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Sample records for refraction profile issa

  1. Auroral interactions with ISSA

    NASA Technical Reports Server (NTRS)

    Purvis, Carolyn K.; Snyder, David B.; Jongeward, Gary A.

    1994-01-01

    Due to its high inclination orbit, International Space Station Alpha (ISSA) will occasionally experience surface charging by the high energy electrons of the auroral environment. This study looks at the frequency of these occurrences and recapitulates a charging model. ISSA should expect about 80 auoral encounters annually. If the plasma contactor is not run continuously, the vehicle may charge several hundred volts. Charge storage on standard space station coatings should not be a problem, but care must be taken that materials are not introduced inadvertently that cannot bleed off accumulated charge in a reasonable time. A conductivity requirement may be used to ensure surface materials do not charge to high voltages, or store charge for long periods of time.

  2. The SPOrt mission on ISSA

    NASA Astrophysics Data System (ADS)

    Cortiglioni, S.; Cecchini, S.; Orsini, M.; Boella, G.; Gervasi, M.; Sironi, G.; Fabbri, R.; Monari, J.; Orfei, A.; Ng, K.-W.; Nicastro, L.; Pisani, U.; Tascone, R.; Popa, L.; Strukov, I. A.

    1999-01-01

    In the framework of the International Space Station (ISSA) utilization a project to measure the sky diffuse polarized emission at microwave frequencies has been presented to the ESA AO. After its selection by ESA the Sky Polarization Observatory (SPOrt) has been slightly modified, within ISSA constrains, to meet better its scientific goal. In this paper the current design of SPOrt is presented with emphasis on changes which have a major impact on the overall performances and that were imposed by the ISSA environment.

  3. The BHVI-EyeMapper: peripheral refraction and aberration profiles.

    PubMed

    Fedtke, Cathleen; Ehrmann, Klaus; Falk, Darrin; Bakaraju, Ravi C; Holden, Brien A

    2014-10-01

    The aim of this article was to present the optical design of a new instrument (BHVI-EyeMapper, EM), which is dedicated to rapid peripheral wavefront measurements across the visual field for distance and near, and to compare the peripheral refraction and higher-order aberration profiles obtained in myopic eyes with and without accommodation. Central and peripheral refractive errors (M, J180, and J45) and higher-order aberrations (C[3, 1], C[3, 3], and C[4, 0]) were measured in 26 myopic participants (mean [±SD] age, 20.9 [±2.0] years; mean [±SD] spherical equivalent, -3.00 [±0.90] diopters [D]) corrected for distance. Measurements were performed along the horizontal visual field with (-2.00 to -5.00 D) and without (+1.00 D fogging) accommodation. Changes as a function of accommodation were compared using tilt and curvature coefficients of peripheral refraction and aberration profiles. As accommodation increased, the relative peripheral refraction profiles of M and J180 became significantly (p < 0.05) more negative and the profile of M became significantly (p < 0.05) more asymmetric. No significant differences were found for the J45 profiles (p > 0.05). The peripheral aberration profiles of C[3, 1], C[3, 3], and C[4, 0] became significantly (p < 0.05) less asymmetric as accommodation increased, but no differences were found in the curvature. The current study showed that significant changes in peripheral refraction and higher-order aberration profiles occurred during accommodation in myopic eyes. With its extended measurement capabilities, that is, permitting rapid peripheral refraction and higher-order aberration measurements up to visual field angles of ±50 degrees for distance and near (up to -5.00 D), the EM is a new advanced instrument that may provide additional insights in the ongoing quest to understand and monitor myopia development.

  4. Tropospheric Refractivity Profiles Inferred from RF Measurements-Passive Refractive Index by Satellite Monitoring (PRISM).

    DTIC Science & Technology

    1980-10-24

    AD-AO95 498 NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA F/6 4 /1 TROPOSPHIERIC REFRACTIVITY PROFILES INFERRED FROM RF MEASUMEMET-ETC(UI OCT 80 K 0...DOCUMENTATION PAGE BEFORE COMPLETING FORM 4 . 11f e d .41Ŕ"t R_ FT &PERIOO COVERED TROPOSPHERIC REFRACTIVITY F-ROFILES INFERRED FROMJ.F ! Final...lirnitation to the applicability of this technique is an uncorrectable rms range error of about 4 km. These errors are caused by small-scale

  5. Two-dimensional refractive index profiling of optical fibers by modified refractive near-field technique

    NASA Astrophysics Data System (ADS)

    El Sayed, A.; Pilz, Soenke; Ryser, Manuel; Romano, Valerio

    2016-02-01

    The refractive index distribution in the core-cladding region of an optical fiber plays an important role in determining the transmission and dispersion properties of the waveguide. The refracted near-field technique (RNF) is among the most widespread techniques used for measuring the refractive index profile of optical fibers and is based on illuminating the end-facet of a fiber with a focused beam whose vertex angle greatly exceeds the acceptance angle of the fiber, which is immersed in an index matching liquid. What one observes are then the refracted unguided rays rather than the guided rays. Nevertheless, the standard refracted near-field technique cannot be applied to a wide range of optical fibers e.g. if their shapes are not axially symmetric. In this work we demonstrate a modified method which allows 2-D imaging of the refractive index profile and thereby overcoming the axial symmetric limitation of the standard RNF. The new system is operating at 630 nm and based on the same principle of the RNF, but the optical path is reversed so that the light at the fiber end-facet is collected by an objective lens and detected by a CCD camera. The method does not require scanning over the fiber end-facet. Thus the system is faster and less sensitive to vibrations and external conditions compared to the standard RNF, furthermore it allows averaging to improve the signal to noise ratio. The spatial resolution of the system is determined by the numerical aperture of the objective and by the resolution of the CCD camera. To calibrate the setup, a reference multi-step index fiber provided by National Physical Laboratory was used.

  6. Two-dimensional refractive index profiling of optical fibers by modified refractive near-field technique

    NASA Astrophysics Data System (ADS)

    El Sayed, A.; Pilz, Soenke; Ryser, Manuel; Romano, Valerio

    2016-04-01

    The refractive index distribution in the core-cladding region of an optical fiber plays an important role in determining the transmission and dispersion properties of the waveguide. The refracted near-field technique (RNF) is among the most widespread techniques used for measuring the refractive index profile of optical fibers and is based on illuminating the end-facet of a fiber with a focused beam whose vertex angle greatly exceeds the acceptance angle of the fiber, which is immersed in an index matching liquid. What one observes are then the refracted unguided rays rather than the guided rays. Nevertheless, the standard refracted near-field technique cannot be applied to a wide range of optical fibers e.g. if their shapes are not axially symmetric. In this work we demonstrate a modified method which allows 2-D imaging of the refractive index profile and thereby overcoming the axial symmetric limitation of the standard RNF. The new system is operating at 630 nm and based on the same principle of the RNF, but the optical path is reversed so that the light at the fiber end-facet is collected by an objective lens and detected by a CCD camera. The method does not require scanning over the fiber end-facet. Thus the system is faster and less sensitive to vibrations and external conditions compared to the standard RNF, furthermore it allows averaging to improve the signal to noise ratio. The spatial resolution of the system is determined by the numerical aperture of the objective and by the resolution of the CCD camera. To calibrate the setup, a reference multi-step index fiber provided by National Physical Laboratory was used.

  7. Refraction in the lower troposphere: Higher order image distortion effects due to refractive profile curvature

    NASA Astrophysics Data System (ADS)

    Short, Daniel J.

    There are many applications that rely on the propagation of light through the atmosphere - all of which are subject to atmospheric conditions. While there are obvious processes such as scattering due to particulates like clouds and dust that affect the received intensity of the radiation, the clear atmosphere can also cause significant effects. Refraction is a clear air effect that can cause a variety of phenomena such as apparent relocation, stretching and compression of objects when viewed through the atmosphere. Recently, there has been significant interest in studying the refractive effects for low angle paths within the troposphere, and in particular, near-horizontal paths in the Earth's boundary layer, which is adjacent to the ground. Refractive effects in this case become problematic for many terrestrial optical applications. For example, the pointing of a free space optical communication or a remote sensing system can suffer wandering effects, high-resolution imagery can present distorted and/or dislocated targets, optical tracking of targets can be inaccurate, and optical geodetic surveying accuracy is also very sensitive to the effects of refraction. The work in this dissertation was inspired by data from a time-lapse camera system that collects images of distant targets over a near-horizontal path along the ground. This system was used previously to study apparent diurnal image displacement and this dissertation extends that work by exploring the higher order effects that result from curvature in the vertical refractive index profile of the atmosphere. There are surprisingly few experiments involving atmospheric refractive effects that carefully correlate field data to analytical expressions and other factors such as meteorological data. In working with the time-lapse data, which is comprised of sequences of hundreds or thousands of images collected over durations of weeks or months, it is important to develop straightforward analysis techniques that can

  8. Interferometric analysis of the ablation profile in refractive surgery

    NASA Astrophysics Data System (ADS)

    Rodríguez-Rodríguez, M. I.; López-Olazagasti, E.; Rosales, M. A.; Ramírez-Zavaleta, G.; Cantú, R.; Tepichín, E.

    2008-08-01

    In ophthalmology, the laser excimer corneal surface ablation used to correct the refractive eye defects, such as myopia, astigmatism and hyperopia and, more recently, presbyopia is known as refractive surgery. Typically, the characterization of the corresponding technique, as well as the laser accuracy, is performed by analyzing standard ablation profiles made on PMMA (polymethylmethacrylate) plates. A drawback of this technique is that those plates do not necessarily represent the dimensions of the cornea during the ablation. On the other hand, due to the time varying process of the eye aberrations, the direct eye refractometric measurements can produce some errors. We report in this work the interferometric analysis of the ablation profile obtained with refractive surgery, applied directly on a contact lens. In this case, the resultant ablation profile might be closer to the real profile as well as time invariant. We use, as a reference, a similar contact lens without ablation. The preliminary results of the characterization of the corresponding ablation profile are also presented.

  9. The BHVI-EyeMapper: Peripheral Refraction and Aberration Profiles

    PubMed Central

    Fedtke, Cathleen; Ehrmann, Klaus; Falk, Darrin; Bakaraju, Ravi C.; Holden, Brien A.

    2014-01-01

    ABSTRACT Purpose The aim of this article was to present the optical design of a new instrument (BHVI-EyeMapper, EM), which is dedicated to rapid peripheral wavefront measurements across the visual field for distance and near, and to compare the peripheral refraction and higher-order aberration profiles obtained in myopic eyes with and without accommodation. Methods Central and peripheral refractive errors (M, J180, and J45) and higher-order aberrations (C[3, 1], C[3, 3], and C[4, 0]) were measured in 26 myopic participants (mean [±SD] age, 20.9 [±2.0] years; mean [±SD] spherical equivalent, −3.00 [±0.90] diopters [D]) corrected for distance. Measurements were performed along the horizontal visual field with (−2.00 to −5.00 D) and without (+1.00 D fogging) accommodation. Changes as a function of accommodation were compared using tilt and curvature coefficients of peripheral refraction and aberration profiles. Results As accommodation increased, the relative peripheral refraction profiles of M and J180 became significantly (p < 0.05) more negative and the profile of M became significantly (p < 0.05) more asymmetric. No significant differences were found for the J45 profiles (p > 0.05). The peripheral aberration profiles of C[3, 1], C[3, 3], and C[4, 0] became significantly (p < 0.05) less asymmetric as accommodation increased, but no differences were found in the curvature. Conclusions The current study showed that significant changes in peripheral refraction and higher-order aberration profiles occurred during accommodation in myopic eyes. With its extended measurement capabilities, that is, permitting rapid peripheral refraction and higher-order aberration measurements up to visual field angles of ±50 degrees for distance and near (up to −5.00 D), the EM is a new advanced instrument that may provide additional insights in the ongoing quest to understand and monitor myopia development. PMID:25105690

  10. Influence of contact lens power profile on peripheral refractive error.

    PubMed

    de la Jara, Percy Lazon; Sankaridurg, Padmaja; Ehrmann, Klaus; Holden, Brien A

    2014-06-01

    To measure the power profile across the optic zone (OZ) of four commercially available soft contact lenses and establish the impact on the peripheral refractive error of the eye. The power profiles of a spherical conventional hydrogel contact lens (etafilcon A, J&J Vistakon, Jacksonville, FL USA) and three spherical silicone hydrogel contact lenses (lotrafilcon A and B, CIBA Vision, Duluth, GA USA; enfilcon A, CooperVision, Pleasanton, CA USA) with a labeled power of -3.00 and -6.00 diopters were measured using a Shack-Hartmann wavefront sensor power mapping device. Central and peripheral refraction across the horizontal meridian (nasal and temporal visual field at 20, 30, and 40 degrees) was measured with an open-field autorefractor (Shin Nippon NVision K5001, Osaka Japan) with and without contact lenses in 26 myopic subjects. The relative peripheral refractive error on the eye was estimated and compared with and without contact lenses and between contact lenses. Differences in the distribution of the power profile across the OZ were apparent between contact lens types and powers. No significant differences (p > 0.05) were found between contact lens types for their effect on on-axis refraction. Significant differences (p < 0.05) were found at all peripheral retinal eccentricities between contact lens types. For a given central power, the four contact lenses exhibited variations in optical power across the OZ of the lens. The distribution of optical power across the OZ has an influence on the peripheral refractive error of the eye.

  11. Measurement of refractive index profile of non-symmetric, complex silica preforms with high refractive index differences

    NASA Astrophysics Data System (ADS)

    Probostova, Jana; Slanicka, Jiri; Mrazek, Jan; Podrazky, Ondrej; Benda, Adam; Peterka, Pavel

    2016-04-01

    Refractive index profile measurement is a key instrument for characterization of optical properties of preforms, which are used for drawing of high-quality optical fibers. Common industrial optical preform analyzers have been designed for measurement of simple symmetric structures such as step-index or graded-index preforms with refractive index close to the silica (n=1.457 at 633 nm). However, these conditions are usually far from more complex structures used in fiber lasers or in fiber sensor area. Preforms for the drawing of advanced optical fibers, such as Bragg, microstructure or photonic crystal fibers, are usually constituted from stacks with non-symmetric internal structure or composed of alternating layers with high refractive index contrasts. In this paper we present comparison of refractive index profile measurements of simple as well as complex structures with high refractive index differences simulating the Bragg structures. Commercial Photon Kinetics 2600 preform analyzer was used for the refractive index profile measurements. A set of concentrically arranged silica tubes was welded to form a complex preforms. Free space between the tubes was filled by immersion with varying refractive indices to simulate the Bragg structure. Up to three tubes were used for the analysis and the refractive indices of immersion were changed from 1.4 to 1.5. When refractive index of immersion was independently measured the structure of preform was defined. Profiles of these "known" structures were compared to measured data processed by originally proposed algorithm. The work provides an extension of issues of refractive index profile measurements in non-symmetric complex silica structures by a commercial preform analyzer and proposes more convenient methods of numeric data processing.

  12. Laser beam refraction traversely through a graded-index preform to determine refractive index ratio and gradient profile.

    PubMed

    Watkins, L S

    1979-07-01

    A technique is described which permits the determination of geometric and refractive index characteristics of graded-index preforms from measurements of the refraction of rays traced through the preform perpendicular to the preform axis. A computer program was developed to trace rays through graded-index preforms to display the refracting effect of the index properties and relate the ray incidence angle to its deflection in traversing the preform. An experimental apparatus has been developed in which a narrow beam of laser radiation is directed at the preform and its deflection angle measured. Comparison between the experimental results and the ray trace calculations using an interative curve-fitting procedure gave nondestructive determinations of the refractive index ratio Delta and index gradient profile parameter alpha as well as measurement of the core dimensions.

  13. International Space Station Alpha (ISSA) Integrated Traffic Model

    NASA Technical Reports Server (NTRS)

    Gates, R. E.

    1995-01-01

    The paper discusses the development process of the International Space Station Alpha (ISSA) Integrated Traffic Model which is a subsystem analyses tool utilized in the ISSA design analysis cycles. Fast-track prototyping of the detailed relationships between daily crew and station consumables, propellant needs, maintenance requirements and crew rotation via spread sheets provide adequate benchmarks to assess cargo vehicle design and performance characteristics.

  14. International Space Station Alpha (ISSA) Integrated Traffic Model

    NASA Technical Reports Server (NTRS)

    Gates, R. E.

    1995-01-01

    The paper discusses the development process of the International Space Station Alpha (ISSA) Integrated Traffic Model which is a subsystem analyses tool utilized in the ISSA design analysis cycles. Fast-track prototyping of the detailed relationships between daily crew and station consumables, propellant needs, maintenance requirements and crew rotation via spread sheets provide adequate benchmarks to assess cargo vehicle design and performance characteristics.

  15. Saudi Arabian seismic deep-refraction profiles; final project report

    USGS Publications Warehouse

    Healy, J.H.; Mooney, W.D.; Blank, H.R.; Gettings, M.E.; Kohler, W.M.; Lamson, R.J.; Leone, L.E.

    1983-01-01

    In February 1978 a seismic deep-refraction profile was recorded by the U.S. Geological Survey along a 1000-km line across the Arabian Shield in western Saudi Arabia. The line begins in Mesozoic cover rocks near Riyadh on the Arabian Platform, leads southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan (Tihamat-Asir), and terminates at the outer edge of the Farasan Bank in the southern Red Sea. More than 500 surveyed recording sites were occupied, including 19 in the Farasan Islands. Six shot points were used: five on land, with most charges placed below the water table in drill holes, and one at sea, with charges placed on the sea floor and detonated from a ship. Slightly more than 61 metric tons of explosives were used in 19 discrete firings. Seismic energy was recorded by 100 newly-developed portable seismic stations deployed in approximately 200 km-long arrays for each firing. Each station consisted of a standard 2-Hz vertical component geophone coupled to a self-contained analog recording instrument equipped with a magnetic-tape cassette. In this final report, we fully document the field and data-processing procedures and present the final seismogram data set as both a digital magnetic tape and as record sections for each shot point. Record sections include a normalized set of seismograms, reduced at 6 km/s, and a true-amplitude set, reduced at 8 km/s, which have been adjusted for amplifier gain, individual shot size, and distance from the shot point. Appendices give recorder station and shot information, digital data set descriptions, computer program listings, arrival times used in the interpretation, and a bibliography of reports published as a result of this project. We used two-dimensional ray-tracing techniques in the data analysis, and our interpretation is based primarily on horizontally layered models. The Arabian Shield is composed, to first-order, of two layers, each about 20 km

  16. ISSA/TSS power preliminary design

    NASA Technical Reports Server (NTRS)

    Main, John A.

    1996-01-01

    A projected power shortfall during the initial utilization flights of the International Space Station Alpha (ISSA) has prompted an inquiry into the use of the Tethered Satellite System (TSS) to provide station power. The preliminary design of the combined ISSA/TSS system is currently underway in the Preliminary Design Office at the Marshall Space Flight Center. This document focuses on the justification for using a tether system on space station, the physical principles behind such a system, and how it might be operated to best utilize its capabilities. The basic components of a simple DC generator are a magnet of some type and a conductive wire. Moving the wire through the magnetic field causes forces to be applied to the electric charges in the conductor, and thus current is induced to flow. This simple concept is the idea behind generating power with space-borne tether systems. The function of the magnet is performed by the earth's magnetic field, and orbiting a conductive tether about the earth effectively moves the tether through the field.

  17. International Space Station Alpha (ISSA) Integrated Traffic Model

    NASA Technical Reports Server (NTRS)

    Gates, Robert E.

    1994-01-01

    The paper discusses the development process of the International Space Station Alpha (ISSA) Integrated Traffic Model which is a subsystem analyses tool utilized in the ISSA design analysis cycles. Fast-track prototyping of the detailed relationships between daily crew and station consumables, propellant needs, maintenance requirements, and crew rotation via spread sheets provides adequate bench marks to assess cargo vehicle design and performance characteristics.

  18. Two-dimensional refractive index and stresses profiles of a homogenous bent optical fiber.

    PubMed

    Ramadan, W A; Wahba, H H; Shams El-Din, M A

    2014-11-01

    We present a significant contribution to the theory of determining the refractive index profile of a bent homogenous optical fiber. In this theory we consider two different processes controlling the index profile variations. The first is the linear index variation due to stress along the bent radius, and the second is the release of this stress on the fiber surface. This release process is considered to have radial dependence on the fiber radius. These considerations enable us to construct the index profile in two dimensions normal to the optical axis, considering the refraction of light rays traversing the fiber. This theory is applied to optical homogenous bent fiber with two bending radii when they are located orthogonal to the light path of the object arm in the holographic setup (like the Mach-Zehnder interferometer). Digital holographic phase shifting interferometry is employed in this study. The recorded phase shifted holograms have been combined, reconstructed, and processed to extract the phase map of the bent optical fiber. A comparison between the extracted optical phase differences and the calculated one indicates that the refractive index profile variation should include the above mentioned two processes, which are considered as a response for stress distribution across the fiber's cross section. The experimentally obtained refractive index profiles provide the stress induced birefringence profile. Thus we are able to present a realistic induced stress profile due to bending.

  19. Fine-scale measurements of microwave refractivity profiles with helicopter and low-cost rocket probes

    NASA Astrophysics Data System (ADS)

    Rowland, John R.; Babin, Steven M.

    1987-12-01

    The recent development of computer models that can accurately predict radar performance under ducting or other anomalous propagation conditions has produced a need for high-resolution profiles of microwave refractivity in the lower troposphere. This article contains a brief description of two systems that can make the required meteorological measurements for use in those models. The first system is helicopter-based and has been used for research purposes to verify model performance. The second uses a low-cost rocket to carry a lightweight telemetry package to the desired altitudes. The rocket system shows promise for shipboard use where accurate, high-resolution refractivity profiles near the ocean surface are required.

  20. Recovery of atmospheric refractivity profiles from simulated satellite-to-satellite tracking data

    NASA Technical Reports Server (NTRS)

    Murray, C. W., Jr.; Rangaswamy, S.

    1975-01-01

    Techniques for recovering atmospheric refractivity profiles from simulated satellite-to-satellite tracking data are documented. Examples are given using the geometric configuration of the ATS-6/NIMBUS-6 Tracking Experiment. The underlying refractivity model for the lower atmosphere has the spherically symmetric form N = exp P(s) where P(s) is a polynomial in the normalized height s. For the simulation used, the Herglotz-Wiechert technique recovered values which were 0.4% and 40% different from the input values at the surface and at a height of 33 kilometers, respectively. Using the same input data, the model fitting technique recovered refractivity values 0.05% and 1% different from the input values at the surface and at a height of 50 kilometers, respectively. It is also shown that if ionospheric and water vapor effects can be properly modelled or effectively removed from the data, pressure and temperature distributions can be obtained.

  1. Reconstruction of fiber grating refractive-index profiles from complex bragg reflection spectra.

    PubMed

    Huang, D W; Yang, C C

    1999-07-20

    Reconstruction of the refractive-index profiles of fiber gratings from their complex Bragg reflection spectra is experimentally demonstrated. The amplitude and phase of the complex reflection spectrum were measured with a balanced Michelson interferometer. By integrating the coupled-mode equations, we built the relationship between the complex coupling coefficient and the complex reflection spectrum as an iterative algorithm for reconstructing the index profile. This method is expected to be useful for reconstructing the index profiles of fiber gratings with any apodization, chirp, or dc structures. An apodized chirped grating and a uniform grating with a depression of index modulation were used to demonstrate the technique.

  2. Enhanced ODR range using exponentially graded refractive index profile of 1D binary photonic crystal

    SciTech Connect

    Sharma, Sanjeev Kumar, Rajendra; Singh, Kh. S.; Jain, Deepti; Kumar, Arun

    2016-05-06

    A simple design of broadband one dimensional dielectric/semiconductor multilayer structure having refractive index profile of exponentially graded material has been proposed. The theoretical analysis shows that the proposed structure works as a perfect mirror within a certain wavelength range (1550 nm). In order to calculate the reflection properties a transfer matrix method (TMM) has been used. This property shows that binary graded photonic crystal structures have widened omnidirectional reflector (ODR) bandgap. Hence a exponentially graded photonic crystal structure can be used as a broadband optical reflector and the range of reflection can be tuned to any wavelength region by varying the refractive index profile of exponentially graded photonic crystal structure.

  3. Airborne GPS radio occultation refractivity profiles observed in tropical storm environments

    NASA Astrophysics Data System (ADS)

    Murphy, B. J.; Haase, J. S.; Muradyan, P.; Garrison, J. L.; Wang, K.-N.

    2015-03-01

    Airborne GPS radio occultation (ARO) data have been collected during the 2010 PRE-Depression Investigation of Cloud systems in the Tropics (PREDICT) experiment. GPS signals received by the airborne Global Navigation Satellite System Instrument System for Multistatic and Occultation Sensing (GISMOS) are used to retrieve vertical profiles of refractivity in the neutral atmosphere. The system includes a conventional geodetic GPS receiver component for straightforward validation of the analysis method in the middle to upper troposphere, and a high-sample rate (10 MHz) GPS recorder for postprocessing complex signals that probe the lower troposphere. The results from the geodetic receivers are presented here. The retrieved ARO profiles consistently agree within ~2% of refractivity profiles calculated from the European Center for Medium-Range Weather Forecasting model Interim reanalyses as well as from nearby dropsondes and radiosondes. Changes in refractivity obtained from ARO data over the 5 days leading to the genesis of tropical storm Karl are consistent with moistening in the vicinity of the storm center. An open-loop tracking method was implemented in a test case to analyze GPS signals from the GISMOS 10 MHz recording system for comparison with geodetic receiver data. The open-loop mode successfully tracked ~2 km deeper into the troposphere than the conventional receiver and can also track rising occultations, illustrating the benefit from the high-rate recording system. Accurate refractivity retrievals are an important first step toward the future goal of assimilating moisture profiles to improve forecasting of developing storms using this new GPS occultation technique.

  4. Full-field measurement of surface reflectivity using a microscopy for refractive index profiling of GRIN lenses

    NASA Astrophysics Data System (ADS)

    Weng, Chun-Jen; Chen, Chih-Yen; Hwang, Chi-Hung; Liu, Da-Ren

    2016-10-01

    This paper outlines an improved technique for profiling the refractive index of Graded-index (GRIN) lenses based on the measurements obtained from a reflectivity image. Reflective cross-sectional image of the GRIN lens were compared with a reflectance reference target under illumination at small incidence angles to obtain the full-field refractive index distribution of the GRIN lens quickly and easily.

  5. The design of analysis system of refractive index profile of optical fiber

    NASA Astrophysics Data System (ADS)

    He, Gao; Liu, Zhihai

    2011-11-01

    This paper developed an intelligent optical fiber refractive index profile measurement system. This system is based on the principle of the refracted near-field measurement. The whole system is the use of a unique high-resolution non-contact capacitive displacement sensor to monitor the scanning position of the fiber measured. At the same time we used a shading screen which was embedded into the sample pool. Using this method, we can totally save space. Finally, we used a high curvature condenser to collection of reflected light which we used a photo detector to collect. The collected signal was brought into the computer to calculate the optical fiber refractive index. The whole system is totally enclosed operating instrument with an easy-to-use software interface for performing measurements of both multi mode and single mode optical fiber, which can easy pick up the signal automatically and processing in computer. Measurement accuracy can reach 10-4. It is fit for measuring the refractive index of single-mode fibers and multi-mode fibers.

  6. Ionospheric refraction effects in slant range profiles of auroral HF coherent echoes

    NASA Astrophysics Data System (ADS)

    Uspensky, M. V.; Kustov, A. V.; Sofko, G. J.; Koehler, J. A.; Villain, J. P.; Hanuise, C.; Ruohoniemi, J. M.; Williams, P. J. S.

    1994-03-01

    The theory of auroral coherent echoes developed for VHF scattering by Uspensky et al. (1988, 1989) is applied to the interpretation of intensity and Doppler velocity slant range profiles of HF radar aurora. The theoretical model includes the effects of irregularity aspect sensitivity, ionospheric refraction of the radar beam, and the reception of signals from different heights. The predicted profiles of HF radar aurora are compared with Schefferville HF radar observations in the frequency interval of 9-18 MHz. Satisfactory agreement is found between theory and experiment for the intensity profiles. However, there are significant discrepancies for the Doppler velocity profiles. We discuss this lack of agreement in light of other recent observations.

  7. Recycling and recovery routes for incinerated sewage sludge ash (ISSA): a review.

    PubMed

    Donatello, Shane; Cheeseman, Christopher R

    2013-11-01

    The drivers for increasing incineration of sewage sludge and the characteristics of the resulting incinerated sewage sludge ash (ISSA) are reviewed. It is estimated that approximately 1.7 milliontonnes of ISSA are produced annually world-wide and is likely to increase in the future. Although most ISSA is currently landfilled, various options have been investigated that allow recycling and beneficial resource recovery. These include the use of ISSA as a substitute for clay in sintered bricks, tiles and pavers, and as a raw material for the manufacture of lightweight aggregate. ISSA has also been used to form high density glass-ceramics. Significant research has investigated the potential use of ISSA in blended cements for use in mortars and concrete, and as a raw material for the production of Portland cement. However, all these applications represent a loss of the valuable phosphate content in ISSA, which is typically comparable to that of a low grade phosphate ore. ISSA has significant potential to be used as a secondary source of phosphate for the production of fertilisers and phosphoric acid. Resource efficient approaches to recycling will increasingly require phosphate recovery from ISSA, with the remaining residual fraction also considered a useful material, and therefore further research is required in this area.

  8. Characterization and estimation of refractive index profile of laser-written photopolymer optical waveguides

    NASA Astrophysics Data System (ADS)

    Dinleyici, Mehmet Salih; Sümer, Can

    2011-10-01

    In this study, channel waveguides fabricated in photopolymer films by direct-writing using a low-power CW laser, are used as phase objects in a simple plane-wave diffraction setup, and the refractive index modulation profiles of the waveguides are characterized using the recorded diffraction patterns. Index profiles are modeled by piece-wisely combining two Gaussian functions representing the central and the tail regions. Measured diffraction patterns are matched with patterns generated using the model. This simple model makes it possible to design various channel waveguides embedded into polymer substrates. The proposed model is tested on three distinctive waveguide profiles written on the same Acrylamide/Polyvinyl Alcohol based photopolymer with different exposures.

  9. Vertical profiling of atmospheric refractivity using GPS STD data from a single ground-based station: Simulations and applications

    NASA Astrophysics Data System (ADS)

    Zus, F.; Dick, G.; Heise, S.; Wickert, J.; Ramatschi, M.

    2013-12-01

    We developed a ray-tracing operator to compute the signal travel time delay due to the neutral atmosphere, known as Slant Total Delay (STD), between a GPS satellite and a ground-based receiving station. Having developed a rapid and precise forward operator we constructed the tangent-linear (adjoint) operator to estimate refractivity in the vicinity of a single station. The refractivity retrievals potentially complement refractivity retrievals from radio occultation data and can be considered a valuable input for Numerical Weather Prediction. In a first experiment (simulation) we study the feasibility for vertical profiling of refractivity using STDs from a single station. The simulation cycle consists of the computation of STDs given a refractivity profile, the addition of noise to mimic observation errors and the retrieval of a refractivity profile from the artificial STDs by a non-linear least-square analysis. Clearly, besides the noise level, the elevation range plays an important role regarding the quality of the refractivity retrieval; near-horizon STDs corrupted by noise allow a significantly better refractivity retrieval than STDs close to the zenith without any noise. The simulation study suggests that near-horizon STDs provide additional information when compared to Zenith Total Delays (ZTDs). In a second experiment (application) we replace the artificial STDs in the simulation by STDs retrieved from GPS phase-observations. The procedure is repeated station-by-station for 200 stations in Germany. We do not find a significant benefit from STDs over ZTDs in the retrieved refractivity profile since near-horizon STDs are rarely available and representative errors due to asymmetry are non-negligable. We attempt to mitigate the latter problem by the additional estimation of horizontal gradients, and indeed, we find strong evidence that STDs retrieved from GPS phase-observations contain asymmetric information. The former problem still poses a serious limitation

  10. Two-dimensional refractive index and birefringence profiles of a graded index bent optical fibre

    NASA Astrophysics Data System (ADS)

    Ramadan, W. A.; Wahba, H. H.; Shams El-Din, M. A.

    2017-07-01

    A theory to recover refractive index profile of the bent graded index (GRIN) optical fibre, in core region, is proposed. This theory is applied to the bent GRIN optical fibre when it is located orthogonal in the light path of the object arm in digital holographic phase shifting interferometer; like Mach-Zehnder interferometer. In the experiment, the fibre is bent with two different bending radii and fixed on a microscope slide keeping it immersed in matching liquid. The produced phase shifted holograms, with the presence of the fibre, are recorded using an attached CCD camera. Two different processes controlling the index profile shape of the bent GRIN optical fibre are assumed. In the first process, a linear index variation is evolved from stresses in the direction of the bent radius. In the second one, there is a release of these stresses near the fibre surface, which depends on the fibre's radius. This will affect the outer free surface of the cladding. Based on these assumptions, we are able to construct the index profile in two dimensions normal to the optical axis. We propose two functions to describe the refractive index profiles in cladding and the core regions of the bent GRIN optical fibre. The recorded phase shifted holograms are combined, reconstructed and analyzed to get the phase map of the bent GRIN optical fibre. Comparing the extracted optical phase differences with the calculated ones, a good agreement between them is found. This means that the used two dimensional proposed functions, which are describing cladding and the core indices profiles, are the most proper in this situation. Thus, we are able to determine a realistic induced birefringence profile inside the fibre which is generated by a bending operation, not only in the cladding but also in graded index core region as well.

  11. Evaluation of Refractivity Profiles from CHAMP and SAC-C GPS Radio Occultation

    NASA Technical Reports Server (NTRS)

    Poli, Paul; Joiner, Joanna; delaTorreJuarez, Manuel; Hoff, Raymond M.; Atlas, Robert (Technical Monitor)

    2002-01-01

    The CHAMP and SAC-C missions are the first missions to carry a second-generation 'Blackjack' GPS receiver. One of the new features of this receiver is its ability to sense the lower troposphere closer to the surface than the proof-of-concept GPS/MET 1995 experiment. Since their launch, CHAMP and SAC-C have collected thousands of GPS radio occultations, representing a wealth of measurements available for data assimilation in Numerical Weather Prediction (NWP) models. In order to evaluate the refractivity data derived by JPL from raw radio occultation measurements, we use Data Assimilation Office (DAO) 6-hour forecasts as an independent state of the atmosphere. We compare CHAMP and SAC-C refractivity (processed by JPL) with refractivity calculated from the DAO global fields of temperature, water vapor content and humidity. We will show statistics of the differences as well as Probability Density Functions (PDFs) of the differences. Depending upon availability of AIRS data, we plan to show individual profile comparisons between GPS radio occultation and AIRS retrievals.

  12. Evaluation of Refractivity Profiles From Champ and SAC-C GPS Radio Occultation

    NASA Technical Reports Server (NTRS)

    Poli, Paul; Joiner, Joanna; delaTorreJuarez, Manuel; Hoff, Raymond M.; Atlas, Robert (Technical Monitor)

    2002-01-01

    The CHAMP and SAC-C missions are the first missions to carry a second-generation 'Blackjack' GPS receiver. One of the new features of this receiver is its ability to sense the lower troposphere closer to the surface than the proof-of-concept GPS/MET 1995 experiment. Since their launch, CHAMP and SAC-C have collected thousands of GPS radio occultations, representing a wealth of measurements available for data assimilation in Numerical Weather Prediction (NWP) models. In order to evaluate the refractivity data derived by JPL from raw radio occultation measurements, we use Data Assimilation Office (DAO) shout forecasts as an independent state of the atmosphere. We compare CHAMP and SAC-C refractivity (processed by JPL) with refractivity calculated from the DAO global fields of temperature, water vapor content and humidity. We will show statistics of the differences as well as Probability Density Functions (PDFs) of the differences. Depending upon availability of AIRS data, we plan to show individual profile comparisons between GPS radio occultation and AIRS retrievals.

  13. Thin-film thickness profile and its refractive index measurements by dispersive white-light interferometry.

    PubMed

    Ghim, Young-Sik; Kim, Seung-Woo

    2006-11-27

    As an extension of the authors' previous report of Ref 1, we describe an improved version of dispersive white-light interferometry that enables us to measure the tomographical thickness profile of a thin-film layer through Fourier-transform analysis of spectrally-resolved interference signals. The group refractive index can also be determined without prior knowledge of the geometrical thickness of the film layer. Owing to fast measurement speed with no need of mechanical depth scanning, the proposed method is well suited for in-line 3-D inspection of dielectric thin film layers particularly for the semiconductor and flat-panel display industry.

  14. Spatially resolved refractive index profiles of electrically switchable computer-generated holographic gratings.

    PubMed

    Zito, Gianluigi; Finizio, Andrea; De Nicola, Sergio

    2009-10-12

    We describe a spatially resolved interferometric technique combined with a phase reconstruction method that provides a quantitative two-dimensional profile of the refractive index and spatial distribution of the optical contrast between the on-off states of electrically switchable diffraction gratings as a function of the external electric field. The studied structures are holographic gratings optically written into polymer/liquid crystal composites through single-beam spatial light modulation by means of computer-generated holograms. The electro-optical response of the gratings is also discussed. The diffraction efficiency results to be dependent on the incident light polarization suggesting the possibility to develop polarization dependent switching devices.

  15. Measurement of two dimensional refractive index profiles of channel waveguides using an interferometric technique.

    PubMed

    Oven, R

    2009-10-20

    Two dimensional refractive index profiles of ion exchanged channel waveguides in glass have been measured using an interferometric method. In order to obtain depth data, a shallow bevel is produced in the glass by polishing. A regularization algorithm for the extraction of the phase data from the interferometer image is presented. The method is applied to waveguides formed by the electric field assisted diffusion of Cu+ ions into a borosilicate glass. The index change obtained from the interferometer is in good agreement with that obtained from measurements on planar waveguides.

  16. Ionosphere Profile Estimation Using Ionosonde & GPS Data in an Inverse Refraction Calculation

    NASA Astrophysics Data System (ADS)

    Psiaki, M. L.

    2014-12-01

    A method has been developed to assimilate ionosonde virtual heights and GPS slant TEC data to estimate the parameters of a local ionosphere model, including estimates of the topside and of latitude and longitude variations. This effort seeks to better assimilate a variety of remote sensing data in order to characterize local (and eventually regional and global) ionosphere electron density profiles. The core calculations involve a forward refractive ray-tracing solution and a nonlinear optimal estimation algorithm that inverts the forward model. The ray-tracing calculations solve a nonlinear two-point boundary value problem for the curved ionosonde or GPS ray path through a parameterized electron density profile. It implements a full 3D solution that can handle the case of a tilted ionosphere. These calculations use Hamiltonian equivalents of the Appleton-Hartree magneto-plasma refraction index model. The current ionosphere parameterization is a modified Booker profile. It has been augmented to include latitude and longitude dependencies. The forward ray-tracing solution yields a given signal's group delay and beat carrier phase observables. An auxiliary set of boundary value problem solutions determine the sensitivities of the ray paths and observables with respect to the parameters of the augmented Booker profile. The nonlinear estimation algorithm compares the measured ionosonde virtual-altitude observables and GPS slant-TEC observables to the corresponding values from the forward refraction model. It uses the parameter sensitivities of the model to iteratively improve its parameter estimates in a way the reduces the residual errors between the measurements and their modeled values. This method has been applied to data from HAARP in Gakona, AK and has produced good TEC and virtual height fits. It has been extended to characterize electron density perturbations caused by HAARP heating experiments through the use of GPS slant TEC data for an LOS through the heated

  17. Crustal structure of Yunnan province, People's Republic of China, from seismic refraction profiles

    USGS Publications Warehouse

    Kan, R.-J.; Hu, H.-X.; Zeng, R.-S.; Mooney, W.D.; McEvilly, T.V.

    1986-01-01

    Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics, on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile, but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy.

  18. Crustal Structure of Yunnan Province, People's Republic of China, from Seismic Refraction Profiles.

    PubMed

    Kan, R J; Hu, H X; Zeng, R S; Mooney, W D; McEvilly, T V

    1986-10-24

    Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy.

  19. Vertical profiles of urban aerosol complex refractive index in the frame of ESQUIF airborne measurements

    NASA Astrophysics Data System (ADS)

    Raut, J.-C.; Chazette, P.

    2007-07-01

    A synergy between lidar, sunphotometer and in situ measurements has been applied to airborne observations performed during the Etude et Simulation de la QUalité de l'air en Ile-de-France (ESQUIF), enabling the retrieval of vertical profiles for the aerosol complex refractive index (ACRI) and single-scattering albedo with a vertical resolution of 200 m over Paris area. The averaged value over the entire planetary boundary layer (PBL) for the ACRI is close to 1.51(±0.02)-i0.017(±0.003) at 532 nm. The single-scattering albedo of the corresponding aerosols is found to be ~0.9 at the same wavelength. A good agreement is found with previous studies for urban aerosols. A comparison of vertical profiles of ACRI with simulations combining in situ measurements and relative humidity (RH) profiles has highlighted a modification in aerosol optical properties linked to their history and the origin of the air mass. The determination of ACRI in the atmospheric column enabled to retrieve vertical profiles of extinction coefficient in accordance with lidar profiles measurements.

  20. Vertical profiles of urban aerosol complex refractive index in the frame of ESQUIF airborne measurements

    NASA Astrophysics Data System (ADS)

    Raut, J.-C.; Chazette, P.

    2008-02-01

    A synergy between lidar, sunphotometer and in situ measurements has been applied to airborne observations performed during the Etude et Simulation de la QUalité de l'air en Ile-de-France (ESQUIF), enabling the retrieval of vertical profiles for the aerosol complex refractive index (ACRI) and single-scattering albedo with a vertical resolution of 200 m over Paris area. The averaged value over the entire planetary boundary layer (PBL) for the ACRI is close to 1.51(±0.02)-i0.017(±0.003) at 532 nm. The single-scattering albedo of the corresponding aerosols is found to be ~0.9 at the same wavelength. A good agreement is found with previous studies for urban aerosols. A comparison of vertical profiles of ACRI with simulations combining in situ measurements and relative humidity (RH) profiles has highlighted a modification in aerosol optical properties linked to their history and the origin of the air mass. The determination of ACRI in the atmospheric column enabled to retrieve vertical profiles of extinction coefficient in accordance with lidar profiles measurements.

  1. Profile of refractive errors in European Caucasian children with Autistic Spectrum Disorder; increased prevalence and magnitude of astigmatism.

    PubMed

    Anketell, Pamela M; Saunders, Kathryn J; Gallagher, Stephen; Bailey, Clare; Little, Julie-Anne

    2016-07-01

    Autistic Spectrum Disorder (ASD) is a common neurodevelopmental disorder characterised by impairment of communication, social interaction and repetitive behaviours. Only a small number of studies have investigated fundamental clinical measures of vision including refractive error. The aim of this study was to describe the refractive profile of a population of children with ASD compared to typically developing (TD) children. Refractive error was assessed using the Shin-Nippon NVision-K 5001 open-field autorefractor following the instillation of cyclopentolate hydrochloride 1% eye drops. A total of 128 participants with ASD (mean age 10.9 ± 3.3 years) and 206 typically developing participants (11.5 ± 3.1 years) were recruited. There was no significant difference in median refractive error, either by spherical equivalent or most ametropic meridian between the ASD and TD groups (Spherical equivalent, Mann-Whitney U307 = 1.15, p = 0.25; Most Ametropic Meridian, U305 = 0.52, p = 0.60). Median refractive astigmatism was -0.50DC (range 0.00 to -3.50DC) for the ASD group and -0.50DC (Range 0.00 to -2.25DC) for the TD group. Magnitude and prevalence of refractive astigmatism (defined as astigmatism ≥1.00DC) was significantly greater in the ASD group compared to the typically developing group (ASD 26%, TD 8%, magnitude U305 = 3.86, p = 0.0001; prevalence (χ12=17.71 , p < 0.0001). This is the first study to describe the refractive profile of a population of European Caucasian children with ASD compared to a TD population of children. Unlike other neurodevelopmental conditions, there was no increased prevalence of spherical refractive errors in ASD but astigmatic errors were significantly greater in magnitude and prevalence. This highlights the need to examine refractive errors in this population. © 2016 The Authors Ophthalmic & Physiological Optics © 2016 The College of Optometrists.

  2. Note: refractive index sensing of turbid media by differentiation of the reflectance profile: does error-correction work?

    PubMed

    Goyal, K G; Dong, M L; Kane, D G; Makkar, S S; Worth, B W; Bali, L M; Bali, S

    2012-08-01

    A widely used method for determining refractive index postulates that the derivative of the angular profile for light reflected from the sample is maximum at the critical angle for total internal reflection (TIR). It is well-known that in turbid media this "differentiation method" yields errors in refractive index. Unexplained anomalies in previous error-calculations are eliminated if one uses a recent model of TIR which departs from traditional Fresnel theory. However we find that, in practical situations, the refractive index obtained by differentiation even after error-correction is significantly different from the best estimate for the refractive index obtained by curve-fitting the reflectance data. Thus the differentiation method lacks scientific validity in turbid media.

  3. Tropospheric profiles of wet refractivity and humidity from the combination of remote sensing data sets and measurements on the ground

    NASA Astrophysics Data System (ADS)

    Hurter, F.; Maier, O.

    2013-11-01

    We reconstruct atmospheric wet refractivity profiles for the western part of Switzerland with a least-squares collocation approach from data sets of (a) zenith path delays that are a byproduct of the GPS (global positioning system) processing, (b) ground meteorological measurements, (c) wet refractivity profiles from radio occultations whose tangent points lie within the study area, and (d) radiosonde measurements. Wet refractivity is a parameter partly describing the propagation of electromagnetic waves and depends on the atmospheric parameters temperature and water vapour pressure. In addition, we have measurements of a lower V-band microwave radiometer at Payerne. It delivers temperature profiles at high temporal resolution, especially in the range from ground to 3000 m a.g.l., though vertical information content decreases with height. The temperature profiles together with the collocated wet refractivity profiles provide near-continuous dew point temperature or relative humidity profiles at Payerne for the study period from 2009 to 2011. In the validation of the humidity profiles, we adopt a two-step procedure. We first investigate the reconstruction quality of the wet refractivity profiles at the location of Payerne by comparing them to wet refractivity profiles computed from radiosonde profiles available for that location. We also assess the individual contributions of the data sets to the reconstruction quality and demonstrate a clear benefit from the data combination. Secondly, the accuracy of the conversion from wet refractivity to dew point temperature and relative humidity profiles with the radiometer temperature profiles is examined, comparing them also to radiosonde profiles. For the least-squares collocation solution combining GPS and ground meteorological measurements, we achieve the following error figures with respect to the radiosonde reference: maximum median offset of relative refractivity error is -16% and quartiles are 5% to 40% for the lower

  4. Epithelial Thickness Profile Changes Following Small Incision Refractive Lenticule Extraction (SMILE) for Myopia and Myopic Astigmatism.

    PubMed

    Ganesh, Sri; Brar, Sheetal; Relekar, Kirti J

    2016-07-01

    To evaluate the epithelial thickness profile changes following small incision refractive lenticule extraction (SMILE) and study their correlation with the amount of myopia corrected. Epithelial thickness was measured in nine zones with spectral-domain anterior segment optical coherence tomography (SD-OCT) across a 6-mm diameter preoperatively and at 1 day, 2 weeks, and 3 months postoperatively. The observed changes were correlated with the degree of myopia corrected. The study included 100 eyes from 50 eligible patients (32 females, 18 males) with a mean age of 24.4 ± 2.8 years. Thirty-eight eyes underwent SMILE for low (spherical equivalent [SE] < -4.00 diopters [D]), 44 eyes for moderate (SE -4.00 to -6.00 D), and 18 eyes for high (SE > -6.00 to -10.00 D) myopia with 6.71 ± 1.65, 6.82 ± 0.21, and 6.44 ± 0.2 mm optical zones, respectively. At 3 months, a statistically significant epithelial thickness increase was observed in the central zone (6.83% for low, 9.26% for moderate, and 12.7% for high myopia, P < .05 for all groups) and superior zone (3.98% for low, 7.82% for moderate, and 9.87% for high myopia) across all three groups, which correlated positively with the degree of myopia corrected (r(2) = 0.723 for central zone, r(2) = 0.585 for superior zone, P < .001 for both zones). None of the other zones showed any statistically significant changes at 3 months. Four eyes of two patients with high myopia (SE > -8.00 D) had regression due to significant epithelial thickening. Preliminary results suggest that epithelial thickness profile changes after SMILE may have an impact on the refractive outcome in the long-term postoperative period, especially in higher degrees of myopia. [J Refract Surg. 2016;32(7):473-478.]. Copyright 2016, SLACK Incorporated.

  5. Crustal structure of the North Iberian continental margin from seismic refraction/wide-angle reflection profiles

    NASA Astrophysics Data System (ADS)

    Ruiz, M.; Díaz, J.; Pedreira, D.; Gallart, J.; Pulgar, J. A.

    2017-10-01

    The structure and geodynamics of the southern margin of the Bay of Biscay have been investigated from a set of 11 multichannel seismic reflection profiles, recorded also at wide angle offsets in an onshore-offshore network of 24 OBS/OBH and 46 land sites. This contribution focuses on the analysis of the wide-angle reflection/refraction data along representative profiles. The results document strong lateral variations of the crustal structure along the margin and provide an extensive test of the crustal models previously proposed for the northern part of the Iberian Peninsula. Offshore, the crust has a typical continental structure in the eastern tip of the bay, which disappears smoothly towards the NW to reach crustal thickness close to 10 km at the edge of the studied area ( 45°N, 6°W). The analysis of the velocity-depth profiles, altogether with additional information provided by the multichannel seismic data and magnetic surveys, led to the conclusion that the crust in this part of the bay should be interpreted as transitional from continental to oceanic. Typical oceanic crust has not been imaged in the investigated area. Onshore, the new results are in good agreement with previous results and document the indentation of the Bay of Biscay crust into the Iberian crust, forcing its subduction to the North. The interpreted profiles show that the extent of the southward indentation is not uniform, with an Alpine root less developed in the central and western sector of the Basque-Cantabrian Basin. N-S to NE-SW transfer structures seem to control those variations in the indentation degree.

  6. Crustal structure of the Southern Rio Grande rift determined from seismic refraction profiling

    NASA Technical Reports Server (NTRS)

    Sinno, Y. A.; Keller, G. R.; Harder, S. H.; Daggett, P. H.; Morgan, P.

    1986-01-01

    As part of a major cooperative seismic experiment, a series of seismic refraction profiles have been recorded in south-central New Mexico with the goal of determining the crustal structure in the southern Rio Grande rift. The data gathered greatly expand the seismic data base in the area, and consist of three interlocking regional profiles: a reversed E-W line across the rift, an unreversed N-S axial line, and an unreversed SW-SE line. The reversed E-W line shows no significant dip along the Moho (32 km thick crust) and a 7.7 km/s Pn velocity. Results from the N-S axial line and the NW-SE line indicate an apparent Pn velocity of 7.95 km/s and significant dip along the Moho with crustal thinning toward the south and southeast. When interpreted together, these data indicate a crustal thinning in the southern rift of 4-6 km with respect to the northern rift and the adjacent Basin and Range province, and establish the regional Pn velocity to be approximately 7.7 km/s. These results suggest that the Rio Grande rift can be identified as a crustal feature separate and distinct from the Basin and Range province.

  7. Crustal structure of the Southern Rio Grande rift determined from seismic refraction profiling

    NASA Technical Reports Server (NTRS)

    Sinno, Y. A.; Keller, G. R.; Harder, S. H.; Daggett, P. H.; Morgan, P.

    1986-01-01

    As part of a major cooperative seismic experiment, a series of seismic refraction profiles have been recorded in south-central New Mexico with the goal of determining the crustal structure in the southern Rio Grande rift. The data gathered greatly expand the seismic data base in the area, and consist of three interlocking regional profiles: a reversed E-W line across the rift, an unreversed N-S axial line, and an unreversed SW-SE line. The reversed E-W line shows no significant dip along the Moho (32 km thick crust) and a 7.7 km/s Pn velocity. Results from the N-S axial line and the NW-SE line indicate an apparent Pn velocity of 7.95 km/s and significant dip along the Moho with crustal thinning toward the south and southeast. When interpreted together, these data indicate a crustal thinning in the southern rift of 4-6 km with respect to the northern rift and the adjacent Basin and Range province, and establish the regional Pn velocity to be approximately 7.7 km/s. These results suggest that the Rio Grande rift can be identified as a crustal feature separate and distinct from the Basin and Range province.

  8. Combined tomographic forward and inverse modeling of active seismic refraction profiling data

    NASA Astrophysics Data System (ADS)

    Koulakov, I.; Kopp, H.

    2008-12-01

    We present a new code for combined forward and inverse tomographic modeling based on first-arrival travel times of active seismic refraction profiling data (PROFIT - Profile Forward and Inverse Tomographic modeling). The main features of the algorithm involve the original version of bending ray tracing, parameterization based on nodes, variable grid size definition determined by the ray density, and regularization of the inversion. The key purpose of applying the PROFIT code is rather not in solely producing the tomographic image of a continuous velocity field, but in creating a geologically reasonable synthetic model. This model then includes first-order velocity changes representing petrophysical boundaries and is thus better suited for a geological-tectonic interpretation than its smoothed tomographic counterpart. After performing forward and inverse modeling, the synthetic model will reproduce a congeneric model to the tomographic inversion result of the observed data. We demonstrate the working ability of the code using two marine datasets acquired in the Musicians Seamount Province (Pacific Ocean). The results of the tomographic inversion clearly resolve the dominating extrusive volcanism. In addition, the combined forward and inverse approach tests a large variety of synthetic models to fit the observed data tomography. Along both profiles, the preferred structural model includes a strong positive velocity anomaly extending into the seamount edifice. We suggest that this anomaly pattern represents secondary intrusive processes, which are only revealed by the combined tomographic forward and inverse modeling and could not be resolved by exclusively applying a tomographic inversion. In addition, we present examples of imaging salt domes in the Precaspian oil province as well as a higher-resolution field study that was conducted as a preinvestigative study for tunnel construction to demonstrate the capability of the code in different regimes and on different

  9. The Refractive Status and Vision Profile: evaluation of psychometric properties and comparison of Rasch and summated Likert-scaling.

    PubMed

    Garamendi, Estibaliz; Pesudovs, Konrad; Stevens, Michael J; Elliott, David B

    2006-04-01

    The psychometric properties of the Refractive Status and Vision Profile (RSVP) questionnaire were evaluated using Rasch analysis. Ninety-one myopic patients from a refractive surgery clinic and general optometric practice completed the RSVP. Rasch analysis of the RSVP ordinal data was performed to examine for unidimensionality and item reduction. The traditional Likert-scoring system was compared with a Rasch-scored RSVP and a reduced item Rasch-scored RSVP. Rasch analysis of the original RSVP showed poor targeting of item difficulty to patient quality of life, items with a ceiling effect and underutilized response categories. Combining the underutilized response scales and removal of redundant and misfitting items improved the internal consistency and targeting of the RSVP, and the reduced 20-item Rasch scored RSVP showed greater relative precision over standard Likert scoring in discriminating between the two subject groups. A Rasch scaled quality of life questionnaire is recommended for use in refractive outcomes research.

  10. ISSA-PS, The Postage Stamp Server for IRAS Imaging Data

    NASA Astrophysics Data System (ADS)

    van Buren, D.; Ebert, R.; Egret, D.

    The \\htmllink{ISSA Postage Stamp Server}{http://astrovr.ipac.caltech.edu:8888/ISSA-PS} is a Web-accessible service that delivers IRAS images to users with a minimum of effort. It is unique in that it will operate by object name as well as celestial position. Users can connect using custom clients to automatically make requests and fetch images for local use.

  11. Comparison of phosphorus recovery from incinerated sewage sludge ash (ISSA) and pyrolysed sewage sludge char (PSSC).

    PubMed

    Kleemann, Rosanna; Chenoweth, Jonathan; Clift, Roland; Morse, Stephen; Pearce, Pete; Saroj, Devendra

    2017-02-01

    This research compares and contrasts the physical and chemical characteristics of incinerator sewage sludge ash (ISSA) and pyrolysis sewage sludge char (PSSC) for the purposes of recovering phosphorus as a P-rich fertiliser. Interest in P recovery from PSSC is likely to increase as pyrolysis is becoming viewed as a more economical method of sewage sludge thermal treatment compared to incineration. The P contents of ISSA and PSSC are 7.2-7.5% and 5.6%, respectively. Relative to the sludge, P concentrations are increased about 8-fold in ISSA, compared to roughly 3-fold in PSSC. Both PSSC and ISSA contain whitlockite, an unusual form of calcium phosphate, with PSSC containing more whitlockite than ISSA. Acid leaching experiments indicate that a liquid/solid ratio of 10 with 30min contact time is optimal to release PO4-P into leachate for both ISSA and PSSC. The proportion of P extracted from PSSC is higher due to its higher whitlockite content. Heavy metals are less soluble from PSSC because they are more strongly incorporated in the particles. The results suggest there is potential for the development of a process to recover P from PSSC.

  12. Saudi Arabian seismic-refraction profile: A traveltime interpretation of crustal and upper mantle structure

    USGS Publications Warehouse

    Mooney, W.D.; Gettings, M.E.; Blank, H.R.; Healy, J.H.

    1985-01-01

    The crustal and upper mantle compressional-wave velocity structure across the southwestern Arabian Shield has been investigated by a 1000-km-long seismic refraction profile. The profile begins in Mesozoic cover rocks near Riyadh on the Arabian Platform, trends southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan, and terminates at the outer edge of the Farasan Bank in the southern Red Sea. More than 500 surveyed recording sites were occupied, and six shot points were used, including one in the Red Sea. Two-dimensional ray-tracing techniques, used to analyze amplitude-normalized record sections indicate that the Arabian Shield is composed, to first order, of two layers, each about 20 km thick, with average velocities of about 6.3 km/s and 7.0 km/s, respectively. West of the Shield-Red Sea margin, the crust thins to a total thickness of less than 20 km, beyond which the Red Sea shelf and coastal plain are interpreted to be underlain by oceanic crust. A major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition. Elsewhere along the profile, several high-velocity anomalies in the upper crust correlate with mapped gneiss domes, the most prominent of which is the Khamis Mushayt gneiss. Based on their velocities, these domes may constitute areas where lower crustal rocks have been raised some 20 km. Two intracrustal reflectors in the center of the Shield at 13 km depth probably represent the tops of mafic intrusives. The Mohorovic??ic?? discontinuity beneath the Shield varies from a depth of 43 km and mantle velocity of 8.2 km/s in the northeast to a depth of 38 km and mantle velocity of 8.0 km/s depth in the southwest near the Shield-Red Sea transition. Two velocity discontinuities occur in the upper mantle, at 59 and 70 km depth. The crustal and upper mantle velocity structure of the Arabian Shield is

  13. Measurement of planar refractive index profiles with rapid variations in glass using interferometry and total variation regularized differentiation

    NASA Astrophysics Data System (ADS)

    Oven, R.

    2015-12-01

    Planar refractive index profiles with rapid variations, formed in glass, are measured with interferometry. This involves forming a bevel in the glass and orientating the fringe pattern to be normal to the bevel edge. The index profile is determined by differentiation of the phase function of the fringe pattern. The differentiation has been performed using the total variation regularization method in order to preserve rapid changes in the derivative. This new approach avoids the necessity of filtering, in order to reduce noise, in the direction perpendicular to the bevel, which would otherwise smooth out the rapid index changes. The method is assessed using a model refractive index profile that contains an index gradient of 0.24 μm-1 and is then applied practically to measure the refractive index profile of electrically poled BK7 glass. The new approach allows the sharp transition in the index between poled and unpoled glass to be observed as well as the accumulation of potassium ions beyond the poled glass region.

  14. Crustal structure of the Central-Eastern Greenland: results from the TopoGreenland refraction profile

    NASA Astrophysics Data System (ADS)

    Shulgin, Alexey; Thybo, Hans

    2014-05-01

    Until present, seismic surveys have only been carried out offshore and near the coasts of Greenland, where the crustal structure is affected by oceanic break-up. We present the deep seismic structure of the crust of the interior of Greenland, based on the new and the only existing so far seismic refraction/wide-angle reflection profile. The seismic data was acquired by a team of six people during a two-month long experiment in summer of 2011 on the ice cap in the interior of central-eastern Greenland. The presence of an up to 3.4 km thick ice sheet, permanently covering most of the land mass, made acquisition of geophysical data logistically complicated. The profile extends 310 km inland in E-W direction from the approximate edge of the stable ice cap near the Scoresby Sund across the center of the ice cap. 350 Reftek Texan receivers recorded high-quality seismic data from 8 equidistant shots along the profile. Explosive charge sizes were 1 ton at the ends and ca. 500 kg along the profile, loaded with about 125 kg at 35-85 m depth in individual boreholes. Given that the data acquisition was affected by the thick ice sheet, we questioned the quality of seismic records in such experiment setup. We have developed an automatic routine to check the amplitudes and spectra of the selected seismic phases and to check the differences/challenges in making seismic experiments on ice and the effects of ice on data interpretation. Using tomographic inversion and forward ray tracing modelling we have obtained the two-dimensional velocity model down to a 50 km depth. The model shows a decrease of crustal thickness from 47 km below the centre of Greenland in the western part of the profile to 40 km in its eastern part. Relatively high lower crustal velocities (Vp 6.8 - 7.3 km/s) in the western part of the TopoGreenland profile may result from past collision tectonics or, alternatively, may be related to the speculated passage of the Iceland mantle plume. Comparison of our results

  15. Influence of refractive profile on the reaction of modes with sensor layer in the planar amplitude chemical sensor

    NASA Astrophysics Data System (ADS)

    Karasinski, Pawel; Rogozinski, Roman

    2003-04-01

    The paper presents the theoretical and experimental results involving the influence of refractive profile on the reaction of modes with the absorption sensor layer. The investigation studies concerned the planar structure in which the waveguides were producd using the ion-exchange technique in glass, and the sensor layer was produced with the application of sol-gel technology. The results of experimental investigations confirm the theoretical predictions.

