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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. A., Shabanov A. V.
Заглавие : Molecular dynamics investigation of the helical structure of smectic C*
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 54, Is. 8. - P.1704-1708. - ISSN 1063-7834, DOI 10.1134/S106378341208015X
Примечания : Cited References: 34
Предметные рубрики: LIQUID-CRYSTALS
SHORT-PITCH
FORCE-FIELD
SIMULATIONS
MODES
PHASE
DOBAMBC
POWER
Аннотация: The numerical simulation of the behavior of the molecules of the DOBAMBC liquid crystal by the molecular dynamics method allowed us to find the change of the the conformation of molecules as a function of temperature and to reveal the helical structures with various pitches in the smectic phase C*. These results explained the anomalous temperature dependences of the order parameter at the molecular level, as well as the optical second harmonic generation in the region of smectic A.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Divin A., Markidis S., Lapenta G., Semenov V. S., Erkaev N. V., Biernat H. K.
Заглавие : Model of electron pressure anisotropy in the electron diffusion region of collisionless magnetic reconnection
Коллективы :
Место публикации : Phys. Plasmas: AMER INST PHYSICS, 2010. - Vol. 17, Is. 12. - Ст.122102. - ISSN 1070-664X, DOI 10.1063/1.3521576
Примечания : Cited References: 42. - The present work is supported partially by the Onderzoekfonds KU Leuven (Research Fund KU Leuven) and by the European Commission's Seventh Framework Programme (FP7/2007-2013) under grant Agreement No. 218816 (SOTERIA project, www.soteria- space.eu). Additional support is provided by RFBR (Grant No. 09-05-91000-ANF-a). V.S.S. thanks ISSI for hospitality and financial support. The simulations were conducted on the resources of the Vlaams Supercomputer Centrum (VSC) at the Katholieke Universiteit Leuven.
Предметные рубрики: CURRENT SHEETS
X-LINE
PLASMA
DISSIPATION
FIELD
SIMULATIONS
ACCELERATION
TRANSPORT
Ключевые слова (''Своб.индексиров.''): analytical results--antiparallel configuration--collisionless--electron diffusion--electron population--electron pressures--magnetic reconnections--neutral line--new model--particle-in-cell simulations--two particles--anisotropy--astrophysics--collisionless plasmas--computer simulation--diffusion--geophysics--magnetic fields--magnetic properties--plasma simulation--electrons
Аннотация: A new model of the electron pressure anisotropy in the electron diffusion region in collisionless magnetic reconnection is presented for the case of antiparallel configuration of magnetic fields. The plasma anisotropy is investigated as source of collisionless dissipation. By separating electrons in the vicinity of the neutral line into two broad classes of inflowing and accelerating populations, it is possible to derive a simple closure for the off-diagonal electron pressure component. The appearance of these two electron populations near the neutral line is responsible for the anisotropy and collisionless dissipation in the magnetic reconnection. Particle-in-cell simulations verify the proposed model, confirming first the presence of two particle populations and second the analytical results for the off-diagonal electron pressure component. Furthermore, test-particle calculations are performed to compare our approach with the model of electron pressure anisotropy in the inner electron diffusion region by Fujimoto and Sydora [Phys. Plasmas 16, 112309 (2009)]. (C) 2010 American Institute of Physics. [doi:10.1063/1.3521576]
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Belyaev B. A., Izotov A. V., Leksikov An. A.
Заглавие : Micromagnetic calculation of the equilibrium distribution of magnetic moments in thin films
Коллективы :
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 52, Is. 8. - P1664-1672. - ISSN 1063-7834, DOI 10.1134/S1063783410080160
Примечания : Cited References: 17. - This study was supported by the Council on Grants from the President of the Russian Federation (grant no. 3818.2008.3), the Siberian Branch of the Russian Academy of Sciences (integration project no. 5), the Presidium of the Russian Academy of Sciences (project no. 27.1), and the Ministry of Education and Science of the Russian federation (state contract nos. 02.740.11.0220 and 02.740.11.0568.
