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Sample records for active wavefront sensing

  1. Hybrid Architecture Active Wavefront Sensing and Control

    NASA Technical Reports Server (NTRS)

    Feinberg, Lee; Dean, Bruce; Hyde, Tupper

    2010-01-01

    A method was developed for performing relatively high-speed wavefront sensing and control to overcome thermal instabilities in a segmented primary mirror telescope [e.g., James Webb Space Telescope (JWST) at L2], by using the onboard fine guidance sensor (FGS) to minimize expense and complexity. This FGS performs centroiding on a bright star to feed the information to the pointing and control system. The proposed concept is to beam split the image of the guide star (or use a single defocused guide star image) to perform wavefront sensing using phase retrieval techniques. Using the fine guidance sensor star image for guiding and fine phasing eliminates the need for other, more complex ways of achieving very accurate sensing and control that is needed for UV-optical applications. The phase retrieval occurs nearly constantly, so passive thermal stability over fourteen days is not required. Using the FGS as the sensor, one can feed segment update information to actuators on the primary mirror that can update the primary mirror segment fine phasing with this frequency. Because the thermal time constants of the primary mirror are very slow compared to this duration, the mirror will appear extremely stable during observations (to the level of accuracy of the sensing and control). The sensing can use the same phase retrieval techniques as the JWST by employing an additional beam splitter, and having each channel go through a weak lens (one positive and one negative). The channels can use common or separate detectors. Phase retrieval can be performed onboard. The actuation scheme would include a coarse stage able to achieve initial alignment of several millimeters of range (similar to JWST and can use a JWST heritage sensing approach in the science camera) and a fine stage capable of continual updates.

  2. Hybrid architecture active wavefront sensing and control system, and method

    NASA Technical Reports Server (NTRS)

    Feinberg, Lee D. (Inventor); Dean, Bruce H. (Inventor); Hyde, Tristram T. (Inventor)

    2011-01-01

    According to various embodiments, provided herein is an optical system and method that can be configured to perform image analysis. The optical system can comprise a telescope assembly and one or more hybrid instruments. The one or more hybrid instruments can be configured to receive image data from the telescope assembly and perform a fine guidance operation and a wavefront sensing operation, simultaneously, on the image data received from the telescope assembly.

  3. Compressed Wavefront Sensing

    PubMed Central

    Polans, James; McNabb, Ryan P.; Izatt, Joseph A.; Farsiu, Sina

    2014-01-01

    We report on an algorithm for fast wavefront sensing that incorporates sparse representation for the first time in practice. The partial derivatives of optical wavefronts were sampled sparsely with a Shack-Hartmann wavefront sensor (SHWFS) by randomly subsampling the original SHWFS data to as little as 5%. Reconstruction was performed by a sparse representation algorithm that utilized the Zernike basis. We name this method SPARZER. Experiments on real and simulated data attest to the accuracy of the proposed techniques as compared to traditional sampling and reconstruction methods. We have made the corresponding data set and software freely available online. Compressed wavefront sensing offers the potential to increase the speed of wavefront acquisition and to defray the cost of SHWFS devices. PMID:24690703

  4. Wavefront sensing, control, and pointing

    NASA Technical Reports Server (NTRS)

    Pitts, Thomas; Sevaston, George; Agronin, Michael; Bely, Pierre; Colavita, Mark; Clampin, Mark; Harvey, James; Idell, Paul; Sandler, Dave; Ulmer, Melville

    1992-01-01

    A majority of future NASA astrophysics missions from orbiting interferometers to 16-m telescopes on the Moon have, as a common requirement, the need to bring light from a large entrance aperture to the focal plane in a way that preserves the spatial coherence properties of the starlight. Only by preserving the phase of the incoming wavefront, can many scientific observations be made, observations that range from measuring the red shift of quasi-stellar objects (QSO's) to detecting the IR emission of a planet in orbit around another star. New technologies for wavefront sensing, control, and pointing hold the key to advancing our observatories of the future from those already launched or currently under development. As the size of the optical system increases, either to increase the sensitivity or angular resolution of the instrument, traditional technologies for maintaining optical wavefront accuracy become prohibitively expensive or completely impractical. For space-based instruments, the low mass requirement and the large temperature excursions further challenge existing technologies. The Hubble Space Telescope (HST) is probably the last large space telescope to rely on passive means to keep its primary optics stable and the optical system aligned. One needs only look to the significant developments in wavefront sensing, control, and pointing that have occurred over the past several years to appreciate the potential of this technology for transforming the capability of future space observatories. Future developments in space-borne telescopes will be based in part on developments in ground-based systems. Telescopes with rigid primary mirrors much larger than 5 m in diameter are impractical because of gravity loading. New technologies are now being introduced, such as active optics, that address the scale problem and that allow very large telescopes to be built. One approach is a segmented design such as that being pioneered by the W.M. Keck telescope now under

  5. Developmental Cryogenic Active Telescope Testbed, a Wavefront Sensing and Control Testbed for the Next Generation Space Telescope

    NASA Technical Reports Server (NTRS)

    Leboeuf, Claudia M.; Davila, Pamela S.; Redding, David C.; Morell, Armando; Lowman, Andrew E.; Wilson, Mark E.; Young, Eric W.; Pacini, Linda K.; Coulter, Dan R.

    1998-01-01

    As part of the technology validation strategy of the next generation space telescope (NGST), a system testbed is being developed at GSFC, in partnership with JPL and Marshall Space Flight Center (MSFC), which will include all of the component functions envisioned in an NGST active optical system. The system will include an actively controlled, segmented primary mirror, actively controlled secondary, deformable, and fast steering mirrors, wavefront sensing optics, wavefront control algorithms, a telescope simulator module, and an interferometric wavefront sensor for use in comparing final obtained wavefronts from different tests. The developmental. cryogenic active telescope testbed (DCATT) will be implemented in three phases. Phase 1 will focus on operating the testbed at ambient temperature. During Phase 2, a cryocapable segmented telescope will be developed and cooled to cryogenic temperature to investigate the impact on the ability to correct the wavefront and stabilize the image. In Phase 3, it is planned to incorporate industry developed flight-like components, such as figure controlled mirror segments, cryogenic, low hold power actuators, or different wavefront sensing and control hardware or software. A very important element of the program is the development and subsequent validation of the integrated multidisciplinary models. The Phase 1 testbed objectives, plans, configuration, and design will be discussed.

  6. Advanced Wavefront Sensing and Control Testbed (AWCT)

    NASA Technical Reports Server (NTRS)

    Shi, Fang; Basinger, Scott A.; Diaz, Rosemary T.; Gappinger, Robert O.; Tang, Hong; Lam, Raymond K.; Sidick, Erkin; Hein, Randall C.; Rud, Mayer; Troy, Mitchell

    2010-01-01

    The Advanced Wavefront Sensing and Control Testbed (AWCT) is built as a versatile facility for developing and demonstrating, in hardware, the future technologies of wave front sensing and control algorithms for active optical systems. The testbed includes a source projector for a broadband point-source and a suite of extended scene targets, a dispersed fringe sensor, a Shack-Hartmann camera, and an imaging camera capable of phase retrieval wavefront sensing. The testbed also provides two easily accessible conjugated pupil planes which can accommodate the active optical devices such as fast steering mirror, deformable mirror, and segmented mirrors. In this paper, we describe the testbed optical design, testbed configurations and capabilities, as well as the initial results from the testbed hardware integrations and tests.

  7. Compressive wavefront sensing with weak values.

    PubMed

    Howland, Gregory A; Lum, Daniel J; Howell, John C

    2014-08-11

    We demonstrate a wavefront sensor that unites weak measurement and the compressive-sensing, single-pixel camera. Using a high-resolution spatial light modulator (SLM) as a variable waveplate, we weakly couple an optical field's transverse-position and polarization degrees of freedom. By placing random, binary patterns on the SLM, polarization serves as a meter for directly measuring random projections of the wavefront's real and imaginary components. Compressive-sensing optimization techniques can then recover the wavefront. We acquire high quality, 256 × 256 pixel images of the wavefront from only 10,000 projections. Photon-counting detectors give sub-picowatt sensitivity.

  8. ARGOS wavefront sensing: from detection to correction

    NASA Astrophysics Data System (ADS)

    Orban de Xivry, Gilles; Bonaglia, M.; Borelli, J.; Busoni, L.; Connot, C.; Esposito, S.; Gaessler, W.; Kulas, M.; Mazzoni, T.; Puglisi, A.; Rabien, S.; Storm, J.; Ziegleder, J.

    2014-08-01

    Argos is the ground-layer adaptive optics system for the Large Binocular Telescope. In order to perform its wide-field correction, Argos uses three laser guide stars which sample the atmospheric turbulence. To perform the correction, Argos has at disposal three different wavefront sensing measurements : its three laser guide stars, a NGS tip-tilt, and a third wavefront sensor. We present the wavefront sensing architecture and its individual components, in particular: the finalized Argos pnCCD camera detecting the 3 laser guide stars at 1kHz, high quantum efficiency and 4e- noise; the Argos tip-tilt sensor based on a quad-cell avalanche photo-diodes; and the Argos wavefront computer. Being in the middle of the commissioning, we present the first wavefront sensing configurations and operations performed at LBT, and discuss further improvements in the measurements of the 3 laser guide star slopes as detected by the pnCCD.

  9. Properties of coherence-gated wavefront sensing.

    PubMed

    Rueckel, Markus; Denk, Winfried

    2007-11-01

    Coherence-gated wavefront sensing (CGWS) allows the determination of wavefront aberrations in strongly scattering tissue and their correction by adaptive optics. This allows, e.g., the restoration of the diffraction limit in light microscopy. Here, we develop a model, based on ray tracing of ballistic light scattered from a set of discrete scatterers, to characterize CGWS performance as it depends on coherence length, scatterer density, coherence-gate position, and polarization. The model is evaluated by using Monte Carlo simulation and verified against experimental measurements. We show, in particular, that all aberrations needed for adaptive wavefront restoration are correctly sensed if circularly polarized light is used. PMID:17975579

  10. Asymmetric cryptography based on wavefront sensing.

    PubMed

    Peng, Xiang; Wei, Hengzheng; Zhang, Peng

    2006-12-15

    A system of asymmetric cryptography based on wavefront sensing (ACWS) is proposed for the first time to our knowledge. One of the most significant features of the asymmetric cryptography is that a trapdoor one-way function is required and constructed by analogy to wavefront sensing, in which the public key may be derived from optical parameters, such as the wavelength or the focal length, while the private key may be obtained from a kind of regular point array. The ciphertext is generated by the encoded wavefront and represented with an irregular array. In such an ACWS system, the encryption key is not identical to the decryption key, which is another important feature of an asymmetric cryptographic system. The processes of asymmetric encryption and decryption are formulized mathematically and demonstrated with a set of numerical experiments.

  11. Recent developments of interferometric wavefront sensing

    NASA Astrophysics Data System (ADS)

    Liu, Dong; Yang, Yongying; Chen, Xiaoyu; Ling, Tong; Zhang, Lei; Bai, Jian; Shen, Yibing

    2015-08-01

    Recent trends of interferometric wavefront sensing tend to focus on high precision, anti-vibration, compact, along with much more involved of electric and computer technology. And the optical principles employed not only limit to interference but also include diffraction, scattering, polarization, etc. In this paper, some selected examples basing on the research works in our group will be given to illustrate the trends mentioned above. To achieve extra high accuracy, phase-shifting point diffraction interferometry (PS-PDI) is believed to be a good candidate as it employs a nearly perfect point diffraction spherical wavefront as the reference and also takes advantage of the high precision of phase-shifting algorithms. Cyclic radial shearing interferometry (C-RSI) successively demonstrate the anti-vibration characteristic and can diagnose transient wavefront with only one single shot by employing a three-mirror common-path configuration and a synchronizing system. In contrast sharply with those early interferometers, interferometers with very compact configuration are more suitable to develop portable wavefront sensing instruments. Cross-grating lateral shearing interferometer (CG-LSI) is a very compact interferometer that adopts a cross-grating of millimeters to produce lateral shearing of the diffraction wave of the test wavefront. Be aware that, computer technique has been used a lot in all of the above interferometers but the non-null annual sub-aperture stitching interferometer (NASSI) for general aspheric surface testing mostly relies on the computer model of the physical interferometer setup and iterative ray-tracing optimization. The principles of the above mentioned interferometric wavefront sensing methods would be given in detail.

  12. Implementation of a Wavefront-Sensing Algorithm

    NASA Technical Reports Server (NTRS)

    Smith, Jeffrey S.; Dean, Bruce; Aronstein, David

    2013-01-01

    A computer program has been written as a unique implementation of an image-based wavefront-sensing algorithm reported in "Iterative-Transform Phase Retrieval Using Adaptive Diversity" (GSC-14879-1), NASA Tech Briefs, Vol. 31, No. 4 (April 2007), page 32. This software was originally intended for application to the James Webb Space Telescope, but is also applicable to other segmented-mirror telescopes. The software is capable of determining optical-wavefront information using, as input, a variable number of irradiance measurements collected in defocus planes about the best focal position. The software also uses input of the geometrical definition of the telescope exit pupil (otherwise denoted the pupil mask) to identify the locations of the segments of the primary telescope mirror. From the irradiance data and mask information, the software calculates an estimate of the optical wavefront (a measure of performance) of the telescope generally and across each primary mirror segment specifically. The software is capable of generating irradiance data, wavefront estimates, and basis functions for the full telescope and for each primary-mirror segment. Optionally, each of these pieces of information can be measured or computed outside of the software and incorporated during execution of the software.

  13. 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.

  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. Robust Image-Based Wavefront Sensing

    NASA Astrophysics Data System (ADS)

    Zielinski, Thomas P.

    2011-12-01

    Several planned future optical systems, such as the James Webb Space Telescope (JWST), rely on image-based wavefront sensing for alignment, testing, and control of optical surfaces during operation. The focus of this work is on characterizing the effects of various non-idealities on the performance of image-based wavefront sensing algorithms, developing techniques to mitigate those effects, and demonstrating these techniques in computer simulations and in the lab. Two new techniques for algorithmically determining the proper sampling factor for optical propagation are presented and tested against experimental data collected in the lab and during JWST ground-based testing. A new method for mitigating against the effects of vibration on phase retrieval is discussed, implemented, and tested in simulation. The use of an alternative type of diversity, called transverse translation, is explored for use in the JWST and shown to be a promising technique through simulation. A method for extending the capture range of phase retrieval algorithms is presented and tested both in simulation and with experimental data collected in the lab. A benchmark of a phase retrieval algorithm running on a graphics card is presented and the practical implications for JWST testing are discussed. Finally, phase retrieval results from a MEMS deformable mirror testbed are presented and compared against interferometry. The improved robustness resulting from this research will not only help to mitigate the risks associated with wavefront sensing for the JWST, but also serve as an enabling technology for future NASA missions.

  16. SAPHIRA detector for infrared wavefront sensing

    NASA Astrophysics Data System (ADS)

    Finger, Gert; Baker, Ian; Alvarez, Domingo; Ives, Derek; Mehrgan, Leander; Meyer, Manfred; Stegmeier, Jörg; Weller, Harald J.

    2014-08-01

    The only way to overcome the CMOS noise barrier of near infrared sensors used for wavefront sensing and fringe tracking is the amplification of the photoelectron signal inside the infrared pixel by means of the avalanche gain. In 2007 ESO started a program at Selex to develop near infrared electron avalanche photodiode arrays (eAPD) for wavefront sensing and fringe tracking. In a first step the cutoff wavelength was reduced from 4.5 micron to 2.5 micron in order to verify that the dark current scales with the bandgap and can be reduced to less than one electron/ms, the value required for wavefront sensing. The growth technology was liquid phase epitaxy (LPE) with annular diodes based on the loophole interconnect technology. The arrays required deep cooling to 40K to achieve acceptable cosmetic performance at high APD gain. The second step was to develop a multiplexer tailored to the specific application of the GRAVITY instrument wavefront sensors and the fringe tracker. The pixel format is 320x256 pixels. The array has 32 parallel video outputs which are arranged in such a way that the full multiplex advantage is available also for small subwindows. Nondestructive readout schemes with subpixel sampling are possible. This reduces the readout noise at high APD gain well below the subelectron level at frame rates of 1 KHz. The third step was the change of the growth technology from liquid phase epitaxy to metal organic vapour phase epitaxy (MOVPE). This growth technology allows the band structure and doping to be controlled on a 0.1μm scale and provides more flexibility for the design of diode structures. The bandgap can be varied for different layers of Hg(1-x)CdxTe. It is possible to make heterojunctions and apply solid state engineering techniques. The change to MOVPE resulted in a dramatic improvement in the cosmetic quality with 99.97 % operable pixels at an operating temperature of 85K. Currently this sensor is deployed in the 4 wavefront sensors and in the

  17. Adaptive wavefront correction in two-photon microscopy using coherence-gated wavefront sensing

    PubMed Central

    Rueckel, Markus; Mack-Bucher, Julia A.; Denk, Winfried

    2006-01-01

    The image quality of a two-photon microscope is often degraded by wavefront aberrations induced by the specimen. We demonstrate here that resolution and signal size in two-photon microcopy can be substantially improved, even in living biological specimens, by adaptive wavefront correction based on sensing the wavefront of coherence-gated backscattered light (coherence-gated wavefront sensing, CGWS) and wavefront control by a deformable mirror. A nearly diffraction-limited focus can be restored even for strong aberrations. CGWS-based wavefront correction should be applicable to samples with a wide range of scattering properties and it should be possible to perform real-time pixel-by-pixel correction even at fast scan speeds. PMID:17088565

  18. Preparing for JWST wavefront sensing and control operations

    NASA Astrophysics Data System (ADS)

    Perrin, Marshall D.; Acton, D. Scott; Lajoie, Charles-Philippe; Knight, J. Scott; Lallo, Matthew D.; Allen, Marsha; Baggett, Wayne; Barker, Elizabeth; Comeau, Thomas; Coppock, Eric; Dean, Bruce H.; Hartig, George; Hayden, William L.; Jordan, Margaret; Jurling, Alden; Kulp, Trey; Long, Joseph; McElwain, Michael W.; Meza, Luis; Nelan, Edmund P.; Soummer, Remi; Stansberry, John; Stark, Christopher; Telfer, Randal; Welsh, Andria L.; Zielinski, Thomas P.; Zimmerman, Neil T.

    2016-07-01

    The James Webb Space Telescopes segmented primary and deployable secondary mirrors will be actively con- trolled to achieve optical alignment through a complex series of steps that will extend across several months during the observatory's commissioning. This process will require an intricate interplay between individual wavefront sensing and control tasks, instrument-level checkout and commissioning, and observatory-level calibrations, which involves many subsystems across both the observatory and the ground system. Furthermore, commissioning will often exercise observatory capabilities under atypical circumstances, such as fine guiding with unstacked or defocused images, or planning targeted observations in the presence of substantial time-variable offsets to the telescope line of sight. Coordination for this process across the JWST partnership has been conducted through the Wavefront Sensing and Control Operations Working Group. We describe at a high level the activities of this group and the resulting detailed commissioning operations plans, supporting software tools development, and ongoing preparations activities at the Science and Operations Center. For each major step in JWST's wavefront sensing and control, we also explain the changes and additions that were needed to turn an initial operations concept into a flight-ready plan with proven tools. These efforts are leading to a robust and well-tested process and preparing the team for an efficient and successful commissioning of JWSTs active telescope.

  19. Wavefront Compensation Segmented Mirror Sensing and Control

    NASA Technical Reports Server (NTRS)

    Redding, David C.; Lou, John Z.; Kissil, Andrew; Bradford, Charles M.; Woody, David; Padin, Stephen

    2012-01-01

    The primary mirror of very large submillimeter-wave telescopes will necessarily be segmented into many separate mirror panels. These panels must be continuously co-phased to keep the telescope wavefront error less than a small fraction of a wavelength, to ten microns RMS (root mean square) or less. This performance must be maintained continuously across the full aperture of the telescope, in all pointing conditions, and in a variable thermal environment. A wavefront compensation segmented mirror sensing and control system, consisting of optical edge sensors, Wavefront Compensation Estimator/Controller Soft ware, and segment position actuators is proposed. Optical edge sensors are placed two per each segment-to-segment edge to continuously measure changes in segment state. Segment position actuators (three per segment) are used to move the panels. A computer control system uses the edge sensor measurements to estimate the state of all of the segments and to predict the wavefront error; segment actuator commands are computed that minimize the wavefront error. Translational or rotational motions of one segment relative to the other cause lateral displacement of the light beam, which is measured by the imaging sensor. For high accuracy, the collimator uses a shaped mask, such as one or more slits, so that the light beam forms a pattern on the sensor that permits sensing accuracy of better than 0.1 micron in two axes: in the z or local surface normal direction, and in the y direction parallel to the mirror surface and perpendicular to the beam direction. Using a co-aligned pair of sensors, with the location of the detector and collimated light source interchanged, four degrees of freedom can be sensed: transverse x and y displacements, as well as two bending angles (pitch and yaw). In this approach, each optical edge sensor head has a collimator and an imager, placing one sensor head on each side of a segment gap, with two parallel light beams crossing the gap. Two sets

  20. Curvature wavefront sensing for the large synoptic survey telescope.

    PubMed

    Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian

    2015-10-20

    The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing. PMID:26560396

  1. Curvature wavefront sensing for the large synoptic survey telescope.

    PubMed

    Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian

    2015-10-20

    The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing.

  2. Laser beacon wave-front sensing without focal anisoplanatism.

    PubMed

    Buscher, D F; Love, G D; Myers, R M

    2002-02-01

    Wave-front sensing from artificial beacons is normally performed by formation of a focused spot in the atmosphere and sensing of the wave-front distortions produced during the beam's return passage. We propose an alternative method that senses the distortions produced during the outgoing path by forming an intensity pattern in the atmosphere that is then viewed from the ground. A key advantage of this method is that a parallel beam is used, and therefore the wave-front measurements will not suffer from the effects of focal anisoplanatism. We also envisage other geometries, all based on the concept of projecting a pupil pattern onto the atmosphere.

  3. Experimental results for correlation-based wavefront sensing

    SciTech Connect

    Poyneer, L A; Palmer, D W; LaFortune, K N; Bauman, B

    2005-07-01

    Correlation wave-front sensing can improve Adaptive Optics (AO) system performance in two keys areas. For point-source-based AO systems, Correlation is more accurate, more robust to changing conditions and provides lower noise than a centroiding algorithm. Experimental results from the Lick AO system and the SSHCL laser AO system confirm this. For remote imaging, Correlation enables the use of extended objects for wave-front sensing. Results from short horizontal-path experiments will show algorithm properties and requirements.

  4. Application of L3 technology to wavefront sensing

    NASA Astrophysics Data System (ADS)

    Tulloch, Simon M.

    2004-10-01

    The new L3 Technology CCDs from E2V combine sub-electron read noise with high pixel rates. This makes them ideal candidates for wavefront sensing. ING's NAOMI adaptive optics instrument is currently limited by the readout noise of its wavefront sensor CCDs. Upgrading to L3 detectors has the potential to give a large increase in performance; simulations suggest a 2 magnitude improvement to the guide star limit. At ING we have explored the behaviour of various L3 devices in applications ranging from fast photometry, fast spectroscopy through to wavefront sensing. The investigations have been done using our own cryogenic cameras containing L3 devices coupled to an SDSU controller. An integral Peltier packaged CCD60 has also been purchased specifically for the WFS upgrade. This paper describes the progress we have made to date on the L3 wavefront sensor upgrade and our future plans for its use with a Rayleigh laser beacon.

  5. Method and apparatus for wavefront sensing

    DOEpatents

    Bahk, Seung-Whan

    2016-08-23

    A method of measuring characteristics of a wavefront of an incident beam includes obtaining an interferogram associated with the incident beam passing through a transmission mask and Fourier transforming the interferogram to provide a frequency domain interferogram. The method also includes selecting a subset of harmonics from the frequency domain interferogram, individually inverse Fourier transforming each of the subset of harmonics to provide a set of spatial domain harmonics, and extracting a phase profile from each of the set of spatial domain harmonics. The method further includes removing phase discontinuities in the phase profile, rotating the phase profile, and reconstructing a phase front of the wavefront of the incident beam.

  6. Direct wavefront sensing in adaptive optical microscopy using backscattered light.

    PubMed

    Rahman, Saad A; Booth, Martin J

    2013-08-01

    Adaptive optics has been used to compensate the detrimental effects of aberrations in a range of high-resolution microscopes. We investigate how backscattered laser illumination can be used as the source for direct wavefront sensing using a pinhole-filtered Shack-Hartmann wavefront sensor. It is found that the sensor produces linear response to input aberrations for a given specimen. The gradient of this response is dependent upon experimental configuration and specimen structure. Cross sensitivity between modes is also observed. The double pass nature of the microscope system leads in general to lower sensitivity to odd-symmetry aberration modes. The results show that there is potential for use of this type of wavefront sensing in microscopes.

  7. UA wavefront control lab: design overview and implementation of new wavefront sensing techniques

    NASA Astrophysics Data System (ADS)

    Miller, Kelsey; Guyon, Olivier; Codona, Johanan; Knight, Justin; Rodack, Alexander

    2015-09-01

    We present an overview of the design of a new testbed for studying coronagraphic imaging and wavefront control using a variety of pupil and coronagraph architectures. The testbed is designed to explore optimal use of starlight (including starlight rejected by the coronagraph) for wavefront control, system self-calibration, and point spread function (PSF) calibration. It is also compatible with coronagraph designs for centrally obscured and segmented apertures, and includes shaped or apodized pupils, a range of focal plane masks and Lyot stops of multiple sizes, and an optional PIAA apodizing stage. Starlight is reflected and imaged from the focal plane mask and Lyot stop for low-order wavefront sensing. Both a segmented and a continuous sheet MEMS DM are included to simulate segmented telescope pupils, apply known test phase patterns, and implement a controllable phase apodization coronagraph. The testbed is adaptable and is currently being used to investigate three different techniques: (1) the differential optical transfer function (dOTF), (2) low-order wavefront sensing (LOWFS) with a hybrid-Lyot coronagraph, and (3) linear dark field control (LDFC).

  8. Wavefront Sensing for WFIRST with a Linear Optical Model

    NASA Technical Reports Server (NTRS)

    Jurling, Alden S.; Content, David A.

    2012-01-01

    In this paper we develop methods to use a linear optical model to capture the field dependence of wavefront aberrations in a nonlinear optimization-based phase retrieval algorithm for image-based wavefront sensing. The linear optical model is generated from a ray trace model of the system and allows the system state to be described in terms of mechanical alignment parameters rather than wavefront coefficients. This approach allows joint optimization over images taken at different field points and does not require separate convergence of phase retrieval at individual field points. Because the algorithm exploits field diversity, multiple defocused images per field point are not required for robustness. Furthermore, because it is possible to simultaneously fit images of many stars over the field, it is not necessary to use a fixed defocus to achieve adequate signal-to-noise ratio despite having images with high dynamic range. This allows high performance wavefront sensing using in-focus science data. We applied this technique in a simulation model based on the Wide Field Infrared Survey Telescope (WFIRST) Intermediate Design Reference Mission (IDRM) imager using a linear optical model with 25 field points. We demonstrate sub-thousandth-wave wavefront sensing accuracy in the presence of noise and moderate undersampling for both monochromatic and polychromatic images using 25 high-SNR target stars. Using these high-quality wavefront sensing results, we are able to generate upsampled point-spread functions (PSFs) and use them to determine PSF ellipticity to high accuracy in order to reduce the systematic impact of aberrations on the accuracy of galactic ellipticity determination for weak-lensing science.

  9. Non-iterative adaptive optical microscopy using wavefront sensing

    NASA Astrophysics Data System (ADS)

    Tao, X.; Azucena, O.; Kubby, J.

    2016-03-01

    This paper will review the development of wide-field and confocal microscopes with wavefront sensing and adaptive optics for correcting refractive aberrations and compensating scattering when imaging through thick tissues (Drosophila embryos and mouse brain tissue). To make wavefront measurements in biological specimens we have modified the laser guide-star techniques used in astronomy for measuring wavefront aberrations that occur as star light passes through Earth's turbulent atmosphere. Here sodium atoms in Earth's mesosphere, at an altitude of 95 km, are excited to fluoresce at resonance by a high-power sodium laser. The fluorescent light creates a guide-star reference beacon at the top of the atmosphere that can be used for measuring wavefront aberrations that occur as the light passes through the atmosphere. We have developed a related approach for making wavefront measurements in biological specimens using cellular structures labeled with fluorescent proteins as laser guide-stars. An example is a fluorescently labeled centrosome in a fruit fly embryo or neurons and dendrites in mouse brains. Using adaptive optical microscopy we show that the Strehl ratio, the ratio of the peak intensity of an aberrated point source relative to the diffraction limited image, can be improved by an order of magnitude when imaging deeply into live dynamic specimens, enabling near diffraction limited deep tissue imaging.

  10. Direct-Solve Image-Based Wavefront Sensing

    NASA Technical Reports Server (NTRS)

    Lyon, Richard G.

    2009-01-01

    A method of wavefront sensing (more precisely characterized as a method of determining the deviation of a wavefront from a nominal figure) has been invented as an improved means of assessing the performance of an optical system as affected by such imperfections as misalignments, design errors, and fabrication errors. The method is implemented by software running on a single-processor computer that is connected, via a suitable interface, to the image sensor (typically, a charge-coupled device) in the system under test. The software collects a digitized single image from the image sensor. The image is displayed on a computer monitor. The software directly solves for the wavefront in a time interval of a fraction of a second. A picture of the wavefront is displayed. The solution process involves, among other things, fast Fourier transforms. It has been reported to the effect that some measure of the wavefront is decomposed into modes of the optical system under test, but it has not been reported whether this decomposition is postprocessing of the solution or part of the solution process.

  11. Broadband Phase Retrieval for Image-Based Wavefront Sensing

    NASA Technical Reports Server (NTRS)

    Dean, Bruce H.

    2007-01-01

    A focus-diverse phase-retrieval algorithm has been shown to perform adequately for the purpose of image-based wavefront sensing when (1) broadband light (typically spanning the visible spectrum) is used in forming the images by use of an optical system under test and (2) the assumption of monochromaticity is applied to the broadband image data. Heretofore, it had been assumed that in order to obtain adequate performance, it is necessary to use narrowband or monochromatic light. Some background information, including definitions of terms and a brief description of pertinent aspects of image-based phase retrieval, is prerequisite to a meaningful summary of the present development. Phase retrieval is a general term used in optics to denote estimation of optical imperfections or aberrations of an optical system under test. The term image-based wavefront sensing refers to a general class of algorithms that recover optical phase information, and phase-retrieval algorithms constitute a subset of this class. In phase retrieval, one utilizes the measured response of the optical system under test to produce a phase estimate. The optical response of the system is defined as the image of a point-source object, which could be a star or a laboratory point source. The phase-retrieval problem is characterized as image-based in the sense that a charge-coupled-device camera, preferably of scientific imaging quality, is used to collect image data where the optical system would normally form an image. In a variant of phase retrieval, denoted phase-diverse phase retrieval [which can include focus-diverse phase retrieval (in which various defocus planes are used)], an additional known aberration (or an equivalent diversity function) is superimposed as an aid in estimating unknown aberrations by use of an image-based wavefront-sensing algorithm. Image-based phase-retrieval differs from such other wavefront-sensing methods, such as interferometry, shearing interferometry, curvature

  12. Common-Path Wavefront Sensing for Advanced Coronagraphs

    NASA Technical Reports Server (NTRS)

    Wallace, J. Kent; Serabyn, Eugene; Mawet, Dimitri

    2012-01-01

    Imaging of faint companions around nearby stars is not limited by either intrinsic resolution of a coronagraph/telescope system, nor is it strictly photon limited. Typically, it is both the magnitude and temporal variation of small phase and amplitude errors imparted to the electric field by elements in the optical system which will limit ultimate performance. Adaptive optics systems, particularly those with multiple deformable mirrors, can remove these errors, but they need to be sensed in the final image plane. If the sensing system is before the final image plane, which is typical for most systems, then the non-common path optics between the wavefront sensor and science image plane will lead to un-sensed errors. However, a new generation of high-performance coronagraphs naturally lend themselves to wavefront sensing in the final image plane. These coronagraphs and the wavefront sensing will be discussed, as well as plans for demonstrating this with a high-contrast system on the ground. Such a system will be a key system-level proof for a future space-based coronagraph mission, which will also be discussed.

  13. Low order wavefront sensing and control for WFIRST coronagraph

    NASA Astrophysics Data System (ADS)

    Shi, Fang; Balasubramanian, Kunjithapatham; Bartos, Randall; Hein, Randall; Lam, Raymond; Mandic, Milan; Moore, Douglas; Moore, James; Patterson, Keith; Poberezhskiy, Ilya; Shields, Joel; Sidick, Erkin; Tang, Hong; Truong, Tuan; Wallace, James K.; Wang, Xu; Wilson, Daniel W.

    2016-07-01

    To maintain the required WFIRST Coronagraph starlight suppression performance in a realistic space environment, a low order wavefront sensing and control (LOWFS/C) subsystem is necessary. The LOWFS/C uses the rejected stellar light from coronagraph to sense and suppress the telescope pointing drift and jitter as well as the low order wavefront errors due to changes in thermal loading on the telescope and the rest of the observatory. In this paper we will present an overview of the low order wavefront sensing and control subsystem for the WFIRST Coronagraph and describe the WFIRST Coronagraph LOWFS function, its design, and modeled performance. We will present experimental results on a dedicated LOWFS/C testbed that show that the LOWFS/C subsystem not only can sense pointing errors better than 0.2 mas but has also experimentally demonstrated closed loop pointing error suppression with residuals better than 0.4 mas rms per axis for the vast majority of observatory reaction wheel speeds.

  14. Scene-based Wave-front Sensing for Remote Imaging

    SciTech Connect

    Poyneer, L A; LaFortune, K; Chan, C

    2003-07-30

    Scene-based wave-front sensing (SBWFS) is a technique that allows an arbitrary scene to be used for wave-front sensing with adaptive optics (AO) instead of the normal point source. This makes AO feasible in a wide range of interesting scenarios. This paper first presents the basic concepts and properties of SBWFS. Then it discusses that application of this technique with AO to remote imaging. For the specific case of correction of a lightweight optic. End-to-end simulation results establish that in this case, SBWFS can perform as well as point-source AO. Design considerations such as noise propagation, number of subapertures and tracking changing image content are analyzed.

  15. Wavefront Sensing Using a Multi-Object Spectrograph (NIRSpec)

    NASA Technical Reports Server (NTRS)

    Dean, Bruce H.; Boucarut, Rene; Hadjimichael, Theo; Smith, Scott

    2004-01-01

    An analysis is presented that illustrates how the James Webb Space Telescope (JWST) fine-phasing process can be carried out using the Near-Infrared Spectrograph (NIRSpec) data collected at the science focal plane. The analysis considers a multi-plane diffraction model which properly accounts for the microshutter diffractive element placed at the first relay position of the spectrograph. Wavefront sensing results are presented based on data collected from the NASA Goddard Microshutter Testbed.

  16. Sparse aperture mask for low order wavefront sensing

    NASA Astrophysics Data System (ADS)

    Subedi, Hari; Zimmerman, Neil T.; Kasdin, N. Jeremy; Cavanagh, Kathleen; Riggs, A. J. E.

    2015-09-01

    A high contrast is required for direct imaging of exoplanets. Ideally, the level of contrast required for direct imaging of exoplanets can be achieved by coronagraphic imaging, but in practice, the contrast is degraded by wavefront aberrations. To achieve the required contrast, low-order wavefront aberrations such as tip-tilt, defocus and coma must be determined and corrected. In this paper, we present a technique that integrates a sparse- aperture mask (SAM) with a shaped pupil coronagraph (SPC) to make precise estimates of these low-order aberrations. Starlight rejected by the coronagraph's focal plane stop is collimated to a relay pupil, where the mask forms an interference fringe pattern on a detector. Using numerical simulations, we show that the SAM can estimate rapidly varying tip-tilt errors in space telescopes arising from line-of-sight pointing oscillations as well as other higher-order modes. We also show that a Kalman filter can be used with the SAM to improve the estimation. At Princetons High Contrast Imaging Laboratory, we have recently created a testbed devoted to low-order wavefront sensing experiments. The testbed incorporates custom-fabricated masks (shaped pupil, focal plane, and sparse aperture) with a deformable mirror and a CCD camera to demonstrate the estimation and correction of low-order aberrations. Our first experiments aim to replicate the results of the SAM wavefront sensor (SAM WFS) Fourier propagation models.

  17. Beam geometry, alignment, and wavefront aberration effects on interferometric differential wavefront sensing

    NASA Astrophysics Data System (ADS)

    Yu, Xiangzhi; Gillmer, S. R.; Ellis, J. D.

    2015-12-01

    Heterodyne interferometry is a widely accepted methodology with high resolution in many metrology applications. As a functionality enhancement, differential wavefront sensing (DWS) enables simultaneous measurement of displacement, pitch, and yaw using a displacement interferometry system and a single beam incident on a plane mirror target. The angular change is measured using a weighted phase average between symmetrically adjacent quadrant photodiode pairs. In this paper, we present an analytical model to predict the scaling of differential phase signals based on fundamental Gaussian beams. Several numerical models are presented to discuss the effects of physical beam parameters, detector size, system alignment errors, and beam wavefront aberrations on the DWS technique. The results of our modeling predict rotational scaling factors and a usable linear range. Furthermore, experimental results show the analytically predicted scaling factor is in good agreement with empirical calibration. Our three degree-of-freedom interferometer can achieve a resolution of 0.4 nm in displacement and 0.2 μrad in pitch and yaw simultaneously.

  18. Analysis of non-linearity in differential wavefront sensing technique.

    PubMed

    Duan, Hui-Zong; Liang, Yu-Rong; Yeh, Hsien-Chi

    2016-03-01

    An analytical model of a differential wavefront sensing (DWS) technique based on Gaussian Beam propagation has been derived. Compared with the result of the interference signals detected by quadrant photodiode, which is calculated by using the numerical method, the analytical model has been verified. Both the analytical model and numerical simulation show milli-radians level non-linearity effect of DWS detection. In addition, the beam clipping has strong influence on the non-linearity of DWS. The larger the beam clipping is, the smaller the non-linearity is. However, the beam walking effect hardly has influence on DWS. Thus, it can be ignored in laser interferometer. PMID:26974079

  19. Wavefront sensing in space from the PICTURE-B sounding rocket

    NASA Astrophysics Data System (ADS)

    Douglas, Ewan S.; Mendillo, Christopher B.; Cook, Timothy A.; Chakrabarti, Supriya

    2016-07-01

    A NASA sounding rocket for high contrast imaging with a visible nulling coronagraph, the Planet Imaging Coronagraphic Technology Using a Reconfigurable Experimental Base (PICTURE-B) payload has made two suborbital attempts to observe the warm dust disk inferred around Epsilon Eridani. We present results from the November 2015 launch demonstrating active wavefront sensing in space with a piezoelectric mirror stage and a micromachine deformable mirror along with precision pointing and lightweight optics in space.

  20. Wavefront Sensing & Control for a Large Segmented Space Telescope

    NASA Astrophysics Data System (ADS)

    Redding, David; ATLAST Concept Study Team

    2009-01-01

    This poster presents an active optics control architecture for ATLAS-T16 - a proposed 16 m aperture space telescope, with a Primary Mirror composed of 32 separate hexagonal segments. ATLAS-T16 is intended to be launched in a in a large ARES rocket in the 2020 time frame. Like the James Webb Space Telescope, it would be launched in a folded configuration, and deployed after orbital insertion. The ATLAS wavefront control problem is to align the PM segments and other optics following deployment, with initial errors in the mm and mrad range, to achieve diffraction limited performance in the UV and visible wavelengths at under 50 nm WF error (RMS) across the field. In this it is similar to JWST, though with considerably tighter WF error requirements. ATLAS differs from JWST by being twice as large, with 4 times the collecting area, and with a correspondingly lighter and more flexible structure - factors that may require a continuous but low bandwidth WF and pointing control system to preserve optical quality throughout extended operational periods. The poster will describe a WFSC architecture that provides both the initial WF control and continuous metrology of the various PM segments and other optics to assure excellent optical quality throughout the mission. Control requirements will be driven by scientific mission objectives, with the most taxing being high dynamic-range imaging for exoplanet observation. Initialization will utilized image- and spectrum-based measurements for WF sensing. Continuous metrology will be provided by an "optical truss," made up of multiple Laser Distance Gauges to measure and maintain the optical state of all major optical elements in the telescope. Results from multiple testbeds and telescopes will be provided to illustrate control performance.

  1. Large viewing field wavefront sensing by using a lightfield system

    NASA Astrophysics Data System (ADS)

    Lv, Yang; Zhang, Xuanzhe; Ma, Haotong; Ning, Yu; Wang, Rui; Xu, Xiaojun

    2013-09-01

    To overcome the shortcomings of Shack-Hartmann wavefront sensor, we developed a lightfield wavefront detection system, which is able to complete the large field of view, multi-perspective wavefront detection in a single photographic exposure. The lightfield wavefront detection system includes an imaging primary mirror, a lenslet array and a photosensitive device. The lenslet array is located on the imaging plane of the imaging primary mirror and the photosensitive device is located on the focal plane of the lenslet array. In this system, each lenslet reimages the aperture and forms a low-resolution image of the aperture. Compared with the Shack-Hartmann sensor, this lightfield measuring method can obtain imaging arrays in different perspectives. By comparing the array information with the standard information, we can obtain the slope matrix of the wavefront in different perspectives and restore the wavefront in a large field of view. Based on Fourier optics, we built the corresponding theoretical model and simulation system. By busing Meade telescope, turbulent phase screen, lenslet array and CCD camera, we founded the experimental lightfield wavefront measuring system. Numerical simulation results and experimental results show that this wavefront measuring method can effectively achieve the wavefront aberration information. This wavefront measurement method can realize the multi-perspective wavefront measurement, which is expected to solve the problem of large viewing field wavefront detection, and can be used for adaptive optics in giant telescopes.

  2. TRL-6 for JWST Wavefront Sensing and Control

    NASA Technical Reports Server (NTRS)

    Feinberg, Lee; Dean, Bruce; Smith, Scott; Aronstein, David; Shiri, Ron; Lyon, Rick; Hayden, Bill; Bowers, Chuck; Acton, D. Scott; Shields, Duncan; Sabatke, Erin; Schwenker, John; Towell, Tim; Carey, Larkin; Contos, Adam; Shi, Fang; Mesa, Luis

    2007-01-01

    NASA's Technology Readiness Level (TRL)-6 is documented for the James Webb Space Telescope (JWST) Wavefront Sensing and Control (WFSC) subsystem. The WFSC subsystem is needed to align the Optical Telescope Element (OTE) after all deployments have occurred, and achieves that requirement through a robust commissioning sequence consisting of unique commissioning algorithms, all of which are part of the WFSC algorithm suite. This paper identifies the technology need, algorithm heritage, describes the finished TRL-6 design platform, and summarizes the TRL-6 test results and compliance. Additionally, the performance requirements needed to satisfy JWST science goals as well as the criterion that relate to the TRL-6 Testbed Telescope (TBT) performance requirements are discussed

  3. System and Method for Null-Lens Wavefront Sensing

    NASA Technical Reports Server (NTRS)

    Hill, Peter C. (Inventor); Thompson, Patrick L. (Inventor); Aronstein, David L. (Inventor); Bolcar, Matthew R. (Inventor); Smith, Jeffrey S. (Inventor)

    2015-01-01

    A method of measuring aberrations in a null-lens including assembly and alignment aberrations. The null-lens may be used for measuring aberrations in an aspheric optic with the null-lens. Light propagates from the aspheric optic location through the null-lens, while sweeping a detector through the null-lens focal plane. Image data being is collected at locations about said focal plane. Light is simulated propagating to the collection locations for each collected image. Null-lens aberrations may extracted, e.g., applying image-based wavefront-sensing to collected images and simulation results. The null-lens aberrations improve accuracy in measuring aspheric optic aberrations.

  4. Wavefront sensing based on phase contrast theory and coherent optical processing

    NASA Astrophysics Data System (ADS)

    Lei, Huang; Qi, Bian; Chenlu, Zhou; Tenghao, Li; Mali, Gong

    2016-07-01

    A novel wavefront sensing method based on phase contrast theory and coherent optical processing is proposed. The wavefront gradient field in the object plane is modulated into intensity distribution in a gang of patterns, making high-density detection available. By applying the method, we have also designed a wavefront sensor. It consists of a classical coherent optical processing system, a CCD detector array, two pieces of orthogonal composite sinusoidal gratings, and a mechanical structure that can perform real-time linear positioning. The simulation results prove and demonstrate the validity of the method and the sensor in high-precision measurement of the wavefront gradient field.

  5. Improving active space telescope wavefront control using predictive thermal modeling

    NASA Astrophysics Data System (ADS)

    Gersh-Range, Jessica; Perrin, Marshall D.

    2015-01-01

    Active control algorithms for space telescopes are less mature than those for large ground telescopes due to differences in the wavefront control problems. Active wavefront control for space telescopes at L2, such as the James Webb Space Telescope (JWST), requires weighing control costs against the benefits of correcting wavefront perturbations that are a predictable byproduct of the observing schedule, which is known and determined in advance. To improve the control algorithms for these telescopes, we have developed a model that calculates the temperature and wavefront evolution during a hypothetical mission, assuming the dominant wavefront perturbations are due to changes in the spacecraft attitude with respect to the sun. Using this model, we show that the wavefront can be controlled passively by introducing scheduling constraints that limit the allowable attitudes for an observation based on the observation duration and the mean telescope temperature. We also describe the implementation of a predictive controller designed to prevent the wavefront error (WFE) from exceeding a desired threshold. This controller outperforms simpler algorithms even with substantial model error, achieving a lower WFE without requiring significantly more corrections. Consequently, predictive wavefront control based on known spacecraft attitude plans is a promising approach for JWST and other future active space observatories.

  6. Wavefront sensing using a liquid-filled photonic crystal fiber.

    PubMed

    Valente, Denise; Rativa, Diego; Vohnsen, Brian

    2015-05-18

    A novel wavefront sensor based on a microstructural array of waveguides is proposed. The method is based on the sensitivity in light-coupling efficiency to the wavefront gradient present at the entrance aperture of each waveguide in an array, and hence the amount of incident light that couples is influenced by wavefront aberrations. The concept is illustrated with wavefront measurements that have been performed using a liquid-filled photonic crystal fiber (LF-PCF) working as a coherent fiber bundle. The pros and cons of the LF-PCF based sensor are discussed. PMID:26074553

  7. Wavefront Sensing Analysis of Grazing Incidence Optical Systems

    NASA Technical Reports Server (NTRS)

    Rohrbach, Scott; Saha, Timo

    2012-01-01

    Wavefront sensing is a process by which optical system errors are deduced from the aberrations in the image of an ideal source. The method has been used successfully in near-normal incidence, but not for grazing incidence systems. This innovation highlights the ability to examine out-of-focus images from grazing incidence telescopes (typically operating in the x-ray wavelengths, but integrated using optical wavelengths) and determine the lower-order deformations. This is important because as a metrology tool, this method would allow the integration of high angular resolution optics without the use of normal incidence interferometry, which requires direct access to the front surface of each mirror. Measuring the surface figure of mirror segments in a highly nested x-ray telescope mirror assembly is difficult due to the tight packing of elements and blockage of all but the innermost elements to normal incidence light. While this can be done on an individual basis in a metrology mount, once the element is installed and permanently bonded into the assembly, it is impossible to verify the figure of each element and ensure that the necessary imaging quality will be maintained. By examining on-axis images of an ideal point source, one can gauge the low-order figure errors of individual elements, even when integrated into an assembly. This technique is known as wavefront sensing (WFS). By shining collimated light down the optical axis of the telescope and looking at out-of-focus images, the blur due to low-order figure errors of individual elements can be seen, and the figure error necessary to produce that blur can be calculated. The method avoids the problem of requiring normal incidence access to the surface of each mirror segment. Mirror figure errors span a wide range of spatial frequencies, from the lowest-order bending to the highest order micro-roughness. While all of these can be measured in normal incidence, only the lowest-order contributors can be determined

  8. Wavefront Sensing with the Fine Guidance Sensor for James Webb Space Telescope

    NASA Technical Reports Server (NTRS)

    Smith, J. Scott; Aronstein, David; Dean, Bruce H.; Howard,Joe; Shiri, Ron

    2008-01-01

    An analysis is presented that utilizes the Fine Guidance Sensor (FGS) for focal-plane wavefront sensing (WFS) for the James Webb Space Telescope (JWST). WFS with FGS increases the number of wavefront measurements taken in field of the telescope, but has many challenges over the other JWST instruments that make it unique, such as; less sampling of the Point Spread Function (PSF), a smaller diversity-defocus range, a smaller image detector size, and a polychromatic object or source. Additionally, presented is an analysis of sampling for wavefront sensing. Results are shown based on simulations of flight and the cryogenic optical testing at NASA Johnson Space Center.

  9. Tomographic wavefront error using multi-LGS constellation sensed with Shack-Hartmann wavefront sensors.

    PubMed

    Robert, Clélia; Conan, Jean-Marc; Gratadour, Damien; Schreiber, Laura; Fusco, Thierry

    2010-11-01

    Noise effects induced by laser guide star (LGS) elongation have to be considered globally in a multi-LGS tomographic reconstruction analysis. This allows a fine estimation of performance and the comparison of different launching options. We present a modal analysis of the wavefront error with Shack-Hartmann wavefront sensors based on quasi-analytical matrix formalism. Including spot elongation and the Rayleigh fratricide effect, edge launching produces similar performance to central launching and avoids the risk of possible underestimation of fratricide scatter. Performance improves slightly with an optimized centroid estimator and is not affected by a slight field-of-view truncation of the subapertures. Finally we discuss detector characteristics for a LGS Shack-Hartmann wavefront sensor.

  10. Binary hologram based high speed zonal wavefront sensing with reduced estimation time

    NASA Astrophysics Data System (ADS)

    Pathak, Biswajit; Boruah, Bosanta R.

    2016-03-01

    Reduced wavefront estimation time in a Shack-Hartmann type wavefront sensor plays an important role in any high speed application of the sensor. Exploiting computer generated holography technique, one can generate an array of binary diffraction grating pattern to produce an array of focal spots, similar to that in a Shack Hartmann wavefront sensor (SHWS). The transmittance functions of each of such a grating pattern can be configured to produce a one dimensional (1D) array of focal spots of a desired order. In this paper, we show that the formation of 1D array, further facilitates in the process of single indexed wavefront estimation in its true sense that considerably reduces the wavefront estimation time.

  11. Binary hologram based high speed zonal wavefront sensing with reduced estimation time

    NASA Astrophysics Data System (ADS)

    Pathak, Biswajit; Boruah, Bosanta R.

    2016-03-01

    Reduced wavefront estimation time in a Shack-Hartmann type wavefront sensor plays an important role in any high speed application of the sensor. Exploiting computer generated holography technique, one can generate an array of binary diffraction grating pattern to produce an array of focal spots, similar to that in a Shack Hartmann wavefront sensor (SHWS). The transmittance functions of each of such a grating pattern can be configured to produce a one dimensional (1D) array of focal spots of a desired order. In this paper, we show that the formation of 1D array, further facilitates in the process of single indexed wavefront estimation in its true sense that considerably reduces the wavefront estimation time.

  12. Adaptive optics confocal microscopy using direct wavefront sensing.

    PubMed

    Tao, Xiaodong; Fernandez, Bautista; Azucena, Oscar; Fu, Min; Garcia, Denise; Zuo, Yi; Chen, Diana C; Kubby, Joel

    2011-04-01

    Optical aberrations due to the inhomogeneous refractive index of tissue degrade the resolution and brightness of images in deep-tissue imaging. We introduce a confocal fluorescence microscope with adaptive optics, which can correct aberrations based on direct wavefront measurements using a Shack-Hartmann wavefront sensor with a fluorescent bead used as a point source reference beacon. The results show a 4.3× improvement in the Strehl ratio and a 240% improvement in the signal intensity for fixed mouse tissues at depths of up to 100 μm.

  13. Maximum-likelihood methods in wavefront sensing: stochastic models and likelihood functions

    PubMed Central

    Barrett, Harrison H.; Dainty, Christopher; Lara, David

    2008-01-01

    Maximum-likelihood (ML) estimation in wavefront sensing requires careful attention to all noise sources and all factors that influence the sensor data. We present detailed probability density functions for the output of the image detector in a wavefront sensor, conditional not only on wavefront parameters but also on various nuisance parameters. Practical ways of dealing with nuisance parameters are described, and final expressions for likelihoods and Fisher information matrices are derived. The theory is illustrated by discussing Shack–Hartmann sensors, and computational requirements are discussed. Simulation results show that ML estimation can significantly increase the dynamic range of a Shack–Hartmann sensor with four detectors and that it can reduce the residual wavefront error when compared with traditional methods. PMID:17206255

  14. Zonal wavefront sensing using a grating array printed on a polyester film

    NASA Astrophysics Data System (ADS)

    Pathak, Biswajit; Kumar, Suraj; Boruah, Bosanta R.

    2015-12-01

    In this paper, we describe the development of a zonal wavefront sensor that comprises an array of binary diffraction gratings realized on a transparent sheet (i.e., polyester film) followed by a focusing lens and a camera. The sensor works in a manner similar to that of a Shack-Hartmann wavefront sensor. The fabrication of the array of gratings is immune to certain issues associated with the fabrication of the lenslet array which is commonly used in zonal wavefront sensing. Besides the sensing method offers several important advantages such as flexible dynamic range, easy configurability, and option to enhance the sensing frame rate. Here, we have demonstrated the working of the proposed sensor using a proof-of-principle experimental arrangement.

  15. Zonal wavefront sensing using a grating array printed on a polyester film.

    PubMed

    Pathak, Biswajit; Kumar, Suraj; Boruah, Bosanta R

    2015-12-01

    In this paper, we describe the development of a zonal wavefront sensor that comprises an array of binary diffraction gratings realized on a transparent sheet (i.e., polyester film) followed by a focusing lens and a camera. The sensor works in a manner similar to that of a Shack-Hartmann wavefront sensor. The fabrication of the array of gratings is immune to certain issues associated with the fabrication of the lenslet array which is commonly used in zonal wavefront sensing. Besides the sensing method offers several important advantages such as flexible dynamic range, easy configurability, and option to enhance the sensing frame rate. Here, we have demonstrated the working of the proposed sensor using a proof-of-principle experimental arrangement.

  16. Zonal wavefront sensing using a grating array printed on a polyester film

    SciTech Connect

    Pathak, Biswajit; Boruah, Bosanta R.; Kumar, Suraj

    2015-12-15

    In this paper, we describe the development of a zonal wavefront sensor that comprises an array of binary diffraction gratings realized on a transparent sheet (i.e., polyester film) followed by a focusing lens and a camera. The sensor works in a manner similar to that of a Shack-Hartmann wavefront sensor. The fabrication of the array of gratings is immune to certain issues associated with the fabrication of the lenslet array which is commonly used in zonal wavefront sensing. Besides the sensing method offers several important advantages such as flexible dynamic range, easy configurability, and option to enhance the sensing frame rate. Here, we have demonstrated the working of the proposed sensor using a proof-of-principle experimental arrangement.

  17. Common-Path Interferometric Wavefront Sensing for Space Telescopes

    NASA Technical Reports Server (NTRS)

    Wallace, James Kent

    2011-01-01

    This paper presents an optical configuration for a common-path phase-shifting interferometric wavefront sensor.1 2 This sensor has a host of attractive features which make it well suited for space-based adaptive optics. First, it is strictly reflective and therefore operates broadband, second it is common mode and therefore does not suffer from systematic errors (like vibration) that are typical in other interferometers, third it is a phase-shifting interferometer and therefore benefits from both the sensitivity of interferometric sensors as well as the noise rejection afforded by synchronous detection. Unlike the Shack-Hartman wavefront sensor, it has nearly uniform sensitivity to all pupil modes. Optical configuration, theory and simulations for such a system will be discussed along with predicted performance.

  18. On the application of background oriented schlieren for wavefront sensing

    NASA Astrophysics Data System (ADS)

    Bichal, A.; Thurow, B. S.

    2014-01-01

    The concept of utilizing a background oriented schlieren (BOS) imaging system to measure the distortion of a wavefront is presented and analyzed. It is shown that the fundamental equations characterizing the image distortion measured using BOS and the distortion of a wavefront are based on the same physical phenomena and can be easily related to one another. An analysis is performed to consider the influence of practical considerations, such as the field-of-view (FOV) and depth-of-field (DOF) on the sensitivity of the BOS measurement. It is found that when the FOV of the schlieren object is held constant and placement of both the medium and background is constrained to the DOF of the imaging system, the sensitivity of the BOS measurement is independent of the focal length of the imaging lens and overall length of the system, both of which are dependent on the FOV and DOF. An equation is derived that expresses the BOS sensitivity as a function of imaging lens f-number and the circle of confusion as these parameters are used in practice to determine the FOV and DOF. It is shown that allowing the background to be slightly out of focus can significantly increase the sensitivity of the measurement. The analysis is tested and confirmed using both computer generated model images and experiments performed to measure the wavefront distortion induced by a plano-convex lens. An uncertainty analysis is performed showing better than 0.1 pixel resolution in the image distortion, which results in an absolute error of the reconstructed wavefront that is better than 5% for the case considered here.

  19. Modeling of high-precision wavefront sensing with new generation of CMT avalanche photodiode infrared detectors.

    PubMed

    Gousset, Silvère; Petit, Cyril; Michau, Vincent; Fusco, Thierry; Robert, Clelia

    2015-12-01

    Near-infrared wavefront sensing allows for the enhancement of sky coverage with adaptive optics. The recently developed HgCdTe avalanche photodiode arrays are promising due to their very low detector noise, but still present an imperfect cosmetic that may directly impact real-time wavefront measurements for adaptive optics and thus degrade performance in astronomical applications. We propose here a model of a Shack-Hartmann wavefront measurement in the presence of residual fixed pattern noise and defective pixels. To adjust our models, a fine characterization of such an HgCdTe array, the RAPID sensor, is proposed. The impact of the cosmetic defects on the Shack-Hartmann measurement is assessed through numerical simulations. This study provides both a new insight on the applicability of cadmium mercury telluride (CMT) avalanche photodiodes detectors for astronomical applications and criteria to specify the cosmetic qualities of future arrays. PMID:26836674

  20. Curvature wavefront sensing based on a single defocused image and intensity compensation.

    PubMed

    Wu, Zhixu; Bai, Hua; Cui, Xiangqun

    2016-04-01

    Curvature wavefront sensing usually requires the measurement of two defocused images at equal distances before and after the focus. In this paper, a new wavefront recovery algorithm based on only one defocused image is proposed. This algorithm contains the following four steps: response matrix calculation, establishment of intensity distribution equations, Zernike coefficients solution derived from the least squares method, and defocused image compensation with the solved Zernike coefficients. The performance of the algorithm in a large obscuration ratio and fast focal ratio optical system on axis and the edge of the field of view (FOV) is examined. Two optical systems of the Hubble telescope and a modified Paul-Baker telescope are employed to test the algorithm. The simulations show that the proposed algorithm outperforms in structural simplicity, and applications are expected in the wavefront recovery of the extreme environment (i.e., in space and the Antarctic). PMID:27139686

  1. Curvature wavefront sensing based on a single defocused image and intensity compensation.

    PubMed

    Wu, Zhixu; Bai, Hua; Cui, Xiangqun

    2016-04-01

    Curvature wavefront sensing usually requires the measurement of two defocused images at equal distances before and after the focus. In this paper, a new wavefront recovery algorithm based on only one defocused image is proposed. This algorithm contains the following four steps: response matrix calculation, establishment of intensity distribution equations, Zernike coefficients solution derived from the least squares method, and defocused image compensation with the solved Zernike coefficients. The performance of the algorithm in a large obscuration ratio and fast focal ratio optical system on axis and the edge of the field of view (FOV) is examined. Two optical systems of the Hubble telescope and a modified Paul-Baker telescope are employed to test the algorithm. The simulations show that the proposed algorithm outperforms in structural simplicity, and applications are expected in the wavefront recovery of the extreme environment (i.e., in space and the Antarctic).

  2. Shack-Hartmann wavefront sensing using interferometric focusing of light onto guide-stars.

    PubMed

    Tao, Xiaodong; Dean, Ziah; Chien, Christopher; Azucena, Oscar; Bodington, Dare; Kubby, Joel

    2013-12-16

    Optical microscopy provides noninvasive imaging of biological tissues at subcellular level. The optical aberrations induced by the inhomogeneous refractive index of biological samples limits the resolution and can decrease the penetration depth. To compensate refractive aberrations, adaptive optics with Shack-Hartmann wavefront sensing has been used in microscopes. Wavefront measurement requires light from a guide-star inside of the sample. The scattering effect limits the intensity of the guide-star, hence reducing the signal to noise ratio of the wavefront measurement. In this paper, we demonstrate the use of interferometric focusing of excitation light onto a guide-star embedded deeply in tissue to increase its fluorescent intensity, thus overcoming the excitation signal loss caused by scattering. With interferometric focusing, we more than doubled the signal to noise ratio of the laser guide-star through scattering tissue as well as potentially extend the imaging depth through using AO microscopy.

  3. Piston and tilt interferometry for segmented wavefront sensing.

    PubMed

    Deprez, M; Bellanger, C; Lombard, L; Wattellier, B; Primot, J

    2016-03-15

    We present a novel interferometric technique dedicated to the measurement of relative phase differences (pistons) and tilts of a periodically segmented wavefront. Potential applications include co-phasing of segmented mirrors of Keck-like telescopes as well as coherent laser beam combining. The setup only requires a holes mask selecting the center part of each element, a diffracting component, and a camera. Recorded interferogram is made of many subareas with sinusoidal fringe pattern. From each pattern, piston is extracted from fringe shift and tilts from fringe frequency and orientation. The pattern analysis is simple enough to enable kilohertz rate operation. The λ ambiguities are solved by a two-wavelength measurement. This technique is compatible with a very high number of elements and can be operated in the presence of atmospheric turbulence. PMID:26977638

  4. Adaptive optics for array telescopes using piston-and-tilt wave-front sensing

    NASA Technical Reports Server (NTRS)

    Wizinowich, P.; Mcleod, B.; Lloyd-Yhart, M.; Angel, J. R. P.; Colucci, D.; Dekany, R.; Mccarthy, D.; Wittman, D.; Scott-Fleming, I.

    1992-01-01

    A near-infrared adaptive optics system operating at about 50 Hz has been used to control phase errors adaptively between two mirrors of the Multiple Mirror Telescope by stabilizing the position of the interference fringe in the combined unresolved far-field image. The resultant integrated images have angular resolutions of better than 0.1 arcsec and fringe contrasts of more than 0.6. Measurements of wave-front tilt have confirmed the wavelength independence of image motion. These results show that interferometric sensing of phase errors, when combined with a system for sensing the wave-front tilt of the individual telescopes, will provide a means of achieving a stable diffraction-limited focus with segmented telescopes or arrays of telescopes.

  5. Review of the latest developments in fast low noise detectors for wavefront sensing in the visible

    NASA Astrophysics Data System (ADS)

    Adkins, Sean M.

    2014-08-01

    In this paper we describe the development of fast low noise detectors intended primarily for use in Shack Hartmann wavefront sensors for natural and laser guide star wavefront sensing in the future adaptive optics systems of the Thirty Meter Telescope Project and the Next Generation Adaptive Optics system at the W. M. Keck Observatory. This work results from collaboration among the W. M. Keck Observatory, the Thirty Meter Telescope Project, the Lincoln Laboratory of the Massachusetts Institute of Technology, and the Starfire Optical Range of the Air Force Research Laboratory. Testing of backside thinned, packaged detectors has been completed and performance results including read noise, readout speed, charge diffusion, dark current, and quantum efficiency will be reported. Proposed developments of readout systems to compliment this detector will be described, and performance compared to alternative detector solutions.

  6. Fine optical alignment correction of astronomical spectrographs via in-situ full-field moment-based wavefront sensing

    NASA Astrophysics Data System (ADS)

    Lee, Hanshin; Hill, Gary J.; Tuttle, Sarah E.; Vattiat, Brian L.

    2012-09-01

    The image moment-based wavefront sensing (IWFS) utilizes moments of focus-modulated focal plane images to determine modal wavefront aberrations. This permits fast, easy, and accurate measurement of wavefront error (WFE) on any available finite-sized isolated targets across the entire focal plane (FP) of an imaging system, thereby allowing not only in-situ full-field image quality assessment, but also deterministic fine alignment correction of the imaging system. We present an experimental demonstration where fine alignment correction of a fast camera system in a fiber-fed astronomical spectrograph, called VIRUS, is accomplished by using IWFS.

  7. Visible and Infrared Wavefront Sensing detectors review in Europe - part I

    NASA Astrophysics Data System (ADS)

    Feautrier, Philippe; Gach, Jean-luc

    2013-12-01

    The purpose of this review is to give an overview of the state of the art wavefront sensor detectors developments held in Europe for the last decade. A major breakthrough has been achieved with the development by e2v technologies of the CCD220 between 2004 and 2012. Another major breakthrough is currently achieved with the very successful development of fast low noise infrared arrays called RAPID. The astonishing results of this device will be showed for the first time in an international conference at AO4ELT3.The CCD220, a 240x240 pixels 8 outputs EMCCD (CCD with internal multiplication), offers less than 0.2 e readout noise at a frame rate of 1500 Hz with negligible dark current. The OCAM2 camera is the commercial product that drives this advanced device. This system, commercialized by First Light Imaging, is quickly described in this paper. An upgrade of OCAM2 is currently developed to boost its frame rate to 2 kHz, opening the window of XAO wavefront sensing for the ELT using 4 synchronized cameras and pyramid wavefront sensing. This upgrade and the results obtained are described extensively elsewhere in this conference (Gach et al).Since this major success, new detector developments started in Europe. The NGSD CMOS device is fully dedicated to Natural and Laser Guide Star AO for the E-ELT with ESO involvement. The spot elongation from a LGS Shack Hartman wavefront sensor necessitates an increase of the pixel format. The NGSD will be a 880x840 pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate. New technologies will be developed for that purpose: advanced CMOS pixel architecture, CMOS back thinned and back illuminated device for very high QE, full digital outputs with signal digital conversion on chip. This innovative device will be used on the European ELT but also interests potentially all giant telescopes.Additional developments also started in 2009 for wavefront sensing in the infrared based on a new technological breakthrough

  8. Wavefront Sensing and Control Technology for Submillimeter and Far-Infrared Space Telescopes

    NASA Technical Reports Server (NTRS)

    Redding, Dave

    2004-01-01

    The NGST wavefront sensing and control system will be developed to TRL6 over the next few years, including testing in a cryogenic vacuum environment with traceable hardware. Doing this in the far-infrared and submillimeter is probably easier, as some aspects of the problem scale with wavelength, and the telescope is likely to have a more stable environment; however, detectors may present small complications. Since this is a new system approach, it warrants a new look. For instance, a large space telescope based on the DART membrane mirror design requires a new actuation approach. Other mirror and actuation technologies may prove useful as well.

