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41.
The axion–photon system in an external magnetic field, when the direction of propagation of axions and photons is orthogonal to the direction of the external magnetic field, displays a continuous axion–photon duality symmetry in the limit the axion mass is neglected. The conservation law that follow in this effective (2+1)-dimensional theory from this symmetry is obtained. The magnetic field interaction is seen to be equivalent to first order to the interaction of a complex charged field with an external electric potential, where this fictitious “electric potential” is proportional to the external magnetic field. This allows one to solve for the scattering amplitudes using already known scalar QED results. From the scalar QED analog the axion and the photon are symmetric and antisymmetric combinations of particle and antiparticle. If one considers therefore scattering experiments in which the two spatial dimensions of the effective theory are involved nontrivially, one observes that both particle and antiparticle components of photons and axions are preferentially scattered in different directions, thus producing the splitting or decomposition of the photon and axion into their particle and antiparticle components in an inhomogeneous magnetic field. This observable in principle effect is of first order in the axion–photon coupling, unlike the “light shining through a wall phenomena”, which is second order. 相似文献
42.
We study a new scenario for baryogenesis due to the spontaneous breaking of the CPT invariance through the interaction between a baryon current and a hypermagnetic helicity. The hypermagnetic helicity (Chern–Simons number) of UY(1) provides a CPT violation background for the generation of baryons via sphaleron processes, which protects these baryons from the sphaleron wash-out effect in thermal equilibrium. It is shown that if the present amplitude of the resultant magnetic fields are sufficiently large, for a wide range mass scale (from TeV to the Planck scale), the observational magnitude of the baryon asymmetry of the Universe can be realized. 相似文献
43.
In this paper, we present the spectral results of Dy3+ and Pr3+ (1.0 mol%) ions doped Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (Tg), crystallization (Tc) and melting (Tm) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy3+:glass has shown two emission transitions 4F7/2→6H15/2 (482 nm) and 4F7/2→6H13/2 (576 nm) with an excitation at 390 nm wavelength and Pr3+:glass has shown a strong emission transition 1D2→3H4 (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy3+ and Pr3+ glasses have shown bright yellow and reddish colors, respectively, from their surfaces. 相似文献
44.
M.S. Al-Assiri 《Physica B: Condensed Matter》2008,403(17):2684-2689
Characterization and electrical properties of vanadium-copper-phosphate glasses of compositions xV2O5-(40−x)CuO-60P2O5 have been reported. X-ray diffraction (XRD) confirms the amorphous nature of these glasses. It was observed that, the density (d) decreases gradually while the molar volume (Vm) increases with the increase of the vanadium oxide content in such glasses. This may be due to the effect of the polarizing power strength, PPS, which is a measure of ratio of the cation valance to its diameter. The dc conductivity increases while the activation energy decreases with the increase of the V2O5 content. The dc conductivity in the present glasses is electronic and depends strongly upon the average distance, R, between the vanadium ions. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. 相似文献
45.
Atsushi Goto Tadashi Shimizu Kenjiro Hashi Shinobu Ohki 《Applied Physics A: Materials Science & Processing》2008,93(2):533-536
We present a scheme of surface-sensitive nuclear magnetic resonance in optically pumped semiconductors, where an NMR signal from a part of the surface of a bulk compound semiconductor is detected
apart from the bulk signal. It utilizes optically oriented nuclei with a long spin-lattice relaxation time as a polarization
reservoir for the second (target) nuclei to be detected. It provides a basis for the nuclear spin polarizer [IEEE Trans. Appl. Supercond. 14:1635, 2004], which is a polarization reservoir at the surface of the optically pumped semiconductor that polarizes nuclear spins in
a target material in contact through the nanostructured interfaces. 相似文献
46.