Предметные рубрики: SIMULATIONS
ANISOTROPY
NANOPARTICLES
MODES
Аннотация: A new approach has been proposed for determining an equilibrium configuration of magnetic moments in condensed matter in terms of its discrete model. The solution to this problem is reduced to a system of linear inhomogeneous equations with undetermined Lagrange multipliers. The possibility of numerically solving these systems has been shown using a modified power method. The efficiency of the method has been demonstrated for the model of a thin magnetic film with a nonuniform distribution of the uniaxial magnetic anisotropy over the area. The dependence of the coercive force on the uniaxial anisotropy of nanocrystallites, their exchange interaction, and other parameters of samples has been investigated.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gunell H., Amerstorfer U. V., Nilsson H., Grima C., Koepke M., Franz M., Winningham J. D., Frahm R. A., Sauvaud J. A., Fedorov A., Erkaev N. V., Biernat H. K., Holmstrom M., Lundin R., Barabash S.
Заглавие : Shear driven waves in the induced magnetosphere of Mars
Место публикации : Plasma Phys. Control. Fusion: IOP PUBLISHING LTD, 2008. - Vol. 50, Is. 7. - Ст.74018. - ISSN 0741-3335, DOI 10.1088/0741-3335/50/7/074018
Примечания : Cited References: 27
Предметные рубрики: SOLAR-WIND INTERACTION
KELVIN-HELMHOLTZ INSTABILITY
MARTIAN ATMOSPHERE
VELOCITY SHEAR
VENUS
PLASMA
MHD
IONOPAUSE
SIMULATIONS
BOUNDARY
Ключевые слова (''Своб.индексиров.''): charged particles--magnetosphere--motion estimation--natural frequencies--plasma stability--shearing machines--p ,p ,t measurements--computational results--electron densities--fundamental frequency (ff)--higher harmonics--ion densities--ion velocities--velocity shear--electrons
Аннотация: We present measurements of oscillations in the electron density, ion density and ion velocity in the induced magnetosphere of Mars. The fundamental frequency of the oscillations is a few millihertz, but higher harmonics are present in the spectrum. The oscillations are observed in a region where there is a velocity shear in the plasma flow. The fundamental frequency is in agreement with computational results from an ideal-MHD model. An interpretation based on velocity-shear instabilities is described.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Komogortsev S. V., Iskhakov R. S.
Заглавие : Magnetization curve and magnetic correlations in a nanochain of ferromagnetic grains with random anisotropy
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 3. - P495-501. - ISSN 1063-7834, DOI 10.1134/1.1884711
Примечания : Cited References: 31
Предметные рубрики: NANOCRYSTALLINE FERROMAGNETS
AMORPHOUS FERROMAGNETS
FIELD
MODEL
MICROSTRUCTURE
SIMULATIONS
DEPENDENCE
SYMMETRY
SYSTEM
MEDIA
Аннотация: The magnetization curve and magnetization correlation function are calculated for a ferromagnetic chain of single-domain nanoparticles with a randomly oriented anisotropy axis for different ratios between the exchange correlation and anisotropy energies. It is shown that the coercive force decreases as the exchange correlations increase. For strong exchange correlations, the magnetization curve is described by the following three successive magnetization processes as the applied field is increased: (i) nonuniform rotation of the magnetization of stochastic domains, (ii) collapse of the magnetic solitons, and (iii) nonuniform rotation of exchange-correlated magnetization vectors of the nanoparticles. For high fields, the calculated correlation function of the transverse magnetization components coincides with that predicted from linear theory. At low and zero fields, the main parameters of the correlation function (the variance and correlation radius) tend to certain finite values rather than diverge (as is the case in linear theory). The irreversible variation in the magnetization at low fields (the hysteresis loop) and the hysteresis of the main parameters of the correlation function are calculated. (c) 2005 Pleiades Publishing, Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Markel V. A., Shalaev V. M., Poliakov E. Y., George T. F.
