Abnormal Refraction Research Articles

Anomalous Propagation Echo Classification of Imbalanced Radar Data with Support Vector Machine

A number of technologically advanced devices, such as radars and satellites, are used in an actual weather forecasting process. Among these devices, the radar is essential equipment in this process because it has a wide observation area and fine resolution in both the time and the space domains. However, the radar can also observe unwanted nonweather phenomena. Anomalous propagation echo is one of the representative nonprecipitation echoes generated by an abnormal refraction phenomenon of a radar beam. Abnormal refraction occurs when the temperature and the humidity change dramatically. In such a case, the radar recognizes either the ground or the sea surface as an atmospheric object. This false observation decreases the accuracy of both quantitative precipitation estimation and weather forecasting. Therefore, a system that can automatically recognize an anomalous propagation echo from the radar data needs to be developed. In this paper, we propose a classification method for separating anomalous propagation echoes from the rest of the weather data by using a combination of a support vector machine classifier and the synthetic minority oversampling technique, to solve the problem of imbalanced data. By using actual cases of anomalous propagation we have confirmed that the proposed method provides good classification results.

Anomalous refraction of heat flux in thermal metamaterials

We discuss the possibility of bending of heat flux in a multilayered composite typical to abnormal negative refraction, according to which the horizontal and the vertical components of the incident and refracted heat flux vectors point in the opposite direction. The engineered anisotropy of the thermal conductivity tensor is integral to such effects. We propose practical designs where such anomalous refraction phenomena may be observed and be used for heat flux redirection.

Abnormal refraction of microwave in ferrite/wire metamaterials

We report the experimentally observed abnormal refraction in metamaterials (MMs) consisting of ferrite rods and metallic wires with two kinds of configurations. Negative refraction (NR) and positive refraction (PR) are demonstrated in an MM constructed with parallel-arranged rods and wires. The frequencies of both NR and PR can be adjusted dynamically and together by an applied magnetic field and the PR occurs at frequencies slightly lower than that of the NR. The NR is attributed to simultaneously negative effective permittivity and permeability, and the PR is resulted from positive effective permittivity and permeability with the positive effective permittivity originating from electromagnetic coupling between the closest rod and wire. By making the rod cross the wire to reduce the coupling, we observed sole NR in an MM consisting of the cross-arranged rods and wires. Theoretical analysis explained qualitatively the abnormal refraction behaviors of microwave for the two kinds of MMs and it is supported by the retrieved effective parameters and field distributions.

The range of visual acuity using the crowded Kay Picture test and the range of refractive error present in children aged 42–48 months

Aims: To establish, using the crowded Kay Picture test, the ranges of visual acuity in children aged 42–48 months which are associated with normal and abnormal refractive status. To identify the visual acuity and refractive error distribution in this age group. Methods: Children attending a primary vision screening service had visual acuity measured and cycloplegic refraction undertaken. Refractive error was pre-defined as normal, borderline and abnormal by using existing evidence. On the basis of the refractive error found, visual acuity ranges associated with each refractive group were established. Children with squint and ocular pathology were excluded. Results: Seven hundred and thirty-three children participated, with a median age of 43 months. Ninety per cent had a normal monocular refractive error. Ninety-three per cent of children had insignificant anisometropia. When anisometropia was insignificant, the median (IQR) visual acuity was 0.05 (0.00–0.10) for both right eye and left eye. Median (IQR) interocular visual acuity difference in this group was 0.025 (0.00–0.05). There was a statistically significant difference between the visual acuity ranges for each of the normal, borderline and abnormal refraction groups ( p < 0.001). The median refractive error was þ0.38D spherical equivalent for the right eye and þ0.50D spherical equivalent for the left eye. Conclusion: Children of 42–48 months with monocular visual acuity of equal to or better than 0.10 and with an interocular visual acuity difference of 0.05 or less when tested with the crowded Kay Picture test are likely to have a normal refractive status.

A Memory-efficient Strategy for the FDTD Implementation Applied to the Photonic Crystals Problems

The Finite Difierence Time Domain (FDTD) method is well suited for the com- putation of the photonic crystals problems. However, this technique has the drawback of high computer memory requirements, when involving complex structures. In this paper, a modifled array implementation for the FDTD algorithm, with increased memory e-ciency, is presented and applied to studies on the abnormal refraction phenomena of the electromagnetic propagat- ing in the photonic crystals. The novel approach is based on memory-mapped flles, which is a mechanism of manipulating memory in Windows or Linux operating system. By using this mechanism, we make use of memory space more availably in allocating and implementing mul- tidimensional arrays for FDTD algorithm. The computed examples are given in the paper to prove the feasibility and accuracy of this strategy. A detailed discussion is presented for the case of the electromagnetic propagating in two-dimensional photonic crystals, formed by parallel air cylinders in a dielectric medium. The results show that some interesting relations can be obtained between the incident and the refraction angles with the group velocity (Vg) and the energy velocity (Ve).