Raman spectroscopy has been used to measure the fraction of tetrahedral silicate units connected at three corners into the network (Q3) in binary lithium silicate glasses and also in the more complex borosilicate glasses used for waste immobilization. Agreement within experimental error was obtained with 29Si MAS NMR measurements of the same samples. Raman provides an alternative method of structural determination for silicon-containing glasses with a high content of paramagnetic species where NMR loses resolution. Analysis was performed on borosilicate glasses containing up to 11.98 mol% Fe2O3 and the Q3 values obtained by Raman spectroscopy agree within error with the published 29Si NMR results from borosilicate glasses containing the equivalent quantity of Al2O3. 相似文献
47.
Using X-ray diffraction and differential scanning calorimetry (DSC), the structure and the crystallization mechanism of Se0.8Te0.2 chalcogenide glass has been studied. The structure of the crystalline phase has been refined using the Rietveld technique. The crystal structure is hexagonal with lattice parameter a = 0.443 nm and c = 0.511 nm. The average crystallite size obtained using Scherrer equation is equal 16.2 nm, so it lies in the nano-range. From the radial distribution function, the short range order (SRO) of the amorphous phase has been discussed. The structure unit of the SRO is regular tetrahedron with (r2/r1) = 1.61. The Se0.8Te0.2 glassy sample obeys the chemical order network model, CONM. Some amorphous structural parameters have been deduced. The crystallization mechanism of the amorphous phase is one-dimensional growth. The calculated value of the glass transition activation energy (Eg) and the crystallization activation energy (Ec) are 159.8 ± 0.3 and 104.3 ± 0.51 kJ/mol, respectively. 相似文献
48.
Transparent amorphous and glass-ceramics waveguides in the system ZrF4-LaF3-ErF3-AlF3 (ZELA) have been fabricated by physical vapor deposition (PVD). The ceramming process was studied by means of X-ray diffraction and transmission electron microscopy for different deposition temperatures. With increasing deposition temperature, formation of LaxEr1−xF3 nanocrystals with x ∼ 0.3 was observed. The decay curves of the 4I13/2 level in the glass-ceramics with 14.5 mol% Er3+ gave evidence of the presence of erbium both in the amorphous matrix (τ = 8.6 ms) and in the crystal phase (τ = 2.2 ms). The decrease of lifetime was due to clustering of erbium incorporated in LaF3 crystal lattice. No significant increase of attenuation loss was detected after waveguide cerammization (1.3 dB/cm at 1304 nm). 相似文献
49.
Michael Burgess 《Journal of Non》2008,354(29):3491-3502
Packing is an intrinsic property of glass, defined as the ratio of ionic volume to molar volume, and is a useful parameter for analyzing structural changes with composition. Alkali based glasses show two trends in packing, one dominated by the oxygen covalent network for the small ions, Li and Na, and one ionically dominated by the metal cations for the large, K, Rb and Cs cases [S. Giri, C. Gaebler, J. Helmus, M. Affatigato, S.A. Feller, J. Non-Cryst. Solids 347 (2004) 87]. We have found that alkaline earth glasses do not display these behaviors, and in this paper we determined the packing fractions of these glasses and compared them with the alkali case. Further, we considered the structural implications of the packing trends. 相似文献
50.
The use of a Carr-Purcell-Meiboom-Gill (CPMG) echotrain to increase the 29Si NMR sensitivity in glasses was investigated. The echo intensity decay follows a stretched exponential behavior M(t) = M0 exp[−(t/t2)β] with values for the exponent β in the range of 0.41-0.65. The signal to noise in the spectra can be increased by a factor of up to 4 by taking the weighted sum of the spectra obtained from the individual echoes. However, differential T2 relaxation for the different Qn species is observed, with a shorter relaxation time for Q4 than Q3. Thus, summing of the echoes leads to distorted spectral intensities and quantitative information can no longer be obtained from the spectra. To circumvent the problem with differential T2 relaxation, an alternative approach is developed in which the spectral intensity for each chemical shift value is determined from the stretched exponential fit to its echo decay. With this approach, the sensitivity can be increased by a factor of up to 2.4, while quantitative information can still be obtained from the spectra. The increased sensitivity permitted the detection of five-coordinated silicon in a potassium silicate glass with natural 29Si abundance at ambient pressure. 相似文献