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At least 1,315 records · Page 73Linked to original sources
PubMed2002

Inertial deposition effects: a study of aerosol mechanics in the trachea using laser Doppler velocimetry and fluorescent dye.

This study characterizes the axial velocity and axial turbulence intensity patterns noted in the tracheal portion of a cadaver-based throat model at two different steady flow rates (18.1 and 41.1 LPM.) This characterization was performed using Phase Doppler Interferometry (Laser Doppler Velocimetry). Deposition, as assessed qualitatively using fluorescent dye, is related to the position of the laryngeal jet within the trachea. The position of the jet is dependent on the downstream conditions of the model. It is proposed therefore that lung/airway conditions may have important effects on aerosol deposition within the throat. There is no correspondence noted between regions of high axial turbulence intensity and deposition.

Administration, Inhalation↗
PubMedDate not supplied

Photomechanical investigations on the stress-strain relationship in dentine macrostructure.

In this study photomechanical experiments were carried out to examine the relationship between macroscopic mechanical stress and strain gradients within the root dentine structure. Three-dimensional digital photoelasticity was used to study the stress distribution patterns in tooth models, while digital moire interferometry was used to study the strain gradients within the natural teeth. The stress analysis showed a distinct bending stress distribution, along faciolingual plane in the coronal and cervical regions of the tooth. There was a reduction in bending towards the apical third of the tooth model. The strain analysis displayed strain gradients in the axial (along the long axis of the tooth) and lateral (perpendicular to the long axis of the tooth) directions in dentine. There was a conspicuous reduction in strains from the cervical to the apical third of the root dentine. The root dentine displayed uniform distribution of normal strains. Although there was a steep increase in stresses from the inner core region to the outer surface of an isotropic tooth model, there were more uniform strain gradients in the natural dentine structure. It is apparent from these observations that complex organization of material properties facilitated distinct strain gradients in dentine structure during mechanical functions.

Anisotropy↗
PubMedDate not supplied

Doppler flow imaging of cytoplasmic streaming using spectral domain phase microscopy.

Spectral domain phase microscopy (SDPM) is a function extension of spectral domain optical coherence tomography. SDPM achieves exquisite levels of phase stability by employing common-path interferometry. We discuss the theory and limitations of Doppler flow imaging using SDPM, demonstrate monitoring the thermal contraction of a glass sample with nanometer per second velocity sensitivity, and apply this technique to measurement of cytoplasmic streaming in an Amoeba proteus pseudopod. We observe reversal of cytoplasmic flow induced by extracellular CaCl2, and report results that suggest parabolic flow of cytoplasm in the A. proteus pseudopod.

Amoeba↗
PubMedDate not supplied

Investigations on the dynamics of water in the macrostructural dentine.

The purpose of this study was twofold: (1) to investigate the nature and degree of water loss at 21 degrees C, 60% relative humidity (dehydration) and at 105 degrees C (desiccation), and to relate these findings with (2) the strains produced in the dentine structure during dehydration and rehydration processes. In stage 1, digital moire interferometry (DMI) was used to study the strain distribution pattern during dehydration and rehydration at 21 degrees C. In stage 2, the nature and degree of water loss was determined using gravimetric analysis and nuclear magnetic resonance spectroscopy. DMI showed that dehydration produced strains in the dentine structure after an initial latent period. Gravimetric analysis showed that dentine exhibited an initial rapid water-loss phase followed by a slow and steady water-loss phase. Though the major portion of water loss occurred in the initial 2 h of dehydration (rapid water-loss phase), no obvious strains were produced during this period. Rehydration lead to the major reversal of dehydration-induced water loss and strains in dentine. Heating at 105 degrees C resulted in further substantial loss of water from dentine. These experiments highlighted that the free water in the dentine surface, porosities and tubules are lost rapidly and constitute the major water lost when dehydrated at 21 degrees C.

Absorption↗
PubMedDate not supplied

Observation of microwave-induced eye lens surface motion in vitro.

Previous experiments have shown that murine ocular lenses immersed in saline in vitro suffered microscopic physical damage (including cataractogenic changes) after exposure to pulsed microwaves under conditions in which the temperature rise was negligible. The suspected coupling mechanism is thermoelastic transduction (TET). To test this hypothesis, laser interferometry was used to measure the lens surface motion induced by pulsed microwaves. Although experimental constraints delayed the recording of surface motion data until 0.5 ms after the microwave pulse, damped oscillatory motion was measured over an interval of several milliseconds. A theoretical model is presented to explain the observed motion as natural oscillation modes of an elastic sphere excited by TET waves produced in the surrounding saline. Effects of the lens capsule are also discussed. The conclusions reached are that the observed motion is TET induced, but the lens damage occurs during the passage of the initial excitatory TET waves through the lens, an event which could not be monitored by this experiment.