  16. Crustal structure of the Kermadec arc from MANGO seismic refraction profiles

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Kopp, Heidrun; Sutherland, Rupert; Henrys, Stuart; Watts, Anthony B.; Timm, Christian; Scherwath, Martin; Grevemeyer, Ingo; Ronde, Cornel E. J.

    2016-10-01

    Three active-source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the Kermadec subduction zone. These observations are used to test contrasting tectonic models for an along-strike transition in margin structure previously known as the 32°S boundary. We use residual bathymetry to constrain the geometry of this boundary and propose the name Central Kermadec Discontinuity (CKD). North of the CKD, the buried Tonga Ridge occupies the fore-arc with VP 6.5-7.3 km s-1 and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110 ± 20 km), and strike ( 005° south of 25°S). South of the CKD the fore-arc is structurally homogeneous downdip with VP 5.7-7.3 km s-1. In the Havre Trough back-arc, crustal thickness south of the CKD is 8-9 km, which is up to 4 km thinner than the northern Havre Trough and at least 1 km thinner than the southern Havre Trough. We suggest that the Eocene arc did not extend along the current length of the Tonga-Kermadec trench. The Eocene arc was originally connected to the Three Kings Ridge, and the CKD was likely formed during separation and easterly translation of an Eocene arc substrate during the early Oligocene. We suggest that the first-order crustal thickness variations along the Kermadec arc were inherited from before the Neogene and reflect Mesozoic crustal structure, the Cenozoic evolution of the Tonga-Kermadec-Hikurangi margin and along-strike variations in the duration of arc volcanism.

  17. Crustal velocities near Coalinga, California, modeled from a combined earthquake/explosion refraction profile

    USGS Publications Warehouse

    Macgregor-Scott, N.; Walter, A.

    1988-01-01

    Crustal velocity structure for the region near Coalinga, California, has been derived from both earthquake and explosion seismic phase data recorded along a NW-SE seismic-refraction profile on the western flank of the Great Valley east of the Diablo Range. Comparison of the two data sets reveals P-wave phases in common which can be correlated with changes in the velocity structure below the earthquake hypocenters. In addition, the earthquake records reveal secondary phases at station ranges of less than 20 km that could be the result of S- to P-wave conversions at velocity interfaces above the earthquake hypocenters. Two-dimensional ray-trace modeling of the P-wave travel times resulted in a P-wave velocity model for the western flank of the Great Valley comprised of: 1) a 7- to 9-km thick section of sedimentary strata with velocities similar to those found elsewhere in the Great Valley (1.6 to 5.2 km s-1); 2) a middle crust extending to about 14 km depth with velocities comparable to those reported for the Franciscan assemblage in the Diablo Range (5.6 to 5.9 km s-1); and 3) a 13- to 14-km thick lower crust with velocities similar to those reported beneath the Diablo Range and the Great Valley (6.5 to 7.30 km s-1). This lower crust may have been derived from subducted oceanic crust that was thickened by accretionary underplating or crustal shortening. -Authors

  18. Analytical expression of giant Goos-Hänchen shift in terms of proper and improper modes in waveguide structures with arbitrary refractive index profile.

    PubMed

    Alishahi, Fatemeh; Mehrany, Khashayar

    2010-06-01

    We analytically relate the giant Goos-Hänchen shift, observed at the interface of a high refractive index prism and a waveguide structure with an arbitrary refractive index profile, to the spatial resonance phenomenon. The proximity effect of the high refractive index prism on modal properties of the waveguide is discussed, and the observed shift is expressed in terms of proper and improper electromagnetic modes supported by the waveguide with no prism. The transversely increasing improper modes are shown playing an increasingly important role as the high refractive index prism comes closer to the waveguide.

  19. Correlation between compositional and refractive index profiles in LiNbO3:Zn diffused optical waveguides

    NASA Astrophysics Data System (ADS)

    Nevado, R.; Cussó, F.; Lifante, G.; Caccavale, F.; Sada, C.; Segato, F.

    2000-12-01

    Waveguides fabrication in Z- and X-cut LiNbO3 crystals by vapor zinc diffusion has been studied by secondary ion mass spectrometry and optical measurements. Compositional analysis of diffused substrates shows the formation of a Zn rich superficial layer, followed by a deeper region with decreasing Zn concentration. A subsequent thermal annealing process has been performed to let zinc ions further diffuse into the substrates. The composition profiles have been correlated with the refractive index profiles, reconstructed by optical reflectivity measurements. The results and the nature of the detected layers are discussed and correlated with previous x-ray studies obtained in the same samples.

  20. Variability of Atmospheric Boundary Layer height over the tropical oceans - A study using atmospheric refractivity profiles from multi campaign in-situ and satellite radio occultation data.

    NASA Astrophysics Data System (ADS)

    Santosh, M.

    2016-07-01

    Atmospheric Boundary Layer (ABL) over the tropical oceans controls and regulates the influx of water vapour into the free atmosphere due to evaporation. The availability of in situ data for determining the ABL characteristics over tropical oceans are limited to different ship based campaigns and hence restricted in spatial and temporal coverage. For ABL studies the Radio Occultation (RO) based satellite data over tropical oceans have good temporal and spatial coverage but limited in temporal and spatial resolution. Atmospheric refractivity profiles are extensively used in many studies to determine the ABL height from both platforms. The present study attempts to use the advantages in both in-situ and satellite (RO) based data to quantify the variability in the ABL height over the tropical oceans. All studies done so far to identify the ABL height from RO derived refractivity profiles rely extensively on the detection of the minimum refractivity gradient (MRG) below ~6 km along with additional threshold criteria. This leads to an over estimation of ABL heights especially in presence of strong subsidence inversion caused by local/ mesoscale/ synoptic scale processes where the MRG lies significantly above the ABL. The present study attempts to quantify this over estimation using atmospheric refractivity profiles derived from thermo-dynamical parameters from radiosonde ascents over the tropical ocean, suggests an improved method of ABL detection and quantifies the variability so deduced. Over 1000 radiosonde ascents from four ship cruises conducted during DYNAMO 2011 field campaign over the tropical Indian Ocean are used for the purpose. ABL heights determined from radiosonde data using traditional methods (using virtual potential temperature and specific humidity) are compared with those identified from simulated atmospheric refractivity profiles from same data (using prevalent methods for RO) to quantify the over estimation. A new method of ABL detection from

  1. Reconstruction of 3D refractive index profiles of PM PANDA optical fiber using digital holographic method

    NASA Astrophysics Data System (ADS)

    Wahba, H. H.

    2014-10-01

    In this paper, the refractive indices distributions on the two birefringent axes of polarization maintaining (PM) PANDA type optical fiber are reconstructed. The local refraction of the incident rays crossing the PM optical fiber is considered. Off-axis digital holographic interferometric phase shifting arrangement is employed in this investigation. The recorded mutual phase shifted holograms, starts with 0° with steps of π/4, are combined and numerically reconstructed in the image plane to obtain the optical interference phase map. Consequently, the optical phase differences due to the PM optical fiber are extracted after unwrapping and background subtraction of the enhanced optical interference phase map. The birefringence and the beat length in the two directions, fast and slow axes of PM optical fiber, of polarizations in the core region are calculated. This holographic technique and the advanced analysis of the phase shifting permit the calculation of the 3D refractive index distributions for PM PANDA optical fiber.

  2. Crustal structure and tectonic history of the Kermadec arc inferred from MANGO seismic refraction profiles

    NASA Astrophysics Data System (ADS)

    Bassett, D.; Kopp, H.; Sutherland, R.; Henrys, S.; Watts, A. B.; Timm, C.; Scherwath, M.; Grevemeyer, I.; de Ronde, C. E. J.

    2016-12-01

    We have analyzed three wide-angle seismic reflection and refraction profiles and applied spectral averaging techniques to regional grids of bathymetry and free-air gravity anomaly to place the first regional constraints on the crustal structure of the Kermadec arc. These observations are used to test contrasting tectonic models for an along-strike transition in margin structure, across which, 1) the remnant Lau-Colville and active Kermadec arc ridges narrow by >50%; 2) the backarc and forearc deepen by 1 km, and 3) the active volcanic arc is deflected west into the deepest known backarc basin. We use residual bathymetric anomalies to constrain the geometry of this boundary and propose the name Central Kermadec Discontinuity (CKD). North of the CKD, the buried Tonga Ridge occupies the forearc with VP 6.5-7.3 km s-1 and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110±20 km) and strike ( 005° south of 25°S). South of the CKD the forearc is structurally homogeneous down-dip with VP 5.7-7.3 km s-1. Lower crustal velocities are similar to the northern Kermadec forearc, but there is no seismic or gravimetric evidence for an extinct arc ridge within the forearc. In the Havre Trough backarc, crustal thickness south of the CKD is 8-9 km, which is up-to 4 km thinner than the northern Havre Trough and at least 1 km thinner than the southern Havre Trough. The northern Kermadec/Tonga arc preserves a substrate of the Eocene arc, the southern Kermadec forearc preserves Mesozoic forearc rocks accreted at the Gondwana margin, and the central Kermadec arc may have fomed in the Kupe Abyssal Plain. The oldest arc related rocks recovered north and south of the CKD are 52 Ma and 16.7 Ma respectively, and plate tectonic reconstruction suggest the Eocene arc was originally conjoined with the Three Kings Ridge. The separation of these ridges during the early Oligocene likely formed the CKD. In contrast to previous interpretations, we

  3. Refraction near the horizon

    NASA Technical Reports Server (NTRS)

    Schaefer, Bradley E.; Liller, William

    1990-01-01

    Variations in astronomical refraction near the horizon are examined. Sunset timings, a sextant mounted on a tripod, and a temperature profile are utilized to derive the variations in refraction data, collected from 7 locations. It is determined that the refraction ranges from 0.234 to 1.678 deg with an rms deviation of 0.16, and it is observed that the variation is larger than previously supposed. Some applications for the variation of refraction value are discussed.

  4. Refraction near the horizon

    NASA Technical Reports Server (NTRS)

    Schaefer, Bradley E.; Liller, William

    1990-01-01

    Variations in astronomical refraction near the horizon are examined. Sunset timings, a sextant mounted on a tripod, and a temperature profile are utilized to derive the variations in refraction data, collected from 7 locations. It is determined that the refraction ranges from 0.234 to 1.678 deg with an rms deviation of 0.16, and it is observed that the variation is larger than previously supposed. Some applications for the variation of refraction value are discussed.

  5. Criticality Safety Evaluation of the LLNL Inherently Safe Subcritical Assembly (ISSA)

    SciTech Connect

    Percher, Catherine

    2012-06-19

    The LLNL Nuclear Criticality Safety Division has developed a training center to illustrate criticality safety and reactor physics concepts through hands-on experimental training. The experimental assembly, the Inherently Safe Subcritical Assembly (ISSA), uses surplus highly enriched research reactor fuel configured in a water tank. The training activities will be conducted by LLNL following the requirements of an Integration Work Sheet (IWS) and associated Safety Plan. Students will be allowed to handle the fissile material under the supervision of LLNL instructors. This report provides the technical criticality safety basis for instructional operations with the ISSA experimental assembly.

  6. Tropospheric Profiles of Total Refractivity Based on Numerical Weather Prediction Model and GNSS Data Using the Collocation Software COMEDIE

    NASA Astrophysics Data System (ADS)

    Wilgan, K. I.; Rohm, W.; Bosy, J.; Geiger, A.; Hurter, F.

    2015-12-01

    The GNSS (Global Navigation Satellite Systems) signal propagation delay in neutral atmosphere can be described in terms of total refractivity which depends on the atmospheric parameters: air pressure, temperature and water vapor partial pressure. In this study we have reconstructed the total refractivity profiles over Poland using the least-squares collocation software COMEDIE (Collocation of Meteorological Data for Interpretation and Estimation of Tropospheric Pathdelays). Profiles were calculated from different combinations of data sets from following sources: meteorological parameters from Numerical Weather Prediction Model WRF (Weather Research and Forecasting) or EUREF Permanent Network (EPN) stations and zenith total delay (ZTD) from ground-based GNSS products on ASG-EUPOS stations. The combinations of data sets included into this study are: 'WRF only', 'WRF/GNSS', 'WRF/GNSS/EPN' and 'GNSS only'. To find the data set with the best accuracy, profiles were compared with the reference radiosonde observations. The data set with the best accuracy is the combined 'WRF/GNSS' with mean bias close to 0 and standard deviation of 3 ppm. The data set 'WRF/GNSS/EPN' shows very similar accuracy so, there is no need to include the additional ground-based meteorological information from EPN stations. The data set 'GNSS only' shows much worse accuracy with the discrepancies at lower altitudes even at the level of -30 ppm. The data set 'WRF only' shows as good agreement with reference data as 'WRF/GNSS' in term of total refractivity, but when we calculated ZTD from all sets, we found that standard deviations from residuals are almost two times larger for the 'WRF only' dataset. We continue advancing the collocation algorithms, so the ZTD from the model can be useful as a priori troposphere information for example in PPP (Precise Point Positioning) technique.

  7. Evaluation of Refractivity Profiles from CHAMP and SAC-C GPS Radio Occultation

    NASA Technical Reports Server (NTRS)

    Poli, Paul; Ao, Chi On; Joiner, Joanna; delaTorreJuarez, Manuel; Hoff, Raymond

    2002-01-01

    The GeoForschungsZentrum's Challenging Minisatellite Payload for Geophysical Research and Application (CHAMP, Germany-US) and the Comision Nacional de Actividades Especiales' Satelite de Aplicaciones Cientificas-C (SAC-C, Argentina-US) missions are the first missions to carry a second-generation Blackjack Global Positioning System (GPS) receiver. One of the new features of this receiver is its ability to sense the lower troposphere closer to the surface than the proof-of-concept GPS Meteorology experiment (GPS/MET). Since their launch, CHAMP and SAC-C have collected thousands of GPS radio occultations, representing a wealth of measurements available for data assimilation and Numerical Weather Prediction (NWP). In order to evaluate the refractivity data derived by the Jet Propulsion Laboratory (JPL) from raw radio occultation measurements, we use Data Assimilation Office (DAO) 6-hour forecasts as an independent state of the atmosphere. We compare CHAMP and SAC-C refractivity (processed by JPL) with refractivity calculated from the DAO global fields of temperature, water vapor content and humidity. We show statistics of the differences as well as histograms of the differences.

  8. Multi-functional antireflective surface-relief structures based on nanoscale porous germanium with graded refractive index profiles.

    PubMed

    Leem, Jung Woo; Yu, Jae Su

    2013-03-21

    We fabricated the multi-stacked graded refractive index (GRIN) porous amorphous germanium (a-Ge) films with linear, quintic, and Gaussian index profiles for their refractive indices at a wavelength of 1.33 μm by e-beam evaporation with a glancing angle deposition technique. The porous a-Ge films with inclined nanocolumnar structures were deposited on Ge substrates at incident vapor flux angles of 40, 55, and 75°. The surface wetting behaviour of the porous a-Ge films was explored, exhibiting the hydrophilic surfaces with water contact angles below 78°. Their optical reflectance properties were investigated, together with the theoretical analysis using the rigorous coupled-wave analysis simulation. For the GRIN a-Ge films with a quintic index profile, a low reflectance band of <2% was shifted towards the longer wavelength with increasing the total thickness (ttotal) of GRIN a-Ge layers. For the GRIN a-Ge films with optimized ttotal values of 350, 333, and 225 nm for linear, quintic, and Gaussian index profiles, respectively, the low reflectance spectra of <10% were obtained at wavelengths of 1.1-1.7 μm, which yielded the lowest average reflectance value (Ravg) of ∼2.2% for Gaussian index profile (compared to the Ravg ∼ 3.7 and 4% for linear and quintic ones, respectively). The angle-dependent reflectance characteristics were also studied at incident angles of 15-85° for s- and p-polarized lights at a wavelength of 1.33 μm. The calculated results showed similar trends to the experimental data.

  9. Seismic refraction profile, Kingdom of Saudi Arabia: field operations, instrumentation, and initial results

    USGS Publications Warehouse

    Blank, H. Richard; Healy, J.H.; Roller, John; Lamson, Ralph; Fisher, Fred; McClearn, Robert; Allen, Steve

    1979-01-01

    In February 1978 a seismic deep-refraction profile was recorded by the USGS along a 1000-km line across the Arabian Shield in western Saudi Arabia. The line begins in Paleozoic and Mesozoic cover rocks near Riyadh on the Arabian Platform, leads southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan (Tihamat Asir), and terminates at the outer edge of the Farasan Bank in the southern Red Sea. More than 500 surveyed recording sites were occupied, including 19 in the Farasan Islands. Six shot points were used--five on land, with charges placed mostly below water table in drill holes, and one at sea, with charges placed on the sea floor and fired from a ship. The total charge consumed was slightly in excess of 61 metric tons in 21 discrete firings. Seismic energy was recorded by means of a set of 100 newly developed portable seismic stations. Each station consists of a standard 2-Hz vertical geophone coupled to a self-contained analog recording instrument equipped with a magnetic-tape cassette. The stations were deployed in groups of 20 by five observer teams, each generally consisting of two scientist-technicians and a surveyor-guide. On the day prior to deployment, the instruments were calibrated and programmed for automatic operation by means of a specially designed device called a hand-held tester. At each of ten pre-selected recording time windows on a designated firing day, the instruments were programmed to turn on, stabilize, record internal calibration signals, record the seismic signals at three levels of amplification, and then deactivate. After the final window in the firing sequence, all instruments were retrieved and their data tapes removed for processing. A specially designed, field tape- dubbing system was utilized at shot point camps to organize and edit data recorded on the cassette tapes. The main functions of this system are to concatenate all data from each shot on any given day

  10. Nondestructive measurement of two-dimensional refractive index profiles by deflectometry

    NASA Astrophysics Data System (ADS)

    Lin, Di; Leger, James R.

    2015-06-01

    We present a method for calculating a two-dimensional refractive index field from measured boundary values of beam position and slope. By initially ignoring the dependence of beam trajectories on the index field and using cubic polynomials to approximate these trajectories, we show that the inverse problem can be reduced to set of linear algebraic equations and solved using a numerical algorithm suited for inverting sparse, ill-conditioned linear systems. The beam trajectories are subsequently corrected using an iterative ray trace procedure so that they are consistent with the ray equation inside the calculated index field. We demonstrate the efficacy of our method through computer simulation, where a hypothetical test index field is reconstructed on a 15 × 15 discrete grid using 800 interrogating rays and refractive index errors (RMS) less than 0.5% of the total index range (nmax-nmin) are achieved. In the subsequent error analysis, we identify three primary sources of error contributing to the reconstruction of the index field and assess the importance of data redundancy. The principles developed in our approach are fully extendable to three-dimensional index fields as well as more complex geometries.

  11. Comparison of P- and S-wave velocity profiles obtained from surface seismic refraction/reflection and downhole data

    USGS Publications Warehouse

    Williams, R.A.; Stephenson, W.J.; Odum, J.K.

    2003-01-01

    High-resolution seismic-reflection/refraction data were acquired on the ground surface at six locations to compare with near-surface seismic-velocity downhole measurements. Measurement sites were in Seattle, WA, the San Francisco Bay Area, CA, and the San Fernando Valley, CA. We quantitatively compared the data in terms of the average shear-wave velocity to 30-m depth (Vs30), and by the ratio of the relative site amplification produced by the velocity profiles of each data type over a specified set of quarter-wavelength frequencies. In terms of Vs30, similar values were determined from the two methods. There is <15% difference at four of the six sites. The Vs30 values at the other two sites differ by 21% and 48%. The relative site amplification factors differ generally by less than 10% for both P- and S-wave velocities. We also found that S-wave reflections and first-arrival phase delays are essential for identifying velocity inversions. The results suggest that seismic reflection/refraction data are a fast, non-invasive, and less expensive alternative to downhole data for determining Vs30. In addition, we emphasize that some P- and S-wave reflection travel times can directly indicate the frequencies of potentially damaging earthquake site resonances. A strong correlation between the simple S-wave first-arrival travel time/apparent velocity on the ground surface at 100 m offset from the seismic source and the Vs30 value for that site is an additional unique feature of the reflection/refraction data that could greatly simplify Vs30 determinations. ?? 2003 Elsevier Science B.V. All rights reserved.

  12. Mapping the megathrust beneath the northern Gulf of Alaska using wide-angle seismic reflection/refraction profiles

    SciTech Connect

    Brocher, T.M.; Fuis, G.S.; Fisher, M.A.; Plafker, G.; Moses, M.J.; Taber, J.J. ); Christensen, N.I. . Dept. of Earth and Atmospheric Sciences)

    1993-04-01

    In the northern Gulf of Alaska and Prince William Sound, wide-angle seismic reflection/refraction profiling, earthquake studies, and laboratory measurements of physical properties are used to determine the geometry of the Prince William and Yakutat terranes, and the subducting Pacific plate. In this complex region, the Yakutat terrane is underthrust beneath the Prince William terrane, and both terranes are interpreted to be underlain by the Pacific plate. Wide-angle seismic reflection/refraction profiles recorded along 5 seismic lines are used to unravel this terrane geometry. Modeled velocities in the upper crust of the Prince William terrane (to 18-km depth) agree closely with laboratory velocity measurements of Orca Group phyllites and quartzofeldspathic graywackes (the chief components of the Prince William terrane) to hydrostatic pressures as high as 600 MPa (6 KBAR). An interpretation consistent with these data extends the Prince William terrane to at least 18-km depth. A landward dipping reflection at depths of 16--24 km is interpreted as the base of the Prince William terrane. This reflector corresponds to the top of the Wadati-Benioff zone seismicity and is interpreted as the megathrust. Beneath this reflector is a 6.9-km/s refractor, that is strongly reflective and magnetic, and is interpreted to be gabbro in Eocene age oceanic crust of the underthrust Yakutat terrane. Both wide-angle seismic and magnetic anomaly data indicate that the Yakutat terrane has been underthrust beneath the Prince William terrane for at least a few hundred kilometers. Wide-angle seismic data are consistent with a 9 to 10[degree] landward dip of the subducting Pacific plate, distinctly different from the inferred average 3 to 4[degree] dip of the overlying 6.9-km/s refractor and Wadati-Benioff seismic zone. The preferred interpretation of the geophysical data is that one composite plate, composed of the Pacific and Yakutat plates, is subducting beneath southern Alaska.

  13. Crustal Structure across The North China Craton from long-range seismic wide angle reflection/refraction profile

    NASA Astrophysics Data System (ADS)

    Tian, Xiaofeng; Wang, Fuyun; Jia, Shixu; Duan, Yonghong

    2014-05-01

    The North China Craton (NCC) is the oldest craton in China, which formed around 2.5Ga and had a 200 km thick lithosphere during the Paleozoic. The cratonic lithosphere of NCC has experienced strong thinning since the Mesozoic. In the past 30 years, a lot of excellent research about NCC have provided some different tectonic models, however, carton destruction is a sophisticated process. Though there have been many deep seismic sounding profiles in North China, but none of them is long enough to sample the complete section of thinned and preserved Craton. Recent long range seismic wide angle reflection/refraction experiment have provided the best opportunities to obtain better knowledge of seismic structure and properties of lithosphere. A 1500 km long wide angle reflection/refraction profile was completed in 2009. Our long range profile extends from west end of Ordos Plateau, across Shanxi Plateau, Taihang Mountains, to Luxi Uplift. We present a hybrid tomographic and layered velocity model of the crust and uppermost mantle along the profile crossed whole the north China craton. The model shows the crustal thickness of the region is very variable. The Moho topography varies more than 10km in the Central part of the north China craton. In particular, the crust appears the thinnest in the North China Plain, where the crust consists of very thick upper-mid crust and very thin lower crust, and the lower crust is with a lower velocity (~6.8km/s). The Moho dip with thinner lower crust beneath the Shanxi plateau may support the Central NCC has been affected at some time since its formation in the Archean. Furthermore, the TFZ is manifested in the deep structure. Our model provide the seismic evidences supporting that the TFZ extend deep into the uppermost mantle. It is the hypothesis that TFZ is a major channel for asthenosphere upwelling accompanying the tectonic extension and lithospheric reactivation in the Mesozoic-Cenozoic time. The different structural features may

  14. Adenovirus infection in savanna chimpanzees (Pan troglodytes schweinfurthii) in the Issa Valley, Tanzania.

    PubMed

    Dadáková, Eva; Brožová, Kristýna; Piel, Alex K; Stewart, Fiona A; Modrý, David; Celer, Vladimír; Hrazdilová, Kristýna

    2017-10-04

    Adenoviruses are a widespread cause of diverse human infections with recently confirmed zoonotic roots in African great apes. We focused on savanna-dwelling chimpanzees in the Issa Valley (Tanzania), which differ from those from forested sites in many aspects of behavior and ecology. PCR targeting the DNA polymerase gene detected AdV in 36.7% (69/188) of fecal samples. We detected five groups of strains belonging to the species Human mastadenovirus E and two distinct groups within the species Human mastadenovirus C based on partial hexon sequence. All detected AdVs from the Issa Valley are related to those from nearby Mahale and Gombe National Parks, suggesting chimpanzee movements and pathogen transmission.

  15. The International Space Station Alpha (ISSA) End-to-End On-Orbit Maintenance Process Flow

    NASA Technical Reports Server (NTRS)

    Zingrebe, Kenneth W., II

    1995-01-01

    As a tool for construction and refinement of the on-orbit maintenance system to sustain the International Space Station Alpha (ISSA), the Mission Operations Directorate (MOD) developed an end to-end on-orbit maintenance process flow. This paper discusses and demonstrates that process flow. This tool is being used by MOD to identify areas which require further work in preparation for MOD's role in the conduct of on-orbit maintenance operations.

  16. Littoral Refractivity Prognostic Advancement

    DTIC Science & Technology

    2010-09-30

    refractivity profiles to the surface at each COAMPS® grid point. Compared COAMPS® . / AREPS modeled propagation to measured propagation from Wallops...Test Range, and Wallops Island, VA. COAMPS® refractivity fields combined with AREPS radar performance models will be used in an FY11-13 program to

  17. Anatomy of a metamorphic core complex: Seismic refraction/wide-angle reflection profiling in southeastern California and western Arizona

    NASA Astrophysics Data System (ADS)

    McCarthy, Jill; Larkin, Steven P.; Fuis, Gary S.; Simpson, Robert W.; Howard, Keith A.

    1991-07-01

    The metamorphic core complex belt in southeastern California and western Arizona is a NW-SE trending zone of unusually large Tertiary extension and uplift. Midcrustal rocks exposed in this belt raise questions about the crustal thickness, crustal structure, and the tectonic evolution of the region. Three seismic refraction/wide-angle reflection profiles, acquired and analyzed as a part of the U.S. Geological Survey's Pacific to Arizona Crustal Experiment, were collected to address these issues. The results presented here, which focus on the Whipple and Buckskin-Rawhide mountains, yield a consistent three-dimensional image of this part of the metamorphic core complex belt. The seismic refraction/wide-angle reflection data are of excellent quality and are characterized by six principal phases that can be observed on all three profiles. These phases include refractions from the near-surface and crystalline basement, reflections from boundaries in the middle and lower crust, and reflections and refractions from the upper mantle. The final model consists of a thin veneer (<2 km) of upper plate and fractured lower plate rocks (1.5-5.5 kms-1) overlying a fairly homogeneous basement (˜6.0 km s-1) and a localized high-velocity (6.4 km s-1) body situated beneath the western Whipple Mountains. A prominent midcrustal reflection is identified beneath the Whipple and Buckskin-Rawhide mountains between 10 and 20 km depth. This reflector has an arch-like shape and is centered beneath, or just west of, the metamorphic core complex belt. This event is underlain by a weaker, approximately subhorizontal reflection at 24 km depth. Together, these two discontinuities define a lens-shaped midcrustal layer with a velocity of 6.35-6.5 km s-1. The apex of this midcrustal layer corresponds roughly to a region of major tectonic denudation and uplift (˜10 km) defined by surface geologic mapping and petrologic barometry studies. The layer thins to the northeast and is absent in the Transition

  18. Direct measurement of the refractive index profile of phase gratings, recorded in silver halide holographic materials by phase-contrast microscopy

    NASA Astrophysics Data System (ADS)

    Bányász, I.

    2003-11-01

    Plane-wave phase holograms recorded in Agfa-Gevaert 8E75HD emulsions and processed by the combination of AAC developer and the R-9 bleaching agent were studied by phase-contrast microscopy, using high-power immersion (100×) objective. Thus the modulation of the refractive index as a function of the bias exposure and the visibility of the recording interference pattern can also be determined. Measured diffraction efficiencies were compared to those predicted by coupled wave theory, using the measured refractive index modulations. Direct measurement of the phase profile of the gratings can be used for optimizing processing.

  19. Analysis of optical fibers with arbitrary refractive index profiles: accuracy, convergence, and effects of finite cladding

    NASA Astrophysics Data System (ADS)

    Tamil, Lakshman S.; Aicklen, Gregory H.

    1993-06-01

    We have formulated a matrix eigenvalue problem for cylindrical optical fibers from a set of finite difference equations. Numerical solution of this problem yields the propagation constants for propagating modes. The method can be used for arbitrary index profiles, does not require the explicit evaluation of Bessel or modified Bessel functions, and does not use iterative methods to search for the propagation constants as was the case in earlier proposed methods using finite differences. The method is accurate, fast, and simple. We have established the convergence and stability of this method, and explored the effects of finite cladding width on the dispersion characteristics.

  20. Capturing a reflective cross-sectional image of an optical fiber with partially coherent laser light to measure the refractive index profile of a multimode optical fiber.

    PubMed

    Sheu, Fang-Wen; Jhang, Heng-Jian

    2013-01-28

    We focused partially coherent laser light onto an optical fiber end-face and captured a high-quality reflective cross-sectional image of the fiber. By analyzing the reflected light intensity distribution of the captured fiber image, we can achieve refractive-index profiling of a step-index multimode optical fiber. The measurement error caused by the reflected light from the other fiber end-face positioned in air can be greatly improved by inserting that end of the fiber into water. This simple and easy technique for fiber index profiling by employing reduced-coherence laser light is very useful in determining the refractive index profiles of various multimode optical fibers.

  1. Anatomy of a metamorphic core complex: seismic refraction/wide-angle reflection profiling in southeastern California and western Arizona

    USGS Publications Warehouse

    McCarthy, J.; Larkin, S.P.; Fuis, G.S.; Simpson, R.W.; Howard, K.A.

    1991-01-01

    The metamorphic core complex belt in southeastern California and western Arizona is a NW-SE trending zone of unusually large Tertiary extension and uplift. Midcrustal rocks exposed in this belt raise questions about the crustal thickness, crustal structure, and the tectonic evolution of the region. Three seismic refraction/wide-angle reflection profiles were collected to address these issues. The results presented here, which focus on the Whipple and Buckskin-Rawhide mountains, yield a consistent three-dimensiional image of this part of the metamorphic core complex belt. The final model consists of a thin veneer (<2 km) of upper plate and fractured lower plate rocks (1.5-5.5 km s-1) overlying a fairly homogeneous basement (~6.0 km s-1) and a localized high-velocity (6.4 km s -1) body situated beneath the western Whipple Mountains. A prominent midcrustal reflection is identified beneath the Whipple and Buckskin Rawhide mountains between 10 and 20km depth. -from Authors

  2. Backarc basin evolution and cordilleran orogenesis: Insights from new ocean-bottom seismograph refraction profiling in Bransfield Strait, Antarctica

    NASA Astrophysics Data System (ADS)

    Barker, Daniel H. N.; Christeson, Gail L.; Austin, James A., Jr.; Dalziel, Ian W. D.

    2003-02-01

    Bransfield Strait, a backarc basin off the northwestern Antarctic Peninsula, is a modern analog for Cretaceous basins inverted in the compressional tectonic regime that initiated the Andean Cordillera. Eight new refraction ocean-bottom seismograph profiles in the strait demonstrate that crustal thickness in the deep central basin increases from northeast to southwest, from ˜10 km to ˜14 16 km. This confirms multichannel seismic interpretation of upper crustal structures suggesting that the Bransfield basin is opening by northeast to southwest rift propagation within arc crust of the Antarctic Peninsula, a process also recorded in the obducted Cretaceous Rocas Verdes basin of the southernmost Andes. Thinning is most prominent along the axis of the strait, where the crust is ˜9 11 km thick. In contrast, thicknesses beneath the Antarctic Peninsula margin and the inactive South Shetland Islands pedestal are ˜18 km and ˜24 km, respectively. Seismic velocities and thicknesses suggest that new oceanic crust is not yet being generated. Extension is focused along the northwest margin, imparting the physiographic asymmetry to the strait. Comparing the Bransfield basin with the inverted Rocas Verdes basin and intraoceanic counterparts in the western Pacific suggests that rift propagation and trench-side focusing of extension may be fundamental features of young backarc basins. Resultant asymmetry may facilitate observed obduction of backarc basin floor and arc rocks onto continental margins during compressional orogenesis.

  3. A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling

    USGS Publications Warehouse

    Wang, Chun-Yong; Zeng, Rong-Sheng; Mooney, W.D.; Hacker, B.R.

    2000-01-01

    We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400-km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0±0.2 km/s, 6.5±0.1 km/s, and 6.8±0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0±0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24±0.02 in the upper crust to 0.27±0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (<5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.

  4. A comparison of photogrammetrically determined astronomical refraction of sunlight at high zenith angles with a ray-tracing computer model employing rawinsonde profiles

    NASA Astrophysics Data System (ADS)

    Sampson, Russell Dean

    2001-11-01

    possible that the VIZ rawinsonde used on December 8 may have been from an old and possibly defective supply. A Modified U.S. Standard Atmosphere (MUSSA) profile produces a better fit between model and observed astronomical refraction than the rawinsonde profiles. The results of this study suggest that the temperature measurements from the rawinsondes may be too inaccurate to improve on a MUSSA model. Nonetheless, both models showed a significant improvement over the Pulkovo Refraction Tables.

  5. A diffraction-limited laser of 25/400 Yb3+/Al3+/P5+/F- silica fiber with a zigzag refractive index profile

    NASA Astrophysics Data System (ADS)

    Lin, Zhiquan; Lou, Fengguang; Wang, Meng; Zhang, Guodong; Zhang, Lei; Feng, Suya; Yu, Chunlei; Chen, Danping; Hu, Lili

    2017-08-01

    In this work, a Yb3+/Al3+/P5+/F- co-doped low-NA preform with larger than 0.4 wt.% Yb3+ doping concentration and zigzag refractive index profile was fabricated based on solution doping modified chemical vapor deposition technology. The modality of the preform refractive index profile was simulated based on a circle-symmetry-distribution fiber model. According to the simulation results a step-index 25/400 double cladding fiber with core NA of ~0.04 was drawn. Pumped with a 970 nm laser diode, a diffraction-limited oscillator-laser output with ~71% slope efficiency and M 2 of ~1.06 were achieved at bending diameter  ⩾50 cm after stripping cladding light. For bending diameters less than 50 cm, the laser efficiency measured at stripping cladding light decreases with decrease in bending diameter.

  6. Refractive Errors

    MedlinePlus

    ... and lens of your eye helps you focus. Refractive errors are vision problems that happen when the shape ... cornea, or aging of the lens. Four common refractive errors are Myopia, or nearsightedness - clear vision close up ...

  7. Refractive keratoplasty

    SciTech Connect

    Schwab, I.R. )

    1987-01-01

    This book contains 12 chapters. Some of the titles are: Perspectives on refractive surgery; Radial keratotomy; The refractive aspects of corneal transplantation; Wedge resection and relating incisions; Laser surgery of the cornea; and All plastic corneal lenses.

  8. Organization Spotlight: The Power of an Association in Early Childhood Education and Care: ISSA--An Engine for Advocacy, Capacity Building, and Creating a Growing Learning Community

    ERIC Educational Resources Information Center

    Ionescu, Mihaela

    2015-01-01

    The International Step by Step Association (ISSA) is an association that believes in learning from each other across cultures and borders, building on each other's strengths, and tapping into the power of a network. Building on the strong legacy of the Open Society Foundations' Step by Step program, ISSA has nurtured a culture of belonging to a…

  9. Organization Spotlight: The Power of an Association in Early Childhood Education and Care: ISSA--An Engine for Advocacy, Capacity Building, and Creating a Growing Learning Community

    ERIC Educational Resources Information Center

    Ionescu, Mihaela

    2015-01-01

    The International Step by Step Association (ISSA) is an association that believes in learning from each other across cultures and borders, building on each other's strengths, and tapping into the power of a network. Building on the strong legacy of the Open Society Foundations' Step by Step program, ISSA has nurtured a culture of belonging to a…

  10. Helicon plasma deposition of a TiO2/SiO2 multilayer optical filter with graded refractive index profiles

    NASA Astrophysics Data System (ADS)

    Wang, Xinrong; Masumoto, Hiroshi; Someno, Yoshihiro; Hirai, Toshio

    1998-06-01

    Thirty one layer TiO2/SiO2 optical filters with graded refractive index profiles were fabricated by helicon plasma sputtering at room temperature. Multilayer films were deposited on glass (BK7) and Si (100) substrates simultaneously and sequentially. The measured transmittance spectrum exhibited a reflectance of 99.8% at a central wavelength of 730 nm and high transmittance over the wavelength region outside of the reflected band as a result of the suppression of the sidelobes. The experimental transmittance spectrum corresponded almost completely with that calculated based on the optical multilayer film theory and using the measured refractive indices of TiO2, SiO2 and TiO2-SiO2 composite films. Transmission electron microscopic observations confirmed the expected microstructure of the filter.

  11. Recovery of refractivity profiles and pressure and temperature distributions in the lower atmosphere from satellite-to-satellite radio occultation data

    NASA Technical Reports Server (NTRS)

    Murray, C. W., Jr.

    1977-01-01

    The feasibility of recovering parameters from one-way range rate between two earth orbiting spacecraft during occultation of the tracking signal by the earth's lower atmosphere. The tracking data is inverted by an integral transformation (Abel transform) to obtain a vertical refractivity profile above the point of closest approach of the ray connecting the satellites. Pressure and temperature distributions can be obtained from values of dry refractivity using the hydrostatic equation and perfect gas law. Two methods are investigated for recovering pressure and temperature parameters. Results show that recovery is much more sensitive to satellite velocity errors than to satellite position errors. An error analysis is performed. An example is given demonstrating recovery of parameters from radio occultation data obtained during satellite-to-satellite tracking of Nimbus 6 by the ATS 6 satellite.

  12. Refractive Surgery

    PubMed Central

    Kellum, Keith

    2000-01-01

    The concept of surgically altering the eye to correct refractive errors has been considered for hundreds of years, but only in the past 60 years has interest grown considerably due to the development of modern refractive surgery techniques such as astigmatic keratotomies to correct astigmatism induced by cataract surgery and future technologies currently being investigated. Modern refractive surgery is more involved than setting the correct parameters on the laser. Patient selection and examination, proper technique, and postoperative follow-up for potential complications are essential for a successful refractive procedure. Critical evaluation of new techniques is vital to avoid the pitfall of overly exuberant enthusiasm for new and unproven methods of refractive surgery. Kellum K. Refractive surgery. The Ochsner Journal 2000; 2:164-167. PMID:21765686

  13. Atmospheric microwave refractivity and refraction

    NASA Technical Reports Server (NTRS)

    Yu, E.; Hodge, D. B.

    1980-01-01

    The atmospheric refractivity can be expressed as a function of temperature, pressure, water vapor content, and operating frequency. Based on twenty-year meteorological data, statistics of the atmospheric refractivity were obtained. These statistics were used to estimate the variation of dispersion, attenuation, and refraction effects on microwave and millimeter wave signals propagating along atmospheric paths. Bending angle, elevation angle error, and range error were also developed for an exponentially tapered, spherical atmosphere.

  14. Production of technical grade phosphoric acid from incinerator sewage sludge ash (ISSA).

    PubMed

    Donatello, S; Tong, D; Cheeseman, C R

    2010-01-01

    The recovery of phosphorus from sewage sludge ash samples obtained from 7 operating sludge incinerators in the UK using a sulfuric acid washing procedure to produce a technical grade phosphoric acid product has been investigated. The influences of reaction time, sulfuric acid concentration, liquid to solid ratio and source of ISSA on P recovery have been examined. The optimised conditions were the minimum stoichiometric acid requirement, a reaction time of 120 min and a liquid to solid ratio of 20. Under these conditions, average recoveries of between 72% and 91% of total phosphorus were obtained. Product filtrate was purified by passing through a cation exchange column, concentrated to 80% H(3)PO(4) and compared with technical grade H(3)PO(4) specifications. The economics of phosphate recovery by this method are briefly discussed.

  15. MEDES clinical research facility as a tool to prepare ISSA space flights

    NASA Astrophysics Data System (ADS)

    Maillet, A.; Traon, A. Pavy-Le

    This new multi-disciplinary medical experimentation center provides the ideal scientific, medical and technical environment required for research programs and to prepare international space station Alpha (ISSA) missions, where space and healthcare industries can share their expertise. Different models are available to simulate space flight effects (bed-rest, confinement,…). This is of particular interest for research in Human psychology, physiology, physiopathology and ergonomics, validation of biomedical materials and procedures, testing of drugs, and other healthcare related products. This clinical research facility (CRF) provides valuable services in various fields of Human research requiring healthy volunteers. CRF is widely accessible to national and international, scientific, medical and industrial organisations. Furthermore, users have at their disposal the multi-disciplinary skills of MEDES staff and all MEDES partners on a single site.

  16. Correlation of Substitutional Hydrogen to Refractive Index Profiles in Annealed Proton-Exchanged Z- and X-Cut LiNbO3

    DTIC Science & Technology

    1998-02-20

    Correlation of substitutional hydrogen to refractive index profiles in annealed proton-exchanged Z- and X- cut LiNbOs J. M. Zavada U. S. Army Research Office...cally active substitutional H and optically inactive interstitial H. The H and Li spa- tial variations in both Z- cut and X- cut crystals were determined...185°C and then were an- nealed at 400° C for times t from 6 to 240 min in wet flowing oxygen. For the Z- cut crystals, fit of the SIMS measured H

  17. Structure of the crust and uppermost mantle beneath the North China Craton from long-range seismic wide angle reflection/refraction profile

    NASA Astrophysics Data System (ADS)

    Tian, X.; Wang, F.; Zhang, X.; Duan, Y.

    2012-12-01

    The North China Craton (NCC) is the oldest craton in China, which formed around 2.5Ga and had a 200 km thick lithosphere during the Paleozoic. The cratonic lithosphere of NCC has experienced strong thinning since the Mesozoic. In the past 30 years, a lot of excellent research about NCC have provided some different tectonic models, however, carton destruction is a sophisticated process. Recent long range seismic wide angle reflection/refraction experiment have been providing new opportunities to obtain better knowledge of seismic structure and properties of lithosphere. A 1500 km long wide angle reflection/refraction profile was completed in 2009. Our long range profile extends from west end of Ordos Plateau, across Shanxi Plateau, Taihang Mountains, to Luxi Uplift. The recording of seismic waves from 11 chemical explorations was conducted in 600 three-component geophones with station spacing of 1~3km. The shooting procedure was employ 2000 ~ 5000kg explosives in 4-5 or 15-23 boreholes at 70-80m depth. The refractions in the upper crust (the Pg phase), the reflections from the Moho (the PmP phase) , the refractions in the uppermost mantle (the Pn phase) and the refractions in the upper mantle (the PL phase) can be easily correlated in all the seismic sections. we focus our attention mainly on the Pg, Pn, PL and PmP arrivals. We follow the standard modelling strategies described by Colin Zelt (Zelt, 1999). The 2D ray-tracing program RAYINVR was used for forward modeling and inversion of travel times (Zelt & Smith, 1992). The travel time modeling was done using'across-and-down' modelling approach layer by layer. Subsequently, the forward model was updated by damped least-squares inversion for the velocity and interface nodes until χ2 less than 1. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. Supported by NSFC (grant No. 90814012 and No. 41104038)

  18. Seismic Wide-Angle Reflection / Refraction Profiling from the DESIRE Project Reveals the Deep Structure Across the Southern Dead Sea Basin

    NASA Astrophysics Data System (ADS)

    Weber, M.; Mechie, J.; Ab-Ayyash, K.; Ben-Avraham, Z.; El-Kelani, R.; Qabbani, I.; DESIRE Group

    2007-12-01

    As part of the DESIRE project a 240 km long seismic wide-angle reflection / refraction (WRR) profile was completed in spring 2006 across the Dead Sea Transform (DST) in the region of the southern Dead Sea basin. The DST with a total of about 105 km multi-stage left-lateral shear since about 18 Ma ago, accommodates the movement between the Arabian and African plates. It connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a length of about 1100 km. With a sedimentary infill of about 10 km in places, the southern Dead Sea basin is the largest pull-apart basin along the DST and one of the largest pull-apart basins on Earth. The WRR measurements comprised 11 shots recorded by 200 three-component and 400 one- component instruments spaced 300 m to 1.2 km apart along the whole length of the E-W trending profile. Models of the P-wave velocity structure derived from the WRR data show that the sedimentary infill associated with the formation of the southern Dead Sea basin is about 8.5 km thick beneath the profile. With around an additional 2 km of older sediments, the depth to the seismic basement beneath the southern Dead Sea basin is about 11 km below sea level beneath the profile. In contrast, the interfaces below about 20 km depth, including the top of the lower crust and the Moho, show less than 3 km variation in depth beneath the profile as it crosses the southern Dead Sea basin. Thus the Dead Sea pull-apart basin is essentially an upper crustal feature with N-S upper crustal extension associated with the left-lateral motion along the DST. The boundary between the upper and lower crust at about 20 km depth must act as a decoupling zone. Thermo-mechanical modelling of the Dead Sea basin supports such a scenario.

  19. Isotropic non-ideal cloaks providing improved invisibility by adaptive segmentation and optimal refractive index profile from ordering isotropic materials.

    PubMed

    Qiu, C W; Hu, L; Zouhdi, S

    2010-07-05

    Mimicking the ideal cloak, which is anisotropic and inhomogeneous, can be achieved by alternating homogeneous isotropic materials, whose permittivity and permeability of each isotropic coating can be determined from effective medium theory. An improved two-fold method is proposed by optimally discretizing the cloak and re-ordering the combination of the effective parameters of each layer to form a smooth step-index profile. The roles of impedance matching and index matching are investigated for cloaking effects. Smoothing the index profile leads to better invisibility than that obtained by smoothing the impedance profile, since the forward scattering can be further diminished. Nonlinear-transformationbased spherical ideal cloaks are studied, and improved design method is explored together with different segmentation schemes. Significant improvement in invisibility is always observed for the optimal segmentation in virtual space with the proposed two-fold design method no matter how nonlinear the coordinate transformation is.

  20. A simple approach for estimating the refractive index structure parameter (Cn²) profile in the atmosphere.

    PubMed

    Basu, Sukanta

    2015-09-01

    Utilizing the so-called Thorpe scale as a measure of the turbulence outer scale, we propose a physically-based approach for the estimation of Cn2 profiles in the lower atmosphere. This approach only requires coarse-resolution temperature profiles (a.k.a., soundings) as input, yet it has the intrinsic ability to capture layers of high optical turbulence. The prowess of this computationally inexpensive approach is demonstrated by validations against observational data from a field campaign over Mauna Kea, Hawaii.

  1. 3D crustal seismic velocity model for the Gulf of Cadiz and adjacent areas (SW Iberia margin) based on seismic reflection and refraction profiles

    NASA Astrophysics Data System (ADS)

    Lozano, Lucía; Cantavella, Juan Vicente; Barco, Jaime; Carranza, Marta; Burforn, Elisa

    2016-04-01

    The Atlantic margin of the SW Iberian Peninsula and northern Morocco has been subject of study during the last 30 years. Many seismic reflection and refraction profiles have been carried out offshore, providing detailed information about the crustal structure of the main seafloor tectonic domains in the region, from the South Portuguese Zone and the Gulf of Cadiz to the Abyssal Plains and the Josephine Seamount. The interest to obtain a detailed and realistic velocity model for this area, integrating the available data from these studies, is clear, mainly to improve real-time earthquake hypocentral location and for tsunami and earthquake early warning. Since currently real-time seismic location tools allow the implementation of 3D velocity models, we aim to generate a full 3D crustal model. For this purpose we have reviewed more than 50 profiles obtained in different seismic surveys, from 1980 to 2008. Data from the most relevant and reliable 2D seismic velocity published profiles were retrieved. We first generated a Moho depth map of the studied area (latitude 32°N - 41°N and longitude 15°W - 5°W) by extracting Moho depths along each digitized profile with a 10 km spacing, and then interpolating this dataset using ordinary kriging method and generating the contour isodepth map. Then, a 3D crustal velocity model has been obtained. Selected vertical sections at different distances along each profile were considered to retrieve P-wave velocity values at each interface in order to reproduce the geometry and the velocity gradient within each layer. A double linear interpolation, both in distance and depth, with sampling rates of 10 km and 1 km respectively, was carried out to generate a (latitude, longitude, depth, velocity) matrix. This database of all the profiles was interpolated to obtain the P-wave velocity distribution map every kilometer of depth. The new 3D velocity model has been integrated in NonLinLoc location program to relocate several representative

  2. Visual inspection of 3-D surface and refractive-index profiles of microscopic lenses using a single-arm off-axis holographic interferometer.

    PubMed

    Kim, Byung-Mok; Kim, Eun-Soo

    2016-05-16

    A single-arm off-axis holographic interferometer (SA-OHI) system for visual inspection of the three-dimensional (3-D) surfaces and refractive-index profiles of micrometer-scale optical lenses is proposed. In this system, a couple of pellicle beam splitters and optical mirrors are employed to generate two sheared off-axis beams from the single object beam by controlling the tilted angle of the optical mirror. Each sheared beam is divided into two areas with and without object data, which are called half-object and half-reference beams, respectively. These sub-divided object and reference beams then make interference patterns, just like the conventional two-arm holographic interferometer. This holographic interferometer system, called SA-OHI, can solve the DC bias, virtual and duplicated image problems occurred in most lateral shearing interferometers, which allow extraction of the hologram data only related to the target object. The operational principle of the proposed system is analyzed based on ray-optics. To confirm the feasibility of the proposed system in the practical application fields, experiments with test lenses are also carried out and the results are comparatively discussed with those of the conventional system.

  3. PCR Based Microbial Monitor for Analysis of Recycled Water Aboard the ISSA: Issues and Prospects

    NASA Technical Reports Server (NTRS)

    Cassell, Gail H.; Lefkowitz, Elliot J.; Glass, John I.

    1995-01-01

    added to a PCR assay; There are not likely to be contaminants in ISSA recycled water that would inhibit PCR resulting in false-negative results; The TaqMan PCR product detection system is the most promising method for developing a rapid, highly automated gene-based microbial monitoring system. The method is inherently quantitative. NASA and other government agencies have invested in other technologies that, although potentially could lead to revolutionary advances, are not likely to mature in the next 5 years into working systems; PCR-based methods cannot distinguish between DNA or RNA of a viable microorganism and that of a non-viable organism. This may or may not be an important issue with reclaimed water on the ISSA. The recycling system probably damages the capacity of the genetic material of any bacteria or viruses killed during processing to serve as a template in a PCR desinged to amplify a large segment of DNA (less than 650 base pairs). If necessary, vital dye staining could be used in addition to PCR, to enumerate the viable cells in a water sample; The quality control methods have been developed to insure that PCR's are working properly, and that reactions are not contaminated with PCR carryover products which could lead to the generation of false-positive results; and The sequences of the small rRNA subunit gene for a large number of microorganisms are known, and they consititue the best database for rational development of the oligonucleotide reagents that give PCR its great specificity. From those gene sequences, sets of oligonucleotide primers for PCR and Taqman detection that could be used in a NASA microbial monitor were constructed using computer based methods. In addition to space utilization, a microbial monitior will have tremendous terrestrial applications. Analysis of patient samples for microbial pathogens, testing industrial effluent for biofouling bacteria, and detection biological warfare agents on the battlefield are but a few of the diverse

  4. Comparisons of refractive index gradient and stability profiles measured by balloons and the MU radar at a high vertical resolution in the lower stratosphere

    NASA Astrophysics Data System (ADS)

    Luce, H.; Hassenpflug, G.; Yamamoto, M.; Fukao, S.

    2007-02-01

    Many experimental studies have demonstrated that VHF Stratosphere-Troposphere (ST) radar echo power is proportional to the generalized refractive index gradient squared M2 when using a vertically oriented beam. Because humidity is generally negligible above the tropopause, VHF ST radars can thus provide information on the static stability (quantified by the squared Brunt-Väisälä frequency N2) at stratospheric heights and this capability is useful for many scientific applications. Most studies have been performed until now at a vertical resolution of 150 m or more. In the present paper, results of comparisons between radar- and (balloon borne) radiosonde-derived M2 and N2 are shown at a better vertical resolution of 50 m with the MU radar (34.85° N, 136.15° E; Japan) by benefiting from the range resolution improvement provided by the multi-frequency range imaging technique, using the Capon processing method. Owing to favorable winds in the troposphere, the radiosondes did not drift horizontally more than about 30 km from the MU radar site by the time they reached an altitude of 20 km. The measurements were thus simultaneous and almost collocated. Very good agreements have been obtained between both high resolution profiles of M2, as well as profiles of N2. It is also shown that this agreement can still be improved by taking into account a frozen-in advection of the air parcels by a horizontally uniform wind. Therefore, it can be concluded that 1) the range imaging technique with the Capon method really provides substantial range resolution improvement, despite the relatively weak Signal-to-Noise Ratios (SNR) over the analyzed region of the lower stratosphere, 2) the proportionality of the radar echo power to M2 at a vertical scale down to 50 m in the lower stratosphere is experimentally demonstrated, 3) the MU radar can provide stability profiles with a vertical resolution of 50 m at heights where humidity is negligible, 4) stable stratospheric layers as thin

  5. Repeatability and Reproducibility of Virtual Subjective Refraction.

    PubMed

    Perches, Sara; Collados, M Victoria; Ares, Jorge

    2016-10-01

    To establish the repeatability and reproducibility of a virtual refraction process using simulated retinal images. With simulation software, aberrated images corresponding with each step of the refraction process were calculated following the typical protocol of conventional subjective refraction. Fifty external examiners judged simulated retinal images until the best sphero-cylindrical refraction and the best visual acuity were achieved starting from the aberrometry data of three patients. Data analyses were performed to assess repeatability and reproducibility of the virtual refraction as a function of pupil size and aberrometric profile of different patients. SD values achieved in three components of refraction (M, J0, and J45) are lower than 0.25D in repeatability analysis. Regarding reproducibility, we found SD values lower than 0.25D in the most cases. When the results of virtual refraction with different pupil diameters (4 and 6 mm) were compared, the mean of differences (MoD) obtained were not clinically significant (less than 0.25D). Only one of the aberrometry profiles with high uncorrected astigmatism shows poor results for the M component in reproducibility and pupil size dependence analysis. In all cases, vision achieved was better than 0 logMAR. A comparison between the compensation obtained with virtual and conventional subjective refraction was made as an example of this application, showing good quality retinal images in both processes. The present study shows that virtual refraction has similar levels of precision as conventional subjective refraction. Moreover, virtual refraction has also shown that when high low order astigmatism is present, the refraction result is less precise and highly dependent on pupil size.

  6. Atmospheric refraction errors in laser ranging systems

    NASA Technical Reports Server (NTRS)

    Gardner, C. S.; Rowlett, J. R.

    1976-01-01

    The effects of horizontal refractivity gradients on the accuracy of laser ranging systems were investigated by ray tracing through three dimensional refractivity profiles. The profiles were generated by performing a multiple regression on measurements from seven or eight radiosondes, using a refractivity model which provided for both linear and quadratic variations in the horizontal direction. The range correction due to horizontal gradients was found to be an approximately sinusoidal function of azimuth having a minimum near 0 deg azimuth and a maximum near 180 deg azimuth. The peak to peak variation was approximately 5 centimeters at 10 deg elevation and decreased to less than 1 millimeter at 80 deg elevation.

  7. ISSA (iterative screening and structure analysis)—a new reduction method and its application to the tropospheric cloud chemical mechanism RACM/CAPRAM2.4

    NASA Astrophysics Data System (ADS)

    Mauersberger, G.

    An automated reduction method ISSA (iterative screening and structure analysis) has been developed. It is aimed at the analysis of complex atmospheric chemical multiphase mechanisms and produces reduced mechanisms for specifiable application purposes. Cyclic and non-cyclic reactions identified by a structure analysis are separately evaluated. The normalized valuation coefficients are calculated in a box model framework by using time-averaged reaction rates. Starting with a set of target species, important reactions and species are selected together in an iteration procedure. So, only one threshold value fixed for all box model scenarios is necessary. For every scenario a specific reduced mechanism is obtained. The sum of reactions and species included in the specific reduced mechanisms generates then the ISSA-reduced mechanism. All reactants in the reduced mechanism are included in the verification procedure where the concentrations simulated with the full and the reduced mechanism are compared. The maximum relative deviation of daily maxima was found to be a suitable deviation measure for atmospheric trace species concentrations. An application of the ISSA method to the large cloud chemical mechanism RACM/CAPRAM2.4 resulted in reduction rates of 55% for reactions (46% gas phase, 60% liquid phase), 23% for species, and 23% for phase transfers. The deviation between full and reduced mechanism averaged over all scenarios and reactants was 2.5%. The liquid-phase part of this application was compared with a condensed version of the CAPARAM2.4 mechanism developed simultaneously with the full version. It was found that these two reduced versions of CAPRAM2.4 differ significantly. Whereas the condensed version achieves good verification results only for the target species, the ISSA-reduced version reproduce very well the complete full mechanism results and should be useful for future large-scale models, which will include both detailed microphysics and complex (reduced

  8. Design of graded refractive index profile for silica multimode optical fibers with improved effective modal bandwidth for short-distance laser-based multi-Gigabit data transmission over "O"-band

    NASA Astrophysics Data System (ADS)

    Bourdine, Anton V.; Zhukov, Alexander E.

    2017-04-01

    High bit rate laser-based data transmission over silica optical fibers with enlarged core diameter in comparison with standard singlemode fibers is found variety infocommunication applications. Since IEEE 802.3z standard was ratified on 1998 this technique started to be widely used for short-range in-premises distributed multi-Gigabit networks based on new generation laser optimized multimode fibers 50/125 of Cat. OM2…OM4. Nowadays it becomes to be in demand for on-board cable systems and industrial network applications requiring 1Gps and more bit rates over fibers with extremely enlarged core diameter up to 100 μm. This work presents an alternative method for design the special refractive index profiles of silica few-mode fibers with extremely enlarged core diameter, that provides modal bandwidth enhancing under a few-mode regime of laser-based data optical transmission. Here some results are presented concerning with refractive index profile synthesis for few-mode fibers with reduced differential mode delay for "O"-band central region, as well as computed differential mode delay spectral curves corresponding to profiles for fibers 50/125 and 100/125 for in-premises and on-board/industrial cable systems.

  9. Refractive corneal surgery - discharge

    MedlinePlus

    Nearsightedness surgery - discharge; Refractive surgery - discharge; LASIK - discharge; PRK - discharge ... You had refractive corneal surgery to help improve your vision. This surgery uses a laser to reshape your cornea. It corrects mild-to-moderate nearsightedness, ...

  10. Refractive error blindness.

    PubMed Central

    Dandona, R.; Dandona, L.

    2001-01-01

    Recent data suggest that a large number of people are blind in different parts of the world due to high refractive error because they are not using appropriate refractive correction. Refractive error as a cause of blindness has been recognized only recently with the increasing use of presenting visual acuity for defining blindness. In addition to blindness due to naturally occurring high refractive error, inadequate refractive correction of aphakia after cataract surgery is also a significant cause of blindness in developing countries. Blindness due to refractive error in any population suggests that eye care services in general in that population are inadequate since treatment of refractive error is perhaps the simplest and most effective form of eye care. Strategies such as vision screening programmes need to be implemented on a large scale to detect individuals suffering from refractive error blindness. Sufficient numbers of personnel to perform reasonable quality refraction need to be trained in developing countries. Also adequate infrastructure has to be developed in underserved areas of the world to facilitate the logistics of providing affordable reasonable-quality spectacles to individuals suffering from refractive error blindness. Long-term success in reducing refractive error blindness worldwide will require attention to these issues within the context of comprehensive approaches to reduce all causes of avoidable blindness. PMID:11285669

  11. Remote Measurement of the Atmospheric Isoplanatic Angle and Determination of Refractive Turbulence Profiles by Direct Inversion of the Scintillation Amplitude Covariance Function with Tikhonov Regularization.

