Vladimir Vedeneev - Academia.edu (original) (raw)

Papers by Vladimir Vedeneev

Research paper thumbnail of Ferromagnetism of low-dimensional Mn-doped III-V semiconductor structures in the vicinity of the insulator-metal transition

Journal of Applied Physics, 2010

The structural and transport properties of GaAs/Mn/GaAs/InxGa1-xAs/GaAs quantum wells (x~0.2) wit... more The structural and transport properties of GaAs/Mn/GaAs/InxGa1-xAs/GaAs quantum wells (x~0.2) with Mn δ-layer (4-10 at. %), separated from the well by a GaAs spacer, have been studied. The hole mobility in the investigated structures has exceeded the values known for magnetic III-V heterostructures by two orders of magnitude. For structures with the conductivity of the metal type, we have succeeded to observe at low temperatures Shubnikov-de Haas oscillations just confirming the two dimensionality (2D) of the hole energy spectrum. Exactly those 2D holes promote the ferromagnetic ordering of the Mn layer. That has been proven by (i) observing maxima (at 25-40 K) in temperature dependencies of the resistance, which positions agree with calculated values of Curie temperatures (for structures with the indirect interaction of Mn atoms via 2D holes), and (ii) revealing the negative spin-dependent magnetoresistance (NMR) as well as the anomalous Hall effect (AHE), which values are also in good agreement with calculations relating to ferromagnetic 2D III-V systems. As for the structures with the insulator type of the conductivity, their NMR and AHE features evidence the phase separation-the sample fragmentation with the formation of mesoscopic ferromagnetic areas separated by paramagnetic strata of the high tunnel conductivity.

Research paper thumbnail of Holographic neuro-predictor for fractional Brownian motion

In this paper we discuss our approach to based on holographic techniques implementation of neuro-... more In this paper we discuss our approach to based on holographic techniques implementation of neuro-fuzzy predictor for processes, described by Fractal Brownian Motion (FBM) model. We use the model of the predictor as a Riemann Stieltjes integral over the observed traffic of specific weight function. We discuss two-layered bi-directional optical neural network to find our solution. To find the weight function we use non-linearity in the correlation layer of the neural network. In our experiments we used air-photograph of forest as this kind of images demonstrates self-similarity property and can be described by the FBM model. As a first step we used approximate solution for the weight function, achieved by using binary filtering function in the correlation layer. We demonstrate experimental results and discuss directions of our future investigations.

Research paper thumbnail of Discovery of the negative temperature coefficient in the reaction of methane oxidation

Kinetics and Catalysis, 1995

Research paper thumbnail of Concerning the dependence of the selectivity of the formation of ethane and ethylene on the degree of methane conversion during its oxidative coupling

Russian Chemical Bulletin, 1995

The dependences of the maximum selectivity and the limiting yield of C2 hydrocarbons on the degre... more The dependences of the maximum selectivity and the limiting yield of C2 hydrocarbons on the degree of methane conversion during its gas-phase oxidative coupling were calculated by means of kinetic simulation. The correlation between the results of the calculations and the rersults obtained in the experimental studies dealing with catalytic oxidative coupling of methane is discussed.

Research paper thumbnail of Dependence of the kinetics of gas phase methane oxidation at high pressures on the concentration of oxygen and on temperature

Russian Chemical Bulletin, 1996

A decrease of the rate of high pressure oxidation of very rich methane-oxygen mixtures with incre... more A decrease of the rate of high pressure oxidation of very rich methane-oxygen mixtures with increasing oxygen concentration was found. The results were confirmed by kinetic simulation of the process. A very distinct temperature dependence of the rate of oxygen conversion can be explained on the basis of a critical change in the reaction mechanism.

Research paper thumbnail of Kinetic limit of C 2 hydrocarbons yield at gas-phase oxidative coupling of methane

Studies in Surface Science and Catalysis, 1997

Research paper thumbnail of Effect of hydrogen, carbon monoxide, and nitrogen on partial oxidation of methane

Theoretical Foundations of Chemical Engineering, 1995

Presently, the partial oxidation of natural gas to methanol at high pressures is considered as th... more Presently, the partial oxidation of natural gas to methanol at high pressures is considered as the most promising alternative to the conventional way of producing this very important chemical product and the component of environmentally safe motor fuels. The conventional way is disadvantageous because it includes a preliminary power-consuming stage of manufacturing synthesis gas. In the partial oxidation, however, a

Research paper thumbnail of Direct high-pressure gas-phase oxidation of natural gas to methanol and other oxygenates

Russian Chemical Reviews, 1996

The published experimental data on the direct gas-phase oxidation of natural gas (methane) to met... more The published experimental data on the direct gas-phase oxidation of natural gas (methane) to methanol are surveyed. The results of kinetic modelling of the process, its mechanism, and its most characteristic features are considered. Prospects of the industrial use of the process and the most important directions for further studies are discussed. The bibliography includes 146 references.

