131 research outputs found
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 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
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