Animals↗
PubMed2003

Musical quality assessment of clarinet reeds using optical holography.

Vibrational modes of 24 clarinet reeds have been observed in both dry and wet conditions using holographic interferometry. Results have been compared with the "musical quality" of the reeds as judged by two professional clarinet players. An excellent correspondence has been demonstrated between specific vibrational behavior and musical quality. The results suggest that the presence and symmetry of a strong first torsional mode are indicative of good or very good musical quality. A second, but less stringent quality criterion is the proximity of frequencies corresponding to the second torsional and the second flexural mode. This proximity leads to the creation of mixed vibrational modes for the very best of the investigated clarinet reeds.

Journal Article↗
PubMed2003

Numerical and experimental modal analysis of the reed and pipe of a clarinet.

A modal computation of a complete clarinet is presented by the association of finite-element models of the reed and of part of the pipe with a lumped-element model of the rest of the pipe. In the first part, we compare modal computations of the reed and the air inside the mouthpiece and barrel with measurements performed by holographic interferometry. In the second part, the complete clarinet is modeled by adjoining a series of lumped elements for the remaining part of the pipe. The parameters of the lumped-resonator model are determined from acoustic impedance measurements. Computed eigenmodes of the whole system show that modal patterns of the reed differ significantly whether it is alone or coupled to air. Some modes exhibit mostly reed motion and a small contribution of the acoustic pressure inside the pipe. Resonance frequencies measured on a clarinet with the mouthpiece replaced by the cylinder of equal volume differ significantly from the computed eigenfrequencies of the clarinet taking the actual shape of the mouthpiece into account and from those including the (linear) dynamics of the reed. This suggests revisiting the customary quality index based on the alignment of the peaks of the input acoustical impedance curve.

Acoustics↗
PubMed2006

Geometrical effects on the tuning of Chinese and Korean stone chimes.

The vibrational mode frequencies and mode shapes of ancient stone chimes are analyzed and their dependence on stone shapes are discussed. Mode shapes and frequencies of several chime models are determined by using finite element methods, and these show good agreement with mode shapes and frequencies observed in Korean pyeongyeong chime stones using holographic interferometry and experimental modal testing. The dependence of mode shapes and frequencies on vertex angle and base curvature suggests that the geometries used in late Chinese bianqing and Korean pyeongyeong may have been selected to give the best sound.

Letter↗
PubMed1990

Direct estimation of aberrating delays in pulse-echo imaging systems.

Nearfield fluctuations in wave propagation velocity and system timing errors are among the sources of focusing aberrations in pulse-echo imaging systems. For situations in which the source of these errors can be modeled by a stationary phase aberrator placed in front of the transmitter and receiver aperture, appropriate electronic delays might be applied to the signals associated with each array element in order to restore the system to focus. A method is described and evaluated for estimating the set of aberrating delays in a linear array utilizing data from a single two-dimensional scan. The underlying principle is analogous to that of phase closure used for one-way passive interferometry and readily generalizes to two-dimensional arrays. Although the following theory is developed in the context of acoustic imaging, the general approach is applicable to other pulse-echo systems, such as radar.

Acoustics↗
PubMed1996

Middle-ear development VII: umbo velocity in the neonatal rat.

Laser interferometry was used to measure umbo velocity in the developing rat. The tympanic membrane was stimulated with pure tones between 0.4 and 40.0 kHz, at intensity levels between 50 and 130 dB SPL. The corresponding umbo velocity response was measured. Umbo velocity responded linearly with respect to sound pressure throughout development. When the stimulus level was held constant at 100 dB SPL, all animals displayed a velocity response that increased with frequency until a peak response was reached at about 20.0 kHz. Above this frequency the response decreased in all age groups. Umbo velocity increased with age at all frequencies, and at 1.0, 2.0, 4.0, 8.0, 16.0, and 32.0 kHz the velocity reached 90% of its mature value by 68, 24, 24, 15, 19, and 50 days after birth, respectively. These age-related increases in tympanic membrane velocity coincided with improvements in compound action potential (CAP) thresholds (as measured by other investigators) at similar frequencies. Both umbo velocity and CAP thresholds showed substantial growth after 10 days of age. The role of middle-ear functional development with respect to overall auditory sensitivity is discussed.

Acoustic Stimulation↗
PubMed1997

Two-tone suppression of basilar membrane vibrations in the base of the guinea pig cochlea using "low-side" suppressors.

