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71.
An experimental and simulation investigation regarding the effect of various CRAMPS parameters (delays interleaved with the decoupling shape, z-rotation symmetry and offset frequency) on the DUMBO decoupling performance is presented using two model compounds, glycine and tyrosine·HCl. Although the conclusions of this work may be extended to the other homonuclear-decoupling schemes, this work focuses essentially on the effect of adding interleaved delays to DUMBO decoupling during the indirect dimension using different 2D pulse-scheme architectures. While the simulations revealed an increasing loss of the spectral resolution with longer delays (from 0 to 6 μs), the experimental 2D (1)H DUMBO NMR correlation spectra revealed that the inclusion of delays, during the indirect dimension, improves the (1)H resolution whether the z-rotation symmetry was used or not. The best experimental spectra are obtained when z-rotation symmetry and windows are combined. 相似文献
72.
73.
Calibration of the relationship between height and phase is of uttermost importance to perform accurate 3D measurements in phase measurement profilometry. This work reports a different approach to this problem by first looking at the analytical expression for this relationship and determining the regime spanned by the fringe analysis method. The conclusions thus ascertained, amply justify confronting the analytical expression with a simple normalization procedure of the experimental data, with a remarkable matching between both results. In light of this, a linear calibration procedure with just one plane is proposed and verified experimentally. 相似文献
74.
75.
The cosmological constant problem is examined within the context of the covariant brane-world gravity, based on Nash’s embedding
theorem for Riemannian geometries. We show that the vacuum structure of the brane-world is more complex than General Relativity’s
because it involves extrinsic elements, in specific, the extrinsic curvature. In other words, the shape (or local curvature)
of an object becomes a relative concept, instead of the “absolute shape” of General Relativity. We point out that the immediate
consequence is that the cosmological constant and the energy density of the vacuum quantum fluctuations have different physical
meanings: while the vacuum energy density remains confined to the four-dimensional brane-world, the cosmological constant
is a property of the bulk’s gravitational field that leads to the conclusion that these quantities cannot be compared, as
it is usually done in General Relativity. Instead, the vacuum energy density contributes to the extrinsic curvature, which
in turn generates Nash’s perturbation of the gravitational field. On the other hand, the cosmological constant problem ceases
to be in the brane-world geometry, reappearing only in the limit where the extrinsic curvature vanishes. 相似文献
76.
D. Wardecki R. Przeniosło A. N. Fitch M. Bukowski R. Hempelmann 《Journal of nanoparticle research》2011,13(3):1151-1161
The microstructure of electrodeposited nanocrystalline chromium (n-Cr) was studied by using synchrotron radiation (SR) diffraction,
SEM, TEM, and EDX techniques. The as-prepared n-Cr samples show the standard bcc crystal structure of Cr with volume-averaged
column lengths varying from 25 to 30 nm. The grain growth kinetics and the oxidation kinetics were studied by time resolved
SR diffraction measurements with n-Cr samples annealed at 400, 600, and 800 °C. The grain growth process is relatively fast
and it occurs within the first 10 min of annealing. The final crystallite size depends only on the annealing temperature and
not on the initial grain size or on the oxygen content. The final volume-averaged column lengths observed after 50 min annealing
are 40(4), 80(1), and 120(2) nm for temperatures 400, 600, and 800 °C, respectively. It is shown that annealing ex situ of
n-Cr at 800 °C both under vacuum and in air gives a grain growth process with the same final crystallite sizes. The formation
of the Cr2O3 and CrH phases is observed during annealing. 相似文献
77.
Miniussi E Pozzo M Baraldi A Vesselli E Zhan RR Comelli G Menteş TO Niño MA Locatelli A Lizzit S Alfè D 《Physical review letters》2011,106(21):216101
We report on a novel approach to determine the relationship between the corrugation and the thermal stability of epitaxial graphene grown on a strongly interacting substrate. According to our density functional theory calculations, the C single layer grown on Re(0001) is strongly corrugated, with a buckling of 1.6 ?, yielding a simulated C 1s core level spectrum which is in excellent agreement with the experimental one. We found that corrugation is closely knit with the thermal stability of the C network: C-C bond breaking is favored in the strongly buckled regions of the moiré cell, though it requires the presence of diffusing graphene layer vacancies. 相似文献
78.
P. M. Ferreira Jo?o P. Silva 《The European Physical Journal C - Particles and Fields》2010,69(1-2):45-52
We analyze generalized CP symmetries of two-Higgs doublet models, extending them from the scalar to the fermion sector of the theory. We show that, other than the usual CP transformation, there is only one of those symmetries which does not imply massless charged fermions. That single model which accommodates a fermionic mass spectrum compatible with experimental data possesses a remarkable feature. Through a soft breaking of the symmetry it displays a new type of spontaneous CP violation, which does not occur in the scalar sector responsible for the symmetry breaking mechanism but, rather, in the fermion sector. 相似文献
79.
We describe an analog model for quantum gravity effects in condensed matter physics. The situation discussed is that of phonons propagating in a fluid with a random velocity wave equation. We consider that there are random fluctuations in the reciprocal of the bulk modulus of the system and study free phonons in the presence of Gaussian colored noise with zero mean. We show that, in this model, after performing the random averages over the noise function a free conventional scalar quantum field theory describing free phonons becomes a self-interacting model. 相似文献
80.
Leitão JM Esteves da Silva JC Girón AJ Muñoz de la Peña A 《Journal of fluorescence》2008,18(6):1065-1076
Excitation emission fluorescence matrices (EEMs) of Verapamil drug were obtained by direct and by derivatization fluorescence
spectroscopy. The fluorescence excitation and emission wavelengths were displaced to longer wavelengths and the fluorescence
intensity was enhanced upon derivation with respect to the native fluorescence of the drug. The complete EEM of the native
fluorescence of the drug and of the derivatization product were rapidly acquired by using a charged-coupled device detector
(CCD), which is advantageous in terms of speed in the analysis, with respect to the use of a conventional photomultiplier
detector. The EEMs were analyzed by several second-order multivariate calibration methods exploiting the second order advantage.
The three-dimensional decomposition methods used, based in different assumptions about the trilinearity of the three way data
structure under analysis, were parallel factor analysis (PARAFAC), bilinear least squares (BLLS), parallel factor analysis
2 (PARAFAC2) and multivariate curve resolution—alternating least squares (MCR-ALS). The determination was performed by using
the standard addition approach. The figures of merit of the PARAFAC and BLLS methods were calculated, obtaining a lower limit
of detection with the derivatization procedure, when compared with the direct measurement of the fluorescence of the drug.
In Verapamil drug the best estimations were found with the BLLS and the MCR-ALS models. In the quantification of Verapamil
in a pharmaceutical formulation the best estimation, when compared with the result obtained by the US Pharmacopeia high performance
liquid chromatography approach, was obtained by direct fluorescence spectroscopy with MCR-ALS and by derivatization fluorescence
spectroscopy with the PARAFAC2 model. 相似文献