S. H. R. Hosseini

Experimental study of Richtmyer-Meshkov instability induced by cylindrical shock waves

The paper describes the results of holographic interferometric flow visualization of the Richtmyer-Meshkov instability induced by cylindrical shock waves propagating across cylindrical interfaces. Experiments were conducted in an annular coaxial vertical diaphragmless shock tube, which can produce converging cylindrical shock waves with minimum disturbances. The shock wave converged and interacted with a cylindrical soap bubble filled with He, Ne, air, Ar, Kr, Xe, or SF6. The soap bubble was placed coaxially in the test section. The effects of density variation on the Richtmyer-Meshkov instability for a wide range of Atwood numbers were determined. Pressure histories at different radii during the shock wave implosion and reflection from the center were measured. Double-exposure holographic interferometry was used and the motion of the converging shock wave and its interaction with the gaseous interface were visualized. The variation of the pressure at the center with interface Atwood number for constant i...

Implosion of a spherical shock wave reflected from a spherical wall

The paper describes results of experiments of a converging spherical shock wave reflected from a spherical wall. In order to visualize the motion and the flow field behind the shock waves, an aspheric lens-shaped transparent test section made of acrylic PMMA (polymethyl methacrylate) with an inner spherical cavity was designed and constructed. This test section made optical flow visualization with collimated object beams possible. Spherical shock waves were produced at the centre of the spherical cavity by explosion of silver azide pellets ranging from 1.0 to 10.0 mg with corresponding energies of 1.9 to 19 J. The charges were ignited by irradiation of a pulsed Nd:YAG laser beam. Pressures were also measured at two points with pressure transducers mounted flush at the inner wall of the test section. The pellet was simultaneously ignited on two sides or was shaped to produce a uniform diverging spherical shock wave. This spherically diverging shock wave was reflected from the spherical inner wall of the test section to form a converging spherical shock wave. We visualized the shock-wave motion by using double exposure holographic interferometry and time-resolved high-speed video recording. The sequence of diverging and converging spherical shock-wave propagations and their interaction with gaseous explosion products were observed. The convergence, acceleration and stability of the imploding shock wave in the test section were studied.

On the efficiency of Gore-Tex layer for brain protection from shock wave damage in cranioplasty

The effectiveness of a Gore-Tex layer for protecting soft tissue from damage in shock wave therapy is investigated analytically, numerically and experimentally. Analytical considerations based on the fundamentals of wave dynamics and two-dimensional numerical simulations based on the elastodynamic equations are carried out for underwater shock wave propagation and interaction with Gore-Tex membrane models of different complexity. The results clearly demonstrate that considerable attenuation of shock waves with Gore-Tex is due to the air trapped inside the membrane. The experimental results confirm that a Gore-Tex sheet placed in the liquid reduces the transmitted shock wave peak overpressure significantly, by up to two orders of magnitude. Another experimental series reveals what kind of damage in the rat brain tissue can be caused by shock waves of different intensity.

Experimental study of micro shock wave focusing for precise medical applications

For applying shock waves to sensitive medical procedures like cranioplasty in a close vicinity of the brain or treatment of myocardial dysfunction, generation of micro underwater shock waves plays an important role. Such delicate applications make limits on usage of conventional shock wave (SW) sources. In the present research a half‐ellipsoidal cavity with 20.0‐mm minor diameter and the ratio of major to minor diameters of 1.41 was designed as a compact extracorporeal SW source. Silver azide AgN3 pellets ranging from 1.0 to 20 μg with their energy ranging from 1.9 to 38 mJ were used to generate shock waves at the first focal point F1 inside the reflector. Irradiation of a Q‐switched Nd:YAG laser beam through a 400‐μm optical fiber was used to ignite the pellet. The whole sequences of the shock wave generation, propagation, and focusing were visualized by quantitative double pulse holographic interferometry and time‐resolved high speed shadowgraph methods. Pressure histories were measured at the shock wav...

Experimental application of Holmium:yttrium‐aluminum‐garnet laser‐induced shock wave as a drug delivery system

One of the possible applications of shock waves is enhancement of drug delivery in the central nervous system. To achieve such a goal, it is necessary to develop a suitable shock wave source with the ability to be integrated with an endoscope or a catheter. We have developed a shock wave generator using a pulsed Ho:YAG laser as the energy source; this device is remarkable for its ability to expose shock wave to target tissue in a localized area. The physical feature and characteristics of the generator were clarified. The overpressures of Ho:YAG laser‐induced cavitational shock waves were measured by using a PVDF needle hydrophone. Maximum overpressure of 19 MPa at 4‐mm distance from tip of the device was obtained. As a preliminary experiment, the device was applied to evaluate the enhancement of chemotherapeutic effects of shock wave in vitro, using human gastric cancer cell (GCIY cell) line and an anticancer drug (Bleomycin: BLM). Proliferation rate of the cells decreased to 90% and 45%, after applicati...

