Michael I. Bell

Miniature valveless ultrasonic pumps and mixers

Abstract Miniature acousto-fluidic devices are described that operate as pumps without valves in channel widths of millimeters and below. These devices can also be configured to produce mixing in low-Reynolds-number flows. The prototypes are based on radio-frequency, ultrasonic piezoelectric transducers that exert a directed body force on the fluid via acoustic attenuation. The process is a type of acoustic streaming termed quartz wind. In microfluidics applications, this mechanism has the advantages of insensitivity to the chemical state of the fluid or walls and greatly reduced crosstalk in a multichannel system. The observed pump flow velocities are on the order of 1 mm/s in 1.6×1.6 mm 2 channels and with a calculated maximum backpressure that can be pumped against of 0.13 Pa. Due to the low backpressure, quartz wind devices are not competitive pumps for open-loop and high-impedance microfluidics systems but could find application in pumping in low-impedance planar and closed-loop systems and for mixing in reservoirs and channels.

Vibrational Analysis of the Dioctahedral Mica: 2M1 Muscovite

Abstract Raman spectra and lattice dynamics calculations are presented for the dioctahedral mica, muscovite. Calculated fundamental mode frequencies for the Raman-active and Ag and Bg species were fit to observed fundamentals assigned to features in the two polarized Raman spectra collected, so that unambiguous vibrational assignments could be made to most peaks in the Raman data. Calculated frequencies for the IR-active Au and Bu modes generally fall within the frequency ranges of bands in the IR spectra for muscovite presented earlier. Factor group analysis indicates that motion from all atom types in the muscovite structure can be found in modes for all four vibrational species. Force constant values determined for muscovite are similar to equivalent values calculated for the trioctahedral mica, phlogopite. Raman and IR-active modes calculated at frequencies greater than 800 cm-1 are dominated by internal sheet T-O stretch and T-O-T bend motions, where T is a tetrahedral site. Modes between 800 and 360 cm-1 have internal tetrahedral sheet motions mixed with K and octahedral Al displacements. Modes at frequencies less than 360 cm-1 have lattice and OH motions. Inter-sheet bonding in the muscovite structure is strong enough to affect modes at frequencies as high as 824 cm-1.

Raman spectra and vibrational analysis of the trioctahedral mica phlogopite

Abstract The use of a direct crystallographic technique is reported for locating Cr atomic sites in a mullite containing 11.5 wt% Cr2O3 by monitoring variations in characteristic X-ray emission rates as a function of fast electron beam orientation. Systematic examination of two dimensional incoherent channeling patterns (ICP), formed from characteristic X-ray emissions from Al, Si, and Cr, and recorded near low index zone axis orientations, has enabled the preferred lattice position of Cr in mullite to be identified as the interstitial site 0, 0.25, 0. Although the method of atom location by channeling enhanced microanalysis (or ALCHEMI) generally has been applied in situations where introduced minority atom species are accommodated in substitutional atomic positions, this study illustrates the identification of an interstitial site of an introduced dopant species. This result does not coincide with that derived from X-ray Rietveld refinement. The ICP method is analytically robust and, unlike Rietveld refinement, does not require a highly accurate model of the host lattice framework and composition. ICP analysis therefore may be more appropriate for this particular application.

Vibrational analysis of beryl (Be3Al2Si6O18) and its constituent ring (Si6O18)

The normal modes of vibration and their frequencies are calculated for beryl, a mineral whose crystal structures (space group D6h2) consists of six-membered silicate rings (Si6O18) linked by Be2+ and Al3+ ions. A valence force potential is used, consisting of central interactions between nearest neighbors and bond-bending interactions centered at the Si4+, Be2+, and Al3+ ions. The force constants are determined by fitting the calculated frequencies to the results of a complete study of the Raman spectra of a large single crystal. The calculated frequencies are in reasonable agreement with experiment, permitting unambiguous assignment of normal modes to the observed spectral lines. In several cases, the resulting interpretation of spectral features differs significantly from those published previously. Considerable mixing of Al and Be motions with those of the ring is found for the Raman-active modes near 750 cm−1 and above 850 cm−1, respectively. The normal modes and frequencies of the hypothetical isolated ring with C6h symmetry are determined by neglecting all interactions between the rings and the surrounding Be and Al atoms. This identification of normal modes characteristic of six-membered silicate rings and the effect of the environment of these modes may prove useful in the interpretation of infrared and Raman spectra of amorphous silicates.

Acousto- and electro-osmotic microfluidic controllers

Acoustic and electroosmotic uni-directional pumping mechanisms for single and multichannel valve-less fluidic pumps and controllers are compared. Geometry, scaling, efficiency and heating, fluid restrictions, and wall materials for the mechanisms are analyzed.

Vibrational analysis of dioptase Cu6Si6O18 · 6(H2O) and its puckered six-membered ring

AbstractThe normal modes of vibration and their frequencies are calculated for dioptase, a mineral whose crystal structure (space group R

Novel X-ray sources and systems using gated electron emitters

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Inclusion of local structure effects in theoretical x-ray resonant scattering amplitudes using ab initio x-ray-absorption spectra calculations

or C3i2) consists of puckered six-membered silicate rings (Si6O18) linked by Cu2+ ions and H2O groups. The calculation employs a valence force potential consisting of central interactions between nearest neighbors and bond-bending interactions centered at the Si4+ and Cu2+ ions. The force constants are determined by fitting the calculated frequencies to values obtained by measuring the single-crystal Raman spectra. The calculated frequencies are in reasonable agreement with experiment, permitting assignment of normal modes to the observed spectral frequencies. Considerable mixing of Cu and H2O motions with those of the ring is found for the Raman-active modes below 430 cm-1. The normal modes and frequencies of the hypothetical isolated ring with C3i symmetry are determined by neglecting all interactions between the rings and the surrounding Cu and H2O. The identification of normal modes characteristic of the puckered six-membered silicate rings and the effect of the environment on these modes may prove useful in the interpretation of the Raman spectra of amorphous silicates.