bluuebunny/crossref_metadata_2025 huggingface dataset:
Amnesty. Pardon. Criminal record
Authors: Grishko Aleksandr , Seliverstov Vyacheslav , Naumov Anatoliy
Published: February 2023

The monograph examines various aspects of the institutions of amnesty, pardon, criminal record: the concept, the history of formation, foreign legislative practice. The features of the personality of the amnestied and pardoned are analyzed. A comparative analysis with related institutions was carried out: parole, rehabilitation. In contrast to the previous edition, new legal realities related to the amendments made to legislative acts, Decree of the President of the Russian Federation No. 1500 of December 28, 2001 "On Pardon commissions in the Territories of the Subjects of the Russian Federation" are taken into account.
It is intended for employees of justice bodies, courts, law enforcement agencies, members of pardon commissions in the territories of the subjects of the Russian Federation. It can be used in the educational process during training, advanced training and retraining of personnel in the direction (specialty) "Jurisprudence". Will provide assistance to researchers, applicants, graduate students (adjuncts).
Control and supervisory activities of customs authorities in the context of digitalization and integration of the economy
Authors: Agamagomedova Saniyat , Bakaeva Ol'ga , Grechkina Ol'ga
Published: February 2023

The monograph is devoted to the implementation of the control and supervisory functions of the customs authorities of the Russian Federation in the context of digital and integration agendas. The theoretical foundations of the construction of control and supervisory activities of customs authorities are investigated, the author's methodology of its doctrinal positioning is proposed, the correlation of various types of state control and supervision in the activities of customs authorities is substantiated. It is of interest to consider the control and supervisory activities of customs authorities in the context of the introduction of digital mechanisms, the use of artificial intelligence, as well as the development of integration processes on the territory of the Eurasian Economic Union.
For teachers, researchers, postgraduates and practitioners interested in the activities of customs authorities.
Flat farms. Schemes and calculation formulas: a reference book. Volume 2
Authors: Kirsanov Mihail , Kozlov Vladimir
Published: February 2023

The handbook contains 99 schemes of flat regular statically definable trusses and exact formulas for calculating the forces in the rods and deflection depending on the number of panels. Algorithms for obtaining analytical solutions in the Maple computer mathematics system are described. Cases of kinematic variability of some truss schemes with a certain number of panels have been noted. An algorithm for analytical calculation of a spatial cantilever truss and an axisymmetric dome is described. An example of farm calculation is considered.
Designed for engineers, researchers, students and postgraduates of technical universities.
Perceptual Consequences of the Trichromatic Cone Mosaic
Authors: Williams David R.
Published: February 2023

That the eye is trichromatic has been known for more than two centuries, and the spectral sensitivity of the cones has been known for nearly three decades. Nonetheless, we have only relatively recently begun to assemble a picture of the topography of the three cone classes across the retina. Trichromacy has been incorporated in the human retina by interleaving three separate submosaics of S, M, L cones in a single tier of receptors. This means that at any single point in the retinal mosaic, the visual system is essentially color blind, and it is only by comparing the responses of different cones at different spatial locations that the visual system can estimate spectral variations in the retinal image. This talk will review what is known about the topography of the three cone submosaics and the perceptual consequences of that topography.
Chromatic Stiles-Crawford effect in normal and anomalous trichromatic color vision
Authors: Walraven Pieter L.
Published: February 2023

Stiles and Crawford (1933) showed that the sensitivity of the retina varies with the place of entry of the light in the pupil, and thus with the direction of incidence of light upon the retina. Sensitivity is generally greatest near the centre of the pupil and progressively decreases for more eccentric entry points. This phenomenon is known as the Stiles-Crawford effect.
Spectral Sensitivity by Increment Threshold during Saccades
Authors: Sato Masayuki , Uchikawa Keiji
Published: February 2023

Images on the retina change rapidly during saccades. The visual system
integrates clear images before and after saccades to produce a stable
perception of the outside scene. It is said that during saccades the
visual system is suppressed to eliminates the smeared images, which
may disturb integration of the retinal images.1) It has not
been well understood how the visual system eliminate the smeared
images. Luminance and chromatic channels in the visual system seem to
play different roles to perceive the outside scene.2) If
the saccadic suppression is useful to integrate images, luminance and
chromatic channels may be suppressed differently during saccades. In
this report, we measured spectral sensitivity functions by the
increment threshold method during saccades and fixation in order to
clarify the effects of saccadic suppression on luminance and chromatic
channels.3),4)
Dynamic neon colors: Perceptual evidence for parallel visual pathways
Authors: Cicerone Carol M. , Hoffman Donald D.
Published: February 2023

There is accumulating neurophysiological evidence that the primate visual system constructs multiple representations of the visual world (1-5). Each of these representations, based on classes of neurons with distinctive properties and roles, provides an analysis of some aspect, for example motion, of the visual world. In everyday life, a smooth interleaving of the information provided by these parallel pathways leaves us unaware of this segregation of function: Effortlessly, we use a complex tapestry of form, color, depth, and motion to make sense of the patterns of light and dark falling upon our retinae.
Lightness Constancy and Adaptation to Illumination Varying as a Temporal Sinusoid
Authors: Shimozaki Steven S. , Thomas James P.
Published: February 2023

