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19 Feb 2001

Volume 78, Issue 8, pp. 1023-1163

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Properties of surface waves determined via bistatic terahertz impulse ranging

M. T. Reiten, D. Grischkowsky, and R. A. Cheville

Appl. Phys. Lett. 78, 1146 (2001); http://dx.doi.org/10.1063/1.1350418 (3 pages) | Cited 9 times

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A bistatic terahertz impulse ranging system has permitted the full isolation and direct measurements of the surface wave loss and dispersion for terahertz frequencies on a dielectric cylinder. This system permits ranging investigations with variable bistatic angles between the source and detector. Direct, frequency dependent comparisons of surface wave loss and propagation velocity are compared to Mie theory and previous measurements of surface wave propagation over a 1 THz bandwidth. The observed radiation from the surface waves is seen to depend on the path of the radiation in and along the scatterer. © 2001 American Institute of Physics.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
43.35.Pt Surface waves in solids and liquids
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.35.Iv Acoustical properties

Electrospinning: A whipping fluid jet generates submicron polymer fibers

Y. M. Shin, M. M. Hohman, M. P. Brenner, and G. C. Rutledge

Appl. Phys. Lett. 78, 1149 (2001); http://dx.doi.org/10.1063/1.1345798 (3 pages) | Cited 213 times

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Polymeric fibers with diameters in the range from 50 nm to 5 μm are produced by accelerating a fluid jet in an electric field, in a process known as “electrospinning.” Here we show that an essential element of the process is a fluid instability, the rapidly whipping jet. The phenomena responsible for the onset of whipping are revealed by a linear instability analysis that describes the jet behavior in terms of known fluid properties and operating conditions. The behavior of two competing instabilities, the Rayleigh mode and the axisymmetric conducting mode, is also described. The results are summarized using operating diagrams, delineating regimes of operation in electrospinning, which are in good agreement with experimental observations. © 2001 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
47.15.Fe Stability of laminar flows
47.27.wg Turbulent jets

Metal foam evolution studied by synchrotron radioscopy

John Banhart, Heiko Stanzick, Lukas Helfen, and Tilo Baumbach

Appl. Phys. Lett. 78, 1152 (2001); http://dx.doi.org/10.1063/1.1350422 (3 pages) | Cited 32 times

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High-intensity synchrotron x-ray radioscopy was used to obtain real-time images of foaming metals, thus allowing the formation, growth, and decay of such systems to be studied. Bubble generation, foam coalescence and drainage of an aluminum-based alloy foam were investigated. Although the foaming process appears to be very similar to the formation of aqueous foams, the observed rupture behavior of thin metal films suggests that the processes responsible for metal foam stabilization and destabilization must be quite different. © 2001 American Institute of Physics.
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82.70.Rr Aerosols and foams

Ultrafast two-dimensional ultrasonic speckle velocimetry: A tool in flow imaging

Laurent Sandrin, Sébastien Manneville, and Mathias Fink

Appl. Phys. Lett. 78, 1155 (2001); http://dx.doi.org/10.1063/1.1350622 (3 pages) | Cited 12 times

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A technique for imaging fluid flows is proposed, based on the ultrafast analysis of the ultrasonic speckle signal backscattered by particles following the flow. Such an “ultrasonic speckle velocimetry” (USV) provides two-dimensional measurements of one component of the fluid velocity field at about 5000 frames per second. USV is applied to three different flows and future improvements of the technique are described. © 2001 American Institute of Physics.
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47.80.-v Instrumentation and measurement methods in fluid dynamics
43.35.Yb Ultrasonic instrumentation and measurement techniques
06.30.Gv Velocity, acceleration, and rotation

Observation of multiple nearly monoenergetic electron production by heated pyroelectric crystals in ambient gas

J. D. Brownridge, S. M. Shafroth, D. W. Trott, B. R. Stoner, and W. M. Hooke

Appl. Phys. Lett. 78, 1158 (2001); http://dx.doi.org/10.1063/1.1342209 (2 pages) | Cited 15 times

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Multiple production of nearly monoenergetic electrons at a given pyroelectric crystal surface charge density is observed on cooling or heating the crystal in ambient gas. Typically, the +z base of a 5 mm diam×5 mm crystal of LiNbO3 is heated to 100 °C and then let cool to 23 °C in dry N2 at 10−2–10−6 Torr. The electron spectrum consists of a series of peaks equally spaced in energy and having decreasing intensity with order superimposed on a continuously decreasing background. The higher-order peaks and the high-energy continuum are due to two or more electrons hitting the surface barrier detector within its resolving time (∼1 μs). © 2001 American Institute of Physics.
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79.75.+g Exoelectron emission
77.70.+a Pyroelectric and electrocaloric effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
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