  9. Active compensation of wavefront aberrations by controllable heating of lens with electric film heater matrix.

    PubMed

    Chen, Hua; Hou, Lv; Zhou, Xinglin

    2016-08-20

    We present a new apparatus for active compensation of wavefront aberrations by controllable heating of a lens using a film heater matrix. The annular electric film heater matrix, comprising 24 individual heaters, is attached to the periphery of a lens. Utilizing the linear superposition, and wavefront change proportional to the heating energy properties induced by heating, a controllable wavefront can be defined by solving a linear function. The two properties of wavefront change of a lens have been confirmed through a specially designed experiment. The feasibility of the compensation method is validated by compensating the wavefront of a plate lens. The results show that the wavefront of the lens changes from 12.52 to 2.95 nm rms after compensation. With a more precise electric controlling board, better results could be achieved. PMID:27556982

  10. Grazing Incidence Wavefront Sensing and Verification of X-Ray Optics Performance

    NASA Technical Reports Server (NTRS)

    Saha, Timo T.; Rohrbach, Scott; Zhang, William W.

    2011-01-01

    Evaluation of interferometrically measured mirror metrology data and characterization of a telescope wavefront can be powerful tools in understanding of image characteristics of an x-ray optical system. In the development of soft x-ray telescope for the International X-Ray Observatory (IXO), we have developed new approaches to support the telescope development process. Interferometrically measuring the optical components over all relevant spatial frequencies can be used to evaluate and predict the performance of an x-ray telescope. Typically, the mirrors are measured using a mount that minimizes the mount and gravity induced errors. In the assembly and mounting process the shape of the mirror segments can dramatically change. We have developed wavefront sensing techniques suitable for the x-ray optical components to aid us in the characterization and evaluation of these changes. Hartmann sensing of a telescope and its components is a simple method that can be used to evaluate low order mirror surface errors and alignment errors. Phase retrieval techniques can also be used to assess and estimate the low order axial errors of the primary and secondary mirror segments. In this paper we describe the mathematical foundation of our Hartmann and phase retrieval sensing techniques. We show how these techniques can be used in the evaluation and performance prediction process of x-ray telescopes.

  11. Comparison of laser ray-tracing and skiascopic ocular wavefront-sensing devices

    PubMed Central

    Bartsch, D-UG; Bessho, K; Gomez, L; Freeman, WR

    2009-01-01

    Purpose To compare two wavefront-sensing devices based on different principles. Methods Thirty-eight healthy eyes of 19 patients were measured five times in the reproducibility study. Twenty eyes of 10 patients were measured in the comparison study. The Tracey Visual Function Analyzer (VFA), based on the ray-tracing principle and the Nidek optical pathway difference (OPD)-Scan, based on the dynamic skiascopy principle were compared. Standard deviation (SD) of root mean square (RMS) errors was compared to verify the reproducibility. We evaluated RMS errors, Zernike terms and conventional refractive indexes (Sph, Cyl, Ax, and spherical equivalent). Results In RMS errors reading, both devices showed similar ratios of SD to the mean measurement value (VFA: 57.5±11.7%, OPD-Scan: 53.9±10.9%). Comparison on the same eye showed that almost all terms were significantly greater using the VFA than using the OPD-Scan. However, certain high spatial frequency aberrations (tetrafoil, pentafoil, and hexafoil) were consistently measured near zero with the OPD-Scan. Conclusion Both devices showed similar level of reproducibility; however, there was considerable difference in the wavefront reading between machines when measuring the same eye. Differences in the number of sample points, centration, and measurement algorithms between the two instruments may explain our results. PMID:17571088

  12. Study of an instrument for sensing errors in a telescope wavefront

    NASA Technical Reports Server (NTRS)

    Golden, L. J.; Shack, R. V.; Slater, P. N.

    1974-01-01

    Focal plane sensors for determining the error in a telescope wavefront were investigated. The construction of three candidate test instruments and their evaluation in terms of small wavefront error aberration measurements are described. A laboratory wavefront simulator was designed and fabricated to evaluate the test instruments. The laboratory wavefront error simulator was used to evaluate three tests; a Hartmann test, a polarization shearing interferometer test, and an interferometric Zernike test.

  13. Wide-field wavefront sensing in solar adaptive optics : modeling and effects on reconstruction

    NASA Astrophysics Data System (ADS)

    Béchet, Clémentine; Tallon, Michel; Montilla, Icíar; Langlois, Maud

    2013-12-01

    The planned 4-meter diameter of the European Solar Telescope (EST) is aimed at providing high spatial resolution and large photon collecting area, in order to understand in particular the mechanisms of magnetic coupling in the chromosphere and the photosphere. To reach its goals in the visible and the near-infrared, EST is designed with both a conventional and a multi-conjugate adaptive optics (AO) of similar complexity than the ones featured for the Extremely Large Telescopes. In addition, the AO on EST has to face a particularity of solar AO: the wavefront sensing on extended sources with measurement fields of about 10'' in size. Reviewing recent literature together with an independent analysis, we investigate the impact of extended-field sensing in AO for large solar telescopes. Sensing modeling and its effect on reconstruction performance are analyzed, thanks to simulations performed with the Fractal Iterative Method for tomography (FRiM-3D), showing the difficulty to correct high altitude turbulence. We introduce a new approximate direct model of extended-source sensing which greatly improves the quality of the end-to-end simulations for EST AO. Next, we try to improve the conventional solar AO correction by using this new model in the reconstruction. Our simulations do not show significant benefits from using such tomographic model in this conventional AO configuration and under typical atmospheric conditions.

  14. Measuring aberrations in the rat brain by coherence-gated wavefront sensing using a Linnik interferometer.

    PubMed

    Wang, Jinyu; Léger, Jean-François; Binding, Jonas; Boccara, A Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-10-01

    Aberrations limit the resolution, signal intensity and achievable imaging depth in microscopy. Coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore the implementation of adaptive corrections. However, CGWS has been demonstrated so far only in weakly scattering samples. We designed a new CGWS scheme based on a Linnik interferometer and a SLED light source, which is able to compensate dispersion automatically and can be implemented on any microscope. In the highly scattering rat brain tissue, where multiply scattered photons falling within the temporal gate of the CGWS can no longer be neglected, we have measured known defocus and spherical aberrations up to a depth of 400 µm. PMID:23082292

  15. Measuring aberrations in the rat brain by coherence-gated wavefront sensing using a Linnik interferometer

    PubMed Central

    Wang, Jinyu; Léger, Jean-François; Binding, Jonas; Boccara, A. Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-01-01

    Aberrations limit the resolution, signal intensity and achievable imaging depth in microscopy. Coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore the implementation of adaptive corrections. However, CGWS has been demonstrated so far only in weakly scattering samples. We designed a new CGWS scheme based on a Linnik interferometer and a SLED light source, which is able to compensate dispersion automatically and can be implemented on any microscope. In the highly scattering rat brain tissue, where multiply scattered photons falling within the temporal gate of the CGWS can no longer be neglected, we have measured known defocus and spherical aberrations up to a depth of 400 µm. PMID:23082292

  16. Measuring aberrations in the rat brain by coherence-gated wavefront sensing using a Linnik interferometer.

    PubMed

    Wang, Jinyu; Léger, Jean-François; Binding, Jonas; Boccara, A Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-10-01

    Aberrations limit the resolution, signal intensity and achievable imaging depth in microscopy. Coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore the implementation of adaptive corrections. However, CGWS has been demonstrated so far only in weakly scattering samples. We designed a new CGWS scheme based on a Linnik interferometer and a SLED light source, which is able to compensate dispersion automatically and can be implemented on any microscope. In the highly scattering rat brain tissue, where multiply scattered photons falling within the temporal gate of the CGWS can no longer be neglected, we have measured known defocus and spherical aberrations up to a depth of 400 µm.

  17. Measuring and modeling intraocular light scatter with Shack-Hartmann wavefront sensing and the effects of nuclear cataract on the measurement of wavefront error

    NASA Astrophysics Data System (ADS)

    Donnelly, William J., III

    Purpose. The purpose of this research is to determine if Shack/Hartmann (S/H) wavefront sensing (SHWS) can be used to objectively quantify ocular forward scatter. Methods. Patient S/H images from an study of nuclear cataract were analyzed to extract scattering data by examining characteristics of the lenslet point spread functions. Physical and computer eye models with simulated cataract were developed to control variables and to test the underlying assumptions for using SHWS to measure aberrations and light scatter from nuclear cataract. Results. (1) For patients with nuclear opalescence (NO) >=2.5, forward scatter metrics in a multiple regression analysis account for 33% of variance in Mesopic Low Contrast acuity. Prediction of visual acuity was improved by employing a multiple regression analysis that included both backscatter and forward scatter metrics (R2 = 51%) for Mesopic High Contrast acuity. (2) The physical and computer models identified areas of instrument noise (e.g., stray light and unwanted reflections) improving the design of a second generation SHWS for measuring both wavefront error and scatter. (3) Exposure time had the most influence on, and pupil size had negligible influence on forward scatter metrics. Scatter metric MAX_SD predicted changes in simulated cataract up to R2 = 92%. There were small but significant differences (alpha = 0.05) between 1.5-pass and 1-pass wavefront measurements inclusive of variable simulated nuclear cataract and exposure; however, these differences were not visually significant. Improvements to the SHWS imaging hardware, software, and test protocol were implemented in a second generation SHWS to be used in a longitudinal cataract study. Conclusions. Forward light scatter in real eyes can be quantified using a SHWS. In the presence of clinically significant nuclear opalescence, forward scatter metrics predicted acuity better than the LOCS III NO backscatter metric. The superiority of forward scatter metrics over back

  18. Study of an instrument for sensing errors in a telescope wavefront

    NASA Technical Reports Server (NTRS)

    Golden, L. J.; Shack, R. V.; Slater, D. N.

    1973-01-01

    Partial results are presented of theoretical and experimental investigations of different focal plane sensor configurations for determining the error in a telescope wavefront. The coarse range sensor and fine range sensors are used in the experimentation. The design of a wavefront error simulator is presented along with the Hartmann test, the shearing polarization interferometer, the Zernike test, and the Zernike polarization test.

  19. Distributed Computing Architecture for Image-Based Wavefront Sensing and 2 D FFTs

    NASA Technical Reports Server (NTRS)

    Smith, Jeffrey S.; Dean, Bruce H.; Haghani, Shadan

    2006-01-01

    Image-based wavefront sensing (WFS) provides significant advantages over interferometric-based wavefi-ont sensors such as optical design simplicity and stability. However, the image-based approach is computational intensive, and therefore, specialized high-performance computing architectures are required in applications utilizing the image-based approach. The development and testing of these high-performance computing architectures are essential to such missions as James Webb Space Telescope (JWST), Terrestial Planet Finder-Coronagraph (TPF-C and CorSpec), and Spherical Primary Optical Telescope (SPOT). The development of these specialized computing architectures require numerous two-dimensional Fourier Transforms, which necessitate an all-to-all communication when applied on a distributed computational architecture. Several solutions for distributed computing are presented with an emphasis on a 64 Node cluster of DSPs, multiple DSP FPGAs, and an application of low-diameter graph theory. Timing results and performance analysis will be presented. The solutions offered could be applied to other all-to-all communication and scientifically computationally complex problems.

  20. Pyramid wavefront sensing with a laser guide star for an ELT

    NASA Astrophysics Data System (ADS)

    Le Roux, Brice

    2010-07-01

    The wavefront sensor [WFS] is a key element of an Adaptive Optics [AO] system. It gives access to a direct measurement of the turbulent phase, its curvature or its slope, from which the mirror voltages are computed. The ability of the system to correct efficiently the atmospheric turbulence is strongly dependent on the performance of the WFS in estimating the turbulent phase. The Shack-Hartmann [SH] WFS has been for a long time the standard used in AO systems. In 1996, it has been proposed1 a new generation WFS, the pyramid WFS. It is a focal plane WFS, based on the principle of a Foucault knife-edge. It has been demonstrated that it provides a consistent gain with respect to the Shack-Hartmann.2,5-7 More recently, improvements were proposed to increase the pyramid performance.3, 4 On the framework of the developpement of extremely large telescopes, the interest of a pyramid wave front sensor appears clearly. But its behaviour with laser guide stars [LGS], most probably necessary in any Extremely Large Telescope [ELT], is still relatively unknown. Some WFS dedicated to LGS wave front sensing has already been proposed8,9 but a full study of the pyramid WFS behaviour is still necessary. This work's aim is to bring answers to this topic.

  1. HIGH-SPEED IMAGING AND WAVEFRONT SENSING WITH AN INFRARED AVALANCHE PHOTODIODE ARRAY

    SciTech Connect

    Baranec, Christoph; Atkinson, Dani; Hall, Donald; Jacobson, Shane; Chun, Mark; Riddle, Reed; Law, Nicholas M.

    2015-08-10

    Infrared avalanche photodiode (APD) arrays represent a panacea for many branches of astronomy by enabling extremely low-noise, high-speed, and even photon-counting measurements at near-infrared wavelengths. We recently demonstrated the use of an early engineering-grade infrared APD array that achieves a correlated double sampling read noise of 0.73 e{sup −} in the lab, and a total noise of 2.52 e{sup −} on sky, and supports simultaneous high-speed imaging and tip-tilt wavefront sensing with the Robo-AO visible-light laser adaptive optics (AO) system at the Palomar Observatory 1.5 m telescope. Here we report on the improved image quality simultaneously achieved at visible and infrared wavelengths by using the array as part of an image stabilization control loop with AO-sharpened guide stars. We also discuss a newly enabled survey of nearby late M-dwarf multiplicity, as well as future uses of this technology in other AO and high-contrast imaging applications.

  2. Shack-Hartmann mask/pupil registration algorithm for wavefront sensing in segmented mirror telescopes.

    PubMed

    Piatrou, Piotr; Chanan, Gary

    2013-11-10

    Shack-Hartmann wavefront sensing in general requires careful registration of the reimaged telescope primary mirror to the Shack-Hartmann mask or lenslet array. The registration requirements are particularly demanding for applications in which segmented mirrors are phased using a physical optics generalization of the Shack-Hartmann test. In such cases the registration tolerances are less than 0.1% of the diameter of the primary mirror. We present a pupil registration algorithm suitable for such high accuracy applications that is based on the one used successfully for phasing the segments of the Keck telescopes. The pupil is aligned in four degrees of freedom (translations, rotation, and magnification) by balancing the intensities of subimages formed by small subapertures that straddle the periphery of the mirror. We describe the algorithm in general terms and then in the specific context of two very different geometries: the 492 segment Thirty Meter Telescope, and the seven "segment" Giant Magellan Telescope. Through detailed simulations we explore the accuracy of the algorithm and its sensitivity to such effects as cross talk, noise/counting statistics, atmospheric scintillation, and segment reflectivity variations.

  3. Laboratory prototype for the demonstration of sodium laser guide star wavefront sensing on the E-ELT

    NASA Astrophysics Data System (ADS)

    Patti, M.; Lombini, M.; Schreiber, L.; Bregoli, G.; Arcidiacono, C.; Cosentino, G.; Diolaiti, E.; Foppiani, I.

    The new class of Extremely Large Telescopes (ELT) relies on Sodium Laser Guide Stars (LGS) to improve the Adaptive Optics performance in terms of correction quality and sky coverage. The time instability and the vertical extension of the atmospheric Sodium layer density have a potential significant impact on the wavefront sensing accuracy. We describe a laboratory prototype which has been developed with the goal to investigate specific algorithms for wavefront sensing with these artificial sources under different conditions of sodium layer density profile, parallactic effects due to laser launch geometry and atmospheric turbulence. The prototype can emulate realistic elongated spots on the focal plane of a Shack-Hartmann wavefront sensor (SHWFS), including their intensity variations due to the time variability of the Sodium density vertical profile. In addition, multiple LGSs can be simulated, one at a time, and a two-layer atmospheric turbulence model is available. Herein we report the verification of prototype performances, including optical performance, accuracy of emulated Sodium density profiles and atmospheric turbulence features.

  4. Application of geometric phase to wavefront sensing for astronomical adaptive optics

    NASA Astrophysics Data System (ADS)

    Bloemhof, E. E.

    2014-02-01

    Modern adaptive optics systems give high performance, both in terms of Strehl ratio (degree of correction) and corrected field of view. Arguably the most important subsystem is the wavefront sensor, which measures the deviation from flatness of the incident wavefront that has been perturbed by the turbulent atmosphere, and commands an actuated mirror to compensate. An aspect of the wavefront sensor essential to achieving high sensitivity is that it perform over a broad spectral bandwidth; operation without correction for guide star color is also desirable. With this in mind, wavefront sensors are considered that make use of the geometric (or topological) phase, which has the property that the value of the phase is independent of wavelength. Conceptual system designs and advantages are discussed.

  5. Correlation Wave-Front Sensing Algorithms for Shack-Hartmann-Based Adaptive Optics using a Point Source

    SciTech Connect

    Poynee, L A

    2003-05-06

    Shack-Hartmann based Adaptive Optics system with a point-source reference normally use a wave-front sensing algorithm that estimates the centroid (center of mass) of the point-source image 'spot' to determine the wave-front slope. The centroiding algorithm suffers for several weaknesses. For a small number of pixels, the algorithm gain is dependent on spot size. The use of many pixels on the detector leads to significant propagation of read noise. Finally, background light or spot halo aberrations can skew results. In this paper an alternative algorithm that suffers from none of these problems is proposed: correlation of the spot with a ideal reference spot. The correlation method is derived and a theoretical analysis evaluates its performance in comparison with centroiding. Both simulation and data from real AO systems are used to illustrate the results. The correlation algorithm is more robust than centroiding, but requires more computation.

  6. Conformal optical elements for correcting wavefront distortions in YAG : Nd{sup 3+} active elements

    SciTech Connect

    Korolkov, V P; Nasyrov, R K; Poleshchuk, A G; Arapov, Yu D; Ivanov, A F

    2013-02-28

    Correction of the wavefront is studied for the light beam passing wide-aperture YAG : Nd3+ single-crystal rods, which are used as active elements in high-power solid-state lasers. A nonideal character of the crystal structure is responsible for the deformation of the wavefront of passing radiation. By using the halftone technology we have developed conformal aberration correctors capable of compensating rod nonuniformities and reducing the laser radiation divergence by an order of magnitude. The results obtained make it possible to employ optically nonuniform active elements in laser constructions. (laser optics 2012)

  7. Implementation of adaptive optics in fluorescent microscopy using wavefront sensing and correction

    NASA Astrophysics Data System (ADS)

    Azucena, Oscar; Crest, Justin; Cao, Jian; Sullivan, William; Kner, Peter; Gavel, Donald; Dillon, Daren; Olivier, Scot; Kubby, Joel

    2010-02-01

    Adaptive optics (AO) improves the quality of astronomical imaging systems by using real time measurement of the turbulent medium in the optical path using a guide star (natural or artificial) as a point source reference beacon [1]. AO has also been applied to vision science to improve the view of the human eye. This paper will address our current research focused on the improvement of fluorescent microscopy for biological imaging utilizing current AO technology. A Shack-Hartmann wavefront sensor (SHWS) is used to measure the aberration introduced by a Drosophila Melanogaster embryo with an implanted 1 micron fluorescent bead that serves as a point source reference beacon. Previous measurements of the wavefront aberrations have found an average peak-to-valley and root-mean-square (RMS) wavefront error of 0.77 micrometers and 0.15 micrometers, respectively. Measurements of the Zernike coefficients indicated that the correction of the first 14 Zernike coefficients is sufficient to correct the aberrations we measured. Here we show that a MEMS deformable mirror with 3.5 microns of stroke and 140 actuators is sufficient to correct these aberrations. The design, assembly and initial results for the use of a MEMS deformable mirror, SHWS and implanted fluorescent reference beacon for wavefront correction are discussed.

  8. On-Sky Demonstration of Low-Order Wavefront Sensing and Control with Focal Plane Phase Mask Coronagraphs

    NASA Astrophysics Data System (ADS)

    Singh, Garima; Lozi, Julien; Guyon, Olivier; Baudoz, Pierre; Jovanovic, Nemanja; Martinache, Frantz; Kudo, Tomoyuki; Serabyn, Eugene; Kuhn, Jonas

    2015-09-01

    The ability to characterize exoplanets by spectroscopy of their atmospheres requires direct imaging techniques to isolate planet signal from the bright stellar glare. One of the limitations with the direct detection of exoplanets, either with ground- or space-based coronagraphs, is pointing errors and other low-order wavefront aberrations. The coronagraphic detection sensitivity at the diffraction limit therefore depends on how well low-order aberrations upstream of the focal plane mask are corrected. To prevent starlight leakage at the inner working angle of a phase mask coronagraph, we have introduced a Lyot-based low-order wavefront sensor (LLOWFS), which senses aberrations using the rejected starlight diffracted at the Lyot plane. In this article, we present the implementation, testing, and results of LLOWFS on the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO) at the Subaru Telescope. We have controlled 35 Zernike modes of a H-band vector vortex coronagraph in the laboratory and 10 Zernike modes on-sky with an integrator control law. We demonstrated a closed-loop pointing residual of 0.02 mas in the laboratory and 0.15 mas on-sky for data sampled using the minimal 2-s exposure time of the science camera. We have also integrated the LLOWFS in the visible high-order control loop of SCExAO, which in closed-loop operation has validated the correction of the noncommon path pointing errors between the infrared science channel and the visible wavefront sensing channel with pointing residual of 0.23 mas on-sky.

  9. Measuring seeing with a Shack-Hartmann wave-front sensor during an active-optics experiment.

    PubMed

    Zhang, Yong; Yang, Dehua; Cui, Xiangqun

    2004-02-01

    We describe the measurement of atmospheric enclosure seeing along a 120-m light path by use of a Shack-Hartmann wave-front sensor (S-H WFS) for the first time to our knowledge in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) outdoor active-optics experiment system, based on the differential image motion method and a S-H WFS. Seeing estimates that were gained with the S-H WFS were analyzed and found to be in close agreement with the actual seeing conditions, the estimates of refractive-index structure constant, and the thin-mirror active optics results, which usually include the shape sensing precision and the active correction precision of the experimental system. Finally, some countermeasures against poor seeing conditions were considered and adopted.

  10. Shack-Hartmann wavefront sensing with elongated sodium laser beacons: centroiding versus matched filtering.

    PubMed

    Gilles, Luc; Ellerbroek, Brent

    2006-09-01

    We describe modeling and simulation results for the Thirty Meter Telescope on the degradation of sodium laser guide star Shack-Hartmann wavefront sensor measurement accuracy that will occur due to the spatial structure and temporal variations of the mesospheric sodium layer. By using a contiguous set of lidar measurements of the sodium profile, the performance of a standard centroid and of a more refined noise-optimal matched filter spot position estimation algorithm is analyzed and compared for a nominal mean signal level equal to 1000 photodetected electrons per subaperture per integration time, as a function of subaperture to laser launch telescope distance and CCD pixel readout noise. Both algorithms are compared in terms of their rms spot position estimation error due to noise, their associated wavefront error when implemented on the Thirty Meter Telescope facility adaptive optics system, their linear dynamic range, and their bias when detuned from the current sodium profile. PMID:16912797

  11. Wave-front sensing by use of a Green's function solution to the intensity transport equation.

    PubMed

    Woods, Simon C; Greenaway, Alan H

    2003-03-01

    A method for reconstructing an unknown wave front from measurements of its intensity distribution on two planes along the direction of propagation is described. The method solves the intensity transport equation by use of Neumann boundary conditions, leading to a solution that requires only matrix multiplication. The method provides real-time wave-front reconstruction with high accuracy and is easily reposed to permit reconstruction of the wave front in any orthonormal basis set. PMID:12630836

  12. Novel Adaptive Optics concepts : wavefront sensing with sodium laser guide stars at Extemely Large Telescopes and simultaneous differential imaging

    NASA Astrophysics Data System (ADS)

    Kellner, Stephan Albert

    2005-12-01

    Since more than 15 years, Adaptive Optics (AO) is a proven concept to reach diffraction limited imaging at modern astronomical telescopes. In the case of next generation telescopes (Extremely Large Telescopes (ELTs)) with aperture diameters of up to 100m, sodium laser guide star based multi-conjugated-AO systems will be a basic requirement to exploit their full capability in terms of resolution and light concentration. A drawback of such an approach emerges in the finite distance and vertical extent of the sodium beacon in the mesosphere with respect to the telescope. This induces effects such as perspective elongation, where conventional wavefront sensing mechanisms will fail. Although several engineering concepts are under development to counteract these constraints at the cost of overall light efficiency and increased system complexity, this thesis proposes a novel kind of wavefront sensing technique to overcome the imposed limitations in a more natural way. The sensing technique is composed of two independently working sensors, a reflective rod and a mask with circular slits, each a representative of a novel wavefront sensor class, the so called z-invariant and Inverse Bessel Beam technique. Both are discussed in this thesis with a focus on the Inverse Bessel Beam technique. The latter is compared to alternative concepts such as temporal gating, with respect to the photon efficiency. Furthermore, the reflective rod was tested for its feasibility in laboratory conditions and in a more realistic environment at the William Herschel Telescope (WHT) at La Palma. With this test run its sensing principle has been verified. A novel technique already intensively used at 8m class telescopes is Simultaneous Differential Imaging. The direct detection of giant extra-solar planets is and will be a major science driver for galactic astronomy in the coming years. Modern telescope facilities such as the VLT reach, by means of adaptive optics, potentially the capability in terms

  13. First Experimental Results Using Sparse Aperture Mask for Low Order Wavefront Sensing

    NASA Astrophysics Data System (ADS)

    Subedi, Hari; Zimmerman, Neil T.; Kasdin, N. Jeremy; Eldorado Riggs, A. J.

    2016-01-01

    We can determine the existence of life outside of earth by analyzing the spectra of exoplanets. Such direct imaging will provide the capability to thoroughly characterize an exoplanet's atmosphere. Direct imaging of exoplanets, however, has many technical challenges and difficulties: scattering and diffraction of light and the large difference in contrast, which is the ratio of brightness between the bright star and the dimmer planet. A coronagraph is an optical device that manipulates the diffraction of starlight and creates a region of high contrast (dark hole) where the dimmer planets can be seen. While in principle the level of contrast required for direct imaging of exoplanets can be achieved by stellar coronagraphic imaging, the resulting dark hole is highly sensitive to phase aberrations. In order to effectively suppress starlight for exoplanet imaging applications, low-order wavefront aberrations entering a coronagraph such as tip-tilt, defocus and coma must be determined and compensated for. A sparse-aperture mask (SAM) can be integrated in the telescopic imaging system to make precise estimate of low-order wavefront aberrations. In this technique, the starlight rejected by the coronagraph's focal plane stop is collimated to a relay pupil, where the mask forms an interference fringe pattern on a detector and the phase aberrations are inferred from this fringe pattern. At Princeton's High Contrast Imaging Lab (HCIL), we have numerically proved this concept and we are currently working on verifying it experimentally.

  14. Open-loop wavefront sensing scheme for specimen aberrations correction in two-photon excited fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Aviles-Espinosa, Rodrigo; Andilla, Jordi; Porcar-Guezenec, Rafael; Levecq, Xavier; Artigas, David; Loza-Alvarez, Pablo

    2011-07-01

    The recent linkage between adaptive optics, a technique borrowed from astronomy and various imaging devices, has enabled to push forward their imaging capabilities by improving its contrast and resolution. A specific case is nonlinear microscopy (NLM) that, although it brings several inherent advantages (compared to linear fluorescence techniques) due to its nonlinear dependence on the excitation beam, its enhanced capabilities can be limited by the sample inhomogeneous structure. In this work, we demonstrate how these imaging capabilities can be enhanced by, employing adaptive optics in a two step correction process. Firstly, a closed-loop methodology aided by Shack-Hartman Wavefront sensing scheme is implemented for compensating the aberrations produced by the laser and the optical elements before the high numerical aperture microscope objective, resulting in a one-time calibration process. Then the residual aberrations are produced by the microscope objective and the sample. These are measured in a similar way as it is done in astronomy (employing a laser guide-star), using the two-photon excited fluorescence. The properties of this incoherent emission produced inside a test sample are compared to a genetically modified Caenorhabditis. elegans nematode expressing GFP showing that the emission of this protein (at 810nm) can be sensed efficiently with our WFS by modifying the exposure time. Therefore the recorded wavefront will capture the sample aberrations which are used to shape a deformable mirror in an open-loop configuration. This correction principle is demonstrated in a test sample by correcting aberrations in a "single-shot" resulting in a reduced sample exposure.

  15. Active touch sensing

    PubMed Central

    Prescott, Tony J.; Diamond, Mathew E.; Wing, Alan M.

    2011-01-01

    Active sensing systems are purposive and information-seeking sensory systems. Active sensing usually entails sensor movement, but more fundamentally, it involves control of the sensor apparatus, in whatever manner best suits the task, so as to maximize information gain. In animals, active sensing is perhaps most evident in the modality of touch. In this theme issue, we look at active touch across a broad range of species from insects, terrestrial and marine mammals, through to humans. In addition to analysing natural touch, we also consider how engineering is beginning to exploit physical analogues of these biological systems so as to endow robots with rich tactile sensing capabilities. The different contributions show not only the varieties of active touch—antennae, whiskers and fingertips—but also their commonalities. They explore how active touch sensing has evolved in different animal lineages, how it serves to provide rapid and reliable cues for controlling ongoing behaviour, and even how it can disintegrate when our brains begin to fail. They demonstrate that research on active touch offers a means both to understand this essential and primary sensory modality, and to investigate how animals, including man, combine movement with sensing so as to make sense of, and act effectively in, the world. PMID:21969680

  16. In-focus wavefront sensing using non-redundant mask-induced pupil diversity.

    PubMed

    Greenbaum, Alexandra Z; Sivaramakrishnan, Anand

    2016-07-11

    Wavefront estimation using in-focus image data is critical to many applications. This data is invariant to a sign flip with complex conjugation of the complex amplitude in the pupil, making for a non-unique solution. Information from an in-focus image taken through a non-redundant pupil mask (NRM) can break this ambiguity, enabling the true aberration to be determined. We demonstrate this by priming a full pupil Gerchberg-Saxton phase retrieval with NRM fringe phase information. We apply our method to measure simulated aberrations on the segmented James Webb space telescope (JWST) mirror using full pupil and NRM data from its near infrared imager and slitless spectrograph (NIRISS). PMID:27410825

  17. Sensing the wavefront of x-ray free-electron lasers using aerosol spheres

    SciTech Connect

    Loh, N.Duane; Starodub, Dimitri; Lomb, Lukas; Hampton, Christina Y.; Martin, Andrew V.; Sierra, Raymond G.; Barty, Anton; Aquila, Andrew; Schulz, Joachim; Steinbrener, Jan; Shoeman, Robert L.; Kassemeyer, Stephan; Bostedt, Christoph; Bozek, John; Epp, Sascha W.; Erk, Benjamin; Hartmann, Robert; Rolles, Daniel; Rudenko, Artem; Rudek, Benedikt; Foucar, Lutz

    2014-04-22

    Characterizing intense, focused x-ray free electron laser (FEL) pulses is crucial for their use in diffractive imaging. We describe how the distribution of average phase tilts and intensities on hard x-ray pulses with peak intensities of 10 21 W/m2 can be retrieved from an ensemble of diffraction patterns produced by 70 nm-radius polystyrene spheres, in a manner that mimics wave-front sensors. Besides showing that an adaptive geometric correction may be necessary for diffraction data from randomly injected sample sources, the paper demonstrates the possibility of collecting statistics on structured pulses using only the diffraction patterns they generate and highlights the imperative to study its impact on single-particle diffractive imaging.

  18. Sensing the wavefront of x-ray free-electron lasers using aerosol spheres.

    PubMed

    Loh, N Duane; Starodub, Dmitri; Lomb, Lukas; Hampton, Christina Y; Martin, Andrew V; Sierra, Raymond G; Barty, Anton; Aquila, Andrew; Schulz, Joachim; Steinbrener, Jan; Shoeman, Robert L; Kassemeyer, Stephan; Bostedt, Christoph; Bozek, John; Epp, Sascha W; Erk, Benjamin; Hartmann, Robert; Rolles, Daniel; Rudenko, Artem; Rudek, Benedikt; Foucar, Lutz; Kimmel, Nils; Weidenspointner, Georg; Hauser, Guenter; Holl, Peter; Pedersoli, Emanuele; Liang, Mengning; Hunter, Mark S; Gumprecht, Lars; Coppola, Nicola; Wunderer, Cornelia; Graafsma, Heinz; Maia, Filipe R N C; Ekeberg, Tomas; Hantke, Max; Fleckenstein, Holger; Hirsemann, Helmut; Nass, Karol; White, Thomas A; Tobias, Herbert J; Farquar, George R; Benner, W Henry; Hau-Riege, Stefan; Reich, Christian; Hartmann, Andreas; Soltau, Heike; Marchesini, Stefano; Bajt, Sasa; Barthelmess, Miriam; Strueder, Lothar; Ullrich, Joachim; Bucksbaum, Philip; Frank, Matthias; Schlichting, Ilme; Chapman, Henry N; Bogan, Michael J

    2013-05-20

    Characterizing intense, focused x-ray free electron laser (FEL) pulses is crucial for their use in diffractive imaging. We describe how the distribution of average phase tilts and intensities on hard x-ray pulses with peak intensities of 10(21) W/m(2) can be retrieved from an ensemble of diffraction patterns produced by 70 nm-radius polystyrene spheres, in a manner that mimics wavefront sensors. Besides showing that an adaptive geometric correction may be necessary for diffraction data from randomly injected sample sources, our paper demonstrates the possibility of collecting statistics on structured pulses using only the diffraction patterns they generate and highlights the imperative to study its impact on single-particle diffractive imaging.

  19. Sensing the wavefront of x-ray free-electron lasers using aerosol spheres.

    PubMed

    Loh, N Duane; Starodub, Dmitri; Lomb, Lukas; Hampton, Christina Y; Martin, Andrew V; Sierra, Raymond G; Barty, Anton; Aquila, Andrew; Schulz, Joachim; Steinbrener, Jan; Shoeman, Robert L; Kassemeyer, Stephan; Bostedt, Christoph; Bozek, John; Epp, Sascha W; Erk, Benjamin; Hartmann, Robert; Rolles, Daniel; Rudenko, Artem; Rudek, Benedikt; Foucar, Lutz; Kimmel, Nils; Weidenspointner, Georg; Hauser, Guenter; Holl, Peter; Pedersoli, Emanuele; Liang, Mengning; Hunter, Mark S; Gumprecht, Lars; Coppola, Nicola; Wunderer, Cornelia; Graafsma, Heinz; Maia, Filipe R N C; Ekeberg, Tomas; Hantke, Max; Fleckenstein, Holger; Hirsemann, Helmut; Nass, Karol; White, Thomas A; Tobias, Herbert J; Farquar, George R; Benner, W Henry; Hau-Riege, Stefan; Reich, Christian; Hartmann, Andreas; Soltau, Heike; Marchesini, Stefano; Bajt, Sasa; Barthelmess, Miriam; Strueder, Lothar; Ullrich, Joachim; Bucksbaum, Philip; Frank, Matthias; Schlichting, Ilme; Chapman, Henry N; Bogan, Michael J

    2013-05-20

    Characterizing intense, focused x-ray free electron laser (FEL) pulses is crucial for their use in diffractive imaging. We describe how the distribution of average phase tilts and intensities on hard x-ray pulses with peak intensities of 10(21) W/m(2) can be retrieved from an ensemble of diffraction patterns produced by 70 nm-radius polystyrene spheres, in a manner that mimics wavefront sensors. Besides showing that an adaptive geometric correction may be necessary for diffraction data from randomly injected sample sources, our paper demonstrates the possibility of collecting statistics on structured pulses using only the diffraction patterns they generate and highlights the imperative to study its impact on single-particle diffractive imaging. PMID:23736456

  20. Wave-front sensing and deformable-mirror control in strong scintillation

    PubMed

    Roggemann; Koivunen

    2000-05-01

    Recent studies of coherent wave propagation through turbulence have shown that under conditions where scintillation is significant a continuous phase function does not in general exist, owing to the presence of branch points in the complex optical field. Because of branch points and the associated branch cuts, least-squares approaches to wave-front reconstruction and deformable-mirror control can have large errors. Branch-point reconstructors are known to provide superior performance to least-squares reconstructors, but they require that branch points be explicitly detected. Detecting branch points is a significant practical impediment owing to spatial sampling and measurement noise in real wave-front sensors. Branch points are associated with real zeros in an optical field, and hence information about the phase of the field is encoded in the amplitude of the wave. We present a new wave-front-sensor processing algorithm that exploits this observation in the wave-front-reconstruction and deformable-mirror-control process. This algorithm jointly processes three intensity measurements by using light from the beacon field to develop a set of deformable-mirror actuator commands that are maximally consistent with three intensity measurements: (1) the entire wave-front-sensor image, (2) a pupil intensity image, and (3) a conventional image. Owing to the nonlinear nature of the resulting algorithm, we have used a simulation to evaluate performance. We find that in a focused laser beam projection paradigm that uses a point-source beacon, the new algorithm provides significantly improved performance over that of conventional Hartmann sensor least-squares deformable-mirror control based on centroid processing of wave-front-sensor outputs. The performance of the new algorithm approaches, the performance of an idealized branch-point reconstructor that requires pointwise phase differences for operation.

  1. Experimental measurements of estimator bias and the signal-to-noise ratio for deconvolution from wave-front sensing.

    PubMed

    Dayton, D; Gonglewski, J; Rogers, S

    1997-06-10

    Deconvolution from wave-front sensing (DWFS) has been proposed as a method for achieving high-resolution images of astronomical objects from ground-based telescopes. The technique consists of the simultaneous measurement of a short-exposure focal-plane speckled image, as well as the wave front, by use of a Shack-Hartmann sensor placed at the pupil plane. In early studies it was suspected that some problems would occur in poor seeing conditions; however, it was usually assumed that the technique would work well as long as the wave-front sensor subaperture spacing was less than r(0) (L/r(0) < 1). Atmosphere-induced phase errors in the pupil of a telescope imaging system produce both phase errors and magnitude errors in the effective short-exposure optical transfer function (OTF) of the system. Recently it has been shown that the commonly used estimator for this technique produces biased estimates of the magnitude errors. The significance of this bias problem is that one cannot properly estimate or correct for the frame-to-frame fluctuations in the magnitude of the OTF but can do so only for fluctuations in the phase. An auxiliary estimate must also be used to correct for the mean value of the magnitude error. The inability to compensate for the magnitude fluctuations results in a signal-to-noise ratio (SNR) that is less favorable for the technique than was previously thought. In some situations simpler techniques, such as the Knox-Thompson and bispectrum methods, which require only speckle gram data from the focal plane of the imaging system, can produce better results. We present experimental measurements based on observations of bright stars and the Jovian moon Ganymede that confirm previous theoretical predictions. PMID:18253416

  2. Bringing it all together: a unique approach to requirements for wavefront sensing and control on the James Webb Space Telescope (JWST)

    NASA Astrophysics Data System (ADS)

    Contos, Adam R.; Acton, D. Scott; Atcheson, Paul D.; Barto, Allison A.; Lightsey, Paul A.; Shields, Duncan M.

    2006-06-01

    The opto-mechanical design of the 6.6 meter James Webb Space Telescope (JWST), with its actively-controlled secondary and 18-segment primary mirror, presents unique challenges from a system engineering perspective. To maintain the optical alignment of the telescope on-orbit, a process called wavefront sensing and control (WFS&C) is employed to determine the current state of the mirrors and calculate the optimal mirror move updates. The needed imagery is downloaded to the ground, where the WFS&C algorithms to process the images reside, and the appropriate commands are uploaded to the observatory. Rather than use a dedicated wavefront sensor for the imagery as is done in most other applications, a science camera is used instead. For the success of the mission, WFS&C needs to perform flawlessly using the assets available among the combination of separate elements (ground operations, spacecraft, science instruments, optical telescope, etc.) that cross institutional as well as geographic borders. Rather than be yet another distinct element with its own set of requirements to flow to the other elements as was originally planned, a novel approach was selected. This approach entails reviewing and auditing other documents for the requirements needed to satisfy the needs of WFS&C. Three actions are taken: (1) when appropriate requirements exist, they are tracked by WFS&C ; (2) when an existing requirement is insufficient to meet the need, a requirement change is initiated; and finally (3) when a needed requirement is missing, a new requirement is established in the corresponding document. This approach, deemed a "best practice" at the customer's independent audit, allows for program confidence that the necessary requirements are complete, while still maintaining the responsibility for the requirement with the most appropriate entity. This paper describes the details and execution of the approach; the associated WFS&C requirements and verification documentation; and the

  3. Application of Shack-Hartmann wavefront sensing technology to transmissive optic metrology

    NASA Astrophysics Data System (ADS)

    Rammage, Ron R.; Neal, Daniel R.; Copland, Richard J.

    2002-11-01

    Human vision correction optics must be produced in quantity to be economical. At the same time every human eye is unique and requires a custom corrective solution. For this reason the vision industries need fast, versatile and accurate methodologies for characterizing optics for production and research. Current methods for measuring these optics generally yield a cubic spline taken from less than 10 points across the surface of the lens. As corrective optics have grown in complexity this has become inadequate. The Shack-Hartmann wavefront sensor is a device that measures phase and irradiance of light in a single snapshot using geometric properties of light. Advantages of the Shack-Hartmann sensor include small size, ruggedness, accuracy, and vibration insensitivity. This paper discusses a methodology for designing instruments based on Shack-Hartmann sensors. The method is then applied to the development of an instrument for accurate measurement of transmissive optics such as gradient bifocal spectacle lenses, progressive addition bifocal lenses, intrarocular devices, contact lenses, and human corneal tissue. In addition, this instrument may be configured to provide hundreds of points across the surface of the lens giving improved spatial resolution. Methods are explored for extending the dynamic range and accuracy to meet the expanding needs of the ophthalmic and optometric industries. Data is presented demonstrating the accuracy and repeatability of this technique for the target optics.

  4. Coronagraphic wavefront sensing with COFFEE: high spatial-frequency diversity and other news

    NASA Astrophysics Data System (ADS)

    Mugnier, L. M.; Sauvage, J.-F.; Herscovici-Schiller, O.; Baudoz, P.; Galicher, R.; Le Duigou, J.-M.

    2016-07-01

    The final performance of current and future instruments dedicated to exoplanet detection and characterization is limited by intensity residuals in the scientific image plane, which originate in uncorrected optical aberrations. In order to reach very high contrasts, these aberrations needs to be compensated for. We have proposed a focalplane wave-font sensor called COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), which consists in an extension of conventional phase diversity to a coronagraphic system. In this communication, we study the extension of COFFEE to the joint estimation of the phase and the amplitude in the context of space-based coronagraphic instruments: we optimize the diversity phase in order to minimize the reconstruction error; we also propose and optimize a novel low-amplitude high-frequency diversity that should allow the phase-diverse images to still be used for science. Lastly, we perform a first experimental validation of COFFEE in the very high, space-like contrast conditions of the THD bench and show that COFFEE is able to distinguish between phase and amplitude aberrations.

  5. Laser guide star wavefront sensing for ground-layer adaptive optics on extremely large telescopes.

    PubMed

    Clare, Richard M; Le Louarn, Miska; Béchet, Clementine

    2011-02-01

    We propose ground-layer adaptive optics (GLAO) to improve the seeing on the 42 m European Extremely Large Telescope. Shack-Hartmann wavefront sensors (WFSs) with laser guide stars (LGSs) will experience significant spot elongation due to off-axis observation. This spot elongation influences the design of the laser launch location, laser power, WFS detector, and centroiding algorithm for LGS GLAO on an extremely large telescope. We show, using end-to-end numerical simulations, that with a noise-weighted matrix-vector-multiply reconstructor, the performance in terms of 50% ensquared energy (EE) of the side and central launch of the lasers is equivalent, the matched filter and weighted center of gravity centroiding algorithms are the most promising, and approximately 10×10 undersampled pixels are optimal. Significant improvement in the 50% EE can be observed with a few tens of photons/subaperture/frame, and no significant gain is seen by adding more than 200 photons/subaperture/frame. The LGS GLAO is not particularly sensitive to the sodium profile present in the mesosphere nor to a short-timescale (less than 100 s) evolution of the sodium profile. The performance of LGS GLAO is, however, sensitive to the atmospheric turbulence profile. PMID:21283238

  6. Laser guide star wavefront sensing for ground-layer adaptive optics on extremely large telescopes.

    PubMed

    Clare, Richard M; Le Louarn, Miska; Béchet, Clementine

    2011-02-01

    We propose ground-layer adaptive optics (GLAO) to improve the seeing on the 42 m European Extremely Large Telescope. Shack-Hartmann wavefront sensors (WFSs) with laser guide stars (LGSs) will experience significant spot elongation due to off-axis observation. This spot elongation influences the design of the laser launch location, laser power, WFS detector, and centroiding algorithm for LGS GLAO on an extremely large telescope. We show, using end-to-end numerical simulations, that with a noise-weighted matrix-vector-multiply reconstructor, the performance in terms of 50% ensquared energy (EE) of the side and central launch of the lasers is equivalent, the matched filter and weighted center of gravity centroiding algorithms are the most promising, and approximately 10×10 undersampled pixels are optimal. Significant improvement in the 50% EE can be observed with a few tens of photons/subaperture/frame, and no significant gain is seen by adding more than 200 photons/subaperture/frame. The LGS GLAO is not particularly sensitive to the sodium profile present in the mesosphere nor to a short-timescale (less than 100 s) evolution of the sodium profile. The performance of LGS GLAO is, however, sensitive to the atmospheric turbulence profile.

  7. Stress activated contractile wavefronts in the mechanically-excitable embryonic heart

    NASA Astrophysics Data System (ADS)

    Chiou, Kevin; Majkut, Stephanie; Discher, Dennis; Lubensky, Tom; Liu, Andrea

    2014-03-01

    The heart is a prime example of a robust, active system with behavior-the heart beat-that is extraordinarily well timed and coordinated. For more than half a century, electrical activity induced by ion release and diffusion has been argued to be the mechanism driving cardiac action. But recent work indicates that this phenomenon is also regulated by mechanical activity. In the embryonic avian heart tube, the speed of the contractile wavefront traversing the heart tube with each beat is measured to be a monotonic, linear function of tissue stiffness. Traditional electrical conduction models of excitation-contraction cannot explain this dependence; such a result indicates that the myocardium is mechanically excitable. Here, we extend this work by using experimental observations of stiffness-dependent behavior in isolated cardiomyocytes as an input to study contractile wavefronts in the tissue as a whole. We model the heart tube as an active, overdamped elastic network where the primary stress mediator is the extracellular matrix. Using this simple model, we explain experimental observations of the systolic wave and predict qualitatively new behavior.

  8. Field application of moment-based wavefront sensing to in-situ alignment and image quality assessment of astronomical spectrographs: results and analysis of aligning VIRUS unit spectrographs

    NASA Astrophysics Data System (ADS)

    Lee, Hanshin; Hill, Gary J.; Tuttle, Sarah E.; Noyola, Eva; Peterson, Trent; Vattiat, Brian L.

    2014-07-01

    Teague introduced a phase retrieval method that uses the image shape moments. More recently, an independent study arrived at a similar technique, which was then applied to in-situ full-field image-quality evaluation of spectroscopic systems. This moment-based wavefront sensing (MWFS) method relies on the geometric relation between the image shape moments and the geometric wavefront modal coefficients. The MWFS method allows a non-iterative determination of the modal coefficients from focus-modulated images at arbitrary spatial resolutions. The determination of image moments is a direct extension of routine centroid and image size calculation, making its implementation easy. Previous studies showed that the MWFS works well in capturing large low-order modes, and is quite suitable for in-situ alignment diagnostics. At the Astronomical Instrumentation conference in 2012, we presented initial results of the application of the moment-based wavefront sensing to a fiber-fed astronomical spectrograph, called VIRUS (a set of replicated 150 identical integral-field unit spectrographs contained in 75 unit pairs). This initial result shows that the MWFS can provide accurate full-field image-quality assessment for efficiently aligning these 150 spectrographs. Since then, we have assembled more than 24 unit pairs using this technique. In this paper, we detail the technical update/progress made so far for the moment-based wavefront sensing method and the statistical estimates of the before/after alignment aberrations, image-quality, and various efficiency indicators of the unit spectrograph alignment process.

  9. Active wavefront control challenges of the NASA Large Deployable Reflector (LDR)

    NASA Technical Reports Server (NTRS)

    Meinel, Aden B.; Meinel, Marjorie P.; Manhart, Paul K.; Hochberg, Eric B.

    1989-01-01

    The 20-m Large Deployable Reflector will have a segmented primary mirror. Achieving diffraction-limited performance at 50 microns requires correction for the errors of tilt and piston of the primary mirror. This correction can be obtained in two ways, the use of an active primary or a correction at a demagnified pupil of the primary. A critical requirement is the means for measurement of the wavefront error and maintaining phasing during the observation of objects that may be too faint for determining the error. Absolute phasing can only be determined using a cooperative source. Maintenance of phasing can be done with an on-board source. A number of options are being explored as discussed below. The many issues concerning the assessment and control of an active segmented mirror will be addressed with an early construction of the Precision Segmented Reflector testbed.

  10. Modeling the effect of high altitude turbulence in wide-field correlating wavefront sensing and its impact on the performance of solar AO systems

    NASA Astrophysics Data System (ADS)

    Montilla, I.; Tallon, M.; Langlois, M.; Béchet, C.; Collados Vera, M.

    2014-08-01

    Solar Adaptive Optics (AO) shares many issues with night-time AO, but it also has its own particularities. The wavefront sensing is performed using correlations to efficiently work on the solar granulation as a reference. The field of view for that measurement usually is around 10". A sensor collecting such a wide field of view averages wavefront information from different sky directions, and the anisoplanatism thus has a peculiar impact on the performance of solar AO and MCAO systems. Since we are entering the era of large solar telescopes (European Solar Telescope, Advanced Technology Solar Telescope) understanding this issue is crucial to evaluate its impact on the performance of future AO systems. In this paper we model the correlating wide field sensor and the way it senses the high altitude turbulence. Thanks to this improved modelling, we present an analysis of the influence of this sensing on the performance of each AO configuration, conventional AO and MCAO. In addition to the analytical study, simulations similar to the case of the EST AO systems with FRiM-3D (the Fractal Iterative Method for Atmospheric tomography) are used in order to highlight the relative influence of design parameters. In particular, results show the performance evolution when increasing the telescope diameter. We analyse the effect of high altitude turbulence correlation showing that increasing the diameter of the telescope does not degrade the performance when correcting on the same spatial and temporal scales.

  11. Target-in-the-loop wavefront sensing and control with a Collett-Wolf beacon: speckle-average phase conjugation.

    PubMed

    Vorontsov, Mikhail A; Kolosov, Valeriy V; Polnau, Ernst

    2009-01-01

    Adaptive optical systems for laser beam projection onto an extended target embedded in an optically inhomogeneous medium are considered. A new adaptive optics wavefront control technique--speckle-average (SA) phase conjugation--is introduced. In this technique mitigation of speckle effects related to laser beam scattering off the rough target surface is achieved by measuring the SA wavefront slopes of the target return wave using a conventional Shack-Hartmann wavefront sensor. For statistically representative speckle averaging we consider the generation of an incoherent light source, referred to here as a Collett-Wolf beacon, directly on the target surface using a rapid steering (scanning) auxiliary laser beam. Our numerical simulations and experiment show that control of the outgoing beam phase using SA phase conjugation can lead to efficient compensation of turbulence effects and results in an increase of the projected laser beam power density on a remote extended target. The impact of both target anisoplanatism and the Collett-Wolf beacon size on adaptive system performance is studied.

  12. Longitudinal chromatic aberration of the human eye in the visible and near infrared from wavefront sensing, double-pass and psychophysics

    PubMed Central

    Vinas, Maria; Dorronsoro, Carlos; Cortes, Daniel; Pascual, Daniel; Marcos, Susana

    2015-01-01

    Longitudinal Chromatic Aberration (LCA) influences the optical quality of the eye. However, the reported LCA varies across studies, likely associated to differences in the measurement techniques. We present LCA measured in subjects using wavefront sensing, double-pass retinal images, and psychophysical methods with a custom-developed polychromatic Adaptive Optics system in a wide spectral range (450-950 nm), with control of subjects’ natural aberrations. LCA measured psychophysically was significantly higher than that from reflectometric techniques (1.51 D vs 1.00 D in the 488-700 nm range). Ours results indicate that the presence of natural aberrations is not the cause for the discrepancies across techniques. PMID:25798317

  13. Wavefront control with a spatial light modulator containing dual-frequency liquid crystal

    NASA Astrophysics Data System (ADS)

    Gu, Dong-Feng; Winker, Bruce; Wen, Bing; Taber, Don; Brackley, Andrew; Wirth, Allan; Albanese, Marc; Landers, Frank

    2004-10-01

    A versatile, scalable wavefront control approach based upon proven liquid crystal (LC) spatial light modulator (SLM) technology was extended for potential use in high-energy near-infrared laser applications. The reflective LC SLM module demonstrated has a two-inch diameter active aperture with 812 pixels. Using an ultra-low absorption transparent conductor in the LC SLM, a high laser damage threshold was demonstrated. Novel dual frequency liquid crystal materials and addressing schemes were implemented to achieve fast switching speed (<1ms at 1.31 microns). Combining this LCSLM with a novel wavefront sensing method, a closed loop wavefront controller is being demonstrated. Compared to conventional deformable mirrors, this non-mechanical wavefront control approach offers substantial improvements in speed (bandwidth), resolution, power consumption and system weight/volume.

  14. High signal-to-noise ratio sensing with Shack-Hartmann wavefront sensor based on auto gain control of electron multiplying CCD

    NASA Astrophysics Data System (ADS)

    Zhu, Zhao-Yi; Li, Da-Yu; Hu, Li-Fa; Mu, Quan-Quan; Yang, Cheng-Liang; Cao, Zhao-Liang; Xuan, Li

    2016-09-01

    High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device (EMCCD) applied in the Shack-Hartmann wavefront sensor (S-H WFS) in adaptive optics (AO). However, when the brightness of the target changes in a large scale, the fixed electron multiplying (EM) gain will not be suited to the sensing limitation. Therefore an auto-gain-control method based on the brightness of light-spots array in S-H WFS is proposed in this paper. The control value is the average of the maximum signals of every light spot in an array, which has been demonstrated to be kept stable even under the influence of some noise and turbulence, and sensitive enough to the change of target brightness. A goal value is needed in the control process and it is predetermined based on the characters of EMCCD. Simulations and experiments have demonstrated that this auto-gain-control method is valid and robust, the sensing SNR reaches the maximum for the corresponding signal level, and especially is greatly improved for those dim targets from 6 to 4 magnitude in the visual band. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174274, 61205021, and 61405194) and the State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.

  15. High signal-to-noise ratio sensing with Shack–Hartmann wavefront sensor based on auto gain control of electron multiplying CCD

    NASA Astrophysics Data System (ADS)

    Zhu, Zhao-Yi; Li, Da-Yu; Hu, Li-Fa; Mu, Quan-Quan; Yang, Cheng-Liang; Cao, Zhao-Liang; Xuan, Li

    2016-09-01

    High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device (EMCCD) applied in the Shack–Hartmann wavefront sensor (S–H WFS) in adaptive optics (AO). However, when the brightness of the target changes in a large scale, the fixed electron multiplying (EM) gain will not be suited to the sensing limitation. Therefore an auto-gain-control method based on the brightness of light-spots array in S–H WFS is proposed in this paper. The control value is the average of the maximum signals of every light spot in an array, which has been demonstrated to be kept stable even under the influence of some noise and turbulence, and sensitive enough to the change of target brightness. A goal value is needed in the control process and it is predetermined based on the characters of EMCCD. Simulations and experiments have demonstrated that this auto-gain-control method is valid and robust, the sensing SNR reaches the maximum for the corresponding signal level, and especially is greatly improved for those dim targets from 6 to 4 magnitude in the visual band. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174274, 61205021, and 61405194) and the State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.

  16. Wavefront Measurement in Ophthalmology

    NASA Astrophysics Data System (ADS)

    Molebny, Vasyl

    Wavefront sensing or aberration measurement in the eye is a key problem in refractive surgery and vision correction with laser. The accuracy of these measurements is critical for the outcome of the surgery. Practically all clinical methods use laser as a source of light. To better understand the background, we analyze the pre-laser techniques developed over centuries. They allowed new discoveries of the nature of the optical system of the eye, and many served as prototypes for laser-based wavefront sensing technologies. Hartmann's test was strengthened by Platt's lenslet matrix and the CCD two-dimensional photodetector acquired a new life as a Hartmann-Shack sensor in Heidelberg. Tscherning's aberroscope, invented in France, was transformed into a laser device known as a Dresden aberrometer, having seen its reincarnation in Germany with Seiler's help. The clinical ray tracing technique was brought to life by Molebny in Ukraine, and skiascopy was created by Fujieda in Japan. With the maturation of these technologies, new demands now arise for their wider implementation in optometry and vision correction with customized contact and intraocular lenses.

  17. Wavefront Control for Extreme Adaptive Optics

    SciTech Connect

    Poyneer, L A

    2003-07-16

    Current plans for Extreme Adaptive Optics systems place challenging requirements on wave-front control. This paper focuses on control system dynamics, wave-front sensing and wave-front correction device characteristics. It may be necessary to run an ExAO system after a slower, low-order AO system. Running two independent systems can result in very good temporal performance, provided specific design constraints are followed. The spatially-filtered wave-front sensor, which prevents aliasing and improves PSF sensitivity, is summarized. Different models of continuous and segmented deformable mirrors are studied. In a noise-free case, a piston-tip-tilt segmented MEMS device can achieve nearly equivalent performance to a continuous-sheet DM in compensating for a static phase aberration with use of spatial filtering.

  18. Optical Modeling Activities for NASA's James Webb Space Telescope (JWST). 3; Wavefront Aberrations due to Alignment and Figure Compensation

    NASA Technical Reports Server (NTRS)

    Howard, Joseph

    2007-01-01

    This is part three of a series describing the ongoing optical modeling activities for James Webb Space Telescope (JWST). The first two discussed modeling JWST on-orbit performance using wavefront sensitivities to predict line of sight motion induced blur, and stability during thermal transients. The work here investigates the aberrations resulting from alignment and figure compensation of the controllable degrees of freedom (primary and secondary mirrors), which may be encountered during ground alignment and on-orbit commissioning of the observatory. The optical design of the telescope is a three-mirror anastigmat, with an active fold mirror at the exit pupil for fine guiding. The primary mirror is over 6.5 meters in diameter, and is composed of 18 hexagonal segments that can individually positioned on hexapods, as well as compensated for radius of curvature. This effectively gives both alignment and figure control of the primary mirror. The secondary mirror can be moved in rigid body only, giving alignment control of the telescope. The tertiary mirror is fixed, however, as well as the location of the science instrumentation. Simulations are performed of various combinations of active alignment corrections of component figure errors, and of primary mirror figure corrections of alignment errors. Single field point and moderate field knowledge is assumed in the corrections. Aberrations over the field are reported for the varying cases, and examples presented.

  19. Proposal for a field experiment of elongated Na LGS wave-front sensing in the perspective of the E-ELT

    NASA Astrophysics Data System (ADS)

    Rousset, G.; Gratadour, D.; Gendron, E.; Buey, T.; Myers, R.; Morris, T.; Basden, A.; Talbot, G.; Bonaccini Calia, D.; Marchetti, E.; Pfrommer, T.

    2014-08-01

    Wavefront (WF) sensing using Sodium (Na) Laser Guide Stars (LGS) is a key concern for the design of a number of first generation Extremely Large Telescope (ELT) Adaptive Optics (AO) modules. One of the main challenges is the mitigation of the effects induced by extreme LGS spot elongation on the WF measurements. Before the final design studies of the E-ELT instruments, a Na LGS WF sensing on-sky experiment at the E-ELT scale is mandatory to achieve the full validation of the proposed mitigation strategies and their performance. This experiment will provide unique spatial and temporal WF measurements on a true Na LGS, perturbed by the atmospheric turbulence and mesospheric variability. The fine comparative analysis of such data with synchronously acquired WF measurements on at least one natural guide star (NGS) will be fundamental to test a number of algorithms, configurations for spot sampling and truncation and WF reconstruction schemes including multi-LGS configurations. A global error budget for the whole experiment will be derived with time to feed into the numerical simulation and the design of subsequent E-ELT LGS-AO modules. The data produced will be made available to the E-ELT community. We propose to use CANARY, the Multi-Object AO demonstrator installed at the 4.2m WHT which is a modular AO platform, equipped with several NGS WF Sensor (WFS) and Rayleigh multi-LGS unit and WFS. The transportable 20W Sodium laser unit (WLGSU), developed at ESO, will be positioned at a varying distance from the WHT to provide off-axis launching (up to 40m), simulating the whole range of LGS spot elongations obtained on the E-ELT. In such a case, the WHT pupil will represent an off-axis sub-pupil of the main E-ELT pupil. In addition, this experiment will include a Na layer profiler and the capability for open and closed loop operations. The experiment is scheduled before the end of 2016.

  20. Wavefront Control Testbed (WCT) Experiment Results

    NASA Technical Reports Server (NTRS)

    Burns, Laura A.; Basinger, Scott A.; Campion, Scott D.; Faust, Jessica A.; Feinberg, Lee D.; Hayden, William L.; Lowman, Andrew E.; Ohara, Catherine M.; Petrone, Peter P., III

    2004-01-01

    The Wavefront Control Testbed (WCT) was created to develop and test wavefront sensing and control algorithms and software for the segmented James Webb Space Telescope (JWST). Last year, we changed the system configuration from three sparse aperture segments to a filled aperture with three pie shaped segments. With this upgrade we have performed experiments on fine phasing with line-of-sight and segment-to-segment jitter, dispersed fringe visibility and grism angle;. high dynamic range tilt sensing; coarse phasing with large aberrations, and sampled sub-aperture testing. This paper reviews the results of these experiments.

  1. Relaying an optical wavefront

    DOEpatents

    Sweatt, William C.; Vawter, G. Allen

    2007-03-06

    A wavefront rely devices samples an incoming optical wavefront at different locations, optically relays the samples while maintaining the relative position of the samples and the relative phase between the samples. The wavefront is reconstructed due to interference of the samples. Devices can be designed for many different wavelengths, including for example the ultraviolet, visible, infrared and even longer wavelengths such as millimeter waves. In one application, the device function as a telescope but with negligible length.

  2. Wave-front analysis of personal eye protection.

    PubMed

    Eppig, Timo; Zoric, Katja; Speck, Alexis; Zelzer, Benedikt; Götzelmann, Jens; Nagengast, Dieter; Langenbucher, Achim

    2012-07-30

    Shack-Hartmann wave-front sensing has been successfully applied to many fields of optical testing including the human eye itself. We propose wave-front measurement for testing protective eye wear for production control and investigation of aberrations. Refractive power data is derived from the wave-front data and compared to a subjective measurement technique based on a focimeter. Additional image quality classification was performed with a multivariate model using objective parameters to resample a subjectively determined visual quality. Wave-front measurement advances optical testing of protective eye wear and may be used for objective quality control.

  3. Fixed mount wavefront sensor

    DOEpatents

    Neal, Daniel R.

    2000-01-01

    A rigid mount and method of mounting for a wavefront sensor. A wavefront dissector, such as a lenslet array, is rigidly mounted at a fixed distance relative to an imager, such as a CCD camera, without need for a relay imaging lens therebetween.

  4. An Improved Wavefront Control Algorithm for Large Space Telescopes

    NASA Technical Reports Server (NTRS)

    Sidick, Erkin; Basinger, Scott A.; Redding, David C.

    2008-01-01

    Wavefront sensing and control is required throughout the mission lifecycle of large space telescopes such as James Webb Space Telescope (JWST). When an optic of such a telescope is controlled with both surface-deforming and rigid-body actuators, the sensitivity-matrix obtained from the exit pupil wavefront vector divided by the corresponding actuator command value can sometimes become singular due to difference in actuator types and in actuator command values. In this paper, we propose a simple approach for preventing a sensitivity-matrix from singularity. We also introduce a new "minimum-wavefront and optimal control compensator". It uses an optimal control gain matrix obtained by feeding back the actuator commands along with the measured or estimated wavefront phase information to the estimator, thus eliminating the actuator modes that are not observable in the wavefront sensing process.

  5. Brazil's remote sensing activities in the Eighties

    NASA Technical Reports Server (NTRS)

    Raupp, M. A.; Pereiradacunha, R.; Novaes, R. A.

    1985-01-01

    Most of the remote sensing activities in Brazil have been conducted by the Institute for Space Research (INPE). This report describes briefly INPE's activities in remote sensing in the last years. INPE has been engaged in research (e.g., radiance studies), development (e.g., CCD-scanners, image processing devices) and applications (e.g., crop survey, land use, mineral resources, etc.) of remote sensing. INPE is also responsible for the operation (data reception and processing) of the LANDSATs and meteorological satellites. Data acquisition activities include the development of CCD-Camera to be deployed on board the space shuttle and the construction of a remote sensing satellite.

  6. A Simplified Approach for Simultaneous Measurements of Wavefront Velocity and Curvature in the Heart Using Activation Times

    PubMed Central

    Mazeh, Nachaat; Haines, David E.; Kay, Matthew W.; Roth, Bradley J.

    2014-01-01

    The velocity and curvature of a wave front are important factors governing the propagation of electrical activity through cardiac tissue, particularly during heart arrhythmias of clinical importance such as fibrillation. Presently, no simple computational model exists to determine these values simultaneously. The proposed model uses the arrival times at four or five sites to determine the wave front speed (v), direction (θ), and radius of curvature (ROC) (r0). If the arrival times are measured, then v, θ, and r0 can be found from differences in arrival times and the distance between these sites. During isotropic conduction, we found good correlation between measured values of the ROC r0 and the distance from the unipolar stimulus (r = 0.9043 and p < 0.0001). The conduction velocity (m/s) was correlated (r = 0.998, p < 0.0001) using our method (mean = 0.2403, SD = 0.0533) and an empirical method (mean = 0.2352, SD = 0.0560). The model was applied to a condition of anisotropy and a complex case of reentry with a high voltage extra stimulus. Again, results show good correlation between our simplified approach and established methods for multiple wavefront morphologies. In conclusion, insignificant measurement errors were observed between this simplified approach and an approach that was more computationally demanding. Accuracy was maintained when the requirement that ε (ε = b/r0, ratio of recording site spacing over wave fronts ROC) was between 0.001 and 0.5. The present simplified model can be applied to a variety of clinical conditions to predict behavior of planar, elliptical, and reentrant wave fronts. It may be used to study the genesis and propagation of rotors in human arrhythmias and could lead to rotor mapping using low density endocardial recording electrodes. PMID:24772193

  7. Curvature sensor for ocular wavefront measurement.

    PubMed

    Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O

    2006-08-01

    We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes. PMID:16832447

  8. Curvature sensor for ocular wavefront measurement.

    PubMed

    Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O

    2006-08-01

    We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes.

