Observations made with the Cookson floating zenith telescope in the years 1919-1927, at the Royal Observatory, Greenwich, for the determination of variation of latitude and the constant of aberration.

At head of title: Supplied for the public service.

A study of chromatic aberration of a coma-corrected zoned mirror /

"Contract AF33(616)-6079 Project No. 9-(13-6278) Task 40572. Sponsored by: Wright Air Development Division"

Directional spectral wave generator basin response to monochromatic waves /

"This report is a product of the Laboratory Simulation of Spectral and Directional Spectral Waves Work Unit, Coastal Flooding and Storm Protection Program, Civil Works Research and Development, at the US Army Engineer Waterways Experiment Station's Coastal Engineering Research Center."--Preface.

Transformation of monochromatic waves from deep to shallow water /

"August 1980."

Théorie du système optique composé d'une lunette astronomique et d'un double miroir plan : application à la mesure précise des distances en vue de l'étude de l'aberration et de la refraction /

Mode of access: Internet.

Clinical evaluation of the Softec HD aberration-free aspheric intraocular lens

Purpose: To compare distance and near visual performance with a zero-aberration aspheric intraocular lens (IOL) (Softec HD, Lenstec, Inc. FL, USA) with that of an otherwise identical, but spherical IOL (Softec 1). Setting: Department of Ophthalmology, Solihull Hospital, West Midlands, United Kingdom. Methods: This prospective study comprised 37 patients with a Softec 1 spherical IOL implanted in one eye, who underwent phacoemulsification and received the Softec HD aspheric IOL in the fellow eye. One month post-operatively, unaided distance and near vision, residual refraction, best spectacle corrected distance and near visual acuity, reading speed, pseudoaccommodation and photopic contrast sensitivity were recorded. Wavefront analysis enabled comparison of higher order aberrations between the IOLs. Results: Prior to surgery, the Softec 1 and Softec HD eyes were not significantly different. Post-operatively, unaided vision, best spectacle corrected visual acuity and residual refraction were not significantly different between the eyes, nor were there significant differences observed between the measured wavefront aberrations. Once implanted, the range of focus was significantly better in the Softec HD IOL eye than the Softec 1 IOL eye and, although reading speed was equivalent to the Softec 1 eye, the print size at which this could be achieved was significantly smaller. Conclusions: Depth of field was significantly improved with the aspheric IOL compared with the spherical IOL, without any compromise in distance visual performance between the two IOLs.

In situ aberration corrected-transmission electron microscopy of magnesium oxide nanocatalysts for biodiesels

Biofuels are promising renewable energy sources and can be derived from vegetable oil feedstocks. Although solid catalysts show great promise in plant oil triglyceride transesterification to biodiesel, the identification of active sites and operating surface nanostructures created during their processing is essential for the development of efficient heterogeneous catalysts. Systematic, direct observations of dynamic MgO nanocatalysts from a magnesium hydroxide-methoxide precursor were performed under controlled calcination conditions using novel in situ aberration corrected-transmission electron microscopy at the 0.1 nm level and quantified with catalytic reactivity and physico-chemical studies. Surface structural modifications and the evolution of extended atomic scale glide defects implicate coplanar anion vacancies in active sites in the transesterification of triglycerides to biodiesel. The linear correlation between surface defect density (and therefore polarisability) and activity affords a simple means to fine tune new, energy efficient nanocatalysts for biofuel synthesis. © 2009 Springer Science+Business Media, LLC.

