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  • Author: Ivan Georgiev x
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Maintenance System Research for Armored Vehicles in Peacekeeping Operation as Close Queueing System in Dynamic Regime

Abstract

The maintenance system for wheel vehicles of 4th infantry battalion from Iraqi stable forces is studied in this article as a close queuing system. The differential equations of the dynamic functioning of the system are derived and solved numerically. The results of the dynamic characteristics and loading of the system are analyzed and compared with the results in stationary regime.

Open access
High Performance Computing Applications
High Performance Computing in Micromechanics with an Application

Abstract

High Performance Computing (HPC) is required for many important applications in chemistry, computational fluid dynamics, etc., see, e.g., an overview in [1]. In this paper we shortly describe an application (a multiscale material design problem) that requires HPC for several reasons. The problem of interest is analysis of the fiber-reinforced concrete and we focus on modelling of stiffness through numerical homogenization and computing local material properties by inverse analysis. Both problems require a repeated solution of large-scale finite element problems up to 200 million degrees of freedom and therefore the importance of HPC computing is evident.

Open access
First record of the “small cave bear” in Bulgaria and the taxonomic status of bears of the Ursus savini Andrews – Ursus rossicus Borissiak group

Abstract

The discovery of rich, well preserved skull material in the latest Middle Pleistocene deposits of Mishin Kamik cave (N-W Bulgaria) presents an opportunity for a new analysis of the taxonomy and the phylogeny of the so called “small cave bears”. Not all the small cave bears known would have necessarily had a common origin, the size decrease could be related in a number of cases to a parallelism. The bear from Mishin Kamik is identical with “Ursus rossicus” Borissiak from Krasnodar (S. Russia). Both these samples must be referred to U. savini Andrews from Bacton near Cromer (England). The specimens from Krasnodar and Mishin Kamik could be classified as U. sa. rossicus, a late form of the species. This species may have affinities with some Middle Pleistocene Siberian forms. U. savini is a small but very robust spelaeoid bear which is more advanced in a number of features than U. deningeri. In several aspects it attained the evolutional adaptations of the cave bears of the U. spelaeus-U. ingressus group and represents an independent lineage of spelaeoid bears. The Mishin Kamik population was adapted to a mosaic landscape of forests and open areas in hilly terrain. This bear had well developed grazing adaptations but had weak motor abilities.

Open access
Postoperative Outcomes of Elective Pancreatic Surgery in a Low-Volume Academic Surgical Clinic

Summary

According to the volume-outcome concept the postoperative outcome after major pancreatic surgery in high-volume institutions compares favorably to low- volume centers. However, it is not clear whether this is applicable to all low-volume institutions nowadays. The aim of the study was to evaluate the postoperative outcome after major elective pancreatic surgery in a low- volume academic surgical clinic. All consecutive elective major pancreatic cases operated within a 10-year period till October 2013 have been retrospectively reviewed. During the studied period, 36 patients (15 females, 21 males, mean age 54 years, age range 37-76) were scheduled for elective pancreatic surgery and underwent pancreatic resection (n=31, 18 proximal and 13 distal pancreatic resections) or complete pancreatic duct drainage procedure (n=5). Eleven patients had chronic pancreatitis and 25 patients had malignant or benign tumors. Vascular or adjacent organ resection was performed in 9 patients (29% of resections). The overall postoperative morbidity was 36% (n=13), and complications requiring re-operation occurred in 5 patients (14%). The median postoperative hospital stay was 11 days for patients without complications vs. 25 days for patients with any complication. There was no 60- day postoperative mortality or hospital readmission. Major elective pancreatic surgery can be safely performed today in a low-volume academic general surgical clinic, with postoperative outcomes similar to those reported by high-volume centers.

Open access
In Vivo Collection and SEM Identification of Oral Biofilm Using Indirect Composite Prototype Restorations. Clinical and Laboratory Study

Abstract

Background: The oral ecosystem is a dynamic environment inhabited by more than 700 microbial taxa. Recent studies report that multispecies oral biofilms develop on the surface of resin composites leading to degradation of its organic matrix and altered structural stability of the restoration.

Aim: To examine the efficacy of a novel clinical approach to investigating in vivo formed biofilms on resin composite surfaces.

Materials and methods: The clinical protocol of this study implemented indirect composite molar restorations (from resin material Filtek Z250, 3M ESPE) as intraoral biofilm carriers (test devices). We recruited for the experiment 5 consenting adult subjects with indications for indirect molar restoration. For each subject we fabricated 4 indirect restorations, 3 of which dedicated to different intraoral duration – 3, 7, and 14 days. All composite carriers were fixed temporarily for the intended time period and consecutively replaced. The detached carriers were prepared for microscope analysis at each time interval. The fourth composite carrier was used as the definitive restoration.

Results: The timeline of the biofilm formation and the microbial morphology were associated with previous studies of in vivo bacterial colonisation. A correlation between the plaque formation cycle and the DMFt indices of the subjects was established.

Conclusions: The implementation of indirect composite restorations as intraoral biofilm carrier offers valuable contribution to the real time investigation of in vivo biofilm accumulation.

Open access
Antioxidant Activity and Antiproliferative Effects of Lycium barbarum’s (Goji berry) Fractions on Breast Cancer Cell Lines

Abstract

Background: Lycium barbarum has gained immense popularity over the past decade because of its antioxidant properties. There are many reports of observed health benefits of juice consumption, including prophylaxis in neoplastic disease and treatment of tumors.

Materials and methods: In this study, we isolated three fractions of Lycium barbarum fruits – total water, pectin-free and polysaccharide, and determined their antioxidant activity by ORAC and HORAC assays. We investigated the antiproliferative effects of Lycium barbarum’s pectin-free and polysaccharide fraction on three different breast cell lines - MCF-10A (non-tumorigenic epithelial breast cell line), MCF-7 (breast cancer cell line, estrogen, progesterone receptors +, HER2-), and MDA-MB-231 (breast cancer cell line, triple negative), by the MTT dye reduction assay.

Results: The Lycium barbarum’s pectin-free fraction showed concentration-dependent growth inhibition on the three cell lines, moreover, on cancer cells (MCF- 7 and MDA-MB-231) it was significantly more pronounced. The polysaccharide fraction showed negligible activity on the three cell lines, only the highest concentration (1000 μg/mL), suppressed the proliferation of MCF-7 cells. The combination of pectin-free and polysaccharide fraction on MCF-7 did not show the expected synergistic effect.

Conclusion: We found a relative correlation between the polyphenolic content of the extracts and the observed effects. The pectin-free extract had the highest content of polyphenols with the best antioxidant and antineoplastic activity against breast cancer cells. Addition of polysaccharide to the pectin-free fraction contributes to its pharmacological activity.

Open access