Scan and deliver : By combining imaging‐based spectral/spatial 2D radiofrequency manipulations (see scheme, left) with Hadamard‐weighting principles, 2D NMR spectra can be retrieved within a single scan (right). This approach can give homo‐ or heteronuclear correlations with an enhanced sensitivity over conventional ultrafast 2D NMR spectroscopy.
Spherical microphone arrays have been recently used for room acoustics analysis, to detect the direction-of-arrival of early room reflections, and compute directional room impulse responses and other spatial room acoustics parameters. Previous works presented methods for room acoustics analysis using spherical arrays that are based on beamforming, e.g., delay-and-sum, regular beamforming, and Dolph-Chebyshev beamforming. Although beamforming methods provide useful directional selectivity, optimal array processing methods can provide enhanced performance. However, these algorithms require an array cross-spectrum matrix with a full rank, while array data based on room impulse responses may not satisfy this condition due to the single frame data. This paper presents a smoothing technique for the cross-spectrum matrix in the frequency domain, designed for spherical microphone arrays, that can solve the problem of low rank when using room impulse response data, therefore facilitating the use of optimal array processing methods. Frequency smoothing is shown to be performed effectively using spherical arrays, due to the decoupling of frequency and angular components in the spherical harmonics domain. Experimental study with data measured in a real auditorium illustrates the performance of optimal array processing methods such as MUSIC and MVDR compared to beamforming. 相似文献
A fundamental study aimed at investigating the stabilization characteristics of edge flames established in the near-wake of two merging streams, one containing fuel and the other oxidizer, is presented, with the main focus placed on the effects of the thermal interaction between the flame and the splitter plate. To this end, a diffusive-thermal model characterized by constant gas density and transport coefficients is used for conditions at which flame liftoff is likely to occur. It is assumed that the incoming streams are of equal strain rates, that the fuel and oxidizer are supplied in stoichiometric proportion, and that the mass diffusivities of the reactants are equal, such that the resulting combustion field is symmetric with respect to the centerline extending from the splitter plate. The results indicate that the plate has a negligible effect on the edge flame unless the tip of the plate intrudes into the preheat zone of the curved premixed flame segment forming the edge flame. In an overall adiabatic system, the heat conducted from the flame to the plate is completely recirculated back to the reactants via the lateral surfaces of the plate, thus supporting an excess enthalpy flame in the near-wake. The average output heat flux, defined as the total heat output through the lateral surfaces of the plate divided by the characteristic length associated with the temperature variation along the plate, is identified as an appropriate measure to characterize the heat recirculation efficiency. 相似文献
Optically active 1, 3-disubstituted propargyl alcohols undergo SNi′ rearrangements with thionyl bromide in the presence of propylene oxide to yield bromoallenes without loss of optical purity. 相似文献
This article addresses a real-life problem - obtaining communication links between multiple base station sites, by positioning
a minimal set of fixed-access relay antenna sites on a given terrain. Reducing the number of relay antenna sites is considered
critical due to substantial installation and maintenance costs. Despite the significant cost saved by eliminating even a single
antenna site, an inefficient manual approach is employed due to the computational complexity of the problem. From the theoretical
point of view we show that this problem is not only NP hard, but also does not have a constant approximation. In this paper
we suggest several alternative automated heuristics, relying on terrain preprocessing to find educated potential points for
positioning relay stations. A large-scale computer-based experiment consisting of approximately 7,000 different scenarios
was conducted. The quality of alternative solutions was compared by isolating and displaying factors that were found to affect
the standard deviation of the solutions supplied by the tested heuristics. The results of the simulation based experiments
show that the saving potential increases when more base stations are needed to be interconnected. The designs of a human expert
were compared to the automatically generated solutions for a small subset of the experiment scenarios. Our studies indicate
that for small networks (e.g., connecting up to ten base stations), the results obtained by human experts are adequate although
they rarely exceed the quality of automated alternatives. However, the process of obtaining these results in comparison to
automated heuristics is longer. In addition, when more base station sites need to be interconnected, the human approach is
easily outperformed by our heuristics, both in terms of better results (fewer antennas) and in significant shorter calculation
times. 相似文献
Pyrolysis of 1,1,1-trimethylamine-2-phenylcarbamoylimide gave sym-diphenylurea, phenylurea, 1,1-dimethyl-4-phenylsemicarbazide, 1,1,2-trimethyl-4-phenylsemicarbazide, aniline, 1,1-dimethylhydrazine, trimethylamine, nitrogen and carbon monoxide as products. Azoformanilide, a possible intermediate, decomposed at lower temperatures and gave diphenylurea, formanilide. and phenyl isocyanate. 1,1,1-Trimethylamine-2-[1-naphthylcarbamoyl]imide behaved s in addition a small amount of naphthalene. Carbarmoylimides involving two substituents in the 2-position behaved differently and gave indazolones. 相似文献