To evaluate the time course of adaptation processes affecting lightness constancy judgments, two subjects performed lightness discriminations between two similar suprathreshold simulated achromatic surfaces while a simulated achromatic illumination varied as a temporal sinusoid with periods varying from 0.7 to 120 sec.
Dual Rayleigh-Like Color Matches Sensitive to Individual Differences in Cone Photopigments
Authors: Shevell Steven K. , He Ji Chang
Published: February 2023

Color matches of normal trichromatic observers reveal substantial individual differences. The Rayleigh match, in which an admixture of 545 and 670 nm lights is matched to 589 nm, is a classical procedure that has been modified recently to explore the cause(s) of normals’ interobserver variation (Neitz and Jacobs, 1986). Three distinct physiological bases may contribute to differences among observers’ Rayleigh matches: (1) pre-receptoral spectrally selective filtering, (2) optical density of cone photopigment, and (3) the wavelength of peak sensitivity of cone photopigment. Rayleigh measurements from a large sample of observers that fall into two or more distinct sub-populations have been interpreted as evidence that some individuals are slightly different than others with respect to the wavelength at which their photopigment is most sensitive. This type of individual difference among normal trichromats has been attributed to an X-linked polymorphism (Neitz and Jacobs, 1990).
The basic building blocks of color vision: A Generalized View of the Opponent Colors Transformation
Authors: Buchsbaum Gershon , Derrico Joel B.
Published: February 2023

Neurophysiology provided color research with a wealth of single unit recordings indicating how color is coded in the early visual system [e.g., 1]. These show that when color is coded in the visual system it is encrypted together with spatial features. An obvious requirement of the coding system is that it be sufficient to contain all image information relevant to the visual system, for processing at higher levels of the visual system [2]. One of the most commonly applied hypotheses to understand the coding strategy is that the visual system is an efficient coder. This term has been used before to investigate whether the coding scheme, using building blocks recorded in physiology, is minimizing error, utilizing minimum transmission resources, combatting noise by improving signal to noise ratio and related criteria [3,4].
The Effects of Backgrounds on Sensitivity and Brightness
Authors: Hayhoe Mary M.
Published: February 2023

One of the primary accomplishments of the retinal circuitry is to transform the light signal to one which reflects contrast, or variation around the mean level, rather than the mean level itself. This transformation determines not only visual sensitivity, but also is an important factor in the suprathreshold visibility, that is the brightness of objects. Historically, most work on the problem has concerned measurements of threshold sensitivity. I will review our current understanding of the determinants of visual sensitivity and then examine how far we can extend these conceptions to the perception of brightness.
Additional Constancy Data Obtained with the Color Naming Method
Authors: Troost Jimmy M. , de Weert Charles M.M.
Published: February 2023

In this paper we present additional data obtained with the naming task. First, the size of the set of (monolexemic) color names from which subjects have to draw their responses is varied. Besides the basic set of 11 color names, we also presented subjects with sets of 6, 2x6 and 19 color names. It was found that if the set of alternatives becomes sufficiently detailed, by increasing the number of color names, responses shift toward colorimetric matches as opposed to constancy matches. Second, we investigated the adaptation component on color naming by either presenting illuminant conditions blockwise or randomized. Obviously, (slow) adaptation mechanisms are more likely to have an effect in the blockwise version than in the randomized version. We conclude that the naming method is not affected by slow adaptation processes.
Color Discrimination Measures and Mechanisms Under Varying Viewing Conditions
Authors: Nagy Allen L.
Published: February 2023

The primary data on which uniform color spaces have been based were collected under nearly optimal viewing conditions. Observers foveally scrutinized a pair of adjacent stimuli of moderate size for extended periods. It is common knowledge that many factors such as the spatial and temporal properties of the stimulus and its location in the visual field greatly influence an observers ability to discriminate colors. Some attempts to characterize these variations within existing uniform color spaces have been made (for example, Judd, 1973). However, uniform color spaces typically are transformations of the CIE chromaticity diagram which is based on imaginary primaries that are not easily relatable to physiological mechanisms. Therefore, it may be difficult to characterize variations in discrimination under different conditions with simple changes in the uniform color space such as scaling the axes.
Nonlinear transformation of color coordinates for color reproduction by a 3-layered neural network
Authors: Arai Yoshifumi , Nakano Yoshiki , Iga Tetsuo , Usui Shiro
Published: February 2023