Shock‐wave‐based biolistic apparatus

A shock‐wave‐based biolistic device has been developed to deliver DNA/drug‐coated micro‐projectiles into soft living targets. The device consists of an Nd:yttrium aluminum garnet laser, equipped with a suitable optical setup and a thin aluminum (Al) foil (typically 100‐μm thick). The powdered vaccines to be delivered are deposited on the anterior surface of the foil and the posterior surface of the foil is ablated using the laser beam. The ablation launches a shock wave through the foil that imparts an impulse to the foil surface, due to which the deposited particles accelerate to high velocities that are sufficient to enable them to penetrate soft targets. The device has been tested for in vivo DNA delivery by delivering plasmid‐coated, 1‐μm size, gold (Au) particles into onion and tobacco cells. The GUS activity was detected in the onion and tobacco cells after the addition of an artificial substrate. The present device is totally nonintrusive in nature and has a potential to get miniaturized to suit the existing medical procedures for drug delivery.

Shock Wave Interaction with Micro-Filament Network in a Cancer Ce1l line

Interaction of shock waves with renal tumor cell line (ACHN) has been studied with regard to their membrane micro-filament structure as a major cellular system to resist mechanical stress. ACHN monolayer cultured on a cover slide glass was treated with 16 MPa peak pressure focused underwater shock waves. The morphological deformations were found to be associated with disorganization of the intracellular cytoskeletal filaments. In order to simulate the interaction of shock waves with fibrillar network structure of cells, thin porous layers of cotton immersed in water were exposed to underwater shock waves. Attenuation of shock over-pressures were measured with needle and fiber optic probe hydrophones. The motion of shock waves was quantitatively visualized. The experimental results were extended to understand the complex process of shock/cell interactions, which would happen during ESW cancer therapy

Study of a tissue protecting system for clinical applications of underwater shock wave

Applications of underwater shock waves have been extended to various clinical therapies during the past two decades. Besides the successful contribution of extracorporeal shock waves, tissue damage especially to the vasculature has been reported. These side effects are believed to be due to the shock wave‐tissue interaction and cavitation. In the present research in order to minimize shock wave induced damage a shock wave attenuating system was designed and studied. The attenuating system consisted of thin gas packed layers immersed in water, which could attenuate more than 90% of shock waves overpressure. Silver azide micro‐pellets (10 mg) were ignited by irradiation of a pulsed Nd:YAG laser to generate shock waves. Pressure histories were measured with fiber optic probe and PVDF needle hydrophones. The strength of incident shock waves was changed by adjusting the distance between the pellets and the layers. The whole sequences of the shock wave attenuation due to the interaction of shock waves with the ...

Study of diverging and converging spherical shock waves induced by micro explosives in an aspherical transplant test section

The paper reports an experimental study of production and propagation of diverging and converging spherical shock waves. In order to quantitatively observe spherical shock waves and the flow field behind them, an aspheric spherical transparent test section was designed and constructed. This 150 mm inner-diameter aspheric lens shaped test section permits the collimated visualization laser light beam to traverse the test section parallel and emerge parallel. Spherical diverging shock waves were produced at the center of the spherical test section. In order to generate shock waves, irradiation of a pulsed Nd:YAG laser beam on micro silver azide pellets were used. The weight of silver azide pellets ranged from 1 to 10 mg, with their corresponding energy of 2.1 to 21 J. Pressure histories at different points over the test section were measured to validate production of uniform shock waves. After reflection of spherical shock wave from the test section, a converging spherical shock wave was produced. Double exposure holographic interferometry and time resolved high speed photography were used for flow visualization. The whole sequence of diverging and converging spherical shock waves propagation and their interaction with product gases were studied.

Interaction of shock waves with cavitation bubble: Application of Ho:YAG pulse laser irradiation for cerebral thrombolysis

This paper reports on the application of underwater shock waves and vapor cavities for cerebral thrombolysis. The energy source was a Q‐switched Ho:YAG laser (Nippon Infrared Industries Co., Ltd.) with 91 and 140 mJ/pulse energy measured at the end of a 0.60‐mm‐diam glass optical fiber, pulse duration of 200 ns, and wavelength of 2100 nm. The whole sequences of the shock‐wave propagation and growth of the cavitation bubbles from the end of the optical fiber were visualized by high‐speed photography using an Imacon 468 camera (Hadland Photonics Ltd.). The shock‐wave generation was associated with the laser breakdown in the water. The laser interaction produced a microplasma and heated the liquid in front of the fiber. The plasma drove spherical shock wave in water, followed by the formation of a high‐temperature vapor cavity. Collapse of the cavity produced a secondary spherical shock wave in water. Successive generation and collapse of the bubbles were visualized. Pressure histories were measured by PVDF ...