Research paper thumbnail of Modeling the self-ignition of methane—Air mixtures in internal combustion engines

Combustion Explosion and Shock Waves, 1994

An approximate method for modeling the self-ignition delay for internal combustion engines is pro... more An approximate method for modeling the self-ignition delay for internal combustion engines is proposed. The method allows the calculation of the time of chemical reaction for self-ignition at a constant volume (or constant pressure), which is equivalent to the real time of engine operation with a moving piston. The self-ignition delay calculated using a detailed kinetic mechanism is compared with corresponding experimental data.

Research paper thumbnail of Modern state of direct high pressure partial oxidation of natural gas to methanol

Industrial & Engineering Chemistry Research, 1995

... Gas to Methanol Vladimir S. Arutyunov,*J Valentin Ya. ... Principal Experimental Results Pres... more ... Gas to Methanol Vladimir S. Arutyunov,*J Valentin Ya. ... Principal Experimental Results Pressure Dependence of the Products Yield. It is well-known that pressure reduces reaction time (Melvin, 1966) or reaction temperature (Burch et al., 1989) and promotes methanol formation. ...

Research paper thumbnail of The role of initiation in oxidative coupling of methane

Applied Catalysis A-general, 1995

A generalized kinetic model, which satisfactory describes the main kinetic features of the gas-ph... more A generalized kinetic model, which satisfactory describes the main kinetic features of the gas-phase oxidative coupling of methane over a wide range of pressures and temperatures, was used to investigate the influence of an additional generation of methyl radicals on the process. It was shown that the additional generation of methyl radicals sufficiently enhances the yield of C2 hydrocarbons up to the values obtained with the use of catalysts, but even with a very high rate of additional generation of radicals by means of an effective reaction CH4 + O2 ~ CH3 + HO2, subsequent gas-phase reactions do not permit to overcome a certain kinetic limit in C2 yield. This is very similar to the results obtained in the catalytic oxidative coupling of methane and it is in good agreement with the assumption that at atmospheric and elevated pressures the main role of most catalysts in this process is an additional generation of methyl radicals.

Research paper thumbnail of Experimental investigation and kinetic modeling of the negative temperature coefficient of the reaction rate in rich propane—oxygen mixtures

Russian Chemical Bulletin, 1997

The phenomenon of the negative temperature coefficient (NTC) of the reaction rate of the oxidatio... more The phenomenon of the negative temperature coefficient (NTC) of the reaction rate of the oxidation of rich propane—oxygen mixtures was experimentally studied. The NTC phenomenon is qualitatively described by a simple kinetic model containing a minimum set of reactions related to the oxidation of the starting hydrocarbon, propane, and the propyl C3H7. radical formed.

Research paper thumbnail of Kinetic limit of the ethane and ethylene yield in the gas phase condensation of methane

Russian Chemical Bulletin, 1995

A kinetic simulation of the initiated oxidative condensation of methane in the gas phase showed t... more A kinetic simulation of the initiated oxidative condensation of methane in the gas phase showed that the additional generation of methyl radicalsvia the reaction CH4 + O2 → CH3 + HO2 causes a nearly tenfold increase in the C2 hydrocarbon yield. However, a kinetic limit of the yield exists that is close to that determined in experiments on the catalytic oxidative condensation of methane.

Research paper thumbnail of Direct high-pressure gas-phase oxidation of natural gas to methanol and other oxygenates

Russian Chemical Reviews, 1996

The published experimental data on the direct gas-phase oxidation of natural gas (methane) to met... more The published experimental data on the direct gas-phase oxidation of natural gas (methane) to methanol are surveyed. The results of kinetic modelling of the process, its mechanism, and its most characteristic features are considered. Prospects of the industrial use of the process and the most important directions for further studies are discussed. The bibliography includes 146 references.