A conventional color reproduction theories widely used in the color reproduction systems have been established by Yule et al.[1]. However, some kinds of problems, such as the difference of the reproduced color between a color monitor and a color printer, have occured because these theories are based on the densitometoric color value and/or other device-dependent color representation. We now require a device-independent representation of color information to reproduce color accurately. That is, we should adopt CIEXYZ value or other colorimetric values for color reproduction theories. Furthermore, we require the mothod of transformation between device-dependent color representation and independent color representations. Laihanen and other investigator[4] [2] attempted to establish the transformation method by using a Look-up-table and/or Neugebauer equations[3] and indicated that these methods cannot be used for practical applications because of the problems such as accuracy of the transformation and/or calculation cost.
A color segmentation method for image registration in automatic face recognition
Authors: Sasaki Tsutomu , Akamatsu Shigeru , Fukamachi Hideo , Suenaga Yasuhito
Published: February 2023

The computer identification of human faces is a fundamental element of high level human-computer interaction. It must be both accurate and easy to use. In order to realize fully automatic facial image processing and face identification based on 2D intensity images, it is necessary to accurately extract the standard face view from the input face image automatically. If the standard face view is not extracted correctly, identification accuracy remains poor. Therefore, manual extraction of the standard face view is used in most previous facial image processing research.
Design of a Color Information Processing System with Spectral Responses Similar to Human Eyes
Authors: Yamaba Kazuo , Miyake Yoichi
Published: February 2023

In recent years, color vision techniques have been gaining attention in various kinds of industrial fields. One reason for its effectiveness, apart from the actual information, is that the information is in color.
Color Image analysis by vector subspace method
Authors: Toyooka S. , Jaaskelainen T. , Izawa S. , Hayasaka N. , Kadono H.
Published: February 2023

Spectral characteristics of a color image is conventionally obtained by multi-spectral imaging(1,2). A color image is illuminated by series of light having narrow spectral band equally divided in the visible spectral region. Spectral distribution for each pixel is directly determined by intensity distribution of images for each illuminating light.
Color appearance of colored lights at light-adapted peripheral retina
Authors: Takase Masanori , Uchikawa Keiji
Published: February 2023

It has been pointed out that, as eccentricity of the peripheral retina is increased, saturation of light is dropped rapidly and its hue changes to blue or yellow in the dark-adapted condition.1-4) The present experiment is performed to find out whether such deterioration is observed in the light- adapted environment.
Color Appearances of Objects at High Illuminance in Natural Environment
Authors: Shibata Tsutomu , Henry Ronald C.
Published: February 2023

Atmospheric visivility is now of concern not only to transportation safety but also to protection of scenic beauty of national parks and certain other areas. There have been air quality visibility models developed that make use of CIE color difference formulae for evaluating the perceptibility of plumes and hazes. We built the Visual Colorimeter for Atomospheric Research (VICAR) that allows one to quantify the subjective experience of color by binocular color matching on site in the natural environment. Objective measurements were also taken simultaneously with a spectrophotometer for comparison and analysis.
Topological Factors in Neon Color Spreading1
Authors: Albert Marc K. , Hoffman Donald D.
Published: February 2023

The human visual system is often confronted with ambiguity in its interpretation of images. Many researchers believe that the visual system can be understood, in part, by investigating the constraints that it uses to arrive at its perceptions. Recently researchers have begun to appreciate the power that these constraints can provide for understanding subjective contours [1] and neon color spreading [2]. In this paper we will study some of the topological factors involved in neon color spreading [3] [4] using the constraint of “general position”.
Indeterminacy of a Privileged Coordinate Frame Based on Discrimination Measures: Analysis and Experimental Tests
Authors: Knoblauch Kenneth , Maloney Laurence T.
Published: February 2023

A basic aim in the study of vision is to determine the fundamental mechanisms that mediate discrimination performance. In color vision, the description of discrimination data by an ellipsoidal representation has been very successful but at the cost of an indeterminacy in the knowledge of which axes in color space correspond to mechanism directions. For example, in the work of Wandell and colleagues (Wandell, 1982; Poirson et al., 1990) color discrimination contours are described by a mapping, A, from receptor coordinates to a privileged coordinate frame in which threshold differences map onto a unit sphere, where v is a color difference vector. As they so indicate, the matrix A is determined by the data only up to an arbitrary orthogonal transform. If the privileged coordinate frame is interpreted as a mechanism space, then the mechanisms mediating discrimination are specified only to within rotations and mirror image reflections. Geometrically, this means that the discrimination mechanisms do not necessarily lie along the principal axes of the ellipsoid that describes threshold but could lie along any set of axes for which the threshold lengths are mapped into unit orthogonal directions by A. Consequently, discrimination thresholds would not be sufficient to specify uniquely mechanism directions. Additional factors must be taken into account to pin down which axes of an ellipsoid correspond to visual mechanisms, e.g., specifying directions along which a mechanism might be null, based on adaptational (Krauskopf et al., 1982) or perceptual (Thornton and Pugh, 1983) criteria.
Combination of Signals from Opponent Color Mechanisms
Authors: Zaidi Qasim , Shapiro Arthur G.
Published: February 2023

