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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. Seismic refraction profile in coral sea basin.

    PubMed

    Shor, G G

    1967-11-17

    A refraction profile near the south edge of Coral Sea Basin shows sediments, "second layer," and oceanic crust all thicker than normal for an oceanic station; normal mantle lies at a depth of 19 kilometers. PMID:17753600

  3. Advanced interferometric profile measurements through refractive media

    SciTech Connect

    Koev, Stephan T.; Ghodssi, Reza

    2008-09-15

    Optical profilers are valuable tools for the characterization of microelectromechanical systems (MEMSs). They use phase sifting interferometry (PSI) or vertical scanning interferometry to measure the topography of microscale structures with nanometer resolution. However, for many emerging MEMS applications, the sample needs to be imaged while placed in a liquid or in a package with a glass window. The increased refractive index of the transparent medium degrades the interference image contrast and prevents any measurement of the sample. We report on the modification of a Veeco NT1100 optical profiler to enable PSI measurements through refractive media. This approach can be applied to any other optical profiler with PSI capability. The modification consists in replacing the original illumination source with a custom-built narrow linewidth source, which increases the coherence length of the light and the contrast of the interference image. We present measurements taken with the modified configuration on samples covered with 3 mm water or 500 {mu}m glass, and we compare them to measurements of uncovered samples. We show that the measurement precision is only slightly reduced by the water and glass, and that it is still sufficiently high for typical MEMS applications. The described method can be readily used for measuring through other types and thicknesses of refractive materials.

  4. Refractive-index-profile determinations by using Lloyd's mirage.

    PubMed

    Allman, B E; Klein, A G; Nugent, K A; Opat, G I

    1994-04-01

    A method is presented for the experimental determination of refractive-index profiles for planar media of monotonically decreasing refractive index, such as those used for optical waveguides. The technique is based on a generalization of the classical experiment of Lloyd's mirror, involving the interference pattern formed by a point source and its mirage, i.e., its reflection in such a graded planar medium. PMID:20885511

  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. Compressive and Shear Wave Velocity Profiles using Seismic Refraction Technique

    NASA Astrophysics Data System (ADS)

    Aziman, M.; Hazreek, Z. A. M.; Azhar, A. T. S.; Haimi, D. S.

    2016-04-01

    Seismic refraction measurement is one of the geophysics exploration techniques to determine soil profile. Meanwhile, the borehole technique is an established way to identify the changes of soil layer based on number of blows penetrating the soil. Both techniques are commonly adopted for subsurface investigation. The seismic refraction test is a non-destructive and relatively fast assessment compared to borehole technique. The soil velocities of compressive wave and shear wave derived from the seismic refraction measurements can be directly utilised to calculate soil parameters such as soil modulus and Poisson’s ratio. This study investigates the seismic refraction techniques to obtain compressive and shear wave velocity profile. Using the vertical and horizontal geophones as well as vertical and horizontal strike directions of the transient seismic source, the propagation of compressive wave and shear wave can be examined, respectively. The study was conducted at Sejagung Sri Medan. The seismic velocity profile was obtained at a depth of 20 m. The velocity of the shear wave is about half of the velocity of the compression wave. The soil profiles of compressive and shear wave velocities were verified using the borehole data and showed good agreement with the borehole data.

  7. The measurement of patient-reported outcomes of refractive surgery: the refractive status and vision profile.

    PubMed Central

    Schein, O D

    2000-01-01

    PURPOSE: To develop a questionnaire, the Refractive Status and Vision Profile (RSVP), to assess health-related quality of life associated with refractive error and its correction. METHODS: The published literature on patient report of visual and overall function was reviewed, and the RSVP was self-administered by 550 participants with refractive error. Cross-sectional validation was performed using standard psychometric techniques. The responsiveness of the RSVP to surgical intervention was assessed prospectively in a subset of 176 patients. The principal outcomes measures were scores on the overall RSVP scale (S) and on 8 RSVP subscales (functioning, driving, concern, expectations, symptoms, glare, optical problems, problems with corrective lenses). RESULTS: The RSVP (S) and its subscales demonstrated very good internal consistency (Cronbach's alpha, 0.70-0.93). S and several subscale scores were independently associated with satisfaction with vision and were more correlated with satisfaction with vision than with either visual acuity or refractive error. Higher refractive error was associated with lower scores on S and on 5 subscales. In the prospective surgical cohort, 15% of patients had some worsening in their total RSVP score; however, substantial variation was seen in the individual subscales where worsening ranged from 7% (problems with corrective lenses) to 41% (driving). The effect size (measure of responsiveness) of the RSVP and most of its subscales was very high. Approximately 14% of patients had significant worsening in 3 or more subscales, and this outcome was found to be independently associated with being dissatisfied with vision following surgery (OR, 5.84; 95% CI, 1.88, 8.13). CONCLUSIONS: The RSVP has been validated as a questionnaire that measures patient-reported quality of life related to refractive error and its correction. It is responsive to surgical intervention and provides important information regarding patient outcomes not available

  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. 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.

  11. Evaporation duct refractivity profile from satellite meteorological data

    NASA Astrophysics Data System (ADS)

    Levadnyi, Iu.; Ivanov, V.; Shalyapin, V.

    The refractivity profile is initial data for the microwave propagation prediction models Evaporation duct height is usually used to characterize refractivity profile in the surface layer over sea The evaporation duct height is calculated using bulk measurement of air temperature wind speed humidity pressure at some level and sea surface temperature Four prevailing models LKB Liu-Katsaros-Businger RSHMU Russian State Hydro-Meteorological University optimized by us ECMWF European Center for Medium range Weather Forecast and COARE Coupled Ocean-Atmosphere Response Experiment were examined The results of computation using above mentioned models were compared with the direct refractometric measurements All measurements meteorological and refractometric were made by us during two marine expeditions First expedition was in the Atlantic ocean from March to May in latitude 22 circ-32° North and longitude 52 circ-65° West 29 measurements Second one was in the Indian ocean from December to February in latitude 0 circ-15° North and longitude 55 circ-80° East 94 measurements The approximation by least square-root method was carried out to compare the direct measurements of evaporation duct height with the results of computations The minimum square-root error is obtained for LKB model 2 59m for negative air-sea temperature difference 2 42m maximum - for ECMWF model 2 72m All models overestimate low evaporation duct heights and underestimate - high values This effect is least of all define in RSHMU

  12. 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

  13. 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. PMID:23820291

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  15. Atmospheric refraction: Applied image analysis and experimental example for index profile with curvature

    NASA Astrophysics Data System (ADS)

    Short, Daniel; Voelz, David; Barraza, Jose; Dragulin, Ivan

    2016-05-01

    In this work we consider atmospheric refractive bending and its effects on long-range imaging along a horizontal path. Refraction can impact the ability of a remote sensing or image system to accurately locate objects and determine their apparent proportions. We use a low-cost commercial camera operating in a time-lapse mode for refraction studies and have been recording images of a building that is 15.3 km west of the camera. Based on the paraxial ray equation, a solution for ray height and angle is obtained for a refractive index profile with curvature. A curved index profile can produce the effects of towering (stretching) and stooping (compression). The curvature parameter for the average atmospheric index profile between the camera and target can be derived from an analysis of the images collected by the camera system. We show example images where the building (33 m height) appears to stretch by 5.1 m and calculate a refractive index curvature parameter of 6.0x10-5 m-2.

  16. Efficient approximations of dispersion relations in optical waveguides with varying refractive-index profiles.

    PubMed

    Li, Yutian; Zhu, Jianxin

    2015-05-01

    In this paper we consider the problem of computing the eigen-modes for the varying refractive-index profile in an open waveguide. We first approximate the refractive-index by a piecewise polynomial of degree two, and the corresponding Sturm-Liouville problem (eigenvalue problem) of the Helmholtz operator in each layer can be solved analytically by the Kummer functions. Then, analytical approximate dispersion equations are established for both TE and TM cases. Furthermore, the approximate dispersion equations converge fast to the exact ones for the continuous refractive-index function as the maximum value of the subinterval sizes tends to zero. Suitable numerical methods, such as Müller's method or the chord secant method, may be applied to the dispersion relations to compute the eigenmodes. Numerical simulations show that our method is very practical and efficient for computing eigenmodes. PMID:25969285

  17. 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.

  18. SEISMIC-REFRACTION PROFILE ACROSS THE SAN ANDREAS, SARGENT, AND CALAVERAS FAULTS, WEST-CENTRAL CALIFORNIA.

    USGS Publications Warehouse

    Mooney, Walter D.; Colburn, Robert H.

    1985-01-01

    Geophysical studies of the upper crustal structure of west-central California are important for the further understanding of the geologic structure and tectonics in this seismically active region. In 1981, the United States Geological Survey recorded a seismic-refraction profile across the southern Santa Cruz Mountains in west-central California to examine the shallow velocity structure of this seismogenic region. This 40-km-long profile, which consisted of three shotpoints, extended northeastward from near Watsonville, California, to Coyote Lake, crossing the San Andreas, Sargent, and Calaveras faults. Refs.

  19. Alteration in refractive index profile during accommodation based on mechanical modelling

    PubMed Central

    Bahrami, Mehdi; Heidari, Ali; Pierscionek, Barbara K.

    2015-01-01

    The lens of the eye has a gradient refractive index (GRIN). Ocular accommodation, which alters the shape of the lens in response to visual demand, causes a redistribution of the internal structure of the lens leading to a change in the GRIN profile. The nature of this redistribution and the consequence of change in the GRIN profile are not understood. A modelling approach that considers how the GRIN profile may change with accommodation needs to take into account optical and mechanical parameters and be cognisant of individual variability in the shape and size of lenses. This study models the normalised axial GRIN profile during accommodation using reduced modelling and incorporating finite element analysis to connect inhomogenous mechanical characteristics of the lens to optical performance. The results show that simulated stretching changes the length of the plateau but does not alter the cortical gradient, which supports clinical findings. There is a very small change to the accommodated and non-accommodated profiles when normalised, yet this yields measurable changes in aberrations with around 11% and almost 13% difference in spherical aberration and astigmatism respectively. The results can be used in reconstruction of the refractive index and for investigating gradual changes with age. PMID:26819821

  20. Alteration in refractive index profile during accommodation based on mechanical modelling.

    PubMed

    Bahrami, Mehdi; Heidari, Ali; Pierscionek, Barbara K

    2016-01-01

    The lens of the eye has a gradient refractive index (GRIN). Ocular accommodation, which alters the shape of the lens in response to visual demand, causes a redistribution of the internal structure of the lens leading to a change in the GRIN profile. The nature of this redistribution and the consequence of change in the GRIN profile are not understood. A modelling approach that considers how the GRIN profile may change with accommodation needs to take into account optical and mechanical parameters and be cognisant of individual variability in the shape and size of lenses. This study models the normalised axial GRIN profile during accommodation using reduced modelling and incorporating finite element analysis to connect inhomogenous mechanical characteristics of the lens to optical performance. The results show that simulated stretching changes the length of the plateau but does not alter the cortical gradient, which supports clinical findings. There is a very small change to the accommodated and non-accommodated profiles when normalised, yet this yields measurable changes in aberrations with around 11% and almost 13% difference in spherical aberration and astigmatism respectively. The results can be used in reconstruction of the refractive index and for investigating gradual changes with age. PMID:26819821

  1. Bent induced refractive index profile variation and mode field distribution of step-index multimode optical fiber

    NASA Astrophysics Data System (ADS)

    Sokkar, T. Z. N.; Ramadan, W. A.; Shams El-Din, M. A.; Wahba, H. H.; Aboleneen, S. S.

    2014-02-01

    The effect of bending of step-index optical fiber on its refractive index profile and the mode field distribution were investigated. An enhanced slab model is suggested in this investigation. A qualitative study has been done on a bent step-index optical fiber. A very small radius of bending curvature (R) has been reached, practically R is 9.25 mm. In this case a dramatic change of the refractive index profile has been observed with an induced birefringence. The refractive index profile is recovered from the interferograms which were generated by Mach-Zehnder interferometer. The interferogram has been analyzed using advanced image analyses software. We have proposed another approach to calculate the refractive index profile of bent optical fiber. In this approach the fiber is divided into layers and slabs, simultaneously. The induced refractive index profile variation of the bent optical fiber, for parallel and perpendicular components of the light beam, is calculated considering the refraction of the light beam traversing the fiber. The mode field distribution and mode numbers in these two directions of polarizations are determined for both straight and bent fibers.

  2. Crustal Structure across The Southwest Longmenshan Fault Zone from Seismic Wide Angle Reflection/Refraction Profile

    NASA Astrophysics Data System (ADS)

    Tian, Xiaofeng; Wang, Fuyun; Wang, Shuaijun; Duan, Yonghong

    2014-05-01

    The Lushan eathquake, which epicenter and focal depth were at 30.308° N, 102.888° E, and 14.0 km, is the latest intense earthquake occurring in the southwest section of the Longmenshan fault zone after the Ms 8.0 Wenchuan earthquake in 2008. According to the emergency field observations, the slip distribution of the Lushan earthquake was concentrated at the hypocenter, and did not rupture to the surface(Chen et al, 2013). The rupture history constrained by inverting waveforms showed that the causative fault plane of the Lushan event is apparently not a simple extension of either the Pengguan fault or the Beichuan fault that ruptured during the 2008 Mw 8.0 Wenchuan earthquake. The focal mechanism using the Cut and Paste algorithm showed this event occurred on a high dip-angle fault, but its dip angle is not steep enough to rupture the surface. All these research is not independent on the heterogeneous crust structure of the Longmenshan fault zone. A 450 km-long wide-angle reflection/refraction profile executed during September and October 2013. This experiment have provided the best opportunities to obtain better knowledge of seismic structure and properties of crust and uppermost mantle beneath the Southwest Longmenshan fault zone. This seismic profile extends from the west Sichuan Plain, through the Longmenshan Fault zone, and into the west Sichuan Plateau. We observed clear Pg, refraction Phase from the upper crust, Pi1/Pi2/Pi3, reflection/refraction Phase from intra-crust, PmP, reflection from the Moho boundary, and the Pn phase, refraction Phase from uppermost mantle. We present a hybrid tomographic and layered velocity model of the crust and uppermost mantle along the profile. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. The model shows the crustal thickness of the region is very variable. The Moho topography varies more than 10km in the southwest

  3. 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

  4. 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. PMID:17792016

  5. 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.

  6. Seismic Refraction Profiles Across Shear Zones: What Can We Expect To See ?

    NASA Astrophysics Data System (ADS)

    Rumpel, H.-M.; Levander, A. R.

    In recent years more high-resolution refraction / wide-angle reflection data sets have been recorded to elucidate our picture of the Earth. For the 1999 seismic refraction/ wide-angle reflection CDROM profile more than 1200 stations were deployed be- tween New Mexico and Wyoming (Southern Rocky Mountain Region) at an average receiver spacing of 800m. A ray tracing code was used to analyse the data set. Though we have a good velocity model for the crust with a vertical resolution of less than 1km for the sediments and circa 2km at Moho depths, explaing more than 90% of the travel time data, we still find features we cannot explain by ray tracing only. One of those is the influence of shear zones on seismic sections. It is well known that the CDROM profile crosses many shear zones which formed in Phanerozoic time or even earlier. Therefore we test this idea in the following study. A two-dimensional visco-elastic finite-difference code was used to calculate synthetic seismogramms. Several models were created. The shear zone was realized as an elongate tabular body with velocities reduced at a constant percentage relative to the positive linear velocity gradient back- ground model. Variable parameters were the thickness of the shear zone, the relative location to the source, the dip angle and the velocity reduction within the shear zone relative to the background model. Recorder spacing was chosen to be comparable to the CDROM wide-angle data set and the source was located along the profile. Beside the normal first arrivals the synthetic seismogramms show diffuse arrivals between the front and back shear zone reflections. The time difference between front and back reflections depends on the shear zone thickness and the amplitudes on the velocity contrast. This band of arrivals comes in steeply crossing other reflections, thus creat- ing ambiguties in the data. A small influence on the first arrivals is seen as well, but might not be resolvable in field data. Varying

  7. 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.

  8. Analyzing refractive index profiles of confined fluids by interferometry part II: Multilayer and asymmetric systems.

    PubMed

    Kienle, Daniel F; Kuhl, Tonya L

    2016-09-14

    Methods for determining the substrate properties and the optical thickness of thin films or any variation in the refractive index of a fluid or film near a surface for unknown 5-layer symmetric and 3-layer asymmetric interferometers are presented. Both systems can be fully resolved without any known layer properties and without contact or confining the films. The method was tested using realistic simulated interferometer data, and was found to consistently yield accurate values for all desired properties. The method was experimentally validated through analysis of an asymmetric three layer interferometer system of linear polyethyleneimine (LPEI) adsorbed onto mica substrates of differing thickness and identical refractive index. The results were in excellent agreement with the dry polymer film properties measured using conventional SFA contact measurements. More complicated systems were also evaluated for feasibility, and any additional parameter specifications required for analysis were determined. The utility of this method is broad, as a single experiment in a laboratory setting can independently provide non-contact film properties and the effects of confinement on the film structure, which can be correlated to a simultaneously measured interaction force profile. PMID:27566361

  9. CRUSTAL REFRACTION PROFILE OF THE LONG VALLEY CALDERA, CALIFORNIA, FROM THE JANUARY 1983 MAMMOTH LAKES EARTHQUAKE SWARM.

    USGS Publications Warehouse

    Luetgert, James H.; Mooney, Walter D.

    1985-01-01

    Seismic-refraction profiles recorded north of Mammoth Lakes, California, using earthquake sources from the January 1983 swarm complement earlier explosion refraction profiles and provide velocity information from deeper in the crust in the area of the Long Valley caldera. Eight earthquakes from a depth range of 4. 9 to 8. 0 km confirm the observation of basement rocks with seismic velocities ranging from 5. 8 to 6. 4 km/sec extending at least to depths of 20 km. The data provide further evidence for the existence of a partial melt zone beneath Long Valley caldera and constrain its geometry. Refs.

  10. Crustal Structure across Northeastern Tibet from Seismic Wide Angle Reflection/Refraction Profile

    NASA Astrophysics Data System (ADS)

    Tian, Xiaofeng; Wang, Fuyun; Liu, Baofeng; Duan, Yonghong

    2014-05-01

    The 2010 Yushu earthquake, located at 33.2°N, 96.6°E at a focal depth of 14 km, was one of the largest earthquakes experienced in the west China since the 2008 Ms8.0 Wenchuan earthquake. This earthquake was one of a series of large recent earthquakes resulting from the northward-moving Indian plate as it uplifts the Tibetan block and causes the eastward extrusion of the Bayan Har active sub-block (Zhang, et al, 2003). A 550 km-long wide-angle reflection/refraction profile which is the densest active source profile in Tibet Plateau up to now executed during July and August 2010. This experiment have provided the best opportunities to obtain better knowledge of seismic structure and properties of crust and uppermost mantle beneath the North Tibet Plateau. This seismic profile extends from the Qang Tang block in Central Tibet, through the Bayan Har block, and into the west Qinling fold. We observed clear Pn phase, refraction Phase from mantle in Tibet Plateau. We present a hybrid tomographic and layered velocity model of the crust and uppermost mantle along the profile. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. We find the deepest Moho is deeper than 70 km in Yushu basin and Qang Tang block, and the shallowest Moho is around 60 km in north part of Bayan Har block. This unusual crust thickness with respect to the continental average value of 41 km (Christensen and Mooney, 1995) indicates that the Bayan Har crust may have thickened either homogeneously or by tectonic superposition. Our crustal model also shows that the Bayan Har Moho segment appears indeed as the southward geometrical continuation and this may indicates the Bayan Har Moho would hence extend further south than the location of the Jinsha suture at the surface. We also observe the presence of one low velocity layer or anomalous body in the middle crust along the profile, which may suggest the

  11. Precision estimation in temperature and refractivity profiles retrieved by GPS radio occultations

    NASA Astrophysics Data System (ADS)

    Alexander, P.; Torre, A.; Llamedo, P.; Hierro, R.

    2014-07-01

    The Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) is a six-satellite Global Positioning System (GPS) radio occultation (RO) mission that started in April 2006. The close proximity of these satellites during some months after launch provided a unique opportunity to evaluate the precision of GPS RO temperature and refractivity profile retrievals in the neutral atmosphere from nearly collocated and simultaneous observations. In order to work with nearly homogeneous sets, data are divided into five groups according to latitude bands during 20 days of July. For all latitude bands and variables, the best precision values (about 0.1%) are found somewhere between 8 and 25 km height. In general, we find that precision degrades significantly with height above 30 km and its performance becomes there worse than 1%. Temperature precision assessment has been generally excluded in previous studies. Refractivity has here, in general, a precision similar to dry temperature but worse than wet temperature in the lower atmosphere and above 30 km. However, it has been shown that the better performance of wet temperature is an artificial effect produced by the use of the same background information in nearly collocated wet retrievals. Performance in refractivity around 1% is found in the Northern Hemisphere at the lowest heights and significantly worse in the southern polar zone above 30 km. There is no strong dependence of the estimated precision in terms of height on day and night, on latitude, on season, or on the homogeneity degree of each group of profiles. This reinforces the usual claim that GPS RO precision is independent of the atmospheric conditions. The roughly 0.1% precision in the 8-25 km height interval should suffice to distinguish between day and night average values, but no significant differences are found through a Student t test for both populations at all heights in each latitude band. It was then shown that the present spatial

  12. 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.

  13. A Stellar Occultation Sensor Using Absorption and Refraction of Starlight for Atmospheric Profile Measurements

    NASA Astrophysics Data System (ADS)

    Morgan, F.; Yee, J.; Murphy, G.; Swartz, W.; Demajistre, R.; Vervack, R.; Morrison, D.

    2008-12-01

    The Self-Calibrating H2O and O3 Nighttime Environmental Remote Sensor (SCHOONERS) is a compact, integrated UV-IR imaging spectrograph and imager for spaceborne stellar occultation measurements, developed under the NASA Instrument Incubator Program and based on the measurement technique and retrieval demonstrated by the MSX/UVISI instrument. The imaging spectrograph, covering a spectral range between 300 and 900 nm, measures the varying absorption of starlight as a star sets through the Earth's atmosphere to determine vertical profiles of atmospheric constituents. The relative star position measured by the co-aligned imager not only provides position feedback to the active-tracking loop but also measures the star refraction angle for determining the atmospheric density and temperature profiles. The instrument has a 25-cm-diameter aperture and employs a two-axis gimbaled telescope to provide acquisition and tracking of the star. It also uses a two-axis high-precision vernier mirror to correct for spacecraft jitter and maintain the star within the field-of-view. SCHOONERS' hardware and accompanying software have been demonstrated in end-to-end laboratory tests. SCHOONERS' built-in image tracking and motion compensation mechanism, coupled with its small size and limited spacecraft resource requirements, makes it suitable for deployment on existing and future spacecraft platforms as an instrument-of-opportunity. In this paper, stellar occultation sensing technique, experiment requirements, and SCHOONERS design and expected performance will be presented.

  14. Propagation of Gaussian beams through inhomogeneous cylinders with shock-like profiles of refractive index: Grazing incidence case

    NASA Astrophysics Data System (ADS)

    Adamovsky, Grigory

    1997-08-01

    Wave propagation in inhomogeneous media has been studied for such diverse applications as propagation of radiowaves in the atmosphere, light propagation through thin films and in inhomogeneous waveguides, flow visualization, and others. In recent years an increased interest has been developed in the wave propagation through shocks generated in supersonic flows. Historically these shocks have been treated as discontinuities in refractive index profiles. However, a profile of the refractive index across the shock possesses a finite thickness and gradient. Geometry of the inhomogeneity also had an impact. This dissertation reports on modeling and numerical analysis of wave propagation through inhomogeneous media with shock-like profiles of refractive indexes. In particular, effects of geometry of inhomogeneities and the refractive index profile are addressed. The subject of study is a dielectric penetrable circular cylinder with a cylindrically symmetric profile of the refractive index illuminated by a two dimensional Gaussian beam. The propagation vector of the beam is normal to the long axis of the cylinder. The beam is a sheet of light with Gaussian profile along a direction normal to both, the propagation vector and the long axis of the cylinder. The incident electromagnetic field is a TM wave with the electric field vector being parallel to the long axis of the cylinder. The refractive index of the cylinder has a shock-like profile. In the dissertation, the refractive index profile of such a medium is described and the wave propagation phenomena through a such medium is formulated. The wavefront that emerges after passing through the inhomogeneous cylinder described above is propagated to a remotely located screen using the Fresnel diffraction equation. The resultant pattern is evaluated. Thus the method is a hybrid one. The first part of the method is to propagate the incident Gaussian beam through an inhomogeneous medium of a given profile. The second part is

  15. 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

  16. 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

  17. 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.

  18. 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

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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…

  5. Planetary boundary layer heights from GPS radio occultation refractivity and humidity profiles

    NASA Astrophysics Data System (ADS)

    Ao, Chi O.; Waliser, Duane E.; Chan, Steven K.; Li, Jui-Lin; Tian, Baijun; Xie, Feiqin; Mannucci, Anthony J.

    2012-08-01

    The height of the planetary boundary layer (PBL) is an important parameter that relates to the various processes associated with the PBL. In this paper, we use Global Positioning System radio occultation (GPSRO) measurements to derive a global climatology of PBL heights. Utilizing the strength of GPSRO in capturing fine vertical structures, the top of the PBL is defined to be the height at which the vertical gradient of the refractivity or water vapor partial pressure is minimum, corresponding to the height where the refractivity or water vapor pressure changes most rapidly. A "sharpness parameter" is defined that quantifies the applicability of these definitions. The sharpness parameter is largest over the subtropical regions characterized by strong subsidence. When the sharpness parameter is large, the refractivity- and moisture-based heights are shown to converge. We derived global PBL height climatology using three years (Dec. 2006-Nov. 2009) of COSMIC/FORMOSAT-3 measurements and compared with values calculated from ECMWF Reanalysis Interim (ERA-Int). We found that the mean PBL heights from GPSRO shared similar spatial and seasonal variations with ERA-Int; however, GPSRO heights were higher by 500 m. The standard deviation was also higher from GPSRO, especially in the tropics. We present detailed comparisons between GPSRO and ERA-Int over the Pacific Ocean and the Sahara desert and examine the PBL height distributions as well as its annual and diurnal variabilities. These results suggest that the underlying causes of the bias between GPSRO and ERA-Int likely vary from region to region.

  6. 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.

  7. 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.

  8. Effect of lower and upper parabolic dips in refractive index profile on performance of coaxial fiber Raman gain amplifier

    NASA Astrophysics Data System (ADS)

    Karak, Anup; Pramanik, Sanchita; Sarkar, Somenath

    2016-03-01

    An investigation on the effect of practically possible upper and lower parabolic dips in the refractive index profile of the inner core of the coaxial fiber Raman gain amplifier is reported using matrix method for single pump. It is seen that for lower parabolic dip, the tolerable limits of dip parameters correspond to dip depth of 0.25% and dip width of 25% of the respective parameters for ideal step index profile case and agree with the earlier predicted linear dip. However, for upper parabolic dip, one gets higher gain and better flatness at these limits. Even up to 1% of the dip depth for 25% of dip width or 75% of dip width for 0.25% of the dip depth or 0.5% of dip depth and 50% of dip width, one can expect performance as good as that of the ideal one. However, since system designers will be aimed to produce ideal profile, our recommendation is to keep tolerable limits within 0.25% of dip depth and 25% of dip width of respective parameters. But one can accept profile with upper parabolic dip if there is deviation within the above relaxation limits for such dip.

  9. 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.

  10. 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.

  11. 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

  12. Research of dispersion slope parameters of single-mode optical fibres depending on radius of a fibre and height of refractive index profile

    NASA Astrophysics Data System (ADS)

    Andreev, Roman V.; Praporshchikov, Denis E.

    2005-06-01

    At the solution of a problem of synthesis of refractive index profile of optical fibres with the set dispersive characteristics by optimization methods it is important at formation of initial conditions with the maximal accuracy to come nearer to a global minimum. It demands preliminary research of dependences of chromatic dispersion slopes from parameters of refractive index profile ofan optical fibre. In the given job results of theoretical researches of chromatic dispersion slopes, its parameters (wavelength of zero dispersion, an inclination of the spectral characteristic) are submitted depending on core radius and profile height. For calculations of dispersion the known analytical expressions received on the basis of the modified Gaussian approximation method were used. Calculations have been executed for single-mode optical fibres with a step, triangular and parabolic refractive index profile in a working range of wavelengths of CWDM systems. The received results allow to predict tendencies of chromatic dispersion changes, give quantitative ratings of its spectral characteristics changes depending on the form and parameters ofrefractive index profile of an optical fibre.

  13. Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams

    NASA Astrophysics Data System (ADS)

    Jimenez, Jose Ramón; González Anera, Rosario; Jiménez del Barco, Luis; Hita, Enrique; Pérez-Ocón, Francisco

    2005-01-01

    We provide a correction factor to be added in ablation algorithms when a Gaussian beam is used in photorefractive laser surgery. This factor, which quantifies the effect of pulse overlapping, depends on beam radius and spot size. We also deduce the expected post-surgical corneal radius and asphericity when considering this factor. Data on 141 eyes operated on LASIK (laser in situ keratomileusis) with a Gaussian profile show that the discrepancy between experimental and expected data on corneal power is significantly lower when using the correction factor. For an effective improvement of post-surgical visual quality, this factor should be applied in ablation algorithms that do not consider the effects of pulse overlapping with a Gaussian beam.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. Refraction test

    MedlinePlus

    ... purpose is to determine whether you have a refractive error (a need for glasses or contact lenses). ... glasses or contact lenses) is normal, then the refractive error is zero (plano) and your vision should ...

  19. Refractive Errors

    MedlinePlus

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

  20. 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.

  1. 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

  2. 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.

  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. Using a Newport refractive beam shaper to generate high-quality flat-top spatial profiles from a flashlamp-pumped commercial Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Armstrong, Darrell J.; Smith, Arlee V.

    2004-09-01

    We've generated high-quality flat-top spatial profiles from a modified Continuum Powerlite 9010 Nd:YAG laser using the Gaussian-to-flat-top refractive beam shaper available from Newport Corporation. The Powerlite is a flashlamp-pumped, Q-switched, injection-seeded Nd:YAG laser manufactured in 1993 that delivers 1.6 J at 10 Hz using an oscillator and two 9 mm diameter amplifier rods. While its pulse energy is impressive, its beam quality is typically poor, an all too common characteristic of research-grade Nd:YAG lasers manufactured in the late 1980's and early 1990's. Structure in its near-field spatial fluence profile is reminiscent of round-aperture diffraction that is superposed with additional hot spots. These characteristics are largely due to poor beam quality from the oscillator coupled with over-filled amplifier rods, and reflect a design philosophy from the era of organic dye lasers. When these older laser systems are used for tasks like pumping optical parametric oscillators (OPO's), or for other applications demanding good beam quality, their designs are simply inadequate. To improve the 9010's beam quality we spatially filter the oscillator beam and remove the resulting Airy rings with an iris, then collimate and magnify the remaining central disk so its diameter is appropriate for input to the refractive shaper. The output of the beam shaper is then double-pass amplified through two amplifier rods with thermally induced focusing compensated by a negative lens before the first pass and by a convex mirror before the second pass. Using this approach we've obtained single-pass energy exceeding 250 mJ with little degradation of the flat-top profile and 950 mJ after double pass amplification. After double-passing the two amplifier rods the beam suffers some degradation in symmetry and uniformity, but is still much improved compared to the beam obtained using the 9010's original factory configuration. We find the modified 9010's flat-top profile improves

  5. 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. PMID:26368729

  6. Facts about Refractive Errors

    MedlinePlus

    ... the lens can cause refractive errors. What is refraction? Refraction is the bending of light as it passes ... rays entering the eye, causing a more precise refraction or focus. In many cases, contact lenses provide ...

  7. How to incorporate generic refraction models into multistatic tracking algorithms

    NASA Astrophysics Data System (ADS)

    Crouse, D. F.

    The vast majority of literature published on target tracking ignores the effects of atmospheric refraction. When refraction is considered, the solutions are generally tailored to a simple exponential atmospheric refraction model. This paper discusses how arbitrary refraction models can be incorporated into tracking algorithms. Attention is paid to multistatic tracking problems, where uncorrected refractive effects can worsen track accuracy and consistency in centralized tracking algorithms, and can lead to difficulties in track-to-track association in distributed tracking filters. Monostatic and bistatic track initialization using refraction-corrupted measurements is discussed. The results are demonstrated using an exponential refractive model, though an arbitrary refraction profile can be substituted.

  8. 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

  9. 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. PMID:27409857

  10. Crustal Structure of the Puget Lowland, Washington State From the Dry SHIPS '99 Seismic Refraction/Wide-Angle Reflection Profile

    NASA Astrophysics Data System (ADS)

    Snelson, C. M.; Miller, K. C.; Brocher, T. M.; Li, Q.; Pratt, T. L.; Wilcock, W. S.; Crosson, R. S.; Trehu, A. M.; Weaver, C. S.

    2001-12-01

    The SHIPS (Seismic Hazards Investigations of Puget Sound) experiments are part of a continuing effort to define basin and fault geometry beneath the populated Puget Lowland. In September 1999, the USGS and a number of university collaborators collected the "Dry SHIPS" seismic profile across the Seattle basin of western Washington State. In March 2000, this group collected additional seismic data in the city of Seattle using the implosion of the Kingdome sports arena as a seismic source. The objectives of the Dry SHIPS study were to define the geometry of the Seattle basin in an E-W direction and to determine the structure of the eastern and western boundaries of the basin. In addition, we were testing the hypothesis that N-S trending faults lie beneath Puget Sound or the adjacent Lowland: one of these faults may form the eastern boundary of the Siletz terrane. The main objective of Kingdome SHIPS was to look at the Seattle fault and shallow strata beneath Seattle to estimate site response in Seattle. The Dry SHIPS data are characterized by travel time advances associated with the Siletz terrane to the west and the Cascades to the east and by delays of as much as 2 s caused by the Seattle basin. P-wave 3-D tomographic results show that the basin is about 70 km wide and contains sedimentary strata with velocities increasing gradually from 1.8 - 4.5 km/s. The contact with underlying basement rocks is characterized by a rapid increase in velocity from 4.5 to 5.0 km/s. At its center the basin is 6 - 7 km deep along this profile. This result is consistent with results from a N-S trending reflection line collected in 1998 during the Wet SHIPS phase of the project that is tied to well control. The symmetry of the Seattle basin is consistent with thrust loading as the major contributor to the formation of the basin. The lower velocities within the upper part of the basement found east of the Puget Sound may be indicative of pre-Tertiary basement rocks of the Cascades. This

  11. Seismotectonics and Seismic Structure of the Alboran Sea, Western Mediterranean - Constraints from Local Earthquake Monitoring and Seismic Refraction and Wide-Angle Profiling

    NASA Astrophysics Data System (ADS)

    Leuchters, W.; Grevemeyer, I.; Ranero, C. R.; Villasenor, A.; Booth-Rea, G.; Gallart, J.

    2011-12-01

    The Alboran Basin is located in the western-most Mediterranean Sea and is surrounded by the Gibraltar-Betic and Rif orogenic arc. Geological evidence suggests that the most important phase of formation started in the early-to-mid-Miocene. Currently two conflicting models are discussed for its formation: One model proposes contractive tectonics producing strike-slip faults and folds with sedimentation occurring in synclinal basins and in regions of subsidiary extension in transtensional fault segments. A second model proposes slab roll back that caused contraction at the front of the arc and coeval overriding plate bending and extension and associated arc magmatism. However, this phase has been partially masked by late Miocene to present contractive structures, caused by the convergence of Africa and Iberia. Two German/Spanish collaborative research projects provided excellent new seismological and seismic data. Onshore/offshore earthquake monitoring received a wealth of local earthquake data to study seismotectonics and yielded the average 1D velocity structure of the Alboran/Betics/Rif domain. In the Alboran Basin most earthquakes occur below 20 km along a diffuse fault zone, crossing the Alboran Sea from the Moroccan to the Spanish coast. Further, earthquakes along the northern portion of the Alboran Ridge show thrust mechanisms and compression roughly normal to the vector of plate convergence between Africa and Iberia. A 250 km long seismic refraction and wide-angle profile was acquired coincident with the existing multi-channel seismic (MCS) ESCI-Alb2 line using the German research vessel Meteor. Shots fired with a 64-litre airgun array were recorded on 24 ocean-bottom seismometer (OBS) and ocean-bottom hydrophone (OBH) stations. The profile run roughly along the axis of the basin, circa 65 km off the coast of Morocco, north of the Alboran Ridge. It continues in an ENE direction to end north of the Algeria coast. Using seismic tomography we mapped the crustal

  12. 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.

  13. Correction of satellite laser ranging for atmospheric refraction.

    NASA Astrophysics Data System (ADS)

    Mironov, N. T.

    Atmospheric refraction causes significant errors in satellite laser ranging (SLR) systems. Numerous formulas have been developed to partially correct laser ranging data for the effects of atmospheric refraction. These formulas were derived under the assumption that atmospheric refraction is spherically symmetric. The accuracy of the Marini-Murray's spherical correction formula are checked. The residual errors in the spherical model are thought to be primarily caused by horizontal gradients in the refractivity. The effects of horizontal refractivity gradients are investigated by ray tracing through spherically symmetric and three-dimensional refractivity profiles.

  14. Shallow architecture of the 2009 Mw 6.1 L'Aquila earthquake fault (Central Italy): Insights from high-resolution multiscale refraction tomography and reflection profiles

    NASA Astrophysics Data System (ADS)

    Villani, F.; Bruno, P. P.; Improta, L.; Castiello, A.; Punzo, M.; Varriale, F.

    2012-04-01

    Central Apennines (Italy) is affected by repeated large normal-faulting crustal earthquakes. The 6th April 2009 Mw 6.1 event damaged L'Aquila town and surroundings, causing 308 deaths. Seismological, geodetic and geological analyses have defined the geometry and kinematics of the source of the 2009 mainshock (Paganica Fault) and of the structures activated during the seismic sequence. They form a ~ 40 km long NW-trending and SW-dipping normal fault system featuring two main right-stepping strands. The hangingwall of the Paganica Fault hosts a deep Quaternary basin (Middle Aterno basin). However, the basin geometry and internal structure, as well as the internal architecture and the fault-system, are poorly unknown. This hinders the reconstruction of the long-term evolution of the fault-system and related basin. With the aim of illuminating the shallow crust, in 2010 we collected 5 dense wide-aperture seismic profiles that run NE-SW across the Middle Aterno basin and the Paganica Fault, for a total survey length of 8 km. Multi-scale refraction tomography and reflection data were merged to investigate extremely complex fault structures. A 216-channel geophone array (5 m spacing) was used to record a narrow spaced (5-10 m) vibratory source progression. The spread is 1075 m long, 3-4 times larger than the presumed depth of the basin substratum. For each line we provide Vp models and stack migrated sections. The overall profiles allowed to depict a reliable cross-section of the Middle Aterno basin and of the normal fault-system, including the source of the 2009 mainshock. Multi-scale tomography details the Vp structure down to ~ 350 m depth, identifying low Vp (1500-2000 m/s) lacustrine sediments (up to 200 m thick) and coarse fluvial and alluvial fan deposits (Vp ~ 3000 m/s) sited above high-Vp regions (Vp > 3500-4000 m/s) corresponding to an articulated Meso-Cenozoic substratum. The main basin depocenter, ~ 350 m deep, is in the SW sector of the basin. It matches the

  15. 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 ...

