211 pages Price $5 9. 50.Hot wire (and hot film) anemometry is a subject involving the experimental measurement of fluid flows (usually turbulent) that is approached from a scientific and technical point of view. In hot wire anemometry, a fine metal wire, typically 1 mm long and 5 ttm in diameter (supported between two prongs) is electronically heated by an amplifier in a feedback circuit. Air going past the wire cools it at a rate that is a complicated function of flow speed (known as King's law). This causes the circuit to rebalance by creating more current, which is measured as the hot wire signal. Hot film probes are used in liquids. They have a protective coating, typically quartz, to prevent chemical reactions.Lomas' book reveals the subject from a practical perspective surrounded by the science and engineering discoveries that have extended the instrument from an era--where experimentalists had to build their own--to the present, where commercial equipment is readily available.Chapter 1 gives a good introduction to the instrument, including the various types of probes and electronics. In Chap. 2, the reader gets an appreciation for the wear and tear the probes are subjected to and the engineering designs that are used for best performance and consistent response. Chapter 3 gets back into the physics of the instrument by studying the cooling laws of wires (and metal films) and their calibration. Electronic circuitry and feedback are discussed from the engineering standpoint in Chap. 4. In Chap. 5, Lomas' book becomes invaluable because his discussion on measuring flows in a variety of liquids reveals a wealth of information that could only be learned by years of laboratory experience. Finally, in Chaps. 6 and 7, he puts the subject all together by discussing the methods of measuring the various flow quantities of turbulence (using physics and engineering equations). The material in Chap. 6, entitled "Types of Measurements," is substantial in dealing with topics such as the measurement of mean flow velocity, turbulent flow velocity, vorticity, and temperature. An account on the technique of measurement of gas mixture concentration and heat transfer phenomenon in compressible flow completes this satisfying chapter. With over 225 references and many figures distributed throughout, this compact text is extremely valuable to students and researchers (both experimentalists and theorists) in the field of fluid mechanics and related areas. MURRAYS. KORMAN

When airborne sound couples into the ground seismic waves can interact with a target buried in the soil and effect the vibration velocity of the surface. Acoustic-to-seismic coupling (using linear acoustic techniques) has proven to be an extremely accurate technology for locating buried land mines [J. M. Sabatier and N. Xiang, IEEE Trans. Geoscience and Remote Sensing 39, 1146-1154 (2001)] . Donskoy [SPIE Proceedings 3392, 211-217 (1998); 3710, 239-246 (1999)] has suggested a nonlinear technique that can detect an acoustically compliant buried mine that is insensitive to relatively noncompliant targets. (Utilizing both techniques could eliminate certain types of false alarms.) Airborne sound at two primary frequencies f 1 and f 2 undergo acoustic-to-seismic coupling and a superimposed seismic wave interacts with the compliant mine and soil to generate a difference frequency component that can effect the vibration velocity at the surface. Geophone measurements scanning the soil's surface at the difference frequency (chosen at a resonance) profile the mine with more relative sensitivity than the linear profiles -but off the mine some nonlinearity exists. Amplitude dependent frequency response curves for a harmonically driven mass-soil oscillator are used to find the nonlinearity of the soil acting as a "soft" spring. Donskoy's nonlinear mechanism (over the mine) involves a simple model of the top surface of the mine-soil planar surface separating two elastic surfaces. During the compression phase of the wave, the surfaces stay together and then separate under the tensile phase due to a relatively high compliance of the mine. This "bouncing" soil-mine interface is thought to be a bi-modular oscillator that is inherently nonlinear.

Acoustic-to-seismic coupling has proven to be an extremely accurate technology for locating buried landmines. Most of the research to date has focused on linear acoustic techniques in which sound couples into the ground, interacts with the buried mine, and causes increased vibration of the ground above the mine. However, Donskoy' has suggested that nonlinear acoustic techniques may be applicable to acoustic mine detection. This technique has recently been used with success in field tests at the University of Mississippi and US Army mine lanes. In the nonlinear acoustic technique, airborne sound is produced at two primary frequencies which couple into the ground and a superimposed compressional wave interacts with the mine and the soil. Because the mine is compliant, contact between the soil and the mine is maintained during the compression phase of the wave, but they separate during the tensile phase. This creates a bimodular oscillator that is inherently non-linear. This effect has been demonstrated on inert landmines at the University of Mississippi and at US Army test lanes. Results of these tests indicate that nonlinear measurements over buried landmines have more sensitivity than linear measurements. Non-compliant objects such as concrete disks do not exhibit nonlinear phenomena but can be located using linear techniques.