Research paper thumbnail of Oxidation of Natural Gas to Methanol in a Cyclic Mode

Theoretical Foundations of Chemical Engineering, 2001

Research paper thumbnail of Kinetic nature of limited yield of principal products at heterogeneous-homogeneous oxidation of methane

Studies in Surface Science and Catalysis, 1998

Research paper thumbnail of Mechanism of gas-phase oxidation of hydrogen sulfide at high temperatures

Russian Chemical Bulletin, 1990

A kinetic model of oxidation of hydrogen sulfide is proposed. The model contains 201 elementary s... more A kinetic model of oxidation of hydrogen sulfide is proposed. The model contains 201 elementary stages, 23 particles, and satisfactorily describes the experimental data in a wide range of temperatures and pressures.

Research paper thumbnail of Mechanism of the gas-phase oxidation of carbon disulfide at elevated temperatures (the CSO system

Russian Chemical Bulletin, 1992

Machine modeling was used to investigate the kinetic mechanism of the gas-phase oxidation of carb... more Machine modeling was used to investigate the kinetic mechanism of the gas-phase oxidation of carbon disulfide at elevated temperatures. The scheme of the process examined includes 70 elementary reactions. On the basis of the kinetic data on these reactions available in the literature the rates of the oxidation process, the concentrations of end products and intermediate particles were calculated as a function of the time under various conditions (composition, pressure, temperature). Comparison of the results obtained with the experimental data showed satisfactory agreement and also revealed some important elementary reactions.

Research paper thumbnail of The mechanism of O(3P) atom reaction with ethylene and other simple olefins

International Journal of Chemical Kinetics, 1992

Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature u... more Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10−13cm3s−1,K = (4.3 ± 0.4) ± 10−12 cm3 s−1, K = (1.4 ± 0.4) · 10−11 cm3 s−1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C2 channels with pressure was found. A mechanism of the O + C2 reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C2 was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.

Research paper thumbnail of Oxidation of methane–ethane mixtures into alcohols under enhanced pressures

Catalysis Today, 1998

Experimental investigation of the direct partial oxidation of methane±ethane mixtures into alcoho... more Experimental investigation of the direct partial oxidation of methane±ethane mixtures into alcohols in the pressure range from 2 to 15 atm and at 100 atm was carried out and compared with the results of kinetic simulation of this process. #

Research paper thumbnail of Ferromagnetism of low-dimensional Mn-doped III-V semiconductor structures in the vicinity of the insulator-metal transition

Journal of Applied Physics, 2010

The structural and transport properties of GaAs/Mn/GaAs/InxGa1-xAs/GaAs quantum wells (x~0.2) wit... more The structural and transport properties of GaAs/Mn/GaAs/InxGa1-xAs/GaAs quantum wells (x~0.2) with Mn δ-layer (4-10 at. %), separated from the well by a GaAs spacer, have been studied. The hole mobility in the investigated structures has exceeded the values known for magnetic III-V heterostructures by two orders of magnitude. For structures with the conductivity of the metal type, we have succeeded to observe at low temperatures Shubnikov-de Haas oscillations just confirming the two dimensionality (2D) of the hole energy spectrum. Exactly those 2D holes promote the ferromagnetic ordering of the Mn layer. That has been proven by (i) observing maxima (at 25-40 K) in temperature dependencies of the resistance, which positions agree with calculated values of Curie temperatures (for structures with the indirect interaction of Mn atoms via 2D holes), and (ii) revealing the negative spin-dependent magnetoresistance (NMR) as well as the anomalous Hall effect (AHE), which values are also in good agreement with calculations relating to ferromagnetic 2D III-V systems. As for the structures with the insulator type of the conductivity, their NMR and AHE features evidence the phase separation-the sample fragmentation with the formation of mesoscopic ferromagnetic areas separated by paramagnetic strata of the high tunnel conductivity.

Research paper thumbnail of Holographic neuro-predictor for fractional Brownian motion

In this paper we discuss our approach to based on holographic techniques implementation of neuro-... more In this paper we discuss our approach to based on holographic techniques implementation of neuro-fuzzy predictor for processes, described by Fractal Brownian Motion (FBM) model. We use the model of the predictor as a Riemann Stieltjes integral over the observed traffic of specific weight function. We discuss two-layered bi-directional optical neural network to find our solution. To find the weight function we use non-linearity in the correlation layer of the neural network. In our experiments we used air-photograph of forest as this kind of images demonstrates self-similarity property and can be described by the FBM model. As a first step we used approximate solution for the weight function, achieved by using binary filtering function in the correlation layer. We demonstrate experimental results and discuss directions of our future investigations.

