Influence of Processing Conditions on PVDF Properties

Lebedev, S.M.,Gefle, O.S.,Semenikhin, M.V. The Korean Powder Metallurgy Institute 2011 한국분말재료학회지 (KPMI) Vol.18 No.2

Study of the main properties of PVDF films produced by two processing technologies such as hot pressing from a melt or solution casting was the aim of this paper. All samples were prepared of as-received PVDF powder. First group of samples was prepared by the hot pressing. Second group of samples was prepared by the solution casting method. PVDF powder was dissolved in dimethylformamide. To characterize properties of samples, different experimental methods such as FRA (dielectric spectroscopy), IR-spectroscopy and DSC/TGA analysis were used in this work. It was found that IR-spectra of both studied groups do not change compared to that for virgin PVDF powder. It confirms that molecular structure is practically independent on the processing technology of samples. The only difference has been found that new band centered at $1723\;cm^{-1}$ appears for samples prepared by the hot pressing method. This absorption band is related with formation of C=C bonds in samples prepared by the hot pressing method in contrast both to PVDF powder and samples prepared by the solution casting method.

Metal-Polymer Composites and their Characterization

Lebedev, S.M.,Gefle, O.S.,Semenikhin, M.V. The Korean Powder Metallurgy Institute 2011 한국분말재료학회지 (KPMI) Vol.18 No.2

PVDF was used as a polymeric matrix material in this work. Nickel powders with average particles size of 200 nm or 72 nm were used as fillers. PVDF/metal submicro- and nanocomposites were prepared by means of a mixing in twin screw extruder and planetary ball mill, respectively. All samples were prepared by hot pressing method. Their electrical, thermal and morphological properties were examined by dielectric spectroscopy, DSC, FTIR, XRD, optical microscopy and scanning electron microscopy. It was found that all properties of composites were strongly modified depending on the content of metal powders and filler particles size. Particularly, specific volume resistivity of PVDF/Ni composite with 0.2 wt.% of Ni was increased by factor of 1.5~4.

State-of-the-art progress of gaseous radiochemical method for detecting of ionizing radiation

Lebedev, S.G.,Yants, V.E. Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.7

The article provides a review of the research results obtained during of more than 20 years concerning using the gaseous radiochemical method (GRCM) for detecting of ionizing radiation. This method based on threshold nuclear reactions with production of radioactive noble gas which does not interact with the materials of gaseous tract. The applications of GRCM in the diagnostics of neutrinos, neutrons, charged particles, thermonuclear plasma thermometry, and the study of the structure and dynamics of astrophysical objects, position-sensitive dosimetry of neutron targets with accelerator driving, spatial distribution of the fast neutron flux density in a nuclear reactor allowing the transformation of longitudinal coordinate of neutron flux distribution into a temporal distribution of the radiochemical gas decay counting rate ("barcode" semblance) and measurement of bombarding particles spectra are described. Experimental testing of the described technologies was made on the neutron target driven with the linear proton accelerator of Institute for Nuclear Research of Russian Academy of Sciences (INR RAS).

The Features of Variable Structure System Application in Conditions of Control Signal Saturation

Alexander Lebedev 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10

The variable structure system with control signal saturation for the position control of second order dynamic object is considered in this paper. The features of system phase trajectories and transition processes at different values of control law coefficients are analyzed. The new conditions of a sliding mode existence in the given areas of a phase plane are formulated. The control systems parameters ensuring the greatest possible fast-action and high dynamic precision are determined. The received conclusions are confirmed by results of control system numerical simulation.

Optically transparent, dense α-Al₂O₃ thick films deposited on glass at room temperature

Maxim Lebedev,Susan Krumdieck 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4

Alumina films up to 5 μm thick have been deposited on fused silica and stainless steel substrates by a novel aerosol-jet depositionprocess at room temperature. The lms are dense, uniform and adherent. Moreover, Al₂O₃ film deposited on fused silica substrate isl m thick alumina lm is 83% measured at 800 nm, and that of 5.5 μm thick lm is 68%. Scanning electron microscopy images and XRD analysis have revealed that the lms have αAl₂O₃ crystallite structure however crystallite size is order of magnitude smaller than that raw material powder. Vickers microhardness of the lms deposited on stainlesssteel has been measured. Aerosol-jet deposition becomes promising method for surface coating.

