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We have previously shown that daily application of 0.05% retinoic acid to the backs of lightly pigmented, hairless HRA:Skh-2 mice increases melanogenesis resulting from exposure to solar-simulated ultraviolet radiation. In this study we show that as early as 1 wk following commencement of treatment, there is a 2- fold increase in the number of epidermal(More)
Because of mechanical aspects of fabrication, launch, and operational environment, space telescope optics can suffer from unforeseen aberrations, detracting from their intended diffraction-limited performance goals. We give the results of simulation studies designed to explore how wave-front aberration information for such near-diffraction-limited(More)
Quadratic aberration is successfully corrected with a segmented microelectromechanical deformable mirror in conjunction with a refractive lenslet array. Use of the lenslet array greatly improves the effective fill factor of the correcting element. Experimental results show correction approaching the diffraction limit for an extreme spherical aberration.
One method for improving the quality of astronomical images measured through a atmospheric turbulence uses simultaneous short-exposure measurements of both an image and the output of a wave-front sensor exposed to an image of the telescope pupil. The wave-front sensor measurements are used to reconstruct an estimate of the instantaneous generalized pupil(More)
We outline a novel method for estimating a fixed aberration that is in the image path but not in the wave-front-sensor (WFS) path of an adaptive optics (AO) imaging system. We accomplish this through a nontraditional application of the Gonsalves [Proc. SPIE 207, 32 (1997)] least-squares phase-diversity technique, using an ensemble of images and WFS data.(More)
Tilt compensation performance is generally suboptimal when phase measurements from natural or laser guide stars are used as the conjugate phase in an adaptive optics system. Optimal compensation is obtained when the conjugate-phase coefficients are estimated from beacon measurements, given knowledge of the correlation between the on-axis object phase and(More)
The performance of ground-based optical imaging systems is severely degraded from the diffraction limit by the random effects of the atmosphere. Adaptive-optics techniques have been used to compensate for atmospheric-turbulence effects. A critical component in the adaptive-optics system is the wave-front sensor. At present, two types of sensors are common:(More)
Turbulence has long been recognized as one of the most signiicant factors limiting the performance of optical systems operating in the presence of atmosphere. Atmospheric turbulence over vertical paths has been well characterized, both theoretically and experimentally. Much less is known about turbulence over long, horizontal paths. Perturbations of the(More)
It is well known that atmospheric turbulence severely degrades the performance of ground-based imaging systems. Techniques to overcome the effects of the atmosphere have been developing at a rapid pace over the past 10 years. These techniques can be grouped into two broad categories: predetection and postdetection techniques. A recent newcomer to the(More)