Despite the long standing interest in stage-theories of human color vision, little thought had been given to the processing of the output of traditional opponent mechanisms until Krauskopf et al (1986a,b) presented the first experiments to address this issue. The original evidence for post-opponent mechanisms came from the habituating effect of prolonged simultaneous stimulation of the two chromatic cardinal mechanisms of Krauskopf et al (1982). Under the hypothesis that prolonged stimulation leads to independent "fatigue" of the two mechanisms, the effect of habituation should be greatest along one or the other of the cardinal directions, irrespective of the habituating color direction. This hypothesis was rejected because the maximum effect was always in the habituating direction. Krauskopf et al (1986a) suggested that the results were compatible with habituation within multiple higher order mechanisms.
Discrimination Ellipsoid of Surface Color
Authors: Indow Tarow
Published: February 2023

Discrimination thresholds in various directions from a standard color stimulus s0 are represented by an ellipsoid in the (x, y, Y) space or, when the luminance Y is kept constant, by an ellipse on the chromaticity diagram. It has been a tradition since MacAdam (1942) to define thresholds by fluctuation of repeated color matchings under the assumption that the distribution of colors indiscriminable from s0 is 3-D or 2-D normal fN(s). This procedure cannot be applied to painted color samples and the discrimination ellipsoid around s0 is defined through paired comparisons of s0 and sj, where sj's are a set of prepared samples, j = 1, 2,…, n. As to method of obtaining an ellipsoid from these data, the situation is chaotic. Indow and Morrison (1991) proposed a procedure that is an extension of the method of constant stimuli for uni-dimensional stimulus continuum. Denote by Pj the rate that sj is judged different from s0 where sj differs from s0 in various directions Λ = 1, 2,…, n.
Spatial reconstruction of signals from short-wavelength cones
Authors: Brainard David H. , Williams David R.
Published: February 2023

Because the retinal cone mosaic samples an image only at discrete locations, our continuous visual percept must arise from a spatial reconstruction process. How this process combines information from the three cone types is presently unclear. To investigate, we asked whether luminance information can modify the visual system's reconstruction of signals from the S cones. In Experiment 1, we used a matching paradigm to measure the effect of luminance information on filling-in at the foveal tritanopic area. In Experiment 2, we asked whether luminance information can modify the splotchy low-frequency alias seen when an observer views fine S cone gratings.
Analysis and Calibration of Natural Guide Star Adaptive Optics Data
Authors: Tessier Eric
Published: February 2023

The point spread function (PSF) calibrator data from the Come-On Plus instrument (COP, see Beuzit et al. 1994) were obtained on the 1st January 1994 at 8:54, 8:59 and 9:03 UT respectively for the KHJ bands as continous series of one-second exposure frames respectively 120 in the K band and 60 in the H band and of three 20-second exposure frame in the J band. Left part of Fig. 1 shows the distribution of the full width half maximum (FWHM) versus Strehl ratio (SR) for each individual exposures of the calibrator in JHK. The FWHM is rescaled by a factor λ/D (which corresponds to the diffraction limit at the wavelength λ for a telescope of diameter D), points clearly gather along a single curve.
Optimization of Closed-Loop Adaptive Optics Wavefront Reconstruction Algorithms Using Experimentally Measured Performance Data: Experimental Results
Authors: Rhoadarmer Troy A. , Ellerbroek Brent L.
Published: February 2023

Experiments have shown the reward adaptive optics provides in improving the resolution of ground-based astronomical telescopes.1-2 A critical contributor to adaptive optics system performance is the reconstruction algorithm that converts wavefront sensor (WFS) measurements into the deformable mirror (DM) actuator commands.3-4 Minimum variance reconstruction algorithms have been developed extensively to optimize the performance of adaptive optics systems given specific atmospheric conditions.5-7 These algorithms depend on atmospheric parameters which are seldom known exactly and are constantly fluctuating. This is especially true for systems incorporating multiple WFS beacons that require knowledge of the wind speed profile, the vertical distribution of atmospheric turbulence, and the intensity of the wavefront sensing beacons to calculate the optimal reconstructor.7 This uncertainty and continual changing of atmospheric conditions implies that an optimal degree of turbulence compensation cannot be achieved or maintained over long time intervals with static reconstructor coefficients. A need exists for a method of updating these coefficients in real time based on actual closed-loop performance.
Initial results from the Lick Observatory laser guide star adaptive optics system
Authors: Olivier Scot S. , An Jong , Avicola Kenneth , Bissinger Horst D. , Brase James M. , Friedman Herbert W. , Gavel Donald T. , Macintosh Bruce , Max Claire E. , Salmon J. Thaddeus , Waltjen Kenneth E.
Published: February 2023

A prototype adaptive optics system has been developed at Lawrence Livermore National Laboratory (LLNL) for use on the 3-m Shane telescope at Lick Observatory. This system is currently based on a 127-actuator continuous-surface deformable mirror developed at LLNL, a high-quantum-efficiency low-noise fast CCD camera built for LLNL by Adaptive Optics Associates using a chip developed by Lincoln Laboratory, and a Mercury VME board containing four Intel i860 processors.
Adaptive Telescope Array for Laser Communications and Astronomy
Authors: Kudielka Klaus H. , Leeb Walter R.
Published: February 2023

