Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “INTERFEROMETRY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,639 records · Page 91Linked to original sources
PubMed1997

Correlation of microhardness and wear in differently eroded bovine dental enamel.

The purpose of the study was to compare the microhardness data of differently eroded enamel surfaces with the wear caused by toothbrushing. Sixty bovine enamel specimens were polished and prepared for microhardness determination. The polished surfaces were covered with tape except for a 1.3 x 10.0 mm window. Fifteen specimens each were stored in an erosive beverage (Sprite Light) for either 1, 5 or 15 min. Each specimen was immersed in 10 ml of the beverage. The remaining 15 specimens were not eroded. Interferometrical analysis revealed that substance loss after 15 min of erosion was negligibly low (about 75 mm). In all specimens Vickers microhardness determinations were conducted on eroded (= final hardness) and non-eroded (= initial hardness) enamel surfaces. The specimens were subsequently submitted to toothbrushing abrasion using a slurry consisting of 1 g non-fluoridated dentifrice in 5 ml artificial saliva. The total amount of tooth wear due to erosion and subsequent abrasion was profilometrically evaluated. Statistical analysis revealed a significant decrease in hardness and a significant increase in wear with increasing time of storage in the erosive beverage. Overall regression analysis yielded a statistically significant correlation between both initial and final hardness and the amount of tooth wear. The correlation of abrasion and final hardness could be described by a quadratic mathematical function. It is concluded that the susceptibility of eroded enamel to toothbrushing abrasion can be correlated with Vickers microhardness values, thereby suggesting an overproportionate increase of abrasion with decreasing hardness values.

Animals↗
PubMed1988

Principal component analysis of intercusp distances on the lower first molars of three human populations.

The distances between the five main cusps of lower first molars were measured on moiré photographs of casts obtained from Japanese, Dutch and Australian Aboriginal children. Principal component analysis of the intercusp distances, log transformed and standardized so that average tooth size was held constant, revealed three sources of shape variation in cusp topography. All populations were similar for scores on component 1 which was concerned with variations in the position of the hypoconulid. The Dutch had lowest scores on component 2 indicating small buccolingual distances compared with mesiodistal, whereas the Australian Aboriginals had the lowest mean score on component 3, expressing the distances between metaconid, entoconid and hypoconulid.

Asian People↗
PubMed1982

Analysis of human back shape using surface curvatures.

A method for the evaluation of surface measurements of the human back is presented. A shape analysis is carried out in terms of surface curvature. This is calculated using differential geometry of surfaces. Similar to other invariant shape parameters, the surface curvature does not depend on a coordinate system and is thus independent of the patient's position. The advantages of such an invariant shape analysis are discussed and first results are presented.

Back↗
PubMed1984

Detection of stimulated back muscle contractions by moiré topography.

The ability to treat scoliosis via surface stimulated trunk muscle contractions is now being evaluated at several treatment centers. In order to make biomechanical analysis of the procedure, so that the technique can be used optimally, data are needed to quantify the muscle contractions and structural changes by different electrode locations. This paper presents the use of a modified shadow moiré technique to quantify geometric changes resulting from electrical stimulation applied to the surface of the back in a healthy subject.

Back↗
PubMed1985

Moiré patterns: an accurate technique for determination of the locus of the centres of rotation.

This study describes an accurate technique for the determination of the centre of rotation of small angles. The moiré fringe method localizes the centre of rotation by defining two primary fringes, each of which is found by the intersection of three lines. The primary fringes intersect at the centre of rotation at 90 degrees to each other, the angle least likely to produce an error in measurement. By utilizing joints with known centres of rotation, we have found that the method is extremely accurate and reproducible to within 2 mm of the real centre for angular changes as small as 3 degrees. This technique is useful in evaluating whether a joint is a simple hinge, i.e. rotating about a single axis of rotation or whether the joint moves about a changing axis of rotation referred to as a locus or centrode.

Arthrography↗
PubMed1990

Fracture mechanics of bone with short cracks.

