Application of Rarebit Perimetry in Preperimetric Glaucoma

Цел: Да се определят диагностичните възможности на Rarebit периметрията за установяване на ранни функционални промени при първична откритоъгълна глаукома.Методи: Включени са общо 47 очи разпределени в две групи: 23 очи с предпериметрична глаукома (ППГ) и контролна група от 24 очи, изследвани чрез Rarebit периметрия (РБП) и стандартна автоматична периметрия (САП). За оценка на разликите между групите са използвани Kruskal Wallis Test, Mann-Whitney Test, Fisher's Exact Test. Чувствителността и специфичността на РБП за установяване на ранни глаукомни промени е оценена чрез ROC анализ с помощта на различни алгоритми.Резултати: Средните стойности за МНR за контролите и групата ППГ са съответно: 94.71% (SD 2.58); 87.61% (SD 4.80). Разликите в стойностите на МНR между групите са статистически значими (Мann-Whitney Test, р<О.ОО1 ). Най-висока стойността на AROC (0. 849) е постигната, когато за абнормен се приема Rarebit тест с МНR<90% при сравняване на здравите очи с тези с ППГ.Заключение: РБП е чувствителен метод спрямо дефекти в зрителното поле при препериметрична глаукома. Тестът е бърз и лесен за изпълнение.Aim: То determine the diagnostic capabilities of Rarebit perimetry for detection of early functional changes in primary open-angle glaucoma.Methods: А total of 47 eyes divided into two groups: 23 eyes with preperimetric glaucoma (PPG) and a control group of 24 eyes were examined with Rarebit perimetry (RBP) and standard automated perimetry (SAP). То evaluate the differences between the groups were used Kruskal Wallis Test, Mann-Whitney Test and Fisher's Exact Test. The sensitivity and specificity of the RBP for detection of early glaucomatous changes were evaluated by ROC analysis using different algorithms.Results: Average МНR for control and PPG group were respectively: 94.71% (SD 2.58); 87.61% (SD 4.80). Differences in МНR between the groups were statistically significant (Мann-Whitney Test, р <0.001). The highest value of AROC (0.849) was achieved when as abnormal was accepted Rarebit test with МНR <90% when comparing healthy eyes to those with PPG.Conclusion: RBP is sensitive method for visual field defects in preperimetric glaucoma. The test is quick and easy to perform

Mean Age of Patients with and without Type 2 Diabetes Mellitus during Surgical Treatment of Age-Related Cataract

Introduction: Age-related cataract is one of the most common causes of preventable blindness. Type 2 diabetes is a non-infectious epidemic disease with an ever-increasing number of diseased patients. Cataract is one of the leading causes of reduced vision in diabetics. The preferred treatment method is phacoemulsification. The aim of the present study was to compare the mean age of patients with and without diabetes type 2 at the time of cataract surgery. Materials and methods: After informed consent and approval by the Ethics Commission of the Medical University of Sofia, 176 patients admitted to the Clinic of Ophthalmology at the University Hospital „Alexandrovska“ for surgical treatment of cataract were randomized. Inclusion criteria: diagnosed age-related cataract, requiring surgical treatment. Patients were divided into two groups – diabetic type 2 and non-diabetic patients. Inclusion criteria for the group of diabetics: medical history of diabetes type 2 and administration of anti diabetic medications. Results: The average age of patients undergoing cataract surgery was 70.81 years. The average ageof patients with diabetes type 2 was 65.89 years, and that of non-diabetics – 71.74 years. Diabetes type 2 was established at 15.91 % of patients (19 men and 9 women). Conclusion: Patients with diabetes type 2 develop age-related cataract, requiring surgical treatment, at an earlier age compared to non-diabetics. The transparency of the lens in diabetic patients is of particular importance for the diagnosis and treatment of the diabetic retinopathy. Follow-up by an ophthalmologist and maintenance of strict blood glucose control are necessary to reduce the incidence of vision loss, caused by cataract and diabetic retinopathy

Re-entrant superconductivity in Nb/Cu(1-x)Ni(x) bilayers

We report on the first observation of a pronounced re-entrant superconductivity phenomenon in superconductor/ferromagnetic layered systems. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu(1-x)Ni(x). The superconducting transition temperature T_{c} drops sharply with increasing thickness d_{CuNi} of the ferromagnetic layer, until complete suppression of superconductivity is observed at d_{CuNi}= 4 nm. Increasing the Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at d_{CuNi}=13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.Comment: 3 pages, 3 figures, REVTEX4/twocolum

Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers

We studied the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state establishing due to the proximity effect in superconducting Nb/Cu41Ni59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device (SQUID) magnetometry. These studies yield precise information about the thickness, and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu41Ni59 layer thickness, Tc(dS) and Tc(dF), were investigated for constant thickness dF of the magnetic alloy layer and dS of the superconducting layer, respectively. All types of non-monotonic behaviors of Tc versus dF predicted by the theory could be realized experimentally: from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, Tc(dF) diagrams of a hypothetical F/S/F spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results.Comment: 34 pages, 9 figure

Experimental and theoretical analysis of the upper critical field in FSF trilayers

The upper critical magnetic field H_{c2} in thin-film FSF trilayer spin-valve cores is studied experimentally and theoretically in geometries perpendicular and parallel to the heterostructure surface. The series of samples with variable thicknesses of the bottom and of the top Cu_{41}Ni_{59} F-layers are prepared in a single run, utilizing a wedge deposition technique. The critical field H_{c2} is measured in the temperature range $0.4-8$ K and for magnetic fields up to 9 Tesla. A transition from oscillatory to reentrant behavior of the superconducting transition temperature versus F-layers thickness, induced by an external magnetic field, has been observed for the first time. In order to properly interpret the experimental data, we develop a quasiclassical theory, enabling one to evaluate the temperature dependence of the critical field and the superconducting transition temperature for an arbitrary set of the system parameters. A fairly good agreement between our experimental data and theoretical predictions is demonstrated for all samples, using a single set of fit parameters. This confirms adequacy of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) physics in determining the unusual superconducting properties of the studied Cu_{41}Ni_{59}/Nb/Cu_{41}Ni_{59} spin-valve core trilayers.Comment: 16 pages, 7 figures; published versio

Memory Effect and Triplet Pairing Generation in the Superconducting Exchange Biased Co/CoOx/Cu41Ni59/Nb/Cu41Ni59 Layered Heterostructure

We fabricated a nanolayered hybrid superconductor-ferromagnet spin-valve structure, the resistive state of which depends on the preceding magnetic field polarity. The effect is based on a strong exchange bias (about -2 kOe) on a diluted ferromagnetic copper-nickel alloy and generation of a long range odd in frequency triplet pairing component. The difference of high and low resistance states at zero magnetic field is 90% of the normal state resistance for a transport current of 250 {\mu}A and still around 42% for 10 {\mu}A. Both logic states of the structure do not require biasing fields or currents in the idle mode.Comment: 9 pages, 4 figures, Accepted to Applied Physics Letter

Reentrant Superconductivity and Superconducting Critical Temperature Oscillations in F/S/F trilayers of Cu41Ni59/Nb/Cu41Ni59 Grown on Cobalt Oxide

Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers constitute the core of a superconducting spin valve. The switching effect of the spin valve is based on interference phenomena occurring due to the proximity effect at the S/F interfaces. A remarkable effect is only expected if the core structure exhibits strong critical temperature oscillations, or most favorable, reentrant superconductivity, when the thickness of the ferromagnetic layer is increased. The core structure has to be grown on an antiferromagnetic oxide layer (or such layer to be placed on top) to pin by exchange bias the magnetization-orientation of one of the ferromagnetic layers. In the present paper we demonstrate that this is possible, keeping the superconducting behavior of the core structure undisturbed.Comment: 22 pages, 12 figures, 1 tabl

Fluctuation conductivity in superconducting MgB2

According to the crystal structure of MgB2 and band structure calculations, quasi-two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical-field and resistance measurements of 5.6-μm-thick MgB2 films grown on a sapphire single-crystal substrate. Resistivity measurements yield a temperature dependence of the fluctuation conductivity above the critical temperature, which agrees with the Aslamazov-Larkin and Maki-Thompson theory of fluctuations in layered superconductors, indicating a quasi-two-dimensional nucleation of superconductivity in MgB2. © 2002 MAIK "Nauka/Interperiodica"

Reentrant superconductivity in Nb/Cu1-xNix bilayers

We report on the first observation of a pronounced reentrant superconductivity phenomenon in a superconductor/ferromagnet layered system. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu1-xNix. The superconducting transition temperature Tc drops sharply with increasing thickness dCuNi of the ferromagnetic layer, until complete suppression of superconductivity is observed at dCuNi≈4nm. Increasing the Cu1-xNix layer thickness further, superconductivity reappears at dCuNi≥13nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one-dimensional Fulde-Ferrell-Larkin- Ovchinnikov-like state in the ferromagnetic layer. © 2006 The American Physical Society