共查询到20条相似文献,搜索用时 31 毫秒
1.
Nguyen Phu Xuan Jean-Louis Ferrier José Gazengel Geneviève Rivoire 《Optics Communications》1984,51(6):433-437
Single frequency Jamin interferometry is used for observation of non-linear susceptibility tensor measurements in the picosecond range (25 ps). At low density, when avoiding the polarization state instabilities, the displacement of the fringes leads to the measurement of two components of the nonlinear susceptibility tensor. It is shown that Xxyyx (ω = ω + ω - ω) decreases when the pulse duration is reduced, whereas Xxxxx (ω = ω + ω - ω) remains constant. This is interpreted by the difference between the orientational and vibrational molecular contributions. 相似文献
2.
The excitation profile of ordinary Raman scattering under steady-state excitation conditions and the time-resolved emission spectrum of ordinary Raman scattering under transient excitation conditions undergo considerable changes when the excitation frequency ω approaches ωmn, where ωmn is the resonance frequency of a two-photon transition from the ground state |n to an excited state |m of a molecule. The appearance of ghost peaks, dips or dispersion-like features centred at ω ? ωmn in the excitation profile and of coherence effects such as Rabi nutations with unusual time-dependence in the time-resolved spectrum are predicted. 相似文献
3.
Further experiments in doped InSb are reported on the anomalous NMR relaxation peak, the B-peak, first reported by Bridges and Clark. Data on the peak now extends up to donor concentrations of 8 × 1021 m?3 and permits a sharp reduction in the number of possible explanations of the peak which remain plausible.The peak occurs well above the critical field required for magnetic freeze-out, and appears to follow a dependence of magnetic field at the peak, BB, against density, nD, of BB ∝ n0.60±0.01D at constant temperature. The possibility that the peak is due to the tuning of the ESR frequency through the typical electron hopping frequency ωH in the crystal is explored; a consequence of this model is that ωH must be dominated by nearest-neighbour hops, involving only a very small minority of the donor centres. 相似文献
4.
A universal mechanism of the Boson peak formation in glasses is proposed. The mechanism is based on the concept of interacting quasilocal oscillators. Even in the case of weak interaction, the low-frequency spectrum becomes unstable. Due to anharmonicity, the system undergoes a transition into a new stable configuration. As a result, below some characteristic frequency ωc, proportional to the typical strength of interaction, the renormalized density of states becomes a universal function of ω with a Boson peak feature; i.e., the reduced density of states g(ω)/ω2 has a maximum at a frequency ωb?ωc. We derive an analytic form of this function. 相似文献
5.
In this paper, the dispersion characteristics of a plasma filled elliptical Bragg waveguide is investigated. The modal characteristic equations of the proposed Bragg waveguide for both ω > ωp and ω < ωp are derived. The effects of plasma frequency, numbers of cladding layers and the eccentricity of elliptical Bragg waveguide on the dispersion characteristics are studied. The analysis shows that the introduction of plasma in the proposed waveguide allows to control the propagation of modes. 相似文献
6.
B. Wende 《Zeitschrift für Physik A Hadrons and Nuclei》1967,206(1):1-17
Optical pumping on Cs133 atoms was performed by means of a new transmission technique. The cesium vapor was pumped towards equilibrium by an intensive circulary polarizedD 1 orD 2 light beam. A weakD 1 detecting beam was polarized alternately σ+, σ? and allowed one to measure continuously amount and sign of the absorption difference between σ+ and σ? light. The measured signals are proportional to the electron spin polarization. The new technique was used to investigate the influence of Cs buffer gas collisions on the pumping cycle and to measure the influence of radio frequency induced Zeeman transitions on the ground state polarization. In addition the variation of magnetic field and of pumping light intensity and polarization was studied. Some measurements demonstrate the high sensitivity of the applied method. The obtained qualitative results are discussed and further experiments are proposed. 相似文献
7.
M. Moresco 《Physics letters. A》1973,45(1):65-67
Measurements of k⊥ for an extraordinary wave near the lower hybrid frequency have been carried out by means of propagation between two dipole antennas into a plasma column. Resonance-like behavior have been observed when plasma parameters and frequency fulfil the condition ω ≈ ωLH. 相似文献
8.
It is previously found that the two-dimensional (2D) electron-pair in a homogeneous magnetic field has a set of exact solutions
for a denumerably infinite set of magnetic fields. Here we demonstrate that as a function of magnetic field a band-like structure
of energy associated with the exact pair states exists. A direct and simple connection between the pair states and the quantum
Hall effect is revealed by the band-like structure of the hydrogen “pseudo-atom”. From such a connection one can predict the
sites and widths of the integral and fractional quantum Hall plateaus for an electron gas in a GaAs-Al
x
Ga1−x
As heterojunction. The results are in good agreement with the existing experimental data. 相似文献
9.