Research paper thumbnail of Discovery of the negative temperature coefficient in the reaction of methane oxidation

Kinetics and Catalysis, 1995

Research paper thumbnail of Concerning the dependence of the selectivity of the formation of ethane and ethylene on the degree of methane conversion during its oxidative coupling

Russian Chemical Bulletin, 1995

The dependences of the maximum selectivity and the limiting yield of C2 hydrocarbons on the degre... more The dependences of the maximum selectivity and the limiting yield of C2 hydrocarbons on the degree of methane conversion during its gas-phase oxidative coupling were calculated by means of kinetic simulation. The correlation between the results of the calculations and the rersults obtained in the experimental studies dealing with catalytic oxidative coupling of methane is discussed.

Research paper thumbnail of Dependence of the kinetics of gas phase methane oxidation at high pressures on the concentration of oxygen and on temperature

Russian Chemical Bulletin, 1996

A decrease of the rate of high pressure oxidation of very rich methane-oxygen mixtures with incre... more A decrease of the rate of high pressure oxidation of very rich methane-oxygen mixtures with increasing oxygen concentration was found. The results were confirmed by kinetic simulation of the process. A very distinct temperature dependence of the rate of oxygen conversion can be explained on the basis of a critical change in the reaction mechanism.

Research paper thumbnail of Kinetic limit of C 2 hydrocarbons yield at gas-phase oxidative coupling of methane

Studies in Surface Science and Catalysis, 1997

Research paper thumbnail of Effect of hydrogen, carbon monoxide, and nitrogen on partial oxidation of methane

Theoretical Foundations of Chemical Engineering, 1995

Presently, the partial oxidation of natural gas to methanol at high pressures is considered as th... more Presently, the partial oxidation of natural gas to methanol at high pressures is considered as the most promising alternative to the conventional way of producing this very important chemical product and the component of environmentally safe motor fuels. The conventional way is disadvantageous because it includes a preliminary power-consuming stage of manufacturing synthesis gas. In the partial oxidation, however, a

Research paper thumbnail of Direct high-pressure gas-phase oxidation of natural gas to methanol and other oxygenates

Russian Chemical Reviews, 1996

The published experimental data on the direct gas-phase oxidation of natural gas (methane) to met... more The published experimental data on the direct gas-phase oxidation of natural gas (methane) to methanol are surveyed. The results of kinetic modelling of the process, its mechanism, and its most characteristic features are considered. Prospects of the industrial use of the process and the most important directions for further studies are discussed. The bibliography includes 146 references.

Research paper thumbnail of Modeling the self-ignition of methane—Air mixtures in internal combustion engines

Combustion Explosion and Shock Waves, 1994

An approximate method for modeling the self-ignition delay for internal combustion engines is pro... more An approximate method for modeling the self-ignition delay for internal combustion engines is proposed. The method allows the calculation of the time of chemical reaction for self-ignition at a constant volume (or constant pressure), which is equivalent to the real time of engine operation with a moving piston. The self-ignition delay calculated using a detailed kinetic mechanism is compared with corresponding experimental data.

Research paper thumbnail of Modern state of direct high pressure partial oxidation of natural gas to methanol

Industrial & Engineering Chemistry Research, 1995

... Gas to Methanol Vladimir S. Arutyunov,*J Valentin Ya. ... Principal Experimental Results Pres... more ... Gas to Methanol Vladimir S. Arutyunov,*J Valentin Ya. ... Principal Experimental Results Pressure Dependence of the Products Yield. It is well-known that pressure reduces reaction time (Melvin, 1966) or reaction temperature (Burch et al., 1989) and promotes methanol formation. ...

Research paper thumbnail of The role of initiation in oxidative coupling of methane

Applied Catalysis A-general, 1995

A generalized kinetic model, which satisfactory describes the main kinetic features of the gas-ph... more A generalized kinetic model, which satisfactory describes the main kinetic features of the gas-phase oxidative coupling of methane over a wide range of pressures and temperatures, was used to investigate the influence of an additional generation of methyl radicals on the process. It was shown that the additional generation of methyl radicals sufficiently enhances the yield of C2 hydrocarbons up to the values obtained with the use of catalysts, but even with a very high rate of additional generation of radicals by means of an effective reaction CH4 + O2 ~ CH3 + HO2, subsequent gas-phase reactions do not permit to overcome a certain kinetic limit in C2 yield. This is very similar to the results obtained in the catalytic oxidative coupling of methane and it is in good agreement with the assumption that at atmospheric and elevated pressures the main role of most catalysts in this process is an additional generation of methyl radicals.