    DTIC Science & Technology

    1985-12-01

    shows Good’s 2 data between 500 m and 40 km. Good obtained thisCn profile by differential temperature measurement between two balloon-borne microthermal ...Cn profiles. However, they are difficult to obtain by remote measurements. In Chapters IV and V, I presented a profile measured by microthermal probes

  12. Spacecraft and Stellar Occultations by Turbulent Planetary Atmospheres. A Theoretical Investigation of Various Wave Propagation Effects and Their Impact on Derived Profiles of Refractivity, Temperature and Pressure,

    DTIC Science & Technology

    1981-05-08

    fluctuations are a small fraction only of the ambient refractivity. The intensity fluctuations also depend on the radiation wavelength X, whereas the...atmospheric 48 Fresnel zone. We also find that for Kolmogorov turbulence the bias in phase path scales with radiation wavelength as X" , implying that an...iII nije Li 2r,,,, a, aIs the( impact parametehr) b\\ thu( solair dix iiti tld !wld. \\wi\\ )Y’l l~iiss Is tw to1mill to) sign ificatitl\\ degrade the mia

  13. Refractivity estimation from sea clutter: An invited review

    NASA Astrophysics Data System (ADS)

    Karimian, Ali; Yardim, Caglar; Gerstoft, Peter; Hodgkiss, William S.; Barrios, Amalia E.

    2011-12-01

    Non-standard radio wave propagation in the atmosphere is caused by anomalous changes of the atmospheric refractivity index. In recent years, refractivity from clutter (RFC) has been an active field of research to complement traditional ways of measuring the refractivity profile in maritime environments which rely on direct sensing of the environmental parameters. Higher temporal and spatial resolution of the refractivity profile, together with a lower cost and convenience of operations have been the promising factors that brought RFC under consideration. Presented is an overview of the basic concepts, research and achievements in the field of RFC. Topics that require more attention in future studies also are discussed.

  14. Analytical models of optical refraction in the troposphere.

    PubMed

    Nener, Brett D; Fowkes, Neville; Borredon, Laurent

    2003-05-01

    An extremely accurate but simple asymptotic description (with known error) is obtained for the path of a ray propagating over a curved Earth with radial variations in refractive index. The result is sufficiently simple that analytic solutions for the path can be obtained for linear and quadratic index profiles. As well as rendering the inverse problem trivial for these profiles, this formulation shows that images are uniformly magnified in the vertical direction when viewed through a quadratic refractive-index profile. Nonuniform vertical distortions occur for higher-order refractive-index profiles.

  15. Atmospheric refraction: a history

    NASA Astrophysics Data System (ADS)

    Lehn, Waldemar H.; van der Werf, Siebren

    2005-09-01

    We trace the history of atmospheric refraction from the ancient Greeks up to the time of Kepler. The concept that the atmosphere could refract light entered Western science in the second century B.C. Ptolemy, 300 years later, produced the first clearly defined atmospheric model, containing air of uniform density up to a sharp upper transition to the ether, at which the refraction occurred. Alhazen and Witelo transmitted his knowledge to medieval Europe. The first accurate measurements were made by Tycho Brahe in the 16th century. Finally, Kepler, who was aware of unusually strong refractions, used the Ptolemaic model to explain the first documented and recognized mirage (the Novaya Zemlya effect).

  16. Atmospheric refraction: a history.

    PubMed

    Lehn, Waldemar H; van der Werf, Siebren

    2005-09-20

    We trace the history of atmospheric refraction from the ancient Greeks up to the time of Kepler. The concept that the atmosphere could refract light entered Western science in the second century B.C. Ptolemy, 300 years later, produced the first clearly defined atmospheric model, containing air of uniform density up to a sharp upper transition to the ether, at which the refraction occurred. Alhazen and Witelo transmitted his knowledge to medieval Europe. The first accurate measurements were made by Tycho Brahe in the 16th century. Finally, Kepler, who was aware of unusually strong refractions, used the Ptolemaic model to explain the first documented and recognized mirage (the Novaya Zemlya effect).

  17. Curvature of iris profile in spectral domain optical coherence tomography and dependency to refraction, age and pupil size - the MIPH Eye&Health Study.

    PubMed

    Schuster, Alexander K; Fischer, Joachim E; Vossmerbaeumer, Urs

    2017-03-01

    Optical coherence tomography (OCT) of the anterior segment allows quantitative analysis of the geometry of the iris. We performed spectral domain OCT examinations in healthy emmetropic, hyperopic and myopic subjects to investigate iris curvature and its associations. In a cross-sectional study, out of 4617 eyes (2309 subjects) those with refractive errors of <-4 or >+3 dioptres were identified by objective refraction. The iris was examined using the anterior segment mode of a spectral domain 3D OCT-2000 (Topcon Inc., Japan) in the temporal meridian, and OCT scans were investigated with respect to presence and amount of convex and concave iris configuration. Ninety-three eyes of 50 subjects served as emmetropic group (-0.5 ≤ x ≤+0.5 dioptres). Previous ocular surgery was exclusion criterion. Six hundred and sixty-eight eyes of 398 persons [292 male (76%); age range; 18-66 years] were included in the study. In the myopic group, 105 eyes had a concave iris configuration (26%), while in the hyperopic group, no eye had this configuration (0%) and in the emmetropic group five eyes (5%). Convex iris configuration was found in 96% of hyperopic, in 85% of the emmetropic and in 67% of the myopic eyes. There was an association between concave iris configuration and myopia, younger age and male gender, and with anterior chamber angle width. Spectral domain OCT images can be used for analysis of the iris structure and geometry. Our results are limited to the properties of the study population having an age range from 18 to 66 years and consisting mainly of men. © 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  18. Gradient Refractive Index Lenses.

    ERIC Educational Resources Information Center

    Morton, N.

    1984-01-01

    Describes the nature of gradient refractive index (GRIN) lenses, focusing on refraction in these materials, focal length of a thin Wood lens, and on manufacturing of such lenses. Indicates that GRIN lenses of small cross section are in limited production with applications suggested for optical communication and photocopying fields. (JN)

  19. Uncorrected refractive errors

    PubMed Central

    Naidoo, Kovin S; Jaggernath, Jyoti

    2012-01-01

    Global estimates indicate that more than 2.3 billion people in the world suffer from poor vision due to refractive error; of which 670 million people are considered visually impaired because they do not have access to corrective treatment. Refractive errors, if uncorrected, results in an impaired quality of life for millions of people worldwide, irrespective of their age, sex and ethnicity. Over the past decade, a series of studies using a survey methodology, referred to as Refractive Error Study in Children (RESC), were performed in populations with different ethnic origins and cultural settings. These studies confirmed that the prevalence of uncorrected refractive errors is considerably high for children in low-and-middle-income countries. Furthermore, uncorrected refractive error has been noted to have extensive social and economic impacts, such as limiting educational and employment opportunities of economically active persons, healthy individuals and communities. The key public health challenges presented by uncorrected refractive errors, the leading cause of vision impairment across the world, require urgent attention. To address these issues, it is critical to focus on the development of human resources and sustainable methods of service delivery. This paper discusses three core pillars to addressing the challenges posed by uncorrected refractive errors: Human Resource (HR) Development, Service Development and Social Entrepreneurship. PMID:22944755

  20. Uncorrected refractive errors.

    PubMed

    Naidoo, Kovin S; Jaggernath, Jyoti

    2012-01-01

    Global estimates indicate that more than 2.3 billion people in the world suffer from poor vision due to refractive error; of which 670 million people are considered visually impaired because they do not have access to corrective treatment. Refractive errors, if uncorrected, results in an impaired quality of life for millions of people worldwide, irrespective of their age, sex and ethnicity. Over the past decade, a series of studies using a survey methodology, referred to as Refractive Error Study in Children (RESC), were performed in populations with different ethnic origins and cultural settings. These studies confirmed that the prevalence of uncorrected refractive errors is considerably high for children in low-and-middle-income countries. Furthermore, uncorrected refractive error has been noted to have extensive social and economic impacts, such as limiting educational and employment opportunities of economically active persons, healthy individuals and communities. The key public health challenges presented by uncorrected refractive errors, the leading cause of vision impairment across the world, require urgent attention. To address these issues, it is critical to focus on the development of human resources and sustainable methods of service delivery. This paper discusses three core pillars to addressing the challenges posed by uncorrected refractive errors: Human Resource (HR) Development, Service Development and Social Entrepreneurship.

  1. Refractive errors and schizophrenia.

    PubMed

    Caspi, Asaf; Vishne, Tali; Reichenberg, Abraham; Weiser, Mark; Dishon, Ayelet; Lubin, Gadi; Shmushkevitz, Motti; Mandel, Yossi; Noy, Shlomo; Davidson, Michael

    2009-02-01

    Refractive errors (myopia, hyperopia and amblyopia), like schizophrenia, have a strong genetic cause, and dopamine has been proposed as a potential mediator in their pathophysiology. The present study explored the association between refractive errors in adolescence and schizophrenia, and the potential familiality of this association. The Israeli Draft Board carries a mandatory standardized visual accuracy assessment. 678,674 males consecutively assessed by the Draft Board and found to be psychiatrically healthy at age 17 were followed for psychiatric hospitalization with schizophrenia using the Israeli National Psychiatric Hospitalization Case Registry. Sib-ships were also identified within the cohort. There was a negative association between refractive errors and later hospitalization for schizophrenia. Future male schizophrenia patients were two times less likely to have refractive errors compared with never-hospitalized individuals, controlling for intelligence, years of education and socioeconomic status [adjusted Hazard Ratio=.55; 95% confidence interval .35-.85]. The non-schizophrenic male siblings of schizophrenia patients also had lower prevalence of refractive errors compared to never-hospitalized individuals. Presence of refractive errors in adolescence is related to lower risk for schizophrenia. The familiality of this association suggests that refractive errors may be associated with the genetic liability to schizophrenia.

  2. Refractive Surgery Survey 2004.

    PubMed

    Sandoval, Helga P; de Castro, Luis E Fernández; Vroman, David T; Solomon, Kerry D

    2005-01-01

    To determine the refractive surgery (RS) preferences of ophthalmologists worldwide, questionnaires were sent to 8897 members of the American Society of Cataract and Refractive Surgery. A total of 1053 questionnaires were returned by the deadline. The practice distribution included 29.5% cataract surgeons, 48.8% comprehensive ophthalmologists, 11.6% RS specialists, 5.1% cornea and external disease specialists, 1.9% glaucoma specialists, 1.1% retina specialists, and <1.0% oculoplastics/pediatrics/researchers/retired. Results were compared with those in the 2003 survey and demonstrate that refractive surgery continues to develop and change.

  3. Reflection, refraction, and the Legendre transform.

    PubMed

    Gutiérrez, Cristian E

    2011-02-01

    We construct in dimension two a mirror that reflects collimated rays into a set of directions that amplify the image and an optical lens so that collimated rays are refracted into a set of directions with a prescribed magnification factor. The profiles of these optical surfaces are given by explicit formulas involving the Legendre transformation.

  4. Refractive-index measurement of high-refractive-index integrated-optic components

    NASA Astrophysics Data System (ADS)

    Oberson, Philippe

    2004-12-01

    The most commonly-used technique for measuring the refractive index profile of an optical fiber is the refracted near-field method. This standard method cannot be directly used for integrated optical waveguides such as silica-on-silicon or LiNbO3 because of the geometrical constraints imposed by the slab waveguide. A modified method was described in previous work and subsequently implemented with some improvements (e.g. use of a calibrated solid refractive-index reference element; a simplified waveguide identification) in a commercial apparatus. However, the non-availability of suitable index-matching liquids having an index of refraction greater than about 1.8 prevent this apparatus being used with high-index DUTs. In this paper, we propose and experimentally verify a modified instrument that permits the characterization of the index profile of high refractive-index waveguides such as LiNbO3. Provided that the waveguide is written in a homogeneous bulk substrate with a known index, this modified approach allows for spatial and refractive-index resolutions that are practically as good as those obtained with the standard technique applied to optical fibers.

  5. Refraction of microwave signals by water vapor

    NASA Technical Reports Server (NTRS)

    Goldfinger, A. D.

    1980-01-01

    Tropospheric water vapor causes a refractive path length effect which is typically 5-10% of the 'dry' tropospheric effect and as large as several meters at elevation angles below 5 deg. The vertical water vapor profile is quite variable, and measurements of intensive atmospheric parameters such as temperature and humidity limited to the surface do not adequately predict the refractive effect. It is suggested that a water vapor refraction model that is a function of the amount of precipitable water alone can be successful at low elevation angles. From an extensive study of numerical ray tracings through radiosonde balloon data, such a model has been constructed. The model predicts the effect at all latitudes and elevation angles between 2 and 10 deg to an accuracy of better than 4% (11 cm at 3 deg elevation angle).

  6. Refraction of microwave signals by water vapor

    NASA Technical Reports Server (NTRS)

    Goldfinger, A. D.

    1980-01-01

    Tropospheric water vapor causes a refractive path length effect which is typically 5-10% of the 'dry' tropospheric effect and as large as several meters at elevation angles below 5 deg. The vertical water vapor profile is quite variable, and measurements of intensive atmospheric parameters such as temperature and humidity limited to the surface do not adequately predict the refractive effect. It is suggested that a water vapor refraction model that is a function of the amount of precipitable water alone can be successful at low elevation angles. From an extensive study of numerical ray tracings through radiosonde balloon data, such a model has been constructed. The model predicts the effect at all latitudes and elevation angles between 2 and 10 deg to an accuracy of better than 4% (11 cm at 3 deg elevation angle).

  7. Negative refraction and superconductivity

    NASA Astrophysics Data System (ADS)

    Amariti, Antonio; Forcella, Davide; Mariotti, Alberto; Siani, Massimo

    2011-10-01

    We discuss exotic properties of charged hydrodynamical systems, in the broken superconducting phase, probed by electromagnetic waves. Motivated by general arguments from hydrodynamics, we observe that negative refraction, namely the propagation in opposite directions of the phase velocities and of the energy flux, is expected for low enough frequencies. We corroborate this general idea by analyzing a holographic superconductor in the AdS/CFT correspondence, where the response functions can be explicitly computed. We study the dual gravitational theory both in the probe and in the backreacted case. We find that, while in the first case the refractive index is positive at every frequency, in the second case there is negative refraction at low enough frequencies. This is in agreement with hydrodynamic considerations.

  8. Excimer laser refractive surgery.

    PubMed Central

    Manche, E E; Carr, J D; Haw, W W; Hersh, P S

    1998-01-01

    Excimer laser photorefractive keratectomy and excimer laser in situ keratomileusis are relatively new treatment modalities that can be used to correct refractive errors of the eye. They are most commonly used to correct myopia (nearsightedness) but can also be used to correct hyperopia (farsightedness) and astigmatism. The excimer laser alters the refractive state of the eye by removing tissue from the anterior cornea through a process known as photoablative decomposition. This process uses ultraviolet energy from the excimer laser to disrupt chemical bonds in the cornea without causing any thermal damage to surrounding tissue. The modified anterior corneal surface enables light to be focused on the retina, thereby reducing or eliminating the dependence on glasses and contact lenses. We discuss in detail all aspects of excimer laser refractive surgery--techniques, indications and contraindications, clinical outcomes, and complications. PMID:9682628

  9. Comparisons between high-resolution profiles of squared refractive index gradient M2 measured by the Middle and Upper Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign

    NASA Astrophysics Data System (ADS)

    Luce, Hubert; Kantha, Lakshmi; Hashiguchi, Hiroyuki; Lawrence, Dale; Yabuki, Masanori; Tsuda, Toshitaka; Mixa, Tyler

    2017-03-01

    New comparisons between the square of the generalized potential refractive index gradient M2, estimated from the very high-frequency (VHF) Middle and Upper Atmosphere (MU) Radar, located at Shigaraki, Japan, and unmanned aerial vehicle (UAV) measurements are presented. These comparisons were performed at unprecedented temporal and range resolutions (1-4 min and ˜ 20 m, respectively) in the altitude range ˜ 1.27-4.5 km from simultaneous and nearly collocated measurements made during the ShUREX (Shigaraki UAV-Radar Experiment) 2015 campaign. Seven consecutive UAV flights made during daytime on 7 June 2015 were used for this purpose. The MU Radar was operated in range imaging mode for improving the range resolution at vertical incidence (typically a few tens of meters). The proportionality of the radar echo power to M2 is reported for the first time at such high time and range resolutions for stratified conditions for which Fresnel scatter or a reflection mechanism is expected. In more complex features obtained for a range of turbulent layers generated by shear instabilities or associated with convective cloud cells, M2 estimated from UAV data does not reproduce observed radar echo power profiles. Proposed interpretations of this discrepancy are presented.

  10. Effect of alpha and Gaussian refractive index profiles on the design of highly nonlinear optical fibre for efficient nonlinear optical signal processing

    NASA Astrophysics Data System (ADS)

    Selvendran, S.; Sivanantharaja, A.; Arivazhagan, S.; Kannan, M.

    2016-09-01

    We propose an index profiled, highly nonlinear ultraflattened dispersion fibre (HN-UFF) with appreciable values of fibre parameters such as dispersion, dispersion slope, effective area, nonlinearity, bending loss and splice loss. The designed fibre has normal zero flattened dispersion over S, C, L, U bands and extends up to 1.9857 μm. The maximum dispersion variation observed for this fibre is as low as 1.61 ps km-1 nm-1 over the 500-nm optical fibre transmission spectrum. This fibre also has two zero dispersion wavelengths at 1.487 and 1.9857 μm and the respective dispersion slopes are 0.02476 and 0.0068 ps nm-2 km-1. The fibre has a very low ITU-T cutoff wavelength of 1.2613 μm and a virtuous nonlinear coefficient of 9.43 W-1 km-1. The wide spectrum of zero flattened dispersion and a good nonlinear coefficient make the designed fibre very promising for different nonlinear optical signal processing applications.

  11. Refraction corrections for surveying

    NASA Technical Reports Server (NTRS)

    Lear, W. M.

    1979-01-01

    Optical measurements of range and elevation angle are distorted by the earth's atmosphere. High precision refraction correction equations are presented which are ideally suited for surveying because their inputs are optically measured range and optically measured elevation angle. The outputs are true straight line range and true geometric elevation angle. The 'short distances' used in surveying allow the calculations of true range and true elevation angle to be quickly made using a programmable pocket calculator. Topics covered include the spherical form of Snell's Law; ray path equations; and integrating the equations. Short-, medium-, and long-range refraction corrections are presented in tables.

  12. Effect of single vision soft contact lenses on peripheral refraction.

    PubMed

    Kang, Pauline; Fan, Yvonne; Oh, Kelly; Trac, Kevin; Zhang, Frank; Swarbrick, Helen

    2012-07-01

    To investigate changes in peripheral refraction with under-, full, and over-correction of central refraction with commercially available single vision soft contact lenses (SCLs) in young myopic adults. Thirty-four myopic adult subjects were fitted with Proclear Sphere SCLs to under-correct (+0.75 DS), fully correct, and over-correct (-0.75 DS) their manifest central refractive error. Central and peripheral refraction were measured with no lens wear and subsequently with different levels of SCL central refractive error correction. The uncorrected refractive error was myopic at all locations along the horizontal meridian. Peripheral refraction was relatively hyperopic compared to center at 30 and 35° in the temporal visual field (VF) in low myopes and at 30 and 35° in the temporal VF and 10, 30, and 35° in the nasal VF in moderate myopes. All levels of SCL correction caused a hyperopic shift in refraction at all locations in the horizontal VF. The smallest hyperopic shift was demonstrated with under-correction followed by full correction and then by over-correction of central refractive error. An increase in relative peripheral hyperopia was measured with full correction SCLs compared with no correction in both low and moderate myopes. However, no difference in relative peripheral refraction profiles were found between under-, full, and over-correction. Under-, full, and over-correction of central refractive error with single vision SCLs caused a hyperopic shift in both central and peripheral refraction at all positions in the horizontal meridian. All levels of SCL correction caused the peripheral retina, which initially experienced absolute myopic defocus at baseline with no correction, to experience absolute hyperopic defocus. This peripheral hyperopia may be a possible cause of myopia progression reported with different types and levels of myopia correction.

  13. Conceptualization of Light Refraction

    ERIC Educational Resources Information Center

    Sokolowski, Andrzej

    2013-01-01

    There have been a number of papers dealing quantitatively with light refraction. Yet the conceptualization of the phenomenon that sets the foundation for a more rigorous math analysis is minimized. The purpose of this paper is to fill that gap. (Contains 3 figures.)

  14. Conceptualization of Light Refraction

    ERIC Educational Resources Information Center

    Sokolowski, Andrzej

    2013-01-01

    There have been a number of papers dealing quantitatively with light refraction. Yet the conceptualization of the phenomenon that sets the foundation for a more rigorous math analysis is minimized. The purpose of this paper is to fill that gap. (Contains 3 figures.)

  15. Refraction corrections for surveying

    NASA Technical Reports Server (NTRS)

    Lear, W. M.

    1980-01-01

    Optical measurements of range and elevation angles are distorted by refraction of Earth's atmosphere. Theoretical discussion of effect, along with equations for determining exact range and elevation corrections, is presented in report. Potentially useful in optical site surveying and related applications, analysis is easily programmed on pocket calculator. Input to equation is measured range and measured elevation; output is true range and true elevation.

  16. Refraction corrections for surveying

    NASA Technical Reports Server (NTRS)

    Lear, W. M.

    1980-01-01

    Optical measurements of range and elevation angles are distorted by refraction of Earth's atmosphere. Theoretical discussion of effect, along with equations for determining exact range and elevation corrections, is presented in report. Potentially useful in optical site surveying and related applications, analysis is easily programmed on pocket calculator. Input to equation is measured range and measured elevation; output is true range and true elevation.

  17. Cross Gradient Based Joint Inversion of 2D Wide Angle Seismic Reflection/Refraction and Gravity Data Along the Profile Through the 2010 Ms 7.1 Yushu Earthquake, China

    NASA Astrophysics Data System (ADS)

    Xiang, S.; Zhang, H.

    2015-12-01

    2D wide-angle seismic reflection/refraction survey has been widely used to investigate crustal structure and Moho topography. Similarly gravity survey is also very important in the study of local and regional earth features. Seismic survey is sensitive to the seismic velocity parameters and interface variations. For gravity survey, it is sensitive to density parameters of the medium but the resolution along the vertical direction is relatively poor. In this study, we have developed a strategy to jointly invert for seismic velocity model, density model and interface positions using the gravity observations and seismic arrival times from different phases. For the joint inversion of seismic and gravity data, it often relies on the empirical relationship between seismic velocity and density. In comparison, our joint inversion strategy also includes the cross-gradient based structure constraint for seismic velocity and density models in addition to the empirical relationship between them. The objective function for the joint inversion includes data misfit terms for seismic travel times and gravity observations, the cross-gradient constraint, the smoothness terms for two models, and the data misfit term between predicted gravity data based on density model converted from velocity model using the empirical relationship. Each term has its respective weight. We have applied the new joint inversion method to the Riwoqe-Yushu-Maduo profile in northwest China. The profile crosses through the Qiangtang block and Bayan Har block from southwest to northeast, respectively. The 2010 Ms 7.1 Yushu earthquake is located on the profile, around the Ganzi-Yushu fault zone. The joint inversion produces the velocity and density models that are similar in structure and at the same time fit their respective data sets well. Compared to separate seismic inversion using seismic travel times, the joint inversion with gravity data gives a velocity model that better delineates the fault zones. Low

  18. Effects of horizontal refractivity gradients on the accuracy of laser ranging to satellites

    NASA Technical Reports Server (NTRS)

    Gardner, C. S.

    1976-01-01

    Numerous formulas have been developed to partially correct laser ranging data for the effects of atmospheric refraction. All the formulas assume the atmospheric refractivity profile is spherically symmetric. The effects of horizontal refractivity gradients are investigated by ray tracing through spherically symmetric and three-dimensional refractivity profiles. The profiles are constructed from radiosonde data. The results indicate that the horizontal gradients introduce an rms error of approximately 3 cm when the satellite is near 10 deg elevation. The error decreases to a few millimeters near zenith.

  19. Profiles.

    ERIC Educational Resources Information Center

    Macintosh, Henry G.

    An introduction to profiles is presented with examples provided to permit an overall appraisal of the potential of profiles, of the principles upon which they might be based, and of the problems that will have to be overcome if their potential is to be realized in practice. The larger scale examples of profiles discussed are the Scottish Pupil…

  20. Multistep ion exchange processes of gradient refractive index rod lens.

    PubMed

    Lv, Hao; Liu, Aimei; Tong, Jufang; Yi, Xunong; Li, Qianguang; Wang, Xinmin; Ding, Yaoming

    2011-01-01

    A mathematical model for research on the refractive index profile (RIP) of multistep ion exchange processes (IEPs) of gradient refractive index rod lenses (GRINs) is established by the different initial condition and boundary condition, based on the Fickian diffusion equation. GRIN rod lenses have been fabricated using the three-step IEPs. Research results indicate that the experimental deviations of refractive index (DRI) are in good agreement with the theoretical data. The DRI of three-step IEPs is superior to the one- and two-step IEPs and smaller than 10(-5).

  1. Precise determination of the refractive index of suspended particles: light transmission as a function of refractive index mismatch

    NASA Astrophysics Data System (ADS)

    McClymer, J. P.

    2016-08-01

    Many fluids appear white because refractive index differences lead to multiple scattering. In this paper, we use safe, low-cost commercial index matching fluids to quantitatively study light transmission as a function of index mismatch, reduce multiple scattering to allow single scattering probes, and to precisely determine the index of refraction of suspended material. The transmission profile is compared with Rayleigh-Gans and Mie theory predictions. The procedure is accessible as a student laboratory project, while providing advantages over other standard methods of measuring the refractive index of an unknown nanoparticle, making it valuable to researchers.

  2. Refraction in adults with diabetes.

    PubMed

    Klein, Barbara E K; Lee, Kristine E; Klein, Ronald

    2011-01-01

    To examine refraction, change in refraction, and risk factors for change in refraction in adults with type 1 and type 2 diabetes mellitus. Population-based study. Modified Early Treatment of Diabetic Retinopathy Study refractions and a standard history were obtained for all participants. Baseline and 10-year follow-up data were available. Age and education were significantly associated with refraction in persons with younger-onset diabetes (T1D) and in those with older-onset diabetes (T2D); refractions were similar for both groups. Persons of similar age with T1D were likely to be more myopic than were those with T2D (P < .01). In those with T1D, on average, there was a -0.28-diopter (D) change in refraction in 10 years. Those with longer duration of diabetes and proliferative retinopathy were more likely to have hyperopic shifts in refraction. In persons with T2D, there was, on average, a +0.48-D change in refraction during the 10 years, but there was little consistency in the amount of change by age at baseline. In persons of similar age, those with T1D were likely to be slightly more myopic than were those with T2D. Overall, mean refraction and the important risk factors of age and education were similar to those reported in nondiabetic populations.

  3. Refractive beam shapers for focused laser beams

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Laskin, Vadim; Ostrun, Aleksei

    2016-09-01

    Focusing of laser radiation is most often used approach in various industrial micromachining applications like scribing, PCB drilling, and is important in scientific researches like laser heating in geophysics experiments with diamond anvil cells (DAC). Control of intensity distribution in focal spot is important task since optimum intensity profiles are rather flat-top, doughnut or "inverse-Gauss" than typical for lasers Gaussian profile. Because of high intensity of modern CW and pulsed lasers it is advisable to use refractive beam shaping optics with smooth optical surfaces providing high radiation resistance. Workable optical solutions can be built on the base of diffraction theory conclusion that flat-top intensity profile in focal plane of a lens is created when input beam has Airy-disk intensity distribution. It is suggested to apply refractive beam shapers converting, with minimum wavefront deformation, Gaussian profile of TEM00 beam to a beam with Airy disk intensity distribution, thereby optimizing conditions of interference near the focal plane of a lens after the beam shaper and providing flat-top, doughnut, "inverse-Gauss" profiles. This approach allows operation with CW and ultra-short pulse lasers, using F-theta lenses and objectives, mirror scanners, provides extended depth of field similar to Rayleigh length of comparable TEM00 beam, easy integration in industrial equipment, simple adjustment procedure and switching between profiles, telescope and collimator implementations. There will be considered design basics of beam shapers, analysis of profile behaviour near focal plane, examples of implementations in micromachining systems and experimental DAC setups, results of profile measurements and material processing.

  4. Refraction in Adults with Diabetes

    PubMed Central

    Klein, Barbara E. K.; Lee, Kristine E.; Klein, Ronald

    2010-01-01

    Objective(s) Examine refraction, change in refraction, and risk factors for change in refraction in adults with type 1 and type 2 diabetes. Methods Population based study. Modified Early Treatment of Diabetic Retinopathy Study refractions and a standard history were obtained for all participants. Baseline and ten-year follow-up data were available. Results Age was significantly associated with refraction in persons with younger-onset diabetes (T1D) and those with older-onset diabetes (T2D); refractions were similar for both groups. Persons of similar age with T1D were likely to be more myopic than those with T2D (P<.01). Years of education were significantly associated with more myopic refraction (P<.0001). In those with T1D on average there was a −.35 diopter (D) change in refraction over 10 years. However, there was a systematic decrease in myopic shift with increasing age at baseline. Those with longer duration of diabetes and with proliferative retinopathy were more likely to have hyperopic shifts in refraction. In those with T2D there was, on average, a +.25D change in refraction over the 10 years but there was little consistency in the amount of change by age at baseline. There were no other significant effects on change in refraction in this group. Conclusions In persons of similar age, those with T1D are likely to be slightly more myopic than those with T2D. Overall, mean refractions and the important risk factors of age and education are similar to those reported in non-diabetic populations. PMID:21220629

  5. Colored Flag by Double Refraction.

    ERIC Educational Resources Information Center

    Reid, Bill

    1994-01-01

    Describes various demonstrations that illustrate double refraction and rotation of the plane of polarization in stressed, transparent plastics, with the consequent production of colored designs. (ZWH)

  6. Causality, Nonlocality, and Negative Refraction.

    PubMed

    Forcella, Davide; Prada, Claire; Carminati, Rémi

    2017-03-31

    The importance of spatial nonlocality in the description of negative refraction in electromagnetic materials has been put forward recently. We develop a theory of negative refraction in homogeneous and isotropic media, based on first principles, and that includes nonlocality in its full generality. The theory shows that both dissipation and spatial nonlocality are necessary conditions for the existence of negative refraction. It also provides a sufficient condition in materials with weak spatial nonlocality. These fundamental results should have broad implications in the theoretical and practical analyses of negative refraction of electromagnetic and other kinds of waves.

  7. Colored Flag by Double Refraction.

    ERIC Educational Resources Information Center

    Reid, Bill

    1994-01-01

    Describes various demonstrations that illustrate double refraction and rotation of the plane of polarization in stressed, transparent plastics, with the consequent production of colored designs. (ZWH)

  8. Profiles.

    ERIC Educational Resources Information Center

    School Arts, 1979

    1979-01-01

    Profiles seven Black, Native American, and Chicano artists and art teachers: Hale A. Woodruff, Allan Houser, Luis Jimenez, Betrand D. Phillips, James E. Pate, I, and Fernando Navarro. This article is part of a theme issue on multicultural art. (SJL)

  9. Profiles.

    ERIC Educational Resources Information Center

    School Arts, 1979

    1979-01-01

    Profiles seven Black, Native American, and Chicano artists and art teachers: Hale A. Woodruff, Allan Houser, Luis Jimenez, Betrand D. Phillips, James E. Pate, I, and Fernando Navarro. This article is part of a theme issue on multicultural art. (SJL)

  10. The refractive group.

    PubMed

    Campbell, C

    1997-06-01

    Spherocylindrical optical elements can be decomposed into a sphere-equivalent component and two cross-cylinder components, oriented at 45 degrees to one another. These components in turn can be represented with a simple matrix formalism. This matrix formalism allows it to be seen that the components also form members of an eight element group, designated the refractive group. The structure of this group is developed including its algebra and its representation with Cayley diagrams. The group is identified as the eight element dihedral group, D4, and is compared to another well-known eight element group, the quaternion group. An example is given using the group formal algebra to develop the transfer equations for spherocylindrical wavefronts. Certain properties of propagating spherocylindrical wavefronts, such as nonrotation of cylinder axes, are seen to come directly as consequences of the group properties.

  11. Can manipulation of orthokeratology lens parameters modify peripheral refraction?

    PubMed

    Kang, Pauline; Gifford, Paul; Swarbrick, Helen

    2013-11-01

    To investigate changes in peripheral refraction, corneal topography, and aberrations induced by changes in orthokeratology (OK) lens parameters in myopes. Subjects were fitted with standard OK lenses that were worn overnight for 2 weeks. Peripheral refraction, corneal topography, and corneal surface aberrations were measured at baseline and after 14 nights of OK lens wear. Subsequent to a 2-week washout period, subjects were refitted with another set of lenses where one eye was randomly assigned to wear an OK lens with a smaller optic zone diameter (OZD) and the other eye with a steeper peripheral tangent. Measurements were taken again at a second baseline and after 14 days of overnight wear of the second OK lens set. Standard OK lenses with a 6-mm OZD and 1/4 peripheral tangent caused significant changes in both peripheral refraction and corneal topography. Significant hyperopic shift occurred in the central visual field (VF) while a myopic shift was found at 35 degrees in the nasal VF. OK induced significant reductions in corneal power at all positions along the horizontal corneal chord except at 2.4 mm nasal where there was no significant change and at 2.8 mm nasal where there was an increase in corneal refractive power. A positive shift in spherical aberration was induced for all investigated lens designs except for the 1/2 tangent design when calculated over a 4-mm pupil. Reducing OZD and steepening the peripheral tangent did not cause significant changes in peripheral refraction or corneal topography profiles across the horizontal meridian. OK lenses caused significant changes in peripheral refraction, corneal topography, and corneal surface aberrations. Modifying OZD and peripheral tangent made no significant difference to the peripheral refraction or corneal topography profile. Attempting to customize refraction and topography changes through manipulation of OK lens parameters appears to be a difficult task.

  12. Refraction, including prisms.

    PubMed

    Hiatt, R L

    1991-02-01

    The literature in the past year on refraction is replete with several isolated but very important topics that have been of interest to strabismologists and refractionists for many decades. The refractive changes in scleral buckling procedures include an increase in axial length as well as an increase in myopia, as would be expected. Tinted lenses in dyslexia show little positive effect in the nonasthmatic patients in one study. The use of spectacles or bifocals as a way to control increase in myopia is refuted in another report. It has been shown that in accommodative esotropia not all patients will be able to escape the use of bifocals in the teenage years, even though surgery might be performed. The hope that disposable contact lenses would cut down on the instance of giant papillary conjunctivitis and keratitis has been given some credence, and the conventional theory that sclerosis alone is the cause of presbyopia is attacked. Also, gas permeable bifocal contact lenses are reviewed and the difficulties of correcting presbyopia by this method outlined. The practice of giving an aphakic less bifocal addition instead of a nonaphakic, based on the presumption of increased effective power, is challenged. In the review of prisms, the majority of articles concern prism adaption. The most significant report is that of the Prism Adaptation Study Research Group (Arch Ophthalmol 1990, 108:1248-1256), showing that acquired esotropia in particular has an increased incidence of stable and full corrections surgically in the prism adaptation group versus the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

  13. GRAVSAT/GEOPAUSE refraction study

    NASA Technical Reports Server (NTRS)

    Llewellyn, S. K.

    1977-01-01

    A ground station network tracked a high altitude spacecraft which in turn tracked a low orbiting satellite. Orbit data are relayed back to the ground stations. A refraction study was performed on this configuration to compute ionospheric and tropospheric refraction effects along the satellite and ground links.

  14. Binocular vision and refractive surgery.

    PubMed

    Finlay, Alison L

    2007-05-01

    Binocular status can have an effect on the outcome of refractive surgery. Some accommodative deviations and anisometropia can be managed effectively. Fully accommodative esotropia has been successfully treated in young patients but the outcome can be less predictable in older patients. High anisometropes are usually unaffected by the change in aniseikonia following refractive surgery but there are exceptions. Failure to recognise and appropriately classify a binocular vision anomaly pre-surgically can result in symptoms that are difficult to manage post-operatively. Refractive surgery producing a binocular vision anomaly where there was none pre-operatively is less common. I present a review of the literature discussing the relationship between binocular vision anomalies and refractive surgery, illustrating the findings with published reports of successful and unsuccessful binocular postoperative outcomes. I argue that predicting the binocular outcome should be considered pre-operatively for every refractive surgery patient.

  15. Imaging techniques with refractive beam shaping optics

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Laskin, Vadim

    2012-10-01

    Applying of the refractive beam shapers in real research optical setups as well as in industrial installations requires very often manipulation of a final laser spot size. In many cases this task can be easily solved by using various imaging optical layouts presuming creating an image of a beam shaper output aperture. Due to the unique features of the refractive beam shapers of field mapping type, like flat wave front and low divergence of the collimated resulting beam with flattop or another intensity profile, there is a freedom in building of various imaging systems with using ordinary optical components, including off-the-shelf ones. There will be considered optical layouts providing high, up to 1/200×, de-magnifying factors, combining of refractive beam shapers like πShaper with scanning systems, building of relay imaging systems with extended depth of field. These optical layouts are widely used in such laser technologies like drilling holes in PCB, welding, various micromachining techniques with galvo-mirror scanning, interferometry and holography, various SLM-based applications. Examples of real implementations and experimental results will be presented as well.

  16. Linearly decayed evanescent optical field in planar refractive index well

    NASA Astrophysics Data System (ADS)

    Liu, Jianhua; Tao, Li

    2017-04-01

    Evanescent optical field with linearly decaying profile is theoretically analyzed at the critical angle of incidence in a planar structure of one dimensional refractive index well (RIW). The linearity of the evanescent field is due to the presence of the second refractive index barrier, which also shifts the position of total internal reflection (TIR) away from the critical angle. The decaying rate is determined by the refractive indices of the two barriers, as well as the width of the well. With this linearly decayed evanescent field (LDEF), various profiles across the well, for example uniform one, can be formed via appropriate combination of the LDEFs, which can promote new applications in fields of material analysis and sensing in the molecular scale.

  17. Barren Acidic Soil Assessment using Seismic Refraction Survey

    NASA Astrophysics Data System (ADS)

    Tajudin, S. A. A.; Abidin, M. H. Z.; Madun, A.; Zawawi, M. H.

    2016-07-01

    Seismic refraction method is one of the geophysics subsurface exploration techniques used to determine subsurface profile characteristics. From past experience, seismic refraction method is commonly used to detect soil layers, overburden, bedrock, etc. However, the application of this method on barren geomaterials remains limited due to several reasons. Hence, this study was performed to evaluate the subsurface profile characteristics of barren acidic soil located in Ayer Hitam, Batu Pahat, Johor using seismic refraction survey. The seismic refraction survey was conducted using ABEM Terraloc MK 8 (seismograph), a sledge hammer weighing 7 kg (source) and 24 units of 10 Hz geophones (receiver). Seismic data processing was performed using OPTIM software which consists of SeisOpt@picker (picking the first arrival and seismic configureuration data input) and SeisOpt@2D (generating 2D image of barren acidic soil based on seismic velocity (primary velocity, Vp) distribution). It was found that the barren acidic soil profile consists of three layers representing residual soil (Vp= 200-400 m/s) at 0-2 m, highly to completely weathered soil (Vp= 500-1800 m/s) at 3-8 m and shale (Vp= 2100-6200 m/s) at 9-20 m depth. Furthermore, result verification was successfully done through the correlation of seismic refraction data based on physical mapping and the geological map of the study area. Finally, it was found that the seismic refraction survey was applicable for subsurface profiling of barren acidic soil as it was very efficient in terms of time, cost, large data coverage and sustainable.

  18. Investigation of a new method for determination of atmospheric refractivity corrections in satellite laser ranging.

    NASA Astrophysics Data System (ADS)

    Mironov, N. T.; Prokopov, A. V.; Remaev, E. V.

    1997-08-01

    A new algorithm is investigated for calculating atmospheric refractivity corrections in satellite laser ranging in the Earth's spherically stratified atmosphere based on results of measuring meteorological parameters on the Earth's surface. A numerical experiment with 125 meteorological sounding profiles shows that the new method allows to determine atmospheric refractivity corrections with the accuracy better than the Marini-Murray method does.

  19. Refractive index modulation in photo-thermo-refractive fibers

    NASA Astrophysics Data System (ADS)

    Rotari, Eugeniu; Glebova, Larissa; Glebov, Leonid

    2005-04-01

    Refractive index decrement was discovered in a fiber made from photo-thermo-refractive (PTR) glass. PTR glass is a fluorosilicate glass doped with cerium and silver which demonstrates refractive index change after UV exposure and thermal development due to precipitation of NaF nanocrystals in the irradiated areas. This glass is widely used for volume holographic optical elements recording. Photosensitivity in PTR optical fibers has been shown after exposure to radiation at 325 nm for about 1 J/cm2 followed by thermal development at 520°C. Refractive index difference between exposed and unexposed areas was about 1000 ppm. A Bragg mirror at 1088 nm was recorded in such fiber which showed narrow band reflection within 1 nm.

  20. Nonlinear refractive index of photo-thermo-refractive glass

    NASA Astrophysics Data System (ADS)

    Santran, Stephane; Martinez-Rosas, Miguel; Canioni, Lionel; Sarger, Laurent; Glebova, Larissa N.; Tirpak, Alan; Glebov, Leonid B.

    2006-03-01

    Nonlinear properties of a photo-thermo-refractive (PTR) glass are studied and compared with those in fused silica and a conventional optical glass. PTR glass is a new photosensitive medium for high-efficiency phase volume hologram recording which manifests a linear refractive index modulation after exposure to UV radiation followed by thermal treatment. Nonlinear optical properties of PTR glass exposed to femtosecond laser pulses are studied. Diffraction patterns in a propagated laser beam focused in the sample were detected by a CCD, while a nonlinear refractive index was measured by a collinear-orthogonal-polarization-pump-probe (COP3) method. It was found that nonlinear refractive index of PTRG is n2 = 3.3 × 10-20 m2/W (0.33 ppm cm2/GW) which is about the same as for the fused silica. It is important that n2 in PTR glass does not vary after UV exposure and thermal development.

  1. Seismic refraction survey of the ANS preferred site

    SciTech Connect

    Davis, R.K.; Hopkins, R.A.; Doll, W.E.

    1992-02-01

    Between September 19, 1991 and October 8, 1991 personnel from Martin Marietta Energy Systems, Inc. (Energy Systems), Automated Sciences Group, Inc., and Marrich, Inc. performed a seismic refraction survey at the Advanced Neutron Source (ANS) preferred site. The purpose of this survey was to provide estimates of top-of-rock topography, based on seismic velocities, and to delineate variations in rock and soil velocities. Forty-four seismic refraction spreads were shot to determine top-of-rock depths at 42 locations. Nine of the seismic spreads were shot with long offsets to provide 216 top-of-rock depths for 4 seismic refraction profiles. The refraction spread locations were based on the grid for the ANS Phase I drilling program. Interpretation of the seismic refraction data supports the assumption that the top-of-rock surface generally follows the local topography. The shallow top-of-rock interface interpreted from the seismic refraction data is also supported by limited drill information at the site. Some zones of anomalous data are present that could be the result of locally variable weathering, a localized variation in shale content, or depth to top-of-rock greater than the site norm.

  2. Effect of refractive error on temperament and character properties

    PubMed Central

    Kalkan Akcay, Emine; Canan, Fatih; Simavli, Huseyin; Dal, Derya; Yalniz, Hacer; Ugurlu, Nagihan; Gecici, Omer; Cagil, Nurullah

    2015-01-01

    AIM To determine the effect of refractive error on temperament and character properties using Cloninger's psychobiological model of personality. METHODS Using the Temperament and Character Inventory (TCI), the temperament and character profiles of 41 participants with refractive errors (17 with myopia, 12 with hyperopia, and 12 with myopic astigmatism) were compared to those of 30 healthy control participants. Here, temperament comprised the traits of novelty seeking, harm-avoidance, and reward dependence, while character comprised traits of self-directedness, cooperativeness, and self-transcendence. RESULTS Participants with refractive error showed significantly lower scores on purposefulness, cooperativeness, empathy, helpfulness, and compassion (P<0.05, P<0.01, P<0.05, P<0.05, and P<0.01, respectively). CONCLUSION Refractive error might have a negative influence on some character traits, and different types of refractive error might have different temperament and character properties. These personality traits may be implicated in the onset and/or perpetuation of refractive errors and may be a productive focus for psychotherapy. PMID:25709911

  3. Refractive index determination in axially symmetric oprtically inhomogeneous media

    NASA Astrophysics Data System (ADS)

    Ionescu-Pallas, Nicholas; Vlad, Valentin I.; Bociort, Florian

    The focussing method from transversally light, put forward by Dietrich Marcuse in view of determining the refractive index profile (RIP) in optical fibers and fiber performs, is revised. A more rigorous derivation of the Marcuse formula is given, establishing the conditions of its validity and a simplified version is initially proposed, able to avoid the systematic errors in the processing of light intensity data.

  4. Experimental verification and simulation of negative index of refraction using Snell's law.

    PubMed

    Parazzoli, C G; Greegor, R B; Li, K; Koltenbah, B E C; Tanielian, M

    2003-03-14

    We report the results of a Snell's law experiment on a negative index of refraction material in free space from 12.6 to 13.2 GHz. Numerical simulations using Maxwell's equations solvers show good agreement with the experimental results, confirming the existence of negative index of refraction materials. The index of refraction is a function of frequency. At 12.6 GHz we measure and compute the real part of the index of refraction to be -1.05. The measurements and simulations of the electromagnetic field profiles were performed at distances of 14lambda and 28lambda from the sample; the fields were also computed at 100lambda.

  5. Measurement of the refractive index of human teeth by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Meng, Zhuo; Yao, X. Steve; Yao, Hui; Liang, Yan; Liu, Tiegen; Li, Yanni; Wang, Guanhua; Lan, Shoufeng

    2009-05-01

    We describe a novel method based on optical coherence tomography (OCT) for the accurate measurement of the refractive index of in vitro human teeth. We obtain the refractive indices of enamel, dentin, and cementum to be 1.631+/-0.007, 1.540+/-0.013, and 1.582+/-0.010, respectively. The profile of the refractive index is readily obtained via an OCT B scan across a tooth. This method can be used to study the refractive index changes caused by dental decay and therefore has great potential for the clinical diagnosis of early dental caries.

  6. Refractive accuracy with light-adjustable intraocular lenses.

    PubMed

    Villegas, Eloy A; Alcon, Encarna; Rubio, Elena; Marín, José M; Artal, Pablo

    2014-07-01

    To evaluate efficacy, predictability, and stability of refractive treatments using light-adjustable intraocular lenses (IOLs). University Hospital Virgen de la Arrixaca, Murcia, Spain. Prospective nonrandomized clinical trial. Eyes with a light-adjustable IOL (LAL) were treated with spatial intensity profiles to correct refractive errors. The effective changes in refraction in the light-adjustable IOL after every treatment were estimated by subtracting those in the whole eye and the cornea, which were measured with a Hartmann-Shack sensor and a corneal topographer, respectively. The refractive changes in the whole eye and light-adjustable IOL, manifest refraction, and visual acuity were obtained after every light treatment and at the 3-, 6-, and 12-month follow-ups. The study enrolled 53 eyes (49 patients). Each tested light spatial pattern (5 spherical; 3 astigmatic) produced a different refractive change (P<.01). The combination of 2 light adjustments induced a maximum change in spherical power of the light-adjustable IOL of between -1.98 diopters (D) and +2.30 D and in astigmatism of up to -2.68 D with axis errors below 9 degrees. Intersubject variability (standard deviation) ranged between 0.10 D and 0.40 D. The 2 required lock-in procedures induced a small myopic shift (range +0.01 to +0.57 D) that depended on previous adjustments. Light-adjustable IOL implantation achieved accurate refractive outcomes (around emmetropia) with good uncorrected distance visual acuity, which remained stable over time. Further refinements in nomograms and in the treatment's protocol would improve the predictability of refractive and visual outcomes with these IOLs. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  7. Evaluation of simplified evaporation duct refractivity models for inversion problems

    NASA Astrophysics Data System (ADS)

    Saeger, J. T.; Grimes, N. G.; Rickard, H. E.; Hackett, E. E.

    2015-10-01

    To assess a radar system's instantaneous performance on any given day, detailed knowledge of the meteorological conditions is required due to the dependency of atmospheric refractivity on thermodynamic properties such as temperature, water vapor, and pressure. Because of the significant challenges involved in obtaining these data, recent efforts have focused on development of methods to obtain the refractivity structure inversely using radar measurements and radar wave propagation models. Such inversion techniques generally use simplified refractivity models in order to reduce the parameter space of the solution. Here the accuracy of three simple refractivity models is examined for the case of an evaporation duct. The models utilize the basic log linear shape classically associated with evaporation ducts, but each model depends on various parameters that affect different aspects of the profile, such as its shape and duct height. The model parameters are optimized using radiosonde data, and their performance is compared to these atmospheric measurements. The optimized models and data are also used to predict propagation using a parabolic equation code with the refractivity prescribed by the models and measured data, and the resulting propagation patterns are compared. The results of this study suggest that the best log linear model formulation for an inversion problem would be a two-layer model that contains at least three parameters: duct height, duct curvature, and mixed layer slope. This functional form permits a reasonably accurate fit to atmospheric measurements as well as embodies key features of the profile required for correct propagation prediction with as few parameters as possible.

  8. Refractive Effects Guidebook (REG)

    DTIC Science & Technology

    1976-09-22

    NORMAL HORIZON (PLOT, EDIT. LIST. SUMRV. RAVS. LOSS , COUER , END if 20K.-1 100 150 PANQf IN NAUTICAL MILES LOCATION 22 02M 159 47U TIME 25...JUL 69 18102 SOURCE HEIGHT - 100 FEET NORMAL HORIZON t PLOT, EDIT. LIST, SUMPV. PAYS , LOSS , COUER , END )? 5-7 PROFILE TYPE G Very...NORMAL HORIZON (PLOT , ED IT. LI ST. SUTRV . PAVS . LOSS. COUER . END )7 5-8 PROFILE TYPE H Multiple ducts with bases at surface and about 5,000

  9. Recent advances in refractive surgery

    PubMed Central

    Yu, E Y; Jackson, W B

    1999-01-01

    Refractive errors are some of the most common ophthalmic abnormalities world-wide and are associated with significant morbidity. Tremendous advances in treating refractive errors have occurred over the past 20 years. The arrival of the excimer laser has allowed a level of accuracy in modifying the cornea that was unattainable before. Although refractive surgery is generally safe and effective, it does carry some risks. Careful patient selection, meticulous surgical technique and frequent follow-up can avoid most complications. The experience of a surgical team can also affect the outcome and the incidence of complications. The future should bring continued improvement in outcomes, fewer complications and exciting new options for treating refractive errors. PMID:10333840

  10. Negative Refraction in Weyl Semimetals

    NASA Astrophysics Data System (ADS)

    Shoufie Ukhtary, Muhammad; Nugraha, Ahmad R. T.; Saito, Riichiro

    2017-10-01

    We theoretically propose that Weyl semimetals may exhibit negative refraction at some frequencies close to the plasmon frequency, allowing transverse magnetic (TM) electromagnetic waves with frequencies smaller than the plasmon frequency to propagate in the Weyl semimetals. The idea is justified by the calculation of reflection spectra, in which negative refractive index at such frequencies gives physically correct spectra. In this case, a TM electromagnetic wave incident to the surface of the Weyl semimetal will be bent with a negative angle of refraction. We argue that the negative refractive index at the specified frequencies of the electromagnetic wave is required to conserve the energy of the wave, in which the incident energy should propagate away from the point of incidence.

  11. Diplopia associated with refractive surgery.

    PubMed

    Kushner, Burton J

    2012-01-01

    When diplopia occurs after refractive surgery, a systematized approach to diagnosis and treatment is useful. First, determine if the problem is monocular or binocular. Monocular diplopia usually is caused by anterior segment complications and should be referred to an anterior segment surgeon. If the problem is binocular, determine if there is iatrogenic monovision. If monovision was created by the refractive surgery, determine if the double vision is due to fixation switch diplopia. If so, the monovision state needs to be reversed. If fixation switch is not the cause of the symptoms, try "optical rescue". If monovision is not present, check old refraction and motility records, and correct any residual refractive error. Strabismus may need to be treated with surgery, orthoptic exercises, or prisms.

  12. Refraction characteristics of phononic crystals

    NASA Astrophysics Data System (ADS)

    Nemat-Nasser, Sia

    2015-08-01

    Some of the most interesting refraction properties of phononic crystals are revealed by examining the anti-plane shear waves in doubly periodic elastic composites with unit cells containing rectangular and/or elliptical multi-inclusions. The corresponding band structure, group velocity, and energy-flux vector are calculated using a powerful mixed variational method that accurately and efficiently yields all the field quantities over multiple frequency pass-bands. The background matrix and the inclusions can be anisotropic, each having distinct elastic moduli and mass densities. Equifrequency contours and energy-flux vectors are readily calculated as functions of the wave-vector components. By superimposing the energy-flux vectors on equifrequency contours in the plane of the wave-vector components, and supplementing this with a three-dimensional graph of the corresponding frequency surface, a wealth of information is extracted essentially at a glance. This way it is shown that a composite with even a simple square unit cell containing a central circular inclusion can display negative or positive energy and phase velocity refractions, or simply performs a harmonic vibration (standing wave), depending on the frequency and the wave-vector. Moreover, that the same composite when interfaced with a suitable homogeneous solid can display: (1) negative refraction with negative phase velocity refraction; (2) negative refraction with positive phase velocity refraction; (3) positive refraction with negative phase velocity refraction; (4) positive refraction with positive phase velocity refraction; or even (5) complete reflection with no energy transmission, depending on the frequency, and direction and the wavelength of the plane-wave that is incident from the homogeneous solid to the interface. For elliptical and rectangular inclusion geometries, analytical expressions are given for the key calculation quantities. Expressions for displacement, velocity, linear momentum

  13. [Reproducibility of subjective refraction measurement].

    PubMed

    Grein, H-J; Schmidt, O; Ritsche, A

    2014-11-01

    Reproducibility of subjective refraction measurement is limited by various factors. The main factors affecting reproducibility include the characteristics of the measurement method and of the subject and the examiner. This article presents the results of a study on this topic, focusing on the reproducibility of subjective refraction measurement in healthy eyes. The results of previous studies are not all presented in the same way by the respective authors and cannot be fully standardized without consulting the original scientific data. To the extent that they are comparable, the results of our study largely correspond largely with those of previous investigations: During repeated subjective refraction measurement, 95% of the deviation from the mean value was approximately ±0.2 D to ±0.65 D for the spherical equivalent and cylindrical power. The reproducibility of subjective refraction measurement in healthy eyes is limited, even under ideal conditions. Correct assessment of refraction results is only feasible after identifying individual variability. Several measurements are required. Refraction cannot be measured without a tolerance range. The English full-text version of this article is available at SpringerLink (under supplemental).

  14. Peripheral refraction and the development of refractive error: a review.

    PubMed

    Charman, W Neil; Radhakrishnan, Hema

    2010-07-01

    It has been suggested that emmetropic and low-hyperopic eyes in which the refractive error in the periphery of the visual field is relatively hyperopic with respect to the axial refraction may be at greater risk of developing myopia than eyes with similar refractions but relatively myopic peripheral refractive errors. The animal and human evidence to support this hypothesis is reviewed. The most persuasive studies are those in which emmetropization has been shown to occur in infant rhesus monkeys with ablated foveas but intact peripheral fields, and the demonstration that, in similar animals, lens-induced relative peripheral hyperopia produces central axial myopia. Evidence for emmetropization in animals with severed optic nerves suggests that emmetropization is primarily controlled at the retinal level but that the higher levels of the visual system play a significant role in refining the process: there appear to be no directly equivalent human studies. Since any contribution of the higher centres to the control of refractive development must depend upon the sensitivity to defocus, the results of human studies of the changes in depth-of-focus across the field and of the contribution of the retinal periphery to the accommodation response are discussed. Although peripheral resolution is relatively insensitive to focus, this is not the case for detection. Moreover accommodation occurs to peripheral stimuli out to a field angle of at least 10 deg, and the presence of a peripheral stimulus can influence the accommodation to a central target. Although the basic hypothesis that a relatively hyperopic peripheral refractive error can drive the development of human myopia remains unproven, the available data support the possibility of an interaction between the states of focus on axis and in the periphery.

  15. Photonic crystal negative refractive optics.

    PubMed

    Baba, Toshihiko; Abe, Hiroshi; Asatsuma, Tomohiko; Matsumoto, Takashi

    2010-03-01

    Photonic crystals (PCs) are multi-dimensional periodic gratings, in which the light propagation is dominated by Bragg diffraction that appears to be refraction at the flat surfaces of the PC. The refraction angle from positive to negative, perfectly or only partially obeying Snell's law, can be tailored using photonic band theory. The negative refraction enables novel prism, collimation, and lens effects. Because PCs usually consist of two transparent media, these effects occur at absorption-free frequencies, affording significant design flexibility for free-space optics. The PC slab, a high-index membrane with a two-dimensional airhole array, must be carefully designed to avoid reflection and diffraction losses. Light focusing based on negative refraction forms a parallel image of a light source, facilitating optical couplers and condenser lenses for wavelength demultiplexing. A compact wavelength demultiplexer can be designed by combining the prism and lens effects. The collimation effect is obtainable not only inside but also outside of the PC by optimizing negative refractive condition.

  16. Refraction effects on the Galileo probe telemetry carrier frequency

    NASA Technical Reports Server (NTRS)

    Atkinson, D. H.; Spilker, T. R.

    1991-01-01

    As the Galileo probe relay radio link (RRL) signal propagates outward through the Jovian atmosphere, the atmosphere will manifest itself in two ways. First, the geometric path length of the signal is increased, resulting in a small change of the RRL signal departure angle from the proble (transmitter). Secondly, the velocity of the signal is decreased. For a spherical, static atmosphere with a known profile of refractivity versus altitude the effects of refraction on the RRL frequency can be found using a variation of standard ray-tracing techniques, whereby the ray departure angle is found by an iterative process. From the dispersive characteristics of a mixture of hydrogen and helium with trace amounts of methane and ammonia a simple model of the Jovian atmosphere is constructed assuming spherical symmetry and uniform mixing. The contribution to the RRL Doppler frequency arising from refraction is calculated, and its effect on the Doppler wind measurements is discussed.

  17. Refraction effects on the Galileo probe telemetry carrier frequency

    NASA Technical Reports Server (NTRS)

    Atkinson, D. H.; Spilker, T. R.

    1991-01-01

    As the Galileo probe relay radio link (RRL) signal propagates outward through the Jovian atmosphere, the atmosphere will manifest itself in two ways. First, the geometric path length of the signal is increased, resulting in a small change of the RRL signal departure angle from the proble (transmitter). Secondly, the velocity of the signal is decreased. For a spherical, static atmosphere with a known profile of refractivity versus altitude the effects of refraction on the RRL frequency can be found using a variation of standard ray-tracing techniques, whereby the ray departure angle is found by an iterative process. From the dispersive characteristics of a mixture of hydrogen and helium with trace amounts of methane and ammonia a simple model of the Jovian atmosphere is constructed assuming spherical symmetry and uniform mixing. The contribution to the RRL Doppler frequency arising from refraction is calculated, and its effect on the Doppler wind measurements is discussed.

  18. Anomalous refraction of guided waves via embedded acoustic metasurfaces

    NASA Astrophysics Data System (ADS)

    Zhu, Hongfei; Semperlotti, Fabio

    2016-04-01

    We illustrate the design of acoustic metasurfaces based on geometric tapers and embedded in thin-plate structures. The metasurface is an engineered discontinuity that enables anomalous refraction of guided wave modes according to the Generalized Snell's Law. Locally-resonant geometric torus-like tapers are designed in order to achieve metasurfaces having discrete phase-shift profiles that enable a high level of control of refraction of the wavefronts. Results of numerical simulations show that anomalous refraction can be achieved on transmitted anti-symmetric modes (A0) either when using a symmetric (S0) or anti-symmetric (A0) incident wave, where the former case clearly involves mode conversion mechanisms.

  19. Refraction of coastal ocean waves

    NASA Technical Reports Server (NTRS)

    Shuchman, R. A.; Kasischke, E. S.

