On some Modifications of the Nekrassov Method for Numerical Solution of Linear Systems of Equations

A modification of the Nekrassov method for finding a solution of a linear system of algebraic equations is given and a numerical example is shown.* This paper is partly supported by project IS–M–4 of Department for Scientific Research, Paisii Hilendarski University of Plovdiv

Afforestation in Bulgaria

The historical development of afforestations in Bulgaria was investigated. Some of the more important decisions and events which determine the correct state policy in the field of afforestations are pointed out. The most significant achievements are in: erosion control, incl. water tank protection from silting up; increasing the tree volume and forest growth; protection of agriculture via forest protection belts; landscape improving. The social importance for more employment and improvement of means of livelihood is mentioned. Proved reasons for decreasing the afforested areas since 1980s are given. The main mistakes and problems are mentioned as well as the changes in the afforestation policy and future challenges

Compliance and knowledge about glaucoma in patients at tertiary glaucoma units

To document the rate of self-reported compliance and glaucoma-related knowledge in Swiss patients and to identify risk factors for their poor compliance. This was an observational study, including a total of 200 consecutive patients already under glaucoma medication in two Swiss tertiary glaucoma clinics (Geneva and Bern). Personal characteristics, presence of systemic disease, compliance with glaucoma medication, attitude to the ophthalmologist, and glaucoma-related attitudes were ascertained by means of a predetermined questionnaire with 40 questions. Patients were subsequently assessed for the ability to correctly instil placebo eye drops. Non-compliance with glaucoma medication was defined as omitting more than two doses a week as reported by the patient. Logistic regression was used to evaluate how patient characteristics and knowledge about the disease were related to compliance. Overall, 81% (n=162) of patients reported to be compliant. Forgetfulness was the most frequently cited reason for non-compliance with dosing regimen (63%). Although 90.5% (n=181) of patients believed glaucoma medication to be efficient, only 28% (n=56) could correctly define glaucoma. Factors positively associated with compliance were ‘knowledge of glaucoma' [adjusted odds ratio (OR) 4.77 (95% CI 1.36-16.70)] and ‘getting help for administration of drops' [OR 2.95 (1.25-6.94)]. These findings indicate that despite the comparatively high compliance rate among glaucoma patients, knowledge of glaucoma remains poor in long-term glaucoma sufferers. Improving knowledge about the disease is important since it is positively associated with compliance in our stud

Nanoscale switching characteristics of nearly tetragonal BiFeO3 thin films

We have investigated the nanoscale switching properties of strain-engineered BiFeO3 thin films deposited on LaAlO3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically-driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material which is promising for a plethora of applications.Comment: 10 pages, 6 figure

Retrograde Maculopathy in Patients With Glaucoma.

PURPOSE Macular optical coherence tomography (OCT) analysis can be used for quantitative measures of optic nerve atrophy at a location far from the optic nerve head. This recently led to the finding of microcystic macular edema (MME), that is vacuolar inclusions in the macular inner nuclear layer, in some glaucoma patients. The involvement of individual retinal layers is yet unclear in glaucoma. In this study we systematically investigated glaucoma-induced changes in macular layers to evaluate whether glaucoma-associated damage extends beyond the macular ganglion cell layer. PATIENTS AND METHODS We included 218 consecutive patients and 282 eyes with confirmed primary open-angle glaucoma or pseudoexfoliation glaucoma, and macular OCT in a cross-sectional observational study. Eyes were screened for presence of MME. Thickness of individual retinal layers was determined using a semiautomatic segmentation algorithm. Peripapillary nerve fiber layer thickness and mean defect in visual field testing were extracted from OCT and medical records, respectively. Results were compared with a small group of eyes with no apparent glaucoma. RESULTS We found MME in 5 eyes from 5 primary open-angle glaucoma patients and 3 eyes of 3 pseudoexfoliation glaucoma patients (2.8%). MME was confined to the inner nuclear layer in a perifoveal ring and was associated with thinning of the ganglion cell layer and thickening of the macular inner nuclear layer. Glaucoma eyes without MME showed a significant inverse correlation of inner nuclear layer thickness with glaucoma severity. CONCLUSIONS Glaucomatous damage leads to a gradual thickening of the inner nuclear layer, which leads to MME in more severe glaucoma cases. These changes, along with nerve fiber loss and ganglion cell loss, may be summarized as glaucoma-associated retrograde maculopathy

Origin of the Superconductivity in the Y-Sr-Ru-O and Y-Sr-Cu-O Systems

We report on the structural, magnetic, and Raman-scattering studies of double perovskite structure Sr2Y(Ru1-xCux)O6-d systems made by systematic synthesis processes with various numbers of doping concentrations and sintering temperatures. We observed different behaviors resulting from the different thermal treatments. In particular, superconductivity in Cu-doped Sr2YRuO6 has been observed only for partially melted ceramic materials. We show that superconductivity is associated with the 1:2:3 phase (YSr2Cu3Ot), similar to that of Y-Sr-Cu-O samples sintered at high temperature