  9. Phase discrepancy induced from least squares wavefront reconstruction of wrapped phase measurements with high noise or large localized wavefront gradients

    NASA Astrophysics Data System (ADS)

    Steinbock, Michael J.; Hyde, Milo W.

    2012-10-01

    Adaptive optics is used in applications such as laser communication, remote sensing, and laser weapon systems to estimate and correct for atmospheric distortions of propagated light in real-time. Within an adaptive optics system, a reconstruction process interprets the raw wavefront sensor measurements and calculates an estimate for the unwrapped phase function to be sent through a control law and applied to a wavefront correction device. This research is focused on adaptive optics using a self-referencing interferometer wavefront sensor, which directly measures the wrapped wavefront phase. Therefore, its measurements must be reconstructed for use on a continuous facesheet deformable mirror. In testing and evaluating a novel class of branch-point- tolerant wavefront reconstructors based on the post-processing congruence operation technique, an increase in Strehl ratio compared to a traditional least squares reconstructor was noted even in non-scintillated fields. To investigate this further, this paper uses wave-optics simulations to eliminate many of the variables from a hardware adaptive optics system, so as to focus on the reconstruction techniques alone. The simulation results along with a discussion of the physical reasoning for this phenomenon are provided. For any applications using a self-referencing interferometer wavefront sensor with low signal levels or high localized wavefront gradients, understanding this phenomena is critical when applying a traditional least squares wavefront reconstructor.

  10. Indicators of international remote sensing activities

    NASA Technical Reports Server (NTRS)

    Spann, G. W.

    1977-01-01

    The extent of worldwide remote sensing activities, including the use of satellite and high/medium altitude aircraft data was studied. Data were obtained from numerous individuals and organizations with international remote sensing responsibilities. Indicators were selected to evaluate the nature and scope of remote sensing activities in each country. These indicators ranged from attendance at remote sensing workshops and training courses to the establishment of earth resources satellite ground stations and plans for the launch of earth resources satellites. Results indicate that this technology constitutes a rapidly increasing component of environmental, land use, and natural resources investigations in many countries, and most of these countries rely on the LANDSAT satellites for a major portion of their data.

  11. MOSAIC: a new wavefront metrology

    SciTech Connect

    Anderson, Christopher; Naulleau, Patrick

    2009-02-02

    MOSAIC is a new wavefront metrology that enables complete wavefront characterization from print or aerial image based measurements. Here we describe MOSAIC and verify its utility with a model-based proof of principle.

  12. Advanced Wavefront Control Techniques

    SciTech Connect

    Olivier, S S; Brase, J M; Avicola, K; Thompson, C A; Kartz, M W; Winters, S; Hartley, R; Wihelmsen, J; Dowla, F V; Carrano, C J; Bauman, B J; Pennington, D M; Lande, D; Sawvel, R M; Silva, D A; Cooke, J B; Brown, C G

    2001-02-21

    Programs at LLNL that involve large laser systems--ranging from the National Ignition Facility to new tactical laser weapons--depend on the maintenance of laser beam quality through precise control of the optical wavefront. This can be accomplished using adaptive optics, which compensate for time-varying aberrations that are often caused by heating in a high-power laser system. Over the past two decades, LLNL has developed a broad capability in adaptive optics technology for both laser beam control and high-resolution imaging. This adaptive optics capability has been based on thin deformable glass mirrors with individual ceramic actuators bonded to the back. In the case of high-power lasers, these adaptive optics systems have successfully improved beam quality. However, as we continue to extend our applications requirements, the existing technology base for wavefront control cannot satisfy them. To address this issue, this project studied improved modeling tools to increase our detailed understanding of the performance of these systems, and evaluated novel approaches to low-order wavefront control that offer the possibility of reduced cost and complexity. We also investigated improved beam control technology for high-resolution wavefront control. Many high-power laser systems suffer from high-spatial-frequency aberrations that require control of hundreds or thousands of phase points to provide adequate correction. However, the cost and size of current deformable mirrors can become prohibitive for applications requiring more than a few tens of phase control points. New phase control technologies are becoming available which offer control of many phase points with small low-cost devices. The goal of this project was to expand our wavefront control capabilities with improved modeling tools, new devices that reduce system cost and complexity, and extensions to high spatial and temporal frequencies using new adaptive optics technologies. In FY 99, the second year of

  13. Early Childhood: Developing Sense-activities.

    ERIC Educational Resources Information Center

    Shirah, Sue; Dorman, Mildred M.

    1989-01-01

    Described are science activities in which students concentrate on their senses and make discoveries with their eyes, ears, noses, mouths, and hands. Suggested experiments include activities involving cooking, tasting, observing, floating and sinking objects, making rain, and stringed musical instruments. (RT)

  14. Remote Sensing of Active Volcanoes

    NASA Astrophysics Data System (ADS)

    Francis, Peter; Rothery, David

    The synoptic coverage offered by satellites provides unparalleled opportunities for monitoring active volcanoes, and opens new avenues of scientific inquiry. Thermal infrared radiation can be used to monitor levels of activity, which is useful for automated eruption detection and for studying the emplacement of lava flows. Satellite radars can observe volcanoes through clouds or at night, and provide high-resolution topographic data. In favorable conditions, radar inteferometery can be used to measure ground deformation associated with eruptive activity on a centimetric scale. Clouds from explosive eruptions present a pressing hazard to aviation; therefore, techniques are being developed to assess eruption cloud height and to discriminate between ash and meterological clouds. The multitude of sensors to be launched on future generations of space platforms promises to greatly enhance volcanological studies, but a satellite dedicated to volcanology is needed to meet requirements of aviation safety and volcano monitoring.

  15. Sensing Human Activity: GPS Tracking

    PubMed Central

    van der Spek, Stefan; van Schaick, Jeroen; de Bois, Peter; de Haan, Remco

    2009-01-01

    The enhancement of GPS technology enables the use of GPS devices not only as navigation and orientation tools, but also as instruments used to capture travelled routes: as sensors that measure activity on a city scale or the regional scale. TU Delft developed a process and database architecture for collecting data on pedestrian movement in three European city centres, Norwich, Rouen and Koblenz, and in another experiment for collecting activity data of 13 families in Almere (The Netherlands) for one week. The question posed in this paper is: what is the value of GPS as ‘sensor technology’ measuring activities of people? The conclusion is that GPS offers a widely useable instrument to collect invaluable spatial-temporal data on different scales and in different settings adding new layers of knowledge to urban studies, but the use of GPS-technology and deployment of GPS-devices still offers significant challenges for future research. PMID:22574061

  16. Wavefront Correction for Large, Flexible Antenna Reflector

    NASA Technical Reports Server (NTRS)

    Imbriale, William A.; Jammejad, Vahraz; Rajagopalan, Harish; Xu, Shenheng

    2010-01-01

    A wavefront-correction system has been proposed as part of an outer-space radio communication system that would include a large, somewhat flexible main reflector antenna, a smaller subreflector antenna, and a small array feed at the focal plane of these two reflector antennas. Part of the wavefront-correction system would reside in the subreflector, which would be a planar patch-element reflectarray antenna in which the phase shifts of the patch antenna elements would be controlled via microelectromechanical systems (MEMS) radio -frequency (RF) switches. The system would include the following sensing-and-computing subsystems: a) An optical photogrammetric subsystem built around two cameras would estimate geometric distortions of the main reflector; b) A second subsystem would estimate wavefront distortions from amplitudes and phases of signals received by the array feed elements; and c) A third subsystem, built around small probes on the subreflector plane, would estimate wavefront distortions from differences among phases of signals received by the probes. The distortion estimates from the three subsystems would be processed to generate control signals to be fed to the MEMS RF switches to correct for the distortions, thereby enabling collimation and aiming of the received or transmitted radio beam to the required precision.

  17. Myopic aberrations: Simulation based comparison of curvature and Hartmann Shack wavefront sensors

    NASA Astrophysics Data System (ADS)

    Basavaraju, Roopashree M.; Akondi, Vyas; Weddell, Stephen J.; Budihal, Raghavendra Prasad

    2014-02-01

    In comparison with a Hartmann Shack wavefront sensor, the curvature wavefront sensor is known for its higher sensitivity and greater dynamic range. The aim of this study is to numerically investigate the merits of using a curvature wavefront sensor, in comparison with a Hartmann Shack (HS) wavefront sensor, to analyze aberrations of the myopic eye. Aberrations were statistically generated using Zernike coefficient data of 41 myopic subjects obtained from the literature. The curvature sensor is relatively simple to implement, and the processing of extra- and intra-focal images was linearly resolved using the Radon transform to provide Zernike modes corresponding to statistically generated aberrations. Simulations of the HS wavefront sensor involve the evaluation of the focal spot pattern from simulated aberrations. Optical wavefronts were reconstructed using the slope geometry of Southwell. Monte Carlo simulation was used to find critical parameters for accurate wavefront sensing and to investigate the performance of HS and curvature sensors. The performance of the HS sensor is highly dependent on the number of subapertures and the curvature sensor is largely dependent on the number of Zernike modes used to represent the aberration and the effective propagation distance. It is shown that in order to achieve high wavefront sensing accuracy while measuring aberrations of the myopic eye, a simpler and cost effective curvature wavefront sensor is a reliable alternative to a high resolution HS wavefront sensor with a large number of subapertures.

  18. Wavefront detection method of a single-sensor based adaptive optics system.

    PubMed

    Wang, Chongchong; Hu, Lifa; Xu, Huanyu; Wang, Yukun; Li, Dayu; Wang, Shaoxin; Mu, Quanquan; Yang, Chengliang; Cao, Zhaoliang; Lu, Xinghai; Xuan, Li

    2015-08-10

    In adaptive optics system (AOS) for optical telescopes, the reported wavefront sensing strategy consists of two parts: a specific sensor for tip-tilt (TT) detection and another wavefront sensor for other distortions detection. Thus, a part of incident light has to be used for TT detection, which decreases the light energy used by wavefront sensor and eventually reduces the precision of wavefront correction. In this paper, a single Shack-Hartmann wavefront sensor based wavefront measurement method is presented for both large amplitude TT and other distortions' measurement. Experiments were performed for testing the presented wavefront method and validating the wavefront detection and correction ability of the single-sensor based AOS. With adaptive correction, the root-mean-square of residual TT was less than 0.2 λ, and a clear image was obtained in the lab. Equipped on a 1.23-meter optical telescope, the binary stars with angle distance of 0.6″ were clearly resolved using the AOS. This wavefront measurement method removes the separate TT sensor, which not only simplifies the AOS but also saves light energy for subsequent wavefront sensing and imaging, and eventually improves the detection and imaging capability of the AOS. PMID:26367988

  19. Remote Sensing Simulation Activities for Earthlings

    ERIC Educational Resources Information Center

    Krockover, Gerald H.; Odden, Thomas D.

    1977-01-01

    Suggested are activities using a Polaroid camera to illustrate the capabilities of remote sensing. Reading materials from the National Aeronautics and Space Administration (NASA) are suggested. Methods for (1) finding a camera's focal length, (2) calculating ground dimension photograph simulation, and (3) limiting size using film resolution are…

  20. Symbol Sense Behavior in Digital Activities

    ERIC Educational Resources Information Center

    Bokhove, Christian; Drijvers, Paul

    2010-01-01

    The algebraic expertise that mathematics education is aiming for includes both procedural skills and conceptual understanding. To capture the latter, notions such as symbol sense, gestalt view and visual salience have been developed. We wonder if digital activities can be designed that not only require procedural algebraic skills, but also invite…

  1. Electrically sensing protease activity with nanopores

    NASA Astrophysics Data System (ADS)

    Kukwikila, Mikiembo; Howorka, Stefan

    2010-11-01

    The enzymatic activity of a protease was electrically detected using nanopore recordings. A peptide substrate was tethered to microscale beads, and cleavage by the enzyme trypsin released a soluble fragment that was electrophoretically driven through the α-hemolysin protein pore, leading to detectable blockades in the ionic current. Owing to its simplicity, this approach to sense enzymatic activity may be applied to other proteases.

  2. A Wavefront Sensor to Detect Dim Objects

    NASA Astrophysics Data System (ADS)

    Mateen, M.; Guyon, O.; Hart, M.; Codona, J.

    2014-09-01

    In this paper we present the progress made towards building the non-linear Curvature wavefront sensor (nlCWFS) to be used in an adaptive optics system for the direct imaging of exoplanets without the use of a laser guide star (LGS). Commonly used wavefront sensors such as the Shack Hartmann wavefront sensor (SHWFS) do a good job of reconstructing high order modes but due to design limitations are poor at reconstructing low order modes. The nlCWFS is able to use the full spatial coherence of the pupil allowing it to reconstruct all spatial frequencies equally well. The nlCWFS senses at the diffraction limit as opposed to the SHWFS which senses at the seeing limit. This awards the nlCWFS a gain in flux of (D/r0)2. In this paper we present results from putting the nlCWFS on the 6.5m MMT Observatory and detail the progress being made to build the nlCWFS for the 1.5 m Air Force Research Laboratory/RDS Optics Division telescope.

  3. Development of a Pyramid Wave-front Sensor

    NASA Astrophysics Data System (ADS)

    El Hadi, Kacem; Vignaux, Mael; Fusco, Thierry

    2013-12-01

    Within the framework of the E-ELT studies, several laboratories are involved on some instruments: HARMONY with its ATLAS adaptive optics [AO] system, EAGLE or EPICS. Most of the AO systems will probably integrate one or several pyramidal wavefront sensors, PWFS (R. Ragazzoni [1]). The coupling in an AO loop and the control in laboratory (then on sky) of this type of sensor is fundamental for the continuation of the projects related to OA systems on the E-ELT. LAM (Laboratory of Astrophysics of Marseille) is involved in particular in the VLT-SPHERE, ATLAS, EPICS projects. For the last few years, our laboratory has been carrying out different R&D activities in AO instrumentation for ELTs. An experimental AO bench is designed and being developed to allow the validation of new wave-front sensing and control concepts [2]. One the objectives of this bench, is the experimental validation of a pyramid WFS. Theoretical investigations on its behavior have been already made. The world's fastest and most sensitive camera system (OCAM2) has been recently developed at LAM (J.L Gach [3], First Light Imaging). Conjugating this advantage with the pyramid concept, we plan to demonstrate a home made Pyramid sensor for Adaptive Optics whose the speed and the precision are the key points. As a joint collaboration with ONERA and Shaktiware, our work aims at the optimization (measurement process, calibration and operation) in laboratory then on the sky of a pyramid sensor dedicated to the first generation instruments for ELTs. The sensor will be implemented on the ONERA ODISSEE AO bench combining thus a pyramid and a Shack-Hartmann wavefront sensors. What would give the possibility to compare strictly these two WFS types and make this bench unique in France and even in Europe. Experimental work on laboratory demonstration is undergoing. The status of our development will presented at the conference.

  4. Adaptive Full Aperture Wavefront Sensor Study

    NASA Technical Reports Server (NTRS)

    Robinson, William G.

    1997-01-01

    This grant and the work described was in support of a Seven Segment Demonstrator (SSD) and review of wavefront sensing techniques proposed by the Government and Contractors for the Next Generation Space Telescope (NGST) Program. A team developed the SSD concept. For completeness, some of the information included in this report has also been included in the final report of a follow-on contract (H-27657D) entitled "Construction of Prototype Lightweight Mirrors". The original purpose of this GTRI study was to investigate how various wavefront sensing techniques might be most effectively employed with large (greater than 10 meter) aperture space based telescopes used for commercial and scientific purposes. However, due to changes in the scope of the work performed on this grant and in light of the initial studies completed for the NGST program, only a portion of this report addresses wavefront sensing techniques. The wavefront sensing techniques proposed by the Government and Contractors for the NGST were summarized in proposals and briefing materials developed by three study teams including NASA Goddard Space Flight Center, TRW, and Lockheed-Martin. In this report, GTRI reviews these approaches and makes recommendations concerning the approaches. The objectives of the SSD were to demonstrate functionality and performance of a seven segment prototype array of hexagonal mirrors and supporting electromechanical components which address design issues critical to space optics deployed in large space based telescopes for astronomy and for optics used in spaced based optical communications systems. The SSD was intended to demonstrate technologies which can support the following capabilities: Transportation in dense packaging to existing launcher payload envelopes, then deployable on orbit to form a space telescope with large aperture. Provide very large (greater than 10 meters) primary reflectors of low mass and cost. Demonstrate the capability to form a segmented primary or

  5. Tomographic wavefront correction for the LSST

    SciTech Connect

    Phillion, D W; Olivier, S S; Baker, K; Seppala, L; Hvisc, S

    2006-05-03

    The Large Synoptic Survey Telescope (LSST) is a three mirror modified Paul-Baker design with an 8.4m primary, a 3.4m secondary, and a 5.0m tertiary followed by a 3-element refractive corrector producing a 3.5 degree field of view. This design produces image diameters of <0.3 arcsecond 80% encircled energy over its full field of view. The image quality of this design is sufficient to ensure that the final images produced by the telescope will be limited by the atmospheric seeing at an excellent astronomical site. In order to maintain this image quality, the deformations and rigid body motions of the three large mirrors must be actively controlled to minimize optical aberrations. By measuring the optical wavefront produced by the telescope at multiple points in the field, mirror deformations and rigid body motions that produce a good optical wavefront across the entire field may be determined. We will describe the details of the techniques for obtaining these solutions. We will show that, for the expected mirror deformations and rigid body misalignments, the solutions that are found using these techniques produce an image quality over the field that is close to optimal. We will discuss how many wavefront sensors are needed and the tradeoffs between the number of wavefront sensors, their layout and noise sensitivity.

  6. Active remote sensing of random media

    SciTech Connect

    Zuniga, M.; Kong, J.A.

    1980-01-01

    Analytical results for the bistatic scattering coefficients and the backscattering cross sections have been derived for active remote sensing of earth terrain with the model of bounded random media which accounts for volume-scattering effects. It is found that as a result of the effect of the second boundary, the horizontally polarized return sigma/sub h/h can be greater than the vertically polarized return sigma/sub v/v, whereas for a half-space random medium sigma/sub v/v is always greater than sigma/sub h/h. We illustrate by matching the theoretical results with experimental data collected from vegetation field.

  7. Propofol effects on atrial fibrillation wavefront delays.

    PubMed

    Cervigón, Raquel; Moreno, Javier; Millet, José; Pérez-Villacastín, Julián; Castells, Francisco

    2010-08-01

    Since the cardiac activity during atrial fibrillation (AF) may be influenced by autonomic modulations, in this study, a novel method to quantify the effects of the most common anesthetic agent (propofol) in AF ablation procedures is introduced. This study has two main objectives: first, to assess whether the sedation earlier to radio frequency ablation affects the arrhythmia itself, and second, to provide new information that contributes to a better understanding of the influence of the autonomic nervous system on AF. The methodology presented is based on the measurement of synchronization and delay indexes between two atrial activations at adjacent intracavitary electrodes. These parameters aim to estimate whether two activations at different sites may be caused by the same propagating wavefront, or otherwise, are the consequence of independent wavefronts. The results showed that the mentioned indexes have a different behavior at both atria: the right atrium becomes more synchronized with propofol administration, whereas the synchronization index decreases at the left atrium.

  8. Dynamics of Active Sensing and perceptual selection.

    PubMed

    Schroeder, Charles E; Wilson, Donald A; Radman, Thomas; Scharfman, Helen; Lakatos, Peter

    2010-04-01

    Sensory processing is often regarded as a passive process in which biological receptors like photoreceptors and mechanoreceptors transduce physical energy into a neural code. Recent findings, however, suggest that: first, most sensory processing is active, and largely determined by motor/attentional sampling routines; second, owing to rhythmicity in the motor routine, as well as to its entrainment of ambient rhythms in sensory regions, sensory inflow tends to be rhythmic; third, attentional manipulation of rhythms in sensory pathways is instrumental to perceptual selection. These observations outline the essentials of an Active Sensing paradigm, and argue for increased emphasis on the study of sensory processes as specific to the dynamic motor/attentional context in which inputs are acquired. PMID:20307966

  9. Hierarchical curiosity loops and active sensing.

    PubMed

    Gordon, Goren; Ahissar, Ehud

    2012-08-01

    A curious agent acts so as to optimize its learning about itself and its environment, without external supervision. We present a model of hierarchical curiosity loops for such an autonomous active learning agent, whereby each loop selects the optimal action that maximizes the agent's learning of sensory-motor correlations. The model is based on rewarding the learner's prediction errors in an actor-critic reinforcement learning (RL) paradigm. Hierarchy is achieved by utilizing previously learned motor-sensory mapping, which enables the learning of other mappings, thus increasing the extent and diversity of knowledge and skills. We demonstrate the relevance of this architecture to active sensing using the well-studied vibrissae (whiskers) system, where rodents acquire sensory information by virtue of repeated whisker movements. We show that hierarchical curiosity loops starting from optimally learning the internal models of whisker motion and then extending to object localization result in free-air whisking and object palpation, respectively. PMID:22386787

  10. Dynamics of Active Sensing and Perceptual Selection

    PubMed Central

    Schroeder, Charles E; Wilson, Donald A.; Radman, Thomas; Scharfman, Helen; Lakatos, Peter

    2010-01-01

    Sensory processing is often regarded as a passive process in which a biological sensors like photo- and mechanoreceptors transducer physical energy into a neural code. Recent findings, however, suggest that: 1) most sensory processing is active, and largely determined by motor/attentional sampling routines, 2) due to rhythmicity in the motor routine, as well as to its entrainment of ambient rhythms in sensory regions, sensory inflow tends to be rhythmic, and 3) attentional manipulation of rhythms in sensory pathways is instrumental to perceptual selection. These observations outline the essentials of an Active Sensing paradigm, and argue for increased emphasis on the study of sensory processes as specific to the dynamic motor/attentional context in which inputs are acquired. PMID:20307966

  11. Optical Modeling Activities for the James Webb Space Telescope (JWST) Project. II; Determining Image Motion and Wavefront Error Over an Extended Field of View with a Segmented Optical System

    NASA Technical Reports Server (NTRS)

    Howard, Joseph M.; Ha, Kong Q.

    2004-01-01

    This is part two of a series on the optical modeling activities for JWST. Starting with the linear optical model discussed in part one, we develop centroid and wavefront error sensitivities for the special case of a segmented optical system such as JWST, where the primary mirror consists of 18 individual segments. Our approach extends standard sensitivity matrix methods used for systems consisting of monolithic optics, where the image motion is approximated by averaging ray coordinates at the image and residual wavefront error is determined with global tip/tilt removed. We develop an exact formulation using the linear optical model, and extend it to cover multiple field points for performance prediction at each instrument aboard JWST. This optical model is then driven by thermal and dynamic structural perturbations in an integrated modeling environment. Results are presented.

  12. JWST Wavefront Control Toolbox

    NASA Technical Reports Server (NTRS)

    Shin, Shahram Ron; Aronstein, David L.

    2011-01-01

    A Matlab-based toolbox has been developed for the wavefront control and optimization of segmented optical surfaces to correct for possible misalignments of James Webb Space Telescope (JWST) using influence functions. The toolbox employs both iterative and non-iterative methods to converge to an optimal solution by minimizing the cost function. The toolbox could be used in either of constrained and unconstrained optimizations. The control process involves 1 to 7 degrees-of-freedom perturbations per segment of primary mirror in addition to the 5 degrees of freedom of secondary mirror. The toolbox consists of a series of Matlab/Simulink functions and modules, developed based on a "wrapper" approach, that handles the interface and data flow between existing commercial optical modeling software packages such as Zemax and Code V. The limitations of the algorithm are dictated by the constraints of the moving parts in the mirrors.

  13. Phase-Controlled Magnetic Mirror for Wavefront Correction

    NASA Technical Reports Server (NTRS)

    Hagopian, John; Wollack, Edward

    2011-01-01

    Typically, light interacts with matter via the electric field and interaction with weakly bound electrons. In a magnetic mirror, a patterned nanowire is fabricated over a metallic layer with a dielectric layer in between. Oscillation of the electrons in the nanowires in response to the magnetic field of incident photons causes a re-emission of photons and operation as a "magnetic mirror." By controlling the index of refraction in the dielectric layer using a local applied voltage, the phase of the emitted radiation can be controlled. This allows electrical modification of the reflected wavefront, resulting in a deformable mirror that can be used for wavefront control. Certain applications require wavefront quality in the few-nanometer regime, which is a major challenge for optical fabrication and alignment of mirrors or lenses. The use of a deformable magnetic mirror allows for a device with no moving parts that can modify the phase of incident light over many spatial scales, potentially with higher resolution than current approaches. Current deformable mirrors modify the incident wavefront by using nano-actuation of a substrate to physically bend the mirror to a desired shape. The purpose of the innovation is to modify the incident wavefront for the purpose of correction of fabrication and alignment-induced wavefront errors at the system level. The advanced degree of precision required for some applications such as gravity wave detection (LISA - Laser Interferometer Space Antenna) or planet finding (FKSI - Fourier-Kelvin Stellar Interferometer) requires wavefront control at the limits of the current state of the art. All the steps required to fabricate a magnetic mirror have been demonstrated. The modification is to apply a bias voltage to the dielectric layer so as to change the index of refraction and modify the phase of the reflected radiation. Light is reflected off the device and collected by a phase-sensing interferometer. The interferometer determines the

  14. Beam characterization by wavefront sensor

    DOEpatents

    Neal, D.R.; Alford, W.J.; Gruetzner, J.K.

    1999-08-10

    An apparatus and method are disclosed for characterizing an energy beam (such as a laser) with a two-dimensional wavefront sensor, such as a Shack-Hartmann lenslet array. The sensor measures wavefront slope and irradiance of the beam at a single point on the beam and calculates a space-beamwidth product. A detector array such as a charge coupled device camera is preferably employed. 21 figs.

  15. Extended scene wavefront sensor for space application

    NASA Astrophysics Data System (ADS)

    Bomer, Thierry; Ravel, Karen; Corlay, Gilles

    2015-10-01

    The spatial resolution of optical monitoring satellites increases continuously and it is more and more difficult to satisfy the stability constraints of the instrument. The compactness requirements induce high sensitivity to drift during storage and launching. The implementation of an active loop for the control of the performances for the telescope becomes essential, in the same way of astronomy telescopes on ground. The active loop requires disposing of informations in real time of optical distortions of the wavefront, due to mirror deformations. It is the role of the Shack-Hartmann wave front sensor studied by Sodern. It is located in the focal plane of the telescope, in edge of field of view, in order not to disturb acquisition by the main instrument. Its particular characteristic, compared to a traditional wavefront sensor is not only to work on point source as star image, but also on extended scenes, as those observed by the instrument. The exit pupil of the telescope is imaged on a micro lenses array by a relay optics. Each element of the micro lenses array generates a small image, drifted by the local wavefront slope. The processing by correlation between small images allows to measure local slope and to recover the initial wavefront deformation according to Zernike decomposition. Sodern has realized the sensor dimensioning and has studied out the comparison of various algorithms of images correlation making it possible to measure the local slopes of the wave front. Simulations, taking into account several types of detectors, enabled to compare the performances of these solutions and a choice of detector was carried out. This article describes the state of progress of the work done so far. It shows the result of the comparisons on the choice of the detector, the main features of the sensor definition and the performances obtained.

  16. The NGS Pyramid wavefront sensor for ERIS

    NASA Astrophysics Data System (ADS)

    Riccardi, A.; Antichi, J.; Quirós-Pacheco, F.; Esposito, S.; Carbonaro, L.; Agapito, G.; Biliotti, V.; Briguglio, R.; Di Rico, G.; Dolci, M.; Ferruzzi, D.; Pinna, E.; Puglisi, A.; Xompero, M.; Marchetti, E.; Fedrigo, E.; Le Louarn, M.; Conzelmann, R.; Delabre, B.; Amico, P.; Hubin, N.

    2014-07-01

    ERIS is the new Single Conjugate Adaptive Optics (AO) instrument for VLT in construction at ESO with the collaboration of Max-Planck Institut fuer Extraterrestrische Physik, ETH-Institute for Astronomy and INAF - Osservatorio Astrofisico di Arcetri. The ERIS AO system relies on a 40×40 sub-aperture Pyramid Wavefront Sensor (PWFS) for two operating modes: a pure Natural Guide Star high-order sensing for high Strehl and contrast correction and a low-order visible sensing in support of the Laser Guide Star AO mode. In this paper we present in detail the preliminary design of the ERIS PWFS that is developed under the responsibility of INAF-Osservatorio Astrofisico di Arcetri in collaboration with ESO.

  17. Estimate Low and High Order Wavefront Using P1640 Calibrator Measurements

    NASA Technical Reports Server (NTRS)

    Zhai, C.; Vasisht, G.; Shao, M.; Lockhart, T.; Cady, E.; Oppenheimer, B.; Burruss, R.; Roberts, J.; Beichman, C.; Brenner, D.; Crepp, J.; Dekany, R.; Hillenbrand, L.; Hinkley, S.; Parry, I.; Pueyo, L.; Rice, E.; Roberts, L. C. Jr.; Sivaramakrishnan, A.; Soummer, R.; Tang, H.; Vescelus, F.; Wallace, K.; Zimmerman, N.

    2013-01-01

    P1640 high contrast imaging system on the Palomar 200 inch Telescope consists of an apodized-pupil Lyot coronagraph, the PALM-3000 adaptive optics (P3K-AO), and P1640 Calibrator (CAL). Science images are recorded by an integral field spectrograph covering J-H bands for detecting and characterizing stellar companions. With aberrations from atmosphere corrected by the P3K-AO, instrument performance is limited mainly by the quasi-static speckles due to noncommon path wavefront aberrations for the light to propagate to the P3K-AO wavefront sensor and to the coronagraph mask. The non-common path wavefront aberrations are sensed by CAL, which measures the post-coronagraph E-field using interferometry, and can be effectively corrected by offsetting the P3K-AO deformable mirror target position accordingly. Previously, we have demonstrated using CAL measurements to correct high order wavefront aberrations, which is directly connected to the static speckles in the image plane. Low order wavefront, on the other hand, usually of larger amplitudes, causes light to leak through the coronagraph making the whole image plane brighter. Knowledge error in low order wavefront aberrations can also affect the estimation of the high order wavefront. Even though, CAL is designed to sense efficiently high order wavefront aberrations, the low order wavefront front can be inferred with less sensitivity. Here, we describe our method for estimating both low and high order wavefront aberrations using CAL measurements by propagating the post-coronagraph E-field to a pupil before the coronagraph. We present the results from applying this method to both simulated and experiment data.

  18. On numerical simulation of high-speed CCD/CMOS-based wavefront sensors in adaptive optics

    NASA Astrophysics Data System (ADS)

    Konnik, Mikhail V.; Welsh, James Stuart

    2011-10-01

    Wavefront sensors, which use solid-state CCD or CMOS photosensors, are sources of errors in adaptive optic systems. Inaccuracy in the detection of wavefront distortions introduces considerable errors into wavefront reconstruction and leads to overall performance degradation of the adaptive optics system. The accuracy of wavefront sensors is significantly affected by photosensor noise. Thus, it is crucial to formulate high-level photosensor models that enable adaptive optic engineers to simulate realistic effects of noise from wavefront sensors. However, the complexity of solid-state photosensors and multiple noise sources makes it difficult to formulate an adequate model of the photosensor. Moreover, the characterisation of the simulated sensor and comparison with real hardware is often incomplete due to lack of comprehensive standards and guidelines. Owe to these difficulties, engineers work with oversimplified models of the wavefront sensors and consequently have imprecise numerical simulation results. The paper presents an approach for the modelling of noise sources for CCD and CMOS sensors that are used for wavefront sensing in adaptive optics. Both dark and light noise such as fixed pattern noise, photon shot noise, and read noises, as well as, charge-to-voltage noises are described. Procedures for characterisation of both light and dark noises of the simulated photosensors are provided. Numerical simulation results of a photosensor for a high-frame rate Shack-Hartmann wavefront sensor are presented.

  19. Optimized plasmonic nanostructures for improved sensing activities.

    PubMed

    Shen, Hong; Guillot, Nicolas; Rouxel, Jérémy; Lamy de la Chapelle, Marc; Toury, Timothée

    2012-09-10

    The paper outlines the optimization of plasmonic nanostructures in order to improve their sensing properties such as their sensitivity and their ease of manipulation. The key point in this study is the optimization of the localized surface plasmon resonance (LSPR) properties essential to the sensor characteristics, and more especially for surface-enhanced Raman scattering (SERS). Two aspects were considered in order to optimize the sensing performance: apolar plasmonic nanostructures for non polarization dependent detection and improvements of SERS sensitivity by using a molecular adhesion layer between gold nanostructures and glass. Both issues could be generalized to all plasmon-resonance-based sensing applications.

  20. A non-linear curvature wavefront sensor reconstruction speed and the broadband design

    NASA Astrophysics Data System (ADS)

    Mateen, Mala; Guyon, Olivier; Sasián, José; Garrel, Vincent; Hart, Michael

    2011-10-01

    In this paper we explain why a non-linear curvature wavefront sensor (nlCWFS) is more sensitive than conventional wavefront sensors such as the Shack Hartmann wavefront sensor (SHWFS) and the conventional curvature wavefront sensor (cCWFS) for sensing mV < 14 natural guide stars. The non-linear approach builds on the successful curvature wavefront sensing concept but uses a non-linear Gerchberg-Saxton (GS) phase diversity algorithm to reconstruct the wavefront. The nonlinear reconstruction algorithm is an advantage for sensitivity but a challenge for fast computation. The current speed is a factor of 10 to 100 times slower than needed for high performance groundbased AO. We present a two step strategy to increase the speed of the algorithm. In the last paper3 we presented laboratory results obtained with a monochromatic source, here we extend our experiment to incorporate a broadband source. The sensitivity of the nlCWFS depends on the ability to extract wavefront phase from diffraction limited speckles therefore it is essential that the speckles do not suffer from chromatic aberration when used with a polychromatic source. We discuss the design for the chromatic re-imaging optics, which through chromatic compensation, allow us to obtain diffraction limited speckles in Fresnel propagated planes on either side of the pupil plane.

  1. Wavefront modifier with integrated sensor

    NASA Astrophysics Data System (ADS)

    Griffith, Mike; Laycock, Leslie; Rowe, Duncan; Cairns, Lee

    2009-09-01

    We present a novel method for integrating a wavefront sensor into a deformable mirror. This development should simplify the design of laser and electro-optic systems, and lead to smart mirrors which need no external control systems. In operation, a small fraction of the incident light is transmitted through the mirror coating and is sampled by a Hartmann Mask. Options include open loop, traditional closed loop or fully integrated operation whereby the wavefront sensor is used to provide direct feedback to the mirror actuators, enabling automatic alignment or phase conjugation.

  2. One-Dimensional Wavefront Sensor Analysis

    1996-04-25

    This software analyzes one-dimensional wavefront sensor data acquired with any of several data acquisition systems. It analyzes the data to determine centroids, wavefront slopes and overall wavefront error. The data can be displayed in many formats, with plots of various parameters vs time and position, including computer generated movies. Data can also be exported for use by other programs.

  3. New CCD imagers for adaptive optics wavefront sensors

    NASA Astrophysics Data System (ADS)

    Schuette, Daniel R.; Reich, Robert K.; Prigozhin, Ilya; Burke, Barry E.; Johnson, Robert

    2014-08-01

    We report on two recently developed charge-coupled devices (CCDs) for adaptive optics wavefront sensing, both designed to provide exceptional sensitivity (low noise and high quantum efficiency) in high-frame-rate low-latency readout applications. The first imager, the CCID75, is a back-illuminated 16-port 160×160-pixel CCD that has been demonstrated to operate at frame rates above 1,300 fps with noise of < 3 e-. We will describe the architecture of this CCD that enables this level of performance, present and discuss characterization data, and review additional design features that enable unique operating modes for adaptive optics wavefront sensing. We will also present an architectural overview and initial characterization data of a recently designed variation on the CCID75 architecture, the CCID82, which incorporates an electronic shutter to support adaptive optics using Rayleigh beacons.

  4. Adaptive wavefront sensor based on the Talbot phenomenon.

    PubMed

    Podanchuk, Dmytro V; Goloborodko, Andrey A; Kotov, Myhailo M; Kovalenko, Andrey V; Kurashov, Vitalij N; Dan'ko, Volodymyr P

    2016-04-20

    A new adaptive method of wavefront sensing is proposed and demonstrated. The method is based on the Talbot self-imaging effect, which is observed in an illuminating light beam with strong second-order aberration. Compensation of defocus and astigmatism is achieved with an appropriate choice of size of the rectangular unit cell of the diffraction grating, which is performed iteratively. A liquid-crystal spatial light modulator is used for this purpose. Self-imaging of rectangular grating in the astigmatic light beam is demonstrated experimentally. High-order aberrations are detected with respect to the compensated second-order aberration. The comparative results of wavefront sensing with a Shack-Hartmann sensor and the proposed sensor are adduced. PMID:27140122

  5. Active microwave remote sensing of oceans, chapter 3

    NASA Technical Reports Server (NTRS)

    1975-01-01

    A rationale is developed for the use of active microwave sensing in future aerospace applications programs for the remote sensing of the world's oceans, lakes, and polar regions. Summaries pertaining to applications, local phenomena, and large-scale phenomena are given along with a discussion of orbital errors.

  6. Terahertz wavefront measurement with a Hartmann sensor

    NASA Astrophysics Data System (ADS)

    Richter, H.; Greiner-Bär, M.; Deßmann, N.; Pfund, J.; Wienold, M.; Schrottke, L.; Hey, R.; Grahn, H. T.; Hübers, H.-W.

    2012-07-01

    The measurement of the wavefront of a terahertz (THz) beam is essential for the development of any optical instrument operating at THz frequencies. We have realized a Hartmann wavefront sensor for the THz frequency range. The sensor is based on an aperture plate consisting of a regular square pattern of holes and a microbolometer camera. The performance of the sensor is demonstrated by characterizing the wavefront of a THz beam emitted by a quantum-cascade laser. The wavefront determined by the sensor agrees well with that expected from a Gaussian-shaped beam. The spatial resolution is 1 mm, and a single-wavefront measurement takes less than 1 s.

  7. Closed-loop focal plane wavefront control with the SCExAO instrument

    NASA Astrophysics Data System (ADS)

    Martinache, Frantz; Jovanovic, Nemanja; Guyon, Olivier

    2016-09-01

    Aims: This article describes the implementation of a focal plane based wavefront control loop on the high-contrast imaging instrument SCExAO (Subaru Coronagraphic Extreme Adaptive Optics). The sensor relies on the Fourier analysis of conventional focal-plane images acquired after an asymmetric mask is introduced in the pupil of the instrument. Methods: This absolute sensor is used here in a closed-loop to compensate for the non-common path errors that normally affects any imaging system relying on an upstream adaptive optics system.This specific implementation was used to control low-order modes corresponding to eight zernike modes (from focus to spherical). Results: This loop was successfully run on-sky at the Subaru Telescope and is used to offset the SCExAO deformable mirror shape used as a zero-point by the high-order wavefront sensor. The paper details the range of errors this wavefront-sensing approach can operate within and explores the impact of saturation of the data and how it can be bypassed, at a cost in performance. Conclusions: Beyond this application, because of its low hardware impact, the asymmetric pupil Fourier wavefront sensor (APF-WFS) can easily be ported in a wide variety of wavefront sensing contexts, for ground- as well space-borne telescopes, and for telescope pupils that can be continuous, segmented or even sparse. The technique is powerful because it measures the wavefront where it really matters, at the level of the science detector.

  8. Feasibility study of a layer-oriented wavefront sensor for solar telescopes.

    PubMed

    Marino, Jose; Wöger, Friedrich

    2014-02-01

    Solar multiconjugate adaptive optics systems rely on several wavefront sensors, which measure the incoming turbulent phase along several field directions to produce a tomographic reconstruction of the turbulent phase. In this paper, we explore an alternative wavefront sensing approach that attempts to directly measure the turbulent phase present at a particular height in the atmosphere: a layer-oriented cross-correlating Shack-Hartmann wavefront sensor (SHWFS). In an experiment at the Dunn Solar Telescope, we built a prototype layer-oriented cross-correlating SHWFS system conjugated to two separate atmospheric heights. We present the data obtained in the observations and complement these with ray-tracing computations to achieve a better understanding of the instrument's performance and limitations. The results obtained in this study strongly indicate that a layer-oriented cross-correlating SHWFS is not a practical design to measure the wavefront at a high layer in the atmosphere.

  9. Remote sensing application to regional activities

    NASA Technical Reports Server (NTRS)

    Shahrokhi, F.; Jones, N. L.; Sharber, L. A.

    1976-01-01

    Two agencies within the State of Tennessee were identified whereby the transfer of aerospace technology, namely remote sensing, could be applied to their stated problem areas. Their stated problem areas are wetland and land classification and strip mining studies. In both studies, LANDSAT data was analyzed with the UTSI video-input analog/digital automatic analysis and classification facility. In the West Tennessee area three land-use classifications could be distinguished; cropland, wetland, and forest. In the East Tennessee study area, measurements were submitted to statistical tests which verified the significant differences due to natural terrain, stripped areas, various stages of reclamation, water, etc. Classifications for both studies were output in the form of maps of symbols and varying shades of gray.

  10. Wavefront-Error Performance Characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Science Instruments

    NASA Technical Reports Server (NTRS)

    Aronstein, David L.; Smith, J. Scott; Zielinski, Thomas P.; Telfer, Randal; Tournois, Severine C.; Moore, Dustin B.; Fienup, James R.

    2016-01-01

    The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES) test chamber. In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing, and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) F-number and pupil-distortion measurements made using a pseudo-nonredundant mask (PNRM), and 3) pupil geometry predictions as a function of SI and field point, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse translation diversity sweeps instead of focus sweeps, in which a sub-aperture is translated and/or rotated across the exit pupil of the system. Several optical-performance requirements that were verified during this ISIM-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also describes the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis of focus-sweep data, used to establish

  11. Wavefront-Error Performance Characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Science Instruments

    NASA Technical Reports Server (NTRS)

    Aronstein, David L.; Smith, J. Scott; Zielinski, Thomas P.; Telfer, Randal; Tournois, Severine C.; Moore, Dustin B.; Fienup, James R.

    2016-01-01

    The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES). In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing (also known as phase retrieval), and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) plate scale measurements made using a Pseudo-Nonredundant Mask (PNRM), and 3) pupil geometry predictions as a function of SI and field point, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse translation diversity sweeps instead of focus sweeps, in which a sub-aperture is translated andor rotated across the exit pupil of the system.Several optical-performance requirements that were verified during this ISIM-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also describes the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis of focus-sweep data, used to establish the

  12. Making Sense of Multiple Physical Activity Recommendations.

    ERIC Educational Resources Information Center

    Corbin, Charles B.; LeMasurier, Guy; Franks, B. Don

    2002-01-01

    This digest provides basic information designed to help people determine which of the many physical activity guidelines are most appropriate for use in specific situations. After an introduction, the digest focuses on: "Factors to Consider in Selecting Appropriate Physical Activity Guidelines" (group credibility and purpose, benefits to be…

  13. Broadband, Common-path, Interferometric Wavefront Sensor

    NASA Technical Reports Server (NTRS)

    Wallace, James Kent (Inventor)

    2015-01-01

    Hybrid sensors comprising Shack-Hartmann Wavefront Sensor (S-HWFS) and Zernike Wavefront Sensor (Z-WFS) capabilities are presented. The hybrid sensor includes a Z-WFS optically arranged in-line with a S-HWFS such that the combined wavefront sensor operates across a wide dynamic range and noise conditions. The Z-WFS may include the ability to introduce a dynamic phase shift in both transmissive and reflective modes.

  14. Sparse aperture mask wavefront sensor testbed results

    NASA Astrophysics Data System (ADS)

    Subedi, Hari; Zimmerman, Neil T.; Kasdin, N. Jeremy; Riggs, A. J. E.

    2016-07-01

    Coronagraphic exoplanet detection at very high contrast requires the estimation and control of low-order wave- front aberrations. At Princeton High Contrast Imaging Lab (PHCIL), we are working on a new technique that integrates a sparse-aperture mask (SAM) with a shaped pupil coronagraph (SPC) to make precise estimates of these low-order aberrations. We collect the starlight rejected from the coronagraphic image plane and interfere it using a sparse aperture mask (SAM) at the relay pupil to estimate the low-order aberrations. In our previous work we numerically demonstrated the efficacy of the technique, and proposed a method to sense and control these differential aberrations in broadband light. We also presented early testbed results in which the SAM was used to sense pointing errors. In this paper, we will briefly overview the SAM wavefront sensor technique, explain the design of the completed testbed, and report the experimental estimation results of the dominant low-order aberrations such as tip/tit, astigmatism and focus.

  15. Wavefront reconstruction from tangential and sagittal curvature.

    PubMed

    Canales, Javier; Barbero, Sergio; Portilla, Javier; López-Alonso, José Manuel

    2014-12-10

    In a previous contribution [Appl. Opt.51, 8599 (2012)], a coauthor of this work presented a method for reconstructing the wavefront aberration from tangential refractive power data measured using dynamic skiascopy. Here we propose a new regularized least squares method where the wavefront is reconstructed not only using tangential but also sagittal curvature data. We prove that our new method provides improved quality reconstruction for typical and also for highly aberrated wavefronts, under a wide range of experimental error levels. Our method may be applied to any type of wavefront sensor (not only dynamic skiascopy) able to measure either just tangential or tangential plus sagittal curvature data.

  16. Microwave remote sensing: Active and passive. Volume 1 - Microwave remote sensing fundamentals and radiometry

    NASA Technical Reports Server (NTRS)

    Ulaby, F. T.; Moore, R. K.; Fung, A. K.

    1981-01-01

    The three components of microwave remote sensing (sensor-scene interaction, sensor design, and measurement techniques), and the applications to geoscience are examined. The history of active and passive microwave sensing is reviewed, along with fundamental principles of electromagnetic wave propagation, antennas, and microwave interaction with atmospheric constituents. Radiometric concepts are reviewed, particularly for measurement problems for atmospheric and terrestrial sources of natural radiation. Particular attention is given to the emission by atmospheric gases, clouds, and rain as described by the radiative transfer function. Finally, the operation and performance characteristics of radiometer receivers are discussed, particularly for measurement precision, calibration techniques, and imaging considerations.

  17. Zernike-like Orthogonal Basis Functions for Wavefront Characterization over Sampled, Irregular Apertures

    NASA Technical Reports Server (NTRS)

    Aronstein, David L.; Dean, Bruce H.; Smith, J. Scott

    2007-01-01

    For optical systems with circular apertures, wavefronts are often analyzed using Zernike polynomials, and individual Zernike functions are associated with familiar optical aberrations. For systems with noncircular apertures, or in practical situations in which wavefronts are measured at a limited number of points in the aperture, the Zernike polynomials are no longer an orthogonal basis for the measured data. Although there are an endless number of ways to create a basis for such measured data, a "Zernike-like" basis is useful to connect with our experience with the usual optical aberrations. In this paper, the steps required to identify a Zernike-like basis for wavefronts over sampled, irregular apertures are presented, based on the Gram-Schmidt orthogonalization technique. The benefits of analyzing optical wavefronts using an orthogonal basis specific to an optical system's aperture shape and wavefront sampling, instead of using the traditional Zernike polynomials, are detailed in two examples, from image-based wavefront sensing on a segmented-aperture telescope (the James Webb Space Telescope Testbed Telescope at Ball Aerospace) and from interferometer characterization for surface metrology of a hexagonal mirror segment.

  18. Passive and Active Sensing Technologies for Structural Health Monitoring

    NASA Astrophysics Data System (ADS)

    Do, Richard

    A combination of passive and active sensing technologies is proposed as a structural health monitoring solution for several applications. Passive sensing is differentiated from active sensing in that with the former, no energy is intentionally imparted into the structure under test; sensors are deployed in a pure detection mode for collecting data mined for structural health monitoring purposes. In this thesis, passive sensing using embedded fiber Bragg grating optical strain gages was used to detect varying degrees of impact damage using two different classes of features drawn from traditional spectral analysis and auto-regressive time series modeling. The two feature classes were compared in detail through receiver operating curve performance analysis. The passive detection problem was then augmented with an active sensing system using ultrasonic guided waves (UGWs). This thesis considered two main challenges associated with UGW SHM including in-situ wave propagation property determination and thermal corruption of data. Regarding determination of wave propagation properties, of which dispersion characteristics are the most important, a new dispersion curve extraction method called sparse wavenumber analysis (SWA) was experimentally validated. Also, because UGWs are extremely sensitive to ambient temperature changes on the structure, it significantly affects the wave propagation properties by causing large errors in the residual error in the processing of the UGWs from an array. This thesis presented a novel method that compensates for uniform temperature change by considering the magnitude and phase of the signal separately and applying a scalable transformation.

  19. NASA's Future Active Remote Sensing Missing for Earth Science

    NASA Technical Reports Server (NTRS)

    Hartley, Jonathan B.

    2000-01-01

    Since the beginning of space remote sensing of the earth, there has been a natural progression widening the range of electromagnetic radiation used to sense the earth, and slowly, steadily increasing the spatial, spectral, and radiometric resolution of the measurements. There has also been a somewhat slower trend toward active measurements across the electromagnetic spectrum, motivated in part by increased resolution, but also by the ability to make new measurements. Active microwave instruments have been used to measure ocean topography, to study the land surface. and to study rainfall from space. Future NASA active microwave missions may add detail to the topographical studies, sense soil moisture, and better characterize the cryosphere. Only recently have active optical instruments been flown in space by NASA; however, there are currently several missions in development which will sense the earth with lasers and many more conceptual active optical missions which address the priorities of NASA's earth science program. Missions are under development to investigate the structure of the terrestrial vegetation canopy, to characterize the earth's ice caps, and to study clouds and aerosols. Future NASA missions may measure tropospheric vector winds and make vastly improved measurements of the chemical components of the earth's atmosphere.

  20. Browsing Image Collections with Representations of Common-Sense Activities.

    ERIC Educational Resources Information Center

    Gordon, Andrew S.

    2001-01-01

    Describes a methodology for creating networks of subject terms by manually representing a large number of common-sense activities that are broadly related to image subject terms. Application of this methodology to the Library of Congress Thesaurus for Graphic Materials produced 768 representations that supported users of a prototype browsing-based…

  1. Active Wave Propagation and Sensing in Plates

    NASA Technical Reports Server (NTRS)

    Ghoshal, Anindya; Martin, William N.; Sundaresan, Mannur J.; Schulz, Mark J.; Ferguson, Frederick

    2001-01-01

    Health monitoring of aerospace structures can be done using an active interrogation approach with diagnostic Lamb waves. Piezoelectric patches are often used to generate the waves, and it is helpful to understand how these waves propagate through a structure. To give a basic understanding of the actual physical process of wave propagation, a model is developed to simulate asymmetric wave propagation in a panel and to produce a movie of the wave motion. The waves can be generated using piezoceramic patches of any size or shape. The propagation, reflection, and interference of the waves are represented in the model. Measuring the wave propagation is the second important aspect of damage detection. Continuous sensors are useful for measuring waves because of the distributed nature of the sensor and the wave. Two sensor designs are modeled, and their effectiveness in measuring acoustic waves is studied. The simulation model developed is useful to understand wave propagation and to optimize the type of sensors that might be used for health monitoring of plate-like structures.

  2. A smooth introduction to the wavefront set

    NASA Astrophysics Data System (ADS)

    Brouder, Christian; Viet Dang, Nguyen; Hélein, Frédéric

    2014-11-01

    The wavefront set of a distribution describes not only the points where the distribution is singular, but also the ‘directions’ of the singularities. Because of its ability to control the product of distributions, the wavefront set was a key element of recent progress in renormalized quantum field theory in curved spacetime, quantum gravity, the discussion of time machines or quantum energy inequalitites. However, the wavefront set is a somewhat subtle concept whose standard definition is not easy to grasp. This paper is a step-by-step introduction to the wavefront set, with examples and motivation. Many different definitions and new interpretations of the wavefront set are presented. Some of them involve a Radon transform.

  3. Tomographic Errors From Wavefront Healing

    NASA Astrophysics Data System (ADS)

    Malcolm, A. E.; Trampert, J.

    2008-12-01

    Despite recent advances in full-waveform modeling ray theory is still, for good reasons, the preferred method in global tomography. It is well known that ray theory is most accurate for anomalies that are large compared to the wavelength. Exactly what errors result from the failure of this assumption is less well understood, in spite of the fact that anomalies found in the Earth from ray-based tomography methods are often outside the regime in which ray theory is known to be valid. Using the spectral element method, we have computed exact delay times and compared them to ray-theoretical traveltimes for two classic anomalies, one large and disk-shaped near the core mantle boundary, and the other a plume-like structure extending throughout the mantle. Wavefront healing is apparent in the traveltime anomalies generated by these structures; its effects are strongly asymmetric between P and S arrivals due to wavelength differences and source directionality. Simple computations in two dimensions allow us to develop the intuition necessary to understand how diffractions around the anomalies explain these results. When inverting the exact travel time anomalies with ray theory we expect wavefront healing to have a strong influence on the resulting structures. We anticipate that the asymmetry will be of particular importance in anomalies in the bulk velocity structure.

  4. High stability wavefront reference source

    DOEpatents

    Feldman, Mark; Mockler, Daniel J.

    1994-01-01

    A thermally and mechanically stable wavefront reference source which produces a collimated output laser beam. The output beam comprises substantially planar reference wavefronts which are useful for aligning and testing optical interferometers. The invention receives coherent radiation from an input optical fiber, directs a diverging input beam of the coherent radiation to a beam folding mirror (to produce a reflected diverging beam), and collimates the reflected diverging beam using a collimating lens. In a class of preferred embodiments, the invention includes a thermally and mechanically stable frame comprising rod members connected between a front end plate and a back end plate. The beam folding mirror is mounted on the back end plate, and the collimating lens mounted to the rods between the end plates. The end plates and rods are preferably made of thermally stable metal alloy. Preferably, the input optical fiber is a single mode fiber coupled to an input end of a second single mode optical fiber that is wound around a mandrel fixedly attached to the frame of the apparatus. The output end of the second fiber is cleaved so as to be optically flat, so that the input beam emerging therefrom is a nearly perfect diverging spherical wave.

  5. High stability wavefront reference source

    DOEpatents

    Feldman, M.; Mockler, D.J.

    1994-05-03

    A thermally and mechanically stable wavefront reference source which produces a collimated output laser beam is disclosed. The output beam comprises substantially planar reference wavefronts which are useful for aligning and testing optical interferometers. The invention receives coherent radiation from an input optical fiber, directs a diverging input beam of the coherent radiation to a beam folding mirror (to produce a reflected diverging beam), and collimates the reflected diverging beam using a collimating lens. In a class of preferred embodiments, the invention includes a thermally and mechanically stable frame comprising rod members connected between a front end plate and a back end plate. The beam folding mirror is mounted on the back end plate, and the collimating lens mounted to the rods between the end plates. The end plates and rods are preferably made of thermally stable metal alloy. Preferably, the input optical fiber is a single mode fiber coupled to an input end of a second single mode optical fiber that is wound around a mandrel fixedly attached to the frame of the apparatus. The output end of the second fiber is cleaved so as to be optically flat, so that the input beam emerging therefrom is a nearly perfect diverging spherical wave. 7 figures.

  6. Optically powered active sensing system for Internet Of Things

    NASA Astrophysics Data System (ADS)

    Gao, Chen; Wang, Jin; Yin, Long; Yang, Jing; Jiang, Jian; Wan, Hongdan

    2014-10-01

    Internet Of Things (IOT) drives a significant increase in the extent and type of sensing technology and equipment. Sensors, instrumentation, control electronics, data logging and transmission units comprising such sensing systems will all require to be powered. Conventionally, electrical powering is supplied by batteries or/and electric power cables. The power supply by batteries usually has a limited lifetime, while the electric power cables are susceptible to electromagnetic interference. In fact, the electromagnetic interference is the key issue limiting the power supply in the strong electromagnetic radiation area and other extreme environments. The novel alternative method of power supply is power over fiber (PoF) technique. As fibers are used as power supply lines instead, the delivery of the power is inherently immune to electromagnetic radiation, and avoids cumbersome shielding of power lines. Such a safer power supply mode would be a promising candidate for applications in IOT. In this work, we built up optically powered active sensing system, supplying uninterrupted power for the remote active sensors and communication modules. Also, we proposed a novel maximum power point tracking technique for photovoltaic power convertors. In our system, the actual output efficiency greater than 40% within 1W laser power. After 1km fiber transmission and opto-electric power conversion, a stable electric power of 210mW was obtained, which is sufficient for operating an active sensing system.

  7. Neural sensing of electrical activity with stretchable microelectrode arrays.

    PubMed

    Yu, Zhe; Graudejus, Oliver; Lacour, Stéphanie P; Wagner, Sigurd; Morrison, Barclay

    2009-01-01

    Sensing neural activity within mechanically active tissues poses particular hurdles because most electrodes are much stiffer than biological tissues. As the tissue deforms, the rigid electrodes may damage the surrounding tissue. The problem is exacerbated when sensing neural activity in experimental models of traumatic brain injury (TBI) which is caused by the rapid and large deformation of brain tissue. We have developed a stretchable microelectrode array (SMEA) that can withstand large elastic deformations (>5% biaxial strain) while continuing to function. The SMEA were fabricated from thin metal conductors patterned on polydimethylsiloxane (PDMS) and encapsulated with a photo-patternable silicone. SMEA were used to record spontaneous activity from brain slice cultures, as well as evoked activity after stimulating through SMEA electrodes. Slices of brain tissue were grown on SMEA in long-term culture and then mechanically injured with our well-characterized in vitro injury model by stretching the SMEA and the adherent culture, which was confirmed by image analysis. Because brain tissue was grown on the substrate-integrated SMEA, post-injury changes in electrophysiological function were normalized to pre-injury function since the SMEA deformed with the tissue and remained in place during mechanical stimulation. The combination of our injury model and SMEA could help elucidate mechanisms responsible for post-traumatic neuronal dysfunction in the quest for TBI therapies. The SMEA may have additional sensing applications in other mechanically active tissues such as peripheral nerve and heart. PMID:19964344

  8. Correction of the wavefront using the irradiance transport equation

    NASA Astrophysics Data System (ADS)

    García, M.; Granados, F.; Cornejo, A.

    2008-07-01

    The correction of the wavefront in optical systems implies the use of wavefront sensors, software, and auxiliary optical systems. We propose evaluated the wavefront using the fact that the wavefront and its intensity are related in the mathematical expression the irradiance transport equation (ITE)

  9. Cholinergic signals in mouse barrel cortex during active whisker sensing.

    PubMed

    Eggermann, Emmanuel; Kremer, Yves; Crochet, Sylvain; Petersen, Carl C H

    2014-12-11

    Internal brain states affect sensory perception, cognition, and learning. Many neocortical areas exhibit changes in the pattern and synchrony of neuronal activity during quiet versus active behaviors. Active behaviors are typically associated with desynchronized cortical dynamics. Increased thalamic firing contributes importantly to desynchronize mouse barrel cortex during active whisker sensing. However, a whisking-related cortical state change persists after thalamic inactivation, which is mediated at least in part by acetylcholine, as we show here by using whole-cell recordings, local pharmacology, axonal calcium imaging, and optogenetic stimulation. During whisking, we find prominent cholinergic signals in the barrel cortex, which suppress spontaneous cortical activity. The desynchronized state of barrel cortex during whisking is therefore driven by at least two distinct signals with opposing functions: increased thalamic activity driving glutamatergic excitation of the cortex and increased cholinergic input suppressing spontaneous cortical activity.

  10. Scalable analog wavefront sensor with subpixel resolution

    NASA Astrophysics Data System (ADS)

    Wilcox, Michael

    2006-06-01

    Standard Shack-Hartman wavefront sensors use a CCD element to sample position and distortion of a target or guide star. Digital sampling of the element and transfer to a memory space for subsequent computation adds significant temporal delay, thus, limiting the spatial frequency and scalability of the system as a wavefront sensor. A new approach to sampling uses information processing principles in an insect compound eye. Analog circuitry eliminates digital sampling and extends the useful range of the system to control a deformable mirror and make a faster, more capable wavefront sensor.

  11. Active sensing without efference copy: referent control of perception.

    PubMed

    Feldman, Anatol G

    2016-09-01

    Although action and perception are different behaviors, they are likely to be interrelated, as implied by the notions of perception-action coupling and active sensing. Traditionally, it has been assumed that the nervous system directly preprograms motor commands required for actions and uses a copy of them called efference copy (EC) to also influence our senses. This review offers a critical analysis of the EC concept by identifying its limitations. An alternative to the EC concept is based on the experimentally confirmed notion that sensory signals from receptors are perceived relative to referent signals specified by the brain. These referents also underlie the control of motor actions by predetermining where, in the spatial domain, muscles can work without preprogramming how they should work in terms of motor commands or EC. This approach helps solve several problems of action and explain several sensory experiences, including position sense and the sense that the world remains stationary despite changes in its retinal image during eye or body motion (visual space constancy). The phantom limb phenomenon and other kinesthetic illusions are also explained within this framework. PMID:27306668

  12. Characteristics of self-sensing actuation for active control

    SciTech Connect

    Barney, P.; Redmond, J.; Smith, D.

    1996-12-31

    The benefits of a collocated sensor actuator pair are well known within the controls community. Generally speaking, collocation offers the use of simple control algorithms with reduced instabilities due to spillover. One method for achieving collocation is the implementation of a ``sentuator`` in which a piezoelectric element functions simultaneously as both a sensor and an actuator. Past work in utilizing a sentuator has primarily been limited to piezoelectric films and patches mounted to flexible structures. Additional papers have provided information and methodology for dealing with the non-linear aspects of a piezoceramic sentuator. The need arises for methods of self-sensing when performing active vibration control of very stiff structures. A method for understanding and using self-sensing lead zirconate titanate stacks for active vibration control is presented. This paper specifically provides a basic understanding of self-sensing methods as applied to stiff structures for the purposes of control. The discussion of the methodology is followed by a simple example in which active vibration control is applied to a model of a boring bar with embedded PZT stacks.

  13. Wavefront Control and Image Restoration with Less Computing

    NASA Technical Reports Server (NTRS)

    Lyon, Richard G.

    2010-01-01

    PseudoDiversity is a method of recovering the wavefront in a sparse- or segmented- aperture optical system typified by an interferometer or a telescope equipped with an adaptive primary mirror consisting of controllably slightly moveable segments. (PseudoDiversity should not be confused with a radio-antenna-arraying method called pseudodiversity.) As in the cases of other wavefront- recovery methods, the streams of wavefront data generated by means of PseudoDiversity are used as feedback signals for controlling electromechanical actuators of the various segments so as to correct wavefront errors and thereby, for example, obtain a clearer, steadier image of a distant object in the presence of atmospheric turbulence. There are numerous potential applications in astronomy, remote sensing from aircraft and spacecraft, targeting missiles, sighting military targets, and medical imaging (including microscopy) through such intervening media as cells or water. In comparison with prior wavefront-recovery methods used in adaptive optics, PseudoDiversity involves considerably simpler equipment and procedures and less computation. For PseudoDiversity, there is no need to install separate metrological equipment or to use any optomechanical components beyond those that are already parts of the optical system to which the method is applied. In Pseudo- Diversity, the actuators of a subset of the segments or subapertures are driven to make the segments dither in the piston, tilt, and tip degrees of freedom. Each aperture is dithered at a unique frequency at an amplitude of a half wavelength of light. During the dithering, images on the focal plane are detected and digitized at a rate of at least four samples per dither period. In the processing of the image samples, the use of different dither frequencies makes it possible to determine the separate effects of the various dithered segments or apertures. The digitized image-detector outputs are processed in the spatial

  14. Zernike wavefront sensor modeling development for LOWFS on WFIRST-AFTA

    NASA Astrophysics Data System (ADS)

    Wang, Xu; Wallace, J. Kent; Shi, Fang

    2015-09-01

    WFIRST-AFTA design makes use of an existing 2.4m telescope for direct imaging of exoplanets. To maintain the high contrast needed for the coronagraph, wavefront error (WFE) of the optical system needs to be continuously sensed and controlled. Low Order Wavefront Sensing (LOWFS) uses the rejected starlight from an immediate focal plane to sense wavefront changes (mostly thermally induced low order WFE) by combining the LOWFS mask (a phase plate located at the small center region with reflective layer) with the starlight rejection masks, i.e. Hybrid Lyot Coronagraph (HLC)'s occulter or Shaped Pupil Coronagraph (SPC)'s field stop. Zernike wavefront sensor (ZWFS) measures phase via the phase-contrast method and is known to be photon noise optimal for measuring low order aberrations. Recently, ZWFS was selected as the baseline LOWFS technology on WFIST/AFTA for its good sensitivity, accuracy, and its easy integration with the starlight rejection mask. In this paper, we review the theory of ZWFS operation, describe the ZWFS algorithm development, and summarize various numerical sensitivity studies on the sensor performance. In the end, the predicted sensor performance on SPC and HLC configurations are presented.

  15. Optical wavefront shaping for the enhancement of Raman signal in scattering media

    NASA Astrophysics Data System (ADS)

    Thompson, Jonathan V.; Throckmorton, Graham A.; Hokr, Brett H.; Yakovlev, Vladislav V.

    2016-03-01

    The ability to non-invasively focus light through scattering media has significant applications in many fields ranging from nanotechnology to deep tissue sensing. Until recently, the multiple light scattering events that occur in complex media such as biological tissue have inhibited the focusing ability and penetration depth of optical tools. Through the use of optical wavefront shaping, the spatial distortions due to these scattering events can be corrected, and the incident light can be focused through the scattering medium. Here, we demonstrate that wavefront shaping can be used to non-invasively enhance the Raman signal of a material through a scattering medium. Raman signal enhancement was achieved using backscattered light and a continuous sequential algorithm. Our results show the potential of wavefront shaping as an important addition to non-invasive detection techniques.

