaram, Valliammai; Brewster, Philip J.; Jordan, Kristine C.; Hurdle, John F.
Fonte: American Medical Informatics Association Publicador: American Medical Informatics Association
Tipo: Artigo de Revista Científica
Publicado em 16/11/2013 EN
Relevância na Pesquisa
55.9%
The United States, indeed the world, struggles with a serious obesity epidemic. The costs of this epidemic in terms of healthcare dollar expenditures and human morbidity/mortality are staggering. Surprisingly, clinicians are ill-equipped in general to advise patients on effective, longitudinal weight loss strategies. We argue that one factor hindering clinicians and patients in effective shared decision-making about weight loss is the absence of a metric that can be reasoned about and monitored over time, as clinicians do routinely with, say, serum lipid levels or HgA1C. We propose that a dietary quality measure championed by the USDA and NCI, the HEI-2005/2010, is an ideal metric for this purpose. We describe a new tool, the quality Dietary Information Extraction Tool (qDIET), which is a step toward an automated, self-sustaining process that can link retail grocery purchase data to the appropriate USDA databases to permit the calculation of the HEI-2005/2010.

Application of Electro-Fenton Technology to Remediation of Polluted Effluents by Self-Sustaining Process

Fernández de Dios, Maria Ángeles; Iglesias, Olaia; Pazos, Marta; Sanromán, Maria Ángeles
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em 26/02/2014 EN
Relevância na Pesquisa
45.75%
The applicability of electro-Fenton technology to remediation of wastewater contaminated by several organic pollutants such as dyes and polycyclic aromatic hydrocarbons has been evaluated using iron-enriched zeolite as heterogeneous catalyst. The electro-Fenton technology is an advanced oxidation process that is efficient for the degradation of organic pollutants, but it suffers from the high operating costs due to the need for power investment. For this reason, in this study microbial fuel cells (MFCs) were designed in order to supply electricity to electro-Fenton processes and to achieve high treatment efficiency at low cost. Initially, the effect of key parameters on the MFC power generation was evaluated. Afterwards, the degradation of Reactive Black 5 dye and phenanthrene was evaluated in an electro-Fenton reactor, containing iron-enriched zeolite as catalyst, using the electricity supplied by the MFC. Near complete dye decolourization and 78% of phenanthrene degradation were reached after 90 min and 30 h, respectively. Furthermore, preliminary reusability tests of the developed catalyst showed high degradation levels for successive cycles. The results permit concluding that the integrated system is adequate to achieve high treatment efficiency with low electrical consumption.

FibronectinEDA Promotes Chronic Cutaneous Fibrosis Through Toll-like Receptor Signaling

Bhattacharyya, Swati; Tamaki, Zenshiro; Wang, Wenxia; Hinchcliff, Monique; Hoover, Paul; Getsios, Spiro; White, Eric S.; Varga, John
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 16/04/2014 EN
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35.8%
Scleroderma is a progressive autoimmune disease affecting multiple organs. Fibrosis, the hallmark of scleroderma, represents transformation of self-limited wound healing into a deregulated self-sustaining process. The factors responsible for maintaining persistent fibroblast activation in scleroderma and other conditions with chronic fibrosis are not well understood. Toll-like receptor 4 (TLR4) and its damage-associated endogenous ligands are implicated in immune and fibrotic responses. We now show that fibronectin extra domain A (FnEDA) is an endogenous TLR4 ligand markedly elevated in the circulation and lesional skin biopsies from patients with scleroderma, as well as in mice with experimentally induced cutaneous fibrosis. Synthesis of FnEDA was preferentially stimulated by transforming growth factor–β in normal fibroblasts and was constitutively up-regulated in scleroderma fibroblasts. Exogenous FnEDA was a potent stimulus for collagen production, myofibroblast differentiation, and wound healing in vitro and increased the mechanical stiffness of human organotypic skin equivalents. Each of these profibrotic FnEDA responses was abrogated by genetic, RNA interference, or pharmacological disruption of TLR4 signaling. Moreover, either genetic loss of FnEDA or TLR4 blockade using a small molecule mitigated experimentally induced cutaneous fibrosis in mice. These observations implicate the FnEDA-TLR4 axis in cutaneous fibrosis and suggest a paradigm in which aberrant FnEDA accumulation in the fibrotic milieu drives sustained fibroblast activation via TLR4. This model explains how a damage-associated endogenous TLR4 ligand might contribute to converting self-limited tissue repair responses into intractable fibrogenesis in chronic conditions such as scleroderma. Disrupting sustained TLR4 signaling therefore represents a potential strategy for the treatment of fibrosis in scleroderma.

