Magnetostriction Oscillator Research Articles

Dynamics of a single cavitation bubble near an oscillating boundary

Cavitation and its effects are well investigated, especially single bubble cavitation and its collapse near rigid and elastic boundaries. In our current article, we investigated novel experiments of a single cavitation bubble near an oscillatory boundary. We generated the cavitation bubble by laser focusing in water. A flat glass plate was fixed to the shaft of the magnetostriction oscillator coil. We investigated the dynamics of bubbles at two relative wall distances (ratio of the distance between the bubble center and plate surface to the maximum radius of the bubble) of the bubble from the glass plate in combination with four modes of oscillation. Each mode has specific frequency and amplitude of oscillation. The high-speed camera captured the dynamics of the bubble using the back-illumination method with a framing rate of 120Kfps and simultaneously we used an optical CMOS sensor to measure the oscillation of the glass plate. We presented a clear comparison among the bubble dynamics near stationary and oscillating plates with parameters such as oscillating modes and direction. We correlated the dynamics of the bubble with the motion of the plate. In addition, we highlighted the differences including the characteristics of bubble shape and jetting that occurred during the collapse phase. The comparison of the time histories of the bubble’s equivalent size postulated that the bubble’s collapse times vary significantly in some cases compared to the bubble’s dynamics near the stationary plate. In all cases, we noticed the shortening of the bubble’s collapsing time, i.e. accelerated collapses. In our findings, we noticed a collapse times reduction of about 4–15%. Our finding signifies the importance of introducing the oscillation of the boundaries to obtain effective energy concentration over the time during the collapse. Our study also suggests that forced oscillation of boundaries is undesirable for destructive cavitation effects. The method we suggested for the manipulation of bubble dynamics holds potential for enhancing the efficiency of applications such as lithotripsy in biomedical devices, actuation and micro pumping in microfluidic devices, and effective semiconductor surface cleaning. Not but least, obtained results can be used as benchmark in future for validating numerical methods.

Investigations of Cavitation Processes in Different Types of Emitters Using Sonochemical Analysis

The application limits of optical and sonochemical methods to determine the sizes of cavitation bubbles and their derivatives have been analyzed. The effect of cavitation fields generated using an ultrasonic magnetostrictive oscillator and jet hydrodynamic emitter on the parameters of their acoustic signals has been examined. The bubbles size depending on emitter type and parameters has been determined using sonochemical analysis. The character of the dependence was estimated according to Minnaert formula. The bubbles dispersity in the flotation zone may be controlled by varying conditions of cavitation excitation.

Angular magnetostriction oscillations in layered conductors with multisheet Fermi surfaces

The dependence of the electrical conductivity of layered conductors with a quasi-two dimensional electron energy spectrum on the orientation of an external magnetic field is studied. The oscillatory dependence of the magnetostriction of conductors with a multisheet Fermi surface (FS) on the angle of inclination of a strong magnetic field to the layers is found to contain valuable information on the shape of the FS. In particular, the period of the oscillations can be used to determine the magnitude of the corrugation in a plane sheet of the Fermi surface.

Effect of Acoustic Standing Wave in a Bubble Column

Experiments using nickel magnetostrictive oscillators as transducers that generate acoustic standing waves in a bubble column were conducted in this study. The acoustic frequencies employed are 16 and 20 kHz with power up to 400 W. The column is operated at a constant room temperature, with the heat generated from acoustic excitation removed by the use of a water jacket. The study examines the fundamental behavior of initial bubble size, bubble rise velocity and movement of a swarm of mesobubbles (2−8 mm in diameter), gas−liquid mass transfer, and turbulence under the influence of the Bjerknes force in the acoustic field. The results indicate a smaller initial bubble size, a slower bubble rise velocity, and more concentrated bubble aggregates in the presence, rather than in the absence, of the acoustic field. Furthermore, the gas−liquid mass transfer rate and the liquid-phase turbulence are found to be significantly enhanced when an acoustic field is present.

Quantum magnetostriction oscillations in a two-dimensional antiferromagnet with spin-phonon interaction in a magnetic field

The ground state of a two-dimensional antiferromagnet with S=1/2 interacting with acoustic phonons in a magnetic field was studied by the quantum Monte Carlo method in the nonadiabatic approximation. Oscillations of the amplitude of the root-mean-square displacement of ions and the average phonon occupation number in a magnetic field were found. Local maxima were revealed in the distribution functions of site magnetic moments and ion displacements. The saturation magnetization was calculated as a function of the spin-phonon coupling constant.