Phased telescope arrays can be used to coherently receive or transmit optical radiation [1], even in the presence of wavefront distortion due to turbulent media [2]. In addition, phased telescope arrays operating in receive mode allow to obtain images with high angular resolution [3] and to implement wide field-of-view imaging systems [4].
High Speed Micro-Machine Device for Adaptive Correction of Aero-Optic Effects
Authors: Clark Rod , Karpinsky John , Borek Gregg , Johnson Eric , Clark Natalie
Published: February 2023

Current adaptive optical 1 systems which provide wavefront correction operate at or below 100 Hz, a frequency response suitable for correcting atmospheric effects for such applications as ground-based astronomy1. These systems are limited to such low frequency operating bandwidths by the speed of the processing and drive electronics, and the large, slow, deformable mirror devices utilized by these system designs. SY Technology, Inc. has developed a micro-machine based, high frequency, adaptive device which, when inserted into the proposed interferometric design, will have the potential to correct wavefronts at frequencies of hundreds of kilohertz2. This tremendous bandwidth is achieved by a device fabricated using photolithographic techniques, with its drive electronics controlled through light-addressed circuitry (see Figure 1). In this paper, a closed-loop adaptive, interferometric micro-machine device to correct for aero-optic effects is described and demonstrated3.
Site Atmospheric Characterization
Authors: Sarazin Marc
Published: February 2023

The past decade has seen the development of new devices to reliably monitor atmospheric seeing and several observatories are now routinely proposing to the observers new services including online visualization of the site seeing as in addition to standard meteorological parameters.
Mesospheric Metals for Guide Star Generation
Authors: Papen George C.
Published: February 2023

Elemental Na has been the tracer of choice for the generation of high altitude (mesospheric) guide stars because of its relatively large natural abundance and large absorption cross section. Dye based systems using Na are currently under development for several large aperture telescopes. However, robust solid state laser technology to generate high power narrow linewidth light at 589nmhas progressed slowly. Here we consider both the tracer and the transmitter technology and show that using either the K D1line at 769nmor the 372nmline of Fe (a5D-z5F°) for the tracer may provide robust solutions until solid state Na transmitter technology can be more fully developed. The comparable performance is primarily due to the fact that both lines can be generated with existing solid state materials (Alexandrite, Ti:Sapphire).
Simulation of Adaptive Optical Correction with Deformable Secondary Mirrors
Authors: Bigelow B. C.
Published: February 2023

Adaptive secondary mirrors offer the promise of maximum throughput and minimum emissivity, when compared to traditional post-secondary adaptive optical systems. Currently, at least five telescope projects (Keck, LBT, MMT Conversion, UKIRT, VLT) are developing secondary mirrors of either the tip/tilt or deformable variety. Tip/tilt secondary mirror systems have already been demonstrated. For example, Close and McCarthy[1] have operated a tip/tilt system on a 2.3-m telescope which provides a factor of 4 improvement in Strehl ratio and nearly diffraction-limited imaging at 1.6μm. The primary objective of this work has been to examine, through detailed simulations, the wavefront correction characteristics of a deformable secondary mirror. This work is part of an on-going development program at the OSL to produce an adaptive secondary mirror system, potentially for the 3.8 m UKIRT.
Rapid Phase Retrieval Using The Fast Fourier Transform
Authors: Gureyev T.E. , Nugent K.A. , Paganin D. , Roberts A.
Published: February 2023

Phase retrieval from intensity data based purely on the Fourier transform is demonstrated experimentally and theoretically. Our method does not require boundary conditions.
The Alternative Large Telescope Construction
Authors: Sychev Victor V. , Kaspersky Valery B.
Published: February 2023

They propose a new conception of the large astronomical telescope with a primary segmented mirror 10 m. Constructively the telescope is supposed to make using an alt-azimuthal scheme as an upper moving part having a sphere-like shape.
New Wavefront Reconstructor for the MMT Adaptive Secondary
Authors: Stahl Steven M. , Barrett Todd K.
Published: February 2023

In this paper we present a reconstructor optimized to fully utilize spatial and temporal correlations of the measured wavefront and a hardware implementation being built for the adaptive optics system for the new 6.5m single-mirror MMT. We compare the projected performance for a closed-loop system which drives the mirror to obtain a wavefront sensor null with a system designed to “optimally” utilize measurements from the source--which may be a laser guide star.
Use of the LBT to study zodiacal emission around other stars
Authors: Woolf N. , Angel J.R.P.
Published: February 2023

Thermal emission from "planetary" discs is known in other stars such as β Pictoris. The emission, discovered by the IRAS satellite, is comparable in strength to that from the star itself at 60 µm wavelength, indicating a large quantity of material at radius ~ 100 AU and temperature ~ 50 K (ref 1). Such discs are uncommonly bright, far more dense and extensive than the known zodiacal dust in our solar system. Here the emission is concentrated mostly within 1 AU, where the dust temperature is ~ 300K and it is optically very thin, causing an increment of only 10-5 in the 10 µm luminosity of the Sun as seen from afar.
Post-Processing of Adaptive Optics Corrected Images
Authors: Christou Julian C. , Drummond Jack D.
Published: February 2023

