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N. Nikolov, D. Pashkouleva and V. Kavardzhikov

Mechanical Behaviour of Conventional Materials at Experimental Conditions of Deep Drawing Technological Process

The paper deals with experimental investigations on the mechanical behaviour of body-centred-cubic (BCC) and face-centred-cubic (FCC)-conventionally structured sheet metalic-metalic materials under stress-strain conditions of a deep drawing process determined by a coefficient close to the limiting one for Steel 08 and punch diameter of 50 mm. The mechanical characteristics of the investigated materials are identified by one-dimensional tension tests. The materials' responses, as results of identical loading conditions, are described by the change of blank sizes and characteristics of the forming processes. The chosen deformation path ensures obtaining a qualitative steel piece and leads to failures of aluminium and brass blanks.

The reported results could be useful for investigations and predictions of the mechanical responses of such type metallic structures applying microscopic instrumented observations and numerical simulations.

Open access

N. Nikolov, T. Avdjieva and I. Altaparmakov

Abstract

Some specially designed metallic alloys crystallize during process of rapid quenching which aims their amorphization. Nevertheless, change in their mechanical properties could be seen compared to these obtained during conventional technological regimes of cooling. That attracts the attention in this elaboration. Full 3-D numerical simulations of nanoindentation process of two material models are performed. The models reflect equivalent elastic and different plastic material properties. The plastic behaviour of the first one is subjected to yield criterion of Dracker-Prager and this of the second one to yield criterion of Mises. The reported numerical results depending on the nanoindentation scale length of 1000 nanometers, suggest different adequacy of the two yield criteria to the data obtained experimentally with a Zr-Al-Cu-Ni-Mo alloy. It could be speculated that the different effects developed depending on the indenter travel of 1000 nanometers and taken into account in the two yield criteria stand behind this fact and determinate three structural levels of plastic deformation.

Open access

V. Lukov, M. Alexandrova and N. Nikolov

Abstract

The article presents the synthesis of a multi-model modal control of single input – single output nonlinear plant, based on Takagi-Sugeno fuzzy controller. For that purpose, the nonlinear static characteristic of the plant is presented by two linear parts. These two linear structures are described in state space. The feedback vectors and the coefficients ki of the modal controllers are calculated. An integral component in the control law is added.

Open access

E. Nikolov, N. G. Nikolova and B. Grasiani

Abstract

The present study systematizes certain methods for analysis at priori un-certainty and proposes new methods for analy-sis of the filtration features of the repetitive gain scheduling control sys-tems under the conditions of periodic harmonic interference. For analysis of the fil-tering features of the repetitive gain scheduling control systems, the following methods have been proposed and applied to a particular example: temporal analy-sis with “test” periodic im-pacts in nomi-nal parametric mode and frequency analysis, using the method of the alge-braic derivative.

Open access

E. Nikolov, N. Nikolova and B. Grasiani

Abstract

The work proposed analytical modeling the processes in laboratory pneumatic FESTO-model. The characteristics of the pro-posed analytical model are simulated and analyzed. Systems for control of laboratory installation are synthesized. Designing control systems are modeled and their performance is analyzed. Is confirmed and proven their efficiency.

Open access

Georgi N. Nikolov, Milena D. Karcheva, Chavdar A. Tsvetkov, Alexandar V. Valkov, , Tihomir R. Rashev and Alexandar B. Blazhev

Summary

Human papillomaviruses (HPVs) are associated with the most common sexually transmitted infections. It is well documented that high-risk (HR)-HPVtypes are etiologically associated with some cancers. The aim of the study was to investigate HPV16-DNApositivity and prevalence of Ig Gantibody against HPV16 in patients with laryngeal carcinoma and precancerous lesions of cervix uteri in Pleven region, Bulgaria. Material/Methods: We performedacross-sectional study and investigated clinical materials. Attached is real-time PCR-analysis for detection of HPV16-DNA. HPVspecific antibody response by enzyme-linked immunosorbent assay (ELISA) test for detection and quantification of specific Ig Gantibodies in serum were used. Results: For the six-month period, 30 samples were collected and tested. Fourteen of them were found in patients with carcinoma of the larynx and sixteen - in patients with various lesions of cervix uteri.We found that six patients (42.8%) in the first group and eight patients (50%) in the second group were HPV16-DNA-positive. Different age groups were affected. The sera analyzed in this study showed that seven patients (50%) with carcinoma of the larynx were seropositive of whom four (57%) were males. Fourteen of the females with dysplasia (88%) were seropositive. Matching DNApositivity and antibody response were found in 29%of the patients with laryngeal cancer. The match was found in 50%of the females with cervical dysplasia. Conclusions: Real-time PCRisarapid, cost-effective method for detection of HPVs.Ahigh level of seropositivity was found in the two groups of patients.

Open access

Nikolay K. Balgaranov, Lachezar S. Nikolov, Nadia I. Kolarova-Yaneva, Vania N. Nedkova, Kristina Ts. Tabakova and Viktor E. Donev

Summary

Asthma and allergic rhinitis are common in childhood. Establishing sensitization to aeroallergens is crucial to effectively prevent exacerbation of these respiratory allergic diseases. The study aimed to evaluate sensitization to the most common aeroallergens in children with asthma and allergic rhinitis.We establishedacorrelation between patients sensitized to indoor, outdoor and simultaneously to both allergens. The study population consisted of 276 patients (168 boys and 108 girls) ages 4 to 16 years with asthma (A) and allergic rhinitis (AR). Skin prick tests were performed with 21 commercial allergen extracts: pollens, mites, epithelia and insects, and molds. We found that 217 patients were sensitized to at least one aeroallergen: 117 patients hadapositive result to mites, 92 to pollens, 72 to epithelia and insects, and 63 - to mold allergens. Dermatophagoides pteronyssinus was the most prevalent aeroallergen. Sensitized only to indoor allergens were 104 patients, 60 - only to outdoor allergens, and 53 were sensitized to both. Mites were the most frequent aeroallergens in children with Aand AR. Lately there has been foundasignificant increase in rates of sensitization to mold allergens, especially to Alternaria alternata. Our study has confirmed the dominant role of indoor allergens in children with respiratory allergic diseases.