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Instability modes of viscoelastic Taylor–Couette flow in the Keplerian regime are investigated using both linear stability analysis and experimental detection of critical states. A generalised Rayl...

To investigate the frequency response characteristics of a push–pull electrostatic speaker (60-mm diameter) and free-edge-like piezoelectric speakers (68-mm and 73-mm diameters), this study was employed optical and acoustic measurements from 20 Hz to 20 kHz. The optical measurements of displacement amplitude and mode shape were used to predict sound pressure levels (SPLs). Comparisons with measured SPL values were used to verify the predictions. When using a mesh with acoustic flow resistance, i.e., unless damped, the electrostatic and piezoelectric speakers both produced numerous resonant frequencies. The two evaluation methods produced SPL values that were in good agreement. The piezoelectric speakers produced jagged SPL curves with peaks steeper than those of the electrostatic speaker. At the first axisymmetric mode, the electrostatic speaker was affected by acoustic resistance, which resulted in the following quality factor (Q) values: without mesh (Q = 6.16) and using a mesh with specific acoustic resistance of 145 rayl (Q = 1.74). By contrast, the piezoelectric speakers at modes (0, 1)–(0, 4) were unaffected by acoustic resistance, which resulted in Q values of 10–11, regardless of whether mesh was applied. Because higher Q performs larger acoustic response and lower Q presents wide broadband, this study concluded that the characteristics make electrostatic speakers suitable for headphones and piezoelectric speakers suitable for audio signaling devices.

Epoxy resin/hollow glass microsphere (HGM) composite acoustic materials for potential applications in the acoustic and electronic fields were prepared with epoxy resin as the matrix and HGMs as the filler. The effects of the HGM content on the sound propagation characteristics and dielectric properties of the composites were investigated. The results show that the specific acoustic impedance of the epoxy resin matrix is reduced effectively by addition of HGMs. The specific acoustic impedance of the composite is 0.72 × 106 rayl when the HGM content is 20 wt%, 70% lower than that of the epoxy resin. The minimum acoustic attenuation coefficient of the composite is 1.35 dB cm−1 when the HGM content is 15 wt%. The acoustic response amplitude in the composite with 20 wt% HGMs is 76% less than that in the epoxy resin in the acoustic transmission test. In addition, the dielectric constant and dielectric loss of the composites are also reduced with addition of HGMs. The epoxy resin/HGM composite acoustic materials have potential applications in the fields of acoustic transducers, sound-absorbing materials, and electronic materials requiring a low dielectric constant.

In the present study, Constrained Interpolated Prof ile (CIP) method was used to simulate the natural c onvection heat transfer and fluid flow in an enclosed square cavity with differ entially heated side walls. The fundamental idea of this method is to solve the advection phase equation with CIP method and th e non-advection phase equation is calculated with finite difference method. CIPNSE is applied to predict the temperature and ve locity profiles in a square cavity for various Rayl eigh number: Ra=10 3 , 10 4 and 10 5 . The streamline and isotherms obtained under these conditions were then compared with those published in literature and found a

Novel anti-cavitation hydrophones were fabricated by depositing a hydrothermally synthesized lead zirconate titanate polycrystalline film on the back of a titanium plate. These hydrophones were not damaged by the measurement of the acoustic field formed by a high-intensity focused ultrasound (HIFU) device. The hydrophones were designed using Mason's equivalent circuit and by numerical simulation to improve their receiving characteristics for the measurement of the HIFU device. High receiving sensitivity with flat frequency characteristics was obtained by using a backing material with a specific acoustic impedance of about 20 × 106 kg/(m2 s) [Rayl]. We developed a new type of hydrophone using a tin and titanium rods as backing materials, which have specific acoustic impedances of 24 × 106 and 27 × 106 kg/(m2 s), respectively. The fabricated anti-cavitation hydrophone showed wide frequency characteristics of the receiving sensitivity. Furthermore, we observed the output waveform with distortion due to nonlinear propagation using the fabricated anti-cavitation hydrophone. This hydrophone was not damaged by exposure to a high-intensity acoustic field of an ultrasound cleaner under acoustic cavitation for duration of about ten times longer than the conventional commercial hydrophone.

