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Open access

I. Jonane, A. Podins and A. Ivanova

Photoluminescence of Neutron-Irradiated LiF Single Crystals

In 1980, a single LiF crystal was irradiated by thermal neutrons up to the exposition dose 1019 n/cm2 at the Salaspils nuclear reactor. The crystal has been kept at room temperature for 29 years. Samples in size of 5×4×1 mm3 were cut from the crystal and some of them annealed at 920 K for 30 min. To study photoluminescence, measurements with a confocal laser scanning microscope Leica TCS SP5 were performed, during which 3D-defects of size of ~1μm3 were revealed. Photoluminescence was observed in the red spectral region with the peak of ~ 655 nm when excited with an argon laser (Δ = 458 nm).

Open access

Tanyana N. Ivanova, Aleksandr I. Korshunov and Pavol Božek

Abstract

The main purpose of processing of tough-to-machine materials is improving of cutting process of steels with different physicochemical properties and alloying by means of various chemical elements in combination with heat treatment. Producing of high quality surface layers depends on properties of material used to make details, that is why reasons of tough machining were identified: influence of chemical composition and resulting structure. The studies of grinding of tough-to-machine materials were undertaken by means of grinding wheels made from synthetic diamonds as they are most resistant and highly-productive. Based on the studies recommendations for using of characteristics of grinding wheels and tough-to machine steel grades are given.

Research on heat processes during grinding allows us to determine patterns showing how cutting speed, detail motion speed, area and action period of contact influence temperature and speed of heat processes in surface layers as well as depth of heating. These patterns also give the chance to show interrelation between temperature and rate of heating and cooling. This gives an opportunity to predict state of structure of surface layer of details made of tough-to-machine steels under different machining conditions reasonably.

Open access

Vesela Ivanova, Milen P. Karaivanov and Tihomir I. Dikov

Open access

Zlatina I. Ivanova and Yavor Y. Ivanov

Abstract

Introduction: Pharmacoeconomics (PE) treats the problems of pharmacotherapy policy, drug marketing and reimbursement and clinical trials. It guides policy makers for effective health resources utilization and determines the profitability of the new drugs on the basis of their price, efficacy and benefits for society.

Types of health costs and pharmacoeconomic analyses: In the current review the main types of health costs are discussed. The main PE analyses with their advantages and disadvantages are presented.

Pharmacoeconomic of bronchial asthma: The main aspects of PE of bronchial asthma are available in the current review. The costs of health services (direct and indirect), the educational programs and asthma medications in different countries are discussed. Recently published data showed correlation between asthma cost and disease severity, control, social status and therapy adherence.

Conclusion: PE analyses provide the benefit of making cost consistent decisions in the field of asthma care. This review adds more data on the cost of current asthma treatment worldwide and in Bulgaria.

Open access

Zhivka D. Stoykova, Lilia I. Ivanova and Tatina T. Todorova

Abstract

Background: Human cytomegalovirus is a ubiquitous, large enveloped DNA β-herpesvirus that, like other herpesviruses, establishes lifelong latency following primary infection. It is the most frequent cause of congenital, neonatal and early postnatal infections with long lasting sequelae.

Aim: The aim of the present study was to assess the prevalence of cytomegalovirus among a cohort of newborns and 1-3-month-old children with neurological symptoms, physical retardation, prolonged jaundice, thrombocytopenic purpura and other disabilities.

Materials and methods: The study was a retrospective cross-sectional analysis of serological screening data for detection of specific anti-cytomegalovirus IgM and IgG in children from Northeastern Bulgaria.

Results: Between 2003 and 2015, average prevalences of 18.8% (95% CI: 15.4 to 22.2) for anti-CMV IgM antibodies (suggesting acute infection) and 84.7% (95% CI: 81.6 to 87.8) for anti-CMV IgG antibodies were measured in a total number of 517 samples. The prevalence rate of anti-CMV IgM in 1-3-month-old children was 4-fold higher than that in newborns [25.8% (95% CI: 21.1 to 30.5) and 6.4% (95% CI: 2.9 to 9.9, respectively]. In contrast, no significant difference was found for anti- CMV IgG positivity between newborns and 1-3-month-old infants (84% and 85%, respectively).

Conclusions: The data obtained strongly encourage screening of pregnant women for anti-CMV IgG and IgM to avoid transmission of the infection and severe complications of congenital infection.

Open access

A. Ivanova, A. Tokmakov, K. Lebedeva, M. Roze and I. Kaulachs

Abstract

Organometal halide perovskites are promising materials for lowcost, high-efficiency solar cells. The method of perovskite layer deposition and the interfacial layers play an important role in determining the efficiency of perovskite solar cells (PSCs). In the paper, we demonstrate inverted planar perovskite solar cells where perovskite layers are deposited by two-step modified interdiffusion and one-step methods. We also demonstrate how PSC parameters change by doping of charge transport layers (CTL). We used dimethylsupoxide (DMSO) as dopant for the hole transport layer (PEDOT:PSS) but for the electron transport layer [6,6]-phenyl C61 butyric acid methyl ester (PCBM)) we used N,N-dimethyl-N-octadecyl(3-aminopropyl)trimethoxysilyl chloride (DMOAP).

