Home About us Contact
|
Home About us Contact | ||
|
|
||
Flow Control (flow + control)
Kinds of Flow Control Selected AbstractsRecent Progress in Dielectric Barrier Discharges for Aerodynamic Flow ControlCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-2 2007G. I. Font Abstract Plasma actuators are electrical devices that use an atmospheric pressure dielectric barrier discharge for flow control. They have been employed successfully to promote boundary layer attachment. Simulations have been carried out of a plasma actuator using Direct-Simulation-Monte-Carlo and Particle-in-Cell methods. This work summarizes some recent results including: 1) the method by which force is imparted by the actuator to the neutral flow, 2) the effect of electronegative gasses, such as oxygen, and 3) the effects on the neutral flow of the plasma force. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Knowledge creation and transfer in a cross-cultural context,empirical evidence from Tyco Flow ControlKNOWLEDGE AND PROCESS MANAGEMENT: THE JOURNAL OF CORPORATE TRANSFORMATION, Issue 3 2007Florian Kohlbacher The capability of multinational corporations (MNCs) to create and efficiently combine knowledge from different locations around the world is becoming increasingly important as a determinant of competitive advantage and will be more and more critical to their success and survival. Consequently, cultural differences and cross-cultural contexts play an essential role for and significantly influence global knowledge creation and management. This paper presents a case study resulting from a current empirical research project on knowledge management and the transfer of knowledge within organizations of MNCs. We describe and analyze the efforts of global market leader Tyco Flow Control (TFC)'s Japanese subsidiary KTM to transfer relevant,and often highly tacit,knowledge to a newly acquired production site in Taiwan. Challenges and difficulties encountered in the process of global knowledge management,in this case the transfer of knowledge from Japan to Taiwan,as well as the creation of new knowledge locally and its feedback,are illustrated and carefully examined. Finally, we discuss our findings and highlight practical implications for managers and international corporations in a global business environment. Copyright © 2007 John Wiley & Sons, Ltd. [source] An analysis of VI Architecture primitives in support of parallel and distributed communicationCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 1 2002Andrew Begel Abstract We present the results of a detailed study of the Virtual Interface (VI) paradigm as a communication foundation for a distributed computing environment. Using Active Messages and the Split-C global memory model, we analyze the inherent costs of using VI primitives to implement these high-level communication abstractions. We demonstrate a minimum mapping cost (i.e. the host processing required to map one abstraction to a lower abstraction) of 5.4 ,s for both Active Messages and Split-C using four-way 550 MHz Pentium III SMPs and the Myrinet network. We break down this cost to the use of individual VI primitives in supporting flow control, buffer management and event processing and identify the completion queue as the source of the highest overhead. Bulk transfer performance plateaus at 44 Mbytes/s for both implementations are due to the addition of fragmentation requirements. Based on this analysis, we present the implications for the VI successor, Infiniband. Copyright © 2002 John Wiley & Sons, Ltd. [source] Recent Progress in Dielectric Barrier Discharges for Aerodynamic Flow ControlCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-2 2007G. I. Font Abstract Plasma actuators are electrical devices that use an atmospheric pressure dielectric barrier discharge for flow control. They have been employed successfully to promote boundary layer attachment. Simulations have been carried out of a plasma actuator using Direct-Simulation-Monte-Carlo and Particle-in-Cell methods. This work summarizes some recent results including: 1) the method by which force is imparted by the actuator to the neutral flow, 2) the effect of electronegative gasses, such as oxygen, and 3) the effects on the neutral flow of the plasma force. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Confinement effects on the morphology of photopatterned porous polymer monoliths for capillary and microchip electrophoresis of proteinsELECTROPHORESIS, Issue 14 2008Mei He Abstract We find that the morphology of porous polymer monoliths photopatterned within capillaries and microchannels is substantially influenced by the dimensions of confinement. Porous polymer monoliths were prepared by UV-initiated free-radical polymerization using either the hydrophilic or hydrophobic monomers 2-hydroxyethyl methacrylate or butyl methacrylate, cross-linker ethylene dimethacrylate and different porogenic solvents to produce bulk pore diameters between 3.2 and 0.4,µm. The extent of deformation from the bulk porous structure under confinement strongly depends on the ratio of characteristic length of the confined space to the monolith pore size. The effects are similar in cylindrical capillaries and D-shaped microfluidic channels. Bulk-like porosity is observed for a confinement dimension to pore size ratio >10, and significant deviation is observed for a ratio <5. At the extreme limit of deformation a smooth polymer layer ,300 nm thick is formed on the surface of the capillary or microchannel. Surface tension or wetting also plays a role, with greater wetting enhancing deformation of the bulk structure. The films created by extreme deformation provide a rapid and effective strategy to create robust wall coatings, with the ability to photograft various surface chemistries onto the coating. This approach is