  16. Refractive surgery and strabismus.

    PubMed

    Kowal, Lionel; Battu, Ravindra; Kushner, Burton

    2005-02-01

    This review discusses the potential for strabismic complications after refractive surgery for hyperopia, myopia, anisomyopia, astigmatism and monovision, and how to avoid these complications. Guidelines are given for assessing patients with strabismus seeking refractive surgery. Screening tests are suggested that lead to stratification of refractive surgery patients into different risk groups each warranting a different intensity of evaluation. PMID:15670088

  17. Refractive errors in children.

    PubMed

    Tongue, A C

    1987-12-01

    Optical correction of refractive errors in infants and young children is indicated when the refractive errors are sufficiently large to cause unilateral or bilateral amblyopia, if they are impairing the child's ability to function normally, or if the child has accommodative strabismus. Screening for refractive errors is important and should be performed as part of the annual physical examination in all verbal children. Screening for significant refractive errors in preverbal children is more difficult; however, the red reflex test of Bruckner is useful for the detection of anisometropic refractive errors. The photorefraction test, which is an adaptation of Bruckner's red reflex test, may prove to be a useful screening device for detecting bilateral as well as unilateral refractive errors. Objective testing as well as subjective testing enables ophthalmologists to prescribe proper optical correction for refractive errors for infants and children of any age. PMID:3317238

  18. 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.

  19. 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).

  20. 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)

  1. 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

  2. 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. PMID:22944755

  3. Lidar measurements of refractive propagation effects

    NASA Astrophysics Data System (ADS)

    Philbrick, C. R.; Blood, D. W.

    1995-02-01

    A multi-wavelength Raman lidar has been developed and used to measure the profiles of atmospheric properties in the troposphere under a wide range of geophysical conditions. The instrument measures the two physical properties which contribute to the refractive index at radio frequencies, water vapor concentration profiles from vibrational Raman measurements and neutral density determined from rotational Raman temperature profiles and surface pressure. The LAMP lidar instrument is transportable and has been used to make measurements at several locations in addition to our local Penn State University site, including shipboard measurements between Arctic and Antarctic and in the coastal environment at Point Mugu, CA. Lidar measurements of the atmospheric refractive environment, which are of particular interest, were made during 1993 at Point Mugu, CA, including the period of Project VOCAR (Variability of Coastal Atmospheric Refractivity). Both the lidar and balloon tropospheric measurements have been used for analyses of the propagation conditions by employing th Navy's RPO, IREPS and EREPS PC programs and comparisons have been made with the measured propagation conditions. On the short term (hour-to-hour throughout the day), the lidar derived profiles permit the examination of refractive layer stratification for guided-wave mode propagation.

  4. 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). PMID:16201423

  5. Seismic refraction exploration

    SciTech Connect

    Ruehle, W.H.

    1980-12-30

    In seismic exploration, refracted seismic energy is detected by seismic receivers to produce seismograms of subsurface formations. The seismograms are produced by directing seismic energy from an array of sources at an angle to be refracted by the subsurface formations and detected by the receivers. The directivity of the array is obtained by delaying the seismic pulses produced by each source in the source array.

  6. Nonlinear Refractive Properties

    NASA Technical Reports Server (NTRS)

    Vikram, Chandra S.; Witherow, William K.

    2001-01-01

    Using nonlinear refractive properties of a salt-water solution at two wavelengths, numerical analysis has been performed to extract temperature and concentration from interferometric fringe data. The theoretical study, using a commercially available equation solving software, starts with critical fringe counting needs and the role of nonlinear refractive properties in such measurements. Finally, methodology of the analysis, codes, fringe counting accuracy needs, etc. is described in detail.

  7. [Refractive development and form-deprivation induced myopic refractive error in CBA/CaJ mice].

    PubMed

    Li, Yun-Yun; Qian, Kang-Wei; Wu, Xiao-Hua; Zhou, Wei; Zhong, Yong-Mei; Weng, Shi-Jun

    2016-04-25

    Due to the advantages in genetic manipulation, mice have become one of the most commonly used mammalian models for the study of mechanisms underlying myopia development. However, the vast majority of laboratory mouse strains are incapable of synthesizing melatonin, a neurohormone that may play an important role in myopia generation in humans. The present study investigated refractive development profiles in the CBA/CaJ mouse, a strain proficient in melatonin, and determined whether and how its refractive development could be affected by form-deprivation. Eccentric infrared photoretinoscopy revealed that this animal could be stably refracted, and the refractive error underwent developmental changes, which increased with age in the hyperopic direction and eventually got stable approximately 9 weeks after birth. The absolute values of refractive error in CBA/CaJ mice were larger than those of age-matched C57BL/6 mice, whereas the time points when refractive error reached steady state were similar between the two strains. Five weeks of form-deprivation applied to 3-week-old CBA/CaJ mice by translucent occluder wear caused a significant myopic shift in refractive error, indicating that this strain could be adequately used as a myopia model. PMID:27108899

  8. Variation in crustal structure along the Kyushu-Palau Ridge at 15-21°N on the Philippine Sea plate based on seismic refraction profiles

    NASA Astrophysics Data System (ADS)

    Nishizawa, A.; Kaneda, K.; Katagiri, Y.; Kasahara, J.

    2007-06-01

    We acquired coincident wide-angle and multi-channel seismic reflection data along four profiles perpendicular to the Kyushu-Palau Ridge (KPR) between 15°N and 20°N on the Philippine Sea plate. The crustal thickness beneath the KPR, which is a remnant arc created in the Late Eocene, varies along the strike from 8 to approximately 20 km and is always thicker than the adjacent oceanic crust of the West Philippine Basin to the west and the Parece Vela Basin to the east. The thickest crust among the four profiles, which is primarily due to a thickening of the lower crust, is found where the KPR adjoins Oki-no-Tori-Shima Island. There is no clear evidence of the thick (>5 km) middle crustal layer with a P-wave velocity of 6.0-6.5 km/s that has been inferred beneath the conjugate rifted counterpart of the Izu-Ogasawara(Bonin)-Mariana Island-arc. Our results suggest that the crust of the KPR at 15-21°N represents a less mature island arc crust relative to that further north along the ridge where a mid-crustal layer of 6 km/s has been reported.

  9. P- and S-wave velocity model along crustal scale refraction and wide-angle reflection profile in the southern Korean peninsula

    NASA Astrophysics Data System (ADS)

    Cho, Hyun-Moo; Baag, Chang-Eob; Lee, Jung Mo; Moon, Wooil M.; Jung, Heeok; Kim, Ki Young

    2013-01-01

    The onshore seismic experiment, KCRT2004, explored the crustal velocity structure of the southern Korean peninsula. We present an interpretation of seismic data along this 340 km long NNW-SSE trending profile. The crust was found to consist of three layers: the upper, middle, and lower crust with P- and S-wave velocities ranging 5.50 to 6.95 km/s and 2.82 to 3.91 km/s, respectively. The average P-wave velocity (6.26 km/s) and Pn velocity (7.82-7.88 km/s) are lower than the worldwide average of continental crust. Moho depths are 29.0-34.9 km, gradually thickening toward south. The Vp/Vs ratio of crustal material is estimated to be 1.73 (σ = 0.249) for the upper and middle crust and the ratio increases with the depth in the lower crust. The Gyeonggi massif in the north of the profile has a lower Vp/Vs ratio than other tectonic units. The average crustal Vp/Vs ratio of 1.74 (σ = 0.253) is remarkably lower than the average value 1.78 (σ = 0.27) for the bulk continental crust. The low average crustal Vp/Vs ratio is similar to that measured in eastern China. The empirical analysis using both P-wave velocity and Vp/Vs ratio shows that the upper and middle crust is dominantly felsic and the lower crust is intermediate in composition. The absence of the mafic material in the lower crust that is also found in eastern China contrasts with the generally accepted global model of the mafic lower crust.

  10. 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).

  11. 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.

  12. The RAMESSES experiment-II. Evidence for accumulated melt beneath a slow spreading ridge from wide-angle refraction and multichannel reflection seismic profiles

    NASA Astrophysics Data System (ADS)

    Navin, D. A.; Peirce, C.; Sinha, M. C.

    1998-12-01

    The RAMESSES study (Reykjanes Axial Melt Experiment: Structural Synthesis from Electromagnetics and Seismics) targeted an apparently magmatically active axial volcanic ridge (AVR), centred on 57°45'N at the Reykjanes Ridge, with the aim of investigating the processes of crustal accretion at a slow spreading mid-ocean ridge. As part of this multicomponent experiment, airgun and explosive wide-angle seismic data were recorded by 10 digital ocean-bottom seismometers (OBSs) along profiles oriented both across- and along-axis. Coincident normal-incidence seismic, bathymetry and underway gravity and magnetic data were also collected. Forward modelling of the seismic and gravity data has revealed layer thicknesses, velocities and densities similar to those observed elsewhere within the oceanic crust near mid-ocean ridges. At 57°45'N, the Reykjanes Ridge has a crustal thickness of approximately 7.5 km on-axis. However, the crust is modelled to decrease in thickness slightly off-axis (i.e. with age), which implies that full crustal thickness is achieved on-axis and that it is subsequently thinned, most likely, by off-axis extension. Modelling also indicates that the AVR is underlain by a thin (~100 m), narrow (~4 km) melt lens some 2.5 km beneath the seafloor, which overlies a broader zone of partial melt approximately 8 km in width. Thus the results of this study provide the first clear evidence for a crustal magma chamber beneath any slow spreading ridge. The size and depth of this magma chamber (the melt lens and underlying zone of partial melt) are similar to those observed beneath fast and intermediate spreading ridges, which implies that the processes of crustal accretion are similar at all spreading rates. Hence the lack of previous observations of magma chambers beneath slow spreading ridges is probably temporally related to the periods of magmatic activity being considerably shorter and more widely spaced in time than at fast and intermediate spreading ridges.

  13. 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.

  14. Scanning focused refractive-index microscopy

    NASA Astrophysics Data System (ADS)

    Sun, Teng-Qian; Ye, Qing; Wang, Xiao-Wan; Wang, Jin; Deng, Zhi-Chao; Mei, Jian-Chun; Zhou, Wen-Yuan; Zhang, Chun-Ping; Tian, Jian-Guo

    2014-07-01

    We present a novel scanning focused refractive-index microscopy (SFRIM) technique to obtain the refractive index (RI) profiles of objects. The method uses a focused laser as the light source, and combines the derivative total reflection method (DTRM), projection magnification, and scanning technique together. SFRIM is able to determine RIs with an accuracy of 0.002, and the central spatial resolution achieved is 1 µm, which is smaller than the size of the focal spot. The results of measurements carried out on cedar oil and a gradient-refractive-index (GRIN) lens agree well with theoretical expectations, verifying the accuracy of SFRIM. Furthermore, using SFRIM, to the best of our knowledge we have extracted for the first time the RI profile of a periodically modulated photosensitive gelatin sample. SFRIM is the first RI profile-resolved reflected light microscopy technique that can be applied to scattering and absorbing samples. SFRIM enables the possibility of performing RI profile measurements in a variety of applications, including optical waveguides, photosensitive materials and devices, photorefractive effect studies, and RI imaging in biomedical fields.

  15. Scanning focused refractive-index microscopy

    PubMed Central

    Sun, Teng-Qian; Ye, Qing; Wang, Xiao-Wan; Wang, Jin; Deng, Zhi-Chao; Mei, Jian-Chun; Zhou, Wen-Yuan; Zhang, Chun-Ping; Tian, Jian-Guo

    2014-01-01

    We present a novel scanning focused refractive-index microscopy (SFRIM) technique to obtain the refractive index (RI) profiles of objects. The method uses a focused laser as the light source, and combines the derivative total reflection method (DTRM), projection magnification, and scanning technique together. SFRIM is able to determine RIs with an accuracy of 0.002, and the central spatial resolution achieved is 1 µm, which is smaller than the size of the focal spot. The results of measurements carried out on cedar oil and a gradient-refractive-index (GRIN) lens agree well with theoretical expectations, verifying the accuracy of SFRIM. Furthermore, using SFRIM, to the best of our knowledge we have extracted for the first time the RI profile of a periodically modulated photosensitive gelatin sample. SFRIM is the first RI profile-resolved reflected light microscopy technique that can be applied to scattering and absorbing samples. SFRIM enables the possibility of performing RI profile measurements in a variety of applications, including optical waveguides, photosensitive materials and devices, photorefractive effect studies, and RI imaging in biomedical fields. PMID:25008374

  16. Scanning focused refractive-index microscopy.

    PubMed

    Sun, Teng-Qian; Ye, Qing; Wang, Xiao-Wan; Wang, Jin; Deng, Zhi-Chao; Mei, Jian-Chun; Zhou, Wen-Yuan; Zhang, Chun-Ping; Tian, Jian-Guo

    2014-01-01

    We present a novel scanning focused refractive-index microscopy (SFRIM) technique to obtain the refractive index (RI) profiles of objects. The method uses a focused laser as the light source, and combines the derivative total reflection method (DTRM), projection magnification, and scanning technique together. SFRIM is able to determine RIs with an accuracy of 0.002, and the central spatial resolution achieved is 1 µm, which is smaller than the size of the focal spot. The results of measurements carried out on cedar oil and a gradient-refractive-index (GRIN) lens agree well with theoretical expectations, verifying the accuracy of SFRIM. Furthermore, using SFRIM, to the best of our knowledge we have extracted for the first time the RI profile of a periodically modulated photosensitive gelatin sample. SFRIM is the first RI profile-resolved reflected light microscopy technique that can be applied to scattering and absorbing samples. SFRIM enables the possibility of performing RI profile measurements in a variety of applications, including optical waveguides, photosensitive materials and devices, photorefractive effect studies, and RI imaging in biomedical fields. PMID:25008374

  17. 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.

  18. 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.)

  19. 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

  20. 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.

  1. STARS: the Stellar Absorption and Refraction Sensor

    NASA Astrophysics Data System (ADS)

    Yee, Jeng-Hwa; Morrison, Daniel; Murphy, Graham A.; Morgan, M. F.; Humm, David C.; Silverglate, Peter R.; Vervack, Ronald; Paxton, Larry J.

    2002-01-01

    The Stellar Absorption and Refraction Sensor (STARS) is a compact, large-aperture instrument that combines a UV-IR imaging spectrograph with a co-aligned visible-light imager to make simultaneous absorptive and refractive stellar occultation measurements. The absorption measurements provided by the spectrograph allow the determination of vertical profiles of atmospheric constituents. The coincident refraction observations made by the image yield high-precision measurements of atmospheric density, pressure, and temperature and provide independent knowledge of both the refracted light path and Rayleigh extinction, which are critical in reducing the uncertainty in the retrieved constituent profiles in the lower atmosphere. STARS employs a two-axis gimbaled telescope to acquire and track the star and a two-axis, high-precision, fast-steering mirror to correct for spacecraft jitter and maintain the star within the spectrograph field of view. The relative star position measured by the imager provides position feedback to the active tracking loop of the fast-steering mirror. With funding from NASA's Instrument Incubator Program, a laboratory facility has been developed to demonstrate the overall instrument performance and, in particular, its capability to acquire and track a setting, refracting, and scintillating star, to compensate for various degrees of platform jitter, and to provide the pointing knowledge required for accurate determination of the atmospheric quantities. The combination of built-in image tracking and motion compensation capabilities, small size, and limited spacecraft resource requirements makes STARS and its tracking mechanism suitable for deployment on existing and future commercial spacecraft platforms for applications that require high-precision pointing. In this paper, we present details of the instrument design and its expected performance based on our laboratory tests.

  2. Photon-Refracting Aerogel

    NASA Astrophysics Data System (ADS)

    Rice, Daniel

    2012-10-01

    A threshold aerogel Cherenkov detector is being constructed at CUA to allow for the study of kaons in experiments at the Jefferson Laboratory. These subatomic particles move faster than light through the aerogel material, emitting Cherenkov radiation. Photomultiplier Tubes (PMTs) convert the photons from the Cherenkov radiation into electrons and multiply the electrons sufficiently to get a readable electronic signal, which can be analyzed. An important part of a threshold aerogel Cherenkov detector is its use of aerogel material of several refractive indices to cover the full dynamic range over which one wants to detect the particles of interest (in this case the kaon). Uniform coverage in refractive index is important as the location of the incoming particle will not be constant throughout the testing. In addition to testing for uniform coverage, we must also verify these refractive indices to ensure that the particles we are detecting are in fact kaons. The last test on the aerogel that needs to be performed is the measurement of transparency. Although aerogel is highly transparent, it is still necessary to find the amount of light being absorbed, reflected, or scattered versus how much will actually be measured by the PMTs used.

  3. Corrections for atmospheric refractivity in satellite laser ranging

    NASA Technical Reports Server (NTRS)

    Iyer, R. S.; Bufton, J. L.

    1977-01-01

    The effects of departures from the spherical symmetry assumption are investigated by describing the refractivity profile on the earth's surface as a generalized function of the surface coordinates. Aspects of satellite ranging geometry are considered and the representation of the true group refractivity of the atmosphere at any point on the earth's surface is discussed. Surface meteorological data obtained from a few east coast weather stations are analyzed to obtain typical values of the higher order bias terms.

  4. 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.

  5. 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)

  6. Comparison of atmospheric refraction at radar and optical wavelengths

    NASA Astrophysics Data System (ADS)

    Kunz, Gerard; Heemskerk, Eric; van Eijk, Lex

    2005-10-01

    A study is carried out to classify possible combinations of refractivity conditions for RF and IR over a wide range of meteorological conditions using different micrometeorological bulk models. The calculated refractivity profiles are analyzed for evaporation duct height (EDH), mainly relevant for RF propagation, and for gradients of the modified refractivity at different heights, relevant for both RF and IR propagation. These refractivity gradients are a direct indicator for the occurrence of sub- or super refraction at the height of interest. The present study reveals that under humid and unstable conditions evaporation ducts are found at approximately 3+/-2 m above cold (5°C) waters and at approximately 8+/-5 m over warm waters (25°C). Under dry conditions, these duct heights are approximately 9+/-5 m and 20+/-10 m, respectively. Duct heights decrease with increasing wind speed. Under humid and near-neutral conditions, duct heights range from 1 to 25 m, and decrease with increasing air temperature and/or wind speed. On the other hand, for dry and near-neutral conditions, and also for neutral conditions, the duct height is not well defined. Values between 1 m and 100 m are found, with an irregular dependence on air temperature and wind speed. Reliable modeling of duct height under these conditions remains questionable due to a lack of vertical mixing in the surface layer. The paper also shows that all four combinations of RF and IR sub- and super-refraction can occur in the atmosphere. The occurrence of a specific combination depends predominantly on temperature and humidity, and to a relatively minor part on wind speed. The magnitude of refraction effects in the two spectral bands is not necessarily coupled but varies with environmental conditions and height. Sub-sub refraction is generally weak and occurs under neutral conditions or at large heights. Super-super refraction occurs under warm and dry conditions and can reach medium strengths. RF

  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. Refraction effects under atmospheric stable conditions in coastal environments

    NASA Astrophysics Data System (ADS)

    Claverie, Jacques; Dion, Denis; Stein, Karin

    2007-10-01

    The performances of Electro-Optical (EO) systems such as visible or infrared cameras, lasers, operating within the Marine Surface Boundary Layer (MSBL), i.e. at heights up to a few tens of meters above the sea surface, are disturbed by various propagation mechanisms: molecular attenuation, aerosol extinction, refraction and turbulence. Refraction is responsible for focusing and defocusing of rays, detection range limitations, mirage formation and angular deviation. These refraction phenomena can be efficiently described using ray-tracing in conjunction with bulk estimations of the refractivity profiles based on the Monin-Obukhov (MO) theory. For stable atmospheric conditions (i.e. air temperature greater than sea temperature), the accuracy of the model predictions has been strongly discussed in the recent years. By using measurements of apparent target elevations recorded during the VAMPIRA trial, this paper aims at clarifying this discussion.

  9. 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.

  10. Designing refractive beam shapers via aberration theory

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Shealy, David

    2014-10-01

    In this paper, we use aberration theory to design a refractive laser beam shaper in the configuration of two-aspheric lenses, whose analytical equations are known, but rather complicated. Specifically, we use results from third order aberration theory to obtain the parameters of the refracting laser beam shaper from the transverse aberration, which are then used as a starting point for further optimization by using optical design software. This approach was developed during the beginning of the twentieth century, works well for systems with a low numerical aperture, and allows one to define the following parameters of an optical system: radii of curvature, indices of refraction, thicknesses or air gaps, and conic constants of second order aspheric surfaces. We shall consider surfaces of the second-order spherical and conic sections and shall consider the example of designing of a two-lens beam shaper of the Keplerian 1-to-1 telescopic design providing a theoretical flat phase front and a flat-top irradiance profile of the output beam, where the ray mapping function from the input aperture to the output aperture is known from the literature. Explicit expression for third order longitudinal aberration and the Seidel coefficients are expressed in terms beam waist and input beam geometrical parameter, indices, lens radii and conic constants.

  11. Spatial variation of stratospheric aerosol acidity and model refractive index - Implications of recent results

    NASA Technical Reports Server (NTRS)

    Russell, P. B.; Hamill, P.

    1984-01-01

    Recent experimental results indicate that little or no solid ammonium sulfate is present in background stratospheric aerosols. Other results allow straightforward calculation of sulfuric acid/water droplet properties (acidity, specific gravity, refractive index) as functions of stratospheric temperature and humidity. These results are combined with a variety of latitudinal and seasonal temperature and humidity profiles to obtain corresponding profiles of droplet properties. These profiles are used to update a previous model of stratospheric aerosol refractive index. The new model retains the simplifying approximation of vertically constant refractive index in the inner stratosphere, but has sulfuric acid/water refractive index values that significantly exceed the previously used room temperature values. Mean conversion ratios (e.g., extinction-to-number, backscatter-to-volume) obtained using Mie scattering calculations with the new refractive indices are very similar to those obtained for the old indices, because the effects of deleting ammonium sulfate and increasing acid indices tend to cancel each other.

  12. 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.

  13. 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.

  14. High refractive index photocurable resins

    NASA Astrophysics Data System (ADS)

    Morford, Robert V.; Mercado, Ramil L.; Planje, Curtis E.; Flaim, Tony D.

    2005-04-01

    The performance of optoelectronic devices can be increased by incorporating a high refractive index layer into the system. This paper describes several potential high refractive index resin candidates. Our materials include the added advantages over other systems because the new materials are cationically photocurable and free flowing, have low shrinkage upon cure, have no (or little) volatile organic components, are applicable by a variety of methods (dip coating, roller coating, injection molding, or film casting), can be applied in a variety of thicknesses (10-100 m), are fast-curing, and possess robust physical properties. Particular attention focuses on the refractive index in the visible spectrum, light transmission, and formulation viscosity.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. Refraction effects and wavelength dependence

    NASA Astrophysics Data System (ADS)

    Claverie, J.; Dion, D.

    2006-09-01

    The performances of Electro-Optical (EO) systems such as visible or infrared cameras, lasers, operating within the Marine Surface Boundary Layer (MSBL), i.e. at heights up to a few tens of meters above the sea surface, are disturbed by various propagation mechanisms: molecular attenuation, aerosol extinction, refraction and turbulence. Refraction is responsible for focusing and defocusing of rays, detection range limitations, mirage formation and angular deviation. The refractive index depends on atmospheric pressure, air temperature and air humidity. Within the optical transmission bands, it also depends on the wavelength. In this paper, the results provided by two different formulations of the refractive index associated with the same ray tracing program are compared and discussed.

  20. 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

  1. Nonlinear refraction in vitreous humor.

    PubMed

    Rockwell, B A; Roach, W P; Rogers, M E; Mayo, M W; Toth, C A; Cain, C P; Noojin, G D

    1993-11-01

    We extend the application of the z-scan technique to determine the nonlinear refractive index (n(2)) for human and rabbit vitreous humor, water, and physiological saline. In these measurements there were nonlinear contributions to the measured signal from the aqueous samples and the quartz cell that held the sample. Measurements were made with 60-ps pulses at 532 nm. To our knowledge, this is the first measurement of the nonlinear refractive properties of biological material. PMID:19829406

  2. Underwater optical wireless communications: depth-dependent beam refraction.

    PubMed

    Johnson, Laura J; Green, Roger J; Leeson, Mark S

    2014-11-01

    Global refractive gradients in seawater cause pointing problems for optical wireless communications. A refractive index depth profile of the Pacific Ocean was calculated from measured salinity, temperature, and pressure, determining the end points of a refracted and nonrefracted 200 m communication link. Numerical ray tracing was used with a point source for angles between 10° and 80° and transmission wavelengths of 500-650 nm; the maximum end-point difference found was 0.23 m. A 500 nm laser with a 0.57° full-angle FOV was traced; the nonrefracted receiver location was outside the FOV for all links angled >15° to the vertical. However, most pointing issues underwater are unlikely to be significant with suitable FOV choice and natural scattering of the source. PMID:25402887

  3. 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.

  4. 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.

  5. Characterizing conical refraction optical tweezers.

    PubMed

    McDonald, C; McDougall, C; Rafailov, E; McGloin, D

    2014-12-01

    Conical refraction occurs when a beam of light travels through an appropriately cut biaxial crystal. By focusing the conically refracted beam through a high numerical aperture microscope objective, conical refraction optical tweezers can be created, allowing for particle manipulation in both Raman spots, and in the Lloyd/Poggendorff rings. We present a thorough quantification of the trapping properties of such a beam, focusing on the trap stiffness, and how this varies with trap power and trapped particle location. We show that the lower Raman spot can be thought of as a single-beam optical gradient force trap, while radiation pressure dominates in the upper Raman spot, leading to optical levitation rather than trapping. Particles in the Lloyd/Poggendorff rings experience a lower trap stiffness than particles in the lower Raman spot, but benefit from rotational control. PMID:25490654

  6. 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.

  7. The Optics of Refractive Substructure

    NASA Astrophysics Data System (ADS)

    Johnson, Michael D.; Narayan, Ramesh

    2016-08-01

    Newly recognized effects of refractive scattering in the ionized interstellar medium have broad implications for very long baseline interferometry (VLBI) at extreme angular resolutions. Building upon work by Blandford & Narayan, we present a simplified, geometrical optics framework, which enables rapid, semi-analytic estimates of refractive scattering effects. We show that these estimates exactly reproduce previous results based on a more rigorous statistical formulation. We then derive new expressions for the scattering-induced fluctuations of VLBI observables such as closure phase, and we demonstrate how to calculate the fluctuations for arbitrary quantities of interest using a Monte Carlo technique.

  8. 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…

  9. 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…

  10. Refractive surgery: keratomileusis and keratophakia.

    PubMed

    Werner, D L

    1986-08-01

    This paper reviews the non-radial keratotomy surgeries that are being performed. The author reviews the literature and suggests an approach toward counseling patients who may be considering these approaches. The paucity of reported studies makes the choice of these alternate procedures somewhat risky, particularly in their refractive predictability. PMID:3528269

  11. Fiber optic refractive index monitor

    DOEpatents

    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.

  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. Refractive Errors - Multiple Languages: MedlinePlus

    MedlinePlus

    ... Are Here: Home → Multiple Languages → All Health Topics → Refractive Errors URL of this page: https://www.nlm.nih. ... V W XYZ List of All Topics All Refractive Errors - Multiple Languages To use the sharing features on ...

  14. Development of refraction and strabismus.

    PubMed

    Thorn, F

    2000-10-01

    Research on the etiology and causes of refractive errors has become a very active field of study during the past few years. Most of this research has focused on myopia. But hyperopia and astigmatism are also being examined both in comparison to myopia and in their own right. Animal models have also been developed for the study of experimentally induced myopia and hyperopia. These studies demonstrate the chain of neural and molecular events that occurs in induced myopia and hyperopia with increasing precision. In the future, these results may elucidate the mechanisms that underlie the refractive errors seen in human populations. Research into the development of strabismus has not progressed with the same vigor. The links among hyperopia, accommodative convergence, and strabismus are well established. Numerous neural, oculomotor, and subjective correlates of strabismus are now well established, but there has been a failure to develop the experimental paradigms needed to demonstrate the causal relations among these different factors. PMID:11148693

  15. 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.

  16. Influence of heterogeneous refractivity on optical wave propagation in coastal environments

    NASA Astrophysics Data System (ADS)

    He, Ping; Nunalee, Christopher G.; Basu, Sukanta; Minet, Jean; Vorontsov, Mikhail A.; Fiorino, Steven T.

    2015-12-01

    Spatial variations of refractivity significantly dictate the characteristics of optical wave propagation through the atmosphere. Consequently, the ability to simulate such propagation is highly dependent upon the accurate characterization of refractivity along the propagation path. Unfortunately, the scarcity of high spatiotemporal resolution observational data has forced many past studies of optical wave propagation to assume horizontally homogeneous (HH) atmospheric conditions. However, the (adverse) impact of such an assumption has not been quantified in the literature. In this paper, we attempt to fill this void by utilizing a mesoscale modeling-based approach to explicitly simulate atmospheric refraction. We then compare the differences of the HH refractivity fields to the mesoscale model-derived refractivity fields by means of a realistic atmospheric event and through ray tracing simulations. In this study, we model a coastal low-level jet, a common coastal atmospheric phenomenon which is associated with heterogeneous thermal and refractivity fields. Observational data from a radiosonde and a radar wind profiler near the northeastern region of the United States are used for model validation. The observed characteristics of low-level jet (e.g., evolution, intensity, location) and associated temperature inversion are found to be reasonably well captured by the mesoscale model. The simulated nighttime refractivity gradient field manifests significant spatial heterogeneity; over land, the refractivity gradient is much stronger and amplified near the ground, whereas it becomes much weaker over the ocean. We quantify the effect of this heterogeneity on optical ray trajectories by simulating a suite of rays and documenting the variability of their altitudes at certain propagation ranges. It is found that the altitude of optical rays may vary tens of meters during a diurnal cycle, and at nighttime the rays may bend downward by more than 150 m at a range of 100 km. We

  17. 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.

  18. 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)

  19. 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.

  20. Refractive beryllium x-ray lens with variable focal length

    NASA Astrophysics Data System (ADS)

    Cederstroem, Bjoern; Danielsson, Mats; Lundqvist, Mats

    2001-01-01

    A refractive lens for hard X-rays comprising two saw-tooth profiles is presented. This lens has the same focusing properties as a parabolic compound refractive lens. One advantage is the remarkably low fabrication cost, since curved surfaces are replaced by planar ones. In addition, the focal length of the lens can be easily varied by adjusting the angle between the two halves. Since the index of refraction depends on the X-ray energy, the lens is chromatic and acts as a band- pass filter for a broad energy spectrum. Combined with the tunability of the focal length, this allows versatile spectral shaping of the X-ray beam. Calculations and numerical examples of the focusing properties are presented. Due to its low atomic number, beryllium is an excellent choice for refractive optics and a prototype in beryllium has been fabricated using diamond turning technique. Surface metrology shows a deviation from the ideal shape of about 400 nm rms, indicating a loss of intensity of between 20% and 50%, depending on the geometry an X-ray energy.

  1. Diffractively Coupled, Refractively Guided Lasers

    NASA Technical Reports Server (NTRS)

    Katz, Joseph; Cser, Jim; Marshall, William K.

    1987-01-01

    Semiconductor-laser arrays more reliable, more powerful, and easier to make. Improved design intended to eliminate undesired electromagnetic modes and mode shifts sometimes occuring in gain-guided variety. Reflected from mirror/window at end of common resonator section of laser, energy refracted from each laser enters adjacent laser. Mutual coupling establishes phase relationships among lasers. Monolithic laser array made by standard epitaxial techniques. Made in part with polymeric materials to mitigate some deleterious effects of all-expitaxial processing. Potential applications include optical communications, ranging, printing, and recording.

  2. 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.

  3. 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.

  4. 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

  5. Centration axis in refractive surgery.

    PubMed

    Arba Mosquera, Samuel; Verma, Shwetabh; McAlinden, Colm

    2015-01-01

    The human eye is an asymmetric optical system and the real cornea is not a rotationally symmetrical volume. Each optical element in the eye has its own optical and neural axes. Defining the optimum center for laser ablation is difficult with many available approaches. We explain the various centration approaches (based on these reference axes) in refractive surgery and review their clinical outcomes. The line-of-sight (LOS) (the line joining the entrance pupil center with the fixation point) is often the recommended reference axis for representing wavefront aberrations of the whole eye (derived from the definition of chief ray in geometrical optics); however pupil centration can be unstable and change with the pupil size. The corneal vertex (CV) represents a stable preferable morphologic reference which is the best approximate for alignment to the visual axis. However, the corneal light reflex can be considered as non-constant, but dependent on the direction of gaze of the eye with respect to the light source. A compromise between the pupil and CV centered ablations is seen in the form of an asymmetric offset where the manifest refraction is referenced to the CV while the higher order aberrations are referenced to the pupil center. There is a need for a flexible choice of centration in excimer laser systems to design customized and non-customized treatments optimally. PMID:26605360

  6. 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.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  10. 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.

  11. Building achromatic refractive beam shapers

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Shealy, David

    2014-10-01

    Achromatic beam shapers can provide beam shaping in a certain spectral band and are very important for various laser techniques, such as, applications based on ultra-short pulse lasers with pulse width <100 fs, confocal microscopy, multicolour holography, life sciences fluorescence techniques, where several lasers in spectrum 405-650 nm are used simultaneously, for example 405-650 nm. Conditions of energy re-distribution and zero wave aberration are strictly fulfilled in ordinary plano-aspheric lens pair beam shapers for a definite wavelength only. Hence, these beam shapers work efficiently in relatively narrow, few nm spectrum. To provide acceptable beam quality for refractive beam shaping over a wide spectrum, an achromatizing design condition should be added. Consequently, the typical beam shaper design contains more than two-lenses, to avoid any damaging and other undesirable effects the lenses of beam shaper should be air-spaced. We suggest a two-step method of designing the beam shaper: 1) achromatizing of each plano-aspheric lens using a buried achromatizing surface ("chromatic radius"), then each beam shaper component presents a cemented doublet lens, 2) "splitting" the cemented lenses and realizing air-spaced lens design using optical systems design software. This method allows for using an achromatic design principle during the first step of the design, and then, refining the design by using optimization software. We shall present examples of this design procedure for an achromatic Keplerian beam shaper and for the design of an achromatic Galilean type of beam shaper. Experimental results of operation of refractive beam shapers will be presented as well.

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

    PubMed

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

    2015-10-13

    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

  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. Ionospheric refraction correction in radio astronomy

    NASA Astrophysics Data System (ADS)

    Chai, Yan; Han, Wen-Jun

    1986-10-01

    Using Snell's law in polar coordinates, the ionospheric refraction effects on the declination and right ascension determination are discussed in this paper. A ray tracing method is also given. With the ionospheric data observed in Beijing, the correction of ionospheric refraction is estimated and some useful conclusions are drawn.

  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. 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. PMID:26938648

  17. 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.

  18. 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

  19. Refraction in electrically thin inhomogeneous media.

    PubMed

    Ruphuy, Miguel; Ramahi, Omar M

    2016-04-01

    This work presents a new formulation for refraction from flat electrically thin lenses and reflectors comprised of inhomogeneous material. Inhomogeneous electrically thin flat lenses and reflectors cannot make use of the Snell law since this classical formulation works solely at interfaces of planar homogeneous media. The refraction of a perpendicularly incident plane wave at a planar interface is physically explained through the phase advance of the rays within the medium. The Huygens principle is then used to construct the refracted wavefront. The formulation is validated using numerical full wave simulation for several examples where the refractive angle is predicted with good accuracy. Furthermore, the formulation gives a physical insight of the phenomenon of refraction from electrically thin inhomogeneous media. PMID:27140761

  20. Upper-crustal velocity structure near Coalinga, as determined from seismic-refraction data

    SciTech Connect

    Walter, A.W.

    1990-01-01

    The May 2 earthquake (M{sub L} = 6.7) was unexpected in that it occurred at the structural transition between the southern Diablo Range and the San Joaquin Valley, part of the 500-km-long Coast Ranges-Great Valley boundary. Since 1981, the US Geological Survey (USGS) has been acquiring both seismic reflection and refraction data along profiles that cross this boundary. The occurrence of the May 2 earthquake provided motivation to acquire additional seismic reflection and refraction data in the hypocentral region with the goal of understanding the structural relations responsible for the unexpected seismicity. This understanding is needed to assess the probability of large earthquakes occurring elsewhere along the Coast Ranges-Great Valley boundary. Sections of this paper describe the following: geologic setting; seismic-refraction experiment, including the east-west profile, northwest-southeast profile, quality of seismic data, velocity modeling, east-west velocity model, and northwest-southeast velocity model; comparison of the velocity models at their point of intersection; comparison between the Coalinga velocity models and the velocity model derived for profile SJ-6; comparison between the refraction velocity structure and nearby seismic-reflection profiles; relation between Coalinga seismicity and the velocity structure; and a summary of modeling results.

  1. Refraction tomography over a buried waste disposal site

    SciTech Connect

    Lanz, E.; Maurer, H.; Green, A.G.

    1998-07-01

    Potential field methods generally lack the necessary depth resolution, and seismic reflection data are usually contaminated by source-generated noise in the time range of interest (<50 ms). To address this problem, the authors have developed a surface 2-D tomographic refraction scheme that is based on a fast finite-difference eikonal solver and an inversion method that incorporates appropriate damping and smoothing constraints. This new scheme has been applied to a first-arrival traveltime data set collected across adjacent landfills in northern Switzerland. High-quality seismic data were collected along five profiles that crossed the landfills and two that sampled undisturbed natural sediments. Seismic waves generated from multiple shots were recorded on large numbers of closely spaced receivers during quiet evening periods. Reliability of the resultant velocity tomograms was estimated on the basis of (1) ray diagrams, (2) plots of synthetic and observed traveltimes, (3) traveltime residual analyses, (4) comparisons of coincident velocity-depth profiles computed from intersecting profiles, (5) inversions with diverse input models, and (6) quantitative error analyses using a bootstrap technique. Although results have demonstrated that the tomographic refraction scheme may be an efficient and cost-effective means of studying the very shallow subsurface (<20 m depth), complementary geological and other geophysical data were required to discriminate between velocity anomalies attributed to the landfills and those attributed to natural variations in the near-surface geology.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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

  7. 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.

  8. Theoretical analysis and numerical experiments of variational adjoint approach for refractivity estimation

    NASA Astrophysics Data System (ADS)

    Zhao, Xiao-Feng; Huang, Si-Xun; Du, Hua-Dong

    2011-02-01

    This paper puts forward possibilities of refractive index profile retrieval using field measurements at an array of radio receivers in terms of variational adjoint approach. The derivation of the adjoint model begins with the parabolic wave equation for a smooth, perfectly conducting surface and horizontal polarization conditions. To deal with the ill-posed difficulties of the inversion, the regularization ideas are introduced into the establishment of the cost function. Based on steepest descent iterations, the optimal value of refractivity could be retrieved quickly at each point over height. Numerical experiments demonstrate that the method works well for low-distance signals, while it is not accurate enough for long-distance propagations. Through curve fitting processing, however, giving a good initial refractivity profile could generally improve the inversions.

  9. Negative Refraction experiments in Photonic Crystal prisms

    NASA Astrophysics Data System (ADS)

    Vodo, Plarenta; Parimi, Patanjali. V.; Lu, Wentao. T.; di Gennaro, Emiliano; Sridhar, Srinivas

    2004-03-01

    We have experimentally demonstrated negative refraction in metallic photonic crystal (PC) prisms [1]. The refracted fields in the parallel plate waveguide (PPW) are measured by an automated dipole antenna, which scans the desired area, while the free space (FS) measurements, performed in a anechoic chamber, are measured by a rectangular X-band horn that swings in an arc in far field area. Both TE and TM excitation modes are used in FS experiments. Numerical calculations of the band structure and equi-frequency surface simulations are used to determine frequency regions of negative refraction of the triangular lattice PC. Angle of refraction determined by theoretical simulations and experimental results, are in exceptional good agreement, yielding the negative refraction index. FS and PPW refraction experimental results agree remarkably with simulations. 1. "Negative Refraction and Left-handed electromagnetism in Microwave Photonic Crystals", P.V Parimi, W.T Lu, P.Vodo J. Sokoloff and S.Sridhar, cond-mat/0306109 (2003)

  10. 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.

  11. 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.