Objective: Cell adhesion phenomenon has been extensively studied in the last decade and was shown to be mediated by specialized molecules and driven by physical forces. Cohesion of the vessel wall cells is also dependent on adhesion molecules but less is known about the physical forces involved. To investigate endothelial cell/endothelial cell interaction from a mechanical point of view, we have used an ultrasonic interferometry device, named EchoCell, which has been previously designed to study red blood cell–red bood cell (RBC–RBC) interaction. Methods: Bovine aortic endothelial (BAE) cells were cultured, detached, then suspended in buffer and their mechanical and geometrical properties studied with the EchoCell system. The ultrasonic apparatus measures both the accumulation rate of cells in suspension on a solid plate and the acoustical impedances of the suspension and the sediment. Results: In suspension, BAE exhibited, in our experimental conditions (3×106 cells per ml), a spherical size evaluated by calculation at a mean radius of 7±2 μm. Moreover, no BAE aggregation occurred at the concentrations used. The acoustical impedance of the BAE suspensions calculated from all the samples studied, in the cell concentration range from 1.5×106 to 6×106 cells per ml, was 1.52×106 Rayl (kg m−2 s−1). Furthermore, the acoustical impedance of the cell sediment was found to be independent on the initial cell suspension concentration and equal to 1.63×106 Rayl (kg m−2 s−1). Estimation of the volume fraction of BAE inside the sediment allows to evaluate the ultrasonic velocity and the elastic bulk modulus of cells. Conclusion: The ultrasonic interferometry method appears particularly interesting to study geometrical and mechanical (acoustical impedance, sound velocity, elastic bulk modulus) properties of BAE cells.

The extrinsic contributions to the dielectric response of 0.5Pb(Yb1∕2Nb1∕2)O3–0.5PbTiO3 thin films with (100) or (111) crystallographic orientation were studied (all indices are given in terms of the pseudocubic cell). Both the nonlinearity in the permittivity as well as the polarization hysteresis are described by the Rayleigh Law in subswitching conditions. It was found that (100) oriented films show a slightly higher extrinsic contribution to their dielectric behavior than (111) oriented films. For example, at 1 kHz and oscillation fields of 20kV∕cm, for (100) and (111) oriented films, respectively, 25% and 21% of the relative dielectric constant is due to irreversible extrinsic contributions. The difference is attributed to the higher concentration of mobile interfaces in the (100) oriented thin films. For frequencies between 20 Hz and 200 kHz both the Rayleigh parameters dropped with frequency approximately logarithmically. The frequency dependent Rayleigh parameters have been used to modify the Rayl...

In general vibration theories of thin elastic plate, the plates have been assumed to be nonpermeable. However, previous work on permeable membranes revealed that the acoustic properties of a membrane are strongly affected by its permeability [Takahashi et al., J. Acoust. Soc. Am. 99, 3003–3009 (1996)]. In this study, permeable elastic‐plate absorbers are proposed and their acoustic performance is examined by means of numerical analysis. For the simplest model, a theory for sound transmission through and sound reflection by a single permeable plate absorber with the oblique incidence of steady‐state plane wave is developed. In this theory, permeability of the plate is represented by unit‐depth flow resistivity [MKS‐rayl/m]. Subsequently, for more complex models, structured absorbers composed of the facing of a permeable plate and several layers of air and/or absorptive materials are investigated theoretically. With these theoretical models, parametric surveys are executed to evaluate the acoustic performance of permeable elastic‐plate absorbers. As a result of numerical calculations, it becomes clear that the flow resistance of the permeable elastic plate has a remarkable influence on its acoustic characteristics, especially at high frequencies.