Ground-based images of astronomical objects typically require some form of post-processing to realize their full information content. The same is true for images obtained with adaptive optics. In order to do this an unresolved source near the target of interest is required.
Imaging exoplanets with the 6.5 m MMT and Magellan telescopes
Authors: Angel Roger , Sandler David
Published: February 2023

Do stars like the sun also have similar planetary systems? No positive detection has been yet made, but observations by various ground based methods may soon produce answers. Gravitational microlensing events observed with high precision should show the presence of planets around distant normal stars1. Indirect searches are also currently being conducted of nearby stars, for stellar reaction motion through astrometry and doppler accelerometry. The sensitivity and length of observations should soon become adequate to sense Jupiter mass planets at a number of stars.
Are scintillations indeed noise for wave front sensing?
Authors: Ribak Erez N.
Published: February 2023

The field of view in adaptive optics is limited by a very narrow isoplanatic angle. A number of deformable mirrors, each conjugated to a different atmospheric layer, might provide phase compensation over an extended field. For this a larger volume need be probed using a multitude of guide stars (see review in [Baharav 1994, 95]). Angel [1994] noticed that the search for planets next to bright stars is limited by scintillation. Scintillation is produced by high turbulence [Tatarski 1971]. If so, why not correct it with a deformable mirror conjugate to that turbulence, whose error signal is provided by the same scintillation? [Ribak 1994, 5].
Sky Coverage Calculations for Astronomical Adaptive Optics
Authors: Ellerbroek Brent L. , Racine René , Tyler David
Published: February 2023

The fraction of the sky over which an adaptive-optics (AO) system will provide a useful level of performance is limited by anisoplanatism. One measure of sky coverage is the probabilty P(P ≥ S*) that the system will provide a Strehl ratio S no smaller than a threshold value S* when observing in a random direction selected without reference to the distribution of guide stars. This probability is a function of the atmospheric turbulence and wind velocity profiles, the telescope aperture diameter, the observing wavelength, the density of guide stars as a function of magnitude, and the characteristics of the adaptive-optics system. Some of these characteristics include the photon efficiency of the wavefront sensor (WFS), the order and efficiency of the AO correction, and bandwidth of the AO control loop. The values of these parameters which will maximize P(P ≥ S*) for a natural guide star (NGS) AO system are strongly dependant upon the choice of the threshold Strehl ratio S*, while current interest in laser guide star (LGS) adaptive-optics is of course motivated by the potential for dramatic increases in P(S > S*) for large values of S* at visible and near infrared wavelengths.
Wavefront estimation by phase diversity and compensation with a liquid crystal wavefront corrector.
Authors: Love Gordon D. , Ebstein Steven M. , Gonsalves Robert A. , Nisenson Peter , Restaino Sergio R. , Carreras Richard C. , Junor. William
Published: February 2023

Nematic liquid crystal spatial light modulators (LC-SLMs) have been proposed as wavefront correctors for adaptive optics (a summary of which is described in ref. 1 and references therein). For example, at the last OSA/ESO meeting on adaptive optics in Garching (1995) we described a high-quality LC-SLM which had 69-direct driven pixels which was custom designed for adaptive optics applications2. Additional work has been done with the goal of producing a polarization insensitive LC-SLM which does not suffer the reduced efficiency of a device which only works with a single polarization3. This paper demonstrates successful application of an LC-SLM to wavefront compensation and the first successful application of phase diversity sensing4 to wavefront compensation, to the best of our knowledge.
Results from the Cassegrain adaptive optics system of the Mount Wilson 100-inch telescope
Authors: Shelton J. C. , Schneider T.G. , McKenna D. , Baliunas S. L.
Published: February 2023

Since June of 1994 we have been operating and improving a natural-guide-star adaptive optics system on the Mount Wilson 100-inch telescope.1,3 The system is routinely operated by one person plus a telescope operator. First astronomical observations have achieved image profiles with a full-width-at-half-max (FWHM) of 0.068 arcsec, using a silicon CCD with no wavelength discrimination (Fig. 1).
Nd:YAG Laser Beam Pointing Stability and Artificial Guide Star Generation
Authors: Parfenov Vadim A. , Rodin Sergei N.
Published: February 2023

Laser beam pointing instability is one of the most actual problem at the artificial guide stars generation, because high angular stability (~1…2 arcsec) of laser beacons is required for atmosphreric compensation with adaptive optics. In our work we investigated the beam pointing stability of frequency-doubled Nd:YAG lasers generating at the wavelength of 532 nm. Such lasers may be used for guide stars generation by Rayleigh optical scattering by air molecules in the stratosphere [1].
First Results of a Polychromatic Artificial Sodium Star for the Correction of Tilt
Authors: Friedman Herbert , Foy Renaud , Talion Michel , Migus Arnold
Published: February 2023

