共查询到20条相似文献,搜索用时 31 毫秒
1.
《Journal of magnetism and magnetic materials》2002,248(2):332-335
The system Co0.6Zn0.4Fe2O4 ferrite was prepared by the usual ceramic method. The resonant frequency and antiresonance of vibrating disc have been studied as a function of temperature. The decrease of resonant frequency with rising temperature was attributed to increase the interaction of domains with the applied AC field. The decrease of the ultrasonic wave velocity with the increase of temperature was ascribed to thermal lattice vibration, which facilitate the domains to interact at lower frequency of the applied AC field. The electromechanical coupling factor of the radial mode was fairly constant with rising temperature. The pyroelectric voltage measured at the transducer electric terminals increases with the increase of temperature. Ferrite transducer is useful for ultrasonic generation to be used in technology. 相似文献
2.
Rotating black holes in the brany universe of the Randall–Sundrum type with infinite additional dimension are described by
the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b < 0 rotating black holes with dimensionless spin a > 1 are allowed. We investigate the role of the tidal charge in the orbital resonance model of quasiperiodic oscillations
(QPOs) in black hole systems. The orbital Keplerian frequency v
K and the radial and vertical epicyclic frequencies v
r, v
θ
of the equatorial, quasicircular geodetical motion are given. Their radial profiles related to Keplerian accretion discs
are discussed, assuming the inner edge of the disc located at the innermost stable circular geodesic. For completeness, naked
singularity spacetimes are considered too. The resonant conditions are given in three astrophysically relevant situations:
for direct (parametric) resonances of the oscillations with the radial and vertical epicyclic frequencies, for the relativistic
precession model, and for some trapped oscillations of the warped discs, with resonant combinational frequencies involving
the Keplerian and radial epicyclic frequencies. It is shown, how the tidal charge could influence matching of the observational
data indicating the 3 : 2 frequency ratio observed in GRS 1915 + 105 microquasar with prediction of the orbital resonance
model; limits on allowed range of the black hole parameters a and b are established. The “magic” dimensionless black hole spin enabling presence of strong resonant phenomena at the radius,
where v
K: v
θ
: v
r = 3 : 2 : 1, is determined in dependence on the tidal charge. Such strong resonances could be relevant even in sources with
highly scattered resonant frequencies, as those expected in Sgr A*. The specific values of the spin and tidal charge are given
also for existence of specific radius where v
K : v
θ
: v
r = s : t : u with 5≥s >t >u being small natural numbers. It is shown that for some ratios such situation is impossible in the field of black holes. We
can conclude that analysing the microquasars high-frequency QPOs in the framework of orbital resonance models, we can put
relevant limits on the tidal charge of brany Kerr black holes. 相似文献
3.
The collisionless dissociation of SF6 has been studied using simultaneous irradiation by two frequencies from a CO2 laser which are both nearly resonant with the SF6v3 absorption band. It was found that the dissociation was enhanced, and occurred over a wider frequency range, than for single frequency dissociation. No threshold effect was observed for a weak resonant and a much higher energy field pumping slightly off-resonance. For such two frequency irradiation, the peak in the dissociation curve was found to be shifted to lower frequencies with respect to that for single frequency dissociation. 相似文献
4.
5.
6.
The dependence of the transformation coefficient of the four-pole network with the toroid core made of the La0.6Pb0.4MnO3 manganite on dc biasing magnetic field and frequency was experimentally investigated. The factors which influence the value of the transmission coefficient are analyzed. In the megahertz frequency range the frequency dependence of the transformation coefficient has a resonant form with the position of the maximum and amplitude increasing with the dc biasing. The dc magnetic field dependence of the phase shift between the voltages in the primary and secondary windings was investigated. The results are interpreted taking into account the imaginary component of magnetic permeability of the core material. 相似文献
7.
J. Ďatlov R. Klíma L. Kryška V. N. Budnikov O. N. Scherbinin 《Czechoslovak Journal of Physics》1973,23(12):1315-1332
In the overdense collisionless plasma column inserted through the narrow sides of a rectangular waveguide, the excited electron cyclotron harmonic waves (CHWs) are studied by means of two movable probes and a phase interferometer in the range of parameters of 2 >ω/ω ce >1; 0·5 < (ω pe /ω)2 < 15. Two kinds of CH waves have been found in the dipole mode:
- Stable backward CH waves with the phase velocity in the direction from the axis to the periphery.
- Unstable backward CH waves with the phase velocity in the opposite direction.
8.
The pump polarization has an evident effect on a superradiant FIR Raman laser both in NH3 and CH3F gases when the pump detuning from the resonant line is larger than the Raby frequency. In particular for R resonant lines the circular polarization shows a spontaneous gain about 1.5 times greater than the linear polarization as expected from the theory. 相似文献
9.