    1981-01-01

    Refraction of gravity waves in the coastal area off Cape Hatteras, NC as documented by synthetic aperture radar (SAR) imagery from Seasat orbit 974 (collected on September 3, 1978) is discussed. An analysis of optical Fourier transforms (OFTs) from more than 70 geographical positions yields estimates of wavelength and wave direction for each position. In addition, independent estimates of the same two quantities are calculated using two simple theoretical wave-refraction models. The OFT results are then compared with the theoretical results. A statistical analysis shows a significant degree of linear correlation between the data sets. This is considered to indicate that the Seasat SAR produces imagery whose clarity is sufficient to show the refraction of gravity waves in shallow water.

  20. Refraction of coastal ocean waves

    NASA Technical Reports Server (NTRS)

    Shuchman, R. A.; Kasischke, E. S.

    1981-01-01

    Refraction of gravity waves in the coastal area off Cape Hatteras, NC as documented by synthetic aperture radar (SAR) imagery from Seasat orbit 974 (collected on September 3, 1978) is discussed. An analysis of optical Fourier transforms (OFTs) from more than 70 geographical positions yields estimates of wavelength and wave direction for each position. In addition, independent estimates of the same two quantities are calculated using two simple theoretical wave-refraction models. The OFT results are then compared with the theoretical results. A statistical analysis shows a significant degree of linear correlation between the data sets. This is considered to indicate that the Seasat SAR produces imagery whose clarity is sufficient to show the refraction of gravity waves in shallow water.

  1. Estimating refractivity from propagation loss in turbulent media

    NASA Astrophysics Data System (ADS)

    Wagner, Mark; Gerstoft, Peter; Rogers, Ted

    2016-12-01

    This paper estimates lower atmospheric refractivity (M-profile) given an electromagnetic (EM) propagation loss (PL) measurement. Specifically, height-independent PL measurements over a range of 10-80 km are used to infer information about the existence and potential parameters of atmospheric ducts in the lowest 1 km of the atmosphere. The main improvement made on previous refractivity estimations is inclusion of range-dependent fluctuations due to turbulence in the forward propagation model. Using this framework, the maximum likelihood (ML) estimate of atmospheric refractivity has good accuracy, and with prior information about ducting the maximum a priori (MAP) refractivity estimate can be found. Monte Carlo methods are used to estimate the mean and covariance of PL, which are fed into a Gaussian likelihood function for evaluation of estimated refractivity probability. Comparisons were made between inversions performed on propagation loss data simulated by a wide angle parabolic equation (PE) propagation model with added homogeneous and inhomogeneous turbulence. It was found that the turbulence models produce significantly different results, suggesting that accurate modeling of turbulence is key.

  2. Imaging of subsurface faults using refraction migration with fault flooding

    NASA Astrophysics Data System (ADS)

    Metwally, Ahmed; Hanafy, Sherif; Guo, Bowen; Kosmicki, Maximillian

    2017-08-01

    We propose a novel method for imaging shallow faults by migration of transmitted refraction arrivals. The assumption is that there is a significant velocity contrast across the fault boundary that is underlain by a refracting interface. This procedure, denoted as refraction migration with fault flooding, largely overcomes the difficulty in imaging shallow faults with seismic surveys. Numerical results successfully validate this method on three synthetic examples and two field-data sets. The first field-data set is next to the Gulf of Aqaba and the second example is from a seismic profile recorded in Arizona. The faults detected by refraction migration in the Gulf of Aqaba data were in agreement with those indicated in a P-velocity tomogram. However, a new fault is detected at the end of the migration image that is not clearly seen in the traveltime tomogram. This result is similar to that for the Arizona data where the refraction image showed faults consistent with those seen in the P-velocity tomogram, except that it also detected an antithetic fault at the end of the line. This fault cannot be clearly seen in the traveltime tomogram due to the limited ray coverage.

  3. Refractive Surgery: New Techniques and Usability for Military Personnel (La chirurgie refractive: Nouvelles techniques et leur application pour le personnel militaire)

    DTIC Science & Technology

    2012-11-01

    targeted, even in the absence of cataract formation, to correct refractive error. The risk profile of intraocular procedures is different than corneal...change the refractive power. If the natural lens is not opaque with cataract , this procedure is termed ‘clear lens extraction’. Generally, such...cystoid macular edema. The long-term risk of cataract progression and corneal decompensation (loss of the cornea’s ability to regulate its own water

  4. Effect of the refractive index change kinetics of photosensitive materials on the diffraction efficiency of reflecting Bragg gratings.

    PubMed

    Lumeau, Julien; Glebov, Leonid B

    2013-06-10

    Experimental and modeled dependencies of the induced refractive index on dosage of UV exposure in photo-thermo-refractive glass for different thermal treatment regimes are presented. Resulting spatial profiles of refractive index modulation in a reflecting Bragg grating recorded by a holographic technique are computed, and corresponding diffraction efficiencies are modeled. It is shown that nonlinearity of the photosensitivity response is responsible for spatial distortions of a recorded grating that result in a decrease of the diffraction efficiency.

  5. Fiber optic refractive index monitor

    SciTech Connect

    Weiss, Jonathan David

    2002-01-01

    A sensor for measuring the change in refractive index of a liquid uses the lowest critical angle of a normal fiber optic to achieve sensitivity when the index of the liquid is significantly less than the index of the fiber core. Another embodiment uses a liquid filled core to ensure that its index is approximately the same as the liquid being measured.

  6. REFLECTION AND REFRACTION, VOLUME 2.

    ERIC Educational Resources Information Center

    KLAUS, DAVID J.; AND OTHERS

    THIS VOLUME 2 OF A TWO-VOLUME SET PROVIDES AUTOINSTRUCTION IN PHYSICS. THE UNITS COVERED IN THIS VOLUME ARE (1) REFLECTION OF LIGHT, (2) PHOTOMETRY, (3) POLARIZATION, (4) REFRACTION OF LIGHT, (5) SNELL'S LAW, (6) LENSES, FOCUS, AND FOCAL POINTS, (7) IMAGE FORMATION, AND (8) ABERRATIONS, THE EYE, AND MAGNIFICATION. THE INTRODUCTION AND UNITS ON…

  7. Index of Refraction without Geometry

    ERIC Educational Resources Information Center

    Farkas, N.; Henriksen, P. N.; Ramsier, R. D.

    2006-01-01

    This article presents several activities that permit students to determine the index of refraction of transparent solids and liquids using simple equipment without the need for geometrical relationships, special lighting or optical instruments. Graphical analysis of the measured data is shown to be a useful method for determining the index of…

  8. Crystalline lens and refractive development.

    PubMed

    Iribarren, Rafael

    2015-07-01

    Individual refractive errors usually change along lifespan. Most children are hyperopic in early life. This hyperopia is usually lost during growth years, leading to emmetropia in adults, but myopia also develops in children during school years or during early adult life. Those subjects who remain emmetropic are prone to have hyperopic shifts in middle life. And even later, at older ages, myopic shifts are developed with nuclear cataract. The eye grows from 15 mm in premature newborns to approximately 24 mm in early adult years, but, in most cases, refractions are maintained stable in a clustered distribution. This growth in axial length would represent a refractive change of more than 40 diopters, which is compensated by changes in corneal and lens powers. The process which maintains the balance between the ocular components of refraction during growth is still under study. As the lens power cannot be measured in vivo, but can only be calculated based on the other ocular components, there have not been many studies of lens power in humans. Yet, recent studies have confirmed that the lens loses power during growth in children, and that hyperopic and myopic shifts in adulthood may be also produced by changes in the lens. These studies in children and adults give a picture of the changing power of the lens along lifespan. Other recent studies about the growth of the lens and the complexity of its internal structure give clues about how these changes in lens power are produced along life.

  9. Refractive Index Enhancement in Gases

    DTIC Science & Technology

    2012-02-29

    experimentally demonstrated the key ingredients of this approach in Rubidium vapor where we have observe enhanced refractive index with vanishing absorption...beam, Ep. We have recently experimentally demonstrated this effect in a 1-mm-long Rubidium (Rb) vapor cell at high vapor densities. Here, we utilize

  10. Index of Refraction without Geometry

    ERIC Educational Resources Information Center

    Farkas, N.; Henriksen, P. N.; Ramsier, R. D.

    2006-01-01

    This article presents several activities that permit students to determine the index of refraction of transparent solids and liquids using simple equipment without the need for geometrical relationships, special lighting or optical instruments. Graphical analysis of the measured data is shown to be a useful method for determining the index of…

  11. REFLECTION AND REFRACTION, VOLUME 2.

    ERIC Educational Resources Information Center

    KLAUS, DAVID J.; AND OTHERS

    THIS VOLUME 2 OF A TWO-VOLUME SET PROVIDES AUTOINSTRUCTION IN PHYSICS. THE UNITS COVERED IN THIS VOLUME ARE (1) REFLECTION OF LIGHT, (2) PHOTOMETRY, (3) POLARIZATION, (4) REFRACTION OF LIGHT, (5) SNELL'S LAW, (6) LENSES, FOCUS, AND FOCAL POINTS, (7) IMAGE FORMATION, AND (8) ABERRATIONS, THE EYE, AND MAGNIFICATION. THE INTRODUCTION AND UNITS ON…

  12. The effects of atmospheric refraction on the accuracy of laser ranging systems

    NASA Technical Reports Server (NTRS)

    Zanter, D. L.; Gardner, C. S.; Rao, N. N.

    1976-01-01

    Correction formulas derived by Saastamoinen and Marini, and the ray traces through the refractivity profiles all assume a spherically symmetric refractivity profile. The errors introduced by this assumption were investigated by ray tracing through three-dimensional profiles. The results of this investigation indicate that the difference between ray traces through the spherically symmetric and three-dimensional profiles is approximately three centimeters at 10 deg and decreases to less than one half of a centimeter at 80 deg. If the accuracy desired in future laser ranging systems is less than a few centimeters, Saastamoinen and Marini's formulas must be altered to account for the fact that the refractivity profile is not spherically symmetric.

  13. Emmetropisation and the aetiology of refractive errors

    PubMed Central

    Flitcroft, D I

    2014-01-01

    The distribution of human refractive errors displays features that are not commonly seen in other biological variables. Compared with the more typical Gaussian distribution, adult refraction within a population typically has a negative skew and increased kurtosis (ie is leptokurtotic). This distribution arises from two apparently conflicting tendencies, first, the existence of a mechanism to control eye growth during infancy so as to bring refraction towards emmetropia/low hyperopia (ie emmetropisation) and second, the tendency of many human populations to develop myopia during later childhood and into adulthood. The distribution of refraction therefore changes significantly with age. Analysis of the processes involved in shaping refractive development allows for the creation of a life course model of refractive development. Monte Carlo simulations based on such a model can recreate the variation of refractive distributions seen from birth to adulthood and the impact of increasing myopia prevalence on refractive error distributions in Asia. PMID:24406411

  14. Efficient physics-based predictive 3D image modeling and simulation of optical atmospheric refraction phenomena

    NASA Astrophysics Data System (ADS)

    Reinhardt, Colin N.; Hammel, Stephen M.; Tsintikidis, Dimitris

    2016-09-01

    We present some preliminary results and discussion of our ongoing effort to develop a prototype volumetric atmospheric optical refraction simulator which uses 3D nonlinear ray-tracing and state-of-art physics-based rendering techniques. The tool will allow simulation of optical curved-ray propagation through nonlinear refractivity gradient profiles in volumetric atmospheric participating media, and the generation of radiometrically accurate images of the resulting atmospheric refraction phenomena, including inferior and superior mirages, over-the-horizon viewing conditions, looming and sinking, towering and stooping of distant objects. The ability to accurately model and predict atmospheric optical refraction conditions and phenomena is important in both defense and commercial applications. Our nonlinear refractive ray-trace method is currently CPU-parallelized and is well-suited for GPU compute implementation.

  15. Evaluations of refraction competencies of ophthalmic technicians in Mozambique.

    PubMed

    Shah, Kajal; Naidoo, Kovin; Chagunda, Margarida; Loughman, James

    2016-01-01

    Ophthalmic technicians (OT) work at health facilities in Mozambique and are trained to provide primary and secondary eye care services including basic refraction. This study was designed to assess OT competence and confidence in refraction, and investigate whether an upskilling programme is effective in developing their competence and confidence at refraction. Thirty-one trainee OTs and 16 qualified OTs were recruited to the study. A background questionnaire was administered to determine the demographic profile of the OTs. A confidence levels questionnaire explored their self-reported skills. Clinical competencies were assessed in relation to knowledge (theory exam) and clinical skills (patient exams). 11 OTs were upskilled and the clinical evaluations carried out post training. Initial evaluations demonstrated that confidence and competence levels varied depending on the OTs training (location and duration), and their location of work (clinical load, availability of equipment and other eye care personnel). The qualified OTs were more competent than trainee OTs in most of the evaluations. Post upskilling results demonstrated significant positive impact on confidence and competence levels. These evaluations identified factors affecting the refraction competencies of the OTs and demonstrated that upskilling is effective in improving confidence and competence levels for refraction. They demonstrate the need for a refraction competency framework. The overarching aim of this research was to inform the development of a nationwide programme of OT mentoring, upskilling and leading to the establishment of clinical competency standards for the new OT curricula, relevant to the professional demands. Copyright © 2014 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.

  16. [Refractive surgery and flight safety].

    PubMed

    Draeger, J

    1998-09-01

    For both VFR and as IFR flight, visual assessment is the major source of information for the pilot. The new possibilities for change of refraction by means of corneal refractive surgery have led to an increasing demand from pilots for these new methods. Can these methods successfully be applied for aviation purposes? The valid regulations for medical standards of pilots, as well as the future international regulations such as JAR and ICAO, are explained in this respect. A report is given on the work of the Advisory Board of the German Federal Government Air Traffic Authority and on the cases treated so far and their outcome, and recommendations are expressed. Concerning the legal situation and clinical experience, advice for pilots, aviation medical examiners and ophthalmologists is given.

  17. Refractive keratoplasty. Keratophakia and keratomileusis.

    PubMed

    Troutman, R C; Swinger, C

    1982-01-01

    Early experience with the refractive keratoplasty techniques of José Barraquer--keratophakia and hypermetropic keratomileusis is presented. In contradistinction to the alloplastic lens substitutes currently being employed for the integral correction of aphakia, Barraquer's techniques would seem to offer a more permanent, more physiologic, full-time optical correction of the aphakic state. Their use is limited only by the condition of the patient's cornea and, in fact, may be applied not only in aphakia but also in phakic eyes with higher degrees of hyperopia or myopia. In the opinion of the authors, the refractive keratoplasty techniques of Barraquer can be performed by any well-instructed ophthalmic surgeon. These techniques offer to many patients a satisfactory, and potentially a physiologically superior alternative to alloplastic lens substitute for aphakic correction.

  18. Refractive keratoplasty: keratophakia and keratomileusis.

    PubMed

    Troutman, R C; Swinger, C

    1978-01-01

    We have presented our early experience with the refractive keratoplasty techniques of Doctor Jose Barraquer--keratophakia and hypermetropic keratomileusis. In contradistinction to the alloplastic lens substitutes currently being employed for the integral correction of aphakia, his techniques would seem to offer a more permanent, more physiologic, full-time optical correction of the aphakic state. Their use is limited only by the condition of the patient's corneaa and, in fact, may be applied not only in aphakia but also in phakic eyes with higher degrees of hyperopia or myopia. In the opinion of the authors, the refractive keratoplasty techniques of Barraquer can be perfored by any well-instructed ophthalmic surgeon. These techniques offer to many patients a satisfactory and potentially a physiologically superior alternative to alloplastic lens substitute for aphakic correction.

  19. Triangulation in Random Refractive Distortions.

    PubMed

    Alterman, Marina; Schechner, Yoav Y; Swirski, Yohay

    2017-03-01

    Random refraction occurs in turbulence and through a wavy water-air interface. It creates distortion that changes in space, time and with viewpoint. Localizing objects in three dimensions (3D) despite this random distortion is important to some predators and also to submariners avoiding the salient use of periscopes. We take a multiview approach to this task. Refracted distortion statistics induce a probabilistic relation between any pixel location and a line of sight in space. Measurements of an object's random projection from multiple views and times lead to a likelihood function of the object's 3D location. The likelihood leads to estimates of the 3D location and its uncertainty. Furthermore, multiview images acquired simultaneously in a wide stereo baseline have uncorrelated distortions. This helps reduce the acquisition time needed for localization. The method is demonstrated in stereoscopic video sequences, both in a lab and a swimming pool.

  20. Electro-refractive photonic device

    SciTech Connect

    Zortman, William A.; Watts, Michael R.

    2015-06-09

    The various technologies presented herein relate to phase shifting light to facilitate any of light switching, modulation, amplification, etc. Structures are presented where a second layer is juxtaposed between a first layer and a third layer with respective doping facilitating formation of p-n junctions at the interface between the first layer and the second layer, and between the second layer and the third layer. Application of a bias causes a carrier concentration change to occur at the p-n junctions which causes a shift in the effective refractive index per incremental change in an applied bias voltage. The effective refractive index enhancement can occur in both reverse bias and forward bias. The structure can be incorporated into a waveguide, an optical resonator, a vertical junction device, a horizontal junction device, a Mach-Zehnder interferometer, a tuneable optical filter, etc.

  1. Interpolation of refractive index data.

    PubMed

    Morrissey, B W; Powell, C J

    1973-07-01

    A comparison of the interpolation of index of refraction data for Czochralski sapphire, cyclohexane, and polystyrene dissolved in cyclohexane using a three-term Sellmeier equation, the Lorentz-Lorenz equation with six terms, third and fifth order polynomials, and a cubic-spline technique indicates that the cubic spline method is extremely valuable for simple interpolation. Not only were the magnitudes of the rms and average absolute residuals the smallest, but the fits showed no systematic errors.

  2. Quantification of scaling exponents and dynamical complexity of microwave refractivity in a tropical climate

    NASA Astrophysics Data System (ADS)

    Fuwape, Ibiyinka A.; Ogunjo, Samuel T.

    2016-12-01

    Radio refractivity index is used to quantify the effect of atmospheric parameters in communication systems. Scaling and dynamical complexities of radio refractivity across different climatic zones of Nigeria have been studied. Scaling property of the radio refractivity across Nigeria was estimated from the Hurst Exponent obtained using two different scaling methods namely: The Rescaled Range (R/S) and the detrended fluctuation analysis(DFA). The delay vector variance (DVV), Largest Lyapunov Exponent (λ1) and Correlation Dimension (D2) methods were used to investigate nonlinearity and the results confirm the presence of deterministic nonlinear profile in the radio refractivity time series. The recurrence quantification analysis (RQA) was used to quantify the degree of chaoticity in the radio refractivity across the different climatic zones. RQA was found to be a good measure for identifying unique fingerprint and signature of chaotic time series data. Microwave radio refractivity was found to be persistent and chaotic in all the study locations. The dynamics of radio refractivity increases in complexity and chaoticity from the Coastal region towards the Sahelian climate. The design, development and deployment of robust and reliable microwave communication link in the region will be greatly affected by the chaotic nature of radio refractivity in the region.

  3. Ray tracing evaluation of a technique for correcting the refraction errors in satellite tracking data

    NASA Technical Reports Server (NTRS)

    Gardner, C. S.; Rowlett, J. R.; Hendrickson, B. E.

    1978-01-01

    Errors may be introduced in satellite laser ranging data by atmospheric refractivity. Ray tracing data have indicated that horizontal refractivity gradients may introduce nearly 3-cm rms error when satellites are near 10-degree elevation. A correction formula to compensate for the horizontal gradients has been developed. Its accuracy is evaluated by comparing it to refractivity profiles. It is found that if both spherical and gradient correction formulas are employed in conjunction with meteorological measurements, a range resolution of one cm or less is feasible for satellite elevation angles above 10 degrees.

  4. Ray tracing evaluation of a technique for correcting the refraction errors in satellite tracking data

    NASA Technical Reports Server (NTRS)

    Gardner, C. S.; Rowlett, J. R.; Hendrickson, B. E.

    1978-01-01

    Errors may be introduced in satellite laser ranging data by atmospheric refractivity. Ray tracing data have indicated that horizontal refractivity gradients may introduce nearly 3-cm rms error when satellites are near 10-degree elevation. A correction formula to compensate for the horizontal gradients has been developed. Its accuracy is evaluated by comparing it to refractivity profiles. It is found that if both spherical and gradient correction formulas are employed in conjunction with meteorological measurements, a range resolution of one cm or less is feasible for satellite elevation angles above 10 degrees.

  5. Laser refractive tomography of phase objects

    SciTech Connect

    Raskovskaya, I L

    2013-06-30

    The principles are outlined of laser refractive tomography - a method for reconstructing the values of the refractive index in the cross sections of phase objects, which involves the use of three-dimensional refractive images (3D refractograms) of structured laser radiation. A simulation algorithm is realised and examples are provided of characteristic 3D refractograms obtained by solving the direct problem of refraction of structured radiation. A method was developed for reconstructing the values of refractive index under conditions of strong refraction, which is based on the visualisation of ray trajectories inside an optically inhomogeneous medium. A classification is made of possible approaches to the solution of the inverse problem of refraction based on the visualisation of ray trajectories. Examples are given of cross section reconstruction and quantitative diagnostics of phase objects. (laser imaging)

  6. Stress-optic coefficients and temperature dependent refractive indices of potassium terbium fluoride (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Zelmon, David E.; Fenstermaker, Steven T.; Poston, William B.; Kunkel, John D.; Stevens, Kevin T.; Foundos, Greg; Payne, Alexis; Chang, Kelvin

    2017-03-01

    Potassium terbium fluoride is a recently developed magneto-optic material which has been proposed for use as an optical isolator. We have performed measurements of the refractive index, thermo-optic coefficient, and stress-optic coefficient of this material. We present a temperature dependent Sellmeier equation along with calculations of temperature and refractive index profiles at various pump power levels in a diode pumped laser. The data are critical to the design of laser systems in which optical isolators are employed.

  7. GEOPHYSICS, ASTRONOMY AND ASTROPHYSICS: Refractivity estimation from radar sea clutter

    NASA Astrophysics Data System (ADS)

    Huang, Si-Xun; Zhao, Xiao-Feng; Sheng, Zheng

    2009-11-01

    This paper addresses the problem of estimating lower atmospheric refractivity under the nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical structure of the refractive environment is modeled by using a five-parameter model, and the horizontal structure is modeled as range-independent. The electromagnetic propagation in the troposphere is simulated by using a split-step fast Fourier transform based on parabolic approximation to the wave equation. A global search marked as a modified genetic algorithm (MGA) for the 5 environmental parameters is performed by using a genetic algorithm (GA) integrated with a simulated annealing technique. The retrieved results from simulated runs demonstrate the ability of this method to make atmospheric refractivity estimations. A comparison with the classical GA and the Bayesian Markov Chain Monte Carlo (Bayesian-MCMC) technique shows that the MGA can not only shorten the inverse time but also improve the inverse precision. For real data cases, the inversion values do not match the reference data very well. The inverted profile, however, can be used to synoptically describe the real refractive structure.

  8. Refraction of cylindrical converging shock wave at an air/helium gaseous interface

    NASA Astrophysics Data System (ADS)

    Zhai, Zhigang; Li, Wei; Si, Ting; Luo, Xisheng; Yang, Jiming; Lu, Xiyun

    2017-01-01

    Refraction of a cylindrical converging shock wave at an inclined air/helium interface is investigated. Experimentally, based on the shock dynamics theory, a special wall profile is designed to generate a perfectly cylindrical converging shock wave. A soap film technique is developed to form an inclined discontinuous air/helium interface, and high-speed schlieren photography is adopted to capture the flow. Numerical simulations are also performed to compare with the experimental counterparts and to show details of refraction. In this work, two initial incident angles (45° and 60°) are considered. As the incident shock converges inward, the shock intensity increases while the incident angle decreases, causing possible transitions among the wave patterns. For the case of 45°, an irregular refraction of free precursor refraction (FPR) first occurs and gradually transits into regular refraction, while for the case of 60°, various irregular refractions of twin von Neumann refraction (TNR), twin regular refraction (TRR), free precursor von Neumann refraction (FNR), and FPR occur in sequence. The transition sequences do not belong to any groups described in the planar counterpart, indicating that the classification of the refraction phenomenon in the planar case is not exhaustive or cannot be applied to the converging case. It is also the first time to observe the transition from FNR to FPR, providing an experimental evidence for the previous numerical results. It is deemed that the difference between the velocities of the incident and transmitted shocks propagating along the interface is the primary factor that induces the transitions among wave patterns.

  9. Negative refraction in a laminate

    NASA Astrophysics Data System (ADS)

    Willis, J. R.

    2016-12-01

    This work is concerned with the reflection and transmission of waves at a plane interface between a homogeneous elastic half-space and a half-space of elastic material that is periodically laminated. The lamination is always in the direction of the x1-coordinate axis and the displacement is always longitudinal shear, so that the only non-zero displacement component is u3(x1 ,x2 , t). After an initial discussion of Floquet-Bloch waves in the laminated material, brief consideration is given to the reflection-transmission problem, when the interface between the two media is the plane x1 = 0. Nothing unusual emerges: there are just a single reflected wave and a single transmitted wave, undergoing positive group-velocity refraction. Then, the problem is considered when the interface between the two media is the plane x2 = 0. The periodic structure of the interface induces an infinite set of reflected waves and an infinite set of transmitted waves. All need to be taken into account, but most decay exponentially away from the interface. It had previously been recognized that, if the incident wave had appropriate frequency and angle of incidence, a propagating transmitted wave would be generated that would undergo negative group-velocity refraction - behaviour usually associated with a metamaterial. It is established by an example in this work that there is, in addition, a propagating transmitted wave with smaller wavelength but larger group velocity that undergoes positive group-velocity refraction. The work concludes with a brief discussion of this finding, including its implications for the utility (or not) of "effective medium" theory.

  10. Influence of refractive index matching on the photon diffuse reflectance.

    PubMed

    Churmakov, D Y; Meglinski, I V; Greenhalgh, D A

    2002-12-07

    Photon migration in a randomly inhomogeneous, highly scattering and absorbing semi-infinite medium with a plane boundary is considered by a Monte Carlo (MC) technique. The employed MC technique combines the statistical weight scheme and real photon paths simulation, allowing the exclusion of the energy conservation problem. The internal reflection of the scattered radiation on the medium interface is taken into account by allowing the trajectories of photon packets to be split into reflected and transmitted parts. The spatial photon sensitivity profile (SPSP), spatially resolved diffuse reflectance and angular and spatial photon detector weight distributions are considered in terms of Fresnel's reflection/refraction on the boundary of the medium. The effect of the refractive index match is predicted correctly by the MC method and by the diffusion approximation. The results demonstrate that matching of the refractive index of the medium significantly improves the contrast and spatial resolution of the spatial photon sensitivity profile (SPSP). The results of simulation of the spatially resolved diffuse reflectance agree well with the results predicted by the diffusion approximation and the experimental results reported earlier.

  11. Effects of refractive index mismatch in optical CT imaging of polymer gel dosimeters

    SciTech Connect

    Manjappa, Rakesh; Makki S, Sharath; Kanhirodan, Rajan; Kumar, Rajesh

    2015-02-15

    reconstructs the dose profiles by estimating refractive indices of multiple inhomogeneities having different refractive indices and optical densities embedded in the dosimeter. This is achieved by tracking the path of the ray that traverses through the dosimeter. Extensive simulation studies have been carried out and results are found to be matching that of experimental results.

  12. Crustal seismic refraction study in West-Central Arizona

    SciTech Connect

    Sinno, Y.A.; Keller, G.R.; Sbar, M.L.

    1981-06-10

    A reversed seismic refraction profile was recorded in the southern Basin and Range Province between Parker and Globe, Arizona. Interpretation of both refracted and reflected phases indicates a two-layered crust 23-25 km thick, and a low Pn velocity (7.67 km/s). PmP/Pn amplitude analysis on individual traces and synthetic seismogram modeling indicate that a positive velocity gradient may exist in the upper mantle. The low Pn velocity is indicative of partial melting in the upper mantle and implies that the crust is identical with the lithosphere. The heat flow data suggest that the lithosphere was about 40 km thick approximately 5 m.y. ago. On the basis of this and a negative free air gravity anomaly we propose that the lithosphere has been thinned from about 40 to 24 km over the past 5 m.y. and will probably thin and uplift further in the southern Basin and Range in Arizona.

  13. Investigation of refracting flows for acoustic suppression

    NASA Technical Reports Server (NTRS)

    Sloan, D.; Purves, R. B.; Farquhar, B. W.

    1977-01-01

    An experimental investigation to determine the possibility of using refracting flows for the suppression of aircraft inlet noise is described. Observations of wave refraction in duct flows and measurements of the increase in effectiveness of acoustic linings due to refraction have suggested methods for the design of engine inlet ducts which can either suppress noise internally or direct it to where it causes less annoyance.

  14. Peripheral refraction in normal infant rhesus monkeys

    PubMed Central

    Hung, Li-Fang; Ramamirtham, Ramkumar; Huang, Juan; Qiao-Grider, Ying; Smith, Earl L.

    2008-01-01

    Purpose To characterize peripheral refractions in infant monkeys. Methods Cross-sectional data for horizontal refractions were obtained from 58 normal rhesus monkeys at 3 weeks of age. Longitudinal data were obtained for both the vertical and horizontal meridians from 17 monkeys. Refractive errors were measured by retinoscopy along the pupillary axis and at eccentricities of 15, 30, and 45 degrees. Axial dimensions and corneal power were measured by ultrasonography and keratometry, respectively. Results In infant monkeys, the degree of radial astigmatism increased symmetrically with eccentricity in all meridians. There were, however, initial nasal-temporal and superior-inferior asymmetries in the spherical-equivalent refractive errors. Specifically, the refractions in the temporal and superior fields were similar to the central ametropia, but the refractions in the nasal and inferior fields were more myopic than the central ametropia and the relative nasal field myopia increased with the degree of central hyperopia. With age, the degree of radial astigmatism decreased in all meridians and the refractions became more symmetrical along both the horizontal and vertical meridians; small degrees of relative myopia were evident in all fields. Conclusions As in adult humans, refractive error varied as a function of eccentricity in infant monkeys and the pattern of peripheral refraction varied with the central refractive error. With age, emmetropization occurred for both central and peripheral refractive errors resulting in similar refractions across the central 45 degrees of the visual field, which may reflect the actions of vision-dependent, growth-control mechanisms operating over a wide area of the posterior globe. PMID:18487366

  15. Investigation of refracting flows for acoustic suppression

    NASA Technical Reports Server (NTRS)

    Sloan, D.; Purves, R. B.; Farquhar, B. W.

    1977-01-01

    An experimental program to determine the possibility of using refracting flows for the suppression of aircraft inlet noise has been completed. Observations of wave behavior in accelerating duct flows have suggested that acoustic wave refraction could be used to direct inlet noise away from the ground upward to where it causes less annoyance. Measurements have also shown that acoustic wave refraction can cause large improvements in the effectiveness of acoustic lining material.

  16. Optical Negative Refraction in Ferrofluids with Magnetocontrollability

    DTIC Science & Technology

    2010-01-22

    Optical Negative Refraction in Ferrofluids with Magnetocontrollability Y. Gao,1,2 J. P. Huang,1,* Y.M. Liu,3 L. Gao,4 K.W. Yu,2 and X. Zhang3...China (Received 5 October 2009; published 20 January 2010) We numerically demonstrate optical negative refraction in ferrofluids containing isotropic...certain soft materials. As a result, we reveal, for the first time, a new class of all-angle broadband optical nega- tive refraction in ferrofluids with

  17. Polymeric nanolayered gradient refractive index lenses: technology review and introduction of spherical gradient refractive index ball lenses

    NASA Astrophysics Data System (ADS)

    Ji, Shanzuo; Yin, Kezhen; Mackey, Matthew; Brister, Aaron; Ponting, Michael; Baer, Eric

    2013-11-01

    A nanolayered polymer films approach to designing and fabricating gradient refractive index (GRIN) lenses with designer refractive index distribution profiles and an independently prescribed lens surface geometry have been demonstrated to produce a new class of optics. This approach utilized nanolayered polymer materials, constructed with polymethylmethacrylate and a styrene-co-acrylonitrile copolymer with a tailorable refractive index intermediate to bulk materials, to fabricate discrete GRIN profile materials. A process to fabricate nanolayered polymer GRIN optics from these materials through thermoforming and finishing steps is reviewed. A collection of technology-demonstrating previously reported nanolayered GRIN case studies is presented that include: (1) the optical performance of a f/# 2.25 spherical GRIN plano-convex singlet with one quarter (2) the weight of a similar BK7 lens and a bio-inspired aspheric human eye GRIN lens. Original research on the fabrication and characterization of a Luneburg inspired GRIN ball lens is presented as a developing application of the nanolayered polymer technology.

  18. Negative refraction in semiconductor metamaterials.

    PubMed

    Hoffman, Anthony J; Alekseyev, Leonid; Howard, Scott S; Franz, Kale J; Wasserman, Dan; Podolskiy, Viktor A; Narimanov, Evgenii E; Sivco, Deborah L; Gmachl, Claire

    2007-12-01

    An optical metamaterial is a composite in which subwavelength features, rather than the constituent materials, control the macroscopic electromagnetic properties of the material. Recently, properly designed metamaterials have garnered much interest because of their unusual interaction with electromagnetic waves. Whereas nature seems to have limits on the type of materials that exist, newly invented metamaterials are not bound by such constraints. These newly accessible electromagnetic properties make these materials an excellent platform for demonstrating unusual optical phenomena and unique applications such as subwavelength imaging and planar lens design. 'Negative-index materials', as first proposed, required the permittivity, epsilon, and permeability, mu, to be simultaneously less than zero, but such materials face limitations. Here, we demonstrate a comparatively low-loss, three-dimensional, all-semiconductor metamaterial that exhibits negative refraction for all incidence angles in the long-wave infrared region and requires only an anisotropic dielectric function with a single resonance. Using reflection and transmission measurements and a comprehensive model of the material, we demonstrate that our material exhibits negative refraction. This is furthermore confirmed through a straightforward beam optics experiment. This work will influence future metamaterial designs and their incorporation into optical semiconductor devices.

  19. Femtosecond laser corneal refractive surgery

    NASA Astrophysics Data System (ADS)

    Kurtz, Ron M.; Spooner, Greg J. R.; Sletten, Karin R.; Yen, Kimberly G.; Sayegh, Samir I.; Loesel, Frieder H.; Horvath, Christopher; Liu, HsiaoHua; Elner, Victor; Cabrera, Delia; Muenier, Marie-Helene; Sacks, Zachary S.; Juhasz, Tibor

    1999-06-01

    We evaluated the efficacy, safety, and stability of femtosecond laser intrastromal refractive procedures in ex vivo and in vivo models. When compared with longer pulsewidth nanosecond or picosecond laser pulses, femtosecond laser-tissue interactions are characterized by significantly smaller and more deterministic photodisruptive energy thresholds, as well as reduced shock waves and smaller cavitation bubbles. We utilized a highly reliable, all-solid-state femtosecond laser system for all studies to demonstrate clinical practicality. Contiguous tissue effects were achieved by scanning a 5 μm focused laser spot below the corneal surface at pulse energies of approximately 2 - 4 microjoules. A variety of scanning patterns was used to perform three prototype procedures in animal eyes; corneal flap cutting, keratomileusis, and intrastromal vision correction. Superior dissection and surface quality results were obtained for lamellar procedures (corneal flap cutting and keratomileusis). Preliminary in vivo evaluation of intrastromal vision correction in a rabbit model revealed consistent and stable pachymetry changes, without significant inflammation or loss of corneal transparency. We conclude that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques.

  20. Detecting motion through dynamic refraction.

    PubMed

    Alterman, Marina; Schechner, Yoav Y; Perona, Pietro; Shamir, Joseph

    2013-01-01

    Refraction causes random dynamic distortions in atmospheric turbulence and in views across a water interface. The latter scenario is experienced by submerged animals seeking to detect prey or avoid predators, which may be airborne or on land. Man encounters this when surveying a scene by a submarine or divers while wishing to avoid the use of an attention-drawing periscope. The problem of inverting random refracted dynamic distortions is difficult, particularly when some of the objects in the field of view (FOV) are moving. On the other hand, in many cases, just those moving objects are of interest, as they reveal animal, human, or machine activity. Furthermore, detecting and tracking these objects does not necessitate handling the difficult task of complete recovery of the scene. We show that moving objects can be detected very simply, with low false-positive rates, even when the distortions are very strong and dominate the object motion. Moreover, the moving object can be detected even if it has zero mean motion. While the object and distortion motions are random and unknown, they are mutually independent. This is expressed by a simple motion feature which enables discrimination of moving object points versus the background.

  1. Statistical Analysis of Refractivity in UAE

    NASA Astrophysics Data System (ADS)

    Al-Ansari, Kifah; Al-Mal, Abdulhadi Abu; Kamel, Rami

    2007-07-01

    This paper presents the results of the refractivity statistics in the UAE (United Arab Emirates) for a period of 14 years (1990-2003). Six sites have been considered using meteorological surface data (Abu Dhabi, Dubai, Sharjah, Al-Ain, Ras Al-Kaimah, and Al-Fujairah). Upper air (radiosonde) data were available at one site only, Abu Dhabi airport, which has been considered for the refractivity gradient statistics. Monthly and yearly averages are obtained for the two parameters, refractivity and refractivity gradient. Cumulative distributions are also provided.

  2. Refractive index of plant cell walls

    NASA Technical Reports Server (NTRS)

    Gausman, H. W.; Allen, W. A.; Escobar, D. E.

    1974-01-01

    Air was replaced with media of higher refractive indices by vacuum infiltration in leaves of cucumber, blackeye pea, tomato, and string bean plants, and reflectance of noninfiltrated and infiltrated leaves was spectrophotometrically measured. Infiltrated leaves reflected less light than noninfiltrated leaves over the 500-2500-nm wavelength interval because cell wall-air interfaces were partly eliminated. Minimal reflectance should occur when the average refractive index of plant cell walls was matched by the infiltrating fluid. Although refractive indices that resulted in minimal reflectance differed among the four plant genera, an average value of 1.425 approximates the refractive index of plant cell walls for the four plant genera.

  3. Refractive index of plant cell walls

    NASA Technical Reports Server (NTRS)

    Gausman, H. W.; Allen, W. A.; Escobar, D. E.

    1974-01-01

    Air was replaced with media of higher refractive indices by vacuum infiltration in leaves of cucumber, blackeye pea, tomato, and string bean plants, and reflectance of noninfiltrated and infiltrated leaves was spectrophotometrically measured. Infiltrated leaves reflected less light than noninfiltrated leaves over the 500-2500-nm wavelength interval because cell wall-air interfaces were partly eliminated. Minimal reflectance should occur when the average refractive index of plant cell walls was matched by the infiltrating fluid. Although refractive indices that resulted in minimal reflectance differed among the four plant genera, an average value of 1.425 approximates the refractive index of plant cell walls for the four plant genera.

  4. Comparison of Aberrations After Standard and Customized Refractive Surgery

    NASA Astrophysics Data System (ADS)

    Fang, L.; He, X.; Wang, Y.

    2013-09-01

    To detect possible differences in residual wavefront aberrations between standard and customized laser refractive surgery based onmathematical modeling, the residual optical aberrations after conventional and customized laser refractive surgery were compared accordingto the ablation profile with transition zone. The results indicated that ablation profile has a significant impact on the residual aberrations.The amount of residual aberrations for conventional correction is higher than that for customized correction. Additionally, the residualaberrations for high myopia eyes are markedly larger than those for moderate myopia eyes. For a 5 mm pupil, the main residual aberrationterm is coma and yet it is spherical aberration for a 7 mm pupil. When the pupil diameter is the same as optical zone or greater, themagnitudes of residual aberrations is obviously larger than that for a smaller pupil. In addition, the magnitudes of the residual fifth orsixth order aberrations are relatively large, especially secondary coma in a 6 mm pupil and secondary spherical aberration in a 7 mm pupil.Therefore, the customized ablation profile may be superior to the conventional correction even though the transition zone and treatmentdecentration are taken into account. However, the customized ablation profile will still induce significant amount of residual aberrations.

  5. Influence of refraction index strength on the light propagation in dielectrics material with periodic refraction index

    SciTech Connect

    Hidayat, Arif Latifah, Eny; Kurniati, Diana; Wisodo, Hari

    2016-04-19

    This study investigated the influence of refraction index strength on the light propagation in refraction index-varied dielectric material. This dielectric material served as photonic lattice. The behavior of light propagation influenced by variation of refraction index in photonic lattice was investigated. Modes of the guiding light were determined numerically using squared-operator iteration method. It was found that the greater the strength of refraction index, the smaller the guiding modes.

  6. Accuracy of the WASCA aberrometer refraction compared to manifest refraction in myopia.

    PubMed

    Reinstein, Dan Z; Archer, Timothy J; Couch, Darren

    2006-03-01

    To evaluate the accuracy of myopic refraction by a single measurement using the Wavefront Supported Custom Ablation (WASCA) aberrometer (Carl Zeiss Meditec AG, Jena, Germany). We retrospectively compared the refractive errors obtained by manifest refraction and wavefront refraction (WASCA) in 50 eyes of 25 consecutive myopic patients undergoing laser refractive surgery. The sphere ranged from -1.00 to -8.25 diopters (D) and cylinder from 0 to -3.75 D. WASCA measurements under cycloplegia were made and WASCA refractions calculated for a 6-mm analysis zone using the Seidel method within the WASCA. We used the manifest refraction as our best estimate of the true refractive error, therefore accuracy was defined as the difference between manifest refraction and that of the WASCA. Correlation coefficients and mean vector errors between manifest and WASCA refraction were calculated. High correlation was shown between manifest and WASCA refractions, with correlation coefficients (R2) of 0.97, 0.85, and 0.79 for M, J180, and J45, respectively. Mean power vector error (standard deviation) was 0.22 D (0.39), +0.03 D (0.21), and +0.03 D (0.13) for M, J180, and J45, respectively. Total dioptric power vector error was 0.43 D with 74% eyes within 0.50 D. When measuring normal myopic eyes, the concordance between manifest and WASCA refractions was found on average to be high; however, outlier measurements occurred.

  7. Hard x-ray nanofocusing by refractive lenses of constant thickness

    NASA Astrophysics Data System (ADS)

    Seiboth, F.; Scholz, M.; Patommel, J.; Hoppe, R.; Wittwer, F.; Reinhardt, J.; Seidel, J.; Knaut, M.; Jahn, A.; Richter, K.; Bartha, J. W.; Falkenberg, G.; Schroer, C. G.

    2014-09-01

    In order to focus light or x rays, the thickness of a refractive lens is typically varied over its aperture. Here, we present a refractive x-ray lens made of lamellae of constant thickness, the refractive lamellar lens. Refractive power is created by a specific bending of the lamellae rather than by a concave lens profile. This very special design has the technological advantage that materials like sapphire or diamond can be used to make lenses by coating techniques. A first lens prototype focused x rays with a photon energy E = 15.25 keV to a lateral beam size of 164 nm × 296 nm full width at half maximum.

  8. Hard x-ray nanofocusing by refractive lenses of constant thickness

    SciTech Connect

    Seiboth, F. Scholz, M.; Patommel, J.; Hoppe, R.; Wittwer, F.; Reinhardt, J.; Seidel, J.; Knaut, M.; Jahn, A.; Richter, K.; Bartha, J. W.; Falkenberg, G.; Schroer, C. G.

    2014-09-29

    In order to focus light or x rays, the thickness of a refractive lens is typically varied over its aperture. Here, we present a refractive x-ray lens made of lamellae of constant thickness, the refractive lamellar lens. Refractive power is created by a specific bending of the lamellae rather than by a concave lens profile. This very special design has the technological advantage that materials like sapphire or diamond can be used to make lenses by coating techniques. A first lens prototype focused x rays with a photon energy E = 15.25 keV to a lateral beam size of 164 nm × 296 nm full width at half maximum.

  9. Long-term measurements of refractive index structure constant in atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Jicha, Otakar; Pechac, Pavel; Zvanovec, Stanislav; Grabner, Martin; Kvicera, Vaclav

    2012-10-01

    Results of long-term measurements of the refractive index structure constant in the boundary layer are introduced. The measurements were made on a 150-meter-high lattice mast equipped by nineteen meteorological sensors and one pressure sensor at the bottom of the mast. The Kolmogorov statistical theory of turbulence was used to calculate the refractive index structure constant C2n, allowing us to present annual cumulative distribution functions (CDFs) and seasonal quantiles. The quantiles of measured height dependence of the refractive index structure constant are also shown and compared with existing models (Hufnagel/Andrews/Phillips, SLC Day and Gurvich). Parameters of a linear model were calculated to fit the measured median height profile of the refractive index structure constant with the uncertainty of measurements also being addressed.

  10. Flexible method of refraction correction in vision measurement systems with multiple glass ports.

    PubMed

    Gong, Zheng; Liu, Zhen; Zhang, Guangjun

    2017-01-23

    Many vision measurement systems, especially in outdoor engineering, usually utilize glass ports to protect sensors against environmental influences. The refraction caused by glass ports lead to measurement errors in traditional single viewpoint model. Most existing methods only deal with the refraction that happens once, and the glass ports are required to be perpendicular to cameras or the orientations of glass ports are obtained by auxiliary equipment. This paper proposes a corrected 3D reconstruction model based on refraction geometry, which can be used for any number of glass ports with any orientations. The orientation of each glass port is obtained only using refracted and unrefracted images of the same scene, which doesn't need any auxiliary equipment. A series of validation experiments are performed. An existing image rectification method is used to make a comparison. The proposed method is also employed in a train wheelset profile measurement application, which proves that the method is effective in actual applications.

  11. Refractive index engineering of high performance coupler for compact photonic integrated circuits

    NASA Astrophysics Data System (ADS)

    Liu, Lu; Zhou, Zhiping

    2017-04-01

    High performance couplers are highly desired in many applications, but the design is limited by nearly unchangeable material refractive index. To tackle this issue, refractive index engineering method is investigated, which can be realized by subwavelength grating. Subwavelength gratings are periodical structures with pitches small enough to locally synthesize the refractive index of photonic waveguides, which allows direct control of optical profile as well as easier fabrication process. This review provides an introduction to the basics of subwavelength structures and pay special attention to the design strategies of some representative examples of subwavelength grating devices, including: edge couplers, fiber-chip grating couplers, directional couplers and multimode interference couplers. Benefited from the subwavelength grating which can engineer the refractive index as well as birefringence and dispersion, these devices show better performance when compared to their conventional counterparts.

  12. Refractive microlenses for ultraflat photolithographic projection systems

    NASA Astrophysics Data System (ADS)

    Voelkel, Reinhard; Eisner, Martin; Ossmann, Christian; Weible, Kenneth J.

    2000-08-01

    We report on the fabrication of high quality microlens arrays on 4', 6' and 8'-fused silica wafers. Refractive, plano-convex microlenses are fabricated by using photolithography; a reflow or melting resist technique and reactive ion etching. A diffraction-limited optical performance (p-v wave aberrations of < (lambda) /8, Strehl ratio GTR 0.97) is achieved. Aspherical lens profiles are obtained by varying the etch parameters during the reactive ion etching transfer. The microlens arrays are used for Microlens Projection Lithography (MPL) and within UV-light illumination systems. Microlens Projection Lithography is an innovative technique using KARL SUSS Mask Aligners equipped with an ultra-flat microlens-based projection system. The projection system consists of 500.000 identical micro-objectives side- by-side. Each micro-objective consists of 3 to 4 microlenses. A fully symmetrical optical design eliminates coma, distortion and lateral color. The lens system is frontal- and backside telecentric to provide a unit magnification (+1) over the whole depth of focus. Each micro- objective images a small part of the photomask pattern onto the wafer. The partial images from different channels overlap consistently and form a complete aerial image of the photomask. Microlens Projection Lithography provides an increased depth of focus (GTR 50 microns) at a larger working distance ($GTR 1 mm)than standard proximity printing. Microlens Projection Lithography allows photolithography on curved on non-planar substrates, in V-grooves, holes, etc. using a KARL SUSS Mask Aligner.

  13. The eye lens: age-related trends and individual variations in refractive index and shape parameters

    PubMed Central

    Pierscionek, Barbara; Bahrami, Mehdi; Hoshino, Masato; Uesugi, Kentaro; Regini, Justyn; Yagi, Naoto

    2015-01-01

    The eye lens grows throughout life by cell accrual on its surface and can change shape to adjust the focussing power of the eye. Varying concentrations of proteins in successive cell layers create a refractive index gradient. The continued growth of the lens and age-related changes in proteins render it less able to alter shape with loss of capacity by the end of the sixth decade of life. Growth and protein ageing alter the refractive index but as accurate measurement of this parameter is difficult, the nature of such alterations remains uncertain. The most accurate method to date for measuring refractive index in intact lenses has been developed at the SPring-8 synchrotron. The technique, based on Talbot interferometry, has an X-ray source and was used to measure refractive index in sixty-six human lenses, aged from 16 to 91 years. Height and width were measured for forty-five lenses. Refractive index contours show decentration in some older lenses but individual variations mask age-related trends. Refractive index profiles along the optic axis have relatively flat central sections with distinct micro-fluctuations and a steep gradient in the cortex but do not exhibit an age-related trend. The refractive index profiles in the equatorial aspect show statistical significance with age, particularly for lenses below the age of sixty that had capacity to alter shape in vivo. The maximum refractive index in the lens centre decreases slightly with age with considerable scatter in the data and there are age-related variations in sagittal thickness and equatorial height. PMID:26416418

  14. Headache and refractive errors in children.

    PubMed

    Roth, Zachary; Pandolfo, Katie R; Simon, John; Zobal-Ratner, Jitka

    2014-01-01

    To investigate the association between uncorrected or miscorrected refractive errors in children and headache, and to determine whether correction of refractive errors contributes to headache resolution. Results of ophthalmic examination, including refractive error, were recorded at initial visit for headache. If resolution of headache on subsequent visits was not documented, a telephone call was placed to their caregivers to inquire whether headache had resolved. Of the 158 patients, 75.3% had normal or unchanged eye examinations, including refractions.Follow-up data were available for 110 patients. Among those, 32 received new or changed spectacle correction and 78 did not require a change in refraction.Headaches improved in 76.4% of all patients, whether with (71.9%) or without (78.2%) a change in refractive correction. The difference between these two groups was not statistically significant (P = .38). Headaches in children usually do not appear to be caused by ophthalmic disease, including refractive error. The prognosis for improvement is favorable, regardless of whether refractive correction is required. Copyright 2014, SLACK Incorporated.

  15. Measuring Variable Refractive Indices Using Digital Photos

    ERIC Educational Resources Information Center

    Lombardi, S.; Monroy, G.; Testa, I.; Sassi, E.

    2010-01-01

    A new procedure for performing quantitative measurements in teaching optics is presented. Application of the procedure to accurately measure the rate of change of the variable refractive index of a water-denatured alcohol mixture is described. The procedure can also be usefully exploited for measuring the constant refractive index of distilled…

  16. Measuring Variable Refractive Indices Using Digital Photos

    ERIC Educational Resources Information Center

    Lombardi, S.; Monroy, G.; Testa, I.; Sassi, E.

    2010-01-01

    A new procedure for performing quantitative measurements in teaching optics is presented. Application of the procedure to accurately measure the rate of change of the variable refractive index of a water-denatured alcohol mixture is described. The procedure can also be usefully exploited for measuring the constant refractive index of distilled…

  17. Achieving target refraction after cataract surgery.

    PubMed

    Simon, Shira S; Chee, Yewlin E; Haddadin, Ramez I; Veldman, Peter B; Borboli-Gerogiannis, Sheila; Brauner, Stacey C; Chang, Kenneth K; Chen, Sherleen H; Gardiner, Matthew F; Greenstein, Scott H; Kloek, Carolyn E; Chen, Teresa C

    2014-02-01

    To evaluate the difference between target and actual refraction after phacoemulsification and intraocular lens implantation at an academic teaching institution's Comprehensive Ophthalmology Service. Retrospective study. We examined 1275 eye surgeries for this study. All consecutive cataract surgeries were included if they were performed by an attending or resident surgeon from January through December 2010. Postoperative refractions were compared with preoperative target refractions. Patients were excluded if they did not have a preoperative target refraction documented or if they did not have a recorded postoperative manifest refraction within 90 days. The main outcome measure was percentage of cases achieving a postoperative spherical equivalent ± 1.0 diopter (D) of target spherical equivalent. We performed 1368 cataract surgeries from January through December of 2010. Of these, 1275 (93%) had sufficient information for analysis. Of the included cases, 94% (1196 of 1275) achieved ± 1.0 D of target refraction by 90 days after cataract surgery. This paper establishes a new benchmark for a teaching hospital, where 94% of patients achieved within 1.0 D of target refraction after cataract surgery. The refractive outcomes after cataract surgery at this academic teaching institution were higher than average international benchmarks. Copyright © 2014 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

  18. Retinal Image Simulation of Subjective Refraction Techniques.

    PubMed

    Perches, Sara; Collados, M Victoria; Ares, Jorge

    2016-01-01

    Refraction techniques make it possible to determine the most appropriate sphero-cylindrical lens prescription to achieve the best possible visual quality. Among these techniques, subjective refraction (i.e., patient's response-guided refraction) is the most commonly used approach. In this context, this paper's main goal is to present a simulation software that implements in a virtual manner various subjective-refraction techniques--including Jackson's Cross-Cylinder test (JCC)--relying all on the observation of computer-generated retinal images. This software has also been used to evaluate visual quality when the JCC test is performed in multifocal-contact-lens wearers. The results reveal this software's usefulness to simulate the retinal image quality that a particular visual compensation provides. Moreover, it can help to gain a deeper insight and to improve existing refraction techniques and it can be used for simulated training.

  19. Retinal Image Simulation of Subjective Refraction Techniques

    PubMed Central

    Perches, Sara; Collados, M. Victoria; Ares, Jorge

    2016-01-01

    Refraction techniques make it possible to determine the most appropriate sphero-cylindrical lens prescription to achieve the best possible visual quality. Among these techniques, subjective refraction (i.e., patient’s response-guided refraction) is the most commonly used approach. In this context, this paper’s main goal is to present a simulation software that implements in a virtual manner various subjective-refraction techniques—including Jackson’s Cross-Cylinder test (JCC)—relying all on the observation of computer-generated retinal images. This software has also been used to evaluate visual quality when the JCC test is performed in multifocal-contact-lens wearers. The results reveal this software’s usefulness to simulate the retinal image quality that a particular visual compensation provides. Moreover, it can help to gain a deeper insight and to improve existing refraction techniques and it can be used for simulated training. PMID:26938648

  20. Refracting surface plasmon polaritons with nanoparticle arrays.

    PubMed

    Radko, Ilya P; Evlyukhin, Andrey B; Boltasseva, Alexandra; Bozhevolnyi, Sergey I

    2008-03-17

    Refraction of surface plasmon polaritons (SPPs) by various structures formed by a 100-nm-period square lattice of gold nanoparticles on top of a gold film is studied by leakage radiation microscopy. SPP refraction by a triangular-shaped nanoparticle array indicates that the SPP effective refractive index increases inside the array by a factor of approximately 1.08 (for the wavelength 800 nm) with respect to the SPP index at a flat surface. Observations of SPP focusing and deflection by circularly shaped areas as well as SPP waveguiding inside rectangular arrays are consistent with the SPP index increase deduced from the SPP refraction by triangular arrays. The SPP refractive index is found to decrease slightly for longer wavelengths within the wavelength range of 700-860 nm. Modeling based on the Green's tensor formalism is in a good agreement with the experimental results, opening the possibility to design nanoparticle arrays for specific applications requiring in-plane SPP manipulation.

  1. Optical Evaluation of a Refractive Secondary Concentrator

    NASA Technical Reports Server (NTRS)

    Jaworske, Donald A.; Wong, Wayne A.; Skowronski, Timothy J.

    1999-01-01

    Refractive secondary concentrators are being considered for solar thermal applications because of their ability to archive maximum efficiency through the use of total internal reflection for the concentration and distribution of solar energy. A prototype refractive secondary concentrator was built based on ray tracing analysis to demonstrate this collection and distribution concept. The design included a conical secondary concentrator and a faceted extractor. The objective of this effort was to functionally evaluate the performance of the refractive secondary concentrator/extractor prototype and to compare the results with modeling. Most of the light was found to exit the refractive secondary concentrator through the extractor. In addition, the degree of attenuation encountered by the light as it passed through the refractive secondary concentrator was of interest. Quantifying optical output and validating the modeling will provide further understanding of the efficiency of the prototype and will provide insight for additional design and materials selection activities.

  2. The Northern Walker Lane Seismic Refraction Experiment

    NASA Astrophysics Data System (ADS)

    Louie, J. N.; Smith, S. B.; Thelen, W.; Scott, J. B.; Clark, M.

    2002-12-01

    We are developing a three-dimensional reference seismic velocity model for the western Great Basin region of Nevada and eastern California. The northern Walker Lane had not been characterized well by previous work. In May 2002 we collected a new crustal refraction profile from Battle Mountain, Nev. across western Nevada, the Reno area, Lake Tahoe, and the northern Sierra to Auburn, Calif. Mine blasts and earthquakes were recorded by 199 Texan instruments (loaned by the PASSCAL Instrument Center) extending across this more than 450-km-long transect. The seismic sources at the eastern end were mining blasts at Barrick's GoldStrike pit. We recorded additional blasts at the Florida Canyon and other mines between Lovelock and Battle Mountain, Nevada. The GoldStrike mine produced several ripple-fired blasts using 10,000-40,000 kg of ANFO each. First arrivals from the larger blasts are obvious to distances exceeding 250 km in the raw records. A M2.4 earthquake near Bridgeport, Calif. also produced pickable P-wave arrivals across at least half the transect, providing fan-shot data. We recorded only during working hours, and so missed an M4 earthquake that occurred at night. Events of M2 occurred during our recording to the west on the San Andreas fault near Pinnacles, Calif.; M3 events occurred near Portola and Mammoth Lakes, Calif. Arrivals from M5 events in the Mariana and Kuril Islands also appear in the records. Time-picks from these earthquakes may be possible after more work on synthetic-time modeling, data filtering, and display. We plan to record blasts at quarries in the western Sierra in future experiments, for a direct refraction reversal. We will compare our time picks against times generated from regional velocity models, to identify potential crustal and upper-mantle velocity anomalies. Such anomalies may be associated with the Battle Mountain heat-flow high, the northern Walker Lane belt, or the northern Sierran block.

  3. The correlation between headache and refractive errors.

    PubMed

    Akinci, Arsen; Güven, Alev; Degerliyurt, Aydan; Kibar, Esin; Mutlu, Murad; Citirik, Mehmet

    2008-06-01

    To compare the prevalence of refractive errors in patients with headache and a control population. Three hundred ten patients with headache and 843 controls were retrospectively evaluated. Complete ophthalmologic examination was performed in the headache group. Autorefraction was performed in all participants (with cycloplegia under 10 years of age). Myopia was defined as the spherical equivalent refraction of at least -0.50 D, hyperopia as the spherical equivalent refraction of at least +2.0 D, and astigmatism as the cylinder of at least 1.0 D. Main outcome measures were refractive error, anisometropia, and previous miscorrection of refractive error. Chi-square and Student's t-tests were used for statistical analysis. Total prevalence of refractive errors was higher in the headache group (p = 0.002). The rate of astigmatism was higher in the headache group (p < 0.0001), while that of myopia and hyperopia were similar in both groups (p = 0.74, p = 0.79, respectively). The rates of compound and mixed astigmatism were higher in the headache group (p = 0.026, p < 0.001, respectively). The rates of anisometropia and previous miscorrection of refractive error were higher in the headache group (p < 0.0001 for both). Children with headache have a statistically significant increased risk of total refractive errors (OR = 1.57, 95% CI: 1.18-2.07), anisometropia (OR = 9.59, 95% CI: 5.72-16.1), and miscorrection of refractive error (OR = 9.57, 95% CI: 5.43-16.9). Compound and mixed types of astigmatism, anisometropia, and miscorrection of refractive error were found more often in patients with headache than in control subjects.

  4. The Refractive Error of Professional Baseball Players.

    PubMed

    Laby, Daniel M; Kirschen, David G

    2017-05-01

    High levels of visual acuity are required to hit a baseball effectively. Research has shown that any decrease in vision is likely caused by low-order optical aberrations. This study is designed to validate the SVOne autorefractor, and describe the amount and type, of low-order optical aberrations present in a large cohort of professional baseball players. A retrospective chart review on the 608 Major League Baseball players evaluated during the 2016 Spring Training Season was performed. Results for a subset of players who had both manifest refraction as well as autorefraction were calculated. Subsequently, after determining the accuracy of the autorefraction system in this population, refractive results for the entire population were determined. There was a borderline statistically significant difference in mean spherical refractive error (M) between the manifest refraction and the SVOne auto refraction (-0.273D in the manifest refraction method vs. -0.503D in the SVOne method, P = .06) in the subset of athletes who underwent both tests. Additionally, there was no difference in the J0 or J45 cylindrical component vectors for each method. For the entire eligible population, the SVOne autorefraction system found a mean spherical refractive error (M) of -0.228D, a J0 value of -0.013D, and a J45 value of -0.040D. These data suggest that the SVOne autorefraction system is generally able to measure the refractive error in the baseball population. The system was slightly biased, often reporting more myopia in myopic subjects. Thus, careful evaluation of the refractive status of these athletes coupled with careful subjective refractive correction for those with less than average vision for baseball is strongly suggested.

