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At least 1,333 records · Page 74Linked to original sources
PubMed2005

A comparison of three different methods for the quantification of the in vitro wear of dental materials.

OBJECTIVE: Different approaches are utilized to quantify the wear generated on flat specimens with a wear simulator. However, there are no systematic studies comparing different wear quantification methods with a series of materials that exhibit different wear rates. METHODS: Sixteen restorative materials, including 14 composites (BelleGlass, Chromasit, Estenia, Esthet-X, Four Seasons, Heliomolar RO, Heliomolar HB, Herculite XRV, InTen-S, Point 4, SureFil, Targis cured at 95 and 130 degrees C, Tetric Ceram) as well as an amalgam (Amalcap) and a ceramic (Empress) material, were subjected to attrition wear against standardized Empress antagonists in the Willytec wear simulator (120,000 cycles, 5 kg, 1.6 Hz). The volume and maximal vertical loss were quantified directly on the specimens with a profilometry device (Perthometer) and the FRT MicroProf optical sensor. After the fabrication of plaster replicas, the loss was also determined with a 3D laser scanning device. For the statistical analysis, the data were subjected to a logarithmic transformation. Intraclass correlation was calculated to measure the agreement among all three methods, while limits of agreement were used to compare one method against another. RESULTS: There was a very good agreement between all three quantification methods for both volume and vertical loss. The mechanical sensor measured consistently higher values compared to the optical sensors for the volume loss (correction factor 0.95), whereas for the vertical loss, consistently lower values were obtained (correction factor 1.17). However, the ranking of the materials was only marginally influenced by the quantification method. SIGNIFICANCE: All three sensors are suitable for the quantification of wear facets. Due to speed and simplicity, the laser sensor has greater advantages over the two other sensors.

Acrylic Resins↗
PubMed2000

Transmission spectra of light to the mammalian retina.

A simple method has been developed to determine the optical properties of the anterior segment of the intact eye. This consists of a probe that is inserted into the posterior sclera and detects light passing through the anterior segment. The probe is connected to a charge-coupled device spectrophotometer via a fiber optic bundle. It was determined that the young rat anterior segment transmits light down to 300 nm, whereas calf and rabbit eyes transmit no UVB and only part of the UVA to the posterior segment. The absorbing species in these animals is most likely NAD(P)H, which has an absorption maximum at approximately 345 nm and is associated with zeta-crystallin. A young primate anterior segment transmits almost no UV with a steep increase in transmission at CA 400 nm. Because some experiments employed a light tube that is used to illuminate the retina during vitrectomies, this method can be used to determine the transmission spectra of the anterior segment of humans in vivo.

Animals↗
PubMed2002

[Reproducibility of measuring retinal nerve fiber density. Comparison of optical coherence tomography with the nerve fiber analyzer and the Heidelberg retinal tomography device].

BACKGROUND: Glaucoma is associated with a progressive loss of retinal ganglion cell axons and the evaluation of the thickness of the retinal nerve fibre layer (RNFL) is important for early diagnosis and follow-up. Results of RNFL thickness measurements may vary according to the devices used. Therefore, the present study has analysed and compared the reproducibility of data obtained with three different instruments. METHODS: RNFL thickness was determined using a circular identification line around the optic nerve head by optical coherence tomography (OCT), a Heidelberg Retina Tomograph (HRT) and a Nerve Fiber Analyser (NFA). Each eye was tested six times. The values for RNFL thickness were calculated for the superior, inferior, nasal and temporal areas. A one-way analysis of variance with random effects was chosen to estimate the variance components. The intraclass correlation coefficient (ICC) as a measure of reliability and the coefficient of variation (CV%) as a measure of precision were determined to estimate the reproducibility of RNFL thickness measurements. RESULTS: With all three instruments, the reproducibility of measurements between the superior, inferior, temporal and nasal areas did not differ significantly suggesting that reproducibility does not depend on the thickness of the RNFL. Data obtained by NFA showed the highest ICC values (0.9) and lowest CV% values (7.0), followed by those obtained by HRT (reliability ICC 0.8; precision CV% 12). A markedly lower degree of reproducibility was found for the OCT compared to NFA and HRT (reliability ICC 0.5; precision CV% 15). CONCLUSION: The comparison of RNFL thickness measurements with OCT, NFA, and HRT showed that the NFA yielded the most reliable results followed by HRT.