With the present state of technology, the tilt component of a aberrated stellar wavefront which has been distorted by atmospheric turbulence cannot be ascertained by an artificial guide star. The absolute position of the artificial guide star cannot be determined since it wanders on the uplink portion of its propagation and there is no way, at least with a single receiving telescope, to distinguish an undetermined position of a guide star from tilt in the wavefront. In conventional adaptive optics systems, a natural star is needed to supply the tilt information in addition to the higher order corrections supplied by an artificial guide star. The probability of finding a suitably bright natural guide star for tilt correction is not significantly higher than for higher order correction despite the fact that the entire telescope area is used and both the tilt anisoplanatic angle and integration time are considerably larger. Since the tilt contributes ≈90% of the phase variance, the accuracy in the tilt measurement has to be much greater than for higher order corrections1. In particular at galactic latitudes above the galactic plane, or at visible wavelengths, the sky coverage for a tilt star becomes unacceptable for most applications.
Subaru Adaptive Optics Program
Authors: Takami Hideki , Iye Masanori , Takato Naruhisa , Otsubo Masashi , Nakashima Koji
Published: February 2023

SUBARU telescope is being constructed atop Mauna Kea in the Hawaii island. It employs an 8.2 m thin-meniscus primary mirror that is supported by 261 actuators and 3 fixed points and will provide an almost perfect surface figure for the near infrared imaging. Under such circumstances, the atmospheric turbulence will become the dominant source of image degradation. Therefore, an adaptive optics (hereafter AO) system is essential in attaining the high resolution imaging capability for large ground-based telescopes.
Laser Systems for the Generation of Sodium Layer Guide Stars
Authors: Friedman H. , Erbert G. , Kuklo T. , Salmon T. , Thompson G. , Wong N. , Malik J.
Published: February 2023

Laser generated guide stars in the mesosphere at 90 km provide an effective beacon for adaptive optics schemes which compensate the effects of atmospheric turbulence. Atomic sodium, the species with the highest product of integrated density and cross section, requires an exciting laser with a stable wavelength of 589 nm, a spectral bandwidth of ≈3 GHz and a peak power incident on the mesosphere of ≤5 W/cm2 in order to reduce the effects of saturation. There are several other attributes of the laser which are desirable from a point of view of overall adaptive optics system performance and operation ease. These include the following: (1) near diffraction limited beam quality which is needed to make a small laser guide star, (2) pointing accuracy in the arcsecond range with resolution in the subarcsecond range, (3) the ability to detune the laser for background subtraction or retune to another wavelength for polychromatic guide stars1, (4) a configuration which simplifies the laser projection optics and does not require beam paths through the telescope bearings and (5) an effective method of removing waste head from the laser before it enters the dome volume. Finally, while lasers with average power in the ten watt range may be sufficient for observations in the near IR, extension to visible observations will require multiple guide stars with total powers in the hundred watt range. Therefore the ability to scale up in power by an order of magnitude in a straightforward manner is certainly desirable.
Applications of Neural Networks in Adaptive Optics
Authors: Aitken George J. M.
Published: February 2023

Artificial neural networks have been successfully applied to a wide variety of practical tasks ranging from the recognition of speech and handwriting to the prediction of future stock prices. Highly refined learning procedures allow these multilayer, nonlinear networks to construct internal representations from examples, thus removing the need for explicit programming. The power of neural networks (NN) derives from their ability to learn nonlinear relationships and to generalize from specific training situations. They are advantageous where a small number of decisions have to be made from a large amount of data, and where nonlinear or very complex mappings must be acquired.
Optimization of Closed-Loop Adaptive-Optics Control Algorithms Using Measured Performance Data: Experimental Results
Authors: Ellerbroek Brent L. , Rhoadarmer Troy A.
Published: February 2023

Experiments have shown the reward adaptive-optics provides in improving the resolution of ground-based astronomical telescopes [1,2,3]. A critical contributor to adaptive-optics system performance is the control algorithm that converts wavefront sensor (WFS) measurements into the deformable mirror (DM) actuator commands. For the adaptive-optics systems in use today this control algorithm consists of a wavefront reconstruction step to estimate the instantaneous phase distortion to be compensated [4], followed by a servo control law to temporally filter this instantaneous estimate before it is applied to the deformable mirror [5]. So-called modal adaptive-optics systems can apply different temporal filters to separate spatial components, or modes, of the overall phase distortion [6]. Extensive analysis has been performed to evaluate and optimize the performance of these adaptive-optics control systems [7,8,9,10,11], but the results obtained depend on atmospheric parameters which are seldom known exactly and are constantly fluctuating. The uncertainty and variability of atmospheric conditions implies that an optimal degree of turbulence compensation cannot be achieved or maintained for long time intervals with a fixed control algorithm. A need exists for methods to update adaptive-optics control algorithms based upon actual system performance. Encouraging results have already been obtained demonstrating the value of emperically optimizing the control bandwidths for a modal adaptive-optics system [12]. In comparison, the subject of real-time adjustments to reconstruction matrices on the basis of measured system performance has received little attention.
Adaptive Correction of Phase-Distorted Extended Source Images: Experimental Results
Authors: Pruidze D.V. , Ricklin J.C. , Voelz D.G. , Vorontsov M.A.
Published: February 2023

