Optomechanical system to induce low-order refractive errors on a biconical surface

2018 ◽  
Author(s):  
Angel S. Cruz-Felix ◽  
Rafael Cruz Amador ◽  
Agustín Santiago-Alvarado
Keyword(s):  
Refractive Errors ◽  
Optomechanical System ◽  
Low Order

the effects of resonance with Jupiter in the system of short-period comets

1974 ◽  
Vol 22 ◽  
pp. 193-203
Author(s):  
L̆ubor Kresák
Keyword(s):  
Structural Effects ◽  
Order Resonance ◽  
Mean Motion ◽  
Short Period ◽  
The Mean ◽  
Compound Effect ◽  
Low Order

AbstractStructural effects of the resonance with the mean motion of Jupiter on the system of short-period comets are discussed. The distribution of mean motions, determined from sets of consecutive perihelion passages of all known periodic comets, reveals a number of gaps associated with low-order resonance; most pronounced are those corresponding to the simplest commensurabilities of 5/2, 2/1, 5/3, 3/2, 1/1 and 1/2. The formation of the gaps is explained by a compound effect of five possible types of behaviour of the comets set into an approximate resonance, ranging from quick passages through the gap to temporary librations avoiding closer approaches to Jupiter. In addition to the comets of almost asteroidal appearance, librating with small amplitudes around the lower resonance ratios (Marsden, 1970b), there is an interesting group of faint diffuse comets librating in characteristic periods of about 200 years, with large amplitudes of about±8% in μ and almost±180° in σ, around the 2/1 resonance gap. This transient type of motion appears to be nearly as frequent as a circulating motion with period of revolution of less than one half that of Jupiter. The temporary members of this group are characteristic not only by their appearance but also by rather peculiar discovery conditions.

Hybrid Reduced Model of Rotor

2013 ◽  
Vol 60 (3) ◽  
pp. 319-333
Author(s):  
Rafał Hein ◽  
Cezary Orlikowski
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Hybrid Model ◽  
Rotor System ◽  
Reduced Model ◽  
Order Model ◽  
Gyroscopic Effect ◽  
Reduced Models ◽  
Rigid Finite Element Method ◽  
Low Order

Abstract In the paper, the authors describe the method of reduction of a model of rotor system. The proposed approach makes it possible to obtain a low order model including e.g. non-proportional damping or the gyroscopic effect. This method is illustrated using an example of a rotor system. First, a model of the system is built without gyroscopic and damping effects by using the rigid finite element method. Next, this model is reduced. Finally, two identical, low order, reduced models in two perpendicular planes are coupled together by means of gyroscopic and damping interaction to form one model of the system. Thus a hybrid model is obtained. The advantage of the presented method is that the number of gyroscopic and damping interactions does not affect the model range

Clinical manifestations and diagnosis of keratoconus. Treatment of iatrogenic keratoconus

2020 ◽  
pp. 37-42
Author(s):  
Fedor Ermolyuk
Keyword(s):  
Research Methods ◽  
Contact Lenses ◽  
Correct Diagnosis ◽  
Clinical Manifestations ◽  
Refractive Errors ◽  
Dry Eyes ◽  
Advanced Stages ◽  
Dystrophic Disease ◽  
Iatrogenic Origin ◽  
Binocular Diplopia

Keratoconus is a dystrophic disease of the cornea, when it is thinned with the formation of a conus-like protrusion (protrusion of the cornea). This disease belongs to the group of keratectasia, it has a multifactorial nature and occurs in approximately 25 % of all corneal pathologies. The disease can be either primary, which is based on dystrophic changes in the cornea, or secondary, which develops against the background of prenatal keratitis. Keratoconus of iatrogenic origin, which develops as a result of refractive eye microsurgery, has become widespread during the last 20 years. Most often primary keratoconus manifests during puberty, progresses to 30–40 years, after which its development slows down. An early clinical manifestation of this corneal pathology is a progressive decrease in visual acuity, development of double vision (binocular diplopia) with the development of a strong headache against this background. Monocular polyopia — images and symbols with multiple contours — develops subsequently. Severe dry eyes, itching, photophobia appear in advanced stages. Diagnosis of keratoconus in some cases can be a significant difficulty, since the use of conventional research methods only allow to suspect refractive errors in the form of myopia or astigmatism. It is necessary to take into account the impossibility of correcting visual impairment using conventional methods — glasses or contact lenses — to make correct diagnosis. As a rule, diagnosis of keratoconus requires use of expanded spectrum of instrumental research methods.

