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In Memoriam - Prof. Emanuel Palamarev, DSc

100%

Ivanov D.

Acta Palaeobotanica

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2004

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tom 44

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nr 1

2

A contribution to the Neogene history of Fagaceae in the Central Balkan area

63%

Palamarev E. , Ivanov D.

Acta Palaeobotanica

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2003

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tom 43

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nr 1

3

Uber einige Besonderheiten der Tertiaren Floren in Bulgarien und ihre Bedeutung fur die Entwicklungsgeschichte der Pflanzenwelt in Europa

63%

Palamarev E. , Ivanov D.

Acta Palaeobotanica

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1998

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tom 38

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nr 1

4

A numerical comparative analysis of ChM and Fixion nails for diaphyseal femur fractures

51%

Ivanov D. , Barabash Y. , Barabash A.

Acta of Bioengineering and Biomechanics

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2016

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tom Vol. 18, no. 3

73--81

EN

Purpose: Today intramedullary locked nails are widespread in treatment of diaphyseal long bone fractures of the lower limb. However, such nails have a number of drawbacks: complexity and duration of the installation, high axial stiffness, as well as the failure of locking screws and nail body. Expandable nails such as Fixion have several advantages over lockable ones. They can be quickly installed without the need of reaming and provide sufficient stabilization of the fracture. However, many studies show their low stability under torsional loads. Methods: In this paper, geometric characteristics of Fixion nail were investigated. Bone-nail systems (with Fixion and locked nail) under the influence of three types of loads were numerically studied. Two types of diaphyseal femoral fractures (type A and B in accordance with AO/ASIF classification) were examined. Results: It was revealed that Fixion nail provides axial stiffness of 489 N/mm for the fractures studied. Expandable nail showed higher compression at fragments junction than locked nail. Torsional stability of Fixion nail was also high. Corrosion was found on inner surface of Fixion nail. Conclusions: Fixion nail showed high stability under influence of the three loads studied. Corrosion on the internal wall of the nail may indicate its relatively low resistance to saline.

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Combustion of Energetic Systems Based on HMX and Aluminum: Infuence of Particle Size and Mixing Technology

38%

Muravyev N. , Frolov Y. , Pivkina A. , Monogarov K. , Ivanov D. , Meerov D. , Fomenkov I.

Central European Journal of Energetic Materials

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2009

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tom Vol. 6, nr 2

195-210

EN

In this work the complex experimental investigation of the microstructure and burning parameters of HMX-monopropellant and 25%Al/75%HMX energetic systems was carried on with the particle size variation. Components, their mixtures, pressed samples, and the combustion products (agglomerates) collected from a burning surface by QPCB (quench particle collection bomb) technique were investigated. Two types of HMX particles: micro-sized (mHMX) and ultrafne (uHMX) and aluminium powders: micro- and ultra-sized (ALEXTM) were used. Morphology and particle size were examined by atomic-force microscopy (AFM), scanning electron microscopy (SEM) and BET-analysis. AFM analysis shows the ALEXTM average volume particle size is 180 nm. It was shown, that the monopropellant's burning rates of the micro- and ultra-sized HMX are almost identical in the pressure range 20-100 atm. Two mixing technologies to prepare Al/HMX compositions were used: (i) conventional "dry" mixing and (ii) "wet" technique with ultrasonic processing in diethyl ether. Applying of ultrasonic technique results in a burning rate increase up to 18% comparing to "dry" mixing (under pressure 60 atm). The highest combustion rate was determined for composition of mHMX/ALEXTM (porosity 13%). Infuence of component N. Muravyev et al. size and composition's microstructure on the burning rate of energetic systems is discussed and analyzed.

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Mechanical Activation of Al/MoO3 Thermite as a Component of Energetic Condensed Systems to Increase Its Effciency

38%

Meerov D. , Ivanov D. , Monogarov K. , Muravyev N. , Pivkina A. , Frolov Y.

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tom Vol. 6, nr 3-4

277-289

EN

In the present work a stoichiometric energetic compositions Al+MoO3 prepared by dry mixing and by reactive milling of micro-scale particles were investigated. Morphology, particle size and surface structure of produced powders were examined using scanning electron microscopy, atomic-force microscopy, laser diffractometry and BET analysis. DSC/TG data were processed to obtain kinetic mechanism of the reaction between Al and MoO3. The combustion rate of Al+MoO3 thermite mixture increases with pressure, reaching a maximum at ~10 atm, and then decreases with further pressure increase. The rise of combustion rate at the low range of pressure is associated with the rise in the extent of the vapour phase penetrating the pores of the pressed sample as the ambient pressure increases. However, at a higher pressure the gas formation is suppressed, and the melt formed in the combustion process can selectively wet the pores resulting in inhibition of reaction. Burning rates of mechanical activated system Al+MoO3 are two times higher then not-activated system at ambient pressure ~10 atm and 8 times higher at ~40 atm. In additional experiments, nano-scale MoO3 powder was prepared by evaporation with a subsequent condensation onto cooled plate in an inert-gas fow. Scanning electron microscopy showed that nano-MoO3 particles are absolutely spherical with mean diameter ~100 nm, and atomic-force microscopy 278 D. Meerov et al. reveals smaller particles with mean diameter ~5-30 nm. DSC/TG data showed that the nano-MoO3 starts to sublime earlier than micro MoO3. The use of nano-sized components could considerably increase the burning rates of energetic condensed systems, because of its large specifc surface, lower temperature of sublimation, and high reaction ability.