We demonstrate a new type of adaptive imaging system capable of improving the quality of phase-distorted images of extended objects. The operational algorithm was based on optimization of the spectral image quality criteria suggested in [1]. For adaptive control of the nine-electrode semi-passive bimorph mirror we used gradient optimization algorithms. To introduce slowly varying large scale phase distortions into the imaging system a second deformable mirror with computer control was used. Small scale phase distortions were created using the nonlinear optics technique described in [2]. Image quality criteria were measured using the optical image quality analyzer described in [1].
Optimized adaptive optics design for low light level, optical-wavelength imaging interferometer arrays
Authors: Tyler David W.
Published: February 2023

Although there have been recent advances in the design and manufacture of large, single-aperture telescopes, the problems and costs involved are formidable enough that imaging interferometer arrays are being developed for such demanding missions as direct detection of extrasolar planets1. Studies of AO-compensated interferometry have been accomplished both with computer simulations2 and approximate analysis3. These studies have shown that even partial wavefront compensation can dramatically improve the limiting magnitude observable by the array. Here, an analysis of AO design for partially-compensating systems is presented. The method here is identical to that used by Angel1, but 1.) more detail is provided, such as treatment of read noise and allowance for different AO and imaging wavelengths, and 2.) the dependence of control-loop bandwidth requirements on degree of AO compensation is accounted for.
CHARM - A tip-tilt tertiary system for the Calar Alto 3.5m telescope
Authors: Glindemann Andreas , McCaughrean Mark J. , Hippier Stefan , Wagner Karl , Rohloff Ralf-Rainer
Published: February 2023

We present a tip-tilt tertiary mirror system for the Calar Alto 3.5m telescope that reduces the rapid image motion from typically 0”2 to <0”03 rms.
Polarization Insensitive 127-Segment Liquid Crystal Wavefront Corrector.
Authors: Love Gordon D. , Restaino Sergio R. , Carreras’ Richard C. , Loos Gary C. , Morrison Rob. V. , Baur Tom , Kopp Greg
Published: February 2023

In the past we have presented work on using nematic liquid crystal spatial light modulators (LC-SLMs) as wavefront correctors for adaptive optics (a summary of which is described in ref. 1 and references therein). For example, at the last OSA/ESO meeting on adaptive optics in Garching (1995) we described a high-quality LC-SLM which had 69-direct driven pixels which was custom designed for adaptive optics applications2. One of the fundamental problems of this device, and of nematic LC-SLMs in general, is that they are inherently polarization sensitive, i.e. they can only phase modulate linearly polarized light. The use of a polarizer, and the associated wastage of light, is unacceptable for many applications, especially astronomy. In this paper we describe an LC-SLM which has been custom designed for adaptive optics and which can phase modulate unpolarized light.
Adaptive Optics Servo-system Performance Estimator: practical implementation
Authors: Prieto E. , Bonaccini D. , Geoffray H. , Prado P. , Demailly L.
Published: February 2023

The evaluation of the quality parameters of the adaptive correction and their evolution with time is important while your adaptive optics system is running. It allows to give an observer a precise feeling of what he will get in the integrated image, it allows the operator to keep an eye on the system performance, and it allows the implementation of adaptive filtering techniques to the servo control laws. These reason have driven us to implement such a tool on the ESO Adonis system. To know the image quality parameters the only possibilities are to directly look at the science image or from the wavefront sensor residuals. Our purpose is to report on our attempts to evaluate the long exposure Strehl ratio and FWHM of the corrected PSF, by using the residual slopes given by the Wave Front Sensor (for us a Shark-Hartmann). We have used the following relation to compute the long exposure strehl1:
Relationship between wave fronts and scintillations
Authors: Ribak Erez
Published: February 2023

Scintillations are a measure of turbulence at high elevations, while most wave front aberrations originate at lower turbulence layers. Thus, inversion of scintillation patterns should allow measurement of high layers [Ribak et al. 1996]. According to this method, the higher turbulence alone is to be estimated from the intensities in the wave front sensor. Using the wave front slopes or curvature from the same data, all of the turbulence is calculated. In this manner we utilize both the amplitude and the phase of the measured wave fronts, whereas until now the amplitude fluctuations were considered noise.
Rapid Phase Retrieval using the Fast Fourier Transform - further developments
Authors: Gureyev T. E. , Nugent K.A. , Roberts A. , Paganin D.
Published: February 2023

Our method of phase retrieval1 is based on the transport of intensity equation which relates the phase of a paraxial wavefield to the longitudinal intensity gradient, and is an extension of the method initially proposed by Teague2 which was later developed into the method of wavefront curvature sensing by Roddier3. Whilst conceptually simple, the problem to date with recovering phase data in real time using systems based on the transport of intensity equation has been that it is computationally intensive and sensitive to the effects of noise, both of which limit its usefulness in adaptive optics applications.