Tensile fracture experiments were performed upon specimens of wet mature bovine Haversian bone, with short, controlled notches. Stress concentration factors were found to be significantly less than values predicted using a maximum stress criterion in the theory of elasticity. Results were also modeled with the aid of linear elastic fracture mechanics. Agreement of experiment with theory was better in this case, however deviations were seen for short notches. Two mechanisms were evaluated for the behavior: plasticity near the crack tip, and effects of the Haversian microstructure, modelled by Cosserat elasticity, a generalized continuum theory. Plastic zone effects were found to be insignificant. Cosserat elasticity, by contrast, predicted stress concentration factors which better approximated observed values. To explore strain redistribution processes, further experiments were conducted upon notched specimens in torsion at small strain. They disclosed a strain redistribution effect consistent with Cosserat elasticity. These microelastic effects were attributed to the Haversian architecture of bone. The implications of the results are that bone resists the effect of stress raisers such as fatigue microcracks and surgical sawcuts to a much greater extent than anticipated on the basis of its elastic or elastoplastic properties.

Animals↗
PubMed1978

Ultrasonic digital interferometer for investigation of blood clotting.

The digital ultrasonic fixed path interferometer designed for testing small amounts of sample was used for the investigation of whole blood coagulation, retraction and clot melting processes. The ultrasound velocity and absorption are determined from the characteristics of an acoustic resonator consisting of an emitter, a column of liquid to be tested and a receiver. The measuring accuracy of the ultrasound velocity is 0.1 ms-1, resolution--0.01 ms-1; the absorption measuring error does not exceed 10%. The device operates automatically giving analogue signals in the output for the recorder and discrete ones for the tape puncher to process the results obtained by computer. This permits employment of the interferometer in complex investigation systems. The whole blood clotting characteristics obtained provide new information which correlates with the results of some biological tests.

Blood Coagulation Tests↗
PubMed1996

Application of neural networks to quantitative nondestructive evaluation.

This paper concentrates on the quantitative analysis of reflection and transmission characteristics of structural waves in notched beams using neural networks. At one end of a rod a piezoelectric transducer excites a flexural guided wave, which propagates through the structure and is reflected from the notch as well as from the ends of the rod. At another point, a laser interferometer measures the resulting displacement versus time, which is recorded and serves as the digital fingerprint of the experiment. Our aim is to obtain quantitative information about the notch characteristics, i.e. its location and depth, on the basis of these digital recordings. This requires an inverse problem to be solved using neural networks. For the training of the network, synthetically produced wave patterns are used. The results of the corresponding wave experiment simulations compare well with experimental data. For fixed location, the calculated wave patterns could be quantitatively analysed to yield the depth of the notch if it is greater than a twentieth of the diameter. Another network could be trained for the localization with an accuracy of 2 cm for 93% of the training patterns. On the basis of these results a strategy is formulated on how neural networks could be trained to evaluate quantitatively both of the notch characteristics.

Algorithms↗
PubMed1985

Aliasing in human foveal vision.

An improved laser interferometer allows forced choice contrast sensitivity measurements that are relatively unaffected by optical blurring in the eye. At spatial frequencies above about 60-70 c/deg, the regular bars of the interference fringe are no longer visible; observers report a pattern resembling zebra stripes centered on the line of sight. The characteristics of this pattern are consistent with the hypothesis that it is a moiré pattern resulting from aliasing by the foveal cone mosaic. Properties of this moiré pattern allow an assessment of the regularity of the foveal lattice, the spacing between cones, and the light-catching area of individual cones.

Form Perception↗
PubMed1988

Topography of the foveal cone mosaic in the living human eye.

Interference fringes whose spatial frequency exceeds the resolution limit form visible moiré patterns with the foveal cone mosaic. This paper describes a model of foveal cone sampling that shows how these moiré patterns depend on the spatial frequency and orientation of an interference fringe imaged on a triangular lattice of cones. The model is tested with two psychophysical experiments. The first experiment shows that the behavior of the moiré patterns is quantitatively consistent with anatomical estimates of cone spacing across the human fovea. These patterns provide a psychophysical method for measuring cone spacing within 1.75 deg of the foveal center. In some observers, cone spacing is larger in a horizontal direction than in a vertical direction at any particular location within the fovea. The second experiment shows that the behavior of the moiré patterns is consistent with the triangular packing of foveal cones observed anatomically, and allows the orientation of the cone mosaic to be determined at the foveal center. These observations demonstrate the rich information that methods based on aliasing can provide about the topography of foveal cones in the living human eye.

