Modeling resonance tests for electrostrictive ceramics

The electromechanical coupling coefficient represents a useful figure-of-merit for comparing the quality of different electroactive materials. However, the coupling coefficient for an electrostrictive ceramic is not a unique material parameter, because it depends strongly on the applied DC bias field, AC field amplitude and frequency, and stress. These dependencies make direct comparison between electrostrictors and piezoelectrics somewhat ambiguous. In this paper, we developed a pair of coupling parameters for electrostrictors that were strictly material constants and completely characterized the material's electromechanical quality. We proposed relatively simple, inexpensive resonance testing to measure these new parameters from the electrical admittance of a vibrating electrostrictive rod. The electromechanical coupling coefficient for a specific loading condition is computed from these parameters, allowing direct comparison between electrostrictive and piezoelectric materials.     

Noninvasive measurement of compliance of human leg arteries

Electrical impedance plethysmography has been evaluated for early detection of peripheral atherosclerosis. A pressure cuff was wrapped around the lower leg and the cuff pressure increased. Two circumferential electrodes glued in the middle of the cuff recorded the impedance pulse, from which the arterial pulse volume was calculated. The ratio of maximal arterial volume change to the pulse pressure was determined as a measure of maximal compliance Cp. Based on the data from 118 human subjects, Cp was found to correlate well with known cardiovascular risk factors. For example, Cp decreased on the average from 3.08 to 1.92 microL.mm Hg-1.cm-1 (1 microL.mm Hg-1.cm-1 = 7.5 x 10(-10) m4.N-1) in groups of subjects of increasing age from 22 to 70 years. Subjects on a regular exercise program had an average value of 3.86, while those with proven peripheral vascular disease had a value of 0.70. In a related pathologic validation study on 15 monkeys fed a cholesterol-control diet a good correlation was found between the limb peak compliance and morphometric data obtained from iliac and carotid arteries.     

Selective flocculation of iron oxide-kaolin mixtures using a modified polyacrylamide flocculant

High molecular weight polyacrylamides were synthesized and successfully modified to contain up to 8·3% hydroxamate functional groups. The selective flocculation tests carried out on 1:1 iron oxide/kaolin mixtures using parent polyacrylamide, polyacrylic acid and the modified polyacrylamide, confirm the possibility of enhancing selectivity through introduction of iron chelating functional groups in commercially available polymers. Starting with a feed grade of 35% iron, 92% recovery with acceptable grade of 60% iron has been achieved using the modified polyacrylamide. NCL communication No. 4415     

Nonlinear surface acoustic waves on an isotropic solid

A systematic derivation of the approximate coupled amplitude equations governing the propagation of a quasi-monochromatic Rayleigh surface wave on an isotropic solid is presented, starting from the non-linear governing differential equations and the non-linear free-surface boundary conditions, using the method of mulitple scales. An explicit solution of these equations for a signalling problem is obtained in terms of hyperbolic functions. In the case of monochromatic excitation, it is shown that the second harmonic amplitude grows initially at the expense of the fundamental and that the amplitudes of the fundamental and second harmonic remain bounded for all time.     

Pulse oximetry theory and calibration for low saturations

Pulse oximetry is a widely used technique in biomedical optics, but currently available pulse oximeters rely on empirical calibration approaches, which perform poorly at low saturations. We present an exact solution for pulse oximetry and show how this can be used as the basis for the development of a semiempirical calibration approach that may be useful, especially at low saturations and variable probe geometries. This new approach was experimentally tested against traditional empirical calibration techniques on transmission pulse oximetry for monitoring of fetal sheep using a minimally invasive spiral probe. The results open the way for the development of more accurate pulse oximetry.     

Variability of mesopause temperature derived from two independent methods using meteor radar and its comparison with SABER and EOS MLS and a collocated multi-wavelength dayglow photometer over an equatorial station,Thumba (8.5° N, 76.5° E)

Two independent methods for deriving mesopause temperature using meteor radar installed at an equatorial station, Thumba (8.5° N, 76.5° E), are discussed in this article. This meteor radar-derived mesopause temperature is then compared with two different types of spaceborne measurement, namely (i) Sounding the Atmosphere using Broadband Emission Radiometry (SABER) and (ii) the Earth Observing System Microwave Limb Sounder (EOS MLS), and a collocated multi-wavelength dayglow photometer (DGPM). The meteor radar-derived temperature is in fairly good agreement with all the three measurement techniques, with an uncertainty of ±10°. This study focuses on a detailed evaluation and inter-comparison of mesopause temperature derived from different measurement techniques. An attempt is also made to compare the suitability of these observations to study planetary waves and other oscillation activities in the mesospheric region.     

A Low Power Photoemission Source for Electrons on Liquid Helium

Electrons on the surface of liquid helium are a widely studied system that may also provide a promising method to implement a quantum computer. One experimental challenge in these studies is to generate electrons on the helium surface in a reliable manner without heating the cryo-system. An electron source relying on photoemission from a zinc film has been previously described using a high power continuous light source that heated the low temperature system. This work has been reproduced more compactly by using a low power pulsed lamp that avoids any heating. About 5×10³ electrons are collected on 1 cm² of helium surface for every pulse of light. A time-resolved experiment suggests that electrons are either emitted over or tunnel through the 1 eV barrier formed by the thin superfluid helium film on the zinc surface. No evidence of trapping or bubble formation is seen.     

A computational method for regularized long wave equation

Quintic spline technique and splitting method have been used to develop a new-finite difference method to solve regularized long wave (RLW) equation. The convergence and the stability of the proposed method are discussed. Then, it is used to model solitary wave motion and undular bore development by solving two test examples.     

Mueller-matrix Ellipsometry on Electroformed Rough Surfaces

Abstract

Automated Mueller-matrix ellipsometry was used to investigate the optical properties of electroformed standard rough surfaces as a function of r.m.s. surface roughness heights and angle of incidence. The r.m.s. roughness of the specimens examined varied from 50 to 12 500 nm. Six different surface finishes and 22 different specimens were examined and Mueller matrices were obtained at angles of incidence that varied from 30 to 80°. Measurements were conducted at a wavelength of 633 nm with the use of a division-of-amplitude photopolarimeter capable of simultaneously measuring all four Stokes parameters of arbitrarily polarized light. Values of ψ and Δ, the ellipsometric parameters, were derived from the measured Mueller matrices. The results demonstrate firstly the monotonic variations in the derived values of Δ with surface roughness for fixed angles of incidence, which include a ‘resonance’ effect for specimens with r.m.s. roughness heights close to the wavelength of light, secondly a systematic variation of ψ with the angle of incidence for different specimen roughness values and a reversal in these trends beyond the pseudo-Brewster angle, thirdly a monotonic variation in Δ values with the angle of incidence for different roughness values, fourthly relatively large variations in ψ values for roughness values close to the wavelength of light and fifthly relatively little change in ψ and Δ values for roughness values that greatly exceeded the wavelength of light.