13,369 research outputs found
Self-excited piezoelectric cantilever oscillators
No full textWe describe a micromachined self-excited piezoelectric cantilever device whose oscillating frequency is in the audio range. The 2000 mu m X 2000 mu m X 2.8 mu m cantilever has a zinc oxide (ZnO) piezoelectric thin film between two aluminum (Al) layers on a supporting layer of low-pressure chemical-vapor-deposited (LPCVD) low-stress silicon nitride. The transducer and an amplifier that drives the cantilever via a driving electrode constitute a self-excited unit. If the gain of the amplifier is sufficient to overcome the loss of the transducer and the resonance frequency is in the amplifier passband, the device oscillates and produces significant acoustic output. The self-excited acoustic output transducer could serve as a sensor for environmental quantities such as relative humidity or chemical vapor concentration. Simulation results show that the gravimetric sensitivity exceeds 5000 cm(2) g(-1) when the whole cantilever is covered with the sorptive film
Piezoelectric cantilever voltage-to-frequency converter
No full textA micromachined piezoelectric cantilever acoustic device that functions as a microspeaker and a voltage-to-frequency converter has been designed, fabricated and tested. The 2 x 2 x 0.0047 mm(3) cantilever has a 1.3-mu m-thick zinc oxide (ZnO) piezoelectric thin film on a supporting layer of LPCVD low-stress silicon nitride. When measured with 8 VP-P (peak-peak) input drive, the sound pressure level (SPL) of the cantilever microspeaker output is higher than 70 dB at 5 kHz at a distance of 0.5 cm. The microspeaker also can be used as a voltage-to-frequency converter by the addition of a silicon top plate and an aluminum (Al) sputtered layer on the backside of the cantilever. The resonant frequency of the microspeaker is changed by the potential applied between the top plate and the backside Al layer. As the potential is changed from 0 to 40 VP-P, the resonant frequency shifts down from 14.5 to 11.5 kHz. In the potential range of 15 to 25 VP-P, the frequency shift is fairly linear with the potential change and the sensitivity (frequency shift/applied potential change) is 200 Hz/V around 13 kHz. (C) 1998 Elsevier Science S.A. All rights reserved
Piezoelectric cantilever acoustic transducer
No full textWe present a piezoelectric acoustic transducer fabricated on a bulk-micromachined cantilever diaphragm. Use of the cantilever as a supporting diaphragm produces a highly sensitive microphone. In addition, when the device is driven electrically as an output transducer, a microspeaker, the relatively large deflections produce significant acoustic output. A voltage-to-frequency converter has also been demonstrated with piezoelectric cantilever transducers. The 2 x 2 x 0.0047 mm(3) micromachined transducer has a zinc oxide (ZnO) piezoelectric thin film on a 1.5 mu m thick cantilever diaphragm, made of LPCVD low-stress silicon nitride. The measured cantilever microphone sensitivity is fairly constant around 3 mV mu bar(-1) in the low-frequency range below the first resonant frequency, which occurs at 1.8 kHz. The microspeaker output is approximately 100 dB SPL at 4.8 kHz and 12 VP-P (peak-peak) input drive. The voltage-to-frequency conversion is accomplished by the addition of a conducting plate and an aluminum (Al) sputtered layer on the underside of the cantilever. The resonant frequency of the microspeaker is changed by the potential applied between the top conducting plate and the lower Al layer. As the potential is changed from 0 to 40 VP-P, the resonant frequency shifts down from 14.5 kHz to 11.5 kHz while the amplitude of the output pressure is increased by 12.5 dB SPL. In the potential range of 15 to 25 VP-P, the frequency shift is fairly linear with the potential change and the sensitivity (frequency shift per unit applied potential change) is 200 Hz V-1 around 13 kHz
The 2D/3D dynamics of wall-bounded low-Rm magnetohydrodynamic (MHD) turbulence
No full textWith this experimental study, we give evidence that the dynamics of low-Rm MHD turbulence depends on the diffusion length l_z, which corresponds to the distance over which the Lorentz force is able to diffuse momentum before it is balanced by inertia
[ICI Photograph - RM Currie?]
