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1.
Rodney Loudon 《物理学进展》2013,62(66):243-280
The contributions of magnons to the optical properties of antiferromagnets having the rutile structure are discussed. The properties considered are electric-dipole active two-magnon absorption in the infra-red, and magnon sidebands on sharp-line exciton transitions in the visible. The discussion is based on a thorough treatment of the properties of excitons and magnons in the antiferromagnetically ordered state. The site-group and space-group symmetries of the magnetic excitations are derived and the selection rules for electric and magnetic dipole transitions are determined. The occurrence of magnetic Davydov splittings of the excitons is investigated, and their symmetry properties throughout the Brillouin zone are derived. The functional dependences of exciton energy on wave vector are calculated. Applications of the theory are made to experimental results on excitons and magnons in MnF2, FeF2 and CoF2. The possible mechanisms for two-magnon and magnon-sideband absorption are discussed, and the influence of crystal symmetry on these mechanisms is described. The two-magnon state responsible for electric-dipole absorption is identified and selection rules for electric-dipole activity are presented. A spin Hamiltonian for the two-magnon process is set up and used to derive expressions for absorption coefficients for electric vector parallel and perpendicular to the crystal c-axis. Comparison with experiment for MnF2 yields numerical values for the parameters of the basic coupling mechanism. The exciton-magnon states which give rise to magnon-sideband absorption are explicitly constructed and electric-dipole selection rules are derived for all possible types of sideband. Spin Hamiltonians for the various magnonsideband absorption processes are presented and used to derive expressions for sideband shapes. The results are applied to the experimental spectra for MnF2 and FeF2 and the sideband shapes in MnF2 are calculated numerically. The sideband shapes observable in emission spectra are also briefly discussed. 相似文献
2.
The yields of photonucleon reactions on the isotope 181Ta that are induced by bremsstrahlung photons whose endpoint energy is 67.7 MeV are measured by the residual-activity method.
The cross sections for photonucleon reactions on the isotope 181Ta are calculated on the basis of the TALYS code and a combined model. The measured reaction yields are compared with their
counterparts rescaled from cross sections obtained in experiments that employed beams of quasimonochromatic and bremsstrahlung
photons. The spectra of neutrons emitted from 181Ta nuclei after the absorption of photons having various energies are calculated within the TALYS code and the combined model
in question. 相似文献
3.
First principle methods for calculation of hyperfine fields in different systems are reviewed. The contributions from energy
states close to the Fermi level are emphasized and are responsible for different observed systematic behaviours in the hyperfine
field, not directly related to the host magnetic moment. Calculations on Fe, on Fe2P, on surfaces, on impurity atoms in Fe and on the muon Knight shift in Sb are discussed. 相似文献
4.
Optical properties of spherical gold particles with diameters of 150–650 nm (mesoparticles) are studied by reflectance spectroscopy.
Particles are fabricated by laser-induced transfer of metallic droplets onto metal and dielectric substrates. Contributions
of higher multipoles (beyond the quadrupole) in the scattering spectra of individual spherical particles are experimentally
observed. These observations are performed for particles in a homogeneous environment and for particles located in air on
a metal surface. Good agreement between calculations on the basis of Mie theory and experimental results obtained in homogeneous
environment is demonstrated. Multipole resonance features in the experimental reflection spectra of particles located on a
gold substrate, in the wavelength range of 500–1000 nm, are discussed and theoretically analyzed on the basis of finite-difference
time-domain simulations. High-resolution Raman images of mesoparticle pairs at different polarizations of light are also presented. 相似文献
5.