Frequency dependence of the real part of the conductivity σ1(ω) in the region of the transition from almost linear (s < 1) to quadratic (s ≈ 2) can indicate a change in the conduction mechanism (the transition from the variable-range to the fixed-range hopping with increasing frequency); in this case, the sharpness of the change in the slope of the frequency characteristic is related to the dependence of the preexponential factor of the resonance integral on the intercenter distance in the pair. The frequency dependence of the imaginary part of the conductivity σ2(ω) has no kink in the vicinity of the transition frequency ωcr, remaining almost linear. A large dielectric loss angle |cotγ| = |σ2|/σ1 can indicate that the imaginary part of the conductivity at ω < ωcr is defined by the larger zero-phonon contribution in σ2res the region of weak variation in the loss angle γ(ω), which significantly exceeds the relaxation contribution σ2res. 相似文献
10.
《Superlattices and Microstructures》2001,29(2):99-104
Quantum wire superlattices (1D) realized by controlled dislocation slipping in quantum well superlattices (2D) (atomic saw method) have already shown Magneto-phonon oscillations. This effect has been used to investigate the electronic properties of such systems and prove the quantum character of the physical properties of the wires. By cooling the temperature and using pulsed magnetic field up to 35 T, we have observed both quantum Hall effect (QHE) and Shubnikov–de Haas (SdH) oscillations for various configurations of the magnetic field. The effective masses deduced from the values of the fundamental fields are coherent with those obtained with Magneto-phonon effect. The field rotation induces a change in the resonance frequencies due to the modification of the mass tensor as in a (3D) electron gas. In view the QHE, the plateaus observed in ρYZare dephased relatively toρZZ minima which seems to be linked to the dephasing of the minima of the density of states of the broadened Landau levels. 相似文献
11.
Spatial nonlocality (dispersion) of transport equations leads to a nonlinear dependence of the voltage drop U on the distance between the points of voltage measurement. For this reason, the results of conventional two-probe measurements of conductivity substantially depend on the relationship between the linear dimensions of the sample L and the characteristic length of spatial dispersion R of the generalized diffusion coefficient D(q, ω). This makes it possible to obtain information on the character of spatial nonlocality of D(q, ω) in the vicinity of the Anderson transition and, in particular, on the magnitude of the correlation multifractal dimension D2 of electron wave functions near the mobility edge. 相似文献
12.
M. E. Gushchin S. V. Korobkov A. V. Kostrov A. V. Strikovsky 《Journal of Experimental and Theoretical Physics》2004,99(5):978-986
We present the results of our experiments in which the propagation of whistler waves in a plasma with a nonstationary magnetic-field perturbation (B=B0+δB(t), δB/B0 ≤ 5%) was investigated. The parametric and dispersive phenomena in a variable magnetic field were studied on the unique Krot plasma bench (the plasma column was 4 m in length and 1.5 m in diameter). A periodic field perturbation is shown to lead to an amplitude-frequency modulation of the whistler wave and to fragmentation of the signal into separate frequency-modulated wavepackets followed by their compression. The formation and compression of pulses is attributable to strong whistler group-velocity dispersion near the electron cyclotron frequency (ω ≤ ωH). The results can be used to interpret the spectral shapes of the signals received from the Earth’s magnetosphere and ionosphere in the electron and ion whistler frequency ranges. 相似文献
13.
Seung-Man Yu Sae-Sark Kim Mun-Young Paek Eun-Hoe Goo Youn-Sang Ji Bo-Young Choe 《Applied magnetic resonance》2013,44(7):791-801
Fat accumulates as droplets in the hepatocyte swelling, distortion of microcirculatory anatomy and compression of sinus. This study aims to investigate the correlation between the T2*-corrected fat fraction (FF) value acquired via gradient echo with a low flip angle and parenchymal pseudorandom blood perfusion (P fraction), microcirculation (D fast), and slow component of diffusion (D slow), acquired via intravoxel incoherent motion (IVIM), and to investigate the blood microcirculation and diffusion components of liver parenchyma, according to fat deposition. A total of 126 patients underwent 3-T magnetic resonance imaging, including a 3-echo three-dimensional (3-D) gradient echo sequence with T2*-corrected Dixon reconstruction and IVIM sequence. Pearson’s correlation analysis was conducted to investigate the correlation of the FF obtained via the Dixon method with the apparent diffusion coefficient (ADC), D slow, P fraction, and D fast obtained via IVIM. Correlation analysis was also conducted for the IVIM mapping images. A confidence level of p < 0.05 was set. A negative correlation was found between the T2*-corrected FF acquired using the 3-echo 3-D Dixon method and D slow acquired via IVIM (r = ?0.181, p < 0.05). It was likely due to the increased extracellular collagen deposition and increased intracellular fat droplets during the progression of liver fibrosis. 相似文献
14.
I. O. Bashkin V. V. Shestakov M. K. Sakharov V. K. Fedotov E. G. Ponyatovskiĭ 《Physics of the Solid State》2008,50(7):1337-1341
Phase separation in the hexagonal ω modification of the Ti-Zr system was observed. The ω → ω1 + ω2 decomposition in an equiatomic TiZr alloy after prolonged thermal treatment at P = 5.5 ± 0.6 GPa and T = 440 ± 30°C was revealed using x-ray diffraction. It is found that the concentration dependence of the specific volume of the ω phase of Ti-Zr alloys deviates from the Vegard law to higher values. An isobaric section of the equilibrium P-T-x phase diagram of the Ti-Zr system is shown to have the shape of an eutectoid diagram at pressures higher than 8 GPa. 相似文献
15.
