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Search Results: 1 - 10 of 241395 matches for " O. F. Vyvenko "
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Aharonov-Bohm resistance magneto-oscillations on single-nanohole graphite and graphene structures
Yu. I. Latyshev,A. P. Orlov,V. A. Volkov,V. V. Enaldiev,I. V. Zagorodnev,O. F. Vyvenko,Yu. V. Petrov,P. Monceau
Physics , 2013,
Abstract: Graphene is a stable single atomic layer material exhibiting two-dimensional electron gas of massless Dirac fermions of high mobility. One of the intriguing properties of graphene is a possibility of realization of the Tamm-type edge states. These states differ from the usual surface states caused by defects, impurities and other imperfections at the edge of the system, as well as they differ from the magnetic edge states caused by skipping cyclotron orbits. The Tamm states result from breaking of periodic crystal potential at the edge, they can exist even at zero magnetic field and form a conducting band. Until recently those states have been observed in graphene only by local STM technique and there were no direct experiments on their contribution to transport measurements. Here we present the experiments on Aharonov-Bohm (AB) oscillations of resistance in a single-nanohole graphite and graphene structures, it indicates the presence of conducting edge states cycling around nanohole. An estimation show the penetration depth of the edge states to be as short as about 2 nm. The oscillations persist up to temperature T=115 K and the T-range of their existence increases with a decrease of the nanohole diameter. The proposed mechanism of the AB oscillations based on the resonant intervalley backscattering of the Dirac fermions by the nanohole via the Tamm states. The experimental results are consistent with such a scenario. Our findings show a way towards interference devices operating at high temperatures on the edge states in graphene
Transport of Massless Dirac Fermions in Non-topological Type Edge States
Yu. I. Latyshev,A. P. Orlov,V. A. Volkov,V. V. Enaldiev,I. V. Zagorodnev,O. F. Vyvenko,Yu. V. Petrov,P. Monceau
Physics , 2015, DOI: 10.1038/srep07578
Abstract: There are two types of intrinsic surface states in solids. The first type is formed on the surface of topological insulators. Recently, transport of massless Dirac fermions in the band of "topological" states has been demonstrated. States of the second type were predicted by Tamm and Shockley long ago. They do not have a topological background and are therefore strongly dependent on the properties of the surface. We study the problem of the conductivity of Tamm-Shockley edge states through direct transport experiments. Aharonov-Bohm magneto-oscillations of resistance are found on graphene samples that contain a single nanohole. The effect is explained by the conductivity of the massless Dirac fermions in the edge states cycling around the nanohole. The results demonstrate the deep connection between topological and non-topological edge states in 2D systems of massless Dirac fermions.
Orbital Quantization in a System of Edge Dirac Fermions in Nanoperforated Graphene
Yu. I. Latyshev,A. P. Orlov,A. V. Frolov,V. A. Volkov,I. V. Zagorodnev,V. A. Skuratov,Yu. V. Petrov,O. F. Vyvenko,D. Yu. Ivanov,M. Konczykowski,P. Monceau
Physics , 2015, DOI: 10.1134/S0021364013170098
Abstract: The dependence of the electric resistance R of nanoperforated graphene samples on the position of the Fermi level, which is varied by the gate voltage Vg, has been studied. Nanoperforation has been performed by irradiating graphene samples on a Si/SiO$_2$ substrate by heavy (xenon) or light (helium) ions. A series of regular peaks have been revealed on the R(Vg) dependence at low temperatures in zero magnetic field. These peaks are attributed to the passage of the Fermi level through an equidistant ladder of levels formed by orbitally quantized states of edge Dirac fermions rotating around each nanohole. The results are in agreement with the theory of edge states for massless Dirac fermions.
A Theoretical Foundation for Understanding Law Subjects and Rights in Igbo Philosophy of Law  [PDF]
F. O. C. Njoku
Open Journal of Philosophy (OJPP) , 2013, DOI: 10.4236/ojpp.2013.31A041
Abstract:

This paper attempts to respond to a call to find an ontological basis for establishing African legal theory. The African world of my choice is the Igbo world of South-east Nigeria. It is a world I want to examine to see how its material and theoretical structures help articulate a philosophy of law in terms of projecting a consistent understanding of law subjects and the foundations of their rights. The article builds on the contributions of F. U. Okafor and his many African critics.