Adult↗
PubMed1993

Visual optics and retinal cone topography in the common marmoset (Callithrix jacchus).

The common marmoset (Callithrix jacchus) is a small, diurnal, New World monkey amenable to vision research. In this paper we describe the visual optics and cone photoreceptor topography of the normal adult marmoset. Paraxial optical ray-tracing shows that the marmoset eye is well represented as a scaled-down version of the human eye. The density of foveal and perifoveal cone photoreceptors in the marmoset is as high, and in peripheral retina higher, than those reported in humans and macaques. The foveal acuity predicted by the Nyquist limits set by the cone mosaic (30 c/deg) is in agreement with behavioral measures of visual acuity. Foveal depth of focus is remarkably small (< 0.2 D) for an eye of this size (axial length about 11 mm). Estimates of the amplitude of accommodation using infrared photorefraction indicate that the marmoset is capable of more than 20 D of accommodation.

Animals↗
PubMed1978

Nucleolar changes in senescing WI-38 cells.

Changes in the area, dry mass and morphology of nucleoli were studied during in vitro aging of WI-38 cells. Interferometric methods were used for nucleolar dry mass determinations. The results show that there is (1) an increase in the fraction of cells with one large nucleolus per nucleus, 17% at population doubling 27.3 vs. 93% at population doubling 41.2, (2) an increase in mean nucleolar dry mass (583% at the last doubling), and (3) an increase in mean nucleolar area (236% at the last doubling) with in vitro senescence of WI-38 fibroblast cells. A strong correlation (r = 0.92) between nucleolar dry mass and nucleolar area was demonstrated.

Cell Division↗
PubMed1992

Determination of three-dimensional morphometry of adherent cells by surface profilometry.

A three-dimensional, non-contacting surface profiler was used to analyse cells that had been previously prepared for scanning electron microscopy. The height of ten attached and spread cells was measured in both two- and three-dimensions (2-D and 3-D). The 2-D scan is a typical, linear profilometer output, while a 3-D image is produced with a 3-D detector. The 3-D contour plots of each cell were then compared with scanning electron microscopy micrographs by digitizing four morphological parameters: perimeter, surface area, long axis and short axis of each cell. A paired Student's t test showed that the two imaging techniques are not equivalent. Non-equivalence was attributed to a difference in the method of calibration. However, when combined with scanning electron microscopy, the profiler allowed complete three-dimensional quantitative analysis of cellular morphology.

Animals↗
PubMed1996

Spectral and interferometrical study of the interaction of haemin with glutathione.

The interaction of haemin with reduced glutathione (GSH) was investigated in vitro and the association constant was determined by both spectrophotometric and interferometric methods. In order to elucidate the nature of this interaction, the reaction of haemin with a typical reductive agent (sodium dithionite) and a typical chelating agent for hem-iron (histidine) was also studied. Haemin-induced haemolysis in the presence and absence of GSH was monitored spectrophotometrically. The results outline the role of GSH at physiological concentration in preventing erythrocyte damage by haemin.

Erythrocyte Membrane↗
PubMed1991

Frequency-specific position shift in the guinea pig organ of Corti.

The organ of hearing is tuned as expressed both in the vibratory response of the cochlear partition and in the resulting receptor potentials of the sensory cells. We now demonstrate a sharply tuned response, consisting of a position shift of the surface of the organ of Corti, occurring during the presentation of a tone. The magnitude of the position shift exceeds that of the vibratory response to the stimulus. The shift is most pronounced in the region of the outer hair cells, and its affected by an inhibitor of outer hair cell motility. We conclude that the response is induced by the action of the outer hair cells.

Acoustic Stimulation↗