MULTIPATH ANTENNA SYSTEM OF THE VHF BAND BASED ON A LENS MADE OF GRANITE RUBBLE

Предложена конструкция приземной многолучевой антенной решетки на основе линзы из гранитного щебня, позволяющая одновременно формировать до нескольких десятков лучей в длинноволновой области УКВ-диапазона волн. Эффективная диэлектрическая проницаемость гранитного щебня оценивалась с помощью формулы Лихтенекера для мелкодисперсных смесей; ее величина приблизительно равна 3. Для оценки величины замедления поверхностных волн в линзе использовалась методика анализа дисперсионных характеристик зеркального диэлектрического волновода; при высоте линзы 1.8 метра эффективная диэлектрическая проницаемость эквивалентного зеркального диэлектрического волновода равна 2.1. В качестве облучателей линзы - несимметричные электрические вибраторы, расположенные на окружности по периметру линзы, диаметр которой составляет 30 метров; диаметр подстилающей стальной поверхности составляет 40 метров. Предложенная антенная система характеризуется потерями в щебне около 3 дБ при диаметре линзы около 3,8 длин волн; показано, что коэффициент направленного действия у каждого луча может составлять около 15,5 дБ, при ширине главного лепестка в азимутальной плоскости по уровню половинной мощности около 10 градусов We propose a design of a surface multi-beam antenna array based on a lens of crushed granite, which makes it possible to simultaneously form up to several tens of beams in the long-wave region of the VHF wave range. We estimated the effective dielectric constant of crushed granite using the Lichtenecker formula for fine mixtures; its value is approximately equal to 3. To estimate the magnitude of the deceleration of surface waves in the lens, we used a technique to analyze the dispersion characteristics of a mirror dielectric waveguide; at a lens height of 1.8 meters, the effective dielectric constant of the equivalent mirror dielectric waveguide is 2.1. As irradiators of the lens - asymmetric electric vibrators located on a circle around the perimeter of the lens, the diameter of which is 30 meters; the diameter of the underlying steel surface is 40 meters. The proposed antenna system is characterized by a loss in rubble of about 3 dB with a lens diameter of about 3.8 wavelengths; the directivity of each beam can be about 15.5 dB, with the width of the main lobe in the azimuthal plane at half power level of about 10 degrees

B- mode ultrasonographic biometry of cataractous eyes in dogs

Cataract is one of the main reasons interfering with examination of the eye in many species of animals. As the opaque lens obscures visualization of the posterior segment of the eye, evaluation of the structures in the posterior segment becomes impossible. B-mode ultrasonography of the eye plays a major role in such conditions to evaluate the posterior segment and to evaluate the biometry of the intraocular structures. In the current study, dogs with cataracts of various stages were subjected to ocular ultrasonographic evaluation and biometry of ocular structures. Biometry for ocular parameters like axial length of the eye (D1), vitreous chamber depth (D2), lens diameter (D3) and lens depth (D4) were recorded in all the dogs with cataractous lens. The ultrasonographic appearance of the lens varied in echogenicity with the stage of the cataract. The changes in the cortex and nucleus part of the lens were also imaged and recorded. B-mode ultrasonography was useful in ruling out structural pathologies related to the vitreous and retina prior to cataract surgery

Influence of scleral lens haptic zone design on lens fit in patients with different scleral toricity

In our practice, we often encounter the issue of centering and stabilizing scleral contact lens (SCL) in the patient's eye. This is due to the fact that the haptic part of the SCL rests on the scleral conjunctiva, which itself is toric. Рurpose. To analyze possibilities of stabilizing scleral and mini-scleral lenses in patients with different scleral toricities. Material and methods. This study was a retrospective review of 17 patient records (34 eyes); 9 patients were male and 8 female. The mean age of the patients was 38 ± 12 years. Results. The horizontal visible iris diameter amounted to 11.85 ± 0.52 mm (11.0 to 12.5 mm). All patients previously underwent fitting of SCLs for correction of ametropia. Lens diameter was chosen based on the corneal diameter, while the shape of the patient's sclera determined stabilization method. This work describes a method for determining scleral toricity. An adequate fit of spherical SCLs was not achieved in patients with toric sclera; however, the correct choice of a stabilization method made it possible to achieve congruence of the lens edge with the scleral surface in all four quadrants and obtain a high visual acuity in all patients included in the study, regardless of the lens diameter. Conclusion. Stabilization of SCLs provided a safe and comfortable wearing experience. Key words: scleral lenses, mini-scleral lenses, lens edges, scleral conjunctiva, toric periphery, limbus