Using the Dual Energy Gamma-Ray Transmission Technique to Measure Soil Bulk Density and Water Content of Central Southwestern Nigerian Soils  [PDF]
O. O. Adejumo, F. A. Balogun
Journal of Environmental Protection (JEP) , 2012, DOI: 10.4236/jep.2012.311160
Abstract: In this work, a radiological technique which simultaneously measures soil bulk density and water contents accurately and quickly in a non-destructive manner at different depths of the soil profile of the major soil series of Central Southwestern Nigeria is developed. Undisturbed samples from Iwo, Ondo, Egbeda, Itagunmodi, Okemessi, Mamu, Origo and Jago soil series of Southwestern Nigeria were collected on monthly intervals from June 2006 to May 2007. Using gamma-ray energy pairs of 122 and 1112 keV; and 344 and 1408 keV obtained from europium-152 (152Eu) radionuclide, the attenuation coefficients for soil and water, μs, μw and consequently ρs and θv at varying soil depths of these series were calculated. Comparative gravimetric measurements of these soil parameters were carried out. Using the XCOM computer algorithm with the soil elemental concentrations obtained using the Energy Dispersive X-Ray Fluorescence analysis (EDXRF) technique, theoretical estimates of μs for the various soil series were obtained and compared with the experimental values. The result of the developed dual energy gamma-ray transmission technique was compared with the gravimetric measurement method and Pearson correlation coefficient (0.987, p < 0.001) was obtained for ρs and (0.996, p < 0.001) for θv. The results of the measurements showed that θv minima with values 0.1931, 0.1987, 0.2377, 0.2111, 0.1738, 0.1701, 0.2334, 0.2341 and minima ρs values of 1.21 g/cm3, 1.20 g/cm3, 1.02 g/cm3, 1.38 g/cm3, 1.12 g/cm3, 1.14 g/cm3, 0.64 g/cm3, 1.33 g/cm3 were obtained respectively for the soil series stated above in January. The maxima θv with values 0.3621, 0.4212, 0.3962, 0.3794, 0.3049, 0.2811, 0.4415, 0.4416 and maxima ρs values of 1.52 g/cm3, 1.67 g/cm3, 1.74 g/cm3, 1.69 g/cm3, 1.70 g/cm3, 1.68 g/cm3, 1.08 g/cm3, 1.54 g/cm3 occurred for these soil series respectively in July except for Mamu soil series which occurred in May. These correlated very well with the occurrence of the Dry and Rainy seasons in the study area. The results of the EDXRF analysis showed that maxima Iron, Fe concentrations of 5.0890 ppm at the depth of 90 - 120 cm into the soil profile, was obtained for Iwo series, 4.4691 ppm at 50 - 70 cm for Ondo, 6.3438 ppm at 15 -
A Novel Statistical AOA Model Pertinent to Indoor Geolocation  [PDF]
F. O. AKGUL, K. PAHLAVAN
Journal of Geographic Information System (JGIS) , 2010, DOI: 10.4236/jgis.2010.21009
Abstract: A novel statistical angle-of-arrival (AOA) model for indoor geolocation applications is presented. The modeling approach focuses on the arrivals of the multipath components with respect to the line-of-sight (LOS) path which is an important component especially when indoor geolocation applications are considered. The model is particularly important for indoor applications where AOA information could be utilized for tracking indirect paths to aid in precise ranging in harsh and dense multipath environments where LOS path might be blocked due to obstructions. The results have been obtained by a measurement calibrated ray-tracing (RT) tool.
Optimizing the Properties of Polyether Based Polyurethane Foam  [PDF]
F. O. Aramide, P. O. Atanda, E. O. Olorunniwo
Open Journal of Polymer Chemistry (OJPChem) , 2013, DOI: 10.4236/ojpchem.2013.34015
Abstract:

Effect of different chemicals and additives used in producing polyester foam was investigated. Reference samples were produced from polyol, toluene di isocyanate (TDI), amine stannous octoate distil water, and silicone oil using laboratory mix formulation based on 500 g polyether based polyol. Other samples were produced by consecutively varying the content of all the additives with the exception of polyol. Standard sample dimensions for density test, indentation test, compression set test, tensile strength and elongation tests were produced from the samples. The various tests were carried out on the samples using the ASTM-D3574 standards. It was observed that the degree of indentation affects the value of indentation hardness and increasing the percentage content of TDI results in acceptable compression set value for the polyester samples. It was concluded that Holding all other parameters constant, reducing the water content and increasing the TDI content will yield polyester foam of optimum properties.