Diamagnetic domains and magnetostriction in beryllium

Magnetostriction was for the first time studied under the conditions of formation of diamagnetic domains (Condon domains). Transverse magnetostriction oscillations on a beryllium single crystalline plate oriented normally to magnetic field were measured in magnetic fields up to 7 T at temperatures down to 1.5 K. The relative amplitude of oscillations increased almost as the square of magnetic field and reached 10−5. The signal had a sawtoothed shape corresponding to alternation of homogeneous and inhomogeneous (domain) states in the region of the existence of magnetic domains. The arising of domains was accompanied by singularities in the observed signals which is explained by an anomalous increase in the compressibility coefficient of the domain state: coefficient oscillations were more than 100 times larger than the value predicted by the standard theory. The observed relation between magnetization current and deformation led us to conclude that the compressibility of the metal was fully determined by conduction electrons. Magnetostriction then exactly compensated Fermi level oscillations. The position of the Fermi level therefore remained constant under magnetic field variations. In addition, the domain wall thickness had to increase as the plate grew thicker.

Magnetization and magnetostriction oscillations in a superconducting 2H-NbSe2 single crystal

The results of a comparative study of the oscillating magnetostriction and absolute magnetization components in the single crystal of the layered superconducting compound 2H-NbSe2 are presented. The measurements were made in the temperature range 1.5–8 K in a magnetic field of 0–20 T with in-plane orientation (normal to the hexagonal axis). The mechanical stress derivative of the extremal cross-sectional area of the Fermi surface is derived from a thermodynamic analysis. The values obtained are considerably higher, by an order of magnitude, than those for other metals, which explains the observed enhancement of the magnetostriction oscillations in comparison with the magnetization oscillations.

709 磁わい振動キャビテーション気泡の挙動特性(オーガナイズドセッション : 流体工学2)

709 磁わい振動キャビテーション気泡の挙動特性(オーガナイズドセッション : 流体工学2)

Anomalous compressibility and magnetostriction of beryllium under the conditions of diamagnetic domain formation

Magnetostriction oscillations are measured for a single-crystal beryllium sample shaped like a plate perpendicular to the direction of the magnetic field. In the range of 2–5 T at a temperature of 1.5 K, i.e., in the region of diamagnetic domain formation (Condon domains), the striction signal has the saw-tooth shape corresponding to the alternation of homogeneous and nonhomogeneous (domain) states. The formation of the domain structure is accompanied by an anomalous increase in compressibility; the oscillations in this coefficient are more than one hundred times greater than the value given by the standard theory. An analysis of the results indicates that the domain wall width should increase with increasing plate thickness.

Magnetic Anisotropy and Magnetostriction Oscillations in Magnetic Multilayers

Interlayer pseuclodipolar coupling between two ferromagnets separated by nonmagnetic spacer is analyzed. It was shown that this type of interaction should induce magnetic anisotropy and magnetostriction oscillations. It was also predicted that both magnetic anisotropy and magnetostriction decrease with an increase in the spacer thickness.' This effect was observed in [permalloy/Cu]1oo multilayers.

RF-photon induced Mössbauer satellites in permalloy

The Mossbauer spectra of a permalloy film placed in an rf magnetic field are measured. The film is so thin that transverse magnetostriction oscillations are not excited in it. This permits the observation of satellites that are due solely to periodic variations of the magnetic field at the nucleus. The data are in good agreement with calculations performed in the model of step-wise field reversals. On application of an additional static magnetic field the splitting of the satellites is observed, as predicted by the model of asymmetric step-wise field reversals.

Stress dependence of the Fermi surface of gold

Derivatives of the five principal extremal cross sections of the Fermi surface of gold with respect to uniaxial stress along various directions have been determined from simultaneous measurements of the amplitudes of magnetostriction and torque quantum oscillations. The accuracy of the measurements is limited by a spurious magnetostriction signal caused by the crystal bending in response to the torque it experiences when its symmetry axis is misaligned with the magnetic field direction. The results are self-consistent and agree with the results of the direct tension measurements and with stress derivatives calculated from the absolute magnetostriction amplitude measurements. Discrepancies with results from other experimental work are discussed

Dynamic characteristics of a subcritical bifurcation with inversion symmetry.

Phase and amplitude dynamics of a subcritical period-doubling bifurcation are experimentally characterized in the nonlinear strain response (at f\ensuremath{\approxeq}10 kHz) of a magnetostrictive oscillator. Low frequency (${\mathit{f}}_{\mathrm{mod}}$\ensuremath{\le}0.1 Hz) modulation of the observed subcritical bifurcation provides a phase-reversing time series whose power spectrum tends to conceal frequency components. An event counting technique developed for characterizing the phase-slip dynamics of the time series reveals a substantial component at half the modulation frequency (f/2) as well as at f. The event counting technique is applied to observe stochastic resonance for the first time in a tristable system.

