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Results for “Optical Devices”

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At least 595 records · Page 33Linked to original sources
PubMed2002

Adaptive restoration of a partially coherent blurred image using an all-optical feedback interferometer with a liquid-crystal device.

A liquid-crystal adaptive optics system using all-optical feedback interferometry is applied to partially coherent imaging through a phase disturbance. A theoretical analysis based on the propagation of the cross-spectral density shows that the blurred image due to the phase disturbance can be restored, in principle, irrespective of the state of coherence of the light illuminating the object. Experimental verification of the theory has been performed for two cases when the object to be imaged is illuminated by spatially coherent light originating from a He-Ne laser and by spatially incoherent white light from a halogen lamp. We observed in both cases that images blurred by the phase disturbance were successfully restored, in agreement with the theory, immediately after the adaptive optics system was activated. The origin of the deviation of the experimental results from the theory, together with the effect of the feedback misalignment inherent in our optical arrangement, is also discussed.

Journal Article↗
PubMed2006

The impact of assistive device use on disability and depression among older adults with age-related vision impairments.

OBJECTIVE: One can conceptualize adaptive technology as a resource used by disabled older adults in order to maintain competence in everyday life. This study examined the independent relationships between optical and adaptive device utilization and change in functional disability and depression among older adults with age-related vision impairments. METHODS: We interviewed older adults (n = 438) with a recent vision impairment applying for vision rehabilitation services both pre-service and at the 6-month follow-up. We conducted hierarchical regression analyses with functional disability and depressive symptoms as criteria. In order to identify their independent direct effects, we entered optical and adaptive device use into the final step, preceded by Time 1 criterion scores, demographics, baseline disability or depression (depending on criterion), and total rehabilitation service hours. RESULT: Optical, but not adaptive, device use was significantly associated with declines in functional disability and depressive symptoms over time. DISCUSSION: We propose that these differential effects result from the fact that optical devices optimize residual vision and thus allow for greater continuity in the way tasks are accomplished (i.e., reading still performed visually), whereas use of adaptive aids (e.g., talking books) involves learning new methods in order to compensate for lost functions and thus is not as desirable either functionally or psychologically.

Activities of Daily Living↗
PubMed2005

Designing optical-fiber modulators by using magnetic fluids.

To reduce interface loss between optical fibers and devices in telecommunication systems, the development of an optical-fiber-based device that can be fused directly with fibers is important. A novel optical modulator consisting of a bare fiber core surrounded by magnetic fluids instead of by a SiO2 cladding layer is proposed. Applying a magnetic field raises the refractive index of the magnetic fluid. Thus we can control the occurrence of total reflection at the interface between the fiber core and the magnetic fluid when light propagates along the fiber. As a result, the intensity of the outgoing light is modulated by variation in field strength. Details of the design, fabrication, and working properties of such a modulator are presented.

Journal Article↗
PubMed2005

p-Hertz excitation spectroscopy of an optical antenna, optical transmitter-receiver mechanism.

o-Xylene sensitized biacetyl fluorescence and phosphorescence have been investigated and photosensitized fluorescence and phosphorescence lifetimes of biacetyl in the vapor phase have been determined. Attempts to detect the triplet of biacetyl by its absorption spectrum were unsuccessful, primarily due to, it is believed, the low extinction coefficients of the triplet, and the low triplet concentrations produced by the optical pumping device at room temperature.

Acetylation↗
PubMed1976

Coherent optical processing of cervical cytologic samples.

Earlier research using a very limited data base gave encouraging results for the automated screening of exfoliated cytologic samples using coherent optical processing techniques to examine individual isolated cells. A more thorough investigation involving a larger data base has confirmed our initial results. This investigation was performed using a specially designed Fourier spectrum analyzer and a solid state optical detector array. An analysis was made to determine the performance of a screening system using such a cell-by-cell discriminating device. This analysis indicated that less than 20,000 cells would have to be examined to obtain a system performance level of 1% false negative and 10% false positive error rates with a 1% probability of occurrence of malignant cells in a malignant sample. This performance figure was inferred from measured statistical performance characteristics of a laboratory cell-by-cell screening device using optically generated Fourier transfrom techniques for cell discrimination. The performance of the system was shown to be much more sensitive to cell-by-cell false error rates than false negative error rates. It was also found that the majority of false positive errors were due to misclassifying parabasal cells as malignant. By eliminating parabasal cells, which comprised more than 25% of our normal cell data base, the number of cells needed to be screened dropped by an order of magnitude. It was also shown that there is an inverse quadratic relationship between the percentage of malignant cells in a malignant sample and the number of cells that must be screened to achieve any desired system performance.