  12. The refractive index of relic gravitons

    NASA Astrophysics Data System (ADS)

    Giovannini, Massimo

    2016-06-01

    The dynamical evolution of the refractive index of the tensor modes of the geometry produces a specific class of power spectra characterized by a blue (i.e. slightly increasing) slope which is directly determined by the competition of the slow-roll parameter and of the rate of variation of the refractive index. Throughout the conventional stages of the inflationary and post-inflationary evolution, the microwave background anisotropies measurements, the pulsar timing limits and the big-bang nucleosynthesis constraints set stringent bounds on the refractive index and on its rate of variation. Within the physically allowed region of the parameter space the cosmic background of relic gravitons leads to a potentially large signal for the ground-based detectors (in their advanced version) and for the proposed space-borne interferometers. Conversely, the lack of direct detection of the signal will set a qualitatively new bound on the dynamical variation of the refractive index.

  13. Nonlinear negative refraction by difference frequency generation

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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. Refractive index measurement using comparative interferometry

    NASA Astrophysics Data System (ADS)

    Bojan, Mihaela; Apostol, D.; Damian, V.; Logofatu, P. C.; Garoi, F.; Iordache, Iuliana

    2007-05-01

    The refractive index of a material medium is an important optical parameter since it exhibits the optical properties of the material. The adulteration problem is increasing day by day and hence simple, automatic and accurate measurement of the refractive index of materials is of great importance these days. For solid thin films materials Abeles method was reconsidered. Quick, measurements of refractive index using simple techniques and refractometers can help controlling adulteration of liquids of common use to a greater extent. Very simple interferometric set-up using Fizeau fringe patterns compares the fringe pitch as obtained in a cell with two levels: one down level with the unknown refractive index liquids and the upper level with gas air. A CCD matrix and a PC can handle the data and produce the results up to for digits.

  15. 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.

  16. 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.

  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. Two Color Interferometry with Nonlinear Refractive Properties

    NASA Technical Reports Server (NTRS)

    Vikram, Chandra S.; Witherow, William K.

    2002-01-01

    Using nonlinear refractive properties of salt-water solution at two wavelengths, numerical analysis has been performed to extract temperature and concentration from virtual interferometric fringe data. The theoretical study, using a commercially available equation solving tool, starts with critical fringe counting needs and the role of nonlinear refractive properties in such measurements. Finally, methodology of the analysis, developed codes, and fringe counting accuracy needs are described in detail.

  19. Classical gravity does not refract negatively.

    PubMed

    McCall, Martin W

    2007-03-01

    We appraise recent claims that classical gravitation can induce negative refraction of electromagnetic radiation in vacuum. By recasting the previous literature in covariant notation, we show that the criterion used hitherto for determining negative refraction in vacuum is inappropriate, and can even be satisfied by parametrized transformations in Minkowski spacetime. Using instead a covariantly acceptable definition, we find that in classical vacuum the power flux of a plane electromagnetic wave points in the direction of phase advance. PMID:17359145

  20. 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.

  1. On the sources of astrometric anomalous refraction

    NASA Astrophysics Data System (ADS)

    Taylor, M. Suzanne

    2009-06-01

    Over 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, now known as "anomalous refraction," is again being observed. Anomalous refraction is described as a low frequency, large angular scale motion of the entire image plane with respect to the celestial coordinate system as observed and defined by previous astrometric catalogs. These motions of typically several tenths of an arcsecond with timescales on the order often minutes are ubiquitous to drift-scan ground-based 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 never 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 coherent dynamical structures in the boundary-layer below 60 meters.

  2. 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.

  3. 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. PMID:23428441

  4. Profile sampling dependence of the MLAYER program

    NASA Astrophysics Data System (ADS)

    Chang, Ting-Hsun

    1991-03-01

    The dependence of the predictions of the MLAYER program on the set of heights at which the refractive index value are sampled from a fixed reference profile are analyzed. A refractivity profile with a four-meter evaporation duct is adopted as a reference. Two variable piecewise linear profiles of four and five segments, respectively, are used to approximate the reference profile for MLAYER computations. The sensitivities of the waveguide mode location, the range attenuation rate, and the height-gain function to the changes of the piece-wise linear profiles are investigated at the frequencies 3, 6, 10, and 15 GHz. The frequency dependence of the dominant mode for one profile is also studied to investigate the fact that the sensitivity to changes in sampling point location is lower at GHz than at other frequencies. A general rule-of-thumb for the change in range attenuation rate due to a slight change in refractivity is suggested.

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. Djibouti: country profile.

    PubMed

    Fozzard, A

    1988-08-01

    The nation of Djibouti lies on the east coast of Africa at the point where the Red Sea and the Gulf of Aden meet. It has been independent since 1977, yet French influence and presence continue. For example, 2000 French troops are in Djibouti to guard its independence from its combative neighbors Somalia and Ethiopia. France also supports the government's constant budget deficit and unstable economy. The nation's 2 main sources of national income include the port and its associated services and the money spent by the unwelcome French garrison. Many of the troops and visitors from the Gulf frequent the many brothels and the Muslim Djiboutians find this sexual activity offensive. Since agriculture is almost nonexistent due to semiarid conditions and the well-paid expatriate community can afford to pay high prices for food, many of the 400,000 Djiboutians live at subsistence level or below. Additionally, the authors claim that perhaps 40% of the population is unemployed. The population consists of 2 main groups, the Afars and the Issas, who feud in the political arena. The Afars dominate the Cabinet, yet President Gouled is an Issas and patronizes Issas rival clans to maintain their support. Not surprisingly, the demands of the Afar community are not the President's top priorities. Consequently' violent protests arise and the President resorts to force. PMID:12315735

  10. 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)

  11. 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

  12. Optimization of torque on an optically driven micromotor by manipulation of the index of refraction

    NASA Astrophysics Data System (ADS)

    Wing, Frank M., III; Mahajan, Satish; Collett, Walter

    2004-12-01

    Since the 1970"s, the focused laser beam has become a familiar tool to manipulate neutral, dielectric micro-objects. A number of authors, including Higurashi and Gauthier, have described the effects of radiation pressure from laser light on microrotors. Collett, et al. developed a wave, rather than a ray optic, approach in the calculation of such forces on a microrotor for the first time. This paper describes a modification to the design of a laser driven, radiation pressure microrotor, intended to improve the optically generated torque. Employing the wave approach, the electric and magnetic fields in the vicinity of the rotor are calculated using the finite difference time domain (FDTD) method, which takes into account the wave nature of the incident light. Forces are calculated from the application of Maxwell"s stress tensor over the surfaces of the rotor. Results indicate a significant increase in torque when the index of refraction of the microrotor is changed from a single value to an inhomogeneous profile. The optical fiber industry has successfully employed a variation in the index of refraction across the cross section of a fiber for the purpose of increasing the efficiency of light transmission. Therefore, it is hoped that various fabrication methods can be utilized for causing desired changes in the index of refraction of an optically driven microrotor. Various profiles of the index of refraction inside a microrotor are considered for optimization of torque. Simulation methodology and results of torque on a microrotor for various profiles of the index of refraction are presented. Guidelines for improvised fabrication of efficient microrotors may then be obtained from these profiles.

  13. 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

  14. Refractive error sensing from wavefront slopes.

    PubMed

    Navarro, Rafael

    2010-01-01

    The problem of measuring the objective refractive error with an aberrometer has shown to be more elusive than expected. Here, the formalism of differential geometry is applied to develop a theoretical framework of refractive error sensing. At each point of the pupil, the local refractive error is given by the wavefront curvature, which is a 2 × 2 symmetric matrix, whose elements are directly related to sphere, cylinder, and axis. Aberrometers usually measure the local gradient of the wavefront. Then refractive error sensing consists of differentiating the gradient, instead of integrating as in wavefront sensing. A statistical approach is proposed to pass from the local to the global (clinically meaningful) refractive error, in which the best correction is assumed to be the maximum likelihood estimation. In the practical implementation, this corresponds to the mode of the joint histogram of the 3 different elements of the curvature matrix. Results obtained both in computer simulations and with real data provide a close agreement and consistency with the main optical image quality metrics such as the Strehl ratio. PMID:21149305

  15. 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.

  16. Refractive index change in dissociating shocked benzene

    SciTech Connect

    Erskine, D.J.

    1994-06-01

    A calculation is made of the refractive index of a shocked solution of hydrocarbon species and spheroidal carbon particles that would be the dissociation products of benzene. The results is evaluated for benzene shocked to 15 GPa, both for an arbitrary endpoint distribution of products and reactant, and for a specific endpoint distribution suggested by a statistical-mechanical calculation. In the case of diamond particles, the refractive index is predicted to decrease by a small amount (from 1.96 to 1.75) as the dissociation proceeds. In the case of graphite particles of large oblateness, the refractive index could increase significantly through the dissociation (from 1.96 to 2.75 for infinitely oblate platelets). Thus the measurement of the time dependent refractive index through the dissociation of shocked benzene can indicate the morphology of the carbon particulates as well as the time scale for this reaction. We propose using the refractive index as a measure of completion of the dissociation reaction. This would allow a determination of the instantaneous amount of carbon in particulate form, information which is valuable in conjunction with Mie scattering experiments for example.

  17. [Refractive changes after Descemet membrane endothelial keratoplasty].

    PubMed

    Röck, T; Bartz-Schmidt, K U; Röck, D; Yoeruek, E

    2014-01-01

    Penetrating keratoplasty has different refractive disadvantages in contrast to posterior lamellar keratoplasty. For example, a decentered corneal trephination and a tilted trephination or unevenly tightened corneal sutures can cause an uncontrolled high astigmatism as well as a refractive change. Also the postoperative refraction may change over time as a result of wound healing, suture loosening or suture removal. The aim of this retrospective study was to investigate a possible refractive change after Descemet membrane endothelial keratoplasty (DMEK). A total of 139 pseudophakic eyes from 125 patients with endothelial decompensation had undergone DMEK surgery at the Tübingen Eye Clinic. After a mean postoperative time of 13.15 ± 2.98 months after DMEK discreet mean changes in the spherical equivalent of + 0.37 ± 0.87 diopters and the cylinder to - 0.45 ± 0.57 diopters were observed. The mean central corneal thickness decreased from 670 ± 70 µm to 544 ± 55 µm. In conclusion after DMEK a discreet induced hyperopic refractive shift due to the reversal of stromal swelling was observed. PMID:23989219

  18. Compression of ultra-short light pulses using the graded refractive index one-dimensional photonic crystals

    NASA Astrophysics Data System (ADS)

    Shiri, R.; Bananej, A.; Safari, E.

    2016-09-01

    The one-dimensional photonic crystals (1D PCs) containing a graded refractive index layer have been theoretically utilized to compress the positively chirped ultra-short pulses of light. Two types of simple and graded index multi-layer structures consisting alternating layers of TiO2 and SiO2 with the same total thicknesses and periodicity have been investigated and compared. For the graded structure, three different refractive index distributions including linear, exponential and parabolic profiles have been considered. The results revealed that replacing one of the homogeneous layers of the unit cells in simple photonic crystal with a graded material having parabolic refractive index profile efficiently improves compression behavior of the structure. The compress factors of as much as 47% and 78% depending on the pulse's initial chirp rate obtained with parabolic profile of such the structures.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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.

  1. 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

  2. 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. PMID:27212938

  3. Pg shingles: preliminary results from the onshore GLIMPCE refraction experiment

    NASA Astrophysics Data System (ADS)

    Mereu, R. F.; Epili, D.; Green, A. G.

    1990-02-01

    In 1986, a series of near vertical Seismic reflection lines and coincident Seismic refraction lines were recorded across the Great Lakes in the GLIMPCE experiment. From a refraction point of view this experiment was unique as this was the first time in North America that long range refraction lines up to 350 km were recorded with a trace spacing of less than 100 metres. The source of energy was a large air gun. Some preliminary results of the nature of the onshore recordings made by the University of Western Ontario are presented in this paper. Observations of many of the in-line profiles show that the character of the Pg crustal phase is not simple but has a "shingle-like" pattern which may be caused by wide-angle reflection effects from numerous long and short reflectors within the crust. Theoretical studies indicate that the amplitudes of the wide-angle reflected signals from thin high-velocity layers are in general much larger than those from thin low-velocity layers. Supercritical reflected waves are not possible from the top of a low-velocity layer. The closely spaced traces show in minute detail the manner in which one travel-time branch fades and the next one arrives. The results seem to indicate that the Pg phase in our data set has little direct wave component but, instead, is made up of a whole series of "shingled or fish-scaled" wide-angle reflection components, each with successively larger apparent velocities. These results are in agreement with the findings of the near-vertical reflection component of the experiment.

  4. Regularized reconstruction of wave fields from refracted images of water

    NASA Astrophysics Data System (ADS)

    Choudhury, K. Roy; O'Sullivan, F.; Samanta, M.; Shrira, V.; Caulliez, G.

    2009-04-01

    Refractive imaging of wave fields is often used for observation of short gravity and gravity-capillary waves in wave tanks and in the field. A light box placed under the waves emits light of spatially graduated intensity. The refracted light intensity image recorded overhead can be related to the wave slope field using a system of equations derived from the laws of refraction. Previous authors have proposed a two stage reconstruction strategy for the recovery of wave slope and height fields: i) estimation of local slope fields ii) global reconstruction of height and slope fields using local estimates. Our statistical analysis of local slope estimates reveals that estimation error variability increases considerably from the bright to the dark ends of the imaging area, with some concomitant bias. The reconstruction problem behaves like an ill posed inverse problem in the dark areas of the image. Illposedness is addressed by a reconstruction method that imposes Tikhonov regularization of directional wave slopes using penalized least squares. Other refinements proposed include a) bias correction of local slope estimates b) spatially weighted reconstruction using estimated variability of local slope estimates and c) more accurate estimates of reference light profiles from time sequence data. A computationally efficient algorithm that exploits sparsity in the resulting system of equations is employed to evaluate the regularized estimator. Simulation studies show that the refinements can result in substantial improvements in the mean squared error of reconstruction. The algorithm is applied to obtain wave field reconstructions from video recordings. Analysis of various video sequences demonstrates distinct spatial patterns at different wind speed and fetch combinations.

  5. Beam shaping in high-power laser systems with using refractive beam shapers

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Laskin, Vadim

    2012-06-01

    Beam Shaping of the spatial (transverse) profile of laser beams is highly desirable by building optical systems of high-power lasers as well in various applications with these lasers. Pumping of the crystals of Ti:Sapphire lasers by the laser radiation with uniform (flattop) intensity profile improves performance of these ultrashort pulse high-power lasers in terms of achievable efficiency, peak-power and stability, output beam profile. Specifications of the solid-state lasers built according to MOPA configuration can be also improved when radiation of the master oscillator is homogenized and then is amplified by the power amplifier. Features of building these high power lasers require that a beam shaping solution should be capable to work with single mode and multimode beams, provide flattop and super-Gauss intensity distributions, the consistency and divergence of a beam after the intensity re-distribution should be conserved and low absorption provided. These specific conditions are perfectly fulfilled by the refractive field mapping beam shapers due to their unique features: almost lossless intensity profile transformation, low output divergence, high transmittance and flatness of output beam profile, extended depth of field, adaptability to real intensity profiles of TEM00 and multimode laser sources. Combining of the refractive field mapping beam shapers with other optical components, like beam-expanders, relay imaging lenses, anamorphic optics makes it possible to generate the laser spots of necessary shape, size and intensity distribution. There are plenty of applications of high-power lasers where beam shaping bring benefits: irradiating photocathode of Free Electron Lasers (FEL), material ablation, micromachining, annealing in display making techniques, cladding, heat treating and others. This paper will describe some design basics of refractive beam shapers of the field mapping type, with emphasis on the features important for building and applications

  6. Meterological correction of optical beam refraction

    SciTech Connect

    Lukin, V.P.; Melamud, A.E.; Mironov, V.L.

    1986-02-01

    At the present time laser reference systems (LRS's) are widely used in agrotechnology and in geodesy. The demands for accuracy in LRS's constantly increase, so that a study of error sources and means of considering and correcting them is of practical importance. A theoretical algorithm is presented for correction of the regular component of atmospheric refraction for various types of hydrostatic stability of the atmospheric layer adjacent to the earth. The algorithm obtained is compared to regression equations obtained by processing an experimental data base. It is shown that within admissible accuracy limits the refraction correction algorithm obtained permits construction of correction tables and design of optical systems with programmable correction for atmospheric refraction on the basis of rapid meteorological measurements.

  7. 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.

  8. 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.

  9. 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

  10. An evaluation of the impact of variable temporal and spatial data resolution upon IREPS (Integrated Refractive Effects Prediction System)

    NASA Astrophysics Data System (ADS)

    Dotson, Michael E.

    1987-06-01

    Atmospheric refractive index gradients significantly modify the path of electromagnetic (EM) waves as they propagate through the atmosphere. Accordingly, the performance of U.S. Navy (EM) systems can be either degraded or enhanced due to atmospheric conditions which effect atmospheric refractive index profiles. The Integrated Refractive Effects Prediction System (IREPS) version 2.2 is the latest software developed by Naval Ocean Systems Center (NOSC) to predict atmospheric refraction and its resulting effect on EM systems. Specific environmental parameters are used as input data to produce various output products to be used by the tactician in planning the optimum use of naval assets. The quality and accuracy of the resulting output is directly related to the quality and timeliness of the input data. This thesis study shows the importance of timely, high resolution data, for input into the IREPS version 2.2 program, in order to obtain realistic atmospheric refractive and corresponding EM system performance predictions. A continentally derived data set is used to compare the results of using high resolution versus low resolution data as input into IREPS, and to qualitatively show how quickly the refractive structure of the atmosphere can vary with time. A second data set from an over ocean experiment attacks the horizontally homogeneous atmosphere assumption which appears to be frequently incorrectly applied. Finally, a statistical comparison can result in significant variations of atmospheric refractivity that could affect Naval EM systems.

  11. Commercial scale fabrication method for fabricating a gradient refractive-index rod: Overcoming volume shrinkage and chemical restrictions.

    PubMed

    Cho, Hansol; Son, Young Mok; Kim, Mu Gyeom; Ra, Byoung Joo; Park, Joon-Yong; Lee, Seung Hui; Choi, Jin Sung; Song, Min Young; Park, O Ok; Kim, Youn Cheol; Hwang, Jin Taek

    2006-10-01

    We report a fabrication method for a gradient refractive-index polymeric object from a binary comonomer system, regardless of the monomers' reactivity ratio and the molar volume criteria of gradient refractive-index development. To fabricate a large gradient refractive-index rod consisting of a methyl methacrylate and 2,2,3,3-tetrafluoropropyl methacrylate comonomer pair that has not been used for fabrication of a copolymer gradient refractive-index rod by previous conventional methods because of chemical restrictions in molar volume and reactivity ratio difference, we use the so-called successive UV polymerization in a controlled radial volume in conjunction with an automatic refill reactor. Simultaneously and automatically, the volume shrinkage problem, an inevitable shortcoming for the fabrication of a large polymeric object in a commercial production scale, is overcome and exploited. The theoretical features of the refractive-index profile generation of this method are also compared with those of conventional methods for which the chemical restrictions of monomers are crucial for the shape of a refractive-index profile. PMID:16983409

  12. 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.

  13. Negative refraction using Raman transitions and chirality

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

    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.

  14. Negative refraction without absorption via quantum coherence

    NASA Astrophysics Data System (ADS)

    Fang, Ai-Ping; Ge, Wenchao; Wang, Meng; Li, Fu-li; Zubairy, M. Suhail

    2016-02-01

    Negative refraction of a probe field is studied in a dense gas consisting of cascade-type four-level atoms. By coupling the magnetic component of the probe field to a Λ scheme with initially prepared coherence in the two lower levels, strong negative permeability with minimal absorption can be obtained. The permittivity of the gas to the electric component of the probe field can be made negative by taking into account the local field effect of the dense atoms. Strong negative refraction with zero absorption can be achieved in a wide range of parameters in our scheme. A possible experimental realization is also discussed.

  15. 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.

  16. 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.

  17. 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. PMID:11801014

  18. Applying field mapping refractive beam shapers to improve holographic techniques

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Williams, Gavin; McWilliam, Richard; Laskin, Vadim

    2012-03-01

    Performance of various holographic techniques can be essentially improved by homogenizing the intensity profile of the laser beam with using beam shaping optics, for example, the achromatic field mapping refractive beam shapers like πShaper. 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 several laser sources with different wavelengths simultaneously. Applying of these beam shapers brings serious benefits to the Spatial Light Modulator based techniques like Computer Generated Holography or Dot-Matrix mastering of security holograms since uniform illumination of an SLM allows simplifying mathematical calculations and increasing predictability and reliability of the imaging results. Another example is multicolour Denisyuk holography when the achromatic πShaper provides uniform illumination of a field at various wavelengths simultaneously. This paper will describe some design basics of the field mapping refractive beam shapers and optical layouts of their applying in holographic systems. Examples of real implementations and experimental results will be presented as well.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Design and testing of a refractive laser beam homogenizer

    NASA Astrophysics Data System (ADS)

    Fernelius, N. C.; Bradley, K. R.; Hoekstra, B. L.

    1984-09-01

    A survey is made of various techniques to create a homogeneous or flat top laser beam profile. A refractive homogenizer was designed for use with a ND:YAG laser with output at its fundamental (1.06 micrometer) and frequency doubled (532 nm) modes. The system consists of a 2X beam expander and two faceted cylindrical lenses with differing focal lengths. Each cylindrical lens focusses its input into a strip the width of a facet. By orienting their axes at a 90 degree angle and focussing them on the same plane, the beam is concentrated into a square focus. Formulae for calculating the facet angles are derived and a FORTRAN computer square focus. Formulae for calculating the facet angles are derived and a FORTRAN computer program was written to calculate them with a precision greater than one is able to fabricate them.

  7. New consideration of atmospheric refraction in laser ranging data

    NASA Astrophysics Data System (ADS)

    Yan, Haojian; Wang, Guangli

    1999-08-01

    In this paper we reconsider the formulae of tropospheric refraction correction for the Satellite Laser Range technique. From the expansion of the complementary error function, a new continued fraction form of the mapping function at optical frequencies is derived. The correction terms related to the operation frequency of the laser beam are considered in both the zenith delay and the mapping function. The correction for low-elevation satellites is briefly reviewed. The theoretical accuracy of the new mapping function has been analysed via the ray tracing integrals under the standard atmospheric profile. With respect to the radiosonde data, the deviations of the new mapping function are investigated in an elevation range down to near 1 deg, which is comparable with the results of the Marini-Murray formulae.

  8. 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.

  9. 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. PMID:24116404

  10. 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.

  11. 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…

  12. 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)

  13. 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.

  14. Refracting boundaries in thin film glass lightguides

    NASA Astrophysics Data System (ADS)

    Turner, A. F.; Browning, S. D.

    1980-02-01

    The paper describes experimental studies of refraction at a straightline boundary between evaporated glass lightguides and evaporated thin film overlays of SbO3 with index 2.10. Attention is given to sample preparation, measurement procedures, and computations. It is noted that Snell's law gives the total change of mode indices on each side of the boundary are used.

  15. 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)

  16. Intraocular Pressure, Ethnicity, and Refractive Error

    PubMed Central

    Manny, Ruth E.; Mitchell, G. Lynn; Cotter, Susan A.; Jones-Jordan, Lisa A.; Kleinstein, Robert N.; Mutti, Donald O.; Twelker, J. Daniel; Zadnik, Karla

    2011-01-01

    Purpose The ethnically-diverse Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study cohort provides a unique opportunity to explore associations among intraocular pressure (IOP), ethnicity, and refractive error while adjusting for potential confounding variables. Methods Mixed linear models were used to examine the effect of age, refractive error (cycloplegic autorefraction), ethnicity, sex, and measurement protocol on IOP (Tono-pen) in 3,777 children, aged 6-14 years at their first CLEERE visit (1995-2009). Children who became myopic during follow-up were used to examine the relationship between time since myopia onset and IOP. Clinically meaningful differences in IOP were preset at > 2 mm Hg. Results IOP differed among refractive error categories with higher IOP in children with low/moderate myopia than those with high hyperopia (differences < 1 mm Hg). There was a statistically significant relationship between age and IOP that depended on ethnicity (interaction p<0.0001) and measurement protocol (interaction p<0.0001). The relationship between sex and IOP depended on measurement protocol (interaction p=0.0004). For children who became myopic during follow-up, the adjusted mean IOP showed a significant decline for only Asian (p=0.024) and White children (p=0.004). As with other statistically significant results, these changes in mean adjusted IOPs from two years before to two years after myopia onset were < 2 mm Hg. Conclusions Small but significant differences in IOP by refractive error category were found in this ethnically diverse cohort of children. Relationships between IOP and age, ethnicity, sex, and measurement protocol were complicated by significant interactions between these parameters. Longitudinal analysis of children before and after myopia onset showed changes in IOP over time that varied by ethnicity. Higher IOPs before and at myopia onset were not present in all ethnic groups, with differences before and after

  17. Dual-band quasi-zero refraction and negative refraction in coin-shaped metamaterial

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Hou, Zhi-Ling; Liu, Ya-Min; Li, Zhong-Jun; Liu, Xingda; Fang, Hui-Min

    2015-05-01

    This paper demonstrates a metamaterial capable of realizing a dual-band quasi-zero refractive index and a negative refractive index, which consists of a coin-shaped slice and two parallel planar wires. The zero refractive index is achieved over a very wide frequency range. The bandwidth of the first band of the quasi-zero index can reach up to 3 GHz, and the width of the second band exhibiting low loss is 0.4 GHz. Between these two bands, the negative refractive index band is 9.0-13.9 GHz. The corresponding formulas of electric plasma frequency and magnetic plasma frequency are established, and the theoretical results agree well with the simulated results. The proposed metamaterial may have potential applications in multiband or broadband devices.

  18. 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.

  19. 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.

  20. 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)

  1. Refractive eye surgery - what to ask your doctor

    MedlinePlus

    Refractive eye surgery helps improve nearsightedness, farsightedness, and astigmatism. Below are some questions you may want to ... What to ask your doctor about refractive eye surgery; ... ask your doctor; Laser-Assisted In Situ Keratomileusis - what to ...

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

    MedlinePlus

    ... were developed with the help of the Federal Trade Commission and the American Society of Cataract and Refractive Surgery. For the complete guidelines, see: www.aao.org/about/policy/upload/Guidelines-for-Refractive-Surgery- Advertising-3-26- ...

  3. 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

  4. 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.

  5. A new method for the removal of refraction artifacts in multibeam echosounder systems

    NASA Astrophysics Data System (ADS)

    Kammerer, Edouard Louis Laurent Marie

    Refraction artifacts are often present in shallow water multibeam surveys and can degrade the quality of the final product if they are not adequately addressed. This thesis consists of the implementation of a systematic analysis and correction software package that addresses refraction artifacts in a post-processing context. The methodology consists of the estimation of the variation in the water sound speed distribution, by using the information given by the multibeam dataset itself. This is done by the evaluation of the appropriately modeled Sound Speed Profiles (SSP), which is applied either in addition to an already existing SSP, or applied directly to the raw data. Refraction errors are most developed in the outer parts of the survey line coverage. The software developed takes advantage of this observation by utilising the nadir data because they are almost unaffected by refraction errors. Two methods of analysis are considered in this study. The first method uses two neighbouring parallel lines to generate corrections. The second uses the crossing check lines. Both methods are used to evaluate the refraction coefficients of a two-layer SSP model, which, when applied, should bring the outer parts of the survey line as close as possible to the real seafloor (as observed at nadir). The software developed is tested on an actual multibeam dataset. This data has been acquired off Saint John Harbor (N.B.) with a SIMRAD EM1000 sonar. The application of the new post-processing tool reduces refraction artifacts. The reduction of such artifacts improves the extraction of useful information contained in the multibeam data. The method used allows as well the computation of correction SSPs that provide characteristics of an equivalent water mass.

  6. Riftogenic structures of the western Arctic shelf investigated by refraction surveys

    SciTech Connect

    Verba, M.L.; Daragan-Sushchova, L.A.; Pavlenkin, A.D.

    1992-08-01

    Marine refraction profiles of a very important prospective petroleum province reveal the deep structure, to the base of the sedimentary section at some 20 km depth in troughs and still deeper to the base of the crust. The general pattern of rifting and trough filling appears to have repeated through Phanerozoic history, although with the rate of sedimentation increasing with time. 15 refs., 5 figs., 1 tab.

  7. Refractive Error, Axial Length, and Relative Peripheral Refractive Error before and after the Onset of Myopia

    PubMed Central

    Mutti, Donald O.; Hayes, John R.; Mitchell, G. Lynn; Jones, Lisa A.; Moeschberger, Melvin L.; Cotter, Susan A.; Kleinstein, Robert N.; Manny, Ruth E.; Twelker, J. Daniel; Zadnik, Karla

    2009-01-01

    Purpose To evaluate refractive error, axial length, and relative peripheral refractive error before, during the year of, and after the onset of myopia in children who became myopic compared with emmetropes. Methods Subjects were 605 children 6 to 14 years of age who became myopic (at least −0.75 D in each meridian) and 374 emmetropic (between −0.25 D and + 1.00 D in each meridian at all visits) children participating between 1995 and 2003 in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study. Axial length was measured annually by A-scan ultrasonography. Relative peripheral refractive error (the difference between the spherical equivalent cycloplegic autorefraction 30° in the nasal visual field and in primary gaze) was measured using either of two autorefractors (R-1; Canon, Lake Success, NY [no longer manufactured] or WR 5100-K; Grand Seiko, Hiroshima, Japan). Refractive error was measured with the same autorefractor with the subjects under cycloplegia. Each variable in children who became myopic was compared to age-, gender-, and ethnicity-matched model estimates of emmetrope values for each annual visit from 5 years before through 5 years after the onset of myopia. Results In the sample as a whole, children who became myopic had less hyperopia and longer axial lengths than did emmetropes before and after the onset of myopia (4 years before through 5 years after for refractive error and 3 years before through 5 years after for axial length; P < 0.0001 for each year). Children who became myopic had more hyperopic relative peripheral refractive errors than did emmetropes from 2 years before onset through 5 years after onset of myopia (P < 0.002 for each year). The fastest rate of change in refractive error, axial length, and relative peripheral refractive error occurred during the year before onset rather than in any year after onset. Relative peripheral refractive error remained at a consistent level of hyperopia each

  8. Refractive index determination by coherence scanning interferometry.

    PubMed

    Yoshino, H; Kaminski, P M; Smith, R; Walls, J M; Mansfield, D

    2016-05-20

    Coherence scanning interferometry is established as a powerful noncontact, three-dimensional, metrology technique used to determine accurate surface roughness and topography measurements with subnanometer precision. The helical complex field (HCF) function is a topographically defined helix modulated by the electrical field reflectance, originally developed for the measurement of thin films. An approach to extend the capability of the HCF function to determine the spectral refractive index of a substrate or absorbing film has recently been proposed. In this paper, we confirm this new capability, demonstrating it on surfaces of silicon, gold, and a gold/palladium alloy using silica and zirconia oxide thin films. These refractive index dispersion measurements show good agreement with those obtained by spectroscopic ellipsometry. PMID:27411157

  9. Regular shock refraction in planar ideal MHD

    NASA Astrophysics Data System (ADS)

    Delmont, P.; Keppens, R.

    2010-03-01

    We study the classical problem of planar shock refraction at an oblique density discontinuity, separating two gases at rest, in planar ideal (magneto)hydrodynamics. In the hydrodynamical case, 3 signals arise and the interface becomes Richtmyer-Meshkov unstable due to vorticity deposition on the shocked contact. In the magnetohydrodynamical case, on the other hand, when the normal component of the magnetic field does not vanish, 5 signals will arise. The interface then typically remains stable, since the Rankine-Hugoniot jump conditions in ideal MHD do not allow for vorticity deposition on a contact discontinuity. We present an exact Riemann solver based solution strategy to describe the initial self similar refraction phase. Using grid-adaptive MHD simulations, we show that after reflection from the top wall, the interface remains stable.

  10. 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.

  11. [The deterioration of refractive accommodative esotropia].

    PubMed

    Yan, J; Yang, S; Wang, Y

    1995-09-01

    137 patients with refractive accommodative esotropia who were followed for at least 5 years were investigated. The results showed that in 23 of the 137 patients (16.8%) occurred the deterioration of esotropia that means esotropia can no longer be controlled by wearing a pair of complete corrective spectacles. The deterioration develops most likely in patients with delay of anti-accommodative therapy or with malfunction of binocular vision. The age of onset, refractive status and the visual acuity difference between bilateral eyes are not etiologic factors in the process of deterioration. We consider that early diagnosis of accommodative esotropia, timely prescription of optical correction and maintenance of normal binocular vision play important roles in preventing the deterioration. PMID:8706583

  12. 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.

  13. Refractive scintillation in the interstellar medium

    NASA Astrophysics Data System (ADS)

    Coles, W. A.; Rickett, B. J.; Codona, J. L.; Frehlich, R. G.

    1987-04-01

    The slow variation in the apparent intensity of pulsars on time scales of days to months was recently shown to be due to a large-scale component of interstellar scintillation (Rickett, Coles, and Bourgois). These variations are greater than one would expect if the turbulence spectrum were a simple Kolmogorov power law. It is shown that this large-scale component can be greatly enhanced when the turbulence spectrum has a limiting "inner scale" of the order of 109m. The authors present a solution for the covariance of refractive scintillation of an extended source in an extended medium. The results show that refractive scintillations are also responsible for slow variations in "low-frequency variables".

  14. Neutrino refraction by the cosmic neutrino background

    NASA Astrophysics Data System (ADS)

    Díaz, J. S.; Klinkhamer, F. R.

    2016-03-01

    We have determined the dispersion relation of a neutrino test particle propagating in the cosmic neutrino background. Describing the relic neutrinos and antineutrinos from the hot big bang as a dense medium, a matter potential or refractive index is obtained. The vacuum neutrino mixing angles are unchanged, but the energy of each mass state is modified. Using a matrix in the space of neutrino species, the induced potential is decomposed into a part which produces signatures in beta-decay experiments and another part which modifies neutrino oscillations. The low temperature of the relic neutrinos makes a direct detection extremely challenging. From a different point of view, the identified refractive effects of the cosmic neutrino background constitute an ultralow background for future experimental studies of nonvanishing Lorentz violation in the neutrino sector.

  15. Interpretation of data from uphole refraction surveys

    NASA Astrophysics Data System (ADS)

    Franklin, A. G.

    1980-06-01

    The conventional interpretation of the data from an uphole refraction survey is based on the similarity between a plot of contours drawn on uphole arrival times and a wave-front diagram, which shows successive positions of the wave front produced by a single shot location at the ground surface. However, the two are alike only when the ground consists solely of homogeneous strata, oriented either horizontally or vertically. In this report, the term 'Meissner diagram' is used for the plot of arrival times from the uphole refraction survey in order to maintain the distinction between it and a true wave-front diagram. Where departures from the case of homogeneous, horizontal strata exist, the interpretation of the Meissner diagram is not straightforward, although a partial interpretation in terms of a horizontally stratified system is usually possible. A systematic approach to the interpretation problem, making use of such a partial interpretation, is proposed.

  16. [Complications of corneal lamellar refractive surgery].

    PubMed

    Kohnen, T; Remy, M

    2015-12-01

    Techniques available for corneal lamellar refractive surgery are laser-assisted in situ keratomileusis (LASIK) using a microkeratome or femtosecond laser incision followed by excimer laser corneal ablation, and femtosecond laser-assisted refractive lenticule extraction (ReLEx). These treatments are nowadays considered to be safe and effective standard procedures for surgical correction of mild to moderate ametropia. Possible complications include too small or decentered optical zones, intraoperative flap cutting errors and postoperative inflammation (e.g. diffuse lamellar keratitis, DLK), epithelial or flap folds, epithelial ingrowths or iatrogenic ectasia. The occurrence of complications may be significantly reduced by compliance to corresponding standards of indication and treatment that are based on current scientific knowledge. PMID:26613941

  17. 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.

  18. 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.

  19. 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.

  20. Matched Index of Refraction Flow Facility

    ScienceCinema

    Mcllroy, Hugh

    2013-05-28

    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.

  1. 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.

  2. 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

  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. Atmospheric refractivity corrections in satellite laser ranging

    NASA Technical Reports Server (NTRS)

    Abshire, J. B.; Gardner, C. S.

    1985-01-01

    Atmospheric refraction can cause significant errors in satellite laser ranging (SLR) systems. There are two techniques which can be used to correct for these errors. Atmospheric models based upon surface measurements of pressure, temperature, and relative humidity have been shown by ray tracing to be accurate to within a few centimeters at 20 deg elevation angle. The residual errors in the models are thought to be primarily caused by horizontal gradients in the refractivity. Although models have been developed to predict the gradient effects, initial studies show that they can be sensitive to local topographic effects. Atmospheric turbulence can introduce random fluctuations in the refractivity, but only introduces centimeter level errors at elevation angles below 10 deg. Pulsed two-color ranging systems can directly measure the atmospheric delay in satellite ranging. These systems require mode-locked multiple-frequency lasers and streak-camera-based receivers and currently appear capable of measuring the atmospheric delay with an accuracy of 0.5 cm or better.

  5. 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.

  6. Tissue refractive index as marker of disease

    NASA Astrophysics Data System (ADS)

    Wang, Zhuo; Tangella, Krishnarao; Balla, Andre; Popescu, Gabriel

    2011-11-01

    The gold standard in histopathology relies on manual investigation of stained tissue biopsies. A sensitive and quantitative method for in situ tissue specimen inspection is highly desirable, as it would allow early disease diagnosis and automatic screening. Here we demonstrate that quantitative phase imaging of entire unstained biopsies has the potential to fulfill this requirement. Our data indicates that the refractive index distribution of histopathology slides, which contains information about the molecular scale organization of tissue, reveals prostate tumors and breast calcifications. These optical maps report on subtle, nanoscale morphological properties of tissues and cells that cannot be recovered by common stains, including hematoxylin and eosin. We found that cancer progression significantly alters the tissue organization, as exhibited by consistently higher refractive index variance in prostate tumors versus normal regions. Furthermore, using the quantitative phase information, we obtained the spatially resolved scattering mean free path and anisotropy factor g for entire biopsies and demonstrated their direct correlation with tumor presence. In essence, our results show that the tissue refractive index reports on the nanoscale tissue architecture and, in principle, can be used as an intrinsic marker for cancer diagnosis.

  7. 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. PMID:17657376

  8. Retrieval of water vapor profiles from atmospheric radio-occultations

    NASA Technical Reports Server (NTRS)

    Juarez, M. de la Torre; Nilsson, P. M.

    2002-01-01

    We illustrate a novel method to extract water vapor with high vertical resolution, using the refractivity profiles without ancillary data. We also discuss the estimated accuracies and sources of error.

  9. Using Seismic Refraction to Assess the Crustal Thickness of the Great Basin and Sierra Nevada

    NASA Astrophysics Data System (ADS)

    Heimgartner, M. N.; Louie, J. N.; Scott, J. B.; Thelen, W.; Pullammanappallil, S.; Lopez, C. T.; Coolbaugh, M. F.

    2006-12-01

    In order to assess the crustal thickness of the Great Basin in poorly constrained areas, we have completed three long-range seismic refraction experiments: the 2002 Northern Walker Lane (NWL) transect, extending from central Nevada to the eastern Sierras; the 2004 Idaho-Nevada-California (INC) experiment, running from central Nevada into Fresno, California; and the 2005 Northern-Nevada-Utah transect (NNUT), stretching from central Nevada through eastern Utah. Our refraction experiments will contribute toward a more accurate crustal model for the northern Great Basin where little previous seismic refraction control exists. The INC and NNUT experiments used a dense spacing of 400 portable seismographs and 4.5-Hz geophones. The instruments were able to record events ranging from large mine blasts to small local earthquakes. Our instruments sensed blast first arrivals out to distances of approximately 400 km. We obtained 99% data recovery and clear first arrivals across the Sierra Nevada and the northern Great Basin regions. From our INC transect, we observe an unexpectedly deep crustal root beneath the northern Sierra Nevada range (>50 km down to a Moho velocity of 7.8 km/s). From the NWL experiment, we observe anomalously thin crust over a limited region approximately 100 km wide, near Battle Mountain, NV, with a crustal thickness of 19-23 km and a southern extent limited by the INC transect. This area of thin crust correlates with regional gravity data. Our NNUT refraction experiment will better constrain crustal thickness and provide insight into the crustal-scale tectonics of the northeastern Great Basin, including the Wasatch Front and eastern Utah. These experiments are a successful demonstration that crustal refraction profiles can be obtained using mine blasts and a dense array of portable seismographs. Costly refraction shots were not needed to find crustal thicknesses, where mine blasts could be recorded. In addition, local earthquakes (approximately M2

  10. Solitary wave propagation and steering through light-induced refractive potentials

    NASA Astrophysics Data System (ADS)

    Assanto, Gaetano; Skuse, Benjamin D.; Smyth, Noel F.