Optimizing the intraocular lens formula constant according to intraocular lens diameter

AIM: To determine whether the different diameters of a specific intraocular lens (IOL) have significantly different optimized SRK/T A constants and whether these new A constants can improve refractive outcomes. METHODS: Data were collected prospectively from Jan. 2011 to Dec. 2012 on all patients undergoing routine cataract surgery at a district general hospital in the UK. Patients were divided into three groups according to the size of the Akreos AO MI60 IOL used. A constants for the SRK/T formula were optimized according to the size of the IOL. These optimized A constants were then used to select future refractive outcomes. RESULTS: A total of 2398 cataract operations were performed during the study period of which 1131 met the inclusion criteria. The three optimized A constants for the different sized IOLs were 118.98, 119.13, 119.32. The difference between them was highly significant (P≤0.0001). Two optimized A constants for three sizes of IOL led to an improvement in refractive outcomes (from 93.4% to 94.6% of refractive outcomes within 1.00 D of predicted spherical equivalent). The optimized A constant for the largest IOL was based on a small number of cases and was not used. CONCLUSION: Optimizing the A constant for the three distinct sizes of the Bausch & Lomb Akreos MI60 lens lead to three significantly different A constants. In our practice, using two different optimized A constants for three different sized IOLs give the least refractive error, however, using three optimized A constants may give better results with a larger dataset.

Isotopic characterization of lifetime movement by two demersal fishes from the northeastern Gulf of Mexico

An understanding of lifetime trophic changes and ontogenetic habitat shifts is essential to the preservation of marine fish species. We used carbon and nitrogen stable isotope values (δ13C and δ15N) recorded within the laminar structure of fish eye lenses, reflecting both diet and location over time, to compare the lifetime trends of 2 demersal mesopredators. Tilefish Lopholatilus chamaeleonticeps inhabit burrows on the outer continental shelf, which results in exceptional site fidelity. Red grouper Epinephelus morio are spawned on the middle to outer continental shelf, move to the inner shelf for the juvenile period, and return offshore upon sexual maturity. Both species inhabit the eastern Gulf of Mexico, a region with a distinctive offshore-inshore gradient in background δ13C values. Within individual tilefish (n = 36), sequences of δ13C values and δ15N values had strong, positive correlations with eye-lens diameter, and strong correlations between the 2 isotopes (mean Spearman r = 0.86), reflecting an increase in trophic position with growth and little lifetime movement. In red grouper (n = 30), δ15N values positively correlated with eye-lens diameter, but correlations between δ15N and δ13C were weak (mean Spearman r = 0.29), suggesting cross-shelf ontogenetic movements. Linear mixed model results indicated strong relationships between δ15N and δ13C values in tilefish eye lenses but no convergence in the red grouper model. Collectively, these results are consistent with previously established differences in the life histories of the 2 species, demonstrating the potential utility of eye-lens isotope records, particularly for investigating the life histories of lesser-known species.

Evaluation of the Relationship between Corneal Diameter and Lens Diameter in Children

Primary intraocular lens (IOL) implantation has gained acceptance for management of infantile cataracts because of the advantage of reduced amblyopia risk. The aim of the study was to investigate the association between corneal diameter as measured from the white-to-white distance and natural lens diameter in children. This association may aid intraocular lens selection following cataract removal in infants and young children. A cross-sectional study was performed on forty eyes from 40 children less than 4 years, who needed to be examined, were planned for a procedure or operation under general anaesthesia. Subjects were recruited from Eye Clinic,Kuala Lumpur General Hospital from January 2010 to September 2011. Corneal diameter was measured with Holladay-Godwin corneal gauge while lens diameter was measured with ultrasound biomicroscope (UBM) during surgery. For the results, mean age of subjects was 24.7 + 12.1 months. Mean corneal diameter was 11.62 + 0.50 mm horizontally and 11.20 + 0.58 mm vertically. Mean horizontal lens diameter was 7.94 + 0.47 mm. A medium positive correlation was found between mean horizontal corneal diameter and lens diameter (r=0.479, p=0.002). Lens diameter had a strong correlation with patient’s age (r=0.718, p<0.001). Lens diameter can be calculated by using this model of equation: [Lens diameter (mm) = 7.010 + 0.021 Corneal Diameter (mm) + 0.028 Age (months)] (r2=0.52). In conclusion, there was a moderate positive correlation between corneal and lens diameter. UBM can be used to measure lens capsular bag size directly preoperatively.