Autoanalysis↗
PubMed1989

Uses and limitations of microcomputers for epidemiological research in occupational health.

The rapid improvements in microcomputer systems have contributed to ease of performance of epidemiological research in occupational health. Computers now available can aid in all stages of research- from the early stages of literature review to data collection, analysis and presentation. Optical storage devices now allow large occupational health data bases to be stored on a single compact disc, with the information accessible by microcomputer. Hand-held computers and optical scanners allow paperless collection of field data. Epidemiological analysis and data presentation is easily done with software packages, some of which are in the public domain. However, there are limitations in the use of computers for any epidemiological research. Investment of time is required to learn the use of a computer. Care needs to be taken to ensure accurate data entry, and correct choice has to be made of methods for subsequent statistical analysis. Microcomputers are valuable as labour saving devices, but cannot replace proper planning, execution and appropriate data analysis in epidemiological research in occupational health.

Health Services Research↗
PubMed2004

Microfabricated polymer analysis chip for optical detection.

A coupling between multimode polymer waveguides and microfluidic channels on a polymethylmethacrylate (PMMA) capillary electrophoresis (CE)-chip for optical analytical applications has been successfully realised. This technology allows the integration of polymer optical waveguides together with hermetically sealed fluidic channels. The microchannels and waveguides are made in PMMA by the approved hot-embossing technology. The technology developed for the fabrication of polymer waveguides on the microfluidic chip offers the possibility of great flexibility in the choice of core materials, design and alignment of the polymer waveguides. The integration of polymer waveguides on an analysis chip enables highly spatially resolved optical detection without the large and expensive conventionally used apparatus. The optical properties of the analytical system developed are verified by transmission and propagation loss measurements. The results of measurements prove the suitability of the presented device for optical applications between 440 and 800 nm. This was shown with absorbance measurements of the dye Sulfanilazochromotrop (SPADNS) within 50 microm fluidic channels.

Journal Article↗
PubMed1999

Inter- and intraobserver variation in the analysis of optic disc images: comparison of the Heidelberg retina tomograph and computer assisted planimetry.

AIMS: The development of imaging and measurement techniques has brought the prospect of greater objectivity in the measurement of optic disc features, and therefore better agreement between observers. The purpose of this study was to quantify and compare the variation between observers using two measurement devices. METHODS: Optic disc photographs and images from the Heidelberg retina tomograph (HRT) of 30 eyes of 30 subjects were presented to six observers for analysis, and to one observer on five separate occasions. Agreement between observers was studied by comparing the analysis of each observer with the median result of the other five, and expressed as the mean difference and standard deviation of differences between the observer and the median. Inter- and intraobserver variation was calculated as a coefficient of variation (mean SD/mean x 100). RESULTS: For planimetry, agreement between observers was dependent on observer experience, for the HRT it was independent. Agreement between observers (SD of differences as a percentage of the median) for optic disc area was 4.0% to 7.2% (planimetry) and 3.3% to 6.0% (HRT), for neuroretinal rim area it was 10.8% to 21.0% (planimetry) and 5.2% to 9.6% (HRT). The mean interobserver coefficient of variation for optic disc area was 8.1% (planimetry) and 4.4% (HRT), for neuroretinal rim area it was 16.3% (planimetry) and 8.1% (HRT), and (HRT only) for rim volume was 16.3%, and reference height 9.1%. HRT variability was greater for the software version 1.11 reference plane than for version 1.10. The intraobserver coefficient of variation for optic disc area was 1.5% (planimetry) and 2.4% (HRT), for neuroretinal rim area it was 4.0% (planimetry) and 4.5% (HRT). CONCLUSIONS: Variation between observers is greatly reduced by the HRT when compared with planimetry. However, levels of variation, which may be clinically significant, remain for variables that depend on the subjective drawing of the disc margin.

Glaucoma↗
PubMed1993

[Present and future of the methods for measurement of intracellular Ca2+ concentration].