  5. Refractive beam shapers for optical systems of lasers

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Laskin, Vadim; Ostrun, Aleksei

    2015-02-01

    Performance of modern high-power lasers can be strongly improved by control of irradiance distribution in laser optical systems: flat-top or super-Gaussian irradiance profiles are optimum for amplification in MOPA lasers and for reduction of thermal effects in crystals of solid-state ultra-short pulse lasers; variable profiles are also important in irradiating of photocathode of Free Electron lasers (FEL). This task can be easily solved with using beam shaping optics, for example, the field mapping refractive beam shapers like Shaper. The operational principle of these devices presumes transformation of laser beam intensity from Gaussian to flattop one with high flatness of output wavefront, saving of beam consistency, providing collimated output beam of low divergence, high transmittance, extended depth of field, negligible residual wave aberration, and achromatic design provides capability to work with ultra-short pulse lasers having broad spectrum. With using the same Shaper it is possible to realize various beam profiles like flattop, inverse Gauss or super Gauss by simple variation of input beam diameter. This paper will describe some design basics of refractive beam shapers of the field mapping type and optical layouts of their applying in optical systems of high-power lasers. Examples of real implementations and experimental results will be presented as well.

  6. 3D refractive index measurements of special optical fibers

    NASA Astrophysics Data System (ADS)

    Yan, Cheng; Huang, Su-Juan; Miao, Zhuang; Chang, Zheng; Zeng, Jun-Zhang; Wang, Ting-Yun

    2016-09-01

    A digital holographic microscopic chromatography-based approach with considerably improved accuracy, simplified configuration and performance stability is proposed to measure three dimensional refractive index of special optical fibers. Based on the approach, a measurement system is established incorporating a modified Mach-Zehnder interferometer and lab-developed supporting software for data processing. In the system, a phase projection distribution of an optical fiber is utilized to obtain an optimal digital hologram recorded by a CCD, and then an angular spectrum theory-based algorithm is adopted to extract the phase distribution information of an object wave. The rotation of the optic fiber enables the experimental measurements of multi-angle phase information. Based on the filtered back projection algorithm, a 3D refraction index of the optical fiber is thus obtained at high accuracy. To evaluate the proposed approach, both PANDA fibers and special elliptical optical fiber are considered in the system. The results measured in PANDA fibers agree well with those measured using S14 Refractive Index Profiler, which is, however, not suitable for measuring the property of a special elliptical fiber.

  7. Peripheral refraction in pseudophakic eyes measured by infrared scanning photoretinoscopy.

    PubMed

    Tabernero, Juan; Ohlendorf, Arne; Fischer, M Dominik; Bruckmann, Anna R; Schiefer, Ulrich; Schaeffel, Frank

    2012-05-01

    To obtain quantitative data of peripheral refractive errors in pseudophakic eyes including measurements up to ±45 degrees on the retina. University Eye Hospital, Tübingen, Germany. Population-based cross-sectional study. Pseudophakic and phakic subjects were measured with a purpose-built scanning photorefractor. The instrument was improved over previous versions. It permits measurement of semicontinuous peripheral profiles over the central 90-degree field of the retina at a faster speed (4 s/scan). Twenty-four pseudophakic and 43 phakic subjects were enrolled. The intraocular lenses (IOLs) induced a mean myopic shift of 2.00 diopters (D) at ±45 degrees of eccentricity in the vertical pupil meridian. Ray-tracing simulations with phakic eye and pseudophakic eye models agreed well with the experimental data. They showed that changes induced by IOLs were a consequence of an increase in astigmatism with eccentricity and a myopic shift in the spherical equivalent. The peripheral refractions in pseudophakic eyes were more myopic than in phakic eyes as a consequence of the optical design of the IOLs. Whether a more myopic refraction of approximately 2.00 D at 45 degrees has significant effects on visual performance must be tested. Perhaps there is room for improvement in the peripheral optics of IOLs. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  8. Microvolume index of refraction determinations by interferometric backscatter

    NASA Astrophysics Data System (ADS)

    Bornhop, Darryl J.

    1995-06-01

    A new method has been applied to the determination of fluid bulk properties in small detection volumes. Through the use of an unfocused He-Ne laser beam and a cylindrical tube of capillary dimensions, relative refractive-index measurements are possible. The backscattered light from the illumination of a tube of capillary dimensions produces an interference pattern that is spatially defined and that contains information related to the bulk properties of the fluid contained in the tube. Positional changes in the intensity-modulated beam profile (interference fringes) are directly related to the refractive index of the fluid in the tube. The determination of dn/n at the 10-7 level is possible in probe volumes of 350 pL. The technique has been applied to tubes as small as 75 mu m inner diameter and as large as 1.0 mm inner diameter. No modification of the simple optical bench is required for facilitating the determination of refractive index for the complete range of tube diameters.

  9. Is LASIK for Me? A Patient's Guide to Refractive Surgery

    MedlinePlus

    ... reading or driving at night. The greater your refractive error (that is, the greater your nearsightedness, farsighted- ness ... thickness of your cornea before surgery. • degree of refractive error . Very high levels of refractive error (nearsighted- ness, ...

  10. Reproducibility of manifest refraction between surgeons and optometrists in a clinical refractive surgery practice.

    PubMed

    Reinstein, Dan Z; Yap, Timothy E; Carp, Glenn I; Archer, Timothy J; Gobbe, Marine

    2014-03-01

    To measure and compare the interobserver reproducibility of manifest refraction according to a standardized protocol for normal preoperative patients in a refractive surgery practice. Private clinic, London, United Kingdom. Retrospective case series. This retrospective study comprised patients attending 2 preoperative refractions before laser vision correction. The first manifest refraction was performed by 1 of 7 optometrists and the second manifest refraction by 1 of 2 surgeons, all trained using a standard manifest refraction protocol. Spherocylindrical data were converted into power vectors for analysis. The dioptric power differences between observers were calculated and analyzed. One thousand nine hundred twenty-two consecutive eyes were stratified into a myopia group and a hyperopia group and then further stratified by each surgeon-optometrist combination. The mean surgeon-optometrist dioptric power difference was 0.21 diopter (D) (range 0.15 to 0.32 D). The mean difference in spherical equivalent refraction was 0.03 D, with 95% of all refractions within ±0.44 D for all optometrist-surgeon combinations. The severity of myopic or hyperopic ametropia did not affect the interobserver reproducibility of the manifest refraction. There was close agreement in refraction between surgeons and optometrists using a standard manifest refraction protocol of less than 0.25 D. This degree of interobserver repeatability is similar to that in intraobserver repeatability studies published to date and may represent the value of training and the use of a standard manifest refraction protocol between refraction observers in a refractive surgery practice involving co-management between surgeons and optometrists. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  11. Planoconcave lens by negative refraction of stacked subwavelength hole arrays.

    PubMed

    Beruete, M; Navarro-Cía, M; Sorolla, M; Campillo, I

    2008-06-23

    This work presents the design of a planoconcave parabolic negative index metamaterial lens operating at millimeter wavelengths fabricated by using stacked subwavelength hole arrays. A staircase approximation to the ideal parabola profile has been done by removing step by step one lattice in each dimension of the transversal section. Theory predicts power concentration at the focal point of the parabola when the refractive index equals -1. Both simulation and measurement results exhibit an excellent agreement and an asymmetrical focus has been observed. The possibility to design similar planoconcave devices in the terahertz and optical wavelengths could be a reality in the near future.

  12. Fully 3D refraction correction dosimetry system.

    PubMed

    Manjappa, Rakesh; Makki, S Sharath; Kumar, Rajesh; Vasu, Ram Mohan; Kanhirodan, Rajan

    2016-02-21

    The irradiation of selective regions in a polymer gel dosimeter results in an increase in optical density and refractive index (RI) at those regions. An optical tomography-based dosimeter depends on rayline path through the dosimeter to estimate and reconstruct the dose distribution. The refraction of light passing through a dose region results in artefacts in the reconstructed images. These refraction errors are dependant on the scanning geometry and collection optics. We developed a fully 3D image reconstruction algorithm, algebraic reconstruction technique-refraction correction (ART-rc) that corrects for the refractive index mismatches present in a gel dosimeter scanner not only at the boundary, but also for any rayline refraction due to multiple dose regions inside the dosimeter. In this study, simulation and experimental studies have been carried out to reconstruct a 3D dose volume using 2D CCD measurements taken for various views. The study also focuses on the effectiveness of using different refractive-index matching media surrounding the gel dosimeter. Since the optical density is assumed to be low for a dosimeter, the filtered backprojection is routinely used for reconstruction. We carry out the reconstructions using conventional algebraic reconstruction (ART) and refractive index corrected ART (ART-rc) algorithms. The reconstructions based on FDK algorithm for cone-beam tomography has also been carried out for comparison. Line scanners and point detectors, are used to obtain reconstructions plane by plane. The rays passing through dose region with a RI mismatch does not reach the detector in the same plane depending on the angle of incidence and RI. In the fully 3D scanning setup using 2D array detectors, light rays that undergo refraction are still collected and hence can still be accounted for in the reconstruction algorithm. It is found that, for the central region of the dosimeter, the usable radius using ART-rc algorithm with water as RI matched

  13. Fully 3D refraction correction dosimetry system

    NASA Astrophysics Data System (ADS)

    Manjappa, Rakesh; Sharath Makki, S.; Kumar, Rajesh; Mohan Vasu, Ram; Kanhirodan, Rajan

    2016-02-01

    The irradiation of selective regions in a polymer gel dosimeter results in an increase in optical density and refractive index (RI) at those regions. An optical tomography-based dosimeter depends on rayline path through the dosimeter to estimate and reconstruct the dose distribution. The refraction of light passing through a dose region results in artefacts in the reconstructed images. These refraction errors are dependant on the scanning geometry and collection optics. We developed a fully 3D image reconstruction algorithm, algebraic reconstruction technique-refraction correction (ART-rc) that corrects for the refractive index mismatches present in a gel dosimeter scanner not only at the boundary, but also for any rayline refraction due to multiple dose regions inside the dosimeter. In this study, simulation and experimental studies have been carried out to reconstruct a 3D dose volume using 2D CCD measurements taken for various views. The study also focuses on the effectiveness of using different refractive-index matching media surrounding the gel dosimeter. Since the optical density is assumed to be low for a dosimeter, the filtered backprojection is routinely used for reconstruction. We carry out the reconstructions using conventional algebraic reconstruction (ART) and refractive index corrected ART (ART-rc) algorithms. The reconstructions based on FDK algorithm for cone-beam tomography has also been carried out for comparison. Line scanners and point detectors, are used to obtain reconstructions plane by plane. The rays passing through dose region with a RI mismatch does not reach the detector in the same plane depending on the angle of incidence and RI. In the fully 3D scanning setup using 2D array detectors, light rays that undergo refraction are still collected and hence can still be accounted for in the reconstruction algorithm. It is found that, for the central region of the dosimeter, the usable radius using ART-rc algorithm with water as RI matched

  14. Long-Term Global Distributions of Mesoscale Variations in Atmospheric Radio Refraction Obtained from the GPS Champ Satellite Data

    NASA Astrophysics Data System (ADS)

    Gavrilov, N. M.; Manuilova, R. O.

    2016-12-01

    We obtain average global distributions of the variances of the mesoscale variations in the atmospheric radio-refraction index (refractive index) at altitudes of 5-35 km from the data of the radio-occultation experiments performed during operation of the low-orbit GPS CHAMP satellite in the period 2001-2009. The filtering of the vertical profiles of the radio-refraction index allows one to determine the variances of the variations with vertical scales below 8 km. The latitudinal-temporal distributions of the zonal-mean variances of the index demonstrate significant interannual variations at various altitudes. Seasonal variations in the variances of radio refraction are studied. Quasi-biennial oscillations at low latitudes are revealed. Acoustic-gravity waves and turbulent and convective motions in the atmosphere can cause a spread of the radio-refraction index.

  15. Reflection and refraction seismic on the great Ancona landslide

    NASA Astrophysics Data System (ADS)

    Stucchi, E.; Mazzotti, A.

    2003-04-01

    The Adriatic coast in Italy is characterised by the occurrence of several landslide bodies, some of which of huge extension. Here we present the results of seismic refraction and reflection studies recently carried out on the Ancona Landslide, which is located immediately westward of the harbour city of Ancona, and interests an area of about 3.5 km^2 with a landslide front of 2 km. The acquired seismic profile crosses the entire landslide body and was performed employing land and marine sources and receivers. Thus it allows the simultaneous acquisition of marine-marine, marine-land, land-marine and land-land data. The most significant acquisition parameters are: nominal maximum source-receiver offset 600 m, receiver group interval 5 m, single airgun and small explosive charges as energy sources, profile length 1.5 km, average reflection coverage on land 4000% and at sea 20000%. Notwithstanding the significant noise contamination due to intense human activities (road, naval and railway traffic) in the area, the data shows good first breaks and reflections which we use for refraction and reflection processing. The refraction study makes use of GRM and other techniques (Lawton) and it leads to a good definition of the shallower landslide bodies but it is not able to depict the deeper decollement surface. It is also very useful in providing a detailed near surface velocity model that is crucial for the determination of accurate static corrections for the reflection data. High quality subsurface images are achieved by applying different processing sequences to the different sets (marine, land or land-marine) of reflection seismic data. The processing steps that turned out as more effective to the achievement of such a quality were the noise removal by means of FX and SVD filtering, the attenuation of the bubble effect for the marine source data, the ground roll attenuation and the computation of accurate statics. The outcomes of the refraction and reflection

  16. Source localization from an elevated acoustic sensor array in a refractive atmosphere.

    PubMed

    Ostashev, Vladimir E; Scanlon, Michael V; Wilson, D Keith; Vecherin, Sergey N

    2008-12-01

    Localization of sound sources on the ground from an acoustic sensor array elevated on a tethered aerostat is considered. To improve estimation of the source coordinates, one should take into account refraction of sound rays due to atmospheric stratification. Using a geometrical acoustics approximation for a stratified moving medium, formulas for the source coordinates are derived that account for sound refraction. The source coordinates are expressed in terms of the direction of sound propagation as measured by the sensor array, its coordinates, and the vertical profiles of temperature and wind velocity. Employing these formulas and typical temperature and wind velocity profiles in the atmosphere, it is shown numerically that sound refraction is important for accurate predictions of the source coordinates. Furthermore, it is shown that the effective sound speed approximation, which is widely used in atmospheric acoustics, fails to correctly predict the source coordinates if the grazing angle of sound propagation is relatively large.

  17. A study of refraction of a cylindrical laser beam in stratified liquid

    NASA Astrophysics Data System (ADS)

    Rinkevichyus, B. S.; Sapronov, M. V.; Pavlov, I. N.

    2016-09-01

    Refraction of a cylindrical laser beam in a transition layer at the interface of two liquids with different optical characteristics is studied theoretically and experimentally. A theoretical basis for calculations of the beam trajectory in the transition layer of stratified liquid is given. Two- and three-dimensional images (2D and 3D refractograms) of a cylindrical laser beam inside and outside the media are obtained on the basis of a tangential model of the refractive index profile. The influence of the parameters of the laser beam and media on the appearance of refractograms is studied and the optimal experimental conditions are selected with the use of computer simulation. A scheme of the setup for recording digital 2D refractogram and experimental results are presented. Algorithms for digitizing experimental images and for their comparison with calculated refractograms to determine the refractive index profile in the transition layer based on the tangential model are developed.

  18. Novel characterization of the nonlinear refractive response of materials using spatially and spectrally resolved interferometry

    NASA Astrophysics Data System (ADS)

    Meier, Amanda; Adams, Daniel; Squier, Jeff; Durfee, Charles

    2010-10-01

    Characterization of the nonlinear refractive index of a material is important in order to fully understand the nonlinear propagation of femtosecond laser pulses. The most common method to obtaining the nonlinear refractive index is Z-scan. However, since it averages over pulse duration and beam profile, Z-scan is not reliable when there is time- and intensity-dependence of the nonlinear response. The new method we are exploring to make these nonlinear refractive index measurements is spatially and spectrally resolved interferometry (SSRI). SSRI is a method that can give a simultaneous measurement of the spatial wave-front across the frequency or temporal profile of the pulse. The SSRI method proves better in measuring response at specific y and t, allowing it to measure both delayed response and saturation effects. The ability to make a measurement in both dimensions enables understanding of spatiotemporal dynamics in other experiments as cross-wave polarization and filamentation.

  19. Negative refraction in anisotropic composites

    NASA Astrophysics Data System (ADS)

    Chui, S. T.

    2004-03-01

    Left-handed materials (LHM) are materials in which the direction of wave propagation S is opposite to the wave vector k . S <0 .[1,2,3] LHM exhibit nagative refraction. Experiments have been carried out on a medium consisting of arrays of metallic rings and wrires.[3] An example of a different class of anisotropic left-handed materials are metallic magnetic granular composites. Based on the effective medium approximation, we show that by incorporating metallic magnetic nanoparticles into an appropriate insulating matrix, it may be possible to prepare a composite medium of low eddy current loss which is left-handed for electromagnetic waves propagating in some special direction and polarization in a frequency region near the ferromagnetic resonance frequency.[4,5] This composite may be easier to make on an industrial scale. In addition, its physical properties may be easily tuned by rotating the magnetization locally. The physics involved seems to be different from the original argument.[1,2] In our argument[5], the imaginary part of the dielectric constant of the metal is much larger than the real part, opposite to the original argument. In anisotropic materials so that some of the susceptibilities are negative, the criterion for LHM may not be the same as that for negative refraction.[6] Ansiotropic materials exhibit a richer manifold of anomlous behaviour[6,7,8] and offers more flexibility in apllications.[8] More recently it was found that negative refraction can occur in anisotropic materials where all the susceptibilities are positive.[9] We found that the range of applicability of this effect is much larger than originally thought.[10] S. T. Chui was supported in part by the Office of Naval Research, by the Army Research Laboratory through the Center of Composite Materials at the University of Delaware, by DARPA and by the NSF. [1] J.B.Pendry, A.J.Holden, W.J.Stewart, and I.Youngs, Phys. Rev. Lett 76, 4773 (1996). [2] V.G.Veselago, Sov. Phys. Usp. 10, 509

  20. [Does refractive surgery really make eyeglasses superfluous?].

    PubMed

    Seiler, T

    2001-06-14

    Spectacles have become a problem of life-style in some societies. In the USA, in 1999 approximately 1 million LASIK operations have been performed to correct myopia and astigmatism and in Europe the frequency of refractive surgery stead by increases. However, only 3 to 5% of these operations are medically indicated. Refractive surgery is evaluated regarding safety and efficacy. Modern laser techniques demonstrate excellent refractive results: photorefractive keratectomy (PRK) achieved refractive success rates of 90% and more with complication rates of 0.5% and less. PRK is, therefore, a valuable technique for corrections of myopia up to -6.0 D. Similar efficacy is obtained with LASIK (laser in situ keratomileusis) in corrections up to -10 D, however, the complication rate is somewhat higher. Laser correction of hyperopia is equally successful regarding the refractive success but shows an even higher complication rate and the patient satisfaction is lower. Modern refractive laser surgery may replace spectacles in the majority of the cases, however, none of the techniques is free of complications. Therefore, we understand refractive surgery still to be inferior to the correction of ametropia by means of spectacles and any such operation should be attempted only after thorough discussion.

  1. J. B. Biot and Refraction Calculations

    NASA Astrophysics Data System (ADS)

    Young, A. T.

    2000-12-01

    The Auer-Standish (AJ 119, 2472, 2000) algorithm, recommended in the revised Explanatory Supplement for calculating refraction in an arbitrary model atmosphere, was derived and used by J. B. Biot (Conn. des Tems pour l'An 1839) a century and a half earlier, using Newton's (wrong) emission theory, and the clumsy notation of Laplace's Mécanique Céleste, which Biot had proof-read. Newton, Laplace, and Biot all describe refraction in terms of the trajectories of ``luminous molecules'' attracted by a central force exerted by the atmosphere; this explains why Laplace considered refraction a topic in celestial mechanics. Fortunately for these authors, the only optics required is Snel's law of refraction, which was discovered before Newton's birth, and which Newton's corpuscular optics was rigged to reproduce. Thus Biot's ``derivation'' of the refractive invariant nr sin z by Laplace's method is a circular and unnecessary argument. While Auer & Standish were reinventing Biot's method, the historian D. T. Whiteside (Centaurus 24, 288, 1980) noticed the mathematical similarity of the refraction theories of Newton and Biot to modern ones, and rashly concluded that ``working astronomers still find computational advantage in maintaining the fiction of a Newtonian emission theory'' --- which is absurd nonsense! Despite being an emissionist, Biot understood atmospheric refraction much better than most astronomers do today: he knew why refraction is almost independent of atmospheric structure, except within a few degrees of the horizon, and that refraction at the horizon depends mostly on the local temperature gradient. His work --- together with that of Lord Rayleigh, who derived his eponymous scattering law from the elastic-solid theory of the luminiferous \\ae ther --- reminds us that a theory's correct results do not make it true. This work was supported by NSF grant ATM-9714357.

  2. [Calculations of mean refraction and variation of refraction using a dioptric space].

    PubMed

    Touzeau, O; Costantini, E; Gaujoux, T; Borderie, V; Laroche, L

    2010-11-01

    Polar notations (sphere, cylinder, and axis) of refraction perfectly characterize a single refraction but are not suitable for statistical analysis or graphic representation. While the spherical component of refraction can be easily analyzed by the spherical equivalent, statistical analysis of astigmatism requires non-polar expressions of refraction. Indeed, the cylinder and axis of astigmatism are not independent data. In addition, axis is a directional data including a non-trigonometric cycle. Refraction can be written in a non-polar notation by three rectangular coordinates (x, y, z), which can also represent the spherocylinder by one point in a dioptric space. These three coordinates constitute three independent (orthogonal) variables that correspond to a sphere-equivalent component and a pair of Jackson cross-cylinder components, oriented at 0°/90° (WTR/ATR astigmatism) and 45°/135° (oblique astigmatism). Statistical analysis and graphical representation become less complicated when using rectangular coordinates of refraction. Rectangular coordinates of the mean refraction are obtained by average rectangular coordinates. Similarly, rectangular coordinates of refraction change are obtained by a single subtraction of rectangular coordinates between the final and initial refractions. After statistical analysis, the rectangular coordinates obtained can be converted into a polar form for a more easily understood result. Finally, non-polar notations including rectangular coordinates are useful for statistical and graphical analysis, which would be difficult with only conventional polar notations of refraction.

  3. Formation of bulk refractive index structures

    DOEpatents

    Potter, Jr., Barrett George; Potter, Kelly Simmons; Wheeler, David R.; Jamison, Gregory M.

    2003-07-15

    A method of making a stacked three-dimensional refractive index structure in photosensitive materials using photo-patterning where first determined is the wavelength at which a photosensitive material film exhibits a change in refractive index upon exposure to optical radiation, a portion of the surfaces of the photosensitive material film is optically irradiated, the film is marked to produce a registry mark. Multiple films are produced and aligned using the registry marks to form a stacked three-dimensional refractive index structure.

  4. Negative refraction in Möbius molecules

    NASA Astrophysics Data System (ADS)

    Fang, Y. N.; Shen, Yao; Ai, Qing; Sun, C. P.

    2016-10-01

    We theoretically show the negative refraction existing in Möbius molecules. The negative refractive index is induced by the nontrivial topology of the molecules. With the Möbius boundary condition, the effective electromagnetic fields felt by the electron in a Möbius ring is spatially inhomogeneous. In this regard, the DN symmetry is broken in Möbius molecules and thus the magnetic response is induced through the effective magnetic field. Our findings provide an alternative architecture for negative refractive index materials based on the nontrivial topology of Möbius molecules.

  5. X-ray refraction effect and density determination of steep-gradient, high-density plasma

    NASA Astrophysics Data System (ADS)

    Miyanaga, N.; Kato, Y.; Yamanaka, C.

    1982-12-01

    X-ray defraction due to the steep density gradient of a laser-produced plasma has been observed. Distribution of the density gradient was determined from the measured refraction angle. Estimation of the radial density profile and the density scale length in the high-density region near the ablation surface are presented.

  6. International Society of Refractive Surgery of the American Academy of Ophthalmology

    MedlinePlus

    ... to Epithelial Thickness Profile Changes" Go to the Journal of Refractive Surgery » Trending on ISRS Now Visit the ISRS Facebook page to read why Irish Open champion Rory McIlroy says having LASIK surgery helped his golf game. Discover the Benefits of ISRS ISRS is the leading organization for ...

  7. Understanding refraction contrast using a comparison of absorption and refraction computed tomographic techniques

    NASA Astrophysics Data System (ADS)

    Wiebe, S.; Rhoades, G.; Wei, Z.; Rosenberg, A.; Belev, G.; Chapman, D.

    2013-05-01

    Refraction x-ray contrast is an imaging modality used primarily in a research setting at synchrotron facilities, which have a biomedical imaging research program. The most common method for exploiting refraction contrast is by using a technique called Diffraction Enhanced Imaging (DEI). The DEI apparatus allows the detection of refraction between two materials and produces a unique ''edge enhanced'' contrast appearance, very different from the traditional absorption x-ray imaging used in clinical radiology. In this paper we aim to explain the features of x-ray refraction contrast as a typical clinical radiologist would understand. Then a discussion regarding what needs to be considered in the interpretation of the refraction image takes place. Finally we present a discussion about the limitations of planar refraction imaging and the potential of DEI Computed Tomography. This is an original work that has not been submitted to any other source for publication. The authors have no commercial interests or conflicts of interest to disclose.

  8. REFractions: The Representing Equivalent Fractions Game

    ERIC Educational Resources Information Center

    Tucker, Stephen I.

    2014-01-01

    Stephen Tucker presents a fractions game that addresses a range of fraction concepts including equivalence and computation. The REFractions game also improves students' fluency with representing, comparing and adding fractions.

  9. Negative index of refraction in optical metamaterials.

    PubMed

    Shalaev, Vladimir M; Cai, Wenshan; Chettiar, Uday K; Yuan, Hsiao-Kuan; Sarychev, Andrey K; Drachev, Vladimir P; Kildishev, Alexander V

    2005-12-15

    A double-periodic array of pairs of parallel gold nanorods is shown to have a negative refractive index in the optical range. Such behavior results from the plasmon resonance in the pairs of nanorods for both the electric and the magnetic components of light. The refractive index is retrieved from direct phase and amplitude measurements for transmission and reflection, which are all in excellent agreement with simulations. Both experiments and simulations demonstrate that a negative refractive index n' approximately -0.3 is achieved at the optical communication wavelength of 1.5 microm using the array of nanorods. The retrieved refractive index critically depends on the phase of the transmitted wave, which emphasizes the importance of phase measurements in finding n'.

  10. A fully automated remote refraction system.

    PubMed

    Dyer, A M; Kirk, A H

    2000-01-01

    Traditional methods of performing refractions depend on a trained refractionist being present with the subject and conducting an interactive form of subjective testing. A fully automated refraction system was installed in 13 optical dispensaries and after 15 months the patient and statistical information was gathered. The data from all operators were consistent and suggested a lack of operator effect on the refraction results. The mean of the SD of subjective sphere measurements was 0.2, or slightly less than a quarter dioptre, which would be an acceptable level of accuracy for ordering corrective lenses. The present study suggests an absence of operator influence on the results of the refractions and a degree of consistency and accuracy compatible with the prescription of lenses.

  11. Isaac Newton and the astronomical refraction.

    PubMed

    Lehn, Waldemar H

    2008-12-01

    In a short interval toward the end of 1694, Isaac Newton developed two mathematical models for the theory of the astronomical refraction and calculated two refraction tables, but did not publish his theory. Much effort has been expended, starting with Biot in 1836, in the attempt to identify the methods and equations that Newton used. In contrast to previous work, a closed form solution is identified for the refraction integral that reproduces the table for his first model (in which density decays linearly with elevation). The parameters of his second model, which includes the exponential variation of pressure in an isothermal atmosphere, have also been identified by reproducing his results. The implication is clear that in each case Newton had derived exactly the correct equations for the astronomical refraction; furthermore, he was the first to do so.

  12. Development of a subjective refraction simulator

    NASA Astrophysics Data System (ADS)

    Perches, S.; Ares, J.; Collados, M. V.

    2013-11-01

    We have developed simulation software by Matlab (MathworksInc.) with a graphical interface designed for non-expert users. This simulator allows you to complete the process of subjective refraction starting from the aberrometry of the patients and analyse the influence of different factors during the exam. In addition to explain the graphical interface and its working, we show two examples about a complete process of subjective refraction with the influence of high order aberrations and without them showing the retinal image obtained in each step of the refraction process. When the Jackson Cross-Cylinder technique is made with this software, it becomes clear the difficulty of chosen between two images when high order aberrations are present. Therefore, the variability of response during the refraction can be a problem when the examiner has to reach an adequate optical prescription.

  13. Nonlinear negative refraction by difference frequency generation

    SciTech Connect

    Cao, Jianjun; Shen, Dongyi; Feng, Yaming; Wan, Wenjie

    2016-05-09

    Negative refraction has attracted much interest for its promising capability in imaging applications. Such an effect can be implemented by negative index meta-materials, however, which are usually accompanied by high loss and demanding fabrication processes. Recently, alternative nonlinear approaches like phase conjugation and four wave mixing have shown advantages of low-loss and easy-to-implement, but associated problems like narrow accepting angles can still halt their practical applications. Here, we demonstrate theoretically and experimentally a scheme to realize negative refraction by nonlinear difference frequency generation with wide tunability, where a thin Beta barium borate slice serves as a negative refraction layer bending the input signal beam to the idler beam at a negative angle. Furthermore, we realize optical focusing effect using such nonlinear negative refraction, which may enable many potential applications in imaging science.

  14. Hybrid high refractive index polymer coatings

    NASA Astrophysics Data System (ADS)

    Wang, Yubao; Flaim, Tony; Mercado, Ramil; Fowler, Shelly; Holmes, Douglas; Planje, Curtis

    2005-04-01

    Thermally curable hybrid high refractive index polymer solutions have been developed. These solutions are stable up to 6 months under room temperature storage conditions and can be easily spin-coated onto a desired substrate. When cured at elevated temperature, the hybrid polymer coating decomposes to form a metal oxide-rich film that has a high refractive index. The resulting films have refractive indices higher than 1.90 in the entire visible region and achieve film thicknesses of 300-900 nm depending on the level of metal oxide loading, cure temperature being used, and number of coatings. The formed films show greater than 90% internal transmission in the visible wavelength (400-700 nm). These hybrid high refractive index films are mechanically robust, are stable upon exposure to both heat and UV radiation, and are currently being investigated for microlithographic patterning potential.

  15. Influence of refractive correction on ocular dominance

    NASA Astrophysics Data System (ADS)

    Nakayama, Nanami; Kawamorita, Takushi; Uozato, Hiroshi

    2010-07-01

    We investigated the effects of refractive correction and refractive defocus on the assessment of sensory ocular dominance. In 25 healthy subjects (4 males and 21 females) aged between 20 and 31 years, a quantitative measurement of sensory ocular dominance was performed with refractive correction and the addition of a positive lens on the dominant eye. Sensory ocular dominance was measured with a chart using binocular rivalry targets. The reversal point changed after the addition of a +1.00 D lens on the dominant eye in all subjects. However, sighting ocular dominance and stereopsis did not change after the addition of a positive lens on the dominant eye ( P > 0:05, Wilcoxon test). These results suggest that refractive correction affects sensory ocular dominance, indicating the possible development of a new type of occlusion for amblyopia in the future.

  16. Intertester agreement in refractive error measurements.

    PubMed

    Huang, Jiayan; Maguire, Maureen G; Ciner, Elise; Kulp, Marjean T; Quinn, Graham E; Orel-Bixler, Deborah; Cyert, Lynn A; Moore, Bruce; Ying, Gui-Shuang

    2013-10-01

    To determine the intertester agreement of refractive error measurements between lay and nurse screeners using the Retinomax Autorefractor and the SureSight Vision Screener. Trained lay and nurse screeners measured refractive error in 1452 preschoolers (3 to 5 years old) using the Retinomax and the SureSight in a random order for screeners and instruments. Intertester agreement between lay and nurse screeners was assessed for sphere, cylinder, and spherical equivalent (SE) using the mean difference and the 95% limits of agreement. The mean intertester difference (lay minus nurse) was compared between groups defined based on the child's age, cycloplegic refractive error, and the reading's confidence number using analysis of variance. The limits of agreement were compared between groups using the Brown-Forsythe test. Intereye correlation was accounted for in all analyses. The mean intertester differences (95% limits of agreement) were -0.04 (-1.63, 1.54) diopter (D) sphere, 0.00 (-0.52, 0.51) D cylinder, and -0.04 (1.65, 1.56) D SE for the Retinomax and 0.05 (-1.48, 1.58) D sphere, 0.01 (-0.58, 0.60) D cylinder, and 0.06 (-1.45, 1.57) D SE for the SureSight. For either instrument, the mean intertester differences in sphere and SE did not differ by the child's age, cycloplegic refractive error, or the reading's confidence number. However, for both instruments, the limits of agreement were wider when eyes had significant refractive error or the reading's confidence number was below the manufacturer's recommended value. Among Head Start preschool children, trained lay and nurse screeners agree well in measuring refractive error using the Retinomax or the SureSight. Both instruments had similar intertester agreement in refractive error measurements independent of the child's age. Significant refractive error and a reading with low confidence number were associated with worse intertester agreement.

  17. Indices of refraction for the HITRAN compilation

    NASA Technical Reports Server (NTRS)

    Massie, S. T.

    1994-01-01

    Indices of refraction of sulfuric acid solutions, water, and ice, which will become part of the HITRAN database, are discussed. Representative calculations are presented for the sulfate aerosol, to illustrate the broadband spectral features of i.r. aerosol extinction spectra. Values of the sulfuric acid mass density are used in an application of the Lorentz-Lorenz equation, which is used to estimate the sensitivity of extinction coefficients to temperature dependent refractive indices.

  18. Controlling plasmon hybridization for negative refraction metamaterials

    NASA Astrophysics Data System (ADS)

    Kanté, B.; Burokur, S. N.; Sellier, A.; de Lustrac, A.; Lourtioz, J.-M.

    2009-02-01

    The hybridization scheme of plasmon modes in cut-wire-based left-handed metamaterials is shown to critically depend on the coupling between paired cut wires. We show that an inverted hybridization scheme obtained with an asymmetric alignment of paired cut wires is the most appropriate to negative refraction. This is validated (numerically and experimentally) by the first demonstration of negative refraction in the microwave domain using only periodic ensembles of cut wires.

  19. [Polar and non polar notations of refraction].

    PubMed

    Touzeau, O; Gaujoux, T; Costantini, E; Borderie, V; Laroche, L

    2010-01-01

    Refraction can be expressed by four polar notations which correspond to four different combinations of spherical or cylindrical lenses. Conventional expressions of refraction (plus and minus cylinder notation) are described by sphere, cylinder, and axis. In the plus cylinder notation, the axis visualizes the most powerful meridian. The axis usually corresponds to the bow tie axis in curvature maps. Plus cylinder notation is also valuable for all relaxing procedures (i.e., selective suture ablation, arcuate keratotomy, etc.). In the cross-cylinder notation, two orthogonal cylinders can describe (without the sphere component) the actual refraction of both the principal meridians. This notation must be made before performing the vertex calculation. Using an association of a Jackson cross-cylinder and a spherical equivalent, refraction can be broken down into two pure components: astigmatism and sphere. All polar notations of refraction may perfectly characterize a single refraction but are not suitable for statistical analysis, which requires nonpolar expression. After doubling the axis, a rectangular projection breaks down the Jackson cross-cylinder, which has a polar axis, into two Jackson cross-cylinders on the 0 degrees /90 degrees and 45 degrees /135 degrees axis. This procedure results in the loss of the directional nature of the data. Refraction can be written in a nonpolar notation by three rectangular coordinates (x,y,z), which can also represent the spherocylinder by one point in a dioptric space. These three independent (orthogonal) variables have a concrete optical significance: a spherical component, a direct/inverse (WTR/ATR) component, and an oblique component of the astigmatism. Finally, nonpolar notations are useful for statistical analysis and graphical representation of refraction.

  20. Indices of refraction for the HITRAN compilation

    NASA Technical Reports Server (NTRS)

    Massie, S. T.

    1994-01-01

    Indices of refraction of sulfuric acid solutions, water, and ice, which will become part of the HITRAN database, are discussed. Representative calculations are presented for the sulfate aerosol, to illustrate the broadband spectral features of i.r. aerosol extinction spectra. Values of the sulfuric acid mass density are used in an application of the Lorentz-Lorenz equation, which is used to estimate the sensitivity of extinction coefficients to temperature dependent refractive indices.

  1. Assessment of the Effects of Refractive Conditions on Electronic Warfare in Central America

    DTIC Science & Technology

    1990-09-01

    charatterize the type uf refracti% e profiles occuring at a station. Radiosonde data collected by coastal stations in the area were used to establish...Gaviria Maldonado Lieutenant, Colombian Navy Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN SYSTEMS...atmospheric ducts and to characterize the type of refractive profiles occurring at a station. Radiosonde data collected by coastal stations in the area were

  2. Origin of crystallization-induced refractive index changes in photo-thermo-refractive glass

    NASA Astrophysics Data System (ADS)

    Lumeau, Julien; Glebova, Larissa; Golubkov, Valerii; Zanotto, Edgar D.; Glebov, Leonid B.

    2009-11-01

    Photo-thermo-refractive (PTR) glass is a multi-component silicate that undergoes localized refractive index decrease after UV-exposure and thermal treatment for partial crystallization. Based on this refractive index change, high efficiency volume Bragg gratings have been developed in PTR glass and have been successfully used for laser beam control. However, despite the fact that this type of glass has been widely studied and used over the last 20 years, the origin of the refractive index change upon crystallization is poorly understood. In this paper, we introduce three possible mechanisms (the precipitation of nano-sized NaF crystals and the associated local chemical changes of the glass matrix, the volumetric changes due to relaxation, and the local residual stresses) for the refractive index decrement in PTR glass and estimate the partial refractive index change due to each mechanism. Refractive index measurements are compared with high temperature XRD experiments and a general approach for the simulation of the refractive index change in PTR glass is proposed. We show that among the studied variables the residual stresses surrounding the crystals are the main responsible for the local refractive index decrement in this glass.

  3. Multimeridional refraction: dependence of the measurement accuracy on the number of meridians refracted.

    PubMed

    Oechsner, U; Kusel, R

    1997-06-01

    A Monte Carlo simulation of multimeridional refraction measurements was used to investigate the dependence of the accuracy of the measurement on the number of meridians refracted, N, and on the standard deviation of a measurement in a single meridian, sigma. For the description of the measurement errors, the residual refraction values were used, i.e., the parameters of the refraction remaining after application of the measured correction. The distributions of the residual refraction values were found to be independent of the "true" refraction values; in addition, by means of a factor square root of N/sigma, reduced residual refraction values could be defined which also were independent of N and sigma. A vector space proposed by Lakshminarayanan and Varadharajan (based on Long's power matrix) was used to represent the joint distribution of the residual refraction values in three-dimensional space. It was found to be a three-variate Gaussian distribution with zero mean and diagonal covariance matrix. It could further be shown that the vector space proposed by Harris is identical to the one used, up to a linear transformation. Several criteria, based on the one- and three-dimensional distributions and corresponding to different levels of accuracy, are discussed resulting in a wide range of answers about the number of meridians to be refracted.

  4. Comparison of objective refraction in darkness to cycloplegic refraction: a pilot study.

    PubMed

    Vasudevan, Balamurali; Ciuffreda, Kenneth J; Meehan, Kelly; Grk, Dejana; Cox, Misty

    2016-03-01

    The aim was to assess non-cycloplegic objective refraction in darkness using an open-field auto-refractor, and furthermore to compare it with distance cycloplegic subjective refraction and distance cycloplegic retinoscopy in the light, in children and young adults. Twenty-three, visually-normal, young-adults (46 eyes) ages 23 to 31 years, and five children (10 eyes) ages five to 12 years, participated in the study. The spherical component of their refraction ranged from -2.25 D to +3.75 D with a mean of +1.80 D, and a mean cylinder of -0.70 D. Three techniques were used to assess refractive error. An objective measure of the non-cycloplegic refractive state was obtained using an open-field autorefractor (WAM-5500) after five minutes in the dark to allow for dissipation of accommodative transients and relaxation of accommodation. In addition, both distance retinoscopy and subjective distance refraction were performed following cycloplegia (Cyclopentolate, 1%) using conventional clinical procedures. All measurements were obtained on the same day within a single session. The spherical component of the refraction was compared among the three techniques in both the children and adults. There was no significant difference in spherical refraction among the three techniques: non-cycloplegic objective refraction in the dark, distance cycloplegic retinoscopy and distance cycloplegic subjective refraction, in either the adults [F(2, 137) = 0.79, p = 0.45] or the children [F(2, 27) = 0.47, p = 0.62]. Mean difference in the spherical component between refraction in the dark and the cycloplegic distance retinoscopy was -0.34 D (r = 0.89) in the adults and +0.14 D (r = 0.96) in the children. The mean difference in spherical component between refraction in the dark and the cycloplegic distance subjective refraction was -0.25 D (r = 0.92) in the adults and -0.05 D (r = 0.95) in the children. Comparison of the spherical refractive component between the three techniques was not

  5. ON THE SOURCE OF ASTROMETRIC ANOMALOUS REFRACTION

    SciTech Connect

    Taylor, M. Suzanne; McGraw, John T.; Zimmer, Peter C.; Pier, Jeffrey R.

    2013-03-15

    More than a century ago, astronomers using transit telescopes to determine precise stellar positions were hampered by an unexplained periodic shifting of the stars they were observing. With the advent of CCD transit telescopes in the past three decades, this unexplained motion, termed 'anomalous refraction' by these early astronomers, is again being observed. Anomalous refraction is described as a low-frequency, large angular scale ({approx}2 Degree-Sign ) motion of the entire image plane with respect to the celestial coordinate system as observed and defined by astrometric catalogs. These motions, of typically several tenths of an arcsecond amplitude with timescales on the order of 10 minutes, are ubiquitous to ground-based drift-scan astrometric measurements regardless of location or telescopes used and have been attributed to the effect of tilting of equal-density layers of the atmosphere. The cause of this tilting has often been attributed to atmospheric gravity waves, but this cause has never been confirmed. Although theoretical models of atmospheric refraction show that atmospheric gravity waves are a plausible cause of anomalous refraction, an observational campaign specifically directed at defining this relationship provides clear evidence that anomalous refraction is not consistent with the passage of atmospheric gravity waves. The source of anomalous refraction is found to be meter-scale, slowly evolving quasi-coherent dynamical structures in the boundary layer below 60 m above ground level.

  6. Heritability of refractive value and ocular biometrics.

    PubMed

    Paget, Sandrine; Vitezica, Zulma G; Malecaze, François; Calvas, Patrick

    2008-02-01

    The aim of this work was to analyse genetic influences on ocular refractive value and axial length using the hypothesis of a polygenic control. The genealogical records of 55 families were used in the analyses. The cohort included 723 individuals and clinical data were collected for 445 individuals with a mean age of 37.86 years. Ocular refraction was determined by standard autorefractometry. Axial length was evaluated by scan ultrasonography. Gender, age and ethnic origin were included as covariates in the statistical analyses. Using variance component analysis via a Markov Chain Monte Carlo (MCMC) method, we estimated the heritability of refractive value and axial length in the pedigree. We then performed a segregation analysis, using Loki, a (MCMC) linkage analysis program for multilocus inheritance models, examining different inheritance models with polygenic components. Polygenic control was modelled under an additive infinitesimal model (which assumes infinite loci with small effects, with additive actions) and under a finite locus model (i.e. several causal loci). The estimates of heritability were 0.20 (95% confidence interval (CI) 0.04-0.36) for refractive value and 0.20 (95% CI 0.03-0.43) for axial length. Segregation analyses suggested that ocular refraction and axial length are under a polygenic control. A finite number of genes were identified with or without a polygenic, infinitesimal component. Ocular refraction is mildly-moderately heritable in the studied population.

  7. On the effective refractive index of blood

    NASA Astrophysics Data System (ADS)

    Nahmad-Rohen, Alexander; Contreras-Tello, Humberto; Morales-Luna, Gesuri; García-Valenzuela, Augusto

    2016-01-01

    We calculated the real and imaginary parts of the effective refractive index {n}{eff} of blood as functions of wavelength from 400 to 800 nm; we employed van de Hulst’s theory, together with the anomalous diffraction approximation, for the calculation. We modelled blood as a mixture of plasma and erythrocytes. Our results indicate that erythrocyte orientation has a strong effect on {n}{eff}, making blood an optically anisotropic medium except when the erythrocytes are randomly oriented. In the case in which their symmetry axis is perpendicular to the wave vector, {n}{eff} equals the refractive index of plasma at certain wavelengths. Furthermore, the erythrocytes’ shape affects their contribution to {n}{eff} in an important way, implying that studies on the effective refractive index of blood should avoid approximating them as spheres or spheroids. Finally, the effective refractive index of blood predicted by van de Hulst’s theory is different from what would be obtained by averaging the refractive indices of its constituents weighted by volume; such a volume-weighted average is appropriate only for haemolysed blood. We then measured the real part of the refractive index of various blood solutions using two different experimental setups. One of the most important results of our expriment is that {n}{eff} is measurable to a good degree of precision even for undiluted blood, although not all measuring apparatuses are appropriate. The experimental data is self-consistent and in reasonable agreement with our theoretical calculations.

  8. Reflective and refractive objects for mixed reality.

    PubMed

    Knecht, Martin; Traxler, Christoph; Winklhofer, Christoph; Wimmer, Michael

    2013-04-01

    In this paper, we present a novel rendering method which integrates reflective or refractive objects into a differential instant radiosity (DIR) framework usable for mixed-reality (MR) applications. This kind of objects are very special from the light interaction point of view, as they reflect and refract incident rays. Therefore they may cause high-frequency lighting effects known as caustics. Using instant-radiosity (IR) methods to approximate these high-frequency lighting effects would require a large amount of virtual point lights (VPLs) and is therefore not desirable due to real-time constraints. Instead, our approach combines differential instant radiosity with three other methods. One method handles more accurate reflections compared to simple cubemaps by using impostors. Another method is able to calculate two refractions in real-time, and the third method uses small quads to create caustic effects. Our proposed method replaces parts in light paths that belong to reflective or refractive objects using these three methods and thus tightly integrates into DIR. In contrast to previous methods which introduce reflective or refractive objects into MR scenarios, our method produces caustics that also emit additional indirect light. The method runs at real-time frame rates, and the results show that reflective and refractive objects with caustics improve the overall impression for MR scenarios.

  9. Electromagnetic waves: Negative refraction by photonic crystals

    NASA Astrophysics Data System (ADS)

    Ozbay, Ekmel

    2004-03-01

    Recently left-handed materials (LHM) attracted great attention since these materials exhibit negative effective index, which is due to simultaneously negative permeability and permittivity. Pendry proposed that negative effective index in left-handed materials can be used for constructing a perfect lens, which is not limited by diffraction(J. B. Pendry, Negative refraction makes a perfect lens, Phys. Rev. Lett. vol. 85, 3966 (2000)). Negative refraction is also achievable in a dielectric photonic crystal (PC) that has a periodically modulated positive permittivity and a permeability of unity. Luo et al. has studied negative refraction and subwavelength imaging in photonic crystals(C. Luo, S. G. Johnson, J. D. Joannopoulos, J. B. Pendry, Subwavelength Imaging in Photonic Crystals Phys. Rev. B 68, 045115 (2003)). In this presentation, we report our experimental and theoretical investigation of negative refraction and subwavelength focusing of electromagnetic waves in a 2D PC. Our structure consists of a square array of dielectric rods in air. Transmission measurements are performed for experimentally verifying the predicted negative refraction behavior in our structure. Negative index of refraction determined from the experiment is -1.94 which is very close to the theoretical value of -2.06. Negative refraction is observed for the incidence angles of > 20°(Ertugrul Cubukcu, Koray Aydin, Ekmel Ozbay, S. Foteinopolou, and Costas Soukoulis, Negative Refraction by Photonic Crystals, Nature, vol. 423, 604 (2003)). Since we know the optimum frequency for a broad angle negative refraction, we can use our crystal to test the superlensing effect that was predicted for negative refractive materials. Scanning transmission measurement technique is used to measure the spatial power distribution of the focused electromagnetic waves that radiate from a point source. Full width at half maximum of the focused beam is measured to be 0.21λ, which is in good agreement with the finite

  10. Virtual edge illumination and one dimensional beam tracking for absorption, refraction, and scattering retrieval

    SciTech Connect

    Vittoria, Fabio A. Diemoz, Paul C.; Endrizzi, Marco; Olivo, Alessandro; Wagner, Ulrich H.; Rau, Christoph; Robinson, Ian K.

    2014-03-31

    We propose two different approaches to retrieve x-ray absorption, refraction, and scattering signals using a one dimensional scan and a high resolution detector. The first method can be easily implemented in existing procedures developed for edge illumination to retrieve absorption and refraction signals, giving comparable image quality while reducing exposure time and delivered dose. The second method tracks the variations of the beam intensity profile on the detector through a multi-Gaussian interpolation, allowing the additional retrieval of the scattering signal.

  11. Near-surface velocity structure from borehole and refraction seismic surveys

    SciTech Connect

    Parry, D.; Lawton, D.C.

    1994-12-31

    Seismic refraction and borehole reflection data have been used in conjunction with other geophysical tools to characterize the near-surface geology in the vicinity of a shallow well near Calgary, Alberta. The investigated section is comprised primarily of glacial tills and gravels. Seismic waves generated in the lower gravel units travel as compressional waves up to the till/gravel interface, where they are converted to shear waves upon transmission. Velocity structure from a reverse vertical seismic profile (RVSP) survey agrees closely with that from refraction surveying.

  12. Is an objective refraction optimised using the visual Strehl ratio better than a subjective refraction?

    PubMed

    Hastings, Gareth D; Marsack, Jason D; Nguyen, Lan Chi; Cheng, Han; Applegate, Raymond A

    2017-05-01

    To prospectively examine whether using the visual image quality metric, visual Strehl (VSX), to optimise objective refraction from wavefront error measurements can provide equivalent or better visual performance than subjective refraction and which refraction is preferred in free viewing. Subjective refractions and wavefront aberrations were measured on 40 visually-normal eyes of 20 subjects, through natural and dilated pupils. For each eye a sphere, cylinder, and axis prescription was also objectively determined that optimised visual image quality (VSX) for the measured wavefront error. High contrast (HC) and low contrast (LC) logMAR visual acuity (VA) and short-term monocular distance vision preference were recorded and compared between the VSX-objective and subjective prescriptions both undilated and dilated. For 36 myopic eyes, clinically equivalent (and not statistically different) HC VA was provided with both the objective and subjective refractions (undilated mean ± S.D. was -0.06 ± 0.04 with both refractions; dilated was -0.05 ± 0.04 with the objective, and -0.05 ± 0.05 with the subjective refraction). LC logMAR VA provided by the objective refraction was also clinically equivalent and not statistically different to that provided by the subjective refraction through both natural and dilated pupils for myopic eyes. In free viewing the objective prescription was preferred over the subjective by 72% of myopic eyes when not dilated. For four habitually undercorrected high hyperopic eyes, the VSX-objective refraction was more positive in spherical power and VA poorer than with the subjective refraction. A method of simultaneously optimising sphere, cylinder, and axis from wavefront error measurements, using the visual image quality metric VSX, is described. In myopic subjects, visual performance, as measured by HC and LC VA, with this VSX-objective refraction was found equivalent to that provided by subjective refraction, and was typically preferred

  13. Linkage Analysis of Quantitative Refraction and Refractive Errors in the Beaver Dam Eye Study

    PubMed Central

    Duggal, Priya; Lee, Kristine E.; Cheng, Ching-Yu; Klein, Ronald; Bailey-Wilson, Joan E.; Klein, Barbara E. K.

    2011-01-01

    Purpose. Refraction, as measured by spherical equivalent, is the need for an external lens to focus images on the retina. While genetic factors play an important role in the development of refractive errors, few susceptibility genes have been identified. However, several regions of linkage have been reported for myopia (2q, 4q, 7q, 12q, 17q, 18p, 22q, and Xq) and for quantitative refraction (1p, 3q, 4q, 7p, 8p, and 11p). To replicate previously identified linkage peaks and to identify novel loci that influence quantitative refraction and refractive errors, linkage analysis of spherical equivalent, myopia, and hyperopia in the Beaver Dam Eye Study was performed. Methods. Nonparametric, sibling-pair, genome-wide linkage analyses of refraction (spherical equivalent adjusted for age, education, and nuclear sclerosis), myopia and hyperopia in 834 sibling pairs within 486 extended pedigrees were performed. Results. Suggestive evidence of linkage was found for hyperopia on chromosome 3, region q26 (empiric P = 5.34 × 10−4), a region that had shown significant genome-wide evidence of linkage to refraction and some evidence of linkage to hyperopia. In addition, the analysis replicated previously reported genome-wide significant linkages to 22q11 of adjusted refraction and myopia (empiric P = 4.43 × 10−3 and 1.48 × 10−3, respectively) and to 7p15 of refraction (empiric P = 9.43 × 10−4). Evidence was also found of linkage to refraction on 7q36 (empiric P = 2.32 × 10−3), a region previously linked to high myopia. Conclusions. The findings provide further evidence that genes controlling refractive errors are located on 3q26, 7p15, 7p36, and 22q11. PMID:21571680

  14. Linkage analysis of quantitative refraction and refractive errors in the Beaver Dam Eye Study.

    PubMed

    Klein, Alison P; Duggal, Priya; Lee, Kristine E; Cheng, Ching-Yu; Klein, Ronald; Bailey-Wilson, Joan E; Klein, Barbara E K

    2011-07-13

    Refraction, as measured by spherical equivalent, is the need for an external lens to focus images on the retina. While genetic factors play an important role in the development of refractive errors, few susceptibility genes have been identified. However, several regions of linkage have been reported for myopia (2q, 4q, 7q, 12q, 17q, 18p, 22q, and Xq) and for quantitative refraction (1p, 3q, 4q, 7p, 8p, and 11p). To replicate previously identified linkage peaks and to identify novel loci that influence quantitative refraction and refractive errors, linkage analysis of spherical equivalent, myopia, and hyperopia in the Beaver Dam Eye Study was performed. Nonparametric, sibling-pair, genome-wide linkage analyses of refraction (spherical equivalent adjusted for age, education, and nuclear sclerosis), myopia and hyperopia in 834 sibling pairs within 486 extended pedigrees were performed. Suggestive evidence of linkage was found for hyperopia on chromosome 3, region q26 (empiric P = 5.34 × 10(-4)), a region that had shown significant genome-wide evidence of linkage to refraction and some evidence of linkage to hyperopia. In addition, the analysis replicated previously reported genome-wide significant linkages to 22q11 of adjusted refraction and myopia (empiric P = 4.43 × 10(-3) and 1.48 × 10(-3), respectively) and to 7p15 of refraction (empiric P = 9.43 × 10(-4)). Evidence was also found of linkage to refraction on 7q36 (empiric P = 2.32 × 10(-3)), a region previously linked to high myopia. The findings provide further evidence that genes controlling refractive errors are located on 3q26, 7p15, 7p36, and 22q11.

  15. Refractive Turbulence, Transient Propagation Disturbances, and Space Situational Awareness

    NASA Astrophysics Data System (ADS)

    Cote, O.; Wroblewski, D.; Hacker, J.

    This paper examines the proposition that mission limiting space situational awareness (SSA) has important and fundamental turbulence and propagation physics issues to be investigated. We propose to call these aspects, propagation situational awareness (PSA). Transient disturbances can be present in communication to and from ground stations and satellites and in the performance of ground based and space based optical and infra-red imaging and tracking systems. Propagation frequency is important in characterizing whether the source of the disturbance lay in the electron density fluctuations of ionosphere or the refractive turbulence of the neutral atmosphere. Over the past ten years high altitude airborne measurements of clear air and refractive turbulence were made in Australia to support design and performance evaluations of the Airborne Laser. More recently in collaboration with the Australian Defence Science & Technology Organization (DSTO) smaller aircraft were used to investigate the effect of ducting layers on the signal strength of an airborne emitter as a low cost simulation of potential for loss of track in the coverage pattern of an airborne radar. From 2002 onward we were also tasked to do fundamental investigations of clear air turbulence for flight safety evaluations of both manned and unmanned high altitude surveillance aircraft. These investigations covered a wide spread in frequency, from infra-red to microwave. Most of these investigations were confined to measurement days and altitudes where strong turbulence was expected. The decision to measure was based on predictions of the location of jet streams relative to the measurement area as well as bulk gradient Richardson (Ri) vertical profiles derived from radio sound measurements from stations surround the potential measurement location. We will show how all these analyses and decision aids, including the Ri profiles, can be used to estimate potential for propagation disturbances to SSA. Current DOD

  16. Deep crustal structure of the Cascade Range and surrounding regions from seismic refraction and magnetotelluric data

    USGS Publications Warehouse

    Stanley, W.D.; Mooney, W.D.; Fuis, G.S.

    1990-01-01

    Several regional seismic refraction and magnetotelluric (MT) profiles have been completed across the Cascade Range and surrounding geologic provinces in California, Oregon, and Washington. Analysis of three MT and two seismic refraction profiles in Oregon and a coincident MT and refraction profile in northern California show a high degree of correlation between resistivity and velocity models. The main feature that is evident in both data sets is a highly conductive (2-20 ohm m) zone that occurs at depths of 6-20 km and largely within a midcrustal velocity layer of 6.4-6.6 km/s, overlying a lower crust with velocities of 7.0-7.4 km/s. Accretionary structures in the southern Washington Cascades have been shown to be related to stress release in the area of Mount St. Helens. In order to explain the similar structures in the MT and refraction models for Oregon and California, a model is proposed involving the effects of metamorphic zonation to produce the velocity structure, combined with metamorphically produced fluids and partial melt to produce the deep conductor. -from Authors

  17. Interferometric Methods of Measuring Refractive Indices and Double-Refraction of Fibres.

    ERIC Educational Resources Information Center

    Hamza, A. A.; El-Kader, H. I. Abd

    1986-01-01

    Presents two methods used to measure the refractive indices and double-refraction of fibers. Experiments are described, with one involving the use of Pluta microscope in the double-beam interference technique, the other employing the multiple-beam technique. Immersion liquids are discussed that can be used in the experiments. (TW)

  18. Interferometric Methods of Measuring Refractive Indices and Double-Refraction of Fibres.

    ERIC Educational Resources Information Center

    Hamza, A. A.; El-Kader, H. I. Abd

    1986-01-01

    Presents two methods used to measure the refractive indices and double-refraction of fibers. Experiments are described, with one involving the use of Pluta microscope in the double-beam interference technique, the other employing the multiple-beam technique. Immersion liquids are discussed that can be used in the experiments. (TW)

  19. Variable beam shaping with using the same field mapping refractive beam shaper

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Laskin, Vadim

    2012-02-01

    Modern laser scientific techniques and industrial technologies require not only simple homogenizing of a beam but also more freedom in manipulation of intensity profile and generating such profiles like super-Gaussian, inverse-Gaussian, skewed flattop and others. In many cases the task of variable beam shaping can be solved by refractive beam shaping optics of field mapping type which operational principle presumes saving of beam consistency, providing collimated output beam of low divergence, high transmittance and flatness of output beam profile, extended depth of field; another important feature is negligible residual wave aberration. Typically the fields mapping refractive beam shapers, like πShaper, are designed to generate flattop intensity profile for a beam of pre-determined size and input intensity profile. Varying of the input beam diameter lets it possible to realize either super-Gaussian (smaller input) or inverse-Gaussian (bigger input) intensity profiles of output beam that are important in pumping of solid-state lasers, hardening, cladding and other techniques. By lateral shift of a beam with respect to a πShaper the output flattop profile gets a skew in direction of that shift, the skew angle corresponds to the shift value. The skewed profile is important, for example, in some acousto-optical techniques where compensation of acoustic wave attenuation is required. All variety of profiles can be provided by the same beam shaper unit. This paper will describe some design basics of refractive beam shapers of the field mapping type and techniques to vary the output intensity profile, experimental results will be presented as well.

  20. Estimation of the Atmospheric Refraction Effect in Airborne Images Using Radiosonde Data

    NASA Astrophysics Data System (ADS)

    Beisl, U.; Tempelmann, U.