Granular silver films deposited on a thin insulating film of amorphous hydrogenated carbon (a-C:H) and transparent conducting electrode (polycrystalline indium tin oxide (ITO) layer) have been investigated by spectroscopy and microscopy methods. The extinction spectra of silver films on the surface of these materials are found to be significantly different. An annealing of silver films causes a blue shift of the peak of plasmon resonance band in the spectrum of silver nanoparticles: by 16 nm on the a-C:H surface and by 94 nm on the ITO surface. Silver films on the surface of a-C:H films are characterized by a narrower band in the extinction spectrum, which is peaked at 446 nm. The changes observed in the optical density of Ag films are related to the change in size and area of nanoparticles. The results of spectral studies of Ag films are in agreement with the data on the nanostructure obtained by scanning electron microscopy and statistical image processing. The spectra of granular silver films are shown to correlate well with the nanoparticle distribution function over the film area. 相似文献
6.
V. F. Khairutdinov F. R. Gabitov F. M. Gumerov B. Le Neindre E. S. Vorob’ev 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(8):1228-1239
Experimental results on the phase equilibria in the dichloromethane-CO2, dichloromethanepolycarbonate, polycarbonate-CO2, and polycarbonate-dichloromethane-CO2 systems are presented. Based on these data, the parameters of the dispersion of polycarbonate by the SAS method are determined.
Experimental data on the dispersion of polycarbonate by the SAS method at pressures of 8.0 to 25.0 MPa and temperatures of
313, 333, and 355 K are obtained and analyzed. 相似文献
7.
Using an electron beam, spontaneous polarization on the surface of +Z cuts of lithium niobate crystals of various compositions is switched. Domains 100–200 nm in size are formed in a thin surface layer, with the thickness dependent on the primary-electron energy. The sizes of segments, on which submicron domains are formed, exceed the sizes of the irradiation region. The distributions of domains on the surface in crystals of various compositions are different and depend on the method of moving the electron beam and irradiation conditions. The results are discussed in the context of notions on the charging of dielectric materials by the electron beam. It is assumed that the spontaneous polarization in the surface layer of +Z cuts of lithium niobates is switched by the field of a double layer of charges formed as a result of the charging process near the surface. 相似文献
8.
Amir Mardani Sadegh Tabejamaat Mohammadreza Baig Mohammadi 《Combustion Theory and Modelling》2013,17(6):753-772
In this paper, the importance of fluctuations in flow field parameters is studied under MILD combustion conditions. In this way, a turbulent non-premixed CH4+H2 jet flame issuing into a hot and deficient co-flow air is modeled using the RANS Axisymmetric equations. The modeling is carried out using the EDC model to describe the turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. Results illustrate that although the fluctuations in temperature field are small and the reaction zone volume are large in the MILD regime, the fluctuations in temperature and species concentrations are still effective on the flow field. Also, inappropriate dealing with the turbulence effect on chemistry leads to errors in prediction of temperature up to 15% in the present flame. By decreasing of O2 concentration of hot co-flow air, the effect of fluctuations in flow field parameters on flame characteristics are still significant and its effect on species reaction rates does not decrease. On the other hand, although decreasing of jet inlet Reynolds number at constant inlet turbulence intensity addresses to smaller fluctuations in flow filed, it does not lead to lower the effect of turbulence on species distribution and temperature field under MILD combustion conditions. 相似文献
9.
Shang Yuan Ren 《Annals of Physics》2002,301(1):22-30
Exact and general results on the electronic states in one-dimensional crystals bounded at τ and τ+L, where L=Na, N is a positive integer, and a is the potential period, are presented. Corresponding to each energy band of the Bloch wave, there are N−1 states in the finite crystal whose energies are dependent on L but not on τ and map the energy band exactly. There is always one and only one electronic state corresponding to each band gap of the Bloch wave, whose energy is dependent on τ but not on L. This state is either a constant-energy confined band-edge state or a surface state in the band gap. 相似文献
10.
Standardization methods of low symmetry – orthorhombic, monoclinic and triclinic – crystal fields are formulated and discussed. Two alternative approaches are presented, the conventional one, based on the second-rank parameters and the standardization based on the fourth-rank parameters. Mainly f-electron systems are considered but some guidelines for d-electron systems and the spin Hamiltonian describing the zero-field splitting are given. The discussion focuses on premises for choosing the most suitable method, in particular on inadequacy of the conventional one. Few examples from the literature illustrate this situation. 相似文献
11.
