Physical and mathematical modelling of ignition of small magnesium particles

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.The distributed mathematical model (nonstationary 1D and 2D) of magnesium particle ignition is developed taking into account the heterogeneous chemical reaction, the domain of particle thermal influence to gas, and the realistic particle temperature after ignition. Solvability of the corresponding mathematical problem in the stationary one-dimensional case in some kinds of symmetry has allowed one to expand classification of regular modes of heating, and also modes of extinction and ignition of a particle. The numerical method for solving the considered class of boundary value problems of magnesium particles ignition is developed, and the mathematical model is verified by the experimental dependences of: ignition delay time on surrounding gas pressure and particle radius; limiting ignition gas temperature on surrounding gas pressure and particle radius. The limiting size of a gas layer near a particle is found that determines an ignition mode in the frame of this realistic mathematical model. The work was supported financially by the Russian Foundation for Basic Research, Grant No 06–01–00299.vk201

Nanocarbons And Quantum Dots Formation In New Hybrid Materials

We present technique of obtaining complex hybrid structures combining the multi-walled carbon nanotubes or multi-layer graphene and luminescent hydrophobic semiconductor core/shell quantum dots CdSe/ZnS. As a result, a formation of quantum dot decorated carbon nanotubes and graphene films is evidenced by 2D microluminescence and micro-Raman mapping of quantum dots and nanocarbons, respectively, where a spatial correlation between the luminescence and Raman signals is found. © 2014 SPIE.912612-02-00938; RFBR; Russian Foundation for Basic Research; 12-02-01263; RFBR; Russian Foundation for Basic ResearchKalantar-Zadeh, K., (2008) Nanotechnology-Enabled Sensors, p. 490. , K. Kalantar-zadeh, B. Fry. New York.: Springer Science & Business Media(1955) Springer Handbook of Nanotechnology, , Ed. B. Bhusha.-New York.: Springer Science & Business Media, 2010, ISBN: 978-3-642-02524-2Cattanach, K., Kulkarni, R.D., Kozlov, M., Manohar, S.K., Flexible carbon nanotube sensors for nerve agent simulants (2006) Nanotechnology, 17, pp. 4123-4128Peng, S., O'Keeffe, J., Wei, C., Cho, K., Kong, J., Chen, R., Franklin, N., Dai, H., Carbon nanotube chemical and mechanical sensors (2001) Proceedings of the 3rd International Workshop on Structural Health Monitoring, pp. 1-8. , USA, September 17-19, 2001, Stanford University, StanfordSnow, E.S., Perkins, F.K., Houser, E.H., Badescu, S.C., Reinecke, T.L., (2005) Science, 307, pp. 1942-1945. , Chemical detection with a single-walled carbon nanotube capacitorStar, A., Joshi, V., Skarupo, S., Thomas, D., Gabriel, J.-C.P., Gas sensor array based on metal-decorated carbon nanotubes (2006) J. Phys. Chem. B, 110, pp. 21014-21020Xu, Z., Gao, H., Guoxin, H., Solution-based synthesis and characterization of a silver nanoparticle-graphene hybrid film Carbon, 49 (14), pp. 4731-4738Cao, A., Liu, Z., Chu, S., Wu, M., Ye, Z., Cai, Z., Chang, Y., Liu, Y., A facile one-step method to produce graphene-cds quantum dot nanocomposites as promising optoelectronic materials (2010) Adv. Mater, 22, pp. 103-106Yang, Y.-K., He, Ch.-E., He, W.-J., Yu, L.-J., Peng, R.-G., Xie, X.-L., Wang, X.-B., Mai, Y.-W., Reduction of silver nanoparticles onto graphene oxide nanosheets with N,Ndimethylformamide and SERS activities of GO/Ag composites (2011) J Nanopart. Res, 13, pp. 5571-5581Lightcap, V., Kamat, P.V., Fortification of cdse quantum dots with graphene oxide. Excited state interactions and light energy conversion (2012) J. Am. Chem. Soc, 134, pp. 7109-7116Ghosh, A., Rao, K.V., Voggu, R., George, S.J., Non-covalent functionalization, solubilization of graphene and single-walled carbon nanotubes with aromatic donor and acceptor molecules (2010) Chemical Physics Letters, 488, pp. 198-201Kim, Y.-T., Han, J.H., Hong, B.H., Kwon, Y.-U., Electrochemical synthesis of cdse quantum-dot arrays on a graphene basal plane using mesoporous silica thin-film templates (2010) Adv. Mater, 22, pp. 515-518Konstantatos, G., Badioli, M., Gaudreau, L., Osmond, J., Bernechea, M., Arquer De Garcia, F.P., Gatti, F., Koppens, L.F.H., Hybrid graphene-quantum dot phototransistors with ultrahigh gain (2012) Nature Nanotechnology, 7, pp. 363-368Wang, Y., Yao, H.-B., Wang, X.-H., Yu, Sh.-H., One-pot facile decoration of CdSe quantum dots on graphene nanosheets: Novel graphene-CdSe nanocomposites with tunable fluorescent properties (2011) J. Mater. Chem, 21, pp. 562-566Murray, C.B., Gaschler, W., Sun, S., Doyle, H., Betley, T.A., Kagan, C.R., Colloidal synthesis of nanocrystals and nanocrystal superlattices IBM J. Res. & Dev., 45 (1), pp. 47-56Ermakov, V.A., Alaferdov, A.V., Vaz, A.R., Baranov, A.V., Moshkalev, S.A., Nonlocal laser annealing to improve thermal contacts between multi-layer graphene and metals (2013) Nanotechnology, 24 (15), p. 15530110Bogdanov, K., Fedorov, A., Osipov, V., Enoki, T., Takai, K., Hayashi, T., Ermakov, V., Moshkalev A, S., Annealing-induced structural changes of carbon onions: High-resolution transmission electron microscopy and Raman studies Baranov Carbon, , 02/201