Amphoteric refraction at the isotropic–anisotropic biaxial media interface: an alternative treatment

Amphoteric refraction of light (refraction that can be positive or negative depending on the angle of incidence) at the interface between isotropic and anisotropic biaxial media is analysed by means of an alternative method previously developed by the authors. Unlike left-handed materials (LHMs), negative (or abnormal) refraction involving anisotropic media is only due to the intrinsic properties of the media and is only exhibited by non-collinear rays (rays that do not follow an isotropic behaviour). Moreover, the axes of wavevector ellipsoids must be rotated with respect to the normal to the incidence plane. In this paper, only planes of incidence lying normal to a principal axis of the dielectric tensor are considered, and consequently comparison between traditional and alternative methods is possible because both geometrical constructions are plane. First, a very simple procedure that allows us to find the direction of wavevector k from the knowledge of non-collinear (n.c.) ray direction is outlined together with the solution of the dual problem: to find the n.c. ray direction from the k one. Then, the abnormal refraction phenomenon is studied and the equivalence between traditional and alternative methods is clearly stated. Finally, two graphical constructions to find the critical angle of incidence and the maximum angle of negative refraction are also proposed.

Refraction in the fixed direction at the surface of dielectric/silver superlattice

We report a novel abnormal refraction, called as refraction in the fixed direction, that occurs for certain dielectric/silver superlattices, in which the ray direction of the refracted wave is perpendicular to the surface of dielectric/silver superlattices, independent on the angle of incidence.

Refraction referral criteria for Hong Kong Chinese preschool children.

The major types of ametropia and visual problems for Hong Kong Chinese and Caucasian children are different. Consequently, the referral criteria developed for Caucasian children may not be applicable to Hong Kong children. Results of our study suggested that the referral criteria for Hong Kong children should be set as hyperopia of > or = +2.0 D, myopia of > or = 1.0 D, astigmatism of > or = 1.0 D and anisometropia of > or = 1.25 D. Sensitivity using only these criteria for abnormal refraction in identifying children with amblyopia, esotropia, exotropia and subnormal vision (< 6/12) was respectively 100%, 84.6%, 45.2% and 95.7%. The overall sensitivity for the identification of visual problems was 86.1% and the overall specificity was 76%. If a cover test or a Hirschberg test was introduced into the screening battery so that all the strabismic cases were identified. the overall sensitivity would increase to 98.6%.

Risk factors in amblyopia

Any intervention to prevent serious amblyopia is based on the knowledge about normal versus subnormal visual development. Our ability to predict with high degree of certainty which children will develop amblyopia will be dependent on the characteristics of various risk factors for initiating the development of squint or amblyopia. We have used longitudinal studies of population based cohorts of young children to define some of these risk factors such as refractive errors. Three hundred and ten children with an astigmatism greater than or equal to 1.0 D at one year of age were refracted yearly between the age one and four years. Astigmatism and anisometropia were found to be highly variable during infancy and early childhood. Longitudinal follow-up seems to be needed to separate the normal from the abnormal refraction development, which initiates the development of the amblyopia. Children with constant or increasing astigmatism or anisometropia between one and four years were 'at risk'. In parallel we have studied important factors for successful treatment of amblyopia. Based on these findings we conclude that a population screening at four years of age seems to be advantageous in Sweden in order detect and successfully treat most cases of amblyopia.

Notes on some abnormal refraction phenomena in the atmosphere

To geodesists and astronomers atmospheric refraction is a phenomenon, which makes it necessary to introduce corrections to the observations of carefully performed measuring series. Such corrections are generally obtained from tables giving values, which are applicable under “normal” or standard conditions. These conditions may be taken as more or less obtaining with a mean variation of temperature with height in the atmosphere - in the troposphere mainly a decrease of 0,6 – 0,7° per 100 m.

An Early Report of Abnormal Refraction over the Gulf of California

An Early Report of Abnormal Refraction over the Gulf of California

The propagation of metre radio waves beyond the normal horizon. Part 1: Some theoretical considerations, with particular reference to propagation over land

The effect on radio wave propagation of departures from the normal variation with height of the refractive index of the lower atmosphere is considered with special reference to frequencies of 90 and 45 Mc/s. The relative importance of changes in refraction near the surface of the earth and of reflection from high-level inversion layers is investigated, and some illustrative examples are worked out. The number of parameters concerned in the problem prevents an all-embracing survey of the many possibilities within the scope of the present work, but a few general conclusions are reached.It is unlikely that radio ducts of sufficient magnitude to be greatly significant at the frequencies in question can be maintained over long distances in broken country. Of the two mechanisms—refraction near the surface of the earth and reflection at an elevated inversion layer—the latter is the one which is likely more often to give abnormally high field strengths at ranges of a few hundred kilometres, especially for relatively low terminal points.Consideration is also given to the effects of scattering of radio energy by turbulent eddies in the atmosphere, and an approximate calculation is made of the magnitude of this scattering for horizontally polarized waves on a frequency of 90 Mc/s, and at distances up to 500 km. It appears likely that such scattering is of less importance in the creation of unusually high field strengths up to distances of the order of 250 km than the mechanisms of abnormal refraction, including reflection at elevated inversion layers.

