The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform

V V Subramaniam - One of the best experts on this subject based on the ideXlab platform.

  • effect of wall shear on the propagation of a weak spark Generated Shock Wave in argon
    Physics of Fluids, 2001
    Co-Authors: A R White, V V Subramaniam
    Abstract:

    Photo-acoustic deflection (PAD) measurements are presented for a weak spark-Generated Shock Wave propagating in argon at 40 Torr in a cylindrical tube. Measurements indicate that for a given Shock strength, there is a maximum distance of travel beyond which the Shock front is nonplanar, consistent with the predictions of numerical calculations reported recently [S. M. Aithal and V. V. Subramaniam, Phys. Fluids 12, 924 (2000)]. The initially planar Shock Wave exhibits curvature at downstream locations in the Shock tube in the absence of any imposed temperature gradients. Since the PAD signal is a line-of-sight measurement, it is sensitive to the axial gradient of density at all radial locations, and Shock curvature manifests itself as a split and spread PAD signal. In contrast, a planar Shock registers a sharp, delta-function-like PAD signal. The curvature of weak Shocks observed in the present experiments is due to viscous action alone, as the wall shear retards the near-wall portions of the front relativ...

  • on the characteristics of a spark Generated Shock Wave
    Physics of Fluids, 2000
    Co-Authors: S Aithal, V V Subramaniam
    Abstract:

    Recent experiments involving Shock Waves propagating through weakly ionized plasmas have raised questions regarding interpretation of the experimental results. In aid of analyzing these experimental results, Shock Waves initiated by a simulated spark and their subsequent propagation in a cylindrical tube containing argon initially at 30 Torr and 300 K, have been analyzed numerically in this paper. Numerical solutions to the compressible Navier–Stokes equations are considered under the four conditions of induced flow (a) without wall friction, (b) with wall friction, (c) with wall friction and purely axial thermal gradients, and (d) with wall friction and both axial and radial thermal gradients. Although plasma processes have not been simulated, it is found that the effects of wall shear and thermal gradients alone are sufficient to explain most of the experimental observations. This work represents a first step in the analysis of this problem before plasma effects can be modeled.

Antonio Ting - One of the best experts on this subject based on the ideXlab platform.

  • Shaping gas jet plasma density profile by laser Generated Shock Waves
    Journal of Applied Physics, 2014
    Co-Authors: Dmitri Kaganovich, Daniel Gordon, Michael Helle, Antonio Ting
    Abstract:

    The Gaussian plasma density profile from a simple cylindrical nozzle jet was modified using laser Generated Shock Wave. This modification provided great variety of density profiles suitable for different applications. The Gaussian plasma density distribution was modified into fast-rise slow-fall profile with adjustable gradients, almost flat-top profiles, and profiles with variable lengths. Position of the Shock Wave center and time delay were the major parameters used for shaping the density profiles. Other easily adjustable parameters such as Shock Wave energy and backing pressure provided linear scaling of the modified plasma densities.

Farrukh S Alvi - One of the best experts on this subject based on the ideXlab platform.

B Sturtevant - One of the best experts on this subject based on the ideXlab platform.

  • mechanical haemolysis in Shock Wave lithotripsy swl ii in vitro cell lysis due to shear
    Physics in Medicine and Biology, 2001
    Co-Authors: Murtuza Lokhandwalla, James A Mcateer, James C Williams, B Sturtevant
    Abstract:

    In this work we report injury to isolated red blood cells (RBCs) due to focused Shock Waves in a cavitation-free environment. The lithotripter-Generated Shock Wave was refocused by a parabolic reflector. This refocused Wave field had a tighter focus (smaller beam width and a higher amplitude) than the lithotripter Wave field, as characterized by a membrane hydrophone. Cavitation was eliminated by applying overpressure to the fluid. A novel passive cavitation detector (HP-PCD) operating at high overpressure (up to 7 MPa) was used to measure acoustic emission due to bubble activity. The typical 'double-bang' emission measured in the lithotripter free-field was replaced by a continuum of weak signals when the fluid was enclosed in a pressure chamber. No acoustic emissions were measured above an overpressure of 5.5 MPa. Aluminium foils were used to study Shock Wave damage and had distinct deformation features corresponding to exposure conditions, i.e. pitting and denting accompanied by wrinkling. Pitting was eliminated by high overpressure and so was due to cavitation bubble collapse, whereas denting and wrinkling were caused by the reflected Shock Wave refocused by the parabolic reflector. RBCs suspended in phosphate-buffered saline (PBS) were exposed to the reflected Wave field from a parabolic reflector and also from a flat reflector. Exposure to the Wave field from the parabolic reflector increased haemolysis four-fold compared with untreated controls and was twice that of cell lysis with the flat reflector. Recently we analysed deformation and rupture of RBCs when subjected to a flow field set up by a focused Shock. The cell lysis results presented here are in qualitative agreement with our theoretical prediction that haemolysis is directly related to the gradient of Shock strength and validates shearing as a cell lysis mechanism in SWL.

  • fracture mechanics model of stone comminution in eswl and implications for tissue damage
    Physics in Medicine and Biology, 2000
    Co-Authors: Murtuza Lokhandwalla, B Sturtevant
    Abstract:

    Focused Shock Waves administered during extracorporeal Shock-Wave lithotripsy (ESWL) cause stone fragmentation. The process of stone fragmentation is described in terms of a dynamic fracture process. As is characteristic of all brittle materials, fragmentation requires nucleation, growth and coalescence of flaws, caused by a tensile or shear stress. The mechanisms, operative in the stone, inducing these stresses have been identified as spall and compression-induced tensile microcracks, nucleating at pre-existing flaws. These mechanisms are driven by the lithotripter-Generated Shock Wave and possibly also by cavitation effects in the surrounding fluid. In this paper, the spall mechanism has been analysed, using a cohesive-zone model for the material. The influence of Shock Wave parameters, and physical properties of stone, on stone comminution is described. The analysis suggests a potential means to exploit the difference between the stone and tissue physical properties, so as to make stone comminution more effective, without increasing tissue damage.

S Aithal - One of the best experts on this subject based on the ideXlab platform.

  • on the characteristics of a spark Generated Shock Wave
    Physics of Fluids, 2000
    Co-Authors: S Aithal, V V Subramaniam
    Abstract:

    Recent experiments involving Shock Waves propagating through weakly ionized plasmas have raised questions regarding interpretation of the experimental results. In aid of analyzing these experimental results, Shock Waves initiated by a simulated spark and their subsequent propagation in a cylindrical tube containing argon initially at 30 Torr and 300 K, have been analyzed numerically in this paper. Numerical solutions to the compressible Navier–Stokes equations are considered under the four conditions of induced flow (a) without wall friction, (b) with wall friction, (c) with wall friction and purely axial thermal gradients, and (d) with wall friction and both axial and radial thermal gradients. Although plasma processes have not been simulated, it is found that the effects of wall shear and thermal gradients alone are sufficient to explain most of the experimental observations. This work represents a first step in the analysis of this problem before plasma effects can be modeled.