    2010-06-01

    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.

  11. 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.

  12. Defocusing properties of Gaussian beams for measuring refractive index of thin transparent samples

    NASA Astrophysics Data System (ADS)

    Cervantes-L, Joel; Cywiak, Moisés; Olvera-R, Octavio; Morales, Arquímedes

    2013-11-01

    We show how the defocusing properties of Gaussian beams can be used to measure the refractive index of solutions in thin transparent samples (less than 2 mm). Additionally, it is possible to predict analytically the shape of the plot for the refractive index as a function of concentration in any range. Our theory is limited for substances whose refractive index increases with concentration. The thin sample is placed between the focusing lens and its back focal plane and the system is adjusted to best focusing conditions. As a result, changes of the refractive index of the sample cause variations of the size of the focused beam. To measure with high accuracy the size of the beam we use the homodyne knife-edge profilometer while profiling a calibrated holographic reflective grating. The recorded vertical heights of the grating provide statistical data for improving even more the accuracy of the measurements. We demonstrate that the sensitivity of the system is a function of the pitch of the grating allowing selecting the range of interest. We apply our method for glucose liquid solutions. We include analytical description of our method and experimental results.

  13. 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

    2016-08-01

    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.

  14. 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.

  15. 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

  16. 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.

  17. Refraction of nonlinear beams by localized refractive index changes in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Assanto, Gaetano; Minzoni, Antonmaria A.; Smyth, Noel F.; Worthy, Annette L.

    2010-11-01

    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.

  18. Refractive index change and curvature in shock waves by angled beam refraction

    NASA Astrophysics Data System (ADS)

    Kiefer, J. H.; Manson, A. C.

    1981-09-01

    Observations of front geometry and refractive index jump across shock waves in rare gases have been made with a new particularly simple technique. The technique involves determination of the angular deflection of a narrow laser beam intersecting the shock front at a shallow angle. Measured refractive index jumps in rare gases are in excellent agreement with those calculated using Snell's law and ideal shock theory. The apparent shock curvature is in close accord with deBoer's theory for loading pressures below 20 Torr, but above this pressure there is evidence of an indentation near tube center.

  19. Enabling novel functionality in heavily doped ZnO:Ga by nanostructuring: an efficient plasmonic refractive index sensor

    NASA Astrophysics Data System (ADS)

    Kuznetsov, Alexander S.; Schäfer, Peter; John, Wilfred; Prasai, Deepak; Sadofev, Sergey; Kalusniak, Sascha

    2016-01-01

    We demonstrate a proof-of-concept refractive index sensor based on heavily doped ZnO:Ga nanostructured in a grating configuration, which supports free space excitation of propagating surface plasmons. The bulk sensitivity of the sensor of 4.9 × 103 nm per refractive index unit, achieved in the mid-infrared spectral range with the first grating prototype, surpasses that of the noble metal counterparts by three to four times. Sensing performance is discussed in the light of numerical simulations of the spatial profile of the near field of surface plasmon polaritons.

  20. Enabling novel functionality in heavily doped ZnO:Ga by nanostructuring: an efficient plasmonic refractive index sensor.

    PubMed

    Kuznetsov, Alexander S; Schäfer, Peter; John, Wilfred; Prasai, Deepak; Sadofev, Sergey; Kalusniak, Sascha

    2016-01-15

    We demonstrate a proof-of-concept refractive index sensor based on heavily doped ZnO:Ga nanostructured in a grating configuration, which supports free space excitation of propagating surface plasmons. The bulk sensitivity of the sensor of 4.9 × 10(3) nm per refractive index unit, achieved in the mid-infrared spectral range with the first grating prototype, surpasses that of the noble metal counterparts by three to four times. Sensing performance is discussed in the light of numerical simulations of the spatial profile of the near field of surface plasmon polaritons. PMID:26629968

  1. Optical waveguiding properties and refractive index analysis of boron nitride (BN) thin films prepared by reactive ion plating

    NASA Astrophysics Data System (ADS)

    Boudiombo, J.; Boudrioua, A.; Loulergue, J. C.; Malhouitre, S.; Machet, J.

    1998-05-01

    Thin films of hexagonal boron nitride (h-BN) have been prepared using a reactive ion plating process. Investigations of guiding and optical properties of films have been performed using m-line spectroscopy. Both ordinary and extraordinary refractive indices are, respectively, determined from TE and TM mode excitation. Furthermore, refractive index profile analysis using an improved inverse WKB method reveals a gradient-like behavior indicating an optical inhomogeneity of the deposited films along the thickness. An optical anisotropy study confirms the films uniaxial nature with a birefringence, Δ n, of about 0.11.

  2. A Mechanical Analogue of the Refracting Telescope

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

    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.1 This has offered the opportunity for addressing in the classroom the basic principles explaining the operation of the telescope. When doing so, a key concept that is faced is magnification. In geometrical optics, the treatment of magnification is generally given in terms of light rays and first-order (Gaussian or paraxial) ray tracing. Computer programs are available with which the light path through the lenses and the whole telescope can be simulated.

  3. 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. PMID:19466190

  4. Prediction of refractive correction with radial keratotomy.

    PubMed

    Kremer, F B; Steer, R A

    1985-10-01

    Multiple regression analysis was employed to estimate the amount of preoperative correction required to achieve emmetropia in 129 spherical radial keratotomy procedures. Age, intraocular pressure, central corneal thickness, number of incisions, number of zones, and central optical zone size are variables that describe the amount of refractive correction required in order to achieve emmetropia. The surgical procedures from which these estimates are derived yield meaningful reductions in myopia. Recommendations for further research on the prediction of optimal response to radial keratotomy are included. PMID:4073725

  5. Femtosecond laser in refractive and cataract surgeries

    PubMed Central

    Liu, Han-Han; Hu, Ying; Cui, Hong-Ping

    2015-01-01

    In the past few years, 9 unique laser platforms have been brought to the market. As femtosecond (FS) laser-assisted ophthalmic surgery potentially improves patient safety and visual outcomes, this new technology indeed provides ophthalmologists a reliable new option. But this new technology also poses a range of new clinical and financial challenges for surgeons. We provide an overview of the evolution of FS laser technology for use in refractive and cataract surgeries. This review describes the available laser platforms and mainly focuses on discussing the development of ophthalmic surgery technologies. PMID:25938066

  6. Effects of refractive index on glories.

    PubMed

    Laven, Philip

    2008-12-01

    Atmospheric glories are caused by backscattering of sunlight from spherical droplets of water (e.g., from fog or clouds). But what would glories look like if they were caused by scattering from more exotic substances, such as clouds of ethane as found on Titan? Examining backscattering as a function of the refractive index n of spherical droplets leads to the surprising conclusion that a glory's appearance is almost independent of n (at least for 1.03

  7. Tomographic reconstruction of wet and total refractivity fields from GNSS receiver networks

    NASA Astrophysics Data System (ADS)

    Notarpietro, Riccardo; Cucca, Manuela; Gabella, Marco; Venuti, Giovanna; Perona, Giovanni

    2011-03-01

    One of the most attractive scientific issues in the use of GNSS (Global Navigation Satellite System) signals, from a meteorological point of view, is the retrieval of high resolution tropospheric water vapour maps. The real-time (or quasi real-time) knowledge of such distributions could be very useful for several applications, from operative meteorology to atmospheric modelling. Moreover, the exploitation of wet refractivity field reconstruction techniques can be used for atmospheric delay compensation purposes and, as a very promising activity, it could be applied for example to calibrate SAR or Interferometric-SAR (In-SAR) observations for land remote sensing. This is in fact one of the objectives of the European Space Agency project METAWAVE (Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water vapour Effects), in which several techniques are investigated and results were compared to identify a strategy to remove the contribution of water vapour induced propagation delays in In-SAR products. Within this project, the tomographic reconstruction of three dimensional wet refractivity fields from tropospheric delays observed by a local GNSS network (9 dual frequency GPS receivers) deployed over Como area (Italy), during 12-18 October, 2008, was performed. Despite limitations due to the network design, internal consistency tests prove the efficiency of the adopted tomographic approach: the rms of the difference between reconstructed and GNSS observed Zenith Wet Delays (ZWD) are in the order of 4 mm. A good agreement is also observed between our ZWDs and corresponding delays obtained by vertically integrating independent wet refractivity fields, taken by co-located meteorological analysis. Finally, during the observing period, reconstructed vertical wet refractivity profiles evolution reveals water vapour variations induced by simple cloud covering. Even if our main goal was to demonstrate the effectiveness in adopting tomographic

  8. Caustics in a field negatively refracted at a plane interface.

    PubMed

    Shendeleva, M L

    2008-03-01

    An electromagnetic field radiated by a line source situated near a plane interface between a medium with positive refractive index and a medium with negative refractive index is considered by using the geometrical optics approach. Rays and wave fronts of the refracted field are constructed using Fermat's principle. It is shown that the negatively refracted rays intersecting in pairs create 2-fold caustics that meet at a cusp point. The cusp of the caustic is directed towards the interface for |n| > 1 and away from the interface for |n| < 1, where n is the relative refractive index. It is also shown that wave fronts of the refracted field propagate towards the interface, in the direction from negative to positive optical path lengths. PMID:18331494

  9. Negative Refraction and Energy Funneling by Hyperbolic Materials: An Experimental Demonstration in Acoustics

    NASA Astrophysics Data System (ADS)

    García-Chocano, Victor M.; Christensen, Johan; Sánchez-Dehesa, José

    2014-04-01

    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.

  10. Tomographic reconstruction of strongly refracting fields and its application to interferometric measurement of boundary layers.

    PubMed

    Cha, S; Vest, C M

    1981-08-15

    An iterative algorithm for tomographic reconstruction of refractive-index fields from measured values of path integrals along rays which have been bent by refraction is presented. The behavior of the algorithm is studied by applying it to path length data obtained by computer simulation of experiments in which holographic or Mach-Zehnder interferograms of the field are recorded for several different viewing directions. A special form of the algorithm is also used to measure concentration profiles in the boundary layer formed at the cathode of an electrolytic cell containing ZnCl(2). The Appendix contains a discussion of series expansion techniques for reconstructing object fields from measured values of line integrals through the field. PMID:20333041

  11. Refining Sunrise/set Prediction Models by Accounting for the Effects of Refraction

    NASA Astrophysics Data System (ADS)

    Wilson, Teresa; Bartlett, Jennifer L.

    2016-01-01

    Current atmospheric models used to predict the times of sunrise and sunset have an error of one to four minutes at mid-latitudes (0° - 55° N/S). At higher latitudes, slight changes in refraction may cause significant discrepancies, including determining even whether 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. Because sunrise/set times and meteorological data from multiple locations will be necessary for a thorough investigation of the problem, we will collect this data using smartphones as part of a citizen science project. This analysis will lead to more complete models that will provide more accurate times for navigators and outdoorsman alike.

  12. 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.

  13. 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.

  14. Autonomous satellite navigation using starlight refraction angle measurements

    NASA Astrophysics Data System (ADS)

    Ning, Xiaolin; Wang, Longhua; Bai, Xinbei; Fang, Jiancheng

    2013-05-01

    An on-board autonomous navigation capability is required to reduce the operation costs and enhance the navigation performance of future satellites. Autonomous navigation by stellar refraction is a type of autonomous celestial navigation method that uses high-accuracy star sensors instead of Earth sensors to provide information regarding Earth's horizon. In previous studies, the refraction apparent height has typically been used for such navigation. However, the apparent height cannot be measured directly by a star sensor and can only be calculated by the refraction angle and an atmospheric refraction model. Therefore, additional errors are introduced by the uncertainty and nonlinearity of atmospheric refraction models, which result in reduced navigation accuracy and reliability. A new navigation method based on the direct measurement of the refraction angle is proposed to solve this problem. Techniques for the determination of the refraction angle are introduced, and a measurement model for the refraction angle is established. The method is tested and validated by simulations. When the starlight refraction height ranges from 20 to 50 km, a positioning accuracy of better than 100 m can be achieved for a low-Earth-orbit (LEO) satellite using the refraction angle, while the positioning accuracy of the traditional method using the apparent height is worse than 500 m under the same conditions. Furthermore, an analysis of the factors that affect navigation accuracy, including the measurement accuracy of the refraction angle, the number of visible refracted stars per orbit and the installation azimuth of star sensor, is presented. This method is highly recommended for small satellites in particular, as no additional hardware besides two star sensors is required.

  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. 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.

  17. Corneal polarimetry after LASIK refractive surgery

    NASA Astrophysics Data System (ADS)

    Bueno, Juan M.; Berrio, Esther; Artal, Pablo

    2006-01-01

    Imaging polarimetry provides spatially resolved information on the polarization properties of a system. In the case of the living human eye, polarization could be related to the corneal biomechanical properties, which vary from the normal state as a result of surgery or pathologies. We have used an aberro-polariscope, which we recently developed, to determine and to compare the spatially resolved maps of polarization parameters across the pupil between normal healthy and post-LASIK eyes. The depolarization distribution is not uniform across the pupil, with post-surgery eyes presenting larger levels of depolarization. While retardation increases along the radius in normal eyes, this pattern becomes irregular after LASIK refractive surgery. The maps of slow axis also differ in normal and post-surgery eyes, with a larger disorder in post-LASIK eyes. Since these changes in polarization indicate subtle structural modifications of the cornea, this approach can be useful in a clinical environment to follow the biomechanical and optical changes of the cornea after refractive surgery or for the early diagnosis of different corneal pathologies.

  18. IOL Power Calculation after Corneal Refractive Surgery

    PubMed Central

    De Bernardo, Maddalena; Capasso, Luigi; Caliendo, Luisa; Rosa, Nicola

    2014-01-01

    Purpose. To describe the different formulas that try to overcome the problem of calculating the intraocular lens (IOL) power in patients that underwent corneal refractive surgery (CRS). Methods. A Pubmed literature search review of all published articles, on keyword associated with IOL power calculation and corneal refractive surgery, as well as the reference lists of retrieved articles, was performed. Results. A total of 33 peer reviewed articles dealing with methods that try to overcome the problem of calculating the IOL power in patients that underwent CRS were found. According to the information needed to try to overcome this problem, the methods were divided in two main categories: 18 methods were based on the knowledge of the patient clinical history and 15 methods that do not require such knowledge. The first group was further divided into five subgroups based on the parameters needed to make such calculation. Conclusion. In the light of our findings, to avoid postoperative nasty surprises, we suggest using only those methods that have shown good results in a large number of patients, possibly by averaging the results obtained with these methods. PMID:25136609

  19. The refractive index of reciprocal electromagnetic media

    NASA Astrophysics Data System (ADS)

    McCall, Martin W.; Kinsler, Paul; Topf, Renè D. M.

    2016-04-01

    We study the electromagnetics of media described by identical inhomogeneous relative dielectric and magnetic tensors, {\\boldsymbol{ε }}={\\boldsymbol{μ }}. Such media occur generically as spatial transformation media, i.e. electromagnetic media that are defined by a deformation of space. We show that such media are completely described by a refractive index n({r},\\hat{{s}}) that depends on position {r} and direction \\hat{{s}}, but is independent of polarization. The phase surface is always ellipsoidal, and n({r},\\hat{{s}}) is therefore represented by the radius vector to the surface of the ellipsoid. We apply our method to calculate the angular dependence of the refractive index in the well-studied cylindrical cloak and to a new kind of structurally chiral medium induced by a twist deformation. By way of a simple example we also show that media for which {\\boldsymbol{ε }}={\\boldsymbol{μ }} do not in general preserve the impedance properties of vacuum. The implications of this somewhat surprising conclusion for the field of transformation optics are discussed.

  20. 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

  1. Effect of atmospheric refraction on radiative transfer in visible and near-infrared band: Model development, validation, and applications

    NASA Astrophysics Data System (ADS)

    Hu, Shuai; Gao, Tai-chang; Li, Hao; Liu, Lei; Liu, Xi-chuan; Zhang, Ting; Cheng, Tian-ji; Li, Wan-tong; Dai, Zhong-hua; Su, Xiaojian

    2016-03-01

    Refraction is an important factor influencing radiative transfer since it can modify the propagation trajectory and polarization states of lights; therefore, it is necessary to quantitively evaluate the effect of atmospheric refraction on radiative transfer process. To this end, a new atmospheric radiative transfer model including refraction process is proposed. The model accuracy is validated against benchmark results, literature results, and well-tested radiative transfer models such as discrete coordinate method and RT3/PolRadtran. The impact of atmospheric refraction on both polarized radiance and fluxes is discussed for pure Rayleigh scattering atmosphere, atmosphere with aerosol, and cloud. The results show that atmospheric refraction has a significant influence on both the radiance and polarization states of diffuse light, where the relative change of the radiance of reflected light and transmitted light due to refraction can achieve 6.3% and 7.4% for Rayleigh scattering atmosphere, 7.2% and 7.8% for atmosphere with aerosol, and 6.2% and 6.8% for cloudy atmosphere, respectively. The relative change of the degree of polarization ranges from near zero in the horizon to 9.5% near neutral points. The angular distribution pattern of the relative change of the radiance for atmosphere with aerosol and cloud is very similar to that for pure Rayleigh scattering case, where its magnitude decreases gradually with the increasing of zenith angle for reflected light; but for transmitted light, the variation characteristics is opposite. The impact of refraction is gradually enhanced with the increasing of solar zenith angles and the optical depth of aerosol and cloud. As the wavelength of incident light increases, the impact declines rapidly for Rayleigh scattering medium. The relative change of the fluxes due to refraction is most notable for Middle Latitude Winter profile (about 8.2043% and 7.3225% for the transmitted and reflected light, respectively, at 0.35 µm). With

  2. Comparison of Ocular Monochromatic Higher-order Aberrations in Normal Refractive Surgery Candidates of Arab and South Asian Origin

    PubMed Central

    Prakash, Gaurav; Srivastava, Dhruv; Choudhuri, Sounak; Bacero, Ruthchel

    2016-01-01

    Purpose: To compare the ocular monochromatic higher-order aberration. (HOA) profile in normal refractive surgery candidates of Arab and South Asian origin. Methods: 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. Results: 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, Z3−1,31, Z4−4, Z4−2, Z40, Z44, 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). Conclusions: 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. PMID:26957850

  3. 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

  4. Floquet-Bloch analysis of refracting Huygens metasurfaces

    NASA Astrophysics Data System (ADS)

    Epstein, Ariel; Eleftheriades, George V.

    2014-12-01

    We investigate the response of passive lossless Huygens metasurfaces (HMS), designed to implement a prescribed refraction, to arbitrary plane-wave excitations. Applying a rigorous Floquet-Bloch (FB) analysis of the cotangent electric and magnetic surface reactance modulations, we discover that the scattered FB modes follow an extraordinary ray-optical model. According to this model, the HMS can be replaced by a virtual region of constant wave impedance; incident power is incoupled into this virtual Fabry-Pérot etalon, gradually leaking to successively higher-order FB modes. Analytical closed-form expressions are derived for the FB coefficients, indicating that the first FB mode in transmission is always dominant; this clarifies previous experimental findings which implied that the HMS retained its functionality over a broad angular range. Furthermore, we point out the implementation problems inherent in the cotangent function and offer a simple, realizable form of the reactive modulation which does not significantly deteriorate the HMS performance. These results provide fundamental physical insight into the working mechanism of passive lossless Huygens metasurfaces in general, revealing a new degree of freedom which enables control of the transmitted field amplitude: the virtual region wave impedance. Importantly, the implied broad acceptance angle of the HMS may be harnessed for synthesis of low-profile multifunctional devices, designed to respond to several excitations with reduced reflections.

  5. Light field optical flow for refractive surface reconstruction

    NASA Astrophysics Data System (ADS)

    Iffa, Emishaw; Wetzstein, Gordon; Heidrich, Wolfgang

    2012-10-01

    This paper discusses a method to reconstruct a transparent ow surface from single camera shot with the aid of a Micro-lens array. An intentionally prepared high frequency background which is placed behind the refractive flow is captured and a curl-free optical flow algorithm is applied between pairs of images taken by different micro-lenses. The computed raw optical ow vector is a blend of motion parallax and background deformation vector due to the underlying flow. Subtracting the motion parallax, which is obtained by calibration, from the total op- optical flow vector yields the background deformation vector. The deflection vectors on each images are used to reconstruct the flow profile. A synthetic data set of fuel injection was used to evaluate the accuracy of the proposed algorithm and good agreement was achieved between the test and reconstructed data. Finally, real light field data of hot air created by a lighter flame is used to reconstruct and show a hot air plume surface.

  6. Microwave gain medium with negative refractive index

    NASA Astrophysics Data System (ADS)

    Ye, Dexin; Chang, Kihun; Ran, Lixin; Xin, Hao

    2014-12-01

    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.

  7. Time-driven superoscillations with negative refraction.

    PubMed

    Dubois, M; Bossy, E; Enoch, S; Guenneau, S; Lerosey, G; Sebbah, P

    2015-01-01

    The flat-lens concept based on negative refraction proposed by Veselago in 1968 has been mostly investigated in the monochromatic regime. It was recently recognized that time development of the superlensing effect discovered in 2000 by Pendry is yet to be assessed and may spring surprises: Time-dependent illumination could improve the spatial resolution of the focusing. We investigate dynamics of flexural wave focusing by a 45°-tilted square lattice of circular holes drilled in a duralumin plate. Time-resolved experiments reveal that the focused image shrinks with time below the diffraction limit, with a lateral resolution increasing from 0.8λ to 0.35λ, whereas focusing under harmonic excitation remains diffraction limited. Modal analysis reveals the role in pulse reconstruction of radiating lens resonances, which repeatedly self-synchronize at the focal spot to shape a superoscillating field. PMID:25615470

  8. Nanofocusing Parabolic Refractive X-Ray Lenses

    SciTech Connect

    Schroer, C.G.; Kuhlmann, M.; Hunger, U.T.; Guenzler, T.F.; Kurapova, O.; Feste, S.; Lengeler, B.; Drakopoulos, M.; Somogyi, A.; Simionovici, A. S.; Snigirev, A.; Snigireva, I.

    2004-05-12

    Parabolic refractive x-ray lenses with short focal distance can generate intensive hard x-ray microbeams with lateral extensions in the 100nm range even at short distance from a synchrotron radiation source. We have fabricated planar parabolic lenses made of silicon that have a focal distance in the range of a few millimeters at hard x-ray energies. In a crossed geometry, two lenses were used to generate a microbeam with a lateral size of 330nm by 110nm at 25keV in a distance of 41.8m from the synchrotron radiation source. First microdiffraction and fluorescence microtomography experiments were carried out with these lenses. Using diamond as lens material, microbeams with lateral size down to 20nm and below are conceivable in the energy range from 10 to 100keV.

  9. Engineer's Refractive Effects Prediction System (EREPS)

    NASA Astrophysics Data System (ADS)

    Hitney, Herbert V.

    1989-09-01

    In recent years, electromagnetic tactical decision aids were developed to assess environmental effects on the performance of operational systems such as shipboard radars. In general, these systems have performed well and are now routinely used by operational forces to optimize their use of sensors and deployment of forces. In many cases, the existing tactical decision aid software was taken and used to assess the performance of proposed new sensors. Since the original software was not designed for this purpose, many deficiencies in such a use were soon identified. For example, most engineers prefer to graphically compare performance results as a single design parameter, such as radar pulse length, is varied over a range of possible values. Also, in designing a new system, one is usually more interested in the long-term statistical performance than in single-event performance that the tactical decision aids are normally designed to assess. The Engineer's Refractive Effects Prediction System (EREPS) is a recent development effort tailored to engineering uses and based on the propagation models of the Integrated Refractive Effects Prediction System (IREPS). EREPS is hosted on IBM PC computers for maximum availability to the engineering community, and was developed using interactive graphics displays for optimum comparison studies. The models are designed in such a way as to give results within a few seconds to allow multiple design trade-off studies to be easily performed. EREPS Revision 1.00 was distributed to interested users in the summer of 1988 and is currently being revised for a summer 1989 distribution. Existing and planned capabilities will be presented along with some examples of applications.

  10. 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…

  11. 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…

  12. 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)

  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. 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)

  15. 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.

  16. 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.

  17. 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)

  18. 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.

  19. 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…

  20. A covariant approach to the gravitational refractive index

    NASA Astrophysics Data System (ADS)

    Simaciu, I.; Ionescu-Pallas, N.

    A covariant formulation of the Maxwell's field equations in a gravitational field, based on the bimetric interpretation of general relativity Theory, is given. The purpose of the work is in adequate definition of the gravitational refractive index in agreement with both wave equations propagation and a relationship between refractive index and the Minkovskian tensor of gravitational permitivity.

  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. Atmospheric Refractive Electromagnetic Wave Bending and Propagation Delay

    NASA Astrophysics Data System (ADS)

    Mangum, Jeffrey G.; Wallace, Patrick

    2015-01-01

    In this tutorial we summarize the physics and mathematics behind refractive electromagnetic wave bending and delay. Refractive bending and delay through the Earth's atmosphere at both radio/millimetric and optical/IR wavelengths are discussed, but with most emphasis on the former, and with Atacama Large Millimeter Array (ALMA) applications in mind. As modern astronomical measurements often require subarcsecond position accuracy, care is required when selecting refractive bending and delay algorithms. For the spherically-uniform model atmospheres generally used for all refractive bending and delay algorithms, positional accuracies lsim1'' are achievable when observing at zenith angles lsim75°. A number of computationally economical approximate methods for atmospheric refractive bending and delay calculation are presented, appropriate for astronomical observations under these conditions. For observations under more realistic atmospheric conditions, for zenith angles lsim75°, or when higher positional accuracy is required, more rigorous refractive bending and delay algorithms must be employed. For accurate calculation of the refractive bending, we recommend the Auer and Standish method, using numerical integration to ray-trace through a two-layer model atmosphere, with an atmospheric model determination of the atmospheric refractivity. For the delay calculation we recommend numerical integration through a model atmosphere.

  3. Comparison Between Radar and Automatic Weather Station Refractivity Variability

    NASA Astrophysics Data System (ADS)

    Hallali, Ruben; Dalaudier, Francis; Parent du Chatelet, Jacques

    2016-03-01

    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.

  4. 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.

  5. 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].

  6. Elliptical-core two mode fiber sensors and devices incorporating photoinduced refractive index gratings

    NASA Technical Reports Server (NTRS)

    Greene, Jonathan A.; Miller, Mark S.; Starr, Suzanne E.; Fogg, Brian R.; Murphy, Kent A.; Claus, Richard O.; Vengsarkar, Ashish M.

    1991-01-01

    Results of experiments performed using germanium-doped, elliptical core, two-mode optical fibers whose sensitivity to strain was spatially varied through the use of chirped, refractive-index gratings permanently induced into the core using Argon-ion laser light are presented. This type of distributed sensor falls into the class of eighted-fiber sensors which, through a variety of means, weight the strain sensitivity of a fiber according to a specified spatial profile. We describe results of a weighted-fiber vibration mode filter which successfully enhances the particular vibration mode whose spatial profile corresponds to the profile of the grating chirp. We report on the high temperature survivability of such grating-based sensors and discuss the possibility of multiplexing more than one sensor within a single fiber.

  7. 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.

  8. 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.

  9. Calculating the surgically induced refractive change following ocular surgery.

    PubMed

    Holladay, J T; Cravy, T V; Koch, D D

    1992-09-01

    Calculating the surgically induced refractive change following ocular surgery is important for evaluating the results of keratore-fractive procedures, smaller incisions and various wound closures for cataract surgery, and the effect of suturing techniques and suture removal following corneal transplant surgery. We present a ten-step method of calculating the spherical- and cylindrical-induced refractive change in a manner suitable for a programmable calculator or personal computer. Several applications are given including (1) adding the overrefraction to the spectacle correction, (2) determining the surgically induced refractive change from the preoperative and postoperative refractions, (3) determining the surgically induced refractive change from the K-readings, (4) rotating axes, (5) determining the power at meridians oblique to the principal meridians of a spherocylinder, (6) determining the coupling ratio, and (7) averaging axes. Standard methods for calculating and reporting aggregate results are also given. PMID:1403745

  10. Optimization of refractive liquid crystal lenses using an efficient multigrid simulation.

    PubMed

    Milton, Harry; Brimicombe, Paul; Morgan, Philip; Gleeson, Helen; Clamp, John

    2012-05-01

    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. PMID:22565739

  11. A numerical approach to sound levels in near-surface refractive shadows.

    PubMed

    Cheinet, Sylvain

    2012-03-01

    The present study formulates a consistent method to simulate the outdoor, near-surface sound propagation through realistic refractive conditions. The correlated atmospheric stratification and turbulence properties are derived from standard meteorological quantities through flux-profile similarity relationships. The propagation of a monochromatic sound field is simulated in presence of the turbulence and stratification effects and an impedance ground. The propagation model uses a numerical solution of a second-order moment parabolic equation, which is introduced and evaluated. The so-formed coupled atmospheric-acoustic model is used to systematically investigate the sound levels in near-surface refractive shadows. In an illustrative propagation scenario, the shadow zone sound levels are predicted to show significant variations with the meteorological conditions. Specifically, the sound levels decrease with the adverse wind, as a consequence of enhanced mean upward refraction. Conversely, they increase with the absolute value of the surface heat flux, as a consequence of enhanced turbulence scattering. Implications for the assessment of the sound levels in shadow zones are discussed. PMID:22423692

  12. Influence of uncorrected refractive error and unmet refractive error on visual impairment in a Brazilian population

    PubMed Central

    2014-01-01

    Background 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. Methods 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. Results 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. Conclusion RE is an important cause of reversible blindness and low vision in the Brazilian population. PMID:24965318

  13. 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.

  14. Crustal structure in the eastern Colorado Plateaus Provence from seismic-refraction measurements

    USGS Publications Warehouse

    Roller, John C.

    1964-01-01

    A reversed seismic-refraction profile was recorded in the Colorado Plateaus Province from Hanksville, Utah, to Chinle, Arizona, The velocity of Pg is 6.2 km/sec, and the true velocity of Pn is 7.8 km/sec, Waves identified as reflections indicate that an intermediate layer in the crust has a velocity of approximately 6.8 km/sec. Thickness of the crust is 43 km at Chinle and 40 km at Hanksville. The Pn velocity in the Colorado Plateaus Province is the same as that in the Basin and Range Province, but is significantly lower than Pn in the High Plains of Colorado.

  15. 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

  16. 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. PMID:25597549

  17. Recursive Bayesian electromagnetic refractivity estimation from radar sea clutter

    NASA Astrophysics Data System (ADS)

    Vasudevan, Sathyanarayanan; Anderson, Richard H.; Kraut, Shawn; Gerstoft, Peter; Rogers, L. Ted; Krolik, Jeffrey L.

    2007-04-01

    Estimation of the range- and height-dependent index of refraction over the sea surface facilitates prediction of ducted microwave propagation loss. In this paper, refractivity estimation from radar clutter returns is performed using a Markov state space model for microwave propagation. Specifically, the parabolic approximation for numerical solution of the wave equation is used to formulate the refractivity from clutter (RFC) problem within a nonlinear recursive Bayesian state estimation framework. RFC under this nonlinear state space formulation is more efficient than global fitting of refractivity parameters when the total number of range-varying parameters exceeds the number of basis functions required to represent the height-dependent field at a given range. Moreover, the range-recursive nature of the estimator can be easily adapted to situations where the refractivity modeling changes at discrete ranges, such as at a shoreline. A fast range-recursive solution for obtaining range-varying refractivity is achieved by using sequential importance sampling extensions to state estimation techniques, namely, the forward and Viterbi algorithms. Simulation and real data results from radar clutter collected off Wallops Island, Virginia, are presented which demonstrate the ability of this method to produce propagation loss estimates that compare favorably with ground truth refractivity measurements.

  18. Refractive Errors Affect the Vividness of Visual Mental Images

    PubMed Central

    Palermo, Liana; Nori, Raffaella; Piccardi, Laura; Zeri, Fabrizio; Babino, Antonio; Giusberti, Fiorella; Guariglia, Cecilia

    2013-01-01

    The hypothesis that visual perception and mental imagery are equivalent has never been explored in individuals with vision defects not preventing the visual perception of the world, such as refractive errors. Refractive error (i.e., myopia, hyperopia or astigmatism) is a condition where the refracting system of the eye fails to focus objects sharply on the retina. As a consequence refractive errors cause blurred vision. We subdivided 84 individuals according to their spherical equivalent refraction into Emmetropes (control individuals without refractive errors) and Ametropes (individuals with refractive errors). Participants performed a vividness task and completed a questionnaire that explored their cognitive style of thinking before their vision was checked by an ophthalmologist. Although results showed that Ametropes had less vivid mental images than Emmetropes this did not affect the development of their cognitive style of thinking; in fact, Ametropes were able to use both verbal and visual strategies to acquire and retrieve information. Present data are consistent with the hypothesis of equivalence between imagery and perception. PMID:23755186

  19. Objective and Subjective Refractive Error Measurements in Monkeys

    PubMed Central

    Hung, Li-Fang; Ramamirtham, Ramkumar; Wensveen, Janice M.; Harwerth, Ronald S.; Smith, Earl L.

    2011-01-01

    Purpose To better understand the functional significance of refractive-error measures obtained using common objective methods in laboratory animals, we compared objective and subjective measures of refractive error in adolescent rhesus monkeys. Methods The subjects were 20 adolescent monkeys. Spherical-equivalent spectacle-plane refractive corrections were measured by retinoscopy and autorefraction while the animals were cyclopleged and anesthetized. The eye’s axial dimensions were measured by A-Scan ultrasonography. Subjective measures of the eye’s refractive state, with and without cycloplegia, were obtained using psychophysical methods. Specifically, we measured spatial contrast sensitivity as a function of spectacle lens power for relatively high spatial frequency gratings. The lens power that produced the highest contrast sensitivity was taken as the subjective refraction. Results Retinoscopy and autorefraction consistently yielded higher amounts of hyperopia relative to subjective measurements obtained with or without cycloplegia. The subjective refractions were not affected by cycloplegia and on average were 1.42 ± 0.61 D and 1.24 ± 0.62 D less hyperopic than the retinoscopy and autorefraction measurements, respectively. Repeating the retinoscopy and subjective measurements through 3 mm artificial pupils produced similar differences. Conclusions The results show that commonly used objective methods for assessing refractive errors in monkeys significantly overestimate the degree of hyperopia. It is likely that multiple factors contributed to the hyperopic bias associated with these objective measurements. However, the magnitude of the hyperopic bias was in general agreement with the “small-eye artifact” of retinoscopy. PMID:22198796

  20. Refractive Error Evaluation in Eccentric Photorefracation

    NASA Astrophysics Data System (ADS)

    Baker, K.; Tan, B.; Shi, L.; Chen, Y.; Lewis, J. W. L.

    2007-11-01

    Eccentric photorefraction (EPR) is a technique to measure eye refractive errors (RE) particularly in non-cooperative children. A camera and a decentered light source are used to illuminate eyes and photograph the reflex. Recently the National Eye Institute VIP study examined 10 methods to screen the crucial children eye disorders including RE. The 3 EPR based devices were found to have lower detection sensitivities. The deficiency is inherent in the current optical designs and a lack of knowledge of parameters that influence RE analysis. The new EPR experimental design includes multi-eccentric-meridian illuminations, pupil finding algorithm, and feedback loop data acquisition. NIR is used to prevent chromatic aberration. A novel integrated intensity analysis is developed to control multiple intraocular scattering/reflection. The RE is calculated from the 21 normalized related intensities of the 2-D array illuminations. Using computer eye modeling and simulations, error analysis is performed for monochromatic aberrations and eye orientation. Experimental data comparison is obtained from a physical model eye.

  1. Analysis of critically refracted longitudinal waves

    SciTech Connect

    Pei, Ning Bond, Leonard J.

    2015-03-31

    Fabrication processes, such as, welding, forging, and rolling can induce residual stresses in metals that will impact product performance and phenomena such as cracking and corrosion. To better manage residual stress tools are needed to map their distribution. The critically refracted ultrasonic longitudinal (LCR) wave is one such approach that has been used for residual stress characterization. It has been shown to be sensitive to stress and less sensitive to the effects of the texture of the material. Although the LCR wave is increasingly widely applied, the factors that influence the formation of the LCR beam are seldom discussed. This paper reports a numerical model used to investigate the transducers' parameters that can contribute to the directionality of the LCR wave and hence enable performance optimization when used for industrial applications. An orthogonal test method is used to study the transducer parameters which influence the LCR wave beams. This method provides a design tool that can be used to study and optimize multiple parameter experiments and it can identify which parameter or parameters are of most significance. The simulation of the sound field in a 2-D 'water-steel' model is obtained using a Spatial Fourier Analysis method. The effects of incident angle, standoff, the aperture and the center frequency of the transducer were studied. Results show that the aperture of the transducer, the center frequency and the incident angle are the most important factors in controlling the directivity of the resulting LCR wave fields.

  2. Climate Absolute Radiance and Refractivity Observatory (CLARREO)

    NASA Technical Reports Server (NTRS)

    Leckey, John P.

    2015-01-01

    The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a mission, led and developed by NASA, that will measure a variety of climate variables with an unprecedented accuracy to quantify and attribute climate change. CLARREO consists of three separate instruments: an infrared (IR) spectrometer, a reflected solar (RS) spectrometer, and a radio occultation (RO) instrument. The mission will contain orbiting radiometers with sufficient accuracy, including on orbit verification, to calibrate other space-based instrumentation, increasing their respective accuracy by as much as an order of magnitude. The IR spectrometer is a Fourier Transform spectrometer (FTS) working in the 5 to 50 microns wavelength region with a goal of 0.1 K (k = 3) accuracy. The FTS will achieve this accuracy using phase change cells to verify thermistor accuracy and heated halos to verify blackbody emissivity, both on orbit. The RS spectrometer will measure the reflectance of the atmosphere in the 0.32 to 2.3 microns wavelength region with an accuracy of 0.3% (k = 2). The status of the instrumentation packages and potential mission options will be presented.

  3. Analysis of critically refracted longitudinal waves

    NASA Astrophysics Data System (ADS)

    Pei, Ning; Bond, Leonard J.

    2015-03-01

    Fabrication processes, such as, welding, forging, and rolling can induce residual stresses in metals that will impact product performance and phenomena such as cracking and corrosion. To better manage residual stress tools are needed to map their distribution. The critically refracted ultrasonic longitudinal (LCR) wave is one such approach that has been used for residual stress characterization. It has been shown to be sensitive to stress and less sensitive to the effects of the texture of the material. Although the LCR wave is increasingly widely applied, the factors that influence the formation of the LCR beam are seldom discussed. This paper reports a numerical model used to investigate the transducers' parameters that can contribute to the directionality of the LCR wave and hence enable performance optimization when used for industrial applications. An orthogonal test method is used to study the transducer parameters which influence the LCR wave beams. This method provides a design tool that can be used to study and optimize multiple parameter experiments and it can identify which parameter or parameters are of most significance. The simulation of the sound field in a 2-D "water-steel" model is obtained using a Spatial Fourier Analysis method. The effects of incident angle, standoff, the aperture and the center frequency of the transducer were studied. Results show that the aperture of the transducer, the center frequency and the incident angle are the most important factors in controlling the directivity of the resulting LCR wave fields.

  4. Failure Analysis of Sapphire Refractive Secondary Concentrators

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Quinn, George D.