Our Astronomical Column

ANOTHER TEST OF THE EINSTEIN BENDING OF LIGHT.—It was suggested by Prof. Chas. Lane Poor and others that the observed light bending at the eclipses of 1919, 1922 might be due not to the Einstein effect but to abnormal refraction in the terrestrial atmosphere, produced by the fall of temperature about the time of totality. While it was unlikely that this would act radially from the centre of the sun throughout totality, it was thought advisable to test the suggestion at the Sumatra eclipse of 1926. This was done by Dr. Miller and Dr. Marriott, their method being to obtain the diameter of the moon by photography during totality. The effect if present would affect the moon as well as the stars, while the Einstein effect would only act on the stars.

THE EVIDENCE OF DIURNAL VARIATION IN CLOCK RATES

there is a systematic difference between the clock corrections as determined at sunset and at sunrise. It amounts to about 08.06 and can evidently be explained in but one of two ways. Either there is some systematic correction required for the observations of transits at the two epochs of the day, or the clock runs faster at night than during the daylight hours. Attempts to explain the effect by the variations in atmospheric refraction which might be due to changes in the barometric gradient, or the thermal gradient, have shown that such causes could not be sufficient to account for the observed deviation. We can shift our point of attack by deriving the observed clock rates during the night hours. It is not feasible to obtain clock rates during the middle of the day that would be precise enough to compare directly with night rates. Nor is this necessary. If the night rates are in excess of the average rate for an interval of twenty-four hours, the excess must be balanced by a deficit in the rates during daylight. At night we have the advantage of the best observing conditions, with no evidence that is conclusive of the existence of any abnormal refraction effects, and we can make a sufficiently large number of observations to obtain a precise result, such as is required by the delicacy of the test. The result is independent of observations made at sunset and sunrise, but appears to be an entirely competent test of the observed deviations at those epochs of the day. Variations of temperature of the clocks do not affect our results by any sensible amount. Our clocks are protected by double cases, in which the diurnal variation rarely exceeds a fraction of one degree, and the temperature at night lies almost invariably between those of the two adjoining days. The following table gives the comparison of clock rates determined during the actual intervals of observation each night

Abnormal refraction of milk serum

Abnormal refraction of milk serum

On the need for a legislative norm for high degrees of hypermetropia in relation to military-combatant services

As for the current Russian laws on anomalies in the organs of vision that allow or restrict the ability to perform military service, hyperopia, for which the law does not specify a predetermined degree, is completely ignored, compatible with the requirements of military service. Any hyperopia, no matter how high its degree of abnormal refraction, is recognised as extremely suitable for military service, unless it has a normal visual acuity without glasses.

EYE TROUBLES WHICH CONSTITUTE A FREQUENT SOURCE OF HEADACHE, VERTIGO AND NAUSEA, AND OTHER NERVOUS DISORDERS.Series of four lectures delivered at the Fourth Special Course of the Chicago Policlinic.

LECTURE II.—STRAIN OF THE OCULAR MUSCLES IN BINOCULAR VISION. Second Group:—The ocular affections to which I wish to invite your attention to-day, create disturbances in the nervous system also by strained muscular action. But while a person with abnormal refraction may suffer from nervous symptoms whether he sees with one eye or with both, the group of affections now before us can trouble the person only when he uses both eyes together.The nervous symptoms caused by this second group are due to unusual demands upon the ocular muscles to maintain binocular vision. Binocular vision is only possible if the visual line of each eye (i. e. the straight line drawn from the macula through the center of rotation of the eye) connects the macula with the object, or as it is usually expressed, both eyes must be turned directly towards the object. The slightest deviation of the one visual

On an Instance of Abnormal Refraction

On an Instance of Abnormal Refraction

3. Laboratory Notes by Professor Tait - 1. On Anomalous Spectra, and on a simple Direct-vision Spectroscope

When I first saw Le Roux's account of his very singular discovery of the abnormal refraction of iodine vapour, I was inclined to attribute the phenomenon to something similar to over-correction of an achromatic combination. In fact, if a hollow prism be filled with a mixture of two gases or vapours, one of which is more refractive than air, the other less refractive; while the second body is more dispersive than the first; it is easy to see that Le Roux's result might be obtained, although each of the substances employed is free from anomalous refractive properties. In a recent conversation with Mr Talbot, I happened to mention the subject, and I learned from him his remarkable observation just laid before the Society.