Focusing, shock wave

By perturbing and focusing shock waves which pass through the explosive [4,5]... 

Kuwahara. M, et.al. "Acoustics Cavitation Bubbles in the Kidney Induced by Focused Shock Waves for the Extracorporeal Shock Wave Lithotripsy(ESWL)",Proc. 17th ISSW T (to appear 1990). ... 

Besides interest in low-frequency shock wave hydrophones, there have also been investigations of shock wave hydrophones for ultrasonic applications. Focused fields of ultrasonic pulses occurring in lithotripsy can be measured using ferroelectric polymer sensors. A Study in a water-filled tank has led to the development of a 2S-p,m PVDF hydrophone. The sensitivity of this sensor is 20 mV/MPa with a bandwidth of 20 MHz. More than 100,000 focused shock wave pulses of 20 MPa have been recorded successfully without a significant decrease in acoustic sensitivity [14],... 

A.A. Borisov, B.E. Gelfand, G.L Skatchkov et al.. Ignition of gaseous combustible mixtures in focused shock waves, in Current topics in shock waves, ed. by Y. Kim. Proceedings of 17th ISSW (AIP, New York, 1990), pp. 696-701... 

A.M. Bartenev, S.V. Khomik, B.E. Gelfand, H. Gronig, H. Olivier, Effect of reflection type on detonation initiation at shock waves focusing. Shock Waves 10(3), 205-215 (2000)... 

In the literature we can now find several papers which establish a widely accepted scenario of the benefits and effects of an ultrasound field in an electrochemical process [13-15]. Most of this work has been focused on low frequency and high power ultrasound fields. Its propagation in a fluid such as water is quite complex, where the acoustic streaming and especially the cavitation are the two most important phenomena. In addition, other effects derived from the cavitation such as microjetting and shock waves have been related with other benefits reported for this coupling. For example, shock waves induced in the liquid cause not only an enhanced convective movement of material but also a possible surface damage. Micro jets of liquid, with speeds of up to 100 ms-1, result from the asymmetric collapse of cavitation bubbles at the solid surface [16] and contribute to the enhancement of the mass transport of material to the solid surface of the electrode. Therefore, depassivation [17], reaction mechanism modification [18], surface activation [19], adsorption phenomena decrease [20] and the mass transport enhancement [21] are effects derived from the presence of an ultrasound field on electrode processes. We have only listed the main phenomena referring to the reader to the specific reviews [22, 23] and reference therein. 

A familiar military use of this principle is the 3.5 inch antitank rocket, or bazooka round. The explosive charge in the head of the rocket has a conical cavity in the forward end. When the charge is detonated against the side of a tank, the shock waves emerging from the conical cavity are focused on one spot where they will penetrate several inches of tough steel. 

Several explosive devices have recently been developed to enhance general safety. Some examples are air bags which protect the driver from injury in car collisions, and seatbelt tensioners which, when tied up with the action of an air bag, hold the driver to the seat. Explosives are also used as a source of shock waves in medical equipment for breaking up gall stones in a patient s body. In yet another application, explosives are used to generate shock waves in a patient s body water which are then focused on a kidney stone to break it. 

The use of sound waves to destroy kidney stones is based on the destructive force generated when a shock wave in fluid suddenly hits a substance that has different properties, such as a kidney stone. The shock waves pass efficiently through fluid mediums and can be focused so they strike small objects. 

In order to focus the shock waves so they pass into the body and strike kidney stones, physicians must first locate the stones by means cf fluoroscopy or ultrasound. 

Alfentanil is an ideal analgesic for focused and ambulatory interventions. In a prospective, uncontrolled study in three consecutive groups of outpatients undergoing shock-wave lithotripsy, group 1 (152 patients) had an induction dose of a combination of propofol 0.8 mg/kg and alfentanil 8 pg/kg in group 2 (78 patients) and group 3 (250 patients), the induction dose was reduced by 20%... 

Beware of artefacts This cautionary remark should always be kept in mind when carrying out flash photolysis. Stray light and fluorescence, acoustic shock waves and inhomogeneous transient distributions produced in the sample by focused laser pulses, extraneous electronic pulses from flash lamps or Q-switches, signal echoes and the like often distort the transient waveforms or spectra. 

One method to achieve the requisite short time resolution is to utilize laser pulses to both initiate the shock process and probe the shocked material. Lasers have been used for decades to drive shocks. [19-33] Direct laser drive is being pursued to achieve fusion, but has not yet succeeded. Nevertheless, such studies produced a wealth of important data on the mechanisms of interaction of high power laser pulses with solid targets. Other researchers have tried to use lasers to initiate high explosives, either directly [34-37] or via the launch of a flyer [38-39]. Again, these studies provided very important background information for the work described in this ehapter, which will focus on shock wave studies utilizing table-top ultrafast laser systems. 

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