R B de Vasconcellos Azeredo

Federal University of Pernambuco, Arrecife, Pernambuco, Brazil

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Publications (3)8.23 Total impact

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    ABSTRACT: Time-domain nuclear magnetic resonance (TD-NMR) is one of the most popular solutions for quality control in the food industry. Despite the recognized success of TD-NMR in quality control and quality assurance, the speed by which samples can be characterized by TD-NMR techniques is still a concern, primarily when considering online or high-throughput applications. Therefore, to enhance the speed of TD-NMR analysis, we developed rapid methods based on steady-state free precession of nuclear spins, which we denoted continuous wave free precession (CWFP). CWFP substantially increases the sensitivity of TD-NMR compared with free induction decay or spin-echo detection, which are traditionally used. The objective of this paper was to present the physical background of CWFP and review its recent developments and applications in fat and oil quantifications in agri-food products.
    Magnetic Resonance in Chemistry 12/2011; 49 Suppl 1:S113-20. · 1.53 Impact Factor
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    ABSTRACT: The use of continuous wave free precession (CWFP) as a practical analytical tool for quantitative determinations in low-resolution nuclear magnetic resonance (LRNMR) is examined. The requirements of this technique are shown to be no more demanding than those prevailing in free-induction decay or spin-echo measurements. It is shown that the substantial gain in signal to noise ratio for a given acquisition time permitted by CWFP, can be exploited with advantage in practically any application of LRNMR. This applies not only to homogeneous low viscosity liquid samples but also to multi-component systems where differences in relaxation times of each component permit a separation of the individual contributions. As an example, the use of CWFP for fast quantitative determination of oil and moisture in various seeds is presented.
    Analytica Chimica Acta 02/2003; · 4.39 Impact Factor
  • R B de Vasconcellos Azeredo, M Engelsberg, L A Colnago
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    ABSTRACT: Steady-state free precession (SSFP) of nuclear spins in the presence of a magnetic field gradient is known to be very sensitive to flow. We present a theoretical and experimental study of flow sensitivity in a regime where the spacing of the radio-frequency pulses is extremely short compared with the free induction decay time and the relaxation times. Under these rather drastic conditions, a truly continuous wave free precession (CWFP) regime is established, in which, unlike standard SSFP, a large degree of coherence is preserved. This leads to a quite different flow sensitivity, which is significant even when very small magnetic field gradients are present. The unspoiled coherence is predicted to cause different flow effects which we confirmed experimentally. Tailored flow sensitivity can be achieved by adjusting the frequency offset from resonance, which plays a dominant role in the CWFP regime.
    Physical Review E 08/2001; 64(1 Pt 2):016309. · 2.31 Impact Factor