Заглавие : Numerical studies of second- and fourth-order correlation functions in cluster-cluster aggregates in application to optical scattering
Место публикации : Phys. Rev. E: AMERICAN PHYSICAL SOC, 1997. - Vol. 55, Is. 6. - P7313-7333. - ISSN 1063-651X, DOI 10.1103/PhysRevE.55.7313
Примечания : Cited References: 21
Предметные рубрики: DIFFUSION-LIMITED AGGREGATION
COLLOIDAL AGGREGATION
FRACTAL CLUSTERS
ANTICORRELATION
SIMULATIONS
Аннотация: Two- and four-point density correlation functions p(2)(r) and p(4)(r) are studied numerically and theoretically in computer-generated three-dimensional lattice cluster-cluster aggregates (CCA) with the number of particles N up to 20 000 in application to the light scattering problem. The ''pure'' aggregation algorithm is used, where subclusters of all possible sizes are allowed to collide. We find that large CCA clusters demonstrate pronounced multiscaling. In particular, the fractal dimension determined from the slope of p(2)(r) at small distances differs from that found from the dependence of the radius of gyration on the number of monomers (according to our data, 1.80 and 1.94, respectively). We also consider different functional forms for p(2) and their general properties and applicability. We find that the best fit to the numerical data is provided by the generalized exponential cutoff function with coefficients depending on N. The latter dependence is a manifestation of multiscaling. We propose some theoretical approaches for calculating p(4)(r), assuming p(2)(r) is known. In particular, we find the small-r asymptote for the p(4)(r) and verify it numerically. In addition, we find that p(4)(r) cannot be represented by a scaling dependence with a cutoff function, like p(2)(r) Instead, p(4)(r) is given by an expansion in terms of integer powers of r(2D-3), where D is the fractal dimension (approximate to 1.8 for CCA clusters).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lundin A. A., Zobov V. E.
Заглавие : Decoherence-induced stabilization of the multiple-quantum NMR-spectrum width
Место публикации : Appl. Magn. Reson.: Springer, 2016. - Vol. 47, Is. 7. - P.701-710. - ISSN 0937-9347, DOI 10.1007/s00723-016-0770-z. - ISSN 1613-7507(eISSN)
Примечания : Cited References:26
Предметные рубрики: SIMULATIONS
DYNAMICS
SYSTEMS
SOLIDS
Аннотация: The time dependence of an increase in the number of correlated spins in cluster was calculated for a particular variant of multiple-quantum (MQ) nuclear magnetic resonance spectroscopy using an effective two-quantum Hamiltonian that includes conventional secular nuclear dipole-dipole interaction as a weak perturbation at the stage of correlation preparation. It was shown that the cluster size grows steadily, while the width of the MQ spectrum stabilizes because the decay rates of the spectral components located at different areas of the MQ spectrum are different. The MQ bandwidth was also calculated as a function of the preparation time for various perturbation strengths. The results obtained are in excellent agreement with the experimental data reported in Alvarez and Suter (Phys Rev A 84:012320, 2011).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Belyaev B. A., Boev N. M., Izotov A. V., Solovev P. N.
Заглавие : Study of Peculiarities of the Microwave Absorption Spectrum of Nanocrystalline Thin Magnetic Films
Коллективы : Ministry of Education and Science of the Russian Federation [RFMEFI60417X0179]
Место публикации : Russ. Phys. J. - 2019. - Vol. 61, Is. 10. - P.1798-1805. - ISSN 1064-8887, DOI 10.1007/s11182-019-01603-4. - ISSN 1573-9228(eISSN)
Примечания : Cited References: 22. - This work was supported by the Ministry of Education and Science of the Russian Federation, project No. RFMEFI60417X0179.