  16. Latest developments in active remote sensing at INO

    NASA Astrophysics Data System (ADS)

    Babin, F.; Forest, R.; Bourliaguet, B.; Cantin, D.; Cottin, P.; Pancrati, O.; Turbide, S.; Lambert-Girard, S.; Cayer, F.; Lemieux, D.; Cormier, J.-F.; Châteauneuf, F.

    2012-09-01

    Remote sensing or stand-off detection using controlled light sources is a well known and often used technique for atmospheric and surface spatial mapping. Today, ground based, vehicle-borne and airborne systems are able to cover large areas with high accuracy and good reliability. This kind of detection based on LiDAR (Light Detection and Ranging) or active Differential Optical Absorption Spectroscopy (DOAS) technologies, measures optical responses from controlled illumination of targets. Properties that can be recorded include volume back-scattering, surface reflectivity, molecular absorption, induced fluorescence and Raman scattering. The various elastic and inelastic backscattering responses allow the identification or characterization of content of the target volumes or surfaces. INO has developed instrumentations to measure distance to solid targets and monitor particles suspended in the air or in water in real time. Our full waveform LiDAR system is designed for use in numerous applications in environmental or process monitoring such as dust detection systems, aerosol (pesticide) drift monitoring, liquid level sensing or underwater bathymetric LiDARs. Our gated imaging developments are used as aids in visibility enhancement or in remote sensing spectroscopy. Furthermore, when coupled with a spectrograph having a large number of channels, the technique becomes active multispectral/hyperspectral detection or imaging allowing measurement of ultra-violet laser induced fluorescence (UV LIF), time resolved fluorescence (in the ns to ms range) as well as gated Raman spectroscopy. These latter techniques make possible the stand-off detection of bio-aerosols, drugs, explosives as well as the identification of mineral content for geological survey. This paper reviews the latest technology developments in active remote sensing at INO and presents on-going projects conducted to address future applications in environmental monitoring.

  17. Advanced Imaging Optics Utilizing Wavefront Coding.

    SciTech Connect

    Scrymgeour, David; Boye, Robert; Adelsberger, Kathleen

    2015-06-01

    Image processing offers a potential to simplify an optical system by shifting some of the imaging burden from lenses to the more cost effective electronics. Wavefront coding using a cubic phase plate combined with image processing can extend the system's depth of focus, reducing many of the focus-related aberrations as well as material related chromatic aberrations. However, the optimal design process and physical limitations of wavefront coding systems with respect to first-order optical parameters and noise are not well documented. We examined image quality of simulated and experimental wavefront coded images before and after reconstruction in the presence of noise. Challenges in the implementation of cubic phase in an optical system are discussed. In particular, we found that limitations must be placed on system noise, aperture, field of view and bandwidth to develop a robust wavefront coded system.

  18. Clustering of solitons in weakly correlated wavefronts

    PubMed Central

    Chen, Zhigang; Sears, Suzanne M.; Martin, Hector; Christodoulides, Demetrios N.; Segev, Mordechai

    2002-01-01

    We demonstrate theoretically and experimentally the spontaneous clustering of solitons in partially coherent wavefronts during the final stages of pattern formation initiated by modulation instability and noise. PMID:16578870

  19. An ocular wavefront sensor based on binary phase element: design and analysis

    NASA Astrophysics Data System (ADS)

    Mishra, Sanjay Kumar; Gupta, Arun Kumar; Sharma, Anurag

    2012-07-01

    A modal wavefront sensor for ocular aberrations exhibits two main advantages compared to a conventional Shack-Hartmann sensor. As the wavefront is detected in the Fourier plane, the method is robust against local loss of information (e.g. local opacity of ocular lens as in the case of cataract), and is not dependent on the spatial distribution of wavefront sampling. We have proposed a novel method of wavefront sensing for ocular aberrations that directly detects the strengths of Zernike aberrations. A multiplexed Fourier computer-generated hologram has been designed as the binary phase element (BPE) for the detection of second-order and higher-order ocular aberrations (HOAs). The BPE design has been validated by comparing the simulated far-field pattern with the experimental results obtained by displaying it on a spatial light modulator. Simulation results have demonstrated the simultaneous wavefront detection with an accuracy better that ∼λ/30 for a measurement range of ±2.1λ with reduced cross-talk. Sensor performance is validated by performing a numerical experiment using the City data set for test waves containing second-order and HOAs and measurement errors of 0.065 µm peak-to-valley (PV) and 0.08 µm (PV) have been obtained, respectively.

  20. Measuring thermal budgets of active volcanoes by satellite remote sensing

    NASA Technical Reports Server (NTRS)

    Glaze, L.; Francis, P. W.; Rothery, D. A.

    1989-01-01

    Thematic Mapper measurements of the total radiant energy flux Q at Lascar volcano in north Chile for December 1984 are reported. The results are consistent with the earlier suggestion that a lava lake is the source of a reported thermal budget anomaly, and with values for 1985-1986 that are much lower, suggesting that fumarolic activity was then a more likely heat source. The results show that satellite remote sensing may be used to monitor the activity of a volcano quantitatively, in a way not possible by conventional ground studies, and may provide a method for predicting eruptions.

  1. Technology advances in active and passive microwave sensing through 1985

    NASA Technical Reports Server (NTRS)

    Barath, F. T.

    1977-01-01

    As a result of a growing awareness by the remote sensing community of the unique capabilities of passive and active microwave sensors, these instruments are expected to grow in the next decade in numbers, versatility and complexity. The Nimbus-G and Seasat-A Scanning Multichannel Microwave Spectrometer (SMMR), the Seasat-A radar altimeter, scatterometer and synthetic aperture radar represent the first systematic attempt at exploring a wide variety of applications utilizing microwave sensing techniques and are indicators of the directions in which the pertinent technology is likely to evolve. The trend is toward high resolution multi-frequency imagers spanning wide frequency ranges and wide swaths requiring sophisticated receivers, real-time data processors and most importantly, complex antennas.

  2. Intracellular sensing of complement C3 activates cell autonomous immunity

    PubMed Central

    Tam, Jerry C.H.; Bidgood, Susanna R.; McEwan, William A.; James, Leo C.

    2014-01-01

    Pathogens traverse multiple barriers during infection including cell membranes. Here we show that during this transition pathogens carry covalently attached complement C3 into the cell, triggering immediate signalling and effector responses. Sensing of C3 in the cytosol activates MAVS-dependent signalling cascades and induces proinflammatory cytokine secretion. C3 also flags viruses for rapid proteasomal degradation, thereby preventing their replication. This system can detect both viral and bacterial pathogens but is antagonized by enteroviruses, such as rhinovirus and poliovirus, which cleave C3 using their 3C protease. The antiviral Rupintrivir inhibits 3C protease and prevents C3 cleavage, rendering enteroviruses susceptible to intracellular complement sensing. Thus, complement C3 allows cells to detect and disable pathogens that have invaded the cytosol. PMID:25190799

  3. Compliant deformable mirror approach for wavefront improvement

    NASA Astrophysics Data System (ADS)

    Clark, James H.; Penado, F. Ernesto

    2016-04-01

    We describe a compliant static deformable mirror approach to reduce the wavefront concavity at the Navy Precision Optical Interferometer (NPOI). A single actuator pressing on the back surface of just one of the relay mirrors deforms the front surface in a correcting convex shape. Our design uses the mechanical advantage gained from a force actuator sandwiched between a rear flexure plate and the back surface of the mirror. We superimpose wavefront contour measurements with our finite element deformed mirror model. An example analysis showed improvement from 210-nm concave-concave wavefront to 51-nm concave-concave wavefront. With our present model, a 100-nm actuator increment displaces the mirror surface by 1.1 nm. We describe the need for wavefront improvement that arises from the NPOI reconfigurable array, offer a practical design approach, and analyze the support structure and compliant deformable mirror using the finite element method. We conclude that a 20.3-cm-diameter, 1.9-cm-thick Zerodur® mirror shows that it is possible to deform the reflective surface and cancel out three-fourths of the wavefront deformation without overstressing the material.

  4. Wageningen UR Unmanned Aerial Remote Sensing Facility - Overview of activities

    NASA Astrophysics Data System (ADS)

    Bartholomeus, Harm; Keesstra, Saskia; Kooistra, Lammert; Suomalainen, Juha; Mucher, Sander; Kramer, Henk; Franke, Jappe

    2016-04-01

    To support environmental management there is an increasing need for timely, accurate and detailed information on our land. Unmanned Aerial Systems (UAS) are increasingly used to monitor agricultural crop development, habitat quality or urban heat efficiency. An important reason is that UAS technology is maturing quickly while the flexible capabilities of UAS fill a gap between satellite based and ground based geo-sensing systems. In 2012, different groups within Wageningen University and Research Centre have established an Unmanned Airborne Remote Sensing Facility. The objective of this facility is threefold: a) To develop innovation in the field of remote sensing science by providing a platform for dedicated and high-quality experiments; b) To support high quality UAS services by providing calibration facilities and disseminating processing procedures to the UAS user community; and c) To promote and test the use of UAS in a broad range of application fields like habitat monitoring, precision agriculture and land degradation assessment. The facility is hosted by the Laboratory of Geo-Information Science and Remote Sensing (GRS) and the Department of Soil Physics and Land Management (SLM) of Wageningen University together with the team Earth Informatics (EI) of Alterra. The added value of the Unmanned Aerial Remote Sensing Facility is that compared to for example satellite based remote sensing more dedicated science experiments can be prepared. This includes for example higher frequent observations in time (e.g., diurnal observations), observations of an object under different observation angles for characterization of BRDF and flexibility in use of camera's and sensors types. In this way, laboratory type of set ups can be tested in a field situation and effects of up-scaling can be tested. In the last years we developed and implemented different camera systems (e.g. a hyperspectral pushbroom system, and multispectral frame cameras) which we operated in projects all

  5. Coronagraphic Wavefront Control for the ATLAST-9.2m Telescope

    NASA Technical Reports Server (NTRS)

    Lyon, RIchard G.; Oegerle, William R.; Feinberg, Lee D.; Bolcar, Matthew R.; Dean, Bruce H.; Mosier, Gary E.; Postman, Marc

    2010-01-01

    The Advanced Technology for Large Aperture Space Telescope (ATLAST) concept was assessed as one of the NASA Astrophysics Strategic Mission Concepts (ASMC) studies. Herein we discuss the 9.2-meter diameter segmented aperture version and its wavefront sensing and control (WFSC) with regards to coronagraphic detection and spectroscopic characterization of exoplanets. The WFSC would consist of at least two levels of sensing and control: (i) an outer coarser level of sensing and control to phase and control the segments and secondary mirror in a manner similar to the James Webb Space Telescope but operating at higher temporal bandwidth, and (ii) an inner, coronagraphic instrument based, fine level of sensing and control for both amplitude and wavefront errors operating at higher temporal bandwidths. The outer loop would control rigid-body actuators on the primary and secondary mirrors while the inner loop would control one or more segmented deformable mirror to suppress the starlight within the coronagraphic field-of view. Herein we discuss the visible nulling coronagraph (VNC) and the requirements it levies on wavefront sensing and control and show the results of closed-loop simulations to assess performance and evaluate the trade space of system level stability versus control bandwidth.

  6. Generalised optical differentiation wavefront sensor: a sensitive high dynamic range wavefront sensor.

    PubMed

    Haffert, S Y

    2016-08-22

    Current wavefront sensors for high resolution imaging have either a large dynamic range or a high sensitivity. A new kind of wavefront sensor is developed which can have both: the Generalised Optical Differentiation wavefront sensor. This new wavefront sensor is based on the principles of optical differentiation by amplitude filters. We have extended the theory behind linear optical differentiation and generalised it to nonlinear filters. We used numerical simulations and laboratory experiments to investigate the properties of the generalised wavefront sensor. With this we created a new filter that can decouple the dynamic range from the sensitivity. These properties make it suitable for adaptive optic systems where a large range of phase aberrations have to be measured with high precision. PMID:27557179

  7. Active microwave remote sensing of earth/land, chapter 2

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Geoscience applications of active microwave remote sensing systems are examined. Major application areas for the system include: (1) exploration of petroleum, mineral, and ground water resources, (2) mapping surface and structural features, (3) terrain analysis, both morphometric and genetic, (4) application in civil works, and (5) application in the areas of earthquake prediction and crustal movements. Although the success of radar surveys has not been widely publicized, they have been used as a prime reconnaissance data base for mineral exploration and land-use evaluation in areas where photography cannot be obtained.

  8. Remote sensing of environmental impact of land use activities

    NASA Technical Reports Server (NTRS)

    Paul, C. K.

    1977-01-01

    The capability to monitor land cover, associated in the past with aerial film cameras and radar systems, was discussed in regard to aircraft and spacecraft multispectral scanning sensors. A proposed thematic mapper with greater spectral and spatial resolutions for the fourth LANDSAT is expected to usher in new environmental monitoring capability. In addition, continuing improvements in image classification by supervised and unsupervised computer techniques are being operationally verified for discriminating environmental impacts of human activities on the land. The benefits of employing remote sensing for this discrimination was shown to far outweigh the incremental costs of converting to an aircraft-satellite multistage system.

  9. Active Chemical Sensing With Partially Observable Markov Decision Processes

    NASA Astrophysics Data System (ADS)

    Gosangi, Rakesh; Gutierrez-Osuna, Ricardo

    2009-05-01

    We present an active-perception strategy to optimize the temperature program of metal-oxide sensors in real time, as the sensor reacts with its environment. We model the problem as a partially observable Markov decision process (POMDP), where actions correspond to measurements at particular temperatures, and the agent is to find a temperature sequence that minimizes the Bayes risk. We validate the method on a binary classification problem with a simulated sensor. Our results show that the method provides a balance between classification rate and sensing costs.

  10. Active microwave remote sensing of an anisotropic random medium layer

    NASA Technical Reports Server (NTRS)

    Lee, J. K.; Kong, J. A.

    1985-01-01

    A two-layer anisotropic random medium model has been developed to study the active remote sensing of the earth. The dyadic Green's function for a two-layer anisotropic medium is developed and used in conjunction with the first-order Born approximation to calculate the backscattering coefficients. It is shown that strong cross-polarization occurs in the single scattering process and is indispensable in the interpretation of radar measurements of sea ice at different frequencies, polarizations, and viewing angles. The effects of anisotropy on the angular responses of backscattering coefficients are also illustrated.

  11. Strategy change in vibrissal active sensing during rat locomotion.

    PubMed

    Arkley, Kendra; Grant, Robyn A; Mitchinson, Ben; Prescott, Tony J

    2014-07-01

    During exploration, rats and other small mammals make rhythmic back-and-forth sweeps of their long facial whiskers (macrovibrissae) [1-3]. These "whisking" movements are modulated by head movement [4] and by vibrissal sensory input [5, 6] and hence are often considered "active" in the Gibsonian sense of being purposive and information seeking [7, 8]. An important hallmark of active sensing is the modification of the control strategy according to context [9]. Using a task in which rats were trained to run circuits for food, we tested the hypothesis that whisker control, as measured by high-speed videography, changes with contextual variables such as environment familiarity, risk of collision, and availability of visual cues. In novel environments, functionally blind rats moved at slow speeds and performed broad whisker sweeps. With greater familiarity, however, they moved more rapidly, protracted their whiskers further, and showed decreased whisking amplitude. These findings indicate a strategy change from using the vibrissae to explore nearby surfaces to using them primarily for "look ahead." In environments with increased risk of collision, functionally blind animals moved more slowly but protracted their whiskers further. Sighted animals also showed changes in whisker control strategy with increased familiarity, but these changes were different to those of the functionally blind strain. Sighted animals also changed their vibrissal behavior when visual cues were subsequently removed (by being placed in darkness). These contextual influences provide strong evidence of active control and demonstrate that the vibrissal system provides an accessible model of purposive behavior in mammals.

  12. Active one-class classification of remote sensing image

    NASA Astrophysics Data System (ADS)

    Liu, Zhigang; Sun, Zhichao

    2008-12-01

    In many remote sensing image classification applications, interest focuses on a specific land-cover class. In these cases, one-class classification (OCC) approach is appropriate, because one classifier can be trained with samples of target class and just few or no samples of classes that are not of interest are required. However, it is always hard to build a training sample set effectively to represent the target class completely. In this paper, an active learning is introduced for OCC based on support vector data description (SVDD). In active SVDD learning, a SVDD classifier is started with a small size of training samples and an expert is asked to label supplementary training data by asking only for the labels of the most informative, unlabeled examples. Thus, it is possible to build a training sample set effectively to represent the target class completely. The effectiveness of active SVDD is proved by preliminary experiments.

  13. CARER: Efficient Dynamic Sensing for Continuous Activity Monitoring

    PubMed Central

    Au, Lawrence K.; Bui, Alex A.T.; Batalin, Maxim A.; Xu, Xiaoyu; Kaiser, William J.

    2016-01-01

    Advancement in wireless health sensor systems has triggered rapidly expanding research in continuous activity monitoring for chronic disease management or promotion and assessment of physical rehabilitation. Wireless motion sensing is increasingly important in treatments where remote collection of sensor measurements can provide an in-field objective evaluation of physical activity patterns. The well-known challenge of limited operating lifetime of energy-constrained wireless health sensor systems continues to present a primary limitation for these applications. This paper introduces CARER, a software system that supports a novel algorithm that exploits knowledge of context and dynamically schedules sensor measurement episodes within an energy consumption budget while ensuring classification accuracy. The sensor selection algorithm in the CARER system is based on Partially Observable Markov Decision Process (POMDP). The parameters for the POMDP algorithm can be obtained through standard maximum likelihood estimation. Sensor data are also collected from multiple locations of the subjects body, providing estimation of an individual's daily activity patterns. PMID:22254783

  14. A Broad-Band Phase-Contrast Wave-Front Sensor

    NASA Technical Reports Server (NTRS)

    Bloemhof, Eric; Wallace, J. Kent

    2005-01-01

    A broadband phase-contrast wave-front sensor has been proposed as a real-time wave-front sensor in an adaptive-optics system. The proposed sensor would offer an alternative to the Shack-Hartmann wave-front sensors now used in high-order adaptive-optics systems of some astronomical telescopes. Broadband sensing gives higher sensitivity than does narrow-band sensing, and it appears that for a given bandwidth, the sensitivity of the proposed phase-contrast sensor could exceed that of a Shack-Hartmann sensor. Relative to a Shack-Hartmann sensor, the proposed sensor may be optically and mechanically simpler. As described below, an important element of the principle of operation of a phase-contrast wave-front sensor is the imposition of a 90deg phase shift between diffracted and undiffracted parts of the same light beam. In the proposed sensor, this phase shift would be obtained by utilizing the intrinsic 90 phase shift between the transmitted and reflected beams in an ideal (thin, symmetric) beam splitter. This phase shift can be characterized as achromatic or broadband because it is 90deg at every wavelength over a broad wavelength range.

  15. Anionic activators for differential sensing with cell-penetrating peptides.

    PubMed

    Montenegro, Javier; Matile, Stefan

    2011-02-01

    The design, synthesis, and evaluation of small peptides with one to three negative charges and one to three hydrazides as key components of membrane-based synthetic sensing systems are reported. Their spontaneous reaction with hydrophobic aldehydes or ketones gives rapid access to small collections of amphiphilic anions. These anionic amphiphiles can activate polycations as anion transporters in lipid-bilayer membranes. Odorants are used as representative hydrophobic aldehydes and ketones, and cell-penetrating peptides (CPPs) as polycationic transporters in fluorogenic vesicles. Different activities obtained with different counterion activators are used to generate multidimensional patterns that can be recognized by principal component and hierarchical cluster analysis to extract unique "fingerprints" for individual analytes (including enantiomers, cis-trans isomers or perfumes as illustrative analyte mixtures). Comparison of the peptide activators reveals that carboxylates perform better than phosphonates. Gemini-like activators containing two carboxylates and two hydrophobic hydrazone tails are best, whereas excessive charges and tails give weaker activities. This result differs from cationic activators of polyanionic transporters such as DNA, which worked best with octopus amphiphiles with one cationic head and four hydrophobic tentacles.

  16. Self-calibration for transmitted wavefront measurements

    SciTech Connect

    Bergner, Brent C.; Davies, Angela

    2007-01-01

    Micro-optic components and subsystems are becoming increasingly important in optical sensors, communications, data storage, and many other diverse applications. To adequately predict the performance of the final system, it is important to understand the element's effect on the wavefront as it propagates through the system. The wavefront can be measured using interferometric means, however, random and systematic errors contribute to the measurement. Self-calibration techniques exploit symmetries of the measurement or averaging techniques to separate the systematic errors of the instrument from the errors in the test lens. If the transmitted wavefront of a ball lens is measured in a number of random orientations and the measurements are averaged, the only remaining deviations from a perfect wavefront will be spherical aberration from the ball lens and the systematic errors of the interferometer. If the radius, aperture, and focal length of the ball lens are known, the spherical aberration can be calculated and subtracted, leaving only the systematic errors of the interferometer. We develop the theory behind the technique and illustrate the approach with a description of the calibration of a microinterferometer used to measure the transmitted wavefront error of micro-optics.

  17. U.S. Geological Survey land remote sensing activities

    USGS Publications Warehouse

    Frederick, Doyle G.

    1983-01-01

    The U.S. Geological Survey (USGS) and the Department of the Interior (DOI) were among the earliest to recognize the potential applications of satellite land remote sensing for management of the country's land and water resources…not only as a user but also as a program participant responsible for final data processing, product generation, and data distribution. With guidance from Dr. William T. Pecora, who was the Survey's Director at that time and later Under Secretary of Interior, the Earth Resources Observation Systems (EROS) Program was established in 1966 as a focal point for these activities within the Department. Dr. Pecora was among the few who could envision a role for the Survey and the Department as active participants in programs yet to come--like the Landsat, Magsat, Seasat and, most recently, Shuttle Imaging Radar programs.

  18. Terahertz active photonic crystals for condensed gas sensing.

    PubMed

    Benz, Alexander; Deutsch, Christoph; Brandstetter, Martin; Andrews, Aaron M; Klang, Pavel; Detz, Hermann; Schrenk, Werner; Strasser, Gottfried; Unterrainer, Karl

    2011-01-01

    The terahertz (THz) spectral region, covering frequencies from 1 to 10 THz, is highly interesting for chemical sensing. The energy of rotational and vibrational transitions of molecules lies within this frequency range. Therefore, chemical fingerprints can be derived, allowing for a simple detection scheme. Here, we present an optical sensor based on active photonic crystals (PhCs), i.e., the pillars are fabricated directly from an active THz quantum-cascade laser medium. The individual pillars are pumped electrically leading to laser emission at cryogenic temperatures. There is no need to couple light into the resonant structure because the PhC itself is used as the light source. An injected gas changes the resonance condition of the PhC and thereby the laser emission frequency. We achieve an experimental frequency shift of 10(-3) times the center lasing frequency. The minimum detectable refractive index change is 1.6 × 10(-5) RIU.

  19. Variability of wavefront aberration measurements in small pupil sizes using a clinical Shack-Hartmann aberrometer

    PubMed Central

    Ginis, Harilaos S; Plainis, Sotiris; Pallikaris, Aristophanis

    2004-01-01

    Background Recently, instruments for the measurement of wavefront aberration in the living human eye have been widely available for clinical applications. Despite the extensive background experience on wavefront sensing for research purposes, the information derived from such instrumentation in a clinical setting should not be considered a priori precise. We report on the variability of such an instrument at two different pupil sizes. Methods A clinical aberrometer (COAS Wavefront Scienses, Ltd) based on the Shack-Hartmann principle was employed in this study. Fifty consecutive measurements were perfomed on each right eye of four subjects. We compared the variance of individual Zernike expansion coefficients as determined by the aberrometer with the variance of coefficients calculated using a mathematical method for scaling the expansion coefficients to reconstruct wavefront aberration for a reduced-size pupil. Results Wavefront aberration exhibits a marked variance of the order of 0.45 microns near the edge of the pupil whereas the central part appears to be measured more consistently. Dispersion of Zernike expansion coefficients was lower when calculated by the scaling method for a pupil diameter of 3 mm as compared to the one introduced when only the central 3 mm of the Shack – Hartmann image was evaluated. Signal-to-noise ratio was lower for higher order aberrations than for low order coefficients corresponding to the sphero-cylindrical error. For each subject a number of Zernike expansion coefficients was below noise level and should not be considered trustworthy. Conclusion Wavefront aberration data used in clinical care should not be extracted from a single measurement, which represents only a static snapshot of a dynamically changing aberration pattern. This observation must be taken into account in order to prevent ambiguous conclusions in clinical practice and especially in refractive surgery. PMID:15018630

  20. Frequency Based Volcanic Activity Detection through Remotely Sensed Data

    NASA Astrophysics Data System (ADS)

    Worden, A. K.; Dehn, J.; Webley, P. W.

    2015-12-01

    Satellite remote sensing has proved to offer a useful and relatively inexpensive method for monitoring large areas where field work is logistically unrealistic, and potentially dangerous. Current sensors are able to detect the majority of explosive volcanic activity; those that tend to effect and represent larger scale changes in the volcanic systems, eventually relating to ash producing periods of extended eruptive activity, and effusive activity. As new spaceborne sensors are developed, the ability to detect activity improves so that a system to gauge the frequency of volcanic activity can be used as a useful monitoring tool. Four volcanoes were chosen for development and testing of a method to monitor explosive activity: Stromboli (Italy); Shishaldin and Cleveland (Alaska, USA); and Karymsky (Kamchatka, Russia). Each volcano studied had similar but unique signatures of pre-cursory and eruptive activity. This study has shown that this monitoring tool could be applied to a wide range of volcanoes and still produce useful and robust data. Our method deals specifically with the detection of small scale explosive activity. The method described here could be useful in an operational setting, especially at remote volcanoes that have the potential to impact populations, infrastructure, and the aviation community. A number of important factors will affect the validity of application of this method. They are: (1) the availability of a continuous and continually populated dataset; (2) appropriate and reasonable sensor resolutions; (3) a recorded history of the volcano's previous activity; and, if available, (4) some ground-based monitoring system. We aim to develop the method further to be able to capture and evaluate the frequency of other volcanic processes such as lava flows, phreatomagmatic eruptions and dome growth and collapse. The work shown here has served to illustrate the capability of this method and monitoring tool for use at remote, un-instrumented volcanoes.

  1. Visual optics under the wavefront perspective.

    PubMed

    Faria-e-Sousa, Sidney Júlio; Victor, Gustavo; Alves, Milton Ruiz

    2014-08-01

    Some intriguing concepts of visual optics cannot be explained by ray tracing. However, they can be clarified using wavefront formalism. Its main advantage is in the use of the concept of vergence, which is very helpful in interpreting the optical phenomena involved in the neutralization of the ametropias. In this line of thinking, the major role of a lens is in the creation of a new light source (the image point) that orientates the refracted waves. Once the nature and position of this source is known, one can easily predict the behavior of the wavefronts. The formalism also allows for an easier understanding on how wavefronts relate to light rays and on how algebraic signs are assigned to optical distances.

  2. Wavefront control for the Gemini Planet Imager

    SciTech Connect

    Poyneer, L A; Veran, J; Dillon, D; Severson, S; Macintosh, B

    2006-04-14

    The wavefront control strategy for the proposed Gemini Planet Imager, an extreme adaptive optics coronagraph for planet detection, is presented. Two key parts of this strategy are experimentally verified in a testbed at the Laboratory for Adaptive Optics, which features a 32 x 32 MEMS device. Detailed analytic models and algorithms for Shack-Hartmann wavefront sensor alignment and calibration are presented. It is demonstrated that with these procedures, the spatially filtered WFS and the Fourier Transform reconstructor can be used to flatten to the MEMS to 1 nm RMS in the controllable band. Performance is further improved using the technique of modifying the reference slopes using a measurement of the static wavefront error in the science leg.

  3. Feedback controlled optics with wavefront compensation

    NASA Technical Reports Server (NTRS)

    Breckenridge, William G. (Inventor); Redding, David C. (Inventor)

    1993-01-01

    The sensitivity model of a complex optical system obtained by linear ray tracing is used to compute a control gain matrix by imposing the mathematical condition for minimizing the total wavefront error at the optical system's exit pupil. The most recent deformations or error states of the controlled segments or optical surfaces of the system are then assembled as an error vector, and the error vector is transformed by the control gain matrix to produce the exact control variables which will minimize the total wavefront error at the exit pupil of the optical system. These exact control variables are then applied to the actuators controlling the various optical surfaces in the system causing the immediate reduction in total wavefront error observed at the exit pupil of the optical system.

  4. Wavefront-error performance characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) science instruments

    NASA Astrophysics Data System (ADS)

    Aronstein, David L.; Smith, J. S.; Zielinski, Thomas P.; Telfer, Randal; Tournois, Severine C.; Moore, Dustin B.; Fienup, James R.

    2016-07-01

    The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES) test chamber. In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing, and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) f/# and pupil-distortion measurements made using a pseudo-nonredundant mask (PNRM), and 3) pupil-geometry predictions for each SI field point tested, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse-translation diversity (TTD) sweeps instead of focus sweeps, in which a subaperture is translated and/or rotated across the exit pupil of the system from one image to the next. Several optical-performance requirements that were verified during this ISIM Element-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also gives an overview of the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis

  5. Hyperspectral imaging camera using wavefront division interference.

    PubMed

    Bahalul, Eran; Bronfeld, Asaf; Epshtein, Shlomi; Saban, Yoram; Karsenty, Avi; Arieli, Yoel

    2016-03-01

    An approach for performing hyperspectral imaging is introduced. The hyperspectral imaging is based on Fourier transform spectroscopy, where the interference is performed by wavefront division interference rather than amplitude division interference. A variable phase delay between two parts of the wavefront emanating from each point of an object is created by a spatial light modulator (SLM) to obtain variable interference patterns. The SLM is placed in the exit pupil of an imaging system, thus enabling conversion of a general imaging optical system into an imaging hyperspectral optical system. The physical basis of the new approach is introduced, and an optical apparatus is built. PMID:26974085

  6. Concepts, laboratory, and telescope test results of the plenoptic camera as a wavefront sensor

    NASA Astrophysics Data System (ADS)

    Rodríguez-Ramos, L. F.; Montilla, I.; Fernández-Valdivia, J. J.; Trujillo-Sevilla, J. L.; Rodríguez-Ramos, J. M.

    2012-07-01

    The plenoptic camera has been proposed as an alternative wavefront sensor adequate for extended objects within the context of the design of the European Solar Telescope (EST), but it can also be used with point sources. Originated in the field of the Electronic Photography, the plenoptic camera directly samples the Light Field function, which is the four - dimensional representation of all the light entering a camera. Image formation can then be seen as the result of the photography operator applied to this function, and many other features of the light field can be exploited to extract information of the scene, like depths computation to extract 3D imaging or, as it will be specifically addressed in this paper, wavefront sensing. The underlying concept of the plenoptic camera can be adapted to the case of a telescope by using a lenslet array of the same f-number placed at the focal plane, thus obtaining at the detector a set of pupil images corresponding to every sampled point of view. This approach will generate a generalization of Shack-Hartmann, Curvature and Pyramid wavefront sensors in the sense that all those could be considered particular cases of the plenoptic wavefront sensor, because the information needed as the starting point for those sensors can be derived from the plenoptic image. Laboratory results obtained with extended objects, phase plates and commercial interferometers, and even telescope observations using stars and the Moon as an extended object are presented in the paper, clearly showing the capability of the plenoptic camera to behave as a wavefront sensor.

  7. Estimating Active Layer Thickness from Remotely Sensed Surface Deformation

    NASA Astrophysics Data System (ADS)

    Liu, L.; Schaefer, K. M.; Zhang, T.; Wahr, J. M.

    2010-12-01

    We estimate active layer thickness (ALT) from remotely sensed surface subsidence during thawing seasons derived from interferometric synthetic aperture radar (InSAR) measurements. Ground ice takes up more volume than ground water, so as the soil thaws in summer and the active layer deepens, the ground subsides. The volume of melted ground water during the summer thaw determines seasonal subsidence. ALT is defined as the maximum thaw depth at the end of a thawing season. By using InSAR to measure surface subsidence between the start and end of summer season, one can estimate the depth of thaw over a large area (typically 100 km by 100 km). We developed an ALT retrieval algorithm integrating InSAR-derived surface subsidence, observed soil texture, organic matter content, and moisture content. We validated this algorithm in the continuous permafrost area on the North Slope of Alaska. Based on InSAR measurements using ERS-1/2 SAR data, our estimated values match in situ measurements of ALT within 1--10 cm at Circumpolar Active Layer Monitoring (CALM) sites within the study area. The active layer plays a key role in land surface processes in cold regions. Current measurements of ALT using mechanical probing, frost/thaw tubes, or inferred from temperature measurements are of high quality, but limited in spatial coverage. Using InSAR to estimate ALT greatly expands the spatial coverage of ALT observations.

  8. Non-invasive UWB sensing of astronauts' breathing activity.

    PubMed

    Baldi, Marco; Cerri, Graziano; Chiaraluce, Franco; Eusebi, Lorenzo; Russo, Paola

    2014-12-30

    The use of a UWB system for sensing breathing activity of astronauts must account for many critical issues specific to the space environment. The aim of this paper is twofold. The first concerns the definition of design constraints about the pulse amplitude and waveform to transmit, as well as the immunity requirements of the receiver. The second issue concerns the assessment of the procedures and the characteristics of the algorithms to use for signal processing to retrieve the breathing frequency and respiration waveform. The algorithm has to work correctly in the presence of surrounding electromagnetic noise due to other sources in the environment. The highly reflecting walls increase the difficulty of the problem and the hostile scenario has to be accurately characterized. Examples of signal processing techniques able to recover breathing frequency in significant and realistic situations are shown and discussed.

  9. Non-Invasive UWB Sensing of Astronauts' Breathing Activity

    PubMed Central

    Baldi, Marco; Cerri, Graziano; Chiaraluce, Franco; Eusebi, Lorenzo; Russo, Paola

    2015-01-01

    The use of a UWB system for sensing breathing activity of astronauts must account for many critical issues specific to the space environment. The aim of this paper is twofold. The first concerns the definition of design constraints about the pulse amplitude and waveform to transmit, as well as the immunity requirements of the receiver. The second issue concerns the assessment of the procedures and the characteristics of the algorithms to use for signal processing to retrieve the breathing frequency and respiration waveform. The algorithm has to work correctly in the presence of surrounding electromagnetic noise due to other sources in the environment. The highly reflecting walls increase the difficulty of the problem and the hostile scenario has to be accurately characterized. Examples of signal processing techniques able to recover breathing frequency in significant and realistic situations are shown and discussed. PMID:25558995

  10. Efficient active depth sensing by laser speckle projection system

    NASA Astrophysics Data System (ADS)

    Yin, Xuanwu; Wang, Guijin; Shi, Chenbo; Liao, Qingmin

    2014-01-01

    An active depth sensing approach by laser speckle projection system is proposed. After capturing the speckle pattern with an infrared digital camera, we extract the pure speckle pattern using a direct-global separation method. Then the pure speckles are represented by Census binary features. By evaluating the matching cost and uniqueness between the real-time image and the reference image, robust correspondences are selected as support points. After that, we build a disparity grid and propose a generative graphical model to compute disparities. An iterative approach is designed to propagate the messages between blocks and update the model. Finally, a dense depth map can be obtained by subpixel interpolation and transformation. The experimental evaluations demonstrate the effectiveness and efficiency of our approach.

  11. Real-Time Wavefront Control for the PALM-3000 High Order Adaptive Optics System

    NASA Technical Reports Server (NTRS)

    Truong, Tuan N.; Bouchez, Antonin H.; Dekany, Richard G.; Guiwits, Stephen R.; Roberts, Jennifer E.; Troy, Mitchell

    2008-01-01

    We present a cost-effective scalable real-time wavefront control architecture based on off-the-shelf graphics processing units hosted in an ultra-low latency, high-bandwidth interconnect PC cluster environment composed of modules written in the component-oriented language of nesC. The architecture enables full-matrix reconstruction of the wavefront at up to 2 KHz with latency under 250 us for the PALM-3000 adaptive optics systems, a state-of-the-art upgrade on the 5.1 meter Hale Telescope that consists of a 64 x 64 subaperture Shack-Hartmann wavefront sensor and a 3368 active actuator high order deformable mirror in series with a 241 active actuator tweeter DM. The architecture can easily scale up to support much larger AO systems at higher rates and lower latency.

  12. Exact wavefront surface refracted by a smooth arbitrary surface considering a plane wavefront incident

    NASA Astrophysics Data System (ADS)

    Avendaño-Alejo, Maximino M.

    2015-08-01

    We study the formation of wavefronts produced by smooth arbitrary surfaces with symmetry of revolution considering a plane wavefront propagating parallel to the optical axis and impinging on the refracting surface. The wavefronts are obtained by using the Malus-Dupin theorem and they represent the monochromatic aberrations which can be called image errors, furthermore their shapes could be modified by changing the parameters of the lens in such a way that if a caustic surface is vanished the optical system produces a perfect image, on the other hand for a caustic possessing a large area it could be applied to design non-imaging optical systems. The shape of the wavefront depends only on the indices of refraction and geometrical properties of the refracting surface such as the first derivative and their parameters associated. This analytic formula has potential applications in the microscopy field, illumination or corrector plates.

  13. Active sensing in the categorization of visual patterns

    PubMed Central

    Yang, Scott Cheng-Hsin; Lengyel, Máté; Wolpert, Daniel M

    2016-01-01

    Interpreting visual scenes typically requires us to accumulate information from multiple locations in a scene. Using a novel gaze-contingent paradigm in a visual categorization task, we show that participants' scan paths follow an active sensing strategy that incorporates information already acquired about the scene and knowledge of the statistical structure of patterns. Intriguingly, categorization performance was markedly improved when locations were revealed to participants by an optimal Bayesian active sensor algorithm. By using a combination of a Bayesian ideal observer and the active sensor algorithm, we estimate that a major portion of this apparent suboptimality of fixation locations arises from prior biases, perceptual noise and inaccuracies in eye movements, and the central process of selecting fixation locations is around 70% efficient in our task. Our results suggest that participants select eye movements with the goal of maximizing information about abstract categories that require the integration of information from multiple locations. DOI: http://dx.doi.org/10.7554/eLife.12215.001 PMID:26880546

  14. Remote sensing for active volcano monitoring in Barren Island, India

    SciTech Connect

    Bhattacharya, A.; Reddy, C.S.S.; Srivastav, S.K. )

    1993-08-01

    The Barren Island Volcano, situated in the Andaman Sea of the Bay of Bengal, erupted recently (March, 1991) after a prolonged period of quiescence of about 188 years. This resumed activity coincides with similar outbreaks in the Philippines and Japan, which are located in an identical tectonic environment. This study addresses (1) remote sensing temporal monitoring of the volcanic activity, (2) detecting hot lava and measuring its pixel-integrated and subpixel temperatures, and (3) the importance of SWIR bands for high temperature volcanic feature detection. Seven sets of TM data acquired continuously from 3 March 1991 to 8 July 1991 have been analyzed. It is concluded that detectable pre-eruption warming took place around 25 March 1991 and volcanic activity started on 1 April 1991. It is observed that high temperature features, such as an erupting volcano, can register emitted thermal radiance in SWIR bands. Calculation of pixel-integrated and sub-pixel temperatures related to volcanic vents has been made, using the dual-band method. 6 refs.

  15. Experimental results of ground-layer and tomographic wavefront reconstruction from multiple laser guide stars.

    PubMed

    Lloyd-Hart, Michael; Baranec, Christoph; Milton, N Mark; Snyder, Miguel; Stalcup, Thomas; Angel, J Roger P

    2006-08-21

    We describe results from the first multi-laser wavefront sensing system designed to support tomographic modes of adaptive optics (AO). The system, now operating at the 6.5 m MMT telescope in Arizona, creates five beacons by Rayleigh scattering of laser beams at 532 nm integrated over a range from 20 to 29 km by dynamic refocus of the telescope optics. The return light is analyzed by a Shack-Hartmann sensor that places all five beacons on a single detector, with electronic shuttering to implement the beacon range gate. A separate high-order Shack-Hartmann sensor records simultaneous measurements of wavefronts from a natural star. From open-loop measurements, we find the average beacon wavefront gives a good estimate of ground layer aberration. We present results of full tomographic wavefront analysis, enabled by supplementing the laser data with simultaneous fast image motion measurements from three stars in the field. We describe plans for an early demonstration at the MMT of closed-loop ground layer AO, and later tomographic AO.

  16. Depth aberrations characterization in linear and nonlinear microscopy schemes using a Shack-Hartmann wavefront sensor

    NASA Astrophysics Data System (ADS)

    Aviles-Espinosa, Rodrigo; Andilla, Jordi; Porcar-Guezenec, Rafael; Levecq, Xavier; Artigas, David; Loza-Alvarez, Pablo

    2012-03-01

    The performance of imaging devices such as linear and nonlinear microscopes (NLM) can be limited by the optical properties of the imaged sample. Such an important aspect has already been described using theoretical models due to the difficulties of implementing a direct wavefront sensing scheme. However, these only stand for simple interfaces and cannot be generalized to biological samples given its structural complexity. This has leaded to the development of sensor-less adaptive optics (AO) implementations. In this approach, aberrations are iteratively corrected trough an image related parameter (aberrations are not measured), being prone of causing sample damage. In this work, we perform a practical implementation of a Shack-Hartman wavefront sensor to compensate for sample induced aberrations, demonstrating its applicability in linear and NLM. We perform an extensive analysis of wavefront distortion effects through different depths employing phantom samples. Aberration effects originated by the refractive index mismatch and depth are quantified using the linear and nonlinear guide-star concept. More over we analyze offaxis aberrations in NLM, an important aspect that is commonly overlooked. In this case spherical aberration behaves similarly to the wavefront error compared with the on-axis case. Finally we give examples of aberration compensation using epi-fluorescence and nonlinear microscopy.

  17. Quorum Sensing Inhibiting Activity of Streptomyces coelicoflavus Isolated from Soil

    PubMed Central

    Hassan, Ramadan; Shaaban, Mona I.; Abdel Bar, Fatma M.; El-Mahdy, Areej M.; Shokralla, Shadi

    2016-01-01

    Quorum sensing (QS) systems communicate bacterial population and stimulate microbial pathogenesis through signaling molecules. Inhibition of QS signals potentially suppresses microbial infections. Antimicrobial properties of Streptomyces have been extensively studied, however, less is known about quorum sensing inhibitory (QSI) activities of Streptomyces. This study explored the QSI potential of Streptomyces isolated from soil. Sixty-five bacterial isolates were purified from soil samples with morphological characteristics of Streptomyces. The three isolates: S6, S12, and S17, exhibited QSI effect by screening with the reporter, Chromobacterium violaceum. Isolate S17 was identified as Streptomyces coelicoflavus by sequencing of the hypervariable regions (V1–V6) of 16S rRNA and was assigned gene bank number KJ855087. The QSI effect of the cell-free supernatant of isolate S17 was not abolished by proteinase K indicating the non-enzymatic activity of QSI components of S17. Three major compounds were isolated and identified, using spectroscopic techniques (1D, 2D NMR, and Mass spectrometry), as behenic acid (docosanoic acid), borrelidin, and 1H-pyrrole-2-carboxylic acid. 1H-pyrrole-2-carboxylic acid inhibited QS and related virulence factors of Pseudomonas aeruginosa PAO1 including; elastase, protease, and pyocyanin without affecting Pseudomonas viability. At the molecular level, 1H-pyrrole-2-carboxylic acid suppressed the expression of QS genes (lasI, lasR, lasA, lasB, rhlI, rhlR, pqsA, and pqsR). Moreover, QSI activity of S17 was assessed under different growth conditions and ISP2 medium supplemented with glucose 0.4% w/v and adjusted at pH 7, showed the highest QSI action. In conclusion, 1H-pyrrole-2-carboxylic acid, one of the major metabolites of Streptomyces isolate S17, inhibited QS and virulence determinants of P. aeruginosa PAO1. The findings of the study open the scope to exploit the in vivo efficacy of this active molecule as anti-pathogenic and anti

  18. Quorum Sensing Inhibiting Activity of Streptomyces coelicoflavus Isolated from Soil.

    PubMed

    Hassan, Ramadan; Shaaban, Mona I; Abdel Bar, Fatma M; El-Mahdy, Areej M; Shokralla, Shadi

    2016-01-01

    Quorum sensing (QS) systems communicate bacterial population and stimulate microbial pathogenesis through signaling molecules. Inhibition of QS signals potentially suppresses microbial infections. Antimicrobial properties of Streptomyces have been extensively studied, however, less is known about quorum sensing inhibitory (QSI) activities of Streptomyces. This study explored the QSI potential of Streptomyces isolated from soil. Sixty-five bacterial isolates were purified from soil samples with morphological characteristics of Streptomyces. The three isolates: S6, S12, and S17, exhibited QSI effect by screening with the reporter, Chromobacterium violaceum. Isolate S17 was identified as Streptomyces coelicoflavus by sequencing of the hypervariable regions (V1-V6) of 16S rRNA and was assigned gene bank number KJ855087. The QSI effect of the cell-free supernatant of isolate S17 was not abolished by proteinase K indicating the non-enzymatic activity of QSI components of S17. Three major compounds were isolated and identified, using spectroscopic techniques (1D, 2D NMR, and Mass spectrometry), as behenic acid (docosanoic acid), borrelidin, and 1H-pyrrole-2-carboxylic acid. 1H-pyrrole-2-carboxylic acid inhibited QS and related virulence factors of Pseudomonas aeruginosa PAO1 including; elastase, protease, and pyocyanin without affecting Pseudomonas viability. At the molecular level, 1H-pyrrole-2-carboxylic acid suppressed the expression of QS genes (lasI, lasR, lasA, lasB, rhlI, rhlR, pqsA, and pqsR). Moreover, QSI activity of S17 was assessed under different growth conditions and ISP2 medium supplemented with glucose 0.4% w/v and adjusted at pH 7, showed the highest QSI action. In conclusion, 1H-pyrrole-2-carboxylic acid, one of the major metabolites of Streptomyces isolate S17, inhibited QS and virulence determinants of P. aeruginosa PAO1. The findings of the study open the scope to exploit the in vivo efficacy of this active molecule as anti-pathogenic and anti

  19. Quorum Sensing Inhibiting Activity of Streptomyces coelicoflavus Isolated from Soil.

    PubMed

    Hassan, Ramadan; Shaaban, Mona I; Abdel Bar, Fatma M; El-Mahdy, Areej M; Shokralla, Shadi

    2016-01-01

    Quorum sensing (QS) systems communicate bacterial population and stimulate microbial pathogenesis through signaling molecules. Inhibition of QS signals potentially suppresses microbial infections. Antimicrobial properties of Streptomyces have been extensively studied, however, less is known about quorum sensing inhibitory (QSI) activities of Streptomyces. This study explored the QSI potential of Streptomyces isolated from soil. Sixty-five bacterial isolates were purified from soil samples with morphological characteristics of Streptomyces. The three isolates: S6, S12, and S17, exhibited QSI effect by screening with the reporter, Chromobacterium violaceum. Isolate S17 was identified as Streptomyces coelicoflavus by sequencing of the hypervariable regions (V1-V6) of 16S rRNA and was assigned gene bank number KJ855087. The QSI effect of the cell-free supernatant of isolate S17 was not abolished by proteinase K indicating the non-enzymatic activity of QSI components of S17. Three major compounds were isolated and identified, using spectroscopic techniques (1D, 2D NMR, and Mass spectrometry), as behenic acid (docosanoic acid), borrelidin, and 1H-pyrrole-2-carboxylic acid. 1H-pyrrole-2-carboxylic acid inhibited QS and related virulence factors of Pseudomonas aeruginosa PAO1 including; elastase, protease, and pyocyanin without affecting Pseudomonas viability. At the molecular level, 1H-pyrrole-2-carboxylic acid suppressed the expression of QS genes (lasI, lasR, lasA, lasB, rhlI, rhlR, pqsA, and pqsR). Moreover, QSI activity of S17 was assessed under different growth conditions and ISP2 medium supplemented with glucose 0.4% w/v and adjusted at pH 7, showed the highest QSI action. In conclusion, 1H-pyrrole-2-carboxylic acid, one of the major metabolites of Streptomyces isolate S17, inhibited QS and virulence determinants of P. aeruginosa PAO1. The findings of the study open the scope to exploit the in vivo efficacy of this active molecule as anti-pathogenic and anti

  20. Design of Optical Systems with Extended Depth of Field: An Educational Approach to Wavefront Coding Techniques

    ERIC Educational Resources Information Center

    Ferran, C.; Bosch, S.; Carnicer, A.

    2012-01-01

    A practical activity designed to introduce wavefront coding techniques as a method to extend the depth of field in optical systems is presented. The activity is suitable for advanced undergraduate students since it combines different topics in optical engineering such as optical system design, aberration theory, Fourier optics, and digital image…

  1. Fourier optics for wavefront engineering and wavelength control of lasers

    NASA Astrophysics Data System (ADS)

    Blanchard, Romain

    Since their initial demonstration in 1994, quantum cascade lasers (QCLs) have become prominent sources of mid-infrared radiation. Over the years, a large scientific and engineering effort has led to a dramatic improvement in their efficiency and power output, with continuous wave operation at room temperature and Watt-level output power now standard. However, beyond this progress, new functionalities and capabilities need to be added to this compact source to enable its integration into consumer-ready systems. Two main areas of development are particularly relevant from an application standpoint and were pursued during the course of this thesis: wavelength control and wavefront engineering of QCLs. The first research direction, wavelength control, is mainly driven by spectroscopic applications of QCLs, such as trace gas sensing, process monitoring or explosive detection. We demonstrated three different capabilities, corresponding to different potential spectroscopic measurement techniques: widely tunable single longitudinal mode lasing, simultaneous lasing on multiple well-defined longitudinal modes, and simultaneous lasing over a broad and continuous range of the spectrum. The second research direction, wavefront engineering of QCLs, i.e. the improvement of their beam quality, is relevant for applications necessitating transmission of the QCL output over a large distance, for example for remote sensing or military countermeasures. To address this issue, we developed plasmonic lenses directly integrated on the facets of QCLs. The plasmonic structures designed are analogous to antenna arrays imparting directionality to the QCLs, as well as providing means for polarization control. Finally, a research interest in plasmonics led us to design passive flat optical elements using plasmonic antennas. All these projects are tied together by the involvement of Fourier analysis as an essential design tool to predict the interaction of light with various gratings and periodic

  2. Method and apparatus for holographic wavefront diagnostics

    DOEpatents

    Toeppen, John S.

    1995-01-01

    A wavefront diagnostic apparatus has an optic and a measuring system. The optic forms a holographic image in response to a beam of light striking a hologram formed on a surface of the optic. The measuring system detects the position of the array of holographic images and compares the positions of the array of holographic images to a reference holographic image.

  3. 2D Wavefront Sensor Analysis and Control

    1996-02-19

    This software is designed for data acquisition and analysis of two dimensional wavefront sensors. The software includes data acquisition and control functions for an EPIX frame grabber to acquire data from a computer and all the appropriate analysis functions necessary to produce and display intensity and phase information. This software is written in Visual Basic for windows.

  4. Method and apparatus for holographic wavefront diagnostics

    DOEpatents

    Toeppen, J.S.

    1995-04-25

    A wavefront diagnostic apparatus has an optic and a measuring system. The optic forms a holographic image in response to a beam of light striking a hologram formed on a surface of the optic. The measuring system detects the position of the array of holographic images and compares the positions of the array of holographic images to a reference holographic image. 3 figs.

  5. High accuracy laboratory spectroscopy to support active greenhouse gas sensing

    NASA Astrophysics Data System (ADS)

    Long, D. A.; Bielska, K.; Cygan, A.; Havey, D. K.; Okumura, M.; Miller, C. E.; Lisak, D.; Hodges, J. T.

    2011-12-01

    Recent carbon dioxide (CO2) remote sensing missions have set precision targets as demanding as 0.25% (1 ppm) in order to elucidate carbon sources and sinks [1]. These ambitious measurement targets will require the most precise body of spectroscopic reference data ever assembled. Active sensing missions will be especially susceptible to subtle line shape effects as the narrow bandwidth of these measurements will greatly limit the number of spectral transitions which are employed in retrievals. In order to assist these remote sensing missions we have employed frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) [2], a high-resolution, ultrasensitive laboratory technique, to measure precise line shape parameters for transitions of O2, CO2, and other atmospherically-relevant species within the near-infrared. These measurements have led to new HITRAN-style line lists for both 16O2 [3] and rare isotopologue [4] transitions in the A-band. In addition, we have performed detailed line shape studies of CO2 transitions near 1.6 μm under a variety of broadening conditions [5]. We will address recent measurements in these bands as well as highlight recent instrumental improvements to the FS-CRDS spectrometer. These improvements include the use of the Pound-Drever-Hall locking scheme, a high bandwidth servo which enables measurements to be made at rates greater than 10 kHz [6]. In addition, an optical frequency comb will be utilized as a frequency reference, which should allow for transition frequencies to be measured with uncertainties below 10 kHz (3×10-7 cm-1). [1] C. E. Miller, D. Crisp, P. L. DeCola, S. C. Olsen, et al., J. Geophys. Res.-Atmos. 112, D10314 (2007). [2] J. T. Hodges, H. P. Layer, W. W. Miller, G. E. Scace, Rev. Sci. Instrum. 75, 849-863 (2004). [3] D. A. Long, D. K. Havey, M. Okumura, C. E. Miller, et al., J. Quant. Spectrosc. Radiat. Transfer 111, 2021-2036 (2010). [4] D. A. Long, D. K. Havey, S. S. Yu, M. Okumura, et al., J. Quant. Spectrosc

  6. A multi-tiered wavefront sensor using binary optics

    SciTech Connect

    Neal, D.R.; Warren, M.E.; Gruetzner, J.K.; Smith, T.G.; Rosenthal, R.R.; McKechnie, T.S.

    1994-05-01

    Wavefront sensors have been used to make measurements in fluid- dynamics and for closed loop control of adaptive optics. In most common Shack-Hartmann wavefront wavefront sensors, the light is broken up into series of rectangular or hexagonal apertures that divide the light into a series of focal spots. The position of these focal spots is used to determine the wavefront slopes over each subaperture. Using binary optics technology, we have developed a hierarchical or fractal wavefront sensor that divides the subapertures up on a more optimal fashion. We have demonstrated this concept for up to four tiers and developed the wavefront reconstruction methods for both segmented adaptive optics and continous wavefront measurement.

  7. Temporal signatures of taste quality driven by active sensing.

    PubMed

    Graham, Dustin M; Sun, Chengsan; Hill, David L

    2014-05-28

    Animals actively acquire sensory information from the outside world, with rodents sniffing to smell and whisking to feel. Licking, a rapid motor sequence used for gustation, serves as the primary means of controlling stimulus access to taste receptors in the mouth. Using a novel taste-quality discrimination task in head-restrained mice, we measured and compared reaction times to four basic taste qualities (salt, sour, sweet, and bitter) and found that certain taste qualities are perceived inherently faster than others, driven by the precise biomechanics of licking and functional organization of the peripheral gustatory system. The minimum time required for accurate perception was strongly dependent on taste quality, ranging from the sensory-motor limits of a single lick (salt, ∼100 ms) to several sampling cycles (bitter, >500 ms). Further, disruption of sensory input from the anterior tongue significantly impaired the speed of perception of some taste qualities, with little effect on others. Overall, our results show that active sensing may play an important role in shaping the timing of taste-quality representations and perception in the gustatory system.

  8. Improving the accuracy of a Shack-Hartmann wavefront sensor on extended scenes

    NASA Astrophysics Data System (ADS)

    Rais, M.; Morel, J.-M.; Thiebaut, C.; Delvit, J.-M.; Facciolo, G.

    2016-10-01

    In order to achieve higher resolutions, current earth-observation satellites use larger lightweight main mirrors which are usually deformed over time, impacting on image quality. In the context of active optics, we studied the problem of correcting this main mirror by performing wavefront estimation in a closed loop environment. To this end, a Shack-Hartman wavefront sensor (SHWFS) used on extended scenes could measure the incoming wavefront. The performance of the SHWFS on extended scenes depends entirely on the accuracy of the shift estimation algorithm employed, which should be fast enough to be executed on-board. In this paper we specifically deal with the problem of fast accurate shift estimation in this context. We propose a new algorithm, based on the global optical flow method, that estimates the shifts in linear time. In our experiments, our method proved to be more accurate and stable, as well as less sensitive to noise than all current state-of-the-art methods.

  9. Predicting eruptions from precursory activity using remote sensing data hybridization

    NASA Astrophysics Data System (ADS)

    Reath, K. A.; Ramsey, M. S.; Dehn, J.; Webley, P. W.

    2016-07-01

    Many volcanoes produce some level of precursory activity prior to an eruption. This activity may or may not be detected depending on the available monitoring technology. In certain cases, precursors such as thermal output can be interpreted to make forecasts about the time and magnitude of the impending eruption. Kamchatka (Russia) provides an ideal natural laboratory to study a wide variety of eruption styles and precursory activity prior to an eruption. At Bezymianny volcano for example, a clear increase in thermal activity commonly occurs before an eruption, which has allowed predictions to be made months ahead of time. Conversely, the eruption of Tolbachik volcano in 2012 produced no discernable thermal precursors before the large scale effusive eruption. However, most volcanoes fall between the extremes of consistently behaved and completely undetectable, which is the case with neighboring Kliuchevskoi volcano. This study tests the effectiveness of using thermal infrared (TIR) remote sensing to track volcanic thermal precursors using data from both the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Advanced Very High Resolution Radiometer (AVHRR) sensors. It focuses on three large eruptions that produced different levels and durations of effusive and explosive behavior at Kliuchevskoi. Before each of these eruptions, TIR spaceborne sensors detected thermal anomalies (i.e., pixels with brightness temperatures > 2 °C above the background temperature). High-temporal, low-spatial resolution (i.e., ~ hours and 1 km) AVHRR data are ideal for detecting large thermal events occurring over shorter time scales, such as the hot material ejected following strombolian eruptions. In contrast, high-spatial, low-temporal resolution (i.e., days to weeks and 90 m) ASTER data enables the detection of much lower thermal activity; however, activity with a shorter duration will commonly be missed. ASTER and AVHRR data are combined to track low

  10. Specific quorum sensing-disrupting activity (A QSI) of thiophenones and their therapeutic potential.

    PubMed

    Yang, Qian; Scheie, Anne Aamdal; Benneche, Tore; Defoirdt, Tom

    2015-01-01

    Disease caused by antibiotic resistant pathogens is becoming a serious problem, both in human and veterinary medicine. The inhibition of quorum sensing, bacterial cell-to-cell communication, is a promising alternative strategy to control disease. In this study, we determined the quorum sensing-disrupting activity of 20 thiophenones towards the quorum sensing model bacterium V. harveyi. In order to exclude false positives, we propose a new parameter (AQSI) to describe specific quorum sensing activity. AQSI is defined as the ratio between inhibition of quorum sensing-regulated activity in a reporter strain and inhibition of the same activity when it is independent of quorum sensing. Calculation of AQSI allowed to exclude five false positives, whereas the six most active thiophenones (TF203, TF307, TF319, TF339, TF342 and TF403) inhibited quorum sensing at 0.25 μM, with AQSI higher than 10. Further, we determined the protective effect and toxicity of the thiophenones in a highly controlled gnotobiotic model system with brine shrimp larvae. There was a strong positive correlation between the specific quorum sensing-disrupting activity of the thiophenones and the protection of brine shrimp larvae against pathogenic V. harveyi. Four of the most active quorum sensing-disrupting thiophenones (TF 203, TF319, TF339 and TF342) were considered to be promising since they have a therapeutic potential of at least 10. PMID:26647822

  11. Specific quorum sensing-disrupting activity (AQSI) of thiophenones and their therapeutic potential

    PubMed Central

    Yang, Qian; Aamdal Scheie, Anne; Benneche, Tore; Defoirdt, Tom

    2015-01-01

    Disease caused by antibiotic resistant pathogens is becoming a serious problem, both in human and veterinary medicine. The inhibition of quorum sensing, bacterial cell-to-cell communication, is a promising alternative strategy to control disease. In this study, we determined the quorum sensing-disrupting activity of 20 thiophenones towards the quorum sensing model bacterium V. harveyi. In order to exclude false positives, we propose a new parameter (AQSI) to describe specific quorum sensing activity. AQSI is defined as the ratio between inhibition of quorum sensing-regulated activity in a reporter strain and inhibition of the same activity when it is independent of quorum sensing. Calculation of AQSI allowed to exclude five false positives, whereas the six most active thiophenones (TF203, TF307, TF319, TF339, TF342 and TF403) inhibited quorum sensing at 0.25 μM, with AQSI higher than 10. Further, we determined the protective effect and toxicity of the thiophenones in a highly controlled gnotobiotic model system with brine shrimp larvae. There was a strong positive correlation between the specific quorum sensing-disrupting activity of the thiophenones and the protection of brine shrimp larvae against pathogenic V. harveyi. Four of the most active quorum sensing-disrupting thiophenones (TF 203, TF319, TF339 and TF342) were considered to be promising since they have a therapeutic potential of at least 10. PMID:26647822

  12. Specific quorum sensing-disrupting activity (A QSI) of thiophenones and their therapeutic potential.

    PubMed

    Yang, Qian; Scheie, Anne Aamdal; Benneche, Tore; Defoirdt, Tom

    2015-12-09

    Disease caused by antibiotic resistant pathogens is becoming a serious problem, both in human and veterinary medicine. The inhibition of quorum sensing, bacterial cell-to-cell communication, is a promising alternative strategy to control disease. In this study, we determined the quorum sensing-disrupting activity of 20 thiophenones towards the quorum sensing model bacterium V. harveyi. In order to exclude false positives, we propose a new parameter (AQSI) to describe specific quorum sensing activity. AQSI is defined as the ratio between inhibition of quorum sensing-regulated activity in a reporter strain and inhibition of the same activity when it is independent of quorum sensing. Calculation of AQSI allowed to exclude five false positives, whereas the six most active thiophenones (TF203, TF307, TF319, TF339, TF342 and TF403) inhibited quorum sensing at 0.25 μM, with AQSI higher than 10. Further, we determined the protective effect and toxicity of the thiophenones in a highly controlled gnotobiotic model system with brine shrimp larvae. There was a strong positive correlation between the specific quorum sensing-disrupting activity of the thiophenones and the protection of brine shrimp larvae against pathogenic V. harveyi. Four of the most active quorum sensing-disrupting thiophenones (TF 203, TF319, TF339 and TF342) were considered to be promising since they have a therapeutic potential of at least 10.

  13. Realistic Instrumentation Platform for Active and Passive Optical Remote Sensing.

    PubMed

    Brydegaard, Mikkel; Merdasa, Aboma; Gebru, Alem; Jayaweera, Hiran; Svanberg, Sune

    2016-02-01

    We describe the development of a novel versatile optical platform for active and passive remote sensing of environmental parameters. Applications include assessment of vegetation status and water quality. The system is also adapted for ecological studies, such as identification of flying insects including agricultural pests. The system is based on two mid-size amateur astronomy telescopes, continuous-wave diode lasers at different wavelengths ranging from violet to the near infrared, and detector facilities including quadrant photodiodes, two-dimensional and line scan charge-coupled device cameras, and a compact digital spectrometer. Application examples include remote Ramanlaser-induced fluorescence monitoring of water quality at 120 m distance, and insect identification at kilometer ranges using the recorded wing beat frequency and its spectrum of overtones. Because of the low cost this developmental platform is very suitable for advanced research projects in developing countries and has, in fact, been multiplied during hands-on workshops and is now being used by a number of groups at African universities.

  14. Realistic Instrumentation Platform for Active and Passive Optical Remote Sensing.

    PubMed

    Brydegaard, Mikkel; Merdasa, Aboma; Gebru, Alem; Jayaweera, Hiran; Svanberg, Sune

    2016-02-01

    We describe the development of a novel versatile optical platform for active and passive remote sensing of environmental parameters. Applications include assessment of vegetation status and water quality. The system is also adapted for ecological studies, such as identification of flying insects including agricultural pests. The system is based on two mid-size amateur astronomy telescopes, continuous-wave diode lasers at different wavelengths ranging from violet to the near infrared, and detector facilities including quadrant photodiodes, two-dimensional and line scan charge-coupled device cameras, and a compact digital spectrometer. Application examples include remote Ramanlaser-induced fluorescence monitoring of water quality at 120 m distance, and insect identification at kilometer ranges using the recorded wing beat frequency and its spectrum of overtones. Because of the low cost this developmental platform is very suitable for advanced research projects in developing countries and has, in fact, been multiplied during hands-on workshops and is now being used by a number of groups at African universities. PMID:26772187

  15. Measurements of Pupillary Diameter and Wavefront Aberrations in Pregnant Women

    PubMed Central

    Altay, Mehmet Metin; Demirok, Gulizar; Balta, Ozgur; Bolu, Hulya

    2016-01-01

    Purpose. To show whether pregnancy affects the measurements of pupillary diameter and wavefront (WF) aberrations. Methods. This was a case-control study including 34 healthy pregnant women in the third trimester and age-matched 34 nonpregnant women. Only women who had no ocular abnormalities and no refractive error were included. We measured photopic and mesopic pupil diameter and WF aberrations at the third trimester and at the second postpartum month. Measurements of the right eyes were used in this study. The differences between groups were analysed by paired t-test and t-test. Results. Pregnant women's mean photopic pupil size in the third trimester was significantly higher than in postpartum period and in control group (3.74 ± 0.77, 3.45 ± 0.53, and 3.49 ± 0.15 mm, p < 0.05, resp.). Mesopic pupil size in the third trimester was also higher than in postpartum period and in control group (6.77 ± 0.52, 6.42 ± 0.55, and 6.38 ± 0.21 mm, p < 0.05, resp.). RMS-3 and RMS-5 values were higher in pregnancy but these differences were not statistically significant. Conclusion. Pregnancy increased photopic and mesopic pupil size significantly but did not increase wavefront aberrations notably. Increased pupil size may be due to increased sympathetic activity during pregnancy. And this activity can be noninvasively determined by measuring pupil size. PMID:26998383

  16. Bioinspired active whisker sensor for robotic vibrissal tactile sensing

    NASA Astrophysics Data System (ADS)

    Ju, Feng; Ling, Shih-Fu

    2014-12-01

    A whisker transducer (WT) inspired by rat’s vibrissal tactile perception is proposed based on a transduction matrix model characterizing the electro-mechanical transduction process in both forward and backward directions. It is capable of acting as an actuator to sweep the whisker and simultaneously as a sensor to sense the force, motion, and mechanical impedance at whisker tip. Its validity is confirmed by numerical simulation using a finite element model. A prototype is then fabricated and its transduction matrix is determined by parameter identification. The calibrated WT can accurately sense mechanical impedance which is directly related to stiffness, mass and damping. Subsequent vibrissal tactile sensing of sandpaper texture reveals that the real part of mechanical impedance sensed by WT is correlated with sandpaper roughness. Texture discrimination is successfully achieved by inputting the real part to a k-means clustering algorithm. The mechanical impedance sensing ability as well as other features of the WT such as simultaneous-actuation-and-sensing makes it a good solution to robotic tactile sensing.