Quasi-Chaplygin Systems and Nonholonimic Rigid Body Dynamics

We show that the Suslov nonholonomic rigid body problem can be regarded almost everywhere as a generalized Chaplygin system. Furthermore, this provides a new example of a multidimensional nonholonomic system which can be reduced to a Hamiltonian form by means of Chaplygin reducing multiplier. Since we deal with Chaplygin systems in the local sense, the invariant manifolds of the integrable examples are not necessary tori.Comment: minor changes, to appear in Letters in Mathematical Physic

Chaplygin ball over a fixed sphere: explicit integration

We consider a nonholonomic system describing a rolling of a dynamically non-symmetric sphere over a fixed sphere without slipping. The system generalizes the classical nonholonomic Chaplygin sphere problem and it is shown to be integrable for one special ratio of radii of the spheres. After a time reparameterization the system becomes a Hamiltonian one and admits a separation of variables and reduction to Abel--Jacobi quadratures. The separating variables that we found appear to be a non-trivial generalization of ellipsoidal (spheroconical) coordinates on the Poisson sphere, which can be useful in other integrable problems. Using the quadratures we also perform an explicit integration of the problem in theta-functions of the new time.Comment: This is an extended version of the paper to be published in Regular and Chaotic Dynamics, Vol. 13 (2008), No. 6. Contains 20 pages and 2 figure

Self-sustaining secondary emission in magnetron guns, beam modulation and feedbacks

This paper reports on computer simulations of an electron cloud formation inside a smooth-bore magnetron. Preliminary results were published in [1-3]. Computer simulations have been performed using 2.5D and 3D electromagnetic PIC code KARAT [4] for the magnetron diode (MD) with parameters close to experimental [5], and with an external voltage source V0(t) connected to MD via an RL-circuit. The yield of secondary electrons from the cathode takes into account the dependence of the yield on the energy of electrons and the angle between the direction of electron velocity and the perpendicular to the cathode surface, and also the threshold of secondary emission