Types of refractive errors and methods for their diagnosis

2020 ◽  
pp. 30-36
Author(s):  
Olga Lemzyakova
Keyword(s):  
Optical System ◽  
Contact Lenses ◽  
Vision Impairment ◽  
Refractive Errors ◽  
Vision Correction ◽  
Light Rays ◽  
Different Types ◽  
Almost All ◽  
Degrees Of Severity ◽  
The Brain

Refraction of the eye means its ability to bend (refract) light in its own optical system. In a normal state, which is called emmetropia, light rays passing through the optical system of the eye focus on the retina, from where the impulse is transmitted to the visual cortex of the brain and is analyzed there. A person sees equally well both in the distance and near in this situation. However, very often, refractive errors develop as a result of various types of influences. Myopia, or short-sightedness, occurs when the light rays are focused in front of the retina as a result of passing through the optical system of the eye. In this case, a person will clearly distinguish close objects and have difficulties in seeing distant objects. On the opposite side is development of farsightedness (hypermetropia), in which the focusing of light rays occurs behind the retina — such a person sees distant objects clearly, but outlines of closer objects are out of focus. Near vision impairment in old age is a natural process called presbyopia, it develops due to the lens thickening. Both myopia and hypermetropia can have different degrees of severity. The variant, when different refractive errors are observed in different eyes, is called anisometropia. In the same case, if different types of refraction are observed in the same eye, it is astigmatism, and most often it is a congenital pathology. Almost all of the above mentioned refractive errors require correction with spectacles or use of contact lenses. Recently, people are increasingly resorting to the methods of surgical vision correction.

Outdoor Activities and Myopia on Junior High School Student in Rural Area of Bali

2018 ◽  
Vol 44 (1) ◽  
pp. 30
Author(s):  
Ni Made Ari Suryathi ◽  
I Putu Budhiastra ◽  
Ariesanti Tri Handayani
Keyword(s):  
High School ◽  
High School Students ◽  
Rural Area ◽  
Junior High School ◽  
Junior High ◽  
Positive Impact ◽  
Natural Habitat ◽  
Capital City ◽  
Refractive Errors ◽  
Outdoor Activities

Introduction and Aims. Refractive errors such as miopia, hyperopia and astigmatism in teenagers are common in Asian country nowadays. Gadget usage also influence the prevalence and incidence of refractive errors specially for miopia and astigmatism. Outdoor activities have positive impact to prevent miopia. The aim of this study is to report the role of outdoor activities as unique school program that could prevent refractive errors in Junior High School in rural area of Bali Method. This is analytic descriptive study with cross sectional approach of 231 Pekutatan II Junior High School students taken in December 2016. This school located in rural area; 35,3 km from Jembarana and 60,5 km from Denpasar, the capital city of Bali. The area of the school is about 1500 m2, where 70% of the land are still vacant to natural habitat and this school had their own garden area that being organized by the students themselves after school hours. This school do not have computer extra curriculum as well. Result. From 231 students there were only 14 students that have refractive errors consist of 5 boys and 9 girls, mostly aged 15 years. Six students (2%) were diagnosed as myopia and 8 students (3.4%) were diagnosed as compound astigmatism myopia. The length of gadget usage in this school were 1.66 hours and outdoor activities time were 4.78 hours per day. The hereditary factors of refractive errors were noted in 12 students (5 %). Outdoor activities associated with refractive errors in this study (p = 0.03). While time using gadget does not have an association with the refractive errors (p = 0.38). Conclusion. Rural area where the outdoor activities are still common have protective effect to prevalence of refractive errors in teenager.

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