L. Gao X. P. Yu 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):403-409
We derive expressions for the effective nonlinear susceptibility
tensors for both the second harmonic generation (SHG) and induced
third harmonic generation (THG) of nonlinear composite materials,
in which nondilute coated particles with radial dielectric
anisotropy are randomly embedded in the linear host. Two types of
coated particles are considered. The first is that the core
possesses a second order nonlinear susceptibility and the shell is
linear and radially anisotropic, while the second is that the
core is linear with radial anisotropy and the shell has a second
order nonlinear susceptibility. We observe greatly enhanced SHG
and THG susceptibilities at several surface plasmon resonant
frequencies. For the second model, due to the coating material
being metallic, there exists two fundamental resonant frequencies
ωc1 and ωc2, whose difference
ωc2-ωc1 is strongly dependent on the interfacial
parameter and the radial dielectric anisotropy. Furthermore, in
both systems, the adjustment of the dielectric anisotropy results
in larger enhancement of both SHG and induced THG susceptibilities
at surface plasmon resonant frequencies than the corresponding
isotropic systems. Therefore, both the core-shell structure and
the dielectric anisotropy play important roles in determining the
nonlinear enhancement and the surface resonant frequencies. 相似文献
10.
Using the idea of “stress-field-controlled graded ferroelectrics”, a ring-shaped composite system of Pb(Zr,Ti)O3/Terfenol-D was fabricated. The magnetoelectric coupling of the composite was investigated. A resonant peak was observed at frequency of 69.6 kHz. The magnetoelectric frequency spectrum was found to relate to the polarity of the applied magnetic field, resulting in positive and negative magnetoelectric effects around the resonant point. Analysis shows that elastic resonance of the composite decides the resonant frequency and the magnetostrictive state of the Terfenol-D was responsible for the magnetoelectric coupling at different frequencies. 相似文献
11.
Joachim Heidberg Ingo Hussla 《Journal of Electron Spectroscopy and Related Phenomena》1983,29(1):105-110
After measuring the linear infrared absorption spectrum of the coadsorbate, selective desorption of CH3F from the binary coadsorbate C2H6CH3FNaCl under ultrahigh vacuum conditions at 12o K stimulated by resonant CO2 laser pulses of small fluence ~ 0.1 J·cmt?2 has been carried out. No desorption of ethane, which is slightly more volatile, but has no significant infrared absorption at the laser frequency, was observed. The primary activation step is the resonant multiphoton excitation of the most intense internal CH3FNaCl adsorbate vibration, the CF stretching mode ν3. The substance separation seems to indicate high localisation of the activation in this desorption and could be of interest for applications. 相似文献
12.
将电子注视为等离子体柱,从填充等离子体柱的谐振腔的物理模型出发,推导了圆柱腔填充中心电子注时TM0m0模式的特征方程,并重点分析了填充电子注的圆柱腔中TM010模式和TM020模式的谐振频率和电磁场分布随等离子频率的变化情况。研究结果表明,随着电子注的等离子体频率不断增大,谐振频率也不断增大,谐振腔内电场和磁场的分布也随之发生改变。当电子注的等离子体频率超过谐振腔的谐振频率时,谐振腔内的电磁场分布将发生很大的变化,出现了电子注内外电场方向相反和趋肤效应等现象。 相似文献
13.
V. V. Kapaev Yu. V. Kopaev S. A. Savinov V. N. Murzin 《Journal of Experimental and Theoretical Physics》2013,116(3):497-515
The characteristics of the high-frequency response of single- and double-well resonant tunneling structures in a dc electric field are investigated on the basis of the numerical solution of a time-dependent Schrödinger equation with open boundary conditions. The frequency dependence of the real part of high frequency conductivity (high-frequency response) in In0.53Ga0.47As/AlAs/InP structures is analyzed in detail for various values of the dc voltage V dc in the negative differential resistance (NDR) region. It is shown that double-well three-barrier structures are promising for the design of terahertz-band oscillators. The presence of two resonant states with close energies in such structures leads to a resonant (in frequency) response whose frequency is determined by the energy difference between these levels and can be controlled by varying the parameters of the structure. It is shown that, in principle, such structures admit narrow-band amplification, tuning of the amplification frequency, and a fine control of the amplification (oscillation) frequency in a wide range of terahertz frequencies by varying a dc electric voltage applied to the structure. Starting from a certain width of the central intermediate barrier in double-well structures, one can observe a collapse of resonances, where the structure behaves like a single-well system. This phenomenon imposes a lower limit on the oscillation frequency in three-barrier resonant tunneling structures. 相似文献
14.
对三明治复合结构TbxDy1-xFe2-y/Pb(Zr, Ti)O3/TbxDy1-xFe2-y的电容与频率及磁场的函数关系进行了实验和理论研究. 实验发现,该复合材料样品的电容随频率的增加而出现多个谐振峰,并且其谐振点随磁场的增加而发生频移. 在谐振点附近,观察到样品的阻抗随磁场的增加由容抗性转变为感抗性,从而同时观察到巨大的正磁电容效应和负磁电容效应. 由复合材料的弹性力学本构方程出发,对该类样品的电容随频率及磁场的变化进行了理论模拟. 结果显示,模拟曲线与实验结果符合得很好. 理论表明该磁致伸缩/压电复合材料的磁电容效应源于磁场诱变的铁磁相柔顺系数.