The development of fluorescent Ca2+ indicators, which have made measurement of the dynamic change in cytosolic free Ca2+ concentration during biological activity feasible, has allowed correlations to be drawn between biochemical changes within cells and their functions. Recently, many new types of Ca2+ indicators with special merit and also new methods for fluorescence measurement have been published. The present technical review summarizes properties of the newly developed indicators and describes the newly developed methods for measuring intracellular Ca2+ concentration. In particular, examples of image analysis applied to single cells and tissue slice preparations are stated in detail. Furthermore, a newly developed single optical fiber device for making measurements in the deep brain region is also introduced.

Animals↗
PubMed2001

Identification of cervical intraepithelial neoplasia (CIN) using UV-excited fluorescence and diffuse-reflectance tissue spectroscopy.

BACKGROUND AND OBJECTIVE: The diagnostic potentials of ultraviolet-excitation fluorescence spectroscopy and diffuse-reflectance spectroscopy of tissue are assessed in a study to identify cervical intraepithelial neoplasia (CIN) in vivo. A multivariate algorithm is used to classify tissue into normal tissues, CIN I, and CIN II/III categories, based on spectral characteristics of biopsied tissue sites. STUDY DESIGN/MATERIALS AND METHODS: An optical instrument with the capability of measuring fluorescence and diffuse-reflectance spectra from 120 locations uniformly distributed over the surface of the cervix is described. Using this device, these optical spectra of the cervix were measured on women referred for colposcopy due to an abnormal Pap smear. RESULTS: UV fluorescence differentiates CIN II/III lesions from normal squamous tissue with a sensitivity and specificity of 91 and 93%, respectively. CIN I is distinguished from normal tissue with a sensitivity of 86% and a specificity of 87%. CONCLUSION: Optical spectroscopy shows promise for the detection of pre-cancerous cervical lesions in vivo. The fluorescence and reflectance methods are complementary in their ability to differentiate different tissue types, making the use of the two techniques together more diagnostic than the use of either method separately.

Algorithms↗
PubMed2005

Light extinction at agglomerates of spheres--a practical test on the submicroscale.

Today's theories applied to the inversion of measurement data from optical measurement devices are restricted to single spherical particles. However, particles formed in industrial processes such as precipitation and crystallization are often nonspherical or agglomerates. Theoretical approaches to describe the optical behavior of such particle systems have already been proposed. The verification of these theories has mostly been done using microwave scattering experiments with agglomerates in the millimeter range. This paper provides a first but surely not all-embracing practical test for a general extension of the Mie theory to agglomerates of submicroscale spheres. For the sake of simplicity and from practical viewpoints of online-sensor development only light extinction of an agglomerated suspension has been examined. The required rigid agglomerates have been produced using a spray-drying method that generates particles with a much higher mechanical stability than can be obtained by the usual procedures. Subsequent fractionation of the suspension delivers systems with only a limited number of agglomerate configurations. Extinction measurements at multiple wavelengths using dynamic extinction spectroscopy have been conducted to determine the extinction cross section of the agglomerated dispersions. These data are compared with computations of agglomerates scattering.

Journal Article↗
PubMed2006

Photosensitive gold-nanoparticle-embedded dielectric nanowires.

Noble-metal nanoparticles embedded in dielectric matrices are considered to have practical applications in ultrafast all-optical switching devices owing to their enhanced third-order nonlinear susceptibility, especially near the surface-plasmon-resonance (SPR) frequency. Here we present the use of a microreactor approach to the fabrication of a self-organized photosensitive gold nanoparticle chain encapsulated in a dielectric nanowire. Such a hybrid nanowire shows pronounced SPR absorption. More remarkably, a strong wavelength-dependent and reversible photoresponse has been demonstrated in a two-terminal device using an ensemble of gold nanopeapodded silica nanowires under light illumination, whereas no photoresponse was observed for the plain silica nanowires. These results show the potential of using gold nanopeapodded silica nanowires as wavelength-controlled optical nanoswitches. The microreactor approach can be applied to the preparation of a range of hybrid metal-dielectric one-dimensional nanostructures that can be used as functional building blocks for nanoscale waveguiding devices, sensors and optoelectronics.

Journal Article↗
PubMed2006

Achieving uniform mixing in a microfluidic device: hydrodynamic focusing prior to mixing.

