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21.
The application of micro-Raman spectroscopy is discussed for the analysis of structural features of human tooth tissues affected by high doses of external ionizing radiation (0.5–1.7 Gy) after the nuclear plant catastrophe in Chernobyl in 1986. The results have shown significant changes in the mineral matrix of dental enamel that lead to the decrease of tooth enamel hardness. Destruction of the collagen chain of the organic matrix has been observed for dentin and cementum. 相似文献
22.
Since 1989, AFMs have been used to map the nanomechanical properties of surfaces using measurements such as force-distance curves. Quantification of the force and elastic parameters are critical to the nanomechanical analysis and positive identification of materials at the nanoscale, as well as for assessing behaviour at surfaces. In recent years, there have been AFM papers publishing “quantitative” values for the indentation modulus, however, many involved large uncertainties arising from the lack of calibration of key components, the use of manufacturers’ nominal values for these components or the use of incorrect models. This paper addresses the quantification issues in modulus measurement at surfaces for homogeneous materials using force-distance curves and how to do this with sufficient accuracy to identify materials at the nanoscale. We review the available theory and describe two routes to quantitative modulus measurement using both the AFM on its own and the AFM combined with a nanoindenter. The first involves the direct measurement of modulus using a fully calibrated instrument and allows depth analysis. The second uses indirect measurement through calibration by reference materials of known reduced modulus. For depth analysis by this second route, these reference moduli need to be known as a function of depth. We show that, using the second route, an unknown polymer may be analysed using the nanoindenter, its modulus determined and, providing the moduli of the polymers to be identified or distinguished differ by more than 20%, identified with 95% confidence. We recommend that users evaluate a set of reference samples using a traceable nanoindenter via the first route, and then use these to calibrate the AFM by the second route for identification of nano-regions using the AFM. 相似文献
23.
The fractal dimensions of six differently mechanically pre-treated stainless steel samples were investigated using five fractal
algorithms. The surfaces were analyzed using a profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM)
and light microscopy (LM), and thereafter adhesively bonded and tested in single-overlap joints to test their tensile strength.
All samples showed different fractal behavior, depending on the microscopic methods and fractal algorithms. However, the overall
relation between fractal dimension and tensile strength is qualitatively the same, except for the SEM images. This verifies
that tensile strength is correlated to fractal dimension, although only within the length-scale of the profiler and the light
microscope (≈0.5–100 μm). The AFM method was excluded in this comparison, since the limitation in the z-direction for the
AFM scanner made it difficult to scan the rougher parts of the blasted samples. The magnitude of the surfaces is a parameter
not often considered in fractal analysis. It is shown that the magnitude, for the Fourier method, is correlated to the arithmetic
average difference, Ra, but only weakly to the fractal dimension. Hence, traditional parameters, such as Ra, tell us very little about the spatial distribution of the elevation data.
Received: 22 December 1999 / Accepted: 9 October 2000 / Published online: 9 February 2001 相似文献
24.
Kostya Trachenko 《Journal of Non》2008,354(32):3903-3906
We propose that the origin of the Vogel-Fulcher-Tammann law is the increase of the range of elastic interaction between local relaxation events in a liquid. In this picture, we discuss the origin of cooperativity of relaxation, the absence of divergence of relaxation time at a finite temperature and the crossover to a more Arrhenius behavior at low temperature. 相似文献
25.
W. Rohrbeck E. Chilla H.-J. Fröhlich J. Riedel 《Applied Physics A: Materials Science & Processing》1991,52(5):344-347
A new method for the investigation of ultrasonic waves on surfaces of solids based on scanning tunneling microscopy is presented. A sinusoidal high frequency signal is added to the tip voltage. Hence the tunneling current contains a component whose frequency is the difference of the frequencies of the acoustic wave field and the ac tip voltage. Amplitude and phase of this component carry the full information about the wave field. 相似文献
26.
Method of frustrated total reflection in spectroscopy of surface polaritons in almost perfectly conducting metals 总被引:1,自引:0,他引:1
The standard technique for surface polaritons excitation by a prism coupling in Otto configuration is applied for investigation of almost perfectly conducting (pec) metals like tantalum irradiated by a collimated He-Ne laser radiation (λ 0 = 632.8 nm). In pec metals the imaginary part of the relative dielectric permittivity (ɛ″) is quite larger than the modulus of the real part of the same quantity (ɛ′ < 0, ɛ″ ≫ | ɛ′ |). Under this condition the single Lorentz dip of the reflectivity coefficient is proven to exist and is given in an analytical form, which follows from simplification of the usual multilayer Fresnel formula. In the case of a deterministically curved metal surface an approximate solution to the reduced Rayleigh integral equation appropriate for the Otto configuration is also given. These two theoretical deductions are compared with experimental data that have been produced by us for the reflectivity into the prism region from a bulk tantalum sample. 相似文献
27.
We investigate a life time broadened and coherently prepared five-state system for multi-wave mixing processes. We show that very efficient wave mixing occurs, producing an unconventional mixing wave that has the characteristics of both conventional four-wave mixing (FWM) and stimulated hyper-Raman (SHR) emission. In addition, we show interesting multiple simultaneous multi-photon interference effects at large propagation distances and demonstrate more than 10 orders of magnitude suppression of populations of the probe wave terminal state and the near three-photon resonance mixing wave generating state. These new type of multi-photon interference based induced transparency effects, which are critically dependent on two distinctive relaxation processes involving both an external supplied and an internally generated fields, are fundamentally different from the conventional three-state electromagnetically induced transparency effect which does not depend on propagation. As a consequence, both the probe and the wave-mixing field to propagate nearly free of absorption and distortions in a highly dispersive medium. 相似文献
28.
29.
Semiclassical expansions derived in the framework of the Extended Thomas-Fermi approach for the kinetic energy density τ(
r) and the spin-orbit density
J(
r) as functions of the local density ρ(
r) are used to determine the central nuclear potentials V
n(
r) and V
p(
r) of the neutron and proton distribution for effective interactions of the Skyrme type. We demonstrate that the convergence
of the resulting semiclassical expansions for these potentials is fast and that they reproduce quite accurately the corresponding
Hartree-Fock average fields.
Received: 12 February 2000 / Accepted: 14 March 2002 相似文献
30.
V. G. Veselago 《Applied physics. B, Lasers and optics》2005,81(2-3):403-407
In the following article some electrodynamical problems of materials with negative refraction are considered. In contrast to the usual case when the index of refraction is positive, for these sorts of materials many laws and equations must be recorded differently. Special note is taken of the fact that most of the books and textbooks are written with the so-called “nonmagnetic approach”, which is only valid for nonmagnetic materials (μ = 1). This approach is undoubtedly unfit for material with a negative index of refraction.It is shown that materials with simultaneously negative dielectric and magnetic permeabilities undoubtedly must possess the frequency dispersion. Correlation is brought between phase and group velocities for these sorts of materials.The question is considered in detail about the so-called “overcoming of the diffraction limit” by means of plates from materials with a negative factor of refraction. It is shown that this effect is indeed reduced to the problem of matching between source and receiver of radiation. Such matching is possible by spreading the so-called evanescent modes, for which a diffraction limit does not exist. These modes fade within a distance of the order of the wavelength, and only at such a distance is the transfer of picture details that are smaller than the wavelength possible. 相似文献