Use of a microelectromechanical mirror for adaptive optics in the human eye

Ophthalmic instrumentation equipped with adaptive optics offers the possibility of rapid and automated correction of the eye's optics for improving vision and for improving images of the retina. One factor that limits the widespread implementation of adaptive optics is the cost of the wave-front corrector, such as a deformable mirror. In addition, the large apertures of these elements require high pupil magnification, and hence the systems tend to be physically large. We present what are believed to be the first closed-loop results when a compact, low-cost, surface micromachined, microelectromechanical mirror is used in a vision adaptive-optics system. The correction performance of the mirror is shown to be comparable to that of a Xinetics mirror for a 4.6-mm pupil size. Furthermore, for a pupil diameter of 6.0-mm, the residual rms error is reduced from 0.36 to 0.12 microm and individual photoreceptors are resolved at a pupil eccentricity of 1 degrees from the fovea.     

Quasi-solitonic behavior of self-written waveguides created by photopolymerization

We investigated the condition of unique self-written channel and multichannel propagation inside bulk photopolymerizable materials. Light was introduced in the medium by a single-mode optical fiber. At a very low beam power of 5 muW , a unique uniform-channel waveguide without any broadening was obtained by polymerization. When the input power is increased to 100 muW , the guide becomes chaotic and multichannel. We connected two fibers separated by a 1-cm distance. The results open the door to studies of the optical and electro-optical properties of photopolymerized guides doped by nonlinear optical chromophores and to possible applications in integrated optical devices.     

Corrosion Products Formed on Mild Steel Samples Submerged in Various Aqueous Solutions

Corroded samples, from the steel shell of an industrial evaporator system were investigated. A protective magnetite layer had formed, which subsequently dissolved in localised areas, resulting in failure of the shell. To clarify the mechanisms involved, mild steel samples of similar composition to the steel shell were submerged in the condensate and experiments were performed at room temperature and at 90°C under both static and dynamic conditions for exposure times up to 30 days. Control samples were submerged in deionised water under similar conditions. The dynamic corrosion rates in the industrial condensate were a factor of 2 higher than the rates for the deionised water, whilst static corrosion rates, measured in both media, were lower by a factor of 3 to 4 found for the dynamic experiments. The corrosion products were identified by means of CEMS analyses. The main components were magnetite and oxyhydroxides of iron. Additional to the species mentioned, -Fe₂O₃, goethite and hematite formed.     

Brain MRI lesion load quantification in multiple sclerosis: a comparison between automated multispectral and semi-automated thresholding computer-assisted techniques

Brain magnetic resonance imaging (MRI) lesion volume measurement is an advantageous tool for assessing disease burden in multiple sclerosis (MS). We have evaluated two computer-assisted techniques: MSA multispectral automatic technique that is based on bayesian classification of brain tissue and NIH image analysis technique that is based on local (lesion by lesion) thresholding, to establish reliability and repeatability values for each technique. Brain MRIs were obtained for 30 clinically definite relapsing-remitting MS patients using a 2.0 Tesla MR scanner with contiguous, 3 mm thick axial, T1, T2 and PD weighted modalities. Digital (Dicom 3) images were analyzed independently by three observers; each analyzed the images twice, using the two different techniques (Total 360 analyses). Accuracy of lesion load measurements using phantom images of known volumes showed significantly better results for the MSA multispectral technique (p < 0.001). The mean intra-and inter-observer variances were, respectively, 0.04 ± 0.4 (range 0.04–0.13), and 0.09 ± 0.6 (range 0.01–0.26) for the multispectral MSA analysis technique, 0.24 ± 2.27 (range 0.23–0.72) and 0.33 ± 3.8 (range 0.47–1.36) for the NIH threshold technique. These data show that the MSA multispectral technique is significantly more accurate in lesion volume measurements, with better results of within and between observers’ assessments, and the lesion load measurements are not influenced by increased disease burden. Measurements by the MSA multispectral technique were also faster and decreased analysis time by 43%. The MSA multispectral technique is a promising tool for evaluating MS patients. Non-biased recognition and delineation algorithms enable high accuracy, low intra-and inter-observer variances and fast assessment of MS related lesion load.     

High resolution 2D 1H-13C correlation of cholesterol in model membrane

High resolution 2D NMR MAS spectra of liposomes, in particular 1H-13C chemical shifts correlations have been obtained on fluid lipid bilayers made of pure phospholipids for several years. We have investigated herein the possibility to obtain high resolution 2D MAS spectra of cholesterol embedded in membranes, i.e. on a rigid molecule whose dynamics is characterized mainly by axial diffusion without internal segmental mobility. The efficiency of various pulse sequences for heteronuclear HETCOR has been compared in terms of resolution, sensitivity and selectivity, using either cross polarization or INEPT for coherence transfer, and with or without MREV-8 homonuclear decoupling during t1. At moderately high spinning speed (9 kHz), a similar resolution is obtained in all cases (0.2 ppm for 1H(3,4), 0.15 ppm for 13C(3,4) cholesterol resonances), while sensitivity increases in the order: INEPT < CP(x4) < CP + MREV. At reduced spinning speed (5 kHz), the homonuclear dipolar coupling between the two geminal protons attached to C(4) gives rise to spinning sidebands from which one can estimate a H-H dipolar coupling of 10 kHz which is in good agreement with the known dynamics of cholesterol in membranes.     

Sur un théorème de connexité de Mumford pour les espaces homogènes

We prove some consequences of an old unpublished connectivity result of Mumford. These mostly deal with the fundamental group of some (ramified) coverings of homogeneous spaces; for example, it is shown that the fundamental group of a complex projective irreducible normal variety which is a covering of a simple (in the sense of 2.2) homogeneous space V, of degree ≤dim (V), is isomorphic to π₁ (V).