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91.
Perturbation differential equations of motion of a general nonholonomic system subjected to the ideal nonholonomic constraints of Chetaev's type are established, and the equation of variation of energy is deduced by using the perturbation equations of the system. A criterion of the stability is obtained and an example is given to illustrate the application of the result. 相似文献
92.
We investigate the linearization of systems of n-component nonlinear diffusion equations; such systems have physical applications in soil science, mathematical biology and invariant curve flows. Equivalence transformations of their auxiliary systems are used to identify the systems that can be linearized. We also provide several examples of systems with two-component equations, and show how to linearize them by nonlocal mappings. 相似文献
93.
We report the long time dynamical behaviour of ac Stark effect in a simple quantum model in which two level atoms interact with quantized coherent radiation field. A new phenomenon of periodic quantum collapse and revival of the ac Stark shift of energy level due to ac Stark effect is expressed accurately by analysing the phase of transition probability amplitude. The analytic prediction is confirmed by the numerical results. 相似文献
94.
The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation (GGA) as well as the on-site Coulomb interaction correction (+U). The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor. 相似文献
95.
At 4.2-350 K, the steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics were studied under excitation in the 2.5-15 eV energy range for the undoped and Ce3+-doped Lu3Al5O12 (LuAG) single-crystalline films grown by liquid phase epitaxy method from the PbO-based flux. The spectral bands arising from the single Pb2+-based centres were identified. The processes of energy transfer from the host lattice to Pb2+ and Ce3+ ions and from Pb2+ to Ce3+ ions were investigated. Competition between Pb2+ and Ce3+ ions in the processes of energy transfer from the LuAG crystal lattice was evidenced especially in the exciton absorption region. Due to overlap of the 3.61 eV emission band of Pb2+ centres with the 3.6 eV absorption band of Ce3+ centres, an effective nonradiative energy transfer from Pb2+ ions to Ce3+ ions takes place, resulting in the appearance of slower component in the luminescence decay kinetics of Ce3+ centres and decrease of the Ce3+-related luminescence intensity. 相似文献
96.
Thin tris(acetylacetonato)iron(III) films were prepared by sublimation in vacuum on glass and p-Si substrates. Then comprehensive studies of X-ray fluorescence (XRF), X-ray diffraction (XRD), optical absorption spectroscopy, AC-conductivity, and dielectric permittivity as a function of frequency and temperature have been performed. The prepared films show a polycrystalline of orthorhombic structure. The optical absorption spectrum of the film was identical with that of the bulk powder layer. For electrical measurements of the complex as insulator, sample in form of metal-insulator-semiconductor (MIS) structure was prepared and characterised by the measurement of the capacitance and AC-conductance as a function of gate voltage. From those measurements, the state density Dit at insulator/semiconductor interface and the density of the fixed charges in the complex film were determined. It was found that Dit was of order 1010 eV−1/cm2 and the surface charge density in the insulator film was of order 1010 cm−2. The frequency dependence of the electrical conductivity and dielectric properties of MIS structures were studied at room temperature. It was observed that the experimental data follow the correlated barrier-hopping (CBH) model, from which the fundamental absorption edge, the cut off hopping distance, and other parameters of the model were determined. It was found that the capacitance of the complex increases as temperature increases. Generally, the present study shows that the tris(acetylacetonato)iron(III) films grown on p-Si is a promising candidate for low-k dielectric applications, it displays low-k value around 2.0. 相似文献
97.
Four kinds of silica-gel supported diethylenetriamine adsorbents with different structures were prepared by so-called heterogeneous-direct-amination, homogeneous-direct-amination, heterogeneous end-group protection and homogeneous end-group protection methods, respectively. Our objective was to use a novel strategy of end-group protection to prepare the adsorbents with high adsorption capacities for metal ions. The structures of the resulting adsorbents were characterized by infrared spectroscopy (FT-IR), porous structure analysis and elemental analysis. Hg(II), Cu(II), Ni(II) and Pb(II) were chosen as representatives to assess their adsorption capability and the utilization ratio of N. The experimental results indicated that the adsorbents prepared by heterogeneous end-group protection and homogeneous end-group protection methods possessed lower contents of diethylenetriamine (DETA), while their adsorption capacities and the utilization ratios of N were much higher than the corresponding counterparts prepared by heterogeneous-direct-amination and homogeneous-direct-amination methods. The end-group protection method exhibited its advantage in preparation of effective adsorbent for metal ions uptake compared to the direct-amination method. 相似文献
98.
M. Donath 《Applied Physics A: Materials Science & Processing》1989,49(4):351-364
Inverse photoemission (IPE) with spin-polarized electrons provides a way to measure separately the exchange-split majority and minority bands in ferromagnets above the Fermi level. Consequently spin-resolved IPE turns out to be an outstanding technique for obtaining information on surface magnetism: the magnetization of the topmost atomic layer may be investigated by measuring the exchange splitting of electronic states that are localized within the surface layer. Theoretical models of ferromagnetism may be tested by observing the temperature behavior of bands which contribute to the ferromagnetism of the material. The magnetic coupling of an adsorbate to the ferromagnetic substrate may be studied by probing adsorbate-induced bands. Results for the Ni(110) surface serve as an illustration to discuss the status of spin-resolved IPE and its application to the field of surface magnetism. 相似文献
99.
M. Marcellini B. Hjörvarsson G. Nowak 《Journal of magnetism and magnetic materials》2009,321(9):1214-1220
The relation between the interlayer exchange coupling and magnetic order is addressed, using Fe/V(0 0 1) superlattices as a model system. Large decrease in the ordering temperature (Tc) is observed with decreasing interlayer exchange coupling. The effective exponents of the magnetization were determined to be larger than 0.5 for all the samples, which is strongly deviating from the classical values of both two- and three-dimensional systems. This effect can partially be ascribed to the presence of boundaries, invoked by the finite number of magnetic layers. 相似文献
100.
T. Kawahara M. Miyazaki A. Kimura Y. Okamoto J. Morimoto T. Miyakawa 《Applied Physics A: Materials Science & Processing》1999,69(3):343-346
The noncontact imaging of the buried structures is carried out in the open-air atmosphere by using the photothermal deflection
(PTD) method. We applied these techniques to the layered samples. Besides the PTD images for the optically opaque buried structures,
the parameters of the materials such as thermal diffusivity can also be calculated from the PTD amplitude and phase signal
in the PTD scanning images. When the PTD signals at two different modulation frequencies are used, the thermal diffusivity
of the buried structure can be obtained from the PTD signal outside of the sample nondestructively.
Received: 27 November 1998 / Accepted: 18 March 1999 / Published online: 7 July 1999 相似文献