Research paper thumbnail of Experimental investigation and kinetic modeling of the negative temperature coefficient of the reaction rate in rich propane—oxygen mixtures

Russian Chemical Bulletin, 1997

The phenomenon of the negative temperature coefficient (NTC) of the reaction rate of the oxidatio... more The phenomenon of the negative temperature coefficient (NTC) of the reaction rate of the oxidation of rich propane—oxygen mixtures was experimentally studied. The NTC phenomenon is qualitatively described by a simple kinetic model containing a minimum set of reactions related to the oxidation of the starting hydrocarbon, propane, and the propyl C3H7. radical formed.

Research paper thumbnail of Kinetic limit of the ethane and ethylene yield in the gas phase condensation of methane

Russian Chemical Bulletin, 1995

A kinetic simulation of the initiated oxidative condensation of methane in the gas phase showed t... more A kinetic simulation of the initiated oxidative condensation of methane in the gas phase showed that the additional generation of methyl radicalsvia the reaction CH4 + O2 → CH3 + HO2 causes a nearly tenfold increase in the C2 hydrocarbon yield. However, a kinetic limit of the yield exists that is close to that determined in experiments on the catalytic oxidative condensation of methane.

Research paper thumbnail of Direct high-pressure gas-phase oxidation of natural gas to methanol and other oxygenates

Russian Chemical Reviews, 1996

The published experimental data on the direct gas-phase oxidation of natural gas (methane) to met... more The published experimental data on the direct gas-phase oxidation of natural gas (methane) to methanol are surveyed. The results of kinetic modelling of the process, its mechanism, and its most characteristic features are considered. Prospects of the industrial use of the process and the most important directions for further studies are discussed. The bibliography includes 146 references.

Research paper thumbnail of Oxidation of Natural Gas to Methanol in a Cyclic Mode

Theoretical Foundations of Chemical Engineering, 2001

Research paper thumbnail of Kinetic nature of limited yield of principal products at heterogeneous-homogeneous oxidation of methane

Studies in Surface Science and Catalysis, 1998

Research paper thumbnail of Mechanism of gas-phase oxidation of hydrogen sulfide at high temperatures

Russian Chemical Bulletin, 1990

A kinetic model of oxidation of hydrogen sulfide is proposed. The model contains 201 elementary s... more A kinetic model of oxidation of hydrogen sulfide is proposed. The model contains 201 elementary stages, 23 particles, and satisfactorily describes the experimental data in a wide range of temperatures and pressures.

Research paper thumbnail of Mechanism of the gas-phase oxidation of carbon disulfide at elevated temperatures (the CSO system

Russian Chemical Bulletin, 1992

Machine modeling was used to investigate the kinetic mechanism of the gas-phase oxidation of carb... more Machine modeling was used to investigate the kinetic mechanism of the gas-phase oxidation of carbon disulfide at elevated temperatures. The scheme of the process examined includes 70 elementary reactions. On the basis of the kinetic data on these reactions available in the literature the rates of the oxidation process, the concentrations of end products and intermediate particles were calculated as a function of the time under various conditions (composition, pressure, temperature). Comparison of the results obtained with the experimental data showed satisfactory agreement and also revealed some important elementary reactions.

Research paper thumbnail of The mechanism of O(3P) atom reaction with ethylene and other simple olefins

International Journal of Chemical Kinetics, 1992

Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature u... more Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10−13cm3s−1,K = (4.3 ± 0.4) ± 10−12 cm3 s−1, K = (1.4 ± 0.4) · 10−11 cm3 s−1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C2 channels with pressure was found. A mechanism of the O + C2 reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C2 was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.

Research paper thumbnail of Oxidation of methane–ethane mixtures into alcohols under enhanced pressures

Catalysis Today, 1998

Experimental investigation of the direct partial oxidation of methane±ethane mixtures into alcoho... more Experimental investigation of the direct partial oxidation of methane±ethane mixtures into alcohols in the pressure range from 2 to 15 atm and at 100 atm was carried out and compared with the results of kinetic simulation of this process. #