demonstrated through cationic films used for electroosmotic flow control and neutral hydrophilic coatings for electrophoresis of proteins. [source] Effects of percutaneous transluminal coronary angioplasty on coronary adenosine concentrations in humansEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2 2000Paganelli Background Even minimal amounts of adenosine is released during myocardial ischemia. Its role in coronary blood flow has been extensively studied, but little is known about its behaviour during percutaneous transluminal angioplasty (PTCA) in man. Material and methods Using in situ samples the aim of this study was to evaluate adenosine plasma concentration before and after PTCA. Ten patients (8 men and 2 women, mean age 65 ± 9 years) with a single stenosis of the left anterior descending coronary artery (LAD) of at least 70% and 10 healthy volunteers (4 men and 6 women, mean age 55 ± 9 years) were included in the study. Results and discussion We found that there is a close relationship between the degree of the stenosis and the adenosine concentrations in the great cardiac vein and in the LAD, and that after PTCA there is a drop in adenosine concentration downstream from the stenosis. This study confirms the crucial role of adenosine in coronary blood flow control. [source] Numerical procedure for fluid flow in a pipe performing transverse oscillationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 5 2007M. Ragulskis Abstract Numerical procedure for the analysis of fluid flow in a tube performing transverse oscillations is developed. The formulation of the problem is presented in differential equation form and a finite element model is developed leading to the first-order matrix differential equation. The fluid flow model incorporates transverse oscillation of the boundary through the convective inertia terms. Modal decomposition of the solution is performed and a technique for numerical solution of the finite element problem incorporating parametric vibrations is developed. Numerical results provide insight into the problem of fluid flow control by transverse vibrations of the tube. Copyright © 2006 John Wiley & Sons, Ltd. [source] Interface tracking finite volume method for complex solid,fluid interactions on fixed meshesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2002H. S. Udaykumar Abstract We present a numerical technique for computing flowfields around moving solid boundaries immersed in fixed meshes. The mixed Eulerian,Lagrangian framework treats the immersed boundaries as sharp solid,fluid interfaces and a conservative finite volume formulation allows boundary conditions at the moving surfaces to be exactly applied. A semi-implicit second-order accurate spatial and temporal discretization is employed with a fractional-step scheme for solving the flow equations. A multigrid accelerator for the pressure Poisson equations has been developed to apply in the presence of multiple embedded solid regions on the mesh. We present applications of the method to two types of problems: (a) solidification in the presence of flows and particles, (b) fluid,structure interactions in flow control. In both these problems, the sharp interface method presents advantages by being able to track arbitrary interface motions, while capturing the full viscous, unsteady dynamics. Copyright © 2001 John Wiley & Sons, Ltd. [source] Optimal flow control for Navier,Stokes equations: drag minimizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2007L. Dedč Abstract Optimal control and shape optimization techniques have an increasing role in Fluid Dynamics problems governed by partial differential equations (PDEs). In this paper, we consider the problem of drag minimization for a body in relative motion in a fluid by controlling the velocity through the body boundary. With this aim, we handle with an optimal control approach applied to the steady incompressible Navier,Stokes equations. We use the Lagrangian functional approach and we consider the Lagrangian multiplier method for the treatment of the Dirichlet boundary conditions, which include the control function itself. Moreover, we express the drag coefficient, which is the functional to be minimized, through the variational form of the Navier,Stokes equations. In this way, we can derive, in a straightforward manner, the adjoint and sensitivity equations associated with the optimal control problem, even in the presence of Dirichlet control functions. The problem is solved numerically by an iterative optimization procedure applied to state and adjoint PDEs which we approximate by the finite element method. Copyright © 2007 John Wiley & Sons, Ltd. [source] Competitive flow control in general multi-node multi-link communication networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2008Ismet Sahin Abstract In this paper, we consider the flow control in a general multi-node multi-link communication network with competing users. Each user has a source node, a destination node, and an existing route for its data flow over any set of links in the network from its source to its destination node. The flow rate for each user is a control variable that is determined by optimizing a user-specific utility function which combines maximizing the flow rate and minimizing the network congestion for that user. A preference parameter in the utility function allows each user to adjust the trade-off between these two objectives. Since all users share the same network resources and are only interested in optimizing their own utility functions, the Nash equilibrium of game theory represents a reasonable solution concept for this multi-user general network. The existence and uniqueness of such an equilibrium is therefore very important for the network to admit an enforceable flow configuration. In this paper, we derive an expression