Adolescent↗
PubMed2002

The optical functional advantages of an intraocular low-vision telescope.

An implantable miniaturized telescope (IMT) for low vision has recently been developed. Surgically inserted into only one eye of patients with bilateral central visual loss, the IMT provides a nominal magnification of 3.0x and a field-of-view of 6.6 degrees (9.2 degrees for the 2.2x magnification version). Theoretical concerns have been raised regarding the ability of patients to function with a large interocular magnification difference, the impact of the monocular restriction of the field-of-view, and the impact of this design on depth perception. This article addresses these concerns regarding the design of the IMT in comparison with spectacle-mounted telescopes and combined intraocular lens/spectacle (or combined contact lens/spectacle) telescopic systems. The effective field-of-view (as determined by the combination of both the field-of-view and the field-of-fixation), the effects of head motion and the vestibular reflex, and the disruption of stereo depth perception with a monocular device are considered here. Physiological optics considerations of these issues show that the IMT may have important advantages over other designs of magnification devices for patients with age-related macular degeneration.

Depth Perception↗
PubMed1996

[Topometry of the optic papilla with the glaucoma-scope].

Reproducibility of measurements of the "Glaucoma-Scope", a new topometric device (software version 3.12), was assessed by optic disk analysis of 10 eyes in 10 healthy subjects. Each analysis was carried out by 4 independent observers. Examinations of one of these eyes were repeated 10 times by each one of the 4 observers. The instrument was also applied to a sample of 117 eyes in 60 patients from a glaucoma clinic. The minimal requirements were determined to be a pupil diameter of 5 mm and lens-related visual acuity > 0.8. The coefficient of variation for the different optic disk parameters in the repeated examinations ranged from 3.5% to 15.7%. The maximal discrepancy between values of vertical C/D ratio within any of the subjects ranged from 0.01 to 0.12 (mean 0.05). Glaucoma-Scope measurements revealed a smaller value for disk area than those from computer-assisted manual planimetry, with a constant factor of 0.81. The measurement of vertical C/D ratio by Glaucoma-Scope and a stereoscopic estimate correlated highly in a subset consisting of 20 glaucoma patients and the 10 healthy subjects (r = 0.786; p < 0.0001). A considerable discrepancy (larger or smaller) was apparent between values found through clinical inspection of 6 of the 117 eyes (4 of 60 patients) and those found with the Glaucoma-Scope. In these 6 eyes subsequent analyses utilizing a more recent software version yielded a good correlation between the two methods. The Glaucoma-Scope allows sufficiently reproducible optic disk topometry.

Adolescent↗
PubMed1992

Acousto-optic tunable filter as a polychromator and its application in multidimensional fluorescence spectrometry.

Acousto-optic tunable filter (AOTF) is an electronically driven dispersive device which operates on the principle of acousto-optic interaction in an anisotropic medium. Incident white light will be diffracted by the AOTF into a specific wavelength when a specific rf is applied to it. The diffracted light needs not be a monochromatic light. Multiwavelength light can be diffracted from the AOTF when several rf signals are simultaneously applied into the filter. Compared to conventional polychromators, advantages of this electronic AOTF polychromator include its ability to individually amplitude-modulate each wavelength of the diffracted multiwavelength light at different frequency. This is accomplished by individually and sinusoidally modulating each applied rf signal at the desired frequency. This feature makes it possible to develop a novel AOTF-based multidimensional fluorimeter in which the sample was simultaneously excited by two different wavelengths (514.5 and 488.0 nm) whose amplitudes were sinusoidally modulated at two different frequencies (100 and 66 Hz). Multicomponent samples, e.g., mixtures of rhodamine 6G and rhodamine B, were successfully analyzed using this novel fluorimeter and the developed data analysis.

Filtration↗
PubMed2006

Device physics vis-à-vis fundamental physics in Cold War America: the case of quantum optics.

Historians have convincingly shown the close ties U.S. physicists had with the military during the Cold War and have raised the question of whether this alliance affected the content of physics. Some have asserted that it distorted physics, shifting attention from fundamental problems to devices. Yet the papers of physicists in quantum electronics and quantum optics, fields that have been exemplary for those who hold the distortion thesis, show that the same scientists who worked on military devices simultaneously pursued fundamental and foundational topics. This essay examines one such physicist, Marlan O. Scully, with attention to both his extensive foundational studies and the way in which his applied and basic researches played off each other.

