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PubMed2002

Vibrometric studies of the middle ear of the bullfrog Rana catesbeiana II. The operculum.

The operculum and stapes footplate, the two moveable elements within the oval window of the frog, have been thought to function independently. In this study, laser interferometry was used to record the vibrations of both structures in response to free-field airborne sound. Contrary to expectation, the operculum appears to be coupled to the footplate. Coupling is achieved both by means of ligaments and by a cartilaginous flange of the footplate that underlies the operculum. The stapes footplate rotates about an axis located ventrolaterally, but the axis for the operculum is dorsomedial. As a result of this unusual morphology, the opercularis muscle, which connects the operculum and shoulder girdle, can potentially affect the movements of both the operculum and footplate. The proposed roles of the opercularis system in seismic signal detection and extratympanic sound transmission are critically reviewed in the light of this new evidence. An alternative or additional role for the opercularis system is proposed, involving the protection of the inner ear from high-amplitude displacements of the stapes footplate during breathing and vocalisation.

Animals↗
PubMed2002

Effects of age and size in the ears of gekkonomorph lizards: middle-ear sensitivity.

Previous studies of electrophysiological audiograms in gekkonomorph lizards revealed greater sensitivity in adults than in juveniles. We investigated whether this difference, as far as it is affected by the middle ear, is due to animal age or size. The velocity transfer function of the tympanic membrane (TM) was examined using laser interferometry in nine samples: adults of three large gekkonomorph species, adults of three small species (each related to one of the former), and juveniles of the large species, their sizes matching those of the small-species adults. Each transfer function exhibited an inverted 'V' or 'U' shape, with the velocity of TM motion peaking in the mid-frequency range and becoming poorer at lower and higher frequencies. Among samples, maximum TM velocity correlated with animal length, perhaps because of a damping change in the larger TM. The frequency at maximum velocity negatively correlated with measurements of TM area. Presumably, with a larger TM area, the best frequency shifted downward because of increased middle-ear mass or decreased stiffness. The bandwidth of the transfer function negatively correlated with animal length, being broader in smaller animals and sharper in larger animals. This effect can be attributed to increased mass, decreased damping, or both. Among the middle-ear morphological measurements, the one most closely correlated with body length was the length of the extracolumellar anchorage at the TM. Among the physiological variables investigated, maximum velocity was negatively correlated with the frequency at which it occurred. The dependence of these transfer function variables on animal and ear size was similar, regardless of whether the comparison was among adults of species of different sizes, or among age classes within a species, so that age differences appear to be largely the result of size differences.

Acoustic Stimulation↗
PubMed2006

The role of the surface amorphous layer of articular cartilage in joint lubrication.

Articular cartilage is a complex soft tissue that performs multiple functions in the joint. In particular, the amorphous layer that covers the surface of articular cartilage is thought to play some role in lubrication. This study aimed to characterize the surface amorphous layer (SAL) using a variety of techniques, including environmental scanning electron microscopy, transmission electron microscopy, white light interferometry, and biochemical analysis of its composition. Friction tests were conducted to investigate the role of the SAL in lubrication. A protocol to remove successfully the SAL without damaging the underlying cartilage was developed and the material removed from healthy cartilage was found to contain approximately equal quantities of glycosaminoglycan (GAG), protein, and lipid. Cartilage-on-cartilage friction tests were conducted on fresh, healthy cartilage with and without the SAL, under both dynamic and static operating conditions. Removal of the SAL was not found to change the friction coefficient. However, subsequent staining of specimens indicated that the SAL had replenished during the test following loading. The replenished SAL was characterized and found to contain lipids and sulphated GAGs with undetectable protein. This study revealed experimental evidence of surface layer replenishment in articular cartilage. It was postulated that the surface layer regeneration mechanism was purely mechanical and associated with movement of GAGs and lipids through the cartilage matrix during deformation, since the experimental set-up did not contain any means of biochemical activation.

Animals↗
PubMed1996

Effect of counterface material on the characteristics of retrieved uncemented cobalt-chromium and titanium alloy total hip replacements.

A number of total hip components explanted at revision with bearing surfaces in either cobalt-chromium-molybdenum alloy or titanium-6% aluminium-4% vanadium alloy were examined and compared to contemporaneously manufactured but unused items; particular attention was paid to the bearing surfaces which were examined visually, by low-power microscopy, scanning electron microscopy (SEM), confocal microscopy, white light interferometry, laser profilometry and conventional stylus profilometry. The cobalt alloy heads maintained their surface finish well over periods up to 12 years. The titanium implants became badly damaged over much shorter periods although even badly scratched heads continued to meet the current standards for titanium alloy heads. Analysis showed that the damage to the titanium alloy heads was not a random but a well-defined process of scarring of a consistent size created by abrasion with small particles of bone. These damaged heads had the potential to wear the matching UHMWPE components rapidly creating large amounts of polymer debris. The finding that measurement of these damaged heads is within current standards raises concerns as to whether current standards incorporate fully the requirements for clinical performance.

Alloys↗
PubMed2005

Optical coherence tomography.