Managing the transition toward self-sustaining alternative fuel vehicle markets : policy analysis using a dynamic behavioral spatial model

Supple, Derek R. (Derek Richard)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 97 p.
ENG
Relevância na Pesquisa
45.9%
Designing public policy or industry strategy to bolster the transition to alternative fuel vehicles (AFVs) is a formidable challenge as demonstrated by historical failed attempts. The transition to new fuels occurs within a dynamically complex system with many distributed actors, long time delays, several important feedback relationships, and multiple tipping points. A broad-boundary, behavioral, dynamic model with explicit spatial structure was previously developed to represent the most important AFV transition barriers. Using California as an illustrative testing region, the model simulates the spatial diffusion of entrant vehicle/fuel technology pairs individually or in competition with other entrants. In this work, the integrated model is carefully parameterized for various specific alternative vehicle technologies. Structural and parametric sensitivity analyses are used to build understanding of system behavior and to identify policy leverage points or the need for further model calibration.; (cont.) The qualitative impacts of policies are tested individually and then in multi-policy combinations to find synergies. Under plausible assumptions and strong policies, AFVs can achieve successful diffusion but this process requires long time periods. Findings indicate some commonly suggested policies may provide little leverage and be very costly. The analysis reveals the importance of designing policy cognizant of the system structure underlying its dynamic behavior. Several examples demonstrate how policy leverage varies with context such as key attributes of the alternative vehicle technology. Broadly...

Short-Term and Long-Term Effects of United Nations Peace Operations

Sambanis, Nicholas
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
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35.69%
Earlier studies have shown that United Nations peace operations make a positive contribution to peacebuilding efforts after civil wars. But do these effects carry over to the period after the peacekeepers leave? And how do the effects of UN peace operations interact with other determinants of peacebuilding in the long run? The author addresses these questions using a revised version of the Doyle and Sambanis dataset and applying different estimation methods to estimate the short-term and long-term effects of UN peace missions. He finds that UN missions have robust, positive effects on peacebuilding in the short term. UN missions can help parties implement peace agreements but the UN cannot fight wars, and UN operations contribute more to the quality of the peace where peace is based on participation, than to the longevity of the peace, where peace is simply the absence of war. The effects of UN missions are also felt in the long run, but they dissipate over time. What is missing in UN peacebuilding is a strategy to foster the self-sustaining economic growth that could connect increased participation with sustainable peace.

State-Community Synergies in Development : Laying the Basis for Collective Action

Das Gupta, Monica; Grandvoinnet, Helene; Romani, Mattia
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research; Publications & Research :: Policy Research Working Paper
EN_US
Relevância na Pesquisa
35.75%
If states would interact more synergistically with communities, they could tap local energies and resources for development-- and help create a development-oriented society and polity in the process. The authors analyze experience in several countries to identify the actions required for state-community synergies in development. Two actions that seem especially important: 1) Broadening the distribution of power within communities, to facilitate collective action and reduce the potential for local capture. In rural areas, much can be done by expanding access to credit, strengthening tenants' rights, and expanding non-crop sources of income. 2) Creating state-community alliances to improve the effectiveness of local public sector institutions and the delivery of services. Case studies from East Asia and Latin America show that such alliances can effect rapid improvements in local institutions, benefiting not only communities but also politicians seeking support and legitimacy. Local bureaucratic reform, combined with more egalitarian community social organizations, allows the creation of powerful coalitions and synergies for rapid, self-sustaining development. This model has been used to achieve outcomes ranging from better health care and drought relief to the generation of agrarian and industrial economic growth. In China and Taiwan...