The highest main PSC parameters (PCE, EQE, VOC) were obtained for cells prepared by the one-step method with fast crystallization and doped CTLs but higher fill factor (FF) and shunt resistance (Rsh) values were obtained for cells prepared by the two-step method with undoped CTLs.

Open access

Izabella K. Ivanova, Matvey E. Semenov, Vladilina V. Koryakina and Igor I. Rozhin

Abstract

The paper considers the research results of natural gas (NG) hydrate formation process in systems consisting of paraffin oil and distilled water at various ratios. Thermobaric conditions of hydrates phase transitions in water-oil emulsions were determined by the method of high-pressure differential scanning calorimetry (DSC). It was ascertained that the equilibrium curve in systems under study, compared to the process of hydrate formation of this gas in distilled water, is shifted in the area of low pressures and high temperatures. According to DSC analysis results and volume analysis, it was determined that with increase of the water content in emulsions by more than 40 % of mass, the degree of water conversion into hydrate in emulsions decreases. It was concluded that the degree of water conversion into hydrate in emulsions can be used as an index of its stability.

Open access

I. Ivanova, B. Atanasova, A. Kostadinova, Y. Bocheva and K. Tzatchev

Summary

Copper (Cu) and zinc (Zn) are essential for life. Body Cu and Zn content depends on variety of factors - age, gender, and diet, type of drinking water, geographical location and genetic predisposition. Copper status becomes even more relevant not only in rare genetic disorders such as Wilson disease but in diseases such as cardiovascular ones, impaired glucose tolerance and neuro-degenerative and tumor diseases. The study aimed to examine the distribution of serum Cu and Zn in a representative group of the Bulgarian population and to describe factors which influence metal content. It also aimed to describe the link between serum Cu levels and the frequency of Alzheimer’s disease (AD) in Bulgarians. Cu and Zn in serum were measured in 379 individuals (172 males and 207 females) from 5 different regions in Bulgaria by flame atomic absorption using AAnalyst 400, Perkin Elmer. Statistical analyses were performed by SPSS, 19. Median and inert-quartile range (IQR) for blood Cu were 15.89 (13.87-7.89) μmol/L and for Zn - 13.00 (11.7-14.68) μmol/L in the examined group. Higher Cu levels in females than in males were found (p < 0.001). Decrease of Zn with aging was established (p > 0.05). Significant difference (p < 0.05) was found in serum Cu between young people (< 30 year old) and adults over 61 year old. Statistically significant difference in Cu and Zn was observed (p < 0.05) in respect of residences. Difference without significance was measured between serum lipids and serum Cu (p = 0.541) and Zn (p = 0.741).

Open access

Vesela Ivanova, Milen P. Karaivanov and Tihomir I. Dikov

Summary

We present a case of a 75-year-old female who underwent a total abdominal hysterectomy with bilateral salpingooophorectomy for an ovarian tumor. Hematoxylin-eosin- stained slides from tumor specimen revealed 1) focci of benign Brenner tumor; 2) mucinous cysts and 3) intracystic papillary projections resembling low-grade papillary transitional cell carcinoma (Grade 1-2) with squamous differentiation and comedo-type necrosis; 4) focal areas resembling noninvasive papillary transitional cell carcinoma Grade 3. Immunohistochemical investigation with a panel of antibodies (p63, p53, Ki-67, Wilms Tumor 1 - WT1, pi 6) was initiated. Areas resembling urothelial carcinoma showed diffuse nuclear positive reaction for p63 and wild-type expression of p53. Ki-67-nuclear positivity varied from less than 5% up to 30% in areas resembling high-grade urothelial carcinoma. WT1 expression was not seen. Weak but still exceeding background staining was observed in predominantly cytoplasmic fashion with few scattered positive nuclei in transitional cell nest of the benign component. No reactivity, however, was seen within the proliferative component. The histopathological diagnosis was a borderline/atypical proliferative Brenner tumor.

The patient has been regularly followed up and is at present disease-free 5 years after diagnosis. In this paper, the authors describe the morphological characteristics of Brenner tumors and address some debatable issues in the light of recent immunohistochemical and molecular studies.

Open access

Mariana Genova, B. Atanasova, I. Ivanova, K. Todorova and D. Svinarov

Abstract

Gestational diabetes mellitus (GDM), one of the most common pregnancy complications, is defined as glucose intolerance with onset or first recognition during pregnancy. Its prevalence varies worldwide in dependence on characteristics of the underlying population and applied diagnostic criteria. The etiology is multifactorial and not sufficiently elucidated. Available evidence suggests that the base of pathogenesis is relatively diminished insulin secretion coupled with pregnancy-induced insulin resistance. Modifiable and non-modifiable risk factors for development have been identified. Trace elements and vitamin D could be contributed to modifiable factors for prediction the risk in a large population. Essential trace elements in pregnancy are necessary to overcome systemic oxidative, metabolic and inflammatory stress. Evidence, still inconclusive, has been accumulated about the relation between higher incidence of vitamin D failure/deficiency during pregnancy and GDM. The lower level of 25-OH vitamin D could be associated with increased risk for anemia development, also including pregnant women. This review intends to provide an overview of the possible link between both vitamin D and trace elements as risk factors for GDM development.