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It is well-known that spectral singularities play a certain critical role in the spectral theory of nonselfadjoint differential operators. Their existence is accompanied by specific phenomenon which are new in the sense that they do not occur either in the spectral theory of self-adjoint or normal operators. So, in this paper, we examine spectrum and spectral singularities of the impulsive quadratic pencil of Schrödinger operators. In particular, we study the dependence of the structure of discrete spectrum and spectral singularities of these operators of the behaviour of the potential functions at infinity. We present some conditions on potential functions which guarantee that the impulsive quadratic pencil of Schrödinger operators have a finite number of eigenvalues and spectral singularities with finite multiplicities. Later, we discuss the properties of principal functions corresponding to the spectral singularities. [ABSTRACT FROM AUTHOR]

Diabetes mellitus is a serious disease worldwide and causes other associated diseases. In this study, we observed the effect of streptozotocin (STZ)-induced diabetes and benfluorex treatment on muscular capillary ultrastructure. Adult male rats were used as the test subjects and each individual was intraperitoneally injected with one dose of STZ (45 mg/kg) to induce diabetes. Doses (50 mg/kg) of benfluorex were given to the subjects with tap water by intragastric gavage application once daily for 21 days. At the end of day 21, muscle tissues were obtained from animals and examined under transmission electron microscopy. From the data obtained with the electron microscope, it was observed that the control group had typical continuous capillary vascular structures in their muscles, while STZ caused disruptive disorder of the muscle cells in the capillary wall of the STZ-diabetic group. Additionally, the thickening of the basement membrane around endothelial cells, loss of mitochondrial crista in the muscle cells, enlarged endothelial cells, and narrowed vessel lumen were observed in the muscle tissue. The findings of our study revealed that STZ-induced diabetes disrupted the vascular structure, while benfluorex partially improved it.

We investigated the distribution of connective tissue fibers in diabetic and vitamin C treated diabetic rat spleen. Rats were divided into three groups: group A, control; group B, diabetic; group C, vitamin C treated diabetic. Diabetes was induced by streptozotocin. Vitamin C was administered intragastrically for 21 days. Spleen tissues were examined by light microscopy after staining with Masson's trichrome, Gomori silver impregnation and van Gieson. In group B, we found accumulation of collagen fibers in the trabeculae, in the capsule and around the central artery and splenic sinusoids. Splenic cord thickening due to fibrosis was observed. Reticular fibers accumulated principally in the white and red pulps of the spleen and focal reticular fiber thickening was observed in the dense fiber areas. Partial elastic fiber rupture was observed among the fibers of the elastic lamina of the arteries in the hilum. By contrast, the distribution of collagen fibers in group C was similar to group A. Collagen fiber accumulation was decreased in group C compared to group B. We found little reticular fiber thickening in group C and elastic fibers maintained their integrity and were better organized than in group B. Our findings suggest that appropriat e doses of vitamin C may exert beneficial effects on the structure of the connective tissue fibers in the diabetic spleen.