G. T. Jones B. W. Kennedy R. P. Middleton S. W. O'Neale A. M. Cooper A. Grant H. Klein J. Mittendorfer D. R. O. Morrison A. Parker P. Schmid H. Wachsmuth F. Hamisi M. M. Mobayyen O. Villalobos-Baillie M. Aderholz L. Deck N. Schmitz W. Wittek G. Corrigan G. Myatt D. Radojicic M. Retter 《Zeitschrift fur Physik C Particles and Fields》1984,25(2):121-127
Data from a neutrino and antineutrino hydrogen experiment with BEBC are used to investigate transverse properties of the produced charged hadrons. Measurements are presented on average transverse momenta of charged pions as functions of Feynman-x and the hadronic mass, on the transverse momentum flow within an event and on jet-related quantities. The main features of the data are well described by the LUND model. The data favour a version of the model in which soft gluon effects are included and the primordial transverse momentum of the quarks in the proton is small. Effects from 1st order QCD (hard gluon emission) are negligible. 相似文献
12.
P. Pieranski L. Sittler P. Sotta M. Imperor-Clerc 《The European physical journal. E, Soft matter》2001,5(3):317-328
Monocrystals of the cubic lyotropic liquid crystal phase V1 are studied in droplets of the mixture C
12
EO
6/water surrounded by water vapor of controlled pressure p. Shapes of monocrystals are found to depend on the conditions of growth from the lamellar phase and on the nature of the
substrate. After the growth, when the lamellar phase is exhausted and crystals are in equilibrium with water vapors, their
shapes are shown to depend on the pressure p. Thermodynamic aspects of these phenomena are discussed.
Received 22 November 2000 相似文献
13.
V. Yu. Bychkov Yu. P. Tulenin M. M. Slinko D. N. Vturina V. N. Korchak 《Russian Journal of Physical Chemistry B, Focus on Physics》2018,12(5):830-835
Self-oscillations of the rate of oxidation reactions of CO and CH4 on nickel foil are compared. It has been shown that, despite significant differences in the stepwise mechanism of the two reactions, the properties of oscillation regimes are very close. In both reactions, oscillation regimes result from oxidation and reduction of nickel and are accompanied by wave processes on the catalyst surface. The similarity in the properties of rate oscillations in the reactions of CO and CH4 oxidation shows that a change in the selectivity and the formation of carbon on the nickel surface are not key factors in the mechanism of the rate oscillations in CH4 oxidation. An observed periodic change in the concentrations of reactants and reaction products when the reaction mixture is supplied in a pulse mode proves that, in both cases, the self-oscillations of the reaction rate are due only to the reaction mechanism and are not caused by a change in the catalyst temperature. 相似文献
14.
A. S. Filippov 《Journal of Engineering Thermophysics》2011,20(1):64-76
Available experimental data on heat transfer of a melt with volumetric heat generation are analyzed in order to use them for
validating the computer codes that describe a core catcher. The problem for CFD simulation of the experiments on heat transfer
by laminar and turbulent natural convection is described. Information that can be obtained from experiments for verifying
the models of convective heat transfer in a melt is analyzed. The effect of variable viscosity on the integral heat flux is
discussed. Calculation results are represented and compared with experimental data on temperature distribution and integral
heat transfer. The calculations are in good agreement with the experiment. The results are numerically extrapolated to the
range of Rayleigh numbers up to 7 · 1016. It is concluded that the CFD calculations with the κ-ɛ turbulence model can be used in problems concerned with analysis of melt convection in a core catcher. 相似文献
15.