The view-obstruction problem for ann-dimensional closed convex bodyC containing the origin in its interior has been formulated by T. W. Cusick in 1973. The problem is to determine the constantK(C) defined to be the infimum of those α>0 such that for any rayL starting from the origin and lying in the positive quadrant there are non-negative integersm1,...,mn for whichL intersects αC+(m1+1/2,...,mn+1/2). Here a conjecture of T. W. Cusick for the 3-dimensional spheres with centre 0 is proved. In fact an infinite sequence of isolated minima is obtained.

An impulse technique has been used to investigate the effect of up to 40% by weight moisture content on the impedance of grassland, barren earth, and sand. Layering of the soil after the addition of water causes resonances in the impedance values at frequencies around 5 kHz which are found to be position dependent. Comparison with layer theory is made although the predicted resonances are much broader than the experimental peaks. The variation of the peak height of the reflected impulse has been used to determine the change of effective flow resistivity of the top surface with moisture content. This may change from 200 cgs rayl at 10% moisture to 1500 cgs rayl at 35% moisture content. Results taken over grassland and sand follow the same trend if normalized to their saturation value.

Abstmct-The electro-acoustic properties of Lead zirconate titanate (PZT) rod-polymer composites relevant for ultrasonic transducer applications are reported. Acoustic impedance of the composite materials was measured by three different techniques in the frequency range 0.33.5 MHz. Dependence of the acoustic impedance as a function of volume fraction of PZT and frequency was also modeled theoretically. Time-delay spectrometry was employed to calibrate the free-field transmitting and receiving voltage responses of the composite materials. The acoustic impedance of the composite materials was in the range of 3-10 M rayl. The figure of merit in the receiving mode of composite materials was three times that of PZT. The figure of merit for a 20percent PZT composite (2 = 7.3 M rayl) was further enhanced by 50 percent using a single-layer impedance transformer of lucite (2 =3.3 M rayl). These composite materials were molded into curved shapes by simple thermal process to fabricate focused transducers. The axial and lateral beam profiles of focused composite transducers are presented.

An airflow resistivity instrument features a novel specimen holder, especially designed for in situ measurement on the earth's ground surface. This capability eliminates the disadvantages of prior intrusive instruments, which necessitate the removal of a test specimen from the ground. A prototype instrument can measure airflow resistivities in the range 10-5000 cgs rayl/cm, at specimen depths up to 15.24 cm (6 in.), and at differential pressures up to 2490.8 dyn sq cm (1 in. H2O) across the specimen. Because of the close relationship between flow resistivity and acoustic impedance, this instrument should prove useful in acoustical studies of the earth's ground surface. Results of airflow resistivity measurements on an uncultivated grass field for varying values of moisture content are presented.

Recently Wojtowicz and Rayl suggested a method for determining β, the exponent describing the behavior of the magnetization below the critical point. We have applied this method to the study of YIG in low magnetic fields ranging from 5 to 350 Oe. The transition temperature was observed to decrease linearly with the square of the applied field (as predicted by the theory) for fields up to 50 Oe. Our data are best interpreted by proposing two values of β, namely, β=0.47 close to Tc (within 1°K) and β=0.36 for the temperature region from 1° to 120°K below Tc. Similar behavior has been reported for nickel and YFeO3. Our results add further support to the suggestion of Callen and Callen that values of β∼⅓ are not truly properties of the phase transition itself.

Fiber‐metal materials are available which can provide virtually any acoustical resistance in the form of thin, strong, formable and joinable sheets. Manufacturing procedures are described briefly. The mechanical, thermal, and fatigue properties of the materials, in both aluminum and stainless steel, are described insofar as these properties are known. Also, the tradeoffs relating to weight, strength, and cost are presented, along with a discussion of material design options and limitations. Within the acoustical‐flow resistance range of 10–60 cgs Rayl, produceability limitations are reviewed statistically in terms of sheet thickness and flow‐resistance tolerances. The effect of particle velocity on flow resistance is described, showing that the resistance increases owing to turbulent flow at equivalent sound‐pressure levels (SPL) above 140 dB. Finally, the effect of flow‐resistance variations on impedance‐tube absorption characteristics is discussed, considering again the range of 10–60 cgs Rayl. The major unresolved question is the effect of very high SPL's on absorption characteristics.