Proceso de reestructuración y fortalecimiento institucional Asociación Santa Cruz

Henao Guáqueta, Felipe
Fonte: Facultad de Administración Publicador: Facultad de Administración
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/acceptedVersion Formato: application/pdf
Publicado em 11/12/2012 SPA
Relevância na Pesquisa
46.04%
La Asociación Santa Cruz es una organización que lleva más de 17 años generando espacios de formación para niños, adolescentes y jóvenes. Los proyectos que ejecuta son programas auténticos para la juventud, atractivos para ellos y para quienes los forman (Entidades educativas y núcleos familiares). Por medio de la educación experiencial y las actividades al aire libre hemos encontrado la herramienta prefecta para formar de una manera actual y profunda. Los resultados del presente proceso se evidencian de la siguiente manera: a) estructuración de un organigrama funcional para la organización. b) Realización de los manuales de funciones y procedimientos de todos los trabajadores de la organización. c) Realización de la proyección financiera por parte del proyecto EKO Campos de verano. d) Análisis del mercado que permite una proyección fiable en ventas. Gracias al trabajo realizado en este proceso de mejora se entrega un plan de acción que potencializa la organización para que cumpliendo con todos los parámetros dados podamos generar una organización autosostenible que aumenta sus clientes anualmente en al menos un 20%, generando un superávit anual de hasta $200.000.000 en los primeros 5 años y de hasta $600.000.000 en los años 5 al 10. Gracias al proceso de mejora la asociación se convertirá en la organización Colombiana que más campos de verano residenciales realiza al año: 8 para el 2012. Es una asociación que puede auntosostenerse gracias a proyectos propios y no depende sino en un 20% de las donaciones que recibe. El medio de la educación no formal es una industria con un potencial muy grande en Colombia ya que es una oferta débil y pequeña para una demanda grande y con una necesidad fácil de identificar. Implementando este proceso de reestructuración la asociación tendrá la oportunidad de atender una población de alrededor de 300 personas para el 2012 y podrá acercarse a las 1.200 para el año 2022.; Centro de Estudios Empresariales para la Perdurabilidad; Santa Cruz Asociation is an organization that throughout 17 years has created formation spaces for children and youth. The running projects are authentic programs for youth...

Turbulent patterns in wall-bounded flows: a Turing instability?

Manneville, Paul
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/05/2012
Relevância na Pesquisa
35.69%
In their way to/from turbulence, plane wall-bounded flows display an interesting transitional regime where laminar and turbulent oblique bands alternate, the origin of which is still mysterious. In line with Barkley's recent work about the pipe flow transition involving reaction-diffusion concepts, we consider plane Couette flow in the same perspective and transform Waleffe's classical four-variable model of self-sustaining process into a reaction-diffusion model. We show that, upon fulfillment of a condition on the relative diffusivities of its variables, the featureless turbulent regime becomes unstable against patterning as the result of a Turing instability. A reduced two-variable model helps us to delineate the appropriate region of parameter space. An {\it intrinsic} status is therefore given to the pattern's wavelength for the first time. Virtues and limitations of the model are discussed, calling for a microscopic support of the phenomenological approach.; Comment: to appear in Europhysics Letters in a different format

Physics of Flow Instability and Turbulent Transition in Shear Flows

Dou, Hua-Shu
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.69%
In this paper, the physics of flow instability and turbulent transition in shear flows is studied by analyzing the energy variation of fluid particles under the interaction of base flow with a disturbance. For the first time, a model derived strictly from physics is proposed to show that the flow instability under finite amplitude disturbance leads to turbulent transition. The proposed model is named as "energy gradient method." It is demonstrated that it is the transverse energy gradient that leads to the disturbance amplification while the disturbance is damped by the energy loss due to viscosity along the streamline. It is also shown that the threshold of disturbance amplitude obtained is scaled with the Reynolds number by an exponent of -1, which exactly explains the recent modern experimental results by Hof et al. for pipe flow. The mechanism for velocity inflection and hairpin vortex formation are explained with reference to analytical results. Following from this analysis, it can be demonstrated that the critical value of the so called energy gradient parameter Kmax is constant for turbulent transition in wall bounded parallel flows, and this is confirmed by experiments and is about 370-389. The location of instability initiation in the flow field accords well with the experiments for both pipe Poiseuille flow (r/R=0.58) and plane Poiseuille flow (y/h=0.58). It is also inferred from the proposed method that the transverse energy gradient can serve as the power for the self-sustaining process of wall bounded turbulence. Finally...