V. Ya. Rudyak A. V. Minakov A. A. Gavrilov A. A. Dekterev 《Thermophysics and Aeromechanics》2010,17(4):565-576
A method is proposed for modelling fluid flows in microchannels. The method is tested on the known experimental data on studying
the flows in microchannels with the aid of the micro-PIV. The flow regimes in micromixers of the Y- and T-types are studied. The passive and active mixers are considered. The dependence of the mixing efficiency on the Reynolds
and Péclet numbers as well as the possibility of using the hydrophobic and ultra-hydrophobic coatings are analysed. A T-mixer is proposed as an active technique of mixing, in which the flow rate in one of the inlet channels varied according
to the harmonic law. The dependence of the mixing efficiency on the frequency of the variation of the flow rate and its amplitude
is established. 相似文献
16.
采用基于密度泛函理论的平面波赝势方法对SnO2:F体系的电子结构进行了第一性原理模拟计算.用广义梯度近似方法优化SnO2:F体系的晶胞结构,计算了体系基态总能.通过确定F掺杂对O的优先替代位置,计算了SnO2:F的能带结构、态密度、分波态密度.分析了F掺杂对SnO2晶体的电子结构和晶体性质及光学吸收边的影响,从理论上得出光学吸收边发生蓝移.对不同掺杂量的体系电子结构进行了分析.
关键词:
F掺杂
2')" href="#">SnO2
电子结构
态密度 相似文献
17.
S. N. Bagayev V. P. Chebotayev A. S. Dychkov V. G. Goldort 《Applied Physics A: Materials Science & Processing》1981,25(2):161-164
The possibility to use narrow optical resonances and highly stable lasers as detectors of gravitational waves are discussed. The methods for measuring small displacements are based on the registration of small variations of a radiation frequency that arise in changing an optical phase. First results on the use of narrow resonances for precision measurements of small displacements are given. The achieved absolute sensitivity of the measurements amounted to 6·10?6 Å on the basis of 5·102 cm. 相似文献
18.
O. V. Bespalova I. N. Boboshin V. V. Varlamov T. A. Ermakova B. S. Ishkhanov E. A. Romanovsky T. I. Spasskaya T. P. Timokhina 《Physics of Atomic Nuclei》2006,69(5):796-809
The neutron and proton single-particle energies and the occupation probabilities for the valence states of the even-even isotopes 90,92,94,96Zr are determined by matching data on nucleon-stripping and nucleon-pickup reactions on the same nucleus. The data obtained in this way suggest the magicity of the number N = 56 for Z = 40. The single-particle energies of all bound neutron and proton states in the 90,92,94,96Zr nuclei are described within the experimental errors on the basis of the dispersive optical model. 相似文献
19.
Adsorption of simple organic molecules on wide band gap insulators is a versatile tool to introduce unoccupied electronic states in the band gap at the surface. Relative energetic positions, varied also by intra-molecular interactions of functional side groups, determine the effective band gap. Specific examples used here are adsorbed molecules of benzoic acid and of its OH-substituted derivates (salicylic acid, etc.) on NaCl, KCl and on MgSO4 · H2O. These acids are mainly physisorbed on NaCl and KCl, whereas on MgSO4 · H2O chemical bond formation is found. Ab initio and semi-empirical calculations are used in order to identify mechanisms of surface-molecule as well as intra-molecular interactions. 相似文献
20.
Yuming Liu 《Solid State Communications》2005,133(2):131-134
Carbon nanotubes are synthesized on the silicon nanowire arrays which are fabricated on silicon substrate by chemical vapor depositing SiCl4 and H2 gases in the presence of Au catalysts. The silicon nanowires are single-crystal with lengths up to 100 μm and diameters ranging from 50 to 500 nm. The tangled carbon nanotubes are grown directly from the surface of Si nanowires. The field emission properties of the carbon nanotubes are investigated at the gap of 200 μm. The low turn on and threshold fields are obtained. The stabilization of the emission currents is also presented. 相似文献