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/450242Black and white portrait photograph of man. Handwritten on verso: "Dunstan 15573 ICI Work study RM Currie". 9x12 cm337172
Item: [2022.0033.00139] "[ICI Photograph - RM Currie?]
The clinical importance of white matter hyperintensities on brain magnetic resonance imaging: systematic review and meta-analysis.
No full textObjectives: To review the evidence for an association of white matter hyperintensities with risk of stroke, cognitive decline, dementia, and death.
Design: Systematic review and meta-analysis.
Data sources: PubMed from 1966 to 23 November 2009.
Study selection: Prospective longitudinal studies that used magnetic resonance imaging and assessed the impact of white matter hyperintensities on risk of incident stroke, cognitive decline, dementia, and death, and, for the meta-analysis, studies that provided risk estimates for a categorical measure of white matter hyperintensities, assessing the impact of these lesions on risk of stroke, dementia, and death.
Data extraction: Population studied, duration of follow-up, method used to measure white matter hyperintensities, definition of the outcome, and measure of the association of white matter hyperintensities with the outcome.
Data synthesis: 46 longitudinal studies evaluated the association of white matter hyperintensities with risk of stroke (n=12), cognitive decline (n=19), dementia (n=17), and death (n=10). 22 studies could be included in a meta-analysis (nine of stroke, nine of dementia, eight of death). White matter hyperintensities were associated with an increased risk of stroke (hazard ratio 3.3, 95% confidence interval 2.6 to 4.4), dementia (1.9, 1.3 to 2.8), and death (2.0, 1.6 to 2.7). An association of white matter hyperintensities with a faster decline in global cognitive performance, executive function, and processing speed was also suggested.
Conclusion: White matter hyperintensities predict an increased risk of stroke, dementia, and death. Therefore white matter hyperintensities indicate an increased risk of cerebrovascular events when identified as part of diagnostic investigations, and support their use as an intermediate marker in a research setting. Their discovery should prompt detailed screening for risk factors of stroke and dementia
The nature of ammonium ion disorder in ammonium tetrafluoroaluminate, NHAlF
No full textPT: J; CR: BERRY LG, 1976, POWDER DIFFRACTION F BRADE RM, 1971, J PHYS C SOLID STATE, V4, P876 BULOU A, 1982, MATER RES BULL, V17, P391 CHIHARA H, 1983, PHYS CHEM, V87, P188 COUZI M, 1983, PHYS CHEM, V87, P232 COUZI M, 1985, J PHYS-PARIS, V46, P435 DAGHORN Y, 1985, J PHYS C SOLID STATE, V18, P383 FOURQUET JL, 1979, REV CHIM MINER, V16, P490 GIRDHAR HL, 1968, J CHEM ENG DATA, V13, P239 KNOP O, 1985, CAN J CHEM, V63, P516 KOBAYASHI K, 1985, SOLID STATE COMMUN, V53, P719 LAUNAY JM, 1984, MATER RES SOC S P, V21, P167 LEBLE A, 1982, PHYS STATUS SOLIDI, V69, P249 MACKOWIAK M, 1984, MAT RES B, V19, P249 NYQUIST RA, 1971, INFRARED SPECTRA INO PARSONAGE NG, 1978, DISORDER CRYSTALS SHINN DB, 1966, INORG CHEM, V5, P1927 SIMON F, 1922, ANN PHYS-BERLIN, V68, P241 VANOORT MJM, J CHEM SOC F1 WAGNER EL, 1950, J CHEM PHYS, V18, P296 WEIR RD, 1980, J CHEM PHYS, V73, P1386 WESTRUM EF, 1969, J CHEM PHYS, V50, P5083 WHITE MA, UNPUB WHITE MA, 1981, J CHEM THERMODYN, V13, P283 WHITE MA, 1984, THERMOCHIM ACTA, V74, P55; NR: 25; TC: 9; J9: J CHEM PHYS; PG: 5; GA: AUR04Source type: Electronic(1
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