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Collective effects for long bunches in dual harmonic RF systems

Chinese Physics C 2008年第2期32卷 139-145页

作者：安世忠 Klaus Bongardt Rudolf Maier 唐靖宇张天爵 China Institute of Atomic Energy Beijing 102413 China IKP FZ Juelich 52425 JuelichGermany Institute of High Energy Physics CAS Beijing 100049China

The storage of long bunches for large time intervals needs flattened stationary buckets with a large bucket height. Collective effects from the space charge and resistive impedance are studied by looking at the incoherent particle motion for the matched and mismatched bunches. Increasing the RF amplitude with particle number provides r.m.s wise matching for modest intensities. The incoherent motion of large amplitude particles depends on the details of the RF system. The resulting debunching process is a combination of the too small full RF acceptance together with the mismatch, enhanced by the collective effects. Irregular single particle motion is not associated with the coherent dipole instability. For the stationary phase space distribution of the Hofmann-Pedersen approach and for the dual harmonic RF system, stability limits are presented, which are too low if using realistic input distributions. For single and dual harmonic RF system with d=0.31, the tracking results are shown for intensities, by a factor of 3 above the threshold values. Small resistive impedances lead to coherent oscillations around the equilibrium phase value, as energy loss by resistive impedance is compensated by the energy gain of the RF system.

关键词： resistive impedance incoherent motion halo formation coherent dipole instability

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A SUSPENSION MODEL FOR BLOOD FLOW THROUGH A CATHETERIZED ARTERY

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International Journal of Biomathematics 2012年第5期5卷 21-35页

作者： SHAILESH MISHRA NARENDRA KUMAR VERMA S. U. SIDDIQUI Department of MathematicsHarcourt Butler Technological Institute Kanpur-208002 India

The present work is concerned with the analysis of an axi-symmetric flow of blood through coaxial tubes where the outer tube has an axially symmetric mild stenosis and the inner tube has a balloon which is axi-symmetric in nature. The mild stenosis approximation is used to solve the present problem. The effect of the volume fraction density of the particles, the maximum height attained by the balloon, the radius of the inner tube, which keeps the balloon in position k, and the axial displacement of the balloon have been studied. Flow parameters such as the resistive impedance, the wall shear stress distribution in the stenotic region and its magnitude at the stenosis throat have been computed for different parameters. It is observed that the resistance to flow decreases with increasing values of the axial displacement of the balloon, while the resistance to flow increases with the volume fraction density of the particles, the radius of the inner tube, which keeps the balloon in position k, and the maximum height attained by the balloon. The wall shear stress distribution in the stenotic region possesses a character similar to the resistance to flow with respect to any parameter.

关键词： Blood now stenosis resistive impedance wall shear stress suspension.

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A Study for Analyzing the Effect of Overlapping Stenosis and Dilatation on Non-Newtonian Blood Flow in an Inclined Artery

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Journal of Biomedical Science and Engineering 2016年第12期9卷 576-596页

作者： Mukesh Kumar Sharma Vinay Nasha P. R. Sharma Department of Mathematics Guru Jambheshwar University of Science & Technology Hisar India Department of Mathematics University of Rajasthan Jaipur India

The stenosis in the artery, which reduces the flow passage to blood, is a common cardiovascular disease that is responsible even for cardiac arrest sometimes. The hemodynaics reveals that the severe blockage in an artery due to stenosis generates pressure tangential stress that impacts adversely on the arterial wall downstream to stenosis and weakens the arterial wall. The site of weakened wall in the artery generates post stenotic dilatation. The objective of this paper is to study flow of blood, of non-Newtonian in nature described by Herschel-Bulkley model, in a diseased artery suffering with partly overlapped two stenoses and a dilatation distal to the stenoses. A mathematical model, describing the blood flow, has been derived using Navier-Stokes equations along with the prescribed geometry of the diseased artery. The expressions of velocity profile, resistive impedance to flow and wall shear stress (skin-friction) are derived. The effect of inclination of the vessel on the resistive impedance to flow is discussed along with the effect of rheological and geometrical parameters on the resistive impedance to flow and skin friction.

关键词： Stenotic Artery Overlapped Stenoses Dilatation Herschel-Bulkley Blood Yield Stress resistive impedance

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