  17. Predictive Analysis of Landslide Activity Using Remote Sensing Data

    NASA Astrophysics Data System (ADS)

    Markuzon, N.; Regan, J.; Slesnick, C.

    2012-12-01

    Landslides are historically one of the most damaging geohazard phenomena in terms of death tolls and socio-economic losses. Therefore, understanding the underlying causes of landslides and how environmental phenomena affect their frequency and severity is of critical importance. Of specific importance for mitigating future damage is increasing our understanding of how climate change will affect landslide severity, occurrence rates, and damage. We are developing data driven models aimed at predicting landslide activity. The models learn multi-dimensional weather and geophysical patterns associated with historical landslides and estimate location-dependent probabilities for landslides under current or future weather and geophysical conditions. Our approach uses machine learning algorithms capable of determining non-linear associations between dependent variables and landslide occurrence without requiring detailed knowledge of geomorphology. Our primary goal in year one of the project is to evaluate the predictive capabilities of data mining models in application to landslide activity, and to analyze if the approach will discover previously unknown variables and/or relationships important to landslide occurrence, frequency or severity. The models include remote sensing and ground-based data, including weather, landcover, slope, elevation and drainage information as well as urbanization data. The historical landslide dataset we used to build our preliminary models was compiled from City of Seattle landslide files, United States Geological Survey reports, newspaper articles, and a verified subset of the Seattle Landslide Database that consists of all reported landslides within Seattle, WA, between 1948 and 1999. Most of the landslides analyzed to-date are shallow. Using statistical analysis and unsupervised clustering methods we have thus far identified subsets of weather conditions that lead to a significantly higher landslide probability, and have developed

  18. Measuring aberrations in the rat brain by a new coherence-gated wavefront sensor using a Linnik interferometer

    NASA Astrophysics Data System (ADS)

    Wang, Jinyu; Leger, Jean-Francois; Binding, Jonas; Boccara, Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-03-01

    Wavefront distortions due to refractive index mismatch and tissue inhomogeneity may limit the resolution, contrast, signal strength and achievable imaging depth of microscope. Traditional Shack-Hartmann wavefront sensors can't be used in strongly scattering biological samples since there is no selection of the ballistic photons originating from the reference point in the sample amongst all the backscattered photons. In contrast, coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore should permit adaptive corrections. We have implemented a new CGWS scheme based on a Linnik interferometer with Super Luminescent Emission Diode as low temporal coherence light source. Compared to the previously described CGWS system based on a femtosecond laser, its main advantages are the automatic compensation of dispersion between the two arms and its easy implementation on any microscope. The configuration of virtual Shack-Hartmann wavefront sensor for wavefront reconstruction was optimized, and the measurement precision was analyzed when multiple scattering was not negligible. In fresh rat brain slices, we successfully measured up to about 400 μm depth a known defocus aberration, obtained by axially displacing the coherence gate with respect to the actual focus in the sample.

  19. A First Order Wavefront Estimation Algorithm for P1640 Calibrator

    NASA Technical Reports Server (NTRS)

    Zhaia, C.; Vasisht, G.; Shao, M.; Lockhart, T.; Cady, E.; Oppenheimer, B.; Burruss, R.; Roberts, J.; Beichman, C.; Brenner, D.; Crepp, J.; Dekany, R.; Hinkley, S.; Hillenbrand, L.; Parry, I.; Pueyo, L.; Rice, E.; Roberts, L. C. Jr.; Sivaramakrishnan, A.; Soummer, R.; Vescelus, F.; Wallace, K.; Zimmerman, N.

    2012-01-01

    P1640 calibrator is a wavefront sensor working with the P1640 coronagraph and the Palomar 3000 actuator adaptive optics system (P3K) at the Palomar 200 inch Hale telescope. It measures the wavefront by interfering post-coronagraph light with a reference beam formed by low-pass filtering the blocked light from the coronagraph focal plane mask. The P1640 instrument has a similar architecture to the Gemini Planet Imager (GPI) and its performance is currently limited by the quasi-static speckles due to non-common path wavefront errors, which comes from the non-common path for the light to arrive at the AO wavefront sensor and the coronagraph mask. By measuring the wavefront after the coronagraph mask, the non-common path wavefront error can be estimated and corrected by feeding back the error signal to the deformable mirror (DM) of the P3K AO system. Here, we present a first order wavefront estimation algorithm and an instrument calibration scheme used in experiments done recently at Palomar observatory. We calibrate the P1640 calibrator by measuring its responses to poking DM actuators with a sparse checkerboard pattern at different amplitudes. The calibration yields a complex normalization factor for wavefront estimation and establishes the registration of the DM actuators at the pupil camera of the P1640 calibrator, necessary for wavefront correction. Improvement of imaging quality after feeding back the wavefront correction to the AO system demonstrated the efficacy of the algorithm.

  20. Upgrading telescopes by active pupil wavefront correction

    NASA Astrophysics Data System (ADS)

    Stacy, J. E.; Meinel, A. B.; Meinel, J. P.

    Exit pupil correction of the Large Deployable Reflector's (a proposed IR to sub-mm space telescope) segmented primary can be done by reimaging it onto a like segmented surface at the exit pupil. This allows the primary to be more flexible, the adaptive element to be smaller, and the supporting structure to be cheaper than if all correction were performed at a stiffly supported primary. Piston, tilt, and decenter errors of an annulus of the primary and the equations for the required corrections are considered. To verify these, the perturbations with spline functions in the lens design program are simulated. Strehl ratios used to measure image quality show that a piston error of 1 mm is fully corrected over a 5 arcmin field for an f/10 system with a 0.7 n.a. primary at 30 micrometers. Limits of correction are also shown for tilt and decenter errors of segments. Tolerances are given for tilt and decenter errors of the remaining optics also.

  1. Real-time wavefront reconstruction from intensity measurements

    NASA Astrophysics Data System (ADS)

    Smith, Carlas; Marinica, Raluca; Verhaegen, Michel

    2013-12-01

    for the rst time puts Adaptive Optics based on intensity measurements in an optimal H2 controller setting. A computationally ecient solution is presented for this H2 controller for the case the mirror dynamics can be considered as a static system. The advantage of this new dynamic aberration correction is also demonstrated in the simulation study. References [1] C. Keller, V. Korkiakoski, N. Doelman, R. Fraanje, R. Andrei, and M. Verhaegen. Extremely fast focal-plane wavefront sensing for extreme adaptive optics. arXiv preprint arXiv:1207.3273, 2012

  2. Study on an oxygen sensing rhenium(I) complex with enlarged sensing/active area: fabrication, photophysical parameters and molecular oxygen sensing performance.

    PubMed

    Xu, Guiying; Lu, Mang; Huang, Can; Wang, Yaoqiong; Ge, Shuping

    2014-04-01

    In this paper, we synthesize a novel 1,10-phenanthroline-derived (Phen-derived) diamine ligand of benzo[f][1,10]phenanthroline-6,7-dicarbonitrile (Phen-CN) with enlarged conjugation planar and its corresponding Re(I) complex of Re(CO)3Cl(Phen-CN), hoping to achieve an optical sensor owing large sensing/active area. Its geometric and electronic structures are investigated, which suggests that the effective sensing/active area of Re(CO)3Cl(Phen-CN) is enlarged by the successful formation of conjugation planar. The promising photophysical parameters of Re(CO)3Cl(Phen-CN), including large sensing/active area and long excited state lifetime, make it a potential probe for oxygen detection. By doping Re(CO)3Cl(Phen-CN) into a polymer matrix of poly(vinylpyrrolidone), oxygen sensing performances of the resulted composite materials are investigated. Finally, a high sensitivity of 17.1 is realized, with short response/recovery time of 9s/32s.

  3. Adaptable Diffraction Gratings With Wavefront Transformation

    NASA Technical Reports Server (NTRS)

    Iazikov, Dmitri; Mossberg, Thomas W.; Greiner, Christoph M.

    2010-01-01

    Diffraction gratings are optical components with regular patterns of grooves, which angularly disperse incoming light by wavelength. Traditional diffraction gratings have static planar, concave, or convex surfaces. However, if they could be made so that they can change the surface curvature at will, then they would be able to focus on particular segments, self-calibrate, or perform fine adjustments. This innovation creates a diffraction grating on a deformable surface. This surface could be bent at will, resulting in a dynamic wavefront transformation. This allows for self-calibration, compensation for aberrations, enhancing image resolution in a particular area, or performing multiple scans using different wavelengths. A dynamic grating gives scientists a new ability to explore wavefronts from a variety of viewpoints.

  4. The Challenge of Active Optical Sensing from Extreme Orbits

    NASA Technical Reports Server (NTRS)

    Spiers, Gary D.

    2004-01-01

    A review of the history and current state of atmospheric sensing lidar from Earth orbit was conducted and it was found that space based earth remote sensing is still in its infancy with only one limited success extended duration autonomous mission to date. An analysis of the basic requirements for some candidate geo-synchronous lidar concepts was completed and it was concluded that significant basic work is required in all areas of lidar development.

  5. Extremely large telescopes' optical design and wavefront correction

    NASA Astrophysics Data System (ADS)

    Goncharov, Alexander Vladimirovich

    An overview of the state of art within optical design of large astronomical telescopes is given. Recent advances within the field are presented. The importance of new computer-controlled mirror-polishing methods is emphasized. Some important aspects of atmospheric optics are presented together with current compensation methods using adaptive optics, with or without laser guide stars. An overview of wavefront sensing, wavefront reconstruction and techniques for compensation is given. Methods for optical design of large, optical telescopes with fast primary mirrors are presented in a systematic way. Three different approaches are outlined and commented. They include an algebraic method, a method based on optimization through ray tracing and an analytical method based on Fermat's principle and the Abbe sine condition. Studies of optical designs for large telescopes with fast, spherical primary mirrors are examined and discussed. For two-mirror designs, an analytical method has been derived using aberration control based on Fermat's principle. Intrinsic apodization for design of extremely fast primary mirrors is analyzed. For four- mirror designs with spherical primary minors, a ray tracing approach has been chosen. A total of fifteen different four-mirror designs have been analyzed and discussed. For the 50 m optical telescope. Euro50, a two-mirror design was chosen. This optical design is presented in detail, together with the optical layout of an adaptive optical system that forms an integrated part of the telescope. An analysis of essential components of the Euro50 is given. Finally, an analytical approach is presented for control of two or more deformable mirrors for adaptive optics in extremely large telescopes for optical wavelengths. The same algorithms are used to evaluate and predict the performance of the adaptive optics for the Euro50.

  6. Transmission-grating-based wavefront tilt sensor.

    PubMed

    Iwata, Koichi; Fukuda, Hiroki; Moriwaki, Kousuke

    2009-07-10

    We propose a new type of tilt sensor. It consists of a grating and an image sensor. It detects the tilt of the collimated wavefront reflected from a plane mirror. Its principle is described and analyzed based on wave optics. Experimental results show its validity. Simulations of the ordinary autocollimator and the proposed tilt sensor show that the effect of noise on the measured angle is smaller for the latter. These results show a possibility of making a smaller and simpler tilt sensor.

  7. Experimental results for absolute cylindrical wavefront testing

    NASA Astrophysics Data System (ADS)

    Reardon, Patrick J.; Alatawi, Ayshah

    2014-09-01

    Applications for Cylindrical and near-cylindrical surfaces are ever-increasing. However, fabrication of high quality cylindrical surfaces is limited by the difficulty of accurate and affordable metrology. Absolute testing of such surfaces represents a challenge to the optical testing community as cylindrical reference wavefronts are difficult to produce. In this paper, preliminary results for a new method of absolute testing of cylindrical wavefronts are presented. The method is based on the merging of the random ball test method with the fiber optic reference test. The random ball test assumes a large number of interferograms of a good quality sphere with errors that are statistically distributed such that the average of the errors goes to zero. The fiber optic reference test utilizes a specially processed optical fiber to provide a clean high quality reference wave from an incident line focus from the cylindrical wave under test. By taking measurements at different rotation and translations of the fiber, an analogous procedure can be employed to determine the quality of the converging cylindrical wavefront with high accuracy. This paper presents and discusses the results of recent tests of this method using a null optic formed by a COTS cylindrical lens and a free-form polished corrector element.

  8. Specialized wavefront sensors for adaptive optics

    NASA Astrophysics Data System (ADS)

    Neal, Daniel R.; Mansell, J. D.; Gruetzner, James K.; Morgan, R.; Warren, Mial E.

    1995-08-01

    The performance of an adaptive optical system is strongly dependent upon correctly measuring the wavefront of the arriving light. The most common wavefront measurement techniques used to date are the shearing interferometer and the Shack-Hartmann sensor. Shack-Hartmann sensors rely on the use of lenslet arrays to sample the aperture appropriately. These have traditionally been constructed using MLM or step and repeat technology, and more recently with binary optics technology. Diffractive optics fabrication methodology can be used to remove some of the limitations of the previous technologies and can allow for low-cost production of sophisticated elements. We have investigated several different specialized wavefront sensor configurations using both Shack-Hartmann and shearing interferometer principles. We have taken advantage of the arbitrary nature of these elements to match pupil shapes of detector and telescope aperture and to introduce magnification between the lenslet array and the detector. We have fabricated elements that facilitate matching the sampling to the current atmospheric conditions. The sensors were designed using a far-field diffraction model and a photolithography layout program. They were fabricated using photolithography and RIE etching. Several different designs are presented with some experimental results from a small-scale adaptive optics brass-board.

  9. Wavefront reconstruction using computer-generated holograms

    NASA Astrophysics Data System (ADS)

    Schulze, Christian; Flamm, Daniel; Schmidt, Oliver A.; Duparré, Michael

    2012-02-01

    We propose a new method to determine the wavefront of a laser beam, based on modal decomposition using computer-generated holograms (CGHs). Thereby the beam under test illuminates the CGH with a specific, inscribed transmission function that enables the measurement of modal amplitudes and phases by evaluating the first diffraction order of the hologram. Since we use an angular multiplexing technique, our method is innately capable of real-time measurements of amplitude and phase, yielding the complete information about the optical field. A measurement of the Stokes parameters, respectively of the polarization state, provides the possibility to calculate the Poynting vector. Two wavefront reconstruction possibilities are outlined: reconstruction from the phase for scalar beams and reconstruction from the Poynting vector for inhomogeneously polarized beams. To quantify single aberrations, the reconstructed wavefront is decomposed into Zernike polynomials. Our technique is applied to beams emerging from different kinds of multimode optical fibers, such as step-index, photonic crystal and multicore fibers, whereas in this work results are exemplarily shown for a step-index fiber and compared to a Shack-Hartmann measurement that serves as a reference.

  10. Fiber coupler end face wavefront surface metrology

    NASA Astrophysics Data System (ADS)

    Compertore, David C.; Ignatovich, Filipp V.; Marcus, Michael A.

    2015-09-01

    Despite significant technological advances in the field of fiber optic communications, one area remains surprisingly `low-tech': fiber termination. In many instances it involves manual labor and subjective visual inspection. At the same time, high quality fiber connections are one of the most critical parameters in constructing an efficient communication link. The shape and finish of the fiber end faces determines the efficiency of a connection comprised of coupled fiber end faces. The importance of fiber end face quality becomes even more critical for fiber connection arrays and for in the field applications. In this article we propose and demonstrate a quantitative inspection method for the fiber connectors using reflected wavefront technology. The manufactured and polished fiber tip is illuminated by a collimated light from a microscope objective. The reflected light is collected by the objective and is directed to a Shack-Hartmann wavefront sensor. A set of lenses is used to create the image of the fiber tip on the surface of the sensor. The wavefront is analyzed by the sensor, and the measured parameters are used to obtain surface properties of the fiber tip, and estimate connection loss. For example, defocus components in the reflected light indicate the presence of bow in the fiber end face. This inspection method provides a contact-free approach for quantitative inspection of fiber end faces and for estimating the connection loss, and can potentially be integrated into a feedback system for automated inspection and polishing of fiber tips and fiber tip arrays.

  11. Coherence gated wavefront sensorless adaptive optics for two photon excited fluorescence retinal imaging (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Jian, Yifan; Cua, Michelle; Bonora, Stefano; Pugh, Edward N.; Zawadzki, Robert J.; Sarunic, Marinko V.

    2016-03-01

    We present a novel system for adaptive optics two photon imaging. We utilize the bandwidth of the femtosecond excitation beam to perform coherence gated imaging (OCT) of the sample. The location of the focus is directly observable in the cross sectional OCT images, and adjusted to the desired depth plane. Next, using real time volumetric OCT, we perform Wavefront Sensorless Adaptive Optics (WSAO) aberration correction using a multi-element adaptive lens capable of correcting up to 4th order Zernike polynomials. The aberration correction is performed based on an image quality metric, for example intensity. The optimization time is limited only by the OCT acquisition rate, and takes ~30s. Following aberration correction, two photon fluorescence images are acquired, and compared to results without adaptive optics correction. This technique is promising for multiphoton imaging in multi-layered, scattering samples such as eye and brain, in which traditional wavefront sensing and guide-star sensorless adaptive optics approaches may not be suitable.

  12. Identification of sewage leaks by active remote-sensing methods

    NASA Astrophysics Data System (ADS)

    Goldshleger, Naftaly; Basson, Uri

    2016-04-01

    The increasing length of sewage pipelines, and concomitant risk of leaks due to urban and industrial growth and development is exposing the surrounding land to contamination risk and environmental harm. It is therefore important to locate such leaks in a timely manner, to minimize the damage. Advances in active remote sensing Ground Penetrating Radar (GPR) and Frequency Domain Electromagnetic (FDEM) technologies was used to identify leaking potentially responsible for pollution and to identify minor spills before they cause widespread damage. This study focused on the development of these electromagnetic methods to replace conventional acoustic methods for the identification of leaks along sewage pipes. Electromagnetic methods provide an additional advantage in that they allow mapping of the fluid-transport system in the subsurface. Leak-detection systems using GPR and FDEM are not limited to large amounts of water, but enable detecting leaks of tens of liters per hour, because they can locate increases in environmental moisture content of only a few percentage along the pipes. The importance and uniqueness of this research lies in the development of practical tools to provide a snapshot and monitoring of the spatial changes in soil moisture content up to depths of about 3-4 m, in open and paved areas, at relatively low cost, in real time or close to real time. Spatial measurements performed using GPR and FDEM systems allow monitoring many tens of thousands of measurement points per hectare, thus providing a picture of the spatial situation along pipelines and the surrounding. The main purpose of this study was to develop a method for detecting sewage leaks using the above-proposed geophysical methods, since their contaminants can severely affect public health. We focused on identifying, locating and characterizing such leaks in sewage pipes in residential and industrial areas.

  13. Wavefronts and mechanical signaling in early Drosophila embryos

    NASA Astrophysics Data System (ADS)

    Idema, Timon; Dubuis, Julien; Manning, Lisa; Nelson, Philip; Liu, Andrea

    2012-02-01

    Mitosis in the early syncytial Drosophila embryo has a high degree of spatial and temporal correlations, visible as mitotic wavefronts that travel across the embryo. This mitosis wavefront is preceded by another wavefront which corresponds to chromosome condensation. The two wavefronts are separated by a time interval that is independent of cell cycle and propagate at the same speed for a given embryo in a given cycle. We study the wavefronts in the context of excitable medium theory, using two different models, one with biochemical signaling and one with mechanical signaling. We find that the dependence of wavefront speed on cell cycle number is most naturally explained via a mechanical signaling, and that the entire process suggests a scenario in which biochemical and mechanical signaling are coupled.

  14. Wavefront sensorless adaptive optics ophthalmoscopy in the human eye.

    PubMed

    Hofer, Heidi; Sredar, Nripun; Queener, Hope; Li, Chaohong; Porter, Jason

    2011-07-18

    Wavefront sensor noise and fidelity place a fundamental limit on achievable image quality in current adaptive optics ophthalmoscopes. Additionally, the wavefront sensor 'beacon' can interfere with visual experiments. We demonstrate real-time (25 Hz), wavefront sensorless adaptive optics imaging in the living human eye with image quality rivaling that of wavefront sensor based control in the same system. A stochastic parallel gradient descent algorithm directly optimized the mean intensity in retinal image frames acquired with a confocal adaptive optics scanning laser ophthalmoscope (AOSLO). When imaging through natural, undilated pupils, both control methods resulted in comparable mean image intensities. However, when imaging through dilated pupils, image intensity was generally higher following wavefront sensor-based control. Despite the typically reduced intensity, image contrast was higher, on average, with sensorless control. Wavefront sensorless control is a viable option for imaging the living human eye and future refinements of this technique may result in even greater optical gains.

  15. Quorum Sensing Inhibitory Activity of Giganteone A from Myristica cinnamomea King against Escherichia coli Biosensors.

    PubMed

    Sivasothy, Yasodha; Krishnan, Thiba; Chan, Kok-Gan; Abdul Wahab, Siti Mariam; Othman, Muhamad Aqmal; Litaudon, Marc; Awang, Khalijah

    2016-03-21

    Malabaricones A-C (1-3) and giganteone A (4) were isolated from the bark of Myristica cinnamomea King. Their structures were elucidated and characterized by means of NMR and MS spectral analyses. These isolates were evaluated for their anti-quorum sensing activity using quorum sensing biosensors, namely Escherichia coli [pSB401] and Escherichia coli [pSB1075], whereby the potential of giganteone A (4) as a suitable anti-quorum sensing agent was demonstrated.

  16. Sub-pixel spatial resolution wavefront phase imaging

    NASA Technical Reports Server (NTRS)

    Stahl, H. Philip (Inventor); Mooney, James T. (Inventor)

    2012-01-01

    A phase imaging method for an optical wavefront acquires a plurality of phase images of the optical wavefront using a phase imager. Each phase image is unique and is shifted with respect to another of the phase images by a known/controlled amount that is less than the size of the phase imager's pixels. The phase images are then combined to generate a single high-spatial resolution phase image of the optical wavefront.

  17. Wavefront Analysis of Adaptive Telescope

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.; Hillman, Lloyd

    1997-01-01

    The motivation for this work came from a NASA Headquarters interest in investigating design concepts for a large space telescope employing active optics technology. The development of telescope optical requirements and potential optical design configurations is reported.

  18. U. S. GEOLOGICAL SURVEY LAND REMOTE SENSING ACTIVITIES.

    USGS Publications Warehouse

    Frederick, Doyle G.

    1983-01-01

    USGS uses all types of remotely sensed data, in combination with other sources of data, to support geologic analyses, hydrologic assessments, land cover mapping, image mapping, and applications research. Survey scientists use all types of remotely sensed data with ground verifications and digital topographic and cartographic data. A considerable amount of research is being done by Survey scientists on developing automated geographic information systems that can handle a wide variety of digital data. The Survey is also investigating the use of microprocessor computer systems for accessing, displaying, and analyzing digital data.

  19. Recent activities of the Priroda State Remote Sensing Center

    USGS Publications Warehouse

    Morrison, J.L.; Bond, A.R.

    1989-01-01

    At present the Priroda State Remote Sensing Center is the largest entity in the USSR responsible for the receipt and processing of space imagery. Besides the aforementioned consulting and training functions, Priroda, upon user request: a) processes multispectral, band-specific, and other remote sensing imagery and supplies a broad range of primary and derivative information in the form of image copies [prints and transparencies] and digital products; and b) cooperates with other GUGK bodies in the compilation of thematic map series on diverse topics. -from Authors

  20. Halogen bonding-enhanced electrochemical halide anion sensing by redox-active ferrocene receptors.

    PubMed

    Lim, Jason Y C; Cunningham, Matthew J; Davis, Jason J; Beer, Paul D

    2015-10-01

    The first examples of halogen bonding redox-active ferrocene receptors and their anion electrochemical sensing properties are reported. Halogen bonding was found to significantly amplify the magnitude of the receptor's metallocene redox-couple's voltammetric responses for halide sensing compared to their hydrogen bonding analogues in both acetonitrile and aqueous-acetonitrile solvent media.

  1. Halogen bonding-enhanced electrochemical halide anion sensing by redox-active ferrocene receptors.

    PubMed

    Lim, Jason Y C; Cunningham, Matthew J; Davis, Jason J; Beer, Paul D

    2015-10-01

    The first examples of halogen bonding redox-active ferrocene receptors and their anion electrochemical sensing properties are reported. Halogen bonding was found to significantly amplify the magnitude of the receptor's metallocene redox-couple's voltammetric responses for halide sensing compared to their hydrogen bonding analogues in both acetonitrile and aqueous-acetonitrile solvent media. PMID:26289779

  2. Active Remote Sensing of Natural Resources: Course Notes. Science Series No. 5. Final Technical Report.

    ERIC Educational Resources Information Center

    Maxwell, Eugene L.

    Presented is a portion of a research project which developed materials for teaching remote sensing of natural resources on an interdisciplinary basis at the graduate level. This volume contains notes developed for a course in active remote sensing. It is concerned with those methods or systems which generate the electromagnetic energy…

  3. Non-uniform dispersion of the source-sink relationship alters wavefront curvature.

    PubMed

    Romero, Lucia; Trenor, Beatriz; Ferrero, Jose M; Starmer, C Frank

    2013-01-01

    The distribution of cellular source-sink relationships plays an important role in cardiac propagation. It can lead to conduction slowing and block as well as wave fractionation. It is of great interest to unravel the mechanisms underlying evolution in wavefront geometry. Our goal is to investigate the role of the source-sink relationship on wavefront geometry using computer simulations. We analyzed the role of variability in the microscopic source-sink relationship in driving changes in wavefront geometry. The electrophysiological activity of a homogeneous isotropic tissue was simulated using the ten Tusscher and Panfilov 2006 action potential model and the source-sink relationship was characterized using an improved version of the Romero et al. safety factor formulation (SFm2). Our simulations reveal that non-uniform dispersion of the cellular source-sink relationship (dispersion along the wavefront) leads to alterations in curvature. To better understand the role of the source-sink relationship in the process of wave formation, the electrophysiological activity at the initiation of excitation waves in a 1D strand was examined and the source-sink relationship was characterized using the two recently updated safety factor formulations: the SFm2 and the Boyle-Vigmond (SFVB) definitions. The electrophysiological activity at the initiation of excitation waves was intimately related to the SFm2 profiles, while the SFVB led to several counterintuitive observations. Importantly, with the SFm2 characterization, a critical source-sink relationship for initiation of excitation waves was identified, which was independent of the size of the electrode of excitation, membrane excitability, or tissue conductivity. In conclusion, our work suggests that non-uniform dispersion of the source-sink relationship alters wavefront curvature and a critical source-sink relationship profile separates wave expansion from collapse. Our study reinforces the idea that the safety factor

  4. Malabaricone C from Myristica cinnamomea exhibits anti-quorum sensing activity.

    PubMed

    Chong, Yee Meng; Yin, Wai Fong; Ho, Chia Yong; Mustafa, Mohamad Rais; Hadi, A Hamid A; Awang, Khalijah; Narrima, Putri; Koh, Chong-Lek; Appleton, David R; Chan, Kok-Gan

    2011-10-28

    A methanol-soluble extract of the bark of Myristica cinnamomea was found to exhibit anti-quorum sensing activity, and subsequent bioassay-guided isolation led to the identification of the active compound malabaricone C (1). Compound 1 inhibited violacein production by Chromobacterium violaceum CV026 when grown in the presence of a cognate signaling molecule, N-3-oxohexanoyl-homoserine lactone. Furthermore, 1 inhibited the quorum sensing-regulated pyocyanin production and biofilm formation in Pseudomonas aeruginosa PAO1. These results suggest that the anti-quorum sensing activity of 1 and related molecules should be investigated further.

  5. Sense of Cohesion among Community Activists Engaging in Volunteer Activity

    ERIC Educational Resources Information Center

    Levy, Drorit; Itzhaky, Haya; Zanbar, Lea; Schwartz, Chaya

    2012-01-01

    The present article attempts to shed light on the direct and indirect contribution of personal resources and community indices to Sense of Cohesion among activists engaging in community volunteer work. The sample comprised 481 activists. Based on social systems theory, three levels of variables were examined: (1) inputs, which included personal…

  6. Activities of the Remote Sensing Information Sciences Research Group

    NASA Technical Reports Server (NTRS)

    Estes, J. E.; Botkin, D.; Peuquet, D.; Smith, T.; Star, J. L. (Principal Investigator)

    1984-01-01

    Topics on the analysis and processing of remotely sensed data in the areas of vegetation analysis and modelling, georeferenced information systems, machine assisted information extraction from image data, and artificial intelligence are investigated. Discussions on support field data and specific applications of the proposed technologies are also included.

  7. Remote sensing research activities related to academic institutions

    NASA Technical Reports Server (NTRS)

    Myers, V. I.

    1980-01-01

    The role of research in the educational setting is discussed. Curriculum developments for integrating teaching and research are described. Remote sensing technology is used as an example of bridging the gap between research and application. Recommendations are presented for strengthing research groups.

  8. Wavefront Analysis of Adaptive Telescope

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.; Hillman, Lloyd

    1997-01-01

    The motivation for this work came from a NASA Headquarters interest in investigating design concepts for a large space telescope employing active optics technology. Current and foreseeable launch vehicles will be limited to carrying around 4-5 meter diameter objects. Thus, if a large, filled-aperture telescope (6-20 meters in diameter) is to be placed in space, it will be required to have a deployable primary mirror. Such a mirror may be an inflatable membrane or a segmented mirror consisting of many smaller pieces. In any case, it is expected that the deployed primary will not be of sufficient quality to achieve diffraction-limited performance for its aperture size. Thus, an active optics system will be needed to correct for initial as well as environmentally-produced primary figure errors. Marshall Space Flight Center has developed considerable expertise in the area of active optics with the PAMELA test-bed. The combination of this experience along with the Marshall optical shop's work in mirror fabrication made MSFC the logical choice to lead NASA's effort to develop active optics technology for large, space-based, astronomical telescopes. Furthermore, UAH's support of MSFC in the areas of optical design, fabrication, and testing of space-based optical systems placed us in a key position to play a major role in the development of this future-generation telescope. A careful study of the active optics components had to be carried out in order to determine control segment size, segment quality, and segment controllability required to achieve diffraction-limited resolution with a given primary mirror. With this in mind, UAH undertook the following effort to provide NASA/MSFC with optical design and analysis support for the large telescope study. All of the work performed under this contract has already been reported, as a team member with MSFC, to NASA Headquarters in a series of presentations given between May and December of 1995. As specified on the delivery

  9. Auto gain control of EMCCD in Shack-Hartmann wavefront sensor for adaptive optics

    NASA Astrophysics Data System (ADS)

    Zhu, Zhaoyi; Li, Dayu; Hu, Lifa; Mu, QuanQuan; Cao, Zhaoliang; Wang, Yukun; Wang, Shaoxin; Xuan, Li

    2016-12-01

    Electron multiplying charge-coupled-device (EMCCD) applied in Shack-Hartmann wavefront sensor (S-H WFS) makes the wavefront sensing more efficient for adaptive optics (AO). However when the brightness of the observed target changes in large ranges in a few minutes, a fixed electron multiplying (EM) gain may not be optimum. Thus an auto-gain-control (AGC) method based on the spots image of the S-H WFS is proposed. The designed control value is the average value of the maximum signals of all the light spots in a frame. It has been demonstrated in the experiments that the control value is sensitive to the change of the target brightness, and is stable in the presence of detecting noises and turbulence influence. The goal value for control is predetermined based on the linear relation of the signal with the EM gain and the number of photons collected in sub-apertures. The conditions of the self-protection of the EMCCD are also considered for the goal value. Simulations and experiments indicate that the proposed control method is efficient, and keeps the sensing in a high SNR which reaches the upper SNR limit when sensing with EMCCD. The self-protection of the EMCCD is avoided during the whole sensing process.

  10. An experimental study on reflector wave-front error correction using PZT actuators

    NASA Astrophysics Data System (ADS)

    Lan, Lan; Jiang, Shuidong; Zhou, Yang; Fang, Houfei; Wu, Zhigang; Du, Jianming

    2016-04-01

    An adaptive control system for correcting wave-front error of a CFRC reflector has been studied. Errors investigated in this paper were mainly introduced by fabrication and gravity. 72 Piezoelectric Ceramic Transducer (PZT) actuators were integrated to the CFRC reflector to conduct wave-front error control. The adaptive CFRC reflector was fixed on an optical platform without any external loads. The temperature and humidity were well controlled during the experimental study. The wave-front error correction algorithm is based on influence matrix approach coupled with least squares optimization method. The linear relationship between the PZT actuator's input voltage and the output displacement of the adaptive CFRC reflector surface is validated. A laser displacement sensor was used for measuring the displacements. The influence matrix was obtained experimentally by measuring the displacements of the associated points while each actuator was activated separately. The wave-front error and influence matrix were measured using a V-Stars photogrammetry system. Experimental investigation validated that this adaptive control system is capable to significantly reduce the reflector surface geometry error. Experimental results are correlated very well with simulation results which were obtained by using a multidisciplinary analytical approach. Conclusions of this study suggest that the adaptive CFRC reflector technology can provide a low cost method to significantly increase the precision of a CFRC reflector.

  11. Wavefront Measurement over an Extended Horizontal Path Using a Wavefront Curvature Sensor

    NASA Astrophysics Data System (ADS)

    Burnett, J.; Woods, S.; Turner, A.; Scott, A.

    This paper reports on the results of wavefront curvature sensor measurements over horizontal paths of 66m and 4 km. The wavefront curvature sensor used has been developed at QinetiQ and is based on the use of a quadratically distorted diffraction grating to enable the simultaneous recording of two symmetrically separated planes about the entrance pupil of a telescope. The measurements allow us to characterize the spatio-temporal nature of the wavefront errors and therefore enable us to estimate the wavefront sensor (WFS) and deformable mirror (DM) requirements for the development of an adaptive optic system (AOS). For the 66m path the dynamic range and frame-rate of the WFS camera was found to be adequate to drive the AOS, although the software based control resulted in intermittent performance. The data for the 4 km path suggested that the frame-rate of the WFS camera was at least a factor of 3 slower than would be necessary to either drive the AOS or make any detailed conclusions about the spatial analysis.

  12. Liquid Crystal on Silicon Wavefront Corrector

    NASA Technical Reports Server (NTRS)

    Pouch, John; Miranda, Felix; Wang, Xinghua; Bos, Philip, J.

    2004-01-01

    A low cost, high resolution, liquid crystal on silicon, spatial light modulator has been developed for the correction of huge aberrations in an optical system where the polarization dependence and the chromatic nature are tolerated. However, the overall system performance suggests that this device is also suitable for real time correction of aberration in human eyes. This device has a resolution of 1024 x 768, and is driven by an XGA display driver. The effective stroke length of the device is 700 nm and 2000 nm for the visible and IR regions of the device, respectively. The response speeds are 50 Hz and 5 Hz, respectively, which are fast enough for real time adaptive optics for aberrations in human eyes. By modulating a wavefront of 2 pi, this device can correct for arbitrary high order wavefront aberrations since the 2-D pixel array is independently controlled by the driver. The high resolution and high accuracy of the device allow for diffraction limited correction of the tip and tilt or defocus without an additional correction loop. We have shown that for every wave of aberration, an 8 step blazed grating is required to achieve high diffraction efficiency around 80%. In light of this, up to 125 waves peak to valley of tip and tilt can be corrected if we choose the simplest aberration. Corrections of 34 waves of aberration, including high order Zernicke terms in a high magnification telescope, to diffraction limited performance (residual wavefront aberration less than 1/30 lambda at 632.8 nm) have been observed at high efficiency.

  13. Modeling Chemical Detection Sensitivities of Active and Passive Remote Sensing Systems

    SciTech Connect

    Scharlemann, E T

    2003-07-28

    During nearly a decade of remote sensing programs under the auspices of the U. S. Department of Energy (DOE), LLNL has developed a set of performance modeling codes--called APRS--for both Active and Passive Remote Sensing systems. These codes emphasize chemical detection sensitivity in the form of minimum detectable quantities with and without background spectral clutter and in the possible presence of other interfering chemicals. The codes have been benchmarked against data acquired in both active and passive remote sensing programs at LLNL and Los Alamos National Laboratory (LANL). The codes include, as an integral part of the performance modeling, many of the data analysis techniques developed in the DOE's active and passive remote sensing programs (e.g., ''band normalization'' for an active system, principal component analysis for a passive system).

  14. Initial Demonstration of Mercury Wavefront Correction System

    SciTech Connect

    Liao, Z M

    2006-02-01

    High average power operation of the Mercury Laser induces dynamic aberrations to the laser beam wavefront. Analysis of recent data indicates that up to 4 waves of low order aberration (mainly focus error or power, with spatial resolution < 0.5 cm{sup -1}) could be expected at each pass. Because of the magnitude of the wavefront error, the logical position is to place a deformable mirror (DM) at the M11 position, where the DM will correct the beam between passes 1 & 2 and 3 & 4. Currently, there are only two established commercial vendors offering complete adaptive optic (AO) systems that can accommodate the Mercury beam size (45 x 75 mm) which are compatible with high damage threshold coatings. Xinetics (MA, USA) offers a complete AO system along with a Shack-Hartmann wavefront sensor. The Xinetics DM is based on lead magnesium niobate (PMN) technology. A number of US aerospace firms as well as NIF use Xinetics PMN technology for their DMs. Phasics (Paris, France) offers a complete AO solution with its proprietary SID-4, a four-way shearing interferometric wavefront sensor capable of high resolution (over 100 x 100 sampling points). The Phasics system includes a bimorph deformable mirror from Night-n-Opt (Moscow, Russia) that uses lead zirconate titanate (PZT) technology. Various high power laser laboratories around the world such as LULI (France), HELEN (UK), and GEKKO (Japan) are using the PZT-based bimorph DM in their system. While both DM technologies are equivalent and have been deployed in high-energy laser systems, the PZT based bimorph DM offers two distinct features that makes it more attractive for high average power laser systems. The bimorph DM uses two layers of PZT actuators with the outer layer acting as power correctors, capable of correcting up to 20 waves of power. The Xinetics DM offers a maximum stroke of 4 waves. In addition, Night-N-Opt has also designed a water-cooled DM with a silicon based substrate (as opposed to a glass substrate

  15. Advanced Techniques for Fourier Transform Wavefront Reconstruction

    SciTech Connect

    Poyneer, L A

    2002-08-05

    The performance of Fourier transform (FT) reconstructors in large adaptive optics systems with Shack-Hartmann sensors and a deformable mirror is analyzed. FT methods, which are derived for point-based geometries, are adapted for use on the continuous systems. Analysis and simulation show how to compensate for effects such as misalignment of the deformable mirror and wavefront sensor gain. Further filtering methods to reduce noise and improve performance are presented. All these modifications can be implemented at the filtering stage, preserving the speed of FT reconstruction. Simulation of a large system shows how compensated FT methods can have equivalent or better performance to slower vector-matrix-multiply reconstructions.

  16. Lenses that provide the transformation between two given wavefronts

    NASA Astrophysics Data System (ADS)

    Criado, C.; Alamo, N.

    2016-12-01

    We give an original method to design four types of lenses solving the following problems: focusing a given wavefront in a given point, and performing the transformation between two arbitrary incoming and outgoing wavefronts. The method to design the lenses profiles is based on the optical properties of the envelopes of certain families of Cartesian ovals of revolution.

  17. Mitotic wavefronts mediated by mechanical signaling in early Drosophila embryos

    NASA Astrophysics Data System (ADS)

    Kang, Louis; Idema, Timon; Liu, Andrea; Lubensky, Tom

    2013-03-01

    Mitosis in the early Drosophila embryo demonstrates spatial and temporal correlations in the form of wavefronts that travel across the embryo in each cell cycle. This coordinated phenomenon requires a signaling mechanism, which we suggest is mechanical in origin. We have constructed a theoretical model that supports nonlinear wavefront propagation in a mechanically-excitable medium. Previously, we have shown that this model captures quantitatively the wavefront speed as it varies with cell cycle number, for reasonable values of the elastic moduli and damping coefficient of the medium. Now we show that our model also captures the displacements of cell nuclei in the embryo in response to the traveling wavefront. This new result further supports that mechanical signaling may play an important role in mediating mitotic wavefronts.

  18. The Object of Activity: Making Sense of the Sense-Maker

    ERIC Educational Resources Information Center

    Kaptelinin, Victor

    2005-01-01

    The concept of "the object of activity" plays a key role in research based on activity theory. However, the usefulness of this concept is somewhat undermined by the fact that a number of problems related to its meaning and its contexts of use remain unsolved. This article is an attempt to address some of these problems. The article focuses on 3…

  19. A New Way of Sensing: Need-Based Activation of Antibiotic Resistance by a Flux-Sensing Mechanism

    PubMed Central

    Fritz, Georg; Dintner, Sebastian; Treichel, Nicole Simone; Radeck, Jara; Gerland, Ulrich; Gebhard, Susanne

    2015-01-01

    ABSTRACT Sensing of and responding to environmental changes are of vital importance for microbial cells. Consequently, bacteria have evolved a plethora of signaling systems that usually sense biochemical cues either via direct ligand binding acting as “concentration sensors” or by responding to downstream effects on bacterial physiology, such as structural damage to the cell. Here, we describe a novel, alternative signaling mechanism that effectively implements a “flux sensor” to regulate antibiotic resistance. It relies on a sensory complex consisting of a histidine kinase and an ABC transporter, in which the transporter fulfills the dual role of both the sensor of the antibiotic and the mediator of resistance against it. Combining systems biological modeling with in vivo experimentation, we show that these systems in fact respond to changes in activity of individual resistance transporters rather than to changes in the antibiotic concentration. Our model shows that the cell thereby adjusts the rate of de novo transporter synthesis to precisely the level needed for protection. Such a flux-sensing mechanism may serve as a cost-efficient produce-to-demand strategy, controlling a widely conserved class of antibiotic resistance systems. PMID:26199330

  20. A tactile vision substitution system for the study of active sensing.

    PubMed

    Hsu, Brian; Hsieh, Cheng-Han; Yu, Sung-Nien; Ahissar, Ehud; Arieli, Amos; Zilbershtain-Kra, Yael

    2013-01-01

    This paper presents a tactile vision substitution system (TVSS) for the study of active sensing. Two algorithms, namely image processing and trajectory tracking, were developed to enhance the capability of conventional TVSS. Image processing techniques were applied to reduce the artifacts and extract important features from the active camera and effectively converted the information into tactile stimuli with much lower resolution. A fixed camera was used to record the movement of the active camera. A trajectory tracking algorithm was developed to analyze the active sensing strategy of the TVSS users to explore the environment. The image processing subsystem showed advantageous improvement in extracting object's features for superior recognition. The trajectory tracking subsystem, on the other hand, enabled accurately locating the portion of the scene pointed by the active camera and providing profound information for the study of active sensing strategy applied by TVSS users.

  1. Young Scientists Explore the Five Senses. Book 4--Intermediate Level. A Good Apple Activity Book.

    ERIC Educational Resources Information Center

    DeBruin, Jerry

    Designed to develop creativity in young learners, this book contains interdisciplinary activities which focus on the theme of the five senses. Activity pages are provided that can serve as front and back covers of a student booklet and the suggested activities can be duplicated for insertion between the covers resulting in a booklet for each…

  2. Quorum sensing activity of Hafnia alvei isolated from packed food.

    PubMed

    Tan, Jia-Yi; Yin, Wai-Fong; Chan, Kok-Gan

    2014-01-01

    Quorum sensing (QS) is a mechanism adopted by bacteria to regulate expression of genes according to population density. N-acylhomoserine lactones (AHLs) are a type of QS signalling molecules commonly found in Gram-negative bacteria which have been reported to play a role in microbial spoilage of foods and pathogenesis. In this study, we isolated an AHL-producing Hafnia alvei strain (FB1) from spherical fish pastes. Analysis via high resolution triple quadrupole liquid chromatography/mass spectrometry (LC/MS) on extracts from the spent supernatant of H. alvei FB1 revealed the existence of two short chain AHLs: N-(3-oxohexanoyl) homoserine lactone (3-oxo-C6-HSL) and N-(3-oxo- octanoyl) homoserine lactone (3-oxo-C8-HSL). To our knowledge, this is the first report of the production of AHLs, especially 3-oxo-C8-HSL, by H. alvei.

  3. Quorum Sensing Activity of Hafnia alvei Isolated from Packed Food

    PubMed Central

    Tan, Jia-Yi; Yin, Wai-Fong; Chan, Kok-Gan

    2014-01-01

    Quorum sensing (QS) is a mechanism adopted by bacteria to regulate expression of genes according to population density. N-acylhomoserine lactones (AHLs) are a type of QS signalling molecules commonly found in Gram-negative bacteria which have been reported to play a role in microbial spoilage of foods and pathogenesis. In this study, we isolated an AHL-producing Hafnia alvei strain (FB1) from spherical fish pastes. Analysis via high resolution triple quadrupole liquid chromatography/mass spectrometry (LC/MS) on extracts from the spent supernatant of H. alvei FB1 revealed the existence of two short chain AHLs: N-(3-oxohexanoyl) homoserine lactone (3-oxo-C6-HSL) and N-(3-oxo- octanoyl) homoserine lactone (3-oxo-C8-HSL). To our knowledge, this is the first report of the production of AHLs, especially 3-oxo-C8-HSL, by H. alvei. PMID:24736131

  4. Quorum sensing activity of Hafnia alvei isolated from packed food.

    PubMed

    Tan, Jia-Yi; Yin, Wai-Fong; Chan, Kok-Gan

    2014-01-01

    Quorum sensing (QS) is a mechanism adopted by bacteria to regulate expression of genes according to population density. N-acylhomoserine lactones (AHLs) are a type of QS signalling molecules commonly found in Gram-negative bacteria which have been reported to play a role in microbial spoilage of foods and pathogenesis. In this study, we isolated an AHL-producing Hafnia alvei strain (FB1) from spherical fish pastes. Analysis via high resolution triple quadrupole liquid chromatography/mass spectrometry (LC/MS) on extracts from the spent supernatant of H. alvei FB1 revealed the existence of two short chain AHLs: N-(3-oxohexanoyl) homoserine lactone (3-oxo-C6-HSL) and N-(3-oxo- octanoyl) homoserine lactone (3-oxo-C8-HSL). To our knowledge, this is the first report of the production of AHLs, especially 3-oxo-C8-HSL, by H. alvei. PMID:24736131

  5. The apparent quorum-sensing inhibitory activity of pyrogallol is a side effect of peroxide production.

    PubMed

    Defoirdt, Tom; Pande, Gde Sasmita Julyantoro; Baruah, Kartik; Bossier, Peter

    2013-06-01

    There currently is more and more interest in the use of natural products, such as tea polyphenols, as therapeutic agents. The polyphenol compound pyrogallol has been reported before to inhibit quorum-sensing-regulated bioluminescence in Vibrio harveyi. Here, we report that the addition of 10 mg · liter(-1) pyrogallol protects both brine shrimp (Artemia franciscana) and giant river prawn (Macrobrachium rosenbergii) larvae from pathogenic Vibrio harveyi, whereas the compound showed relatively low toxicity (therapeutic index of 10). We further demonstrate that the apparent quorum-sensing-disrupting activity is a side effect of the peroxide-producing activity of this compound rather than true quorum-sensing inhibition. Our results emphasize that verification of minor toxic effects by using sensitive methods and the use of appropriate controls are essential when characterizing compounds as being able to disrupt quorum sensing. PMID:23545532

  6. AIS wavefront sensor: a robust optical test of exposure tools using localized wavefront curvature

    NASA Astrophysics Data System (ADS)

    Miyakawa, Ryan; Zhou, Xibin; Goldstein, Michael; Ashworth, Dominic; Cummings, Kevin; Fan, Yu-Jen; Shroff, Yashesh; Denbeaux, Greg; Kandel, Yudhi; Naulleau, Patrick

    2014-04-01

    We present an update of the AIS wavefront sensor, a diagnostic sensor set for insertion in the upgraded 0.5 NA SEMATECH Albany and Berkeley METs. AIS works by using offset monopole illumination to probe localized regions of the test optic pupil. Variations in curvature manifest as focus shifts, which are measured using a photodiode- based grating-on- grating contrast monitor, and the wavefront aberrations are reconstructed using a least-squares approach. We present results from an optical prototype of AIS demonstrating an accuracy of better than λ/30 rms for Zernike polynomials Z4 through Z10. We also discuss integration strategies and requirements as well as specifications on system alignment.

  7. High resolution wavefront measurement of aspheric optics

    NASA Astrophysics Data System (ADS)

    Erichsen, I.; Krey, S.; Heinisch, J.; Ruprecht, A.; Dumitrescu, E.

    2008-08-01

    With the recently emerged large volume production of miniature aspheric lenses for a wide range of applications, a new fast fully automatic high resolution wavefront measurement instrument has been developed. The Shack-Hartmann based system with reproducibility better than 0.05 waves is able to measure highly aspheric optics and allows for real time comparison with design data. Integrated advanced analysis tools such as calculation of Zernike coefficients, 2D-Modulation Transfer Function (MTF), Point Spread Function (PSF), Strehl-Ratio and the measurement of effective focal length (EFL) as well as flange focal length (FFL) allow for the direct verification of lens properties and can be used in a development as well as in a production environment.

  8. Manipulation of wavefront using helical metamaterials.

    PubMed

    Yang, Zhenyu; Wang, Zhaokun; Tao, Huan; Zhao, Ming

    2016-08-01

    Helical metamaterials, a kind of 3-dimensional structure, has relatively strong coupling effect among the helical nano-wires. Therefore, it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. In this paper, using the finite-difference time-domain (FDTD) method, we studied the phase shift properties in the helical metamaterials. It is found that the phase shift occurs for both transmitted and reflected light waves. And the maximum of reflection coefficients can reach over 60%. In addition, the phase shift (φ) is dispersionless in the range of 600 nm to 860 nm, that is, it is only dominated by the initial angle (θ) of the helix. The relationship between them is φ = ± 2θ. Using Jones calculus we give a further explanation for these properties. Finally, by arranging the helixes in an array with a constant phase gradient, the phenomenon of anomalous refraction was also observed in a broad wavelength range.

  9. Telescope Multi-Field Wavefront Control with a Kalman Filter

    NASA Technical Reports Server (NTRS)

    Lou, John Z.; Redding, David; Sigrist, Norbert; Basinger, Scott

    2008-01-01

    An effective multi-field wavefront control (WFC) approach is demonstrated for an actuated, segmented space telescope using wavefront measurements at the exit pupil, and the optical and computational implications of this approach are discussed. The integration of a Kalman Filter as an optical state estimator into the wavefront control process to further improve the robustness of the optical alignment of the telescope will also be discussed. Through a comparison of WFC performances between on-orbit and ground-test optical system configurations, the connection (and a possible disconnection) between WFC and optical system alignment under these circumstances are analyzed. Our MACOS-based computer simulation results will be presented and discussed.

  10. Propagation of aberrated wavefronts using a ray transfer matrix.

    PubMed

    Raasch, Thomas W

    2014-05-01

    A ray transfer matrix is used to calculate the propagation of aberrated wavefronts across a homogeneous refractive index. The wavefront is represented by local surface normals, i.e., by a ray bundle, and the propagation is accomplished by transferring those rays across the space. Wavefront shape is generated from the slopes and positions of the collection of rays. Calculation methods are developed for the paraxial case, for higher-order expansions, and for the exact tangent case. A numerical example is used to compare results between an analytical method and the methods developed here.

  11. Initial Performance of the Keck AO Wavefront Controller System

    SciTech Connect

    Johansson, E M; Acton, D S; An, J R; Avicola, K; Beeman, B V; Brase, J M; Carrano, C J; Gathright, J; Gavel, D T; Hurd, R L; Lai, O; Lupton, W; Macintosh, B A; Max, C E; Olivier, S S; Shelton, J C; Stomski, P J; Tsubota, K; Waltjen, K E; Watson, J A; Wizinowich, P L

    2001-03-01

    The wavefront controller for the Keck Observatory AO system consists of two separate real-time control loops: a tip-tilt control loop to remove tilt from the incoming wavefront, and a deformable mirror control loop to remove higher-order aberrations. In this paper, we describe these control loops and analyze their performance using diagnostic data acquired during the integration and testing of the AO system on the telescope. Disturbance rejection curves for the controllers are calculated from the experimental data and compared to theory. The residual wavefront errors due to control loop bandwidth are also calculated from the data, and possible improvements to the controller performance are discussed.

  12. Sensing network for electromagnetic fields generated by seismic activities

    NASA Astrophysics Data System (ADS)

    Gershenzon, Naum I.; Bambakidis, Gust; Ternovskiy, Igor V.

    2014-06-01

    The sensors network is becoming prolific and play now increasingly more important role in acquiring and processing information. Cyber-Physical Systems are focusing on investigation of integrated systems that includes sensing, networking, and computations. The physics of the seismic measurement and electromagnetic field measurement requires special consideration how to design electromagnetic field measurement networks for both research and detection earthquakes and explosions along with the seismic measurement networks. In addition, the electromagnetic sensor network itself could be designed and deployed, as a research tool with great deal of flexibility, the placement of the measuring nodes must be design based on systematic analysis of the seismic-electromagnetic interaction. In this article, we review the observations of the co-seismic electromagnetic field generated by earthquakes and man-made sources such as vibrations and explosions. The theoretical investigation allows the distribution of sensor nodes to be optimized and could be used to support existing geological networks. The placement of sensor nodes have to be determined based on physics of electromagnetic field distribution above the ground level. The results of theoretical investigations of seismo-electromagnetic phenomena are considered in Section I. First, we compare the relative contribution of various types of mechano-electromagnetic mechanisms and then analyze in detail the calculation of electromagnetic fields generated by piezomagnetic and electrokinetic effects.

  13. Characteristics of active spectral sensor for plant sensing

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Plant stress has been estimated by spectral signature using both passive and active sensors. As optical sensors measure reflected light from a target, changes in illumination conditions critically affect sensor response. Active spectral sensors minimize the illumination effects by producing their ...

  14. A Self-Sensing Active Magnetic Bearing Based on a Direct Current Measurement Approach

    PubMed Central

    Niemann, Andries C.; van Schoor, George; du Rand, Carel P.

    2013-01-01

    Active magnetic bearings (AMBs) have become a key technology in various industrial applications. Self-sensing AMBs provide an integrated sensorless solution for position estimation, consolidating the sensing and actuating functions into a single electromagnetic transducer. The approach aims to reduce possible hardware failure points, production costs, and system complexity. Despite these advantages, self-sensing methods must address various technical challenges to maximize the performance thereof. This paper presents the direct current measurement (DCM) approach for self-sensing AMBs, denoting the direct measurement of the current ripple component. In AMB systems, switching power amplifiers (PAs) modulate the rotor position information onto the current waveform. Demodulation self-sensing techniques then use bandpass and lowpass filters to estimate the rotor position from the voltage and current signals. However, the additional phase-shift introduced by these filters results in lower stability margins. The DCM approach utilizes a novel PA switching method that directly measures the current ripple to obtain duty-cycle invariant position estimates. Demodulation filters are largely excluded to minimize additional phase-shift in the position estimates. Basic functionality and performance of the proposed self-sensing approach are demonstrated via a transient simulation model as well as a high current (10 A) experimental system. A digital implementation of amplitude modulation self-sensing serves as a comparative estimator. PMID:24030681

  15. Head-mounted active noise control system with virtual sensing technique

    NASA Astrophysics Data System (ADS)

    Miyazaki, Nobuhiro; Kajikawa, Yoshinobu

    2015-03-01

    In this paper, we apply a virtual sensing technique to a head-mounted active noise control (ANC) system we have already proposed. The proposed ANC system can reduce narrowband noise while improving the noise reduction ability at the desired locations. A head-mounted ANC system based on an adaptive feedback structure can reduce noise with periodicity or narrowband components. However, since quiet zones are formed only at the locations of error microphones, an adequate noise reduction cannot be achieved at the locations where error microphones cannot be placed such as near the eardrums. A solution to this problem is to apply a virtual sensing technique. A virtual sensing ANC system can achieve higher noise reduction at the desired locations by measuring the system models from physical sensors to virtual sensors, which will be used in the online operation of the virtual sensing ANC algorithm. Hence, we attempt to achieve the maximum noise reduction near the eardrums by applying the virtual sensing technique to the head-mounted ANC system. However, it is impossible to place the microphone near the eardrums. Therefore, the system models from physical sensors to virtual sensors are estimated using the Head And Torso Simulator (HATS) instead of human ears. Some simulation, experimental, and subjective assessment results demonstrate that the head-mounted ANC system with virtual sensing is superior to that without virtual sensing in terms of the noise reduction ability at the desired locations.

  16. A self-sensing active magnetic bearing based on a direct current measurement approach.

    PubMed

    Niemann, Andries C; van Schoor, George; du Rand, Carel P

    2013-09-11

    Active magnetic bearings (AMBs) have become a key technology in various industrial applications. Self-sensing AMBs provide an integrated sensorless solution for position estimation, consolidating the sensing and actuating functions into a single electromagnetic transducer. The approach aims to reduce possible hardware failure points, production costs, and system complexity. Despite these advantages, self-sensing methods must address various technical challenges to maximize the performance thereof. This paper presents the direct current measurement (DCM) approach for self-sensing AMBs, denoting the direct measurement of the current ripple component. In AMB systems, switching power amplifiers (PAs) modulate the rotor position information onto the current waveform. Demodulation self-sensing techniques then use bandpass and lowpass filters to estimate the rotor position from the voltage and current signals. However, the additional phase-shift introduced by these filters results in lower stability margins. The DCM approach utilizes a novel PA switching method that directly measures the current ripple to obtain duty-cycle invariant position estimates. Demodulation filters are largely excluded to minimize additional phase-shift in the position estimates. Basic functionality and performance of the proposed self-sensing approach are demonstrated via a transient simulation model as well as a high current (10 A) experimental system. A digital implementation of amplitude modulation self-sensing serves as a comparative estimator.

  17. Active microwave sensing of the atmosphere, chapter 4

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The use of active microwave systems to study atmospheric phenomena is studied. Atmospheric pollution, weather prediction, climate and weather modification, weather danger and disaster warning, and atmospheric processes and interactions are covered.

  18. Development of a pyramidal wavefront sensor test-bench at INO

    NASA Astrophysics Data System (ADS)

    Turbide, Simon; Wang, Min; Gauvin, Jonny; Martin, Olivier; Savard, Maxime; Bourqui, Pascal; Veran, Jean-Pierre; Deschenes, William; Anctil, Genevieve; Chateauneuf, François

    2013-12-01

    The key technical element of the adaptive optics in astronomy is the wavefront sensing (WFS). One of the advantages of the pyramid wavefront sensor (P-WFS) over the widely used Shack-Hartmann wavefront sensor seems to be the increased sensitivity in closed-loop applications. A high-sensitivity and large dynamic-range WFS, such as P-WFS technology, still needs to be further investigated for proper justification in future Extremely Large Telescopes application. At INO, we have recently carried out the optical design, testing and performance evaluation of a P-WFS bench setup. The optical design of the bench setup mainly consists of the super-LED fiber source, source collimator, spatial light modulator (SLM), relay lenses, tip-tilt mirror, Fourier-transforming lens, and a four-faceted glass pyramid with a large vertex angle as well as pupil re-imaged optics. The phase-only SLM has been introduced in the bench setup to generate atmospheric turbulence with a maximum phase shift of more than 2π at each pixel (256 grey levels). Like a modified Foucault knife-edge test, the refractive pyramid element is used to produce four images of the entrance pupil on a CCD camera. The Fourier-transforming lens, which is used before the pyramid prism, is designed for telecentric output to allow dynamic modulation (rotation of the beam around the pyramid-prism center) from a tip-tilt mirror. Furthermore, a P-WFS diffraction-based model has been developed. This model includes most of the system limitations such as the SLM discrete voltage steps and the CCD pixel pitch. The pyramid effects (edges and tip) are considered as well. The modal wavefront reconstruction algorithm relies on the construction of an interaction matrix (one for each modulation's amplitude). Each column of the interaction matrix represents the combination of the four pupil images for a given wavefront aberration. The nice agreement between the data and the model suggest that the limitation of the system is not the P

  19. Advantages and Limitations in using Active Remote Sensing Technology for Disaster Damage Assessment

    NASA Astrophysics Data System (ADS)

    Tauhidur Rahman, Muhammad

    2013-04-01

    Following any major natural or man-made disaster, rapid monitoring and assessment of infrastructures and environmental damages are essential for successful rescue and relief operations. While pre- and post-disaster data from passive remote sensing imageries have played a major role in assessing damages on a damage/no damage basis for over four decades, latest advances in active remote sensing technologies such as Radar and Lidar are also becoming quite useful. The goal of this paper is to first explain the basic theories and analytical techniques involved in using active remote sensing data for assessing damages following a major natural disaster. It will then discuss some of the advantages and limitations often faced by researchers and disaster management personnel when using data from these sensors. Finally, it will highlight how data from Lidar and other active sensors were used to assess damages from three recent major disasters.

  20. Zinc activates damage-sensing TRPA1 ion channels

    PubMed Central

    Hu, Hongzhen; Bandell, Michael; Petrus, Matt J.; Zhu, Michael X.; Patapoutian, Ardem

    2009-01-01

    Zinc is an essential biological trace element. It is required for the structure or function of over 300 proteins, and is increasingly recognized for its role in cell signaling. However, high concentrations of zinc have cytotoxic effects, and overexposure to zinc can cause pain and inflammation through unknown mechanisms. Here we show that zinc excites nociceptive somatosensory neurons and causes nociception in mice through TRPA1, a cation channel previously shown to mediate the pungency of wasabi and cinnamon through cysteine-modification. Zinc activates TRPA1 through a novel mechanism that requires zinc influx through TRPA1 channels and subsequent activation via specific intracellular cysteine and histidine residues. TRPA1 is highly sensitive to intracellular zinc, as low nanomolar concentrations activate TRPA1 and modulate its sensitivity. These findings identify TRPA1 as a major target for the sensory effects of zinc, and support an emerging role for zinc as a signaling molecule that can modulate sensory transmission. PMID:19202543

  1. Thermal lensing measurement from the coefficient of defocus aberration using Shack-Hartmann wavefront sensor

    NASA Astrophysics Data System (ADS)

    Bell, Teboho; Naidoo, Darryl; Ngcobo, Sandile; Forbes, Andrew

    2016-03-01

    In this paper we experimentally demonstrate the measurement of thermally induced lensing, using a Shack-Hartmann wavefront sensor. We measured the thermally induced lens from the coefficient of defocus aberration using a Shack-Hartmann wavefront sensor (SHWFS). As a calibration technique, we infer the focal length of standard lenses probed by a collimated Gaussian beam of wavelength 633 nm. The technique was applied to an Nd:YAG crystal that is actively pumped by a diode laser operating at 808 nm. The results were compared to the results obtained by changing the properties of the end-pumped solid-state laser resonator operating at 1064 nm, where the length of an unstable plane-parallel laser resonator cavity is varied, and the laser output power was measured.

  2. Wavefront control of the Large Optics Test and Integration Site (LOTIS) 6.5m Collimator

    SciTech Connect

    West, Steven C.; Bailey, Samuel H.; Burge, James H.; Cuerden, Brian; Hagen, Jeff; Martin, Hubert M.; Tuell, Michael T.

    2010-06-20

    The LOTIS Collimator provides scene projection within a 6.5m diameter collimated beam used for optical testing research in air and vacuum. Diffraction-limited performance (0.4 to 5{mu}m wavelength) requires active wavefront control of the alignment and primary mirror shape. A hexapod corrects secondary mirror alignment using measurements from collimated sources directed into the system with nine scanning pentaprisms. The primary mirror shape is controlled with 104 adjustable force actuators based on figure measurements from a center-of-curvature test. A variation of the Hartmann test measures slopes by monitoring the reflections from 36 small mirrors bonded to the optical surface of the primary mirror. The Hartmann source and detector are located at the f/15 Cassegrain focus. Initial operation has demonstrated a closed-loop 110nmrms wavefront error in ambient air over the 6.5mcollimated beam.

  3. Wavefront sensor sampling plane fabricated by maskless grayscale lithography

    NASA Astrophysics Data System (ADS)

    Cirino, G. A.; Amaral, F. T.; Lopera, S. A.; Montagnolil, A. N.; Arruda, A.; Mansano, R. D.; M.-Brahim, T.; Monteiro, D. W. L.

    2014-05-01

    In this work we report the design and characterization of a Shack-Hartmann wavefront sampling plane based on a microlens array (MLA) composed of 12 X 12 hexagonal contiguous diffractive lenslet, with 355 μm pitch, 4.5 mm focal length, and 4.3 X 4.3 mm lateral dimensions. The device was fabricated by maskless grayscale lithography based on Digital Light Projector (DLP) technology. Optical characterization was performed in order to measure wavefront aberrations in Zernike polynomials terms. Intraocular lenses were used as test elements because they yield well-known optical aberrations, such as defocus and spherical aberration. For the wavefront reconstruction, the modal approach was used, in which the first derivatives of Zernike polynomials are used as the set of orthogonal basis functions. The corresponding polynomial coefficients up to the first 10 Zernike terms were obtained and the resulting reconstructed wavefront presents an RMS reconstruction error compliant to most optical systems of interest.

  4. Manipulating acoustic wavefront by inhomogeneous impedance and steerable extraordinary reflection.

    PubMed

    Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

    2013-01-01

    We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717

  5. Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection

    NASA Astrophysics Data System (ADS)

    Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

    2013-08-01

    We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.

  6. Lens testing with a simple wavefront shearing interferometer.

    PubMed

    Nyyssonen, D; Jerke, J M

    1973-09-01

    A lens-testing system using a simple wavefront shearing interferometer is described. This simple cube interferometer has all the interferometric adjustments built in at manufacture. In contrast to most interferometric test systems, the wavefront shearing interferometer is inexpensive, portable, relatively insensitive to vibration, does not need laser illumination, and requires only a minimum of experimental time and operational expertise. Reading of the interferograms and subsequent data reduction require the major effort in testing with the wavefront shearing interferometer. However, with automatic scanning of the interferograms and a high-speed electronic computer to perform the analysis, the data reduction may be completely automated. Operation of the wavefront shearing interferometer is described together with the method of data reduction. Experimental results are also presented.