Repeatability of ocular aberration measurements in patients with keratoconus

Purpose: To explore the repeatability of lower-order and higher-order ocular aberrations measured in patients with keratoconus. Methods: The IRX-3 (Imagine Eyes, Paris, France) aberrometer was used to record lower-order and higher-order aberrations in 31 eyes of 31 patients with keratoconus. Four monocular measurements were taken consecutively for each patient. The aberrometry data were analysed up to the 5th Zernike order for a 4-mm pupil diameter. The data were evaluated using repeated-measures anova and Friedman analyses. Repeatability was analysed using within-subject standard deviation (SW) and the repeatability limit (r) calculated as 1.96 ×√2×Sw. Results: Of the 11 aberration terms evaluated, the repeatability of Z (2,0) (mean= 1.36μm; SW=0.09μm; r=0.26μm); Z (2,±2) RMS (mean=1.05μm; SW= 0.09μm; r=0.24μm) and Z (4,0) aberrations (mean=0.34μm; SW=0.09 μm; r=0.24μm) showed the highest variability. In contrast, Z (3,±1) RMS aberrations (mean=0.85μm; SW=0.06μm; r=0.16μm) and Z (4,±2) RMS aberrations (mean=0.40μm; SW=0.07μm; r=0.18μm) showed comparatively better repeatability. Conclusions: The lower-order and higher-order aberrations measured in this group of keratoconic patients showed higher levels of variability compared to previous investigations of visually-normal subjects. These results may be of interest to eyecare practitioners involved in the design and fitting of aberration-controlling contact lenses for patients with keratoconus. © 2011 The College of Optometrists.

On-screen pre-deblurring of digital images using the wavefront aberration function of the human eye to improve computer access for the visually impaired

Traditional Optics has provided ways to compensate some common visual limitations (up to second order visual impairments) through spectacles or contact lenses. Recent developments in wavefront science make it possible to obtain an accurate model of the Point Spread Function (PSF) of the human eye. Through what is known as the "Wavefront Aberration Function" of the human eye, exact knowledge of the optical aberration of the human eye is possible, allowing a mathematical model of the PSF to be obtained. This model could be used to pre-compensate (inverse-filter) the images displayed on computer screens in order to counter the distortion in the user's eye. This project takes advantage of the fact that the wavefront aberration function, commonly expressed as a Zernike polynomial, can be generated from the ophthalmic prescription used to fit spectacles to a person. This allows the pre-compensation, or onscreen deblurring, to be done for various visual impairments, up to second order (commonly known as myopia, hyperopia, or astigmatism). The technique proposed towards that goal and results obtained using a lens, for which the PSF is known, that is introduced into the visual path of subjects without visual impairment will be presented. In addition to substituting the effect of spectacles or contact lenses in correcting the loworder visual limitations of the viewer, the significance of this approach is that it has the potential to address higher-order abnormalities in the eye, currently not correctable by simple means.

Primary Immunodeficiency Associated with Chromosomal Aberration - an ESID Survey

Patients with syndromic features frequently suffer from recurrent respiratory infections, but little is known about the spectrum of immunological abnormalities associated with their underlying chromosomal aberrations outside the well-known examples of Down and DiGeorge syndromes. Therefore, we performed this retrospective, observational survey study.

Five Prime Ministers : a crisis, a political aberration or the new normal

Quantitative phase Analisis: A comparative study of Mo and Cu strictly monochromatic radiations

A comparison of the Rietveld quantitative phase analyses (RQPA) obtained using Cu-Kα1, Mo-Kα1, and synchrotron strictly monochromatic radiations is presented. The main aim is to test a simple hypothesis: high energy Mo-radiation, combined with high resolution laboratory X-ray powder diffraction optics, could yield more accurate RQPA, for challenging samples, than well-established Cu-radiation procedure(s). In order to do so, three set of mixtures with increasing amounts of a given phase (spiking-method) were prepared and the corresponding RQPA results have been evaluated. Firstly, a series of crystalline inorganic phase mixtures with increasing amounts of an analyte was studied in order to determine if Mo-Kα1 methodology is as robust as the well-established Cu-Kα1 one. Secondly, a series of crystalline organic phase mixtures with increasing amounts of an organic compound was analyzed. This type of mixture can result in transparency problems in reflection and inhomogeneous loading in narrow capillaries for transmission studies. Finally, a third series with variable amorphous content was studied. Limit of detection in Cu-patterns, ~0.2 wt%, are slightly lower than those derived from Mo-patterns, ~0.3 wt%, for similar recording times and limit of quantification for a well crystallized inorganic phase using laboratory powder diffraction was established ~0.10 wt%. However, the accuracy was comprised as relative errors were ~100%. Contents higher than 1.0 wt% yielded analyses with relative errors lower than 20%. From the obtained results it is inferred that RQPA from Mo-Kα1 radiation have slightly better accuracies than those obtained from Cu-Kα1. This behavior has been established with the calibration graphics obtained through the spiking method and also from Kullback-Leibler distance statistic studies. We explain this outcome, in spite of the lower diffraction power for Mo-radiation (compared to Cu-radiation), due to the larger volume tested with Mo, also because higher energy minimize pattern systematic errors and the microabsorption effect.