A review is presented of different scanning, acquisition and processing techniques used to obtain depth-resolved information in optical-coherence tomography (OCT). The principles and performances of different OCT techniques are discussed and images from different types of tissue are presented. Special attention is devoted to the progress in using the time-domain flying spot OCT technique and combination of the en face OCT imaging with confocal microscopy. Although OCT is based on white light interferometry, which is a well established and an old technology, the quest for higher resolution and faster acquisition of in vivo images has ensured OCT a rapid evolution in the last decade. Highly adventurous avenues to expand the OCT capabilities and trends are presented at the end of the review.

Contrast Media↗
PubMed2002

Form assessment of hollow cylindrical specimens.

Grazing-incidence interferometry that makes use of diffractive axicons for the measurement of cylindrical mantle surfaces has already been reported. However, measurement of concave rod structures poses a severe problem because these structures are subject to spurious fringes caused by parasitic diffraction orders of the diffractive axicons. By breaking the symmetry of the interferometric setup it is possible to obtain unique interferograms of the inner mantle surfaces of hollow cylinders as cages for roller bearings or other workpieces produced on lathe machines that have a suitable surface finish. Special design issues for the computer-generated holograms and the interferometric setup are discussed, and test examples are given.

Journal Article↗
PubMed2002

Internal stress and optical properties of Nb2O5 thin films deposited by ion-beam sputtering.

The influence on the internal stress and optical properties of Nb2O5 thin films with ion-beam energy was investigated. Nb2O5 thin films were deposited on unheated glass substrates by means of ion-beam sputtering with different ion-beam voltage, Vb. The refractive index, extinction coefficient, and surface roughness were found to depend on the ion-beam energy. The stresses in thin films were measured by the phase-shifting interferometry technique. The film stress was also found to be related to Vb, and a high compressive stress of -0.467 GPa was measured at Vb = 850 V. The Nb2O5-SiO2 multilayer coatings had smaller average compressive stress as compared with single-layer Nb2O5 film.

Journal Article↗
PubMed2002

Least-mean-squares phase unwrapping by use of an incomplete set of residue branch cuts.

A new technique for the least-mean-squares (LMS) phase-unwrapping method is developed that incorporates the concept of branch cuts between phase singularities (residues), which are usually associated with the path-following gradient integration technique. These branch cuts are introduced by decomposition of the least-mean-squares unwrapped phase into two separate components. The first results from the transverse part of the wrapped phase gradient, which is induced by residues of the original phase, and the second component is due to a potential component, independent of the residues. This decomposition allows the reconstruction of phase patterns with a high level of accuracy and consistency with the initial (wrapped) phase, even when only partial knowledge of the placement of branch cuts between residues is available. We show how the residue-induced phase, ignored by conventional LMS phase estimators, is reconstructed for a given boundary-value problem. The method is illustrated with interferometric quality-control measurements of optical fiber-connector terminations and also with synthetic aperture radar interferometry. These experiments demonstrate the high accuracy of the method in practical situations in which only a limited number of branch cuts are available.

Journal Article↗
PubMed2002

Polarization-mode dispersion measurements in high-birefringence fibers by means of stimulated Raman scattering.

A convenient technique for polarization-mode dispersion measurements in short lengths of high-birefringence fibers is reported. The technique is based on spectral interferometry with a frequency-doubled Nd:YAG laser, which is frequency shifted and broadened by self-stimulated Raman scattering in an optical fiber. The different Raman Stokes beams permit accurate measurements over a 40-nm wavelength range in the visible spectrum.

Journal Article↗
PubMed2002

Error sources and algorithms for white-light fringe estimation at low light levels.

We address the problem of highly accurate phase estimation at low light levels, as required by the Space Interferometry Mission (SIM). The most stringent SIM requirement in this regard is that the average phase error over a 30-s integration time correspond to a path-length error of approximately 30 pm. Most conventional phase-estimation algorithms exhibit significant enough bias at the signal levels at which the SIM will be operating so that some correction is necessary. Several algorithms are analyzed, and methods of compensating for their bias are developed. Another source of error in phase estimation occurs because the phase is not constant over the integration period. Errors that are due to spacecraft motion, the motion of compensating optical elements, and modulation errors are analyzed and simulated. A Kalman smoothing approach for compensating for these errors is introduced.

Journal Article↗
PubMed2002

Microgravity materials and life sciences research applications of digital holography.

We investigate the utility of digital holographic interferometry for analyzing gravity-dependent mass transport phenomena as applicable to materials and life science research topics. Digital holography is useful for measurement of parameters that introduce phase changes in light traversing the material of interest, such as temperature or concentration variations in an aqueous environment. We have constructed, tested, and verified a compact, portable digital holographic monitor (DHM) suitable for characterization of transparent samples. It has proved useful for the study of systems such as protein crystal growth solutions and has been proposed for further application into studies involving microbial metabolism. The DHM is also sufficiently rugged for field operation in challenging environments a s may be encountered in a spacecraft or industrial setting. We discuss some system capabilities and limitations.

Biological Science Disciplines↗
PubMed2002

Automatic alignment of a displacement-measuring heterodyne interferometer.