Empirical Determination of the Tolerable Sample Size for Ols Estimator in the Presence of Multicollinearity (ρ)  [PDF]
O. O. Alabi, T. O. Olatayo, F. R. Afolabi
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.513180
Abstract:

This paper investigates the tolerable sample size needed for Ordinary Least Square (OLS) Estimator to be used when there is presence of Multicollinearity among the exogenous variables of a linear regression model. A regression model with constant term (β0) and two independent variables (with β1 and β2 as their respective regression coefficients) that exhibit multicollinearity was considered. A Monte Carlo study of 1000 trials was conducted at eight levels of multicollinearity (0, 0.25, 0.5, 0.7, 0.75, 0.8, 0.9 and 0.99) and sample sizes (10, 20, 40, 80, 100, 150, 250 and 500). At each specification, the true regression coefficients were set at unity while 1.5, 2.0 and 2.5 were taken as the hypothesized value. The power value rate was obtained at every multicollinearity level for the aforementioned sample sizes. Therefore, whether the hypothesized values highly depart from the true values or not once the multicollinearity level is very high (i.e. 0.99), the sample size needed to work with in order to have an error free estimation or the inference result must be greater than five hundred.

Corrosion Characteristics of Ascast Ductile Iron in Lime Juice  [PDF]
F.O. Aramide, E.O. Olorunniwo, P.O. Atanda, J.O. Borode
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2010, DOI: 10.4236/jmmce.2010.910063
Abstract: A study on the corrosion characteristics of ascast ductile iron in lime juice was conducted using the common weight loss method. Five standard tensile samples were prepared from the ascast condition of the alloy. One of them was taken to be for control, while the others were labeled A, B, C, and D. These labeled samples were then immersed in freshly extracted lime juice for a period of four weeks, having noted their respective initial weights. A sample was withdrawn from the medium at the end of each week for microstructural and tensile properties (using INSTRON 1195 at a fixed crosshead speed of 10mm min-1) examination for comparison with those of the control sample. It was observed that the mechanical properties of the alloy were deteriorating due to pitting corrosion and that the corrosion rate increases with increase in the pH of the medium. It was concluded that corrosion rate can be kept to the minimum by controlling the pH of the media within the range 2.0 to 3.05.
In-Vitro Metabolite Colonic Production from Otili (Sphenostylis stenocarpa) as Influenced by Selected Gastrointestinal Microbes  [PDF]
O. A. Awoyinka, T. R. Omodara, F. C. Oladele, O. O. Aina, O. E. Ajayi
Advances in Bioscience and Biotechnology (ABB) , 2018, DOI: 10.4236/abb.2018.911041
Abstract: In human nutrition, dietary fibers are un-degradable by mammalian enzymes, and are therefore potentially available for fermentation by micro-organisms living in the gastrointestinal tract. It is thought that these fermentable carbohydrates affect fermentation by stimulating the growth or metabolism of specific bacterial species, which are potentially beneficial for health. Hence in this study three gut associated microbes—Escherichia coli, Bacillus subtilis, and Lactobacillus acidophilus were made to ferment the non-digestible fraction of OtiliSphenostylis stenocarpa, a well-established underutilized wild bean with high economic importance. After 18 hours’ fermentation period short chain fatty acids (SCFAs) and medium chain fatty acids (MCFAs) were detected and evaluated by GC-MS analysis. Metabolic products were relatively dependent on the fermenter. This present study affirmed butyric acid as the main SCFAs after 18 hours’ fermentation. The clinical significance of thirteen other MCFAs detected and quantified was also explored thus conferring a valuable prebiotic on Otili.
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