Equipment Design↗
PubMed2004

Supramolecular optical chemosensors for organic analytes.

Supramolecular optical chemosensors are abiotic molecular devices that bind analytes by noncovalent interactions, producing a change in light absorption or fluorescence. This review summarizes recent progress in the development of such chemosensors for organic analytes based on artificial receptors. Important design considerations, such as analyte affinity, choice of chromophore or fluorophore, binding selectivity, and optical signaling mechanism are briefly discussed. Chemists have fashioned chemosensors from a wide range of molecular structures, including polyalcohols, crown ethers, calixarenes, helicenes, sterically geared tripods, metal complexes, pinwheels, porphyrins, and fused-ring heterocycles. Analytes of interest include amines, carboxylic acids, amino acids, hydroquinones, alkaloids, carbohydrates, peptides, urea and creatinine.

Biosensing Techniques↗
PubMed1999

Determination of stresses in aluminum alloy using optical detection of Rayleigh waves

In this paper, a non-destructive method for the determination of residual stress profiles as a function of depth in laminated aluminium alloy sheets is presented. An ultrasonic method using Rayleigh waves propagating along the sides of the sheet is proposed. The determination of residual stresses is based on the measurement of the relative variation of the ultrasonic wave velocity versus the depth. An experimental device, using the acousto-optic interaction, has been developed to measure the velocity of the Rayleigh wave. Several residual stress profiles obtained by this technique are shown. The latter are compared to other stress profiles obtained by other methods: layer removal method and acoustic detection using wedge transducer.

Journal Article↗
PubMed2002

Cavity solitons as pixels in semiconductor microcavities.

Cavity solitons are localized intensity peaks that can form in a homogeneous background of radiation. They are generated by shining laser pulses into optical cavities that contain a nonlinear medium driven by a coherent field (holding beam). The ability to switch cavity solitons on and off and to control their location and motion by applying laser pulses makes them interesting as potential 'pixels' for reconfigurable arrays or all-optical processing units. Theoretical work on cavity solitons has stimulated a variety of experiments in macroscopic cavities and in systems with optical feedback. But for practical devices, it is desirable to generate cavity solitons in semiconductor structures, which would allow fast response and miniaturization. The existence of cavity solitons in semiconductor microcavities has been predicted theoretically, and precursors of cavity solitons have been observed, but clear experimental realization has been hindered by boundary-dependence of the resulting optical patterns-cavity solitons should be self-confined. Here we demonstrate the generation of cavity solitons in vertical cavity semiconductor microresonators that are electrically pumped above transparency but slightly below lasing threshold. We show that the generated optical spots can be written, erased and manipulated as objects independent of each other and of the boundary. Numerical simulations allow for a clearer interpretation of experimental results.

Journal Article↗
PubMed2005

Optical sectioning microscopy.

Confocal scanning microscopy, a form of optical sectioning microscopy, has radically transformed optical imaging in biology. These devices provide a powerful means to eliminate from images the background caused by out-of-focus light and scatter. Confocal techniques can also improve the resolution of a light microscope image beyond what is achievable with widefield fluorescence microscopy. The quality of the images obtained, however, depends on the user's familiarity with the optical and fluorescence concepts that underlie this approach. We describe the core concepts of confocal microscopes and important variables that adversely affect confocal images. We also discuss data-processing methods for confocal microscopy and computational optical sectioning techniques that can perform optical sectioning without a confocal microscope.

Animals↗
PubMed2005

Optical design in beam steering environments with emphasis on laser transmission measurements.

Optical sensors applied to practical devices often encounter beam steering: the wander and/or diffusion of laser light. Here we provide a framework for minimizing the sensitivity of transmission-based sensors to beam steering without quantitative prediction of the severity of the beam-steering field. Typical goals are increased transmission and/or minimized fluctuations in transmission; such features can improve optical sensor performance (e.g., improved signal-to-noise ratio, response time, or spectral resolution). In our framework, we introduce a parameter for characterizing beam-steering severity. We then compare two approaches for absorption spectroscopy and show that the preferred approach depends on the total spectral range monitored, the spectral resolution desired, and the severity of the beam steering.