The responses of the basilar membrane (BM) in the basal section of the guinea pig cochlea were measured by laser interferometry. The stimuli were pairs of harmonically related tones, presented simultaneously. One tone, at the BM's characteristic frequency (CF) of about 17 kHz, was presented at a low intensity. The other tone, presented at various intensities, was a "low-side" suppressor, with a frequency of 0.2-8 kHz. As observed by many others, the suppressor tone, when presented at high enough intensity, reduced the magnitude of the CF component of BM displacement, sometimes dramatically. However, regardless of whether the CF component was suppressed or not, the sum of the displacement amplitudes of the CF and suppressor components was always greater than the displacement amplitude of the unsuppressed CF component. For suppressor frequencies up to 4 kHz, the suppression was both tonic and phasic, and synchronized to the suppressor period. For higher suppressor frequencies, principally tonic suppression was seen.

Acoustic Stimulation↗
PubMed2001

Phase-coherent optical pulse synthesis from separate femtosecond lasers.

We generated a coherently synthesized optical pulse from two independent mode-locked femtosecond lasers, providing a route to extend the coherent bandwidth available for ultrafast science. The two separate lasers (one centered at 760 nanometers wavelength, the other at 810 nanometers) are tightly synchronized and phase-locked. Coherence between the two lasers is demonstrated via spectral interferometry and second-order field cross-correlation. Measurements reveal a coherently synthesized pulse that has a temporally narrower second-order autocorrelation width and that exhibits a larger amplitude than the individual laser outputs. This work represents a new and flexible approach to the synthesis of coherent light.

Journal Article↗
PubMed2002

Rapid bottom melting widespread near Antarctic Ice Sheet grounding lines.

As continental ice from Antarctica reaches the grounding line and begins to float, its underside melts into the ocean. Results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed. The melting rate is positively correlated with thermal forcing, increasing by 1 meter per year for each 0.1 degrees C rise in ocean temperature. Where deep water has direct access to grounding lines, glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature.

Journal Article↗
PubMed2002

Formation of a matter-wave bright soliton.

We report the production of matter-wave solitons in an ultracold lithium-7 gas. The effective interaction between atoms in a Bose-Einstein condensate is tuned with a Feshbach resonance from repulsive to attractive before release in a one-dimensional optical waveguide. Propagation of the soliton without dispersion over a macroscopic distance of 1.1 millimeter is observed. A simple theoretical model explains the stability region of the soliton. These matter-wave solitons open possibilities for future applications in coherent atom optics, atom interferometry, and atom transport.

Journal Article↗
PubMed2004

InSAR observations of low slip rates on the major faults of western Tibet.

Two contrasting views of the active deformation of Asia dominate the debate about how continents deform: (i) The deformation is primarily localized on major faults separating crustal blocks or (ii) deformation is distributed throughout the continental lithosphere. In the first model, western Tibet is being extruded eastward between the major faults bounding the region. Surface displacement measurements across the western Tibetan plateau using satellite radar interferometry (InSAR) indicate that slip rates on the Karakoram and Altyn Tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in Tibet.

Journal Article↗
PubMed2004

Discovery of a compact radio component in the center of supernova 1986J.

Very-long-baseline interferometry observations have revealed a bright, compact radio component near the center of the expanding shell of supernova 1986J. The component, not present in earlier images, has an inverted radio spectrum different from that of the shell. Such an inversion has not been seen in the spectrum of any other supernova. The new component is likely radio emission associated either with accretion onto a black hole or with the nebula formed around an energetic young neutron star in the center of SN 1986J, which would directly link either a black hole or a neutron star to a modern supernova.

Journal Article↗
PubMed2005

Light scattering to determine the relative phase of two Bose-Einstein condensates.

We demonstrated an experimental technique based on stimulated light scattering to continuously sample the relative phase of two spatially separated Bose-Einstein condensates of atoms. The phase measurement process created a relative phase between two condensates with no initial phase relation, read out the phase, and monitored the phase evolution. This technique was used to realize interferometry between two trapped Bose-Einstein condensates without need for splitting or recombining the atom cloud.

Journal Article↗
PubMed2006

Changes in the velocity structure of the Greenland Ice Sheet.

Using satellite radar interferometry observations of Greenland, we detected widespread glacier acceleration below 66 degrees north between 1996 and 2000, which rapidly expanded to 70 degrees north in 2005. Accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year. As more glaciers accelerate farther north, the contribution of Greenland to sea-level rise will continue to increase.

Journal Article↗