  7. Wavefront shaping through emulated curved space in waveguide settings

    PubMed Central

    Sheng, Chong; Bekenstein, Rivka; Liu, Hui; Zhu, Shining; Segev, Mordechai

    2016-01-01

    The past decade has witnessed remarkable progress in wavefront shaping, including shaping of beams in free space, of plasmonic wavepackets and of electronic wavefunctions. In all of these, the wavefront shaping was achieved by external means such as masks, gratings and reflection from metasurfaces. Here, we propose wavefront shaping by exploiting general relativity (GR) effects in waveguide settings. We demonstrate beam shaping within dielectric slab samples with predesigned refractive index varying so as to create curved space environment for light. We use this technique to construct very narrow non-diffracting beams and shape-invariant beams accelerating on arbitrary trajectories. Importantly, the beam transformations occur within a mere distance of 40 wavelengths, suggesting that GR can inspire any wavefront shaping in highly tight waveguide settings. In such settings, we demonstrate Einstein's Rings: a phenomenon dating back to 1936. PMID:26899285

  8. Wavefront shaping through emulated curved space in waveguide settings.

    PubMed

    Sheng, Chong; Bekenstein, Rivka; Liu, Hui; Zhu, Shining; Segev, Mordechai

    2016-01-01

    The past decade has witnessed remarkable progress in wavefront shaping, including shaping of beams in free space, of plasmonic wavepackets and of electronic wavefunctions. In all of these, the wavefront shaping was achieved by external means such as masks, gratings and reflection from metasurfaces. Here, we propose wavefront shaping by exploiting general relativity (GR) effects in waveguide settings. We demonstrate beam shaping within dielectric slab samples with predesigned refractive index varying so as to create curved space environment for light. We use this technique to construct very narrow non-diffracting beams and shape-invariant beams accelerating on arbitrary trajectories. Importantly, the beam transformations occur within a mere distance of 40 wavelengths, suggesting that GR can inspire any wavefront shaping in highly tight waveguide settings. In such settings, we demonstrate Einstein's Rings: a phenomenon dating back to 1936. PMID:26899285

  9. Zonal wavefront estimation using an array of hexagonal grating patterns

    SciTech Connect

    Pathak, Biswajit E-mail: brboruah@iitg.ernet.in; Boruah, Bosanta R. E-mail: brboruah@iitg.ernet.in

    2014-10-15

    Accuracy of Shack-Hartmann type wavefront sensors depends on the shape and layout of the lenslet array that samples the incoming wavefront. It has been shown that an array of gratings followed by a focusing lens provide a substitution for the lensslet array. Taking advantage of the computer generated holography technique, any arbitrary diffraction grating aperture shape, size or pattern can be designed with little penalty for complexity. In the present work, such a holographic technique is implemented to design regular hexagonal grating array to have zero dead space between grating patterns, eliminating the possibility of leakage of wavefront during the estimation of the wavefront. Tessellation of regular hexagonal shape, unlike other commonly used shapes, also reduces the estimation error by incorporating more number of neighboring slope values at an equal separation.

  10. Zonal wavefront estimation using an array of hexagonal grating patterns

    NASA Astrophysics Data System (ADS)

    Pathak, Biswajit; Boruah, Bosanta R.

    2014-10-01

    Accuracy of Shack-Hartmann type wavefront sensors depends on the shape and layout of the lenslet array that samples the incoming wavefront. It has been shown that an array of gratings followed by a focusing lens provide a substitution for the lensslet array. Taking advantage of the computer generated holography technique, any arbitrary diffraction grating aperture shape, size or pattern can be designed with little penalty for complexity. In the present work, such a holographic technique is implemented to design regular hexagonal grating array to have zero dead space between grating patterns, eliminating the possibility of leakage of wavefront during the estimation of the wavefront. Tessellation of regular hexagonal shape, unlike other commonly used shapes, also reduces the estimation error by incorporating more number of neighboring slope values at an equal separation.

  11. Adaptive Wavefront Calibration and Control for the Gemini Planet Imager

    SciTech Connect

    Poyneer, L A; Veran, J

    2007-02-02

    Quasi-static errors in the science leg and internal AO flexure will be corrected. Wavefront control will adapt to current atmospheric conditions through Fourier modal gain optimization, or the prediction of atmospheric layers with Kalman filtering.

  12. Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection

    PubMed Central

    Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

    2013-01-01

    We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717

  13. Dynamical quorum sensing and clustering dynamics in a population of spatially distributed active rotators

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu; Maeyama, Satomi

    2013-02-01

    A model of clustering dynamics is proposed for a population of spatially distributed active rotators. A transition from excitable to oscillatory dynamics is induced by the increase of the local density of active rotators. It is interpreted as dynamical quorum sensing. In the oscillation regime, phase waves propagate without decay, which generates an effectively long-range interaction in the clustering dynamics. The clustering process becomes facilitated and only one dominant cluster appears rapidly as a result of the dynamical quorum sensing. An exact localized solution is found to a simplified model equation, and the competitive dynamics between two localized states is studied numerically.

  14. Making Sense of Total VET Activity: An Initial Market Analysis

    ERIC Educational Resources Information Center

    National Centre for Vocational Education Research (NCVER), 2016

    2016-01-01

    Following the successful first national publication of total vocational education and training (VET) activity and presentation of various informative data products, NCVER has continued to undertake further analysis of the submitted data. This paper is the first in a suite of the National Centre for Vocational Education Research (NCVER) authored…

  15. Making Sense of Participation in Cultural Activities for Children

    ERIC Educational Resources Information Center

    Hultgren, Frances; Johansson, Barbro

    2013-01-01

    Introduction: This paper investigates participatory practices in library activities for young children and their care-givers in a specific cultural context. Method: Using an ethnographic approach data were collected through participant observations of songtimes for babies and toddlers, and interviews and group interviews with staff and…

  16. On the haptic nature of the active electric sense of fish.

    PubMed

    Caputi, Angel A; Aguilera, Pedro A; Carolina Pereira, Ana; Rodríguez-Cattáneo, Alejo

    2013-11-01

    Electroreception is a sensory modality present in chondrichthyes, actinopterygii, amphibians, and mammalian monotremes. The study of this non-intuitive sensory modality has provided insights for better understanding of sensory systems in general and inspired the development of innovative artificial devices. Here we review evidence obtained from the analysis of electrosensory images, neurophysiological data from the recording of unitary activity in the electrosensory lobe, and psychophysical data from analysis of novelty responses provoked in well-defined stimulus conditions, which all confirm that active electroreception has a short range, and that the influence of exploratory movements on object identification is strong. In active electric images two components can be identified: a "global" image profile depending on the volume, shape and global impedance of an object and a "texture" component depending on its surface attributes. There is a short range of the active electric sense and the progressive "blurring" of object image with distance. Consequently, the lack of precision regarding object location, considered together, challenge the current view of this sense as serving long range electrolocation and the commonly used metaphor of "electric vision". In fact, the active electric sense shares more commonalities with human active touch than with teleceptive senses as vision or audition. Taking into account that other skin exteroceptors and proprioception may be congruently stimulated during fish exploratory movements we propose that electric, mechanoceptive and proprioceptive sensory modalities found in electric fish could be considered together as a single haptic sensory system. This article is part of a Special Issue entitled Neural Coding 2012.

  17. Bidirectional phase-shifting point diffraction interferometer for wavefronts testing

    NASA Astrophysics Data System (ADS)

    Chen, Sanbin; Zhou, Shouhuan; Tang, Xiaojun; Hong, Zhao

    2015-10-01

    The wavefront of the laser beam was tested by a point-diffraction interferometer with bidirectional phase-shifting. The phase-shifting is obtained by the bidirectional modulated of the electro-optic effect lithium niobate crystal combining with a pinhole filter in half-wave film. The wavefront aberration of incoming beam is directly measured by analyzing five frames phase-shifted interferograms captured by a CCD camera.

  18. Optical differentiation wavefront sensor based on binary pixelated transmission filters

    NASA Astrophysics Data System (ADS)

    Qiao, J.; Travinsky, A.; Ding, G.; Dorrer, C.

    2015-03-01

    High-resolution wavefront sensors are used in a wide range of applications. The Shack-Hartmann sensor is the industry standard and mostly used for this kind of analysis. However, with this sensor the analysis can only be performed for narrowband radiation, the recoverable curvature of the wavefront slopes is also restricted by the size of a single lens in the microlens array. The high-resolution Shack Hartmann wavefront sensor (>128×128) is also significantly expensive. The optical differentiation wavefront sensor, on the other hand, consists of only simple and therefore inexpensive components, offers greater signal to noise ratio, allows for high-resolution analysis of wavefront curvature, and is potentially capable of performing broadband measurements. When a transmission mask with linear attenuation along a spatial direction modulates the far field of an optical wave, the spatial wavefront slope along that direction can be recovered from the fluence in the near field after modulation. With two orthogonal measurements one can recover the complete wavefront of the optical wave. In this study the characteristics of such a wavefront sensor are investigated when the linear transmission modulation is implemented with a pixelated binary filter. Such a filter can be produced as a gray-scale quasi-continuous transmission pattern constructed using arrays of small (e.g., 10-micron) transparent or opaque pixels and therefore it can simply be fabricated by conventional lithography techniques. Simulations demonstrate the potential ability of such a pixelated filter to match the performance of a filter with continuously varying transmission, while offering the advantage of better transmission control and reduction of fabrication costs.

  19. Cumulative Reconstructor: fast wavefront reconstruction algorithm for Extremely Large Telescopes.

    PubMed

    Rosensteiner, Matthias

    2011-10-01

    The Cumulative Reconstructor (CuRe) is a new direct reconstructor for an optical wavefront from Shack-Hartmann wavefront sensor measurements. In this paper, the algorithm is adapted to realistic telescope geometries and the transition from modified Hudgin to Fried geometry is discussed. After a discussion of the noise propagation, we analyze the complexity of the algorithm. Our numerical tests confirm that the algorithm is very fast and accurate and can therefore be used for adaptive optics systems of Extremely Large Telescopes.

  20. Advanced wavefront measurement and analysis of laser system modeling

    SciTech Connect

    Wolfe, C.R.; Auerback, J.M.

    1994-11-15

    High spatial resolution measurements of the reflected or transmitted wavefronts of large aperture optical components used in high peak power laser systems is now possible. These measurements are produced by phase shifting interferometry. The wavefront data is in the form of 3-D phase maps that reconstruct the wavefront shape. The emphasis of this work is on the characterization of wavefront features in the mid-spatial wavelength range (from 0.1 to 10.0 mm) and has been accomplished for the first time. Wavefront structure from optical components with spatial wavelengths in this range are of concern because their effects in high peak power laser systems. At high peak power, this phase modulation can convert to large magnitude intensity modulation by non-linear processes. This can lead to optical damage. We have developed software to input the measured phase map data into beam propagation codes in order to model this conversion process. We are analyzing this data to: (1) Characterize the wavefront structure produced by current optical components, (2) Refine our understanding of laser system performance, (3) Develop a database from which future optical component specifications can be derived.

  1. Active resonant subwavelength grating devices for high speed spectroscopic sensing

    NASA Astrophysics Data System (ADS)

    Gin, A. V.; Kemme, S. A.; Boye, R. R.; Peters, D. W.; Ihlefeld, J. F.; Briggs, R. D.; Wendt, J. R.; Marshall, L. H.; Carter, T. R.; Samora, S.

    2009-02-01

    In this paper, we describe progress towards a multi-color spectrometer and radiometer based upon an active resonant subwavelength grating (RSG). This active RSG component acts as a tunable high-speed optical filter that allows device miniaturization and ruggedization not realizable using current sensors with conventional bulk optics. Furthermore, the geometrical characteristics of the device allow for inherently high speed operation. Because of the small critical dimensions of the RSG devices, the fabrication of these sensors can prove challenging. However, we utilize the state-of-the-art capabilities at Sandia National Laboratories to realize these subwavelength grating devices. This work also leverages previous work on passive RSG devices with greater than 98% efficiency and ~1nm FWHM. Rigorous coupled wave analysis has been utilized to design RSG devices with PLZT, PMN-PT and BaTiO3 electrooptic thin films on sapphire substrates. The simulated interdigitated electrode configuration achieves field strengths around 3×107 V/m. This translates to an increase in the refractive index of 0.05 with a 40V bias potential resulting in a 90% contrast of the modulated optical signal. We have fabricated several active RSG devices on selected electro-optic materials and we discuss the latest experimental results on these devices with variable electrostatic bias and a tunable wavelength source around 1.5μm. Finally, we present the proposed data acquisition hardware and system integration plans.

  2. Does Active Learning through an Antisense Jigsaw Make Sense?

    NASA Astrophysics Data System (ADS)

    Seetharaman, Mahadevan; Musier-Forsyth, Karin

    2003-12-01

    Three journal articles on nucleic acid antisense modification strategies were assigned to 12 students as part of an active learning "jigsaw" exercise for a graduate-level chemistry course on nucleic acids. Each student was required to read one of the three articles. This assignment was preceded by an hour-long lecture on the basic concepts in antisense antigene technology. On the day of the jigsaw, the students with the same article (three groups of four students) discussed their article briefly, and then formed four new groups where no one had read the same article. Each student spent about five minutes teaching his or her article to the other group members, using specific questions provided to guide the discussion. This exercise laid the foundation for bringing the discussion to the entire class, where most of the students actively participated. To test the students' comprehension of the reading materials, a problem set was designed that required not only an understanding of the three articles, but also application of the concepts learned. The effectiveness of this active learning strategy and its applicability to other topics are discussed in this article.

  3. Active sensing associated with spatial learning reveals memory-based attention in an electric fish.

    PubMed

    Jun, James J; Longtin, André; Maler, Leonard

    2016-05-01

    Active sensing behaviors reveal what an animal is attending to and how it changes with learning. Gymnotus sp, a gymnotiform weakly electric fish, generates an electric organ discharge (EOD) as discrete pulses to actively sense its surroundings. We monitored freely behaving gymnotid fish in a large dark "maze" and extracted their trajectories and EOD pulse pattern and rate while they learned to find food with electrically detectable landmarks as cues. After training, they more rapidly found food using shorter, more stereotyped trajectories and spent more time near the food location. We observed three forms of active sensing: sustained high EOD rates per unit distance (sampling density), transient large increases in EOD rate (E-scans) and stereotyped scanning movements (B-scans) were initially strong at landmarks and food, but, after learning, intensified only at the food location. During probe (no food) trials, after learning, the fish's search area and intense active sampling was still centered on the missing food location, but now also increased near landmarks. We hypothesize that active sensing is a behavioral manifestation of attention and essential for spatial learning; the fish use spatial memory of landmarks and path integration to reach the expected food location and confine their attention to this region. PMID:26961107

  4. Characterization of Deep Tunneling Activity through Remote-Sensing Techniques

    SciTech Connect

    R. G. Best, P. J. Etzler, and J. D. Bloom

    1997-10-01

    This work is a case study demonstrating the uses of multispectral and multi-temporal imagery to characterize deep tunneling activity. A drainage tunnel excavation in Quincy, MA is the case locality. Data used are aerial photographs (digitized) and Daedalus 3600 MSS image data that were collected in July and October of 1994. Analysis of the data includes thermal characterization, spectral characterization, multi-temporal analysis, and volume estimation using digital DEM generation. The results demonstrate the type of information that could be generated by multispectral, multi-temporal data if the study locality were a clandestine excavation site with restricted surface access.

  5. Passive and active EO sensing of small surface vessels

    NASA Astrophysics Data System (ADS)

    Steinvall, Ove; Berglund, Folke; Allard, Lars; Öhgren, Johan; Larsson, Hâkan; Amselem, Elias; Gustafsson, Frank; Repasi, Endre; Lutzmann, Peter; Göhler, Benjamin; Hammer, Marcus; McEwen, Kennedy; McEwan, Ken

    2015-10-01

    The detection and classification of small surface targets at long ranges is a growing need for naval security. This paper will present an overview of a measurement campaign which took place in the Baltic Sea in November 2014. The purpose was to test active and passive EO sensors (10 different types) for the detection, tracking and identification of small sea targets. The passive sensors were covering the visual, SWIR, MWIR and LWIR regions. Active sensors operating at 1.5 μm collected data in 1D, 2D and 3D modes. Supplementary sensors included a weather station, a scintillometer, as well as sensors for positioning and attitude determination of the boats. Three boats in the class 4-9 meters were used as targets. After registration of the boats at close range they were sent out to 5-7 km distance from the sensor site. At the different ranges the target boats were directed to have different aspect angles relative to the direction of observation. Staff from IOSB Fraunhofer in Germany and from Selex (through DSTL) in UK took part in the tests beside FOI who was arranging the trials. A summary of the trial and examples of data and imagery will be presented.

  6. Dielectric elastomer vibrissal system for active tactile sensing

    NASA Astrophysics Data System (ADS)

    Conn, Andrew T.; Pearson, Martin J.; Pipe, Anthony G.; Welsby, Jason; Rossiter, Jonathan

    2012-04-01

    Rodents are able to dexterously navigate confined and unlit environments by extracting spatial and textural information with their whiskers (or vibrissae). Vibrissal-based active touch is suited to a variety of applications where vision is occluded, such as search-and-rescue operations in collapsed buildings. In this paper, a compact dielectric elastomer vibrissal system (DEVS) is described that mimics the vibrissal follicle-sinus complex (FSC) found in rodents. Like the vibrissal FSC, the DEVS encapsulates all sensitive mechanoreceptors at the root of a passive whisker within an antagonistic muscular system. Typically, rats actively whisk arrays of macro-vibrissae with amplitudes of up to +/-25°. It is demonstrated that these properties can be replicated by exploiting the characteristic large actuation strains and passive compliance of dielectric elastomers. A prototype DEVS is developed using VHB 4905 and embedded strain gauges bonded to the root of a tapered whisker. The DEVS is demonstrated to produce a maximum rotational output of +/-22.8°. An electro-mechanical model of the DEVS is derived, which incorporates a hyperelastic material model and Euler- Bernoulli beam equations. The model is shown to predict experimental measurements of whisking stroke amplitude and whisker deflection.

  7. Extension of the modal wave-front reconstruction algorithm to non-uniform illumination.

    PubMed

    Ma, Xiaoyu; Mu, Jie; Rao, ChangHui; Yang, Jinsheng; Rao, XueJun; Tian, Yu

    2014-06-30

    Attempts are made to eliminate the effects of non-uniform illumination on the precision of wave-front measurement. To achieve this, the relationship between the wave-front slope at a single sub-aperture and the distributions of the phase and light intensity of the wave-front were first analyzed to obtain the relevant theoretical formulae. Then, based on the principle of modal wave-front reconstruction, the influence of the light intensity distribution on the wave-front slope is introduced into the calculation of the reconstruction matrix. Experiments were conducted to prove that the corrected modal wave-front reconstruction algorithm improved the accuracy of wave-front reconstruction. Moreover, the correction is conducive to high-precision wave-front measurement using a Hartmann wave-front sensor in the presence of non-uniform illumination.

  8. Anti-Quorum Sensing Activity of the Traditional Chinese Herb, Phyllanthus amarus

    PubMed Central

    Priya, Kumutha; Yin, Wai-Fong; Chan, Kok-Gan

    2013-01-01

    The discovery of quorum sensing in Proteobacteria and its function in regulating virulence determinants makes it an attractive alternative towards attenuation of bacterial pathogens. In this study, crude extracts of Phyllanthus amarus Schumach. & Thonn, a traditional Chinese herb, were screened for their anti-quorum sensing properties through a series of bioassays. Only the methanolic extract of P. amarus exhibited anti-quorum sensing activity, whereby it interrupted the ability of Chromobacterium violaceum CVO26 to response towards exogenously supplied N-hexanoylhomoserine lactone and the extract reduced bioluminescence in E. coli [pSB401] and E. coli [pSB1075]. In addition to this, methanolic extract of P. amarus significantly inhibited selected quorum sensing-regulated virulence determinants of Pseudomonas aeruginosa PA01. Increasing concentrations of the methanolic extracts of P. amarus reduced swarming motility, pyocyanin production and P. aeruginosa PA01 lecA∷lux expression. Our data suggest that P. amarus could be useful for attenuating pathogens and hence, more local traditional herbs should be screened for its anti-quorum sensing properties as their active compounds may serve as promising anti-pathogenic drugs. PMID:24169540

  9. Interactive Change Detection Using High Resolution Remote Sensing Images Based on Active Learning with Gaussian Processes

    NASA Astrophysics Data System (ADS)

    Ru, Hui; Yu, Huai; Huang, Pingping; Yang, Wen

    2016-06-01

    Although there have been many studies for change detection, the effective and efficient use of high resolution remote sensing images is still a problem. Conventional supervised methods need lots of annotations to classify the land cover categories and detect their changes. Besides, the training set in supervised methods often has lots of redundant samples without any essential information. In this study, we present a method for interactive change detection using high resolution remote sensing images with active learning to overcome the shortages of existing remote sensing image change detection techniques. In our method, there is no annotation of actual land cover category at the beginning. First, we find a certain number of the most representative objects in unsupervised way. Then, we can detect the change areas from multi-temporal high resolution remote sensing images by active learning with Gaussian processes in an interactive way gradually until the detection results do not change notably. The artificial labelling can be reduced substantially, and a desirable detection result can be obtained in a few iterations. The experiments on Geo-Eye1 and WorldView2 remote sensing images demonstrate the effectiveness and efficiency of our proposed method.

  10. Passive and active EO sensing close to the sea surface

    NASA Astrophysics Data System (ADS)

    Steinvall, Ove; Persson, Rolf; Berglund, Folke; Öhgren, Johan; Gustafsson, Frank

    2014-10-01

    The present paper investigates the use of an eye-safe laser rangefinder at 1.5 μm and TV/IR imaging to obtain information on atmospheric properties at various paths close to the sea surface. On one day active/passive imaging NIR and SWIR systems were also used. The paper will describe the experimental equipment and the results from measurements of atmospheric backscatter as well as TV and IR images of test targets along a 1.8 km path close to the Baltic Sea. The site also contained a weather station and a scintillometer for logging weather and turbulence parameters. Results correlating the lidar attenuation with the imaging performance will be given and compared with models.

  11. Active and Passive Sensing from Geosynchronous and Libration Orbits

    NASA Technical Reports Server (NTRS)

    Schoeberl, Mark; Raymond, Carol; Hildebrand, Peter

    2003-01-01

    The development of the LEO (EOS) missions has led the way to new technologies and new science discoveries. However, LEO measurements alone cannot cost effectively produce high time resolution measurements needed to move the science to the next level. Both GEO and the Lagrange points, L1 and L2, provide vantage points that will allow higher time resolution measurements. GEO is currently being exploited by weather satellites, but the sensors currently operating at GEO do not provide the spatial or spectral resolution needed for atmospheric trace gas, ocean or land surface measurements. It is also may be possible to place active sensors in geostationary orbit. It seems clear, that the next era in earth observation and discovery will be opened by sensor systems operating beyond near earth orbit.

  12. More than Activities: Using a "Sense of Place" to Enrich Student Experience in Adventure Sport

    ERIC Educational Resources Information Center

    Leather, Mark; Nicholls, Fiona

    2016-01-01

    There has been increasing interest in recent years in the significance of a sense of place in the literature of outdoor adventure education. In the UK relationships between outdoor education and the environment still appear largely focused on the science of the natural environment and the activity in question. In this paper, we present empirical…

  13. Active Teaching Strategies for a Sense of Salience: End-of-Life Communication

    ERIC Educational Resources Information Center

    Kopp, Mary L.

    2013-01-01

    This study compared active teaching strategies with passive lecture by evaluating cognitive, affective, and psychomotor learning outcomes, while highlighting end-of-life communication in nursing education. The problem addressed was twofold: First, passive lecture prevents transfer to situational decision-making, or a sense of salience (Benner,…

  14. Photon counting arrays for AO wavefront sensors

    NASA Astrophysics Data System (ADS)

    Vallerga, John; Tremsin, Anton; McPhate, Jason; Mikulec, Bettina; Clark, Allan; Siegmund, Oswald

    2005-08-01

    Future wavefront sensors for AO on large telescopes will require a large number of pixels and must operate at high frame rates. Unfortunately for CCDs, there is a readout noise penalty for operating faster, and this noise can add up rather quickly when considering the number of pixels required for the extended shape of a sodium laser guide star observed with a large telescope. Imaging photon counting detectors have zero readout noise and many pixels, but have suffered in the past with low QE at the longer wavelengths (> 500 nm). Recent developments in GaAs photocathode technology, CMOS ASIC readouts and FPGA processing electronics have resulted in noiseless WFS detector designs that are competitive with silicon array detectors, though at ~ 40% the QE of CCDs. We review noiseless array detectors and compare their centroiding performance with CCDs using the best available characteristics of each. We show that for sub-aperture binning of 6x6 and greater that noiseless detectors have a smaller centroid error at fluences of 60 photons or less, though the specific number is dependent on seeing conditions and the centroid algorithm used. We then present the status of a 256x256 noiseless MCP/Medipix2 hybrid detector being developed for AO.

  15. Manipulation of wavefront using helical metamaterials.

    PubMed

    Yang, Zhenyu; Wang, Zhaokun; Tao, Huan; Zhao, Ming

    2016-08-01

    Helical metamaterials, a kind of 3-dimensional structure, has relatively strong coupling effect among the helical nano-wires. Therefore, it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. In this paper, using the finite-difference time-domain (FDTD) method, we studied the phase shift properties in the helical metamaterials. It is found that the phase shift occurs for both transmitted and reflected light waves. And the maximum of reflection coefficients can reach over 60%. In addition, the phase shift (φ) is dispersionless in the range of 600 nm to 860 nm, that is, it is only dominated by the initial angle (θ) of the helix. The relationship between them is φ = ± 2θ. Using Jones calculus we give a further explanation for these properties. Finally, by arranging the helixes in an array with a constant phase gradient, the phenomenon of anomalous refraction was also observed in a broad wavelength range. PMID:27505790

  16. Electrochemical strategy for sensing DNA methylation and DNA methyltransferase activity.

    PubMed

    Wang, Gang Lin; Zhou, Long Yin; Luo, Hong Qun; Li, Nian Bing

    2013-03-20

    The present work demonstrates a novel signal-off electrochemical method for the determination of DNA methylation and the assay of methyltransferase activity using the electroactive complex [Ru(NH3)6](3+) (RuHex) as a signal transducer. The assay exploits the electrostatic interactions between RuHex and DNA strands. Thiolated single strand DNA1 was firstly self-assembled on a gold electrode via Au-S bonding, followed by hybridization with single strand DNA2 to form double strand DNA containing specific recognition sequence of DNA adenine methylation MTase and methylation-responsive restriction endonuclease Dpn I. The double strand DNA may adsorb lots of electrochemical species ([Ru(NH3)6](3+)) via the electrostatic interaction, thus resulting in a high electrochemical signal. In the presence of DNA adenine methylation methyltransferase and S-adenosyl-l-methionine, the formed double strand DNA was methylated by DNA adenine methylation methyltransferase, then the double strand DNA can be cleaved by methylation-responsive restriction endonuclease Dpn I, leading to the dissociation of a large amount of signaling probes from the electrode. As a result, the adsorption amount of RuHex reduced, resulting in a decrease in electrochemical signal. Thus, a sensitive electrochemical method for detection of DNA methylation is proposed. The proposed method yielded a linear response to concentration of Dam MTase ranging from 0.25 to 10UmL(-1) with a detection limit of 0.18UmL(-1) (S/N=3), which might promise this method as a good candidate for monitoring DNA methylation in the future. PMID:23473252

  17. Comparative study of active and passive sensing with AE and PWAS transducers

    NASA Astrophysics Data System (ADS)

    Yu, Lingyu; Giurgiutiu, Victor; Yu, Jianguo; Ziehl, Paul; Zhao, Liuxian

    2012-04-01

    Monitoring of fatigue cracking in bridges using a combined passive and active scheme has been approached by the authors. Passive Acoustic Emission (AE) monitoring has shown to be able to detect crack growth behavior by picking up the stress waves resulting from the breathing of cracks while active ultrasonic pulsing can quantitatively assess structural integrity by sensing out an interrogating pulse and receive the structural reflections from the discontinuity. In this paper, we present a comparative study of active and passive sensing with two types of transducers: (a) AE transducers, and (b) embeddable piezoelectric wafer active sensors (PWAS). The study was performed experimentally on steel plates. Both pristine and damaged (notched) conditions were considered. For active sensing, pitchcatch configuration was examined in which one transducer was the transmitter and another transducer acted as the receiver. The ping signal was generated by the AE hardware/software package AEwin. For passive sensing, 0.5-mm lead breaks were executed both on top and on the edge of the plate. The comparative nature of the study was achieved by having the AE and PWAS transducers placed on the same location but on the opposite sides of the plate. The paper presents the main findings of this study in terms of (a) signal strength; (b) signal-to-noise (S/N) ratio; (c) waveform clarity; (d) waveform Fourier spectrum contents and bandwidth; (e) capability to detect and localize AE source; (f) capability to detect and localize damage. The paper performs a critical discussion of the two sensing methodologies, conventional AE transducers vs. PWAS transducers.

  18. Active Microwave Remote Sensing Observations of Weddell Sea Ice

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.

    1997-01-01

    Since July 1991, the European Space Agency's ERS-1 and ERS-2 satellites have acquired radar data of the Weddell Sea, Antarctica. The Active Microwave Instrument on board ERS has two modes; SAR and Scatterometer. Two receiving stations enable direct downlink and recording of high bit-rate, high resolution SAR image data of this region. When not in an imaging mode, when direct SAR downlink is not possible, or when a receiving station is inoperable, the latter mode allows normalized radar cross-section data to be acquired. These low bit-rate ERS scatterometer data are tape recorded, downlinked and processed off-line. Recent advances in image generation from Scatterometer backscatter measurements enable complementary medium-scale resolution images to be made during periods when SAR images cannot be acquired. Together, these combined C-band microwave image data have for the first time enabled uninterrupted night and day coverage of the Weddell Sea region at both high (25 m) and medium-scale (-20 km) resolutions. C-band ERS-1 radar data are analyzed in conjunction with field data from two simultaneous field experiments in 1992. Satellite radar signature data are compared with shipborne radar data to extract a regional and seasonal signature database for recognition of ice types in the images. Performance of automated sea-ice tracking algorithms is tested on Antarctic data to evaluate their success. Examples demonstrate that both winter and summer ice can be effectively tracked. The kinematics of the main ice zones within the Weddell Sea are illustrated, together with the complementary time-dependencies in their radar signatures. Time-series of satellite images are used to illustrate the development of the Weddell Sea ice cover from its austral summer minimum (February) to its winter maximum (September). The combination of time-dependent microwave signatures and ice dynamics tracking enable various drift regimes to be defined which relate closely to the circulation of the

  19. Activities of Asian Students and Young Scientists on Photogrammetry and Remote Sensing

    NASA Astrophysics Data System (ADS)

    Miyazaki, H.; Lo, C.-Y.; Cho, K.

    2012-07-01

    This paper reports a history and future prospects of the activities by Asian students and young scientists on photogrammetry and remote sensing. For future growths of academic fields, active communications among students and young scientists are indispensable. In some countries and regions in Asia, local communities are already established by youths and playing important roles of building networks among various schools and institutes. The networks are expected to evolve innovative cooperations after the youths achieve their professions. Although local communities are getting solid growth, Asian youths had had little opportunities to make contacts with youths of other countries and regions. To promote youth activities among Asian regions, in 2007, Asian Association on Remote Sensing (AARS) started a series of programs involving students and young scientists within the annual conferences, the Asian Conference on Remote Sensing (ACRS). The programs have provided opportunities and motivations to create networks among students and young scientists. As a result of the achievements, the number of youth interested and involved in the programs is on growing. In addition, through the events held in Asian region by ISPRS Student Consortium (ISPRSSC) and WG VI/5, the Asian youths have built friendly partnership with ISPRSSC. Currently, many Asian youth are keeping contacts with ACRS friends via internet even when they are away from ACRS. To keep and expand the network, they are planning to establish an Asian youth organization on remote sensing. This paper describes about the proposals and future prospects on the Asian youth organization.

  20. Sensing performance of electrically conductive fabrics and dielectric electro active polymers for parachutes

    NASA Astrophysics Data System (ADS)

    Favini, Eric; Niezrecki, Christopher; Manohar, Sanjeev K.; Willis, David; Chen, Julie; Niemi, Eugene; Desabrais, Kenneth; Charette, Christine

    2011-04-01

    This paper quantifies the sensing capabilities of novel smart materials in an effort to improve the performance, better understand the physics, and enhance the safety of parachutes. Based upon a recent review of actuation technologies for parachute applications, it was surmised that the actuators reviewed could not be used to effectively alter the drag or lift (i.e. geometry, porosity, or air vent openings) of a parachute during flight. However, several materials showed potential for sensing applications within a parachute, specifically electrically conductive fabrics and dielectric electro-active polymers. This paper introduces several new conductive fabrics and provides an evaluation of the sensing performance of these smart materials based upon test results using mechanical testing and digital image correlation for comparison.

  1. Structural sensing of interior sound for active control of noise in structural-acoustic cavities.

    PubMed

    Bagha, Ashok K; Modak, S V

    2015-07-01

    This paper proposes a method for structural sensing of acoustic potential energy for active control of noise in a structural-acoustic cavity. The sensing strategy aims at global control and works with a fewer number of sensors. It is based on the established concept of radiation modes and hence does not add too many states to the order of the system. Acoustic potential energy is sensed using a combination of a Kalman filter and a frequency weighting filter with the structural response measurements as the inputs. The use of Kalman filter also makes the system robust against measurement noise. The formulation of the strategy is presented using finite element models of the system including that of sensors and actuators so that it can be easily applied to practical systems. The sensing strategy is numerically evaluated in the framework of Linear Quadratic Gaussian based feedback control of interior noise in a rectangular box cavity with a flexible plate with single and multiple pairs of piezoelectric sensor-actuator patches when broadband disturbances act on the plate. The performance is compared with an "acoustic filter" that models the complete transfer function from the structure to the acoustic domain. The sensing performance is also compared with a direct estimation strategy.

  2. Beamlet pulse-generation and wavefront-control system

    SciTech Connect

    Van Wonterghem, B.M.; Salmon, J.T.; Wilcox, R.W.

    1996-06-01

    The Beamlet pulse-generation system (or {open_quotes}front end{close_quotes}) refers to the laser hardware that generates the spatially and temporally shaped pulse that is injected into the main laser cavity. All large ICF lasers have pulse-generation systems that typically consist of a narrow-band oscillator, elector-optic modulators for temporal and bandwidth shaping, and one or more preamplifiers. Temporal shaping is used to provide the desired laser output pulse shape and also to compensate for gain saturation effects in the large-aperture amplifiers. Bandwidth is applied to fulfill specific target irradiation requirements and to avoid stimulated Brillouin scattering (SBS) in large-aperture laser components. Usually the sharp edge of the beam`s spatial intensity profile is apodized before injection in the main amplifier beam line. This prevents large-amplitude ripples on the intensity profile. Here the authors briefly review the front-end design and discuss improvements to the oscillator and modulator systems. Their main focus, however, is to describe Beamlet`s novel beam-shaping and wavefront-control systems that have recently been fully activated and tested.

  3. Spatiotemporal analysis of soil moisture in using active and passive remotely sensed data and ground observations

    NASA Astrophysics Data System (ADS)

    Li, H.; Fang, B.; Lakshmi, V.

    2015-12-01

    Abstract: Soil moisture plays a vital role in ecosystem, biological processes, climate, weather and agriculture. The Soil Moisture Active Passive (SMAP) improves data by combining the advantages and avoiding the limitation of passive microwave remote sensing (low resolution), and active microwave (challenge of soil moisture retrieval). This study will advance the knowledge of the application of soil moisture by using the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) data as well as data collected at Walnut Gulch Arizona in August 2015 during SMAPVEX15. Specifically, we will analyze the 5m radar data from Unmanned Airborne Vehicle Synthetic Aperture Radar (UAVSAR) to study spatial variability within the PALS radiometer pixel. SMAPVEX12/15 and SMAP data will also be analyzed to evaluate disaggregation algorithms. The analytical findings will provide valuable information for policy-makers to initiate and adjust protocols and regulations for protecting land resources and improving environmental conditions. Keywords: soil moisture, Remote Sensing (RS), spatial statistic

  4. A discussion of two wavefront aberration correction procedures.

    PubMed

    Steinberg, B D

    1992-10-01

    This review paper discusses the basic properties of two adaptive signal processing procedures for dealing with weak scattering in a phased array transducer system. A fundamental improvement in the lateral resolution of ultrasonic echo scanners will result if the weight vector of a large phased array transducer can be modified to account for distortion in the propagation medium. Lateral resolution in most tissue is limited to a few mm by wavefront-distortion-induced sound-speed variations. One important wavefront-distortion source is scattering from local speed variations within large and reasonably homogeneous tissue beds such as the liver. Scattering disperses some energy from the beam and perturbs the wavefront, thereby distorting the image and limiting the resolution to the scale of the distortion. Often, such scattering is weak, meaning that most of the energy in the beam is unscattered. The total field at the receiving transducer is the vector sum of the unscattered and scattered fields. In weak scattering the unscattered field is dominant and the resultant field can be treated as the unscattered field plus a perturbation. The net effect is primarily a distorted phasefront, while the amplitude or modulus of the wavefront remains reasonably intact. Refraction and strong scattering effect the wavefront more severely and are less responsive to these algorithms.

  5. Mid-Infrared Laser Beam Diagnostic Wavefront Analyzer

    NASA Astrophysics Data System (ADS)

    Goranson, Rex; Blea, Joe; Chipps, Art; Denton, Grant; Houchard, Jeff

    1988-08-01

    The Rockwell Wavefront Analyzer (RWA) is an integrated beam diagnostic tool developed for the US Army, STEWS, WSMR, for the MIRACL device. It accepts a 2.5 cm square nominally collimated DF laser beam input of approximately 5 W power level. The electrical signals are reduced and analyzed by an on-line computer processor. The ultimate outputs are plots including total beam power and angular jitter in the x and y axes, an irradiance map of the beam on a 32 X 32 square grid, and a wavefront map of the beam on the same grid. Wavefront aberration poly-nomial coefficient listings are also generated. The wavefront is obtained from measurements of its local slope in two axes by means of a classical Hartmann test done by scanning the pupil with holes in a rotating drum. Earlier versions of this instrument we called SHAPE, for Scanning Hartmann Analyzer Plate Experiment. This design would be SHAPE IV. A single indium antimonide photopot detector measures the transverse ray aberrations, which are then subjected to elaborate processing to extract the polynomial wavefront coefficients. Another photopot is the jitter sensor. Each photopot measures power to normalize the X and Y signals; these "Z" signals also provide the beam power and local irradiance signals.

  6. Wavefront measurement of plastic lenses for mobile-phone applications

    NASA Astrophysics Data System (ADS)

    Huang, Li-Ting; Cheng, Yuan-Chieh; Wang, Chung-Yen; Wang, Pei-Jen

    2016-08-01

    In camera lenses for mobile-phone applications, all lens elements have been designed with aspheric surfaces because of the requirements in minimal total track length of the lenses. Due to the diffraction-limited optics design with precision assembly procedures, element inspection and lens performance measurement have become cumbersome in the production of mobile-phone cameras. Recently, wavefront measurements based on Shack-Hartmann sensors have been successfully implemented on injection-molded plastic lens with aspheric surfaces. However, the applications of wavefront measurement on small-sized plastic lenses have yet to be studied both theoretically and experimentally. In this paper, both an in-house-built and a commercial wavefront measurement system configured on two optics structures have been investigated with measurement of wavefront aberrations on two lens elements from a mobile-phone camera. First, the wet-cell method has been employed for verifications of aberrations due to residual birefringence in an injection-molded lens. Then, two lens elements of a mobile-phone camera with large positive and negative power have been measured with aberrations expressed in Zernike polynomial to illustrate the effectiveness in wavefront measurement for troubleshooting defects in optical performance.

  7. Genesis of return stroke current evolution at the wavefront

    NASA Astrophysics Data System (ADS)

    Kumar, Udaya; Raysaha, Rosy Balaram

    2013-07-01

    The channel dynamics at the wavefront is complex and is primarily responsible for the evolution of return stroke current. The enhancement of channel conductance at the wavefront is necessary for the evolution of current and hence, return stroke. In this regard several questions arise like: (i) what causes the enhancement of conductance, (ii) as the channel core temperature and electrical conductance are closely related, does one support the other and (iii) is the increase in core temperature on the nascent section of the channel the result of free burning arc of the wavefront just below. The present work investigates on these issues with appropriate transient thermal analysis and a macroscopic physical model for the lightning return stroke. Results clearly indicate that the contribution from the thermal field of the wavefront region to the adjacent nascent channel section is negligible as compared to the field enhancement brought in by the same. In other words, the whole process of return stroke evolution is dependent on the local heat generation at the nascent section caused by the enhancement of electric field due to the arrival of the wavefront.

  8. Aero-optical jitter estimation using higher-order wavefronts

    NASA Astrophysics Data System (ADS)

    Whiteley, Matthew R.; Goorskey, David J.; Drye, Richard

    2013-07-01

    Wavefront measurements from wind tunnel or flight testing of an optical system are affected by jitter sources due to the measurement platform, system vibrations, or aero-mechanical buffeting. Depending on the nature of the testing, the wavefront jitter will be a composite of several effects, one of which is the aero-optical jitter; i.e., the wavefront tilt due to random air density fluctuations. To isolate the aero-optical jitter component from recent testing, we have developed an estimation technique that uses only higher-order wavefront measurements to determine the jitter. By analogy with work done previously with free-stream turbulence, we have developed a minimum mean-square error estimator using higher-order wavefront modes to compute the current-frame tilt components through a linear operation. The estimator is determined from computational fluid dynamics evaluation of aero-optical disturbances, but does not depend on the strength of such disturbances. Applying this technique to turret flight test data, we found aero-optical jitter to be 7.7±0.8 μrad and to scale with (ρ/ρSL)M2 (˜1 μrad in the actual test cases examined). The half-power point of the aero-optical jitter variance was found to be ˜2u∞/Dt and to roll off in temporal frequency with a power law between f and f.

  9. On the haptic nature of the active electric sense of fish.

    PubMed

    Caputi, Angel A; Aguilera, Pedro A; Carolina Pereira, Ana; Rodríguez-Cattáneo, Alejo

    2013-11-01

    Electroreception is a sensory modality present in chondrichthyes, actinopterygii, amphibians, and mammalian monotremes. The study of this non-intuitive sensory modality has provided insights for better understanding of sensory systems in general and inspired the development of innovative artificial devices. Here we review evidence obtained from the analysis of electrosensory images, neurophysiological data from the recording of unitary activity in the electrosensory lobe, and psychophysical data from analysis of novelty responses provoked in well-defined stimulus conditions, which all confirm that active electroreception has a short range, and that the influence of exploratory movements on object identification is strong. In active electric images two components can be identified: a "global" image profile depending on the volume, shape and global impedance of an object and a "texture" component depending on its surface attributes. There is a short range of the active electric sense and the progressive "blurring" of object image with distance. Consequently, the lack of precision regarding object location, considered together, challenge the current view of this sense as serving long range electrolocation and the commonly used metaphor of "electric vision". In fact, the active electric sense shares more commonalities with human active touch than with teleceptive senses as vision or audition. Taking into account that other skin exteroceptors and proprioception may be congruently stimulated during fish exploratory movements we propose that electric, mechanoceptive and proprioceptive sensory modalities found in electric fish could be considered together as a single haptic sensory system. This article is part of a Special Issue entitled Neural Coding 2012. PMID:23727613

  10. Wavefront reconstruction and piston measurement using Ronchi test

    NASA Astrophysics Data System (ADS)

    Penalver, Dayana H.; Granados-Agustin, Fermin; Romero-Antequera, David L.

    2011-10-01

    Ronchi test represents an economical alternative, with ease implementation and uncertainties in the order of wavelength, to measure the piston between the elements of a segmented mirror. The current trend of using non monolithic surfaces as imaging systems in telescopes or adaptive optical systems in medical devices, open the field for the development of new wavefront sensors that would retrieve information allowing an optimal disposition of the segments to form an image with minimum of optical aberration. This paper uses the Ronchi test to reconstruct the wavefront, and measure the piston between two adjacent mirrors. Based on a geometrical relation, we have developed a computer software that determine the distance between the mirrors and the light source using a nonlinear optimization algorithm. In order to achieve this goal, it is necessary to perform a several stages processing to the input images. Finally, the wavefront reconstruction is carried out using a combined nonlinear optimization and least square algorithm.

  11. Reflected wavefront manipulation based on ultrathin planar acoustic metasurfaces

    PubMed Central

    Li, Yong; Liang, Bin; Gu, Zhong-ming; Zou, Xin-ye; Cheng, Jian-chun

    2013-01-01

    The introduction of metasurfaces has renewed the Snell's law and opened up new degrees of freedom to tailor the optical wavefront at will. Here, we theoretically demonstrate that the generalized Snell's law can be achieved for reflected acoustic waves based on ultrathin planar acoustic metasurfaces. The metasurfaces are constructed with eight units of a solid structure to provide discrete phase shifts covering the full 2π span with steps of π/4 by coiling up the space. By careful selection of the phase profiles in the transverse direction of the metasurfaces, some fascinating wavefront engineering phenomena are demonstrated, such as anomalous reflections, conversion of propagating waves into surface waves, planar aberration-free lens and nondiffracting Bessel beam generated by planar acoustic axicon. Our results could open up a new avenue for acoustic wavefront engineering and manipulations. PMID:23986034

  12. Hartmann wavefront sensors and their application at FLASH.

    PubMed

    Keitel, Barbara; Plönjes, Elke; Kreis, Svea; Kuhlmann, Marion; Tiedtke, Kai; Mey, Tobias; Schäfer, Bernd; Mann, Klaus

    2016-01-01

    Different types of Hartmann wavefront sensors are presented which are usable for a variety of applications in the soft X-ray spectral region at FLASH, the free-electron laser (FEL) in Hamburg. As a typical application, online measurements of photon beam parameters during mirror alignment are reported on. A compact Hartmann sensor, operating in the wavelength range from 4 to 38 nm, was used to determine the wavefront quality as well as aberrations of individual FEL pulses during the alignment procedure. Beam characterization and alignment of the focusing optics of the FLASH beamline BL3 were performed with λ(13.5 nm)/116 accuracy for wavefront r.m.s. (w(rms)) repeatability, resulting in a reduction of w(rms) by 33% during alignment. PMID:26698044

  13. Hartmann wavefront sensors and their application at FLASH.

    PubMed

    Keitel, Barbara; Plönjes, Elke; Kreis, Svea; Kuhlmann, Marion; Tiedtke, Kai; Mey, Tobias; Schäfer, Bernd; Mann, Klaus

    2016-01-01

    Different types of Hartmann wavefront sensors are presented which are usable for a variety of applications in the soft X-ray spectral region at FLASH, the free-electron laser (FEL) in Hamburg. As a typical application, online measurements of photon beam parameters during mirror alignment are reported on. A compact Hartmann sensor, operating in the wavelength range from 4 to 38 nm, was used to determine the wavefront quality as well as aberrations of individual FEL pulses during the alignment procedure. Beam characterization and alignment of the focusing optics of the FLASH beamline BL3 were performed with λ(13.5 nm)/116 accuracy for wavefront r.m.s. (w(rms)) repeatability, resulting in a reduction of w(rms) by 33% during alignment.

  14. Accelerated wavefront determination technique for optical imaging through scattering medium

    NASA Astrophysics Data System (ADS)

    He, Hexiang; Wong, Kam Sing

    2016-03-01

    Wavefront shaping applied on scattering light is a promising optical imaging method in biological systems. Normally, optimized modulation can be obtained by a Liquid-Crystal Spatial Light Modulator (LC-SLM) and CCD hardware iteration. Here we introduce an improved method for this optimization process. The core of the proposed method is to firstly detect the disturbed wavefront, and then to calculate the modulation phase pattern by computer simulation. In particular, phase retrieval method together with phase conjugation is most effective. In this way, the LC-SLM based system can complete the wavefront optimization and imaging restoration within several seconds which is two orders of magnitude faster than the conventional technique. The experimental results show good imaging quality and may contribute to real time imaging recovery in scattering medium.

  15. High-contrast imager for complex aperture telescopes (HiCAT): 3. first lab results with wavefront control

    NASA Astrophysics Data System (ADS)

    N'Diaye, Mamadou; Mazoyer, Johan; Choquet, Élodie; Pueyo, Laurent; Perrin, Marshall D.; Egron, Sylvain; Leboulleux, Lucie; Levecq, Olivier; Carlotti, Alexis; Long, Chris A.; Lajoie, Rachel; Soummer, Rémi

    2015-09-01

    HiCAT is a high-contrast imaging testbed designed to provide complete solutions in wavefront sensing, control and starlight suppression with complex aperture telescopes. The pupil geometry of such observatories includes primary mirror segmentation, central obstruction, and spider vanes, which make the direct imaging of habitable worlds very challenging. The testbed alignment was completed in the summer of 2014, exceeding specifications with a total wavefront error of 12nm rms over a 18mm pupil. The installation of two deformable mirrors for wavefront control is to be completed in the winter of 2015. In this communication, we report on the first testbed results using a classical Lyot coronagraph. We also present the coronagraph design for HiCAT geometry, based on our recent development of Apodized Pupil Lyot Coronagraph (APLC) with shaped-pupil type optimizations. These new APLC-type solutions using two-dimensional shaped-pupil apodizer render the system quasi-insensitive to jitter and low-order aberrations, while improving the performance in terms of inner working angle, bandpass and contrast over a classical APLC.

  16. Asphericity analysis using corneal wavefront and topographic meridional fits

    NASA Astrophysics Data System (ADS)

    Arba-Mosquera, Samuel; Merayo-Lloves, Jesús; de Ortueta, Diego

    2010-03-01

    The calculation of corneal asphericity as a 3-D fit renders more accurate results when it is based on the corneal wavefront aberrations rather than on the corneal topography of the principal meridians. A more accurate prediction could be obtained for hyperopic treatments compared to myopic treatments. We evaluate a method to calculate corneal asphericity and asphericity changes after refractive surgery. Sixty eyes of 15 consecutive myopic patients and 15 consecutive hyperopic patients (n=30 each) are retrospectively evaluated. Preoperative and 3-month-postoperative topographic and corneal wavefront analyses are performed using corneal topography. Ablations are performed using a laser with an aberration-free profile. Topographic changes in asphericity and corneal aberrations are evaluated for a 6-mm corneal diameter. The induction of corneal spherical aberrations and asphericity changes correlates with the achieved defocus correction. Preoperatively as well as postoperatively, asphericity calculated from the topography meridians correlates with asphericity calculated from the corneal wavefront in myopic and hyperopic treatments. A stronger correlation between postoperative asphericity and the ideally expected/predicted asphericity is obtained based on aberration-free assumptions calculated from corneal wavefront values rather than from the meridians. In hyperopic treatments, a better correlation can be obtained compared to the correlation in myopic treatments. Corneal asphericity calculated from corneal wavefront aberrations represents a 3-D fit of the corneal surface; asphericity calculated from the main topographic meridians represents a 2-D fit of the principal corneal meridians. Postoperative corneal asphericity can be calculated from corneal wavefront aberrations with higher fidelity than from corneal topography of the principal meridians. Hyperopic treatments show a greater accuracy than myopic treatments.

  17. Reading as Active Sensing: A Computational Model of Gaze Planning in Word Recognition

    PubMed Central

    Ferro, Marcello; Ognibene, Dimitri; Pezzulo, Giovanni; Pirrelli, Vito

    2010-01-01

    We offer a computational model of gaze planning during reading that consists of two main components: a lexical representation network, acquiring lexical representations from input texts (a subset of the Italian CHILDES database), and a gaze planner, designed to recognize written words by mapping strings of characters onto lexical representations. The model implements an active sensing strategy that selects which characters of the input string are to be fixated, depending on the predictions dynamically made by the lexical representation network. We analyze the developmental trajectory of the system in performing the word recognition task as a function of both increasing lexical competence, and correspondingly increasing lexical prediction ability. We conclude by discussing how our approach can be scaled up in the context of an active sensing strategy applied to a robotic setting. PMID:20577589

  18. Reading as active sensing: a computational model of gaze planning in word recognition.

    PubMed

    Ferro, Marcello; Ognibene, Dimitri; Pezzulo, Giovanni; Pirrelli, Vito

    2010-01-01

    WE OFFER A COMPUTATIONAL MODEL OF GAZE PLANNING DURING READING THAT CONSISTS OF TWO MAIN COMPONENTS: a lexical representation network, acquiring lexical representations from input texts (a subset of the Italian CHILDES database), and a gaze planner, designed to recognize written words by mapping strings of characters onto lexical representations. The model implements an active sensing strategy that selects which characters of the input string are to be fixated, depending on the predictions dynamically made by the lexical representation network. We analyze the developmental trajectory of the system in performing the word recognition task as a function of both increasing lexical competence, and correspondingly increasing lexical prediction ability. We conclude by discussing how our approach can be scaled up in the context of an active sensing strategy applied to a robotic setting.

  19. Broadband manipulation of acoustic wavefronts by pentamode metasurface

    NASA Astrophysics Data System (ADS)

    Tian, Ye; Wei, Qi; Cheng, Ying; Xu, Zheng; Liu, Xiaojun

    2015-11-01

    An acoustic metasurface with a sub-wavelength thickness can manipulate acoustic wavefronts freely by the introduction of abrupt phase variation. However, the existence of a narrow bandwidth and a low transmittance limits further applications. Here, we present a broadband and highly transparent acoustic metasurface based on a frequency-independent generalized acoustic Snell's law and pentamode metamaterials. The proposal employs a gradient velocity to redirect refracted waves and pentamode metamaterials to improve impedance matching between the metasurface and the background medium. Excellent wavefront manipulation based on the metasurface is further demonstrated by anomalous refraction, generation of non-diffracting Bessel beam, and sub-wavelength flat focusing.

  20. Broadband manipulation of acoustic wavefronts by pentamode metasurface

    SciTech Connect

    Tian, Ye; Wei, Qi Cheng, Ying; Xu, Zheng; Liu, Xiaojun

    2015-11-30

    An acoustic metasurface with a sub-wavelength thickness can manipulate acoustic wavefronts freely by the introduction of abrupt phase variation. However, the existence of a narrow bandwidth and a low transmittance limits further applications. Here, we present a broadband and highly transparent acoustic metasurface based on a frequency-independent generalized acoustic Snell's law and pentamode metamaterials. The proposal employs a gradient velocity to redirect refracted waves and pentamode metamaterials to improve impedance matching between the metasurface and the background medium. Excellent wavefront manipulation based on the metasurface is further demonstrated by anomalous refraction, generation of non-diffracting Bessel beam, and sub-wavelength flat focusing.

  1. One dimensional wavefront distortion sensor comprising a lens array system

    DOEpatents

    Neal, D.R.; Michie, R.B.

    1996-02-20

    A 1-dimensional sensor for measuring wavefront distortion of a light beam as a function of time and spatial position includes a lens system which incorporates a linear array of lenses, and a detector system which incorporates a linear array of light detectors positioned from the lens system so that light passing through any of the lenses is focused on at least one of the light detectors. The 1-dimensional sensor determines the slope of the wavefront by location of the detectors illuminated by the light. The 1 dimensional sensor has much greater bandwidth that 2 dimensional systems. 8 figs.

  2. One dimensional wavefront distortion sensor comprising a lens array system

    DOEpatents

    Neal, Daniel R.; Michie, Robert B.

    1996-01-01

    A 1-dimensional sensor for measuring wavefront distortion of a light beam as a function of time and spatial position includes a lens system which incorporates a linear array of lenses, and a detector system which incorporates a linear array of light detectors positioned from the lens system so that light passing through any of the lenses is focused on at least one of the light detectors. The 1-dimensional sensor determines the slope of the wavefront by location of the detectors illuminated by the light. The 1 dimensional sensor has much greater bandwidth that 2 dimensional systems.

  3. Generation of atmospheric wavefronts using binary micromirror arrays.

    PubMed

    Anzuola, Esdras; Belmonte, Aniceto

    2016-04-10

    To simulate in the laboratory the influence that a turbulent atmosphere has on light beams, we introduce a practical method for generating atmospheric wavefront distortions that considers digital holographic reconstruction using a programmable binary micromirror array. We analyze the efficiency of the approach for different configurations of the micromirror array and experimentally demonstrate the benchtop technique. Though the mirrors on the digital array can only be positioned in one of two states, we show that the holographic technique can be used to devise a wide variety of atmospheric wavefront aberrations in a controllable and predictable way for a fraction of the cost of phase-only spatial light modulators. PMID:27139872

  4. Adaptive optics in ophthalmology: human eye wavefront generator

    NASA Astrophysics Data System (ADS)

    Galetskiy, Sergey O.; Cherezova, Tatyana Y.; Kudryashov, Alexis V.

    2008-02-01

    We present human eye wavefront generator (HEWG) introduced inside aberrometer for dynamic reproduction of human eye aberrations. It's main element is bimorph deformable mirror and a telescope. Deformable mirror generates human eye aberrations in real time. We have recorded aberrations time traces for plurality of subjects using aberrometer and reproduced them with the help of the generator at 10Hz frequency, that is inherit to human eye aberrations dynamics. Experimental results indicate that HEWG can reproduce dynamics of human eye aberrations with residual error less than λ/10 microns. Such a model can be useful for testing, for example, customized contact lenses or wavefront guided aberrometers.

  5. Measurement of wavefront aberrations of diffractive imaging elements

    NASA Astrophysics Data System (ADS)

    Zajac, Marek; Dubik, Boguslawa

    1998-01-01

    Diffractive optics is more and more widely used nowadays. One of its most important applications is diffractive imaging element (DIE). The DIE can be a lens (Holo-lens, diffractive lens, hybrid lens) or a part of complex imaging system (e.g. an aberration corrector). Apart of such problems occurring when dealing with DIE as its design, manufacture or copying the problem of its control is important. By this we mean the measurement of wavefront generated by DIE, i.e. the evaluation of wavefront aberrations. To this aim we propose two different experimental methods: one of them employs diffraction interferometer, the other one holographic shearing interferometer.

  6. Geographic information systems, remote sensing, and spatial analysis activities in Texas, 2002-07

    USGS Publications Warehouse

    Pearson, D.K.; Gary, R.H.; Wilson, Z.D.

    2007-01-01

    Geographic information system (GIS) technology has become an important tool for scientific investigation, resource management, and environmental planning. A GIS is a computer-aided system capable of collecting, storing, analyzing, and displaying spatially referenced digital data. GIS technology is particularly useful when analyzing a wide variety of spatial data such as with remote sensing and spatial analysis. Remote sensing involves collecting remotely sensed data, such as satellite imagery, aerial photography, or radar images, and analyzing the data to gather information or investigate trends about the environment or the Earth's surface. Spatial analysis combines remotely sensed, thematic, statistical, quantitative, and geographical data through overlay, modeling, and other analytical techniques to investigate specific research questions. It is the combination of data formats and analysis techniques that has made GIS an essential tool in scientific investigations. This document presents information about the technical capabilities and project activities of the U.S. Geological Survey (USGS) Texas Water Science Center (TWSC) GIS Workgroup from 2002 through 2007.

  7. Self-sensing ionic electromechanically active actuator with patterned carbon electrodes

    NASA Astrophysics Data System (ADS)

    Kruusamäe, Karl; Kaasik, Friedrich; Punning, Andres; Aabloo, Alvo

    2013-04-01

    In comparison to other ionic electromechanically active polymers (ionic EAP), carbon-polymer composite (CPC) actuators are considered especially attractive due to possibility of producing completely metal-free devices. However, mechanical response of ionic EAP-s is, in addition to voltage and frequency, dependent on environmental variables such as humidity and temperature. Therefore, similarly to other EAPs, one of the major challenges lies in achieving controlled actuation of the CPC sample. Due to their size and added complexity, external feedback devices (e.g. laser displacement sensors and video cameras) tend to inhibit the application of micro-scale actuators. Hence, self-sensing EAP actuators - capable for simultaneous actuation and sensing - are often desired. A thin polyvinylidene fluoride-cohexafluoropropylene film with ionic liquid (EMIMBF4) was prepared and masked coincidently on opposite surfaces prior to spray painting carbide-derived carbon electrodes. The purpose of masking was to create different electrically insulated electrodes on the same surface of polymer in order to achieve separate sections for actuator and sensor on one piece of CPC material. Solution of electrode paint consisting of carbide-derived carbon, EMIMBF4 and dimethylacetamide was applied to the polymer film. After removing the masking tape, a completely metal-free CPC actuator with sophisticated electrode geometry was achieved to foster simultaneous sensing and actuation, i.e. self-sensing carbon-polymer actuator was created.

  8. A structural perspective on the mechanisms of quorum sensing activation in bacteria.

    PubMed

    Lixa, Carolina; Mujo, Amanda; Anobom, Cristiane D; Pinheiro, Anderson S

    2015-01-01

    Bacteria are able to synchronize the population behavior in order to regulate gene expression through a cell-to-cell communication mechanism called quorum sensing. This phenomenon involves the production, detection and the response to extracellular signaling molecules named autoinducers, which directly or indirectly regulate gene expression in a cell density-dependent manner. Quorum sensing may control a wide range of biological processes in bacteria, such as bioluminescence, virulence factor production, biofilm formation and antibiotic resistance. The autoinducers are recognized by specific receptors that can either be membrane-bound histidine kinase receptors, which work by activating cognate cytoplasmic response regulators, or cytoplasmic receptors acting as transcription factors. In this review, we focused on the cytosolic quorum sensing regulators whose three-dimensional structures helped elucidate their mechanisms of action. Structural studies of quorum sensing receptors may enable the rational design of inhibitor molecules. Ultimately, this approach may represent an effective alternative to treat infections where classical antimicrobial therapy fails to overcome the microorganism virulence.

  9. Crack identification for reinforced concrete using PZT based smart rebar active sensing diagnostic network

    NASA Astrophysics Data System (ADS)

    Song, N. N.; Wu, F.

    2016-04-01

    An active sensing diagnostic system using PZT based smart rebar for SHM of RC structure has been currently under investigation. Previous test results showed that the system could detect the de-bond of concrete from reinforcement, and the diagnostic signals were increased exponentially with the de-bonding size. Previous study also showed that the smart rebar could function well like regular reinforcement to undertake tension stresses. In this study, a smart rebar network has been used to detect the crack damage of concrete based on guided waves. Experimental test has been carried out for the study. In the test, concrete beams with 2 reinforcements have been built. 8 sets of PZT elements were mounted onto the reinforcement bars in an optimized way to form an active sensing diagnostic system. A 90 kHz 5-cycle Hanning-windowed tone burst was used as input. Multiple cracks have been generated on the concrete structures. Through the guided bulk waves propagating in the structures from actuators and sensors mounted from different bars, crack damage could be detected clearly. Cases for both single and multiple cracks were tested. Different crack depths from the surface and different crack numbers have been studied. Test result shows that the amplitude of sensor output signals is deceased linearly with a propagating crack, and is decreased exponentially with increased crack numbers. From the study, the active sensing diagnostic system using PZT based smart rebar network shows a promising way to provide concrete crack damage information through the "talk" among sensors.

  10. Development of an integrated software solution for piezoelectric active-sensing in structural health monitoring

    NASA Astrophysics Data System (ADS)

    Jacobs, Laura D.; Park, Gyuhae; Farrar, Charles R.

    2007-04-01

    In this study, a novel approach of integrating data interrogation algorithms of active sensing methods for structural health monitoring (SHM) applications, including Lamb wave propagation, impedance method, and sensor-diagnostics, is presented. Contrary to most active-sensing SHM techniques, which utilize only a single signal processing method for damage identification, a suite of signal processing algorithms are employed and grouped into one package to improve the damage detection capability. A MatLab-based user interface called H.O.P.S. (Health Of Plate Structures) was created, which allows the analyst to configure the data acquisition system and display the results from each damage identification algorithm for side-by-side comparison. This side-by-side comparison of results simplifies the task of identifying the relative effectiveness and sensitivity of each algorithm. By grouping a suite of algorithms into one package, this study contributes to and enhances the visibility and interpretation of the active-sensing methods related to damage identification in a structure.

  11. Mini Review of Phytochemicals and Plant Taxa with Activity as Microbial Biofilm and Quorum Sensing Inhibitors.

    PubMed

    Ta, Chieu Anh Kim; Arnason, John Thor

    2015-01-01

    Microbial biofilms readily form on many surfaces in nature including plant surfaces. In order to coordinate the formation of these biofilms, microorganisms use a cell-to-cell communication system called quorum sensing (QS). As formation of biofilms on vascular plants may not be advantageous to the hosts, plants have developed inhibitors to interfere with these processes. In this mini review, research papers published on plant-derived molecules that have microbial biofilm or quorum sensing inhibition are reviewed with the objectives of determining the biosynthetic classes of active compounds, their biological activity in assays, and their families of occurrence and range. The main findings are the identification of plant phenolics, including benzoates, phenyl propanoids, stilbenes, flavonoids, gallotannins, proanthocyanidins and coumarins as important inhibitors with both activities. Some terpenes including monoterpenes, sesquiterpenes, diterpenes and triterpenes also have anti-QS and anti-biofilm activities. Relatively few alkaloids were reported. Quinones and organosulfur compounds, especially from garlic, were also active. A common feature is the polar nature of these compounds. Phytochemicals with these activities are widespread in Angiosperms in temperate and tropical regions, but gymnosperms, bryophytes and pteridophytes were not represented. PMID:26712734

  12. Personalized foot orthoses with embedded temperature sensing: Proof of concept and relationship with activity.

    PubMed

    Telfer, Scott; Munguia, Javier; Pallari, Jari; Dalgarno, Kenneth; Steultjens, Martijn; Woodburn, James

    2014-01-01

    Plantar foot surface temperature has been identified as a clinically relevant physiological variable. Embedding sensors in foot orthoses (FOs) may allow long term monitoring of these temperatures, with compliance via the detection of periods of activity being a potential clinical utilization. This study aimed to test novel designs for FOs with embedded sensing that were produced via additive manufacturing and determine if foot temperature measurements could be used to detect periods of increased activity. FOs with embedded temperature sensors were developed and tested in 10 healthy participants over four day wear periods. Activity monitoring was used to estimate energy expenditure during testing. A threshold-based algorithm was developed to identify time periods of high activity from foot temperature data. Group differences in estimated energy expenditure between time periods below and above the threshold were significant in both the training and validation sets (p<0.001). Significant differences were also seen at individual participant level (p<0.001 in all cases). These results demonstrate the feasibility of using FOs with embedded sensing to monitor plantar surface foot temperatures during normal daily activities and for extended periods and show that periods of increased activity can be identified using foot temperature data. PMID:23981438

  13. Mini Review of Phytochemicals and Plant Taxa with Activity as Microbial Biofilm and Quorum Sensing Inhibitors.

    PubMed

    Ta, Chieu Anh Kim; Arnason, John Thor

    2015-12-26

    Microbial biofilms readily form on many surfaces in nature including plant surfaces. In order to coordinate the formation of these biofilms, microorganisms use a cell-to-cell communication system called quorum sensing (QS). As formation of biofilms on vascular plants may not be advantageous to the hosts, plants have developed inhibitors to interfere with these processes. In this mini review, research papers published on plant-derived molecules that have microbial biofilm or quorum sensing inhibition are reviewed with the objectives of determining the biosynthetic classes of active compounds, their biological activity in assays, and their families of occurrence and range. The main findings are the identification of plant phenolics, including benzoates, phenyl propanoids, stilbenes, flavonoids, gallotannins, proanthocyanidins and coumarins as important inhibitors with both activities. Some terpenes including monoterpenes, sesquiterpenes, diterpenes and triterpenes also have anti-QS and anti-biofilm activities. Relatively few alkaloids were reported. Quinones and organosulfur compounds, especially from garlic, were also active. A common feature is the polar nature of these compounds. Phytochemicals with these activities are widespread in Angiosperms in temperate and tropical regions, but gymnosperms, bryophytes and pteridophytes were not represented.