Sergei Witte and the Russo-Japanese War

B.V. Anan?ich,S.A. Lebedev 고려대학교 한국사연구소 2005 International Journal of Korean History Vol.7 No.-

Magnetohydrodynamic Simulation of Tungsten Wire in Wire-Array Z Pinch

Kim, D.-K.,Chittenden, J. P.,Lebedev, S. V.,Marocchino, A.,Suzuki-Vidal, F. WILEY-VCH Verlag 2010 Contributions to plasma physics Vol.50 No.2

<P>The magnetohydrodynamic behavior of tungsten wire ablating in wire-array Z pinch discharge on MAGPIE is simulated in a two-dimensional fine-grid domain using the GORGON code. A nonideal resistivity model has been implemented in the simulation to obtain plasma transport coefficients in the high density regime along with a screened hydrogenic model to calculate the radiative cooling. Starting from the initial state of warm dense plasma, the evolution of ablated wire is demonstrated to show its explosion and implosion dynamics as a function of discharge time and then the computed profile of electron density is compared with the contour lines reproduced from the measurement by a laser interferometer during the early stage of discharge. The comparison overall shows a fair agreement in terms of the magnitude and the profile shape while some discrepancies can be attributed to the simplified description of the internal wire core physics (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Intrinsic antiferromagnetic coupling underlies colossal magnetoresistance effect: Role of correlated polarons

Moshnyaga, V.,Belenchuk, A.,Hü,hn, S.,Kalkert, C.,Jungbauer, M.,Lebedev, O. I.,Merten, S.,Choi, K.-Y.,Lemmens, P.,Damaschke, B.,Samwer, K. American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.2

A commonly believed picture of colossal magnetoresistance (CMR) effect is related to a first-order phase transition and electronic phase separation with coexisting ferromagnetic metallic and antiferromagnetic insulating phases. However, the underlying mechanism, i.e., the characteristic energy scale of the interacting phases and their spatial extent, is still under debate. Here we present experimental evidence on the existence of an effective antiferromagnetic coupling between the ferromagnetic nanodomains in epitaxial thin films of a classical CMR material (La1-yPry)(0.67)Ca0.33MnO3 with Pr doping, y = 0.375 and 0.4. This coupling yields to peculiar low-field CMR behavior with magnetic hysteresis and slow resistance relaxation, both induced by the magnetization reversal. The coercive field obeys a square-root temperature dependence for T << T-C and increases anomalously close to the phase transition. We modeled the magnetic structure within the phase-separation scenario as an assembly of single-domain ferromagnetic nanoparticles, antiferromagnetically coupled (pinned) by correlated Jahn-Teller polarons. The concentration of polarons increases drastically close to phase transition as indicated by the third harmonic of the electrical conductivity as well as Raman spectroscopy.

The superconducting bismuth-based mixed oxides

E.V.Antipov,N.R.Khasanova,J.S.Pshirkov,S.N.Putilin,C.Bougerol,O.I.Lebedev,G.VanTendeloo,A.N.Baranov,Y.W.Park 한국물리학회 2002 Current Applied Physics Vol.2 No.5

The present paper describes the synthesis, characterization of mixed-valence bismuthates with three- or two-dimensional per-ovskite-like structures and structural criteria that inuence superconductivity in these compounds.Single-phase samples of Sr1. xKxBiO3 were prepared for the broad range of K-content: 0:256 x6 0:65. For these bismuthates thesymmetry of the structure changes from monoclinic to orthorhombic and nally to tetragonal upon increasing the K-content thusTc ¼ 12K exists in the narrow range (x . 0:50.6) within the stability eld of the tetragonal phase (0:336 x6 0:65), when the three-dimensional octahedral framework has close to the ideal perovskite structure arrangement.The layered type (Ba,K)3Bi2O7 and (Ba,K)2BiO4 bismuthates belonging to the Anþ 1BnO3nþ 1 homologous series were investi-gated. Buckling of the (BiO2 n ¼ 2 member occurs due to the ordering of alkaline- and alkaline-earthcations between two independent positions. The formation of the one-layer bismuthate was revealed by Electron Microscopy andXRPD studies. Both types of compounds are considered to be possible candidates for new superconducting materials amongbismuthates.. 2002 Published by Elsevier Science B.V.