    2016-06-01

    The influence of the atmospheric refraction on the geometric accuracy of airborne photogrammetric images was already considered in the days of analogue photography. The effect is a function of the varying refractive index on the path from the ground to the image sensor. Therefore the effect depends on the height over ground, the view zenith angle and the atmospheric constituents. It is leading to a gradual increase of the scale towards the borders of the image, i.e. a magnification takes place. Textbooks list a shift of several pixels at the borders of standard wide angle images. As it was the necessity of that time when images could only be acquired at good weather conditions, the effect was calculated using standard atmospheres for good atmospheric conditions, leading to simple empirical formulas. Often the pixel shift caused by refraction was approximated as linear with height and compensated by an adjustment of the focal length. With the advent of sensitive digital cameras, the image dynamics allows for capturing images at adverse weather conditions. So the influence of the atmospheric profiles on the geometric accuracy of the images has to be investigated and the validity of the standard correction formulas has to be checked. This paper compares the results from the standard formulas by Saastamoinen with the results calculated from a broad selection of atmospheres obtained from radiosonde profile data. The geometric deviation is calculated by numerical integration of the refractive index as a function of the height using the refractive index formula by Ciddor. It turns out that the effect of different atmospheric profiles (including inversion situations) is generally small compared to the overall effect except at low camera heights. But there the absolute deviation is small. Since the necessary atmospheric profile data are often not readily available for airborne images a formula proposed by Saastamoinen is verified that uses only camera height, the pressure

  1. Preliminary results from the retrieval and assimilation of GPS radio occultation refractivity observations during tropical storm development

    NASA Astrophysics Data System (ADS)

    Haase, J. S.; Murphy, B.; Chen, X.; Chen, S.; Muradyan, P.; Nievinski, F. G.; Larson, K. M.; Garrison, J. L.; Wang, E. K.; Chen, S.

    2012-12-01

    Airborne GPS radio occultation (RO) data have been collected by the GNSS Instrument System for Multi-static and Occultation Sensing (GISMOS) during the 2010 PRE-Depression Investigation of Cloud systems in the Tropics (PREDICT) experiment to study developing Atlantic tropical storms. This airborne system is designed to receive and record radio signals from setting and rising GPS satellites. The additional phase delay of the GPS radio signals due to refraction in the atmosphere is used to retrieve vertical profiles of refractivity, which depend strongly on moisture. A large airborne RO dataset was acquired from twenty-six research flights and refractivity profiles have been derived from the GISMOS geodetic GPS receivers. The airborne RO profiles consistently agree within ~2% with refractivity profiles calculated from ECMWF model analyses above 5 km altitude and with nearby dropsonde profiles. Accurate refractivity results are an important first step in investigating the impact of assimilating moisture profiles within the mesoscale environment of developing storms. A case study is conducted for pre-Hurricane Karl. The evolution of refractivity derived from RO data over the five days leading to the genesis of tropical storm Karl are consistent with mid-tropospheric moistening in the vicinity of the storm center. The algorithm to assimilate airborne GPS observations has been implemented in the Three-Dimensional Variational (3DVAR) Data Assimilation (DA) system of the Weather Research and Forecasting (WRF) model. We use a non-local operator for the integrated excess phase, defined as the integrated value of refractivity along the GPS radio ray path. One observation per horizontal and vertical model grid point is assimilated instead of only one per vertical model level, so that the horizontal drift of the occultation points within each model level is considered. Three data assimilation experiments were conducted: 1) NONE: No data are assimilated during data cycling. 2

  2. Refractive Secondary Concentrators for Solar Thermal Applications

    NASA Technical Reports Server (NTRS)

    Wong, Wayne A.; Macosko, Robert P.

    1999-01-01

    The NASA Glenn Research Center is developing technologies that utilize solar energy for various space applications including electrical power conversion, thermal propulsion, and furnaces. Common to all of these applications is the need for highly efficient, solar concentration systems. An effort is underway to develop the innovative single crystal refractive secondary concentrator, which uses refraction and total internal reflection to efficiently concentrate and direct solar energy. The refractive secondary offers very high throughput efficiencies (greater than 90%), and when used in combination with advanced primary concentrators, enables very high concentration ratios (10,0(X) to 1) and very high temperatures (greater than 2000 K). Presented is an overview of the refractive secondary concentrator development effort at the NASA Glenn Research Center, including optical design and analysis techniques, thermal modeling capabilities, crystal materials characterization testing, optical coatings evaluation, and component testing. Also presented is a discussion of potential future activity and technical issues yet to be resolved. Much of the work performed to date has been in support of the NASA Marshall Space Flight Center's Solar Thermal Propulsion Program. The many benefits of a refractive secondary concentrator that enable efficient, high temperature thermal propulsion system designs, apply equally well to other solar applications including furnaces and power generation systems such as solar dynamics, concentrated thermal photovoltaics, and thermionics.

  3. Cryogenic Refractive Index of Heraeus Homosil Glass

    NASA Technical Reports Server (NTRS)

    Miller, Kevin H.; Quijada, Manuel A.; Leviton, Douglas B.

    2017-01-01

    This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.34-3.16 microns and temperature range of 120-335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASAs Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a field-widened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitivity performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dn/dT) and dispersion relation (dn/d(lamda)) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in literature.

  4. [Retinal detachment in various myopic refractions].

    PubMed

    Alimanović-Halilović, Emina

    2009-01-01

    The basic aim of this study was to find the group of "critical" myopic refraction with the highest occurrence of retinal detachment. In the study, 180 myopic eyes were analyzed. Upon the targeted ophthalmological anamnesis, definition of the objective refraction, and indirect binocular ophthalmoscopy, we analyzed the distribution of retinal detachment and the area affected in relation to refraction. All the eyes were divided into groups according to the refraction height. Average age of our patients ranged from 48.43 to 51.60 years with SD from 13.88 to 18.45. We did not find a statistically significant difference for a certain age. The study covered 102 (56.6%) male and 78 (43.3%) female patients. The highest occurrence of retinal detachment was found in Refraction Group from 3.5 to 7.49 dsph, total 21 (11.6%). The retinal detachments usually affected 2/4 or 3/4 of the eye fundus surface respectively.

  5. Cryogenic Refractive Index of Heraeus Homosil Glass

    NASA Technical Reports Server (NTRS)

    Miller, Kevin H.; Quijada, Manuel A.; Leviton, Douglas B.

    2017-01-01

    This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.343.16 m and temperature range of 120335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASAs Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a field-widened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitivity performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dndT) and dispersion relation (dnd) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in literature.

  6. Refractive index dispersion sensing using an array of photonic crystal resonant reflectors

    SciTech Connect

    Hermannsson, Pétur G.; Vannahme, Christoph; Smith, Cameron L. C.; Sørensen, Kristian T.; Kristensen, Anders

    2015-08-10

    Refractive index sensing plays a key role in various environmental and biological sensing applications. Here, a method is presented for measuring the absolute refractive index dispersion of liquids using an array of photonic crystal resonant reflectors of varying periods. It is shown that by covering the array with a sample liquid and measuring the resonance wavelength associated with transverse electric polarized quasi guided modes as a function of period, the refractive index dispersion of the liquid can be accurately obtained using an analytical expression. This method is compact, can perform measurements at arbitrary number of wavelengths, and requires only a minute sample volume. The ability to sense a material's dispersion profile offers an added dimension of information that may be of benefit to optofluidic lab-on-a-chip applications.

  7. Inversion for Refractivity Parameters Using a Dynamic Adaptive Cuckoo Search with Crossover Operator Algorithm.

    PubMed

    Zhang, Zhihua; Sheng, Zheng; Shi, Hanqing; Fan, Zhiqiang

    2016-01-01

    Using the RFC technique to estimate refractivity parameters is a complex nonlinear optimization problem. In this paper, an improved cuckoo search (CS) algorithm is proposed to deal with this problem. To enhance the performance of the CS algorithm, a parameter dynamic adaptive operation and crossover operation were integrated into the standard CS (DACS-CO). Rechenberg's 1/5 criteria combined with learning factor were used to control the parameter dynamic adaptive adjusting process. The crossover operation of genetic algorithm was utilized to guarantee the population diversity. The new hybrid algorithm has better local search ability and contributes to superior performance. To verify the ability of the DACS-CO algorithm to estimate atmospheric refractivity parameters, the simulation data and real radar clutter data are both implemented. The numerical experiments demonstrate that the DACS-CO algorithm can provide an effective method for near-real-time estimation of the atmospheric refractivity profile from radar clutter.

  8. Inversion for Refractivity Parameters Using a Dynamic Adaptive Cuckoo Search with Crossover Operator Algorithm

    PubMed Central

    Zhang, Zhihua; Sheng, Zheng; Shi, Hanqing; Fan, Zhiqiang

    2016-01-01

    Using the RFC technique to estimate refractivity parameters is a complex nonlinear optimization problem. In this paper, an improved cuckoo search (CS) algorithm is proposed to deal with this problem. To enhance the performance of the CS algorithm, a parameter dynamic adaptive operation and crossover operation were integrated into the standard CS (DACS-CO). Rechenberg's 1/5 criteria combined with learning factor were used to control the parameter dynamic adaptive adjusting process. The crossover operation of genetic algorithm was utilized to guarantee the population diversity. The new hybrid algorithm has better local search ability and contributes to superior performance. To verify the ability of the DACS-CO algorithm to estimate atmospheric refractivity parameters, the simulation data and real radar clutter data are both implemented. The numerical experiments demonstrate that the DACS-CO algorithm can provide an effective method for near-real-time estimation of the atmospheric refractivity profile from radar clutter. PMID:27212938

  9. Linear parabolic single-crystal diamond refractive lenses for synchrotron X-ray sources.

    PubMed

    Terentyev, Sergey; Polikarpov, Maxim; Snigireva, Irina; Di Michiel, Marco; Zholudev, Sergey; Yunkin, Vyacheslav; Kuznetsov, Sergey; Blank, Vladimir; Snigirev, Anatoly

    2017-01-01

    Linear parabolic diamond refractive lenses are presented, designed to withstand high thermal and radiation loads coming from upgraded accelerator X-ray sources. Lenses were manufactured by picosecond laser treatment of a high-quality single-crystal synthetic diamond. Twelve lenses with radius of curvature at parabola apex R = 200 µm, geometrical aperture A = 900 µm and length L = 1.5 mm were stacked as a compound refractive lens and tested at the ESRF ID06 beamline. A focal spot of size 2.2 µm and a gain of 20 were measured at 8 keV. The lens profile and surface quality were estimated by grating interferometry and X-ray radiography. In addition, the influence of X-ray glitches on the focusing properties of the compound refractive lens were studied.

  10. Lower troposphere refractivity bias in GPS occultation retrievals

    NASA Astrophysics Data System (ADS)

    Ao, C. O.; Meehan, T. K.; Hajj, G. A.; Mannucci, A. J.; Beyerle, G.

    2003-09-01

    Analysis of atmospheric occultation data from the GPS Meteorology experiment has revealed that the refractivity retrievals in the lower troposphere were systematically smaller than those obtained with numerical weather prediction models. It has been suggested that the bias was due to a combination of atmospheric multipath, critical refraction, and receiver tracking errors. In this paper, we show that a similar bias exists in the CHAMP and SAC-C data and describe the characteristics of the bias based on over 6700 soundings from October 2001. Retrievals obtained using the recently introduced canonical transform method are shown to markedly reduce the refractivity bias; however, a significant bias still remains below 2 km altitude. To better understand the underlying causes of the bias, we perform an end-to-end simulation study that incorporates full-wave signal propagation and realistic receiver tracking effects using an ensemble of atmospheric profiles. We find that atmospheric ducting effects associated with the top of the planetary boundary layer (PBL) at 1-2 km altitude would cause retrieval errors at and below the PBL even in the absence of the receiver errors. Furthermore, current implementation of the receiver tracking algorithm based on an enhanced version of the phase-locked loop could introduce additional errors under the low signal-to-noise ratio conditions that are often encountered in the lower troposphere. The latter problem is expected to be resolved in the near future through the adoption of open-loop tracking and the removal of the navigation modulation from the GPS signal.

  11. Refraction by a spherical nematic bubble

    NASA Astrophysics Data System (ADS)

    Sherman, Richard David

    1989-08-01

    A formalism is developed to study refraction by a spherical nematic bubble. It is applicable to bubbles that are larger than light wavelengths, but smaller than the dimensions for excitation of director-fluctuation-induced scattering. The technique yields a nonlinear differential equation and an associated integral which govern the trajectory of a ray inside a nematic region for an arbitrary director configuration. Explicit solutions are provided for five simple interior arrangements-isotropic, onion skin, radial star, horizontal (bottle brush), and vertical. It is then demonstrated that for extraordinary-ordinary refractive-index difference small compared to either, interfacial refraction at the bubble surface is the dominant contribution; deviations from a rectilinear path are small. When ranked in terms of decreasing scattering effectiveness, the sequence is horizontal, onion, isotropic, radial, and vertical if the light is linearly polarized and coupling optimally to the extraordinary index component; for unpolarized incoherent light the order becomes isotropic, horizontal, onion, radial, and vertical.

  12. Cosmology with a dark refraction index

    NASA Astrophysics Data System (ADS)

    Chen, B.; Kantowski, R.

    2008-08-01

    We review Gordon’s optical metric and the transport equations for the amplitude and polarization of a geometrical optics wave traveling in a gravity field. We apply the theory to the Friedmann-Lemaître-Robertson-Walker cosmologies by associating a refraction index with the cosmic fluid. We then derive an expression for the accumulated effect of a refraction index on the distance-redshift relations and fit the Hubble curve of current supernova observations with a nonaccelerating cosmological model. We also show that some observational effects caused by inhomogeneities, e.g., the Sachs-Wolfe effect, can be interpreted as being caused by an effective index of refraction, and hence this theory could extend to other speed of light communications such as gravitational radiation and neutrino fluxes.

  13. Seismic refraction analysis: the path forward

    USGS Publications Warehouse

    Haines, Seth S.; Zelt, Colin; Doll, William

    2012-01-01

    Seismic Refraction Methods: Unleashing the Potential and Understanding the Limitations; Tucson, Arizona, 29 March 2012 A workshop focused on seismic refraction methods took place on 29 May 2012, associated with the 2012 Symposium on the Application of Geophysics to Engineering and Environmental Problems. This workshop was convened to assess the current state of the science and discuss paths forward, with a primary focus on near-surface problems but with an eye on all applications. The agenda included talks on these topics from a number of experts interspersed with discussion and a dedicated discussion period to finish the day. Discussion proved lively at times, and workshop participants delved into many topics central to seismic refraction work.

  14. Fiber optic liquid refractive index sensor

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Vanita; Gangwar, Rahul Kumar; Singh, Vinod Kumar

    2015-08-01

    In this present work we report fabrication of fiber optic liquid refractive index (RI) measurement sensor based on Michelson Interferometer method. This sensor was assembled by using graded index multimode (MM) fiber with core diameter 50 µm and the cladding of fiber was removed by simple chemical method. To perform this experiment a 2×2 3dB coupler is used. The fiber ends are then immersed in solvent and solution to provide reference and refractive index measurements, respectively. This method was successfully used to measure refractive index of Sodium Chloride (NaCl)-Water solution at different concentrations. The fringe contrast sensitivity of device is 92.90 dB/RIU measured in the RI range from 1.34 to 1.42 which is better than Mach-Zehnder Interferometer sensor [1] and Fabry perot based sensor [2]. The fabrication of sensor is simple, low cost and highly sensitive.

  15. Removing singular refractive indices with sculpted surfaces

    PubMed Central

    Horsley, S. A. R.; Hooper, I. R.; Mitchell–Thomas, R. C.; Quevedo–Teruel, O.

    2014-01-01

    The advent of Transformation Optics established the link between geometry and material properties, and has resulted in a degree of control over electromagnetic fields that was previously impossible. For waves confined to a surface it is known that there is a simpler, but related, geometrical equivalence between the surface shape and the refractive index, and here we demonstrate that conventional devices possessing a singularity — that is, the requirement of an infinite refractive index — can be realised for waves confined to an appropriately sculpted surface. In particular, we redesign three singular omnidirectional devices: the Eaton lens, the generalized Maxwell Fish–Eye, and the invisible sphere. Our designs perfectly reproduce the behaviour of these singular devices, and can be achieved with simple isotropic media of low refractive index contrast. PMID:24786649

  16. Tunable Terahertz Device Using Refractive Index Control

    NASA Astrophysics Data System (ADS)

    Nakanishi, Atsushi; Yasuda, Takashi; Horita, Kazuki; Takahashi, Hironori

    2017-08-01

    We measured the thermal dependencies of the refractive index and the absorption coefficient of high-resistivity silicon. We found that the refractive index varied slightly with temperature, and the absorption coefficient was very low and remained approximately constant as the temperature was changed. As a result, the conditions for terahertz propagation in silicon could be controlled by changing the refractive index without any absorption loss. As one application of this effect, we developed a terahertz time delay generator that can generate a terahertz time delay by changing the temperature of the medium through which the terahertz beam passes, without the need for any mechanical delay. We demonstrated generation of a terahertz time delay of approximately 6.6 ps.

  17. Acquisition of long-offset seismic refraction data in the Chukchi Borderlands and Mendeleev Ridge

    NASA Astrophysics Data System (ADS)

    Vermeesch, P. M.; van Avendonk, H. J.; Lawver, L. A.; Hornbach, M. J.; Wiederspahn, M.; Saustrup, S.; Mironov, A.; Stevenoski, S.; Asher, C.; Bain, K.; McDonald, M.; Young, R.

    2006-12-01

    The deep structure of the Chukchi Borderlands and Mendeleev Ridge is important for our understanding of the tectonic history of the western Arctic Ocean. Our constraints on the crustal structure of this region are sparse because the nearly continuous ice cover makes the acquisition of marine seismic refraction data difficult. In July and August of 2006 we gathered a unique seismic refraction data set on the Chukchi Borderlands and Mendeleev Ridge utilizing USCGC Healy and two helicopters. In order to obtain seismic refractions from an air- gun source over long offsets, we placed seismic instruments on the sea ice by helicopter. Each of the stations was equipped with a geophone, hydrophone, GPS unit and radio. The instruments were left on ice for several days, making occasional radio contact with either the ship or the helicopter to give us their latest location. We deployed an array of 12 instruments across the Northwind Escarpment into the Canada Basin, 13 instruments on an east-west transect across Chukchi Cap, and 14 seismometers on a refraction line parallel to the crest of Mendeleev Ridge. One instrument on the Chukchi Cap was lost at sea, but the other instruments were successfully retrieved with their refraction data. The instrument arrays recorded air-gun shots over distances up to 150 km. We will use the first-arrival time data to estimate the two-dimensional seismic velocity structure along the three profiles that were gathered on this cruise.

  18. Precise control of dispersion flatness in silicon nitride waveguides by cladding refractive index engineering

    NASA Astrophysics Data System (ADS)

    Bodenmüller, D.; Chavez Boggio, J. M.; Fernando, H. N. J.; Haynes, R.; Roth, M. M.

    2012-06-01

    A technique for flattening the chromatic dispersion in silicon nitride waveguides with silica cladding is proposed and numerically investigated. By modifying the transversal dimensions of the silicon nitride core and by adding several cladding layers with appropriate refractive indices and thicknesses, we demonstrate dispersion flattening over large spectral bandwidths in the near infrared. We analyze several cladding refractive index profiles that could be realistically fabricated by using existing materials and doping procedures. We show that cladding engineering allows for much more dispersion control (and flattening) in comparison with optimizing only the core transversal dimensions. For the latter case it is demonstrated that while the zero dispersion wavelength can be shifted to a great extent, the effect of the cross-section adjustment in the flatness is very limited. In sharp contrast, by adding two cladding layers and decreased refractive index values, the dispersion ripple can be strongly reduced. By further adding one more layer and by adjusting their refractive indices it is possible to obtain nearly constant chromatic dispersion (only +/- 3 ps/nm-km variation) over the spectral region from 1.8 to 2.4 microns. In our calculations, the analyzed change in the silica or silicon nitride refractive index is up to +/-3%. Our technique should open new avenues for the demonstration of high-performance nonlinear devices on a chip. Furthermore highly dispersive integrated photonic components can be envisaged for slow light applications and integrated photonics spectrographs.

  19. Negative Refraction Angular Characterization in One-Dimensional Photonic Crystals

    PubMed Central

    Lugo, Jesus Eduardo; Doti, Rafael; Faubert, Jocelyn

    2011-01-01

    Background Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs. Methodology/Principal Findings By using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snell's law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone. Conclusions/Significance Since both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications. PMID:21494332

  20. Negative refraction angular characterization in one-dimensional photonic crystals.

    PubMed

    Lugo, Jesus Eduardo; Doti, Rafael; Faubert, Jocelyn

    2011-04-06

    Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs. By using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snell's law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone. Since both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications.

  1. Negative refraction using Raman transitions and chirality

    SciTech Connect

    Sikes, D. E.; Yavuz, D. D.

    2011-11-15

    We present a scheme that achieves negative refraction with low absorption in far-off resonant atomic systems. The scheme utilizes Raman resonances and does not require the simultaneous presence of an electric-dipole transition and a magnetic-dipole transition near the same wavelength. We show that two interfering Raman tran-sitions coupled to a magnetic-dipole transition can achieve a negative index of refraction with low absorption through magnetoelectric cross-coupling. We confirm the validity of the analytical results with exact numerical simulations of the density matrix. We also discuss possible experimental implementations of the scheme in rare-earth metal atomic systems.

  2. Ray Curvature and Refraction of Wave Packets.

    DTIC Science & Technology

    1978-09-01

    1!~~~~~ _ ‘ AD AOM 302 FLORIDA STATE UNIV TALLAHASSEE DEPT OF OCEANOGRAPHY FIG B/3 RAY CURVATURE AND REFRACTION OF WAVE PACKETS. (U) SEP 78 .J E...BREEDING N00014—77—C—0329 UNCLASSIFIED TR JE6 3 NL _ _ _ rwii__ _ ~iU ir!I I -~~ RAYOJR\\1L~[UREAND REFRACI ION OF WAVE F1~\\CKET~S ~y J. Ernest Breeding...01 29 014 -~ Technical Report No. JEB-3 Department of Oceanography • Florida State University RAY CURVATURE AND REFRACTION OF WAVE PACKETS b O G • J

  3. A Liquid Prism for Refractive Index Studies

    NASA Astrophysics Data System (ADS)

    Edmiston, Michael D.

    2001-11-01

    A hollow glass prism filled with liquid becomes a "liquid prism". A simple method for constructing hollow glass prisms is presented. A method is given for a demonstration that uses the liquid prism with a laser or laser pointer so the audience can observe differences in refractive index for various liquids. The demonstration provides a quick and easy determination of the sugar content of soft drinks and juices. The prism makes it easy to determine a numerical value for the refractive index of a liquid.

  4. Refractive acoustic devices for airborne sound.

    PubMed

    Cervera, F; Sanchis, L; Sánchez-Pérez, J V; Martínez-Sala, R; Rubio, C; Meseguer, F; López, C; Caballero, D; Sánchez-Dehesa, J

    2002-01-14

    We show that a sonic crystal made of periodic distributions of rigid cylinders in air acts as a new material which allows the construction of refractive acoustic devices for airborne sound. It is demonstrated that, in the long-wave regime, the crystal has low impedance and the sound is transmitted at subsonic velocities. Here, the fabrication and characterization of a convergent lens are presented. Also, an example of a Fabry-Perot interferometer based on this crystal is analyzed. It is concluded that refractive devices based on sonic crystals behave in a manner similar to that of optical systems.

  5. Plasmonic crystal enhanced refractive index sensing

    SciTech Connect

    Stein, Benedikt; Devaux, Eloïse; Genet, Cyriaque Ebbesen, Thomas W.

    2014-06-23

    We demonstrate experimentally how the local anisotropy of the dispersion relation of surface plasmon modes propagating over periodic metal gratings can lead to an enhancement of the figure of merit of refractive index sensors. Exploiting the possibility to acquire defocused images of the Fourier space of a highly stable leakage radiation microscope, we report a twofold increase in sensing sensitivity close to the band gap of a one-dimensional plasmonic crystal where the anisotropy of the band structure is the most important. A practical sensing resolution of O(10{sup −6}) refractive index units is demonstrated.

  6. Stabilisation of refraction following cataract surgery.

    PubMed Central

    Baranyovits, P R

    1988-01-01

    Refraction was performed at frequent, regular intervals for six months following routine intracapsular cataract extraction. Patients were divided into two groups, those whose limbal sections were closed with 8-0 virgin silk or with 9-0 nylon. The stabilisation of refraction was observed, and the most suitable time to prescribe 'first glasses' was estimated retrospectively. In the silk group this was found to be at three months in the nylon group at four months. However, results in the latter were less predictable with greater variation. PMID:3061448

  7. Optical negative refraction in ferrofluids with magnetocontrollability.

    PubMed

    Gao, Y; Huang, J P; Liu, Y M; Gao, L; Yu, K W; Zhang, X

    2010-01-22

    We numerically demonstrate optical negative refraction in ferrofluids containing isotropic Fe3O4 nanoparticles, each having an isotropic Ag shell, in the presence of an external dc magnetic field H. The all-angle broadband optical negative refraction with magnetocontrollability arises from H-induced chains or columns. They result in hyperbolic equifrequency contour for transverse magnetic waves propagating in the system. The finite element simulations verify the analyses using the effective medium approximation. Experimental demonstration and potential applications are suggested and discussed.

  8. Sensitivity analysis and performance estimation of refractivity from clutter techniques

    NASA Astrophysics Data System (ADS)

    Yardim, Caglar; Gerstoft, Peter; Hodgkiss, William S.

    2009-02-01

    Refractivity from clutter (RFC) refers to techniques that estimate the atmospheric refractivity profile from radar clutter returns. A RFC algorithm works by finding the environment whose simulated clutter pattern matches the radar measured one. This paper introduces a procedure to compute RFC estimator performance. It addresses the major factors such as the radar parameters, the sea surface characteristics, and the environment (region, time of the day, season) that affect the estimator performance and formalizes an error metric combining all of these. This is important for applications such as calculating the optimal radar parameters, selecting the best RFC inversion algorithm under a set of conditions, and creating a regional performance map of a RFC system. The performance metric is used to compute the RFC performance of a non-Bayesian evaporation duct estimator. A Bayesian estimator that incorporates meteorological statistics in the inversion is introduced and compared to the non-Bayesian estimator. The performance metric is used to determine the optimal radar parameters of the evaporation duct estimator for six scenarios. An evaporation duct inversion performance map for a S band radar is created for the larger Mediterranean/Arabian Sea region.

  9. Radiation pressure cross sections and optical forces over negative refractive index spherical particles by ordinary Bessel beams.

    PubMed

    Ambrosio, Leonardo A; Hernández-Figueroa, Hugo E

    2011-08-01

    When impinged by an arbitrary laser beam, lossless and homogeneous negative refractive index (NRI) spherical particles refract and reflect light in an unusual way, giving rise to different scattered and internal fields when compared to their equivalent positive refractive index particles. In the generalized Lorenz-Mie theory, the scattered fields are dependent upon the Mie scattering coefficients, whose values must reflect the metamaterial behavior of an NRI scatterer, thus leading to new optical properties such as force and torque. In this way, this work is devoted to the analysis of both radial and longitudinal optical forces exerted on lossless and simple NRI particles by zero-order Bessel beams, revealing how the force profiles are changed whenever the refractive index becomes negative.

  10. Fabrication of gradient refractive index ball lenses using the method of combination of ion exchanging and sagging

    NASA Astrophysics Data System (ADS)

    Hao, Lv; Bangren, Shi; Jijiang, Wu; Lijun, Guo; Aimei, Liu

    2007-08-01

    Based on the Fick's diffusion equations, the distribution function of refractive index of a gradient refractive index ball lens (GRIN ball lens/GBL) is derived. Lithium containing silicate glass is fabricated and GRIN ball lenses (GBLs) which diameters are from 0.3 mm to 3.0 mm are made by the method of combination of Ion exchanging and sagging in sodium nitrate. Refractive index profiles of these GBLs are measured by interferometer, and the performances such as effective focal length (EFL), back focal length (BFL) and numerical aperture (NA) between GBLs and homogeneous ball lenses (HBLs) are compared. Results show that the distribution of the index of refraction is parabolic curve and its Δn is about 0.0002, the performances of the former are super to the latter.

  11. Implantable collamer lens for residual refractive error after corneal refractive surgery

    PubMed Central

    Chen, Xun; Wang, Xiao-Ying; Zhang, Xi; Chen, Zhi; Zhou, Xing-Tao

    2016-01-01

    AIM To assess the safety, efficacy, predictability and stability of implantable collamer lens (ICL) for residual refractive error after corneal refractive surgery. METHODS This study evaluated 19 eyes of 12 patients who underwent ICL implantation after corneal refractive surgeries. They were followed up for 1y to 5y of uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refractive error, flat and steep K value, axial length, intraocular pressure, corneal endothelial cell density, adverse events after ICL surgery. RESULTS The mean follow-up period was 39.05±19.22 mo (range, 1-5y). Spherical equivalent refractive error changed from -7.45±3.02 D preoperatively to -0.85±1.10 D 1wk to 1mo after ICL implantation, with the safety and efficacy indices being 1.12 and 1.15, respectively. A total of 52.63% of eyes were within ±0.5 D of the predicted spherical equivalents, 73.68% were within ±1.0 D. A trend of mild regression towards myopia with axial elongation after 5y was observed. One eye with mild anterior capsule opacity and retinal detachment 1y after surgery were observed. CONCLUSION ICL implantation is safe and effective for the correction of residual refractive error after corneal refractive surgeries, especially in moderate to high residual myopia. PMID:27803858

  12. Refractive index of air: 3. The roles of CO2, H2O, and refractivity virials.

    PubMed

    Ciddor, Philip E

    2002-04-20

    The author's recent studies of the refractive index of air are extended, and several assumptions made therein are further examined. It is shown that the alternative dispersion equations for CO2, which are due to Edlen [Metrologia 2, 71 (1966)] and Old et al. [J. Opt. Soc. Am. 61, 89 (1971)] result in differences of less than 2 x 10(-9) in the phase refractive index and less than 3 x 10(-9) in the group refractive index for current and predicted concentrations of CO2. However, because the dispersion equation given by Old et al. is consistent with experimental data in the near infrared, it is preferable to the equation used by Edlen, which is valid only in the ultraviolet and the visible. The classical measurement by Barrell and Sears [Philos. Trans. R. Soc. London Ser. A 238, 1 (1939)] on the refractivity of moist air is shown to have some procedural errors in addition to the one discussed by Birch and Downs [Metrologia 30, 155 (1993)]. It is shown that for normal atmospheric conditions the higher refractivity virial coefficients related to the Lorentz-Lorenz relation are adequately incorporated into the empirically determined first refractivity virial. As a guide to users the practical limits to the calculation of the refractive index of the atmosphere that result from the uncertainties in the measurement of the various atmospheric parameters are summarized.

  13. Calculations of atmospheric refraction for spacecraft remote-sensing applications

    NASA Technical Reports Server (NTRS)

    Chu, W. P.

    1983-01-01

    Analytical solutions to the refraction integrals appropriate for ray trajectories along slant paths through the atmosphere are derived in this paper. This type of geometry is commonly encountered in remote-sensing applications utilizing an occultation technique. The solutions are obtained by evaluating higher-order terms from expansion of the refraction integral and are dependent on the vertical temperature distributions. Refraction parameters such as total refraction angles, air masses, and path lengths can be accurately computed. It is also shown that the method can be used for computing refraction parameters in astronomical refraction geometry for large zenith angles.

  14. Calculations of atmospheric refraction for spacecraft remote-sensing applications

    NASA Technical Reports Server (NTRS)

    Chu, W. P.

    1983-01-01

    Analytical solutions to the refraction integrals appropriate for ray trajectories along slant paths through the atmosphere are derived in this paper. This type of geometry is commonly encountered in remote-sensing applications utilizing an occultation technique. The solutions are obtained by evaluating higher-order terms from expansion of the refraction integral and are dependent on the vertical temperature distributions. Refraction parameters such as total refraction angles, air masses, and path lengths can be accurately computed. It is also shown that the method can be used for computing refraction parameters in astronomical refraction geometry for large zenith angles.

  15. Modal study of refractive effects on x-ray laser coherence

    SciTech Connect

    Amendt, P.; London, R.A. ); Strauss, M. . Nuclear Research Center-Negev)

    1991-04-05

    The role of smoothly varying transverse gain and refraction profiles on x-ray laser intensity and coherence is analyzed by modally expanding the electric field within the paraxial approximation. Comparison with a square transverse profile reveals that smooth-edged profiles lead to: (1) a greatly reduced number of guided modes, (2) the continued cancellation of local intensity from a loosely guided mode by resonant free modes, (3) and the absence of extraneous (or anomalous) free mode resonances. These generic spectral properties should enable a considerable simplification in analyzing and optimizing the coherence properties of laboratory soft x-ray lasers. 6 refs., 3 figs.

  16. Joint analysis of refractions with surface waves: An inverse solution to the refraction-traveltime problem

    USGS Publications Warehouse

    Ivanov, J.; Miller, R.D.; Xia, J.; Steeples, D.; Park, C.B.

    2006-01-01

    We describe a possible solution to the inverse refraction-traveltime problem (IRTP) that reduces the range of possible solutions (nonuniqueness). This approach uses a reference model, derived from surface-wave shear-wave velocity estimates, as a constraint. The application of the joint analysis of refractions with surface waves (JARS) method provided a more realistic solution than the conventional refraction/tomography methods, which did not benefit from a reference model derived from real data. This confirmed our conclusion that the proposed method is an advancement in the IRTP analysis. The unique basic principles of the JARS method might be applicable to other inverse geophysical problems. ?? 2006 Society of Exploration Geophysicists.

  17. Accuracy of refractive outcomes in myopic and hyperopic laser in situ keratomileusis: Manifest versus aberrometric refraction.

    PubMed

    Reinstein, Dan Z; Morral, Merce; Gobbe, Marine; Archer, Timothy J

    2012-11-01

    To compare the achieved refractive accuracy of laser in situ keratomileusis (LASIK) performed based on manifest refraction with the predicted accuracy that would have been achieved using WASCA aberrometric refraction with and without Seidel correction factor for sphere. London Vision Clinic, London, United Kingdom. Comparative case series. Myopic eyes and hyperopic eyes had LASIK based on manifest refraction. Two aberrometric refractions were obtained preoperatively: Seidel, which includes spherical aberration in the sphere calculation, and non-Seidel. Bland-Altman plots were used to show the agreement between aberrometric and manifest refractions. Predicted LASIK outcomes had aberrometric refraction been used were modeled by shifting the postoperative manifest refraction by the vector difference between the preoperative manifest and aberrometric refractions. This study included 869 myopic eyes and 413 hyperopic eyes. The mean differences (manifest minus aberrometric) in spherical equivalent were +0.03 diopters (D) ± 0.48 (SD) (Seidel aberrometric) and +0.45 ± 0.42 D (non-Seidel aberrometric) for myopia and -0.20 ± 0.39 D and +0.39 ± 0.34 D, respectively, for hyperopia. The mean differences in cylinder magnitude were -0.10 ± 0.27 D and 0.00 ± 0.25 D, respectively. The percentage of eyes within ±0.50 D of the attempted correction was 81% (manifest), 70% (Seidel), and 67% (non-Seidel) for myopia and 71% (manifest), 61% (Seidel), and 64% (non-Seidel) for hyperopia. The achieved refractive accuracy by manifest refraction was better than the predicted accuracy had Seidel or non-Seidel aberrometric refractions been used for surgical planning. Using the Seidel method improved the accuracy in myopic eyes but not in hyperopic eyes. Dr. Reinstein is a consultant to Carl Zeiss Meditec AG and has a proprietary interest in the Artemis technology (Arcscan Inc., Morrison, Colorado, USA) through patents administered by the Cornell Center for Technology Enterprise and

  18. Temperature Humidity and Sea Level Pressure Increments Induced by 1DVAR Analysis of GPS Refractivity

    NASA Technical Reports Server (NTRS)

    Poli, Paul; Joiner, Joanna; Kursinski, Emil Robert; Einaudi, Franco (Technical Monitor)

    2001-01-01

    The Global Positioning System (GPS) transmitted signals are affected by the atmosphere. Using the radio occultation technique, where a receiver is placed on a low-Earth-orbiting platform. it is possible to perform soundings. by measuring the bending angles of the rays. The information can be converted into atmospheric refractivity. We have developed a one dimensional variational (1DVAR) analysis that uses GPS/MET 1995 refractivity and 6-hour FVDAS (Finite Volume Data Assimilation System) forecasts as background information to constrain the retrievals. The analysis increments are defined as 1DVAR minus background temperature, humidity and sea level pressure. Before assimilating the 1DVAR profiles into the FVDAS. the increments need to be understood. First, some bias could be induced in the retrievals when confronted with actual biased data: second. bias in the back-round could create undesired bias in the retrievals. Anv bias in the analyses will ultimately change the climatology of the model the retrievals will be assimilated into. We relate the increments to the reduction of the difference between observed minus computed refractivity profiles. We also point out the difference in the mean increments using backgrounds which have assimilated either NESDIS TIROS Operational Vertical Sounder (TOVS) operational retrievals or Data Assimilation Office (DAO) TOVS interactive retrievals. The climatology of the model in terms of refractivity is significantly different and this impacts the GPS 1DVAR increments. This testifies that changing the basic load of assimilated data has an influence on the impact the GPS data may have in a DAS.

  19. Temperature Humidity and Sea Level Pressure Increments Induced by 1DVAR Analysis of GPS Refractivity

    NASA Technical Reports Server (NTRS)

    Poli, Paul; Joiner, Joanna; Kursinski, Emil Robert; Einaudi, Franco (Technical Monitor)

    2001-01-01

    The Global Positioning System (GPS) transmitted signals are affected by the atmosphere. Using the radio occultation technique, where a receiver is placed on a low-Earth-orbiting platform. it is possible to perform soundings. by measuring the bending angles of the rays. The information can be converted into atmospheric refractivity. We have developed a one dimensional variational (1DVAR) analysis that uses GPS/MET 1995 refractivity and 6-hour FVDAS (Finite Volume Data Assimilation System) forecasts as background information to constrain the retrievals. The analysis increments are defined as 1DVAR minus background temperature, humidity and sea level pressure. Before assimilating the 1DVAR profiles into the FVDAS. the increments need to be understood. First, some bias could be induced in the retrievals when confronted with actual biased data: second. bias in the back-round could create undesired bias in the retrievals. Anv bias in the analyses will ultimately change the climatology of the model the retrievals will be assimilated into. We relate the increments to the reduction of the difference between observed minus computed refractivity profiles. We also point out the difference in the mean increments using backgrounds which have assimilated either NESDIS TIROS Operational Vertical Sounder (TOVS) operational retrievals or Data Assimilation Office (DAO) TOVS interactive retrievals. The climatology of the model in terms of refractivity is significantly different and this impacts the GPS 1DVAR increments. This testifies that changing the basic load of assimilated data has an influence on the impact the GPS data may have in a DAS.

  20. The estimation of lower refractivity uncertainty from radar sea clutter using the Bayesian—MCMC method

    NASA Astrophysics Data System (ADS)

    Sheng, Zheng

    2013-02-01

    The estimation of lower atmospheric refractivity from radar sea clutter (RFC) is a complicated nonlinear optimization problem. This paper deals with the RFC problem in a Bayesian framework. It uses the unbiased Markov Chain Monte Carlo (MCMC) sampling technique, which can provide accurate posterior probability distributions of the estimated refractivity parameters by using an electromagnetic split-step fast Fourier transform terrain parabolic equation propagation model within a Bayesian inversion framework. In contrast to the global optimization algorithm, the Bayesian—MCMC can obtain not only the approximate solutions, but also the probability distributions of the solutions, that is, uncertainty analyses of solutions. The Bayesian—MCMC algorithm is implemented on the simulation radar sea-clutter data and the real radar sea-clutter data. Reference data are assumed to be simulation data and refractivity profiles are obtained using a helicopter. The inversion algorithm is assessed (i) by comparing the estimated refractivity profiles from the assumed simulation and the helicopter sounding data; (ii) the one-dimensional (1D) and two-dimensional (2D) posterior probability distribution of solutions.

  1. Compound refractive X-ray lens

    DOEpatents

    Nygren, David R.; Cahn, Robert; Cederstrom, Bjorn; Danielsson, Mats; Vestlund, Jonas

    2000-01-01

    An apparatus and method for focusing X-rays. In one embodiment, his invention is a commercial-grade compound refractive X-ray lens. The commercial-grade compound refractive X-ray lens includes a volume of low-Z material. The volume of low-Z material has a first surface which is adapted to receive X-rays of commercially-applicable power emitted from a commercial-grade X-ray source. The volume of low-Z material also has a second surface from which emerge the X-rays of commercially-applicable power which were received at the first surface. Additionally, the commercial-grade compound refractive X-ray lens includes a plurality of openings which are disposed between the first surface and the second surface. The plurality of openings are oriented such that the X-rays of commercially-applicable power which are received at the first surface, pass through the volume of low-Z material and through the plurality openings. In so doing, the X-rays which emerge from the second surface are refracted to a focal point.

  2. Refraction in TYCHO Brahe's Small Universe

    NASA Astrophysics Data System (ADS)

    Moesgaard, K. P.

    Tycho Brahe's work set a new standard of objectivity in empirical science. Aiming at an observational accuracy of one minute of arc he had to introduce corrections of atmospheric refraction. This proved to be anything but trivial, mainly because Tycho adopted the traditional value of 3arcmin for the parallax of the sun.

  3. Validation of Ray Tracing Code Refraction Effects

    NASA Technical Reports Server (NTRS)

    Heath, Stephanie L.; McAninch, Gerry L.; Smith, Charles D.; Conner, David A.

    2008-01-01

    NASA's current predictive capabilities using the ray tracing program (RTP) are validated using helicopter noise data taken at Eglin Air Force Base in 2007. By including refractive propagation effects due to wind and temperature, the ray tracing code is able to explain large variations in the data observed during the flight test.

  4. Blending History with Physics: Acoustic Refraction.

    ERIC Educational Resources Information Center

    Ross, Charles D.

    2000-01-01

    Argues that the study of refraction of sound waves, although usually neglected, is an excellent ancillary to the normal optical approach in physics courses. Discusses the historical context of interest in the science behind outdoor sound propagation, particularly during the Civil War in the United States. (WRM)

  5. Blending History with Physics: Acoustic Refraction.

    ERIC Educational Resources Information Center

    Ross, Charles D.

    2000-01-01

    Argues that the study of refraction of sound waves, although usually neglected, is an excellent ancillary to the normal optical approach in physics courses. Discusses the historical context of interest in the science behind outdoor sound propagation, particularly during the Civil War in the United States. (WRM)

  6. A Mechanical Analogue of the Refracting Telescope

    ERIC Educational Resources Information Center

    Vannoni, Maurizio; Molesini, Giuseppe; Sordini, Andrea; Straulino, Samuele

    2011-01-01

    The recent celebration of the discoveries made by Galileo four centuries ago has attracted new attention to the refracting telescope and to its use as an instrument for the observation of the night sky. This has offered the opportunity for addressing in the classroom the basic principles explaining the operation of the telescope. When doing so, a…

  7. Refractive Surgery in Systemic and Autoimmune Disease

    PubMed Central

    AlKharashi, Majed; Bower, Kraig S.; Stark, Walter J.; Daoud, Yassine J.

    2014-01-01

    Patients with underlying systemic disease represent challenging treatment dilemma to the refractive surgeon. The refractive error in this patient population is accompanied by a systemic disease that may have an ocular or even a corneal component. The literature is rather sparse about the use of laser refractive surgery (LRS) and such procedure is not approved by the United States Food and Drug Administration (FDA) in this patient population. Patients with collagen vascular disease, diabetes mellitus (DM), allergic and atopic disease, or human immunodeficiency virus (HIV) are never ideal for LRS. Patients with uncontrolled systemic disease or ocular involvement of the disease should not undergo LRS. However, a patient with well-controlled and mild disease, no ocular involvement, and not on multidrug regimen may be a suitable candidate if they meet stringent criteria. There is a need for a large, multicenter, controlled trial to address the safety and efficacy of LRS in patients with systemic disease before such technology can be widely adopted by the refractive surgery community. PMID:24669141

  8. A Mechanical Analogue of the Refracting Telescope

    ERIC Educational Resources Information Center

    Vannoni, Maurizio; Molesini, Giuseppe; Sordini, Andrea; Straulino, Samuele

    2011-01-01

    The recent celebration of the discoveries made by Galileo four centuries ago has attracted new attention to the refracting telescope and to its use as an instrument for the observation of the night sky. This has offered the opportunity for addressing in the classroom the basic principles explaining the operation of the telescope. When doing so, a…

  9. Subjective refraction: the mechanism underlying the routine.

    PubMed

    Harris, W F

    2007-11-01

    The routine of subjective refraction is usually understood, explained and taught in terms of the relative positions of line or point foci and the retina. This paper argues that such an approach makes unnecessary and sometimes invalid assumptions about what is actually happening inside the eye. The only assumption necessary in fact is that the subject is able to guide the refractionist to (or close to) the optimum power for refractive compensation. The routine works even in eyes in which the interval of Sturm does not behave as supposed; it would work, in fact, regardless of the structure of the eye. The idealized subjective refraction routine consists of two steps: the first finds the best sphere (the stigmatic component) and the second finds the remaining Jackson cross-cylinder (the antistigmatic component). The model makes use of the concept of symmetric dioptric power space. The second part of the refraction routine can be performed with Jackson cross-cylinders alone. However, it is usually taught and practiced using spheres, cylinders and Jackson cross-cylinders in a procedure that is not easy to understand and learn. Recognizing that this part of the routine is equivalent to one involving Jackson cross-cylinders only allows one to teach and understand the procedure more naturally and easily.

  10. Refraction of light by light in vacuum

    NASA Astrophysics Data System (ADS)

    Sarazin, Xavier; Couchot, François; Djannati-Ataï, Arache; Guilbaud, Olivier; Kazamias, Sophie; Pittman, Moana; Urban, Marcel

    2016-01-01

    In very intense electromagnetic fields, the vacuum refractive index is expected to be modified due to nonlinear quantum electrodynamics (QED) properties. Several experimental tests using high intensity lasers have been proposed to observe electromagnetic nonlinearities in vacuum, such as the diffraction or the reflection of intense laser pulses. We propose a new approach which consists in observing the refraction, i.e. the rotation of the waveplanes of a probe laser pulse crossing a transverse vacuum index gradient. The latter is produced by the interaction of two very intense and ultra short laser pulses, used as pump pulses. At the maximum of the index gradient, the refraction angle of the probe pulse is estimated to be 0.2 × (w0/10 μm)-3 × I/1J prad, where I is the total energy of the two pump pulses and w0 is the minimum waist (fwhm) at the interaction area. Assuming the most intense laser pulses attainable by the LASERIX facility (I = 25 J, 30 fs fwhm duration, 800 nm central wavelength) and assuming a minimum waist of w = 10 μm (fwhm) (corresponding to an intensity of the order of 1021 W/cm2), the expected maximum refraction angle is about 5 prad. An experimental setup, using a Sagnac interferometer, is proposed to perform this measurement.

  11. Refractive Indices of Gases at Microwave Frequencies

    ERIC Educational Resources Information Center

    Goodhead, D. T.; And Others

    1976-01-01

    Describes a simple microwave interferometer capable of measuring small phase shifts. Proposes laboratory exercises involving the use of the interferometer in the determination of refractive indices of gases and the analysis of the reflection in a test chamber. (Author/CP)

  12. Non-interferometric phase retrieval using refractive index manipulation

    NASA Astrophysics Data System (ADS)

    Chen, Chyong-Hua; Hsu, Hsin-Feng; Chen, Hou-Ren; Hsieh, Wen-Feng

    2017-04-01

    We present a novel, inexpensive and non-interferometric technique to retrieve phase images by using a liquid crystal phase shifter without including any physically moving parts. First, we derive a new equation of the intensity-phase relation with respect to the change of refractive index, which is similar to the transport of the intensity equation. The equation indicates that this technique is unneeded to consider the variation of magnifications between optical images. For proof of the concept, we use a liquid crystal mixture MLC 2144 to manufacture a phase shifter and to capture the optical images in a rapid succession by electrically tuning the applied voltage of the phase shifter. Experimental results demonstrate that this technique is capable of reconstructing high-resolution phase images and to realize the thickness profile of a microlens array quantitatively.

  13. Infrasonic interferometry of stratospherically refracted microbaroms--a numerical study.

    PubMed

    Fricke, Julius T; El Allouche, Nihed; Simons, Dick G; Ruigrok, Elmer N; Wapenaar, Kees; Evers, Läslo G

    2013-10-01

    The atmospheric wind and temperature can be estimated through the traveltimes of infrasound between pairs of receivers. The traveltimes can be obtained by infrasonic interferometry. In this study, the theory of infrasonic interferometry is verified and applied to modeled stratospherically refracted waves. Synthetic barograms are generated using a raytracing model and taking into account atmospheric attenuation, geometrical spreading, and phase shifts due to caustics. Two types of source wavelets are implemented for the experiments: blast waves and microbaroms. In both numerical experiments, the traveltimes between the receivers are accurately retrieved by applying interferometry to the synthetic barograms. It is shown that microbaroms can be used in practice to obtain the traveltimes of infrasound through the stratosphere, which forms the basis for retrieving the wind and temperature profiles.

  14. Effects of refractive index mismatch on SRS and CARS microscopy.

    PubMed

    van der Kolk, Jarno; Lesina, Antonino Calà; Ramunno, Lora

    2016-10-31

    An inhomogeneous linear refractive index profile, such as that occurring in biological tissues, is shown to significantly alter stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) microscopy images. Our finite-difference time-domain simulations show that near-field enhancement and microlensing can lead to an increase of an object's perceived molecular density by a factor of nine and changes in its perceived position by 0.4 μm up to 1.0 μm. Thus the assumption that SRS scales linearly and CARS quadratically with density does not always hold. Furthermore, the inhomogeneous linear index can cause false CARS and AM-SRS signals, even for a homogeneous nonlinear susceptibility.

  15. Semiconductor laser devices having lateral refractive index tailoring

    DOEpatents

    Ashby, Carol I. H.; Hadley, G. Ronald; Hohimer, John P.; Owyoung, Adelbert

    1990-01-01

    A broad-area semiconductor laser diode includes an active lasing region interposed between an upper and a lower cladding layer, the laser diode further comprising structure for controllably varying a lateral refractive index profile of the diode to substantially compensate for an effect of junction heating during operation. In embodiments disclosed the controlling structure comprises resistive heating strips or non-radiative linear junctions disposed parallel to the active region. Another embodiment discloses a multi-layered upper cladding region selectively disordered by implanted or diffused dopant impurities. Still another embodiment discloses an upper cladding layer of variable thickness that is convex in shape and symmetrically disposed about a central axis of the active region. The teaching of the invention is also shown to be applicable to arrays of semiconductor laser diodes.

  16. Non-interferometric phase retrieval using refractive index manipulation

    PubMed Central

    Chen, Chyong-Hua; Hsu, Hsin-Feng; Chen, Hou-Ren; Hsieh, Wen-Feng

    2017-01-01

    We present a novel, inexpensive and non-interferometric technique to retrieve phase images by using a liquid crystal phase shifter without including any physically moving parts. First, we derive a new equation of the intensity-phase relation with respect to the change of refractive index, which is similar to the transport of the intensity equation. The equation indicates that this technique is unneeded to consider the variation of magnifications between optical images. For proof of the concept, we use a liquid crystal mixture MLC 2144 to manufacture a phase shifter and to capture the optical images in a rapid succession by electrically tuning the applied voltage of the phase shifter. Experimental results demonstrate that this technique is capable of reconstructing high-resolution phase images and to realize the thickness profile of a microlens array quantitatively. PMID:28387382

  17. Loop-mirror-based slot waveguide refractive index sensor

    NASA Astrophysics Data System (ADS)

    Kou, Jun-long; Xu, Fei; Lu, Yan-qing

    2012-12-01

    Loop mirror has been widely used in fiber optical devices and systems for it provides a smart way to make use of the fiber birefringence properties and can enhance the sensitivity greatly. On the other hand, slot waveguide is very promising for optical sensing applications because of their peculiar spatial mode profile. In this paper, we propose and analyze a loop-mirror-based slot waveguide (LMSW) sensor which can be routinely fabricated in modern high-volume complementary metal-oxide-semiconductor (CMOS) process. The finite element method (FEM) simulation results show that the birefringence can be as high as 0.8 which is orders of magnitude than that in conventional birefringent fiber loop mirror. High sensitivity up to 6 × 103 nm/RIU (refractive index unit) is achieved by this scheme.

  18. Refractive outcomes after multifocal intraocular lens exchange.

    PubMed

    Kim, Eric J; Sajjad, Ahmar; Montes de Oca, Ildamaris; Koch, Douglas D; Wang, Li; Weikert, Mitchell P; Al-Mohtaseb, Zaina N

    2017-06-01

    To evaluate the refractive outcomes after multifocal intraocular lens (IOL) exchange. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Retrospective case series. Patients had multifocal IOL explantation followed by IOL implantation. Outcome measures included type of IOL, surgical indication, corrected distance visual acuity (CDVA), and refractive prediction error. The study comprised 29 patients (35 eyes). The types of IOLs implanted after multifocal IOL explantation included in-the-bag IOLs (74%), iris-sutured IOLs (6%), sulcus-fixated IOLs with optic capture (9%), sulcus-fixated IOLs without optic capture (9%), and anterior chamber IOLs (3%). The surgical indication for exchange included blurred vision (60%), photic phenomena (57%), photophobia (9%), loss of contrast sensitivity (3%), and multiple complaints (29%). The CDVA was 20/40 or better in 94% of eyes before the exchange and 100% of eyes after the exchange (P = .12). The mean refractive prediction error significantly decreased from 0.22 ± 0.81 diopter (D) before the exchange to -0.09 ± 0.53 D after the exchange (P < .05). The median absolute refractive prediction error significantly decreased from 0.43 D before the exchange to 0.23 D after the exchange (P < .05). Multifocal IOL exchange can be performed safely with good visual outcomes using different types of IOLs. A lower refractive prediction error and a higher likelihood of 20/40 or better vision can be achieved with the implantation of the second IOL compared with the original multifocal IOL, regardless of the final IOL position. Copyright © 2017 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  19. Specific features of measuring the optical power of artificial refractive and diffractive-refractive eye lenses

    NASA Astrophysics Data System (ADS)

    Lenkova, G. A.

    2016-08-01

    Methods for monitoring the optical power of artificial refractive eye lenses (intraocular lenses) based on measuring focal lengths in air and in medium are analyzed. The methods for determining the refraction of diffractive-refractive lenses (in particular, of MIOL-Akkord type), with allowance for the specific features of the diffractive structure, are considered. A computer simulation of the measurement of the focal length of MIOL-Akkord lenses is performed. The effective optical power of the diffractive component of these lenses is shown to depend on the diaphragm diameter. The optimal diaphragm diameter, at which spherical aberrations do not affect the position of foci, is found to be 3 mm. Possible errors in measuring the focal lengths are analyzed, and the necessary corrections that must be introduced into measurement results and calculations of refractions are determined.

  20. Effects of myopic spectacle correction and radial refractive gradient spectacles on peripheral refraction.

    PubMed

    Tabernero, Juan; Vazquez, Daniel; Seidemann, Anne; Uttenweiler, Dietmar; Schaeffel, Frank

    2009-08-01

    The recent observation that central refractive development might be controlled by the refractive errors in the periphery, also in primates, revived the interest in the peripheral optics of the eye. We optimized an eccentric photorefractor to measure the peripheral refractive error in the vertical pupil meridian over the horizontal visual field (from -45 degrees to 45 degrees ), with and without myopic spectacle correction. Furthermore, a newly designed radial refractive gradient lens (RRG lens) that induces increasing myopia in all radial directions from the center was tested. We found that for the geometry of our measurement setup conventional spectacles induced significant relative hyperopia in the periphery, although its magnitude varied greatly among different spectacle designs and subjects. In contrast, the newly designed RRG lens induced relative peripheral myopia. These results are of interest to analyze the effect that different optical corrections might have on the emmetropization process.

  1. Electrodynamics of moving media inducing positive and negative refraction

    SciTech Connect

    Grzegorczyk, Tomasz M.; Kong, Jin Au

    2006-07-15

    Negative refraction is a phenomenon that has been recently reported with left-handed media (either isotropic or not), photonic crystals, and rotated uniaxial media. In this Brief Report, we identify another origin of negative refraction, due to the motion of the transmitted medium parallel to the interface at which refraction occurs. Previous works in this domain have concentrated on media velocities that are above the Cerenkov limit, while we show here that negative refraction is in fact achievable at any velocities of the transmitted medium. A possible experimental implementation is proposed to verify this effect. Next, we consider an isotropic frequency-dispersive medium for which the index of refraction can take negative values, and we study the wave refraction phenomenon as a function of frequency and medium velocity. It is found that the motion of the medium induces a rotation of refraction, which can either enhance or attenuate the natural negative refraction of the medium.

  2. Automatic Refraction: How It Is Done: Some Clinical Results

    ERIC Educational Resources Information Center

    Safir, Aran; And Others

    1973-01-01

    Compaired are methods of determining visual refraction needs of young children or other unreliable observers by means of retinosocopy or the Opthalmetron, an automatic instrument which can be operated by a technician with no knowledge of refraction. (DB)

  3. Design of Amphoteric Refraction Models Using WAVICA and RAYICA

    NASA Technical Reports Server (NTRS)

    Su, Richard

    2004-01-01

    The phenomenon of refraction of light is due to refractive index mismatches in two different media. However, to achieve this effect, a finite reflection loss is inevitable. A recent finding presented a unique type of interface, ferroelastic materials, that enables refraction without any reflection for either an electron or a light beam. This property is called total refraction. The same type of interface that yields total refraction can also yield amphoteric refraction, where the index of refraction can be either positive or negative depending on the incident angle. This interface could potentially be used to steer light without reflections which could have major applications in high power optics. My goal this summer is to first familiarize myself with the Mathematica software, especially the Wavica and Rayica packages. I will then model the amphoteric refraction by either modifying the Wavica and Rayica packages or using the built-in functions in these packages.

  4. Automatic Refraction: How It Is Done: Some Clinical Results

    ERIC Educational Resources Information Center

    Safir, Aran; And Others

    1973-01-01

    Compaired are methods of determining visual refraction needs of young children or other unreliable observers by means of retinosocopy or the Opthalmetron, an automatic instrument which can be operated by a technician with no knowledge of refraction. (DB)

  5. Design of Amphoteric Refraction Models Using WAVICA and RAYICA

    NASA Technical Reports Server (NTRS)

    Su, Richard

    2004-01-01

    The phenomenon of refraction of light is due to refractive index mismatches in two different media. However, to achieve this effect, a finite reflection loss is inevitable. A recent finding presented a unique type of interface, ferroelastic materials, that enables refraction without any reflection for either an electron or a light beam. This property is called total refraction. The same type of interface that yields total refraction can also yield amphoteric refraction, where the index of refraction can be either positive or negative depending on the incident angle. This interface could potentially be used to steer light without reflections which could have major applications in high power optics. My goal this summer is to first familiarize myself with the Mathematica software, especially the Wavica and Rayica packages. I will then model the amphoteric refraction by either modifying the Wavica and Rayica packages or using the built-in functions in these packages.

  6. Goos-Hänchen shift in negatively refractive media.

    PubMed

    Berman, P R

    2002-12-01

    The Goos-Hänchen shift is calculated when total internal reflection occurs at an interface between "normal" and negatively refractive media. The shift is negative, consistent with the direction of energy flow in the negatively refractive medium.

  7. Negative light refraction in a gradient medium with ultrasound-modulated refractive index

    NASA Astrophysics Data System (ADS)

    Naimi, E. K.; Vekilov, Yu. Kh.

    2015-01-01

    The conditions of the formation of a spatially ordered optical structure with an ultrasound-modulated refractive index in a gradient medium have been considered. It has been shown that the excitation of a standing ultrasonic wave in the medium creates a structure consisting of trajectories of separate light beams, which is a superlattice of the "dynamic 4D photonic crystal." Regions corresponding to negative light refraction have been revealed in beam trajectories. Possible fields of application of such structures have been discussed.

  8. Methodes avancees pour le design de filtres optiques avec des indices de refraction intermediaires arbitraires

    NASA Astrophysics Data System (ADS)

    Larouche, Stephane

    Optical interference filters can be found everywhere. Their applications range from antireflective coatings present on almost every optical element to narrowband filters used in telecommunication networks and in astronomy. Most optical filters consist of a stack of homogeneous layers of two or a few materials with discrete refractive indices. They are called multilayer filters. If an appropriate process is available, it is also possible to fabricate graded-index filters, in which the refractive index varies continuously. Another less explored avenue is the conception of multilayer filters, but with layer of arbitrary intermediate refractive indices. At normal incidence, it has been demonstrated the optimal filter for a given application consists of only two materials with the greatest refractive index contrast. At oblique incidence, the situation is more complex. Electric and magnetic fields continuity conditions at interfaces are different for s and p polarizations, which leads to the definition of different pseudo refractive indices. It is generally accepted that the optimal solution maximizes the pseudo refractive index contrast, and it is therefore probable that the optimal design includes intermediate refractive indices. The conception of optical filters relies on the use of design, optimization, and synthesis methods. There exist many very effective methods for the conception of multilayer filters with discrete refractive indices. However, the methods are less adapted to the conception of filters with intermediate refractive indices. Graded-index filters can be designed using the approximate Fourier transform relationship between the refractive index profile and the desired spectrum. However, this method has two important drawbacks: (1) it is only approximate and (2) it does not account for the effect of the refractive index dispersion. The former is usually addressed by an iterative approach. However, there was no general solution to the problem of the

  9. [Results of refractive surgery in hyperopic and combined astigmatism].