    2009-01-01

    Failure analysis was performed on two sapphire, refractive secondary concentrators (RSC) that failed during elevated temperature testing. Both concentrators failed from machining/handling damage on the lens face. The first concentrator, which failed during testing to 1300 C, exhibited a large r-plane twin extending from the lens through much of the cone. The second concentrator, which was an attempt to reduce temperature gradients and failed during testing to 649 C, exhibited a few small twins on the lens face. The twins were not located at the origin, but represent another mode of failure that needs to be considered in the design of sapphire components. In order to estimate the fracture stress from fractographic evidence, branching constants were measured on sapphire strength specimens. The fractographic analysis indicated radial tensile stresses of 44 to 65 MPa on the lens faces near the origins. Finite element analysis indicated similar stresses for the first RSC, but lower stresses for the second RSC. Better machining and handling might have prevented the fractures, however, temperature gradients and resultant thermal stresses need to be reduced to prevent twinning.

  5. Variable thickness double-refracting plate

    DOEpatents

    Hadeishi, Tetsuo

    1976-01-01

    This invention provides an A.C., cyclic, current-controlled, phase retardation plate that uses a magnetic clamp to produce stress birefringence. It was developed for an Isotope-Zeeman Atomic Absorption Spectrometer that uses polarization modulation to effect automatic background correction in atomic absorption trace-element measurements. To this end, the phase retardation plate of the invention is a variable thickness, photoelastic, double-refracting plate that is alternately stressed and released by the magnetic clamp selectively to modulate specific components selected from the group consisting of circularly and plane polarized Zeeman components that are produced in a dc magnetic field so that they correspond respectively to Zeeman reference and transmission-probe absorption components. The polarization modulation changes the phase of these polarized Zeeman components, designated as .sigma. reference and .pi. absorption components, so that every half cycle the components change from a transmission mode to a mode in which the .pi. component is blocked and the .sigma. components are transmitted. Thus, the Zeeman absorption component, which corresponds in amplitude to the amount of the trace element to be measured in a sample, is alternately transmitted and blocked by a linear polarizer, while the circularly polarized reference components are continuously transmitted thereby. The result is a sinusoidally varying output light amplitude whose average corresponds to the amount of the trace element present in the sample.

  6. Computed tomography of refractive index by low-coherence interferometry

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Ma, Zhenhe; Zhou, Hongxian

    2015-03-01

    We present a 3D imaging system for simultaneously imaging the distributions of refractive index and optical absorption using a transmission Fourier-domain low-coherence interferometer. The forward-scattering light travelling through a sample interferes with a reference light beam. The projections of refractive index and optical absorption within the sample are calculated from measured interference fringes. We acquire the projections at sufficient angular views and reconstruct the distributions of refractive index and optical absorption using the filter back-projection algorithm. The proposed method is experimentally verified by using a plastic tube phantom.

  7. Refractive index and temperature nanosensor with plasmonic waveguide system

    NASA Astrophysics Data System (ADS)

    Kong, Yan; Qiu, Peng; Wei, Qi; Quan, Wei; Wang, Shouyu; Qian, Weiying

    2016-07-01

    A surface plasmon polariton sensor consisting of two metal-insulator-metal waveguides and a transverse rectangular resonator is proposed. Both refractive index and temperature sensing characteristics are analyzed by investigating the transmission spectra which demonstrates that the transmission peak wavelength shifting satisfies linear relation with environmental refractive index and temperature, respectively. The proposed design provides high refractive index and temperature sensitivity as 3.38×106%/RIU and 82%/K estimated by integrated response of the sensor, and owns the potentials for high-throughput array sensing. It is believed that the nanoscale sensor can be applied in spot detection for high speed multi-parameter sensing and accurate measurements.

  8. Black and gray Helmholtz-Kerr soliton refraction

    SciTech Connect

    Sanchez-Curto, Julio; Chamorro-Posada, Pedro; McDonald, Graham S.

    2011-01-15

    Refraction of black and gray solitons at boundaries separating different defocusing Kerr media is analyzed within a Helmholtz framework. A universal nonlinear Snell's law is derived that describes gray soliton refraction, in addition to capturing the behavior of bright and black Kerr solitons at interfaces. Key regimes, defined by beam and interface characteristics, are identified, and predictions are verified by full numerical simulations. The existence of a unique total nonrefraction angle for gray solitons is reported; both internal and external refraction at a single interface is shown possible (dependent only on incidence angle). This, in turn, leads to the proposal of positive or negative lensing operations on soliton arrays at planar boundaries.

  9. Studies of atmospheric refraction effects on laser data

    NASA Technical Reports Server (NTRS)

    Dunn, P. J.; Pearce, W. A.; Johnson, T. S.

    1982-01-01

    The refraction effect from three perspectives was considered. An analysis of the axioms on which the accepted correction algorithms were based was the first priority. The integrity of the meteorological measurements on which the correction model is based was also considered and a large quantity of laser observations was processed in an effort to detect any serious anomalies in them. The effect of refraction errors on geodetic parameters estimated from laser data using the most recent analysis procedures was the focus of the third element of study. The results concentrate on refraction errors which were found to be critical in the eventual use of the data for measurements of crustal dynamics.

  10. Refractive phenomena in the shock wave dispersion with variable gradients

    SciTech Connect

    Markhotok, A.; Popovic, S.

    2010-06-15

    In this article the refraction effects in the weak shock wave (SW) dispersion on an interface with a temperature variation between two mediums are described. In the case of a finite-gradient boundary, the effect of the SW dispersion is remarkably stronger than in the case of a step change in parameters. In the former case the vertical component of velocity for the transmitted SW (the refraction effect) must be taken into account. Results of comparative calculations based on the two-dimensional model corrected for the refraction effect show significant differences in the shapes of the dispersed SW fronts.

  11. Polarized light transport in refractive weak scattering media.

    PubMed

    Soloviev, Vadim Y

    2016-07-01

    This paper is devoted to modeling of the light transport in refractive and weak scattering media by means of the vector radiative transfer equation. In refractive media polarization of light depends not only on the law of scattering but also on the refractive index distribution and can change along curved light trajectories according to the Rytov law of the polarization ellipse rotation. Results of numerical simulations are presented in the form of CCD camera images, which is how data are acquired in tomographic imaging experiments. PMID:27409689

  12. Using neural nets to measure ocular refractive errors: a proposal

    NASA Astrophysics Data System (ADS)

    Netto, Antonio V.; Ferreira de Oliveira, Maria C.

    2002-12-01

    We propose the development of a functional system for diagnosing and measuring ocular refractive errors in the human eye (astigmatism, hypermetropia and myopia) by automatically analyzing images of the human ocular globe acquired with the Hartmann-Schack (HS) technique. HS images are to be input into a system capable of recognizing the presence of a refractive error and outputting a measure of such an error. The system should pre-process and image supplied by the acquisition technique and then use artificial neural networks combined with fuzzy logic to extract the necessary information and output an automated diagnosis of the refractive errors that may be present in the ocular globe under exam.

  13. Studies of atmospheric refraction effects on laser data

    NASA Astrophysics Data System (ADS)

    Dunn, P. J.; Pearce, W. A.; Johnson, T. S.

    1982-06-01

    The refraction effect from three perspectives was considered. An analysis of the axioms on which the accepted correction algorithms were based was the first priority. The integrity of the meteorological measurements on which the correction model is based was also considered and a large quantity of laser observations was processed in an effort to detect any serious anomalies in them. The effect of refraction errors on geodetic parameters estimated from laser data using the most recent analysis procedures was the focus of the third element of study. The results concentrate on refraction errors which were found to be critical in the eventual use of the data for measurements of crustal dynamics.

  14. Refractive effects from VHF to EHF. Part A: Propagation Mechanisms

    NASA Astrophysics Data System (ADS)

    Hitney, Herbert V.

    1994-09-01

    Radio wave propagation in the very high frequency (VHF) to extremely high frequency (EHF) bands at low elevation angles and near the earth's surface is almost always affected by refraction. This lecture details these effects and the various methods used to model them, from simple effective-earth-radius factors for standard refraction to parabolic-equation methods for range-dependent ducting environments. Refraction and Snell's law are discussed and standard and nonstandard propagation mechanisms are defined. To establish the significance of nonstandard propagation effects, some statistics on the occurrence of ducting around the world are presented.

  15. A novel acousto-optic modulation-deflection mechanism using refractive index grating as graded index beam router

    NASA Astrophysics Data System (ADS)

    Jangjoo, Alireza; Reza Baezzat, Mohammad; Razavizadeh, Ahmad

    2014-03-01

    A novel acousto-optic modulation mechanism will be addressed in this paper. Focused Gaussian beam passing through acousto-optic media experiences different refractive index regions arising from acoustic waves generated by ultrasonic source. In this way according to the snell's law of refraction the beam propagation path will be altered when these periodic traveling waves reach the incoming radiation where a typical p-n junction photodiode located inside the rising or falling lobe of the undiffracted Gaussian beam senses these small lateral deflections. Due to small variations of the refractive index the magnitude of deflection will be up to tens of micron outside the modulator. Hence, sharp intensity gradient is required for detecting such small beam movements by appropriate lens configuration to focus the Gaussian profile on the detector junction area. In the other words intensity profile of zero order beam oscillates proportional to the time dependent amplitude of the acoustic waves versus previous methods that intensity of diffracted beam changes with applied ultrasonic intensity. The extracted signal properties depend on the beam collimation, quality of beam profile and depth of focus inside the modulator. The first experimental approach was proceeded using a collimated 532 nm diode laser source (TEM00), distilled water as interaction media and 10 MHz transducer as ultrasonic generator where a cylindrical glass column with input-output flat windows was used for liquid support. The present method has advantages over common acoustooptical techniques as low cost, simplicity of operation, direct modulation of the signal and minimum alignment requirement.

  16. Refractive cylinder outcomes after calculating toric intraocular lens cylinder power using total corneal refractive power

    PubMed Central

    Davison, James A; Potvin, Richard

    2015-01-01

    Purpose To determine whether the total corneal refractive power (TCRP) value, which is based on measurement of both anterior and posterior corneal astigmatism, is effective for toric intraocular lens (IOL) calculation with AcrySof® Toric IOLs. Patients and methods A consecutive series of cataract surgery cases with AcrySof toric IOL implantation was studied retrospectively. The IOLMaster® was used for calculation of IOL sphere, the Pentacam® TCRP 3.0 mm apex/ring value was used as the keratometry input to the AcrySof Toric IOL Calculator and the VERION™ Digital Marker for surgical orientation. The keratometry readings from the VERION reference unit were recorded but not used in the actual calculation. Vector differences between expected and actual residual refractive cylinder were calculated and compared to simulated vector errors using the collected VERION keratometry data. Results In total, 83 eyes of 56 patients were analyzed. Residual refractive cylinder was 0.25 D or lower in 58% of eyes and 0.5 D or lower in 80% of eyes. The TCRP-based calculation resulted in a statistically significantly lower vector error (P<0.01) and significantly more eyes with a vector error ≤0.5 D relative to the VERION-based calculation (P=0.02). The TCRP and VERION keratometry readings suggested a different IOL toric power in 53/83 eyes. In these 53 eyes the TCRP vector error was lower in 28 cases, the VERION error was lower in five cases, and the error was equal in 20 cases. When the anterior cornea had with-the-rule astigmatism, the VERION was more likely to suggest a higher toric power and when the anterior cornea had against-the-rule astigmatism, the VERION was less likely to suggest a higher toric power. Conclusion Using the TCRP keratometry measurement in the AcrySof toric calculator may improve overall postoperative refractive results. Consideration of measured posterior corneal astigmatism, rather than a population-averaged value, appears advantageous. PMID:26316693

  17. The application of wave field continuation for seismic refraction

    NASA Astrophysics Data System (ADS)

    Wu, Lijun; Feng, Rui; Huang, Zhiming

    1992-02-01

    Based on wave equation a fundamental formula for plane wave propagaton is derived, the theoretical method of inverting wave volocity structure of earth interior through the observational wave field is discussed in this paper. The observational wave field can be decomposed into the surface plane wave field by using τ - p transform. The maximum amplitude curve in the plane wave field can show stably the change tendency of wave velocity with depth in the Earth. This property can be used to restrict the solution space. By using the wave field continuation method more useful information from the observational wave field can be extracted and the inverion solution not only can be obtained simply and quickly, but also is stable and less influenced by the subjective factor. The wave field continuation is a fine inversion method. Theoretical analysis and numerical modelling are carried out in the study of wave field continuation. By applying homomorphic decovolution the signal — to — noese ratio is improved. Finaly a sonar refraction profile in the northern part of the South China Sea is interpreted and computed. It is found as a result that there is a velocity interface from 1.76 km/s to 2.21 km/s at the depth of 1.4 km. The velocity gradients in the upper and lower layers are 0.54 km · s-1/km and 0.63 km · s-1/km respectively. A discussion of the characteristics of shallow sea structure in the view of tectonic movements is geven.

  18. Seismic reflection data imaging and interpretation from Braniewo2014 experiment using additional wide-angle refraction and reflection and well-logs data

    NASA Astrophysics Data System (ADS)

    Trzeciak, Maciej; Majdański, Mariusz; Białas, Sebastian; Gaczyński, Edward; Maksym, Andrzej

    2015-04-01

    Braniewo2014 reflection and refraction experiment was realized in cooperation between Polish Oil and Gas Company (PGNiG) and the Institute of Geophysics (IGF), Polish Academy of Sciences, near the locality of Braniewo in northern Poland. PGNiG realized a 20-km-long reflection profile, using vibroseis and dynamite shooting; the aim of the reflection survey was to characterise Silurian shale gas reservoir. IGF deployed 59 seismic stations along this profile and registered additional full-spread wide-angle refraction and reflection data, with offsets up to 12 km; maximum offsets from the seismic reflection survey was 3 km. To improve the velocity information two velocity logs from near deep boreholes were used. The main goal of the joint reflection-refraction interpretation was to find relations between velocity field from reflection velocity analysis and refraction tomography, and to build a velocity model which would be consistent for both, reflection and refraction, datasets. In this paper we present imaging results and velocity models from Braniewo2014 experiment and the methodology we used.

  19. Photoresist Exposure Parameter Extraction from Refractive Index Change during Exposure

    NASA Astrophysics Data System (ADS)

    Sohn, Young-Soo; Sung, Moon-Gyu; Lee, Young-Mi; Lee, Eun-Mi; Oh, Jin-Kyung; Byun, Sung-Hwan; Jeong, Yeon-Un; Oh, Hye-Keun; An, Ilsin; Lee, Kun-Sang; Park, In-Ho; Cho, Joon-Yeon; Lee, Sang-Ho

    1998-12-01

    The refractive indices of photoresist are usually measured byan ellipsometer or spectrophotometer, but the values are limited to pre-exposure. It is known thatthe real and imaginary indices are changed during the exposure.But there is little report on these variations since itis difficult to measure this refractive index change at deep ultraviolet. The DillABC parameters show a significant variation with the resist and substrate thicknessas well as the experimental conditions.A method is suggested to extract the parameters from the refractive index changes.We can get the refractive index change and extract the Dill ABC exposure parameters from that.The multiple thin film interference calculation is used to fit the measured transmittance data.The results of our experiments and calculations for several resists including193 nm chemically amplified resists are compared with other methods.The results are agreed well with the full multilayer thin film simulation.

  20. Multiple scattering induced negative refraction of matter waves

    PubMed Central

    Pinsker, Florian

    2016-01-01

    Starting from fundamental multiple scattering theory it is shown that negative refraction indices are feasible for matter waves passing a well-defined ensemble of scatterers. A simple approach to this topic is presented and explicit examples for systems of scatterers in 1D and 3D are stated that imply negative refraction for a generic incoming quantum wave packet. Essential features of the effective scattering field, densities and frequency spectrum of scatterers are considered. Additionally it is shown that negative refraction indices allow perfect transmission of the wave passing the ensemble of scatterers. Finally the concept of the superlens is discussed, since it is based on negative refraction and can be extended to matter waves utilizing the observations presented in this paper which thus paves the way to ‘untouchable’ quantum systems in analogy to cloaking devices for electromagnetic waves. PMID:26857266

  1. Helping secondary school students develop a conceptual understanding of refraction

    NASA Astrophysics Data System (ADS)

    Ashmann, Scott; Anderson, Charles W.; Boeckman, Heather

    2016-07-01

    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 refraction occur. The use of ray diagrams can be useful in (a) the teacher modelling a correct explanation to a situation where refraction occurs and (b) for students to create as they practice other examples. This paper includes eight examples of increasing complexity that use a cognitive apprenticeship cycle approach to scaffold student learning. The first examples (rock fish, floating penny) are shown and a solution is modeled using a ray diagram. Three more examples (bent pencil, dropping an item in water, sunrise/sunset) are presented for students to practice, with each becoming more sophisticated. Three assessment exercises are then provided (two dots, three coins, broken tube).

  2. Dielectric Optical-Controllable Magnifying Lens by Nonlinear Negative Refraction.

    PubMed

    Cao, Jianjun; Shang, Ce; Zheng, Yuanlin; Feng, Yaming; Chen, Xianfeng; Liang, Xiaogan; Wan, Wenjie

    2015-01-01

    A simple optical lens plays an important role for exploring the microscopic world in science and technology by refracting light with tailored spatially varying refractive indices. Recent advancements in nanotechnology enable novel lenses, such as, superlens and hyperlens, with sub-wavelength resolution capabilities by specially designed materials' refractive indices with meta-materials and transformation optics. However, these artificially nano- or micro-engineered lenses usually suffer high losses from metals and are highly demanding in fabrication. Here, we experimentally demonstrate, for the first time, a nonlinear dielectric magnifying lens using negative refraction by degenerate four-wave mixing in a plano-concave glass slide, obtaining magnified images. Moreover, we transform a nonlinear flat lens into a magnifying lens by introducing transformation optics into the nonlinear regime, achieving an all-optical controllable lensing effect through nonlinear wave mixing, which may have many potential applications in microscopy and imaging science. PMID:26149952

  3. Dielectric Optical-Controllable Magnifying Lens by Nonlinear Negative Refraction

    NASA Astrophysics Data System (ADS)

    Cao, Jianjun; Shang, Ce; Zheng, Yuanlin; Feng, Yaming; Chen, Xianfeng; Liang, Xiaogan; Wan, Wenjie

    2015-07-01

    A simple optical lens plays an important role for exploring the microscopic world in science and technology by refracting light with tailored spatially varying refractive indices. Recent advancements in nanotechnology enable novel lenses, such as, superlens and hyperlens, with sub-wavelength resolution capabilities by specially designed materials’ refractive indices with meta-materials and transformation optics. However, these artificially nano- or micro-engineered lenses usually suffer high losses from metals and are highly demanding in fabrication. Here, we experimentally demonstrate, for the first time, a nonlinear dielectric magnifying lens using negative refraction by degenerate four-wave mixing in a plano-concave glass slide, obtaining magnified images. Moreover, we transform a nonlinear flat lens into a magnifying lens by introducing transformation optics into the nonlinear regime, achieving an all-optical controllable lensing effect through nonlinear wave mixing, which may have many potential applications in microscopy and imaging science.

  4. Chirality-induced negative refraction in magnetized plasma

    SciTech Connect

    Guo, B.

    2013-09-15

    Characteristic equations in magnetized plasma with chirality are derived in simple formulations and the dispersion relations for propagation parallel and perpendicular to the external magnetic field are studied in detail. With the help of the dispersion relations of each eigenwave, the author explores chirality-induced negative refraction in magnetized plasma and investigates the effects of parameters (i.e., chirality degree, external magnetic field, etc.) on the negative refraction. The results show that the chirality is the necessary and only one factor which leads to negative refraction without manipulating electrical permittivity and magnetic permeability. Both increasing the degree of chirality and reducing the external magnetic field can result in greater range negative refraction. Parameter dependence of the effects is calculated and discussed.

  5. Asronomical refraction: Computational methods for all zenith angles

    NASA Technical Reports Server (NTRS)

    Auer, L. H.; Standish, E. M.

    2000-01-01

    It is shown that the problem of computing astronomical refraction for any value of the zenith angle may be reduced to a simple, nonsingular, numerical quadrature when the proper choice is made for the independent variable of integration.

  6. Spatially Varying Index of Refraction: An Open Ended Undergraduate Topic.

    ERIC Educational Resources Information Center

    Krueger, David A.

    1980-01-01

    Presents an experiment on the bending of light in a medium with a continuously varying index of refraction. Several theoretical approaches for the analysis of this experiment, designed for college physics students, are also presented. (HM)

  7. An Analogue Model for Teaching Reflection and Refraction of Waves.

    ERIC Educational Resources Information Center

    Bates, Harry E.

    1980-01-01

    Describes a concrete model for teaching the concepts of reflection and refraction without the use of formal mathematics. The model has been tested in five sections of a physics course for nonscience majors at Towson State University, Baltimore, Maryland. (HM)

  8. Refraction-dependent kinematic shift of spectral lines

    NASA Astrophysics Data System (ADS)

    Chyla, W. T.

    2015-04-01

    If a luminous source moves with respect to the medium in which it is embedded, the kinematic shift of spectral lines depends both on the relative velocity and on the (relativistic) index of refraction of the medium. This effect is frequency-dependent, which makes it distinguishable from the cosmological redshift, the gravitational redshift and the regular Doppler shift in vacuum, which are all achromatic. The refraction-dependent shift of spectral lines is considered in more detail in the case of Ia supernovae, where the thermally generated electron-positron plasma ball, which expands with relativistic speeds, constitutes the refractive medium; it turns out that the discussed effect is relatively small at the UV and visible frequencies, but it can be significantly larger at longer wavelengths (the IR band). Other examples are given in optics and in other situations, where the refraction-dependent kinematic shift of frequency can be of significance.

  9. Indications, results, and complications of refractive corneal surgery with lasers.

    PubMed

    Stevens, J D; Steele, A D

    1993-08-01

    Large numbers of patients are being treated for myopia, hyperopia, and astigmatism using the excimer laser. For many patients who are treated for myopia and hyperopia, the procedure is elective and these treatments remain investigational. The use of other lasers for refractive surgery is at an earlier stage, with human trials commencing for infrared lasers. Animal studies are being performed for pulsed picosecond and solid-state ultraviolet lasers. The indications for refractive treatment should be clearly defined, although the results of laser application remain the subject of investigation. Complications of laser application to the cornea occur in the immediate, short-term, and long-term posttreatment period. A continual improvement in refractive results along with a reduction in complications remains the goal of laser refractive research. PMID:10148871

  10. Miniature interferometer for refractive index measurement in microfluidic chip

    NASA Astrophysics Data System (ADS)

    Chen, Minghui; Geiser, Martial; Truffer, Frederic; Song, Chengli

    2012-12-01

    The design and development of the miniaturized interferometer for measurement of the refractive index or concentration of sub-microliter volume aqueous solution in microfludic chip is presented. It is manifested by a successful measurement of the refractive index of sugar-water solution, by utilizing a laser diode for light source and the small robust instrumentation for practical implementation. Theoretically, the measurement principle and the feasibility of the system are analyzed. Experimental device is constructed with a diode laser, lens, two optical plate and a complementary metal oxide semiconductor (CMOS). Through measuring the positional changes of the interference fringes, the refractive index change are retrieved. A refractive index change of 10-4 is inferred from the measured image data. The entire system is approximately the size of half and a deck of cards and can operate on battery power for long time.

  11. 2D seismic residual statics derived from refraction interferometry

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Zhang, Jie

    2016-07-01

    Refraction traveltimes have long been applied for deriving long-wavelength statics solutions. These traveltimes are also applied for the derivation of residual statics, but they must be sufficiently accurate at short wavelengths. In this study, we present a seismic residual statics method that applies interferometric theory to produce four stacked virtual refraction gathers with a significantly improved signal-to-noise ratio. These gathers are composed of forward and backward virtual refraction gathers for receivers and shots. By picking the first arrivals on these four gathers followed by the application of a set of refraction equations, reliable residual statics solutions can be derived. This approach can help deal with noisy data and also avoid using traveltime picks from shot gathers. We demonstrate the approach by applying it to synthetic data as well as real data.

  12. A Simple Method to Determine the Refractive Index of Glass.

    ERIC Educational Resources Information Center

    Mak, Se-yuen

    1988-01-01

    Describes an experiment for determining the refractive index. Discusses the experiment procedure and mathematical expression for calculating the index. Provides two geometrical diagrams and a graph for determining the index with a typical data. (YP)

  13. Multiple scattering induced negative refraction of matter waves.

    PubMed

    Pinsker, Florian

    2016-01-01

    Starting from fundamental multiple scattering theory it is shown that negative refraction indices are feasible for matter waves passing a well-defined ensemble of scatterers. A simple approach to this topic is presented and explicit examples for systems of scatterers in 1D and 3D are stated that imply negative refraction for a generic incoming quantum wave packet. Essential features of the effective scattering field, densities and frequency spectrum of scatterers are considered. Additionally it is shown that negative refraction indices allow perfect transmission of the wave passing the ensemble of scatterers. Finally the concept of the superlens is discussed, since it is based on negative refraction and can be extended to matter waves utilizing the observations presented in this paper which thus paves the way to 'untouchable' quantum systems in analogy to cloaking devices for electromagnetic waves. PMID:26857266

  14. Dielectric Optical-Controllable Magnifying Lens by Nonlinear Negative Refraction

    PubMed Central

    Cao, Jianjun; Shang, Ce; Zheng, Yuanlin; Feng, Yaming; Chen, Xianfeng; Liang, Xiaogan; Wan, Wenjie

    2015-01-01

    A simple optical lens plays an important role for exploring the microscopic world in science and technology by refracting light with tailored spatially varying refractive indices. Recent advancements in nanotechnology enable novel lenses, such as, superlens and hyperlens, with sub-wavelength resolution capabilities by specially designed materials’ refractive indices with meta-materials and transformation optics. However, these artificially nano- or micro-engineered lenses usually suffer high losses from metals and are highly demanding in fabrication. Here, we experimentally demonstrate, for the first time, a nonlinear dielectric magnifying lens using negative refraction by degenerate four-wave mixing in a plano-concave glass slide, obtaining magnified images. Moreover, we transform a nonlinear flat lens into a magnifying lens by introducing transformation optics into the nonlinear regime, achieving an all-optical controllable lensing effect through nonlinear wave mixing, which may have many potential applications in microscopy and imaging science. PMID:26149952

  15. Refractive eye surgery - what to ask your doctor

    MedlinePlus

    ... Fam Physician Mimura T, Azar DT. Current concepts, classification, and history of refractive surgery. In: Yanoff M, ... MedlinePlus Connect for EHRs For Developers U.S. National Library of Medicine 8600 Rockville Pike, Bethesda, MD 20894 ...

  16. Engineering a resonant nanocoating for an optical refractive index sensor

    NASA Astrophysics Data System (ADS)

    Bialiayeu, A.; Ianoul, A.; Albert, J.

    2014-03-01

    We proposing to boost the performance of refractive index sensors based on the tilted fiber Bragg grating (TFBG) structure by resonant coupling of small spherical nanoparticles to the TFBG resonances. The optimal choice of nanoparticle parameters is discussed.

  17. Ectasia risk factors in refractive surgery

    PubMed Central

    Santhiago, Marcony R; Giacomin, Natalia T; Smadja, David; Bechara, Samir J

    2016-01-01

    This review outlines risk factors of post-laser in situ keratomileusis (LASIK) ectasia that can be detected preoperatively and presents a new metric to be considered in the detection of ectasia risk. Relevant factors in refractive surgery screening include the analysis of intrinsic biomechanical properties (information obtained from corneal topography/tomography and patient’s age), as well as the analysis of alterable biomechanical properties (information obtained from the amount of tissue altered by surgery and the remaining load-bearing tissue). Corneal topography patterns of placido disk seem to play a pivotal role as a surrogate of corneal strength, and abnormal corneal topography remains to be the most important identifiable risk factor for ectasia. Information derived from tomography, such as pachymetric and epithelial maps as well as computational strategies, to help in the detection of keratoconus is additional and relevant. High percentage of tissue altered (PTA) is the most robust risk factor for ectasia after LASIK in patients with normal preoperative corneal topography. Compared to specific residual stromal bed (RSB) or central corneal thickness values, percentage of tissue altered likely provides a more individualized measure of biomechanical alteration because it considers the relationship between thickness, tissue altered through ablation and flap creation, and ultimate RSB thickness. Other recognized risk factors include low RSB, thin cornea, and high myopia. Age is also a very important risk factor and still remains as one of the most overlooked ones. A comprehensive screening approach with the Ectasia Risk Score System, which evaluates multiple risk factors simultaneously, is also a helpful tool in the screening strategy. PMID:27143849

  18. Ectasia risk factors in refractive surgery.

    PubMed

    Santhiago, Marcony R; Giacomin, Natalia T; Smadja, David; Bechara, Samir J

    2016-01-01

    This review outlines risk factors of post-laser in situ keratomileusis (LASIK) ectasia that can be detected preoperatively and presents a new metric to be considered in the detection of ectasia risk. Relevant factors in refractive surgery screening include the analysis of intrinsic biomechanical properties (information obtained from corneal topography/tomography and patient's age), as well as the analysis of alterable biomechanical properties (information obtained from the amount of tissue altered by surgery and the remaining load-bearing tissue). Corneal topography patterns of placido disk seem to play a pivotal role as a surrogate of corneal strength, and abnormal corneal topography remains to be the most important identifiable risk factor for ectasia. Information derived from tomography, such as pachymetric and epithelial maps as well as computational strategies, to help in the detection of keratoconus is additional and relevant. High percentage of tissue altered (PTA) is the most robust risk factor for ectasia after LASIK in patients with normal preoperative corneal topography. Compared to specific residual stromal bed (RSB) or central corneal thickness values, percentage of tissue altered likely provides a more individualized measure of biomechanical alteration because it considers the relationship between thickness, tissue altered through ablation and flap creation, and ultimate RSB thickness. Other recognized risk factors include low RSB, thin cornea, and high myopia. Age is also a very important risk factor and still remains as one of the most overlooked ones. A comprehensive screening approach with the Ectasia Risk Score System, which evaluates multiple risk factors simultaneously, is also a helpful tool in the screening strategy. PMID:27143849

  19. Crustal structure along the coast of California from seismic-refraction measurements

    USGS Publications Warehouse

    Healy, J.H.

    1962-01-01

    Two reversed seismic-refraction profiles were recorded between Los Angeles and San Francisco in 1961. The three shotpoints were located in Santa Monica Bay, offshore near San Francisco, and at Camp Roberts, about halfway between Los Angeles and San Francisco. The velocity of Pg along these profiles is 6.1 ± 0.1 km/sec, with possible exceptions near San Francisco and near Los Angeles, where the scatter in the arrival times indicates complex near-surface velocity variations. The velocity of Pn between Los Angeles and Camp Roberts is 8.2 ± 0.1 km/sec, and between Camp Roberts and San Francisco 8.0 ± 0.2 km/sec. There is no indication of an intermediate crustal layer in the traveltimes of first arrivals. Computed depths to the Mohorovicic discontinuity, if the crust consists of a single layer, are: 35 km at Los Angeles, 23 km at Camp Roberts, and 23 km at San Francisco. Refractions from crustal layers of intermediate velocity need not appear as first arrivals, and in the extreme, the depth to the Mohorovicic discontinuity may be one-third greater than the thickness of a one-layer crust.

  20. Investigation of refractive index sensing based on Fano resonance in fiber Bragg grating ring resonators.

    PubMed

    Campanella, Carlo Edoardo; De Leonardis, Francesco; Mastronardi, Lorenzo; Malara, Pietro; Gagliardi, Gianluca; Passaro, Vittorio M N

    2015-06-01

    In this paper we theoretically investigate a ring resonant cavity obtained by closing on itself a π-shifted fiber Bragg grating, to be used for refractive index sensing applications. Differently from a conventional π-shifted fiber Bragg grating, the spectral structure of this cavity is characterized by an asymmetric splitting doublet composed by a right side resonance having an asymmetric Fano profile and a left side resonance having a symmetric Lorentzian profile. The right side resonance shows a narrower and sharper peak than all the other kinds of resonance achievable with both conventional ring resonators and π-shifted fiber Bragg gratings. A reduction of the resonant linewidth with respect to a conventional π-shifted Fiber Bragg grating and a fiber ring resonator, having the same physical parameters, is theoretically proved, achieving up to five orders of magnitude improvement with respect to the usual ring resonator. Due to these resonance features, the π-shifted Bragg grating ring resonator results suitable for RI sensing applications requiring extremely narrow resonances for high resolution measurements. In particular, by assuming a refractive index sensing to detect the presence of sugar in water, the sensor can show a theoretical resolution better than 10-9 RIU. PMID:26072795

  1. Data report for the 1985 seismic-refraction experiment at Yucca Mountain and vicinity, southwestern Nevada

    SciTech Connect

    Sutton, V.D.

    1985-12-31

    In February 1985, the US Geological Survey (USGS) conducted a seismic-refraction survey in the vicinity of Yucca Mountain, southwestern Nevada to better define the P(compressional)-wave velocity structure of the upper crust in this area. This experiment is a continuation of seismic investigations at the Nevada Test Site (NTS) by the USGS on behalf of the Nevada Nuclear Waste Storage Investigations Project (NNWSI) to assess the feasibility of a proposed nuclear waste disposal site at Yucca Mountain. The 1985 seismic-refraction survey consisted of three separate deployments: two East-West profiles, Line A and Line B, and a North-South profile (Plate 1). Thirty-one shots were recorded by 120 portable seismographs, where recorder station spacing averaged .3 km, and the shotpoints averaged 5 to 8 km apart. Additionally, off set shots were fired at shotpoints located about 7 to 15 km from the endpoints of the deployment lines. This report includes record sections from the twenty-nine shotpoints (Plates 2 to 17), a list of seismograph locations (Appendix A), a list of shotpoint locations and shot times, DKDAT data files and Tape Grade Code (Appendix B), and a list of first-arrival traveltime picks (Appendix C). Detailed interpretation of these data will be published in a subsequent report.

  2. Recent developments in refractive concentrators for space photovoltaic power systems

    NASA Technical Reports Server (NTRS)

    Piszczor, Michael F.; Oneill, Mark J.

    1993-01-01

    Since SPRAT 11, significant progress has been made in the development of refractive concentrator elements and components designed specifically for space applications. The status of the mini-dome Fresnel lens concentrator array is discussed and then the results of work recently completed in the area of prismatic cell covers for concentrator systems are summarized. This is followed by a brief discussion of some work just starting in the area of line-focus refractive concentrators for space.

  3. Refractive Interstellar Scintillation for Flux Density Variations of Two Pulsars

    NASA Astrophysics Data System (ADS)

    Zhou, Ai-Zhi; Wu, Xin-Ji; Esamdin, A.

    2003-08-01

    The flux density structure functions of PSRs B0525+21 and B2111+46 are calculated with the refractive interstellar scintillation (RISS) theory. The theoretical curves are in good agreement with observations [Astrophys. J. 539 (2000) 300] (hereafter S2000). The spectra of the electron density fluctuations both are of Kolmogorov spectra. We suggest that the flux density variations observed for these two pulsars are attributed to refractive interstellar scintillation, not to intrinsic variability.

  4. Steering and collimating ballistic electrons with amphoteric refraction

    SciTech Connect

    Radu, A.; Dragoman, D.; Iftimie, S.

    2012-07-15

    We show that amphoteric refraction of ballistic electrons, i.e., positive or negative refraction depending on the incidence angle, occurs at an interface between an isotropic and an anisotropic medium and can be employed to steer and collimate electron beams. The steering angle is determined by the materials' parameters, but the degree of collimation can be tuned in a significant range by changing the energy of ballistic electrons.

  5. Apparatus and method to compensate for refraction of radiation

    DOEpatents

    Allen, Gary R.; Moskowitz, Philip E.

    1990-01-01

    An apparatus to compensate for refraction of radiation passing through a curved wall of an article is provided. The apparatus of a preferred embodiment is particularly advantageous for use in arc tube discharge diagnostics. The apparatus of the preferred embodiment includes means for pre-refracting radiation on a predetermined path by an amount equal and inverse to refraction which occurs when radiation passes through a first wall of the arc tube such that, when the radiation passes through the first wall of the arc tube and into the cavity thereof, the radiation passes through the cavity approximately on the predetermined path; means for releasably holding the article such that the radiation passes through the cavity thereof; and means for post-refracting radiation emerging from a point of the arc tube opposite its point of entry by an amount equal and inverse to refraction which occurs when radiation emerges from the arc tube. In one embodiment the means for pre-refracting radiation includes a first half tube comprising a longitudinally bisected tube obtained from a tube which is approximately identical to the arc tube's cylindrical portion and a first cylindrical lens, the first half tube being mounted with its concave side facing the radiation source and the first cylindrical lens being mounted between the first half tube and the arc tube and the means for post-refracting radiation includes a second half tube comprising a longitudinally bisected tube obtained from a tube which is approximately identical to the arc tube's cylindrical portion and a second cylindrical lens, the second half tube being mounted with its convex side facing the radiation source and the second cylindrical lens being mounted between the arc tube and the second half tube. Methods to compensate for refraction of radiation passing into and out of an arc tube is also provided.

  6. Apparatus and method to compensate for refraction of radiation

    DOEpatents

    Allen, G.R.; Moskowitz, P.E.

    1990-03-27

    An apparatus to compensate for refraction of radiation passing through a curved wall of an article is provided. The apparatus of a preferred embodiment is particularly advantageous for use in arc tube discharge diagnostics. The apparatus of the preferred embodiment includes means for pre-refracting radiation on a predetermined path by an amount equal and inverse to refraction which occurs when radiation passes through a first wall of the arc tube such that, when the radiation passes through the first wall of the arc tube and into the cavity thereof, the radiation passes through the cavity approximately on the predetermined path; means for releasably holding the article such that the radiation passes through the cavity thereof; and means for post-refracting radiation emerging from a point of the arc tube opposite its point of entry by an amount equal and inverse to refraction which occurs when radiation emerges from the arc tube. In one embodiment the means for pre-refracting radiation includes a first half tube comprising a longitudinally bisected tube obtained from a tube which is approximately identical to the arc tube's cylindrical portion and a first cylindrical lens, the first half tube being mounted with its concave side facing the radiation source and the first cylindrical lens being mounted between the first half tube and the arc tube and the means for post-refracting radiation includes a second half tube comprising a longitudinally bisected tube obtained from a tube which is approximately identical to the arc tube's cylindrical portion and a second cylindrical lens, the second half tube being mounted with its convex side facing the radiation source and the second cylindrical lens being mounted between the arc tube and the second half tube. Methods to compensate for refraction of radiation passing into and out of an arc tube is also provided. 4 figs.

  7. Light refraction in the Swiss-cheese model

    NASA Astrophysics Data System (ADS)

    Csapó, Adelinda; Bene, Gyula

    2012-08-01

    We investigate light propagation in the Swiss-cheese model. On both sides of Swiss-cheese sphere surfaces, observers resting in the flat Friedmann-Robertson-Walker (FRW) space and the Schwarzschild space respectively, see the same light ray enclosing different angles with the normal. We examine light refraction at each crossing of the boundary surfaces, showing that the angle of refraction is larger than the angle of incidence for both directions of the light.

  8. Development of a contact lens for refracting aquatic animals.

    PubMed

    Spielman, S L; Gruber, S H

    1983-01-01

    Development of a new technique for refracting the eye of unwieldy and large aquatic organisms in air is presented. The technique employs a contact lens to simulate underwater conditions. Refraction is performed through a flat front surface with an ophthalmoscope or a streak retinoscope. Data from 11 carcharhinid sharks (four species) indicate that the smaller eyes of inshore species are defocused relative to the eyes of offshore species. PMID:6646759

  9. Coherent laser radar performance for general atmospheric refractive turbulence

    NASA Technical Reports Server (NTRS)

    Frehlich, Rod G.; Kavaya, Michael J.

    1991-01-01

    A general theory for the signal-to-noise ratio (SNR) of a coherent detection laser radar is developed using the path-integral formulation (Fresnel approximation), which is valid for any typical path-integrated atmospheric refractive turbulence. The principal effects of refractive turbulence are discussed, and analytical expressions are presented for the case of untruncated Gaussians for the transmitted field, local oscillator field, and transmitter/receiver optics. The physical mechanisms that reduce heterodyne efficiency are identified.