for the Nash equilibrium and prove its uniqueness. We illustrate the results with an example and discuss some properties and observations related to the network performance when in the Nash equilibrium. Copyright © 2007 John Wiley & Sons, Ltd. [source] A simple, scalable and provably stable explicit rate computation scheme for flow control in communication networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2001James Aweya Abstract This paper describes fast rate computation (FASTRAC), an explicit rate flow control algorithm for available bit rate (ABR) traffic. Using digital control theory, we develop a simple rate controller for the ABR flow control process. We prove that the controller is stable, fair to all participating sources and configurable with respect to responsiveness. The analysis presented shows that stability of the flow control process depends primarily on two factors, the control update rate and the feedback delay. The implementation of the proposed algorithm is much simpler than other fair rate allocation algorithms. The proposed algorithm demonstrates the ability to scale with speed, distance, different feedback delays, number of users, and number of nodes while remaining robust, efficient, and fair under stressing and dynamic traffic conditions. Copyright © 2001 John Wiley & Sons, Ltd. [source] Microfluidic Valves Comprising Nanolayered Thermoresponsive Polymer-Grafted Capillaries,ADVANCED MATERIALS, Issue 22 2005N. Idota Thermally regulated flow control using a thermoresponsive polymer grafted onto surfaces of capillary lumen facilitates rapid, reliable, and repeatable open,close cycles (see Figure). Hydration of the grafted polymer chains on the internal surfaces may increase the microviscosity of the hydration layers at the wall interfaces without physically occluding the lumen, producing complete and reversible on/off flow valving in microchannels under hydrostatic pressures relevant for microfluidics approaches. [source] Linear quadratic optimal sliding mode flow control for connection-oriented communication networksINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 4 2009Przemys, aw Ignaciuk Abstract In this paper, a new sliding mode flow controller for multi-source connection-oriented communication networks is proposed. The networks are modelled as discrete time, nth-order systems. On the basis of the system state space description, novel sliding mode controllers with linear quadratic (LQ) optimal and sub-optimal switching planes are designed. The control law derivation focuses on the minimization of the LQ cost functional and solving the resultant matrix Riccati equation. Closed-loop system stability is demonstrated, and conditions for no data loss and full bottleneck link bandwidth utilization in the network are presented and strictly proved. To the best of our knowledge, this paper presents the first attempt to design a discrete time sliding mode flow control algorithm for connection-oriented communication networks. Copyright © 2008 John Wiley & Sons, Ltd. [source] Molecular control of blood flow and angiogenesis: role of nitric oxideJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2009W. C. SESSA Summary., In the past decade, the importance of the vascular endothelium as a multifunctional regulator of vascular smooth muscle physiology and pathophysiology has been appreciated. Indeed, the endothelium responds to hemodynamic stimuli (pressure, shear stress and wall strain) and locally manufactured mediators (such as bradykinin, prostaglandins, angiotensin II and nitric oxide) that can influence blood flow, cell trafficking into tissue and angiogenesis. In this chapter, the importance of nitric oxide (NO) as a mediator of blood flow control, vascular permeability and angiogenesis will be discussed. [source] Regulation of Blood Flow in the MicrocirculationMICROCIRCULATION, Issue 1 2005STEVEN S. SEGAL ABSTRACT The regulation of blood flow has rich history of investigation and is exemplified in exercising skeletal muscle by a concerted interaction between striated muscle fibers and their microvascular supply. This review considers blood flow control in light of the regulation of capillary perfusion by and among terminal arterioles, the distribution of blood flow in arteriolar networks according to metabolic and hemodynamic feedback from active muscle fibers, and the balance between peak muscle blood flow and arterial blood pressure by sympathetic nerve activity. As metabolic demand increases, the locus of regulating oxygen delivery to muscle fibers "ascends" from terminal arterioles, through intermediate distributing arterioles, and into the proximal arterioles and feed arteries, which govern total flow into a muscle. At multiple levels, venules are positioned to provide feedback to nearby arterioles regarding the metabolic state of the tissue through the convection and production of vasodilator stimuli. Electrical signals initiated on smooth muscle and endothelial cells can travel rapidly for millimeters through cell-to-cell conduction via gap junction channels, rapidly coordinating vasodilator responses that govern the distribution and magnitude of blood flow to active muscle fibers. Sympathetic constriction of proximal arterioles and feed arteries can restrict functional hyperemia while dilation prevails in distal arterioles to promote oxygen extraction. With vasomotor tone reflecting myogenic contraction of smooth muscle cells modulated by flow-induced vasodilator production by endothelium, the initiation of functional vasodilation and its modulation by shear stress and sympathetic innervation dictate how and where blood flow is distributed in microvascular networks. A remarkable ensemble of signaling pathways underlie the integration of smooth muscle and endothelial cell function in microvascular networks. These