We describe a microfluidic mixer that is well-suited for kinetic studies of macromolecular conformational change under a broad range of experimental conditions. The mixer exploits hydrodynamic focusing to create a thin jet containing the macromolecules of interest. Kinetic reactions are triggered by molecular diffusion into the jet from adjacent flow layers. The ultimate time resolution of these devices can be restricted by premature contact between co-flowing solutions during the focusing process. Here, we describe the design and characterization of a mixer in which hydrodynamic focusing is decoupled from the diffusion of reactants, so that the focusing region is free from undesirable contact between the reactants. Uniform mixing on the microsecond time scale is demonstrated using a device fabricated by imprinting optical-grade plastic. Device characterization is carried out using fluorescence correlation spectroscopy (FCS) and two-photon microscopy to measure flow speeds and to quantify diffusive mixing by monitoring the collisional fluorescence quenching, respectively. Criteria for achieving microsecond time resolution are described and modeled.

Microfluidics↗
PubMed2005

Discontinuous spectral element method modeling of optical coupling by whispering gallery modes between microcylinders.

We introduce a high-order time-domain discontinuous spectral element method for the study of the optical coupling by evanescent whispering gallery modes between two microcylinders, the building blocks of coupled resonator optical waveguide devices. By using the discontinuous spectral element method with a Dubiner orthogonal polynomial basis on triangles and a Legendre nodal orthogonal basis on quadrilaterals, we conduct a systematic study of the optical coupling by whispering gallery modes between two microcylinders and demonstrate the successful coupling between the microcylinders and also the dependence of such a coupling on the separation and the size variation of the microcylinders.

Journal Article↗
PubMed1994

[Response rate, missing values, validity and reproducibility of responses in mark-sheet and conventional questionnaires].

A self-administered questionnaire using the mark-sheet method (MSM), in which responses of subjects are computer processed directly through an optical scanning device, has recently been utilized in epidemiologic surveys. Compared to the data coding process for a conventional questionnaire, in which a keypuncher enters the responses manually into a computer (manual method; MM), optical scanning requires less time and cost. Accuracy of the MSM for use in the general population in Japan, however, remains uncertain. Therefore the response rates, frequencies of missing values, validity and reproducibility of the answers in self-administered questionnaires were compared between the MSM and MM. Subjects were 463 residents aged 40-69 years living in 6 local districts of a rural town in northeastern Japan. They were randomly allocated, by district basis, to the MSM group (n = 242) or the MM group (n = 221). The questionnaire was delivered and collected at the subject's home by volunteers. Two weeks after collecting the original questionnaire, the same type of questionnaire was again distributed to half of the responders randomly chosen to investigate reproducibility. The overall response rate did not differ in MSM and MM (96.7% vs 98.2%, p = 0.312). Among questions with a multiple-choice type of answer, proportions of missing values were not different for most of the items, but it was lower in MSM for all of the 33 food frequency items. Reproducibilities of food frequency items measured by Spearman's rank correlation did not differ substantially in two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2006

Multipoint holographic optical velocimetry in microfluidic systems.

We show how holographic optical trapping can be used for the multipoint measurement of fluid flow in microscopic geometries. An array of microprobes can be simultaneously trapped and used to map out the fluid flow in a microfluidic device. The optical traps are alternately turned on and off such that the probe particles are displaced by the flow of the surrounding fluid and then retrapped. The particles' displacements are monitored by digital video microscopy and directly converted into velocity field values. This technique enables the measurement of a two-dimensional flow field at points arbitrarily distributed in a three-dimensional volume. The validity of the technique is demonstrated for the case of the flow around a spinning sphere and the flow at the outlet of a microchannel.

Journal Article↗
PubMed1993

Distinct patterns of spatial frequency response by normal, recovered optic neuritis, and normal fellow eyes to a new linearly variable neutral density device.

Upon apparent recovery from optic neuropathy, structural damage to the optic nerve may remain while usual measures of visual function appear normal. To test for such damage, the logarithm of optical density to cause a pattern to disappear is read directly on the scale of our device. Patients in the first study observed the disappearance of a red Amsler grid; this Threshold Amsler Score, used jointly with acuity scores, separates normal eyes from eyes with optic neuropathies. Patients in the second study used the device to measure the disappearance of the highest contrast Vistech patterns to show that this device, used over a range of spatial frequencies, differentiates "subclinical" neuropathies (recovered optic neuritis eye; never symptomatic fellow eye to a diagnosed eye) from normal eyes. This device may measure the functional photopic brightness of the stimulus pattern; when the score from our device is higher, the range of photopic brightness for the stimulus is wider, and the retina is more sensitive to contrast.

Adolescent↗