关键词:
层状复合材料
界面弹性耦合
磁电容效应 相似文献
15.
V. G. Alpatov Yu. D. Bayukov A. V. Davydov Yu. N. Isaev G. R. Kartashov M. M. Korotkov V. V. Migachev I. N. Rozantsev M. G. Shchepkin 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(6):769-772
Experiments on the search for the effect of resonant screening on the Mössbauer absorption of 119m Sn γ rays of energy 23.8 keV emitted by a standard Mössbauer Ca119m SnO3 γ source in the resonant SnO2 absorber of natural isotopic composition are described. Intensities of tin γ rays and X-rays that passed through the absorber were measured with and without a resonant cylindrical screen (which was a black absorber for the 23.8-keV Mössbauer γ line) around the absorber and their ratios were calculated for each radiation separately. No difference beyond the experimental error was found between these ratios measured with the γ source both at rest and when oscillating with a frequency and amplitude enough to completely break the conditions for Mössbauer resonant absorption of 23.8-keV γ rays. The upper limit for the relative decrease, due to the influence of the resonant screen, in the intensities of these γ rays after their passing through the resonant absorber was 0.00030. 相似文献
16.
Pedro J. Castro Joaquim J. Barroso Rafael A. Corrêa 《International Journal of Infrared and Millimeter Waves》2000,21(4):633-645
A study of the electrodynamical properties of a Ka-band gyrotron open resonator was experimentally conducted. Experiments were accomplished to measure resonant frequencies and their respective loaded quality factors for TE modes in the frequency range from 26 to 40 GHz. In particular, a perturbation technique was used to determine the axial, radial and azimuthal electric field profiles, as an identification method of the TE021 mode operating around 35 GHz. In any experimental event, good agreement with the values predicted by theory was found. 相似文献
17.
Michael K. Skrehot Kai Chang 《International Journal of Infrared and Millimeter Waves》1990,11(12):1355-1376
A two-gap floating resonant strip is used for characterization of the high-temperature superconductor, YBa2Cu3O7–. The method has the advantages of simplicity, no electrical contact, operation at various resonant frequencies, and of requiring only a small sample. An analysis was devised that allows for the accurate design of the strip dimensions to produce a desired resonant frequency. Experimental measurements in X and Kuband (8–18 GHz) agree well with the calculations. The sensitivities of the circuit to positional errors and size variations of the resonant strip were investigated. The surface resistance was measured and compared favorably with the theory. 相似文献
18.
The radial density distribution of metastable Ar(3P2) and resonant Ar(1P1) atoms is determined experimentally in two types of electrical discharges of cylindrical shape: the positive column plasma of a DC discharge and the plasma produced by an electromagnetic surface wave. The exitation and deexcitation rates for Ar(3P2) by electron collisions are determined as a function of radius from the measured radial population density profile using a population density balance equation. These rate coefficients are obtained for various electron density values on the axis. The published values for these coefficients in the positive column plasma assume that they are independent of the discharge current. In this work, it is shown that these coefficients actually decrease as the electron density increases. In a more general way, the results obtained indicate that the examination of the radial density distributions of exited atoms is a powerful method for determining the kinetics of their creation and destruction. 相似文献
19.
The resonant and nonresonant part of χ(3) are distinguished by their different time behavior. The medium is coherently excited by two picosecond light pulses of defined frequency difference and the state of the system is monitored by a third properly delayed probe pulse. Results are presented on neat liquids of carbontetrachloride and cyclohexane and on the mixture of CCl4: C6H12. 相似文献
20.
Results of a numerical study of the Faraday effect arising upon propagation of the light beams with the frequencies ω L1 (resonant to the nS 1/2-nP 1/2, 3/2 transitions) and ω L2 (resonant to the nP 1/2, 3/2-(n+2)S 1/2 transitions) through alkali-metal vapors are presented. Characteristics of the magneto-optical rotation spectra at each of the frequencies are strongly affected by the second intense radiation field resonant to the adjacent transition. When the atoms interact with two strong light waves, resonant to adjacent transitions, and with a magnetic field, the shape of the Faraday rotation spectra depends on the energy shifts of the atomic states that arise due to the dynamic Stark effect and the Zeeman effect (the Paschen-Back or an intermediate-type effect), as well as due to the difference of populations of these states caused by the interaction of the atoms with the fields. The results obtained show that in the frequency selection method, based on the resonance Faraday effect, the frequency of the generated narrow-band beam can be tuned by the intensity of the strong wave, resonant to the transition between the excited states. 相似文献