On self-sustaining processes in Rayleigh-stable rotating plane Couette flows and subcritical transition to turbulence in accretion disks

Rincon, F.; Ogilvie, G. I.; Cossu, C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/12/2006
Relevância na Pesquisa
56.07%
Subcritical transition to turbulence in Keplerian accretion disks is still a controversial issue and some theoretical progress is required in order to determine whether or not this scenario provides a plausible explanation for the origin of angular momentum transport in non-magnetized accretion disks. Motivated by the recent discoveries of exact nonlinear steady self-sustaining solutions in linearly stable non-rotating shear flows, we attempt to compute similar solutions in Rayleigh-stable rotating plane Couette flows and to identify transition mechanisms in such flows by combining nonlinear continuation methods and asymptotic theory. We obtain exact nonlinear solutions for Rayleigh-stable cyclonic regimes but show that it is not possible to compute solutions for Rayleigh-stable anticyclonic regimes, including Keplerian flow, using similar techniques. We also present asymptotic descriptions of these various problems at large Reynolds numbers that provide some insight into the differences between the non-rotating and Rayleigh-stable anticyclonic regimes and derive some necessary conditions for mechanisms analogous to the non-rotating self-sustaining process to be present in flows on the Rayleigh line. Our results demonstrate that subcritical transition mechanisms cannot be identified in wall-bounded Rayleigh-stable anticyclonic shear flows by transposing directly the phenomenology of subcritical transition in cyclonic and non-rotating wall-bounded shear flows. Asymptotic developments...

Turbulent bands in a planar shear flow without walls

Chantry, Matthew; Tuckerman, Laurette S.; Barkley, Dwight
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/06/2015
Relevância na Pesquisa
35.69%
Turbulent bands are a ubiquitous feature of transition in wall-bounded shear flows. We show that these are also a robust feature of Waleffe flow -- a shear flow driven by a sinusoidal body force between stress-free boundaries -- thus demonstrating that rigid walls are not a prerequisite for band formation. Exploiting the Fourier dependence of Waleffe forcing, we construct a model flow that uses only four wavenumbers in the shear direction and yet captures uniform turbulence, turbulent bands, and spot expansion. The model is simultaneously a reduction of the full Navier-Stokes equations and an extension of minimal models of the self-sustaining process of shear turbulence.; Comment: 5 pages, 4 figures

Disruption of SSP/VWI states by a stable stratification

Eaves, T. S.; Caulfield, C. P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.69%
We identify `minimal seeds' for turbulence, i.e. initial conditions of the smallest possible total perturbation energy density $E_c$ that trigger turbulence from the laminar state, in stably stratified plane Couette flow using the `direct-adjoint-looping' (DAL) method for finding nonlinear optimal perturbations that optimise the time averaged total dissipation of energy in the flow. These minimal seeds are located adjacent to the edge manifold, the manifold in state space that separates trajectories which transition to turbulence from those which eventually decay to the laminar state. The edge manifold is also the stable manifold of the system's `edge state'. The trajectories from the minimal seed initial conditions spend a large amount of time in the vicinity of some states: the edge state; another state contained within the edge manifold; or even in dynamically slowly varying regions of the edge manifold, allowing us to investigate the effects of a stable stratification on any coherent structures associated with such states. In unstratified plane Couette flow, these coherent structures are manifestations of the self-sustaining process (SSP) deduced on physical grounds by Waleffe (1997), or equivalently finite Reynolds number solutions of the vortex-wave interaction (VWI) asymptotic equations initially derived mathematically by Hall & Smith (1991). The stratified coherent states we identify at moderate $Re$ display an altered form from their unstratified counterparts for bulk Richardson numbers $Ri_B=\textit{O}(Re^{-1})$...

A self-sustaining nonlinear dynamo process in Keplerian shear flows

Rincon, F.; Ogilvie, G. I.; Proctor, M. R. E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/05/2007
Relevância na Pesquisa
56%
A three-dimensional nonlinear dynamo process is identified in rotating plane Couette flow in the Keplerian regime. It is analogous to the hydrodynamic self-sustaining process in non-rotating shear flows and relies on the magneto-rotational instability of a toroidal magnetic field. Steady nonlinear solutions are computed numerically for a wide range of magnetic Reynolds numbers but are restricted to low Reynolds numbers. This process may be important to explain the sustenance of coherent fields and turbulent motions in Keplerian accretion disks, where all its basic ingredients are present.; Comment: 4 pages, 7 figures, accepted for publication in Physical Review Letters