Observation of stochastic resonance near a subcritical bifurcation

A hysteretic Subcritical period-doubling bifurcation is observed in the nonlinear strain dynamics of a magnetostrictive oscillator. The dynamic strain response of the magnetostrictive oscillator was observed with a high-resolution fiber optic interferometer. The effects of low-frequency modulation and band-limited stochastic fluctuations on such a bifurcation are investigated. Power spectral density measurements show that for an optimal value of externally injected noise the signal-to-noise ratio of a low-frequency modulation signal is enhanced by greater than 14 dB, thus indicating the first experimental observation of stochastic resonance near a bistable period-doubling bifurcation.

Characteristics of a parametric magnetostrictive oscillator

Parametric properties of a magnetostrictive oscillator are characterized by observing the strain dynamics of a magnetically excited metallic glass ribbon. A magnetostrictive ribbon excited by a total magnetic field H=H/sub dc/+h/sub p/ cos( omega t)+h/sub Omega / cos( Omega t) generates strain responses at frequencies omega , Omega , omega +or- Omega , thereby making the device resemble a parametric oscillator operating in the three-photon mode. Close to an instability in the nonlinear strain dynamics of such materials, the authors observed dependence of the gain of the strain e/sub Omega / on pump amplitude h/sub p/ and detuning frequency, while DC field dependent gain was observed in the strain e/sub omega +or- Omega /. This behavior is generic to parametric devices and is not predicted by the quadratic coherent rotation model of magnetostriction. Experimental verification of greater than 35-dB small signal gain in a fiber-optic AC magnetometer is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Deformation and Fracture of Single-Crystal and Sintered Polycrystalline Silicon Carbide Produced by Cavitation

An investigation was conducted to examine the deformation and fracture behavior of single-crystal and sintered polycrystalline SiC surfaces exposed to cavitation. Cavitation erosion experiments were conducted in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (1 mm) to the surface of SiC. The horn frequency was 20 kHz, and the double amplitude of the vibrating disk was 50 microns. The results of the investigation indicate that the SiC (0001) surface could be deformed in a plastic manner during cavitation. Dislocation etch pits were formed when the surface was chemically etched. The number of defects, including dislocations in the SiC (0001) surface, increased with increasing exposure time to cavitation. The presence of intrinsic defects such as voids in the surficial layers of the sintered polycrystalline SiC determined the zones at which fractured grains and fracture pits (pores) were generated. Single-crystal SiC had superior erosion resistance to that of sintered polycrystalline SiC.

A study of the cavitation erosion behaviour of a Ti-Ni alloy coating

A low pressure plasma spray process (LPPS) has been used to make a Ti-Ni alloy coating on bronze. This paper reports on studies of the structure and mechanical properties of the Ti-Ni coating, and also discusses the behaviour of the coating during cavitation erosion by means of X-ray diffraction, electron microprobe, microhardness testing and scanning electron microscopy. The cavitation erosion tests were carried out using a magnetostrictive oscillator operating at 19 kHz in distilled water. The investigation shows that the Ti-Ni coating can improve the cavitation erosion resistance of bronze.

Observations of sonoluminescence using image intensification

A high-gain image intensifier system has been applied to the study of the light emitted when cavitation occurs in a liquid (sonoluminescence). Observations of sonoluminescence from several different magnetostrictive oscillators show that spatial and temporal distributions can be recorded in a few seconds in cases where recording on conventional film would not be possible. In the present experiments, the spectral transmission properties of the optics precluded recording of the light in ultraviolet. The spatial details of the cavitation process would not be available from photomultiplier records.

36] Cyclic AMP phosphodiesterase of Escherichia coli

Publisher Summary Escherichia colt strain K12 is used for the preparation of the cAMP phosphodiesterase. Conditions of growth, e.g., the use of either mineral salts-based or complex media, do not appear to affect the specific cyclic AMP phosphodiesterase activity significantly. Cells may be stored frozen at -20°C or below for prolonged periods of time. E. colt strain Crookes (American Type Culture Collection 8739) when grown on a mineral salts medium is devoid of detectable cAMP phosphodiesterase activity and serves as source of the activator. The bacteria of both strains K12 and Crookes are extracted by any one of three equally effective methods. Extraction and all following operations are carried out at 0–4°C. The bacteria are suspended in a volume (ml) of buffer A equal to their wet weight in grams. They are then disrupted either by passage through a French press at 5000 psi, or by treatment in a Raytheon 10-kcycles/sec magnetostrictive oscillator for two consecutive 15-minute periods, or by grinding with an approximately equal weight of levigated alumina.

Oscillatory Magnetostriction in Multivalley Semiconductors: Application top- Type PbTe

Magnetostriction oscillations of de Haas---van Alphen origin are observed in $p$-type PbTe, a single-band multivalley semiconductor. The hole concentration of the material studied is 3\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The amplitude of the oscillations is related not only to the usual shear deformation potential ${\ensuremath{\Xi}}_{u}$, which causes intervalley charge transfer as the valleys rigidly shift relative to each other in energy, but also to six strain masses, which describe rotations and distortions of the hole valleys.