Solutions to the pion dispersion equation in the complex plane of the pion frequency ω are obtained for symmetric nuclear matter. Three well-known solution branches—a sound, a pion, and an isobar one—exist on the physical sheet at the medium density below its critical value (ρ<ρc). For ρ>ρc, the fourth branch ωc appears on the physical sheet. The condition ω c 2 ≤0 is valid for this branch (in general, Re ω c 2 ≤0). This suggests ground-state instability, possibly associated with pion condensation. The behavior of these solutions is analyzed for various medium densities. The appearance of each solution on the physical sheet of the complex frequency plane and its disappearance are also studied. 相似文献
16.
We have previously calculated the Faraday rotation θ and ellipticity δ due to the two-dimensional electron gas at the oxide-semiconductor interface of a metal-oxide-semiconductor system. The results depend on such parameters of the system as the effective mass m1, the relaxation time τ, and the electron surface concentration N, and in fact the motivation is to enable one to determine such parameters from measurements of θ and δ. Here we discuss the optimum method for the determination of these parameters from the data. In particular, we argue that it is more desirable to carry out measurements at fixed magnetic field B and variable photon frequency ω, rather than at fixed ω and variable B. We also demonstrate how our analysis can be used to determine the predicted dependence of τ on magnetic field, without explicit knowledge of m1 or N. 相似文献
17.
B. Wannberg G. Engdahl A. Sköllermo 《Journal of Electron Spectroscopy and Related Phenomena》1976,9(2):111-127
Numerical values of the second-order aberration coefficients are given for two classes of toroidal fields, namely (1) the “quasi-spherical” field with c = 1, c′ ≠ ? 1, and (2) fields with c in the region 1.6–1.8. For the “quasi-spherical” fields, the second-order coefficients are given as functions of the deflection angles ω for 90° ≤ ω ≤ 180°. The third-order coefficients for the spherical field are given in the same region.For the devices in the second class, which have one intermediary axial image, the second-order coefficients are studied as functions of c and ω, subject to the condition that double-focussing should be obtained. The conditions under which the radial and axial image planes coincide are considered. The influence of axially curved entrance and exit surfaces is investigated. One special case (ω = 180°, c = 1.691, c′= ? 1.11), which may be favourable for an electron monochromator is discussed. 相似文献
18.
We determine and study the ground states of a focusing Schrödinger equation in dimension one with a power nonlinearity |ψ|2μ ψ and a strong inhomogeneity represented by a singular point perturbation, the so-called (attractive) δ′ interaction, located at the origin. The time-dependent problem turns out to be globally well posed in the subcritical regime, and locally well posed in the supercritical and critical regime in the appropriate energy space. The set of the (nonlinear) ground states is completely determined. For any value of the nonlinearity power, it exhibits a symmetry breaking bifurcation structure as a function of the frequency (i.e., the nonlinear eigenvalue) ω. More precisely, there exists a critical value ω* of the nonlinear eigenvalue ω, such that: if ω0 < ω < ω*, then there is a single ground state and it is an odd function; if ω > ω* then there exist two non-symmetric ground states. We prove that before bifurcation (i.e., for ω < ω*) and for any subcritical power, every ground state is orbitally stable. After bifurcation (ω = ω* + 0), ground states are stable if μ does not exceed a value ${\mu^\star}$ that lies between 2 and 2.5, and become unstable for μ > μ*. Finally, for μ > 2 and ${\omega \gg \omega^*}$ , all ground states are unstable. The branch of odd ground states for ω < ω* can be continued at any ω > ω*, obtaining a family of orbitally unstable stationary states. Existence of ground states is proved by variational techniques, and the stability properties of stationary states are investigated by means of the Grillakis-Shatah-Strauss framework, where some non-standard techniques have to be used to establish the needed properties of linearization operators. 相似文献
19.
Experiments on the propagation of TG-modes in a weakly inhomogeneous plasma are reported. The modes travel from the high density part (ω < ωpe) to that of lower density (ω > ωpe). The wavelength decreases as expected but an increase of the longitudinal fieldstrength predicted by collisionless theory could not be observed. Two nonlinear effects appear one after another with increasing wave amplitude. These are the sideband instability and a decay into the drift frequency range occuring in the whole plasma column. Neither the region ω ≈ ωpe nor the very vicinity of the exciter antenna are distinguished. The second instability is accompanied by effective electron heating. 相似文献
20.
Two three-dimensional models exhibiting coexistence of superconductivity and lattice distortion are discussed. One of the models, studied in detail by Rusinov, Do Chan Kat and Kopayev, takes into account the superconductivity inter- and intra-band pairing phenomenologically. The other has been derived by Mattis and Langer from a Fröhlich-type hamiltonian by eliminating the linear electron-phonon coupling in the presence of a “condensing” phonon mode. Both approaches are shown to agree in the limit ωD å μ, where ωD is the cut-off energy and ω is the deviation of the chemical potential from the band centre. 相似文献