Charged plasma interaction with a surface in crossed fields

Problems of non-linear dynamics and non-stationary behaviour of charged plasma interacting with secondary emission surfaces in crossed E×B-fields are discussed from the point of view of the investigation of new approaches for microwave electronic devices. Self-organisation of flows and formation of regular space structures due to the feedback at the emitting surface is shown. The results of computer simulations of electron clouds formation due to non-linear azimuthal instability inside coaxial systems embedded inside in external magnetic field under the condition of strong non-uniform secondary self-sustaining emission are described. The existence of quasi-stationary, rotating state of charged flow has been shown under conditions of conservation of full power and full momentum of the system. It is emphasised the dominant influence of a feedback due to non-uniform secondary emission on dynamics of plasma flow modulation and on arising of a leakage current across external magnetic field.Обговорюються проблеми нелінійної динаміки і нестаціонарного поводження зарядженої плазми, взаємодіючою з повторно-емісійною поверхнею в схрещених полях, з позиції дослідження нових підходів для пристроїв мікрохвильової електроніки. Показано можливість самоорганізації потоків і формування регулярних просторових структур, обумовлена зворотним зв'язком на емітувальній поверхні. Дано опис результатів чисельного моделювання формування електронних структур у коаксіальних системах, що знаходяться в зовнішньому магнітному полі, в умовах неоднорідної самопідтримної вторинної емісії. Показано можливість існування стаціонарно обертових станів в умовах збереження повної потужності і повного моменту системи. Звертається особлива увага на домінуючий вплив зворотного зв'язку і неоднорідності вторинної емісії на динаміку модуляції потоків і виникнення струмів витоку поперек зовнішнього магнітного поля.Обсуждаются проблемы нелинейной динамики и нестационарного поведения заряженной плазмы, взаимодействующей с вторично-эмиссионной поверхностью в скрещенных полях, с позиции исследования новых подходов для устройств микроволновой электроники. Показана возможность самоорганизации потоков и формирования регулярных пространственных структур, обусловленная обратной связью на эмитирующей поверхности. Дано описание результатов численного моделирования формирования электронных структур в коаксиальных системах, находящихся во внешнем магнитном поле, в условиях неоднородной самоподдерживающейся вторичной эмиссии. Показана возможность существования стационарно вращающихся состояний в условиях сохранения полной мощности и полного момента системы. Обращается особое внимание на доминирующее влияние обратной связи и неоднородности вторичной эмиссии на динамику модуляции потоков и возникновение токов утечки поперек внешнего магнитного поля

Selforganisation and dynamics peculiarities of intense electron beams in compact crossed fields systems

The review of the results of computer simulations of electron flow self-organisation inside magnetically isolated coaxial diodes (magnetron gun) is given. Magnetron guns of usual and inverted polarities are considered

Nanocavity formation processes in MgO(100) by light ion (D, He, Li) and heavy ion (Kr, Cu, Au) implantation

In studies on the controlled growth of metallic precipitates in MgO it is attempted to use nanometer size cavities as precursors for formation of metallic precipitates. In MgO nanocavities can easily be generated by light gas ion bombardment at room temperature with typically 30 keV ion energy to a dose of 10^16 cm–2, followed by annealing to 1300 K. It has been shown earlier by transmission electron microscopy (TEM) that the cavities (thickness 2–3 nm and length/width 5–10 nm) have a perfectly rectangular shape bounded by {100} faces. The majority of the gas has been released at this temperature and the cavities are stable until annealing at 1500 K. The depth location of the cavities and the implanted ions is monitored by positron beam analysis, neutron depth profiling, RBS/channeling and energy dispersive spectroscopy. The presence of metallic nanoprecipitates is detected by optical absorption measurements and by high-resolution XTEM. Surprisingly, all the metallic implants induce, in addition to metallic precipitates in a band at the mean ion range, small rectangular and cubic nanocavities. These are most clearly observed at a depth shallower than the precipitate band. In the case of gold the cavities are produced in close proximity to the crystal surface. The results indicate that in MgO vacancy clustering dominates over Frenkel-pair recombination. Results of molecular dynamics calculations will be used to discuss the observed defect recovery and clustering processes in MgO

A Generalization of Chaplygin's Reducibility Theorem

In this paper we study Chaplygin's Reducibility Theorem and extend its applicability to nonholonomic systems with symmetry described by the Hamilton-Poincare-d'Alembert equations in arbitrary degrees of freedom. As special cases we extract the extension of the Theorem to nonholonomic Chaplygin systems with nonabelian symmetry groups as well as Euler-Poincare-Suslov systems in arbitrary degrees of freedom. In the latter case, we also extend the Hamiltonization Theorem to nonholonomic systems which do not possess an invariant measure. Lastly, we extend previous work on conditionally variational systems using the results above. We illustrate the results through various examples of well-known nonholonomic systems.Comment: 27 pages, 3 figures, submitted to Reg. and Chaotic Dy

Collisions of three-dimensional bipolar optical solitons in an array of carbon nanotubes

We study interactions of extremely short three-dimensional bipolar electromagnetic pulses propagating towards each other in an array of semiconductor carbon nanotubes, along any direction perpendicular to their axes. The analysis provides a full account of the effects of the nonuniformity of the pulses’ fields along the axes. The evolution of the electromagnetic field and charge density in the sample is derived from the Maxwell’s equations and the continuity equation, respectively. In particular, we focus on indirect interaction of the pulses via the action of their fields on the electronic subsystem of the nanotube array. Changes in the shape of pulses in the course of their propagation and interaction are analyzed by calculating and visualizing the distribution of the electric field in the system. The numerical analysis reveals a possibility of stable post-collision propagation of pulses over distances much greater than their sizes