  14. Synthesis and quorum sensing inhibitory activity of key phenolic compounds of ginger and their derivatives.

    PubMed

    Kumar, N Vijendra; Murthy, Pushpa S; Manjunatha, J R; Bettadaiah, B K

    2014-09-15

    Phenolic components of ginger (Zingiber officinale Roscoe) viz. [6]-gingerol, [6]-shogaol and zingerone exhibited quorum sensing inhibitory activity (QSI) against Chromobacterium violaceum and Pseudomonas aeruginosa. The inhibitory activity of all the compounds was studied by zone inhibition, pyocyanin, and violacein assay. All the compounds displayed good inhibition at 500ppm. [6]-Azashogaol, a new derivative of [6]-shogaol has been synthesized by Beckmann rearrangement of its oxime in the presence of ZnCl2. The structure elucidation of this new derivative was carried out by 1D ((1)H NMR and (13)C NMR) and 2D-NMR (COSY, HSQC and NOESY) spectral studies. This compound showed good QSI activity against P. aeruginosa. An isoxazoline derivative of [6]-gingerol was prepared and it exhibited good QSI activity. Present study illustrated that, the phenolic compounds of ginger and their derivatives form a class of compounds with promising QSI activity. PMID:24767081

  15. Quorum sensing activity of Aeromonas caviae strain YL12, a bacterium isolated from compost.

    PubMed

    Lim, Yan-Lue; Ee, Robson; Yin, Wai-Fong; Chan, Kok-Gan

    2014-04-22

    Quorum sensing is a well-studied cell-to-cell communication method that involves a cell-density dependent regulation of genes expression mediated by signalling molecules. In this study, a bacterium isolated from a plant material compost pile was found to possess quorum sensing activity based on bioassay screening. Isolate YL12 was identified using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry and molecular typing using rpoD gene which identified the isolate as Aeromonas caviae. High resolution tandem mass spectrometry was subsequently employed to identify the N-acyl homoserine lactone profile of Aeromonas caviae YL12 and confirmed that this isolate produced two short chain N-acyl homoserine lactones, namely C4-HSL and C6, and the production was observed to be cell density-dependent. Using the thin layer chromatography (TLC) bioassay, both AHLs were found to activate C. violaceum CV026, whereas only C6-HSL was revealed to induce bioluminescence expression of E. coli [pSB401]. The data presented in this study will be the leading steps in understanding the role of quorum sensing in Aeromonas caviae strain YL12.

  16. Geographic information systems, remote sensing, and spatial analysis activities in Texas, 2008-09

    USGS Publications Warehouse

    ,

    2009-01-01

    Geographic information system (GIS) technology has become an important tool for scientific investigation, resource management, and environmental planning. A GIS is a computer-aided system capable of collecting, storing, analyzing, and displaying spatially referenced digital data. GIS technology is useful for analyzing a wide variety of spatial data. Remote sensing involves collecting remotely sensed data, such as satellite imagery, aerial photography, or radar images, and analyzing the data to gather information or investigate trends about the environment or the Earth's surface. Spatial analysis combines remotely sensed, thematic, statistical, quantitative, and geographical data through overlay, modeling, and other analytical techniques to investigate specific research questions. It is the combination of data formats and analysis techniques that has made GIS an essential tool in scientific investigations. This fact sheet presents information about the technical capabilities and project activities of the U.S. Geological Survey (USGS) Texas Water Science Center (TWSC) GIS Workgroup during 2008 and 2009. After a summary of GIS Workgroup capabilities, brief descriptions of activities by project at the local and national levels are presented. Projects are grouped by the fiscal year (October-September 2008 or 2009) the project ends and include overviews, project images, and Internet links to additional project information and related publications or articles.

  17. Volcanology 2020: How will thermal remote sensing of volcanic surface activity evolve over the next decade?

    NASA Astrophysics Data System (ADS)

    Ramsey, Michael S.; Harris, Andrew J. L.

    2013-01-01

    Volcanological remote sensing spans numerous techniques, wavelength regions, data collection strategies, targets, and applications. Attempting to foresee and predict the growth vectors in this broad and rapidly developing field is therefore exceedingly difficult. However, we attempted to make such predictions at both the American Geophysical Union (AGU) meeting session entitled Volcanology 2010: How will the science and practice of volcanology change in the coming decade? held in December 2000 and the follow-up session 10 years later, Looking backward and forward: Volcanology in 2010 and 2020. In this summary paper, we assess how well we did with our predictions for specific facets of volcano remote sensing in 2000 the advances made over the most recent decade, and attempt a new look ahead to the next decade. In completing this review, we only consider the subset of the field focused on thermal infrared remote sensing of surface activity using ground-based and space-based technology and the subsequent research results. This review keeps to the original scope of both AGU presentations, and therefore does not address the entire field of volcanological remote sensing, which uses technologies in other wavelength regions (e.g., ultraviolet, radar, etc.) or the study of volcanic processes other than the those associated with surface (mostly effusive) activity. Therefore we do not consider remote sensing of ash/gas plumes, for example. In 2000, we had looked forward to a "golden age" in volcanological remote sensing, with a variety of new orbital missions both planned and recently launched. In addition, exciting field-based sensors such as hand-held thermal cameras were also becoming available and being quickly adopted by volcanologists for both monitoring and research applications. All of our predictions in 2000 came true, but at a pace far quicker than we predicted. Relative to the 2000-2010 timeframe, the coming decade will see far fewer new orbital instruments with

  18. Induced Voltage Linear Extraction Method Using an Active Kelvin Bridge for Disturbing Force Self-Sensing

    PubMed Central

    Yang, Yuanyuan; Wang, Lei; Tan, Jiubin; Zhao, Bo

    2016-01-01

    This paper presents an induced voltage linear extraction method for disturbing force self-sensing in the application of giant magnetostrictive actuators (GMAs). In this method, a Kelvin bridge combined with an active device is constructed instead of a conventional Wheatstone bridge for extraction of the induced voltage, and an additional GMA is adopted as a reference actuator in the self-sensing circuit in order to balance the circuit bridge. The linear fitting of the measurement data is done according to the linear relationship between the disturbing forces and the integral of the induced voltage. The experimental results confirm the good performance of the proposed method, and the self-sensitivity of the disturbing forces is better than 2.0 (mV·s)/N. PMID:27213399

  19. Validity of PALMS GPS Scoring of Active and Passive Travel Compared to SenseCam

    PubMed Central

    Carlson, Jordan A.; Jankowska, Marta M.; Meseck, Kristin; Godbole, Suneeta; Natarajan, Loki; Raab, Fredric; Demchak, Barry; Patrick, Kevin; Kerr, Jacqueline

    2014-01-01

    Purpose To assess validity of the Personal Activity Location Measurement System (PALMS) for deriving time spent walking/running, bicycling, and in vehicle, using SenseCam as the comparison. Methods 40 adult cyclists wore a Qstarz BT-Q1000XT GPS data logger and SenseCam (camera worn around neck capturing multiple images every minute) for a mean of 4 days. PALMS used distance and speed between GPS points to classify whether each minute was part of a trip (yes/no), and if so, the trip mode (walking/running, bicycling, in vehicle). SenseCam images were annotated to create the same classifications (i.e., trip yes/no and mode). 2×2 contingency tables and confusion matrices were calculated at the minute-level for PALMS vs. SenseCam classifications. Mixed-effects linear regression models estimated agreement (mean differences and intraclass correlations [ICCs]) between PALMS and SenseCam with regards to minutes/day in each mode. Results Minute-level sensitivity, specificity, and negative predictive value were ≥88%, and positive predictive value was ≥75% for non mode-specific trip detection. 72–80% of outdoor walking/running minutes, 73% of bicycling minutes, and 74–76% of in-vehicle minutes were correctly classified by PALMS. For minutes/day, PALMS had a mean bias (i.e., amount of over or under estimation) of 2.4–3.1 minutes (11–15%) for walking/running, 2.3–2.9 minutes (7–9%) for bicycling, and 4.3–5 minutes (15–17%) for vehicle time. ICCs were ≥.80 for all modes. Conclusions PALMS has validity for processing GPS data to objectively measure time walking/running, bicycling, and in vehicle in population studies. Assessing travel patterns is one of many valuable applications of GPS in physical activity research that can improve our understanding of the determinants and health outcomes of active transportation as well as its impact on physical activity. PMID:25010407

  20. Quorum Sensing Inhibition and Structure-Activity Relationships of β-Keto Esters.

    PubMed

    Forschner-Dancause, Stephanie; Poulin, Emily; Meschwitz, Susan

    2016-07-25

    Traditional therapeutics to treat bacterial infections have given rise to multi-drug resistant pathogens, which pose a major threat to human and animal health. In several pathogens, quorum sensing (QS)-a cell-cell communication system in bacteria-controls the expression of genes responsible for pathogenesis, thus representing a novel target in the fight against bacterial infections. Based on the structure of the autoinducers responsible for QS activity and other QS inhibitors, we hypothesize that β-keto esters with aryl functionality could possess anti-QS activity. A panel of nineteen β-keto ester analogs was tested for the inhibition of bioluminescence (a QS-controlled phenotype) in the marine pathogen Vibrio harveyi. Initial screening demonstrated the need of a phenyl ring at the C-3 position for antagonistic activity. Further additions to the phenyl ring with 4-substituted halo groups or a 3- or 4-substituted methoxy group resulted in the most active compounds with IC50 values ranging from 23 µM to 53 µM. The compounds additionally inhibit green fluorescent protein production by E. coli JB525. Evidence is presented that aryl β-keto esters may act as antagonists of bacterial quorum sensing by competing with N-acyl homoserine lactones for receptor binding. Expansion of the β-keto ester panel will enable us to obtain more insight into the structure-activity relationships needed to allow for the development of novel anti-virulence agents.

  1. Quorum Sensing Inhibition and Structure-Activity Relationships of β-Keto Esters.

    PubMed

    Forschner-Dancause, Stephanie; Poulin, Emily; Meschwitz, Susan

    2016-01-01

    Traditional therapeutics to treat bacterial infections have given rise to multi-drug resistant pathogens, which pose a major threat to human and animal health. In several pathogens, quorum sensing (QS)-a cell-cell communication system in bacteria-controls the expression of genes responsible for pathogenesis, thus representing a novel target in the fight against bacterial infections. Based on the structure of the autoinducers responsible for QS activity and other QS inhibitors, we hypothesize that β-keto esters with aryl functionality could possess anti-QS activity. A panel of nineteen β-keto ester analogs was tested for the inhibition of bioluminescence (a QS-controlled phenotype) in the marine pathogen Vibrio harveyi. Initial screening demonstrated the need of a phenyl ring at the C-3 position for antagonistic activity. Further additions to the phenyl ring with 4-substituted halo groups or a 3- or 4-substituted methoxy group resulted in the most active compounds with IC50 values ranging from 23 µM to 53 µM. The compounds additionally inhibit green fluorescent protein production by E. coli JB525. Evidence is presented that aryl β-keto esters may act as antagonists of bacterial quorum sensing by competing with N-acyl homoserine lactones for receptor binding. Expansion of the β-keto ester panel will enable us to obtain more insight into the structure-activity relationships needed to allow for the development of novel anti-virulence agents. PMID:27463706

  2. Device for wavefront correction in an ultra high power laser

    DOEpatents

    Ault, Earl R.; Comaskey, Brian J.; Kuklo, Thomas C.

    2002-01-01

    A system for wavefront correction in an ultra high power laser. As the laser medium flows past the optical excitation source and the fluid warms its index of refraction changes creating an optical wedge. A system is provided for correcting the thermally induced optical phase errors.

  3. Dispersionless Manipulation of Reflected Acoustic Wavefront by Subwavelength Corrugated Surface

    PubMed Central

    Zhu, Yi-Fan; Zou, Xin-Ye; Li, Rui-Qi; Jiang, Xue; Tu, Juan; Liang, Bin; Cheng, Jian-Chun

    2015-01-01

    Free controls of optic/acoustic waves for bending, focusing or steering the energy of wavefronts are highly desirable in many practical scenarios. However, the dispersive nature of the existing metamaterials/metasurfaces for wavefront manipulation necessarily results in limited bandwidth. Here, we propose the concept of dispersionless wavefront manipulation and report a theoretical, numerical and experimental work on the design of a reflective surface capable of controlling the acoustic wavefront arbitrarily without bandwidth limitation. Analytical analysis predicts the possibility to completely eliminate the frequency dependence with a specific gradient surface which can be implemented by designing a subwavelength corrugated surface. Experimental and numerical results, well consistent with the theoretical predictions, have validated the proposed scheme by demonstrating a distinct phenomenon of extraordinary acoustic reflection within an ultra-broad band. For acquiring a deeper insight into the underlying physics, a simple physical model is developed which helps to interpret this extraordinary phenomenon and predict the upper cutoff frequency precisely. Generations of planar focusing and non-diffractive beam have also been exemplified. With the dispersionless wave-steering capability and deep discrete resolution, our designed structure may open new avenue to fully steer classical waves and offer design possibilities for broadband optical/acoustical devices. PMID:26077772

  4. Dispersionless Manipulation of Reflected Acoustic Wavefront by Subwavelength Corrugated Surface.

    PubMed

    Zhu, Yi-Fan; Zou, Xin-Ye; Li, Rui-Qi; Jiang, Xue; Tu, Juan; Liang, Bin; Cheng, Jian-Chun

    2015-01-01

    Free controls of optic/acoustic waves for bending, focusing or steering the energy of wavefronts are highly desirable in many practical scenarios. However, the dispersive nature of the existing metamaterials/metasurfaces for wavefront manipulation necessarily results in limited bandwidth. Here, we propose the concept of dispersionless wavefront manipulation and report a theoretical, numerical and experimental work on the design of a reflective surface capable of controlling the acoustic wavefront arbitrarily without bandwidth limitation. Analytical analysis predicts the possibility to completely eliminate the frequency dependence with a specific gradient surface which can be implemented by designing a subwavelength corrugated surface. Experimental and numerical results, well consistent with the theoretical predictions, have validated the proposed scheme by demonstrating a distinct phenomenon of extraordinary acoustic reflection within an ultra-broad band. For acquiring a deeper insight into the underlying physics, a simple physical model is developed which helps to interpret this extraordinary phenomenon and predict the upper cutoff frequency precisely. Generations of planar focusing and non-diffractive beam have also been exemplified. With the dispersionless wave-steering capability and deep discrete resolution, our designed structure may open new avenue to fully steer classical waves and offer design possibilities for broadband optical/acoustical devices. PMID:26077772

  5. Dispersionless Manipulation of Reflected Acoustic Wavefront by Subwavelength Corrugated Surface

    NASA Astrophysics Data System (ADS)

    Zhu, Yi-Fan; Zou, Xin-Ye; Li, Rui-Qi; Jiang, Xue; Tu, Juan; Liang, Bin; Cheng, Jian-Chun

    2015-06-01

    Free controls of optic/acoustic waves for bending, focusing or steering the energy of wavefronts are highly desirable in many practical scenarios. However, the dispersive nature of the existing metamaterials/metasurfaces for wavefront manipulation necessarily results in limited bandwidth. Here, we propose the concept of dispersionless wavefront manipulation and report a theoretical, numerical and experimental work on the design of a reflective surface capable of controlling the acoustic wavefront arbitrarily without bandwidth limitation. Analytical analysis predicts the possibility to completely eliminate the frequency dependence with a specific gradient surface which can be implemented by designing a subwavelength corrugated surface. Experimental and numerical results, well consistent with the theoretical predictions, have validated the proposed scheme by demonstrating a distinct phenomenon of extraordinary acoustic reflection within an ultra-broad band. For acquiring a deeper insight into the underlying physics, a simple physical model is developed which helps to interpret this extraordinary phenomenon and predict the upper cutoff frequency precisely. Generations of planar focusing and non-diffractive beam have also been exemplified. With the dispersionless wave-steering capability and deep discrete resolution, our designed structure may open new avenue to fully steer classical waves and offer design possibilities for broadband optical/acoustical devices.

  6. Wavefront Derived Refraction and Full Eye Biometry in Pseudophakic Eyes

    PubMed Central

    Mao, Xinjie; Banta, James T.; Ke, Bilian; Jiang, Hong; He, Jichang; Liu, Che; Wang, Jianhua

    2016-01-01

    Purpose To assess wavefront derived refraction and full eye biometry including ciliary muscle dimension and full eye axial geometry in pseudophakic eyes using spectral domain OCT equipped with a Shack-Hartmann wavefront sensor. Methods Twenty-eight adult subjects (32 pseudophakic eyes) having recently undergone cataract surgery were enrolled in this study. A custom system combining two optical coherence tomography systems with a Shack-Hartmann wavefront sensor was constructed to image and monitor changes in whole eye biometry, the ciliary muscle and ocular aberration in the pseudophakic eye. A Badal optical channel and a visual target aligning with the wavefront sensor were incorporated into the system for measuring the wavefront-derived refraction. The imaging acquisition was performed twice. The coefficients of repeatability (CoR) and intraclass correlation coefficient (ICC) were calculated. Results Images were acquired and processed successfully in all patients. No significant difference was detected between repeated measurements of ciliary muscle dimension, full-eye biometry or defocus aberration. The CoR of full-eye biometry ranged from 0.36% to 3.04% and the ICC ranged from 0.981 to 0.999. The CoR for ciliary muscle dimensions ranged from 12.2% to 41.6% and the ICC ranged from 0.767 to 0.919. The defocus aberrations of the two measurements were 0.443 ± 0.534 D and 0.447 ± 0.586 D and the ICC was 0.951. Conclusions The combined system is capable of measuring full eye biometry and refraction with good repeatability. The system is suitable for future investigation of pseudoaccommodation in the pseudophakic eye. PMID:27010674

  7. Synergistic effect and antiquorum sensing activity of Nymphaea tetragona (water lily) extract.

    PubMed

    Hossain, Md Akil; Park, Ji-Yong; Kim, Jin-Yoon; Suh, Joo-Won; Park, Seung-Chun

    2014-01-01

    Salmonellosis is a common and widely distributed food borne disease where Salmonella typhimurium is one of the most important etiologic agents. The purpose of this study was to investigate the antimicrobial activity of Nymphaea tetragona alone and in combination with antibiotics against S. typhimurium. It also aimed to assess the plant for quorum sensing inhibition (QSI) activity and to identify the bioactive compounds. The antibacterial activities of the extract were assessed using broth microdilution method. Disk agar diffusion method was employed to determine the QSI and bioactive compounds were identified by GC-MS analysis. Ethyl acetate fraction of N. tetragona extract (EFNTE) demonstrated good antimicrobial activity (MIC 781 μg/mL) against 4 strains out of 5. FIC index ranged from 0.375 to 1.031 between EFNTE/tylosin and 0.515 to 1.250 between EFNTE/streptomycin against S. typhimurium. Among all extracts, EFNTE and butanol fraction more significantly inhibited pigment production of C. violaceum. Polyphenols were identified as major compound of EFNTE and butanol fraction. These results indicate that combination among N. tetragona extract and antibiotics could be useful to combat drug-resistance Salmonella infections and polyphenols are promising new components from N. tetragona that warrant further investigation as a candidate anti-Salmonella agent and quorum sensing inhibitor.

  8. Synergistic effect and antiquorum sensing activity of Nymphaea tetragona (water lily) extract.

    PubMed

    Hossain, Md Akil; Park, Ji-Yong; Kim, Jin-Yoon; Suh, Joo-Won; Park, Seung-Chun

    2014-01-01

    Salmonellosis is a common and widely distributed food borne disease where Salmonella typhimurium is one of the most important etiologic agents. The purpose of this study was to investigate the antimicrobial activity of Nymphaea tetragona alone and in combination with antibiotics against S. typhimurium. It also aimed to assess the plant for quorum sensing inhibition (QSI) activity and to identify the bioactive compounds. The antibacterial activities of the extract were assessed using broth microdilution method. Disk agar diffusion method was employed to determine the QSI and bioactive compounds were identified by GC-MS analysis. Ethyl acetate fraction of N. tetragona extract (EFNTE) demonstrated good antimicrobial activity (MIC 781 μg/mL) against 4 strains out of 5. FIC index ranged from 0.375 to 1.031 between EFNTE/tylosin and 0.515 to 1.250 between EFNTE/streptomycin against S. typhimurium. Among all extracts, EFNTE and butanol fraction more significantly inhibited pigment production of C. violaceum. Polyphenols were identified as major compound of EFNTE and butanol fraction. These results indicate that combination among N. tetragona extract and antibiotics could be useful to combat drug-resistance Salmonella infections and polyphenols are promising new components from N. tetragona that warrant further investigation as a candidate anti-Salmonella agent and quorum sensing inhibitor. PMID:24895589

  9. Synergistic Effect and Antiquorum Sensing Activity of Nymphaea tetragona (Water Lily) Extract

    PubMed Central

    Hossain, Md. Akil; Park, Ji-Yong; Kim, Jin-Yoon; Suh, Joo-Won; Park, Seung-Chun

    2014-01-01

    Salmonellosis is a common and widely distributed food borne disease where Salmonella typhimurium is one of the most important etiologic agents. The purpose of this study was to investigate the antimicrobial activity of Nymphaea tetragona alone and in combination with antibiotics against S. typhimurium. It also aimed to assess the plant for quorum sensing inhibition (QSI) activity and to identify the bioactive compounds. The antibacterial activities of the extract were assessed using broth microdilution method. Disk agar diffusion method was employed to determine the QSI and bioactive compounds were identified by GC-MS analysis. Ethyl acetate fraction of N. tetragona extract (EFNTE) demonstrated good antimicrobial activity (MIC 781 μg/mL) against 4 strains out of 5. FIC index ranged from 0.375 to 1.031 between EFNTE/tylosin and 0.515 to 1.250 between EFNTE/streptomycin against S. typhimurium. Among all extracts, EFNTE and butanol fraction more significantly inhibited pigment production of C. violaceum. Polyphenols were identified as major compound of EFNTE and butanol fraction. These results indicate that combination among N. tetragona extract and antibiotics could be useful to combat drug-resistance Salmonella infections and polyphenols are promising new components from N. tetragona that warrant further investigation as a candidate anti-Salmonella agent and quorum sensing inhibitor. PMID:24895589

  10. Recent Developments in Active and Passive Distributed Temperature Sensing for Soil Moisture Monitoring

    NASA Astrophysics Data System (ADS)

    Steele-Dunne, S. C.; Dong, J.; Hoes, O.; Van De Giesen, N.; Sayde, C.; Ochsner, T. E.; Selker, J. S.

    2015-12-01

    In this presentation we will review recent developments in both active and passive Distributed Temperature Sensing (DTS) for soil moisture monitoring. DTS involves using fiber-optic cables to measure temperature at sub-meter resolution along cables up to several kilometers in length. Soil thermal properties depend on soil moisture. Hence, temperature variations either in response to externally-applied heating (active) or the response to net radiation (passive) can be monitored and used to infer soil moisture. DTS occupies a unique measurement niche, potentially providing soil moisture information at sub-meter resolution over extents on the order of km at sub-daily time steps. It complements observations from point sensors to other innovative measurement techniques like cosmic ray neutron detection methods and GPS reflectometry. DTS is being developed as a tool for the validation of soil moisture observations from remote sensing and for hydrological field investigations. Here, we will discuss both technological and theoretical advances in active and passive DTS for soil moisture monitoring. We will present data from new installations in the Netherlands and the USA to illustrate recent developments. In particular, we will focus on the value of combining temperature observations from DTS with physical models using data assimilation. In addition to yielding improved soil moisture and temperature profile estimates, recent research has shown the potential to also derive information on the soil thermal and hydraulic properties. We will conclude by outlining the current challenges, with particular emphasis on combining active and passive DTS.

  11. Horizon: A Proposal for Large Aperture, Active Optics in Geosynchronous Orbit

    NASA Technical Reports Server (NTRS)

    Chesters, Dennis; Jenstrom, Del

    2000-01-01

    In 1999, NASA's New Millennium Program called for proposals to validate new technology in high-earth orbit for the Earth Observing-3 (NMP EO3) mission to fly in 2003. In response, we proposed to test a large aperture, active optics telescope in geosynchronous orbit. This would flight-qualify new technologies for both Earth and Space science: 1) a future instrument with LANDSAT image resolution and radiometric quality watching continuously from geosynchronous station, and 2) the Next Generation Space Telescope (NGST) for deep space imaging. Six enabling technologies were to be flight-qualified: 1) a 3-meter, lightweight segmented primary mirror, 2) mirror actuators and mechanisms, 3) a deformable mirror, 4) coarse phasing techniques, 5) phase retrieval for wavefront control during stellar viewing, and 6) phase diversity for wavefront control during Earth viewing. Three enhancing technologies were to be flight- validated: 1) mirror deployment and latching mechanisms, 2) an advanced microcontroller, and 3) GPS at GEO. In particular, two wavefront sensing algorithms, phase retrieval by JPL and phase diversity by ERIM International, were to sense optical system alignment and focus errors, and to correct them using high-precision mirror mechanisms. Active corrections based on Earth scenes are challenging because phase diversity images must be collected from extended, dynamically changing scenes. In addition, an Earth-facing telescope in GEO orbit is subject to a powerful diurnal thermal and radiometric cycle not experienced by deep-space astronomy. The Horizon proposal was a bare-bones design for a lightweight large-aperture, active optical system that is a practical blend of science requirements, emerging technologies, budget constraints, launch vehicle considerations, orbital mechanics, optical hardware, phase-determination algorithms, communication strategy, computational burdens, and first-rate cooperation among earth and space scientists, engineers and managers

  12. Long distance active hyperspectral sensing using high-power near-infrared supercontinuum light source.

    PubMed

    Manninen, Albert; Kääriäinen, Teemu; Parviainen, Tomi; Buchter, Scott; Heiliö, Miika; Laurila, Toni

    2014-03-24

    A hyperspectral remote sensing instrument employing a novel near-infrared supercontinuum light source has been developed for active illumination and identification of targets. The supercontinuum is generated in a standard normal dispersion multi-mode fiber and has 16 W total optical output power covering 1000 nm to 2300 nm spectral range. A commercial 256-channel infrared spectrometer was used for broadband infrared detection. The feasibility of the presented hyperspectral measurement approach was investigated both indoors and in the field. Reflection spectra from several diffusive targets were successfully measured and a measurement range of 1.5 km was demonstrated.

  13. New Active Remote-sensing Capabilities: Laser Ablation Spectrometer and Lidar Atmospheric Species Profile Measurements

    NASA Technical Reports Server (NTRS)

    DeYoung, R. J.; Bergstralh, J. T.

    2005-01-01

    Introduction: With the anticipated development of high-capacity fission power and electric propulsion for deep-space missions, it will become possible to propose experiments that demand higher power than current technologies (e.g. radioisotope power sources) provide. Jupiter Icy Moons Orbiter (JIMO), the first mission in the Project Prometheus program, will explore the icy moons of Jupiter with a suite of high-capability experiments that take advantage of the high power levels (and indirectly, the high data rates) that fission power affords. This abstract describes two high-capability active-remote-sensing experiments that will be logical candidates for subsequent Prometheus-class missions.

  14. Preliminary methods for wearable neuro-vascular assessment with non-invasive, active sensing.

    PubMed

    Carek, Andrew M; Töreyin, Hakan; Hersek, Sinan; Inan, Omer T

    2015-01-01

    In this study, a non-invasive and active sensing scheme that is ultimately aimed to be integrated in a wearable system for neuro-vascular health assessment is presented with preliminary results. With this system, vascular tone is modulated by local heating and cooling of the palm, and the resulting changes in local hemodynamics are monitored via impedance plethysmography (IPG) and photoplethysmography (PPG) sensors interfaced with custom analog electronics. Proof-of-concept measurements were conducted on three subjects using hot packs/ice bags to modulate the palmar skin temperature. From ensemble averaged and smoothed versions of pulsatile IPG and PPG signals, the effects of local changes in skin temperature on a series of parameters associated with neuro-vascular mechanisms (heart rate, blood volume, blood flow rate, blood volume pulse inflection point area ratio, and local pulse transit time) have been observed. The promising experimental results suggest that, with different active temperature modulation schemes (consisting of heating/cooling cycles covering different temperature ranges at different rates), it would be possible to enhance the depth and specificity of the information associated with neuro-vascular health by using biosensors that can fit inside a wearable device (such as a sleeve). This study sets the foundation for future studies on designing and testing such a wearable neuro-vascular health assessment system employing active sensing. PMID:26736951

  15. Anti-quorum sensing activity of essential oils from Colombian plants.

    PubMed

    Jaramillo-Colorado, Beatriz; Olivero-Verbel, Jesus; Stashenko, Elena E; Wagner-Döbler, Irene; Kunze, Brigitte

    2012-01-01

    Essential oils from Colombian plants were characterised by GC-MS, and assayed for anti-quorum sensing activity in bacteria sensor strains. Two major chemotypes were found for Lippia alba, the limonene-carvone and the citral (geranial-neral). For other species, the main components included α-pinene (Ocotea sp.), β-pinene (Swinglea glutinosa), cineol (Elettaria cardamomun), α-zingiberene (Zingiber officinale) and pulegone (Minthostachys mollis). Several essential oils presented promising inhibitory properties for the short chain AHL quorum sensing (QS) system, in Escherichia coli containing the biosensor plasmid pJBA132, in particular Lippia alba. Moderate activity as anti-QS using the same plasmid, were also found for selected constituents of essential oils studied here, such as citral, carvone and α-pinene, although solely at the highest tested concentration (250 µg mL(-1)). Only citral presented some activity for the long chain AHL QS system, in Pseudomonas putida containing the plasmid pRK-C12. In short, essential oils from Colombian flora have promising properties as QS modulators. PMID:21936639

  16. A Host-Produced Autoinducer-2 Mimic Activates Bacterial Quorum Sensing.

    PubMed

    Ismail, Anisa S; Valastyan, Julie S; Bassler, Bonnie L

    2016-04-13

    Host-microbial symbioses are vital to health; nonetheless, little is known about the role crosskingdom signaling plays in these relationships. In a process called quorum sensing, bacteria communicate with one another using extracellular signal molecules called autoinducers. One autoinducer, AI-2, is proposed to promote interspecies bacterial communication, including in the mammalian gut. We show that mammalian epithelia produce an AI-2 mimic activity in response to bacteria or tight-junction disruption. This AI-2 mimic is detected by the bacterial AI-2 receptor, LuxP/LsrB, and can activate quorum-sensing-controlled gene expression, including in the enteric pathogen Salmonella typhimurium. AI-2 mimic activity is induced when epithelia are directly or indirectly exposed to bacteria, suggesting that a secreted bacterial component(s) stimulates its production. Mutagenesis revealed genes required for bacteria to both detect and stimulate production of the AI-2 mimic. These findings uncover a potential role for the mammalian AI-2 mimic in fostering crosskingdom signaling and host-bacterial symbioses.

  17. A framework for nowcasting and forecasting of rainfall-triggered landslide activity using remotely sensed data

    NASA Astrophysics Data System (ADS)

    Kirschbaum, Dalia; Stanley, Thomas

    2016-04-01

    Remote sensing data offers the unique perspective to provide situational awareness of hydrometeorological hazards over large areas in a way that is impossible to achieve with in situ data. Recent work has shown that rainfall-triggered landslides, while typically local hazards that occupy small spatial areas, can be approximated over regional or global scales in near real-time. This work presents a regional and global approach to approximating potential landslide activity using the landslide hazard assessment for situational awareness (LHASA) model. This system couples remote sensing data, including Global Precipitation Measurement rainfall data, Shuttle Radar Topography Mission and other surface variables to estimate where and when landslide activity may be likely. This system also evaluates the effectiveness of quantitative precipitation estimates from the Goddard Earth Observing System Model, Version 5 to provide a 24 forecast of potential landslide activity. Preliminary results of the LHASA model and implications for are presented for a regional version of this system in Central America as well as a prototype global approach.

  18. Discrimination of active and inactive sand from remote sensing - Kelso dunes, Mojave Desert, California

    NASA Technical Reports Server (NTRS)

    Paisley, Elizabeth C. I.; Lancaster, Nicholas; Gaddis, Lisa R.; Greeley, Ronald

    1991-01-01

    Landsat TM images, field data, and laboratoray reflectance spectra were examined for the Kelso dunes, Mojave Desert, California to assess the use of visible and near-infrared (VNIR) remote sensing data to discriminate aeolian sand populations on the basis of spectral brightness. Results show that areas of inactive sand have a larger percentage of dark, fine-grained materials compared to those composed of active sand, which contain less dark fines and a higher percentage of quartz sand-size grains. Both areas are spectrally distinct in the VNIR, suggesting that VNIR spectral data can be used to discriminate active and inactive sand populations in the Mojave Desert. Analysis of laboratory spectra was complicated by the presence of magnetite in the active sands, which decreases their laboratory reflectance values to those of inactive sands. For this application, comparison of TM and laboratory spectra suggests that less than 35 percent vegetation cover does not influence the TM spectra.

  19. Antimicrobial and quorum sensing inhibitory activities of the pericarp of Garcinia mangostana.

    PubMed

    Asfour, Hani Z

    2016-07-01

    A prenylated xanthone, α-mangostin was separated from the alcoholic extract of Garcinia mangostana pericarp. Its structure was established by different spectroscopic analysis. The total methanolic extract (TME) and different fractions of G. mangostana pericarp as well as α-mangostin were assessed for their antimicrobial and quorum sensing inhibitory effects (QSI). The TME, CHCl3 fraction, and α-mangostin exhibited strong activity against all tested strains. While, EtOAc, n-BuOH, and aqueous fractions showed moderate activity against some of the tested organisms. In addition TME, CHCl3, EtOAc, and α-mangostin showed promising QSI, while n-BuOH and aqueous fractions showed moderate activity. Minimal inhibitory concentration (MIC) for TME, CHCl3 fractions, and α-mangostin was also assessed. PMID:27592485

  20. Electrochemical Sensing, Photocatalytic and Biological Activities of ZnO Nanoparticles: Synthesis via Green Chemistry Route

    NASA Astrophysics Data System (ADS)

    Yadav, L. S. Reddy; Archana, B.; Lingaraju, K.; Kavitha, C.; Suresh, D.; Nagabhushana, H.; Nagaraju, G.

    2016-05-01

    In this paper, we have successfully synthesized ZnO nanoparticles (Nps) via solution combustion method using sugarcane juice as the novel fuel. The structure and morphology of the synthesized ZnO Nps have been analyzed using various analytical tools. The synthesized ZnO Nps exhibit excellent photocatalytic activity for the degradation of methylene blue dye, indicating that the ZnO Nps are potential photocatalytic semiconductor materials. The synthesized ZnO Nps also show good electrochemical sensing of dopamine. ZnO Nps exhibit significant bactericidal activity against Klebsiella aerogenes, Pseudomonas aeruginosa, Eschesichia coli and Staphylococcus aureus using agar well diffusion method. Furthermore, the ZnO Nps show good antioxidant activity by potentially scavenging 1-diphenyl-2-picrylhydrazyl (DPPH) radicals. The above studies clearly demonstrate versatile applications of ZnO synthesized by simple eco-friendly route.

  1. Modulation of BK channel activities by calcium-sensing receptor in rat bronchopulmonary sensory neurons.

    PubMed

    Vysotskaya, Zhanna V; Moss, Charles R; Gilbert, Carolyn A; Gabriel, Sabry A; Gu, Qihai

    2014-11-01

    This study was carried out to investigate the expression of large-conductance Ca(2+)-activated potassium (BK) channels and to explore the possible modulation of BK channel activities by calcium-sensing receptors (CaSR) in rat bronchopulmonary sensory neurons. The expression of BK channels was demonstrated by immunohistochemistry and RT-PCR. Results from whole-cell patch-clamp recordings demonstrated that activation of CaSR with its agonist spermine or NPS R-568 showed a dual regulating effect on BK channel activities: it potentiated BK currents in cells exhibiting low baseline BK activity while slightly inhibited BK currents in cells with high baseline BK activity. Blocking CaSR with its antagonist NPS 2143 significantly inhibited BK currents. Our results further showed that the modulation of BK currents by CaSR activation or blockade was completely abolished when the intracellular Ca(2+) was chelated by BAPTA-AM. In summary, our data suggest that CaSR plays an integrative role in bronchopulmonary afferent signaling, at least partially through the regulation of BK channel activities.

  2. Antibacterial and quorum sensing regulatory activities of some traditional Eastern-European medicinal plants.

    PubMed

    Tolmacheva, Anna A; Rogozhin, Eugene A; Deryabin, Dmitry G

    2014-06-01

    The objective of this study was to screen extracts of twenty Eastern European medicinal plants, using wild-type and reporter Chromobacterium violaceum bioassays, for novel components that target bacterial cells and their quorum sensing (QS) communication systems. Three types of activity and their combinations were revealed: (i) direct antimicrobial growth-inhibitory activity, (ii) non-specific and specific pro-QS activities, (iii) anti-QS activity. Among seven plant extracts showing direct growth-inhibitory activity, the strongest effect was shown by Arctostaphylos uva-ursi (bearberry) leaves. Many plants stimulated violacein production by wild-type C. violaceum ATCC 31532 in a non-specific manner, and only the herb Bidens tripartita (three-lobe beggarticks) contained compounds that mimic acyl-homoserine lactone and operated as a QS agonist. Anti-QS activity was found in eleven plants including Quercus robur (oak) cortex, Betula verrucosa (birch) buds and Eucalyptus viminalis (Manna Gum) leaves. Subsequent statistical analysis showed differences between antimicrobial and anti-QS activities, whereas both activities were defined by phylogenetic position of medical resource plant. Finally, extract from Quercus robur cortex revealed at least two fractions, showing different anti-QS mechanisms. These data confirm that multicomponent anti-infectious mechanisms are used by plants, which may be useful for drug development.

  3. Realizing the full potential of Remotely Sensed Active Layer Thickness (ReSALT) Products

    NASA Astrophysics Data System (ADS)

    Schaefer, K. M.; Chen, A.; Liu, L.; Parsekian, A.; Jafarov, E. E.; Panda, S. K.; Zebker, H. A.

    2015-12-01

    The Remotely Sensed Active Layer Thickness (ReSALT) product uses the Interferometric Synthetic Aperture Radar (InSAR) technique to measure ground subsidence, active layer thickness (ALT), and thermokarst activity in permafrost regions. ReSALT supports research for the Arctic-Boreal Vulnerability Experiment (ABoVE) field campaign in Alaska and northwest Canada and is a precursor for a potential Nasa-Isro Synthetic Aperture Radar (NISAR) product. ALT is a critical parameter for monitoring the status of permafrost and thermokarst activity is one of the key drivers of change in permafrost regions. The ReSALT product currently includes 1) long-term subsidence trends resulting from the melting and subsequent drainage of excess ground ice in permafrost-affected soils, 2) seasonal subsidence resulting from the expansion of soil water into ice as the active layer freezes and thaws, and 3) ALT estimated from the seasonal subsidence assuming a vertical profile of water within the soil column. ReSALT includes uncertainties for all parameters and is validated against in situ measurements from the Circumpolar Active Layer Monitoring (CALM) network, Ground Penetrating Radar and mechanical probe measurements. We present high resolution ReSALT products on the North Slope of Alaska: Prudhoe Bay, Barrow, Toolik Lake, Happy Valley, and the Anaktuvuk fire zone. We believe that the ReSALT product could be expanded to include maps of individual thermokarst features identified as spatial anomalies in the subsidence trends, with quantified expansion rates. We illustrate the technique with multiple examples of thermokarst features on the North Slope of Alaska. Knowing the locations and expansion rates for individual features allows us to evaluate risks to human infrastructure. Our results highlight the untapped potential of the InSAR technique to remotely sense ALT and thermokarst dynamics over large areas of the Arctic.

  4. Multisensor of Remotely Sensed Data for Characterizing Seismotectonic Activities in Malaysia

    NASA Astrophysics Data System (ADS)

    Abu Bakar, Rabieahtul; Azahari Razak, Khamarrul; Anuar Jamaludin, Tajul; Tongkul, Felix; Mohamad, Zakaria; Ramli, Zamri; Abd Manap, Mohamad; Rahman, Muhammad Zulkarnain Abdul

    2015-04-01

    Seismically induced events pose serious hazards yet are difficult to predict. Despite remarkable efforts of mapping, monitoring and modelling of such great events at regional or local scales, the understanding of the processes in the Earth's dynamic system remains elusive. Although Malaysia is in a relatively low seismic hazard zone, the current trend and pattern of seismotectonic activities triggered a series of fundamental study to better understand the relationship between the earthquakes, recent tectonics and seismically active fault zones. Several conventional mapping techniques have been intensively used but shown some limitations. Remote sensing is the preferable mean to quantify the seismic activity accurately in a larger area within a short period. Still, only few of such studies have been carried out in this subduction region. Characterization of seismotectonic activities from space in a tropical environment is very challenging given the complexity of its physiographic, climatic, geologic conditions and anthropogenic activities. There are many factors controlling the success rate of the implementation mainly due to the lack of historical earthquakes, geomorphological evidence, and proper identification of regional tectonic patterns. In this study, we aim at providing better insight to extract and characterize seismotectonic activities by integrating passive and active remotely-sensed data, geodetic data, historical records, GIS-based data analysis and in-situ measurements as well quantify them based on field investigation and expert knowledge. It is crucial to perform spatiotemporal analysis of its activities in the most seismically induced region in North-Western Sabah. A comprehensive geodatabase of seismotectonic events are developed and allowed us to analyse the spatiotemporal activities. A novelty of object-based image method for extracting tropical seismically active faults and related seismotectonic features are introduced and evaluated. We aim to

  5. Real-time phasing and co-phasing of a ground-based interferometer with a pyramid wavefront sensor.

    NASA Astrophysics Data System (ADS)

    Vérinaud, Christophe; Esposito, Simone

    The feasibility and remarkable performances of pyramid wavefront sensing in adaptive optics have already been demonstrated. In this paper, we investigate another potential of the pyramid wavefront sensor which is differential piston sensing in interferometry: this can be done by using a glass pyramid placed in a combined focal plane of the interferometer, and a CCD sampling the usual four diffracted images of the pupil, composed here by the interferometer apertures. From a purely geometrical point of view, no information about the differential phase between two pupils could be retrieved. However, as the sensor main component, the pyramid, is located directly in the interference pattern of the interferometer, the piston information present in the electric field of the combined focal plane modifies, after diffraction by the pyramid, the intensity distribution in the pupil plane. Thus, with only one sensor, the differential piston can be measured, in addition to the classical local tilts determination. In this paper we present the concept and give some simulation results showing the performances of a closed-loop adaptive optics correction for a ground-based two-telescope interferometer like the Large Binocular Telescope.

  6. Active landslide monitoring using remote sensing data, GPS measurements and cameras on board UAV

    NASA Astrophysics Data System (ADS)

    Nikolakopoulos, Konstantinos G.; Kavoura, Katerina; Depountis, Nikolaos; Argyropoulos, Nikolaos; Koukouvelas, Ioannis; Sabatakakis, Nikolaos

    2015-10-01

    An active landslide can be monitored using many different methods: Classical geotechnical measurements like inclinometer, topographical survey measurements with total stations or GPS and photogrammetric techniques using airphotos or high resolution satellite images. As the cost of the aerial photo campaign and the acquisition of very high resolution satellite data is quite expensive the use of cameras on board UAV could be an identical solution. Small UAVs (Unmanned Aerial Vehicles) have started their development as expensive toys but they currently became a very valuable tool in remote sensing monitoring of small areas. The purpose of this work is to demonstrate a cheap but effective solution for an active landslide monitoring. We present the first experimental results of the synergistic use of UAV, GPS measurements and remote sensing data. A six-rotor aircraft with a total weight of 6 kg carrying two small cameras has been used. Very accurate digital airphotos, high accuracy DSM, DGPS measurements and the data captured from the UAV are combined and the results are presented in the current study.

  7. Development of Optically Active Nanostructures for Potential Applications in Sensing, Therapeutics and Imaging

    NASA Astrophysics Data System (ADS)

    Joshi, Padmanabh

    Materials at nanoscale are finding manifold applications in the various fields like sensing, plasmonics, therapeutics, to mention a few. Large amount of development has taken place regarding synthesis and exploring the novel applications of the various types of nanomaterials like organic, inorganic and hybrid of both. Yet, it is believed that the full potential of different nanomaterials is yet to be fully established stimulating researchers to explore more in the field of nanotechnology. Building on the same premise, in the following studies we have developed the nanomaterials in the class of optically active nanoparticles. First part of the study we have successfully designed, synthesized, and characterized Ag-Fe3O4 nanocomposite substrate for potential applications in quantitative Surface Enhanced Raman Scattering (SERS) measurements. Quantitative SERS-based detection of dopamine was performed successfully. In subsequent study, facile, single-step synthesis of polyethyleneimine (PEI) coated lanthanide based NaYF4 (Yb, Er) nanoparticles was developed and their application as potential photodynamic therapy agent was studied using excitations by light in near infra-red and visible region. In the following and last study, synthesis and characterization of the conjugated polymer nanoparticles was attempted successfully. Functionalization of the conjugated nanoparticles, which is a bottleneck for their potential applications, was successfully performed by encapsulating them in the silica nanoparticles, surface of which was then functionalized by amine group. Three types of optically active nanoparticles were developed for potential applications in sensing, therapeutics and imaging.

  8. Composition, anti-quorum sensing and antimicrobial activity of essential oils from Lippia alba

    PubMed Central

    Olivero-Verbel, Jesus; Barreto-Maya, Ana; Bertel-Sevilla, Angela; Stashenko, Elena E.

    2014-01-01

    Many Gram-negative pathogens have the ability to produce N-acylhomoserine lactones (AHLs) as signal molecules for quorum sensing (QS). This cell-cell communication system allows them to coordinate gene expression and regulate virulence. Strategies to inhibit QS are promising for the control of infectious diseases or antibiotic resistant bacterial pathogens. The aim of the present study was to evaluate the anti-quorum sensing (anti-QS) and antibacterial potential of five essential oils isolated from Lippia alba on the Tn-5 mutant of Chromobacterium violaceum CV026, and on the growth of the gram-positive bacteria S. aureus ATCC 25923. The anti-QS activity was detected through the inhibition of the QS-controlled violacein pigment production by the sensor bacteria. Results showed that two essential oils from L. alba, one containing the greatest geranial:neral and the other the highest limonene:carvone concentrations, were the most effective QS inhibitors. Both oils also had small effects on cell growth. Moreover, the geranial/neral chemotype oil also produced the maximum zone of growth inhibition against S. aureus ATCC 25923. These data suggest essential oils from L. alba have promising properties as QS modulators, and present antibacterial activity on S. aureus. PMID:25477905

  9. Branch-point reconstruction in laser beam projection through turbulence with finite-degree-of-freedom phase-only wave-front correction.

    PubMed

    Roggemann, M C; Koivunen, A C

    2000-01-01

    Wave-front sensing and deformable mirror control algorithms in adaptive optics systems are designed on the premise that a continuous phase function exists in the telescope pupil that can be conjugated with a deformable mirror for the purpose of projecting a laser beam. However, recent studies of coherent wave propagation through turbulence have shown that under conditions where scintillation is not negligible, a truly continuous phase function does not in general exist as a result of the presence of branch points in the complex optical field. Because of branch points and the associated branch cuts, least-squares wave-front reconstruction paradigms can have large errors. We study the improvement that can be obtained by implementing wave-front reconstructors that can sense the presence of branch points and reconstruct a discontinuous phase function in the context of a laser beam projection system. This study was conducted by fitting a finite-degree-of-freedom deformable mirror to branch-point and least-squares reconstructions of the phase of the beacon field, propagating the corrected field to the beacon plane, and evaluating performance in the beacon plane. We find that the value of implementing branch-point reconstructors with a finite-degree-of-freedom deformable mirror is significant for optical paths that cause saturated log-amplitude fluctuations.

  10. Active Thermal Extraction and Temperature Sensing of Near-field Thermal Radiation

    PubMed Central

    Ding, D.; Kim, T.; Minnich, A. J.

    2016-01-01

    Recently, we proposed an active thermal extraction (ATX) scheme that enables thermally populated surface phonon polaritons to escape into the far-field. The concept is based on a fluorescence upconversion process that also occurs in laser cooling of solids (LCS). Here, we present a generalized analysis of our scheme using the theoretical framework for LCS. We show that both LCS and ATX can be described with the same mathematical formalism by replacing the electron-phonon coupling parameter in LCS with the electron-photon coupling parameter in ATX. Using this framework, we compare the ideal efficiency and power extracted for the two schemes and examine the parasitic loss mechanisms. This work advances the application of ATX to manipulate near-field thermal radiation for applications such as temperature sensing and active radiative cooling. PMID:27595609

  11. Novel error sensing microphone arrays for active control of turbofan rotor/stator tones

    NASA Astrophysics Data System (ADS)

    Walker, Bruce E.; Hersh, Alan S.; Rice, Edward J.; Sutliff, Daniel L.

    2003-10-01

    Active control of turbofan rotor/stator interaction tones is complicated by the simultaneous presence of multiple duct propagation modes. In-duct error sensing microphone arrays that can adequately resolve these modes typically require duct lengths that are incompatible with modern compact engine design. Two alternative approaches have been investigated. For inlet noise, an external linear array of microphones was positioned in the near/far radiation field transition region and weighted to provide error signals resolved either by duct mode or by radiation angle. For the exhaust, radially spaced microphones have been placed on duct bifurcation panels to provide supplemental radial-mode resolution. The concepts were tested in combination with an adaptive segmented liner in a static duct and as part of an active stator-vane system in the ANCF research facility at NASA/Glenn Research Center. [Work sponsored by NASA/Langley Research Center.

  12. Active Thermal Extraction and Temperature Sensing of Near-field Thermal Radiation

    NASA Astrophysics Data System (ADS)

    Ding, D.; Kim, T.; Minnich, A. J.

    2016-09-01

    Recently, we proposed an active thermal extraction (ATX) scheme that enables thermally populated surface phonon polaritons to escape into the far-field. The concept is based on a fluorescence upconversion process that also occurs in laser cooling of solids (LCS). Here, we present a generalized analysis of our scheme using the theoretical framework for LCS. We show that both LCS and ATX can be described with the same mathematical formalism by replacing the electron-phonon coupling parameter in LCS with the electron-photon coupling parameter in ATX. Using this framework, we compare the ideal efficiency and power extracted for the two schemes and examine the parasitic loss mechanisms. This work advances the application of ATX to manipulate near-field thermal radiation for applications such as temperature sensing and active radiative cooling.

  13. ESA activities in the use of microwaves for the remote sensing of the Earth

    NASA Technical Reports Server (NTRS)

    Maccoll, D.

    1984-01-01

    The program of activities under way in the European Space Agency (ESA) directed towards Remote Sensing of the oceans and troposphere is discussed. The initial project is the launch of a satellite named ERS-1 with a primary payload of microwave values in theee C- and Ku-bands. This payload is discussed in depth. The secondary payload includes precision location experiments and an instrument to measure sea surface temperature, which are described. The important topic of calibration is extensively discussed, and a review of activities directed towards improvements to the instruments for future satellites is presented. Some discussion of the impact of the instrument payload on the spacecraft design follows and the commitment of ESA to the provision of a service of value to the ultimate user is emphasized.

  14. Active Thermal Extraction and Temperature Sensing of Near-field Thermal Radiation.

    PubMed

    Ding, D; Kim, T; Minnich, A J

    2016-01-01

    Recently, we proposed an active thermal extraction (ATX) scheme that enables thermally populated surface phonon polaritons to escape into the far-field. The concept is based on a fluorescence upconversion process that also occurs in laser cooling of solids (LCS). Here, we present a generalized analysis of our scheme using the theoretical framework for LCS. We show that both LCS and ATX can be described with the same mathematical formalism by replacing the electron-phonon coupling parameter in LCS with the electron-photon coupling parameter in ATX. Using this framework, we compare the ideal efficiency and power extracted for the two schemes and examine the parasitic loss mechanisms. This work advances the application of ATX to manipulate near-field thermal radiation for applications such as temperature sensing and active radiative cooling. PMID:27595609

  15. Applications of ultrafast wavefront rotation in highly nonlinear optics

    NASA Astrophysics Data System (ADS)

    Quéré, F.; Vincenti, H.; Borot, A.; Monchocé, S.; Hammond, T. J.; Taec Kim, Kyung; Wheeler, J. A.; Zhang, Chunmei; Ruchon, T.; Auguste, T.; Hergott, J. F.; Villeneuve, D. M.; Corkum, P. B.; Lopez-Martens, R.

    2014-06-01

    This paper provides an overview of ultrafast wavefront rotation of femtosecond laser pulses and its various applications in highly nonlinear optics, focusing on processes that lead to the generation of high-order harmonics and attosecond pulses. In this context, wavefront rotation can be exploited in different ways, to obtain new light sources for time-resolved studies, called ‘attosecond lighthouses’, to perform time-resolved measurements of nonlinear optical processes, using ‘photonic streaking’, or to track changes in the carrier-envelope relative phase of femtosecond laser pulses. The basic principles are explained qualitatively from different points of view, the experimental evidence obtained so far is summarized, and the perspectives opened by these effects are discussed.

  16. Synthetic holography in microscopy: opportunities arising from advanced wavefront shaping

    NASA Astrophysics Data System (ADS)

    Jesacher, Alexander; Ritsch-Marte, Monika

    2016-01-01

    The advent of computer-generated or synthetic holography has created a wealth of possibilities for wavefront shaping in optics. We discuss the impact this has had on optical microscopy. Synthetic Holographic Microscopy utilises wavefront shaping by a computer-generated 'hologram' (CGH) to modify light on the illumination or the detection side, or both. This enables modifications of the general sample appearance concerning contrast, resolution and other aspects. Multiplexing CGHs can perform several tasks at once, for instance splitting the image into sub-images corresponding to different depths in the sample, or displaying differently contrasted images of the sample, e.g. bright field, darkfield or (spiral) phase contrast, in different sub-images. We give an overview of the options and discuss the advantages and disadvantages of using programmable holographic elements inside an optical microscope.

  17. Analysis of optical wavefront reconstruction and deconvolution in adaptive optics

    NASA Astrophysics Data System (ADS)

    Luke, David Russell

    2001-11-01

    It was in the spirit of ``reuniting divergent trends by clarifying the common features and interconnections of many distinct and diverse scientific facts'' that Courant and Hilbert published their book Methods of Mathematical Physics [43]. This thesis is written in the same spirit and with the same goal. We focus our attention on the problem of wavefront reconstruction and deconvolution in adaptive optics. This is an ill-posed, non-linear inverse problem that touches on the theory of harmonic analysis, variational analysis, signal processing, nonconvex optimization, regularization, statistics and probability. Numerical solutions rely on spectral and operator-splitting methods as well as limited memory and multi-resolution techniques. We introduce novel methods for wavefront reconstruction and compare our results against common techniques. Previous work on this problem is reviewed and unified in a non-parametric, analytic framework.

  18. Ultrasonically encoded wavefront shaping for focusing into random media

    PubMed Central

    Tay, Jian Wei; Lai, Puxiang; Suzuki, Yuta; Wang, Lihong V.

    2014-01-01

    Phase distortions due to scattering in random media restrict optical focusing beyond one transport mean free path. However, scattering can be compensated for by applying a correction to the illumination wavefront using spatial light modulators. One method of obtaining the wavefront correction is by iterative determination using an optimization algorithm. In the past, obtaining a feedback signal required either direct optical access to the target region, or invasive embedding of molecular probes within the random media. Here, we propose using ultrasonically encoded light as feedback to guide the optimization dynamically and non-invasively. In our proof-of-principle demonstration, diffuse light was refocused to the ultrasound focal zone, with a focus-to-background ratio of more than one order of magnitude after 600 iterations. With further improvements, especially in optimization speed, the proposed method should find broad applications in deep tissue optical imaging and therapy. PMID:24472822

  19. Terahertz wavefront control by tunable metasurface made of graphene ribbons

    SciTech Connect

    Yatooshi, Takumi; Ishikawa, Atsushi Tsuruta, Kenji

    2015-08-03

    We propose a tunable metasurface consisting of an array of graphene ribbons on a silver mirror with a SiO{sub 2} gap layer to control reflected wavefront at terahertz frequencies. The graphene ribbons exhibit localized plasmon resonances depending on their Fermi levels to introduce abrupt phase shifts along the metasurface. With interference of the Fabry-Perot resonances in the SiO{sub 2} layer, phase shift through the system is largely accumulated, covering the 0-to-2π range for full control of the wavefront. Numerical simulations prove that wide-angle beam steering up to 53° with a high reflection efficiency of 60% is achieved at 5 THz within a switching time shorter than 0.6 ps.

  20. Wavefront scanning method for minimum traveltime calculations in 3-D

    SciTech Connect

    Meng, F.; Liu, H.; Li, Y.

    1994-12-31

    This paper proposes an efficient way to calculate the shortest travel-time and its correspondent ray-path in three dimension, by using point secondary approximation to depict the wavefront and propagate the travel-time computation along recursively expanding and contracting cubic boxes. Due to its following advantages: (1) the computation order is O(N), where N is the total number of discrete secondary nodes; (2) the memory occupation is relatively small; (3) the algorithm is robust even for high velocity contrast; (4) the minimum travel-time and raypath are computed accurately, this 3-D wavefront scanning raytracing method promises to be real tool for 3-D seismic prestack migration, velocity analysis as well as forward waveform modeling by Maslov asymptotic ray theory.

  1. Optimization-based wavefront sensorless adaptive optics for multiphoton microscopy.

    PubMed

    Antonello, Jacopo; van Werkhoven, Tim; Verhaegen, Michel; Truong, Hoa H; Keller, Christoph U; Gerritsen, Hans C

    2014-06-01

    Optical aberrations have detrimental effects in multiphoton microscopy. These effects can be curtailed by implementing model-based wavefront sensorless adaptive optics, which only requires the addition of a wavefront shaping device, such as a deformable mirror (DM) to an existing microscope. The aberration correction is achieved by maximizing a suitable image quality metric. We implement a model-based aberration correction algorithm in a second-harmonic microscope. The tip, tilt, and defocus aberrations are removed from the basis functions used for the control of the DM, as these aberrations induce distortions in the acquired images. We compute the parameters of a quadratic polynomial that is used to model the image quality metric directly from experimental input-output measurements. Finally, we apply the aberration correction by maximizing the image quality metric using the least-squares estimate of the unknown aberration.

  2. An adaptive optic for correcting low-order wavefront aberrations

    SciTech Connect

    Thompson, C A; Wilhelmsen, J

    1999-09-02

    Adaptive Optics used for correcting low-order wavefront aberrations were tested and compared using interferometry, beam propagation, and a far-field test. Results confirm that the design and manufacturing specifications were met. Experimental data also confirms theoretical performance expectations, indicating the usefulness of these optics (especially in a laser-beam processing system), and identifying the resulting differences between the two fabrication methods used to make the optics.

  3. The entire beam wavefront control of high power laser facility

    NASA Astrophysics Data System (ADS)

    Dai, Wanjun; Wang, Deen; Hu, Dongxia; Zhang, Xin; Zhou, Wei; Yuan, Qiang; Deng, Xuewei; Wang, Yuancheng; Deng, Wu; Yang, Ying; Zhu, Qihua; Jing, Feng

    2015-02-01

    Experiment of entire beam wavefront compensation was carried out in a beamline of a high power laser facility, and two adaptive optics systems with different intentions were applied in the chosen beamline. After correction, the far-filed irradiance distribution is concentrated evidently and the entrance rate of 3ω focal spot to a 500-μm hole is improved to be about 95% under number kilojoules energy.

  4. Ophthalmic Shack-Hartmann Wavefront Sensor Applications - Oral Paper

    NASA Astrophysics Data System (ADS)

    Neal, Daniel R.

    2008-01-01

    One of the most common applications of the Shack-Hartmann wavefront sensor is to measure the human eye. There are a number of instruments that have been designed for this purpose and are used extensively in laser refractive surgery. While conceptually the sensor is similar to those used for astronomy applications, there are key differences adaptive optic and measurement sensors. These sensors have led to a range of applications and diagnostics that are providing key new information about how the eye functions.

  5. Research on technique of wavefront retrieval based on Foucault test

    NASA Astrophysics Data System (ADS)

    Yuan, Lvjun; Wu, Zhonghua

    2010-05-01

    During finely grinding the best fit sphere and initial stage of polishing, surface error of large aperture aspheric mirrors is too big to test using common interferometer. Foucault test is widely used in fabricating large aperture mirrors. However, the optical path is disturbed seriously by air turbulence, and changes of light and dark zones can not be identified, which often lowers people's judging ability and results in making mistake to diagnose surface error of the whole mirror. To solve the problem, the research presents wavefront retrieval based on Foucault test through digital image processing and quantitative calculation. Firstly, real Foucault image can be gained through collecting a variety of images by CCD, and then average these image to eliminate air turbulence. Secondly, gray values are converted into surface error values through principle derivation, mathematical modeling, and software programming. Thirdly, linear deviation brought by defocus should be removed by least-square method to get real surface error. At last, according to real surface error, plot wavefront map, gray contour map and corresponding pseudo color contour map. The experimental results indicates that the three-dimensional wavefront map and two-dimensional contour map are able to accurately and intuitively show surface error on the whole mirrors under test, and they are beneficial to grasp surface error as a whole. The technique can be used to guide the fabrication of large aperture and long focal mirrors during grinding and initial stage of polishing the aspheric surface, which improves fabricating efficiency and precision greatly.

  6. One dimensional wavefront sensor development for tomographic flow measurements

    SciTech Connect

    Neal, D.; Pierson, R.; Chen, E.

    1995-08-01

    Optical diagnostics are extremely useful in fluid mechanics because they generally have high inherent bandwidth, and are non-intrusive. However, since optical probe measurements inherently integrate all information along the optical path, it is often difficult to isolate out-of-plane components in 3-dimensional flow events. It is also hard to make independent measurements of internal flow structure. Using an arrangement of one-dimensional wavefront sensors, we have developed a system that uses tomographic reconstruction to make two-dimensional measurements in an arbitrary flow. These measurements provide complete information in a plane normal to the flow. We have applied this system to the subsonic free jet because of the wide range of flow scales available. These measurements rely on the development of a series of one-dimensional wavefront sensors that are used to measure line-integral density variations in the flow of interest. These sensors have been constructed using linear CCD cameras and binary optics lenslet arrays. In designing these arrays, we have considered the coherent coupling between adjacent lenses and have made comparisons between theory and experimental noise measurements. The paper will present examples of the wavefront sensor development, line-integral measurements as a function of various experimental parameters, and sample tomographic reconstructions.

  7. Real-time simulation of ultrasound refraction phenomena using ray-trace based wavefront construction method.

    PubMed

    Szostek, Kamil; Piórkowski, Adam

    2016-10-01

    Ultrasound (US) imaging is one of the most popular techniques used in clinical diagnosis, mainly due to lack of adverse effects on patients and the simplicity of US equipment. However, the characteristics of the medium cause US imaging to imprecisely reconstruct examined tissues. The artifacts are the results of wave phenomena, i.e. diffraction or refraction, and should be recognized during examination to avoid misinterpretation of an US image. Currently, US training is based on teaching materials and simulators and ultrasound simulation has become an active research area in medical computer science. Many US simulators are limited by the complexity of the wave phenomena, leading to intensive sophisticated computation that makes it difficult for systems to operate in real time. To achieve the required frame rate, the vast majority of simulators reduce the problem of wave diffraction and refraction. The following paper proposes a solution for an ultrasound simulator based on methods known in geophysics. To improve simulation quality, a wavefront construction method was adapted which takes into account the refraction phenomena. This technique uses ray tracing and velocity averaging to construct wavefronts in the simulation. Instead of a geological medium, real CT scans are applied. This approach can produce more realistic projections of pathological findings and is also capable of providing real-time simulation. PMID:27586490

  8. Real-time simulation of ultrasound refraction phenomena using ray-trace based wavefront construction method.

    PubMed

    Szostek, Kamil; Piórkowski, Adam

    2016-10-01

    Ultrasound (US) imaging is one of the most popular techniques used in clinical diagnosis, mainly due to lack of adverse effects on patients and the simplicity of US equipment. However, the characteristics of the medium cause US imaging to imprecisely reconstruct examined tissues. The artifacts are the results of wave phenomena, i.e. diffraction or refraction, and should be recognized during examination to avoid misinterpretation of an US image. Currently, US training is based on teaching materials and simulators and ultrasound simulation has become an active research area in medical computer science. Many US simulators are limited by the complexity of the wave phenomena, leading to intensive sophisticated computation that makes it difficult for systems to operate in real time. To achieve the required frame rate, the vast majority of simulators reduce the problem of wave diffraction and refraction. The following paper proposes a solution for an ultrasound simulator based on methods known in geophysics. To improve simulation quality, a wavefront construction method was adapted which takes into account the refraction phenomena. This technique uses ray tracing and velocity averaging to construct wavefronts in the simulation. Instead of a geological medium, real CT scans are applied. This approach can produce more realistic projections of pathological findings and is also capable of providing real-time simulation.