    PubMed

    Vlaicu, Valeria

    2013-01-01

    The refractive surgery includes a lot of procedures for changing the refraction of the eye to obtain a better visual acuity with no glasses or contact lenses. LASIK is the most commonly performed laser refractive surgery today. The goal is to present the postoperative evolution of the refraction and visual acuity after LASIK for Mixed and Hyperopic Astigmatism. The results show that LASIK is safe and predictible if we have well performed interventions and well-selected patients.

  10. Visual acuity through fresnel, refractive, and hybrid diffractive/refractive prisms.

    PubMed

    Katz, Milton

    2004-08-01

    This article compares the effect on visual acuity of the Fresnel and wedge-shaped refractive prisms with newly developed hybrid diffractive/refractive prisms (ComPrisms), which combine a wedge-shaped refractive prism with a diffractive component. The diffractive component of hybrid elements can be designed to correct the chromatic aberration of the refractive component. The monocular visual acuity of 21 subjects and binocular acuity of 20 subjects were measured with computer-generated logMAR charts. Visual acuity was measured without prisms (NP) and through ComPrisms, 3M Press-on Fresnel, and acrylic refractive prisms of 20delta, 30delta, and 40delta powers. A repeated measures analysis of variance indicates a significant main effect of treatment (without prisms and through the three types of prisms) at each prism power, both monocularly and binocularly. Results of the Scheffé test for all possible comparisons between pairs of means of the treatments are provided. Although all the prisms reduced visual acuity, the ComPrisms provide significantly better visual acuity than acrylic refractive or 3M Press-on Fresnel prisms of equivalent power

  11. Shuttle program: Computing atmospheric scale height for refraction corrections

    NASA Technical Reports Server (NTRS)

    Lear, W. M.

    1980-01-01

    Methods for computing the atmospheric scale height to determine radio wave refraction were investigated for different atmospheres, and different angles of elevation. Tables of refractivity versus altitude are included. The equations used to compute the refraction corrections are given. It is concluded that very accurate corrections are determined with the assumption of an exponential atmosphere.

  12. Postoperative refraction in the second eye having cataract surgery.

    PubMed

    Leffler, Christopher T; Wilkes, Martin; Reeves, Juliana; Mahmood, Muneera A

    2011-01-01

    Introduction. Previous cataract surgery studies assumed that first-eye predicted and observed postoperative refractions are equally important for predicting second-eye postoperative refraction. Methods. In a retrospective analysis of 173 patients having bilateral sequential phacoemulsification, multivariable linear regression was used to predict the second-eye postoperative refraction based on refractions predicted by the SRK-T formula for both eyes, the first-eye postoperative refraction, and the difference in IOL selected between eyes. Results. The first-eye observed postoperative refraction was an independent predictor of the second eye postoperative refraction (P < 0.001) and was weighted more heavily than the first-eye predicted refraction. Compared with the SRK-T formula, this model reduced the root-mean-squared (RMS) error of the predicted refraction by 11.3%. Conclusions. The first-eye postoperative refraction is an independent predictor of the second-eye postoperative refraction. The first-eye predicted refraction is less important. These findings may be due to interocular symmetry.

  13. Refractive Changes Induced by Strabismus Corrective Surgery in Adults

    PubMed Central

    Leshno, Ari; Ziv-Baran, Tomer; Stolovitch, Chaim

    2017-01-01

    Purpose. To investigate refractive changes after strabismus correction procedures among adults. Methods. Retrospective chart review of adult patients who had horizontal recti muscles surgery with preoperative and postoperative cycloplegic refraction measurements. The preoperative refraction was mathematically subtracted from the postoperative refraction, and the induced refractive changes were statistically analyzed. Vector analysis was used to examine the magnitude of the toric change. The proportion of clinically significant refractive change was evaluated as well. Results. Thirty-one eyes from 22 subjects met the criteria and were included in the final analysis. A significant postoperative refractive change of the spherical equivalent towards myopia and a change of the astigmatism in the with-the-rule direction were observed. In a subset of 9 cases a third cycloplegic refraction measurement demonstrated stable refraction compared to the 1-month postoperative measurement. In 10 cases of single eye surgery, significant refractive changes were observed only in the operated side when compared to the sound eye. The induced surgical refractive change was of clinical significance (≥0.5 D) in 11 eyes of 9 patients (40.9% of patients). Conclusions. Refractive changes are a significant side effect of horizontal strabismus corrective surgery among adults. Therefore, patients should be informed about it prior to surgery and should be rerefracted in the postoperative period. PMID:28191347

  14. Postoperative Refraction in the Second Eye Having Cataract Surgery

    PubMed Central

    Leffler, Christopher T.; Wilkes, Martin; Reeves, Juliana; Mahmood, Muneera A.

    2011-01-01

    Introduction. Previous cataract surgery studies assumed that first-eye predicted and observed postoperative refractions are equally important for predicting second-eye postoperative refraction. Methods. In a retrospective analysis of 173 patients having bilateral sequential phacoemulsification, multivariable linear regression was used to predict the second-eye postoperative refraction based on refractions predicted by the SRK-T formula for both eyes, the first-eye postoperative refraction, and the difference in IOL selected between eyes. Results. The first-eye observed postoperative refraction was an independent predictor of the second eye postoperative refraction (P < 0.001) and was weighted more heavily than the first-eye predicted refraction. Compared with the SRK-T formula, this model reduced the root-mean-squared (RMS) error of the predicted refraction by 11.3%. Conclusions. The first-eye postoperative refraction is an independent predictor of the second-eye postoperative refraction. The first-eye predicted refraction is less important. These findings may be due to interocular symmetry. PMID:24533181

  15. Cosmology with a dark refraction index

    NASA Astrophysics Data System (ADS)

    Chen, Bin

    2009-09-01

    In this dissertation we review Gordon's optical metric theory, generalize it, and apply it to modern cosmology. In Chapter 1, we build the notation, define important quantities (luminosity distance, angular diameter distance, etc.), derive a few key equations (reciprocity relation, transport equations of optical scalars, etc.), and develop some basic techniques which will be useful later on. In Chapter 2 we apply Gordon's optical metric theory to Friedman-Lemaître- Robertson-Walker cosmologies. We associate a refraction index with the cosmic fluid and derive the refraction-corrected distance redshift relations. We then fit the Hubble curve of current supernova observations with a non-accelerating cosmological model. We also show that some observational effects caused by inhomogeneities, e.g., the Sachs-Wolfe effect, can be interpreted as being caused by an effective index of refraction, and hence this theory could extend to other speed of light communications such as gravitational radiation and neutrino fluxes. In Chapter 3 we show that Gordon's optical metric on a curved spacetime can be generalized to include absorption by allowing the metric to become complex. We distinguish two different cases, i.e., strong and weak absorption, and demonstrate the use of the complex optical metric theory by giving three examples. We use one of these examples to compute corrected distance-redshift relations for Friedman-Lemaître-Robertson-Walker models in which the cosmic fluid possesses a complex index of refraction that represents grey extinction. We then fit this corrected Hubble curve to the same supernovae data used in Chapter 2 by assuming pure absorption. In Chapter 4 we equate the physical intensity reduction of a light wave caused by weak absorption with a geometrical reduction in intensity caused by a "transverse" conformal transformation of the spacetime metric in which the wave travels. We then modify Gordon's optical metric to include absorption via a totally

  16. Holographic Refraction and the Measurement of Spherical Ametropia.

    PubMed

    Nguyen, Nicholas Hoai Nam

    2016-10-01

    To evaluate the performance of a holographic logMAR chart for the subjective spherical refraction of the human eye. Bland-Altman analysis was used to assess the level of agreement between subjective spherical refraction using the holographic logMAR chart and conventional autorefraction and subjective spherical refraction. The 95% limits of agreement (LoA) were calculated between holographic refraction and the two standard methods (subjective and autorefraction). Holographic refraction has a lower mean spherical refraction when compared to conventional refraction (LoA 0.11 ± 0.65 D) and when compared to autorefraction (LoA 0.36 ± 0.77 D). After correcting for systemic bias, this is comparable between autorefraction and conventional subjective refraction (LoA 0.45 ± 0.79 D). After correcting for differences in vergence distance and chromatic aberration between holographic and conventional refraction, approximately 65% (group 1) of measurements between holography and conventional subjective refraction were similar (MD = 0.13 D, SD = 0.00 D). The remaining 35% (group 2) had a mean difference of 0.45 D (SD = 0.12 D) between the two subjective methods. Descriptive statistics showed group 2's mean age (21 years, SD = 13 years) was considerably lower than group 1's mean age (41 years, SD = 17), suggesting accommodation may have a role in the greater mean difference of group 2. Overall, holographic refraction has good agreement with conventional refraction and is a viable alternative for spherical subjective refraction. A larger bias between holographic and conventional refraction was found in younger subjects than older subjects, suggesting an association between accommodation and myopic over-correction during holographic refraction.

  17. Uncladded sensing fiber for refractive index measurement

    SciTech Connect

    Bhardwaj, V. Gangwar, R. K.; Pathak, A. K.; Singh, V. K.

    2016-05-06

    The formation of chemically etched optical fiber for use in refractive index sensor is addressed. This presented design of a refractive index (RI) sensor is based on recording the power loss exhibited by radiation propagating through an etched multimode fiber (MMF) immersed in the liquid under study. The decreasing diameters of fibers are found to be strongly dependent on the temperature and etchant composition. This experiment was performed for different unclad etched fibers for same sensing length and the RI changes from 1.33 RIU to 1.38 RIU. When the multimode fiber (MMF) is etched for 12 hours the sensitivity of the sensor is approximately 204.25dBm/RIU, which is larger than without etched fiber having sensitivity 127.2dBm/RIU.

  18. Uncladded sensing fiber for refractive index measurement

    NASA Astrophysics Data System (ADS)

    Bhardwaj, V.; Gangwar, R. K.; Pathak, A. K.; Singh, V. K.

    2016-05-01

    The formation of chemically etched optical fiber for use in refractive index sensor is addressed. This presented design of a refractive index (RI) sensor is based on recording the power loss exhibited by radiation propagating through an etched multimode fiber (MMF) immersed in the liquid under study. The decreasing diameters of fibers are found to be strongly dependent on the temperature and etchant composition. This experiment was performed for different unclad etched fibers for same sensing length and the RI changes from 1.33 RIU to 1.38 RIU. When the multimode fiber (MMF) is etched for 12 hours the sensitivity of the sensor is approximately 204.25dBm/RIU, which is larger than without etched fiber having sensitivity 127.2dBm/RIU.

  19. Effective spectral dispersion of refractive index modulation

    NASA Astrophysics Data System (ADS)

    Vojtíšek, Petr; Květoň, Milan; Richter, Ivan

    2017-04-01

    For diffraction effects inside photopolymer materials, which act as volume diffraction systems (e.g. gratings), refractive index modulation is one of the key parameters. Due to its importance it is necessary to study this parameter from many perspectives, one of which is its value for different spectral components, i.e. its spectral dispersion. In this paper, we discuss this property and present an approach to experimental and numerical extraction and analysis (via rigorous coupled wave analysis and Cauchy’s empirical relation) of the effective dispersion of refractive index modulation based on an analysis of transmittance maps measured in an angular-spectral plane. It is indicated that the inclusion of dispersion leads to a significantly better description of the real grating behavior (which is often necessary in various design implementations of diffraction gratings) and that this estimation can be carried out for all the diffraction orders present.

  20. Analytical properties of the effective refractive index

    NASA Astrophysics Data System (ADS)

    Puzko, R. S.; Merzlikin, A. M.

    2017-01-01

    The propagation of a plane wave through a periodic layered system is considered in terms of the effective parameters. The problem of introduction of effective parameters is discussed. It was demonstrated that although the effective admittance cannot be introduced, it is possible to introduce the effective refractive index, which tends toward the Rytov value when the system size increases. It was shown that the effective wave vector derivative is an analytical function of frequency. In particular, the Kramers-Kronig-like relations for real and imaginary parts of the effective wave vector derivative were obtained. The Kramers-Kronig-like relations for the effective refractive index were also considered. The results obtained numerically were proved by exact solution of Maxwell's equations in the specific case of an "equi-impedance" system.

  1. Transverse chromatic aberration after corneal refractive surgery

    NASA Astrophysics Data System (ADS)

    Anera, R. G.; Jiménez, J. R.; Jiménez del Barco, L.; Hita, E.

    2005-05-01

    An expression has been deduced theoretically from a schematic-eye model, for the transverse or lateral chromatic aberration (TCA) after refractive surgery. The aim was to investigate analytically how chromatic aberration varies after the emmetropization process. These changes in the TCA have been characterized from changes in corneal asphericity. The results indicate that TCA after refractive surgery diminishes as the degree of myopia increases, a trend contrary to that occurring with monochromatic aberrations, such as spherical or coma. These results can explain the fact that the real deterioration of the visual function under photopic conditions detected in those operated on for myopia is less than expected when only monochromatic aberrations are taken into account.

  2. The use of measured RF power signals to evaluate feasibility of inverse methods to retrieve refractivity parameters

    NASA Astrophysics Data System (ADS)

    Gustafsson, Ove K. S.; Eriksson, Gunnar; Holm, Peter; Waern, Åsa; von Schoenberg, Pontus; Thaning, Lennart; Nordstrand, Melker; Persson, Rolf

    2006-09-01

    Radio wave propagation over sea paths is influenced by the local meteorological condition at the atmospheric layer near the surface, especially during ducts. Duct condition can be determined by measurements of local meteorological parameters, by weather forecast models or by using inverse methods. In order to evaluate the feasibility of using inverse methods to retrieve the refractivity profiles a measurement of RF signals and meteorological parameters were carried out at a test site in the Baltic. During the measurements, signal power from two broadcast antennas, one at Visby and one at Vastervik, were received at Musko, an island south of Stockholm. The measurements were performed during the summer 2005 and the data was used to test the software package for inversion methods, SAGA (Seismo Acoustic inversion using Genetic Algorithms, by Peter Gerstoft UCSD, US). Refractivity profiles retrieved by SAGA were compared with the refractivity profiles calculated from measured parameters, during parts of the experiment, from rocket sounding, radio sounding, local meteorological measurements using bulk model calculations, and also obtained by the Swedish operational weather forecast model HIRLAM. Surface based duct height are predicted in relative many situations even though the number of frequencies or antennas height has to be increased to diminish the ambiguous of the refractive index profile.

  3. Refraction effects of atmosphere on geodetic measurements to celestial bodies

    NASA Technical Reports Server (NTRS)

    Joshi, C. S.

    1973-01-01

    The problem is considered of obtaining accurate values of refraction corrections for geodetic measurements of celestial bodies. The basic principles of optics governing the phenomenon of refraction are defined, and differential equations are derived for the refraction corrections. The corrections fall into two main categories: (1) refraction effects due to change in the direction of propagation, and (2) refraction effects mainly due to change in the velocity of propagation. The various assumptions made by earlier investigators are reviewed along with the basic principles of improved models designed by investigators of the twentieth century. The accuracy problem for various quantities is discussed, and the conclusions and recommendations are summarized.

  4. Optofluidic two-dimensional grating volume refractive index sensor.

    PubMed

    Sarkar, Anirban; Shivakiran Bhaktha, B N; Khastgir, Sugata Pratik

    2016-09-10

    We present an optofluidic reservoir with a two-dimensional grating for a lab-on-a-chip volume refractive index sensor. The observed diffraction pattern from the device resembles the analytically obtained fringe pattern. The change in the diffraction pattern has been monitored in the far-field for fluids with different refractive indices. Reliable measurements of refractive index variations, with an accuracy of 6×10-3 refractive index units, for different fluids establishes the optofluidic device as a potential on-chip tool for monitoring dynamic refractive index changes.

  5. Survey of Radar Refraction Error Corrections

    DTIC Science & Technology

    2016-11-01

    Science Laboratory. “Data Systems Manual, Meteorology and Timing.” Prepared for White Sands Missile Range under contract DAAD07-76-0007, September, 1979...reflect the different meteorological layers within the troposphere. Atmospheric Modeling Parameters 5.1 Earth Model Refraction correction models use...dissertations/AAIEP00334/. Physical Science Laboratory. “Data Systems Manual, Meteorology and Timing.” Prepared for White Sands Missile Range under

  6. Lens Design Using Group Indices of Refraction

    NASA Technical Reports Server (NTRS)

    Vaughan, A. H.

    1995-01-01

    An approach to lens design is described in which the ratio of the group velocity to the speed of light (the group index) in glass is used, in conjunction with the more familiar phase index of refraction, to control certain chromatic properties of a system of thin lenses in contact. The first-order design of thin-lens systems is illustrated by examples incorporating the methods described.

  7. The ionospheric refraction at 38 MHz.

    NASA Astrophysics Data System (ADS)

    Milogradov-Turin, J.

    The investigation of the observed shift of the North Polar Spur (NPS) at the 38 MHz survey of Milogradov-Turin and Smith (1973) in respect to the position of the NPS on the survey at 408 MHz convolved to the same resolution (Haslam and Salter 1977) has shown that there is no dependence of the NPS position on frequency and that the ionospheric refraction should be larger than believed.

  8. Matched Index of Refraction Flow Facility

    ScienceCinema

    Mcllroy, Hugh

    2016-07-12

    What's 27 feet long, 10 feet tall and full of mineral oil (3000 gallons' worth)? If you said INL's Matched Index of Refraction facility, give yourself a gold star. Scientists use computers to model the inner workings of nuclear reactors, and MIR helps validate those models. INL's Hugh McIlroy explains in this video. You can learn more about INL energy research at the lab's facebook site http://www.facebook.com/idahonationallaboratory.

  9. Matched Index of Refraction Flow Facility

    SciTech Connect

    Mcllroy, Hugh

    2010-01-01

    What's 27 feet long, 10 feet tall and full of mineral oil (3000 gallons' worth)? If you said INL's Matched Index of Refraction facility, give yourself a gold star. Scientists use computers to model the inner workings of nuclear reactors, and MIR helps validate those models. INL's Hugh McIlroy explains in this video. You can learn more about INL energy research at the lab's facebook site http://www.facebook.com/idahonationallaboratory.

  10. Autonomous satellite navigation by stellar refraction

    NASA Technical Reports Server (NTRS)

    Gounley, R.; White, R.; Gai, E.

    1983-01-01

    This paper describes an error analysis of an autonomous navigator using refraction measurements of starlight passing through the upper atmosphere. The analysis is based on a discrete linear Kalman filter. The filter generated steady-state values of navigator performance for a variety of test cases. Results of these simulations show that in low-earth orbit position-error standard deviations of less than 0.100 km may be obtained using only 40 star sightings per orbit.

  11. Lens Design Using Group Indices of Refraction

    NASA Technical Reports Server (NTRS)

    Vaughan, A. H.

    1995-01-01

    An approach to lens design is described in which the ratio of the group velocity to the speed of light (the group index) in glass is used, in conjunction with the more familiar phase index of refraction, to control certain chromatic properties of a system of thin lenses in contact. The first-order design of thin-lens systems is illustrated by examples incorporating the methods described.

  12. Emerging Technology in Refractive Cataract Surgery

    PubMed Central

    Saraiva, João; Neatrour, Kristin; Waring IV, George O.

    2016-01-01

    Technology in cataract surgery is constantly evolving to meet the goals of both surgeons and patients. Recent major advances in refractive cataract surgery include innovations in preoperative and intraoperative diagnostics, femtosecond laser-assisted cataract surgery (FLACS), and a new generation of intraocular lenses (IOLs). This paper presents the latest technologies in each of these major categories and discusses how these contributions serve to improve cataract surgery outcomes in a safe, effective, and predictable manner. PMID:27433353

  13. Emerging Technology in Refractive Cataract Surgery.

    PubMed

    Saraiva, João; Neatrour, Kristin; Waring Iv, George O

    2016-01-01

    Technology in cataract surgery is constantly evolving to meet the goals of both surgeons and patients. Recent major advances in refractive cataract surgery include innovations in preoperative and intraoperative diagnostics, femtosecond laser-assisted cataract surgery (FLACS), and a new generation of intraocular lenses (IOLs). This paper presents the latest technologies in each of these major categories and discusses how these contributions serve to improve cataract surgery outcomes in a safe, effective, and predictable manner.

  14. Autonomous satellite navigation by stellar refraction

    NASA Technical Reports Server (NTRS)

    Gounley, R.; White, R.; Gai, E.

    1983-01-01

    This paper describes an error analysis of an autonomous navigator using refraction measurements of starlight passing through the upper atmosphere. The analysis is based on a discrete linear Kalman filter. The filter generated steady-state values of navigator performance for a variety of test cases. Results of these simulations show that in low-earth orbit position-error standard deviations of less than 0.100 km may be obtained using only 40 star sightings per orbit.

  15. Nonlinear refraction and reflection travel time tomography

    USGS Publications Warehouse

    Zhang, Jiahua; ten Brink, U.S.; Toksoz, M.N.

    1998-01-01

    We develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid. For travel time and ray path calculations, we apply a wave front method employing graph theory. The first-arrival refraction travel times are calculated on the basis of cell velocities, and the later refraction and reflection travel times are computed using both cell velocities and given interfaces. We solve a regularized nonlinear inverse problem. A Laplacian operator is applied to regularize the model parameters (cell slownesses and reflector geometry) so that the inverse problem is valid for a continuum. The travel times are also regularized such that we invert travel time curves rather than travel time points. A conjugate gradient method is applied to minimize the nonlinear objective function. After obtaining a solution, we perform nonlinear Monte Carlo inversions for uncertainty analysis and compute the posterior model covariance. In numerical experiments, we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry. This combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust. We apply this approach to model the crustal structure of the California Borderland using ocean bottom seismometer and land data collected during the Los Angeles Region Seismic Experiment along two marine survey lines. Details of our image include a high-velocity zone under the Catalina Ridge, but a smooth gradient zone between. Catalina Ridge and San Clemente Ridge. The Moho depth is about 22 km with lateral variations. Copyright 1998 by the American Geophysical Union.

  16. Compound Refractive Lenses for Thermal Neutron Applications

    SciTech Connect

    Gary, Charles K.

    2013-11-12

    This project designed and built compound refractive lenses (CRLs) that are able to focus, collimate and image using thermal neutrons. Neutrons are difficult to manipulate compared to visible light or even x rays; however, CRLs can provide a powerful tool for focusing, collimating and imaging neutrons. Previous neutron CRLs were limited to long focal lengths, small fields of view and poor resolution due to the materials available and manufacturing techniques. By demonstrating a fabrication method that can produce accurate, small features, we have already dramatically improved the focal length of thermal neutron CRLs, and the manufacture of Fresnel lens CRLs that greatly increases the collection area, and thus efficiency, of neutron CRLs. Unlike a single lens, a compound lens is a row of N lenslets that combine to produce an N-fold increase in the refraction of neutrons. While CRLs can be made from a variety of materials, we have chosen to mold Teflon lenses. Teflon has excellent neutron refraction, yet can be molded into nearly arbitrary shapes. We designed, fabricated and tested Teflon CRLs for neutrons. We demonstrated imaging at wavelengths as short as 1.26 ? with large fields of view and achieved resolution finer than 250 μm which is better than has been previously shown. We have also determined designs for Fresnel CRLs that will greatly improve performance.

  17. Adjustable hybrid diffractive/refractive achromatic lens

    PubMed Central

    Valley, Pouria; Savidis, Nickolaos; Schwiegerling, Jim; Dodge, Mohammad Reza; Peyman, Gholam; Peyghambarian, N.

    2011-01-01

    We demonstrate a variable focal length achromatic lens that consists of a flat liquid crystal diffractive lens and a pressure-controlled fluidic refractive lens. The diffractive lens is composed of a flat binary Fresnel zone structure and a thin liquid crystal layer, producing high efficiency and millisecond switching times while applying a low ac voltage input. The focusing power of the diffractive lens is adjusted by electrically modifying the sub-zones and re-establishing phase wrapping points. The refractive lens includes a fluid chamber with a flat glass surface and an opposing elastic polydimethylsiloxane (PDMS) membrane surface. Inserting fluid volume through a pump system into the clear aperture region alters the membrane curvature and adjusts the refractive lens’ focal position. Primary chromatic aberration is remarkably reduced through the coupling of the fluidic and diffractive lenses at selected focal lengths. Potential applications include miniature color imaging systems, medical and ophthalmic devices, or any design that utilizes variable focal length achromats. PMID:21503055

  18. Refractive surgery: the future of perfect vision?

    PubMed

    Fong, C S

    2007-08-01

    The history of refractive eye surgery is recent, but has seen rapid advancement. Older technologies, such as radial keratectomy, had the problem of overcorrection and epithelial complications. Newer technologies, such as photorefractive keratectomy, laser-assisted in-situ keratomileusis (LASIK) and laser-assisted subepithelial keratomileusis (LASEK), which require the use of laser, has revolutionised eye surgery. However, there are complications, such as corneal hazing, postoperative pain, regression, and poorer correction for high myopes. If not contraindicated, wavefront analysis and femtosecond laser are useful adjuncts to laser photoablation for better visual results. Wavefront analysis improves the precision of laser photoablation by measuring the individual's wavefront aberrations, while femtosecond laser offers an instrument-free means of creating the corneal hinge. Lastly, implantation of intraocular lenses, with or without extraction of the crystalline lens, provides an alternative to laser photoablation for the treatment of high myopia. Clear lens exchange offers refractive correction to presbyopes and people with cataracts. However, complications, such as endothelial cell loss, cataract formation and retinal detachment, exist. In conclusion, refractive eye surgery provides an alternative to wearing spectacles or contact lenses. However, potential patients must be warned of the complications and long-term effects on the eyes.

  19. [Infection post Excimer Laser Corneal Refractive Surgery].

    PubMed

    Hieda, Osamu; Sotozono, Chie; Nakamura, Takahiro; Kinoshita, Shigeru

    2015-12-01

    To report the cases with severe infection post excimer laser refractive surgery. This study involved 6 eyes of 4 women (mean age 38 years, range : 27-51 years) who underwent excimer laser corneal refractive surgery. In all 4 cases, the respective primary causative organisms of the infection were quinolone-resistant methicillin-sensitive Staphylococcus aureus, quinolone-resistant methicillin-resistant Staphylococcus aureus, yeast type fungus, and in 1 case, penicillin-resistant Streptococcus pneumoniae. We initiated topical antibiotics or intensive antifungal treatment, yet due to severe inflammation and ophthalmalgia, analgesic drugs were needed. An average hospitalization period was 38.5 days (range : 22-77 days), and the best spectacle-corrected visual acuity was 0.5 or more than 0.5 post discharge. In the treatment of severe corneal infection post refractive surgery, it is important to identify the primary causative organism. If the response to the initial treatment is poor, such patients should immediately be referred to a special clinic to obtain a better visual outcome.

  20. Telescope resolution using negative refractive index materials

    NASA Astrophysics Data System (ADS)

    May, Jack L.; Jennetti, Tony

    2004-02-01

    Concepts are presented for using negative refractive index (NRI) materials to design parabolic reflector telescopes and antennas with resolutions significantly better than the diffractions limit. The main question we are attempting to answer is can negative refractive material be used to improve performance of parabolic systems even when the signal or light source is far away and no evanescent fields are present when they arrive at the parabolic reflector. The main approach is to take advantage of any knowledge that we have to recreate the evanescent fields. Fields are then adapted to improve a performance measure such a sharper focus or antenna rejection of interference. A negative refraction index lens is placed between the conventional reflector and focal plane to shape the point spread function. To produce telescope resolutions that are better than the diffraction limit, evanescent fields created by the reflection off of the parabolic surface are amplified and modified to generate fields that sharpen the focus. A second approach use available knowledge of an emitting aperture to synthesize a field at a distance that matches as closely as possible the field of the emitting aperture. The yet unproven conclusion is that techniques can be developed that will improve antenna and telescopes resolution that is better than the diffraction limit.

  1. Correction of subtle refractive error in aviators.

    PubMed

    Rabin, J

    1996-02-01

    Optimal visual acuity is a requirement for piloting aircraft in military and civilian settings. While acuity can be corrected with glasses, spectacle wear can limit or even prohibit use of certain devices such as night vision goggles, helmet mounted displays, and/or chemical protective masks. Although current Army policy is directed toward selection of pilots who do not require spectacle correction for acceptable vision, refractive error can become manifest over time, making optical correction necessary. In such cases, contact lenses have been used quite successfully. Another approach is to neglect small amounts of refractive error, provided that vision is at least 20/20 without correction. This report describes visual findings in an aviator who was fitted with a contact lens to correct moderate astigmatism in one eye, while the other eye, with lesser refractive error, was left uncorrected. Advanced methods of testing visual resolution, including high and low contrast visual acuity and small letter contrast sensitivity, were used to compare vision achieved with full spectacle correction to that attained with the habitual, contact lens correction. Although the patient was pleased with his habitual correction, vision was significantly better with full spectacle correction, particularly on the small letter contrast test. Implications of these findings are considered.

  2. Topography-guided laser refractive surgery.

    PubMed

    Pasquali, Theodore; Krueger, Ronald

    2012-07-01

    Topography-guided laser refractive surgery seeks to correct vision by altering the major refractive surface of the eye. Whereas results are not significantly different from current treatment options for primary surgery, topography-guided treatment is uniquely effective in eyes with corneal irregularity. This review highlights topography-guided ablations, emphasizing recent advances in treating highly aberrated eyes, including treatment for corneal ectasia in conjunction with collagen cross-linking (CXL). Studies continue to document similar outcomes between topography-guided and wavefront-guided customized corneal ablations while exploring the indications for each modality. Topography-guided ablations demonstrate good outcomes for the correction of astigmatism after penetrating keratoplasty, laser-assisted in-situ keratomileusis (LASIK) flap or interface complications, post-radial keratotomy eyes, and other highly aberrated corneas, many of which are poor candidates for wavefront-guided therapy. The use of topography-guided ablations with CXL seeks to address both the refractive and structural abnormalities of corneal ectasias. This combination therapy has shown promising results for keratoconus, post-LASIK ectasia, and pellucid marginal degeneration. Topography-guided customized corneal ablation is well tolerated and effective. Recent attention has been focused on the unique therapeutic benefits of this treatment for highly irregular and ectatic corneas with encouraging results.

  3. Surgical options for correction of refractive error following cataract surgery.

    PubMed

    Abdelghany, Ahmed A; Alio, Jorge L

    2014-01-01

    Refractive errors are frequently found following cataract surgery and refractive lens exchange. Accurate biometric analysis, selection and calculation of the adequate intraocular lens (IOL) and modern techniques for cataract surgery all contribute to achieving the goal of cataract surgery as a refractive procedure with no refractive error. However, in spite of all these advances, residual refractive error still occasionally occurs after cataract surgery and laser in situ keratomileusis (LASIK) can be considered the most accurate method for its correction. Lens-based procedures, such as IOL exchange or piggyback lens implantation are also possible alternatives especially in cases with extreme ametropia, corneal abnormalities, or in situations where excimer laser is unavailable. In our review, we have found that piggyback IOL is safer and more accurate than IOL exchange. Our aim is to provide a review of the recent literature regarding target refraction and residual refractive error in cataract surgery.

  4. A Direct Spectral Domain Method for Near-ground Microwave Radiation by a Vertical Dipole above Earth in the Presence of Atmospheric Refractivity

    DTIC Science & Technology

    2013-08-01

    Electromagnetic (EM) modeling of refractive and terrain effects over long links has been mod- eled by ray tracing [1, 17, 20] or by using the parabolic...REFERENCES 1. Akbarpour, R. and A. R. Webster, “ Ray - tracing and parabolic equation methods in the mod- eling of a tropospheric microwave link,” IEEE...No. 2, 131–140, Jan. 2008. 20. Valtr, P. and P. Pechac, “Analytic tropospheric ray - tracing model for constant refractivity gradient profiles,” First

  5. LASIK for spherical refractive myopia: effect of topographic astigmatism (ocular residual astigmatism, ORA) on refractive outcome.

    PubMed

    Frings, Andreas; Richard, Gisbert; Steinberg, Johannes; Skevas, Christos; Druchkiv, Vasyl; Katz, Toam; Linke, Stephan J

    2015-01-01

    In eyes with a preoperative plano refractive cylinder, it would appear that there is no rationale for astigmatic treatment. The aim of this retrospective, cross-sectional data analysis was to determine the amount of topographic astigmatism in refractive plano eyes that results in reduced efficacy after myopic laser in situ keratomileusis (LASIK). This study included 267 eyes from 267 consecutive myopic patients with a refractive plano cylinder. Receiver operating characteristic analysis was used to find the cut-off values of preoperative ocular residual astigmatism (= topographic astigmatism) that can best discriminate between groups of efficacy and safety indices in preoperative plano refractive cylinder eyes. Preoperative ocular residual astigmatism (ORA) (or topographic astigmatism) of ≤0.9 diopters (D) resulted in an efficacy index of at least 0.8 statistically significantly more frequently than eyes with a preoperative ORA of >0.9 D. Eyes with a high ORA preoperatively also had a high ORA postoperatively. Regression analysis showed that each diopter of preoperative ORA reduced efficacy by 0.07. A preoperative corneal astigmatism of ≥0.9 D could (partially) be taken into account in the LASIK design, even if the subjective refractive astigmatism is neutral.

  6. Estimation of contrast of refraction contrast imaging compared with absorption imaging-basic approach.

    PubMed

    Hirano, Masatsugu; Yamasaki, Katsuhito; Okada, Hiroshi; Kitazawa, Sohei; Kitazawa, Riko; Ohno, Yoshiharu; Sakurai, Takashi; Kondoh, Takeshi; Ohbayashi, Chiho; Katafuchi, Tetsuro; Maeda, Sakan; Sugimura, Kazuro; Tamura, Shinichi

    2005-03-01

    We discuss the usefulness of the refraction contrast method using highly parallel X-rays as a new approach to minute lung cancer detection. The advantages of refraction contrast images are discussed in terms of contrast, and a comparison is made with absorption images. We simulated refraction contrast imaging using globules with the density of water in air as models for minute lung cancer detection. The contrast intensified by bright and dark lines was compared on a globule with the contrast of absorption images. We adopted the Monte Carlo simulation to determine the strength of the profile curve of the photon counts at the detector. The obtained contrasts were more intense by two to three digits than those obtainable with the absorption contrast imaging method. The contrast in refraction contrast imaging was more intense than that obtainable with absorption contrast imaging. A two to three digit improvement in contrast means that it is possible to greatly reduce the exposure dose necessary for imaging. Therefore, it is expected to become possible to detect the interfaces of soft tissues, which are difficult to capture with conventional absorption imaging, at low dosages and high resolution.

  7. What Time Is Sunrise? Revisiting the Refraction Component of Sunrise/set Prediction Models

    NASA Astrophysics Data System (ADS)

    Wilson, Teresa; Bartlett, Jennifer L.; Hilton, James Lindsay

    2017-01-01

    Algorithms that predict sunrise and sunset times currently have an error of one to four minutes at mid-latitudes (0° - 55° N/S) due to limitations in the atmospheric models they incorporate. At higher latitudes, slight changes in refraction can cause significant discrepancies, even including difficulties determining when the Sun appears to rise or set. While different components of refraction are known, how they affect predictions of sunrise/set has not yet been quantified. A better understanding of the contributions from temperature profile, pressure, humidity, and aerosols could significantly improve the standard prediction. We present a sunrise/set calculator that interchanges the refraction component by varying the refraction model. We then compare these predictions with data sets of observed rise/set times to create a better model. Sunrise/set times and meteorological data from multiple locations will be necessary for a thorough investigation of the problem. While there are a few data sets available, we will also begin collecting this data using smartphones as part of a citizen science project. The mobile application for this project will be available in the Google Play store. Data analysis will lead to more complete models that will provide more accurate rise/set times for the benefit of astronomers, navigators, and outdoorsmen everywhere.

  8. In vivo measurements of thermal load during ablation in high-speed laser corneal refractive surgery.

    PubMed

    de Ortueta, Diego; Magnago, Thomas; Triefenbach, Nico; Arba Mosquera, Samuel; Sauer, Udo; Brunsmann, Ulrich

    2012-01-01

    To evaluate the thermal load of ablation in high-speed laser corneal refractive surgery with the AMARIS excimer laser (SCHWIND eye-tech-solutions). Thermal load from refractive corrections on human corneas using a 500-Hz laser system with a fluence of 500 mJ/cm(2) and aspheric ablation profiles was recorded with an infrared thermography camera. Each single in vivo measurement was analyzed and temperature values were evaluated. Overall, the maximum temperature change of the ocular surface induced by the refractive ablations was ≤4°C. The increase in the peak temperature of the ocular surface never exceeded 35°C in any case. This low thermal load was independent of the amount of correction the eye achieved. The thermal load of the ablation in high-speed laser corneal refractive surgery was minimized using a computer algorithm to control the peak temperature to avoid corneal collagen denaturation with minimal compromise on treatment duration. Copyright 2012, SLACK Incorporated.

  9. Solitary wave propagation and steering through light-induced refractive potentials

    SciTech Connect

    Assanto, Gaetano; Skuse, Benjamin D.; Smyth, Noel F.

    2010-06-15

    The steering of a self-guided beam in a dye-doped nematic liquid crystal caused by an external illumination (control beam) that induces changes in the refractive index of the medium is theoretically analyzed. The interaction between the control beam and the dye molecules modifies the anchoring of the nematic molecules, so changing the director orientation in the bulk of the medium. Beam evolution is investigated by use of a modulation theory approach. It is found that the beam trajectory is independent of the beam profile, as long as this profile is self-similar. Solutions obtained from the modulation theory approach are in excellent agreement with numerical solutions.

  10. Tropospheric refractivity and zenith path delays from least-squares collocation of meteorological and GNSS data

    NASA Astrophysics Data System (ADS)

    Wilgan, Karina; Hurter, Fabian; Geiger, Alain; Rohm, Witold; Bosy, Jarosław

    2017-02-01

    Precise positioning requires an accurate a priori troposphere model to enhance the solution quality. Several empirical models are available, but they may not properly characterize the state of troposphere, especially in severe weather conditions. Another possible solution is to use regional troposphere models based on real-time or near-real time measurements. In this study, we present the total refractivity and zenith total delay (ZTD) models based on a numerical weather prediction (NWP) model, Global Navigation Satellite System (GNSS) data and ground-based meteorological observations. We reconstruct the total refractivity profiles over the western part of Switzerland and the total refractivity profiles as well as ZTDs over Poland using the least-squares collocation software COMEDIE (Collocation of Meteorological Data for Interpretation and Estimation of Tropospheric Pathdelays) developed at ETH Zürich. In these two case studies, profiles of the total refractivity and ZTDs are calculated from different data sets. For Switzerland, the data set with the best agreement with the reference radiosonde (RS) measurements is the combination of ground-based meteorological observations and GNSS ZTDs. Introducing the horizontal gradients does not improve the vertical interpolation, and results in slightly larger biases and standard deviations. For Poland, the data set based on meteorological parameters from the NWP Weather Research and Forecasting (WRF) model and from a combination of the NWP model and GNSS ZTDs shows the best agreement with the reference RS data. In terms of ZTD, the combined NWP-GNSS observations and GNSS-only data set exhibit the best accuracy with an average bias (from all stations) of 3.7 mm and average standard deviations of 17.0 mm w.r.t. the reference GNSS stations.

  11. Deep crustal structure of the Cascade Range and surrounding regions from seismic refraction and magnetotelluric data

    SciTech Connect

    Stanley, W.D. ); Mooney, W.D.; Fuis, G.S. )

    1990-11-10

    Analysis of three MT and two seismic refraction profiles in Oregon and a coincident MT and refraction profile in northern California show a high degree of correlation between resistivity and velocity models. The main feature that is evident in both data sets is a highly conductive (2-20 ohm m) zone that occurs at depths of 6-20 km and largely within a midcrustal velocity layer of 6.4-6.6 km/s, overlying a lower crust with velocities of 7.0-7.4 km/s. Although this conductor and the midcrustal zone of 6.4-6.6 km/s velocities are generally rather horizontal, important structures do occur. For instance, near the boundary of Western Cascades and High Cascades the MT midcrustal conductor rises to within 6 km of the surface. In addition, on the coincident MT-refraction profile in northern California a significant westward downdip occurs on both the MT deep conductor and the 6.4-km/s velocity layer, with both occurring at very similar depths. However, in the Columbia Plateau of Washington, no deep crustal conductors occur shallower than 25 km; also, the velocity structure is quite different, with a 6.8-km/s midcrust and a 7.5-km/s lower crust. Complex accretionary structures occur on MT models for the southern Washington Cascades. The accretionary structures in the southern Washington Cascades have been shown to be related to stress release in the area of Mount St. Helens. In order to explain the similar structures in the MT and refraction models for Oregon and California, the authors propose a model involving the effects of metamorphic zonation to produce the velocity structure, combined with metamorphically produced fluids and partial melt to produce the deep conductor.

  12. Gradients of refractive index in the crystalline lens and transient changes in refraction among patients with diabetes

    PubMed Central

    Charman, W. Neil; Adnan; Atchison, David A.

    2012-01-01

    Transient hyperopic refractive shifts occur on a timescale of weeks in some patients after initiation of therapy for hyperglycemia, and are usually followed by recovery to the original refraction. Possible lenticular origin of these changes is considered in terms of a paraxial gradient index model. Assuming that the lens thickness and curvatures remain unchanged, as observed in practice, it appears possible to account for initial hyperopic refractive shifts of up to a few diopters by reduction in refractive index near the lens center and alteration in the rate of change between center and surface, so that most of the index change occurs closer to the lens surface. Restoration of the original refraction depends on further change in the refractive index distribution with more gradual changes in refractive index from the lens center to its surface. Modeling limitations are discussed. PMID:23243557

  13. Deviations of Lambert-Beer's law affect corneal refractive parameters after refractive surgery

    NASA Astrophysics Data System (ADS)

    Jiménez, José R.; Rodríguez-Marín, Francisco; Anera, Rosario G.; Jiménez Del Barco, Luis

    2006-06-01

    We calculate whether deviations of Lambert-Beer’s law, which regulates depth ablation during corneal ablation, significantly influence corneal refractive parameters after refractive surgery and whether they influence visual performance. For this, we compute a point-to-point correction on the cornea while assuming a non-linear (including a quadratic term) fit for depth ablation. Post-surgical equations for refractive parameters using a non-linear fit show significant differences with respect to parameters obtained from a linear fit (Lambert-Beer’s law). Differences were also significant for corneal aberrations. These results show that corneal-ablation algorithms should include analytical information on deviations from Lambert-Beer’s law for achieving an accurate eye correction.

  14. EDITORIAL: Sensitive structures: refractive indices in nanotechnology Sensitive structures: refractive indices in nanotechnology

    NASA Astrophysics Data System (ADS)

    Demming, Anna

    2012-12-01

    Refractive index effects using nanoscale systems are frequently applied in new imaging, sensing and even visibility cloaking technology. In this issue, researchers in Japan use simulations and experiments to describe the confinement of optical vortices in nanoscale fin structures and the sensitivity of these systems to the refractive index of the surrounding media [1]. The effects of refraction as light rays pass between different media were recorded as long ago as the first century AD, by Ptolemy [2]. Over the following centuries the phenomena inspired Ibn Sahl in 984 [3], Thomas Harriot in 1602 [4], Willebrord Snellius in 1621 [5] and Rene Descartes in 1637 [6] to independently derive the more accurate and elegant equation for refraction so familiar to us today. Recent studies of the interactions between light and matter continue to reveal a wealth of phenomena that originate in the effects of the refractive indices of materials. Nanostructures can be used to manipulate conditions that affect the refractive indices of materials, such as temperature. A E Aliev et al at the University of Texas reported a striking demonstration of temperature-dependent refractive index effects using a free-standing, highly aligned carbon nanotube aerogel sheet [7]. They used the extremely low thermal capacitance and high heat transfer ability of transparent carbon nanotube sheets to enable high-frequency modulation of the sheet temperature over an enormous temperature range. The resulting sharp, rapidly changing gradient of the refractive index in the surrounding liquid or gas makes objects seem to disappear and can be used for visibility cloaking. Light-matter interaction resonances, where light is confined at the nanoscale, can be extremely sensitive to changes in the refractive index of the surrounding media [8], even allowing single-molecule detection [9]. Plasmons, the collective oscillations of electrons in response to incident light, are a typical example. Researchers at Rice

  15. Refraction of nonlinear beams by localized refractive index changes in nematic liquid crystals

    SciTech Connect

    Assanto, Gaetano; Minzoni, Antonmaria A.; Smyth, Noel F.; Worthy, Annette L.

    2010-11-15

    The propagation of solitary waves in nematic liquid crystals in the presence of localized nonuniformities is studied. These nonuniformities can be caused by external electric fields, other light beams, or any other mechanism which results in a modified director orientation in a localized region of the liquid-crystal cell. The net effect is that the solitary wave undergoes refraction and trajectory bending. A general modulation theory for this refraction is developed, and particular cases of circular, elliptical, and rectangular perturbations are considered. The results are found to be in excellent agreement with numerical solutions.

  16. Measurement of refractive index distribution of biotissues by scanning focused refractive index microscopy

    NASA Astrophysics Data System (ADS)

    Sun, Tengqian; Ye, Qing; Wang, Xiao-Wan; Wang, Jin; Deng, Zhi-Chao; Mei, Jian-Chun; Zhou, Wen-Yuan; Zhang, Chun-Ping; Tian, Jian-Guo

    2014-11-01

    We adapt the improved scanning focused refractive-index microscopy (SFRIM) technique to the quantitative study of biological tissues. Delicate refractive index (RI) imaging of a porcine muscle tissue is obtained in a reflection mode. Some modifications are made to the SFRIM for better two dimension (2-D) observation of the tissues. The RI accuracy is 0.002. The central spatial resolution of SFRIM achieves 1μm, smaller than the size of the focal spot. Our method is free from signal distortion. The experimental result demonstrates that SFRIM is a potential technique in a wide field of biomedical research.

  17. Ketamine-xylazine anesthesia causes hyperopic refractive shift in mice

    PubMed Central

    Tkatchenko, Tatiana V.; Tkatchenko, Andrei V.

    2010-01-01

    Mice have increasingly been used as a model for studies of myopia. The key to successful use of mice for myopia research is the ability to obtain accurate measurements of refractive status of their eyes. In order to obtain accurate measurements of refractive errors in mice, the refraction needs to be performed along the optical axis of the eye. This represents a particular challenge, because mice are very difficult to immobilize. Recently, ketamine-xylazine anesthesia has been used to immobilize mice before measuring refractive errors, in combination with tropicamide ophthalmic solution to induce mydriasis. Although these drugs have increasingly been used while refracting mice, their effects on the refractive state of the mouse eye have not yet been investigated. Therefore, we have analyzed the effects of tropicamide eye drops and ketamine-xylazine anesthesia on refraction in P40 C57BL/6J mice. We have also explored two alternative methods to immobilize mice, i.e. the use of a restraining platform and pentobarbital anesthesia. We found that tropicamide caused a very small, but statistically significant, hyperopic shift in refraction. Pentobarbital did not have any substantial effect on refractive status, whereas ketamine-xylazine caused a large and highly significant hyperopic shift in refraction. We also found that the use of a restraining platform represents good alternative for immobilization of mice prior to refraction. Thus, our data suggest that ketamine-xylazine anesthesia should be avoided in studies of refractive development in mice and underscore the importance of providing appropriate experimental conditions when measuring refractive errors in mice. PMID:20813132

  18. Refractive index matching and clear emulsions.

    PubMed

    Sun, James Ziming; Erickson, Michael C E; Parr, James W

    2005-01-01

    Refractive index (RI) matching is a unique way of making clear emulsions to meet market trends. However, RI matching has not been sufficiently investigated in terms of physical principles and methodologies. Snell's law (n2 sin r2= n1 sin r1) is applicable to cosmetic emulsions. When oil phase and water phase have equal RI (n2 = n1) values, light will not bend as it strikes obliquely at the emulsion interface. Instead, light is transmitted through the emulsion without refraction, which produces clarity. Theoretical RI values in solution can be calculated with summation of the product of the weight percentage and refractive index of each ingredient (RI(mix) = [W1 x n1 + W2 x n2 + W3 x n3 + + Wn x nn]Wtau). Oil-phase RI values are normally at 1.4 or higher. Glycols are used to adjust the water phase RI, since they typically have larger RI values than water. Noticeable deviations from calculated RI values are seen in experimentally prepared solutions. Three basic deviation types are observed: negative, positive, and slightly negative or positive, which can occur in glycol aqueous solutions at different concentrations. The deviations are attributed to changes in molecular interaction between molecules in solution, which can lead to changes in specific gravity. Negative RI deviation corresponds to a decrease in specific gravity, and positive RI deviation corresponds to an increase in specific gravity. RI values will deviate from calculated values since an increase or decrease in specific gravity leads to a change in optical density.

  19. Seismic refraction methodology for groundwater level determination: “Water seismic index”

    NASA Astrophysics Data System (ADS)

    Grelle, Gerardo; Guadagno, Francesco Maria

    2009-07-01

    Recently, there has been increased interest in the use of refraction seismic data for the exploration and development of hydrological reservoirs. The aim of this study is to provide a procedure in order to identify groundwater levels by means of seismic refraction profiles. Assuming that the velocity of shear waves increases much less than the velocity of compressional waves in a saturated soil, seismic refraction surveys were performed for the determination of the water table. In order to have a perfect overlay of the tomography 2D grids, P and S wave seismic profiles were obtained with the same geometrical configuration. Based on the propagation of the P and S waves in the unsaturated and saturated media, a "Water Seismic Index" (WSI) was defined. WSI is related to the local variations of the P and S wave velocities and, in theoretical terms, it is correlated to groundwater level. Preliminary results indicate that there is a good agreement between the depth of the ground water and the WSI parameter.

  20. The Alvarez and Lohmann refractive lenses revisited.

    PubMed

    Barbero, Sergio

    2009-05-25

    Alvarez and Lohmann lenses are variable focus optical devices based on lateral shifts of two lenses with cubic-type surfaces. I analyzed the optical performance of these types of lenses computing the first order optical properties (applying wavefront refraction and propagation) without the restriction of the thin lens approximation, and the spot diagram using a ray tracing algorithm. I proposed an analytic and numerical method to select the most optimum coefficients and the specific configuration of these lenses. The results show that Lohmann composite lens is slightly superior to Alvarez one because the overall thickness and optical aberrations are smaller.

  1. Methods for Correction of Refractive Errors.

    DTIC Science & Technology

    1984-12-31

    on arcingline for different rotational positions of the object ’ vr :,)w() J -. rvr-. Mueller (t al.’s method gives the values of the Fourir 0 rai-f...take u. defined as the scattered field in Eq. (2.16), to be the scattered pressure field. By imposing the boundary conditions (continuity of Vr and P...n()-lI u(-) + Vr (,,"rl Vu(T) (3.9) PO where the refractive index n(-?) is defined as ~~n (r PY)Kt (3.10) In most practical situations the second term

  2. Refraction and reflection of diffusion fronts.

    PubMed

    Remhof, A; Wijngaarden, R J; Griessen, R

    2003-04-11

    Diffusion waves form the basis of several measurement technologies in materials science as well as in biological systems. They are, however, so heavily damped that their observation is a real challenge to the experimentalist. We show that accurate information about the refraction-like and reflection-like behavior of diffusion waves can be obtained by studying diffusion fronts. For this we use hydrogen in a metal as a model system and visualize its 2D migration with an optical indicator. The similarities between classical optics and diffusion, in particular, the applicability of Snell's law to diffusive systems are discussed. Our measurements are in good agreement with numerical simulations.

  3. Near-zero refractive index photonics

    NASA Astrophysics Data System (ADS)

    Liberal, Iñigo; Engheta, Nader

    2017-03-01

    Structures with near-zero parameters (for example, media with near-zero relative permittivity and/or relative permeability, and thus a near-zero refractive index) exhibit a number of unique features, such as the decoupling of spatial and temporal field variations, which enable the exploration of qualitatively different wave dynamics. This Review summarizes the underlying principles and salient features, physical realizations and technological potential of these structures. In doing so, we revisit their distinctive impact on multiple optical processes, including scattering, guiding, trapping and emission of light. Their role in emphasizing secondary responses of matter such as nonlinear, non-reciprocal and non-local effects is also discussed.

  4. Conical refraction in magneto-optical crystals

    NASA Astrophysics Data System (ADS)

    Kuznetsov, E. V.; Merzlikin, A. M.

    2017-09-01

    The paper investigates the influence of an external magnetic field on light propagation through a magneto-optical biaxial, biaxial hyperbolic and anisotropic magnetophotonic crystal. It is demonstrated that the application of a magnetic field results in splitting and reconnection of an isofrequency near the self-intersection point and thus it leads to the disappearance of conical refraction in a crystal. This effect makes it possible to control light propagation by means of a magnetic field. In addition, it is demonstrated that the diffraction divergence of a beam is suppressed in a homogeneous magneto-optical biaxial crystal.

  5. Interferometric measurement of refractive index modification in a single mode microfiber

    NASA Astrophysics Data System (ADS)

    Ahmed, Farid; Ahsani, Vahid; Jun, Martin B. G.

    2017-02-01

    Efficient and cost effective measurement of the refractive index profile in an optical fiber is a significant technical job to design and manufacture in-fiber photonic devices and communication systems. For instance, to design fiber gratings, it is required to estimate the refractive index modulation to be inscribed by the fabrication apparatus such as ultraviolet or infrared lasers. Mach-Zehnder interferometer (MZI) based quantification of refractive index change written in single mode microfiber by femtosecond laser radiation is presented in this study. The MZI is constructed by splicing a microfiber (core diameter: 3.75 μm, cladding diameter: 40 μm) between standard single mode fibers. To measure the RI inscribed by infrared femtosecond laser, 200 μm length of the core within the MZI was scanned with laser radiation. As the higher index was written within 200 μm length of the core, the transmission spectrum of the interferometer displayed a corresponding red shift. The observed spectral shift was used to calculate the amount of refractive index change inscribed by the femtosecond irradiation. For the MZI length of 3.25 mm, and spectral shift of 0.8 nm, the calculated refractive index was found to be 0.00022. The reported results display excellent agreement between theory and experimental findings. Demonstrated method provides simple yet very effective on-site measurement of index change in optical fibers. Since the MZI can be constructed in diverse fiber types, this technique offers flexibility to quantify index change in various optical fibers.

  6. Fabrication of refractive microlens array by etching ammonium dichromate gelatin (ADG) with enzyme

    NASA Astrophysics Data System (ADS)

    Yao, Jun; Gao, Fuhua; Gao, Feng; Zhang, Yixiao; Su, Jingqin; Guo, Yongkang; Cui, Zheng

    2000-08-01

    A new method has been developed to fabricate refractive microlens by etching ammonium dichromate gelatin (ADG) with enzyme solution. Unlike previous methods which are used to fabricate refractive microlens with photoresist, the process of fabricating microlens by etching ADG with enzyme solution doesn't require the use of expensive equipment, and it isn't sophisticated and time consuming. The light exposes ADG through a high contrast binary mask, then the exposed parts of ADS generate cross- linking reaction. Usually, the relief achieved by water developing is very shallow (<1um) when nonpre-harden gelatin is used, so we compound a certain concentration enzyme solution, and because of surface tension, ADG turns to spherical structure after developing. The optimum technique parameters of this process are presented. Results are presented for experiments and evaluated by profile meter and interference microscope.

  7. Negative refraction and energy funneling by hyperbolic materials: an experimental demonstration in acoustics.

    PubMed

    García-Chocano, Victor M; Christensen, Johan; Sánchez-Dehesa, José

    2014-04-11

    This Letter reports the design, fabrication, and experimental characterization of hyperbolic materials showing negative refraction and energy funneling of airborne sound. Negative refraction is demonstrated using a stack of five holey Plexiglas plates where their thicknesses, layer separation, hole diameters, and lattice periodicity have been determined to show hyperbolic dispersion around 40 kHz. The resulting hyperbolic material shows a flat band profile in the equifrequency contour allowing the gathering of acoustic energy in a broad range of incident angles and its funneling through the material. Our demonstrations foresee interesting developments based on both phenomena. Acoustic imaging with subwavelength resolution and spot-size converters that harvest and squeeze sound waves irradiating from many directions into a collimated beam are just two possible applications among many.

  8. Correction of laser range tracking data for atmospheric refraction at elevations above 10 degrees

    NASA Technical Reports Server (NTRS)

    Marini, J. W.; Murray, C. W., Jr.

    1973-01-01

    A formula for correcting laser measurements of satellite range for the effect of atmospheric refraction is given. The corrections apply above 10 deg elevation to satellites whose heights exceed 70 km. The meteorological measurements required are the temperature, pressure, and relative humidity of the air at the laser site at the time of satellite pass. The accuracy of the formula was tested by comparison with corrections obtained by ray-tracing radiosonde profiles. The standard deviation of the difference between the refractive retardation given by the formula and that calculated by ray-tracing was less than about 0.04% of the retardation or about 0.5 cm at 10 deg elevation, decreasing to 0.04 cm near zenith.

  9. Data report for seismic refraction surveys conducted from 1980 to 1982 in the Livermore Valley and the Santa Cruz Mountains, California

    USGS Publications Warehouse

    Williams, Angela J.; Brocher, Thomas M.; Mooney, Walter D.; Boken, Annette

    1999-01-01

    We provide documentation for two seismic refraction profiles acquired by the U.S. Geological Survey in the San Francisco Bay area between 1980 and 1982 in Livermore Valley and the Santa Cruz Mountains. We also include the waveforms and travel times from five aftershocks of the April 1980 Livermore earthquake that were recorded on temporary seismic stations and that have not been published. Although seismic refraction profiles from the 1980 Livermore study have been published, none of the other data for this experiment, including shot times and locations, receiver locations, data quality, and travel times, have been reported. Similarly, such data from the 1981 to 1982 seismic refraction survey in the Santa Cruz Mountains included here have not been published. The first-arrival travel times from these profiles are reported in the hope that they can be used for three-dimensional velocity models in the San Francisco Bay area, particularly for the Livermore Valley and Santa Cruz Mountains.

  10. Negative Refraction in Rare-Earth Doped Crystals

    DTIC Science & Technology

    2016-06-09

    practical implications. The key challenge in observing negative refraction in the optical region of the spectrum is the weakness of the magnetic response...Our central experimental result during this project has been the first observation of Rabi flopping of a magnetic dipole transition in the optical...refraction. Because of these achievements, observing negative refraction and left-handed electromagnetic waves in atomic systems seem within

  11. Optimizing Refractivity from Clutter (RFC) for Surface-Based Ducts

    DTIC Science & Technology

    2011-09-30

    This model is named the Advanced Propagation Model (APM) and is the primary model used in the Advanced Refractive Effects Prediction System ( AREPS ...120 which has funded the development of the Advanced Refractive Effects Prediction System ( AREPS ). Current and new software, along with information...refractivity from clutter (RFC) integration plans. Academia and other U.S. government are also utilizing APM/ AREPS . The APM is currently being used by

  12. Determination of refractive index by Moiré deflectometry

    NASA Astrophysics Data System (ADS)

    Ahmadi, Mohammad; Madanipour, Khosro; Javadianvarjovi, Soheila

    2015-06-01

    Determination of refractive index is an important characteristic of material which is crucial parameter for physicists and engineers. Moiré deflectometry technique is convenient, easy-aligning, nondestructive, non-contact and fairly accurate method for refractive index measurement of gas, liquid, solid. In this paper we investigate the theory of the technique and simulate some relations then finally measure refractive index of a glassy lamella, n=1.536.

  13. Refractive index fiber sensor based on Brillouin fast light

    NASA Astrophysics Data System (ADS)

    Chen, Jiali; Gan, Jiulin; Zhang, Zhishen; Yang, Tong; Deng, Huaqiu; Yang, Zhongmin

    2014-01-01

    A new type of refractive index fiber sensor was invented by combining the evanescent-field scattering sensing mechanism with the Brillouin fast light scheme. Superluminal light was realized using Brillouin lasing oscillation in a fiber ring cavity. The refractive index of the solution around the microfiber within the cavity is related to the group velocity of the fast light. This fast light refractive index sensor offers an alternative for high-accuracy sensing applications.

  14. Retinal evaluation and treatment after refractive corneal surgery.

    PubMed

    Swinger, C A; Kraushar, M F

    1985-08-01

    Refractive corneal surgery (a collective term used to describe a variety of surgical procedures that alter the refractive status of the eye through the surgical modification of corneal curvature) shows promise for use in situations where current methods of optical correction do not meet the patient's needs. This article reviews our experiences with the retinal evaluation of patients who have undergone corneal refractive surgery and offers recommendations for the treatment of retinal pathology after such surgery.

  15. Negative-Refraction Metamaterials: Fundamental Principles and Applications

    NASA Astrophysics Data System (ADS)

    Eleftheriades, G. V.; Balmain, K. G.