pathways are being defined with new insight as novel approaches are applied to understanding the cellular and molecular mechanisms of blood flow control. [source] Measurement of exhaled nitric oxide in young children during tidal breathing through a facemaskPEDIATRIC ALLERGY AND IMMUNOLOGY, Issue 3 2005Peter Fleng Daniel Measurement of exhaled nitric oxide (eNO) offers a non-invasive means for assessment of airway inflammation. The currently available methods are difficult to apply in preschool children. We evaluated four methods potentially applicable for eNO measurement during tidal breathing in young children. eNO was assessed during tidal breathing in 24 children, 2,7 yr old, using a facemask which separated nasal and oral airflow. Facemasks with and without a one-way valve allowing exhalation through the nose were used. Expiratory flow control was not attempted. Measurements of eNO were performed both on-line and off-line. In 11 children, 8,12 yr old, measurements were compared with the standard single breath on-line method. eNO was significantly lower applying the one-way valve in on-line and off-line measurements in comparison with measurements without the valve [4.6 and 3.9 parts per billion (ppb) vs. 6.9 ppb and 6.5 ppb]. The mean within subject coefficient of variation (CV) was significantly lower in on-line measurements with the one-way valve (9.6%) compared with the other three methods (18.8, 27.7 and 29.3% respectively). Measurements with a facemask fitted with a one-way valve yielded similar eNO levels as the standard single breath method (7.0 ppb vs. 6.9 ppb) and reproducibility (9.8% vs. 7.1%). In conclusion, reproducible measurements of eNO can be obtained without control of expiration flow using a facemask fitted with a one-way valve on the nasal compartment. The likely explanation to this is that the one-way valve reduces the admixture of nasal NO, thereby improving the reliability of eNO measurements. [source] Arteriolar network architecture and vasomotor function with ageing in mouse gluteus maximus muscleTHE JOURNAL OF PHYSIOLOGY, Issue 2 2004Shawn E. Bearden Physical diminishes with ageing, but little is known of how the microvascular supply to skeletal muscle fibres is affected. To test the hypothesis that ageing alters blood flow control, we investigated network architecture and vasomotor responses of arterioles in the gluteus maximus muscle of young (2,3 months), adult (12,14 months) and old (18,20 months) C57BL6 male mice (n= 83) (Young, Adult and Old, respectively). Microvascular casts revealed that the total number, length and surface area of arteriolar segments (diameter, 10,50 ,m) were not significantly different across age-groups. However, for arterioles with diameter of 30 ,m, tortuosity and branch angles increased with age (P < 0.05). In anaesthetized mice, second-order (2A) distributing arterioles had similar resting (17 ± 1 ,m) and maximal (37 ± 1 ,m) diameters and similar responsiveness to cumulative (10,10,10,4m) superfusion of acetylcholine or phenylephrine. With superfusate oxygen level raised from 0 to 21%, 2A arteriolar constriction in Young (11 ± 1 ,m) was greater (P < 0.05) than Adult and Old (5 ± 1 ,m). Observed 1 mm upstream from microiontophoresis of ACh (1 ,A, 1 s), conducted vasodilatation was 10 ± 1 ,m in Young, 17 ± 1 ,m in Adult and 6 ± 1 ,m in Old (P < 0.05). With muscle contractions (2, 4 and 8 Hz; 30 s) arteriolar diameter increased similarly across age-groups (6 ± 1, 11 ± 1 and 18 ± 1 ,m, respectively). Muscle mass and active tension were similar across age-groups yet postcontraction vasodilatation recovered more rapidly in Old versus Adult and Young (P < 0.05). With arteriolar network architecture maintained during ageing, the impairment in conducted vasodilatation and attenuation of postcontraction vasodilatation may compromise exercise tolerance. [source] Determining friction coefficients for interrill flows: the significance of flow filaments and backwater effectsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2003Dr David L. Dunkerley Abstract Friction coefficients in overland flows are customarily estimated from mean flow properties (depth, velocity, slope) that subsume spatial variations in flow arising from two major causes: microtopography and obstacles. This paper uses laboratory experiments in shallow flumes to examine the extent of non-uniformity in flow conditions associated with each cause. Randomly placed emergent obstacles in a flume with a shallow axial channel generally yielded higher hydraulic roughness than the same pattern of obstacles on a planar flume, as well as greater variation in roughness as the obstacle locations were altered. In both flumes, hydraulic roughness fell with increasing Reynolds number for 10% obstacle cover, showed a flattening trend at 20% cover, and exhibited a convex-downward trend at 30% obstacle cover. These results indicate the progressive onset of flow controls at narrow gaps in the obstacle field. In such flows, the use of mean flow properties conceals the existence of two main subdivisions of flow: flow filaments and backwater flows. In the experiments, flow filaments involved velocities more than twice the overall mean, whereas backwater flows were much slower than the mean. The existence of fast-moving flow filaments may be significant in understanding soil transport in surface runoff, and backwater depths may modify splash detachment. Similarly, friction coefficients that fail to reflect these important non-uniform flow components may not be optimal for hydraulic calculations or in erosion models. It is concluded that new approaches to observing and processing flow data may be required, in order to avoid the loss of important flow detail that is entailed in assuming uniform flow conditions. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||||||||