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22 May 2006

Volume 88, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 88, 211101 (2006); http://dx.doi.org/10.1063/1.2206087 (3 pages)

Kengo Nozaki and Toshihiko Baba
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Quasistatic transduction of the fundamental symmetric Lamb mode in longitudinal wave transducers

Ventsislav Yantchev and Ilia Katardjiev

Appl. Phys. Lett. 88, 214101 (2006); http://dx.doi.org/10.1063/1.2206092 (3 pages) | Cited 2 times

Online Publication Date: 22 May 2006

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The Green’s function formalism has been applied to the analysis of the fundamental symmetric Lamb mode excited by means of longitudinal wave (LW) transducers. The Lamb wave Green’s function has been related to the properties of the effective permittivity defined as a function of the wave slowness and the relative plate thickness. An electrostatic analysis that neglects the piezoelectric coupling is employed to relate the charge density to the applied voltage. This analysis is subsequently used to calculate the radiation conductance of a LW transducer. The results obtained are consistent with the equivalent circuit approach and define the device coupling as a function of the plate thickness and the intrinsic Lamb wave coupling.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
43.38.Fx
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Effect of normal vibration on friction in the atomic force microscopy experiment

Sangmin Jeon, Thomas Thundat, and Yehuda Braiman

Appl. Phys. Lett. 88, 214102 (2006); http://dx.doi.org/10.1063/1.2203741 (3 pages) | Cited 10 times

Online Publication Date: 23 May 2006

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We studied the effect of periodic normal (out-of-plane) surface vibrations on friction in an atomic force microscope experiment. Vibration frequency was varied in the range of 1–100 kHz, and vibration amplitude was varied in the range of a few nanometers. We observed a reduction of a few orders of magnitude in friction coefficient due to the periodic vibrations. Friction reduction is over a wide range of vibration frequencies and amplitudes. Very low values (of the order of 0.01) of friction coefficient were measured. Our numerical simulation based on a minimalist modeling qualitatively agrees with the experimental results. Based on numerical simulations, a mechanism of friction reduction and/or increase with normal vibrations is proposed.
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07.79.Lh Atomic force microscopes
68.35.Ja Surface and interface dynamics and vibrations
81.40.Pq Friction, lubrication, and wear
68.35.Af Atomic scale friction

Percolating ion transport in binary mixtures with high dielectric loss

U. Brohede and M. Strømme

Appl. Phys. Lett. 88, 214103 (2006); http://dx.doi.org/10.1063/1.2201556 (3 pages) | Cited 1 time

Online Publication Date: 24 May 2006

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We investigate the ion transport percolation properties of a binary system of an ion conductor (NaCl) and an insulator (ethyl cellulose) for which the ac component of the conductivity is non-negligible over the entire measured frequency range. We find that the dc conductivity, extracted from a well-defined range of frequencies, can be described by a low percolation threshold, ϕc = 0.06 three-dimensional conducting network. The low ϕc was explained by the water-layer-assisted ion conduction in micrometer-sized ethyl cellulose channels between NaCl grains. The present findings provide valuable knowledge for the analysis and design of a broad class of ion conducting functional materials.
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66.30.Dn Theory of diffusion and ionic conduction in solids
77.22.Gm Dielectric loss and relaxation

Phase contrast tomography: An alternative approach

A. Groso, M. Stampanoni, R. Abela, P. Schneider, S. Linga, and R. Müller

Appl. Phys. Lett. 88, 214104 (2006); http://dx.doi.org/10.1063/1.2207221 (3 pages) | Cited 16 times

Online Publication Date: 25 May 2006

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Conventional microtomography is widely used for reconstructing the three-dimensional (3D) distribution of the absorption coefficient of a sample from a set of radiographic projections. The question here is whether the 3D distribution of the phase (refractive index) of a weakly absorbing object can be, alternatively to the combined phase retrieval-backprojection methods presented up to now, directly reconstructed from a single tomographic data set. In this letter a solution to this problem based on a direct filtered backprojection approach, derived from the transport of intensity equation, is investigated numerically and experimentally for monochromatic and polychromatic x rays. The results show that the contrast is increased, while keeping dose minimal and spatial resolution equivalent to the conventional absorption based technique. This method is therefore very promising for imaging of biological specimens.
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87.59.bd Computed radiography
87.57.N- Image analysis
87.57.C- Image quality

Parametric generation of multimegahertz acoustic oscillations in laser-generated multibubble system in bulk water

Sergey I. Kudryashov, Kevin Lyon, and Susan D. Allen

Appl. Phys. Lett. 88, 214105 (2006); http://dx.doi.org/10.1063/1.2206094 (3 pages) | Cited 3 times

Online Publication Date: 25 May 2006

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Using a nanosecond CO2 laser for explosive surface boiling of bulk water, oscillatory acoustic transients from steam bubbles were recorded using a contact photoacoustic technique. Multiple well-resolved, high-amplitude multimegahertz spectral features reflecting parametric interactions between oscillations of cavitating steam bubbles were revealed in the fast Fourier transformation spectra of these transients. A potential parametric generation mechanism for these oscillation modes of steam bubbles is discussed.
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43.35.Ud
43.35.Ei
47.55.dd Bubble dynamics
47.55.dp Cavitation and boiling
62.60.+v Acoustical properties of liquids
64.70.F- Liquid-vapor transitions

History effects on the viscous motion of acoustically forced particles

J. S. Allen, M. H. Kobayashi, and C. F. M. Coimbra

Appl. Phys. Lett. 88, 214106 (2006); http://dx.doi.org/10.1063/1.2208265 (3 pages)

Online Publication Date: 26 May 2006

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We examine memory viscous effects on the motion of a particle in the vicinity of nodal points. The Basset history force has a fractional derivative dependence of order 3/2 on the particle displacement, and its contribution to the dynamics of acoustically forced particles is demonstrated for typical conditions occurring in acoustic separation devices. The inclusion of the Basset history force in the formulation has the net effect of changing the eigenfunctions of the problem from exponential to Mittag-Leffler functions, thus affecting the overall balance of forces considered.
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47.61.Jd Multiphase flows
43.35.Bf
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