THERMOREFLECTANCE, PHOTOCONDUCTANCE AND RAMAN SCATTERING OF FERROMAGNETIC SPINELS MCr 2X4 (M=Cd, Hg ; X=S, Se) NEAR THE MAGNETIC PHASE TRANSITION

Le compte rendu présent a pour but d'étudier certains résultats des expériences faites récemment sur la thermoréflexion, la photoconductibilité et la diffusion Raman de résonance des spinelles ferromagnétiques (CdCr2Se4, CdCr2S4, HgCr2Se4) près et au-dessus du seuil d'absorbtion. Le comportement critique près de la transition de phase magnétique des éléments particuliers du spectre de la thermoréflectibilité associés aux bandes des électrons itinérants met en évidence l'existence d'un fort couplage entre les sous-systèmes des électrons et des spins. Ceci est confirmé aussi par les variations en température du spectre de photoconductibilité et la section efficace de la diffusion Raman. Le mécanisme réel des processus éléctroniques dépendants du spin paraît donc plus compliqué que celui prévu par les modèles les plus simples. Les Raman spectres eux-mêmes aussi bien que leur dépendance de la température et de l'énergie des photons incidents mettent en cause le concept actuel sur la diffusion Raman dépendant du spin dans les spinelles ferromagnétiques. Les résultats prouvent que les intensités des phonons Raman actifs sont déterminées par les formes des courbes de résonance et leur variation avec la température.The results of recent experiments on thermoreflectance, photoconductance and resonant Raman scattering of CdCr2Se4, CdCr2S4 and HgCr2Se4 at photon energies near and above the absorption edge are reviewed. The critical behaviour near the magnetic phase transition of the thermoreflectance (TR) spectral features associated with the bands of itinerant electrons provide evidence of a strong coupling between electrons and spins. The latter is supported by the temperature variation of both the photoconductivity spectra and the resonance of the Raman scattering cross section. The actual mechanism of spin-dependent electronic processes seems to be more complex than predicted by the simplest models. The Raman spectra and their dependence on temperature and incident photon energy show that the concept of spin dependent Raman scattering in the ferromagnetic spinels has to be revised. The results allow to conclude that the intensities of the Raman-active phonons are determined mainly by the line shapes of the resonance curves and their changes with temperature

Raman spectroscopy of M₃B₇O₁₃X boracites (M = Cr,Co,Ni,Cu,Zn,Cd; X = Cl,Br,I)

We report results of a Raman study on single crystals of 16 boracites M3B7O13X (M= Cr,Co,Ni,Cu,Zn,Cd; X = Cl,Br,I) over a broad temperature range. The Ramanmodes for all boracites in their high-temperature prototype cubic (F43c) phase are compared. With decreasing temperature,most (but not all) compounds present a transition to the low-temperature orthorhombic phase (Pca21) or to a sequence of orthorhombic, monoclinic (Pa), and trigonal (R3c) phases. The variations of the Raman spectra through different phases are studied in detail. Special attention is paid to the temperature hysteresis near the transitions and the dependence of transition temperature on the direction of crystal growth for the same material

Investigation of Phonon Vibrational Modes in Ga, Al, Fe, Co, Ni, and Zn Doped (110)-Oriented PBCO Thin Films

We performed Raman scattering measurements and a comprehensive study of different types of Raman modes associated with phonon vibrations on pure and Ga, Al, Fe, Co, Ni, and Zn doped (110)-oriented PrBa2Cu3O7 (PBCO) thin films to identify the substitution of Cu (1) or Cu (2) ions in PBCO lattice. In Raman spectrum of (110)–oriented PBCO thin film, we observed four prominent Ag type Raman modes at ∼130 cm−1, ∼150 cm−1, ∼440 cm−1, and ∼520 cm−1 corresponding to Ba, Cu (2), O (2)–O (3) in-phase, and O (4) apical oxygen vibration along c-axis, respectively. The Raman mode of pure PBCO at ∼520 cm−1 softened on Ga, Al, Fe, and Co doped PBCO thin films while it remained unaffected on Zn and Ni doped PBCO thin films. We explain these results in the context of their correlation with Cu (1)–O (4) and Cu (2)–O (4) bond lengths. In addition, we observed a new Raman mode near 610 cm−1 in the Raman spectra of Ga, Al, Fe, and Co doped PBCO thin films, an infrared (IR) active mode that became Raman active when the symmetry was broken at the Cu-O chain site after the partial substitution of Cu (1) ion. Moreover, the “O (2)–O (3) in-phase Raman mode” near 440 cm−1 remained unaffected in Fe, Co, Ga, and Al doped PBCO thin films but softened in Zn and Ni doped PBCO thin films. Based on these results, we argue that Ga, Al, Fe, and Co ions replace Cu (1) ion at the Cu-O chain site, break the crystal symmetry, and produce disorder locally, whereas Zn and Ni ions replace Cu (2) ion at the CuO2 plane of the PBCO lattice structure