Предметные рубрики: MICROMAGNETIC CALCULATION
SIMULATIONS
PARTICLES
MODES
Ключевые слова (''Своб.индексиров.''): micromagnetic modeling--nanocrystallites--random magnetic anisotropy--ferromagnetic resonance--microwave
Аннотация: Based on the micromagnetic model which takes into account the random distribution of the uniaxial magnetic anisotropy directions in crystallites of a nanocrystalline film, an effective method has been implemented for calculation of the magnetization dynamics in microwave fields. For a certain range of crystallite sizes, when the energy of the random magnetic anisotropy is comparable to the exchange energy, a significant change of the ferromagnetic resonance field, broadening of the resonance line, and the appearance of an asymmetry in the shape of the resonance curve were found. With an increase of the crystallite sizes, the resonance field first grows, then, it quickly decreases to its minimum, and then, it grows again to reach saturation. In this case, the steepness of the left slope of the broadening resonance curve first decreases faster than that of the right slope, leading to the symmetry breaking of the resonance curve shape, then, the curve becomes symmetrical again, and then, the steepness of the left slope becomes greater than that of the right slope.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Belyaev B. A., Izotov A. V., Skomorokhov G. V., Solovev P. N.
Заглавие : Micromagnetic analysis of edge effects in a thin magnetic film during local excitation of magnetization oscillations
Место публикации : Russ. Phys. J. - 2020. - Vol. 63, Is. 5. - P.837-843. - ISSN 1064-8887, DOI 10.1007/s11182-020-02106-3. - ISSN 1573-9228(eISSN)
Примечания : Cited References: 19. - This research was performed with financial support of the Russian Foundation for Basic Research within the research project No. 18-32-00086
Предметные рубрики: ANISOTROPIES
SIMULATIONS
FIELDS
Аннотация: The method of numerical micromagnetic simulation was used to study the magnetization dynamics of a thin film with uniaxial magnetic anisotropy during ferromagnetic resonance (FMR) excitation in it on the local sites by a linearly polarized high-frequency magnetic field emitted from the 1 mm opening in the metallic screen of the transmission line. It was established that non-uniformities of demagnetizing fields emerging near the film edges lead not only to the change in the FMR field, but also to the change in the value and direction of the uniaxial anisotropy field. The distribution of non-uniformities of the magnetic anisotropy characteristics over the area of 60 nm thick permalloy film that was measured on the scanning FMR spectrometer agrees well with the micromagnetic simulation results. Demagnetizing fields were proved to be the main cause for the edge effects in magnetic films.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Reversible and Irreversible propagation of quantum information and its manifestation in multiple-quantum NMR spectra in solids
Коллективы : Ministry of Science and Higher Education of the Russian Federation [0082-2019-0001, AAAA-A19-119012890064-7]
Место публикации : J. Exp. Theor. Phys. - 2020. - Vol. 131, Is. 2. - P.273-279. - ISSN 1063-7761, DOI 10.1134/S1063776120060096. - ISSN 1090-6509(eISSN)
Примечания : Cited References: 33. - This work was supported by the Ministry of Science and Higher Education of the Russian Federation within the State Task 0082-2019-0001 (State Registration Number AAAA-A19-119012890064-7)
Предметные рубрики: DYNAMICS
LOCALIZATION
SIMULATIONS
COHERENCES
Аннотация: On the basis of the earlier developed statistical theory of the growth of the effective size of correlated clusters (the number of correlated spins), an expression for the shape of the multiple-quantum (MQ) NMR spectrum is obtained that takes into account the loss of coherence in a spin system due, for example, to the controlled intervention of the experimenter. It is shown that the scrambling and decoherence processes in the MQ spectrum of the multiparticle system of a solid are not separated, unlike the corresponding spectra of some large isolated molecules [27] in a solution. The relations obtained allow one to extract the necessary information about the above processes (scrambling and decoherence) from the dependence of the MQ spectra on experimental parameters.
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