  10. Refractive error among urban preschool children in Xuzhou, China.

    PubMed

    Wang, Xiaojuan; Liu, Dan; Feng, Ruifang; Zhao, Huashuo; Wang, Qinmei

    2014-01-01

    The prevalence of refractive errors in urban preschool children in Xuzhou, China remains unknown. Children attending twelve randomly selected kindergartens participated in this study. Visual acuity, ocular alignment, cover-uncover test, cycloplegic refraction, slit-lamp and funduscopy were performed under a standardized testing environment. Cycloplegic streak retinoscopy was performed for all subjects. The mean spherical equivalent (SE) refractive error was the main outcome measure. Emmetropia was defined as refractive status between +1.75 diopters (D) and -0.75D. Myopia, hyperopia, astigmatism and anisometropia were defined as SE < -0.50D, SE > +2.0 D, cylindrical error > 1.0 D and SE difference ≥ 1 D between fellow eyes, respectively. Out of 2349 eligible children, 2255 (96%) children completed a refractive examination. Of the 2255 children, the mean SE of right eyes was +1.14 ± 0.95 diopters (D). Mean SE of the right eyes did not decline with age (r = -0.01; P = 0.56). The majority (86.6%) of children were emmetropia. The prevalence of myopia and hyperopia was 0.9% and 14.3%, respectively. The mean astigmatism for the right eyes was 0.87 ± 0.62 D. The prevalence of With-the-rule, against the rule and oblique astigmatism was 93.8%, 4.7% and 1.5%, respectively. The mean anisometropia between two eyes was 0.14 ± 0.38 D. The most common type of refractive error was hyperopia (14.3%), followed by astigmatism (8.8%), anisometropia (3.2%), and myopia (0.9%). The refractive status in this population of urban Xuzhou preschool children was stable and there was no evidence of a myopic refractive shift over this age range in our cross-sectional study. PMID:25674266

  11. Steering and collimating ballistic electrons with amphoteric refraction

    NASA Astrophysics Data System (ADS)

    Radu, A.; Dragoman, D.; Iftimie, S.

    2012-07-01

    We show that amphoteric refraction of ballistic electrons, i.e., positive or negative refraction depending on the incidence angle, occurs at an interface between an isotropic and an anisotropic medium and can be employed to steer and collimate electron beams. The steering angle is determined by the materials' parameters, but the degree of collimation can be tuned in a significant range by changing the energy of ballistic electrons.

  12. Ducting and Boundary Layer Refractivity Bias Correction in GPS Radio Occultation Soundings with MODIS over the Subtropical Eastern Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Xie, F.; Ao, C. O.; Adhikari, L.; Yu, X.

    2015-12-01

    Over the subtropical eastern Pacific, a large stratus cloud deck is often trapped below a strong inversion layer resulting from the combination of strong free tropospheric subsidence and the cool sea surface temperature underneath. The stable inversion leads to a sharp moisture decrease and a large negative refractivity gradient that often causes ducting right above the cloudy boundary layer (CBL). The presence of duct results in systematically negative biases in the GPS radio occultation (RO) refractivity (i.e., N-bias) inside the CBL due to a non-unique retrieval problem. An independent physical constraint is required to extract a unique and bias-free RO refractivity observation. In the overcast scenario, the inversion base temperature corresponds well to the cloud-top-temperature (CTT) of the stratus, which can be precisely measured from MODIS (Moderate Resolution Imaging Spectroradiometer) longwave infrared window channel. In this presentation, the MODIS CTT measurements are used as an independent constraint to correct the systematic biases in the near co-incident RO refractivity soundings from COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate). The sensitivity analysis on the reconstruction technique and the comparison of the reconstructed (bias-free) RO profiles with the radiosonde and ECMWF reanalysis will be presented. The synergy of GPS RO and MODIS cloud measurements provides model-independent observation of CBL thermodynamic structures that are crucial for understanding the boundary layer and low cloud processes in global weather and climate model simulations.

  13. Assimilation Experiments of One-Dimensional Variational Analyses with GPS/MET Refractivity

    NASA Technical Reports Server (NTRS)

    Poli, Paul; Joiner, Joanna; Atlas, Robert (Technical Monitor)

    2002-01-01

    The GPS/MET 1995 experiment demonstrated the feasibility of remote soundings of the Earth's atmosphere using the GPS radio occultation technique. Subsequent studies assessed the information content of such measurements. Several groups have attempted to assimilate the GPS radio occultation measurements into a global Data Assimilation System (DAS). These attempts followed in general the methodology proposed by Eyre, and range from die act four-dimensional variational assimilation of bending angles to assimilation of inverted profiles of temperature and/or humidity. We present here an hybrid approach. We attempted to take advantage of the accuracy of current, weather models to constrain one-dimensional variational analyses using GPS refractivity. Retrieved profiles of atmospheric parameters were then assimilated like other types of observations in a global DAS for issuing the next forecast period.

  14. Total Negative Refraction: A New Frontier in Optics

    NASA Astrophysics Data System (ADS)

    Mascarenhas, Angelo

    2003-10-01

    We are all familiar with positive refraction, in which the incident and transmitted light through an interface of two media with different refractive indices are on opposite sides of the interface normal. If the refractive index is negative for one medium, the refracted light would remain on the same side of the interface normal as the incident light. There have been several recent experimental demonstrations of negative refraction but these are in a small band of microwave frequencies for materials made out of split rings and rods of copper, or photonic lattices. NREL scientists have discovered a new way to realize negative refraction using visible light and real crystals. This new method, utilizing a ferroelastic-twin domain boundary, is applicable to any frequency of the electromagnetic spectrum. The beauty of this new method is that it eliminates all reflection loss and so could be of enormous value for steering high power laser beams as well as electron beams in nano-electronic devices. This talk will present an overview of this exciting new phenomenon.

  15. Biexciton induced refractive index changes in a semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    Shojaei, S.

    2015-06-01

    We present a detailed theoretical study of linear and third order nonlinear refractive index changes in a optically driven disk-like GaN quantum dot. In our numerical calculations, we consider the three level system containing biexciton, exciton, and ground states and use the compact density matrix formalism and iterative method to obtain refractive index changes. Variational method through effective mass approximation are employed to calculate the ground state energy of biexciton and exciton states. The evolution of refractive index changes around one, two and three photon resonance is investigated and discussed for different quantum dot sizes and light intensities. Size-dependent three-photon nonlinear refractive index change versus incident photon energy compared to that of two-photon is obtained and analyzed. As main result, we found that around resonance frequency at exciton-biexciton transition the quantum confinement has great influence on the linear change in refractive index so that for very large quantum dots, it decreases. Moreover, it was found that third order refractive index changes for three photon process is strongly dependent on QD size and light intensity. Our study reveals that considering our simple model leads to results which are in good agreement with other rare numerical results. Comparison with experimental results has been done.

  16. Objective evaluation of refractive data and astigmatism: quantification and analysis.

    PubMed

    Kaye, S B

    2014-02-01

    The aim of this study was to present methods to improve the analysis of refractive data. A comparison of methods is used to analyse refractive powers using individual powers and aggregate data. Equations are also developed for the representation of the average power of a lens or refractive data as a univariate measure, which includes spherical, coma, and/or other aberrations. The equations provide a precise representation of refractive power, which is useful for comparing individual and aggregate data. Average lens power in the principal meridian can be adequately computed as can the average lens power through orthogonal and oblique meridians, providing a good univariate representation of astigmatism and refractive power. Although these formulae are perhaps not as easy to use as, for example, the spherical equivalent, they are more precise and superior in principle involving fewer approximations and are not subject to systematic bias. These effects are of significance when dealing with high-powered lenses such as intraocular lenses or the cornea. They need to be taken into account particularly for calculations of intraocular lens power, toric intraocular lenses, and cornea refractive surgery, especially if outcomes are to be improved. Such issues are of particular importance when dealing with aggregate data and determining statistical significance of treatment effects. PMID:24336294

  17. Seismic reflection and refraction data acquired in Canada Basin, Northwind Ridge and Northwind Basin, Arctic Ocean in 1988, 1992 and 1993

    USGS Publications Warehouse

    Grantz, Arthur; Hart, Patrick E.; May, Steven D.

    2004-01-01

    Seismic reflection and refraction data were collected in generally ice-covered waters of the Canada Basin and the eastern part of the Chukchi Continental Borderland of the Amerasia Basin, Arctic Ocean, during the late summers of 1988, 1992, and 1993. The data were acquired from a Polar class icebreaker, the U.S. Coast Guard Cutter Polar Star, using a seismic reflection system designed by the U.S. Geological Survey (USGS). The northernmost data extend to 78? 48' N latitude. In 1988, 155 km of reflection data were acquired with a prototype system consisting of a single 195 cubic inch air gun seismic source and a two-channel hydrophone streamer with a 150-m active section. In 1992 and 1993, 500 and 1,900 km, respectively, of seismic reflection profile data were acquired with an improved six air gun, 674 to 1303 cubic inch tuned seismic source array and the same two-channel streamer. In 1993, a 12-channel streamer with a 150-m active section was used to record five of the reflection lines and one line was acquired using a three air gun, 3,000 cubic inch source. All data were recorded with a DFS-V digital seismic recorder. Processed sections feature high quality vertical incidence images to more than 6 km of sub-bottom penetration in the Canada Basin. Refraction data were acquired with U.S. Navy sonobuoys recorded simultaneously with the seismic reflection profiles. In 1988 eight refraction profiles were recorded with the single air gun, and in 1992 and 1993 a total of 47 refraction profiles were recorded with the six air gun array. The sonobuoy refraction records, with offsets up to 35 km, provide acoustic velocity information to complement the short-offset reflection data. The report includes trackline maps showing the location of the data, as well as both digital data files (SEG-Y) and images of all of the profiles.

  18. Deep seismic refraction experiment in northeast Brazil: New constraints for Borborema province evolution

    NASA Astrophysics Data System (ADS)

    Lima, Marcus Vinicius A. G. de; Berrocal, Jesus; Soares, José E. P.; Fuck, Reinhardt A.

    2015-03-01

    The Borborema Province of northeastern Brazil is a major Proterozoic crustal province that, until now, has never been explored using deep crustal seismic methods. Here are reported the first results obtained from a high-quality seismic refraction/wide-angle reflection profile that has defined the internal seismic velocity structure and thickness of the crust in this region. Almost 400 recording stations were deployed in the Deep Seismic Refraction (DSR) experiment through an NW-SE ca. 900 km linear array and 19 shots were exploded at every 50 km along the line. Data from the 10 southeastern most shots of the seismic profile were processed in this work. The main features and geological structures crossed by the studied portion of the profile belong to the so-called Central Sub-province of the Borborema tectonic province. The crustal model obtained is compatible with a typical structure of extended crust. The model was essentially divided into three layers: upper crust, lower crust, and a half-space represented by the shallower portion of the mantle. The Moho is an irregular interface with depth ranging between 31.7 and 34.5 km, and beneath the Central Sub-province it varies from 31.5 to 33 km depth, where its limits are related to major crustal discontinuities. The distribution of velocities within the crust is heterogeneous, varying vertically from 5.7 to 6.3 km/s in the upper crust and from 6.45 to 6.9 km/s in the lower crust. From the average crustal velocity distribution it is evident that the Central Sub-province has seismic characteristics different from neighboring domains. The crust is relatively thin and crustal thickness variations in the profile are subtle due to stretching that occurred in the Cretaceous, during the fragmentation of Pangaea, opening of the South Atlantic Ocean and separation of South America from Africa.

  19. Assembly and alignment of infrared refractive system

    NASA Astrophysics Data System (ADS)

    Yang, Lin; Lin, Jian-chun; Wang, Ya-jing; Chen, Fan-sheng

    2013-09-01

    Optical systems for scientific instrumentation frequently include lens or mirrors with critical mechanical requirements. Position issues of those components are inextricably bound to the efficiency of the instrument. The position referring to the lens system mainly means spacer and rotation of all elements concerned. Instrument could not be completed without the accuracy assembly even the previous design was top one. The alignment of infrared optical system always is a tough thing due to the IR material being opaque to visible light which hardly effect on the imaging ability of the system. In this paper a large-aperture IR refractive system was described in details and the alignment of this system was presented. The brief work describes the assembly and integration of the camera barrel in lab. First of all, all the mechanical elements must be manufactured with high accuracy requirements to meet alignment tolerances and minimum errors mostly could be ignored. The rotations relative to the optical axis were hardy restricted by the space between barrel and cells. The lens vertex displacements were determined through high accuracy titanium alloy spacer. So the actual shape data of the optical lenses were obtained by coordinate measuring machining (CMM) to calculate the real space between lenses after alignment1 done. All the measured results were critical for instruction of the practical assemble. Based on the properties and tolerances of the system, the camera barrel includes sets of six lenses with their respective supports and cells which are composed of two parts: the flied lens group and the relay lenses group. The first one was aligned by the geometry centering used CMM. And the relay lenses were integrated one by one after centered individually with a classical centering instrument. Then the two separate components were assembled under the monitor of the CMM with micron precision. Three parameters on the opti-mechanical elements which include decenter, tilt and

  20. Using Resistivity and Seismic Refraction to Image Surface-Ground Water Interaction in the Snowy Range, Wyoming

    NASA Astrophysics Data System (ADS)

    Provart, M.; Holbrook, W.; Carr, B.; Miller, S. N.; Traver, E.; Hall, R.

    2013-12-01

    Closing the water balance in mountain watersheds is often difficult due to uncertainties about the role of surface/groundwater interactions. We have initiated a combined hydrological/geophysical study of a mountain watershed in the Snowy Range of Wyoming in order to test the efficacy of near-surface geophysical techniques in assessing the pathways that connect surface water to groundwater. Here we present initial results of subsurface structure inferred from electrical resistivity and seismic refraction data. The Snowy Range represents the northern extent of the Medicine Bow Mountains, a subset of the Rockies, that originated from the Laramide Orogeny. Bedrock varies from quartzite, to metasedimentary gneisses and schists, to igneous rock. Our data set consists of DC-resistivity and seismic refraction surveys in a valley containing a spring, as well as a saline tracer experiment in the No Name watershed consisting of time-lapse resistivity profiles along both banks of the stream. Our resistivity transects show highly conductive regions immediately below the spring with resistivities <100 Ω-m at depths ranging from 0 to 25 meters. We conclude these sections are saturated with highly ionized water that has filtered downwards through the ridgelines to the north and south of the valley. Seismic refraction surveys along the same profiles show P-velocities <1500 m/s (the seismic velocity of water) in the upper 10 meters. One possible explanation is that water occupies discrete fracture systems in an otherwise partially saturated subsurface. A saline tracer experiment also shows clear evidence for surface/groundwater interactions. We injected a salt water mixture into the stream and conducted time-lapse resistivity profiling on stream-parallel profiles downstream over five hours to test for hyporheic flow from the stream into the adjacent banks. We imaged increasing conductivity in sections of our profiles which we attribute to saline water infiltrating the subsurface

  1. Global cost of correcting vision impairment from uncorrected refractive error

    PubMed Central

    Fricke, TR; Wilson, DA; Schlenther, G; Naidoo, KS; Resnikoff, S; Frick, KD

    2012-01-01

    Abstract Objective To estimate the global cost of establishing and operating the educational and refractive care facilities required to provide care to all individuals who currently have vision impairment resulting from uncorrected refractive error (URE). Methods The global cost of correcting URE was estimated using data on the population, the prevalence of URE and the number of existing refractive care practitioners in individual countries, the cost of establishing and operating educational programmes for practitioners and the cost of establishing and operating refractive care facilities. The assumptions made ensured that costs were not underestimated and an upper limit to the costs was derived using the most expensive extreme for each assumption. Findings There were an estimated 158 million cases of distance vision impairment and 544 million cases of near vision impairment caused by URE worldwide in 2007. Approximately 47 000 additional full-time functional clinical refractionists and 18 000 ophthalmic dispensers would be required to provide refractive care services for these individuals. The global cost of educating the additional personnel and of establishing, maintaining and operating the refractive care facilities needed was estimated to be around 20 000 million United States dollars (US$) and the upper-limit cost was US$ 28 000 million. The estimated loss in global gross domestic product due to distance vision impairment caused by URE was US$ 202 000 million annually. Conclusion The cost of establishing and operating the educational and refractive care facilities required to deal with vision impairment resulting from URE was a small proportion of the global loss in productivity associated with that vision impairment. PMID:23109740

  2. Ray-path concepts for converted-wave seismic refraction

    NASA Astrophysics Data System (ADS)

    Hearn, Steve; Meulenbroek, Alan

    2011-06-01

    P-wave reflection-statics solutions typically incorporate P-wave refraction data, derived from the first breaks of the production data. Similarly, converted-wave refractions, taken from inline-component recordings, can be exploited to yield S-wave receiver statics, required in the processing of converted-wave reflection data. This methodology requires extensions to well known P-wave refraction analysis methods. This paper outlines extensions of the slope-intercept method and the reciprocal method, required to analyse converted-wave refractions. We discuss the computation of S-wave time-depths and describe how the observed ratio of S-wave to P-wave time-depths can provide a useful estimate of the near-surface VP/VS ratio, which is of interest in the analysis of engineering rock strengths. We also include discussion of several related practical issues, with particular reference to dynamite sources. When the source is buried in the refractor, the required reciprocal times cannot be directly measured from the raw travel-time data. They can, however, be easily derived via correction using measured intercept times. Often converted-wave refractions are of poorer quality than conventional P-wave refractions, such that reversed refractions may not be available over some parts of the spread. In this situation, the preferred time-depth quantity cannot be computed. However, delay-times derived from single-ended data can be substituted, particularly if lateral variations in refractor velocity are allowed for. The concepts outlined here are used in a companion paper to correct S-wave receiver statics in a coal-scale dataset from the Bowen Basin in central Queensland.

  3. Refraction near the horizon-an empirical approach. Part 1: terrestrial refraction of the dip.

    PubMed

    Tschudin, Marcel E

    2016-04-20

    This study aims at providing improved closed-form refraction estimates for observations near the horizon. In this first part, over 1800 previously published direct measurements of the horizon's depression (dip) over the sea are reanalyzed using a nonconventional robust procedure for coping with numerous real, large, and asymmetric outliers from abnormal dips. The derived 1-parameter function agrees with those proposed in modern almanacs and for land surveying. It is found that the dips of warmer and colder sea surfaces vs. air are best described with two different functions. The two proposed 3-parameter functions, also using temperature difference between air and sea and wind speed, reduce the estimated error of the 1-parameter function by ∼⅓ and the number of outliers by ∼⅔. PMID:27140075

  4. Measurement of the index of refraction of μm crystals by a confocal laser microscope--potential application for the refractive index mapping of μm scale.

    PubMed

    Kimura, Keisaku; Sato, Seiichi

    2014-05-01

    A conventional laser microscope can be used to derive the index of refractivity by the ratio of geometrical height of the transparent platelet to the apparent height of the normal incident light for very small crystals in the wide size range. We demonstrate that the simple method is effective for the samples from 100 μm to 16 μm in size using alkali halide crystals as a model system. The method is also applied for the surface fractured micro-crystals and an inclined crystal with microscopic size regime. Furthermore, we present two-dimensional refractive index mapping as well as two-dimensional height profile for the mixture of three alkali halides, KCl, KI, and NaCl, all are μm in size. PMID:24880379

  5. Fermat's principle and the formal equivalence of local light-ray rotation and refraction at the interface between homogeneous media with a complex refractive index ratio.

    PubMed

    Sundar, Bhuvanesh; Hamilton, Alasdair C; Courtial, Johannes

    2009-02-01

    We derive a formal description of local light-ray rotation in terms of complex refractive indices. We show that Fermat's principle holds, and we derive an extended Snell's law. The change in the angle of a light ray with respect to the normal of a refractive index interface is described by the modulus of the refractive index ratio; the rotation around the interface normal is described by the argument of the refractive index ratio. PMID:19183663

  6. Refractive index dependence of Papilio Ulysses butterfly wings reflectance spectra

    NASA Astrophysics Data System (ADS)

    Isnaeni, Muslimin, Ahmad Novi; Birowosuto, Muhammad Danang

    2016-02-01

    We have observed and utilized butterfly wings of Papilio Ulysses for refractive index sensor. We noticed this butterfly wings have photonic crystal structure, which causes blue color appearance on the wings. The photonic crystal structure, which consists of cuticle and air void, is approximated as one dimensional photonic crystal structure. This photonic crystal structure opens potential to several optical devices application, such as refractive index sensor. We have utilized small piece of Papilio Ulysses butterfly wings to characterize refractive index of several liquid base on reflectance spectrum of butterfly wings in the presence of sample liquid. For comparison, we simulated reflectance spectrum of one dimensional photonic crystal structure having material parameter based on real structure of butterfly wings. We found that reflectance spectrum peaks shifted as refractive index of sample changes. Although there is a slight difference in reflectance spectrum peaks between measured spectrum and calculated spectrum, the trend of reflectance spectrum peaks as function of sample's refractive index is the similar. We assume that during the measurement, the air void that filled by sample liquid is expanded due to liquid pressure. This change of void shape causes non-similarity between measured spectrum and calculated spectrum.

  7. Empirical modelling to predict the refractive index of human blood.

    PubMed

    Yahya, M; Saghir, M Z

    2016-02-21

    Optical techniques used for the measurement of the optical properties of blood are of great interest in clinical diagnostics. Blood analysis is a routine procedure used in medical diagnostics to confirm a patient's condition. Measuring the optical properties of blood is difficult due to the non-homogenous nature of the blood itself. In addition, there is a lot of variation in the refractive indices reported in the literature. These are the reasons that motivated the researchers to develop a mathematical model that can be used to predict the refractive index of human blood as a function of concentration, temperature and wavelength. The experimental measurements were conducted on mimicking phantom hemoglobin samples using the Abbemat Refractometer. The results analysis revealed a linear relationship between the refractive index and concentration as well as temperature, and a non-linear relationship between refractive index and wavelength. These results are in agreement with those found in the literature. In addition, a new formula was developed based on empirical modelling which suggests that temperature and wavelength coefficients be added to the Barer formula. The verification of this correlation confirmed its ability to determine refractive index and/or blood hematocrit values with appropriate clinical accuracy. PMID:26807785

  8. On the anodic aluminium oxide refractive index of nanoporous templates

    NASA Astrophysics Data System (ADS)

    Hierro-Rodriguez, A.; Rocha-Rodrigues, P.; Valdés-Bango, F.; Alameda, J. M.; Jorge, P. A. S.; Santos, J. L.; Araujo, J. P.; Teixeira, J. M.; Guerreiro, A.

    2015-11-01

    In the present study, we have determined the intrinsic refractive index of anodic aluminium oxide, which is originated by the formation of nanoporous alumina templates. Different templates have been fabricated by the conventional two-step anodization procedure in oxalic acid. Their porosities were modified by chemical wet etching allowing the tuning of their effective refractive indexes (air-filled nanopores  +  anodic aluminium oxide). By standard spectroscopic light transmission measurements, the effective refractive index for each different template was extracted in the VIS-NIR region. The determination of the intrinsic anodic aluminium oxide refractive index was performed by using the Maxwell-Garnett homogenization theory. The results are coincident for all the fabricated samples. The obtained refractive index (~1.55) is quite lower (~22%) than the commonly used Al2O3 handbook value (~1.75), showing that the amorphous nature of the anodic oxide structure strongly conditions its optical properties. This difference is critical for the correct design and modeling of optical plasmonic metamaterials based on anodic aluminium oxide nanoporous templates.

  9. Application of seismic-refraction techniques to hydrologic studies

    USGS Publications Warehouse

    Haeni, F.P.

    1986-01-01

    Seismic-refraction methods have been extensively used in petroleum, mineral, and engineering investigations and to some extent, for hydrologic applications during the past 30 years. Recent advances in equipment, sound sources, and computer-interpretation techniques make seismic-refraction methods a highly effective and economical means of obtaining subsurface data in hydrologic studies. Aquifers that can be defined by one or more high seismic-velocity surfaces, such as alluvial or glacial deposits in consolidated rock valleys, limestone or sandstone underlain by metamorphic or igneous rock, or saturated unconsolidated deposits overlain by unsaturated unconsolidated deposits, are ideally suited for applying seismic-refraction methods. These methods allow the economical collection of subsurface data and provide the basis for more efficient collection of subsurface data by test drilling or aquifer tests and results in improved hydrologic studies. This manual briefly reviews the basics of seismic refraction theory and principles. It emphasizes the use of this technique in hydrologic investigations and describes the planning, equipment, field procedures, and interpretation techniques needed for this type of study. Examples of the use of seismic refraction techniques in a wide variety of hydrologic studies are presented. (USGS)

  10. Water absorption in a refractive index model for bacterial spores

    NASA Astrophysics Data System (ADS)

    Siegrist, K. M.; Thrush, E.; Airola, M.; Carr, A. K.; Limsui, D. M.; Boggs, N. T.; Thomas, M. E.; Carter, C. C.

    2009-05-01

    The complexity of biological agents can make it difficult to identify the important factors impacting scattering characteristics among variables such as size, shape, internal structure and biochemical composition, particle aggregation, and sample additives. This difficulty is exacerbated by the environmentally interactive nature of biological organisms. In particular, bacterial spores equilibrate with environmental humidity by absorption/desorption of water which can affect both the complex refractive index and the size/shape distributions of particles - two factors upon which scattering characteristics depend critically. Therefore accurate analysis of experimental data for determination of refractive index must take account of particle water content. First, spectral transmission measurements to determine visible refractive index done on suspensions of bacterial spores must account for water (or other solvent) uptake. Second, realistic calculations of aerosol scattering cross sections should consider effects of atmospheric humidity on particle water content, size and shape. In this work we demonstrate a method for determining refractive index of bacterial spores bacillus atropheus (BG), bacillus thuringiensis (BT) and bacillus anthracis Sterne (BAs) which accounts for these effects. Visible index is found from transmission measurements on aqueous and DMSO suspensions of particles, using an anomalous diffraction approximation. A simplified version of the anomalous diffraction theory is used to eliminate the need for knowledge of particle size. Results using this approach indicate the technique can be useful in determining the visible refractive index of particles when size and shape distributions are not well known but fall within the region of validity of anomalous dispersion theory.

  11. Negative refraction, gain and nonlinear effects in hyperbolic metamaterials.

    PubMed

    Argyropoulos, Christos; Estakhri, Nasim Mohammadi; Monticone, Francesco; Alù, Andrea

    2013-06-17

    The negative refraction and evanescent-wave canalization effects supported by a layered metamaterial structure obtained by alternating dielectric and plasmonic layers is theoretically analyzed. By using a transmission-line analysis, we formulate a way to rapidly analyze the negative refraction operation for given available materials over a broad range of frequencies and design parameters, and we apply it to broaden the bandwidth of negative refraction. Our analytical model is also applied to explore the possibility of employing active layers for loss compensation. Nonlinear dielectrics can also be considered within this approach, and they are explored in order to add tunability to the optical response, realizing positive-to-zero-to-negative refraction at the same frequency, as a function of the input intensity. Our findings may lead to a better physical understanding and improvement of the performance of negative refraction and subwavelength imaging in layered metamaterials, paving the way towards the design of gain-assisted hyperlenses and tunable nonlinear imaging devices. PMID:23787691

  12. Transient Thermal Analysis of a Refractive Secondary Solar Concentrator

    NASA Technical Reports Server (NTRS)

    Geng, Steven M.; Macosko, Robert P.

    1999-01-01

    A secondary concentrator is an optical device that accepts solar energy from a primary concentrator and further intensifies and directs the solar flux. The refractive secondary is one such device; fabricated from an optically clear solid material that can efficiently transmit the solar energy by way of refraction and total internal reflection. When combined with a large state-of-the-art rigid or inflatable primary concentrator, the refractive secondary enables solar concentration ratios of 10,000 to 1. In support of potential space solar thermal power and propulsion applications, the NASA Glenn Research Center is developing a single-crystal refractive secondary concentrator for use at temperatures exceeding 2000K. Candidate optically clear single-crystal materials like sapphire and zirconia are being evaluated for this application. To support this evaluation, a three-dimensional transient thermal model of a refractive secondary concentrator in a typical solar thermal propulsion application was developed. This paper describes the model and presents thermal predictions for both sapphire and zirconia prototypes. These predictions are then used to establish parameters for analyzing and testing the materials for their ability to survive thermal shock and stress.

  13. Application of seismic-refraction techniques to hydrologic studies

    USGS Publications Warehouse

    Haeni, F.P.

    1988-01-01

    During the past 30 years, seismic-refraction methods have been used extensively in petroleum, mineral, and engineering investigations and to some extent for hydrologic applications. Recent advances in equipment, sound sources, and computer interpretation techniques make seismic refraction a highly effective and economical means of obtaining subsurface data in hydrologic studies. Aquifers that can be defined by one or more high-seismic-velocity surface, such as (1) alluvial or glacial deposits in consolidated rock valleys, (2) limestone or sandstone underlain by metamorphic or igneous rock, or (3) saturated unconsolidated deposits overlain by unsaturated unconsolidated deposits, are ideally suited for seismic-refraction methods. These methods allow economical collection of subsurface data, provide the basis for more efficient collection of data by test drilling or aquifer tests, and result in improved hydrologic studies. This manual briefly reviews the basics of seismic-refraction theory and principles. It emphasizes the use of these techniques in hydrologic investigations and describes the planning, equipment, field procedures, and interpretation techniques needed for this type of study. Further-more, examples of the use of seismic-refraction techniques in a wide variety of hydrologic studies are presented.

  14. On the refraction of longitudinal waves in compressible media

    SciTech Connect

    Henderson, L.F.

    1988-07-01

    The refraction of plane shock waves in media with arbitrary equations of state is discussed. Previous work is reviewed briefly, and a rigorous definition of wave impedance is formulated. Earlier definitions are shown to be unsatisfactory. The impedance is combined with the boundary conditions at the media interface in order to study both head-on and oblique shock incidence. The impedance determines the nature of the reflected and transmitted waves, their intensities, and the fractions of energy and power that are reflected and transmitted. The refractive index is also defined; it determines whether or not a wave will be refracted and also helps to determine whether the wave system will be regular or irregular. The fundamental law of refraction is derived and shown to be a consequence of the fact that an arbitrary point on a shock or an expansion wave follows a ray path of minimum time between any points on the path. This is a generalization of Fermat's principle to media that are deformed and convected by the waves propagating through them. There is also a detailed discussion of a wide variety of refractions at head-on and at glancing incidence. 40 refs., 19 figs.

  15. Empirical modelling to predict the refractive index of human blood

    NASA Astrophysics Data System (ADS)

    Yahya, M.; Saghir, M. Z.

    2016-02-01

    Optical techniques used for the measurement of the optical properties of blood are of great interest in clinical diagnostics. Blood analysis is a routine procedure used in medical diagnostics to confirm a patient’s condition. Measuring the optical properties of blood is difficult due to the non-homogenous nature of the blood itself. In addition, there is a lot of variation in the refractive indices reported in the literature. These are the reasons that motivated the researchers to develop a mathematical model that can be used to predict the refractive index of human blood as a function of concentration, temperature and wavelength. The experimental measurements were conducted on mimicking phantom hemoglobin samples using the Abbemat Refractometer. The results analysis revealed a linear relationship between the refractive index and concentration as well as temperature, and a non-linear relationship between refractive index and wavelength. These results are in agreement with those found in the literature. In addition, a new formula was developed based on empirical modelling which suggests that temperature and wavelength coefficients be added to the Barer formula. The verification of this correlation confirmed its ability to determine refractive index and/or blood hematocrit values with appropriate clinical accuracy.

  16. A pitfall in shallow shear-wave refraction surveying

    USGS Publications Warehouse

    Xia, J.; Miller, R.D.; Park, C.B.; Wightman, E.; Nigbor, R.

    2002-01-01

    The shallow shear-wave refraction method works successfully in an area with a series of horizontal layers. However, complex near-surface geology may not fit into the assumption of a series of horizontal layers. That a plane SH-wave undergoes wave-type conversion along an interface in an area of nonhorizontal layers is theoretically inevitable. One real example shows that the shallow shear-wave refraction method provides velocities of a converted wave rather than an SH- wave. Moreover, it is impossible to identify the converted wave by refraction data itself. As most geophysical engineering firms have limited resources, an additional P-wave refraction survey is necessary to verify if velocities calculated from a shear-wave refraction survey are velocities of converted waves. The alternative at this time may be the surface wave method, which can provide reliable S-wave velocities, even in an area of velocity inversion (a higher velocity layer underlain by a lower velocity layer). ?? 2002 Elsevier Science B.V. All rights reserved.

  17. Refractive status of mountain aborigine schoolchildren in southern Taiwan.

    PubMed

    Hsu, Shiuh-Liang; Chang, Cheng-Hsien; Lai, Yu-Hung; Wen, Mei-Hong; Cheng, Kai-Chun; Ho, Chi-Kung

    2008-03-01

    Myopia is an epidemic health problem in Taiwan's schoolchildren. The prevalence of myopia has been increasing yearly, and the average age at which myopia develops has also become younger. Due to insufficient eye care in remote areas, the refractive status of aboriginal schoolchildren has not been well established. In 2005 and 2006, under the sponsorship of the Bureau of Health Promotion, we surveyed the ocular refraction of aboriginal schoolchildren in southern Taiwan mountain townships. From five primary schools in two townships, 371 children aged from 7 to 13 years of age were enrolled in our study. Refractive status under cycloplegia and subjective visual acuity were obtained. The crude prevalence of myopia (< -0.25 diopter [D]) was 25.6%. Although the prevalence increased with age, the annual change in mean refractive status was slower in the schoolchildren of mountain aborigines. The spherical equivalents of 93% of children were within +/- 1 D. The highest myopia was only -2.50 D. Seven children (1.82%) were refractive amblyopic, for which high hyperopia, astigmatism or anisometropia were the main causes. As aboriginal children were noted to be more myopic in this study than in the past, better eye care should be implemented in these remote areas. PMID:18364272

  18. Scattering of light passing through a statistically rough interface between media with different refractive indices after laser correction of vision

    SciTech Connect

    Semchishen, A V; Seminogov, V N; Semchishen, V A

    2012-04-30

    Forward scattering of light passing through large-scale irregularities of the interface between two media having different refractive indices is considered. An analytical expression for the ratio of intensities of directional and diffusion components of scattered light in the far-field zone is derived. It is theoretically shown that the critical depth of possible interface relief irregularities, starting from which the intensity of the diffuse component in the passing light flow becomes comparable with the directional light component, responsible for the image formation on the eye retina, is 3 - 4 {mu}m, with the increase in the refractive index in the postoperational zone taken into account. These profile depth values agree with the experimentally measured ones and may affect the contrast sensitivity of vision.

  19. Scattering of light passing through a statistically rough interface between media with different refractive indices after laser correction of vision

    NASA Astrophysics Data System (ADS)

    Semchishen, A. V.; Seminogov, V. N.; Semchishen, V. A.

    2012-04-01

    Forward scattering of light passing through large-scale irregularities of the interface between two media having different refractive indices is considered. An analytical expression for the ratio of intensities of directional and diffusion components of scattered light in the far-field zone is derived. It is theoretically shown that the critical depth of possible interface relief irregularities, starting from which the intensity of the diffuse component in the passing light flow becomes comparable with the directional light component, responsible for the image formation on the eye retina, is 3 — 4 μm, with the increase in the refractive index in the postoperational zone taken into account. These profile depth values agree with the experimentally measured ones and may affect the contrast sensitivity of vision.

  20. Polarizing phase shifting interferometry of total internal reflection light for measurement of refractive index and its spatial variation in liquid samples

    NASA Astrophysics Data System (ADS)

    Das, Tania; Bhattacharya, Kallol

    2016-07-01

    It is well known that the phase change in total internal reflection (TIR) is a function of the refractive indices of the pair of media involved. The spatial phase variations in a totally internally reflected beam are accurately measured using a Mach Zehnder interferometer employing polarization phase shifting technique. The evaluated phase change is then related to the refractive index variations of the rarer medium. One of the salient features of the proposed technique is that, unlike most interferometric methods where the measured phase is a function of the sample thickness, TIR phase is independent of the sample thickness as long as the evanescent wave field is fully confined within the sample. The theory of the technique is discussed and experimental results showing the three-dimensional profiles of the measured refractive indices and its spatial variations are presented.

  1. Radar and aircraft observations of a layer of strong refractivity turbulence

    NASA Astrophysics Data System (ADS)

    Eaton, Frank D.; Nastrom, Gregory D.; Masson, Bruce S.; Hahn, Ila L.; McCrae, Kimberley A.; Nowlin, Scott R.; Berkopec, Timothy L.

    1998-09-01

    The Air Force Research Laboratory at Kirtland Air Force Base examined the characteristics of the refractive index structure parameter (C2n) within a strong and persistent layer of turbulence using observations obtained from a 49.25 MHz radar and an instrumented C-135E aircraft at the Atmospheric Profiler Research Facility at White Sands Missile Range, NM on January 23, 1997. The aircraft measurements sensed the atmospheric temperature structure parameter (C2T) with fine-wire aerothermal probes for deriving C2n while the radar measurements provided C2n from Bragg scatter at turbulent scales in the clear air. The aircraft results provide horizontal spatial information at the specific altitudes flown while the radar-obtained values show temporal profile information. Flight legs approximately 200 km long were flown along the wind direction at eight different altitudes from 11.01 km to 12.21 km MSL. The turbulent layer and direction of flights were selected from the VHF radar-obtained C2n and wind measurements prior to take-off. Presentations include a range-height display of the patterns of refractivity turbulence obtained from the aircraft measurements and a range-height display derived from the radar observations corresponding to the aircraft results. Both range-height displays were produced by assuming Taylor's hypothesis and applying the actual wind profile to the time-height data. The evolution and persistency of features is discussed. A statistical evaluation comparing the two different methods of sensing C2n is presented. Salient features of the aircraft sensors and radar are discussed.

  2. Determining the refractive index of shocked [100] lithium fluoride to the limit of transmissibility

    SciTech Connect

    Rigg, P. A. Scharff, R. J.; Hixson, R. S.; Knudson, M. D.

    2014-07-21

    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.

  3. Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol in Situ and Remote Sensing Measurements During TARFOX

    NASA Technical Reports Server (NTRS)

    Redemann, J.; Turco, R. P.; Liou, K. N.; Russell, P. B.; Bergstrom, R. W.; Schmid, B.; Livingston, J. M.; Hobbs, P. V.; Hartley, W. S.; Ismail, S.; Ferrare, R. A.; Browell, E. V.

    2000-01-01

    The largest uncertainty in estimates of the effects of atmospheric aerosols on climate stems from uncertainties in the determination of their microphysical properties, including the aerosol complex index of refraction, which in turn determines their optical properties. A novel technique is used to estimate the aerosol complex index of refraction in distinct vertical layers from a combination of aerosol in situ size distribution and remote sensing measurements during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). In particular, aerosol backscatter measurements using the NASA Langley LASE (Lidar Atmospheric Sensing Experiment) instrument and in situ aerosol size distribution data are utilized to derive vertical profiles of the "effective" aerosol complex index of refraction at 815 nm (i.e., the refractive index that would provide the same backscatter signal in a forward calculation on the basis of the measured in situ particle size distributions for homogeneous, spherical aerosols). A sensitivity study shows that this method yields small errors in the retrieved aerosol refractive indices, provided the errors in the lidar-derived aerosol backscatter are less than 30% and random in nature. Absolute errors in the estimated aerosol refractive indices are generally less than 0.04 for the real part and can be as much as 0.042 for the imaginary part in the case of a 30% error in the lidar-derived aerosol backscatter. The measurements of aerosol optical depth from the NASA Ames Airborne Tracking Sunphotometer (AATS-6) are successfully incorporated into the new technique and help constrain the retrieved aerosol refractive indices. An application of the technique to two TARFOX case studies yields the occurrence of vertical layers of distinct aerosol refractive indices. Values of the estimated complex aerosol refractive index range from 1.33 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part. The methodology devised in this study

  4. Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol in Situ and Remote Sensing Measurements During TARFOX

    NASA Technical Reports Server (NTRS)

    Redemann, J.; Turco, R. P.; Liou, K. N.; Russell, P. B.; Bergstrom, R. W.; Schmid, B.; Livingston, J. M.; Hobbs, P. V.; Hartley, W. S.; Ismail, S.