A technique to align automatically the beams of displacement-measuring interferometric gauges is described. The pointing of the launched beam is modulated in a circular pattern, and the resulting displacement signal is demodulated synchronously to determine the alignment error. This error signal is used in a control system that maintains the alignment for maximum path between a pair of fiducial hollow-cube corner retroreflectors, which minimizes sensitivity to alignment drift. The technique is tested on a developmental gauge of the type intended for the Space Interferometry Mission. The displacement signal for the gauge is generated in digital form; and the lock-in amplifier functions of modulation, demodulation, and filtering are all implemented digitally.

Journal Article↗
PubMed2002

One-beam interferometer by beam folding.

A novel one-beam interferometer based on beam folding is described. The device resembles a Mach-Zehnder interferometer in which the two arms are located together in one collimated beam. Different halves of the same beam interfere with the help of a mirror--with its reflecting surface along the axis of the optical system--placed near the focal plane of the imaging lens. Phase-delay control is achieved by application of an electrical potential to a Pockels cell, which permits the use of techniques of phase-stepping interferometry.

Journal Article↗
PubMed2002

High-accuracy position and orientation measurement of extended two-dimensional surfaces by a phase-sensitive vision method.

We introduced recently phase measurements usually performed in interferometry to the domain of image processing and intelligent vision [IEEE Trans. Instrum. Meas. 49, 867 (2000)]. Our purpose is to sense with a high accuracy the position, orientation, and displacement of two-dimensional (2D) surfaces observed by a static vision system. We report on significant improvements of the method. Experimental measurements reveal a peak-valley noise of approximately 10(-2) CCD pixel, corresponding approximately to a 10(-3) period of the phase reference pattern. Then the observation of 10 microm scaled features enables an accuracy of a few nm in the position sensing of the phase reference pattern for the extended 2D measurement range.

Journal Article↗
PubMed2002

Differential wavelength-scanning heterodyne interferometer for measuring large step height.

An interferometer based on the differential heterodyne configuration and wavelength-scanning interferometry for measuring large step heights is presented. The proposed interferometer is less sensitive to environmental disturbances than other interferometers and can accurately measure interference phases. A tunable diode laser is utilized to illuminate the interferometer and thus solve the phase ambiguity problem. Counting the interference fringes as the wavelength is scanned through a known change in wavelength directly determines the step height. Three gauge blocks of different lengths, 5, 10, and 50 mm, are individually wrung on a steel plate to simulate large step heights. Comparing the results measured by the proposed interferometer with those by the gauge block interferometer reveals that the accuracy is approximately 100 nm.

Journal Article↗
PubMed2002

X-ray-ultraviolet beam splitters for the Michelson interferometer.

With the aim of realizing a Michelson interferometer working at 13.9 nm, we have developed a symmetrical beam splitter with multilayers deposited on the front and back sides of a silicon nitride membrane. On the basis of the experimental optical properties of the membrane, simulations have been performed to define the multilayer structure that provides the highest reflectivity-transmission product. Optimized Mo-Si multilayers have been successfully deposited on both sides of t he membrane by use of the ion-beam sputtering technique, with a thickness-period reproducibility of 0.1 nm. Measurements by means of synchrotron radiation at 13.9 nm and at an angle of 45 degrees provide a reflectivity of 14.2% and a transmission of 15.2% for a 60% s-polarized light, close to the simulated values. Such a beam splitter has been used for x-ray laser Michelson interferometry at 13.9 nm. The first interferogram is discussed.

Journal Article↗
PubMed2002

Oxygen 630.0- and 557.7-nm line source for thermospheric dynamics studies.

A novel design of a rf afterglow source of the oxygen forbidden lines at 630.0 and 557.7 nm for use in thermospheric dynamics studies is presented. With a repetitive discharge-afterglow excitation cycle, the source yields adequate afterglow intensities of the OI lines that are sufficiently free of background continuum for use in Fabry-Perot interferometer measurements of spectral line profiles. These lines provide accurate zero-velocity references in Fabry-Perot determinations of Doppler shifts in the OI thermospheric lines. The design considerations for the rf source are described, together with its preparation and filling by an ultrahigh-vacuum gas-handling system. Examples are given of the source's output spectrum, as measured by a grating spectrometer, and its spectral line profiles, as determined by a Fabry-Perot interferometer. Comparative interferometry between the OI afterglow source lines and nearby (within approximately 0.01-0.02-nm) lines from hollow-cathode sources illustrates the means of establishing secondary reference sources in cases in which the primary OI afterglow source is not available.

Journal Article↗
PubMed2003

Analytical modeling of the white-light fringe.

An analytical technique for extracting phase, visibility, and amplitude information as needed for interferometric astrometry for the Space Interferometry Mission (SIM) is presented. This model accounts for a number of physical and instrumental effects and is valid for the general case of a bandpass filter. I was able to obtain a general solution for polychromatic phasors and to address the properties of unbiased fringe estimators in the presence of noise. For demonstration purposes I studied a rectangular bandpass filter with two different methods of optical path difference (OPD) modulation: stepping and ramping OPD modulation. A number of areas for further studies relevant to instrument design and simulations are outlined and discussed.

Journal Article↗