  9. ‘Progressive Development of International Law’ on Remote Sensing Activities: from the View of International Cooperation

    NASA Astrophysics Data System (ADS)

    Fukunaga, Masatoshi

    The objective of this paper is to investigate into the development of international law on remote sensing activities. There is one general United Nations General Assembly Resolution concerning remote sensing activities, but the problems remain to be solved. Considering international cooperation on remote sensing activities, it seems that there is a common direction that data exchange/sharing should be taken place based on ‘non-discriminatory’ principle, ‘free or no more than the cost of reproduction and delivery,’ and ‘best endeavours.’ It is also mentioned that the remote sensing data exchange/sharing on international cooperation have indirectly been engaging in the harmonization among interests of sensing States, developing countries and sensed States. It is assumed that the data exchange/sharing principles have been contributing to the development of customary international law as “limited in the peacetime and for civil use, every State shall enjoy the access in the manner of nondiscriminatory and reasonable cost and time to the data owned by governmental entities substantially.”

  10. Simulation of wavefront reconstruction in beam reshaping system for rectangular laser beam

    NASA Astrophysics Data System (ADS)

    Zhou, Qiong; Liu, Wenguang; Jiang, Zongfu

    2014-05-01

    A new method to calculating the wavefront of slap laser is studied in this paper. The method is based on the ray trace theory of geometrical optics. By using the Zemax simulation software and Matlab calculation software, the wavefront of rectangular beam in beam reshaping system is reconstructed. Firstly, with the x- and y-slope measurement of reshaping beam the direction cosine of wavefront can be calculated. Then, the inverse beam path of beam reshaping system is built by using Zemax simulation software and the direction cosine of rectangular beam can be given, too. Finally, Southwell zonal model is used to reconstruct the wavefront of rectangular beam in computer simulation. Once the wavefront is received, the aberration of laser can be eliminated by using the proper configuration of beam reshaping system. It is shown that this method to reconstruct the wavefront of rectangular beam can evidently reduce the negative influence of additional aberration induced by beam reshaping system.

  11. High-precision method for submicron-aperture fiber point-diffraction wavefront measurement.

    PubMed

    Wang, Daodang; Xu, Yangbo; Liang, Rongguang; Kong, Ming; Zhao, Jun; Zhang, Baowu; Li, Wei

    2016-04-01

    It is a key issue to measure the point-diffraction wavefront error, which determines the achievable accuracy of point-diffraction interferometer (PDI). A high-precision method based on shearing interferometry is proposed to measure submicron-aperture fiber point-diffraction wavefront with high numerical aperture (NA). To obtain the true shearing point-diffraction wavefront, a double-step calibration method based on three-dimensional coordinate reconstruction and symmetric lateral displacement compensation is proposed to calibrate the geometric aberration in the case of high NA and large lateral wavefront displacement. The calibration can be carried out without any prior knowledge about the system configuration parameters. With the true shearing wavefront, the differential Zernike polynomials fitting method is applied to reconstruct the point-diffraction wavefront. Numerical simulation and experiments have been carried out to demonstrate the accuracy and feasibility of the proposed measurement method, and a good measurement accuracy is achieved. PMID:27137002

  12. Structural mechanism of ligand activation in human calcium-sensing receptor

    PubMed Central

    Geng, Yong; Mosyak, Lidia; Kurinov, Igor; Zuo, Hao; Sturchler, Emmanuel; Cheng, Tat Cheung; Subramanyam, Prakash; Brown, Alice P; Brennan, Sarah C; Mun, Hee-chang; Bush, Martin; Chen, Yan; Nguyen, Trang X; Cao, Baohua; Chang, Donald D; Quick, Matthias; Conigrave, Arthur D; Colecraft, Henry M; McDonald, Patricia; Fan, Qing R

    2016-01-01

    Human calcium-sensing receptor (CaSR) is a G-protein-coupled receptor (GPCR) that maintains extracellular Ca2+ homeostasis through the regulation of parathyroid hormone secretion. It functions as a disulfide-tethered homodimer composed of three main domains, the Venus Flytrap module, cysteine-rich domain, and seven-helix transmembrane region. Here, we present the crystal structures of the entire extracellular domain of CaSR in the resting and active conformations. We provide direct evidence that L-amino acids are agonists of the receptor. In the active structure, L-Trp occupies the orthosteric agonist-binding site at the interdomain cleft and is primarily responsible for inducing extracellular domain closure to initiate receptor activation. Our structures reveal multiple binding sites for Ca2+ and PO43- ions. Both ions are crucial for structural integrity of the receptor. While Ca2+ ions stabilize the active state, PO43- ions reinforce the inactive conformation. The activation mechanism of CaSR involves the formation of a novel dimer interface between subunits. DOI: http://dx.doi.org/10.7554/eLife.13662.001 PMID:27434672

  13. Activation of the MAP Kinase Cascade by Exogenous Calcium-Sensing Receptor

    SciTech Connect

    Hobson, Susan A.; Wright, Jay W.; Lee, Fred; Mcneil, Scott; Bilderback, Tim R.; Rodland, Karin D.

    2003-02-01

    In Rat-1 fibroblasts and ovarian surface epithelial cells, extracellular calcium induces a proliferative response which appears to be mediated by the G-protein coupled Calcium-sensing Receptor (CaR), as expression of the non-functional CaR-R795W mutant inhibits both thymidine incorporation and activation of the extracellular-regulated kinase (ERK) in response to calcium. In this report we utilized CaR-transfected HEK293 cells to demonstrate that functional CaR is necessary and sufficient for calcium-induced ERK activation. CaR-dependent ERK activation was blocked by co-expression of the Ras dominant-negative mutant, Ras N17, and by exposure to the phosphatidyl inositol 3' kinase inhibitors wortmannin and LY294002. In contrast to Rat-1 fibroblasts, CaR-mediated in vitro kinase activity of ERK2 was unaffected by tyrosine kinase inhibitor herbimycin in CaR-transfected HEK293 cells. These results suggest that usage of distinct pathways downstream of the CaR varies in a cell-type specific manner, suggesting a potential mechanism by which activation of the CaR could couple to distinct calcium-dependent responses.

  14. Structural mechanism of ligand activation in human calcium-sensing receptor.

    PubMed

    Geng, Yong; Mosyak, Lidia; Kurinov, Igor; Zuo, Hao; Sturchler, Emmanuel; Cheng, Tat Cheung; Subramanyam, Prakash; Brown, Alice P; Brennan, Sarah C; Mun, Hee-Chang; Bush, Martin; Chen, Yan; Nguyen, Trang X; Cao, Baohua; Chang, Donald D; Quick, Matthias; Conigrave, Arthur D; Colecraft, Henry M; McDonald, Patricia; Fan, Qing R

    2016-01-01

    Human calcium-sensing receptor (CaSR) is a G-protein-coupled receptor (GPCR) that maintains extracellular Ca(2+) homeostasis through the regulation of parathyroid hormone secretion. It functions as a disulfide-tethered homodimer composed of three main domains, the Venus Flytrap module, cysteine-rich domain, and seven-helix transmembrane region. Here, we present the crystal structures of the entire extracellular domain of CaSR in the resting and active conformations. We provide direct evidence that L-amino acids are agonists of the receptor. In the active structure, L-Trp occupies the orthosteric agonist-binding site at the interdomain cleft and is primarily responsible for inducing extracellular domain closure to initiate receptor activation. Our structures reveal multiple binding sites for Ca(2+) and PO4(3-) ions. Both ions are crucial for structural integrity of the receptor. While Ca(2+) ions stabilize the active state, PO4(3-) ions reinforce the inactive conformation. The activation mechanism of CaSR involves the formation of a novel dimer interface between subunits. PMID:27434672

  15. A Bayesian approach to optimal sensor placement for structural health monitoring with application to active sensing

    NASA Astrophysics Data System (ADS)

    Flynn, Eric B.; Todd, Michael D.

    2010-05-01

    This paper introduces a novel approach for optimal sensor and/or actuator placement for structural health monitoring (SHM) applications. Starting from a general formulation of Bayes risk, we derive a global optimality criterion within a detection theory framework. The optimal configuration is then established as the one that minimizes the expected total presence of either type I or type II error during the damage detection process. While the approach is suitable for many sensing/actuation SHM processes, we focus on the example of active sensing using guided ultrasonic waves by implementing an appropriate statistical model of the wave propagation and feature extraction process. This example implements both pulse-echo and pitch-catch actuation schemes and takes into account line-of-site visibility and non-uniform damage probabilities over the monitored structure. The optimization space is searched using a genetic algorithm with a time-varying mutation rate. We provide three actuator/sensor placement test problems and discuss the optimal solutions generated by the algorithm.

  16. Silicon nanowire based biosensing platform for electrochemical sensing of Mebendazole drug activity on breast cancer cells.

    PubMed

    Shashaani, Hani; Faramarzpour, Mahsa; Hassanpour, Morteza; Namdar, Nasser; Alikhani, Alireza; Abdolahad, Mohammad

    2016-11-15

    Electrochemical approaches have played crucial roles in bio sensing because of their Potential in achieving sensitive, specific and low-cost detection of biomolecules and other bio evidences. Engineering the electrochemical sensing interface with nanomaterials tends to new generations of label-free biosensors with improved performances in terms of sensitive area and response signals. Here we applied Silicon Nanowire (SiNW) array electrodes (in an integrated architecture of working, counter and reference electrodes) grown by low pressure chemical vapor deposition (LPCVD) system with VLS procedure to electrochemically diagnose the presence of breast cancer cells as well as their response to anticancer drugs. Mebendazole (MBZ), has been used as antitubulin drug. It perturbs the anodic/cathodic response of the cell covered biosensor by releasing Cytochrome C in cytoplasm. Reduction of cytochrome C would change the ionic state of the cells monitored by SiNW biosensor. By applying well direct bioelectrical contacts with cancer cells, SiNWs can detect minor signal transduction and bio recognition events, resulting in precise biosensing. Our device detected the trace of MBZ drugs (with the concentration of 2nM) on electrochemical activity MCF-7 cells. Also, experimented biological analysis such as confocal and Flowcytometry assays confirmed the electrochemical results.

  17. Region-based geometric active contour for classification using hyperspectral remote sensing images

    NASA Astrophysics Data System (ADS)

    Yan, Lin

    2011-12-01

    The high spectral resolution of hyperspectral imaging (HSI) systems greatly enhances the capabilities of discrimination, identification and quantification of objects of different materials from remote sensing images, but they also bring challenges to the processing and analysis of HSI data. One issue is the high computation cost and the curse of dimensionality associated with the high dimensions of HSI data. A second issue is how to effectively utilize the information including spectral and spatial information embedded in HSI data. Geometric Active Contour (GAC) is a widely used image segmentation method that utilizes the geometric information of objects within images. One category of GAC models, the region-based GAC models (RGAC), have good potential for remote sensing image processing because they use both spectral and geometry information in images are robust to initial contour placement. These models have been introduced to target extractions and classifications on remote sensing images. However, there are some restrictions on the applications of the RGAC models on remote sensing. First, the heavy involvement of iterative contour evolutions makes GAC applications time-consuming and inconvenient to use. Second, the current RGAC models must be based on a certain distance metric and the performance of RGAC classifiers are restricted by the performance of the employed distance metrics. According to the key features of the RGAC models analyzed in this dissertation, a classification framework is developed for remote sensing image classifications using the RGAC models. This framework allows the RGAC models to be combined with conventional pixel-based classifiers to promote them to spectral-spatial classifiers and also greatly reduces the iterations of contour evolutions. An extended Chan-Vese (ECV) model is proposed that is able to incorporate the widely used distance metrics in remote sensing image processing. A new type of RGAC model, the edge-oriented RGAC model

  18. Volumetric imaging of fast biological dynamics in deep tissue via wavefront engineering

    NASA Astrophysics Data System (ADS)

    Kong, Lingjie; Tang, Jianyong; Cui, Meng

    2016-03-01

    To reveal fast biological dynamics in deep tissue, we combine two wavefront engineering methods that were developed in our laboratory, namely optical phase-locked ultrasound lens (OPLUL) based volumetric imaging and iterative multiphoton adaptive compensation technique (IMPACT). OPLUL is used to generate oscillating defocusing wavefront for fast axial scanning, and IMPACT is used to compensate the wavefront distortions for deep tissue imaging. We show its promising applications in neuroscience and immunology.

  19. Active optics system of the VLT Survey Telescope.

    PubMed

    Schipani, Pietro; Noethe, Lothar; Magrin, Demetrio; Kuijken, Konrad; Arcidiacono, Carmelo; Argomedo, Javier; Capaccioli, Massimo; Dall'Ora, Massimo; D'Orsi, Sergio; Farinato, Jacopo; Fierro, Davide; Holzlöhner, Ronald; Marty, Laurent; Molfese, Cesare; Perrotta, Francesco; Ragazzoni, Roberto; Savarese, Salvatore; Rakich, Andrew; Umbriaco, Gabriele

    2016-03-01

    This paper describes the active optics system of the VLT Survey Telescope, the 2.6-m survey telescope designed for visible wavelengths of the European Southern Observatory at Cerro Paranal, in the Atacama desert. The telescope is characterized by a wide field of view (1.42 deg diameter), leading to tighter active optics than in conventional telescopes, in particular for the alignment requirements. We discuss the effects of typical error sources on the image quality and present the specific solutions adopted for wavefront sensing and correction of the aberrations, which are based on the shaping of a monolithic primary mirror and the positioning of the secondary in five degrees of freedom.

  20. Wavefront Imaging in Fractured Transversely-Isotropic Media

    NASA Astrophysics Data System (ADS)

    Shao, S.; Pyrak-Nolte, L. J.

    2013-12-01

    Fractures in the Earth's crust are a source of stress-dependent mechanical anisotropy that affect seismic wave attenuation and velocity. While many theoretical and experimental studies have investigated seismic wave propagation in single or multi- fractured isotropic rocks, few studies have examined the seismic response of a fractured anisotropic medium. Fractures and layering each contribute to the mechanical anisotropy of the crust. The coexistence of these two sources of anisotropy complicates the interpretation of the seismic properties of crustal rock. In this study, laboratory wavefront imaging was performed to capture the seismic response of layered media containing multiple parallel fractures. We determined that whether the observed anisotropy is dominated by the matrix anisotropy or by the fracture orientation depends on the applied stress and that late-arriving guided-modes provide information on the orientation of the fractures. Four cubic garolite samples (~102 mm on edge) each containing 5 parallel fractures were used in this study. The fractures were oriented normal, parallel or at acute angles (30 degrees, 60 degrees) to the layering. The fracture and layer spacing were approximately 10mm and 0.5mm, respectively. An intact sample containing no fractures was used as a standard orthorhombic medium for reference. Stress was applied to the samples with a servo-controlled loading machine. Two spherically-focused water-coupled transducers (central frequency 1MHz) were used; one as a fixed-source and the other as a translating receiver. Each sample was scanned over a 60mm×60mm region in 1 mm increments to map out the arriving wavefront (i.e. 3600 signals were recorded) as a function of time. The measured wavefront in the intact reference sample (which contained no fractures) was elliptical with the major axis parallel to the layers as expected and was stress-independent. When the fracture samples were subjected to low stress (<4 MPa), the observed seismic

  1. High-accuracy wavefront control for retinal imaging with Adaptive-Influence-Matrix Adaptive Optics

    PubMed Central

    Zou, Weiyao; Burns, Stephen A.

    2010-01-01

    We present an iterative technique for improving adaptive optics (AO) wavefront correction for retinal imaging, called the Adaptive-Influence-Matrix (AIM) method. This method is based on the fact that the deflection-to-voltage relation of common deformable mirrors used in AO are nonlinear, and the fact that in general the wavefront errors of the eye can be considered to be composed of a static, non-zero wavefront error (such as the defocus and astigmatism), and a time-varying wavefront error. The aberrated wavefront is first corrected with a generic influence matrix, providing a mirror compensation figure for the static wavefront error. Then a new influence matrix that is more accurate for the specific static wavefront error is calibrated based on the mirror compensation figure. Experimental results show that with the AIM method the AO wavefront correction accuracy can be improved significantly in comparison to the generic AO correction. The AIM method is most useful in AO modalities where there are large static contributions to the wavefront aberrations. PMID:19997241

  2. A Phase-Shifting Zernike Wavefront Sensor for the Palomar P3K Adaptive Optics System

    NASA Technical Reports Server (NTRS)

    Wallace, J. Kent; Crawford, Sam; Loya, Frank; Moore, James

    2012-01-01

    A phase-shifting Zernike wavefront sensor has distinct advantages over other types of wavefront sensors. Chief among them are: 1) improved sensitivity to low-order aberrations and 2) efficient use of photons (hence reduced sensitivity to photon noise). We are in the process of deploying a phase-shifting Zernike wavefront sensor to be used with the realtime adaptive optics system for Palomar. Here we present the current state of the Zernike wavefront sensor to be integrated into the high-order adaptive optics system at Mount Palomar's Hale Telescope.

  3. Calcium-sensing receptor activation in chronic kidney disease: effects beyond parathyroid hormone control.

    PubMed

    Massy, Ziad A; Hénaut, Lucie; Larsson, Tobias E; Vervloet, Marc G

    2014-11-01

    Secondary hyperparathyroidism (SHPT) is an important complication of advanced chronic kidney disease (CKD). Cinacalcet, an allosteric modulator of the calcium-sensing receptor (CaSR) expressed in parathyroid glands, is the only calcimimetic approved to treat SHPT in patients on dialysis. By enhancing CaSR sensitivity for plasma extracellular calcium (Ca(2+)0), cinacalcet reduces serum parathyroid hormone, Ca(2+)0, and serum inorganic phosphorous concentrations, allowing better control of SHPT and CKD-mineral and bone disorders. Of interest, the CaSR also is expressed in a variety of tissues where its activation regulates diverse cellular processes, including secretion, apoptosis, and proliferation. Thus, the existence of potential off-target effects of cinacalcet cannot be neglected. This review summarizes our current knowledge concerning the potential role(s) of the CaSR expressed in various tissues in CKD-related disorders, independently of parathyroid hormone control.

  4. Estimating the amount of Ship Recycling Activity Using Remote Sensing Application

    NASA Astrophysics Data System (ADS)

    Watagawa, M.; Shinoda, T.; Hasegawa, K.

    2016-06-01

    The Advanced Land Observing Satellite (ALOS) was launched for earth observation and there are more than 6 million scenes of archives including coastal areas during period of five years. The wealth of satellite imagery is noticeable for investigating monitoring methods such as ship detection in wide ocean area. Especially, it is useful way to estimate past behaviour from satellite imagery compared to reference data. We collected satellite imagery and analysis breaking process in major ship breaking yards between year 2009 and 2011. Comparing the number of recycling ships by satellite imagery to the world statistics is in good agreement. In this study, Remote Sensing Application has been discussed in order to assess the potential to be used for economic activities such as ship recycling in wide coastal area. It was used to evaluate the performance of ship recycling monitoring by Satellite imagery. Additionally, an approach for recognizing ships by SAR imagery regardless of weather conditions is presented.

  5. Sensing surface mechanical deformation using active probes driven by motor proteins

    PubMed Central

    Inoue, Daisuke; Nitta, Takahiro; Kabir, Arif Md. Rashedul; Sada, Kazuki; Gong, Jian Ping; Konagaya, Akihiko; Kakugo, Akira

    2016-01-01

    Studying mechanical deformation at the surface of soft materials has been challenging due to the difficulty in separating surface deformation from the bulk elasticity of the materials. Here, we introduce a new approach for studying the surface mechanical deformation of a soft material by utilizing a large number of self-propelled microprobes driven by motor proteins on the surface of the material. Information about the surface mechanical deformation of the soft material is obtained through changes in mobility of the microprobes wandering across the surface of the soft material. The active microprobes respond to mechanical deformation of the surface and readily change their velocity and direction depending on the extent and mode of surface deformation. This highly parallel and reliable method of sensing mechanical deformation at the surface of soft materials is expected to find applications that explore surface mechanics of soft materials and consequently would greatly benefit the surface science. PMID:27694937

  6. Sensing surface mechanical deformation using active probes driven by motor proteins

    NASA Astrophysics Data System (ADS)

    Inoue, Daisuke; Nitta, Takahiro; Kabir, Arif Md. Rashedul; Sada, Kazuki; Gong, Jian Ping; Konagaya, Akihiko; Kakugo, Akira

    2016-10-01

    Studying mechanical deformation at the surface of soft materials has been challenging due to the difficulty in separating surface deformation from the bulk elasticity of the materials. Here, we introduce a new approach for studying the surface mechanical deformation of a soft material by utilizing a large number of self-propelled microprobes driven by motor proteins on the surface of the material. Information about the surface mechanical deformation of the soft material is obtained through changes in mobility of the microprobes wandering across the surface of the soft material. The active microprobes respond to mechanical deformation of the surface and readily change their velocity and direction depending on the extent and mode of surface deformation. This highly parallel and reliable method of sensing mechanical deformation at the surface of soft materials is expected to find applications that explore surface mechanics of soft materials and consequently would greatly benefit the surface science.

  7. Structural damage identification in wind turbine blades using piezoelectric active sensing with ultrasonic validation

    SciTech Connect

    Claytor, Thomas N; Ammerman, Curtt N; Park, Gyu Hae; Farinholt, Kevin M; Farrar, Charles R; Atterbury, Marie K

    2010-01-01

    This paper gives a brief overview of a new project at LANL in structural damage identification for wind turbines. This project makes use of modeling capabilities and sensing technology to understand realistic blade loading on large turbine blades, with the goal of developing the technology needed to automatically detect early damage. Several structural health monitoring (SHM) techniques using piezoelectric active materials are being investigated for the development of wireless, low power sensors that interrogate sections of the wind turbine blade using Lamb wave propagation data, frequency response functions (FRFs), and time-series analysis methods. The modeling and sensor research will be compared with extensive experimental testing, including wind tunnel experiments, load and fatigue tests, and ultrasonic scans - on small- to mid-scale turbine blades. Furthermore, this study will investigate the effect of local damage on the global response of the blade by monitoring low-frequency response changes.

  8. Active Ground Optical Remote Sensing for Improved Monitoring of Seedling Stress in Nurseries

    PubMed Central

    Eitel, Jan U. H.; Keefe, Robert F.; Long, Dan S.; Davis, Anthony S.; Vierling, Lee A.

    2010-01-01

    Active ground optical remote sensing (AGORS) devices mounted on overhead irrigation booms could help to improve seedling quality by autonomously monitoring seedling stress. In contrast to traditionally used passive optical sensors, AGORS devices operate independently of ambient light conditions and do not require spectral reference readings. Besides measuring red (590–670 nm) and near-infrared (>760 nm) reflectance AGORS devices have recently become available that also measure red-edge (730 nm) reflectance. We tested the hypothesis that the additional availability of red-edge reflectance information would improve AGORS of plant stress induced chlorophyll breakdown in Scots pine (Pinus sylvestris). Our results showed that the availability of red-edge reflectance information improved AGORS estimates of stress induced variation in chlorophyll concentration (r2 > 0.73, RMSE < 1.69) when compared to those without (r2 = 0.57, RMSE = 2.11). PMID:22319275

  9. Modelling Rift Valley fever (RVF) disease vector habitats using active and passive remote sensing systems

    NASA Technical Reports Server (NTRS)

    Ambrosia, Vincent G.; Linthicum, K. G.; Bailey, C. L.; Sebesta, P.

    1989-01-01

    The NASA Ames Ecosystem Science and Technology Branch and the U.S. Army Medical Research Institute of Infectious Diseases are conducting research to detect Rift Valley fever (RVF) vector habitats in eastern Africa using active and passive remote-sensing. The normalized difference vegetation index (NDVI) calculated from Landsat TM and SPOT data is used to characterize the vegetation common to the Aedes mosquito. Relationships have been found between the highest NDVI and the 'dambo' habitat areas near Riuru, Kenya on both wet and dry data. High NDVI values, when combined with the vegetation classifications, are clearly related to the areas of vector habitats. SAR data have been proposed for use during the rainy season when optical systems are of minimal use and the short frequency and duration of the optimum RVF mosquito habitat conditions necessitate rapid evaluation of the vegetation/moisture conditions; only then can disease potential be stemmed and eradication efforts initiated.

  10. Bond slip detection of concrete-encased composite structure using shear wave based active sensing approach

    NASA Astrophysics Data System (ADS)

    Zeng, Lei; Parvasi, Seyed Mohammad; Kong, Qingzhao; Huo, Linsheng; Lim, Ing; Li, Mo; Song, Gangbing

    2015-12-01

    Concrete-encased composite structure exhibits improved strength, ductility and fire resistance compared to traditional reinforced concrete, by incorporating the advantages of both steel and concrete materials. A major drawback of this type of structure is the bond slip introduced between steel and concrete, which directly reduces the load capacity of the structure. In this paper, an active sensing approach using shear waves to provide monitoring and early warning of the development of bond slip in the concrete-encased composite structure is proposed. A specimen of concrete-encased composite structure was investigated. In this active sensing approach, shear mode smart aggregates (SAs) embedded in the concrete act as actuators and generate desired shear stress waves. Distributed piezoceramic transducers installed in the cavities of steel plates act as sensors and detect the wave response from shear mode SAs. Bond slip acts as a form of stress relief and attenuates the wave propagation energy. Experimental results from the time domain analysis clearly indicate that the amplitudes of received signal by lead zirconate titanate sensors decreased when bond slip occurred. In addition, a wavelet packet-based analysis was developed to compute the received signal energy values, which can be used to determine the initiation and development of bond slip in concrete-encased composite structure. In order to establish the validity of the proposed method, a 3D finite element analysis of the concrete-steel bond model is further performed with the aid of the commercial finite element package, Abaqus, and the numerical results are compared with the results obtained in experimental study.

  11. Activation of calcium-sensing receptor increases TRPC3 expression in rat cardiomyocytes

    SciTech Connect

    Feng, Shan-Li; Sun, Ming-Rui; Li, Ting-Ting; Yin, Xin; Xu, Chang-Qing; Sun, Yi-Hua

    2011-03-11

    Research highlights: {yields} Calcium-sensing receptor (CaR) activation stimulates TRP channels. {yields} CaR promoted transient receptor potential C3 (TRPC3) expression. {yields} Adult rat ventricular myocytes display capacitative calcium entry (CCE), which was operated by TRPCs. {yields} TRPC channels activation induced by CaR activator sustained the increased [Ca{sup 2+}]{sub i} to evoke cardiomyocytes apoptosis. -- Abstract: Transient receptor potential (TRP) channels are expressed in cardiomyocytes, which gate a type of influx of extracellular calcium, the capacitative calcium entry. TRP channels play a role in mediating Ca{sup 2+} overload in the heart. Calcium-sensing receptors (CaR) are also expressed in rat cardiac tissue and promote the apoptosis of cardiomyocytes by Ca{sup 2+} overload. However, data about the link between CaR and TRP channels in rat heart are few. In this study, reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting were used to examine the expression of the TRP canonical proteins TRPC1 and TRPC3 in adult and neonatal rat cardiomyocytes. Laser scan confocal microscopy was used to detect intracellular [Ca{sup 2+}]{sub i} levels in isolated adult rat ventricular myocytes. The results showed that, in adult rat cardiomyocytes, the depletion of Ca{sup 2+} stores in the endoplasmic/sarcoplasmic reticulum (ER/SR) by thapsigargin induced a transient increase in [Ca{sup 2+}]{sub i} in the absence of [Ca{sup 2+}]{sub o} and the subsequent restoration of [Ca{sup 2+}]{sub o} sustained the increased [Ca{sup 2+}]{sub i} for a few minutes, whereas, the persisting elevation of [Ca{sup 2+}]{sub i} was reduced in the presence of the TRPC inhibitor SKF96365. The stimulation of CaR by its activator gadolinium chloride (GdCl{sub 3}) or spermine also resulted in the same effect and the duration of [Ca{sup 2+}]{sub i} increase was also shortened in the absence of [Ca{sup 2+}]{sub o}. In adult and neonatal rat cardiomyocytes, GdCl{sub 3

  12. Tissue redox activity as a sensing platform for imaging of cancer based on nitroxide redox cycle.

    PubMed

    Zhelev, Zhivko; Aoki, Ichio; Gadjeva, Veselina; Nikolova, Biliana; Bakalova, Rumiana; Saga, Tsuneo

    2013-04-01

    The experience in free radical biology and medicine shows the crucial role of redox signalling in carcinogenesis. The cells and tissues of healthy mammals are characterised by a low level of reactive oxygen species (ROS) and some constant (reference) level of reducing equivalents. Increasing of ROS above the critical level provokes genomic instability. The present study describes universal methodology for direct imaging of tissue redox activity in carcinogenesis, which allows a differentiation of cancer development from normal condition. The experiments were conducted on: neuroblastoma-bearing mice; colon cancer-bearing mice; and healthy mice. The tissue redox activity was visualised in vivo by nitroxide-enhanced magnetic resonance imaging (MRI) on anesthetised animals. The method is based on nitroxide redox cycle, coupled with appearance/disappearance of MRI signal. The half-life (τ1/2) of nitroxide-enhanced MRI signal in the respective tissue was used as a diagnostic marker. The study provides direct evidence that healthy and cancer-bearing mammalian tissues are characterised by different redox activities - a basis for cancer diagnosis. The tissues (cancer and 'normal') of cancer-bearing mammals were characterised by a long-lived MRI signal (τ1/2>14 min), indicating a high oxidative activity. The tissues of healthy organism were characterised by a short-lived MRI signal (τ1/2=1-3 min), indicating a high reducing activity. The study shows that tissue redox activity is a sensing platform for imaging of cancer using nitroxide-enhanced MRI. It also suggests that 'normal' tissues of cancer-bearing organism are susceptible to oxidative damage.

  13. Empowering Prospective Teachers to Become Active Sense-Makers: Multimodal Modeling of the Seasons

    NASA Astrophysics Data System (ADS)

    Kim, Mi Song

    2015-10-01

    Situating science concepts in concrete and authentic contexts, using information and communications technologies, including multimodal modeling tools, is important for promoting the development of higher-order thinking skills in learners. However, teachers often struggle to integrate emergent multimodal models into a technology-rich informal learning environment. Our design-based research co-designs and develops engaging, immersive, and interactive informal learning activities called "Embodied Modeling-Mediated Activities" (EMMA) to support not only Singaporean learners' deep learning of astronomy but also the capacity of teachers. As part of the research on EMMA, this case study describes two prospective teachers' co-design processes involving multimodal models for teaching and learning the concept of the seasons in a technology-rich informal learning setting. Our study uncovers four prominent themes emerging from our data concerning the contextualized nature of learning and teaching involving multimodal models in informal learning contexts: (1) promoting communication and emerging questions, (2) offering affordances through limitations, (3) explaining one concept involving multiple concepts, and (4) integrating teaching and learning experiences. This study has an implication for the development of a pedagogical framework for teaching and learning in technology-enhanced learning environments—that is empowering teachers to become active sense-makers using multimodal models.

  14. Natural compounds regulate energy metabolism by the modulating the activity of lipid-sensing nuclear receptors.

    PubMed

    Goto, Tsuyoshi; Kim, Young-Il; Takahashi, Nobuyuki; Kawada, Teruo

    2013-01-01

    Obesity causes excess fat accumulation in various tissues, most notoriously in the adipose tissue, along with other insulin-responsive organs such as skeletal muscle and the liver, which predisposes an individual to the development of metabolic abnormalities. The molecular mechanisms underlying obesity-induced metabolic abnormalities have not been completely elucidated; however, in recent years, the search for therapies to prevent the development of obesity and obesity-associated metabolic disorders has increased. It is known that several nuclear receptors, when activated by specific ligands, regulate carbohydrate and lipid metabolism at the transcriptional level. The expression of lipid metabolism-related enzymes is directly regulated by the activity of various nuclear receptors via their interaction with specific response elements in promoters of those genes. Many natural compounds act as ligands of nuclear receptors and regulate carbohydrate and lipid metabolism by regulating the activities of these nuclear receptors. In this review, we describe our current knowledge of obesity, the role of lipid-sensing nuclear receptors in energy metabolism, and several examples of food factors that act as agonists or antagonists of nuclear receptors, which may be useful for the management of obesity and the accompanying energy metabolism abnormalities.

  15. Structural Domains Underlying the Activation of Acid-Sensing Ion Channel 2a

    PubMed Central

    Schuhmacher, Laura-Nadine; Srivats, Shyam; Smith, Ewan St. John

    2015-01-01

    The acid-sensing ion channels (ASICs) are a family of ion channels expressed throughout the mammalian nervous system. The principal activator of ASICs is extracellular protons, and ASICs have been demonstrated to play a significant role in many physiologic and pathophysiologic processes, including synaptic transmission, nociception, and fear. However, not all ASICs are proton-sensitive: ASIC2a is activated by acid, whereas its splice variant ASIC2b is not. We made a series of chimeric ASIC2 proteins, and using whole-cell electrophysiology we have identified the minimal region of the ASIC2a extracellular domain that is required for ASIC2 proton activation: the first 87 amino acids after transmembrane domain 1. We next examined the function of different domains within the ASIC2b N-terminus and identified a region proximal to the first transmembrane domain that confers tachyphylaxis upon ASIC2a. We have thus identified domains of ASIC2 that are crucial to channel function and may be important for the function of other members of the ASIC family. PMID:25583083

  16. Tracking SERS-active nanoprobe intracellular uptake for chemical and biological sensing

    NASA Astrophysics Data System (ADS)

    Gregas, Molly K.; Yan, Fei; Scaffidi, Jonathan; Wang, Hsin-Neng; Khoury, Christopher; Zhang, Yan; Vo-Dinh, Tuan

    2007-09-01

    A critical aspect of the use of nanoprobes for intracellular studies in chemical and biological sensing involves a fundamental understanding of their uptake and trajectory in cells. In this study, we describe experiments using surface-enhanced Raman scattering (SERS) spectroscopy and mapping to track cellular uptake of plasmonics-active labeled nanoparticles. Three different Raman-active labels with positive, negative, and neutral charges were conjugated to silver colloidal nanoparticles with the aim of spatially and temporally profiling intracellular delivery and tracking of nanoprobes during uptake in single mammalian cells. 1-D Raman spectra and 2-D Raman mapping are used to identify and locate the probes via their SERS signal intensities. Because Raman spectroscopy is very specific for identification of chemical and molecular signatures, the development of functionalized plasmonics-active nanoprobes capable of exploring intracellular spaces and processes has the ability to provide specific information on the effects of biological and chemical pollutants in the intracellular environment. The results indicate that this technique will allow study of when, where, and how these substances affect cells and living organisms.

  17. Pyrophosphate-regulated Zn(2+)-dependent DNAzyme activity: an amplified fluorescence sensing strategy for alkaline phosphatase.

    PubMed

    Kong, Rong-Mei; Fu, Ting; Sun, Ni-Na; Qu, Feng-Li; Zhang, Shu-Fang; Zhang, Xiao-Bing

    2013-12-15

    In this work, based on the fact that pyrophosphate (PPi) could regulate the activity of Zn(2+)-dependent DNAzyme, we for the first time report a fluorescence turn-on sensing system for alkaline phosphatase (ALP) with improved sensitivity via nonprotein-enzymatic signal amplification. A catalytic and molecular beacon (CAMB) design was employed to further improve its sensitivity. Taking advantage of the strong interactions between PPi and the Zn(2+), the cofactor Zn(2+) was caged, and the DNAzyme activity was effectively inhibited. The introduction of ALP, however, could catalyze the hydrolysis of PPi and release free Zn(2+), resulting in the activation of DNAzyme to catalyze the cleavage of the molecular beacon substrate with a remarkable increase of fluorescent signal. These optimized designs together allow a high sensitivity for ALP, with a detection limit of 20 pM observed, much lower than previously reported methods. It has also been used for detection of ALP in human serum with satisfactory results, demonstrating its potential applications in clinical diagnosis.

  18. The Jellyfish: smart electro-active polymers for an autonomous distributed sensing node

    NASA Astrophysics Data System (ADS)

    Blottman, John B.; Richards, Roger T.

    2006-05-01

    The US Navy has recently placed emphasis on deployable, distributed sensors for Force Protection, Anti-Terrorism and Homeland Defense missions. The Naval Undersea Warfare Center has embarked on the development of a self-contained deployable node that is composed of electro-active polymers (EAP) for use in a covert persistent distributed surveillance system. Electro-Active Polymers (EAP) have matured to a level that permits their application in energy harvesting, hydrophones, electro-elastic actuation and electroluminescence. The problem to resolve is combining each of these functions into an autonomous sensing platform. The concept presented here promises an operational life several orders of magnitude beyond what is expected of a Sonobuoy due to energy conservation and harvesting, and at a reasonable cost. The embodiment envisioned is that of a deployed device resembling a jellyfish, made in most part of polymers, with the body encapsulating the necessary electronic processing and communications package and the tentacles of the jellyfish housing the sonar sensors. It will be small, neutrally buoyant, and will survey the water column much in the manner of a Cartesian Diver. By using the Electro-Active Polymers as artificial muscles, the motion of the jellyfish can be finely controlled. An increased range of detection and true node autonomy is achieved through volumetric array beamforming to focus the direction of interrogation and to null-out extraneous ambient noise.

  19. Remote sensing and tectonic analysis of active volcanoes in continental arcs

    NASA Astrophysics Data System (ADS)

    Wessels, Rick Lee

    Variations in arc volcano spatial distribution and morphology are influenced by the crustal structure beneath the arc. In Colombia and Ecuador, most of the active volcanoes lie on or near regional arc-parallel fault zones, and many of the major volcanoes are aligned or elongated parallel to the faults. Two dominant volcano-fault geometry patterns exist: (1) From north to south, the orientation of the fractures and volcano-shapes changes along the arc from primarily north-northwest trending to east-northeast trending; and (2) From west to east, the fault and volcano alignment patterns vary from north-northwest trends at the outer edges of the arc to east-northeast trending in the middle of the arc. The fault and volcano orientation patterns are related to the age and type of crust being faulted during oblique subduction. The regionally active strike-slip faults in the Northern Andes and other arcs provide long-lasting paths for magma ascent that penetrate much deeper through the lithosphere than the secondary features. Local zones of extension and pre-existing fractures in the last several kilometers of lithosphere provide the plumbing that diverts magma slightly away from the primary linear volcanic front. The dissertation also describes a technique for merging multiple remote sensing data sets over the extremely rough terrain of silicic volcanoes. The major focus of this work was on overcoming coregistration errors from geometric distortion induced by local topography. The geometric distortion was compensated for by first creating an accurate base image with a combination of global positioning system (GPS) ground control, high resolution digital elevation models (DEM), and orthorectified aerial photographs. The individual sensor data were then rectified to the new reference base using triangulation geocoding. The final multi-layered, geocoded product is being used to enhance an existing thermal infrared technique for mapping complex textural patterns in silicic

  20. Visualization of cardiac wavefronts using data fusion

    NASA Astrophysics Data System (ADS)

    Kynor, David B.; Dietz, Anthony; Friets, Eric; Peterson, Jon; Bergstrom, Ursula; Triedman, John; Hammer, Peter

    2002-05-01

    Catheter ablation has emerged as a highly effective treatment for arrhythmias that are constrained by known, easily located, anatomic landmarks. However, this treatment has enjoyed limited success for arrhythmias that are characterized by complex activation patterns or are not anatomically constrained. This class of arrhythmias, which includes atrial fibrillation and ventricular tachycardia resulting from ischemic heart disease, demands improved mapping tools. Current technology forces the cardiologist to view cardiac anatomy independently from the functional information contained in the electrical activation patterns. This leads to difficulties in interpreting the large volumes of data provided by high-density recording catheters and in mapping patients with abnormal anatomy (e.g., patients with congenital heart disease). The goal of this is work is development of new data processing and display algorithms that will permit the clinician to view activation sequences superimposed onto existing fluoroscopic images depicting the location of recording catheters within the heart. In cases where biplane fluoroscopic images and x-ray camera position data are available, the position of the catheters can be reconstructed in three-dimensions.

  1. Non-Invasive Microbial Metabolic Activity Sensing at Single Cell Level by Perfusion of Calcein Acetoxymethyl Ester

    PubMed Central

    Krämer, Christina E. M.; Singh, Abhijeet; Helfrich, Stefan; Grünberger, Alexander; Wiechert, Wolfgang; Nöh, Katharina; Kohlheyer, Dietrich

    2015-01-01

    Phase contrast microscopy cannot give sufficient information on bacterial metabolic activity, or if a cell is dead, it has the fate to die or it is in a viable but non-growing state. Thus, a reliable sensing of the metabolic activity helps to distinguish different categories of viability. We present a non-invasive instantaneous sensing method using a fluorogenic substrate for online monitoring of esterase activity and calcein efflux changes in growing wild type bacteria. The fluorescent conversion product of calcein acetoxymethyl ester (CAM) and its efflux indicates the metabolic activity of cells grown under different conditions at real-time. The dynamic conversion of CAM and the active efflux of fluorescent calcein were analyzed by combining microfluidic single cell cultivation technology and fluorescence time lapse microscopy. Thus, an instantaneous and non-invasive sensing method for apparent esterase activity was created without the requirement of genetic modification or harmful procedures. The metabolic activity sensing method consisting of esterase activity and calcein secretion was demonstrated in two applications. Firstly, growing colonies of our model organism Corynebacterium glutamicum were confronted with intermittent nutrient starvation by interrupting the supply of iron and carbon, respectively. Secondly, bacteria were exposed for one hour to fatal concentrations of antibiotics. Bacteria could be distinguished in growing and non-growing cells with metabolic activity as well as non-growing and non-fluorescent cells with no detectable esterase activity. Microfluidic single cell cultivation combined with high temporal resolution time-lapse microscopy facilitated monitoring metabolic activity of stressed cells and analyzing their descendants in the subsequent recovery phase. Results clearly show that the combination of CAM with a sampling free microfluidic approach is a powerful tool to gain insights in the metabolic activity of growing and non

  2. Revisiting the comparison between the Shack-Hartmann and the pyramid wavefront sensors via the Fisher information matrix.

    PubMed

    Plantet, C; Meimon, S; Conan, J-M; Fusco, T

    2015-11-01

    Exoplanet direct imaging with large ground based telescopes requires eXtreme Adaptive Optics that couples high-order adaptive optics and coronagraphy. A key element of such systems is the high-order wavefront sensor. We study here several high-order wavefront sensing approaches, and more precisely compare their sensitivity to noise. Three techniques are considered: the classical Shack-Hartmann sensor, the pyramid sensor and the recently proposed LIFTed Shack-Hartmann sensor. They are compared in a unified framework based on precise diffractive models and on the Fisher information matrix, which conveys the information present in the data whatever the estimation method. The diagonal elements of the inverse of the Fisher information matrix, which we use as a figure of merit, are similar to noise propagation coefficients. With these diagonal elements, so called "Fisher coefficients", we show that the LIFTed Shack-Hartmann and pyramid sensors outperform the classical Shack-Hartmann sensor. In photon noise regime, the LIFTed Shack-Hartmann and modulated pyramid sensors obtain a similar overall noise propagation. The LIFTed Shack-Hartmann sensor however provides attractive noise properties on high orders.

  3. OCAM2S: an integral shutter ultrafast and low noise wavefront sensor camera for laser guide stars adaptive optics systems

    NASA Astrophysics Data System (ADS)

    Gach, Jean-Luc; Feautrier, Philippe; Balard, Philippe; Guillaume, Christian; Stadler, Eric

    2014-07-01

    To date, the OCAM2 system has demonstrated to be the fastest and lowest noise production ready wavefront sensor, achieving 2067 full frames per second with subelectron readout noise. This makes OCAM2 the ideal system for natural as well as continuous wave laser guide star wavefront sensing. In this paper we present the new gated version of OCAM2 named OCAM2-S, using E2V's CCD219 sensor with integral shutter. This new camera offers the same superb characteristics than OCAM2 both in terms of speed and readout noise but also offers a shutter function that makes the sensor only sensitive to light for very short periods, at will. We will report on gating time and extinction ratio performances of this new camera. This device opens new possibilities for Rayleigh pulsed lasers adaptive optics systems. With a shutter time constant well below 1 microsecond, this camera opens new solutions for pulsed sodium lasers with backscatter suppression or even spot elongation minimization for ELT LGS.

  4. Revisiting the comparison between the Shack-Hartmann and the pyramid wavefront sensors via the Fisher information matrix.

    PubMed

    Plantet, C; Meimon, S; Conan, J-M; Fusco, T

    2015-11-01

    Exoplanet direct imaging with large ground based telescopes requires eXtreme Adaptive Optics that couples high-order adaptive optics and coronagraphy. A key element of such systems is the high-order wavefront sensor. We study here several high-order wavefront sensing approaches, and more precisely compare their sensitivity to noise. Three techniques are considered: the classical Shack-Hartmann sensor, the pyramid sensor and the recently proposed LIFTed Shack-Hartmann sensor. They are compared in a unified framework based on precise diffractive models and on the Fisher information matrix, which conveys the information present in the data whatever the estimation method. The diagonal elements of the inverse of the Fisher information matrix, which we use as a figure of merit, are similar to noise propagation coefficients. With these diagonal elements, so called "Fisher coefficients", we show that the LIFTed Shack-Hartmann and pyramid sensors outperform the classical Shack-Hartmann sensor. In photon noise regime, the LIFTed Shack-Hartmann and modulated pyramid sensors obtain a similar overall noise propagation. The LIFTed Shack-Hartmann sensor however provides attractive noise properties on high orders. PMID:26561131

  5. Implementation of Active Teaching Methods and Emerging Topics in Photogrammetry and Remote Sensing Subjects

    NASA Astrophysics Data System (ADS)

    Kosmatin Fras, M.; Grigillo, D.

    2016-06-01

    Fast technological developments in photogrammetry and remote sensing areas demand quick and steady changes in the education programme and its realization. The university teachers and assistants are faced with ensuring the learning materials, data and software for practical lessons, as well as project proposals for student's team work and bachelor or master thesis. In this paper the emerging topics that already have a considerable impact in the practice are treated mostly from the educational aspect. These relatively new topics that are considered in this paper are unmanned aerial systems for spatial data collection, terrestrial and aerial laser scanning, mobile mapping systems, and novelties in satellite remote sensing. The focus is given to practical implementation of these topics into the teaching and learning programme of Geodesy and Geoinformation at the University of Ljubljana, Faculty of Civil and Geodetic Engineering, and experiences gained by the authors so far. Together with the technological advances, the teaching approaches must be modernized as well. Classical approaches of teaching, where a lecturer gives lecture ex cathedra and students are only listeners, are not effective enough. The didactics science of teaching has developed and proved in the practice many useful approaches that can better motivate students for more active learning. We can use different methods of team work like pro et contra debate, buzzing groups, press conference, moderated discussion etc. An experimental study on active teaching methods in the class of students of the Master programme of Geodesy and Geoinformation has been made and the results are presented. After using some new teaching methods in the class, the students were asked to answer two types of a questionnaire. First questionnaire was the standard form developed by Noel Entwistle, an educational psychologist who developed the Approaches to Studying Inventory (ASI) for identifying deep and surface approaches to

  6. Focal plane wavefront sensor achromatization: The multireference self-coherent camera

    NASA Astrophysics Data System (ADS)

    Delorme, J. R.; Galicher, R.; Baudoz, P.; Rousset, G.; Mazoyer, J.; Dupuis, O.

    2016-04-01

    Context. High contrast imaging and spectroscopy provide unique constraints for exoplanet formation models as well as for planetary atmosphere models. But this can be challenging because of the planet-to-star small angular separation (<1 arcsec) and high flux ratio (>105). Recently, optimized instruments like VLT/SPHERE and Gemini/GPI were installed on 8m-class telescopes. These will probe young gazeous exoplanets at large separations (≳1 au) but, because of uncalibrated phase and amplitude aberrations that induce speckles in the coronagraphic images, they are not able to detect older and fainter planets. Aims: There are always aberrations that are slowly evolving in time. They create quasi-static speckles that cannot be calibrated a posteriori with sufficient accuracy. An active correction of these speckles is thus needed to reach very high contrast levels (>106-107). This requires a focal plane wavefront sensor. Our team proposed a self coherent camera, the performance of which was demonstrated in the laboratory. As for all focal plane wavefront sensors, these are sensitive to chromatism and we propose an upgrade that mitigates the chromatism effects. Methods: First, we recall the principle of the self-coherent camera and we explain its limitations in polychromatic light. Then, we present and numerically study two upgrades to mitigate chromatism effects: the optical path difference method and the multireference self-coherent camera. Finally, we present laboratory tests of the latter solution. Results: We demonstrate in the laboratory that the multireference self-coherent camera can be used as a focal plane wavefront sensor in polychromatic light using an 80 nm bandwidth at 640 nm (bandwidth of 12.5%). We reach a performance that is close to the chromatic limitations of our bench: 1σ contrast of 4.5 × 10-8 between 5 and 17 λ0/D. Conclusions: The performance of the MRSCC is promising for future high-contrast imaging instruments that aim to actively minimize the

  7. Utilization of the Wavefront Sensor and Short-exposure Images for Simultaneous Estimation of Quasi-static Aberration and Exoplanet Intensity

    NASA Astrophysics Data System (ADS)

    Frazin, Richard A.

    2013-04-01

    Heretofore, the literature on exoplanet detection with coronagraphic telescope systems has paid little attention to the information content of short exposures and methods of utilizing the measurements of adaptive optics wavefront sensors. This paper provides a framework for the incorporation of the wavefront sensor measurements in the context of observing modes in which the science camera takes millisecond exposures. In this formulation, the wavefront sensor measurements provide a means to jointly estimate the static speckle and the planetary signal. The ability to estimate planetary intensities in as little as a few seconds has the potential to greatly improve the efficiency of exoplanet search surveys. For simplicity, the mathematical development assumes a simple optical system with an idealized Lyot coronagraph. Unlike currently used methods, in which increasing the observation time beyond a certain threshold is useless, this method produces estimates whose error covariances decrease more quickly than inversely proportional to the observation time. This is due to the fact that the estimates of the quasi-static aberrations are informed by a new random (but approximately known) wavefront every millisecond. The method can be extended to include angular (due to diurnal field rotation) and spectral diversity. Numerical experiments are performed with wavefront data from the AEOS Adaptive Optics System sensing at 850 nm. These experiments assume a science camera wavelength λ of 1.1 μ, that the measured wavefronts are exact, and a Gaussian approximation of shot-noise. The effects of detector read-out noise and other issues are left to future investigations. A number of static aberrations are introduced, including one with a spatial frequency exactly corresponding the planet location, which was at a distance of ≈3λ/D from the star. Using only 4 s of simulated observation time, a planetary intensity, of ≈1 photon ms-1, and a stellar intensity of ≈105 photons ms-1

  8. Spliceosome SNRNP200 Promotes Viral RNA Sensing and IRF3 Activation of Antiviral Response

    PubMed Central

    Tremblay, Nicolas; Baril, Martin; Chatel-Chaix, Laurent; Es-Saad, Salwa; Park, Alex Young; Koenekoop, Robert K.; Lamarre, Daniel

    2016-01-01

    Spliceosomal SNRNP200 is a Ski2-like RNA helicase that is associated with retinitis pigmentosa 33 (RP33). Here we found that SNRNP200 promotes viral RNA sensing and IRF3 activation through the ability of its amino-terminal Sec63 domain (Sec63-1) to bind RNA and to interact with TBK1. We show that SNRNP200 relocalizes into TBK1-containing cytoplasmic structures upon infection, in contrast to the RP33-associated S1087L mutant, which is also unable to rescue antiviral response of SNRNP200 knockdown cells. This functional rescue correlates with the Sec63-1-mediated binding of viral RNA. The hindered IFN-β production of knockdown cells was further confirmed in peripheral blood cells of RP33 patients bearing missense mutation in SNRNP200 upon infection with Sendai virus (SeV). This work identifies a novel immunoregulatory role of the spliceosomal SNRNP200 helicase as an RNA sensor and TBK1 adaptor for the activation of IRF3-mediated antiviral innate response. PMID:27454487

  9. Acid-sensing ion channels regulate spontaneous inhibitory activity in the hippocampus: possible implications for epilepsy.

    PubMed

    Ievglevskyi, O; Isaev, D; Netsyk, O; Romanov, A; Fedoriuk, M; Maximyuk, O; Isaeva, E; Akaike, N; Krishtal, O

    2016-08-01

    Acid-sensing ion channels (ASICs) play an important role in numerous functions in the central and peripheral nervous systems ranging from memory and emotions to pain. The data correspond to a recent notion that each neuron and many glial cells of the mammalian brain express at least one member of the ASIC family. However, the mechanisms underlying the involvement of ASICs in neuronal activity are poorly understood. However, there are two exceptions, namely, the straightforward role of ASICs in proton-based synaptic transmission in certain brain areas and the role of the Ca(2+)-permeable ASIC1a subtype in ischaemic cell death. Using a novel orthosteric ASIC antagonist, we have found that ASICs specifically control the frequency of spontaneous inhibitory synaptic activity in the hippocampus. Inhibition of ASICs leads to a strong increase in the frequency of spontaneous inhibitory postsynaptic currents. This effect is presynaptic because it is fully reproducible in single synaptic boutons attached to isolated hippocampal neurons. In concert with this observation, inhibition of the ASIC current diminishes epileptic discharges in a low Mg(2+) model of epilepsy in hippocampal slices and significantly reduces kainate-induced discharges in the hippocampus in vivo Our results reveal a significant novel role for ASICs.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'. PMID:27377725

  10. Improved Infrared-Sensing Running Wheel Systems with an Effective Exercise Activity Indicator

    PubMed Central

    Chen, Chi-Chun; Chang, Ming-Wen; Chang, Ching-Ping; Chang, Wen-Ying; Chang, Shin-Chieh; Lin, Mao-Tsun; Yang, Chin-Lung

    2015-01-01

    This paper describes an infrared-sensing running wheel (ISRW) system for the quantitative measurement of effective exercise activity in rats. The ISRW system provides superior exercise training compared with commercially available traditional animal running platforms. Four infrared (IR) light-emitting diode/detector pairs embedded around the rim of the wheel detect the rat’s real-time position; the acrylic wheel has a diameter of 55 cm and a thickness of 15 cm, that is, it is larger and thicker than traditional exercise wheels, and it is equipped with a rubber track. The acrylic wheel hangs virtually frictionless, and a DC motor with an axially mounted rubber wheel, which has a diameter of 10 cm, drives the acrylic wheel from the outer edge. The system can automatically train rats to run persistently. The proposed system can determine effective exercise activity (EEA), with the IR sensors (which are connected to a conventional PC) recording the rat exercise behavior. A prototype of the system was verified by a hospital research group performing ischemic stroke experiments on rats by considering middle cerebral artery occlusion. The experimental data demonstrated that the proposed system provides greater neuroprotection in an animal stroke model compared with a conventional treadmill and a motorized running wheel for a given exercise intensity. The quantitative exercise effectiveness indicator showed a 92% correlation between an increase in the EEA and a decrease in the infarct volume. This indicator can be used as a noninvasive and objective reference in clinical animal exercise experiments. PMID:25875841

  11. Study for urbanization corresponding to socio-economic activities in Savannaket, Laos using satellite remote sensing

    NASA Astrophysics Data System (ADS)

    Kimijiama, S.; Nagai, M.

    2014-06-01

    In Greater Mekong Sub-region (GMS), economic liberalization and deregulation facilitated by GMS Regional Economic Corporation Program (GMS-ECP) has triggered urbanization in the region. However, the urbanization rate and its linkage to socio-economic activities are ambiguous. The objectives of this paper are to: (a) determine the changes in urban area from 1972 to 2013 using remote sensing data, and (b) analyse the relationships between urbanization with respect to socio-economic activities in central Laos. The study employed supervised classification and human visible interpretation to determine changes in urbanization rate. Regression analysis was used to analyze the correlation between the urbanization rate and socio-economic variables. The result shows that the urban area increased significantly from 1972 to 2013. The socio-economic variables such as school enrollment, labour force, mortality rate, water source and sanitation highly correlated with the rate of urbanization during the period. The study concluded that identifying the highly correlated socio-economic variables with urbanization rate could enable us to conduct a further urbanization simulation. The simulation helps in designing policies for sustainable development.

  12. Improved infrared-sensing running wheel systems with an effective exercise activity indicator.

    PubMed

    Chen, Chi-Chun; Chang, Ming-Wen; Chang, Ching-Ping; Chang, Wen-Ying; Chang, Shin-Chieh; Lin, Mao-Tsun; Yang, Chin-Lung

    2015-01-01

    This paper describes an infrared-sensing running wheel (ISRW) system for the quantitative measurement of effective exercise activity in rats. The ISRW system provides superior exercise training compared with commercially available traditional animal running platforms. Four infrared (IR) light-emitting diode/detector pairs embedded around the rim of the wheel detect the rat's real-time position; the acrylic wheel has a diameter of 55 cm and a thickness of 15 cm, that is, it is larger and thicker than traditional exercise wheels, and it is equipped with a rubber track. The acrylic wheel hangs virtually frictionless, and a DC motor with an axially mounted rubber wheel, which has a diameter of 10 cm, drives the acrylic wheel from the outer edge. The system can automatically train rats to run persistently. The proposed system can determine effective exercise activity (EEA), with the IR sensors (which are connected to a conventional PC) recording the rat exercise behavior. A prototype of the system was verified by a hospital research group performing ischemic stroke experiments on rats by considering middle cerebral artery occlusion. The experimental data demonstrated that the proposed system provides greater neuroprotection in an animal stroke model compared with a conventional treadmill and a motorized running wheel for a given exercise intensity. The quantitative exercise effectiveness indicator showed a 92% correlation between an increase in the EEA and a decrease in the infarct volume. This indicator can be used as a noninvasive and objective reference in clinical animal exercise experiments.

  13. Electrochemical sensing chemical oxygen demand based on the catalytic activity of cobalt oxide film.

    PubMed

    Wang, Jinqi; Wu, Can; Wu, Kangbing; Cheng, Qin; Zhou, Yikai

    2012-07-29

    Cobalt oxide sensing film was in situ prepared on glassy carbon electrode surface via constant potential oxidation. Controlling at 0.8 V in NaOH solution, the high-valence cobalt catalytically oxidized the reduced compounds, decreasing its surface amount and current signal. The current decline was used as the response signal of chemical oxygen demand (COD) because COD represents the summation of reduced compounds in water. The surface morphology and electrocatalytic activity of cobalt oxide were readily tuned by variation of deposition potential, time, medium and Co(2+) concentration. As confirmed from the atomic force microscopy measurements, the cobalt oxide film, that prepared at 1.3 V for 40 s in pH 4.6 acetate buffer containing 10 mM Co(NO(3))(2), possesses large surface roughness and numerous three-dimensional structures. Electrochemical tests indicated that the prepared cobalt oxide exhibited high electrocatalytic activity to the reduced compounds, accompanied with strong COD signal enhancement. As a result, a novel electrochemical sensor with high sensitivity, rapid response and operational simplicity was developed for COD. The detection limit was as low as 1.1 mg L(-1). The analytical application was studied using a large number of lake water samples, and the accuracy was tested by standard method.

  14. Oxidative DNA damage protective activity, antioxidant and anti-quorum sensing potentials of Moringa oleifera.

    PubMed

    Singh, Brahma N; Singh, B R; Singh, R L; Prakash, D; Dhakarey, R; Upadhyay, G; Singh, H B

    2009-06-01

    The aqueous extract of leaf (LE), fruit (FE) and seed (SE) of Moringa oleifera was assessed to examine the ability to inhibit the oxidative DNA damage, antioxidant and anti-quorum sensing (QS) potentials. It was found that these extracts could significantly inhibit the OH-dependent damage of pUC18 plasmid DNA and also inhibit synergistically with trolox, with an activity sequence of LE > FE > SE. HPLC and MS/MS analysis was carried out, which showed the presence of gallic acid, chlorogenic acid, ellagic acid, ferulic acid, kaempferol, quercetin and vanillin. The LE was with comparatively higher total phenolics content (105.04 mg gallic acid equivalents (GAE)/g), total flavonoids content (31.28 mg quercetin equivalents (QE)/g), and ascorbic acid content (106.95 mg/100 g) and showed better antioxidant activity (85.77%), anti-radical power (74.3), reducing power (1.1 ascorbic acid equivalents (ASE)/ml), inhibition of lipid peroxidation, protein oxidation, OH-induced deoxyribose degradation, and scavenging power of superoxide anion and nitric oxide radicals than did the FE, SE and standard alpha-tocopherol. Eventually, LE and FE were found to inhibit violacein production, a QS-regulated behavior in Chromobacterium violaceum 12472.

  15. Switch of SpnR function from activating to inhibiting quorum sensing by its exogenous addition.

    PubMed

    Takayama, Yuriko; Kato, Norihiro

    2016-09-01

    The opportunistic human pathogen Serratia marcescens AS-1 produces the N-hexanoylhomoserine lactone (C6HSL) receptor SpnR, a homologue of LuxR from Vibrio fischeri, which activates pig clusters to produce the antibacterial prodigiosin. In this study, we attempted to artificially regulate quorum sensing (QS) by changing the role of SpnR in N-acylhomoserine lactone (AHL)-mediated QS. SpnR was obtained as a fusion protein tagged with maltose-binding protein (MBP) from overexpression in Escherichia coli, and its specific affinity to C6HSL was demonstrated by quartz crystal microbalance analysis and AHL-bioassay with Chromobacterium violaceum CV026. Prodigiosin production was effectively inhibited by externally added MBP-SpnR in both wild-type AS-1 and the AHL synthase-defective mutant AS-1(ΔspnI). For the mutant, the induced amount of prodigiosin was drastically reduced to approximately 4% with the addition of 18 μM MBP-SpnR to the liquid medium, indicating 81% trapping of C6HSL. A system for inhibiting QS can be constructed by adding exogenous AHL receptor to the culture broth to keep the concentration of free AHL low, whereas intracellular SpnR naturally functions as the activator in response to QS. PMID:27387237

  16. Switch of SpnR function from activating to inhibiting quorum sensing by its exogenous addition.

    PubMed

    Takayama, Yuriko; Kato, Norihiro

    2016-09-01

    The opportunistic human pathogen Serratia marcescens AS-1 produces the N-hexanoylhomoserine lactone (C6HSL) receptor SpnR, a homologue of LuxR from Vibrio fischeri, which activates pig clusters to produce the antibacterial prodigiosin. In this study, we attempted to artificially regulate quorum sensing (QS) by changing the role of SpnR in N-acylhomoserine lactone (AHL)-mediated QS. SpnR was obtained as a fusion protein tagged with maltose-binding protein (MBP) from overexpression in Escherichia coli, and its specific affinity to C6HSL was demonstrated by quartz crystal microbalance analysis and AHL-bioassay with Chromobacterium violaceum CV026. Prodigiosin production was effectively inhibited by externally added MBP-SpnR in both wild-type AS-1 and the AHL synthase-defective mutant AS-1(ΔspnI). For the mutant, the induced amount of prodigiosin was drastically reduced to approximately 4% with the addition of 18 μM MBP-SpnR to the liquid medium, indicating 81% trapping of C6HSL. A system for inhibiting QS can be constructed by adding exogenous AHL receptor to the culture broth to keep the concentration of free AHL low, whereas intracellular SpnR naturally functions as the activator in response to QS.

  17. Twisted speckle entities inside wave-front reversal mirrors

    SciTech Connect

    Okulov, A. Yu

    2009-07-15

    The previously unknown property of the optical speckle pattern reported. The interference of a speckle with the counterpropagating phase-conjugated (PC) speckle wave produces a randomly distributed ensemble of a twisted entities (ropes) surrounding optical vortex lines. These entities appear in a wide range of a randomly chosen speckle parameters inside the phase-conjugating mirrors regardless to an internal physical mechanism of the wave-front reversal. These numerically generated interference patterns are relevant to the Brillouin PC mirrors and to a four-wave mixing PC mirrors based upon laser trapped ultracold atomic cloud.

  18. Towards feasible and effective predictive wavefront control for adaptive optics

    SciTech Connect

    Poyneer, L A; Veran, J

    2008-06-04

    We have recently proposed Predictive Fourier Control, a computationally efficient and adaptive algorithm for predictive wavefront control that assumes frozen flow turbulence. We summarize refinements to the state-space model that allow operation with arbitrary computational delays and reduce the computational cost of solving for new control. We present initial atmospheric characterization using observations with Gemini North's Altair AO system. These observations, taken over 1 year, indicate that frozen flow is exists, contains substantial power, and is strongly detected 94% of the time.

  19. Intracellular Ca(2+) mobilization and kinase activity during acylated homoserine lactone-dependent quorum sensing in Serratia liquefaciens.

    PubMed

    Werthén, M; Lundgren, T

    2001-03-01

    Quorum sensing in Gram-negative bacteria involves acylated homoserine lactones (AHLs) and a transcription factor, activated by the AHLs. In this study, a possible involvement of intracellular Ca(2+) as second messenger and/or protein kinase activity during signal transduction is analyzed. When N-hexanoyl-l-homoserine lactone was added to a suspension of Fura-2-loaded Serratia liquefaciens, there was a decline in [Ca(2+)](i), measured as a decrease in the Fura-2 fluorescence ratio. As controls, the addition of the signal molecule N-3-oxohexanoyl-l-homoserine lactone, which is not produced by S. liquefaciens, did not induce changes in [Ca(2+)](i). Using a protein kinase activity assay on AHL-stimulated cells, an increase in kinase activity after N-butanoyl-l-homoserine lactone stimulation of S. liquefaciens cells was detected, whereas the kinase activity induced by N-3-oxohexanoyl-l-homoserine lactone was not statistically significant. The conclusion from this study is that changes in [Ca(2+)](i) are involved in quorum sensing signal transduction in the Gram-negative bacteria S. liquefaciens. We also conclude that kinase activity is induced in S. liquefaciens upon AHL stimulation. We suggest that the transient intracellular [Ca(2+)] changes and kinase activity, activated by the AHL signal, are critical for the quorum-sensing signal transduction.

  20. Expected gain in the pyramid wavefront sensor with limited Strehl ratio

    NASA Astrophysics Data System (ADS)

    Viotto, V.; Ragazzoni, R.; Bergomi, M.; Magrin, D.; Farinato, J.

    2016-09-01

    Context. One of the main properties of the pyramid wavefront sensor is that, once the loop is closed, and as the reference star image shrinks on the pyramid pin, the wavefront estimation signal-to-noise ratio can considerably improve. This has been shown to translate into a gain in limiting magnitude when compared with the Shack-Hartmann wavefront sensor, in which the sampling on the wavefront is performed before the light is split into four quadrants, which does not allow the quality of the focused spot to increase. Since this property is strictly related to the size of the re-imaged spot on the pyramid pin, the better the wavefront correction, the higher the gain. Aims: The goal of this paper is to extend the descriptive and analytical computation of this gain that was given in a previous paper, to partial wavefront correction conditions, which are representative for most of the wide field correction adaptive optics systems. Methods: After focusing on the low Strehl ratio regime, we analyze the minimum spatial sampling required for the wavefront sensor correction to still experience a considerable gain in sensitivity between the pyramid and the Shack-Hartmann wavefront sensors. Results: We find that the gain can be described as a function of the sampling in terms of the Fried parameter.