    2000-01-01

    The largest uncertainty in estimates of the effects of atmospheric aerosols on climate stems from uncertainties in the determination of their microphysical properties, including the aerosol complex index of refraction, which in turn determines their optical properties. A novel technique is used to estimate the aerosol complex index of refraction in distinct vertical layers from a combination of aerosol in situ size distribution and remote sensing measurements during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). In particular, aerosol backscatter measurements using the NASA Langley LASE (Lidar Atmospheric Sensing Experiment) instrument and in situ aerosol size distribution data are utilized to derive vertical profiles of the 'effective' aerosol complex index of refraction at 815 nm (i.e., the refractive index that would provide the same backscatter signal in a forward calculation on the basis of the measured in situ particle size distributions for homogeneous, spherical aerosols). A sensitivity study shows that this method yields small errors in the retrieved aerosol refractive indices, provided the errors in the lidar derived aerosol backscatter are less than 30% and random in nature. Absolute errors in the estimated aerosol refractive indices are generally less than 0.04 for the real part and can be as much as 0.042 for the imaginary part in the case of a 30% error in the lidar-derived aerosol backscatter. The measurements of aerosol optical depth from the NASA Ames Airborne Tracking Sunphotometer (AATS-6) are successfully incorporated into the new technique and help constrain the retrieved aerosol refractive indices. An application of the technique to two TARFOX case studies yields the occurrence of vertical layers of distinct aerosol refractive indices. Values of the estimated complex aerosol refractive index range from 1.33 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part. The methodology devised in this study

  5. New vistas in refractive laser beam shaping with an analytic design approach

    NASA Astrophysics Data System (ADS)

    Duerr, Fabian; Thienpont, Hugo

    2014-05-01

    Many commercial, medical and scientific applications of the laser have been developed since its invention. Some of these applications require a specific beam irradiance distribution to ensure optimal performance. Often, it is possible to apply geometrical methods to design laser beam shapers. This common design approach is based on the ray mapping between the input plane and the output beam. Geometric ray mapping designs with two plano-aspheric lenses have been thoroughly studied in the past. Even though analytic expressions for various ray mapping functions do exist, the surface profiles of the lenses are still calculated numerically. In this work, we present an alternative novel design approach that allows direct calculation of the rotational symmetric lens profiles described by analytic functions. Starting from the example of a basic beam expander, a set of functional differential equations is derived from Fermat's principle. This formalism allows calculating the exact lens profiles described by Taylor series coefficients up to very high orders. To demonstrate the versatility of this new approach, two further cases are solved: a Gaussian to at-top irradiance beam shaping system, and a beam shaping system that generates a more complex dark-hollow Gaussian (donut-like) irradiance profile with zero intensity in the on-axis region. The presented ray tracing results confirm the high accuracy of all calculated solutions and indicate the potential of this design approach for refractive beam shaping applications.

  6. Internal characteristics of refractive-index matched debris flows

    NASA Astrophysics Data System (ADS)

    Gollin, Devis; Bowman, Elisabeth; Sanvitale, Nicoletta

    2016-04-01

    Debris flows are channelized masses of granular material saturated with water that travel at high speeds downslope. Their destructive character represents a hazard to lives and properties, especially in regions of high relief and runoff. The characteristics that distinguish their heterogeneous, multi-phase, nature are numerous: non-uniform surge formation, particle size ranging from clay to boulders, flow segregation with larger particles concentrating at the flow front and fluid at the tail making the composition and volume of the bulk varying with time and space. These aspects render these events very difficult to characterise and predict, in particular in the area of the deposit spread or runout - zones which are generally of most interest in terms of human risk. At present, considerable gaps exist in our understanding of the flow dynamics of debris flows, which originates from their complex motion and relatively poor observations available. Flume studies offer the potential to examine in detail the behaviour of model debris flows, however, the opaque nature of these flows is a major obstacle in gaining insight of their internal behaviour. Measurements taken at the sidewalls may be poorly representative leading to incomplete or misleading results. To probe internally to the bulk of the flow, alternative, nonintrusive techniques can be used, enabling, for instance, velocities and solid concentrations within the flowing material to be determined. We present experimental investigations into polydisperse granular flows of spherical immersed particles down an inclined flume, with specific attention directed to their internal behavior. To this end, the refractive indices of solids and liquid are closely matched allowing the two phases to be distinguished. Measurements are then made internally at a point in the channel via Plane Laser Induced Fluorescence, Particle Tracking Velocimetry, PTV and Particle Image Velocimetry, PIV. The objective is to to increase our

  7. The posterior chamber phakic refractive lens (PRL): a review

    PubMed Central

    Pérez-Cambrodí, R J; Piñero, D P; Ferrer-Blasco, T; Cerviño, A; Brautaset, R

    2013-01-01

    Implantation of phakic intraocular lenses (pIOLs) is a reversible refractive procedure, preserving the patient's accommodative function with minimal induction of higher order aberrations compared with corneal photoablative procedures. Despite this, as an intraocular procedure, it has potential risks such as cataracts, chronic uveitis, pupil ovalization, corneal endothelial cell loss, pigmentary dispersion syndrome, pupillary block glaucoma, astigmatism, or endophthalmitis. Currently, only two models of posterior chamber pIOLs are commercially available, the implantable collammer lens (STAAR Surgical Co.) and the phakic refractive lens (PRL; Zeiss Meditec). The number of published reports on the latter is very low, and some concerns still remain about its long-term safety. The present article reviews the published literature on the outcomes after PRL implantation in order to provide a general overview and evaluate its real potential as a surgical refractive option. PMID:23222559

  8. Refraction of acoustic duct waveguide modes by exhaust jets.

    NASA Technical Reports Server (NTRS)

    Mani, R.

    1973-01-01

    The refraction of acoustic duct waveguide modes emitted from the open end of a semiinfinite rectangular duct by a jet-like exhaust flow is studied theoretically. The problem is formulated as a Wiener-Hopf problem and is ultimately solved by an approximate method due to Carrier and Koiter. Continuity of transverse acoustic particle displacement and of acoustic pressure is assumed at the jet/still-air interface. The solution exhibits several features of the acoustics of moving media such as a source convection effect, zones of relative silence, and simple refraction. Plots of far-field directivity patterns are presented for several cases and show refraction effects to be important even at modest exhaust Mach numbers of order 0.3. Only subsonic exhaust Mach numbers are considered.

  9. SH-wave refraction/reflection and site characterization

    USGS Publications Warehouse

    Wang, Z.; Street, R.L.; Woolery, E.W.; Madin, I.P.

    2000-01-01

    Traditionally, nonintrusive techniques used to characterize soils have been based on P-wave refraction/reflection methods. However, near-surface unconsolidated soils are oftentimes water-saturated, and when groundwater is present at a site, the velocity of the P-waves is more related to the compressibility of the pore water than to the matrix of the unconsolidated soils. Conversely, SH-waves are directly relatable to the soil matrix. This makes SH-wave refraction/reflection methods effective in site characterizations where groundwater is present. SH-wave methods have been used extensively in site characterization and subsurface imaging for earthquake hazard assessments in the central United States and western Oregon. Comparison of SH-wave investigations with geotechnical investigations shows that SH-wave refraction/reflection techniques are viable and cost-effective for engineering site characterization.

  10. Enhanced Nonlinear Refractive Index in ɛ -Near-Zero Materials

    NASA Astrophysics Data System (ADS)

    Caspani, L.; Kaipurath, R. P. M.; Clerici, M.; Ferrera, M.; Roger, T.; Kim, J.; Kinsey, N.; Pietrzyk, M.; Di Falco, A.; Shalaev, V. M.; Boltasseva, A.; Faccio, D.

    2016-06-01

    New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here, we demonstrate a universal approach based on the low linear permittivity values attained in the ɛ -near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a sixfold increase of the Kerr nonlinear refractive index (n2) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics.

  11. How To Prepare Materials With a Desired Refraction Coefficient?

    SciTech Connect

    Ramm, A. G.

    2010-05-21

    In this talk a method is described for preparing materials with a desired refraction coefficient. The method consists of embedding into a material with known refraction coefficient many small particles of size a. The number of particles per unit volume around any point is prescribed, the distance between neighboring particles is O(a{sup (2-kappa/3)}) as a->0, 00. The refraction coefficient is the coefficient n{sup 2}(x) in the wave equation [nabla{sup 2}+kappa{sup 2}n{sup 2}(x)]u = 0.

  12. Terahertz refractive index sensors using dielectric pipe waveguides.

    PubMed

    You, Borwen; Lu, Ja-Yu; Yu, Chin-Ping; Liu, Tze-An; Peng, Jin-Long

    2012-03-12

    A dielectric pipe waveguide is successfully demonstrated as a terahertz refractive index sensor for powder and liquid-vapor sensing. Without additional engineered structures, a simple pipe waveguide can act as a terahertz resonator based on anti-resonant reflecting guidance, forming multiple resonant transmission-dips. Loading various powders in the ring-cladding or inserting different vapors into the hollow core of the pipe waveguide leads to a significant shift of resonant frequency, and the spectral shift is related to the refractive-index change. The proven detection limit of molecular density could be reduced to 1.6nano-mole/mm3 and the highest sensitivity is demonstrated at around 22.2GHz/refractive-index-unit (RIU), which is comparable to the best THz molecular sensor [Appl. Phys. Lett. 95, 171113 (2009)]. PMID:22418463

  13. Calculation of turbulence effects in an upward-refracting atmosphere

    NASA Astrophysics Data System (ADS)

    Gilbert, Kenneth E.; di, Xiao; Raspet, Richard

    1990-06-01

    The effect of atmospheric turbulence on sound propagation was investigated for both nonrefractive and refractive atmospheres, using the parabolic equation method of Gilbert and White (1989) in conjunction with a two-dimensional atmospheric turbulence model. The calculations for a nonrefractive atmosphere gave good agreement with experimental data and with Daigle's (1979) theory, while calculations for an upward-refractive atmosphere gave reasonable agreement with the data of Weiner and Keast (1959). It is concluded that, for a receiver deep in a shadow zone and for frequencies greater than a few hundred hertz, the measured sound-pressure level is due almost entirely to the sound scattered into the shadow zone by atmospheric turbulence. Consequently, for upward refraction and frequencies above a few hundred hertz, turbulence must be included in long-range propagation calculations.

  14. Enhanced Nonlinear Refractive Index in ε-Near-Zero Materials.

    PubMed

    Caspani, L; Kaipurath, R P M; Clerici, M; Ferrera, M; Roger, T; Kim, J; Kinsey, N; Pietrzyk, M; Di Falco, A; Shalaev, V M; Boltasseva, A; Faccio, D

    2016-06-10

    New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here, we demonstrate a universal approach based on the low linear permittivity values attained in the ε-near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a sixfold increase of the Kerr nonlinear refractive index (n_{2}) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics. PMID:27341234

  15. The posterior chamber phakic refractive lens (PRL): a review.

    PubMed

    Pérez-Cambrodí, R J; Piñero, D P; Ferrer-Blasco, T; Cerviño, A; Brautaset, R

    2013-01-01

    Implantation of phakic intraocular lenses (pIOLs) is a reversible refractive procedure, preserving the patient's accommodative function with minimal induction of higher order aberrations compared with corneal photoablative procedures. Despite this, as an intraocular procedure, it has potential risks such as cataracts, chronic uveitis, pupil ovalization, corneal endothelial cell loss, pigmentary dispersion syndrome, pupillary block glaucoma, astigmatism, or endophthalmitis. Currently, only two models of posterior chamber pIOLs are commercially available, the implantable collammer lens (STAAR Surgical Co.) and the phakic refractive lens (PRL; Zeiss Meditec). The number of published reports on the latter is very low, and some concerns still remain about its long-term safety. The present article reviews the published literature on the outcomes after PRL implantation in order to provide a general overview and evaluate its real potential as a surgical refractive option. PMID:23222559

  16. Peripheral Refraction with and without Contact Lens Correction

    PubMed Central

    Shen, Jie; Clark, Christopher A.; Soni, P. Sarita; Thibos, Larry N.

    2011-01-01

    Purpose Peripheral refractive error degrades the quality of retinal images and has been hypothesized to be a stimulus for the development of refractive error. The purpose of this study was to investigate the changes in refractive error across the horizontal visual field produced by contact lenses (CLs) and to quantify the effect of CLs on peripheral image blur. Methods A commercial Shack-Hartmann aberrometer measured ocular wavefront aberrations in 5° steps across the central 60° of visual field along the horizontal meridian before and after CLs correction. Wavefront refractions for peripheral lines-of-sight were based on the full elliptical pupil encountered in peripheral measurements. Curvature of field is the change in peripheral spherical equivalent relative to the eye’s optical axis. Results Hyperopic curvature of field in the naked eye increases with increasing amounts central myopic refractive error as predicted by Atchison (2006). For an eccentricity of E degrees, field curvature is approximately E percent of foveal refractive error. Rigid gas permeable (RGP) lenses changed field curvature in the myopic direction twice as much as soft contact lenses (SCLs). Both of these effects varied with CLs power. For all lens powers, SCL cut the degree of hyperopic field curvature in half whereas RGP lenses nearly eliminated field curvature. The benefit of reduced field curvature was partially offset by increased oblique astigmatism. The net reduction of retinal blur due to CLs is approximately constant across the visual field. Conclusions Both SCL and RGP lenses reduced the degree of hyperopic field curvature present in myopic eyes, with RGP lenses having greater effect. The tradeoff between field curvature and off-axis astigmatism with RGP lenses may limit their effectiveness for control of myopia progression. These results suggest that axial growth mechanisms that depend on retinal image quality will be affected more by RGP than by SCL lenses. PMID:20601913

  17. Automated measurement of the refractive index of fluids

    SciTech Connect

    Pixton, Bruce M.; Greivenkamp, John E

    2008-04-01

    A method for automating refractive-index measurements of fluids has been developed. An encoded rotation stage and position-sensitive detector enable automated reading of angles typically acquired by visual means. Two tunable lasers are used to obtain index measurements at ten discrete wavelengths across the visible spectrum. This method has been implemented on a Hilger-Chance refractometer from which the bulk refractive-index values for various transparent fluids have been measured. An index measurement accuracy of better than one part in the fourth decimal place for distilled water and a few parts in the fourth decimal place for higher index fluids is obtained.

  18. Quantum dot-embedded microspheres for remote refractive index sensing.

    PubMed

    Pang, Shuo; Beckham, Richard E; Meissner, Kenith E

    2008-06-01

    We present a refractometric sensor based on quantum dot-embedded polystyrene microspheres. Optical resonances within a microsphere, known as whispering-gallery modes (WGMs), produce narrow spectral peaks. For sensing applications, spectral shifts of these peaks are sensitive to changes in the local refractive index. In this work, two-photon excited luminescence from the quantum dots couples into several WGMs within the microresonator. By optimizing the detection area, the spectral visibility of the WGMs is improved. The spectral shifts are measured as the surrounding index of the refraction changes. The experimental sensitivity is about five times greater than that predicted by the Mie theory. PMID:19488403

  19. Overlapping illusions by transformation optics without any negative refraction material

    PubMed Central

    Sun, Fei; He, Sailing

    2016-01-01

    A novel method to achieve an overlapping illusion without any negative refraction index material is introduced with the help of the optic-null medium (ONM) designed by an extremely stretching spatial transformation. Unlike the previous methods to achieve such an optical illusion by transformation optics (TO), our method can achieve a power combination and reshape the radiation pattern at the same time. Unlike the overlapping illusion with some negative refraction index material, our method is not sensitive to the loss of the materials. Other advantages over existing methods are discussed. Numerical simulations are given to verify the performance of the proposed devices. PMID:26751285

  20. Inter-tester Agreement in Refractive Error Measurements

    PubMed Central

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

    2014-01-01

    Purpose To determine the inter-tester agreement of refractive error measurements between lay and nurse screeners using the Retinomax Autorefractor (Retinomax) and the SureSight Vision Screener (SureSight). Methods 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. Inter-tester 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 inter-tester difference (lay minus nurse) was compared between groups defined based on 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. Inter-eye correlation was accounted for in all analyses. Results The mean inter-tester 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 inter-tester 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. Conclusions 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 inter-tester 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 inter

  1. Refraction of sound by a shear layer - Experimental assessment

    NASA Technical Reports Server (NTRS)

    Schlinker, R. H.; Amiet, R. K.

    1979-01-01

    An experimental study was conducted to determine the refraction angle and amplitude changes associated with sound transmission through a circular, open jet shear layer. Both on-axis and off-axis acoustic source locations were used. Source frequency varied from 1 kHz to 10 kHz while freestream Mach number varied from 0.1 to 0.4. The experimental results were compared with an existing refraction theory which was extended to account for off-axis source positions. A simple experiment was also conducted to assess the importance of turbulence scattering between 1 kHz and 25 kHz.

  2. Measurements of photoinduced refractive index changes in bacteriorhodopsin films

    NASA Astrophysics Data System (ADS)

    Banyal, Ravinder Kumar; Raghavendra Prasad, B.

    2007-03-01

    We report the pump--probe measurements of nonlinear refractive index changes in photochromic bacteriorhodopsin films. The photoinduced absorption is caused by pump beam at 532 nm and the accompanying refractive index changes are studied using a probe beam at 633 nm. The proposed technique is based on a convenient and accurate determination of optical path difference using digital interferometry-based local fringe shift. The results are presented for the wild-type as well as genetically modified D96N variant of the bacteriorhodopsin.

  3. Additive manufacturing of a trifocal diffractive-refractive lens

    NASA Astrophysics Data System (ADS)

    Hinze, Ulf; El-Tamer, Ayman; Doskolovich, Leonid L.; Bezus, Evgeni A.; Reiß, Stefan; Stolz, Heinrich; Guthoff, Rudolf F.; Stachs, Oliver; Chichkov, Boris

    2016-08-01

    The application of two-photon polymerization and molding for the fabrication of a multifocal diffractive-refractive lens operating in water is studied. The fabricated lens is of aspheric shape and combines diffractive and refractive parts in a single element to generate three foci. The lens performance is characterized by visualization of the beam propagation in a transparent basin filled with water containing fluorescein. The experimental measurements are in good agreement with the theoretical description. The obtained results are promising for the realization of trifocal intraocular lenses with predetermined light intensity distribution between the foci.

  4. Experimental verification of electro-refractive phase modulation in graphene

    NASA Astrophysics Data System (ADS)

    Mohsin, Muhammad; Neumaier, Daniel; Schall, Daniel; Otto, Martin; Matheisen, Christopher; Lena Giesecke, Anna; Sagade, Abhay A.; Kurz, Heinrich

    2015-06-01

    Graphene has been considered as a promising material for opto-electronic devices, because of its tunable and wideband optical properties. In this work, we demonstrate electro-refractive phase modulation in graphene at wavelengths from 1530 to 1570 nm. By integrating a gated graphene layer in a silicon-waveguide based Mach-Zehnder interferometer, the key parameters of a phase modulator like change in effective refractive index, insertion loss and absorption change are extracted. These experimentally obtained values are well reproduced by simulations and design guidelines are provided to make graphene devices competitive to contemporary silicon based phase modulators for on-chip applications.

  5. Quantum dot-embedded microspheres for remote refractive index sensing

    PubMed Central

    Pang, Shuo; Beckham, Richard E.; Meissner, Kenith E.

    2008-01-01

    We present a refractometric sensor based on quantum dot-embedded polystyrene microspheres. Optical resonances within a microsphere, known as whispering-gallery modes (WGMs), produce narrow spectral peaks. For sensing applications, spectral shifts of these peaks are sensitive to changes in the local refractive index. In this work, two-photon excited luminescence from the quantum dots couples into several WGMs within the microresonator. By optimizing the detection area, the spectral visibility of the WGMs is improved. The spectral shifts are measured as the surrounding index of the refraction changes. The experimental sensitivity is about five times greater than that predicted by the Mie theory. PMID:19488403

  6. Experimental verification of electro-refractive phase modulation in graphene

    PubMed Central

    Mohsin, Muhammad; Neumaier, Daniel; Schall, Daniel; Otto, Martin; Matheisen, Christopher; Lena Giesecke, Anna; Sagade, Abhay A.; Kurz, Heinrich

    2015-01-01

    Graphene has been considered as a promising material for opto-electronic devices, because of its tunable and wideband optical properties. In this work, we demonstrate electro-refractive phase modulation in graphene at wavelengths from 1530 to 1570 nm. By integrating a gated graphene layer in a silicon-waveguide based Mach-Zehnder interferometer, the key parameters of a phase modulator like change in effective refractive index, insertion loss and absorption change are extracted. These experimentally obtained values are well reproduced by simulations and design guidelines are provided to make graphene devices competitive to contemporary silicon based phase modulators for on-chip applications. PMID:26061415

  7. Diffraction of sound by a refracting cylindrical barrier

    NASA Astrophysics Data System (ADS)

    Cole, John E., III

    1987-02-01

    The effect of refraction caused by a sound-speed gradient at the surface of a diffracting obstacle is investigated by examining both exact and asymptotic solutions for the sound field behind a rigid cylinder. Depending on the sign of the gradient, the curvature due to refraction over the surface of the obstacle either adds or subtracts from the geometric surface curvature and thereby alters the shadow zone of the obstacle. Results of exact and asymptotic solutions are found to display similar trends. Implications regarding improved acoustic performance of barriers are discussed.

  8. Extreme Brightness Temperatures and Refractive Substructure in 3C273 with RadioAstron

    NASA Astrophysics Data System (ADS)

    Johnson, Michael D.; Kovalev, Yuri Y.; Gwinn, Carl R.; Gurvits, Leonid I.; Narayan, Ramesh; Macquart, Jean-Pierre; Jauncey, David L.; Voitsik, Peter A.; Anderson, James M.; Sokolovsky, Kirill V.; Lisakov, Mikhail M.

    2016-03-01

    Earth-space interferometry with RadioAstron provides the highest direct angular resolution ever achieved in astronomy at any wavelength. RadioAstron detections of the classic quasar 3C 273 on interferometric baselines up to 171,000 km suggest brightness temperatures exceeding expected limits from the “inverse-Compton catastrophe” by two orders of magnitude. We show that at 18 cm, these estimates most likely arise from refractive substructure introduced by scattering in the interstellar medium. We use the scattering properties to estimate an intrinsic brightness temperature of 7× {10}12 {{K}}, which is consistent with expected theoretical limits, but which is ˜15 times lower than estimates that neglect substructure. At 6.2 cm, the substructure influences the measured values appreciably but gives an estimated brightness temperature that is comparable to models that do not account for the substructure. At 1.35 {{cm}}, the substructure does not affect the extremely high inferred brightness temperatures, in excess of {10}13 {{K}}. We also demonstrate that for a source having a Gaussian surface brightness profile, a single long-baseline estimate of refractive substructure determines an absolute minimum brightness temperature, if the scattering properties along a given line of sight are known, and that this minimum accurately approximates the apparent brightness temperature over a wide range of total flux densities.

  9. An overview of an intensive observation period on variability of coastal atmospheric refractivity

    NASA Astrophysics Data System (ADS)

    Paulus, Richard A.

    1995-02-01

    This paper is an overview of an experiment called Variability of Coastal Atmospheric Refractivity (VOCAR). VOCAR was designed to be conducted under a larger program called Coastal Variability Analysis, Measurements, and Prediction and is a multi-year experimental effort to investigate the variability of atmospheric refractivity with emphasis on the coastal zone. The experiment is being conducted jointly with the Naval Air Warfare Center Weapons Division, Point Mugu, CA, the Naval Research Laboratory, and the Naval Postgraduate School. In addition, the National Oceanic and Atmospheric Administration Environmental Technology Laboratory and Penn State University/Applied Research Laboratory are participating in the measurement phase of VOCAR. The propagation measurements being made during VOCAR consist of monitoring signal strength variations of VHF/UHF transmitters in the southern California coastal region. Corresponding meteorological measurements are made during routine, special, and intensive observation periods. During an intensive measurement period from 23 August to 3 September 1993, radio data were collected at two receiver sites and meteorological data were collected from three profiler sites, eight radiosonde sites, three aircraft, and numerous surface weather sites. Samples of the data will be shown.

  10. Avalon terane in eastern coastal Maine: seismic refraction-wide- angle reflection data

    USGS Publications Warehouse

    Luetgert, J.; Mann, C.E.

    1990-01-01

    A 145-km-long seismic refraction line recorded parallel to the eastern coastline of Maine within the Avalon terrane provides information about the crustal velocity structure within the Avalon block and its relation to other Appalachian terranes. A crustal velocity model for the upper 8 km shows that, except for a thin surficial layer of velocity 5.0-5.3 km/s, upper crustal granites and country rocks have velocities in the range 6.0-6.3 km/s and gabbros have a 6.5 km/s velocity. To determine the lower crustal structure, deep reflections were analyzed by applying normal moveout corrections routinely used in reflection data processing. Major reflective boundaries at approximately 3-4, 7, and 10-11 s two-way traveltime are easily distinguished, and are similar to those observed in a near-vertical seismic reflection survey crossing the refraction profile at its southwestern end. The deepest reflections correspond to the crust-mantle boundary at a depth of 34-35 km. -from Authors

  11. High refractive index substrates for fluorescence microscopy of biological interfaces with high z contrast

    PubMed Central

    Ajo-Franklin, Caroline M.; Kam, Lance; Boxer, Steven G.

    2001-01-01

    Total internal reflection fluorescence microscopy is widely used to confine the excitation of a complex fluorescent sample very close to the material on which it is supported. By working with high refractive index solid supports, it is possible to confine even further the evanescent field, and by varying the angle of incidence, to obtain quantitative information on the distance of the fluorescent object from the surface. We report the fabrication of hybrid surfaces consisting of nm layers of SiO2 on lithium niobate (LiNbO3, n = 2.3). Supported lipid bilayer membranes can be assembled and patterned on these hybrid surfaces as on conventional glass. By varying the angle of incidence of the excitation light, we are able to obtain fluorescent contrast between 40-nm fluorescent beads tethered to a supported bilayer and fluorescently labeled protein printed on the surface, which differ in vertical position by only tens of nm. Preliminary experiments that test theoretical models for the fluorescence-collection factor near a high refractive index surface are presented, and this factor is incorporated into a semiquantitative model used to predict the contrast of the 40-nm bead/protein system. These results demonstrate that it should be possible to profile the vertical location of fluorophores on the nm distance scale in real time, opening the possibility of many experiments at the interface between supported membranes and living cells. Improvements in materials and optical techniques are outlined. PMID:11717428

  12. Generation of doughnut spot for high-power laser technologies using refractive beam shaping

    NASA Astrophysics Data System (ADS)

    Laskin, Alexander; Laskin, Vadim; Ostrun, Aleksei

    2015-03-01

    Doughnut and inverse-Gauss intensity distributions of laser spot are required in laser technologies like welding, cladding where high power fiber coupled diode or solid-state lasers as well as fiber lasers are used. In comparison to Gaussian and flat-top distributions the doughnut and inverse-Gauss profiles provide more uniform temperature distribution on a work piece - this improves the technology, increase stability of processes and efficiency of using the laser energy, reduce the heat affected zone (HAZ). This type of beam shaping has become frequently asked by users of multimode lasers, especially multimode fiber coupled diode lasers. Refractive field mapping beam shapers are applied as one of solutions for the task to manipulate intensity distribution of multimode lasers. The operation principle of these devices presumes almost lossless transformation of laser beam irradiance from Gaussian to flat-top, doughnut or inverse-Gauss through controlled wavefront manipulation inside a beam shaper using lenses with smooth optical surfaces. This paper will describe some design basics of refractive beam shapers of the field mapping type and optical layouts of their applying with high-power multimode lasers. Examples of real implementations and experimental results will be presented as well.

  13. Waveguides and nonlinear index of refraction of borate glass doped with transition metals

    NASA Astrophysics Data System (ADS)

    Almeida, Juliana M. P.; Fonseca, Ruben D.; De Boni, Leonardo; Diniz, Andre Rosa S.; Hernandes, Antonio C.; Ferreira, Paulo H. D.; Mendonca, Cleber R.

    2015-04-01

    The ability to write 3D waveguides by femtosecond laser micromachining and the nonlinear refractive index (n2) spectrum of a new borate glass matrix, containing zinc and lead oxides - (BZP) have been investigated. The transparent matrix was doped with transition metals (CdCl2, Fe2O3, MnO2 and CoO) in order to introduce electronic transitions in visible spectrum, aiming to evaluate their influence on the waveguides and n2 spectrum. We observed that n2 is approximately constant from 600 to 1500 nm, exhibiting an average value of 4.5 × 10-20 m2/W, which is about twice larger than the one for fused silica. The waveguide profile is influenced by the self-focusing effect of the matrix owing to its positive nonlinear index of refraction in the wavelength used for micromachining. A decrease in the waveguide loss of approximately four times was observed for the sample doped with Fe in comparison to the other ones, which may be associated with the change in the optical gap energy.

  14. Self correction of refractive error among young people in rural China: results of cross sectional investigation

    PubMed Central

    Zhang, Mingzhi; Zhang, Riping; He, Mingguang; Liang, Wanling; Li, Xiaofeng; She, Lingbing; Yang, Yunli; MacKenzie, Graeme; Silver, Joshua D; Ellwein, Leon; Moore, Bruce

    2011-01-01

    Objective To compare outcomes between adjustable spectacles and conventional methods for refraction in young people. Design Cross sectional study. Setting Rural southern China. Participants 648 young people aged 12-18 (mean 14.9 (SD 0.98)), with uncorrected visual acuity ≤6/12 in either eye. Interventions All participants underwent self refraction without cycloplegia (paralysis of near focusing ability with topical eye drops), automated refraction without cycloplegia, and subjective refraction by an ophthalmologist with cycloplegia. Main outcome measures Uncorrected and corrected vision, improvement of vision (lines on a chart), and refractive error. Results Among the participants, 59% (384) were girls, 44% (288) wore spectacles, and 61% (393/648) had 2.00 dioptres or more of myopia in the right eye. All completed self refraction. The proportion with visual acuity ≥6/7.5 in the better eye was 5.2% (95% confidence interval 3.6% to 6.9%) for uncorrected vision, 30.2% (25.7% to 34.8%) for currently worn spectacles, 96.9% (95.5% to 98.3%) for self refraction, 98.4% (97.4% to 99.5%) for automated refraction, and 99.1% (98.3% to 99.9%) for subjective refraction (P=0.033 for self refraction v automated refraction, P=0.001 for self refraction v subjective refraction). Improvements over uncorrected vision in the better eye with self refraction and subjective refraction were within one line on the eye chart in 98% of participants. In logistic regression models, failure to achieve maximum recorded visual acuity of 6/7.5 in right eyes with self refraction was associated with greater absolute value of myopia/hyperopia (P<0.001), greater astigmatism (P=0.001), and not having previously worn spectacles (P=0.002), but not age or sex. Significant inaccuracies in power (≥1.00 dioptre) were less common in right eyes with self refraction than with automated refraction (5% v 11%, P<0.001). Conclusions Though visual acuity was slightly worse with self refraction than automated or

  15. A seismic refraction survey of the Imperial Valley Region, California

    NASA Astrophysics Data System (ADS)

    Fuis, G. S.; Mooney, W. D.; Healy, J. H.; McMechan, G. A.; Lutter, W. J.

    1984-02-01

    The U.S. Geological Survey conducted an extensive seismic refraction survey in the Imperial Valley region of California in 1979. The Imperial Valley is located in the Salton Trough, an active rift between the Pacific and North American plates. Forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0.5-1 km. More than 1300 recording locations were occupied, and more than 3000 usable seismograms were obtained. We analyzed five profiles using a standard ray-tracing program, constructed a contour map of reduced travel times from our most widely recorded shot point, and modeled an existing gravity profile across the Salton Trough. Results are itemized: (1) All models have in common a sedimentary layer (Vp = 1.8-5.0 km/s), a "transition zone" (Vp = 5.0-5.65 km/s), a basement (Vp = 5.65 km/s in the Imperial Valley, 5.9 km/s on the bordering mesas), and subbasement (Vp = 7.2 km/s). (2) The sedimentary layer ranges in thickness along the axis of the Salton Trough from 3.7 km (Salton Sea) to 4.8 km (U.S.-Mexican border). On the bordering mesas it is quite variable in thickness. (3) The "transition" zone is about 1 km thick in most places. In the Imperial Valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement. On the bordering mesas, however, there is a discontinuity at the top of this zone. (4) There are apparently two types of basement. On the bordering mesas, basement is crystalline igneous and metamorphic rocks. In the Imperial Valley, basement is mostly lower-greenshist-facies sedimentary rocks, based primarily on the smooth transition in character from sediment to basement arrivals, the low value of basement velocity, and the fact that deep (4 km) wells in the valley penetrate only the upper part of the known Cenozoic stratigraphic column for the Salton Trough. (5) The subbasement, or intermediate crustal layer, ranges in depth along the axis of the Salton Trough

  16. Hidden quantum mirage by negative refraction in semiconductor P-N junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Shu-Hui; Zhu, Jia-Ji; Yang, Wen; Lin, Hai-Qing; Chang, Kai

    2016-08-01

    We predict a robust quantum interference phenomenon in a semiconductor P-N junction: with a local pump on one side of the junction, the response of a local probe on the other side behaves as if the disturbance emanates not from the pump but instead from its mirror image about the junction. This phenomenon follows from the matching of Fermi surfaces of the constituent materials, thus it is robust against the details of the junction (e.g., width, potential profile, and even disorder), in contrast to the widely studied anomalous focusing caused by negative refraction. The recently fabricated P-N junctions in 2D semiconductors provide ideal platforms to explore this phenomenon and its applications to dramatically enhance charge and spin transport as well as carrier-mediated long-range correlation.

  17. DC resistivity and seismic refraction survey across the SE margin of Lake Ngami, NW Botswana

    NASA Astrophysics Data System (ADS)

    Shemang, Elisha; Molwalefhe, Loago

    2009-09-01

    Seismic refraction survey and DC resistivity measurements were made across the margin of the Lake Ngami. The structure and stratigraphy at the lake were determined. High resolution aeromagnetic data showed a prominent anomaly coinciding with the Kunyere Fault. Estimated depths to magnetic sources are increasing towards the lake. Two velocity layers were mapped. The top layer (500 m/s) is thin outside the lake and thicker inside the lake. The underlying layer (3125 m/s) has undeterminable thickness. Resistivity sounding results inside the lake showed that the low velocity layer has four sub-units: dry hard clays; diatomaceous earth; soft clays interlayered with silts; and wet whitish clays interlayered with silts. Normal faults were mapped along the profile with a total displacement up to 50 m. The results of the study indicate that the formation of the Lake Ngami basin was structurally controlled and probably initiated by the tectonics of the Okavango Rift Zone.

  18. Deep crustal structure of the Tuamotu plateau and Tahiti (French Polynesia) based on seismic refraction data

    NASA Astrophysics Data System (ADS)

    Patriat, Martin; Klingelhoefer, Frauke; Aslanian, Daniel; Contrucci, Isabelle; Gutscher, Marc-André; Talandier, Jacques; Avedik, Felix; Francheteau, Jean; Weigel, Wilfried

    2002-07-01

    In French Polynesia, the young (<5Ma) Society Islands appear to result from intraplate volcanism, while the old (>50 Ma) Tuamotu plateau was likely created at or near the ridge axis. The structure of the crust between those two archipelagoes is constrained by a 300 km long refraction seismic profile. Crustal and upper mantle arrivals recorded by 6 OBHs and 3 land stations were used to provide a 2D model of the crust. Results of our study, combined with that of Grevemeyer et al. [2001] show a slight flexure below the Tahiti apron, while a deep crustal root (21 km) underlies the Tuamotu plateau. These structures reflect the different modes of load emplacement and compensation mechanisms between these two volcanic edifices, consistent with an increasing elastic thickness of the oceanic lithosphere with age.

  19. Unidirectional transmission using array of zero-refractive-index metamaterials

    SciTech Connect

    Fu, Yangyang; Xu, Lin; Hong Hang, Zhi; Chen, Huanyang

    2014-05-12

    In this Letter, we find that high efficient unidirectional transmission occurs for an array of prisms made of zero-refractive-index metamaterials. As a specific demonstration, we further design the device using Dirac-cone-like photonic crystals. The device can function for a broadband of spectrum. Numerical simulations are performed to verify the one-way wave functionality.

  20. Nano-imprint gold grating as refractive index sensor

    NASA Astrophysics Data System (ADS)

    Kumari, Sudha; Mohapatra, Saswat; Moirangthem, Rakesh S.

    2016-05-01

    Large scale of fabrication of plasmonic nanostructures has been a challenging task due to time consuming process and requirement of expensive nanofabrication tools such as electron beam lithography system, focused ion beam system, and extreme UV photolithography system. Here, we present a cost-effective fabrication technique so called soft nanoimprinting to fabricate nanostructures on the larger sample area. In our fabrication process, a commercially available optical DVD disc was used as a template which was imprinted on a polymer glass substrate to prepare 1D polymer nano-grating. A homemade nanoimprinting setup was used in this fabrication process. Further, a label-free refractive index sensor was developed by utilizing the properties of surface plasmon resonance (SPR) of a gold coated 1D polymer nano-grating. Refractive index sensing was tested by exposing different solutions of glycerol-water mixture on the surface of gold nano-grating. The calculated bulk refractive index sensitivity was found to be 751nm/RIU. We believed that our proposed SPR sensor could be a promising candidate for developing low-cost refractive index sensor with high sensitivity on a large scale.

  1. Optical glass: refractive index change with wavelength and temperature

    NASA Astrophysics Data System (ADS)

    Englert, Marion; Hartmann, Peter; Reichel, Steffen

    2014-05-01

    With the catalog of 1992 SCHOTT introduced two formulae each with six parameters for a better representation of the refractive index of optical glasses. The Sellmeier-equation improved the characterization of dispersion at room temperature and the Hoffmann equation that of its temperature dependence. Better representation had been expected because both formulae were derived from general dispersion theory. The original publication of Hoffmann et al. from 1992 contains first results on the accuracy of the fits. The extended use of the formulae has led to a collection of data allowing reviewing the adequacy of the Sellmeier-equation approach on a much broader basis. We compare fitted refractive index values with measured values for all wavelengths used at our precision refractive index goniometer. Data sets are available for specific melts of the four representative glass types N-BK7, N-FK5, LF5 and IRG2. For some materials, the optical glass N-LAF21, the IR glass IRG2 and the crystal CaF2, several sets of data for the temperature dependence of the refractive index are available thus giving evidence for the variation of these properties among melts of the same material.

  2. Refraction-enhanced tomography of mouse and rabbit lungs

    SciTech Connect

    Sera, T.; Uesugi, K.; Yagi, N.

    2005-09-15

    In order to evaluate the effectiveness of edge enhancement by refraction in computed tomography, images of a cross section of a euthanized mouse thorax were recorded at low (20 keV) and high (72 keV) x-ray energies at a spatial resolution of about 40 {mu}m. Compared with the images obtained with the detector at 30 cm from an object, when the object was located at 113 cm from the detector, the contrast between tissues and air was improved at both energies. The improvement was more pronounced at 72 keV where the absorption contrast was weaker. This effect was due to refraction at the surfaces of alveolar membranes and small airways which creates areas with apparently high and low linear attenuation coefficients within tissues. The edge enhancement by refraction was also effective in images of a euthanized rabbit thorax at x-ray energies of 40 and 70 keV at a spatial resolution of about 0.15 mm. These results raise the possibility that the refraction contrast may be utilized to obtain a high-resolution tomographic image of human lung and bone with low dose.