A minimal model of self-sustaining turbulence

Thomas, Vaughan; Farrell, Brian F.; Ioannou, Petros J.; Gayme, Dennice F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/01/2015
Relevância na Pesquisa
56.07%
In this work we examine the turbulence maintained in a Restricted Nonlinear (RNL) model of plane Couette flow. This model is a computationally efficient approximation of the second order statistical state dynamics (SSD) obtained by partitioning the flow into a streamwise averaged mean flow and perturbations about that mean, a closure referred to herein as the RNL$_\infty$ model. The RNL model investigated here employs a single member of the infinite ensemble that comprises the covariance of the RNL$_\infty$ dynamics. The RNL system has previously been shown to support self-sustaining turbulence with a mean flow and structural features that are consistent with DNS. This paper demonstrates that the RNL system's self-sustaining turbulent state is supported by a small number of streamwise varying modes, which form the natural support for the self-sustaining process maintaining RNL turbulence. Remarkably, truncation of the RNL system's support to a single streamwise varying mode can suffice to sustain the turbulent state. The close correspondence between RNL simulations and DNS that has been previously observed along with the results presented here suggest that the fundamental mechanisms underlying wall-turbulence can be analyzed using these highly simplified RNL systems.; Comment: 9 Figures...

Clean (“Green”) Ion-Exchange Technologies. 4. High-Ca-Selectivity Ion-Exchange Material for Self-Sustaining Decalcification of Mineralized Waters Process

Muraviev, Dmitri; Khamizov, Ruslan Kh.; Tikhonov, Nikolai A.; Gómez-Morales, J.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
Relevância na Pesquisa
46%
This paper (the fourth in a series) reports the results of a theoretical and experimental study of the decalcification of seawater on different ion-exchange sorbents by simultaneous use of electroselectivity reversal and ion-exchange isothermal supersaturation (IXISS) effects. A detailed evaluation of the influence of the sorbent properties on the efficiency of the IXISS-based self-sustaining seawater decalcification process was carried out through a series of computer experiments using a mathematical model of the dynamics of ion exchange. It was found that the best sorbent to be used in the process is a modified A-type zeolite. The modification of the zeolite includes sequential treatment of the initial ion exchanger with dilute magnesium-containing solution (or seawater) and concentrated sodium salt solution. The first treatment was carried out at elevated temperature [15−20 °C higher than the temperature at which the modified zeolite (MZ) is expected to be used, Tex], and the second was performed at Tex. The complete regeneration of the MZ after the calcium sorption cycle was carried out with the calcium-free brine produced by the seawater desalination unit. The process is continuous and operates in the closed-cycle mode.; Part of this work was supported by Research Grants ND-2000 and ND-2300 from the International Science Foundation and by grants from the Science and Technology Programs of Russian Federation “Global Ocean” (Grant 02.08.1) and the Russian Foundation for Basic Research (Grant 02-03-33144). The Ministry of Science and Technology of Spain is acknowledged with thanks for the financial support of D.M. within the Program “Ramon y Cajal”.; Peer reviewed

A streamwise-constant model of turbulent pipe flow

Bourguignon, Jean-Loup; McKeon, Beverley J.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /09/2011
Relevância na Pesquisa
35.9%
A streamwise-constant model is presented to investigate the basic mechanisms responsible for the change in mean flow occuring during pipe flow transition. The model is subject to two different types of forcing: a simple forcing of the axial momentum equation via a deterministic form for the streamfunction and a stochastic forcing of the streamfunction equation. Using a single forced momentum balance equation, we show that the shape of the velocity profile is robust to changes in the forcing profile and that both linear non-normal and nonlinear effects are required to capture the change in mean flow associated with transition to turbulence. The particularly simple form of the model allows for the study of the momentum transfer directly by inspection of the equations. The distribution of the high- and low-speed streaks over the cross-section of the pipe produced by our model is remarkably similar to one observed in the velocity field near the trailing edge of the puff structures present in pipe flow transition. Under stochastic forcing, the model exhibits a quasi-periodic self-sustaining cycle characterized by the creation and subsequent decay of “streamwise-constant puffs,” so-called due to the good agreement between the temporal evolution of their velocity field and the projection of the velocity field associated with three-dimensional puffs in a frame of reference moving at the bulk velocity. We establish that the flow dynamics are relatively insensitive to the regeneration mechanisms invoked to produce near-wall streamwise vortices...