The use of mo and cu monochromatic radiations for quantitative phase analysis: study of the accuracy

Cement hydration is a very complex process in which crystalline phases are dissolving in water and after supersaturation hydrated crystalline and amorphous phases precipitate. Great efforts are being made to develop analytical tools to accurately quantify these processes and X-ray Powder Diffraction (XRPD) combined with Rietveld methodology is a suitable tool to quantify these complex mixtures and their time evolutions. However, some problems/drawbacks should be overcome to fully apply it to cement pastes characterization in order to get accurate phase analyses. In order to tackle this issue, a comparison of the Rietveld quantitative phase analyses (RQPA) obtained using Cu-Kα1, Mo-Kα1, and synchrotron strictly monochromatic radiations of three set of mixtures with increasing amounts of a given phase (spiking-method) is presented. The main aim is to test a simple hypothesis: high energy Mo-radiation, combined with high resolution laboratory X-ray powder diffraction optics, could yield more accurate RQPA, for challenging samples, than well-established Cu-radiation procedure(s). Firstly, a series of crystalline inorganic phase mixtures with increasing amounts of an analyte was studied in order to determine if Mo-Kα1 methodology is as robust as the well-established Cu-Kα1 one. Secondly, a series of crystalline organic phase mixtures with increasing amounts of an organic compound was analyzed. This type of mixture can result in transparency problems in reflection and inhomogeneous loading in narrow capillaries for transmission studies. Finally, a third series with variable amorphous content was studied. Limit of detection in Cu-patterns, ~0.2 wt%, are slightly lower than those derived from Mo-patterns, ~0.3 wt%, for similar recording times and limit of quantification for a well crystallized inorganic phase using laboratory powder diffraction was established ~0.10 wt%. From the obtained results it is inferred that RQPA from Mo-Kα1 radiation have slightly better accuracies than those obtained from Cu-Kα1. The results obtained in the previous comparison have been taken into account to obtain accurate RQPA, including the amorphous component with internal standard methodology, of hydrating cement pastes. The final goal of this second study was understanding the early-stage hydration mechanisms of a variety of cementing systems (Ordinary Portland Cement or Belite Alite Ye’elimite cement) as a function of water content, superplasticizer additives and type and content of sulfate source. In order to do so, X-ray powder diffraction data were taken in-situ with the humidity chamber coupled to the Mo-Kα1 powder diffractometer. Some results of this ongoing investigation will be reported and discussed.

Chitosan/tripolyphosphate Nanoparticles Loaded With Paraquat Herbicide: An Environmentally Safer Alternative For Weed Control.

Paraquat is a fast acting nonselective contact herbicide that is extensively used worldwide. However, the aqueous solubility and soil sorption of this compound can cause problems of toxicity in nontarget organisms. This work investigates the preparation and characterization of nanoparticles composed of chitosan and sodium tripolyphosphate (TPP) to produce an efficient herbicidal formulation that was less toxic and could be used for safer control of weeds in agriculture. The toxicities of the formulations were evaluated using cell culture viability assays and the Allium cepa chromosome aberration test. The herbicidal activity was investigated in cultivations of maize (Zea mays) and mustard (Brassica sp.), and soil sorption of the nanoencapsulated herbicide was measured. The efficiency association of paraquat with the nanoparticles was 62.6 ± 0.7%. Encapsulation of the herbicide resulted in changes in its diffusion and release as well as its sorption by soil. Cytotoxicity and genotoxicity assays showed that the nanoencapsulated herbicide was less toxic than the pure compound, indicating its potential to control weeds while at the same time reducing environmental impacts. Measurements of herbicidal activity showed that the effectiveness of paraquat was preserved after encapsulation. It was concluded that the encapsulation of paraquat in nanoparticles can provide a useful means of reducing adverse impacts on human health and the environment, and that the formulation therefore has potential for use in agriculture.