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Introduction to Quantum Mechanics
Published in Caroline Desgranges, Jerome Delhommelle, A Mole of Chemistry, 2020
Caroline Desgranges, Jerome Delhommelle
Let us add that refraction (or refractometry) is also the name of a clinical test during an eye exam. The idea is to determine if the eye has a refractive error, and if so, what best corrective lenses should be prescribed. In practice, several test lenses with different optical powers are presented to the patient. The one giving the sharpest, clearest, vision is then selected, and the refractive error can be determined. For example, an eye that has no refraction error when viewing a distant object 6 meters or 20 feet away is said to have emmetropia (Greek: en- (in) + metron (measure) + -ops (eye)). It means that the eye can focus parallel rays of light in the retina without using any accommodation. Therefore, one will score “6/6” (meters) or “20/20” (feet). For example, a person with “20/80” vision can only see clearly an object at 20 feet whereas others who do not need corrective lenses can see at 80 feet, meaning that this person is nearsighted or has myopia. The purpose of the corrective lenses is to compensate for refractive errors of the eyes including myopia, hyperopia and astigmatism (see Figure 3.2). The concept of corrective lenses is to help focus the ray of light on the retina, thus allowing a person to have a clear image of the object. More specifically, for an eye exhibiting myopia, the eye focuses the ray of light before it actually reaches the retina, giving a blurred image. Therefore, the corrective lens should be concave in order to make the ray diverge, allowing the eye to focus exactly on the retina. For hyperopia, the eye focuses beyond the retina surface. To compensate for that, the corrective lens should be convex in order to make the ray converge, again helping the eye to focus on the retina. In practice, the corrective lenses are characterized by their optical power measured in diopter units (D) with 1 D = 1 m–1. For example, –2.0 D corresponds to a power for the corrective lens of 2 m–1 meaning that it creates a focal point at 0.5 m or 50 cm. The negative sign indicates that the focal point is located 50 cm before the eye, implying that this prescription is intended to correct myopia. On the other hand, there is no negative sign in the case of corrective lenses for hyperopia, since the focal point should be after the eye. But the story does not end there. How about distance and depth perception? 3D vision is achieved through our ability to have binocular vision (two eyes). Both eyes help us see an image from two different points and angles. Then, the brain processes the information from optic nerves and uses different techniques to assess distance and depth perception. For example, convergence and accommodation are two different techniques the brain uses to estimate distances, based on efforts made by eye muscles. For instance, an object close to us requires more effort than the accommodation needed to see an object further away. More information can be obtained through parallax and geometry pattern recognition, which we acquire as we grow up. This gigantic database is then used by the brain to apprehend the world surrounding us, in 3D. Let us not forget that 33% of our cerebral cortex plays a role in processing vision!
Assistive technology needs, functional difficulties, and services utilization and coordination of children with developmental disabilities in the United States
Published in Assistive Technology, 2018
With regards to functional difficulties, we selected three composite measures from the NS-CSHCN that examined parental report of multiple functional difficulties among CSHCN: (1) difficulties in one or more bodily functions such as respiratory problems, swallowing or metabolism, blood circulation, repeated or chronic physical pain, seeing even with corrective lens, and hearing even with hearing devices; (2) difficulties in activities or participation such as self-care, moving around, and limited hand use; and (3) difficulties in emotional or behavioral factors such as anxiety or depression, behavior problems (e.g., acting out, fighting, bullying, or arguing), and friendships. Finally, services utilization and coordination looked at parental responses (yes/no) to the following: (1) Does the child receive special education services; (2) Does the child need or use more medical care or educational service than their peers; and (3) Do the medical providers of the child need to coordinate and communicate with educational, vocational, or rehabilitation programs?
Characterization and damage assessment of stones used in the Pasargadae World Heritage Site, Achaemenian period
Published in International Journal of Architectural Heritage, 2019
Atefeh Shekofteh, Eduardo Molina, Anna Arizzi, Giuseppe Cultrone, Hossein Ahmadi, Mehdi Yazdi
The observation of the stone microstructure was carried out on thin sections on intact samples by means of polarized optical microscopy (POM), using a CarlZeiss Jenapol-U microscope equipped with a digital microphotography camera (Nikon D7000). A Leica videomicroscope model DVM2000 with a 50–400x lens (and a corrective lens of 0.4x) was used to perform surface observations on the weathered samples listed in Table 1, and the images were processed using the Leica Application Suite v3.8.0 (Leica Microsystems©).