Journal Article↗
PubMed1992

Use of interferometric visual stimulators in optometry.

Professor Fergus Campbell and colleagues pioneered the use of the interferometric visual stimulator as a tool for separating optical from neural factors which limit spatial vision. The device is now commercially available as a clinical instrument which 'bypasses the optics of the eye' to measure the potential visual acuity of the neural portion of the visual system. However, the clinician needs to be aware of limitations of current instrument designs and recent advances in our understanding of peripheral vision, to correctly interpret patient data gathered with these devices.

Humans↗
PubMed2005

Lab-on-a-chip with integrated optical transducers.

Taking the next step from individual functional components to higher integrated devices, we present a feasibility study of a lab-on-a-chip system with five different components monolithically integrated on one substrate. These five components represent three main domains of microchip technology: optics, fluidics and electronics. In particular, this device includes an on-chip optically pumped liquid dye laser, waveguides and fluidic channels with passive diffusive mixers, all defined in one layer of SU-8 polymer, as well as embedded photodiodes in the silicon substrate. The dye laser emits light at 576 nm, which is directly coupled into five waveguides that bring the light to five different locations along a fluidic channel for absorbance measurements. The transmitted portion of the light is collected at the other side of this cuvette, again by waveguides, and finally detected by the photodiodes. Electrical read-out is accomplished by integrated metal connectors. To our knowledge, this is the first time that integration of all these components has been demonstrated.

Equipment Design↗
PubMed2003

A volumetric method for estimation of breast density on digitized screen-film mammograms.

A method is described for the quantitative volumetric analysis of the mammographic density (VBD) from digitized screen-film mammograms. The method is based on initial calibration of the imaging system with a tissue-equivalent plastic device and the subsequent correction for variations in exposure factors and film processing characteristics through images of an aluminum step wedge placed adjacent to the breast during imaging. From information about the compressed breast thickness and technique factors used for taking the mammogram as well as the information from the calibration device, VBD is calculated. First, optical sensitometry is used to convert images to Log relative exposure. Second, the images are corrected for x-ray field inhomogeneity using a spherical section PMMA phantom image. The effectiveness of using the aluminum step wedge in tracking down the variations in exposure factors and film processing was tested by taking test images of the calibration device, aluminum step wedge and known density phantoms at various exposure conditions and also at different times over one year. Results obtained on known density phantoms show that VBD can be estimated to within 5% accuracy from the actual value. A first order thickness correction is employed to correct for inaccuracy in the compression thickness indicator of the mammography units. Clinical studies are ongoing to evaluate whether VBD can be a better indicator for breast cancer risk.

Absorptiometry, Photon↗
PubMed2002

Microfluidic devices fabricated in poly(methyl methacrylate) using hot-embossing with integrated sampling capillary and fiber optics for fluorescence detection.

High-aspect-ratio microstructures have been prepared using hot-embossing techniques in poly(methyl methacrylate) (PMMA) from Ni-based molding dies prepared using LIGA (Lithographie, Galvanoformung, Abformung). Due to the small amount of mask undercutting associated with X-ray lithography and the high energy X-ray beam used during photoresist patterning, deep structures with sharp and smooth sidewalls have been prepared. The Ni-electroforms produced devices with minimal replication errors using hot-embossing at a turn around time of approximately 5 min per device. In addition, several different polymers (with different glass transition temperatures) could be effectively molded with these Ni-electroforms and many devices (>300) molded with the same master without any noticeable degradation. The PMMA devices consisted of deep and narrow channels for insertion of a capillary for the automated electrokinetic loading of sample into the microfluidic device and also, a pair of optical fibers for shuttling laser light to the detection zone and collecting the resulting emission for fluorescence analysis. Electrophoretic separations of double-stranded DNA ladders Phi X174 digested with Hae III) were performed with fluorescence detection accomplished using near-IR excitation. It was found that the narrow width of the channels did not contribute significantly to electrophoretic zone broadening and the plate numbers generated in the extended length separation channel allowed sorting of the 271/281 base pair fragments associated with this sizing ladder when electrophoresed in methylcellulose entangled polymer solutions. The dual fiber detector produced sub-attomole detection limits with the entire detector, including laser source, electronics and photon transducer, situated in a single box measuring 3'' x 10" x 14".

Dinitrobenzenes↗