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21.
We find that the optical properties of carbon nanotubes reflect remarkably strong effects of exciton-phonon coupling. Tight-binding calculations show that a significant fraction of the spectral weight of the absorption peak is transferred to a distinct exciton+phonon sideband, which is peaked at around 200 meV above the main absorption peak. This sideband provides a distinctive signature of the excitonic character of the optical transition. The exciton-phonon coupling is reflected in a dynamical structural distortion, which contributes a binding energy of up to 100 meV. The distortion is surprisingly long ranged, and is strongly dependent on chirality. 相似文献
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M. Vasilić 《General Relativity and Gravitation》2002,34(9):1383-1391
In Kaluza-Klein geometric sigma models, the scalar fields coupled to higher-dimensional gravity are pure gauge. The gauge fixed theory contains no matter fields, and can consistently be reduced to 4 dimensions, provided the internal space is chosen in the form of a group manifold. The effective 4-dimensional theory includes standard Einstein and Yang-Mills sectors, and is free of the classical cosmological constant problem. In this paper, the stability of the internal excitations is analyzed. It is shown that the initial Lagrangian can be modified to lead to a classically stable effective 4-dimensional theory, independently of the particular group used, and retaining all the basic features of the unmodified theory. 相似文献
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M. Petkovi?S. Stojadinovi? R. Vasili?I. Bel?a Z. Nedi?B. Kasalica U.B. Mio? 《Applied Surface Science》2011,257(22):9555-9561
The growth of silicate tungsten bronzes on aluminum by plasma electrolytic oxidation in 12-tungstosilicic acid is experimentally investigated and discussed. Real time imaging and optical emission spectroscopy characterization of plasma electrolytic oxidation show that spatial density of microdischarges is the highest in the early stage of the process, while the percentage of oxide coating area covered by active discharge sites decreases slowly with time. Emission spectrum of microdischarges has several intensive band peaks originating either from aluminum electrode or from the electrolyte. Surface roughness of obtained oxide coatings increases with prolonged time of plasma electrolytic oxidation, as their microhardness decreases. Raman spectroscopy and energy dispersive X-ray spectroscopy are employed to confirm that the outer layer of oxide coatings formed during the plasma electrolytic oxidation process is silicate tungsten bronzes. 相似文献
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Two-sample (Allan) variance with a modified algorithm was applied to the determination of the experimental linewidth of a thermoelectrically-cooled continuous-wave distributed feedback quantum cascade laser at a wavelength of 4.333 μm. From successive laser transmittance scans over the CO2 ν3, (0111 − 0110) P(33) absorption line at 2307.653 cm− 1, two-sample variances were calculated for the laser frequency difference between different points on the sides of the absorption peak. From the minimum two-sample variance of the laser frequency difference between two adjacent points (5 μs between the points) on the same side of the absorption line the experimental laser linewidth was estimated to be less than 36(7) kHz at a laser power of ~ 25 mW, a laser current of 976 mA and a laser temperature of + 19.5 °C. 相似文献
25.
Oxide coatings were formed on tantalum by plasma electrolytic oxidation (PEO) process in 12-tungstosilicic acid. The PEO process can be divided into three stages with respect to change of the voltage-time response. The contribution of electron current density in total current density during anodization results in the transformation of the slope of voltage-time curve. The surface morphology, chemical and phase composition of oxide coatings were investigated by AFM, SEM-EDX, XRD and Raman spectroscopy. Oxide coating morphology is strongly dependent of PEO time. The elemental components of PEO coatings are Ta, O, Si and W. The oxide coatings are partly crystallized and mainly composed of WO3, Ta2O5 and SiO2. Raman spectroscopy showed that the outer layer of oxide coatings formed during the PEO process is silicate tungsten bronze. 相似文献
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Shekurov R. P. Gilmanova L. H. Zagidullin A. A. Miluykov V. A. 《Russian Chemical Bulletin》2021,70(7):1415-1417
Russian Chemical Bulletin - Racemic 2-[1-(dimethylamino)ethyl]ferrocenylphosphinic acid was tested as an organocatalyst in the Michael and Friedel—Crafts reactions. The use of this zwitterion... 相似文献
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R. P. Shekurov D. R. Islamov D. B. Krivolapov V. A. Miluykov O. N. Kataeva T. P. Gerasimova S. A. Katsyuba O. G. Sinyashin 《Russian Chemical Bulletin》2015,64(8):1819-1822
The previously unknown isomorphous tris{µ2-[1,1´-ferrocenediylbis(phenylphosphinato)]}-iron(iii) complexes as solvates with methanol and DMSO were synthesized and characterized. 相似文献
30.
A laser spectrometer based on a continuous-wave thermoelectrically-cooled distributed feedback quantum cascade laser at ∼2308 cm−1 has been evaluated for measurement of 13CO2/12CO2 isotopic ratio (δ13C) changes in exhaled breath samples and in CO2 gas flows in the concentration range 1-5%. Mid-infrared CO2 absorption spectra were measured in a 54.2-cm long optical cell using balanced detection whereby the beam passing through the cell was ratioed against a reference beam split-off from the main beam before the cell. Signal-to-noise ratios (SNR) were estimated for CO2 concentration measurements determined from either absorption peak amplitude or absorption peak area. The highest SNR were achieved in the measurements based upon a fitted absorption peak area. Typical short-term δ13C precisions of 1.10/00 (1-s integration time) and 0.50/00 (8-12-s integration time) were estimated from the two-sample (Allan) variance plots of data recorded in the optical cell at a pressure of 20 Torr and with no active temperature stabilization of the cell and gas flow. The best precision of 0.120/00 was achieved for averaging 80 successive 1-s integration time measurements. 相似文献