  3. Refraction effects in soft x-ray multilayer blazed gratings.

    PubMed

    Voronov, D L; Salmassi, F; Meyer-Ilse, J; Gullikson, E M; Warwick, T; Padmore, H A

    2016-05-30

    A 2500 lines/mm Multilayer Blazed Grating (MBG) optimized for the soft x-ray wavelength range was fabricated and tested. The grating coated with a W/B4C multilayer demonstrated a record diffraction efficiency in the 2nd blazed diffraction order in the energy range from 500 to 1200 eV. Detailed investigation of the diffraction properties of the grating demonstrated that the diffraction efficiency of high groove density MBGs is not limited by the normal shadowing effects that limits grazing incidence x-ray grating performance. Refraction effects inherent in asymmetrical Bragg diffraction were experimentally confirmed for MBGs. The refraction affects the blazing properties of the MBGs and results in a shift of the resonance wavelength of the gratings and broadening or narrowing of the grating bandwidth depending on diffraction geometry. The true blaze angle of the MBGs is defined by both the real structure of the multilayer stack and by asymmetrical refraction effects. Refraction effects can be used as a powerful tool in providing highly efficient suppression of high order harmonics. PMID:27410064

  4. Statistics of the residual refraction errors in laser ranging data

    NASA Technical Reports Server (NTRS)

    Gardner, C. S.

    1977-01-01

    A theoretical model for the range error covariance was derived by assuming that the residual refraction errors are due entirely to errors in the meteorological data which are used to calculate the atmospheric correction. The properties of the covariance function are illustrated by evaluating the theoretical model for the special case of a dense network of weather stations uniformly distributed within a circle.

  5. Refractive index modification of polymers using nanosized dopants

    NASA Astrophysics Data System (ADS)

    Hanemann, Thomas; Boehm, Johannes; Müller, Claas; Ritzhaupt-Kleissl, Eberhard

    2008-04-01

    The addition of nanosized inorganic or organic dopants to polymers allows the modification of the polymers physical properties enabling the realization of functionalized polymers with new application fields e.g. in microoptics. Exemplarily electron rich organic dopants, solved in polymers, cause a pronounced increase of the refractive index. Polymer based reactive resins like PMMA, solved in MMA, or unsaturated polyester, solved in styrene, can be cured to thermoplastic polymers. The resin's low viscous flow behaviour enables an easy composite formation by solving the organic dopants in the liquid up to a dopant content of 50 wt%, followed by solidification to a thermoplastic. The addition of simple organic molecules like phenanthrene or benzochinoline allows a refractive index elevation at 633 nm from 1.56 up to 1.60 retaining the good transmission properties. In comparison the refractive index of PMMA can be increased from the initial value of 1.49 up to values around 1.58 (@633 nm). All composites show an almost linear correlation between dopant content and refractive index. Using these composites devices like 3dB-couplers or an electrooptical modulator applying injection molded or hot embossed substrates have been realized.

  6. Indications, results, and complications of refractive corneal surgery with lasers.

    PubMed

    Brancato, R; Carones, F

    1994-08-01

    The applications of the current laser technology in refractive surgery have developed during the past year. Several techniques to correct ametropia with various laser sources have been proposed and investigated. To date, using the myopic photorefractive keratectomy excimer laser is the most common technique; it has already been performed on more than 100,000 eyes worldwide. Refractive results on large series of patients with long-term follow-up indicate that the technique is safe, effective, and highly predictable in the correction of low to moderate myopia. Concerns about the treatment of high myopia still arise, especially regarding regression toward myopia and stability of achieved refraction; multizone treatments have been proposed to reach better results. The correction of compound myopic astigmatism with the excimer laser seems to be promising, although long-term results on large series are still pending. Among the patients treated, very few complications occurred. We believe that laser technology will play the most important role in refractive surgery in the future. PMID:10147334

  7. Studies of the Reflection, Refraction and Internal Reflection of Light

    ERIC Educational Resources Information Center

    Lanchester, P. C.

    2014-01-01

    An inexpensive apparatus and associated experiments are described for studying the basic laws of reflection and refraction of light at an air-glass interface, and multiple internal reflections within a glass block. In order to motivate students and encourage their active participation, a novel technique is described for determining the refractive…

  8. VOCAR: An experiment in Variability of Coastal Atmospheric Refractivity

    NASA Astrophysics Data System (ADS)

    Paulus, Richard A.

    1994-10-01

    A previous radio-meteorological experiment conducted along the coast of southern California showed a high correlation between UHF signals and the base of the elevated temperature inversion. A reanalysis of this experimental data with a recently developed hybrid propagation model confirmed this correlation and a method to remotely sense the refractive structure was proposed. An experiment called Variability of Coastal Atmospheric Refractivity (VOCAR) was designed under a larger program called Coastal Variability Analysis, Measurements, and Prediction. VOCAR is a multi-year experimental effort to investigate the variability of atmospheric refractivity with emphasis on the coastal zone. The experiment is being conducted by the Naval Command, Control and Ocean Surveillance Center RDT&E Division jointly with the Naval Air Warfare Center Weapons Division, Point Mugu, CA, the Naval Research Laboratory (Washington, DC and Monterey), and the Naval Postgraduate School. In addition, the National Oceanic and Atmospheric Administration Environmental Technology Laboratory, Penn State University Applied Research Laboratory and Johns Hopkins University Applied Physics Laboratory participated in the intensive measurement phase of VOCAR. The objectives of VOCAR are to provide an assessment capability for horizontally varying refractivity conditions in a coastal environment and to develop a remote sensing capability. The propagation measurements being made during VOCAR consist of monitoring signal strength variations of VHF/UHF transmitters in the southern California coastal region. Corresponding meteorological measurements are made during routine, special, and intensive observation periods. Measurements began in May 1993 and will be conducted periodically through 1994.

  9. [ETHICAL ASPECTS OF INFORMED CONSENT IN REFRACTIVE SURGERY].

    PubMed

    Van Cauwenberge, F; Rakic, J-M; Rorive, G

    2016-03-01

    With the introduction of the use of Laser assisted surgery, refractive eye surgery knows a very large success. Surgery of well being, it requires that an extensive information is delivered to the patient concerning the benefit and possible side-effects of the available treatments. This information process may reduce the frequency of negligence claims relating to Laser eye surgery. PMID:27311245

  10. Giant Kerr nonlinearities using refractive-index enhancement

    SciTech Connect

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

    2010-03-15

    By utilizing refractive-index enhancement with vanishing absorption, a scheme is suggested that achieves giant Kerr nonlinearities between two weak laser beams. One application of this scheme is discussed and an all-optical distributed Bragg reflector is proposed that works at very low light levels.

  11. Average refractive powers of an alexandrite laser rod

    NASA Astrophysics Data System (ADS)

    Driedger, K. P.; Krause, W.; Weber, H.

    1986-04-01

    The average refractive powers (average inverse focal lengths) of the thermal lens produced by an alexandrite laser rod optically pumped at repetition rates between 0.4 and 10 Hz and with electrical flashlamp input pulse energies up to 500 J have been measured. The measuring setup is described and the measurement results are discussed.

  12. Refractive index of Lithosil and Suprasil 312 at cryogenic temperature

    NASA Astrophysics Data System (ADS)

    Vannoni, Maurizio; Olivieri, Monica; Mondello, Giuseppe; Sordini, Andrea; Molesini, Giuseppe

    2010-06-01

    Measurements of the refractive index of two different Lithosil samples and a sample of Suprasil 312 at cryogenic temperature and at 293 K are reported for the spectral range from 480 nm to 894 nm. Such data are useful for the design of fused silica optical components and systems destined for space missions.

  13. Basement configuration of on-land Kutch basin from seismic refraction studies and modeling of first arrival travel time skips

    NASA Astrophysics Data System (ADS)

    Prasad, B. Rajendra; Venkateswarlu, N.; Prasad, A. S. S. S. R. S.; Murthy, A. S. N.; Sateesh, T.

    2010-10-01

    The Kutch basin is one of the three (Narmada, Cambay and Kutch) major marginal rift basins that are close to each other in mid-western part of the Indian subcontinent. The seismic refraction and wide-angle reflection data were acquired and a first order velocity structure of the Kutch sedimentary basin along Jakhau-Mandvi, Mandvi-Mundra, Mundra-Adesar and Hamirpur-Halvad profiles is derived. The travel time skip phenomenon has been noticed in the travel time plots and record sections indicating presence of low velocity sediments. Derived two-dimensional velocity-depth models revealed a Mesozoic sedimentary sequence sandwiched between Trap and Limestone layers, in some of the profiles. Two thick low velocity layers (that corresponds early to late Mesozoic era) have been identified. These are dipping towards Mandvi along Jakhau-Mandvi profile. The early Mesozoic layer that is thinning towards southeast is completely missing in Mandvi-Mundra profile. It is also noticed that the early Mesozoic Bhuj formation exists in the northern parts of the Mundra-Adesar and Hamirpur-Halvad profiles, where it directly overlies the granitic basement. The derived velocity-depth model suggests that the basement is about 3 km deep near Jakhau and reaches a depth of about 6 km near Mandvi. The layered structure may correspond to the Tertiary, Trap, Late Mesozoic sediments and Mesozoic limestone. The velocity-depth model obtained in Kutch is very similar to earlier derived model for Jamnagar and Dwarka sub-basins of northwestern Saurashtra peninsula suggesting probable continuity/linkage between southern on-land Kutch and, across the Gulf of Kutch to Saurashtra peninunsula. We also conclude that the evolution of Kutch basin, as a peri-cratonic rift basin, is essentially controlled by the four (F1-F4) faults inferred from obvious abrupt changes in layer thickness/velocity along the seismic refraction profiles.

  14. A Role for Epha2 in Cell Migration and Refractive Organization of the Ocular Lens

    PubMed Central

    Shi, Yanrong; De Maria, Alicia; Bennett, Thomas; Shiels, Alan

    2012-01-01

    Purpose. The Epha2 receptor is a surprisingly abundant component of the membrane proteome of vertebrate lenses. In humans, genetic studies have linked mutations in EPHA2 to inherited and age-related forms of cataract, but the function of Epha2 in the lens is obscure. To gain insights into the role of Epha2, a comparative analysis of lenses from wild-type and Epha2−/− mice was performed. Methods. Epha2 distribution was examined using immunocytochemistry and Western blot analysis. Lens optical quality was assessed by laser refractometry. Confocal microscopy was used to analyze cellular phenotypes. Results. In wild-type lenses, Epha2 was expressed by lens epithelial cells and elongating fibers but was degraded during the later stages of fiber differentiation. Epha2-null lenses retained their transparency, but two key optical parameters, lens shape and internal composition, were compromised in Epha2−/− animals. Epha2-null lenses were smaller and more spherical than age-matched wild-type lenses, and laser refractometry revealed a significant decrease in refractive power of the outer cell layers of mutant lenses. In the absence of Epha2, fiber cells deviated from their normal course and terminated at sutures that were no longer centered on the optical axis. Patterning defects were also noted at the level of individual cells. Wild-type fiber cells had hexagonal cross-sectional profiles with membrane protrusions extending from the cell vertices. In contrast, Epha2−/− cells had irregular profiles, and protrusions extended from all membrane surfaces. Conclusions. These studies indicate that Epha2 is not required for transparency but does play an indispensable role in the cytoarchitecture and refractive quality of the lens. PMID:22167091

  15. Crust structure of the North China Craton from a long-range seismic wide-angle-reflection/refraction data

    NASA Astrophysics Data System (ADS)

    Tian, Xiaofeng; Zelt, Colin A.; Wang, Fuyun; Jia, Shixu; Liu, Qiaoxia

    2014-11-01

    We present an interpretation of a 1530-km-long wide-angle seismic reflection/refraction profile that extends across the North China Craton (NCC) approximately from east to west. This profile is the longest and the densest wide-angle seismic reflection/refraction profile in China up to now. Parameterizing the velocity model as layers with variable thickness, we perform seismic travel time tomography to resolve the velocity variation within layers and velocity contrast across Moho. Our model shows crustal thickness that varies from 35 km under the Shandong peninsula, to 30 km under the North China Plain (NCP) and 32-40 km under central NCC, to 45 km under the Ordos plateau. These results indicate obvious crustal thinning beneath the NCP in comparison with the ~ 35 km crustal thicknesses typical of most cratonic regions. In particular, an abrupt Moho step of ∼ 10 km is detected at the junction of the eastern block and western block of the NCC. These crustal characteristics are consistent with studies of lithosphere-asthenosphere boundary (LAB) with the method of receiver function migration, and they indicate a close correlation with lithospheric thickness and surface tectonics of the northeastern NCC. These results provide robust seismological evidence that the lithosphere from NCC to the western edge of the Taihang Mountain, might have been widely affected and thinned since its formation in the Archean era.

  16. Refractive Secondary Solar Concentrator Demonstrated High-Temperature Operation

    NASA Technical Reports Server (NTRS)

    Wong, Wayne A.

    2002-01-01

    Space applications that utilize solar thermal energy--such as electric power conversion systems, thermal propulsion systems, and furnaces--require highly efficient solar concentration systems. The NASA Glenn Research Center is developing the refractive secondary concentrator, which uses refraction and total internal reflection to efficiently concentrate and direct solar energy. When used in combination with advanced lightweight primary concentrators, such as inflatable thin films, the refractive secondary concentrator enables very high system concentration ratios and very high temperatures. Last year, Glenn successfully demonstrated a secondary concentrator throughput efficiency of 87 percent, with a projected efficiency of 93 percent using an antireflective coating. Building on this achievement, Glenn recently successfully demonstrated high-temperature operation of the secondary concentrator when it was used to heat a rhenium receiver to 2330 F. The high-temperature demonstration of the concentrator was conducted in Glenn's 68-ft long Tank 6 thermal vacuum facility equipped with a solar simulator. The facility has a rigid panel primary concentrator that was used to concentrate the light from the solar simulator onto the refractive secondary concentrator. NASA Marshall Space Flight Center provided a rhenium cavity, part of a solar thermal propulsion engine, to serve as the high-temperature receiver. The prototype refractive secondary concentrator, measuring 3.5 in. in diameter and 11.2 in. long, is made of single-crystal sapphire. A water-cooled splash shield absorbs spillage light outside of the 3.5-in. concentrator aperture. Multilayer foil insulation composed of tungsten, molybdenum, and niobium is used to minimize heat loss from the hightemperature receiver. A liquid-cooled canister calorimeter is used to measure the heat loss through the multilayer foil insulation.

  17. Treatment of Anisometropic Amblyopia in Children with Refractive Correction

    PubMed Central

    2006-01-01

    Objective: To evaluate the effectiveness of refractive correction alone for the treatment of untreated anisometropic amblyopia in children 3 to <7 years old. Design: Prospective, multicenter, noncomparative intervention. Participants: 84 children 3 to <7 years old with untreated anisometropic amblyopia ranging from 20/40 to 20/250. Methods: Optimal refractive correction was provided and visual acuity was measured with the new spectacle correction at baseline, and at 5-week intervals until visual acuity stabilized or amblyopia resolved. Main Outcome Measures: Maximum improvement in best-corrected visual acuity in the amblyopic eye and proportion of children whose amblyopia resolved (interocular difference of 1 line or less) with refractive correction alone. Results: Amblyopia improved with optical correction by 2 or more lines in 77% of the patients and resolved in 27%. Improvement took up to 30 weeks for stabilization criteria to be met. After stabilization, additional improvement occurred with spectacles alone in 21 of 34 patients followed in a control group of a subsequent randomized trial, with amblyopia resolving in 6. Treatment outcome was not related to age, but was related to better baseline visual acuity and lesser amounts of anisometropia. Conclusion: Refractive correction alone improves visual acuity in many cases and results in resolution of amblyopia in at least one third of 3 to <7-year-old children with untreated anisometropic amblyopia. While most cases of resolution occur with moderate (20/40 to 20/100) amblyopia, the average 3-line improvement in visual acuity resulting from treatment with spectacles may lessen the burden of subsequent amblyopia therapy for those with denser levels of amblyopia. Precis Refractive correction alone improves visual acuity in many cases and results in resolution of amblyopia in at least one third of children 3 to <7 years old with untreated anisometropic amblyopia. PMID:16751032

  18. Dual interferometer system for measuring index of refraction

    NASA Astrophysics Data System (ADS)

    Goodwin, Eric Peter

    The optical power of a lens is determined by the surface curvature and the refractive index, n. Knowledge of the index is required for accurate lens design models and for examining material variations from sample to sample. The refractive index of glass can be accurately measured using a prism spectrometer, but measuring the index of soft contact lens materials presents many challenges. These materials are non-rigid, thin, and must remain hydrated in a saline solution during testing. Clearly an alternative to a prism spectrometer must be used to accurately measure index. A Dual Interferometer System has been designed, built and characterized as a novel method for measuring the refractive index of transparent optical materials, including soft contact lens materials. The first interferometer is a Low Coherence Interferometer in a Twyman-Green configuration with a scanning reference mirror. The contact lens material sample is placed in a measurement cuvette, where it remains hydrated. By measuring the locations of the multiple optical interfaces, the physical thickness t of the material is measured. A new algorithm has been developed for processing the low coherence signals obtained from the reflection at each optical interface. The second interferometer is a Mach-Zehnder interferometer with a tunable HeNe laser light source. This interferometer measures the optical path length (OPL) of the test sample in the cuvette in transmission as a function of five wavelengths in the visible spectrum. This is done using phase-shifting interferometry. Multiple thickness regions are used to solve 2pi phase ambiguities in the OPL. The outputs of the two interferometers are combined to determine the refractive index as a function of wavelength: n(lambda) = OPL(lambda)/t. Since both t and OPL are measured using a detector array, n is measured at hundreds of thousands of data points. A measurement accuracy of 0.0001 in refractive index is achieved with this new instrument, which is

  19. Discriminating between Cloudy, Hazy, and Clear Sky Exoplanets Using Refraction

    NASA Astrophysics Data System (ADS)

    Misra, Amit K.; Meadows, Victoria S.

    2014-11-01

    We propose a method to distinguish between cloudy, hazy, and clear sky (free of clouds and hazes) exoplanet atmospheres that could be applicable to upcoming large aperture space- and ground-based telescopes such as the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT). These facilities will be powerful tools for characterizing transiting exoplanets, but only after a considerable amount of telescope time is devoted to a single planet. A technique that could provide a relatively rapid means of identifying haze-free targets (which may be more valuable targets for characterization) could potentially increase the science return for these telescopes. Our proposed method utilizes broadband observations of refracted light in the out-of-transit spectrum. Light refracted through an exoplanet atmosphere can lead to an increase of flux prior to ingress and subsequent to egress. Because this light is transmitted at pressures greater than those for typical cloud and haze layers, the detection of refracted light could indicate a cloud- or haze-free atmosphere. A detection of refracted light could be accomplished in <10 hr for Jovian exoplanets with JWST and <5 hr for super-Earths/mini-Neptunes with E-ELT. We find that this technique is most effective for planets with equilibrium temperatures between 200 and 500 K, which may include potentially habitable planets. A detection of refracted light for a potentially habitable planet would strongly suggest the planet was free of a global cloud or haze layer, and therefore a promising candidate for follow-up observations.

  20. DISCRIMINATING BETWEEN CLOUDY, HAZY, AND CLEAR SKY EXOPLANETS USING REFRACTION

    SciTech Connect

    Misra, Amit K.; Meadows, Victoria S.

    2014-11-01

    We propose a method to distinguish between cloudy, hazy, and clear sky (free of clouds and hazes) exoplanet atmospheres that could be applicable to upcoming large aperture space- and ground-based telescopes such as the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT). These facilities will be powerful tools for characterizing transiting exoplanets, but only after a considerable amount of telescope time is devoted to a single planet. A technique that could provide a relatively rapid means of identifying haze-free targets (which may be more valuable targets for characterization) could potentially increase the science return for these telescopes. Our proposed method utilizes broadband observations of refracted light in the out-of-transit spectrum. Light refracted through an exoplanet atmosphere can lead to an increase of flux prior to ingress and subsequent to egress. Because this light is transmitted at pressures greater than those for typical cloud and haze layers, the detection of refracted light could indicate a cloud- or haze-free atmosphere. A detection of refracted light could be accomplished in <10 hr for Jovian exoplanets with JWST and <5 hr for super-Earths/mini-Neptunes with E-ELT. We find that this technique is most effective for planets with equilibrium temperatures between 200 and 500 K, which may include potentially habitable planets. A detection of refracted light for a potentially habitable planet would strongly suggest the planet was free of a global cloud or haze layer, and therefore a promising candidate for follow-up observations.

  1. Temperature-dependent Refractive Index of Silicon and Germanium

    NASA Technical Reports Server (NTRS)

    Frey, Bradley J.; Leviton, Douglas B.; Madison, Timothy J.

    2006-01-01

    Silicon and germanium are perhaps the two most well-understood semiconductor materials in the context of solid state device technologies and more recently micromachining and nanotechnology. Meanwhile, these two materials are also important in the field of infrared lens design. Optical instruments designed for the wavelength range where these two materials are transmissive achieve best performance when cooled to cryogenic temperatures to enhance signal from the scene over instrument background radiation. In order to enable high quality lens designs using silicon and germanium at cryogenic temperatures, we have measured the absolute refractive index of multiple prisms of these two materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For silicon, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 20 to 300 K at wavelengths from 1.1 to 5.6 pin, while for germanium, we cover temperatures ranging from 20 to 300 K and wavelengths from 1.9 to 5.5 microns. We compare our measurements with others in the literature and provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. Citing the wide variety of values for the refractive indices of these two materials found in the literature, we reiterate the importance of measuring the refractive index of a sample from the same batch of raw material from which final optical components are cut when absolute accuracy greater than k5 x 10" is desired.

  2. An experimental investigation of the effect of boundary layer refraction on the noise from a high-speed propeller

    NASA Technical Reports Server (NTRS)

    Dittmar, J. H.; Burns, R. J.; Leciejewski, D. J.

    1984-01-01

    Models of supersonic propellers were previously tested for acoustics in the Lewis 8- by 6-Foot Wind Tunnel using pressure transducers mounted in the tunnel ceiling. The boundary layer on the tunnel ceiling is believed to refract some of the propeller noise away from the measurement transducers. Measurements were made on a plate installed in the wind tunnel which had a thinner boundary layer than the ceiling boundary layer. The plate was installed in two locations for comparison with tunnel ceiling noise data and with fuselage data taken on the NASA Dryden Jetstar airplane. Analysis of the data indicates that the refraction increases with: increasing boundary layer thickness; increasing free stream Mach number; increasing frequency; and decreasing sound radiation angle (toward the inlet axis). At aft radiation angles greater than about 100 deg there was little or no refraction. Comparisons with the airplane data indicated that not only is the boundary layer thickness important but also the shape of the velocity profile. Comparisons with an existing two-dimensional theory, using an idealized shear layer to approximate the boundary layer, showed that the theory and data had the same trends. Analysis of the data taken in the tunnel at two different distances from the propeller indicates a decay with distance in the wind tunnel at high Mach numbers but the decay at low Mach numbers is not as clear.

  3. Radar coverage predictions through time- and range-dependent refractive atmospheres with planetary boundary layer and electromagnetic parabolic equation models

    NASA Astrophysics Data System (ADS)

    Skura, J. P.; Schemm, C. E.; Ko, H. W.; Manzi, L. P.

    The enhancement of the capability of electromagnetic parabolic equation (EMPE) and other propagation codes by using predictions from an atmospheric forecast model to provide refractivity data for range-dependent and time-varying situations is demonstrated. Starting from measured temperature and humidity data at one location and time, the JHU/APL planetary boundary layer (PBL) model is used to obtained predictions for a 24-h forecast period. Predicted fields of temperature, humidity, and refractivity after 12 and 24 h are compared with measured data to verify the forecast, and vertical profiles of refractivity for each hour are provided, along with appropriate radar parameters, as input to EMPE. The EMPE calculations of expected radiation patterns as functions of height and range at selected times demonstrate the effects of hourly changes in the structure of the lower atmosphere on radar propagation. The radar propagation calculations have been repeated using the IREPS code to illustrate the similarities and differences between the two models when applied to this somewhat idealized, horizontally homogeneous situation.

  4. Parameter estimation of atmospheric refractivity from radar clutter using the particle swarm optimization via Lévy flight

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi-Hua; Sheng, Zheng; Shi, Han-Qing

    2015-01-01

    Estimating refractivity profiles from radar sea clutter is a complex nonlinear optimization problem. To deal with the ill-posed difficulties, an inversion algorithm, particle swarm optimization with a Lévy flight (LPSO), was proposed to be applied in the refractivity from clutter (RFC) technique to retrieve atmospheric duct in this paper. PSO has many advantages in solving continuous optimization problems, while in its late period it has slow convergence speed and low precision. Therefore, we integrate the Lévy flights into the standard PSO algorithm to improve the precision and enhance the capability of jumping out of the local optima. To verify the feasibility and validation of the LPSO for estimating atmospheric duct parameters based on the RFC method, the synthetic and Wallops98 experimental data are implemented. Numerical experiments demonstrate that the optimal solutions obtained from the hybrid algorithm are more precise and efficient. Additionally, to test the algorithm inversion performance, the antinoise ability of LPSO is analyzed. The results indicate that the LPSO algorithm has a certain antinoise ability. Finally, according to the experiment results, it can be concluded that the LPSO algorithm can provide a more precise and efficient method for near-real-time inversion of atmospheric refractivity from radar clutter.

  5. Joint French-German radar measurements for the determination of the refractive index in the maritime boundary layer

    NASA Astrophysics Data System (ADS)

    Essen, Helmut; Danklmayer, Andreas; Förster, Jörg; Behn, Mario; Hurtaud, Yvonick; Fabbro, Vincent; Castanet, Laurent

    2012-10-01

    To predict the performance of coastal and shipborne radars, it is essential to assess the propagation characteristics of electromagnetic waves in the maritime boundary layer. To be independent upon environmental measurements, which are generally not as precise and reliable as they have to be for a proper input to simulation programs, usually based upon parabolic equation models, a method to retrieve the refractive index gradients in the low troposphere is the Refractivity from Clutter (RFC) algorithm. The propagation factor is computed from the received clutter power and is iteratively processed in order to retrieve the refractive index profiles. Under a respective French-German technical agreement a measurement program concerning radar propagation in the maritime boundary layer has been initiated, with contributions from ONERA-CERT, DGA MI / TN, Fraunhofer-FHR and the German Technical Center for Ships and Naval Weapons (WTD 71). The paper gives an overview on the RFC method with examples from the previous campaigns. It describes the experimental set-up and its methodology.

  6. Retrieval of refractive index fields in two-dimensional gradient-index elements from external deflectometry data.

    PubMed

    Lin, Di; Leger, James R

    2016-03-01

    In a previous work, we presented a numerical method for retrieving inhomogeneous refractive index fields in rectangular gradient-index elements from boundary positions and internal boundary slopes associated with a set of interrogating probe beams that transit the medium. The present work extends this method to external boundary beam slopes without knowledge of the refractive index along the surface of the optical element, requiring minimal additional information (outside of beam position and slope data) such as a single known index point inside the medium. The inverse problem is cast as a linear algebraic system describing the deflection of probe beams inside the optical material, and an iterative inversion algorithm is used to generate an index field that produces the boundary value data. By incorporating Snell's law into the system equation through surface values derived from tentative reconstructions of the refractive index, we show in simulation that a series of inversion cycles applied to the system equation accurately recovers the index profile used to generate the test data. PMID:26974909

  7. Measurement of gradient index profile using deflectometry

    NASA Astrophysics Data System (ADS)

    Sekh, Md. Asraful; Biswas, Nisha Sood; Sarkar, Samir; Basuray, Amitabha

    2013-10-01

    The present paper reports a simple technique for measurement of one dimensional graded index (GRIN) profile using deflectometry. In this method the linear fringe pattern generated by a lateral shear interferometer using a Wollaston prism is made incident on the GRIN sample and the profile is measured from the deflection of the fringes. The method is simple and also gives a visual display of the GRIN profiles. Computation of the profile from the deflection of fringes is also simple. Measured data is compared with the theoretical ones obtained from the solution of the diffusion equation. Results are reported for negative refractive index profiles made by exchanging Na+ for Li+ ions in Na2O-Li2O-Al2O3-ZrO2-SiO2 glasses.

  8. Predicted and measured boundary layer refraction for advanced turboprop propeller noise

    NASA Technical Reports Server (NTRS)

    Dittmar, James H.; Krejsa, Eugene A.

    1990-01-01

    Currently, boundary layer refraction presents a limitation to the measurement of forward arc propeller noise measured on an acoustic plate in the NASA Lewis 8- by 6-Foot Supersonic Wind Tunnel. The use of a validated boundary layer refraction model to adjust the data could remove this limitation. An existing boundary layer refraction model is used to predict the refraction for cases where boundary layer refraction was measured. In general, the model exhibits the same qualitative behavior as the measured refraction. However, the prediction method does not show quantitative agreement with the data. In general, it overpredicts the amount of refraction for the far forward angles at axial Mach number of 0.85 and 0.80 and underpredicts the refraction at axial Mach numbers of 0.75 and 0.70. A more complete propeller source description is suggested as a way to improve the prediction method.

  9. At-wavelength characterization of refractive x-ray lenses using a two-dimensional grating interferometer

    SciTech Connect

    Rutishauser, Simon; David, Christian; Zanette, Irene; Weitkamp, Timm; Donath, Tilman

    2011-11-28

    We report on the application of a two-dimensional hard x-ray grating interferometer to x-ray optics metrology. The interferometer is sensitive to refraction angles in two perpendicular directions with a precision of 10 nrad. It is used to observe the wavefront changes induced by a single parabolic beryllium focusing lens of large radius of curvature. The lens shape is reconstructed and its residual aberrations are analyzed. Its profile differs from an ideal parabolic shape by less than 2 {mu}m or {lambda}/50 at {lambda} = 0.54 A wavelength.

  10. Measurement of near-surface seismic compressional wave velocities using refraction tomography at a proposed construction site on the Presidio of Monterey, California

    USGS Publications Warehouse

    Powers, Michael H.; Burton, Bethany L.

    2012-01-01

    The U.S. Army Corps of Engineers is determining the feasibility of constructing a new barracks building on the U.S. Army Presidio of Monterey in Monterey, California. Due to the presence of an endangered orchid in the proposed area, invasive techniques such as exploratory drill holes are prohibited. To aid in determining the feasibility, budget, and design of this building, a compressional-wave seismic refraction survey was proposed by the U.S. Geological Survey as an alternative means of investigating the depth to competent bedrock. Two sub-parallel profiles were acquired along an existing foot path and a fence line to minimize impacts on the endangered flora. The compressional-wave seismic refraction tomography data for both profiles indicate that no competent rock classified as non-rippable or marginally rippable exists within the top 30 feet beneath the ground surface.

  11. Refraction measurements and modeling over the Chesapeake Bay during the NATO (TG-51) SAPPHIRE trials, June 2006

    NASA Astrophysics Data System (ADS)

    de Jong, Arie N.; Fritz, Peter J.

    2007-10-01

    Optical refraction tends to occur frequently in the atmospheric boundary layer. Due to a gradient in the temperature as function of height, rays are bending down towards the earth (super-refraction), or up towards to the sky (sub-refraction). As a consequence, images of targets at long range may be distorted and mirages may occur, while the maximum detection range may be affected. In addition the irradiance, received from a point target at a sensor pupil, may increase or decrease due to atmospheric focusing effects. Sub-refraction tends to occur more frequently over sea-paths, as the air is normally cooler than the water. Currently available propagation models, like IRBLEM [1] and EOSTAR [2] adequately describe the mentioned effects for this condition. However sparse data are available for model validation in super-refractive conditions, when the air is warmer than the water. For this reason, the SAPPHIRE trial, (Ship and Atmospheric Propagation Phenomena Infrared Experiment), was organized in the Chesapeake Bay near Washington DC by NATO Task Group TG51 in June 2006. At this location and in this time of the year, the probability for having positive ASTD (Air to Sea Temperature Difference) conditions is high. In the bay a buoy was positioned, on which a set of precision temperature sensors was mounted. They provided as well ASTD values as temperature gradients at a height of 3.7 m. By means of a geodetic theodolite, absolute AOA's (Angle Of Arrival) were measured for a set of lights at various altitudes, located on the other side of the bay at a distance of 16.2 km. The buoy was located at about mid-path position. Positive ASTD conditions did occur on a number of days allowing validation of the values of the AOA, predicted by the models, based upon the meteorological data, simultaneously collected at the buoy. It was found, that the temperature profile, generated by the bulk model for the marine surface layer [3] is incorrect, resulting in deviations in the AOA

  12. Polarization beam splitters based on a two-dimensional photonic crystal of negative refraction.

    PubMed

    Ao, Xianyu; He, Sailing

    2005-08-15

    A two-dimensional metallo-dielectric photonic crystal of negative refraction was designed for the application of polarization beam splitters. To match the refractive index of air, the effective refractive index of the designed photonic crystal is -1 for TE polarization and +1 for TM polarization. Two types of polarization beam splitter are presented. PMID:16127940

  13. Inversion of the anomalous diffraction approximation for variable complex index of refraction near unity. [numerical tests for water-haze aerosol model

    NASA Technical Reports Server (NTRS)

    Smith, C. B.

    1982-01-01

    The Fymat analytic inversion method for retrieving a particle-area distribution function from anomalous diffraction multispectral extinction data and total area is generalized to the case of a variable complex refractive index m(lambda) near unity depending on spectral wavelength lambda. Inversion tests are presented for a water-haze aerosol model. An upper-phase shift limit of 5 pi/2 retrieved an accurate peak area distribution profile. Analytical corrections using both the total number and area improved the inversion.

  14. Ambient illuminance, retinal dopamine release and refractive development in chicks.

    PubMed

    Cohen, Yuval; Peleg, Edna; Belkin, Michael; Polat, Uri; Solomon, Arieh S

    2012-10-01

    Form deprivation and low illuminance of ambient light are known to induce myopia in chicks. Low concentrations of retinal dopamine, a light-driven neurohormone, was previously shown to be associated with form deprivation myopia. In the present study we examined the dependence of retinal dopamine release in chicks on illuminance during light-dark cycles and in continuous light, and the role of retinal dopamine release in illuminance dependent refractive development. Newly hatched chicks (n = 166) were divided into two experimental groups, a dopamine (n = 88) and a refraction group (n = 78). Both groups were further divided into six illumination groups for exposure of chicks to illuminances of 50, 500 or 10,000 lux of incandescent illumination (referred to throughout as low, medium, and high illuminance, respectively), either under a light-dark cycle with lights on between 7 AM and 7 PM or under continuous illumination. For the dopamine experiment, chicks were euthanized and vitreous was extracted on day 14 post-hatching at 7, 8 AM and 1 PM. Vitreal dihydroxyphenylacetic acid (DOPAC) and dopamine concentrations were quantified by high-performance liquid chromatography coupled to electrochemical detection. For the refraction experiment, chicks underwent refraction, keratometry and A-scan ultrasonography on days 30, 60 and 90 post-hatching, and each of those measurements was correlated with vitreal DOPAC concentration measured at 1 PM (representing the index of retinal dopamine release). The results showed that under light-dark cycles, vitreal DOPAC concentration was strongly correlated with log illuminance, and was significantly correlated with the developing refraction, corneal radius of curvature, and axial length values. On day 90, low vitreal DOPAC concentrations were associated with myopia (-2.41 ± 1.23 D), flat cornea, deep anterior and vitreous chambers, and thin lens. Under continuous light, vitreal DOPAC concentrations measured at 1 PM in the low, medium

  15. Empirical estimates of cumulative refraction errors associated with procedurally constrained levelings based on the Gaithersburg-Tucson Refraction Tests of the National Geodetic Survey

    NASA Astrophysics Data System (ADS)

    Castle, Robert O.; Gilmore, Thomas D.; Mark, Robert K.; Shaw, Roger H.

    1985-05-01

    Analyses of results of the National Geodetic Survey's leveling refraction tests indicate that the standard deviation about the mean (σ) for high-scale minus low-scale rod readings closely correlates with measured refraction error. Use of this relation in conjunction with values for σ obtained from routinely constrained surveys provides a basis for estimating the refraction error associated with levelings of stipulated order and class.

  16. Empirical estimates of cumulative refraction errors associated with procedurally constrained levelings based on the Gaithersburg- Tucson refraction tests of the National Geodetic Survey.

    USGS Publications Warehouse

    Castle, R.O.; Gilmore, T.D.; Mark, R.K.; Shaw, R.H.

    1985-01-01

    Analyses of results of the National Geodetic Survey's leveling refraction tests indicate that the standard deviation about the mean (sigma) for high-scale minus low-scale rod readings closely correlates with measured refraction error. Use of this relation in conjunction with values for sigma obtained from routinely constrainted surveys provides a basis for estimating the refraction error associated with levelings of stipulated order and class. -Authors

  17. INDEX OF REFRACTION OF SHOCK LOADED SODA-LIME GLASS

    SciTech Connect

    Alexander, C. S.

    2009-12-28

    Soda-lime glass (SLG) is a potential low-cost VISAR window for use at moderate shock pressures (up to 2430 GPa) where the material remains transparent. In order for SLG to be practical as a VISAR window, the correction factor, which describes the frequency correction related to the strain dependence of the refractive index, and hence the index of refraction itself, must be characterized as a function of pressure. Characterization data are reported in this paper and compared to previous results. The present data show good agreement with those of Dandekar [J. Appl. Phys. 84, 6614 (1998)] and separate study results by Gibbons and Ahrens [J. Geophys. Res. 76, 5489 (1971)] up to 7 GPa. However, at stresses over 7 GPa, marked discrepancies are evident between the present data and that of Gibbons and Ahrens. Differences in test methods may explain these discrepancies.

  18. Nonlinear refraction of silver hydrosols during their aggregation

    SciTech Connect

    Karpov, S V; Kodirov, M K; Ryasnyansky, A I; Slabko, V V

    2001-10-31

    The relation between the degree of aggregation of silver hydrosols and their nonlinear refractive index n{sub 2} is studied experimentally. It is found that the sign of n{sub 2} at a wavelength of 1.064 {mu}m changes with increasing the aggregation degree, which corresponds to the replacing of self-focusing by self-defocusing. The observed effects are explained based on the analysis of a change in nonlinear dispersion of the medium, taking into account the interaction between phases and the photochromic effects, which are typical for colloidal structures with fractal geometry. It is shown that the change in the sign of the nonlinear refractive index of hydrosols upon irradiation by laser pulses of duration of less than 10{sup -7} s is caused by the perturbation of resonances of silver and water and by the competition between Kerr nonlinear polarisations involving these resonances. (nonlinear optical phenomena and devices)

  19. Cataract Surgery with a Refractive Corneal Inlay in Place

    PubMed Central

    Stojanovic, N. R.; Panagopoulou, S. I.; Pallikaris, I. G.

    2015-01-01

    Purpose. To present a case of cataract surgery performed in a patient with a refractive corneal inlay in place. Methods. A 48-year-old female patient presented to our institute with bilateral cataract. The patient had undergone refractive corneal inlay implantation three years ago in her right, nondominant eye for presbyopia correction. Biometry and intraocular lens (IOL) power calculation were performed without removing the inlay. Phacoemulsification and IOL insertion were carried out in both eyes in a usual manner. Results. On day one postoperatively, the patient achieved binocular uncorrected distance visual acuity 20/20 and uncorrected near visual acuity J1. The vision remained stable during the one-year follow-up period. Conclusion. Cataract surgery was performed in a standard manner in a patient with Presbia Microlens corneal inlay in place. Visual outcomes for both near and distance vision were satisfactory. PMID:26171265

  20. Effect of parallel refraction on magnetospheric upper hybrid waves

    NASA Technical Reports Server (NTRS)

    Engel, J.; Kennel, C. F.

    1984-01-01

    Large amplitude (not less than 10 mV/m) electrostatic plasma waves near the upper hybrid (UH) frequency have been observed from 0 to 50 deg magnetic latitude (MLAT) during satellite plasma-pause crossings. A three-dimensional numerical ray-tracing calculation, based on an electron distribution measured during a GEOS 1 dayside intense upper-hybrid wave event, suggests how UH waves might achieve such large amplitudes away from the geomagnetic equator. Refractive effects largely control the wave amplification and, in particular, the unavoidable refraction due to parallel geomagnetic field gradients restricts growth to levels below those observed. However, a cold electron density gradient parallel to the field can lead to upper hybrid wave growth that can account for the observed emission levels.