R J Baxter 1982 London: Academic xii + 486 pp price £43.60 Over the past few years there has been a growing belief that all the twodimensional lattice statistical models will eventually be solved and that it will be Professor Baxter who solves them. Baxter has inherited the mantle of Onsager who started the process by solving exactly the two-dimensional Ising model in 1944.

Exactly Solved Models in Statistical Mechanics

A three-dimensional spatial input apparatus including a series of coplanar, single axis accelerometers configured to provide information on translation along and rotation around a set of orthogonal axes. A preprocessing computer determines the acceleration values output by the accelerometers and converts these values into a series of acceleration, velocity and position values in relation to the axis system, with corrections based on a change in the influence of gravity on the device as it rotates. The values are transmitted to an object control computer which takes appropriate action, including moving a cursor, rotating a displayed object, and controlling remote devices. The spatial input apparatus can have an attached pointer and be used as a three-dimensional digitizer in conjunction with the object control computer.

Spatial input apparatus

An ultrasonic manipulation apparatus to move objects (41; 42; 45) comprising a host fluid as acoustic medium and the object(s) to be moved, wherein a plurality of ultrasonic wave oscillators is arranged in at least one line. The wave oscillators are connected to a control unit (50) adapted to generate control signals (51, 52) for the wave oscillators (21, 22) to generate a gradient force by superposing one over another the gradient force fields generated by ultrasonic waves produced by the wave oscillators. Drive signals for two adjacent wave oscillators have amplitudes of the sinusoidal inputs for these two adjacent wave oscillators which maintain an essentially constant acoustic potential magnitude during transition of an object between these two wave oscillators (21, 22).

https://www.pnas.org/content/pnas/110/31/12549.full.pdf

Acoustophoretic contactless transport and handling of matter in air

Silicon fusion and eutectic bonding processes based on the technique of localized heating have been successfully demonstrated. Phosphorus-doped polysilicon and gold films are applied separately in the silicon-to-glass fusion bonding and silicon-to-gold eutectic bonding experiments. These films are patterned as line-shape resistive heaters with widths of 5 or 7 /spl mu/m for the purpose of heating and bonding. In the experiments, silicon-to-glass fusion bonding and silicon to gold eutectic bonding are successfully achieved at temperatures above 1000/spl deg/C and 800/spl deg/C, respectively, by applying 1-MPa contact pressure. Both bonding processes can achieve bonding strength comparable to the fracture toughness of bulk silicon in less than 5 min. Without using global heating furnaces, localized bonding process is conducted in the common environment of room temperature and atmospheric pressure. Although these processes are accomplished within a confined bonding region and under high temperature, the substrate temperature remains low. This new class of bonding scheme has potential applications for microelectromechanical systems fabrication and packaging that require low-temperature processing at the wafer level, excellent bonding strength, and hermetic sealing characteristics.

/pdf/localized-silicon-fusion-and-eutectic-bonding-for-mems-5ad5sczb1r.pdf

Localized silicon fusion and eutectic bonding for MEMS fabrication and packaging

A new method is reported on how to measure the local pressure amplitude and the Q factor of ultrasound resonances in microfluidic chips designed for acoustophoresis of particle suspensions. The method relies on tracking individual polystyrene tracer microbeads in straight water-filled silicon/glass microchannels. The system is actuated by a PZT piezo transducer attached beneath the chip and driven by an applied ac voltage near its eigenfrequency of 2 MHz. For a given frequency a number of particle tracks are recorded by a CCD camera and fitted to a theoretical expression for the acoustophoretic motion of the microbeads. From the curve fits we obtain the acoustic energy density, and hence the pressure amplitude as well as the acoustophoretic force. By plotting the obtained energy densities as a function of applied frequency, we obtain Lorentzian line shapes, from which the resonance frequency and the Q factor for each resonance peak are derived. Typical measurements yield acoustic energy densities of the order of 10 J/m3, pressure amplitudes of 0.2 MPa, and Q factors around 500. The observed half wavelength of the transverse acoustic pressure wave is equal within 2% to the measured width w = 377 μm of the channel.

/pdf/measuring-the-local-pressure-amplitude-in-microchannel-2a6eyc4ien.pdf

Measuring the local pressure amplitude in microchannel acoustophoresis

The method of Gor'kov is applied for deriving the acoustic radiation potential on a sphere in an arbitrary sound field. Generalized potential and force expressions are derived for arbitrary standing wave modes in rectangular, cylindrical, and spherical geometries for the case where the sphere radius is much smaller than the wavelength. Criteria for determining radiation-potential minima are derived and examples of characteristic spatial radiation-potential profiles are presented. Single modes that can sustain stable positioning are discussed for each geometry. The localizing force strengths for representative standing wave modes in the three geometries are also compared. The positioning of samples due to acoustic forces only are considered. However, the method developed is general and is extended to include gravity or other external forces.

http://www.csun.edu/%7Evcphy00d/PDFPublications/1985%20Barmatz-Collas.pdf

Acoustic radiation potential on a sphere in plane, cylindrical, and spherical standing wave fields

This review provides an overview of the progress in using the low-gravity environment of space to explore critical phenomena and test modern theoretical predictions. Gravity-induced variations in the hydrostatic pressure and the resulting density gradients adversely affect ground-based measurements near fluid critical points. Performing measurements in a low-gravity environment can significantly reduce these difficulties. A number of significant experiments have been performed in low-Earth orbit. Experiments near the lambda transition in liquid helium explored the regime of large correlation lengths and tested the theoretical predictions to a level of precision that could not be obtained on Earth. Other studies have validated theoretical predictions for the divergence in the viscosity as well as the unexpected critical speeding up of the thermal equilibrium process in pure fluids near the liquid-gas critical point. We describe the scientific content of previously flown low-gravity investigations of critical phenomena as well as those in the development stage, and associated ground-based work.

Critical phenomena in microgravity: Past, present, and future

A method enabling controlled selective heating of workpiece components during microwave brazing. Two workpiece components are joined by melting an adhesion interlayer material between the two components. An indication of when the interlayer has melted is provided. The temperature difference across the braze assembly is monitored and adjusted via a feedback loop to reduce stresses in the braze joint resulting in a stronger braze joint.

Microwave technique for brazing materials

/pdf/acoustic-particle-separation-9uf3s0pwtq.pdf

Acoustic particle separation

An extension of standard results for the acoustic force on an object in a single‐mode resonant chamber yields predictions for the onset of oscillational instabilities when objects are levitated or positioned in these chambers. The results are consistent with experimental investigations. The present approach accounts for the effect of time delays on the response of a cavity to the motion of an object inside it. Quantitative features of the instabilities are investigated. The experimental conditions required for sample stability, saturation of sample oscillations, hysteretic effects, and the loss of the ability to levitate are discussed.

Martin B. Barmatz

Papers

Acoustic radiation potential on a sphere in plane, cylindrical, and spherical standing wave fields

Critical phenomena in microgravity: Past, present, and future

Microwave technique for brazing materials

Acoustic particle separation

Oscillational instabilities in single-mode acoustic levitators