    2005-06-01

    Learn about the revolutionary new technology of negative-refraction metamaterials Negative-Refraction Metamaterials: Fundamental Principles and Applications introduces artificial materials that support the unusual electromagnetic property of negative refraction. Readers will discover several classes of negative-refraction materials along with their exciting, groundbreaking applications, such as lenses and antennas, imaging with super-resolution, microwave devices, dispersion-compensating interconnects, radar, and defense. The book begins with a chapter describing the fundamentals of isotropic metamaterials in which a negative index of refraction is defined. In the following chapters, the text builds on the fundamentals by describing a range of useful microwave devices and antennas. Next, a broad spectrum of exciting new research and emerging applications is examined, including: Theory and experiments behind a super-resolving, negative-refractive-index transmission-line lens 3-D transmission-line metamaterials with a negative refractive index Numerical simulation studies of negative refraction of Gaussian beams and associated focusing phenomena Unique advantages and theory of shaped lenses made of negative-refractive-index metamaterials A new type of transmission-line metamaterial that is anisotropic and supports the formation of sharp steerable beams (resonance cones) Implementations of negative-refraction metamaterials at optical frequencies Unusual propagation phenomena in metallic waveguides partially filled with negative-refractive-index metamaterials Metamaterials in which the refractive index and the underlying group velocity are both negative This work brings together the best minds in this cutting-edge field. It is fascinating reading for scientists, engineers, and graduate-level students in physics, chemistry, materials science, photonics, and electrical engineering.

  16. Fiber in-line Michelson Interferometer for refractive index sensing

    NASA Astrophysics Data System (ADS)

    Liao, C. R.; Wang, D. N.; Wang, Min; Yang, Minghong; Wang, Yiping

    2013-09-01

    A fiber in-line Michelson interferometer based on open micro-cavity is demonstrated, which is fabricated by femtosecond laser micromachining and thin film coating technique. In refractive index sensing, this interferometer operates in a reflection mode of detection, exhibits compact sensor head, good mechanical reliability, wide operation range and high sensitivity of 975nm/RIU (refractive index unit) at the refractive index value of 1.484.

  17. Near field imaging of refraction via the magnetic field

    NASA Astrophysics Data System (ADS)

    Kanté, Boubacar; Germain, Dylan; de Lustrac, André

    2014-01-01

    We experimentally map positive and negative refractions by probing the magnetic field after the interaction of a complex metallo-dielectric composite with electromagnetic wave. The structure consists of coupled electric dipoles and negative refractive index is achieved exclusively from coupled localized resonances. By mapping out the magnetic field, negative refraction is directly observed from the three dimensional composite using a small magnetic antenna as local probe. Our work shows that light meta-matter interaction can be equally probed from magnetic light.

  18. Calculation of electron wave functions and refractive index of Ne

    NASA Astrophysics Data System (ADS)

    Zhu, Min; Liu, Wei; Zhang, Tao

    2008-10-01

    The radial wave functions of inner electron shell and outer electron shell of a Ne atom were obtained by the approximate analytical method and tested by calculating the ground state energy of the Ne atom. The equivalent volume of electron cloud and the refractive index of Ne were calculated. The calculated refractive index agrees well with the experimental result. Relationship between the refractive index and the wave function of Ne was discovered.

  19. Experimental analysis of distributed pump absorption and refractive index changes in Yb-doped fibers using acousto-optic interaction.

    PubMed

    Alcusa-Sáez, E P; Díez, A; Andrés, M V

    2015-03-01

    In-fiber acousto-optic interaction is used to characterize the refractive index changes at the C band in a single-mode ytterbium-doped optical fiber under 980 nm pumping. The transmission notch created by the acoustic-induced coupling between the core mode and a cladding mode shifts to longer wavelengths when the pump is delivered to the fiber. The electronic contribution to the refractive index change is quantified from the wavelength shift. Using a time-resolved acousto-optic method, we investigate the distribution of pump absorption, and the resulting refractive index change profile, along sections of ytterbium-doped fiber exceeding 1 m long under different pump power levels.

  20. Ultrarefraction and negative refraction in metamaterials

    NASA Astrophysics Data System (ADS)

    Maystre, Daniel R.; Enoch, Stefan; Tayeb, Gerard

    2004-07-01

    In the recent years, many experimental and theoretical achievements have shown that meta-materials can simulate homogeneous materials with optical index less than unity or even negative. For example, a dielectric photonic crystal, used at the edge of a band gap, can generate phenomena of ultra-refraction (positive index less than unity) or negative refraction (negative index). Some applications of these phenomena will be shown, specially the design of directive antenna in the microwaves region. More recently, experimental and theoretical studies have been published on left-handed materials. These materials, which have a permittivity and a permeability equal to -1, have been the subject of controversies about their alleged property of making perfect lenses. It will be shown that such a perfect lens cannot exist. However, this kind of meta-material could be used for making better lenses than the best classical ones, a fact which could explain some experimental results. The vital influence of the size of the elementary cell on the performance of the lens will be pointed out. Finally, it will be shown that surprisingly, a left-handed material can be interpreted as a means to go through the mirror, as Alice in the novel of Lewis Carrol...

  1. Achromatic doublets using group indices of refraction

    NASA Astrophysics Data System (ADS)

    Rosete-Aguilar, M.; Estrada-Silva, F. C.; Román-Moreno, C. J.; Ortega-Martínez, R.

    2008-03-01

    One main function of short pulses is to concentrate energy in time and space [1]. The use of refractive lenses allows us to concentrate energy in a small volume of focusing around the focal point of the lens. When using refractive lenses, there are three effects that affect the concentration of energy around the focal point of the lens. These are the group velocity dispersion (GVD), the propagation time difference (PTD), and the aberrations of the lens. In this paper, we study lenses which are diffraction limited so that the monochromatic aberrations are negligible; the group velocity dispersion and the propagation time difference are the main effects affecting the spreading of the pulse at the focus. We will show that for 100-fs pulses the spatial spreading is larger than the temporal spreading of the pulse. It is already known that the effect of spatial spreading of the pulse due to PTD can be reduced by using achromatic optics. We use the theory proposed by A. Vaughan to analyze simple lenses and normal achromatic doublets, where normal means doublets that we can buy from catalogs. We then use the Vaughan theory to design achromatic doublets in phase and group, which produce no spatial spreading of the pulse, i.e., PTD = 0, when the doublet is designed for the carrier of the pulse. We compare these phase and group achromatic doublets with normal achromatic doublets. Finally, we show that apochromatic optics can give a much better correction of PTD than using normal achromatic doublets.

  2. Mathematics of Radiation Propagation in Planetary Atmospheres: Absorption, Refraction, Time Delay, Occultation, and Abel Inversion

    NASA Astrophysics Data System (ADS)

    Huestis, D. L.

    Forward integration calculation of air mass, refraction, and time delay requires care even for very smooth model atmospheres. The literature abounds in examples of injudicious approximations, assumptions, transformations, variable substitutions, and failures to verify that the formulas work with unlimited accuracy for simple cases and also survive challenges from mathematically pathological but physically realizable cases. A few years ago we addressed the problem of evaluation of the Chapman function for attenuation along a straight line path in an exponential atmosphere. In this presentation we will describe issues and approaches for integration over light paths curved by refraction. The inverse problem, determining the altitude profile of mass density (index of refraction) or the concentration of an individual chemical species (absorption), from occultation data, also has its mathematically interesting (i.e., difficult) aspects. Now we automatically have noise and thus statistical analysis is just as important as calculus and numerical analysis. Here we will describe a new approach of least-squares fitting occultation data to an expansion over compact basis functions. This approach, which avoids numerical differentiation and singular integrals, was originally developed to analyze laboratory imaging data.Forward integration calculation of air mass, refraction, and time delay requires care even for very smooth model atmospheres. The literature abounds in examples of injudicious approximations, assumptions, transformations, variable substitutions, and failures to verify that the formulas work with unlimited accuracy for simple cases and also survive challenges from mathematically pathological but physically realizable cases. A few years ago we addressed the problem of evaluation of the Chapman function for attenuation along a straight line path in an exponential atmosphere. In this presentation we will describe issues and approaches for integration over light paths

  3. Comparison of Ocular Monochromatic Higher-order Aberrations in Normal Refractive Surgery Candidates of Arab and South Asian Origin.

    PubMed

    Prakash, Gaurav; Srivastava, Dhruv; Choudhuri, Sounak; Bacero, Ruthchel

    2016-01-01

    To compare the ocular monochromatic higher-order aberration. (HOA) profile in normal refractive surgery candidates of Arab and South Asian origin. This cross-sectional, observational, comparative study was performed in the cornea department of a specialty hospital. Normal refractive surgery candidates with no ocular morbidity except refractive error were recruited. Refractive surgery candidates underwent a preoperative evaluation, including wavefront aberrometry with the iDesign aberrometer (AMO, Inc., Santa Ana, California, United States). The HOA from right eyes were analyzed for HOA signed, absolute, and polar Zernike coefficients. Two hundred Arab participants (group 1) and 200 participants of South-Asian origin (group 2) comprised the study sample. The age and refractive status were comparable between groups. The mean of the HOA root mean square (RMS) was 0.36 ± 17 μ and 0.38 ± 18 μ for Arab and South-Asian eyes, respectively (P < 0.05, rank sum test [RST]). Of the 22 higher order signed Zernike modes, only Z3 (-3), Z3 (-1),3 (1), Z4 (-4), Z4 (-2), Z4 (0), Z4 (4), and Z5 (-5) were significantly different from zero (one sample t-test, P < 0.002, with a Bonferroni correction of 0.05/22). All the signed and absolute Zernike terms were comparable between groups (RST, P > 0.002 [0.05/22]). The polar coefficients for coma, trefoil, spherical aberration, and tetrafoil were comparable between groups (P > 0.05, RST). Combined RMS values of third, fourth, fifth, and sixth order also were comparable between groups (P > 0.05, RST). Preoperative whole eye HOA were similar for refractive surgery candidates of Arab and South-Asian origin. The values were comparable to historical data for Caucasian eyes and were lower than Asian (Chinese) eyes. These findings may aid in refining refractive nomograms for wavefront ablations.

  4. Influence of uncorrected refractive error and unmet refractive error on visual impairment in a Brazilian population.

    PubMed

    Ferraz, Fabio H; Corrente, José E; Opromolla, Paula; Schellini, Silvana A

    2014-06-25

    The World Health Organization (WHO) definitions of blindness and visual impairment are widely based on best-corrected visual acuity excluding uncorrected refractive errors (URE) as a visual impairment cause. Recently, URE was included as a cause of visual impairment, thus emphasizing the burden of visual impairment due to refractive error (RE) worldwide is substantially higher. The purpose of the present study is to determine the reversal of visual impairment and blindness in the population correcting RE and possible associations between RE and individual characteristics. A cross-sectional study was conducted in nine counties of the western region of state of São Paulo, using systematic and random sampling of households between March 2004 and July 2005. Individuals aged more than 1 year old were included and were evaluated for demographic data, eye complaints, history, and eye exam, including no corrected visual acuity (NCVA), best corrected vision acuity (BCVA), automatic and manual refractive examination. The definition adopted for URE was applied to individuals with NCVA > 0.15 logMAR and BCVA ≤ 0.15 logMAR after refractive correction and unmet refractive error (UREN), individuals who had visual impairment or blindness (NCVA > 0.5 logMAR) and BCVA ≤ 0.5 logMAR after optical correction. A total of 70.2% of subjects had normal NCVA. URE was detected in 13.8%. Prevalence of 4.6% of optically reversible low vision and 1.8% of blindness reversible by optical correction were found. UREN was detected in 6.5% of individuals, more frequently observed in women over the age of 50 and in higher RE carriers. Visual impairment related to eye diseases is not reversible with spectacles. Using multivariate analysis, associations between URE and UREN with regard to sex, age and RE was observed. RE is an important cause of reversible blindness and low vision in the Brazilian population.

  5. Two different looks at Kepler’s refraction experiment

    NASA Astrophysics Data System (ADS)

    Grusche, Sascha; Wagner, Steffen

    2016-11-01

    Most refraction experiments are theory-laden and far from everyday experience. Accordingly, many students fail to apply the law of refraction to phenomena. To guide students from phenomena to theory, teachers can use a refraction experiment proposed by Kepler, where measurements are based on shadow images. For a different look at Kepler’s experiment, one can use the principle of reversibility to get equivalent results, but based on apparent depth. For this reversal, rays of light are reinterpreted as lines of sight, and vice versa. The principle allows students to relate refracted rays to shifted images, and applies to other optical phenomena.

  6. Demonstration of optical interference filters utilizing tunable refractive index layers.

    PubMed

    Poxson, David J; Mont, Frank W; Schubert, Martin F; Kim, Jong Kyu; Cho, Jaehee; Schubert, E Fred

    2010-11-08

    Optical interference filters utilizing tunable refractive index layers are shown to have higher spectral fidelity as compared to conventional filters consisting of non-tunable refractive index layers. To demonstrate this increase in spectral fidelity, we design and compare a variety of optical interference filters employing both tunable and non-tunable refractive index layers. Additionally, a five-layer optical interference filter utilizing tunable refractive index layers is designed and fabricated for use with a Xenon lamp to replicate the Air Mass 0 solar irradiance spectrum and is shown to have excellent spectral fidelity.

  7. The urgency for the study of the abnormal refraction.

    NASA Astrophysics Data System (ADS)

    Wei, Mao; Peng, Qingyu; Wang, Xiaobin

    The effects from the atmosphere of our earth on the astrometry are classified and some processing methods in the observations of traditional meridian circles are introduced. In comparison, the corresponding processing methods of the LLMC are also introduced. Since the LLMC can absolutely determine the normal refraction and the slope of the atmospheric isopyknic, it is pointed out that the short periodic and irregular refractions will be the main obstacle to raise the observatinal accuracy and the determination of the abnormal refraction in real time is urgent to clear away the obstacle of the refraction.

  8. Baseline peripheral refractive error and changes in axial refraction during one year in a young adult population

    PubMed Central

    Hartwig, Andreas; Charman, William Neil; Radhakrishnan, Hema

    2015-01-01

    Purpose To determine whether the initial characteristics of individual patterns of peripheral refraction relate to subsequent changes in refraction over a one-year period. Methods 54 myopic and emmetropic subjects (mean age: 24.9 ± 5.1 years; median 24 years) with normal vision were recruited and underwent conventional non-cycloplegic subjective refraction. Peripheral refraction was also measured at 5° intervals over the central 60° of horizontal visual field, together with axial length. After one year, measurements of subjective refraction and axial length were repeated on the 43 subjects who were still available for examination. Results In agreement with earlier studies, higher myopes tended to show greater relative peripheral hyperopia. There was, however, considerable inter-subject variation in the pattern of relative peripheral refractive error (RPRE) at any level of axial refraction. Across the group, mean one-year changes in axial refraction and axial length did not differ significantly from zero. There was no correlation between changes in these parameters for individual subjects and any characteristic of their RPRE. Conclusion No evidence was found to support the hypothesis that the pattern of RPRE is predictive of subsequent refractive change in this age group. PMID:26188389

  9. Baseline peripheral refractive error and changes in axial refraction during one year in a young adult population.

    PubMed

    Hartwig, Andreas; Charman, William Neil; Radhakrishnan, Hema

    2016-01-01

    To determine whether the initial characteristics of individual patterns of peripheral refraction relate to subsequent changes in refraction over a one-year period. 54 myopic and emmetropic subjects (mean age: 24.9±5.1 years; median 24 years) with normal vision were recruited and underwent conventional non-cycloplegic subjective refraction. Peripheral refraction was also measured at 5° intervals over the central 60° of horizontal visual field, together with axial length. After one year, measurements of subjective refraction and axial length were repeated on the 43 subjects who were still available for examination. In agreement with earlier studies, higher myopes tended to show greater relative peripheral hyperopia. There was, however, considerable inter-subject variation in the pattern of relative peripheral refractive error (RPRE) at any level of axial refraction. Across the group, mean one-year changes in axial refraction and axial length did not differ significantly from zero. There was no correlation between changes in these parameters for individual subjects and any characteristic of their RPRE. No evidence was found to support the hypothesis that the pattern of RPRE is predictive of subsequent refractive change in this age group. Copyright © 2015 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.

  10. Refractive shift of silicone oil tamponade in pseudophakic eye.

    PubMed

    Fang, Wei; Li, Jiuke; Jin, Xiaohong; Zhai, Jing; Dai, Yuanmin; Li, Yumin

    2016-08-16

    Refraction change of silicone oil (SO) tamponade in phakic and aphakic eye has been studied thoroughly; however, it is rarely studied in pseudophakic eye. In this paper we aimed to deduce a theoretical formula predicting refractive shift of silicone oil tamponade in pseudophakic eye and compared it with clinical findings. A theoretical formula was deduced through strict geometric optical principles under the Helmholtz Schematic eye model. Pre/postoperative refractive status of patients who previously underwent phacoemulsification, intraocular lens (IOL) implant, vitrectomy, SO tamponade and required SO extraction was studied. Twenty-six patients (27 eyes, 13 males and 13 females) were studied. Refractive error of SO-off was -1.88 ± 2.73D, and of SO-in was 2.02 ± 3.90. Refractive shift of SO tamponade was -3.90 ± 1.74D. Refractive shift was significantly associated with refractive power of IOL (r = -0.7903, p < 0.0001, Pearson correlation test) and anterior chamber distance (ACD, r = 0.3840, p = 0.0480, Pearson correlation test). Theoretical refractive shift was -4.10 ± 1.51D, and there was no significant difference between the theoretical and the clinical refractive shift (p = 0.3329, Paired T test). Refractive shift of SO tamponade in pseudophakic eye correlates with refractive power of implanted IOL and ACD, and strong correlation between theoretical formula and clinical findings was detected.

  11. Predicting postoperative intraocular lens position and refraction.

    PubMed

    Preussner, Paul-Rolf; Wahl, Jochen; Weitzel, Daniela; Berthold, Silke; Kriechbaum, Katharina; Findl, Oliver

    2004-10-01

    To predict the postoperative IOL position and refraction as accurately as possible independent of individualization of the parameters. Universitats-Augenklinik, Mainz, Germany, and Vienna, Austria. One patient cohort (189 eyes, Vienna) was used to calibrate the prediction method, which was then applied to a second cohort (65 eyes, Mainz). All calculations were based on consistent numerical ray tracing of the pseudophakic eye using the original manufacturer's intraocular lens (IOL) data (radii, thickness, refractive index). A new algorithm to predict IOL position was developed. Ultrasound (US) axial lengths were calibrated relative to partial coherence interferometry (PCI). Corneal radii extracted from topography were checked against radii measured with the IOLMaster (Zeiss) and by Littmann keratometry. Zero mean prediction errors for IOL position and refraction were obtained without adjusting the parameters and with PCI lengths or US lengths calibrated relative to the PCI values. There was no significant loss of accuracy of US data compared to PCI data. Corneal radii extracted from topography were slightly but statistically significantly different from the Littmann values, and they were more accurate than the latter with respect to prediction error. The measured mean central IOL position (distance from posterior corneal surface) for all IOL types was 4.580 mm, a value very close to the mean recalculated from A-constants (4.587 mm). The difference in the individual central IOL position relative to the mean value depended only linearly (ie, no higher orders such as square or cubic are needed) on axial length, with the mean central IOL position as a free parameter. This parameter should be 4.6 +/- 0.2 mm (the same value as independently measured or recalculated) to obtain zero steepness of the prediction error as a function of axial length, producing zero bias for long and short eyes. Calculation errors from formulas and confusing adjusting parameters can be avoided

  12. A noble refractive optical scanner with linear response

    NASA Astrophysics Data System (ADS)

    Mega, Yair J.; Lai, Zhenhua; DiMarzio, Charles A.

    2013-03-01

    Many applications in various fields of science and engineering use steered optical beam systems. Currently, many methods utilize mirrors in order to steer the beam. However, this approach is an off-axis solution, which normally increases the total size of the system as well as its error and complexity. Other methods use a "Risely Prisms" based solution, which is on-axis solution, however it poses some difficulties from an engineering standpoint, and therefore isn't widely used. We present here a novel technique for steering a beam on its optical axis with a linear deflection response. We derived the formulation for the profile required of the refractive optical component necessary for preforming the beam steering. The functionality of the device was simulated analytically using Matlab, as well as using a ray-tracing software, Zemax, and showed agreement with the analytical model. An optical element was manufactured based on the proposed design and the device was tested. The results show agreement with our hypothesis. We also present some proposed geometries of the several other devices, all based on the same concept, which can be used for higher performance applications such as two-dimensional scanner, video rate scanner etc.

  13. Porous Silicon Gradient Refractive Index Micro-Optics.

    PubMed

    Krueger, Neil A; Holsteen, Aaron L; Kang, Seung-Kyun; Ocier, Christian R; Zhou, Weijun; Mensing, Glennys; Rogers, John A; Brongersma, Mark L; Braun, Paul V

    2016-12-14

    The emergence and growth of transformation optics over the past decade has revitalized interest in how a gradient refractive index (GRIN) can be used to control light propagation. Two-dimensional demonstrations with lithographically defined silicon (Si) have displayed the power of GRIN optics and also represent a promising opportunity for integrating compact optical elements within Si photonic integrated circuits. Here, we demonstrate the fabrication of three-dimensional Si-based GRIN micro-optics through the shape-defined formation of porous Si (PSi). Conventional microfabrication creates Si square microcolumns (SMCs) that can be electrochemically etched into PSi elements with nanoscale porosity along the shape-defined etching pathway, which imparts the geometry with structural birefringence. Free-space characterization of the transmitted intensity distribution through a homogeneously etched PSi SMC exhibits polarization splitting behavior resembling that of dielectric metasurfaces that require considerably more laborious fabrication. Coupled birefringence/GRIN effects are studied by way of PSi SMCs etched with a linear (increasing from edge to center) GRIN profile. The transmitted intensity distribution shows polarization-selective focusing behavior with one polarization focused to a diffraction-limited spot and the orthogonal polarization focused into two laterally displaced foci. Optical thickness-based analysis readily predicts the experimentally observed phenomena, which strongly match finite-element electromagnetic simulations.

  14. Negative Refractive Index Metasurfaces for Enhanced Biosensing.

    PubMed

    Jakšić, Zoran; Vuković, Slobodan; Matovic, Jovan; Tanasković, Dragan

    2010-12-23

    In this paper we review some metasurfaces with negative values of effective refractive index, as scaffolds for a new generation of surface plasmon polariton-based biological or chemical sensors. The electromagnetic properties of a metasurface may be tuned by its full immersion into analyte, or by the adsorption of a thin layer on it, both of which change its properties as a plasmonic guide. We consider various simple forms of plasmonic crystals suitable for this purpose. We start with the basic case of a freestanding, electromagnetically symmetrical plasmonic slab and analyze different ultrathin, multilayer structures, to finally consider some two-dimensional "wallpaper" geometries like split ring resonator arrays and fishnet structures. A part of the text is dedicated to the possibility of multifunctionalization where a metasurface structure is simultaneously utilized both for sensing and for selectivity enhancement. Finally we give an overview of surface-bound intrinsic electromagnetic noise phenomena that limits the ultimate performance of a metasurfaces sensor.

  15. Microwave gain medium with negative refractive index.

    PubMed

    Ye, Dexin; Chang, Kihun; Ran, Lixin; Xin, Hao

    2014-12-19

    Artificial effective media are attractive because of the fantastic applications they may enable, such as super lensing and electromagnetic invisibility. However, the inevitable loss due to their strongly dispersive nature is one of the fundamental challenges preventing such applications from becoming a reality. In this study, we demonstrate an effective gain medium based on negative resistance, to overcompensate the loss of a conventional passive metamaterial, meanwhile keeping its original negative-index property. Energy conservation-based theory, full-wave simulation and experimental measurement show that a fabricated sample consisting of conventional sub-wavelength building blocks with embedded microwave tunnel diodes exhibits a band-limited Lorentzian dispersion simultaneously with a negative refractive index and a net gain. Our work provides experimental evidence to the assertion that a stable net gain in negative-index gain medium is achievable, proposing a potential solution for the critical challenge current metamateiral technology faces in practical applications.

  16. Refraction in Terms of the Deviation of the Light.

    ERIC Educational Resources Information Center

    Goldberg, Fred M.

    1985-01-01

    Discusses refraction in terms of the deviation of light. Points out that in physics courses where very little mathematics is used, it might be more suitable to describe refraction entirely in terms of the deviation, rather than by introducing Snell's law. (DH)

  17. Optimizing Refractivity from Clutter (RFC) for Surface-Based Ducts

    DTIC Science & Technology

    2010-09-30

    System ( AREPS ). The specific technical objectives are to develop algorithms to extract surface clutter only from weather files provided by the...Propagation Model (APM), currently integrated in the Advanced Refractive Effects Prediction System ( AREPS ) and included in the Oceanographic and...PMW 120 which has produced the Advanced Refractive Effects Prediction System ( AREPS ). Current and new software, along with information displays will

  18. Index of Refraction Measurements Using a Laser Distance Meter

    ERIC Educational Resources Information Center

    Ochoa, Romulo; Fiorillo, Richard; Ochoa, Cris

    2014-01-01

    We present a simple method to determine the refractive indices of transparent media using a laser distance meter. Indices of refraction have been obtained by measuring the speed of light in materials. Some speed of light techniques use time-of-flight measurements in which pulses are emitted by lasers and the time interval is measured for the pulse…

  19. Modification of the DSN radio frequency angular tropospheric refraction model

    NASA Technical Reports Server (NTRS)

    Berman, A. L.

    1977-01-01

    The previously derived DSN Radio Frequency Angular Tropospheric Refraction Model contained an assumption which was subsequently seen to be at a variance with the theoretical basis of angular refraction. The modification necessary to correct the model is minor in that the value of a constant is changed.

  20. Refraction in Terms of the Deviation of the Light.

    ERIC Educational Resources Information Center

    Goldberg, Fred M.

    1985-01-01

    Discusses refraction in terms of the deviation of light. Points out that in physics courses where very little mathematics is used, it might be more suitable to describe refraction entirely in terms of the deviation, rather than by introducing Snell's law. (DH)

  1. Determining the Thickness and Refractive Index of a Mirror

    ERIC Educational Resources Information Center

    Uysal, Ahmet

    2010-01-01

    When a laser beam reflects from a back surface glass mirror and falls on a screen, a pattern of discrete bright spots is created by partial reflection and refraction of the light at the air-glass interface and reflection at the mirror surface (Fig. 1). This paper explains how this phenomenon can be used to determine the refractive index and the…

  2. Negative Refraction in a Uniaxial Absorbent Dielectric Material

    ERIC Educational Resources Information Center

    Jen, Yi-Jun; Lakhtakia, Akhlesh; Yu, Ching-Wei; Lin, Chin-Te

    2009-01-01

    Refraction of light from an isotropic dielectric medium to an anisotropic dielectric material is a complicated phenomenon that can have several different characteristics not usually discussed in electromagnetics textbooks for undergraduate students. With a simple problem wherein the refracting material is uniaxial with its optic axis normal to the…

  3. Helping Secondary School Students Develop a Conceptual Understanding of Refraction

    ERIC Educational Resources Information Center

    Ashmann, Scott; Anderson, Charles W.; Boeckman, Heather

    2016-01-01

    Using real-world examples, ray diagrams, and a cognitive apprenticeship cycle, this paper focuses on developing students' conceptual (not mathematical) understanding of refraction. Refraction can be a difficult concept for students to comprehend if they do not have well-designed opportunities to practice explaining situations where reflection and…

  4. Comparison Between Radar and Automatic Weather Station Refractivity Variability

    NASA Astrophysics Data System (ADS)

    Hallali, Ruben; Dalaudier, Francis; Parent du Chatelet, Jacques

    2016-08-01

    Weather radars measure changes in the refractive index of air in the atmospheric boundary layer. The technique uses the phase of signals from ground targets located around the radar to provide information on atmospheric refractivity related to meteorological quantities such as temperature, pressure and humidity. The approach has been successfully implemented during several field campaigns using operational S-band radars in Canada, UK, USA and France. In order to better characterize the origins of errors, a recent study has simulated temporal variations of refractivity based on Automatic Weather Station (AWS) measurements. This reveals a stronger variability of the refractivity during the summer and in the afternoon when the refractivity is the most sensitive to humidity, probably because of turbulence close to the ground. This raises the possibility of retrieving information on the turbulent state of the atmosphere from the variability in radar refractivity. An analysis based on a 1-year dataset from the operational C-band radar at Trappes (near Paris, France) and AWS refractivity variability measurements was used to measure those temporal and spatial variabilities. Particularly during summer, a negative bias increasing with range is observed between radar and AWS estimations, and is well explained by a model based on Taylor's hypotheses. The results demonstrate the possibility of establishing, depending on season, a quantitative and qualitative link between radar and AWS refractivity variability that reflects low-level coherent turbulent structures.

  5. String and Sticky Tape Experiments: Refractive Index of Liquids.

    ERIC Educational Resources Information Center

    Edge, R. D., Ed.

    1979-01-01

    Describes a simple method of measuring the refractive index of a liquid using a paper cup, a liquid, a pencil, and a ruler. Uses the ratio between the actual depth and the apparent depth of the cup to calculate the refractive index. (GA)

  6. Measurement of Refractive Index Using a Michelson Interferometer.

    ERIC Educational Resources Information Center

    Fendley, J. J.

    1982-01-01

    Describes a novel and simple method of measuring the refractive index of transparent plates using a Michelson interferometer. Since it is necessary to use a computer program when determining the refractive index, undergraduates could be given the opportunity of writing their own programs. (Author/JN)

  7. Unbiased Estimation of Refractive State of Aberrated Eyes

    PubMed Central

    Martin, Jesson; Vasudevan, Balamurali; Himebaugh, Nikole; Bradley, Arthur; Thibos, Larry

    2011-01-01

    To identify unbiased methods for estimating the target vergence required to maximize visual acuity based on wavefront aberration measurements. Experiments were designed to minimize the impact of confounding factors that have hampered previous research. Objective wavefront refractions and subjective acuity refractions were obtained for the same monochromatic wavelength. Accommodation and pupil fluctuations were eliminated by cycloplegia. Unbiased subjective refractions that maximize visual acuity for high contrast letters were performed with a computer controlled forced choice staircase procedure, using 0.125 diopter steps of defocus. All experiments were performed for two pupil diameters (3mm and 6mm). As reported in the literature, subjective refractive error does not change appreciably when the pupil dilates. For 3 mm pupils most metrics yielded objective refractions that were about 0.1D more hyperopic than subjective acuity refractions. When pupil diameter increased to 6 mm, this bias changed in the myopic direction and the variability between metrics also increased. These inaccuracies were small compared to the precision of the measurements, which implies that most metrics provided unbiased estimates of refractive state for medium and large pupils. A variety of image quality metrics may be used to determine ocular refractive state for monochromatic (635nm) light, thereby achieving accurate results without the need for empirical correction factors. PMID:21777601

  8. Cylindrical radiant energy direction device with refractive medium

    DOEpatents

    Winston, Roland

    1978-01-01

    A device is provided for directing radiant energy and includes a refractive element and a reflective boundary. The reflective boundary is so contoured that incident energy directed thereto by the refractive element is directed to the exit surface thereof or onto the surface of an energy absorber positioned at the exit surface.

  9. Determining the Thickness and Refractive Index of a Mirror

    ERIC Educational Resources Information Center

    Uysal, Ahmet

    2010-01-01

    When a laser beam reflects from a back surface glass mirror and falls on a screen, a pattern of discrete bright spots is created by partial reflection and refraction of the light at the air-glass interface and reflection at the mirror surface (Fig. 1). This paper explains how this phenomenon can be used to determine the refractive index and the…

  10. Surface refractivity measurements at NASA spacecraft tracking sites

    NASA Technical Reports Server (NTRS)

    Schmid, P. E.

    1972-01-01

    High-accuracy spacecraft tracking requires tropospheric modeling which is generally scaled by either estimated or measured values of surface refractivity. This report summarizes the results of a worldwide surface-refractivity test conducted in 1968 in support of the Apollo program. The results are directly applicable to all NASA radio-tracking systems.

  11. Refractive properties of the healthy human eye during acute hyperglycemia.

    PubMed

    Wiemer, Nanouk G M; Eekhoff, Elisabeth M W; Simsek, Suat; Heine, Robert J; Ringens, Peter J; Polak, Bettine C P; Dubbelman, Michiel

    2008-07-01

    To measure the refractive properties of the healthy human eye during acute hyperglycemia by means of Scheimpflug imaging and Hartmann-Shack aberrometry. Acute hyperglycemia was induced in five healthy subjects (two males, three females, mean age +/-SD 24.8 years +/- 4.6) by means of an oral glucose tolerance test (OGTT) after subcutaneous somatostatin injection. Before and every 30 minutes after the OGTT, measurements with Scheimpflug imaging and Hartmann-Shack aberrometry were performed. The main outcome measures were the thickness and shape of the lens, and the ocular refractive error and higher order aberrations. The equivalent refractive index of the lens was calculated from these parameters. Measurements at baseline and during hyperglycemia were analyzed by means of Wilcoxon signed rank sum tests. During hyperglycemia (mean blood glucose level at baseline: 4.0 mmol/l; mean maximal blood glucose level: 18.4 mmol/l) no changes could be found in the refractive properties within the group. In one subject, a hyperopic shift (0.4 D) was observed, together with a more convex shape of the anterior lens surface and a decrease in the equivalent refractive index of the lens. This study shows that hyperglycemia generally does not cause changes in the refractive properties of the healthy eye. Nevertheless, in one subject a hyperopic shift accompanied by a change in shape and refractive index of the lens was measured. This finding could provide an explanation for the mechanism underlying the refractive changes that are often observed during hyperglycemia.

  12. String and Sticky Tape Experiments: Refractive Index of Liquids.

    ERIC Educational Resources Information Center

    Edge, R. D., Ed.

    1979-01-01

    Describes a simple method of measuring the refractive index of a liquid using a paper cup, a liquid, a pencil, and a ruler. Uses the ratio between the actual depth and the apparent depth of the cup to calculate the refractive index. (GA)

  13. Modification of the DSN radio frequency angular tropospheric refraction model

    NASA Technical Reports Server (NTRS)

    Berman, A. L.

    1977-01-01

    The previously derived DSN Radio Frequency Angular Tropospheric Refraction Model contained an assumption which was subsequently seen to be at a variance with the theoretical basis of angular refraction. The modification necessary to correct the model is minor in that the value of a constant is changed.

  14. Anterior segment surgery IOLs, lasers, and refractive keratoplasty

    SciTech Connect

    Stark, W.J.; Terry, A.C.; Maumenee, A.E.

    1987-01-01

    The contributors to this text combine their expertise to make this book available on intraocular lenses, refractive corneal surgery, and the use of the YAG laser. Included is information on; IOL power calculations; the use of the YAG laser; retinal damage by short wavelength light; reviews of corneal refractive surgery; possibilities for the medical prevention of cataracts; and more.

  15. Negative Refraction in a Uniaxial Absorbent Dielectric Material

    ERIC Educational Resources Information Center

    Jen, Yi-Jun; Lakhtakia, Akhlesh; Yu, Ching-Wei; Lin, Chin-Te

    2009-01-01

    Refraction of light from an isotropic dielectric medium to an anisotropic dielectric material is a complicated phenomenon that can have several different characteristics not usually discussed in electromagnetics textbooks for undergraduate students. With a simple problem wherein the refracting material is uniaxial with its optic axis normal to the…

  16. Index of Refraction Measurements Using a Laser Distance Meter

    ERIC Educational Resources Information Center

    Ochoa, Romulo; Fiorillo, Richard; Ochoa, Cris

    2014-01-01

    We present a simple method to determine the refractive indices of transparent media using a laser distance meter. Indices of refraction have been obtained by measuring the speed of light in materials. Some speed of light techniques use time-of-flight measurements in which pulses are emitted by lasers and the time interval is measured for the pulse…

  17. Measurement of Refractive Index Using a Michelson Interferometer.

    ERIC Educational Resources Information Center

    Fendley, J. J.

    1982-01-01

    Describes a novel and simple method of measuring the refractive index of transparent plates using a Michelson interferometer. Since it is necessary to use a computer program when determining the refractive index, undergraduates could be given the opportunity of writing their own programs. (Author/JN)

  18. [Influence of axial length in refractive outcome after cataract surgery].

    PubMed

    de Juan, V; Martín, R; Pérez, I; Herreras, J M

    2010-04-01

    To analyse the influence of axial length (AL) and age on refractive outcome after cataract surgery in terms of uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA) and subjective refraction. A retrospective review of 171 consecutive cases of uncomplicated cataract surgery was done. The refractive outcome was analysed (UCVA, BCVA and postoperative retraction) according AL before surgery (AL < 22 mm, between 22 and 25 mm and AL > 25 mm) and age (< 40, between 40-60 years and > 60 years). After surgery mean UCVA was 0.6 ± 0.33 Diopters (D) and mean BCVA was 0.93 ± 0.23 D. Mean refractive outcome was 0.89 ± 0.78 D. There were no significant differences in post-operative UCVA, BCVA and refraction between the three age groups. There were statistically significant differences (p = 0.004) in UCVA between the three AL groups. The group with AL between 22 and 25 mm had better UCVA. Mean refractive outcome was -0.95 ± 1.91 D in the group with AL < 22 mm, -0.36 ± 0.88 D in the group with AL between 22 and 25 mm and 0.23 ± 1.15 D in the group with AL > 25 mm. AL influences refractive outcome and UCVA after cataract surgery. Eyes with AL < 22 mm have a worse refractive outcome.

  19. Diffractive-refractive correction units for plastic compact zoom lenses.

    PubMed

    Greisukh, Grigoriy I; Ezhov, Evgeniy G; Kalashnikov, Alexander V; Stepanov, Sergei A

    2012-07-10

    A method of designing a plastic zoom lens with a diffractive-refractive hybrid corrector, comprising one diffractive lens and one refractive lens, is described. The efficiency of this method is demonstrated by designing a compact zoom lens for a mobile phone. This zoom design, incorporating lenses made only of two commercial optical plastics (polymethylmethacrylate and polycarbonate), provides high optical performance.

  20. Helping Secondary School Students Develop a Conceptual Understanding of Refraction

    ERIC Educational Resources Information Center

    Ashmann, Scott; Anderson, Charles W.; Boeckman, Heather

    2016-01-01

    Using real-world examples, ray diagrams, and a cognitive apprenticeship cycle, this paper focuses on developing students' conceptual (not mathematical) understanding of refraction. Refraction can be a difficult concept for students to comprehend if they do not have well-designed opportunities to practice explaining situations where reflection and…

  1. Comment on "Refractive indices of biaxial crystals evaluated from the refractive indices ellipsoid equation"

    NASA Astrophysics Data System (ADS)

    Hernández-Rodríguez, Cecilio; Fragoso-López, Ana Belén

    2014-02-01

    In 2007 Yin, Zhang and Tian [1] [Yin et al., 2007] derived the expressions of the refractive indices of biaxial crystals evaluated from the refractive indices ellipsoid equation. In the past we have researched about the simultaneous measurement of birefringence and optical activity in different crystals [2] [Hernández-Rodríguez et al., 2000], [3] [Hernández-Rodríguez and Gómez-Garrido, 2000], [4] [Herreros-Cedrés et al., 2003], [5] [Herreros-Cedrés et al., 2005] and [6] [Herreros-Cedrés et al., 2007], and recently, when we used their methods for the study of nonlinear crystals such as KTiOAsO4 (KTA) and KTiOPO4 (KTP), we found some errors in some expressions in their paper which were used by other authors [7] [Gao et al., 2003].

  2. Human resources for refraction services in Central Nepal.

    PubMed

    Kandel, Himal; Murthy, G V S; Bascaran, Covadonga

    2015-07-01

    Uncorrected refractive error is a public health problem globally and in Nepal. Planning of refraction services is hampered by a paucity of data. This study was conducted to determine availability and distribution of human resources for refraction, their efficiency, the type and extent of their training; the current service provision of refraction services and the unmet need in human resources for refraction in Central Nepal. This was a descriptive cross-sectional study. All refraction facilities in the Central Region were identified through an Internet search and interviews of key informants from the professional bodies and parent organisations of primary eye centres. A stratified simple random sampling technique was used to select 50 per cent of refraction facilities. The selected facilities were visited for primary data collection. Face-to-face interviews were conducted with the managers and the refractionists available in the facilities using a semi-structured questionnaire. Data was collected in 29 centres. All the managers (n=29; response rate 100 per cent) and 50 refractionists (Response rate 65.8 per cent) were interviewed. Optometrists and ophthalmic assistants were the main providers of refraction services (n=70, 92.11 per cent). They were unevenly distributed across the region, highly concentrated around urban areas. The median number of refractions per refractionist per year was 3,600 (IQR: 2,400 - 6,000). Interviewed refractionists stated that clients' knowledge, attitude and practice related factors such as lack of awareness of the need for refraction services and/or availability of existing services were the major barriers to the output of refraction services. The total number of refractions carried out in the Central Region per year was 653,176. An additional 170 refractionists would be needed to meet the unmet need of 1,323,234 refractions. The study findings demand a major effort to develop appropriately trained personnel when planning

  3. CRUSTAL STRUCTURE OF THE SOUTHERN CALAVERAS FAULT ZONE, CENTRAL CALIFORNIA, FROM SEISMIC REFRACTION INVESTIGATIONS.

    USGS Publications Warehouse

    Blumling, Peter; Mooney, Walter D.; Lee, W.H.K.

    1985-01-01

    A magnitude 5. 7 earthquake on August 6, 1979, within the Calaveras fault zone, near Coyote Lake of west-central California, motivated a seismic-refraction investigation in this area. A northwest-southeast profile along the fault, as well as two fan profiles across the fault were recorded to examine the velocity structure of this region. The analysis of the data reveals a complicated upper crustal velocity structure with strong lateral variations in all directions. Velocities within the fault zone were determined from the fan profiles. Near Anderson Lake, a pronounced delay of first arrivals on the fan records indicates a vertical 1- to 2-km-wide near-surface, low-velocity zone along the fault. Near Coyote Lake, the delays observed in the fan records correlate with two subsurface en-echelon fault planes which have been previously identified from lineations in the seismicity pattern. Refs.

  4. CHARMS: The Cryogenic, High-Accuracy Refraction Measuring System

    NASA Technical Reports Server (NTRS)

    Frey, Bradley; Leviton, Douglas

    2004-01-01

    The success of numerous upcoming NASA infrared (IR) missions will rely critically on accurate knowledge of the IR refractive indices of their constituent optical components at design operating temperatures. To satisfy the demand for such data, we have built a Cryogenic, High-Accuracy Refraction Measuring System (CHARMS), which, for typical 1R materials. can measure the index of refraction accurate to (+ or -) 5 x 10sup -3 . This versatile, one-of-a-kind facility can also measure refractive index over a wide range of wavelengths, from 0.105 um in the far-ultraviolet to 6 um in the IR, and over a wide range of temperatures, from 10 K to 100 degrees C, all with comparable accuracies. We first summarize the technical challenges we faced and engineering solutions we developed during the construction of CHARMS. Next we present our "first light," index of refraction data for fused silica and compare our data to previously published results.

  5. Refractive changes following corrective surgery for thyroid-related orbitopathy.

    PubMed

    Kinori, Michael; Godfrey, Kyle J; Whipple, Katherine M; Kikkawa, Don O; Granet, David B

    2017-02-01

    Thyroid-related orbitopathy (TRO) is a common and recognizable manifestation of Graves' disease, caused by an increase in orbital fat volume, increased extraocular muscle diameter, and fibrosis. Together, within the bony confines of the orbit, these changes might alter the shape and position of the globe, potentially inducing refractive shifts. These refractive changes may then be affected by corrective surgical interventions for TRO such as orbital decompression and strabismus surgery. We studied refractive changes in patients with TRO who underwent strabismus surgery with or without orbital decompression. Manifest refraction was performed preoperatively and postoperatively in 33 patients who met inclusion criteria. Statistically significant postoperative refractive changes were found for cylinder, axis, and spherical equivalent. Copyright © 2017 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.

  6. Software for teaching refraction of light with the semicircle

    NASA Astrophysics Data System (ADS)

    Mihas, Pavlos

    2016-11-01

    Software is presented for teaching elementary optics using a transparent semicircle. We demonstrate the use of the semicircle to investigate Snell’s lawand students can are presented with the difficulties involved in experiments. An Excel spreadsheet can show to students that small errors in positioning of the semicircle can result in a non-constant index of refraction. Students can study the effect of changing some of the parameters of placement of a semicircle on the accuracy of the experimental results. They can see from the analysis of data that much better results are obtained by doing regression analysis rather than by just taking the average value of the index of refraction. Measuring the critical angle also gives a method of calculating the index of refraction. Another way to measure the index of refraction is the use of the semicircle as a lens and from its focal length we can deduce the index of refraction.

  7. The effect of multifocal soft contact lenses on peripheral refraction.

    PubMed

    Kang, Pauline; Fan, Yvonne; Oh, Kelly; Trac, Kevin; Zhang, Frank; Swarbrick, Helen A

    2013-07-01

    To compare changes in peripheral refraction with single-vision (SV) and multifocal (MF) correction of distance central refraction with commercially available SV and MF soft contact lenses (SCLs) in young myopic adults. Thirty-four myopic adult subjects were fitted with Proclear Sphere and Proclear Multifocal SCLs to correct their manifest central refractive error. Central and peripheral refraction were measured with no lens wear and subsequently with the two different types of SCL correction. At baseline, refraction was myopic at all locations along the horizontal meridian. Peripheral refraction was relatively hyperopic compared with center at 30 and 35 degrees in the temporal visual field (VF) in low myopes, and at 30 and 35 degrees in the temporal VF, and 10, 30, and 35 degrees in the nasal VF in moderate myopes. Single-vision and MF distance correction with Proclear Sphere and Proclear Multifocal SCLs, respectively, caused a hyperopic shift in refraction at all locations in the horizontal VF. Compared with SV correction, MF SCL correction caused a significant relative myopic shift at all locations in the nasal VF in both low and moderate myopes and also at 35 degrees in the temporal VF in moderate myopes. Correction of central refractive error with SV and MF SCLs caused a hyperopic shift in both central and peripheral refraction at all positions in the horizontal meridian. Single-vision SCL correction caused the peripheral retina, which initially experienced absolute myopic defocus at baseline with no correction to experience an absolute hyperopic defocus. Multifocal SCL correction resulted in a relative myopic shift in peripheral refraction compared with SV SCL correction. This myopic shift may explain recent reports of reduced myopia progression rates with MF SCL correction.

  8. Fabrication and modeling of the gray-scale mask-based aspheric refraction microlens array

    NASA Astrophysics Data System (ADS)

    Wang, Gou-Jen; Wang, Shuh-Yi; Chin, Chi-Hsian

    2002-04-01

    In this research, the manufacturing processes of non- spherical refraction microles array by gray-scale mask is investigated. Compared to the conventional multi-lithography fabricating method, the gray-scale mask approach requires only a single lithography action to fabricate a non- spherical refraction microlens array. In the firs part of this research, we emphasize the gray-scale mask based microlens array fabrication processes through the UV-LIGA approach. Furthermore, a two-stage process-modeling scheme is proposed to reduce the time-consuming trial-and-error parameters tuning labor works. At the first stage, a multi- layer feedforward neural-network is employed to model the relationships between the diameter and height of the microlens are obtained, the surface profile of this microlens can be predicted by an empirical equation. The empirical equation is derived through the regressing analysis method with data points sampled from the real microlens surface profile. Experimental results demonstrate that the proposed two-stage scheme can precisely predict the surface profile of the gray-scale mask based microlens.

  9. Crustal structure of Shatsky Rise from joint refraction and reflection seismic tomography

    NASA Astrophysics Data System (ADS)

    Korenaga, J.; Sager, W. W.

    2011-12-01

    Shatsky Rise in the western Pacific is one of a few gigantic oceanic plateaus in the world, with a surface area of ˜ 4.8 ± 105~km2 (about the same size as California). In contrast to other large oceanic plateaus formed during the Cretaceous Quite Period, Shatsky Rise formed during the frequent reversals of magnetic polarity, allowing its tectonic environment to be resolved in detail. It was formed at a rapidly spreading ridge-ridge-ridge triple junction, so the effect of lithospheric lid on magma migration is expected to be minimal, thereby facilitating the petrological interpretation of its seismic structure in terms of parental mantle processes. In the summer of 2010, a seismic refraction survey combined with multichannel seismic profiling was conducted across Shatsky Rise. Twenty eight ocean-bottom seismometers were deployed along two crossing perpendicular lines, and all of the instruments were recovered successfully, yielding a large volume of high-quality wide-angle refraction and reflection data, with the source-receiver distance often exceeding 200~km. In this contribution, we present the P-wave velocity structure of the Shatsky Rise crust, which is constructed by joint refraction and reflection travel time tomography, and also discuss its implications for the origin of Shatsky Rise.

  10. Parabolic refractive X-ray lenses: a breakthrough in X-ray optics

    NASA Astrophysics Data System (ADS)

    Lengeler, Bruno; Schroer, Christian G.; Benner, Boris; Günzler, Til Florian; Kuhlmann, Marion; Tümmler, Johannes; Simionovici, Alexandre S.; Drakopoulos, Michael; Snigirev, Anatoly; Snigireva, Irina

    2001-07-01

    Refractive X-ray lenses, considered for a long time as unfeasible, have been realized with a rotational parabolic profile at our institute: The main features of the new lenses are: they focus in two directions and are free of spherical aberration. By varying the number of individual lenses in the stack the focal length can be chosen in a typical range from 0.5 to 2 m for photon energies between about 6 and 60 keV. The aperture of the lens is about 1 mm matching the angular divergence of undulator beams at 3d generation synchrotron radiation sources. They cope without problems with the heat load from the white beam of an undulator. Finally, they are easy to align and to operate. Refractive X-ray lenses can be used with hard X-rays in the same way as glass lenses can be used for visible light, if it is take into account that the numerical aperture is small (of the order 10 -4). Being high-quality optical elements, the refractive X-ray lenses can be used for generating a focal spot in the μm range with a gain of a factor 1000 and more, or for imaging purposes as in a hard X-ray microscope. Recent examples from microanalysis, microtomography, fluorescence tomography, X-ray microscopy will be shown to demonstrate the state of the art. Possible new developments will be discussed.

  11. Determining the refractive index of shocked [100] lithium fluoride to the limit of transmissibility

    NASA Astrophysics Data System (ADS)

    Rigg, P. A.; Knudson, M. D.; Scharff, R. J.; Hixson, R. S.

    2014-07-01

    Lithium fluoride (LiF) is a common window material used in shock- and ramp-compression experiments because it displays a host of positive attributes in these applications. Most commonly, it is used to maintain stress at an interface and velocimetry techniques are used to record the particle velocity at that interface. In this application, LiF remains transparent to stresses up to 200 GPa. In this stress range, LiF has an elastic-plastic response with a very low (<0.5 GPa) elastic precursor and exhibits no known solid-solid phase transformations. However, because the density dependence of the refractive index of LiF does not follow the Gladstone-Dale relation, the measured particle velocity at this interface is not the true particle velocity and must be corrected. For that reason, the measured velocity is often referred to as the apparent velocity in these types of experiments. In this article, we describe a series of shock-compression experiments that have been performed to determine the refractive index of LiF at the two most commonly used wavelengths (532 nm and 1550 nm) between 35 and 200 GPa to high precision. A modified form of the Gladstone-Dale relation was found to work best to fit the determined values of refractive index. In addition, we provide a direct relationship between the apparent and true particle velocity to correct experimentally obtained wave profiles by others using these velocimetry techniques.

  12. Optimization of refractive liquid crystal lenses using an efficient multigrid simulation.

    PubMed

    Milton, Harry; Brimicombe, Paul; Morgan, Philip; Gleeson, Helen; Clamp, John

    2012-05-07

    A multigrid computational model has been developed to assess the performance of refractive liquid crystal lenses, which is up to 40 times faster than previous techniques. Using this model, the optimum geometries producing an ideal parabolic voltage distribution were deduced for refractive liquid crystal lenses with diameters from 1 to 9 mm. The ratio of insulation thickness to lens diameter was determined to be 1:2 for small diameter lenses, tending to 1:3 for larger lenses. The model is used to propose a new method of lens operation with lower operating voltages needed to induce specific optical powers. The operating voltages are calculated for the induction of optical powers between + 1.00 D and + 3.00 D in a 3 mm diameter lens, with the speed of the simulation facilitating the optimization of the refractive index profile. We demonstrate that the relationship between additional applied voltage and optical power is approximately linear for optical powers under + 3.00 D. The versatility of the computational simulation has also been demonstrated by modeling of in-plane electrode liquid crystal devices.

  13. The inverse problem of refraction travel times, part II: Quantifying refraction nonuniqueness using a three-layer model

    USGS Publications Warehouse

    Ivanov, J.; Miller, R.D.; Xia, J.; Steeples, D.

    2005-01-01

    This paper is the second of a set of two papers in which we study the inverse refraction problem. The first paper, "Types of Geophysical Nonuniqueness through Minimization," studies and classifies the types of nonuniqueness that exist when solving inverse problems depending on the participation of a priori information required to obtain reliable solutions of inverse geophysical problems. In view of the classification developed, in this paper we study the type of nonuniqueness associated with the inverse refraction problem. An approach for obtaining a realistic solution to the inverse refraction problem is offered in a third paper that is in preparation. The nonuniqueness of the inverse refraction problem is examined by using a simple three-layer model. Like many other inverse geophysical problems, the inverse refraction problem does not have a unique solution. Conventionally, nonuniqueness is considered to be a result of insufficient data and/or error in the data, for any fixed number of model parameters. This study illustrates that even for overdetermined and error free data, nonlinear inverse refraction problems exhibit exact-data nonuniqueness, which further complicates the problem of nonuniqueness. By evaluating the nonuniqueness of the inverse refraction problem, this paper targets the improvement of refraction inversion algorithms, and as a result, the achievement of more realistic solutions. The nonuniqueness of the inverse refraction problem is examined initially by using a simple three-layer model. The observations and conclusions of the three-layer model nonuniqueness study are used to evaluate the nonuniqueness of more complicated n-layer models and multi-parameter cell models such as in refraction tomography. For any fixed number of model parameters, the inverse refraction problem exhibits continuous ranges of exact-data nonuniqueness. Such an unfavorable type of nonuniqueness can be uniquely solved only by providing abundant a priori information

  14. Swift and heavy ion implanted chalcogenide laser glass waveguides and their different refractive index distributions

    SciTech Connect

    Qiu Feng; Narusawa, Tadashi; Zheng Jie

    2011-02-10

    Planar waveguides have been fabricated in Nd- or Ho-doped gallium lanthanum sulfide laser glasses by 60 MeV Ar or 20 MeV N ion implantation. The refractive index profiles were reconstructed based on the results of prism coupling. The Ar implanted waveguides exhibit an approximate steplike distribution, while the N implanted ones show a ''well + barrier'' type. This difference can be attributed to the much lower dose of Ar ions. After annealing, the N implanted waveguides can support two modes at 1539 nm and have low propagation loss, which makes them candidates for novel waveguide lasers.

  15. Transmission and refractive index sensing based on Fano resonance in MIM waveguide-coupled trapezoid cavity

    NASA Astrophysics Data System (ADS)

    Zhou, Jinli; Chen, Huibin; Zhang, Zhidong; Tang, Jun; Cui, Jiangong; Xue, Chenyang; Yan, Shubin

    2017-01-01

    A metal-insulator-metal (MIM) waveguide-coupled trapezoid cavity is presented, and the transmission properties are investigated by finite-element method. Results show that an asymmetric Fano profile emerged in the transmission spectrum, which was caused by the asymmetrical break of the MIM waveguide-coupled trapezoid cavity system. A refractive index sensitivity, Q-factor and FOM of approximately 750nm/RIU, 68.3 and 65.2 were measured based on the Fano resonance. The effect of the structural parameters on the transmission properties is also investigated. The results provide a new possibility for designing high-performance plasmonic devices.

  16. Improving directivity of laser beams by employing the effect of conical refraction in biaxial crystals.

    PubMed

    Peet, V

    2010-09-13

    The far-field pattern of Gaussian beams transformed by conical refraction in biaxial crystal is analyzed. It is shown that one of the two outgoing beam components acquires, under certain conditions, a profile with a dominating central peak. The width of this peak can be made significantly smaller than the width of the parent diffraction-limited Gaussian beam at the same propagation distance. The formation of such structurally-stable sub-diffraction beam core improves the beam directivity. Another component is a charge-one optical vortex, that forms the annular shell of the beam and carries the rest of the beam power.

  17. On application of shirt formula method for index profile reconstruction of a planar waveguide

    NASA Astrophysics Data System (ADS)

    Espinosa-Ortis, N.; Shevchenko, V. V.

    1994-03-01

    There is solved a problem of finding refractive index profile of the waveguiding layer of a near-surface waveguide on the basis of the measured values of effective refractive indexes of waveguide modes using selection of the model function parameters by the shift formulas method.

  18. Using refractive optics to broaden the focus of an X-ray mirror.

    PubMed

    Laundy, David; Sawhney, Kawal; Dhamgaye, Vishal

    2017-07-01

    X-ray mirrors are widely used at synchrotron radiation sources for focusing X-rays into focal spots of size less than 1 µm. The ability of the beamline optics to change the size of this spot over a range up to tens of micrometres can be an advantage for many experiments such as X-ray microprobe and X-ray diffraction from micrometre-scale crystals. It is a requirement that the beam size change should be reproducible and it is often essential that the change should be rapid, for example taking less than 1 s, in order to allow high data collection rates at modern X-ray sources. In order to provide a controlled broadening of the focused spot of an X-ray mirror, a series of refractive optical elements have been fabricated and installed immediately before the mirror. By translation, a new refractive element is moved into the X-ray beam allowing a variation in the size of the focal spot in the focusing direction. Measurements using a set of prefabricated refractive structures with a test mirror showed that the focused beam size could be varied from less than 1 µm to over 10 µm for X-rays in the energy range 10-20 keV. As the optics is in-line with the X-ray beam, there is no effect on the centroid position of the focus. Accurate positioning of the refractive optics ensures reproducibility in the focused beam profile and no additional re-alignment of the optics is required.

  19. Seismic refraction and downhole velocity surveys for investigation of the Tinemaha Dam Inyo County, California

    SciTech Connect

    Olson, M.; Inel, S.; Prashar, Y.

    1997-10-01

    Seismic refraction and downhole velocity surveys were conducted as part of a geotechnical investigation of the Tinemaha Dam. Thirteen P and S-wave velocity surveys were conducted concurrently with cone penetration testing along the crest and downstream toe of this dam. One additional velocity survey was conducted from a borehole on the crest of the dam using a downhole geophone array. The shear wave velocities estimated for the dam and its underlying alluvium ranged from 345 to 2008 ft/sec. A depth profile of these velocities indicates areas within the dam and its foundation where the shear wave velocities are less than 600 ft/sec. These velocity estimates were used with other geotechnical data, to calculate the dynamic elastic moduli for the dam and its foundation, to evaluate the stability of the dam in the event of a local earthquake on the Owens Valley fault. To further investigate the location of this active strike-slip fault, seismic refraction surveys were conducted at two locations. The first refraction survey was positioned south of the dam across the expected trend of the Owens Valley fault. A velocity analysis of the upper refracting horizon was conducted using the generalized reciprocal method. This revealed changes in lateral velocity that were interpreted as due to a fault-transition from saturated alluvium to volcanic bedrock. The second survey was positioned along the dam`s crest at the west abutment to help locate a possible fault beneath this area. The interpreted depth section from this survey locates a point where the deeper bedrock unit appears to be truncated by faulting. This information will help locate additional boreholes to evaluate lithologic conditions.

  20. Cycloplegic refraction is the gold standard for epidemiological studies.

    PubMed

    Morgan, Ian G; Iribarren, Rafael; Fotouhi, Akbar; Grzybowski, Andrzej

    2015-09-01

    Many studies on children have shown that lack of cycloplegia is associated with slight overestimation of myopia and marked errors in estimates of the prevalence of emmetropia and hyperopia. Non-cycloplegic refraction is particularly problematic for studies of associations with risk factors. The consensus around the importance of cycloplegia in children left undefined at what age, if any, cycloplegia became unnecessary. It was often implicitly assumed that cycloplegia is not necessary beyond childhood or early adulthood, and thus, the protocol for the classical studies of refraction in older adults did not include cycloplegia. Now that population studies of refractive error are beginning to fill the gap between schoolchildren and older adults, whether cycloplegia is required for measuring refractive error in this age range, needs to be defined. Data from the Tehran Eye Study show that, without cycloplegia, there are errors in the estimation of myopia, emmetropia and hyperopia in the age range 20-50, just as in children. Similar results have been reported in an analysis of data from the Beaver Dam Offspring Eye Study. If the only important outcome measure of a particular study is the prevalence of myopia, then cycloplegia may not be crucial in some cases. But, without cycloplegia, measurements of other refractive categories as well as spherical equivalent are unreliable. In summary, the current evidence suggests that cycloplegic refraction should be considered as the gold standard for epidemiological studies of refraction, not only in children, but in adults up to the age of 50.